JP4199366B2 - Dispersion method of foamable microcapsule wet cake - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for dispersing a foamable microcapsule wet cake in which a foamable microcapsule wet cake in which a volatile substance is encapsulated in a thermoplastic resin outer shell can be dissociated and dispersed to form foamable fine particles.
[0002]
[Prior art]
Expandable microcapsules encapsulating a volatile substance in a thermoplastic resin shell have the property of easily foaming by heating to form fine foamed particles, and thus are used in various applications. For example, use as a paint additive, plastic filler, etc. for weight reduction, use of a sealing agent additive by utilizing volume expansion by foaming, or use of surface irregularities formed by foaming Thus, it is widely used in various fields such as an additive for foaming ink and wallpaper, and an additive for textile processing agents.
[0003]
This type of expandable microcapsule has almost a solvent action on a monomer that can be polymerized to form a thermoplastic resin and a thermoplastic resin, as described in JP-B-42-26524. It is obtained by a method (suspension polymerization method) or the like of preparing a suspension containing a non-liquid volatile substance (foaming agent) and a dispersion stabilizer and polymerizing monomers in the suspension.
[0004]
According to the suspension polymerization method as described above, fine foamable microcapsules having a particle size of about 10 to 100 μm are obtained, and the obtained foamable microcapsules are stored in a plastic bag or a container bag and distributed. ing. Since the foamable microcapsules obtained by the suspension polymerization method are usually in a wet state containing about 20 to 40% of moisture, the fine foamable microcapsules are aggregated to form a huge wet cake. .
[0005]
The foamable microcapsule that has become such a huge wet cake is dissociated and dispersed into fine foamable particles when used as an additive for paints, plastics, sealing agents, foamable inks, etc. For this reason, conventionally, water is added to a wet cake and stirred with a homomixer, a disper, a propeller stirrer, ultrasonic waves or the like to obtain an aqueous dispersion of about 2 to 30%. Added to various uses.
[0006]
[Problems to be solved by the invention]
However, it is not easy to disperse the wet cake of expandable microcapsules into the expandable particle state again, and even if redispersion is attempted by the above-described method, the aggregated particles are difficult to loosen and there is a variation in particle size. Become very large. There has been a problem in that good results cannot be obtained even when such expandable particles having a very large variation in particle size are used in various applications. In addition, when stirring strongly to increase dispersibility, the foamable microcapsules are foamed or broken due to heat or mechanical impact generated during stirring, and the foamability is not lowered. .
[0007]
Furthermore, since the conventional methods as described above are those in which water is further added to a wet cake containing 20 to 40% of water to obtain an aqueous dispersion, the purpose is to add to an aqueous system. However, it cannot be used for the purpose of addition to a non-aqueous system. For the purpose of addition to a non-aqueous system, it is necessary to dry the wet cake to remove moisture and then disperse it in a non-aqueous solvent. Even if a homogenizer, a disper, a propeller stirrer, an ultrasonic wave or the like as described above is used, it is extremely difficult to dissociate and disperse the foam into uniform foamable particles.
[0008]
The present invention has been made in view of the above points. The microcapsule can be obtained by simply drying the foamed microcapsule wet cake under normal pressure or a reduced pressure of 50 mmHg or more while applying vibration. Dispersion method of foamable microcapsule wet cake that can dissociate and disperse wet cake into uniform foamable fine particle state without foaming or breaking, and without performing operations such as grinding after drying Is intended to provide.
[0009]
[Means for Solving the Problems]
That is, the method for dispersing the foamable microcapsule wet cake of the present invention is performed under a reduced pressure of normal pressure to 50 mmHg or more while applying vibration to the wet cake of the foamable microcapsule encapsulating a volatile substance in the outer shell of the thermoplastic resin. Thus, the wet cake is dissociated and dispersed by drying treatment so that the moisture content in the wet cake is 5% or less to obtain expandable microparticles.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Examples of the thermoplastic resin constituting the outer shell of the foamable microcapsule in the present invention include homopolymers and copolymers obtained from monomers such as acrylonitrile, vinyl chloride, methacrylate, vinylidene chloride, and styrene. It is not limited to these as long as it can form an outer shell that encloses the substance.
[0011]
On the other hand, as the volatile substance encapsulated in the outer shell of the thermoplastic resin, a compound that does not substantially dissolve the thermoplastic resin but can expand by heating to foam the thermoplastic outer shell is used. . As such a compound, for example, a compound similar to a compound usually used as a foaming agent for a thermoplastic resin can be used, such as hydrocarbons such as butane, pentane and hexane. Foamable microcapsules enclosing such a volatile substance in the outer shell of a thermoplastic resin can be obtained by the method described in Japanese Patent Publication No. 42-26524, etc., but Matsumoto Microsphere (Matsumoto Wet cakes containing about 15 to 40% moisture under the trade names such as Yushi Seiyaku Co., Ltd. and Expancel (Expancel) are also commercially available.
[0012]
In the method of the present invention, the foamable microcapsule obtained by the method described in the above Japanese Patent Publication No. 42-26524 or a wet cake of a commercially available foamable microcapsule is subjected to normal pressure or a reduced pressure of 50 mmHg or more while applying vibration. In order to obtain foamable fine particles by dissociating and dispersing the wet cake by drying the wet cake so that the moisture content is 5% or less, if the temperature inside the dryer is too low, It takes a long time until the water content becomes 5% or less, and if the temperature is too high, the foamable microcapsules will foam. Therefore, the foaming microcapsule has a foaming start temperature of −60 ° C. or lower. It is preferable to dry-process with. When the inside of the dryer is decompressed to less than 50 mmHg when the wet cake is dried, the foaming agent is volatilized from the foamable microcapsules, and the microcapsules cannot be uniformly foamed. The inside of the dryer when drying the microcapsule wet cake is more preferably set to a normal pressure or a reduced pressure of 80 mmHg or more.
[0013]
As a dryer used for drying the microcapsule wet cake in the present invention, a commercially available vibratory dryer (for example, manufactured by Chuo Kako) can also be used. Any wet cake can be applied as long as it can be vibrated and can be dried at normal or reduced pressure. For example, a dryer provided with a pressure reducing mechanism may be set in a separate vibrator and used. As described above, the temperature during the drying treatment is preferably 25 ° C. or more and the foaming start temperature of the foamable microcapsule is −60 ° C. or less. Therefore, heating means such as hot water heating, steam heating, and electric heating are provided. Preferably it is. The frequency of vibration applied to the wet cake by the vibration type dryer during the drying process is preferably 30 times / minute or more when the amount of the wet cake to be processed is about 1 kg or less, and particularly when the amount is larger than that, the wet cake When the amount is 10 kg or more, it is preferable to apply vibration of 1000 to 2000 times / minute.
[0014]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1
The dryer has a double structure of an inner container and an outer container (inner container inner diameter: 15 cm, length 20 cm), and is provided with a stainless steel container configured to supply hot water between the inner and outer containers, and the inner container A structure having a pressure-removing line for removing moisture generated from the wet cake was used. In the inner container of this dryer, a wet cake of a foamable microcapsule (Matsumoto Microsphere F-80S: Matsumoto Yushi Seiyaku Co., Ltd., average particle size 26.7μ) having an acrylonitrile-based copolymer as an outer shell (containing water) (Rate 30%) 500 g was added and the inner container was closed, and then the dryer was set on a vibrator. The inside of the container was depressurized to 200 mmHg, and 40 ° C. warm water was supplied between the inner and outer containers to heat the wet cake stored in the inner container, and drying treatment was performed while applying 50 reciprocating vibrations for 3 hours per minute. The water content of the obtained dried product was 1.2%. The dried product was dispersed in ion-exchanged water, and the size of the dispersed particles was measured with a laser analysis particle size measuring device (manufactured by Shimadzu Corporation). The average particle size was 26.9 μm, which is the average of the original foamable microcapsules. It was a fine particle having a particle size substantially equal to the particle size. After preparing a 1% dioctyl phthalate dispersion of these microparticles and heating them in a drier prepared at 170 ± 2 ° C. for 2 minutes, the foamed state was observed with a microscope. It was foamed and almost no foam was destroyed and foamed aggregated particles were not recognized.
[0015]
Comparative Example 1
The same treatment as in Example 1 was performed except that the inside of the container was depressurized to 40 mmHg during the drying treatment. The water content of the obtained dried product was 0.6%. When this dried product was dispersed in ion-exchanged water and the size of the dispersed particles was measured in the same manner as in Example 1, the average particle size was 26.8 μm, which was substantially equal to the average particle size of the original foamable microcapsules. It was a fine particle with a particle size. A 1% dioctyl phthalate dispersion of these microparticles was prepared, heated in a dryer adjusted to 170 ± 2 ° C. for 2 minutes, and then observed for foaming with a microscope. The foaming agent was volatilized from the inside of the foamable microcapsules, so that particles having a particle diameter of 20 to 30 μm which seemed to be insufficiently foamed were mixed.
[0016]
Comparative Example 2
The same treatment as in Example 1 was performed except that no vibration was applied during the drying treatment. The water content of the obtained dried product was 2.1%. When this dried product was dispersed in ion-exchanged water and the size of the dispersed particles was measured in the same manner as in Example 1, a large amount of large aggregates were present. A 1% dioctyl phthalate dispersion of this dried product was prepared, heated for 2 minutes in a dryer adjusted to 170 ± 2 ° C., and then observed for a foamed state with a microscope. And a spherical and single-particle foam were mixed together.
[0017]
【The invention's effect】
As described above, the method of the present invention performs a drying process on a wet cake of foamable microcapsules under a reduced pressure of normal pressure to 50 mmHg or more while applying vibration so that the moisture content in the wet cake is 5% or less. By dissociating and dispersing the wet cake to obtain expandable microparticles, the wet cake can be surely and easily dissociated and dispersed into expandable microparticles without destroying the expandable microcapsules. Can do. The foamable microparticles obtained by dispersing the wet cake of the foamable microcapsules by the method of the present invention are applied to a coating additive, a plastic filler for the purpose of weight reduction, and a sealing agent utilizing volume expansion by foaming. It can be suitably used as an additive, an additive for foaming ink, wallpaper, etc. utilizing the formation of surface irregularities by foaming, an additive for textile processing agents, and the like.

Claims (1)

The moisture content in the wet cake is 5% or less under normal pressure or a reduced pressure of 50 mmHg or more while applying vibration to the wet cake of foamable microcapsules encapsulating a volatile substance in the thermoplastic resin shell. A method for dispersing a foamable microcapsule wet cake, wherein the wet cake is dissociated and dispersed by drying to obtain foamable microparticles.