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 being insufficiently impregnated with the solvent during the dissolution, and ensure excellent uniformity of the resin components.SOLUTION: A polyvinyl acetal resin particle contains a polyvinyl acetal resin and has a voidage of 50% or more and a proportion of voids with a pore radius of 7.5-0.075 μm of 98% or more, and has a specific surface area of 15 m2 / g 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 due to their excellent toughness, film-forming properties, dispersibility of particles and the like, and adhesion 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 for these applications are generally used as solutions dissolved in organic solvents such as methyl ethyl ketone, toluene, alcohol, and mixtures 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; however, in practice, the particles float on the liquid surface of the solvent, resulting in a slow dissolution rate in the solvent. Furthermore, if a 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, 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. Patent Document 2 discloses polyvinyl acetal resin particles comprising a polyvinyl acetal resin having a degree of polymerization 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 Documents

[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 exhibit 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 lead to the particles floating during addition, and poor solvent impregnation of the particles during dissolution can occur, potentially reducing the uniformity of the resin components.

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

[0008] This invention relates to a material containing polyvinyl acetal resin, having a porosity of 50% or more, a porosity ratio of 98% or more for pores with a pore radius of 7.5 to 0.075 μm, and a specific surface area of ​​15 m². 2 These are polyvinyl acetal resin particles weighing 1 / g or more. 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. Therefore, the inventors have found that polyvinyl acetal resin particles, which have a high porosity, a large proportion of pores with a large pore radius, and a high specific surface area, can be easily dissolved in organic solvents even when added in large quantities, and that poor solvent impregnation of the particles during dissolution is less likely to occur, resulting in excellent uniformity of the resin components. Furthermore, they have found that such polyvinyl acetal resin particles adhere less to containers after dissolution, thus completing the present invention.

[0010] The polyvinyl acetal resin particles of the present invention have a porosity of 50% or more. A lower limit of 50% for the porosity makes it possible to improve solubility in organic solvents. A preferred lower limit for the porosity is 55%, and a more preferred lower limit is 60%. Furthermore, while there is no particular upper limit for the porosity, 80% 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 98% or more for pores with a pore radius of 7.5 to 0.075 μm. A lower limit of 98% 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 98.5%, and a more preferred lower limit is 99%. 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 preferably have a void ratio of 80% or more with a pore radius of 7.5 to 1.0 μm. A preferred lower limit of 80% for the void ratio with a pore radius of 7.5 to 1.0 μm makes it easier for organic solvents to penetrate, thus improving solubility in organic solvents. A more preferred lower limit for the void ratio with a pore radius of 7.5 to 1.0 μm is 83%, and an even more preferred lower limit is 85%. Furthermore, there is no particular upper limit for the preferred upper limit of the void ratio with a pore radius of 7.5 to 1.0 μm, but it is preferably 100%. In this specification, the void ratio for pore radii of 7.5 to 1.0 μm refers to the ratio of the void volume for pore radii of 7.5 to 1.0 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 1.0 μm can be measured, for example, using a porosimeter (Thermo Pascal 14B, Thermo Fisher Scientific) by the mercury intrusion method.

[0013] The polyvinyl acetal resin particles of the present invention have a specific surface area of ​​15 m². 2 The minimum specific surface area is 15 m². 2 The value of / g allows for easier impregnation with organic solvents, thus improving solubility in organic solvents. A more preferable lower limit for the specific surface area is 17m². 2 / g, a more preferable lower limit is 20mg 2 The value is / g. Furthermore, the upper limit of the specific surface area is not particularly limited, but 40m² 2 It is preferable that it be / g. In this specification, the specific surface area refers to the surface area per unit weight, and can be measured, for example, using a porosimeter (Thermo Pascal 14B, manufactured by Thermo Fisher Scientific) by the mercury intrusion method.

[0014] The preferred lower limit for the D90 particle size of the polyvinyl acetal resin particles of the present invention is 30 μm, and the preferred upper limit is 1000 μm. A D90 particle size of 30 μm or more improves solubility in organic solvents. A D90 particle size of 1000 μm or less allows for easy dispersion when dissolved in organic solvents. A more preferred lower limit for the D90 particle size is 50 μm, and a more preferred upper limit is 800 μm. Furthermore, the preferred lower limit for the D50 particle diameter of the polyvinyl acetal resin particles of the present invention is 30 μm, and the preferred upper limit is 500 μm. A more preferred lower limit for the above D50 particle diameter is 40 μm, and a more preferred upper limit is 400 μm. Furthermore, the preferred lower limit for the D10 particle diameter of the polyvinyl acetal resin particles of the present invention is 10 μm, and the preferred upper limit is 300 μm. A more preferred lower limit for the above D10 particle diameter is 20 μm, and a more preferred upper limit is 100 μm. The above-mentioned "D90 particle size (D90)" refers to the particle size at which the cumulative frequency of the distribution from the small particle side reaches 90% in particle size distribution measurement, "D50 particle size (D50)" refers to the particle size at which the cumulative frequency of the distribution reaches 50%, and "D10 particle size (D10)" refers to the particle size at which the cumulative frequency of the distribution reaches 10%. The above-mentioned D90, D50, and D10 can be measured, for example, using a laser diffraction particle size distribution analyzer (Mastersizer 3000, manufactured by Malvern Panalytical).

[0015] The preferred lower limit of the particle size distribution ε of the polyvinyl acetal resin particles of the present invention is 0.01, and the preferred upper limit is 4.00. When the particle size distribution ε is 0.01 or higher, the solubility in organic solvents is improved. When the particle size distribution ε is 4.00 or lower, the particles can be easily dispersed when dissolved in organic solvents. From a similar viewpoint, the more preferred lower limit of the particle size distribution ε is 0.01, the more preferred upper limit is 3.00, and the still more preferred upper limit is 2.00. The particle size distribution ε is calculated from [(D90-D10) / D50].

[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 10000 or less. When the degree of polymerization of the above polyvinyl acetal resin is 200 or more and 10000 or less, the resin can be easily dissolved in an organic solvent even when added in a large amount, and a solution having excellent uniformity of resin components can be obtained. Therefore, it is possible to shorten the tact time in the dissolution step of the polyvinyl acetal resin and stabilize the variation in mechanical strength of various obtained sheets. From the same viewpoint, the preferred lower limit of the degree of polymerization of the above polyvinyl acetal resin is 300, the preferred upper limit is 8500, the more preferred upper limit is 5500, and the even more preferred upper limit is 5000.

[0017] Regardless of whether the aldehyde is used alone or two or more aldehydes are used in combination, the preferred lower limit of the acetal group content of the above polyvinyl acetal resin is 40 mol%, and the preferred upper limit is 80 mol%. When the acetal group content is 40 mol% or more and 80 mol% or less, the polyvinyl acetal resin does not aggregate, dissolves in a wide variety of solvents, can impart dispersibility to inks and dyes, and can impart sufficient flexibility to various obtained sheets. From the same viewpoint, the more preferred lower limit of the acetal group content is 60 mol%, and the more preferred upper limit is 78 mol%. Regarding the calculation method of the acetal group content, since the acetal groups of the polyvinyl acetal resin are obtained by acetalizing two hydroxyl groups of polyvinyl alcohol, a method of counting the two acetalized hydroxyl groups is employed. In addition, in the present specification, when the acetal group is an acetoacetal group, it is also referred to as acetoacetal 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 above 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. From a similar viewpoint, the more preferred lower limit for the amount of hydroxyl groups is 22 mol%, and the more preferred 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. From a similar viewpoint, the more preferred lower limit for the amount of acetyl groups is 0.5 mol%, and the more preferred 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. From a similar viewpoint, the content of the polyvinyl acetal resin is more preferably 20% by weight as the lower limit and more preferably 80% by weight as the upper limit.

[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). 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 and the polyvinyl alcohol content (concentration) of the polyvinyl alcohol solution.

[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, 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 suitably produced. From a similar viewpoint, the polyvinyl alcohol content has a more preferable lower limit of 2.0% by mass and a more preferable upper limit of 6.0% by mass. The polyvinyl alcohol resin content can be determined 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 resin obtained through the above manufacturing method may be used as the polyvinyl acetal resin particles of the present invention, and may be further granulated. The granulation method described above is not particularly limited and includes, for example, rolling granulation, extrusion granulation, compression granulation, stirring granulation, spray drying, dissolution and solidification, and crushing granulation. [Effects of the Invention]

[0030] 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. Furthermore, according to the present invention, it is possible to provide polyvinyl acetal resin particles that have excellent solubility and do not adhere to containers after dissolution. [Modes for carrying out the invention]

[0031] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0032] (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 approximately 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 35% by weight hydrochloric acid (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. Subsequently, the solution temperature was raised to 25°C and maintained for 3 hours to complete the reaction. Neutralization, washing with water, and drying were performed 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.

[0033] (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).

[0034] (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.

[0035] (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).

[0036] (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.

[0037] (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).

[0038] (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.

[0039] (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).

[0040] (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.

[0041] (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.

[0042] (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).

[0043] (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 3300 and a degree of saponification of 99.2 mol% was added to 3440 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 5.3% by mass). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0044] (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 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 4.9 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) 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 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 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 10) 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 Table 1.

[0052] (1) Porosity, void ratio of pores with a radius of 7.5 to 0.075 μm, void ratio of pores with a radius of 7.5 to 1.0 μm, specific surface area The obtained polyvinyl acetal resin particles were measured using a porosimeter (Thermo Pascal 14B) by mercury intrusion to determine porosity, pore ratio of pores with pore radii of 7.5 to 0.075 μm, pore ratio of pores with pore radii of 7.5 to 1.0 μm, and specific surface area. Porosity refers to the volume of pores with pore radii of 7.5 to 0.0038 μm relative to the volume of pores with pore radii of 7.5 to 0.0038 μm. The pore ratio of pores with pore radii of 7.5 to 1.0 μm refers to the ratio of the pore volume of pores with pore radii of 7.5 to 1.0 μm relative to the volume of pores with pore radii of 7.5 to 0.0038 μm.

[0053] (2) Particle size (D10, D50, D90) The obtained polyvinyl acetal resin particles were measured for particle size distribution (D10, D50, D90) using a laser diffraction particle size distribution analyzer (Mastersizer 3000). The particle size distribution ε[(D90-D10) / D50] was calculated from the measured D10, D50, and D90 values.

[0054] (3)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 while stirring with two impellers at a rotation speed of 200 rpm, 48.0g of the obtained polyvinyl acetal resin particles (concentration 20% by weight) were added and 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. "Undissolved" means that the particles did not dissolve even after 600 minutes, or that the viscosity when dissolved in the organic solvent was 5000 mPa·s or higher. If 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 dissolution time multiples (multiples of dissolution time) for each concentration other than the lowest concentration were calculated and shown in the table. A "-" in the table indicates that the dissolution time multiple could not be calculated.

[0055] (4) Confirmation of the solvent impregnation state of the particles [Polyvinyl acetal resin particles obtained in Comparative Examples 1, 2, and 5 and Examples 1, 2, and 6] 192 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) was placed in a 500 mL beaker. The temperature was maintained at 25°C, and while stirring with two stirring blades at a rotation speed of 200 rpm, 48.0 g of the obtained polyvinyl acetal resin particles were added to the solution to a concentration of 20% by weight, and the polyvinyl acetal resin particles were dissolved. The state of the resin particles was observed visually, and the time until the resin particles became transparent (the resin particles were impregnated with the solvent) was measured at 5-minute intervals. [Polyvinyl acetal resin particles obtained in Comparative Examples 3, 4, 6, 7 and Examples 3, 4, 5, 7, 8] 228 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) was placed in a 500 mL beaker. The temperature was maintained at 25°C, and 12.0 g of the obtained polyvinyl acetal resin particles were added while stirring with two stirring blades at a rotation speed of 200 rpm, so that the solution concentration was 5% by weight, and the polyvinyl acetal resin particles were dissolved. The state of the resin particles was observed visually, and the time until the resin particles became transparent (the resin particles were impregnated with the solvent) was measured at 5-minute intervals. [Polyvinyl acetal resin particles obtained in Comparative Examples 8, 9, and 10, and Examples 9 and 10] 235.2 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) was placed in a 500 mL beaker. The temperature was maintained at 25°C, and while stirring with two stirring blades at a rotation speed of 200 rpm, 4.8 g of the obtained polyvinyl acetal resin particles were added to the solution to a concentration of 2% by weight, and the polyvinyl acetal resin particles were dissolved. The state of the resin particles was observed visually, and the time until the resin particles became transparent (the resin particles were impregnated with the solvent) was measured at 5-minute intervals.

[0056] (5) Evaluation of container adhesion during particle dissolution [Polyvinyl acetal resin particles obtained in Comparative Examples 1-7 and Examples 1-8] 228 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) was placed in a 500 mL beaker. The temperature was maintained at 25°C, and while stirring with two stirring blades at a rotation speed of 200 rpm, 12.0 g of the obtained polyvinyl acetal resin particles were added to the solution to a concentration of 5% by weight, and the dissolution of the polyvinyl acetal resin particles was visually confirmed. Subsequently, the 500 mL beaker was inverted for 1 minute to remove the solution, and the area of ​​the transparent resin particles remaining undissolved and adhering to the inside of the beaker was calculated as a ratio to the area of ​​the beaker in contact with the liquid during dissolution, which was set to 100%. [Polyvinyl acetal resin particles obtained in Comparative Examples 8, 9, and 10, and Examples 9 and 10] 235.2 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) as an organic solvent was placed in a 500 mL beaker. The temperature was maintained at 25°C, and while stirring with two stirring blades at a rotation speed of 200 rpm, 4.8 g of the obtained polyvinyl acetal resin particles were added to the solution to a concentration of 2% by weight, and the dissolution of the polyvinyl acetal resin particles was visually confirmed. Subsequently, the 500 mL beaker was inverted for 1 minute to remove the solution, and the area of ​​the transparent resin particles remaining undissolved and adhering to the inside of the beaker was calculated as a ratio to the area of ​​the beaker in contact with the liquid during dissolution, which was set to 100%.

[0057] [Table 1]

[0058] [Table 2]

[0059] [Table 3]

[0060] [Table 4]

[0061] [Table 5] [Industrial applicability]

[0062] 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, Porosity of 50% or more, porosity of pores with a pore radius of 7.5 to 0.075 μm of 98% or more, and specific surface area of ​​15 m². ２ Polyvinyl acetal resin particles having a concentration of 0.1 mol% to 20 mol% of acetyl groups in the polyvinyl acetal resin, and a degree of polymerization of 3300 to 8300.

2. Polyvinyl acetal resin particles according to claim 1, wherein the particle size distribution ε is 0.01 to 3.

00.

3. Polyvinyl acetal resin particles according to claim 1, wherein the particle size distribution ε is 0.01 to 2.

00.

4. Polyvinyl acetal resin particles according to claim 1 or 2, wherein the void ratio of pores with a pore radius of 7.5 to 1.0 μm is 80% or more.

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