Method for producing ethylene-vinyl alcohol copolymer resin composition pellets

Abstract

This invention provides a method for producing ethylene-vinyl alcohol resin pellets with excellent thermal stability. [Solution] A method for producing ethylene-vinyl alcohol resin composition pellets comprising a pelletizing step and a drying step, wherein intermediate pellets of an ethylene-vinyl alcohol copolymer resin composition are produced in the pelletizing step, the volatile content of the intermediate pellets from the pelletizing step to the drying step is 5 to 90% by mass, the lower alcohol content of the intermediate pellets brought into the drying step is 0.005 to 15% by mass, and the organic acid content is 10 to 3000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer resin in the intermediate pellets.

Description

Technical Field

[0001] The present invention relates to a method for producing ethylene-vinyl alcohol copolymer resin composition pellets, and more particularly, to a method for producing ethylene-vinyl alcohol copolymer resin composition pellets having excellent thermal stability.

Background Art

[0002] Conventionally, when there is residual solvent such as lower alcohol used in the production of ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as "EVOH") resin composition pellets, it causes problems during molding processing into films or the like. Therefore, it is usually required to minimize these. Also, from the viewpoints of economy and safety, it is required to recover them as much as possible. In particular, since it becomes a problem from the viewpoint of environmental protection when released into the atmosphere in the drying process, it has been carried out to reduce it as much as possible before the drying process (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, it has been found that there is room for improvement in the thermal stability of EVOH resin composition pellets obtained by drying intermediate pellets of an EVOH resin composition with the lower alcohol content minimized before drying.

[0005] Therefore, under such circumstances, the present invention provides a method for producing EVOH resin composition pellets having excellent thermal stability. [Means for solving the problem]

[0006] However, in view of these circumstances, the inventors conducted extensive research and found that by setting the lower alcohol content of the intermediate pellets of the EVOH resin composition introduced into the drying process to a range of 0.005 to 15% by mass, and by ensuring that the EVOH resin in the intermediate pellets contains 10 to 1000 ppm of organic acid by mass, the thermal stability of the EVOH resin composition pellets obtained after drying is improved.

[0007] In other words, the present invention has the following aspects. [1] A method for producing ethylene-vinyl alcohol copolymer resin composition pellets, comprising a pelletizing step and a drying step, In the pelletizing process described above, intermediate pellets of the ethylene-vinyl alcohol copolymer resin composition are produced. The volatile content of the intermediate pellets from the pelletizing process to the drying process is 5 to 90% by mass. The lower alcohol content of the intermediate pellets introduced into the drying process is 0.005 to 15% by mass. The intermediate pellets brought into the drying process contain an organic acid. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets, wherein the content of the organic acid is 10 to 3000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer resin in the intermediate pellets brought into the drying step. [2] A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to [1], comprising the step of washing the intermediate pellets produced in the pelletizing step with a solvent containing at least water. [3] A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to [1] or [2], comprising the step of contacting the intermediate pellet produced in the pelletizing step with a solvent containing at least a lower alcohol. [4] The pelletizing process involves pelletizing a fluid ethylene-vinyl alcohol copolymer resin composition to produce intermediate pellets, The aforementioned fluid ethylene-vinyl alcohol copolymer resin composition contains an ethylene-vinyl alcohol copolymer resin and a solvent. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to any one of [1] to [3], wherein the lower alcohol content in the solvent is 5% by mass or more. [5] A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to any one of [1] to [4], wherein the lower alcohol content of the intermediate pellets brought into the drying step is 0.03 to 9% by mass. [6] A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to any one of [1] to [5], wherein the drying step is carried out in a sealed space. [7] A method for producing ethylene-vinyl alcohol copolymer resin composition pellets, comprising a pelletizing step and a drying step, In the pelletizing process described above, intermediate pellets of the ethylene-vinyl alcohol copolymer resin composition are produced. Multiple drying steps are provided, Of the multiple drying processes described above, the lower alcohol content of the intermediate pellets brought into the first drying process is 0.005 to 15% by mass. The aforementioned intermediate pellet contains an organic acid, A method for producing ethylene vinyl alcohol copolymer resin composition pellets, wherein the content of the organic acid is 10 to 3000 ppm relative to the mass of the ethylene vinyl alcohol copolymer resin in the intermediate PET. [8] The method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to [7], wherein the lower alcohol content of the intermediate pellets introduced into the first drying step is 0.03 to 9% by mass. [9] A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to [7] or [8], wherein the first drying step is carried out in a sealed space.

[10] A method for producing ethylene vinyl alcohol copolymer resin composition pellets according to any one of [1] to [9], wherein the content of the organic acid is 30 to 800 ppm relative to the mass of the ethylene vinyl alcohol copolymer resin in the intermediate pellets brought into the drying step.

[11] A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to any one of [1] to

[10] , wherein the organic acid is acetic acid.

[12] A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to any one of [7] to

[11] , wherein the first drying step is performed using explosion-proof equipment. [Effects of the Invention]

[0008] In this invention, the lower alcohol content of the intermediate pellets of the EVOH resin composition introduced into the drying process is set in the range of 0.005 to 15% by mass, and the organic acid content of the EVOH resin in the intermediate pellets is set in the range of 10 to 3000 ppm by mass, so that the resulting EVOH resin composition pellets have excellent thermal stability. [Brief explanation of the drawing]

[0009] [Figure 1] This is a flowchart illustrating one embodiment of the present invention. [Modes for carrying out the invention]

[0010] The present invention will be described below based on examples of embodiments for carrying out the present invention. However, the present invention is not limited to the embodiments described below.

[0011] In this invention, when "X~Y" (where X and Y are any numbers) is used, unless otherwise specified, it includes the meaning of "greater than or equal to X and less than or equal to Y," as well as the meaning of "preferably greater than X" or "preferably less than Y." When expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the meaning that "it is preferably greater than X" or "it is preferably less than Y".

[0012] Regarding the numerical ranges described stepwise in this specification, the upper limit value or lower limit value of a numerical range at a certain step can be arbitrarily combined with the upper limit value or lower limit value of a numerical range at another step. Also, in the numerical ranges described in this specification, the upper limit value or lower limit value of the numerical range can also be replaced with the value shown in the examples.

[0013] <EVOH resin composition> The pellets produced by the present invention are composed of an EVOH resin composition containing a specific trace amount of organic acid. That is, in this EVOH resin composition, the base resin is an EVOH resin, and the content of the EVOH resin in this EVOH resin composition is usually 70% by mass or more, preferably 90% by mass or more, particularly preferably 95% by mass or more of the resin components. The upper limit value is 99.999% by mass. The EVOH resin composition will be described in detail below. [EVOH resin] 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 usually a water-insoluble thermoplastic resin.

[0014] As the vinyl ester monomer, vinyl acetate is typically used due to its market availability and efficient impurity removal during manufacturing. Other vinyl ester monomers besides vinyl acetate include, for example, aliphatic vinyl esters such as vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, and vinyl versatate, and aromatic vinyl esters such as vinyl benzoate. However, aliphatic vinyl esters having 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms are usually used. These are usually used individually, but multiple types may be used simultaneously as needed.

[0015] The polymerization method for copolymerizing the ethylene and vinyl ester monomer can be any known polymerization method, such as solution polymerization, suspension polymerization, or emulsion polymerization, but generally, solution polymerization using a lower alcohol, preferably methanol, as the solvent is used. The saponification of the obtained ethylene-vinyl ester copolymer can also be carried out by known methods. The EVOH resin produced in this manner mainly consists of ethylene-derived structural units and vinyl alcohol structural units, and contains a small amount of vinyl ester structural units that remain unsaponified.

[0016] The ethylene structural unit content in the EVOH resin is typically 20 to 60 mol%, preferably 25 to 50 mol%, and particularly preferably 25 to 35 mol%. The ethylene structural unit content can be controlled by the pressure of the ethylene when copolymerizing the vinyl ester monomer and ethylene. If the content is above the lower limit, the gas barrier properties and melt moldability under high humidity conditions are less likely to decrease, while if it is below the upper limit, the gas barrier properties are less likely to decrease. The content of such ethylene structural units is usually, 1 It is measured by 1H-NMR. For example, 1 A measurement method using 1H-NMR is employed, employing d-DMSO as the measurement solvent and a measurement temperature of 50°C.

[0017] The degree of saponification in the EVOH resin is typically 90-100 mol%, preferably 95-100 mol%, and particularly preferably 99-100 mol%. The degree of saponification can be controlled by the amount of saponification catalyst (usually an alkaline catalyst) used to saponify the ethylene-vinyl ester copolymer, the temperature, the time, etc. If the degree of saponification is too low, the gas barrier properties, thermal stability, moisture resistance, etc. tend to decrease. The degree of saponification of such EVOH resin is usually, 1 It is measured by 1H-NMR. For example, 1 A measurement method using 1H-NMR is employed, employing d-DMSO as the measurement solvent and a measurement temperature of 50°C.

[0018] The melt flow rate (MFR) (210°C, 2160g load) of the EVOH resin is typically 0.5 to 100 g / 10 min, preferably 1 to 50 g / 10 min, and particularly preferably 3 to 35 g / 10 min. Having an MFR below the upper limit reduces the likelihood of impaired stability during manufacturing, while having an MFR above the lower limit reduces the likelihood of excessive viscosity making melt extrusion difficult. The aforementioned MFR is an indicator of the degree of polymerization of the EVOH resin and can be adjusted by the amount of polymerization initiator and solvent used when copolymerizing ethylene and vinyl ester monomers.

[0019] Furthermore, the EVOH resin may further contain structural units derived from the following comonomers, within a range that does not impair the effects of the present invention (for example, 10 mol% or less of the EVOH resin). Examples of the comonomers include olefins such as propylene, 1-butene, and isobutene; hydroxyl group-containing α-olefins such as 3-buten-1-ol, 3-buten-1,2-diol, 4-penten-1-ol, and 5-hexen-1,2-diol, and their esterified and acylated derivatives; hydroxyalkylvinylidenes such as 2-methylenepropane-1,3-diol and 3-methylenepentane-1,5-diol; 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyl Hydroxyalkylvinylidene diacetates such as ruoxy-2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, (anhydride) phthalic acid, (anhydride) maleic acid, (anhydride) itaconic acid, or their salts, or mono or dialkyl esters with 1 to 18 carbon atoms in the alkyl group; acrylamide, N-alkylacrylamide with 1 to 18 carbon atoms in the alkyl group, N,N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or its salts, acrylamidopropyldimethylamine or its salts or its quaternary salts Acrylamides such as methacrylamide, N-alkylmethacrylamide with 1 to 18 C1 of the alkyl group, N,N-dimethylmethacrylamide, 2-methacrylamidepropanesulfonic acid or its salts, methacrylamidopropyldimethylamine or its salts or its quaternary salts, etc.; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, etc.; vinyl cyanides such as acrylonitrile, methacrylnitrile, etc.; alkyl vinyl ethers with 1 to 18 C1 of the alkyl group, hydro Examples include vinyl ethers such as xyalkyl vinyl ethers and alkoxyalkyl vinyl ethers; vinyl halogenated compounds such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; vinyl silanes such as trimethoxyvinylsilane; allyl halogenated compounds such as allyl acetate and allyl chloride; allyl alcohols such as allyl alcohol and dimethoxyallyl alcohol; and comonomers such as trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride and acrylamide-2-methylpropanesulfonic acid.These can be used individually or in combination of two or more types.

[0020] Among these, hydroxyl group-containing α-olefins are preferred, and 3-butene-1,2-diol and 5-hexene-1,2-diol are particularly preferred. When the hydroxyl group-containing α-olefins are copolymerized, the resulting EVOH resin has primary hydroxyl groups in its side chains. Such EVOH resins having primary hydroxyl groups in their side chains, and especially EVOH resins having a 1,2-diol structure in their side chains, are preferred because they maintain gas barrier properties while exhibiting good secondary moldability.

[0021] When the EVOH resin has a primary hydroxyl group in its side chain, the content of structural units derived from the monomer having the primary hydroxyl group is typically 0.1 to 20 mol%, preferably 0.5 to 15 mol%, and particularly preferably 1 to 10 mol% of the EVOH resin.

[0022] Furthermore, as the EVOH resin, EVOH resins that have undergone "post-modification" such as esterification, urethaneization, acetalization, cyanoethylation, or oxyalkyleneization can also be used.

[0023] When using the post-modified EVOH resin described above, the modification rate is usually 10 mol% or less, preferably 4 mol% or less. Having a modification rate of EVOH resin below the upper limit reduces thermal degradation and prevents a decrease in long-run performance.

[0024] Furthermore, the EVOH resin may be a mixture of EVOH resins with different ethylene structural unit content, degree of saponification, degree of polymerization, copolymer components, etc.

[0025] [Organic acid] Examples of organic acids used in the present invention include linear saturated aliphatic carboxylic acids, branched saturated aliphatic carboxylic acids, unsaturated aliphatic carboxylic acids, aromatic carboxylic acids, heterocyclic carboxylic acids, dicarboxylic acids, tricarboxylic acids, etc., with linear saturated aliphatic carboxylic acids being preferred. These organic acids may be used individually or in combination of two or more types.

[0026] Examples of the linear saturated aliphatic carboxylic acids include formic acid, acetic acid, propionic acid, n-butyric acid, n-valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid. Among these, carboxylic acids having 2 to 4 carbon atoms are preferred due to their excellent thermal stability.

[0027] Carboxylic acids having 2 to 4 carbon atoms may be monocarboxylic acids, dicarboxylic acids, saturated carboxylic acids, or unsaturated carboxylic acids. Furthermore, as long as the number of carbon atoms in the molecule is within the range of 2 to 4, they may be branched or have substituents such as hydroxyl groups. Specifically, examples include monocarboxylic acids such as acetic acid, butyric acid, and propionic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, maleic acid, and fumaric acid; hydroxy acids such as glycolic acid, lactic acid, tartaric acid, and malic acid; and unsaturated fatty acids such as acrylic acid, crotonic acid, and methacrylic acid. In particular, from the viewpoint of dispersibility in EVOH resin, mono- or dicarboxylic acids having 2 to 4 carbon atoms are preferred, and from an economic standpoint, monocarboxylic acids having 2 to 4 carbon atoms are more preferred, and acetic acid is especially preferred.

[0028] The molecular weight of the organic acid is usually 40 to 400, preferably 45 to 300, and particularly preferably 45 to 90.

[0029] The content of the organic acid is preferably 10 to 3000 ppm, more preferably 20 to 1500 ppm, still more preferably 30 to 800 ppm, particularly preferably 40 to 300 ppm, and especially preferably 50 to 200 ppm, based on the mass of the EVOH resin in the EVOH resin composition. When the content of the organic acid is within the above range, the thermal stability of the obtained EVOH resin composition pellets is improved, and the moldability of the EVOH resin composition tends to be improved.

[0030] The EVOH resin composition may contain a resin other than the EVOH resin. In that case, the content of the resin other than the EVOH resin is, for example, 20% by mass or less, preferably 10% by mass or less of the EVOH resin composition.

[0031] The EVOH resin composition may contain additives generally blended with EVOH resins, such as heat stabilizers, antioxidants, antistatic agents, colorants, ultraviolet absorbers, plasticizers, light stabilizers, surfactants, antibacterial agents, desiccants, antiblocking agents, flame retardants, crosslinking agents, curing agents, foaming agents, crystal nucleating agents, antifogging agents, biodegradable additives, silane coupling agents, oxygen absorbers, etc. These can be used alone or in combination of two or more.

[0032] <Method for producing EVOH resin composition pellets> The method for producing EVOH resin composition pellets of the present invention is a method for producing EVOH resin composition pellets having a drying step, wherein the lower alcohol content in the intermediate pellets of the EVOH resin composition introduced into the drying step is set to 0.005 to 15% by mass, and the content of the organic acid in the EVOH resin composition in the intermediate pellets is set to 10 to 3000 ppm by mass. The EVOH resin composition pellets thus obtained can be produced, for example, as shown in FIG. 1, through the following steps.

[0033] In the present invention, lower alcohols refer to aliphatic alcohols having 1 to 10 carbon atoms, such as methanol, ethanol, propanol, n-butanol, and t-butanol, and more preferably methanol, ethanol, propanol, and t-butanol, and even more preferably methanol.

[0034] [Pelletization process] First, as described above, an ethylene copolymer is produced by copolymerizing ethylene and vinyl ester elastomer, and this copolymer is saponified with alkali to produce a fluid EVOH resin composition. Then, the fluid EVOH resin composition is pelletized to obtain an intermediate pellet (A) of the EVOH resin composition.

[0035] To pelletize the fluid EVOH resin composition, examples include a method in which the fluid EVOH resin composition is extruded from the discharge port of an extruder, cut in a molten state, and then cooled and solidified to produce pellets (hot cut method), and a method in which the fluid EVOH resin composition is extruded into a solidification bath and the EVOH resin composition strands obtained by cooling and solidification are cut (strand cut method). Among these, the strand cut method is preferred because it yields porous pellets.

[0036] Whether using the hot-cut method or the strand-cut method, the fluid EVOH resin composition used as the pellet raw material can also be an EVOH resin composition solution, an EVOH resin composition pellet (dried EVOH composition) that has been melted, or a molten EVOH resin composition.

[0037] The EVOH resin composition solution is obtained by dissolving the EVOH resin composition using a solvent, and the concentration of EVOH resin in the EVOH resin composition solution is usually 20 to 60% by mass.

[0038] As the solvent, water, lower alcohols, water / lower alcohol mixed solvents, etc., can be used, of which water / lower alcohol mixed solvents are preferably used, and the mass ratio of the water / lower alcohol mixture is preferably 95 / 5 to 1 / 99, and more preferably 80 / 20 to 5 / 95. That is, it is preferable that the lower alcohol content in the solvent is 5% by mass or more. Furthermore, methanol is particularly preferred as the lower alcohol.

[0039] The EVOH resin composition solution preferably contains 0 to 100 parts by mass of lower alcohol and 10 to 500 parts by mass of water per 100 parts by mass of EVOH resin.

[0040] The method for adjusting the water content of the EVOH resin composition solution is not particularly limited, but to increase the water content, for example, a method of spraying the solvent onto the solution or slurry of the EVOH resin composition obtained by solution polymerization, a method of mixing the solution or slurry of the EVOH resin composition with the solvent, or a method of contacting the solution or slurry of the EVOH resin composition with the vapor of the solvent can be used. To decrease the water content, it can be dried as appropriate, for example, using a fluidized bed hot air dryer or a static hot air dryer.

[0041] [Hot cut method] In the aforementioned hot-cut method, when the EVOH resin composition solution is fed into the extruder as a pellet raw material for production using the hot-cut method, the temperature of the EVOH resin composition solution in the extruder is preferably 70 to 170°C, more preferably 80 to 170°C, and even more preferably 90 to 170°C. If the temperature of the EVOH resin composition solution is above the lower limit, the EVOH resin becomes less likely to melt completely, and if it is below the upper limit, the EVOH resin becomes less susceptible to thermal degradation. On the other hand, when a dried EVOH resin composition is fed into an extruder as a pellet raw material, the temperature of the dried EVOH resin composition inside the extruder is preferably 150 to 300°C, more preferably 160 to 280°C, and even more preferably 170 to 250°C. The temperature of the EVOH resin composition solution and the dried EVOH resin composition inside the extruder refers to the temperature detected near the discharge port at the tip of the extruder by a temperature sensor installed in the extruder cylinder.

[0042] The EVOH resin composition solution or dried EVOH resin composition, i.e., the molten EVOH resin, extruded from the extruder die is cut before it cools and solidifies. The cutting method may be either a hot cutting method (air hot cutting method) in which the resin is cut in the air, or an underwater cutting method in which the resin is extruded into a cutter-mounted container filled with cooling water and cut in the cooling water.

[0043] In the underwater cutting method, the temperature of the cooling water is such that the EVOH resin extruded in a molten state does not solidify instantly. When using an EVOH resin composition solution as a raw material, the temperature of the cooling water is preferably -20 to 50°C, and more preferably -5 to 30°C. Furthermore, when using a dried EVOH resin composition as a raw material, it solidifies more easily than when using an EVOH resin composition solution as a raw material. Therefore, the temperature of the cooling water in the underwater cutting method is higher than when using an EVOH resin composition solution as a raw material, usually between 0 and 90°C, and preferably between 20 and 70°C.

[0044] The cooling water is not limited to water; other substances such as water / alcohol mixtures, aromatic hydrocarbons such as benzene, ketones such as acetone and methyl ethyl ketone, ethers such as dipropyl ether, and organic esters such as methyl acetate, ethyl acetate, and methyl propionate can also be used. Of these, water or water / alcohol mixtures are used because they are easy to handle. In water / alcohol mixtures, the water / alcohol (mass ratio) is usually 90 / 10 to 99 / 1. As the alcohol, lower alcohols such as methanol, ethanol, and propanol can be used, and methanol is preferred industrially.

[0045] [Strand cut method] In the aforementioned strand-cutting method, when an EVOH resin composition solution is fed into an extruder as pellet raw material, the temperature of the EVOH resin composition solution extruded into the solidification bath is typically 10 to 100°C, the temperature of the solidification bath is typically -10 to 40°C, which is the temperature at which the extruded EVOH resin can cool and solidify, and the residence time is typically about 10 to 400 seconds. On the other hand, when a dried EVOH resin composition is fed into an extruder as a pellet raw material, the temperature at which the EVOH resin composition is extruded into the solidification bath is typically 150 to 300°C, the temperature of the solidification bath is typically 0 to 90°C, and the residence time is approximately 2 to 400 seconds. As the coagulation solution used in the coagulation bath, the same solution as the cooling water used in the hot-cut method described above can be used.

[0046] In this way, an intermediate pellet (A) of the EVOH resin composition is obtained, but from the viewpoint of adjusting the lower alcohol and organic acid content described later, it is preferable that the intermediate pellet (A) is a porous pellet. The porous pellets can be obtained, for example, by using an alcohol or water / alcohol solution (EVOH resin composition solution) of an EVOH resin composition as the pellet raw material in a strand-cutting method. If the intermediate pellet (A) is porous, the content of lower alcohol and organic acid can be efficiently adjusted in the "lower alcohol and organic acid content adjustment process" described later by permeating the pores with lower alcohol and organic acid at predetermined concentrations.

[0047] The shape of the intermediate pellet (A) usually depends on its manufacturing method and can be of various shapes. Examples of the shapes of the intermediate pellet (A) include spherical, oval, cylindrical, cubic, rectangular, and irregular shapes, but it is usually oval or cylindrical. Furthermore, in terms of convenience when used later as a molding material, the size is such that, in the case of an oval 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; 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.

[0048] If the lower alcohol and organic acid content of the intermediate pellet (A) is within a predetermined range, the process may proceed to the drying step without going through the "washing step" and / or the "lower alcohol and organic acid content adjustment step" described below.

[0049] [Washing process] The fluid EVOH resin composition used as the pellet raw material typically contains the alkaline catalyst used during saponification, by-product salts, and other impurities. Therefore, the intermediate pellets (A) typically contain these impurities. Consequently, the intermediate pellets (A) are usually subjected to a washing process to remove these impurities.

[0050] The cleaning solution used in the cleaning step is usually an aqueous solution. The cleaning method may include, for example, adding the intermediate pellets (A) to the cleaning solution and stirring them together. The cleaning step may be performed multiple times.

[0051] As mentioned above, in the washing step, it is common technical knowledge to those skilled in the art to wash the intermediate pellet (A) in such a way that the amount of lower alcohol contained in it is reduced as much as possible. In this washing step, by washing the intermediate pellet (A), it is usually possible to obtain intermediate pellet (B) of an EVOH resin composition with an extremely low lower alcohol content (usually 0.005% by mass or less). The volatile content of the intermediate pellet (B) is typically 10 to 90% by mass, preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 45 to 65% by mass.

[0052] Furthermore, in the washing process, it is also possible to obtain intermediate pellets (B) containing predetermined amounts of lower alcohol and organic acid by washing with a washing solution in which the concentrations of lower alcohol and organic acid have been adjusted. However, it is preferable to include the lower alcohol and organic acid content adjustment step described later, as this allows for highly precise adjustment of the lower alcohol and organic acid content of the intermediate pellets brought into the drying process.

[0053] [Process for adjusting the content of lower alcohols and organic acids] In order to convert the intermediate pellet (B) into an intermediate pellet (C) of an EVOH resin composition containing predetermined amounts of lower alcohol and organic acid, it is preferable to include a "lower alcohol and organic acid content adjustment step," for example, in which the intermediate pellet (B) is brought into contact with a solvent (processing solution) containing lower alcohol and organic acid at predetermined concentrations.

[0054] In other words, in the "lower alcohol and organic acid content adjustment step," an intermediate pellet (C) of an EVOH resin composition having a predetermined amount of lower alcohol and organic acid can be obtained by contacting the intermediate pellet (B) with a treatment solution containing a predetermined concentration of lower alcohol and organic acid. In this way, an intermediate pellet (C) of an EVOH resin composition having a predetermined amount of lower alcohol and organic acid can be easily produced simply by adjusting the lower alcohol concentration and organic acid concentration contained in the treatment solution.

[0055] As a method for bringing the processing liquid into contact with the intermediate pellet (B), for example, a method of immersing the intermediate pellet (B) in the processing liquid or a method of spraying the processing liquid onto the intermediate pellet (B) can be used. However, a method of immersing the intermediate pellet (B) in the processing liquid and stirring the processing liquid together is preferred because it allows for the uniform inclusion of lower alcohols and organic acids.

[0056] The lower alcohol concentration of the processing solution used in the "lower alcohol and organic acid content adjustment step" depends on the lower alcohol content of the intermediate pellet (B) to be contacted, the mass ratio of the pellet to the processing solution, and the contact time, but is preferably 0.01 to 40% by mass, more preferably 0.02 to 25% by mass, even more preferably 0.05 to 15% by mass, and particularly preferably 0.1 to 10% by mass.

[0057] Furthermore, the organic acid concentration of the treatment solution depends on the mass ratio of the intermediate pellet (B) to the treatment solution and the contact time, but for example, it is preferably 30 to 2000 ppm by mass ratio, more preferably 40 to 1500 ppm, even more preferably 50 to 1200 ppm, and especially preferably 60 to 1000 ppm.

[0058] When the intermediate pellet (B) is immersed in the processing liquid, the immersion time (time in contact with the processing liquid) is preferably, for example, 1 minute to 6 hours, and more preferably 30 minutes to 3 hours. Furthermore, the temperature of the processing liquid is preferably, for example, 1 to 60°C, and more preferably 10 to 40°C.

[0059] The processing solution is usually a solvent (aqueous solution) containing at least water. Alternatively, the cleaning solution used in the cleaning step may be modified to include a predetermined amount of lower alcohol and organic acid.

[0060] In this way, intermediate pellets (C) of an EVOH resin composition containing a predetermined amount of lower alcohol and organic acid can be easily obtained. The lower alcohol content of the intermediate pellets (C) is 0.005 to 15% by mass, preferably 0.015 to 15% by mass, more preferably 0.025 to 12% by mass, particularly preferably 0.03 to 9% by mass, and especially preferably 0.035 to 7% by mass.

[0061] If the intermediate pellet (B) already contains a predetermined amount of lower alcohol and organic acid at the end of the washing process, this "lower alcohol and organic acid content adjustment process" is unnecessary. However, since adjusting the lower alcohol and organic acid content to a predetermined range during the washing process is a complicated process, it is preferable to provide a separate lower alcohol and organic acid content adjustment process.

[0062] [Drying process] The volatile content of the intermediate pellets (C) of the EVOH resin composition obtained in this way is typically 10 to 90% by mass, preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 45 to 65% by mass. For this reason, the present invention requires a drying step to dry the intermediate pellets (C). Multiple such drying steps may be provided.

[0063] The drying process can be any method as long as it can dry the intermediate pellets (C), but it is preferable, for example, to carry it out in a sealed space, as this makes it easier to recover volatile components (such as water and lower alcohols), thus protecting the environment. Examples of devices capable of drying in a sealed space include fluidized bed dryers using cylindrical / groove type agitator dryers, cylindrical dryers, rotary dryers, fluidized bed dryers, vibrating fluidized bed dryers, and conical rotary dryers, as well as static drying devices using batch vacuum dryers, continuous vacuum dryers, ventilated box dryers, batch box dryers, band dryers, tunnel dryers, and vertical silo dryers. Among these, drying using explosion-proof equipment is preferred. Various drying methods may also be used in combination. In this invention, a sealed space refers to a space in which the entry and exit of air or gas is restricted. In other words, in such a space, it is possible to circulate air or gas to restrict the discharge of gas to the outside, or to set the amount of air or gas coming out (discharge) and the amount coming in (input) to be the same to maintain a constant pressure within the space. Furthermore, in this invention, explosion-proof equipment refers to all equipment in which explosion-proof measures have been taken for electrical equipment that could be an ignition source. In other words, when the drying process is carried out using explosion-proof equipment, explosions and fires caused by leakage of flammable materials can be effectively prevented, which is preferable from the standpoint of environmental protection.

[0064] The drying temperature in the drying process is preferably set to 40-190°C, more preferably 60-170°C, and even more preferably 80-150°C. Furthermore, drying can be efficiently achieved by passing a gas such as air or gas at 80-150°C through the dryer. The drying time in the drying process is preferably set to 5 minutes to 100 hours, more preferably 30 minutes to 90 hours, even more preferably 1 to 80 hours, and particularly preferably 10 to 70 hours.

[0065] The volatile content of the EVOH resin composition pellets obtained in this way is typically 0.01 to 0.5% by mass, preferably 0.05 to 0.35% by mass, and particularly preferably 0.1 to 0.3% by mass.

[0066] In other words, drying in this invention means adjusting the volatile content contained in the resulting EVOH resin composition pellets to 0.5% by mass or less.

[0067] The volatile content of the aforementioned intermediate pellets (B), (C) and EVOH resin composition pellets is measured and calculated by the following method. In other words, in this invention, volatile matter is calculated by the drying residue method, specifically by weighing the intermediate pellet (B) or (C) of the EVOH resin composition and the pre-drying mass (W1) of the EVOH resin composition pellet using an electronic balance, drying in a hot air dryer at 150°C for 5 hours, weighing the mass (W2) after cooling in a desiccator for 30 minutes, and calculating it using the following formula. Volatile content (mass%) = [(W1-W2) / W1] × 100

[0068] Thus, contrary to the common technical practice of introducing intermediate pellets (B) of an EVOH resin composition with a sufficiently low lower alcohol content into the drying process, the present invention introduces intermediate pellets (C) of an EVOH resin composition containing a predetermined amount of lower alcohol and an organic acid into the drying process. This makes it possible to obtain EVOH resin composition pellets with excellent thermal stability. The reason for this is not entirely clear, but it is presumed that the thermal stability of the resulting EVOH resin composition pellets is improved because the water evaporation process is different from normal, and the presence of a predetermined amount of organic acid leads to a more organized molecular arrangement during drying and a higher degree of crystallinity. Therefore, the content of organic acids in the EVOH resin composition is set within a predetermined range, and if there are multiple drying steps, the content of lower alcohols and organic acids in the intermediate pellets (C) of the EVOH resin composition brought into the first drying step is set within a predetermined range.

[0069] The EVOH resin composition pellets obtained in this way can be prepared in various forms, such as as is, or in powder or liquid form, and provided as molding materials for various molded products. [Examples]

[0070] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. In the examples, "parts," "%," and "ppm" refer to mass.

[0071] [Example 1] (Pelletization process) First, an EVOH resin solution [water / methanol mixed solution (water / methanol = 42 / 58 mixed mass ratio, EVOH resin concentration 40%, solution temperature 60°C)] was prepared with an ethylene content of 32 mol%, a degree of saponification of 99.7 mol%, and an MFR of 12 g / 10 min (210°C, load 2160 g)]. Next, this EVOH resin solution was extruded in strand form into a tank containing a solidification solution (water / methanol = 97 / 3 mixed mass ratio) maintained at 2°C and allowed to solidify. After solidification, it was cut with a cutter to obtain cylindrical intermediate pellets (A) of the EVOH resin composition. (Washing process) Then, as a washing step, 100 parts of the intermediate pellet (A) of the EVOH resin composition were added to 300 parts of a washing solution (0.5% aqueous acetic acid solution), stirred at 30-35°C for 1 hour, then the washing solution was replaced, and the washing was repeated a total of two times. After that, it was added to 300 parts of pure water, stirred at 30-35°C for 30 minutes, then the pure water was replaced, and the washing was repeated a total of four times to obtain intermediate pellet (B). The volatile content of the intermediate pellet (B) was 58.0% (resin concentration 42.0%). (Process for adjusting the content of lower alcohols and organic acids) Furthermore, as a step to adjust the lower alcohol and organic acid content, 100 parts of the intermediate pellet (B) were added to 300 parts of a treatment solution (an aqueous solution containing 86 ppm acetic acid and 0.21% methanol), stirred at 30-35°C for 4 hours, and the lower alcohol and organic acid content was adjusted once to obtain intermediate pellet (C) with adjusted lower alcohol and organic acid content. The methanol content of the intermediate pellet (C) was 0.082%, and the acetic acid content of the EVOH resin in the intermediate pellet (C) was 103 ppm. The volatile content was 57.9% (resin concentration 42.1%). (drying process) The intermediate pellets (C), whose lower alcohol and organic acid content was adjusted, were dried at 120°C for 3 hours in an explosion-proof batch vacuum dryer, and then dried for 10 hours in a batch ventilated box dryer with nitrogen gas blown in at 118°C to obtain EVOH resin composition pellets with a volatile content of 0.3%.

[0072] [Example 2] In Example 1, the procedure was carried out in the same manner as in Example 1, except that the acetic acid concentration of the treatment solution in the lower alcohol and organic acid content adjustment step was changed to 346 ppm, and EVOH resin composition pellets were obtained. In Example 2, the methanol content of the intermediate pellet (C) in which the lower alcohol and organic acid content was adjusted was 0.082%, and the acetic acid content of the EVOH resin in the intermediate pellet (C) was 430 ppm.

[0073] [Example 3] In Example 1, the procedure was carried out in the same manner as in Example 1, except that the acetic acid concentration of the treatment solution in the lower alcohol and organic acid content adjustment step was changed to 864 ppm, and EVOH resin composition pellets were obtained. In Example 3, the methanol content of the intermediate pellet (C) in which the lower alcohol and organic acid content was adjusted was 0.082%, and the acetic acid content of the EVOH resin in the intermediate pellet (C) was 1115 ppm.

[0074] [Comparative Example 1] In Example 1, the procedure was carried out in the same manner as in Example 1, except that acetic acid was not added to the treatment solution in the lower alcohol and organic acid content adjustment step, to obtain EVOH resin composition pellets. In Comparative Example 1, the methanol content of the intermediate pellet (C) in which the lower alcohol and organic acid content was adjusted was 0.082%, and the acetic acid content of the EVOH resin in the intermediate pellet (C) was 0 ppm.

[0075] [Comparative Example 2] In Example 1, the procedure was carried out in the same manner as in Example 1, except that the acetic acid concentration of the treatment solution in the lower alcohol and organic acid content adjustment step was changed to 2592 ppm, and EVOH resin composition pellets were obtained. In Comparative Example 2, the methanol content of the intermediate pellet (C) in which the lower alcohol and organic acid content was adjusted was 0.082%, and the acetic acid content of the EVOH resin in the intermediate pellet (C) was 3220 ppm.

[0076] [Comparative Example 3] In Example 2, the procedure was carried out in the same manner as in Example 2, except that methanol was not added to the treatment solution in the lower alcohol and organic acid content adjustment step, to obtain EVOH resin composition pellets. In Comparative Example 3, the methanol content of the intermediate pellet (C) in which the lower alcohol and organic acid content was adjusted was 0.002%, and the acetic acid content of the EVOH resin in the intermediate pellet (C) was 430 ppm.

[0077] The volatile content (%) of these intermediate pellets (B) and (C), and the methanol content (%) of intermediate pellet (C) are shown in Table 1 below. The methods for measuring the methanol content and organic acid content in the intermediate pellets (B) and (C) are as follows.

[0078] <Methanol content> Measurements were taken using gas chromatography (external standard method). Specifically, 5.0 g of intermediate pellet (C) and 20.0 g of distilled water were weighed out, and methanol was extracted from the intermediate pellet (C) by stirring in the distilled water for 3 hours. The extract was filtered to prepare the sample, and the methanol concentration was quantified using gas chromatography (GC) under the following conditions. • Gas chromatography conditions Evaporation chamber temperature: 160℃ (split ratio 10:1) Carrier gas: He (64.2 kPa) Column: Supel-Q PLOT (length 30m, inner diameter 0.32mm) Column temperature: 90°C (equilibrium time: 3 minutes) Temperature program: 90°C (hold for 10 minutes) → Heat increase by 10.0°C / min → 150°C (hold for 2 minutes) • Detector: FID Detector temperature: 160℃ Makeup gas: N2 (30 mL / min) H2 flow rate: 40mL / min Air flow rate: 400mL / min

[0079] Then, based on the values ​​quantified by gas chromatography (GC), the methanol content per intermediate pellet (C) was calculated using the following formula. • "Methanol content per pellet (%)" = "Methanol concentration of GC sample (GC analysis value) (%)" × "Weighed distilled water mass (g) + Weighed pellet volatile matter mass (g)" ÷ Weighed pellet mass (g) = "GC analysis value (%)" × "Weighed distilled water mass (g) + [Weighed pellet mass (g) × (Volatile content of pellets (%) / 100)]" ÷ Weighed pellet mass (g)

[0080] <Acetic acid content> The amount of free acetic acid present in the intermediate pellet (C) was measured by the following method. 10 g of intermediate pellet (C) was weighed into a plastic container, and 50 g of the adjustment solution was added thereto. The adjustment solution was prepared by dissolving 0.339 g of sodium bicarbonate and 0.336 g of sodium carbonate in 2000 g of pure water. The mixture of the intermediate pellet (C) and the preparation solution was stirred at 25°C for 1 hour to extract free acetic acid. The resulting extract was filtered, and the amount of free acetic acid in the filtrate was quantified by ion chromatography using an external standard method with a standard aqueous acetic acid solution. Next, based on the obtained ion chromatography analysis values, the amount of free acetic acid per unit of EVOH resin in the intermediate pellet (C) was calculated using the following formula (1). The intermediate pellet (C) and the preparation solution were weighed to three decimal places, and the amount of free acetic acid (acetic acid content) was calculated. In this specification, "free acetic acid" means acetic acid that is not covalently bonded to the EVOH resin. The amount of free acetic acid per EVOH resin (ppm) = P × (Q + R) / S ... (1) In equation (1), P, Q, R, and S are as follows: P: Analytical value obtained by ion chromatography (ppm) Q: What is the mass (g) of the weighed preparation solution? R: Mass of volatile matter in the weighed intermediate pellet (C) (g) (= Mass of weighed intermediate pellet (C) (g) × Volatile matter (%) / 100) S: This is the mass of resin content (g) in the weighed intermediate pellet (C) (= mass of weighed intermediate pellet (C) (g) × resin content (%) / 100).

[0081] The EVOH resin composition pellets of Examples 1-3 and Comparative Examples 1-3 were evaluated for color and thermal stability as follows. These results are shown in Table 1 below.

[0082] <Coloring Evaluation> EVOH resin composition pellets (1g) were used as samples, and their coloration was evaluated using a visual analyzer IRIS VA400 (Alphamos) under the following conditions. • Data analysis software: Alpha Soft V14.3 • Objective lens: 25mm (Basler) • Lighting Mode: Up and down lighting • Evaluation method: An EVOH resin composition pellet (1g) was used as a sample, placed in a tray inside the chamber of a visual analyzer, and a planar image of the entire sample was captured with a CCD camera. The color pattern of the sample was then evaluated by performing image processing using data analysis software. Then, the ratio of color numbers "1911" (R:120, G:120, B:120) and "1621" (R:104, G:88, B:88) among the obtained color patterns was evaluated. Since smaller color numbers indicate darker colors, a larger ratio of these color numbers indicates that heat-induced coloration is suppressed and that the thermal stability is high.

[0083] [Table 1]

[0084] Examples 1-3 all showed a small proportion of dark colors in the color evaluation and demonstrated excellent thermal stability. In contrast, as shown in Comparative Examples 1 and 2, both too much and too little acetic acid content in the EVOH resin of the intermediate pellet (C) resulted in a large proportion of dark colors in the color evaluation and poor thermal stability. Furthermore, in Comparative Example 3, where the methanol content of the intermediate pellet (C) of the EVOH resin composition brought into the drying process was too low, it was found that even though the EVOH resin in the intermediate pellet (C) contained a predetermined amount of organic acid, the proportion of dark-colored areas in the color evaluation was large, indicating poor thermal stability. Furthermore, similar results were obtained even when the drying process was carried out using explosion-proof equipment.

[0085] While the above embodiments illustrate specific forms of the present invention, these embodiments are merely illustrative and should not be interpreted restrictively. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention. [Industrial applicability]

[0086] This invention makes it possible to produce EVOH resin composition pellets with excellent thermal stability.

Claims

1. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets, comprising a pelletizing step and a drying step, In the pelletizing process described above, intermediate pellets of the ethylene-vinyl alcohol copolymer resin composition are produced. The volatile content of the intermediate pellets from the pelletizing process to the drying process is 5 to 90% by mass. The lower alcohol content of the intermediate pellets introduced into the drying process is 0.005 to 15% by mass. The intermediate pellets brought into the drying process contain an organic acid. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets, wherein the content of the organic acid is 10 to 3000 ppm relative to the mass of the ethylene-vinyl alcohol copolymer resin in the intermediate pellets brought into the drying step.

2. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to claim 1, comprising the step of washing the intermediate pellets produced in the pelletizing step with a solvent containing at least water.

3. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to claim 1, comprising the step of contacting the intermediate pellet produced in the pelletizing step with a solvent containing at least a lower alcohol.

4. The pelletizing process involves pelletizing a fluid ethylene-vinyl alcohol copolymer resin composition to produce intermediate pellets. The aforementioned fluid ethylene-vinyl alcohol copolymer resin composition contains an ethylene-vinyl alcohol copolymer resin and a solvent. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to claim 1, wherein the lower alcohol content in the solvent is 5% by mass or more.

5. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to claim 1, wherein the lower alcohol content of the intermediate pellets brought into the drying step is 0.03 to 9% by mass.

6. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to claim 1, wherein the drying step is carried out in a sealed space.

7. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets, comprising a pelletizing step and a drying step, In the pelletizing process described above, intermediate pellets of the ethylene-vinyl alcohol copolymer resin composition are produced. Multiple drying steps are provided, Of the multiple drying processes described above, the lower alcohol content of the intermediate pellets brought into the first drying process is 0.005 to 15% by mass. The aforementioned intermediate pellet contains an organic acid, A method for producing ethylene vinyl alcohol copolymer resin composition pellets, wherein the content of the organic acid is 10 to 3000 ppm relative to the mass of the ethylene vinyl alcohol copolymer resin in the intermediate PET.

8. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to claim 7, wherein the lower alcohol content of the intermediate pellets introduced into the first drying step is 0.03 to 9% by mass.

9. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to claim 7, wherein the first drying step is carried out in a sealed space.

10. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to claim 1 or 7, wherein the content of the organic acid is 30 to 800 ppm relative to the mass of the ethylene-vinyl alcohol copolymer resin in the intermediate pellets brought into the drying step.

11. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to claim 1 or 7, wherein the organic acid is acetic acid.

12. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets according to any one of claims 7 to 9, wherein the first drying step is carried out using explosion-proof equipment.

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