Polyvinyl acetal resin particle

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 Art

[0002] Polyvinyl acetal resins such as polyvinyl butyral resin are used in various applications because they are excellent in toughness, film-forming property, dispersibility of particles, adhesiveness to a coating surface, and the like. As one of the uses of polyvinyl acetal resin, for example, a slurry composition or a conductive paste using a polyvinyl acetal resin such as polyvinyl butyral resin as a binder resin is disclosed.

[0003] The polyvinyl acetal resin used for these applications is generally used as a solution dissolved in an organic solvent such as methyl ethyl ketone, toluene, alcohol, or a mixture thereof. At that time, if the dissolution in the solvent is fast, the workability is improved. Increasing the surface area of the polyvinyl acetal resin particles is thought to improve the solubility because the contact area with the solvent increases, but actually, the particles will float on the liquid surface of the solvent, and the dissolution rate in the solvent is slow. In addition, if the polyvinyl acetal resin is inferior in solubility in an organic solvent, a small amount of undissolved matter will be generated when dissolved in the organic solvent, and the dispersibility of the particles will decrease.

[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 made of a polyvinyl acetal resin having a degree of polymerization of 500 or more, in which 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 Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-38456 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-225842 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] However, even the polyvinyl acetal resin particles disclosed in Patent Documents 1 and 2 actually have insufficient solubility in organic solvents, especially when the resin addition amount is large, the solubility is low. Further, simply reducing the average particle diameter makes the particles likely to float during addition, and it is likely that the solvent impregnation of the particles is poor during dissolution, and the uniformity of the resin component may decrease.

[0007] An object of the present invention is to provide polyvinyl acetal resin particles in which poor solvent impregnation of particles hardly occurs during dissolution, can be easily dissolved in an organic solvent even when the addition amount is large, and has excellent uniformity of the resin component. [Means for Solving the Problems]

[0008] The present invention is polyvinyl acetal resin particles containing a polyvinyl acetal resin, having a porosity of 50% or more, a porosity ratio of pores with 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 simply defining the particle diameter and bulk specific gravity as in the 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 with a high porosity, a large proportion of voids with a large pore radius, and a high specific surface area can be easily dissolved in an organic solvent even when the addition amount is large, and it is difficult for poor solvent impregnation of the particles to occur during dissolution, and the uniformity of the resin component is excellent. Further, it has been found that such polyvinyl acetal resin particles have little adhesion to the container after dissolution, and the present invention has been completed.

[0010] The polyvinyl acetal resin particles of the present invention have a porosity of 50% or more. By setting the lower limit of the porosity to 50%, it becomes possible to enhance the solubility in an organic solvent. The preferable lower limit of the porosity is 55%, and the more preferable lower limit is 60%. Further, the upper limit of the porosity is not particularly limited, but it is preferably 80%. In the present specification, the above porosity means the volume of voids with a pore radius of 7.5 to 0.0038 μm occupying the volume of the resin particles. The above porosity can be measured, for example, by the mercury intrusion method 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 with a pore radius of 7.5 to 0.075 μm. By setting the lower limit of the void ratio with a pore radius of 7.5 to 0.075 μm to 98%, the organic solvent is easily impregnated, so the solubility in the organic solvent is improved. The preferable lower limit of the void ratio with a pore radius of 7.5 to 0.075 μm is 98.5%, and the more preferable lower limit is 99%. Further, the upper limit of the void ratio with a pore radius of 7.5 to 0.075 μm is not particularly limited, but it is preferably 100%. In the present specification, the above void ratio with a pore radius of 7.5 to 0.075 μm represents the ratio of the void volume with a pore radius of 7.5 to 0.075 μm to the void volume with a pore radius of 7.5 to 0.0038 μm. The void ratio with a pore radius of 7.5 to 0.075 μm can be measured, for example, using a porosimeter (Thermo Pascal 14B, manufactured by Thermo Fisher Scientific.) by 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. When the lower limit of the void ratio with a pore radius of 7.5 to 1.0 μm is 80%, the organic solvent is easily impregnated, so the solubility in the organic solvent is improved. A more preferable lower limit of the void ratio with a pore radius of 7.5 to 1.0 μm is 83%, and a further preferable lower limit is 85%. The upper limit of the void ratio with a pore radius of 7.5 to 1.0 μm is not particularly limited, but is preferably 100%. In the present specification, the void ratio with a pore radius of 7.5 to 1.0 μm represents the ratio of the void volume with a pore radius of 7.5 to 1.0 μm to the void volume with a pore radius of 7.5 to 0.0038 μm. The void ratio with a pore radius of 7.5 to 1.0 μm can be measured, for example, using a porosimeter (Thermo Pascal 14B, manufactured by 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 m 2 / g or more. When the lower limit of the specific surface area is 15 m 2 / g, the organic solvent is easily impregnated, so the solubility in the organic solvent is improved. A more preferable lower limit of the specific surface area is 17 m 2 / g, and a further preferable lower limit is 20 m 2 / g. The upper limit of the specific surface area is not particularly limited, but is preferably 40 m 2 / g. In the present 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 of 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. When the D90 particle size is 30 μm or more, the solubility in an organic solvent is improved. When the D90 particle size is 1000 μm or less, it can be easily dispersed when dissolved in an organic solvent. The more preferred lower limit of the D90 particle size is 50 μm, and the more preferred upper limit is 800 μm. Also, the preferred lower limit of the D50 particle size of the polyvinyl acetal resin particles of the present invention is 30 μm, and the preferred upper limit is 500 μm. The more preferred lower limit of the D50 particle size is 40 μm, and the more preferred upper limit is 400 μm. Furthermore, the preferred lower limit of the D10 particle size of the polyvinyl acetal resin particles of the present invention is 10 μm, and the preferred upper limit is 300 μm. The more preferred lower limit of the D10 particle size is 20 μm, and the more preferred upper limit is 100 μm. The "D90 particle size (D90)" is the particle size at the point where the cumulative frequency of the distribution from the small particle side reaches 90% in the particle size distribution measurement. The "D50 particle size (D50)" is the particle size at the point where the cumulative frequency of the distribution reaches 50% in the same way. The "D10 particle size (D10)" is the particle size at the point where the cumulative frequency of the distribution reaches 10% in the same way. The above D90, D50, and D10 can be measured using, for example, a laser diffraction particle size distribution measuring device (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 more, the solubility in an organic solvent is improved. When the particle size distribution ε is 4.00 or less, it can be easily dispersed when dissolved in an organic solvent. From the same 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 further 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 10,000 or less. When the degree of polymerization of the polyvinyl acetal resin is 200 or more and 10,000 or less, even when the addition amount is large, it can be easily dissolved in an organic solvent, and a solution excellent in the uniformity of the resin component can be obtained. Therefore, it is possible to shorten the tact time in the dissolution step of the polyvinyl acetal resin and to stabilize the variation in the mechanical strength of various obtained sheets. 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 8,500, the more preferable upper limit is 5,500, and the further preferable upper limit is 5,000.

[0017] The amount of acetal groups in the polyvinyl acetal resin preferably has a lower limit of 40 mol% and an upper limit of 80 mol%, whether aldehyde is used alone or in combination of two or more. When the amount of acetal groups 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 of ink and dyes, and can impart sufficient flexibility to various obtained sheets. From the same viewpoint, the more preferable lower limit of the amount of acetal groups is 60 mol%, and the more preferable upper limit is 78 mol%. Regarding the calculation method of the amount of acetal groups, 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 adopted. In addition, 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 preferable lower limit of the amount of hydroxyl groups in the polyvinyl acetal resin is 20 mol%, and the preferable upper limit is 50 mol%. When the amount of hydroxyl groups is 20 mol% or more and 50 mol% or less, even when the addition amount is large, it can be easily dissolved in an organic solvent, and a solution excellent in the uniformity of the resin component can be obtained. Therefore, it is possible to shorten the tact time in the dissolution step of the polyvinyl acetal resin and to stabilize the variation in the mechanical strength of various obtained sheets. From the same viewpoint, the more preferable lower limit of the amount of hydroxyl groups is 22 mol%, and the more preferable upper limit is 45 mol%.

[0019] The preferable lower limit of the amount of acetyl groups in the polyvinyl acetal resin is 0.1 mol%, and the preferable upper limit is 20 mol%. When the amount of acetyl groups is 0.1 mol% or more, the compatibility with an organic solvent can be improved. When the amount of acetyl groups is 20 mol% or less, it is less likely to form lumps during dissolution. From the same viewpoint, the more preferable lower limit of the amount of acetyl groups is 0.5 mol%, and the more preferable upper limit is 15 mol%.

[0020] The content of the polyvinyl acetal resin in the polyvinyl acetal resin particles of the present invention preferably has a lower limit of 10% by weight and a preferable upper limit of 90% by weight. When the content of the polyvinyl acetal resin is within the above range, even when the addition amount is large, it can be easily dissolved in an organic solvent, and a polyvinyl acetal resin composition excellent in the uniformity of the resin component can be obtained. From the same viewpoint, the content of the polyvinyl acetal resin preferably has a 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 step of acetalizing polyvinyl alcohol (acetal step). Examples of the method for acetalizing the above polyvinyl alcohol include a method of adding various aldehydes to the above polyvinyl alcohol solution in the presence of an acid catalyst, etc. In particular, the polyvinyl acetal resin particles of the present invention having a predetermined degree of polymerization, porosity, void ratio of pores 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 acetalization step and the polyvinyl alcohol content (concentration) of the polyvinyl alcohol solution.

[0023] The polyvinyl alcohol content of the polyvinyl alcohol solution in the above acetalization 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, void ratio of pores with a pore radius of 7.5 to 0.075 μm, and specific surface area can be suitably produced. From the same viewpoint, the lower limit of the above polyvinyl alcohol content is more preferably 2.0% by mass, and the upper limit is more preferably 6.0% by mass. Note that the content of the above polyvinyl alcohol resin can be determined in consideration of the degree of polymerization of the polyvinyl alcohol resin used.

[0024] The preferable lower limit of the saponification degree of the above polyvinyl alcohol is 80 mol%. When the saponification degree of the above polyvinyl alcohol is less than 80 mol%, the water solubility deteriorates, making acetalization difficult, and also the amount of hydroxyl groups decreases, making acetalization itself difficult. The more preferable lower limit is 85 mol%. The upper limit is not particularly limited, but it is 99.9 mol%.

[0025] If the saponification degree of the polyvinyl alcohol at the time of acetalization is 80 mol% or more, the above polyvinyl alcohol may be used alone, or a polyvinyl alcohol with a saponification degree of 80 mol% or more and a polyvinyl alcohol with a saponification degree of less than 80 mol% may be mixed and used after adjusting the saponification degree to 80 mol% or more.

[0026] The above acid catalyst is not particularly limited, and either organic acid or inorganic acid can be used. Examples include acetic acid, p-toluenesulfonic acid, nitric acid, sulfuric acid, hydrochloric acid, etc. Among them, a non-halogenated acid catalyst is preferred.

[0027] The aldehyde used in the above acetalization is not particularly limited. For example, formaldehyde (including paraformaldehyde), acetaldehyde (including paraldehyde), propionaldehyde, butyraldehyde, amyl aldehyde, hexyl aldehyde, heptyl aldehyde, 2-ethylhexyl aldehyde, cyclohexyl aldehyde, furfural, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropionaldehyde, etc. can be mentioned. Among them, it is preferable to perform acetalization using acetaldehyde and / or butyraldehyde. These aldehydes may be used alone or in combination of two or more.

[0028] In order to stop the reaction of the above acetalization, it is preferable to perform neutralization with an alkali. The above alkali is not particularly limited. Examples include sodium hydroxide, potassium hydroxide, ammonia, sodium acetate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, etc. Also, before and after the above neutralization step, it is preferable to wash the modified polyvinyl acetal resin obtained using water or the like. In order to prevent the mixing of impurities contained in the washing water, it is more preferable to perform the washing with pure water.

[0029] The resin obtained through the above production method may be used as the polyvinyl acetal resin particles of the present invention, or may be further granulated. The method of the above granulation is not particularly limited. Examples include rolling granulation method, extrusion granulation method, compression granulation method, stirring granulation method, spray drying method, dissolution coagulation method, crushing granulation method, etc.

Advantages of the Invention

[0030] According to the present invention, even when the addition amount is large, it is possible to easily dissolve in an organic solvent, and it is possible to provide polyvinyl acetal resin particles that are less likely to have poor solvent impregnation of particles during dissolution and have excellent resin component uniformity. Further, according to the present invention, in addition to excellent solubility, it is possible to provide polyvinyl acetal resin particles with less adhesion to a container after dissolution.

Mode for Carrying Out the Invention

[0031] Examples will be given below to explain the present invention in more detail, but the present invention is not limited to these examples only.

[0032] (Example 1) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 300 and a saponification degree of 98.7 mol% was added to 3050 g of pure water, and stirred and dissolved at a temperature of 90 ° C for about 2 hours to obtain a polyvinyl alcohol solution (polyvinyl alcohol concentration 5.9 mass%). This solution was cooled to 40 ° C, and 240 g of 35% hydrochloric acid and 116 g of n-butyl aldehyde corresponding to a concentration of 7.9% by weight based on the amount of pure water added were added thereto. The liquid temperature was lowered to 5 ° C and this temperature was maintained to carry out an acetalization reaction, and the reaction product was precipitated. Then, the liquid temperature was set to 25 ° C and held for 3 hours to complete the reaction, and neutralization, washing with water, and drying were carried out by a conventional method 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 measured using C-NMR (nuclear magnetic resonance spectrum) was 35.7 mol%, the amount of acetyl groups was 1.3 mol%, and the degree of butyralization was 63.0 mol%.

[0033] (Comparative Example 1) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 300 and a saponification degree of 98.7 mol% was added to 1300 g of pure water and stirred at 90 °C for about 2 hours to dissolve, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 12.9 mass%). Then, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0034] (Example 2) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 700 and a saponification degree of 98.5 mol% was added to 3200 g of pure water and stirred at 90 °C for about 2 hours to dissolve, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 5.7 mass%). Then, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0035] (Comparative Example 2) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 700 and a saponification degree of 98.5 mol% was added to 1000 g of pure water and stirred at 90 °C for about 2 hours to dissolve, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 16.1 mass%). Then, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0036] (Example 3) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 1700 and a saponification degree of 98.8 mol% was added to 3300 g of pure water and stirred at 90 °C for about 2 hours to dissolve, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 5.5 mass%). Then, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0037] (Comparative Example 3) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 1700 and a saponification degree of 98.8 mol% was added to 1400 g of pure water and stirred at 90 °C for about 2 hours to dissolve, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 12.1 mass%). Then, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0038] (Example 4) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 3300 and a saponification degree of 99.2 mol% was added to 4300 g of pure water, and stirred at 90 °C for about 2 hours to dissolve, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 4.3 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0039] (Example 5) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 3300 and a saponification degree of 99.2 mol% was added to 5700 g of pure water, and stirred at 90 °C for about 2 hours to dissolve, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 3.3 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0040] (Comparative Example 4) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 3300 and a saponification degree of 99.2 mol% was added to 2300 g of pure water, and stirred at 90 °C for about 2 hours to dissolve, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 7.7 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0041] (Example 6) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 500 and a saponification degree of 98.8 mol% was added to 2600 g of pure water, and stirred at 90 °C for about 2 hours to dissolve, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 6.9 mass%). After that, except that 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 with a degree of polymerization of 500 and a saponification degree of 98.8 mol% (purity 96.5%) was added to 1050 g of pure water, and the mixture was stirred at 90 °C for about 2 hours to dissolve it, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 15.4 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 6 except that this solution was used.

[0043] (Example 7) 200 g of polyvinyl alcohol with a degree of polymerization of 3300 and a saponification degree of 99.2 mol% (purity 96.5%) was added to 3440 g of pure water, and the mixture was stirred at 90 °C for about 2 hours to dissolve it, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 5.3 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0044] (Example 8) 200 g of polyvinyl alcohol with a degree of polymerization of 4000 and a saponification degree of 99.1 mol% (purity 96.5%) was added to 6000 g of pure water, and the mixture was stirred at 90 °C for about 2 hours to dissolve it, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 4.9 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

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

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

[0047] (Example 9) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 5400 and a saponification degree of 99.3 mol% was added to 6700 g of pure water, and the mixture was stirred at 90 °C for about 2 hours to dissolve it, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 2.8 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0048] (Example 10) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 8300 and a saponification degree of 99.0 mol% was added to 13600 g of pure water, and the mixture was stirred at 90 °C for about 2 hours to dissolve it, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 1.4 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0049] (Comparative Example 8) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 5400 and a saponification degree of 99.3 mol% was added to 4200 g of pure water, and the mixture was stirred at 90 °C for about 2 hours to dissolve it, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration: 4.4 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

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

[0051] (Evaluation) The following evaluations were performed on the polyvinyl acetal resin particles obtained in the examples and comparative examples. The results are shown in Table 1.

[0052] (1) Porosity, void ratio with pore radius of 7.5 to 0.075 μm, void ratio with pore radius of 7.5 to 1.0 μm, specific surface area For the obtained polyvinyl acetal resin particles, a porosimeter (Thermo Pascal 14B) was used to measure the porosity, void ratio with pore radius of 7.5 to 0.075 μm, void ratio with pore radius of 7.5 to 1.0 μm, and specific surface area by mercury intrusion method. The porosity means the volume of voids with pore radius of 7.5 to 0.0038 μm in the volume of the resin particles, and the void ratio with pore radius of 7.5 to 0.075 μm means the ratio of the volume of voids with pore radius of 7.5 to 0.075 μm to the volume of voids with pore radius of 7.5 to 0.0038 μm. Also, the void ratio with pore radius of 7.5 to 1.0 μm means the ratio of the volume of voids with pore radius of 7.5 to 1.0 μm to the volume of voids with pore radius of 7.5 to 0.0038 μm.

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

[0054] (3) Solubility 192 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 at 200 rpm using two stirring blades, 48.0 g (concentration 20 wt%) of the obtained polyvinyl acetal resin particles was added to dissolve the polyvinyl acetal resin particles. Visual observation was carried out, and the dissolution time from the addition of the obtained polyvinyl acetal resin particles until no undissolved resin remained was measured. Similarly, the dissolution times were also measured for concentrations of 10 wt%, 5 wt%, 3 wt%, and 2 wt%. Note that "insoluble" means that it did not dissolve even after 600 minutes had passed or the viscosity when dissolved in the organic solvent was 5000 mPa·s or more. When the viscosity is 5000 mPa·s or more, due to the Weissenberg effect, the solution wraps around the stirring shaft and the same evaluation cannot be performed. Furthermore, the multiple of the dissolution time with respect to the dissolution time at the lowest concentration (dissolution time multiple) was calculated for each concentration other than the lowest concentration and shown in a table. Note that "-" in the table means that the dissolution time multiple could not be calculated.

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

[0056] (5) Evaluation of container adhesion during particle dissolution [Polyvinyl acetal resin particles obtained in Comparative Examples 1 to 7 and Examples 1 to 8] Put 228 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) as an organic solvent into a 500 mL beaker, keep the temperature at 25°C, use two stirring blades, and while stirring at a rotation speed of 200 rpm, add 12.0 g of the obtained polyvinyl acetal resin particles so that the solution concentration becomes 5% by weight, and visually confirm the dissolution of the polyvinyl acetal resin particles. Then, turn the 500 mL beaker upside down for 1 minute to remove the solution, and determine the ratio of the area of the transparent resin particles remaining undissolved and adhering to the inside of the beaker with respect to the contact area of the beaker during dissolution, assuming the contact area of the beaker during dissolution is 100%. [Polyvinyl acetal resin particles obtained in Comparative Examples 8, 9, 10 and Examples 9, 10] Put 235.2 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) as an organic solvent into a 500 mL beaker, keep the temperature at 25°C, use two stirring blades, and while stirring at a rotation speed of 200 rpm, add 4.8 g of the obtained polyvinyl acetal resin particles so that the solution concentration becomes 2% by weight, and visually confirm the dissolution of the polyvinyl acetal resin particles. Then, turn the 500 mL beaker upside down for 1 minute to remove the solution, and determine the ratio of the area of the transparent resin particles remaining undissolved and adhering to the inside of the beaker with respect to the contact area of the beaker during dissolution, assuming the contact area of the beaker during dissolution is 100%.

[0057]

Table 1

[0058]

Table 2

[0059]

Table 3

[0060]

Table 4

[0061]

Table 5

Industrial Applicability

[0062] According to the present invention, even when the addition amount is large, it is possible to easily dissolve in an organic solvent, and it is possible to provide polyvinyl acetal resin particles that are less likely to cause poor solvent impregnation of particles during dissolution and have excellent resin component uniformity.

Claims

1. containing a polyvinyl acetal resin, Polyvinyl acetal resin particles having a porosity of 50% or more, a void ratio of 98% or more with a pore radius of 7.5 to 0.075 μm, and a specific surface area of 15 m ２ / g or more.

2. The polyvinyl acetal resin particles according to Claim 1, wherein the particle size distribution ε is from 0.01 to 3.

00.

3. The polyvinyl acetal resin particles according to Claim 1 or 2, wherein the void ratio with a pore radius of 7.5 to 1.0 μm is 80% or more.

4. The polyvinyl acetal resin particles according to any one of Claims 1 to 3, wherein the degree of polymerization of the polyvinyl acetal resin is 200 or more and 10,000 or less.

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