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

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.SOLUTION: This crosslinkable resin composition contains a resin component comprising an ethylene-(meth)acrylic acid ester copolymer and a crosslinking agent component, and 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 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 crosslinkable resin composition comprising an ethylene copolymer capable of performing reversible crosslinking, a resin crosslinked body, a recycled copolymer, a recyclable crosslinkable resin composition, and methods for producing these.

Background Art

[0002] Crosslinked polyethylene is excellent in insulation, heat resistance, durability, chemical stability, etc., and is therefore used in a wide variety of applications such as coating materials for various electric wires and cables, various electrical products, packaging materials, cushioning materials, (heat insulation) sheets, tubes and containers for chemicals and pharmaceuticals, chemical tanks, water supply and hot water supply pipes, automobile parts, and sealing materials for solar cells. There is also a demand to effectively utilize (recycle) crosslinked polyethylene waste materials generated during production or at the time of disposal after use as recycled resources. However, crosslinked polyethylene cannot be melted by heat or a solvent, and its recycling method is limited. Therefore, methods of forcibly cutting carbon chains by water in a supercritical state (see Patent Documents 1 and 2 below) or shear by a twin-screw extruder (see Patent Documents 3 and 4 below) have been studied. However, these methods inevitably involve new introduction of equipment and deterioration of quality, and have hardly reached industrialization.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] A first object of the present invention is to provide a crosslinkable resin composition capable of performing reversible crosslinking. A second object of the present invention is to provide a resin crosslinked body excellent in recyclability capable of returning at least a part of the crosslinked structure 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 part 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.

Means for Solving the Problems

[0005] The crosslinkable resin composition of the present invention contains a resin component composed of an ethylene-(meth)acrylate copolymer and a crosslinking agent component. When the content ratio (comonomer amount) 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 the resin composition is in the range represented by the following formula.

[0006] ·25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ·25 ≦ C ≦ 95 (where 8.0 < A)

[0007] In the crosslinkable resin composition of the present invention, it is preferable that the resin component is composed of ethylene-ethyl acrylate (EEA). Further, it is preferable that the crosslinking agent component is a peroxide crosslinking agent. Further, the crosslinking agent component may be a silane crosslinking agent. Further, the content ratio A (comonomer amount) of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is preferably 1.5 to 16 mol%, particularly preferably 2.0 to 13 mol%. Also, it is preferable that the crosslinking temperature (T1) is in the range of 20 to 250°C, the de-crosslinking temperature (T2) is in the range of 300 to 400°C, and the temperature difference (T2 - T1) is 50°C or more.

[0008] The resin crosslinked product of the present invention is composed of a crosslinked ethylene-(meth)acrylate copolymer. When the content ratio (comonomer amount) 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.

[0009] ·25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ·25 ≦ C ≦ 95 (where 8.0 < A)

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

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

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

[0013] The recyclable 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 recyclable crosslinkable resin composition of the present invention, it is preferable that the resin component is composed of 100 to 1% by mass of the recycled copolymer and 0 to 99% by mass of a virgin ethylene-(meth)acrylate copolymer. Further, it is preferable that the crosslinking degree of the entire resin component in the recyclable crosslinkable resin composition of the present invention is less than 15%.

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

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

[0017] The method for producing a recyclable crosslinkable resin composition of the present invention includes a step (decrosslinking step) of heating the resin crosslinked body of the present invention 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 a virgin ethylene-(meth)acrylate copolymer to prepare a resin component.

Advantages of the Invention

[0018] The crosslinkable resin composition of the present invention can perform 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, at a predetermined temperature (relatively low temperature), the crosslinking reaction of the crosslinkable resin composition occurs, and thereby, a resin crosslinked body (the resin crosslinked body of the present invention) can be preferably produced.

[0019] The resin crosslinked body of the present invention can return at least a part of the crosslinked structure to an uncrosslinked state by a decrosslinking reaction. According to the resin crosslinked product of the present invention, without using a special additive or applying a high shearing force, the crosslinking reaction of the resin crosslinked product occurs simply by heating to a predetermined temperature (relatively high temperature), whereby a recycled copolymer can be produced, and consequently, the crosslinkable resin composition can be suitably reproduced.

[0020] The recycled copolymer of the present invention has at least a part of the crosslinked structure of the resin crosslinked product depolymerized and a crosslinking degree of less than 15%, so that it can be suitably used as a resin component constituting the crosslinkable resin composition (the recyclable crosslinkable resin composition of the present invention).

[0021] The recyclable crosslinkable resin composition of the present invention contains a resin component including the recycled copolymer of the present invention, and thus can be melt-molded.

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

[0023] According to the method for producing the recycled copolymer of the present invention, the recycled copolymer of the present invention in which at least a part of the crosslinked structure in the resin crosslinked product is depolymerized can be suitably produced.

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

Embodiments for Carrying Out the Invention

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

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

[0027] The de-crosslinking reaction of the resin composition (resin crosslinked product) is important for the structure of the polymer side chain, and it is necessary to have an atomic group containing a heteroatom. Therefore, ethylene homopolymers and copolymers, such as ethylene-α-olefin copolymers which are hydrocarbon compounds (for example, propylene, butene-1, 1-hexene, etc. as α-olefins), are not suitable. Furthermore, even for an ethylene-α-olefin copolymer containing a heteroatomic group, when a vinyl alcohol ester such as ethylene-vinyl acetate copolymer (EVA) is used as a copolymer component, it is well known that a decarboxylation reaction, formation of main chain double bonds, and subsequent crosslinking reaction occur upon heating, and the heat resistance at the de-crosslinking temperature is insufficient. Therefore, the de-crosslinking reaction does not proceed sufficiently, and a crosslinkable resin composition that can be melt-molded cannot be produced (recycled) (see Comparative Example 6 described later). Also, when (meth)acrylic acid such as ethylene-(meth)acrylic acid copolymer (EAA, EMAA) is used as a copolymer component, it is well known that a crosslinking reaction occurs due to an intermolecular dehydration reaction and formation of an acid anhydride upon heating, and similarly the heat resistance is insufficient. Therefore, the de-crosslinking reaction does not proceed sufficiently, and a crosslinkable resin composition that can be melt-molded cannot be produced (recycled) (see Comparative Example 7 described later). On the other hand, in the case of an ethylene-(meth)acrylate copolymer, such side reactions do not occur, so the de-crosslinking reaction proceeds efficiently by heating at a predetermined temperature.

[0028] Examples of the ethylene-(meth)acrylate copolymer as 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 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 the 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.

[0030] In the ethylene-(meth)acrylate copolymer, the content ratio (comonomer amount) of the (meth)acrylate ester unit is preferably 1.5 to 16 mol%, more preferably 2.0 to 13 mol%. If the content ratio of the (meth)acrylate ester unit is too small, the de-crosslinking reaction does not proceed sufficiently, so that a crosslinkable resin composition that can be melt-molded cannot be produced (recycled). On the other hand, if this ratio is too large, properties such as the mechanical strength and electrical insulation properties of polyethylene may be impaired.

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

[0032] 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.

[0033] 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.

[0034] As the amount of the crosslinking agent component used in the crosslinkable resin composition of the present invention, it is an amount such that the crosslinking degree of the resin crosslinked body obtained by crosslinking the crosslinkable resin composition falls within the range represented by the following formula. Although it varies depending on the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer which is the resin component, it is preferably 0.25 to 4.5 parts by mass, more preferably 0.3 to 4.0 parts by mass with respect to 100 parts by mass of the resin component.

[0035] The crosslinkable 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 crosslinkable resin composition of the present invention, by simply heating to a predetermined temperature (relatively low temperature), the crosslinking reaction of the crosslinkable resin composition occurs, and thereby, the resin crosslinked body of the present invention can be produced. The crosslinking temperature (T1) of the crosslinkable resin composition of the present invention (the 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 resin crosslinked body (the resin crosslinked body of the present invention) having a crosslinking degree C (%) within the range represented by the following formula can be obtained.

[0037] ·25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ·25 ≦ C ≦ 95 (where 8.0 < A)

[0038] 〔A is the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer which is the resin component.〕

[0039] The crosslinkable resin composition of the present invention can contain, as optional components, 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 fibers, carbon fibers), plasticizers (phthalic acid esters, trimellitic acid esters, polyesters), softeners (mineral oils, process oils, fatty acids), antioxidants (hindered phenol stabilizers, sulfur stabilizers, amine stabilizers), ultraviolet absorbers (benzophenone-based UVA, benzotriazole-based UVA, salicylic acid ester-based UVA), antistatic agents (glycerin fatty acid esters, alkyl sulfonic acids, tetraalkylammonium salts), flame retardants (metal hydroxides, phosphorus compounds, halogen compounds), lubricants (fatty acid amides, zinc stearate, silicones), foaming agents [azodicarbonamide (ADCA), sodium bicarbonate, 4,4'-oxybis(benzenesulfonylhydrazide) (OBSH)], 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.

[0040] <Resin crosslinked body> The resin crosslinked body of the present invention is composed of a crosslinked ethylene-(meth)acrylate copolymer having a specific degree of crosslinking within the range represented by the above formula. The degree of crosslinking of the resin crosslinked body of the present invention can be adjusted by appropriately adjusting the amount of the crosslinking agent component according to the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer which is the resin component of the crosslinkable resin composition of the present invention. Also, in the resin crosslinked body of the present invention crosslinked by electron beam, the degree of crosslinking can be adjusted by appropriately adjusting the irradiation conditions of the electron beam irradiated to the ethylene-(meth)acrylate copolymer.

[0041] The resin crosslinked body of the present invention is obtained by subjecting the crosslinkable resin composition of the present invention to a crosslinking treatment. The crosslinking method for producing the resin crosslinked product 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.

[0042] In the crosslinking methods (1) and (2) above, the crosslinking temperature (T1) of the crosslinkable resin composition of the present invention [the 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 the heat treatment method for crosslinking, various methods can be adopted according to the form of the resin crosslinked product, 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.

[0043] The crosslinking degree of the resin crosslinked product of the present invention (the crosslinking degree measured by the method described below) is 25% or more, preferably 45% or more, more preferably 70% or more. A resin crosslinked product with too small a crosslinking degree cannot exhibit sufficient heat resistance and will melt and deform under temperature conditions exceeding the melting point of the resin (see Comparative Example 1 described below).

[0044] The upper limit value of the crosslinking degree of the resin crosslinked product of the present invention (hereinafter, also referred to as the "upper limit crosslinking degree") is defined from the viewpoint of sufficiently advancing the de-crosslinking reaction of the resin crosslinked product. Here, the de-crosslinking reaction of the resin crosslinked body proceeds more easily as the content ratio (comonomer amount) of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is higher. The upper limit crosslinking degree of the resin crosslinked body 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%.

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

[0046] By heating the resin crosslinked body of the present invention at a predetermined temperature, at least a part of the crosslinked structure is de-crosslinked.

[0047] The de-crosslinking temperature (T2) [the de-crosslinking temperature measured by the method described in the examples below] of the resin crosslinked body is preferably in the range of 300 to 400 °C, and more preferably in the range of 320 to 380 °C.

[0048] A resin crosslinked body with a de-crosslinking temperature (T2) 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. Also, if the de-crosslinking temperature (T2) is in the range of 400 °C or lower, de-crosslinking (decomposition of the crosslinked structure) proceeds while suppressing thermal degradation of the obtained recycled copolymer, so that a decrease in the physical properties of the recycled copolymer can be prevented.

[0049] The temperature difference (T2 - T1) between the de-crosslinking temperature and the crosslinking temperature is preferably 50 °C or higher, and more preferably 70 °C or higher. If the temperature difference (T2 - T1) is 50 °C or higher, in each of the crosslinking step of the resin composition and the de-crosslinking step of the resin crosslinked body, the setting of the treatment temperature and the temperature control can be easily performed.

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

[0051] The resin crosslinked product of the present invention can be used in all applications of conventional crosslinked polyethylene. Specifically, it is preferably used as a coating material for various electric wires and cables, various electrical products, packaging materials, cushioning materials, (heat insulation) sheets, tubes and containers for chemical and pharmaceutical products, chemical tanks, water supply and hot water supply pipes, automotive parts, solar cell encapsulants, etc. Here, the electric wires and cables include electric wires and cables for power transmission or communication. Also, the coating material for the electric wires and cables may be an insulator (layer), a semiconductor (layer), or a foam (layer). Further, the resin crosslinked product of the present invention can also constitute a flame-retardant coating material.

[0052] <Recycled copolymer> The recycled copolymer of the present invention is formed by at least partially de-crosslinking the crosslinked structure of the resin crosslinked product of the present invention. Here, the crosslinking degree of the recycled copolymer of the present invention is usually less than 15%, preferably less than 10%. A recycled copolymer with an excessive crosslinking degree cannot be subjected to remelting and molding by heating and cannot be reused.

[0053] <Recyclable crosslinkable resin composition> The recyclable crosslinkable resin composition of the present invention contains the recycled copolymer of the present invention as a resin component. The resin component constituting the recyclable crosslinkable resin composition may consist only of the recycled copolymer of the present invention, but may also contain a virgin ethylene-(meth)acrylate copolymer.

[0054] Here, the mass ratio of the recycled copolymer to the virgin ethylene-(meth)acrylate copolymer is 100 to 1:0 to 99, and can be appropriately adjusted according to the properties and costs required for the application of the recycled copolymer (recyclable crosslinkable resin composition).

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

[0056] Illustrating an example of the method for producing the crosslinkable recycled resin composition of the present invention, the resin crosslinked product of the present invention is heated at a predetermined temperature to be de-crosslinked to prepare the recycled copolymer of the present invention, and the obtained recycled copolymer is mixed with virgin ethylene-(meth)acrylate copolymer to prepare a resin component, and a method of adding a crosslinking agent component as necessary can be mentioned.

Examples

[0057] 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 (co)polymers and crosslinking agents constituting the resin component.

[0058] ·Copolymer (EEA-1) Density = 0.93 g / cm 3 , Ethylene-ethyl acrylate copolymer with MFR (190 ° C, 2.16 kg) = 4 g / 10 min and EA content ratio = 2.0 mol%.

[0059] ·Copolymer (EEA-2) Density = 0.93 g / cm 3 , Ethylene-ethyl acrylate copolymer with MFR (190 ° C, 2.16 kg) = 1.5 g / 10 min and EA content ratio = 4.7 mol%.

[0060] ·Copolymer (EEA-3) Density = 0.93 g / cm 3 , Ethylene-ethyl acrylate copolymer with MFR (190 ° C, 2.16 kg) = 0.5 g / 10 min and EA content ratio = 7.7 mol%.

[0061] · Copolymer (EEA-4) Density = 0.94 g / cm 3 , Ethylene-ethyl acrylate copolymer with MFR (190 °C, 2.16 kg) = 1.5 g / 10 min and EA content ratio = 8.1 mol%.

[0062] · Copolymer (EEA-5) Density = 0.95 g / cm 3 , Ethylene-ethyl acrylate copolymer with MFR (190 °C, 2.16 kg) = 20 g / 10 min and EA content ratio = 13 mol%.

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

[0064] · Polymer (LDPE) Density = 0.92 g / cm 3 , Low-density polyethylene with MFR (190 °C, 2.16 kg) = 5.0 g / 10 min.

[0065] · Polymer (L-LDPE) Density = 0.92 g / cm 3 , Linear low-density polyethylene with MFR (190 °C, 2.16 kg) = 0.7 g / 10 min.

[0066] · Copolymer (EVA) Density = 0.94 g / cm 3 , Ethylene-vinyl acetate copolymer with MFR (190 °C, 2.16 kg) = 12 g / 10 min and VA content ratio = 5.4 mol%.

[0067] · Copolymer (EAA) Density = 0.94 g / cm 3 , Ethylene-acrylic acid copolymer with MFR (190 °C, 2.16 kg) = 12 g / 10 min and AA content ratio = 6.4 mol%.

[0068] · Crosslinking agent (PO-1) Peroxide crosslinking agent composed of dicumyl peroxide

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

[0070] · Crosslinking agent (Silane) Silane crosslinking agent composed of vinyltriethoxysilane, 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 at 60°C for 12 hours while heating, and then cooled to room temperature to obtain the resin composition (crosslinkable resin composition) of the present invention.

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

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

[0074] 〔Example 4〕 The resin composition of the present invention was obtained in the same manner as in Example 1, except that 100 parts by mass of copolymer (EEA-4) and 1.73 parts by mass of 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 a copolymer (EEA-5) and 2.88 parts by mass of a 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 a copolymer (EEA-2) and 0.92 parts by mass of a 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 a copolymer (EEA-4) and 0.50 parts by mass of a crosslinking agent (Silane) were mixed at 60 °C for 12 hours and then cooled to room temperature. This was charged into a twin-screw kneader (TEM-35B manufactured by Toshiba Machine Co., Ltd.) and extruded and kneaded at a rotational 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 a copolymer (EMMA) and 1.83 parts by mass of a 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 the crosslinking agent (PO-1) used was changed to 0.10 parts by mass according to the formulation shown in Table 2 below. This Comparative Example 1 is a comparative example in which the degree of crosslinking of the resin crosslinked body obtained by crosslinking the resin composition is too small.

[0080] [Comparative Example 2] A comparative resin composition was obtained in the same manner as in Example 1, except that the amount of the crosslinking agent (PO-1) used was changed to 1.83 parts by mass according to the formulation shown in Table 2 below. This Comparative Example 2 is a comparative example in which the degree of crosslinking of the resin crosslinked body obtained by crosslinking the resin composition is too large.

[0081] [Comparative Example 3] A comparative resin composition was obtained in the same manner as in Example 2, except that the amount of the crosslinking agent (PO-1) was changed to 2.05 parts by mass according to the formulation shown in Table 2 below. This Comparative Example 3 is a comparative example in which the degree of crosslinking of the resin crosslinked body obtained by crosslinking the resin composition is excessive.

[0082] 〔Comparative Examples 4 to 7〕 A comparative resin composition was obtained in the same manner as in Example 1, except that the type of the (co)polymer and the amount of the crosslinking agent (PO-1) were changed according to the formulation shown in Table 2 below. These Comparative Examples 4 to 7 are comparative examples in which a (co)polymer other than the ethylene-(meth)acrylate copolymer is used as the resin component.

[0083] <Manufacture of Resin Crosslinked Body (Crosslinking Reaction)> Each of the crosslinkable resin compositions obtained in Examples 1 to 6, 8 and Comparative Examples 1 to 7 was pressed at 180 ° C for 15 minutes using a hot press machine (manufactured by Toho Machinery, model TBD-50) to be crosslinked, and a sheet-like resin crosslinked body with a thickness of 1 mm was obtained.

[0084] Also, the crosslinkable resin composition obtained in Example 7 was pressed at 120 ° C for 5 minutes using a hot press machine (manufactured by Toho Machinery, model TBD-50) to obtain a sheet-like resin crosslinked body with a thickness of 1 mm. This was immersed in warm water at 80 ° C for 2 hours to be further crosslinked, and a resin crosslinked body was obtained.

[0085] 〔Example 9〕 The copolymer (EEA-5) was molded into a sheet with a thickness of 1 mm by pressing at 120 ° C for 5 minutes using a hot press machine (manufactured by Toho Machinery, model TBD-50). The obtained molded product was irradiated with an electron beam 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 using an electron beam irradiation device (manufactured by NHV Corporation, EPS-750 kV) to crosslink the copolymer (EEA-5) by electron beam irradiation, and a sheet-like resin crosslinked body was obtained.

[0086] [Example 10] A copolymer (EMMA) was formed into a 1-mm-thick sheet instead of the copolymer (EEA-5), and the copolymer (EMMA) was electron beam crosslinked by changing the irradiation dose to the obtained molded article to 200 kGy. A sheet-like resin crosslinked body was obtained in the same manner as in Example 9 except for this.

[0087] <Measurement of crosslinking temperature (T1)> For each of the crosslinkable resin compositions obtained in Examples 1 to 10, the crosslinking temperature (T1) was measured as follows. The results are also shown in Table 1 below.

[0088] (Measurement method) Both peroxide crosslinking and silane crosslinking have a temperature-dependent crosslinking reaction rate. 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 warm water or steam at normal pressure, but generally it is preferably carried out at 60 to 90°C. Therefore, in the silane crosslinking of Example 7, the temperature of the warm water when crosslinking progress was confirmed by warm water treatment was defined as the crosslinking temperature. In electron beam irradiation, crosslinking is carried out at room temperature or a temperature below the resin melting point, but generally crosslinking is promoted at a high temperature. Therefore, in the electron beam crosslinking of Examples 9 and 10, the material temperature when crosslinking progress was confirmed by electron beam irradiation was defined as the crosslinking temperature.

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

[0090] <Evaluation of heat distortion resistance of resin crosslinked body> Test pieces were prepared from the sheet-like resin crosslinked bodies obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 7, and using the test pieces, the heat distortion rate and the hot set (maximum elongation under load) were measured to evaluate the heat resistance of the resin crosslinked body. Here, if the heat distortion rate and the hot set are excessive, sufficient heat resistance cannot be exhibited. For example, in the case of cable applications, the resin is greatly deformed under high temperature conditions, which becomes a problem.

[0091] The measuring methods for the heat distortion rate and the hot set are as follows. As the evaluation criteria for heat resistance, when the heat distortion rate is 40% or less or the hot set is 175% or less, it is regarded as "qualified (○)", and when neither is satisfied, it is regarded as "unqualified (×)". The results are shown in Tables 1 and 2 below.

[0092] (Measurement method) (1) Measuring method for heat distortion rate of resin crosslinked body The heat distortion rate (reduction rate of thickness due to heating) was measured in accordance with JIS C3005 except that the above test pieces were used.

[0093] (2) Measuring method for hot set of resin crosslinked body The maximum elongation under load of the hot set was measured in accordance with JIS C3660-507 except that the above test pieces were used.

[0094] <Manufacture of recycled copolymer (depolymerization reaction)> For each of the sheet-like resin crosslinked bodies obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 7, a recycling 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 heating temperature of 350 °C for 2 minutes.

[0095] <Measurement of depolymerization temperature (T2)> For each resin crosslinked body obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 10, the de-crosslinking temperature (T2) was measured as follows.

[0096] (Measurement method) Using a rheometer (MCR302 manufactured by Anton Paar), a sample composed of a resin crosslinked body was measured for dynamic viscoelasticity while increasing the temperature from an initial temperature of 130 °C under the conditions of a constant frequency (angular frequency 0.1 rad / s, strain 1%), and the temperature at which the storage elastic modulus (G') and the loss elastic modulus (G") intersect (gelation point) was defined as the de-crosslinking temperature (T2).

[0097] (Evaluation of recyclability of resin crosslinked body) Regarding each of the sheet-like resin crosslinked bodies obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 10 and Comparative Examples 1 to 7, the recyclability of the resin crosslinked body was evaluated by measuring the crosslinking degree (gel fraction) after the regeneration treatment (350 °C × 2 minutes). As the evaluation criteria for recyclability, when the crosslinking degree of the regenerated product after the regeneration treatment (regenerated copolymer) is less than 15%, it is regarded as "qualified (○)", and when it is 15% or more, it is regarded as "unqualified (×)". If it is less than 15%, there are no lumps or roughness on the surface of the tape or strand made from the regenerated copolymer, and it can be molded with a good appearance. The results are shown in Tables 1 and 2 below.

[0098] [Table 1]

[0099] [Table 2]

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.

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%.

6. Crosslinking temperature (T 1 ) is in the range of 20 to 250 °C, Unloading bridge temperature (T 2 ) is in the range of 300 to 400 °C, The temperature difference (T 2 - T 1 ) is 50°C or higher. The crosslinkable resin composition according to claim 1.

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%), the crosslinking degree C (%) thereof 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, composed of crosslinked ethylene-ethyl acrylate (EEA).

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

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

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

12. The resin crosslinked body according to Claim 7, which, when heated at 350°C, has a crosslinking degree reduced 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, comprising: A method for producing a resin crosslinked body, comprising 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, comprising: A method for producing a recycled copolymer, comprising 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, comprising: 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 in the above step and 0 to 99% by mass of virgin ethylene-(meth)acrylate copolymer to prepare a resin component.

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