Polyvinyl acetal resin particles

Abstract

To provide polyvinyl acetal resin particles that can be easily dissolved in organic solvent even with a large amount of addition of resin, and prevent the particles from floating at the time of addition, and ensure excellent uniformity of the resin components.SOLUTION: A polyvinyl acetal resin particle contains a polyvinyl acetal resin and has a voidage of 30% or more and a proportion of voids with a pore radius of 7.5-0.075 μm of 90% or more. The content of particles passing through a JIS standard sieve with an opening of 250 μm is 10 wt.% or less, the content of particles not passing through a JIS standard sieve with an opening of 2830 μm is 10 wt.% or less, and the content of particles passing through a JIS standard sieve with an opening of 2830 μm but not passing through a JIS standard sieve with an opening of 1700 μm is 45 wt.% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to polyvinyl acetal resin particles that can be easily dissolved in an organic solvent. [Background technology]

[0002] Polyvinyl acetal resins such as polyvinyl butyral resins are used in a variety of applications due to their excellent toughness, film-forming properties, dispersibility of particles, and adhesion to coated surfaces. As one of the uses of polyvinyl acetal resins, for example, slurry compositions and conductive pastes using polyvinyl acetal resins such as polyvinyl butyral resins as binder resins have been disclosed.

[0003] The polyvinyl acetal resins used for these applications are generally used as a solution dissolved in an organic solvent such as methyl ethyl ketone, toluene, alcohol, or a mixture thereof. In this case, if the dissolution in the solvent is quick, the workability is improved. It is thought that increasing the surface area of ​​the polyvinyl acetal resin particles will improve the solubility because the contact area with the solvent increases, but in reality, the particles sit on the surface of the solvent, and the dissolution rate in the solvent is slow. Furthermore, if the polyvinyl acetal resin has poor solubility in organic solvents, a small amount of undissolved matter is generated when the resin is dissolved in an organic solvent, and the dispersibility of the particles is reduced.

[0004] Patent Document 1 discloses polyvinyl acetal resin particles in which the smallest constituent particles (primary particles) have an average particle size of 5 μm or less. Patent Document 2 discloses polyvinyl acetal resin particles made of a polyvinyl acetal resin having a degree of polymerization of 500 or more, having a content of particles passing through a 60 mesh sieve of 20% by weight or less, a bulk specific gravity of 0.20 or less, and an average particle diameter of 100 to 500 μm. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-38456 A [Patent Document 2] JP 2011-225842 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, even the polyvinyl acetal resin particles disclosed in Patent Documents 1 and 2 have insufficient solubility in organic solvents, particularly when a large amount of resin is added. In addition, by only reducing the average particle size, the particles tend to float when added, and the uniformity of the resin component may decrease.

[0007] An object of the present invention is to provide polyvinyl acetal resin particles which can be easily dissolved in an organic solvent even when added in a large amount, are less likely to cause floating of particles during addition, and have excellent uniformity of the resin component. [Means for solving the problem]

[0008] The present invention relates to polyvinyl acetal resin particles which contain a polyvinyl acetal resin, have a porosity of 30% or more, a void ratio of pores with a pore radius of 7.5 to 0.075 μm of 90% or more, a content of particles passing through a JIS standard sieve with a mesh size of 250 μm of 10% by weight or less, a content of particles not passing through a JIS standard sieve with a mesh size of 2830 μm of 10% by weight or less, and a content of particles passing through a JIS standard sieve with a mesh size of 2830 μm but not passing through a JIS standard sieve with a mesh size of 1700 μm of 45% by weight or more. The present invention will be described in detail below.

[0009] The present inventors have found that, as in the polyvinyl acetal resin particles disclosed in Patent Documents 1 and 2, simply specifying the particle size or bulk specific gravity results in insufficient solubility in organic solvents. The inventors have found that polyvinyl acetal resin particles having a low porosity, a high proportion of pores with a large pore radius, and a specified ratio of particles that pass or do not pass through a specified JIS standard sieve can be easily dissolved in an organic solvent even when added in a large amount. They have also found that the particles are less likely to be impregnated with the solvent during dissolution, and have excellent uniformity of the resin component, which has led to the completion of the present invention.

[0010] The polyvinyl acetal resin particles of the present invention have a porosity of 30% or more. The lower limit of the porosity is 30%, so that the solubility in organic solvents can be increased. The lower limit of the porosity is preferably 32%, and more preferably 35%. The upper limit of the porosity is not particularly limited, but is preferably 40%. In this specification, the porosity refers to the volume of pores with a pore radius of 7.5 to 0.0038 μm in the volume of the resin particles. The porosity can be measured, for example, by mercury intrusion porosimetry using a porosimeter (Thermo Pascal 14B, manufactured by Thermo Fisher Scientific).

[0011] The polyvinyl acetal resin particles of the present invention have a void ratio of 90% or more for a pore radius of 7.5 to 0.075 μm. When the lower limit of the void ratio for the pore radius of 7.5 to 0.075 μm is 90%, the organic solvent is easily impregnated, and the solubility in the organic solvent is improved. The lower limit of the void ratio for the pore radius of 7.5 to 0.075 μm is preferably 92%, and more preferably 95%. The upper limit of the void ratio for the pore radius of 7.5 to 0.075 μm is not particularly limited, but is preferably 100%. In this specification, the void ratio of pores having a pore radius of 7.5 to 0.075 μm indicates the ratio of the pore volume of pores having a pore radius of 7.5 to 0.075 μm to the pore volume of pores having a pore radius of 7.5 to 0.0038 μm. The void ratio of the pores having a pore radius of 7.5 to 0.075 μm can be measured by mercury intrusion porosimetry using, for example, a porosimeter (Thermo Pascal 14B, manufactured by Thermo Fisher Scientific).

[0012] The polyvinyl acetal resin particles of the present invention have a content of particles passing through a JIS standard sieve with a mesh size of 250 μm of 10% by weight or less. By having the content of particles passing through a JIS standard sieve with a mesh size of 250 μm of 10% by weight or less, floating of particles during addition can be suppressed, and the occurrence of lumps during dissolution can be prevented. The preferred upper limit of the content of particles passing through a JIS standard sieve with a mesh size of 250 μm is 5.0% by weight, and the more preferred upper limit is 3.0% by weight. In addition, the lower limit of the content of particles passing through a JIS standard sieve with a mesh size of 250 μm is not particularly limited, but is preferably 0% by weight. In this specification, the sieve is in accordance with JIS Z8801. In addition, the passage of the JIS standard sieves was judged by visual inspection. The content ratio of particles passing through the JIS standard sieve with a mesh size of 250 μm was calculated by [(weight of particles passing through all JIS standard sieves) / (weight of all particles)]×100 when particles were sieved through JIS standard sieves with mesh sizes of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm, and 250 μm, placed in that order.

[0013] The polyvinyl acetal resin particles of the present invention have a content ratio of particles that do not pass through a JIS standard sieve with an opening of 2830 μm of 10% by weight or less. By having the content ratio of the above particles be 10% by weight or less, particles with a large aspect ratio can be removed. The upper limit of the content ratio of particles that do not pass through a JIS standard sieve with an opening of 2830 μm is preferably 8.0% by weight, more preferably 7.0% by weight. The lower limit is not particularly limited, but is preferably 0% by weight. In this specification, the sieve is in accordance with JIS Z8801. The content ratio of particles that do not pass through the JIS standard sieve with a mesh size of 2830 μm is calculated from the following formula when particles are sieved through JIS standard sieves with mesh sizes of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm and 250 μm, arranged in this order. "(Total weight of particles that do not pass through JIS standard sieves with mesh sizes of 4000 μm, 3350 μm, and 2830 μm) / (Weight of all particles)] x 100"

[0014] The polyvinyl acetal resin particles of the present invention have a content of particles that pass through a JIS standard sieve having an opening of 2830 μm but do not pass through a JIS standard sieve having an opening of 1700 μm of 45% by weight or more. By making the content of the particles 45% by weight or more, it is possible to obtain particles with a uniform aspect ratio. The upper limit of the content of the particles is preferably 100% by weight. The lower limit of the content of the particles is preferably 48% by weight, and more preferably 50% by weight. In this specification, the sieve is in accordance with JIS Z8801. In addition, the content ratio of particles that pass through the JIS standard sieve with a mesh size of 2830 μm and do not pass through the JIS standard sieve with a mesh size of 1700 μm is calculated from the following formula when particles are sieved through JIS standard sieves with mesh sizes of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm and 250 μm, arranged in this order. [(Weight of particles that do not pass through a JIS standard sieve with a mesh size of 1700 μm) / (Weight of all particles)]×100

[0015] The polyvinyl acetal resin particles of the present invention have a content of particles passing through a rattra tester (JIS standard sieve with a mesh size of 1180 μm) of 3.0% by weight or less. By making the content of the above particles 3.0% by weight or less, it is possible to obtain particles that are less likely to break and have a uniform aspect ratio. The lower limit of the content of the above particles is preferably 1.0% by weight, and the more preferred upper limit is 2.0% by weight. In this specification, the above sieve is in accordance with JIS Z8801. When passing through the above-mentioned Rattler tester (JIS standard sieve with mesh size of 1180 μm), the conditions are, for example, 87 rpm and 1000 revolutions.

[0016] The polyvinyl acetal resin particles of the present invention preferably contain a polyvinyl acetal resin having a degree of polymerization of 200 or more and 10,000 or less. Within the above range, even if the amount of resin added is large, the resin can be easily dissolved in an organic solvent, and a solution with excellent uniformity of the resin component can be obtained. Therefore, the tact time in the dissolving process of the polyvinyl acetal resin can be shortened, and the variation in mechanical strength of the various sheets obtained can be stabilized. The more preferred lower limit of the polymerization degree of the polyvinyl acetal resin is 300, the more preferred upper limit is 8500, the even more preferred upper limit is 5500, and the particularly preferred upper limit is 5000.

[0017] The amount of acetal groups in the polyvinyl acetal resin is preferably 40 mol% at the lower limit and 80 mol% at the upper limit, regardless of whether an aldehyde is used alone or in combination of two or more kinds. When the amount of acetal groups is 40 mol% to 80 mol%, the polyvinyl acetal resin does not aggregate and dissolves in a wide variety of solvents, and can impart dispersibility of inks and dyes and sufficient flexibility to the various sheets obtained. A more preferred lower limit of the amount of acetal groups is 60 mol %, and a more preferred upper limit is 78 mol %. Regarding the method for calculating the amount of acetal groups, since the acetal groups of polyvinyl acetal resin are obtained by acetalizing two hydroxyl groups of polyvinyl alcohol, the method of counting the two acetalized hydroxyl groups is used. In this specification, when the acetal group is an acetoacetal group, it is also referred to as the amount of acetoacetal groups, and when the acetal group is a butyral group, it is also referred to as the amount of butyral groups.

[0018] The preferred lower limit of the amount of hydroxyl groups in the polyvinyl acetal resin is 20 mol%, and the preferred upper limit is 50 mol%. When the amount of hydroxyl groups is 20 mol% to 50 mol%, the resin can be easily dissolved in an organic solvent even when the amount added is large, and a solution having excellent uniformity of the resin component can be obtained. Therefore, the tact time in the dissolving process of the polyvinyl acetal resin can be shortened, and the variation in mechanical strength of the obtained various sheets can be stabilized. A more preferred lower limit of the amount of hydroxyl groups is 22 mol %, and a more preferred upper limit is 45 mol %.

[0019] The polyvinyl acetal resin has an acetyl group content of preferably 0.1 mol% (lower limit) and 20 mol% (upper limit). When the acetyl group content is 0.1 mol% or more, the compatibility with organic solvents can be improved. When the acetyl group content is 20 mol% or less, the resin is less likely to form lumps during dissolution. A more preferred lower limit of the amount of acetyl groups is 0.5 mol %, and a more preferred upper limit is 15 mol %.

[0020] The content of the polyvinyl acetal resin in the polyvinyl acetal resin particles of the present invention is preferably such that the lower limit is 10% by weight and the upper limit is 90% by weight. When the content of the polyvinyl acetal resin is within the above range, even when a large amount is added, the polyvinyl acetal resin can be easily dissolved in an organic solvent, and a polyvinyl acetal resin composition having excellent uniformity of the resin components can be obtained. The content of the polyvinyl acetal resin is more preferably 20% by weight in the lower limit and 80% by weight in the upper limit.

[0021] The polyvinyl acetal resin particles of the present invention can be used for applications such as inks, paints, baking enamels, wash primers, lacquers, dispersants, adhesives, laminated ceramic capacitors, and thermally developable photosensitive materials.

[0022] The polyvinyl acetal resin particles of the present invention are obtained by carrying out a step of acetalizing polyvinyl alcohol (acetalization step) and a granulation step. The method for acetalizing the polyvinyl alcohol includes, for example, a method in which various aldehydes are added to the polyvinyl alcohol solution in the presence of an acid catalyst. In particular, the polyvinyl acetal resin particles of the present invention having a predetermined degree of polymerization, porosity, pore radius of 7.5 to 0.075 μm, and specific surface area can be prepared by adjusting the degree of polymerization of polyvinyl alcohol used in the acetal process, the polyvinyl alcohol content (concentration) of the polyvinyl alcohol solution, and the granulation process.

[0023] The polyvinyl alcohol content of the polyvinyl alcohol solution in the acetal step is preferably 1.0 to 7.0% by mass. By adjusting the content within the above range, the polyvinyl acetal resin particles of the present invention having a predetermined degree of polymerization, porosity, pore ratio with a pore radius of 7.5 to 0.075 μm, content of particles passing through a JIS standard sieve with an opening of 250 μm, and proportion of particles passing / not passing through a predetermined JIS standard sieve can be suitably produced. The content of the polyvinyl alcohol resin is more preferably 2.0% by mass at the lower limit and 6.0% by mass at the upper limit. The content of the polyvinyl alcohol resin can be determined in consideration of the degree of polymerization of the polyvinyl alcohol resin used.

[0024] The preferred lower limit of the saponification degree of the polyvinyl alcohol is 80 mol%. If the saponification degree of the polyvinyl alcohol is less than 80 mol%, the water solubility is deteriorated, making acetalization difficult, and the amount of hydroxyl groups is reduced, making acetalization itself difficult. A more preferred lower limit is 85 mol%. The preferred upper limit is not particularly limited, but is 99.9 mol%.

[0025] As for the polyvinyl alcohol, so long as the saponification degree of the polyvinyl alcohol at the time of acetalization is 80 mol % or more, the polyvinyl alcohol may be used alone, or a polyvinyl alcohol having a saponification degree of 80 mol % or more may be mixed with a polyvinyl alcohol having a saponification degree of less than 80 mol % to adjust the saponification degree to 80 mol % or more before use.

[0026] The acid catalyst is not particularly limited, and either an organic acid or an inorganic acid can be used, and examples thereof include acetic acid, paratoluenesulfonic acid, nitric acid, sulfuric acid, hydrochloric acid, etc. Among them, a non-halogen acid catalyst is preferable.

[0027] The aldehyde used in the acetalization is not particularly limited, and examples thereof include formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, butyraldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2-ethylhexylaldehyde, cyclohexylaldehyde, furfural, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde. Among these, it is preferable to use acetaldehyde and / or butyraldehyde for the acetalization. These aldehydes may be used alone or in combination of two or more.

[0028] In order to terminate the acetalization reaction, it is preferable to neutralize the reaction mixture with an alkali, which is not particularly limited and may, for example, be sodium hydroxide, potassium hydroxide, ammonia, sodium acetate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, or potassium hydrogen carbonate. In addition, it is preferable to wash the obtained modified polyvinyl acetal resin with water or the like before or after the neutralization step. In order to prevent contamination with impurities contained in the washing water, it is more preferable to wash with pure water.

[0029] The granulation step in the above-mentioned manufacturing method is not particularly limited, and examples thereof include a method of compressing and crushing particulate raw resin, a method of heating the raw resin to a temperature range in which the resin softens but does not fuse, a method of mixing a raw resin having a low softening temperature, and a method of using a raw resin containing a small amount of an organic solvent, water, etc. Specifically, a rolling type (drum type, inclined plate type, etc.), a vibration type (horizontal type, inclined type, etc.), a compression molding type (tablet press, briquette machine, roll machine, etc.), a crushing type (crusher), a mixing type (blender type, pin type, etc.), a fluid type (fluidized bed type, spouted bed type, etc.), an extrusion molding type (screw type, hot cut pellet type, etc.), or a combination of two or more types can be used. Among these, a method of using a two-roll compression molding machine and a crusher in combination of two or more types is preferred.

[0030] The above-mentioned crusher is not particularly limited, but a flake breaker, a hammer mill, a feather mill, a cutter mill, a roll mill, a rotating disk mill, or the like is preferable, and in order to prevent the resin from fusing due to heat generated during crushing, it is preferable that the crushing part of the crusher has a cooling function such as a water-cooled jacket. The crushing conditions (rotation speed, screen, etc.) are not particularly limited, and can be selected so that the resulting granulated resin has a desired particle shape. Effect of the Invention

[0031] According to the present invention, it is possible to provide polyvinyl acetal resin particles which can be easily dissolved in an organic solvent even when a large amount is added, which are less likely to suffer from poor solvent impregnation of the particles during dissolution, and which have excellent uniformity of the resin component. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0033] Example 1 200g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 300 and a degree of saponification of 98.7 mol% was added to 3050g of pure water, and stirred at a temperature of 90°C for about 2 hours to dissolve, to obtain a polyvinyl alcohol solution (polyvinyl alcohol concentration 5.9% by mass). This solution was cooled to 40°C, and 240g of hydrochloric acid with a concentration of 35% by weight, which corresponds to a concentration of 7.9% by weight relative to the amount of pure water added, and 116g of n-butyl aldehyde were added to it, and the liquid temperature was lowered to 5°C and maintained at this temperature to carry out an acetalization reaction, and the reaction product was precipitated. Thereafter, the liquid temperature was set to 25°C and maintained for 3 hours to complete the reaction, and the reaction was neutralized, washed with water, and dried by a conventional method to obtain a white powder of polyvinyl acetal resin. The obtained polyvinyl acetal resin was dissolved in DMSO-d 6 (dimethyl sulfoxide), 13 The amount of hydroxyl groups, the amount of acetyl groups, and the degree of butyralization, measured using C-NMR (nuclear magnetic resonance spectroscopy), were 35.7 mol %, 1.3 mol %, and 63.0 mol %, respectively. The obtained raw material powder of polyvinyl acetal resin was rolled at a unit area pressure of 5 kg / cm by two rolls. 2 The mixture was compression molded with a pressure of 1000 psi and pulverized with a crusher to obtain polyvinyl acetal resin particles.

[0034] Comparative Example 1 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 300 and a degree of saponification of 98.7 mol% was added to 1,300 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 12.9 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0035] Example 2 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 700 and a degree of saponification of 98.5 mol% was added to 3,200 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 5.7% by mass). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0036] Comparative Example 2 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 700 and a degree of saponification of 98.5 mol% was added to 1000 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 16.1 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0037] Example 3 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 1700 and a degree of saponification of 98.8 mol% was added to 3300 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 5.5% by mass). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0038] Comparative Example 3 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 1700 and a degree of saponification of 98.8 mol% was added to 1400 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 12.1 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0039] Example 4 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 3,300 and a degree of saponification of 99.2 mol% was added to 4,300 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 4.3 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0040] Example 5 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 3,300 and a degree of saponification of 99.2 mol% was added to 5,700 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 3.3 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0041] Comparative Example 4 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 3,300 and a degree of saponification of 99.2 mol% was added to 2,300 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 7.7% by mass). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0042] Example 6 200 g of polyvinyl alcohol (purity 96.5%) with a polymerization degree of 500 and a saponification degree of 98.8 mol% was added to 2600 g of pure water, and dissolved by stirring at a temperature of 90°C for about 2 hours to obtain a polyvinyl alcohol solution (polyvinyl alcohol concentration 6.9 mass%). Except for using this solution, the amount of n-butyl aldehyde in Example 1 was changed to 144 g. Polyvinyl acetal resin particles were obtained in the same manner as in Example 1.

[0043] Comparative Example 5 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 500 and a degree of saponification of 98.8 mol% was added to 1,050 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 15.4 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 6, except that this solution was used.

[0044] Example 7 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 4000 and a degree of saponification of 99.1 mol% was added to 6000 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 3.1 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0045] Comparative Example 6 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 4000 and a degree of saponification of 99.1 mol% was added to 3700 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 4.9% by mass). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0046] Comparative Example 7 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 4000 and a degree of saponification of 99.1 mol% was added to 2480 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 7.2 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0047] Example 8 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 5,400 and a degree of saponification of 99.3 mol% was added to 6,700 g of pure water and stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol solution (polyvinyl alcohol concentration 2.8% by mass). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0048] Example 9 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 8,300 and a degree of saponification of 99.0 mol% was added to 13,600 g of pure water, and the mixture was stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 1.4 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0049] Comparative Example 8 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 5,400 and a degree of saponification of 99.3 mol% was added to 4,200 g of pure water, and the mixture was stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 4.4 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0050] Comparative Example 9 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 8,300 and a degree of saponification of 99.0 mol% was added to 6,400 g of pure water, and the mixture was stirred at a temperature of 90°C for approximately 2 hours to dissolve the polyvinyl alcohol, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 2.9% by mass). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0051] <Evaluation> The polyvinyl acetal resin particles obtained in the examples and comparative examples were evaluated as follows. The results are shown in Tables 1 to 4.

[0052] (1) Porosity, pore ratio of pores with a pore radius of 7.5 to 0.075 μm The porosity and the ratio of pores with a pore radius of 7.5 to 0.075 μm of the obtained polyvinyl acetal resin particles were measured by mercury intrusion using a porosimeter (Thermo Pascal 14B). Note that the porosity means the volume of pores with a pore radius of 7.5 to 0.0038 μm in the volume of the resin particles, and the ratio of pores with a pore radius of 7.5 to 0.075 μm means the ratio of the volume of pores with a pore radius of 7.5 to 0.075 μm to the volume of pores with a pore radius of 7.5 to 0.0038 μm.

[0053] (2) JIS standard sieve passing test The obtained polyvinyl acetal resin particles were classified at a rotation speed of 200 rpm for 1 minute using a horizontal rotating sieve (manufactured by AS ONE, turning radius φ30 mm) equipped with JIS standard sieves with openings of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm, and 250 μm arranged in seven consecutive stages in this order. Then, the content ratio of particles that did not pass through each JIS standard sieve (φ200 × height 45 mm) and the content ratio of particles that passed through all JIS standard sieves were measured. The presence or absence of particles passing through each of the JIS standard sieves was judged by visual inspection, and the content of particles that did not pass through each JIS standard sieve was calculated by "[(weight of particles that did not pass through each JIS standard sieve) / (total particle weight)]×100". The table shows the "total content ratio that does not pass through 4000μm, 3350μm, and 2830μm mesh sizes." This indicates the "content ratio of particles that do not pass through the JIS standard sieve with a mesh size of 2830μm." In addition, the "content proportion passing through all sieves" in the table indicates the "content proportion of particles passing through a JIS standard sieve with a mesh size of 250 μm," and the "content proportion not passing through a JIS standard sieve with a mesh size of 1700 μm" in the table indicates the "content proportion of particles passing through a JIS standard sieve with a mesh size of 2830 μm but not passing through a JIS standard sieve with a mesh size of 1700 μm."

[0054] (3) Rattler test The obtained polyvinyl acetal resin particles were passed through a sieve at 87 rpm and 1000 revolutions using a Rator Tester (Minerva Instruments, JIS standard sieve with 1180 μm mesh), and the content of particles that passed through the JIS standard sieve with 1180 μm mesh and the content of particles that did not pass through were measured. The presence or absence of passing was judged by visual inspection, and the content of particles that passed through the JIS standard 1180 μm mesh was calculated from [(weight passing through 1180 μm mesh / total particle weight)]×100.

[0055] (4)Solubility In a 500 mL beaker, 192 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) was placed as an organic solvent, and the temperature was kept at 25°C. 48.0 g of the obtained polyvinyl acetal resin particles (concentration 20 wt%) was added while stirring at 200 rpm using two stirring blades, and the polyvinyl acetal resin particles were dissolved. The dissolution time from the addition of the obtained polyvinyl acetal resin particles to the time when no undissolved resin remained was measured by visual observation. Similarly, the dissolution time was measured for concentrations of 10 wt%, 5 wt%, 3 wt%, and 2 wt%. Note that "not dissolved" means that the solution did not dissolve even after 600 minutes had passed, or the viscosity when dissolved in the organic solvent was 5000 mPa·s or more. When the viscosity was 5000 mPa·s or more, the solution wrapped around the stirring shaft due to the Weissenberg effect, and the same evaluation could not be performed. In addition, the multiple of the dissolution time relative to the dissolution time at the lowest concentration (dissolution time multiple) was calculated for each concentration except for the lowest concentration, and is shown in the table. Note that "-" in the table means that the dissolution time multiple could not be calculated.

[0056] [Table 1]

[0057] [Table 2]

[0058] [Table 3]

[0059] [Table 4]

[0060] [Table 5] [Industrial Applicability]

[0061] According to the present invention, it is possible to provide polyvinyl acetal resin particles which can be easily dissolved in an organic solvent even when a large amount is added, which are less likely to suffer from poor solvent impregnation of the particles during dissolution, and which have excellent uniformity of the resin component.

Claims

1. Contains polyvinyl acetal resin, The porosity is 30% or more and 40% or less, and the pore ratio of pores having a pore radius of 7.5 to 0.075 μm is 90% or more, The content of particles passing through a JIS standard sieve with an opening of 250 μm is 10% by weight or less, The content of particles that do not pass through a JIS standard sieve having an opening of 2830 μm is 10% by weight or less, and The content of particles passing through a JIS standard sieve having an opening of 2830 μm but not passing through a JIS standard sieve having an opening of 1700 μm is 45% by weight or more; the polyvinyl acetal resin has a hydroxyl group content of 20 mol % or more and 50 mol % or less and a polymerization degree of 200 or more and 3,300 or less; Polyvinyl acetal resin particles.

2. 2. The polyvinyl acetal resin particles according to claim 1, wherein the polyvinyl acetal resin has an acetal group content of 40 mol % or more and 78 mol % or less.

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