CN112111083B

CN112111083B - Polypropylene resin foam particles and molded article of polypropylene resin foam particles

Info

Publication number: CN112111083B
Application number: CN202010556363.9A
Authority: CN
Inventors: 太田肇; 坂村拓映
Original assignee: JSP Corp
Current assignee: JSP Corp
Priority date: 2019-06-20
Filing date: 2020-06-17
Publication date: 2023-09-22
Anticipated expiration: 2040-06-17
Also published as: CN112111083A

Abstract

The present invention relates to polypropylene resin expanded particles and a polypropylene resin expanded particle molded article, wherein the polypropylene resin expanded particles have a particle-like expanded body comprising, as a base resin, a polypropylene resin comprising an ethylene-propylene-butene copolymer a having a butene content of 7 to 20% by mass and a ratio of the butene content [ mass% ] to the ethylene content [ mass% ] of 7 or more.

Description

Polypropylene resin foam particles and molded article of polypropylene resin foam particles

Technical Field

The present invention relates to polypropylene resin expanded beads and molded articles of polypropylene resin expanded beads, each of which comprises a polypropylene resin containing an ethylene-propylene-butene copolymer as a base resin.

Background

The expanded particle molded article obtained by in-mold molding the polypropylene resin expanded particles is excellent in chemical resistance, impact resistance, compressive strain recovery and the like as compared with the polystyrene resin expanded particle molded article. Accordingly, the polypropylene resin foam particle molded product is used in a wide range of fields such as impact absorbing materials, heat insulating materials, various packaging materials, etc., as food containers, packaging cushioning materials for electric and electronic parts, automobile bumpers, interior parts, building parts such as house heat insulating materials, and sundry goods.

In order to improve the physical properties of the obtained expanded particle molded product, a copolymer obtained by copolymerizing propylene with another monomer is used as a resin constituting the expanded particles of the propylene resin. Among them, a terpolymer obtained by copolymerizing 1-butene and a comonomer component of ethylene is used as a resin constituting the propylene resin expanded beads.

For example, patent document 1 discloses a polypropylene resin expanded particle molded article having a specific density, which comprises a propylene random copolymer containing a comonomer component of 1-butene and ethylene as a base resin. Patent document 2 discloses polypropylene resin expanded particles containing a low-melting polypropylene resin containing a structural unit composed of 1-butene and a high-melting polypropylene resin. Further, patent document 3 discloses polypropylene resin pre-expanded particles in which an ethylene-propylene random copolymer or an ethylene-propylene-1-butene random copolymer having a specific melting point and Melt Index (Melt Index) is used as a base resin.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 7-258455

Patent document 2: international publication No. 2016/60162

Patent document 3: japanese patent laid-open No. 10-316791

Disclosure of Invention

Technical problem to be solved by the invention

However, in recent years, various properties such as strength have been demanded for expanded particles used for expanded particle molded bodies for application to various applications. Among them, it is required that the expanded beads can be molded by a wide range of molding pressures. In these respects, expanded beads comprising the copolymer described in patent documents 1 to 3 as a base material have technical problems in the compression properties of expanded bead molded articles obtained from the expanded beads, the moldability of the expanded beads, and the like.

The present invention has an object to provide expanded particles which can produce an expanded particle molded article excellent in moldability and strength of the obtained molded article, and a molded article excellent in strength.

Solution to the above technical problems

The present inventors have found that the above problems can be solved by providing a specific relationship between the copolymer ratio of the ethylene-propylene-butene copolymer and the butene component and the ethylene component to the polypropylene-based resin constituting the base resin of the expanded beads.

Specifically, the present invention provides polypropylene resin expanded particles having a particle-like expanded body comprising, as a base resin, a polypropylene resin comprising an ethylene-propylene-butene copolymer a having a butene content of 7 to 20% by mass and a ratio of the butene content to the ethylene content (butene content [ mass% ]/ethylene content [ mass% ]) of 7 or more, and an expanded particle molded body obtained by in-mold molding the polypropylene resin expanded particles.

Effects of the invention

According to the present invention, expanded beads which can produce a molded article of expanded beads excellent in moldability and also excellent in strength of the molded article obtained, and a molded article of expanded beads having the above excellent characteristics can be obtained.

Detailed Description

Hereinafter, preferred embodiments of the expanded beads and expanded bead molded articles of the present invention will be described. In the present specification, when "to" are used to express numerical values or physical property values before and after the numerical values or physical property values, the numerical values or physical property values are used as a range including the numerical values before and after the numerical values. Further, the upper limit value and the lower limit value of the preferable range, the more preferable range, or the like for the numerical value and the physical property value may be determined and used in the range. All combinations of the upper limit value and the lower limit value of these ranges can be selected and determined. Therefore, the combination of the preferable upper limit value and the lower limit value, the more preferable combination of the upper limit value and the lower limit value, and the more preferable combination of the upper limit value and the lower limit value are preferable, but are not necessarily limited to these combinations.

In the present specification, when "consisting of …" and "consisting of …" are used, they do not mean "consisting of … only" and "consisting of … only".

The invention provides polypropylene resin expanded particles and a molded article of expanded particles obtained by molding the polypropylene resin expanded particles in a mold, wherein the polypropylene resin expanded particles have a particle-shaped expanded body comprising, as a base resin, a polypropylene resin comprising an ethylene-propylene-butene copolymer a having a butene content of 7 to 20% by mass and a ratio of the butene content [ mass% ] to the ethylene content [ mass% ] of 7 or more.

[ Polypropylene resin foam particles ]

The polypropylene resin foam particles of the present invention are provided with a polypropylene resin comprising an ethylene-propylene-butene copolymer a having a butene component content of 7 to 20 mass% and a ratio of the butene component content [ mass% to the ethylene component content [ mass% ] of 7 or more as a base resin in the form of particles.

In the present invention, the polypropylene resin may be a propylene homopolymer, a propylene copolymer, or a mixture thereof, and the polypropylene resin preferably contains 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 80% by weight or more of a structural unit derived from propylene. Examples of the propylene-based copolymer include a copolymer of propylene and ethylene and/or an α -olefin such as 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-butene having 4 to 20 carbon atoms, and the ethylene-propylene-butene copolymer a. In addition, the ethylene-propylene-butene copolymer a may be used in combination with other propylene resins.

The polypropylene resin constituting the foam of the polypropylene resin foam particles of the present invention contains the copolymer a. The content of the copolymer a is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and still more preferably 99% by mass or more. Further, the upper limit is 100 mass%.

To the base resin constituting the polypropylene-based resin expanded particles of the present invention, other resins than the polypropylene-based resin containing the ethylene-propylene-butene copolymer a may be added. The content of the other resin is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 1% by mass or less. Even more preferably, the resin composition contains only polypropylene resin. For example, a styrene resin such as a polyethylene resin, polystyrene, or a styrene-maleic anhydride copolymer may be added; ethylene-propylene rubber, ethylene-1-butene rubber, propylene-1-butene rubber, ethylene-propylene-diene rubber, isoprene rubber, chloroprene rubber, nitrile rubber, and the like; other resins include thermoplastic elastomers such as styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, hydrogen addition products of styrene-butadiene-styrene block copolymers, and hydrogen addition products of styrene-isoprene-styrene block copolymers.

(ethylene-propylene-butene copolymer a)

The ethylene-propylene-butene copolymer a used in the polypropylene resin expanded beads of the present invention has a butene content of 7 to 20% by mass and a ratio of butene content [ mass% ] to ethylene content [ mass% ] of 7 or more.

The copolymer a satisfying such a copolymer ratio can produce expanded particles having good moldability capable of being molded into expanded particle molded bodies even under a low molding pressure, and can produce expanded particle molded bodies having excellent rigidity. In addition, when the butene content of the copolymer a is too small, there is a possibility that it is difficult to obtain expanded particles which can be molded by low molding pressure or expanded particle molded products having good compression characteristics, as in the conventional technique.

The lower limit of the butene content of the ethylene-propylene-butene copolymer a is 7% by mass, preferably 8% by mass. The upper limit of the butene content of the ethylene-propylene-butene copolymer a is 20% by mass, preferably 15% by mass, and more preferably 12% by mass. The butene used in the butene component of the copolymer is preferably linear 1-butene as an alpha-olefin.

The lower limit of the ethylene component content of the ethylene-propylene-butene copolymer a is preferably 0.1 mass%, more preferably 0.3 mass%, and still more preferably 0.4 mass%. The upper limit of the ethylene component content of the ethylene-propylene-butene copolymer a is preferably 2 mass%, more preferably 1.5 mass%, and still more preferably 1.2 mass%.

The lower limit of the propylene component content of the ethylene-propylene-butene copolymer a is preferably 78 mass%, more preferably 80 mass%, and still more preferably 85 mass%. The upper limit of the propylene component content is preferably 91.7 mass%, more preferably 91 mass%.

The total of the butene component content, the ethylene component content and the propylene component content was set to 100 mass%.

The ethylene-propylene-butene copolymer a may contain a monomer component other than an ethylene component, a propylene component and a butene component, but is preferably composed substantially of these 3 monomer components, more preferably composed of only these 3 monomer components.

The content of these monomer components can be determined by IR spectrum measurement based on a polypropylene resin having a known copolymerization composition. Specifically, the method described in the examples can be used to obtain the product.

In the present invention, the ethylene component, the propylene component and the butene component of the ethylene-propylene-butene copolymer a refer to structural units derived from ethylene, structural units derived from propylene and structural units derived from butene in the ethylene-propylene-butene copolymer a. The monomer components other than the ethylene component, the propylene component and the butene component refer to structural units derived from ethylene, structural units derived from propylene and structural units derived from monomers other than structural units derived from butene.

Further, the content of each monomer component in the copolymer represents the content of structural units derived from each monomer in the copolymer.

The ratio of the butene content to the ethylene content (butene content [ mass% ]/ethylene content [ mass% ]) of the ethylene-propylene-butene copolymer a is 7 or more, preferably 9 or more, more preferably 10 or more, and even more preferably 13 or more.

On the other hand, the upper limit of the above ratio is preferably 50 or less, more preferably 30 or less, and further preferably 20 or less.

The copolymer having such a polymer ratio is considered to have a low melting point due to the composition of the butene component/ethylene component ratio and the like, but also to have excellent rigidity.

When the ratio is satisfied, the expanded particles have the following effects. In the case of producing the expanded beads, a good bubble film can be formed during the generation of bubbles at the time of foaming. Further, in the case where the expanded beads are secondarily expanded at the time of in-mold molding, the bubble film of the expanded beads is also hardly broken, so that the expanded beads have good moldability. In addition, even in the case of molding with a high molding pressure, the cell structure of the expanded beads can be maintained, and thus the molding of the expanded bead molded body at a high molding pressure can be performed.

Further, even when molding is performed with a low molding pressure, the expanded particle molded body can be molded, and therefore the expanded particle can be molded with a wide range of molding conditions. Further, since the obtained expanded particle molded product exhibits high rigidity, the following characteristics are combined: the expanded beads are expanded beads having moldability under a wide range of molding pressure conditions, and can give expanded bead molded articles having high compressive strength.

The lower limit of the melting point of the ethylene-propylene-butene copolymer a is preferably 136 ℃, more preferably 137 ℃, and even more preferably 138 ℃ from the viewpoint of both in-mold formability and heat resistance of the expanded particles. The upper limit of the melting point of the ethylene-propylene-butene copolymer a is preferably 148 ℃, more preferably 145 ℃, and even more preferably 142 ℃ from the viewpoint of heat resistance of the expanded particles.

The melting point can be determined according to JIS K7121:1987. Specifically, the method was used to obtain the product described in the examples.

The Melt Flow Rate (MFR) of the ethylene-propylene-butene copolymer a is preferably 2 to 10g/10 min, more preferably 5 to 9g/10 min.

(melting Heat of Polypropylene resin foam particles)

The polypropylene resin expanded particles of the present invention preferably have 1 or more melting peaks (high temperature peaks) on the high temperature side of melting peaks (resin-inherent peaks) inherent to the resin in a Differential Scanning Calorimetry (DSC) curve.

These melting peaks can be obtained by the method shown in the examples.

Specifically, the expanded particles were measured at a temperature rise of from 23 ℃ to 200 ℃ at 10 ℃/min by a differential scanning calorimeter, and a DSC curve having 2 or more melting peaks was obtained. Then, the peak having the largest heat of fusion was regarded as a melting peak inherent to the resin (resin inherent peak), and the melting peak appearing on the higher temperature side than that was regarded as a high temperature peak.

The DSC curve in this case refers to the DSC curve of the 1 st heating obtained by the measurement method. The endothermic peak (resin-inherent peak) due to melting inherent to the resin is an endothermic peak due to melting inherent to the polypropylene resin constituting the expanded particles, and is considered to be a peak due to heat absorption at the time of melting of crystals inherent to the polypropylene resin.

On the other hand, the endothermic peak (high temperature peak) on the high temperature side of the resin intrinsic peak means an endothermic peak that appears on the high temperature side of the resin intrinsic peak in the 1 st DSC curve. When this high temperature peak occurs, it is presumed that secondary crystallization exists in the resin. In addition, in a DSC curve (DSC curve of the 2 nd heating) obtained when the temperature is raised from 23℃to 200℃at a temperature-raising rate of 10℃per minute, then cooled from 200℃to 23℃at a cooling rate of 10℃per minute, and then heated again from 23℃to 200℃at a temperature-raising rate of 10℃per minute, only an endothermic peak due to melting inherent to the polypropylene resin constituting the polypropylene resin expanded particles was observed. The inherent peak of the resin appears in both the DSC curve for the 1 st and 2 nd heats, sometimes with a slight difference in peak apex temperature between the 1 st and 2 nd heats, but typically with a difference of less than 5 ℃. This can confirm which peak is the inherent peak of the resin. The endothermic peak varies depending on the polymer ratio of the polypropylene resin and the like.

Accordingly, in the polypropylene resin expanded particles of the present invention, it is preferable that 2 or more melting peaks including a high temperature peak appear in a DSC curve obtained by Differential Scanning Calorimetry (DSC), wherein the high temperature peak is a peak which does not appear in a 2 nd DSC curve measured when melting is performed by obtaining a 1 st DSC curve, then holding the temperature at 30 ℃ higher than the temperature at the end of the melting peak for 10 minutes, cooling the temperature to 30 ℃ at a cooling rate of 10 ℃/minute, and heating the temperature at a heating rate of 10 ℃/minute to 30 ℃ higher than the temperature at the end of the melting peak.

The upper limit of the melting heat of the high temperature peak of the polypropylene resin foam particles is preferably 40J/g, more preferably 30J/g, and still more preferably 20J/g. On the other hand, the lower limit is preferably 5J/g, more preferably 7J/g, still more preferably 10J/g.

The upper limit of the ratio of the heat of fusion of the high temperature peak to the heat of fusion of the total melting peak of the DSC curve (heat of fusion of the high temperature peak/heat of fusion of the total melting peak) is preferably 0.3, more preferably 0.25, and even more preferably 0.2. On the other hand, the lower limit thereof is preferably 0.05, more preferably 0.1, and further preferably 0.15.

When the ratio of the heat of fusion of the high temperature peaks to the heat of fusion of the total melting peaks is in such a range, it is considered that the expanded particles are particularly excellent in mechanical strength and excellent in-mold formability due to the presence of secondary crystals which are expressed as the high temperature peaks.

The heat of fusion of the total melting peak is the sum of the heat of fusion obtained from the sum of the areas of all melting peaks of the DSC curve.

The heat of fusion of each peak can be specifically determined by the method described in the examples.

From the viewpoint of both formability and strength of the molded article, the upper limit of the tensile elastic modulus of the base resin constituting the expanded particles is preferably 900MPa, more preferably 890MPa, and further preferably 880MPa. On the other hand, the lower limit is preferably 700MPa, more preferably 730MPa, and still more preferably 740MPa. In the present invention, particularly when the base resin is substantially composed of an ethylene-propylene-butene copolymer, since a large amount of butene is contained as a copolymer component and the ratio of ethylene to butene is in a specific range, the rigidity of the expanded particle molded product is excellent even in the case of a copolymer having a low tensile elastic modulus. The tensile elastic modulus can be obtained by measuring the specimen at a test speed of 0.25 mm/min using a specimen No. 2 having a sample thickness of 1mm based on JIS K6758.

The upper limit of the flexural modulus of the base resin constituting the expanded particles is preferably 1200MPa, more preferably 1000MPa, and even more preferably 1000MPa. On the other hand, the lower limit is preferably 800MPa, more preferably 850MPa, and still more preferably 900MPa. By setting the flexural modulus in the above range, the bubble film becomes firm at the time of foaming, and the strength of the expanded particle molded product obtained by molding the expanded particles can be further increased. The flexural modulus can be obtained based on JIS K7171 (2008).

[ Polypropylene resin multilayer foam particles (multilayer particles) ]

The polypropylene resin expanded particles may be a particle-shaped foam comprising a polypropylene resin containing an ethylene-propylene-butene copolymer a as a base resin, wherein the ethylene-propylene-butene copolymer a has a butene content of 7 to 20 mass%, a ratio of the butene content [ mass% to the ethylene content [ mass% is 7 or more, and an outer layer made of a thermoplastic resin B formed on the surface of the foam. The polypropylene resin foam particles of the present invention having an outer layer are preferable because the foam particles having a single layer composed of only a foam can be imparted with functionality without impairing the physical properties and foamability of the foam as an inner layer. Hereinafter, expanded beads having such an outer layer may be referred to as polypropylene resin multilayer expanded beads.

< inner layer >

The foamed layer (inner layer) of the foamed article present inside the multilayered polypropylene resin multilayered foamed particles is in a foamed state, and the substrate resin constituting the foamed particles of the foamed article is a polypropylene resin containing an ethylene-propylene-butene copolymer a having a butene content of 7 to 20% by mass and a ratio of a butene content [ mass% ] to an ethylene content [ mass% ] of 7 or more. In the following, in the multilayer expanded beads, polypropylene resin a, which is a base resin constituting the expanded body, may be referred to as polypropylene resin a in order to distinguish the polypropylene resin from the resin constituting the outer layer.

< outer layer >

The outer layer, which is a resin layer formed on the outer surface of the foam of the polypropylene resin multilayer foam particles, is composed of a thermoplastic resin B. In the multilayer expanded beads of the present invention, by forming the outer layer, it is possible to impart functionality to the expanded beads of a single layer composed of only the expanded body of the inner layer without impeding the physical properties and foamability of the expanded layer as the inner layer. For example, since the additive imparting functionality to the outer layer can be added at a high concentration, the amount of the additive as a whole can be reduced to effectively exhibit functionality.

(thermoplastic resin B)

The thermoplastic resin B is not particularly limited as long as it is a resin having thermoplastic properties. The thermoplastic resin B may be, for example, a crystalline resin, an amorphous resin, or a mixture of a crystalline resin and an amorphous resin, and among these, a crystalline resin and a mixture of a crystalline resin and an amorphous resin are preferable, and a crystalline resin is more preferable. Examples of the thermoplastic resin include polyester resins, polycarbonate resins, acrylic resins, polyphenylene ether resins, polymethacrylimide resins, polyolefin resins, polystyrene resins, and polyamide resins. Among thermoplastic resins, polyolefin-based resins are preferred from the viewpoint of adhesion to the inner layer.

The thermoplastic resin B preferably has different properties from the polypropylene resin a in the inner layer of the polypropylene resin multilayer foam particles.

The polypropylene resin constituting the outer layer may be a propylene homopolymer or a propylene copolymer, and is preferably a propylene copolymer, more preferably an ethylene-propylene copolymer, and even more preferably an ethylene-propylene copolymer having an ethylene content of 2 to 5% by mass.

Examples of the polyethylene resin constituting the outer layer include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear ultra-low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer. The proportion of the ethylene component in the ethylene copolymer is not particularly limited, but the content of the structural unit derived from ethylene in the copolymer is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 80 to 99.5% by mass.

In the case where the thermoplastic resin B is a crystalline resin having a melting point, the melting point is preferably 5 to 30 ℃, more preferably 8 to 20 ℃, still more preferably 10 to 15 ℃ lower than the copolymer a constituting the inner layer.

In addition, from the viewpoint of improving the formability of expanded particles and the appearance of the obtained expanded particle molded article, the melting point of the thermoplastic resin B is preferably 116 to 143 ℃, more preferably 120 to 140 ℃, and even more preferably 120 to 130 ℃.

The case where the melting point of the thermoplastic resin constituting the outer layer is lower than the melting point of the resin constituting the inner layer of the multilayer expanded beads can be determined by comparing the melting point of the resin raw material constituting the outer layer of the surface layer portion of the multilayer expanded beads with the melting point of the resin raw material constituting the inner layer of the inside of the expanded beads.

In addition, the surface layer portion of the multilayer expanded beads and the inside of the multilayer expanded beads may be directly measured. Specifically, the melting point of the outer layer of the surface layer portion of the multilayer foam particles can be measured by the method described in Japanese patent application laid-open No. 2003-335892 using a micro thermal analysis system "2990 micro thermal analyzer" of TA Instruments Japan. On the other hand, the melting point of the inner layer of the multilayer expanded beads can be measured by a usual thermal energy differential scanning calorimetric method by cutting the inner layer from the inside of the multilayer expanded beads so as not to contain the outer layer portion as a sample.

In the case where the thermoplastic resin B is amorphous, the softening temperature of the thermoplastic resin B is preferably 5 to 30 ℃, more preferably 8 to 20 ℃, and even more preferably 10 to 17 ℃ lower than that of the copolymer a, from the viewpoint of moldability of the expanded particles.

Further, from the viewpoint of improving the moldability of the expanded beads and the appearance of the obtained expanded bead molded article, the softening temperature of the thermoplastic resin B is preferably 116 to 143 ℃, more preferably 120 to 140 ℃, and even more preferably 120 to 130 ℃. In addition, in the present specification, the softening point is a vicat (vicat) softening point measured by the a50 method based on JIS K7206 (1999). Whether or not the thermoplastic resin B is amorphous can be confirmed by a DSC curve obtained by performing a heat flux differential scanning calorimetry using the thermoplastic resin B as a sample, and can be judged by: when the thermoplastic resin B is crystalline, an endothermic peak appears on the DSC curve, and when the thermoplastic resin B is amorphous, no endothermic peak appears on the DSC curve.

The multilayer expanded beads have the copolymer a in the inner layer, and therefore, as described above, are excellent in moldability and rigidity. Further, since the outer layer is formed on the multilayer foam particles, the functionality can be imparted without interfering with the above-described characteristics of the inner layer. In particular, from the viewpoint of excellent moldability of the expanded particles, it is preferable that the thermoplastic resin B constituting the outer layer has a lower melting point and softening temperature than the copolymer a constituting the inner layer. It is considered that by using the thermoplastic resin B excellent in heat sealing property, the molding property at low temperature can be improved by molding at a lower pressure than the molding steam pressure of the single-layer expanded particles obtained by expanding the single-layer particles composed of the resin forming the inner layer.

In the case of imparting another specific function to the multilayer expanded beads of the present invention, for example, a thermoplastic resin having characteristics corresponding to the function is preferably used as the thermoplastic resin B constituting the outer layer.

The thermoplastic resin B constituting the outer layer may contain additives such as flame retardants, flame retardant aids, plasticizers, antistatic agents, antioxidants, ultraviolet absorbers, light stabilizers, and antibacterial agents, and other resins. In particular, in the present invention, it is preferable to add the above additive only to the outer layer. By adding only to the outer layer, the function derived from the additive can be efficiently exhibited.

These additives may be added in the step of obtaining the multilayer resin particles to be contained in the multilayer expanded particles. For example, the proportion of the additive in the outer layer is preferably 0.01 to 20 parts by mass per 100 parts by mass of the thermoplastic resin B.

< Structure of multilayer foam particles of Polypropylene resin >

The polypropylene resin multilayer foam particles have an inner layer in a foam state composed of a polypropylene resin A containing an ethylene-propylene-butene copolymer a having a butene content of 7 to 20 mass% and a ratio of the butene content to the ethylene content (butene content [ mass% ]/ethylene content [ mass% ]) of 7 or more, and an outer layer composed of a thermoplastic resin B. Further, the multilayer expanded beads are preferably capable of being molded with a lower vapor pressure than corresponding single-layer expanded beads obtained by expanding single-layer resin beads comprising the polypropylene-based resin a constituting the inner layer. That is, it is preferable that the polypropylene resin multilayer expanded beads of the present invention can be molded with a lower steam pressure than a single-layer expanded bead obtained by expanding a single-layer resin bead composed of the polypropylene resin a constituting the inner layer when conditions other than the steam pressure are the same.

The term "corresponding single-layer expanded beads formed by expanding single-layer resin beads comprising polypropylene resin a constituting the inner layer" means expanded beads comprising: the expanded particles of the present invention having the same or substantially the same expansion ratio, expanded particle diameter, average cell diameter, and high temperature peak heat of the expanded particles as those of the expanded particles of the present invention having an inner layer and an outer layer are expanded particles having the same corresponding characteristics as those of the expanded particles of the present invention except for a single layer. In the present specification, such single-layer expanded beads may be referred to as "corresponding single-layer expanded beads formed by expanding single-layer resin beads comprising polypropylene resin a constituting the inner layer". The term "can be molded with a low vapor pressure" means that a molded article having the same characteristics as a molded article obtained by using expanded beads as a standard is obtained with a vapor pressure lower than that of the expanded beads as a standard. The characteristics of the molded article are, for example, surface appearance, weldability, and restorability.

In the polypropylene resin multilayer foam particles of the present invention, the melting point and softening temperature of the thermoplastic resin B constituting the outer layer are lower than those of the copolymer a constituting the inner layer. Therefore, it is considered that, when the thermoplastic resin B having excellent weldability is used as the resin constituting the outer layer, in particular, the polypropylene resin multilayer expanded beads have improved moldability at low temperatures.

More preferably, the polypropylene resin multilayer expanded beads of the present invention can be molded at a steam pressure of 0.01MPa or more lower, and even more preferably at a steam pressure of 0.02MPa or more lower, than the corresponding single-layer expanded beads obtained by expanding single-layer resin beads comprising the polypropylene resin a constituting the inner layer.

Examples of the shape of the expanded beads include various shapes such as a cylindrical shape, a rugby shape, a spherical shape, and a tubular shape.

The inner layer has a foamed layer in a foamed state. The foaming layer as the inner layer and the outer layer present on the surface side of the foaming layer are not limited to a 2-layer structure, respectively. For example, a multilayer structure may be formed in which an inner layer is composed of 2 layers of a foamed layer and a non-foamed layer, an outer layer is composed of a non-foamed resin layer, or the like.

On the other hand, the outer layer is formed in a foamed state or a non-foamed state, preferably in a foamed state. The non-foaming state herein includes not only a state in which no bubbles are present in the layer but also a substantially non-foaming state in which very small bubbles are present only in a very small amount. The state in which no bubbles are present in the layer includes a state in which temporarily formed bubbles are broken by melting and the bubbles disappear.

Examples of the method for forming the outer layer include a method in which a resin forming the outer layer is attached to the inner layer by coating or the like, and a method in which a resin constituting the inner layer and the outer layer is laminated by coextrusion.

The outer layer preferably covers 50% or more of the surface area of the inner layer, more preferably 70% or more of the surface area, still more preferably 90% or more of the surface area, and still more preferably substantially 100% of the surface area.

The thickness of the outer layer is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more, from the viewpoint of excellent weldability between the expanded particles. On the other hand, the upper limit is preferably 25 μm or less, more preferably 18 μm or less, and still more preferably 15 μm or less.

The mass ratio of the inner layer to the outer layer (inner layer/outer layer) is more preferably 99.5/0.5 to 85/15, still more preferably 99/1 to 90/10.

[ method for producing polypropylene resin foam particles ]

As a preferred method for producing the polypropylene resin foam particles of the present invention, the following method can be used: polypropylene resin particles containing a polypropylene resin of an ethylene-propylene-butene copolymer a having a butene component content of 7 to 20 mass% and a ratio of the butene component content [ mass% to the ethylene component content [ mass% ] of 7 or more are dispersed in a dispersion medium, and a foaming agent is permeated into the resin particles and released at a low pressure (dispersion medium release foaming method).

More preferably, the method for producing the polypropylene resin particles comprises dispersing polypropylene resin particles comprising a base resin of an ethylene-propylene-butene copolymer a having a butene content of 7 to 20% by mass and a ratio of the butene content [ mass% ] to the ethylene content [ mass% ] in a dispersion medium in a closed vessel, heating the dispersion medium, and then pressing a foaming agent into the dispersion medium to allow the foaming agent to permeate the resin particles. Then, after a holding step of growing secondary crystals at a predetermined temperature, the content is released to a low pressure to foam the content, thereby obtaining foam particles.

(production of Polypropylene resin particles)

The resin particles used for producing the polypropylene resin expanded beads of the present invention are obtained by the following method. First, a polypropylene resin containing an ethylene-propylene-butene copolymer a is supplied as a base resin into an extruder, and then heated and kneaded to prepare a resin melt. At this time, other additives such as a bubble nucleating agent blended as necessary are blended into the base resin. Then, the resin melt is extruded from the extruder and pelletized by a strand cutting method, a thermal cutting method, an underwater cutting method, or the like, to obtain polypropylene resin pellets.

On the other hand, when producing polypropylene resin multilayer foam particles having an outer layer formed on the surface of a particulate foam, multilayer resin particles having an inner layer and an outer layer are produced by the following method.

First, a polypropylene resin a as a base resin for the inner layer of the copolymer a is fed into a first extruder, heated, and kneaded to obtain a resin melt for the inner layer. At this time, other additives such as a bubble nucleating agent are blended into the inner layer as necessary.

Further, the thermoplastic resin B is supplied as an outer layer into the second extruder, and heated and kneaded to thereby form a resin melt of the outer layer. At this time, other additives are also blended in the outer layer as necessary.

Then, the resin melt of the inner layer and the resin melt of the outer layer are supplied to a coextrusion die, and the flow of the resin melt of the outer layer and the flow of the resin melt of the inner layer are merged in the die, and the two are laminated. The resin melt after lamination is extruded from an extruder and pelletized by a strand cutting method, a thermal cutting method, an underwater cutting method, or the like.

The particle diameter of the resin particles is preferably 0.1 to 3.0mm, more preferably 0.3 to 1.5mm. The ratio of the length to the diameter of the resin particles is preferably 0.5 to 5.0, more preferably 1.0 to 3.0. The average mass of each 1 resin particle (the arithmetic average of 1 obtained by measuring the mass of 200 randomly selected resin particles) is preferably adjusted to 0.1 to 20mg, more preferably 0.2 to 10mg, still more preferably 0.3 to 5mg, and particularly preferably 0.4 to 2mg.

In the wire harness cutting method, the extrusion speed, the drawing speed, the cutting speed, and the like can be appropriately changed to cut the resin melt when extruding the resin melt, and the particle diameter, the length/diameter ratio, and the average mass of the resin particles can be adjusted.

(production of polypropylene resin foam particles)

As a dispersion medium for dispersing the resin particles obtained as described above in a closed vessel, an aqueous dispersion medium may be used. The aqueous dispersion medium is a dispersion medium containing water as a main component. The proportion of water in the aqueous dispersion medium is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more. Examples of the dispersion medium other than water in the aqueous dispersion medium include ethylene glycol, glycerin, methanol, and ethanol.

In the dispersion medium releasing foaming method preferably used in the present invention, it is preferable to add a dispersing agent to the dispersion medium so that polypropylene resin particles heated in the container do not weld with each other in the container. The dispersant may be any dispersant that prevents the polypropylene resin particles from being welded to the dispersion medium in the container. Therefore, the dispersant may be an organic compound or an inorganic compound, and is preferably a particulate inorganic material in view of ease of handling. For example, natural or synthetic clay minerals such as kaolin, mica and clay, alumina, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate and iron oxide may be mentioned, and combinations of 1 or 2 or more may be used. Among them, natural or synthetic clay minerals are preferably used. Preferably, about 0.001 to 5 parts by mass of the dispersant is added to 100 parts by mass of the resin particles.

In the case of using a dispersant, an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylsulfonate, or sodium oleate is preferably used as a dispersing aid. Preferably, about 0.001 to 1 part by mass of the dispersion aid is added to 100 parts by mass of the resin particles.

The foaming agent used for foaming the polypropylene resin particles is preferably a physical foaming agent. Examples of the physical blowing agent include inorganic physical blowing agents and organic physical blowing agents. Examples of the inorganic physical blowing agent include carbon dioxide, air, nitrogen, helium, and argon. Examples of the organic physical blowing agent include aliphatic hydrocarbons such as propane, butane, and hexane; alicyclic hydrocarbons such as cyclopentane and cyclohexane; halogenated hydrocarbons such as chlorofluoromethane, trifluoromethane, 1-difluoromethane, 1-chloro-1, 1-dichloroethane, 1, 2-tetrafluoroethane, chloromethane, chloroethane, and dichloromethane. In addition, the physical foaming agent may be used alone or in combination of two or more. In addition, an inorganic physical blowing agent and an organic physical blowing agent may be used in combination. Among these blowing agents, from the viewpoints of environmental load and handling properties, an inorganic physical blowing agent is preferably used, and carbon dioxide is more preferably used. In the case of using another organic physical blowing agent, n-butane, isobutane, n-pentane, isopentane are preferably used from the viewpoints of compatibility with polypropylene resin and foamability.

The amount of the foaming agent to be added is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 15 parts by mass, based on 100 parts by mass of the base resin.

In the expanded bead production step, as a method for allowing the foaming agent to permeate the resin beads, the resin beads are dispersed in an aqueous dispersion medium in a closed vessel, and the foaming agent is pressed into the resin beads while heating the resin beads, thereby allowing the foaming agent to permeate the resin beads.

The internal pressure of the closed vessel at the time of foaming is preferably 0.5MPa (G) or more. On the other hand, the upper limit of the internal pressure of the closed vessel is preferably 4.0MPa (G). If the amount is within the above range, the expanded beads can be produced safely without risk of breakage, explosion, or the like of the closed container.

The temperature of the aqueous dispersion medium in the expanded particle production step may be set to an appropriate range by raising the temperature at 1 to 5 ℃/min.

The polypropylene resin expanded particles, which are preferable polypropylene resin expanded particles of the present invention, that is, polypropylene resin expanded particles having 1 or more melting peaks (high temperature peaks) on the high temperature side of the melting peak (resin inherent peak) inherent to the resin in a DSC curve obtained by Differential Scanning Calorimetry (DSC) can be obtained as follows.

In the heating in the expanded particle production step, the temperature is stopped at a temperature of not less than (melting point of polypropylene resin-20 ℃) and less than (melting end temperature of polypropylene resin), and the temperature is kept at that temperature for a sufficient time, preferably about 10 to 60 minutes (first-stage holding step), and then the temperature is adjusted from (melting point of polypropylene resin-15 ℃) to (melting end temperature of polypropylene resin +10℃), and the temperature is kept for a sufficient time, preferably about 10 to 60 minutes (second-stage holding step), as required. Then, the foamable resin particles impregnated with the foaming agent are released from the inside of the closed container to a low pressure to foam them.

Further, it is preferable to foam the inside of the closed vessel after the temperature is reached to a temperature of not less than (the melting point of the polypropylene resin-10 ℃), and it is more preferable to foam the inside of the closed vessel after the temperature is reached to a temperature of not more than (the melting point of the polypropylene resin-20 ℃) and not more than (the melting point of the polypropylene resin +20℃).

In the heating in the multilayer expanded beads production step, the temperature is stopped at a temperature of (the melting point of the propylene resin a in the inner layer-20 ℃) or higher and lower than (the melting end temperature of the propylene resin a in the inner layer), and the temperature is maintained for a sufficient period of time, preferably about 10 to 60 minutes (one-stage maintaining step), and then the temperature is adjusted from (the melting point of the propylene resin a in the inner layer-15 ℃) to (the melting end temperature of the propylene resin a in the inner layer +10 ℃) and further maintained at that temperature for a sufficient period of time as needed, preferably about 10 to 60 minutes (two-stage maintaining step). Then, the foamable resin particles impregnated with the foaming agent are released from the inside of the closed container to a low pressure to foam them.

The foaming is preferably performed after the temperature in the closed vessel is set to a temperature of (the melting point of the propylene resin a in the inner layer is-10 ℃) or higher, and more preferably after the temperature is set to a temperature of (the melting point of the propylene resin a in the inner layer is not higher than +20℃).

The average cell diameter of the expanded particles is preferably 20 to 400. Mu.m. If the average cell diameter is within the above range, the in-mold formability is excellent, and the expanded particle molded article after the forming is excellent in dimensional recovery. Further, a foam particle molded body excellent in mechanical properties such as compression properties can be obtained.

The upper limit of the apparent density of the polypropylene resin foam particles of the present invention is preferably 300kg/m ³ More preferably 15 to 200kg/m ³ More preferably 100kg/m ³ More preferably 50kg/m ³ . On the other hand, the lower limit of the apparent density is preferably 10kg/m ³ More preferably 15kg/m ³ More preferably 20kg/m ³ . If the amount is within the above range, the obtained expanded beads are preferable because they have excellent heat insulating properties and sufficient lightweight properties.

The polypropylene resin expanded beads obtained as described above can be further produced into expanded beads having a high expansion ratio (low apparent density) by increasing the internal pressure by a pressurization treatment with air and then foaming the beads by heating with steam or the like (two-stage foaming).

[ Polypropylene resin foam particle molded article ]

The polypropylene resin expanded beads molded article of the present invention can be obtained by in-mold molding the expanded beads.

The expanded particle molded article comprises a polypropylene resin containing an ethylene-propylene-butene copolymer a having a butene content of 7 to 20% by mass and a butene content [ mass% to ethylene content [ mass% ] ratio of 7 or more as a base resin.

The expanded particle molded body of the present invention is preferably obtained by molding the expanded particles in a mold.

The in-mold molding method can be performed by filling the foaming particles into a molding die and performing heat molding using a heating medium such as steam. Specifically, after the expanded beads are filled into the molding die, a heating medium such as steam is introduced into the molding die, the expanded beads are heated and foamed, and the expanded beads are welded to each other, whereby a molded article of expanded beads having a shape of the space to be molded is obtained. In the present invention, the in-mold molding is preferably performed by a press molding method described in, for example, japanese patent application laid-open No. 51-22951. The pressure molding method is to perform a pressure treatment in advance on expanded particles by a pressurized gas such as air to raise the pressure in the cells of the expanded particles, adjust the pressure in the expanded particles to a relatively high pressure of 0.01 to 0.3MPa, fill the expanded particles into a molding die under atmospheric pressure or reduced pressure, and then supply a heating medium such as steam into the die to heat and weld the expanded particles. Further, the molding can be performed by a compression filling molding method described in the following japanese patent application publication No. 4-46217: after the expanded beads pressurized to the pressure equal to or higher than the atmospheric pressure are filled in the molding die pressurized to the pressure equal to or higher than the atmospheric pressure by the compressed gas, a heating medium such as steam is supplied into the cavity to heat the expanded beads, thereby heat-welding the expanded beads. In addition, the molding can be performed by the normal pressure filling molding method described in Japanese patent application laid-open No. 6-49795: the expanded beads having a high secondary foaming power obtained under special conditions are filled into a cavity of a molding die under atmospheric pressure or reduced pressure, and then heated by supplying a heating medium such as steam, whereby the expanded beads are heat-welded, or molded by a method combining the above methods as described in JP-A-6-22919.

The density of the expanded particle molded product of the present invention is preferably 5 to 50kg/m ³ More preferably 10 to 40kg/m ³ . When the density of the expanded particle molded product is within the above range, the compression characteristics are excellent.

In the production of the expanded particle molded article, the expanded particles of the present invention are excellent in moldability particularly at low temperatures, and therefore the following effects can be obtained: the range of molding pressure in which a good molded article can be obtained is widened.

The 50% compressive stress of the expanded particle molded article of the present invention is preferably 0.10 to 0.55MPa, more preferably 0.15 to 0.40MPa. The above 50% compressive stress is a compressive stress (MPa) at 50% deformation when compressed at a speed of 10 mm/min, measured in accordance with JIS K6767:1999.

Examples (example)

Next, the present invention will be described in further detail by way of the present examples, but the present invention is not limited to these examples.

The resins, expanded beads, and expanded bead molded articles used in examples and comparative examples were subjected to the following measurement and evaluation. The expanded beads or expanded bead molded articles were evaluated after being left for 2 days under conditions of a relative humidity of 50%, 23℃and 1atm, and then subjected to a state adjustment.

(monomer component content of Polypropylene resin)

The polypropylene resin having a known copolymer composition was hot-pressed at 180℃to prepare a film having a thickness of about 100. Mu.m. By IR spectroscopic measurement of the fabricated film, 810cm derived from propylene was read ^-1 Absorbance under (I) ₈₁₀ ) 733cm from ethylene ^-1 Absorbance under (I) ₇₃₃ ) 766cm from butene ^-1 Absorbance under (I) ₇₆₆ ). Then, the absorbance ratio (I ₇₃₃ /I ₈₁₀ ) As the horizontal axis, willThe ethylene content was taken as the vertical axis, whereby a standard curve of the ethylene content was prepared. Similarly, the absorbance ratio (I ₇₆₆ /I ₈₁₀ ) The horizontal axis represents the butene component content, and the vertical axis represents the butene component content, thereby preparing a standard curve of butene component content. Next, as in the case of the sample preparation method in the standard curve preparation, the polypropylene resin used in examples and comparative examples was hot-pressed to prepare a film having a thickness of about 100. Mu.m, and I was read by IR spectrum measurement ₈₁₀ 、I ₇₃₃ 、I ₇₆₆ And calculating the ethylene component content and the butene component content according to the standard curve established before.

(melting Point of Polypropylene resin)

The melting point of the polypropylene resin was determined according to JIS K7121:1987. Specifically, a substrate resin in the form of pellets of 2mg was used as a test piece, and the temperature at the peak of the endothermic peak determined by DSC curve, which was obtained by heating the substrate resin from 30℃to 200℃at a heating rate of 10℃per minute, cooling the substrate resin to 30℃at a cooling rate of 10℃per minute, and heating the substrate resin from 30℃to 200℃at a heating rate of 10℃per minute, was used as the melting point of the substrate resin, based on the heat flux differential scanning calorimetry described in JIS K7121:1987. The measuring device used was a heat flux differential scanning calorimeter (model: DSC7020, manufactured by Seiko NanoTech (SII NanoTech)) Co., ltd.

(crystallization temperature and crystallization Heat of Polypropylene resin)

The crystallization temperature and the crystallization heat of the polypropylene resin were measured according to JIS K7121:2012.

(melt flow Rate (MFR) of Polypropylene-based resin)

The melt flow rate of the polypropylene-based resin was measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 190℃and a load of 2.16 kg.

(flexural modulus of base resin and resin for outer layer)

According to JIS K7171:2008, the flexural modulus of elasticity of the base resin and the resin for the outer layer were obtained. As a test piece, a 4mm sheet was produced by hot-pressing the foamed particles at 230℃and a test piece having a length of 80 mm. Times.10 mm. Times.4 mm in thickness was cut from the sheet (standard test piece) Is a test piece of (a). In addition, the radius R of the pressure head ₁ Radius R of support table ₂ All are 5mm, the distance between the fulcrums is 64mm, and the test speed is 2mm/min.

(tensile elastic modulus of base resin)

The tensile elastic modulus of the base resin was measured under conditions of a sample thickness of 1mm, a test piece No. 2, and a test speed of 0.25mm/min according to JIS K6758 by forming the expanded particles into a sheet at 230 ℃.

(melting Heat of each peak of DSC curve of expanded polypropylene-based resin particles)

1 to 3mg of the expanded particles were collected, and a temperature rise measurement was performed at 10℃to 200℃at 10℃per minute by a differential scanning calorimeter (DSC Q1000 manufactured by TA Instruments Co.), to obtain a DSC curve having 1 or more melting peaks. The resin inherent peak in the following description is denoted as a, and the high temperature peak appearing on the higher temperature side than the resin inherent peak is denoted as B.

A straight line (α - β) connecting a point α corresponding to 80 ℃ on the DSC curve and a point β on the DSC curve corresponding to the melting end temperature T of the expanded particles is drawn. The melting end temperature T is the intersection point of the DSC curve on the high temperature side of the high temperature peak B and the high temperature side base line. Next, a straight line parallel to the vertical axis of the graph is drawn from a point γ on the DSC curve corresponding to the valley between the above-mentioned resin intrinsic peak a and high temperature peak B, and a point intersecting the straight line (α - β) is defined as δ.

The area of the resin intrinsic peak a is the area of the portion surrounded by the curve of the resin intrinsic peak a portion of the DSC curve, the line segment (α - δ) and the line segment (γ - δ), and is taken as the melting heat of the resin intrinsic peak.

The area of the high temperature peak B is the area of the portion surrounded by the curve of the high temperature peak B portion, the line segment (δ - β) and the line segment (γ - δ) of the DSC curve, and is taken as the heat of fusion of the high temperature peak.

The area of the total melting peak is the area of the portion surrounded by the curve of the resin intrinsic peak A portion, the curve of the high temperature peak B portion, and the line segment (. Alpha. - β) of the DSC curve, and is taken as the melting heat of the total melting peak.

(evaluation of in-mold formability (formability range) of Polypropylene resin foam particles)

By the method of < manufacturing of expanded molded particle > described later, expanded molded particle is molded by changing the molding vapor pressure between 0.20 and 0.38MPa to 0.02MPa, and the in-mold moldability is evaluated for the items of weldability, surface appearance (degree of gap=void), and recovery (recovery of expansion or contraction after in-mold molding) of the obtained molded article. The vapor pressure obtained by the following method was used as the vapor pressure for molding. The wider the width from the lower limit value to the upper limit value of the formable vapor pressure, the wider the formable range, and thus preferable.

(weldability)

The number of expanded particles (C1) and the number of broken expanded particles (C2) present on the fracture surface were obtained by bending and breaking the expanded particle molded body, and the ratio (C2/C1×100) of the broken expanded particles to the expanded particles was calculated as the material breakage rate. The above measurement was performed 5 times using different test pieces, and the respective material failure rates were determined, and the material failure rates obtained by arithmetic averaging the material failure rates were found to be acceptable when the material failure rates were 90% or more. In table 6, the material failure rate was set to be 90% or more as pass (a), and less than 90% as fail (B).

(surface appearance)

A square of 100mm by 100mm was drawn at the center of the molded foam of expanded beads, a line was drawn from one corner of the square to the diagonal line, the number of voids (gaps) of 1mm by 1mm or more on the line was counted, and the number of voids was set to be less than 5 and no surface irregularities were found to be acceptable. In table 6, the number of voids was less than 5, and the number of voids was determined to be acceptable (a) when the surface had no irregularities, but was determined to be unacceptable (B).

(restorability)

The thickness of the expanded particle molded body in the vicinity of four corners (10 mm inward from the corner in the center direction) and the thickness of the center portion (the portion dividing both the longitudinal direction and the transverse direction by 2 equal parts) corresponding to the dimensions of a flat plate-shaped mold having a length of 250mm, a width of 200mm, and a thickness of 20mm used for in-mold molding were measured, respectively. Then, the ratio (%) of the thickness of the center portion to the thickness of the thickest portion in the vicinity of the four corners was calculated, and the ratio was found to be acceptable when the ratio was 95% or more. In table 6, the ratio was set to be 95% or more as acceptable (a), and less than 95% as unacceptable (B).

Examples 1-1 to 1-12 and comparative examples 1-1 to 1-9 (monolayer particles)

In the following, for examples 1-1 to 1-12, single-layer expanded particles having a particulate foam comprising a polypropylene-based resin containing the ethylene-propylene-butene copolymer a as a base resin were produced.

< production of expanded Polypropylene resin particles >

Example 1-1

Polypropylene resin 1 (ethylene-propylene-butene copolymer, butene component content 9.0 mass%, ethylene component content 1.0 mass%. Other properties are shown in table 1.) was melt-kneaded in an extruder at 200 to 230 ℃, then extruded into strands and water-cooled, cut with a granulator at a mass of about 1.3mg, and dried to obtain polypropylene resin particles. In addition, in the production of the resin particles, zinc borate as a bubble regulator was supplied to an extruder, and 500 mass ppm of zinc borate was contained in the base resin.

1kg of the polypropylene resin particles was put into a 5L sealed container together with 3L of water as a dispersion medium, and 0.3 part by mass of kaolin as a dispersant and 0.004 part by mass of a surfactant (sodium alkylbenzenesulfonate) were added to the sealed container with respect to 100 parts by mass of the resin particles. Carbon dioxide was added as a blowing agent to a closed vessel so that the pressure in the vessel became 3.7MPa (carbon dioxide pressure), and the vessel was heated to 142.3 ℃ (foaming temperature) with stirring, and after holding at this temperature for 15 minutes, the vessel content was released to atmospheric pressure to obtain expanded particles 1-1. The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 1, and the in-mold formability (formable range) is shown in table 2.

Examples 1 to 2

Expanded particles 1-2 were obtained in the same manner as in example 1-1, except that the polypropylene resin 1 was changed to the polypropylene resin 2 (ethylene-propylene-butene copolymer, butene content was 9.4 mass%, ethylene content was 0.5 mass%. Other characteristics are shown in table 1.) and the carbon dioxide pressure and the expansion temperature were changed to the values shown in table 1. The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 1, and the in-mold formability (formable range) is shown in table 2.

Comparative example 1-1

Expanded particles 1-3 were obtained in the same manner as in example 1-1, except that the polypropylene resin 1 was changed to the polypropylene resin 3 (ethylene-propylene-butene copolymer, butene content: 9.1 mass%, ethylene content: 6.5 mass%. Other characteristics are shown in table 1.) and the carbon dioxide pressure and the expansion temperature were changed to the values shown in table 1. The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 1, and the in-mold formability (formable range) is shown in table 2.

Comparative examples 1 to 2

Expanded particles 1 to 4 were obtained in the same manner as in example 1-1, except that the polypropylene resin 1 was changed to the polypropylene resin 4 (ethylene-propylene-butene copolymer, butene content: 8.8 mass%, ethylene content: 1.6 mass%. Other characteristics are shown in table 1.) and the carbon dioxide pressure and the expansion temperature were changed to the values shown in table 1. The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 1, and the in-mold formability (formable range) is shown in table 2.

In addition, in the expanded beads obtained in this comparative example, a molded article formed 30 times was not obtained.

Examples 1 to 3

Expanded beads 1-5 and expanded bead molded articles were produced in the same manner as in example 1-1, except that the carbon dioxide pressure and the expansion temperature were changed to the values shown in table 1 in order to change the heat of fusion of the high temperature peak of the DSC curve of the expanded beads (presumably derived from secondary crystallization). The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 1, and the in-mold formability (formable range) is shown in table 2.

Examples 1 to 4

Expanded beads 1 to 6 and expanded bead molded articles were produced in the same manner as in examples 1 to 2, except that the carbon dioxide pressure and the expansion temperature were changed to the values shown in table 1. The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 1, and the in-mold formability (formable range) is shown in table 2.

Comparative examples 1 to 3

Expanded beads 1 to 7 and expanded bead molded articles were produced in the same manner as in comparative example 1 to 1, except that the carbon dioxide pressure and the expansion temperature were changed to the values shown in Table 1. The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 1, and the in-mold formability (formable range) is shown in table 2.

TABLE 1

Butene/ethylene: mass ratio of butene component content to ethylene component content (butene component content/ethylene component content)

High temperature peak/total peak: ratio of heat of fusion of high temperature peak to heat of fusion of total melting peak (heat of fusion of high temperature peak/heat of fusion of total melting peak)

TABLE 2

(compressive Strength of expanded particle molded article)

Test pieces 5cm long by 5cm wide by 2.5cm high were collected from the molded bodies obtained in examples and comparative examples, and the test pieces were compressed at a compression rate of 10 mm/min to measure stress at 50% strain. The higher the stress, the more excellent the strength of the expanded particle molded body.

< production of expanded particle molded article (15-fold Molding) >)

Examples 1 to 5

After the expanded beads were subjected to an internal pressure of 0.25MPa (G) by air, the polypropylene resin expanded beads 1-1 obtained in example 1-1 were filled into a flat sheet molding die having a length of 250 mm. Times. A width of 200 mm. Times. A thickness of 50mm so that the resulting molded article became 15 times molded, and after preheating by supplying steam from both sides of the die for 5 seconds (air discharge step), one side of the die was heated until steam having a pressure of 0.08MPa (G) lower than the molding pressure of 0.30MPa (G) was reached, and then one side of the die was heated until steam having a pressure of 0.04MPa (G) lower than the molding pressure was reached (main heating). After the heating was completed, the pressure was released, water cooling was performed until the surface pressure generated by the foaming force of the molded article reached 0.04MPa (G), and then the mold was opened to take out the molded article. The obtained molded body was cured in an oven at 80℃for 12 hours to obtain a molded body of expanded particles. The compressive strength of the obtained expanded particle molded product is shown in table 3.

(examples 1-6 to 1-8 and comparative examples 1-4 to 1-6)

Expanded particle molded articles were produced in the same manner as in examples 1 to 5, except that the polypropylene resin expanded particles 1-1 were changed to the polypropylene resin expanded particles 1-2 to 1-7 obtained in examples and comparative examples shown in Table 3 and the molding pressure was changed to the values shown in Table 3. The compressive strength of the obtained expanded particle molded product is shown in table 3.

TABLE 3

< production of expanded particle molded article (30-fold Molding) >)

(examples 1-9 to 1-12 and comparative examples 1-7 to 1-9)

Expanded particle molded articles were produced in the same manner as in examples 1 to 5, except that the polypropylene resin expanded particles 1-1 to 1-7 were charged into a flat plate molding die so that the resulting molded article was molded 30 times, and the molding pressure was changed to the value shown in table 4. The compressive strength of the obtained expanded particle molded product is shown in table 4.

TABLE 4

It was found that the polypropylene resin expanded beads of the examples have a wide molding range, and therefore have excellent moldability, and the resulting expanded bead molded article has excellent compressive strength.

Examples 2-1 to 2-2 and comparative examples 2-1 to 2-2 (multilayered particles)

In the following, for examples 2-1 to 2-2, expanded particles having a multilayer structure were produced, and the expanded particles formed an outer layer on the surface of a particulate foam having a polypropylene-based resin containing the ethylene-propylene-butene copolymer a as a base resin.

< production of expanded Polypropylene resin particles >

Example 2-1

An ethylene-propylene-butene copolymer A1 (butene content 9.0 mass% and ethylene content 1.0 mass%. Other properties are shown in table 5) as a polypropylene resin was melt-kneaded in an extruder at 200 to 230 ℃ to obtain a resin melt for an inner layer. Meanwhile, an ethylene-propylene copolymer B1 (ethylene component content: 3.5 mass%) as a polypropylene-based resin was melt-kneaded at 200 to 230 ℃ in an extruder to obtain a resin melt for an outer layer. Next, the resin melt for the inner layer and the resin melt for the outer layer were supplied to a coextrusion die, and in the die, the resin melt for the outer layer was laminated so as to cover the periphery of the resin melt for the inner layer, extruded in a strand shape, water-cooled, cut by a granulator so as to have a mass of about 1.3mg, and dried to obtain polypropylene resin particles. The mass ratio of the discharge amount of the resin melt for the inner layer to the resin melt for the outer layer at this time was set to 20/1. In addition, in the production of the resin particles, zinc borate as a bubble regulator was supplied to an extruder, and 500 mass ppm of zinc borate was contained in the ethylene-propylene-butene copolymer A1.

1kg of the polypropylene resin particles was put together with 3L of water as a dispersion medium into a 5L sealed container, 0.3 parts by mass of kaolin as a dispersant and 0.004 parts by mass of a surfactant (sodium alkylbenzenesulfonate) were further added to the sealed container relative to 100 parts by mass of the resin particles, carbon dioxide was added as a foaming agent to the sealed container so that the pressure in the container became 3.3MPa (carbon dioxide pressure), the container was heated to 143℃with stirring, and the temperature was maintained at that temperature for 15 minutes, and then the container content was released to atmospheric pressure, whereby foamed particles 2-1 were obtained. The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 5, and the in-mold formability (formable range) is shown in table 6.

Comparative example 2-1

Expanded beads 2-2 were obtained in the same manner as in example 2-1, except that in example 2-1, resin pellets were obtained by using only the resin melt for the inner layer without using the resin melt for the outer layer, and the carbon dioxide pressure and the expansion temperature were changed to the values shown in table 5. The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 5, and the in-mold formability (formable range) is shown in table 6.

Examples 2 to 2

Expanded particles 2-3 were obtained in the same manner as in example 2-1, except that the ethylene-propylene-butene copolymer A1 was changed to the ethylene-propylene-butene copolymer A2 (butene content: 9.4 mass% and ethylene content: 0.5 mass%. Other characteristics are shown in table 5.) and the carbon dioxide pressure and the expansion temperature were changed to the values shown in table 5. The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 5, and the in-mold formability (formable range) is shown in table 6.

Comparative examples 2-2

Expanded beads 2-4 were obtained in the same manner as in example 2-2, except that in example 2-2, resin pellets were obtained by using only the resin melt for the inner layer without using the resin melt for the outer layer, and the carbon dioxide pressure and the expansion temperature were changed to the values shown in table 5. The heat of fusion of each peak of the DSC curve of the obtained expanded particles is shown in table 5, and the in-mold formability (formable range) is shown in table 6.

TABLE 5

TABLE 6

(compressive stress of expanded particle molded article)

< production of expanded particle molded article (30-fold Molding) >)

Examples 2 to 3

After an internal pressure of 0.25MPa (G) was applied with air, the polypropylene resin foam particles 2-1 obtained in example 2-1 were filled into a flat sheet molding die having a length of 250 mm. Times. A width of 200 mm. Times. A thickness of 50mm so that the resulting molded article became 30 times molded, and after 5 seconds of steam was supplied from both sides of the die to perform preheating (vent step), one side of the die was heated until steam having a pressure of 0.08MPa (G) lower than the molding pressure of 0.22MPa (G) was reached, and then the other side of the die was heated until steam having a pressure of 0.04MPa (G) lower than the molding pressure was reached, and then heating was performed until the molding pressure reached 0.22MPa (main heating). After the heating was completed, the pressure was released, water cooling was performed until the surface pressure generated by the foaming force of the molded article reached 0.04MPa (G), and then the molded article was taken out by opening the mold. The obtained molded body was cured in an oven at 80℃for 12 hours to obtain a molded body of expanded particles. Table 7 shows the compressive stress of the obtained expanded particle molded product.

(examples 2-4 and comparative examples 2-3 to 2-4)

A multilayer expanded particle molded article was produced in the same manner as in example 2-3, except that the polypropylene resin multilayer expanded particles 2-1 were changed to the polypropylene resin multilayer expanded particles 2-2 to 2-4 obtained in examples and comparative examples shown in Table 8 and the molding pressure was changed to the values shown in Table 7. Table 7 shows the compressive stress of the obtained multilayer expanded particle molded article.

TABLE 7

The polypropylene resin multilayer expanded beads of the examples have an outer layer while maintaining the compression properties exhibited by the inner layer (expanded layer) in the expanded state, and thus can expand the moldable range compared with expanded beads having a single-layer structure, and can give an excellent expanded bead molded article even under low pressure. Therefore, it was found that the obtained multilayer expanded particle molded article was also excellent in compressive strength.

Industrial applicability

The molded article obtained from the expanded beads of the present invention has excellent strength and can be produced into expanded beads molded articles having characteristics other than strength such as moldability, and therefore can be suitably used for automobile parts, seat cushion materials, sports cushion materials, soles, and the like.

Claims

1. A polypropylene resin foam particle characterized by comprising a polypropylene resin comprising an ethylene-propylene-butene copolymer a as a base resin, wherein the ethylene-propylene-butene copolymer a has a butene component content of 8 to 20 mass%, wherein the ratio of the butene component content by mass to the ethylene component content by mass is 9 to 50 inclusive, wherein the ethylene component content is 0.1 to 2 mass%, and wherein the base resin has a flexural modulus of 800 to 1000MPa.

2. The polypropylene resin foam particles according to claim 1, wherein 2 or more melting peaks including a high temperature peak, which is a peak that does not appear in the 2 nd DSC curve when measured at the time of melting by heating at a heating rate of 10 ℃/min to a temperature of 30 ℃ higher than the temperature of 30 ℃ at the end of the melting peak after the DSC curve obtained by differential scanning calorimetry, i.e., DSC, are obtained, and the melting heat of the high temperature peak is 5 to 40J/g after the DSC curve of the 1 st time is obtained and then the temperature is kept at 30 ℃ higher than the temperature of the end of the melting peak for 10 minutes.

3. The polypropylene resin foam particles according to claim 2, wherein the ratio of the amount of heat of fusion of the high temperature peak to the amount of heat of fusion of the total melting peak of the DSC curve is 0.05 to 0.3.

4. The polypropylene resin foam particles according to claim 1, wherein the ethylene-propylene-butene copolymer a has a melting point of 136 to 148 ℃.

5. The polypropylene resin foam particles according to claim 1, wherein the base resin has a tensile elastic modulus of 700 to 900MPa.

6. The polypropylene resin foam particles as defined in claim 1, wherein the foam particles have an apparent density of 10 to 300kg/m ³ 。

7. The polypropylene resin foam particle according to claim 1, wherein the polypropylene resin foam particle has an outer layer formed on the surface of the foam body and made of a thermoplastic resin B.

8. The polypropylene-based resin foam particle according to claim 1, wherein the melt flow rate MFR of the ethylene-propylene-butene copolymer a is 2 to 10g/10 min.

9. A foam particle molded article obtained by molding the foam particle molded article according to any one of claims 1 to 8 in a mold.

10. The expanded-particle molded body as claimed in claim 9, wherein the density of the expanded-particle molded body is 5 to 50kg/m ³ 。

11. The expanded-particle molded body according to claim 9 or 10, wherein 50% compressive stress of the expanded-particle molded body is 0.10 to 0.55MPa.