CN110093107B - Adhesive sheet, method for producing same, and method for producing image display device - Google Patents

Abstract

The invention relates to an adhesive sheet, a method for manufacturing the same, and a method for manufacturing an image display device. The adhesive sheet (5) is a photocurable adhesive sheet comprising a layer-shaped adhesive composition containing a base polymer and a photocurable compound. The adhesive sheet (5) has a haze of 1% or less, an adhesive strength to glass of 1.5N/10mm or less, and a shear storage modulus at 25 ℃ of 0.15MPa or less. The adhesive sheet (5) has a glass transition temperature of-3 ℃ or lower when the polymerization rate is 99% by curing and a shear storage modulus of 0.16MPa or higher at a temperature of 25 ℃.

Description

Adhesive sheet, method for producing same, and method for producing image display device

Technical Field

The present invention relates to a photocurable adhesive sheet and a method for producing the same. The present invention also relates to a method for manufacturing an image display device using the adhesive sheet.

Background

Liquid crystal display devices and organic electroluminescence (organic EL) display devices are widely used as various image display devices such as mobile phones, smart phones, car navigation devices, personal computer monitors, and televisions. For the purpose of preventing damage to the image display panel due to impact from the outer surface, a front surface transparent plate (also referred to as a "cover window") such as a transparent resin plate or a glass plate may be provided on the viewing side of the image display panel. In recent years, devices having a touch panel on the viewing side of an image display panel have become widespread.

As a method of disposing a front surface transparent member such as a front surface transparent plate or a touch panel on the front surface of an image display panel, an "interlayer filling structure" in which an image display panel and a front surface transparent member are bonded to each other via an adhesive sheet has been proposed. An adhesive sheet may be provided between the touch panel and the front surface transparent plate. In the interlayer filling structure, the voids between the members are filled with the adhesive, so that the refractive index difference at the interface is reduced, and the deterioration of visibility due to reflection and scattering can be suppressed. In addition, in the interlayer filling structure, since the members are bonded and fixed by the adhesive sheet, there is an advantage that the front surface transparent member is less likely to be peeled off by an impact such as dropping, as compared with a case where the front surface transparent member is fixed only to the case.

A colored layer (decorative printed layer) may be formed on the periphery of the front surface transparent member for the purpose of decoration and light shielding. When an adhesive is applied to a transparent member having a decorative print layer, bubbles are likely to be generated around the printed step portion. By using a thick adhesive sheet, the adhesive sheet has a level difference absorption property, and can suppress troubles such as air bubble mixing. Further, the use of a thick adhesive sheet tends to improve impact resistance.

Since a thick adhesive sheet can be formed with a uniform thickness, solvent-free photocurable adhesives are widely used as an adhesive sheet for interlayer filling (see, for example, patent documents 1 and 2). In the case of using a photocurable pressure-sensitive adhesive, a pressure-sensitive adhesive sheet in which a part of the pressure-sensitive adhesive composition is in an uncured state (semi-cured) may be attached to an adherend and then photocured. In this method, the semi-cured adhesive sheet has high fluidity, and therefore, the step absorption at the time of bonding is high, and the adhesive holding force can be improved by the subsequent photo-curing.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2014-125524

Patent document 2: international publication No. 2013/161666

Disclosure of Invention

Problems to be solved by the invention

Conventionally, a front surface transparent member such as a cover window has a size larger than that of a display panel, and is bonded to a case with an adhesive tape or the like in a region outside an outer peripheral edge of the display panel. That is, the front surface transparent member is fixed by bonding to the case and bonding to the surface of the display panel with the interlayer filling adhesive sheet in combination.

In recent years, a display device has been made narrower and borderless, mainly for mobile devices such as smartphones. With the narrow framing and the borderless, the size of the display panel 10 is equal to or larger than the size of the front surface transparent member 7. In such a configuration, the case 9 and the front surface transparent member 7 cannot be fixed by an adhesive tape or the like, and the front surface transparent member 7 needs to be fixed by the adhesive sheet 5 for only interlayer filling (see fig. 2). Accordingly, the pressure-sensitive adhesive sheet for filling the interlayer is required to have higher adhesive strength and to be free from peeling due to an impact such as dropping in a wide temperature range.

When the size of the display panel is equal to or larger than the size of the front surface transparent member 7, the display panel may be sealed with a resin material to fill the gap 90 between the case 9 and the front surface transparent member 7. For example, the resin material in a molten state is poured into the gap 90, and then cooled to room temperature to solidify the resin, thereby performing sealing with the resin material. When the high-temperature resin is flowed into the gap 90, the front transparent member 7, the case 9, and the adhesive sheet 5 reach high temperatures in the vicinity of the gap 90, and are cooled when the resin is cured. Adhesive durability against deformation stress is required for the adhesive sheet 5 so that peeling between adherends does not occur even in the case where dimensional deformation occurs in the front surface transparent member, the case, and the like accompanying such a temperature change.

The conventional pressure-sensitive adhesive sheet for interlayer filling disclosed in patent document 1 and the like has a high glass transition temperature, and therefore has poor adhesiveness and impact resistance at low temperatures. On the other hand, the low glass temperature pressure-sensitive adhesive sheet disclosed in patent document 2 has low adhesive durability against deformation stress, and it is difficult to achieve both impact resistance at low temperature and durability against deformation stress at the time of heating and cooling such as resin sealing.

In view of the above circumstances, an object of the present invention is to provide an adhesive sheet having a level difference absorption property and excellent impact resistance in a wide temperature range and adhesive durability against deformation stress.

Means for solving the problems

The present invention relates to a pressure-sensitive adhesive sheet obtained by forming a pressure-sensitive adhesive containing a base polymer into a sheet form. The haze of the adhesive sheet is 1% or less.

In one embodiment, the pressure-sensitive adhesive sheet is a photocurable pressure-sensitive adhesive sheet obtained by forming a pressure-sensitive adhesive composition containing a base polymer and a photocurable compound into a layer. The photocurable adhesive sheet has an adhesive strength to glass of 1.5N/10mm or more and a shear storage modulus at 25 ℃ of 0.15MPa or less.

The photocurable adhesive composition is preferably in a so-called semi-cured state and has a polymerization rate of 90% to 98%. The glass transition temperature of the semi-cured adhesive sheet is preferably-5 ℃ or lower. The peak value of the loss tangent of the semi-cured adhesive sheet is preferably 1.6 or more.

In one embodiment of the adhesive sheet of the present invention, the polymerization rate of the adhesive composition is about 99% or more. Such a completely cured adhesive sheet can be obtained, for example, by photocuring the above semi-cured adhesive sheet. A fully cured adhesive sheet can also be obtained by photocuring a photocurable adhesive sheet having a polymerization rate of less than 90%.

The glass transition temperature of the fully cured adhesive sheet is preferably-3 ℃ or lower. Shear storage modulus G 'at temperature of 25 ℃ of fully cured adhesive sheet' _25℃ Preferably 0.16MPa or more. The peak top value of loss tangent of the fully cured adhesive sheet is preferably 1.5 or more. The semi-cured adhesive sheet preferably has a glass transition temperature and G 'when the polymerization degree is increased to 99% by curing' _25℃ Within the above range, and preferably, the peak top value of the loss tangent is within the above range.

As the base polymer contained in the pressure-sensitive adhesive sheet, for example, a polymer obtained by crosslinking an acrylic polymer chain with a urethane segment is used. In order to satisfy the above characteristics, the content of the urethane segment is preferably 3 to 30 parts by weight with respect to 100 parts by weight of the acrylic polymer chain. The weight average molecular weight of the urethane segment is preferably 4000 to 50000.

The base polymer obtained by crosslinking the acrylic polymer chain with the urethane segment is obtained, for example, by copolymerization of a monomer component constituting the acrylic polymer chain and a urethane (meth) acrylate having a (meth) acryloyl group at least at both ends. As the polyfunctional urethane (meth) acrylate, urethane di (meth) acrylates having (meth) acryloyl groups at both ends are preferred.

The weight average molecular weight of the urethane (meth) acrylate is preferably 4000 to 50000. The glass transition temperature of the urethane (meth) acrylate is preferably 0 ℃ or lower.

An adhesive sheet containing a base polymer obtained by crosslinking an acrylic polymer chain with a urethane segment is obtained, for example, by coating a composition containing an acrylic monomer and/or a partial polymer thereof and a urethane (meth) acrylate in a layer form on a substrate, and then irradiating the composition with active light to perform photocuring. In the adhesive composition, the content of the urethane (meth) acrylate is preferably 3 to 30 parts by weight based on 100 parts by weight of the total of the acrylic monomer and the partial polymer thereof.

The adhesive sheet of the present invention is used for bonding a transparent member in an image display device in which the transparent member is disposed on a viewing side surface, for example. In the case of using a semi-cured adhesive sheet, an image display device can be formed by bonding the adhesive sheet to the transparent member, and then irradiating the adhesive sheet with active light to perform photocuring of the adhesive sheet.

Effects of the invention

The pressure-sensitive adhesive sheet of the present invention has a low glass transition temperature after complete curing and a high shear storage modulus, and therefore can achieve both impact resistance such as dropping and adhesive durability against deformation stress in a wide temperature range. In addition, in a semi-cured state, the shear storage modulus is small, and therefore the level difference absorption is excellent. An image display device in which a cover window or the like is bonded to a viewing side surface using the adhesive sheet of the present invention has excellent adhesion reliability, and can be applied to a narrow frame or a frameless frame.

Drawings

Fig. 1 is a cross-sectional view showing an example of the structure of a release film-attached pressure-sensitive adhesive sheet.

Fig. 2 is a sectional view showing a configuration example of the image display device.

Fig. 3 and 4 are cross-sectional views showing examples of the laminated structure of the optical film with the adhesive sheet.

Fig. 5A is a photograph showing the case of the interlayer adhesiveness test, and fig. 5B is a photograph of an observation of a sample in which striped bubbles are generated in the interlayer adhesiveness test.

Fig. 6 is a schematic diagram showing the arrangement of the test pieces in the impact resistance test.

Reference numerals

5. Adhesive sheet

1. 2 mold release film

3. Polarizing plate

4. Adhesive sheet

6. Image display unit

10. Image display panel

7. Front surface transparent plate

9. Shell body

100. Image display device

Detailed Description

Fig. 1 shows a release film-equipped pressure-sensitive adhesive sheet in which release films 1 and 2 are temporarily attached to both surfaces of a pressure-sensitive adhesive sheet 5. Fig. 2 is a cross-sectional view showing an example of the configuration of the image display apparatus in which the front surface transparent plate 7 is fixed by using an adhesive sheet.

[ Properties of adhesive sheet ]

The pressure-sensitive adhesive sheet of the present invention is a pressure-sensitive adhesive sheet obtained by forming a pressure-sensitive adhesive into a sheet form. The adhesive sheet is a transparent adhesive sheet having a haze of 1.0% or less.

In one embodiment, the adhesive constituting the adhesive sheet is a photocurable adhesive containing a monomer or oligomer (photopolymerizable compound) having a photopolymerizable functional group. The polymerization rate of the photocurable adhesive sheet is preferably 90% to 98%. In other words, the photocurable adhesive sheet is preferably in a semi-cured state and contains 2 to 10 wt% of a photopolymerizable compound. The polymerization rate of the adhesive sheet was calculated from the weight of the adhesive sheet before and after heating when the sheet was heated at 130 ℃ for 3 hours according to the following formula. The polymerization ratio of the prepolymer to be described later is also calculated by the same method.

Polymerization rate (%) = weight after drying/weight before drying × 100

Shear storage modulus G 'at 25 ℃ of semi-cured adhesive sheet from the viewpoint of imparting level difference absorbency to the adhesive sheet and preventing air bubbles from being mixed in the vicinity of printing level difference' _25℃ Preferably 0.15MPa or less. On the other hand, G 'of the semi-cured pressure-sensitive adhesive sheet from the viewpoint of moldability and workability of the pressure-sensitive adhesive sheet' _25℃ Preferably 0.03MPa or more, more preferably 0.05MPa or more, and still more preferably 0.07MPa or more.

When photocuring (post-curing) is performed after bonding a semi-cured adhesive sheet to an adherend, the polymerization rate is increased by the polymerization reaction of the photopolymerizable compound, and the adhesive sheet is shearedThe storage modulus increases. Shear storage modulus G 'at 25 ℃ of a completely cured (when the polymerization degree is adjusted to 99% or more) pressure-sensitive adhesive sheet obtained by post-curing' _25℃ Preferably 0.16MPa or more. G 'through the adhesive sheet after complete curing' _25℃ The pressure is 0.16MPa or more, and the adhesion reliability is improved. Shear storage modulus G 'at 80 ℃ of the pressure-sensitive adhesive sheet after complete curing from the viewpoint of improving adhesive reliability at high temperature' _80℃ Preferably 0.11MPa or more.

On the other hand, G 'of the adhesive sheet after complete curing from the viewpoint of ensuring wettability by imparting appropriate tackiness to the adhesive sheet' _25℃ Preferably 1MPa or less, more preferably 0.5MPa or less, and still more preferably 0.4MPa or less. From the same viewpoint, G 'of the adhesive sheet after complete curing' _80℃ Preferably 0.6MPa or less, more preferably 0.4MPa or less, and still more preferably 0.3MPa or less.

The glass transition temperature of the semi-cured adhesive sheet is preferably-5 ℃ or lower. The glass transition temperature of the semi-cured adhesive sheet is preferably-25 ℃ or higher, more preferably-20 ℃ or higher, and still more preferably-18 ℃ or higher. The glass transition temperature of the pressure-sensitive adhesive sheet after complete curing is preferably-3 ℃ or lower. The glass transition temperature of the pressure-sensitive adhesive sheet after complete curing is preferably-20 ℃ or higher, more preferably-15 ℃ or higher, and still more preferably-13 ℃ or higher. When the glass transition temperature is within the above range, the pressure-sensitive adhesive sheet tends to have excellent impact resistance because it has appropriate tackiness even in a low temperature range.

The semi-cured adhesive sheet preferably has a peak value of loss tangent tan δ (i.e., tan δ at the glass transition temperature) of 1.6 or more, more preferably 1.7 or more, and still more preferably 1.8 or more. The peak value of tan δ of the pressure-sensitive adhesive sheet after complete curing is preferably 1.5 or more, more preferably 1.6 or more, and still more preferably 1.7 or more. A pressure-sensitive adhesive sheet having a large peak top value of tan δ tends to have a large tack behavior and excellent impact resistance.

The shear storage modulus G', the glass transition temperature, and the peak top value of tan δ of the pressure-sensitive adhesive sheet were determined by viscoelasticity measurement at a frequency of 1 Hz. The glass transition temperature is a temperature at which tan δ reaches a maximum (peak top temperature). tan delta is the ratio G '/G' of the loss modulus G 'to the storage modulus G'. The storage modulus G' corresponds to a portion stored as elastic energy when the material is deformed, and is an index representing the degree of hardness. The larger the storage modulus of the pressure-sensitive adhesive sheet, the higher the adhesive holding power, and peeling due to deformation tends to be suppressed. The loss modulus G "corresponds to a loss energy portion lost by internal friction or the like when the material is deformed, and indicates a degree of viscosity. the larger the tan δ, the stronger the tendency to be viscous, the deformation behavior becomes liquid behavior, and the rebound energy tends to decrease.

The upper limit of the peak top value of tan δ is not particularly limited, and is usually 3.0 or less, for any of the semi-cured adhesive sheet and the fully cured adhesive sheet. From the viewpoint of adhesive holding power, the peak value of tan δ is preferably 2.7 or less, more preferably 2.5 or less.

The adhesive strength of the semi-cured adhesive sheet is preferably 3N/10mm or more, more preferably 4N/10mm or more, and still more preferably 5N/10mm or more. When the adhesive strength of the semi-cured adhesive sheet is within the above range, peeling of the interface between the adherend and the adhesive sheet 5 can be suppressed when the release film 2 (light release film) temporarily attached to one surface of the adhesive sheet 5 is peeled off to bond the adhesive sheet 5 to the adherend and then the release film 1 (heavy release film) temporarily attached to the other surface is peeled off.

The adhesive strength of the pressure-sensitive adhesive sheet after complete curing is preferably 2N/10mm or more, more preferably 2.5N/10mm or more, and still more preferably 3N/10mm or more. When the adhesive strength of the pressure-sensitive adhesive sheet after complete curing is within the above range, the pressure-sensitive adhesive sheet can be prevented from peeling off from an adherend when stress due to deformation or impact due to dropping or the like occurs.

The adhesive strength was determined by a peeling test at a drawing speed of 60 mm/min and a peeling angle of 180 degrees, using a glass plate as an adherend. Unless otherwise specified, the adhesive force was measured at 25 ℃.

The adhesive strength at 65 ℃ of the semi-cured adhesive sheet is preferably 1N/10mm or more, more preferably 1.5N/10mm or more, and still more preferably 2N/10mm or more. The adhesive force at 65 ℃ of the adhesive sheet after complete curing is preferably 1N/10mm or more, more preferably 1.5N/10mm or more, and still more preferably 2N/10mm or more.

The thickness of the pressure-sensitive adhesive sheet is not particularly limited, and may be set according to the type, shape, and the like of the adherend. When a member having a printing step, such as a front surface transparent plate, is used as the adherend, the thickness of the pressure-sensitive adhesive sheet is preferably larger than the thickness of the printing step. The thickness of the adhesive sheet for bonding the front surface transparent plate (covering the window) is preferably 30 μm or more, more preferably 40 μm or more, and further preferably 50 μm or more. By increasing the thickness of the pressure-sensitive adhesive sheet, the level difference absorption property and impact resistance tend to be increased. The upper limit of the thickness of the pressure-sensitive adhesive sheet is not particularly limited, but is preferably 500 μm or less, more preferably 300 μm or less, and still more preferably 250 μm or less, from the viewpoint of productivity of the pressure-sensitive adhesive sheet and the like.

[ composition of adhesive ]

The composition of the pressure-sensitive adhesive is not particularly limited as long as the pressure-sensitive adhesive sheet of the present invention satisfies the above-mentioned properties, and a pressure-sensitive adhesive containing a polymer such as an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyamide, a polyvinyl ether, a vinyl acetate/vinyl chloride copolymer, a modified polyolefin, an epoxy type, a fluorine type, a natural rubber, or a synthetic rubber as a base polymer can be appropriately selected and used.

In particular, an acrylic pressure-sensitive adhesive containing an acrylic polymer as a base polymer is preferably used because it has excellent optical transparency, exhibits appropriate adhesive properties such as wettability, cohesiveness, and adhesiveness, and has excellent weather resistance and heat resistance. Among these, an acrylic base polymer having a structure in which an acrylic polymer chain is crosslinked by a urethane segment is preferable.

[ base Polymer ]

The acrylic polymer chains are crosslinked by urethane-based segments, thereby enabling high adhesive retention at low glass transition temperatures. In the base polymer, the content of the urethane segment is preferably 3 parts by weight or more with respect to 100 parts by weight of the acrylic polymer chain.

When the amount of the urethane segment is excessively increased, the tackiness of the adhesive decreases with an increase in the crosslinking density, and the level difference absorbability and the impact resistance may decrease. If the amount of the urethane segment is excessively increased, the transparency of the pressure-sensitive adhesive sheet may be decreased, and the haze may be increased. Therefore, the amount of the urethane segment in the base polymer is preferably 30 parts by weight or less, more preferably 25 parts by weight or less, relative to 100 parts by weight of the acrylic polymer chain.

< acrylic Polymer chain >

The acrylic polymer chain contains an alkyl (meth) acrylate as a main constituent monomer component. In the present specification, "(meth) acrylic acid" means acrylic acid and/or methacrylic acid.

As the alkyl (meth) acrylate, an alkyl (meth) acrylate in which the alkyl group has 1 to 20 carbon atoms is preferably used. In the alkyl (meth) acrylate, the alkyl group may have a branched or cyclic alkyl group.

Specific examples of the alkyl (meth) acrylate having a chain alkyl group include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, neopentyl (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, dodecyl (meth) acrylate, isotridecyl (meth) acrylate, tetradecyl (meth) acrylate, isotetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, isostearyl (meth) acrylate, and nonadecyl (meth) acrylate.

Specific examples of the alkyl (meth) acrylate having an alicyclic alkyl group include cycloalkyl (meth) acrylates such as cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, and cyclooctyl (meth) acrylate; (meth) acrylic esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth) acrylate; (meth) acrylates having three or more aliphatic hydrocarbon rings, such as tetrahydrodicyclopentadiene (meth) acrylate, tetrahydrodicyclopentadiene oxyethyl (meth) acrylate, tetrahydrotricyclopentadienyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl-2-adamantyl (meth) acrylate, and 2-ethyl-2-adamantyl (meth) acrylate.

The amount of the alkyl (meth) acrylate is preferably 40% by weight or more, more preferably 50% by weight or more, and still more preferably 60% by weight or more, based on the total amount of the monomer components constituting the acrylic polymer chain. From the viewpoint of adjusting the glass transition temperature (Tg) of the polymer chain to be within an appropriate range, the amount of the alkyl (meth) acrylate having a chain alkyl group having 4 to 10 carbon atoms in the acrylic polymer chain is preferably 30% by weight or more, more preferably 40% by weight or more, and still more preferably 45% by weight or more, relative to the total amount of the constituent monomer components. The monomer component constituting the acrylic polymer chain means a monomer component other than urethane (meth) acrylate or the like as a constituent component of the urethane segment.

The acrylic polymer chain may contain a hydroxyl group-containing monomer and a carboxyl group-containing monomer as constituent monomer components. The acrylic polymer chain has a tendency that transparency of the adhesive sheet can be improved and white turbidity in a high-temperature and high-humidity environment can be suppressed by having a hydroxyl group-containing monomer as a constituent monomer component.

Examples of the hydroxyl group-containing monomer include (meth) acrylic acid esters such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, and (4-hydroxymethylcyclohexyl) methyl (meth) acrylate. Among them, from the viewpoint of high compatibility with the urethane segment and improvement in transparency of the adhesive sheet, the acrylic polymer chain preferably contains a (meth) acrylate having a hydroxyalkyl group having 4 to 8 carbon atoms as a constituent monomer component.

The amount of the hydroxyl group-containing monomer is preferably 1 to 35% by weight, more preferably 3 to 30% by weight, and still more preferably 5 to 25% by weight, based on the total amount of the monomer components constituting the acrylic polymer chain.

Examples of the carboxyl group-containing monomer include acrylic monomers such as (meth) acrylic acid, carboxyethyl (meth) acrylate, and carboxypentyl (meth) acrylate, and itaconic acid, maleic acid, fumaric acid, and crotonic acid.

The acrylic polymer chain may contain a nitrogen-containing monomer as a constituent monomer component. Examples of the nitrogen-containing monomer include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole and vinyl

Vinyl monomers such as oxazole, vinyl morpholine, (meth) acryloyl morpholine, N-vinylcarboxylic acid amides and N-vinylcaprolactam, and cyano-containing acrylic monomers such as acrylonitrile and methacrylonitrile.

The acrylic polymer chain contains a high-polarity monomer such as a hydroxyl group-containing monomer or a carboxyl group-containing monomer as a constituent monomer component, whereby the cohesive force of the adhesive tends to be increased and the adhesive holding property at high temperatures tends to be improved. On the other hand, when the content of the highly polar monomer is too large, the glass transition temperature is increased, and the adhesiveness and impact resistance at low temperatures may be lowered. Therefore, the amount of the high-polarity monomer (the total of the hydroxyl group-containing monomer, the carboxyl group-containing monomer, and the nitrogen-containing monomer) relative to the total amount of the monomer components constituting the acrylic polymer chain is preferably 3 to 40% by weight, more preferably 5 to 35% by weight, and still more preferably 10 to 30% by weight. The amount of the nitrogen-containing monomer is preferably 1 to 25% by weight, more preferably 2 to 20% by weight, and still more preferably 3 to 15% by weight, based on the total amount of the monomer components constituting the acrylic polymer chain.

The acrylic polymer chain may contain, as monomer components other than those described above, a monomer containing an acid anhydride group, a caprolactone adduct of (meth) acrylic acid, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, a vinyl-based monomer such as vinyl acetate, vinyl propionate, styrene, α -methylstyrene, or the like; cyano group-containing acrylic monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing monomers such as glycidyl (meth) acrylate; glycol acrylic ester monomers such as polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, methoxyethylene glycol (meth) acrylate, and methoxypolypropylene glycol (meth) acrylate; acrylic ester monomers such as tetrahydrofurfuryl (meth) acrylate, fluorine-containing (meth) acrylate, polysiloxane (meth) acrylate, and 2-methoxyethyl (meth) acrylate.

The acrylic polymer chain may contain multifunctional monomers or oligomers. The polyfunctional compound has two or more polymerizable functional groups having an unsaturated double bond such as a (meth) acryloyl group or a vinyl group in one molecule. Examples of the polyfunctional compound include polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, bisphenol a ethylene oxide-modified di (meth) acrylate, bisphenol a propylene oxide-modified di (meth) acrylate, alkanediol di (meth) acrylate, tricyclodecane dimethanol di (meth) acrylate, ethoxylated isocyanuric acid triacrylate, pentaerythritol tri (meth) acrylate, pentaerythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, ethoxylated pentaerythritol tetra (meth) acrylate, dipentaerythritol poly (meth) acrylate, dipentaerythritol hexa (meth) acrylate, neopentyl glycol di (meth) acrylate, glycerol di (meth) acrylate, epoxy (meth) acrylate, butadiene (meth) acrylate, isoprene (meth) acrylate, and the like.

The acrylic polymer chain contains a polyfunctional monomer as a constituent monomer component, thereby introducing a branched structure (crosslinked structure) into the polymer chain. As described later, in the adhesive of the present invention, a crosslinked structure is introduced into the acrylic polymer chain through the urethane segment. When the amount of the cross-linked structure formed by the polyfunctional monomer component other than the urethane segment is increased, the low-temperature adhesive force of the adhesive may be reduced. Therefore, the amount of the polyfunctional compound (excluding the urethane acrylate) is preferably 3% by weight or less, more preferably 1% by weight or less, further preferably 0.5% by weight or less, and particularly preferably 0.3% by weight or less, based on the total amount of the monomer components constituting the acrylic polymer chain.

The acrylic polymer chain preferably contains the alkyl (meth) acrylate in the largest amount among the above monomer components. The properties of the adhesive sheet can be easily controlled by the kind of the monomer (main monomer) having the largest content among the constituent monomers of the acrylic polymer chain. For example, when the main monomer of the acrylic polymer chain is an alkyl (meth) acrylate having a chain alkyl group having 6 or less carbon atoms, the peak value of tan δ tends to be large, and the impact resistance tends to be improved. In particular in the case of acrylic acid C such as butyl acrylate ₄ When the alkyl ester is a main monomer, the peak top value of tan δ tends to be high. The amount of the alkyl (meth) acrylate having a chain alkyl group having 6 or less carbon atoms is preferably 30 to 80% by weight, more preferably 35 to 75% by weight, and still more preferably 40 to 70% by weight, based on the total amount of the monomer components constituting the acrylic polymer chain. In particular, the content of butyl acrylate as a constituent monomer component is preferably within the above range.

The theoretical Tg of the acrylic polymer chain is preferably-50 ℃ or higher. The theoretical Tg of the acrylic polymer chain is preferably-10 ℃ or lower, more preferably-20 ℃ or lower, and still more preferablyIs below-25 ℃. The theoretical Tg is the glass transition temperature Tg of the homopolymer of the monomer component consisting of the acrylic polymer chain _i And weight fraction W of each monomer component _i Calculated by the following Fox equation.

1/Tg＝Σ(W _i /Tg _i )

Tg is the glass transition temperature (unit: K) of the polymer chain, W _i The Tg is the weight fraction (copolymerization ratio on the weight basis) of the monomer component i constituting the segment _i The glass transition temperature (unit: K) of the homopolymer of the monomer component i. As the glass transition temperature of the homopolymer, a Polymer Handbook (Polymer Handbook), 3 rd edition (John Wiley) can be used&Sons, inc., 1989). The Tg of the homopolymer of the monomer not described in the above document may be the peak top temperature of loss tangent (tan δ) obtained by dynamic viscoelasticity measurement.

< urethane segment >

The urethane segment is a molecular chain having a urethane bond, and is covalently bonded to the acrylic polymer chain through both ends of the urethane segment, thereby introducing a crosslinked structure into the acrylic polymer chain.

(Structure of urethane segment)

The urethane-based segment typically comprises a polyurethane chain obtained by reacting a diol with a diisocyanate. From the viewpoint of obtaining a pressure-sensitive adhesive that can achieve both low-temperature adhesiveness and high-temperature holding power, the molecular weight of the polyurethane chain in the urethane segment is preferably 4000 to 50000, more preferably 4500 to 40000, and still more preferably 5000 to 30000.

The larger the molecular weight of the polyurethane chain in the urethane-based segment is, the longer the distance between the crosslinking points of the acrylic polymer chain is. When the molecular weight of the polyurethane chain is too small and the distance between the crosslinking points is short, the storage modulus increases as the cohesive force increases. This reduces the tackiness of the pressure-sensitive adhesive sheet and decreases tan δ, which tends to reduce the level difference absorption property and impact resistance. When the molecular weight of the polyurethane chain is too large and the distance between the crosslinking points is long, the storage modulus may be small and the adhesive holding force may be insufficient. When the molecular weight of the polyurethane chain is within the above range, the binder has appropriate cohesiveness, and therefore, impact resistance and adhesive holding power can be simultaneously achieved.

Examples of the diol for forming a polyurethane chain include low molecular weight diols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, and hexamethylene glycol; high molecular weight polyols such as polyester polyols, polyether polyols, polycarbonate polyols, acrylic polyols, epoxy polyols, caprolactone polyols, and the like.

Polyether polyols are obtained by ring-opening addition polymerization of alkylene oxides in polyols. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and tetrahydrofuran. Examples of the polyhydric alcohol include the above-mentioned diols, glycerin, and trimethylolpropane.

The polyester polyol is a polyester having a hydroxyl group at the end, and is obtained by reacting a polybasic acid with a polyhydric alcohol in such a manner that the alcohol equivalent is in excess relative to the carboxylic acid equivalent. The polybasic acid component and the polyhydric alcohol component constituting the polyester polyol are preferably a combination of a dibasic acid and a diol.

Examples of the dibasic acid component include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and the like; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, and eicosanedioic acid; anhydrides of these dicarboxylic acids, lower alcohol esters, and the like.

Examples of the diol component include: ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, and the like.

Examples of the polycarbonate polyol include polycarbonate polyols obtained by polycondensation of a diol component with phosgene; polycarbonate polyols obtained by ester exchange condensation of a diol component with a carbonic acid diester such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, ethylbutyl carbonate, ethylene carbonate, propylene carbonate, diphenyl carbonate, or dibenzyl carbonate; and a copolymerized polycarbonate polyol obtained by using two or more polyol components; polycarbonate polyols obtained by subjecting the above-mentioned various polycarbonate polyols and a carboxyl group-containing compound to an esterification reaction; polycarbonate polyols obtained by etherification of the above-mentioned various polycarbonate polyols with a hydroxyl group-containing compound; polycarbonate polyols obtained by subjecting the above-mentioned various polycarbonate polyols and an ester compound to an ester exchange reaction; polycarbonate polyols obtained by subjecting the above-mentioned various polycarbonate polyols and a hydroxyl group-containing compound to an ester exchange reaction; polyester-based polycarbonate polyols obtained by polycondensation of the above-mentioned various polycarbonate polyols with dicarboxylic acid compounds; and a copolymerized polyether polycarbonate polyol obtained by copolymerizing the above-mentioned various polycarbonate polyols with an alkylene oxide.

The polyacrylic polyol is obtained by copolymerizing a (meth) acrylate and a monomer component having a hydroxyl group. Examples of the monomer having a hydroxyl group include hydroxyalkyl esters of (meth) acrylic acid such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 2-hydroxypentyl (meth) acrylate; (meth) acrylic acid monoesters of polyhydric alcohols such as glycerin and trimethylolpropane; n-methylol (meth) acrylamide and the like. Examples of the (meth) acrylic acid ester include methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and cyclohexyl (meth) acrylate.

The polyacrylic polyol may contain a monomer component other than the above as a copolymerization component. Examples of the other comonomer components include unsaturated monocarboxylic acids such as (meth) acrylic acid; unsaturated dicarboxylic acids such as maleic acid, anhydrides thereof, and monoesters or diesters thereof; unsaturated nitriles such as (meth) acrylonitrile; unsaturated amides such as (meth) acrylamide and N-methylol (meth) acrylamide; vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether; α -olefins such as ethylene and propylene; halogenated α, β -unsaturated aliphatic monomers such as vinyl chloride and vinylidene chloride; and α, β -unsaturated aromatic monomers such as styrene and α -methylstyrene.

The diisocyanate for forming a polyurethane chain may be any of an aromatic diisocyanate and an aliphatic diisocyanate. Examples of the aromatic diisocyanate include 1,5-naphthalene diisocyanate, 4,4' -diphenylmethane diisocyanate (MDI), 2,2-bis (4-isocyanatophenyl) propane, tetramethyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2-chloro-1,4-phenyl diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, xylylene diisocyanate, 4,4' -diphenyl ether diisocyanate, 4,4' -diphenyl sulfoxide diisocyanate, 4,4' -diphenylsulfone diisocyanate, 4,4' -biphenyl diisocyanate, and the like. Examples of the aliphatic diisocyanate include butane-1,4-diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4' -diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, methylcyclohexane diisocyanate, and the like.

Derivatives of isocyanate compounds may also be used as diisocyanates. Examples of the derivative of the isocyanate compound include a dimer of polyisocyanate, a trimer of isocyanate (isocyanurate), polymeric MDI, an adduct with trimethylolpropane, a biuret modified product, an allophanate modified product, and a urea modified product. As the diisocyanate component, a urethane prepolymer having an isocyanate group at the end can be used.

(introduction of a crosslinked structure into an acrylic Polymer chain by urethane segment)

By using a compound having a functional group copolymerizable with the monomer components constituting the acrylic polymer chain at the end of the polyurethane chain or a compound having a functional group reactive with a carboxyl group, a hydroxyl group, or the like contained in the acrylic polymer chain at the end of the polyurethane chain, a crosslinked structure composed of a urethane segment can be introduced into the acrylic polymer chain. It is preferable to introduce a crosslinked structure formed of a urethane segment using a urethane di (meth) acrylate having a (meth) acryloyl group at both ends of a urethane chain because crosslinking points are easily introduced uniformly on an acrylic polymer chain and compatibility of the acrylic polymer chain and the urethane segment is excellent. For example, by copolymerizing a monomer component constituting the acrylic polymer chain with urethane di (meth) acrylate, a crosslinked structure formed of a urethane segment can be introduced into the acrylic polymer chain.

The urethane di (meth) acrylate having a (meth) acryloyl group at both ends is obtained, for example, by using a (meth) acrylic compound having a hydroxyl group in addition to a diol component in the polymerization of polyurethane. From the viewpoint of controlling the chain length (molecular weight) of the urethane segment, it is preferable to synthesize an isocyanate-terminated polyurethane by reacting a diol with a diisocyanate so that the isocyanate is excessive, and then add a (meth) acrylic compound having a hydroxyl group to react the terminal isocyanate group of the polyurethane with the hydroxyl group of the (meth) acrylic compound.

By reacting a polyol with a polyisocyanate compound in such a manner that the polyisocyanate compound is in excess, a polyurethane chain having an isocyanate group at the terminal is obtained. In order to obtain the isocyanate-terminated polyurethane, the diol component and the diisocyanate component may be used so that NCO/OH (equivalent ratio) is preferably 1.1 to 2.0, more preferably 1.15 to 1.5. The diisocyanate component may be additionally added after approximately equal amounts of the diol component and the diisocyanate component are mixed and reacted.

Examples of the (meth) acrylic compound having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyhexyl (meth) acrylate, methylolacrylamide, and hydroxyethylacrylamide.

As the urethane (meth) acrylate, commercially available products sold by various companies such as Mikan chemical industry, sinkian chemical industry, toyo Synthesis, kyoho chemical, nippon Chemicals, nippon Synthesis chemical industry, gentianshu industry, and Daicel allnex can be used. The weight average molecular weight of the urethane (meth) acrylate is preferably 4000 to 50000, more preferably 4500 to 40000, and further preferably 5000 to 30000.

The glass transition temperature of the urethane (meth) acrylate is preferably 0 ℃ or lower, more preferably-10 ℃ or lower, and still more preferably-20 ℃ or lower. By using a urethane (meth) acrylate having a low Tg, a pressure-sensitive adhesive having excellent low-temperature adhesive strength can be obtained even when the cohesive force of the base polymer is increased by introducing a crosslinked structure with a urethane segment. The lower limit of the glass transition temperature of the urethane (meth) acrylate is not particularly limited, but is preferably-100 ℃ or higher, more preferably-90 ℃ or higher, and still more preferably-80 ℃ or higher, from the viewpoint of obtaining a binder excellent in high-temperature holding power.

When a crosslinked structure formed of a urethane segment is introduced into an acrylic polymer chain using a urethane (meth) acrylate, the glass transition temperature of the urethane segment of the base polymer is substantially equal to the glass transition temperature of the urethane (meth) acrylate.

< preparation of base Polymer >

The polymer having the crosslinked structure formed by the urethane segment introduced into the acrylic polymer chain can be polymerized by various known methods. When a urethane (meth) acrylate is used as a constituent component of the urethane segment, a monomer component for constituting the acrylic polymer chain may be copolymerized with the urethane (meth) acrylate.

The amount of the urethane (meth) acrylate used is preferably 3 to 30 parts by weight, more preferably 4 to 25 parts by weight, based on 100 parts by weight of the monomer component constituting the acrylic polymer chain. By adjusting the amount of the urethane (meth) acrylate used, a base polymer having a urethane segment content within the above range can be prepared. When the content of the urethane segment is too small, the adhesive holding power of the adhesive sheet tends to decrease due to the decrease in the cohesive property of the base polymer. When the content of the urethane segment is too large, the tackiness of the pressure-sensitive adhesive sheet tends to decrease with an increase in the cohesive property of the base polymer, and the impact resistance tends to decrease.

As a polymerization method of the base polymer, photopolymerization is preferable. In photopolymerization, since a polymer can be prepared without using a solvent, a pressure-sensitive adhesive sheet having a large thickness can be uniformly formed without drying and removing the solvent when the pressure-sensitive adhesive sheet is formed. Further, photopolymerization is suitable for the formation of a semi-cured adhesive sheet because the degree of polymerization can be easily adjusted and polymerization can be restarted by re-irradiation with light.

In the preparation of the base polymer, the whole amount of the monomer component constituting the acrylic polymer chain and the whole amount of the urethane (meth) acrylate for introducing the crosslinked structure may be reacted at once or may be polymerized in multiple stages. As the method of carrying out the polymerization by multistage, the following method is preferred: the monomer having a monofunctional structure constituting the acrylic polymer chain is polymerized to form a prepolymer composition (prepolymerization), and a polyfunctional compound such as urethane di (meth) acrylate is added to a slurry of the prepolymer composition to polymerize the prepolymer composition with the polyfunctional monomer (main polymerization). The prepolymer composition is a partial polymer containing a polymer of low degree of polymerization and unreacted monomers.

By performing the preliminary polymerization of the constituent components of the acrylic polymer, branch points (crosslinking points) obtained by a polyfunctional compound such as urethane di (meth) acrylate can be uniformly introduced into the acrylic polymer chain. Further, a pressure-sensitive adhesive sheet can also be formed by applying a mixture (pressure-sensitive adhesive composition) of a low-molecular-weight polymer or a partial polymer and an unpolymerized monomer component onto a substrate and then performing main polymerization on the substrate.

Since a low-polymerization-degree composition such as a prepolymer composition has a low viscosity and is excellent in coatability, a method of applying an adhesive composition that is a mixture of a prepolymer composition and a polyfunctional compound and then performing main polymerization on a substrate can improve productivity of an adhesive sheet and can make the thickness of the adhesive sheet uniform. Further, by adjusting the polymerization rate of main polymerization, a semi-cured adhesive sheet having excellent level difference absorption properties can be formed.

[ adhesive sheet ]

As described above, a prepolymer composition having a low polymerization degree is prepared by prepolymerization, and a pressure-sensitive adhesive composition obtained by adding a polyfunctional compound or the like to the prepolymer composition is applied to a substrate in a layer form, and polymerization (main polymerization) of the pressure-sensitive adhesive composition on the substrate is carried out, whereby a semi-cured pressure-sensitive adhesive sheet can be obtained.

< prepolymerization >

The prepolymer composition can be prepared, for example, by polymerizing a composition obtained by mixing a monomer component constituting the acrylic polymer chain with a polymerization initiator. The prepolymer-forming composition may contain a polyfunctional compound (polyfunctional monomer or polyfunctional oligomer). For example, a part of the polyfunctional compound as a raw material of the polymer may be contained in the composition for forming a prepolymer, and the remaining part of the polyfunctional compound may be added after the polymerization of the prepolymer to perform main polymerization.

The prepolymer-forming composition preferably contains a photopolymerization initiator. Examples of the photopolymerization initiator include benzoin ether type photopolymerization initiators, acetophenone type photopolymerization initiators, α -ketol type photopolymerization initiators, aromatic sulfonyl chloride type photopolymerization initiators, photoactive oxime type photopolymerization initiators, benzoin type photopolymerization initiators, benzil type photopolymerization initiators, benzophenone type photopolymerization initiators, ketal type photopolymerization initiators, thioxanthone type photopolymerization initiators, and acylphosphine oxide type photopolymerization initiators.

In the polymerization, a chain transfer agent, a polymerization inhibitor (polymerization retarder), or the like may be used for the purpose of adjusting the molecular weight or the like. Examples of the chain transfer agent include thiols such as α -thioglycerol, lauryl mercaptan, glycidyl mercaptan, thioglycolic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and α -methylstyrene dimer.

The prepolymer-forming composition may contain a chain transfer agent and the like as necessary in addition to the monomer and the polymerization initiator. The polymerization initiator or chain transfer agent used in the preliminary polymerization is not particularly limited, and for example, the above photopolymerization initiator or chain transfer agent can be used.

The polymerization rate of the prepolymer is not particularly limited, but is preferably 3 to 50 wt%, more preferably 5 to 40 wt%, from the viewpoint of adjusting the viscosity suitable for coating on the substrate. The polymerization rate of the prepolymer can be adjusted to a desired range by adjusting the type and amount of the photopolymerization initiator, the irradiation intensity and irradiation time of active light such as UV light, and the like.

< preparation of adhesive composition >

In the prepolymer composition, the urethane (meth) acrylate, and if necessary, the remainder of the monomer components constituting the acrylic polymer chain, a polymerization initiator, a chain transfer agent, other additives, and the like are mixed to prepare an adhesive composition. The adhesive composition preferably has a viscosity suitable for coating on a substrate (e.g., from about 0.5Pa · s to about 20Pa · s). The viscosity of the adhesive composition can be adjusted to an appropriate range by adjusting the polymerization rate of the prepolymer, the amount of the urethane (meth) acrylate added, the composition, the molecular weight, the amount added of other components (for example, oligomer), and the like. For the purpose of adjusting viscosity or the like, a thickening additive or the like may be used.

The polymerization initiator or chain transfer agent used in the main polymerization is not particularly limited, and for example, the above photopolymerization initiator or chain transfer agent can be used. When the polymerization initiator used in the prepolymerization remains in the prepolymer composition without being deactivated, the addition of the polymerization initiator used in the main polymerization may be omitted.

(oligomer)

The adhesive composition may contain various oligomers for the purpose of adjusting the adhesive force of the adhesive sheet, adjusting the viscosity, and the like. As the oligomer, for example, an oligomer having a weight average molecular weight of about 1000 to about 30000 can be used. The oligomer is preferably an acrylic oligomer because of its excellent compatibility with the acrylic base polymer.

The acrylic oligomer contains an alkyl (meth) acrylate as a main constituent monomer component. Among them, an acrylic oligomer containing, as a constituent monomer component, a monomer of an alkyl (meth) acrylate having a chain alkyl group (a chain alkyl (meth) acrylate) and an alkyl (meth) acrylate having an alicyclic alkyl group (an alicyclic alkyl (meth) acrylate) is preferable. Specific examples of the chain alkyl (meth) acrylate and alicyclic alkyl (meth) acrylate are as exemplified above as the constituent monomers of the acrylic polymer chain.

The glass transition temperature of the acrylic oligomer is preferably 20 ℃ or higher, more preferably 30 ℃ or higher, and still more preferably 40 ℃ or higher. By using a low Tg base polymer having a cross-linked structure formed by a urethane segment and a high Tg acrylic oligomer in combination, the adhesive holding power of the adhesive sheet tends to be improved. The upper limit of the glass transition temperature of the acrylic oligomer is not particularly limited, but is usually 200 ℃ or lower, preferably 180 ℃ or lower, and more preferably 160 ℃ or lower. The glass transition temperature of the acrylic oligomer is calculated by the above Fox formula.

Among the alkyl (meth) acrylates exemplified above, methyl methacrylate is preferred as the chain alkyl (meth) acrylate because of its high glass transition temperature and excellent compatibility with the base polymer. As the alicyclic alkyl (meth) acrylate, tetrahydrodicyclopentadiene methacrylate, cyclohexyl acrylate and cyclohexyl methacrylate are preferable. That is, the acrylic oligomer preferably contains one or more selected from the group consisting of tetrahydrodicyclopentadiene acrylate, tetrahydrodicyclopentadiene methacrylate, cyclohexyl acrylate and cyclohexyl methacrylate, and methyl methacrylate as constituent monomer components.

The amount of the alicyclic alkyl (meth) acrylate is preferably 10 to 90 wt%, more preferably 20 to 80 wt%, and still more preferably 30 to 70 wt% based on the total amount of the monomer components constituting the acrylic oligomer. The amount of the chain alkyl (meth) acrylate is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, and still more preferably 30 to 70% by weight, based on the total amount of the monomer components constituting the acrylic oligomer.

The weight average molecular weight of the acrylic oligomer is preferably 1000 to 30000, more preferably 1500 to 10000, and further preferably 2000 to 8000. By using the acrylic oligomer having a molecular weight within this range, the adhesive strength and adhesive holding power of the adhesive tend to be improved.

The acrylic oligomer can be obtained by polymerizing the above monomer components by various polymerization methods. In the polymerization of the acrylic oligomer, various polymerization initiators can be used. In addition, a chain transfer agent may be used for the purpose of adjusting the molecular weight.

When an oligomer component such as an acrylic oligomer is contained in the pressure-sensitive adhesive composition, the content thereof is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight, and still more preferably 2 to 10 parts by weight, based on 100 parts by weight of the base polymer. When the content of the oligomer in the pressure-sensitive adhesive composition is within the above range, adhesiveness at high temperature and high-temperature holding power tend to be improved.

(silane coupling agent)

For the purpose of adjusting the adhesive force, a silane coupling agent may be added to the adhesive composition. When the silane coupling agent is added to the adhesive composition, the amount thereof is usually about 0.01 to about 5.0 parts by weight, preferably about 0.03 to about 2.0 parts by weight, based on 100 parts by weight of the base polymer.

(crosslinking agent)

The base polymer may have a crosslinked structure other than the above-mentioned polyfunctional compound as necessary. By containing a crosslinking agent in the adhesive composition, a crosslinked structure can be introduced into the base polymer. Examples of the crosslinking agent include compounds that react with functional groups such as hydroxyl groups and carboxyl groups contained in the polymer. Specific examples of the crosslinking agent include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and the like,

Oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, metal chelate crosslinking agents, and the like.

When the amount of the crosslinked structure formed of a substance other than the urethane segment is increased, the viscosity may be lowered and the impact resistance may be lowered. Therefore, the amount of the crosslinking agent used is preferably 3 parts by weight or less, more preferably 2 parts by weight or less, and further preferably 1 part by weight or less, based on 100 parts by weight of the base polymer.

(other additives)

The pressure-sensitive adhesive composition may contain additives such as a tackifier, a plasticizer, a softening agent, a deterioration inhibitor, a filler, a colorant, an ultraviolet absorber, an antioxidant, a surfactant, and an antistatic agent, in addition to the above-mentioned components.

< coating of adhesive composition and actual polymerization >

The photo-curing is performed by coating the adhesive composition on a substrate in a layer form and then irradiating active light. In the case of photocuring, it is preferable to provide a cover sheet on the surface of the coating layer and irradiate the adhesive composition with active light while sandwiching the adhesive composition between two sheets, thereby preventing inhibition of polymerization by oxygen.

As the substrate and the cover sheet used for forming the adhesive sheet, any suitable substrate may be used. The substrate and the cover sheet may be release films having a release layer on the surface in contact with the adhesive sheet.

As the film base material of the release film, films containing various resin materials can be used. Examples of the resin material include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, polyarylate resins, and polyphenylene sulfide resins. Among them, polyester resins such as polyethylene terephthalate are particularly preferable. The thickness of the film substrate is preferably 10 to 200 μm, more preferably 25 to 150 μm. Examples of the material of the release layer include silicone release agents, fluorine-containing release agents, long-chain alkyl release agents, fatty acid amide release agents, and the like. The release layer typically has a thickness of about 10nm to about 2000nm.

As a method for coating the adhesive composition on the substrate, various methods such as a roll coating method, a roll-and-scrape coating method, a gravure coating method, a reverse coating method, a roll brush method, a spray coating method, a dip roll coating method, a bar coating method, a blade coating method, an air knife coating method, a curtain coating method, a lip die coating method, a die coater, and the like can be used.

The adhesive composition applied in a layer form to a substrate is irradiated with actinic light to effect main polymerization. In the main polymerization, unreacted monomer components in the prepolymer composition react with urethane (meth) acrylate to obtain a base polymer having a crosslinked structure formed of urethane segments introduced into an acrylic polymer chain. By adjusting the polymerization rate in the main polymerization, a part of the polymerizable compound remains unreacted, whereby a semi-cured adhesive sheet can be obtained.

The active light is selected according to the type of the polymerizable component such as a monomer or urethane (meth) acrylate, the type of the photopolymerization initiator, and the likeUltraviolet and/or short-wavelength visible light may be generally used. The cumulative amount of light irradiated is preferably about 100mJ/cm ² About 5000mJ/cm ² . The light source used for the light irradiation is not particularly limited as long as it can irradiate light in a wavelength range in which the photopolymerization initiator contained in the adhesive composition has sensitivity, and an LED light source, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a metal halide lamp, a xenon lamp, or the like is preferably used. After the polymerization rate reaches a predetermined polymerization rate, the light irradiation is stopped, whereby the polymerization rate can be adjusted to a predetermined range. As described above, the polymerization rate of the semi-cured adhesive sheet is preferably 90% to 98%.

By bonding the release films 1 and 2 to the surface of the semi-cured adhesive sheet 5, an adhesive sheet having release films temporarily attached to both sides as shown in fig. 1 can be obtained. Release films used as substrates or cover sheets in the formation of adhesive sheets can be used as they are as release films 1 and 2.

When the release films 1 and 2 are provided on both surfaces of the psa sheet 5, the thickness of one release film 1 may be the same as or different from the thickness of the other release film 2. The peeling force when peeling the release film temporarily attached to one side from the psa sheet 5 may be the same as or different from the peeling force when peeling the release film temporarily attached to the other side from the psa sheet 5. When the two are different in peel strength, the release film 2 (light release film) having a relatively small peel strength is peeled from the pressure-sensitive adhesive sheet 5 and then bonded to the first adherend, and the release film 1 (heavy release film) having a relatively large peel strength is peeled off and bonded to the second adherend, which is excellent in workability.

[ image display apparatus ]

The adhesive sheet of the present invention can be used for bonding various transparent members and opaque members. The kind of the adherend is not particularly limited, and various resin materials, glass, metal, and the like can be cited. The pressure-sensitive adhesive sheet of the present invention has high transparency, and is therefore suitable for bonding optical members such as image display devices. In particular, the adhesive sheet of the present invention is excellent in level difference absorption and impact resistance, and therefore is preferably used for bonding a transparent member such as a front surface transparent plate or a touch panel to a viewing side surface of an image display device.

Fig. 2 is a cross-sectional view showing an example of a laminated structure of an image display device in which a front transparent plate 7 is bonded to a viewing-side surface of an image display panel 10 via an adhesive sheet 5. The image display panel 10 includes a polarizing plate 3 bonded to a surface of an image display unit 6 such as a liquid crystal unit or an organic EL unit on the side of viewing through an adhesive sheet 4. The front-surface transparent plate 7 has a printed layer 76 provided on the periphery of one surface of the transparent flat plate 71. The transparent plate 71 is made of, for example, a transparent resin plate such as acrylic resin or polycarbonate resin, or a glass plate. The transparent plate 71 may have a touch panel function. As the touch panel, any type of touch panel such as a resistive type, a capacitive type, an optical type, an ultrasonic type, or the like is used.

The polarizing plate 3 provided on the surface of the image display panel 10 and the printed layer 76-formed surface of the front transparent plate 7 are bonded via an adhesive sheet 5. The order of application is not particularly limited, and the adhesive sheet 5 may be applied to the image display panel 10 first, or the adhesive sheet 5 may be applied to the front surface transparent plate 7 first. In addition, the two may be bonded at the same time. From the viewpoint of workability of bonding and the like, it is preferable to peel off one release film (light release film) 2, bond the exposed surface of the adhesive sheet 5 to the image display panel 10, peel off the other release film 1 (heavy release film), and bond the exposed surface of the adhesive sheet to the front surface transparent plate 7.

After the adhesive sheet 5 and the front surface transparent plate 7 are bonded to each other, it is preferable to perform deaeration for removing air bubbles in the vicinity of an uneven portion such as the interface between the adhesive sheet 5 and the flat plate 71 portion of the front surface transparent plate 7 and the printed layer 76. As the defoaming method, an appropriate method such as heating, pressurization, and depressurization can be employed. For example, it is preferable to bond the substrates while suppressing mixing of bubbles under reduced pressure and heating, and then to apply pressure while heating by autoclave treatment or the like for the purpose of suppressing delayed foaming or the like. When defoaming is performed by heating, the heating temperature is usually about 40 ℃ to about 150 ℃. When the pressurization is carried out, the pressure is usually about 0.05MPa to about 2MPa.

The adhesive sheet of the present invention has a shear storage modulus of 0.15MPa or less in a semi-cured state, and therefore easily follows the step shape of the print layer 76 and the like, and therefore, the generation of voids can be suppressed.

The semi-cured adhesive sheet is bonded to an adherend such as a front surface transparent plate, and then photocuring (post-curing) of the adhesive sheet is performed. The polymerization rate is increased by the post-curing, and the storage modulus of the adhesive sheet is increased, and the adhesion reliability between the adhesive sheet 5 and the front surface transparent member 70 is improved. The polymerization rate of the pressure-sensitive adhesive sheet after post-curing is preferably 99% or more.

When the gap 90 exists between the case 9 and the front transparent plate 7, it is preferable to fill the gap 90 with a resin material or the like and seal the gap. As described above, the adhesive sheet after post-curing has a large shear storage modulus, and therefore has excellent adhesion reliability over a wide temperature range. Therefore, even when stress deformation occurs at the bonding interface of the adhesive sheet due to a temperature change at the time of sealing with a resin material or the like, peeling at the bonding interface can be suppressed. In addition, the pressure-sensitive adhesive sheet after post-curing has a low glass transition temperature and a large peak top value of tan δ, and therefore has excellent impact resistance in a wide temperature range, and is less likely to peel off due to impact such as dropping.

As described above, when the pressure-sensitive adhesive sheet is in a semi-cured state containing an unreacted photopolymerizable compound, the shear storage modulus is small and the step absorption property is excellent. Therefore, it is preferably used for bonding to the surface of an image display panel such as a front surface transparent plate or a touch panel having a printing step.

The description has been focused on a method of laminating a front surface transparent plate having a print step caused by a print layer with a semi-cured adhesive sheet and then post-curing the laminated sheet, but in the case where the step absorption property is not required, a completely cured adhesive sheet can be laminated to an adherend. For example, a psa composition is applied in a layer form to a substrate and then subjected to main polymerization so that the polymerization rate is 99% or more, thereby obtaining a psa sheet with the psa completely cured. Even in the case of using a completely cured adhesive sheet, peeling due to stress deformation or impact such as dropping is less likely to occur in the same manner as in the case of performing post-curing after bonding using a semi-cured adhesive sheet, and adhesion with excellent reliability can be achieved.

[ optical film with adhesive sheet ]

The pressure-sensitive adhesive sheet of the present invention can be used as a film with a pressure-sensitive adhesive for fixing the pressure-sensitive adhesive sheet to an optical film or the like, in addition to the form in which release films are temporarily attached to both surfaces as shown in fig. 1. For example, in the embodiment shown in fig. 3, the release film 1 is temporarily attached to one surface of the adhesive sheet 5, and the polarizing plate 3 is fixed to the other surface of the adhesive sheet 5. In the embodiment shown in fig. 4, an adhesive sheet 4 is further provided on the polarizing plate 3, and the release film 2 is temporarily attached thereon.

In the case where an optical film such as a polarizing plate is bonded to the adhesive sheet in advance, the release film 1 temporarily attached to the surface of the adhesive sheet 5 is peeled off and bonded to the front surface transparent member, and then the adhesive sheet 5 is post-cured as necessary.

Examples

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[ production of acrylic acid oligomer ]

60 parts by weight of tetrahydrodicyclopentadiene methacrylate (DCPMA), 40 parts by weight of Methyl Methacrylate (MMA), 3.5 parts by weight of α -thioglycerol as a chain transfer agent, and 100 parts by weight of toluene as a polymerization solvent were mixed, and stirred at 70 ℃ for 1 hour under a nitrogen atmosphere. Then, 2,2' -Azobisisobutyronitrile (AIBN), 0.2 part by weight, was charged as a thermal polymerization initiator, reacted at 70 ℃ for 2 hours, and then heated to 80 ℃ for 2 hours. Then, the reaction solution was heated to 130 ℃ to dry and remove toluene, chain transfer agent and unreacted monomer, thereby obtaining a solid acrylic oligomer. The weight average molecular weight of the acrylic oligomer was 5100.

[ example 1]

(polymerization of prepolymer)

A prepolymer composition was obtained by blending 52.8 parts by weight of Butyl Acrylate (BA), 10.9 parts by weight of cyclohexyl acrylate (CHA), 9.7 parts by weight of N-vinyl-2-pyrrolidone (NVP), 14.8 parts by weight of 4-hydroxybutyl acrylate (4 HBA), 11.8 parts by weight of isostearyl acrylate (ISTA), and a photopolymerization initiator ("Irgacure 184" manufactured by BASF: 0.035 parts by weight and "Irgacure 651" manufactured by BASF: 0.035 parts by weight, and irradiating ultraviolet light to polymerize the composition so that the viscosity (BH No.5 rotor, 10rpm viscometer, measurement temperature 30 ℃) became about 20 Pa.s (polymerization rate: about 9%).

(preparation of Photocurable adhesive composition)

To the prepolymer composition, a terminal acrylic-modified polyether urethane ("UV-3300B" manufactured by japan synthetic chemical industry) as a urethane (meth) acrylate was added: 7 parts by weight and a terminal acrylic-modified polyester urethane ("UV-3010B" manufactured by Nippon synthetic chemical industry): 3 parts by weight of the acrylic oligomer: 5 parts by weight of Irgacure 184 as a photopolymerization initiator: 0.05 parts by weight and Irgacure 651:0.57 parts by weight of α -methylstyrene dimer ("Nofmer MSD" manufactured by Nichigan oil) as a chain transfer agent: 0.1 parts by weight, and "KBM403" manufactured by Beacon chemistry as a silane coupling agent): 0.3 parts by weight, and then they were uniformly mixed, thereby preparing an adhesive composition.

(preparation of adhesive sheet)

The coating layer was formed by applying the photocurable adhesive composition onto a substrate (double release film) having a polyethylene terephthalate (PET) film (refer to "diol MRF75" manufactured by mitsubishi chemical) with a thickness of 75 μm, on the surface of which a silicone release layer was provided, as a substrate, so as to have a thickness of 150 μm. A PET film (refer MRE75 manufactured by mitsubishi chemical) having a thickness of 75 μm, on one side of which a silicone release treatment was performed, was laminated on the coating layer as a cover sheet (also a light release film). So that the irradiation intensity of the irradiation surface directly below the lamp is 5mW/cm ² The black light lamp with the position adjusted in the mode of (1) irradiated the ultraviolet ray for 130 seconds from the cover sheet side to the laminate for photocuringThus, a pressure-sensitive adhesive sheet having a thickness of 150 μm and a polymerization rate of 94% was obtained.

Examples 2 to 7 and comparative examples 1 to 10

The monomer composition charged during the polymerization of the prepolymer, and the types and amounts of the polyfunctional compound (urethane acrylate and/or polyfunctional acrylate), acrylic oligomer, photopolymerization initiator, and chain transfer agent added to the adhesive composition were as shown in tables 1-1 and 1-2. Except for this, a photocurable adhesive composition was prepared in the same manner as in example 1, and coating on a substrate and photocuring were performed to obtain an adhesive sheet. In example 4, comparative example 4 and comparative example 5, the same adhesive compositions as in example 3 were used, and the irradiation time of ultraviolet rays was changed, thereby obtaining adhesive sheets having the polymerization ratios shown in table 1-1.

[ evaluation ]

< weight average molecular weight >

The weight average molecular weights (Mw) of the acrylic oligomer and the urethane (meth) acrylate were measured by a GPC (gel permeation chromatography) apparatus (product name "HLC-8120 GPC") manufactured by Tosoh. For the measurement sample, a filtrate obtained by filtering a substance obtained by dissolving a base polymer in tetrahydrofuran to obtain a 0.1 wt% solution by using a 0.45 μm membrane filter was used. The measurement conditions of GPC are as follows.

(measurement conditions)

Column: g7000HXL + GMHXL manufactured by Tosoh corporation

Column size: each one of

(total column length: 90 cm)

Column temperature: 40 ℃ flow rate: 0.8 mL/min

Sample introduction amount: 100 μ L

Eluent: tetrahydrofuran (THF)

A detector: differential Refractometer (RI)

Standard sample: polystyrene

< storage modulus, glass transition temperature and tan delta Peak value of pressure-sensitive adhesive sheet >

10 adhesive sheets were laminated to a thickness of about 1.5mm to obtain a sample for measurement. The dynamic viscoelasticity was measured under the following conditions using the Advanced Rheological Extension System (ARES) manufactured by Rheometric Scientific.

(measurement conditions)

Deformation mode: torsion

Measuring frequency: 1Hz

Temperature rise rate: 5 deg.C/min

Shape: parallel plates

The shear storage modulus was determined by reading the storage modulus G' at each temperature from the measurement results. The temperature (peak top temperature) at which the loss tangent (tan δ) becomes maximum was taken as the glass transition temperature of the adhesive sheet. In addition, the value of tan δ at the glass transition temperature (peak top value) was read.

< adhesive force >

The light release film was peeled from the pressure-sensitive adhesive sheet, a 50 μm thick PET film was laminated, cut into a width of 10mm × a length of 100mm, and the heavy release film was peeled off and pressed against a glass plate with a 5kg roller to prepare a sample for measuring adhesive strength. The sample for measuring adhesive force was kept at 25 ℃ or 65 ℃ for 30 minutes, and then a tensile tester was used to peel the test piece from the glass plate at a tensile speed of 300 mm/minute and a peel angle of 180 °, to measure the peel force.

< haze >

The haze was measured using a haze meter ("HM-150" manufactured by mura color technology research) using a test piece obtained by bonding a pressure-sensitive adhesive sheet to alkali-free glass (total light transmittance 92%, haze 0.4%) having a thickness of 800 μm. The haze value of the alkali-free glass (0.4%) was subtracted from the measured value to obtain a value as the haze value of the pressure-sensitive adhesive sheet.

< differential absorption Property >

The pressure-sensitive adhesive sheet was cut into a size of 75mm × 45mm, the light release film was peeled from the pressure-sensitive adhesive sheet, and the light release film was bonded to the center of a 125 μm thick PET film cut into a size of 100mm × 50mm by a roll laminator (roll pressure: 0.2MPa, carrying speed: 100 mm/min). Then, the heavy release film was peeled off, and the film was laminated on a 500 μm thick glass plate (100 mm. Times.50 mm) having a peripheral portion on which a black ink having a thickness of 20 μm was frame-printed by a roll laminator (nip pressure: 0.2MPa, transport speed: 100 mm/min). The ink printed area of the glass plate was 5mm from both ends in the short side direction and 15mm from both ends in the long side direction, and the black ink layer was in contact with the area 5mm from the end of the four sides of the adhesive sheet. The sample was treated in an autoclave (50 ℃ C., 0.5 MPa) for 30 minutes, and then observed by a digital microscope at a magnification of 20 times to confirm the presence or absence of bubbles in the vicinity of the boundary of the printing region of the black ink.

< releasability from mold Release film >

The adhesive sheet was cut into a size of 75mm × 45mm, the light release film was peeled from the adhesive sheet, and the sheet was bonded to a glass plate (100 mm × 50 mm) having a thickness of 500 μm using a roll laminator (roll pressure: 0.2MPa, transport speed: 100 mm/min). The pickup tape was bonded to the end of the heavy release film temporarily attached to the adhesive sheet, and the peeling was performed at a peeling angle of 90 °, and the sample in which the peeling occurred at the interface between the adhesive sheet and the heavy release film was regarded as OK, and the sample in which the peeling occurred at the interface between the glass plate and the heavy release film was regarded as NG.

< interlayer adhesiveness >

(preparation of test sample)

The pressure-sensitive adhesive sheet was cut into a size of 75mm × 45mm, the light release film was peeled from the pressure-sensitive adhesive sheet, and the sheet was bonded to the center of a glass plate (100 mm × 50 mm) having a thickness of 500 μm by means of a roll laminator (roll pressure: 0.2MPa, conveying speed: 100 mm/min). The heavy release film was peeled from the pressure-sensitive adhesive sheet, and a 500 μm thick glass plate having a peripheral edge portion on which black ink having a thickness of 30 μm was printed in a frame shape (50 mm. Times.100 mm, ink printed region the same as that used in the level difference absorption test) was bonded by vacuum pressure bonding (surface pressure 0.3MPa, pressure 100 Pa). The sample was treated in an autoclave (50 ℃ C., 0.5 MPa) for 30 minutes and then treated with a metal halide lamp (300 mW/cm) ² ) From having a black colorThe glass plate side of the ink printed layer was cured by irradiation with ultraviolet rays, and the polymerization rate was increased to 99%.

The sample was held at 60 ℃ for 30 minutes, and then, as shown in FIG. 5A, a polystyrene sheet having a thickness of 200 μm was inserted between two glass plates to a distance of 1mm from the end of the adhesive sheet and held for 10 seconds. The end of the adhesive sheet was observed with a digital microscope at 20 times magnification. The sample in which streaky blisters (see fig. 5B) occurred or peeling of the adhesive sheet from the glass plate occurred was denoted as NG, and the sample in which neither blisters nor peeling occurred was denoted as OK.

< impact resistance >

In the same manner as in the preparation of the sample for interlayer adhesiveness test described above except that the size of the glass plate on which the black ink-not-provided print layer was changed to 100mm × 70mm, glass plates were bonded to both surfaces of the adhesive sheet, and autoclave treatment and curing of the adhesive were performed to prepare a sample for test. As shown in fig. 6, both ends in the short side direction of the test sample 95 were placed on a stage 93 disposed at an interval of 60mm so that the glass plate 7 provided with the printed layer 76 was positioned on the lower side, and the upper surface of the end of the glass plate 5 not provided with the printed layer was fixed to the stage 80 by an adhesive tape (not shown). The test specimen 95 fixed on the stage 93 by the adhesive tape was kept at-5 ℃ for 24 hours, and then was taken out to room temperature and dropped onto the glass plate 7 from a height of 300mm by a mass of 11g within 40 seconds, thereby carrying out an impact resistance test.

In the impact resistance test, in order to keep the falling position of the metal ball constant, the metal ball 97 was dropped using a cylindrical guide 99 at a position spaced apart from the corner by 10mm in each of the short side direction and the long side direction of the inner edge of the frame in the printing region of the printing layer 76. The test was conducted twice, and a sample in which the glass plate was not peeled off in any of the tests was regarded as "OK", and a sample in which the glass plate was peeled off in either or both of the tests was regarded as "NG".

< physical Properties of cured adhesive sheet >

In the production of the pressure-sensitive adhesive sheets of the examples and comparative examples, a pressure-sensitive adhesive sheet having a polymerization rate of 99% was produced by changing the irradiation time of ultraviolet rays, and viscoelasticity (storage modulus, glass transition temperature, and tan δ peak), haze, and adhesive force were measured in the same manner as described above. In example 4, comparative example 4 and comparative example 5, the physical properties of the cured adhesive sheet were not measured because the composition of the adhesive was the same as in example 6.

[ evaluation results ]

The compounding of the adhesive compositions used for producing the respective adhesive sheets are shown in tables 1-1 and 1-2, and the evaluation results are shown in tables 2-1 and 2-2. In tables 1-1 and 1-2, the components are described below.

< acrylic monomer >

BA: acrylic acid butyl ester

2HEA: 2-ethylhexyl acrylate

CHA: acrylic acid cyclohexyl ester

NVP: n-vinyl-2-pyrrolidone

4HBA: acrylic acid 4-hydroxybutyl ester

2HEA: 2-Hydroxyethyl acrylate

And (3) ISTA: acrylic acid isostearyl ester

< urethane acrylate >

UV-3300B: "UV-3300B" (polyether urethane diacrylate having a weight average molecular weight of about 12000 and a glass transition temperature of-30 ℃ C.) manufactured by Nippon synthetic chemical industry

3400: polyether urethane diacrylate with weight average molecular weight of about 3400

UA-4200: "UA-4200" (polyether urethane diacrylate having a weight average molecular weight of about 1000) manufactured by Xinzhongcun chemical industry

UN-350: "ArtResinUN-350" (polyester urethane diacrylate having a weight average molecular weight of about 12500 and a glass transition temperature of-57 ℃ C.) commercially manufactured

UV-3000B: "UV-3000B" (polyester urethane diacrylate having a weight average molecular weight of about 18000 and a glass transition temperature of-39 ℃ C.) manufactured by Nippon synthetic chemical industry

UV-3010B: "UV-3010B" (polyester urethane diacrylate having a weight average molecular weight of about 11000) manufactured by Nippon synthetic chemical industry

Urethane monoacrylate: polyether urethane monoacrylate having a weight average molecular weight of about 1300)

< polyfunctional acrylate >

HDDA: hexanediol diacrylate

< photopolymerization initiator >

Irg651: irgacure 651 (2,2-dimethoxy-1,2-diphenylethan-1-one)

Irg184: irgacure 184 (1-hydroxycyclohexyl phenyl ketone)

In examples 1 and 2 using a pressure-sensitive adhesive composition in which urethane diacrylate or the like was added to a prepolymer composition obtained by prepolymerization of an acrylic monomer containing butyl acrylate as a main monomer, the semi-cured pressure-sensitive adhesive sheet was excellent in level difference absorption and free from adhesive residue, and in the evaluation using a fully cured pressure-sensitive adhesive sheet, both the interlayer adhesiveness and the drop impact durability were good.

In comparative example 1 using a low molecular weight urethane diacrylate, tackiness was observed before and after photocuringThe adhesive strength of the adhesive sheet to an adherend was small, and the interlayer adhesiveness and the drop impact durability were poor. In comparative example 2 in which the amount of urethane diacrylate added was increased, the haze of the adhesive sheet was high and the transparency was decreased. G 'of the adhesive sheet before curing' _25℃ Large, and therefore poor in high-absorbency. In comparative example 3 using a urethane monoacrylate, the shear storage modulus of the pressure-sensitive adhesive sheet after photocuring was low, and the adhesive durability was poor.

Examples 3 and 5, and examples 6 and 7, in which the composition of the acrylic monomer in the prepolymer forming composition was changed, exhibited good adhesive properties in the same manner as examples 1 and 2.

In example 4 in which the polymerization rate was reduced to 92% by using the same adhesive composition as in example 3, the glass transition temperature of the semi-cured adhesive sheet was reduced as compared with example 3, and G 'was accompanied therewith' _25℃ And G' _80℃ And (4) reducing. In comparative example 4 in which the polymerization rate was further decreased, the glass transition temperature, G' _25℃ And G' _80℃ Further decrease in the adhesive strength. On the other hand, in comparative example 5 in which the polymerization rate was adjusted to 99%, factor G' _{At 25 ℃ of} The increase results in insufficient differential absorbency.

Comparative example 6 in which the glass transition temperature was lowered by adjusting the composition of the acrylic monomer without using a urethane material, the adhesive sheet after photocuring had G' _25℃ And G' _80℃ Small, poor adhesion reliability. In comparative example 7 in which the cohesive property was improved by increasing the ratio of the polar monomers (NVB and 4 HBA) in the acrylic monomer component, the tackiness was good, but the impact resistance was lowered because the glass transition temperature was high. The same tendency was observed in comparative example 10.

In comparative example 8 in which the ratio of the polyfunctional acrylate in the pressure-sensitive adhesive composition was increased, the peak top value of tan δ was small and the tackiness was low, so that the adhesive strength was insufficient and the impact resistance was also poor. In the introduction of crosslinks through low molecular weight urethane diacrylatesThe same tendency was observed in comparative example 9 having the above-mentioned structure. In these comparative examples, it is considered that the main monomer of the acrylic polymer chain is acrylic acid C ₈ The alkyl ester (2-ethylhexyl acrylate) is also reacted with the main monomer C acrylate ₄ Examples 1 to 7 of the alkyl ester (butyl acrylate) and the like have one of the factors that tan δ is small.

From these results, it is understood that a pressure-sensitive adhesive sheet containing a base polymer having a crosslinked structure introduced into an acrylic polymer chain using a urethane diacrylate having a predetermined molecular weight exhibits a high shear storage modulus even at a low glass transition temperature and has a large tan δ, and therefore can achieve both adhesive durability and impact resistance.

Claims (11)

1. A pressure-sensitive adhesive sheet which is a photocurable pressure-sensitive adhesive sheet obtained by forming a pressure-sensitive adhesive composition comprising an acrylic base polymer, an acrylic oligomer having a weight-average molecular weight of 1000 to 30000, and a photocurable compound into a layer,

in the base polymer, an acrylic polymer chain is crosslinked by a urethane segment having a weight average molecular weight of 4000 to 50000,

the adhesive sheet has a haze of 1% or less,

the adhesive force of the adhesive sheet to glass is more than 1.5N/10mm,

the adhesive sheet has a shear storage modulus of 0.15MPa or less at a temperature of 25 ℃ and

when the adhesive composition is cured and the polymerization rate is adjusted to 99%, the glass transition temperature of the adhesive sheet is-3 ℃ or less, and the shear storage modulus at a temperature of 25 ℃ is 0.16MPa or more.

2. The adhesive sheet according to claim 1, wherein the adhesive composition has a polymerization rate of 90% to 98%.

3. The adhesive sheet according to claim 1 or 2, wherein the glass transition temperature of the adhesive sheet is-5 ℃ or lower.

4. The adhesive sheet according to claim 1 or 2, wherein the peak top value of loss tangent of the adhesive sheet is 1.6 or more.

5. The adhesive sheet according to claim 1 or 2, wherein the peak top value of the loss tangent of the adhesive sheet is 1.5 or more when the adhesive composition is cured and the polymerization rate is adjusted to 99%.

6. The adhesive sheet according to claim 1 or 2, wherein the content of the urethane segment is 3 to 30 parts by weight with respect to 100 parts by weight of the acrylic polymer chain.

7. The adhesive sheet according to claim 1 or 2, wherein in the base polymer, a crosslinked structure formed from the urethane-based segment is introduced into the acrylic polymer chain by copolymerization of a monomer component constituting the acrylic polymer chain and a urethane (meth) acrylate having a (meth) acryloyl group at a terminal.

8. A method for manufacturing an image display device in which a transparent member having a step portion is disposed on a viewing-side surface,

the adhesive sheet according to any one of claims 1 to 7 is bonded to the transparent member, and then the adhesive sheet is irradiated with active light, whereby photocuring of the adhesive sheet is performed.

9. A method for producing the adhesive sheet according to any one of claims 1 to 7, wherein,

a composition containing an acrylic monomer and/or a partial polymer thereof and a urethane (meth) acrylate having a weight average molecular weight of 4000 to 50000 is applied in a layer form to a substrate, and then the composition is irradiated with active light to be photocured.

10. The method for producing an adhesive sheet according to claim 9, wherein the composition contains 3 to 30 parts by weight of the urethane (meth) acrylate per 100 parts by weight of the total of the acrylic monomer and the partial polymer thereof.

11. The method for producing an adhesive sheet according to claim 9 or 10, wherein the urethane (meth) acrylate has a glass transition temperature of 0 ℃ or lower.

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