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 organic solvents.

Background Art

[0002] Polyvinyl acetal resins such as polyvinyl butyral resin are used in various applications because of their excellent toughness, film-forming properties, dispersibility for particles and the like, and adhesiveness to coated surfaces. As one of the applications of polyvinyl acetal resins, for example, slurry compositions and conductive pastes using a polyvinyl acetal resin such as polyvinyl butyral resin as a binder resin are disclosed.

[0003] Polyvinyl acetal resins used in 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, faster dissolution in the solvent improves workability. It is considered that increasing the surface area of polyvinyl acetal resin particles increases the contact area with the solvent, thereby improving solubility, but in practice, the particles float on the liquid surface of the solvent, resulting in a slow dissolution rate in the solvent. Further, when a polyvinyl acetal resin has poor solubility in organic solvents, a trace amount of undissolved matter is generated when the resin is dissolved in an organic solvent, which reduces the dispersibility of particles.

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

Prior Art Literature

Patent Literature

[0005] [Patent Document 1] Japanese Patent Publication No. 2000-38456 [Patent Document 2] Japanese Patent Publication No. 2011-225842 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the polyvinyl acetal resin particles disclosed in Patent Documents 1 and 2 actually have insufficient solubility in organic solvents, and their solubility is particularly low when the amount of resin added is large. Furthermore, simply reducing the average particle size can cause the particles to float during addition, which can reduce the uniformity of the resin components.

[0007] The present invention aims to provide polyvinyl acetal resin particles that can be easily dissolved in organic solvents even in large amounts, are less prone to particle floating during addition, and exhibit excellent uniformity of resin components. [Means for solving the problem]

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

[0009] The present inventors have found that simply specifying particle size and bulk density, as in the case of polyvinyl acetal resin particles disclosed in Patent Documents 1 and 2, results in insufficient solubility in organic solvents. Furthermore, we discovered that polyvinyl acetal resin particles with low porosity and a high proportion of pores with large pore radii, and with a defined ratio of particles that pass through and do not pass through a specified JIS standard sieve, can be easily dissolved in organic solvents even in large amounts. We also found that poor solvent impregnation of particles during dissolution is less likely to occur, and that the uniformity of the resin components is excellent, thus completing the present invention.

[0010] The polyvinyl acetal resin particles of the present invention have a porosity of 30% or more. A lower limit of 30% for the porosity makes it possible to improve solubility in organic solvents. A preferred lower limit for the porosity is 32%, and a more preferred lower limit is 35%. Furthermore, while there is no particular upper limit for the porosity, 40% is preferred. In this specification, the porosity refers to the volume of voids with pore radii of 7.5 to 0.0038 μm relative to the volume of the resin particles. The above porosity can be measured, for example, using a porosimeter (Thermo Pascal 14B, manufactured by Thermo Fisher Scientific) by the mercury intrusion method.

[0011] The polyvinyl acetal resin particles of the present invention have a void ratio of 90% or more for pores with a pore radius of 7.5 to 0.075 μm. A lower limit of 90% for the void ratio of pores with a pore radius of 7.5 to 0.075 μm facilitates impregnation with organic solvents, thereby improving solubility in organic solvents. A preferred lower limit for the void ratio of pores with a pore radius of 7.5 to 0.075 μm is 92%, and a more preferred lower limit is 95%. Furthermore, there is no particular upper limit for the void ratio of pores with a pore radius of 7.5 to 0.075 μm, but 100% is preferred. In this specification, the void ratio for pore radii of 7.5 to 0.075 μm refers to the ratio of the void volume for pore radii of 7.5 to 0.0038 μm to the void volume for pore radii of 7.5 to 0.0038 μm. The void ratio for pores with pore radii of 7.5 to 0.075 μm can be measured, for example, using a porosimeter (Thermo Pascal 14B, Thermo Fisher Scientific) and the mercury intrusion method.

[0012] The polyvinyl acetal resin particles of the present invention have a particle content of 10% by weight or less that passes through a JIS standard sieve with a mesh size of 250 μm. By having a particle content of 10% by weight or less that passes through the JIS standard sieve with a mesh size of 250 μm, floating of the particles during addition can be suppressed, and the generation of clumps during dissolution can be prevented. The preferred upper limit for the particle content that passes through the 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. Furthermore, there is no particular lower limit for the particle content that passes through the JIS standard sieve with a mesh size of 250 μm, but it is preferably 0% by weight. In this specification, the sieve described above conforms to JIS Z8801. Furthermore, whether or not a particle passed through the above-mentioned JIS standard sieve was determined by visual inspection. The percentage of particles that passed through the above-mentioned JIS standard sieve with a mesh size of 250 μm was calculated as follows: [(weight of particles that passed through all JIS standard sieves) / (weight of all particles)] × 100, when JIS standard sieves with mesh sizes of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm, and 250 μm were set up in this order and the particles were sieved.

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

[0014] The polyvinyl acetal resin particles of the present invention have a content of 45% by weight or more of particles that pass through a JIS standard sieve with a mesh size of 2830 μm but do not pass through a JIS standard sieve with a mesh size of 1700 μm. By having a particle content of 45% by weight or more, particles with a uniform aspect ratio can be obtained. The preferred upper limit for the particle content is 100% by weight. Furthermore, the preferred lower limit for the particle content is 48% by weight, and more preferably 50% by weight. In this specification, the sieve described above conforms to JIS Z8801. Furthermore, the percentage of particles that pass through the JIS standard sieve with a mesh size of 2830 μm but not through the JIS standard sieve with a mesh size of 1700 μm is calculated using the following formula when particles are sieved using JIS standard sieves with mesh sizes of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm, and 250 μm, set up in this order. [(Weight of particles that do not pass through a JIS standard sieve with a mesh size of 1700 μm) / (Total weight of particles)] × 100

[0015] The polyvinyl acetal resin particles of the present invention have a particle content of 3.0% by weight or less that passes through a ratrol tester (JIS standard sieve with a mesh size of 1180 μm). By ensuring that the content of the above particles is 3.0% by weight or less, it is possible to obtain particles that are less prone to breaking and have a uniform aspect ratio. The preferred lower limit for the content of the above particles is 1.0% by weight, and the more preferred upper limit is 2.0% by weight. In this specification, the sieve used conforms to JIS Z8801. Further, when passing through the above-mentioned Ro-Tap tester (JIS standard sieve with an opening of 1180 µm), the passage is performed, for example, under conditions of 87 rpm and 1000 rotations.

[0016] The polyvinyl acetal resin particles of the present invention preferably contain a polyvinyl acetal resin having a polymerization degree of 200 or more and 10000 or less. When the polymerization degree falls within the above range, the resin can be easily dissolved in an organic solvent even when the addition amount of the resin is large, and a solution having excellent uniformity of resin components can be obtained. Therefore, the tact time in the dissolution step of the polyvinyl acetal resin can be shortened, and variation in the mechanical strength of the obtained various sheets can be stabilized. A more preferable lower limit of the polymerization degree of the polyvinyl acetal resin is 300, a more preferable upper limit is 8500, a further more preferable upper limit is 5500, and a particularly preferable upper limit is 5000.

[0017] With respect to the acetal group content of the above polyvinyl acetal resin, whether an aldehyde is used alone or two or more aldehydes are used in combination, a preferable lower limit is 40 mol% and a preferable upper limit is 80 mol%. When the acetal group content is from 40 mol% to 80 mol%, the polyvinyl acetal resin does not aggregate and can be dissolved in a wide variety of solvents, which can impart dispersibility to inks and dyes, and impart sufficient flexibility to various obtained sheets. A more preferable lower limit of the acetal group content is 60 mol%, and a more preferable upper limit thereof is 78 mol%. Note that, regarding the calculation method of the acetal group content, since acetal groups of the polyvinyl acetal resin are obtained by acetalizing two hydroxyl groups of polyvinyl alcohol, a method of counting two acetalized hydroxyl groups is adopted. In addition, in the present specification, when the acetal group is an acetaldehyde acetal group, it is also referred to as acetaldehyde acetal group content, and when the acetal group is a butyral group, it is also referred to as butyral group content.

[0018] The preferred lower limit for 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 between 20 mol% and 50 mol%, it can be easily dissolved in organic solvents even when the amount added is large, and a solution with excellent uniformity of resin components can be obtained. Therefore, the cycle time in the dissolution process of polyvinyl acetal resin can be shortened, and the variation in the mechanical strength of the resulting sheets can be stabilized. A more preferable lower limit for the amount of hydroxyl groups is 22 mol%, and a more preferable upper limit is 45 mol%.

[0019] The preferred lower limit for the amount of acetyl groups in the above polyvinyl acetal resin is 0.1 mol%, and the preferred upper limit is 20 mol%. When the amount of acetyl groups is 0.1 mol% or more, the compatibility with organic solvents can be improved. When the amount of acetyl groups is 20 mol% or less, the formation of lumps during dissolution becomes less likely. A more preferable lower limit for the amount of acetyl groups is 0.5 mol%, and a more preferable upper limit is 15 mol%.

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

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

[0022] The polyvinyl acetal resin particles of the present invention are obtained by performing a process of acetalizing polyvinyl alcohol (acetal process) and a granulation process. One example of a method for acetalizing the polyvinyl alcohol is to add various aldehydes 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, porosity ratio with a pore radius of 7.5 to 0.075 μm, and specific surface area can be produced by adjusting the degree of polymerization of the 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 process described above is preferably 1.0 to 7.0% by mass. By keeping it within this range, it is possible to suitably produce polyvinyl acetal resin particles of the present invention that have a predetermined degree of polymerization, porosity, porosity ratio of pores with a pore radius of 7.5 to 0.075 μm, a content ratio of particles that pass through a JIS standard sieve with a mesh size of 250 μm, and a ratio of particles that pass through and do not pass through the predetermined JIS standard sieve. The content of the polyvinyl alcohol resin described above has a more preferable lower limit of 2.0% by mass and a more preferable upper limit of 6.0% by mass. The content of the polyvinyl alcohol resin can be determined by considering the degree of polymerization of the polyvinyl alcohol resin used.

[0024] The preferred lower limit of the degree of saponification of the above polyvinyl alcohol is 80 mol%. If the degree of saponification of the above polyvinyl alcohol is less than 80 mol%, the water solubility deteriorates, making acetalization difficult, and the amount of hydroxyl groups decreases, making acetalization itself difficult. A more preferred lower limit is 85 mol%. There is no particular upper limit, but a preferred upper limit is 99.9 mol%.

[0025] The above-mentioned polyvinyl alcohol may be used alone, provided that the degree of saponification of the polyvinyl alcohol during acetalization is 80 mol% or more, or it may be used after mixing polyvinyl alcohol with a degree of saponification of 80 mol% or more and polyvinyl alcohol with a degree of saponification of less than 80 mol% to adjust the degree of saponification to 80 mol% or more.

[0026] The above-mentioned acid catalyst is not particularly limited and can be either an organic or inorganic acid, such as acetic acid, p-toluenesulfonic acid, nitric acid, sulfuric acid, or hydrochloric acid. Among these, non-halogenated acid catalysts are preferred.

[0027] The aldehyde used in the above acetalization is not particularly limited, and examples 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, β-phenylpropionaldehyde, etc. Among these, acetaldehyde and / or butyraldehyde are preferred for acetalization. These aldehydes may be used individually or in combination of two or more.

[0028] To stop the acetalization reaction described above, neutralization with an alkali is preferable. The alkali is not particularly limited and examples include sodium hydroxide, potassium hydroxide, ammonia, sodium acetate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, etc. Furthermore, it is preferable to wash the modified polyvinyl acetal resin obtained using water or the like before and after the neutralization process described above. In addition, it is more preferable to wash with pure water to prevent contamination by impurities contained in the washing water.

[0029] The granulation process in the above manufacturing method is not particularly limited, and for example, methods such as compressing and crushing particulate raw material resin, heating the raw material resin to a temperature range in which the resin softens but does not fuse, mixing in raw material resin with a low softening temperature, or using raw material resin containing a small amount of organic solvent or water can be used. Specifically, rolling type (drum type, inclined pan type, etc.), vibrating type (horizontal type, inclined type, etc.), compression molding type (tablet press, briquette press, roll press, etc.), crushing type (crusher), mixing type (blender type, pin type, etc.), fluidized bed type (fluidized bed type, jet bed type, etc.), 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 crushing machine described above is not particularly limited, but flake breakers, hammer mills, feather mills, cutter mills, roll mills, and rotary mills are preferred. Furthermore, in order to prevent the resin from fusing together due to the heat generated during crushing, it is preferable that the crushing part of the crushing machine has a cooling function such as a water-cooled jacket. Furthermore, the crushing conditions (rotation speed, screen size, etc.) are not particularly limited and can be selected to ensure that the resulting granulated resin has the desired particle shape. [Effects of the Invention]

[0031] According to the present invention, it is possible to provide polyvinyl acetal resin particles that can be easily dissolved in organic solvents even when a large amount is added, and that are less prone to poor solvent impregnation of particles during dissolution, and have excellent uniformity of resin components. [Modes for carrying out the invention]

[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) 200 g of polyvinyl alcohol (96.5% purity) with a degree of polymerization of 300 and a degree of saponification of 98.7 mol% was added to 3050 g of pure water and stirred at 90°C for about 2 hours to dissolve, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 5.9% by mass). This solution was cooled to 40°C, and 240 g of hydrochloric acid with a concentration of 35% by weight (corresponding to 7.9% by weight relative to the amount of pure water added) and 116 g of n-butyraldehyde were added. The solution temperature was lowered to 5°C and maintained at this temperature to carry out the acetalization reaction, and the reaction product was precipitated. After that, the solution temperature was raised to 25°C and maintained for 3 hours to complete the reaction, and neutralization, washing with water, and drying were carried out by conventional methods to obtain a white powder of polyvinyl acetal resin. The obtained polyvinyl acetal resin was dissolved in DMSO-d6 (dimethyl sulfoxide), 13 The amount of hydroxyl groups, the amount of acetyl groups, and the degree of butyralization were measured using 13C-NMR (nuclear magnetic resonance spectroscopy) to be 35.7 mol%, 1.3 mol%, and 63.0 mol%, respectively. The resulting polyvinyl acetal resin raw material powder is passed through a two-roller system at a unit area pressure of 5 kg / cm². 2 Polyvinyl acetal resin particles were obtained by compression molding and crushing with a crusher.

[0034] (Comparative Example 1) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 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 1300 g of pure water and stirred at 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 12.9% by mass).

[0035] (Example 2) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 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 3200 g of pure water and stirred at 90°C for about 2 hours to dissolve it, thereby obtaining a 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) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 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 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 16.1% by mass).

[0037] (Example 3) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 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 90°C for about 2 hours to dissolve it, thereby obtaining a 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) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 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 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 12.1% by mass).

[0039] (Example 4) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 3300 and a degree of saponification of 99.2 mol% was added to 4300 g of pure water and stirred at 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 4.3% by 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) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 3300 and a degree of saponification of 99.2 mol% was added to 5700 g of pure water and stirred at 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 3.3% by mass).

[0041] (Comparative Example 4) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 3300 and a degree of saponification of 99.2 mol% was added to 2300 g of pure water and stirred at 90°C for about 2 hours to dissolve it, thereby obtaining a 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 (96.5% purity) with a degree of polymerization of 500 and a degree of saponification of 98.8 mol% was added to 2600 g of pure water and stirred at 90°C for about 2 hours to dissolve, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 6.9% by mass). Except for using this solution, the amount of n-butyraldehyde 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) Polyvinyl acetal resin particles were obtained in the same manner as in Example 6, except that 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 1050 g of pure water and stirred at 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 15.4% by mass).

[0044] (Example 7) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 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 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 3.1% by mass).

[0045] (Comparative Example 6) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 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 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 4.9 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) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 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 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 7.2% by 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) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 5400 and a degree of saponification of 99.3 mol% was added to 6700 g of pure water and stirred at 90°C for about 2 hours to dissolve it, thereby obtaining a 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) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 8300 and a degree of saponification of 99.0 mol% was added to 13600 g of pure water and stirred at 90°C for about 2 hours to dissolve it, 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) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 5400 and a degree of saponification of 99.3 mol% was added to 4200 g of pure water and stirred at 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 4.4% by mass).

[0050] (Comparative Example 9) Polyvinyl acetal resin particles were obtained in the same manner as in Example 1, except that 200 g of polyvinyl alcohol (purity 96.5%) with a degree of polymerization of 8300 and a degree of saponification of 99.0 mol% was added to 6400 g of pure water and stirred at 90°C for about 2 hours to dissolve it, thereby obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 2.9 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0051] <Rating> 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, void ratio of pores with a pore radius of 7.5 to 0.075 μm The porosity and void ratio of pores with pore radii of 7.5 to 0.075 μm were measured for the obtained polyvinyl acetal resin particles using a porosimeter (Thermo Pascal 14B) and the mercury intrusion method. Porosity refers to the volume of voids with pore radii of 7.5 to 0.0038 μm relative to the volume of the resin particles, and the void ratio of voids with pore radii of 7.5 to 0.075 μm refers to the ratio of the volume of voids with pore radii of 7.5 to 0.0038 μm to the volume of voids with pore radii of 7.5 to 0.0038 μm.

[0053] (2) Pass test of JIS standard sieve The obtained polyvinyl acetal resin particles were classified for 1 minute at 200 rpm using a horizontal sieving machine (manufactured by AS ONE, with a swivel radius of φ30 mm) equipped with seven consecutive JIS standard sieves with mesh sizes of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm, and 250 μm, in that order. The percentage of particles that did not pass through each JIS standard sieve (φ200 × height 45 mm) and the percentage of particles that passed through all JIS standard sieves were then measured. Whether or not particles passed through each of the above JIS standard sieves was determined by visual inspection, and the percentage of particles that did not pass through each JIS standard sieve was calculated using the formula "[(Weight of particles that did not pass through each JIS standard sieve) / (Total particle weight)] × 100". The table shows the "total percentage of particles that do not pass through sieves with mesh sizes of 4000 μm, 3350 μm, and 2830 μm." This represents the "percentage of particles that do not pass through a JIS standard sieve with a mesh size of 2830 μm." Note that in the table, "Percentage of particles passing through all sieves" refers to "the percentage of particles that pass through a JIS standard sieve with a mesh size of 250 μm," and "Percentage of particles that do not pass through a 1700 μm sieve" refers to "the percentage of particles that pass through a JIS standard sieve with a mesh size of 2830 μm but do not pass through a JIS standard sieve with a mesh size of 1700 μm."

[0054] (3) Rattle test The obtained polyvinyl acetal resin particles were passed through a rattle tester (manufactured by Minerva Kiki Co., Ltd., JIS standard sieve with a mesh size of 1180 μm) at 87 rpm and 1000 rpm. The percentage of particles that passed through the JIS standard sieve with a mesh size of 1180 μm and the percentage of particles that did not pass through were measured. Whether or not a particle passed was determined by visual inspection, and the percentage of particles that passed through the JIS standard sieve with a mesh size of 1180 μm was calculated using the formula [(weight of particles that passed through the 1180 μm sieve / total particle weight)] × 100.

[0055] (4)Solubility 192g of a mixed solvent of ethanol and toluene (weight ratio 1:1) was placed in a 500mL beaker. The temperature was maintained at 25°C, and 48.0g of the obtained polyvinyl acetal resin particles (concentration 20% by weight) were added while stirring at 200 rpm using two stirring blades, and the polyvinyl acetal resin particles were dissolved. The dissolution time was measured by visual observation, from the time the obtained polyvinyl acetal resin particles were added until no undissolved resin remained. Similarly, the dissolution time was measured for concentrations of 10% by weight, 5% by weight, 3% by weight, and 2% by weight. Note that "Unacceptable" means that the solution did not dissolve even after 600 minutes, or that the viscosity when dissolved in the organic solvent was 5000 mPa·s or higher. When the viscosity is 5000 mPa·s or higher, the Weissenberg effect causes the solution to wrap around the stirring shaft, making it impossible to perform the same evaluation. Furthermore, the multiples of dissolution time relative to the dissolution time at the lowest concentration (dissolution time multiples) were calculated for each concentration other than the lowest concentration and are shown in the table. Note that "-" in the table indicates 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 that can be easily dissolved in organic solvents even when a large amount is added, and that are less prone to poor solvent impregnation of particles during dissolution, and have excellent uniformity of resin components.

Claims

1. It contains polyvinyl acetal resin, The porosity is 30% or more and 40% or less, and the proportion of voids with a pore radius of 7.5 to 0.075 μm is 90% or more. The content of particles that pass through a JIS standard sieve with a mesh size of 250 μm is 10% by weight or less. The content of particles that do not pass through a JIS standard sieve with a mesh size of 2830 μm is 10% by weight or less, The content of particles that pass through a JIS standard sieve with a mesh size of 2830 μm but do not pass through a JIS standard sieve with a mesh size 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, an acetyl group content of 0.1 mol% or more and 20 mol% or less, and a degree of polymerization of 3300 or more and 8300 or less. Polyvinyl acetal resin particles.

2. The polyvinyl acetal resin particles according to claim 1, wherein the amount of acetal groups in the polyvinyl acetal resin is 40 mol% or more and 78 mol% or less.

Images