JPS6315924B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for efficiently saponifying particulate ethylene-vinyl acetate copolymer in a methanol solution of sodium hydroxide.

In general, saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as saponified EVA) has a higher melting point, hardness, tensile strength,
High bending strength, bending rigidity, etc., and solvent resistance.
It has many features such as excellent abrasion resistance and gas permeation resistance, the ability to be spun, and the surface gloss of molded and painted products. Furthermore, it has excellent adhesive properties with various inorganic and organic substrates including metals, and is widely used as a coating agent such as powder paint, a fiber adhesive, or a lamination adhesive with various substrates.

As a method for producing saponified EVA,
Conventionally, for example, the raw material resin EVA was dissolved in a mixed solvent of a good solvent such as toluene or xylene and an alcohol such as methanol, and after being alkaline saponified in a homogeneous solution system, a non-solvent was added to precipitate the saponified product. A method of recovering it as a powder is known. However, this method not only requires a large amount of non-solvent such as methanol to precipitate the saponified product after the reaction, but also separates the saponified product.
Since the washing and drying steps are very complicated, it is not an economically advantageous method. On the other hand, as an improvement on this method, a number of methods have been proposed in which powdered, granular, or pelleted EVA is saponified in a lower alcohol such as methanol while maintaining its original shape under conditions that do not allow the EVA to fuse with each other.
(For example, Japanese Patent Publication No. 44-27902,
Publication No. 102893, Japanese Patent Publication No. 126291/1983, Japanese Patent Application Publication No. 1983-126291
53-85888). The advantage of this method is that the raw material EVA
The saponified product can be directly recovered while maintaining its form, that is, in the form of granules or pellets. As described above, the method of saponification using a solid-liquid heterogeneous system is generally recommended as an industrially advantageous method because the saponified product after the reaction is easy to wash, separate, and dry in the drying step.

As a specific method for saponification, a stirring tank is used exclusively as a reactor, and a predetermined amount of raw material EVA and a methanol solution of sodium hydroxide are charged all at once into the tank for saponification. However, the conventional method in which a predetermined amount of raw materials, especially the entire amount of sodium hydroxide, is charged at once and saponified during saponification has the following problems.

(1) In order to produce a product with a high saponification rate, it is necessary to increase the amount of sodium hydroxide added.
For this reason, saponified products tend to be colored yellow or brown. This trend is observed when the vinyl acetate content is high.
This is more noticeable when EVA is used as a raw material.

(2) In order to saponify EVA, a raw material with a high content of vinyl acetate, to a high saponification rate, a large amount of sodium hydroxide is required as described above. As a result, a large amount of sodium acetate is produced as a by-product through the saponification reaction, but its solubility in methanol used as a medium is low (approximately 14% by weight at 30°C).
Therefore, a large amount of methanol is required to completely dissolve the by-product sodium acetate. As a result, the concentration of solid content (EVA) decreases, and the productivity of saponified products per unit volume of the reactor decreases.

(3) If a large amount of sodium acetate is produced as a by-product in the saponification reaction, a large amount of washing solvent (methanol) is required to remove it from the saponified product. Furthermore, separation, recovery, treatment, etc. of these solvents and by-products are complicated.

The inventors of the present invention have carried out intensive studies to solve the above problems, and as a result, the entire amount of the methanol solution of sodium hydroxide used in saponification was extracted from the system during the reaction, and a new solution was prepared. By performing an operation of replacing sodium hydroxide with a methanol solution at least once before the reaction is completed, the inventors have discovered a method of producing a high-quality saponified product extremely efficiently, and have completed the present invention.

Here, when the saponification method of the present invention is compared with the conventional method, the following features can be mentioned.

(1) Because the sodium hydroxide used in saponification is added in portions, there is very little coloration of the saponified product.

(2) Since the amount of methanol used as a medium can be reduced, the solid content concentration can be increased.
Therefore, the productivity of saponified products per unit volume of the reactor is increased. This effect becomes greater when raw material EVA with a higher vinyl acetate content is used.

(3) Since the methanol medium is replaced during the reaction, there is no accumulation of by-products such as sodium acetate in the reaction system. As a result, saponified products can be easily washed and high quality products can be obtained.

(4) Saponification can be achieved to a high saponification rate with a small amount of sodium hydroxide. In other words, as is well known, the saponification reaction involves a transesterification reaction between the vinyl acetate group of EVA and methanol (producing methyl acetate as a by-product) through the catalytic action of sodium hydroxide.
It occurs through a direct reaction between the vinyl acetate group of EVA and sodium hydroxide (sodium acetate is produced as a by-product). Here, a particularly recommended method in the present invention is to first add a small amount of sodium hydroxide at a relatively low temperature range (for example, 40°C) where the transesterification reaction is dominant at the start of the saponification reaction. When the saponification rate reaches an appropriate saponification rate (for example, 30% or more), the entire amount of the methanol solution is extracted from the system, leaving the granular partially saponified products in the reactor. This is because the transesterification reaction becomes extremely slow in a relatively high saponification rate region. Therefore, at the stage where a high saponification rate is reached, saponification by the direct reaction of unreacted vinyl acetate groups in the EVA saponified product with sodium hydroxide (sodium acetate is produced as a by-product) is dominant. Then, a methanol solution of sodium hydroxide in an amount sufficient to complete the reaction (usually about the same molar amount as the unreacted acetic acid group) is added to complete the saponification at a high reaction rate. By this method, high quality saponified products can be efficiently produced.

Embodiments of the present invention will be described in detail below.

The present invention is a method for saponifying granular ethylene-vinyl acetate copolymer in a methanol solution of sodium hydroxide at a temperature at which the granular copolymer does not fuse with each other. A method for saponifying an ethylene-vinyl acetate copolymer, characterized in that the operation of extracting the system from the system and restarting the reaction by replacing it with a freshly prepared methanol solution of sodium hydroxide is performed at least once before the reaction is completed. It is related to.

In the present invention, the raw material resin EVA generally has a vinyl acetate content of 10 to 50% by weight, and preferably 20 to 45% by weight. Further, it is preferable that the raw material EVA has a melt index in the range of 5 to 500.
In addition to EVA, raw material resins include monomers that can be copolymerized with ethylene and vinyl acetate, such as unsaturated hydrocarbons such as propylene, butene-1, and styrene, and unsaturated hydrocarbons such as (meth)acrylic acid and methyl (meth)acrylate. A copolymer of about 10% by weight or less of saturated carboxylic acid and its derivatives can also be used. The amount of unreacted vinyl acetate monomer contained in these EVA and ethylene copolymers is
From the viewpoint of preventing coloring of the saponified product during the saponification reaction, the content is desirably 1% by weight or less.

The shape of the raw material EVA used in the present invention is as follows:
In general, these are pellets obtained by granulation using a screw extruder or the like, or granules obtained by further pulverizing the pellets by freeze-pulverization or the like. The median diameter of the granules (particle diameter when the cumulative value is 50% in the cumulative weight distribution curve) is generally 0.5 to 7 mm, but 2 to 5 mm is particularly preferred.

The saponification reaction is carried out in a methanol solution of sodium hydroxide using the above granular EVA as a raw material. Various types of saponification reactors can be used, such as a stirred tank, fluidized bed, and fixed bed. However, in order to produce homogeneous saponified products efficiently and with a high yield, the fluidized bed type is particularly suitable. A reactor is recommended. Further, the saponification reaction is generally carried out in a nitrogen atmosphere under normal pressure or increased pressure.

The sodium hydroxide used in the saponification reaction is used as a methanol solution. The present invention is characterized in that the methanol solution of sodium hydroxide is replaced during the reaction at least once before the reaction is completed. Here, the amount of sodium hydroxide added at the first time, that is, at the start of the saponification reaction, is
It is desirable that the amount is 0.5 molar equivalent or less relative to the amount of vinyl acetate in EVA. In this way, by adding a relatively small amount of sodium hydroxide, the saponification reaction
It is desirable to start the reaction in a low temperature range where the production of methyl acetate through the transesterification reaction between the vinyl acetate group of EVA and methanol is dominant. The temperature at that time needs to be a temperature at which the EVA particles during saponification do not cause mutual fusion, and is generally in the range of 30 to 55°C. Once the saponification reaction has progressed to a certain extent, the entire amount of the methanol solution is removed from the system during the reaction, replaced with a freshly prepared methanol solution of sodium hydroxide, and saponification is restarted. The first saponification is usually carried out until the saponification rate reaches 30 to 80%.

The amount of sodium hydroxide added in the second or more times is larger by molar equivalent than the amount added in the first time based on the unreacted vinyl acetate groups in the saponified EVA product, and 1.5 It is desirable that the amount is less than the molar equivalent. Further, the reaction temperature is desirably set at a high temperature (usually 55 to 80°C) at which saponification by direct reaction between the vinyl acetate groups in EVA and sodium hydroxide becomes predominant. In this case, the amount of sodium hydroxide added in the area where a particularly high saponification rate (approximately 80% or more) has been reached is
It is usually appropriate to add about 1 molar amount or slightly in excess of the unreacted vinyl acetate group in the saponified EVA product. On the other hand, even if the amount of sodium hydroxide added is greater than 1.5 molar equivalents, the effect will not change, and unreacted sodium hydroxide will remain, making washing the saponified product troublesome, which is not preferable. As mentioned above, in a relatively low temperature range, the saponification reaction by transesterification between EVA and methanol is predominant, and methyl acetate is produced as a by-product in this reaction. This methyl acetate has a good affinity with the EVA particles during saponification and causes the particles to swell. As a result, saponification is promoted, and it is effective in uniformly saponifying the inner layer of the particles. However, in the second and subsequent saponifications,
When saponifying to a high saponification rate in a high-temperature region where the direct reaction between vinyl acetate groups in EVA and sodium hydroxide becomes dominant, it is necessary to Since sodium acetate is also produced by the reaction between methyl acetate and sodium hydroxide, it is necessary to add an extra amount of sodium hydroxide corresponding to the amount of dissolved methyl acetate (usually about the same mole as the amount of methyl acetate). There is. Further, sodium hydroxide is usually added as a methanol solution in a predetermined amount at once during each charging operation, but it can also be added in portions or continuously during the reaction if necessary.

As mentioned above, saponification in the present invention is carried out in a methanol solution of sodium hydroxide,
Sometimes relatively small amounts of ethyl alcohol,
Lower alcohols such as n-propyl alcohol, isopropyl alcohol, and n-butyl alcohol, or other solvents such as toluene, xylene, acetone, and methyl ethyl ketone may also be added. Furthermore, in order to effectively proceed with saponification, it is desirable that the amount of water contained in the reaction system be 0.5% by weight or less.

The saponification in the present invention is carried out throughout the granular
This is carried out at a temperature at which the EVA does not fuse with each other, and the higher the content of vinyl acetate in the EVA, the lower the melting temperature becomes. On the other hand, as the saponification reaction progresses, the melting point of the saponified product gradually rises, so the fusion temperature becomes higher. Therefore, efficient saponification can be achieved by raising the temperature stepwise or continuously by taking advantage of the increase in melting point. Furthermore, for the purpose of preventing particle fusion, a methanol-soluble surfactant or dispersion stabilizer can be added. In addition, in order to prevent coloring of the EVA saponified product produced by the saponification reaction, a coloring inhibitor such as hydrazine and its derivatives, ammonia and its derivatives, cyanacetic acid esters, acetone, and ketones such as methyl ethyl ketone may be added to the reaction system. , aldehydes, etc. can be added.

The saponification rate of the saponified EVA product obtained by the saponification reaction depends on the purpose of use, but is generally 50% or more, preferably 80% or more. The saponification rate can be easily controlled to a desired value by adjusting the reaction conditions.
In particular, when used as a powder coating or fiber adhesive, EVA with a high vinyl acetate content of about 35 to 45% by weight is preferably saponified to 90% or more.

After the saponification reaction is completed, the saponified product can be washed once or twice with methanol if necessary, but it is possible to wash the saponified product with methanol once or twice, but the saponified product may be washed with unreacted sodium hydroxide or by-produced sodium acetate contained in the saponified product. It is desirable to wash until the sodium content is 0.5% by weight or less, particularly 0.2% by weight or less. Generally, the appropriate washing temperature is between room temperature and 80°C, but washing under heating is more effective. In addition, a small amount of inorganic acid or organic acid can be added for the purpose of reducing the sodium content in the saponified product during washing. In this way, a saponified product with excellent adhesiveness, precipitation resistance, etc. can be obtained. After washing, the saponified product separated from the methanol medium is dried under a stream of heated air or nitrogen, etc.
Drying can be carried out by various methods, such as drying under normal air or drying using a vented screw extruder. It is desirable that drying be carried out until the content of methanol in the saponified product is approximately 0.5% by weight or less.

For the saponified product produced in this way, antioxidants, light stabilizers, heat stabilizers, inorganic or organic colorants, rust preventives, crosslinking agents, foaming agents, lubricants, and plasticizers are added as necessary. Various inorganic or organic additives or fillers can be added, such as nucleating agents, surface smoothing agents, surface gloss improvers, fluorescent agents, inorganic or organic fillers, and polymer compounds. These additives or fillers are used in the manufacturing process of the raw material EVA,
It can also be added during the saponified product manufacturing process or subsequent processing steps.

The saponified EVA produced by the method of the present invention is particularly useful as a powder coating and a fiber adhesive, but can also be used as a coating agent or lamination adhesive for various inorganic or organic substrates. Also,
It can be widely used as packaging materials and various molded products.

The present invention will be explained below with reference to examples.
The present invention is not limited thereby.

The measured values for EVA and its saponified products shown in the present invention were determined by the following methods.

(1) Vinyl acetate content and saponification rate It was determined in accordance with JIS-K-6730.

(2) Sodium content Determined by flame photometry in accordance with JIS-K-0102-1974.

(3) Melt index According to JIS-K-6760, under a load of 2.16 kg
Measured at 190°C. The unit of measurement value is g/10min.
It is.

(4) Volatile content: EVA saponified pellets in air under normal pressure.
The weight loss when heated at 105℃ for 2 hours is
The value divided by the weight of the saponified material before heating was expressed as a percentage.

(5) Median diameter Using a JIS standard sieve, a cumulative weight distribution curve with respect to particle size was determined, and from this, the particle size was expressed as the particle size at which the cumulative distribution was 50% by weight.

Example 1 A pressure-resistant fluidized bed reactor made of stainless steel and having an inner diameter of 250 mmφ and a length of 2000 mm was used as a reactor. At the bottom of this device, a perforated plate made of stainless steel with a diameter of 1 mm is installed at an angle of 50° with respect to the horizontal plane. 1.5 of
An inch piston valve is installed. In addition, the top of this reactor opens upward at an internal angle of 30°,
It is connected to a stainless steel cylinder with an inner diameter of 30 mmφ. A methanol solution outlet pipe is attached to the side wall of the cylinder, and a raw material inlet is provided at the head. The methanol solution is heated with an external heat exchanger, supplied from the bottom of the reactor with a pump, and circulated. Furthermore, a viewing window made of pressure-resistant glass is attached to the cylindrical portion of the reactor for observing the inside.

Into this reactor, 40% of EVA pellets, which had been prepared in advance in a mixing tank with a stirrer and preheated to 40°C, were added.
A mixture of 80 kg/methanol solution of sodium hydroxide (weight ratio 1/2) was charged from the top of the reactor. Here, EVA has a median diameter of 3.3 mm, a melt index of 77, and a vinyl acetate content of 43% by weight.
I used the one from Further, sodium hydroxide was added in an amount of 0.15 molar equivalent to vinyl acetate in the raw material EVA. Note that the following saponification and cleaning were performed under a nitrogen atmosphere.

A methanol solution of sodium hydroxide charged into the reactor was circulated using a pump, and the pellets in the reactor were saponified at 40° C. for 8 hours while fluidizing the pellets. The saponification rate of EVA at this time was 72%.
Next, after extracting the entire amount of the methanol solution used in the reaction from the bottom of the reactor, the EVA was newly added.
Charge the same amount of methanol solution (preheated to 70°C) containing 1.2 molar equivalents of sodium hydroxide to unreacted vinyl acetate in the saponified product as in the first saponification, and proceed as above. The mixture was saponified at 70° C. under a gauge pressure of 0.5 kg/cm ² for 5 hours. After cooling to 40°C, the entire amount of the methanol solution was extracted, and then methanol preheated to 60°C was charged and washed at 60°C for 2 hours while circulating with a pump. Thereafter, this washing operation was repeated once.

After washing, only methanol was extracted from the reactor, and then the reactor was dried for 8 hours while blowing nitrogen heated to 90° C. from the bottom of the reactor. As a result, uncolored, translucent saponified pellets with a melt index of 17, a saponification rate of 97.7%, a sodium content of 0.06% by weight, and a volatile content of 0.3% by weight were obtained.

Comparative Example 1 In the reactor used in Example 1, 200
Prepared in a mixing tank with a stirrer and preheated to 40°C.
A mixture of 30 kg of EVA pellets and 90 kg of a methanol solution of sodium hydroxide (weight ratio 1/3) was charged from the top of the reactor. Here, the same EVA as in Example 1 was used. On the other hand, sodium hydroxide is 1.2% of the vinyl acetate in the raw material EVA.
A molar equivalent was added.

Thereafter, saponification was carried out under the same reaction conditions at the same temperature and time as in Example 1, except that the methanol solution was not replaced during the reaction, followed by washing and drying. As a result, the melt index
28. A saponified product with a saponification rate of 98.2% was obtained, but the sodium content was 0.24% by weight, which was higher than that of the saponified product of Example 1, and the pellets were colored yellowish brown.

Example 2 Sodium hydroxide (raw material EVA
42 kg of methanol solution (0.2 molar equivalent added to vinyl acetate) was charged, and while stirring at 150 rpm with a fan turbine blade, a methanol solution with a median diameter of 3.2 mm, a melt index of 150, and a vinyl acetate content of 35% by weight was charged.
After adding 28 kg of EVA pellets and purging the inside of the reactor with nitrogen gas, it was saponified at 50°C for 5 hours. The saponification rate at this time was 66%. Next, the entire methanol solution in the reactor was extracted from the bottom of the reactor through a 16-mesh wire mesh, and then freshly prepared sodium hydroxide (1.1 molar equivalent added to unreacted vinyl acetate in the EVA saponification product) was added. 42 kg of methanol solution was charged and saponified at 80°C under a gauge pressure of 1.1 kg/cm ² for 3 hours. After the reaction, remove the methanol solution in its entirety while leaving the granular partially saponified product in the reactor, and then remove the methanol.
42 kg was charged and washed at 70°C for 2 hours. After washing, the saponified product was collected from the reactor and dried in a vacuum dryer until the content of volatile matter was 0.1% by weight. As a result, the melt index was 54, the saponification rate was 98.6%,
A white saponified pellet with a sodium content of 0.07% by weight was obtained.

Comparative Example 2 In Example 2, quenching was carried out under the same conditions as in Example 1, except that the amount of sodium hydroxide added was 1.1 molar equivalent to the vinyl acetate in the raw material EVA, and the methanol solution was not replaced during the reaction. It became. After saponification, when only the methanol solution was extracted from the reactor, it was found that the sodium acetate produced as a by-product of the reaction was not completely dissolved in methanol, and that more than its saturated solubility (approximately 14% by weight at 30°C) had precipitated. Ta. Meanwhile, the saponified product in the reactor was washed twice with methanol under the same conditions as in Example 2. As a result, a saponified product with a melt index of 65 and a saponification rate of 98.9% was obtained, but the sodium content was 0.21% by weight, which was higher than the saponified product of Example 2, and the pellets were colored yellow. .

Example 3 46 kg of methanol solution of sodium hydroxide (0.5 molar equivalent added to vinyl acetate in the raw material EVA) was charged into the stirring tank used in Example 2, and the stirring tank was heated at 150 rpm.
While stirring, 23 kg of EVA pellets having a median diameter of 3.6 mm, a melt index of 80, and a vinyl acetate content of 45% by weight were added, and the mixture was saponified at 45°C in a nitrogen atmosphere for 5 hours. At this time, the saponification rate was 75%. Next, after extracting only the methanol solution in its entirety from the bottom of the reactor, 46 kg of a freshly prepared methanol solution of sodium hydroxide (1.2 molar equivalent added to unreacted vinyl acetate in the saponified EVA product) was charged, and 60 kg of methanol solution was added. The mixture was saponified for 8 hours at a temperature of 0.degree. C. under normal pressure in a nitrogen atmosphere. After the reaction, only the methanol solution was extracted completely, and then 46 kg of methanol was added and heated at 70℃ for 2 hours.
Washed for hours. After repeating this washing operation once, the saponified product was dried by the method of Example 2. As a result, white saponified pellets with a melt index of 21, a saponification rate of 97.7%, and a sodium content of 0.06% by weight were obtained.

Comparative Example 3 34 kg of methanol solution of sodium hydroxide (0.5 molar equivalent added to vinyl acetate in the raw material EVA) was charged into the stirring tank used in Example 2, and the stirring tank was heated at 150 rpm.
Same as that used in Example 3 under stirring of
17 kg of EVA was added and saponified at 45°C for 5 hours. Next, 17 kg of a freshly prepared methanol solution of sodium hydroxide (0.7 molar equivalent added to the vinyl acetate in the raw material EVA) was added to the reactor, and the temperature was heated at 60°C.
It was saponified for 8 hours. Thereafter, the saponified product was washed and dried by the method of Example 3. As a result, a saponified product with a melt index of 30 and a saponification rate of 97.6% was obtained, but the sodium content was 0.26% by weight, which was higher than that obtained in Example 3, and the pellets were colored yellow. Ta. In order to remove the sodium acetate contained in this saponified product, washing with methanol was repeated three times according to the method of Example 3, but it was difficult to remove, and the sodium acetate content was 0.13% by weight. Ta.

Example 4 40 kg of methanol solution of sodium hydroxide (0.1 molar equivalent added to vinyl acetate in the raw material EVA) was charged into the stirring tank used in Example 2, and the stirring tank was heated at 120 rpm.
While stirring, 30 kg of the same EVA pellets used in Example 3 and 400 g of methyl ethyl ketone were added.
Saponification was carried out at 40°C for 7 hours under a nitrogen atmosphere. The saponification rate at this time was 45%. Next, after extracting only the methanol solution in its entirety from the bottom of the reactor, freshly prepared sodium hydroxide (the EVA
Add 36 kg of methanol solution (0.35 molar equivalent added to unreacted vinyl acetate in the saponified product) and heat at 45°C.
It was saponified for 8 hours. The saponification rate at this time is 85%
It was hot. After extracting the entire methanol solution again, 36 kg of a freshly prepared methanol solution of sodium hydroxide (1.4 molar equivalent added to unreacted vinyl acetate in the saponified EVA product) was added, and the mixture was heated at 62°C for 9 hours. Saponified. After the reaction, only the methanol solution was extracted in its entirety, and then 36 kg of methanol was added and washed at 60°C for 2 hours. After repeating this washing operation once, the saponified product was dried by the method of Example 2. As a result, white saponified pellets with a melt index of 19, a saponification rate of 98.0%, and a sodium content of 0.07% by weight were obtained.

Example 5 In the reactor used in Example 1, 200
46Kg of EVA pellets/sodium hydroxide mixed in a stirring tank (based on vinyl acetate in the raw EVA)
A mixture of 74 kg of methanol solution (0.15 molar equivalent added) was charged. Here, the same raw material EVA as in Example 1 was used. The methanol solution of sodium hydroxide charged into this reactor was saponified at 40° C. for 8 hours while being circulated with a pump. The saponification rate of EVA at this time was 73%. Then,
After extracting the entire amount of the methanol solution used in the reaction from the bottom of the reactor, 74 kg of a new methanol solution containing 0.8 molar equivalent of sodium hydroxide to the unreacted vinyl acetate in the saponified EVA product was added.
The mixture was charged and saponified in the same manner as above at 50°C under normal pressure for 3 hours. After cooling to 40°C, the entire amount of methanol solution was extracted, washed twice with methanol under the same conditions as in Example 1, and then dried. As a result, translucent, uncolored saponified pellets with a melt index of 24, a saponification rate of 91.0%, and a sodium content of 0.04% by weight were obtained.

Claims (1)

[Claims] 1. In a method in which granular ethylene-vinyl acetate copolymer is saponified in a methanol solution of sodium hydroxide at a temperature at which the granular copolymer does not fuse with each other, the methanol is removed during the reaction. A method of producing an ethylene-vinyl acetate copolymer characterized in that the operation of extracting only the solution from the system and restarting the reaction by replacing it with a freshly prepared methanol solution of sodium hydroxide is carried out at least once before the reaction is completed. Saponification method. 2 The amount of sodium hydroxide in the methanol solution of sodium hydroxide used initially is 0.5 molar equivalent or less with respect to the amount of vinyl acetate in the ethylene-vinyl acetate copolymer, and the newly prepared hydroxide The amount of sodium hydroxide in the methanol solution of sodium is greater than the amount used in the first time with respect to the amount of unreacted vinyl acetate in the saponified ethylene-vinyl acetate copolymer, and is 1.5 molar equivalent or less. A method for saponifying an ethylene-vinyl acetate copolymer according to claim 1.