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

Description

Technical Field

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

Background 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 in 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, a content ratio 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 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, and particularly have low solubility when the resin addition amount is large. Further, simply reducing the average particle diameter may cause the particles to easily float during addition, and the uniformity of the resin component may decrease.

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

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

[0009] The present inventors have found that 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. It has been found that polyvinyl acetal resin particles having a low porosity, a large proportion of voids with a large pore radius, and defining the ratio of passing and non-passing particles when passing through a predetermined JIS standard sieve can be easily dissolved in an organic solvent even when the addition amount is large. Further, it has been found that poor solvent impregnation of the particles hardly occurs during dissolution and the resin component has excellent uniformity, leading to the completion of the present invention.

[0010] The polyvinyl acetal resin particles of the present invention have a porosity of 30% or more. By setting the lower limit of the porosity to 30%, it becomes possible to enhance the solubility in an organic solvent. The preferable lower limit of the porosity is 32%, and the more preferable lower limit is 35%. Further, the upper limit of the porosity is not particularly limited, but is preferably 40%. In the present specification, the porosity means the volume of voids 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 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 90% 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 90%, the organic solvent is easily impregnated, so that 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 92%, and the more preferable lower limit is 95%. Further, the upper limit of the void ratio with a pore radius of 7.5 to 0.075 μm is not particularly limited, but is preferably 100%. In the present specification, the 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 have a content ratio of particles passing through a JIS standard sieve with an opening of 250 μm of 10% by weight or less. By having a content ratio of particles passing through the JIS standard sieve with an opening of 250 μm of 10% by weight or less, floating of the particles during addition can be suppressed, and the generation of lumps during dissolution can be prevented. The preferable upper limit of the content ratio of particles passing through the JIS standard sieve with an opening of 250 μm is 5.0% by weight, and the more preferable upper limit is 3.0% by weight. Further, the lower limit of the content ratio of particles passing through the JIS standard sieve with an opening of 250 μm is not particularly limited, but it is preferably 0% by weight. In this specification, the sieve conforms to JIS Z8801. Also, the presence or absence of passing through the JIS standard sieve was visually determined. The content ratio of particles passing through the JIS standard sieve with an opening of 250 μm is calculated by "[(weight of particles that passed through all JIS standard sieves) / (weight of all particles)]×100" when sieving the particles by installing JIS standard sieves with openings of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm, and 250 μm in this order.

[0013] The polyvinyl acetal resin particles of the present invention have a content ratio of particles not passing through a JIS standard sieve with an opening of 2830 μm of 10% by weight or less. By having a content ratio of the particles of 10% by weight or less, particles with a large aspect ratio can be removed. The preferable upper limit of the content ratio of particles not passing through the JIS standard sieve with an opening of 2830 μm is 8.0% by weight, and the more preferable upper limit is 7.0% by weight. Further, the lower limit is not particularly limited, but it is preferably 0% by weight. In this specification, the sieve conforms to JIS Z8801. In addition, the content ratio of particles that do not pass through the JIS standard sieve with an aperture of 2830 μm is calculated from the following formula when sieving the particles by sequentially installing JIS standard sieves with apertures of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm, and 250 μm. "[(Total weight of particles that do not pass through the JIS standard sieves with apertures of 4000 μm, 3350 μm, and 2830 μm) / (Total weight of all particles)] × 100"

[0014] The polyvinyl acetal resin particles of the present invention pass through the JIS standard sieve with an aperture of 2830 μm, and the content ratio of particles that do not pass through the JIS standard sieve with an aperture of 1700 μm is 45% by weight or more. By having the content ratio of the above particles be 45% by weight or more, particles with a uniform aspect ratio can be obtained. The preferable upper limit of the content ratio of the above particles is 100% by weight. Also, the lower limit of the content ratio of the above particles is preferably 48% by weight, and more preferably 50% by weight. In this specification, the above sieves conform to JIS Z8801. In addition, the content ratio of particles that pass through the JIS standard sieve with an aperture of 2830 μm and do not pass through the JIS standard sieve with an aperture of 1700 μm is calculated from the following formula when sieving the particles by sequentially installing JIS standard sieves with apertures of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm, and 250 μm. [(Weight of particles that do not pass through the JIS standard sieve with an aperture of 1700 μm) / (Total weight of all particles)] × 100

[0015] The polyvinyl acetal resin particles of the present invention have a content ratio of particles that pass through a rat tester (JIS standard sieve with an aperture of 1180 μm) of 3.0% by weight or less. By having the content ratio of the above particles be 3.0% by weight or less, it is possible to obtain powder that is difficult to break and particles with a uniform aspect ratio. The preferable lower limit of the content ratio of the above particles is 1.0% by weight, and the more preferable upper limit is preferably 2.0% by weight. In this specification, the above sieves conform to JIS Z8801. When passing through the above-mentioned rattler tester (JIS standard sieve with an aperture of 1180 μm), for example, it is carried out under the conditions of 87 rpm and 1000 rotations.

[0016] The polyvinyl acetal resin particles of the present invention preferably contain a polyvinyl acetal resin having a degree of polymerization of 200 or more and 10,000 or less. When within the above range, even when the amount of the resin added 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. The more preferable lower limit of the degree of polymerization of the polyvinyl acetal resin is 300, the more preferable upper limit is 8500, the further preferable upper limit is 5500, and the particularly preferable upper limit is 5000.

[0017] The amount of acetal groups in the above polyvinyl acetal resin preferably has a lower limit of 40 mol% and an upper limit of 80 mol%, whether aldehyde is used alone or two or more kinds are used in combination. When the amount of acetal groups is from 40 mol% to 80 mol%, the polyvinyl acetal resin can be dissolved in a wide variety of solvents without aggregation, and can impart dispersibility of ink and dyes, and sufficient flexibility to various obtained sheets. 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 group, and when the acetal group is a butyral group, it is also referred to as the amount of butyral group.

[0018] The preferable lower limit of the amount of hydroxyl groups in the above polyvinyl acetal resin is 20 mol%, and the preferable upper limit is 50 mol%. When the amount of hydroxyl groups is from 20 mol% to 50 mol%, even when the addition amount is large, it can be easily dissolved in an organic solvent, and a solution with excellent resin component uniformity can be obtained. Therefore, it is possible to shorten the tact time in the dissolution process of the polyvinyl acetal resin and stabilize the variation in the mechanical strength of various obtained sheets. A more preferable lower limit of the amount of hydroxyl groups is 22 mol%, and a more preferable upper limit is 45 mol%.

[0019] The preferable lower limit of the amount of acetyl groups in the above 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. A more preferable lower limit of the amount of acetyl groups is 0.5 mol%, and a more preferable upper limit is 15 mol%.

[0020] The content of the above 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 above 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 with excellent resin component uniformity can be obtained. The content of the above 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 can be obtained by performing an acetalization step (acetal step) of polyvinyl alcohol and a granulation step. Examples of the method for acetalizing the polyvinyl alcohol include a method of adding 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, void ratio of pore radius 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 step, the polyvinyl alcohol content (concentration) of the polyvinyl alcohol solution, and the granulation step.

[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, void ratio of pore radius 7.5 to 0.075 μm, content ratio of particles passing through a JIS standard sieve with an aperture of 250 μm, and ratio of passing and non-passing particles when passing through a predetermined JIS standard sieve can be preferably produced. The more preferable lower limit of the content of the polyvinyl alcohol resin is 2.0% by mass, and the more preferable upper limit is 6.0% by mass. The content of the polyvinyl alcohol resin can be determined in consideration of the degree of polymerization of the polyvinyl alcohol resin used.

[0024] The preferable lower limit of the saponification degree of the polyvinyl alcohol is 80 mol%. When the saponification degree of the 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 preferable upper limit is not particularly limited, but is 99.9 mol%.

[0025] When acetalizing, if the saponification degree of the polyvinyl alcohol is 80 mol% or more, the 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 an organic acid or an inorganic acid can be used. For example, acetic acid, p-toluenesulfonic acid, nitric acid, sulfuric acid, hydrochloric acid, etc. can be mentioned. Among them, a non-halogenated acid catalyst is preferred.

[0027] The aldehyde used for the above acetalization is not particularly limited. For example, formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), 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. For example, sodium hydroxide, potassium hydroxide, ammonia, sodium acetate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, etc. can be mentioned. 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 granulation process in the above manufacturing method is not particularly limited. For example, methods such as compressing and crushing particulate raw resin, heating the raw resin to a temperature at which the resin softens but does not fuse, mixing raw resins with a low softening temperature, using a raw resin containing a small amount of organic solvent, water, etc. can be used. Specifically, a rolling type (drum type, inclined pan type, etc.), a vibration type (horizontal type, inclined type, etc.), a compression molding type (tablet press, briquetting machine, roll machine, etc.), a crushing type (crusher), a mixing type (blender type, pin type, etc.), a fluidized type (fluidized bed type, jet fluidized bed type, etc.), an extrusion molding type (screw type, hot cut pellet type, etc.) or a combination of two or more types can be used. Among them, a method of using a two-roll compression molding machine and a crusher in combination with two or more types is preferred.

[0030] The above-mentioned crusher is not particularly limited, but a flake breaker, a hammer mill, a feather mill, a cutter mill, a roll mill, a rotary disk mill, etc. are preferred. In addition, in order to prevent the resin from fusing due to heat generation during crushing, those having a cooling function such as a water-cooled jacket in the crushing part of the crusher are preferred. Also, the crushing conditions (rotation speed, screen, etc.) are not particularly limited and can be selected so that the obtained granulated resin has a desired particle shape.

Advantages of the Invention

[0031] According to the present invention, even when the addition amount is large, it can be easily dissolved in an organic solvent, and it is possible to provide polyvinyl acetal resin particles in which poor solvent impregnation of particles hardly occurs during dissolution and which are excellent in the uniformity of the resin component.

Embodiments for Carrying Out the Invention

[0032] Examples are given below to explain the present invention in more detail, but the present invention is not limited only to these examples.

[0033] (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 hydrochloric acid with a concentration of 35 wt% corresponding to a concentration of 7.9 wt% based on the amount of pure water added and 116 g of n-butylaldehyde 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. Thereafter, the liquid temperature was set to 25 °C and maintained 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 13C-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%. The raw material powder of the obtained polyvinyl acetal resin was compression-molded by two rolls at a unit area pressure of 5 kg / cm 2 and pulverized with a crusher to obtain polyvinyl acetal resin particles.

[0034] (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 and dissolved at a temperature of 90 °C for about 2 hours to obtain a polyvinyl alcohol solution (polyvinyl alcohol concentration 12.9 mass%). Thereafter, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0035] (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 and dissolved at a temperature of 90 °C for about 2 hours to obtain a polyvinyl alcohol solution (polyvinyl alcohol concentration 5.7 mass%). Thereafter, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0036] (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 a temperature of 90°C for about 2 hours to dissolve it, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 16.1 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0037] (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 a temperature of 90°C for about 2 hours to dissolve it, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 5.5 mass%). After that, polyvinyl acetal resin particles were obtained in the same manner as in Example 1 except that this solution was used.

[0038] (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 a temperature of 90°C for about 2 hours to dissolve it, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 12.1 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 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 a temperature of 90°C for about 2 hours to dissolve it, 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.

[0040] (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.

[0041] (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.

[0042] (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.

[0043] (Comparative Example 5) 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 1050 g of pure water and stirred at 90 °C for about 2 hours to dissolve, 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.

[0044] (Example 7) 200 g (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 4000 and a saponification degree of 99.1 mol% was added to 6000 g of pure water and stirred at 90 °C for about 2 hours to dissolve it, obtaining a polyvinyl alcohol solution (polyvinyl alcohol concentration 3.1 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 (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 4000 and a saponification degree of 99.1 mol% was added to 3700 g of pure water and 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 (purity 96.5%) of polyvinyl alcohol with a degree of polymerization of 4000 and a saponification degree of 99.1 mol% was added to 2480 g of pure water and 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 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 6700 g of pure water and 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 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 13600 g of pure water and 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 of polyvinyl alcohol with a polymerization degree of 5400 and a saponification degree of 99.3 mol% (purity 96.5%) was added to 4200 g of pure water, and the mixture was stirred and dissolved at 90 °C for about 2 hours to obtain 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 of polyvinyl alcohol with a polymerization degree of 8300 and a saponification degree of 99.0 mol% (purity 96.5%) was added to 6400 g of pure water, and the mixture was stirred and dissolved at 90 °C for about 2 hours to obtain 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 Tables 1 to 4.

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

[0053] (2) Passing test of JIS standard sieve For the obtained polyvinyl acetal resin particles, a horizontal gyratory sieve machine (manufactured by AS ONE, gyration radius φ30 mm) with JIS standard sieves having mesh openings of 4000 μm, 3350 μm, 2830 μm, 1700 μm, 1000 μm, 710 μm, and 250 μm installed in seven consecutive stages in this order was used, and classification was performed for 1 minute at a rotation speed of 200 rpm. Then, the content ratio of the particles that did not pass through each JIS standard sieve (φ200 × height 45 mm), and the content ratio of the particles that passed through all the JIS standard sieves were measured. The presence or absence of passing through each of the above JIS standard sieves was determined visually, and the content ratio of the particles that did not pass through each JIS standard sieve was calculated from "[(weight of the passing particles that did not pass through each JIS standard sieve) / (total particle weight)] × 100". The table showed the "total content ratio of those not passing through mesh openings of 4000 μm, 3350 μm, and 2830 μm". This indicates the "content ratio of the particles that did not pass through the JIS standard sieve with a mesh opening of 2830 μm". In addition, the "content ratio of passing through all the sieves" in the table indicates the "content ratio of the particles that passed through the JIS standard sieve with a mesh opening of 250 μm", and the "content ratio of not passing through a mesh opening of 1700 μm" in the table indicates the "content ratio of the particles that passed through the JIS standard sieve with a mesh opening of 2830 μm and did not pass through the JIS standard sieve with a mesh opening of 1700 μm".

[0054] (3) Rattray test For the obtained polyvinyl acetal resin particles, a Rattray tester (manufactured by Minerva Instruments, JIS standard sieve with a mesh opening of 1180 μm) was used, and the sieve was passed through at 87 rpm for 1000 rotations, and the content ratio of the particles that passed through the JIS standard sieve with a mesh opening of 1180 μm, and the content ratio of the particles that did not pass through were measured. The presence or absence of passing was determined visually, and the content ratio of the particles that passed through the JIS standard mesh opening of 1180 μm was calculated from "[(weight passing through a mesh opening of 1180 μm) / (total particle weight)] × 100".

[0055] (4) Solubility Place 192 g of a mixed solvent of ethanol and toluene (weight ratio 1:1) as an organic solvent in a 500 mL beaker, keep the temperature at 25°C, and while stirring at 200 rpm using two stirring blades, add 48.0 g (concentration 20% by weight) of the obtained polyvinyl acetal resin particles to dissolve the polyvinyl acetal resin particles. Visually observe and measure the dissolution time from the addition of the obtained polyvinyl acetal resin particles until no undissolved resin remains. Similarly, the dissolution times were measured for concentrations of 10% by weight, 5% by weight, 3% by weight, and 2% by weight. Note that "not possible" 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 case and shown in a table. Note that "-" in the table means that the dissolution time multiple could not be calculated.

[0056]

Table 1

[0057]

Table 2

[0058]

Table 3

[0059]

Table 4

[0060]

Table 5

Industrial Applicability

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

Claims

1. containing a polyvinyl acetal resin, having a porosity of 30% or more and a void ratio of 90% or more with a pore radius of 7.5 to 0.075 μm, the content ratio of particles passing through a JIS standard sieve with an opening of 250 μm being 10% by weight or less, the content ratio of particles not passing through a JIS standard sieve with an opening of 2830 μm being 10% by weight or less, and the content ratio of particles passing through a JIS standard sieve with an opening of 2830 μm and not passing through a JIS standard sieve with an opening of 1700 μm being 45% by weight or more, polyvinyl acetal resin particles.

2. The polyvinyl acetal resin particles according to claim 1, wherein the degree of polymerization of the polyvinyl acetal is 200 or more and 10,000 or less.

Images