JP6898725B2 - Foam particle moldings and cushions for soles - Google Patents

Description

The present invention relates to a foamed particle molded product and a cushion for soles.

In recent years, in order to obtain a foam having excellent flexibility, a foam containing an ethylene / α-olefin multi-block copolymer having specific physical properties has been disclosed (see, for example, Patent Document 1).
On the other hand, in order to obtain a good foamed molded product having a large compressive strength and a water permeability coefficient, excellent fusion property, and no shrinkage, a polyolefin-based resin foamed molded product having a specific shape and having communicating voids is disclosed. (See, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2013-64137 Japanese Unexamined Patent Publication No. 08-108441

However, Patent Document 1 has not sufficiently studied a foamed particle molded product obtained by molding foamed particles in a mold.
Further, although various forms are shown as examples of the base resin of the foamed particles in Patent Document 2, the molded product made of the thermoplastic elastomer foamed particles has not been sufficiently studied, and the recoverability against compression has not been made. From this point of view, it left a problem.

An object of the present invention is to provide a foamed particle molded product that has both light weight and recoverability in a short time after compression / release (hereinafter, may be simply abbreviated as recoverability).

As a result of diligent research, the present inventors have found that the above problems can be solved by adopting the configuration shown below, and have completed the present invention.
That is, the present invention is as follows.
[1]
A foamed particle molded product of olefin-based thermoplastic elastomer foamed particles.
The foamed particle molded product has a porosity of 5 to 40%.
The density of the foamed particle molded product is 30 to 150 g / L, and the foamed particle molded product has a density of 30 to 150 g / L.
A foamed particle molded product having a flexural modulus of 10 to 100 MPa of the olefin-based thermoplastic elastomer constituting the foamed particle molded product.
[2]
The foamed particle molded product according to 1 above, wherein the olefin-based thermoplastic elastomer is a block copolymer of a polyethylene block and an ethylene / α-olefin copolymer block.
[3]
The foamed particle molded product according to 1 or 2 above, wherein the olefin-based thermoplastic elastomer has a melting point of 100 to 130 ° C.
[4]
The foamed particle molded product according to any one of 1 to 3 above, wherein the olefin-based thermoplastic elastomer is a multi-block copolymer of a polyethylene block and an ethylene / α-olefin copolymer block.
[5]
The foamed particle molded product according to any one of 1 to 4 above, wherein the foamed particles have through holes.
[6]
A cushion for soles made of the foamed particle molded product according to any one of 1 to 5 above.

According to the present invention, it is possible to provide a foamed particle molded product (hereinafter, may be simply referred to as a molded product) that has both light weight and recoverability in a short time after compression and release.
The foamed particle molded product of the present invention is a foamed particle molded product of olefin-based thermoplastic elastomer foamed particles, the void ratio of the foamed particle molded product is 5 to 40%, and the density of the foamed particle molded product is 30 to 30 to. It is 150 g / L, and the flexural modulus of the olefin-based thermoplastic elastomer constituting the foamed particle molded product is 10 to 100 MPa.
The density of the foamed particle molded product is 30 to 150 g / L, and the olefin-based thermoplastic elastomer constituting the foamed particle molded product has a specific flexural modulus, so that the voids that have been crushed during compression can be recovered. According to the present invention, it is possible to provide a foamed particle molded product that is both lightweight and recoverable in a short time.

The foamed particle molded product of the present invention is a foamed particle molded product of olefin-based thermoplastic elastomer foamed particles, in which the void ratio of the molded product is 5 to 40% and the density of the molded product is 30 to 150 g / L. , The flexural modulus of the olefin-based thermoplastic elastomer constituting the molded product is 10 to 100 MPa.

(Molded body density)
The foamed particle molded product of the present invention has a molded product density of 30 to 150 g / L. If the density of the foamed particle molded product exceeds 150 g / L, the lightness and flexibility of the foamed particle molded product may be impaired. On the other hand, if it is less than 30 g / L, the foam has a high foaming ratio, so that the strength of the bubble film is insufficient, it becomes difficult to withstand compression, and it becomes difficult for the molded product to recover after compression.
From the above viewpoint, the density of the foamed particle molded product is preferably 40 to 125 g / L, and more preferably 45 to 100 g / L.

The foamed particles forming the foamed particle molded product of the present invention are made of an olefin-based thermoplastic elastomer. Then, since the bubble film of the foamed particles is formed by the olefin-based thermoplastic elastomer, the voids and bubbles that are crushed when the molded product is compressed can be easily restored to the state before compression.

The flexural modulus of the olefin-based thermoplastic elastomer constituting the foamed particle molded product is 10 to 100 MPa. When it is within the above range, voids and air bubbles that have been crushed when a load is applied to the molded body can be easily recovered. From the above viewpoint, the flexural modulus is preferably 11 to 90 MPa, more preferably 12 to 50 MPa.
The flexural modulus can be measured in accordance with JIS K6767 (1999) in a test piece obtained by sufficiently defoaming a foamed molded product by a hot press several times.

The type A durometer hardness (generally sometimes referred to as “shore A hardness”) of the olefin-based thermoplastic elastomer constituting the foamed particle molded product is preferably 65 to 90, more preferably 75 to 88. is there. When the durometer hardness type A is in the above range, the foamed particle molded product has excellent recoverability and flexibility. The type A durometer hardness is a value measured based on ASTM D2240 in a test piece obtained by sufficiently defoaming a foamed molded product with a hot press several times.

The density of the olefin-based thermoplastic elastomer constituting the foamed particle molded product is preferably 800 to 1000 g / L, more preferably 850 to 900 g / L, and further preferably 860 to 890 g / L. preferable.
The melting point of the olefin-based thermoplastic elastomer constituting the foamed particle molded product is preferably 100 to 130 ° C, more preferably 115 to 125 ° C. Within the above range, the compression set at high temperature can be made smaller.

The olefin-based thermoplastic elastomer constituting the foamed particle molded product includes a mixture composed of a hard segment made of a propylene-based resin and a soft segment made of an ethylene-based rubber, a hard segment made of a polyethylene block, and ethylene / α-olefin. Examples thereof include a block copolymer with a soft segment composed of a polymer block.

In the mixture composed of a propylene-based resin and an ethylene-based rubber, examples of the propylene-based resin include a propylene homopolymer, a copolymer of propylene and ethylene or an α-olefin having 4 to 8 carbon atoms. .. On the other hand, examples of the ethylene-based rubber include a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms, and further, 5-vinyl-2-norbornene, 5-ethylidene-2-norbornene, and 5-methylene-. Copolymers of non-conjugated diene such as 2-norbornene and disynchropentadiene can be mentioned.

In the block copolymer of the polyethylene block and the ethylene / α-olefin copolymer block, as the polyethylene block, for example, an ethylene homopolymer, a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms can be used. Can be mentioned. On the other hand, the ethylene / α-olefin copolymer block is a block of a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, and the α-olefin copolymerizing with ethylene is, for example, propylene and 1 -Buten, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 3-methyl-1-butene, 4-methyl-1-pentene and the like, among which propylene, 1-Butene, 1-Hexene, 1-octene, particularly 1-octene are preferred. The proportion of the ethylene component in the polyethylene block is preferably 95% by weight or more, more preferably 98% by weight or more, based on the weight of the polyethylene block. On the other hand, the ratio of the α-olefin component in the ethylene / α-olefin copolymer block is preferably 5% by weight or more, more preferably 10% by weight or more, based on the weight of the ethylene / α-olefin copolymer block. , More preferably 15% by weight or more. The proportion of polyethylene blocks and the proportion of ethylene / α-olefin copolymer blocks can be calculated based on data obtained from differential scanning calorimetry (DSC) or nuclear magnetic resonance (NMR).

Examples of the olefin-based thermoplastic elastomer include the product name "Thermoran" (manufactured by Mitsubishi Chemicals), the product name "Milastomer" (manufactured by Mitsui Chemicals), the product name "Sumitomo TPE" (manufactured by Sumitomo Chemicals), and the product name "In". Examples include those commercially available as "fuse" (manufactured by Dow Chemicals).

(Multi-block copolymer)
The block copolymer may have a diblock structure, a triblock structure, and a multiblock structure, but a multiblock structure is particularly preferable.
Among the above, from the viewpoint of improving the recoverability at high temperature, a multi-block copolymer of a polyethylene block and an ethylene / α-olefin copolymer block (hereinafter, may be simply referred to as “multi-block copolymer”). Is particularly preferable. The polyethylene block corresponds to a hard block, and the ethylene / α-olefin copolymer block corresponds to a soft block. The hard blocks and soft blocks are preferably arranged in a straight line.

Examples of the multi-block copolymer include the ethylene / α-olefin copolymer described in Patent Document 1. Examples of commercially available multi-block copolymers include the trade name "Infuse" manufactured by Dow Chemical Co., Ltd.

(Xylene insoluble content by thermal xylene extraction method of foamed particle molded product)
The xylene insoluble content (hereinafter, simply referred to as “xylene insoluble content”) of the foamed particle molded product by the thermal xylene extraction method is preferably 30 to 70% by weight.
Within the above range, the thermoplastic elastomer having a specific apparent density and constituting the foamed particle molded product has a crosslinked structure, so that the thermoplastic elastomer does not "sag" even with respect to the compressive force. It becomes easy to restore to the shape of, and it becomes particularly excellent in recoverability. From the above viewpoint, the xylene insoluble content of the foamed particle molded product is preferably 35 to 60% by weight, more preferably 40 to 55% by weight.

(Fusionability)
For the fusion property of the foamed particle molded product, the ratio of the foamed particles whose material is broken to the foamed particles exposed on the fracture surface by bending and breaking the foamed particle molded product is defined as the material fracture rate, and the material fracture rate (fusion rate) is defined as the material fracture rate. ) Can be evaluated. The material destruction rate is preferably 80% or more, more preferably 90% or more. When the meltability of the foamed particle molded product is within the above range, the molded product is excellent in physical properties such as maximum tensile stress and tensile fracture elongation, and is suitable for applications such as seat cushion materials, sports pad materials, and sole materials.

(Compression set)
The foamed particle molded product of the present invention is measured 22 hours after being compressed at 23 ° C. for 22 hours and then opened at atmospheric pressure to a temperature of 23 ° C. in a state in which the molded product is distorted by 25%. The compression set is preferably 5% or less, more preferably 3% or less, and even more preferably 2% or less. Further, it is preferable that the compression set 30 minutes after compression and opening in the same manner as described above is 15% or less.
Further, the foamed particle molded product of the present invention is measured 22 hours after being compressed at 50 ° C. for 22 hours in a state where the molded product is distorted by 25% and then opened at atmospheric pressure at a temperature of 50 ° C. The compression set is preferably 10% or less, more preferably 8% or less, and even more preferably 7% or less. Further, it is preferable that the compression set 30 minutes after compression and opening in the same manner as described above is 20% or less.
Within the above range, the foamed particle molded product is excellent in shape recovery after compression, and is therefore suitable for applications such as seat cushion materials, sports pad materials, and sole materials.
In particular, since the foamed particle molded product of the present invention recovers in a faster time because voids are formed in the molded product, the compression set 30 minutes after compression release becomes smaller. In addition, the foamed particle molded product of the present invention has excellent recoverability even under compression conditions at high temperatures.
The compression set must be measured in accordance with JIS K6767 (1999).

(Porosity)
The foamed particle molded product of the present invention has a porosity of 5 to 40%. If the porosity of the foamed particle molded body is less than 5%, the air bubbles of the foamed particles are likely to be crushed together with the voids when the molded body is compressed, so that the recoverability of the molded body may be reduced when compressed and released. .. If the porosity of the foamed particle molded body exceeds 40%, the voids become excessive, the adhesion between the foamed particles becomes weak, and the strength may not be maintained when the molded body is compressed.
Therefore, from the viewpoint of improving the recoverability, the porosity of the foamed particle molded product is preferably 8 to 35%, more preferably 10 to 32%, and preferably 12 to 30%. More preferred.
Examples of the voids formed in the molded body include voids existing between the foamed particles constituting the foamed particle molded body and voids formed as through holes or the like in the foamed particles themselves. From the viewpoint of recoverability, it is preferable that these voids are formed so as to communicate with the outside of the molded product.

The foamed particles forming the foamed particle molded product of the present invention preferably have through holes or non-through holes.
The shape of the foamed particles having non-through holes is the same as that of the foamed particles having through holes except that one of the holes is closed. The same applies to the preferred embodiment of the cross-sectional shape, the preferred combination of the preferred embodiment of the cross-sectional shape of the pore and the preferred embodiment of the cross-sectional shape of the foamed particles, and the preferred range of the inner diameter of the foamed particles.
Among the above, the foamed particles are preferably those having through holes from the viewpoint of having recoverability and uniform physical properties.

When the foamed particles have through holes, voids are present in the pores of the foamed particles forming the foamed particle molded product. By forming the foamed particle molded product by in-mold molding of the foamed particles having such through holes, more uniform and non-directional voids are formed in the foamed particle molded body, so that the recoverability is further improved. It is thought that.

When a load is applied to the foamed particle molded body, the void portion of the molded body, that is, the portion of the pores of the foamed particles is preferentially crushed, so that the bubble portion of the foamed particles is relatively difficult to be crushed. When released from the load, the void portion preferentially and quickly recovers the original volume, so that it is considered that excellent recovery as a foamed particle molded body can be exhibited.

The shape of the through hole of the foamed particles is not particularly limited, and the contour of the surface orthogonal to the axial direction of the hole (hereinafter referred to as "cross-sectional shape of the hole") is usually circular, but elliptical, rectangular, trapezoidal, etc. It may be a triangle, a polygon having a pentagon or more, an indefinite shape, or the like. The shape of the foamed particles is not particularly limited, and may be spherical or polyhedral, or may have a circular, rectangular, trapezoidal, triangular, pentagonal or more polygonal, or irregular columnar cross-sectional shape. ..
Among the above, it is more preferable that the foamed particles having through holes have a circular cross-sectional shape of the foamed particles and a cylindrical shape having a circular cross-sectional shape of the holes. The circular shape includes a substantially circular shape.

The inner diameter of the foamed particles (the major axis of the cross-sectional shape of the pores) is preferably 1 to 7 mm, more preferably 1.5 to 5 mm, from the viewpoint of recoverability of the foamed particle molded product in a short time. The inner diameter of the foamed particles does not have to be constant, for example, one inner diameter of the end of the through hole may be small and the other inner diameter may be large, or both ends of the through hole on the surface side of the foamed particles. The pores may have different diameters that are larger or smaller in the vicinity of the center of the foamed particles than the inner diameter.
The axial length of the through hole is preferably 1 to 10 mm, preferably 1 to 7 mm, from the viewpoint of easy charging of the foamed particles into the mold when the foamed particles are molded in the mold. Is more preferable.

The apparent density of the foamed particles is preferably 40 to 200 g / L, more preferably 60 to 195 g / L. When the apparent density of the foamed particles is 40 g / L or more, the foamed particles and the molded product have excellent recoverability, and it is easy to obtain a molded product having a desired shape. In addition, the molded product has excellent compression set recovery, and it is easy to obtain mechanical performance suitable for the purpose. When the apparent density is 200 g / L or less, sufficient cushioning characteristics can be obtained, and even if the product weight increases, the product is lightweight.

The apparent density of the foamed particles is such that 100 ml of ethanol is placed in a 200 ml graduated cylinder, and foamed particles having a bulk volume of about 50 ml, which weighs Wa (g) in advance, are submerged in ethanol using a wire net or the like to raise the water level. Read the volume Va (L) of the increased amount. It can be calculated by obtaining Wa / Va.

The bulk density of the foamed particles is preferably 25 to 120 g / L, more preferably 30 to 110 g / L, further preferably 35 to 105 g / L, and particularly preferably 35 to 100 g / L. By setting the bulk density of the foamed particles in the above range, the lightness, flexibility and resilience of the foamed particle molded product produced by in-mold molding of the foamed particles can be further improved.

For the bulk density of the foamed particles, the foamed particles were randomly taken out from the foamed particle group and placed in a female cylinder having a volume of 1 L, and a large number of foamed particles were accommodated up to a scale of 1 L so as to be in a naturally deposited state. It can be calculated from the weight (Wb) of the contained foamed particles and the contained volume (1 L).

The average particle size of the foamed particles is preferably 0.5 to 10 mm, more preferably 1 to 8 mm, still more preferably 2 to 5 mm. When the average particle size of the foamed particles is in the above range, the foamed particles can be easily produced, and when the foamed particles are molded in the mold, the foamed particles can be easily filled in the mold. The average particle size of the foamed particles can be controlled by adjusting, for example, the amount of the foaming agent, the foaming conditions, the particle size of the polymer particles, and the like.

As a method for producing foamed particles, for example, an olefin-based thermoplastic elastomer and a foaming agent are supplied to an extruder to be melted, and the olefin-based thermoplastic elastomer is extruded and foamed from a die attached to the tip of the extruder. A method of producing a foam of a thermoplastic elastomer and cutting it into particles by pelletizing. After producing particles of an olefin-based thermoplastic elastomer, the particles are impregnated with a foaming agent in a closed container to obtain foaming particles. A method of obtaining foamed particles by discharging the sex particles from a closed container. The foamable particles of an olefin-based thermoplastic elastomer are taken out from the closed container, dehydrated and dried, and then the foamable particles are heated by a heating medium to foam. Examples thereof include a method of forming foamed particles.

Further, by cross-linking the olefin-based thermoplastic elastomer, foamability and moldability can be improved. Specific examples thereof include a method of obtaining foamed particles by discharging the foamable crosslinked particles obtained in the steps (A) to (C) described later in a closed container, but the method is not limited to the one using an organic peroxide. Crosslinked particles or foamed particles can be obtained by performing a crosslinking treatment using another known method, for example, an electron beam crosslinking method or the like.

In order to form the through hole, a desired through hole can be formed in the particles by providing a slit having a specific shape at the outlet of the extruder. Further, a through hole can be formed in the particle by pressing a protrusion having a specific cross-sectional shape against the melt-extruded particle.

(Foaming agent)
The foaming agent is not particularly limited as long as it foams the crosslinked particles. Examples of the foaming agent include inorganic physical foaming agents such as air, nitrogen, carbon dioxide, argon, helium, oxygen and neon, aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane and normal hexane, and cyclohexane. , Cyclopentane and other alicyclic hydrocarbons, chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride and other halogenated hydrocarbons. Examples thereof include organic physical foaming agents such as dialkyl ethers such as hydrogen, dimethyl ether, diethyl ether and methyl ethyl ether. Among these, an inorganic physical foaming agent that does not destroy the ozone layer and is inexpensive is preferable, nitrogen, air, and carbon dioxide are more preferable, and carbon dioxide is particularly preferable. These can be used alone or in combination of two or more.
The blending amount of the foaming agent is determined in consideration of the apparent density of the target foamed particles, the type of the olefin-based thermoplastic elastomer, the type of the foaming agent, etc., but is usually determined with respect to 100 parts by weight of the olefin-based thermoplastic elastomer. Therefore, it is preferable to use 2 to 20 parts by weight of the organic physical foaming agent, and it is preferable to use 0.5 to 20 parts by weight of the inorganic physical foaming agent.

(Other additives)
Other additives can be added to the particles of the olefin-based thermoplastic elastomer as long as the objective effects of the present invention are not impaired. Other additives include, for example, antioxidants, UV absorbers, antistatic agents, flame retardants, flame retardants, bubble nucleating agents, plasticizers, light stabilizers, antibacterial agents, metal deactivators, and conductive. Examples include fillers and bubble modifiers. Examples of the bubble adjusting agent include inorganic powders such as zinc borate, talc, calcium carbonate, boric acid, aluminum hydroxide, silica, zeolite, and carbon, phosphoric acid-based nucleating agents, phenol-based nucleating agents, and amine-based nucleating agents. Examples thereof include organic powders such as polyfluorinated ethylene resin powders. The total amount of these additives is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, still more preferably 5 parts by weight or less, based on 100 parts by weight of the olefin-based thermoplastic elastomer. In particular, the ratio of the bubble adjusting agent is preferably 0.01 to 1 part by weight per 100 parts by weight of the olefin-based thermoplastic elastomer. In addition, these additives are usually used in the minimum necessary amount. Further, these additives can be contained in the particles by adding and kneading them together with the olefin-based thermoplastic elastomer in the extruder, for example, when producing the polymer particles.

Hereinafter, a method for producing foamed particles composed of a block copolymer of a polyethylene block and an ethylene / α-olefin copolymer block, which is an olefin-based thermoplastic elastomer, will be described in detail, but the method is not limited to the following method. Absent.
As the foamed particles of the block copolymer, for example, foamed particles having through holes can be produced by going through the following steps (A) to (D). The foamed particles can be produced at the same time as a series of steps in a single closed container, but after each step, the block copolymer particles are extracted and put into the closed container again to perform the next step. It is also possible to carry out a separate process such as processing.

Step (A): A dispersion step of dispersing block copolymer particles having through holes and a cross-linking agent in a dispersion medium in a closed container.
Step (B): A cross-linking step of softening the block copolymer particles having through holes and heating the block copolymer particles to a temperature equal to or higher than a temperature at which the cross-linking agent is substantially decomposed to obtain block copolymer cross-linked particles.
Step (C): An impregnation step of adding a foaming agent to the dispersion medium and impregnating the block copolymer particles with the foaming agent to obtain foamable particles.
Step (D): A foaming step of producing foamed particles by releasing crosslinked block copolymer particles in an atmosphere having a pressure lower than the pressure in the closed container.

(1) Step (A)
In the step (A), the block copolymer particles having through holes and the cross-linking agent are dispersed in the dispersion medium in the closed container.
Specifically, for the block copolymer particles, the block copolymer is supplied to an extruder and kneaded to obtain a melt-kneaded product, and the melt-kneaded product is extruded from the extruder into a strand shape to foam the strands. Block copolymer particles are produced by known granulation methods such as a method of cutting into particles having a size suitable for forming particles. For example, in the above-mentioned method, polymer particles can be obtained by cooling the melt-kneaded product extruded into a strand shape by water cooling and then cutting it to a predetermined length. When cutting to a predetermined length, for example, a strand cut method can be adopted. In addition, block copolymer particles can be obtained by a hot-cut method in which the melt-kneaded product is extruded immediately after extrusion, an underwater-cut method in which the melt-kneaded product is cut in water, or the like.

The method of forming through holes in the block copolymer particles is not particularly limited.
For example, in order to obtain block copolymer particles having through holes, one having a slit at the outlet of the extruder die having a slit similar to the cross-sectional shape of the desired hole may be selected.

The average weight of each block copolymer particle is usually preferably 0.01 to 10 mg, more preferably 0.1 to 5 mg. The average weight of the polymer particles is a value obtained by dividing the weight (mg) of 100 randomly selected polymer particles by 100.

When obtaining the block copolymer particles, the melt flow rate (MFR) of the multi-block copolymer at 190 ° C. and a load of 2.16 kg is preferably 2 to 10 g / 10 minutes, more preferably. Is 3 to 8 g / 10 minutes, and more preferably can be selected from the range of 4 to 7 g / 10 minutes. The melt flow rate can be measured under the conditions of a temperature of 190 ° C. and a load of 2.16 kg in accordance with JIS K7210-1 (2014).

(Dispersion medium)
The dispersion medium used in the step (A) is not particularly limited as long as it is a dispersion medium that does not dissolve the multi-block copolymer particles. Examples of the dispersion medium include water, ethylene glycol, glycerin, methanol, ethanol and the like. The preferred dispersion medium is water.

In the step (A), the dispersant may be further added to the dispersion medium. Examples of the dispersant include organic dispersants such as polyvinyl alcohol, polyvinylpyrrolidone and methylcellulose; and sparingly soluble inorganic salts such as aluminum oxide, zinc oxide, kaolin, mica, magnesium phosphate and tricalcium phosphate. Further, the surfactant can be further added to the dispersion medium. Examples of the surfactant include sodium oleate, sodium dodecylbenzenesulfonate, other anionic surfactants generally used in suspension polymerization, nonionic surfactants and the like.

Further, when a divalent or trivalent water-soluble metal salt is added to the dispersion medium, the reason is not clear, but the through-holes or non-through-holes of the foamed particles obtained in the step (D) are the metal salt. It tends to be larger than the foamed particles produced without the addition of. As the divalent or trivalent water-soluble metal salt, it is preferable to use a compound having a low water content, and for example, aluminum sulfate can be used. The amount of aluminum sulfate added is preferably 0.001 to 0.1 parts by weight, more preferably 0.005 to 0.08 parts by weight, based on 100 parts by weight of the block copolymer particles.

(Sealed container)
The closed container used in the step (A) is not particularly limited as long as it can be closed. Since the copolymer particles are heated in the step (B) described later and the pressure inside the closed container rises, the closed container needs to be able to withstand the rise in pressure in the step (B). As the closed container, for example, an autoclave is used.

(Crosslinking agent)
A cross-linking agent is used to cross-link the block copolymer particles in step (B). The cross-linking agent may be added to the dispersion medium in advance, or the block copolymer particles may be dispersed and then added to the dispersion medium.
The cross-linking agent is not particularly limited as long as it cross-links the block copolymer. Examples of the cross-linking agent include 2,5-t-butylperbenzoate (10-hour half-life temperature 104 ° C.), 1,1-bis-t-butylperoxycyclohexane (10-hour half-life temperature 91 ° C.), 1, Peroxides such as 1-di (t-hexyl peroxy) cyclohexane (10-hour half-life temperature: 87 ° C.), t-butylperoxy-2-ethylhexyl monocarbonate (10-hour half-life temperature: 99 ° C.), etc. Can be mentioned. These can be used alone or in combination of two or more.
Among the above, the 10-hour half-life temperature is preferably 75 to 105 ° C. By using a cross-linking agent having such a half-life half-life temperature, even if the cross-linked particles are foamed in the step (D), the through holes are not easily crushed. The one-and-a-half-hour half-life temperature is more preferably 80 to 100 ° C.

The amount of the cross-linking agent blended is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 2.5 parts by weight, based on 100 parts by weight of the block copolymer. When the blending amount of the cross-linking agent is within the above range, the efficiency of cross-linking is improved, cross-linked particles having an appropriate xylene insoluble content can be obtained, and the cross-linked particles can be sufficiently foamed and can withstand foaming sufficiently. The resulting strength can be imparted to the polymer particles.

(2) Step (B)
In step (B), it is preferable to impregnate the block copolymer particles with an organic peroxide at a temperature lower than the temperature at which cross-linking of the block copolymer having through holes begins (sometimes referred to as an impregnation temperature). The impregnation temperature is not particularly limited as long as it is lower than the decomposition temperature of the organic peroxide used in the step (B) (when a plurality of types of organic peroxides are used, the lowest decomposition temperature is used as a reference). It depends on the type of organic peroxide used, but is usually 90 to 130 ° C.
Next, the block copolymer particles having through holes are softened and heated to a temperature equal to or higher than the temperature at which the cross-linking agent is substantially decomposed (sometimes referred to as a cross-linking temperature) to obtain a cross-linked block copolymer having through holes. Get particles. Specifically, the block copolymer is softened in a closed container and heated to a temperature equal to or higher than the temperature at which the cross-linking agent is substantially decomposed. The heating temperature for crosslinking (crosslinking temperature) is not particularly limited, but is, for example, in the range of 100 to 170 ° C. This causes cross-linking of the block copolymer. The xylene insoluble content of the obtained foamed particles is preferably 30 to 70% by weight. It is preferable to use an organic peroxide that satisfies the relationship of the following equation.
5 ≦ Tm-Th ≦ 45
[Tm: melting point (° C.) of the block copolymer, Th: 10-hour half-life temperature (° C.) of the organic peroxide]
Further, the cross-linking temperature is preferably a temperature equal to or higher than the melting point of the block copolymer constituting the polymer particles and lower than the melting point of the total k position + 80 ° C.

(3) Step (C)
In the step (C), a foaming agent is added into the closed container, and the block copolymer particles having through holes are impregnated with the foaming agent.
Specifically, a foaming agent for foaming block copolymer particles is added to the closed container, and the softened particles are impregnated with the foaming agent. The temperature at which the foaming agent is impregnated is not particularly limited as long as it is at least the temperature at which the multi-block copolymer particles are in a softened state, but is, for example, in the range of 100 to 170 ° C. As the foaming agent, the above-mentioned foaming agent can be used, an inorganic physical foaming agent is more preferable, and carbon dioxide is further preferable.
The step (C) may be performed before the step (D), and may be performed during the step (A), after the step (A), during the step (B), or after the step (B).

(4) Step (D)
In step (D), multi-block copolymer particles having through-holes are released under an atmosphere of a pressure lower than the pressure in the closed container to produce foamed particles having through-holes.
Specifically, the block copolymer crosslinked particles impregnated with the foaming agent in the step (C) (hereinafter, may be referred to as “foamable crosslinked particles”) have an atmosphere of a pressure lower than the pressure in the closed container. Release down to make foamed particles. The above-mentioned cross-linking, foaming agent impregnation, and foaming step described later, that is, steps (A) to (D) are preferably performed as a series of steps in a single closed container.

[Molded product]
The foamed particle molded body of the present invention is preferably the in-mold molded body of the foamed particles described above, but for example, it may be a molded body in which the foamed particles are adhered with an adhesive or the like. From the viewpoint of environmental compatibility and the like, an in-mold foamed particle molded product is preferable.
The foamed particle molded product can be obtained by filling the foamed particles in a molding die and heat-molding using a heating medium such as steam by a conventionally known method. Specifically, after the foamed particles are filled in the molding mold, a heating medium such as steam is introduced into the molding mold to heat the foamed particles to foam them and fuse them with each other to form a molding space. It is possible to obtain a foamed particle molded product in which is shaped.
Further, in the in-mold molding in the present invention, the foamed particles are pressure-treated in advance with a pressurized gas such as air to increase the pressure inside the foamed particles, and the pressure inside the foamed particles is 0.01 to 0.2 MPa (G). ) (G means gauge pressure), fill the mold cavity with foamed particles under atmospheric pressure or reduced pressure to close the mold, and then supply a heating medium such as steam into the mold. It is preferable to mold the foamed particles by a pressure molding method (for example, the method described in Japanese Patent Publication No. 51-22951). Further, after filling the cavity pressurized to the atmospheric pressure or more by the compressed gas with the foamed particles pressurized to the pressure or more, a heat medium such as steam is supplied to the cavity to heat the cavity, and the foamed particles are heated. Can also be molded by a compression filling molding method (Japanese Patent Publication No. 4-46217) in which heat-sealing is performed. In addition, foamed particles having high secondary foaming power obtained under special conditions are filled in a pair of male and female molded cavities under atmospheric pressure or reduced pressure, and then a heat medium such as steam is supplied. It can also be molded by an atmospheric pressure filling molding method (Japanese Patent Publication No. 6-49795) in which the foamed particles are heated and fused by heating, or a method in which the above methods are combined (Japanese Patent Publication No. 6-22919). it can.

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

<Physical characteristics of olefin-based thermoplastic elastomers>
Olefin-based thermoplastic elastomers used to prepare the foamed particles of Examples and Comparative Examples [Multiblock copolymers (copolymer 1) in Examples 1 to 5, Comparative Examples 1 and 2, and Comparative Example 5). The melting point of polypropylene (PP) in Comparative Examples 3 and 4], melt flow rate, durometer hardness type A, bending elasticity, and inner diameter of through-holes of the copolymer particles were measured as follows. ..

(Melting point)
The melting point of the olefin-based thermoplastic elastomer was determined in accordance with JIS K7121: 1987. Specifically, based on the heat flux differential scanning calorimetry method described in JIS K7121: 1987 using 2 mg of pellet-shaped base resin as a test piece, the temperature rises from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min. The heat absorption peak determined by the DSC curve obtained when the temperature is raised to 30 ° C. at a cooling rate of 10 ° C./min, then lowered to 30 ° C. at a cooling rate of 10 ° C./min, and then raised again from 30 ° C. to 200 ° C. at a heating rate of 10 ° C./min. The peak temperature was taken as the melting point of the base resin. As the measuring device, a heat flux differential scanning calorimetry device (manufactured by SII Nanotechnology Co., Ltd., model number: DSC7020) was used.

(Melt flow rate)
The melt flow rate of the olefin-based thermoplastic elastomer was measured according to JIS K7210-1: 2014 under the conditions of a temperature of 190 ° C. and a load of 2.16 kg.

(Type A durometer hardness)
Type A durometer hardness of olefin-based thermoplastic elastomers was measured according to ASTM D2240.

(Flexural modulus)
The flexural modulus was measured according to the measuring method described in JIS K 7171 (2016). For the measurement, a test piece of 80 × 10 × 4 mm was prepared, and three-point bending was performed using a load cell of 10 kg under the conditions of a distance between fulcrums of 64 mm and a bending speed of 2 mm / min. The flexural modulus was calculated from the gradient between the displacements of 0.5 to 1.0 mm.
The results are shown in the "Bending elastic modulus of the polymer constituting the molded product" column in the "Molded product" column of Tables 1 and 2.

(Inner diameter of through hole of polymer particles)
For the inner diameter of the through hole, the particles are placed on the measurement stage so that the through hole is perpendicular to the measurement stage, a photograph is taken using a microscope, and the inner diameter (diameter) of the through hole in the cross-sectional photograph is measured. And calculated. The inner diameters of the through-holes of the particles are shown in "Inner diameters of through-holes of the polymer particles used" in Tables 1 and 2.

<Physical characteristics of foamed particles>
The apparent density, bulk density, porosity, and inner diameter of the through hole of the foamed particles were measured as follows, and the results are shown in the "foamed particles" column of Tables 1 and 2.

(Apparent density of foamed particles)
100 ml of ethanol is placed in a 200 ml graduated cylinder, and foamed particles having a bulk volume of about 50 ml, which are weighed in advance with a weight of Wa (g), are submerged in ethanol using a wire mesh or the like, and the volume of Va (L) corresponding to the rise in water level. ) Was read. The apparent density (g / L) of the foamed particles was determined by determining Wa / Va.
The measurement was performed under an atmospheric pressure of 23 ° C. and 50% relative humidity.

(Bulk density of foamed particles)
Effervescent particles were randomly taken out from the effervescent particle group and placed in a graduated cylinder having a volume of 1 L, and a large number of effervescent particles were accommodated up to a scale of 1 L so as to be in a naturally deposited state while removing static electricity. Next, the weight of the contained foamed particles was measured, and the bulk density (g / L) of the foamed particles was calculated from the weight of the foamed particles and the contained volume (1 L).
The measurement was performed under an atmospheric pressure of 23 ° C. and 50% relative humidity.
In addition, the "apparent density / bulk density" was calculated from the obtained bulk density and the apparent density.

(Porosity of foamed particles)
The void ratio x (%) of the foamed particles is the apparent volume A (cm ³ ) indicated by the scale of the measuring cylinder when the foamed particles are placed in the measuring cylinder, and this amount of foamed particles is submerged in the measuring cylinder containing alcohol. ^{The true volume B (cm 3} ) indicated by the scale of the graduated cylinder for the increased amount was obtained, and was obtained from the relationship of x (%) = [(AB) / A] × 100.

(Inner diameter of through hole of foamed particles)
The inner diameter of the through hole of the foamed particles is such that the foamed particles are placed on the measurement stage so that the through holes are perpendicular to the measurement stage, a photograph is taken using a microscope, and the inner diameter of the through hole in the cross-sectional photograph thereof ( Diameter) was measured and calculated.

<Physical characteristics of foamed particle molded product>
The density, xylene insoluble matter and porosity of the foamed particle compacts produced in Examples and Comparative Examples were measured as follows.

(Density of foamed particle molded product)
Randomly cut three test pieces from the foamed particle molded body into a shape of 50 mm in length × 50 mm in width × 25 mm in thickness so as to have a rectangular parallelepiped shape excluding the skin layer at the time of molding, and measure the weight and volume of each test piece. Then, the apparent densities of the three test pieces were calculated, and the arithmetic mean value was used as the density of the foamed particle compact, which is shown in the "mold density" column in the table.

(Xylene insoluble content of foamed particle molded product)
For the xylene insoluble content of the foamed particle molded product, about 1.0 g of a sample was cut from the foamed particle molded product, and the sample was weighed to obtain a sample weight W1b. The weighed foamed particle compact was placed in a 150 ml round bottom flask, 100 ml of xylene was added, the mixture was heated with a mantle heater and refluxed for 6 hours, and then the undissolved residue was filtered through a 100 mesh wire mesh to separate it. , It was dried in a vacuum dryer at 80 ° C. for 8 hours or more. The dry matter weight W2b obtained at this time was measured. The weight percentage [(W2b / W1b) × 100] (% by weight) of the weight W2b with respect to the sample weight W1b was defined as the xylene insoluble content of the foamed particle molded product. In the step of in-mold molding of the foamed particles, the xylene insoluble content does not change, and the xylene insoluble content of the molded product is almost the same as that of the foamed particles.

(Porosity of foamed particle molded product)
The cube-shaped test piece cut out from the foamed particle molded body was submerged in a volume containing ethanol for 20 seconds, and the true volume Vc (L) of the test piece was determined from the amount of increase in the liquid level of ethanol. Further, the apparent volume Vd (L) was obtained from the external dimensions of the test piece (length x width x height). From the obtained true volume Vc and the apparent volume Vd, the porosity of the foamed particle molded product was determined based on the following equation.
Porosity (%) = [(Vd-Vc) / Vd] x 100

<Evaluation of foamed particle molded product>
(Compression set of foamed particle molded product)
Three test pieces were cut out from the foamed particle molded body to a length of 50 mm, a width of 50 mm, and a thickness of 25 mm so as to have a rectangular shape excluding the skin layer at the time of molding, and based on JIS K6767: 1999, the temperatures were 23 ° C. and 50 ° C., respectively. In an environment with a relative humidity of 50%, the sample was left to be compressed by 25% in the thickness direction for 22 hours, and the thickness was measured 30 minutes and 24 hours after the compression release, and the compression set (%) of each test piece was measured. The arithmetic mean value was calculated and used as the compression set (%).

(Fusionability)
The fusion property of the foamed particle molded product was evaluated by the following method.
The foamed particle molded body was bent and broken, and the number of foamed particles (C1) present in the fracture surface and the number of destroyed foamed particles (C2) were determined, and the ratio of the destroyed foamed particles to the foamed particles (C2 / C1). × 100) was calculated as the material destruction rate. The above measurement was performed 5 times using different test pieces, the material fracture rate of each was determined, and they were arithmetically averaged to evaluate the fusion property based on the following evaluation criteria.
[Evaluation criteria]
⊚: Material destruction rate 95% or more ○: Material destruction rate 80% or more and less than 95% Δ: Material destruction rate 20% or more and less than 80% ×: Material destruction rate less than 20%

[Example 1]
(Preparation of olefin-based thermoplastic elastomer particles)
As an olefin-based thermoplastic elastomer, both polyethylene block and ethylene / α-olefin having a melting point of 120 ° C., a melt flow rate of 5.4 g / 10 minutes (190 ° C., a load of 2.16 kg), a durometer hardness type A86, and a bending elasticity of 28 MPa. A multi-block copolymer (polymer 1) with a polymer block was prepared.
The polymer 1 is put into an extruder, melt-kneaded, extruded into a strand shape from a tubular die having a circular slit, cooled in water, and then cut with a pelletizer so that the particle weight is about 5 mg. Granulated to obtain tubular polymer particles 1 of a multi-block copolymer having through holes.

(Preparation of foamed particles)
1 kg of the obtained polymer particles are 3 liters of water as a dispersion medium, 3 g of kaolin as a dispersant, 0.04 g of sodium alkylbenzene sulfonate, 0.1 g of aluminum sulfate as a cationic species, and carbon dioxide (dry) as a foaming agent. 8 parts by weight (80 g) of ice) with respect to 100 parts by weight of the multi-block copolymer, t-butylperoxy-2-ethylhexyl monocarbonate as a cross-linking agent (Trigonox 117 (Tri117); 10-hour half-life temperature: 99 ° C. ) Was mixed with 100 parts by weight of the multi-block copolymer and stirred at 110 ° C., which is the impregnation temperature, to impregnate the polymer particles 1 with a cross-linking agent. Then, the temperature was raised to 160 ° C., which is the crosslinked foaming temperature, under stirring, and the mixture was held for 30 minutes, and then the contents were released under atmospheric pressure to obtain crosslinked foamed particles. The pressure inside the container at this time was 4.0 MPa (G).

(Preparation of foamed particle molded product)
The obtained foamed particles were put into a closed container, pressurized with compressed air of 0.2 MPa (G) for 12 hours to apply an internal pressure of 0.10 MPa to the foamed particles, and after being taken out, 250 mm in length and 200 mm in width. The foamed particles were packed in a flat plate-shaped mold having a thickness of 50 mm by cracking 5 mm (that is, 10%). The inside of the mold is heated with steam so that the molding pressure becomes 0.10 MPa, then air-cooled to take out the molded product from the mold, and the foamed particle molded product is further heated in an oven adjusted to 60 ° C. for 12 hours. Then, it was dried, cured, and then taken out to obtain a foamed particle molded product.
The density, porosity, and xylene insoluble matter of the obtained foamed particle molded product were measured, and the compression set and the meltability at 23 ° C. and 50 ° C. were evaluated.

[Example 2]
In the production of the tubular polymer particles 1 of Example 1, the tubular polymer particles (heavy weight) were operated in the same manner as in Example 1 except that the inner diameter of the through hole was reduced by reducing the slit diameter of the extruder. Combined particles 2) were obtained. Next, in the preparation of the foamed particles of Example 1, foamed particles were obtained by the same operation as in Example 1 except that the polymer particles 2 were used instead of the polymer particles 1, and the “molding conditions” column in Table 1 Molding was carried out under the conditions shown in (1) to obtain a foamed particle molded product.

[Example 3]
In the "preparation of foamed particles" of Example 1, the cross-linking agent type was changed to 1,1-di (t-hexyl peroxy) cyclohexane (perhexa HC; 10-hour half-life temperature: 87 ° C.). Foamed particles were obtained by the same operation as in Example 2, and molding was performed under the conditions shown in the "molding conditions" column of Table 1 to obtain a foamed particle molded product.

[Example 4]
In the preparation of the tubular polymer particles 2 of Example 2, tubular polymer particles (polymer particles 3) were obtained by the same operation as in Example 2 except that aluminum sulfate was not added. Next, in the preparation of the foamed particles of Example 1, the foamed particles were obtained by the same operation as in Example 1 except that the polymer particles 3 were used instead of the polymer particles 1, and the “molding conditions” column in Table 1 Molding was carried out under the conditions shown in (1) to obtain a foamed particle molded product.

[Example 5]
In Example 1, the foaming conditions were changed to the conditions shown in Table 1, and carbon dioxide (dry ice) as a foaming agent was set to 3 parts by weight (30 g) with respect to 100 parts by weight of the multi-block copolymer. Foamed particles were obtained by the same operation as in Example 1, and molding was performed under the conditions shown in the "molding conditions" column of Table 1 to obtain a foamed particle molded product.

[Example 6]
In Example 1, foamed particles were obtained by the same operation as in Example 1 except that the foaming conditions were changed to the conditions shown in Table 2, and molding was performed under the conditions shown in the “molding conditions” column of Table 2 to mold the foamed particles. I got a body.

[Comparative Example 1]
Foamed particles were obtained by the same operation as in Example 1 except that n-butyl 4,4-di (t-butyl peroxy) valerate (perhexa V; 10-hour half-life temperature: 72 ° C.) was used as the cross-linking agent. , The molding was carried out under the conditions shown in Table 1 to obtain a foamed particle molded product.

[Comparative Example 2]
In the "preparation of particles of a multi-block copolymer" of Example 1, the "cylindrical die having a circular slit" is changed to a "die having no circular slit", and the multi having no through hole. Polymer particles 101 of block copolymers were obtained. Foamed particles were obtained in the same manner as in Example 1 except that the polymer particles 101 were used and dicumyl peroxide (Parkmill D; 10-hour half-life temperature: 116 ° C.) was used as a cross-linking agent. Molding was carried out under the conditions shown to obtain a foamed particle molded product.

[Comparative Example 3]
Polymer particles of polypropylene (PP) (melting point 142 ° C., flexural modulus 870 MPa) having through holes were prepared in the same manner as in Example 1. 1 kg of the polypropylene particles were charged in a closed container of 5 L together with 3 L of water as a dispersion medium, and 0.3 parts by weight of kaolin as a dispersant and a surfactant (sodium alkylbenzene sulfonate) were further charged with respect to 100 parts by weight of the polymer particles. ) 0.004 parts by weight was added into the closed container, carbon dioxide as a foaming agent was added into the closed container so that the pressure inside the container became the value shown in Table 1, and the foaming temperature was reached to the foaming temperature shown in Table 1 under stirring. After heating and raising the temperature and holding at the same temperature for 15 minutes, the contents of the container were released under atmospheric pressure to obtain foamed particles. Further, a foamed particle molded product was obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were set.

[Comparative Example 4]
In the same manner as in Comparative Example 2, polymer particles of polypropylene (PP) having no through holes (melting point 142 ° C., flexural modulus 870 MPa) were produced. Further, foamed particles were obtained in the same manner as in Comparative Example 3, and a foamed particle molded product was obtained in the same manner as in Comparative Example 2 except that the conditions shown in Table 1 were set.

[Comparative Example 5]
In Comparative Example 2, a foamed particle molded product was obtained in the same manner except that the foaming conditions were changed to the conditions shown in the “foaming conditions” column of Table 2.

As shown in Table 1, when Examples 1 to 5 and Comparative Examples 1 and 2 having the same molded body density are compared, the porosity of the foamed particle molded body is in a range other than 5 to 30%. Is obtained with a low compression set at the time of 25% compression, and it can be seen that the recoverability is excellent.
Further, comparing Examples 1 and 3 with Examples 2 and 4, the foamed particle molded product having a high porosity of the molded product has a lower compression set at a high temperature and is more excellent in recoverability. You can see that.

Comparing Comparative Examples 3 and 4, in the polypropylene resin, an in-mold molded product of foamed particles having no through holes (Comparative Example 4) and an in-mold molded product of foamed particles having through holes (Comparative Example 3) Then, it can be seen that the in-mold molded product of the foamed particles having through holes has a higher compression set at the time of 25% compression.
On the other hand, when Example 1 and Comparative Example 1 are compared, the compression set of the foamed particles having through holes (Example 1) at the time of 25% compression has almost no through holes. It can be seen that the foamed particles (Comparative Example 1) are smaller than the in-mold molded product. That is, it can be seen that the foamed particles made of an olefin-based thermoplastic elastomer exhibit the characteristics completely opposite to those of the foamed particles made of polypropylene. This is because the voids formed in the foamed particle molded product have an effect of improving the recoverability, and the bubble film is made of a specific elastomer, so that the voids can be easily recovered and the recoverability when the bubbles are crushed is also obtained. It is shown that the improvement makes the entire foamed particle molded product particularly excellent in recoverability for the first time.

As shown in Table 2, when Example 6 and Comparative Example 5, which have a relatively high density of the molded product, are compared, the porosity of the foamed particle molded product is in the range other than 5 to 40% (Example 6). ) Has a low compression set at the time of 25% compression, and it can be seen that the recoverability is excellent.
Further, the compression set at 25% compression of Comparative Example 5 having a molded body density of 137 g / L is about the same as that of the molded body having a molded body density of 50 g / L in Examples, and the compression set at 25% compression. When the above is used as a reference, the same physical properties can be exhibited even if the density of the molded body is lowered, so that the weight of the cushion body or the like can be further reduced.

Claims (6)

A foamed particle molded product of olefin-based thermoplastic elastomer foamed particles.
The foamed particle molded product has a porosity of 5 to 40%.
The density of the foamed particle molded product is 30 to 150 g / L, and the foamed particle molded product has a density of 30 to 150 g / L.
The flexural modulus of the olefin thermoplastic elastomer constituting the foamed bead molded article is Ri 10~100MPa der,
The expanded particles, that having a through hole, PP bead molding. The foamed particle molded product according to claim 1, wherein the olefin-based thermoplastic elastomer is a block copolymer of a polyethylene block and an ethylene / α-olefin copolymer block. The foamed particle molded product according to claim 1 or 2, wherein the olefin-based thermoplastic elastomer has a melting point of 100 to 130 ° C. The foamed particle molded product according to any one of claims 1 to 3, wherein the olefin-based thermoplastic elastomer is a multi-block copolymer of a polyethylene block and an ethylene / α-olefin copolymer block. The foamed particle molded product according to any one of claims 1 to 4, wherein the xylene insoluble content of the foamed particle molded product by the thermal xylene extraction method is 30 to 70% by weight. A cushion for soles made of the foamed particle molded product according to any one of claims 1 to 5.