Polyvinyl alcohol resin, water-soluble film, extrusion molded product, film, nonwoven

Abstract

Provided are: a polyvinyl alcohol resin which is capable of obtaining a water-soluble film having good cold water solubility and mechanical strength, has good biodegradability, and has excellent filterability when made into an aqueous solution; a water-soluble film, an extrusion-molded article, a filament, a nonwoven fabric, a container, a method for producing a water-soluble film, and an aqueous solution, each of which contains the polyvinyl alcohol resin; a polyvinyl alcohol resin which contains, as a main component, a modified polyvinyl alcohol containing an N-vinylamide unit, and which is characterized in that the ratio (N1 / N2) of the number of particles (N1) having a size of 1 [mu] m to the number of particles (N2) having a size of 2 [mu] m contained in 1 mL of a 2 mass% aqueous solution of the polyvinyl alcohol resin is 0.1-50.

Description

Technical Field

[0001] The present invention relates to a polyvinyl alcohol resin, a water-soluble film, an extruded product, a filament, a nonwoven fabric, a container, a method for producing the water-soluble film, and an aqueous solution. Background Art

[0002] As a packaging format for various chemicals, such as pesticides, detergents, bleaches, toiletries, and industrial chemicals, known packaging formats include unit packs, which contain a predetermined amount of each chemical, each sealed with a water-soluble film. Unit packs can be placed directly into water at the time of use, where the contents, along with the packaging film, dissolve or disperse in the water. Advantages of unit packs include: they allow for safe handling without direct contact with hazardous chemicals; they contain a predetermined amount of contents, eliminating the need for metering; and they eliminate the need for post-use disposal of the chemical container.

[0003] Water-soluble films used in unit packaging, etc., are required to have good solubility in cold water, sufficient mechanical strength, and good biodegradability. Among them, water-soluble films using various modified polyvinyl alcohols (hereinafter also referred to as "PVA") have been developed. Patent Document 1 describes a water-soluble film comprising a modified polyvinyl alcohol containing 1 to 10 mol% of N-vinylamide units, 0.020 to 4.0 mol% of a carboxyl group and a lactone ring in total, a degree of polymerization of 300 to 3000, and a degree of saponification of 75 to 99.5 mol%.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2003-171424 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] In the manufacture of water-soluble films, PVA aqueous solutions are generally used as film-making stock solutions. In the film-making process using the PVA aqueous solution, in order to remove the dirt, dust, foreign matter, etc. mixed in, the PVA aqueous solution is sometimes filtered before film-making. During filtration, if the mesh of the filter becomes clogged, the filtration rate (the speed at which the liquid passes through the filter) decreases, resulting in a decrease in productivity or an increase in cost due to the replacement of the filter. The modified PVA containing N-vinylamide units described in Patent Document 1 is not considered for filterability when made into an aqueous solution.

[0009] The present invention aims to provide a polyvinyl alcohol resin that can produce a water-soluble film having good cold water solubility and mechanical strength, good biodegradability, and excellent filterability when converted into an aqueous solution, as well as a water-soluble film, an extruded product, a filament, a nonwoven fabric, a container, a method for producing the water-soluble film, and an aqueous solution comprising the polyvinyl alcohol resin.

[0010] Means used to solve problems

[0011] The above-mentioned problems are solved by providing any one of the following solutions.

[0012] [1] A polyvinyl alcohol resin containing a modified polyvinyl alcohol containing an N-vinylamide unit as a main component, wherein the ratio (N1 / N2) of the number of particles having a size of 1 μm (N1) to the number of particles having a size of 2 μm (N2) contained in 1 mL of a 2% by mass aqueous solution of the polyvinyl alcohol resin is 0.1 or more and 50 or less;

[0013] [2] The polyvinyl alcohol resin according to [1], wherein the content of N-vinylamide units in the modified polyvinyl alcohol is 0.3 mol% to 10 mol%, the degree of saponification is 70 mol% to 99.9 mol%, and the average degree of polymerization is 200 to 4,500.

[0014] [3] The polyvinyl alcohol resin according to [1] or [2], wherein the total volume of particles with a size of 1 μm and particles with a size of 2 μm contained in 1 mL of a 2% by mass aqueous solution of the polyvinyl alcohol resin is 1 μm 3 Above and 10,000μm 3 the following;

[0015] [4] The polyvinyl alcohol resin according to any one of [1] to [3], wherein the biodegradability is 60% or more;

[0016] [5] The polyvinyl alcohol resin according to any one of [1] to [4], wherein a cast film having an average thickness of 50 μm obtained from the polyvinyl alcohol resin is subjected to a water dissolution test at 5°C after humidity conditioning at 20°C and 65% RH for one week, and the dissolution time is 5 seconds or more and 3,000 seconds or less;

[0017] [6] The polyvinyl alcohol resin according to any one of [1] to [5], further comprising a polymerization inhibitor;

[0018] [7] A water-soluble film comprising the polyvinyl alcohol resin according to any one of [1] to [6];

[0019] [8] The water-soluble film according to [7], which is formed by molding the polyvinyl alcohol resin using at least one method selected from the group consisting of solvent casting, calendaring, blow molding, extrusion, and blow extrusion;

[0020] [9] An extruded article obtained by extrusion molding of the polyvinyl alcohol resin according to any one of [1] to [6], in the form of a film or a filament;

[0021]

[10] A filament comprising the polyvinyl alcohol resin according to any one of [1] to [6];

[0022]

[11] A nonwoven fabric comprising the filaments of

[10] ;

[0023]

[12] A container comprising the water-soluble film of [7] as a packaging material;

[0024]

[13] The container according to

[12] , containing at least one selected from the group consisting of a pesticide, an oxidizing agent, and a detergent;

[0025]

[14] A method for producing a water-soluble film, comprising: preparing an aqueous solution containing the polyvinyl alcohol resin according to any one of [1] to [6]; and forming a film using the aqueous solution;

[0026]

[15] The method for producing a water-soluble film according to

[14] , further comprising, before the film forming step, filtering the aqueous solution using a filter;

[0027]

[16] An aqueous solution comprising the polyvinyl alcohol resin according to any one of [1] to [6], wherein the content of the polyvinyl alcohol resin is 0.1 ppm to 50 ppm;

[0028]

[17] The aqueous solution according to

[16] , wherein the temperature is 20°C or higher and 25°C or lower;

[0029]

[18] The aqueous solution according to

[16] or

[17] , further comprising at least one selected from magnesium ions and calcium ions, wherein the total content of the magnesium ions and calcium ions is 10 ppm or more and 400 ppm or less;

[0030]

[19] An aqueous solution comprising the polyvinyl alcohol resin according to any one of [1] to [6], wherein the content of the polyvinyl alcohol resin is 3% by mass or more and 12% by mass or less.

[0031] Effects of the Invention

[0032] According to the present invention, there are provided a polyvinyl alcohol resin capable of producing a water-soluble film having good cold water solubility and mechanical strength, good biodegradability, and excellent filterability when prepared as an aqueous solution, as well as a water-soluble film, an extruded product, a filament, a nonwoven fabric, a container, a method for producing the water-soluble film, and an aqueous solution comprising the polyvinyl alcohol resin. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present invention will be described in detail. It should be noted that the present invention is not limited to the following embodiments. It should be noted that in this specification, the upper limit and lower limit of the numerical range (the content of each component, the value calculated based on each component, and each physical property, etc.) can be appropriately combined. In addition, the numerical range represented by "to" means including the upper limit and lower limit. That is, "A to B" means "above A and below B".

[0034] <Polyvinyl alcohol resin>

[0035] The polyvinyl alcohol (PVA) resin described in one embodiment of the present invention is a PVA resin containing a modified PVA containing an N-vinylamide unit as a main component, and the ratio (N1 / N2) of the number of particles with a size of 1 μm (N1) to the number of particles with a size of 2 μm (N2) contained in 1 mL of a 2 mass% aqueous solution of the above-mentioned PVA resin is greater than 0.1 and less than 50.

[0036] The PVA resin is a modified PVA comprising an N-vinylamide unit as a main component, so that a water-soluble film with good cold water solubility and mechanical strength can be obtained, and biodegradability is good. In addition, by making the ratio (N1 / N2) of the number of particles (N1) with a size of 1 μm and the number of particles (N2) with a size of 2 μm contained in 1 mL of a 2% by mass aqueous solution of the PVA resin be 0.1 or more and 50 or less, the filterability when the PVA resin is made into an aqueous solution is excellent. The reason for giving play to this effect is still uncertain, but it can be inferred to be the following reasons. In general, it can be considered that when filtering the PVA aqueous solution using a filter with a pore size of a specified size (such as 1 μm), first, a part of the hole is blocked by particles with a size sufficiently large relative to the pore size, and the remaining gap is completely blocked by smaller particles, whereby the mesh of the filter is clogged. In the PVA resin of the present invention, by setting the ratio (N1 / N2) of the number of relatively small particles, i.e., particles of 1 μm in size, to the number of relatively large particles, i.e., particles of 2 μm in size, to 50 or less, the gaps are prevented from being completely clogged by relatively small particles, i.e., particles of 1 μm in size. It should be noted that if the ratio (N1 / N2) is less than 50, even when the number of particles of 1 μm in size (N1) and the number of particles of 2 μm in size (N2) are both large, clogging of the filter mesh can be suppressed. This is believed to be due to the following effect: when the number of particles of 2 μm in size (N2) is large, the particles of 2 μm in size accumulate on the filter surface, thereby easily forming gaps between the particles. In other words, it is believed that in order to fill the gaps between the particles of 2 μm in size, some of the particles of 1 μm in size are consumed, thereby suppressing the gaps of the filter pores from being completely clogged by the particles of 1 μm in size. For the reasons described above, it is presumed that the PVA resin suppresses clogging of the filter when filtering an aqueous solution, thereby exhibiting excellent filterability.

[0037] The technical solution disclosed in this specification can provide a PVA resin, a water-soluble film containing such a PVA resin, a method for manufacturing a water-soluble film, and an aqueous solution. The PVA resin can obtain a water-soluble film with good cold water solubility and mechanical strength, has good biodegradability, and when prepared as an aqueous solution, has excellent filterability for a filter with a specified pore size (for example, a filter with a pore size of 0.5 μm or more and 2 μm or less, typically, a filter with a pore size of 1 μm).

[0038] It should be noted that the "main component" refers to the component with the largest content based on mass. The PVA resin may contain optional components other than the modified PVA as the main component. The following is a detailed description of the PVA resin.

[0039] (Modified PVA)

[0040] The modified PVA is a polymer containing vinyl alcohol units. The lower limit of the content of vinyl alcohol units in the modified PVA relative to all structural units is, for example, preferably 60 mol%, more preferably 70 mol%, further preferably 75 mol%, and further preferably 80 mol%. On the other hand, the upper limit of the content of vinyl alcohol units is, for example, preferably 99.9 mol%, more preferably 99 mol%, and further preferably 95 mol%.

[0041] Modified PVA contains N-vinylamide units. N-vinylamide units are structural units derived from N-vinylamide compounds (hereinafter also referred to as "N-vinylamide monomers"). Examples of N-vinylamide monomers (monomers that provide N-vinylamide units) include the monomer represented by the following formula (I), N-vinyl-2-pyrrolidones, and N-vinylcaprolactams.

[0042] CH2=CH-NR 1 -C(=O)-R 2 (I)

[0043] In formula (I), R 1 R is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. 2 It is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

[0044] As R 1 Examples of the alkyl group having 1 to 3 carbon atoms include methyl, ethyl, propyl, isopropyl, and the like. 2 Examples of the alkyl group having 1 to 5 carbon atoms include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, and isopentyl.

[0045] Examples of the monomer represented by formula (I) include N-vinylformamide, N-methyl-N-vinylformamide, N-vinylacetamide, and N-methyl-N-vinylacetamide. The monomer represented by formula (I) is preferably N-vinylacetamide.

[0046] N-vinyl-2-pyrrolidones are those in which one or more of the hydrogen atoms on the pyrrolidone ring are replaced with an organic group, preferably an alkyl group, more preferably an alkyl group having 1 to 8 carbon atoms. Examples thereof include N-vinyl-2-pyrrolidone, N-vinyl-3-propyl-2-pyrrolidone, N-vinyl-5,5-dimethyl-2-pyrrolidone, N-vinyl-3,5-dimethyl-2-pyrrolidone, and N-vinyl-5-methyl-2-pyrrolidone. N-vinyl-2-pyrrolidone is preferred.

[0047] As N-vinylcaprolactams, one or more arbitrary hydrogen atoms on the caprolactam ring may be replaced with an organic group, preferably an alkyl group, more preferably an alkyl group having 1 to 8 carbon atoms. Examples thereof include N-vinylcaprolactam, N-vinyl-4-methylcaprolactam, N-vinyl-6-methylcaprolactam, N-vinyl-6-propylcaprolactam, and N-vinyl-7-butylcaprolactam. As the N-vinylcaprolactam, N-vinylcaprolactam is preferred.

[0048] Among the N-vinylamide monomers, N-vinyl-2-pyrrolidone or N-vinyl caprolactam are preferred, and N-vinyl-2-pyrrolidone is more preferred. In addition, N-vinylacetamide, N-vinyl-2-pyrrolidone or N-vinyl caprolactam are also preferred, and N-vinyl-2-pyrrolidone or N-vinyl caprolactam are more preferred, and N-vinyl-2-pyrrolidone is particularly preferred. By using such N-vinylamide monomers, the cold water solubility, mechanical strength, biodegradability, etc. of the obtained water-soluble film can be further improved. For example, when using N-vinyl-2-pyrrolidone, there is a tendency that cold water solubility, biodegradability, etc. become particularly good. In addition, when using N-vinyl caprolactam, there is a tendency that mechanical strength is particularly good.

[0049] In addition, for example, N-vinyl caprolactam (boiling point of about 267°C) has a relatively high boiling point, and in the case of unreacted residues, it may not be fully removed. From this point of view, N-vinyl-2-pyrrolidones with relatively low boiling points (typically N-vinyl-2-pyrrolidone (boiling point of about 148°C / 13.3kPa) are preferred. From this point of view, the N-vinylamide monomer preferably has a boiling point of 200°C or less at 13.3kPa, and more preferably has a boiling point of 160°C or less. The lower limit of the boiling point of the N-vinylamide monomer at 13.3kPa may be, for example, 80°C, 100°C, or 120°C.

[0050] As the content (modification rate) of the N-vinylamide unit in the modified PVA, it is preferably 0.3 mol % or more and 10 mol % or less, more preferably 0.5 mol % or more and 5 mol % or less, further preferably 0.7 mol % or more and 3.9 mol % or less, more preferably 1.0 mol % or more and 3.2 mol % or less. By the content of the N-vinylamide unit in the modified PVA being within the above-mentioned range, the cold water solubility, mechanical strength, biodegradability, etc. in the obtained water-soluble film can be further improved. For example, when the content of the N-vinylamide unit in the modified PVA is above the above-mentioned lower limit, there is a tendency to improve the cold water solubility, etc. On the other hand, when the content of the N-vinylamide unit in the modified PVA is below the above-mentioned upper limit, there is a tendency to improve the biodegradability, etc. It should be noted that the content of the N-vinylamide unit in the modified PVA is the content of the N-vinylamide unit relative to the total structural units in the modified PVA.

[0051] As the saponification degree of the modified PVA, it is preferably 70 mol% or more and 99.9 mol% or less, more preferably 75 mol% or more and 99.5 mol% or less, further preferably 81.5 mol% or more and 97.5 mol% or less, and even more preferably 83.5 mol% or more and 96.0 mol% or less. By making the saponification degree of the modified PVA be within the above range, the cold water solubility, mechanical strength and biodegradability of the resulting water-soluble film can be further improved. For example, when the saponification degree of the modified PVA is above the above lower limit, there is a tendency for mechanical strength, biodegradability, etc. to be improved. On the other hand, when the saponification degree of the modified PVA is below the above upper limit, there is a tendency for cold water solubility, etc. to be improved. The saponification degree of the modified PVA is a value measured by the method described in JIS-K6726-1994.

[0052] As the average degree of polymerization of modified PVA, it is preferably more than 200 and less than 4,500, more preferably more than 550 and less than 4,200, further preferably more than 700 and less than 4,000, and even more preferably more than 1,100 and less than 3,500. By making the average degree of polymerization of modified PVA be the above-mentioned range, the cold water solubility, mechanical strength and biodegradability of the obtained water-soluble film can be further improved. For example, when the average degree of polymerization of modified PVA is above the above-mentioned lower limit, there is a tendency for mechanical strength and the like to improve. On the other hand, when the average degree of polymerization of modified PVA is below the above-mentioned upper limit, there is a tendency for cold water solubility, biodegradability and the like to improve. The average degree of polymerization of modified PVA is the viscosity-average degree of polymerization measured by the method described in JIS-K6726-1994.

[0053] The modified PVA may have structural units other than vinyl alcohol units, vinyl ester units, and N-vinyl amide units. The lower limit of the total content of the vinyl alcohol units, vinyl ester units, and N-vinyl amide units relative to all structural units in the modified PVA is sometimes preferably 90 mol%, more preferably 95 mol%, and even more preferably 99 mol% or 99.9 mol%. When the modified PVA is substantially composed of vinyl alcohol units, vinyl ester units, and N-vinyl amide units, the effects of the present invention are more fully exerted.

[0054] The lower limit of the content of the modified PVA in the PVA resin may be preferably 50% by mass, more preferably 70% by mass, further preferably 80% by mass, and still more preferably 90% by mass, 95% by mass, 99% by mass, or 99.9% by mass. On the other hand, the upper limit of the content may be 100% by mass, or 99.9% by mass, 99% by mass, 95% by mass, or 90% by mass.

[0055] (Number of particles in aqueous solution, etc.)

[0056] The ratio (N1 / N2) of the number of particles (N1) with a size of 1 μm to the number of particles (N2) with a size of 2 μm contained in 1 mL of a 2% by mass aqueous solution of the PVA resin is 0.1 or more and 50 or less. The upper limit of the above ratio (N1 / N2) is preferably 40, more preferably 30, even more preferably 20, and even more preferably 10. By setting the above ratio (N1 / N2) below the upper limit, the filterability of the PVA resin in the form of an aqueous solution can be improved. On the other hand, the lower limit of the above ratio (N1 / N2) can be 0.2, 0.5, or 1.0.

[0057] The ratio (N1 / N2) of the number of particles (N1) with a size of 1 μm to the number of particles (N2) with a size of 2 μm contained in 1 mL of a 2 mass % aqueous solution of a PVA resin is a value measured by the following method.

[0058] Deionized water and PVA resin were added to a 110 mL sample tube equipped with a magnetic stirrer to a PVA resin concentration (content) of 2% by mass. The solution was then heated on a steam bath until the liquid temperature reached 95°C and stirred for 2 hours to dissolve the PVA resin. The sample tube was then immersed in a 20°C water bath and stirred for 30 minutes, then cooled until the liquid temperature reached 20°C. This 2% by mass aqueous solution of PVA resin at 20°C was used for the following measurements.

[0059] In the measurement, a particle counting device (a device formed by connecting a liquid particle counter "LIQUILAZ S05" manufactured by PARTICLE MEASURING SYSTEMS Co., Ltd. and a syringe sampling system "LS-200" manufactured by the same company) was used. It should be noted that other devices can be used if the same measurement can be performed. As a particle size distribution (channel), as a distribution corresponding to particles with a size of 1 μm, a size distribution of 1.00 μm or more and less than 1.41 μm is set, and as a distribution corresponding to particles with a size of 2 μm, a size distribution of 2.00 μm or more and less than 2.82 μm is set. That is, in the present invention, particles with a size of 1 μm are particles with a particle size of 1.00 μm or more and less than 1.41 μm, and particles with a size of 2 μm are particles with a particle size of 2.00 μm or more and less than 2.82 μm. The sample flow rate is set to 20 mL / min, the sample volume is set to 5 mL, and the measurement is repeated 5 times. For the number of particles detected in the size distribution of 1.00 μm or more and less than 1.41 μm and the distribution of 2.00 μm or more and less than 2.82 μm, the average value of the total of 3 times after excluding the first and second measurements (the number of particles per 5 mL) is divided by 5 (mL) and the values ​​obtained are respectively set as N1 (the number of particles with a size of 1 μm contained in 1 mL of a 2 mass% aqueous solution of PVA resin) and N2 (the number of particles with a size of 2 μm contained in 1 mL of a 2 mass% aqueous solution of PVA resin).

[0060] The above ratio (N1 / N2) can be adjusted according to the manufacturing conditions. Specifically, for example, in the manufacturing method of the modified PVA described below, after copolymerizing the vinyl ester monomer and the N-vinyl amide monomer, a polymerization inhibitor is added to stop the polymerization reaction, and the residual N-vinyl amide monomer is removed under reduced pressure and then saponified to obtain the modified PVA. In this way, a PVA resin with the above ratio (N1 / N2) of 0.1 or more and 50 or less can be effectively obtained. The reason for this is still uncertain, but it is believed that after the polymerization reaction is completed, when the unreacted vinyl acetate (vinyl ester compound) is removed by methods such as decompression, the N-vinyl amide monomer with a boiling point higher than that of vinyl acetate is concentrated. By allowing the free radical initiator remaining in this state to undergo polymerization, a polymer with a high content of N-vinyl amide monomer units is generated. In addition, by reacting with the base catalyst used in the saponification reaction, particles of 1 μm in size become more numerous. Therefore, by adding a polymerization inhibitor to stop the polymerization reaction and removing as much residual N-vinylamide monomer as possible before saponification, the formation of 1 μm particles is suppressed, and the above ratio (N1 / N2) tends to decrease. Furthermore, even under the above production conditions, when the N-vinylamide unit content is high or the degree of saponification is high, the number of 1 μm particles (N1) and the number of 2 μm particles (N2) tend to be relatively large. Furthermore, when residual N-vinylamide monomer is removed at a relatively high temperature, the number of 1 μm particles (N1) tends to decrease, while the number of 2 μm particles (N2) tends to increase.

[0061] The 1 μm and 2 μm particles contained in 1 mL of a 2% by mass aqueous solution of the PVA resin are considered to be insoluble matter in the modified PVA, but are not limited to such substances. The particles may also be composed of reaction products of the modified PVA with other components, or components other than the modified PVA.

[0062] The number of particles having a size of 1 μm (N1) contained in 1 mL of a 2% by mass aqueous solution of the PVA resin is not particularly limited, but is preferably 10 or more and 10,000 or less, more preferably 30 or more and 5,000 or less, further preferably 50 or more and 3,000 or less, even more preferably 70 or more and 2,000 or less, 90 or more and 1,000 or less, or 110 or more and 500 or less. The number of particles having a size of 2 μm (N2) contained in 1 mL of a 2% by mass aqueous solution of the PVA resin is preferably 10 or more and 10,000 or less, preferably 10 or more and 1,000 or less, more preferably 20 or more and 500 or less, further preferably 30 or more and 300 or less, and even more preferably 40 or more and 200 or less.

[0063] The total volume of particles with a size of 1 μm and particles with a size of 2 μm contained in 1 mL of a 2% by mass aqueous solution of the PVA resin is preferably 1 μm. 3 Above and 10,000μm 3 less than 10 μm, more preferably 10 μm 3 Above and 5,000μm 3 Below, more preferably 30 μm 3 Above and 3,000μm 3 Below, more preferably 100 μm 3 Above and 2,000μm 3 By setting the total volume of the 1 μm-sized particles and the 2 μm-sized particles within the above range, the filterability and the like of the aqueous solution of the PVA resin can be improved.

[0064] The total volume of particles having a size of 1 μm and particles having a size of 2 μm contained in 1 mL of a 2% by mass aqueous solution of a PVA resin was determined as follows.

[0065] The 1 μm particles and 2 μm particles detected in 1 mL of a 2% by mass aqueous solution of PVA resin detected in the method for calculating the ratio (N1 / N2) are each assumed to be spherical. The diameter of the 1 μm particles detected in a size distribution of 1.00 μm or more and less than 1.41 μm is set to 1.20 μm, and the diameter of the 2 μm particles detected in a size distribution of 2.00 μm or more and less than 2.82 μm is set to 2.41 μm. The total volume is calculated using the following formula based on the detected N1 and N2 values.

[0066] [Mathematical formula 1]

[0067]

[0068] (Method for producing modified PVA)

[0069] Modified PVA can be produced, for example, by copolymerizing vinyl ester monomers and N-vinylamide monomers and saponifying the resulting vinyl ester copolymer in an alcohol solution using an alkaline or acidic catalyst. By adjusting these production conditions (e.g., copolymerization reaction conditions, the amount of N-vinylamide monomer used, saponification reaction conditions, etc.), the average degree of polymerization, modification rate (N-vinylamide unit content), and degree of saponification of the resulting modified PVA can be controlled.

[0070] Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among these, vinyl acetate is preferred.

[0071] As a method for copolymerizing a vinyl ester monomer and an N-vinyl amide monomer, known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be cited. Among these methods, bulk polymerization carried out under solvent-free conditions or solution polymerization carried out using a solvent such as alcohol is preferred, and solution polymerization in the presence of a lower alcohol is more preferred. As the lower alcohol, an alcohol having 3 or less carbon atoms is preferred, more preferably methanol, ethanol, n-propanol, or isopropanol, and even more preferably methanol. When the polymerization reaction is carried out using bulk polymerization or solution polymerization, the reaction method can also be either batch or continuous.

[0072] Examples of initiators used in the polymerization reaction include azo initiators such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile); and known initiators such as organic peroxide initiators such as benzoyl peroxide and n-propyl peroxycarbonate. The polymerization temperature during the polymerization reaction is not particularly limited, but is preferably in the range of 5°C to 200°C, more preferably in the range of 30°C to 100°C. When methanol is used as the solvent, the polymerization is preferably carried out at a temperature near its boiling point.

[0073] When copolymerizing a vinyl ester monomer with an N-vinylamide monomer, a copolymerizable monomer may be copolymerized within a range that does not impair the effects of the present invention. Examples of such monomers include α-olefins such as ethylene, propylene, 1-butene, isobutylene, and 1-hexene; acrylamide derivatives such as N-methylacrylamide and N-ethylacrylamide; methacrylamide derivatives such as N-methylmethacrylamide and N-ethylmethacrylamide; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and n-butyl vinyl ether; vinyl ethers containing hydroxyl groups such as ethylene glycol vinyl ether, 1,3-propylene glycol vinyl ether, and 1,4-butanediol vinyl ether; allyl acetate; allyl ethers such as propyl allyl ether, butyl allyl ether, and hexyl allyl ether; monomers having an oxyalkylene group; isopropenyl acetate; 3-butene-1-ol, 4-pentene-1-ol, 5-hexene-1-ol, Hydroxyl-containing α-olefins such as 7-octen-1-ol, 9-decen-1-ol, and 3-methyl-3-buten-1-ol; silyl-containing monomers such as vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3-(meth)acrylamidopropyltrimethoxysilane, and 3-(meth)acrylamidopropyltriethoxysilane; unsaturated carboxylic acid compounds such as maleic acid, fumaric acid, itaconic acid, acrylic acid, and methacrylic acid, and their chlorides; unsaturated carboxylic acid ester compounds such as monomethyl maleate, dimethyl maleate, methyl acrylate, and methyl methacrylate; and unsaturated carboxylic acid anhydride compounds such as maleic anhydride and itaconic anhydride. The upper limit of the amount of these monomers used is, for example, preferably 20 mol%, more preferably 10 mol%, and may be 5 mol%, 3 mol%, 1 mol%, or 0.1 mol%, relative to the total monomers used in the copolymerization.

[0074] As described above, the copolymerization reaction of the vinyl ester monomer and the N-vinyl amide monomer is preferably stopped by adding a polymerization inhibitor. Examples of the polymerization inhibitor include compounds that stabilize free radicals and hinder the polymerization reaction and have conjugated double bonds with a molecular weight of 1000 or less, and aromatic compounds. Among them, aromatic compounds, especially compounds having a phenolic hydroxyl group, are particularly preferred.

[0075] Specific examples of compounds having conjugated double bonds that can be used as polymerization inhibitors include isoprene, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-tert-butyl-1,3-butadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-pentadiene, 2,4-dimethyl-1,3-pentadiene, 3,4-dimethyl-1,3-pentadiene, 3-ethyl-1,3-pentadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 1,3-hexadiene, 2,4-hexadiene, 2,5-dimethyl-2,4-hexadiene, 1,3-octadiene, 1,3-cyclopentadiene, 1,3-cyclohexadiene, 1-methoxy-1,3-butadiene, 2-methoxy-1,3-pentadiene, -1,3-butadiene, 1-ethoxy-1,3-butadiene, 2-ethoxy-1,3-butadiene, 2-nitro-1,3-butadiene, chloroprene, 1-chloro-1,3-butadiene, 1-bromo-1,3-butadiene, 2-bromo-1,3-butadiene, fulvene, tropinone, ocimene, phellandrene, myrcene, farnesene, cembrene, sorbic acid, sorbate, sorbate, abies Conjugated dienes formed by a conjugated structure of two carbon-carbon double bonds, such as 1,3,5-hexatriene, 2,4,6-octatriene-1-carboxylic acid, eleostearic acid, tung oil, and cholesterol; conjugated polyenes formed by a conjugated structure of four or more carbon-carbon double bonds, such as cyclooctatetraene, 2,4,6,8-tetradecene-1-carboxylic acid, retinol, and retinoic acid.

[0076] Specific examples of aromatic compounds that can be used as polymerization inhibitors include p-benzoquinone, hydroquinone, tert-butylhydroquinone, hydroquinone monomethyl ether, 2-phenyl-1-propene, 2-phenyl-1-butene, 2,4-diphenyl-4-methyl-1-pentene, 3,5-diphenyl-5-methyl-2-heptene, 2,4,6-triphenyl-4,6-dimethyl-1-heptene, 3,5,7-triphenyl-5-ethyl-7-methyl- 1,3-diphenyl-2-nonene, 1,3-diphenyl-1-butene, 2,4-diphenyl-4-methyl-2-pentene, 3,5-diphenyl-5-methyl-3-heptene, 1,3,5-triphenyl-1-hexene, 2,4,6-triphenyl-4,6-dimethyl-2-heptene, 3,5,7-triphenyl-5-ethyl-7-methyl-3-nonene, 1-phenyl-1,3-butadiene, 1,4-diphenyl-1,3-butadiene, etc.

[0077] The copolymerization reaction of the vinyl ester monomer and the N-vinylamide monomer can be stopped by cooling the reaction solution. However, from the viewpoint of obtaining the polyvinyl alcohol resin of the present invention, it is preferred to perform both cooling the reaction solution and adding a polymerization inhibitor.

[0078] As described above, it is preferred to remove as much residual unreacted monomers, particularly N-vinylamide monomers, as possible from the solution containing the obtained vinyl ester copolymer. Removal of the residual monomers is preferably performed under reduced pressure. The solution temperature during this removal operation is preferably, for example, 20°C to 60°C, and preferably 25°C to 55°C. The lower limit of the solution temperature may be 35°C. Alternatively, the upper limit of the solution temperature may be 45°C or 35°C.

[0079] The obtained vinyl ester copolymer is saponified in, for example, an alcohol solvent and then dried to obtain a modified PVA.

[0080] Examples of solvents that can be used in the saponification reaction include methanol, methyl acetate, dimethyl sulfoxide, diethyl sulfoxide, and dimethylformamide. Among these solvents, methanol is preferred.

[0081] As a catalyst for the saponification reaction of the vinyl ester copolymer, an alkaline substance is generally used. Examples of the alkaline substance include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; alkali metal alcoholates such as sodium methoxide, etc. The lower limit of the amount of the catalyst used is preferably 0.002, more preferably 0.004, in terms of the molar ratio relative to the vinyl ester unit of the vinyl ester copolymer. On the other hand, the upper limit of the amount of the catalyst used is preferably 0.2, more preferably 0.1, in terms of the molar ratio relative to the vinyl ester unit of the vinyl ester copolymer. The saponification catalyst may be added all at once at the beginning of the saponification reaction, or a portion may be added at the beginning of the saponification reaction, and the remainder may be added during the saponification reaction.

[0082] The reaction temperature during the saponification reaction is not particularly limited, but is preferably 5°C to 80°C. Furthermore, the reaction time during the saponification reaction is preferably 5 minutes to 10 hours. The saponification reaction can be carried out in either a batch or continuous manner. After the saponification reaction, the residual catalyst can be neutralized as needed. Examples of usable neutralizing agents include organic acids such as acetic acid and lactic acid, and ester compounds such as methyl acetate.

[0083] After saponification, the modified PVA may be washed as needed. As a washing solution, a solution containing a lower alcohol such as methanol as a main component and further containing water and / or an ester such as methyl acetate, which is the same as that generated in the saponification step, may be used.

[0084] If necessary, the modified PVA can be obtained by drying after washing. The substance obtained after these steps can be a PVA resin containing the modified PVA as a main component. In other words, the above-mentioned method for producing modified PVA can be a method for producing PVA resin.

[0085] (Other ingredients, physical properties, etc.)

[0086] The PVA resin may contain other components in addition to the modified PVA. Examples of other components include N-vinylamide compounds, methanol, polymerization inhibitors, and water.

[0087] When manufacturing the polyvinyl alcohol resin of the present invention, it is preferred to suppress the generation of polymers with a high content of N-vinylamide monomer in the process after the completion of polymerization. From this viewpoint, by using a polymerization inhibitor after the completion of polymerization, the ratio of the number of particles (N1 / N2) becomes smaller and can be adjusted to the range specified in the present invention. Therefore, when the PVA resin contains a polymerization inhibitor, the ratio of the number of particles (N1 / N2) is small, and the filterability when the aqueous solution is prepared is higher. As the polymerization inhibitor that can be contained in the PVA resin, the above-mentioned substances in the manufacture of modified PVA can be cited. As the content of the polymerization inhibitor in the PVA resin, it can be, for example, 0.0001 mass % or more and 1 mass % or less, or it can be 0.001 mass % or more and 0.1 mass % or less.

[0088] The biodegradability of the PVA resin is preferably 60% or higher, more preferably 70% or higher, and even more preferably 80% or higher. This excellent biodegradability makes the PVA resin particularly useful as a material for forming water-soluble films used in unit packaging, etc. The upper limit of the biodegradability may be 100%, 99%, 95%, or 92%.

[0089] Specifically, the biodegradation rate is a value measured by the following method.

[0090] To 800 mL of deionized water, 10 mL of Solution A (a solution prepared by dissolving 8.5 g of potassium dihydrogen phosphate, 21.75 g of dipotassium hydrogen phosphate, 33.4 g of disodium hydrogen phosphate dihydrate, and 0.5 g of ammonium chloride in deionized water, adjusting the liquid volume to 1 L) was added in that order; 1 mL of Solution B (a solution prepared by dissolving 27.5 g of calcium chloride in deionized water, adjusting the liquid volume to 1 L); 1 mL of Solution C (a solution prepared by dissolving 22.5 g of magnesium sulfate heptahydrate in deionized water, adjusting the liquid volume to 1 L); and 1 mL of Solution D (a solution prepared by dissolving 0.25 g of iron (III) chloride hexahydrate in deionized water, adjusting the liquid volume to 1 L) were added. Furthermore, an aqueous solution of PVA resin was added to achieve a DOC concentration of 15 mg / L. Furthermore, activated sludge collected from a sewage treatment plant was added to achieve a solids concentration of 30 mg / L, and the liquid volume was adjusted to 1 L. 600 mL of this solution was placed in a 1,100 mL glass bottle equipped with a magnetic stirrer. A sleeve was attached to the mouth of the glass bottle, and approximately 0.5 g of sodium hydroxide was added as a carbon dioxide absorber. Furthermore, an Oxitop (manufactured by Central Scientific) was attached to the top of the glass bottle mouth. The solution was stored at 22°C for 28 days while stirring. The oxygen consumption within the bottle (oxygen consumption (PVA)) was measured based on the pressure drop within the bottle. A glass bottle identical to the above was prepared, except that no PVA resin was added. Similarly, the solution was stored at 22°C for 28 days while stirring, and the oxygen consumption (oxygen consumption (blank)) was measured. The biodegradation rate of the PVA resin was calculated using the following formula.

[0091] Biodegradation rate (%) = 100 × (oxygen consumption (PVA) - oxygen consumption (blank)) / ThOD It should be noted that ThOD represents the theoretical oxygen demand of modified PVA.

[0092] When a cast film having an average thickness of 50 μm obtained from this PVA resin is subjected to a water dissolution test at 5°C after humidity conditioning at 20°C and 65% RH for one week, the dissolution time is preferably 5 seconds to 3,000 seconds. The upper limit of this dissolution time is more preferably 1,000 seconds, even more preferably 400 seconds, and even more preferably 100 seconds. When the dissolution time falls within this range, a water-soluble film having particularly excellent cold-water solubility can be obtained.

[0093] Specifically, the dissolution time is a value measured by the following method.

[0094] 4g of PVA resin is put into 96g of deionized water and dissolved in 2 hours at 95°C. The obtained aqueous solution is flowed into a mold frame and dried at room temperature to obtain a cast film with an average thickness of 50μm. The obtained cast film is cut into a size of 3.8cm×3.5cm and humidified for 1 week at 20°C and 65%RH. The cast film is clamped in a slide rail fixture (Slide Mount) (the size of the mold frame and the inner side of the frame is 3.5cm×2.3cm), immersed in 5°C water (320mL) stirred at 300rpm, and the time from immersion to complete dissolution of the cast film is measured. It should be noted that "complete dissolution" refers to: the cast film cannot be visually confirmed and the state of a transparent aqueous solution can be obtained.

[0095] The lower limit of the tensile elongation at break (elongation at break) of the cast film having an average thickness of 50 μm obtained from the PVA resin is preferably 120%, more preferably 150%, and still more preferably 180%. On the other hand, the upper limit of the tensile elongation at break is not particularly limited, and may be, for example, 400% or 300%. In addition, the lower limit of the Young's modulus of the cast film is preferably 10 N / mm 2 , more preferably 15N / mm 2 On the other hand, the upper limit of the Young's modulus is not particularly limited, and may be, for example, 50 N / mm 2 .

[0096] Specifically, the tensile elongation at break and the Young's modulus are values ​​measured by the following method.

[0097] PVA resin was dissolved in 95°C deionized water at a concentration of 4% over 2 hours. The resulting aqueous solution was dried at 20°C and 65% RH to produce a cast film with an average thickness of 50 μm. The resulting cast film was cut into 1 cm × 10 cm pieces at 20°C and 65% RH and subjected to a tensile test with a clamp distance of 50 mm and a tensile speed of 100 mm / min. The Young's modulus of the film at an elongation of 10-20% and the elongation at break (elongation at break) were calculated.

[0098] The form of the PVA resin is not particularly limited, and examples thereof include powder, chip, and block forms, etc. Furthermore, the PVA resin may be in the form of a film such as a water-soluble film described later, or other molded products.

[0099] The applications of the PVA resin are not particularly limited, and in addition to the water-soluble film described below, it can be used in various applications such as adhesives, stabilizers for emulsion polymerization and suspension polymerization, paper processing agents, fiber processing agents, and inorganic binders. Among these applications, the PVA resin is particularly suitable as a molding material for water-soluble films.

[0100] <Water-soluble film>

[0101] The water-soluble film according to one embodiment of the present invention comprises the PVA resin according to one embodiment of the present invention. The water-soluble film comprises the PVA resin according to one embodiment of the present invention, and therefore has excellent cold-water solubility, mechanical strength, and biodegradability. Furthermore, the water-soluble film can be manufactured using an aqueous solution of the PVA resin, which has excellent filterability, as a raw material, resulting in excellent productivity. Therefore, the water-soluble film can be suitably used as a packaging material for various chemicals such as clothing detergents, bleaching agents, and pesticides. In particular, the water-soluble film can be particularly suitably used as a packaging material in unit packs.

[0102] It should be noted that the water-soluble film can be produced using a filtered aqueous solution of the PVA resin or an unfiltered aqueous solution of the PVA resin. In addition, the water-soluble film can be produced by other methods that do not use an aqueous solution of the PVA resin, as long as it contains the PVA resin according to one embodiment of the present invention.

[0103] The lower limit of the content of the PVA resin according to one embodiment of the present invention in the water-soluble film is preferably 30% by mass, more preferably 50% by mass, further preferably 70% by mass, and may be 80% by mass or 90% by mass. On the other hand, the upper limit of the content of the PVA resin may be 100% by mass, or may be 99% by mass, 95% by mass, 90% by mass, or 80% by mass.

[0104] The lower limit of the modified PVA content in the water-soluble film is preferably 30% by mass, more preferably 50% by mass, further preferably 70% by mass, and may be 80% by mass or 90% by mass. On the other hand, the upper limit of the modified PVA content may be 100% by mass, or may be 99% by mass, 95% by mass, 90% by mass, or 80% by mass.

[0105] The water-soluble film may contain additives and processing aids other than the PVA resin, for example, appropriate amounts of plasticizers, plasticizer compatibilizers, surfactants, lubricants, release agents, fillers, crosslinking agents, anti-blocking agents, antioxidants, adhesion reducers, defoaming agents, nanoparticles such as layered silicate-type nanoclay (such as sodium montmorillonite), bleaching agents (such as sodium metabisulfite, sodium sulfate, etc.), bittering agents and other aversive agents (such as denatonium benzoate, denatonium saccharin, denatonium chloride, sucrose octaacetate, quinine, or flavonoids such as quercetin and naringenin), stimulants (such as capsaicin, piperine, allyl isothiocyanate, resiniferatoxin, etc.), sugars, and other substances, depending on the purpose.

[0106] The water-soluble film may contain 5-50% by mass, preferably 5-40% by mass, and more preferably 10-40% by mass of a plasticizer. The plasticizer may include one or more selected from sorbitol, glycerol, diglycerol, propylene glycol, dipropylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol with a molecular weight of 400 or less, 2-methyl-1,3-propanediol, ethanolamine, trimethylolpropane, polyether polyols, isomalt, maltitol, xylitol, erythritol, aconitol, galactitol, pentaerythritol, mannitol, and sugar alcohols. The plasticizer may be a bio-based material. Examples of bio-based plasticizers include, but are not limited to, glycerol and sorbitol. Generally speaking, water-soluble films require strength and toughness sufficient to withstand high-temperature, high-humidity environments and cold regions, and sometimes require impact resistance at low temperatures. When the water-soluble film contains a plasticizer, the impact resistance at low temperatures can be improved, the glass transition temperature of the water-soluble film can be lowered, or the cold water solubility can be improved.

[0107] The water-soluble film may contain a surfactant. The surfactant is used to improve the dispersibility of the solution of the PVA resin when making the film. As a surfactant, any surfactant such as nonionic, cationic, anionic, and amphoteric can be used. Suitable surfactants include propylene glycol, diethylene glycol, monoethanolamine, ethylene oxide adducts of polypropylene glycol, ethylene oxide adducts of alcohol, ethylene oxide adducts of alkylphenols, tertiary acetylene glycol, alkanolamide (nonionic), ethylene oxide adducts of amines, quaternary ammonium salts, ethylene oxide adducts of quaternary amines (cationic), alkali metal salts of fatty acids having 8 to 24 carbon atoms, alkylated sulfonates, alkyl polyethoxylated sulfonates, alkylbenzene sulfonates (anionic), amine oxides, N-alkylated betaines, sulfobetaines (zwitterions), etc., but are not limited to them. In addition, other suitable surfactants include dialkyl sulfosuccinates, lactated fatty acid esters of glycerol or propylene glycol, lactated esters of fatty acids, sodium salts of alkylsulfonic acids, polysorbate 20, polysorbate 60, polysorbate 65, polysorbate 80, alkylated polyethylene glycols, lecithin, acetylated fatty acid esters of glycerol or propylene glycol, sodium salts of laurylsulfonic acid, acetylated esters of fatty acids, myristyl dimethylamine oxide, trimethyl tallow alkylammonium chloride, quaternary ammonium compounds, salts thereof, and any combination thereof. In a preferred embodiment, the surfactants include polyoxyethylated polypropylene glycol, ethylene oxide adducts of alcohols, ethylene oxide adducts of alkylphenols, tertiary acetylenediol, alkanolamides, ethylene oxide adducts of amines, quaternary ammonium salts, ethylene oxide adducts of quaternary amines, amine oxides, N-alkyl betaines, sulfobetaines, and combinations thereof. The content of the surfactant is not particularly limited and may be 0.1 to 8.0% by mass, preferably 1.0 to 7.0% by mass, more preferably 3.0 to 7.0% by mass, further preferably 5.0 to 7.0% by mass or 0.1 to 2.5% by mass. By setting the content of the surfactant within the above range, film pore formation can be further suppressed during film formation by solvent casting, and stickiness or oiliness of the resulting film surface upon touch can be further suppressed.

[0108] Suitable lubricants and release agents that may be optionally included in the water-soluble film include, but are not limited to, fatty acids or fatty acid salts, fatty alcohols, fatty esters, fatty amines, fatty amine acetates, and fatty amides. Among these, fatty acids, fatty acid salts, and fatty amine acetates may be included. In a preferred embodiment of the present invention, the lubricant and release agent may be present in the water-soluble film in an amount of 0.01 to 1.5% by mass, preferably 0.1 to 1.0% by mass.

[0109] The defoaming agent used in the water-soluble film is not particularly limited, and examples thereof include hydrophobic silica such as silicone dioxide, siloxane, and silicone ether, particulate fumed silica, and the registered trademark "FoamBlast" available from Emerald Performance Materials, namely, "Foam Blast 327," "FoamBlast UVD," "FoamBlast 163," "Foam Blast 269," "Foam Blast 338," "Foam Blast 290," "FoamBlast 332," "Foam Blast 349," "Foam Blast 550," and "Foam Blast 339." In a preferred embodiment of the present invention, the defoaming agent may be 0.01 to 0.5 parts by mass, for example, 0.05 to 0.1 parts by mass, 0.04 to 0.1 parts by mass, 0.03 to 0.1 parts by mass, or 0.02 to 0.1 parts by mass, based on 100 parts by mass of the PVA resin or modified PVA.

[0110] The water-soluble film can contain an antioxidant as, for example, a chloride scavenger. Preferred antioxidants (chloride scavengers) include sulfite compounds, pyrosulfite compounds, thiosulfite compounds, thiosulfate compounds, iodide, nitrite compounds, carbamate compounds, ascorbate compounds, and combinations thereof. In addition, in a preferred embodiment, the antioxidant is suitable for use with propyl gallate, citric acid, sodium pyrosulfite (SMBS), carbamate compounds, ascorbate, and combinations thereof. The amount of the antioxidant added is not particularly limited, but is preferably 0.25 to 1.5 parts by mass relative to 100 parts by mass of the PVA resin or modified PVA. For example, it can be 0.25 to 1.5 parts by mass, 0.3 to 1.5 parts by mass, 0.35 to 1.5 parts by mass, 0.4 to 1.5 parts by mass, 0.45 to 1.5 parts by mass, 0.5 to 1.5 parts by mass, 0.75 to 1.5 parts by mass, 1.0 to 1.5 parts by mass, 1.25 to 1.5 parts by mass, etc.

[0111] The water-soluble film can include filler, chain extender (Extender), filler, antiblocking agent, adhesion reducer and their combination. As filler, there is no particular limitation, and metal stearates such as starch, modified starch, cross-linked polyvinyl pyrrolidone, cross-linked cellulose, crystallized cellulose, silicon dioxide, metal oxide, calcium carbonate, talc, mica, magnesium stearate, etc. can be listed. In a preferred embodiment of the present invention, the content of the filler, chain extender, filler, antiblocking agent, adhesion reducer in the water-soluble film can be 1 to 6 mass % each independently, preferably 1 to 4 mass %, more preferably 2 to 4 mass %.

[0112] Examples of sugars include monosaccharides such as glucose; oligosaccharides, polysaccharides, and chain sugar alcohols. Examples of polysaccharides include starch, cellulose, chitin, chitosan, hemicellulose, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, pectin, pullulan, agar, alginic acid, carrageenan, dextrin, and trehalose. Examples of chain sugar alcohols include tetrasaccharides with four carbon atoms such as threol and erythrol; pentasaccharides with five carbon atoms such as arabinose and xylose; and hexasaccharides with six carbon atoms such as sorbose, mannose, and sorbose. One or more sugars may be used.

[0113] When the water-soluble film contains saccharide, the lower limit of the content of saccharide relative to 100 mass parts of PVA resin or modified PVA is preferably 1 mass part, more preferably 2 mass parts, and further preferably 3 mass parts. On the other hand, the upper limit of the content of saccharide is preferably 100 mass parts, and can be 50 mass parts or 30 mass parts. If the content of saccharide is more than the above-mentioned lower limit, the cold water solubility of the water-soluble film improves. On the other hand, if the content of saccharide is below the above-mentioned upper limit, the impact resistance of the water-soluble film at low temperatures improves.

[0114] The water-soluble film may further contain other additives such as colorants, fragrances, extenders, and ultraviolet absorbers as needed. Furthermore, the water-soluble film may contain a water-soluble polymer such as a different type of PVA from the modified PVA, polyacrylamide, polyacrylic acid, or a salt thereof. Furthermore, the water-soluble film may contain a metal salt such as an alkali metal salt such as sodium acetate or an alkaline earth metal salt such as magnesium acetate.

[0115] The lower limit of the average thickness of the water-soluble film is preferably 10 μm, more preferably 20 μm, and even more preferably 30 μm. The upper limit of the average thickness of the water-soluble film is preferably 200 μm, more preferably 150 μm, and even more preferably 120 μm. If the average thickness of the water-soluble film is greater than or equal to the lower limit, the mechanical strength of the water-soluble film is improved. On the other hand, if the average thickness of the water-soluble film is less than or equal to the upper limit, cold water solubility is improved, and the water-soluble film can be produced at low cost.

[0116] In order to improve the blocking resistance of the water-soluble film, the surface of the water-soluble film can be roll-matted as needed, or an anti-blocking powder such as silicon dioxide or starch can be applied to the water-soluble film, or an embossing treatment can be performed. The roll-matting of the surface of the water-soluble film can be implemented by pre-forming fine concave-convex surfaces on the roller that contacts the water-soluble film before drying during film formation. The embossing treatment can generally be performed after the film is formed by applying heat and pressure while squeezing with an embossing roller and a rubber roller.

[0117] <Method for producing water-soluble film>

[0118] The method for producing the water-soluble film is not particularly limited and can be produced by known methods such as casting (solvent casting), calendaring, blow molding, extrusion, blow extrusion, and melt extrusion. For example, the method for producing the water-soluble film comprises: a step of preparing an aqueous solution containing the PVA resin according to one embodiment of the present invention; and a step of forming a film using the aqueous solution. The method for producing the water-soluble film may further comprise, before the film forming step, a step of filtering the aqueous solution using a filter.

[0119] In the process of preparing an aqueous solution, the PVA resin and, if desired, other ingredients are dissolved in water. It should be noted that the aqueous solution may contain solvents other than water. The concentration of the PVA resin or modified PVA in the aqueous solution may be, for example, from 1% to 20% by mass, or from 3% to 12% by mass. This aqueous solution can be referred to as a film-forming stock solution, etc., for the production of water-soluble films.

[0120] After adjusting the aqueous solution in which the PVA resin is dissolved and before film making, a filter can be used to filter the aqueous solution as needed. For example, when dirt, dust, foreign matter, etc. are present in the solution, in order to remove them, the solution is sometimes filtered. As the filter used in the filtration, an existing known filter can be used. As the pore size of the filter, there is no particular limitation, for example, it can be more than 0.5 μm and less than 2 μm. As the material of the filter, there is no particular limitation, and it can be a synthetic resin such as a fluororesin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF). An unfiltered aqueous solution can be used for film making.

[0121] In the film-forming process, the obtained solution is placed on a smooth casting surface by coating or the like. After the solvent evaporates, the dried product is peeled off from the casting surface. After peeling, it is dried in an oven or the like as needed to obtain a water-soluble film.

[0122] <Extrusion Molding>

[0123] The extruded article according to one embodiment of the present invention is obtained by extrusion molding the PVA resin and has a film shape or a filament shape.

[0124] <filament>

[0125] The filament according to one embodiment of the present invention is a filament containing the PVA resin.

[0126] <Nonwoven fabrics>

[0127] The nonwoven fabric according to one embodiment of the present invention comprises the filaments.

[0128] <Container>

[0129] A container according to one embodiment of the present invention is a container comprising the water-soluble film as a packaging material. The water-soluble film can be used in a container comprising the water-soluble film as a packaging material. The container thus obtained is not particularly limited, but examples thereof include a container comprising at least a portion of the flexible bag disclosed in paragraphs 0090 to 0118 of JP-A-2021-523257 using the water-soluble film of the present invention.

[0130] The container is preferably filled with at least one chemical selected from pesticides, oxidants, and detergents, and the chemical can be sealed in the container. The container can be a container for at least one chemical selected from pesticides, oxidants, and detergents. The chemical loaded or sealed in the container is not particularly limited, and examples thereof include conventionally known pesticides, oxidants, detergents, and the like. Examples of pesticides include, but are not limited to, those disclosed in paragraph 0119 of Japanese Patent Application No. 2021-526563. Examples of oxidants include, but are not limited to, halogenated isocyanurates such as hypochlorite and sodium dichloroisocyanurate, trichloroisocyanuric acid, chlorates, chlorites, perchlorates, bromates, perbromates, halogenated hydantoins, perborates, periodates, persulfates, permanganates, chromates, dichromates, nitrates, nitrites, peroxides, ketone peroxides, peroxyacids, inorganic acids, or combinations thereof, but are not limited to these. Examples of the detergent include, but are not limited to, components described in paragraphs 0123 to 0149 of JP-A No. 2021-523257.

[0131] <Aqueous solution>

[0132] In one embodiment of the present invention, the aqueous solution according to one embodiment of the present invention comprises a PVA resin.

[0133] In the aqueous solution according to one embodiment of the present invention, the content of the PVA resin is preferably 0.1 ppm to 50 ppm. Aqueous solutions containing the PVA resin in such a content tend to have particularly good biodegradability.

[0134] The temperature of the aqueous solution is not particularly limited, but is preferably 20° C. to 25° C. Aqueous solutions adjusted to such a temperature also tend to have particularly good biodegradability.

[0135] The aqueous solution may contain, for example, the water-soluble film according to one embodiment of the present invention dissolved therein. The aqueous solution may contain components other than the PVA resin.

[0136] The aqueous solution preferably further comprises at least one of magnesium ion and calcium ion, more preferably comprises both magnesium ion and calcium ion. When the aqueous solution comprises these ions, there is a particularly good tendency for biodegradability. As the total content of magnesium ion and calcium ion in the aqueous solution, it is preferably more than 10ppm and less than 400ppm, and can be more than 10ppm and less than 100ppm. These ions can be contained in the PVA resin, and can also be contained in the components other than the PVA resin.

[0137] In another embodiment of the present invention, the aqueous solution preferably contains 3% to 12% by mass of PVA resin. Aqueous solutions containing this amount of PVA resin can be suitably used as a stock solution for forming a water-soluble film. For example, the aqueous solution may contain other components of the water-soluble film in addition to the PVA resin, as needed.

[0138] Example

[0139] Hereinafter, the present invention will be described in more detail using Examples, but the present invention is not limited to these Examples at all.

[0140] [Example 1] Production of PVA resin

[0141] In a 5L reactor equipped with a stirring blade, a reflux condenser, a nitrogen inlet, and a thermometer, 2040g of vinyl acetate, 905g of methanol, and 58.9g of a 50% methanol solution of N-vinyl-2-pyrrolidone (NVP) were added, and deaeration was performed by bubbling nitrogen for 30 minutes. The reactor temperature was raised, and when the internal temperature reached 60°C, 1.5g of 2,2'-azobis(isobutyronitrile) was added to initiate polymerization. Polymerization was continued while the 50% methanol solution of N-vinyl-2-pyrrolidone was added sequentially to maintain a constant molar ratio with the vinyl acetate monomer. After 5 hours, the mixture was cooled. The solids concentration at this point was 34%. Next, 10g of a 10% methanol solution of tert-butylhydroquinone was added as a polymerization inhibitor to terminate the reaction. Unreacted monomer was then removed under reduced pressure at 30°C while methanol was occasionally added, yielding a methanol solution of a vinyl acetate copolymer (33% concentration).

[0142] Next, a 10% NaOH methanol solution with an alkali molar ratio (moles of NaOH / moles of vinyl acetate monomer units) of 0.03 was added to a methanol solution of a vinyl acetate copolymer adjusted to a 25% concentration for saponification. The resulting gel was pulverized in a grinder and allowed to stand for 1 hour for saponification. Then, 500 g of methyl acetate was added to neutralize the residual alkali. A white solid was obtained by filtration, to which 2000 g of methanol was added and washed at room temperature for 3 hours. This washing process was repeated three times, and the resulting white solid was centrifuged and stored in a dryer at 65°C for 2 days to obtain a PVA resin primarily composed of modified PVA (PVA-1).

[0143] The average degree of polymerization (viscosity-average degree of polymerization) and degree of saponification of PVA-1 were measured in accordance with JIS-K6726-1994. Furthermore, the N-vinylamide unit content of the vinyl acetate copolymer (i.e., the N-vinylamide unit content in PVA-1: modification ratio) was determined using proton NMR. These results are shown in Table 1.

[0144] (Measurement of N1 and N2, calculation of total volume of particles)

[0145] The number of particles with a size of 1 μm (N1) and the number of particles with a size of 2 μm (N2) contained in 1 mL of a 2% by mass aqueous solution of the resulting PVA resin were determined using the above method, and their ratio (N1 / N2) was calculated. Furthermore, the total volume of particles with a size of 1 μm and particles with a size of 2 μm contained in 1 mL of a 2% by mass aqueous solution of the resulting PVA resin was calculated using the above method. These results are shown in Table 2.

[0146] (Determination of biodegradation rate)

[0147] The biodegradability of the resulting PVA resin was measured using the above method. Note that the calcium concentration in the solution used for the measurement was 9 ppm, and the magnesium concentration was 2 ppm. A biodegradability of 60% or greater was considered good. The measured biodegradability is shown in Table 3.

[0148] (Water Solubility Test: Evaluation of Cold Water Solubility)

[0149] Using the above method, cast films with an average thickness of 50 μm obtained from the resulting PVA resin were subjected to water dissolution testing at 5°C after conditioning at 20°C and 65% RH for one week. The dissolution times were evaluated according to the following criteria. Cases A to D were judged to have good cold water solubility. The results are shown in Table 3.

[0150] A: More than 5 seconds and less than 100 seconds

[0151] B: More than 100 seconds and less than 400 seconds

[0152] C: More than 400 seconds and less than 1,000 seconds

[0153] D: More than 1,000 seconds and less than 3,000 seconds

[0154] E: More than 3,000 seconds

[0155] (Determination of mechanical strength (Young's modulus and elongation at break))

[0156] The Young's modulus and elongation at break of a cast film having an average thickness of 50 μm obtained from the obtained PVA resin were measured by the above method. 2 When the elongation at break was 150% or higher, the mechanical strength was judged to be good.

[0157] (Filtration test: evaluation of filterability)

[0158] Deionized water and the obtained PVA resin were added to a 500 mL separable flask equipped with a stirring blade and treated at 95°C for 2 hours while stirring to prepare 400 mL of a 2% aqueous solution. The solution was temperature-controlled to 20°C and injected into a suction filtration apparatus (filtration area 9.6 cm) equipped with a PTFE membrane filter ("T100A" manufactured by ADVANTEC) with a pore size of 1 μm. 2 ), use an aspirator, keep the reduced pressure during suction to 0.020-0.022MPa, and perform suction filtration. Measure the time (t50) from the start of filtration to the time when 50mL of solution is filtered, the time (t100) from the time when 100mL of solution is filtered, the time (t150) from the time when 150mL of solution is filtered, and the time (t200) from the time when 200mL of solution is filtered. Calculate the ratio (T1 / T2) of the time required from the time when 50mL of solution is filtered to the time when 100mL of solution is filtered (T1=t100-t50) to the time required from the time when 150mL of solution is filtered to the time when 200mL of solution is filtered (T2=t200-t150). The closer the ratio (T1 / T2) is to 1, the better the filterability. When the ratio (T1 / T2) is 0.70 or more, it is judged that the filterability is excellent, and when it is 0.80 or more, it is judged that the filterability is particularly excellent. The results are shown in Table 3.

[0159] [Examples 2 to 22, Comparative Examples 1 to 5]

[0160] The production conditions were adjusted to obtain modified PVA having the average polymerization degree, saponification degree, and modification ratio shown in Table 1. The same procedures as in Example 1 were followed, except that the type of N-vinylamide, the presence or absence of a polymerization inhibitor at the end of polymerization, and the temperature for removing unreacted monomers after polymerization were as shown in Table 1. PVA resins containing modified PVA (PVA-2 to PVA-19) as the main component were obtained. In Table 1, "NVC" stands for N-vinylcaprolactam. The resulting modified PVA and PVA resins were subjected to various measurements and evaluations as in Example 1. The results are shown in Tables 1 to 3.

[0161] [Table 1]

[0162]

[0163] [Table 2]

[0164]

[0165] [Table 3]

[0166]

[0167] As shown in Tables 1 to 3, each PVA resin of Examples 1 to 22 can obtain a water-soluble film with good cold water solubility and mechanical strength, and exhibits good biodegradability and excellent filterability when prepared as an aqueous solution. On the other hand, each PVA resin of Comparative Examples 1 to 5 exhibits a ratio (N1 / N2) exceeding 50 and poor filterability. It should be noted that each PVA resin of Comparative Examples 1 to 5 is a resin obtained by not adding a polymerization inhibitor at the end of polymerization, as in the examples described in Patent Document 1. When no polymerization inhibitor is added at the end of polymerization, the obtained PVA resin exhibits a ratio (N1 / N2) exceeding 50.

[0168] Industrial applicability

[0169] The PVA resin of the present invention can be suitably used as a material for water-soluble films, extruded products, filaments, nonwoven fabrics, containers, and the like.

Claims

1. A polyvinyl alcohol resin comprising a modified polyvinyl alcohol containing an N-vinylamide unit as a main component, The ratio (N1 / N2) of the number of particles (N1) with a size of 1 μm to the number of particles (N2) with a size of 2 μm contained in 1 mL of a 2 mass % aqueous solution of the polyvinyl alcohol resin is 0.1 or more and 50 or less.

2. The polyvinyl alcohol resin according to claim 1, wherein The modified polyvinyl alcohol has an N-vinylamide unit content of 0.3 mol% to 10 mol%, a saponification degree of 70 mol% to 99.9 mol%, and an average polymerization degree of 200 to 4,500.

3. The polyvinyl alcohol resin according to claim 1 or 2, wherein The total volume of particles with a size of 1 μm and particles with a size of 2 μm contained in 1 mL of a 2% by mass aqueous solution of the polyvinyl alcohol resin is 1 μm. 3 Above and 10,000μm 3 the following.

4. The polyvinyl alcohol resin according to any one of claims 1 to 3, wherein The biodegradation rate is over 60%.

5. The polyvinyl alcohol resin according to any one of claims 1 to 4, wherein A cast film having an average thickness of 50 μm obtained from the polyvinyl alcohol resin was subjected to a water dissolution test at 5° C. after humidity conditioning at 20° C. and 65% RH for one week. The dissolution time was 5 seconds to 3,000 seconds. The polyvinyl alcohol resin according to any one of claims 1 to 5, wherein Further comprising a polymerization inhibitor. 7 . A water-soluble film comprising the polyvinyl alcohol resin according to claim 1 .

8. The water-soluble film according to claim 7, wherein the polyvinyl alcohol resin is molded by at least one method selected from the group consisting of solvent casting, calendaring, inflation molding, extrusion, and blow extrusion. 9 . An extruded article obtained by extrusion molding the polyvinyl alcohol resin according to claim 1 , the article being in the form of a film or a filament. 10 . A filament comprising the polyvinyl alcohol resin according to claim 1 .

11. A nonwoven fabric comprising the filaments according to claim 10.

12. A container comprising the water-soluble film according to claim 7 as a packaging material.

13. The container according to claim 12, containing at least one selected from the group consisting of pesticides, oxidants, and detergents.

14. A method for producing a water-soluble film, comprising: preparing an aqueous solution containing the polyvinyl alcohol resin according to any one of claims 1 to 6; and forming a film using the aqueous solution.

15. The method for producing a water-soluble film according to claim 14, wherein Prior to the membrane forming step, the method further includes filtering the aqueous solution using a filter. 16 . An aqueous solution comprising the polyvinyl alcohol resin according to claim 1 , wherein the content of the polyvinyl alcohol resin is 0.1 ppm to 50 ppm. The aqueous solution according to claim 16 , wherein the temperature is 20° C. or higher and 25° C. or lower. 18 . The aqueous solution according to claim 16 , further comprising at least one selected from magnesium ions and calcium ions, wherein the total content of the magnesium ions and calcium ions is 10 ppm to 400 ppm. 19 . An aqueous solution comprising the polyvinyl alcohol resin according to claim 1 , wherein the content of the polyvinyl alcohol resin is 3% by mass or more and 12% by mass or less.

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