Powder product

Abstract

Provided is a powder product comprising: polymer particles formed by saponifying a polymer of a vinyl ester monomer or a copolymer of a vinyl ester monomer and another monomer, the particle size distribution of the polymer particles being less than the particle size distribution of the polymer particles, and the particle size distribution of the polymer particles being less than the particle size distribution of the polymer particles; the content of particles having a particle diameter of 180 [mu] m or less is 50 mass% or more and the content of particles having a particle diameter of 500 [mu] m or more is 10 mass% or less; and a water-soluble additive, the mass of the water-soluble additive being in the range of 0.1-10 mass% (inclusive) based on the mass of the polymer particles, the viscosity of the water-soluble additive at 20 DEG C being in the range of 30-200 mPa.s, and the viscosity of the water-soluble additive at 20 DEG C being in the range of 30-200 mPa.s. The surface tension measured by a hanging drop method for a 0.05 mass% aqueous solution of the water-soluble additive at 20 DEG C is in the range of 50-72 mN / m, and the angle of repose measured by a funnel injection method in accordance with JIS R9301-2-2: 1999 of the powder product is 60 DEG or less.

Description

Technical Field

[0001] This invention relates to powder products. Background Technology

[0002] Polymers with a polyvinyl alcohol (PVA) backbone (hereinafter, in this specification, they are also collectively referred to as "polyvinyl alcohol polymers", "vinyl alcohol polymers", or simply "PVA") are known as hydrophilic synthetic resins, and various applications that effectively utilize their properties are being developed.

[0003] Depending on the intended use, it is sometimes conceivable to disperse PVA in water as a powder. The degree of saponification of PVA has been adjusted to improve its solubility, as described in, for example, the description of the Denka Poval product submitted by the applicant.

[0004] Prior art literature

[0005] Non-patent literature

[0006] Non-patent document 1: "Denka Poval", Denka Co., Ltd., published in 2016, https: / / www.denka.co.jp / pdf / product / detail / 00009 / poval_catalog.pdf Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Generally speaking, it is known that the larger the surface area of ​​a solute, the faster it dissolves in a solvent. Therefore, it is desirable for PVA particles to have a small particle size. However, if the PVA particles are small, the following problems arise: even if it is desired to dissolve them in water, so-called lumps (floating on the water as powdery lumps) or aggregates will form in the water.

[0009] The formation of clumps and agglomerates on the water surface significantly reduces the solubility of PVA particles in water. Existing technologies also present the following challenges: dissolving clumps and agglomerates requires vigorous stirring with high-power mixers, which can lead to unwanted foaming. Furthermore, it is difficult to achieve the performance required for a powder product that dissolves in water.

[0010] In addition, the prior art has the following problem: even with only gentle stirring, PVA particles are promoted to aggregate, which easily forms aggregates in water.

[0011] The aforementioned problems cannot be solved simply by adjusting the degree of saponification using existing technologies; new PVA products are desired.

[0012] Methods for solving problems

[0013] To address the aforementioned issues, the present invention can provide the following approach.

[0014] Method 1.

[0015] The powder product is characterized by comprising:

[0016] Polymer particles, wherein the polymer particles are formed by saponification of a polymer of vinyl ester monomers or a copolymer of vinyl ester monomers with other monomers, wherein the particle size distribution of the polymer particles comprises 50% by mass or more of particles with a particle size of 180 μm or less and 10% by mass or less of particles with a particle size of 500 μm or more; and

[0017] The water-soluble additive, wherein the mass of the water-soluble additive is in the range of 0.1% to 10% by mass based on the mass of the aforementioned polymer particles.

[0018] The viscosity of the aforementioned water-soluble additive at 20°C is in the range of 30–200 mPa·s, and the surface tension of a 0.05% (w / w) aqueous solution of the aforementioned water-soluble additive at 20°C, measured using the pendant drop method, is in the range of 50–72 mN / m.

[0019] The angle of repose of the aforementioned powdered product, as determined by the funnel injection method according to JIS R9301-2-2:1999, is 60° or less.

[0020] Method 2.

[0021] The powder product as described in Method 1, wherein the difference angle measured by the funnel injection method is 10° or more.

[0022] Method 3.

[0023] The powder product as described in method 1 or 2 has a compressibility of 45% or less, which is calculated by the following formula based on the initial bulk density and tapped bulk density determined according to the method in accordance with JIS R1628:1997.

[0024] [Compressibility] (%) = 100 × ([Tap Bulk Density] - [Initial Bulk Density]) / [Tap Bulk Density]

[0025] Method 4.

[0026] The powder product as described in any one of methods 1 to 3, wherein the aforementioned polymer particles are formed from a polymer of vinyl ester monomers.

[0027] Method 5.

[0028] The powder product as described in any one of methods 1 to 3, wherein the aforementioned polymer particles are formed by copolymerization of vinyl ester monomers and other monomers.

[0029] Method 6.

[0030] The powder product as described in any one of methods 1 to 3 and 5, wherein the aforementioned other monomers are multifunctional monomers.

[0031] Method 7.

[0032] The powder product as described in Method 6, wherein the aforementioned multifunctional monomer is a compound having two or more polymerizable unsaturated bonds within the molecule.

[0033] Effects of the Invention

[0034] According to the present invention, not only can the powder product exhibit high solubility in water even under gentle mixing conditions, but it can also achieve the effect of having the adaptability required for a powder product. Detailed Implementation

[0035] Unless otherwise specified, numerical ranges in this specification include both upper and lower limits. The term "polymer" in this specification follows the definition of a polymer as prescribed by the Polymer Nomenclature Committee of the International Union of Pure and Applied Chemistry (IUPAC), which defines a polymer molecule as "a molecule with a large relative molecular mass, having a structure composed of the repeated formation of units substantially or conceptually derived from molecules with small relative molecular masses."

[0036] The powder product according to embodiments of the present invention is characterized by comprising, in a predetermined mass ratio, polymer particles formed by saponifying a polymer of vinyl ester monomers or a copolymer of vinyl ester monomers and other monomers, and a water-soluble additive. This powder product is primarily intended for dissolution in water, but can also be used for dissolution in aqueous solvents other than pure water (tap water, aqueous solutions of hydrophilic solutes, etc.).

[0037] [Polymer particles]

[0038] The aforementioned polymer particles are PVA polymer particles, possessing a specific particle size distribution that satisfies the prerequisite for rapid dissolution in aqueous solvents. The particle size distribution of the polymer particles can be determined by sieving using sieves with a mesh size of 180 μm and 500 μm, as described in JIS Z8815:1994. For rapid dissolution in aqueous solvents, it is necessary that the polymer particles do not contain a large number of excessively large particles. Specifically, it is necessary that, as a particle proportion, the content of particles with a diameter of 500 μm or larger (on the 500 μm sieve) is 10% by mass or less, and the content of particles with a diameter of 180 μm or smaller (under the 180 μm sieve) is 50% by mass or more. If the particle size distribution does not meet this condition, it will adversely affect solubility.

[0039] In a preferred embodiment, the polymer particle size distribution is 5% or less by mass on a 500 μm sieve, more preferably 3% or less by mass, even more preferably 1% or less by mass, and even more preferably 0.1% or less by mass. Furthermore, in a preferred embodiment, the polymer particle size distribution is 60% or more by mass on a 180 μm sieve, more preferably 70% or more by mass, even more preferably 80% or more by mass, and even more preferably 85% or more by mass.

[0040] In a preferred embodiment, the degree of saponification of the PVA constituting the polymer particles can be 70–100 mol%, more preferably 75–95 mol%, even more preferably 80–95 mol%, and even more preferably 80–90 mol%. If the degree of saponification is within this range, the effect of easily improving solubility in aqueous solvents can be obtained. This degree of saponification can be determined using the method described in JIS K 6726:1994.

[0041] In a preferred embodiment, the viscosity of a 4% by mass aqueous solution of PVA constituting the polymer particles at 20°C is determined according to the rotational viscometer method described in JIS K6726:1994 and JIS K7117-1999, with a shear rate of 10 s. -1 The viscosity can be in the range of 1–1000 mPa·s, more preferably in the range of 1–500 mPa·s, and even more preferably in the range of 1–300 mPa·s. If the viscosity is within this range, the effect of improved solubility in aqueous solvents can be obtained.

[0042] Regarding the vinyl ester monomers used as raw materials for PVA, which constitute polymer particles, for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl decanoate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, etc., or mixtures thereof may be used. From the viewpoint of ease of polymerization, vinyl acetate is preferred.

[0043] The PVA can be obtained by saponifying a homopolymer of vinyl ester monomers, or by saponifying a copolymer of vinyl ester monomers with other monomers.

[0044] In addition, examples of monofunctional monomers (i.e., monofunctional monomers other than vinyl esters) that can copolymerize with vinyl ester monomers include: α-olefin monomers such as ethylene and propylene; alkyl methacrylate monomers such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate; unsaturated amide monomers such as methacrylamide and N-hydroxymethylacrylamide; unsaturated carboxylic acid monomers such as methacrylic 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; salts of unsaturated carboxylic acids such as sodium, potassium, and ammonium; monomers containing sulfonic acid groups such as 2-acrylamido-2-methylpropanesulfonic acid, or their salts; and alkyl vinyl ether monomers.

[0045] Other monomers that can copolymerize with vinyl ester monomers include polyfunctional and monofunctional monomers. As polyfunctional monomers, compounds having two or more polymerizable unsaturated bonds within the molecule are preferred. The number of polymerizable unsaturated sites in the polyfunctional monomer is preferably 2 to 5. Examples of polyfunctional monomers include the following: divinyl ethers such as ethanediol divinyl ether, propylene glycol 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; divinyl sulfonic acid compounds such as pentadiene, hexadiene, heptaadiene, octadiene, nonadiene, and decadiene. Diallyl ether compounds include glycerol diallyl ether, diethylene glycol diallyl ether, ethylene glycol diallyl ether, triethylene glycol diallyl ether, polyethylene glycol diallyl ether, trimethylolpropane diallyl ether, pentaerythritol diallyl ether, etc. Triallyl ether compounds include glycerol triallyl ether, trimethylolpropane triallyl ether, pentaerythritol triallyl ether, etc. Tetraallyl ether compounds include pentaerythritol tetraallyl ether, etc. Polyfunctional monomers containing allyl ester groups include diallyl phthalate, diallyl maleate, diallyl itaconic acid, diallyl terephthalate, diallyl adipate, etc. Diallylamine compounds include diallylamine and diallyl methylamine, etc., and polyfunctional monomers containing allyl amino groups include triallylamine, etc. Polyfunctional monomers containing allyl ammonium groups, such as diallyl dimethyl ammonium chloride and diallyl ammonium salts. 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, glycerol di(meth)acrylate, glycerol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, bis(trimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and isocyanurate tri(meth)acrylate. N,N'-methylenebis(meth)acrylamide, N,N'-ethylidenebis(meth)acrylamide, and other polyfunctional monomers containing (meth)acrylamide. Divinylbenzene, trivinylbenzene, and other polyfunctional aromatic monomers. Allyl glycidyl ether, glycidyl (meth)acrylate, and other polyfunctional monomers containing glycidyl groups.

[0046] Other monomers that can copolymerize with vinyl ester monomers are preferably multifunctional monomers, more preferably compounds having two or more polymerizable unsaturated bonds in the molecule, and even more preferably compounds having three or more polymerizable unsaturated bonds in the molecule.

[0047] [Water-soluble additives]

[0048] The water-soluble additives (hereinafter also referred to as "additives") contained in this powder product are liquid at room temperature (e.g., 20°C) as defined by JIS Z8703:1983. The viscosity at 20°C is measured using a cone-plate rotational viscometer (rheometer) according to JIS Z8803:2011 with a shear rate of 10 s. -1 The viscosity must be in the range of 30 to 200 mPa·s. If the viscosity is outside this range, the mixing with the polymer particles becomes insufficient, and the solubility deteriorates. From the viewpoint of improving solubility, in a preferred embodiment, the viscosity of the additive under the above conditions can be in the range of 30 to 150 mPa·s, and more preferably in the range of 30 to 100 mPa·s.

[0049] Furthermore, for this additive, the surface tension of its 0.05% by mass aqueous solution, measured using the pendant drop method at 20°C, must be in the range of 50–72 mN / m. It should be noted that in this specification, the pendant drop method refers to the ds / de method. If the surface tension is outside the above range, the solubility of the powder product will deteriorate.

[0050] The mass of additives in powder products is in the range of 0.1% to 10% by mass, based on the mass of polymer particles. If the mass of the additive is less than 0.1% by mass, the solubility deteriorates under gentle stirring conditions. Furthermore, if the mass of the additive is greater than 10% by mass, the powder product becomes sticky, hindering operation during use and transportation, and adversely affecting the performance of the powder product.

[0051] As an additive, there are no particular limitations as long as it is water-soluble and its viscosity and surface tension meet the above-mentioned conditions. Examples of additives include polyethers, polyols, polyoxyethylenes, alcohol alkoxylates, phenol alkoxylates, organosilicon compounds, and mineral oils. Among these, additives that can be used 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.

[0052] [Powder Products]

[0053] The powder product containing the aforementioned polymer particles and additives has properties suitable for dissolution in pure water and other aqueous solvents. This powder product is characterized by an angle of repose of 60° or less, measured using the funnel injection method as described in JIS R9301-2-2:1999 (in this specification, the measurement is performed using a protractor). If the angle of repose is outside this range, the powder agglomerates excessively, hindering operation during use and conveying, and adversely affecting the performance of the powder product. In a preferred embodiment, the angle of repose can be 20° or more and 60° or less, more preferably 30° or more and 60° or less.

[0054] In a preferred embodiment, the difference angle of this powder product can be 10° or more, and more preferably 10° or more and 40° or less. It should be noted that, in this specification, the difference angle is equivalent to the following value: for a sample whose angle of repose has been determined using the funnel injection method described above, the hammer is dropped and the angle of collapse is measured, and the value obtained by subtracting the angle of collapse from the angle of repose. If the difference angle is within the above range, an improvement in solubility in aqueous solvents can be achieved.

[0055] In a preferred embodiment, the compressibility of the powder product can be 45% or less, more preferably 10% to 45% or less, and even more preferably 10% to 40% or less. It should be noted that, in this specification, compressibility is a percentage calculated using the following formula.

[0056] [Compressibility] (%) = 100 × ([Tap Bulk Density] - [Initial Bulk Density]) / [Tap Bulk Density]

[0057] Here, the initial bulk density and tapped bulk density refer to the values ​​measured according to JIS R1628:1997. If the compressibility is within the above range, the effect of improved solubility in aqueous solvents can be obtained.

[0058] Example

[0059] The present invention will now be described in more detail based on embodiments. It should be noted that the embodiments described below illustrate examples of representative embodiments of the present invention, and the present invention is not limited to these embodiments.

[0060] [Example 1]

[0061] The polymer particles were synthesized through the following steps. 100 parts by mass of vinyl acetate, 117 parts by mass of methanol, and 0.016 parts by mass of Peroyl (registered trademark) NPP (manufactured by Nippon Yushu Co., Ltd.) as an initiator were added to a polymerization tank equipped with a reflux condenser, a dropping funnel, and a stirrer. Polymerization was carried out at boiling point for 5 hours under a nitrogen atmosphere (polymerization rate 88%). Next, unreacted vinyl acetate monomers were removed from the polymerization system to obtain a methanol solution of polyvinyl acetate polymer. A methanol solution of sodium hydroxide (equivalent to 0.007 mol of sodium hydroxide relative to the structural units from vinyl acetate) was added to this solution, and a saponification reaction was carried out at 45°C for 90 minutes to obtain PVA with a saponification degree of 88.1 mol%.

[0062] The obtained PVA was pulverized using an ACM pulverizer. The PVA particles obtained after grading were sieved using sieves with a mesh size of 180 μm and 500 μm, according to JIS Z8815:1994, and the particle size distribution was determined. The particles above the 500 μm sieve accounted for 0.1% by mass, and the particles below the 180 μm sieve accounted for 99.1% by mass. Following the rotational viscometer method described in JIS K6726:1994 and JIS K7117-1:1999, a Brookfield type (Type B) rotational viscometer was used at 20°C with a rotational speed of 30 rpm and a shear rate of 10 s. -1 The viscosity of a 4% by mass aqueous solution of this PVA was determined under the specified conditions, and the result was 5.4 mPa·s.

[0063] As an additive, polyethylene glycol (PEG-300) with a number average molecular weight of 300 was prepared, and the shear rate was set to 10 s according to JIS Z8803:2011. -1 The viscosity was measured using a rheometer, and the result was 70 mPa·s. Additionally, a 0.05% (w / w) aqueous solution of the additive was prepared, and the surface tension was measured using a DMs-301 (manufactured by Kyowa Interface Science Co., Ltd.) at 20°C using the pendant drop method, and the result was 68.8 mN / m. As a control, the surface tension of the water used in this process was measured, and the result was 70.2 mN / m.

[0064] The additives were mixed in a manner that was 3% by mass relative to the mass of the PVA described above, to obtain the powder product described in Example 1. It should be noted that, as shown in the table, the physical properties were also measured in the same manner as in Example 1 in the following examples.

[0065] [Example 2]

[0066] The following steps were used to manufacture the polymer particles, except that the powder product of Example 2 was obtained by the same steps as in Example 1. 100 parts by weight of vinyl acetate, 15 parts by weight of methanol, and 5.0 × 10⁻⁶ Peroyl NPP (manufactured by Nippon Yushi Co., Ltd.) as an initiator were added to a polymerization tank equipped with a reflux condenser, a dropping funnel, and a stirrer. -3 Polymerization was carried out at boiling point for 5 hours with stirring under 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 (equivalent to 0.007 mol of sodium hydroxide relative to the structural units from vinyl acetate) was added to this solution, and a 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.

[0067] [Example 3]

[0068] The following steps were used to manufacture the polymer particles, except that the powder product of Example 3 was obtained by the same steps as in Example 1. 100 parts by weight of vinyl acetate, 5 parts by weight of methanol, and 1.0 × 10⁻⁶ Peroyl NPP (manufactured by Nippon Yushi Co., Ltd.) as an initiator were added to a polymerization tank equipped with a reflux condenser, a dropping funnel, and a stirrer. -3 Polymerization was carried out at boiling point for 5 hours with stirring under 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 (equivalent to 0.007 mol of sodium hydroxide relative to the structural units from vinyl acetate) was added to this solution, and a 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.

[0069] [Examples 4-6]

[0070] Polymer particles were prepared according to the manufacturing method of Example 1 in International Publication No. 2019 / 163490. Specifically, 100 parts by mass of vinyl acetate, 0.16 parts by mass of triallyl isocyanurate (TAIC), 66.7 parts by mass of methanol, and 0.07 parts by mass of Peroyl NPP (manufactured by Nippon Yushu Co., Ltd.) as an initiator were added to a polymerization tank equipped with a reflux condenser, a dropping funnel, and a stirrer. Polymerization was carried out at boiling point for 5 hours (polymerization rate 50%) while stirring under a nitrogen atmosphere. Then, unreacted vinyl acetate monomers were removed from the polymerization system to obtain a methanol solution of polyvinyl acetate-TAIC copolymer. A methanol solution of sodium hydroxide (equivalent to 0.007 mol of sodium hydroxide relative to the structural units from vinyl acetate) was added to this solution, and a saponification reaction was carried out at 45°C for 90 minutes to obtain PVA with a saponification degree of 89.5 mol%.

[0071] The same pulverization and classification process as in Example 1 was performed to obtain PVA particles. The additives and PVA particles were then mixed separately at the ratios shown in the table to obtain the powder products described in Examples 4 to 6.

[0072] [Comparative Example 1]

[0073] No additives were added, except that the powder product involved in Comparative Example 1 was obtained by the same steps as in Example 1.

[0074] [Comparative Example 2]

[0075] No additives were added, except that the powder product involved in Comparative Example 2 was obtained by the same steps as in Example 4.

[0076] [Comparative Example 3]

[0077] As an additive, ADEKANOL UH-420 (manufactured by ADEKA Corporation, a special nonionic polymeric surfactant) was used. Otherwise, the powder product involved in Comparative Example 3 was obtained by the same steps as in Example 1.

[0078] [Comparative Example 4]

[0079] Glycerol was used as an additive, and otherwise the powder product involved in Comparative Example 4 was obtained by the same steps as in Example 4.

[0080] [Comparative Examples 5-6]

[0081] As an additive, SN Deformer 485 (manufactured by SAN NOPCO, a mixture of polyoxyethylene-type nonionic surfactants, etc.) was used. Otherwise, the powder products involved in Comparative Examples 5 and 6 were obtained by the same steps as in Example 4.

[0082] [Comparative Examples 7-8]

[0083] As an additive, SN Deformer PC (manufactured by SAN NOPCO, a polyoxyethylene type nonionic surfactant) was used. Otherwise, the powder products involved in Comparative Examples 7 and 8 were obtained by the same steps as in Example 4.

[0084] [Comparative Example 9]

[0085] As an additive, Noptam 740A (manufactured by SAN NOPCO, a mixture of polyoxyethylene-type nonionic surfactant, silica, water, etc.) was used. Otherwise, the powder product involved in Comparative Example 9 was obtained by the same steps as in Example 4.

[0086] [Comparative Example 10]

[0087] The amount of additives is made excessive, and otherwise, the powder product involved in Comparative Example 10 is obtained by the same steps as in Example 4.

[0088] [Determination of the angle of repose and the angle of difference]

[0089] A funnel was set up on the funnel-pouring method platform of the Powder Tester (registered trademark) PT-E (manufactured by HOSOKAWA MICRON). 80 grams of each of the powder products involved in each example were poured into the funnel, allowing them to accumulate on a tray. The angle of repose of the accumulated powder product on the tray was measured using a protractor. Next, for the pile of powder product with the measured angle of repose, the hammer for measuring the angle of collapse of the testing device was dropped three times according to the instruction manual. The angle of collapse of the collapsed pile was measured using a protractor. The difference angle was calculated by subtracting the angle of collapse from the angle of repose. The results are shown in the table.

[0090] [Determination of compressibility]

[0091] Evaluation was performed using a Powder Tester PT-E (manufactured by HOSOKAWA MICRON). Each example of the powder product was filled completely into a 100mL metal container provided with this apparatus, the surface was leveled using a scraper, and the mass of the metal container was measured. The initial bulk density (also known as loose bulk density) was obtained by subtracting the container's mass from the filled mass and dividing the result by the container's volume.

[0092] Next, a special lid was placed on the aforementioned metal container, and the powder products of each example were filled in. The measurement mode of the device was switched to tapping mode, and the container was tapped for 180 seconds. After tapping, the surface was smoothed with a scraper, and the mass of the container was measured. The tapped bulk density (also known as compacted bulk density) was calculated in the same manner as above.

[0093] Calculate the compressibility using the following formula. The results are shown in the table.

[0094] [Compressibility] (%) = 100 × ([Tap Bulk Density] - [Initial Bulk Density]) / [Tap Bulk Density]

[0095] [Solubility Evaluation under Strong Stirring Conditions]

[0096] Add 200 mL of water at 20°C and 2.0 g of the powder product to a 1 L flask. Stir for 20 minutes using a mechanical stirrer with anchor-shaped blades (300 rpm). Then, filter through a 150-mesh nylon sieve, dry, and determine the mass of the solid component of the residue to ascertain the percentage of the original powder product that had dissolved. The results are shown in the table. A solution of more than 90% dissolved is considered acceptable, while a solution of less than 90% is considered unacceptable.

[0097] [Solubility evaluation under weak stirring conditions]

[0098] Add 200 mL of water (20°C) and a stir bar to a 200 mL beaker, and rotate the stir bar at 200 rpm. The stir bar speed was previously measured using a non-contact laser tachometer. Add 2.0 g of each example powdered product from the top of the beaker at a time, and stir for 20 minutes. Then, filter the solution through a 150-mesh nylon sieve. Dry the nylon sieve at 150°C for at least 1 hour, and determine the amount of solid content in the residue. Solubility was evaluated in the same manner as above. The results are shown in the table. A solution with more than 80% dissolved was considered acceptable, while a solution with less than 80% dissolved was considered unacceptable.

[0099] [Table 1]

[0100]

[0101] [Table 2]

[0102]

[0103] Examples 1 through 6 all showed adequate solubility even under weak stirring conditions.

[0104] On the other hand, although Comparative Examples 1-9 dissolved under strong stirring conditions, their solubility deteriorated under weak stirring conditions. Comparative Example 10 showed sufficient solubility, but it was viscous and therefore unqualified as a product.

Claims

1. A powder product, characterized in that, Include: Polymer particles, wherein the polymer particles are formed by saponification of a polymer of vinyl ester monomers or a copolymer of vinyl ester monomers with other monomers, wherein the particle size distribution of the polymer particles comprises 50% by mass or more of particles with a particle size of 180 μm or less and 10% by mass or less of particles with a particle size of 500 μm or more; and The water-soluble additive, wherein the mass of the water-soluble additive is in the range of 0.1% to 10% by mass based on the mass of the polymer particles. The viscosity of the water-soluble additive at 20°C is in the range of 30–200 mPa·s, and the surface tension of a 0.05% (w / w) aqueous solution of the water-soluble additive at 20°C, measured using the pendant drop method, is in the range of 50–72 mN / m. The angle of repose of the powdered product, as determined by the funnel injection method according to JIS R9301-2-2:1999, is less than 60°.

2. The powder article as described in claim 1, wherein, The difference angle measured using the funnel injection method is greater than 10°.

3. The powder article as described in claim 1 or 2, wherein the compressibility is 45% or less, said compressibility being calculated by the following formula based on the initial bulk density and tapped bulk density determined according to the method in accordance with JIS R1628:1997. [Compression] (%) = 100 × ([Tap Bulk Density] - [Initial Bulk Density]) / [Tap Bulk Density].

4. The powder article according to any one of claims 1 to 3, wherein, The polymer particles are formed from polymers of vinyl ester monomers.

5. The powder article according to any one of claims 1 to 3, wherein, The polymer particles are formed by copolymerization of vinyl ester monomers with other monomers.

6. The powder article according to any one of claims 1 to 3 and 5, wherein, The other monomers are multifunctional monomers.

7. The powder article as described in claim 6, wherein, The multifunctional monomer is a compound having two or more polymerizable unsaturated bonds within its molecule.

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