JP5814551B2 - Foam molding - Google Patents

Description

The present invention relates to a foamed molded article having excellent fatigue resistance against repeated compression.

Conventionally, as a member for medical use or automobiles, railways, railroads, railways, bridges, buildings, etc., a base resin such as rubber or thermoplastic elastomer is formed into a plate shape, etc., cushioning properties, vibration damping properties, etc. A molded body having excellent performance is used. In addition, in order to further improve performance such as cushioning properties and vibration damping properties, it has been studied to foam-mold the base resin.

As a method of foam-molding the base resin, for example, a method of foam-molding by adding a chemical foaming agent such as azodicarbonamide, which decomposes when heated to generate a gas, solubility of gas such as carbon dioxide gas For example, a method in which gas is generated by increasing the solubility in the base resin and then lowering the solubility of the gas. According to these methods, for example, it is possible to obtain a foamed molded article having relatively large bubbles having a diameter exceeding 500 μm.
However, the foamed molded article obtained by these methods has a problem that the cushioning property is good, but fatigue resistance against repeated compression cannot be sufficiently obtained, and the strength as a molded article is low, so that it can be used at the time of use. The surface of the molded body may swell, be torn, or peel off.

In order to solve such a problem, a method of foam molding by adding a heat-expandable microcapsule containing a volatile liquid as a core agent to a shell containing a polymer to a base resin has been proposed. For example, Patent Document 1 discloses that spherical hollow shell-shaped microspheres (B) having an average diameter of 200 μm or less are uniformly dispersed three-dimensionally in a matrix made of a rubber material (A). A vibration-proof material is described which is formed of a molded article having a composite structure and has a ratio of expanded hollow microspheres (B) of 0.3 to 5 parts by weight to 100 parts by weight of the rubber material (A).
However, even with the vibration isolator described in Patent Document 1, fatigue resistance against repeated compression is still not sufficiently obtained.

JP-A-8-303524

An object of this invention is to provide the foaming molding excellent in the fatigue resistance with respect to repeated compression.

The present invention relates to a foam molded article in which bubbles are dispersed in a base resin, wherein the base resin is a thermoplastic elastomer, and the bubbles include a volatile liquid as a core agent in a polymer-containing shell. The thermally expandable microcapsule is formed by thermal expansion, and the foamed molded article has a static stiffness of 35 N / mm or less and a dynamic stiffness of 45 N / mm or less. and the capsule shell state, and are the average adhesion index is 7 or more and the base resin, the thermally expandable microcapsule is foamed molded shell contains a thermosetting resin.
The present invention is described in detail below.

When a thermally expandable microcapsule is used, bubbles formed by thermal expansion of the thermally expandable microcapsule are dispersed in the obtained foamed molded product, and these bubbles are thermally expanded after thermal expansion. The microcapsule shell is formed. Therefore, compared to the case of using a chemical foaming agent that decomposes when heated and generates gas, the use of thermally expandable microcapsules improves fatigue resistance against repeated compression. However, the present inventor, when the adhesion between the thermally expandable microcapsule shell after thermal expansion and the base resin is low, is fatigue resistance to repeated compression in the same manner as when a chemical foaming agent is used. Was found to be insufficient.
In the foamed molded product in which bubbles formed by thermal expansion of thermally expandable microcapsules enclosing a volatile liquid as a core agent in a polymer-containing shell are dispersed in a base resin, We found that the shell of the thermally expandable microcapsule after expansion and the adhesion between the base resin and the shell sufficiently function as a reinforcing material, and can greatly improve the fatigue resistance against repeated compression. The present invention has been completed.

The foamed molded product of the present invention is a foamed molded product in which bubbles are dispersed in a base resin. In the present specification, air bubbles mean pore portions dispersed in the base resin.
Although the said base resin will not be specifically limited if it is a base resin normally used for foam molding, Rubber | gum or a thermoplastic elastomer is preferable.
In the present specification, rubber means a polymer substance exhibiting elasticity at room temperature. The rubber is not particularly limited, and may be natural rubber (NR) or synthetic rubber. Examples of the synthetic rubber include isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene acrylo rubber (CR), nitrile butadiene rubber (NBR), butyl rubber (IIR), and ethylene propylene rubber ( EPDM), urethane rubber (U), silicone rubber (Q), fluoro rubber (FKM), chlorosulfonated polyethylene rubber (CSM), chlorinated polyethylene (CM), acrylic rubber (ACM, ANM), epichlorohydrin rubber ( CO, ECO), polysulfide rubber (T) and the like. Among these, isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene acrylo rubber (CR), butyl rubber (IIR), and ethylene propylene rubber (EPDM) are preferable.

In the present specification, the thermoplastic elastomer means a substance that exhibits properties of an elastomer, that is, a vulcanized rubber, at normal temperature and exhibits thermoplasticity at a high temperature. The thermoplastic elastomer is not particularly limited. For example, styrene elastomer (TPS), olefin elastomer (TPO), ester elastomer (TPEE), urethane elastomer (TPU), amide elastomer (TPAE), and vinyl chloride elastomer. (TPVC). Of these, styrene elastomer (TPS), olefin elastomer (TPO), and ester elastomer (TPEE) are preferable.

The bubbles are formed by thermal expansion of thermally expandable microcapsules enclosing a volatile liquid as a core agent in a shell containing a polymer.
The heat-expandable microcapsules are expanded by heating, so that the shell is plasticized and the core agent is vaporized to increase the vapor pressure. Therefore, by adding the thermally expandable microcapsules to the base resin and performing foam molding, bubbles formed by the thermal expansion of the thermally expandable microcapsules are dispersed in the obtained foamed molded article. It becomes. Such bubbles are formed by the thermally expandable microcapsule shell after thermal expansion, whereby the foamed molded article of the present invention is excellent in fatigue resistance against repeated compression.

Although the said polymer is not specifically limited, For example, it is preferable to have a component derived from a nitrile monomer. Since the polymer contains a component derived from the nitrile monomer, the shell has high heat resistance and gas barrier properties.
The nitrile monomer is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, or a mixture thereof. Of these, acrylonitrile and methacrylonitrile are particularly preferred.

The polymer preferably has a component derived from a monomer having a carboxyl group.
The monomer having a carboxyl group is not particularly limited, and examples thereof include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, and cinnamic acid. Among these, acrylic acid and methacrylic acid capable of obtaining a polymer having a high glass transition temperature are preferable.

Especially, it is preferable that the polymer has a component derived from acrylonitrile and a component derived from acrylic acid, or a component derived from methacrylonitrile and a component derived from methacrylic acid.
In these cases, the cyclization reaction between the nitrile group contained in acrylonitrile or methacrylonitrile and the carboxyl group contained in acrylic acid or methacrylic acid proceeds by heating during molding, and a polyacrylimide structure or a polymethacrylamide structure is formed. Since it is formed, the shell has high heat resistance and durability.
In these cases, compared with other combinations of a component having a nitrile group and a component having a carboxyl group, the reactivity of the copolymerization reaction when obtaining the polymer, and the reaction of the cyclization reaction It is estimated that a polyacrylimide structure or a polymethacrylimide structure is easily formed.

The content of the component derived from the monomer having a carboxyl group in the polymer is not particularly limited. However, when the polymer is obtained, the amount of the monomer having a carboxyl group is 100 parts by weight of the nitrile monomer. A preferred lower limit is 5 parts by weight and a preferred upper limit is 100 parts by weight. When the blending amount of the monomer having a carboxyl group is less than 5 parts by weight, the effect of blending the monomer having a carboxyl group cannot be sufficiently obtained, and the heat resistance, durability, and the like of the shell are lowered. There is. If the amount of the monomer having a carboxyl group exceeds 100 parts by weight, the gas barrier property of the shell may be lowered.
The more preferable lower limit of the compounding amount of the monomer having a carboxyl group with respect to 100 parts by weight of the nitrile monomer is 10 parts by weight, and the more preferable upper limit is 70 parts by weight.

Moreover, when the said polymer has a component derived from the monomer which has the said carboxyl group, it is preferable to have a component derived from the monomer which has a functional group which can react with a carboxyl group further.
In this case, the reaction between the carboxyl group and the functional group capable of reacting with the carboxyl group proceeds by heating at the time of molding, and the shell is highly crosslinked. Therefore, the shell has high heat resistance and durability. .

The monomer having a functional group capable of reacting with the carboxyl group is not particularly limited. For example, N-methylol (meth) acrylamide, glycidyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) Acrylate, 2-hydroxybutyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, magnesium mono Examples include acrylate and zinc monoacrylate. Of these, glycidyl (meth) acrylate and zinc monoacrylate are preferred. In the present specification, (meth) acrylate means both methacrylate and acrylate.

The content of the component derived from the monomer having a functional group capable of reacting with the carboxyl group in the polymer is not particularly limited, but when obtaining the polymer, the carboxyl group with respect to 100 parts by weight of the nitrile monomer and A preferable lower limit of the amount of the monomer having a reactive functional group is 0.01 part by weight, and a preferable upper limit is 30 parts by weight. When the blending amount of the monomer having a functional group capable of reacting with the carboxyl group is less than 0.01 parts by weight, the degree of crosslinking of the shell during molding may be lowered. If the amount of the monomer having a functional group capable of reacting with the carboxyl group exceeds 30 parts by weight, the gas barrier property of the shell may be lowered.
The more preferable lower limit of the amount of the monomer having a functional group capable of reacting with the carboxyl group with respect to 100 parts by weight of the nitrile monomer is 0.1 part by weight, and the more preferable upper limit is 10 parts by weight.

In addition, the polymer has a component derived from the nitrile monomer, the monomer having a carboxyl group, a monomer having a functional group capable of reacting with the carboxyl group, and the like, which can be copolymerized with other monomers. Also good.
Examples of the other monomer include divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, and 1,4-butanediol di (Meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, di (meth) acrylate of polyethylene glycol having a molecular weight of 200 to 600, glycerin di (meth) acrylate , Trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meta) Acrylate, triallyl formal tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dimethylol - tricyclodecane (meth) acrylate. Examples of the other monomers include acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and dicyclopentenyl acrylate, and methacrylic acid such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and isobornyl methacrylate. Examples also include vinyl monomers such as esters, vinyl chloride, vinylidene chloride, vinyl acetate, and styrene. These may be used independently and 2 or more types may be used together.

The content of the component derived from the other monomer in the polymer is not particularly limited, but when obtaining the polymer, the preferred upper limit of the blending amount of the other monomer with respect to 100 parts by weight of the nitrile monomer is 40. Parts by weight. When the blending amount of the other monomer exceeds 40 parts by weight, the heat resistance, durability, gas barrier property and the like of the shell may be lowered.
A more preferable upper limit of the blending amount of the other monomer with respect to 100 blending amount of the nitrile monomer is 30 parts by weight.

The shell is preferably highly crosslinked at the time of molding, for example, by adjusting the constituent components of the polymer, or has a high elastic modulus, gas barrier property, durability, and the like. As a result, the thermally expandable microcapsules are not easily crushed, that is, are not easily shrunk even when subjected to heat and shear during molding, and are not easily destroyed even after repeated compression. Fatigue resistance against repeated compression is improved.
The shell preferably contains a thermosetting resin when the polymer has a component derived from the monomer having a carboxyl group.
In this case, the reaction between the carboxyl group and the thermosetting resin proceeds by heating during molding, and the shell is highly crosslinked, so that the shell has high heat resistance and durability.

Although it will not specifically limit if the said thermosetting resin can react with a carboxyl group, It is preferable to have two or more functional groups which can react with a carboxyl group in a molecule | numerator. Examples of the thermosetting resin include an epoxy resin, a phenol resin, a melamine resin, a urea resin, a polyimide resin, and a bismaleimide resin. Of these, epoxy resins and phenol resins are preferred.
The epoxy resin is not particularly limited, and examples thereof include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, dicyclopentadiene type epoxy resin, glycidylamine type epoxy resin and the like. It is done.

The said phenol resin is not specifically limited, For example, a novolak type phenol resin, a resol type phenol resin, a benzylic ether type phenol resin etc. are mentioned. Of these, novolac type phenol resins are preferred.

Although content of the said thermosetting resin in the said shell is not specifically limited, A preferable minimum is 0.01 weight% and a preferable upper limit is 30 weight%. When the content of the thermosetting resin is less than 0.01% by weight, thermosetting characteristics may not appear in the shell during molding. When the content of the thermosetting resin exceeds 30% by weight, the gas barrier property of the shell may be deteriorated.
The minimum with more preferable content of the said thermosetting resin in the said shell is 0.1 weight%, and a more preferable upper limit is 10 weight%.

In addition, when the polymer has a component derived from a monomer having the carboxyl group, the shell is also formed by having the component derived from a monomer having a functional group capable of reacting with the carboxyl group. Even in the case of containing a thermosetting resin, the shell is highly crosslinked at the time of molding in any case, and the shell has high heat resistance and durability.
However, in order to prevent the subsequent thermal expansion from being inhibited by the reaction between the carboxyl group and the functional group capable of reacting with the carboxyl group when obtaining the polymer, the polymer is It is more preferable that the shell contains the thermosetting resin than a component derived from a monomer having a functional group capable of reacting with a group.

The volatile liquid is not particularly limited, for example, low ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether, etc. molecular weight _{hydrocarbons, CCl 3 F, CCl 2 F} 2, CClF 3, CClF 2 -CClF 2 such chlorofluorocarbons, tetramethylsilane, trimethylethyl silane, trimethyl isopropyl silane, tetraalkyl silane such as trimethyl -n- propyl silane Is mentioned. Of these, isobutane, n-butane, n-pentane, isopentane, n-hexane, petroleum ether, and mixtures thereof are preferred. These may be used independently and 2 or more types may be used together.

The said heat-expandable microcapsule has a preferable lower limit of heat durability of 50 ° C. When the thermal durability is less than 50 ° C., the thermally expandable microcapsules cannot maintain an expanded state even when expanded by heating during molding, and dents are generated, resulting in the thermal expansion after thermal expansion. In some cases, the interface between the shell of the conductive microcapsule and the base resin is peeled off and the adhesion is lowered.
A more preferable lower limit of the thermal durability of the thermally expandable microcapsule is 55 ° C.

The said heat-expandable microcapsule has a preferable lower limit of the maximum foaming displacement of 500 μm. When the maximum foaming displacement is less than 500 μm, the average diameter of the bubbles is reduced, and the cushioning property of the foamed molded product may be lowered.
A more preferable lower limit of the maximum foaming displacement of the thermally expandable microcapsule is 800 μm.

In the present specification, the maximum foaming displacement and thermal durability of the thermally expandable microcapsule are the maximum foaming displacement (Dmax) obtained using a thermomechanical analyzer (TMA) such as “TMA2940” manufactured by TAinstruments. , And a temperature range (ΔT1 / 2) at which a displacement of ½ of the maximum foaming displacement (Dmax) can be obtained.

The thermally expandable microcapsules preferably have a high affinity with the base resin, that is, are easily compatible with the base resin (the solubility parameter is close). Thereby, the adhesiveness of the shell of the said thermally expansible microcapsule after thermal expansion and the said base resin can be improved.
For example, when an ester elastomer is used as the base resin, since the ester elastomer and methacrylic acid have close solubility parameters and high affinity, the polymer contained in the shell is a component derived from methacrylic acid. It is preferable to have.

Further, the thermally expandable microcapsule preferably has chemical reactivity with the base resin. Thereby, the adhesiveness of the shell of the said thermally expansible microcapsule after thermal expansion and the said base resin can further be improved.
For example, when an ester elastomer having a carboxyl group or an amide elastomer having an amide group is used as the base resin, the epoxy contained in the shell is chemically reactive with the carboxyl group or amide group. It is preferable to include a component derived from a resin, a phenol resin, or glycidyl (meth) acrylate.

The above-mentioned bubbles have a preferable lower limit of the average diameter of 50 μm and a preferable upper limit of 300 μm. When the average diameter of the bubbles is less than 50 μm, the foamed molded article has a reduced cushioning property, and in particular, the static stiffness, that is, the static spring property may be increased and become hard. If the average diameter of the bubbles exceeds 300 μm, the strength of the foamed molded product is lowered, and the surface of the molded product may swell, tear or peel off during use.
A more preferable lower limit of the average diameter of the bubbles is 70 μm, and a more preferable upper limit is 200 μm.

The upper limit of the CV value of the diameter of the bubbles is preferably 50%. When the CV value of the diameter of the bubbles exceeds 50%, the foamed molded product has a reduced cushioning property, and in particular, the dynamic stiffness, that is, the dynamic spring property is increased and may be hardened against quick compression.
A more preferable upper limit of the CV value of the bubble diameter is 40%.

In this specification, the average diameter of the bubbles and the CV value of the diameter of the bubbles are obtained by cutting a foamed molded article using a sharp blade such as a razor, a microtome, a focused ion beam, etc. After sputtering with platinum, gold, etc., when observed with an electron microscope at a magnification of 150 times or the like and the diameter di of any 50 (n = 50) bubbles was measured using a caliper, the following formula (1 ) And the value calculated by (2). When the bubbles are not spherical, the bubble diameter means the longest diameter of the bubbles.
Average diameter = (Σdi) / n (1)
CV value of diameter (%) = (standard deviation of diameter / average diameter) × 100 (2)

In the foamed molded article of the present invention, the average adhesion index between the shell of the thermally expandable microcapsule after thermal expansion and the base resin is 7 or more.
When the average adhesion index is 7 or more, the thermal expansion microcapsule shell after thermal expansion and the base resin have high adhesion, and the thermal expansion microcapsule shell after thermal expansion is reinforced. Since it can function sufficiently as a material, the foamed molded article of the present invention is excellent in fatigue resistance against repeated compression.

If the average adhesion index between the shell of the thermally expandable microcapsule after thermal expansion and the base resin is less than 7, the shell of the thermally expandable microcapsule after thermal expansion functions sufficiently as a reinforcing material. As in the case where a chemical foaming agent is used, the foamed molded article has insufficient fatigue resistance against repeated compression.
The average adhesion index between the shell of the thermally expandable microcapsule after thermal expansion and the base resin is preferably 8 or more, and more preferably 9 or more.
The upper limit of the average adhesion index between the thermally expandable microcapsule shell after thermal expansion and the base resin is not particularly limited, and is preferably closer to 10 which is the maximum value.

In this specification, the average adhesion index is a foamed article cut with a sharp blade such as a razor, a microtome, a focused ion beam, etc., and after sputtering the obtained cross section with platinum, gold, etc. Observed with an electron microscope at a magnification of 150 times, etc., the length A of the part of the thermally expandable microcapsule shell after thermal expansion that is in close contact with the base resin in any of a plurality of bubbles, and Means the average value of the adhesion index of each bubble calculated by the following equation (3) when the circumferential length B of the cell in which the thermally expandable microcapsules after thermal expansion are measured is measured. To do. In addition, a cell means the space in which the thermally expansible microcapsule after thermal expansion is arrange | positioned in a foaming molding.
Adhesion index of each bubble = (A / B) × 10 (3)
The length A of the portion of the thermally expandable microcapsule shell that has been thermally expanded is in close contact with the base resin, and the circumference of the cell in which the thermally expandable microcapsule after the thermal expansion is disposed The length B in the direction can be measured, for example, by placing a free curve ruler along a measurement location in a cross-sectional observation image of bubbles printed out on paper.

The average adhesiveness index in this specification is demonstrated with reference to FIGS. (A) of FIGS. 1-10 is an example of the electron micrograph of the cross section of the bubble in the foaming molding in which the bubble formed when the thermally expansible microcapsule was thermally expanded in base resin, respectively. is there. (B) in FIGS. 1 to 10, with respect to the electron micrograph of (a), the length B in the circumferential direction of the cell in which the thermally expandable microcapsules after thermal expansion are arranged is a solid line, It is the photograph which traced the length C of the circumferential direction of the shell of the thermally expansible microcapsule after thermal expansion with the dotted line.
For example, in FIG. 5B, the length B (solid line) and C (dotted line) are overlapped by about half, while in FIG. 10B, the length B (solid line) and C (dotted line) are Are almost entirely overlapping. That is, the air bubbles shown in FIG. 10 have higher adhesion between the shell of the thermally expandable microcapsule after thermal expansion and the base resin than the air bubbles shown in FIG.
The average adhesion index in this specification is an index indicating the adhesion between the shell of the thermally expandable microcapsule after such thermal expansion and the base resin. In addition, the number described in the bubble shown by (b) of FIGS. 1-10 has shown the adhesiveness index of the bubble.

The foamed molded article of the present invention has an indenter with a diameter of 20 mm, and a preferable upper limit of fatigue resistance when a cycle load of a lower limit setting of 165N and an upper limit setting of 661N is applied for 3 million cycles is 10%. If the fatigue resistance at 3 million cycles exceeds 10%, the fatigue resistance to repeated compression of the foamed molded product may be insufficient.
A more preferable upper limit of the fatigue resistance of the foamed molded article of the present invention when the cycle weight of the lower limit setting 165N and the upper limit setting 661N is applied for 3 million cycles with an indenter having a diameter of 20 mm is 8%.

In this specification, fatigue resistance is static after the fatigue test is performed on the static spring property (static stiffness) before the predetermined fatigue test calculated from the following formula (4). It means the rate of change of natural springiness (stiffness after fatigue).
Fatigue resistance (%) = (Static stiffness after fatigue-Static stiffness) / Static stiffness x 100 (4)

In the foamed molded article of the present invention, the preferable upper limit of static stiffness, that is, static springiness is 35 N / mm. When the static stiffness exceeds 35 N / mm, the foamed molded product becomes hard and the cushioning property may be lowered.
The upper limit with more preferable static rigidity of the foaming molding of this invention is 30 N / mm.

In the foamed molded article of the present invention, the preferable upper limit of the dynamic stiffness, that is, the dynamic spring property is 45 N / mm. When the dynamic stiffness exceeds 45 N / mm, the foamed molded product becomes hard against rapid compression, and the cushioning property may be lowered.
The upper limit with more preferable dynamic rigidity of the foaming molding of this invention is 40 N / mm.

The method for producing the foamed molded product of the present invention is not particularly limited. For example, the above thermal expansion microcapsules are added to the base resin and mixed, and the mixture is injected into a molding machine or the like, and foamed and molded. A heat-kneaded microcapsule with a masterbatch base resin such as polyethylene or ethylene-vinyl acetate copolymer to produce a pellet-shaped masterbatch, then add the masterbatch to the above base resin, mix and mold For example, a foam molding method may be used. In particular, in order to enhance the adhesion between the shell of the thermally expandable microcapsule after thermal expansion and the base resin and to make the average adhesive index within the above range, the thermally expandable microcapsule and the base material It is preferred to select the resins so that their affinity is high or they are chemically reactive.
The molding method used for foam molding is not particularly limited, and examples thereof include extrusion molding, injection molding, and press molding. Moreover, the shape and rotation speed of the screw at the time of foam molding are not particularly limited, and may be appropriately designed in consideration of the shearing force due to the rotation of the screw and the residence time.

Further, when foam-molding, it is preferable to perform foam-molding with a low load so that the thermally expandable microcapsules are not crushed. More specifically, the base resin at the time of extrusion molding or injection molding Therefore, it is preferable to use a low-viscosity base resin or lower the viscosity of the base resin by raising the molding temperature.

When the foamed molded article of the present invention is produced, the amount of the thermally expandable microcapsule is not particularly limited, but the preferred lower limit with respect to 100 parts by weight of the base resin is 1 part by weight, and the preferred upper limit is 10 parts by weight. When the blending amount of the thermally expandable microcapsule is less than 1 part by weight, the number of the bubbles may be reduced, and the cushioning property of the foamed molded product may be lowered and become hard. When the blending amount of the thermally expandable microcapsule exceeds 10 parts by weight, the number of the bubbles increases, the strength of the foamed molded product decreases, and the surface of the molded product swells, tears, or peels off during use. Such a problem may occur easily.
The blending amount of the thermally expandable microcapsule is more preferably 1.5 parts by weight and more preferably 8 parts by weight based on 100 parts by weight of the base resin.

When the foamed molded article of the present invention is produced, chemical foaming of azodicarbonamide or the like that decomposes and generates gas when heated, in addition to the above-described thermally expandable microcapsules, within the range that does not impair the effects of the present invention. An agent may be blended.
The upper limit of the compounding amount of the chemical foaming agent is preferably 50 parts by weight with respect to 100 parts by weight of the thermally expandable microcapsules so as not to impair fatigue resistance against repeated compression of the foamed molded product.

Since the foamed molded article of the present invention is excellent in fatigue resistance against repeated compression, it is useful, for example, as a medical member or a member used in automobiles, railways, railroad tracks, bridges, buildings, and the like. More specifically, the foamed molded product of the present invention includes medical tubes, automobile instrument panel displays, grips, glass run channels, boots, hoses and tires, railway damping plates and rail pads for railways, tracks and bridges, building It is preferably used for damping materials, shoe soles, electric cables and the like.

ADVANTAGE OF THE INVENTION According to this invention, the foaming molding excellent in the fatigue resistance with respect to repeated compression can be provided.

1 (a) and 1 (b) show an example of an electron micrograph of a cross section of a bubble in a foamed molded product in which bubbles formed by thermal expansion of thermally expandable microcapsules are dispersed in a base resin. . 2 (a) and 2 (b) show an example of an electron micrograph of a cross section of a bubble in a foamed molded article in which bubbles formed by thermal expansion of thermally expandable microcapsules are dispersed in a base resin. . 3 (a) and 3 (b) show an example of an electron micrograph of a cross section of a bubble in a foamed molded product in which bubbles formed by thermal expansion of thermally expandable microcapsules are dispersed in a base resin. . 4 (a) and 4 (b) show an example of an electron micrograph of a cross section of a bubble in a foamed molded article in which bubbles formed by thermal expansion of thermally expandable microcapsules are dispersed in a base resin. . 5 (a) and 5 (b) show an example of an electron micrograph of a cross section of a bubble in a foamed molded product in which bubbles formed by thermal expansion of thermally expandable microcapsules are dispersed in a base resin. . FIGS. 6A and 6B show an example of an electron micrograph of a cross section of a bubble in a foamed molded product in which bubbles formed by thermal expansion of thermally expandable microcapsules are dispersed in a base resin. . FIGS. 7A and 7B show an example of an electron micrograph of a cross section of a bubble in a foamed molded product in which bubbles formed by thermal expansion of thermally expandable microcapsules are dispersed in a base resin. . FIGS. 8A and 8B show an example of an electron micrograph of a cross section of a bubble in a foam molded product in which bubbles formed by thermal expansion of thermally expandable microcapsules are dispersed in a base resin. . 9 (a) and 9 (b) show an example of an electron micrograph of a cross section of a bubble in a foamed molded product in which bubbles formed by thermal expansion of thermally expandable microcapsules are dispersed in a base resin. . FIGS. 10A and 10B show an example of an electron micrograph of a cross section of a bubble in a foamed molded product in which bubbles formed by thermal expansion of a thermally expandable microcapsule in a base resin are dispersed. . FIGS. 11A and 11B show electron micrographs of a cross section of the foam molded article obtained in Example 1. FIG. FIGS. 11A and 11B show electron micrographs of a cross section of the foam molded article obtained in Example 2. FIGS. FIGS. 11A and 11B show electron micrographs of a cross section of the foam molded article obtained in Comparative Example 3. FIG.

Examples of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

(Production Example 1)
In a polymerization reaction vessel, 250 parts by weight of water, 25 parts by weight of colloidal silica (manufactured by Asahi Denka Co., 20% by weight) and 0.8 parts by weight of polyvinylpyrrolidone (manufactured by BASF) as dispersion stabilizers, 90 parts by weight of sodium chloride And an aqueous dispersion medium was prepared.
Next, 30 parts by weight of acrylonitrile (AN), 50 parts by weight of methacrylonitrile (MAN) and 20 parts by weight of methacrylic acid (MAA), and N, N-bis (2,3-epoxypropyl) -4 as a thermosetting resin -0.2 parts by weight of (2,3-epoxypropoxy) aniline and 1 part by weight of a polycondensate of 4,4'-isopropylidenediphenol and 1-chloro-2,3-epoxypropane; .3 parts by weight, 27 parts by weight of pentane and 5 parts by weight of isooctane as a volatile liquid, 0.8 parts by weight of 2,2′-azobis (isobutyronitrile) and 2,2′-azobis ( An oily mixture composed of 0.6 part by weight of 2,4-dimethylvaleronitrile) was added to an aqueous dispersion medium and suspended to prepare a dispersion.
The resulting dispersion is stirred and mixed with a homogenizer, charged into a pressure polymerizer purged with nitrogen, and reacted at 60 ° C. for 6 hours and at 80 ° C. for 5 hours while being pressurized (0.5 MPa). I got a thing. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules A.

(Production Example 2)
In a polymerization reaction vessel, 250 parts by weight of water, 25 parts by weight of colloidal silica (manufactured by Asahi Denka Co., 20% by weight) and 0.8 parts by weight of polyvinylpyrrolidone (manufactured by BASF) as dispersion stabilizers, 90 parts by weight of sodium chloride And an aqueous dispersion medium was prepared.
Next, 50 parts by weight of acrylonitrile (AN), 30 parts by weight of methacrylonitrile (MAN) and 20 parts by weight of acrylic acid (AA), 27 parts by weight of pentane and 5 parts by weight of isooctane as a volatile liquid, and 2 as a polymerization initiator , 2'-azobis (isobutyronitrile) 0.8 parts by weight and 2,2'-azobis (2,4-dimethylvaleronitrile) 0.6 parts by weight are added to the aqueous dispersion medium, A dispersion was prepared by suspending.
The resulting dispersion is stirred and mixed with a homogenizer, charged into a pressure polymerizer purged with nitrogen, and reacted at 60 ° C. for 6 hours and at 80 ° C. for 5 hours while being pressurized (0.5 MPa). I got a thing. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules B.

(Production Example 3)
In a polymerization reaction vessel, 250 parts by weight of water, 25 parts by weight of colloidal silica (manufactured by Asahi Denka Co., 20% by weight) and 0.8 parts by weight of polyvinylpyrrolidone (manufactured by BASF) as dispersion stabilizers, 90 parts by weight of sodium chloride And an aqueous dispersion medium was prepared.
Next, 60 parts by weight of acrylonitrile (AN) and 40 parts by weight of methacrylonitrile (MAN), 27 parts by weight of pentane and 5 parts by weight of isooctane as a volatile liquid, and 2,2′-azobis (isobutyro) as a polymerization initiator Nitrile) 0.8 parts by weight and 2,2'-azobis (2,4-dimethylvaleronitrile) 0.6 parts by weight are added to an aqueous dispersion medium and suspended to prepare a dispersion. did.
The resulting dispersion is stirred and mixed with a homogenizer, charged into a pressure polymerizer purged with nitrogen, and reacted at 60 ° C. for 6 hours and at 80 ° C. for 5 hours while being pressurized (0.5 MPa). I got a thing. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules C.

(Production Example 4)
In a polymerization reaction vessel, 250 parts by weight of water, 25 parts by weight of colloidal silica (manufactured by Asahi Denka Co., 20% by weight) and 0.8 parts by weight of polyvinylpyrrolidone (manufactured by BASF) as dispersion stabilizers, 90 parts by weight of sodium chloride And an aqueous dispersion medium was prepared.
Next, 20 parts by weight of acrylonitrile (AN), 30 parts by weight of methacrylonitrile (MAN), 40 parts by weight of methyl methacrylate (MMA) and 10 parts by weight of methacrylic acid (MAA), 27 parts by weight of pentane and isooctane as a volatile liquid 5 parts by weight, and 0.8 parts by weight of 2,2′-azobis (isobutyronitrile) and 0.6 parts by weight of 2,2′-azobis (2,4-dimethylvaleronitrile) as a polymerization initiator The oily mixture was added to the aqueous dispersion medium and suspended to prepare a dispersion.
The resulting dispersion is stirred and mixed with a homogenizer, charged into a pressure polymerizer purged with nitrogen, and reacted at 60 ° C. for 6 hours and at 80 ° C. for 5 hours while being pressurized (0.5 MPa). I got a thing. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules D.

<Evaluation of thermally expandable microcapsules>
The following evaluation was performed on the thermally expandable microcapsules obtained in the production examples. The results are shown in Table 1.

(1) Thermal durability Thermomechanical analyzer (TMA) ("TMA2940" manufactured by TA instruments) can be used to obtain a thermal durability of the thermally expandable microcapsules (1/2 of the maximum foaming displacement (Dmax)). The temperature width, ΔT1 / 2) was measured.
Specifically, 25 μg of thermally expandable microcapsules are placed in an aluminum container having a diameter of 7 mm and a depth of 1 mm, and a force of 0.1 N is applied from the top at a temperature increase rate of 5 ° C./min. It heated to 300 degreeC and the displacement in the vertical direction of a measurement terminal was measured. The temperature at which the displacement begins to rise and reaches 1/2 of the maximum foaming displacement is changed to T1 / 2, and then the maximum foaming displacement (Dmax) is changed. Let T1 / 2 *. At this time, thermal durability (temperature range at which a displacement of 1/2 of the maximum foaming displacement (Dmax) can be obtained, ΔT1 / 2) was calculated by the following formula (5).
ΔT1 / 2 = T1 / 2 * −T1 / 2 (5)

(Examples 1-7 and Comparative Examples 1-4)
Kneading 100 parts by weight of a base resin for masterbatch in powder or pellet form shown in Table 2 or 3 and 10 parts by weight of stearic acid as a lubricant with a conical twin screw extruder (“OSC-30” manufactured by Nagata Seisakusho) When the temperature reached about 100 ° C., 100 parts by weight of the foaming agent shown in Table 2 or 3 was added, and the mixture was further kneaded for 30 seconds, then extruded and pelletized at the same time to obtain master batch pellets.
In Table 2 or 3, PE means low density polyethylene resin ("Sunfine PAK00720" manufactured by Asahi Kasei Co., Ltd.), EMMA means ethylene-methyl methacrylate copolymer, and EVA means ethylene-acetic acid. A vinyl copolymer is meant.

100 parts by weight of a pellet-type ester elastomer (“Hytrel # 3078” manufactured by Toray DuPont), a masterbatch having a blending amount shown in Table 2 or 3, and 3 parts by weight of a pigment masterbatch (“Color MB” manufactured by Tokyo Ink) Are mixed with a molding machine ("USV30-20 EXTORUDER" manufactured by Union Plastics Co., Ltd.), and extrusion molding is performed under the conditions shown in Table 2 or 3 under conditions of molding temperature, residence time of 1 minute, and screw rotation speed of 30 rpm. A 12 mm foamed molded article was obtained.

The obtained foamed molded product was cut using a single-blade razor (manufactured by Feather), and the resulting cross-section was sputtered with gold, and then observed with an electron microscope at a magnification of 150 times. The length A of the portion of the thermally expandable microcapsule shell that is in close contact with the base resin, and the circumferential length of the cell in which the thermally expandable microcapsule after the thermal expansion is disposed The average adhesion index was calculated by measuring the thickness B and calculating the average value of the five bubbles of the adhesion index of each bubble calculated by the above-described equation (3).
The length A of the portion of the shell of the thermally expandable microcapsule after thermal expansion that is in close contact with the base resin, and the circumferential direction of the cell in which the thermally expandable microcapsule after the thermal expansion is disposed The length B was measured by placing a free curve ruler along the measurement location in a cross-sectional observation image of bubbles printed out on paper.

<Evaluation of foam molding>
The following evaluation was performed about the foaming molding obtained by the Example and the comparative example. The results are shown in Table 2 or 3.
11, 12 and 13, (a) shows electron micrographs of the cross-sections of the foam molded bodies obtained in Examples 1 and 2 and Comparative Example 3, respectively, and (b) shows the electron of (a). With respect to the micrograph, the circumferential length B of the cell in which the thermally expandable microcapsules after thermal expansion are arranged is indicated by a solid line, and the circumferential length of the shell of the thermally expandable microcapsules after thermal expansion The photograph which traced C with the dotted line was shown. The numbers written in the bubbles shown in FIGS. 11, 12 and 13 (b) indicate the adhesion index of the bubbles.

(1) Cushioning property The cushioning property was evaluated by determining the static stiffness and dynamic stiffness of the foamed molded product as follows.
(1-1) Measurement of Static Stiffness An indenter (made of stainless steel, cylindrical shape of Φ15 mm × 10 mm) was placed on the surface of the foamed molded product, and the height of the indenter at this time was set to zero. Using a static material testing machine (“EZGraph”, manufactured by Shimadzu Corporation), the displacement (S1) of the indenter when a 91.5 N load was applied to the indenter for 60 seconds was measured, and then the indenter was loaded with a 320 N load. Was measured for 60 seconds, and the static stiffness was calculated from the following equation (6).
Static stiffness (N / mm) = (320-91.5) / (S2-S1) (6)

(1-2) Measurement of dynamic stiffness An indenter (made of stainless steel, Φ15 mm × 10 mm column) was placed on the surface of the foamed molded article, and the height of the indenter at this time was set to zero. Using the Tensilon Universal Material Test ("UTA-500", manufactured by A & D), the indenter is subjected to 1000 cycles of a lower limit setting of 91.5N and an upper limit setting of 320N, with an upper limit load from 900 cycles to 1000 cycles. The average weight (FU) and the average displacement (SU) of the indenter, and the average weight (FD) and the average displacement (SD) of the lower limit weight were measured, and the dynamic stiffness was calculated from the following formula (7).
Dynamic stiffness (N / mm) = (FU−FD) / (SU−SD) (7)

(2) Fatigue resistance against repeated compression Place an indenter (Φ20mm) on the surface of the foamed molded product, and use a repeated fatigue tester (manufactured by Shimadzu Corporation) to apply a cycle load of lower limit setting 165N and upper limit setting 661N to the indenter. It took 3 million cycles. Thereafter, the static stiffness of the molded article after 3 million cycles was measured, and fatigue resistance was calculated from the above formula (4).

ADVANTAGE OF THE INVENTION According to this invention, the foaming molding excellent in the fatigue resistance with respect to repeated compression can be provided.

Claims (8)

A foam molded article in which bubbles are dispersed in a base resin,
The base resin is a thermoplastic elastomer,
The bubbles are formed by thermal expansion of thermally expandable microcapsules enclosing a volatile liquid as a core agent in a shell containing a polymer,
The foamed molded article has a static stiffness of 35 N / mm or less and a dynamic stiffness of 45 N / mm or less.
And the shell of the thermally expandable microcapsules after thermal expansion state, and are the average adhesion index is 7 or more and the base resin,
The foam-molded article, wherein the thermally expandable microcapsule has a shell containing a thermosetting resin . The foamable molded article according to claim 1, wherein the thermally expandable microcapsule has a polymer contained in a shell having a component derived from acrylic acid or a component derived from methacrylic acid. The foamable molded article according to claim 1 or 2, wherein the thermally expandable microcapsule further comprises a component derived from a monomer having a functional group capable of reacting with a carboxyl group in the polymer contained in the shell. The foamable molded article according to claim 1 or 2, wherein the thermally expandable microcapsule has a polymer contained in a shell having a component derived from acrylonitrile and a component derived from acrylic acid. The foamable molded article according to claim 1 or 2, wherein the thermally expandable microcapsule has a polymer contained in the shell having a component derived from methacrylonitrile and a component derived from methacrylic acid. The foam-molded article according to claim 1, 2, 3, 4, or 5 , wherein the thermosetting resin is an epoxy resin. In indenter diameter 20 mm, the lower limit setting 165 N, also claim 1,2,3,4,5 fatigue resistance when the cycle load of the upper limit setting 661N multiplied 3,000,000 cycle equal to or less than 10% Is a foamed molded article according to 6 . Thermally expandable microcapsules, foamed molding of claim 1,2,3,4,5,6 or 7, wherein the heat resistance is characterized in that at 50 ° C. or higher.