JP2013221070A - Hollow polymer minute particle and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing hollow polymer minute particles by which the formation of crushed concave-shaped minute particles having low percentages of hollowness is reduced, and the minute particles having high percentages of the hollowness are increased.SOLUTION: A method for producing hollow polymer minute particles including emulsifying and dispersing a mixture containing a polymerizable monomer for forming shells of the polymer minute particles, and an organic solvent in an aqueous medium, subjecting the polymerizable monomer to suspension polymerization in the presence of a polymerization initiator to afford polymer minute particles including the organic solvent, and removing the organic solvent included in the polymer minute particles through the shells of the minute particles by evaporating the organic solvent, is characterized by carrying out the step for making the minute particles hollow by evaporating and removing the organic solvent included in the polymer minute particles, in a state of the polymer minute particles dispersed in an aqueous medium.

Description

  The present invention relates to a method for producing a hollow polymer fine particle capable of producing a non-expandable and high hollow ratio hollow polymer fine particle, and a non-expandable and high hollow ratio hollow polymer fine particle obtained by the production method. The hollow polymer fine particles of the present invention include, for example, a weight reducing material, a light scattering improver, and a heat insulating material contained in an intermediate layer formed between the support and the thermosensitive coloring layer in order to increase the recording sensitivity of the thermosensitive recording medium. Used as. The method for producing hollow polymer fine particles of the present invention increases the generation of non-expandable and high hollowness fine particles, has good water dispersibility, is easy to prepare paints, and does not scatter during handling, and is environmentally friendly. It is said.

  Conventionally, Patent Document 1 and Patent Document 2 are known as methods for producing hollow polymer fine particles. The hollow polymer fine particles described in these documents are expanded hollow fine particles. That is, after forming a microsphere having an outer shell of a thermoplastic polymer and containing a volatile foaming agent therein by suspension polymerization, the foaming agent contained therein is volatilized by heating the microsphere to form a microsphere. The internal pressure is increased to expand (expand) the outer shell.

  The expanded hollow polymer fine particles produced by the methods described in Patent Document 1 and Patent Document 2 have a drawback that the particle diameters after expansion are different and uneven. When the particle diameters are not uniform, the field where the stability of the coating composition using the hollow polymer fine particles is required, or the field where the controlled particle diameter is required (for example, the thermal recording material where the stability of the recording sensitivity is required). Has a drawback that lacks suitability for use.

  Patent Document 3 is known as a method for producing hollow polymer fine particles having a uniform particle diameter. The hollow fine particles described in this document are called a so-called seed polymerization method. The basic technique of the seed polymerization method starts by first emulsifying a polymerizable monomer (eg, styrene) in water in the presence of an emulsifier to form fine particles and polymerize to form seeds (nuclei). Next, another polymerizable monomer (eg, acrylate ester) is adsorbed on the seed, and thereafter, an outer shell layer made of the other polymerizable monomer is formed around the seed. Next, a substance that passes through the outer shell layer and swells and dissolves the inner seed (eg, aqueous ammonia solution) is added to the system to dissolve the seed, replace the dissolved substance with external water, and further heat. It is a method of drying and removing the internal water to make it hollow.

  In general, hollow polymer fine particles by this seed polymerization method are obtained by emulsifying in the presence of an emulsifier to form fine particles, and the particle diameter is as small as 1 μm or less and the hollow ratio is only about 50%. . For example, when the hollow fine particles are used as a heat insulating material for a heat-sensitive recording material, there is a drawback that the heat insulating effect is not sufficient. For this reason, the problem with the seed polymerization method is how to increase the hollow ratio by setting the particle diameter to several μm.

  In Patent Document 4, non-foamed polymer hollow fine particles having an average particle diameter of 0.1 to 20 μm (preferably 2 to 10 μm) and a hollow ratio of 60 (preferably 90)% or more, a support, a thermosensitive coloring layer, and Describes a heat-sensitive recording material contained in a hollow layer formed between the two. However, this document has no technical disclosure on how to produce non-foamed hollow polymer fine particles satisfying such conditions.

  Patent Document 5 discloses a method for producing hollow polymer fine particles by preparing a suspension in which a volatile hydrocarbon, a hydrophilic monomer, and a crosslinkable monomer coexist, polymerizing the monomer component in the suspension, After obtaining a dispersion of polymer fine particles containing volatile hydrocarbons, the polymer fine particles are separated from this dispersion and dried, or air, nitrogen gas, steam, etc. are blown into the dispersion without separation. Alternatively, a method for producing hollow particles by evaporating and separating volatile hydrocarbons in polymer fine particles by using them together is disclosed.

  However, the hollow polymer fine particles produced by the method described in Patent Document 5 have a drawback in that a part or a part of the polymer wall (outer shell) is greatly depressed, resulting in a lazy concave fine particle. This is caused by the vaporized transpiration separation of the volatile hydrocarbons included, and the inside of the particles is depressurized, that is, the polymer film (outer shell) constituting the spherical particles is drawn in without resisting the internal depressurization. This phenomenon is thought to be due to the lack of hardness and strength of the polymer film. The hollow concave polymer fine particles have a reduced hollowness and do not sufficiently exhibit the expected heat insulating effect even when used as a heat insulating agent in the intermediate layer of the heat-sensitive recording material.

Japanese Examined Patent Publication No. 42-26524 Japanese Patent Publication No. 5-86746 JP-A-56-32513 JP-A-5-169818 JP-A-61-87734

As described above, the already known expansion type hollow polymer fine particles are difficult to have a uniform and uniform particle diameter. The hollow polymer fine particles produced by the seed polymerization method are not suitable when a particle having a particle diameter of several μm and a high hollow ratio is expected. The non-expandable hollow polymer fine particles have a problem that a part of the fine particles or some of the fine particles are depressed and become concave concave fine particles with a low hollow ratio. In addition, the hollow rate described here is the ratio of the volume of the hollow part in the hollow particles to the volume of the hollow particles, and is represented by the following formula (1).
Hollow ratio (%) = [(radius of hollow part) ³ / (radius of hollow particles) ³ ] × 100 (1)

  The present invention reduces the generation of clogged concave fine particles with a low hollow ratio and increases the fine particles with a high hollow ratio when the organic solvent is vaporized and removed from the non-expandable polymer fine particles encapsulating the organic solvent to hollow out the fine particles. The main object is to provide a method for producing hollow polymer fine particles. Furthermore, in addition to such problems, the present invention provides an environment-friendly non-expandable type that forms a water-based coating composition, has good water compatibility and dispersibility, is easy to prepare a coating, and does not scatter during handling. It is an object to provide a method for producing hollow polymer fine particles.

  As a result of intensive investigations on the means for solving the above problems, the present inventors have conducted a conventional method (filtering and separating polymer fine particles from a polymer fine particle dispersion having a thermoplastic resin as an outer shell, and, for example, a drying apparatus such as a conical dryer. When the powder is dried by heating in a vacuum, the organic solvent is not vaporized and removed by evaporation, and the polymer fine particles are dispersed to vaporize, remove and hollow the organic solvent contained in the non-expandable polymer fine particles. The present invention was completed by conceiving and investigating a new method of performing in an aqueous dispersion (solvent removal in liquid).

  The present invention is characterized in that, in the production of non-expandable polymer fine particles, the introduction of such a new method increases the number of hollow polymer fine particles having a high hollow ratio, and the polymer fine particles encapsulating the organic solvent of the conventional method are obtained from the aqueous dispersion. This is fundamentally different from the conventional method in which it is once taken out and dried and then hollowed out at the same time as the powder.

  The present invention emulsifies and disperses a mixture of a polymer monomer for forming the outer shell of polymer fine particles and an organic solvent in an aqueous medium, suspension polymerizes the polymerizable monomer in the presence of a polymerization disclosure agent, Forming polymer fine particles encapsulating the solvent, evaporating the organic solvent encapsulated in the polymer fine particles and removing it through the outer shell of the fine particles, in the method for producing hollow polymer fine particles, vaporizing the organic solvent encapsulated in the polymer fine particles, There is provided a method for producing hollow polymer fine particles, wherein the step of removing and hollowing the fine particles is performed in a state where the polymer fine particles are dispersed in an aqueous medium.

  In the method for producing hollow polymer fine particles of the present invention, when the polymerizable monomer is subjected to suspension polymerization, one or more selected from the group consisting of a crosslinking agent, a dispersing agent, and a dispersing aid in an aqueous medium. It is preferable to add an additive.

  In the method for producing hollow polymer fine particles of the present invention, when the organic solvent encapsulated in the polymer fine particles is vaporized and removed, the volume concentration of the polymer fine particles in the aqueous dispersion in which the polymer fine particles are dispersed is 20 to 65. % Is preferable.

  In the method for producing hollow polymer fine particles of the present invention, when the organic solvent encapsulated in the polymer fine particles is vaporized and removed, the liquid temperature of the aqueous dispersion in which the polymer fine particles are dispersed is changed between the aqueous medium and the organic solvent. It is preferable to carry out under conditions set at a temperature higher than the azeotropic point.

  In the method for producing hollow polymer fine particles of the present invention, an aqueous dispersion of hollow polymer fine particles obtained by vaporizing and removing the organic solvent encapsulated in the polymer fine particles to hollow out the fine particles has a solid content concentration of 12 to 70 mass. It is preferable to separate water so that it is within the range of%.

  In the method for producing hollow polymer fine particles of the present invention, when the mixture containing a polymer monomer for forming the outer shell of polymer fine particles and an organic solvent is emulsified and dispersed in an aqueous medium, the polymerizability for forming the outer shell of the polymer fine particles is obtained. The volume concentration of the mixture containing the monomer and the organic solvent is preferably emulsified and dispersed within a range of 20 to 65%.

  In the method for producing hollow polymer fine particles of the present invention, after forming the polymer fine particles encapsulating the organic solvent, a diluent is added so that the volume concentration of the aqueous dispersion of the polymer fine particles is in the range of 20 to 65%. It is preferred to dilute.

  In the method for producing hollow polymer fine particles of the present invention, room temperature water is used as the diluent, and after adding the room temperature water to dilute the aqueous dispersion, the liquid temperature is higher than the azeotropic point of the aqueous medium and the organic solvent. It is preferable to evaporate and remove the organic solvent encapsulated in the polymer fine particles by raising the temperature.

  Further, as the diluent, warm water having a temperature higher than the azeotropic point of the aqueous medium and the organic solvent is used, and the temperature of the aqueous dispersion is raised to a temperature higher than the azeotropic point to vaporize the organic solvent encapsulating the polymer fine particles. Alternatively, it may be configured to be removed.

  The present invention also provides hollow polymer fine particles obtained by the above-described method for producing hollow polymer fine particles.

The method for producing hollow polymer fine particles of the present invention comprises emulsifying and dispersing a mixture of a polymer fine particle-forming polymerizable monomer and an organic solvent in an aqueous medium, and the polymerizable monomer in the presence of a polymerization disclosure agent. In the method for producing hollow polymer fine particles, the polymer fine particles encapsulating the organic solvent are formed, polymer fine particles encapsulating the organic solvent are vaporized, and the organic solvent encapsulated in the polymer fine particles is vaporized and removed through the outer shell of the fine particles. The process of vaporizing and removing the encapsulated organic solvent to hollow out the fine particles is performed in a state where the polymer fine particles are dispersed in the aqueous medium, thereby reducing the formation of crunchy concave fine particles, non-foaming and highly hollow This has the effect of increasing the production of hollow polymer fine particles.
Further, according to the method for producing hollow polymer fine particles of the present invention, in addition to reducing the formation of crunchy concave fine particles and increasing the production of high hollow ratio wet hollow polymer fine particles, the obtained wet hollow polymer fine particles Since it is excellent in water compatibility and dispersibility, it is easy to prepare paints, and since it does not scatter during handling, there is no fear of aspiration that impairs the health of handling workers and has an environmentally friendly effect.

  Since the hollow polymer fine particles obtained by the present invention contain a large amount of polymer fine particles having a high hollow ratio, for example, if this is contained as a heat insulating material in the intermediate layer of the heat-sensitive recording material, Joule heat applied from the thermal head during recording can be reduced. The heat insulating effect is improved, and the recording sensitivity can be remarkably improved.

It is an electron microscope enlarged image of the polymer fine particle group manufactured in Comparative Example 1 based on a conventional method in which the polymer fine particles are separated from an aqueous dispersion of polymer fine particles encapsulating an organic solvent, and then dried and hollowed. It is an electron microscope enlarged image of the hollow polymer fine particle group manufactured in Example 1 based on the present invention (use of room temperature water as a diluent). It is an electron microscope enlarged image of the non-expandable hollow polymer fine particle group manufactured in Example 2 based on the present invention (use of warm water capable of raising the temperature to a temperature higher than the azeotropic point of the aqueous medium and the organic solvent in the diluent). .

  As the polymerizable monomer for forming the outer shell of polymer fine particles used in the present invention, vinylpyridine, glycidyl acrylate, glycidyl methacrylate, (meth) acrylic acid ester, (meth) acrylic acid, acrylonitrile, acrylamide, methacrylamide, N- Selected from methylol acrylamide, N-methylol methacrylamide, itaconic acid, fumaric acid, dimethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, styrene, among others (meth) Acrylic acid, (meth) acrylic acid ester or (meth) acrylonitrile is more soluble in water than the organic solvent to be encapsulated. It is more preferred because of excellent formation of polymerization film.

  These polymerizable monomers may be used alone or, for example, (meth) acrylic acid and (meth) acrylic acid ester, or (meth) acrylic acid and acrylonitrile may be used in combination.

  In order to form polymer fine particles encapsulating an organic solvent by using the polymerizable monomers alone or in combination, a cross-linking agent, a polymerization initiator, a dispersant, and a dispersion aid are preferably used in combination.

  The organic solvent used in the present invention is selected from diethyl ether, neohexane, pentane, hexane, heptane, isooctane, octane, cyclohexane, methylcyclohexane, during polymerization of the polymerizable monomer and Hexane that does not evaporate in the state of being encapsulated in the fine particles after the polymerization is completed, and can be smoothly removed from the polymerized film (outer shell) of the fine particles by evaporating by heating the dispersion of the fine particles to 60 to 130 ° C., Heptane, octane and the like can be preferably used.

  The organic solvent is used in an amount of 400 to 2000 parts by mass, preferably 800 to 1700 parts by mass, and more preferably 1200 to 1400 parts by mass with respect to 100 parts by mass of the polymerizable monomer. Incidentally, when the amount is less than 400 parts by mass, the thickness of the outer shell of the fine particles to be formed is relatively increased, the hollowness is lowered, and polymer fine particles having a high hollowness cannot be formed. On the other hand, even if 2000 parts by mass or more are used, it is difficult to expect a technical effect corresponding to the excess amount, and this is not economical.

The mixture of the polymerizable monomer for forming the outer shell of the polymer fine particles and the organic solvent is emulsified and dispersed in an aqueous medium.
Various additives can be added to the aqueous medium in addition to the polymerizable monomer and the organic solvent. As the additive, it is preferable to add one or more additives selected from the group consisting of a crosslinking agent, a dispersant, and a dispersion aid. In the suspension polymerization of the polymerizable monomer, a polymerization initiator for the polymerizable monomer is added.

  The crosslinking agent is selected in relation to the polymerizable monomer because it affects the hardness and strength of the polymerized film. Specific examples include divinylbenzene, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, trimethylolpropane trimethacrylate, 1,3-butylene (meth) acrylate, and allyl (meth) acrylate. However, when (meth) acrylic acid, (meth) acrylic acid ester, (meth) acrylic acid, acrylonitrile or a combination thereof is selected as the polymerizable monomer, the crosslinking agent may be ethylene glycol di (meth) acrylate or (Meth) trimethylolpropane acrylate is preferred.

  Although the usage-amount of a crosslinking agent is examined in relation to the polymerizable monomer to be used, it is 10 mass parts-200 mass parts with respect to 100 mass parts of polymerizable monomers, Preferably it is 40 mass parts-150 mass parts, More preferably, it is 60. Used in parts by mass to 100 parts by mass. Incidentally, if it is less than 10 parts by mass, it is difficult to form non-expandable hollow polymer fine particles that are hard and excellent in strength, and it is difficult to expect a technical effect corresponding to the amount exceeding 200 parts by mass, It is not economically advantageous.

  The dispersant is necessary for maintaining a stable dispersibility of the fine particles after forming the fine particle dispersion containing the organic solvent. Any substance having such a function can be used as a dispersant, but the present inventors have investigated the effects of phosphorus dispersants, water-soluble polymer dispersants, colloidal silica, etc. It was confirmed that the silica-like silica itself has a positive charge and adheres to the outer periphery of the polymer film of the fine particles to exert an excellent dispersion effect that repels each other and prevents aggregation.

  In the present invention, the reason why colloidal silica exhibits an excellent dispersion effect is that the colloidal silica is positively charged by polymerizing a polymerizable monomer under acidic conditions. The positively charged silica is incorporated into a fine particle polymer film, and each fine particle becomes a positively charged particle. It can be considered that the positively charged fine particles repel each other and prevent aggregation.

  When the dispersant is colloidal silica, the amount of the dispersant used is 30 to 100 parts by weight, preferably 40 to 80 parts by weight, and more preferably 50 to 70 parts by weight with respect to 100 parts by weight of the polymerizable monomer. Use parts by mass. Incidentally, if it is less than 30 parts by mass, the dispersion effect cannot be obtained. Moreover, even if it uses 100 mass parts or more, it is hard to expect the technical effect corresponding to the excess amount, and it is not economically advantageous.

  Dispersing aids exhibit a synergistic effect in the formation and maintenance of more stable dispersions when used in combination with dispersants, such as condensates of adipic acid and diethanolamine, adipic acid and 2-amino-2-methyl, for example. A condensate of -1,3-propanediol, a condensate of adipic acid and monoethanolamine, and the like are preferable.

  When the dispersion aid is a condensate of adipic acid and diethanolamine, the amount of the dispersion aid used is 1 to 10 parts by weight, preferably 2 to 7 parts by weight, more preferably 100 parts by weight of the polymerizable monomer. Preferably 3 to 5 parts by weight are used. Incidentally, if it is less than 1 part by mass, the effect of the dispersion aid cannot be obtained. Moreover, even if it uses 10 mass parts or more, it is hard to expect the technical effect corresponding to the excess amount, and it is not economically advantageous.

  The polymerization initiator can be used as long as it is oil-soluble and generates radicals, and the polymerizable monomer completes the polymerization reaction in an optimal time under a temperature range in which the organic solvent to be included does not vaporize. For example, 2,2′-azobisisobutyronitrile, cumene hydroperoxide, t-butyl hydroperoxide, dicumyl peroxide, di-t-butyl hydroperoxide, benzoyl peroxide, lauroyl peroxide, etc. can be used. It is. When n-heptane is used as the organic solvent, 2,2'-azobisisobutyronitrile having a half-life at 60 ° C of 10 hours is preferable.

  In order to obtain hollow polymer fine particles according to the present invention, the mixture containing each material is emulsified, dispersed, and suspension-polymerized to form polymer fine particles that enclose an organic solvent. It depends on whether hollow polymer fine particles are obtained, and is not specified.

  In the emulsification dispersion method, first, an emulsification stirrer such as a homomixer is used. Suspension polymerization proceeds while stirring is continued by another stirrer in a state where the temperature of the emulsified dispersion is raised to a predetermined temperature.

  The polymer fine particles formed by suspension polymerization proceed to vaporize / remove / hollow the organic solvent contained in the fine particles. The feature of the present invention is to vaporize / remove / hollow the organic solvent. In an aqueous dispersion in which the liquid is dispersed and the temperature of the dispersion is set to a temperature higher than the azeotropic point of the aqueous medium and the organic solvent (desolvation in liquid). .

  The volume concentration of the aqueous dispersion in which the polymer fine particles are dispersed is 20 to 65%, preferably 30 to 50%, more preferably 40 to 45%. Incidentally, when the volume concentration is 20% or less, the production efficiency is drastically reduced due to the low concentration. On the other hand, when the volume concentration is 65% or more, the viscosity of the dispersion becomes high and the vaporized organic solvent is removed in the dispersion. This is because the removal efficiency is deteriorated and the production efficiency is extremely lowered to facilitate foaming when distilling out of the system.

  In order to obtain an aqueous dispersion of polymer fine particles having a volume concentration of 20 to 65%, the volume concentration of a mixture comprising an aqueous medium, a polymerizable monomer for forming fine polymer particles, a crosslinking agent, an organic solvent, a dispersant and a dispersion aid is 20 to 20%. A method of emulsifying and dispersing under a blending condition of 65%, and a method of adjusting by adding a diluent so that the volume concentration of an aqueous dispersion in which the polymer fine particles are dispersed is 20 to 65% after the polymer fine particles are formed. There is. Any method can be adopted, but the latter method is advantageous when the emulsification and dispersion efficiency of the mixture is taken into consideration.

  In the case of the method of adding a diluent after forming polymer fine particles as described above, the diluent is for normal temperature water and hot water, but reduces the formation of concave fine particles with a low hollow ratio and has a high hollow ratio. The use of warm water is more effective for increasing the production of fine particles.

  Incidentally, the temperature for suspension polymerization of the fine particles encapsulating the organic solvent is set based on the organic solvent to be encapsulated. For example, when n-heptane is used as the organic solvent, the temperature is set to 79 ° C. or lower.

  When room temperature water is used as the diluent here, the outer shell film in a state where the crosslinking does not reach the completion range does not have sufficient hardness and strength, and thus shrinks by rapid cooling. The internal pressure of the fine particles is further reduced by evaporating, removing and hollowing out the organic solvent contained therein. When these factors overlap, the outer shell is drawn into the interior, and the fine particles are likely to be crushed concave fine particles.

  However, regarding the problem of the present invention to increase the generation of fine particles having a high hollow ratio, the organic solvent encapsulated in the polymer fine particles is vaporized, removed, and hollowed in an aqueous dispersion in which the polymer fine particles are dispersed. Therefore, it is clear from (FIG. 2) that the effect is improved as compared with the hollow polymer fine particles (FIG. 1) produced based on the conventional method.

  On the other hand, in the case of using warm water in which the liquid temperature of the suspension polymerization solution can be set to a temperature higher than the azeotropic point of the aqueous medium and the organic solvent, the polymer film (outer shell) that forms fine particles is crosslinked. Progresses continuously, its hardness and strength are further improved, the internal pressure of the fine particles is reduced and it can withstand the force of the outer shell being pulled inside, the number of lazy concave fine particles is reduced, and the high hollow The rate of fine particles increases. This is also evident when comparing (FIG. 3) with hollow polymer particles (FIG. 1) produced according to the conventional method and with hollow polymer particles (FIG. 2) produced using room temperature water.

  As described above, almost all the polymer fine particle groups produced based on the conventional method are formed into concave fine particles, and spherical fine particles having a high hollow ratio are hardly seen. On the other hand, it is clear that the hollow polymer fine particle group (FIG. 2) and (FIG. 3) produced based on the present invention produces a large amount of fine particles having a high hollow ratio as compared with FIG.

  Incidentally, the present inventors consider the reason why the above effect is obtained as follows. The hollow polymer fine particle according to the present invention has a volume concentration of 20 to 65% in an aqueous dispersion in which the fine particle is dispersed, and the liquid temperature of the dispersion is low. This is closely related to performing under conditions set at a temperature higher than the azeotropic point of the aqueous medium and the organic solvent.

When the organic solvent is vaporized / removed / hollowed under the above conditions, the organic solvent contained in the fine particles is vaporized and escapes to the outside through the outer shell of the fine particles. Slow with water pressure. Therefore, the internal pressure of the fine particles increases due to the residence of the vaporized organic solvent, and the pressure is applied to the inner walls of the fine particles. At this time, the internal pressure increase due to the residence of the vaporized organic solvent is superior to the internal pressure reduction accompanying the escape of the vaporized organic solvent.
The internal pressure gradually decreases as the organic solvent evaporated with time escapes. In the meantime, however, the outer shell of the fine particles also undergoes cross-linking, and it is thought that the number of fine particles of hardness and strength that can withstand the internal decompression and maintain a spherical shape increases.

  On the other hand, in the conventional method, the polymer fine particles encapsulating the organic solvent are once taken out from the aqueous dispersion, dried by heating and simultaneously hollowed. At this time, there is no factor that is suppressed when the vaporized organic solvent escapes to the outside through the outer shell of the fine particles. Therefore, it is considered that the organic solvent in the fine particles gradually escapes while vaporizing, the internal pressure is reduced, and the outer shell is drawn into the inside, and as a result, most of the fine particles become cramped concave fine particles.

  Next, it is important that the liquid temperature of the dispersion when the organic solvent encapsulated in the polymer fine particles is vaporized / removed / hollowed is set to a temperature higher than the azeotropic point of the aqueous medium and the organic solvent. Specifically, it depends on the type of organic solvent used.

  For example, when octane is used as the organic solvent, 89.6 ° C. or higher, when heptane is used, 79.2 ° C. or higher, when cyclohexane is used, 69.5 ° C. or higher, and when hexane is used, 61.6 ° C. or higher. The liquid temperature of the dispersion is set to be equal to or higher than ° C.

  By setting the liquid temperature of the polymer fine particle dispersion containing the organic solvent as described above, the organic solvent contained in the polymer fine particles is vaporized and escapes from the outer shell of the polymer fine particles to make the polymer fine particles hollow. To do.

  The obtained hollow polymer fine particle dispersion in which spherical particles having a high hollow ratio are increased can be arranged in a form suitable for the application. For example, after separating water, it can be dried to form powdered hollow polymer particles, or wet hollow polymer particles. For example, in the form of wet hollow polymer fine particles, it is easy to prepare a coating because it is gentle to the environment that does not scatter to the outside during handling, and is excellent in water compatibility and dispersibility. Incidentally, in order to obtain wet hollow polymer fine particles, water may be separated and removed so that the solid content concentration is 12 to 70%, preferably 20 to 50%, more preferably 30 to 40%. Incidentally, if it is 12% or less, it is in a water dispersed state and does not become a wet state. On the other hand, if it is 70% or more, the hollow polymer fine particles are likely to be scattered, and there is a fear of sucking that is harmful to the health of the handling worker, which makes it difficult to handle.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited at all by these Examples.

[Example 1]
In a 1000 ml four-necked flask containing 201.2 g of deionized water, 0.6 g of a condensate of adipic acid and diethanolamine was dissolved as a dispersing aid, and 8.5 g of colloidal silica was added as a dispersing agent. This aqueous solution was adjusted to pH 3.0 with 4.5 g of 3% dilute sulfuric acid aqueous solution to obtain an aqueous phase.

  An oil phase was prepared by mixing 11.2 g of methyl methacrylate as a polymerizable monomer, 1.3 g of acrylonitrile, 12.5 g of trimethylolpropane trimethacrylate as a crosslinking agent, and 150.0 g of n-heptane as an organic solvent.

  A water phase and an oil phase are mixed. The mixture was stirred for 6 minutes at 12000 rpm with a K auto homomixer M type (manufactured by Tokushu Kika Kogyo Co., Ltd.) and the particle size was adjusted to 1 to 10 μm, and then 2,2′-azobisiso as a polymerization initiator. 0.1 g of butyronitrile was added, the atmosphere was replaced with nitrogen, and polymerization was performed for 4 hours while stirring at a reaction temperature of 78 ° C. and a rotation speed of 180 rpm.

  To the aqueous polymer dispersion after the polymerization, 385.0 g of room temperature water was added, and the dispersion was heated to 79-100 ° C. under normal pressure while stirring and n-heptane encapsulated in polymer fine particles over 8 hours. Vaporization and removal were performed to hollow out the polymer fine particles (desolvation in liquid). At this time, the dispersion was cooled once from 78 ° C. to 40 ° C. when the polymerization reaction was performed by adding room temperature water.

  The amount of n-heptane removed from the polymer fine particles was 141 g, and it was confirmed that n-heptane in an amount almost equal to the charged amount was vaporized in the polymer fine particles and removed from the outer shell.

  After evaporating and removing n-heptane, the aqueous polymer dispersion was subjected to suction filtration to obtain 155.3 g of wet polymer fine particles having a solid content of 18.7%. The obtained polymer fine particles had a particle size of 4.0 μm. (The particle size is a particle size measured by a laser diffraction particle size distribution measuring device “SALD-2000 (manufactured by Shimadzu Corporation)” and means a particle size of 50% of the cumulative volume particle size distribution.)

  FIG. 2 shows an enlarged image of the obtained non-expandable hollow polymer fine particles taken with an electron microscope. From this image, it was confirmed that the obtained polymer fine particles had fewer hollow fine particles and higher high hollow rate fine particles than the hollow polymer fine particles produced according to the conventional method (FIG. 1). .

  Since the obtained non-expandable hollow polymer fine particles were in a wet state, they were environmentally friendly fine particles having good water compatibility and dispersibility, easy preparation of a paint, and no scattering during handling.

  The visual shape of the fine particles obtained in Example 1 is shown in Table 1, and the recording sensitivity of the thermosensitive recording material when the fine particles are used as a heat insulating material is shown in Table 2.

[Example 2]
Example 1 except that 385.0 g of warm water (85 ° C.) of 79 ° C. or higher, which is the azeotropic point of n-heptane and water, was added as a dilute dispersion of the fine particle dispersion encapsulating n-heptane and finishing polymerization. Similarly, polymer particles having a high hollow ratio in a wet state were produced.

  Maintaining a state in which the temperature of the dispersion is never cooled from the polymerization reaction to vaporization / removal of the organic solvent, and in a wet state in which n-heptane encapsulated in the fine particles is vaporized / removed in the same manner as in Example 1. Fine particles were obtained.

  An enlarged image of the obtained polymer fine particles taken with an electron microscope is shown in FIG. From FIG. 3, the obtained polymer fine particles were compared with the hollow polymer fine particles produced according to the conventional method (FIG. 1), and the hollow polymer fine particles according to Example 1 produced using room temperature water as the diluent (FIG. 1). Compared to FIG. 2), it was confirmed that the number of hollow concave fine particles decreased and the hollow polymer fine particles having a high hollow ratio further increased.

  In addition, when the obtained particles are embedded with an epoxy resin, and a cross-sectional view is observed with an electron microscope, the shape of the particles is larger than that of the lazy concave fine particles obtained by the conventional method, and the average particle size The diameter was 4.0 μm, the thickness of the outer shell membrane was about 0.05 μm, and the hollow rate was high, exceeding 90%. The resulting hollow polymer fine particles had a bulk specific gravity of 0.1 g / ml.

  This effect is achieved by using warm water to maintain the dispersion temperature in a state where it is never cooled from the polymerization reaction to the vaporization / removal / hollowization of the organic solvent. It is considered that the cross-linking of the formed polymer film proceeds continuously and the hardness and strength of the polymer fine particles are improved.

  The visual shape of the fine particles obtained in Example 2 is shown in Table 1, and the recording sensitivity of the thermal recording material using the fine particles as a heat insulating material is shown in Table 2.

[Example 3]
N-heptane encapsulated in microparticles in the same manner as in Example 2 except that 586.2 g of deionized water used for preparing the aqueous phase was prepared, and after emulsion dispersion and suspension polymerization, no diluent was used. Vaporization and removal were performed to obtain hollow fine particles.

  It was confirmed that the obtained fine polymer particles were reduced in the number of hollow concave fine particles and the hollow polymer fine particles having a high hollow ratio were further increased, and the degree thereof was almost the same as in Example 2.

  The visual shape of the fine particles obtained in Example 3 is shown in Table 1, and the recording sensitivity of the thermal recording material using the fine particles as a heat insulating material is shown in Table 2.

[Comparative Example 1]
The same water phase and oil phase as in Example 1 were mixed. The mixture was stirred for 6 minutes at 12000 rpm with a K auto homomixer M type (manufactured by Tokushu Kika Kogyo Co., Ltd.) and the particle size was adjusted to 1 to 10 μm. 0.1 g of butyronitrile was added, the atmosphere was replaced with nitrogen, and polymerization was performed for 4 hours while stirring at a reaction temperature of 78 ° C. and a rotation speed of 180 rpm.

  From the polymer fine particle aqueous dispersion containing n-heptane after polymerization, the polymer fine particles were subjected to solid-liquid separation by suction filtration to obtain polymer fine particles containing n-heptane.

  N-heptane contained in the fine particles of the polymer was vaporized and removed under normal pressure at 40 ° C. for 24 hours to obtain dry polymer fine particles.

  An enlarged image of the obtained polymer fine particles taken with an electron microscope is shown in FIG. As is apparent from this image, this polymer fine particle group was concave fine particles in which almost all the particles were crushed.

  The visual shape of the fine particles obtained in Comparative Example 1 is shown in Table 1, and the recording sensitivity of the thermal recording material using the fine particles as a heat insulating material is shown in 2.

[Comparative Example 2]
A dispersion of fine particles of n-heptane-containing polymer having a volume concentration of 70% by emulsion dispersion and suspension polymerization in the same manner as in Example 2 except that 72.6 g of deionized water used for preparing the aqueous phase was used. Got.

  Attempts were made to vaporize and remove n-heptane encapsulated in polymer fine particles by heating to 79-100 ° C. under atmospheric pressure while stirring this dispersion. However, the concentration of the dispersion aid increased and the surface activity was increased. The ability as an agent is increased, and the encapsulated n-heptane is removed from the outer shell of the polymer fine particles into the dispersion, and when distilling out of the system, the inside of the flask is bubbling vigorously, making it difficult to vaporize and remove n-heptane. Met.

[Comparative Example 3]
In the same manner as in Example 1, n-heptane-containing polymer fine particles were obtained. Add 385.0 g of warm water (85 ° C.) of 79 ° C. or higher, which is the azeotropic point of n-heptane and water, and vaporize and remove n-heptane encapsulated in polymer fine particles under a reduced pressure of 300 mmHg. However, the temperature in the flask did not rise to 79 ° C. or higher, and only the water in the dispersion was vaporized and removed, making it difficult to vaporize and remove n-heptane.
The reason for this is that the vapor pressure of water was lowered and the temperature in the flask was lower than 79 ° C. by placing the dispersion under a reduced pressure condition of 300 mmHg. In the fine particles formed with this composition, it is necessary to vaporize n-heptane in order to remove n-heptane from the outer shell of the fine polymer particles. At this time, since n-heptane is encapsulated in the polymer fine particles, it is difficult for the vapor pressure to decrease due to the reduced pressure. Even under reduced pressure conditions, the boiling point of n-heptane containing the temperature inside the flask is reduced by lowering the vapor pressure of water under reduced pressure conditions because it cannot be vaporized and removed unless the inside of the flask is heated to near the boiling point of n-heptane. It is thought that it was difficult to vaporize and remove n-heptane.

[Hollow rate and thermal insulation effect]
The wet microparticles obtained in Examples 1 to 3, the dry microparticles obtained in Comparative Example 1 and the hollow microparticles obtained by the seed polymerization method were each mixed as a heat insulating material in the intermediate layer of the thermal recording body, and the color development sensitivity of the thermal recording body was examined. It was.

The composition of the thermal recording material was prepared by preparing the coating composition for the undercoat layer and the coating composition for the thermal recording layer with the following composition.
(Preparation of paint for undercoat layer)
Hollow polymer fine particles obtained in Examples 1 to 3, hollow polymer fine particles obtained in Comparative Example 1, and hollow fine particles synthesized by a commercially available seed polymerization method (Rohm & Haas Co., Ltd., “trade name: Ropaque SN-1055 : For each of the particle diameter 1 μm and the hollow ratio of about 50%, an undercoat paint was prepared with the following composition.

(Composition) (Mass)
Hollow fine particles 100
Gocelan L-3266 (Nihon Gosei Co., Ltd.) 5
Latex L-1571 (manufactured by Asahi Kasei Corporation) 7
Oji Ace C (Oji Cornstarch Co., Ltd.) 5
Deionized water 800

(Preparation of recording layer paint)
As a recording layer coating material, a coating material having the following composition was prepared.

(Composition) (Mass)
Calcium carbonate 50
Zinc stearate 10
3-butylamino-6-methyl-N-anilinofluorane 10
4,4′-diphenylsulfone 20
Oji Ace C (Oji Cornstarch Co., Ltd.) 10
PVA-105 5
Deionized water 395

(Preparation of thermal recording material)
On one side of high-quality neutral paper with a basis weight of 64 g / m ^2, the coating for the undercoat layer is 4 g / m ² by dry weight, and the coating for the recording layer on the undercoat layer is 3 g / m ² by dry weight. And dried to obtain a heat-sensitive recording material. In addition, after forming each layer, the super calendar process was carried out.

(Color development test)
The following color developability test was performed on each of the obtained thermal recording materials.
Using the product name “TH-PMD (thermal head 1653Ω)” manufactured by Okura Electric Co., Ltd., the thermal recording medium was colored at 24 V, 0.6 msec, 0.8 msec and 1.6 msec, and the recording density was set to Macbeth densitometer “ RD-914 ". The results are shown in Table 2.

(Evaluation)
Table 2 also shows that the non-foaming hollow polymer fine particles obtained by the present invention have a higher heat insulating effect than the hollow fine particles produced by the seed polymerization method such as “Ropeke”, and the color development sensitivity of the heat-sensitive recording material. Contributes effectively to improvement, and even in non-foaming hollow polymer particles, the number of hollow concave fine particles decreases, and as the number of hollow polymer particles with high hollowness increases, the heat insulation effect increases, and the color sensitivity of the thermal recording medium It is clear from the data that the improvement contributes effectively.

  The non-expandable type of hollow polymer fine particle production method according to the present invention in which particles with a high hollow ratio increase increases the production of hollow polymer fine particles with a low hollow ratio as much as possible and reduces the production of hollow polymer fine particles with a high hollow ratio. The non-expandable hollow polymer fine particles obtained by the present invention are useful as a method for producing a fine hollow polymer fine particle. In order to enhance the sensitivity, it is useful as a heat insulating material or the like contained in an intermediate layer formed between the support and the thermosensitive coloring layer. Further, the wet non-expandable hollow polymer fine particles obtained by the present invention are compatible with water and water. It has good dispersibility, is easy to prepare paint, and does not scatter during handling and is useful for environmentally friendly use.

Claims (10)

In a water medium, a mixture containing a polymerizable monomer for forming the outer shell of polymer fine particles and an organic solvent is emulsified and dispersed, and the polymerizable monomer is subjected to suspension polymerization in the presence of a polymerization disclosure agent to enclose the organic solvent. In a method for producing hollow polymer fine particles by forming polymer fine particles, evaporating an organic solvent encapsulated in the polymer fine particles and removing the vapor through an outer shell of the fine particles,
A method for producing hollow polymer fine particles, wherein the step of vaporizing and removing the organic solvent contained in the polymer fine particles to hollow the fine particles is performed in a state where the polymer fine particles are dispersed in an aqueous medium.   The one or more additives selected from the group consisting of a crosslinking agent, a dispersing agent, and a dispersing aid are added to the aqueous medium when the polymerizable monomer is subjected to suspension polymerization. 2. The method for producing hollow polymer fine particles according to 1.   When the organic solvent encapsulated in the polymer fine particles is vaporized and removed, the volume concentration of the polymer fine particles in the aqueous dispersion in which the polymer fine particles are dispersed is in the range of 20 to 65%. The manufacturing method of the hollow polymer microparticles of Claim 1 or 2.   When the organic solvent contained in the polymer fine particles is vaporized and removed, the temperature of the aqueous dispersion in which the polymer fine particles are dispersed is set to a temperature higher than the azeotropic point of the aqueous medium and the organic solvent. The method for producing hollow polymer fine particles according to any one of claims 1 to 3, wherein   Water is separated from the aqueous dispersion of the hollow polymer fine particles obtained by vaporizing and removing the organic solvent encapsulated in the fine polymer particles to hollow out the fine particles so that the solid concentration is in the range of 12 to 70% by mass. The method for producing hollow polymer fine particles according to any one of claims 1 to 4.   The volume of the mixture containing the polymerizable monomer for forming the outer shell of the polymer fine particle and the organic solvent when emulsifying and dispersing the mixture containing the polymerizable monomer for forming the outer shell of the polymer fine particle and the organic solvent in an aqueous medium. The method for producing hollow polymer fine particles according to any one of claims 1 to 5, wherein the concentration is emulsified and dispersed within a range of 20 to 65%.   The polymer fine particles encapsulating the organic solvent are formed, and then diluted by adding a diluent so that the volume concentration of the aqueous dispersion of the polymer fine particles is within the range of 20 to 65%. 6. The method for producing hollow polymer fine particles according to any one of 6 above.   After using room temperature water as the diluent and diluting the aqueous dispersion by adding the room temperature water, the liquid temperature is raised to a temperature higher than the azeotropic point of the aqueous medium and the organic solvent to enclose the polymer fine particles. The method for producing fine hollow polymer particles according to claim 7, wherein the organic solvent is vaporized and removed.   As the diluent, warm water having a temperature higher than the azeotropic point of the aqueous medium and the organic solvent is used, and the temperature of the aqueous dispersion is raised to a temperature higher than the azeotropic point to vaporize and remove the organic solvent contained in the polymer fine particles. The method for producing hollow polymer fine particles according to claim 7, wherein:   Hollow polymer fine particles obtained by the method for producing hollow polymer fine particles according to any one of claims 1 to 9.