Resin composition containing ethylene-vinyl alcohol copolymer, method for producing the same, and pellets made therefrom

Abstract

To provide a resin composition capable of stably melt-molding, and capable of suppressing defects in a molded product after melt-molding.SOLUTION: A resin composition includes: 20-60 mol% of an ethylene unit content; and an ethylene-vinyl alcohol copolymer having a saponification degree of 99 mol% or more, where a light transmittance T1 of a solution obtained by dissolving 5 pts.mass of the resin composition in 95 pts.mass of a 1-propanol / water mixed solvent (1-propanol content of 60 mass%) is 95% or more, and a light transmittance T2 of a solution obtained by dissolving 5 pts.mass of the resin composition in 95 pts.mass of a 1-propanol / water mixed solvent (1-propanol content of 40 mass%) is 95% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a resin composition containing an ethylene-vinyl alcohol copolymer and a method for producing the same. Further, the present invention relates to pellets made of the resin composition and a method for producing the same. Furthermore, the present invention relates to a multilayer structure having a layer made of the resin composition.

Background Art

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as EVOH) is a thermoplastic resin excellent in gas barrier properties, fuel barrier properties, chemical resistance, stain resistance, non-chargeability, mechanical strength, etc. Taking advantage of such characteristics, EVOH is formed into forms such as films, sheets, bottles, cups, tubes, pipes, etc., and is used in various applications including packaging containers.

[0003] EVOH is usually produced as follows. First, an ethylene-vinyl acetate copolymer is synthesized by copolymerizing ethylene and vinyl acetate in a solution such as methanol. Next, a solution of EVOH is obtained by saponifying the obtained ethylene-vinyl acetate copolymer in a solution. Then, the solvent is removed from the obtained EVOH solution, and then cut and dried to produce EVOH pellets, which are subjected to melt molding. At this time, various improvements have been proposed in the production process of EVOH pellets in order to suppress defects in the molded product after melt molding and perform stable melt molding.

[0004] Patent Document 1 describes a method for producing a saponified ethylene-vinyl acetate copolymer, which involves copolymerizing ethylene and vinyl acetate in a methanol solution to obtain an ethylene-vinyl acetate copolymer, saponifying the copolymer in a methanol solution, adding water to the methanol solution containing the saponified copolymer to prepare a mixed solution, removing insoluble matter from the mixed solution, and obtaining a saponified ethylene-vinyl acetate copolymer from the mixed solution from which the insoluble matter has been removed. In its examples, it is described that polyvinyl alcohol, which is an insoluble matter, was removed by filtering a mixed solution with a weight ratio of methanol / water of 49 / 51 to 70 / 30 through a filter with a mesh size of 60 μm. It is also described that the film obtained by melt-molding at 240 °C using the EVOH pellets obtained by solidifying the filtered solution into strands, cutting them, and drying them had few fish eyes. However, with such a filtration method, suppression of defects in the molded article after melt-molding was sometimes insufficient.

[0005] Patent Document 2 describes a method for producing saponified ethylene-vinyl acetate copolymer pellets, which involves extruding a solution of a saponified ethylene-vinyl acetate copolymer in a strand shape from a nozzle made of any one of an aluminum compound, a glass compound, and a thermosetting resin into a coagulation liquid, and then cutting the strand. By selecting the material of the nozzle, it is said that the strand is less likely to break compared to when using a conventional stainless steel nozzle, uniform-sized EVOH pellets can be obtained, and fluctuations in the charge and load of the extruder can be suppressed. In its examples, nozzles made of glass, an aluminum-silicon alloy, and a silicone resin are used, but nozzles made of these materials are insufficient in strength and durability compared to stainless steel nozzles and were difficult to use industrially.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made to solve the above problems, and an object thereof is to provide an EVOH resin composition capable of suppressing defects in a molded article after melt molding and a method for producing the same. Another object is to provide pellets that can be stably melt-molded and a method for producing the same, which are made of such an EVOH resin composition.

Means for Solving the Problems

[0008] The above problems are solved by providing a resin composition containing an ethylene-vinyl alcohol copolymer having an ethylene unit content of 20 to 60 mol% and a saponification degree of 99 mol% or more; the light transmittance T1 of a solution obtained by dissolving 5 parts by mass of the resin composition in 95 parts by mass of a 1-propanol / water mixed solvent (1-propanol content: 60% by mass) is 95% or more, and the light transmittance T2 of a solution obtained by dissolving 5 parts by mass of the resin composition in 95 parts by mass of a 1-propanol / hydrate solvent (1-propanol content: 40% by mass) is 95% or more.

[0009] At this time, it is preferable that the resin composition contains at least one additive selected from carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts.

[0010] A pellet made of the resin composition is a preferred embodiment. At this time, it is preferable that the shape of the pellet is a cylinder or an ellipsoid, and the half-value width of the particle size distribution of the pellet is 0.7 mm or less. Also, a multilayer structure having at least one layer made of the resin composition is a preferred embodiment.

[0011] The above problem is also solved by providing a method for producing the resin composition, which includes a step of adding an alkali catalyst to a methanol solution of an ethylene-vinyl ester copolymer to saponify the ethylene-vinyl ester copolymer to obtain a methanol solution of an ethylene-vinyl alcohol copolymer, a step of adding water to the saponified solution and then performing a first filtration, a step of adding methanol to the solution after the first filtration and then performing a second filtration, and a step of removing a solvent from the solution after the second filtration.

[0012] The above problem is also solved by providing a method for producing the resin composition, which includes a step of adding an alkali catalyst to a methanol solution of an ethylene-vinyl ester copolymer to saponify the ethylene-vinyl ester copolymer to obtain a methanol solution of an ethylene-vinyl alcohol copolymer, a step of adding water to the saponified solution and then performing a first filtration, a step of adding more water to the solution after the first filtration and then performing a second filtration, and a step of removing a solvent from the solution after the second filtration.

[0013] The above problem is also solved by providing a method for producing the pellet, which includes a step of adding an alkali catalyst to a methanol solution of an ethylene-vinyl ester copolymer to saponify the ethylene-vinyl ester copolymer to obtain a methanol solution of an ethylene-vinyl alcohol copolymer, a step of adding water to the saponified solution and then performing a first filtration, a step of adding methanol to the solution after the first filtration and then performing a second filtration, a step of removing a solvent from the solution after the second filtration, a cutting step, and a drying step.

[0014] The above problems are also solved by providing a method for producing the pellets, which includes a step of adding an alkali catalyst to a methanol solution of an ethylene-vinyl ester copolymer to saponify the ethylene-vinyl ester copolymer to obtain a methanol solution of an ethylene-vinyl alcohol copolymer; a step of adding water to the solution after saponification and then performing a first filtration; a step of adding more water to the solution after the first filtration and then performing a second filtration; a step of removing the solvent from the solution after the second filtration; a cutting step; and a drying step.

[0015] In these methods for producing the pellets, it is preferable to have a sieving step after the drying step, and remove pellets that are too large and pellets that are too small in the sieving step.

Advantages of the Invention

[0016] According to the EVOH resin composition of the present invention, defects in the molded article after melt molding can be suppressed. Further, the pellets of the present invention can be stably melt-molded, thereby obtaining a molded article with suppressed defects.

Brief Description of the Drawings

[0017]

Figure 1

Embodiments for Carrying Out the Invention

[0018] The resin composition of the present invention is a resin composition containing an ethylene-vinyl alcohol copolymer having an ethylene unit content of 20 to 60 mol% and a saponification degree of 99 mol% or more; the light transmittance T1 of a solution obtained by dissolving 5 parts by mass of the resin composition in 95 parts by mass of a 1-propanol / water mixed solvent (1-propanol content 60% by mass) is 95% or more, and the light transmittance T2 of a solution obtained by dissolving 5 parts by mass of the resin composition in 95 parts by mass of a 1-propanol / water mixed solvent (1-propanol content 40% by mass) is 95% or more.

[0019] A major feature is that both the light transmittance T1 when dissolved in a 1-propanol / water mixed solvent with a 1-propanol content of 60% by mass and the light transmittance T2 when dissolved in a 1-propanol / water mixed solvent with a 1-propanol content of 40% by mass are 95% or more. This means that the EVOH resin composition of the present invention has few insoluble substances when dissolved in a 1-propanol / water mixed solvent with a 1-propanol content of 60% by mass and also when dissolved in a 1-propanol / water mixed solvent with a 1-propanol content of 40% by mass.

[0020] There are few solvents capable of dissolving EVOH, and the 1-propanol / water mixed solvent is one of the few good solvents. EVOH does not dissolve in either water or 1-propanol, but it dissolves in a solvent obtained by mixing water and 1-propanol in an appropriate ratio. At this time, in the case of EVOH with a high ethylene unit content, it is easily soluble in a mixed solvent with a high 1-propanol content, and in the case of EVOH with a high vinyl alcohol unit content, it is easily soluble in a mixed solvent with a high water content.

[0021] EVOH is a random copolymer containing ethylene units and vinyl alcohol units, but ethylene units and vinyl alcohol units are not evenly contained in all molecular chains. Molecular chains with a high ethylene unit content and molecular chains with a high vinyl alcohol unit content are also included. By both the light transmittances T1 and T2 being 95% or more, it is possible to obtain an EVOH resin composition from which both molecular chains with an overly high ethylene unit content and molecular chains with an overly high vinyl alcohol unit content are removed.

[0022] Conventionally, in the manufacturing process of EVOH, a method has been proposed to remove insoluble matter by filtering a solution in which EVOH is dissolved in a methanol / water mixed solvent (see Patent Document 1). However, it has not been possible to sufficiently remove both molecular chains with an ethylene unit content that is too high and molecular chains with a vinyl alcohol unit content that is too high. This time, it has been found that by performing multiple filtrations using mixed solvents with different compositions, impurities can be effectively removed, and defects in the molded product after melt molding can be suppressed. In particular, when melt molding at a high temperature, it has been found that bumps, streaks, and flow marks can be suppressed, and the amount of adhesion in the die during long-term operation can be suppressed.

[0023] The light transmittance T1 of a solution obtained by dissolving 5 parts by mass of the resin composition of the present invention in 95 parts by mass of a 1-propanol / water mixed solvent (1-propanol content: 60% by mass) is 95% or more. When the light transmittance T1 is less than 95%, impurities containing molecular chains with a vinyl alcohol unit content that is too high cannot be sufficiently removed, and defects in the molded product after melt molding cannot be suppressed. The light transmittance T1 is preferably 97% or more, and more preferably 98% or more. The light transmittance T1 is the light transmittance at 25°C with a wavelength ranging from 350 nm to 600 nm, and is the relative light transmittance (%) when the light transmittance measured for a cell containing only the solvent in which EVOH is not dissolved is set to 100%.

[0024] Also, the light transmittance T2 of a solution obtained by dissolving 5 parts by mass of the resin composition of the present invention in 95 parts by mass of a 1-propanol / water mixed solvent (1-propanol content: 40% by mass) is also 95% or more. When the light transmittance T2 is less than 95%, impurities containing molecular chains with an ethylene unit content that is too high cannot be sufficiently removed, and defects in the molded product after melt molding cannot be suppressed. The light transmittance T2 is preferably 97% or more, and more preferably 98% or more. The light transmittance T2 is measured in the same manner as the light transmittance T1.

[0025] The resin composition of the present invention contains an ethylene-vinyl alcohol copolymer having an ethylene unit content of 20 to 60 mol% and a saponification degree of 99 mol% or more.

[0026] The EVOH contained in the resin composition of the present invention is obtained by saponifying an ethylene-vinyl ester copolymer. Among them, those obtained by saponifying an ethylene-vinyl acetate copolymer are preferred. The ethylene unit content is 20 to 60 mol%. When the ethylene unit content is less than 20 mol%, the melt moldability becomes insufficient. On the other hand, when the ethylene unit content exceeds 60 mol%, the gas barrier property becomes insufficient. The ethylene unit content is preferably 25 mol% or more, more preferably 30 mol% or more. Also, the ethylene unit content is preferably 55 mol% or less, more preferably 50 mol% or less.

[0027] Also, the saponification degree of EVOH is 99 mol% or more. When the saponification degree is less than 99 mol%, the barrier property and melt moldability are insufficient. More preferably, it is 99.3 mol% or more. Especially when manufacturing an EVOH composition with excellent melt stability and good long-run properties, it is important to have a high saponification degree.

[0028] In addition to EVOH, the resin composition of the present invention preferably contains at least one additive selected from carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts. Thereby, qualities such as thermal stability can be improved.

[0029] Examples of the carboxylic acid include oxalic acid, succinic acid, benzoic acid, citric acid, acetic acid, lactic acid and the like. Among these, acetic acid is preferred in terms of cost, availability and the like. If the content of the carboxylic acid in the EVOH resin pellet after drying of the present invention is too small, coloring may occur during melt molding, and if it is too large, the interlayer adhesiveness may become insufficient. Therefore, 10 to 5000 ppm is preferred. The content of the carboxylic acid is preferably 30 ppm or more, more preferably 50 ppm or more. Also, the content of the carboxylic acid is preferably 1000 ppm or less, more preferably 500 ppm or less.

[0030] Examples of the boron compound include, but are not limited to, boric acids, boric acid esters, borates, boron hydrides and the like. Specifically, examples of the boric acids include orthoboric acid, metaboric acid, tetraboric acid and the like, examples of the boric acid esters include triethyl borate, trimethyl borate and the like, and examples of the borates include alkali metal salts, alkaline earth metal salts of the above various boric acids, borax and the like. Among these compounds, orthoboric acid (hereinafter simply referred to as boric acid) is preferred. If the content of the boron compound in the EVOH resin pellet after drying of the present invention is too small, the effect of improving the thermal stability is small, and if it is too large, it may gel and the moldability may become poor. Therefore, 10 to 2000 ppm in terms of boron is preferred, and 50 to 1000 ppm is more preferred.

[0031] Examples of the phosphate compound include various acids such as phosphoric acid and phosphorous acid, and salts thereof. The phosphate may be contained in any form of primary phosphate, secondary phosphate, or tertiary phosphate, and the cation species thereof is not particularly limited, but is preferably an alkali metal salt or an alkaline earth metal salt. Among them, 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. The content of the phosphate compound in the dried EVOH resin pellets of the present invention is preferably 1 to 1000 ppm in terms of phosphate radical. By adding in such a range, it is possible to suppress the coloring of the molded product and the generation of gel lumps. When the content of the phosphate compound is less than 1 ppm, there is a risk that the coloring during melt molding becomes intense. When it exceeds 1000 ppm, there is a risk that gel lumps are likely to occur in the molded product.

[0032] Examples of the alkali metal salt include monovalent metal aliphatic carboxylates, aromatic carboxylates, phosphates, metal complexes, etc. For example, sodium acetate, potassium acetate, sodium phosphate, lithium phosphate, sodium stearate, potassium stearate, sodium salt of ethylenediaminetetraacetic acid, etc. are mentioned. Among them, sodium acetate, potassium acetate, and sodium phosphate are preferable. The content of the alkali metal salt in the dried EVOH resin pellets of the present invention is preferably 5 to 5000 ppm in terms of alkali metal element. More preferably, it is 20 to 1000 ppm, and even more preferably, it is 30 to 750 ppm.

[0033] Examples of the alkaline earth metal salts include magnesium salts, calcium salts, barium salts, beryllium salts, etc., and magnesium salts and calcium salts are particularly preferred. The anion species of the alkaline earth metal salt is not particularly limited, but acetates and phosphates are preferred. The content of the alkaline earth metal in the EVOH resin pellets after drying of the present invention is preferably 10 to 1000 ppm in terms of metal, more preferably 20 to 500 ppm. When the content of the alkaline earth metal is less than 10 ppm, the effect of improving the long-term performance may be insufficient. On the other hand, when it exceeds 1000 ppm, the coloring during resin melting may become intense.

[0034] Among the resin components constituting the EVOH resin composition of the present invention, the proportion occupied by EVOH is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and may even be 99% by mass or more, or may consist essentially of only EVOH, or may consist of only EVOH. Also, in the EVOH resin composition of the present invention, the proportion occupied by EVOH is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and may even be 99% by mass or more.

[0035] The preferred melt flow rate (MFR) (measured at 190 °C under a load of 2160 g; however, for those with a melting point near 190 °C or exceeding 190 °C, it is measured at a plurality of temperatures above the melting point, plotted with the reciprocal of the absolute temperature on the horizontal axis and the melt flow rate on the vertical axis (logarithmic) in a semi-logarithmic graph, and the value extrapolated to 190 °C) of the EVOH resin composition of the present invention is preferably 0.1 to 200 g / 10 min. The MFR is more preferably 0.2 g / 10 min or more, still more preferably 0.5 g / 10 min or more, and particularly preferably 1 g / 10 min or more. Also, the MFR is more preferably 50 g / 10 min or less, still more preferably 30 g / 10 min or less, and particularly preferably 15 g / 10 min or less. When the MFR is too small, the torque of the extruder motor may become too high during molding, making melt extrusion difficult. On the other hand, when the MFR is too large, the mechanical strength of the resulting molded product may be insufficient.

[0036] The manufacturing method of the EVOH resin composition of the present invention will be described below. A preferred manufacturing method of the resin composition of the present invention is to add an alkali catalyst to a methanol solution of an ethylene-vinyl ester copolymer and saponify the ethylene-vinyl ester copolymer to obtain a methanol solution of an ethylene-vinyl alcohol copolymer, a step of adding water to the solution after saponification and then performing the first filtration, a step of adding methanol or water to the solution after the first filtration and then performing the second filtration, and a step of removing the solvent from the solution after the second filtration.

[0037] First, using a radical initiator as a catalyst, ethylene and vinyl ester are copolymerized to obtain an ethylene-vinyl ester copolymer. Preferably, vinyl acetate is used as the vinyl ester to obtain an ethylene-vinyl acetate polymer. At this time, solution polymerization is carried out using methanol as a solvent. Either a continuous method or a batch method may be used. The polymerization temperature is 20 to 90°C, preferably 40 to 70°C. The polymerization time (average residence time in the case of the continuous method) is 2 to 15 hours, preferably 3 to 11 hours. The polymerization rate is 10 to 90% with respect to the charged vinyl ester, preferably 30 to 80%. The resin content in the solution after polymerization is 5 to 85%, preferably 20 to 70%.

[0038] The catalysts used include azonitrile-based initiators such as 2,2-azobisisobutyronitrile, 2,2-azobis-(2,4-dimethylvaleronitrile), 2,2-azobis-(4-methyl-2,4-dimethylvaleronitrile), 2,2-azobis-(4-methoxy-2,4-dimethylvaleronitrile), 2,2-azobis-(2-cyclopropylpropionitrile), and isobutyryl peroxide, cumyl peroxyneodecanoate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxyneodecanoate, lauroyl peroxide, benzoyl peroxide, t-butyl hydroperoxide, etc.

[0039] In addition to ethylene and vinyl esters, monomers that can copolymerize with these, such as alkenes like propylene, butylene, pentene, hexene, etc.; alkenes having an ester group such as 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, 1,3-diacetoxy-2-methylenepropane, or their enolates; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, or their anhydrides, salts, or mono- or dialkyl esters, etc.; nitriles such as acrylonitrile, methacrylonitrile, etc.; amides such as acrylamide, methacrylamide, etc.; olefin sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, or their salts; vinyl silane compounds such as vinyl trimethoxysilane, vinyl triethoxysilane, vinyl tri(β-methoxy-ethoxy)silane, γ-methacryloxypropylmethoxysilane, etc.; alkyl vinyl ethers, vinyl ketones, N-vinyl pyrrolidone, vinyl chloride, vinylidene chloride, etc. can also be copolymerized in a small amount. In that case, the copolymerization amount is usually 5 mol% or less, and it is preferably substantially not contained.

[0040] After polymerization for a predetermined time and reaching a predetermined polymerization rate, a polymerization inhibitor is added as necessary. After evaporating and removing unreacted ethylene gas, unreacted vinyl ester is expelled. As a method for expelling unreacted vinyl ester from an ethylene-vinyl ester copolymer solution from which ethylene has been evaporated and removed, for example, the copolymer solution is continuously supplied at a constant rate from the upper part of a tower filled with Raschig rings, methanol vapor is blown in from the lower part of the tower, a mixed vapor of methanol and unreacted vinyl ester is distilled out from the top of the tower, and an ethylene-vinyl ester copolymer solution from which unreacted vinyl ester has been removed is taken out from the bottom of the tower.

[0041] An alkali catalyst is added to a methanol solution of an ethylene-vinyl ester copolymer from which unreacted vinyl ester has been removed, and the vinyl ester component in the copolymer is saponified to obtain a methanol solution of an ethylene-vinyl alcohol copolymer. The saponification method can be either continuous or batchwise. As the alkali catalyst, sodium hydroxide, potassium hydroxide, an alkali metal alcoholate, etc. are used. The saponification conditions are as follows. The ethylene-vinyl ester copolymer concentration is preferably 10 to 50% by mass. The saponification reaction temperature is preferably 30 to 150 °C. The amount of alkali catalyst used is preferably 0.005 to 0.6 equivalent (per vinyl ester unit). Also, the saponification time (in the case of continuous operation, the average residence time) is preferably 10 minutes to 6 hours.

[0042] Water is added to the thus obtained methanol solution of EVOH and then filtration is carried out. Suitable methods for filtration include a method of adding water during the first filtration and adding methanol during the second filtration, and a method of adding water during both the first filtration and the second filtration.

[0043] When adding water during the first filtration and adding methanol during the second filtration, first, by adding water, it is preferable to set the methanol content in the methanol / water mixed solvent in the EVOH solution to 50 to 70% by mass. By setting the methanol content in the mixed solvent within this range, only the insoluble matter derived from the molecular chains with an excessive ethylene unit content contained in EVOH can be effectively removed. The methanol content is more preferably 52% by mass or more, and even more preferably 54% by mass or more. On the other hand, the methanol content is more preferably 68% by mass or less, even more preferably 66% by mass or less, and particularly preferably 64% by mass or less.

[0044] The type of filter used at this time is not particularly limited, but a filter having a mesh size of about 20 to 150 μm is preferably used. The differential pressure before and after the filter is preferably 0.1 to 0.7 MPa. When the differential pressure is less than 0.1 MPa, there is a risk of reduced productivity. The differential pressure is more preferably 0.15 MPa or more, and even more preferably 0.2 MPa or more. On the other hand, when the differential pressure exceeds 0.7 MPa, impurities cannot be sufficiently filtered out and may be mixed into the product. The differential pressure is more preferably 0.6 MPa or less, and even more preferably 0.5 MPa or less.

[0045] After adding methanol to the solution after the first filtration, the second filtration is performed. At this time, by adding methanol, it is preferable to set the methanol content in the methanol / water mixed solvent in the EVOH solution to 70 to 90% by mass. By setting the methanol content within this range, only the insoluble matter derived from the molecular chains with an excessive vinyl alcohol unit content contained in EVOH can be effectively removed. The methanol content is more preferably 72% by mass or more, even more preferably 74% by mass or more, and particularly preferably 76% by mass or more. On the other hand, the methanol content is more preferably 88% by mass or less, and even more preferably 86% by mass or less.

[0046] The type of filter used at this time is not particularly limited, but a filter having a mesh size of 20 to 100 μm is preferably used. The differential pressure before and after the filter is preferably 0.2 to 1.5 MPa. If the differential pressure is less than 0.2 MPa, the productivity may decrease. The differential pressure is more preferably 0.3 MPa or more, and even more preferably 0.4 MPa or more. On the other hand, if the differential pressure exceeds 1.5 MPa, impurities may not be sufficiently filtered out and may be mixed into the product. The differential pressure is more preferably 1.2 MPa or less, and even more preferably 1.0 MPa or less.

[0047] When water is added during the first filtration and the second filtration, first, by adding water, the methanol content in the methanol / water mixed solvent in the EVOH solution is preferably set to 70 to 90% by mass. By setting the methanol content within this range, only the insoluble matter derived from the molecular chains with too high a content of vinyl alcohol units contained in EVOH can be effectively removed. The methanol content is more preferably 72% by mass or more, even more preferably 74% by mass or more, and particularly preferably 76% by mass or more. On the other hand, the methanol content is more preferably 88% by mass or less, and even more preferably 86% by mass or less.

[0048] The type of filter used at this time is not particularly limited, but a filter having a mesh size of 20 to 100 μm is preferably used. The differential pressure before and after the filter is preferably 0.2 to 1.5 MPa. If the differential pressure is less than 0.2 MPa, the productivity may decrease. The differential pressure is more preferably 0.3 MPa or more, and even more preferably 0.4 MPa or more. On the other hand, if the differential pressure exceeds 1.5 MPa, impurities may not be sufficiently filtered out and may be mixed into the product. The differential pressure is more preferably 1.2 MPa or less, and even more preferably 1.0 MPa or less.

[0049] Water is further added to the solution after the first filtration, followed by the second filtration. At this time, by adding water, the methanol content in the methanol / water mixed solvent in the EVOH solution is preferably set to 50 to 70% by mass. By setting the methanol content in the mixed solvent within this range, only the insoluble matter derived from the molecular chains with an excessive ethylene unit content contained in EVOH can be effectively removed. The methanol content is more preferably 52% by mass or more, and even more preferably 54% by mass or more. On the other hand, the methanol content is more preferably 68% by mass or less, even more preferably 66% by mass or less, and particularly preferably 64% by mass or less.

[0050] The type of filter used at this time is not particularly limited, but a filter having a mesh size of about 20 to 150 μm is preferably used. The differential pressure before and after the filter is preferably 0.1 to 0.7 MPa. If the differential pressure is less than 0.1 MPa, there is a risk of reduced productivity. The differential pressure is more preferably 0.15 MPa or more, and even more preferably 0.2 MPa or more. On the other hand, if the differential pressure exceeds 0.7 MPa, impurities cannot be sufficiently filtered out and may be mixed into the product. The differential pressure is more preferably 0.6 MPa or less, and even more preferably 0.5 MPa or less.

[0051] The difference in the methanol content in the EVOH solution between the first filtration and the second filtration is preferably 10 to 30% by mass. By providing an appropriate difference, different impurities can be effectively removed. The difference in the methanol content is more preferably 12% by mass or more, and even more preferably 14% by mass or more. On the other hand, the difference in the methanol content is more preferably 28% by mass or less, and even more preferably 26% by mass or less.

[0052] As described above, in the industrial EVOH manufacturing process, the EVOH solution dissolved in the methanol / water mixed solvent is filtered. However, in the present invention, the performance of the EVOH resin composition is evaluated using the light transmittance of the EVOH solution dissolved in the 1-propanol / water mixed solvent. This is because once dried and crystallized EVOH pellets are difficult to dissolve in the methanol / water mixed solvent, whereas they can be dissolved relatively easily in the 1-propanol / water mixed solvent. If the content of 1-propanol in the 1-propanol / water mixed solvent is made less than the content of methanol, the solubility can be evaluated in the same manner as when using the methanol / water mixed solvent.

[0053] After filtration, the solvent is removed. The method for removing the solvent may be any method that can reduce the solvent content and is not particularly limited. By extruding the EVOH solution into a poor solvent such as water and coagulating it, the solvent content can be reduced and solidified. Also, in an extruder or kneader, water may be mechanically squeezed out or water vapor may be evaporated from the vent. After removing the solvent in this way, it is cut. The method for cutting to obtain pellets is not particularly limited. The coagulated water-containing strands can be cut with a cutter, or the water content-reduced material in the extruder or kneader can be cut with a hot cutter or an under-water cutter while in a flowing state.

[0054] When the EVOH resin composition pellets contain at least one additive selected from carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts, the method for adding the additive is not particularly limited. Methods such as immersing the water-containing pellets in an aqueous solution containing the additive for impregnation, or injecting an aqueous solution containing the additive into the water-containing and flowing EVOH in an extruder or the like, kneading, and then cutting to produce pellets are employed.

[0055] After cutting the EVOH resin composition into pellet form, it is dried. The drying method is not particularly limited, and a hot air dryer or the like can be used. The dryer may be a fluidized dryer or a stationary dryer, or a combination of these may be used. Among these, a method of first drying by the fluidized drying method and subsequently drying by the stationary drying method is preferred. The drying temperature is not particularly limited, but a temperature of usually about 70 to 120°C is adopted, and the temperature can be increased as the drying progresses. The moisture content after drying is usually 1% by weight or less, preferably 0.5% by weight or less. The dried pellets thus obtained are subjected to the molding process.

[0056] The shape of the resulting pellets is not particularly limited, but is preferably a cylinder or an ellipsoid. Here, the ellipsoid includes a spheroid with equal radii of two orthogonal axes and a sphere with equal radii of three orthogonal axes. When cutting after forming a strand, cylindrical pellets are obtained. Also, when cutting with a hot cutter or an under-water cutter, ellipsoids, particularly slightly flattened spheroidal pellets, are obtained. Here, the terms cylinder or ellipsoid are not used in a strict sense and may be slightly distorted. The average particle size of the pellets is usually 2 to 7 mm. The average particle size here refers to the equivalent circle diameter (diameter) obtained from the area of the pellet image observed two-dimensionally.

[0057] It is preferable that the half-value width of the particle size distribution of the EVOH resin composition pellets of the present invention is 0.7 mm or less. By making the pellets with a small half-value width and uniform particle size, it is possible to suppress pressure fluctuations in the extruder during melt molding. As a result, a homogeneous melt-molded product can be continuously obtained over a long period of time. The half-value width of the particle size distribution can be determined from the distribution of the diameter values obtained as the equivalent circle diameter from the areas of a large number of pellet images observed two-dimensionally. Specifically, it can be measured using a dynamic image analysis device. The half-value width is preferably 0.6 mm or less, and more preferably 0.5 mm or less.

[0058] Thus, as a method for obtaining pellets with uniform particle size, there are methods such as devising a cutting method and a method of sieving. Among them, the sieving method is preferable because it can reliably and simply reduce the half-value width of the particle size distribution. When sieving, it is preferable to use at least two types of sieves with different mesh sizes to remove pellets that are too large and too small.

[0059] By using the EVOH resin composition pellets of the present invention thus obtained and performing melt molding, various molded articles such as films, sheets, containers, pipes, and fibers can be obtained. As the melt molding method, extrusion molding, inflation extrusion, blow molding, melt spinning, injection molding, etc. are possible. The melting temperature varies depending on the melting point of EVOH, etc., but is preferably about 150 to 270°C.

[0060] The obtained molded article may be a molded article composed of a single layer of only the EVOH resin composition of the present invention, but it is preferably a multilayer structure including at least one layer composed of the EVOH resin composition. As the layer structure of the multilayer structure, when the resin composition of the present invention is represented by E, the adhesive resin by Ad, and other thermoplastic resins by T, examples include E / T, T / E / T, E / Ad / T, T / Ad / E / Ad / T, etc., but are not limited thereto. Each layer shown here may be a single layer or a multilayer.

[0061] The method for manufacturing the above multilayer structure is not particularly limited. For example, a method of co-extruding or co-injecting the EVOH resin composition of the present invention and a thermoplastic resin, a method of melt-extruding a thermoplastic resin onto a molded article (film, sheet, etc.) composed of the EVOH resin composition, conversely, a method of co-extruding the EVOH resin composition and another thermoplastic resin onto a substrate such as a thermoplastic resin, and further, a method of laminating a molded article obtained from the EVOH resin composition of the present invention and a film or sheet of another substrate using a known adhesive, etc. Among them, the co-extrusion or co-injection method is preferable.

[0062] The multilayer structure thus obtained can be used as various packaging materials such as films, sheets, and containers. Since it has excellent barrier properties and moldability, it is suitable for food packaging containers, fuel containers, medicine containers, etc.

Examples

[0063] Hereinafter, the present invention will be described more specifically using examples. The evaluation methods in the examples are as follows.

[0064] (1) Light transmittance A mixed solvent with a 1-propanol content of 60% by mass and a water content of 40% by mass was prepared. EVOH composition pellets of the sample were put into this, and while stirring, they were dissolved at 80 °C over 6 hours to prepare a 5% by mass EVOH solution. The EVOH solution in which the pellets were completely dissolved was cooled and put into a measurement cell (made of quartz: optical path length 10 mm). Using a spectrophotometer UV-2450 manufactured by Shimadzu Corporation, the light transmittance at 25 °C with wavelengths from 350 nm to 600 nm was measured, and the average value was taken as the light transmittance (T1). Also, the light transmittance (T2) was measured in the same manner as above except that a mixed solvent with a 1-propanol content of 40% by mass and a water content of 60% by mass was used. When measuring T1 and T2, the light transmittance when only the solvent in which EVOH was not dissolved was put into the cell was taken as 100%, and the relative light transmittance (%) was determined.

[0065] (2) Full width at half maximum in the particle size distribution of the pellets The particle size distribution of the dry pellets obtained in the examples and comparative examples was determined from the equivalent circle diameter (diameter) calculated by the dynamic image analysis method in accordance with ISO 13322-2 (2006) using 500 g of the pellets as the sample and "CAMSIZER XT" from VERDER Scientific. The equivalent circle diameter refers to the equivalent circle diameter (diameter) obtained from the area of the pellet image observed two-dimensionally. The full width at half maximum (mm) was determined from the obtained particle size distribution.

[0066] (3) Defects in the film A single-layer film-forming test was conducted using the dried pellets obtained in the examples and comparative examples. A film with a thickness of 20 μm was obtained using an extruder and a T-die with the following specifications. · Extruder: "GT-40-A" manufactured by Plastic Engineering Laboratory Co., Ltd. · Type: Single-screw extruder (non-vent type) · L / D: 26 · CR: 2.8 · Caliber: 40 mm φ · Screw: Double flight type · Rotation speed: 40 rpm · Driving machine: DC motor "SCR-DC218B" manufactured by Sumitomo Heavy Industries, Ltd. · Motor capacity: DC 7.5 KW (rated 45 A) · Extruder heater: Three-division type · C1 / C2 / C3 = 190 °C / 240 °C / 260 °C · Ten resin pressure gauges were installed in the cylinder at equal intervals. · Die width: 550 mm · Resin temperature inside the die: 260 °C · Take-up speed: 10 m / min

[0067] The lumps (with a diameter of about 100 μm or more that can be visually confirmed) in the film 1 hour after the start of film formation were counted and converted to the number per 1.0 m. The film was judged as follows based on this number. 2 A: Less than 20 B: 20 or more and less than 100 C: 100 or more and less than 500 D: 500 or more D: 500 or more

[0068] (4) Streaks in the film (3) A single-layer film-forming test was conducted in the same manner as above. The streaks (with a width of about 100 μm or more that can be visually confirmed) in the film 1 hour after the start of film formation were counted and converted to the number per 1.0 m. 2 Based on this number, the appearance of the film was judged as follows. A: Less than 2 B: 2 or more and less than 6 C: 6 or more and less than 21 D: 21 or more

[0069] (5) Flow marks in the film (3) A single-layer film-forming test was conducted in the same manner as above. After 1 hour from the start of film formation, the number of flow marks in the film (when the film was held against a fluorescent lamp and those with a width of about 1 cm or more whose refractive index change could be visually confirmed with the naked eye) was counted and converted per 1.0 m 2 The appearance of the film was judged as follows based on the number. A: Less than 1 place B: 1 or more and less than 3 places C: 3 or more and less than 10 places D: 10 or more

[0070] (6) Amount of adhesion inside the die (3) A single-layer film-forming test was conducted in the same manner as above. After 8 hours from the start of film formation, after replacing the EVOH resin composition in the extruder with low-density polyethylene (LDPE) with an MFR (190 °C, 2160 g load) of 1 g / 10 minutes over 10 minutes, the mass of the resin in which the EVOH adhering to the inside of the die had thermally deteriorated was measured and evaluated according to the following criteria. A: Less than 3 g B: 3 g or more and less than 5 g C: 5 g or more and less than 10 g D: 10 g or more

[0071] Here, the amount of adhesion inside the die is an index indicating the long-term performance in melt molding using the EVOH resin composition. The die deposits continuously accumulate on the surface of the metal after the start of melt molding, and as the molding time progresses, thermal deterioration progresses and adheres inside the die. Since the deposits have undergone thermal deterioration, coloring and crosslinking are progressing, and when they are mixed into the molded product, they cause poor appearance. The amount of adhesion inside the die is the quantification of the die deposits after a certain period of time and is an index for evaluating long-term performance. The amount of adhesion inside the die depends on the shear rate of the molten resin inside the die and indicates the accumulation of the retained material in the low shear region of 1 to 30 (1 / S).

[0072] (7) Pressure fluctuation A single-layer film-forming test was carried out in the same manner as in (3). In the continuous film formation for 6 hours from 1 hour after the start of film formation to 7 hours after the start of film formation, the maximum pressure P and the minimum pressure P of the resin pressure P10 measured by the pressure gauge at the tip of the extruder (the 10th) were used. The difference ΔP between them was evaluated according to the following criteria. MAX and the minimum pressure P MIN was evaluated according to the following criteria. A: ΔP ≦ 0.3 B: 0.3 < ΔP ≦ 0.6 C: 0.6 < ΔP ≦ 1.0 D: 1.0 < ΔP

[0073] Example 1 100 parts by mass of an ethylene-vinyl acetate copolymer having an ethylene unit content of 32 mol% and 400 parts by mass of methanol were charged into a saponification reactor, and further 0.16 part by mass of a methanol solution of sodium hydroxide (80 g / L) (sodium hydroxide / vinyl acetate unit = 0.4 / 1 (molar ratio)) was charged. Nitrogen gas was blown into this reactor, and while removing by-produced methyl acetate out of the system together with methanol, the reaction was carried out at 60 °C for 4 hours. Then, the reaction was stopped by neutralizing with acetic acid, and an EVOH methanol solution composed of 57 parts by mass of EVOH and 75 parts by mass of methanol was obtained. The saponification degree of this EVOH was 99.95 mol%.

[0074] Next, water was added to the EVOH methanol solution to make the mass ratio of the solvent in the EVOH solution (methanol / water) 60 / 40. The EVOH solution in this state at 60 °C was withdrawn from the bottom of the above reactor by a gear pump and supplied to a bucket-type first filter (first filtration step). The differential pressure between the inlet pressure and the discharge pressure of the first filter was set to 0.3 MPa, and a metal element with an opening of 100 μm was arranged in the filtration section. After filtration, methanol was added to the EVOH solution to make the mass ratio of the solvent in the EVOH solution (methanol / water) 80 / 20. This EVOH solution was kept at 60 °C and supplied to a bucket-type second filter by a gear pump (second filtration step). The differential pressure between the inlet pressure and the discharge pressure of the second filter was set to 0.5 MPa, and a metal element with an opening of 60 μm was arranged in the filtration section.

[0075] The EVOH solution that had passed through the first filtration step 1 and the second filtration step 2 was extruded into water through a metal plate with a circular opening to solidify into strands, which were then cut into pellets with a diameter of about 3 mm and a length of about 5 mm. The pellets were deliquified in a centrifuge, and the deliquification process was repeated by adding a large amount of water.

[0076] The EVOH pellets thus obtained (ethylene unit content 32 mol%, saponification degree 99.95 mol%, moisture content 26% by mass) were fed into the cylinder barrel 10 from the raw material supply section 1 of the twin-screw extruder 20 shown in FIG. 1. The water-containing EVOH in a fluidized state was sent forward by the full-flight screw section 2, kneaded by the reverse-flight screw section 3, and the moisture content was adjusted by removing excess moisture at the vent 7. Thereafter, the pellets were sent forward by the full-flight screw section 4, and an aqueous solution of acetic acid / boric acid / sodium acetate / magnesium acetate / potassium dihydrogen phosphate was injected from the additive injection section 8. Thereafter, the pellets were kneaded by the reverse-flight screw section 5, passed through the full-flight screw section 6, and discharged from the discharge port 11. The temperature of the resin composition measured by the temperature sensor 9 provided near the discharge port was 100°C.

[0077] The amount of EVOH fed per unit time was 10 kg / hr (including the mass of water contained), and the amount of additive fed per unit time was 0.65 L / hr. The additive composition was an aqueous solution containing 4.3 g / L of acetic acid, 15 g / L of boric acid, 4.6 g / L of sodium acetate, 3.0 g / L of magnesium acetate, and 1.4 g / L of potassium dihydrogen phosphate.

[0078] The specifications of the twin-screw extruder 20 are as follows: Length: 45.5 ·Aperture: 30mmφ Screw: Same direction full intermeshing type Rotational speed: 300 rpm Motor capacity: DC22kW Heater: 13-split type

[0079] The EVOH resin composition derived from the discharge port 11 was discharged from a die with six 3-mm-diameter holes. The temperature of the EVOH resin composition in the die at this time was 105°C. The discharged EVOH resin composition was cut with a center hot cutter while in a flowing state. The rotational speed of the cutter blade was 2700 rpm.

[0080] The moisture content of the obtained EVOH resin composition pellets was 17% by mass. These pellets were dried at 100°C for 15 hours using a fluidized dryer and subsequently dried at 100°C for 15 hours using a static dryer. As a result, the moisture content was 0.3% by mass. The acetic acid content in the dried EVOH resin composition pellets was 300 ppm, the boron compound content was 270 ppm in terms of boron, the phosphoric acid compound content was 100 ppm in terms of phosphate radical, the alkali metal salt content was 40 ppm in terms of potassium as the metal, the sodium content was 130 ppm in terms of sodium as the metal, and the alkaline earth metal salt content was 50 ppm in terms of magnesium as the metal. Also, the MFR (190°C, 2160 g load) was 1.5 g / 10 min.

[0081] Thereafter, the dried EVOH resin composition pellets were sieved through sieves stacked in the order of 6.5 mesh, 7 mesh, and 8 mesh over 10 minutes, and the pellets remaining on the 8-mesh sieve were collected to obtain pellets for molding. The obtained pellets were slightly flattened ellipsoids, with a length in the longitudinal direction of 3.2 mm and a length in the short transverse direction of 2.1 mm. The obtained pellets were evaluated according to the above evaluation method. The evaluation results are shown in Table 1.

[0082] Example 2 、3、5、 8. Comparative Examples 1 to 6 Resin composition pellets were prepared and evaluated in the same manner as in Example 1, except that the ethylene unit content, filtration conditions, and sieving conditions of the synthesized EVOH were changed as shown in Table 1. The evaluation results are summarized in Table 1. Here, Example 2 、3、5 and Comparative Examples 1 to 6Then, EVOH was synthesized in the same manner as in Example 1. The EVOH synthesized in Example 8 had an ethylene unit content of 44 mol%, a saponification degree of 99.7 mol%, and an MFR (190 °C, 2160 g load) of 4 g / 10 min. In Comparative Example 1, the first filtration step in Example 1 was omitted. In Comparative Example 2, the second filtration step in Example 1 was omitted.

[0083]

Table 1

Explanation of Symbols

[0084] 1 Raw material supply section 2, 4, 6 Full flight screw section 3, 5 Reverse flight screw section 7 Vent 8 Additive injection section 9 Temperature sensor 10 Cylinder barrel 11 Discharge port 20 Twin-screw extruder

Claims

1. A resin composition comprising an ethylene-vinyl alcohol copolymer having an ethylene unit content of 20 to 60 mol% and a saponification degree of 99 mol% or more; The light transmittance T1 of a solution obtained by dissolving 5 parts by mass of the resin composition in 95 parts by mass of a 1-propanol / water mixed solvent (1-propanol content: 60% by mass) is 96% or more, and A resin composition in which the light transmittance T2 of a solution obtained by dissolving 5 parts by mass of the resin composition in 95 parts by mass of a 1-propanol / water mixed solvent (1-propanol content: 40% by mass) is 97% or more.

2. The resin composition according to claim 1, containing at least one additive selected from carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts.

3. Pellets comprising the resin composition according to claim 1 or 2.

4. The pellets according to claim 3, wherein the shape of the pellets is cylindrical or ellipsoidal, and the half-value width of the particle size distribution of the pellets is 0.7 mm or less.

5. A multilayer structure having at least one layer comprising the resin composition according to claim 1 or 2.

6. A process for producing the resin composition according to claim 1 or 2, comprising the steps of adding an alkali catalyst to a methanol solution of an ethylene-vinyl ester copolymer to saponify the ethylene-vinyl ester copolymer to obtain a methanol solution of an ethylene-vinyl alcohol copolymer, adding water to the solution after saponification to adjust the methanol content to 54 to 66% by mass and then performing a first filtration, adding methanol to the solution after the first filtration to adjust the methanol content to 74 to 86% by mass and then performing a second filtration, and removing the solvent from the solution after the second filtration.

7. A process for producing the resin composition according to claim 1 or 2, comprising the steps of adding an alkali catalyst to a methanol solution of an ethylene-vinyl ester copolymer to saponify the ethylene-vinyl ester copolymer to obtain a methanol solution of an ethylene-vinyl alcohol copolymer, adding water to the solution after saponification to adjust the methanol content to 74 to 86% by mass and then performing a first filtration, adding further water to the solution after the first filtration to adjust the methanol content to 54 to 66% by mass and then performing a second filtration, and removing the solvent from the solution after the second filtration.

8. A step of adding an alkali catalyst to a methanol solution of an ethylene-vinyl ester copolymer to saponify the ethylene-vinyl ester copolymer to obtain a methanol solution of an ethylene-vinyl alcohol copolymer; a step of adding water to the solution after saponification to make the methanol content 54 to 66% by mass and then performing the first filtration; a step of adding methanol to the solution after the first filtration to make the methanol content 74 to 86% by mass and then performing the second filtration; a step of removing the solvent from the solution after the second filtration; a cutting step; and a drying step, the method for producing pellets according to claim 3 or 4.

9. A step of adding an alkali catalyst to a methanol solution of an ethylene-vinyl ester copolymer to saponify the ethylene-vinyl ester copolymer to obtain a methanol solution of an ethylene-vinyl alcohol copolymer; a step of adding water to the solution after saponification to make the methanol content 74 to 86% by mass and then performing the first filtration; a step of further adding water to the solution after the first filtration to make the methanol content 54 to 66% by mass and then performing the second filtration; a step of removing the solvent from the solution after the second filtration; a cutting step; and a drying step, the method for producing pellets according to claim 3 or 4.

10. The method for producing pellets according to claim 8 or 9, further comprising a sieving step after the drying step, wherein pellets that are too large and pellets that are too small are removed in the sieving step.

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