Crosslinkable resin foam-forming resin composition and crosslinked resin foam

Abstract

To provide a resin composition that is capable of forming a crosslinked resin foam having good compression characteristics and that is capable of reversible crosslinking (de-crosslinking of the formed crosslinked resin foam).SOLUTION: A resin composition comprises an ethylene-(meth)acrylic acid ester copolymer, a foaming agent, and a crosslinking agent, wherein, when the content proportion of (meth)acrylic acid ester unit in the ethylene-(meth)acrylic acid ester copolymer is represented by A (mol%), the crosslinking degree C (%) of a crosslinked resin foam obtained by crosslinking and foaming the resin composition is within a range represented by the following formulae: 25≤C≤2.3A+77 (where 1.5≤A≤8.0) and 25≤C≤95 (where 8.0<A).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a crosslinked resin foam-forming resin composition capable of performing reversible crosslinking, and a crosslinked resin foam having good compression properties, capable of undergoing de-crosslinking and having excellent recyclability.

Background Art

[0002] Crosslinked resin foams made of ethylene copolymers are required to have good compression properties, particularly low compression set. As such a crosslinked resin foam, a foam obtained by crosslinking a resin composition containing an ethylene-α-olefin copolymer, a foaming agent, and a crosslinking agent that satisfies specific requirements has been proposed (see Patent Document 1 below).

[0003] Recently, it has been demanded to effectively utilize (recycle) waste materials of resin crosslinked bodies such as crosslinked resin foams as recycled resources. However, conventionally known crosslinked polyethylene cannot be melted by heat or a solvent, and its recycling method is limited. Therefore, methods of forcibly cutting carbon chains by supercritical water (see Patent Documents 2 and 3 below) or shear by a twin-screw extruder (see Patent Documents 4 and 5 below) have been studied. However, these methods inevitably require new introduction of equipment and deterioration of quality, and have hardly reached industrialization.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] The present invention has been made based on the above circumstances. An object of the present invention is to provide a resin composition capable of forming a crosslinked resin foam having good compression characteristics and capable of performing reversible crosslinking. Another object of the present invention is to provide a crosslinked resin foam having good compression characteristics and excellent recyclability capable of returning at least a part of the crosslinked structure to an uncrosslinked state.

MEANS FOR SOLVING THE PROBLEMS

[0006] The resin composition of the present invention is a resin composition containing an ethylene-(meth)acrylate copolymer, a foaming agent, and a crosslinking agent. When the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is A (mol%), the crosslinking degree C (%) of the crosslinked resin foam obtained by crosslinking and foaming this is in the range represented by the following formula. Here, the crosslinking degree C is the crosslinking degree (gel fraction) measured according to JIS C 3005.

[0007] ·25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ·25 ≦ C ≦ 95 (where 8.0 < A)

[0008] It is preferable that the resin composition of the present invention can obtain a crosslinked resin foam having a crosslinking degree C of 45% or more, particularly 50% or more. Further, it is preferable that the ethylene-(meth)acrylate copolymer is ethylene-ethyl acrylate (EEA). Further, the content ratio A (comonomer amount) of the (meth)acrylic acid ester unit in the ethylene-(meth)acrylic acid ester copolymer is preferably 1.5 to 16 mol%, particularly preferably 2.0 to 13 mol%.

[0009] The crosslinked resin foam of the present invention is a crosslinked foam of an ethylene-(meth)acrylic acid ester copolymer, When the content ratio of the (meth)acrylic acid ester unit in the ethylene-(meth)acrylic acid ester copolymer is A (mol%), the crosslinking degree C (%) is in the range represented by the following formula.

[0010] ·25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ·25 ≦ C ≦ 95 (where 8.0 < A)

[0011] The crosslinked resin foam of the present invention preferably has a crosslinking degree C of 45% or more, particularly preferably 50% or more. Further, the ethylene-(meth)acrylic acid ester copolymer is preferably ethylene-ethyl acrylate (EEA). Further, when heated at 350°C, it is preferable that the crosslinking degree decreases to less than 15%, particularly less than 10%.

Advantages of the Invention

[0012] According to the resin composition of the present invention, a crosslinked resin foam having good compression characteristics (low compression set) can be formed, and reversible crosslinking (crosslinking reaction and de-crosslinking reaction) can be performed. Here, the crosslinking reaction is carried out at a relatively low temperature, and the de-crosslinking reaction is carried out at a relatively high temperature. According to the resin composition of the present invention, crosslinked foaming occurs at a predetermined temperature (relatively low temperature), and thereby, a crosslinked resin foam (the crosslinked resin foam of the present invention) can be suitably produced.

[0013] The crosslinked resin foam of the present invention can return at least a part of the crosslinked structure to an uncrosslinked state by a de-crosslinking reaction. According to the crosslinked resin foam of the present invention, without using special additives or applying high shear force, just by heating to a predetermined temperature (relatively high temperature), the crosslinking reaction of the crosslinked resin foam occurs, and thereby, an uncrosslinked or low-crosslinked resin composition can be suitably recycled. Also, as is clear from the results of the examples described later, the crosslinked resin foam of the present invention has good compression properties (low compression set).

Embodiments for Carrying Out the Invention

[0014] <Crosslinked Resin Foam-Forming Resin Composition> The resin composition of the present invention contains an ethylene-(meth)acrylate copolymer, a foaming agent, and a crosslinking agent.

[0015] The resin composition of the present invention can perform reversible crosslinking (crosslinking reaction and de-crosslinking reaction). The de-crosslinking reaction of the resin composition (crosslinked resin foam) is important for the structure of the polymer side chain, and it is necessary to have an atomic group containing a heteroatom. Therefore, an ethylene homopolymer and an ethylene-α-olefin copolymer in which the copolymer is a hydrocarbon compound (for example, propylene, butene-1, 1-hexene, etc. as α-olefins) are not suitable. Furthermore, even in the case of an ethylene-α-olefin copolymer containing a heteroatom group, when a vinyl alcohol ester such as an ethylene-vinyl acetate copolymer (EVA) is used as a copolymer component, it is well known that a decarboxylation reaction, the formation of a main chain double bond, and subsequently a crosslinking reaction occur upon heating, and the heat resistance at the de-crosslinking temperature is insufficient. For this reason, the de-crosslinking reaction does not proceed sufficiently, and a resin composition that can be melt-molded cannot be produced (recycled). Also, when (meth)acrylic acid is used as a copolymer component such as an ethylene-(meth)acrylic acid copolymer (EAA, EMAA), it is well known that a crosslinking reaction occurs due to an intermolecular dehydration reaction and the formation of an acid anhydride upon heating, and similarly, the heat resistance is insufficient. For this reason, the de-crosslinking reaction does not proceed sufficiently, and a resin composition that can be melt-molded cannot be produced (recycled). On the other hand, in the ethylene-(meth)acrylate copolymer, such side reactions do not occur, and thus the de-crosslinking reaction proceeds efficiently by heating at a predetermined temperature.

[0016] Examples of the ethylene-(meth)acrylate copolymer contained in the resin composition of the present invention include ethylene-methyl acrylate, ethylene-ethyl acrylate, ethylene-propyl acrylate, ethylene-butyl acrylate, ethylene-2-ethylhexyl acrylate, ethylene-methyl methacrylate, ethylene-ethyl methacrylate, ethylene-propyl methacrylate, ethylene-butyl methacrylate, and ethylene-2-ethylhexyl methacrylate.

[0017] Here, since the ethylene-(meth)acrylate copolymer is less likely to undergo a disintegration reaction with radicals, a high degree of crosslinking is easily obtained mainly by peroxide crosslinking, and the crosslinking efficiency can be higher than that using an ethylene-methacrylate copolymer as a resin component. Also, from the viewpoint of obtaining a resin composition having a well-balanced combination of high mechanical strength and good flexibility, the copolymer component of the resin component is preferably an ethyl ester of (meth)acrylic acid. From the above, among the ethylene-(meth)acrylate copolymers exemplified above, ethylene-ethyl acrylate (EEA) is particularly preferred from the viewpoints of high crosslinking efficiency and excellent physical property balance.

[0018] In the ethylene-(meth)acrylate copolymer, the content ratio (comonomer amount) of the (meth)acrylate unit is 1.5 mol% or more, preferably 1.5 to 16 mol%, more preferably 2.0 to 13 mol%. If the content ratio of the (meth)acrylate unit is too small, the de-crosslinking reaction of the crosslinked resin foam obtained by crosslinking and foaming the resin composition does not proceed sufficiently, and thus a melt-moldable resin composition cannot be produced (recycled). On the other hand, if this ratio is too large, the mechanical strength of the crosslinked resin foam obtained by crosslinking and foaming the resin composition may be impaired.

[0019] As the foaming agent contained in the resin composition of the present invention, either a chemical foaming agent or a physical foaming agent can be used. Examples of the chemical foaming agent include azo-based compounds such as azodicarbonamide and barium azodicarboxylate, nitroso-based compounds such as dinitrosomethylenetetramine and trinitrotriethylenetriamine, hydrazide-based compounds such as 4,4'-oxybisbenzenesulfonylhydrazide, and sulfonyl semicarbazide-based compounds such as 4,4'-oxybisbenzenesulfonyl semicarbazide and toluenesulfonyl semicarbazide, etc., organic thermally decomposable foaming agents; and inorganic thermally decomposable foaming agents such as bicarbonates such as sodium bicarbonate and ammonium bicarbonate, and carbonates such as sodium carbonate and ammonium carbonate. Examples of the physical foaming agent include methanol, propane, butane, pentane, dichloroethane, dichloromethane, water, chlorofluorocarbons, air, carbon dioxide, nitrogen, argon, and the like.

[0020] The content of the foaming agent in the resin composition of the present invention is preferably 0.1 to 40 parts by mass, more preferably 0.5 to 20 parts by mass, based on 100 parts by mass of the ethylene-(meth)acrylate copolymer. If the content of the foaming agent is too small, a crosslinked resin foam having the desired foaming ratio cannot be formed. On the other hand, if the content of the foaming agent is excessive, the properties against compression such as the compression set and compression recovery of the crosslinked resin foam obtained by crosslinking and foaming the resin composition may be impaired.

[0021] Examples of the crosslinking agent contained in the resin composition of the present invention include peroxide crosslinking agents and silane crosslinking agents, and it is preferable to use a peroxide crosslinking agent from the viewpoint of obtaining a crosslinked resin foam with a high degree of crosslinking.

[0022] The peroxide crosslinking agent is not particularly limited, and examples thereof include bis(t-butylperoxyisopropyl)benzene, t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, etc. Among these, dicumyl peroxide is preferred.

[0023] Examples of the silane crosslinking agent include compounds having a functional group reactive with an ethylene-(meth)acrylate copolymer and a plurality of alkoxy groups. Specifically, vinylsilane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane; aminosilane compounds such as γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)γ-aminopropyltrimethoxysilane, β-(aminoethyl)γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane; epoxy silane compounds such as β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane; acrylic silane compounds such as γ-methacryloxypropyltrimethoxysilane; polysulfide silane compounds such as bis(3-methacryloxysilyl)propyl)disulfide, bis(3-(triethoxysilyl)propyl)tetrasulfide; mercapto silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, etc. can be exemplified.

[0024] As the content of the crosslinking agent in the resin composition of the present invention, it is adjusted so that the crosslinking degree (C) of the crosslinked resin foam obtained by crosslinking and foaming the resin composition falls within the range represented by the above formula, and it varies depending on the content ratio (A) of the (meth)acrylic acid ester unit in the contained ethylene-(meth)acrylic acid ester copolymer, but it is preferably 0.25 to 4.5 parts by mass, more preferably 0.3 to 4.0 parts by mass, and particularly preferably 0.4 to 2.0 parts by mass with respect to 100 parts by mass of the resin component.

[0025] The resin composition of the present invention can perform reversible crosslinking (crosslinking reaction and de-crosslinking reaction). Here, the crosslinking reaction is carried out at a relatively low temperature, and the de-crosslinking reaction is carried out at a relatively high temperature. According to the resin composition of the present invention, by heating to a predetermined temperature (relatively low temperature), crosslinking foaming occurs, and thereby, the crosslinked resin foam of the present invention can be produced.

[0026] By subjecting the resin composition of the present invention to a crosslinking treatment, a crosslinked resin foam (the crosslinked resin foam of the present invention) having a crosslinking degree C (%) within the range represented by the above formula can be obtained.

[0027] The resin composition of the present invention can contain, as optional components, components used in conventional resin foam products as required. These optional components, excluding the components consumed during crosslinking foaming, become the constituent components of the crosslinked resin foam of the present invention.

[0028] Examples of such optional components include inorganic fillers (e.g., calcium carbonate, clay, diatomaceous earth, metal oxides, silica, carbon black, glass fibers, carbon fibers), plasticizers (phthalic acid esters, trimellitic acid esters, polyesters), softeners (mineral oils, process oils, fatty acids), antioxidants (hindered phenol-based stabilizers, sulfur-based stabilizers, amine-based stabilizers), ultraviolet absorbers (benzophenone-based UVA, benzotriazole-based UVA, salicylic acid ester-based UVA), antistatic agents (glycerin fatty acid esters, alkylsulfonic acids, tetraalkylammonium salts), flame retardants (metal hydroxides, phosphorus compounds, halogen compounds), lubricants (fatty acid amides, zinc stearate, silicones), colorants (azo compounds, anthraquinone compounds, phthalocyanine compounds, titanium oxide, carbon black), crosslinking aids [trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate (TMPTM), triallyl isocyanurate (TAIC), triallyl cyanurate (TAC)], light stabilizers (hindered amine-type compounds, hindered piperidine-type compounds), and the like.

[0029] <Crosslinked resin foam> The crosslinked resin foam of the present invention is a crosslinked foam of an ethylene-(meth)acrylate copolymer and is composed of a crosslinked resin foam having a specific degree of crosslinking within the range represented by the above formula. The degree of crosslinking C (%) of the crosslinked resin foam of the present invention can be adjusted by appropriately adjusting the content of the crosslinking agent to prepare a resin composition (the resin composition of the present invention) according to the content ratio A (mol%) of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer. Further, the degree of crosslinking C (%) of the crosslinked resin foam by electron beam crosslinking described later can be adjusted by appropriately adjusting the irradiation conditions of the electron beam irradiated to the ethylene-(meth)acrylate copolymer according to the content ratio A (mol%).

[0030] The crosslinked resin foam of the present invention is obtained by subjecting the resin composition of the present invention to a crosslinking treatment. The crosslinking method for producing the crosslinked resin foam of the present invention is not particularly limited. For example, (1) A method of chemically crosslinking by heating the resin composition of the present invention containing a peroxide crosslinking agent at a predetermined temperature, (2) A method of performing silane crosslinking by heating the resin composition of the present invention containing a silane crosslinking agent at a predetermined temperature, (3) A method of performing electron beam crosslinking by irradiating an ethylene-(meth)acrylate copolymer with an electron beam can be mentioned.

[0031] In the crosslinking methods (1) and (2) above, the heating temperature for crosslinking the crosslinked resin foam-forming resin composition varies depending on the type of foaming agent used, but is preferably 50 to 220°C, more preferably 80 to 200°C. As the heat treatment method for crosslinking, various methods can be adopted according to the form of the crosslinked resin foam, such as a method of heating in an atmosphere of nitrogen, steam, silicone oil, molten salt, etc., and a method of heating during molding with a hot press or an injection molding machine.

[0032] The lower limit value of the crosslinking degree of the crosslinked resin foam of the present invention is set at 25%, preferably 45%, more preferably 50%. A resin foam with an excessively small crosslinking degree (less than 25%) has a high compression set and cannot exhibit good compression properties (see Comparative Example 1 described later).

[0033] The upper limit value of the crosslinking degree of the crosslinked resin foam of the present invention (hereinafter, also referred to as the "upper crosslinking degree") is defined from the viewpoint of sufficiently advancing the de-crosslinking reaction of the crosslinked resin foam. Here, the de-crosslinking reaction of the crosslinked resin foam proceeds more easily as the content ratio (comonomer amount) of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is higher. The upper crosslinking degree of the crosslinked resin foam of the present invention is 2.3A + 77% when the content ratio A of the (meth)acrylate unit is 1.5 to 8.0 mol%, and 95% when the content ratio A exceeds 8.0 mol%.

[0034] If the degree of crosslinking of the crosslinked foam is excessive (exceeding the upper limit of the degree of crosslinking), the de-crosslinking reaction does not proceed sufficiently, and a resin composition that can be melt-molded (recycled) cannot be produced (see Comparative Example 2 described later).

[0035] By heating the crosslinked resin foam of the present invention at a predetermined temperature, at least a part of the crosslinked structure is de-crosslinked.

[0036] The heating temperature for de-crosslinking the crosslinked resin foam of the present invention is preferably 300 to 400°C, more preferably 320 to 380°C.

[0037] The crosslinked resin foam of the present invention preferably has a degree of crosslinking that decreases to less than 15%, particularly less than 10% when heated at 350°C.

[0038] The resin (ethylene-(meth)acrylate copolymer) with a degree of crosslinking reduced to less than 15% can be subjected to remelting and molding by heating and can be suitably used as a recycled resin.

[0039] The crosslinked resin foam of the present invention can be used in all applications of conventional resin foams. Specifically, it is suitably used for automotive parts (such as vehicle interiors), footwear parts (such as shoe soles, soles), building parts, interior materials for transportation, packaging cushioning materials, heat insulating materials, backup materials, sports protectors (protectors, sports mats, etc.).

Examples

[0040] Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto. In the following examples and comparative examples, the following compounds were used as the copolymer, foaming agent, antioxidant, and crosslinking agent constituting the resin component.

[0041] ·Copolymer (EEA-1) Density = 0.94 g / cm 3An ethylene-ethyl acrylate copolymer having MFR (190°C, 2.16 kg) = 1.6 g / 10 min and EA content = 8.1 mol%.

[0042] Copolymer (EEA-2) Density=0.93g / cm 3 An ethylene-ethyl acrylate copolymer having MFR (190°C, 2.16 kg) = 4.0 g / 10 min and EA content = 2.1 mol%.

[0043] Foaming agent (FA-1) Azodicarbonamide (ADCA) Product name: "Vinihole" (manufactured by Eiwa Chemical Industry Co., Ltd.)

[0044] Antioxidant (AO-1) Hindered phenol type stabilizer, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]

[0045] · Crosslinking agent (PO-1) Peroxide crosslinking agent consisting of dicumyl peroxide

[0046] <Production of crosslinked resin foam> Example 1 According to the formulation shown in Table 1 below, 100 parts by mass of the copolymer (EEA-1), 2.0 parts by mass of the foaming agent (FA-1), 0.15 parts by mass of the antioxidant (AO-1), and 0.8 parts by mass of the crosslinking agent (PO-1) were melt-kneaded to obtain a resin composition (the crosslinked resin foam-forming resin composition of the present invention). The obtained resin composition was supplied to a press mold and pressed at 170° C. for 15 minutes to cause crosslinking and foaming, thereby obtaining a sheet-like crosslinked resin foam (the crosslinked resin foam of the present invention).

[0047] Example 2 According to the formulation shown in Table 1 below, a resin composition (the crosslinked resin foam-forming resin composition of the present invention) was obtained in the same manner as in Example 1, except that copolymer (EEA-2) was used instead of copolymer (EEA-1), and the compounding amount of crosslinking agent (PO-1) was 0.5 parts by mass with respect to 100 parts by mass of copolymer (EEA-2). The obtained resin composition was crosslinked and foamed in the same manner as in Example 1 to obtain a sheet-like crosslinked resin foam (the crosslinked resin foam of the present invention).

[0048] [Comparative Example 1] According to the formulation shown in Table 1 below, a resin composition (a crosslinked resin foam-forming resin composition for comparison) was obtained in the same manner as in Example 2, except that the compounding amount of crosslinking agent (PO-1) was 1.5 parts by mass with respect to 100 parts by mass of copolymer (EEA-2). The obtained resin composition was crosslinked and foamed in the same manner as in Example 1 to obtain a sheet-like crosslinked resin foam (a crosslinked resin foam for comparison). This Comparative Example 1 is a comparative example in which the degree of crosslinking of the crosslinked resin foam is excessive.

[0049] [Comparative Example 2] According to the formulation shown in Table 1 below, a resin composition (a crosslinked resin foam-forming resin composition for comparison) was obtained in the same manner as in Example 2, except that the compounding amount of crosslinking agent (PO-1) was 0.2 parts by mass with respect to 100 parts by mass of copolymer (EEA-2). The obtained resin composition was crosslinked and foamed in the same manner as in Example 1 to obtain a sheet-like crosslinked resin foam (a crosslinked resin foam for comparison). This Comparative Example 1 is a comparative example in which the degree of crosslinking of the crosslinked resin foam is too small.

[0050] <Measurement of the degree of crosslinking of the crosslinked resin foam> Test pieces were prepared from each of the crosslinked resin foams obtained in Examples 1 to 2 and Comparative Examples 1 to 2, and the degree of crosslinking (gel fraction) was measured in accordance with JIS C3005, except that the test pieces were used. The results are shown in Table 1 below together.

[0051] <Measurement of Foaming Ratio of Crosslinked Resin Foam> For each of the resin compositions and crosslinked resin foams obtained in Examples 1 to 2 and Comparative Examples 1 to 2, the specific gravity was measured according to JIS K7222, and the foaming ratio of the crosslinked resin foam was calculated by the following formula. The results are shown in Table 1 below.

[0052] Formula: Foaming ratio = (Specific gravity of resin composition / Specific gravity of crosslinked resin foam)

[0053] <Evaluation of Compressive Properties of Crosslinked Resin Foam (Measurement of Compression Set)> Test pieces were prepared from each of the crosslinked resin foams obtained in Examples 1 to 2 and Comparative Examples 1 to 2, and using these test pieces, the compression set of the crosslinked resin foam was evaluated by measuring the compression set according to JIS K 6262 under the conditions of a temperature of 50°C and 50% compression for 6 hours. As the evaluation criteria, when the compression set was 60% or less, it was judged as "pass (○)", and when it exceeded 60%, it was judged as "fail (×)". The results are shown in Table 1 below.

[0054] <Evaluation of Recyclability of Crosslinked Resin Foam (Degradation Treatment)> For each of the crosslinked resin foams obtained in Examples 1 to 2 and Comparative Examples 1 to 2, a degradation treatment (regeneration treatment) was performed using a lab plastomill single-screw extruder (manufactured by Toyo Seiki Seisakusho, main body model 4C150, extruder model D2025) at a rotational speed of 50 rpm and a temperature of 350°C for 2 minutes. For each of the resins after the degradation treatment, the crosslinking degree (gel fraction) was measured according to JIS C3005 to evaluate the recyclability. As the evaluation criteria, when the crosslinking degree after the degradation treatment was less than 15%, it was judged as "pass (○)", and when it was 15% or more, it was judged as "fail (×)". If it is less than 15%, a molded article with a good appearance can be obtained without lumps or roughness on the surface of the tape or strand made from the recycled copolymer. The results are shown in Table 1 below.

[0055]

Table 1

Claims

1. A resin composition containing an ethylene-(meth)acrylate copolymer, a foaming agent, and a crosslinking agent, wherein when the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is A (mol%), the crosslinking degree C (%) of the crosslinked resin foam obtained by crosslinking and foaming this is in the range represented by the following formula. A crosslinked resin foam-forming resin composition. - 25 ≤ C ≤ 2.3A + 77 (where 1.5 ≤ A ≤ 8.0) - 25 ≤ C ≤ 95 (where A > 8.0)

2. The crosslinked resin foam-forming resin composition according to Claim 1, wherein a crosslinked resin foam having a crosslinking degree C of 45% or more can be obtained.

3. The crosslinked resin foam-forming resin composition according to Claim 1 or 2, wherein the ethylene-(meth)acrylate copolymer is ethylene-ethyl acrylate.

4. The crosslinked resin foam-forming resin composition according to Claim 1 or 2, wherein the content ratio A of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is 1.5 to 16 mol%.

5. A crosslinked foam of an ethylene-(meth)acrylate copolymer, wherein when the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is A (mol%), the crosslinking degree C (%) thereof is in the range represented by the following formula. A crosslinked resin foam. - 25 ≤ C ≤ 2.3A + 77 (where 1.5 ≤ A ≤ 8.0) - 25 ≤ C ≤ 95 (where A > 8.0)

6. The crosslinked resin foam according to Claim 5, wherein the crosslinking degree C is 45% or more.

7. The crosslinked resin foam according to Claim 5, wherein the ethylene-(meth)acrylate copolymer is ethylene-ethyl acrylate.

8. The crosslinked resin foam according to Claim 5, which, when heated at 350°C, has a crosslinking degree that decreases to less than 15%.

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