Method for producing ethylene-vinyl ester copolymer saponified pellets

Abstract

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

Description

Technical Field

[0001] The present invention relates to a method for producing saponified ethylene-vinyl ester copolymer pellets.

Background Art

[0002] The saponified ethylene-vinyl ester copolymer (hereinafter sometimes abbreviated as EVOH) is a material excellent in oxygen barrier property, oil resistance, non-charging property, mechanical strength, etc., and is widely used after being formed into films, sheets, containers, etc. As a method for producing EVOH, a method of saponifying 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 is common.

[0003] As a post-treatment method for the alcohol solution of EVOH obtained by saponification, a method of extruding the alcohol solution of EVOH in a strand shape into a coagulating liquid such as water or a water / methanol solution and then cutting the strand to produce pellets is widely used (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when cutting the strand, cutting mistakes occurred, resulting in a decrease in productivity or insufficient dimensional stability of the obtained pellets. For these reasons, improvement in the cutability of strands made of water-containing EVOH has been demanded.

[0006] This invention was made to solve the above problems and aims to provide a method for manufacturing EVOH pellets with high dimensional stability and productivity. [Means for solving the problem]

[0007] The above problem is solved by providing a method for producing EVOH pellets, which includes a solidification step of obtaining a solid by extruding an EVOH solution in a strand shape into a solidifying liquid and allowing it to solidify, and a cutting step of cutting the solidified product to obtain pellets, wherein in the solidification step the solidifying liquid has two or more different temperature ranges, and the EVOH extruded in a strand shape comes into contact with a solidifying liquid having a temperature range 1 of -10°C to 40°C, and then comes into contact with a solidifying liquid having a temperature range 2 of 45°C to 80°C.

[0008] In this case, it is preferable that the coagulation solution contains water and methanol. It is also preferable that the EVOH extruded in strand form comes into contact with a coagulation solution having a temperature range 2, and then further comes into contact with a coagulation solution having a temperature range 3 of -10°C to 40°C. It is also preferable that the coagulation solution contains 2% by mass or more 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. [Effects of the Invention]

[0009] The manufacturing method of the present invention produces EVOH pellets with high productivity because the strand-like solidified material containing EVOH has good cutability. The EVOH pellets thus obtained can be suitably used as a material for various molded products. [Modes for carrying out the invention]

[0010] The present invention relates to a method for producing ethylene-vinyl ester copolymer saponified pellets, comprising a solidification step of obtaining a solidified product by extruding an EVOH solution in a strand-like manner into a solidifying liquid and allowing it to solidify, and a cutting step of cutting the solidified product to obtain pellets, wherein the solidifying liquid has two or more different temperature ranges in the solidification step, and the ethylene-vinyl ester copolymer saponified product extruded in a strand-like manner comes into contact with a solidifying liquid having a temperature range 1 of -10°C to 40°C, and then comes into contact with a solidifying liquid having a temperature range 2 of 45°C to 80°C. In this method, the strand-like solidified product containing EVOH has good cutability, resulting in high productivity, and the resulting EVOH pellets also have high dimensional stability. The present invention will be described in detail below.

[0011] First, the method for synthesizing EVOH will be described. 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, but vinyl acetate is preferred. Polymerization of ethylene and vinyl ester may be carried out by solution polymerization, suspension polymerization, emulsion polymerization, or bulk polymerization, but solution polymerization is preferred. It may also be carried out in a continuous or batch manner.

[0012] In solution polymerization, alcohols are preferred as the solvent, but other organic solvents capable of dissolving ethylene, vinyl esters, and ethylene-vinyl acetate copolymers (such as dimethyl sulfoxide) can also be used. Suitable alcohols include methanol, ethanol, 1-propanol, and 2-propanol, with methanol being industrially preferred.

[0013] As polymerization catalysts, azonitrile-based initiators such as 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), and 2,2-azobis-(2-cyclopropylpropionitrile), as well as organic peroxide-based initiators such as isobutyryl peroxide, cumyl peroxyneodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxyneodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide can be used.

[0014] 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 polymerization) 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%, relative to the input vinyl ester. 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 that of EVOH, which will be described later. In addition, the ethylene-vinyl ester copolymer can also be copolymerized with small amounts of other monomers, but the type and amount of other monomers used are the same as those used for EVOH, which will be described later.

[0015] After polymerization for a predetermined time and reaching a predetermined polymerization rate, a polymerization inhibitor is added as needed, and unreacted ethylene gas is evaporated and removed, followed by the removal of unreacted vinyl ester. As a method for removing unreacted vinyl ester from the ethylene-vinyl ester copolymer solution from which ethylene has been evaporated, for example, the copolymer solution is continuously supplied at a constant rate from the top of a column packed with Raschig rings, and an organic solvent vapor such as methanol is blown in from the bottom of the column, causing a mixed vapor of the organic solvent such as methanol and unreacted vinyl ester to distill out from the top of the column, and the copolymer solution from which the unreacted vinyl ester has been removed is taken out from the bottom of the column.

[0016] An alkaline 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 continuous or batch, but it is preferable to carry out the saponification reaction continuously using a tower reactor and collect the EVOH solution from the bottom of the tower. Sodium hydroxide, potassium hydroxide, alkali metal alcohols, etc., can be used as the alkaline catalyst. Alcohols such as methanol and ethanol are preferred as the solvent used for saponification, and methanol is more preferred industrially. When using a tower reactor, it is preferable to supply methanol vapor from the bottom of the tower and distill off methyl acetate from the top of the tower.

[0017] The preferred saponification conditions are as follows: The concentration of ethylene-vinyl ester copolymer in the reaction solution is preferably 10 to 50% by mass, and more preferably 20 to 45% by mass. The reaction temperature is preferably 70 to 150°C, and more preferably 80 to 140°C. The amount of catalyst used is preferably 0.005 to 1 equivalent, and more preferably 0.01 to 0.5 equivalents, relative to the number of moles of vinyl ester units. The reaction time (average residence time in the case of a continuous reaction) is preferably 10 minutes to 6 hours, and more preferably 15 minutes to 2 hours. The saponification reaction is carried out in this manner to obtain a solution of EVOH. The EVOH content in the solution is preferably 10 to 50% by mass, and more preferably 20 to 45% by mass.

[0018] The degree of saponification of the vinyl ester units of the EVOH obtained in this way is preferably 80 to 100 mol%. From the viewpoint of obtaining a molded product with excellent barrier properties, it is more preferably 95 mol% or more, even more preferably 98 mol% or more, and particularly preferably 99 mol% or more. If the degree of saponification is less than 80 mol%, the barrier properties, long-run properties, and moisture resistance may be poor.

[0019] 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 be poor. More preferably, the ethylene unit content is 23 mol% or more. On the other hand, if the ethylene unit content exceeds 60 mol%, the barrier properties may be insufficient. More preferably, the ethylene unit content is 55 mol% or less, and even more preferably 50 mol% or less.

[0020] EVOH can also be copolymerized with small amounts of other monomers, as long as the objectives of the present invention are not hindered. 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-diasiloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, and 4-acyloxy-3-methyl -1-butene, 3,4-diasiloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diasiloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diasiloxy-1-hexene, 1,3-diacetoxy-2-methyl Examples include alkenes having ester groups such as npropane or their saponides; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, and itaconic acid, or their anhydrides, salts, or mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as vinylsulfonic acid, allylsulfonic acid, and methallylsulfonic acid, or their salts; vinylsilane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, and γ-methacryloxypropylmethoxysilane; alkyl vinyl ethers, vinyl ketones, N-vinylpyrrolidone, vinyl chloride, and vinylidene chloride. When EVOH has other monomer units, the copolymerization amount is preferably 10 mol% or less, and more preferably 5 mol% or less.

[0021] The solvent used in the EVOH solution subjected to the solidification 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 solidification 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 alcohols that can be used in this case include methanol, ethanol, propanol, butanol, etc., with methanol being industrially preferred.

[0022] The method for producing the EVOH solution used in the solidification step is not particularly limited. The EVOH solution after the saponification reaction may be used directly in the solidification step, or a solvent may be added to the EVOH solution after the saponification reaction, or at least a portion of the solvent in the EVOH solution after the saponification reaction may be replaced with the same or a different solvent before being used in the solidification step.

[0023] As the water / alcohol solution of the EVOH to be subjected to the coagulation step, the one obtained by replacing a part 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 of replacing a part of the alcohol in the alcohol solution of the EVOH with water, a method of adding a mixed vapor of a solvent (alcohol) and water to the alcohol solution in a container and vaporizing the solvent (alcohol) from the solution is preferable. As the container at this time, a tower-type container such as a tray column or a packed column is preferable. In this case, the alcohol solution of the EVOH is introduced from the upper part of the tower, a mixed vapor of a solvent (alcohol) and water is introduced from the lower part of the tower-type container, and they are brought into countercurrent contact. Then, the mixed vapor of the solvent (alcohol) and water is led out from the upper part of the tower, and a part of the solvent existing in the supplied alcohol solution of the EVOH is replaced with water, and a high-concentration water / alcohol solution of the EVOH can be obtained from the bottom of the tower. Further, it is preferable that the water content in the mixed vapor 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. Examples of such alcohols include alcohols such as methanol, ethanol, propanol, and butanol. An alcohol having a boiling point of 100°C or lower is more preferable, and among them, methanol is preferable in terms of being easily available, inexpensive, having a low boiling point, and being easy to handle. By performing the solvent replacement in this way, a water / alcohol solution of the EVOH can be obtained. The mass ratio of water / alcohol of the water / alcohol solution of the EVOH to be subjected to the coagulation step is preferably 10 / 90 to 60 / 40, and more preferably 20 / 80 to 50 / 50.

[0024] The content of the EVOH in the EVOH solution to be subjected to the coagulation step is preferably 20 to 50% by mass. By setting the content of the EVOH 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 the EVOH and the solvent in the EVOH solution is usually 10% by mass or less.

[0025] As the coagulation liquid used in the coagulation step, a coagulation liquid containing a poor solvent for the EVOH is used. As the poor solvent, water and a mixed solvent containing water and alcohol are preferable, and a mixed solvent containing water and alcohol is more preferable. As the alcohol used in the mixed solvent, methanol, ethanol, propanol, etc. are used, but methanol is preferably used industrially. The mass ratio of water to alcohol (water / alcohol) contained in the mixed solvent is preferably from 70 / 30 to 98 / 2. The mass ratio (water / alcohol) is more preferably 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 still more preferably 90% by mass or more.

[0026] From the viewpoint of further improving the cuttability, it is preferable that the coagulation liquid contains at least one kind of 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, etc., and among them, sulfates, nitrates, and carbonates are preferable. Examples of the organic salts include carboxylates, sulfonates, etc., and among them, carboxylates are preferable. Further, it is preferable that the cation constituting the salt is 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 the cation of a metal belonging to Group 1 of the periodic table include sodium ion, potassium ion, lithium ion, etc., sodium ion and potassium ion are preferable, and sodium ion is more preferable. Examples of the cation of a metal belonging to Group 2 of the periodic table include calcium ion, magnesium ion, etc. Specifically, sodium acetate is preferable from the viewpoint of handleability.

[0027] When the coagulation liquid contains the salt, the content is preferably 2% by mass or more. If the content is less than 2% by mass, there is a risk that the effect of improving the cuttability cannot be obtained. The content is 40% by mass or less from the viewpoint of suppressing the precipitation of the salt in the coagulation liquid.

[0028] In the present invention, the solidification solution must have two or more different temperature ranges. Specifically, the solidification solution must have at least a temperature range 1 of -10°C to 40°C and a temperature range 2 of 45°C to 80°C. In the solidification process, the EVOH extruded in strand form comes into contact with the solidification solution having temperature range 1, and then comes into contact with the solidification solution having temperature range 2. By obtaining a strand-shaped solid containing EVOH in this way, surprisingly, the cutability of the solid is improved in the cutting process described later. As a result, EVOH pellets with high dimensional stability can be produced with high productivity. The reason for this is not clear, but it is thought that one reason is that the EVOH solution extruded in strand form solidifies upon contact with the solidification solution having a low temperature range 1, and then the solid is dehydrated and moderately hardened upon contact with the solidification solution having a high temperature range 2.

[0029] The EVOH solution is extruded in strand form into the solidification liquid by a nozzle having any shape. The shape of the nozzle is not particularly limited, but a cylindrical shape is preferred. The inner diameter of the nozzle can 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 strand form. At this time, the strand does not necessarily have to be a single strand, and any number between a few and several hundred strands can be extruded.

[0030] The EVOH, extruded in strand form, is brought into contact with a solidifying solution having temperature range 1, and then into contact with a solidifying solution having temperature range 2. This process is performed as follows: (1) Using a coagulation bath 1 containing a coagulation solution having a temperature range 1 of -10°C to 40°C and a coagulation bath 2 containing a coagulation solution having a temperature range 2 of 45°C to 80°C, the strand-shaped EVOH is immersed in the coagulation solution having temperature range 1 in coagulation bath 1, and then immersed in the coagulation solution having temperature range 2 in coagulation bath 2. (2) This can be done by adjusting the temperature of the upstream coagulation solution to a temperature range 1 of -10°C to 40°C in a single coagulation bath, adjusting the temperature of the downstream coagulation solution to a temperature range 2 of 45°C to 80°C, immersing the strand-shaped EVOH in the coagulation solution from the upstream side, and then pulling it out from the downstream side. Among these, (1) is preferred because it is easier to control the temperature of the coagulation solution in contact with the EVOH and the contact time.

[0031] The temperature range 1 of the coagulation solution must be between -10°C and 40°C. If the lower limit of temperature range 1 is below -10°C, the coagulation solution may freeze. The lower limit of temperature range 1 is preferably -5°C, and more preferably 0°C. On the other hand, if the upper limit of temperature range 1 exceeds 40°C, the EVOH will not coagulate 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.

[0032] The contact time between the strand-shaped extruded EVOH and the coagulation solution 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 coagulate 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.

[0033] The temperature range 2 of the coagulation solution must be between 45°C and 80°C. When the coagulation solution in this temperature range comes into contact with the solidified material containing EVOH, the water content of the solidified material decreases and its cutability improves. From the viewpoint of easily reducing the water content, the lower limit of the temperature range 2 is preferably 55°C, more preferably 60°C, and even more preferably 65°C. On the other hand, if the upper limit of the temperature range 2 exceeds 80°C, the solidified material containing EVOH becomes soft due to the high temperature, making it difficult to cut. The upper limit of the temperature range 2 is preferably 75°C.

[0034] The contact time between the strand-shaped extruded EVOH and the coagulation solution having a temperature range of 2 is preferably 5 seconds or more. If the contact time is less than 5 seconds, there is a risk that the water content of the coagulated product containing EVOH will not decrease, or that the effect of improving cutability 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.

[0035] To further improve the cutability of the solidified material, it is preferable that the EVOH, extruded in strand form, contacts a solidifying solution having a temperature range 2, and then further contacts a solidifying solution having a temperature range 3 of -10°C to 40°C. This step is performed as follows: (3) Furthermore, using a coagulation bath 3 containing a coagulation solution having a temperature range 3 of -10°C to 40°C, EVOH that has been in contact with a coagulation solution having a temperature range 2 is immersed in the coagulation solution having a temperature range 3 in the coagulation bath 3. (4) In a coagulation bath in which the coagulation solution is adjusted to temperature range 2, the coagulation solution downstream of the portion adjusted to temperature range 2 is adjusted to temperature range 3, the strand-shaped EVOH is immersed in the coagulation solution from the upstream side, and then pulled out from the downstream side, and so on. (3) is preferred because it is easy to control the temperature of the coagulation solution in which the EVOH comes into contact with it and the contact time. These steps may be combined with either (1) or (2) described above as steps to bring the EVOH into contact with a coagulation solution having temperature range 1 and a coagulation solution having temperature range 2. The combination of (1) and (3) is preferred because it is easy to control the temperature of the coagulation solution in which the EVOH comes into contact with it and the contact time. The combination of (2) and (4) is preferred because the steps to bring the EVOH into contact with coagulation solutions having each temperature range can be performed in a single coagulation bath.

[0036] The temperature range 3 of the coagulation solution is -10°C to 40°C. If the lower limit of temperature range 3 is below -10°C, the coagulation solution may freeze. The lower limit of temperature range 3 is preferably -5°C, and more preferably 0°C. On the other hand, if the upper limit of temperature range 3 exceeds 40°C, the temperature of the coagulated material containing EVOH will not decrease sufficiently, and the effect of improving cutting performance by contacting it with the coagulation solution having temperature range 3 will not be obtained. 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.

[0037] When bringing strand-shaped extruded EVOH into contact with a solidifying solution having a temperature range of 3, the contact time is preferably 5 seconds or more. If the contact time is less than 5 seconds, the temperature of the solidified material containing EVOH will not decrease sufficiently, and the effect of improving cutting performance by contacting it with a solidifying solution having a temperature range of 3 will not be obtained. 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.

[0038] The EVOH extruded in strand form is pulled out of the coagulation bath by a take-up roller attached to the edge of the coagulation bath, then cut to obtain EVOH pellets. The take-up speed of the take-up roller can be adjusted to control the contact time with the coagulation liquid and the diameter of the resulting EVOH pellets. 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, and even more preferably 2.5 to 4.5 m / min.

[0039] The strand-like solidified material containing EVOH obtained in this way is cut to obtain EVOH pellets. The method of cutting the solidified material is not particularly limited, and methods using a strand cutter, hot cutter, underwater cutter, etc. are possible. Among these, it is preferable to cut the solidified material using a strand cutter. The length of the EVOH pellet immediately after cutting is preferably 1 to 10 mm. If the EVOH pellet is cylindrical, its diameter is preferably 1 to 10 mm.

[0040] From the standpoint of further improving cutability, the moisture content of the EVOH pellets immediately after cutting is preferably 30 to 80% by mass. A moisture content of 35% by mass or more is more preferable. On the other hand, a moisture content of 70% by mass or less is more preferable, 50% by mass or less is even more preferable, and 45% by mass or less is particularly preferable.

[0041] The resulting hydrated EVOH pellets may be subjected to washing and drying steps as needed. Washing solutions used in the washing step include water, aqueous solutions containing acids such as acetic acid, and aqueous solutions containing alcohols such as methanol. Drying methods for the hydrated EVOH pellets used in the drying step include hot air drying and infrared irradiation.

[0042] The hydrated EVOH pellets may be subjected to chemical treatment as necessary. This treatment may include impregnating the hydrated 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.

[0043] The resulting EVOH pellets are then molded into various types of molded products such as films, sheets, containers, pipes, and fibers by melt molding. [Examples]

[0044] The present invention will be described in more detail below using examples, but the present invention is not limited in any way by these examples.

[0045] [Evaluation Method] (1) Strand cutability evaluation In the manufacturing process of the hydrated EVOH pellets obtained in the examples and comparative examples, approximately 2,500 pellets were obtained by cutting 10m of strand-shaped hydrated EVOH (coagulated material) and visually inspected them, and evaluated for the following items. Can the strand be cut continuously? (Yes / No) • Number of times the cutter was stopped due to a cutting defect where pellets were stuck together for 3 cm or more in a row. • Number of pellets that are connected and cannot be cut (pieces) • Number of hydrated EVOH pellets with crushed cross-sections (pieces)

[0046] (2) Moisture content of water-containing EVOH pellets The moisture content of the hydrated EVOH pellets obtained in the examples and comparative examples immediately after cutting was measured using a Mettler HR73 halogen moisture meter.

[0047] (3) Dimensional stability One hundred EVOH pellets obtained in the examples and comparative examples were arbitrarily selected, and their diameter and length were measured. The percentage of pellets whose diameter and length fell within the range of ±0.2 mm of the average value was then determined.

[0048] [Examples] (Example 1) 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 was filled with an EVOH solution (water / methanol solution (mass ratio 50 / 50)) containing 40% by mass of EVOH (ethylene-vinyl acetate copolymer saponified product) with an ethylene unit content of 27 mol% and a degree of saponification of 99 mol%. By controlling the amount of nitrogen introduced through the nitrogen inlet, the EVOH solution was discharged in strand form from the cylindrical nozzle at a speed of 1 kg / h into a solidification bath 1 consisting of a 5°C water / methanol solution (mass ratio 95 / 5). The strand was then passed through a solidification bath 2 consisting of a 50°C water / methanol solution (mass ratio 95 / 5). The strand was drawn out of the solidification solution at a speed of 2.8 m / min using a take-up roller attached to the end of the solidification bath 2, so that the residence time in each solidification bath was 60 seconds. The strand drawn out of the solidification solution was cut with a cutter to obtain porous, water-containing EVOH pellets. A φ60mm / 100mm rotary blade with eight equally spaced blades was used to cut the strand. The rotation speed of the blade was adjusted so that the peripheral speed of the blade was the take-up speed + 0.05 m / min, and the strand was cut. The obtained water-containing EVOH pellets were evaluated for their 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 in a water bath at 30°C for 1 hour, this was repeated four times, and then washed again in acetic acid water at 30°C for 1 hour. After drying, the EVOH pellets of the present invention (cylindrical white pellets with an average diameter of 3.8 mm and an average length of 4 mm) were obtained.

[0049] (Examples 2-14, Comparative Examples 1-4) Except for changing the ethylene unit content, solution concentration, strand diameter, discharge rate, solidification bath conditions, and take-up rate as shown in Table 1, hydrated EVOH pellets and EVOH pellets were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. The solvent composition of solidification bath 3 is a water / methanol solution (mass ratio 95 / 5). In the examples and comparative examples equipped with solidification bath 3, the material passes through solidification bath 2 and then solidification bath 3 in that order, and the take-up roller is attached to the end of solidification bath 3, not the end of solidification bath 2. When only solidification bath 1 is used, the take-up roller is attached to the end of solidification bath 1.

[0050] [Table 1]

[0051] (Examples 15-17) Hydrated 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 the concentrations shown in Table 2. The results are shown in Table 2.

[0052] (Comparative Example 5) Hydrated EVOH pellets and EVOH pellets were prepared and evaluated using the same method as in Comparative Example 1, except that sodium acetate was dissolved in coagulation bath 1 to the concentrations shown in Table 2. The results are shown in Table 2.

[0053] [Table 2]

[0054] Comparing Example 1 with Example 2, it can be seen that the water content decreases more easily as the temperature of solidification bath 2 increases. Comparing Example 2 with Example 3, it can be seen that cutting performance is extremely good after passing through solidification bath 3 at a lower temperature. Comparing Example 2 with Examples 4-6, it can be seen that cutting performance tends to worsen as the ethylene unit content decreases, but all show good cutting performance. Comparing Example 2 with Example 7, it can be seen that cutting performance improves as the solution concentration decreases, although productivity per unit time decreases. Comparing Example 2 with Example 8, it can be seen that good cutting performance can be maintained even when the solution concentration is increased. Comparing Example 2 with Examples 9 and 10, it can be seen that a faster pull-up speed results in a smaller strand diameter and better cutting performance. Comparing Example 2 with Examples 11-14, it can be seen that the residence time in the solidification bath affects cutting performance. Comparative Example 1 can be seen that cutting performance is poor (cutter stops) without a solidification bath of 45°C or higher. Furthermore, Comparative Examples 2 and 4 show that cutting is not possible when passing through a solidification bath exceeding 80°C. Comparative Example 3 shows that cutting performance is poor (cutter stops) when the solidification bath temperature 2 is below 45°C. These evaluations of cutting performance are conducted as indicators that may affect continuous production, and even if the EVOH pellets have good dimensional stability, comparative examples that perform poorly in this cutting performance evaluation may experience cutting defects during continuous production.

Claims

1. A method for producing ethylene-vinyl ester copolymer saponified pellets, comprising a solidification step of obtaining a solidified product by extruding a solution of ethylene-vinyl ester copolymer saponified in strand form into a solidification liquid and allowing it to solidify, and a cutting step of cutting the solidified product to obtain pellets, wherein in the solidification step the solidification liquid has two or more different temperature ranges, and the ethylene-vinyl ester copolymer saponified, extruded in strand form, comes into contact with a solidification liquid having a temperature range 1 of -10°C to 15°C, and then comes into contact with a solidification liquid having a temperature range 2 of 45°C to 80°C.

2. The method for producing ethylene-vinyl ester copolymer saponified pellets according to claim 1, wherein the coagulation solution contains water and methanol.

3. A method for producing ethylene-vinyl ester copolymer saponified pellets according to claim 1 or 2, wherein the ethylene-vinyl ester copolymer saponified, extruded in strand form, is brought into contact with a coagulation solution having a temperature range 2, and then further into contact with a coagulation solution having a temperature range 3 of -10°C to 40°C.

4. The method for producing ethylene-vinyl ester copolymer saponified 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.

5. The method for producing ethylene-vinyl ester copolymer saponified pellets according to claim 4, wherein the salt is at least one selected from the group consisting of carboxylates, sulfates, nitrates, and carbonates.

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