Powder product

Abstract

This powder product contains: polymer particles obtained by saponifying a polymer of a vinyl ester-based monomer or a copolymer of a vinyl ester-based monomer and another monomer, which have a particle size distribution in which the content of particles having diameters of 180 µm or less is 50 mass% or more and the content of particles having diameters of 500 µm or more is 10 mass% or less; and a water-soluble additive at a quantity of 0.1-10 mass% relative to the mass of the polymer particles. The water-soluble additive has a viscosity of 30-200 mPa·s at 20°C and a surface tension of 50-72 mN / m when a 0.05 mass% aqueous solution of the water-soluble additive is measured at 20°C using a hanging drop method. The angle of repose of the powder product is 60° or less when measured using a funnel injection method according to JIS R9301-2-2:1999.

Description

powder products

[0001] The present invention relates to powder products.

[0002] Polymers having a polyvinyl alcohol (PVA) skeleton (hereinafter, in this specification, these are collectively referred to as "polyvinyl alcohol-based polymers," "vinyl alcohol-based polymers," or simply "PVA") are known as hydrophilic synthetic resins, and various applications that take advantage of these properties are being developed.

[0003] Depending on the application, PVA may be in powder form and dispersed in water. Adjusting the degree of saponification of PVA has been a common practice to improve its solubility, as described, for example, in the introduction of the Denka Poval product by the applicant.

[0004] "Denka Poval," Denka Company Limited, 2016, https: / / www.denka.co.jp / pdf / product / detail / 00009 / poval_catalog.pdf

[0005] It is generally known that the larger the surface area of ​​a solute, the faster it dissolves in a solvent, so it is desirable for the PVA particles to be small in size.However, when PVA particles are too small in size, there are issues such as the formation of lumps (lumps of powder floating on the water surface) or the formation of aggregates in the water when trying to dissolve them in water.

[0006] The formation of these aggregates on the water surface and in the water significantly reduces the solubility of PVA particles in water. Conventional technology requires vigorous mixing using a high-power mixer to break down the aggregates and particles, which also creates the problem of undesirable foaming. It is also difficult to achieve the performance required for a powder product that dissolves in water.

[0007] Furthermore, with conventional techniques, weak stirring alone can actually promote the aggregation of PVA particles, resulting in the problem of aggregates easily forming in the water.

[0008] The above-mentioned problems cannot be solved by simply adjusting the degree of saponification according to conventional techniques, and there is a demand for new PVA products.

[0009] In order to solve the above problems, the present invention can provide the following.

[0010] Aspect 1. A powder product comprising: polymer particles obtained by saponifying a polymer of a vinyl ester monomer or a copolymer of a vinyl ester monomer and another monomer, the polymer particles having a particle size distribution in which particles with a particle size of 180 μm or less account for 50 mass% or more and particles with a particle size of 500 μm or more account for 10 mass% or less; and a water-soluble additive in an amount ranging from 0.1 mass% to 10 mass% based on the mass of the polymer particles, wherein the water-soluble additive has a viscosity at 20°C of 30 to 200 mPa s and a surface tension of 50 to 72 mN / m as measured by the hanging drop method for a 0.05 mass% aqueous solution of the water-soluble additive at 20°C; and an angle of repose of the powder product measured by the funnel injection method in accordance with JIS R9301-2-2:1999 of 60° or less.

[0011] Aspect 2. The powder product of Aspect 1, wherein the difference angle measured by the funnel injection method is 10° or greater.

[0012] Aspect 3. The powder product of Aspect 1 or 2, wherein the compressibility calculated from the initial bulk density and tapped bulk density measured according to a method in accordance with JIS R1628:1997 using the following formula: [Compressibility] (%) = 100 × ([Taped Bulk Density] - [Initial Bulk Density]) / [Taped Bulk Density] is 45% or less.

[0013] Aspect 4. The powder product according to any one of Aspects 1 to 3, wherein the polymer particles are made of a polymer of a vinyl ester monomer.

[0014] Aspect 5. A powder product according to any one of Aspects 1 to 3, wherein the polymer particles are made of a copolymer of a vinyl ester monomer and another monomer.

[0015] Aspect 6. The powder product according to any one of Aspects 1 to 3 and 5, wherein the other monomer is a polyfunctional monomer.

[0016] Aspect 7. The powder product according to Aspect 6, wherein the polyfunctional monomer is a compound having two or more polymerizable unsaturated bonds in the molecule.

[0017] According to the present invention, not only can the powder product have high solubility in water even under weak mixing conditions, but also the powder product has the suitability required for the powder product.

[0018] In this specification, unless otherwise specified, numerical ranges include the upper and lower limits. The term "polymer" in this specification follows the definition of polymer by the International Union of Pure and Applied Chemistry (IUPAC) Commission on Macromolecular Nomenclature, namely, "a polymer molecule is a molecule of high relative molecular mass whose structure is composed of multiple repetitions of units derived, substantially or conceptually, from molecules of low relative molecular mass."

[0019] The powder product according to an embodiment of the present invention is characterized by containing polymer particles obtained by saponifying a polymer of a vinyl ester-based monomer or a copolymer of a vinyl ester-based monomer and another monomer, and a water-soluble additive in a predetermined mass ratio. The powder product is primarily intended to be dissolved in water, but can also be dissolved in aqueous solvents other than pure water (tap water, aqueous solutions of hydrophilic solutes, etc.).

[0020] [Polymer Particles] The polymer particles are PVA polymer particles, and by having a specific particle size distribution, they can satisfy the prerequisites for rapid dissolution in aqueous solvents. The particle size distribution of the polymer particles can be measured by sieving using sieves with 180 μm and 500 μm meshes in accordance with JIS Z8815:1994. For rapid dissolution in aqueous solvents, the polymer particles must not contain many particles of excessively large size. Specifically, the particle ratio must be such that the content of particles with a particle size of 500 μm or more (over a 500 μm sieve) is 10% by mass or less, and the content of particles with a particle size of 180 μm or less (under a 180 μm sieve) is 50% by mass or more. If the particle size distribution does not satisfy this condition, solubility may be adversely affected.

[0021] In a preferred embodiment, the particle size distribution of the polymer particles may be such that the proportion of particles sieving a 500 μm sieve is 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and even more preferably 0.1% by mass or less. Also, in a preferred embodiment, the particle size distribution of the polymer particles may be such that the proportion of particles sieving a 180 μm sieve is 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more.

[0022] In a preferred embodiment, the degree of saponification of the PVA constituting the polymer particles may be 70 to 100 mol%, more preferably 75 to 95 mol%, even more preferably 80 to 95 mol%, and even more preferably 80 to 90 mol%. A saponification degree within this range effectively improves solubility in aqueous solvents. The saponification degree can be measured by the method described in JIS K6726:1994.

[0023] In a preferred embodiment, the viscosity of a 4% by mass aqueous solution of PVA constituting the polymer particles at 20°C is measured at a shear rate of 10 s in accordance with the rotational viscometer method described in JIS K6726:1994 and JIS K7117-1999. -1 When calculated as above, the viscosity may be in the range of 1 to 1000 mPa s, more preferably in the range of 1 to 500 mPa s, and even more preferably in the range of 1 to 300 mPa s. When the viscosity is in this range, the effect of improving the solubility in aqueous solvents can be obtained.

[0024] Examples of vinyl ester monomers used as raw materials for PVA constituting polymer particles include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, etc., and mixtures thereof may also be used. From the viewpoint of ease of polymerization, vinyl acetate is preferred.

[0025] The PVA may be a saponified homopolymer of a vinyl ester monomer, or a saponified copolymer of a vinyl ester monomer and another monomer.

[0026] Furthermore, examples of monofunctional monomers copolymerizable with vinyl ester monomers (i.e., monofunctional monomers other than vinyl esters) include the following compounds: α-olefin monomers such as ethylene and propylene; (meth)acrylic acid alkyl ester monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; unsaturated amide monomers such as (meth)acrylamide and N-methylolacrylamide; unsaturated carboxylic acid monomers such as (meth)acrylic acid, crotonic acid, maleic acid, itaconic acid, and fumaric acid; alkyl (methyl, ethyl, propyl, etc.) ester monomers of unsaturated carboxylic acids; anhydrides of unsaturated carboxylic acids such as maleic anhydride; sodium, potassium, ammonium, etc. salts of unsaturated carboxylic acids; sulfonic acid group-containing monomers or salts thereof such as 2-acrylamido-2-methylpropanesulfonic acid; and alkyl vinyl ether monomers.

[0027] Other monomers copolymerizable with vinyl ester monomers include polyfunctional and monofunctional monomers. Polyfunctional monomers are preferably compounds with two or more polymerizable unsaturated bonds in the molecule. The number of polymerizable unsaturated sites in the polyfunctional monomer is preferably 2 to 5. Examples of polyfunctional monomers include: divinyl ethers such as ethanediol divinyl ether, propanediol divinyl ether, butanediol divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, and polypropylene glycol divinyl ether; and divinyl sulfonic acid compounds. Diene compounds such as pentadiene, hexadiene, heptadiene, octadiene, nonadiene, and decadiene. Diallyl ether compounds such as glycerin diallyl ether, diethylene glycol diallyl ether, ethylene glycol diallyl ether, triethylene glycol diallyl ether, polyethylene glycol diallyl ether, trimethylolpropane diallyl ether, and pentaerythritol diallyl ether. Triallyl ether compounds such as glycerin triallyl ether, trimethylolpropane triallyl ether, and pentaerythritol triallyl ether. Tetraallyl ether compounds such as pentaerythritol tetraallyl ether. Polyfunctional monomers containing an allyl ester group such as diallyl phthalate, diallyl maleate, diallyl itaconate, diallyl terephthalate, and diallyl adipate. Diallylamine compounds such as diallylamine and diallylmethylamine, and polyfunctional monomers containing an allylamino group such as triallylamine. Polyfunctional monomers containing an allylammonium group such as diallylammonium salts such as diallyldimethylammonium chloride. Polyfunctional monomers containing two or more allyl groups, such as triallyl isocyanurate, 1,3-diallyl urea, triallyl phosphate, and diallyl disulfide.Polyfunctional monomers containing (meth)acrylic acid, such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, glycerin di(meth)acrylate, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and isocyanuric acid tri(meth)acrylate. Polyfunctional monomers containing (meth)acrylamides, such as N,N'-methylenebis(meth)acrylamide and N,N'-ethylenebis(meth)acrylamide. Polyfunctional aromatic monomers, such as divinylbenzene and trivinylbenzene. Glycidyl group-containing polyfunctional monomers such as allyl glycidyl ether and glycidyl (meth)acrylate.

[0028] As the other monomer copolymerizable with the vinyl ester-based monomer, a polyfunctional monomer is preferable, a compound having two or more polymerizable unsaturated bonds in the molecule is more preferable, and a compound having three or more polymerizable unsaturated bonds in the molecule is even more preferable.

[0029] [Water-soluble additives] The water-soluble additives contained in this powder product (hereinafter also referred to simply as "additives") are liquid at room temperature (e.g., 20°C) as defined by JIS Z8703:1983, and have a viscosity at 20°C of 10 s at a shear rate of 10 s as measured by a cone-and-plate rotational viscometer (rheometer) conforming to JIS Z8803:2011. -1 When calculated as above, the viscosity must be in the range of 30 to 200 mPa s. If the viscosity is outside this range, miscibility with the polymer particles will be insufficient, resulting in poor solubility. In a preferred embodiment from the viewpoint of improving solubility, the viscosity of the additive under the above conditions may be in the range of 30 to 150 mPa s, more preferably in the range of 30 to 100 mPa s.

[0030] The additive must also have a surface tension of 50 to 72 mN / m when measured by the pendant drop method at 20°C for a 0.05% by mass aqueous solution. In this specification, the pendant drop method refers to the ds / de method. If the surface tension is outside this range, the solubility of the powder product will be poor.

[0031] The mass of the additive in the powder product is in the range of 0.1% by mass to 10% by mass, based on the mass of the polymer particles. If the mass of the additive is less than 0.1% by mass, the solubility under weak stirring conditions will be poor. If the mass of the additive is more than 10% by mass, the powder product will be sticky, which will hinder the operation during use and transportation, and will adversely affect the performance of the powder product.

[0032] The additives are not particularly limited as long as they are water-soluble and satisfy the above-mentioned viscosity and surface tension requirements, and examples include polyethers, polyhydric alcohols, polyoxyalkylenes, alcohol alkoxylate compounds, phenol alkoxylate compounds, silicone compounds, and mineral oils. Among these, those usable as nonionic surfactants are preferred, and / or polyethers are preferred. Among polyethers, polyethylene glycol (polyethylene oxide) and polypropylene glycol are preferred. The number-average molecular weight of the additive is preferably in the range of 100 to 20,000, more preferably in the range of 200 to 2,000, and even more preferably in the range of 200 to 1,500.

[0033] [Powder Product] The powder product containing the polymer particles and additives has properties suitable for dissolving in pure water or other aqueous solvents. This powder product is characterized by an angle of repose of 60° or less, measured by the funnel injection method in accordance with JIS R9301-2-2:1999 (measurement is performed using a protractor in this specification). If the angle of repose is outside this range, the powder will have excessive cohesion, which can cause problems during use and transportation, adversely affecting the performance of the powder product. In a preferred embodiment, the angle of repose may be 20° or more and 60° or less, and more preferably 30° or more and 60° or less.

[0034] In a preferred embodiment, the difference angle of the powder product may be 10° or more, and more preferably 10° to 40°. In this specification, the difference angle refers to the value obtained by subtracting the collapse angle from the repose angle, measured by dropping a weight onto a sample whose repose angle has been measured using the funnel injection method. When the difference angle is within the above range, the effect of improving solubility in aqueous solvents is obtained.

[0035] In a preferred embodiment, the compressibility of the powder product may be 45% or less, more preferably 10% to 45%, and even more preferably 10% to 40%. In this specification, the compressibility is a percentage calculated by the following formula: [Compressibility] (%) = 100 × ([Tapped Bulk Density] - [Initial Bulk Density]) / [Tapped Bulk Density]. Here, the initial bulk density and tapped bulk density refer to values ​​measured in accordance with the description of JIS R1628:1997. When the compressibility is within the above range, the effect of improving solubility in aqueous solvents is obtained.

[0036] The present invention will be described in more detail below with reference to examples. Note that the examples described below are representative examples of the present invention, and the present invention is not limited to the following examples.

[0037] Example 1 Polymer particles were synthesized according to the following procedure. A polymerization vessel equipped with a reflux condenser, a dropping funnel, and a stirrer was charged with 100 parts by weight of vinyl acetate, 117 parts by weight of methanol, and 0.016 parts by weight of Perloyl® NPP (manufactured by NOF Corporation) as an initiator. Polymerization was carried out for 5 hours at boiling point while stirring under a nitrogen atmosphere (polymerization rate: 88%). Unreacted vinyl acetate monomer was then removed from the polymerization system to obtain a methanol solution of polyvinyl acetate polymer. A methanol solution of sodium hydroxide was added to this solution (equivalent to 0.007 moles of sodium hydroxide relative to the structural units derived from vinyl acetate), and the resulting solution was saponified at 45°C for 90 minutes to obtain PVA with a degree of saponification of 88.1 mol%.

[0038] The resulting PVA was pulverized in an ACM pulverizer, and the resulting PVA particles were sieved using sieves with 180 μm and 500 μm openings according to JIS Z8815:1994 to measure particle size distribution. The particle size on the 500 μm sieve was 0.1 mass%, and the particle size on the 180 μm sieve was 99.1 mass%. The viscosity of a 4 mass% aqueous solution of the PVA was measured at 20°C using a Brookfield (Type B) rotational viscometer at a rotational speed of 30 rpm and a shear rate of 10 s in accordance with the rotational viscometer method described in JIS K6726:1994 and JIS K7117-1:1999. -1 The measured value was 5.4 mPa·s.

[0039] Polyethylene glycol (PEG-300) with a number average molecular weight of 300 was prepared as an additive, and the mixture was stirred at a shear rate of 10 s in accordance with the description in JIS Z8803:2011. -1 The viscosity was measured using a rheometer and found to be 70 mPa s. A 0.05% by mass aqueous solution of the additive was prepared, and the surface tension was measured at 20°C using a DMs-301 (Kyowa Interface Science Co., Ltd.) by the hanging drop method, which was found to be 68.8 mN / m. The surface tension of the water used as a control was also measured and found to be 70.2 mN / m.

[0040] The additive was mixed in an amount of 3% by mass relative to the mass of the PVA to obtain a powder product according to Example 1. As shown in the table, the physical properties of the following examples were measured in the same manner as in Example 1.

[0041] [Example 2] A powder product of Example 2 was obtained in the same manner as in Example 1, except that the following procedure was used to produce polymer particles: 100 parts by mass of vinyl acetate, 15 parts by mass of methanol, and 5.0 x 10 parts of Perloyl NPP (manufactured by NOF Corporation) as an initiator were added to a polymerization vessel equipped with a reflux condenser, a dropping funnel, and a stirrer. -3Parts by mass were charged and polymerized at boiling point for 5 hours while stirring in a nitrogen atmosphere (polymerization rate: 55%). Unreacted vinyl acetate monomer was then removed from the polymerization system to obtain a methanol solution of polyvinyl acetate polymer. A methanol solution of sodium hydroxide was added to this solution (calculated as 0.007 moles of sodium hydroxide relative to the vinyl acetate-derived structural units), and the saponification reaction was carried out at 45°C for 90 minutes to obtain PVA with a saponification degree of 87.9 mol%. The viscosity of a 4% by mass aqueous solution of this PVA was 56.8 mPa·s.

[0042] [Example 3] A powder product of Example 3 was obtained in the same manner as in Example 1, except that the following procedure was used to produce polymer particles: 100 parts by mass of vinyl acetate, 5 parts by mass of methanol, and 1.0 x 10 parts by mass of Perloyl NPP (manufactured by NOF Corporation) as an initiator were added to a polymerization vessel equipped with a reflux condenser, a dropping funnel, and a stirrer. -3 Parts by mass were charged and polymerized at boiling point for 5 hours while stirring in a nitrogen atmosphere (polymerization rate: 40%). Unreacted vinyl acetate monomer was then removed from the polymerization system to obtain a methanol solution of polyvinyl acetate polymer. A methanol solution of sodium hydroxide was added to this solution (calculated as 0.007 moles of sodium hydroxide relative to the structural units derived from vinyl acetate), and the saponification reaction was carried out at 45°C for 90 minutes to obtain PVA with a saponification degree of 88.8 mol%. The viscosity of a 4% by mass aqueous solution of this PVA was 114.3 mPa·s.

[0043] Examples 4-6 Polymer particles were prepared according to the manufacturing method of Example 1 of WO 2019 / 163490. Specifically, a polymerization vessel equipped with a reflux condenser, a dropping funnel, and a stirrer was charged with 100 parts by weight of vinyl acetate, 0.16 parts by weight of triallyl isocyanurate (TAIC), 66.7 parts by weight of methanol, and 0.07 parts by weight of Perloyl NPP (manufactured by NOF Corporation) as an initiator. The mixture was stirred under a nitrogen atmosphere and subjected to polymerization at boiling point for 5 hours (polymerization rate: 50%). Next, unreacted vinyl acetate monomer was removed from the polymerization system to obtain a methanol solution of polyvinyl acetate-TAIC copolymer. A methanol solution of sodium hydroxide was added to this solution (equivalent to 0.007 moles of sodium hydroxide relative to the structural units derived from vinyl acetate), and the resulting solution was subjected to a saponification reaction at 45°C for 90 minutes to obtain a PVA with a degree of saponification of 89.5 mol%.

[0044] PVA particles were obtained by pulverization and classification in the same manner as in Example 1, and the additives and PVA particles were mixed in the ratios shown in the table to obtain powder products according to Examples 4 to 6.

[0045] Comparative Example 1 A powder product according to Comparative Example 1 was obtained in the same manner as in Example 1, except that no additives were added.

[0046] Comparative Example 2 A powder product according to Comparative Example 2 was obtained in the same manner as in Example 4, except that no additives were added.

[0047] Comparative Example 3 A powder product according to Comparative Example 3 was obtained in the same manner as in Example 1, except that ADEKA NOL UH-420 (manufactured by ADEKA Corporation, special nonionic polymer surfactant) was used as the additive.

[0048] Comparative Example 4 A powder product according to Comparative Example 4 was obtained in the same manner as in Example 4, except that glycerin was used as the additive.

[0049] [Comparative Examples 5 and 6] Powder products according to Comparative Examples 5 and 6 were obtained in the same manner as in Example 4, except that SN Deformer 485 (manufactured by San Nopco, a mixture of polyoxyalkylene-type nonionic surfactants, etc.) was used as the additive.

[0050] [Comparative Examples 7 and 8] Powder products according to Comparative Examples 7 and 8 were obtained in the same manner as in Example 4, except that SN Deformer PC (a polyoxyalkylene-type nonionic surfactant manufactured by San Nopco Ltd.) was used as the additive.

[0051] Comparative Example 9 A powder product according to Comparative Example 9 was obtained in the same manner as in Example 4, except that NOPTUM 740A (manufactured by San Nopco, a mixture of a polyoxyalkylene-type nonionic surfactant, silica, water, etc.) was used as the additive.

[0052] Comparative Example 10 A powder product according to Comparative Example 10 was obtained in the same manner as in Example 4, except that the amount of additive was excessive.

[0053] [Measurement of Angle of Repose and Difference Angle] A funnel was set on the funnel injection platform of a Powder Tester (registered trademark) PT-E (manufactured by Hosokawa Micron Corporation), and 80 grams of each powder product according to the example was poured from the funnel and allowed to accumulate in a tray. The angle of repose was measured for the pile of powder product accumulated on the tray using a protractor. Next, a collapse angle measuring weight attached to the measuring device was dropped three times onto the pile for which the angle of repose was measured according to the specifications of the measuring device, and the angle of the collapsed pile was measured with the protractor to obtain the collapse angle. The difference angle was calculated by subtracting the collapse angle from the angle of repose. The results are shown in the table.

[0054] [Measurement of Compressibility] Evaluation was performed using a Powder Tester PT-E (manufactured by Hosokawa Micron Corporation). Each powder product was heapedly filled into a 100 mL metal container equipped with the device, the surface was leveled using a blade, and the mass of the metal container was measured. The mass after filling was subtracted from the mass of the container and divided by the volume of the container to obtain the initial bulk density (also called loose bulk density).

[0055] Next, a dedicated cap was attached to the metal container, and each powder product was filled heapingly. The measurement mode of the device was switched to tapping mode, and the container was tapped for 180 seconds. After that, the surface was scraped with a blade and the mass of the container was measured. The tapped bulk density (also called compacted bulk density) was calculated in the same manner as above.

[0056] The compressibility was calculated according to the following formula: [Compressibility] (%) = 100 × ([Tap bulk density] - [Initial bulk density]) / [Tap bulk density]. The results are shown in the table.

[0057] [Evaluation of Solubility Under Strong Stirring Conditions] 200 mL of water at 20°C and 2.0 g of each powder product were added to a 1 L flask and stirred for 20 minutes using a mechanical stirrer (300 rpm) with an anchor-type stirring blade. The mixture was then filtered through a 150 mesh nylon screen, dried, and the mass of the solid content of the residue was measured to determine the percentage of the original powder product that had dissolved. The results are shown in the table. A dissolution of 90% or more was evaluated as acceptable, and a dissolution of less than 90% was evaluated as unacceptable.

[0058] [Evaluation of Solubility Under Weak Stirring Conditions] 200 mL of water at 20°C and a stirrer were added to a 200 mL beaker, and the stirrer was rotated at 200 rpm. The stirrer rotation speed was measured in advance using a non-contact laser tachometer. 2.0 g of each powder product was added all at once from the top of the beaker, and the mixture was stirred for 20 minutes. The solution was then filtered using a 150-mesh nylon screen. The nylon screen was dried at 150°C for at least 1 hour, and the solid content of the residue was measured. The solubility was evaluated in the same manner as above. The results are shown in the table. A solution with 80% or more dissolution was evaluated as acceptable, and a solution with less than 80% dissolution was evaluated as unacceptable.

[0059]

[0060]

[0061] All of Examples 1 to 6 showed sufficient solubility even under weak stirring conditions.

[0062] On the other hand, Comparative Examples 1 to 9 were soluble under strong stirring conditions, but the solubility was poor under weak stirring conditions. Comparative Example 10 showed sufficient solubility, but was sticky and unsuitable for use as a product.

Claims

1. A powder product comprising: polymer particles obtained by saponifying a polymer of a vinyl ester monomer or a copolymer of a vinyl ester monomer and another monomer, the polymer particles having a particle size distribution in which the content of particles having a particle size of 180 μm or less is 50 mass % or more and the content of particles having a particle size of 500 μm or more is 10 mass % or less; a water-soluble additive in an amount of 0.1% by mass or more and 10% by mass or less based on the mass of the polymer particles; Including, the water-soluble additive has a viscosity at 20°C in the range of 30 to 200 mPa s, and a surface tension of a 0.05 mass% aqueous solution of the water-soluble additive at 20°C measured by the hanging drop method in the range of 50 to 72 mN / m; The powder product has an angle of repose of 60° or less as measured by the funnel injection method in accordance with JIS R9301-2-2:1999 A powder product characterized by:

2. 2. The powder product of claim 1, wherein the difference angle measured by the funnel injection method is 10° or more.

3. From the initial bulk density and tapped bulk density measured by a method conforming to JIS R1628:1997, the following formula is used: [Compressibility] (%) = 100 x ([Tapped bulk density] - [Initial bulk density]) / [Tapped bulk density] 3. The powder product according to claim 1 or 2, wherein the degree of compression calculated by is 45% or less.

4. 3. The powder product according to claim 1, wherein the polymer particles are made of a polymer of a vinyl ester monomer.

5. 3. The powder product according to claim 1, wherein the polymer particles are made of a copolymer of a vinyl ester monomer and another monomer.

6. 3. The powder product according to claim 1, wherein the other monomer is a polyfunctional monomer.

7. 7. The powder product according to claim 6, wherein the polyfunctional monomer is a compound having two or more polymerizable unsaturated bonds in the molecule.