JP2006219541A - Resin composition for foam and foam using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an open cell foam which has an excellent wear resistance and is usable for a long period of time. <P>SOLUTION: The foam composition is constituted of (A) a polyolefin resin (a low density polyethylene, etc. ) and (B) a specific polyethylene resin such as an ethylene-vinyl acetate copolymer. The ratio of the melt flow index MIa of the polyolefin resin (A) to the melt flow index MIb of the polyethylene resin (B) is adjusted to be ≥3. The foam is obtained by expanding (and crosslinking) the composition and has an open cell structure. The open cell foam is favorably used for a filter medium (a microbe carrier) for bio filtration, as the foam is excellent in wear resistance and usable for a long period of time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a resin composition useful for forming a foam excellent in abrasion resistance (particularly, an open-cell foam) and a foam using the composition.

  Foams are used in various applications depending on their cell structure. Among such foams, in particular, an open-cell foam having an open-cell structure is used for a filtering material (microorganism carrier) using a biological filtration system such as a microorganism by utilizing characteristics such as water absorption. It has been. For example, JP-A-6-285484 (Patent Document 1) discloses an inorganic carrier (perlite, foamed concrete, activated carbon, porous ceramics, etc.) as a microbial support for filling a biological filtration tank of a sewage purification tank. And synthetic resin carriers (polyethylene, polyvinyl chloride, polyurethane, foamed molded products such as polyvinyl alcohol acetal compounds, fiber masses, nonwoven fabrics, etc.) are described.

  In recent years, such a microorganism-supported body has been required to improve various properties (such as abrasion resistance, chemical resistance, water resistance, open cell property, and microorganism adsorption property). Among these characteristics, the carrier is easily miniaturized due to the collision between the microorganism carriers, and a high level of wear resistance is required. In addition, in such a microorganism carrier, a large amount of microorganisms enter and adhere to the bubbles, so that excellent open cell properties are required.

  On the other hand, a cross-linked polyolefin obtained by cross-linking a polyolefin introduced with a silane coupling agent by graft polymerization or the like with water can improve heat resistance, mechanical strength, etc. as compared with non-cross-linked ones, and attempts to use it as a foam. Has been made. For example, in Japanese Patent Publication No. 1-444499 (Patent Document 2), an amount of a crosslinking agent and an organic decomposable foaming agent adjusted so as to achieve a specific crosslinking rate at a foaming temperature is added to polyolefin and kneaded. The foamable composition obtained in this way is molded into a desired shape without decomposing the foaming agent, and this is heated to 145 ° C. to 210 ° C. and foamed to form a foam containing ultrathin gas bubbles. In addition, a method for producing a crosslinked polyolefin open cell body in which the cell body is mechanically deformed to allow the cell membrane to communicate with each other is disclosed. That is, in this document, the crosslinking rate of the polyolefin resin and the decomposition rate of the foaming agent are adjusted, the foam film of the foam foamed in a block shape in the mold is ruptured by mechanical deformation, and the foam film is made continuous or continuous. Open-celled bodies are produced by a two-stage process.

  However, in such an open cell body, not only is the open cell property sufficient, but it is difficult to improve the wear resistance.

  Attempts have also been made to form foams using a plurality of different resins. For example, in Japanese Patent Publication No. 60-55290 (Patent Document 3), by extruding a mixed resin in which a high density polyethylene having a melt index of 10 or more and a low density polyethylene having a melt index of 1 or less are mixed at a specific ratio. A method of producing a polyethylene foam having an open cell structure and a high expansion ratio is disclosed. That is, in the method of this document, foaming is performed in a one-step process in which high-density polyethylene having a high melt flow rate and low-density polyethylene are mixed at a specific ratio and a resin in which a volatile organic liquid is mixed at high temperature and pressure is extruded and foamed. I'm getting a body.

  However, since such a foam is made of polyethylene resin, it has low wear resistance.

  JP-A-7-278365 (Patent Document 4) discloses an olefin polymer resin such as an ethylene homopolymer, 3 to 30 parts by weight of an elastomer with respect to 100 parts by weight of the olefin polymer resin, and a specific stabilizer. There is disclosed a polyolefin foam obtained by foaming a composition comprising: However, since such a foam contains an elastomer, even if the cushioning property can be improved, characteristics such as wear resistance are still insufficient and easily deteriorated. It is difficult.

  A foam composed of a crosslinked polyolefin resin and a non-crosslinked resin is also known. For example, Japanese Patent Laid-Open No. 2000-7817 (Patent Document 5) discloses that a polyolefin resin having a melting point of 120 ° C. or less, 50 to 900 parts by weight, a low melting point of 115 ° C. or less and a melt flow rate value of 20 g / 10 min or more. A polyolefin-based resin open cell foam is disclosed in which 50 to 10 parts by weight of density polyethylene is mixed, heated and melted, and then mixed with a volatile organic foaming agent and extruded and foamed in a low pressure region. This document describes that the polyolefin resin may be a polyolefin resin obtained by kneading vinylmethoxysilane and an organic peroxide and adding silane. Specifically, in Example 4, a composition containing 30 parts by weight of low-density polyethylene having a high melt flow rate was extruded into 70 parts by weight of grafted polyethylene obtained by adding silane to low-density polyethylene to obtain an open-cell foam. It is described that it was obtained. In this document, when the open-cell foam is used as a carrier for filling a biological filtration septic tank, bubbles composed of small hexahedrons communicate with each other. It is described that it becomes easy and is excellent in decomposition of organic matter and removal of suspended matter in physical filtration.

  JP-B-2-48023 (Patent Document 6) discloses a polyethylene resin containing a crosslinkable ethylene polymer (silylated ethylene polymer) having a silyl group in a side chain which gives a cross-linked site by contact with moisture. A method for producing a crosslinked foam is disclosed in which a foaming agent and a hydroxyl group-free fatty acid amide are kneaded under pressure, extruded and foamed, and further, the foam is brought into contact with water under a silanol condensation catalyst to advance a crosslinking reaction. Has been. In this document, in addition to silylated ethylene polymer, if necessary, ethylene polymer, ethylene polymer as main component and polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, ethylene-propylene rubber, butyl rubber It is described that styrene-butadiene rubber or the like may be blended. Specifically, in Example 3, a silylated ethylene polymer (a copolymer of γ-methacryloxypropyltrimethoxysilane and ethylene by a high-pressure radical polymerization method), a low-density polyethylene containing no unsaturated compound, and In addition, it is described that a foamed sheet was prepared by extrusion foaming a composition containing a silanol catalyst.

In the foam obtained by these methods, mechanical strength can be improved to some extent by using a crosslinked polyolefin resin. However, since the wear resistance is still insufficient in applications such as filter media, it is easy to deteriorate and difficult to use for a long time. Moreover, since resin which has low hydrophilicity and affinity with respect to microorganisms, such as polyethylene, is used as resin which comprises a foam, it is difficult to carry | support microorganisms efficiently.
JP-A-6-285484 (claims, paragraph number [0028]) Japanese Patent Publication No. 1-44499 (Claims) Japanese Patent Publication No. 60-55290 (Claims) JP-A-7-278365 (Claims) JP 2000-7817 A (claims, paragraph number [0005], Example 4) JP-B-2-48023 (Claims, page 5, lines 10 to 35, Example 3)

  Accordingly, an object of the present invention is to provide a resin composition that is excellent in wear resistance and can efficiently form a foam (particularly, open-cell foam) that can be used for a long period of time, and a foam using the composition. There is to do.

  Another object of the present invention is to provide a resin composition useful for obtaining a foam having excellent mechanical properties (abrasion resistance, tensile strength, etc.) and excellent open cell properties, and foaming using the composition. The object is to provide a body (open cell foam).

  Still another object of the present invention is to provide an open-cell foam (microorganism support) that can efficiently support (or retain) microorganisms and can be used for a long period of time.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that a polyolefin resin (such as a low-density polyethylene resin that may have a crosslinkable group) and an ethylene copolymer (such as an ethylene-vinyl acetate copolymer). ) In combination with a specific melt flow index (melt flow rate) ratio, it has been found that a foam (especially an open-cell foam) that can be used over a long period of time can be obtained. Completed the invention.

That is, the foam resin composition of the present invention is a resin composition composed of a polyolefin resin (A) and a polyethylene resin (B), and the polyethylene resin (B) is ethylene (b ₁ ) And at least one copolymerizable monomer (b ₂ ) selected from a carboxylic acid vinyl ester monomer and a (meth) acrylic monomer, or a metal salt thereof, The ratio (or ratio) MIb / MIa of the melt flow index MIa of the polyolefin resin (A) and the melt flow index MIb of the polyethylene resin (B) is 3 or more.

The polyolefin resin (A) may be a crosslinkable (or condensable) resin. For example, a polyolefin resin having a crosslinkable group [particularly a hydrolytic condensable group (such as an alkoxysilyl group)] (particularly, , Low density polyethylene resin, polyethylene resin polymerized using metallocene catalyst). The ratio of the crosslinkable group (hydrolytic condensable group) contained in such a polyolefin resin (A) may be, for example, about 1 to 20% by weight in terms of a crosslinkable monomer. The copolymerizable monomer (b ₂ ) is at least one selected from C _2-3 carboxylic acid vinyl ester (particularly vinyl acetate), (meth) acrylic acid and (meth) acrylic acid C _1-2 alkyl ester. You may comprise. A typical polyolefin resin (A) is a low density polyethylene resin (non-crosslinkable or crosslinkable low density polyethylene resin) which may have a crosslinkable group, and a metallocene which may have a crosslinkable group. You may be comprised with at least 1 type selected from the polyethylene resin (or the polyethylene resin polymerized using the metallocene catalyst, for example, the linear low density polyethylene resin polymerized using the metallocene catalyst).

In the polyethylene resin (B), the ratio (weight ratio) of ethylene (b ₁ ) and copolymerizable monomer (b ₂ ) was about the former / the latter = 90/10 to 65/35. May be. Furthermore, the ratio (weight ratio) between the polyolefin resin (A) and the polyethylene resin (B) may be about the former / the latter = 10/90 to 90/10. Furthermore, in a preferred embodiment, MIa may be about 0.1 to 10 g / 10 minutes, and MIb / MIa may be 4 or more.

  Typical resin compositions include non-crosslinkable or crosslinkable low density polyethylene resins having MIa of 0.2 to 8 g / 10 min (for example, low density polyethylene resin, low density polyethylene resin and silane coupling agent). Graft polymer, etc.) (A) and at least one polyethylene resin selected from ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer and ionomer resin (B And the resin composition having a MIb / MIa of about 4.5 to 40.

  In the present invention, wear resistance can be imparted (improved) or improved by combining the polyolefin resin (A) and the specific polyethylene resin (B). Therefore, the present invention also includes a method for improving the abrasion resistance of the foam by forming the foam using the resin composition for foam.

  The foam of the present invention can be formed by foaming the resin composition. For example, the foam (open cell foam) of the present invention is obtained by melt-kneading the resin composition (for example, the polyolefin resin (A), the polyethylene resin (B), and a foaming agent), and extruding. You may manufacture by making it foam.

  Moreover, the foam formed with the said resin composition is also contained in this invention. Such a foam may have an open cell structure. In the present invention, a foam (open cell foam) having a uniform open cell structure can be formed efficiently. Such an open cell foam can be suitably used as a microorganism carrier.

  In the present invention, a polyolefin resin (for example, a low density polyethylene resin that may have a crosslinkable group) and a specific polyethylene resin (ethylene copolymer) are combined at a specific melt flow index ratio. It is possible to efficiently form a foam (particularly an open-cell foam) that is excellent in wear resistance and can be used for a long period of time. Moreover, in this invention, while being excellent in mechanical characteristics (abrasion resistance etc.), the foam excellent in open cell property can be formed. Furthermore, in the present invention, a specific polyethylene resin (ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer) having excellent affinity for microorganisms and hydrophilicity as compared with polyethylene resin is used. Therefore, it is possible to provide an open-cell foam (microorganism support) that can efficiently support (or hold) microorganisms and that has excellent wear resistance and can be used for a long period of time.

  The resin composition for foams of the present invention is composed of a polyolefin resin (A) and a specific polyethylene resin (B).

[Polyolefin resin (A)]
Examples of the polyolefin resin (A) (hereinafter sometimes simply referred to as polyolefin resin) include olefin homopolymers or copolymers, copolymers of olefins and copolymerizable monomers, and the like.

Examples of the olefin (or the monomer of the polyolefin resin) include ethylene, propylene, 1-butylene, isobutylene, 1-pentene, 3-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, Α-C _2-20 olefins such as 1-nonene, 1-decene, 1-undecene and 1-dodecene (preferably α-C _2-10 olefins, more preferably α-C _2-4 olefins, especially α-C _2-3 olefins). These olefins may be used alone or in combination of two or more.

As the copolymerizable monomer, for example, (meth) acrylic acid, (meth) acrylic acid ester [for example, (meth) acrylic acid methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, etc. ) acrylic acid C _1-6 alkyl esters, vinyl esters (e.g., vinyl acetate, vinyl propionate, etc.), cyclic olefins (norbornene, ethylidene norbornene, cyclopentene, cyclopentadiene, cyclohexene, etc.), dienes (butadiene, isoprene , 1,4-pentadiene, etc.). A copolymerizable monomer can be used individually or in combination of 2 or more types. The ratio (weight ratio) between the olefin and the copolymerizable monomer can be selected in the range of the former / the latter = 100/0 to 50/50, for example, about 95/5 to 60/40, preferably 90 / About 10-65 / 35, More preferably, about 80 / 20-60 / 40 may be sufficient.

  The polyolefin resin may be a random copolymer or a block copolymer.

Typical polyolefin resins (or polyolefin units constituting non-crosslinkable or crosslinkable polyolefin resins) include, for example, polyethylene resins [for example, low, medium or high density polyethylene resins, linear low density polyethylene resins. , Ethylene-propylene copolymer, ethylene-butene-1 copolymer, ethylene-propylene-butene-1 copolymer, ethylene- (4-methylpentene-1) copolymer], polypropylene resin (for example, Polypropylene, propylene-ethylene copolymer, propylene-butene-1 copolymer, propylene-containing propylene-α-olefin copolymer such as propylene-ethylene-butene-1 copolymer and the like having 80 mol% or more), poly ( Methylpentene-1) resin, ethylene-vinyl acetate copolymer, ethylene- (methyl ) Acrylic acid copolymer or its metal salt, ethylene - (meth) acrylic acid C _1-4 alkyl ester copolymer (ethylene - methyl methacrylate copolymer), maleic anhydride grafted polypropylene can be exemplified. These polyolefin resins may be used alone or in combination of two or more.

  Among the polyolefin resins, polyethylene resins (low density polyethylene resin, medium density polyethylene resin, high density polyethylene resin, linear low density polyethylene resin, etc.) are preferable, especially low density polyethylene resin, metallocene catalyst (Kaminsky catalyst). Also included are metallocene polyolefin-based resins polymerized by using (for example, metallocene polyethylene resins such as linear low-density polyethylene resins polymerized using a metallocene catalyst).

  The polyolefin resin (A) may be a non-crosslinkable resin (resin having no crosslinkable group) or a crosslinkable (or condensable) resin. The crosslinkable polyolefin resin (or polyolefin resin having a crosslinkable group) can improve the mechanical strength of the foam by crosslinking (for example, water crosslinking). The crosslinkable polyolefin resin usually has a crosslinkable group, and such a crosslinkable group is a thermally crosslinkable group (for example, a polymerizable unsaturated group such as a vinyl group or a (meth) acryloyl group), Although it may be a photocrosslinkable group or the like, it may usually be a hydrolytic condensable group. When a polyolefin resin having such a hydrolyzable condensable group is used, the entire foam can be efficiently crosslinked by water crosslinking.

  As long as the crosslinkable polyolefin resin has a crosslinkability (or a crosslinkable group), its production method is not particularly limited. For example, an olefin and a crosslinkable monomer (crosslinkable) corresponding to the crosslinkable group. A monomer having a group) (a random copolymer, etc.), and a graft copolymer of a polyolefin resin (the polyolefin resin exemplified above) and a crosslinkable monomer. May be.

As mentioned above, the crosslinkable group is often a hydrolytic condensable group. Examples of such a hydrolytic condensable group include a hydrolyzable group [for example, C ₁ such as an alkoxy group (for example, a methoxy group, an ethoxy group, etc.) on a metal atom (aluminum, silicon, titanium, zirconium, etc., particularly silicon). _-4 alkoxy groups, preferably lower alkoxy groups such as C _1-2 alkoxy groups), halogen atoms (chlorine atoms, bromine atoms, especially chlorine atoms) etc.] directly bonded groups (eg alkoxysilyl groups, halosilyl groups) Etc.

  The crosslinkable monomer (monomer having a crosslinkable group) corresponding to such a crosslinkable group can be appropriately selected according to the type of the crosslinkable group, for example, the crosslinkability corresponding to the hydrolytic condensable group. Examples of the monomer include a hydrolytic condensable compound (such as a silane coupling agent, a titanium coupling agent, a zirconium coupling agent, and an aluminum coupling agent).

Examples of the hydrolytic condensable compound include a silane compound (silane coupling agent) having a polymerizable group [vinyl group, allyl group, (meth) acryloyl group, etc.], for example, a vinyl group-containing silane compound [vinyl trimethoxy. Vinyl tri-C _1-4 alkoxy silanes such as silane and vinyl triethoxy silane; Vinyl di C _1-4 alkoxy mono C _1-4 alkyl silanes such as vinyl dimethoxymethyl silane and vinyl diethoxymethyl silane; Vinyl methoxy dimethyl silane and vinyl ethoxy dimethyl vinyl C _1-4 alkoxydi C _1-4 alkyl silanes such as silane; such as vinyl chloroacetate dimethoxysilane; divinyl dimethoxysilane, divinyl diethoxy silane, Jibiniruji (2-methoxyethoxy) Jibiniruji C _1-4 alkoxysilane such as a silane Vinyl monochrome Di C _1-4 alkoxy silanes; vinyl C _1-4 alkyl dichlorosilane such as vinyl methyl dichlorosilane; vinyl di C _1-4 alkyl chlorosilane such as vinyl dimethylchlorosilane; vinyl dichloro C _1-4 alkyl silane such as vinyl dichloromethylsilane ; vinyl trichlorosilane, allyl group-containing silane compound [Arirutori C _1-4 alkoxysilane such as allyltrimethoxysilane; allyl methoxydimethylsilyl; Ariruji C _1-4 Arukokishimono C _1-4 alkyl silane such as allyl dimethoxymethylsilane allylbis (dimethylamino) methylsilane; allyl C _1-4 alkoxydi C _1-4 alkyl silanes such as silane allyl methyl dichlorosilane, etc.], such as (meth) acryloyl group-containing silane compound [(meth) acryloxy trimethoxy silane ( Data) Akurirokishitori C _1-4 alkoxysilane; (meth) such as acryloxy dimethoxymethylsilane (meth) Akurirokishiji C _1-4 Arukokishimono C _1-4 alkyl silane; (meth) such as acryloxy-methoxy dimethylsilane (meth) acryloxy C _1-4 alkoxydi C _1-4 alkyl silanes; 2- (meth) acryloxyethyl trimethoxysilane, etc.] silane coupling link such as, the corresponding titanium compound in these silane coupling agents (titanium (Coupling agent), zirconium compound (zirconium coupling agent), aluminum compound and the like. These crosslinkable monomers (hydrolytic condensable compounds) can be used alone or in combination of two or more. As the crosslinkable monomer, a silane coupling agent is usually used in many cases because it is excellent in hydrolysis condensation property.

  In the polyolefin resin having a crosslinkable group, the graft copolymer can be usually produced by graft polymerization of the polyolefin resin and the crosslinkable monomer using a radical generator. Such radical generators are not particularly limited. For example, organic peroxides, diacyl peroxides (lauroyl peroxide, benzoyl peroxide, 4-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, etc.) Dialkyl peroxides (di-t-butyl peroxide, 2,5-di (t-butylperoxy) -2,5-dimethylhexane, 1,1-bis (t-butylperoxy) -3, 3,5-trimethylcyclohexane, 2,5-di (t-butylperoxy) -2,5-dimethylhexene-3, 1,3-bis (t-butylperoxyisopropyl) benzene, dicumyl peroxide, etc. ), Alkyl peroxides (t-butyl hydroperoxide, cumene hydroperoxide, 2,5-dimethylhexa -2,5-dihydroperoxide, diisopropylbenzene hydroperoxide, etc.), alkylidene peroxides (ethyl methyl ketone peroxide, cyclohexanone peroxide, 1,1-bis (t-butylperoxy) -3, 3, 5 -Trimethylcyclohexane) and peresters (t-butyl peracetate, t-butyl perpivalate, etc.). These radical generators may be used alone or in combination of two or more.

  The ratio of the crosslinkable group (particularly the hydrolytic condensable group) contained in the polyolefin-based resin (A) having a crosslinkable group is calculated in terms of a crosslinkable monomer (monomer having a hydrolytic condensable group). For example, it may be about 0.1 to 25% by weight, preferably about 1 to 20% by weight (for example, about 1 to 15% by weight), and more preferably about 2 to 10% by weight.

  A preferred polyolefin resin (A) is a polyethylene resin (non-crosslinkable or crosslinkable polyethylene resin) which may have a crosslinkable group (particularly a hydrolytic condensable group). Low-density polyethylene resin (for example, low-density polyethylene resin, graft polymer of silane coupling agent and low-density polyethylene resin), metallocene polyethylene resin that may have a crosslinkable group (Particularly, a linear low density polyethylene resin polymerized using a metallocene catalyst) is preferred.

The density of the low-density polyethylene resin (LDPE) that may have a crosslinkable group can usually be selected from a range of 0.95 g / cm ³ or less, for example, 0.945 g / cm ³ or less (for example, 0.8. 9 to 0.940 g / cm ³ ), preferably 0.905 to 0.93 g / cm ³ , and more preferably about 0.91 to 0.925 g / cm ³ .

  The linear low density polyethylene resin (L-LDPE) may be a linear low density polyethylene resin obtained by a gas phase method, a linear low density polyethylene resin obtained by a solution method, or the like. In particular, a linear low density polyethylene resin (metallocene polyethylene resin) polymerized using a metallocene catalyst is preferred.

The density of the linear low density polyethylene resin (particularly metallocene polyethylene resin) is, for example, 0.90 to 0.970 g / cm ³ , preferably 0.91 to 0.96 g / cm ³ , and more preferably 0.915. It may be about ˜0.95 g / cm ³ . Further, the molecular weight distribution of the metallocene polyolefin resin (particularly metallocene polyethylene resin) is, for example, 1.01 to 3.0, preferably 1.02 to 2.0 (for example, 1.05 to 1.8), Preferably about 1.1-1.5 (for example, 1.15-1.4) may be sufficient.

  The melting point of the polyolefin-based resin (A) can be selected from, for example, 140 ° C. or lower, 130 ° C. or lower (for example, about 80 to 125 ° C.), preferably 120 ° C. or lower (for example, about 90 to 122 ° C.), and more preferably May be 115 ° C. or lower (for example, about 95 to 110 ° C.).

  The melt flow index value MIa of the polyolefin resin (A) is, for example, 0.1 to 10 g / 10 minutes (for example, 0.15 to 9 g / 10 minutes), preferably 0.2 to 8 g / 10 minutes ( For example, it may be about 0.2 to 7 g / 10 min), more preferably about 0.25 to 6 g (for example, 0.3 to 5 g / 10 min). The melt flow index value can be measured by a conventional method. MIa hardly changes before and after the crosslinking of the crosslinkable polyolefin resin.

[Polyethylene resin (B)]
The polyethylene resin (B) is composed of ethylene (b ₁ ) and at least one copolymerizable monomer (b ₂ ) selected from a carboxylic acid vinyl ester monomer and a (meth) acrylic monomer. It is comprised with the copolymer or its metal salt. In the present invention, since the specific polyethylene-based resin and the polyolefin-based resin are combined, mechanical properties such as wear resistance can be greatly improved or improved, and used as a microorganism support for a long period of time. Possible foams, in particular open-cell foams, can be obtained. In addition, since it uses a resin (for example, ethylene-carboxylic acid vinyl ester, ethylene-methacrylic acid ester copolymer, etc.) that is relatively superior in hydrophilicity and affinity to microorganisms compared to polyethylene, it is resistant to abrasion. It is possible to impart a good balance between mechanical properties such as property and microbial support (or microbial retention).

Examples of the carboxylic acid vinyl ester monomer include C _1-4 carboxylic acid vinyl esters (for example, C _2-3 carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate), preferably vinyl acetate. Carboxylic acid vinyl esters may be used alone or in combination of two or more.

Examples of (meth) acrylic monomers include (meth) acrylic acid, (meth) acrylic acid esters [for example, (meth) acrylic acid methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, etc. ) Acrylic acid C _1-6 alkyl ester, preferably (meth) acrylic acid C _1-4 alkyl ester, more preferably (meth) acrylic acid C _1-2 alkyl ester; ) Hydroxy C _1-4 alkyl acrylate, etc.]. The (meth) acrylic monomers may be used alone or in combination of two or more.

  Although it does not specifically limit as a metal which comprises the said metal salt, For example, an alkali metal (sodium, potassium, etc.), alkaline-earth metal (magnesium, etc.), zinc, etc. are mentioned.

  The polyethylene resin (B) may be a random copolymer, a block copolymer or a graft copolymer, and may usually be a random copolymer.

  Preferred polyethylene resins (B) are, for example, ethylene-vinyl acetate copolymers, copolymers of ethylene and (meth) acrylic acid or metal salts thereof (for example, ionomers), ethylene and (meth) acrylic acid alkyl esters. (For example, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, etc.). These polyethylene resins (B) may be used alone or in combination of two or more.

The ratio (weight ratio) of ethylene (b ₁ ) and copolymerizable monomer (b ₂ ) can be appropriately selected according to the use of the foam. For example, the former / the latter = 98/2 to 50/50, Preferably, it may be about 95/5 to 60/40, more preferably about 90/10 to 65/35 (for example, 90/10 to 70/30).

  The melt flow index value MIb of the polyethylene resin (B) is, for example, 1 to 50 g / 10 minutes (for example, 1.5 to 45 g / 10 minutes), preferably 2 to 40 g / 10 minutes (for example, 2.5 to 35 g / min), more preferably about 3 to 30 g / 10 min (for example, 5 to 25 g / min).

  The ratio (weight ratio) between the polyolefin resin (A) and the polyethylene resin (B) is, for example, the former / the latter = 10/90 to 90/10, preferably 20/80 to 80/20 (for example, 35/65 to 75/25), more preferably about 30/70 to 70/30 (for example, 40/60 to 70/30).

  In the present invention, by setting the melt flow index ratio of the polyethylene resin (B) to the polyolefin resin (A) to a predetermined value, it is possible to efficiently form a foam (particularly, a foam having an open cell structure). The melt flow index ratio (or the ratio of the melt index) between the melt flow index value MIa of the polyolefin resin (A) and the melt flow index value MIb of the polyethylene resin (B), that is, MIb / MIa is 3 or more ( For example, about 3 to 60), for example, 3.5 or more (for example, about 3.5 to 50), preferably 4 or more (for example, about 4 to 40), more preferably 4.5 or more ( For example, it may be about 4.5 to 30), and usually about 4.5 to 40. The melt flow index ratio can be calculated based on melt flow indexes MIa and MIb measured under the same measurement conditions (temperature and load).

The resin composition may contain a biodegradable component. Such biodegradable components are environmentally advantageous because they improve the biodegradability of the foam after disposal. Examples of the biodegradable component include aliphatic polyester resins [for example, polycondensates of aliphatic diols (for example, C _2-6 alkane diols) and aliphatic dicarboxylic acids (for example, C _2-10 dicarboxylic acids) (for example, , Polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, etc., polyhydroxy acids (eg, polylactic acid, polyhydroxyacetic acid, polyhydroxybutyrate (polyhydroxybutyric acid), β-hydroxybutyric acid and β-hydroxy Poly (hydroxy C _2-10 carboxylic acid) such as polyester copolymerized with valeric acid), polylactone (such as polycaprolactone)], cellulose or cellulose derivatives (eg, alkyl cellulose such as ethyl cellulose, alkyl such as ethyl hydroxyethyl cellulose) -Hydroxy Alkylcellulose, hydroxyethylcellulose, hydroxypropylcellulose such as hydroxypropylcellulose, cellulose ethers such as carboxyalkylcellulose such as carboxymethylcellulose; cellulose ester resins such as cellulose acetate), vinyl alcohol resins (eg, polyvinyl alcohol) Natural polymers (starch, amylose, amylopectin, dextrin, etc.) and the like. The biodegradable components may be used alone or in combination of two or more. Of these, natural polymers, particularly starch, are preferred.

  The biodegradable component may be added to the resin composition as it is, or may be added to the resin composition in combination with a general-purpose resin (for example, a polyolefin resin such as a polyethylene resin). For example, a mixture of the biodegradable component (such as starch) and a general-purpose resin may be added to the resin composition, or a general-purpose resin modified with a biodegradable component (such as starch) may be added to the resin composition. May be. In the former embodiment, a mixture in which a biodegradable component and a part of the resin are mixed in advance may be added.

  The ratio (addition amount) of the biodegradable component is, for example, 1 to 150 parts by weight, preferably 3 to 80 parts by weight (for example, 4 to 4 parts) with respect to 100 parts by weight of the total amount of the resin (A) and the resin (B). 60 parts by weight), more preferably about 5 to 30 parts by weight (for example, 6 to 20 parts by weight).

  The resin composition may contain a foaming agent. As the foaming agent, various foaming agents such as an evaporating foaming agent and a decomposable foaming agent can be used.

  Examples of evaporating foaming agents include gas [carbon dioxide, hydrocarbons (propane, butane, isobutane, pentane, etc.), halogenated hydrocarbons (trichlorofluoromethane, etc.), methyl ether, nitrogen, etc.], volatilization Liquid (acetone, hexane, toluene, etc.). The evaporative blowing agent may be used alone or in combination of two or more.

  Examples of the decomposable foaming agent include organic acids (such as citric acid), azo compounds (such as 2,2′-azobisisobutyronitrile, azohexahydrobenzonitrile, azodicarboxylic amide, diazoaminobenzene), and sulfonyl. Hydrazide compounds [benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, 4,4′-oxybis (benzenesulfonylhydrazide), etc.], nitroso compounds (N, N′-dinitropentamethylenetetramine, N, N′-dinitroso-N, N And organic compounds such as azide compounds (terephthalazide, p-tert-butylbenzazide, etc.) and inorganic compounds (sodium bicarbonate, ammonium carbonate, etc.). You may use the said decomposition-type foaming agent individually or in combination of 2 or more types.

  The addition amount (ratio) of the foaming agent is 0.1 to 30 parts by weight (for example, 0.5 to 25 parts by weight) with respect to 100 parts by weight of the total amount of the polyolefin resin (A) and the polyethylene resin (B). For example, 1 to 30 parts by weight (for example, 3 to 20 parts by weight), preferably 3 to 25 parts by weight (for example, 5 to 20 parts by weight), and more preferably about 10 to 20 parts by weight. There may be.

  The foaming agent can be contained in the resin composition by a conventional method depending on the type, and for example, mixed (and kneaded) with resin components (for example, polyolefin resin (A) and polyethylene resin (B)). The resin component may be impregnated, or may be added or pressed into the melt-kneaded resin.

  In order to obtain a uniform foam structure (open cell structure), the resin composition may further contain a foaming aid (or foam nucleating agent) as necessary in addition to the foaming agent. Examples of foaming aids include silicon compounds (talc, silica, zeolite, etc.), inorganic acid metal salts (calcium carbonate, magnesium carbonate, barium sulfate, potassium titanate, etc.), metal hydroxides (such as aluminum hydroxide), Examples thereof include metal oxides (such as zinc oxide, titanium oxide, and alumina). These foaming aids (or foaming nucleating agents) may be used alone or in combination of two or more.

  The addition amount (ratio) of the foaming auxiliary agent (or foaming nucleating agent) is not particularly limited, and is, for example, 0.1 to 100 parts by weight based on the total amount of the polyolefin resin (A) and the polyethylene resin (B). It may be about 5 parts by weight, preferably about 0.2 to 4 parts by weight, and more preferably about 0.5 to 3 parts by weight.

  The amount of the foaming aid added is, for example, about 1 to 1500 parts by weight, preferably about 5 to 300 parts by weight, and more preferably about 10 to 100 parts by weight with respect to 100 parts by weight of the foaming agent. May be.

  Furthermore, the resin composition may contain a surfactant as necessary. Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants. Of these surfactants, nonionic surfactants are particularly preferable. In addition, the foam which has moderate water absorption is obtained by adding surfactant.

Examples of the nonionic surfactant include ether type, ester ether type, ester type, and nitrogen-containing type surfactants. In particular, ester type nonionic surfactants are preferably used. Examples of the ester type nonionic surfactant include polyhydric alcohol fatty acid esters [for example, polyhydric alcohols such as (poly) glycerin, trimethylolpropane, propylene glycol, pentaerythritol, sorbitan, sorbitol, glycerin, sucrose, and higher fatty acids. esters of, for example, sorbitan, such as glycerine C _8-24 fatty acid ester, sucrose C _8-24 fatty acid esters, sorbitan monooleate, such as sucrose monostearate, such as glycerol monostearate C _{8- And 24} fatty acid esters. Among these nonionic surfactants, glycerin C _8-24 fatty acid esters (for example, glyceryl monostearate, glyceryl distearate, glyceryl monobenzoate), sorbitan C _8-24 fatty acid esters (for example, sorbitan monooleate, sorbitan) Geolate, sorbitan trioleate, etc.) are preferred. These surfactants may be used alone or in combination of two or more.

  The addition amount (ratio) of the surfactant is not particularly limited, but is 0.3 to 50 parts by weight (for example, for example) with respect to 100 parts by weight of the total amount of the polyolefin resin (A) and the polyethylene resin (B). 1 to 50 parts by weight), preferably 0.5 to 30 parts by weight (for example, 1 to 15 parts by weight), more preferably about 1 to 10 parts by weight.

  The resin composition includes various additives such as stabilizers [antioxidants (hindered phenol-based antioxidants), ultraviolet absorbers, heat stabilizers, weather stabilizers, described in Japanese Patent No. 3380816]. Stabilizers (fatty acid amides, etc.)], lubricants, mold release agents, lubricants, colorants such as dyes and pigments, impact modifiers, plasticizers, shrinkage inhibitors, antistatic agents, flame retardants, silanol condensation catalysts described below Etc. may be contained. The additives may be used alone or in combination of two or more.

  The resin composition usually mixes (or kneads) a polyolefin-based resin (A), a polyethylene-based resin (B), and other components (for example, a foaming agent, a surfactant, etc.) as necessary. Can be obtained. In addition, when utilizing the below-mentioned extrusion foaming method etc., polyolefin-type resin (A) and polyethylene-type resin (B) (with other components, such as surfactant, as needed) in an extruder. It is also possible to obtain a foam by mixing (and kneading), further forming a resin composition (or a resin mixture) by press-fitting a foaming agent (evaporating foaming agent such as isobutane) in an extruder, and then extruding it. it can.

[Foam]
The foam of the present invention can be formed by foaming the resin composition (for example, a resin composition containing a polyolefin resin (A), the polyethylene resin (B), and a foaming agent). The foaming method is not particularly limited, and examples thereof include a method of using a reaction product gas, a method of using a foaming agent, and a method of removing soluble substances. Among the above methods, a method using a foaming agent is preferable from the viewpoints of moldability and versatility.

  Examples of the foam molding method include various methods such as extrusion molding (or extrusion foam molding) and injection molding. Among the molding methods, an extrusion molding method is preferable from the viewpoint of moldability. For example, when a volatile foaming agent is used, a composition containing the polyolefin resin (A) and the polyethylene resin (B) is melt-kneaded with an extruder and the volatile foaming agent is injected from the middle of the extruder. Further, it may be melt-kneaded and extruded into a low pressure region (usually under atmospheric pressure) for foaming.

  The extruder (extruder) is not particularly limited as long as it can form a foam, and may be a single-screw extruder, a twin-screw extruder, a multi-screw extruder, or the like, but a single-screw extruder is usually used. . The single-screw extruder may be a single-stage extruder, but may be a multi-stage extruder (tandem extruder) in order to improve kneadability.

  The foaming conditions can be selected according to the foam molding method and the like. For example, in the extrusion method, the melt kneading temperature may be, for example, about 120 to 300 ° C, preferably about 130 to 280 ° C, and more preferably about 140 to 260 ° C. The molding pressure may be, for example, about 1 to 50 MPa, preferably 2 to 40 MPa, more preferably about 2.5 to 20 MPa (for example, 5 to 10 MPa).

  The cell structure of the foam may be an open cell structure, a closed cell structure, a structure in which these are mixed, or the like. In the present invention, the polyolefin-based resin (A) and the specific polyethylene-based resin (B) are compatible with each other, and a foam having a uniform and stable open-cell structure having moderate flexibility and resilience is efficiently obtained. be able to. Therefore, the said foam can be utilized suitably as a foam which has an open cell structure at least, especially an open cell foam. The shape (or cross-sectional shape) of the open cell is not particularly limited and may be an indefinite shape, but is usually a circular shape (for example, a circular shape or an elliptical shape) or a polygonal shape (for example, a triangular shape or a rectangular shape). , Pentagonal shape, hexagonal shape, etc.), and two or more of these shapes may be mixed.

  When a crosslinkable polyolefin resin is used as the polyolefin resin (A), the foam may be uncrosslinked or crosslinked. The crosslinking is usually performed by using a crosslinkable group of the crosslinkable polyolefin resin (A). The crosslinking method of the crosslinkable polyolefin resin (A) can be selected according to the type of the crosslinkable group. For example, in the case of the polyolefin resin having the heat crosslinkable group or the photocrosslinkable group, an organic peroxide or an electron beam is used. Crosslinking may be performed using a crosslinking reaction by irradiation, and the polyolefin resin having a hydrolytic condensable group can be crosslinked (hydrocrosslinking or condensation) by hydrolysis (hydrolysis condensation). The hydrolyzable condensable group is crosslinked by bringing the foam into contact with water (a component containing water) (for example, immersion in water, spraying with water, leaving in an environment containing water). be able to. Crosslinking (or contact with water) is not particularly limited, but can usually be performed at an appropriate stage after foaming.

  Hydrolytic condensation may be performed in the presence of a catalyst. The catalyst can be selected depending on the kind of the crosslinkable group, and examples thereof include a silanol condensation catalyst. Examples of such silanol condensation catalysts include conventional tin catalysts such as dibutyltin diacetates such as dibutyltin diacetate, dibutyltin dilaurate, and dioctyltin dilaurate, and tin diacylates such as tin diacetate, tin dicaprylate, and tin naphthate. It is done. These silanol condensation catalysts may be used alone or in combination of two or more.

  As a crosslinking method using a catalyst, for example, (1) a method in which a catalyst (for example, a silanol condensation catalyst) is premixed in a resin composition before foaming and water-crosslinking is performed after foaming, and (2) after foaming (in particular, extrusion). (3) after foaming (especially extrusion foaming), after applying a catalyst (for example, a solution of silanol catalyst) to the foam after foaming) by applying (or contacting) a catalyst (for example, a solution of silanol catalyst). A method such as a method of applying water cross-linking by applying a liquid in which a catalyst is dispersed or emulsified in water to the foamed product in the latter case may be mentioned.

  The amount of silanol condensation catalyst added is, for example, 0.05 to 3 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the polyolefin resin (A) (crosslinkable polyolefin resin). Preferably it may be about 0.15 to 1 part by weight.

The density of the foam is, for example, 0.01 to 0.15 g / cm ³ , preferably 0.02 to 0.12 g / cm ³ , more preferably about 0.03 to 0.08 g / cm ^3. Usually, it may be about 0.07 g / cm ³ or less (for example, 0.015 to 0.06 g / cm ³ ).

When the foam is a foam having an open-cell structure (in particular, open-cell foam), the open-cell ratio is, for example, 35 to 99%, preferably 40 to 95%, more preferably about 45 to 90%. It may be 50 to 80% (for example, about 50 to 70%). The water absorption (rate) of the foam (particularly, open-cell foam) is, for example, 0.3 to 0.8 g / cm ³ , preferably 0.35 to 0.75 g / cm ³ , and more preferably 0. It may be about 4 to 0.7 g / cm ³ .

  The shape of the foam (particularly, open-cell foam) is not particularly limited, and can be selected according to the application. For example, a two-dimensional shape such as a sheet shape or a plate shape (board shape), a columnar shape, or a cylindrical shape The shape may be a three-dimensional shape such as a shape, a rod shape, or a prism shape. For applications such as filter media (microorganism carrier, etc.), it may be suitably used in a three-dimensional shape (for example, cylindrical shape, rod shape, etc.).

  In the present invention, by forming a foam using the resin composition, the mechanical properties of the foam (particularly, the abrasion resistance of the foam) can be improved or improved. Therefore, such a foam of the present invention is excellent in mechanical strength such as wear resistance and can be used for various applications. For example, among the foams of the present invention, a foam having an open-cell structure (particularly an open-cell foam) has an open-cell structure and is excellent in wear resistance and water resistance (water resistance life), Since it can be used for a long time even in an environment where it is exposed to running water, it is suitable for use as a filtering material for sewage or wastewater (such as domestic wastewater) (for example, a carrier for a biological filtration septic tank). it can.

  In particular, in the present invention, polyolefin (such as low-density polyethylene which may have a crosslinkable group) and a specific ethylene copolymer are combined with each other, so that it has higher hydrophilicity (and water absorption than polyethylene). In addition, it has an excellent affinity for microorganisms, and can efficiently carry (invade and hold or adhere) a large amount of microorganisms in the bubbles. Therefore, the foam (particularly, open-cell foam) of the present invention has an environment suitable for the expression of the activity of microorganisms, and can be suitably used as a microorganism carrier (biological filtration type filter medium). Such a microorganism carrier has an excellent effect on decomposition of organic matter and removal of suspended solids by physical filtration by being incorporated in a biological filtration type sewage purification apparatus, and moreover, the support of the carrier due to collision between carriers. Miniaturization can be efficiently prevented, long-term use is possible, and durability is high.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

  The resins, foam nucleating agents, and surfactants used in Examples and Comparative Examples are shown below, and the characteristics of the molded foam were measured by the following methods.

[resin]
(Polyolefin resin (A))
LDPE1: Crosslinkable low density polyethylene [low density polyethylene (manufactured by Nippon Polyethylene Co., Ltd., “Novatec LF423”, melt flow index MI value 1.5 g / 10 min) 100 parts by weight vinyl trimethoxysilane 3 parts by weight A resin obtained by graft polymerization. MI value 1.5g / 10min]
LDPE2: Low density polyethylene (manufactured by Sumitomo Chemical Co., Ltd., “Sumikasen F101-1”, MI value 0.3 g / 10 min)
LDPE3: Crosslinkable low density polyethylene [low density polyethylene (Tosoh Co., Ltd., “Petrocene 186”, MI value 3.0 g / 10 min) 100 parts by weight of vinyl trimethoxysilane 3 parts by weight Resin. MI value 3.0 g / 10 min]
LDPE4: Polyethylene polymerized using a metallocene catalyst (metallocene polyethylene) [manufactured by Sumitomo Chemical Co., Ltd., “Excellen GMH GX2005G”, MI value 0.5 g / 10 min]
(Polyethylene resin (B))
EVA1: ethylene-vinyl acetate copolymer (manufactured by Sumitomo Chemical Co., Ltd., “H1011”, vinyl acetate content 15% by weight, MI value 0.6 g / 10 min)
EVA2: ethylene-vinyl acetate copolymer (manufactured by Sumitomo Chemical Co., Ltd., “H4021”, vinyl acetate content 13% by weight, MI value 20 g / 10 min)
EVA3: ethylene-vinyl acetate copolymer (manufactured by Sumitomo Chemical Co., Ltd., “KA-31”, vinyl acetate content 28 wt%, MI value 7 g / 10 min)
The melt flow index values MI of these resins were measured under conditions of a temperature of 190 ° C. and a load of 2.16 kg.

[Surfactant]
Hyd 325: Boehringer Ingelheim Co., Ltd., “Hydrocelol 325”

[Foaming nucleating agent]
Talc: Nihon Talc Co., Ltd., "Microace K-1"
In the table, the amount of “Hyd 325” and talc added is the amount (parts by weight) relative to the total amount of “LDPE” and “EVA” of 100 parts by weight, respectively.

[Abrasion resistance]
The abrasion resistance of the foams obtained in Examples and Comparative Examples was measured by measuring the wear rate (weight after 1 hour wear / weight before wear × 100) according to JIS A1451.

○: Wear rate of less than 6% △: Wear rate of 6% or more and less than 20% ×: Wear rate of 20% or more

[Open cell]
The open cell properties of the foams obtained in Examples and Comparative Examples were evaluated by visual observation based on the following criteria.

A: Most of the bubbles are formed of open cells. O: The cells are formed of open cells, and no closed cells or broken bubbles are mixed.

[Open cell ratio]
The foams obtained in Examples and Comparative Examples were weighed in advance and allowed to stand in water, and then left under a reduced pressure of −400 mmHg for 1 minute to allow water to penetrate into the open cell structure. The pressure was returned to atmospheric pressure from the reduced pressure state, the water adhering to the surface of the foam was removed and the weight was measured.

Open cell ratio (%) = {(w ₂ −w ₁ ) / d ₃ } / (w ₁ / d ₁ −w ₁ / d ₂ ) (1)
(W ₂ is the foam weight after water absorption, w ₁ is the foam weight before water absorption, d ₁ is the apparent density of the foam, d ₂ is the apparent density of the resin composition used in the foam, d ₃ is the density of water at the time of measurement)

[density]
The density (g / cm ³ ) of the foams obtained in Examples and Comparative Examples was measured according to JIS K6767.

[Water absorption]
The water absorption (g / cm ³ ) of the foams obtained in the examples and comparative examples was calculated by the following formula (2).

Water absorption (g / cm ³ ) = (Wi−Wf) / V (2)
(Wi: weight before water absorption or immersion (g), Wf: total amount of foam and water absorbed after immersion of the foam in water at a water temperature of 25 ° C. for 20 hours, V: volume of the foam (cm ³ ))
(Examples 1-8, Comparative Examples 1-3)
The polyolefin resin (A), polyethylene resin (B), foam nucleating agent, and surfactant were melt-kneaded at a temperature of 180 ° C. and a pressure of 3 MPa in a ratio shown in the table using a single screw extruder of φ40 mm, and an extruder. A resin composition in which 13 parts by weight of isobutane was injected into a total amount of 100 parts by weight of the polyolefin resin (A) and the polyethylene resin (B) from a foaming agent inlet provided near the tip of the resin was extruded into the atmosphere from a die. The product was extruded into a cylindrical shape (diameter 10 mm) to obtain a foam. In Examples 1 to 4, Comparative Example 1 and Comparative Example 3, the obtained foams were further heated and allowed to stand for 24 hours under conditions of a temperature of 40 ° C. and a humidity of 60%. ) Was water cross-linked.

  And the abrasion resistance of the foam obtained by the Example and the comparative example and open cell property were evaluated, and the water absorption amount and the open cell rate were measured.

  The results are shown in Table 1.

Claims (12)

A resin composition comprising a polyolefin resin (A) and a polyethylene resin (B), wherein the polyethylene resin (B) comprises ethylene (b ₁ ), a carboxylic acid vinyl ester monomer, and ( A copolymer of at least one copolymerizable monomer (b ₂ ) selected from (meth) acrylic monomers or a metal salt thereof, and a melt flow index MIa of the polyolefin resin (A); The resin composition for foams, wherein the ratio MIb / MIa of the polyethylene resin (B) to the melt flow index MIb is 3 or more.   The resin composition according to claim 1, wherein the polyolefin resin (A) has a hydrolytic condensable group.   The resin composition according to claim 2, wherein the ratio of the hydrolytic condensable group contained in the polyolefin resin (A) is 1 to 20% by weight in terms of a crosslinkable monomer corresponding to the hydrolytic condensable group. .   The polyolefin resin (A) is composed of at least one selected from a low density polyethylene resin which may have a crosslinkable group and a metallocene polyethylene resin which may have a crosslinkable group. 1. The resin composition according to 1. The copolymerizable monomer (b ₂ ) is composed of at least one selected from C _2-3 carboxylic acid vinyl ester, (meth) acrylic acid and (meth) acrylic acid C _1-2 alkyl ester. _2. The resin composition according to claim 1, wherein the ratio (weight ratio) between b ₁ ) and the copolymerizable monomer (b ₂ ) is the former / the latter = 90/10 to 65/35.   The resin composition according to claim 1, wherein the ratio (weight ratio) of the polyolefin resin (A) and the polyethylene resin (B) is the former / the latter = 10/90 to 90/10.   The resin composition according to claim 1, wherein MIa is 0.1 to 10 g / 10 min, and MIb / MIa is 4 or more.   Non-crosslinkable or crosslinkable low density polyethylene resin (A) with MIa of 0.2 to 8 g / 10 min, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer The resin composition according to claim 1, wherein the resin composition is composed of at least one polyethylene-based resin (B) selected from coalescence and ionomer resin, and MIb / MIa is 4.5 to 40.   The method to improve the abrasion resistance of a foam by forming a foam using the resin composition for foams of Claim 1.   A method for producing a foam by melt-kneading the foam resin composition according to claim 1 and extrusion-foaming.   A foam formed of the resin composition according to claim 1, wherein the foam has an open cell structure.   The foam according to claim 11, which is used as a microorganism support.