JP5308013B2 - Olefin resin composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an olefin-based resin composition which is excellent in the mechanical characteristics such as the toughness or the like when being in the form of a foamed body and which is suitable for a foam molding. <P>SOLUTION: The resin composition is comprised of a polyethylene-based resin and the cyclic olefin-based resin having a glass transition temperature of 40-180&deg;C, by using them in a ratio (a weight ratio) of the polyethylene-based resin/the cyclic olefin-based resin of 1/99-70/30. Sometimes, the above cyclic olefin-based resin is a copolymer of a cyclic olefin and a chain olefin, and the cyclic olefin-based resin has a cyclic olefin content of about 60-80% by mole relative to the whole cyclic olefin-based resin. The above cyclic olefin-based resin may be a copolymer of a bicyclic olefin and a chain olefin. The above polyethylene-based resin may be a polyethylene, and the above cyclic olefin-based resin has a glass transition temperature of 60-180&deg;C, and a ratio (a weight ratio) of the above polyethylene-based resin to the above cyclic olefin-based resin, that is, of the polyethylene-based resin/the cyclic olefin-based resin, may be 10/90-20/80. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an olefin-based resin composition useful for forming a foam, a foam formed from the resin composition, and a method for producing the foam.

  Olefin-based resin foams have characteristics such as excellent flexibility and are widely studied in various fields. On the other hand, the olefin resin foam is usually inferior in rigidity. Therefore, attempts have been made to improve rigidity by forming closed cells or foaming at a low expansion ratio. It has also been proposed to use a highly rigid cyclic olefin resin.

For example, in JP-A-6-172572 (Patent Document 1), (A) an ethylene / α-olefin copolymer (such as an ethylene-propylene copolymer) is graft copolymerized with a monomer having a hydrocarbon ring. Modified ethylene / α-olefin copolymer, (B) cyclic olefin random copolymer obtained by random copolymerization of ethylene and cyclic olefin monomer, and (C) ethylene / α-olefin copolymer (ethylene-propylene copolymer) Cyclic olefin resin foams composed of coalesced or the like are disclosed. This document describes that the ethylene content of the cyclic olefin random copolymer (B) is preferably 40 to 90 mol%. In the examples, the foam has closed cells, and the expansion ratio is 10. It is described that it is 4 to 22.3 times. Although the foam of this document has resilience, even if it is foamed at a low foaming ratio, the rigidity is low, and deformation easily occurs with respect to the load. Therefore, the cushioning performance is insufficient as a weight cushioning material.
JP-A-6-172572 (Claim 1, paragraph number [0011] and examples)

  Accordingly, an object of the present invention is to provide a resin composition that is excellent in mechanical properties such as rigidity in the form of a foam and is suitable for foam molding, a foam formed from the resin composition, and a method for producing the foam. It is to provide.

  Another object of the present invention is to provide a foam having mechanical properties such as rigidity and high resilience, and a method for producing the foam.

  Still another object of the present invention is to provide a foam having high rigidity while maintaining high resilience even at a high foaming ratio, and a method for producing the foam having reduced strain with respect to load. There is to do.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventor has improved mechanical properties such as rigidity when a polyethylene resin and a cyclic olefin resin having a specific glass transition temperature are used at a specific ratio. The inventors have found that a useful foam having a high restorability can be obtained, thereby completing the present invention.

  That is, the olefin resin composition of the present invention is composed of a polyethylene resin and a cyclic olefin resin. The glass transition temperature of the cyclic olefin resin is 40 to 180 ° C., and the ratio (weight ratio) between the polyethylene resin and the cyclic olefin resin is polyethylene resin / cyclic olefin resin = 10/90 to 70. / 30. The cyclic olefin resin is a copolymer of a cyclic olefin and a chain olefin, and the cyclic olefin content of the cyclic olefin resin is about 60 to 80 mol% with respect to the entire cyclic olefin resin. It may be. The cyclic olefin resin may be a copolymer of a bicyclic olefin and a chain olefin. Further, the polyethylene resin is polyethylene, the glass transition temperature of the cyclic olefin resin is 60 to 180 ° C., and the ratio (weight ratio) between the polyethylene resin and the cyclic olefin resin is a polyethylene type. Resin / cyclic olefin resin = 10/90 to 20/80 may be used.

  The present invention also includes a foam formed from the resin composition. The foam may have a closed cell ratio of 80% or more. Since the said foam has a high closed cell ratio, it is excellent in mechanical characteristics, maintaining a high resilience. The foaming ratio of the foam may be about 20 to 120 times.

  Moreover, this invention also includes the method of foam-molding the said resin composition and manufacturing the said foam.

  In the present invention, since the resin composition is constituted using a polyethylene resin and a cyclic olefin resin having a specific glass transition temperature at a specific ratio, it is excellent in mechanical properties such as rigidity in the form of a foam, Suitable for foam formation. Moreover, the foam formed of the resin composition has mechanical properties such as rigidity and high resilience. Furthermore, even if the foam has a high foaming ratio, the foam has excellent mechanical properties while maintaining high resilience, and strain with respect to a load is reduced.

  The olefin resin composition of the present invention (hereinafter sometimes referred to as “resin composition”) is composed of a polyethylene resin and a cyclic olefin resin.

(Polyethylene resin)
Examples of the polyethylene resin include ethylene homopolymers and copolymers. Examples of the homopolymer of ethylene include polyethylene [low density polyethylene (LDPE), medium density polyethylene, high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and the like]. The ethylene homopolymers may be used alone or in combination.

The polyethylene resin may be a copolymer of a monomer copolymerizable with ethylene. Examples of the copolymerizable monomer include chain olefins (1-propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1 C _3-20 α-linear olefins such as octadecene and 1-eicosene; 3-methyl-1-butene, 2-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene C _3-20 such as 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, etc. α-branched olefins, etc.); alkadienes (1,4-hexadiene, 1,7-octadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene) Any non-conjugated alkadiene, conjugated alkadiene such as butadiene, isoprene, etc.); ethylenically unsaturated carboxylic acid and its anhydride [(meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, crotonic acid, isocrotonic acid , Mesaconic acid, angelic acid, etc.]; (meth) acrylic acid ester [(meth) acrylic acid alkyl ester, glycidyl (meth) acrylate, etc.]; carboxylic acid vinyl ester (saturated carboxylic acid vinyl ester such as vinyl acetate and vinyl propionate) Etc.). These copolymerizable monomers can be used alone or in combination of two or more. Among the copolymerizable monomers, C _3-10 α-linear olefins such as 1-propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene and the like are preferable.

  The ratio of ethylene units (ethylene content) of the polyethylene resin is 50 mol% or more (for example, 60 to 100 mol%), preferably 70 mol% or more (for example, 80 to 99), based on the entire polyethylene resin. Mol%), more preferably 90 mol% or more (for example, about 95 to 98 mol%). The ethylene content of the polyethylene resin is particularly preferably 95 to 100 mol% (for example, 97 to 100 mol%).

  Among these polyethylene resins, polyethylene (low density polyethylene (LDPE), linear low density polyethylene (LLDPE), etc.), a copolymer with a monomer copolymerizable with ethylene (ethylene- (meth) acrylic acid copolymer) Etc.) are preferred. These polyethylene resins may be used alone or in combination of two or more.

  The ethylene copolymer may be a graft copolymer, but is usually a random copolymer or an alternating copolymer.

  The number average molecular weight of the polyethylene resin may be about 8,000 to 300,000, preferably about 10,000 to 200,000, and more preferably about 15,000 to 100,000.

  The number average molecular weight of the polyethylene resin can be measured by a gel permeation chromatography method (GPC method). The number average molecular weight of the polyethylene-based resin is a value measured using orthodichlorobenzene as a solvent at a measurement temperature of 140 ° C. in the GPC method.

  The melting point or softening point of the polyethylene resin may be about 70 to 200 ° C, preferably about 80 to 170 ° C, more preferably about 90 to 150 ° C (particularly 100 to 130 ° C).

  The melt flow rate of the polyethylene resin under the conditions of a temperature of 190 ° C. and a load of 21.2 N is, for example, 0.2 to 5 g / 10 minutes, preferably 0.25 to 4.5 g / 10 minutes, more preferably It may be about 0.3 to 4 g / 10 minutes.

(Cyclic olefin resin)
The cyclic olefin-based resin may be a resin having at least a polymerizable cyclic olefin having an ethylenic double bond in the ring as a polymerization component. The cyclic olefin may be a monocyclic olefin or a polycyclic olefin.

  Typical cyclic olefins include, for example, monocyclic olefins such as cycloalkene; norbornenes, cyclopentadiene or dicyclopentadiene, 1,4,5,8-obtained by condensation of norbornenes and cyclopentadiene. Dimethano-1,2,3,4,4a, 5,8,8a-octahydronaphthalenes, hexacyclo [6.6.1.1.1.1.0.0] heptadecene-4s, 1-butene and cyclopentadiene And polycyclic olefins such as 6-ethylbicyclo [2.2.1] hept-2-ene synthesized from

In addition, the cyclic olefin includes a substituent {eg, a hydrocarbon group [eg, an alkyl group (eg, a C _1-10 alkyl group such as a methyl group, preferably a C _1-5 alkyl group), a cycloalkyl group (eg, cyclohexyl group]). A C _5-10 cycloalkyl group such as a group), an aryl group (eg, a C _6-10 aryl group such as a phenyl group), an alkenyl group (eg, a C _2-10 alkenyl group such as a propenyl group), a cycloalkenyl group (For example, C _5-10 cycloalkenyl group such as cyclopentenyl group and cyclohexenyl group), alkylidene group (for example, C _2-10 alkylidene group such as ethylidene group, preferably C _2-5 alkylidene group, etc.) An alkoxy group (for example, a C _1-10 alkoxy group such as a methoxy group, preferably a C _1-6 Lucoxy group), acyl group (for example, C _2-5 acyl group such as acetyl group), alkoxycarbonyl group (for example, C _1-10 alkoxy-carbonyl group such as methoxycarbonyl group), hydroxyl group, carboxyl group, amino group Group, substituted amino group, halogen atom, haloalkyl group, nitro group, cyano group, oxo group (═O), heterocyclic group (nitrogen atom-containing heterocyclic group such as pyridyl group), etc.} . The cyclic olefin may have a substituent alone or in combination of two or more.

Specific cyclic olefins include monocyclic olefins [eg, cycloalkenes (eg, cycloC _3-10 alkenes such as cyclobutene, cyclopentene, cycloheptene, cyclooctene, etc.), cycloalkadienes (eg, cyclopentadiene, etc. Cyclocyclo C _3-10 alkadiene etc.]; bicyclic olefins {eg bicycloalkenes [eg norbornenes (eg 2-norbornene, 5-methyl-2-norbornene, 5,5 or 5,6-dimethyl-2] -Norbornene, 5-ethylidene-2-norbornene, 5-cyano-2-norbornene, 5-methoxycarbonyl-2-norbornene, 5-phenyl-2-norbornene, 5-methyl-5-methoxycarbonyl-2-norbornene, 5 , 6-Dimethoxycarbonyl 2-norbornene, 5,6-di (trifluoromethyl) -2-norbornene, 7-oxo-2-norbornene, etc.) _{C 4-20} bicycloalkane such as, bicyclo alkadiene [e.g., norbornadiene (e.g., 2,5-norbornadiene, 5-methyl-2,5-norbornadiene, 5-cyano-2,5-norbornadiene, 5-methoxycarbonyl-2,5-norbornadiene, 5-phenyl-2,5-norbornadiene, 5,6 -Dimethyl-2,5-norbornadiene, 5,6-di (trifluoromethyl) -2,5-norbornadiene, 7-oxo-2-norbornadiene, etc.)], etc.], tricyclic olefin {eg tricycloalkene [For example, dihydrodicyclopentadiene (dihydrodicyclopentadiene Etc.), etc. _{C 6-25} tricycloalkyl alkenes, etc.], tri cycloalkadiene [e.g., a dicyclopentadiene compound (dicyclopentadiene, methyl dicyclopentadiene, etc.), tricyclo [4.4.0.12,5] undec -3,7-diene, C _6-25 tricycloalkadiene such as tricyclo [4.4.0.12,5] undeca-3,8-diene, etc.]}, tetracyclic olefins [eg tetracyclo Alkenes (eg, tetracyclo [4.4.0.12,5.17,10] -3-dodecene, 8-methyltetracyclo [4.4.0.12,5.17,10] -3-dodecene, 8,9-dimethyl-tetracyclo [4.4.0.12,5.17,10] -3- _{C 8-30} tetra cycloalkene such as dodecene, etc.), etc.], pentacyclic olefins Emissions [e.g., penta cycloalkadiene (e.g., _{C 10-35} penta cycloalkadiene such as tricyclopentadiene), etc.], six cyclic olefins [e.g., hexa cycloalkenes (e.g., hexacyclo [6.6.1.13 , 6.02,7.09,14] -4- _{C 12-40} hexa cycloalkene such heptadecene)], and others polycyclic olefins such.

  These cyclic olefins can be used alone or in combination of two or more. Of these cyclic olefins, polycyclic olefins (especially bicyclic olefins such as norbornenes) are preferred.

  The cyclic olefin-based resin may be a cyclic olefin homopolymer or a copolymer (for example, a copolymer of a monocyclic olefin and a polycyclic olefin), and a copolymer of a cyclic olefin and a copolymerizable monomer. It may be a polymer.

  The copolymerizable monomer is not particularly limited as long as it can be copolymerized with a cyclic olefin, and examples include monomers exemplified in the section of the polyethylene resin. These copolymerizable monomers may be used alone or in combination of two or more. Among the copolymerizable monomers, chain olefins (such as linear olefins such as ethylene), ethylenically unsaturated carboxylic acids and acid anhydrides thereof (such as (meth) acrylic acid) are preferable.

  In the cyclic olefin copolymer, the ratio of the cyclic olefin (particularly, bicyclic olefin such as norbornene) unit (cyclic olefin content) is selected from a range of about 40 to 100 mol% with respect to the entire cyclic olefin resin. For example, it may be 50 to 90 mol% (for example, 55 to 87 mol%), preferably 60 to 85 mol% (for example, 65 to 83 mol%), more preferably about 70 to 80 mol%. .

  Preferred cyclic olefin-based resins include copolymers of cyclic olefins and chain (linear or branched) olefins, such as polycyclic olefins (such as bi to hexacyclic olefins) and chain olefins. And a copolymer [a copolymer of a bicyclic olefin and a chain olefin (particularly, a copolymer of norbornenes and ethylene, etc.)] and the like.

  The number average molecular weight of the cyclic olefin resin is, for example, 5,000 to 300,000, preferably 10,000 to 200,000, more preferably 20,000 to 150,000 (particularly 30,000 to 120,000). ) Degree.

  The glass transition temperature of the cyclic olefin resin is 40 to 180 ° C. (eg 45 to 175 ° C.), preferably 60 to 170 ° C. (eg 65 to 165 ° C.), more preferably 70 to 160 ° C. (eg 80 ˜155 ° C.), in particular, about 90 to 150 ° C. (for example, 100 to 145 ° C.), and usually about 60 to 180 ° C. When the glass transition temperature of the cyclic olefin resin is too low, mechanical properties such as rigidity are lowered, and when the glass transition temperature is too high, elasticity is lowered.

  The cyclic olefin-based resin may be a resin obtained by addition polymerization or a resin obtained by ring-opening polymerization (ring-opening metathesis polymerization or the like). In addition, the cyclic olefin-based resin (for example, a resin obtained by ring-opening metathesis polymerization) may be a hydrogenated hydrogenated resin. In addition, the cyclic olefin resin may be a crystalline or amorphous resin, and may usually be an amorphous resin. The cyclic olefin resin may be prepared by a conventional polymerization method (for example, addition polymerization using a Ziegler type catalyst, addition polymerization using a metallocene catalyst, ring-opening metathesis polymerization using a metathesis polymerization catalyst, etc.). Good.

  The ratio (weight ratio) between the polyethylene resin and the cyclic olefin resin is polyethylene resin / cyclic olefin resin = 10/90 to 70/30 (for example, 12/88 to 60/40), preferably 15 / 85 to 50/50, more preferably about 18/82 to 40/60 (for example, 19/81 to 30/70), and usually 10/90 to 60/40 (for example, 10/90 to 20/80). ) If the ratio of the polyethylene-based resin and the cyclic olefin-based resin is smaller than the above ratio, the elasticity is lowered, and if it is larger than the above ratio, the mechanical characteristics are lowered.

  The resin composition includes a compatibilizing agent (for example, a polyethylene resin in which a cyclic olefin monomer or a cyclic olefin polymer is graft-polymerized) in order to enhance the compatibility between the polyethylene resin and the cyclic olefin resin. Even if it does not contain, it has high compatibility.

  In addition, the resin composition may contain a thermoplastic elastomer (for example, an olefin-based thermoplastic elastomer, a styrene-based thermoplastic elastomer, etc.) in order to improve flexibility, buffering property, etc., but does not contain it. Even with high buffering properties.

  Furthermore, the resin composition may contain an additive. Examples of the additives include stabilizers [antioxidants (hindered phenol-based antioxidants, etc.), antistatic agents, ultraviolet absorbers, heat stabilizers, weathering stabilizers, etc.], organic or inorganic fillers (powder or (Including fibrous reinforcing agents), lubricants, mold release agents, lubricants, impact modifiers, colorants (such as dyes and pigments), plasticizers, surface smoothing agents, antishrink agents, flame retardants, antibacterial agents, preservatives Examples include antifungal agents, insect repellents and deodorants.

  These additives may be used alone or in combination of two or more. The ratio of each additive is 0.1 to 30 parts by weight, preferably 0.15 to 20 parts by weight (for example, 0 to 100 parts by weight of the total amount of the polyethylene resin and the cyclic olefin resin). .2 to 15 parts by weight), more preferably about 0.5 to 10 parts by weight.

(Foam)
The resin composition is useful for forming a foam because it has high mechanical properties such as rigidity and resilience in the form of a foam.

  The foam structure of the foam may be an open-cell structure or a closed-cell structure. In the present invention, since a polyethylene resin and a cyclic olefin resin having a specific glass transition temperature are used at a specific ratio, a closed cell structure can be suitably formed.

  The foam has a closed cell ratio of 80% or more (for example, 80 to 100%), preferably 83% or more (for example, 84 to 99%), more preferably 85% or more (for example, about 86 to 98%). It may be. Since the foam has a high closed cell ratio, it has both mechanical properties and high resilience.

  In addition, the average diameter in particular of a foam cell is not restrict | limited, For example, it can select from the range of about 0.5-2.1 mm.

  The foaming ratio of the foam can be selected from, for example, about 2 to 120 times, for example, 20 to 120 times, preferably 25 to 115 times, more preferably 30 to 110 times (for example, 40 to 100 times, In particular, it may be about 50 to 80 times. Olefin-based resin foams usually have low rigidity when they have high resilience, and conversely they have high rigidity and do not have resilience. However, the foam of the present invention has high rigidity while maintaining high resilience even at a high expansion ratio, and has reduced strain with respect to load.

  The shape of the foam is not particularly limited, for example, a one-dimensional shape such as a rod shape or a string shape, a sheet shape, a film shape, a two-dimensional shape such as a two-dimensional mesh (net) shape, a block shape, a plate shape, It may be a three-dimensional shape such as a columnar shape or a pipe shape. Of these shapes, the shape is often a three-dimensional shape such as a block shape or a column shape. When the foam is columnar, the cross-sectional shape in the thickness direction (radial direction) of the columnar foam is circular, elliptical, polygonal (triangular, quadrangular, pentagonal, etc.), radial (clover, petal) (Flower shape) etc.).

(Method for producing foam)
The foam of the present invention can be produced by foam-molding the resin composition. In an appropriate process for producing a foam, a foaming agent (or foaming aid), a foam nucleating agent, or the like may be used as necessary.

  Examples of the foaming agent include volatile foaming agents used for physical foaming and degradable foaming agents used for chemical foaming. Examples of volatile blowing agents include inert or non-flammable gases (nitrogen, carbon dioxide, chlorofluorocarbon, alternative chlorofluorocarbon, etc.), water, organic physical blowing agents [for example, aliphatic hydrocarbons (propane, n-butane, isobutane). , Pentane (n-pentane, isopentane etc.), hexane (n-hexane etc.), aromatic hydrocarbon (toluene etc.), halogenated hydrocarbon (trichlorofluoromethane etc.), ethers (dimethyl ether, petroleum ether) Etc.) and ketones (acetone etc.). Examples of the decomposable foaming agent include inorganic carbonates such as sodium bicarbonate and ammonium carbonate or salts thereof; organic acids such as citric acid or salts thereof (sodium citrate, etc.); 2,2′-azobisiso Azo compounds such as butyronitrile and azodicarboxylic amide; sulfonyl hydrazide compounds such as benzenesulfonyl hydrazide; nitroso compounds such as N, N′-dinitrosopentamethylenetetramine (DNPT); and azide compounds such as terephthalazide . Of these blowing agents, aliphatic hydrocarbons such as butane and pentane, organic acids such as citric acid, or salts thereof (such as sodium citrate) are often used. These foaming agents may be used alone or in combination of two or more.

  The ratio of the blowing agent is 0.1 to 40 parts by weight, preferably 0.3 to 35 parts by weight, and more preferably 0.5 to 100 parts by weight of the total amount of the polyethylene resin and the cyclic olefin resin. About 30 parts by weight may be used.

  Examples of the foam nucleating agent include inorganic carbonates such as sodium bicarbonate and ammonium carbonate exemplified in the section of the foaming agent or salts thereof; organic acids such as citric acid or salts thereof (sodium citrate, etc.), Examples include acid compounds (such as talc, silica, zeolite), metal hydroxides (such as aluminum hydroxide), and metal oxides (such as zinc oxide, titanium oxide, and alumina). These foam nucleating agents may be used alone or in combination of two or more. Among the foam nucleating agents, in particular, when a silicate compound such as talc is used, the cell structure can be made uniform.

  The ratio of the foam nucleating agent is not particularly limited and is, for example, 0.1 to 10 parts by weight, preferably 0.2 to 8 parts by weight with respect to 100 parts by weight of the total amount of the polyethylene resin and the cyclic olefin resin. Part, more preferably about 0.3 to 5 parts by weight.

  Each of the foaming agent and the foaming nucleating agent may be previously contained in the resin composition (including resin pellets), or may be added or press-fitted into the resin composition in the foam molding process. In addition, the above-described additives and the like may be added to the resin composition at an appropriate stage of foam molding if necessary.

  The resin composition may be a mixture of components or may be in the form of pellets.

  Usually, a foam can be obtained by melt-kneading the resin composition and foam molding.

  Melt-kneading can be performed using a conventional melt-kneader, for example, a single-screw or vented twin-screw extruder. Prior to melt-kneading, polyethylene resins and cyclic olefins are used using conventional methods such as mixers (tumblers, V-type blenders, Henschel mixers, Nauta mixers, ribbon mixers, mechanochemical devices, extrusion mixers, etc.). The system resin and other components (compatibility agent, foaming agent, foaming nucleating agent, additive, etc.) may be premixed.

  As the foam molding method, a conventional method such as an extrusion molding method (for example, a T-die method, an inflation method, etc.), an injection molding method, or the like can be used.

  The foaming temperature may be, for example, 70 to 300 ° C, preferably 80 to 280 ° C, and more preferably about 85 to 260 ° C.

  Since the olefin resin composition of the present invention is excellent in mechanical properties such as rigidity in the form of a foam, it is useful for forming a foam. Further, since the foam has not only rigidity but also high resilience, various articles, particularly heavy bodies [eg, electrical appliances (televisions, personal computers, refrigerators, etc.), electrical parts (motors, control equipment parts, etc.) Etc.) and furniture (tables, chairs, bags, etc.)].

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

[Compression strength]
In accordance with JIS K6767, the test pieces obtained in Examples and Comparative Examples were put into a SUS beaker (inner diameter 105 mm × height 125 mm) and filled. Using a compression tester LLOYD LR5K (manufactured by LLOYD INSTRUMENT LTD.), The test piece was compressed at a constant speed of 12 mm / min with a disc having a diameter of 100 mm, and the compression strength of the foams obtained in the examples and comparative examples Was measured.

[Compression creep (distortion)]
In accordance with JIS K6767, the test pieces obtained in Examples and Comparative Examples were put into a SUS beaker (inner diameter 300 mm × height 300 mm) and filled, and a load of 17 g / cm ² was applied with a 290 mm diameter disk. It applied to the test piece and the distortion was computed by the following formula.

Strain (%) = (t ₀ −t ₁ ) / t ₀ × 100
(In the formula, t ₀ represents the thickness (mm) of the test piece before loading, and t ₁ represents the thickness (mm) of the test piece after loading.)
[Apparent density]
The apparent density of the test pieces obtained in Examples and Comparative Examples was measured by an underwater substitution method.

[Restorability]
After compressing for 60 seconds to 50% in the thickness direction (radial direction) of the test pieces obtained in Examples and Comparative Examples, the compression was immediately released, and the restoration property after 120 seconds was calculated by the following formula.

Restorability (%) = d ₁ / d ₀ × 100
(In the formula, d ₀ represents the thickness (mm) before compression, and d ₁ represents the thickness (mm) 120 seconds after releasing the compression.)
[Buffer performance]
The buffer performance of the test pieces obtained in Examples and Comparative Examples was evaluated according to the following criteria. The compression strength is a, and the compression creep is b.

○ ... 100 g / cm ² ≦ a and b <30%
Δ: 90 g / cm ² <a <100 g / cm ² and b <30%
X: a ≦ 90 g / cm ² and 30% ≦ b.

Reference Examples 1 to 17, 7, 21, Example 1 8 to 20, and Comparative Examples 1 to 7
Using a polyethylene-based resin, a cyclic olefin-based resin, and a foaming agent in the proportions shown in Tables 1 to 3, using an extruder (die 6 mmΦ), the resin was extruded into a columnar shape to obtain a foam. The cross-sectional shape in the radial direction of the foam was a flower shape. The obtained foam was cut into a length of 30 mm to prepare a test piece, and the compression strength, compression creep, apparent density, expansion ratio, and resilience were measured, and the buffer performance was evaluated.

  The results are shown in Tables 1 to 3.

The polyethylene resin, cyclic olefin resin, and foaming agent used in Examples and Comparative Examples are shown below.
(Polyethylene resin)
Low density polyethylene (LDPE): F101-1, manufactured by Sumitomo Chemical Co., Ltd.
(Cyclic olefin resin)
Cyclic olefin resin A: manufactured by Polyplastics Co., Ltd., TOPAS 8007
Cyclic olefin resin B: manufactured by Polyplastics Co., Ltd., TOPAS 9506
Cyclic olefin resin C: manufactured by Polyplastics Co., Ltd., TOPAS 6013
(Foaming agent)
Butane / pentane (weight ratio) = 50/50 mixed foaming agent

  As is clear from Tables 1 to 3, in Examples, polyethylene resin and cyclic olefin resin having a specific glass transition temperature are used in a specific ratio, so that high resilience is maintained. However, a foam having excellent mechanical properties such as rigidity and reduced strain with respect to the load was obtained.

Claims (5)

A foam obtained by melt-kneading a resin composition composed of a polyethylene-based resin and a cyclic olefin-based resin and extrusion-foaming,
The expansion ratio is 20 to 120 times,
The polyethylene resin is a polyethylene resin having an ethylene content of 90 mol% or more,
The cyclic olefin-based resin is a copolymer of norbornenes and ethylene ,
The glass transition temperature of the cyclic olefin resin is 60 to 180 ° C. , and the ratio (weight ratio) between the polyethylene resin and the cyclic olefin resin is polyethylene resin / cyclic olefin resin = 18/82 to 40/60. Foam. A polyethylene resin polyethylene, the proportion of the previous SL polyethylene resin and the cyclic olefin resin (weight ratio), according to claim 1, wherein the polyethylene resin / cyclic olefin resin = 19 / 81-30 / 70 Foam.   The foam according to claim 1 or 2, wherein the closed cell ratio is 80% or more.   The foam according to any one of claims 1 to 3, wherein the expansion ratio is 50 to 80 times.   The method of manufacturing the foam in any one of Claims 1-4 by melt-kneading the resin composition comprised by polyethylene-type resin and cyclic olefin-type resin, and carrying out extrusion foam molding.