CN112400001B

CN112400001B - Adhesive sheet

Info

Publication number: CN112400001B
Application number: CN201980045742.7A
Authority: CN
Inventors: 加藤直宏; 伊神俊辉; 樋口真觉; 定司健太
Original assignee: Nitto Denko Shanghai Songjiang Co Ltd; Nitto Denko Corp
Current assignee: Nitto Denko Shanghai Songjiang Co Ltd; Nitto Denko Corp
Priority date: 2018-07-10
Filing date: 2019-07-09
Publication date: 2023-03-17
Anticipated expiration: 2039-07-09
Also published as: KR20210031472A; JP2020012108A; WO2020013168A1; CN112400001A; CN110699008A; JPWO2020013168A1; JP7469856B2; CN110699008B

Abstract

[ problem ] to provide an adhesive sheet that exhibits good deformation resistance even under severe environments and also has excellent impact resistance. [ solution ] to provide an adhesive sheet comprising: a foam base material and an adhesive layer provided on at least one surface of the foam base material. The adhesive layer contains an acrylic polymer as a base polymer. Furthermore, the aforementioned adhesive layer has a storage modulus G' (65 ℃) at 65 ℃ of more than 30000Pa.

Description

Adhesive sheet

Technical Field

The present invention relates to an adhesive sheet. More particularly, the present invention relates to an adhesive sheet suitable for fixing members constituting a portable device.

Background

In general, a pressure-sensitive adhesive (also referred to as a pressure-sensitive adhesive hereinafter) is in a soft solid (viscoelastic body) state in a temperature range around room temperature, and has a property of being easily adhered to an adherend by pressure. By utilizing such properties, adhesives are widely used for the purpose of bonding, fixing, protecting, etc. members in mobile phones and other portable devices, typically in the form of adhesive sheets. Patent documents 1 to 5 are cited as technical documents related to an adhesive tape used in a portable electronic device. Patent document 5 is a technical document relating to an adhesive sheet with a foam substrate.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2009-215355

Patent document 2: japanese laid-open patent publication No. 2013-100485

Patent document 3: japanese patent No. 6153635

Patent document 4: japanese patent No. 6113889

Patent document 5: japanese patent laid-open publication No. 2017-002292

Disclosure of Invention

Problems to be solved by the invention

For example, the adhesive sheet has a small adhesion area due to restrictions on size, weight, and the like in fixing members in a portable electronic device. The pressure-sensitive adhesive sheet used for this application is required to have an adhesive force capable of achieving good fixation even in a small area, and the required performance thereof is becoming higher level due to the demands for weight reduction and size reduction. In particular, in portable electronic devices of touch panel display mounting type represented by smartphones, while the size and thickness of the products themselves are reduced, the screen size is gradually increased from the viewpoint of visibility and operability of the display, and due to such unique circumstances, the adhesive used is required to have adhesive fixing performance under more severe conditions.

As an example of the fixing of the member in the portable electronic device, there is an application as follows: an elastic member such as a circuit board of an organic EL display is bent, stored in a limited internal space in a portable electronic device, and fixed by an adhesive sheet. The adhesive used for fixing the member is required to have a deformation resistance (specifically, a durability against a continuous peeling deformation load applied in the thickness direction (Z-axis direction) of the adhesive sheet) that can continuously resist the elastic rebound of the member under the conditions inside the portable electronic device. The temperature and humidity in the portable electronic device may be in a high temperature state exceeding 50 ℃ or may be in a high humidity state due to the influence of external environment as well as the influence of heat in the electronic device. The adhesive used for this purpose is required to exhibit stable deformation resistance in the Z-axis direction even under such an environment. Therefore, the adhesive used in this application is designed to have a relatively high degree of crosslinking from the viewpoint of ensuring high cohesion that can achieve deformation resistance.

On the other hand, portable electronic devices are at risk of falling from their use forms, and therefore, improvement of impact resistance is strongly demanded. The impact absorbability can be improved by reducing the crosslinking degree of the adhesive, but the reduction in crosslinking degree tends to reduce the cohesive property and the deformation resistance. As described above, the deformation resistance and the impact resistance are contradictory characteristics, and it is difficult to achieve both of them.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a pressure-sensitive adhesive sheet which exhibits excellent deformation resistance even under severe environments and also has excellent impact resistance.

Means for solving the problems

According to the present specification, there is provided an adhesive sheet comprising a foam base and an adhesive layer provided on at least one surface of the foam base. The adhesive layer contains an acrylic polymer as a base polymer. Furthermore, the aforementioned adhesive layer has a storage modulus G' (65 ℃) at 65 ℃ of more than 30000Pa. According to the above configuration, good deformation resistance is exhibited even under severe environments such as high temperature conditions, and impact resistance is also excellent.

In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the monomer component constituting the acrylic polymer containsMore than 50% by weight of an alkyl (meth) acrylate having an alkyl group having 1 to 6 carbon atoms at the ester terminal. By reacting (meth) acrylic acid C _1-6 The alkyl ester as a main constituent monomer component can be preferably designed to be an acrylic polymer that can achieve resistance to deformation against a continuous load in the Z-axis direction.

In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the monomer component constituting the acrylic polymer contains a carboxyl group-containing monomer. Thereby, the cohesive force of the adhesive layer is increased. The monomer component containing the carboxyl group-containing monomer can also contribute favorably to improvement of adhesion of the pressure-sensitive adhesive layer to an adherend. The content of the carboxyl group-containing monomer in the monomer component is preferably about 1 to 10% by weight from the viewpoint of compatibility with other components.

In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent. By using the isocyanate-based crosslinking agent, the cohesive force of the pressure-sensitive adhesive layer tends to be obtained, and further, the impact resistance tends to be more excellent than that of other crosslinking systems.

In a preferred embodiment, the adhesive layer contains, as an adhesion-promoting component, at least one selected from the group consisting of an adhesion-promoting resin and a (meth) acrylic oligomer in addition to the base polymer. Such a binder can easily realize good Z-axis deformation resistance even under severe environments such as high-temperature conditions. In one embodiment, the pressure-sensitive adhesive layer contains a tackifier resin as a tackifier component and does not substantially contain a (meth) acrylic oligomer. In the pressure-sensitive adhesive layer according to another embodiment, the tackifier component is substantially not contained in the tackifier resin, but contains a (meth) acrylic oligomer. In yet another embodiment, the pressure-sensitive adhesive layer contains a tackifier resin and a (meth) acrylic oligomer as tackifier components.

In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the pressure-sensitive adhesive layer contains a tackifier resin having a hydroxyl value of 70mgKOH/g or more. By including the above tackifier resin, excellent deformation resistance can be easily obtained. For example, in an adhesive using an isocyanate-based crosslinking agent, by using a tackifier resin having a high hydroxyl value as described above, not only can the adhesive strength be improved by using the tackifier resin, but also an adhesive layer having a high cohesive strength can be realized by the interaction between the high hydroxyl value tackifier resin and the isocyanate-based crosslinking agent. In some embodiments, the tackifier resin comprises a phenolic tackifier resin. The phenolic tackifier resin has excellent compatibility with the acrylic polymer. By using a phenolic tackifier resin as the tackifier resin, an effect of improving the adhesiveness to an adherend can be preferably achieved.

In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the content of the tackifier resin in the pressure-sensitive adhesive layer is 10 parts by weight or more and 60 parts by weight or less based on 100 parts by weight of the base polymer in the pressure-sensitive adhesive layer. By setting the amount of the tackifier resin to 10 parts by weight or more based on 100 parts by weight of the base polymer, good adhesion can be easily obtained. Further, by setting the amount of the tackifier resin to 60 parts by weight or less, good compatibility with the base polymer is achieved, and good adhesive properties are easily obtained.

The total thickness of the pressure-sensitive adhesive sheet of the preferred embodiment is 100 μm or more. The adhesive sheet having the above total thickness tends to have improved impact resistance.

In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the foam substrate is a polyolefin foam substrate. The effects of the technology disclosed herein can be preferably achieved by using an adhesive sheet provided with a polyolefin foam substrate.

The pressure-sensitive adhesive sheet disclosed herein exhibits excellent resistance to deformation even under severe environments and also has excellent impact resistance, and therefore, can be preferably used for applications for joining components of portable electronic devices. The pressure-sensitive adhesive sheet can exhibit excellent resistance to deformation under a continuous load in the Z-axis direction, and therefore can be suitably used for fixing an elastic adherend such as a circuit board of an organic EL display, for example. The pressure-sensitive adhesive sheet can be fixed in a state in which an elastic adherend is bent even in a high-temperature environment, for example, and can maintain the fixed state continuously. Further, for example, by using the adhesive sheet disclosed herein for the purpose of fixing a circuit board of an organic EL display disposed in a portable electronic device, the efficiency of housing components in the portable electronic device can be improved.

Drawings

Fig. 1 is a sectional view schematically showing one configuration example of an adhesive sheet.

FIG. 2 is a schematic diagram illustrating the method of the Z-axis direction deformation resistance test (65 ℃ 90% RH).

Detailed Description

Suitable embodiments of the present invention are described below. It is to be noted that matters necessary for carrying out the present invention other than the matters specifically mentioned in the present specification can be understood by those skilled in the art based on the teaching of the carrying out of the invention described in the present specification and the common general knowledge at the time of the application. The present invention can be implemented based on the contents disclosed in the present specification and the common general knowledge in the art. In the following drawings, members and portions that exhibit the same function are sometimes described with the same reference numerals, and redundant description may be omitted or simplified. The embodiments shown in the drawings are schematic for the purpose of clearly illustrating the present invention, and do not necessarily show the size or scale of the pressure-sensitive adhesive sheet of the present invention actually provided as a product.

In the present specification, the "pressure-sensitive adhesive" refers to a material that exhibits a soft solid (viscoelastic material) state in a temperature range around room temperature and has a property of easily adhering to an adherend by pressure as described above. As used herein, an adhesive such as "c.a. dahlquist," bonding: foundation and Practice ("Adhesion: fundamental and Practice"), mcLaren&Sons, (1966) P.143", generally speaking, can be a compound having a complex tensile modulus E (1 Hz)<10 ⁷ dyne/cm ² A material having the above properties (typically a material having the above properties at 25 ℃).

< construction of adhesive sheet >

The adhesive sheet disclosed herein (which may be in the form of a tape or the like) includes a foam base and an adhesive layer provided on at least one surface of the foam base. The pressure-sensitive adhesive sheet may be in the form of: the foam base material is in the form of a one-sided pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on only one side and having an adhesive surface (pressure-sensitive adhesive surface) on only one side. Such a one-sided pressure-sensitive adhesive sheet can be used for joining or fixing members by fixing the side having no pressure-sensitive adhesive layer to an adherend by a method other than adhesion (for example, a method using an adhesive, a method of thermal fusion, or the like). The pressure-sensitive adhesive sheet disclosed herein is typically preferably implemented in the form of a double-sided pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet with a foam substrate) having pressure-sensitive adhesive layers on both sides of the foam substrate. Such a double-sided pressure-sensitive adhesive sheet is advantageous from the viewpoints of, for example, ease of joining operations of parts, stability of joining quality, and the like. The term "pressure-sensitive adhesive sheet" as used herein includes articles such as pressure-sensitive adhesive tapes, pressure-sensitive adhesive labels, and pressure-sensitive adhesive films. The pressure-sensitive adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, the pressure-sensitive adhesive sheet may be processed into various shapes.

The adhesive sheet disclosed herein may be, for example, an adhesive sheet having a cross-sectional structure schematically shown in fig. 1. The adhesive sheet 1 comprises: a foam base 10, and a1 st adhesive layer 21 and a2 nd adhesive layer 22 supported by the 1 st surface 10A and the 2 nd surface 10B of the foam base 10, respectively. The 1 st surface 10A and the 2 nd surface 10B are both non-peelable surfaces (non-peelable surfaces). The psa sheet 1 is used by attaching a surface (1 st psa surface) 21A of a1 st psa layer 21 and a surface (2 nd psa surface) 22A of a2 nd psa layer 22 to an adherend. The pressure-sensitive adhesive sheet 1 before use has a structure in which the 1 st pressure-sensitive adhesive surface 21A and the 2 nd pressure-sensitive adhesive surface 22A are protected by

release liners

31 and 32, respectively, at least the pressure-sensitive adhesive surface side of which is a releasable surface (release surface). Alternatively, the following configuration may be adopted: the release liner 32 is omitted, and an object having both surfaces serving as release surfaces is used as the release liner 31, and the psa sheet 1 is wound so that the 2 nd adhesive surface 22A comes into contact with the back surface of the release liner 31, whereby the 2 nd adhesive surface 22A is also protected by the release liner 31.

< adhesive layer >

(storage modulus at 65 ℃ C.)

The pressure-sensitive adhesive layer disclosed herein (the 1 st pressure-sensitive adhesive layer and the 2 nd pressure-sensitive adhesive layer are both included, and the same applies hereinafter unless otherwise specified) is characterized by a storage modulus G' (65 ℃) at 65 ℃ of more than 30000Pa. By using the binder having the above G' (65 ℃ C.), excellent deformation resistance is exhibited even under severe environments such as high temperature conditions. The G' (65 ℃) is preferably higher than 40000Pa, more preferably higher than 50000Pa, and further preferably higher than 55000 Pa. When the pressure-sensitive adhesive layer has a G' (65 ℃) of at least a predetermined value, the high-temperature holding power tends to be excellent. The upper limit of G' (65 ℃) is not limited to a specific range, and is preferably 1.0MPa or less, and from the viewpoint of compatibility between initial adhesion (for example, low-temperature adhesion) and deformation resistance, it is preferably about 500000Pa or less, may be about 200000Pa or less, may be about 100000Pa or less, and may be about 80000Pa or less. In the embodiment disclosed herein in which the psa sheet is a double-sided psa sheet, the storage modulus G' (65 ℃) of the 1 st psa layer and the 2 nd psa layer may be the same or different. The storage modulus G' (65 ℃) can be adjusted by the binder composition (for example, the monomer composition of the base polymer, the molecular weight, the softening point of the tackifier resin, the kind of the crosslinking agent, the content ratio of these components), and the production method (polymerization conditions of the polymer, etc.). The 65 ℃ storage modulus can be measured by the method described in examples described later.

(65 ℃ loss modulus)

Further, although not particularly limited, the loss modulus G' at 65 ℃ (65 ℃) of the adhesive layer disclosed herein is suitably about 500000Pa or less. From the viewpoint of processability and handling, G' (65 ℃) is preferably about 100000Pa or less, may be about 50000Pa or less, or may be about 30000Pa or less. The G' (65 ℃) is preferably about 1000Pa or more, and is preferably about 5000Pa or more, and may be about 10000Pa or more from the viewpoint of wettability to the surface of the adherend, initial adhesiveness, and the like. When the pressure-sensitive adhesive layer has a G' (65 ℃) of a predetermined value or more, the impact resistance tends to be excellent. In the embodiment disclosed herein in which the psa sheet is a double-sided psa sheet, the loss modulus G ″ (65 ℃) of the 1 st psa layer and the 2 nd psa layer may be the same or different. The loss modulus G' (65 ℃) can be adjusted by the adhesive composition (for example, the monomer composition of the base polymer, the molecular weight, the softening point of the tackifier resin, the kind of the crosslinking agent, and the content ratio of these components) and the production method (polymerization conditions of the polymer, etc.). The loss modulus at 65 ℃ can be measured by the method described in examples described later.

(storage modulus at 25 ℃ C.)

The storage modulus at 25 ℃ of the adhesive layer disclosed herein is not particularly limited, and may be, for example, about 1MPa or less. The adhesive layer may have a storage modulus at 25 ℃ of about 0.5MPa or less, preferably about 0.3MPa or less (e.g., about 0.25MPa or less). When the storage modulus at 25 ℃ of the pressure-sensitive adhesive layer is low, the flexibility of the pressure-sensitive adhesive layer is high in the normal temperature region, and therefore, the pressure-sensitive adhesive surface can be easily brought into close contact with the surface of the adherend. Further, good impact resistance is easily obtained by using a binder whose storage modulus is limited to a predetermined value or less. The storage modulus at 25 ℃ may be about 0.01MPa or more. When a pressure-sensitive adhesive exhibiting a storage modulus at 25 ℃ of not less than a predetermined value is used, the adhesive strength is easily improved because the pressure-sensitive adhesive has appropriate cohesive properties in a normal temperature region. From such a viewpoint, the storage modulus at 25 ℃ is preferably about 0.02MPa or more, more preferably about 0.05MPa or more, still more preferably about 0.1MPa or more, yet more preferably about 0.14MPa or more (e.g., 0.15MPa or more), and particularly preferably about 0.18MPa or more (e.g., about 0.2MPa or more). The storage modulus at 25 ℃ of the adhesive layer can be adjusted by the composition, manufacturing method, and the like of the adhesive layer. The storage modulus at 25 ℃ can be measured by the method described in examples described later.

The loss modulus at 25 ℃ of the pressure-sensitive adhesive layer disclosed herein is not particularly limited, and may be, for example, about 0.01MPa or more. The loss modulus at 25 ℃ of the pressure-sensitive adhesive layer is preferably about 0.02MPa or more, more preferably about 0.05MPa or more, still more preferably about 0.15MPa or more, and particularly preferably about 0.17MPa or more (for example, about 0.2MPa or more). The adhesive exhibiting a loss modulus at 25 ℃ of a predetermined value or more is improved in adhesion to an adherend based on the viscosity term (loss modulus). When the loss modulus at 25 ℃ of the pressure-sensitive adhesive layer is high, the impact resistance tends to be improved. The adhesive layer may have a loss modulus at 25 ℃ of about 1MPa or less, for example. The loss modulus at 25 ℃ of the pressure-sensitive adhesive layer may be about 0.5MPa or less, preferably about 0.3MPa or less (for example, about 0.25MPa or less), from the viewpoint of cohesiveness and the like. The 25 ℃ loss modulus of the adhesive layer can be adjusted by the composition of the adhesive layer, the manufacturing method, and the like. The loss modulus at 25 ℃ can be measured by the method described in examples described later.

(Tg of adhesive layer)

Although not particularly limited, the Tg of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet disclosed herein is preferably controlled to about 25 ℃ or lower from the viewpoint of adhesion to an adherend and impact resistance. The adhesive layer preferably has a Tg of about 20 ℃ or less (typically about 15 ℃ or less, e.g., about 10 ℃ or less). The Tg of the pressure-sensitive adhesive layer is suitably about-25 ℃ or higher, preferably about-15 ℃ or higher, more preferably about-10 ℃ or higher (for example, about-5 ℃ or higher), and may be about 0 ℃ or higher (for example, about 5 ℃ or higher), from the viewpoint of impact resistance and the like. By having the above Tg, desired adhesive properties (e.g., adhesive strength, impact resistance) can be preferably achieved by the technique disclosed herein. In the embodiment in which the required properties are satisfied by selecting the type of the tackifier resin (for example, a high hydroxyl value resin), the Tg in the above range can be preferably used to exert the effects of the viscoelastic properties of the adhesive and the chemical properties of the tackifier resin. In the present specification, the Tg of the pressure-sensitive adhesive layer refers to a glass transition temperature determined from a peak temperature of tan δ in the dynamic viscoelasticity measurement. The Tg of the pressure-sensitive adhesive layer can be adjusted by the composition of the pressure-sensitive adhesive (for example, tg of the base polymer, softening point of the tackifier resin, kind of the crosslinking agent, content ratio of these components), and the production method (polymerization conditions of the polymer, etc.). The Tg of the pressure-sensitive adhesive layer can be measured by the method described in the examples described later.

(Peak Strength of tan. Delta. Of adhesive layer)

The value (peak strength) of the adhesive layer at the peak of tan δ is typically 1.0 or more, preferably about 1.5 or more, more preferably about 1.8 or more, and still more preferably about 2.0 or more. An adhesive having a peak of tan δ in a relatively low temperature region (typically, in the range of-25 ℃ to 25 ℃) can have excellent impact resistance when the adhesive has a peak strength of a predetermined value or more. The peak intensity of tan δ is preferably about 3.0 or less, more preferably about 2.5 or less, and may be about less than 2.2 (e.g., less than 2.0). The peak strength of tan δ of the pressure-sensitive adhesive layer can be adjusted by the composition of the pressure-sensitive adhesive (for example, tg of the base polymer, softening point of the tackifier resin, kind of the crosslinking agent, content ratio of these components), and the production method (polymerization conditions of the polymer, etc.). The peak strength of tan δ of the pressure-sensitive adhesive layer can be measured by the method described in the examples described later.

(base Polymer)

The adhesive constituting the adhesive layer disclosed herein is an acrylic adhesive containing an acrylic polymer as a base polymer. The base polymer is a main component of a rubbery polymer (a polymer exhibiting rubber elasticity in a temperature range around room temperature) contained in the pressure-sensitive adhesive layer. In this specification, the term "main component" means a component having a content of more than 50% by weight unless otherwise specified. In the present specification, the term "acrylic adhesive" refers to an adhesive containing an acrylic polymer as a base polymer (a main component in the polymer component, that is, a component accounting for 50% by weight or more). The "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least 1 (meth) acryloyl group in 1 molecule. Hereinafter, a monomer having at least 1 (meth) acryloyl group in 1 molecule is also referred to as an "acrylic monomer". Accordingly, the acrylic polymer in this specification is defined as a polymer containing a monomer unit derived from an acrylic monomer. In this specification, "(meth) acryloyl group" is intended to cover both acryloyl groups and methacryloyl groups. Similarly, "(meth) acrylate" is meant to inclusively refer to both acrylate and methacrylate, and "(meth) acrylic acid" is meant to inclusively refer to both acrylic acid and methacrylic acid.

(acrylic acid Polymer)

The acrylic polymer is preferably a polymer of a monomer raw material containing, for example, an alkyl (meth) acrylate as a main monomer and further containing a sub-monomer copolymerizable with the main monomer. The main monomer herein means a component in an amount of more than 50% by weight based on the monomer composition of the monomer raw material.

As the alkyl (meth) acrylate, for example, a compound represented by the following formula (1) can be suitably used.

CH ₂ ＝C(R ¹ )COOR ² (1)

Here, R in the above formula (1) ¹ Is a hydrogen atom or a methyl group. In addition, R ² Is a chain alkyl group having 1 to 20 carbon atoms. Hereinafter, such a range of the number of carbon atoms may be represented by "C _1-20 ". From the viewpoint of storage modulus of the binder, etc., R is ² Is C _1-14 (e.g. C) _2-10 Or C _4-8 ) The alkyl (meth) acrylate of (a) a chain alkyl group is suitable as a main monomer. From the viewpoint of adhesive properties, R is preferably ¹ Is a hydrogen atom, R ² Is C _4-8 Alkyl acrylate having a chain alkyl group (hereinafter, also simply referred to as acrylic acid C) _4-8 An alkyl ester. ) As the main monomer.

As R ² Is C _1-20 Examples of the alkyl (meth) acrylate having a chain alkyl group of (a) include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, pentyl (meth) acrylate, isoamyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, and isodecyl (meth) acrylateOctadecyl) acrylate, nonadecyl (meth) acrylate, eicosyl (meth) acrylate, and the like. These alkyl (meth) acrylates may be used singly in 1 kind or in combination in 2 or more kinds. Preferred alkyl (meth) acrylates include n-Butyl Acrylate (BA) and 2-ethylhexyl acrylate (2 EHA).

The proportion of the alkyl (meth) acrylate in the total monomer components used for synthesis of the acrylic polymer is preferably 70% by weight or more, more preferably 85% by weight or more, and still more preferably 90% by weight or more. The upper limit of the proportion of the alkyl (meth) acrylate is not particularly limited, and is preferably 99.5% by weight or less (for example, 99% by weight or less), and is preferably about 98% by weight or less (for example, 97% by weight or less) from the viewpoint of properly exhibiting the action of the side monomer such as the carboxyl group-containing monomer.

A preferable acrylic polymer is one containing (meth) acrylic acid C _1-6 The polymer may contain a monomer component of an alkyl ester as a main monomer and a sub-monomer copolymerizable with the main monomer. (meth) acrylic acid C _1-6 The alkyl ester may be used alone in 1 kind or in combination of 2 or more kinds. By using (meth) acrylic acid C _1-6 Alkyl ester, and a binder having good deformation resistance and impact resistance can be easily obtained.

The acrylic polymer is preferably obtained by using (meth) acrylic acid C as a main monomer _1-5 Alkyl esters, more preferably (meth) acrylic acid C _1-4 An alkyl ester. From the viewpoint of adhesion to an adherend, and the like, a preferred embodiment of the main monomer of the acrylic polymer is (meth) acrylic acid C _2-6 Alkyl esters, more preferably (meth) acrylic acid C _4-6 An alkyl ester. From the viewpoint of the improvement of the adhesion, a preferred main monomer of the acrylic polymer of another embodiment is acrylic acid C _1-6 Alkyl esters, more preferably acrylic acid C _1-4 Alkyl esters (e.g. acrylic acid C) _2-4 Alkyl esters).

As the above (meth) acrylic acid C _1-6 The alkyl ester is preferably used from the viewpoint of improving impact resistance and adhesion to an adherend or a substrate(meth) acrylic acid C having a homopolymer glass transition temperature (Tg) of approximately 20 ℃ or lower (typically approximately 10 ℃ or lower, preferably approximately 0 ℃ or lower, more preferably approximately-10 ℃ or lower, and still more preferably approximately-15 ℃ or lower) _1-6 An alkyl ester. The technique disclosed herein can be preferably carried out, for example, in such a manner that the main monomer of the acrylic polymer is BA.

Further, the (meth) acrylic acid C is preferably used _1-6 In view of the effect of the alkyl ester, the (meth) acrylic acid C in the monomer components constituting the acrylic polymer _1-6 Alkyl esters (typically acrylic acid C) _1-6 Alkyl ester, such as BA) is preferably about 60 wt% or more, more preferably about 75 wt% or more, and more preferably about 85 wt% or more. The technique disclosed herein can be preferably performed, for example, in such a manner that about 70% by weight or more (more preferably about 80% by weight or more, still more preferably about 85% by weight or more, and may be about 90% by weight or more, or about 95% by weight or more) of the monomer components is BA.

In the acrylic polymer in the technique disclosed herein, monomers (other monomers) other than the above-described monomers may be copolymerized as necessary within a range not significantly impairing the effect of the present invention. The other monomer can be used for the purpose of, for example, adjusting Tg of the acrylic polymer, improving cohesive force, adjusting initial adhesiveness, and the like. Examples of the monomer capable of improving the cohesive force and heat resistance of the adhesive include sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, vinyl esters, and aromatic vinyl compounds. Among these, preferable examples include vinyl esters. Specific examples of the vinyl esters include vinyl acetate (VAc), vinyl propionate, and vinyl laurate. Among them, VAc is preferred.

Examples of the other monomer that can introduce a functional group that can serve as a crosslinking base point into the acrylic polymer or can contribute to improvement of peel strength include a hydroxyl group-containing monomer, a carboxyl group-containing monomer, an acid anhydride group-containing monomer, an amide group-containing monomer, an amino group-containing monomer, an imide group-containing monomer, an epoxy group-containing monomer, (meth) acryloyl morpholine, and vinyl ethers.

As a suitable example of the acrylic polymer in the technique disclosed herein, there is an acrylic polymer obtained by copolymerizing a carboxyl group-containing monomer as the other monomer. This tends to facilitate the formation of a pressure-sensitive adhesive layer having a high cohesive strength. The carboxyl group-containing monomer contained in the monomer component can also contribute to an improvement in adhesion of the pressure-sensitive adhesive layer to an adherend or a substrate. For example, it is possible to exhibit improved adhesiveness to an adherend made of a polyester resin such as polyethylene terephthalate (PET). Examples of the carboxyl group-containing monomer include Acrylic Acid (AA), methacrylic acid (MAA), carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. The carboxyl group-containing monomers may be used alone in 1 kind or in combination of 2 or more kinds. Among them, preferred carboxyl group-containing monomers include AA and MAA. AA is particularly preferred. AA is considered to be the most suitable monomer material in terms of achieving deformation resistance to a continuous load in the Z-axis direction under high temperature conditions among the carboxyl group-containing monomers disclosed herein due to the combined action of the polarity of the carboxyl group, the action as a crosslinking point, tg (106 ℃ C.), and the like.

As another suitable example of the acrylic polymer in the technique disclosed herein, there can be mentioned an acrylic polymer obtained by copolymerizing a hydroxyl group-containing monomer as the other monomer. A hydroxyl group-containing monomer may be copolymerized together with the carboxyl group-containing monomer. Examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate; polypropylene glycol mono (meth) acrylate; n-hydroxyethyl (meth) acrylamide, and the like. Among these, preferable examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth) acrylates having a hydroxyl group at the end of a linear alkyl group having about 2 to 4 carbon atoms, such as 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4-HBA).

The "other monomers" can be used alone in 1 or a combination of 2 or more. The total content of the other monomers may be, for example, about less than 50% by weight (typically about 0.001 to 40% by weight) of the total monomer components, and preferably about 25% by weight or less (typically about 0.01 to 25% by weight, for example about 0.1 to 20% by weight).

When the carboxyl group-containing monomer is used as the other monomer, the content thereof is suitably about 0.1% by weight or more of the total monomer components, preferably about 0.2% by weight or more, more preferably about 0.5% by weight or more, still more preferably about 1% by weight or more, and particularly preferably about 2% by weight or more (for example, about 3% by weight or more, and further 4% by weight or more). When the content of the carboxyl group-containing monomer is increased, the cohesive force of the pressure-sensitive adhesive layer tends to be generally increased, and the Z-axis deformation resistance under high-temperature conditions tends to be increased. The amount of the carboxyl group-containing monomer is suitably about 20% by weight or less of the total monomer components, preferably about 15% by weight or less, more preferably about 12% by weight or less, still more preferably about 10% by weight or less, and particularly preferably about 8% by weight or less (for example, about 7% by weight or less). By setting the amount of the carboxyl group-containing monomer to the above range, for example, when a tackifier resin described later is blended, the blending effect thereof is suitably exhibited, and a pressure-sensitive adhesive layer exhibiting good adhesion to an adherend or a substrate can be suitably realized.

When a hydroxyl group-containing monomer is used as the other monomer, the content thereof is suitably about 0.001 wt% or more, preferably about 0.01 wt% or more (for example, about 0.02 wt% or more) of the total monomer components. The content of the hydroxyl group-containing monomer is suitably about 10% by weight or less, preferably about 5% by weight or less, and more preferably about 2% by weight or less, of the total monomer components.

The copolymerization composition of the acrylic polymer is suitably designed so that the Tg of the polymer is about-15 ℃ or lower (typically about-70 ℃ or higher and-15 ℃ or lower). Here, the Tg of the acrylic polymer is the Tg obtained from the Fox equation based on the composition of the monomer components used for synthesizing the polymer. The Fox formula is a relational expression between Tg of a copolymer and glass transition temperature Tgi of a homopolymer obtained by homopolymerizing monomers constituting the copolymer.

1/Tg＝Σ(Wi/Tgi)

In the above Fox formula, tg represents the glass transition temperature (unit: K) of the copolymer, wi represents the weight fraction of the monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi represents the glass transition temperature (unit: K) of a homopolymer of the monomer i.

As the glass transition temperature of the homopolymer used in calculating Tg, the values described in the publicly known data were used. For example, the following values are used for the monomers listed below as the glass transition temperatures of the homopolymers of the monomers.

Regarding the glass transition temperature of a homopolymer of a monomer other than those exemplified above, the values described in "Polymer Handbook" (3 rd edition, john Wiley & Sons, inc., 1989) were used. The highest value is used for monomers having various values described in this document.

The above documents do not describe a monomer having a glass transition temperature of a homopolymer, and the following measurement method is used.

Specifically, 100 parts by weight of a monomer, 0.2 part by weight of 2,2' -azobisisobutyronitrile and 200 parts by weight of ethyl acetate as a polymerization solvent were put into a reactor equipped with a thermometer, a stirrer, a nitrogen introduction tube and a reflux condenser, and stirred for 1 hour while flowing nitrogen. After the oxygen in the polymerization system was removed in this manner, the temperature was raised to 63 ℃ and the reaction was carried out for 10 hours. Subsequently, the mixture was cooled to room temperature to obtain a homopolymer solution having a solid content of 33% by weight. Subsequently, the homopolymer solution was cast on a release liner, and dried to prepare a test sample (sheet-like homopolymer) having a thickness of about 2 mm. The test sample was punched out into a disk shape having a diameter of 7.9mm, and sandwiched between parallel plates, and viscoelasticity was measured in a shear mode at a temperature range of-70 ℃ to 150 ℃ and a temperature rise rate of 5 ℃/min while applying a shear strain having a frequency of 1Hz to the test sample using a viscoelasticity tester (model name "ARES" manufactured by TA Instruments Japan Inc.), and the peak top temperature of tan δ (loss tangent) was defined as Tg of the homopolymer.

Although not particularly limited, the Tg of the acrylic polymer is favorably about-25 ℃ or lower, preferably about-35 ℃ or lower, more preferably about-40 ℃ or lower, from the viewpoint of adhesion to an adherend or a substrate and impact resistance. From the viewpoint of the cohesive force of the pressure-sensitive adhesive layer, the Tg of the acrylic polymer is favorably about-65 ℃ or higher, preferably about-60 ℃ or higher, and more preferably about-55 ℃ or higher. The technique disclosed herein can be preferably carried out in such a manner that the Tg of the acrylic polymer is about-65 ℃ or higher and-35 ℃ or lower (for example, about-55 ℃ or higher and-40 ℃ or lower). The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (i.e., the kind and amount ratio of the monomers used in the synthesis of the polymer).

The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as a method for synthesizing an acrylic polymer, such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, and a photopolymerization method, can be suitably used. For example, the solution polymerization method can be preferably employed. As a method of supplying the monomer in the case of performing the solution polymerization, a one-shot method of supplying all of the monomer raw materials at once, a continuous supply (dropwise) method, a batch supply (dropwise) method, and the like can be suitably employed. The polymerization temperature may be appropriately selected depending on the types of monomers and solvents used, the type of polymerization initiator, and the like, and may be, for example, about 20 ℃ to 170 ℃ (typically about 40 ℃ to 140 ℃). In a preferred embodiment, the polymerization temperature may be set to about 75 ℃ or lower (more preferably about 65 ℃ or lower, for example, about 45 ℃ to 65 ℃).

The solvent (polymerization solvent) used for the solution polymerization can be appropriately selected from conventionally known organic solvents. For example, aromatic compounds (typically aromatic hydrocarbons) selected from toluene and the like; acetic acid esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1, 2-dichloroethane; lower alcohols (e.g., monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol; ethers such as t-butyl methyl ether; ketones such as methyl ethyl ketone; and the like, or a mixed solvent of 2 or more.

The initiator used for the polymerization may be suitably selected from conventionally known polymerization initiators depending on the kind of the polymerization method. For example, 1 or 2 or more azo polymerization initiators such as 2,2' -Azobisisobutyronitrile (AIBN) can be preferably used. Other examples of the polymerization initiator include persulfates such as potassium persulfate; peroxide initiators such as Benzoyl Peroxide (BPO) and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; an aromatic carbonyl compound; and the like. As another example of the polymerization initiator, a redox-type initiator based on a combination of a peroxide and a reducing agent can be cited. Such polymerization initiators may be used alone in 1 kind or in combination of 2 or more kinds. The amount of the polymerization initiator to be used may be any amount generally used, and may be selected from a range of about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) based on 100 parts by weight of the total monomer components.

The solution polymerization described above can provide a polymerization reaction solution in which an acrylic polymer is dissolved in an organic solvent. The pressure-sensitive adhesive layer in the technique disclosed herein may be formed from a pressure-sensitive adhesive composition containing the above-mentioned polymerization reaction liquid or an acrylic polymer solution obtained by subjecting the reaction liquid to an appropriate post-treatment. As the acrylic polymer solution, a solution obtained by adjusting the polymerization reaction solution to an appropriate viscosity (concentration) as needed can be used. Alternatively, an acrylic polymer solution prepared by synthesizing an acrylic polymer by a polymerization method other than solution polymerization (for example, emulsion polymerization, photopolymerization, bulk polymerization, or the like) and dissolving the acrylic polymer in an organic solvent may be used.

The weight average molecular weight (Mw) of the base polymer (preferably, acrylic polymer) in the technique disclosed herein is not particularly limited, and may be, for example, about 10 × 10 ⁴ ～500×10 ⁴ In (c) is used. The upper limit of the Mw is set from the viewpoint of the adhesive performance, the adhesive productivity and the like,preferably about 200X 10 ⁴ Hereinafter, more preferably about 150X 10 ⁴ Hereinafter, more preferably about 140 × 10 ⁴ Hereinafter, the value may be about 130 × 10 ⁴ The following. From the viewpoint of adhesive properties, the Mw of the base polymer is preferably about 30 × 10 in several ways ⁴ Above, more preferably about 45 × 10 ⁴ More preferably about 50X 10 or more ⁴ Above (e.g., about 60 × 10) ⁴ Above). In a preferred embodiment, the Mw is about 110X 10 ⁴ The following (e.g., about 90X 10) ⁴ The following, and further about 80X 10 ⁴ Below). For example, using the techniques disclosed herein, a Mw of 70X 10 may be used ⁴ The following acrylic polymer composition achieves the intended high-temperature deformation resistance, high-temperature holding power, and impact resistance. In some other embodiments, the Mw is 70 × 10 from the viewpoint of deformation resistance to a continuous load in the Z-axis direction due to improvement in cohesion of the high molecular weight material ⁴ Above, more preferably about 75 × 10 ⁴ Above, more preferably about 90X 10 ⁴ Above, particularly preferably about 95X 10 ⁴ The above. In still another embodiment, the Mw is about 100X 10 ⁴ Above (e.g., about 110 × 10) ⁴ Above), may be 120 × 10 ⁴ Above (e.g., 130 × 10) ⁴ Above).

The dispersity (Mw/Mn) of the acrylic polymer disclosed herein is not particularly limited. The term "dispersity (Mw/Mn)" as used herein means a dispersity (Mw/Mn) in terms of the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn). In a preferred embodiment, the acrylic polymer has a dispersity (Mw/Mn) of less than 15. An Mw/Mn of the acrylic polymer of less than 15 means that the polymer contains a relatively uniform high molecular weight material in a considerable amount, and cohesion by the high molecular weight material tends to be accurately expressed, and excellent deformation resistance tends to be expressed. The Mw/Mn is preferably less than 12, more preferably less than 10, and still more preferably less than 8 (for example, 7.5 or less). In several ways, the Mw/Mn is less than 6 (e.g., less than 5.5). The Mw/Mn is theoretically 1 or more, for example, 2 or more, 3 or more, or 4 or more. In another preferred embodiment, the dispersity (Mw/Mn) of the acrylic polymer is 8 or more and 40 or less. The Mw/Mn of the acrylic polymer is 8 or more and 40 or less means that the molecular weight distribution is broad and the acrylic polymer contains a low molecular weight material and a high molecular weight material in a considerable amount. The low molecular weight material contributes to the expression of initial adhesiveness due to good wettability to an adherend, and the high molecular weight material expresses resistance to a continuous deformation load (deformation resistance) due to its cohesive property. When the Mw/Mn is 8 or more, initial adhesiveness is preferably exhibited. Further, when the Mw/Mn is 40 or less, the molecular weight distribution is preferably limited to an appropriate range, and stable characteristics (initial adhesion and deformation resistance) can be obtained. The Mw/Mn is preferably 10 or more, more preferably 12 or more, and further preferably 15 or more. The Mw/Mn is preferably 35 or less, more preferably 30 or less, further preferably 25 or less, and may be 20 or less (for example, less than 20).

The Mw, mn, and Mw/Mn can be adjusted by polymerization conditions (time, temperature, etc.), use of a chain transfer agent, selection of a polymerization solvent based on a chain transfer constant, and the like. The Mw and Mn are determined from values in terms of standard polystyrene obtained by GPC (gel permeation chromatography). As the GPC apparatus, for example, the model name "HLC-8320GPC" (column: TSKgelGMH-H (S), manufactured by Tosoh corporation) can be used.

(tackifying resin)

The adhesive layer disclosed herein preferably contains a tackifying resin in addition to the base polymer described above. As the tackifier resin, 1 or 2 or more kinds selected from known various tackifier resins such as rosin-based resins, terpene-based resins, modified terpene-based resins, phenol-based resins, styrene-based resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastic-based tackifier resins, and ketone-based resins can be used. Among them, a phenolic tackifier resin is preferable.

Examples of the phenolic tackifying resins include terpene phenol resins, hydrogenated terpene phenol resins, alkyl phenol resins, and rosin phenol resins.

The terpene-phenol resin is a polymer containing a terpene residue and a phenol residue, and is a concept including both a copolymer of a terpene and a phenol compound (terpene-phenol copolymer resin) and a resin obtained by phenol-modifying a homopolymer or a copolymer of a terpene (phenol-modified terpene resin). Suitable examples of terpenes constituting such a terpene-phenol resin include: monoterpenes such as α -pinene, β -pinene, limonene (including d-isomer, l-isomer, and d/l-isomer (dipentene)). The hydrogenated terpene-phenol resin refers to a hydrogenated terpene-phenol resin having a structure obtained by hydrogenating such a terpene-phenol resin. Sometimes also referred to as hydrogenated terpene phenol resins.

The alkylphenol resin is a resin (oleo-phenolic resin) obtained from alkylphenol and formaldehyde. Examples of the alkylphenol resin include novolak-type and resol-type resins.

The rosin phenol resin is typically a rosin or a phenol-modified product of the above rosin derivatives (including rosin esters, unsaturated fatty acid-modified rosins, and unsaturated fatty acid-modified rosin esters). Examples of the rosin phenol resin include rosin phenol resins obtained by a method of adding phenol to rosins or the various rosin derivatives described above with an acid catalyst and performing thermal polymerization, and the like.

The rosin-based resin (rosin-based tackifier resin) referred to herein includes both rosin-based and rosin derivative resins. Among them, a resin corresponding to a rosin phenol resin described later is treated not as a rosin resin but as a resin belonging to a phenol resin.

Examples of rosins include: unmodified rosins (raw rosins) such as gum rosin, wood rosin, tall oil rosin and the like: modified rosins obtained by modifying these unmodified rosins by hydrogenation, disproportionation, polymerization, or the like (hydrogenated rosins, disproportionated rosins, polymerized rosins, other chemically modified rosins, or the like).

Rosin derivative resins are typically derivatives of such rosins as described above. The rosin-based resin referred to herein includes derivatives of unmodified rosins and derivatives of modified rosins (including hydrogenated rosins, disproportionated rosins and polymerized rosins).

Examples of the rosin derivative resin include: rosin esters such as an unmodified rosin ester as an ester of an unmodified rosin and an alcohol, and a modified rosin ester as an ester of a modified rosin and an alcohol; for example, unsaturated fatty acid-modified rosins obtained by modifying rosins with unsaturated fatty acids; for example, unsaturated fatty acid-modified rosin esters obtained by modifying rosin esters with unsaturated fatty acids; for example, rosin alcohols obtained by reducing carboxyl groups of rosins or the various rosin derivatives described above (including rosin esters, unsaturated fatty acid-modified rosins, and unsaturated fatty acid-modified rosin esters); for example, metal salts of rosins or various rosin derivatives described above; and the like.

Specific examples of the rosin esters include, but are not particularly limited to, methyl esters, triethylene glycol esters, glycerol esters, pentaerythritol esters of unmodified rosins and modified rosins (hydrogenated rosins, disproportionated rosins, polymerized rosins, and the like).

Examples of the terpene resin (terpene-based tackifier resin) include polymers of terpenes (typically monoterpenes) such as α -pinene, β -pinene, d-limonene, l-limonene, and dipentene. The terpene may be a homopolymer of 1 type, or a copolymer of 2 or more types. Examples of the homopolymer of 1 terpene include an α -pinene polymer, a β -pinene polymer, and a dipentene polymer.

Examples of the modified terpene resin include those obtained by modifying the above terpene resins. Specifically, a styrene-modified terpene resin, a hydrogenated terpene resin, and the like can be exemplified. The resin corresponding to the terpene-phenol resin or hydrogenated terpene-phenol resin described later is not a modified terpene resin but a resin belonging to a phenol resin.

Examples of the hydrocarbon-based tackifier resin include: various hydrocarbon-based resins such as aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic/aromatic petroleum resins (e.g., styrene/olefin copolymers), aliphatic/alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone-based resins, and coumarone/indene-based resins.

A preferable embodiment includes an embodiment in which the tackifier resin contains 1 or 2 or more kinds of phenol-based tackifier resins (typically, terpene phenol resins). The use of the phenolic tackifier resin improves the adhesion of the pressure-sensitive adhesive layer to the adherend. In addition, the phenol-based tackifier resin tends to have excellent compatibility in the mode using an acrylic polymer as a base polymer, and has an advantage that desired adhesive properties are easily exhibited.

The techniques disclosed herein may be preferably implemented in such a manner that about 25 wt% or more (more preferably about 30 wt% or more) of the total amount of the tackifier resin is a terpene-phenol resin, for example. The terpene phenol resin may be present in an amount of about 50 wt% or more of the total amount of the tackifier resin, or about 80 wt% or more (for example, about 90 wt% or more) of the total amount of the tackifier resin. Substantially all (e.g., about 95 to 100 wt%, and further about 99 to 100 wt%) of the tackifier resin may be a terpene-phenol resin.

The content of the phenolic tackifier resin (e.g., terpene-phenol resin) is not particularly limited, and is preferably about 5 parts by weight or more relative to 100 parts by weight of the base polymer, and from the viewpoint of adhesiveness, is preferably about 10 parts by weight or more, more preferably about 15 parts by weight or more, and particularly preferably about 20 parts by weight or more (e.g., about 25 parts by weight or more). The content of the phenolic tackifier resin (e.g., terpene-phenol resin) is preferably about 80 parts by weight or less, and from the viewpoint of adhesion characteristics such as compatibility with a base polymer, adhesion, and impact resistance, it is preferably less than 70 parts by weight, more preferably about 60 parts by weight or less, still more preferably about 55 parts by weight or less, and particularly preferably about 45 parts by weight or less (e.g., about 40 parts by weight or less).

Although not particularly limited, as the tackifier resin in the technique disclosed herein, a tackifier resin having a hydroxyl value of less than 30mgKOH/g (for example, less than 20 mgKOH/g) can be used. Hereinafter, a tackifier resin having a hydroxyl value of less than 30mgKOH/g may be referred to as a "low hydroxyl value resin". The hydroxyl value of the low hydroxyl value resin may be about 15mgKOH/g or less, or may be about 10mgKOH/g or less. The lower limit of the hydroxyl value of the low hydroxyl value resin is not particularly limited, and may be substantially 0mgKOH/g.

Although not particularly limited, a tackifier resin having a hydroxyl value of 30mgKOH/g or more may be used as the tackifier resin in the technique disclosed herein. Hereinafter, a tackifier resin having a hydroxyl value of 30mgKOH/g or more may be referred to as a "high hydroxyl value resin". The hydroxyl value is preferably 40mgKOH/g or more, more preferably 50mgKOH/g or more, and still more preferably 60mgKOH/g or more. The upper limit of the hydroxyl value of the high hydroxyl value resin is not particularly limited. From the viewpoint of compatibility with an acrylic polymer, the hydroxyl value of the high hydroxyl resin is suitably about 200mgKOH/g or less, preferably about 180mgKOH/g or less, more preferably about 160mgKOH/g or less, and still more preferably about 140mgKOH/g or less.

In a preferred embodiment, the adhesive layer contains a tackifier resin having a hydroxyl value of 70mgKOH/g or more. By using such a high hydroxyl value resin, excellent deformation resistance can be easily obtained. For example, in an adhesive using an isocyanate-based crosslinking agent, by using a tackifier resin having a high hydroxyl value as described above, not only can the adhesive strength by using a tackifier resin be improved, but also an adhesive layer having a high cohesive strength can be realized by the interaction between the high hydroxyl value tackifier resin and the isocyanate-based crosslinking agent. The hydroxyl value of the high hydroxyl resin may be about 80mgKOH/g or more (e.g., about 100mgKOH/g or more). The upper limit of the hydroxyl value of the high hydroxyl value resin is not particularly limited. From the viewpoint of compatibility with the base polymer, the hydroxyl value of the high hydroxyl resin is preferably about 350mgKOH/g or less, more preferably about 300mgKOH/g or less (for example, about 250mgKOH/g or less), still more preferably about 200mgKOH/g or less, and may be about 150mgKOH/g or less (for example, about 120mgKOH/g or less).

Here, as the value of the hydroxyl value, a value obtained by JIS K0070:1992, the values determined by potentiometric titration. Specific measurement methods are shown below.

[ method for measuring hydroxyl value ]

1. Reagent

(1) As the acetylating reagent, about 12.5g (about 11.8 mL) of acetic anhydride was taken, and pyridine was added thereto so that the total amount was 50mL, followed by sufficient stirring. Alternatively, about 25g (about 23.5 mL) of acetic anhydride was taken, and pyridine was added thereto so that the total amount became 100mL, followed by sufficiently stirring.

(2) As a measuring reagent, 0.5mol/L ethanol solution of potassium hydroxide was used.

(3) In addition, toluene, pyridine, ethanol, and distilled water were prepared.

2. Operation of

(1) About 2g of the collected sample was accurately weighed and placed in a flat-bottomed flask, 5mL of an acetylating reagent and 10mL of pyridine were added, and an air condenser tube was attached.

(2) The flask was heated in a bath at 100 ℃ for 70 minutes, then left to cool, 35mL of toluene was added as a solvent from the top of the condenser tube, and after stirring, 1mL of distilled water was added and stirred, thereby decomposing acetic anhydride. To complete the decomposition, the bath was again heated for 10 minutes and allowed to cool.

(3) The condenser tube was rinsed with 5mL of ethanol and removed. Subsequently, 50mL of pyridine was added as a solvent and stirred.

(4) 25mL of 0.5mol/L ethanolic potassium hydroxide solution was added using a full-volume pipette (vollpipette).

(5) Potentiometric titration was performed with 0.5mol/L ethanolic potassium hydroxide. The inflection point of the resulting titration curve was used as the endpoint.

(6) The above (1) to (5) were carried out without adding a test sample to the blank test.

3. Calculating out

The hydroxyl value was calculated from the following formula.

Hydroxyl value (mgKOH/g) = [ (B-C) × f × 28.05]/S + D

Here, the number of the first and second electrodes,

b: the amount (mL) of 0.5mol/L KOH/ethanol solution used in the blank test,

C: the amount (mL) of 0.5mol/L ethanolic potassium hydroxide solution used in the sample,

f: factor of 0.5mol/L potassium hydroxide ethanol solution,

S: the weight (g) of the sample,

D: acid value,

28.05: the molecular weight of the potassium hydroxide is 1/2 of 56.11.

As the high hydroxyl value resin, a resin having a hydroxyl value of a predetermined value or more among the above various tackifier resins can be used. The high hydroxyl value resin can be used alone 1 or a combination of 2 or more. For example, as the high hydroxyl value resin, a phenolic tackifier resin having a hydroxyl value of 70mgKOH/g or more can be preferably used. In a preferred embodiment, a terpene-phenol resin having a hydroxyl value of 70mgKOH/g or more is used as the tackifier resin. The terpene-phenol resin is suitable because the hydroxyl value can be arbitrarily controlled by the copolymerization ratio of phenol.

Although not particularly limited, the proportion of the high hydroxyl value resin (e.g., terpene-phenol resin) in the entire tackifier resin contained in the adhesive layer may be, for example, about 25% by weight or more, preferably about 30% by weight or more, and more preferably about 50% by weight or more (e.g., about 80% by weight or more, and typically about 90% by weight or more). Substantially all (for example, about 95 to 100% by weight, and further about 99 to 100% by weight) of the tackifier resin may be a high hydroxyl value resin. Therefore, the adhesive layer disclosed herein may contain a tackifier resin not belonging to the high hydroxyl value resin (specifically, a tackifier resin having a hydroxyl value of less than 70 mgKOH/g) within a range not impairing the effects of the invention.

The content of the high hydroxyl resin is preferably about 5 parts by weight or more (for example, 10 parts by weight or more) based on 100 parts by weight of the base polymer. Thus, a pressure-sensitive adhesive sheet exhibiting adhesion to an adherend and excellent deformation resistance can be preferably realized. From the viewpoint of obtaining more excellent effects, the content of the high hydroxyl value resin is preferably about 15 parts by weight or more, more preferably about 20 parts by weight or more, further preferably about 25 parts by weight or more, and particularly preferably about 30 parts by weight or more, relative to 100 parts by weight of the base polymer. The upper limit of the content of the high hydroxyl value resin is not particularly limited, and in one embodiment, is suitably about 80 parts by weight or less relative to 100 parts by weight of the base polymer from the viewpoints of compatibility with the base polymer and initial adhesiveness, and is preferably less than 70 parts by weight, more preferably about 60 parts by weight or less, still more preferably about 55 parts by weight or less, particularly preferably about 50 parts by weight or less (for example, about 45 parts by weight or less), and may be about 40 parts by weight or less (for example, about 35 parts by weight or less) from the viewpoints of adhesion characteristics such as adhesive force and impact resistance.

The softening point of the tackifier resin is not particularly limited. In one embodiment, a tackifier resin having a softening point (softening temperature) of about 80 ℃ or higher (preferably about 100 ℃ or higher) can be preferably used from the viewpoint of improving the cohesive force. The softening point is more preferably about 110 ℃ or higher (for example, about 120 ℃ or higher). For example, a phenolic tackifier resin (terpene-phenol resin or the like) having the above softening point can be preferably used. In a preferred embodiment, a terpene-phenol resin having a softening point of about 135 ℃ or higher (further about 140 ℃ or higher) can be used. The technique disclosed herein can be preferably carried out in such a manner that the tackifier resin having the above softening point is more than 50 wt% (more preferably more than 70 wt%, for example, more than 90 wt%) of the entire tackifier resin contained in the pressure-sensitive adhesive layer. For example, a phenolic tackifier resin (terpene phenol resin or the like) having the above softening point can be preferably used. The upper limit of the softening point of the tackifier resin is not particularly limited. In one embodiment, a tackifier resin having a softening point of about 200 ℃ or less (more preferably about 180 ℃ or less) can be preferably used from the viewpoint of adhesion to an adherend or a base material. The adhesive layer disclosed herein may contain the tackifier resin having a softening point of, for example, about 150 ℃ or lower and about 140 ℃ or lower, or may not substantially contain the tackifier resin having a softening point of 150 ℃ or lower (for example, 140 ℃ or lower). The softening point of the tackifier resin can be measured by a softening point test method (ring and ball method) specified in JIS K2207.

The content of the tackifier resin is not particularly limited, and is preferably about 5 parts by weight or more (for example, 10 parts by weight or more) with respect to 100 parts by weight of the base polymer. This can suitably exhibit the effect of improving the adhesion to the adherend. From the viewpoint of obtaining higher adhesion, the content of the tackifier resin is preferably about 15 parts by weight or more, more preferably about 20 parts by weight or more, further preferably about 25 parts by weight or more, and particularly preferably about 30 parts by weight or more, relative to 100 parts by weight of the base polymer. The upper limit of the content of the tackifier resin is not particularly limited. From the viewpoint of compatibility with the base polymer and deformation resistance, in one embodiment, it is appropriate to set the amount to about 80 parts by weight or less, preferably about 60 parts by weight or less, more preferably about 55 parts by weight or less, further preferably about 50 parts by weight or less (for example, about 45 parts by weight or less), and also about 40 parts by weight or less (for example, about 35 parts by weight or less) with respect to 100 parts by weight of the base polymer.

((meth) acrylic acid-based oligomer)

The pressure-sensitive adhesive composition (and the pressure-sensitive adhesive layer) disclosed herein may contain a (meth) acrylic oligomer from the viewpoint of improving the adhesive strength and the like. As the (meth) acrylic oligomer, a polymer having a higher Tg than the Tg of the copolymer corresponding to the composition of the monomer component (typically, a polymer having a Tg approximately corresponding to the Tg of an acrylic polymer contained in a pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition) is preferably used. The (meth) acrylic oligomer can improve the adhesive strength of the adhesive.

The (meth) acrylic oligomer preferably has a Tg of about 0 ℃ or higher and about 300 ℃ or lower, preferably about 20 ℃ or higher and about 300 ℃ or lower, and more preferably about 40 ℃ or higher and about 300 ℃ or lower. When Tg is within the above range, the adhesion can be suitably improved. In a preferred embodiment, the Tg of the (meth) acrylic oligomer is about 30 ℃ or higher, more preferably about 50 ℃ or higher (e.g., about 60 ℃ or higher), from the viewpoint of the cohesive property of the adhesive, and is preferably about 200 ℃ or lower, more preferably about 150 ℃ or lower, and still more preferably about 100 ℃ or lower (e.g., about 80 ℃ or lower), from the viewpoint of the initial adhesiveness. The Tg of the (meth) acrylic oligomer is the same as the Tg of the copolymer corresponding to the composition of the monomer component, and is a value calculated based on the Fox formula.

The weight average molecular weight (Mw) of the (meth) acrylic oligomer may typically be about 1000 or more and less than about 30000, preferably about 1500 or more and less than about 20000, and more preferably about 2000 or more and less than about 10000. When Mw is within the above range, favorable adhesion and holding properties can be obtained, which is preferable. In a preferred embodiment, the Mw of the (meth) acrylic oligomer is about 2500 or more (e.g., about 3000 or more) from the viewpoint of the deformation resistance against the continuous load in the Z-axis direction, and is preferably about 7000 or less, and more preferably about 5000 or less (e.g., about 4500 or less, and further about 400 or less) from the viewpoint of the initial adhesiveness. The Mw of the (meth) acrylic oligomer can be measured by Gel Permeation Chromatography (GPC) and determined as a value in terms of standard polystyrene. Specifically, the HPLC8020 manufactured by Tosoh corporation was measured using TSKgelGMH-H (20). Times.2 columns in a tetrahydrofuran solvent at a flow rate of about 0.5 mL/min.

Examples of the monomer constituting the (meth) acrylic oligomer include: alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, and dodecyl (meth) acrylate; esters of (meth) acrylic acid and alicyclic alcohol (alicyclic hydrocarbon group-containing (meth) acrylate) such as cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and dicyclopentanyl (meth) acrylate; aryl (meth) acrylates such as phenyl (meth) acrylate and benzyl (meth) acrylate; (meth) acrylic acid esters derived from alcohols which are terpene compound derivatives; and the like. Such (meth) acrylates may be used singly in 1 kind or in combination in 2 or more kinds.

The (meth) acrylic oligomer preferably contains an alkyl (meth) acrylate having a branched structure with an alkyl group such as isobutyl (meth) acrylate or t-butyl (meth) acrylate from the viewpoint of further improving the adhesiveness of the pressure-sensitive adhesive layer; esters of (meth) acrylic acid and alicyclic alcohol (alicyclic hydrocarbon group-containing (meth) acrylic acid esters) such as cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and dicyclopentanyl (meth) acrylate; acrylic monomers having a bulky structure represented by (meth) acrylic esters having a cyclic structure such as aryl (meth) acrylates including phenyl (meth) acrylate and benzyl (meth) acrylate are used as monomer units. In addition, when ultraviolet light is used for synthesis of the (meth) acrylic oligomer or production of the pressure-sensitive adhesive layer, it is preferable to have a saturated bond in view of preventing inhibition of polymerization, and an alkyl (meth) acrylate having a branched structure in an alkyl group or an ester with an alicyclic alcohol (an alicyclic hydrocarbon group-containing (meth) acrylate) may be used as a monomer constituting the (meth) acrylic oligomer. The branched alkyl (meth) acrylate, the alicyclic alkyl (meth) acrylate, and the aryl (meth) acrylate are all (meth) acrylate monomers in the art disclosed herein. The alicyclic hydrocarbon group may be a saturated or unsaturated alicyclic hydrocarbon group.

The proportion of the (meth) acrylate monomer (for example, an alicyclic hydrocarbon group-containing (meth) acrylate) in the total monomer components constituting the (meth) acrylic oligomer is typically more than 50% by weight, preferably 60% by weight or more, and more preferably 70% by weight or more (for example, 80% by weight or more, and further 90% by weight or more). In a preferred embodiment, the (meth) acrylic oligomer has a monomer composition substantially containing only the (meth) acrylate monomer.

As the constituent monomer component of the (meth) acrylic oligomer, a functional group-containing monomer can be used in addition to the above (meth) acrylate monomer. Suitable examples of the functional group-containing monomer include: monomers having a nitrogen atom-containing ring (typically, a nitrogen atom-containing heterocycle) such as N-vinyl-2-pyrrolidone and N-acryloylmorpholine; amino group-containing monomers such as N, N-dimethylaminoethyl (meth) acrylate; amide group-containing monomers such as N, N-diethyl (meth) acrylamide; AA. Carboxyl group-containing monomers such as MAA; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth) acrylate. These functional group-containing monomers may be used alone in 1 kind or in combination of 2 or more kinds. Among them, carboxyl group-containing monomers are preferable, and AA is particularly preferable.

When the functional group-containing monomer is contained in the entire monomer components constituting the (meth) acrylic oligomer, the proportion of the functional group-containing monomer (for example, a carboxyl group-containing monomer such as AA) in the entire monomer components is suitably about 1% by weight or more, preferably 2% by weight or more, and more preferably 3% by weight or more, and is suitably about 15% by weight or less, preferably 10% by weight or less, and more preferably 7% by weight or less.

The (meth) acrylic oligomer can be formed by polymerizing its constituent monomer components. The polymerization method and polymerization method are not particularly limited, and various conventionally known polymerization methods (for example, solution polymerization, emulsion polymerization, bulk polymerization, photopolymerization, and radiation polymerization) can be used in a suitable manner. The type of the polymerization initiator (e.g., azo polymerization initiator such as AIBN) that can be used as needed is generally as exemplified in the synthesis of acrylic polymers, and the amount of the polymerization initiator and the amount of the chain transfer agent such as n-dodecylmercaptan that is optionally used are appropriately set based on technical common knowledge so as to have a desired molecular weight, and detailed description thereof is omitted here.

From the above-mentioned viewpoint, examples of suitable (meth) acrylic oligomers include: dicyclopentyl methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBXMA), isobornyl acrylate (IBXA), dicyclopentyl acrylate (DCPA), 1-adamantyl methacrylate (ADMA), the individual homopolymers of 1-adamantyl acrylate (ADA), as well as copolymers of CHMA with isobutyl methacrylate (IBMA), copolymers of CHMA with IBXMA, copolymers of CHMA with Acryloylmorpholine (ACMO), copolymers of CHMA with Diethylacrylamide (DEAA), copolymers of CHMA with AA, copolymers of ADA with Methyl Methacrylate (MMA), copolymers of DCPMA with IBXMA, copolymers of DCPMA with MMA, and the like.

When the (meth) acrylic oligomer is contained in the adhesive composition disclosed herein, the content thereof is preferably, for example, 0.1 part by weight or more (for example, 1 part by weight or more) based on 100 parts by weight of the acrylic polymer. From the viewpoint of more favorably exhibiting the effects of the (meth) acrylic oligomer, the content of the (meth) acrylic oligomer is preferably about 5 parts by weight or more, more preferably about 8 parts by weight or more, still more preferably about 10 parts by weight or more, and particularly preferably about 12 parts by weight or more. From the viewpoint of compatibility with an acrylic polymer, deformation resistance, and the like, the content of the (meth) acrylic oligomer is suitably less than 50 parts by weight (for example, less than 40 parts by weight), preferably less than 30 parts by weight, more preferably about 25 parts by weight or less, further preferably about 20 parts by weight or less, and may be about 10 parts by weight or less, or may be about 3 parts by weight or less (for example, about 1 part by weight or less). The technology disclosed herein may be implemented in such a manner that the adhesive layer contains substantially no (meth) acrylic oligomer.

(crosslinking agent)

The adhesive composition used to form the adhesive preferably comprises a crosslinking agent. The adhesive composition contains a crosslinking agent, whereby a crosslinked structure is introduced into the adhesive. The kind of the crosslinking agent is not particularly limited, and for example, it can be suitably selected from an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an oxazoline-based crosslinking agent, an aziridine-based crosslinking agent, a melamine-based crosslinking agent, a peroxide-based crosslinking agent, a urea-based crosslinking agent, a metal alkoxide-based crosslinking agent, a metal chelate-based crosslinking agent, a metal salt-based crosslinking agent, a carbodiimide-based crosslinking agent, an amine-based crosslinking agent, and the like, and used. The crosslinking agent can be used alone in 1 or a combination of more than 2. From the viewpoint of adhesion to an adherend and impact resistance, an isocyanate-based crosslinking agent is preferred, and from the viewpoint of retention performance in an adhered state (including retention of a layer shape), an epoxy-based crosslinking agent is preferred. By the technique disclosed herein, a pressure-sensitive adhesive sheet having higher performance can be provided without using an epoxy-based crosslinking agent or with a reduced amount of the crosslinking agent. For example, the use of an isocyanate-based crosslinking agent as the main crosslinking agent component can improve the adhesion to an adherend or the impact resistance. The use of the isocyanate-based crosslinking agent is advantageous in improving the adhesion to an adherend made of a polyester resin such as PET, for example.

As the epoxy crosslinking agent, a compound having 2 or more epoxy groups in 1 molecule can be used without particular limitation. An epoxy crosslinking agent having 3 to 5 epoxy groups in 1 molecule is preferable. The epoxy crosslinking agent may be used alone in 1 kind or in combination of 2 or more kinds.

Specific examples of the epoxy-based crosslinking agent include, but are not particularly limited to, N' -tetraglycidyl m-xylylenediamine, 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane, 1, 6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polyglycerol polyglycidyl ether. Commercially available products of the epoxy-based crosslinking agent include a trade name "TETRAD-C" and a trade name "TETRAD-X" manufactured by Mitsubishi gas chemical Corporation, a trade name "EPICLON CR-5L" manufactured by DIC Corporation, a trade name "DENACOL EX-512" manufactured by Nagase ChemteX Corporation, and a trade name "TEPIC-G" manufactured by Nissan chemical Corporation.

When the epoxy crosslinking agent is used, the amount thereof is not particularly limited, and may be, for example, 3 parts by weight or less based on 100 parts by weight of the base polymer. From the viewpoint of improving the adhesion to an adherend or a substrate and the anchoring strength, the amount of the epoxy-based crosslinking agent is preferably 1 part by weight or less, more preferably 0.5 part by weight or less (typically 0.2 part by weight or less, for example 0.1 part by weight or less, further 0.05 part by weight or less) with respect to 100 parts by weight of the base polymer, and may be 0.03 part by weight or less (for example 0.02 part by weight or less). When the amount of the epoxy crosslinking agent to be used is reduced, the impact resistance tends to be improved. From the viewpoint of suitably exhibiting the effect of improving the cohesive force, the amount of the epoxy-based crosslinking agent may be 0.001 parts by weight or more (for example, 0.005 parts by weight or more) relative to 100 parts by weight of the base polymer.

As the isocyanate-based crosslinking agent, polyfunctional isocyanates (compounds having an average of 2 or more isocyanate groups per 1 molecule, including those having an isocyanurate structure) can be preferably used. The isocyanate-based crosslinking agent may be used alone in 1 kind or in combination of 2 or more kinds.

Examples of the polyfunctional isocyanate include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates.

Specific examples of the aliphatic polyisocyanate include 1, 2-ethylene diisocyanate; tetramethylene diisocyanates such as 1, 2-tetramethylene diisocyanate, 1, 3-tetramethylene diisocyanate, and 1, 4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 1, 2-hexamethylene diisocyanate, 1, 3-hexamethylene diisocyanate, 1, 4-hexamethylene diisocyanate, 1, 5-hexamethylene diisocyanate, 1, 6-hexamethylene diisocyanate, and 2, 5-hexamethylene diisocyanate; 2-methyl-1, 5-pentane diisocyanate, 3-methyl-1, 5-pentane diisocyanate, lysine diisocyanate, and the like.

Specific examples of the alicyclic polyisocyanate include isophorone diisocyanate; cyclohexyl diisocyanates such as 1, 2-cyclohexyl diisocyanate, 1, 3-cyclohexyl diisocyanate and 1, 4-cyclohexyl diisocyanate; cyclopentyl diisocyanates such as 1, 2-cyclopentyl diisocyanate and 1, 3-cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, 4' -dicyclohexylmethane diisocyanate, and the like.

As specific examples of the aromatic polyisocyanates, examples thereof include 2, 4-tolylene diisocyanate, 2, 6-tolylene diisocyanate, 4' -diphenylmethane diisocyanate, 2' -diphenylmethane diisocyanate, 4' -diphenyl ether diisocyanate, 2-nitrodiphenyl-4, 4' -diisocyanate, 2' -diphenylpropane-4, 4' -diisocyanate 3,3' -dimethyldiphenylmethane-4, 4' -diisocyanate, 4' -diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthalene-1, 4-diisocyanate, naphthalene-1, 5-diisocyanate, 3' -dimethoxydiphenyl-4, 4' -diisocyanate, xylylene-1, 4-diisocyanate, xylylene-1, 3-diisocyanate, and the like.

As a preferred polyfunctional isocyanate, a polyfunctional isocyanate having an average of 3 or more isocyanate groups per 1 molecule can be exemplified. The 3 or more functional isocyanate may be a polymer (typically a dimer or trimer) of a2 or more functional isocyanate, a derivative (for example, an addition reaction product of a polyol and 2 or more molecules of a polyfunctional isocyanate), a polymer, or the like. Examples thereof include polyfunctional isocyanates such as dimers and trimers of diphenylmethane diisocyanate, isocyanurate bodies of hexamethylene diisocyanate (trimer adducts having isocyanurate structures), reaction products of trimethylolpropane and tolylene diisocyanate, reaction products of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanates, polyether polyisocyanates, and polyester polyisocyanates. Examples of the commercially available product of the polyfunctional isocyanate include trade name DURANATE TPA-100 manufactured by asahi chemie corporation, trade name "cornate L" manufactured by Nippon Polyurethane Industry co., ltd, trade name "Nippon Polyurethane Industry co., ltd," cornate HL "manufactured by ltd, trade name" Nippon Polyurethane Industry co., ltd, "cornate HK" manufactured by ltd, trade name "Nippon Polyurethane Industry co., ltd," cornate HX "manufactured by ltd, trade name" cornate 2096 "manufactured by ltd, and the like.

When the isocyanate-based crosslinking agent is used, the amount thereof is not particularly limited, and may be, for example, more than 0 part by weight and about 10 parts by weight or less (typically, 0.01 to 10 parts by weight) relative to 100 parts by weight of the base polymer. From the viewpoint of achieving both of the cohesive force and the adhesion, the impact resistance, and the like, the amount of the isocyanate-based crosslinking agent is preferably about 0.5 parts by weight or more, more preferably about 1 part by weight or more, and still more preferably about 1.5 parts by weight or more, relative to 100 parts by weight of the base polymer. From the same viewpoint, the amount of the isocyanate-based crosslinking agent is preferably about 8 parts by weight or less, more preferably about 6 parts by weight or less, still more preferably about 5 parts by weight or less, and particularly preferably about 4 parts by weight or less (for example, about 3 parts by weight or less) with respect to 100 parts by weight of the base polymer.

The technique disclosed herein is preferably carried out by using an epoxy-based crosslinking agent and an isocyanate-based crosslinking agent in combination. In the above embodiment, the relationship between the content of the epoxy-based crosslinking agent and the content of the isocyanate-based crosslinking agent is not particularly limited. The content of the epoxy-based crosslinking agent may be, for example, about 1/50 or less of the content of the isocyanate-based crosslinking agent. From the viewpoint of more suitably satisfying both the adhesiveness to an adherend or a base material and the cohesive force, the content of the epoxy crosslinking agent is suitably about 1/75 or less, preferably about 1/100 or less (for example, 1/150 or less) of the content of the isocyanate crosslinking agent. From the viewpoint of appropriately exhibiting the effect of using the epoxy-based crosslinking agent and the isocyanate-based crosslinking agent in combination, it is preferable that the content of the epoxy-based crosslinking agent is about 1/1000 or more, for example, about 1/500 or more of the content of the isocyanate-based crosslinking agent.

The total amount of the crosslinking agent is not particularly limited, and may be selected from, for example, about 0.005 parts by weight or more (e.g., about 0.01 parts by weight or more, typically about 0.1 parts by weight or more) and about 10 parts by weight or less (e.g., about 8 parts by weight or less, preferably about 5 parts by weight or less) relative to 100 parts by weight of the base polymer.

(other additives)

The pressure-sensitive adhesive composition may contain, in addition to the above-described components, various additives generally used in the field of pressure-sensitive adhesives, such as a leveling agent, a crosslinking assistant, a plasticizer, a softening agent, an antistatic agent, an anti-aging agent, an ultraviolet absorber, an antioxidant, and a light stabilizer, as required. Since conventionally known substances can be used for such various additives by a conventional method and are not characteristic of the present invention, detailed description thereof is omitted.

The pressure-sensitive adhesive layer (layer formed of a pressure-sensitive adhesive) disclosed herein may be a pressure-sensitive adhesive layer formed of a water-based pressure-sensitive adhesive composition, a solvent-based pressure-sensitive adhesive composition, a hot-melt pressure-sensitive adhesive composition, or an active energy ray-curable pressure-sensitive adhesive composition. The aqueous pressure-sensitive adhesive composition is a pressure-sensitive adhesive composition in a form in which a pressure-sensitive adhesive (pressure-sensitive adhesive layer forming component) is contained in a solvent (aqueous solvent) mainly containing water, and typically includes a composition called an aqueous dispersion type pressure-sensitive adhesive composition (a composition in which at least a part of a pressure-sensitive adhesive is dispersed in water) or the like. The solvent-based adhesive composition is in a form containing an adhesive in an organic solvent. From the viewpoint of adhesive properties and the like, the technique disclosed herein can be preferably implemented to include an adhesive layer formed from a solvent-based adhesive composition.

The adhesive layer disclosed herein can be formed by a conventionally known method. For example, a method of forming an adhesive layer by applying an adhesive composition to a surface having releasability (release surface) or a non-releasable surface and drying the adhesive composition can be employed. For example, a method (direct method) of forming a pressure-sensitive adhesive layer by directly applying (typically, coating) a pressure-sensitive adhesive composition to a substrate and drying the composition can be used for a pressure-sensitive adhesive sheet having a substrate structure. Further, a method (transfer method) of applying a pressure-sensitive adhesive composition to a surface having releasability (release surface) and drying the pressure-sensitive adhesive composition to form a pressure-sensitive adhesive layer on the surface and transferring the pressure-sensitive adhesive layer to a substrate may be employed. From the viewpoint of productivity, the transfer method is preferred. As the release surface, a surface of a release liner, a back surface of a base material subjected to release treatment, or the like can be used. The pressure-sensitive adhesive layer disclosed herein is typically formed continuously, but is not limited to this form, and may be formed in a regular or irregular pattern such as dots or stripes, for example.

The application of the adhesive composition can be performed using a conventionally known coater such as a gravure roll coater, die coater, or bar coater. Alternatively, the adhesive composition may be applied by impregnation, curtain coating, or the like.

From the viewpoints of accelerating the crosslinking reaction, improving the production efficiency, and the like, the drying of the binder composition is preferably performed under heating. The drying temperature may be, for example, about 40 to 150 ℃, preferably about 60 to 130 ℃. After drying the adhesive composition, the curing may be further performed for the purpose of adjusting the transfer of components in the adhesive layer, advancing the crosslinking reaction, relaxing strain that may be present in the adhesive layer, and the like.

(thickness of adhesive layer)

The thickness of the adhesive layer is not particularly limited. From the viewpoint of avoiding the psa sheet from becoming too thick, the thickness of the psa layer is suitably about 100 μm or less, preferably about 70 μm or less, more preferably about 60 μm or less, and even more preferably about 50 μm or less. The lower limit of the thickness of the pressure-sensitive adhesive layer is not particularly limited, but from the viewpoint of adhesiveness to an adherend, it is favorably about 3 μm or more, preferably about 10 μm or more, and more preferably about 20 μm or more (for example, about 30 μm or more). When the pressure-sensitive adhesive sheet disclosed herein is configured as a double-sided pressure-sensitive adhesive sheet, the pressure-sensitive adhesive sheet may have a pressure-sensitive adhesive layer having the above thickness on both sides of a substrate. In the double-sided pressure-sensitive adhesive sheet with a substrate having the 1 st pressure-sensitive adhesive layer and the 2 nd pressure-sensitive adhesive layer on each side of the substrate, the 1 st pressure-sensitive adhesive layer and the 2 nd pressure-sensitive adhesive layer may have the same thickness or different thicknesses.

(gel fraction)

Although not particularly limited, the gel fraction of the pressure-sensitive adhesive layer disclosed herein (the pressure-sensitive adhesive layers when the 1 st pressure-sensitive adhesive layer and the 2 nd pressure-sensitive adhesive layer are provided) may be, for example, 20% or more, preferably 30% or more, on a weight basis, and is preferably 35% or more. By increasing the gel fraction of the pressure-sensitive adhesive layer in an appropriate range, the deformation resistance to a continuous load in the Z-axis direction tends to be easily obtained. In the technique disclosed herein, it is more preferable to form a pressure-sensitive adhesive layer having a gel fraction of 40% or more. The gel fraction may be 45% or more, 50% or more, for example, 55% or more. On the other hand, the gel fraction of the pressure-sensitive adhesive layer is preferably 90% or less, more preferably 80% or less, further preferably 70% or less (for example, 65% or less), and may be 60% or less, or 50% or less, from the viewpoint of initial adhesiveness or the like. When the psa sheet disclosed herein is a double-sided psa sheet with a substrate, the gel fractions of the 1 st psa layer and the 2 nd psa layer may be the same or different.

< foamed substrate >

The adhesive sheet disclosed herein comprises a foam base. Specifically, the adhesive sheet is configured as an adhesive sheet having an adhesive layer on at least one surface of a foam base. In the technology disclosed herein, the foam base is a base having a portion having cells (cell structure), and typically means a base including at least 1 layer of a foam (foam layer). The foam base may be a base comprising 1 or 2 or more foam layers. The foam base may be a base substantially composed of only 1 or 2 or more foam layers. Although not particularly limited, a preferable example of the foam base in the technology disclosed herein is a foam base composed of a single-layer (1-layer) foam layer. By using the foam base material, more excellent impact resistance can be obtained than a structure using a resin film base material without a base material.

The density D (which means the apparent density. Hereinafter, the same as long as no particular description is given) of the foam base is not particularly limited, and may be, for example, about 0.1 to 0.9g/cm ³ . The density D of the foam base material was about 0.8g/cm from the viewpoint of impact resistance ³ The following is appropriate, preferably about 0.7g/cm ³ Below (e.g., about 0.6 g/cm) ³ Below). In one embodiment, the density D of the foam base material may be less than 0.5g/cm ³ Or less than 0.45g/cm ³ . Further, the density D of the foam base material is preferably about 0.12g/cm from the viewpoint of impact resistance ³ Above, more preferably about 0.15g/cm ³ Above, more preferably about 0.2g/cm ³ Above (e.g., about 0.3 g/cm) ³ Above). In one embodiment, the foam base material can have a density D of about 0.4g/cm ³ Above, and may be about 0.5g/cm ³ Above (e.g., more than 0.5 g/cm) ³ ) Further, it may be 0.55g/cm ³ The above. The density D (apparent density) of the foam base material can be measured in accordance with JIS K6767.

The average cell diameter of the foam base is not particularly limited, but is preferably about 300 μm or less, more preferably about 200 μm or less, and still more preferably about 150 μm or less, from the viewpoint of stress dispersion. In some embodiments, the average cell diameter of the foam base material may be about 120 μm or less, or about 100 μm or less (typically about 90 μm or less, for example about 80 μm or less, or further about 70 μm or less). The lower limit of the average cell diameter is not particularly limited, and is suitably about 10 μm or more, preferably about 20 μm or more, more preferably about 30 μm or more, and further preferably about 40 μm or more (for example, about 50 μm or more). In one embodiment, the average cell diameter may be 55 μm or more, or 60 μm or more. The impact resistance tends to be improved by increasing the average cell diameter. The average cell diameter referred to herein is an average cell diameter converted into a sphere obtained by observing the cross section of the foam base material with an electron microscope.

The cells contained in the foam base material are preferably relatively nearly circular in a plan view of the foam base material. That is, it is preferable that the average cell diameter in the moving direction (hereinafter also referred to as "MD") of the foam base is not greatly different from the average cell diameter in the width direction (hereinafter also referred to as "CD"). The degree of difference between the shape and the circular shape of the cells can be understood by using, as an index, the ratio of the average cell diameter with respect to MD (MD average cell diameter) to the average cell diameter with respect to CD (CD average cell diameter), that is, the "aspect ratio (MD/CD)" represented by the following formula. As the aspect ratio (MD/CD) is closer to 1, the shape of the cells contained in the foam base material in a plan view is said to be closer to a circle.

Aspect ratio (MD/CD) = MD average cell diameter/CD average cell diameter

In one embodiment of the technology disclosed herein, the aspect ratio (MD/CD) of the cells contained in the foam base is preferably 0.7 or more, more preferably 0.75 or more, further preferably 0.8 or more, and may be 0.85 or more, for example. In one embodiment, the aspect ratio may be 0.9 or more, or may be 0.95 or more (for example, about 1.0 or more). The aspect ratio (MD/CD) is preferably 1.3 or less, more preferably 1.25 or less, further preferably 1.2 or less, and may be 1.15 or less, for example. By making the aspect ratio (MD/CD) not too small as compared with 1, the workability of the psa sheet using the foam substrate can be improved. Further, it is preferable that the aspect ratio (MD/CD) is not too large as compared with 1.

Here, the MD of the foam base refers to the extrusion direction in the production process of the foam base. The MD of the foam base material in the form of a strip or the like is not particularly limited, and is aligned with the longitudinal direction. The CD of the foam base material is a direction perpendicular to the MD of the foam base material and along the surface of the foam base material. The thickness direction (hereinafter also referred to as "VD") of the foam base is a direction perpendicular to both MD and CD.

The MD average cell diameter of the foam substrate was measured as follows. That is, the foam base material was cut along a plane parallel to MD and VD (i.e., a plane in which the direction of the perpendicular line coincides with CD) at the substantially center portion of CD, and the center portion of the cut surface was photographed by a Scanning Electron Microscope (SEM). The photographed image was printed on A4-size paper, and a line having a length of 60mm parallel to the MD was drawn on the image. At this time, the magnification of the SEM was adjusted so that about 10 to 20 bubbles were present on a 60mm straight line. The number of cells present on the straight line was visually counted, and the MD average cell diameter was calculated by the following equation.

MD average cell diameter (μm) =60 (mm) × 10 ³ /(number of cells) × magnification)

The CD average cell diameter of the foam substrate was measured as follows. That is, the foam base material was cut along a plane parallel to the CD and VD (i.e., a plane in which the direction of the perpendicular line coincides with the MD), and the central portion of the cut surface was photographed by SEM. The photographed image was printed on A4-size paper, and a line having a length of 60mm parallel to the CD was drawn on the image. At this time, the magnification of the SEM was adjusted so that about 10 to 20 bubbles were present on a 60mm straight line. The number of bubbles present on the straight line was visually counted, and the CD average bubble diameter was calculated by the following formula.

CD average bubble diameter (μm) =60 (mm) × 10 ³ /(number of air bubbles(s) × magnification)

When drawing a straight line, the straight line penetrates the bubble as much as possible, and the straight line does not make point contact with the bubble. When some of the bubbles were in point contact with a straight line, the number of the bubbles was 1. Further, when both ends of the straight line were located in the bubbles and did not penetrate the bubbles, the number of the bubbles was counted as 0.5.

The average cell diameter of the foam base material in each direction can be controlled by adjusting the composition of the foam base material (the amount of the foaming agent used, etc.) and the production conditions (conditions in the foaming step, the stretching step, etc.), for example.

As the foam base material in the technology disclosed herein, a 10% compressive strength C may be preferably adopted ₁₀ [kPa]And 30% compressive strength C ₃₀ [kPa]Satisfies the following equation: (C) ₃₀ /C ₁₀ ) A foam base material of less than or equal to 5.0. Here, the 10% compressive strength of the foam base refers to a load (load at a compression rate of 10%) when the foam base is cut into a square shape of 30mm square, the obtained foam base is stacked to obtain a measurement sample having a thickness of about 2mm, and the measurement sample is compressed by a thickness amount corresponding to 10% of the initial thickness by sandwiching the measurement sample between a pair of flat plates. That is, the load is applied when the measurement sample is compressed to a thickness corresponding to 90% of the initial thickness. About 30% compressive strength C ₃₀ [kPa]And 25% compressive strength C described later ₂₅ [kPa]Similarly, the load when the measurement sample is compressed by a thickness amount corresponding to 30% or 25% of the initial thickness is referred to.

The compressive strength at any compression ratio of the foam base material was measured in accordance with JIS K6767. As a specific measurement procedure, the measurement sample is attached to the center of the pair of flat plates, the distance between the flat plates is reduced to continuously compress the sample to an arbitrary compression ratio, and then the flat plates are stopped to measure the load after 10 seconds have elapsed. The compressive strength of the foam base material can be controlled by, for example, the degree of crosslinking, density, size, shape of cells, and the like of the material constituting the foam base material.

Compressive strength ratio (C) ₃₀ /C ₁₀ ) Small means that the difference in degree of compression has little effect on the compressive strength. For example, when the bonding surface of the adhesive sheet has irregularities such as a level difference and a scratch; in the case where the width of the adhesive sheet is partially different; or in the case where a part of the joint portion using the adhesive sheet is subjected to a larger stress than other portions, the part of the adhesive sheet may be compressed more greatly than other portions. When the width of the adhesive sheet is narrowed, the adhesive sheet is composed ofThe difference in the degree of compression due to the height difference, the difference in the width of the portion, and the like tends to become more significant. If the difference in compressive strength due to the difference in degree of compression is too large, strain may concentrate on the portion where the degree of compression changes, and this portion may become a starting point for peeling of the adhesive sheet or damage to the foam base. Use (C) ₃₀ /C ₁₀ ) Since the adhesive sheet having a small foam base has a small difference in compressive strength due to the difference in degree of compression, the peeling and damage to the foam base are unlikely to occur. This is advantageous from the viewpoint of improving impact resistance. From the viewpoint of obtaining a more favorable effect, (C) ₃₀ /C ₁₀ ) More preferably 4.5 or less, and still more preferably 4.0 or less. (C) ₃₀ /C ₁₀ ) May be 3.5 or less. (C) ₃₀ /C ₁₀ ) The lower limit of (b) is not particularly limited, and is preferably 2.5 or more, for example, and may be 3.0 or more.

25% compression strength C of foam base ₂₅ The pressure is not particularly limited, and may be, for example, 20kPa or higher (typically 40kPa or higher). C ₂₅ It is preferably 250kPa or more, more preferably 300kPa or more (for example, 400kPa or more), and may be 500kPa or more, and further may be 700kPa or more (for example, 900kPa or less). The pressure-sensitive adhesive sheet having such a foam base material can exhibit excellent durability against impact such as dropping. For example, the adhesive sheet can be more preferably prevented from being broken by impact. C ₂₅ The upper limit of (B) is not particularly limited, but is preferably 1300kPa or less (for example, 1200kPa or less). In one mode, C ₂₅ May be 1000kPa or less. By means of an arrangement of C ₂₅ [kPa]And apparent density D [ g/cm ] ³ ]Satisfies the following equation: c is not less than 150 ₂₅ XD.ltoreq.400 (e.g., 200. Ltoreq.C) ₂₅ xXD.ltoreq.350, preferably 240. Ltoreq.C ₂₅ XD is less than or equal to 300); the foam substrate adhesive sheet of (3) can achieve more favorable results.

In still another preferred embodiment, C of the foam base ₂₅ The pressure may be set to 20kPa to 200kPa (typically 30kPa to 150kPa, for example, 40kPa to 120 kPa). The pressure-sensitive adhesive sheet having such a foam base material has a lower compressive strength than that corresponding to the density, and therefore, the pressure-sensitive adhesive sheet can be used even in the case of a pressure-sensitive adhesive sheet having such a foam base materialExcellent cushioning properties can be achieved even with a narrow width. For example, peeling of the adhesive sheet can be more effectively prevented by allowing the foam base to absorb a drop impact. By means of an arrangement of C ₂₅ [kPa]And apparent density D [ g/cm [) ³ ]Satisfies the following relationship: c is more than or equal to 100 ₂₅ D ≦ 400 (e.g., 150 ≦ C) ₂₅ D.ltoreq.350, preferably 200. Ltoreq.C ₂₅ D is less than or equal to 300); the pressure-sensitive adhesive sheet for foam substrate according to (1) can achieve further improved results.

The tensile elongation of the foam base is not particularly limited. For example, a foam base material having a tensile elongation in the Machine Direction (MD) of 200% to 800% (more preferably 400% to 600%) can be suitably used. The foam base material preferably has a tensile elongation in the width direction (TD) of 50% to 800% (more preferably 200% to 500%). The elongation of the foam base material was measured according to JIS K6767. The elongation of the foam base material can be controlled by, for example, the degree of crosslinking, the apparent density (expansion ratio), and the like.

The tensile strength (tensile strength) of the foam base is not particularly limited. For example, a foam base material having a tensile strength in the Moving Direction (MD) of 5MPa to 35MPa (preferably 10MPa to 30 MPa) can be suitably used. Further, the foam base material has a tensile strength in the width direction (TD) of 1MPa to 25MPa (more preferably 5MPa to 20 MPa). The tensile strength of the foam base material was measured in accordance with JIS K6767. The tensile strength of the foam base material can be controlled by, for example, the degree of crosslinking, the apparent density (expansion ratio), and the like.

The material of the foam base is not particularly limited. For example, a foam base including a foam layer formed of a foam of a plastic material (plastic foam) is preferable. The plastic material (including the rubber material) used for forming the plastic foam is not particularly limited, and may be appropriately selected from known plastic materials. The plastic materials may be used alone in 1 kind or in a suitable combination of 2 or more kinds.

Specific examples of the plastic foam include foams made of polyolefin resins such as polyethylene foams and polypropylene foams; polyester resin foams such as polyethylene terephthalate foams, polyethylene naphthalate foams and polybutylene terephthalate foams; foamed products made of polyvinyl chloride resin such as foamed products made of polyvinyl chloride; a vinyl acetate resin foam; a polyphenylene sulfide resin foam; amide resin foams such as foams made of aliphatic polyamide (nylon) resins and foams made of wholly aromatic polyamide (aramid) resins; a foam made of a polyimide resin; a polyether ether ketone (PEEK) foam; a styrene resin foam such as a polystyrene foam; urethane resin foams such as polyurethane resin foams; and the like. As the plastic foam, a foam made of a rubber resin such as a foam made of polychloroprene rubber can be used.

As a preferred foam, a foam made of a polyolefin resin (hereinafter also referred to as "polyolefin foam") is exemplified. As the plastic material (i.e., polyolefin resin) constituting the polyolefin foam, various known or conventional polyolefin resins can be used without particular limitation. Examples thereof include polyethylene such as Low Density Polyethylene (LDPE), linear Low Density Polyethylene (LLDPE), and High Density Polyethylene (HDPE), polypropylene, ethylene-propylene copolymer, and ethylene-vinyl acetate copolymer. Examples of LLDPE include ziegler-natta catalyst type linear low-density polyethylene, metallocene catalyst type linear low-density polyethylene, and the like. These polyolefin resins may be used alone in 1 kind or in combination of 2 or more kinds as appropriate.

Suitable examples of the foam base in the technology disclosed herein include polyolefin foam bases such as a polyethylene foam base substantially composed of a polyethylene resin foam and a polypropylene foam base substantially composed of a polypropylene resin foam, from the viewpoints of impact resistance, water repellency, dust resistance, and the like. The polyethylene resin herein refers to a resin containing ethylene as a main monomer (i.e., a main component in the monomer), and may contain an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer, and the like, in which the copolymerization ratio of ethylene exceeds 50% by weight, in addition to HDPE, LDPE, LLDPE, and the like. Similarly, the polypropylene resin refers to a resin containing propylene as a main monomer. As the foam base in the technology disclosed herein, a polyethylene-based foam base can be preferably used.

The method for producing the plastic foam (typically, polyolefin foam) is not particularly limited, and various known methods can be suitably used. For example, the plastic foam can be produced by the above-mentioned plastic material or a method including the above-mentioned molding step, crosslinking step and foaming step of the plastic foam. Further, a stretching step may be included as necessary.

Examples of the method for crosslinking the plastic foam include a chemical crosslinking method using an organic peroxide or the like, an ionizing radiation crosslinking method by irradiating an ionizing radiation, and the like, and these methods may be used in combination. Examples of the ionizing radiation include electron beams, α -rays, β -rays, and γ -rays. The dose of the ionizing radiation is not particularly limited, and may be set to an appropriate dose in consideration of the target physical properties (for example, the degree of crosslinking) of the foam base material.

The foam base material may contain various additives such as a filler (inorganic filler, organic filler, etc.), an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a plasticizer, a flame retardant, and a surfactant, as required.

The foam base in the art disclosed herein may be colored in order to allow the adhesive sheet having the foam base to exhibit desired design properties and optical properties (e.g., light-shielding properties, light-reflecting properties, etc.). The coloring may be carried out by using 1 kind of known organic or inorganic coloring agent alone or 2 or more kinds of known organic or inorganic coloring agents in a suitable combination.

For example, when the adhesive sheet disclosed herein is used for light-shielding applications, the visible light transmittance of the foam base is not particularly limited, but is preferably 0% to 15%, more preferably 0% to 10%, as is the visible light transmittance of the adhesive sheet described below. When the adhesive sheet disclosed herein is used for light reflection applications, the visible light reflectance of the foam base is preferably 20% to 100%, more preferably 25% to 100%, as in the case of the adhesive sheet.

The visible light transmittance of the foam base material can be determined by measuring the intensity of light irradiated from one surface side of the foam base material and transmitted to the other surface side at a wavelength of 550nm using a spectrophotometer (for example, a spectrophotometer manufactured by Hitachi High-Technologies Corporation, model "U-4100"). The visible light reflectance of the foam base can be determined by measuring the intensity of light irradiated to one surface of the foam base and reflected at a wavelength of 550nm using the above-mentioned spectrophotometer. The visible light transmittance and the visible light reflectance of the pressure-sensitive adhesive sheet can be determined by the same method.

When the adhesive sheet disclosed herein is used for light-shielding applications, the foam base is preferably colored black. The black color is preferably 35 or less (for example, 0 to 35), and more preferably 30 or less (for example, 0 to 30) in terms of L (luminance) defined in the chromaticity system. Note that a and b defined in the chromaticity system may be appropriately selected depending on the value of L. The values a and b are not particularly limited, but both preferably range from-10 to 10 (more preferably from-5 to 5, particularly preferably from-2.5 to 2.5). For example, it is preferred that a and b are both 0 or about 0.

In the present specification, L, a, b defined in the colorimetric system may be measured by using a color difference meter (for example, color difference meter manufactured by MINOLTA corporation, trade name "CR-200"). Note that the L × a × b chromaticity system is a color space recommended by the international commission on illumination (CIE) in 1976, and refers to a color space called CIE1976 (L × a × b) chromaticity system. Further, L a b color system is specified by JIS Z8729 in japanese industrial standards.

Examples of the black coloring agent used for coloring the foam base material black include carbon black (furnace black, channel black, acetylene black, thermal black, lamp black, etc.), graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanine black, activated carbon, ferrite (nonmagnetic ferrite, magnetic ferrite, etc.), magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complex, composite oxide-based black pigment, and anthraquinone-based organic black pigment. From the viewpoint of cost and availability, carbon black is exemplified as a preferable black colorant. The amount of the black colorant to be used is not particularly limited, and may be adjusted as appropriate so as to impart desired optical characteristics.

When the adhesive sheet disclosed herein is used for light reflection applications, the foam base is preferably white in color. The color white is preferably 87 or more (e.g., 87 to 100), and more preferably 90 or more (e.g., 90 to 100) in terms of L (luminance) defined in the color system. The predetermined values a and b in the L × a × b chromaticity system may be appropriately selected depending on the value of L. Both a and b are preferably in the range of-10 to 10 (more preferably-5 to 5, particularly preferably-2.5 to 2.5), for example. For example, it is preferred that a and b are both 0 or about 0.

Examples of the white colorant used for coloring the foam base material to white include organic white colorants such as titanium oxide (titanium dioxide such as rutile type titanium dioxide and anatase type titanium dioxide), zinc oxide, aluminum oxide, silicon oxide, zirconium oxide, magnesium oxide, calcium oxide, tin oxide, barium oxide, cesium oxide, yttrium oxide, magnesium carbonate, calcium carbonate (light calcium carbonate, heavy calcium carbonate, etc.), barium carbonate, zinc carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, aluminum silicate, magnesium silicate, calcium silicate, barium sulfate, calcium sulfate, barium stearate, zinc white, zinc sulfide, talc, silica, aluminum oxide, clay, kaolin, titanium phosphate, mica, gypsum, white carbon, diatomaceous earth, bentonite, lithopone, zeolite, sericite, halloysite, etc., acrylic resin particles, polystyrene resin particles, polyurethane resin particles, amide resin particles, polycarbonate resin particles, organosilicon resin particles, urea-formalin resin particles, melamine resin particles, and the like. The amount of the white colorant to be used is not particularly limited, and may be adjusted as appropriate so as to impart desired optical characteristics.

The surface of the foamed base material may be subjected to an appropriate surface treatment as required. The surface treatment may be, for example, a chemical treatment or a physical treatment for improving adhesion to an adjacent material (e.g., an adhesive layer). Examples of the surface treatment include corona discharge treatment, chromic acid treatment, ozone exposure, flame exposure, ultraviolet irradiation treatment, plasma treatment, and coating with a primer (primer).

The thickness of the foam base is not particularly limited, and may be appropriately set according to the strength, flexibility, purpose of use, and the like of the pressure-sensitive adhesive sheet. From the viewpoint of thinning the junction portion, the thickness of the foam base is suitably about 700 μm or less, preferably about 400 μm or less, and more preferably about 300 μm or less. The technique disclosed herein can be preferably implemented so that the thickness of the foam base is about 200 μm or less (for example, 180 μm or less, and further 160 μm or less). The thickness of the foam base is suitably about 50 μm or more, preferably about 60 μm or more, and more preferably about 70 μm or more (for example, about 80 μm or more). The technique disclosed herein can be preferably carried out so that the thickness of the foam base is about 100 μm or more (e.g., more than 100 μm, preferably 120 μm or more, for example, 130 μm or more). When the thickness of the foam base material is increased, impact resistance is also improved, and desired impact resistance tends to be exhibited even in a narrow structure, for example.

< Release liner >

In the technique disclosed herein, a release liner may be used for formation of the adhesive layer, production of the adhesive sheet, storage, distribution, shape processing, and the like of the adhesive sheet before use. The release liner is not particularly limited, and examples thereof include a release liner having a release treatment layer on the surface of a liner base material such as a resin film or paper, and a release liner made of a low-adhesive material such as a fluorine-based polymer (polytetrafluoroethylene or the like) or a polyolefin-based resin (polyethylene, polypropylene or the like). The release treatment layer may be formed by surface-treating the backing material with a release treatment agent such as silicone, long-alkyl, fluorine, or molybdenum sulfide.

< Total thickness of adhesive sheet >

The total thickness of the pressure-sensitive adhesive sheet disclosed herein (including the pressure-sensitive adhesive layer, and may further include a base layer, but does not include a release liner.) is not particularly limited. The total thickness of the pressure-sensitive adhesive sheet may be set to, for example, about 800 μm or less, and is preferably about 500 μm or less, and more preferably about 350 μm or less (for example, about 300 μm or less), from the viewpoint of thinning of the portable device. The technique disclosed herein may be implemented in the form of a pressure-sensitive adhesive sheet (typically, a double-sided pressure-sensitive adhesive sheet) having a total thickness of about 250 μm or less (more preferably about 200 μm or less, still more preferably about 150 μm or less, for example, about 120 μm or less). The lower limit of the thickness of the pressure-sensitive adhesive sheet is not particularly limited, and is preferably about 60 μm or more, and from the viewpoint of impact resistance and the like, it is preferably about 100 μm or more, may be about 150 μm or more, may be about 180 μm or more, and may be about 200 μm or more (for example, about 220 μm or more).

< Property of adhesive sheet >

The impact resistance of the adhesive sheet disclosed herein may be about 0.2J or more, as measured by the method described in examples described later. The adhesive sheet exhibiting higher energy can exert more excellent impact resistance. From such a viewpoint, the impact resistance is suitably about 0.3J or more, preferably about 0.4J or more, more preferably about 0.5J or more, and still more preferably about 0.6J or more (for example, 0.7J or more). The upper limit of the impact resistance is not particularly limited, and may be about 1.5J or less (for example, about 1.2J or less) from the viewpoint of compatibility with other characteristics.

The pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and the 180-degree peel strength (low-temperature adhesive strength) at 10 ℃ may be about 5N/20mm or more. The pressure-sensitive adhesive sheet exhibiting such adhesive force can exhibit excellent adhesion to an adherend even in a low-temperature region in addition to the Z-axis deformation resistance in a high-temperature region. The low-temperature adhesive strength is preferably 7N/20mm or more, more preferably about 9N/20mm or more, further preferably about 11N/20mm or more, and may be about 13N/20mm or more (for example, about 14N/20mm or more). The upper limit of the low-temperature adhesive strength is not particularly limited, and may be about 30N/20mm or less (for example, about 20N/20mm or less), from the viewpoint that the higher the adhesiveness to an adherend is, the better. The low-temperature adhesive strength is measured by the method described in the examples described later.

The pressure-sensitive adhesive sheet disclosed herein is typically judged as "acceptable" in a Z-axis deformation resistance test (65 ℃ 90% rh) performed by the method described in the examples described later. An adhesive sheet satisfying these characteristics is excellent in resistance to permanent deformation under high-temperature and high-humidity conditions.

The pressure-sensitive adhesive sheet disclosed herein is judged to be "acceptable" in a high-temperature holding power evaluation test carried out by the method described in the examples described below. The adhesive sheet satisfying these characteristics is excellent in holding power under high temperature conditions.

< use >)

The pressure-sensitive adhesive sheet disclosed herein exhibits excellent resistance to deformation even under severe environments such as high-temperature conditions and also has excellent impact resistance. By utilizing such a feature, the adhesive sheet can be preferably used for fixing members in various portable devices (portable apparatuses). For example, the present invention is suitable for fixing members (including various wiring) in portable electronic devices. Non-limiting examples of the portable electronic devices include a mobile phone, a smartphone, a tablet personal computer, a notebook personal computer, various wearable devices (e.g., a wrist-worn type worn on a wrist such as a watch, a modular type worn on a part of a body with a clip, a band, or the like, an eye-worn (eyewear) type including a spectacle type (a single-eye type, a binocular type, or a helmet type), a clothing type attached to a shirt, a sock, a hat, or the like in the form of an ornament, an ear-worn type attached to an ear such as an earphone, or the like), a digital camera, a digital video camera, an audio device (a portable music player, a recording pen, or the like), a calculator (a desktop calculator, or the like), a portable game device, an electronic dictionary, an electronic organizer, an electronic book, an in-vehicle-mounted information device, a portable radio, a portable television, a portable printer, a portable scanner, a portable modem, and the like. Non-limiting examples of portable devices other than portable electronic devices include mechanical watches, pocket watches, flashlights, hand glasses, card cases, and the like. In the present specification, "portable" is not sufficient if it is interpreted as being merely portable, and means having a level of portability at which an individual (a standard adult) can be relatively easily carried.

The pressure-sensitive adhesive sheet (typically, a double-sided pressure-sensitive adhesive sheet) disclosed herein can be used for fixing members constituting the portable electronic device as a bonding material processed into various shapes. For example, the organic EL display device can be preferably used for a liquid crystal display device or a portable electronic apparatus having an organic EL display. The adhesive sheet disclosed herein has excellent impact resistance, and therefore can be preferably used for fixing members in portable electronic devices equipped with organic EL displays, which are likely to require higher impact resistance. The pressure-sensitive adhesive sheet disclosed herein can be preferably used for fixing an elastic adherend in an electronic device (for example, a portable electronic device such as a smartphone) having a display unit (which may be a display unit of a liquid crystal display device or an organic EL display) such as a touch panel display, and in a device in which an elastic member such as a circuit board is folded and stored in an internal space for the purpose of enlarging a screen or the like. By using the pressure-sensitive adhesive sheet disclosed herein, the elastic adherend can be fixed in a folded state, and the fixed state can be maintained continuously even under severe environments such as high-temperature conditions. Accordingly, the elastic member, which is housed in a limited internal space in a portable electronic device in a bent state, can be accurately positioned by the adhesive sheet disclosed herein, and can be held in a stable fixed state. Further, as a material to be disposed inside the portable electronic device as described above, a material having polarity such as PET, PC (polycarbonate), and PI (polyimide) and rigidity may be mentioned. The adhesive sheet disclosed herein can adhere well to such a material (polar and rigid resin material). In a particularly preferred embodiment, the pressure-sensitive adhesive sheet disclosed herein can exert an excellent effect on a material to be adhered made of PET.

A preferred embodiment of the bonding material includes an embodiment having a width of 20mm or less (e.g., 15mm or less, and further less than 10 mm). The adhesive sheet disclosed herein can fix a member well even if used as a joining material in a region where the width is limited. The lower limit of the width of the pressure-sensitive adhesive sheet is not particularly limited, and is preferably 1mm or more (for example, 3mm or more) from the viewpoint of workability of the pressure-sensitive adhesive sheet.

The matters disclosed in this specification include the following.

(1) A portable electronic device is provided with a portable electronic device,

which includes a touch panel having a display section functioning also as an input section,

the member(s) constituting the aforementioned portable electronic apparatus are joined by means of an adhesive sheet,

the adhesive sheet comprises a foam base and an adhesive layer provided on at least one surface of the foam base,

the adhesive layer contains an acrylic polymer as a base polymer,

the adhesive layer has a storage modulus G' (65 ℃) at 65 ℃ of greater than 30000Pa.

(2) The portable electronic device according to the item (1), wherein a circuit board is stored in an inner space of the portable electronic device so as to be folded, and the adhesive sheet fixes the circuit board in a folded state.

(3) The portable electronic device according to the above (1) or (2), which has an organic EL display.

(4) The portable electronic device according to any one of the above (1) to (3), which is a mobile phone.

(5) The portable electronic device according to any one of the above (1) to (3), which is a smartphone.

(6) The portable electronic device according to any one of the above (1) to (3), which is a tablet computer.

(7) The portable electronic device according to any one of the above (1) to (3), which is a wearable device.

(8) The portable electronic device according to any one of the above (1) to (3), which is a portable game device.

(9) The portable electronic device according to any one of the above (1) to (3), which is an electronic dictionary.

(10) The portable electronic device according to any one of the above (1) to (3), which is an electronic book.

(11) An adhesive sheet comprising a foam base and an adhesive layer provided on at least one surface of the foam base,

the adhesive layer contains an acrylic polymer as a base polymer,

(12) The adhesive sheet according to the item (11), wherein the monomer component constituting the acrylic polymer contains more than 50% by weight of an alkyl (meth) acrylate having an alkyl group having 1 to 6 carbon atoms at an ester terminal.

(13) The pressure-sensitive adhesive sheet according to the above (11) or (12), wherein the monomer component constituting the acrylic polymer contains a carboxyl group-containing monomer.

(14) The adhesive sheet according to the item (13), wherein the amount of the carboxyl group-containing monomer in the monomer component is 1 to 10% by weight.

(15) The adhesive sheet according to any one of the above (11) to (14), wherein the adhesive composition for forming the adhesive layer contains an isocyanate-based crosslinking agent.

(16) The adhesive sheet according to any one of (11) to (15), wherein the adhesive layer contains at least one selected from a tackifier resin and a (meth) acrylic oligomer as a tackifier component in addition to the base polymer.

(17) The adhesive sheet according to any one of (11) to (16) above, wherein the adhesive layer contains a tackifier resin having a hydroxyl value of 70mgKOH/g or more.

(18) The adhesive sheet according to any one of the above (11) to (17), wherein the tackifier resin comprises a phenol-based tackifier resin.

(19) The adhesive sheet according to any one of the above (11) to (18), wherein the content of the tackifier resin in the adhesive layer is 10 parts by weight or more and 60 parts by weight or less with respect to 100 parts by weight of the base polymer.

(20) The pressure-sensitive adhesive sheet according to any one of the above (11) to (19), wherein the pressure-sensitive adhesive layer has a glass transition temperature determined from a peak temperature of tan δ in a range of-25 ℃ to 25 ℃.

(21) The adhesive sheet according to any one of (11) to (20) above, which has a total thickness of 100 μm or more.

(22) The adhesive sheet according to any one of the above (11) to (21), wherein the foam substrate is a polyolefin foam substrate.

(23) The adhesive sheet according to any one of the above (11) to (22), wherein the foam base has a density of 0.1 to 0.9g/cm ³ 。

(24) The adhesive sheet according to any one of the above (11) to (23), wherein the foam base has an average cell diameter of 10 to 200 μm.

(25) The adhesive sheet according to any one of the above (11) to (24), which is used for joining components of a portable electronic device.

(26) The adhesive sheet according to any one of the above (11) to (25), which is used for fixing a circuit board in a portable electronic device.

(27) The adhesive sheet according to any one of the above (11) to (26), which is used for fixing a circuit board housed in a folded state in a portable electronic device.

(28) The adhesive sheet according to any one of the above (11) to (27), which is used for joining components of a portable electronic device having an organic EL display.

(29) A portable device comprising the adhesive sheet according to any one of (11) to (28) above and a member joined by the adhesive sheet.

(30) The portable electronic apparatus described in (29) above, wherein a circuit board is housed in a folded state in an internal space of the portable electronic apparatus, and the adhesive sheet fixes the circuit board in the folded state.

Examples

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the examples. In the following description, "part" and "%" are based on weight unless otherwise specified.

Evaluation method

[ measurement of dynamic viscoelasticity ]

A pressure-sensitive adhesive layer having a thickness of 50 μm was formed on a release surface of a 38 μm PET film, which was release-treated on one side with a silicone release treatment agent, by applying a pressure-sensitive adhesive composition to the release surface and drying the pressure-sensitive adhesive composition at 100 ℃ for 2 minutes. By overlapping the adhesive layers having a thickness of 50 μm, a laminated adhesive sample having a thickness of about 2mm was produced. The laminated adhesive sample was punched out into a disk-like specimen having a diameter of 7.9mm by being sandwiched and fixed between parallel plates, and dynamic viscoelasticity was measured under the following conditions by a viscoelasticity tester (TA Instruments, manufactured by inc., model name "ARES"), and a storage modulus [ Pa ] at 65 ℃ and a loss modulus [ Pa ] at 65 ℃ were obtained. By this measurement method, the Tg (peak temperature of tan δ), the peak strength at the peak of tan δ (G "/G '), the 25 ℃ storage modulus (G' (25 ℃), and the 25 ℃ loss modulus (G" (25 ℃)) of the pressure-sensitive adhesive layer can also be obtained.

(measurement conditions)

Measurement mode: shear mode

Temperature range: -70 ℃ to 150 DEG C

Temperature increase rate: 5 ℃/min

Measurement frequency: 1Hz

[ gel fraction ]

With a porous polytetrafluoroethylene membrane having an average pore diameter of 0.2 μm (weight Wg) ₂ ) About 0.1g of the adhesive sample (weight Wg) ₁ ) Wrapped into a purse shape by kite string (weight Wg) ₃ ) The mouth is pricked. As the porous Polytetrafluoroethylene (PTFE) membrane, a product name "NITOFLON (registered trademark) NTF1122" (average pore diameter 0.2. Mu.m, porosity 75%, thickness 85 μm) available from Nindon electric Co., ltd., or a product equivalent thereof was used.

The pouch was immersed in 50mL of ethyl acetate, kept at room temperature (typically 23 ℃) for 7 days to elute only the sol component in the adhesive layer out of the film, and then the pouch was taken out and wiped off the ethyl acetate attached to the outer surface, dried at 130 ℃ for 2 hours, and the weight of the pouch (Wg) was measured ₄ ). Gel fraction F of adhesive layer _G Each value is obtained by substituting the following equation. The same method is also adopted in the examples described later.

GelRate F _G (％)＝[(Wg ₄ -Wg ₂ -Wg ₃ )/Wg ₁ ]×100

[ Z-axis direction deformation resistance test (65 ℃ 90% RH) ]

As shown in FIG. 2 (a), a PET film 52 having a thickness of 125 μm was laminated and fixed so as to cover the entire surface of a PC board 50 having a length of 30mm, a width of 10mm and a thickness of 2 mm. Further, a PET film 60 having a length of 70mm, a width of 10mm and a thickness of 125 μm was prepared, and the PC board 50 and the PET film 60 were overlapped so that one end in the longitudinal direction of the PC board 50 and the PET film 60 were aligned, and the PC board 50 and the PET film 60 were fixed in a state where the remaining portion of the PET film 60 protruded from the other end of the PC board 50. A commercially available double-sided adhesive tape (manufactured by Nindon electric Co., ltd. "No. 5000NS") was used for the fixation.

Adhesive sheet samples 70 were prepared by cutting the adhesive sheet with both adhesive faces protected by 2 release liners into a size of 3mm in width and 10mm in length. The surface of the PET film 52 laminated on the PC board 50 was set on the upper side, one release liner was peeled from the adhesive sheet sample 70, the width direction of the PC board 50 was aligned with the length direction of the adhesive sheet sample 70, and the adhesive sheet sample 70 was adhered and fixed to the upper surface of the PET film 52 such that both ends in the width direction of the adhesive sheet sample 70 were on the line 7mm and 10mm from the other end among the upper surface of the PET film 52 laminated and fixed to the PC board 50. The fixing is performed by reciprocating a 2kg roller once on the upper surface of the adhesive sheet sample 70 protected by the other release liner.

Next, the other release liner of the adhesive sheet sample 70 attached to the PET film 52 was peeled off in an environment of 23 ℃ and 50% rh, and as shown in fig. 2 (b), the protruding portion (length 40 mm) of the PET film 60 fixed to the PC board 50, which protruded from the PC board 50, was folded back toward the PC board 50 side, the adhesive sheet sample 70 was aligned with the other end (free end) of the PET film 60, and the other end of the folded PET film 60 was fixed to the upper surface of the PET film 52 on the PC board 50 via the adhesive sheet sample 70 by pressure bonding using a press under conditions of 0.5MPa and 0.5 seconds. After the pressure-bonding, the sheet was left to stand in an environment of 65 ℃ 90% rh for 72 hours to evaluate whether or not the PET film 60 was peeled from the adhesive sheet sample piece 70 as the Z-axis direction deformation resistance (65 ℃ 90% rh). The adhesive state between the adhesive sheet sample sheet 70 and the PET film 60 was judged as "good", and the peeling of the PET film 60 as shown in fig. 2 (c) was judged as "bad".

This evaluation method makes it possible to evaluate the deformation resistance under high-temperature and high-humidity conditions including substantially only the peeling load in the thickness direction (Z-axis direction) of the adhesive sheet, unlike the conventional evaluation of the repulsion resistance, and makes it possible to evaluate the continuous deformation resistance by observing the pressure-sensitive adhesive sheet in one step over time.

[ impact resistance ]

The pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet) whose pressure-sensitive adhesive surface was protected by a release liner was punched out into a frame shape having an outer diameter of 24.5mm square at a width of 2mm to obtain a sash-shaped pressure-sensitive adhesive sheet. Further, a stainless steel plate having a hole opened in the center of a square having a thickness of 2mm and an outer shape of 50mm × 50mm and a square PET plate (having an outer shape of 25mm square and a thickness of 2 mm) were prepared, and a sash-shaped adhesive sheet with a release liner removed was disposed therebetween, and pressure-bonded under conditions of 62N and 10 seconds so as to uniformly apply pressure, whereby the stainless steel plate and the PET plate were fixed by the sash-shaped adhesive sheet. The mixture was allowed to stand at 50 ℃ for 2 hours, and then taken out and returned to 23 ℃. This was used as a sample for evaluation. A cylindrical measuring table having a length of 50mm, an outer diameter of 49mm and an inner diameter of 43mm was mounted on a base of a DuPont impact tester (manufactured by Toyo Seiki Seisaku-Sho Ltd.). The evaluation sample was placed on a square PET plate as the lower side. The evaluation samples were prepared as follows: the upper stainless steel plate is supported by the measurement table, and the lower PET plate is fitted into a hollow portion in the measurement table in a state of being bonded to the stainless steel plate by the window frame-shaped adhesive sheet. A shot core (shot type) made of stainless steel having a 3.1mm tip radius was placed on a PET plate on the lower side of the evaluation sample, and the weight was dropped onto the shot core under the following conditions (weight and drop height) at 23 ℃ and 50% RH. The weight and the weight drop height gradually change the conditions in such a way that the energy increases from the condition of minimum energy. The weight drop height was increased at 50mm intervals. When the weight was changed, the weight drop test was performed by setting the conditions (weight x weight drop height) under which the energy did not overlap, without measuring the measured energy (energy obtained from the weight of the weight and the weight drop height).

The energy (J) under the previous condition that separation between the stainless steel plate and the PET plate occurred was calculated from the weight (load) and the falling height, and recorded as a measured value of the impact resistance. When the measured value is 0.2J or more, the impact resistance is excellent.

[ evaluation test for holding force at high temperature ]

The release liner covering one adhesive surface of the double-sided adhesive sheet was peeled off and attached to a PET film having a thickness of 50 μm to back the sheet. The backed adhesive sheet was cut into a size of 10mm in width and 100mm in length to prepare a measurement sample. The release liner covering the other adhesive surface of the above measurement sample was peeled off, and the other adhesive surface was pressure-bonded to a bakelite plate as an adherend by reciprocating a 2kg roller 1 time. Thereafter, the length of the bond to the bakelite plate was set to 20mm (therefore, the bonding area was 200 mm) ² :10mm width x 20mm length). The measurement sample thus attached to the adherend was left hanging and left standing at 80 ℃ for 30 minutes, and then a load of 1kg was applied to the free end of the measurement sample, and left standing at 80 ℃ for 1 hour in a state where the load was applied. The case where the measurement sample was held on the adherend after 1 hour was judged as "acceptable", and the case where the measurement sample was peeled off from the adherend within 1 hour and dropped was judged as "unacceptable".

In the case of a single-sided pressure-sensitive adhesive sheet, the backing of the PET film is not necessary.

[ Low-temperature adhesive Strength ]

A PET film having a thickness of 50 μm was attached to one adhesive surface of the double-sided adhesive sheet in an environment of measuring 23 ℃ and 50% RH, and the sheet was backed and cut into a size of 20mm in width and 100mm in length to prepare a measurement sample. The other adhesive surface of the above measurement sample was pressure-bonded to the surface of a stainless steel plate (SUS 304BA plate) by reciprocating a 2kg roller 1 time at 23 ℃ and 50% RH. After leaving it under the same atmosphere for 30 minutes, the peel strength [ N/20mm ] was measured under conditions of a tensile speed of 1000 mm/minute and a peel angle of 180 degrees at 10 ℃ using a universal tensile compression tester. It is recorded as low temperature adhesion. As the universal tensile compression tester, a tensile compression tester manufactured by Minebea Mitsumi, inc., TG-1kN, or a product equivalent thereof was used. In the case of a single-sided pressure-sensitive adhesive sheet, the backing of the PET film is not necessary.

< example 1 >

95 parts of BA and 5 parts of AA as monomer components and 233 parts of ethyl acetate as a polymerization solvent were charged into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen-introducing tube, a reflux condenser and a dropping funnel, and stirred for 2 hours while introducing nitrogen. After oxygen in the polymerization system was thus removed, 0.2 part of AIBN as a polymerization initiator was added thereto, and solution polymerization was carried out at 60 ℃ for 8 hours to obtain a solution of an acrylic polymer A1. The Mw of the acrylic polymer A1 was about 60X 10 ⁴ ～70×10 ⁴ And Mw/Mn is about 4 to 5.

To the solution of the acrylic polymer A1, 30 parts of a tackifier resin B1 (product name "YS polymer S145", YASUHARA chemcal co., ltd. Manufactured, terpene phenol resin, softening point 145 ℃, hydroxyl value 70 to 110 mgKOH/g), 2 parts (solid content conversion) of an isocyanate-based crosslinking agent (trade name "CORONATE L", 75% ethyl acetate solution of trimethylolpropane/tolylene diisocyanate trimer adduct, manufactured by toyobo co.), 0.01 part (solid content conversion) of an epoxy-based crosslinking agent (trade name "TETRAD-C", 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane, manufactured by mitsubishi CHEMICAL corporation) were mixed and stirred with 100 parts of the acrylic polymer to prepare an adhesive composition of this example.

2 commercially available release liners (trade name "SLB-80W3D", manufactured by Takara Shuzo paper Co., ltd.) were prepared, and one surface (release surface) of each of these release liners was coated with an adhesive composition so that the thickness after drying was 40 μm, and the adhesive composition was dried at 100 ℃ for 2 minutes to thereby form a release surface of each of the 2 release linersThe adhesive layers are formed separately. These pressure-sensitive adhesive layers were respectively bonded to a polyethylene foam sheet (thickness 200 μm, density 0.43 g/cm) having both surfaces subjected to corona discharge treatment ³ 10% compressive strength (C) ₁₀ ) 330kPa, 25% compressive strength (C) ₂₅ ) 942kPa, 30% compressive strength (C) ₃₀ ) 1235kPa, average bubble diameter 55 μm). The release liner remains directly on the pressure-sensitive adhesive layer and protects the surface (pressure-sensitive adhesive surface) of the pressure-sensitive adhesive layer. The resulting structure was passed through a 80 ℃ laminator (0.3 MPa, speed 0.5 m/min) 1 time, and then cured in an oven at 50 ℃ for 1 day. Thus, the pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet with foam substrate) of this example was obtained.

< examples 2 to 5 >

A double-sided adhesive sheet with a foam base material was obtained in each example in the same manner as in example 1 except that the thickness of the adhesive layer and the thickness of the foam base material were changed.

< example 6 >

Basically the same operation as in example 1 was carried out except that the monomer composition was changed to 100 parts of BA, 3 parts of VAc, 5 parts of AA and 0.1 part of HEA and toluene was used as a polymerization solvent, to obtain Mw 50X 10 ⁴ ～60×10 ⁴ A solution of the acrylic polymer A2.

To the solution of the acrylic polymer A2, 35 parts of a tackifier resin and 2 parts (in terms of solid content) of an isocyanate-based crosslinking agent (trade name "CORONATE L", manufactured by tokyo co., ltd.) were added to 100 parts of the acrylic polymer, and the mixture was stirred and mixed to prepare an acrylic adhesive composition of this example.

As the tackifier RESIN, 15 parts of tackifier RESIN B2 (product name "SURILITE RESIN PR-12603N", manufactured by Sumitomo Bakko Corp., terpene-modified phenolic RESIN having a softening point of 130 to 140 ℃ and a hydroxyl value of 1 to 20 mgKOH/g), 10 parts of tackifier RESIN B3 (product name "HARITACK SE10", harima Chemicals Group, manufactured by Inc., hydrogenated rosin glycerin ester having a softening point of 75 to 85 ℃ and a hydroxyl value of 25 to 40 mgKOH/g), and 10 parts of tackifier RESIN B4 (product name "HARITACK PCJ", harima Chemicals Group, manufactured by Inc., polymerized rosin ester having a softening point of 118 to 128 ℃) were used.

A pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet with foam substrate) having pressure-sensitive adhesive layers of 25 μm thickness on both sides of a foam substrate (thickness 150 μm) was obtained in the same manner as in example 2, except that the acrylic pressure-sensitive adhesive composition was used.

< example 7 >

Mw 44X 10 was obtained in substantially the same manner as in example 6 except that the monomer composition was changed to 70 parts of BA, 30 parts of 2EHA, 3 parts of AA and 0.05 part of 4-HBA ⁴ A solution of the acrylic polymer A3.

To the solution of the acrylic polymer A3, 30 parts of a tackifier resin B5 (product name "Pensel D-125", manufactured by Seawa chemical Co., ltd., rosinate-based resin, softening point 120 to 130 ℃) and 3 parts of an isocyanate-based crosslinking agent (product name "CORONATE L", manufactured by Caoton chemical Co., ltd.) (in terms of solid content) were added and mixed with stirring to prepare an acrylic adhesive composition of this example, based on 100 parts of the acrylic polymer.

An adhesive sheet (double-sided adhesive sheet with a foam substrate) having adhesive layers with a thickness of 25 μm on both sides of a foam substrate (thickness 150 μm) was obtained in the same manner as in example 2 except that the acrylic adhesive composition was used.

< example 8 >

Using the adhesive composition prepared in example 1, a PET film having a thickness of 50 μm was used as a substrate in place of the foam substrate, and adhesive layers having a thickness of 50 μm were formed on both sides of the PET film substrate to obtain a double-sided adhesive sheet with a PET film substrate according to this example.

For the adhesive sheets of the respective examples, a storage modulus at 65 ℃ [ Pa ], a loss modulus at 65 ℃ [ Pa ], a gel fraction [% ], a Z-axis direction deformation resistance evaluation test (65 ℃ 90% RH), an impact resistance [ J ], a high-temperature holding power evaluation test, and a low-temperature adhesive strength [ N/20mm ] were measured. The obtained results are shown in table 1 together with the summary of the adhesive composition and the sheet structure.

[ Table 1]

TABLE 1

* Parts per 100 parts of acrylic polymer

As shown in table 1, the adhesive sheets of examples 1 to 5, which had an adhesive layer having a storage modulus at 65 ℃ of more than 30000 and a foam base, were acceptable in the evaluation of the Z-axis direction deformation resistance under high temperature and high humidity conditions, and also had excellent impact resistance. The pressure-sensitive adhesive sheets of examples 1 to 5 also passed the 80 ℃ high temperature holding power test result, and had excellent 10 ℃ low temperature adhesive strength. On the other hand, in examples 6 and 7 in which the 65 ℃ storage modulus was 30000 or less, the above-mentioned evaluation result of the Z-axis direction deformation resistance was no good. In example 8 in which a PET film substrate was used instead of the foam substrate, the ratio of the results of the impact resistance test was 1 to 5. From the above results, it is clear that the pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer having a 65 ℃ storage modulus of more than 30000 and the foam base material exhibits excellent resistance to deformation even when used under severe environments and also has excellent impact resistance.

Specific examples of the present invention have been described above in detail, but these are merely examples and do not limit the claims of the patent application. The embodiments described in the claims of the patent application include various modifications and changes made to the specific examples illustrated above.

Description of the reference numerals

1. Adhesive sheet

10. Foamed base material

10A 1 st surface

10B No. 2

21. 1 st adhesive layer

22. 2 nd adhesive layer

21A 1 st adhesive surface

22A 2 nd adhesive surface

31. 32 Release liner

Claims

1. An adhesive sheet comprising a foam base and an adhesive layer provided on at least one surface of the foam base,

the adhesive layer comprises an acrylic polymer as a base polymer,

the monomer component constituting the acrylic polymer contains more than 50% by weight of an alkyl (meth) acrylate having an alkyl group having 1 to 6 carbon atoms at the ester end,

the tackifying resin of the adhesive layer is terpene phenol resin with a hydroxyl value of more than 70mgKOH/g,

the softening point of the tackifier resin is above 80 ℃, the content of the tackifier resin is above 25 weight parts and below 80 weight parts relative to 100 weight parts of the acrylic polymer,

2. The adhesive sheet according to claim 1, wherein the monomer component constituting the acrylic polymer comprises a carboxyl group-containing monomer.

3. The adhesive sheet according to claim 2, wherein the amount of the carboxyl group-containing monomer in the monomer component is 1 to 10% by weight.

4. The adhesive sheet according to claim 1 or 2, wherein the adhesive composition for forming the adhesive layer comprises an isocyanate-based crosslinking agent.

5. The adhesive sheet according to claim 1 or 2, wherein the content of the tackifier resin in the adhesive layer is 25 parts by weight or more and 60 parts by weight or less with respect to 100 parts by weight of the base polymer.

6. The adhesive sheet according to claim 1 or 2, wherein the total thickness is 100 μm or more.

7. The adhesive sheet according to claim 1 or 2, wherein the foam substrate is a polyolefin-based foam substrate.

8. The adhesive sheet according to claim 1 or 2, which is used for joining components of portable electronic devices.