Pellet, manufacturing method thereof, and molding using the same

Abstract

To provide a pellet capable of stable fusion molding and suppressed formation of die build-up on fusion molding.SOLUTION: In a pellet including EVOH, and in an IR spectrum of a surface and a cut surface of the pellet at each temperature of a range of 1,120 cm-1 to 1,150 cm-1 measured in every 5°C from 30°C to 200°C, the pellet satisfies the formulae (1) to (3): 40≤Tcmin≤100 (1), 10≤Tcmin-Tsmin≤70 (2), -15<Tcmax-Tsmax<15 (3), wherein Tcmin (°C) is the minimum temperature where the IR spectrum of the pellet cut surface has the maximum point, Tsmin (°C) is the minimum temperature where the IR spectrum of the pellet surface has the maximum point, Tcmax (°C) is the maximum temperature where the IR spectrum of pellet cut surface has the maximum point, and Tsmax (°C) is the maximum temperature where the IR spectrum of the pellet surface has the maximum point.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to pellets containing an ethylene-vinyl alcohol copolymer, a method for producing the same, and molded articles using the same. [Background technology]

[0002] Ethylene-vinyl alcohol copolymer (hereinafter also referred to as "EVOH") has excellent gas barrier properties, transparency, oil resistance, anti-static properties, mechanical strength, etc., and is widely used as a material for molded products such as films, sheets, and containers. Molded products of EVOH are usually molded by melt molding. Therefore, EVOH is required to have stability during melt molding and excellent appearance properties (no discoloration such as yellowing, and the ability to obtain transparent molded products).

[0003] In order to improve the various properties required of EVOH, particularly appearance properties, various EVOH compositions containing acids such as carboxylic acids and phosphoric acids, and metal salts such as alkali metal salts and alkaline earth metal salts in appropriate contents have been proposed (Patent Document 1).It is said that these EVOH compositions improve appearance properties and stability during melt molding, and allow molded articles with excellent appearance to be obtained. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-146539 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the melt stability of the pellets described in Patent Document 1 during melt molding is still insufficient.

[0006] Furthermore, in recent years, with the diversification of layer configurations, there has been an increasing trend to produce multilayer structures by co-extruding an EVOH layer as the outermost layer, with the aim of achieving a synergistic effect of improving barrier properties through lamination with an inorganic vapor deposition layer. When EVOH is co-extruded as the outermost layer of a multilayer structure or when EVOH is extruded as a single-layer film, die buildup (i.e., deposits on the outer surface of the die lip) on the outer surface of the discharge port of the molten resin composition can easily cause bumps, streaks, and other defects in the film due to die buildup. Applying inorganic vapor deposition to a film with bumps or streaks is undesirable, as it is prone to defects and tends to reduce the adhesion of the inorganic vapor deposition layer. It has been found that the EVOH composition described in Patent Document 1 is insufficient in terms of die buildup and leaves room for improvement.

[0007] The present invention has been made in light of the above circumstances, and provides pellets that can be stably melt-molded and that suppress the occurrence of die build-up during melt-molding, and molded articles such as multilayer structures using the pellets. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have completed the present invention, which comprises the following items [1] to

[12] .

[0009] [1] A pellet containing EVOH, the surface and cut surface of the pellet are measured at 5°C intervals from 30°C to 200°C, and the 1120cm -1 ~1150cm -1 A pellet that satisfies equations (1) to (3) in the IR spectrum at each temperature in the range. 40≦Tcmin≦100 (1) 10≦Tcmin-Tsmin≦70 (2) -15 <Tcmax-Tsmax<15 (3) however, Tcmin (℃) is the minimum temperature at which the IR spectrum of the pellet cross section has a maximum point. Tsmin (℃) is the minimum temperature at which the IR spectrum of the pellet surface has a maximum. Tcmax (℃) is the maximum temperature at which the IR spectrum of the pellet cross section reaches a maximum point. Tsmax (°C) is the maximum temperature at which the IR spectrum of the pellet surface has a maximum point.

[0010] [2] The pellet according to [1], which satisfies formula (4). 0.95≦(Tsmax-Tsmin) / (Tcmax-Tcmin)<2.5 (4) [3] The pellet according to [1] or [2], which satisfies formula (5). 40≦Tcmax-Tcmin<130 (5) [4] The pellet according to any one of [1] to [3], wherein the EVOH has an ethylene unit content of 20 to 60 mol %. [5] The pellet according to any one of [1] to [4], wherein the EVOH has a degree of saponification of 99 mol % or more. [6] A molded article obtained by extrusion molding the pellets according to any one of [1] to [5]. [7] A molded article obtained by injection molding the pellets according to any one of [1] to [5]. [8] A molded article obtained by blow molding the pellets according to any one of [1] to [5]. [9] A multilayer structure obtained by co-extrusion molding the pellets according to any one of [1] to [5] and other thermoplastic resin pellets.

[10] The multilayer structure according to [9], wherein the layer formed by extrusion molding the pellets is the outermost layer.

[11] A method for producing pellets according to any one of [1] to [5], comprising: a first drying step (I) of introducing EVOH hydrous pellets having a moisture content W0 of 25 to 50% by mass into a dryer to reduce the moisture content W1 of the hydrous pellets to 5 to 25% by mass; a melt-kneading step (II) of introducing the water-containing pellets obtained in the first drying step (I) into an extruder and melt-kneading them; A cutting step (III) of cutting the molten resin discharged from the extruder to obtain wet pellets having a moisture content W2 of 5 to 25% by mass; a second drying step (IV) of drying the wet pellets obtained in the cutting step (III) to obtain pellets having a moisture content W3 of 0.5% by mass or less; A method for producing pellets, wherein the reduction in moisture content (W0-W1) in the first drying step (I) is 10 to 45% by mass.

[12] A method for producing a multilayer structure, comprising co-extrusion molding the pellets according to any one of [1] to [5] and other thermoplastic resin pellets. [Effects of the Invention]

[0011] The pellets of the present invention enable stable melt molding and suppress the occurrence of die build-up during melt molding. Therefore, the pellets are suitable for use in producing molded articles such as multilayer structures. The production method of the present invention is suitable for producing such pellets. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing IR spectra at each temperature obtained by measuring the cross section of the pellet of Example 1 at 5° C. intervals from 30° C. to 200° C. DETAILED DESCRIPTION OF THE INVENTION

[0013] The pellet of the present invention is a pellet containing EVOH, and the surface and cut surface of the pellet are measured at 5°C intervals from 30°C to 200°C using a 1120cm -1 ~1150cm -1 The pellets satisfy the formulas (1) to (3) in the IR spectrum at each temperature in the range of 100 to 150° C. The use of such pellets allows stable melt molding, and suppresses the occurrence of die buildup during melt molding. 40≦Tcmin≦100 (1) 10≦Tcmin-Tsmin≦70 (2) -15 <Tcmax-Tsmax<15 (3) however, Tcmin (℃) is the minimum temperature at which the IR spectrum of the pellet cross section has a maximum point. Tsmin (℃) is the minimum temperature at which the IR spectrum of the pellet surface has a maximum. Tcmax (℃) is the maximum temperature at which the IR spectrum of the pellet cross section reaches a maximum point. Tsmax (°C) is the maximum temperature at which the IR spectrum of the pellet surface has a maximum point.

[0014] The method for producing the pellets is not particularly limited, but preferably includes a first drying step (I) in which EVOH hydrous pellets with a moisture content W0 of 25-50% by mass are introduced into a dryer to reduce the moisture content W1 of the hydrous pellets to 5-25% by mass, a melt-kneading step (II) in which the hydrous pellets obtained in the first drying step (I) are introduced into an extruder and melt-kneaded, a cutting step (III) in which the molten resin discharged from the extruder is cut to obtain hydrous pellets with a moisture content W2 of 5-25% by mass, and a second drying step (IV) in which the hydrous pellets obtained in the cutting step (III) are dried to obtain pellets with a moisture content W3 of 0.5% by mass or less, and the moisture content reduction (W0 - W1) in the first drying step (I) is 10-45% by mass. It is more preferable to adjust the cooling method after cutting in the cutting step (III) (e.g., the temperature of the cooling water, the length of the line transporting the cooling water, etc.). By appropriately adjusting not only the moisture content in each step but also the cooling method in the cutting step (III), it becomes easier to produce pellets whose Tcmin (°C), Tsmin (°C), Tcmax (°C), and Tsmax (°C) satisfy the formulas (1) to (3).

[0015] First, the method for producing the EVOH used in the present invention will be described. EVOH is usually obtained by saponifying an ethylene-vinyl ester copolymer. The copolymerization of ethylene and vinyl ester may be any of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization. It may also be either continuous or batchwise. An example of the polymerization conditions for solution polymerization is shown below.

[0016] The solvent used is preferably an alcohol having a boiling point of 100° C. or less, from the viewpoints of solubility of the ethylene-vinyl ester copolymer and EVOH, ease of handling, and ability to efficiently replace alcohol with water. The boiling point is more preferably 80° C. or less, and even more preferably 70° C. or less. Examples of alcohols having a boiling point of 100° C. or less include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and t-butyl alcohol, with methanol being particularly preferred.

[0017] Examples of initiators that can be used in the polymerization include azonitrile initiators such as 2,2-azobisisobutyronitrile, 2,2-azobis-(2,4-dimethylvaleronitrile), 2,2-azobis-(4-methoxy-2,4-dimethylvaleronitrile), and 2,2-azobis-(2-cyclopropylpropionitrile), and organic peroxide initiators such as isobutyryl peroxide, cumyl peroxy neodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxy neodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide.

[0018] Examples of vinyl esters include fatty acid vinyl esters such as vinyl acetate, vinyl propionate, and vinyl pivalate, with vinyl acetate being preferred. In addition to ethylene and vinyl esters, monomers copolymerizable therewith, such as α-olefins such as propylene, butylene, isobutylene, pentene, hexene, α-octene, and α-dodecene, 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4- Acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy-1-hexene Polymerization can also be performed in the presence of small amounts of alkenes having ester groups such as 1,3-diacetoxy-2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid, as well as their anhydrides, salts, and mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallylsulfonic acid, or their salts; vinyl silanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, and γ-methacryloxypropylmethoxysilane; alkyl vinyl ethers; vinyl ketones; N-vinylpyrrolidone; vinyl chloride; and vinylidene chloride. The content of other monomer units in the EVOH other than ethylene, vinyl ester, and vinyl alcohol is preferably 20 mol% or less, and in some cases, 10 mol% or less, 5 mol% or less, 3 mol% or less, 1 mol% or less, or 0.1 mol% or less may be preferred. The EVOH may not contain the other monomer units.

[0019] The polymerization conditions are preferably as follows: (1) Temperature: preferably 20 to 90°C, more preferably 40 to 70°C. (2) Time (average residence time in the case of a continuous system): preferably 2 to 15 hours, more preferably 3 to 11 hours. (3) Polymerization rate: preferably 10 to 90%, more preferably 30 to 80%, based on the charged vinyl ester. (4) Resin content in the solution after polymerization: preferably 5 to 85% by mass, more preferably 20 to 70% by mass.

[0020] After polymerization for a predetermined time has reached a predetermined polymerization rate, a polymerization inhibitor is added as necessary, unreacted ethylene gas is evaporated and removed, and then unreacted vinyl ester is purged. For example, a method for purging the unreacted vinyl ester may be employed in which the polymerization solution from which ethylene has been removed is continuously fed at a constant rate from the top of a column packed with Raschig rings, vapor of an organic solvent, preferably an alcohol having a boiling point of 100°C or less, and most preferably methanol, is blown into the bottom of the column, a mixed vapor of the organic solvent and unreacted vinyl ester is distilled from the top of the column, and the copolymer solution from which unreacted vinyl ester has been removed is taken out from the bottom of the column.

[0021] An alkali catalyst is added to the copolymer solution from which the unreacted vinyl ester has been removed, and the vinyl ester component in the copolymer is saponified. The saponification method can be either continuous or batchwise. Examples of alkali catalysts that can be used include sodium hydroxide, potassium hydroxide, and alkali metal alcoholates. Methanol is preferred as the solvent for saponification. For example, the saponification conditions are as follows: (1) Concentration of ethylene-vinyl ester copolymer in the solution: 10 to 50% by mass (2) Reaction temperature: 30 to 150°C (3) Amount of catalyst used: 0.005 to 0.6 equivalents (per vinyl ester component) (4) Time (average residence time in the case of continuous type): 10 minutes to 6 hours

[0022] Generally, when saponification is carried out in a continuous system, methyl acetate produced by saponification can be removed more efficiently, and therefore a resin with a higher degree of saponification can be obtained with a smaller amount of catalyst than in a batch system. Furthermore, in the case of a continuous system, saponification must be carried out at a higher temperature to prevent the precipitation of EVOH produced by saponification. Therefore, in a continuous system, it is preferable to use a reaction temperature and catalyst amount within the following ranges: Reaction temperature: 70 to 150°C. Amount of catalyst used: 0.005 to 0.1 equivalents (per vinyl ester component).

[0023] The saponification degree of the EVOH used in the present invention is preferably 95 mol% or more. A saponification degree of 95 mol% or more further improves the gas barrier properties and thermal stability of the resulting molded article. The saponification degree is more preferably 98 mol% or more, even more preferably 99 mol% or more, and even more preferably 99.5 mol% or more. On the other hand, the saponification degree may be 100 mol% or less, 99.97 mol% or less, or 99.94 mol% or less. Note that the saponification degree does not substantially change in any of the first drying step (I), the melt-kneading step (II), the cutting step (III), and the second drying step (IV). Therefore, the saponification degree of the EVOH may be considered to be the same in the EVOH hydrous pellets introduced in the first drying step (I) and in the pellets after the second drying step (IV).

[0024] The ethylene unit content of the EVOH used in the present invention is preferably 20 to 60 mol%. When the ethylene unit content is 20 mol% or more, the melt moldability of the resulting pellets is further improved. The ethylene unit content is more preferably 24 mol% or more, and even more preferably 28 mol% or more. On the other hand, an ethylene unit content of 60 mol% or less improves the gas barrier properties of the EVOH. The ethylene unit content is more preferably 50 mol% or less, and even more preferably 45 mol% or less. Since the ethylene unit content does not substantially change in any of the first drying step (I), the melt-kneading step (II), the cutting step (III), and the second drying step (IV), the ethylene unit content of the EVOH may be considered to be the same in the EVOH water-containing pellets introduced in the first drying step (I) and in the pellets after the second drying step (IV).

[0025] The saponification process yields a solution containing EVOH. Hereinafter, the EVOH-containing solution will be referred to simply as the EVOH solution. However, the term "EVOH solution" also includes solutions that are not completely homogeneous and have undergone phase separation, resulting in a paste-like structure. A post-treatment method for the EVOH solution after the saponification reaction involves supplying a mixed vapor of solvent and water from the bottom of a tower vessel and supplying the EVOH solution from a position above the supply position of the mixed vapor. This replaces a portion of the solvent in the supplied EVOH solution with water, resulting in a highly concentrated EVOH solution. The EVOH concentration in the EVOH solution supplied to the tower vessel is preferably 15 to 50% by mass, more preferably 25 to 40% by mass. It is also preferable that the ratio of the supply rate of the EVOH solution to the supply rate of the mixed vapor (solution supply rate / steam supply rate) be 100 / 400 to 100 / 8 by mass. Furthermore, it is preferable that the water content in the mixed vapor be 20 to 70% by mass. The solvent used for the mixed vapor is preferably an alcohol having a boiling point of 130° C. or less, and examples of such alcohol include alcohols such as methanol, ethanol, propanol, butanol, etc. Alcohols having a boiling point of 100° C. or less are more preferred, and among these, methanol is preferred because it is easily available, inexpensive, has a low boiling point, and is easy to handle.

[0026] The high-concentration EVOH solution thus obtained typically contains 50 parts by mass or more of an alcohol with a boiling point of 100°C or less per 100 parts by mass of EVOH. The alcohol content is preferably 1,000 parts by mass or less, and more preferably 500 parts by mass or less. By keeping the alcohol content within this range, the fluidity of the EVOH solution is ensured and efficient resin production becomes possible. The alcohol used here is preferably methanol. The EVOH solution may also contain water together with the alcohol, and preferably contains 10 to 500 parts by mass of water.

[0027] A suitable method for obtaining the hydrous EVOH pellets to be subjected to the first drying step (I) is, for example, a method in which the high-concentration aqueous EVOH solution obtained as described above is subjected to the following steps (A), (B), and (C) in this order. Specifically, the hydrous EVOH pellets used in the present invention are obtained by the following steps: (A) introducing an EVOH solution containing 100 parts by mass of EVOH and 50 parts by mass or more of an alcohol having a boiling point of 100°C or less into a vessel, contacting the EVOH with steam in the vessel to extract the alcohol together with the steam, and extracting the hydrous EVOH from the vessel; (B) feeding the hydrous EVOH into an extruder, melt-kneading the extruder, and then discharging the copolymer from the extruder; and (C) cutting the hydrous EVOH discharged from the extruder. This method not only efficiently replaces the alcohol in the EVOH solution with water, but also facilitates adjustment of the water content and temperature of the EVOH.

[0028] In step (A), the method for contacting the EVOH solution introduced into the vessel with water vapor within the vessel is not particularly limited, and may be either a continuous or batch method. The vessel shape is also not particularly limited, but a tower-type vessel is preferred for the continuous method, and a tank-type vessel is preferred for the batch method. Considering production efficiency, the continuous method is industrially preferred. Examples of tower-type vessels include plate towers such as perforated plate towers and bubble cap towers, and packed towers containing ring-type packing.

[0029] It is preferable to supply steam from the bottom of a tower vessel and supply the EVOH solution from a position above the steam supply position, thereby extracting the solvent (alcohol) present in the supplied EVOH solution together with the steam, and extracting a water-containing EVOH having a water content of 10 to 90% by mass from the vessel. The amount of steam introduced is preferably 0.3 to 30 times the amount of the EVOH solution introduced, expressed by mass ratio.

[0030] The alcohol vapor and water vapor discharged from the top of the column are condensed in a condenser and recovered as an aqueous alcohol solution, which can be purified and reused as necessary. The EVOH solution comes into direct contact with water vapor in the vessel, gradually reducing the solvent (alcohol) content. During this time, the EVOH remains in a swollen, paste-like state, allowing it to be discharged from the vessel while maintaining its fluidity and without gelation. EVOH dissolves in a methanol / water mixed solvent at atmospheric pressure, for example, at temperatures of approximately 60 to 70°C, but does not dissolve in water alone. However, in the presence of pressurized water vapor at temperatures above 90°C, for example, EVOH can maintain its fluidity even when it contains essentially only water. The temperature inside the vessel is preferably 100 to 150°C, and the pressure is preferably 0.1 to 0.6 MPa.

[0031] After the EVOH solution is brought into contact with water vapor as described above, the fluid, water-containing EVOH is discharged from the vessel. In step (B), the water-containing EVOH discharged from the vessel is fed to an extruder, where it is melt-kneaded, and the copolymer is then discharged from the extruder.

[0032] In step (B), the water content of the hydrous EVOH introduced into the extruder is 10 to 90% by mass. The content of alcohol having a boiling point of 100°C or less in the hydrous EVOH is preferably 10% by mass or less. The hydrous EVOH may also contain, for example, alkali metal salts, such as residues of the catalyst used in the saponification step, in an amount of about 0.1 to 5% by mass in terms of metal, as well as by-product salts and other impurities.

[0033] The extruder used in step (B) may be a single-screw or multi-screw extruder, but a twin-screw extruder is preferred. The L / D of the extruder is preferably 8 to 30. The cylinder of the extruder is provided with an inlet for the hydrous EVOH, through which the hydrous EVOH is introduced. The screw disposed inside the cylinder rotates, melting and kneading the hydrous EVOH, and the hydrous EVOH is then discharged from the discharge port at the tip of the cylinder. At this time, it is preferable to provide a dewatering slit in the cylinder to remove moisture.

[0034] The water content of the water-containing EVOH discharged from the extruder is preferably 25 to 50% by mass. When the water content is 25% by mass or more, the melt viscosity of the water-containing EVOH decreases, tending to make it easier to discharge the water-containing EVOH. The water content is more preferably 30% by mass or more. On the other hand, when the water content is 50% by mass or less, the melt viscosity of the water-containing EVOH increases, tending to make it easier to prevent the EVOH from leaking. The water content is more preferably 40% by mass or less.

[0035] Following step (B), in step (C), the hydrous EVOH discharged from the extruder is cut to obtain hydrous EVOH pellets. The method for this is not particularly limited, and examples include a method in which the hydrous EVOH (molten state) discharged from the extruder is directly cut, or a method in which the hydrous EVOH discharged from the extruder is extruded into a coagulation liquid in the form of strands, solidified, and then cut. Of these, the method of directly cutting the hydrous EVOH is preferred. Methods for directly cutting the hydrous EVOH discharged from the extruder include hot cutting and underwater cutting. When the hydrous EVOH is extruded in the form of strands, solidified, and then cut, cylindrical pellets are obtained, while when the hydrous EVOH is directly cut in the molten state, spherical (or nearly spherical) pellets are obtained. The size of the produced hydrous EVOH pellets can be, for example, a diameter of 1 mm to 10 mm for spherical (or nearly spherical) pellets, or a diameter of 1 mm to 10 mm and a length of 1 mm to 10 mm for cylindrical pellets. The hydrous EVOH pellets obtained in this manner are subjected to the first drying step (I).

[0036] Another method for obtaining the EVOH hydrous pellets used in the present invention is to extrude the high-concentration EVOH aqueous solution from a nozzle into a coagulation liquid in the form of strands, coagulate them in a water bath, and then cut them. Water is used as the coagulation liquid, but a small amount of alcohol may be included. The coagulated strands are cut into pellets with a cutter. A strand cutter is preferably used as the cutter. The size of the obtained pellets can be, for example, 1 mm to 10 mm in diameter and 1 mm to 10 mm in length for cylindrical pellets, or 1 mm to 10 mm in diameter for spherical pellets. The EVOH hydrous pellets obtained in this manner can also be subjected to the first drying step (I).

[0037] The EVOH hydrous pellets obtained as described above contain an alkali catalyst, by-product salts such as sodium acetate and potassium acetate, and other impurities, which may be removed by neutralization and washing as necessary. In this case, some catalyst residues such as sodium acetate may remain in the EVOH hydrous pellets.

[0038] In the first drying step (I), the thus obtained EVOH hydrous pellets having a moisture content W0 of 25 to 50% by mass are introduced into a dryer, where the moisture content W1 of the pellets is reduced to 5 to 25% by mass. The EVOH hydrous pellets introduced into the dryer are porous and dry quickly, allowing them to be dried at a low drying temperature in a short time.

[0039] The moisture content W0 when introduced into the dryer is 25 to 50% by mass. When the moisture content W0 is 25% by mass or more, the color of the obtained pellets becomes good, and it is preferably 30% by mass or more. When the moisture content W0 is less than 25% by mass, the average residence time can be shortened even if the pellets are directly subjected to the melt-kneading step (II), so there is little point in adopting the first drying step (I). On the other hand, when the moisture content W0 exceeds 50% by mass, there is a risk of the pellets sticking in the dryer and the drying efficiency may decrease. The moisture content W0 is preferably 45% by mass or less.

[0040] The dryer used in the first drying step (I) is not particularly limited as long as it can dry the pellets while maintaining their shape. A hot air dryer or the like can be used. The drying method may be fluidized drying using a fluidized dryer or static drying using a static dryer, but fluidized drying is preferred to prevent the pellets from sticking together. These methods may also be used in combination, or a method may be used in which the pellets are first dried using fluidized drying and then dried using static drying.

[0041] The drying temperature is not particularly limited, but is preferably 40 to 150°C for 0.1 to 15 hours. The EVOH hydrous pellets introduced into the dryer can be dried quickly even at low temperatures, and thermal degradation can be suppressed. The drying temperature is more preferably 50°C or higher, and even more preferably 60°C or higher. The drying temperature is more preferably 120°C or lower, even more preferably 100°C or lower, and optimally 90°C or lower. The drying time varies depending on the drying temperature and the target moisture content, but is more preferably 0.2 hours or longer, even more preferably 0.5 hours or longer. It is also more preferably 5 hours or shorter, and even more preferably 3 hours or shorter. Drying may be performed in air or in an inert gas such as nitrogen. When drying in an inert gas, thermal degradation is less likely to occur even if the drying temperature is set higher.

[0042] The moisture content W1 of the EVOH hydrous pellets obtained by drying in the first drying step (I) is 5 to 25% by mass, and the decrease in moisture content (W0-W1) in this step is 10 to 45% by mass. If the moisture content W1 is less than 5% by mass, the resin temperature in the extruder in the melt-kneading step (II) becomes too high, and the hydrous EVOH discharged from the extruder is likely to foam. The moisture content W1 is preferably 7% by mass or more, more preferably 10% by mass or more. On the other hand, if the moisture content W1 exceeds 25% by mass, the moisture content in the extruder in the melt-kneading step (II) becomes too high, causing leakage of EVOH through the dewatering slit and foaming of the discharged EVOH composition. The moisture content W1 is preferably 22% by mass or less, more preferably 18% by mass or less. Furthermore, if the decrease in moisture content (W0-W1) is less than 10% by mass, there is little point in providing the first drying step (I). The decrease in moisture content (W0-W1) is preferably 15% by mass or more, more preferably 20% by mass or more. On the other hand, if the decrease in moisture content (W0-W1) exceeds 45% by mass, it is difficult to dry the pellets in a short time while maintaining their shape. The decrease in moisture content (W0-W1) is preferably 35% by mass or less, more preferably 30% by mass or less. Furthermore, when the moisture content W1 and the decrease in moisture content (W0-W1) are within the above ranges, it becomes easier to adjust the moisture content W2 of the EVOH hydrous pellets to be subjected to the second drying step (IV) within a predetermined range, which in turn makes it easier to obtain pellets that satisfy the formulas (1) to (3).

[0043] In the melt-kneading step (II), the water-containing pellets obtained in the first drying step (I) are introduced into an extruder, and an aqueous solution or aqueous dispersion containing additives is added as needed, followed by melt-kneading. The additives may be dissolved in water in the form of an aqueous solution or a dispersion in water. For example, an aqueous solution containing at least one additive selected from carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts may be used.

[0044] The carboxylic acid contained in the aqueous solution is not particularly limited. Examples include acetic acid, lactic acid, oxalic acid, succinic acid, benzoic acid, and citric acid, with carboxylic acids having four or fewer carbon atoms being preferred. Among these, acetic acid is preferred from the standpoints of cost and availability. When the pellets of the present invention contain a carboxylic acid, the content is preferably 10 to 5,000 ppm. The carboxylic acid content is more preferably 30 ppm or more, and even more preferably 50 ppm or more. The carboxylic acid content is more preferably 1,000 ppm or less, and even more preferably 500 ppm or less. The content of components other than EVOH in the pellets of the present invention is preferably 30% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less.

[0045] Examples of boron compounds contained in the aqueous solution include, but are not limited to, boric acids, boric acid esters, borate salts, and boron hydrides. Specific examples of boric acids include orthoboric acid, metaboric acid, and tetraboric acid. Examples of borate esters include triethyl borate and trimethyl borate. Examples of borates include alkali metal salts, alkaline earth metal salts, and borax of the above-mentioned various boric acids. Among these compounds, orthoboric acid (hereinafter simply referred to as boric acid) is preferred. When the pellets of the present invention contain a boron compound, the content thereof is preferably 10 to 2000 ppm, more preferably 50 to 1000 ppm, calculated as boron.

[0046] Examples of the phosphate compound contained in the aqueous solution include various acids such as phosphoric acid and phosphorous acid, and their salts. The phosphate may be contained in the form of any of monophosphate, diphosphate, and triphosphate, and the cation species is not particularly limited, but alkali metal salts and alkaline earth metal salts are preferred. Among these, it is preferable to add the phosphate compound in the form of sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, or dipotassium hydrogen phosphate. When the pellet of the present invention contains a phosphate compound, the content thereof is preferably 1 to 1,000 ppm in terms of phosphate radical.

[0047] Examples of alkali metal salts contained in the aqueous solution include aliphatic carboxylates, aromatic carboxylates, and phosphates. Examples include sodium acetate, potassium acetate, sodium phosphate, lithium phosphate, sodium stearate, potassium stearate, and the sodium salt of ethylenediaminetetraacetic acid. Among these, sodium acetate, potassium acetate, and sodium phosphate are preferred. When the pellets of the present invention contain an alkali metal salt, the content thereof is preferably 5 to 5,000 ppm, calculated as the alkali metal element, more preferably 20 to 1,000 ppm, and even more preferably 30 to 750 ppm.

[0048] Examples of alkaline earth metal salts contained in the aqueous solution include magnesium salts, calcium salts, barium salts, and beryllium salts, with magnesium salts and calcium salts being particularly preferred. The anion species of the alkaline earth metal salt is not particularly limited, but acetate and phosphate are preferred. When the pellets of the present invention contain an alkaline earth metal salt, the content thereof is preferably 10 to 1000 ppm, more preferably 20 to 500 ppm, calculated as the metal.

[0049] On the other hand, the dispersion to be added to the hydrous EVOH may be a colloid of inorganic particles such as colloidal silica, colloidal titania, or colloidal zirconia, or a dispersion of inorganic particles with a larger particle size.

[0050] The extruder used in the melt-kneading step (II) may be a single-screw extruder or a multi-screw extruder, but a twin-screw extruder is preferred. The L / D of the extruder is preferably 10 to 55, more preferably 20 to 47. The cylinder of the extruder is provided with an inlet for EVOH hydrous pellets, through which the EVOH hydrous pellets are introduced, melt-kneaded by the rotation of a screw disposed inside the cylinder, and discharged from a discharge port at the tip of the cylinder. The screw configuration inside the cylinder is not particularly limited, but it is preferable to provide a full-flight screw and a partial reverse-flight screw to thoroughly knead the molten resin.

[0051] The resin temperature in the extruder is preferably 120 to 210°C. If the resin temperature is too low, the screw torque may become too large, so the resin temperature is more preferably 140°C or higher, and even more preferably 150°C or higher. On the other hand, if the resin temperature is too high, the resulting pellets tend to foam, and if melt-kneaded for a long period of time, coloring or gel formation may occur. Therefore, the resin temperature is more preferably 200°C or lower, and even more preferably 190°C or lower.

[0052] The extruder used in the melt-kneading step (II) may be provided with an additive introduction section downstream of the pellet introduction port. An aqueous solution or dispersion containing additives is injected from the additive introduction section into the molten, water-containing EVOH (molten resin) and melt-kneaded. When the aqueous solution or dispersion is added, the amount added is preferably 1 to 30 parts by mass per 100 parts by mass of the dry mass of EVOH. If the amount added is less than 1 part by mass, uniform blending may be difficult; more preferably, it is 2 parts by mass or more, and even more preferably, it is 5 parts by mass or more. On the other hand, if the amount added exceeds 30 parts by mass, the water content of the water-containing EVOH becomes too high, making it more likely to leak from the dewatering slit and increasing the energy required for drying. Therefore, the amount added is more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.

[0053] In the melt-kneading step (II), it is preferable to discharge liquid water or water vapor from at least one location in the extruder. This can reduce the moisture content of the water-containing EVOH in the extruder. The method for discharging liquid water or water vapor is not particularly limited, and a dewatering slit or vacuum vent can be used. In the melt-kneading step of the present invention, the moisture content of the molten resin discharged from the extruder is not particularly low, so a vacuum vent is often unnecessary, and a dewatering slit is preferably used. Either water vapor or liquid water can be discharged from the dewatering slit, but discharging water vapor is preferred from the viewpoint of removing the latent heat of vaporization and removing heat. Furthermore, when an aqueous solution or aqueous dispersion is added in the melt-kneading step (II) of the present invention, it is preferable to discharge liquid water or water vapor from a position downstream of the position where the aqueous solution or aqueous dispersion is added. This can effectively reduce the moisture content of the discharged molten resin and suppress foaming.

[0054] In the cutting step (III), the molten resin discharged from the extruder is cut to obtain hydrous EVOH pellets having a moisture content W2 of 5 to 25% by mass. The cutting method is not particularly limited, and examples include a method in which the molten hydrous EVOH (molten resin) discharged from the extruder is directly cut, or a method in which the hydrous EVOH discharged from the extruder is extruded into a coagulation liquid in the form of a strand, solidified, and then cut. Of these, the method of directly cutting the hydrous EVOH is preferred. Methods for directly cutting the hydrous EVOH discharged from the extruder include a hot-cut method and an underwater cutting method. When the hydrous EVOH is extruded in the form of a strand, solidified, and then cut, cylindrical pellets are obtained, while when the hydrous EVOH is directly cut in the molten state, spherical (or nearly spherical) pellets are obtained. The size of the produced hydrous EVOH pellets can be, for example, 1 mm to 10 mm in diameter if spherical (or nearly spherical), or 1 mm to 10 mm in diameter and 1 mm to 10 mm in length if cylindrical.

[0055] Not only can the moisture content be kept within a predetermined range in each step, but also by adjusting the cooling method after cutting in the cutting step (III) (such as the temperature of the cooling water and the length of the line along which the cooling water is transported), it becomes easier to obtain pellets that satisfy the above formulas (1) to (3). The temperature of the cooling water is preferably 0 to 50°C, more preferably 5 to 40°C, and even more preferably 10 to 30°C. The cut EVOH hydrous pellets are appropriately cooled by being transported along the line along with the cooling water. The length of such a line is preferably 1 to 20 m, more preferably 2 to 10 m, and even more preferably 3 to 8 m. However, the cooling method is not limited to the above, as long as pellets that satisfy the above formulas (1) to (3) can be obtained.

[0056] The moisture content W2 of the EVOH hydrous pellets obtained in the cutting step (III) is 5 to 25% by mass. By setting the moisture content W2 to 5% by mass or more, the temperature of the molten resin in the melt-kneading step (II) can be lowered, thereby suppressing thermal degradation of the EVOH during melt-kneading. Furthermore, if the moisture content W2 is 5% by mass or more, it is not necessary to provide a vacuum vent in the extruder to reduce the moisture content, thereby simplifying the equipment. On the other hand, by setting the moisture content W2 to 25% by mass or less, leakage of EVOH from the dewatering slit can be suppressed even when the extruder is operated at high speed, thereby improving productivity. Furthermore, foaming of the obtained pellets can be suppressed, and energy consumption in the subsequent second drying step (IV) can also be reduced. Furthermore, by setting the moisture content W2 within the above range, pellets satisfying the above formulas (1) to (3) can be easily obtained.

[0057] The EVOH hydrous pellets thus obtained in the cutting step (III) are subjected to the second drying step (IV). The dryer used in the second drying step (IV) is not particularly limited as long as it can dry the pellets while maintaining their shape. A hot air dryer or the like can be used. The drying method may be a fluidized drying method using a fluidized dryer or a static drying method using a static dryer, or a combination of these methods may be used. A method that first dries at a relatively low temperature using a fluidized dryer, and then dries at a high temperature using a static dryer is preferably used.

[0058] Since pellets satisfying the above formulas (1) to (3) can be more easily obtained, the drying temperature is preferably 50 to 150°C, and the drying time is preferably 1 hour to 7 days. When both fluidized drying and static drying are employed, the drying temperatures of both methods are included in the above temperature range, and the total drying time of both methods is included in the above drying time. The drying temperature is more preferably 60°C or higher, even more preferably 70°C or higher, and particularly preferably 80°C or higher. The drying temperature is more preferably 140°C or lower, even more preferably 130°C or lower, and particularly preferably 120°C or lower. The drying time is more preferably 2 hours or longer, even more preferably 5 hours or longer. It is also more preferably 5 days or shorter, and even more preferably 3 days or shorter. When both fluidized drying and static drying are employed, the drying temperature of the latter method is preferably 5°C or higher, and more preferably 10°C or higher, than the drying temperature of the former method. Drying may be performed in air or in an inert gas such as nitrogen. When drying is performed in an inert gas, thermal degradation is unlikely to occur even if the drying temperature is set high.

[0059] The moisture content W3 of the EVOH-containing pellets of the present invention obtained by drying in the second drying step (IV) is preferably 0.5% by mass or less. When the moisture content W3 is 0.5% by mass or less, problems such as foaming do not occur even if the pellets are subjected to melt molding without further drying. The moisture content W3 is more preferably 0.4% by mass or less, and even more preferably 0.3% by mass or less. Meanwhile, the moisture content W3 is usually 0.01% by mass or more, and reducing the moisture content W3 more than necessary only increases energy consumption.

[0060] The pellets of the present invention thus obtained are measured on their surfaces and cut surfaces at 5°C intervals from 30°C to 200°C using a 1120cm -1 ~1150cm -1 In the IR spectrum at each temperature in the range, the formulas (1) to (3) are satisfied. 40≦Tcmin≦100 (1) 10≦Tcmin-Tsmin≦70 (2) -15 <Tcmax-Tsmax<15 (3) however, Tcmin (℃) is the minimum temperature at which the IR spectrum of the pellet cross section has a maximum point. Tsmin (℃) is the minimum temperature at which the IR spectrum of the pellet surface has a maximum. Tcmax (℃) is the maximum temperature at which the IR spectrum of the pellet cross section reaches a maximum point. Tsmax (°C) is the maximum temperature at which the IR spectrum of the pellet surface has a maximum point.

[0061] The IR spectrum of the pellet is measured as follows. In the present invention, the IR spectrum of the surface and the cut surface of the pellet is measured by the ATR method (attenuated total reflection method). The wave number range for measurement is 1120 cm -1 ~1150cm -1 The range is set to include the above. Measurements are performed at 5°C intervals from 30°C to 200°C, and an IR spectrum is obtained at each temperature. Specific measurement conditions for the IR spectrum of the pellet and a method for determining whether or not there is a maximum point are those described in the Examples.

[0062] FIG. 1 shows the IR spectra at each temperature obtained by measuring the cross section of a pellet in Example 1 described later from 30°C to 200°C at 5°C intervals. In the present invention, the IR spectrum of the pellet cross section measured at each temperature is -1 ~1150cm -1 The lowest temperature with a maximum point in this range is Tcmin (°C), and the highest temperature is Tcmax (°C). In Figure 1, IR spectrum 1 is one measured at 65°C or below. Thus, the IR spectrum measured at 65°C or below has a wavenumber of 1120 cm -1 ~1150cm -1 IR spectrum 2 is an IR spectrum at 70 °C and has no maximum at 1120 cm -1 ~1150cm -1 In other words, 70°C is the minimum temperature Tcmin at which the IR spectrum of the cross section of the pellet in Example 1 has a maximum. The IR spectrum of the cross section of the pellet in the range of 75 to 165°C also has a maximum at 1120cm. -1 ~1150cm -1 IR spectrum 3 is one of those measured at 170°C or higher. Thus, the IR spectrum of the cross section of the pellet measured at 170°C or higher has a maximum point in the range of 1120cm. -1 ~1150cm -1 In other words, at 165°C, the IR spectrum of the pellet cut surface of Example 1 is 1120 cm -1 ~1150cm -1 is the maximum temperature Tcmax that has a maximum point in the range.

[0063] The IR spectrum of the pellet surface at each temperature was measured at 1120 cm -1 ~1150cm -1 The minimum temperature Tsmin (°C) and maximum temperature Tsmax (°C) having maximum points in this range are also determined in the same manner as the minimum temperatures Tcmin (°C) and Tcmax (°C) in the IR spectrum of the pellet cross section.

[0064] In the present invention, the IR spectrum of the cut surface of the pellet at each temperature is 1120 cm -1 ~1150cm -1 The minimum temperature Tcmin having a maximum point in this range must satisfy the above formula (1). When Tcmin is 40 to 100°C, the melting initiation temperature inside the pellet increases and the distribution of the melting temperature throughout the pellet becomes smaller, thereby reducing uneven melting in the extruder and stabilizing fluidity. The minimum temperature Tcmin is preferably 48°C or higher, more preferably 55°C or higher, and even more preferably 65°C or higher, and may be 75°C or higher, 85°C or higher, or 90°C or higher. The minimum temperature Tcmin may be 90°C or lower.

[0065] In the present invention, the lowest temperature Tcmin at which the IR spectrum of the cut surface of the pellet at each temperature has a maximum and the lowest temperature Tsmin at which the IR spectrum of the pellet surface at each temperature has a maximum must satisfy the above formula (2). When the difference (Tcmin - Tsmin) is 10 to 70°C, die buildup is less likely to occur when the resulting pellets are molded. The difference (Tcmin - Tsmin) is preferably 15°C or more, more preferably 25°C or more, and even more preferably 35°C or more, and may be 45°C or more, 50°C or more, or 55°C or more. On the other hand, the difference (Tcmin - Tsmin) is preferably 65°C or less, and may be 55°C or less.

[0066] In the present invention, the difference (Tcmax - Tsmax) between the maximum temperature Tcmax at which the IR spectrum of the cut surface of the pellet at each temperature has a maximum and the maximum temperature Tsmax at which the IR spectrum of the pellet surface at each temperature has a maximum must satisfy the above formula (3). When the difference (Tcmax - Tsmax) is more than -15°C and less than 15°C, die buildup is less likely to occur when the resulting pellets are molded. The difference (Tcmax - Tsmax) is preferably -10°C or more, more preferably -5°C or more, and even more preferably -1°C or more. On the other hand, the difference (Tcmax - Tsmax) is preferably 10°C or less, more preferably 7°C or less, even more preferably 4.5°C or less, and particularly preferably 3.5°C or less.

[0067] The present inventors have conducted extensive research to improve the melt stability of EVOH-containing pellets, and have surprisingly found that pellets satisfying the above formulas (1) to (3) have excellent melt stability. The reason for this is unclear, but the following is thought to be the case. -1 ~1150cm -1 The peak with a maximum at this point is known as the crystalline band of EVOH and serves as an indicator of crystallinity. It has been known that the crystallinity at low temperatures differs between the interior and exterior of EVOH-containing pellets. However, the crystalline state upon heating and melting and its effect on melt-formability were unknown. Therefore, the inventors measured IR spectra of the cross-section and surface of pellets at 30 to 200°C to confirm the relationship between the crystalline state of the interior and exterior of the pellets and melt-formability. As a result, it was found that the crystalline state of the interior and exterior of pellets upon heating and melting differs depending on the pellet manufacturing method. Furthermore, the inventors discovered that pellets manufactured by a predetermined method and satisfying the above formulas (1) to (3) have a narrow melting temperature distribution and are less likely to experience melting unevenness inside the extruder, resulting in stable fluidity. Furthermore, the exterior of the pellets is relatively less likely to melt, shortening the contact time with the extruder wall, thereby suppressing die buildup and enabling the production of molded products with good appearance and high barrier properties.

[0068] In the present invention, it is preferable that the minimum temperature Tcmin and maximum temperature Tcmax at which the IR spectrum of the cut surface of the pellet at each temperature has a maximum, and the minimum temperature Tsmin and maximum temperature Tsmax at which the IR spectrum of the pellet surface at each temperature has a maximum, satisfy the following formula (4). This further improves the appearance of molded articles obtained using the pellets. "(Tsmax - Tsmin) / (Tcmax - Tcmin)" is more preferably 1 or more, and even more preferably 1.05 or more. Meanwhile, "(Tsmax - Tsmin) / (Tcmax - Tcmin)" is more preferably 2.3 or less. 0.95≦(Tsmax-Tsmin) / (Tcmax-Tcmin)<2.5 (4)

[0069] In the present invention, it is preferable that the minimum temperature Tcmin and maximum temperature Tcmax at which the IR spectrum of the cut surface of the pellet has a maximum point satisfy the following formula (5). This further reduces the occurrence of die buildup when the resulting pellets are melt-molded. The difference (Tcmax - Tcmin) is more preferably 50°C or higher, and even more preferably 55°C or higher. On the other hand, the difference (Tcmax - Tcmin) is more preferably 120°C or lower, even more preferably 115°C or lower, even more preferably 100°C or lower, particularly preferably 90°C or lower, and most preferably 80°C or lower. 40≦Tcmax-Tcmin<130 (5)

[0070] The pellet size may be, for example, 0.8 mm to 9.8 mm in diameter if spherical (or approximately spherical), or 0.8 mm to 9.8 mm in diameter and 0.8 mm to 9.8 mm in length if cylindrical.

[0071] From the viewpoint of improving melt moldability, the melt flow rate (MFR) of the pellets measured in accordance with the method described in JIS K7210 (2014) (210°C, under a load of 2160 g) is preferably 0.1 to 30 g / 10 min, more preferably 0.3 to 25 g / 10 min, and even more preferably 0.5 to 20 g / 10 min.

[0072] A preferred embodiment of the present invention is a molded article obtained by melt-molding the pellets of the present invention. Examples of such molded articles include films, sheets, tubes, bags, bottles, packaging materials, and containers. When the pellets of the present invention are used, stable melt-molding is possible, and die buildup during melt-molding is suppressed. The resulting molded article has a good appearance and excellent gas barrier properties. The molded article may have a portion formed from the pellets of the present invention. That is, the molded article may be a molded article consisting solely of the pellets of the present invention, or a molded article consisting solely of the pellets of the present invention and other portions. Examples of methods for melt-molding the pellets include extrusion molding, cast molding, inflation extrusion molding, blow molding, melt spinning, injection molding, injection blow molding, and co-extrusion blow molding. Of these, extrusion molding, injection molding, and blow molding are preferred. A molded article obtained by molding the pellets by these methods is a more preferred embodiment of the present invention. The melt-molding temperature varies depending on the melting point of the pellets, but is preferably about 150 to 270°C. These molded articles can also be crushed and remolded for reuse. Furthermore, films, sheets, etc. can be uniaxially or biaxially stretched.

[0073] The molded article is preferably a multilayer structure having a barrier layer made of the pellets of the present invention and a layer made of a thermoplastic resin other than EVOH. The multilayer structure has excellent gas barrier properties. The multilayer structure may further have a layer made of a component other than resin, such as a layer made of paper, a metal layer, or an inorganic vapor deposition layer. Examples of the multilayer structure include a multilayer film, a multilayer sheet, a multilayer pipe, and a multilayer fiber, with a multilayer film being preferred.

[0074] The layer structure of the multilayer structure is not particularly limited, and examples thereof include structures such as T / E / T, E / Ad / T, T / Ad / E / Ad / T, E / Ad / T / Ad / E, E / Ad / T / Ad / E / Ad / T / Ad / E, etc., where E represents a barrier layer, Ad represents a layer made of an adhesive resin, T represents a layer made of another thermal adhesive resin, and " / " represents direct lamination. Each of these layers may be a single layer or multiple layers.

[0075] From the viewpoint of improving the gas barrier property, the content of components other than EVOH in the barrier layer is preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 1% by mass or less.

[0076] Examples of thermoplastic resins other than EVOH include linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, polypropylene, propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymer, polybutene, polypentene, and other olefin homopolymers or copolymers thereof; polyesters such as polyethylene terephthalate; polyester elastomers; polyamides such as nylon-6 and nylon-66; polystyrene; polyvinyl chloride, polyvinylidene chloride, acrylic resins, vinyl ester resins, polyurethane elastomers, polycarbonate, chlorinated polyethylene, chlorinated polypropylene, etc. Among these, polypropylene, polyethylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, polyamide, polystyrene, and polyester are preferably used.

[0077] The adhesive resin is not particularly limited as long as it has adhesive properties with the barrier layer and other thermoplastic resin layers, but an adhesive resin containing a carboxylic acid-modified polyolefin is preferred. The carboxylic acid-modified polyolefin is preferably a modified olefin polymer containing a carboxyl group formed by chemically bonding an ethylenically unsaturated carboxylic acid, its ester, or its anhydride to an olefin polymer. Here, the olefin polymer refers to polyolefins such as polyethylene, linear low-density polyethylene, polypropylene, and polybutene, as well as copolymers of olefins with other monomers. Among these, linear low-density polyethylene, ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer are preferred, with linear low-density polyethylene and ethylene-vinyl acetate copolymer being particularly preferred.

[0078] It is preferable that the barrier layer be the outermost layer of the multilayer structure. Conventionally, when EVOH is co-extruded as the outermost layer of a multilayer structure, the EVOH contacts a large area with the die lip, which can lead to die buildup (a deposit on the outer surface of the die lip) on the outer surface of the die lip, resulting in the problem of lumps, streaks, and the like appearing in the film. In contrast, the pellets of the present invention make such die buildup less likely to occur. The outermost layer refers to a layer that is in contact with other layers of the multilayer structure on only one side. When a multilayer structure has an inner and outer surface, the outermost layer may be the layer on the outer surface (outermost layer) or the layer on the inner surface (innermost layer). The multilayer structure is preferably a multilayer film obtained by co-extrusion molding the pellets of the present invention and pellets of another thermoplastic resin. In this case, it is preferable that the outermost layer of the multilayer film is a barrier layer made of the pellets of the present invention. The multilayer structure may also be a vapor-deposited multilayer film obtained by forming an inorganic vapor-deposited layer on the barrier layer of the multilayer film. In this case, an inorganic vapor deposition layer may be formed on the uniaxially or biaxially stretched multilayer film by the method described below. The multilayer structure may also have a barrier layer on which a layer composed of another component is laminated. EVOH has a high affinity with inorganic vapor deposition layers, particularly aluminum or aluminum oxide vapor deposition layers, and therefore tends to provide good interlayer adhesion between the barrier layer and the inorganic vapor deposition layer. Examples of layer configurations in which a barrier layer is the outermost layer include E for the barrier layer, Ad for the layer composed of an adhesive resin, and T for the layer composed of a thermoplastic resin, with " / " representing direct lamination, such as E / Ad / T, E / Ad / T / Ad / E, and E / Ad / T / Ad / E / Ad / T / Ad / E. In the case of a multilayer structure in which a barrier layer is the outermost layer, T is preferably a polyolefin from the viewpoint of improving recyclability.

[0079] In the multilayer structure, the thickness of the barrier layer is preferably 0.2 μm or more and 20 μm or less, more preferably 0.4 μm or more and 16 μm or less, and even more preferably 0.6 μm or more and 12 μm or less, and the ratio of the thickness of the barrier layer to the total thickness of all layers of the multilayer structure is preferably 25% or less, more preferably 20% or less, and even more preferably 15% or less.

[0080] The method for producing the multilayer structure is not particularly limited, and examples thereof include a method of melt-extruding other components onto a molded article (film, sheet, etc.) made of the pellets, a method of co-extruding the pellets with other thermoplastic resin pellets, a method of coinjection molding the pellets with other thermoplastic resin pellets, and a method of laminating a barrier layer made of the pellets with a layer made of other components using a known adhesive such as an organic titanium compound, an isocyanate compound, or a polyester-based compound.

[0081] The method for co-extruding the pellets with other thermoplastic resin pellets is not particularly limited, and examples thereof include a multi-manifold confluence type T-die method, a feed block confluence type T-die method, and an inflation method.

[0082] The multilayer structure has excellent thermoformability and can therefore be suitably used as a material for thermoforming of thermoformed containers and the like.

[0083] The multilayer structure may be in the form of a film or a sheet, and may be molded into various shapes. Examples of methods for further molding a molded article using the film- or sheet-like multilayer structure include heat-stretch molding, vacuum molding, pressure molding, vacuum-pressure molding, and blow molding. The multilayer structure subjected to various secondary moldings may be a multilayer sheet. The multilayer structure can be used for packaging materials, containers, tubes, and the like. The multilayer structure may be a non-stretched multilayer sheet or a stretched multilayer sheet.

[0084] The multilayer structure may be stretched at least uniaxially by 2 times or more and 12 times or less. This stretching ratio may be 3 times or more and 10 times or less, or 4 times or more and 8 times or less. A multilayer structure uniaxially stretched in this manner has excellent gas barrier properties, break resistance, etc. Such a uniaxially stretched multilayer structure can be suitably used for packaging materials, etc. The uniaxial stretching of the multilayer structure can be carried out by a conventionally known method.

[0085] The multilayer structure may be biaxially stretched by 2 times or more and 12 times or less. This stretching ratio may be 10 times or less, 8 times or less, or 6 times or less. A multilayer structure biaxially stretched in this manner has excellent gas barrier properties, break resistance, etc. Such a biaxially stretched multilayer structure can be suitably used for packaging materials, etc. The biaxial stretching of the multilayer structure can be carried out by a conventionally known method.

[0086] The multilayer structure can be molded by vacuum pressure molding to obtain a container. Vacuum pressure molding is a method in which the multilayer structure is heated and molded using a combination of vacuum and pressure. Containers molded from the multilayer structure by vacuum pressure molding can be produced simply and reliably, and are excellent in appearance, gas barrier properties, etc.

[0087] In the vacuum and pressure molding method, for example, a multilayer structure is heated to soften it and then molded into the shape of a mold. Examples of molding methods include methods in which a vacuum or compressed air is used, and optionally a plug is also used, to mold the structure into the shape of the mold (straight method, drape method, air slip method, snapback method, plug assist method, etc.), and press molding. Various molding conditions, such as molding temperature, degree of vacuum, compressed air pressure, and molding speed, are appropriately set depending on the plug shape, mold shape, and properties of the raw material film and multilayer structure.

[0088] The molding temperature is not particularly limited, and may be any temperature at which the resin is softened sufficiently for molding. For example, when thermoforming a multilayer structure, it is desirable not to use a temperature so high that the multilayer structure melts due to heating or that the irregularities on the metal surface of the heater plate are transferred to the multilayer sheet, but also not to use a temperature so low that the shaping is insufficient. Specifically, the temperature of the multilayer structure is 50°C to 180°C, preferably 60°C to 160°C. [Example]

[0089] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. In the examples and comparative examples described below, analyses and evaluations were carried out by the methods shown below.

[0090] (1) Measurement of the moisture content of pellets The moisture content of the pellets obtained in the examples and comparative examples was measured by a heating and drying mass measurement method using a halogen moisture analyzer under the conditions of a drying temperature of 180°C, a drying time of 20 minutes, and a sample weight of 10 g. The moisture content of the pellets was calculated using the following formula. Moisture content (mass%) = [(mass before drying - mass after drying) / mass before drying] × 100

[0091] (2) Melt flow rate (MFR) The EVOH pellets obtained in the Examples and Comparative Examples were filled into a cylinder of a Melt Indexer L244 (manufactured by Takara Kogyo Co., Ltd.) with an inner diameter of 9.55 mm and a length of 162 mm, and melted at 210°C. A load was then applied uniformly to the molten resin composition using a plunger with a mass of 2,160 g and a diameter of 9.48 mm. The amount of resin composition extruded per unit time (g / 10 min) through an orifice with a diameter of 2.1 mm provided in the center of the cylinder was measured and defined as the MFR.

[0092] (3) Measurement of IR spectrum The surface of one EVOH pellet obtained in each of the Examples and Comparative Examples, or the central portion of a cross section of an EVOH pellet cut into two equal parts with a slicer, was subjected to IR measurement by the ATR method (attenuated total reflection absorption spectroscopy) under the following conditions. If the EVOH pellet was spherical, it was cut into a hemisphere. If it was spheroidal, it was cut at half the long side in a direction perpendicular to the long axis. If it was cylindrical, it was cut at a position equidistant from the two bases so that the cut surface was parallel to the bases. The infrared absorption spectra obtained at each temperature were analyzed for the 1140 cm band, which is known as the crystallization band. -1 The presence or absence of a maximum point in the absorption band of 1120cm -1 ~1150cm -1 The spectrum in this range was first differentiated, and the presence or absence of a maximum point was determined by checking whether there was a wavenumber where the positive and negative signs of the differential value were reversed, and Tcmin (°C), Tsmin (°C), Tcmax (°C), and Tsmax (°C) were calculated for each sample. (Measurement conditions) Equipment: Fourier transform infrared spectrophotometer FT-IR-6000 (JASCO Corporation) Wavenumber resolution: 4cm -1 Cell: Diamond Measurement mode: Heating single reflection ATR method Number of times accumulated: 16 times at each temperature Measurement area: 500~4000cm -1 Heating rate: 5℃ / min from 30℃ to 200℃ Measurement temperature: Set temperature ±1℃ Measurement interval: 5℃ Measurement atmosphere: Air

[0093] (4) Preparation of multilayer film Using each of the EVOH pellets obtained in the examples and comparative examples, a three-type, three-layer multilayer structure (EVOH / Ad / PE = 10 μm / 10 μm / 100 μm) was produced under the following conditions using low-density polyethylene "INNATE (trademark) TF80" (PE) as the material for the other thermoplastic resin layer and maleic anhydride-modified polyethylene "Admer (trademark) NF518" (Ad) as the adhesive layer. EVOH extruder: Single-screw extruder (Toyo Seiki Co., Ltd., Lab Machine ME Type CO-EXT) Diameter 20mmφ, L / D20, full flight screw Feeding section / compression section / metering section / die = 175 / 220 / 220 / 220℃ Ad extruder: Single screw extruder (Technovel Co., Ltd. SZW20GT-20MG-S TD) Diameter 20mmφ, L / D20, full flight screw Feeding section / compression section / metering section / die = 175 / 220 / 220 / 220℃ PE extruder: Single-screw extruder (Plastic Engineering Research Institute Co., Ltd. GT-32-A) Diameter 32mmφ, L / D28, full flight screw Feeding section / compression section / metering section / die = 175 / 220 / 220 / 220℃ Die: 300mm wide, 3-type, 3-layer coat hanger die (manufactured by Plastics Engineering Research Institute)

[0094] (5) Die build-up evaluation The multilayer film (4) was produced continuously for 2 hours, and after 2 hours, the die buildup around the die (die lip) on the EVOH layer side was visually inspected and evaluated according to the following criteria. In the cases of A to C, it was determined that die buildup was suppressed. (Evaluation: Criteria) A: No die buildup was observed over the entire width even after 2 hours of operation. B: Very little die buildup was observed after 2 hours of operation. C: A small amount of die buildup was observed after 2 hours of operation. D: Die buildup was observed after 1.5 hours of operation, and then an increase in die buildup was observed. E: Die buildup was observed after 1 hour of operation, and then an increase in die buildup was observed.

[0095] (6) Appearance evaluation of multilayer film The multilayer film obtained in (4) above was stretched 5 times in the machine direction (MD) to obtain a multilayer film with an average thickness of EVOH / Ad1 / PE = 2 μm / 2 μm / 20 μm. The appearance characteristics of the uniaxially stretched co-extruded film were evaluated according to the following criteria. Cases A to C were judged to have good appearance. (Evaluation: Criteria) A: No streaks were seen. B: Slight streaks were observed C: Some streaks were observed D: Many streaks were observed

[0096] (7) Oxygen transmission rate (OTR) measurement Aluminum was vacuum-deposited onto the surface of the EVOH of the uniaxially stretched co-extruded film obtained in (6) above using a vacuum deposition apparatus "EWA-105" manufactured by Nippon Vacuum Engineering Co., Ltd., to an average thickness of 50 nm, producing a vapor-deposited multilayer film (Al / EVOH / Ad1 / PE = 50 nm / 2 μm / 2 μm / 20 μm) with an aluminum vapor-deposited layer. The oxygen transmission rate was measured with the PE layer as the oxygen supply side. Specifically, the oxygen transmission rate (unit: cc / (m)) was measured using an oxygen transmission rate measuring device ("MOCON OX-TRAN2 / 21" manufactured by Modern Control Co., Ltd.) under the following conditions: temperature 20°C, humidity on the oxygen supply side 65% RH, humidity on the carrier gas side 65% RH, oxygen pressure 1 atmosphere, and carrier gas pressure 1 atmosphere. 2 The gas barrier properties were evaluated based on the following criteria. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. A rating of C was given, indicating poor gas barrier properties. (Evaluation: Criteria) A: 0.1cc / (m 2 ·day·atm) B: 0.1cc / (m 2 ·day · atm) or more, 0.5cc / (m 2 ·day·atm) C: 0.5cc / (m 2 ·day · atm) or more

[0097] [Example 1] EVOH hydrous pellets (ethylene unit content: 32 mol%, saponification degree: 99.9 mol%) with a moisture content of 40% by mass (W0) were fed into a fluidized bed dryer and dried at 80°C for 60 minutes. The resulting EVOH hydrous pellets with a moisture content of 13% by mass (W1) were fed into a twin-screw extruder. The resin temperature was adjusted to 160°C, and an aqueous solution of acetic acid, boric acid, sodium acetate, magnesium acetate, and potassium dihydrogen phosphate was added through the additive inlet. The aqueous solution was fed at a rate of 20.8 L / hr. The aqueous solution contained 3.5 g / L of acetic acid, 15 g / L of boric acid, 7.7 g / L of sodium acetate trihydrate, 3.1 g / L of magnesium acetate tetrahydrate, and 1.7 g / L of potassium dihydrogen phosphate.

[0098] The specifications of the twin-screw extruder are as follows: Type: Twin-screw extruder L / D: 45.5 Caliber: 30mmφ Screw: Same direction full intermeshing type Rotation speed: 300 rpm Die diameter: 3.0mmφ

[0099] The molten hydrous EVOH discharged from the twin-screw extruder was cut with a hot cutter to obtain hydrous EVOH pellets. The temperature of the cutter circulating water (cooling water) was 15°C, and the cutter blade rotation speed was 3,000 rpm. The obtained pellets were transported along a 5-m line together with the cooling water and deliquored using a centrifuge. The moisture content W2 of the hydrous EVOH pellets immediately after their production was 10% by mass, and the output rate of the EVOH from the twin-screw extruder was 208 kg / h (excluding the amount of water contained). The obtained hydrous EVOH pellets were dried in a fluidized-bed dryer at 90°C for 15 hours and then at 105°C for 15 hours using a static dryer to obtain spherical EVOH pellets with a diameter of 3 mm and a moisture content W3 of 0.2% by mass. The obtained EVOH pellets were evaluated according to the methods described in (2) to (7) above. The results are shown in Table 2.

[0100] [Example 2] EVOH pellets were prepared in the same manner as in Example 1, except that the ethylene unit content and moisture content W0 of the EVOH hydrous pellets, the drying temperature in the first drying step, and the amount of aqueous solution added in the melt-kneading step were changed as shown in Table 1, and the aqueous solution added was changed to an acetic acid / sodium acetate / magnesium acetate / potassium dihydrogen phosphate aqueous solution. The results are shown in Table 2.

[0101] [Examples 3 and 4] EVOH pellets were prepared in the same manner as in Example 1, except that the ethylene unit content and moisture content W0 of the EVOH hydrous pellets, the drying temperature and drying time in the first drying step, the resin temperature in the melt-kneading step, the amount of aqueous solution added, and the cooling water temperature and cooling length in the cutting step were changed as shown in Table 1. The results are shown in Table 2.

[0102] [Example 5] Pellets were prepared in the same manner as in Example 1, except that the drying temperature in the first drying step, the resin temperature and the amount of aqueous solution added in the melt-kneading step, and the cooling water temperature in the cutting step were changed as shown in Table 1, and the aqueous solution containing additives was changed to an aqueous solution containing 1.8 g / L of acetic acid, 3.8 g / L of sodium acetate trihydrate, 1.5 g / L of magnesium acetate tetrahydrate, and 0.9 g / L of potassium dihydrogen phosphate. The results are shown in Table 2.

[0103] [Comparative Example 1] A solution of EVOH with an ethylene unit content of 32 mol% and a saponification degree of 99.9 mol% in a methanol-water mixed solvent (methanol / water = 65 / 35, mass ratio) (EVOH concentration: 40% by mass) was extruded through a die with a 2 mm diameter hole into a coagulation bath containing a 5°C aqueous methanol solution (methanol / water = 10 / 90, mass ratio) to coagulate into strands. The strands were then cut with a cutter to obtain cylindrical hydrous EVOH pellets with a base diameter and height of 2.5 to 3.5 mm. The obtained hydrous pellets were washed in a water bath at 30°C for 1 hour, this process was repeated four times, and then washed in acetic acid water at 30°C for 1 hour. After that, the pellets were immersed in an aqueous solution containing acetic acid, boric acid, sodium acetate trihydrate, magnesium acetate tetrahydrate, and potassium dihydrogen phosphate to incorporate additives, yielding hydrous EVOH pellets with a water content of 57% by mass. The composition of the aqueous solution was adjusted so that the additive composition in the dried EVOH pellets would be the same as in Example 1. The obtained EVOH water-containing pellets were dried using a fluidized bed dryer at 80°C for 15 hours, and then dried using a static dryer at 107°C for 24 hours to obtain cylindrical EVOH pellets with a moisture content of 0.2% by mass. The obtained EVOH pellets were evaluated according to the methods described in (2) to (7) above. The results are shown in Table 2.

[0104] Comparative Example 2 A solution (EVOH concentration: 41% by mass) of EVOH with an ethylene unit content of 32% by mole and a saponification degree of 99.9% by mole in a methanol-water mixed solvent (methanol / water = 65 / 35, mass ratio) was cut using a rotary knife by the underwater pelletization method. At the same time, the EVOH pellets were cooled using circulating cooling water at 5°C to obtain oblong hydrous EVOH pellets with a long side of 3.0 mm and a short side of 2.4 mm. The obtained hydrous EVOH pellets were washed, additives were added, and dried in the same manner as in Comparative Example 1 to obtain EVOH pellets with a moisture content of 0.2% by mass. The obtained EVOH pellets were evaluated according to the methods described in (2) to (7) above. The results are shown in Table 2.

[0105] [Table 1]

[0106] [Table 2] [Explanation of symbols]

[0107] 1, 2, 3 IR spectrum

Claims

1. A pellet containing an ethylene-vinyl alcohol copolymer, the surface and cut surface of the pellet being measured at 5°C intervals from 30°C to 200°C, and －１ ~1150cm －１ A pellet that satisfies formulas (1) to (3) in the IR spectrum at each temperature in the range of 40≦Tcmin≦100 (1) 10≦Tcmin−Tsmin≦70 (2) -15<Tcmax-Tsmax<15 (3) however, Tcmin (°C) is the minimum temperature at which the IR spectrum of the pellet cross section has a maximum point. Tsmin (°C) is the minimum temperature at which the IR spectrum of the pellet surface has a maximum point. Tcmax (°C) is the maximum temperature at which the IR spectrum of the pellet cross section has a maximum point. Tsmax (°C) is the maximum temperature at which the IR spectrum of the pellet surface has a maximum point.

2. The pellet according to claim 1, which satisfies formula (4). 0.95≦(Tsmax-Tsmin) / (Tcmax-Tcmin)<2.5 (4)

3. The pellet according to claim 1, which satisfies formula (5). 40≦Tcmax−Tcmin<130 (5)

4. 2. The pellet according to claim 1, wherein the ethylene-vinyl alcohol copolymer has an ethylene unit content of 20 to 60 mol %.

5. 2. The pellet according to claim 1, wherein the ethylene-vinyl alcohol copolymer has a degree of saponification of 99 mol % or more.

6. A molded article obtained by extrusion molding the pellets according to any one of claims 1 to 5.

7. A molded article obtained by injection molding the pellets according to any one of claims 1 to 5.

8. A molded article obtained by blow molding the pellets according to any one of claims 1 to 5.

9. A multilayer structure obtained by co-extrusion molding the pellets according to any one of claims 1 to 5 and pellets of another thermoplastic resin.

10. 10. The multilayer structure according to claim 9, wherein the layer formed by extrusion molding the pellets is the outermost layer.

11. The method for producing pellets according to any one of claims 1 to 5, wherein the water content W ０ 25 to 50% by mass of ethylene-vinyl alcohol copolymer water-containing pellets are introduced into a dryer, and the water content W of the water-containing pellets is １ a first drying step (I) in which the a melt-kneading step (II) of introducing the water-containing pellets obtained in the first drying step (I) into an extruder and melt-kneading them; The molten resin discharged from the extruder is cut to obtain a water content W ２ A cutting step (III) to obtain water-containing pellets having a water content of 5 to 25% by mass; The water-containing pellets obtained in the cutting step (III) are dried to have a water content W ３ a second drying step (IV) for obtaining the pellets having a content of 0.5% by mass or less, The reduction in moisture content (W ０ -W １ ) is 10 to 45 mass%.

12. A method for producing a multilayer structure, comprising co-extrusion molding the pellets according to any one of claims 1 to 5 and pellets of another thermoplastic resin.

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