Polyvinyl alcohol-based resin composition pellet group

Abstract

To provide a polyvinyl alcohol-based resin composition pellet group having excellent transportation stability without residence in piping on air transport as well as having excellent fusion processing stability using an extruder, and producing a film having excellent appearance.SOLUTION: In a pellet group comprising a polyvinyl alcohol-based resin composition containing a polyvinyl alcohol-based resin, the polyvinyl alcohol-based resin composition pellet group is characterized by that the pellet group contains a pellet and a fine powder passing a sieve having a 500-μm opening, and a content of the fine powder is 0.6 to 4,500 ppm per mass of the polyvinyl alcohol-based resin composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a group of polyvinyl alcohol resin composition pellets. [Background technology]

[0002] Polyvinyl alcohol-based resins are usually in the form of powder after production, but when powdered polyvinyl alcohol-based resins are supplied to a melt molding machine such as an extruder, it is difficult to achieve a uniform molten state due to the influence of volatile components and particle size, making it difficult to produce molded products such as films. Therefore, conventionally, polyvinyl alcohol-based resin powders have been melt-kneaded and formed into pellets, which are then melt-molded.

[0003] Furthermore, the melting point and decomposition temperature of polyvinyl alcohol resins are close to each other, and pellets of polyvinyl alcohol resins produced by melt-kneading may be discolored by heat or may contain degraded materials. When such pellets are used to produce a molded product, further melt-molding may accelerate thermal degradation of the polyvinyl alcohol resin, which may cause coloration and lead to poor appearance of the molded product, or may cause fisheyes when the resin is made into a film.

[0004] Furthermore, polyvinyl alcohol-based resin pellets are required to have a certain degree of hardness. If the polyvinyl alcohol-based resin has low hardness, it may become powdery in the screw during melt molding, making it impossible to extrude through the screw, or the powdered resin may cause fisheyes in the molded product. Furthermore, the pellets are prone to crushing during transportation.

[0005] For this reason, it has been proposed to provide polyvinyl alcohol resin composition pellets with little coloration and improved hardness properties (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 7167711 Summary of the Invention [Problem to be solved by the invention]

[0007] However, no improvement in the air transportability of polyvinyl alcohol-based resin composition pellets is found in Patent Document 1. Specifically, there is no consideration of the possibility that pellets may become stuck in piping during air transport of such melt-molding pellets in a production line, which may cause contamination with foreign matter.

[0008] If there is retention or contamination with foreign matter, not only is there a concern that stability may be reduced when such pellets are melt-molded in an extruder, but fish eyes may also occur in the molded product.

[0009] In recent years, requirements for the appearance of packaging materials and the like have become increasingly stringent, and there is a demand for further suppression of fisheyes while ensuring melt moldability. In particular, there is a demand for polyvinyl alcohol-based resin composition pellets that can sufficiently suppress the occurrence of even minute fisheyes with a diameter of 200 μm or less.

[0010] Under these circumstances, an object of the present invention is to provide a group of polyvinyl alcohol resin composition pellets which do not stagnate in piping during pneumatic transport and have excellent transport stability, as well as excellent melt processing stability in an extruder, and which produce films with excellent appearance. [Means for solving the problem]

[0011] However, in view of the above circumstances, the present inventors have conducted extensive research and have found that, when a certain amount of fine powder is contained in a group of polyvinyl alcohol-based resin composition pellets containing a polyvinyl alcohol-based resin, the pellets have excellent air transportability and melt processing stability, and the resulting film has excellent appearance, and have completed the present invention.

[0012] That is, the present invention has the following aspects. [1] A group of pellets made of a polyvinyl alcohol-based resin composition containing a polyvinyl alcohol-based resin, The pellet group includes pellets and fine powder passing through a 500 μm mesh sieve, A group of polyvinyl alcohol-based resin composition pellets, wherein the fine powder content is 0.6 to 4500 ppm based on the mass of the polyvinyl alcohol-based resin composition. [2] The group of polyvinyl alcohol-based resin composition pellets according to [1], wherein the polyvinyl alcohol-based resin has a degree of saponification of 70 to 99.9 mol %. [3] A group of polyvinyl alcohol-based resin composition pellets according to [1] or [2], wherein the angle of repose of the roughly conical pellets obtained by allowing the pellets to flow from a funnel with a stem diameter of 8 mm into a circular container with a diameter of 9.5 cm is 30 to 40°. [4] The group of polyvinyl alcohol-based resin composition pellets according to any one of [1] to [3], wherein the polyvinyl alcohol-based resin contains a primary hydroxyl group-modified polyvinyl alcohol-based resin. [5] The group of polyvinyl alcohol-based resin composition pellets according to [4], wherein the modification amount of the primary hydroxyl group-modified polyvinyl alcohol-based resin is 4 to 12 mol %. [Effects of the Invention]

[0013] The polyvinyl alcohol resin composition pellets of the present invention do not stagnate in piping during pneumatic transport and have excellent transport stability, as well as excellent melt processing stability in an extruder, and films obtained using the same have excellent appearance. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a process diagram schematically illustrating a process for producing polyvinyl alcohol-based resin composition pellets. [Figure 2] FIG. 2 is a diagram for explaining an angle of repose. [Figure 3]FIG. 1 is a diagram for explaining a method for measuring an angle of repose. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described below based on examples of embodiments for carrying out the present invention, but the present invention is not limited to the embodiments described below.

[0016] In this specification, "x and / or y (x and y are optional configurations)" means at least one of x and y, and can mean three possibilities: x only, y only, or x and y. In this specification, when the expression "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it means "X or more and Y or less," as well as "preferably larger than X" or "preferably smaller than Y." In this specification, when it is expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also means that "it is preferably greater than X" or "it is preferably less than Y." In the present specification, when numerical ranges are described in stages, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In addition, in the numerical ranges described in this specification, the upper or lower limit of the numerical range can also be replaced with the values ​​shown in the examples.

[0017] In this specification, the term "film" includes "tape" and "sheet." In this specification, the term "main component" means a component that has a significant effect on the properties of the target object, and the content of the component is usually 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, and may be 100% by mass.

[0018] A group of polyvinyl alcohol (hereinafter sometimes referred to as "PVA")-based resin composition pellets according to one embodiment of the present invention (hereinafter sometimes referred to as "the present PVA-based resin composition pellets") is made of a PVA-based resin composition. The PVA-based resin composition contains a PVA-based resin as a main component.

[0019] The PVA resin composition pellet group contains pellets (hereinafter sometimes referred to as "raw material pellets") that serve as raw materials for melt-molded products such as films, and fine powder that passes through a 500 μm mesh sieve.

[0020] <Raw material pellets> First, the PVA resin used in the raw material pellets will be described.

[0021] [PVA resin] PVA resins are resins primarily composed of vinyl alcohol structural units, obtained by saponifying polyvinyl ester resins obtained by polymerizing vinyl ester monomers. The PVA resins contain vinyl alcohol structural units corresponding to the degree of saponification, and when the degree of saponification is not 100 mol%, the PVA resins also contain vinyl ester structural units that remain unsaponified.

[0022] Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, and vinyl versatate, with vinyl acetate being economically preferred. These may be used alone or in combination of two or more.

[0023] The average degree of polymerization (measured in accordance with JIS K 6726) of the PVA resin used in this embodiment is usually 150 to 4,000, preferably 200 to 2,000, more preferably 250 to 800, and even more preferably 300 to 600.

[0024] In the pelletizing method used in this embodiment, the raw material powder of the PVA resin can be pelletized without any problems whether the average degree of polymerization is low or high. However, when the resulting pellets are subjected to a melt molding machine, if the average degree of polymerization is too high, they tend to undergo thermal decomposition due to heat generated by shear, and if the average degree of polymerization is too low, the melt viscosity is too low and kneading may not be possible.

[0025] The saponification degree of the PVA resin used in this embodiment is usually 70 mol% or more, preferably 70 to 99.9 mol%, more preferably 72 to 99.5 mol%, and even more preferably 85 to 99.0 mol%. If the saponification degree is too low, the pellets may become too soft. However, if the saponification degree is too high, the water solubility of the PVA resin tends to decrease. In this specification, the degree of saponification of the PVA resin is measured in accordance with JIS K 6726.

[0026] The melting point of the PVA resin is usually 150 to 230° C., preferably 170 to 220° C., and more preferably 180 to 200° C. If the melting point is too high, the melting point and the decomposition temperature become close to each other, which tends to make melt molding difficult, whereas if the melting point is too low, the properties of the PVA resin (gas barrier properties, water solubility, etc.) tend to be impaired.

[0027] In addition, in the case of ordinary PVA-based resins, the main chain bonding mode is mainly 1,3-diol bonds, and the content of 1,2-diol bonds is approximately 1.5 to 1.7 mol %. However, by raising the polymerization temperature when polymerizing vinyl ester-based monomers, the content of 1,2-diol bonds can be increased to 1.8 mol % or more, or even 2.0 to 3.5 mol %.

[0028] In this embodiment, the PVA resin may be a copolymer-modified PVA resin obtained by copolymerizing various monomers with a vinyl ester monomer during the production of the vinyl ester resin and then saponifying the copolymer, or a post-modified PVA resin obtained by introducing various functional groups into unmodified PVA by post-modification. Such modification can be carried out to the extent that the water solubility of the PVA resin is not lost, and is usually less than 20 mol %.

[0029] Examples of monomers used for copolymerization with vinyl ester monomers include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid, or their salts; mono- or di-alkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, or their salts; alkyl vinyl ethers; N-acrylamidomethyltrimethylammonium chloride; allyl trimethylammonium chloride; dimethyl allyl vinyl ketone; N-vinyl pyrrolidone; vinyl chloride; vinylidene chloride; polyoxyethylene (meth)allyl ether; polyoxypropylene (meth)allyl ether; Examples of the hydroxyl group-containing α-olefins include polyoxyalkylene (meth)allyl ethers such as α)allyl ether, polyoxyalkylene (meth)acrylates such as polyoxyethylene (meth)acrylate and polyoxypropylene (meth)acrylate, polyoxyalkylene (meth)acrylamides such as polyoxyethylene (meth)acrylamide and polyoxypropylene (meth)acrylamide, polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl)ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine, hydroxyl group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, and 5-hexen-1-ol, and derivatives thereof, such as acylated products. These may be used alone or in combination of two or more.

[0030] Examples of post-modified PVA resins into which functional groups have been introduced by a post-reaction include those having acetoacetyl groups by reaction with diketene, those having polyalkylene oxide groups by reaction with ethylene oxide, those having hydroxyalkyl groups by reaction with an epoxy compound, and those obtained by reacting an aldehyde compound having various functional groups with a PVA resin.

[0031] The amount of modification in such modified PVA-based resins, i.e., the content of structural units derived from various monomers in the copolymer or functional groups introduced by post-reaction, cannot be generalized because the properties vary greatly depending on the type of modification, but is usually in the range of 0.1 to 20 mol %, and particularly preferably in the range of 0.5 to 12 mol %.

[0032] Among these various modified PVA resins, in this embodiment, PVA resins having a primary hydroxyl group in the side chain and ethylene-modified PVA resins are preferred. In particular, PVA resins having a primary hydroxyl group in the side chain are preferred because of their excellent melt-processability, and among these, PVA resins having a 1,2-diol structure in the side chain are preferred.

[0033] In particular, a PVA resin having a 1,2-diol structure in the side chain, represented by the following general formula (1), is preferred in terms of its high melt moldability. In general formula (1), R 1 , R 2 , and R 3 each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, X represents a single bond or a bonded chain, and R 4 , R 5 , and R 6 each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0034] [ka]

[0035] The content (modification rate) of the 1,2-diol structural unit represented by general formula (1) of such PVA resins having 1,2-diol structures in their side chains is usually 0.1 to 20 mol%, preferably 2 to 15 mol%, more preferably 4 to 12 mol%, even more preferably 5 to 10 mol%, and particularly preferably 6 to 9 mol%. If the modification rate is too high or too low, melt molding tends to become difficult. The portions other than the 1,2-diol structural units are vinyl alcohol structural units and unsaponified vinyl ester structural units, as in ordinary PVA resins.

[0036] R in the 1,2-diol structural unit represented by general formula (1) 1 ~R 3 , and R 4 ~R 6 are preferably all hydrogen atoms, since this results in a primary hydroxyl group at the end of the side chain, further improving reactivity, but may be substituted with an alkyl group having 1 to 4 carbon atoms in an amount that does not significantly impair the resin properties. Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. The alkyl group having 1 to 4 carbon atoms may have a substituent such as a halogen group, a hydroxyl group, an ester group, a carboxylic acid group, or a sulfonic acid group, as necessary.

[0037] Furthermore, X in the 1,2-diol structural unit represented by general formula (1) is most preferably a single bond in terms of thermal stability and stability under high temperatures and acidic conditions, but may be a linking chain as long as it does not impair the effects of the present invention. Examples of such linking chains include hydrocarbons such as alkylene, alkenylene, alkynylene, phenylene, and naphthylene (these hydrocarbons may be substituted with halogens such as fluorine, chlorine, and bromine), as well as -O-, -(CHO) m -, -(OCH2) m -, -(CHO) m CH2-, -CO-, -COCO-, -CO(CH2) mExamples include CO-, -CO(CH)CO-, -S-, -CS-, -SO-, -SO-, -NR-, -CONR-, -NRCO-, -CSNR-, -NRCS-, -NRNR-, -HPO-, -Si(OR)-, -OSi(OR)-, -OSi(OR)O-, -Ti(OR)-, -OTi(OR)-, -OTi(OR)O-, -Al(OR)-, -OAl(OR)-, -OAl(OR)O-, and the like (each R independently represents an arbitrary substituent, preferably a hydrogen atom or an alkyl group, and m is an integer of 1 to 5). Among these, alkylene groups having 6 or less carbon atoms, particularly a methylene group, or -CHOCH- are preferred in terms of stability during production or use.

[0038] The method for producing such a PVA resin having a 1,2-diol structure in the side chain is not particularly limited, but preferred methods include (i) saponifying a copolymer of a vinyl ester monomer and a compound represented by the following general formula (2), (ii) saponifying and decarboxylating a copolymer of a vinyl ester monomer and a compound represented by the following general formula (3), and (iii) saponifying and deketalizing a copolymer of a vinyl ester monomer and a compound represented by the following general formula (4). For example, the PVA resin can be produced by the method described in paragraphs

[0011] to

[0019] of JP 2004-285143 A.

[0039] R in the following general formulas (2), (3), and (4) 1 , R 2 , R 3 , X, R 4 , R 5 , R 6 are the same as those in the general formula (1). 7 and R 8 are each independently a hydrogen atom or R 9 -CO-(wherein, R 9 is an alkyl group). 10 and R 11 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0040] [ka]

[0041] [ka]

[0042] [ka]

[0043] The PVA-based resin used in the present embodiment may be one type or a mixture of two or more types. In this case, combinations such as the above-mentioned unmodified PVAs, an unmodified PVA and a PVA-based resin having a structural unit represented by general formula (1), PVA-based resins having structural units represented by general formula (1) but differing in saponification degree, average degree of polymerization, degree of modification, etc., an unmodified PVA, or a PVA-based resin having a structural unit represented by general formula (1) and another modified PVA-based resin may be used.

[0044] [Optional ingredients] In addition to the PVA resin, the PVA resin composition may contain plasticizers and other additives within the range that does not impair the effects of the present invention (for example, 10% by mass or less of the PVA resin composition). These may be used alone or in combination of two or more.

[0045] (plasticizer) Examples of plasticizers include compounds in which ethylene oxide is added to polyhydric alcohols such as aliphatic polyhydric alcohols (e.g., ethylene glycol, hexanediol, glycerin, trimethylolpropane, diglycerin, etc.), various alkylene oxides (e.g., ethylene oxide, propylene oxide, mixed adducts of ethylene oxide and propylene oxide, etc.), sugars (e.g., sorbitol, mannitol, pentaerythritol, dipentaerythritol, xylol, arabinose, ribulose, etc.), phenol derivatives such as bisphenol A and bisphenol S, amide compounds such as N-methylpyrrolidone, and glucosides such as α-methyl-D-glucoside, among which polyhydric alcohols are preferred. These can be used alone or in combination of two or more.

[0046] When a plasticizer is contained, the blending amount is preferably 0.1 to 8 parts by mass, more preferably 1 to 7 parts by mass, and even more preferably 2 to 6 parts by mass, per 100 parts by mass of the PVA-based resin. If the plasticizer content is too low, the melt moldability tends to decrease, while if the content is too high, the properties of the PVA-based resin (gas barrier property, water solubility, etc.) tend to be impaired.

[0047] (Other additives) Other additives that can be appropriately blended include, for example, thermoplastic resins (e.g., polyethylene, polypropylene, polyester (aliphatic polyester, aliphatic-aromatic copolymer polyester, etc.) in the presence of a compatibilizer), fragrances, foaming agents, deodorants, extenders, fillers (e.g., inorganic fillers such as talc, clay, montmorillonite, calcium carbonate, glass beads, glass fiber, silica, mica, alumina, hydrotalcite, titanium oxide, zirconium oxide, boron nitride, and aluminum nitride, and organic fillers such as starch, starch derivatives, cellulose, cellulose derivatives, and melamine-formaldehyde resins), release agents, ultraviolet absorbers, antioxidants, processing stabilizers, weather resistance stabilizers, mildew inhibitors, and preservatives.

[0048] The PVA-based resin composition preferably contains, as an optional component, at least one selected from the group consisting of polyhydric alcohols, aliphatic polyesters, aliphatic-aromatic copolymer polyesters, starch, and cellulose.

[0049] <Manufacturing method of raw material pellets> Examples of methods for producing raw material pellets in this embodiment include (i) a method in which a PVA-based resin is melted in a melt extruder, cooled, and cut, (ii) a method in which a PVA-based resin powder is compressed under pressure and cut, (iii) a method in which an aqueous PVA-based resin solution is poured into a mold, dried, molded, and cut, and (iv) a method in which a binder resin is incorporated into a PVA-based resin composition and then molded. While method (i) is preferred in terms of production efficiency and moldability, this method is not limited thereto. Furthermore, the pellet shape can also be selected depending on the method for producing the raw material pellets, taking into consideration the subsequent use as a molding material.

[0050] The raw material pellets of this embodiment may be spherical, oval, cylindrical, cubic, rectangular, or the like, but are usually oval or cylindrical. From the viewpoint of convenience when used later as a molding material, the sizes of the raw material pellets are, in the case of an oval shape, usually 1 to 10 mm, preferably 2 to 6 mm, and more preferably 2.5 to 5.5 mm in minor axis and usually 1.5 to 30 mm, preferably 3 to 20 mm, and more preferably 3.5 to 10 mm in major axis. In the case of a cylindrical shape, the diameter of the base is usually 0.5 to 4 mm, preferably 1 to 3 mm, and the length is usually 0.5 to 4 mm, preferably 1 to 3 mm.

[0051] The steps of the method for producing raw material pellets according to this embodiment will be described in order based on the process diagram shown in Fig. 1 as an example. However, the method for producing raw material pellets according to the present invention is not limited to the steps shown in Fig. 1.

[0052] <Melt extrusion process> Powdered PVA is fed into an inlet 2 of a melt extruder 1 shown in Figure 1, melt-kneaded, and extruded into one or more roughly rod-shaped strands 5. The diameter of the extruded strands 5 is set appropriately depending on the size of the holes in the mold attached to the extrusion outlet of the melt extruder 1 and the strand take-up speed, but is usually 0.5 to 4 mm, preferably 1 to 3 mm, and more preferably 1.5 to 2.5 mm.

[0053] The temperature condition for the melt-kneading is preferably set to 250° C. or lower, more preferably 150 to 240° C., and even more preferably 180 to 230° C. If the melt-kneading temperature is too high, the PVA will thermally decompose, making it difficult to extrude the desired strands 5.

[0054] The melt extruder 1 is not particularly limited in appearance, etc., as long as it is provided with a vent at a stage after the PVA begins to melt but before it is completely melted. It may be a twin-screw type or an extruder usually called a 1.5-screw extruder in which there are twin screws below the hopper and a single screw toward the tip, but usually a twin-screw melt extruder is used.

[0055] The melt extruder 1 used in this embodiment is provided with a vent 3 at a stage after the PVA begins to melt but before it is completely melted. The number of vents 3 is not limited as long as they are capable of degassing volatile components generated from the PVA, and at least one vent may be provided, but one vent is preferred.

[0056] The vent 3 may be installed at a position after the PVA begins to melt but before it is completely melted, preferably at a position between about half-melted and just before it is completely melted. If the vent 3 is installed before the PVA is in a molten state, there is a possibility that unmelted raw materials will blow out, and if the vent 3 is installed at a position after the PVA is completely melted, the generated volatile matter will flow back and blow out from the inlet as back pressure, which may prevent the raw materials from being charged.

[0057] The shape of the opening (mouth) of the vent 3 is usually circular, elliptical, or polygonal such as triangular, rectangular, or pentagonal, and is preferably circular or rectangular. The size of the mouth is usually 1 to 150 cm. 2 , preferably 2 to 80 cm 2 , more preferably 3 to 10 cm 2 If the opening is too large, the unmelted powdered PVA raw material tends to spray out easily, and if it is too small, the unmelted powdered PVA raw material tends to clog up easily.

[0058] Furthermore, a general vent (a degassing port, a vacuum vent port) 4 may be provided in addition to the above-mentioned vent 3. The general vent 4 may be provided in one stage or in multiple stages of two or more stages.

[0059] The state after the PVA starts to melt but before it is completely melted is specifically a state in which a part of the PVA powder starts to melt and unmelted powder is kneaded into the molten resin, forming a white viscous mass, which can actually be confirmed by visual inspection, etc.

[0060] <Strand cooling process> As shown in Figure 1, the melt-extruded strand 5 is cooled by conventional methods such as wind cooling or air cooling. However, since PVA is water-soluble, cooling with a water bath or shower is not possible. Among these, a method using a water-cooled metallic endless belt 6 and mist is preferred. Specifically, the strand 5 is placed on the surface of the water-cooled metallic endless belt 6, and the strand 5 is moved by rotating the metallic endless belt 6, cooling the side that comes into contact with the strand 5. At the same time, mist is sprayed onto the surface of the strand 5, and then dry gas is sprayed to cool the entire strand 5.

[0061] For example, a stainless steel belt using a conventionally known water-cooled cooling method is preferably used as the water-cooled metallic endless belt 6. In the drawing, one cooling process using the metallic endless belt 6 is provided, but this is not limitative, and two or more cooling processes using the metallic endless belt 6 may be provided in succession to form a multi-stage system.

[0062] The surface temperature of the water-cooled metallic endless belt 6 is preferably 2 to 80° C., more preferably 5 to 60° C., and even more preferably 20 to 40° C. If the surface temperature is too high, it becomes difficult to cool the strands 5 effectively in a short time.

[0063] On the other hand, a method of cooling the entire strand 5 by spraying mist onto the surface of the strand 5 can be exemplified by a method in which a spraying device 7 for spraying mist is provided above the strand 5, which is moved by the rotational drive of the metal endless belt 6, as shown in Fig. 1, and mist is sprayed onto the surface of the strand 5 from above to cause moisture to adhere to the surface of the strand 5, which then evaporates due to the heat of the strand, efficiently removing the latent heat of evaporation and cooling the strand 5. When using the device 7, the amount of mist sprayed varies depending on the speed of the cooling belt, but is usually 0.5 to 10 L / hr, preferably 1 to 4 L / hr, and more preferably 2 to 3 L / hr. The average droplet size of the sprayed mist is usually 0.1 to 30 μm, preferably 0.5 to 20 μm, and more preferably 1 to 10 μm. If the particle size is too large, the strands may become wet, causing the PVA to dissolve. The mist described above can be sprayed using, for example, a two-fluid spray nozzle (for example, AKIJet manufactured by Ikeuchi Co., Ltd.) that sprays compressed air and water simultaneously.

[0064] Next, it is preferable to inject a dry gas 8 onto the strands 5 that have been subjected to the cooling step, thereby cooling the surface of the strands 5 based on the latent heat of vaporization. Examples of the dry gas 8 include air and inert gases (e.g., nitrogen gas, carbon dioxide gas, etc.), but an air-cooling method using air injection is preferably used. The amount of the dry gas 8 is usually 5 to 5 m 3 / min, preferably 10 to 40 m 3 / min, preferably 20-30m 3 The temperature of the dry gas 8 used is usually 5 to 40°C, preferably 10 to 30°C, and more preferably 15 to 25°C.

[0065] The cooling distance in the cooling step in which the mist is sprayed and the dry gas is injected is usually 4 to 20 m, preferably 6 to 15 m, and more preferably 8 to 10 m. If the cooling distance is too short, cooling will be insufficient, and the strands will be too soft to be cut by the pelletizer, and may become entangled around gears or the like of the pelletizer, causing the equipment to stop. If the cooling distance is too long, workability during production tends to deteriorate.

[0066] The temperature of the strand 5 obtained through the cooling step and the dry gas injection step is set in the range of 35 to 95°C. More preferably, it is 70 to 95°C, and even more preferably, 80 to 90°C. If the temperature of the strand 5 is too high, the strand 5 cannot be cut and efficiently pelletized in the next step. Specifically, if the temperature of the strand 5 is too high, when the strand 5 is cut into pellets in the next step, the strand 5 is too soft, making it impossible to produce pellets with a uniform cut surface. Alternatively, the strand 5 may not be cut and may wrap around the blades of the pelletizer. On the other hand, if the temperature of the strand 5 is too low, the strand 5 is too hard, and the cut surface tends to be uneven when cut.

[0067] The water content of the strand 5 obtained through the cooling step and the dry gas injection step is preferably less than 0.1% by weight, more preferably 0.08% by weight or less, and even more preferably 0.05% by weight or less. The lower limit of the water content is usually 0.02% by weight. If the water content is too high, the strand 5 will be too soft when cut into pellets, making it impossible to produce pellets with a uniform cut surface.

[0068] <Strand cutting (pelletization) process> The strand 5 cooled by the above process is fed to a cutting device 9 for cutting into pellets, whereby the strand 5 is cut and molded into pellets (pelletization process). Examples of the cutting device 9 include a device such as a pelletizer that continuously cuts the strand 5 into pellets using a rotary blade. During this cutting process, a cooling gas 10 is preferably supplied to the cut portion to suppress a temperature rise in the strand 5 due to frictional heat during cutting and to cool the strand 5 to an appropriate temperature. As with the dry gas described above, examples of the cooling gas 10 include air and inert gases (e.g., nitrogen gas, carbon dioxide gas, etc.). Preferably, an air-cooling method using air injection is employed. The supply rate of the cooling gas 10 is typically 150 to 1200 NL / min, preferably 300 to 1000 NL / min, and particularly preferably 500 to 800 NL / min. The temperature of the supplied cooling gas 10 is typically 5 to 30°C, preferably 8 to 20°C, and particularly preferably 10 to 15°C.

[0069] <Pellet cooling process> The PVA pellets (hereinafter sometimes simply referred to as "pellets") 11 cut and shaped through the strand cutting (pelletizing) process are preferably subjected to a pellet cooling process to fix the pelletized shape. As shown in FIG. 1 , the pellet cooling process is preferably performed in a pellet cooler 14, in which the cut and shaped pellets 11 are placed on a metal mesh 12 and moved in the direction of the arrow while vibrating the metal mesh 12 itself, from the viewpoints of preventing adhesion of the pellets 11 to the surface of the metal mesh 12 and effectively cooling the pellets 11. Additionally, a preferred cooling method is to supply the pellets 11 to the pellets 11 by passing the cooling gas 13 through the metal mesh 12 from below, and to circulate the cooling gas 13 outside the pellet cooler 14 from above, thereby preventing the cooling gas 13 from stagnating within the pellet cooler 14. As with the dry gas described above, the cooling gas 13 may be, for example, air or an inert gas (e.g., nitrogen gas, carbon dioxide gas, etc.), but air is preferred. The amount of the cooling gas 13 is usually 5 to 60 m 3 / min, preferably 20 to 50 m 3 / min, preferably 30-40m 3 The temperature of the cooling gas 13 to be supplied is usually 5 to 35°C, preferably 10 to 30°C, and more preferably 15 to 25°C.

[0070] The pellets 11 cooled through the pellet cooling device 14 are preferably at a temperature of, for example, less than 35° C., more preferably 10 to 30° C., and even more preferably 20 to 25° C. If the temperature of the cooled pellets 11 is too high, it becomes difficult to efficiently classify the pellets 11 in the next step, and the accuracy of classification tends to decrease.

[0071] <Classification process> The cooled pellets 11 are generally sorted into desired shapes and sizes through a classification process, thereby obtaining the final product, pellets 11 made of PVA.

[0072] The finally obtained pellets 11 are usually approximately cylindrical in shape. The size of the pellets 11 is appropriately set depending on the application, but usually has a diameter of 0.5 to 4 mm, preferably 1 to 3 mm, and more preferably 1.5 to 2.5 mm, and the length of the pellets 11 is usually 0.5 to 4 mm, preferably 1 to 3 mm, and more preferably 1.5 to 2.5 mm.

[0073] <Fine powder> In addition to the raw material pellets, the PVA-based resin composition pellet group contains fine powder that passes through a 500 μm mesh sieve (hereinafter, sometimes referred to as "PVA-based fine powder"). The PVA-based fine powder preferably contains the PVA-based resin composition as the main component, more preferably consists of only the PVA-based resin composition, and even more preferably is the same PVA-based resin composition as the raw material pellets.

[0074] The content of PVA fine powder in the PVA resin composition pellets is 0.6 to 4500 ppm, more preferably 1 to 4000 ppm, even more preferably 1.5 to 3000 ppm, and particularly preferably 2 to 2000 ppm, based on the mass of the polyvinyl alcohol resin composition. If there is finely powdered resin in the pellets before melt molding, it can cause fisheyes in the molded product, so it is common to try to remove the finely powdered resin. However, in this embodiment, it has been discovered that, rather than removing such fine powder, controlling a specific amount of the resin can improve the transportation stability of the pellets and the processing stability during melt molding.

[0075] The amount of fine powder in the pellets of the PVA resin composition may be measured for the entire amount of the packaging bag containing the pellets, or a portion may be taken and measured to ensure uniformity. When measuring a portion, it is preferable to measure at least 5 kg or more.

[0076] [Production of fine powder] The obtained raw material pellets are sieved through a sieve with a nominal mesh size of 500 μm (JIS Z8801-1:2000 "standard sieve"), and the fine powder that passes through is used as the PVA-based fine powder of this embodiment. In the production of PVA-based fine powder, the average particle size of the PVA-based fine powder is 500 μm or less, and typically 1 to 400 μm. If the average particle size is too small, the powder tends to scatter and become difficult to handle, while if it is too large, the discharge rate during molding processing tends to become unstable. The average particle size is measured by sieving, and the particle size at which the cumulative value of the particle size distribution is 50% by mass is taken as the average particle size.

[0077] <Group of pellets of the present PVA-based resin composition> The PVA resin composition pellet group contains the raw material pellets obtained as described above and fine powder, and has an angle of repose of 30 to 40°. The angle of repose is the angle α formed by the generatrix of a cone and the horizontal plane when a group of PVA resin pellets is dropped onto a flat surface from above using a funnel or the like, as shown in Figure 2. Specifically, as shown in Fig. 3, pellet group 23 is allowed to freely fall into a horizontally placed glass container (internal dimensions: diameter (D) 9.5 cm, height 2 cm) through a glass funnel 22 with a base diameter (a) of 8 mm from a height of 10 cm from the top surface of container 21 until it overflows from container 21. For approximately conical pellet group 24 formed by the accumulation of pellet group, the distance from the bottom surface inside container 21 to the apex (height of the cone: H) is measured, and the arctangent function (Arctan) shown in the following equation is calculated. Angle of repose (°) = Arctan (H / 4.75)

[0078] It is believed that the smaller the angle of repose, the less likely the pellets are to pile up, i.e., the easier the pellets are to slide, and therefore the better the feedability. Although the reason is not clear, it is presumed that the pellets of this PVA resin composition have different shapes and sizes, which makes it difficult to pile up densely, in other words, the pellets are more likely to flow without piling up.

[0079] The PVA resin composition pellets described above have excellent lubricity and do not remain in piping, resulting in excellent air transportability. Even when raw material pellets are prepared by cutting the molten material into so-called cornerless pellets with a substantially circular or elliptical cross section, the air transportability is not satisfactory if the raw material pellets consist solely of cornerless pellets. Furthermore, even in the case of a pellet mixture combining cornerless pellets and cylindrical pellets, the air transportability is poor if the mixture does not contain fine powder.

[0080] The PVA resin composition pellets preferably have a maximum standard deviation of resin pressure in the extruder of less than 1.05, more preferably 1.00 or less. The maximum standard deviation of the resin pressure in the extruder is calculated as follows by continuously measuring the resin pressure in the extruder during continuous film production and examining the fluctuations. Resin pressure refers to the pressure detected by a resin pressure sensor installed in the extruder cylinder. When the overall screw length is L / D=28, resin pressure sensors are installed at 10 locations: L / D=10, 12, 14, 16, 18, 20, 22, 24, 26, and 28. The resin pressure at each location is measured for 5 minutes at a screw rotation speed of 60 rpm, and the standard deviation of pressure fluctuations is calculated. The largest standard deviation of the pressure fluctuation data at 10 points is considered to be the maximum standard deviation.

[0081] If the standard deviation of the resin pressure fluctuations inside the extruder is too large (above the upper limit), the discharge rate of the molten resin becomes unstable, and it tends to be difficult to stably mold molded products such as films and sheets, resulting in poor extrusion processability.On the other hand, if the standard deviation is small (below the upper limit), the discharge rate of the molten resin becomes stable, and therefore extrusion processability tends to improve.

[0082] The number of fish eyes measured using the pellets of the PVA resin composition under the conditions described in the Examples below is preferably less than 60, more preferably 40 or less, and even more preferably 20 or less. If the fine powder content is too high (above the upper limit), many fisheyes will occur, which tends to deteriorate the film appearance. On the other hand, if the fine powder content is low (below the upper limit), the occurrence of fisheyes will be suppressed, and the film appearance will tend to be excellent.

[0083] The shape of the melt-molded product formed from the pellets of the PVA resin composition is not particularly limited, and may be formed into a film, sheet, container, rod, tube, melt-spun fiber or nonwoven fabric, or any other melt-molded product. The melt molding methods used to obtain such melt-molded products include compression molding, transfer molding, extrusion molding, injection molding, inflation molding, hollow molding, blow molding, calendar molding, foam molding, and vacuum molding. The melting temperature is usually selected from the range of 150 to 250°C. Even if the PVA resin has a high degree of saponification, it can be melt-molded at a low temperature of 150 to 220°C (or even 185 to 210°C). Furthermore, if the degree of saponification of the PVA resin is reduced, molding at an even lower temperature is possible.

[0084] In particular, the PVA resin composition pellets can be used for melt-molded products that require gas barrier properties, such as melt-molded films, stretched films, and sheets, as well as bags and containers and lids made of cups, trays, tubes, bottles, and the like. The film, sheet, or container may be a film, sheet, or container made solely (single layer) of the PVA resin composition, or may be a multilayer structure made by laminating two or more layers of other thermoplastic resins, papers, etc. In the multilayer structure, the layer made of pellets of the PVA resin composition (resin composition layer) serves as a gas barrier layer.

[0085] Examples of multilayer structures containing a layer of the present PVA-based resin composition as a gas barrier layer include food packaging materials such as coffee capsules and shrink films, medicine packaging materials, cosmetic packaging materials such as cases for lotion and foundation, packaging materials for metal parts, packaging materials for electronic parts, packaging materials for items in which deterioration of properties due to oxidation or moisture absorption should be suppressed, packaging materials for substances in which odor transfer or odor leakage is a concern, and multilayer structures used for various agricultural sheets and agricultural materials such as mulch sheets, fumigation sheets, seedling trays, and covering sheets.

[0086] The melt-molded products obtained using the pellets of the PVA resin composition can also be used for water-soluble films (particularly for packaging agricultural chemicals, detergents, laundry detergents, civil engineering additives, disinfectants, dyes, pigments, etc.), sheets, pipes, tubes, leak-proof films, temporary coatings, water-soluble fibers for chemical lace, and PVDC substitute films for food packaging.

[0087] Furthermore, the PVA resin composition pellets can be added to other molding resins and molded into various shapes of molded articles or single-layer and multi-layer films, thereby imparting the properties specific to PVA to the molded articles. [Example]

[0088] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" and "%" are by mass.

[0089] First, various PVA-based resins were produced as follows.

[0090] [Production of PVA resin 1] A reactor equipped with a reflux condenser and a stirrer was charged with 76.6 parts vinyl acetate (initial charge: 40%), 14.2 parts methanol, and 9.2 parts 3,4-diacetoxy-1-butene (initial charge: 40%), and 0.068 mol% azobisisobutyronitrile (relative to the vinyl acetate charge) was added. The temperature was raised under a nitrogen stream while stirring, and the remaining vinyl acetate and 3,4-diacetoxy-1-butene were added dropwise at a constant rate for 13.5 hours to initiate polymerization. When the vinyl acetate conversion reached 91%, m-dinitrobenzene was added to terminate the polymerization. Subsequently, unreacted vinyl acetate monomer was removed from the system by blowing in methanol vapor, leaving a methanol solution of the copolymer.

[0091] Next, the methanol solution was further diluted with methanol to a concentration of 50%, and charged into a kneader. While maintaining the solution temperature at 35°C, a methanol solution of sodium hydroxide with a sodium concentration of 2% was added in a proportion of 4.5 mmol per mole of the total amount of vinyl acetate structural units and 3,4-diacetoxy-1-butene structural units in the copolymer, and saponification was carried out. As the saponification proceeded, the saponified product precipitated, and when it became particulate, it was filtered out, washed thoroughly with methanol, and dried in a hot air dryer to obtain PVA resin 1 having 1,2-diol structures in its side chains.

[0092] The degree of saponification of the resulting PVA resin 1 having a 1,2-diol structure in its side chain was 99 mol % as determined by the alkali consumption required for hydrolysis of the remaining vinyl acetate and 3,4-diacetoxy-1-butene in the resin. The average degree of polymerization was 450 as determined according to JIS K 6726.

[0093] The content of the 1,2-diol structural unit represented by the general formula (1) is 1 Calculation from the integrated value measured by 1 H-NMR (300 MHz proton NMR, d6-DMSO solution, internal standard: tetramethylsilane, 50° C.) revealed that the content was 6 mol %.

[0094] [Production of PVA resin 2] A reactor equipped with a reflux condenser and a stirrer was charged with 76.6 parts vinyl acetate (initial charge: 40%), 14.2 parts methanol, and 9.2 parts 3,4-diacetoxy-1-butene (initial charge: 40%). Azobisisobutyronitrile (0.068 mol % relative to the vinyl acetate charge) was then added. The temperature was raised under a nitrogen stream while stirring, and polymerization was initiated by adding vinyl acetate and 3,4-diacetoxy-1-butene dropwise at a constant rate for 13.5 hours. When the conversion of vinyl acetate reached 91%, m-dinitrobenzene was added to terminate the polymerization. Subsequently, unreacted vinyl acetate monomer was removed from the system by blowing in methanol vapor, leaving a methanol solution of the copolymer.

[0095] Next, the methanol solution was further diluted with methanol to a concentration of 50%, and charged into a kneader. While maintaining the solution temperature at 35°C, a 2% methanol solution of sodium hydroxide was added at a ratio of 4.5 mmol per mole of the total amount of vinyl acetate structural units and 3,4-diacetoxy-1-butene structural units in the copolymer, thereby carrying out saponification. As the saponification proceeded, the saponified product precipitated, and when it became particulate, it was filtered off, thoroughly washed with methanol, and dried in a hot air dryer to produce the desired PVA.

[0096] The degree of saponification of the obtained PVA was analyzed based on the amount of alkali consumed for hydrolysis of the remaining vinyl acetate and 3,4-diacetoxy-1-butene, and was found to be 88 mol %. The average degree of polymerization was analyzed according to JIS K 6726 and was found to be 450. The content of 1,2-diol structural units in the side chains was also found to be 450. 1 Calculation from the integrated value measured by 1 H-NMR (300 MHz proton NMR, d6-DMSO solution, internal standard: tetramethylsilane, 50° C.) revealed that the content was 6 mol %.

[0097] [Production of unmodified PVA] A reactor equipped with a reflux condenser, dropping funnel, and stirrer was charged with 1300 parts of vinyl acetate, 2200 parts of methanol, and 0.05 mol% azobisisobutyronitrile (relative to the vinyl acetate charged). The temperature was raised while stirring under a nitrogen stream, and polymerization was carried out at the boiling point. When the conversion of vinyl acetate reached 90%, m-dinitrobenzene was added to terminate the polymerization. Subsequently, unreacted vinyl acetate monomer was removed from the system by blowing in methanol vapor, yielding a methanol solution of PVA.

[0098] Next, the methanol solution was further diluted with methanol to a concentration of 35% and charged into a kneader. While maintaining the solution temperature at 40°C, a 2% methanol solution of sodium hydroxide was added at a ratio of 4 mmol per 1 mol of vinyl acetate structural units in the polymer to carry out saponification. As the saponification proceeded, the saponified product precipitated, and when it became particulate, it was filtered out by solid-liquid separation.

[0099] The degree of saponification of the resulting unmodified PVA was analyzed based on the amount of alkali consumed for hydrolysis of the remaining vinyl acetate, and was found to be 73 mol %. The average degree of polymerization was analyzed in accordance with JIS K 6726 and was found to be 550.

[0100] Example 1 The obtained PVA resin 1 was fed to a twin-screw co-rotating extruder and pelletized under the following conditions to obtain raw material pellets. (Pelletizing conditions) Screw inner diameter 32mm L / D 56 Screw rotation speed: 250 rpm ·Discharge amount 15kg / h ·Extrusion temperature C1 / C2 / C3 / C4 / C5 / C6 / C7~C16 / H / D =50 / 50 / 100 / 160 / 190 / 210 / 220 / 220 / 220℃

[0101] The raw material pellets were passed through a sieve with 500 μm openings to separate them into pellets remaining on the sieve and fine powder that passed through the sieve. These were mixed so that the fine powder content was as shown in Table 1, and the desired PVA resin composition pellets for melt molding (hereinafter, sometimes referred to as "PVA pellets") were obtained.

[0102] [Examples 2 to 7, Comparative Examples 1 and 2] A group of PVA pellets for melt molding was obtained in the same manner as in Example 1, except that the fine powder content in Example 1 was changed to the content shown in Table 1.

[0103] [Example 8] A group of PVA pellets for melt molding was obtained in the same manner as in Example 1, except that PVA resin 1 in Example 1 was changed to PVA resin 2 and the fine powder content was changed to the content shown in Table 1.

[0104] [Example 9] A group of PVA pellets for melt molding was obtained in the same manner as in Example 1, except that the PVA resin 1 in Example 1 was changed to unmodified PVA and the fine powder content was changed to the content shown in Table 1.

[0105] The angle of repose of the resulting group of PVA pellets for melt molding was measured by the following method, and the feedability was evaluated.

[0106] <Measurement of angle of repose> As shown in Figure 3, a group of PVA pellets 23 was allowed to fall freely into a horizontally placed glass container (internal dimensions: diameter (D) 9.5 cm, height 2 cm) through a glass funnel 22 with a base diameter (a) of 8 mm from a height of 10 cm above the top of the container 21 until it overflowed the container 21, and the height (H) of the cone-shaped group of PVA pellets 24 formed, with its base being the horizontal plane of the top surface of the container, was measured and calculated as the arctangent function (Arctan) shown in the following formula. The results are shown in Table 1. Angle of repose (°) = Arctan (H / 4.75)

[0107] [Film production] The obtained PVA pellets were used to form a film using an extruder under the following film-forming conditions to prepare a single layer film having a thickness of 30 μm. The extrusion processing stability during film formation and the fisheyes in the obtained film were measured according to the following methods. The results are shown in Table 1.

[0108] (Film forming conditions) Extruder diameter (D) 40mm Screw: Full flight type, compression ratio = 3.1, L / D = 28 Screen pack: 90 / 90 mesh Die: Width 450mm, coat hanger type ·Set temperature: C1 / C2 / C3 / C4 / H / AD / D=190 / 200 / 210 / 210 / 210 / 210 / 210(℃) Screw rotation speed: 60 rpm Roll temperature: 80℃

[0109] <Extrusion processing stability> The resin pressure of the extruder during continuous film production was continuously measured, and fluctuations were investigated and evaluated as follows. Resin pressure refers to the pressure detected by a resin pressure sensor installed in the extruder cylinder. When the overall screw length is L / D=28, resin pressure sensors are installed at 10 locations: L / D=10, 12, 14, 16, 18, 20, 22, 24, 26, and 28. The resin pressure was measured at each location for 5 minutes at a screw rotation speed of 60 rpm, and the standard deviation of pressure fluctuations was calculated. The largest standard deviation of the pressure fluctuation data at 10 points was taken as the maximum standard deviation.

[0110] <Fisheye> The number of fisheyes in the obtained single layer film was measured using a digital defect inspection device (GX-70LT, manufactured by Mamiya OP Co., Ltd.). The fisheyes were measured by shining light from the bottom of the single-layer film, and counting the area where the light did not pass through (0.1 to 0.2 mm in diameter) as one fisheye. 2The number of fish eyes per area (size: 10 cm x 10 cm) was counted at a reading speed of 3 m / min.

[0111] [Table 1]

[0112] From the results in Table 1 above, it can be seen that the PVA pellets of the examples had good lubricity and did not remain in the piping, and therefore had excellent pneumatic transportability. Furthermore, when such PVA pellets were used for extrusion molding, the extrusion process was stable, and the molded products obtained had few fish eyes and an excellent appearance.

[0113] In contrast, the PVA pellet group of Comparative Example 1 had a fine powder content of less than 0.6 ppm, and therefore had poor air transportability and poor extrusion stability.The PVA pellet group of Comparative Example 2 had a fine powder content of more than 4,500 ppm, and therefore had many fish eyes and poor appearance. [Industrial Applicability]

[0114] The PVA resin composition pellets of the present invention exhibit excellent transport stability without retention in piping during pneumatic transport, excellent extrusion processing stability during melt molding, and can reduce the occurrence of fish eyes and other defects, resulting in molded products with good appearance. They are therefore suitable as materials for water-soluble films (for packaging pesticides, detergents, civil engineering additives, disinfectants, dyes, pigments, etc.), various packaging materials (clothing, etc.), PVDC substitute films for food packaging, wallpaper, water-disintegrable paper, sheets, pipes, tubes, leak-proof films, temporary coatings, water-soluble fibers for chemical lace, etc. [Explanation of symbols]

[0115] 1. Melt extruder 2 Inlet 3,4 Vent 5 strands 6 Metal endless belt 7 Spraying device 8 Dry Gas 9 Cutting device 10 Cooling Gas 11 pellets 12 Metal mesh 13 Cooling gas 14 Pellet cooling device 21 Container 22 Roth 23 pellet group 24 Approximately conical pellet group

Claims

1. A group of pellets made of a polyvinyl alcohol-based resin composition containing a polyvinyl alcohol-based resin, The pellet group includes pellets and fine powder passing through a sieve with an opening of 500 μm, A group of polyvinyl alcohol-based resin composition pellets, wherein the fine powder content is 0.6 to 4500 ppm per mass of the polyvinyl alcohol-based resin composition.

2. 2. The group of polyvinyl alcohol-based resin composition pellets according to claim 1, wherein the polyvinyl alcohol-based resin has a degree of saponification of 70 to 99.9 mol %.

3. The polyvinyl alcohol-based resin composition pellet group according to claim 1 or 2, wherein the pellet group is allowed to flow from a funnel having a base diameter of 8 mm into a circular container having a diameter of 9.5 cm, and the resulting substantially conical pellet group has an angle of repose of 30 to 40°.

4. The group of polyvinyl alcohol-based resin composition pellets according to claim 1 or 2, wherein the polyvinyl alcohol-based resin contains a primary hydroxyl group-modified polyvinyl alcohol-based resin.

5. The group of polyvinyl alcohol-based resin composition pellets according to claim 4, wherein the modification amount of the primary hydroxyl group-modified polyvinyl alcohol-based resin is 4 to 12 mol%.

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