Crosslinkable resin composition, resin crosslinked product and method for producing same, regenerated copolymer and method for producing same, and recycled crosslinkable resin composition and method for producing same

Abstract

The purpose of this invention is to provide a crosslinkable resin composition comprising an ethylene copolymer capable of reversible crosslinking, and a resin crosslinked product excellent in recyclability and capable of returning at least a part of a crosslinked structure to an uncrosslinked state.　This crosslinkable resin composition contains a resin component comprising an ethylene-(meth) acrylic acid ester copolymer and a crosslinking agent component. 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 the resin crosslinked product obtained by crosslinking the ethylene-(meth) acrylic acid ester copolymer is in the range represented by the following formula.　25 ≤ C ≤ 2.3A + 77 (where 1.5 ≤ A ≤ 8.0) 25 ≤ C ≤ 95 (where 8.0 < A)

Description

Crosslinkable resin composition, crosslinked resin product and method for producing the same, recycled copolymer and method for producing the same, recycled crosslinkable resin composition and method for producing the same

[0001] The present invention relates to a crosslinkable resin composition comprising an ethylene copolymer capable of undergoing reversible crosslinking, a crosslinked resin, a recycled copolymer, a recycled crosslinkable resin composition, and methods for producing these.

[0002] Cross-linked polyethylene has excellent insulation properties, heat resistance, durability, chemical stability, and the like, and is therefore used in a wide variety of applications, including coating materials for various electric wires and cables, various electrical appliances, packaging materials, cushioning materials, (thermal) sheets, tubes and containers for chemicals and medicines, chemical tanks, water and hot water supply pipes, automotive parts, and solar cell encapsulants. There is a demand for the effective utilization (recycling) of cross-linked polyethylene waste generated during production and disposal after use as a recyclable resource. However, cross-linked polyethylene cannot be melted with heat or solvents, and recycling methods are limited. Therefore, methods of forcibly severing carbon chains using supercritical water (see Patent Documents 1 and 2 below) or shearing with a twin-screw extruder (see Patent Documents 3 and 4 below) have been investigated. However, these methods inevitably require the introduction of new equipment and result in quality degradation, and have hardly been commercialized.

[0003] JP 2002-187976 JP 2001-192495 JP 2008-69209 JP 2018-35247

[0004] A first object of the present invention is to provide a crosslinkable resin composition capable of undergoing reversible crosslinking. A second object of the present invention is to provide a crosslinked resin product with excellent recyclability in which at least a portion of the crosslinked structure can be returned to an uncrosslinked state, and a method for producing the same. A third object of the present invention is to provide a recycled copolymer in which at least a portion of the crosslinked structure has been returned to an uncrosslinked state, and a method for producing the same. A fourth object of the present invention is to provide a recycled crosslinkable resin composition containing a recycled copolymer as a resin component, and a method for producing the same.

[0005] The crosslinkable resin composition of the present invention is characterized in that it contains a resin component consisting of an ethylene-(meth)acrylic acid ester copolymer and a crosslinker component, and when the content ratio of (meth)acrylic acid ester units (comonomer amount) in the ethylene-(meth)acrylic acid ester copolymer is A (mol %), the degree of crosslinking C (%) of a crosslinked resin product obtained by crosslinking the resin composition is in the range represented by the following formula:

[0006] ・25≦C≦2.3A+77 (however, 1.5≦A≦8.0) ・25≦C≦95 (however, 8.0<A)

[0007] In the crosslinkable resin composition of the present invention, the resin component preferably comprises ethylene-ethyl acrylate (EEA). The crosslinker component preferably comprises a peroxide crosslinker. The crosslinker component may also comprise a silane crosslinker. 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 %. The crosslinking temperature (T 1 ) is in the range of 20 to 250°C, and the decrosslinking temperature (T 2 ) is in the range of 300 to 400°C, and the temperature difference (T 2 -T 1 ) is preferably 50°C or higher.

[0008] The crosslinked resin product of the present invention comprises a crosslinked ethylene-(meth)acrylic acid ester copolymer, and is characterized in that, when the content ratio of (meth)acrylic acid ester units (comonomer amount) in the ethylene-(meth)acrylic acid ester copolymer is A (mol %), its degree of crosslinking C (%) is in the range represented by the following formula:

[0009] ・25≦C≦2.3A+77 (however, 1.5≦A≦8.0) ・25≦C≦95 (however, 8.0<A)

[0010] The crosslinked resin product of the present invention is preferably made of crosslinked ethylene-ethyl acrylate (EEA). The crosslinked resin product of the present invention is preferably made of a peroxide-crosslinked ethylene-(meth)acrylic acid ester copolymer. The crosslinked resin product of the present invention may be made of a silane-crosslinked ethylene-(meth)acrylic acid ester copolymer. The crosslinked resin product of the present invention may be made of an electron beam-crosslinked ethylene-(meth)acrylic acid ester copolymer.

[0011] The crosslinked resin product of the present invention preferably has a degree of crosslinking of 50% or more, particularly 75 to 95%, as measured by the method described below. It is also preferable that the degree of crosslinking is reduced to less than 15%, particularly less than 10%, by heating at 350°C.

[0012] The recycled copolymer of the present invention is characterized in that at least a part of the crosslinked structure of the crosslinked resin product of the present invention has been decrosslinked, and the degree of crosslinking is less than 15%.

[0013] The recycled crosslinkable resin composition of the present invention is characterized by containing the recycled copolymer of the present invention as a resin component.

[0014] In the recycled crosslinkable resin composition of the present invention, the resin component preferably comprises 100 to 1 mass % of the recycled copolymer and 0 to 99 mass % of a virgin ethylene-(meth)acrylic acid ester copolymer. Furthermore, it is preferable that the degree of crosslinking of the entire resin component in the recycled crosslinkable resin composition of the present invention is less than 15%.

[0015] The method for producing a crosslinked resin product of the present invention is characterized by including a step of heating the crosslinkable resin composition of the present invention at 20 to 250° C. (crosslinking step).

[0016] The method for producing the recycled copolymer of the present invention is characterized by including a step of heating the crosslinked resin of the present invention at 300 to 400° C. (decrosslinking step).

[0017] The method for producing a recycled crosslinkable resin composition of the present invention is characterized by comprising: a step of heating the crosslinked resin of the present invention at 300 to 400°C to prepare a recycled copolymer (decrosslinking step); and a step of mixing 100 to 1 mass % of the recycled copolymer obtained in the above step with 0 to 99 mass % of a virgin ethylene-(meth)acrylic acid ester copolymer to prepare a resin component.

[0018] The crosslinkable resin composition of the present invention is capable of undergoing reversible crosslinking (crosslinking reaction and decrosslinking reaction). Here, the crosslinking reaction is carried out at a relatively low temperature, and the decrosslinking reaction is carried out at a relatively high temperature. According to the crosslinkable resin composition of the present invention, the crosslinking reaction of the crosslinkable resin composition occurs at a predetermined temperature (relatively low temperature), thereby making it possible to suitably produce a crosslinked resin product (the crosslinked resin product of the present invention).

[0019] The crosslinked resin product of the present invention can be subjected to a decrosslinking reaction to return at least a portion of the crosslinked structure to an uncrosslinked state. According to the crosslinked resin product of the present invention, the decrosslinking reaction of the crosslinked resin product occurs simply by heating to a predetermined temperature (a relatively high temperature) without using any special additives or applying high shear force, thereby making it possible to produce a recycled copolymer and, in turn, to suitably reproduce a crosslinkable resin composition.

[0020] The recycled copolymer of the present invention can be suitably used as a resin component constituting a crosslinkable resin composition (the recycled crosslinkable resin composition of the present invention) because at least a portion of the crosslinked structure of the crosslinked resin product has been decrosslinked and the degree of crosslinking is less than 15%.

[0021] The recycled crosslinkable resin composition of the present invention can be melt molded because it contains a resin component containing the recycled copolymer of the present invention.

[0022] According to the method for producing a crosslinked resin product of the present invention, the crosslinked resin product of the present invention made of a crosslinked ethylene-(meth)acrylic acid ester copolymer can be suitably produced.

[0023] According to the method for producing a recycled copolymer of the present invention, it is possible to suitably produce the recycled copolymer of the present invention in which at least a portion of the crosslinked structures in the crosslinked resin product have been decrosslinked.

[0024] According to the method for producing a recycled crosslinkable resin composition of the present invention, a melt-moldable crosslinkable resin composition can be produced (reproduced), which can greatly contribute to material recycling.

[0025] <Crosslinkable Resin Composition> The crosslinkable resin composition of the present invention contains a resin component consisting of an ethylene-(meth)acrylic acid ester copolymer and a crosslinking agent component.

[0026] The resin component used is an ethylene-(meth)acrylic acid ester copolymer. The crosslinkable resin composition of the present invention can undergo reversible crosslinking (crosslinking reaction and decrosslinking reaction), and is decrosslinked particularly by heating at a predetermined temperature.

[0027] The structure of the polymer side chain is important for the decrosslinking reaction of a resin composition (crosslinked resin), and it is necessary for the copolymer to have an atomic group containing a heteroatom. For this reason, ethylene-α-olefin copolymers in which the ethylene homopolymer and copolymer are hydrocarbon compounds (e.g., propylene or butene-1,1-hexene as the α-olefin) are not suitable. Furthermore, even in the case of ethylene-α-olefin copolymers containing a heteroatom group, when a vinyl alcohol ester such as ethylene-vinyl acetate copolymer (EVA) is used as the copolymer component, it is well known that heating causes a decarboxylation reaction and the generation of main chain double bonds, followed by a crosslinking reaction. Heat resistance at the decrosslinking temperature is insufficient, and as a result, the decrosslinking reaction does not proceed sufficiently, making it impossible to produce (recycle) a melt-moldable crosslinkable resin composition (see Comparative Example 6 below). Furthermore, when (meth)acrylic acid is used as a copolymer component, such as ethylene-(meth)acrylic acid copolymers (EAA, EMAA), it is well known that heating causes an intermolecular dehydration reaction and a crosslinking reaction due to the production of acid anhydrides, and similarly, heat resistance is insufficient, and therefore the decrosslinking reaction does not proceed sufficiently, making it impossible to produce (recycle) a melt-moldable crosslinkable resin composition (see Comparative Example 7 described below).In contrast, such side reactions do not occur in ethylene-(meth)acrylic acid ester copolymers, and the decrosslinking reaction proceeds efficiently by heating at a predetermined temperature.

[0028] Examples of the ethylene-(meth)acrylic acid ester copolymer that is the resin component 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.

[0029] Here, since ethylene-acrylic acid ester copolymers are less likely to undergo a destructive reaction with radicals, a high degree of crosslinking can be easily achieved mainly by peroxide crosslinking, and crosslinking efficiency can be increased compared to when an ethylene-methacrylic acid ester copolymer is used as the resin component. Furthermore, from the viewpoint of obtaining a resin composition that has a good balance between high mechanical strength and good flexibility, the copolymer component of the resin component is preferably an ethyl ester of (meth)acrylic acid. For these reasons, of the ethylene-(meth)acrylic acid ester copolymers exemplified above, ethylene-ethyl acrylate (EEA) is particularly preferred from the viewpoint of high crosslinking efficiency and excellent balance of physical properties.

[0030] In the ethylene-(meth)acrylic acid ester copolymer, the content ratio of (meth)acrylic acid ester units (comonomer amount) is preferably 1.5 to 16 mol%, more preferably 2.0 to 13 mol%. If the content ratio of (meth)acrylic acid ester units is too low, the decrosslinking reaction does not proceed sufficiently, making it impossible to produce (recycle) a melt-moldable crosslinkable resin composition. On the other hand, if this ratio is too high, properties such as the mechanical strength and electrical insulation characteristics of the polyethylene may be impaired.

[0031] As the crosslinking agent component, a peroxide crosslinking agent or a silane crosslinking agent can be used, and it is preferable to use a peroxide crosslinking agent from the viewpoint of obtaining a crosslinked resin product with a high degree of crosslinking.

[0032] The peroxide crosslinking agent is not particularly limited, but 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, and 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, and of these, dicumyl peroxide is preferred.

[0033] Examples of the silane crosslinking agent include compounds having a functional group reactive with an ethylene-(meth)acrylic acid ester copolymer and a plurality of alkoxy groups, and specific examples thereof include vinylsilane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltris(β-methoxyethoxy)silane; and aminosilanes such as γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)γ-aminopropyltrimethoxysilane, β-(aminoethyl)γ-aminopropylmethyldimethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane. Examples of compounds include epoxy silane compounds such as β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane; acrylic silane compounds such as γ-methacryloxypropyltrimethoxysilane; polysulfide silane compounds such as bis(3-methacryloxysilyl)propyl)disulfide and bis(3-(triethoxysilyl)propyl)tetrasulfide; and mercaptosilane compounds such as 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane.

[0034] The amount of the crosslinking agent component used in the crosslinkable resin composition of the present invention is an amount such that the degree of crosslinking of the crosslinked resin product obtained by crosslinking the crosslinkable resin composition falls within the range represented by the following formula, and although it varies depending on the content of (meth)acrylic acid ester units in the ethylene-(meth)acrylic acid ester copolymer, which is the resin component, it is preferably 0.25 to 4.5 parts by mass, and more preferably 0.3 to 4.0 parts by mass, per 100 parts by mass of the resin component.

[0035] The crosslinkable resin composition of the present invention is capable of undergoing reversible crosslinking (crosslinking reaction and decrosslinking reaction). Here, the crosslinking reaction is carried out at a relatively low temperature, and the decrosslinking reaction is carried out at a relatively high temperature. According to the crosslinkable resin composition of the present invention, the crosslinking reaction of the crosslinkable resin composition occurs simply by heating to a predetermined temperature (relatively low temperature), thereby making it possible to produce the crosslinked resin product of the present invention. The crosslinking temperature (T 1 ) [crosslinking temperature measured by the method described in the Examples below] is preferably in the range of 20 to 250°C.

[0036] By subjecting the crosslinkable resin composition of the present invention to a crosslinking treatment, a crosslinked resin product (crosslinked resin product of the present invention) having a degree of crosslinking C (%) in the range shown by the following formula can be obtained.

[0037] ・25≦C≦2.3A+77 (however, 1.5≦A≦8.0) ・25≦C≦95 (however, 8.0<A)

[0038] (A is the content ratio of (meth)acrylic acid ester units in the ethylene-(meth)acrylic acid ester copolymer, which is the resin component.)

[0039] The crosslinkable resin composition of the present invention may contain optional components used in ordinary resin compositions, as needed. Examples of such optional components include inorganic fillers (e.g., calcium carbonate, clay, diatomaceous earth, metal oxides, silica, carbon black, glass fiber, carbon fiber), plasticizers (phthalate esters, trimellitate esters, polyesters), softeners (mineral oil, process oil, fatty acid), antioxidants (hindered phenol stabilizers, sulfur stabilizers, amine stabilizers), ultraviolet absorbers (benzophenone-based UVA, benzotriazol-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, silicone), foaming agents (azodicarboxamides, methyl methacrylates, methyl methacrylates, methyl methacrylates), methyl methacrylates, ... Examples of suitable crosslinking agents include trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate (TMPTM), triallyl isocyanurate (TAIC), triallyl cyanurate (TAC), and light stabilizers (hindered amine-type compounds, hindered piperidine-type compounds).

[0040] <Crosslinked Resin> The crosslinked resin of the present invention comprises a crosslinked ethylene-(meth)acrylic acid ester copolymer having a specific degree of crosslinking within the range represented by the above formula. The degree of crosslinking of the crosslinked resin of the present invention can be adjusted by appropriately adjusting the amount of the crosslinking agent component used in accordance with the content of (meth)acrylic acid ester units in the ethylene-(meth)acrylic acid ester copolymer, which is the resin component of the crosslinkable resin composition of the present invention. Furthermore, in the case of the crosslinked resin of the present invention that has been crosslinked by electron beam, the degree of crosslinking can be adjusted by appropriately adjusting the irradiation conditions for irradiating the ethylene-(meth)acrylic acid ester copolymer with the electron beam.

[0041] The crosslinked resin product of the present invention can be obtained by crosslinking the crosslinkable resin composition of the present invention. The crosslinking method for producing the crosslinked resin product of the present invention is not particularly limited, and examples thereof include: (1) a method in which a resin composition of the present invention containing a peroxide crosslinking agent is heated at a predetermined temperature to perform chemical crosslinking, (2) a method in which a resin composition of the present invention containing a silane crosslinking agent is heated at a predetermined temperature to perform silane crosslinking, and (3) a method in which an ethylene-(meth)acrylic acid ester copolymer is irradiated with an electron beam to perform electron beam crosslinking.

[0042] In the crosslinking methods (1) and (2), the crosslinking temperature (T 1 ) [crosslinking temperature measured by the method described in the Examples below] is preferably in the range of 20 to 250° C., more preferably in the range of 25 to 240° C. As a heat treatment method for crosslinking, various methods can be adopted depending on the form of the crosslinked resin product, such as a method of heating in an atmosphere of nitrogen, water vapor, silicone oil, molten salt, etc., or a method of heating during molding in a heat press or injection molding machine.

[0043] The degree of crosslinking of the crosslinked resin of the present invention (as measured by the method described below) is 25% or more, preferably 45% or more, and more preferably 70% or more. A crosslinked resin with an insufficient degree of crosslinking cannot exhibit sufficient heat resistance, and melts and deforms at temperatures exceeding the melting point of the resin (see Comparative Example 1 described below).

[0044] The upper limit of the crosslinking degree of the crosslinked resin material of the present invention (hereinafter also referred to as the "upper limit crosslinking degree") is specified from the viewpoint of sufficiently progressing the de-crosslinking reaction of the crosslinked resin material. Here, the de-crosslinking reaction of the crosslinked resin material proceeds more easily as the content ratio (comonomer amount) of (meth)acrylic acid ester units in the ethylene-(meth)acrylic acid ester copolymer increases, and the upper limit of the crosslinking degree of the crosslinked resin material of the present invention is 2.3A+77% when the content ratio A of the (meth)acrylic acid ester units is 1.5 to 8.0 mol%, and is 95% when the content ratio A exceeds 8.0 mol%, where A is the content ratio of the (meth)acrylic acid ester units.

[0045] If the degree of crosslinking of the crosslinked resin is excessive (exceeding the upper limit of the crosslinking degree), the de-crosslinking reaction does not proceed sufficiently, and a melt-moldable crosslinkable resin composition cannot be produced (recycled) (see Comparative Examples 2 and 3 described below).

[0046] By heating the crosslinked resin product of the present invention at a predetermined temperature, at least a portion of the crosslinked structure is decrosslinked.

[0047] The decrosslinking temperature of the crosslinked resin (T 2 ) [decrosslinking temperature measured by the method described in the Examples below] is preferably in the range of 300 to 400°C, more preferably in the range of 320 to 380°C.

[0048] Decrosslinking temperature (T 2 A crosslinked resin having a decrosslinking temperature (T) in the range of 300°C or higher can suppress melt deformation even in a wide high temperature range below 300°C, and has excellent heat resistance. 2 ) is in the range of 400°C or less, de-crosslinking (decomposition of the crosslinked structure) proceeds while suppressing thermal degradation of the resulting recycled copolymer, thereby preventing deterioration of the physical properties of the recycled copolymer.

[0049] The temperature difference between the decrosslinking temperature and the crosslinking temperature (T 2 -T 1 The temperature difference (T 2 -T 1 ) is 50°C or higher, it is possible to easily set and control the treatment temperature in each of the crosslinking step of the resin composition and the de-crosslinking step of the crosslinked resin product.

[0050] The crosslinked resin of the present invention is preferably one whose degree of crosslinking decreases to less than 15%, particularly less than 10%, when heated at 350°C.

[0051] The crosslinked resin of the present invention can be used in all applications for conventional crosslinked polyethylene. Specifically, it is suitable for use as a coating material for various electric wires and cables, various electrical appliances, packaging materials, cushioning materials, (thermal insulation) sheets, tubes and containers for chemicals and medicines, chemical tanks, water and hot water supply pipes, automobile parts, solar cell encapsulants, etc. Here, electric wires and cables include electric wires and cables for power transmission or communication. Furthermore, the coating material for electric wires and cables may be an insulator (layer) or a semiconductive material (layer), or may be a foam (layer). Furthermore, the crosslinked resin of the present invention can also constitute a flame-retardant coating material.

[0052] <Recycled Copolymer> The recycled copolymer of the present invention is obtained by decrosslinking at least a portion of the crosslinked structure of the crosslinked resin product of the present invention. The degree of crosslinking of the recycled copolymer of the present invention is usually less than 15%, preferably less than 10%. A recycled copolymer with an excessively high degree of crosslinking cannot be subjected to remelt molding by heating and cannot be reused.

[0053] <Recycled Crosslinkable Resin Composition> The recycled crosslinkable resin composition of the present invention contains the recycled copolymer of the present invention as a resin component. The resin component constituting the recycled crosslinkable resin composition may consist solely of the recycled copolymer of the present invention, or may also contain a virgin ethylene-(meth)acrylic acid ester copolymer.

[0054] Here, the mass ratio of the recycled copolymer to the virgin ethylene-(meth)acrylic acid ester copolymer is 100 to 1:0 to 99, and can be appropriately adjusted depending on the properties and cost required for the application of the recycled copolymer (recycled crosslinkable resin composition).

[0055] The recycled crosslinkable resin composition of the present invention may contain a crosslinking agent component depending on the crosslinking method used. The crosslinking agent component contained in the recycled crosslinkable resin composition may be the peroxide crosslinking agent or silane crosslinking agent exemplified as those contained in the crosslinkable resin composition of the present invention.

[0056] An example of a method for producing the recycled crosslinkable resin composition of the present invention is a method in which the crosslinked resin of the present invention is heated at a predetermined temperature to decrosslink the crosslinked resin to prepare a recycled copolymer of the present invention, and a virgin ethylene-(meth)acrylic acid ester copolymer is mixed with the resulting recycled copolymer to prepare a resin component, and a crosslinking agent component is added as needed.

[0057] Examples of the present invention will be described below, but the present invention is not limited to these. In the following examples and comparative examples, the following compounds were used as the (co)polymers constituting the resin components and the crosslinking agents.

[0058] ・Copolymer (EEA-1) Density = 0.93g / cm 3 , MFR (190°C, 2.16 kg) = 4 g / 10 min, EA content = 2.0 mol%.

[0059] ・Copolymer (EEA-2) Density = 0.93g / cm 3 , MFR (190°C, 2.16 kg) = 1.5 g / 10 min, EA content = 4.7 mol%.

[0060] ・Copolymer (EEA-3) Density = 0.93g / cm 3 , MFR (190°C, 2.16 kg) = 0.5 g / 10 min, EA content = 7.7 mol%.

[0061] ・Copolymer (EEA-4) Density = 0.94g / cm 3 , MFR (190°C, 2.16 kg) = 1.5 g / 10 min, EA content = 8.1 mol%.

[0062] ・Copolymer (EEA-5) Density = 0.95g / cm 3 , MFR (190°C, 2.16 kg) = 20 g / 10 min, EA content = 13 mol%.

[0063] ・Copolymer (EMMA) Density = 0.94g / cm 3 , MFR (190°C, 2.16 kg) = 2.0 g / 10 min, MMA content = 6.5 mol% Ethylene-methyl methacrylate copolymer.

[0064] ・Polymer (LDPE) density = 0.92g / cm 3 , low-density polyethylene having MFR (190°C, 2.16 kg) = 5.0 g / 10 min.

[0065] ・Polymer (L-LDPE) Density = 0.92g / cm 3 , a linear low-density polyethylene having an MFR (190°C, 2.16 kg) of 0.7 g / 10 min.

[0066] ・Copolymer (EVA) density = 0.94g / cm 3 , MFR (190°C, 2.16 kg) = 12 g / 10 min, VA content = 5.4 mol%.

[0067] ・Copolymer (EAA) density = 0.94g / cm 3 , MFR (190°C, 2.16 kg) = 12 g / 10 min, AA content = 6.4 mol%.

[0068] Crosslinking agent (PO-1): Peroxide crosslinking agent consisting of dicumyl peroxide

[0069] Crosslinking agent (PO-2): Peroxide crosslinking agent consisting of 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane

[0070] Crosslinking agent (Silane): A silane crosslinking agent consisting of vinyltriethoxylane, dicumyl peroxide, and dibutyltin dilaurate.

[0071] <Production of Crosslinkable Resin Composition> [Example 1] According to the formulation shown in Table 1 below, 100 parts by mass of copolymer (EEA-1) and 1.01 parts by mass of crosslinking agent (PO-1) were mixed for 12 hours while heating at 60°C, and then cooled to room temperature to obtain a resin composition (crosslinkable resin composition) of the present invention.

[0072] Example 2 A resin composition of the present invention was obtained in the same manner as in Example 1, except that 100 parts by mass of the copolymer (EEA-2) and 1.32 parts by mass of the crosslinking agent (PO-1) were used according to the formulation shown in Table 1 below.

[0073] Example 3 A resin composition of the present invention was obtained in the same manner as in Example 1, except that 100 parts by mass of the copolymer (EEA-3) and 1.63 parts by mass of the crosslinking agent (PO-1) were used according to the formulation shown in Table 1 below.

[0074] Example 4 A resin composition of the present invention was obtained in the same manner as in Example 1, except that 100 parts by mass of the copolymer (EEA-4) and 1.73 parts by mass of the crosslinking agent (PO-1) were used according to the formulation shown in Table 1 below.

[0075] Example 5 A resin composition of the present invention was obtained in the same manner as in Example 1, except that 100 parts by mass of the copolymer (EEA-5) and 2.88 parts by mass of the crosslinking agent (PO-1) were used according to the formulation shown in Table 1 below.

[0076] Example 6 A resin composition of the present invention was obtained in the same manner as in Example 1, except that 100 parts by mass of the copolymer (EEA-2) and 0.92 parts by mass of the crosslinking agent (PO-2) were used according to the formulation shown in Table 1 below.

[0077] Example 7 According to the formulation shown in Table 1 below, 100 parts by mass of copolymer (EEA-4) and 0.50 parts by mass of crosslinking agent (Silane) were mixed for 12 hours while heated to 60°C, and then cooled to room temperature. The mixture was charged into a twin-screw kneader (TEM-35B manufactured by Toshiba Machine Co., Ltd.) and extrusion-kneaded at a rotation speed of 50 rpm and 200°C to obtain a resin composition (crosslinkable resin composition) of the present invention.

[0078] Example 8 A resin composition of the present invention was obtained in the same manner as in Example 1, except that 100 parts by mass of the copolymer (EMMA) and 1.83 parts by mass of the crosslinking agent (PO-1) were used according to the formulation shown in Table 1 below.

[0079] Comparative Example 1 A comparative resin composition was obtained in the same manner as in Example 1, except that the amount of crosslinking agent (PO-1) used was changed to 0.10 parts by mass according to the formulation shown in Table 2 below. In Comparative Example 1, the crosslinked resin obtained by crosslinking the resin composition had an insufficient degree of crosslinking.

[0080] Comparative Example 2 A comparative resin composition was obtained in the same manner as in Example 1, except that the amount of crosslinking agent (PO-1) used was changed to 1.83 parts by mass according to the formulation shown in Table 2 below. In Comparative Example 2, the crosslinked resin obtained by crosslinking the resin composition had an excessively high degree of crosslinking.

[0081] A comparative resin composition was obtained in the same manner as in Example 2, except that the amount of crosslinking agent (PO-1) used was changed to 2.05 parts by mass, according to the formulation shown in Table 2. In Comparative Example 3, the crosslinked resin obtained by crosslinking the resin composition had an excessively high degree of crosslinking.

[0082] Comparative Examples 4 to 7 Comparative resin compositions were obtained in the same manner as in Example 1, except that the type of (co)polymer and the amount of crosslinking agent (PO-1) used were changed according to the formulations shown in Table 2. These Comparative Examples 4 to 7 are comparative examples in which a (co)polymer other than an ethylene-(meth)acrylic acid ester copolymer was used as the resin component.

[0083] <Production of Crosslinked Resin Product (Crosslinking Reaction)> Each of the crosslinkable resin compositions obtained in Examples 1 to 6 and 8 and Comparative Examples 1 to 7 was crosslinked by pressing at 180°C for 15 minutes using a hot press (Toho Machinery, TBD-50 model), to obtain a sheet-like crosslinked resin product having a thickness of 1 mm.

[0084] Furthermore, the crosslinkable resin composition obtained in Example 7 was pressed at 120°C for 5 minutes using a heated press (Toho Machinery, TBD-50 model) to obtain a 1 mm-thick sheet-like crosslinked resin product, which was then immersed in 80°C warm water for 2 hours to further crosslink the composition, thereby obtaining a crosslinked resin product.

[0085] Example 9 The copolymer (EEA-5) was molded into a sheet having a thickness of 1 mm by pressing it at 120°C for 5 minutes using a heated press (Toho Machinery, TBD-50 model). The obtained molded product was irradiated with electron beams using an electron beam irradiation device (NHV Corporation, EPS-750kV) at an acceleration voltage of 750 kV, a temperature of 30°C, an electron current of 4.9 A, and a dose of 100 kGy, thereby crosslinking the copolymer (EEA-5) with electron beams, and a sheet-like crosslinked resin product was obtained.

[0086] Example 10 A sheet-like crosslinked resin product was obtained in the same manner as in Example 9, except that the copolymer (EMMA) was molded into a sheet having a thickness of 1 mm instead of the copolymer (EEA-5), and the irradiation dose of the obtained molded product was changed to 200 kGy, and the copolymer (EMMA) was crosslinked with an electron beam.

[0087] <Crosslinking temperature (T 1 Measurement of the crosslinking temperature (T) for each of the crosslinkable resin compositions obtained in Examples 1 to 10 was measured as follows. 1 The results are also shown in Table 1 below.

[0088] (Measurement Method) The crosslinking reaction rate of both peroxide crosslinking and silane crosslinking is temperature dependent. Therefore, in the peroxide crosslinking of Examples 1 to 6 and 8, the one-minute half-life temperature of the peroxide used was defined as the crosslinking temperature. In silane crosslinking, crosslinking is carried out in hot water or water vapor at normal pressure, and a temperature of 60 to 90°C is generally preferred. Therefore, in the silane crosslinking of Example 7, the temperature of the hot water at which crosslinking progress was confirmed by hot water treatment was defined as the crosslinking temperature. In electron beam irradiation, crosslinking is carried out at room temperature or a temperature below the melting point of the resin, but crosslinking is generally promoted at higher temperatures. Therefore, in the electron beam crosslinking of Examples 9 and 10, the material temperature at which crosslinking progress was confirmed by electron beam irradiation was defined as the crosslinking temperature.

[0089] <Measurement of Degree of Crosslinking of Crosslinked Resin Product> Test specimens were prepared from the sheet-like crosslinked resin products obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 7, and the degree of crosslinking (gel fraction) was measured in accordance with JIS C3005, except that the test specimens were used. The results are also shown in Tables 1 and 2 below.

[0090] <Evaluation of Heat Distortion Resistance of Crosslinked Resin Product> Test specimens were prepared from the sheet-like crosslinked resin products obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 7, and the heat distortion resistance of the crosslinked resin products was evaluated by measuring the heat distortion rate and hot set (maximum elongation under load) using the test specimens. If the heat distortion rate and hot set are excessive, sufficient heat resistance cannot be exhibited, and the resin will deform significantly under high temperature conditions in cable applications, for example, which will be a problem.

[0091] The methods for measuring the heat deformation rate and hot set are as follows. The evaluation criteria for heat deformation resistance were as follows: a heat deformation rate of 40% or less or a hot set of 175% or less was rated "pass (◯)", and a failure to meet either criteria was rated "fail (×)". The results are also shown in Tables 1 and 2 below.

[0092] (Measurement Method) (1) Method for Measuring Heat Deformation Rate of Crosslinked Resin Body The heat deformation rate (rate of reduction in thickness due to heating) was measured in accordance with JIS C3005, except that the above test specimen was used.

[0093] (2) Method for measuring hot set of crosslinked resin product The maximum elongation under load of the hot set was measured in accordance with JIS C3660-507, except that the above test specimen was used.

[0094] <Production of Recycled Copolymer (Decrosslinking Reaction)> The sheet-like crosslinked resin bodies obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 7 were subjected to a regeneration treatment in which they were heated at 350°C for 2 minutes at a rotation speed of 50 rpm using a Laboplastomill single-screw extruder (manufactured by Toyo Seiki Seisaku-sho, main body Model 4C150, extruder Model D2025).

[0095] <Decrosslinking temperature (T 2 Measurement of decrosslinking temperature (T) for each of the crosslinkable resin compositions obtained in Examples 1 to 10 was measured as follows. 2 ) was measured.

[0096] (Measurement Method) Using a rheometer (MCR302, manufactured by Anton Paar), a sample made of a crosslinked resin was measured for dynamic viscoelasticity while increasing the temperature from an initial temperature of 130°C under conditions of a constant frequency (angular frequency 0.1 rad / s, strain 1%), and the temperature (gel point) at which the storage modulus (G') and loss modulus (G") intersect was determined as the de-crosslinking temperature (T 2 )

[0097] <Evaluation of Recyclability of Crosslinked Resin Product> The recyclability of the crosslinked resin product was evaluated by measuring the degree of crosslinking (gel fraction) after a recycling treatment (350°C x 2 minutes) for the sheet-shaped crosslinked resin products obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 7. The evaluation criteria for recyclability were as follows: a crosslinking degree of less than 15% after the recycling treatment (recycled copolymer) was rated as "pass (◯)," and a crosslinking degree of 15% or more was rated as "fail (×)." If the crosslinking degree was less than 15%, the tape or strand produced from the recycled copolymer was free of bumps or roughness on the surface and could be molded with a good appearance. The results are also shown in Tables 1 and 2 below.

[0098]

[0099]

Claims

1. A crosslinkable resin composition containing a resin component composed of an ethylene-(meth)acrylate copolymer and a crosslinking agent component, 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 resin crosslinked body obtained by crosslinking this is in the range represented by the following formula. - 25 ≤ C ≤ 2.3A + 77 (where 1.5 ≤ A ≤ 8.0) - 25 ≤ C ≤ 95 (where 8.0 < A) 2. The crosslinkable resin composition according to claim 1, wherein the resin component is composed of ethylene-ethyl acrylate (EEA).

3. The crosslinkable resin composition according to claim 1, wherein the crosslinking agent component is a peroxide crosslinking agent.

6. The crosslinking temperature (T 1 ), is in the range of 20 to 250 °C, and the de-crosslinking temperature (T 2 ), is in the range of 300 to 400 °C, and the temperature difference (T 2 - T 1 ) is 50 °C or more. The crosslinkable resin composition according to claim 1.

4. The crosslinkable resin composition according to claim 1, wherein the crosslinking agent component is a silane crosslinking agent.

5. The crosslinkable resin composition according to claim 1, wherein the content ratio A of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is 1.5 to 16 mol%.

7. A resin crosslinked body composed of a crosslinked ethylene-(meth)acrylate copolymer, and when the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is A (mol%), its crosslinking degree C (%) is in the range represented by the following formula. - 25 ≤ C ≤ 2.3A + 77 (where 1.5 ≤ A ≤ 8.0) - 25 ≤ C ≤ 95 (where 8.0 < A) 8. The resin crosslinked body according to claim 7, which is composed of crosslinked ethylene-ethyl acrylate (EEA).

9. The resin crosslinked body according to claim 7, which is composed of a peroxide-crosslinked ethylene-(meth)acrylate copolymer.

10. The resin crosslinked body according to claim 7, which is composed of a silane-crosslinked ethylene-(meth)acrylate copolymer.

11. The resin crosslinked body according to claim 7, which is composed of an electron beam-crosslinked ethylene-(meth)acrylate copolymer.

12. The resin crosslinked body according to claim 7, wherein when heated at 350 °C, the crosslinking degree decreases to less than 15%.

13. A recycled copolymer in which at least a part of the crosslinked structure of the resin crosslinked body according to claim 7 is de-crosslinked and the crosslinking degree is less than 15%.

14. A recyclable crosslinkable resin composition containing the recycled copolymer according to claim 13 as a resin component.

15. The recycled crosslinkable resin composition according to claim 14, wherein the resin component comprises 100 to 1% by mass of the recycled copolymer and 0 to 99% by mass of virgin ethylene-(meth)acrylate copolymer.

16. A method for producing a resin crosslinked body according to claim 7, the method for producing a resin crosslinked body including a step of heating the crosslinkable resin composition according to claim 1 at 20 to 250°C.

17. A method for producing the recycled copolymer according to claim 13, the method for producing the recycled copolymer including a step of heating the resin crosslinked body according to claim 7 at 300 to 400°C.

18. A method for producing the recycled crosslinkable resin composition according to claim 14, the method for producing the recycled crosslinkable resin composition including: a step of heating the resin crosslinked body according to claim 7 at 300 to 400°C to prepare a recycled copolymer; and a step of mixing 100 to 1% by mass of the recycled copolymer obtained by the above step and 0 to 99% by mass of virgin ethylene-(meth)acrylate copolymer to prepare a resin component.

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