Saponified ethylene-vinyl acetate-based copolymer and production method thereof

Abstract

To provide a high-quality saponified ethylene-vinyl acetate-based copolymer which is useful as an adhesive, a compatibility accelerator, a resin modifier or the like for plastics and rubbers, and a simple and efficient production method of the saponified ethylene-vinyl acetate-based copolymer from a used or wasted cross-linked ethylene-vinyl acetate copolymer.SOLUTION: A saponified ethylene-vinyl acetate-based copolymer satisfies following requirements (1) to (3). (1) A vinyl acetate residue unit is 2.0-25.0 mol%. (2) A melt mass flow rate is 0.5-200 g / 10 minutes. (3) A distribution of molecular weight (a ratio of Z-average molecular weight to number average molecular weight (Mz / Mn) is 30 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a saponified ethylene-vinyl acetate copolymer made from a crosslinked resin or waste plastic as a raw material, and a method for producing the saponified ethylene-vinyl acetate copolymer. [Background technology]

[0002] Ethylene-vinyl acetate copolymer (hereinafter sometimes abbreviated as EVA) is a material that has flexibility, It is a type of polyethylene resin that has excellent transparency and adhesive properties, and is used in films due to its usefulness. It is used in a wide range of products and packaging, including mattresses, sheets, adhesives, toys, mats, and insoles. On the other hand, there are issues such as achieving carbon neutrality, marine plastic waste, and climate change. As the need for stronger responses to the issue increases, the importance of promoting the recycling of plastics is increasing. In addition, ethylene-vinyl acetate copolymers are crosslinked to improve mechanical properties, transparency, heat resistance, etc. Since it has even better properties, it is also used as a sealant for cross-linked foams and solar panels. On the other hand, cross-linked materials do not melt and have poor processability, making them difficult to recycle. Furthermore, there is a problem that waste plastic (hereinafter sometimes abbreviated as waste plastic) is thermally Using naphtha cracker and polymerization plant, polyethylene is produced from decomposed and synthesized naphtha. Chemical recycling, which produces polyethylene (PE) and polypropylene (PP), etc., involves cross-linking and deterioration. It is also possible to recycle waste plastics, and to produce plastics from monomer and oligomer raw materials. Because it is synthesized, recycled products have the advantage of being of the same quality as virgin products. The process is long and complicated, and it has been pointed out that it lacks economic rationality. Since the introduction of the Feed-in Tariff (FIT) scheme for renewable energy in 2012, solar power generation has rapidly increased, but the product lifespan of solar panels is approximately 25 to 30 years, and it is predicted that a large amount of waste containing solar panels will be generated around 2040, raising concerns about abandoned or illegal dumping and a shortage of disposal sites. Furthermore, because solar panels use cross-linked EVA as a sealant for the cells, technology has been proposed to separate the sealant made of cross-linked EVA from the glass panel (see, for example, Patent Documents 1 to 5).

[0003] Ethylene-vinyl acetate copolymer is easily affected by bases, acids, alcohols, esters, catalysts, etc. It was found that the copolymer could be converted into an ethylene-vinyl alcohol copolymer by hydrolysis using The ethylene-vinyl alcohol copolymer is generally known as an adhesive, a compatibilizer, a resin, and the like. It is used as a modifier, etc. In particular, the reaction of hydrolysis using a base is called saponification. (See, for example, Patent Document 6.) Furthermore, a crosslinked ethylene-vinyl acetate copolymer is A resin composition for a hot melt adhesive characterized by containing a compound has been proposed (for example, (See Patent Document 7.) Also, a method for producing a copolymer of ethylene-vinyl acetate copolymer with water and / or alcohol is disclosed. and reacting them in a fluid in a supercritical state or a subcritical state. -A method for producing a vinyl alcohol copolymer has been proposed (see, for example, Patent Document 8). Furthermore, in a solvent mainly composed of alcohol, in the absence of a catalyst, the critical temperature of the solvent Temperature (Tc) + 5℃ to 295℃, pressure (Pc) of the solvent to 40MPa, Fluid density at the start of reaction: 0.1 to 0.4 g / cm 3 The vinyl ester polymer is saponified with A method for producing a vinyl alcohol polymer characterized by the above has been proposed (see, for example, Patent Document 9). In addition, in the method of treating a polymer compound and a drug by maintaining them under high temperature and pressure, The polymer compound and the drug are thoroughly mixed and stirred inside the extruder, and the inside of the extruder is heated to a high temperature. The pressure is adjusted to react the polymer compound with the drug, and the reaction product is placed in the downstream of the extruder. The reactants are continuously fed into the high-pressure vessel, and maintained at high temperature and pressure for a certain period of time. Then, the reactant is decompressed by a pressure adjusting means including a resistor having a plurality of holes, and the reactant is then mixed with the chemical. The polymer treated material is continuously fed to a chemical separation tank to be separated into the polymer treated material and the chemical. The polymer treated material is continuously fed to a molding means to form a molded product. A method for treating a polymer compound has been proposed (see, for example, Patent Document 10). The compound is described as a crosslinked polymer. [Prior art documents] [Patent documents]

[0004] [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]

[0005] The cross-linked EVA sealing material containing the cells proposed in Patent Documents 1 to 5 is attached to the glass panel. In the peeling technology, the cross-linked EVA sealant is burned or crushed after peeling, and then separated by gravity. There is no mention of EVA recycling. In the method for producing a saponified ethylene-vinyl acetate copolymer proposed in Patent Document 6, There is no mention of recycling crosslinked EVA. A hot melt adhesive characterized by containing a saponified product of a crosslinked ethylene-vinyl acetate copolymer. In the adhesive resin composition, the degree of crosslinking of the crosslinked ethylene-vinyl acetate copolymer is low, and the crosslinking It cannot be used as a foam or a sealant for solar panels, but it can be recycled as cross-linked EVA. Furthermore, the ethylene-vinyl acetate copolymer proposed in Patent Document 8 is not disclosed. The coalescence is mixed with water and / or alcohol, and reacted in a supercritical or subcritical fluid state. In the method for producing an ethylene-vinyl alcohol copolymer, Saponified EVA, i.e., ethylene-vinyl alcohol copolymer, using crosslinked EVA as the raw material Furthermore, the vinyl acetate proposed in Patent Document 9 is not disclosed in any detail. In the production of alcohol polymers, the vinyl acetate units in polyvinyl acetate are It does not mention anything about saponification using crosslinked EVA as a raw material. In addition, in the method for treating a polymer compound proposed in Patent Document 10, Compounds include cross-linked polymers, synthetic polymers such as thermosetting resins, plastics, and elastomers. Natural polymer compounds such as compounds, lignin, cellulose, and proteins, or synthetic polymer compounds Only a mixture of natural polymer compounds and cross-linked EVA is listed. There is no mention of saponification.

[0006] Furthermore, there have been no reports to date on the method of producing a saponified ethylene-vinyl acetate copolymer by saponifying used crosslinked EVA and then reacetylating it, nor on the structure of the saponified ethylene-vinyl acetate copolymer obtained in this manner.

[0007] Therefore, an object of the present invention is to provide a high-quality novel saponified ethylene-vinyl acetate copolymer obtained by simply and efficiently saponifying and reacetylating a crosslinked ethylene-vinyl acetate copolymer, such as a crosslinked EVA encapsulant separated from used or discarded crosslinked foam or a solar panel, and a method for producing the saponified ethylene-vinyl acetate copolymer. More specifically, an object of the present invention is to provide a novel saponified ethylene-vinyl acetate copolymer useful as an adhesive, compatibilizer, resin modifier, etc. for plastics and rubber, and a method for producing the novel saponified ethylene-vinyl acetate copolymer.

[0008] Highly efficient recycling of molded and used resins and moldings, including reuse, regeneration, raw material recycling, and oil recycling. This will contribute to the promotion of inclusive and sustainable industrialization, which has been called for in recent years. It is one of the technologies necessary for a sustainable society, such as the SDGs. [Means for solving the problem]

[0009] As a result of intensive investigations aimed at solving the above-mentioned problems, the present inventors have found that a high-quality novel ethylene-vinyl acetate copolymer can be produced simply and efficiently by saponifying a crosslinked ethylene-vinyl acetate copolymer and then reacetylating it, thereby completing the present invention.

[0010] That is, the embodiments of the present invention are [1] to [6] shown below. [1] A saponified ethylene-vinyl acetate copolymer that satisfies the following requirements (1) to (3): (1) vinyl acetate residue units are 2.0 to 25.0 mol %; (2) A melt mass flow rate at 190°C measured in accordance with JIS K6924-2 is 0.5 to 200 g / 10 min. (3) Molecular weight distribution (ratio of Z-average molecular weight to number-average molecular weight (Mz / Mn)) is 30 or more. [2] The saponified ethylene-vinyl acetate copolymer according to [1], which satisfies the following requirements (4) and (5): (4) vinyl alcohol residue units are 0.0 to 15.0 mol %, (5) Gel fraction is 0 to 20 wt%. [3] A method for producing a saponified ethylene-vinyl acetate copolymer according to [1] or [2], comprising saponifying a crosslinked ethylene-vinyl acetate copolymer using a solution comprising a solvent containing one or more alcohols and an acid or alkali component (1), followed by reacetylating the copolymer. [4] The method for producing a saponified ethylene-vinyl acetate copolymer according to [3], 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%. [5] The method for producing a saponified ethylene-vinyl acetate copolymer according to [3] or [4], wherein the crosslinked ethylene-vinyl acetate copolymer contains 50% by weight or more of the crosslinked ethylene-vinyl acetate copolymer recovered from used or discarded crosslinked foam or solar panels. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a high-quality novel saponified ethylene-vinyl acetate copolymer that is useful for applications such as adhesives for plastics and rubber, compatibilizers, and resin modifiers. Furthermore, it is possible to provide a method for producing a novel saponified ethylene-vinyl acetate copolymer by simply and efficiently saponifying a used or discarded crosslinked ethylene-vinyl acetate copolymer as a raw material and subsequently reacetylating it, and the industrial value of this method is extremely high. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an IR spectrum diagram of a saponified ethylene-vinyl acetate copolymer according to Example 1 of the present invention. [Figure 2] 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 3] FIG. 1 is a GPC chart showing the raw material ethylene vinyl acetate copolymer (uncrosslinked) and the saponified ethylene-vinyl acetate copolymer after crosslinking reaction, saponification treatment, and reacetylation treatment in Example 1 of the present invention. [Figure 4] 1 is a 1H-NMR chart of the raw material ethylene vinyl acetate copolymer (uncrosslinked) in Example 1 of the present invention and the saponified ethylene-vinyl acetate copolymer after crosslinking reaction, saponification treatment, and reacetylation treatment. FIG. [Figure 5] FIG. 10 is an IR spectrum diagram of a saponified ethylene-vinyl acetate copolymer before and after saponification / reacetylation of a solar cell encapsulating film according to Example 21 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below.

[0014] The saponified ethylene-vinyl acetate copolymer according to one embodiment of the present invention is (1) vinyl acetate residue units are 2.0 to 25.0 mol %; (2) A melt mass flow rate of 0.5 to 200 g / 10 min at 190°C measured in accordance with JIS K6924-2; (3) Molecular weight distribution (ratio of Z-average molecular weight to number-average molecular weight (Mz / Mn)) is 30 or more. It satisfies the following conditions.

[0015] In addition, it can be used as an adhesive, compatibilizer, resin modifier, etc., with excellent transparency, heat resistance, flexibility, and adhesiveness. (4) vinyl alcohol residue units are 0.0 to 15 mol %; (5) Gel fraction is 0 to 20 wt%. It is preferable that the following is satisfied.

[0016] The vinyl acetate residue unit of the saponified ethylene-vinyl acetate copolymer can be determined by a measurement method in accordance with JIS K7192 (1999).

[0017] Furthermore, the vinyl acetate residue units of the ethylene-vinyl acetate copolymer of the present invention are in the range of 2.0 to 25.0 mol %, preferably 2.5 to 20.0 mol %, since the ethylene-vinyl acetate copolymer can be effectively used as an adhesive, compatibilizer, resin modifier, etc., which has excellent transparency, heat resistance, flexibility, adhesiveness, etc.

[0018] The melt mass flow rate of the saponified ethylene-vinyl acetate copolymer is measured at 190°C in accordance with JIS K6924-2 and is in the range of 0.5 to 200 g / 10 min, preferably 1.0 to 60 g / 10 min, because the saponified ethylene-vinyl acetate 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.

[0019] The molecular weight distribution of the saponified ethylene-vinyl acetate copolymer, that is, the ratio of Z-average molecular weight to number-average molecular weight (Mz / Mn), can be determined by gel permeation chromatography (GPC).

[0020] The saponified ethylene-vinyl acetate copolymer has an Mz / Mn of 30 or more, which allows it to be easily recycled as a thermoplastic resin, and if the Mz / Mn is 30 or more, it can be used as a normal thermoplastic resin. In particular, since the processability is good, it is preferably 35 or more and 90 or less.

[0021] The vinyl alcohol residue units of the saponified ethylene-vinyl acetate copolymer can be determined by a known NMR method.

[0022] Furthermore, the vinyl alcohol residue unit of the ethylene-vinyl acetate copolymer is preferably in the range of 0.0 to 15.0 mol %, particularly preferably in the range of 0.0 to 10.0 mol %, since it can be effectively used as a saponified ethylene-vinyl acetate copolymer used as an adhesive, compatibilizer, resin modifier, etc., which has excellent transparency, heat resistance, flexibility, adhesiveness, etc.

[0023] The gel fraction of a saponified ethylene-vinyl acetate 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.

[0024] The saponified ethylene-vinyl acetate copolymer preferably has a gel fraction of 0 to 20% by weight, since it can be easily reused as a thermoplastic resin, and if the gel fraction is 20% by weight or less, it can be used as a normal thermoplastic resin. In particular, a gel fraction of 15% by weight or less is preferred, since it provides good processability.

[0025] The ethylene-vinyl acetate copolymer of the present invention can be produced by any of these methods. However, a preferred method for producing a saponified ethylene-vinyl acetate copolymer is one that involves saponifying a crosslinked ethylene-vinyl acetate copolymer using a solution comprising one or more alcoholic solvents and an acid or alkali component (1) and then reacetylating the copolymer. Furthermore, a preferred method for producing a saponified ethylene-vinyl acetate copolymer is one in which the crosslinked ethylene-vinyl acetate copolymer has a gel fraction of 1 to 100% by weight and a vinyl acetate residue content of 2.0 to 25.0 mol%. The present invention is also effective in recycling waste plastics, and can be expanded and utilized in a method for producing a saponified ethylene-vinyl acetate copolymer in which 50% by weight or more of the crosslinked ethylene-vinyl acetate copolymer is recovered from used or discarded crosslinked foams or solar panels.

[0026] The crosslinked ethylene-vinyl acetate copolymer may have any gel fraction in the range of 1 to 100% by weight, and preferably has a gel fraction in the range of 1 to 85% by weight, and more preferably has a gel fraction in the range of 1 to 50% by weight, since this allows the treatment to be carried out under mild conditions.

[0027] 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 2.2 to 20.0 mol %, since it allows the production of saponified ethylene-vinyl acetate copolymers that are used as adhesives, compatibilizers, resin modifiers, etc. that are excellent in transparency, heat resistance, flexibility, adhesiveness, etc.

[0028] Furthermore, the form of the crosslinked ethylene-vinyl acetate copolymer (crosslinked EVA) is not limited to pellets or powder, but may also be in the form of films, sheets, bottles, fibers, pipes, molded products such as injection-molded products, foams, and their crushed products. Examples of crosslinked EVA include process-loss products, used products, non-standard products, and discarded products. When the crosslinked EVA is a resin composition containing other plastics or rubbers, light stabilizers, UV absorbers, nucleating agents, lubricants, antioxidants, antiblocking agents, flow improvers, mold release agents, flame retardants, flame retardant aids, 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, antifouling agents, rust inhibitors, and ion-trapping agents, the components may be mixed together in a melted state or may be physically mixed in the form of solids such as pellets or scraps. 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 of stable quality.

[0029] Furthermore, the cross-linked ethylene-vinyl acetate copolymer can be preferably used as a cross-linked foam used as a mat or an insole for a shoe sole, or as a sealant for a solar panel. In particular, cross-linked foams and sealants for solar panels are preferred for reasons such as the stability of quality and the ease of ensuring a stable supply quantity.

[0030] The crosslinked ethylene-vinyl acetate copolymer 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 pulverization can also be preferably used, and freezing and pulverization is preferably performed at a temperature of -150°C to -100°C.

[0031] Examples of the acid include acetic acid, sulfuric acid, phosphoric acid, phenol, etc. Particularly preferred are acetic acid and phosphoric acid, which are less corrosive.

[0032] Examples of the alkaline component (1) include sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium methoxide, lithium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, etc. Particularly preferred are sodium hydroxide and potassium hydroxide, which are strong alkalis, and lithium methoxide and sodium methoxide, which are easily soluble in organic solvents.

[0033] The amount of the acid or alkali component (1) used is 0.01 to 100% by weight, preferably 0.5 to 25% by weight, based on the crosslinked EVA.

[0034] The alcohol solvent is not particularly limited as long as it is an industrially available alcohol, but those having 1 to 8 carbon atoms can be preferably used. Examples of the alcohol solvent include, in general, 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, octanol and its isomers, and decanol and its isomers. In particular, examples of the solvent include 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, which have 4 or less carbon atoms and can be efficiently reused and handled during production. The solvent containing one or more alcohols may contain at least one of these, and may also contain, in addition to alcohols, aliphatic hydrocarbons, ether compounds, aromatic hydrocarbons, and the like.

[0035] Furthermore, by hydrolysis using an acid or alkali as a catalyst in a mixed solvent of the alcohol and aliphatic hydrocarbons having 5 to 8 carbon atoms, the raw material crosslinked EVA and the resulting saponified ethylene-vinyl acetate copolymer do not fuse together during the reaction and swell well, resulting in uniform hydrolysis and efficient production of a saponified ethylene-vinyl acetate copolymer with excellent transparency. Examples of the aliphatic hydrocarbons 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. These can be added singly or in combination. Furthermore, the amount of the aliphatic hydrocarbons having 5 to 8 carbon atoms added is preferably 1 to 50 wt. % of the alcohol, and particularly preferably 5 to 30 wt. %. 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 hydrocarbons such as benzene, toluene, xylene, ethylbenzene, cumene, and methylethylbenzene can also be used.

[0036] Furthermore, the addition of conventional color inhibitors during the reaction to prevent coloration due to hydrolysis of the 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.

[0037] The concentration of the crosslinked EVA in the alcohol-containing solvent during the saponification reaction is usually preferably 5 to 80% by weight, and particularly preferably 10 to 60% by weight.

[0038] The saponification treatment of the crosslinked ethylene-vinyl acetate copolymer is usually carried out in the range of 40 to 300°C, more preferably 55 to 300°C. The saponification treatment time is usually 10 to 300 minutes, and the apparatus used for the saponification treatment can be either a continuous or batch type. The solid component produced after the saponification treatment contains alkali, by-product salts, other impurities, etc., and it is preferable to remove these by neutralization and washing as necessary.

[0039] In the reacetylation treatment, the solid component obtained in the saponification treatment is acetylated using an acetylating agent.

[0040] The acetylating agent used is acetic anhydride, which is preferably used in an amount of 1 to 1000 times by weight relative to the amount of the crosslinked ethylene-vinyl acetate copolymer, and more preferably 0.5 to 200 times from the viewpoint of production costs.

[0041] In addition to acetic anhydride, glacial acetic acid and / or acetic acid are preferably used for dilution and reaction promotion. The amount of glacial acetic acid and / or acetic acid used is preferably 1 to 1000 times the amount of the crosslinked ethylene-vinyl acetate copolymer, and more preferably 0.5 to 200 times the amount from the viewpoint of production costs. Sodium acetate (alkali component (2)) is used to promote the reaction. The amount of alkali component (2) used is preferably 0.001 to 1000 times the amount of the crosslinked ethylene-ethyl acetate copolymer, and more preferably 0.01 to 50 times the amount from the viewpoint of efficient removal of catalyst residues.

[0042] In addition to sodium acetate, alkali catalysts such as sodium hydroxide, and acid catalysts such as hydrochloric acid and sulfuric acid can also be used to promote the reaction. The amount of these catalysts used is preferably 0.01 to 10 times the amount of the crosslinked ethylene-vinyl acetate copolymer, and more preferably 0.01 to 1 time from the viewpoint of efficient removal of catalyst residues.

[0043] Furthermore, a hydrocarbon solvent having 5 to 8 carbon atoms may be used in the reacetylation treatment. Examples of aliphatic hydrocarbons having 5 to 8 carbon atoms include n-pentane, i.e., n-pentane, cyclopentane, n-hexane, 2-methylpentane, methylcyclopentane, cyclohexane, n-heptane, 2-methylhexane, 3-methylhexane, methylcyclohexane, n-octane, and 2,2,4-trimethylpentane. These may be added singly or in combination. Furthermore, the amount of the aliphatic hydrocarbon having 5 to 8 carbon atoms used is preferably 0 to 50 wt. % relative to acetic anhydride, and particularly preferably 5 to 30 wt. Furthermore, instead of the aliphatic hydrocarbon 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 hydrocarbons, such as benzene, toluene, xylene, ethylbenzene, cumene, and methylethylbenzene, may also be used.

[0044] The ethylene-vinyl acetate 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]

[0045] 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.

[0046] 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 content in ethylene-vinyl acetate copolymer> Measurements were made in accordance with JIS K7192 (1999). <Melt Mass Flow Rate (MFR)> Measurements were made in accordance with JIS K6922-1 (1997). <Molecular weight distribution (Mz / Mn)> The molecular weight was measured using a GPC system (Tosoh Corporation, product name: HLC-8121GPC / HT) and a column (Tosoh Corporation, product name: TSKgel® GMHhr-H(20)HT), with the column temperature set to 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. The weighted average molecular weight Mz and number average molecular weight Mz were determined from the chromatogram obtained as a result of the measurement, and Mz / Mn was calculated from the ratio of these. <Recyclability> The saponified ethylene-vinyl acetate copolymer obtained in the examples was pulverized and melt-kneaded using a twin-screw extruder (manufactured by Technovel, product name ULTnano25TW) with a screw diameter of 25 mm at a resin temperature of 160°C and a screw rotation speed of 300 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 (△).

[0047] Example 1 100 g of commercially available ethylene-vinyl acetate copolymer (vinyl acetate content 11.2 mol%) was mixed with 1 g of cross-linking agent (Perhexa C) at 120°C for 30 minutes, and then heated and mixed in a calendar molding machine at 180°C for 10 minutes to produce 100 g of cross-linked ethylene-vinyl acetate copolymer with a gel fraction of 76%.

[0048] Next, 10 g of cross-linked ethylene-vinyl acetate copolymer and 5 g of sodium hydroxide were dissolved in 130 mL of methanol and placed in a 1.1 L stainless steel vessel equipped with a stirrer. The reaction was carried out at 250 °C for 3 hours with stirring. After the reaction was completed, the contents were poured into 10 L of 1% dilute hydrochloric acid in methanol to recover 9.1 g of solid component (A). The solid component was freeze-pulverized and washed with a large amount of methanol and then water. NMR spectroscopy confirmed that solid component (A) was an ethylene-vinyl alcohol copolymer (Figure 1). The degree of saponification was over 95% based on the raw material EVA.

[0049] Next, 7 g of the solid component (A) was freeze-pulverized to a powder, which was then placed in a 1 L flask equipped with a magnetic stirrer and chips. 200 g of acetic anhydride and 20 g of sodium acetate were added, and the mixture was allowed to react at 130 °C for 3 hours under a nitrogen atmosphere. The resulting solid was then recovered and washed with a large amount of water, yielding 6 g of a yellow solid. A comparison of the ethylene-vinyl acetate copolymer before crosslinking (11.2 mol% vinyl acetate residue units, gel fraction of 1 wt% or less) with the saponified ethylene-vinyl acetate copolymer (vinyl acetate content 10.8 mol%, vinyl alcohol residue units 0.8 mol%, gel fraction of 1 wt% or less) revealed that the yellow solid obtained in Example 1 exhibited the same carbonyl groups and main chain (CH2) vibrations as the raw material, but also exhibited a different absorption pattern and additional hydroxyl groups, indicating that it was not the same substance (Figures 1 and 2). The presence of acetoxy and hydroxyl groups was also confirmed by 1H-NMR analysis, indicating that the yellow solid obtained in this Example 1 was a copolymer of ethylene and vinyl acetate (Figure 3). Furthermore, in the GPC measurements, a significant difference was observed in the high molecular weight region, above 100,000 (Figure 4, MFR and GPC measurement results are shown in Table 1). 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 also evaluated as good (◯).

[0050] Examples 2 to 17 Table 1 shows the results of varying the raw materials and conditions.

[0051] Comparative Example 1 Except for replacing methanol with water, a reaction was carried out in the same manner as in Example 1. The gel fraction decreased from 76% by weight to 68% by weight, but the resin did not dissolve and could not be recycled as a thermoplastic resin.

[0052] Comparative Example 2 Except for not using sodium hydroxide, the same reaction as in Example 1 was carried out. The saponification reaction did not proceed, and the resin was not dissolved, so it was not possible to regenerate it as a thermoplastic resin.

[0053] Comparative Example 3 A reaction was carried out in the same manner as in Comparative Example 2, except that the temperature was changed from 250° C. to 340° C. The vinyl acetate residue content was 1 mol % or less, and a saponified ethylene-vinyl acetate copolymer could not be obtained.

[0054] Comparative Example 4 Except for using decane instead of methanol, the reaction was carried out in the same manner as in Example 1. The gel fraction was as high as 58%, and it was not possible to regenerate the resin as a thermoplastic resin.

[0055] Comparative Example 5 When a non-crosslinked ethylene-vinyl acetate copolymer was used as the raw material, the Mz / Mn ratio measured by GPC was 11, which was a very sharp molecular weight distribution, and it was not possible to obtain the saponified ethylene-vinyl acetate copolymer of the present invention.

[0056] Comparative Example 6 Except for not carrying out the reacetylation treatment, the same reaction as in Example 1 was carried out. The ethyl acetate residue was 1 mol % or less, and a saponified ethylene-vinyl acetate copolymer of the present invention could not be obtained.

[0057] [Table 1]

[0058] Example 18 The same reaction as in Example 1 was carried out, except that freeze-pulverized foamed used sandal soles (vinyl acetate residue: 7.2 mol %, gel fraction: 55 wt %) were used as the raw material. A meltable thermoplastic resin was obtained. The analytical results are shown in Table 2.

[0059] [Table 2]

[0060] Example 19 The same reaction as in Example 1 was carried out, except that the raw material used was a freeze-pulverized encapsulant from used solar cell panels (vinyl acetate residue: 9.1 mol %, gel fraction: 81 wt %). A meltable thermoplastic resin was obtained. The analytical results are shown in Table 2.

[0061] The IR spectrum of the yellow solid obtained in this Example 19 is shown in Figure 5, and similarly to Example 1, it was confirmed that the solid was a saponified ethylene-vinyl acetate copolymer having a carbonyl group and a hydroxyl group in the main chain portion.

[0062] Example 20 The same reaction as in Example 1 was carried out, except that phosphoric acid and 1-butanol were used instead of sodium hydroxide and methanol. A meltable thermoplastic resin was obtained. The analytical results are shown in Table 3.

[0063] Example 21 The same reaction as in Example 1 was carried out, except that sodium hydroxide was used in the reacetylation reaction. A meltable thermoplastic resin was obtained. The analysis results are shown in Table 3.

[0064] [Table 3] [Industrial Applicability]

[0065] The present invention provides a method for recycling used or discarded crosslinked ethylene-vinyl acetate copolymers by simply and efficiently subjecting them to saponification and subsequent reacetylation, thereby producing high-quality ethylene-vinyl acetate copolymers that are useful as adhesives for plastics and rubbers, compatibilizers, resin modifiers, and the like. [Explanation of symbols]

[0066] 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 acetoxy group (proton absorption of methine group in the main chain) 6 Absorption due to hydroxyl groups (proton absorption of hydroxyl groups in the main chain) 7. Absorption due to acetoxy group (proton absorption of methyl group)

Claims

1. A saponified ethylene-vinyl acetate copolymer that satisfies the following requirements (1) to (3): (1) vinyl acetate residue units are 2.0 to 25.0 mol %, (2) A melt mass flow rate at 190°C measured in accordance with JIS K6924-2 of 0.5 to 200 g / 10 min; (3) The molecular weight distribution (the ratio of Z-average molecular weight to number-average molecular weight (Mz / Mn)) is 30 or more.

2. The saponified ethylene-vinyl acetate copolymer according to claim 1, which satisfies the following requirements (4) and (5): (4) vinyl alcohol residue units are 0.0 to 15.0 mol %; (5) Gel fraction is 0 to 20% by weight.

3. The method for producing a saponified ethylene-vinyl acetate copolymer according to claim 1, wherein a crosslinked ethylene-vinyl acetate copolymer is saponified using a solution containing one or more alcohols and an acid or alkali component (1), and then reacetylated.

4. The method for producing a saponified ethylene-vinyl acetate copolymer according to claim 3, 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%.

5. The method for producing a saponified ethylene-vinyl acetate copolymer according to claim 3, wherein the crosslinked ethylene-vinyl acetate copolymer contains 50% by weight or more of the crosslinked ethylene-vinyl acetate copolymer recovered from used or discarded crosslinked foam or solar panels.

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