JP4674004B2 - Process for producing ethylene-vinyl acetate copolymer and saponified product thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ethylene-vinyl acetate copolymer and a method for producing a saponified product thereof.
[0002]
[Prior art]
Saponified ethylene-vinyl acetate copolymer (hereinafter referred to as “EVOH”) is excellent in melt moldability, gas barrier properties, water resistance, oil resistance, non-charging properties and mechanical strength, and is a film, sheet, container It is used as various packaging materials. In these packaging materials, appearance defects that occur during molding, such as coloring, fish eyes, and rough skin, are one of the important issues to be overcome. For this reason, several improvements have been proposed in the EVOH production process (for example, JP-B 43-14958, JP-B 47-38558, JP-A 61-197603, JP-A 9-71620). No. 11-140136).
[0003]
On the other hand, in order to reduce manufacturing costs, it is desirable to recover and reuse unreacted raw materials and used solvents in the EVOH manufacturing process. In particular, in the production of EVOH on a commercial scale, it is extremely important to reuse alcoholic solvents such as methanol. However, the recovered solvent contains impurities that are by-produced in the copolymerization, saponification, and purification steps. For this reason, when the recovered solvent is reused and copolymerization is performed, the above-mentioned appearance defect occurs at the time of molding, and there is a problem that the commercial value of the molded body as a packaging material is lowered.
[0004]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide an ethylene-vinyl acetate copolymer and a method for producing a saponified product thereof, which can suppress poor appearance during molding even when a recovered solvent is used.
[0005]
[Means for Solving the Problems]
The present inventor found that the aldehyde compound contained in the recovered solvent induces the above-mentioned poor appearance, and completed the present invention.
[0006]
The first method for producing an ethylene-vinyl acetate copolymer of the present invention is a method for producing an ethylene-vinyl acetate copolymer in which ethylene and vinyl acetate are copolymerized in an alcohol solvent, the alcohol solvent At least a part of the solvent is a solvent that has been subjected to an aldehyde reduction treatment in advance. Examples of the aldehyde reduction treatment include contact with a solid acid. According to this production method, copolymerization can be carried out in a solvent having a reduced aldehyde compound concentration.
[0007]
In the first production method, at least a part of the alcohol solvent is a solvent that is used for copolymerization of ethylene and vinyl acetate, separated from the product and unreacted raw material, recovered, and subjected to aldehyde reduction treatment. It is preferable. Thus, according to the present invention, the recovered solvent can be reused while preventing the quality degradation of the target EVOH molded product.
[0008]
In the first production method, for example, an alcohol solvent having an aldehyde compound concentration of 1 ppm to 500 ppm (ppm is based on weight, the same applies hereinafter), preferably 150 to 500 ppm is subjected to aldehyde reduction treatment. The alcohol solvent treated by contact with a solid acid or the like preferably has an aldehyde compound concentration of 100 ppm or less. In order to sufficiently suppress the appearance defect at the time of molding, the concentration of the aldehyde compound in the solvent after the treatment is more preferably 30 ppm or less, and further preferably 5 ppm or less.
[0010]
In the above production method, the alcohol solvent preferably has an acetal compound concentration of 0.1 ppm or more and 10,000 ppm or less.
[0011]
The present invention also provides a production method for continuously obtaining an ethylene-vinyl acetate copolymer by copolymerizing ethylene and vinyl acetate in an alcohol solvent. In this method, ethylene and vinyl acetate are copolymerized in an alcohol solvent to obtain an ethylene-vinyl acetate copolymer, at least a part of the alcohol solvent is recovered, and the recovered alcohol solvent is recovered. An aldehyde-reducing treatment, and using the alcohol solvent treated with aldehyde as at least part of the alcohol-based solvent used for copolymerization, the ethylene-vinyl acetate copolymer is obtained continuously. . The alcohol-based solvent used for copolymerization may contain an acetal compound, preferably at the concentration described above.
[0012]
The present invention also provides a method for producing EVOH. This production method is characterized by saponifying an ethylene-vinyl acetate copolymer obtained by the method described above.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described.
In a preferred embodiment of the present invention, the aldehyde compound contained in the recovered alcohol solvent is acetalized by, for example, contact with a solid acid.
[0014]
Any solid acid can be used without particular limitation as long as it does not dissolve in an alcohol solvent, has an acid site on the surface, and can act as an acetalization catalyst. Examples of solid acids include metal oxides (eg, Al ₂ O ₃ , V ₂ O ₅ ), sulfates (eg, NiSO ₄ , CuSO ₄ ), phosphates (eg, AlPO ₄ ), chlorides (eg, AlCl ₃ , CuCl ₃ ). A typical solid acid catalyst such as a zeolite catalyst or a silica-alumina catalyst may be used. In addition, a mineral such as montmorillonite can be used. However, cation exchange resins are particularly suitable for commercial scale implementation.
[0015]
The cation exchange resin functions as an insoluble solid acid, and various products suitable for a large amount of liquid treatment and repeated use are commercially available. As the cation exchange resin, a weak acid cation exchange resin may be used, but a strong acid cation exchange resin is preferred.
[0016]
As a result of confirmation by the present inventor, the concentration of the aldehyde compound in the alcohol solvent used for the copolymerization of ethylene and vinyl acetate greatly affects the appearance characteristics of the EVOH molded article. If the concentration of the aldehyde compound present in the solvent is 100 ppm or less, the appearance characteristics of the molded product can be greatly improved.
[0017]
The concentration of the aldehyde compound in the recovered alcohol solvent varies depending on the recovery method and other recovery conditions, but is generally in the range of 150 to 500 ppm. If the recovered alcohol solvent is pretreated to an aldehyde compound concentration of 100 ppm or less, preferably 30 ppm or less, more preferably 5 ppm or less, the above copolymerization can be performed using only the recovered solvent. . Even in the case where the aldehyde compound concentration in the recovered alcohol solvent is in the range of 1 to 150 ppm, it is preferable to treat the alcohol solvent in advance in order to further reduce the aldehyde compound concentration. As will be described later, in the EVOH production process, an alcohol solvent such as methanol is used to recover unreacted vinyl acetate. If the alcoholic solvent for vinyl acetate recovery is recovered together with the alcoholic solvent for copolymerization, and all the recovered solvent is subjected to aldehyde reduction treatment, the total amount of the solvent for copolymerization is supplemented with the recovered alcoholic solvent. It is also possible.
[0018]
As described above, in one embodiment of the present invention, acetalization with a solid acid is performed as a reduction treatment of the aldehyde compound. However, the object of the present invention can also be achieved by acetalizing an aldehyde compound using means other than contact with a solid acid. Examples of the acetalization method include contact with a liquid acid, for example, an inorganic acid such as sulfuric acid, nitric acid or phosphoric acid; a carboxylic acid such as formic acid, acetic acid or oxalic acid; or an aqueous solution of a Lewis acid such as zinc chloride or aluminum chloride. A method is mentioned.
[0019]
Acetaldehyde is mentioned as an aldehyde which becomes a problem in manufacture of an ethylene-vinyl acetate copolymer. When acetaldehyde is acetalized with methanol, dimethyl acetal (acetaldehyde dimethyl acetal) is produced.
[0020]
Hereinafter, a preferable example is demonstrated about each process of manufacture and saponification of an ethylene-vinyl acetate copolymer, and collection | recovery of a solvent, and a process.
For copolymerization of ethylene and vinyl acetate, any of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization may be used, but solution polymerization is preferred. Moreover, you may employ | adopt any method of a continuous type and a batch type.
[0021]
As the alcohol solvent, alcohols having 1 to 4 carbon atoms such as methanol, ethanol, n-butanol and t-butanol, particularly methanol is suitable. A solvent in which two or more kinds of alcohols are mixed may be used. The alcohol solvent may contain other trace components as long as alcohol is the main component. The alcohol solvent preferably contains, for example, 60% by weight or more, preferably 70% by weight or more of alcohol.
[0022]
As the catalyst, any radical initiator can be used without particular limitation. Preferred catalysts include 2,2′-azobisisobutyronitrile, 2,2′-azobis- (2,4-dimethylvaleronitrile), 2,2′-azobis- (4-methyl-2,4- Azonitrile-based initiators such as dimethylvaleronitrile), 2,2′-azobis- (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis- (2-cyclopropylpropionitrile), and Isobutyryl peroxide, cumylperoxyneodecanoate, diisopropylperoxycarbonate, di-n-propylperoxydicarbonate, t-butylperoxyneodecanoate, lauroyl peroxide, benzoyl peroxide, t-butylhydro An organic peroxide-based initiator such as peroxide may be used.
[0023]
In addition to ethylene and vinyl acetate, a monomer copolymerizable therewith may coexist. Examples of such monomers include (1) α-olefins such as propylene, isobutylene, α-octene, and α-dodecene, and (2) unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid. Acids, salts thereof, anhydrides thereof or mono- or dialkyl esters, (3) nitriles such as acrylonitrile and methacrylonitrile, (4) amides such as acrylamide and methacrylamide, (5) ethylenesulfonic acid, allylsulfonic acid, Examples thereof include olefin sulfonic acids such as methallyl sulfonic acid or salts thereof. In addition, alkyl vinyl ethers, vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinylidene chloride and the like may coexist. However, it is preferable to add these third monomers in a range that does not inhibit the effects of the present invention.
[0024]
The ethylene content in the copolymer is preferably 20 mol% or more and 70 mol% or less. This is because if the ethylene content is too low, sufficient water resistance cannot be obtained, and if it is too high, sufficient gas barrier properties cannot be obtained. From this viewpoint, the ethylene content is more preferably 25 to 60 mol%. But when using as a coating material etc., it is good also considering ethylene content rate as less than 20 mol%.
[0025]
The polymerization temperature is preferably 50 ° C. or more and 80 ° C. or less, and the pressure (ethylene pressure) in the gas phase part in the polymerization tank is preferably 20 to 80 kg / cm ² . In the case of a batch system, the reaction time is suitably 3 to 24 hours. Even in the case of the continuous type, it is preferable that the average residence time is approximately the same. The polymerization rate is suitably about 30 to 80% based on the supplied vinyl acetate.
[0026]
Next, a polymerization inhibitor is added to the liquid (copolymer solution) containing the ethylene-vinyl acetate copolymer, the unreacted ethylene gas is removed by evaporation, and the unreacted vinyl acetate is further expelled. The removal of vinyl acetate can be carried out, for example, by continuously supplying the copolymer solution from the upper part of the tower filled with Raschig rings at a predetermined rate and continuously blowing alcohol solvent vapor from the lower part of the tower. As the solvent to be blown in, the alcohols exemplified above as the solvent, particularly methanol, are suitable. By expelling vinyl acetate using such a column-type recovery device, unreacted vinyl acetate is taken out from the top of the tower together with the vapor of the alcohol solvent, and a copolymer solution in which unreacted vinyl acetate is removed from the bottom of the tower can be obtained. it can.
[0027]
The mixed liquid taken out from the top of the tower contains unreacted vinyl acetate and the alcohol solvent blown in, as well as the alcohol solvent contained in the copolymer solution. This mixed solution is introduced into another tower-type recovery device, subjected to extractive distillation with water to separate vinyl acetate (this vinyl acetate is also reused), and taken out as a mixed solution of alcohol and water. Furthermore, when the water / alcohol mixture is separated and purified, the alcohol solvent can be recovered.
[0028]
Since the recovered alcohol solvent contains an aldehyde compound as described above, it is acetalized. When acetalization is performed with a cation exchange resin, for example, an alcohol solvent may be introduced into a tower packed with a bead-shaped cation exchange resin. In this case, the temperature in the tower is not particularly limited as long as the alcohol solvent is in a liquid temperature range, and usually a temperature around room temperature may be adopted. Moreover, it is preferable that the residence time in the tower | column of alcohol solvent is 1 to 30 minutes from a viewpoint of the efficiency of solvent processing. The recovered and treated solvent thus obtained is reused as the solvent for the copolymerization.
[0029]
On the other hand, an alkali catalyst is added to the copolymer solution from which unreacted vinyl acetate has been removed to saponify the acetate ester component of the ethylene-vinyl acetate copolymer. Saponification may be performed by either a continuous method or a batch method. As the alkali catalyst, sodium hydroxide, potassium hydroxide, alkali metal alcoholate, or the like can be used. For example, when saponification is performed by a batch system, the copolymer solution temperature is preferably 30 ° C. or higher and 65 ° C. or lower, and the reaction time is preferably 1 to 6 hours. The concentration of the copolymer solution is suitably 10 to 50%, and the catalyst usage is suitably 0.02 to 1.0 equivalent per acetate component (per acetate group). Since the saponified product (EVOH) thus obtained contains an alkali catalyst, by-product salts and other impurities, these are neutralized and washed as necessary.
[0030]
The saponification degree of EVOH is preferably 95 mol% or more, more preferably 99% mol or more. If saponification is not sufficiently performed, sufficient gas barrier properties may not be obtained. However, the degree of saponification may be about 80 to 95 mol% in order to improve, for example, interlayer adhesion. EVOH having this saponification degree may be used alone, or may be used by blending with EVOH having a saponification degree of 99 mol% or more.
[0031]
The melt index (MI) of EVOH is preferably 0.1 to 200 g / 10 minutes. Here, a measured value under a load of 190 ° C. and 2160 g is adopted as MI. However, for those having a melting point near 190 ° C. or exceeding 190 ° C., a single logarithm with the horizontal axis representing the reciprocal of the absolute temperature and the vertical axis (logarithmic scale) representing the reciprocal of the absolute temperature from a plurality of measured values at the temperature above the melting point under the above load. A value plotted as a graph and extrapolated to 190 ° C. is used.
[0032]
The EVOH thus obtained is molded into various shapes such as a film, a sheet, a container, a pipe, and a fiber by melt molding. As melt molding, extrusion molding, inflation method, blow molding, melt spinning, injection molding and the like can be applied. The melting temperature is preferably 150 to 270 ° C. Two or more types of EVOH having different degrees of polymerization, ethylene content, and saponification degree may be blended and melt-molded. In addition, reinforcing agents such as plasticizers, stabilizers, surfactants, crosslinking agents, metal salts, fillers, and various fibers may be added to EVOH in advance.
[0033]
A thermoplastic resin other than EVOH may be blended with EVOH. Thermoplastic resins include polyolefin (polyethylene, polypropylene, poly 1-butene, poly 4-methyl-1 pentene, ethylene-propylene copolymer, copolymer of ethylene and α-olefin having 4 or more carbon atoms, polyolefin Copolymer of ethylene and maleic anhydride, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, modified polyolefin obtained by graft-modifying these with unsaturated carboxylic acid or derivatives thereof, and various nylons (nylon 6 , Nylon 66, nylon 6/66 copolymer, etc.), polyvinyl chloride, polyvinylidene chloride, polyester, polystyrene, polyacrylonitrile, polyurethane, polyacetal, modified polyvinyl alcohol resin, and the like.
[0034]
Moreover, you may shape | mold as a laminated body by coextruding EVOH and the thermoplastic resin which was illustrated above, for example. Furthermore, EVOH may be a laminate with a base film such as paper, plastic film, metal foil, etc., and may be coated on the surface of the base film by coextrusion coating, solution coating or the like.
[0035]
As described above, the present invention recovers an alcohol-based solvent while continuously copolymerizing ethylene and vinyl acetate, further processes this solvent, and reuses it as a solvent for the copolymerization. On the other hand, it is particularly suitable for a form in which EVOH is produced from the obtained copolymer. In the embodiment described above, ethylene and vinyl acetate are copolymerized in an alcohol solvent to obtain an ethylene-vinyl acetate copolymer, and an alcohol solvent is further supplied to the alcohol solvent containing the copolymer. While recovering unreacted vinyl acetate, separating the vinyl acetate from the alcoholic solvent recovered together with the vinyl acetate, and acetalizing the aldehyde compound contained in the alcoholic solvent from which the vinyl acetate has been separated Including. Preferably, the total amount of the solvent used in the step of producing the ethylene-vinyl acetate copolymer is supplemented by the recovered and treated alcohol solvent.
[0036]
However, the form described above is only an example of the present invention. The present invention can also be applied to, for example, the case where an alcohol solvent in which an aldehyde compound is mixed and generated is used as an initial raw material. In the step of producing an ethylene-vinyl acetate copolymer by copolymerizing ethylene and vinyl acetate in an alcohol solvent, for example, the present invention sets the concentration of the aldehyde compound in the alcohol solvent to 100 ppm or less, and The present invention can also be applied to a form in which the concentration is 0.1 ppm to 10,000 ppm.
[0037]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to a following example.
[0038]
(Example)
Using a polymerization tank with a stirrer having an internal volume of 100 L and a cooling coil inside, continuous copolymerization of an ethylene-vinyl acetate copolymer was performed under the following conditions.
[0039]
・ Vinyl acetate supply amount: 5.0 kg / hour ・ Initiator; 2,2′-azobis (2,4-dimethylvaleronitrile)
Initiator supply amount: 0.3 L / hour (as a 2.8 g / L methanol solution)
-Polymerization temperature: 60 ° C
-Ethylene pressure in the polymerization tank: 45 kg / cm ²
・ Average residence time: 7 hours ・ Solvent: Recovery ・ Solid acid-treated methanol (details are described later)
[0040]
The polymerization reaction liquid (copolymer solution) extracted continuously from the bottom of the polymerization tank was sampled and the composition was analyzed. The results are shown below.
-Ethylene-vinyl acetate copolymer (ethylene content 34 mol%); 46 wt%
-Vinyl acetate; 32% by weight
・ Ethylene; 8.7% by weight
・ Methanol: 10% by weight
・ Others; 3.3% by weight
The vinyl acetate polymerization rate was 55%.
[0041]
After adding β-myrcene as a polymerization inhibitor to the copolymer solution, ethylene was removed by flash evaporation. Furthermore, the copolymer solution from which ethylene has been removed is introduced from the top of the tower-type recovery unit (tray tower), and methanol vapor is blown from the bottom of the tower, and unreacted vinyl acetate is partially removed from the top of the tower. It was taken out with. On the other hand, a methanol solution of ethylene-vinyl acetate copolymer was taken out from the bottom of the column. The composition of the liquid mixture taken out from the top of the column was vinyl acetate: 60% by weight and methanol: 40% by weight. The concentration of the copolymer in the methanol solution taken out from the bottom of the tower was 45% by weight.
[0042]
Methanol was recovered from the mixed solution taken out from the top of the tower by the following method.
First, this solution was introduced into another tower-type recovery device (tray tower) and subjected to extractive distillation with water, whereby a mixed liquid of methanol and water was taken out from the lower part of the tower. The weight ratio of methanol to water in this mixture was 30:70. Next, this water / methanol mixture was separated and purified in another tower-type collector, and methanol was recovered.
[0043]
Further, the recovered methanol was treated with a cation exchange resin. Specifically, the recovered methanol is continuously charged at a rate of 1.0 kg / hour into a filling tank (10 L) of an H ⁺ type strongly acidic cation exchanger (manufactured by Dow Chemical Co., Ltd .: “DOWEX G25”). Processed.
[0044]
Thus, recovered and treated methanol was obtained. The concentration of aldehyde and acetal in this treated methanol was measured by gas chromatography (detector: FID). As a result, the concentration of the acetal compound (mainly dimethyl acetal) was 380 ppm. Moreover, an aldehyde compound (mainly acetaldehyde was assumed) could not be detected.
[0045]
In addition, when the same density | concentration measurement was performed also about the collection | recovery methanol before processing with a cation exchange resin, the density | concentration of the aldehyde compound (mainly acetaldehyde) was 200 ppm. No acetal compound could be detected.
[0046]
The treated methanol thus obtained and unused methanol were mixed at a ratio of 9: 1 (weight ratio), and this mixture was used as a solvent to further continue the continuous copolymerization of the ethylene-vinyl acetate copolymer. went. As described above, while recovering and treating methanol and reusing it as a solvent, the above series of steps was continuously performed to continuously produce a methanol solution of the copolymer.
[0047]
This ethylene-vinyl acetate copolymer was saponified and melt-molded by the following steps.
First, 1 part by weight of caustic soda was added to 100 parts by weight of the methanol solution, and the copolymer was saponified while blowing methanol vapor at 110 ° C. and 3.5 kg / cm ² . By-product methyl acetate was distilled out together with a part of methanol and removed out of the system. Water-methanol vapor was further blown into the saponified product (EVOH) solution thus obtained to distill the solvent, thereby obtaining an EVOH solution (methanol / water = 65/35, weight ratio) having a polymer concentration of 35% by weight.
[0048]
Next, this EVOH solution is discharged from a die having a 2 mm diameter hole into a coagulating liquid (methanol / water = 10/90: weight ratio) at 5 ° C., solidified into a strand shape, cut with a cutter and long. A 2.5 to 3.5 mm pellet was obtained. The pellet was washed with 15 parts by weight of water with respect to 1 part by weight of the pellet and drained. Furthermore, the washed pellets were treated with an aqueous solution of acetic acid and sodium dihydrogen phosphate, drained and dried. Thus, EVOH pellets having a saponification degree of 99.5 mol% and MI of 2.1 g / 10 min (load: 2160 g, temperature: 190 ° C.) were obtained.
[0049]
This EVOH pellet was formed into a single layer film having a thickness of 30 μm by the following method.
・ Model: Single screw extruder (non-vent type)
・ L / D; 20
・ Diameter: 60mmφ
・ Screw: One-flight full flight type, surface nitrided steel ・ Screw rotation speed: 40 rpm
・ Die: 300mm wide coat hanger die ・ Lip gap: 0.3mm
Cylinder (C1 to C3), die temperature setting C1 / C2 / C3 / die; 195/230/230/230 (° C.)
[0050]
Fish eyes (thickness of about 150 μm or more that can be confirmed with the naked eye) in the film after 1 hour from the start of film formation were counted. Fish eye, was in terms of per 1.0m ² less than 10 / m ^2. Moreover, when the end surface of the wound film was observed, it was colorless.
[0051]
(Comparative example)
Except for using recovered methanol not treated with a cation exchange resin as a solvent, the steps of polymerization, saponification, pelletization, and film formation were carried out in the same manner as in the above Example. A 30 μm monolayer film was obtained.
[0052]
Was counted fish eyes in the same manner as in Example, fisheyes, converted to have about 150 / m ² occurred per 1.0 m ^2. Moreover, when the end surface of the wound film was observed, it was colored yellow.
[0053]
【The invention's effect】
As described above in detail, according to the present invention, even if the recovered alcohol solvent is used as a solvent for copolymerization, it is possible to suppress the appearance defect of the molded product that is the final product. The present invention that realizes not only reduction of manufacturing cost but also effective use of resources while maintaining product quality has great utility value in this technical field.

Claims (11)

  A method for producing an ethylene-vinyl acetate copolymer in which ethylene and vinyl acetate are copolymerized in an alcohol solvent, wherein at least a part of the alcohol solvent is a solvent that has been subjected to aldehyde reduction treatment in advance. A method for producing an ethylene-vinyl acetate copolymer.   The method for producing an ethylene-vinyl acetate copolymer according to claim 1, wherein the aldehyde reduction treatment is contact with a solid acid.   The method for producing an ethylene-vinyl acetate copolymer according to claim 2, wherein the solid acid is a cation exchange resin.   4. The solvent according to claim 1, wherein at least a part of the alcohol solvent is a solvent that is used as a solvent for copolymerization of ethylene and vinyl acetate, separated from the product and unreacted raw material, recovered, and subjected to aldehyde reduction treatment. The manufacturing method of the ethylene-vinyl acetate copolymer in any one.   The method for producing an ethylene-vinyl acetate copolymer according to any one of claims 1 to 4, wherein the alcohol solvent before the aldehyde reduction treatment has an aldehyde compound concentration of 1 ppm to 500 ppm.   The method for producing an ethylene-vinyl acetate copolymer according to any one of claims 1 to 5, wherein the alcohol solvent subjected to aldehyde reduction treatment has an aldehyde compound concentration of 100 ppm or less.   The method for producing an ethylene-vinyl acetate copolymer according to claim 6, wherein the alcohol solvent subjected to the aldehyde reduction treatment has an aldehyde compound concentration of 30 ppm or less.   The method for producing an ethylene-vinyl acetate copolymer according to any one of claims 1 to 7, wherein the alcohol solvent contains an acetal compound. The method for producing an ethylene-vinyl acetate copolymer according to claim 8, wherein the alcohol solvent has an acetal compound concentration of 0.1 ppm or more and 10,000 ppm or less.   A method for producing the above copolymer by continuously copolymerizing ethylene and vinyl acetate in an alcohol solvent to obtain an ethylene-vinyl acetate copolymer, wherein ethylene and vinyl acetate are copolymerized in an alcohol solvent. An alcohol solvent that has been subjected to an aldehyde reduction treatment, comprising a step of obtaining an ethylene-vinyl acetate copolymer, a step of recovering at least a portion of the alcohol solvent, and a step of subjecting the recovered alcohol solvent to an aldehyde reduction treatment A method for producing an ethylene-vinyl acetate copolymer is characterized by continuously obtaining an ethylene-vinyl acetate copolymer while using at least a part of an alcohol solvent used for copolymerization. Method for producing a vinyl acetate copolymer saponification product - either obtained ethylene by the production method according to claim 1-10 - ethylene vinyl acetate copolymer, characterized in that saponification.