Method for producing aqueous pellets of ethylene-vinyl alcohol copolymer

Abstract

A method for producing water-containing EVOH pellets, said method comprising: a first step in which water-containing EVOH having a water content (W1) of 10-90 mass% is introduced into an extruder and melt-kneaded; and a second step for obtaining EVOH-containing pellets by cutting the water-containing EVOH extruded from the extruder, the extruder having a rear slit from which water is discharged while the rear slit is decompressed by a decompressing device, the temperature of the water-containing EVOH extruded from the extruder being 80-120 DEG C, the water content (W2) being 5-50 mass%, and the water content (W3) being 5-50 mass%. The ratio (W2 / W1) of the water content (W2) to the water content (W1) is 0.2 or more and less than 1. According to this production method, the elution of EVOH can be suppressed and the water in the water-containing EVOH can be efficiently reduced, and therefore, the water-containing EVOH pellets can be produced with good productivity.

Description

Technical Field

[0001] The present invention relates to a method for preparing aqueous pellets of ethylene-vinyl alcohol copolymer. Background Art

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as EVOH) is a polymer material excellent in oxygen barrier properties, aroma retention, oil resistance, non-static properties, mechanical strength, etc., and is widely used by being formed into films, sheets, containers, etc. As a method for producing EVOH, generally, an ethylene-vinyl ester copolymer obtained by copolymerizing ethylene with a vinyl ester such as vinyl acetate is saponified in the presence of a saponification catalyst and in an organic solvent containing an alcohol.

[0003] As one of the post-treatment methods for the alcohol solution of EVOH obtained by saponification, the following method is known: the alcohol solution of EVOH is introduced into a device, brought into contact with water in the aforementioned device, the alcohol in the aforementioned solution is replaced with water, the water content in the hydrous EVOH discharged from the aforementioned device is reduced, and then cutting is performed, thereby obtaining EVOH hydrous pellets (Patent Document 1).

[0004] Patent Document 1 describes a method in which a water-containing EVOH composition obtained by replacing alcohol with water is subjected to a kneading machine having a liquid discharge port to reduce the water content of the water-containing composition, and then extruded from a die and cut to obtain water-containing EVOH pellets. Patent Document 2 describes a method in which a water-containing EVOH obtained by contacting a water / methanol solution of EVOH with water vapor is kneaded using a twin-screw extruder (front section) having a vent hole provided at a portion downstream of an inlet (die side) to obtain water-containing EVOH with reduced water content.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2002-284811

[0008] Patent Document 2: Japanese Patent Application Publication No. 2010-132881 Summary of the invention

[0009] Problems to be solved by the invention

[0010] However, EVOH is hydrophilic, so these methods cannot be used to fully reduce the water content in the hydrous EVOH. When the hydrous EVOH containing a large amount of water extruded from the extruder is cut, poor cutting sometimes occurs, resulting in poor shape of the resulting hydrous EVOH pellets. In addition, when the water content of the hydrous EVOH is reduced, EVOH sometimes dissolves into the discharged water and is discharged from the liquid outlet of the kneader and the vent of the twin-screw extruder together with the water. If it is operated continuously, the liquid outlet and the vent will have traces of EVOH dissolution. If it is left for a long time, there is a possibility that the liquid outlet and the vent will be blocked, which will affect the manufacturing. In order to suppress poor cutting and EVOH dissolution, it is necessary to operate at a low speed. Therefore, a method of increasing the production speed and obtaining a good pellet shape is sought.

[0011] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing hydrous EVOH pellets having a good shape, which can suppress the elution of EVOH and efficiently reduce the water in the hydrous EVOH.

[0012] Means used to solve problems

[0013] This is achieved by providing the following technical solutions:

[0014] [1] A method for producing EVOH hydrous pellets, comprising: a first step of introducing hydrous EVOH having a moisture content W1 of 10 to 90% by mass into an extruder for melt kneading; and a second step of cutting the hydrous EVOH extruded from the extruder to obtain EVOH hydrous pellets, wherein the extruder has a back slit, and water is discharged from the back slit while the back slit is depressurized by a decompression device.

[0015] The temperature of the water-containing EVOH extruded from the extruder is 80 to 120° C., the water content W2 is 5 to 50% by mass, and the ratio of the water content W2 to the water content W1 (W2 / W1) is 0.2 or more and less than 1;

[0016] [2] The method according to [1], wherein the degree of decompression by the decompression device is -0.07 MPa to -0.005 MPa;

[0017] [3] The method according to [1] or [2], wherein the temperature of the aqueous EVOH introduced into the extruder is 80 to 130°C;

[0018] [4] The production method according to any one of [1] to [3], wherein the extruder does not have a liquid discharge port at a location downstream of the introduction port for the aqueous EVOH;

[0019] [5] The method according to any one of [1] to [4], wherein the screw rotation speed of the extruder is 10 to 2000 rpm;

[0020] [6] The production method according to any one of [1] to [5], further comprising the steps of: introducing an EVOH solution into a container, bringing the EVOH solution into contact with water vapor in the container, removing the alcohol together with the water vapor, removing the water-containing EVOH from the container, wherein the EVOH solution contains 50 parts by mass or more of an alcohol having a boiling point of 100° C. or less per 100 parts by mass of the EVOH, and introducing the water-containing EVOH removed from the container into the extruder;

[0021] [7] The production method according to any one of [1] to [6], wherein the EVOH has an ethylene unit content of 20 to 40 mol%.

[0022] Effects of the Invention

[0023] According to the production method of the present invention, the elution of EVOH can be suppressed and the water in the hydrous EVOH can be reduced efficiently, so that the hydrous EVOH pellets can be produced with good productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a figure which shows the barrel structure, screw structure, and installation position of the decompression device of the twin-screw extruder in Examples 1-11.

[0025] Figure 2 It is a diagram showing the barrel structure, screw structure and installation position of the decompression device of the twin-screw extruder in Example 12.

[0026] Figure 3 It is a figure which shows the barrel structure and the screw structure of the twin-screw extruder in Comparative Example 1.

[0027] Figure 4 It is a diagram showing the barrel structure, screw structure, and installation position of the pressure reducing device of the twin-screw extruder in Comparative Example 2.

[0028] Figure 5 It is a diagram showing the barrel structure and screw structure of the twin-screw extruder in Comparative Example 3.

[0029] Figure 6 It is a figure which shows the structure of the thermal cutting machine in Example 1-12 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0030] The present invention is a method for producing EVOH hydrous pellets, which comprises: a first step of introducing hydrous EVOH having a water content W1 of 10 to 90% by mass into an extruder for melt kneading; and a second step of cutting the hydrous EVOH extruded from the extruder to obtain EVOH hydrous pellets, wherein the extruder has a rear slit, and water is discharged from the rear slit while the rear slit is depressurized by a decompression device, the temperature of the hydrous EVOH extruded from the extruder is 80 to 120° C., the water content W2 is 5 to 50% by mass, and the ratio of the water content W2 to the water content W1 (W2 / W1) is 0.2 or more and less than 1. According to the production method, the elution of EVOH can be suppressed and the water in the hydrous EVOH can be efficiently reduced, and the hydrous EVOH pellets with good shape can be produced with good productivity. In particular, by providing the extruder with a rear slit, there is a tendency that the elution of EVOH can be suppressed and the water in the hydrous EVOH can be efficiently reduced. Furthermore, by reducing the pressure of the rear seam using a decompression device, there is a tendency to suppress dehydration failure that may occur when producing EVOH with a low ethylene unit content (for example, an ethylene unit content of 20 to 40 mol%), thereby obtaining EVOH hydrous pellets with good shape.

[0031] In this specification, the hydrous EVOH introduced into the extruder may be referred to as the hydrous EVOH used in the present invention, and the hydrous EVOH obtained by extrusion from the extruder may be referred to as the hydrous EVOH obtained in the present invention.

[0032] The water-containing EVOH used in the present invention is preferably in the form of a paste containing EVOH and water. The water content W1 of the water-containing EVOH is 10 to 90% by mass. In addition, as described later, the water-containing EVOH may contain other components such as alcohols and alkali metal salts.

[0033] The EVOH constituting the hydrous EVOH used in the present invention (hereinafter sometimes referred to as "EVOH used in the present invention" or "the aforementioned EVOH") is generally obtained by saponifying an ethylene-vinyl ester copolymer. The ethylene content in the aforementioned EVOH is preferably 20 to 60 mol%. If the ethylene content of EVOH is 20 mol% or more, the water content of the hydrous EVOH supplied to the extruder is reduced, and it is easy to prevent the melt viscosity of the hydrous EVOH in the extruder from becoming too low, thereby further suppressing the dissolution of EVOH. The aforementioned ethylene content is more preferably 23 mol% or more, and further preferably 25 mol% or more. On the other hand, if the ethylene content of the aforementioned EVOH is 60 mol% or less, the gas barrier properties are improved. The aforementioned ethylene content is more preferably 50 mol% or less, further preferably 45 mol% or less, and particularly preferably 40 mol% or less. In addition, from the viewpoint of efficiently reducing the water in EVOH by using a decompression device, the ethylene unit content of the aforementioned EVOH is preferably 20 mol% or more and 40 mol% or less, more preferably 20 mol% or more and 35 mol% or less, and further preferably 20 mol% or more and 33 mol% or less. If the ethylene unit content of the aforementioned EVOH exceeds 40 mol%, there is a tendency that the effect of reducing the water in EVOH by dehydration from the rear seam becomes sufficient, and the improvement effect based on the decompression device becomes smaller. It should be noted that the ethylene content and saponification degree of EVOH do not substantially change at the end of the saponification process and the end of the subsequent process described later, and are usually measured after all processes are completed.

[0034] The following is a specific description of the method for producing the EVOH. As described above, the EVOH is generally obtained by saponifying an ethylene-vinyl ester copolymer. The copolymerization of ethylene and vinyl ester may be any one of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization. In addition, it may be any one of continuous and intermittent polymerization. An example of polymerization conditions in solution polymerization is shown below.

[0035] The solvent used is preferably an alcohol having a boiling point of 100° C. or lower from the viewpoints of solubility of the ethylene-vinyl ester copolymer and EVOH, handleability, and ability to efficiently replace alcohol with water. The boiling point is more preferably 80° C. or lower, and further preferably 70° C. or lower.

[0036] Examples of the alcohol having a boiling point of 100° C. or lower include methanol, ethanol, n-propanol, isopropanol, tert-butanol, and the like, with methanol being particularly preferred.

[0037] As the initiator used in the polymerization, for example, azonitrile-based initiators such as 2,2-azobisisobutyronitrile, 2,2-azobis(2,4-dimethylvaleronitrile), 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 2,2-azobis(2-cyclopropylpropionitrile) can be used; as well as organic peroxide-based initiators such as isobutyryl peroxide, cumyl peroxyneodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, tert-butyl peroxyneodecanoate, lauroyl peroxide, benzoyl peroxide, and tert-butyl hydroperoxide can be used.

[0038] As the vinyl ester, fatty acid vinyl esters such as vinyl acetate, vinyl propionate, and vinyl pivalate can be listed, and vinyl acetate is suitable. In addition, EVOH can contain 0.0002 to 0.2 mol% of a vinyl silane compound as a copolymer component. Here, as the vinyl silane-based compound, for example, vinyl trimethoxy silane, vinyl triethoxy silane, vinyl tri (β-methoxy-ethoxy) silane, and γ-methacryloxypropyl methoxy silane can be listed. Among them, vinyl trimethoxy silane and vinyl triethoxy silane are suitable.

[0039] The polymerization conditions are preferably as follows.

[0040] (1) Temperature: preferably 20 to 90°C, more preferably 40 to 70°C.

[0041] (2) Time (in the case of a continuous method, average residence time): preferably 2 to 15 hours, more preferably 3 to 11 hours.

[0042] (3) Polymerization rate: preferably 10 to 90%, more preferably 30 to 80%, based on the charged vinyl ester.

[0043] (4) Resin content in the solution after polymerization: preferably 5 to 85% by mass, more preferably 20 to 70% by mass.

[0044] It should be noted that, in addition to ethylene and vinyl ester, a small amount of monomers copolymerizable with these monomers may also coexist, for example, α-olefins such as propylene, butene, isobutylene, pentene, hexene, α-octene, and α-dodecene; 3-acyloxy-1-propylene, 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-acyloxy-1-hexene, 5,6-diacyloxy-1-hexene, 1,3-diacetoxy-2-methylenepropane and other olefins having ester groups; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, their anhydrides, salts, monoalkyl esters or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, methyl allyl sulfonic acid or their salts; alkyl vinyl ethers, vinyl ketones, N-vinyl pyrrolidone, vinyl chloride, vinylidene chloride, etc. and polymerize. The content of other monomer units other than ethylene, vinyl ester and vinyl alcohol in the above-mentioned EVOH is preferably 20 mol% or less, and sometimes preferably 10 mol% or less, 5 mol% or less, 3 mol% or less, 1 mol% or less, 0.1 mol% or less. The above-mentioned EVOH may not contain the above-mentioned other monomer units.

[0045] After the polymerization is carried out for a predetermined time and a predetermined polymerization rate is reached, a polymerization inhibitor is added as needed, and the unreacted ethylene gas is evaporated and removed, and then the unreacted vinyl ester is discharged. As a method for discharging the unreacted vinyl ester, for example, the following method can be adopted: a polymerization solution from which ethylene has been removed is continuously supplied at a constant rate from the upper part of a tower filled with Raschig rings, a vapor of an organic solvent is blown in from the lower part of the tower, vapor of an alcohol having a boiling point of 100° C. or less is preferably blown in, and vapor of methanol is most preferably blown in, a mixed vapor of the organic solvent and the unreacted vinyl ester is distilled out from the top of the tower, and a copolymer solution from which the unreacted vinyl ester has been removed is taken out from the bottom of the tower.

[0046] An alkali catalyst is added to the copolymer solution after the unreacted vinyl ester is removed, and the vinyl ester component in the copolymer is saponified. The saponification method may be either continuous or intermittent. As the alkali catalyst, sodium hydroxide, potassium hydroxide, alkali metal alkoxide, etc. may be used. In addition, methanol is preferably used as the solvent used in the saponification. For example, the saponification conditions are as follows.

[0047] (1) Concentration of ethylene-vinyl ester copolymer in solution: 10 to 50% by mass

[0048] (2) Reaction temperature: 30~150℃

[0049] (3) Catalyst dosage: 0.005 to 0.6 equivalents (relative to the vinyl ester component)

[0050] (4) Time (in the case of continuous mode, average residence time): 10 minutes to 6 hours

[0051] Generally speaking, when saponification is performed by a continuous process, methyl acetate generated by saponification can be removed more effectively, and therefore, a resin with a high degree of saponification can be obtained with a small amount of catalyst compared to the case of a batch process. In addition, in the case of a continuous process, in order to prevent the precipitation of EVOH generated by saponification, it is necessary to perform saponification at a higher temperature. Therefore, it is preferable to set the reaction temperature and catalyst amount in the continuous process to the following ranges.

[0052] Reaction temperature: 70~150℃.

[0053] Catalyst dosage: 0.005 to 0.1 equivalent (relative to the vinyl ester component).

[0054] The saponification degree of the obtained EVOH varies depending on the purpose, but is preferably 80 mol% or more of the vinyl ester component, more preferably 95 mol% or more, further preferably 98 mol% or more, and particularly preferably 99 mol% or more from the viewpoint of further improving the gas barrier properties. The saponification degree can be arbitrarily adjusted according to the conditions.

[0055] As described above, especially in the case of manufacturing EVOH pellets with excellent melt stability and good long-term operating properties, the saponification degree of EVOH is preferably 99.7 mol% or more, more preferably 99.8 mol% or more, further preferably 99.9 mol% or more, and particularly preferably 99.95 mol% or more. In order to obtain such EVOH, it is preferred to further adjust the saponification conditions as follows.

[0056] As a method for obtaining EVOH with a high saponification degree of 99.9 mol% or more, a continuous method is preferred. As a method for obtaining a high saponification degree by a continuous method, for example, a method of adding a catalyst from multiple locations in a saponification reaction tower, a method of increasing the amount of catalyst, a method of increasing the amount of methanol blown in from the lower part of the saponification reaction tower, etc. can be cited. In addition, as a method for obtaining EVOH with a high saponification degree of 99.9 mol% or more by an intermittent method, for example, a method of adding a catalyst in multiple times, a method of increasing the amount of catalyst, a method of increasing the amount of methanol vapor or nitrogen blown into the saponification reaction tank, etc. can be cited.

[0057] A solution or paste containing EVOH can be obtained by the saponification process. EVOH after the saponification reaction contains alkali catalysts, by-product salts such as sodium acetate and potassium acetate, and other impurities, so they can be removed by neutralization and washing as needed. Here, when the EVOH after the saponification reaction is washed with ion exchange water that contains almost no metal ions, chloride ions, etc., a part of the catalyst residues such as sodium acetate and potassium acetate can remain in the EVOH.

[0058] As a post-treatment method for the EVOH solution or paste after the saponification reaction, it is suitable to supply a mixed vapor of solvent and water from the lower part of the container in a tower container, and supply an EVOH solution or paste from a position higher than the supply position of the mixed vapor, thereby replacing a part of the solvent present in the supplied EVOH solution or paste with water to prepare a high-concentration EVOH solution. The EVOH concentration in the EVOH solution supplied to the tower container is preferably 15 to 50% by mass, and more preferably 25 to 40% by mass. In addition, the ratio of the supply amount of the EVOH solution to the supply amount of the mixed vapor (solution supply amount / vapor supply amount) is also suitable to be 100 / 400 to 100 / 8 in terms of mass ratio. Furthermore, the water content in the mixed vapor is preferably 20 to 70% by mass. The solvent used in the mixed vapor is preferably an alcohol having a boiling point of 130°C or less, and as such an alcohol, alcohols such as methanol, ethanol, propanol, and butanol can be exemplified. Alcohols having a boiling point of 100° C. or lower are more preferred, and methanol is preferred from the viewpoints of easy availability, low price, low boiling point, and easy handling.

[0059] The EVOH solution or paste obtained in this way usually contains 50 parts by mass or more of alcohol having a boiling point of 100°C or less relative to 100 parts by mass of EVOH. In addition, the content of alcohol is preferably 1000 parts by mass or less, and more preferably 500 parts by mass or less. By setting the content of alcohol to this range, the fluidity of the EVOH solution is ensured, and the resin can be efficiently manufactured. The alcohol is preferably methanol. It should be noted that the above-mentioned saponified EVOH solution can be not only an alcohol solution, but also a solution of a mixed solvent to which other solvents such as water are added to a degree that EVOH does not precipitate as required.

[0060] The aforementioned manufacturing method as a method for obtaining the hydrous EVOH used in the present invention preferably further comprises, for example, the following steps: introducing an EVOH solution into a container, bringing it into contact with water vapor in the aforementioned container, removing the aforementioned alcohol together with the water vapor, and removing the hydrous EVOH from the aforementioned container, wherein the EVOH solution contains 50 parts by mass or more of an alcohol having a boiling point of 100° C. or less relative to 100 parts by mass of the EVOH obtained by the above operation, and the hydrous EVOH removed from the aforementioned container is introduced into an extruder described later. According to this method, the alcohol in the aforementioned EVOH solution can be efficiently replaced with water, and the water content and temperature of the EVOH can also be easily adjusted.

[0061] The method of contacting the EVOH solution introduced into the container with water vapor in the container is not particularly limited, and any method of continuous or intermittent type can be used. In addition, the form of the container is not particularly limited, and in the case of a continuous method, a tower-type container is suitable, and in the case of an intermittent method, a tank-type container is suitable. If production efficiency is taken into consideration, a continuous method is preferred in industry. Examples of the tower-type container include a perforated plate tower, a disc tower such as a bubble tower, and a packed tower equipped with a ring-type filler.

[0062] It is suitable that: in a tower-type container, water vapor is supplied from the lower part of the container, and EVOH solution or paste is supplied from a position higher than the aforementioned water vapor supply position, thereby extracting the solvent (alcohol) present in the supplied EVOH solution or paste together with the water vapor, and extracting water-containing EVOH with a water content of 10 to 90% by mass from the aforementioned container. If the amount of water vapor introduced is too small, the removal efficiency of the solvent (alcohol) is poor, and conversely, if it is too much, it becomes disadvantageous in terms of cost. Therefore, relative to the amount of EVOH solution or paste introduced, expressed as a mass ratio, it is preferably 0.3 to 30 times, more preferably 0.5 to 10 times, and further preferably 0.7 to 5 times. The water vapor in contact with the EVOH solution or paste may contain 10 parts by mass or less of the solvent (alcohol) relative to 100 parts by mass of the water vapor. In order to efficiently remove the solvent (alcohol), the water vapor preferably does not contain the solvent (alcohol). The water-containing EVOH may contain 0 to 10 parts by mass of the aforementioned solvent (alcohol) relative to 100 parts by mass of EVOH. Furthermore, the hydrous EVOH may contain saponification catalyst residues and the like.

[0063] The alcohol vapor and water vapor extracted from the upper part of the tower are condensed in the condenser and recovered in the form of an alcohol aqueous solution, which can be purified and reused as needed. The EVOH solution or paste is in direct contact with water vapor in the container, and the content of the solvent (alcohol) slowly decreases, but during this period, the EVOH is in a swollen paste state and can be extracted from the container while maintaining fluidity without gelation. EVOH dissolves in a methanol / water mixed solvent at a temperature of about 60 to 70°C at normal pressure, for example, but does not dissolve at normal pressure when the solvent is only water. However, in the presence of pressurized water vapor at a temperature of, for example, above 90°C, even if EVOH is essentially in a state of containing only water, it can maintain fluidity.

[0064] The temperature in the container is preferably 100 to 150°C. When the temperature in the container is lower than 100°C, the fluidity of the aqueous EVOH may become insufficient, and gelation or clogging may occur in the container. It is more preferably 110°C or higher, and further preferably 120°C or higher. On the other hand, when the temperature in the container exceeds 150°C, EVOH may deteriorate. It is more preferably 140°C or lower.

[0065] In addition, if the pressure in the container is too low, the alcohol removal efficiency may become poor. The pressure in the container is preferably 0.1 MPa or more, more preferably 0.15 MPa or more, and even more preferably 0.2 MPa or more. On the other hand, if the pressure in the container is too high, the water content of the hydrous EVOH extracted from the container becomes too high, and thus, the melt viscosity of the hydrous EVOH introduced into the extruder described later may become too low. Therefore, the pressure in the container is preferably 0.6 MPa or less, more preferably 0.5 MPa or less, and even more preferably 0.4 MPa or less.

[0066] As described above, after the EVOH solution is brought into contact with water vapor, the water-containing EVOH is taken out from the container. This water-containing EVOH is preferably used as the water-containing EVOH supplied to the extruder in the first step described below.

[0067] In the first step, water-containing EVOH having a water content W1 of 10 to 90% by mass is introduced into an extruder for melt kneading. The form of the water-containing EVOH introduced into the extruder is not particularly limited, and a paste-like form may be cited. As described above, a paste-like water-containing EVOH can be obtained by directly contacting an EVOH solution with water vapor in a container. The EVOH is extracted from the container while maintaining fluidity without gelation.

[0068] The water content W1 of the water-containing EVOH introduced into the extruder is 10 to 90% by mass. When the water content W1 is less than 10% by mass, the melt viscosity of the water-containing EVOH becomes too high, and the water-containing EVOH cannot be extruded from the front end of the extruder, or the dissolution amount of EVOH increases. In addition, in order to ensure fluidity, the melting temperature of the water-containing EVOH becomes high, the EVOH deteriorates, and the hue of the obtained EVOH deteriorates. The water content W1 is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and particularly preferably 45% by mass or more. On the other hand, if the water content W1 exceeds 90% by mass, the melt viscosity of the water-containing EVOH becomes too low, and the dissolution amount of EVOH increases. The water content W1 is preferably 80% by mass or less, more preferably 70% by mass or less, further preferably 60% by mass or less, and particularly preferably 55% by mass or less. The water content W1 of the water-containing EVOH introduced into the extruder is measured by the method described in the examples described later. The water content W1 can be adjusted by, for example, the conditions when the EVOH solution or paste is post-treated, the conditions when the water-containing EVOH is obtained from the EVOH solution or paste, and the like.

[0069] The temperature of the aqueous EVOH supplied to the aforementioned extruder is preferably 80 to 130°C. If the temperature is within the above range, the melt viscosity of the aqueous EVOH tends to be within an appropriate range, the aqueous EVOH tends to be able to be stably extruded from the front end of the extruder, and the EVOH dissolution tends to be suppressed. The aforementioned temperature is more preferably above 90°C, and further preferably above 95°C. In addition, the aforementioned temperature is more preferably below 125°C, and further preferably below 115°C. The temperature of the aqueous EVOH can be adjusted by, for example, the conditions when the aqueous EVOH is obtained from an EVOH solution or paste.

[0070] From the viewpoint of protecting the working environment and the surrounding environment and from the viewpoint of preventing the obtained EVOH hydrous pellets from sticking to each other, the content of alcohol with a boiling point below 100°C in the hydrous EVOH introduced into the extruder is preferably 10 mass % or less, more preferably 5 mass % or less, further preferably 1 mass % or less, and particularly preferably 0.5 mass % or less.

[0071] The hydrous EVOH introduced into the extruder may contain, for example, alkali metal salts such as the residue of the catalyst used in the saponification process in an amount of about 0.1 to 5% by mass in terms of metal, and may contain by-product salts, other impurities, etc. The content of components other than EVOH, water, and alcohol having a boiling point of 100° C. or less in the hydrous EVOH supplied to the extruder is preferably 10% by mass or less, more preferably 5% by mass or less, further preferably 3% by mass or less, and particularly preferably 1% by mass or less.

[0072] Figure 1This shows the barrel structure of the extruder used in Example 1 described later. Figure 1 The upper side) and the screw rod ( Figure 1 Use Figure 1 , the first step will be further described.

[0073] The extruder used in the first step can be a single-screw extruder or a multi-screw extruder, preferably a twin-screw extruder. In addition, the L / D of the extruder is preferably 8 to 30, more preferably 9 to 25, and further preferably 10 to 20. As the barrel 1, a block cylinder or the like is used. The barrel 1 of the extruder is provided with an inlet 2 for water-containing EVOH. After the water-containing EVOH is introduced into the inlet 2, the screw arranged in the barrel 1 rotates, thereby gradually flowing toward the front end side (downstream side 3) of the barrel 1 along the axis of the barrel 1. At this time, the liquid discharge port (rear slit 4) provided in the barrel 1 is depressurized by the decompression device 5, and the water in the water-containing EVOH is discharged from the liquid discharge port, thereby reducing the water content of the water-containing EVOH. As such, the extruder used in the first step has a rear slit 4, and the water in the water-containing EVOH is discharged from the rear slit 4 while the rear slit 4 is depressurized by the decompression device 5, which is a significant feature of the present invention. The rear slit 4 is a drainage slit (liquid outlet) provided on the upstream side 8 of the flow path 6 of the water-containing EVOH, compared with the introduction port 2 of the water-containing EVOH. Conventionally, the drainage slit (liquid outlet 10) of the extruder is provided below the introduction port 2 ( Figure 5), the liquid outlet 10 is located at a position downstream 3 of the flow path 6 of the water-containing EVOH more than the inlet 2. If it is operated continuously, EVOH dissolution marks will appear in the liquid outlet 10. If it is left for a long time, there is a possibility that the liquid outlet 10 will be blocked and affect the production. Therefore, it needs to be cleaned regularly. As a result of repeated and in-depth research by the inventors to suppress the occurrence of EVOH dissolution marks and produce EVOH water-containing pellets, by setting the above-mentioned back seam 4 in the barrel 1 and draining water from there, it was surprisingly found that the dissolution of EVOH in the discharged water is suppressed. In addition, EVOH is hydrophilic. Therefore, when using water-containing EVOH with a low ethylene unit content (for example, an ethylene unit content of 20 mol% to 40 mol%), the water in the water-containing EVOH cannot be fully reduced. When cutting the water-containing EVOH containing a large amount of water extruded from the extruder, poor cutting sometimes occurs. Poor cutting means that the hydrated EVOH containing a large amount of water has a low melt viscosity, so the hydrated EVOH cannot be cut, and EVOH hydrated pellets with a shape of connected pellets and a length of several centimeters are produced. If continuous operation is performed in a state where the amount of the poorly cut hydrated EVOH pellets generated is large, the transfer pump and piping will be blocked during the transfer of the hydrated EVOH pellets, which may affect the production. Therefore, it is necessary to reduce the production speed. The inventors have repeatedly conducted in-depth research to suppress the occurrence of EVOH dissolution marks and poor cutting and produce EVOH hydrated pellets with good shapes. As a result, it was found that by installing a decompression device 5 in the aforementioned back seam 4 and performing decompression, it is possible to suppress the dissolution of EVOH into the discharged water and produce EVOH hydrated pellets with good shapes.

[0074] It is preferred that: when the extruder is viewed from above from a direction perpendicular to the axis of the barrel 1, the rear slit 4 is provided at a position closer to the upstream side 8 of the flow path 6 of the water-containing EVOH than the introduction port 2 of the water-containing EVOH, and the introduction port 2 and the rear slit 4 do not overlap, that is, the most downstream side 3 of the rear slit 4 is arranged upstream compared to the most upstream side 8 of the introduction port 2. The extruder also preferably does not have a liquid discharge port 10 at a position closer to the downstream than the introduction port 2 of the water-containing EVOH, and more preferably does not have a liquid discharge port 10 other than the rear slit 4. In the case where the extruder does not have a liquid discharge port 10 other than the rear slit 4, there is a tendency that the dissolution of EVOH can be further suppressed. The type of the rear slit 4 used in the present invention is not particularly limited, and a general dewatering slit can be used, specifically, a wedge-type dewatering slit, a mesh-type dewatering slit, etc. can be used.

[0075] A decompression device 5 is provided for decompressing the rear seam 4 of the extruder. By decompressing the rear seam 4 using the decompression device 5, the dissolution of EVOH can be suppressed and the water content of the hydrous EVOH can be effectively reduced, showing a tendency to reduce poor cutting when cutting the hydrous EVOH with a low ethylene unit content (for example, an ethylene unit content of 20 mol% to 40 mol%). The decompression degree of the rear seam 4 is preferably -0.07MPa to -0.005MPa. Here, the decompression degree refers to the gauge pressure of the difference from the atmospheric pressure, and the atmospheric pressure is set to zero, and the degree of decompression relative to the atmospheric pressure is expressed in the form of a negative value. Therefore, "a large decompression degree" means that the absolute value of the negative value is large. In the case of too small a decompression degree, the amount of water in the hydrous EVOH is reduced less, and poor cutting is likely to occur. Therefore, the decompression degree of the rear seam 4 is preferably below -0.005MPa, and can be below -0.015MPa. On the other hand, in the case of too large a decompression degree, the amount of EVOH dissolved increases. Therefore, the decompression degree of the rear seam 4 is preferably -0.07MPa or more, more preferably -0.055MPa or more, further preferably -0.04MPa or more, and can be -0.025MPa or more. The type of decompression device used in the present invention is not particularly limited, and examples thereof include vacuum pumps, aspirators, and exhausters.

[0076] The barrel temperature of the extruder is preferably 70 to 110°C. By setting the barrel temperature in this range, the dissolution of EVOH is further suppressed and EVOH hydrous pellets with good shape are obtained. The temperature is preferably 105°C or less, more preferably 100°C or less, and further preferably 95°C or less. Here, the barrel temperature refers to the maximum temperature of the portion downstream of the hydrous EVOH inlet 2.

[0077] As the screw of the aforementioned extruder, a segment type screw or the like can be used. The screw rotation speed is preferably 10 to 2000 rpm. By setting the screw rotation speed to this range, the dissolution of EVOH is further suppressed and EVOH water-containing pellets with good shape are obtained. The screw rotation speed is more preferably 50 rpm or more, more preferably 120 rpm or more, more preferably 150 rpm or more, and particularly preferably 200 rpm or more. On the other hand, the screw rotation speed is more preferably 1500 rpm or less, more preferably 1000 rpm or less, more preferably 800 rpm or less, and particularly preferably 500 rpm or less. It should be noted that when the rear seam 4 is further decompressed by the decompression device 5, by increasing the screw rotation speed and increasing the production speed, there is a tendency to suppress the dissolution of EVOH. On the contrary, when the rear seam 4 is not much decompressed, by reducing the screw rotation speed and reducing the production speed, there is a tendency to improve the cutting performance.

[0078] The water content W2 of the water-containing EVOH extruded from the aforementioned extruder must be 5 to 50% by mass. When the water content W2 is less than 5% by mass, the melt viscosity of the water-containing EVOH becomes too high, and the water-containing EVOH cannot be extruded from the front end of the extruder, or the dissolved EVOH increases. The water content W2 is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 30% by mass or more. On the other hand, if the water content W2 exceeds 50% by mass, the melt viscosity of the water-containing EVOH becomes too low, the dissolved EVOH increases, and poor cutting occurs. The water content W2 is preferably 45% by mass or less, more preferably 40% by mass or less.

[0079] In the present invention, the ratio (W2 / W1) of the water content W2 of the water-containing EVOH extruded from the aforementioned extruder to the water content W1 of the water-containing EVOH introduced into the aforementioned extruder must be 0.2 or more and less than 1. By making the ratio (W2 / W1) in this range, the dissolution of EVOH is further suppressed, and EVOH water-containing pellets with good shape can be obtained. The ratio (W2 / W1) is preferably 0.3 or more, more preferably 0.4 or more, more preferably 0.5 or more, more preferably 0.55 or more, and particularly preferably 0.6 or more. On the other hand, the ratio (W2 / W1) is preferably 0.9 or less, more preferably 0.85 or less, more preferably 0.8 or less, more preferably 0.75 or less, and particularly preferably 0.7 or less. The water content W2 can be adjusted by, for example, the water content W1, the barrel temperature and the screw speed. In addition, as described above, by setting a rear slit, the water can be further discharged while decompressing using a decompression device, so that the water content W2 can be adjusted.

[0080] The temperature of the hydrous EVOH extruded from the aforementioned extruder must be 80-120°C. When the aforementioned temperature is lower than 80°C, the melt viscosity of the hydrous EVOH becomes too high, and the hydrous EVOH cannot be extruded from the front end of the extruder, or the dissolved EVOH increases. The aforementioned temperature is preferably above 85°C. On the other hand, when the aforementioned temperature exceeds 120°C, the melt viscosity of the hydrous EVOH becomes too low, the dissolved EVOH increases, and poor cutting occurs. The aforementioned temperature is preferably below 115°C, more preferably below 110°C, further preferably below 100°C, and particularly preferably below 93°C. The temperature and water content W2 of the hydrous EVOH extruded from the aforementioned extruder are measured by the method described in the examples.

[0081] From the viewpoint of further suppressing the dissolution of EVOH and obtaining EVOH hydrous pellets with good shape, the temperature of the hydrous EVOH introduced into the aforementioned extruder is preferably higher than the temperature of the hydrous EVOH extruded from the aforementioned extruder. The temperature of the hydrous EVOH introduced into the aforementioned extruder is more preferably higher than the temperature of the hydrous EVOH extruded from the aforementioned extruder by more than 1°C, further preferably higher by more than 5°C, and particularly preferably higher by more than 10°C.

[0082] In the second step, EVOH aqueous pellets are obtained by cutting the aqueous EVOH extruded from the aforementioned extruder. The method is not particularly limited, and examples thereof include: a method of directly cutting the aqueous EVOH (molten state) extruded from the aforementioned extruder; a method of extruding the aqueous EVOH extruded from the aforementioned extruder in the form of strands into a coagulation liquid to coagulate it, and then cutting it. Among them, a method of directly cutting the aqueous EVOH is preferred. As a method for directly cutting the aqueous EVOH extruded from the aforementioned extruder, a heating cutting method or an underwater cutting method can be used. As a suitable method, the method for cutting the aqueous EVOH composition obtained by step 1 described in Patent Document 1 is used. From the viewpoint of the ease of handling of the aqueous EVOH pellets, the nozzle diameter is suitably ( is the diameter. The same applies below). Regarding the size of the manufactured EVOH hydrous pellets, for example, in the case of spherical (or roughly spherical) shape, the diameter can be set to be greater than 1 mm and less than 10 mm, in the case of cylindrical shape, the diameter can be set to be greater than 1 mm and less than 10 mm, and the length can be set to be greater than 1 mm and less than 10 mm. It should be noted that in the case of extruding in the form of strands and then cutting after solidification, cylindrical pellets can be obtained, and in the case of direct cutting in a molten state, spherical (or roughly spherical) pellets can be obtained. In this way, compared with the method of extruding into a coagulation liquid, extruding in the form of strands and then solidifying and then cutting, the method of cutting the hydrous EVOH in a molten state does not need to consider the traction speed that can stably form the strands, and therefore has excellent productivity. For example, even in the case where it is not easy to form strands, such as EVOH with a low ethylene content, it is easy to manufacture EVOH hydrous pellets by cutting in a molten state.

[0083] As the method of extruding in the form of strands and then cutting after solidification, there can be cited a method of extruding the aforementioned aqueous EVOH in the form of strands into a coagulation liquid. Water is used as the aforementioned coagulation liquid, but a small amount of alcohol may be contained. The temperature of the coagulation liquid is preferably 0 to 50°C, and the temperature of the aqueous EVOH during extrusion is 80 to 120°C. By utilizing this temperature difference, the aqueous EVOH can be solidified in a short time. The temperature of the coagulation liquid is preferably 0 to 30°C. The solidified strands are cut by a cutter to form pellets. As the cutter, a strand cutter is preferably used.

[0084] Using a nozzle of any shape, the aqueous EVOH is extruded into the above-mentioned coagulation liquid in the form of strands. The shape of the nozzle is not particularly limited, but is preferably a cylindrical shape. In this way, the aqueous EVOH is extruded from the nozzle in the form of strands. At this time, the strand does not necessarily need to be one strand, and can be extruded in any number ranging from a few to hundreds. Then, after the EVOH extruded in the form of strands is fully coagulated, it is cut to obtain EVOH aqueous pellets. Thereafter, it can be cleaned as described below as needed. Regarding the size of the pellets, for example, in the case of a cylindrical shape, the diameter can be set to be greater than 1 mm and less than 10 mm, and the length can be set to be greater than 1 mm and less than 10 mm. In the case of a spherical shape, the diameter can be set to be greater than 1 mm and less than 10 mm.

[0085] Before drying the EVOH aqueous pellets obtained in this way, washing and additives are added as needed. As a washing method and an additive adding method, the method described in Patent Document 1 for the pellets of the EVOH aqueous composition obtained in step 1 can be adopted. In addition, before drying and after melt-kneading the aforementioned EVOH aqueous pellets again using an extruder, they can be cut to achieve pelletization. As the melt-kneading method, cutting method, and drying method of the obtained pellets at this time, the melt-kneading method of step 2 described in Patent Document 1, the pelletizing method of the EVOH resin obtained in step 2, the drying method of the obtained pellets, etc. can be adopted.

[0086] The melt flow rate (MFR) (210°C, load 2160g) of the EVOH resin composition pellets obtained using the above-mentioned EVOH water-containing pellets is preferably 0.1 to 200g / 10 minutes, more preferably 0.5 to 50g / 10 minutes, and further preferably 1 to 30g / 10 minutes. If the MFR is 0.1g / 10 minutes or more, the moldability tends to be good, and if the MFR is 200g / 10 minutes or less, the mechanical properties of the resulting molded product tend to be good. The above-mentioned MFR can be measured by the method described in the examples described later.

[0087] The EVOH thus obtained can be used for various purposes in addition to being formed into various molded products such as films, sheets, containers, tubes, fibers, etc. by melt molding. The production method of the present invention can improve the productivity of such EVOH.

[0088] Example

[0089] Hereinafter, the present invention will be described in more detail using examples.

[0090] [Evaluation method]

[0091] (1) Determination of moisture content

[0092] Using 3 g of the hydrous EVOH and hydrous EVOH pellets obtained in the Examples and Comparative Examples, the moisture content of the hydrous EVOH and hydrous EVOH pellets was measured using a halogen moisture analyzer "HR73" manufactured by METTLER at a drying temperature of 180°C and a drying time of 15 minutes.

[0093] (2) Evaluation of cutting properties

[0094] Using 100 g of the EVOH hydrous pellets obtained in the examples and comparative examples, measure the mass of the EVOH hydrous pellets with a length exceeding 2 cm, and calculate the ratio as the cutting unevenness. Evaluate according to the following evaluation criteria. Runnability refers to the transferability after cutting. If the evaluation is A to C, it is judged that there is no problem with the cutting performance.

[0095] A: Cutting unevenness is less than 5%, and the running performance is good

[0096] B: Cutting unevenness is more than 5% and less than 30%, and can be operated

[0097] C: Cutting unevenness is more than 30% and less than 50%, and can be operated

[0098] D: Cutting unevenness is more than 50%, and the operation is unstable

[0099] (3) Evaluation of EVOH dissolution

[0100] EVOH water-containing pellets were continuously produced by the method described in the examples and comparative examples. The liquid discharge port of the twin-screw extruder was visually checked to see whether white EVOH dissolution marks were produced. The evaluation was performed according to the following evaluation criteria. It can be considered that the EVOH dissolution marks were produced at the liquid discharge port due to the EVOH dissolving into the discharged water. If the evaluation is A to C, it is judged that the dissolution of EVOH can be suppressed.

[0101] A: Even if it is operated continuously for more than 10 days, no trace of EVOH dissolution is observed at the liquid discharge outlet.

[0102] B: During continuous operation for more than 7 days and less than 10 days, traces of EVOH dissolution were observed at the liquid discharge port

[0103] C: During continuous operation for more than 5 days and less than 7 days, traces of EVOH dissolution were observed at the liquid discharge port

[0104] D: During continuous operation for less than 5 days, traces of EVOH dissolution were observed at the liquid discharge port

[0105] (4) Melt flow rate (MFR)

[0106] The EVOH hydrous pellets obtained by the examples and comparative examples were put into ion exchange water (bath ratio of 20), stirred and washed for 2 hours, and deliquored, and the above operation was repeated 3 times. For the pellets after deliquoring, a centrifugal separator was used to remove surface water. Centrifugal dehydration was performed, and the hydrous pellets with a moisture content of 33% by mass were put into the twin-screw extruder shown below, and the resin temperature of the extrusion port was set to 100°C. While adding a treatment liquid containing acetic acid / sodium acetate / phosphoric acid aqueous solution from the trace component addition part of the front end of the extrusion port side, melt kneading was performed under the following conditions. The input amount of EVOH per unit time was 10kg / hr (including the mass of the contained water), and the input amount of the treatment liquid per unit time was 0.67L / hr, which was an aqueous solution containing 6.7g / L of acetic acid, 11.3g / L of sodium acetate, and 1g / L of phosphoric acid in the composition of the treatment liquid.

[0107] (Twin screw extruder conditions)

[0108] ·Device: 30mmΦ twin-screw extruder

[0109] L / D: 45.5

[0110] Screw: Fully meshing in the same direction

[0111] Screw speed: 300rpm

[0112] Cylinder temperature: 100℃

[0113] Mold temperature: 105℃

[0114] Number of mold holes: 5 holes (3mmΦ)

[0115] Thereafter, the molten EVOH resin extruded from the twin-screw extruder was cut by a heat cutter to obtain approximately spherical pellets. The moisture content of the approximately spherical pellets was 20% by mass. The pellets were dried at 90° C. for 15 hours and at 105° C. for 15 hours under a nitrogen stream to obtain approximately spherical EVOH pellets (moisture content of 0.3% by mass) with a short diameter of 2.7 mm and a long diameter of 3.7 mm.

[0116] The MFR of the EVOH pellets obtained above was measured according to the method described in JIS K7210:2014. Specifically, the EVOH pellets were filled into a cylinder with an inner diameter of 9.55 mm and a length of 162 mm of a melt indexer L244 (manufactured by Takara Industries) and melted at 210°C. Then, a plunger with a mass of 2,160 g and a diameter of 9.48 mm was used to uniformly apply a load to the melted resin composition. The amount of the resin composition extruded per unit time from an orifice with a diameter of 2.1 mm set in the center of the cylinder was measured (g / 10 minutes).

[0117] (5) Determination of alcohol content

[0118] 5 g of the hydrous EVOH used in the examples and comparative examples was freeze-pulverized in liquid nitrogen, and immediately after pulverization, a sample (about 500 mg) was taken into a HSS vial and analyzed for methanol under the following conditions: For each sample, two measurements were performed, and the alcohol content was calculated from the average.

[0119] Headspace (HSS)-GC / MS

[0120] Oven temperature: 120°C (MHE method: [120°C × 30 minutes] × 5 times)

[0121] Quantitative loop temperature: 200°C

[0122] Transfer temperature: 200°C, with oscillation

[0123] GC / MS

[0124] Column: DB-WAXetr (30m-0.25mm-0.5μm)

[0125] Oven: 50°C (hold for 5 minutes) → 10°C / minute → 200°C (hold for 10 minutes)

[0126] Inlet: 230℃ (split ratio 20:1)

[0127] Measurement mode: SIM (m / z=31)

[0128] (Example 1)

[0129] An EVOH solution containing 100 parts by mass of EVOH having an ethylene unit content of 27 mol% and a saponification degree of 99.98 mol%, 55 parts by mass of methanol and 45 parts by mass of water was continuously supplied from the top section of a disk tower having a tower diameter of 0.3 m and 10 stages, and water vapor was blown in from the bottom section to make the EVOH solution contact with the water vapor in a countercurrent manner. The temperature in the tower was 130°C and the pressure in the tower was 0.3 MPa. The water-containing EVOH obtained by contacting the water vapor in a countercurrent manner was taken out from the bottom of the tower. The temperature of the obtained water-containing EVOH was 120°C, and the water content (W1) measured according to the above evaluation method was 54.5% by mass. In addition, the alcohol content was 0.05% by mass. The results are shown in Table 1.

[0130] The obtained water-containing EVOH having a moisture content (W1) of 54.5% by mass was supplied to a 110° C. resin at a rate of 42 kg / hr. Figure 1 The twin-screw extruder shown has a liquid discharge port (rear seam 4) arranged more upstream 8 than the inlet 2 for water-containing EVOH. In order to reduce the pressure of the rear seam 4, a vacuum pump as a pressure reducing device 5 is connected to the rear seam 4 via a pipe, and the pressure is reduced to -0.02 MPa. Under the following conditions, the melt is extruded from a die with an aperture of 30 mm and 8 holes installed at the front end of the extruder, and the melt is cut at a position 0.05 mm away from the die using a heat cutter ( Figure 6 ) was cut to obtain flat spherical EVOH hydrous pellets. The resin temperature at this time was 95°C, and the moisture content (W2) measured according to the above evaluation method was 36% by mass. The resin temperature was measured using a temperature sensor that was arranged near the extrusion outlet at the front end of the barrel and in contact with the melt. EVOH hydrous pellets were continuously manufactured under the above conditions, and the dissolution of EVOH in water discharged from the twin-screw extruder was evaluated according to the above evaluation method. In addition, for a part of the obtained EVOH hydrous pellets, the cuttability and MFR were determined according to the above evaluation method. Their results are shown in Table 1. The flow rate of the circulating water of the cutter was 300 liters / min, and the rotation speed of the cutting blade was 3000 rpm. Furthermore, the obtained EVOH hydrous pellets were put into ion exchange water (bath ratio of 20), stirred and washed for 2 hours, and deliquored, and the above operation was repeated 3 times. The deliquored pellets were centrifuged to remove surface water and then dried at 95° C. for 3 hours in a nitrogen gas stream having an oxygen concentration of 1% by volume or less to obtain dry resin composition pellets having a moisture content of 0.5% by mass.

[0131] <Conditions of Twin Screw Extruder>

[0132] L / D: 14

[0133] Diameter: 30mm

[0134] Screw: Full thread

[0135] Speed: 200rpm

[0136] Cylinder temperature: 90°C (maximum temperature at the downstream side of the aqueous EVOH inlet 2)

[0137] Mold temperature: 120℃

[0138] Number of holes: 8

[0139] (Examples 2 to 12, Comparative Examples 1 to 3)

[0140] The conditions were adjusted so that the ethylene unit content, the temperature and water content W1 of the resin supplied to the extruder, the degree of decompression of the decompression device, the configuration of the liquid discharge port and the configuration of the decompression device, the screw rotation speed, and the temperature and water content W2 of the resin extruded from the extruder were as described in Table 1. The same method as in Example 1 was used to produce and evaluate the water-containing EVOH pellets. The results are shown in Table 1. It should be noted that Figure 2 The barrel structure of the twin-screw extruder in Example 12 is shown. The twin-screw extruder in Example 12 has a liquid discharge outlet (rear seam 4) arranged on the upstream side 8 than the inlet 2 for water-containing EVOH and a liquid discharge outlet 10 arranged on the lower side of the inlet 2 for water-containing EVOH, and the pressure reducing device 5 is arranged in a manner to reduce the pressure on the rear seam 4. Figure 3 The barrel structure of the twin-screw extruder in Comparative Example 1 is shown. The twin-screw extruder in Comparative Example 1 has a liquid discharge port (rear slit 4) disposed on the upstream side 8 of the introduction port 2 for aqueous EVOH. Figure 4 The barrel structure of the twin-screw extruder in Comparative Example 2 is shown. The twin-screw extruder in Comparative Example 2 has a liquid discharge port 10 arranged below the introduction port 2 for water-containing EVOH, and the decompression device 5 is arranged in a manner to decompress the liquid discharge port 10 below the introduction port 2 for water-containing EVOH. Figure 5 The barrel structure of the twin-screw extruder in Comparative Example 3 is shown. The twin-screw extruder in Comparative Example 3 has a liquid discharge port 10 disposed below an introduction port 2 for water-containing EVOH.

[0141]

[0142] According to the comparison between Examples 1 to 9 and Comparative Examples 1 to 2, it can be seen that when the back seam of the extruder is depressurized by a vacuum pump, the dissolution of EVOH in the water discharged from the extruder is suppressed, the cuttability of the hydrous EVOH is good, and hydrous EVOH pellets with good shapes can be obtained. In more detail, according to the comparison between Examples 1 to 3, 9 and 11, it can be considered that when the degree of decompression based on the decompression device is large to a certain extent, the cuttability and the suppression of EVOH dissolution are excellent, when the degree of decompression is small, the cuttability is affected, and when the degree of decompression is large, the dissolution of EVOH is affected. According to the comparison between Examples 1 to 3, 9 and 11, it can be considered that when the ratio (W2 / W1) is within the specified range, the cuttability and the suppression of EVOH dissolution are excellent, when the ratio (W2 / W1) is small, the dissolution of EVOH is affected, and when the ratio (W2 / W1) is large, the cuttability is affected. In addition, according to the comparison between Example 2 and Example 5, it can be considered that when the degree of decompression is low, if the production speed is reduced, the cuttability will be improved. On the other hand, from the comparison between Example 3 and Example 6, it can be considered that when the degree of decompression is high, if the production speed is increased, the dissolution of EVOH can be suppressed. From the comparison between Examples 1, 7 and 8, it can be considered that even if the ethylene unit content changes, the cuttability and the effect of suppressing the dissolution of EVOH are shown. From the comparison between Examples 1, 2 and 10, it can be considered that when the water content W2 is within the specified range, the cuttability and the suppression of the dissolution of EVOH are excellent, and when the water content W2 is large, there is an influence on the cuttability. From the comparison between Example 1 and Example 12, it can be considered that when a liquid discharge port is also arranged on the lower side of the water-containing EVOH inlet in addition to the back seam, the dissolution of EVOH is affected. From the comparison between Example 1 and Comparative Example 1, it can be considered that when the back seam is not decompressed, there is a tendency that the cuttability is deteriorated and the effect of suppressing the dissolution of EVOH is also reduced. From the comparison between Example 1 and Comparative Example 2, it can be considered that when the liquid discharge port arranged on the lower side of the water-containing EVOH inlet, which is not the back seam, is decompressed, the dissolution of EVOH cannot be suppressed, and the cuttability is also reduced. From the comparison between Comparative Examples 1 and 3, it is considered that the use of an extruder having a rear slit can suppress the elution of EVOH compared with the case of using an extruder having a liquid discharge port other than the rear slit.

[0143] Description of Reference Numerals

[0144] 1 Barrel

[0145] 2. Import port

[0146] 3 Downstream side

[0147] 4 Back seam

[0148] 5 Pressure relief device

[0149] 6 Flow path of aqueous EVOH

[0150] 7 Temperature Sensor

[0151] 8 Upstream side

[0152] 9 Full-thread screw

[0153] 10 Liquid outlet

[0154] 30 Thermal cutting machine

[0155] 31 Melt supply port

[0156] 32 Mould

[0157] 33 Spinning Blade

[0158] 34 Rotation axis

[0159] 35 Cutting the chassis

[0160] 36 Cooling water supply port

[0161] 37 Cooling water

[0162] 38 Water film

[0163] 39 Pellet discharge port

[0164] 40 Cooling water and pellets

Claims

1. A method for producing aqueous pellets of ethylene-vinyl alcohol copolymer, comprising: A first step is to introduce a water-containing ethylene-vinyl alcohol copolymer having a water content W1 of 10 to 90% by mass into an extruder and perform melt kneading; and The second step is to obtain aqueous pellets of the ethylene-vinyl alcohol copolymer by cutting the aqueous ethylene-vinyl alcohol copolymer extruded from the extruder. The extruder has a rear slit, and water is discharged from the rear slit while the rear slit is decompressed by a decompression device. The temperature of the water-containing ethylene-vinyl alcohol copolymer extruded from the extruder is 80 to 120° C., the water content W2 is 5 to 50% by mass, and The ratio of the water content W2 to the water content W1 (W2 / W1) is 0.2 or more and less than 1.

2. The manufacturing method according to claim 1, wherein: The degree of reduced pressure by the above-mentioned pressure reducing device is -0.07 MPa to -0.005 MPa.

3. The manufacturing method according to claim 1 or 2, wherein: The temperature of the aqueous ethylene-vinyl alcohol copolymer introduced into the extruder is 80 to 130°C.

4. The production method according to any one of claims 1 to 3, wherein The extruder does not have a liquid discharge port at a location downstream of an inlet for the aqueous ethylene-vinyl alcohol copolymer.

5. The production method according to any one of claims 1 to 4, wherein The screw rotation speed of the extruder is 10 to 2000 rpm.

6. The production method according to any one of claims 1 to 5, further comprising the following step: The ethylene-vinyl alcohol copolymer solution is introduced into a container, brought into contact with water vapor in the container, the alcohol is discharged together with the water vapor, and the water-containing ethylene-vinyl alcohol copolymer is discharged from the container, wherein the ethylene-vinyl alcohol copolymer solution contains 50 parts by mass or more of an alcohol having a boiling point of 100° C. or less relative to 100 parts by mass of the ethylene-vinyl alcohol copolymer, The aqueous ethylene-vinyl alcohol copolymer discharged from the container is introduced into the extruder.

7. The production method according to any one of claims 1 to 6, wherein The ethylene unit content of the ethylene-vinyl alcohol copolymer is 20 to 40 mol%.

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