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 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, if the average particle size is only reduced, the particles tend to float when added, and poor solvent impregnation of the particles tends to occur during dissolution, which may reduce the uniformity of the resin component.

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

[0008] The present invention relates to a porous porous material that contains a polyvinyl acetal resin, has a porosity of 50% or more, a porosity ratio of pores having a pore radius of 7.5 to 0.075 μm of 98% or more, and a specific surface area of ​​15 m 2 / g 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 present inventors have found that polyvinyl acetal resin particles having a high porosity, a large proportion of pores with a large pore radius, and a high specific surface area can be easily dissolved in an organic solvent even when added in a large amount, and are less likely to cause poor solvent impregnation during dissolution, resulting in excellent uniformity of the resin component. Furthermore, they have found that such polyvinyl acetal resin particles are less likely to adhere to a container after dissolution, and have completed the present invention.

[0010] The polyvinyl acetal resin particles of the present invention have a porosity of 50% or more. The lower limit of the porosity is 50%, so that the solubility in organic solvents can be increased. The lower limit of the porosity is preferably 55%, and more preferably 60%. The upper limit of the porosity is not particularly limited, but is preferably 80%. 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 98% 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 98%, 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 98.5%, and more preferably 99%. 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 preferably have a void ratio of pores having a radius of 7.5 to 1.0 μm of 80% or more. The lower limit of the void ratio of the pores having a radius of 7.5 to 1.0 μm is preferably 80%, which facilitates impregnation with an organic solvent and improves the solubility in the organic solvent. The lower limit of the void ratio of the pores having a radius of 7.5 to 1.0 μm is more preferably 83%, and even more preferably 85%. The upper limit of the void ratio of the pores having a radius of 7.5 to 1.0 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 1.0 μm refers to the ratio of the pore volume of pores having a pore radius of 7.5 to 1.0 μm to the pore volume of pores having a pore radius of 7.5 to 0.0038 μm. The void ratio of pores with a pore radius of 7.5 to 1.0 μm can be measured by mercury intrusion porosimetry using, for example, a porosimeter (Thermo Pascal 14B, manufactured by Thermo Fisher Scientific).

[0013] The polyvinyl acetal resin particles of the present invention have a specific surface area of ​​15 m 2 / g or more. The lower limit of the specific surface area is 15 m 2 A more preferable lower limit of the specific surface area is 17 m / g, which allows the organic solvent to easily penetrate the carbon fiber, thereby improving the solubility in the organic solvent. 2 / g, and a more preferable lower limit is 20m 2 The upper limit of the specific surface area is not particularly limited, but is preferably 40 m 2 It is preferred that the molecular weight is / g. In this specification, the specific surface area refers to the surface area per unit weight, and can be measured by mercury intrusion porosimetry using, for example, a porosimeter (Thermo Pascal 14B, manufactured by Thermo Fisher Scientific).

[0014] The polyvinyl acetal resin particles of the present invention preferably have a lower limit of D90 particle size of 30 μm and a higher limit of 1000 μm. The D90 particle size of 30 μm or more improves the solubility in organic solvents. The D90 particle size of 1000 μm or less allows the particles to be easily dispersed when dissolved in an organic solvent. The more preferred lower limit of D90 particle size is 50 μm and a more preferred upper limit is 800 μm. The polyvinyl acetal resin particles of the present invention preferably have a lower limit of 30 μm and an upper limit of 500 μm in terms of D50 particle size, more preferably a lower limit of 40 μm and an upper limit of 400 μm in terms of D50 particle size. Furthermore, the polyvinyl acetal resin particles of the present invention preferably have a lower limit of 10 μm and an upper limit of 300 μm in terms of the D10 particle size, more preferably a lower limit of 20 μm and an upper limit of 100 μm. The above "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, the "D50 particle size (D50)" refers to the particle size at which the cumulative frequency of the distribution reaches 50%, and the "D10 particle size (D10)" refers to the particle size at which the cumulative frequency of the distribution reaches 10%. The above D90, D50, and D10 can be measured, for example, using a laser diffraction particle size distribution measuring device (Mastersizer 3000, manufactured by Malvern Panalytical).

[0015] The polyvinyl acetal resin particles of the present invention preferably have a lower limit of 0.01 and an upper limit of 4.00. When the particle size distribution ε is 0.01 or more, the solubility in organic solvents is improved. When the particle size distribution ε is 4.00 or less, the particles can be easily dispersed when dissolved in an organic solvent. From the same viewpoint, the particle size distribution ε is more preferably 0.01 in lower limit, more preferably 3.00 in upper limit, and even more preferably 2.00 in upper limit. 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 10,000 or less. When the degree of polymerization of the polyvinyl acetal resin is 200 or more and 10000 or less, even if a large amount is added, the resin can be easily dissolved in an organic solvent, 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 mechanical strength variation of the obtained various sheets can be stabilized. From the same viewpoint, the preferable lower limit of the degree of polymerization of the polyvinyl acetal resin is 300, the preferable upper limit is 8500, the more preferable upper limit is 5500, and the even more preferable 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% or more and 80 mol% or less, 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. From the same viewpoint, the lower limit of the amount of acetal groups is more preferably 60 mol %, and the upper limit thereof is more preferably 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% or more and 50 mol% or less, even if the amount added is large, the resin can be easily dissolved in an organic solvent, 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 various sheets obtained can be stabilized. From the same viewpoint, the more preferred lower limit of the amount of hydroxyl groups is 22 mol%, and the more preferred upper limit is 45 mol%.

[0019] The polyvinyl acetal resin has a preferred lower limit of 0.1 mol% and a preferred upper limit of 20 mol% for the amount of acetyl groups. When the amount of acetyl groups is 0.1 mol% or more, compatibility with organic solvents can be improved. When the amount of acetyl groups is 20 mol% or less, the resin is less likely to become viscous during dissolution. From the same viewpoint, the more preferred lower limit of the amount of acetyl groups is 0.5 mol% and the 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 if a large amount is added, the polyvinyl acetal resin composition can be easily dissolved in an organic solvent and has excellent uniformity of the resin component. From the same viewpoint, the content of the polyvinyl acetal resin is more preferably 20% by weight at the lower limit and 80% by weight at 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 can be obtained by carrying out a step of acetalizing polyvinyl alcohol (acetalization 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 and the polyvinyl alcohol content (concentration) of the polyvinyl alcohol solution.

[0023] The polyvinyl alcohol content of the polyvinyl alcohol solution in the acetal step is preferably 1.0 to 7.0% by mass. By setting it within the above range, 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 suitably produced. From the same viewpoint, the polyvinyl alcohol content 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 taking into consideration 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 resin obtained through the above-mentioned production method may be used as the polyvinyl acetal resin particles of the present invention, and may further be granulated. The granulation method is not particularly limited, and examples thereof include a rolling granulation method, an extrusion granulation method, a compression granulation method, an agitation granulation method, a spray drying method, a dissolution solidification method, and a crushing granulation method. Effect of the Invention

[0030] 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. Furthermore, according to the present invention, it is possible to provide polyvinyl acetal resin particles that not only have excellent solubility but also show little adhesion to a container after dissolution. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 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 35% by weight hydrochloric acid, 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Example 7 200 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 3,440 g of pure water, and dissolved by stirring at a temperature of 90°C for approximately 2 hours to obtain a polyvinyl alcohol solution (polyvinyl alcohol concentration 5.3 mass%). Polyvinyl acetal resin particles were then obtained in the same manner as in Example 1, except that this solution was used.

[0044] Example 8 200 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 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.

[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 9 200 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 10 200 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, and the results are shown in Table 1.

[0052] (1) Porosity, pore ratio of pore radius 7.5 to 0.075 μm, pore ratio of pore radius 7.5 to 1.0 μm, specific surface area The obtained polyvinyl acetal resin particles were measured for porosity, pore ratio of pore radius 7.5 to 0.075 μm, pore ratio of pore radius 7.5 to 1.0 μm, and specific surface area by mercury intrusion method 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 pore ratio of pore radius 7.5 to 0.075 μm means the ratio of the pore volume of pore radius 7.5 to 0.0038 μm to the pore volume of pore radius 7.5 to 0.075 μm. In addition, the pore ratio of pore radius 7.5 to 1.0 μm means the ratio of the pore volume of pore radius 7.5 to 1.0 μm to the pore volume of pore radius 7.5 to 0.0038 μm.

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

[0054] (3)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% by weight) 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 resin did not dissolve even after 600 minutes had passed, or the viscosity of the resin when dissolved in the organic solvent was 5000 mPa·s or more. If the viscosity is 5000 mPa·s or higher, the solution will wrap around the stirring shaft due to the Weissenberg effect, making it impossible to perform a uniform evaluation. 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.

[0055] (4) Check the solvent impregnation state of particles [Polyvinyl acetal resin particles obtained in Comparative Examples 1, 2, and 5 and Examples 1, 2, and 6] 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 while keeping the temperature at 25°C and stirring at 200 rpm using two stirring blades, 48.0 g of the obtained polyvinyl acetal resin particles were added so that the solution concentration was 20 wt%, 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, and 7 and Examples 3, 4, 5, 7, and 8] 228 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) was placed in a 500 mL beaker as an organic solvent, and while keeping the temperature at 25°C and stirring at 200 rpm using two stirring blades, 12.0 g of the obtained polyvinyl acetal resin particles were added so that the solution concentration was 5 wt%, 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 as an organic solvent, and 4.8 g of the obtained polyvinyl acetal resin particles were added to the mixture at a solution concentration of 2 wt % while stirring at 200 rpm using two stirring blades while keeping the temperature at 25°C, and the polyvinyl acetal resin particles were dissolved. The state of the resin particles was visually observed, 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 adhesion to containers when particles dissolve [Polyvinyl acetal resin particles obtained in Comparative Examples 1 to 7 and Examples 1 to 8] A 500 mL beaker was charged with 228 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) as an organic solvent, the temperature was kept at 25°C, and 12.0 g of the obtained polyvinyl acetal resin particles were added while stirring at 200 rpm using two stirring blades so that the solution concentration was 5 wt%, and the dissolution of the polyvinyl acetal resin particles was visually confirmed. The 500 mL beaker was then inverted for one minute to remove the solution, and the area of ​​the transparent resin particles that remained undissolved and adhered to the inside of the beaker was calculated as a ratio with the area of ​​the beaker exposed to the liquid during dissolution being taken as 100%. [Polyvinyl acetal resin particles obtained in Comparative Examples 8, 9, and 10 and Examples 9 and 10] A 500 mL beaker was charged with 235.2 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) as an organic solvent, and the temperature was kept at 25°C. While stirring at 200 rpm using two stirring blades, 4.8 g of the obtained polyvinyl acetal resin particles were added so that the solution concentration was 2 wt%, and the dissolution of the polyvinyl acetal resin particles was confirmed visually. The 500 mL beaker was then inverted for one minute to remove the solution, and the area of ​​the transparent resin particles that remained undissolved and adhered to the inside of the beaker was calculated as a ratio with the area of ​​the beaker exposed to the liquid during dissolution being taken as 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 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 50% or more, the pore ratio of pores with a pore radius of 7.5 to 0.075 μm is 98% or more, and the specific surface area is 15 m ２ / g or more, and the polymerization degree of the polyvinyl acetal resin is 200 or more and 3,300 or less.

2. 2. The polyvinyl acetal resin particles according to claim 1, having a particle size distribution ε of 0.01 to 3.

00.

3. 3. The polyvinyl acetal resin particles according to claim 1, wherein the void ratio of pores having a pore radius of 7.5 to 1.0 μm is 80% or more.

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