JPS5941445B2 - Method for producing ethylene-vinyl alcohol copolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an ethylene-vinyl alcohol copolymer, that is, a saponified ethylene-vinyl acetate copolymer. This invention relates to a method for precipitating spherical particles of uniform size without any sharp tips from an ethylene-vinyl alcohol copolymer solution obtained by saponification using an alkaline catalyst in a solvent system. .

Ethylene-vinyl alcohol copolymer refers to ethylene-vinyl acetate copolymer or a multicomponent copolymer obtained by copolymerizing ethylene-vinyl acetate and one or more other polymerizable third components. Those manufactured using ethylene and vinyl alcohol components in appropriate amounts are useful thermoplastics that provide mechanically strong films and molded products with good thermal stability and excellent oxygen gas barrier properties. It is well known that it is a polymer. The saponification reaction of an ethylene-vinyl acetate copolymer is industrially advantageously carried out in a methanol solvent system using an alkali catalyst, and requires a step of precipitating the polymer from the solution after saponification. In this case, the precipitated polymer must be porous so that residual alkali salts and other impurities can be easily removed during washing, and it must also have a shape convenient for processing into films, molded products, etc., and a high filling specific gravity. required. More importantly, the tips of the polymer particles, especially the thin and sharp parts, tend to change in quality during heat treatment such as drying and become foreign polymers for reasons that are not clear, and these become so-called fish eyes in films and molded products. In addition, polymer particles without sharp tips are required since this may cause problems such as die contamination during film formation.

In addition, it is required that there is little polymer loss during precipitation, and that workability and process stability are good not only in the precipitation process but also in subsequent processes such as washing and drying.

Several methods are known to precipitate an ethylene-vinyl alcohol copolymer from a saponification solution.

However, there is no method that satisfies all of the above requirements, and in particular, there is no known method for obtaining polymer particles completely free of sharp edges. For example, Japanese Patent Publication No. 43-17980 discloses a method of cooling the saponified solution and adding water or a water-methanol solution to precipitate it into particles, and a method of obtaining porous precipitates by spraying the saponified solution. Special Public Service No. 45-3119
It is stated in No. 7.

However, with these methods, the particles obtained often have extremely sharp tips and are not uniform in shape. For example, Japanese Patent No. 725 discloses a method in which the solution after saponification is discharged in the form of a sheet or strand into water or water-methanol.
, No. 519 and No. 725,520.

However, in these methods, polymer particles are obtained by cutting a sheet or strand, but the cut portion inevitably has a thin and sharp shape, which causes deterioration in the quality of the polymer. The present inventors have discovered that ethylene which satisfies all of the above-mentioned performance requirements, such as the shape of the precipitated particles, particularly the absence of sharp tips, excellent workability and stability in the washing and processing steps, and no polymer loss during precipitation, has been developed. As a result of various studies on the production method of vinyl alcohol copolymer, we discovered that a saponified solution of ethylene-vinyl alcohol copolymer is discharged from the pores of a die into water or water-methanol, and comes into contact with the pores of the die. However, the present inventors have found that a method of separating the discharged solution from the die part using a sharp cutting mechanism moving at high speed and depositing it while being moved by a water stream is extremely satisfactory, and has completed the present invention.

The ethylene-vinyl alcohol copolymer used in the present invention has the general formula (C2H4)X(CH2CH)Y
(CH2CRR/)Z [However, X/CCOCH3Y+Z=
0.3 to 1.5, Z/Y=0 to 0.1, R is hydrogen or a methyl group, and R/ is a methyl group or COOR], or an ethylene monovinyl acetate copolymer mainly composed of these It is obtained by saponifying 90 moles or more of a multicomponent copolymer with an alkaline catalyst in a solution mainly containing methanol.

A copolymer with the above X/Y+Z of 0.3 or less or 1.5 or more, and a copolymer with a saponification degree of 90 mol% or less even if X/Y+Z=0.3 to 1.5 were used. , the shape of the precipitated particles becomes poor and satisfactory results cannot be obtained. In carrying out the present invention, the ethylene-vinyl alcohol copolymer is saponified in the form of methanol or a methanol-based solution, but in some cases water may be added to form a methanol-water mixed solvent. It is preferable that

In this case, the appropriate copolymer concentration is 15 to 60% by weight, preferably 30 to 45% by weight. 15 layers, hands? If it is less than 60% by weight, the particle shape will be poor, and if it exceeds 60% by weight, the viscosity of the solution will become extremely high, making it difficult to handle, and the washability of the precipitated particles will deteriorate.

The dice are made of water or water with a methanol content of 30% by weight or less.
The contact liquid is constantly circulated, with part of it being replaced with fresh water, so that the saponified solution that is in contact with the methanol mixture and separated from the dice is quickly transferred.

The temperature of the contact liquid is kept below 40'C, preferably below 2'C, and a cooler etc. is provided if necessary. Is the methanol ratio of the circulating fluid 30% by weight? If the temperature exceeds 40° C. or the liquid temperature exceeds 40° C., not only will polymer loss during precipitation be large and pose a practical problem, but the shape of the precipitated particles will also deteriorate. The cross-sectional shape of the die pores is usually circular, but may be square, star-shaped, etc. depending on the case, and the diameter depends on the required particle size, but is usually about 0.1 to 4 mm. It is. The saponified solution is discharged from the die pores into water or water-methanol solution, but the discharge linear velocity at the pores is 2.
00cm/'Sec or less, preferably 20 to 50CT
! Let it be L/Sec.

If it exceeds 200 cm//Sec, the particles after cutting may recombine or sag may occur in the particles, resulting in deterioration of the particle shape.

The dispensed solution must be separated by a cutting mechanism that moves at high speed in contact with the die pores when the dispensed length reaches 1 to 2 times the die pore diameter.

As the cutting mechanism, a rotary blade that rotates around the center of the die is generally used, and the pores are arranged around the center of the die.

When the number of pores is small, it is possible to use a blade that simply moves the pores up and down or left and right. In any case, it is necessary for the blade to move at high speed while contacting the pores of the die to separate the saponification solution continuously discharged from the pores from the die. In this case, the blade needs to be in contact with the pores of the die, and even if there is a slight gap between the blade and the pores of the die, the particles tend to have a sharp tip. The discharged solution separated from the die part progresses in precipitation while being carried by the evolving water or water-methanol solution, and becomes uniform spherical polymer particles with no sharp tips.

The polymer loss during precipitation is negligible, at most 0.3% by weight, and the washability of the polymer particles is also good.
According to the method of the present invention, there is very little deterioration in the quality of the polymer during heat treatment such as drying, and the film obtained from this polymer has a hardness of 1/10 to 1/50 of that of a film made from a polymer produced by a known precipitation method. Decreased,
A film with an extremely good appearance can be obtained, and die contamination during film forming is also significantly reduced.

The method of the present invention will be explained in more detail below with reference to Examples.

Example 1 Ethylene content 32.1 moles? A solution consisting of 45 parts of ethylene monovinyl acetate copolymer, 50 parts of methanol, and 1 part of caustic soda was subjected to a saponification reaction at 110°C for 30 minutes while blowing methanol vapor under 3.5 kG, and methyl acetate was produced during the reaction. is distilled off along with a portion of methanol and removed from the system.

Water and methanol vapor were further blown into the obtained saponified solution to distill out a mixed vapor of methanol and water, resulting in a copolymer with a degree of saponification of 99.2 mol%, a saponified product concentration of 35% by weight, and a temperature of 82°C. Mixed saponification solution (methanol/water-7/
3 weight ratio) was obtained. This solution is pumped using a gear pump.
A die with 26 holes with a hole diameter of 2 mm (each hole has 10
arranged around the center of the die with a pitch of mm)
Therefore, 1001 methanol is added to a mixed solution of water and methanol at a temperature of 5°C and 10 weights of methanol are circulated at a rate of 15 m3/Hr.
It was discharged at a flow rate of /Hr. The die hole linear velocity at this time is 3
It was 4CTIL/Sec. At the same time, the discharged saponification solution is separated from the die by a rotary blade (1200 revolutions/min) with 6 blades that rotates around the center of the die while contacting the die pores, and is converted into the circulating water-methanol mixture. Precipitation progressed while being moved, and was separated from the liquid after about 10 seconds. The circulating fluid has a methanol ratio of 10%.
Water is added to maintain the temperature, and the mixture is returned to the die section through a cooler. The obtained polymer particles were extremely uniform spherical particles, had no sharp tips, and had good washability.

Polymer loss during precipitation is 0.2 weight? It was negligible. After precipitation, the polymer particles were washed with 10 times the amount of water for 1 hour, and then with 10 times the amount of an acetic acid aqueous solution having an acetic acid concentration of 1.59/l for 1 hour, and then dried at 110° C. for 16 hours. Even after washing and drying, the shape remains unchanged except for some volume shrinkage, and the diameter is 1.8
It becomes a spherical polymer of 2.3mm to 2.3mm, and the filling specific gravity is 0.
．． 72, this polymer was extruded to form a film at 220°C to obtain a film with a thickness of 25μ, which had a very small number of fish eyes (4 pieces/m゛) and had an extremely good appearance. Control Example 1 The saponified solution obtained in Example 1 was added to a water-methanol mixture solution of 10 weights of methanol and a temperature of 5°C using a die having 10 holes with a pore size of 2 m and 71 L at 101/H.
The mixture was discharged at a flow rate of r and taken out in the form of a strand, immersed in this mixture for 1 minute, taken out, cut into lengths of about 3 mm, washed and dried under the same conditions as in Example 1.

This polymer was extruded to form a film at 220° C. to obtain a film with a thickness of 25 μm, and the number of fish eyes was 150 per film. In fact, leprosy case 2 ethylene content 43.5 moles? A solution consisting of 42 parts of ethylene monovinyl acetate copolymer, 55 parts of methanol, and 1 part of caustic soda was treated in the same manner as in Example 1, and the degree of saponification was 9.
A methanol/water mixed saponification solution (methanol/
Water-8/2 weight ratio) was obtained.

This solution was prepared using a device similar to that shown in Example 1, with a discharge rate of 1501/Hrl, a number of blade rotations of 18/JO rotations/min, a circulating amount of water-methanol solution of 10 m3/Hrl, a methanol concentration of 5%, and a temperature of Uniform spherical polymer particles were obtained by processing under 5-ring C conditions.

The polymer loss during precipitation was 0.08% by weight, and the washability of the polymer particles was good. The polymer particles were washed and dried in the same manner as in Example 1, and spherical polymer particles with a diameter of 1.6 to 2.1 mm and no sharp tips were obtained.

This polymer was extruded to form a film at 180'C to obtain a film with a thickness of 25 microns, and the number of fish eyes was 3/M2. Example 3 Ethylene content 45 moles? Example 5 A solution consisting of 40 parts of a copolymer of 3 mol% propylene and 52 mol% vinyl acetate, 50 parts of methanol, and 2 parts of caustic soda was treated in the same manner as in Example 1 to obtain a degree of saponification of 97.5 mol 7.
A methanol/water mixed saponification solution (methanol/7K9/1 weight ratio) was obtained at a saponified copolymer concentration of 30% and a temperature of 72°C.

Of the apparatus shown in Example 1, only the die had a pore diameter of 4 m77! Using a device replaced with a die that fills 6 holes, the discharge amount is 2001/Hrl and the hole linear velocity is 74CT.
! L/Sec. Uniform spherical polymer particles were obtained under the conditions of a rotary blade rotation speed of 1850 rpm, a circulating water-methanol solution circulation rate of 15 g/hr, a methanol concentration of 15% by weight, and a temperature of 10°C.

The polymer loss during precipitation was 0.05% by weight, and the washability of the polymer particles was good, and when washed and dried in the same manner as in Example 1, the particles had a diameter of 2.9 to 3.5% without any sharp tips. 4
mm spherical polymer was obtained. This polymer is 180
EXAMPLE 4 Ethylene content 55 mol? A solution consisting of 55 parts of ethylene vinyl acetate copolymer, 55 parts of methanol, and 2 parts of caustic soda was treated in the same manner as in Example 1 (however, water and methanol vapor were not blown in after the saponification reaction). degree 9
5 mol% copolymer saponified product concentration 40 weight? , temperature 67℃
A methanol-based saponification solution was obtained.

This solution was prepared using a device similar to that shown in Example 1, with a discharge rate of 1001/Hrl, a rotary blade rotation speed of 1100 revolutions/min, a circulating water-methanol liquid circulation rate of 10g/Hrl, and a methanol concentration of 15% by weight. A uniform spherical polymer was obtained by processing at a temperature of 7°C.

Polymer loss during precipitation is 0.04 weight? The washing of the polymer particles was good. After washing and drying in the same manner as in Example 1, a spherical polymer with a diameter of 1.9 to 2.3 mm without any sharp tips was obtained. This polymer was extruded at 17"C to form a film with a thickness of 25μ. When I obtained the film, there were 2 fish eyes per eye. Example 5 Example 1 was carried out using a device comprising a die having two horizontally arranged holes with a hole diameter of 3 mm and a pitch of 10 mm, and a knife that moved vertically up and down while contacting the die holes. The indicated saponification solution was treated 〇 That is, the saponification solution was circulated through the die hole by a gear pump at a rate of 25 d/Hr with a methanol ratio of 5 weight? , water at a temperature of 5°C -
It was discharged into the methanol solution at a rate of 101/hr.

Is the die hole linear velocity at this time 20? /Sec. At the same time, the knife is moved up and down at a rate of 2000 times/minute, and the saponified solution discharged is separated from the die and carried by the circulating water-methanol solution, and the polymer becomes uniform spherical particles. It was done. The polymer particles, which were washed and dried in the same manner as in Example 1, had a diameter of 2 without any sharp tips.
．． It was a 7 to 3.3 mm spherical polymer. This polymer was extruded to form a film at 220° C. to obtain a film with a thickness of 25 μm, and the number of fish eyes was 5/eye. Control examples 2 to 4

Claims (1)

[Claims] 1. A copolymer represented by the general formula ▲ Numerical formula, chemical formula, table, etc. ▼ [However, X/Y+Z=0.3 to 1.5, Z
/Y=0 to 0.1, R is hydrogen or methyl group, R'
is a methyl group or COOR] in a methanol-based solution using an alkaline catalyst to saponify the ethylene-vinyl alcohol copolymer to a saponified solution of 90 mol% or more. The solution is discharged into a water-methanol mixture, separated from the die by a sharp cutting mechanism that moves at high speed while contacting the pores of the die, and precipitated while being moved by a water stream, resulting in a saponified copolymer. A method for producing an ethylene-vinyl alcohol copolymer, characterized in that it is obtained as spherical particles having no sharp tips.