Method for producing ethylene-vinyl alcohol copolymer resin pellets

Abstract

In order to provide a method for producing ethylene-vinyl alcohol resin pellets having excellent thermal stability, this method for producing ethylene-vinyl alcohol resin pellets comprises a granulation step in which ethylene-vinyl alcohol copolymer resin intermediate pellets are produced, and a drying step in which the ethylene-vinyl alcohol copolymer resin intermediate pellets are dried. The volatile content of the intermediate particles from the granulation step to the drying step is 10-90 mass%, and the lower alcohol content of the ethylene-vinyl alcohol resin intermediate particles fed to the drying step is 0.005-15 mass%.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for producing ethylene-vinyl alcohol copolymer resin particles, and more particularly to a method for producing ethylene-vinyl alcohol copolymer resin particles having excellent heat stability. BACKGROUND

[0002] Conventionally, in ethylene-vinyl alcohol copolymer (hereinafter, sometimes referred to as "EVOH") resin particles, when a solvent such as a lower alcohol used at the time of production thereof remains, the solvent becomes a cause of producing an undesirable condition at the time of processing into a film or the like, and thus it is generally required to reduce these solvents as much as possible. In addition, from the economic and safety aspects, it is required to recover these solvents as much as possible.

[0003] In particular, when these solvents are discharged to the atmosphere in the drying step, the solvents become a problem from the aspect of environmental protection, and thus it is required to reduce them as much as possible before the drying step (for example, refer to Patent Documents 1 and 2).

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 9-316258

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2002-060413 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] However, it was found that EVOH resin particles obtained by drying EVOH resin intermediate particles in which the content of a lower alcohol is reduced as much as possible before drying have room for improvement in heat stability.

[0010] Therefore, in the present application, in such a background, a method for producing EVOH resin particles having excellent heat stability is provided.

[0011] SOLUTION TO THE PROBLEM

[0012] However, the present inventors and others have conducted intensive research in view of this situation, and as a result, it was found that when the content of a lower alcohol of EVOH resin intermediate particles sent to a drying step is set to a range of 0.005 to 15 mass%, the heat stability of EVOH resin particles obtained after drying is improved.

[0013] That is, the present application has the following solution.

[0014] [1] A method for producing ethylene-vinyl alcohol copolymer resin particles, having a pelletizing step and a drying step, wherein ethylene-vinyl alcohol copolymer resin intermediate particles are produced in the pelletizing step, the volatile component of the intermediate particles between the pelletizing step and the drying step is 5 to 90 mass%, and the lower alcohol content of the ethylene-vinyl alcohol copolymer resin intermediate particles fed to the drying step is 0.005 to 15 mass%.

[0015] [2] A method for producing ethylene-vinyl alcohol copolymer resin particles, having a pelletizing step and a drying step, wherein ethylene-vinyl alcohol copolymer resin intermediate particles are produced in the pelletizing step, and a plurality of the drying step is provided, and the lower alcohol content of the ethylene-vinyl alcohol copolymer resin intermediate particles fed to the first drying step of the plurality of drying steps is 0.005 to 15 mass%.

[0016] [3] The method for producing ethylene-vinyl alcohol copolymer resin particles according to [1] or [2], wherein the lower alcohol content of the ethylene-vinyl alcohol copolymer resin intermediate particles fed to the drying step is 0.03 to 9 mass%.

[0017] [4] The method for producing ethylene-vinyl alcohol copolymer resin particles according to any one of [1] to [3], wherein the volatile component of the ethylene-vinyl alcohol copolymer resin intermediate particles is 10 to 90 mass%.

[0018] [5] The method for producing ethylene-vinyl alcohol copolymer resin particles according to any one of [1] to [4], wherein the drying step is performed in a closed space.

[0019] [6] The method for producing ethylene-vinyl alcohol copolymer resin particles according to [2], wherein the first drying step of the plurality of drying steps is performed in a closed space.

[0020] [7] The method for producing ethylene-vinyl alcohol copolymer resin particles according to [2] or [6], wherein the first drying step of the plurality of drying steps is performed using an explosion-proof device.

[0021] Effects of the Invention

[0022] In the present invention, the lower alcohol content of the EVOH resin intermediate particles fed to the drying step is set to 0.0005 to 15 mass%, and thus the heat stability of the resulting EVOH resin particles is excellent. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a flowchart illustrating one embodiment of the present invention. DETAILED DESCRIPTION

[0024] Hereinafter, the present application will be described based on examples of modes for carrying out the present application. However, the present application is not limited to the modes for carrying out the present application described below.

[0025] Note that, in the present application, in the case where the expression "X to Y" (X, Y are arbitrary numbers) is used, unless otherwise specified, the meaning of "X or more and Y or less" and the meaning of "preferably more than X" or "preferably less than Y" are also included.

[0026] In the case where the expression "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number) is used, the meaning of "preferably more than X" or "preferably less than Y" is also included.

[0027] <EVOH resin>

[0028] The granules manufactured by the present application are formed of an EVOH resin.

[0029] The EVOH resin is a resin obtained by saponifying an ethylene-vinyl ester copolymer which is a copolymer of ethylene and a vinyl ester monomer, and is generally a non-water-soluble thermoplastic resin.

[0030] As the vinyl ester monomer, from the viewpoint of market availability and efficiency of impurity treatment at the time of manufacture, vinyl acetate is typically used. As other vinyl ester monomers other than vinyl acetate, for example, aliphatic vinyl esters such as vinyl formate, vinyl propionate, vinyl pentanoate, vinyl butyrate, vinyl isobutyrate, vinyl neopentanoate, vinyl decanoate, vinyl laurate, vinyl stearate, vinyl versatate, and aromatic vinyl esters such as vinyl benzoate, and the like are exemplified, and an aliphatic vinyl ester having 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms is generally used. They are generally used alone, but a plurality of them can be used simultaneously as needed.

[0031] As the polymerization method for copolymerizing the ethylene and the vinyl ester monomer, any of the known polymerization methods such as solution polymerization, suspension polymerization, emulsion polymerization, and the like can be used, and generally, solution polymerization using a lower alcohol, preferably methanol, as a solvent is used. Furthermore, saponification of the obtained ethylene-vinyl ester copolymer can also be performed by a known method.

[0032] The EVOH resin thus manufactured is mainly composed of structural units derived from ethylene and ethylene alcohol units, and contains a small amount of vinyl ester structural units which are not saponified and remain.

[0033] The content of the ethylene structural unit in the EVOH resin is usually 20 to 60 mol%, preferably 25 to 50 mol%, and particularly preferably 25 to 35 mol%. The content of the ethylene structural unit can be controlled by the pressure of ethylene when the ethylene ester monomer is copolymerized with ethylene, and by making the content be higher than the lower limit value, the gas barrier property under high humidity and the melt formability are not easily reduced, and on the contrary, by making the content be lower than the upper limit value, the gas barrier property is not easily reduced.

[0034] Note that the content of the ethylene structural unit can be measured based on ISO 14663.

[0035] The saponification degree of the EVOH resin is usually 90 to 100 mol%, preferably 95 to 100 mol%, and particularly preferably 99 to 100 mol%. The saponification degree can be controlled by the amount, temperature, and time of the saponification catalyst (usually, an alkali catalyst is used) when the ethylene-ethylene ester copolymer is saponified, and in the case where the saponification degree is too low, there is a tendency that the gas barrier property, heat stability, moisture resistance, and the like are reduced.

[0036] The saponification degree of the EVOH resin can be measured based on JIS K 6726 (in which the EVOH resin is used in the form of a solution uniformly dissolved in a water / methanol solvent).

[0037] The melt flow rate (MFR) (210°C, load 2160 g) of the EVOH resin is usually 0.5 to 100 g / 10 minutes, preferably 1 to 50 g / 10 minutes, and particularly preferably 3 to 35 g / 10 minutes. By making the MFR be lower than the upper limit value, the stability at the time of film formation is not easily impaired, and by making the MFR be higher than the lower limit value, the viscosity does not easily become too high to make melt extrusion difficult.

[0038] The MFR is an index of the degree of polymerization of the EVOH resin, and can be adjusted by the amount of the polymerization initiator and the amount of the solvent when ethylene is copolymerized with the ethylene ester monomer.

[0039] Further, in the EVOH resin, a structural unit derived from a comonomer shown below can also be contained within a range that does not hinder the effects of the present application (for example, 10 mol% or less of the EVOH resin).

[0040] As the comonomer, for example, there can be mentioned: olefins such as propylene, 1-butene, isobutene, etc.; α-olefins containing a hydroxyl group such as 3-buten-1-ol, 3-buten-1,2-diol, 4-penten-1-ol, 5-hexen-1,2-diol, etc.; derivatives thereof such as esterification products, acylated products, etc.; hydroxyalkylvinylidene compounds such as 2-methylenepropane-1,3-diol, 3-methylene pentane-1,5-diol, etc.; hydroxyalkylvinylidene diacetate compounds such as 1,3-diacetyloxy-2-methylene propane, 1,3-dipropionyloxy-2-methylene propane, 1,3-dibutyryloxy-2-methylene propane, etc.; unsaturated acids or salts thereof or mono- or di-alkyl esters having an alkyl group having 1 to 18 carbon atoms such as acrylic acid, methacrylic acid, crotonic acid, phthalic acid (anhydride), maleic acid (anhydride), itaconic acid (anhydride), etc.; acrylamides such as acrylamide, N-alkyl acrylamides having an alkyl group having 1 to 18 carbon atoms, N,N-dimethyl acrylamide, 2-acrylamidoglycolic acid or a salt thereof, acrylamidopropyl dimethylamine or an acid salt thereof or a quaternary salt thereof, etc.; methacrylamides such as methacrylamide, N-alkyl methacrylamides having an alkyl group having 1 to 18 carbon atoms, N,N-dimethyl methacrylamide, 2-methacrylamidoglycolic acid or a salt thereof, methacrylamidopropyl dimethylamine or an acid salt thereof or a quaternary salt thereof, etc.; N-vinyl amides such as N-vinyl pyrrolidone, N-vinyl formamide, N-vinyl acetamide, etc.; cyano vinyl compounds such as acrylonitrile, methacrylonitrile, etc.; vinyl ethers such as alkyl vinyl ethers having an alkyl group having 1 to 18 carbon atoms, hydroxyalkyl vinyl ethers, alkoxyalkyl vinyl ethers, etc.; halogenated ethylene compounds such as chloroethylene, vinylidene chloride, fluoroethylene, vinylidene fluoride, bromoethylene, etc.; vinyl silanes such as trimethoxyvinyl silane, etc.; haloallyl compounds such as allyl acetate, allyl chloride, etc.; allyl alcohols such as allyl alcohol, dimethoxyallyl alcohol, etc.; and comonomers such as trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride, acrylamido-2-methylpropane sulfonic acid, etc. These can be used alone or in combination of two or more.

[0041] Among them, α-olefins containing a hydroxyl group are preferred, and 3-buten-1,2-diol and 5-hexen-1,2-diol are particularly preferred. In the case where the α-olefins containing a hydroxyl group are copolymerized, the resulting EVOH resin has a primary hydroxyl group in the side chain. Such an EVOH resin having a primary hydroxyl group in the side chain, particularly an EVOH resin having a 1,2-diol structure in the side chain, is preferred in terms of maintaining gas barrier properties and good secondary molding properties.

[0042] In the case where the EVOH resin has a primary hydroxyl group in the side chain, the content of the structural unit derived from the monomer having the primary hydroxyl group is usually 0.1 to 20 mol%, preferably 0.5 to 15 mol%, and particularly preferably 1 to 10 mol% of the EVOH resin.

[0043] Further, as the EVOH resin, a "post-modified" EVOH resin subjected to esterification, carbamoylation, acetalization, cyanoethylation, oxyalkylenation, or the like can also be used.

[0044] In the case of using the post-modified EVOH resin, the modification rate thereof is usually 10 mol% or less, and preferably 4 mol% or less. By making the modification rate of the EVOH resin be the upper limit value or less, thermal deterioration is less likely to occur, and long-term operability is less likely to decrease.

[0045] Further, the EVOH resin can also be a mixture of EVOH resins differing in the content of ethylene structural units, the saponification degree, the polymerization degree, copolymerization components, or the like.

[0046] The EVOH resin particles obtained by the present application can contain a resin composition obtained by mixing a resin other than the mixed EVOH resin. In this case, the content of the resin composition obtained by mixing a resin other than the mixed EVOH resin is, for example, 20% by mass or less, and preferably 10% by mass or less.

[0047] The EVOH resin particles obtained by the present application can contain a compounding agent that is usually compounded in an EVOH resin, such as a heat stabilizer, an antioxidant, an antistatic agent, a colorant, an ultraviolet absorber, a plasticizer, a light stabilizer, a surfactant, an antibacterial agent, a drying agent, an anti-blocking agent, a flame retardant, a crosslinking agent, a curing agent, a foaming agent, a crystallization nucleating agent, an antifogging agent, a biodegradation additive, a silane coupling agent, an oxygen absorber, or the like. These can be used alone or in combination with two or more.

[0048]

[0049] The production method of the EVOH resin particles of the present application is a production method of EVOH resin particles having a drying step, in which the lower alcohol content of the EVOH resin intermediate particles fed into the drying step is set to 0.005 to 15 mass%. The EVOH resin particles thus obtained can be produced, for example, as shown in Figure 1

[0050] In the present application, lower alcohol refers to a fatty alcohol having 1 to 10 carbon atoms, such as methanol, ethanol, propanol, n-butanol, t-butanol, or the like.

[0051] [Particle formation step]

[0052] First, as described above, an ethylene copolymer is produced by copolymerization of ethylene and an ethylene ester elastomer, and the copolymer is saponified with a base to produce a flowable EVOH resin. Then, the flowable EVOH resin is particulated to obtain EVOH resin intermediate particles (A).

[0053] ​​As a method for pelletizing the flowable EVOH resin, for example, a method in which the flowable EVOH resin is extruded from a discharge port of an extruder, cut in a molten state, and then cooled and solidified to produce pellets (hot cutting method), a method in which the flowable EVOH resin is extruded into a coagulation bath, and the EVOH resin thread obtained by cooling and solidification is cut (thread cutting method), and the like can be exemplified, of which the thread cutting method is preferred from the viewpoint of obtaining porous pellets.

[0054] In either of the hot cutting method and the thread cutting method, as the flowable EVOH resin used as a pellet raw material, a molten EVOH resin obtained by melting an EVOH resin aqueous composition, EVOH resin pellets (dry EVOH composition), or the like can also be used.

[0055] The EVOH resin aqueous composition refers to a substance obtained by dissolving an EVOH resin using a solvent, and the concentration of the EVOH resin in the EVOH resin aqueous composition is usually 20 to 60 mass %.

[0056] As the solvent, a lower alcohol, a water / lower alcohol mixed solvent, or the like can be used, of which a water / lower alcohol mixed solvent is preferred, and the water / lower alcohol mixed mass ratio is preferably 80 / 20 to 5 / 95.

[0057] Further, as the lower alcohol, methanol is particularly preferred.

[0058] The EVOH resin aqueous composition preferably contains 0 to 100 parts by mass of a lower alcohol and 10 to 500 parts by mass of water with respect to 100 parts by mass of an EVOH resin.

[0059] As a method for adjusting the water content of the EVOH resin aqueous composition, there is no particular limitation, and in order to increase the water content, for example, a method in which the solvent is sprayed to a solution or slurry of an EVOH resin obtained by solution polymerization, a method in which the solvent is mixed with a solution or slurry of an EVOH resin, a method in which a solution or slurry of an EVOH resin is brought into contact with a vapor of the solvent, and the like can be used. In order to decrease the water content, drying is appropriately performed, and for example, a flow type hot air drier or a stationary type hot air drier can be used for drying.

[0060] [Hot cutting method]

[0061] In the case where the EVOH resin aqueous composition is fed to the extruder as a pellet raw material produced by the hot cutting method, the temperature of the EVOH resin aqueous composition in the extruder is preferably 70 to 170°C, more preferably 80 to 170°C, and further preferably 90 to 170°C. By making the temperature of the EVOH resin aqueous composition higher than the lower limit, the EVOH resin is less likely to be completely melted, and by making the temperature of the EVOH resin aqueous composition lower than the upper limit, the EVOH resin is less likely to be deteriorated by heat.

[0062] On the other hand, in the case where the dried EVOH resin composition is fed to the extruder as a pellet raw material, the temperature of the dried EVOH resin composition in the extruder is preferably 50 to 300°C, more preferably 160 to 280°C, and further preferably 170 to 250°C.

[0063] Note that the temperature of the EVOH resin aqueous composition and the dried EVOH resin composition in the extruder refers to the temperature detected by a temperature sensor provided to the cylinder of the extruder near the top end portion discharge port of the extruder.

[0064] The EVOH resin aqueous composition or the dried EVOH resin composition extruded from the die of the extruder, i.e., the EVOH resin in a molten state, is cut before being cooled and solidified. The cutting method can be either of a hot cutting method (air hot cutting method) in which cutting is performed in the air or a water cutting method in which the extrusion is performed into a cutter setting container filled with cooling water and cutting is performed in the cooling water.

[0065] The temperature of the cooling water in the water cutting method is a temperature at which the EVOH resin extruded in a molten state does not instantaneously solidify (set), and the temperature of the cooling water is preferably set to -20 to 50°C, and more preferably -5 to 30°C, in the case where the EVOH resin aqueous composition is used as a raw material.

[0066] Further, in the case where the dried EVOH resin composition is used as a raw material, solidification is more likely to occur compared to the case where the EVOH resin aqueous composition is used as a raw material, and therefore, the temperature of the cooling water in the water cutting method is higher than in the case where the EVOH resin aqueous composition is used as a raw material, and is usually 0 to 90°C, and preferably 20 to 70°C.

[0067] The cooling water is not limited to water, and water / alcohol mixed solution, aromatic hydrocarbons such as benzene, ketones such as acetone and methyl ethyl ketone, ethers such as dipropyl ether, organic esters such as methyl acetate, ethyl acetate and methyl propionate, and the like can also be used. Among them, from the viewpoint of easy operability, water or water / alcohol mixed solution is used. In the water / alcohol mixed solution, the water / alcohol (mass ratio) is usually 90 / 10 to 99 / 1. Note that, as the alcohol, lower alcohols such as methanol, ethanol and propanol can be used, and industrially, methanol is preferably used.

[0068] [Strand cutting method]

[0069] In the strand cutting method, in the case where the EVOH resin aqueous composition is supplied to the extruder as a pellet raw material, the temperature of the EVOH resin aqueous composition extruded into the coagulation bath is usually 10 to 100°C, the temperature of the coagulation bath is a temperature at which the extruded EVOH resin can be cooled and solidified, and is usually -10 to 40°C, and the residence time is usually about 10 to 400 seconds.

[0070] On the other hand, in the case where the dried EVOH resin composition is supplied to the extruder as a pellet raw material, the temperature of the EVOH resin extruded into the coagulation bath is usually 150 to 300°C, the temperature of the coagulation bath is usually 0 to 90°C, and the residence time is about 2 to 400 seconds.

[0071] As the coagulation liquid used in the coagulation bath, the same solution as the cooling water in the hot cutting method can be used.

[0072] In this way, the EVOH resin intermediate pellets (A) are obtained, but from the viewpoint of adjustment of the lower alcohol content described later, the EVOH resin intermediate pellets (A) are preferably porous pellets.

[0073] The porous pellets can be obtained, for example, by using an alcohol or water / alcohol solution of EVOH resin (EVOH resin aqueous composition) as a pellet raw material in the strand cutting method.

[0074] In the case where the EVOH resin intermediate pellets (A) are porous, by allowing a lower alcohol of a prescribed concentration to permeate into the pores, the lower alcohol content can be effectively adjusted in the "lower alcohol content adjustment step" described later.

[0075] The shape of the EVOH resin intermediate pellets (A) is usually determined by the manufacturing method thereof, and can be set to various shapes. As the shape of the EVOH resin intermediate pellets (A), for example, there are spherical, ellipsoidal, cylindrical, cubic, cuboid, irregular, and the like, and is usually ellipsoidal or cylindrical.

[0076] Further, in terms of the size, from the viewpoint of convenience in the case of later use as a molding material, in the case of an elliptical shape, the major axis is usually 1 to 10 mm, preferably 2 to 7 mm, and the minor axis is usually 1 to 6 mm, preferably 2 to 5 mm, and in the case of a cylindrical shape, the diameter of the base is usually 1 to 10 mm, preferably 2 to 7 mm, and the length is usually 1 to 10 mm, preferably 3 to 8 mm.

[0077] In the case where the lower alcohol content of the resultant EVOH resin intermediate particles (A) satisfies the prescribed concentration range, the "drying step" can be entered without passing through the "cleaning step" and / or the "lower alcohol content adjustment step" described later.

[0078] [Cleaning Step]

[0079] The flowable EVOH resin used as the raw material of the particles generally contains an alkaline catalyst used at the time of saponification, by-product salts, other impurities, and the like.

[0080] Therefore, the resultant EVOH resin intermediate particles (A) generally contain these impurities and the like. For this reason, generally, the EVOH resin intermediate particles (A) are subjected to the cleaning step for removing these impurities and the like.

[0081] The cleaning liquid used in the cleaning step is generally an aqueous solution. Further, as the cleaning method, for example, the EVOH resin intermediate particles (A) can be put into the cleaning liquid and stirred, or the like. The cleaning step can be performed a plurality of times.

[0082] In the cleaning step, as described above, it is common knowledge for those skilled in the art to perform cleaning in such a manner that the lower alcohol contained in the EVOH resin intermediate particles (A) is reduced as much as possible, and in the cleaning step, by performing cleaning of the EVOH resin intermediate particles (A), generally, the EVOH resin intermediate particles (B) having an extremely low lower alcohol content (generally, 0.005 mass% or less) can be obtained.

[0083] Note that, in the cleaning step, the cleaning liquid is adjusted so as to become the prescribed lower alcohol content in the present application, and cleaning is performed, and the prescribed amount of lower alcohol content can be achieved.

[0084] However, from the aspect of being able to adjust the lower alcohol content with high precision, it is preferable to provide the lower alcohol content adjustment step described later.

[0085] [Lower Alcohol Content Adjustment Step]

[0086] In order to produce the EVOH resin intermediate particles (C) containing a prescribed amount of the lower alcohol from the EVOH resin intermediate particles (B), for example, a lower alcohol content adjusting step of bringing the EVOH resin intermediate particles (B) into contact with a treatment liquid containing a prescribed concentration of the lower alcohol is preferably provided.

[0087] That is, in the lower alcohol content adjusting step, by bringing the EVOH resin intermediate particles (B) into contact with the treatment liquid containing a prescribed concentration of the lower alcohol, the EVOH resin intermediate particles (C) having a prescribed lower alcohol content can be obtained. In this way, by adjusting only the concentration of the lower alcohol contained in the treatment liquid, the EVOH resin intermediate particles (C) having a prescribed lower alcohol content can be easily produced.

[0088] As the method of bringing the treatment liquid containing a prescribed concentration of the lower alcohol into contact with the EVOH resin intermediate particles (B), for example, a method of immersing the EVOH resin intermediate particles (B) in the treatment liquid, a method of spraying the treatment liquid in mist form onto the EVOH resin intermediate particles (B), and the like can be used, and from the viewpoint of being able to uniformly contain the lower alcohol, a method of immersing the EVOH resin intermediate particles (B) in the treatment liquid and stirring together with the treatment liquid is preferred.

[0089] The concentration of the lower alcohol of the treatment liquid used in the lower alcohol content adjusting step also depends on the lower alcohol content of the EVOH resin intermediate particles (B) that are the contact object, the weight ratio of the particles to the treatment liquid, the contact time, and for example, is preferably set to 0.01 to 40 mass%, more preferably to 0.02 to 25 mass%, and further preferably to 0.05 to 15 mass%.

[0090] Furthermore, in the case of immersing the EVOH resin intermediate particles (B) in the treatment liquid, the immersion time (the time of contact with the treatment liquid) is for example preferably 1 minute to 6 hours, and more preferably 30 minutes to 3 hours.

[0091] Furthermore, the liquid temperature of the treatment liquid is for example preferably 1 to 60°C, and more preferably 10 to 40°C.

[0092] The treatment liquid is usually an aqueous solution. Furthermore, a treatment liquid containing a prescribed amount of the lower alcohol in the cleaning liquid used in the cleaning step can also be used.

[0093] In this way, the EVOH resin intermediate particles (C) containing a prescribed amount of the lower alcohol can be easily obtained. The lower alcohol content of the EVOH resin intermediate particles (C) is 0.005 to 15 mass%, preferably 0.015 to 15 mass%, more preferably 0.025 to 12 mass%, particularly preferably 0.03 to 9 mass%, and especially preferably 0.035 to 7 mass%.

[0094] Note that, in the cleaning step, the lower alcohol content adjustment step is not required when the lower alcohol content has been adjusted to a predetermined amount. However, adjustment of the lower alcohol content to a predetermined range in the cleaning step requires complicated operations, and thus it is preferable to additionally provide the lower alcohol content adjustment step.

[0095] [ Drying Step ]

[0096] The volatile component in the EVOH resin intermediate particles (C) thus obtained is usually 10 to 90% by mass, preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and further preferably 45 to 65% by mass. Therefore, in the present application, a drying step for drying the EVOH resin intermediate particles (C) is required. Such a drying step can be provided in plural.

[0097] The drying step can be any mode as long as the EVOH resin intermediate particles (C) are dried, and, for example, when performed in a closed space, the volatile component (water, lower alcohol, etc.) is easily recovered, and thus is preferable from the viewpoint of environmental protection.

[0098] As the drying mode that can be performed in a closed space, for example, there can be mentioned flow drying using a cylindrical / tank type stirring dryer, a cylindrical dryer, a rotary dryer, a flow layer dryer, a vibrating flow layer dryer, a conical rotary type dryer, and the like, static drying using an intermittent box type dryer, a belt type dryer, a tunnel type dryer, a vertical silo dryer, and the like, and the like, and among them, drying performed using an explosion-proof device is preferable. In addition, various drying methods can be used in combination.

[0099] Note that, in the present application, the closed space means a space in which the entry and exit of air and gas are restricted. That is, when it is such a space, air and gas can be circulated to restrict the discharge of gas to the outside, or the amount of air and gas discharged (discharge amount) and the amount of air and gas introduced (introduction amount) can be set to the same amount to maintain the pressure in the space to be constant.

[0100] In addition, in the present application, the explosion-proof device means all devices that take explosion-proof measures against an electrical device that becomes an ignition source. That is, when the drying step is performed using an explosion-proof device, explosion and fire due to leakage of a flammable substance or the like can be effectively prevented, and thus is preferable from the viewpoint of environmental protection.

[0101] The drying temperature in the drying step is preferably set to 40 to 190°C, more preferably 60 to 170°C, and further preferably 80 to 150°C. In addition, drying can be effectively performed by passing a gas such as air or gas at 80 to 150°C through the dryer.

[0102] The drying time in the drying step is preferably set to 5 minutes to 100 hours, more preferably 30 minutes to 90 hours, further preferably 1 to 80 hours, and particularly preferably 10 to 70 hours.

[0103] The volatile component of the EVOH resin particles thus obtained is usually 0.01 to 0.5 mass%, preferably 0.05 to 0.35 mass%, and particularly preferably 0.1 to 0.3 mass%.

[0104] That is, the drying in the present application means adjusting the volatile component contained in the obtained EVOH resin particles to 0.5 mass% or less.

[0105] The volatile components of the EVOH resin intermediate particles (C) and the EVOH resin particles are measured / calculated by the following method (Comparative Example 1 is the EVOH resin intermediate particles (B)).

[0106] That is, in the present application, the volatile component means the component calculated by the drying residue method, and specifically, the mass (Wl) of the EVOH resin intermediate particles (B) or (C), the EVOH resin particles before drying is measured using an electronic balance, dried in a hot air drier at 150°C for 5 hours, and the mass (W2) after being cooled for 30 minutes in a drier is measured, and calculated by the following formula.

[0107]

[0108] Thus, the present application, contrary to the conventional technical common sense that the EVOH resin intermediate particles (B) having a sufficiently low lower alcohol content are introduced into the drying step, instead introduces the EVOH resin intermediate particles (C) containing a prescribed amount of lower alcohol into the drying step. Thereby, the EVOH resin particles having excellent thermal stability can be obtained.

[0109] The reason for this is not certain, but it is presumed that because the volatilization state of water is different from usual, the molecular arrangement is neat during drying, the crystallinity becomes high, and thereby the thermal stability of the obtained EVOH resin particles is improved.

[0110] Therefore, in the case where a plurality of drying steps are provided, the lower alcohol content of the EVOH resin intermediate particles (C) introduced into the first drying step can be set to the prescribed range.

[0111] The EVOH resin particles thus obtained are provided as is as the molding material for various molded articles or provided in various forms such as powder, liquid, and the like as the molding material for various molded articles.

[0112] Example

[0113] The following examples further specifically illustrate the present application, but the present application is not limited to the following examples as long as it does not deviate from the gist thereof. Note that in the examples, "parts" and "%" refer to mass basis.

[0114] [Example 1]

[0115] First, an EVOH resin solution [water / methanol mixed solution (mixed mass ratio of water / methanol = 42 / 58, EVOH resin concentration = 40%, solution temperature = 60°C)] having an ethylene content of 32 mol%, a saponification degree of 99.7 mol%, and an MFR of 12 g / 10 minutes (210°C, load 2160 g) was prepared.

[0116] Next, the EVOH resin solution was extruded in a strand shape into a water tank containing a coagulation liquid (mixed mass ratio of water / methanol = 97 / 3) maintained at 2°C and allowed to coagulate, and then cut with a knife to obtain a cylindrical EVOH resin intermediate particle (A).

[0117] Then, as a washing step, 100 parts of the EVOH resin intermediate particle (A) was put into 200 parts of a water washing liquid, and after stirring for 1 hour at 30 to 35°C, the washing liquid was changed, and the washing was similarly performed a total of 5 times.

[0118] The methanol content of the EVOH resin intermediate particle (B) after the washing treatment was analyzed using a gas chromatography method, and the result was 0.004%.

[0119] Then, as a lower alcohol content adjustment step, 100 parts of the EVOH resin intermediate particle (B) was put into 200 parts of a treatment liquid (aqueous solution containing 0.04% of methanol) for 2 hours at 30 to 35°C, and the lower alcohol content adjustment was performed once.

[0120] The methanol content of the EVOH resin intermediate particle (C) after the lower alcohol content adjustment was analyzed using a gas chromatography method, and the result was 0.02%. In addition, the resin concentration was 40.7%, and the volatile component was 59.3%.

[0121] The EVOH resin intermediate particle (C) after the lower alcohol content adjustment was dried at 120°C for 18 hours using a batch-type vacuum drier, and then dried for 10 hours using a batch-type air-through box drier with nitrogen gas blown at a temperature of 118°C to obtain an EVOH resin particle having a volatile component of 0.2%.

[0122] [Example 2]

[0123] An EVOH resin particle was obtained in the same manner as in Example 1 except that in the lower alcohol content adjustment step of Example 1, the methanol concentration of the treatment liquid was set to 0.1%.

[0124] [Example 3]

[0125] Except that the methanol concentration of the treatment liquid was set to 0.2% in the lower alcohol content adjustment step of Example 1, the same procedure as Example 1 was performed to obtain EVOH resin particles.

[0126] [Example 4]

[0127] Except that the methanol concentration of the treatment liquid was set to 0.4% in the lower alcohol content adjustment step of Example 1, the same procedure as Example 1 was performed to obtain EVOH resin particles.

[0128] [Example 5]

[0129] Except that the methanol concentration of the treatment liquid was set to 11.0% in the lower alcohol content adjustment step of Example 1, the same procedure as Example 1 was performed to obtain EVOH resin particles.

[0130] [Example 6]

[0131] Except that the methanol concentration of the treatment liquid was set to 22.0% in the lower alcohol content adjustment step of Example 1, the same procedure as Example 1 was performed to obtain EVOH resin particles.

[0132] [Comparative Example 1]

[0133] Except that the lower alcohol content adjustment step of Example 1 was not performed, the same procedure as Example 1 was performed to obtain EVOH resin particles. That is, Comparative Example 1 is a prior art example itself in which the methanol content of the EVOH resin intermediate particles before drying in the drying step is extremely low.

[0134] The methanol content (%) and volatile component (%) of these EVOH resin intermediate particles and the volatile component (%) of the EVOH resin particles are shown in Table 1 described later.

[0135] Note that the measurement method of the physical properties of the EVOH resin intermediate particles and the EVOH resin particles is shown below.

[0136] [Methanol content]

[0137] The measurement was performed by gas chromatography (external standard method).

[0138] That is, 5.0 g of the EVOH resin intermediate particles or the EVOH resin particles and 20.0 g of distilled water were weighed, the particles were stirred in the distilled water for 3 hours, and the methanol in the particles was extracted.

[0139] The extract was filtered, the sample was adjusted, and the methanol concentration was quantified using gas chromatography (GC) under the following conditions.

[0140] ・Gas chromatography conditions

[0141] Vaporization chamber temperature: 160°C (split ratio 10:1).

[0142] Carrier gas: He (64.2 kPa).

[0143] Column: Supel-Q PLOT (length 30 m, inner diameter 0.32 mm).

[0144] Column temperature: 90°C (equilibrium time 3 minutes).

[0145] Temperature program: 90°C (hold for 10 minutes) → increase at 10.0°C / minute → 150°C (hold for 2 minutes).

[0146] Detector: FID.

[0147] Detector temperature: 160°C.

[0148] Make up gas: N2 (30 mL / minute).

[0149] H2flow rate: 40 mL / minute.

[0150] Air flow rate: 400 mL / minute.

[0151] Then, based on the value quantified by gas chromatography (GC), the methanol content per unit of the intermediate particles or the EVOH resin particles was calculated using the following equation.

[0152] ・"Methanol content per unit of the particles (%)"

[0153]

[0154]

[0155]

[0156] For the EVOH resin particles of Examples 1 to 6 and Comparative Example 1, the coloration evaluation was performed in the following manner, and the thermal stability was evaluated. The results thereof are shown together in Table 2 described later. It can be said that the lower the value of the coloration evaluation, the smaller the proportion of deep color tone, and the higher the thermal stability.

[0157] <Coloration evaluation>

[0158] For the EVOH resin particles, the proportion of color number "2167" (R: 136, G: 120, B: 120) to color number "2440" (R: 152, G: 136, B: 136) was evaluated using a visual analyzer IRIS VA400 (manufactured by Alpha MOS) ("2167" / "2440"). Color number "2167" is a color having a dark shade, and color number "2440" is a color having a light shade. The greater the proportion of the dark shade (the greater the value of the coloration evaluation), the more the sample deteriorated due to heat and colored.

[0159]

[0160] It was found that the proportions of the dark shade in the coloration evaluation were small in Examples 1 to 6 compared to the existing example (Comparative Example 1), and the heat stability was excellent.

[0161] In the above-described examples, specific modes in the present application were shown, but the above-described examples are mere examples and are not to be construed as limiting. It is intended that various modifications apparent to those skilled in the art fall within the scope of the present application.

[0162] Industrial Applicability

[0163] The present application enables the production of EVOH resin particles having excellent heat stability.

Claims

1. A method of producing ethylene-vinyl alcohol copolymer resin particles, having a pelletizing step and a drying step, wherein, in the pelletizing step, ethylene-vinyl alcohol copolymer resin intermediate particles are produced, the volatile component of the intermediate particles between the pelletizing step and the drying step is 5 to 90 mass%, and the lower alcohol content of the ethylene-vinyl alcohol copolymer resin intermediate particles fed to the drying step is 0.005 to 15 mass%.

2. A method of producing ethylene-vinyl alcohol copolymer resin particles, having a pelletizing step and a drying step, wherein, in the pelletizing step, ethylene-vinyl alcohol copolymer resin intermediate particles are produced, the method is provided with a plurality of the drying steps, and the lower alcohol content of the ethylene-vinyl alcohol copolymer resin intermediate particles fed to the first drying step of the plurality of drying steps is 0.005 to 15 mass%.

3. The method of producing ethylene-vinyl alcohol copolymer resin particles according to claim 1 or 2, wherein the lower alcohol content of the ethylene-vinyl alcohol copolymer resin intermediate particles fed to the drying step is 0.03 to 9 mass%.

4. The method of producing ethylene-vinyl alcohol copolymer resin particles according to claim 2, wherein the volatile component of the ethylene-vinyl alcohol copolymer resin intermediate particles is 10 to 90 mass%.

5. The method of producing ethylene-vinyl alcohol copolymer resin particles according to claim 1 or 2, wherein the drying step is performed in a closed space.

6. The method of producing ethylene-vinyl alcohol copolymer resin particles according to claim 2, wherein the first drying step of the plurality of drying steps is performed in a closed space.

7. The method of producing ethylene-vinyl alcohol copolymer resin particles according to claim 2 or 6, wherein the first drying step of the plurality of drying steps is performed using an explosion-proof device. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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