Method for producing ethylene-based copolymer and ethylene-based copolymer

Abstract

To provide a high-quality ethylenic copolymer useful as an adhesive for plastics and rubbers, a compatibilizer, a resin modifier, etc., and to provide a method for simply and efficiently producing the ethylenic copolymer from a crosslinked ethylene-vinyl acetate copolymer.SOLUTION: To provide a method for producing an ethylenic copolymer by subjecting a crosslinked ethylene-vinyl acetate copolymer to transesterification treatment using a solution composed of a solvent containing one or more fatty acid esters and an acid or alkali component.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a crosslinked resin, an ethylene copolymer made from waste plastics as a raw material, and a method for producing the ethylene copolymer. [Background technology]

[0002] Ethylene-vinyl acetate copolymer (EVA) is a type of polyethylene resin that excels in flexibility, transparency, and adhesive properties. Due to its usefulness, it is used in a wide range of products and packaging, including films, sheets, adhesives, toys, mats, and insoles. Meanwhile, promoting the recycling of plastics is becoming increasingly important amid calls for achieving carbon neutrality and strengthening efforts to address marine plastic waste and climate change. Furthermore, crosslinking ethylene-vinyl acetate copolymer improves its mechanical properties, transparency, heat resistance, and other properties, making it suitable for use in crosslinked foams and solar panel encapsulants. However, crosslinked products do not melt and are difficult to process, making them difficult to recycle. Furthermore, chemical recycling, which uses naphtha synthesized by thermal decomposition of waste plastic (hereinafter sometimes abbreviated as waste plastic) as a raw material to produce polyethylene (PE) and polypropylene (PP) using naphtha crackers and polymerization plants, is also capable of recycling cross-linked and degraded waste plastic. Furthermore, because plastic is synthesized from raw materials such as monomers and oligomers, the recycled products have the advantage of being of the same quality as virgin products. However, the long and complex recycling process has been criticized as being economically unreasonable. Meanwhile, solar power generation has rapidly increased since the introduction of the Feed-in Tariff (FIT) system for renewable energy in 2012. However, solar panels have a product lifespan of approximately 25 to 30 years, and it is predicted that a large amount of waste, including solar panels, will be generated around 2040, raising concerns about abandoned or illegal dumping and the shortage of disposal sites.

[0003] Furthermore, since solar panels use cross-linked EVA as a sealant for the cells, techniques have been proposed for separating the sealant made of cross-linked EVA from the glass panel (see, for example, Patent Documents 1 to 5).

[0004] It is generally known that ethylene-vinyl acetate copolymer can be converted to ethylene-vinyl alcohol copolymer by hydrolysis using a base, acid, alcohol, ester, catalyst, or the like, and the ethylene-vinyl alcohol copolymer is used as an adhesive, compatibilizer, resin modifier, or the like. In particular, the hydrolysis reaction using a base is called saponification (see, for example, Patent Document 6). Furthermore, a resin composition for a hot-melt adhesive, characterized by containing a saponified product of a crosslinked ethylene-vinyl acetate copolymer, has been proposed (see, for example, Patent Document 7). Furthermore, a method for producing an ethylene-vinyl alcohol copolymer has been proposed (see, for example, Patent Document 8), characterized by mixing an ethylene-vinyl acetate copolymer with water and / or alcohol and reacting the mixture in a supercritical or subcritical fluid. Furthermore, in a solvent containing an alcohol as the main component, in the absence of a catalyst, at a temperature of the critical temperature (Tc) of the solvent + 5°C to 295°C, a pressure of the critical pressure (Pc) of the solvent to 40 MPa, and a fluid density at the start of the reaction of 0.1 to 0.4 g / cm. 3 A method for producing a vinyl alcohol polymer has been proposed (see, for example, Patent Document 9), which comprises saponifying a vinyl ester polymer by a process comprising: (a) mixing a vinyl alcohol polymer with a vinyl ester polymer by a process comprising: (i) saponifying a vinyl ester polymer by a process comprising: (a) mixing a vinyl alcohol polymer with a vinyl ester polymer by a process comprising: (i) saponifying a vinyl ester polymer by a process comprising: (a) saponifying ...ii) saponifying a vinyl ester polymer by a process comprising: (ii) saponifying a vinyl ester polymer by a process comprising: (i) saponifying a vinyl ester polymer by a process comprising: (ii) saponifying a vinyl ester polymer by a process comprising: (i) saponifying a vinyl ester polymer by a process comprising: (ii) saponifying a vinyl [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 203026 [Patent Document 2] Patent No. 6599469 [Patent Document 3] Patent No. 6068948 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-214058 [Patent Document 5] Japanese Patent Application Laid-Open No. 2015-229126 [Patent Document 6] Japanese Patent Application Publication No. 55-5942 [Patent Document 7] Patent No. 6855820 [Patent Document 8] Japanese Patent Application Laid-Open No. 2006-028459 [Patent Document 9] Patent No. 4132467 [Patent Document 10] Patent No. 4081454 Summary of the Invention [Problem to be solved by the invention]

[0006] The techniques proposed in Patent Documents 1 to 5 for peeling a crosslinked EVA encapsulant containing cells from a glass panel merely involve burning, crushing, or gravity separation of the peeled crosslinked EVA encapsulant, but do not mention recycling the EVA. Furthermore, Patent Document 6 proposes a method for producing an ethylene-vinyl acetate copolymer, but does not mention recycling the crosslinked EVA. Patent Document 7 proposes a resin composition for hot-melt adhesives containing a saponified crosslinked ethylene-vinyl acetate copolymer, but the crosslinked ethylene-vinyl acetate copolymer has a low degree of crosslinking and is not suitable for use as an encapsulant for crosslinked foams or solar panels, and does not mention recycling the crosslinked EVA. Patent Document 8 proposes a method for producing an ethylene-vinyl alcohol copolymer, which involves mixing an ethylene-vinyl acetate copolymer with water and / or alcohol and reacting the mixture in a supercritical or subcritical fluid, but does not mention a method for producing a saponified EVA, i.e., an ethylene-vinyl alcohol copolymer, using crosslinked EVA as a raw material. Furthermore, in the method for producing a vinyl alcohol polymer proposed in Patent Document 9, saponification is performed on vinyl acetate units in polyvinyl acetate, and there is no mention of saponification using crosslinked EVA as a raw material. And in the method for treating a polymer compound proposed in Patent Document 10, only crosslinked polymers, synthetic polymer compounds such as thermosetting resins such as plastics and elastomers, natural polymer compounds such as lignin, cellulose, and proteins, or mixtures of synthetic polymer compounds and natural polymer compounds are mentioned as polymer compounds, and there is no mention of saponification using crosslinked EVA as a raw material.

[0007] Furthermore, there have been no reports to date on a method for producing an ethylene copolymer in which crosslinked EVA or used crosslinked EVA is converted into a thermoplastic resin having an aliphatic carboxylic acid substituent by transesterification, or on the structure of the ethylene copolymer obtained thereby.

[0008] Therefore, an object of the present invention is to provide a high-quality novel ethylene-based copolymer obtained by simply and efficiently transesterifying a crosslinked ethylene-vinyl acetate copolymer, such as crosslinked EVA-containing processing waste generated during crosslinking or molding, a used or discarded crosslinked foam containing crosslinked EVA, or a crosslinked EVA encapsulant separated from a solar panel, and a method for producing the ethylene-based copolymer. More specifically, an object of the present invention is to provide a novel ethylene-based copolymer useful as an adhesive, compatibilizer, resin modifier, etc. for plastics and rubber, and a method for producing the novel ethylene-based copolymer.

[0009] Increasing the efficiency of reuse, regeneration, conversion into raw materials, and oil conversion of molded and used resins and molded bodies will contribute to the promotion of inclusive and sustainable industrialization, and is one of the technologies necessary for a sustainable society, such as the SDGs that have been called for in recent years. [Means for solving the problem]

[0010] As a result of intensive investigations aimed at solving the above problems, the present inventors have found that a high-quality novel ethylene-based copolymer can be produced simply and efficiently by transesterifying a crosslinked ethylene-vinyl acetate copolymer, and have thus completed the present invention.

[0011] That is, the embodiments of the present invention are [1] to [6] shown below. [1] A method for producing an ethylene copolymer, which comprises transesterifying a crosslinked ethylene-vinyl acetate copolymer using a solution containing one or more fatty acid esters and an acid or alkali component. [2] The method for producing an ethylene copolymer according to [1], wherein the crosslinked ethylene-vinyl acetate copolymer has a gel fraction of 1 to 100% by weight and a vinyl acetate residue unit content of 2.0 to 25.0% by mole. [3] The method for producing an ethylene-based copolymer according to [1] or [2], wherein the cross-linked ethylene-vinyl acetate copolymer contains 50% by weight or more of a material derived from processing waste materials generated during cross-linking treatment or molding, used or discarded cross-linked foam, or encapsulant recovered from solar panels. [4] The method for producing an ethylene copolymer according to any one of [1] to [3], wherein the alkali component is sodium hydroxide, potassium hydroxide, lithium hydroxide, or an alkali metal alcoholate having 8 or less carbon atoms. [5] An ethylene-fatty acid vinyl ester-vinyl alcohol copolymer having an ethylene residue, a structural unit represented by the following general formula (1), and a structural unit represented by the following general formula (2), which satisfies the following requirements (1) to (5):

[0012] [ka]

[0013] [ka]

[0014] (wherein R1 is a hydrocarbon group having 1 to 30 carbon atoms) (1) 2.0 to 25.0 mol % of the structural unit represented by general formula (1), (2) the structural unit represented by general formula (2) is 0.1 to 25.0 mol %, (3) A melt mass flow rate of 0.01 to 2,000 g / 10 min at 190°C and a load of 21.18 N, as measured in accordance with JIS K6924-2; (4) Weight average molecular weight (Mw) is 15,000 to 300,000; (5) The molecular weight distribution (the ratio of Z-average molecular weight to number-average molecular weight (Mz / Mn)) satisfies the requirement of the following general formula (3).

[0015] Mz / Mn≦0.09×MW 2 -0.25×MW+5.5 (3) (Here, MW stands for weight average molecular weight divided by 10,000.) [6] The ethylene copolymer according to [5], which satisfies the following requirements (6) to (7): (6) The ratio of the structural unit represented by the general formula (1) to the structural unit represented by the general formula (2) is an aliphatic vinyl / vinyl alcohol unit ratio of 1 or more; (7) Gel fraction is 0 to 20 wt%. [Effects of the Invention]

[0016] The present invention provides a novel high-quality ethylene-based copolymer obtained by simply and efficiently subjecting a crosslinked ethylene-vinyl acetate copolymer to transesterification, and a method for producing the ethylene-based copolymer. The ethylene-based copolymer is useful as an adhesive, compatibilizer, resin modifier, or the like for plastics and rubber. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an IR spectrum diagram of the raw material ethylene-vinyl acetate copolymer (uncrosslinked) used in Example 1 of the present invention. [Figure 2] 1 is a diagram comparing the IR spectra of the raw material ethylene-vinyl acetate copolymer (uncrosslinked) used in Example 1 of the present invention and the ethylene copolymer obtained in Example 1. FIG. [Figure 3] FIG. 1 is a 1H-NMR chart of the ethylene copolymer of Example 1 of the present invention. [Figure 4] FIG. 1 is an enlarged view of a 1H-NMR chart of the ethylene copolymer of Example 1 of the present invention. [Figure 5] FIG. 1 is a GPC chart showing the raw material ethylene vinyl acetate copolymer (uncrosslinked) and the ethylene copolymer after crosslinking reaction and transesterification treatment in Example 1 of the present invention. [Figure 6] FIG. 1 is a diagram comparing IR spectra of the ethylene copolymer obtained in Example 5 of the present invention and the commercially available ethylene-vinyl acetate copolymer used as the raw material in Example 1. [Figure 7] FIG. 1 is a 1H-NMR chart of the ethylene copolymer of Example 5 of the present invention. [Figure 8]FIG. 1 is a GPC chart showing the raw material ethylene vinyl acetate copolymer (uncrosslinked) of Example 5 of the present invention and the ethylene copolymer obtained in Example 5 after the crosslinking reaction and transesterification treatment. [Figure 9] FIG. 1 is a diagram showing the Mw-Mw / Mn relationship between the ethylene copolymer of the present invention, a commercially available ethylene-vinyl acetate copolymer, and a saponified ethylene-vinyl acetate copolymer. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below.

[0019] A method for producing an ethylene-based copolymer, which is one aspect of the present invention, is a production method that promotes transesterification of a crosslinked ethylene-vinyl acetate copolymer using a solution containing one or more fatty acid esters and an acid or alkali component, and is simple and enables efficient production of an ethylene-based copolymer.

[0020] The crosslinked ethylene-vinyl acetate copolymer preferably has a gel fraction of 1 to 100% by weight and a vinyl acetate residue unit content of 2.0 to 25.0 mol %, since this provides an ethylene-based copolymer with excellent properties and is easy to produce.

[0021] The vinyl acetate residue unit of the crosslinked ethylene-vinyl acetate copolymer is preferably in the range of 2.0 to 25.0 mol %, particularly preferably in the range of 2.5 to 20.0 mol %, since it is possible to produce an ethylene-based copolymer that can be used as an adhesive, compatibilizer, resin modifier, etc., having excellent transparency, heat resistance, flexibility, adhesiveness, etc.

[0022] The present invention is also effective in recycling waste plastics, and examples of cross-linked ethylene-vinyl acetate copolymer (cross-linked EVA) include cross-linked EVA (so-called recycled products) derived from processing scraps, process loss, work-in-progress, non-standard products, and discarded products generated during cross-linking and molding, used or discarded agricultural sheets, packaging and cushioning materials made of cross-linked EVA, cushioning materials used in sandals and shoe soles, cross-linked foam sheets, cross-linked foams, and sealants recovered from solar panels. Among these, cross-linked EVA (so-called recycled products) derived from process loss, work-in-progress, non-standard products, and discarded products, cross-linked foams made of cross-linked EVA, and solar panel sealants are preferred, particularly because of the ease of ensuring stable quality and stable supply.

[0023] The crosslinked EVA may be in the form of not only pellets or powder, but also films, sheets, bottles, fibers, pipes, injection-molded products, wire coating materials, and other molded products, foams, and crushed products thereof. The crosslinked EVA can be used as is, but is preferably crushed or pulverized into fine particles before use. Crushing or pulverization can be performed using a conventional crusher or pulverizer, or shear crushing using an extruder. Freezing and crushing is also preferably used, and freezing and crushing is preferably performed at a temperature of -150 to -100°C.

[0024] The crosslinked EVA may contain other plastics or rubbers, light stabilizers, ultraviolet absorbers, nucleating agents, lubricants, antioxidants, antiblocking agents, flow improvers, mold release agents, flame retardants, flame retardant assistants, inorganic neutralizing agents, chlorine absorbers, inorganic fillers, organic fillers, conductive agents, dyes, organic pigments, inorganic pigments, inorganic reinforcing agents, plasticizers, waxes, antistatic agents, antifogging agents, antifogging agents, rust inhibitors, ion trapping agents, etc. In such cases, the components may be in a mixed state by dissolving with each other, or may be in a physically mixed state in the form of solid contents such as pellets or scraps.

[0025] The content of the crosslinked EVA is preferably 50% by weight or more, and particularly preferably 60% by weight or more, in order to obtain a saponified ethylene-vinyl acetate copolymer and a composition thereof with stable quality.

[0026] The fatty acid ester is not particularly limited, and the ester group is not particularly limited, but typically, an alkyl ester having 1 to 8 carbon atoms or an aralkyl ester having 7 to 12 carbon atoms is used, preferably an alkyl ester having 1 to 6 carbon atoms, and more preferably an alkyl ester having 1 to 4 carbon atoms. For example, melissic acid ester, montanic acid ester, cerotic acid ester, lignoceric acid ester, behenic acid ester, arachidic acid ester, n-nonadecylenic acid ester, stearic acid ester, margaric acid ester, palmitic acid ester, n-pentadecylenic acid ester, myristate, n-tridecylenic acid ester, lauric acid ester, n-undecylenic acid ester, capric acid ester, pelargonic acid ester, caprylic acid ester, heptanoic acid ester, caproic acid ester, valeric acid ester, butanoic acid ester, propionic acid ester, acetate ester, or formate ester. and unsaturated fatty acid esters and structural isomers thereof, such as acrylates, butenoates, crotonates, isocrotonic acids, vinyl acetate esters, methacrylates, pentenoates, angelic acids, tiglic acids, 2-pentenoates, 3-pentenoates, hexenoates, heptenoates, octenoates, undecenoates, dodecenoates, tetradecenoates, hexadecenoates, octadecenoates, and pentadienoates. Preferred are stearates, caproates, butanoates, acetates, formates, acrylates, and methacrylates, and more preferred are butanoates, propionates, and acetates.

[0027] Specific examples of the butanoate ester include methyl butanoate, ethyl butanoate, propyl butanoate, isopropyl butanoate, butyl butanoate, isobutyl butanoate, sec-butyl butanoate, pentyl butanoate, isopentyl butanoate, sec-hexyl butanoate, cyclohexyl butanoate, and benzyl butanoate. Preferred are methyl butanoate, ethyl butanoate, propyl butanoate, isopropyl butanoate, butyl butanoate, isobutyl butanoate, sec-butyl butanoate, pentyl butanoate, isopentyl butanoate, sec-hexyl butanoate, and cyclohexyl butanoate. More preferred are methyl butanoate, ethyl butanoate, propyl butanoate, isopropyl butanoate, butyl butanoate, and isobutyl butanoate, and most preferred is ethyl butanoate.

[0028] Specific examples of the propionic acid ester include methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, butyl propionate, isobutyl propionate, sec-butyl propionate, pentyl propionate, isopentyl propionate, sec-hexyl propionate, cyclohexyl propionate, and benzyl propionate. Preferred are methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, butyl propionate, isobutyl propionate, sec-butyl propionate, pentyl propionate, isopentyl propionate, sec-hexyl propionate, and cyclohexyl propionate. More preferred are methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, butyl propionate, and isobutyl propionate, and most preferred is ethyl propionate.

[0029] Specific examples of the acetate ester include methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, sec-butyl acetate, pentyl acetate, isopentyl acetate, sec-hexyl acetate, cyclohexyl acetate, and benzyl acetate. Preferred are methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, sec-butyl acetate, pentyl acetate, isopentyl acetate, sec-hexyl acetate, and cyclohexyl acetate. More preferred are methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, and isobutyl acetate, and most preferred is methyl acetate or ethyl acetate.

[0030] Specific examples of the formate ester include methyl formate, ethyl formate, propyl formate, isopropyl formate, butyl formate, isobutyl formate, sec-butyl formate, and pentyl formate. Preferred are methyl formate, ethyl formate, propyl formate, butyl formate, isobutyl formate, and pentyl formate. Most preferred is ethyl formate. Examples of the acid component include inorganic acids such as sulfuric acid, nitric acid, phosphoric acid, and hydrofluoric acid, as well as formic acid, acetic acid, citric acid, and benzoic acid.

[0031] Examples of the acid component include mineral acids and oxo acids, such as sulfuric acid, hydrochloric acid, and hydrogen bromide. Examples of suitable acid include sulfuric acid, hydrochloric acid, phosphoric acid, fluorosulfonic acid, boric acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, formic acid, acetic acid, and butanoic acid. Particularly preferred are sulfuric acid, hydrochloric acid, phosphoric acid, formic acid, and acetic acid, which are easily available industrially and inexpensively.

[0032] Examples of the alkaline component include alkali metal or alkaline earth metal compounds, and alkali metal alkoxides, such as lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, magnesium hydroxide, and calcium hydroxide, as well as alkali metal alkoxides such as lithium methoxide, sodium methoxide, potassium methoxide, lithium ethoxide, sodium ethoxide, potassium ethoxide, lithium propoxide, sodium propoxide, potassium propoxide, lithium t-butoxide, sodium t-butoxide, potassium t-butoxide, lithium phenoxide, sodium phenoxide, and potassium phenoxide. Particularly preferred are strong alkalis such as sodium hydroxide and potassium hydroxide, and alkali metal alkoxides having 8 or less carbon atoms which are easily soluble in organic solvents, such as lithium methoxide, sodium methoxide, potassium methoxide, lithium ethoxide, sodium ethoxide, potassium ethoxide, lithium propoxide, sodium propoxide, potassium propoxide, lithium t-butoxide, sodium t-butoxide, and potassium t-butoxide.

[0033] The amount of the acid or alkali component used is 0.01 to 100% by weight, preferably 0.5 to 25% by weight, based on the crosslinked EVA.

[0034] Furthermore, not only one type of acid component but two or more types of acid components can be used, and not only one type of alkaline component but also two or more types of alkaline components can be used.

[0035] When using an acid component or an alkali component, a solvent such as alcohol, aliphatic hydrocarbon, ether compound, or aromatic hydrocarbon can be used as a reaction aid to facilitate handling or to accelerate the reaction. The use of an alcohol solvent is particularly useful for improving production efficiency because it accelerates the progress of the reaction.

[0036] The alcohol solvent is not particularly limited as long as it is an industrially available alcohol, but those having 1 to 8 carbon atoms are preferably used, and examples thereof include methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, isobutanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, pentanol and its isomers, hexanol and its isomers, heptanol and its isomers, octanol and its isomers, decanol and its isomers, etc. In particular, those having 4 or less carbon atoms that can be efficiently recycled and handled during production, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, isobutanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, and 1,2-butanediol, are mentioned. The solvent containing one or more alcohols may contain at least one of these, and may also contain aliphatic hydrocarbons, ether compounds, aromatic hydrocarbon compounds, etc. in addition to alcohols. Examples of aliphatic hydrocarbons include butane, n-pentane, isopentane, n-hexane, 2-methylpentane, heptane, octane, cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, and petroleum ethers. Examples of ether compounds include dimethyl ether, diethyl ether, methylbutyl ether, diisopropyl ether, diamyl ether, tetrahydrofuran, furan, and dioxane. Examples of aromatic hydrocarbon compounds include benzene, toluene, xylene, ethylbenzene, and methylethylbenzene.

[0037] Furthermore, by conducting transesterification using an acid or alkali as a catalyst in a mixed solvent of the alcohol and an aliphatic hydrocarbon having 5 to 8 carbon atoms, the raw material crosslinked EVA and the resulting ethylene-based copolymer do not fuse together during the reaction, and they swell well, allowing the transesterification reaction to proceed uniformly, resulting in the efficient production of an ethylene-based copolymer with excellent transparency. Examples of the aliphatic hydrocarbon having 5 to 8 carbon atoms include n-pentane, isopentane, cyclopentane, n-hexane, 2-methylpentane, methylcyclopentane, cyclohexane, n-heptane, 2-methylhexane, 3-methylhexane, methylcyclohexane, n-octane, and 2,2,4-trimethylpentane, and these can be added alone or in combination. Furthermore, the amount of the aliphatic hydrocarbon having 5 to 8 carbon atoms added is preferably 0.01 to 50 times the amount of the alcohol, and particularly preferably 0.05 to 30 times the amount of the alcohol. Furthermore, instead of the aliphatic hydrocarbons having 5 to 8 carbon atoms, ether compounds having 4 to 10 carbon atoms such as diethyl ether, dipropyl ether, dibutyl ether, cyamyl ether, tetrahydrofuran, furan, and dioxane, or aromatic hydrocarbon compounds such as benzene, toluene, xylene, ethylbenzene, cumene, and methylethylbenzene can also be used.

[0038] Furthermore, the addition of conventional color inhibitors during the transesterification reaction to prevent coloration of crosslinked EVA does not prevent the effects of the present invention. Examples of such color inhibitors include ammonia, ammonia derivatives, aliphatic amines, acetone, and chlorine-based oxidizing agents. Examples of chlorine-based oxidizing agents include sodium hypochlorite, lithium hypochlorite, calcium hypochlorite, chlorine dioxide, trichloroisocyanuric acid, dichloroisocyanuric acid, sodium dichloroisocyanurate, and potassium dichloroisocyanurate. Examples of ammonia derivatives include ammonium salts of inorganic acids such as ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium nitrate, ammonium phosphate, diammonium phosphate, triammonium phosphate, and ammonium sulfate; ammonium salts of organic acids such as ammonium xanthanate, ammonium oxalate, ammonium tartrate, and ammonium citrate; hydroxylamine; hydrazine; urea; and urea derivatives.

[0039] The concentration of the crosslinked EVA in the solvent during the transesterification reaction is usually preferably 5 to 80% by weight, and particularly preferably 10 to 60% by weight.

[0040] The transesterification of the crosslinked ethylene-vinyl acetate copolymer is usually carried out at a temperature in the range of 30 to 300°C, more preferably 45 to 300°C. The transesterification time is usually 1 to 300 minutes, and the transesterification apparatus can be either continuous or batchwise. If a solid component is generated after the transesterification, the solid component may contain alkali, by-product salts, other impurities, etc., and it is therefore preferable to remove these by neutralization and washing as necessary.

[0041] In the above-mentioned method for producing an ethylene copolymer, an ethylene-fatty acid vinyl ester-vinyl alcohol copolymer having an ethylene residue and a residue of the following general formula (1) or (2) can be produced.

[0042] [ka]

[0043] [ka]

[0044] (wherein R1 is a hydrocarbon group having 1 to 30 carbon atoms.) The ethylene copolymer according to one embodiment of the present invention is an ethylene-fatty acid vinyl ester-vinyl alcohol copolymer having the above-mentioned ethylene residue and residues of general formulas (1) and (2), and satisfies the requirements (1) to (5). (1) 2.0 to 25.0 mol % of the structural unit represented by general formula (1), (2) the structural unit represented by general formula (2) is 0.1 to 25.0 mol %, (3) A melt mass flow rate of 0.01 to 2,000 g / 10 min at 190°C and a load of 21.18 N, as measured in accordance with JIS K6924-2. (4) Weight average molecular weight (Mw) of 15,000 to 300,000; (5) The molecular weight distribution (the ratio of Z-average molecular weight to number-average molecular weight (Mz / Mn)) satisfies the requirement of general formula (3).

[0045] Mz / Mn≦0.09×MW 2 -0.25×MW+5.5 (3) (Here, MW stands for weight average molecular weight divided by 10,000.) It is preferable that the following is satisfied.

[0046] The constitutional units represented by the general formulae (1) and (2) in the ethylene copolymer can be measured by any known method, and can be determined by a method for measuring by nuclear magnetic resonance spectroscopy.

[0047] R1 in the general formula (1) of the ethylene copolymer is not particularly limited as long as it is a hydrocarbon group having 1 to 30 carbon atoms, and examples thereof include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, alkyl groups having 9 to 30 carbon atoms and their structural isomers, cyclopentyl, cyclohexyl, methylcyclopentyl, methylcyclohexyl, and their structural isomers. R1 may also contain multiple types of hydrocarbon groups, for example, two different alkyl groups such as methyl and ethyl, or methyl and propyl, or a combination of three or four types such as methyl, ethyl, propyl, or pentyl, and the ratio and combination may be any value. R1 may also have a crosslinked structure with another R1, or a crosslinked structure may exist between R1 and a carbon atom in the main chain.

[0048] The constituent unit of the ethylene copolymer represented by general formula (1) is in the range of 2.0 to 25.0 mol % because the ethylene copolymer can be effectively used as an adhesive, compatibilizer, resin modifier, etc., which has excellent transparency, heat resistance, flexibility, adhesiveness, etc., and is preferably in the range of 2.5 to 20.0 mol % because it has excellent strength and elasticity.

[0049] Furthermore, the constituent unit of the ethylene copolymer represented by general formula (2) is preferably in the range of 0.1 to 25.0 mol %, particularly preferably in the range of 0.5 to 10.0 mol %, since the ethylene copolymer can be effectively used as an adhesive, compatibilizer, resin modifier, etc., which has excellent transparency, heat resistance, flexibility, adhesiveness, etc.

[0050] The aliphatic vinyl / vinyl alcohol unit ratio, which is the ratio of the structural unit represented by general formula (1) to the structural unit represented by general formula (2) of the ethylene copolymer, is preferably 1 or more in order to provide excellent flexibility, rigidity, strength, moisture absorption, and weather resistance, and is particularly preferably 3 or more in order to provide excellent flexibility, rigidity, and weather resistance.

[0051] The melt mass flow rate of the ethylene copolymer is measured in accordance with JIS K6924-2 at 190°C and a load of 21.18 N. The melt mass flow rate is in the range of 0.01 to 2,000 g / 10 min because the ethylene copolymer can be effectively used as an adhesive, compatibilizer, resin modifier, etc. that is excellent in transparency, heat resistance, flexibility, adhesion, etc., and can exhibit strength and properties, and is preferably in the range of 0.2 to 500 g / 10 min because it provides an excellent balance between processability and strength.

[0052] The weight-average molecular weight (Mw) and molecular weight distribution of the ethylene copolymer, i.e., the ratio of Z-average molecular weight to number-average molecular weight (Mz / Mn), can be determined by gel permeation chromatography (GPC). The weight-average molecular weight (Mw) is preferably in the range of 15,000 to 300,000 in view of the balance between processability and product properties.

[0053] The ethylene copolymer is preferably one represented by formula (3) because it has excellent mechanical strength and processability as a thermoplastic resin. If it falls within the range of formula (3), it can be used as a normal thermoplastic resin and also becomes an excellent new material that combines unprecedented mechanical strength and processability with the resin properties provided by fatty acid esters and hydroxyl groups.

[0054] The right-hand equation of formula (3) defines the region through which the Mw-Mw / Mn curves in the examples described below pass, and is a numerical representation, by the least squares method, of the upper limit curve for the region in which differences were observed compared with commercially available ethylene-vinyl acetate copolymers and saponified ethylene-vinyl acetate copolymers. The Mw-Mw / Mn curves of the ethylene-vinyl acetate copolymers and saponified ethylene-vinyl acetate copolymers used for comparison are shown in Figure 9.

[0055] The vinyl alcohol residue units of the ethylene copolymer can be determined by a known NMR method.

[0056] The gel fraction of an ethylene copolymer is calculated by adding 50 mg of polymer to 50 ml of xylene, dissolving it at 120°C for 12 hours, filtering the solution through a 200-mesh stainless steel mesh (75 μm), and drying the unmelted portion on the wire mesh at 105°C for 5 hours.

[0057] The ethylene copolymer preferably has a gel fraction of 0 to 20% by weight, as this facilitates recycling as a thermoplastic resin. If the gel fraction is 20% by weight or less, it can be used as a normal thermoplastic resin. Furthermore, a gel fraction of 15% by weight or less is preferable, as this improves processability. In particular, a gel fraction of 5% by weight or less is even more preferable, as it can be used in applications where commercially available ethylene-vinyl acetate copolymers are used, as it can be adapted to a wider range of uses.

[0058] The ethylene copolymer according to one embodiment of the present invention can be used as a composition for adhesives such as hot-melt adhesives, compatibilizers, resin modifiers, etc., and can be molded into a sheet, film, pipe, block, or any other shape by methods such as extrusion molding, blow molding, sheet molding, injection molding, compression molding, calendar molding, vacuum molding, air-cooled inflation molding, water-cooled inflation molding, and cast molding. [Example]

[0059] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. It is not something that is done. <Gel fraction measurement> 50 mg of polymer was added to 50 mL of xylene and dissolved at 120°C for 12 hours. The solution was then filtered through a 200-mesh stainless steel mesh (75 μm), and the unmelted portion on the wire mesh was dried at 105°C for 5 hours to calculate the mass fraction. <Measurement of Saponification Degree> It was calculated according to the following formula.

[0060] Degree of saponification (wt%) = 100 × {(acetic acid of ethylene-vinyl acetate copolymer before hydrolysis)} Vinyl content (wt%) - (Vinyl acetate content of ethylene-vinyl acetate copolymer after hydrolysis) Vinyl acetate content (wt%)} / (Vinyl acetate content of ethylene-vinyl acetate copolymer before hydrolysis (weight%)) <Vinyl acetate residue content in ethylene-vinyl acetate copolymer> Measurements were made in accordance with JIS K7192 (1999). <Aliphatic vinyl residue content> Using a known NMR method, 1H-NMR was measured and the ratio was calculated from the peak area ratio. <Vinyl alcohol residue content> Using a known NMR method, 1H-NMR was measured and the ratio was calculated from the peak area ratio. <Melt Mass Flow Rate (MFR)> Measurements were made in accordance with JIS K6922-1 (1997). <Molecular weight> The molecular weight was measured using a GPC system (Tosoh Corporation (trade name) HLC-8121GPC / HT) and a column (Tosoh Corporation (trade name) TSKgel® GMHhr-H(20)HT) at a column temperature of 140°C and 1,2,4-trichlorobenzene as the eluent. The measurement sample was prepared at a concentration of 1.0 mg / ml, and 0.3 ml was injected for measurement. The molecular weight calibration curve was calibrated using a polystyrene sample with a known molecular weight. From the measurement results, the Z-average molecular weight Mz, number-average molecular weight Mn, and weight-average molecular weight Mw were determined from the obtained chromatogram. <Recyclability> The ethylene copolymer obtained in each example was freeze-pulverized and melt-kneaded using a twin-screw extruder with a screw diameter of 11 mm (Fisher Scientific, trade name Process 11, multi-function small twin-screw extruder) at a resin temperature of 160°C and a screw rotation speed of 100 rpm to obtain strands. The surface of the obtained strand was visually observed, and if no protruding foreign matter was found, it was evaluated as having excellent recyclability (◯), and if there was a significant amount of protruding foreign matter, it was evaluated as having poor recyclability (×). If a small amount of such foreign matter was found, it was evaluated as (△).

[0061] Example 1 100 g of a commercially available ethylene-vinyl acetate copolymer (vinyl acetate content 11.2 mol%) was mixed with 1 g of a cross-linking agent (Perhexa C) and heated and kneaded in a calendar molding machine at 180°C for 10 minutes to produce 100 g of a cross-linked ethylene-vinyl acetate copolymer with a gel fraction of 73 wt%.

[0062] Next, 10 g of the resulting cross-linked ethylene-vinyl acetate copolymer and 200 mL of methyl acetate were placed in a 1.1 L stainless steel vessel equipped with a stirrer and stirred vigorously. Next, an alkali component was prepared in a separate vessel by dissolving 100 mg of sodium methoxide in 0.4 mL of methanol. This was then transferred to the stainless steel vessel using a microsyringe and allowed to react for 16 hours with stirring at an internal temperature of 56–58°C. After the reaction was completed, the contents were poured into 10 L of a 1% dilute hydrochloric acid / methanol solution to recover 9.4 g of solid component (A). The resulting mass was freeze-pulverized and washed with a large amount of methanol and then water. Solid component (A) was confirmed to be an ethylene-fatty acid vinyl ester-vinyl alcohol copolymer based on its IR spectrum (the raw material EVA is shown by the dashed line in Figure 1; the resulting ethylene-based polymer is shown by the solid line in Figure 2; for reference, the raw material EVA is also shown by the dashed line in Figure 2) and NMR spectrum (the resulting ethylene-based polymer is shown in Figure 3). A comparison of the ethylene-vinyl acetate copolymer before crosslinking (vinyl acetate residue content 11.2 mol%, gel fraction 1 wt% or less) with the resulting ethylene copolymer (vinyl acetate residue content 7.7 mol%, vinyl alcohol residue content 3.5 mol%, aliphatic vinyl / vinyl alcohol unit ratio 2.2, gel fraction 2 wt%) revealed that the white solid obtained in Example 1 exhibited carbonyl groups and main chain (CH2) vibrations similar to the raw material, but also showed a different absorption pattern and newly detected hydroxyl groups, indicating that it was not the same substance (Figures 1 and 2). The presence of ethyl, acetoxy, and hydroxyl groups was also confirmed by H-NMR analysis, indicating that the white solid obtained in Example 1 is similar to a copolymer of ethylene, vinyl acetate, and vinyl alcohol (FIG. 3, enlarged view in FIG. 4). Furthermore, the MFR measurement was 0.1 g / 10 min (measured at 190°C), and GPC measurements (Figure 5) showed Mz 940,000, Mn 41,000, and Mw 200,000. The molecular weight distribution (Mz / Mn) was 23, which is smaller than the value of 36.5 calculated from the weight-average molecular weight using equation (3), and therefore satisfies the conditions of equation (3).

[0063] Visual observation of the strand surface obtained in the molding test using the twin-screw kneader revealed no protruding foreign matter, and the recyclability was evaluated as good (◯).

[0064] Example 2 The same reaction as in Example 1 was carried out, except that methyl acetate was changed to methyl butanoate and the reaction temperature was changed to 102°C.

[0065] H-NMR analysis of the resulting white solid (yield: 111 g, 103%) confirmed the presence of alkyl groups, vinyl butanoate residues, and vinyl alcohol residues, indicating that the white solid obtained in Example 2 was an ethylene-based copolymer, which is a copolymer of ethylene, vinyl acetate, vinyl butanoate, and vinyl alcohol (FIGS. 6 and 7). The resulting ethylene copolymer had a vinyl butanoate residue content of 9.9 mol%, a vinyl alcohol residue content of 1.3 mol%, an aliphatic vinyl / vinyl alcohol unit ratio of 7.3, a gel fraction of 1 wt% or less, an MFR of 250 g / 10 min (measured at 190°C), Mz of 88,000, Mn of 18,000, and Mw of 43,000. The molecular weight distribution (Mz / Mn, Figure 8) was 5, which is smaller than the value of 6.1 calculated from the weight-average molecular weight by equation (3), satisfying the conditions of equation (3). The recyclability was also evaluated as good (○).

[0066] Example 3 The same reaction as in Example 1 was carried out, except that methyl acetate was changed to ethyl acetate, the reaction temperature was changed to 77°C, and the reaction time was changed to 6 hours.

[0067] The obtained ethylene copolymer had a vinyl acetate residue content of 8.5 mol%, a vinyl alcohol residue content of 2.7 mol%, an aliphatic vinyl / vinyl alcohol unit ratio of 3.2, a gel fraction of 1 wt% or less, an MFR of 4.0 g / 10 min (measured at 190°C), Mz of 490,000, Mn of 39,000, and Mw of 150,000, and a molecular weight distribution (Mz / Mn) of 13, which is smaller than the value of 22 calculated from the weight-average molecular weight by equation (3), satisfying the conditions of equation (3). The recyclability was also evaluated as good (○).

[0068] Example 4 The same reaction as in Example 3 was carried out, except that 20 mL of xylene was added as the solvent.

[0069] The resulting ethylene copolymer had a vinyl acetate residue content of 8.3 mol%, a vinyl alcohol residue content of 2.9 mol%, an aliphatic vinyl / vinyl alcohol unit ratio of 2.8, a gel fraction of 1 wt% or less, an MFR of 18 g / 10 min (measured at 190°C), Mz of 320,000, Mn of 31,000, and Mw of 110,000. The molecular weight distribution (Mz / Mn) was 10, which is smaller than the value of 13.6 calculated from the weight-average molecular weight by equation (3), satisfying the conditions of equation (3). The recyclability was also evaluated as good (○).

[0070] Example 5 The same reaction as in Example 1 was carried out, except that the reaction temperature was changed to 250°C and the reaction time was changed to 30 minutes.

[0071] The resulting ethylene copolymer had a vinyl acetate content of 7.5 mol%, a vinyl alcohol residue content of 3.7 mol%, an aliphatic vinyl / vinyl alcohol unit ratio of 2.0, a gel fraction of 1 wt% or less, an MFR of 24 g / 10 min (measured at 190°C), Mz of 140,000, Mn of 22,000, and Mw of 61,000. The molecular weight distribution (Mz / Mn) was 6, which is smaller than the value of 7.3 calculated from the weight-average molecular weight by equation (3), satisfying the conditions of equation (3). The recyclability was also evaluated as good (○).

[0072] Example 6 The same reaction as in Example 1 was carried out, except that the reaction temperature was changed to 250°C and the reaction time was changed to 60 minutes.

[0073] The obtained ethylene copolymer had a vinyl acetate residue content of 8.5 mol%, a vinyl alcohol residue content of 2.7 mol%, an aliphatic vinyl / vinyl alcohol unit ratio of 3.2, a gel fraction of 1 wt% or less, an MFR of 8.0 g / 10 min (measured at 190°C), Mz of 270,000, Mn of 31,000, and Mw of 100,000. The molecular weight distribution (Mz / Mn) was 9, which is smaller than the value of 12 calculated from the weight-average molecular weight by equation (3), satisfying the conditions of equation (3). The recyclability was also evaluated as good (○).

[0074] Example 7 The same reaction as in Example 1 was carried out, except that the reaction temperature was changed to 250°C and the reaction time was changed to 180 minutes.

[0075] The resulting ethylene copolymer had a vinyl acetate content of 8.5 mol%, a vinyl alcohol residue content of 2.7 mol%, an aliphatic vinyl / vinyl alcohol unit ratio of 3.2, a gel fraction of 1 wt% or less, an MFR of 8.0 g / 10 min (measured at 190°C), Mz of 240,000, Mn of 28,000, and Mw of 91,000. The molecular weight distribution (Mz / Mn) was 9, which is smaller than the value of 10.7 calculated from the weight-average molecular weight by equation (3), satisfying the conditions of equation (3). The recyclability was also evaluated as good (○).

[0076] Reference example The measured values ​​of the saponified products of commercially available ethylene vinyl vinyl acetate copolymers are shown below. Tosoh Corporation, product name: H3051R Vinyl acetate residue content 3.3 mol%, vinyl alcohol residue content 7.7 mol%, aliphatic vinyl / vinyl alcohol unit ratio 2.3, gel fraction 0 wt%, MFR 5g / 10 min (measured at 190°C), Mz 150,000, Mn 12,000, Mw 55,000, molecular weight distribution (Mz / Mn) 12.5, and the value calculated from equation (3) using the weight average molecular weight was greater than 6.8, thereby not satisfying the condition of equation (3). Tosoh Corporation, product name: H6410 Vinyl acetate content 7 mol%, vinyl alcohol residue content 4 mol%, aliphatic vinyl / vinyl alcohol unit ratio 1.7, gel fraction 0 wt%. MFR 17.5 g / 10 min (measured at 190°C). Mz 160,000, Mn 7,400, Mw 47,000, molecular weight distribution (Mz / Mn) 21.6. The value calculated from equation (3) using the weight-average molecular weight was greater than 6.3, and did not satisfy the condition of equation (3). [Industrial Applicability]

[0077] The present invention provides a novel ethylene-based copolymer obtained by simply and efficiently transesterifying used or discarded crosslinked ethylene-vinyl acetate copolymer, and a method for recycling the copolymer into a high-quality ethylene-based copolymer useful as an adhesive, compatibilizer, resin modifier, etc. for plastics and rubber. [Explanation of symbols]

[0078] 1 Hydroxyl group-derived absorption (3370cm -1 ) 2 Absorption due to the main chain (CH2) (2920, 2850 cm -1 ) 3 Absorption due to carbonyl group (1740cm -1 ) 4 Absorption due to ether bond (1241 cm -1 ) 5 Absorption due to ether bond (1182cm -1 ) 6 Absorption due to vinyl fatty acid residues (proton absorption of methine groups in the main chain) 7. Absorption due to hydroxyl residues (proton absorption of hydroxyl groups in the main chain) 8 Absorption from vinyl residues of fatty acids (proton absorption of methyl groups) 9 Absorption from vinyl residues of fatty acids (proton absorption of propyl groups)

Claims

1. A method for producing an ethylene copolymer, comprising transesterifying a crosslinked ethylene-vinyl acetate copolymer using a solution containing one or more fatty acid esters and an acid or alkali component.

2. 2. The method for producing an ethylene copolymer according to claim 1, wherein the crosslinked ethylene-vinyl acetate copolymer has a gel fraction of 1 to 100% by weight and a vinyl acetate residue unit content of 2.0 to 25.0 mol%.

3. 2. The method for producing an ethylene-based copolymer according to claim 1, wherein the crosslinked ethylene-vinyl acetate copolymer contains 50% by weight or more of a material derived from processing waste materials generated during crosslinking treatment or molding, used or discarded crosslinked foam, or sealant recovered from solar panels.

4. 2. The method for producing an ethylene copolymer according to claim 1, wherein the alkali component is sodium hydroxide, potassium hydroxide, lithium hydroxide, or an alkali metal alkoxide having 8 or less carbon atoms.

5. An ethylene-fatty acid vinyl ester-vinyl alcohol copolymer having an ethylene residue, a structural unit represented by the following general formula (1), and a structural unit represented by the following general formula (2), which satisfies the following requirements (1) to (5): 【Chemistry 1】 【Chemistry 2】 (where R １ is a hydrocarbon group having 1 to 30 carbon atoms. (1) the structural unit represented by general formula (1) is 2.0 to 25.0 mol %, (2) the structural unit represented by general formula (2) is 0.1 to 25.0 mol %, (3) A melt mass flow rate of 0.01 to 2,000 g / 10 min at 190°C and a load of 21.18 N, as measured in accordance with JIS K6924-2; (4) a weight average molecular weight (Mw) of 15,000 to 300,000; (5) The molecular weight distribution (the ratio of Z-average molecular weight to number-average molecular weight (Mz / Mn)) satisfies the requirement of the following general formula (3). Mz / Mn≦0.09×MW ２ -0.25×MW+5.5 (3) (Here, MW represents the weight average molecular weight divided by 10,000.)

6. The ethylene copolymer according to claim 5, which satisfies the following requirements (6) to (7): (6) The ratio of the structural unit represented by the general formula (1) to the structural unit represented by the general formula (2) is an aliphatic vinyl / vinyl alcohol unit ratio of 1 or more; (7) Gel fraction is 0 to 20% by weight.

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