JPH0967411A - Production of ethylene-vinyl acetate copolymer saponification product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an ethylene-vinyl acetate copolymer saponification product uniform in shape and excellent in melt moldability. SOLUTION: This method for producing an ethylene-vinyl acetate copolymer saponification product comprises saponifying ethylene-vinyl acetate copolymer having an ethylene content of 15-60mol.% in the presence of an alkali catalyst in an alcohol solvent until reaching a vinyl acetate saponification degree of 70-98mol.%, adding water or water/an alcohol to the obtained partial ethylene- vinyl acetate copolymer saponification product solution, again saponifying the obtained mixture solution in the presence of an alkali catalyst, depositing the obtained highly saponified ethylene-vinyl acetate copolymer saponification product solution having a saponification degree of >=99.4% in a coagulation bath, treating the obtained deposits with an acid and subsequently pelletizing the treated deposits.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a saponified ethylene-vinyl acetate copolymer having a uniform shape and excellent melt moldability.

[0002]

2. Description of the Related Art Saponified ethylene-vinyl acetate copolymers are widely used for various purposes such as films, sheets, containers and fibers because they are excellent in various properties such as oxygen barrier property and mechanical strength. Among them, when producing a sheet or film by melt molding, the saponified product of the copolymer is preferably in the form of pellets from the viewpoint of handling and molding, and as a method for producing the pellets, for example, Japanese Patent Publication No.
No. 7-38634, a water and / or methanol mixed solution of a saponified product of an ethylene-vinyl acetate copolymer is extruded in a strand shape into a coagulating liquid of water or a water system containing methanol, and the obtained strand is cut to produce pellets. And a method of using as the coagulating liquid an organic solvent which is compatible with methanol as a coagulating liquid for the strands but does not dissolve the saponified copolymer, as disclosed in JP-A-62-116614. Is disclosed, and further, JP-A-6
Japanese Patent Laid-Open No. 2-106904 discloses a method of producing pellets by dry blending the saponified product of the copolymer and a lubricant and then extruding the strands into a strand in order to improve the melt moldability of the pellets.

[0003]

However, according to the technique disclosed in Japanese Patent Publication No. 47-38634, the hardness of the solidified strand is not always sufficient, so that when cut and pelletized, its shape becomes non-uniform or deforms. In the technique disclosed in Japanese Patent Laid-Open No. 62-116614, since an organic solvent such as methyl acetate is used, there is a drawback that equipment for improving the working environment is required and the cost becomes high. Japanese Patent Laid-Open No. 62-10690
In the technology disclosed in Japanese Patent Publication No. 4, when the obtained pellets are melt-molded to produce a film or sheet, it is difficult to say that the moldability is good, and the layer thickness accuracy of the molded film or sheet is still insufficient. Met. In the market in recent years, layer thickness accuracy of films and sheets is particularly required, but when pellets with defective shape or non-uniform diameter are used for extrusion molding, fluctuations in charging to the extruder, fluctuations in load on the extruder, etc. As a result, it is difficult to stably obtain a uniform molded product, and therefore, a saponified ethylene-vinyl acetate copolymer having a uniform shape and excellent melt moldability with less heat history is desired. ing.

[0004]

Means for Solving the Problems As a result of intensive studies by the present inventors in order to solve the above-mentioned problems, (1) ethylene-containing alcohol having an ethylene content of 15 to 60 mol%
The vinyl acetate copolymer is saponified with an alkali catalyst to give an ethylene-containing vinyl acetate component having a saponification degree of 70 to 98 mol%.
Obtaining a vinyl acetate copolymer partially saponified solution,
(2) A mixed solution obtained by adding water or water / alcohol to the partially saponified ethylene-vinyl acetate copolymer solution is re-saponified in the presence of an alkali catalyst to obtain a saponification degree of 99.4 mol%. The step of obtaining a saponified ethylene-vinyl acetate copolymer saponified solution having a high degree of saponification as described above, (3) the saponified ethylene-vinyl acetate copolymer saponified solution is extruded into a strand in a coagulation bath to precipitate, and then cut. In order to complete the present invention, it was found that the saponified ethylene-vinyl acetate copolymer can be obtained by combining the above-mentioned three steps (1) to (3) of pelletizing and acid treatment. Arrived

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below for each step. Step (1) The ethylene-vinyl acetate copolymer used in the present invention needs to have an ethylene content of 15 to 60 mol%, preferably 20 to 55 mol%, and more preferably 25.
~ 50 mol%.

If the ethylene content is less than 15 mol%, precipitation of the product after re-saponification in the subsequent step (2) with water is not complete, resulting in emulsification, which is not preferable in operation. In order to keep the methanol solution of the copolymer in a uniform solution state, it is necessary to pressurize it and heat it to a considerably high temperature. Further, depending on the residence time, there is a drawback that quality deterioration occurs, and when a film or sheet is produced by melt molding, scorching or gel is likely to occur, which is not preferable.

On the other hand, if it exceeds 60 mol%, it will not dissolve in the alcohol / water mixed solvent in the step (2) and it will be difficult to carry out re-saponification uniformly, and the saponification reaction will proceed when molding after re-saponification. Even if such a difficult method is used, a considerably large amount of catalyst is required. Therefore, when the produced saponified product is melt-molded, fish eyes are likely to occur, and it is difficult to improve mechanical strength, which is not preferable.

In addition to ethylene and vinyl acetate, the ethylene-vinyl acetate copolymer of the present invention may contain an ethylenically unsaturated monomer copolymerizable therewith as a copolymerization component. Examples of the monomer include olefins such as propylene, isobutylene, α-octene, α-dodecene, and α-octadecene, acrylic acid, methacrylic acid,
Crotonic acid, maleic acid, maleic anhydride, unsaturated acids such as itaconic acid or salts thereof or mono- or dialkyl esters thereof, acrylonitrile, nitriles such as methacrylonitrile, amides such as acrylamide and methacrylamide, ethylenesulfonic acid, allyl Olefin sulfonic acids such as sulfonic acid and methallyl sulfonic acid or salts thereof, alkyl vinyl ethers, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride,
Polyoxyalkylene (meth) allyl ethers such as vinylidene chloride, polyoxyethylene (meth) allyl ether, polyoxypropylene (meth) allyl ether,
Polyoxyalkylene (meth) acrylates such as polyoxyethylene (meth) acrylate and polyoxypropylene (meth) acrylate; polyoxyalkylene (meth) acrylamides such as polyoxyethylene (meth) acrylamide and polyoxypropylene (meth) acrylamide; Polyoxyethylene (1- (meth) acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinyl Examples include amines.

In step (1), the ethylene-vinyl acetate copolymer is saponified in an alcohol solvent with an alkali catalyst. The alcohol used at this time is methanol, ethanol, n-propanol or isopropanol. , N-butanol, t-butanol and the like can be mentioned, but methanol, n-propanol and t-butanol are preferably used. It is also preferable to use an aliphatic polyhydric alcohol such as glycerin, ethylene glycol or hexanediol together with the alcohol.

The saponification reaction in the step (1) is carried out in the presence of an alkali catalyst, and the alkali catalyst used in the saponification reaction of polyvinyl acetate or an ethylene-vinyl acetate copolymer with an alkali catalyst. The conventionally known catalyst can be used as it is. Specifically, sodium hydroxide,
Typical examples are alkali metal hydroxides such as potassium hydroxide and lithium hydroxide, sodium methylate, alkali metal alcoholates such as potassium t-butoxy, and 1,8-diazabicyclo [5,4,10] undecene-7 (DBU). Examples of the co-basic amine include alkali metal carbonates, hydrogen carbonate alkali metal salts and the like, but sodium hydroxide is preferably used from the viewpoint of easy handling, catalyst cost and the like.

The amount of the catalyst used varies depending on the degree of saponification required, the reaction temperature, etc., but is 0.03 equivalent or less, preferably 0.02 equivalent, based on the residual acetic acid groups in the ethylene-vinyl acetate copolymer. It is the following. It is also possible to use an acid catalyst such as hydrochloric acid or sulfuric acid instead of the alkali catalyst.

Upon saponification, the above ethylene-vinyl acetate copolymer is dissolved in alcohol or an alcohol-containing medium to a concentration of usually about 20 to 60% by weight, and an alkali catalyst or an acid catalyst is added. 40-1
The reaction is carried out at a temperature of 40 ° C. There is no particular limitation on the concentration of the partially saponified product so long as the ethylene-vinyl acetate copolymer partially saponified product (hereinafter abbreviated as partially saponified product) does not precipitate at the solution temperature. Is 10 to 50% by weight, preferably 15 to 45% by weight
It should be so.

The degree of saponification of the vinyl acetate component of the partially saponified product obtained by such saponification needs to be 70 to 98 mol%, preferably 80 to 98 mol%. When the degree of saponification exceeds 98 mol%, the partially saponified product produced becomes insoluble in the reaction medium and precipitates to form a heterogeneous system, and it is generally difficult to further increase the degree of saponification in the next step. On the other hand, when the saponification degree is less than 70 mol%, the amount of the alkali catalyst used in the step (2) increases, and the thermal stability of the product deteriorates.

The partially saponified solution thus obtained is preferably used as it is in the next step (2) because it is easier in production and is preferable. However, if necessary, an acetic acid ester by-produced by the saponification reaction, such as methyl acetate, etc. Can be removed to such an extent that the reaction solution can be maintained in a solution state, and the partially saponified product separated from the reaction medium by means of steam distillation, centrifugation, pressing, drying, etc. is re-saponified in the next step (2). It may be prepared so as to have a solution composition suitable for the reaction and then subjected to the re-saponification reaction. If necessary, ethylene glycol or the like may be added for the re-saponification reaction.

Step (2) In this step, in the step of re-saponifying the partially saponified solution obtained in Step (1), water or water / water is added to the partially saponified solution.
The reaction is carried out in an alcohol / water mixed solvent by adding alcohol. Alcohol 10 to dissolve the partially saponified product
The reaction is carried out in a mixed solvent in which both are mixed at a ratio of 15 to 150 volumes of water with respect to 0 volumes. As the alcohol, water-soluble lower alcohols such as methanol, ethanol, n-propanol, isopropanol and t-butanol may be used, but the use of methanol is most preferable from the viewpoint of reaction rate and economy. Further, a mixed solvent of two or more kinds of alcohol and water may be used, and a small amount of another solvent may be mixed as long as it does not hinder the saponification reaction and does not cause an obstacle to the coloring property of the product.

Since the above partially saponified product can be uniformly dissolved in the alcohol / water mixture having the above-mentioned specific ratio, the saponification reaction can be carried out in a homogeneous system.

Water 15 to 15 per 100 volumes of alcohol
In the case where a molded product is made from saponified ethylene-vinyl acetate copolymer obtained by re-saponification reaction in a mixed solvent by adding water and / or alcohol in a proportion of 0 volume, preferably 15-120 volume It is suitable from the viewpoint of preventing the formation of fish eyes, and even if the amount of water is more or less than the above range, the saponified solution may become unstable and precipitate saponified, which is not practical. In addition, it is difficult to avoid formation of fish eyes when the saponified product is molded.

In such re-saponification, a solution obtained by dissolving a partially saponified product in an alcohol / water mixed solvent is added with an alkali catalyst or an acid catalyst and re-saponified at a temperature of 50 to 145 ° C. The amount of the catalyst used is 0.001 to 0.5 equivalents in the case of alkali with respect to the vinyl acetate group, and 0.00 in the case of acid.
It is suitable to use about 5 to 0.5 equivalents. However, the re-saponification conditions are not limited to the above numerical range.

In such re-saponification, the saponification degree of the vinyl acetate component of the high saponification ethylene-vinyl acetate copolymer saponification product obtained is required to be 99.4 mol% or more, and it is 99.5. It is preferably at least mol%.
When the saponification degree is less than 99.4 mol%, acetic acid odor is generated during melt molding and fish eyes frequently occur, which is not preferable.

Step (3) In this step, first, water is added directly to the saponified solution of the ethylene-vinyl acetate copolymer having a high degree of saponification obtained in the above step (2), or the saponified solution is appropriately concentrated or A solution for strand production is prepared by adding water after dilution.
At this point, lubricants such as saturated aliphatic amides (such as stearic acid amide), unsaturated fatty acid amides (such as olefinic acid amide), bis fatty acid amides (such as ethylene bisstearic acid amide), fatty acid metal salts (such as calcium stearate) Etc.), low molecular weight polyolefins (for example, low molecular weight polyethylene having a molecular weight of about 500 to 10,000, or low molecular weight polypropylene), inorganic salts (for example, hydrotalcite, etc.), plasticizers (for example, ethylene glycol, glycerin, hexanediol, etc.) (Eg, aliphatic polyhydric alcohol).

Next, the saponified solution of the ethylene-vinyl acetate copolymer having a high degree of saponification is extruded and precipitated in a coagulating solution in a strand form. The concentration of the saponified product is preferably 15 to 55% by weight, more preferably 20 to 50% by weight. If the amount is less than 15% by weight, coagulation in the coagulating liquid becomes difficult, and conversely, if it exceeds 55% by weight, the porosity of the pellet decreases, which adversely affects the thermal stability during molding, which is not preferable. The weight mixing ratio of water and alcohol in the saponified solution is 1/9 to 7/3,
It is desirable to adjust so as to be preferably 2/8 to 6/4. If the ratio of water to alcohol is less than 1/9, the solution becomes a little unstable, and the porosity at the time of strand precipitation decreases a little, while if it exceeds 7/3, the solution becomes unstable and precipitation of a saponified product may occur. is there.

Water or a water / alcohol mixed solvent is used as the coagulating liquid, and the alcohol concentration when alcohol is used is preferably equal to or lower than the alcohol content of the alcohol / water mixed liquid in the saponified copolymer solution. However, when the content exceeds the above range, polymer loss at the time of strand precipitation in the coagulating liquid increases, which is not preferable.

Further, it is also possible to use an organic solvent as a coagulating liquid, which has a boiling point of 100 ° C. or lower and is compatible with alcohol, but does not dissolve the saponified ethylene-vinyl acetate copolymer having a high degree of saponification. . Examples of the above organic solvent include aromatic hydrocarbons such as benzene, ketones such as acetone and methyl ethyl ketone, ethers such as dipropyl ether, organic acid esters such as methyl acetate, ethyl acetate and methyl propionate. The temperature at which the saponified ethylene-vinyl acetate copolymer saponification solution is brought into contact with the coagulating liquid is -10 to 40 ° C, preferably 0 to 20 ° C.
It is. Since the above-mentioned organic solvent is a non-solvent for the saponified product, there is almost no risk of the saponified product being dissolved in the coagulating liquid to cause resin loss, but operation at a temperature as low as possible is safe.

The high saponification degree ethylene-vinyl acetate copolymer saponification solution is extruded in a strand form into a coagulating liquid through a nozzle or die having an arbitrary shape, usually circular holes. The cross-sectional shape of the pores is usually circular, but in some cases it may be elliptical, prismatic, rhombic, star-shaped, etc.
About 5 mm is suitable. Also, the number of strands is not necessarily one, and can be extruded in any number between several and hundreds.

After being extruded in the form of a strand and sufficiently solidified, the strand is cut and pelletized.

As washing conditions, the pellets are washed in a water bath having a bath ratio (which represents the weight ratio of the saponified ethylene-vinyl acetate copolymer to the weight of the bath coagulation liquid) of 1 to 10 and a temperature of 10 to 60 ° C. By washing with water, oligomers and impurities in EVOH are removed, and especially sodium acetate is removed up to 0.5% by weight or less.

From the viewpoint of workability and handling in molding, it is practical that the diameter is 2 to 5 mm and the length is 2 to 5 mm in the case of a cylindrical shape, and the diameter is 2 to 5 mm in the case of a spherical shape. . The washed pellets need to be treated with an acid, and examples thereof include acetoacetic acid, formic acid, acetic acid, adipic acid, phosphoric acid and boric acid, and more preferably acetic acid. As conditions for the acid treatment, for example, washing is performed in an acetic acid aqueous solution of 3% by weight or less, and the treatment is performed so that the pH of the washing liquid becomes 3 to 8.

In the present invention, the method is not particularly limited as long as it is a method of sequentially performing the above steps (1) to (3), but in industrial production, the above steps (1) and (2) are known column type. It is also effective to carry out the saponification reaction continuously by using two or more reactors (saponification tower). In the present invention, the operation of the above step (1) can be performed in the first tower reactor. The partially saponified solution is continuously supplied to the second column reactor and the above step (2) is performed to obtain a highly saponified ethylene-vinyl acetate copolymer saponified solution.

The first tower type reactor can be used
Although it is a common distillation column such as a perforated plate column, a plate column such as a bubble column, and a packed column, it is generally preferable to use a plate column capable of taking a long residence time. In the first tower type reactor, an alcohol solution of an ethylene-vinyl acetate copolymer and an alkali catalyst are supplied from the upper part of the tower, while a water-soluble lower alcohol vapor is blown from the lower part or the bottom of the tower to form a uniform liquid phase in the tower. Is used to obtain a partially saponified product.

The ethylene-vinyl acetate copolymer is fed as an alcoholic solution to the upper part of the tower type reactor as described above. In this case, the concentration of the copolymer is not particularly limited,
When the content is extremely high, such as 60% by weight or more, the viscosity of the alcohol solution becomes high and the operation becomes difficult, which is not preferable. The alcohol solution concentration of the copolymer depends on the degree of polymerization of the copolymer and the reaction temperature, but is generally 25 to 60% by weight.
Is preferred.

Examples of the water-soluble lower alcohol blown into the tower include methanol, ethanol, butanol, isopropanol and the like, but methanol is preferably used. The operation of step (1) using methanol will be described below, but the operation is not limited to this.
The temperature of the methanol vapor blown into the column is usually the boiling point of methanol under the pressure in the column reactor, but it does not matter even if it is under heating, and preferably 100 to 140.
° C.

The pressure in the tower during the reaction is 1 to 15 kg / cm.
The range of ² G is preferable, and the temperature inside the column is not higher than the boiling point determined by the pressure inside the column and the composition, and is within the range of 60 to 150 ° C. The blowing position of the methanol vapor is preferably right below the lower stage of the column and above the liquid level at the bottom of the column.

The composition of the partially saponified solution after completion of the reaction in the first tower reactor is adjusted to 20 to 45% by weight of the partially saponified product in order to improve the supply to the second tower reactor. The saponification degree of the vinyl acetate unit of the partially saponified product is preferably 70 to 98 mol%, and preferably 80 to 98 mol% in order to make the resaponification reaction in the second column reactor efficient.
97 mol% is more preferable.

The partially saponified solution obtained by such an operation is then continuously fed to the second column reactor for re-saponification, which can be used as the column reactor in this case. Is a normal distillation column such as a perforated plate column, a plate column such as a bubble column, and a packed column, but it is preferable to use a plate column such as a bubble column. The alkaline catalyst is fed to the top of the reactor.

Thus, a saponified ethylene-vinyl acetate copolymer solution having a vinyl acetate component saponification degree of 99.5 mol% or more as described above can be obtained. Then, it is pelletized by the step (3) as described above.

The pellets obtained by the production method of the present invention are melt-molded into a desired molded article.
The temperature condition for melt molding is about 160 to 260
C is desirable. At the time of molding, if necessary, known additives such as a reinforcing material such as glass fiber and carbon fiber, a filler, a colorant, a stabilizer such as hydrotalcite, a foaming agent and a desiccant may be appropriately blended. Also, ethylene-
The saponified vinyl acetate copolymer may be blended with an appropriate amount of a modifying thermoplastic resin.

As the melt molding method, any molding method such as injection molding method, compression molding method and extrusion molding method can be adopted. Among them, examples of the extrusion molding method include a T-die method, a hollow molding method, a pipe extrusion method, a linear extrusion method, a profile die extrusion method, an inflation method, and the like, and a molding of a saponified ethylene-vinyl acetate copolymer alone. Thing (film, sheet, tape,
(Bottles, pipes, filaments, atypical cross-section extrudates, etc.)
Not only is it possible to coextrude the saponified ethylene-vinyl acetate copolymer layer with another thermoplastic resin layer.

In the case of coextrusion molding, the other resin is low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ionomer, ethylene-α-olefin (α-C3-20).
(Olefin) copolymer, ethylene-acrylic acid ester copolymer, polypropylene, propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymer, polybutene, homopolymers or copolymers of olefins such as polypentene, Or a polyolefin resin in a broad sense such as those obtained by graft-modifying homo- or copolymers of these olefins with unsaturated carboxylic acids or their esters, polyester,
Examples thereof include polyamide, copolyamide, polyvinyl chloride, polyvinylidene chloride, acrylic resin, styrene resin, vinyl ester resin, polyester elastomer, polyurethane elastomer, chlorinated polyethylene, chlorinated polypropylene and the like. Coextrusion with a composition in the saponified ethylene-vinyl acetate copolymer different from that of the present application is also possible.

Further, a molded product such as a film or sheet is once obtained from a saponified product of an ethylene-vinyl acetate copolymer, and another thermoplastic resin such as polyolefin is extrusion coated on the molded product, or a film or sheet of another thermoplastic resin. When using an adhesive to laminate, any substrate (paper, metal foil, stretched or unstretched plastics film or sheet, woven fabric, non-woven fabric, metal foil, wood surface, etc.)
Coating with saponified vinyl acetate copolymer by extrusion coating
(In addition, another resin such as a heat-sealable resin may be extrusion coated).

A molded product after melt molding, a coextrusion molded product,
The melt-coated molded product is heat-treated, cooled, rolled, uniaxially or biaxially stretched, printed, dry laminated, solution or melt-coated, bag making, deep squeezing, boxing, tube processing, if necessary. Split processing etc. can be performed.

[0041]

EXAMPLES The present invention will be specifically described below with reference to examples. In the examples, “part” and “%” are based on weight unless otherwise specified.

Example 1 Step (1) A methanol solution containing an ethylene content of 35 mol% and an ethylene-vinyl acetate copolymer of 50% was fed at a rate of 10 kg / hour to the upper part of a plate column (saponification column). At the same time, a methanol solution containing 0.002 equivalent of sodium hydroxide was supplied from the upper part of the tower to the residual acetic acid group in the polymer.
On the other hand, methanol vapor was fed from the bottom of the column at a rate of 15 kg / hr at the boiling point. Tower temperature is 128 ℃, tower pressure is 5kg /
It was cm ² G. 10 minutes after the start of preparation, ethylene-
A partially saponified vinyl acetate copolymer solution was taken out. The ethylene-vinyl acetate copolymer partially saponified solution obtained from the bottom of the column was a completely transparent and homogeneous solution, and the composition was 35% ethylene-vinyl acetate copolymer partially saponified, 65% methanol.
%, And the saponification degree of the vinyl acetate component of the partially saponified ethylene-vinyl acetate copolymer was 88.0 mol%.

Step (2) Subsequently, the partially saponified solution is supplied to the upper part of another tray column (saponification column), and at the same time, 0.015 equivalent of water is added to the acetic acid group in the copolymer. A methanol solution containing sodium oxide was supplied from the top of the tower. Meanwhile, from the bottom of the tower, methanol 10
Both of them were mixed in a ratio of 0 part to 30 parts of water, and they were supplied under an azeotropic point. The temperature inside the tower is 140 ° C at the bottom and 128 at the top.
The tower pressure was 5 kg / cm ² G. The highly saponified ethylene-vinyl acetate copolymer saponified solution obtained from the bottom of the column was a completely transparent and homogeneous solution, and the saponification degree of the vinyl acetate component of the ethylene-vinyl acetate copolymer saponified product was 99.8 mol. %Met.

Step (3) Subsequently, the saponified ethylene-vinyl acetate copolymer solution is extruded in a strand form from a nozzle having a pore diameter of 4 mm into a coagulating liquid tank of 5% methanol and 95% water maintained at 5 ° C. did. The time required for the strand to cure was 30 seconds. After the completion of coagulation, the strand-shaped material was cut with a cutter to obtain white, porous pellets having a diameter of 3.8 mm and a length of 4 mm. The obtained pellet had a uniform shape and had no deformation. The coagulation liquid was not turbid at all and the resin loss was 1% or less. The porous pellets at a temperature of 30
After washing with water for 1 hour in a water bath at ℃, repeat this 4 times to remove sodium acetate, and then in water at 30 ℃ for 1 hour.
The product that had been washed for a period of time was dried to obtain a product.

(1) Strand Evaluation Curing Time The hardness of the strand was measured according to JIS K 6301 with a spring hardness tester (Shimadzu Corporation) until the hardness reached 30 degrees or more, and evaluated as follows. did. ○ ・ ・ ・ 80 seconds or less × ・ ・ ・ 81 seconds or more

Strand break The number of strand breaks during 36 hours of operation was measured and
It was expressed by the number of cuts per 0 piece.

Precision of Pellet Size The diameter and length of 100 pellets were measured with a caliper, and the proportion of pellets in which the diameter and length of the pellets were within ± 0.2 mm was measured and evaluated as follows. . ◎ ・ ・ ・ 95% or more ○ ・ ・ ・ 80 to less than 95% △ ・ ・ ・ 60 to less than 80% × ・ ・ ・ less than 60%

Coagulation liquid stain and resin loss The coagulation liquid stain was visually observed, and the resin loss into the coagulation liquid was calculated by the following formula. Resin loss (% by weight) = ((A−B) / A) × 100 A: High saponification degree before entering coagulation liquid ethylene-vinyl acetate copolymer High saponification degree in solution of saponified ethylene-acetic acid Weight of saponified vinyl copolymer B: Weight of saponified ethylene-vinyl acetate copolymer having a high degree of saponification in the obtained strand-shaped pellets

(2) Performance of film The obtained product pellet was formed into a film under the following conditions, and the appearance of the obtained film was observed.

Fish Eyes The number of fish eyes per 100 cm ^{2 of} film was measured. ◎ ・ ・ ・ 1 or less ○ ・ ・ ・ 2-5 or less △ ・ ・ ・ 6-9 or less × ・ ・ ・ 10 or more

Load fluctuation of extruder It was determined by fluctuation of motor load (screw torque A (ampere) at a screw rotation speed of 60 rpm) of the extruder during continuous film formation for 5 hours. ◯: 5% or less Δ: 5 to less than 10% ×: 10% or more The results are shown in Tables 1 to 3.

Example 2 Step (1) A methanol solution containing 27 mol% of ethylene and 40% of ethylene-vinyl acetate copolymer was supplied to a kneader reactor. A methanol solution containing 0.004 equivalent of sodium hydroxide was added to the residual acetic acid group in the polymer to give 1
After pressure reaction at 30 ° C., a partially saponified ethylene-vinyl acetate copolymer partially saponified solution was obtained, and a saponification of the vinyl acetate component of the partially saponified ethylene-vinyl acetate copolymer was obtained. The degree of conversion was 95.0 mol%.

Step (2) To this partially saponified ethylene-vinyl acetate copolymer solution, water was added to a methanol solution containing 0.008 equivalent of sodium hydroxide with respect to the acetic acid groups in the copolymer, and methanol / The weight ratio of water was 70/30. 140 this solution
The mixture was stirred at 1.5 ° C. for 1.5 hours to obtain a saponified ethylene-vinyl acetate copolymer saponification solution. The saponification degree of the vinyl acetate component of the saponified ethylene-vinyl acetate copolymer is 99.
It was 6 mol%.

Step (3) The above-mentioned saponified solution of ethylene-vinyl acetate copolymer having a high degree of saponification whose liquid temperature is 50.degree.
Coagulation bath maintained at ℃ (width 100 mm, length 4,000
mm, height 100 mm). After the solidification, the attached water was removed, and the strand-like material was cut by a cutter through a take-up roller attached to the end of the solidification liquid tank to produce a white, porous pellet having a diameter of 3.7 mm and a length of 4 mm. .

Comparative Example 1 In the re-saponification step of Example 1, the procedure was changed so that only 100 parts of methanol was fed from the bottom of the column under the azeotropic temperature.
Was evaluated in the same way as

Example 3 The same experiment as in Example 1 was carried out except that an ethylene-vinyl acetate copolymer having an ethylene content of 31 mol% was charged in the upper part of the plate column (saponification column) according to Example 1. It carried out and evaluated like Example 1.

Comparative Example 2 An experiment was conducted in the same manner as in Example 1 except that the ethylene content of the ethylene-vinyl acetate copolymer of Example 1 was changed to 13 mol%, and the same evaluation as in Example 1 was performed.

Comparative Example 3 An experiment was conducted in the same manner as in Example 1 except that the ethylene content of the ethylene-vinyl acetate copolymer of Example 1 was changed to 65 mol%, and the same evaluation as in Example 1 was performed.

Comparative Example 4 In step (1) of Example 1, ethylene was added to the upper part of the column at a rate of 0.25 kg / hour, and the saponification degree of the vinyl acetate component was 60.0 mol%. A partially saponified product was obtained, and in the following steps (2) and (3), an experiment was conducted according to Example 1, and the same evaluation as in Example 1 was performed.

Comparative Example 5 A saponified ethylene-vinyl acetate copolymer having a saponification degree of the vinyl acetate component of 90.0 mol% was obtained without adding sodium hydroxide in the step (2) of Example 1. The experiment was performed according to Example 1 except that the evaluation was performed in the same manner as in Example 1.

Comparative Example 6 An experiment was conducted in the same manner as in Example 1 except that the amount of sodium hydroxide used in the step (1) of Example 1 was changed to 0.02 equivalent, and ethylene with a saponification degree of 99.5 mol% was used. -An experiment was conducted in the same manner as in Example 1 except that a partially saponified vinyl acetate copolymer was obtained, and the same evaluation as in Example 1 was performed.

[0062]

Table 1 Ethylene Content Saponification Degree (mol%) (mol%) Partially Saponified Saponified Example 1 35 88.0 99.8 Example 2 27 95.0 99.6 Example 3 31 97.8 99 9.9 Comparative Example 1 35 88.0 99.9 Comparative Example 2 13 97.0 99.9 Comparative Example 3 65 78.0 99.5 Comparative Example 4 35 60.0 90.0 Comparative Example 5 35 88.0 90 0.0 Comparative Example 6 35 * 99.5 * In step (1), the degree of saponification was 99.5%, and a partial saponification product was not obtained.

[0063]

[Table 2] Strand coagulating liquid curing time Out Pellets Stains Resin loss size accuracy (%) Example 1 ○ 0 ◎ Transparent 0.5 Example 2 ○ 0 ◎ Transparent 1.5 Example 3 ○ 0 ◎ Transparent 0.8 Comparison Example 1 ○ 0 ◎ Transparent 0.6 Comparative example 2 × 5 ◎ White turbidity 15.0 Comparative example 3 (Measurement not possible) * 1 Comparative example 4 (Measurement not possible) * 2 Comparative example 5 ○ 8 × Some white turbidity 8 .4 Comparative Example 6 (Measurement not possible) * 1 * 1: If the saponified ethylene-vinyl acetate copolymer had already precipitated in step (1) and the reaction solution was a solution before entering step (3). It cannot be extruded from the nozzle. * 2: Strand does not cure.

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[Table 3] * Pellets cannot be obtained as described above, and measurement is not possible.

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EFFECT OF THE INVENTION In the present invention, since the saponified product of ethylene-vinyl acetate copolymer is produced by a specific method, it is possible to obtain a saponified product of ethylene-vinyl acetate copolymer which is uniform and excellent in melt moldability. Pellets can be obtained, which are useful as pesticide bottles, fuel tank containers, etc., in combination with organic solvent containers, especially HDPE.

Claims (3)

[Claims] 1. A saponification degree of a vinyl acetate component of an ethylene-vinyl acetate copolymer having an ethylene content of 15 to 60 mol% in an alcohol solvent is 70 to 98 with an alkali catalyst.
Saponification to obtain a mol% to obtain an ethylene-vinyl acetate copolymer partially saponified solution, (2) water or water / alcohol is added to the ethylene-vinyl acetate copolymer partially saponified solution and mixed A step of forming a solution and re-saponifying in the presence of an alkali catalyst to obtain a high saponification degree ethylene-vinyl acetate copolymer saponified solution having a saponification degree of a vinyl acetate component of 99.4 mol% or more, (3) A step of extruding and precipitating the saponified solution of the ethylene-vinyl acetate copolymer having a high degree of saponification in a coagulation bath, followed by acid treatment, and a combination of the above three steps (1) to (3). A method for producing a saponified ethylene-vinyl acetate copolymer, which comprises: 2. The step (1) of obtaining a partially saponified ethylene-vinyl acetate copolymer solution is characterized in that a saponification reaction is carried out by forming a uniform liquid phase in the tower using a tower reactor. The method for producing a saponified ethylene-vinyl acetate copolymer according to claim 1. 3. The step (2) of obtaining a saponified solution of a highly saponified ethylene-vinyl acetate copolymer having a saponification degree of 99.4 mol% or more is carried out by using a tower type reactor, and a uniform liquid is provided in the tower. The method for producing a saponified ethylene-vinyl acetate copolymer according to claim 1 or 2, wherein a saponification reaction is carried out by forming a phase.