CN110945059A

CN110945059A - Melt-molding material

Info

Publication number: CN110945059A
Application number: CN201880054441.6A
Authority: CN
Inventors: 野中康弘; 米谷英里子
Original assignee: Kuraray Co Ltd
Current assignee: Kuraray Co Ltd
Priority date: 2017-08-21
Filing date: 2018-08-21
Publication date: 2020-03-31
Anticipated expiration: 2038-08-21
Also published as: WO2019039458A1; TWI793152B; CN110945059B; TW201920432A; JP7160816B2; JPWO2019039458A1

Abstract

Provided is a melt molding material which can suppress the occurrence of sudden particles during continuous melt molding. The present invention is a melt-molding material, wherein the maximum height roughness (Rz) of the side surface of the columnar, flat or spherical melt-molding material comprising an ethylene-vinyl alcohol copolymer is 300 [ mu ] m or less. The arithmetic average roughness (Ra) of the side surface is preferably 50 μm or less. The full width at half maximum in the particle size distribution of the melt molding material having the same circle diameter is preferably 1mm or less. The ethylene unit content of the ethylene-vinyl alcohol copolymer is preferably 20 mol% or more and 60 mol% or less.

Description

Melt-molding material

Technical Field

The present invention relates to a melt-molding material.

Background

Ethylene-vinyl alcohol copolymers (hereinafter also referred to as "EVOH") are excellent in gas barrier properties, transparency, oil resistance, non-charging properties, mechanical strength, and the like, and are widely used as various packaging materials for films, sheets, containers, and the like.

These various packaging materials and the like are generally formed by a melt forming method. Therefore, a melt-molding material containing EVOH is generally required to have excellent appearance characteristics, long-term run stability, and the like at the time of melt-molding. The appearance characteristics are: in general, a molded article having excellent appearance such as no occurrence of gels or particulates and no occurrence of coloring such as yellowing can be obtained. Further, long-term runnability means: the physical properties such as viscosity do not change even after long-term molding, and a molded article free from streaks or the like can be obtained.

The reason why the appearance characteristics and long-term workability are deteriorated is said to be thermal deterioration of EVOH. In order to improve these various properties, particularly appearance properties, required for melt-molding materials containing EVOH,

patent documents

1 and 2 propose various EVOH compositions in which EVOH is added with an appropriate content of an acid such as a carboxylic acid or a phosphoric acid, an alkali metal salt, an alkaline earth metal salt, or other metal salt. These EVOH compositions are said to provide molded articles having suppressed thermal deterioration, improved appearance characteristics and long-term workability, and excellent appearance even in long-term continuous molding.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. Sho 64-66262

Patent document 2: japanese patent laid-open No. 2001-146539.

Disclosure of Invention

Problems to be solved by the invention

In addition to the properties related to the appearance and long-term running properties due to the thermal degradation, it is required to suppress the generation of shot (sudden shot) which occurs suddenly during continuous melt molding of a melt-molding material containing EVOH. The present inventors confirmed that the formation of carbonyl groups in the sudden particulate matter was hardly caused by thermal degradation by infrared spectroscopy. That is, according to the findings of the present inventors, the sudden particulate matter is generated by a factor different from the gel, the particulate matter, the coloring, and the like generated due to the thermal degradation, and cannot be sufficiently solved by adding an additive such as an acid or a metal salt.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a melt molding material capable of suppressing generation of sudden granular objects at the time of continuous melt molding.

Means for solving the problems

The present invention has been made to solve the above problems, and an object of the present invention is to provide a melt-molded material having a columnar shape, a flat shape, or a spherical shape, which contains an ethylene-vinyl alcohol copolymer (EVOH), and which has a maximum height roughness (Rz) of a side surface of 300 μm or less.

The inventors of the present invention found that: the burst particles are generated by the following reasons. In the continuous melt molding, the following phenomenon occurs when a melt molding material (EVOH) is transported by gas flow through a pipe and sent to a hopper of a melt molding machine. During the air flow conveyance, a part of the molten molding material is ground and pulverized by the impact of the molten molding material on the inner surface of the pipe and the impact of the molten molding materials with each other. In a retention portion such as a curved portion of the pipe, the EVOH in which the fine powder is generated is melted by frictional heat generated during air flow conveyance, and thereby, a band-shaped foreign matter is formed. The foreign matter is discontinuously discharged from the retention section during continuous melt molding, and is supplied to the melt molding machine together with the molten molding material. However, since the foreign matter is in the form of a band, it is difficult to apply shear, and it is difficult to melt the foreign matter in the melt molding machine. Therefore, the foreign matter remains in the obtained molten molded body, that is, particulate matter derived from the foreign matter is abruptly generated. In particular, EVOH is a hard resin having a high glass transition temperature and hydroxyl groups, and therefore, is easily pulverized during air transportation, and is likely to generate sudden particles. In contrast, according to the melt molding material of the present invention, the maximum height roughness (Rz) of the side surface is set to 300 μm or less, so that grinding is less likely to occur when the material impacts the inner surface of the pipe during gas flow conveyance. Therefore, according to the melt molding material, generation of fine powder during air-stream conveyance is suppressed, and as a result, generation of sudden particulate matter is suppressed.

The arithmetic average roughness (Ra) of the side surface is preferably 50 μm or less. By setting the arithmetic mean roughness (Ra) of the side surface to 50 μm or less, generation of fine powder during air flow conveyance can be further suppressed, and generation of sudden particulate matter can be further reduced. In addition, by doing so, the amount of fine powder generated is reduced, and the generation of band-like foreign matter is also reduced, so that the thickness unevenness of the obtained molten molded body can also be suppressed.

The full width at half maximum in the particle size distribution of the melt molding material having the same circle diameter is preferably 1mm or less. By thus making the particle size of the melt-molding material relatively uniform, the biting into the extruder from the hopper at the time of melt-molding is stabilized, and the thickness unevenness of the obtained melt-molded article can be suppressed.

The ethylene unit content of the ethylene-vinyl alcohol copolymer is preferably 20 mol% or more and 60 mol% or less. By setting the ethylene unit content in the above range, melt moldability, gas barrier properties, and the like can be exhibited in a good balance.

When the melt molding material is cylindrical, the height is 1 to 20mm and the diameter is 1 to 20mm, whereby the biting property and the like during melt molding can be improved.

When the melt molding material is flat or spherical, the length in the longitudinal direction is 1 to 20mm, and the length in the width direction is 1 to 20mm, whereby the biting property and the like at the time of melt molding can be improved.

ADVANTAGEOUS EFFECTS OF INVENTION

The melt molding material of the present invention can suppress the generation of sudden particles during continuous melt molding.

Drawings

Fig. 1 (a) is a perspective view of a columnar molten molding material according to an embodiment of the present invention. Fig. 1 (b) is a front view of a flat molten molding material according to an embodiment of the present invention.

Fig. 2 (a) is a photograph of a band-shaped foreign matter collected from a hopper in the production of a single-layer film from the molten molding material obtained in comparative example 1. Both ends of the foreign matter were fixed with tape and photographed together with a ruler (cm mark). Fig. 2 (b) is an enlarged photograph of the above-mentioned band-shaped foreign matter obtained in comparative example 1.

Detailed Description

Hereinafter, a melt molding material according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings as appropriate.

(shape, etc.)

The melt molding material 1 shown in fig. 1 (a) is a columnar melt molding material containing EVOH. The melt-formed material 1 may be a granular substance called a pellet. Here, "columnar" refers to a shape having substantially parallel upper and lower surfaces. Substantially parallel means that the angle formed by the upper surface and the lower surface is within ± 10 °. The upper and lower surfaces may be substantially planar or may be curved. The upper and lower surfaces are typically substantially the same shape, and may be different. The upper surface and the lower surface may be substantially the same size or may be different. The molten molding material 1 may be a straight column or an oblique column, and is preferably a straight column.

Specifically, the molten molding material 1 in fig. 1 (a) has a cylindrical shape. The columnar shape means a columnar shape having a circular cross section in a direction perpendicular to the central axis (axial direction) X. The circular shape is not limited to a perfect circle, and may be an ellipse, or a circle having a concave portion or a convex portion. The molten molding material may be in the form of a columnar, quadrangular prism, hexagonal prism, or the like. Among them, a cylindrical shape is preferable from the viewpoint of further suppressing the pulverization at the time of air flow conveyance.

The cylindrically shaped melt-formed material 1 has an upper surface 3a, a lower surface 3b, and a side surface 2. The upper surface 3a and the lower surface 3b may be rounded in the same size. The edge of the upper surface 3a or the lower surface 3b that contacts the side surface 2 may have a curvature.

The size of the molten molding material 1 is not particularly limited, and the lower limit of the height a is preferably 1mm, more preferably 2 mm. On the other hand, the upper limit of the height a is preferably 20mm, more preferably 10mm, and further preferably 5 mm. The lower limit of the diameter B of the molten molding material 1 is preferably 1mm, and more preferably 2 mm. On the other hand, the upper limit of the diameter B is preferably 20mm, more preferably 10mm, and still more preferably 5 mm. When the molten molding material 1 has such a size, handling properties, conveyance properties during air flow conveyance, and biting properties into the extruder can be improved.

The upper limit of the maximum height roughness (Rz) of the side surface 2 of the molten molding material 1 is 300. mu.m, preferably 200. mu.m, more preferably 150. mu.m, still more preferably 120. mu.m, and particularly preferably 100. mu.m. By setting the maximum height roughness (Rz) to 300 μm or less, generation of band-like foreign matter is suppressed by reduction of fine powder generated during air flow conveyance in the pipe, and as a result, generation of sudden particulates during continuous melt molding can be suppressed, and unevenness in thickness of the obtained melt molded article can be suppressed.

On the other hand, the lower limit of the maximum height roughness (Rz) of the side face 2 is preferably 10 μm, more preferably 30 μm, and still more preferably 50 μm. By setting the maximum height roughness (Rz) of the side surface 2 of the molten molding material 1 to 10 μm or more, for example, the biting of the molten molding material into the extruder from the hopper is stabilized, the torque variation and the discharge variation in the melt molding machine are suppressed, and the thickness unevenness of the obtained molten molded article can be reduced. On the other hand, if the surface smoothness of the molten molding material 1 is too high, the material tends to slip, and the material may not be stably bitten into the extruder. Further, by setting the maximum height roughness (Rz) of the side surface of the melt-molded material 1 to 10 μm or more, it is possible to suppress an increase in cost at the time of manufacturing the melt-molded material 1 itself.

The upper limit of the arithmetic mean roughness (Ra) of the side surface 2 of the molten molding material 1 is preferably 50 μm, more preferably 40 μm, still more preferably 30 μm, yet more preferably 25 μm, yet more preferably 20 μm, and most preferably 10 μm. By setting the arithmetic average roughness (Ra) to 50 μm or less, generation of fine powder during air flow conveyance can be further suppressed, and generation of sudden particulate matter can be further reduced. Further, since the amount of fine powder generated is reduced and the generation of band-like foreign matter is also reduced, the thickness unevenness of the obtained molten molded body can be suppressed.

On the other hand, the lower limit of the arithmetic average roughness (Ra) of the side surface 2 is preferably 1 μm, more preferably 3 μm, still more preferably 3.5 μm, and still more preferably 5 μm. By setting the arithmetic mean roughness (Ra) of the side surface 2 of the melt molding material 1 to 1 μm or more, the biting into the extruder is stabilized, and the thickness unevenness of the obtained melt molding can be reduced. Further, by setting the arithmetic average roughness (Ra) of the side surface 2 of the molten molding material 1 to 1 μm or more, it is possible to suppress an increase in cost in manufacturing the molten molding material 10 itself.

Here, in the present specification, the maximum height roughness (Rz) and the arithmetic average roughness (Ra) of the melt-molded material are each an average value of measured values of 100 optional melt-molded materials. The measured values of the maximum height roughness (Rz) and the arithmetic mean roughness (Ra) of the melt-molded material were measured by a cutoff value (λ c) of 2.5mm in accordance with JIS B0601 (2001). In the present specification, the term "evaluation surface" means a non-contact surface, and the evaluation surface has a maximum width of 1414 μm and a height of 1060 μm. When the molten molding material is small, the evaluation area may be appropriately adjusted.

The melt-molded material 11 shown in fig. 1 (b) is a flat melt-molded material containing EVOH. The melt-formed material 11 may be a particulate matter called a pellet. Here, the "flat shape" refers to a shape in which a cross section having a section including the rotation axis (central axis) Y as a cut section is elliptical. The flat molten molding material 11 may be a rotational ellipsoid. When the flat melt-molding material 11 is left standing on a horizontal surface, a direction along a portion having the longest linear distance along the horizontal direction is referred to as a longitudinal direction d (parallel to the horizontal direction in fig. 1 (b)), and a direction perpendicular to the horizontal surface is referred to as a width direction c. The width direction c is the same as the direction of the rotation axis Y. In general, in the flat melt-formed material 11, the length C in the width direction C is shorter than the length D in the length direction D. The melt molding material may be a spherical melt molding material containing EVOH. The "spherical shape" refers to a shape having a circular cross section with a section including the rotation axis Y as a cut section. In fig. 1 (b), when the length C in the width direction C and the length D in the longitudinal direction D are the same, the melt-molding material 11 is spherical.

In the flat or spherical melt-molded material 11, the maximum height roughness (Rz) of the side surface 12 is 300 μm or less. Here, in the flat or spherical melt-molded material 11, the side surface 12 means: the surface of the molten molding material 11 has a curved surface portion whose normal line is substantially perpendicular to the rotation axis Y (width direction c). The side surface 12 is a curved surface portion including the so-called equator and extending in the circumferential direction. In fig. 1 (b), the side surface 12 is a region surrounded by a broken line along the longitudinal direction d (the same applies to the region corresponding to the back side of the paper surface in fig. 1 (b)). When the molten molding material is spherical, any portion of the surface is a side surface.

The size of the melt-molding material 11 is not particularly limited, and the lower limit of the length C in the width direction of the melt-molding material 11 is preferably 1mm, more preferably 1.5 mm. On the other hand, the upper limit of the width direction length C is preferably 20mm, more preferably 10mm, and further preferably 5 mm. The lower limit of the longitudinal length D is preferably 1mm, and more preferably 1.5 mm. On the other hand, the upper limit of the longitudinal length D is preferably 20mm, more preferably 10mm, and still more preferably 5 mm. When the molten molding material 11 has such a size, the handling property, the conveyance property during air flow conveyance, the biting property into the extruder, and the like can be further improved.

The upper limit of the maximum height roughness (Rz) of the side surface 12 of the melt molding material 11 is 300 μm, preferably 200 μm, more preferably 150 μm, still more preferably 120 μm, and particularly preferably 100 μm. By setting the maximum height roughness (Rz) to 300 μm or less, generation of band-like foreign matter is suppressed by reduction of fine powder generated during air flow conveyance in the pipe, and as a result, generation of sudden particulates during continuous melt molding can be suppressed, and unevenness in thickness of the obtained melt molded article can be suppressed.

On the other hand, the lower limit of the maximum height roughness (Rz) of the side surface 12 is preferably 10 μm, more preferably 30 μm, and still more preferably 50 μm. By setting the maximum height roughness (Rz) of the side surface 12 of the melt molding material 11 to 10 μm or more, for example, the biting of the melt molding material into the extruder from the hopper is stabilized, the torque variation and the discharge variation in the melt molding machine are suppressed, and the thickness unevenness of the obtained melt molding can be reduced. On the other hand, if the surface smoothness of the melt-molding material 11 is too high, the material tends to slip, and the material may not be stably bitten into the extruder. Further, by setting the maximum height roughness (Rz) of the side surface of the melt-molded material 11 to 10 μm or more, it is possible to suppress an increase in cost at the time of manufacturing the melt-molded material 11 itself.

The upper limit of the arithmetic mean roughness (Ra) of the side surface 12 of the melt molding material 11 is preferably 50 μm, more preferably 40 μm, still more preferably 30 μm, still more preferably 25 μm, still more preferably 20 μm, and most preferably 10 μm. By setting the arithmetic average roughness (Ra) to 50 μm or less, generation of fine particles during air flow conveyance can be further suppressed, and generation of sudden particulate matter can be further reduced. Further, since the amount of fine powder generated is reduced and the generation of band-like foreign matter is also reduced, the thickness unevenness of the obtained molten molded body can be suppressed.

On the other hand, the lower limit of the arithmetic average roughness (Ra) of the side surface 12 is preferably 1 μm, more preferably 3 μm, still more preferably 3.5 μm, and still more preferably 5 μm. By setting the arithmetic mean roughness (Ra) of the side surface 12 of the melt molding material 11 to 1 μm or more, the biting into the extruder is stabilized, and the thickness unevenness of the obtained melt molding can be reduced. Further, by setting the arithmetic mean roughness (Ra) of the side surface 12 of the melt-molded material 11 to 1 μm or more, it is possible to suppress an increase in cost in manufacturing the melt-molded material 11 itself.

The maximum height roughness (Rz) and the arithmetic mean roughness (Ra) of the side surface 2 of the molten molding material 1 and the side surface 12 of the molten molding material 11 can be adjusted by controlling the surface roughness of the inner surface of the mold when molding the molten molding material, the drying conditions of the molten molding material, and the like, as described later.

The upper limit of the full width at half maximum (FWHM) in the particle size distribution of the equivalent circle diameter (diameter) of the melt molding material (hereinafter, the melt molding material in the form of a pillar, a plate, or a sphere may be simply referred to as the melt molding material) is preferably 1mm, more preferably 0.6mm, still more preferably 0.5mm, and particularly preferably 0.4 mm. The size of the molten molding material can be made uniform by setting the half width of the molten molding material in the particle size distribution to 1mm or less, and the biting into the extruder can be stabilized, so that the thickness unevenness of the obtained molten molded article can be suppressed. On the other hand, the lower limit of the full width at half maximum in the particle size distribution may be 0.1mm, 0.2mm, or 0.3 mm.

In the present specification, the particle size distribution of the circle equivalent diameter (radius) of the molten molding material is a particle size distribution of the circle equivalent diameter calculated by a moving image analysis method according to ISO 13322-2 (2006) using 500g of the molten molding material.

The particle size distribution of the melt-molding material can be adjusted by sieving the produced melt-molding material or the like.

（EVOH）

Next, EVOH contained in the melt molding material will be described. EVOH is a copolymer having an ethylene unit and a vinyl alcohol unit as a main structural unit. The EVOH may contain 1 or more kinds of other structural units in addition to the ethylene unit and the vinyl alcohol unit. EVOH is generally obtained by polymerizing ethylene with a vinyl ester, and saponifying the resulting ethylene-vinyl ester copolymer. The polymerization and saponification can be carried out by a conventionally known method.

The lower limit of the ethylene unit content of the EVOH (i.e., the proportion of the number of ethylene units in the EVOH relative to the total number of monomer units) is preferably 20 mol%, more preferably 22 mol%, and still more preferably 24 mol%. On the other hand, the upper limit of the ethylene unit content of the EVOH is preferably 60 mol%, more preferably 55 mol%, and still more preferably 50 mol%. When the ethylene unit content of the EVOH is in the above range, sufficient melt moldability, gas barrier properties, and the like can be exhibited. More specifically, by setting the ethylene unit content of the EVOH to 20 mol% or more, for example, the water resistance, hot water resistance, gas barrier properties under high humidity, and melt moldability of the obtained melt-molded article can be improved. On the other hand, by setting the ethylene unit content of EVOH to 60 mol% or less, the gas barrier property and the like of the obtained molded article can be improved.

The lower limit of the saponification degree of EVOH (i.e., the ratio of the number of vinyl alcohol units in EVOH to the total number of vinyl alcohol units and vinyl ester units) is preferably 80 mol%, more preferably 95 mol%, and still more preferably 99 mol%. On the other hand, the upper limit of the saponification degree of EVOH is preferably 100 mol%, more preferably 99.99 mol%. By setting the saponification degree of EVOH to 80 mol% or more, the gas barrier property, the coloring resistance, and the like of the melt-molded article can be improved.

The lower limit of the melt flow rate of EVOH (measured in accordance with JIS K7210 under conditions of a temperature of 210 ℃ and a load of 2160 g) is preferably 0.1g/10 min, more preferably 0.5g/10 min, still more preferably 1g/10 min, and particularly preferably 3g/10 min. On the other hand, the upper limit of the melt flow rate of EVOH is preferably 200g/10 minutes, more preferably 50g/10 minutes, still more preferably 30g/10 minutes, particularly preferably 15g/10 minutes, and most preferably 10g/10 minutes. When the melt flow rate of EVOH is set to a value within the above-mentioned range, the melt-moldability of the melt-moldable material is further improved.

The lower limit of the content of EVOH in the melt molding material is preferably 50 mass%, more preferably 90 mass%, still more preferably 99 mass%, and particularly preferably 99.9 mass%. By setting the content of EVOH in the melt molding material to 50 mass% or more, various properties based on EVOH, such as gas barrier properties and transparency, of the obtained melt molded article can be improved. The content of EVOH may be 100 mass%.

(other Components)

The melt-molding material may contain other components than EVOH. Examples of the other components include carboxylic acids, carboxylic acid salts, phosphoric acid compounds, and boron compounds. When these components are contained, the appearance characteristics and long-term operability can be improved.

The carboxylic acid may be a monocarboxylic acid or a polycarboxylic acid.

Examples of the monocarboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, caproic acid, capric acid, acrylic acid, methacrylic acid, benzoic acid, and 2-naphthoic acid. These monocarboxylic acids may have a hydroxyl group or a halogen atom. Examples of the monocarboxylate ion include ions obtained by removing a hydrogen ion from a carboxyl group of each monocarboxylic acid.

The polycarboxylic acid may have 2 or more carboxyl groups in the molecule, and examples thereof include aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, malic acid, glutaric acid, adipic acid, and pimelic acid; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid; tricarboxylic acids such as citric acid, isocitric acid, aconitic acid, and the like; carboxylic acids having 4 or more carboxyl groups such as 1,2,3, 4-butanetetracarboxylic acid and ethylenediaminetetraacetic acid; hydroxycarboxylic acids such as citric acid, isocitric acid, tartaric acid, malic acid, mucic acid, tartronic acid, citramalic acid, etc.; ketocarboxylic acids such as oxaloacetic acid, acetonic acid, 2-ketoglutaric acid, and 3-ketoglutaric acid; amino acids such as glutamic acid, aspartic acid, and 2-aminoadipic acid.

Examples of the phosphoric acid compound include various phosphorus oxyacids such as phosphoric acid and phosphorous acid, and salts thereof. The phosphate may be contained in any form of, for example, dihydrogen phosphate, hydrogen phosphate, or phosphate, and the kind of counter cation is not particularly limited, but is preferably an alkali metal salt or an alkaline earth metal salt.

Examples of the boron compound include boric acids, boric acid esters, boric acid salts, boron hydrides, and the like. Specifically, doExamples of the boric acids include orthoboric acid (H)₃BO₃) Metaboric acid, tetraboric acid, and the like. Examples of the boric acid ester include triethyl borate and trimethyl borate. Examples of the borate include alkali metal salts, alkaline earth metal salts, and borax of the above-described various boric acids.

The melt-molding material may contain additives such as a lubricant, a plasticizer, a stabilizer, a surfactant, a colorant, an ultraviolet absorber, an antistatic agent, a drying agent, a crosslinking agent, a filler, and various fibers in an appropriate amount. Further, a lubricant or the like may adhere to the surface of the molten molding material. Further, the melt molding material may contain a thermoplastic resin other than EVOH.

Examples of the thermoplastic resin other than EVOH include polyolefin, nylon, polyvinyl chloride, polyvinylidene chloride, polyester, polystyrene, polyacrylonitrile, polyurethane, polyacetal, modified polyvinyl alcohol, etc. examples of the polyolefin include polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, copolymer of ethylene and α -olefin having 4 or more carbon atoms, copolymer of polyolefin and maleic anhydride, ethylene-vinyl ester copolymer, ethylene-acrylic ester copolymer, modified polyolefin obtained by graft-modifying these with unsaturated carboxylic acid or a derivative thereof, etc. examples of the nylon include nylon-6, nylon-66, nylon-6/66 copolymer, etc. when the melt molding material contains a thermoplastic resin other than EVOH, the content of the other thermoplastic resin is preferably 50 mass% or less, more preferably 10 mass% or less, and still more preferably 1 mass% or less.

These other components may be mixed with EVOH by a known method. The EVOH can be mixed by, for example, a method of melt-kneading the EVOH with other components, a method of immersing EVOH in a solution containing other components, or the like.

(method of producing melt Molding Material)

The melt-formed material can be obtained by subjecting to the following steps: for example, a granulating step (step 1 (a), step 1 (b) or step 1 (c)) of obtaining hydrous pellets of EVOH from a solution containing EVOH by a granulating operation; and a drying step (step 2) of drying the water-containing pellets.

After the step 2, a sieving step (step 3) may be further provided. The EVOH to be supplied to the step 1 can be obtained by going through a polymerization step and a saponification step as conventionally known methods, as described above.

(step 1 (a))

In the production of a melt-molded material, EVOH is usually obtained as a solution dissolved in a solvent or the like used in the saponification reaction. In step 1 (a), the solution is pelletized to obtain hydrous pellets containing EVOH. The granulation operation for obtaining such water-containing pellets is not particularly limited. For example, a method of extruding a solution of EVOH into a strand shape in a coagulation bath containing a cooled poor solvent using a die and cooling and solidifying the strand shape may be mentioned. Thereafter, the strand-shaped cured product was cut by a strand cutter, whereby columnar hydrous pellets of EVOH were obtained. As the coagulation bath, for example, a mixed solvent of water and methanol can be used. The water content of the hydrous pellets obtained can be adjusted by, for example, the mass ratio of the mixed solvent to EVOH.

(step 1 (b))

In addition, as the granulation step, the following method can be used: a known method such as a method in which immediately after extruding a solution of an ethylene-vinyl alcohol copolymer into a coagulation bath, the solution is cut with a rotating cutter or the like to obtain hydrous pellets of EVOH in a flat (go-ball) or spherical shape.

(step 1 (c))

Further, as the granulating step, the following methods can be suitably used: a method in which a solution of an ethylene-vinyl alcohol copolymer is brought into contact with water vapor to prepare a water-containing resin composition of EVOH in advance by the method described in Japanese unexamined patent publication No. 2002-121290, and then the composition is extruded into a coagulation bath and cut to obtain water-containing pellets of EVOH.

In the granulation step (step 1 (a), step 1 (b) and step 1 (c)), the surface roughness (maximum height roughness (Rz) and arithmetic mean roughness (Ra)) of the side surface 2 of the finally obtained molten molded material 1 and the side surface 12 of the molten molded material 11 can be adjusted by controlling the surface roughness of the inner surface of the die, particularly the inner surface of the outlet portion (die) used when the EVOH solution is extruded. The surface shape of the inner surface of the outlet portion of the die was transferred to a solution (hydrous pellets) of the EVOH extruded. Therefore, the surface roughness of the resulting molten molding material can be reduced by improving the smoothness of the inner surface of the outlet portion of the mold.

The upper limit of the maximum height roughness (Rz) of the inner surface of the outlet portion of the die is preferably 15 μm, more preferably 5 μm, still more preferably 3 μm, and particularly preferably 1 μm. On the other hand, the lower limit of the maximum height roughness (Rz) may be 0.1 μm or 0.3 μm. The upper limit of the arithmetic average roughness (Ra) of the inner surface of the die exit portion is preferably 1.2 μm, more preferably 1 μm, still more preferably 0.5 μm, particularly preferably 0.2 μm, and most preferably 0.1 μm. On the other hand, the lower limit of the arithmetic average roughness (Ra) may be 0.01. mu.m, or 0.03. mu.m.

Here, the maximum height roughness (Rz) and the arithmetic average roughness (Ra) of the inner surface of the die exit portion are set as the average values of the measurement values at optional 10 points, respectively. In the present specification, the measured values of the maximum height roughness (Rz) and the arithmetic mean roughness (Ra) of the inner surface of the die exit portion were measured under contact conditions with a cut-off value (. lamda.c) of 2.5mm and an evaluation length (l) of 7.5mm in accordance with JIS B0601 (1994).

The hydrous pellets thus obtained can be washed as necessary. By washing, for example, by-products generated at the time of saponification can be removed. Further, the aqueous pellets may be subjected to a treatment of dipping in a solution containing an additive such as a carboxylic acid, a phosphoric acid compound, a boron compound, or the like. By this treatment, the obtained melt molding material can contain an additive such as a carboxylic acid.

(step 2)

The hydrous pellets of EVOH obtained through the above steps are subjected to a drying step to prepare a melt-molded material (pellet) containing EVOH.

The upper limit of the water content of the hydrous pellets of EVOH to be subjected to the drying step is preferably 200 mass%, more preferably 150 mass%, further preferably 120 mass%, and particularly preferably 80 mass% based on the dry mass of EVOH. By setting the water content of the water-containing pellets to 200 mass% or less, drying can be performed under gentle conditions, and the surface roughness of the obtained molten molding material can be reduced. On the other hand, the lower limit of the water content may be, for example, 30 mass% or 50 mass%. By setting the water content to 30 mass% or more, the drying efficiency and the like can be improved.

The method for drying the water-containing pellets is not particularly limited, and various known methods can be used, and examples of suitable methods include standing drying, fluidized drying, and the like. These drying methods may be used alone, for example, fluidized drying may be performed first, and then standing drying may be performed, or a plurality of drying methods may be used in combination. The drying treatment may be carried out by any of a continuous method and a batch method, and when a plurality of drying methods are combined, the continuous method and the batch method can be freely selected for each drying method. The drying may be performed in an air atmosphere, and is preferably performed in a low oxygen concentration or an oxygen-free state from the viewpoint of reducing deterioration due to oxygen during drying.

For example, the surface roughness of the obtained molten molding material can be reduced by controlling the atmosphere temperature (temperature of the blowing gas), the dew point temperature of the blowing gas, the drying rate, and the like when using a hot air dryer, particularly, when drying in the initial stage. The initial stage of drying means, for example, a stage until the water content of the water-containing pellets reaches 10 mass%.

The upper limit of the atmospheric temperature (temperature of the blast gas) in the initial stage of drying is preferably 90 ℃, more preferably 75 ℃, and still more preferably 65 ℃. By setting the atmospheric temperature to 90 ℃ or lower, volatilization of moisture occurs gradually, and the surface of the obtained molten molding material can be inhibited from becoming rough. On the other hand, the lower limit of the atmospheric temperature is preferably 40 ℃ and more preferably 50 ℃. By setting the atmosphere temperature to 40 ℃ or higher, the drying efficiency can be improved.

The lower limit of the dew point temperature of the gas (air or the like) used for drying in the initial stage of drying is preferably-35 ℃, more preferably-25 ℃, and still more preferably-15 ℃. By setting the dew point temperature to-35 ℃ or higher, the volatilization of water is gradually caused, and the surface of the obtained molten molding material can be inhibited from becoming rough. On the other hand, the upper limit of the dew point temperature is preferably 10 ℃, more preferably 0 ℃, and still more preferably-5 ℃. By setting the dew point temperature to 10 ℃ or lower, the drying efficiency can be improved.

The upper limit of the drying rate in the initial stage of drying is preferably 50g/hr & lt 100 g-dry base (dry base), more preferably 30g/hr & lt 100 g-dry base, and further preferably 20g/hr & lt 100 g-dry base. When the drying rate is 50g/hr or less and 100g or less is used as a drying base, the volatilization of water occurs slowly, and the surface of the resulting molten molding material 10 can be inhibited from becoming rough. On the other hand, the lower limit of the drying rate is preferably 5 g/hr-seeded 100 g-dried matter, more preferably 10 g/hr-seeded 100 g-dried matter. By setting the drying rate to 5g/hr or more and seeding 100 g-or more of the drying base, the drying efficiency can be improved. For example, a drying rate of 50 g/hr-100 g-drying medium means that 50g of water is volatilized per 1 hour per 100g of EVOH dry mass basis.

In addition, after the initial stage, that is, for example, when the water content of the pellets is less than 10 mass%, the amount of water volatilized is reduced, and the influence on the surface roughness is reduced, so that the drying can be performed under the condition that the drying rate is increased. That is, drying can be performed at high and low dew point temperatures. By doing so, the drying efficiency can be improved.

The upper limit of the moisture content in the pellets (melt-molded material) obtained through the drying step is preferably 1 mass%, more preferably 0.8 mass%, and still more preferably 0.5 mass% of the total pellets. By setting the water content to 1 mass% or less, molding failures such as voids due to foaming or the like during melt molding can be suppressed.

(step 3)

The pellets (melt-molded material) obtained through the drying step may be further subjected to sieving to adjust the particle size distribution. The mesh number of the screen to be used may be appropriately set according to the size of the melt molding resin, and may be, for example, 4 mesh or more and 10 mesh or less. In addition, the particle size can be adjusted by placing the sieve in a plurality of sieves having different sieve numbers (the number of meshes).

The lower limit of the sieving time is preferably 1 minute, more preferably 5 minutes. On the other hand, the upper limit may be, for example, 1 hour, preferably 20 minutes, and more preferably 15 minutes. When the resin is passed through the sieve for a long period of time, the particle size distribution becomes narrower, but the surface of the melt-molded resin is likely to be damaged, and the surface roughness may become large. Further, fine powder may be generated by sieving for a long period of time.

(method of use)

The melt molding material is melt molded to form various molded articles such as films, sheets, containers, tubes, and fibers. These molded bodies may be pulverized and then molded again depending on the purpose of reuse. Further, the film, sheet, fiber, etc. may be uniaxially or biaxially stretched. The melt molding method may be extrusion molding, inflation extrusion, blow molding, melt spinning, injection molding, or the like.

In addition, in the continuous melt molding, the melt molding material is usually continuously conveyed by air flow to an inlet such as a hopper of a melt molding machine. The gas to be used for gas flow conveyance is not particularly limited, and air may be used in general, or an inert gas such as nitrogen may be used.

The lower limit of the temperature of the gas to be passed through may be, for example, 0 ℃ or 10 ℃. The upper limit is, for example, 100 ℃ and may be 80 ℃ or 60 ℃. The flow rate of the gas to be flowed varies depending on the size, pipe diameter and the like of the molten molding material, and is usually 10 m/sec to 100 m/sec.

Examples

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

In the following examples and comparative examples, the measurement and evaluation were performed by the methods shown below.

(1) Measurement of surface roughness of melt Molding Material (pellet)

A maximum height roughness (Rz) and an arithmetic mean roughness (Ra) of a side surface of a melt-molded material were measured using a shape measurement laser microscope "VK-X200" (noncontact type) manufactured by キーエンス, with a cutoff value of (λ c) 2.5mm, an evaluation area of 1414 μm in width and 1060 μm in height, according to JIS B0601 (2001), and the values were recorded as an average of 100 values.

(2) Measurement of particle size distribution and full Width half maximum of melt-formed Material

The particle size distribution of the circle equivalent diameter (radius) of the molten molding material was determined as follows: the molten molding material 500g was evaluated by dynamic image analysis based on ISO 13322-2 (2006) using "camsize XT" from ヴァーダー seed サイエンティフィック, and found from the calculated circle equivalent diameter. The full width at half maximum (mm) was determined from the particle size distribution obtained.

(3) Measurement of Water content of melt Molding Material

The water content of the molten molding material was measured under conditions of a drying temperature of 180 ℃, a drying time of 20 minutes and a sample amount of about 10g using a halogen water content analyzer "HR 73" manufactured by メトラー & seedings トレド. The water content of the melt molding material was set to be the dry-basis mass%.

(4) Number of times of generation of burst granular material

Using the obtained melt-molded material, a single-layer film was produced by a single-screw extruder, and the number of particles on the film was counted. The amount of particulate matter occurring in the film was measured every 10 minutes. Usually, every 1m²Is 10 or less, but every 1m²When the number of the particles reached 100 or more, the number of the formation of the film was examined by continuous film formation for 48 hours. The number of generation of the burst particulates was evaluated according to the following criteria. In the continuous film formation, the film is conveyed by a gas flow to a hopper provided in a single-screw extruderThe molten molding material is continuously supplied.

A: 0 time

B: 1-2 times

C: 3-4 times

D: the treatment is carried out for more than 5 times.

(5) Uneven thickness

In the continuous film formation of the above (3), a sample was taken in the MD direction 1 hour after the start of film formation, and the thickness in the 2m length range was examined by a continuous thickness meter. The number of dots was counted at intervals of 25mm, and the standard deviation (. mu.m) was determined, and the thickness unevenness was evaluated according to the following criteria.

A: 2 μm or less

B: more than 2 μm and not more than 4 μm

C: more than 4 μm and not more than 6 μm

D: more than 6 μm and not more than 8 μm

E: more than 8 μm.

(6) Amount of micropowder

A total of 5L-shaped pipes were disposed every 10m in a pipe 50m having an inner diameter of 100 mm. The molten molding material 5t is conveyed by air flow through the L-shaped pipe by an air conveyance facility having a hopper with a dust separator. At this time, the fine powder is collected by the filter by the air recovered from the upper part of the dust separator. The captured fine powder was measured by a balance. The ratio (ppm) of the amount of collected fine powder to the amount of carried fine powder was obtained and evaluated according to the following criteria. It should be noted that the wind speed in the air stream conveyance is 20 m/sec. The molten molding material used in the test was obtained by removing fine powder by a fine powder remover until the amount of fine powder was 10ppm or less.

A: less than 100ppm

B: more than 100ppm and not more than 200ppm

C: more than 200ppm and not more than 300ppm

D: over 300 ppm.

(7) Surface roughness of mold

The measurement was carried out using a small-sized surface roughness measuring instrument サーフテスト "SJ-400" (contact type) manufactured by ミツトヨ under the conditions of a cut-off value (. lamda.c) of 2.5mm and an evaluation length (. lamda.c) of 7.5mm in accordance with JIS B0601 (1994).

< Synthesis example 1> Synthesis of EVOH

(polymerization of ethylene-vinyl acetate copolymer)

83.0kg of vinyl acetate and 26.6kg of methanol were charged into a 250L pressure reaction vessel equipped with a stirrer, a nitrogen inlet, an ethylene inlet, an initiator addition port and a delayed (sequential) solution addition port, the temperature was raised to 60 ℃ and then the nitrogen in the system was replaced by bubbling nitrogen for 30 minutes. Subsequently, ethylene was charged so that the pressure in the reaction tank became 3.6 MPa. 2, 2' -azobis (4-methoxy-2, 4-dimethylvaleronitrile) (AMV) was dissolved in methanol to prepare an initiator solution having a concentration of 2.5g/L, and the solution was purged with nitrogen by bubbling with nitrogen. After the internal temperature of the polymerization vessel was adjusted to 60 ℃, 362mL of the initiator solution was injected to start polymerization. During the polymerization, ethylene was introduced to maintain the pressure in the reaction tank at 3.6MPa and the polymerization temperature at 60 ℃ and AMV was continuously added thereto at 1120mL/hr using the above-mentioned initiator solution to carry out polymerization. After 5.0 hours, the polymerization was stopped by cooling when the polymerization rate reached 40%. After the reaction tank was opened to carry out deethylenization, nitrogen bubbling was carried out to completely carry out deethylenization. Subsequently, the copolymer solution obtained from the upper part of the column packed with raschig rings was continuously supplied, methanol was blown from the lower part of the column, and a mixed vapor of methanol and unreacted vinyl acetate monomer was distilled off from the top of the column to obtain a methanol solution of an ethylene-vinyl acetate copolymer (EVAc) from which unreacted vinyl acetate monomer was removed from the bottom of the column.

(saponification)

To 253.4kg (38 kg of EVAc in solution) of the EVAc methanol solution adjusted so that the concentration thereof became 15 mass% by adding methanol to the obtained EVAc solution, 76.6L (0.4 Molar Ratio (MR) to the vinyl acetate unit in EVAc) of an alkali solution (10 mass% methanol solution of NaOH) was added, and the mixture was stirred at 60 ℃ for 4 hours, thereby saponifying the EVAc. After 6 hours from the start of the reaction, 9.2kg of acetic acid and 60L of water were added to neutralize the reaction solution and terminate the reaction.

(cleaning and drying)

Transferring the neutralized reaction solution from the reactor to a rotary drum kettle, standing at room temperature for 16 hours, and cooling and solidifying into a filter cake shape. Thereafter, the cake-like resin was subjected to liquid removal using a centrifuge ("H-130" from domestic centrifuges, having a rotation speed of 1200 rpm). Then, the resin was washed with water for 10 hours while continuously supplying ion-exchanged water from above to the center of the centrifuge. The conductivity of the cleaning solution 10 hours after the start of cleaning was 30. mu.S/CM (measured by "CM-30 ET" from Toyo electric wave industries, Ltd.). The powdery EVOH thus obtained was dried at 60 ℃ for 48 hours using a dryer, to obtain a dried powdery EVOH. The ethylene unit content of the EVOH obtained was 32 mol%.

< example 1>

20kg of the above-described powdery EVOH was dissolved in a 32-L water/methanol mixed solution (mass ratio: water/methanol: 4/6) at 80 ℃ for 12 hours while stirring. Subsequently, the temperature of the dissolution tank was lowered to 65 ℃ while stopping stirring, and the solution was left for 5 hours to defoam the EVOH water/methanol solution. Then, the EVOH solution was extruded through a die having a circular opening with a diameter of 3.5mm into a 5 ℃ water/methanol mixed solution (mass ratio: water/methanol: 9/1) to precipitate the EVOH solution into strands, which were cut into hydrous EVOH pellets with a diameter of about 4mm and a length of about 5 mm. The mold was hard chrome-plated, and had a maximum height roughness (Rz) of the inner surface of the die (outlet portion) of 0.6 μm and an arithmetic mean roughness (Ra) of 0.05 μm.

40kg of the hydrous EVOH pellets thus obtained and 150L of ion-exchanged water were put into a metallic drum having a height of 900mm and an opening diameter of 600mm, and the washing and draining operations were repeated 2 times while stirring at 25 ℃ for 2 hours. Subsequently, 150L of a 1g/L aqueous acetic acid solution was added to 40kg of the hydrous EVOH pellets, and the operations of washing and draining were repeated 2 times while stirring at 25 ℃ for 2 hours. Furthermore, 150L of ion-exchanged water was added to 40kg of the hydrous EVOH pellets, and washing and liquid removal were repeated 6 times while stirring at 25 ℃ for 2 hours, thereby obtaining hydrous EVOH pellets (w-EVOH-1) from which impurities were removed. The conductivity of the cleaning solution after the 6 th cleaning was measured by "CM-30 ET" available from Toyama electric wave industries, and as a result, the conductivity of the cleaning solution was 3. mu.S/CM.

10.5kg of water-containing EVOH pellets (w-EVOH-1) were put into 94.5L of an aqueous solution in which the components were dissolved so that acetic acid content was 0.6g/L, sodium acetate content was 0.55g/L, phosphoric acid content was 0.015g/L, and boric acid content was 0.20g/L, and the mixture was immersed while continuously stirring at 25 ℃ for 6 hours. The water-containing EVOH pellets (w-EVOH-1) after the impregnation treatment were dewatered by centrifugation. The water content of the obtained hydrous EVOH pellets (w-EVOH-1) was 60 mass%.

The obtained hydrous EVOH pellets (w-EVOH-1) were dried by the following procedure. First, air having a dew point temperature of-10 ℃ was used, and the mixture was dried in a hot air dryer at 60 ℃ for 5 hours to give a water content of 10 mass%. Next, the mixture was dried at 120 ℃ for 24 hours in a hot air drying atmosphere using air having a dew point temperature of-20 ℃.

Thereafter, the dried pellets were sieved through 6.5 mesh, 7 mesh and 8 mesh screens in this order for 10 minutes, and the pellets remaining on the 8 mesh screen were collected to obtain pellets of the dried EVOH of example 1 (melt-molded material). The obtained melt-molded material had a cylindrical shape, a height of 3.2mm and a diameter of 2.8 mm.

< example 2>

A hydrous pellet (w-EVOH-2) having a water content of 100 mass% was obtained in the same manner as in example 1, except that 20kg of the powdery EVOH after drying was dissolved in 43L of a water/methanol mixed solution (mass ratio: water/methanol: 4/6) while stirring at 80 ℃ for 12 hours. The hydrous pellets (w-EVOH-2) were dried by the following procedure. First, air having a dew point temperature of-20 ℃ was used, and the mixture was dried in a hot air dryer at 70 ℃ for 4 hours to give a water content of 10 mass%. Next, the mixture was dried at 120 ℃ for 24 hours in a hot air drying atmosphere using air having a dew point temperature of-20 ℃. Thereafter, pellets of dry EVOH (melt-molded material) were obtained by sieving in the same manner as in example 1.

< example 3>

A hydrous pellet (w-EVOH-3) having a water content of 140 mass% was obtained in the same manner as in example 1, except that 20kg of the powdery EVOH after drying was dissolved in 55L of a water/methanol mixed solution (mass ratio: water/methanol: 4/6) while stirring at 80 ℃ for 12 hours. The hydrous pellets (w-EVOH-3) were dried by the following procedure. First, air having a dew point temperature of-30 ℃ was used, and the mixture was dried in a hot air dryer at 80 ℃ for 4 hours to give a water content of 10 mass%. Next, the mixture was dried at 120 ℃ for 24 hours using air having a dew point temperature of-20 ℃. Thereafter, pellets of dry EVOH (melt-molded material) were obtained by sieving in the same manner as in example 1.

< example 4>

Pellets (molten materials) of dry EVOH were obtained in the same manner as in example 2, except that a hard chromium-plated die having a maximum height roughness (Rz) of the inner surface of the die head (outlet portion) of 1.5 μm and an arithmetic mean roughness (Ra) of 0.43 μm was used as the die for extruding the EVOH solution.

< example 5>

Pellets of dry EVOH (melt-molded material) were obtained in the same manner as in example 4, except that the dried pellets were sieved through a 5-mesh, 7-mesh and 8-mesh sieve for 10 minutes in this order to collect pellets remaining on the 8-mesh sieve.

< example 6>

Pellets of dry EVOH (melt-molded material) were obtained in the same manner as in example 4, except that the dried pellets were sieved through a 5-mesh, 7-mesh and 9-mesh sieve for 10 minutes in this order to collect pellets remaining on the 9-mesh sieve.

< example 7>

Pellets of dry EVOH (melt-molded material) were obtained in the same manner as in example 4, except that the dried pellets were sieved through a 4-mesh, 7-mesh and 9-mesh sieve for 10 minutes in this order to collect pellets remaining on the 9-mesh sieve.

< example 8>

Pellets (molten materials) of dry EVOH were obtained in the same manner as in example 2, except that a hard chromium-plated die having a maximum height roughness (Rz) of the inner surface of the die head (outlet portion) of 14.5 μm and an arithmetic mean roughness (Ra) of 0.99 μm was used as the die for extruding the EVOH solution.

< example 9>

Pellets of dry EVOH (melt-molded material) were obtained in the same manner as in example 8, except that the dried pellets were sieved for 30 minutes.

< example 10>

A hydrous pellet (w-EVOH-4) having a water content of 45 mass% was obtained in the same manner as in example 1, except that 20kg of the dried powdery EVOH was dissolved while being stirred at 80 ℃ for 12 hours in 26L of a water/methanol mixed solution (mass ratio: water/methanol: 4/6), and a mold having a maximum height roughness (Rz) of the inner surface of the die head (outlet portion) of 0.5 μm and an arithmetic average roughness (Ra) of 0.05 μm for deposition into a strand shape was used. The hydrous pellets (w-EVOH-4) were dried by the following procedure. First, air having a dew point temperature of-10 ℃ was used, and the mixture was dried in a hot air dryer at 60 ℃ for 4 hours to give a water content of 10 mass%. Next, the mixture was dried in a hot air drying atmosphere at 100 ℃ for 36 hours using air having a dew point temperature of-20 ℃. Thereafter, pellets of dry EVOH (melt-molded material) were obtained by sieving in the same manner as in example 1.

< comparative example 1>

Pellets of dry EVOH (melt-molded material) were obtained in the same manner as in example 2, except that a hard chromium-plated die having a maximum height roughness (Rz) of the inner surface of the die head (outlet portion) of 18.2 μm and an arithmetic average roughness (Ra) of 1.34 μm was used as the die for extruding the EVOH solution, and the dried pellets were sieved in the order of 4 mesh, 7 mesh and 9 mesh for 10 minutes to collect pellets remaining in the 9 mesh.

< example 11>

The hydrous EVOH pellets w-EVOH-1 obtained in example 1 were dried at 80 ℃ for 1 hour in a hot air dryer using air having a dew point temperature of-30 ℃ to obtain hydrous EVOH pellets having a water content of 50 mass%. The resulting hydrous EVOH pellets were fed into a twin-screw extruder (details are shown below) at a rate of 10kg/hr, and an aqueous solution containing 10.0g/L of acetic acid, 7.1g/L of sodium acetate, 0.11g/L of phosphoric acid and 9.8g/L of boric acid was added at a rate of 0.6L/hr from a solution addition part shown in FIG. 1 at the tip of the side of the spout, with the resin temperature at the spout being 100 ℃. As a mold for extruding the EVOH solution, hard chrome plating was used, and the maximum height roughness (Rz) of the inner surface of the die (outlet portion) was 1.5 μm and the arithmetic average roughness (Ra) was 0.43. mu.m. Immediately after the ethylene-vinyl alcohol copolymer solution was extruded into a coagulation bath, the solution was cut with a rotary cutter to obtain flat hydrous EVOH pellets (water content: 25 mass%).

Specification details of twin-screw extruder

Caliber of 30mm phi

L/D 45.5

Screw arbor synclastic complete combined type food

Screw rotation speed 300rpm

3mm phi and 5-hole folded yarn die head

The drawing speed is 5 m/min.

The water-containing EVOH pellets thus obtained were dried at 60 ℃ for 102 minutes in a hot air dryer using air having a dew point temperature of-10 ℃ to a water content of 10 mass%. Next, the mixture was dried at 120 ℃ for 24 hours in a hot air drying atmosphere using air having a dew point temperature of-20 ℃. Thereafter, the dried pellets were sieved through 6.5 mesh, 7 mesh and 8 mesh screens in this order for 10 minutes, and the pellets remaining on the 8 mesh screen were collected to obtain pellets of dry EVOH (melt-molded material). The resulting molten molding material was flat, and had a length of 3.2mm in the longitudinal direction and a length of 2.1mm in the width direction.

< comparative example 2>

The hydrous EVOH pellets w-EVOH-1 obtained in example 1 were dried at 80 ℃ for 1 hour in a hot air dryer using air having a dew point temperature of-30 ℃ to obtain hydrous EVOH pellets having a water content of 50 mass%. The obtained hydrous EVOH pellets were fed into a twin-screw extruder (details are shown below) at 8kg/hr, and an aqueous solution containing 5.0g/L of acetic acid, 3.6g/L of sodium acetate, 0.06g/L of phosphoric acid and 4.9g/L of boric acid was added at 1.2L/hr from a solution addition part shown in FIG. 1 at the tip of the spout side with the resin temperature at the spout port set at 100 ℃. As a mold for extruding the EVOH solution, hard chromium plated and die (outlet portion) inner surface having a maximum height roughness (Rz) of 19.2 μm and an arithmetic average roughness (Ra) of 1.45 μm was used. Immediately after the ethylene-vinyl alcohol copolymer solution was extruded into a coagulation bath, the solution was cut with a rotary cutter to obtain flat hydrous EVOH pellets (water content: 42 mass%).

The water-containing EVOH pellets thus obtained were dried at 80 ℃ for 48 minutes in a hot air dryer using air having a dew point temperature of-40 ℃ to a water content of 10 mass%. Next, the mixture was dried at 120 ℃ for 24 hours in a hot air drying atmosphere using air having a dew point temperature of-20 ℃. Thereafter, the dried pellets were sieved in the order of 4 mesh, 7 mesh and 9 mesh for 10 minutes, and the pellets remaining on the 9 mesh were collected, thereby obtaining pellets of dry EVOH (melt-molded material).

< example 12>

Pellets of dried EVOH (melt-molded materials) were obtained in the same manner as in example 3, except that the water-containing pellets (w-EVOH-3) were first dried at 60 ℃ for 3.7 hours in a hot air dryer using air having a dew point temperature of-35 ℃ to a water content of 10% by mass, and then dried at 120 ℃ for 24 hours in a hot air drying atmosphere using air having a dew point temperature of-20 ℃.

< example 13>

Pellets of dried EVOH (melt-molded materials) were obtained in the same manner as in example 3, except that the water-containing pellets (w-EVOH-3) were first dried at 60 ℃ for 13 hours in a hot air dryer to have a water content of 10 mass% using air having a dew point temperature of-30 ℃ and then dried at 120 ℃ for 24 hours in a hot air drying atmosphere using air having a dew point temperature of-20 ℃.

< example 14>

Pellets of dried EVOH (melt-molded materials) were obtained in the same manner as in example 10, except that the water-containing pellets (w-EVOH-4) were dried in a hot air dryer at 55 ℃ for 5 hours to give a water content of 10% by mass using air having a dew point temperature of-10 ℃ and then dried in a hot air drying atmosphere at 100 ℃ for 36 hours using air having a dew point temperature of-20 ℃.

< comparative example 3>

A hydrous pellet (w-EVOH-5) having a water content of 50 mass% was obtained in the same manner as in example 1, except that 20kg of the dried powdery EVOH was dissolved while stirring at 80 ℃ for 12 hours in 28L of a water/methanol mixed solution (mass ratio: water/methanol: 4/6), and a mold having a maximum height roughness (Rz) of the inner surface of the die (outlet portion) of 18.2 μm and an arithmetic average roughness (Ra) of 1.34 μm was used to precipitate the powdery EVOH. The hydrous pellets (w-EVOH-5) were dried by the following procedure. First, air having a dew point temperature of-10 ℃ was used, and the mixture was dried at 75 ℃ for 3 hours in a nitrogen atmosphere to have a water content of 20 mass%. Next, the film was dried at 120 ℃ for 12 hours in a nitrogen atmosphere using nitrogen having a dew point temperature of-20 ℃. Thereafter, pellets of dry EVOH (melt-molded material) were obtained by sieving in the same manner as in example 1.

< evaluation >

The surface roughness (maximum height roughness (Rz) and arithmetic mean roughness (Ra)) of the side surface and the full width at half maximum of the grain size distribution of each of the obtained melt-molded materials were measured by the methods described above. The measurement results are shown in table 1. Table 1 also shows the drying conditions in the initial stage of drying in the production of each of the above-described molten molding materials. Further, the number of generation of sudden granular particles, thickness unevenness, and the amount of fine powder were evaluated by the above-described method using each of the obtained melt molding materials. The evaluation results are shown in table 1.

As shown in Table 1, the molten molding materials of examples 1 to 14 having a maximum height roughness (Rz) of the side surface of 300 μm or less suppressed the occurrence of sudden particles during continuous melt molding. The thickness unevenness of the obtained molten molded article can be further reduced by reducing the maximum height roughness (Rz) and the arithmetic mean roughness (Ra) of the side surface of the molten molded article, reducing the full width at half maximum of the molten molded article, and the like. Further, by reducing the arithmetic average roughness (Ra) and the like of the side surface of the molten molding material, the amount of generation of fine powder is reduced.

Fig. 2 (a) is a photograph showing a band-shaped foreign matter collected from a hopper when a single-layer film is produced from the molten molding material obtained in comparative example 1. Both ends of the foreign matter were fixed with tape and photographed together with a ruler (cm mark). Fig. 2 (b) is an enlarged photograph of the foreign matter in the form of a band. It can be confirmed that: such foreign matter causes particulate matter to be generated suddenly.

Industrial applicability

The melt-molding material of the present invention can be suitably used as a continuous melt-molding material for films, sheets, containers, and the like.

Description of the reference numerals

1. 11 melting the molding material

2. 12 side surface

3a upper surface

3b lower surface.

Claims

1. A melt-molding material having a columnar shape, a flat shape or a spherical shape, which comprises an ethylene-vinyl alcohol copolymer, wherein the maximum height roughness (Rz) of the side surface is 300 [ mu ] m or less.

2. The molten molding material according to claim 1, wherein the arithmetic average roughness (Ra) of the side surface is 50 μm or less.

3. The melt-formable material according to claim 1 or 2, having a full width at half maximum in a particle size distribution of a circle equivalent diameter of 1mm or less.

4. The melt-molding material according to any one of claims 1 to 3, wherein the ethylene-vinyl alcohol copolymer has an ethylene unit content of 20 mol% or more and 60 mol% or less.

5. The melt-molding material according to any one of claims 1 to 4, which is a cylindrical shape having a height of 1 to 20mm and a diameter of 1 to 20 mm.

6. The melt-molding material according to any one of claims 1 to 4, which is flat or spherical having a length in the longitudinal direction of 1 to 20mm and a length in the width direction of 1 to 20 mm.