JP2024005771A - Method for producing pellets of ethylene-vinyl ester copolymer saponification product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing EVOH pellets having high dimensional stability and productivity.

SOLUTION: There is provided a method for producing pellets of an ethylene-vinyl ester copolymer saponification product, which comprises: a coagulation step in which a solution of an ethylene-vinyl ester copolymer saponification product is extruded in a strand shape into a coagulation liquid to obtain a coagulated product; and a cutting step of cutting the coagulated product to obtain pellets, wherein the coagulation liquid has two or more different temperature ranges in the coagulation step and the ethylene-vinyl ester copolymer saponification product extruded in a strand shape contacts with a coagulant having a temperature range 1 of -10°C or more and 40°C or less, followed by contacting with a coagulant having a temperature range 2 of 45°C or more and 80°C or less.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method for producing saponified ethylene-vinyl ester copolymer pellets.

Saponified ethylene-vinyl ester copolymer (hereinafter sometimes abbreviated as EVOH) is a material with excellent oxygen barrier properties, oil resistance, non-static properties, mechanical strength, etc., and is used for films, sheets, containers, etc. It is molded and widely used. A common method for producing EVOH is to saponify an ethylene-vinyl ester copolymer obtained by polymerizing ethylene and a vinyl ester such as vinyl acetate in an organic solvent containing alcohol in the presence of a saponification catalyst. It is true.

As a post-treatment method for the EVOH alcohol solution obtained by saponification, the EVOH alcohol solution is extruded into a coagulating liquid such as water or a water/methanol solution in the form of a strand, and then the strand is cut to produce pellets. A method is widely used (Patent Document 1).

Japanese Patent Application Publication No. 11-216725

However, when cutting the strands, cutting errors may occur, resulting in reduced productivity and insufficient dimensional stability of the resulting pellets. For this reason, there has been a demand for improvement in the cuttability of strands made of hydrous EVOH.

The present invention was made to solve the above problems, and an object of the present invention is to provide a method for producing EVOH pellets with high dimensional stability and high productivity.

The above-mentioned problem includes a coagulation step in which a solution of EVOH is extruded into a coagulation liquid in the form of a strand and coagulated to obtain a coagulated product, and a cutting process in which the coagulated product is cut to obtain pellets, and in the coagulation step, the coagulated solution has two or more different temperature ranges, and after the EVOH extruded into a strand comes into contact with a coagulation liquid having a temperature range 1 of -10°C to 40°C, a temperature range of 45°C to 80°C is applied. The problem is solved by providing a method for manufacturing EVOH pellets in which the EVOH pellets are brought into contact with a coagulation liquid having a temperature range 2.

At this time, it is preferable that the coagulating liquid contains water and methanol. It is also preferable that the EVOH extruded into a strand comes into contact with the coagulating liquid having the temperature range 2 and then further contacting the coagulating liquid having the temperature range 3 of -10° C. or more and 40° C. or less. It is also preferable that the coagulating liquid contains at least 2% by mass of at least one salt selected from the group consisting of inorganic salts and organic salts. It is also preferable that the salt is at least one selected from the group consisting of carboxylates, sulfates, nitrates, and carbonates.

In the production method of the present invention, EVOH pellets with high dimensional stability can be produced with good productivity because the strand-shaped coagulated material containing EVOH can be easily cut. The EVOH pellets thus obtained are suitably used as materials for various molded products.

The present invention includes a coagulation step of obtaining a coagulated product by extruding an EVOH solution into a coagulating solution in the form of a strand, and a cutting step of cutting the coagulated product to obtain pellets, and in the coagulating step, the coagulating solution has two or more different temperature ranges, and after the saponified ethylene-vinyl ester copolymer extruded into a strand comes into contact with a coagulation liquid having a temperature range 1 of -10°C or more and 40°C or less. , a method for producing saponified ethylene-vinyl ester copolymer pellets in which the pellets are brought into contact with a coagulating liquid having a temperature range 2 of 45° C. or higher and 80° C. or lower. In this method, since the strand-shaped coagulated material containing EVOH has good cutting properties, not only is productivity high, but also the resulting EVOH pellets have high dimensional stability. The present invention will be explained in detail below.

First, a method for synthesizing EVOH will be explained. EVOH is obtained by saponifying an ethylene-vinyl ester copolymer. As the vinyl ester, fatty acid vinyl esters such as vinyl acetate, vinyl propionate, and vinyl pivalate can be used, and vinyl acetate is preferred. The polymerization of ethylene and vinyl ester may be carried out by any of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization, but solution polymerization is preferred. Further, either a continuous type or a batch type may be used.

The solvent used in solution polymerization is preferably alcohol, but other organic solvents (such as dimethyl sulfoxide) that can dissolve ethylene, vinyl ester, and ethylene-vinyl acetate copolymer can also be used. As the alcohol, methanol, ethanol, 1-propanol, 2-propanol, etc. can be used, and methanol is industrially preferred.

As a polymerization catalyst, 2,2-azobisisobutyronitrile, 2,2-azobis-(2,4-dimethylvaleronitrile), 2,2-azobis-(4-methyl-2,4-dimethylvaleronitrile) ), 2,2-azobis-(4-methoxy-2,4-dimethylvaleronitrile), azonitrile-based initiators such as 2,2-azobis-(2-cyclopropylpropionitrile), and isobutyryl peroxide, Organic compounds such as cumyl peroxyneodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxyneodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide. A peroxide-based initiator or the like can be used.

The polymerization temperature is preferably 20 to 90°C, more preferably 40 to 70°C. The polymerization time (average residence time in the case of continuous system) is preferably 2 to 15 hours, more preferably 3 to 11 hours. The polymerization rate is preferably 10 to 90 mol%, more preferably 30 to 80 mol%, based on the vinyl ester charged. The polymer concentration in the solution after polymerization is preferably 5 to 85% by mass, more preferably 20 to 70% by mass. The ethylene unit content of the ethylene-vinyl ester copolymer is the same as the ethylene unit content of EVOH, which will be explained later. In addition, the ethylene-vinyl ester copolymer can be copolymerized with a small amount of other monomers, but the type and amount of the other monomers are the same as in the case of EVOH, which will be explained later. .

After polymerization for a predetermined time and reaching a predetermined polymerization rate, a polymerization inhibitor is added as necessary, unreacted ethylene gas is removed by evaporation, and unreacted vinyl ester is expelled. As a method for expelling unreacted vinyl ester from an ethylene-vinyl ester copolymer solution in which ethylene has been removed by evaporation, for example, the copolymer solution is continuously fed at a constant rate from the upper part of a column packed with a Raschig ring. A method of blowing organic solvent vapor such as methanol from the bottom of the column, distilling a mixed vapor of the organic solvent such as methanol and unreacted vinyl ester from the top of the column, and taking out the copolymer solution from which unreacted vinyl ester has been removed from the bottom of the column. etc. will be adopted.

An alkali catalyst is added to the ethylene-vinyl ester copolymer solution from which unreacted vinyl ester has been removed, and the vinyl ester component in the copolymer is saponified. The saponification method can be either a continuous method or a batch method, but it is preferable to carry out the saponification reaction continuously using a tower reactor and take out the EVOH solution from the bottom of the tower. As the alkali catalyst, sodium hydroxide, potassium hydroxide, alkali metal alcoholate, etc. are used. Moreover, as the solvent used for saponification, alcohols such as methanol and ethanol are preferable, and methanol is more preferable from an industrial standpoint. When using a column reactor, it is preferable to supply methanol vapor from the bottom of the column and distill methyl acetate from the top of the column.

Suitable saponification conditions are as follows. The concentration of the ethylene-vinyl ester copolymer in the reaction solution is preferably 10 to 50% by mass, more preferably 20 to 45% by mass. The reaction temperature is preferably 70 to 150°C, more preferably 80 to 140°C. The amount of the catalyst used is preferably 0.005 to 1 equivalent, more preferably 0.01 to 0.5 equivalent, relative to the number of moles of vinyl ester units. The reaction time (average residence time in the case of a continuous system) is preferably 10 minutes to 6 hours, more preferably 15 minutes to 2 hours. In this way, the saponification reaction is allowed to proceed, and a solution of EVOH is obtained. The content of EVOH in the solution is preferably 10 to 50% by mass, more preferably 20 to 45% by mass.

The degree of saponification of the vinyl ester unit of EVOH thus obtained is preferably 80 to 100 mol%. From the viewpoint of obtaining a molded product with excellent barrier properties, the content is more preferably 95 mol% or more, still more preferably 98 mol% or more, and particularly preferably 99 mol% or more. If the degree of saponification is less than 80 mol%, barrier properties, long-run properties, and moisture resistance may deteriorate.

In the present invention, the ethylene unit content of EVOH is preferably 20 to 60 mol% from the viewpoint of obtaining a molded product with excellent barrier properties and melt moldability. If the ethylene unit content is less than 20 mol%, melt moldability may deteriorate. The ethylene unit content is more preferably 23 mol% or more. On the other hand, if the ethylene unit content exceeds 60 mol%, the barrier properties may become insufficient. The ethylene unit content is more preferably 55 mol% or less, still more preferably 50 mol% or less.

EVOH can also be copolymerized with a small amount of other monomers as long as the purpose of the present invention is not impaired. Examples of copolymerizable monomers include alkenes such as propylene, butylene, pentene, and hexene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4- Diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2- Methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6- Alkenes having ester groups such as acyloxy-1-hexene, 5,6-diasiloxy-1-hexene, 1,3-diacetoxy-2-methylenepropane, or saponified products thereof; acrylic acid, methacrylic acid, crotonic acid, itaconic acid, etc. unsaturated acids or their anhydrides, salts, or mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefins such as vinylsulfonic acid, allylsulfonic acid, and methalylsulfonic acid. Sulfonic acid or its salt; vinyl silane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, γ-methacryloxypropylmethoxysilane; alkyl vinyl ethers, vinyl ketone, N-vinylpyrrolidone, vinyl chloride , vinylidene chloride, etc. When EVOH has other monomer units, the copolymerized amount thereof is preferably 10 mol% or less, more preferably 5 mol% or less.

The solvent used in the EVOH solution to be subjected to the coagulation step is not particularly limited as long as it is a good solvent for EVOH, but a mixed solvent containing water and alcohol is preferred. That is, it is preferable to use a water/alcohol solution of EVOH in the coagulation step. Here, the water/alcohol solution of EVOH refers to a solution in which EVOH is dissolved in the mixed solvent containing water and alcohol. Examples of the alcohol used at this time include methanol, ethanol, propanol, butanol, and the like, with methanol being industrially preferred.

The method for producing the EVOH solution to be subjected to the coagulation step is not particularly limited. The EVOH solution after the saponification reaction may be directly subjected to the coagulation step, or the EVOH solution after the saponification reaction may be further added with a solvent, or at least a part of the solvent in the EVOH solution after the saponification reaction may be used. A solvent substituted with the same or different solvent may be subjected to the coagulation step.

As the EVOH water/alcohol solution to be subjected to the coagulation step, one obtained by replacing a portion of the alcohol in the EVOH solution after the saponification reaction with water can be subjected to the coagulation step. . At this time, as a method to replace a portion of the alcohol in the EVOH alcohol solution with water, a mixed vapor of solvent (alcohol) and water is added to the alcohol solution in the container to remove the solvent (alcohol) from the solution. A method of vaporization is preferred. As the container at this time, a column-type container such as a tray column or a packed column is preferable. In this case, the alcoholic solution of EVOH is introduced from the upper part of the tower, a mixed vapor of solvent (alcohol) and water is introduced from the lower part of the tower type container, and the solvent (alcohol) and water are brought into countercurrent contact, and the solvent (alcohol) and water are introduced from the upper part of the tower. The mixed vapor is discharged and a portion of the solvent present in the supplied alcoholic solution of EVOH is replaced with water, so that a highly concentrated water/alcoholic solution of EVOH can be obtained from the bottom of the column. Furthermore, it is preferable that the water content in the mixed steam is 20 to 70% by mass. The solvent used for the mixed vapor is preferably an alcohol having a boiling point of 130° C. or lower, and examples of such alcohol include alcohols such as methanol, ethanol, propanol, and butanol. Alcohols having a boiling point of 100° C. or less are more preferred, and methanol is particularly preferred because it is easily available, inexpensive, has a low boiling point, and is easy to handle. By replacing the solvent in this way, a water/alcohol solution of EVOH can be obtained. The water/alcohol mass ratio of the EVOH water/alcohol solution to be subjected to the coagulation step is preferably 10/90 to 60/40, more preferably 20/80 to 50/50. .

The EVOH content in the EVOH solution to be subjected to the coagulation step is preferably 20 to 50% by mass. By setting the EVOH content within this range, the fluidity of the EVOH solution is ensured, and efficient resin production is possible. From the viewpoint of increasing the production amount per unit time, the content is more preferably 25% by mass or more, and even more preferably 35% by mass or more. The content of components other than EVOH and the solvent in the EVOH solution is usually 10% by mass or less.

As the coagulating liquid used in the coagulating step, one containing a poor solvent for the EVOH is used. The poor solvent is preferably water or a mixed solvent containing water and alcohol, and more preferably a mixed solvent containing water and alcohol. As the alcohol used in the mixed solvent, methanol, ethanol, propanol, etc. are used, and methanol is preferably used industrially. The mass ratio of water and alcohol (water/alcohol) contained in the mixed solvent is preferably 70/30 to 98/2. It is more preferable that the mass ratio (water/alcohol) is 80/20 or more. The content of the poor solvent in the coagulation liquid is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

From the viewpoint of further improving cutting performance, the coagulating liquid preferably contains at least one salt selected from the group consisting of inorganic salts and organic salts, and more preferably contains an organic salt. Examples of the inorganic salts include sulfates, nitrates, carbonates, hydrochlorides, phosphates, and the like, with sulfates, nitrates, and carbonates being preferred. Examples of the organic salts include carboxylates, sulfonates, and the like, with carboxylates being preferred. Further, the cation constituting the salt is preferably a cation of a metal belonging to Group 1 or 2 of the periodic table, and more preferably a cation of a metal belonging to Group 1 of the periodic table. Examples of cations of metals belonging to Group 1 of the periodic table include sodium ions, potassium ions, and lithium ions, with sodium ions and potassium ions being preferred, and sodium ions being more preferred. Examples of cations of metals belonging to Group 2 of the periodic table include calcium ions and magnesium ions. Specifically, sodium acetate is preferred from the viewpoint of ease of handling.

When the coagulating liquid contains the salt, the content thereof is preferably 2% by mass or more. If the content is less than 2% by mass, the effect of improving cuttability may not be obtained. The content is 40% by mass or less from the viewpoint of suppressing salt precipitation in the coagulation liquid.

In the present invention, the coagulating liquid needs to have two or more different temperature ranges. Specifically, the coagulating liquid needs to have at least a temperature range 1 of -10°C or more and 40°C or less, and a temperature range 2 of 45°C or more and 80°C or less. Then, in the coagulation step, the EVOH extruded into a strand comes into contact with a coagulation liquid having a temperature range 1, and then comes into contact with a coagulation liquid having a temperature range 2. Surprisingly, by obtaining the EVOH-containing strand-shaped coagulated material by such a method, the cuttability of the coagulated material is improved in the cutting step described below. As a result, EVOH pellets with high dimensional stability can be manufactured with high productivity. The reason for this is not clear, but after the EVOH solution extruded into a strand is solidified by contacting with a coagulating liquid having a low temperature range 1, the coagulated product is mixed with a coagulating liquid having a high temperature range 2. This is thought to be due to the fact that it is dehydrated and moderately hardened upon contact.

The EVOH solution is extruded into the coagulation liquid in the form of a strand through a nozzle having an arbitrary shape. The shape of such a nozzle is not particularly limited, but a cylindrical shape is preferable. The inner diameter of the nozzle may be adjusted as appropriate depending on the diameter of the target EVOH pellet, but is usually 1 to 10 mm. The discharge rate of the EVOH solution is usually 0.1 to 5 kg/h per nozzle. In this way, the EVOH solution is extruded from the nozzle in the form of a strand. At this time, the number of strands does not necessarily have to be one, and any number between several to several hundred can be extruded.

The EVOH extruded into a strand is brought into contact with a coagulating liquid having a temperature range 1, and then brought into contact with a coagulating liquid having a temperature range 2. This process is
(1) Using a coagulation bath 1 containing a coagulating liquid having a temperature range 1 of -10°C or more and 40°C or less and a coagulating bath 2 containing a coagulating liquid having a temperature range 2 of 45°C or more and 80°C or less, immersing the EVOH extruded into a strand in a coagulating liquid having a temperature range 1 in a coagulating bath 1, and then immersing it in a coagulating liquid having a temperature range 2 in a coagulating bath 2;
(2) In one coagulation bath, the upstream coagulating liquid is adjusted to a temperature range 1 of -10°C or more and 40°C or less, and the downstream coagulating liquid is adjusted to a temperature range 2 of 45°C or more and 80°C or less, This can be carried out by immersing the EVOH extruded into a strand in a coagulating liquid from the upstream side and then pulling it out from the downstream side. Among these, (1) is preferable because it is easy to control the temperature and contact time of the coagulating liquid with which the EVOH comes into contact.

The temperature range 1 of the coagulating liquid needs to be -10°C or higher and 40°C or lower. If the lower limit of temperature range 1 is less than -10°C, the coagulating liquid may freeze. The lower limit of temperature range 1 is preferably -5°C, more preferably 0°C. On the other hand, if the upper limit of temperature range 1 exceeds 40°C, the EVOH will not solidify sufficiently. The upper limit of temperature range 1 is preferably 30°C, more preferably 25°C, even more preferably 20°C, even more preferably 15°C, and particularly preferably 10°C.

The contact time between the EVOH extruded into a strand and the coagulating liquid having a temperature range of 1 is preferably 5 seconds or more. If the contact time is less than 5 seconds, the EVOH solution may not solidify sufficiently. The contact time is more preferably 10 seconds or more, even more preferably 20 seconds or more, even more preferably 30 seconds or more, and particularly preferably 40 seconds or more. On the other hand, from the viewpoint of productivity, the contact time is preferably 30 minutes or less, more preferably 10 minutes or less, and even more preferably 5 minutes or less.

The temperature range 2 of the coagulating liquid needs to be 45°C or higher and 80°C or lower. By contacting the coagulated liquid in such a temperature range with the EVOH-containing coagulated material, the water content of the coagulated material is reduced and the cuttability is improved. From the viewpoint that the moisture content tends to decrease, the lower limit of temperature range 2 is preferably 55°C, more preferably 60°C, and even more preferably 65°C. On the other hand, when the upper limit of temperature range 2 exceeds 80° C., the EVOH-containing coagulated material becomes high temperature and softens, making it difficult to cut. The upper limit of temperature range 2 is preferably 75°C.

The contact time between the EVOH extruded into a strand and the coagulating liquid having temperature range 2 is preferably 5 seconds or more. If the contact time is less than 5 seconds, there is a risk that the moisture content of the EVOH-containing coagulum will not decrease or that the effect of improving cuttability will not be obtained. The contact time is more preferably 10 seconds or more, and even more preferably 20 seconds or more. On the other hand, from the viewpoint of productivity, the contact time is preferably 30 minutes or less, more preferably 10 minutes or less, and even more preferably 5 minutes or less.

In order to further improve the cutting properties of the coagulated product, after the EVOH extruded into a strand comes into contact with a coagulating liquid having a temperature range 2, it is further coagulated in a temperature range 3 of -10°C or more and 40°C or less. It is preferable to contact the liquid. This process is
(3) Furthermore, using a coagulation bath 3 containing a coagulation liquid having a temperature range 3 of -10°C or more and 40°C or less, the EVOH that has come into contact with the coagulation liquid having a temperature range 2 is 3, immersing in a coagulating liquid having
(4) In the coagulation bath in which the coagulation liquid was adjusted to temperature range 2, the coagulation liquid downstream of the part adjusted to temperature range 2 was adjusted to temperature range 3, and the EVOH extruded in a strand shape was coagulated from the upstream side. This can be carried out by immersing the EVOH in a liquid and then pulling it out from the downstream side, and (3) is preferred from the viewpoint of easy control of the temperature and contact time of the coagulating liquid with which the EVOH comes into contact. These steps may be combined with either (1) or (2) described above as a step of bringing the EVOH into contact with a coagulating liquid having a temperature range 1 and a coagulating liquid having a temperature range 2. The combination of (1) and (3) is preferable because it is easy to control the temperature and contact time of the coagulating liquid with which the EVOH comes into contact. Further, the combination of (2) and (4) is preferable since the step of bringing the EVOH into contact with coagulating liquids having different temperature ranges can be performed in one coagulating bath.

Temperature range 3 of the coagulating liquid is -10°C or higher and 40°C or lower. If the lower limit of temperature range 3 is less than -10°C, the coagulation liquid may freeze. The lower limit of temperature range 3 is preferably -5°C, more preferably 0°C. On the other hand, if the upper limit of temperature range 3 exceeds 40°C, the temperature of the EVOH-containing coagulum does not decrease sufficiently, and the effect of improving cutting performance by contacting with the coagulation liquid having temperature range 3 cannot be obtained. do not have. The upper limit of temperature range 3 is preferably 30°C, more preferably 25°C, even more preferably 20°C, even more preferably 15°C, and particularly preferably 10°C.

The contact time when the EVOH extruded into a strand is brought into contact with the coagulation liquid having a temperature range of 3 is preferably 5 seconds or more. If the contact time is less than 5 seconds, the temperature of the EVOH-containing coagulum will not be sufficiently lowered, and the effect of improving cuttability by contacting with the coagulation liquid having temperature range 3 will not be obtained. The contact time is more preferably 10 seconds or more, further preferably 20 seconds or more, even more preferably 30 seconds or more, and particularly preferably 40 seconds or more. On the other hand, from the viewpoint of productivity, the contact time is preferably 30 minutes or less, more preferably 10 minutes or less, and even more preferably 5 minutes or less.

The EVOH extruded into a strand is pulled out from the coagulation bath by a take-up roller attached to the end of the coagulation bath, and then cut to obtain EVOH pellets. Depending on the take-up speed of the take-up roller, the contact time with the coagulation liquid, the diameter of the EVOH pellets obtained, etc. can be adjusted. The take-up speed of the take-up roller is preferably 1.5 to 5.0 m/min, more preferably 2.0 to 4.5 m/min, even more preferably 2.5 to 4.5 m/min.

The EVOH-containing strand-shaped coagulated material thus obtained is cut to obtain EVOH pellets. The method for cutting the coagulated material is not particularly limited, and examples thereof include methods using a strand cutter, hot cutter, underwater cutter, and the like. Among these, it is preferable to cut the coagulated material using a strand cutter. The length of the EVOH pellet immediately after cutting is preferably 1 to 10 mm. When the EVOH pellet is cylindrical, it is preferable that its diameter is 1 to 10 mm.

In order to further improve cuttability, the moisture content of the EVOH pellets immediately after cutting is preferably 30 to 80% by mass. The moisture content is more preferably 35% by mass or more. On the other hand, the moisture content is more preferably 70% by mass or less, further preferably 50% by mass or less, and particularly preferably 45% by mass or less.

The water-containing EVOH pellets thus obtained may be subjected to a washing step and a drying step, if necessary. Examples of the cleaning liquid used in the cleaning step include water, an aqueous solution containing an acid such as acetic acid, an aqueous solution containing an alcohol such as methanol, and the like. The drying method for the water-containing EVOH pellets used in the drying step includes hot air drying, infrared irradiation, and the like.

The water-containing EVOH pellets may be subjected to chemical treatment, if necessary. Examples of the treatment include a method of impregnating the water-containing EVOH pellets with an aqueous solution containing an arbitrary additive. Examples of such additives include carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts.

The EVOH pellets thus obtained are melt-molded into various molded bodies such as films, sheets, containers, pipes, and fibers.

Hereinafter, the present invention will be explained in more detail using Examples, but the present invention is not limited to these Examples in any way.

[Evaluation method]
(1) Strand cutability evaluation During the manufacturing process of the hydrous EVOH pellets obtained in Examples and Comparative Examples, the hydrous EVOH pellets (approximately 2500 pellets) obtained by cutting 10 m of strand-shaped hydrous EVOH (coagulated material) were visually inspected. and evaluated the following items.
・Is it possible to cut the strands continuously?
・Number of times (times) the cutter was stopped due to a defective cut in which pellets continued for 3 cm or more
・Number of pellets that cannot be cut and are a series of water-containing EVOH pellets
・Number of hydrous EVOH pellets with a crushed cross section (units)

(2) Water content of water-containing EVOH pellets The water content of the water-containing EVOH pellets obtained in Examples and Comparative Examples immediately after cutting was measured using a halogen moisture meter "HR73" manufactured by Mettler.

(3) Dimensional stability 100 EVOH pellets obtained in Examples and Comparative Examples were arbitrarily selected, the diameter and length were measured, and the diameter and length of the pellets were within ±0.2 mm of the average value. The percentage of pellets entering was measured.

[Example]
(Example 1)
EVOH (saponified ethylene-vinyl acetate copolymer) with an ethylene unit content of 27 mol% and a saponification degree of 99 mol% is placed in a container having a nitrogen inlet and a cylindrical nozzle with an inner diameter of 0.3 cm and a length of 6.0 cm. By adding an EVOH solution (water/methanol solution (mass ratio 50/50)) containing 40% by mass of The strands are discharged into a coagulation bath 1 consisting of a 5°C water/methanol solution (mass ratio 95/5) at a rate of Coagulation bath 2 was passed through. The strands were pulled out from the coagulation liquid at a take-up speed of 2.8 m/min using a take-off roller attached to the end of the coagulation bath 2 so that the residence time of each coagulation bath was 60 seconds. The strand pulled out from the coagulation liquid was cut with a cutter to obtain porous water-containing EVOH pellets. To cut the strands, use a φ60mm/100mm rotary blade with 8 equally spaced blades, adjust the rotational speed of the blade so that the circumferential speed of the blade is equal to the take-up speed + 0.05m/min, and cut the strand. did. The resulting water-containing EVOH pellets were evaluated for strand cutability and water content according to the methods described in evaluation methods (1) and (2) above. The results are shown in Table 1. The water-containing EVOH pellets were washed with water for 1 hour in a water tank at a temperature of 30°C, this process was repeated 4 times, and further washed in acetic acid water at a temperature of 30°C for 1 hour, dried, and the EVOH pellets of the present invention (average A cylindrical white pellet with a diameter of 3.8 mm and an average length of 4 mm was obtained.

(Examples 2 to 14, Comparative Examples 1 to 4)
Water-containing EVOH pellets and EVOH pellets were produced in the same manner as in Example 1, except that the ethylene unit content, solution concentration, strand diameter, discharge speed, coagulation bath conditions, and withdrawal speed were changed as shown in Table 1. and evaluated. The results are shown in Table 1. The solvent composition of the coagulation bath 3 is a water/methanol solution (mass ratio 95/5), and in the examples and comparative examples that include the coagulation bath 3, the coagulation bath 2 and the coagulation bath 3 are passed in this order. The take-off roller is attached not to the end of the coagulation bath 2 but to the end of the coagulation bath 3. Further, when only the coagulation bath 1 is used, a take-up roller is attached to the end of the coagulation bath 1.

(Examples 15 to 17)
Water-containing EVOH pellets and EVOH pellets were prepared and evaluated in the same manner as in Example 1, except that sodium acetate was dissolved in coagulation bath 2 to have the concentration shown in Table 2. The results are shown in Table 2.

(Comparative example 5)
Water-containing EVOH pellets and EVOH pellets were prepared and evaluated in the same manner as in Comparative Example 1, except that sodium acetate was dissolved in coagulation bath 1 to the concentration shown in Table 2. The results are shown in Table 2.

From the comparison between Example 1 and Example 2, it can be seen that as the temperature of the coagulation bath 2 increases, the water content is more likely to decrease. From the comparison between Example 2 and Example 3, it can be seen that the cuttability becomes extremely good when the material passes through the coagulation bath 3 having a low temperature. A comparison between Example 2 and Examples 4 to 6 shows that, although the cuttability tends to deteriorate as the ethylene unit content decreases, all of them show good cuttability. A comparison between Example 2 and Example 7 shows that as the solution concentration becomes thinner, the productivity per unit time decreases, but the cutting performance improves. A comparison between Example 2 and Example 8 shows that good cutting performance can be maintained even if the solution concentration is increased. Comparing Example 2 with Examples 9 and 10, it can be seen that the faster the take-up speed is, the smaller the strand diameter is and the better the cuttability is. Comparison of Example 2 and Examples 11 to 14 shows that the residence time in the coagulation bath affects the cuttability. From Comparative Example 1, it can be seen that without a coagulation bath of 45° C. or higher, cutting performance is poor (cutter stops). Further, from Comparative Examples 2 and 4, it can be seen that it cannot be cut if it passes through a coagulation bath at a temperature exceeding 80°C. Comparative Example 3 shows that when the coagulation bath temperature 2 is less than 45° C., the cutting performance is poor (the cutter stops). These cutability evaluations are performed as evaluations of indicators that may affect continuous production, and even if EVOH pellets have good dimensional stability, comparative examples that are inferior to this cutability evaluation are , cutting defects may occur during continuous production.

Claims (5)

The coagulating step includes a coagulating step of obtaining a coagulated product by extruding a solution of saponified ethylene-vinyl ester copolymer into a coagulating liquid in the form of a strand and coagulating it, and a cutting step of cutting the coagulated product to obtain pellets. The coagulating liquid has two or more different temperature ranges, and the saponified ethylene-vinyl ester copolymer extruded into a strand has a temperature range 1 of -10°C to 40°C. A method for producing saponified ethylene-vinyl ester copolymer pellets, which comprises contacting with a coagulating liquid having a temperature range 2 of 45° C. or higher and 80° C. or lower. The method for producing saponified ethylene-vinyl ester copolymer pellets according to claim 1, wherein the coagulation liquid contains water and methanol. The saponified ethylene-vinyl ester copolymer extruded into a strand comes into contact with the coagulating liquid having the temperature range 2, and then further comes into contact with the coagulating liquid having the temperature range 3 of -10°C or more and 40°C or less. A method for producing saponified ethylene-vinyl ester copolymer pellets according to claim 1 or 2. The method for producing saponified ethylene-vinyl ester copolymer pellets according to claim 1 or 2, wherein the coagulation liquid contains 2% by mass or more of at least one salt selected from the group consisting of inorganic salts and organic salts. The method for producing saponified ethylene-vinyl ester copolymer pellets according to claim 4, wherein the salt is at least one selected from the group consisting of carboxylates, sulfates, nitrates, and carbonates.