CN116783240A

CN116783240A - Polypropylene resin foam particles and polypropylene resin foam molded article

Info

Publication number: CN116783240A
Application number: CN202180089689.8A
Authority: CN
Inventors: 松宫丰
Original assignee: Kaneka Corp
Current assignee: Kaneka Corp
Priority date: 2021-01-08
Filing date: 2021-12-28
Publication date: 2023-09-19
Also published as: WO2022149538A1; JPWO2022149538A1

Abstract

The object is to (a) provide a polypropylene resin foam molded article which hardly shrinks or deforms after molding, and (b) provide polypropylene resin foam particles excellent in foamability. A polypropylene resin foam particle comprising a specific amount of a polypropylene resin, a copolymer comprising acrylonitrile units and styrene units, and a hydrogenated styrene copolymer, respectively.

Description

Polypropylene resin foam particles and polypropylene resin foam molded article

Technical Field

The present invention relates to polypropylene resin foam particles and polypropylene resin foam molded articles.

Background

Polypropylene resin foam molded articles are used for various applications such as heat insulating materials including automobile interior parts and automobile bumper cores, cushioning packaging materials, and shipping boxes.

However, since the polypropylene resin is a crystalline thermoplastic resin, the polypropylene resin foam molded body obtained by molding the polypropylene resin foam particles has a larger shrinkage after molding than the amorphous thermoplastic resin such as polystyrene. Therefore, in particular, in the case of integrally molding other raw materials such as metal (insert molding), there is a case where the metal member is deformed by shrinkage of the polypropylene resin foam molded body after molding. That is, in the prior art, when other raw materials such as metal are integrally molded, it is difficult to control the size and/or shape of the polypropylene resin foam molded body.

As a method for controlling shrinkage of a polypropylene resin foam molded article after molding, a method of mixing an amorphous thermoplastic resin to a polypropylene resin for use is known.

For example, patent document 1 discloses a technique of using a polypropylene resin, an amorphous thermoplastic resin, and a compatibilizer in combination.

Patent document 2 discloses a technique in which a polystyrene resin and a polymer mainly composed of a vinyl aromatic compound are mixed with a polypropylene resin.

Prior art literature

Patent literature

Patent document 1: japanese laid-open patent publication No. 2001-302837

Patent document 2: japanese laid-open patent publication No. 6-100740

Disclosure of Invention

Problems to be solved by the invention

In view of the above, an object of one embodiment of the present invention is to (a) provide a polypropylene resin foam molded article which hardly shrinks or deforms after molding, and (b) provide polypropylene resin foam particles excellent in foamability.

Solution for solving the problem

The present inventors have conducted intensive studies to solve the above problems, and as a result, have completed the present invention.

Specifically, the polypropylene resin foam particles according to one embodiment of the present invention comprise: 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer comprising an acrylonitrile unit and a styrene unit, and 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer.

The method for producing polypropylene resin foam particles according to one embodiment of the present invention includes a foaming step of foaming polypropylene resin particles, the polypropylene resin particles including: 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer comprising an acrylonitrile unit and a styrene unit, and 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer.

ADVANTAGEOUS EFFECTS OF INVENTION

According to one embodiment of the present invention, there are exhibited the effects that (a) a polypropylene resin foam molded article which hardly shrinks or deforms after molding and (b) polypropylene resin foam pellets which are excellent in foamability can be provided.

Drawings

Fig. 1 is a schematic view of a foam molded body 100 for evaluating deformation amount.

Detailed Description

Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications can be made within the scope shown in the claims. Further, embodiments or examples obtained by combining technical means disclosed in the different embodiments or examples are also included in the technical scope of the present invention. Further, by combining the technical means disclosed in the respective embodiments, new technical features can be formed. All of the academic documents and patent documents described in the present specification are incorporated by reference into the present specification. In the present specification, "a to B" representing a numerical range means "a or more (including a and more than a) and B or less (including B and less than B)", unless otherwise specified.

In addition, in the present descriptionThe term "X" is intended to include all those derived from X unless otherwise specified ¹ Structural units of monomers, derived from X ² Monomeric building blocks … and X ⁿ Copolymers having monomers (n is an integer of 2 or more) as structural units are referred to as "X ¹ /X ² /…/X ⁿ A copolymer. As X ¹ /X ² /…/X ⁿ The polymerization system of the copolymer is not particularly limited except that it has been already described, and may be a random copolymer, a block copolymer, or a graft copolymer.

In this specification, a structural unit derived from an X monomer contained in a polymer or copolymer is sometimes referred to as an "X unit".

[ 1. Polypropylene resin foam particles ]

The polypropylene resin foam particles according to one embodiment of the present invention comprise: 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer comprising an acrylonitrile unit and a styrene unit, and 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer.

The polypropylene resin foam pellets according to one embodiment of the present invention can be molded by a known method to provide a polypropylene resin foam molded body.

In the present specification, "polypropylene-based resin expanded beads" are sometimes referred to as "expanded beads", polypropylene-based resin expanded beads according to one embodiment of the present invention are sometimes referred to as "present expanded beads", and "polypropylene-based resin expanded molded article" is sometimes referred to as "expanded molded article".

The polypropylene resin foam particles according to one embodiment of the present invention have the following advantages because they have the aforementioned constitution: (a) Can provide a polypropylene resin foam molded body which hardly shrinks or deforms after molding; and (b) excellent foamability. It can be said that the polypropylene resin foam particles according to one embodiment of the present invention can provide a polypropylene resin foam molded article reduced in shrinkage and deformation after molding as compared with conventional articles. In the present specification, the shrinkage of the molded foam after molding is also referred to as reduced, and is excellent in shrinkage.

In the present specification, the polypropylene resin means: the resin contains 75 mol% or more of structural units derived from propylene monomers, based on 100 mol% of the total structural units contained in the resin. In this specification, the "structural unit derived from propylene monomer" is sometimes referred to as "propylene unit".

(Polypropylene resin)

The polypropylene resin may be (a) a homopolymer of propylene, may be (b) a block copolymer, a random copolymer or a graft copolymer of propylene and a monomer other than propylene, or may be (c) a mixture of 2 or more of these.

The polypropylene resin may have 1 unit or more of a structural unit derived from a monomer other than propylene monomer, or 1 unit or more of a structural unit derived from a monomer other than propylene monomer, in addition to the propylene unit. The "monomer other than propylene monomer" used for producing the polypropylene resin is sometimes referred to as "comonomer". The "structural unit derived from a monomer other than propylene monomer" contained in the polypropylene resin is sometimes referred to as a "comonomer unit".

Examples of the comonomer include alpha-olefins having 2 or 4 to 12 carbon atoms such as ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3, 4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene and the like.

Specific examples of the polypropylene resin include polypropylene homopolymers, ethylene/propylene random copolymers, 1-butene/ethylene/propylene random copolymers, ethylene/propylene block copolymers, 1-butene/propylene block copolymers, propylene/vinyl chloride copolymers, propylene/maleic anhydride copolymers, and styrene-modified polypropylene resins. As the polypropylene resin, 1 kind of the polypropylene resins may be used alone, or 2 or more kinds thereof may be used in combination. Among these, ethylene/propylene random copolymers and 1-butene/ethylene/propylene random copolymers are suitable from the viewpoint of good foamability of the obtained expanded beads and good moldability of the molded article. The meaning of 1-butene and butene-1 is the same.

As the polypropylene resin, a case of using an ethylene/propylene random copolymer or a 1-butene/ethylene/propylene random copolymer (referred to as case a) is considered. In the case of A, the ethylene content in the ethylene/propylene random copolymer or the 1-butene/ethylene/propylene random copolymer is preferably 0.2 to 10.0% by weight based on 100% by weight of each copolymer. The ethylene content means the content of structural units derived from ethylene (ethylene units). When the content of the ethylene unit in the ethylene/propylene random copolymer or the 1-butene/ethylene/propylene random copolymer is (i) 0.2% by weight or more, the foamability of the expanded beads and/or the moldability of the obtained expanded beads tend to be good at the time of producing the expanded beads, and when (ii) 10.0% by weight or less, there is no fear that the mechanical properties of the expanded molded article obtained from the expanded beads will be lowered.

In case a, the 1-butene content of the 1-butene/ethylene/propylene random copolymer is preferably 0.2 to 10.0% by weight based on 100% by weight of the copolymer. The 1-butene content refers to the content of structural units derived from 1-butene (1-butene units). When the content of 1-butene units in the 1-butene/ethylene/propylene random copolymer is (i) 0.2% by weight or more, the foamability of the expanded beads and/or the moldability of the obtained expanded beads tend to be good when the expanded beads are produced, and when (ii) 10.0% by weight or less, there is no fear that the mechanical properties of the expanded molded article obtained from the expanded beads will be lowered.

In case a, the total content of the ethylene unit and the 1-butene unit in the 1-butene/ethylene/propylene random copolymer is preferably 0.5 to 10.0% by weight based on 100% by weight of the 1-butene/ethylene/propylene random copolymer. When the total content of the ethylene units and 1-butene units in the 1-butene/ethylene/propylene random copolymer is (i) 0.5% by weight or more, the foamability of the expanded beads and/or the moldability of the obtained expanded beads tend to be good when the expanded beads are produced, and when (ii) 10.0% by weight or less, there is no fear that the mechanical properties of the expanded molded article obtained from the expanded beads will be lowered.

The melting point of the polypropylene resin is preferably 135.0 to 160.0 ℃, more preferably 138.0 to 158.0 ℃, more preferably 140.0 to 156.0 ℃, more preferably 143.0 to 154.0 ℃, still more preferably 145.0 to 152.0 ℃, and particularly preferably 148.0 to 150.0 ℃. When the melting point of the polypropylene resin is (i) 135.0 ℃ or higher, the expanded molded article obtained from the expanded beads has excellent heat resistance, and when (ii) 160.0 ℃ or lower, the expansion ratio of the expanded beads is easily increased during the production of the expanded beads.

In the present specification, the melting point of the polypropylene resin is a value obtained by measurement by a differential scanning calorimeter (hereinafter referred to as "DSC method"). The specific operation steps are as follows: (1) Melting the polypropylene resin by heating the polypropylene resin from 40.0 ℃ to 220.0 ℃ at a heating rate of 10.0 ℃/min at a temperature of 5mg to 6 mg; (2) Thereafter, the temperature of the melted polypropylene resin was lowered from 220.0 ℃ to 40.0 ℃ at a lowering rate of 10.0 ℃/minute, whereby the polypropylene resin was crystallized; (3) Thereafter, the temperature of the crystallized polypropylene resin was further raised from 40.0℃to 220.0℃at a temperature-raising rate of 10℃per minute. The melting point of the polypropylene resin can be obtained by determining the peak (melting peak) of the DSC curve of the polypropylene resin obtained at the second temperature rise (i.e., at the time of (3)). When there are a plurality of peaks (melting peaks) in the DSC curve of the polypropylene resin obtained by the above method at the second temperature rise, the temperature of the peak (melting peak) having the largest amount of heat of fusion is taken as the melting point of the polypropylene resin. As the differential scanning calorimeter, for example, type DSC6200 manufactured by Seiko Instruments inc.

The Melt Flow Rate (MFR) of the polypropylene resin is not particularly limited, but is preferably 3.0g/10 min to 30.0g/10 min, more preferably 4.0g/10 min to 20.0g/10 min, still more preferably 5.0g/10 min to 15.0g/10 min, and particularly preferably 6.0g/10 min to 13.0g/10 min. The MFR may be referred to as "Melt Index (MI)".

When the MFR of the polypropylene resin is 3g/10 min or more, the expansion ratio of the foam particles tends to be easily increased when the foam particles are produced. When the MFR of the polypropylene resin is 30g/10 min or less, there is no fear of the occurrence of communication of bubbles of the obtained foam particles, and as a result, (i) the compression strength of a foam molded article obtained from the present foam particles tends to be good or (ii) the surface of the foam molded article tends to be good.

In the present specification, the MFR value of the polypropylene resin is a value measured under the following conditions using an MFR measuring instrument described in JIS K7210:1999: the orifice has a diameter of 2.0959 + -0.005 mm phi, a length of 8.000+ -0.025 mm, a load of 2.16kgf and a temperature of 230deg.C (230+ -0.2deg.C).

The polypropylene resin can be obtained by a known method. The polymerization catalyst used in the synthesis of the polypropylene resin is not particularly limited, and for example, a ziegler-based catalyst, a metallocene catalyst, or the like can be used.

(copolymer comprising acrylonitrile unit and styrene unit)

The expanded beads contain 5 to 60 parts by weight of a copolymer containing an acrylonitrile unit and a styrene unit per 100 parts by weight of a polypropylene resin. The expanded beads have the following advantages by having the above constitution: expanded beads excellent in foamability can be obtained, and a foam molded article having reduced shrinkage and deformation after molding as compared with conventional products can be obtained. In the present specification, the "copolymer comprising an acrylonitrile unit and a styrene unit" is sometimes referred to AS "AS copolymer". The AS copolymer is an amorphous resin.

In the present specification, AS copolymer means: the total of 100 mol% of the total structural units contained in the AS copolymer is at least 50 mol% or more of the structural units derived from acrylonitrile units or styrene units. The AS copolymer is not particularly limited AS long AS it contains at least 50 mol% or more of a structural unit comprising an acrylonitrile unit and a styrene unit, and may be, for example, (a) a block copolymer, a random copolymer or a graft copolymer, or may be a mixture of 2 or more of these.

The styrene unit contained in the AS copolymer is a structural unit derived from a styrene monomer. Examples of the styrene monomer include (a) styrene; and (b) styrene derivatives such as α -methylstyrene, p-methylstyrene, m-methylstyrene, o-methylstyrene, 2, 4-dimethylstyrene, p-ethylstyrene, m-ethylstyrene, o-ethylstyrene, t-butylstyrene and chlorostyrene. These styrene monomers may be used in an amount of 1 or 2 or more. That is, the styrene unit contained in the AS copolymer may be 1 kind or 2 or more kinds.

The styrene unit contained in the AS copolymer preferably contains an alpha-methylstyrene unit. The amount of the α -methylstyrene unit in the styrene unit contained in the AS copolymer is preferably 70% by weight or more, more preferably 80% by weight or more, still more preferably 90% by weight or more, particularly preferably 95% by weight or more, and most preferably 100% by weight, based on 100% by weight of the styrene unit contained in the AS copolymer. That is, the styrene unit contained in the AS copolymer is most preferably an alpha-methylstyrene unit. The AS copolymer has the following advantages when the amount of the alpha-methylstyrene unit in the styrene unit is large: the obtained expanded beads (a) provide a polypropylene resin expanded molded article which hardly shrinks or deforms after molding, and (b) are excellent in foamability.

The amount of the styrene unit (hereinafter, sometimes referred to AS "styrene content") contained in the AS copolymer is preferably 20 to 95% by weight, more preferably 50 to 90% by weight, still more preferably 55 to 85% by weight, still more preferably 60 to 80% by weight, and particularly preferably 65 to 75% by weight, based on 100% by weight of the AS copolymer. This structure has an advantage that an AS copolymer having excellent productivity and heat resistance can be obtained.

The amount of the α -methylstyrene unit (hereinafter, sometimes referred to AS "α -methylstyrene content") AS the styrene unit contained in the AS copolymer is preferably 20 to 95% by weight, more preferably 50 to 90% by weight, still more preferably 55 to 85% by weight, still more preferably 60 to 80% by weight, and particularly preferably 65 to 75% by weight, based on 100% by weight of the AS copolymer. This structure has an advantage that an AS copolymer having excellent productivity and heat resistance can be obtained.

The AS copolymer may have structural units other than the acrylonitrile unit and the styrene unit (hereinafter sometimes referred to AS "structural units other than AS"). Examples of the structural unit other than AS include vinyl esters such AS vinyl acetate and vinyl propionate; acrylic esters such as methyl acrylate and ethyl acrylate; methacrylate esters such as methyl methacrylate and ethyl methacrylate; olefins such as ethylene and propylene; maleic anhydride; vinyl chloride; vinylidene chloride; and monomers other than the above monomers which can be copolymerized with an acrylonitrile unit and/or a styrene unit. The amount of the structural unit other than AS contained in the AS copolymer is preferably 10 wt% or less, more preferably 5 wt% or less, further preferably 1 wt% or less, and particularly preferably 0 wt% of 100 wt% of the AS copolymer, from the viewpoint that the heat resistance of the AS copolymer is improved. Specifically, the AS copolymer is particularly preferably a copolymer composed of an acrylonitrile unit and a styrene unit.

Specific examples of the AS copolymer include acrylonitrile/styrene copolymer, acrylonitrile/α -methylstyrene copolymer, acrylonitrile/p-methylstyrene copolymer, acrylonitrile/m-methylstyrene copolymer, acrylonitrile/o-methylstyrene copolymer, acrylonitrile/2, 4-dimethylstyrene copolymer, acrylonitrile/p-ethylstyrene copolymer, acrylonitrile/m-ethylstyrene copolymer, acrylonitrile/o-ethylstyrene copolymer, acrylonitrile/t-butylstyrene copolymer, and acrylonitrile/chlorostyrene copolymer. Among the above copolymers, acrylonitrile/α -methylstyrene copolymer is preferable because it can give expanded particles excellent in foamability. Only 1 kind of these AS copolymers may be used, or 2 or more kinds may be used in combination.

The glass transition temperature (sometimes referred to AS "Tg") of the AS copolymer is not particularly limited, but is preferably 95℃to 140℃and more preferably 100℃to 135℃and even more preferably 103℃to 130℃and particularly preferably 105℃to 125 ℃. When the Tg of the AS copolymer is (i) 95 ℃ or higher, there is an advantage that expanded particles and expanded molded articles excellent in heat resistance can be obtained, and when (ii) 140 ℃ or lower, expanded particles having a low open cell ratio can be obtained.

In the present specification, tg of the AS copolymer is a value measured using a differential scanning calorimeter [ Seiko Instruments Inc., DSC6200 type ], and in accordance with JIS-K-7121. The specific operation steps are as follows (1) to (5): (1) measuring 5mg of AS copolymer; (2) Heating the AS copolymer from room temperature to 250 ℃ at 10 ℃/min under nitrogen atmosphere; (3) Cooling the temperature of the warmed AS copolymer from 250 ℃ to room temperature at 10 ℃/min; (4) Again, the temperature of the AS copolymer was raised from room temperature to 250 ℃ at 10 ℃/min; (5) The temperature of the peak (melting peak) of the DSC curve of the AS copolymer obtained at the second temperature rise (i.e., at the time of (4)) was taken AS the Tg of the AS copolymer.

The MFR of the AS copolymer is not particularly limited, but is preferably 2.0g/10 min to 15.0g/10 min, more preferably 3.0g/10 min to 12.0g/10 min, and still more preferably 4.0g/10 min to 10.0g/10 min. When the MFR of the AS copolymer is 2.0g/10 min to 15.0 g/min, the AS copolymer has excellent compatibility with the polypropylene resin, and can reduce foam communication when foaming the obtained resin particles. As a result, there is an advantage that expanded beads having a low open cell ratio can be obtained.

In the present specification, the value of MFR of the AS copolymer is a value measured under the following conditions using an MFR measuring instrument described in JIS K7210:1999: the orifice has a diameter of 2.0959 + -0.005 mm phi, a length of 8.000+ -0.025 mm, a load of 2.16kgf and a temperature of 230deg.C (230+ -0.2deg.C).

The content of the AS copolymer in the expanded beads is 5 to 60 parts by weight, more preferably 5 to 50 parts by weight, still more preferably 8 to 50 parts by weight, still more preferably 10 to 40 parts by weight, still more preferably 13 to 40 parts by weight, still more preferably 15 to 35 parts by weight, and particularly preferably 20 to 30 parts by weight, based on 100 parts by weight of the polypropylene resin. When the content of the AS copolymer is (a) 5 parts by weight or more based on 100 parts by weight of the polypropylene resin, there is an advantage that expanded particles excellent in foamability can be obtained and expanded molded articles having shrinkage and deformation after molding reduced more than conventional products can be obtained, and when (b) 60 parts by weight or less, there is an advantage that expanded particles having a low continuous cell ratio and excellent foamability can be obtained.

(hydrogenated styrene copolymer)

The polypropylene resin foam particles according to one embodiment of the present invention contain 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer. In one embodiment of the present invention, the hydrogenated styrene copolymer has the compatibilizing effect of the polypropylene resin and the AS copolymer. In other words, the hydrogenated styrenic copolymer may function as a compatibilizer. The present expanded beads have the following advantages by containing the hydrogenated styrenic copolymer in the above-mentioned range: expanded beads excellent in foamability can be obtained, and a foam molded article having reduced shrinkage and deformation after molding as compared with conventional products can be obtained.

In the present specification, "hydrogenated styrenic copolymer" means: a copolymer obtained by hydrogenating a block copolymer (hereinafter also referred to as a copolymer X) comprising a styrene block composed of only styrene units and a conjugated diene block composed of only conjugated diene units. In this specification, "hydrogenation" is sometimes referred to as "hydrogenation". More specifically, "hydrogenated styrenic copolymer" means: and a copolymer obtained by hydrogenating the copolymer X so that at least a part of the carbon-carbon double bonds in the conjugated diene units of the copolymer X are saturated.

The conjugated diene unit included in the copolymer X includes, but is not particularly limited to, a butadiene unit, an isoprene unit, a 1, 3-pentadiene unit, a 2, 3-dimethyl-1, 3-butadiene unit, a 3-methyl-1, 3-octadiene unit, a 4-ethyl-1, 3-hexadiene unit, and the like.

In the production of the hydrogenated styrene copolymer, at least a part of carbon-carbon double bonds in the conjugated diene unit of the copolymer X may be saturated, and the whole is not necessarily saturated. In other words, the hydrogenated styrenic copolymer may comprise conjugated diene units comprised by copolymer X used in the production of the hydrogenated styrenic copolymer. More specifically, when the copolymer X contains a butadiene unit as a conjugated diene unit, the hydrogenated styrene copolymer obtained by hydrogenating the copolymer X may contain (a) an unhydrogenated butadiene unit, may contain (b-1) a butene unit obtained by addition polymerization of hydrogen 1,2 to a carbon-carbon double bond of a butadiene unit, and may contain (b-2) an ethylene unit obtained by addition polymerization of hydrogen 1,4 to a carbon-carbon double bond of a butadiene unit.

The hydrogenated styrene copolymer preferably has a proportion of conjugated diene units having hydrogenated carbon-carbon double bonds (hereinafter, sometimes referred to as "hydrogenation rate") of 50% or more, more preferably 70% to 100%, and still more preferably 80% to 100% of the total conjugated diene units of the copolymer X used in the production. When the hydrogenation ratio of the hydrogenated styrene copolymer is in the above range, the following tends to occur: the hydrogenated styrene copolymer is easily present at the interface between the polypropylene resin and the AS copolymer, and the compatibilizing effect of the hydrogenated styrene copolymer is improved. The hydrogenation rate of the hydrogenated styrenic copolymer may be 100%.

Specific examples of the hydrogenated styrene copolymer include styrene/ethylene/butylene/styrene block copolymer (SEBS) and styrene/ethylene/propylene/styrene block copolymer (SEPS). SEBS is a copolymer obtained by hydrogenating a copolymer (copolymer X) in which (a) a styrene block composed only of styrene units, (b) a butadiene block composed only of butadiene units, and (c) a styrene block composed only of styrene units are bonded in this order. More specifically, SEBS is a copolymer in which (a) a styrene block composed of only styrene units, (b) a block in which (b-1) a butene unit obtained by hydrogenating a 1,2 addition-polymerized butadiene unit and (b-2) an ethylene unit obtained by hydrogenating a 1,4 addition-polymerized butadiene unit are bonded in this order, and (c) the styrene block are randomly bonded. The block of SEBS having randomly bonded butene units and ethylene units may contain butadiene units. SEPS is a copolymer obtained by hydrogenating a copolymer (copolymer X) in which (a) a styrene block composed of only styrene units, (b) an isoprene block composed of only isoprene units, and (c) a styrene block composed of only styrene units are bonded in this order. More specifically, SEPS is a copolymer in which (a) a styrene block composed of only styrene units, (b) a block in which an ethylene unit and a propylene unit are randomly bonded by hydrogenation of an isoprene unit, and (c) the styrene block are sequentially bonded. Among these, the hydrogenated styrenic copolymer preferably contains SEBS, particularly preferably SEBS, from the viewpoint of having a higher strength.

The styrene unit content (hereinafter sometimes referred to as "styrene content") of the hydrogenated styrene copolymer is preferably 5 to 90% by weight, more preferably 10 to 85% by weight, still more preferably 15 to 80% by weight, and still more preferably 25 to 55% by weight, based on 100% by weight of the hydrogenated styrene copolymer. This structure has an advantage that the compatibility between the polypropylene resin and the AS copolymer can be improved. In particular, when the styrene unit content of the hydrogenated styrene copolymer is 15% by weight or more based on 100% by weight of the hydrogenated styrene copolymer, there is a tendency that a foam molded article having reduced shrinkage and deformation after molding can be obtained as compared with conventional products.

The content of the hydrogenated styrene copolymer in the expanded beads is 3.0 to 30.0 parts by weight, preferably 4.0 to 25.0 parts by weight, more preferably 5.0 to 20.0 parts by weight, still more preferably 5.0 to 15.0 parts by weight, particularly preferably 5.0 to 10.0 parts by weight, based on 100 parts by weight of the polypropylene resin. When the content of the hydrogenated styrene copolymer is 3.0 parts by weight or more based on 100 parts by weight of the polypropylene resin, there is an advantage that the compatibilizing effect of the polypropylene resin and the AS copolymer can be sufficiently exhibited by using the hydrogenated styrene copolymer. When the content of the hydrogenated styrene-based copolymer is 30.0 parts by weight or less based on 100 parts by weight of the polypropylene-based resin, there are the following advantages: (a) expanded beads excellent in foamability can be obtained, (b) the rigidity of a foam molded article obtained by molding the expanded beads can be made sufficient, and (c) the shrinkage and deformation after molding can be further reduced as compared with conventional products.

(other resins, etc.)

The expanded beads may further contain, AS a resin component, resins other than polypropylene-based resins, AS copolymers and hydrogenated styrene-based copolymers (sometimes referred to AS other resins, etc.) within a range that does not impair the effects described in one embodiment of the present invention. Examples of the other resins include (a) vinyl resins such as 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; (b) Styrene resins such as polystyrene, styrene/maleic anhydride copolymer and styrene/ethylene copolymer; (c) polyphenylene ether resins such as polyphenylene ether and modified polyphenylene ether; (d) polyolefin waxes such as propylene/α -olefin waxes; olefin rubber such as ethylene/propylene rubber, ethylene/butene rubber, ethylene/hexene rubber, and ethylene/octene rubber. The styrene resin and the polyphenylene ether resin are amorphous resins.

The content of the other resin or the like in the expanded beads is preferably more than 0 part by weight and 50 parts by weight or less, more preferably more than 0 part by weight and 30 parts by weight or less, relative to 100 parts by weight of the polypropylene resin. In addition, the present expanded beads may not contain other resins or the like. That is, the content of the other resin or the like in the present expanded beads may be 0 parts by weight.

(additive)

The expanded beads may further optionally contain additives in addition to the resin component containing the polypropylene-based resin, AS copolymer and hydrogenated styrene-based copolymer. Examples of the additives include colorants, water-absorbing materials, foam nucleating agents, antistatic agents, flame retardants, antioxidants, light stabilizers, crystal nucleating agents, conductive agents, lubricants, and the like. Such an additive may be used in the production of the resin particles to be contained in the resin particles at the time of producing the present expanded beads, and may be directly added to the dispersion in a foaming step described later.

The water-absorbent material is a material used for the purpose of increasing the water penetration amount in the resin particles at the time of manufacturing the present expanded particles. By using a water-absorbing substance in the production of the present expanded beads, foamability can be imparted to the resin beads. In the case of using water as the foaming agent, the effect of imparting foamability to the resin particles by the water-absorbent material becomes particularly remarkable.

Examples of the water-absorbing substance that can be used in one embodiment of the present invention include glycerin, diglycerin, polyethylene glycol, C12-C18 aliphatic alcohols (e.g., pentaerythritol, cetyl alcohol, stearyl alcohol), melamine, isocyanuric acid, melamine-isocyanuric acid condensate, zinc borate, and the like. These water-absorbing materials may be used alone in an amount of 1 or in an amount of 2 or more. In addition, when 2 or more water-absorbing substances are used in combination, the mixing ratio can be appropriately adjusted according to the purpose.

Glycerin and polyethylene glycol (a) do not promote the miniaturization of the average cell diameter of the expanded beads, and (b) have good affinity with polypropylene resins. Therefore, among the above water-absorbent materials, glycerin and/or polyethylene glycol are preferable.

The amount of the water-absorbent material used in the production of the present expanded particles, in other words, the content of the water-absorbent material in the present expanded particles will be described. The content of the water-absorbent material in the expanded beads is preferably 0.01 to 1.00 parts by weight, more preferably 0.05 to 0.70 parts by weight, and even more preferably 0.10 to 0.60 parts by weight, based on 100 parts by weight of the total of the polypropylene resin, AS copolymer and hydrogenated styrene copolymer. When the content of the water-absorbent material is (i) 0.01 parts by weight or more, the effect of imparting foamability by the water-absorbent material can be sufficiently obtained, and when (ii) 1.00 parts by weight or less, there is no concern that the resulting expanded particles shrink.

The foam nucleating agent is a substance which can be used in the production of the present expanded beads and which can form a foam core when the resin beads are expanded. In the production of the present expanded beads, a foam nucleating agent is preferably used, in other words, the present expanded beads preferably contain a foam nucleating agent.

Examples of the foam nucleating agent that can be used in one embodiment of the present invention include silica (Silicon dioxide), silicate, alumina, diatomaceous earth, calcium carbonate, magnesium carbonate, calcium phosphate, feldspar apatite, and barium sulfate. Examples of the silicate include talc, magnesium silicate, kaolin, halloysite, dickite, aluminum silicate, and zeolite. The foaming nucleating agent may be used alone or in combination of 1 or more than 2 kinds. In addition, when 2 or more kinds of the foam nucleating agents are used in combination, the mixing ratio can be appropriately adjusted according to the purpose.

The amount of the foam nucleating agent used in the production of the expanded beads, in other words, the content of the foam nucleating agent in the expanded beads will be described. From the viewpoint of uniformity of average cell diameters, the content of the foam nucleating agent in the present expanded beads is preferably 0.005 to 2.000 parts by weight, more preferably 0.010 to 1.000 parts by weight, and even more preferably 0.030 to 0.500 parts by weight, relative to 100 parts by weight of the total amount of the polypropylene resin, the AS copolymer and the hydrogenated styrene copolymer.

The total amount of the additives used in producing the expanded beads, in other words, the total content of the additives in the expanded beads is preferably more than 0 parts by weight and not more than 10 parts by weight, more preferably more than 0 parts by weight and not more than 5 parts by weight, relative to 100 parts by weight of the polypropylene resin. In addition, the expanded beads may not contain any additives. That is, the content of each additive in the present expanded beads may be 0 parts by weight.

< physical Properties >

The physical properties of the expanded beads will be described below.

(expansion ratio of expanded beads)

The expansion ratio of the expanded beads is preferably 15.0 to 50.0 times, more preferably 15.0 to 40.0 times, still more preferably 15.0 to 25.0 times, particularly preferably 15.0 to 20.0 times. If the expansion ratio of the expanded beads is (i) 15.0 times or more, a lightweight foam molded article can be obtained with good productivity, and if it is (ii) 50.0 times or less, there is no fear that the strength of the obtained foam molded article is insufficient. In the present specification, the "expanded beads excellent in foamability" means expanded beads (primary expanded beads described later) obtained by directly expanding resin beads, and the expansion ratio of the expanded beads is 15.0 times or more.

In the present specification, the expansion ratio of the expanded beads is calculated by the following methods (1) to (6): (1) Accurately measuring the weight Gi of the predetermined amount of the expanded beads to a unit of 0.001g (rounding the fourth digit after the decimal place); (2) Next, all of the expanded beads for measuring the weight Gi were immersed in 100mL of ethanol at 23 ℃ contained in a measuring cylinder; (3) The volume yi (cm) of the expanded beads was measured from the amount of rise in the liquid level position of the measuring cylinder ³ ) The method comprises the steps of carrying out a first treatment on the surface of the (4) By dividing the weight Gi (g) of the expanded particles by the volume yi (cm) of the expanded particles ³ ) And converting it into g/L units, thereby calculating the apparent density di (g/L) of the expanded particles; (5) Using resin particles for producing expanded beads instead of expanded beads, the density ds (g/L) of the resin particles is calculated by performing the same operations as (1) to (4); (6) the expansion ratio of the expanded beads was calculated by the following formula:

foaming ratio ki=ds/di.

(DSC ratio of expanded particles)

The expanded beads preferably have at least two melting peaks in a DSC curve obtained by Differential Scanning Calorimetry (DSC) described later. Among the melting peaks, the heat of fusion obtained from the melting peak at the high temperature side is referred to as "high temperature side heat of fusion", and the heat of fusion obtained from the melting peak at the low temperature side is referred to as "low temperature side heat of fusion". When the number of melting peaks is 3 or more, the amount of heat of melting obtained from the highest temperature melting peak is referred to as "high temperature side heat of melting", and the amount of heat of melting obtained from the other melting peaks is referred to as "low temperature side heat of melting".

The DSC ratio of the expanded beads is not particularly limited, but is preferably 10.0% to 50.0%, more preferably 20.0% to 40.0%, and even more preferably 22.0% to 30.0%. When the DSC ratio of the expanded beads is 10.0% or more, there is an advantage that the foamed molded article obtained by molding the expanded beads has sufficient strength. On the other hand, when the DSC ratio of the expanded beads is 40% or less, there is an advantage that the expanded beads can be molded at a relatively low molding temperature.

In the present specification, the DSC ratio refers to a ratio of the heat of fusion at the high temperature side calculated from the DSC curve of the present expanded beads to the total heat of fusion. In the present specification, a DSC curve is obtained using a differential scanning calorimeter (for example, model DSC6200, manufactured by Seiko Instruments inc.). More specifically, in the present specification, the method of measuring (calculating) the DSC ratio of foamed particles using a differential scanning calorimeter (for example, model DSC6200, manufactured by Seiko Instruments inc.) is as follows (1) to (5): (1) weighing 5 mg-6 mg of foaming particles; (2) Heating the temperature of the foaming particles from 40 ℃ to 220 ℃ at a heating rate of 10 ℃/min, and melting the foaming particles; (3) In the DSC curve of the expanded beads obtained in the above (2), the maximum point between the highest temperature melting peak and the melting peak adjacent to the highest temperature melting peak (low temperature side) is connected to the point indicating the temperature before the start of melting by a straight line, and the maximum point is connected to the point indicating the temperature after the end of melting by a straight line; (4) The method comprises (a) setting a heat amount calculated from a high-temperature side region surrounded by (a-1) a line segment obtained by connecting the maximum point with a point indicating a temperature after completion of melting and (a-2) a DSC curve as a high-temperature side melting heat amount, (b) setting a heat amount calculated from a line segment obtained by connecting the maximum point with a point indicating a temperature before start of melting and (b-2) a low-temperature side region surrounded by a DSC curve as a low-temperature side melting heat amount, and (c) setting a sum of the high-temperature side melting heat amount and the low-temperature side melting heat amount as a total melting heat amount (=high-temperature side melting heat amount+low-temperature side melting heat amount); (5) calculating a DSC ratio according to the following formula:

DSC ratio (%) = (high temperature side heat of fusion/total heat of fusion) ×100.

The DSC ratio of the expanded beads may be a value that serves as a reference for the amount of crystals having a high melting point contained in the expanded beads. That is, a DSC ratio of 10.0% to 50.0% of the expanded beads means that the expanded beads contain a large number of crystals having a high melting point. In addition, the DSC ratio of the expanded particles is significantly related to the viscoelasticity of the resin particles and the expanded particles when the resin particles are expanded and when the expanded particles are expanded. That is, when the DSC ratio of the expanded beads is 10.0% to 50.0%, the resin beads and the expanded beads can exhibit excellent foamability and expandability, respectively, when the resin beads are expanded and when the expanded beads are molded. As a result, the following advantages are obtained: a foam molded article having excellent internal fusion properties at a low molding pressure and excellent mechanical strength such as compression strength can be obtained.

In the present expanded beads, as a method for controlling the DSC ratio to a predetermined range, there are: a method of adjusting the conditions (in particular, the foaming temperature, the foaming pressure, the holding time, the temperature of the region (space) where the dispersion is released, etc.) at the time of producing the present expanded beads. From the viewpoint of easy adjustment, a method of adjusting the foaming temperature, foaming pressure, and/or holding time is preferable as a method of controlling the DSC ratio to a predetermined range.

For example, if the foaming temperature is increased, the DSC ratio of the obtained expanded beads tends to be small, whereas if the foaming temperature is decreased, the DSC ratio of the obtained expanded beads tends to be large. This is because: the amount of unmelted crystals contained in the expanded beads varies depending on the foaming temperature. Further, if the foaming pressure is increased, the DSC ratio of the obtained expanded beads tends to be small, whereas if the foaming pressure is decreased, the DSC ratio of the obtained expanded beads tends to be large. This is because: the degree of plasticization changes due to the foaming pressure, and thus the amount of unmelted crystals contained in the expanded beads changes. In addition, the DSC ratio of the obtained expanded beads tends to be larger as the holding time is longer. This is because: the growth amount of unmelted crystals contained in the expanded beads varies depending on the holding time.

(continuous bubble ratio)

The lower the open cell ratio of the expanded beads is, the more preferable. The continuous cell ratio of the expanded beads is preferably 15.0% or less, more preferably 10.0% or less, more preferably 9.0% or less, more preferably 8.0% or less, more preferably 7.0% or less, more preferably 6.0% or less, more preferably 5.0% or less, more preferably 4.0% or less, and particularly preferably 3.0% or less. The lower limit of the continuous bubble ratio of the expanded beads is not particularly limited, but is, for example, 0.0% or more. According to this constitution, there are the following advantages: (a) In the molding of the expanded beads, the cells hardly break and shrink, and therefore, the expanded beads are excellent in moldability; and (b) further exhibits characteristics such as shape discretionary, cushioning property, lightweight property, compression strength, and heat insulation property in the foamed molded article obtained by using the foamed particles. The ratio of open cells of the present expanded beads can be controlled by, for example, the amount of AS copolymer used.

In the present specification, the ratio of open cells of the expanded beads was determined by using an air comparative densitometer [ Tokyo science Co., ltd., 1000 type ]]The values obtained by measurement were measured according to the method described in step C (PROSEDURE C) of ASTM D2856-87. Specifically, the open cell percentage of the expanded beads was calculated by sequentially carrying out the following (1) to (4): (1) Measurement of the volume Vc (cm) of the expanded particles Using an air comparison densitometer ³ ) The method comprises the steps of carrying out a first treatment on the surface of the (2) Then, the total amount of the foaming particles after Vc measurement is immersed into ethanol contained in a measuring cylinder; (3) Thereafter, the apparent volume Va (cm) of the foamed particles was obtained from the amount of rise in the ethanol position in the measuring cylinder ³ ) The method comprises the steps of carrying out a first treatment on the surface of the (4) The open cell ratio of the expanded particles was calculated using the following formula: continuous bubble ratio (%) = ((Va-Vc) ×100)/Va. The above-described method of measuring the volume Va is also referred to as a water immersion method.

< method for producing expanded Polypropylene resin particles >

The method for producing the expanded beads is not particularly limited, and known methods can be suitably used. As a method for producing the present expanded beads, it is preferable that: the method comprises a foaming step of foaming polypropylene resin particles, wherein the polypropylene resin particles comprise: 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer comprising an acrylonitrile unit and a styrene unit, and 3 to 30 parts by weight of a hydrogenated styrene copolymer. Hereinafter, one embodiment of the present method for producing expanded beads will be described in detail, and the above description (for example, description of one item < ingredient >) is appropriately referred to in addition to the matters described in detail below. The method for producing the expanded beads is not limited to the following production method.

(granulation step)

In producing the expanded beads, a step of producing polypropylene resin beads (pelletization step) is first performed. In the present specification, the "polypropylene-based resin particles" are sometimes referred to as "resin particles". The granulating step may be a step of producing resin pellets containing 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer containing an acrylonitrile unit and a styrene unit, and 3 to 30 parts by weight of a hydrogenated styrene copolymer.

As a method for producing the resin pellets, a method using an extruder is exemplified. Specifically, the resin particles can be produced by, for example, the following methods (1) to (5): (1) Blending a polypropylene resin, an AS copolymer and a hydrogenated styrene copolymer, and optionally 1 or more selected from the group consisting of other resins and additives to prepare a blend; (2) Feeding the blend into an extruder, and melt-kneading the blend to prepare a polypropylene resin composition; (3) Extruding the polypropylene resin composition from a die provided in an extruder; (4) The extruded polypropylene resin composition is cooled by being introduced into water or the like, thereby solidifying the composition; (5) Thereafter, the cured polypropylene resin composition is finely cut into a desired shape such as a cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, or the like by a cutter. Alternatively, in (3), the polypropylene resin composition to be melt-kneaded may be extruded directly into water from a die provided in an extruder, and immediately after the extrusion, the polypropylene resin composition may be cut into a pellet shape, cooled and solidified. In this way, by melt-kneading the blend, more uniform resin particles can be obtained.

The weight of each of the resin particles obtained in the above-described manner is preferably 0.5 mg/particle to 3.0 mg/particle, more preferably 0.7 mg/particle to 2.5 mg/particle. When the weight of each of the resin particles is 0.5 mg/particle or more, the handleability of the resin particles tends to be improved, and when it is 3.0 mg/particle or less, the mold filling property in the in-mold foam molding step tends to be improved.

The amounts of the polypropylene-based resin, AS copolymer and hydrogenated styrene-based copolymer, and other resins and additives supplied to the granulating step (blending and melt-kneading) are the contents of the respective components in the produced resin pellets. Therefore, the granulation step preferably includes: and a step of blending at least 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer containing an acrylonitrile unit and a styrene unit, and 3 to 30 parts by weight of a hydrogenated styrene copolymer, and melt-kneading the blend.

(foaming Process)

The foaming step in the method for producing expanded beads is not particularly limited as long as the resin beads can be foamed. In one embodiment of the present invention, the foaming step preferably includes:

(a) A dispersing step of dispersing the resin particles, the aqueous dispersion medium, the foaming agent, and if necessary, the dispersant and/or the dispersing aid in a container;

(b) A temperature raising-pressure raising step of raising the temperature in the container to a predetermined temperature and raising the pressure in the container to a predetermined pressure;

(c) A holding step of holding the temperature and pressure in the container at a predetermined temperature and a predetermined pressure; and

(d) And a releasing step of opening one end of the container and releasing the dispersion liquid in the container into a region (space) having a pressure lower than the foaming pressure (i.e., the pressure in the container).

In this way, the step of producing expanded beads from resin beads is referred to as a "one-stage expansion step", and the expanded beads thus obtained are referred to as "one-stage expanded beads".

The amounts of the polypropylene resin, the AS copolymer and the hydrogenated styrene copolymer contained in the resin particles supplied to the foaming step are the amounts of the polypropylene resin, the AS copolymer and the hydrogenated styrene copolymer in the obtained foamed particles. Therefore, the foaming step in the method for producing expanded beads is preferably a step of foaming resin beads comprising 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer comprising an acrylonitrile unit and a styrene unit, and 3 to 30 parts by weight of a hydrogenated styrene copolymer.

(dispersing step)

The dispersion step may also be a step of preparing a dispersion in which, for example, resin particles, a foaming agent, and if necessary, a dispersant and/or a dispersion aid are dispersed in an aqueous dispersion medium.

The container used in the dispersing step is not particularly limited, and a container that can withstand a foaming temperature and a foaming pressure described later is preferable. The vessel is preferably a pressure-resistant vessel, for example, and more preferably an autoclave-type pressure-resistant vessel.

The aqueous dispersion medium is not particularly limited as long as it can uniformly disperse the resin particles, the foaming agent, and the like. Examples of the aqueous dispersion medium include (a) a dispersion medium obtained by adding methanol, ethanol, ethylene glycol, glycerin, and the like to water; and (b) water such as tap water and industrial water. From the viewpoint of stably producing expanded beads, pure water such as RO water (water purified by reverse osmosis membrane method), distilled water, deionized water (water purified by ion exchange resin), ultrapure water, and the like are preferably used as the aqueous dispersion medium.

The amount of the aqueous dispersion medium to be used is not particularly limited, but is preferably 100 parts by weight to 400 parts by weight based on 100 parts by weight of the resin particles. When the amount of the aqueous dispersion medium is (a) 100 parts by weight or more, there is no concern that the stability of the dispersion is lowered (in other words, the dispersion of the resin particles becomes good), and when (b) 400 parts by weight or less, there is no concern that the productivity of the expanded particles is lowered.

Examples of the foaming agent include: (a) (a-1) an inorganic gas such as nitrogen, carbon dioxide, or air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a-2) an inorganic foaming agent such as water; and (b) saturated hydrocarbons having 3 to 5 carbon atoms such as propane, n-butane, isobutane, n-pentane, isopentane, neopentane, etc., (b-2) ethers such as dimethyl ether, diethyl ether, methylethyl ether, etc., (b-3) halogenated hydrocarbons such as monochloromethane, methylene chloride, dichlorodifluoroethane, etc., etc. As the foaming agent, at least 1 or more selected from the group consisting of the above-mentioned inorganic foaming agents and organic foaming agents can be used. When 2 or more foaming agents are used in combination, the mixing ratio can be appropriately adjusted according to the purpose. From the viewpoints of environmental load and foaming power, among the above, an inorganic foaming agent is preferable. Among the inorganic foaming agents, carbon dioxide is preferred from the viewpoint of appropriately improving plasticizing effect and easily improving foamability of the expanded beads when the expanded beads are produced.

The amount of the foaming agent is not particularly limited as long as it is appropriately used according to the kind of (a) the foaming agent and/or the desired expansion ratio of (b) the expanded beads. The amount of the foaming agent to be used is preferably 1 to 10000 parts by weight, more preferably 1 to 5000 parts by weight, still more preferably 1 to 1000 parts by weight, based on 100 parts by weight of the resin particles, for example. When the amount of the blowing agent is 1 part by weight or more based on 100 parts by weight of the resin particles, expanded particles having a suitable density can be obtained. On the other hand, when the amount of the foaming agent is 10000 parts by weight or less relative to 100 parts by weight of the resin particles, an effect corresponding to the amount of the foaming agent can be obtained, and therefore, no economic waste occurs. The amount of the foaming agent may be, for example, 1 to 100 parts by weight or 1 to 10 parts by weight based on 100 parts by weight of the resin particles.

In the case of using water as the foaming agent, water in the dispersion in the container may be used as the foaming agent. Specifically, when water in the dispersion is used as the foaming agent, the water-absorbent material is preferably contained in the resin particles in advance. As a result, the resin particles easily absorb water of the dispersion liquid in the container, and as a result, water is easily used as the foaming agent.

In the method for producing the expanded beads, a dispersing agent is preferably used. By using a dispersant, there are the following advantages: the adhesion (sometimes referred to as blocking) of the resin particles to each other can be reduced, and the expanded beads can be stably produced. Examples of the dispersant include inorganic substances such as calcium phosphate, magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, clay, alumina, titanium oxide, and aluminum hydroxide. These dispersants may be used alone or in combination of at least 2. In the case where 2 or more dispersants are used in combination, the mixing ratio can be appropriately adjusted according to the purpose.

The amount of the dispersant used in the dispersion liquid according to one embodiment of the present invention is preferably 0.01 to 3.00 parts by weight, more preferably 0.05 to 2.00 parts by weight, and even more preferably 0.10 to 1.00 parts by weight, based on 100 parts by weight of the resin particles. When the amount of the dispersant is not less than 0.01 parts by weight, there is no fear of causing dispersion failure of the resin particles, and when it is not more than 3.00 parts by weight, there is no fear of causing fusion failure of the expanded particles to each other when in-mold foam molding is performed using the obtained expanded particles.

In the present method for producing expanded beads, (a) in order to improve the effect of reducing the adhesion between resin beads and/or (b) in order to improve the stability of the dispersion in the container, a dispersing aid is preferably used. Examples of the dispersion aid include anionic surfactants. Examples of the anionic surfactant include sodium alkylbenzenesulfonate such as sodium dodecylbenzenesulfonate; sodium alkane sulfonate, sodium alkyl diphenyl ether disulfonate, sodium alpha-olefin sulfonate, and the like. These dispersing aids may be used alone or in combination of 1 or more than 2. In the case where 2 or more dispersing aids are used in combination, the mixing ratio can be appropriately adjusted according to the purpose.

The amount of the dispersing aid in the dispersion used in one embodiment of the present invention is preferably 0.001 to 0.500 parts by weight, more preferably 0.001 to 0.200 parts by weight, and still more preferably 0.010 to 0.200 parts by weight, based on 100 parts by weight of the resin particles. When the amount of the dispersing aid is within the above range, there is no fear of causing dispersion failure of the resin particles.

If the stability of the dispersion is lowered, there are cases where a plurality of resin particles in the container adhere to each other or agglomerate. As a result, there are cases where (i) bonded expanded particles are obtained; or (ii) a block of resin particles remaining in the container, failing to produce expanded particles; or (iii) a decrease in the productivity of the expanded beads.

(heating-boosting step and holding step)

The temperature-increasing step is preferably performed after the dispersing step, and the holding step is preferably performed after the temperature-increasing step. In the present specification, (a) a predetermined temperature in the temperature raising/increasing step and the holding step is sometimes referred to as a foaming temperature, and (b) a predetermined pressure is sometimes referred to as a foaming pressure.

The foaming temperature varies depending on the types of polypropylene resin, AS copolymer and hydrogenated styrene copolymer, the type of foaming agent, the desired apparent density of the expanded beads, and the like, and therefore cannot be approximated. The foaming temperature is preferably (i) a mixture of (a) a polypropylene-based resin, an AS copolymer and a hydrogenated styrene-based copolymer, (b) a polypropylene-based resin composition or (c) a melting point of the resin particles of-20.0 ℃ to +10.0 ℃; more preferably, (ii) a mixture of (a) a polypropylene resin, an AS copolymer and a hydrogenated styrene copolymer, (b) a polypropylene resin composition or (c) a resin particle having a melting point of-15.0 ℃ to a melting point +8.0 ℃, still more preferably (iii) a mixture of (a) a polypropylene resin, an AS copolymer and a hydrogenated styrene copolymer, (b) a polypropylene resin composition or (c) a resin particle having a melting point of-10.0 ℃ to a melting point +6.0 ℃.

The foaming pressure is preferably 1.0MPa (gauge pressure) to 10.0MPa (gauge pressure), more preferably 2.0MPa (gauge pressure) to 5.0MPa (gauge pressure), and still more preferably 2.5MPa (gauge pressure) to 3.5MPa (gauge pressure). If the foaming pressure is 1.0MPa (gauge pressure) or more, foamed particles having a suitable density can be obtained.

In the holding step, the time (holding time) for holding the dispersion liquid in the container at around the foaming temperature and foaming pressure is not particularly limited. The holding time is preferably 10 minutes to 60 minutes, more preferably 12 minutes to 55 minutes, and still more preferably 15 minutes to 50 minutes. When the holding time is 10 minutes or longer, there are a sufficient amount of unmelted crystals (crystals of the polypropylene resin), and as a result, there is an advantage that shrinkage of the obtained expanded beads and/or an increase in the open cell ratio can be reduced. On the other hand, when the holding time is 60 minutes or less, there is no excessive unmelted crystal, and therefore there is an advantage that the expanded beads can be molded at a low molding temperature.

(release step)

Regarding the releasing step, it is preferable that: the temperature raising and pressure increasing step is performed after the holding step is not performed, and the holding step is performed after the holding step is performed. The resin particles can be foamed by the releasing step, and as a result, foamed particles can be obtained.

In the release step, "a region having a pressure lower than the foaming pressure" means "a region having a pressure lower than the foaming pressure" or "a space having a pressure lower than the foaming pressure", and may be said to be "an atmosphere having a pressure lower than the foaming pressure". The region of lower pressure than the foaming pressure is not particularly limited as long as it is lower pressure than the foaming pressure, and may be, for example, a region at atmospheric pressure.

In the release step, when the dispersion is released into a region having a pressure lower than the foaming pressure, the dispersion may be released through an opening having a diameter of 1mm to 5mm for the purposes of adjusting the flow rate of the dispersion, reducing the variation in the expansion ratio of the obtained expanded particles, and the like. In addition, for the purpose of improving foamability, the low-pressure region (space) may be filled with saturated steam.

(two-stage foaming Process)

However, in order to obtain expanded beads having a high expansion ratio, there is a method of increasing the amount of the inorganic foaming agent used in the primary foaming step (hereinafter referred to as method 1). Further, as a method other than the method 1, the following method may be adopted: a method of obtaining expanded beads (primary expanded beads) having a low expansion ratio (expansion ratio of about 2.0 to 35.0) in the primary expansion step, and then re-expanding the primary expanded beads to thereby increase the expansion ratio (hereinafter referred to as method 2).

As the method 2, for example, a method including the following (a 1) to (a 3) in this order is exemplified: (a1) Manufacturing a first-stage foaming particle with a foaming multiplying power of 2.0-35.0 times in a first-stage foaming process; (a2) The first-stage expanded beads are put into a pressure-resistant vessel, and pressurized under 0.2MPa (gauge pressure) to 0.6MPa (gauge pressure) with nitrogen, air, carbon dioxide or the like, whereby the pressure in the first-stage expanded beads (hereinafter sometimes referred to as "internal pressure") is made higher than normal pressure; (a3) Thereafter, a method of heating and foaming the expanded beads at a stage where the internal pressure is increased by steam or the like is employed. The step of increasing the expansion ratio of the primary expanded beads as in method 2 is referred to as a "secondary expansion step", and the polypropylene resin expanded beads obtained by the method of method 2 are referred to as "secondary expanded beads".

In the above (a 3) of the two-stage foaming step, the pressure of the steam for heating the primary expanded beads is preferably adjusted to 0.03 to 0.20MPa (gauge pressure) in consideration of the expansion ratio of the two-stage expanded beads. When the pressure of the steam in the two-stage foaming step is 0.03MPa (gauge pressure) or more, the foaming ratio tends to be easily increased, and when the pressure is 0.20MPa (gauge pressure) or less, the possibility of bonding the obtained two-stage foam particles to each other is reduced. In the case where the two-stage expanded beads are bonded to each other, the obtained two-stage expanded beads may not be subjected to in-mold foam molding in some cases.

The internal pressure of the primary expanded beads obtained by impregnating the primary expanded beads with nitrogen, air, carbon dioxide, or the like is desirably appropriately changed in consideration of the expansion ratio of the secondary expanded beads and the steam pressure in the secondary expansion step. The internal pressure of the primary expanded beads is preferably 0.15MPa (absolute pressure) to 0.60MPa (absolute pressure), more preferably 0.20MPa (absolute pressure) to 0.60MPa (absolute pressure), still more preferably 0.30MPa (absolute pressure) to 0.60MPa (absolute pressure). When the internal pressure of the primary expanded beads is 0.15MPa (absolute pressure) or more, high-pressure steam is not required to increase the expansion ratio, and therefore the possibility of binding the secondary expanded beads is reduced. When the internal pressure of the primary expanded beads is 0.60MPa (absolute pressure) or less, the probability of the secondary expanded beads becoming connected by bubbles is reduced. As a result, the final in-mold foam molded body may have a reduced possibility of decreasing rigidity such as compression strength. The "bubble communication" may be also referred to as "communication of bubbles".

[ 2 ] Polypropylene resin foam molded article ]

The polypropylene resin foam molded article according to one embodiment of the present invention is a foam molded article obtained by molding the polypropylene resin foam particles described in [ 1 ] above. The polypropylene resin foam molded article according to one embodiment of the present invention may be said to contain the polypropylene resin foam particles described in [ 1 ] above. The present expanded molded article may be a foam molded article obtained by molding polypropylene-based resin expanded particles obtained by the present expanded particle production method (for example, the production method of polypropylene-based resin expanded particles described in the above < production method of polypropylene-based resin expanded particles > one item), or a foam molded article comprising polypropylene-based resin expanded particles obtained by the present expanded particle production method. The foam molded article may be a foam molded article obtained by molding the foam particles described in the item [ 1 ] above, namely, polypropylene resin foam particles, or a foam molded article comprising the foam particles.

In the present specification, the "polypropylene resin foam molded body according to one embodiment of the present invention" may be referred to as "the present foam molded body".

The foam molded article has the above-described structure, and thus has an advantage of hardly shrinking or deforming after molding.

(shrinkage rate)

In the present specification, the term "hardly shrink after molding" as used in the foamed molded article means: the shrinkage ratio obtained by measurement by the following methods (1) to (3) was small: (1) The expanded beads were molded by in-mold foaming using a mold having a known size (for example, 369mm in the longitudinal direction. Times.319 mm in the width direction. Times.50 mm in the thickness direction). Here, the length of the mold in the longitudinal direction is L0; (2) Measuring the length L1 of the obtained foam molding in the length direction; (3) the shrinkage (%) was calculated according to the following formula:

shrinkage (%) = ((L1-L0) ×100)/L0.

The shrinkage of the foam molded article is preferably 1.2% or less, more preferably 1.0% or less, still more preferably 0.8% or less, and particularly preferably 0.6% or less. The foam molded article having a shrinkage of 1.2% or less means that the foam molded article produced by the production is less likely to have dimensional variations, and is excellent in dimensional stability. The expanded beads which provide a foam molded article having excellent dimensional stability and the foam molded article have the advantage of being suitably usable in the field of insert molding in which the expanded beads are integrally molded with other materials such as metal.

(deformation amount)

The deformation amount of the foam molded body will be described below with reference to fig. 1. Fig. 1 is a schematic view of a foam molded body 100 for evaluating deformation amount. The foam molded body 100 was produced using a mold (length direction 350mm×width direction 320mm×thickness direction (movable driving direction) 180 mm) having a baffle plate in the center of the mold. In fig. 1, the X direction is referred to as the thickness direction of the foam molded body 100, and is also referred to as the moving driving direction. The Y direction is a longitudinal direction of the foam molded body 100, and is a direction perpendicular to the X direction. The Z direction is a width direction of the foam molded body 100, and is a direction perpendicular to the X direction and the Y direction. As shown in fig. 1, in the foam molded body 100, the Z-direction dimensions (length) of both ends in the longitudinal direction are denoted by K1 and K2, respectively, and the Z-direction dimension of the central portion in the longitudinal direction is denoted by K3.

In the present specification, the term "hardly deformed" means that the foam molded body: the deformation amount obtained by measurement by the following methods (1) to (3) is small: (1) Using a mold having a dimension (length) of 350mm in a longitudinal direction (Y direction), 320mm in a width direction (Z direction) and 180mm in a thickness direction (X direction) and having a baffle plate in a center portion of the mold, foam-molding the foamed particles in the mold; (2) The dimensions (mm) in the Z direction of both ends in the longitudinal direction of the obtained foam molded body (foam molded body 100) (K1, K2) and the dimensions (mm) in the Z direction of the central part in the longitudinal direction (K3) were measured; (3) calculating the deformation amount according to the following formula:

Deformation (mm) = { (k1+k2)/2 } -K3.

The deformation amount of the foam molded article is preferably 14.0mm or less, more preferably 13.0mm or less, more preferably 12.0mm or less, more preferably 11.0mm or less, more preferably 10.0mm or less, more preferably 9.0mm or less, more preferably 8.0mm or less, more preferably 7.0mm or less, more preferably 6.0mm or less, and particularly preferably 5.0mm or less. The foam molded article having a deformation of 14.0mm or less is not likely to have a dimensional deviation in the foam molded article produced, and is excellent in dimensional stability.

< method for producing foam molded article >

The method for producing the foam molded article is not particularly limited, and a known method can be applied. The method for producing the foam molded article preferably includes a step of in-mold foam molding the foam particles of the present invention described in item [ 1 ] or the foam particles obtained by the production method described in item < production method of polypropylene resin foam particles >. Specific examples of the method for producing the foam molded article include, for example, the following production methods (in-mold foam molding methods) including the following (b 1) to (b 6) in order, and the method is not limited to the production method:

(b1) A mold composed of a fixed type that cannot be driven and a movable type that can be driven is mounted on an in-mold foam molding machine. Here, the fixed type and the movable type can form the inside of the fixed type and the movable type by driving the movable type toward the fixed type (this operation is sometimes referred to as "mold clamping");

(b2) Driving the movable mold toward the fixed mold in such a manner that a slight gap (also referred to as a crack) is formed in such a manner that the fixed mold and the movable mold are not completely clamped;

(b3) Filling foaming particles into a molding space formed inside the fixed type and the movable type by, for example, a filling machine;

(b4) Driving the movable mold (i.e., fully mold-closing) in a manner of fully mold-closing the fixed mold and the movable mold;

(b5) Preheating the mold by utilizing steam, heating one side and the opposite side of the mold by utilizing the steam, and further heating two sides of the mold by utilizing the steam, thereby performing in-mold foaming molding;

(b6) The in-mold foam molded product is taken out of the mold and dried (for example, dried at 75 ℃) to obtain a foam molded product.

In the above (b 3), as a method of filling the expanded beads into the molding space, the following methods (b 3-1) to (b 3-4) are exemplified:

(b 3-1) a method in which expanded beads (including the two-stage expanded beads, hereinafter the same) are subjected to a pressure treatment with an inorganic gas in a vessel, the expanded beads are impregnated with the inorganic gas, a predetermined internal pressure of the expanded beads is applied, and then the expanded beads are filled into a molding space;

(b 3-2) a method of compressing the expanded beads so that the volume in the mold is reduced by 10 to 75% after filling the expanded beads into the molding space;

(b 3-3) a method of compressing the expanded particles by means of gas pressure and filling into the molding space;

(b 3-4) A method of filling the expanded beads into the molding space without any particular pretreatment.

In the method for producing a foam molded article of the present invention, at least 1 selected from the group consisting of air, nitrogen, oxygen, carbon dioxide, helium, neon, argon, and the like can be used as the inorganic gas in the method (b 3-1). Among these inorganic gases, air and/or carbon dioxide are preferable.

In the method for producing a foam molded article of the present invention, the internal pressure of the foam particles in the method (b 3-1) is preferably 0.10MPa (absolute pressure) to 0.30MPa (absolute pressure), and more preferably 0.11MPa (absolute pressure) to 0.25MPa (absolute pressure).

In the method for producing a foam molded article of the present invention, the temperature in the container at the time of impregnating the expanded beads with the inorganic gas in the method (b 3-1) is preferably 10 to 90 ℃, more preferably 40 to 90 ℃.

In the methods (b 3-2) and (b 3-3), in the subsequent step (b 5), the restoring force of the expanded beads compressed by the gas pressure is used for fusing the expanded beads.

One embodiment of the present invention may have the following configuration.

[ 1 ] A polypropylene resin foam particle comprising: 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer comprising an acrylonitrile unit and a styrene unit, and 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer.

The polypropylene resin foam particles according to [ 1 ], wherein the styrene unit is an α -methylstyrene unit.

The polypropylene resin foam particles according to [ 1 ] or [ 2 ], wherein the hydrogenated styrene copolymer is a styrene/ethylene/butylene/styrene copolymer (SEBS).

The polypropylene resin foam particles according to any one of [ 1 ] to [ 3 ], wherein the styrene unit content of the hydrogenated styrene copolymer is 15 to 80% by weight based on 100% by weight of the hydrogenated styrene copolymer.

The polypropylene resin foam particles according to any one of [ 1 ] to [ 4 ], wherein the copolymer comprising an acrylonitrile unit and a styrene unit has a glass transition temperature of 95℃to 140 ℃.

[ 6 ] A polypropylene resin foam molded article obtained by molding the polypropylene resin foam particles described in any one of [ 1 ] to [ 5 ].

[ 7 ] A method for producing polypropylene resin foam particles, comprising a foaming step of foaming polypropylene resin particles, wherein the polypropylene resin particles comprise: 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer comprising an acrylonitrile unit and a styrene unit, and 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer.

The method for producing expanded polypropylene resin beads according to [ 7 ], wherein the styrene unit is an α -methylstyrene unit.

The method for producing expanded polypropylene resin beads according to [ 7 ] or [ 8 ], wherein the hydrogenated styrene copolymer is a styrene/ethylene/butylene/styrene copolymer (SEBS).

The method for producing expanded polypropylene resin particles according to any one of [ 7 ] to [ 9 ], wherein the styrene unit content of the hydrogenated styrene copolymer is 15 to 80% by weight based on 100% by weight of the hydrogenated styrene copolymer.

The method for producing expanded polypropylene resin particles according to any one of [ 7 ] to [ 10 ], wherein the copolymer comprising an acrylonitrile unit and a styrene unit has a glass transition temperature of 95℃to 140 ℃.

[ 12 ] A method for producing a polypropylene resin foam molded article, comprising: molding the polypropylene resin foam particles of any one of [ 1 ] to [ 5 ] or the polypropylene resin foam particles obtained by the method of any one of [ 7 ] to [ 11 ].

Examples

Hereinafter, an embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the examples.

[ Material ]

Hereinafter, materials used in examples and comparative examples will be described.

< resin component >

(Polypropylene resin)

Polypropylene resin: 1-butene/ethylene/propylene random copolymer [ melting point 149 ℃ C., 1-butene content 3.8 wt%, ethylene content 0.5 wt%, MFR=10 g/10 min ]

(AS copolymer)

AS copolymer 1: acrylonitrile/α -methylstyrene copolymer [ Tg 121 ℃, α -methylstyrene content 70% by weight (styrene content 70% by weight), MFR=4.9 g/10 min ]

AS copolymer 2: acrylonitrile/styrene copolymer [ Tg of 108 ℃, styrene content of 75 wt% (styrene content of 75 wt%), MFR=6.1 g/10 min ]

AS copolymer 3: acrylonitrile/styrene copolymer [ Tg of 115 ℃ and styrene content of 50 wt% (styrene content of 50 wt%) ] MFR=8.1 g/10 min ]

(hydrogenated styrene copolymer)

Hydrogenated styrenic copolymer 1: SEBS (styrene/ethylene/butene/styrene copolymer, dylaron 9901P manufactured by JSR Co.) [ styrene content 53% ]

Hydrogenated styrenic copolymer 2: SEBS (styrene/ethylene/butene/styrene copolymer, dynaron8300P manufactured by JSR Co.) [ styrene content 9% ]

(other resins)

(amorphous resin)

Amorphous resin 1: polystyrene [ Tg 101 ℃, MFR=7.0 ]

Amorphous resin 2: mixture of polyphenylene ether and polystyrene [ Tg 120 ℃, MFR=1.8 g/10 min ]

(Compatibilizing agent)

And (3) a compatilizer: polypropylene/(acrylonitrile/styrene) graft copolymer [ backbone: polypropylene, side chain: acrylonitrile/styrene copolymer, polypropylene: acrylonitrile/styrene copolymer=70 (mol%): 30 (mol%) ] (ModiperA 3400 manufactured by daily oil company)

< additive >

(Water-absorbent Material)

Glycerin (lion king company made, refined glycerin D)

(foam nucleating agent)

Talc (Talc powder (registered trademark) PK-S manufactured by Linne chemical Co., ltd.)

[ method of measurement ]

The measurement and evaluation of each item were performed as follows.

(melting Point of Polypropylene resin)

The melting point of the polypropylene resin was determined by a DSC method using a differential scanning calorimeter (model DSC6200, manufactured by Seiko Instruments Inc.). The specific operation steps are as follows (1) - (4): (1) Melting the polypropylene resin by heating the polypropylene resin from 40.0 ℃ to 220.0 ℃ at a heating rate of 10.0 ℃/min at a temperature of 5mg to 6 mg; (2) Thereafter, the temperature of the melted polypropylene resin was lowered from 220.0 ℃ to 40.0 ℃ at a lowering rate of 10.0 ℃/minute, whereby the polypropylene resin was crystallized; (3) Thereafter, the temperature of the crystallized polypropylene resin was further raised from 40.0 ℃ to 220.0 ℃ at a temperature raising rate of 10.0 ℃/min; (4) The temperature of the peak (melting peak) of the DSC curve of the polypropylene-based resin obtained at the second temperature rise (i.e., at the time of (3)) was taken as the melting point of the polypropylene-based resin. When there are a plurality of peaks (melting peaks) in the DSC curve of the polypropylene resin obtained by the above method at the second temperature rise, the temperature of the peak having the largest amount of heat of fusion (melting peak) is taken as the melting point of the polypropylene resin.

(glass transition temperature (Tg) of AS copolymer)

The glass transition temperature (Tg) of the AS copolymer was measured by using a differential scanning calorimeter [ Seiko Instruments Inc.. Made, DSC6200 type ], according to JIS-K-7121 and by the following methods (1) to (5): (1) measuring 5mg of AS copolymer; (2) Heating the AS copolymer from room temperature to 250 ℃ at 10 ℃/min under nitrogen atmosphere; (3) Cooling the temperature of the warmed AS copolymer from 250 ℃ to room temperature at 10 ℃/min; (4) Again, the temperature of the AS copolymer was raised from room temperature to 250 ℃ at 10 ℃/min; (5) The temperature of the peak (melting peak) of the DSC curve of the AS copolymer obtained at the second temperature rise (i.e., at the time of (4)) was taken AS the Tg of the AS copolymer.

(MFR of Polypropylene-based resin and AS copolymer)

The MFR of the polypropylene resin or AS copolymer was measured under the following conditions using an MFR measuring instrument described in JIS K7210:1999: the orifice has a diameter of 2.0959 + -0.005 mm phi, a length of 8.000+ -0.025 mm, a load of 2.16kgf and a temperature of 230deg.C (230+ -0.2deg.C).

(expansion ratio of expanded beads (first-stage expanded beads, second-stage expanded beads))

The method for measuring the expansion ratio of the expanded beads is as shown in the following (1) to (6): (1) Accurately measuring the weight Gi of a predetermined amount of expanded beads (primary expanded beads or secondary expanded beads) to a unit of 0.001g (rounding the fourth digit after the decimal place); (2) Next, all the expanded beads for measuring the weight Gi were immersed in water of 100mL at 23 ℃ contained in a measuring cylinder; (3) The volume yi (cm) of the expanded beads was measured from the amount of rise in the liquid level position of the measuring cylinder ³ ) The method comprises the steps of carrying out a first treatment on the surface of the (4) By dividing the weight Gi (g) of the expanded particles by the volume yi (cm) of the expanded particles ³ ) And converting it into g/L units, thereby calculating the apparent density di (g/L) of the expanded particles; (5) Using resin particles for producing expanded beads instead of expanded beads, the density ds (g/L) of the resin particles is calculated by performing the same operations as (1) to (4); (6) the expansion ratio of the expanded beads was calculated by the following formula:

foaming ratio ki=ds/di.

(foamability)

The foamability of the expanded beads was evaluated based on the expansion ratio of the primary expanded beads obtained by performing the primary foaming step under the same conditions. The evaluation criteria are shown below.

(good): the foaming multiplying power of the first section of foaming particles is more than 15.0 times.

X (bad): the foaming multiplying power of the first section of foaming particles is less than 15.0 times.

Here, the expansion ratio of the expanded particles is affected by the DSC ratio of the expanded particles. For example, when expanded beads are produced by adjusting the foaming temperature so that the DSC ratio of the expanded beads becomes low, expanded beads with a high expansion ratio tend to be obtained. Therefore, in the case of comparing the expansion ratio of different expanded particles, it is necessary to compare the expansion ratio in consideration of the influence of the DSC ratio of the expanded particles. That is, when the expansion ratio is compared between different expanded beads, the expanded beads are produced so that the DSC ratio is a similar value, whereby the expansion ratio of the expanded beads can be compared relatively accurately.

(DSC ratio of expanded particles)

For measurement (calculation) of the DSC ratio of the foamed particles, a differential scanning calorimeter (model DSC6200, manufactured by Seiko Instruments inc. Was used). The method of measuring (calculating) the DSC ratio of the foamed particles using a differential scanning calorimeter is as shown in the following (1) to (5): (1) weighing 5 mg-6 mg of foaming particles; (2) Heating the temperature of the foaming particles from 40 ℃ to 220 ℃ at a heating rate of 10 ℃/min, and melting the foaming particles; (3) In the DSC curve of the expanded beads obtained in the above (2), the maximum point between the highest temperature melting peak and the melting peak adjacent to the highest temperature melting peak (low temperature side) is connected to the point indicating the temperature before the start of melting by a straight line, and the maximum point is connected to the point indicating the temperature after the end of melting by a straight line; (4) The method comprises (a) setting a heat amount calculated from a high-temperature side region surrounded by (a-1) a line segment obtained by connecting the maximum point with a point indicating a temperature after completion of melting and (a-2) a DSC curve as a high-temperature side melting heat amount, (b) setting a heat amount calculated from a line segment obtained by connecting the maximum point with a point indicating a temperature before start of melting and (b-2) a low-temperature side region surrounded by a DSC curve as a low-temperature side melting heat amount, and (c) setting a sum of the high-temperature side melting heat amount and the low-temperature side melting heat amount as a total melting heat amount (=high-temperature side melting heat amount+low-temperature side melting heat amount); (5) calculating a DSC ratio according to the following formula:

(ratio of continuous cells of expanded particles)

The ratio of continuous bubbles in the polypropylene resin foam particles was determined by using an air comparative densitometer [ 1000 type, manufactured by Tokyo science Co., ltd.)]The measurement was performed according to the method described in step C (PROSEDURE C) of ASTM D2856-87. More specifically, the continuity of the expanded particlesThe bubble ratio was calculated by sequentially carrying out the following (1) to (4): (1) Measurement of the volume Vc (cm) of the expanded particles Using an air comparison densitometer ³ ) The method comprises the steps of carrying out a first treatment on the surface of the (2) Then, the total amount of the foaming particles after Vc measurement is immersed into ethanol contained in a measuring cylinder; (3) Thereafter, the apparent volume Va (cm) of the foamed particles was obtained from the amount of rise in the ethanol position in the measuring cylinder ³ ) The method comprises the steps of carrying out a first treatment on the surface of the (4) The open cell ratio of the expanded particles was calculated using the following formula:

continuous bubble ratio (%) = ((Va-Vc) ×100)/Va.

(shrinkage of foam molded article)

The method for measuring the shrinkage of the foam molded article is as shown in the following (1) to (3): (1) The expanded beads were molded by in-mold foaming using a mold having a known size (for example, 369mm in the longitudinal direction. Times.319 mm in the width direction. Times.50 mm in the thickness direction). Here, the length of the mold in the longitudinal direction is L0; (2) Measuring the length L1 of the obtained foam molding in the length direction; (3) the shrinkage (%) was calculated according to the following formula:

Shrinkage (%) = ((L1-L0) ×100)/L0

The mold for measuring the shrinkage is sometimes referred to as a mold for evaluating the shrinkage.

(deformation amount of foam molded article)

The method for measuring the deformation of the foam molded body is as follows (1) to (3): (1) The foamed particles were subjected to in-mold foam molding using a mold having dimensions (length) of 350mm in the longitudinal direction (Y direction), 320mm in the width direction (Z direction) and 180mm in the thickness direction (X direction) and having a baffle plate in the center portion of the mold; (2) The dimensions (mm) in the Z direction of both ends in the longitudinal direction of the obtained foam molded body (foam molded body 100) (K1, K2) and the dimensions (mm) in the Z direction of the central part in the longitudinal direction (K3) were measured; (3) calculating the deformation amount according to the following formula:

deformation (mm) = { (k1+k2)/2 } -K3.

The mold for measuring the deformation amount may be referred to as a deformation amount evaluation mold.

[ example 1 ]

(production of Polypropylene resin particles)

100 parts by weight (10 kg) of a polypropylene resin, 1.12 parts by weight (1.2 kg) of an AS copolymer, 7.0 parts by weight (700 g) of a hydrogenated styrene copolymer, 0.050 parts by weight (5 g) of talc AS a foam nucleating agent, and 0.2 parts by weight (20 g) of glycerin AS a water-absorbing substance were dry-blended.

The obtained blend was fed into a twin screw extruder (TEM 26-SX, manufactured by Toshiba machinery Co., ltd.) and melt-kneaded at a resin temperature of 250 ℃. The melt-kneaded polypropylene resin composition was extruded into strands through a die having circular holes and attached to the tip of an extruder. The extruded polypropylene resin composition was water-cooled, and then cut by a cutter to obtain columnar resin particles (1.2 mg/pellet).

(production of polypropylene resin foam particles (one-stage foam particles))

100 parts by weight of the obtained resin particles, 200 parts by weight of pure water, 0.2 part by weight of kaolin (ASP-170, manufactured by Engelhard corporation) as a poorly water-soluble inorganic compound, and 0.03 part by weight of sodium dodecylbenzenesulfonate as a surfactant were put into a pressure-resistant airtight container. Thereafter, 6.7 parts by weight of carbon dioxide as a foaming agent was introduced into the pressure-tight vessel while stirring the raw materials in the pressure-tight vessel, to prepare a dispersion. Then, the temperature in the pressure-tight vessel was heated to a foaming temperature of 151.0 ℃. Thereafter, carbon dioxide was additionally introduced into the pressure-tight vessel, and the pressure in the pressure-tight vessel was increased to a foaming pressure of 3.2MPa (gauge pressure) (temperature-increasing step). Then, after the pressure-tight container was kept at the foaming temperature and the foaming pressure for 30 minutes (keeping step), a valve at the lower part of the pressure-tight container was opened, and the dispersion was discharged into a foaming cylinder at atmospheric pressure through an orifice having a diameter of 3.6mm, whereby foam particles (one stage of foam particles) were obtained. At this time, in order to prevent the pressure in the pressure-tight vessel from decreasing from the foaming pressure during release of the dispersion, carbon dioxide was additionally introduced into the pressure-tight vessel, and the pressure in the pressure-tight vessel was maintained at 3.2MPa (gauge pressure). The foaming ratio, foamability, DSC ratio and open cell ratio of the obtained expanded beads were measured, and the results are shown in Table 1.

(production of polypropylene resin foam particles (two-stage foam particles))

The resulting expanded beads were dried at 60℃for 6 hours and then placed in a pressure-tight vessel. Air is introduced into the pressure-tight container, so that the first stage of expanded beads in the pressure-tight container is impregnated with the pressurized air, and an inner pressure (absolute pressure) of expanded beads of 0.24MP (absolute pressure) is applied to the first stage of expanded beads. About 20L of a length of expanded beads impregnated with air (the inner pressure of the expanded beads was applied) was fed into the foaming machine. Next, the primary expanded beads in the foaming machine were heated with steam at 0.06MPa (gauge pressure) for 30 seconds, whereby the primary expanded beads were further expanded (secondary expanded), to obtain expanded beads (secondary expanded beads).

(production of Polypropylene resin foam molded article)

The obtained expanded beads (two-stage expanded beads) were put into a pressure-tight vessel. Air was introduced into the pressure-tight vessel, and the two-stage expanded beads in the pressure-tight vessel were impregnated with the pressurized air, whereby an expanded bead internal pressure (absolute pressure) of 0.20MP (absolute pressure) was applied to the two-stage expanded beads. The two-stage expanded beads impregnated with air were heated and molded with steam at 0.30MPa (gauge pressure) using a molding machine (polypropylene in-mold expansion molding machine manufactured by DAISEN company), a shrinkage rate evaluation mold, and a deformation amount evaluation mold, to obtain a foam molded article. After each of the obtained foam molded bodies was left at room temperature for 1 hour, curing and drying were performed in a constant temperature room at 75℃for 12 hours, and left at room temperature for 4 hours again. Thereafter, the shrinkage and the deformation amount of the obtained foam molded body were evaluated by the above-described methods. The results are shown in Table 1.

Examples 2 to 7 and comparative examples 1 to 9

Expanded beads and expanded molded articles were obtained in the same manner as in example 1, except that the types of the respective materials, the amounts of the respective materials, and/or the respective production conditions were changed as described in table 1. The physical properties of the obtained expanded beads and the expanded molded article were measured and evaluated. The results are shown in Table 1.

TABLE 1

There was no significant difference in DSC ratio of the expanded beads according to the examples and comparative examples. Therefore, according to the examples and the comparative examples, the expansion ratio of the expanded beads can be compared with accuracy.

[ summary ]

The following is apparent from table 1:

(1) From the comparison of examples 1 to 7 with comparative example 1, it is clear that: when only the polypropylene resin is used alone, the amount of deformation of the foam molded body is large, and the shrinkage of the foam molded body is not sufficiently reduced.

(2) From the comparison of examples 1 to 7 with comparative example 2, it is clear that: when polystyrene is used AS an amorphous resin instead of an AS copolymer, the foamability of the expanded beads is low.

(3) From the comparison of examples 1 to 7 with comparative example 3, it is clear that: when a mixture of polyphenylene ether and polystyrene is used AS the amorphous resin instead of the AS copolymer, the foamability of the expanded beads is low, and the shrinkage of the resulting expanded molded article is not sufficiently reduced.

(4) From the comparison of examples 1 to 7 with comparative example 4, it is clear that: when the amount of the AS copolymer is more than the range of the present application, the foamability and the open cell ratio of the expanded beads become poor (become low).

(5) From the comparison of examples 1 to 7 with comparative example 5, it is seen that: when the hydrogenated styrene copolymer is not used, the shrinkage of the resulting foam molded body is not sufficiently reduced.

(6) From the comparison of examples 1 to 7 with comparative example 6, it is seen that: when the amount of the hydrogenated styrene copolymer is more than the range of the present application, the foamability of the expanded beads is low, and the shrinkage of the resulting expanded molded article is not sufficiently reduced.

(7) From the comparison of examples 1 to 7 with comparative example 7, it is clear that: when a non-hydrogenated styrene-based copolymer is used instead of the hydrogenated styrene-based copolymer, the shrinkage of the resulting foam molded body is not sufficiently reduced.

(8) From the comparison of examples 1 to 7 with comparative example 8, it is seen that: when the amount of the AS copolymer is less than the range of the present application, the shrinkage of the resulting foam molded body is not sufficiently reduced.

(9) From the comparison of examples 1 to 7 with comparative example 9, it is seen that: when the amount of the hydrogenated styrene copolymer is less than the range of the present application, the shrinkage of the resulting foam molded body is not sufficiently reduced.

Industrial applicability

The polypropylene resin foam particles according to one embodiment of the present invention can provide a polypropylene resin foam molded body which has excellent foamability and hardly shrinks or deforms after molding. The polypropylene resin foam molded article is suitably used for various applications such as cushioning packaging materials, materials for logistics, heat insulating materials, civil engineering and construction elements, and automobile elements.

Claims

1. A polypropylene resin foam particle comprising:

100 parts by weight of polypropylene resin;

5 to 60 parts by weight of a copolymer comprising an acrylonitrile unit and a styrene unit; and

3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer.

2. The polypropylene-based resin foam particles according to claim 1, wherein the styrene-based unit is an α -methylstyrene unit.

3. The polypropylene-based resin foam particles according to claim 1 or 2, wherein the hydrogenated styrene-based copolymer is a styrene/ethylene/butylene/styrene copolymer (SEBS).

4. The polypropylene resin foam particles according to any one of claims 1 to 3, wherein the styrene unit content of the hydrogenated styrene copolymer is 15 to 80% by weight based on 100% by weight of the hydrogenated styrene copolymer.

5. The polypropylene-based resin foam particles according to any one of claims 1 to 4, wherein the copolymer comprising an acrylonitrile unit and a styrene unit has a glass transition temperature of 95 ℃ to 140 ℃.

6. A polypropylene resin foam molded article obtained by molding the polypropylene resin foam particles according to any one of claims 1 to 5.

7. A process for producing polypropylene resin foam particles, which comprises a foaming step of foaming polypropylene resin particles,

the polypropylene resin particles comprise:

100 parts by weight of polypropylene resin;

3 to 30 parts by weight of a hydrogenated styrene copolymer.

8. The method for producing polypropylene resin foam particles according to claim 7, wherein the styrene unit is an α -methylstyrene unit.

9. The method for producing polypropylene resin foam particles according to claim 7 or 8, wherein the hydrogenated styrene copolymer is a styrene/ethylene/butylene/styrene copolymer (SEBS).

10. The method for producing polypropylene resin foam particles according to any one of claims 7 to 9, wherein the styrene unit content of the hydrogenated styrene copolymer is 15 to 80% by weight based on 100% by weight of the hydrogenated styrene copolymer.

11. The method for producing polypropylene resin foam particles according to any one of claims 7 to 10, wherein the copolymer comprising an acrylonitrile unit and a styrene unit has a glass transition temperature of 95 ℃ to 140 ℃.

12. A method for producing a polypropylene resin foam molded body, comprising: a step of in-mold foam molding the polypropylene resin foam particles according to any one of claims 1 to 5 or the polypropylene resin foam particles obtained by the method for producing polypropylene resin foam particles according to any one of claims 7 to 11.