JPH01180242A - Production of minute particle formed to microcapsule - Google Patents

Abstract

PURPOSE:To improve negative chargeability of the title minute particles by stirring mother particles having a specified number average particle size together at high speed with daughter particles having a specified number average particle size prepd. by polymerizing monomers for forming the daughter particles in an aq. medium contg. an anionic surface active agent. CONSTITUTION:Mother particles having 1-200mum number average particle size are prepd. On one hand, daughter particles having <=1/5 number average particle size of that of the mother particles are prepd. by polymerizing 100pts.wt. mono mer compsn. for forming the daughter particles in an aq. medium contg. 0.01-0.2 pts.wt. anionic surface active agent in the presence of 0.03-0.15pt.wt. persulfate, adding further 0.15-1.0pts.wt. persulfate when the coversion of the monomer reaches 65%. The mother particles and the daughter particles are stirred at high speed in an air stream. Thus, a covering layer consisting of the daughter particles is formed on the surface of the mother particles, and minute particles formed to microcapsules are obtd.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for producing microencapsulated fine particles, and more specifically, a method for uniformly modifying the particle surface by forming or immobilizing specific polymer fine particles on the particle surface. The present invention also relates to a method for producing microencapsulated particles that impart negative chargeability to the particles.

The microencapsulated fine particles obtained by the present invention are
It can be used in many fields including toner for developing electrostatic images in electrophotography and the like.

[Prior Art] So-called encapsulation methods for coating particle surfaces with other substances include chemical methods such as interfacial polymerization, in 5 in situ polymerization, and in-liquid curing coating methods, phase separation methods from aqueous solutions, It is well known that there are physicochemical methods such as a phase separation method from an organic solvent system and a liquid drying method, and mechanical methods such as a fluidized air bed method and a spray drying method. However, with these conventional encapsulation methods, it is difficult to uniformly coat individual particles and aggregates are likely to form, so delicate control of conditions is required for industrial production. There was a problem.

Therefore, recently, methods have been proposed to modify the particle surface using the so-called mechanochemical effect, or to microencapsulate the particles as a core substance (Kagaku Kisatsu, March 1986 issue, p. 27-). 33). According to this method, coating child particles having a predetermined particle size ratio to the mother particles are electrostatically attached to the mother particles, and are strongly mixed by a ball mill, an automatic mortar, or high-speed stirring under an air flow. By embedding child particles in a mother particle and fixing them, the aim is to modify the particle surface or to achieve microencapsulation using the mother particle as a core material.

[Problems to be Solved by the Invention] By the way, polymer particles are typical of child particles to be fixed and formed into a film on the surface of a mother particle. Such polymer particles are usually produced by emulsion polymerization or suspension polymerization in an aqueous medium, and in this case, a large amount of surfactant or suspension protectant is used to ensure polymerization stability.

It has also been found that problems arise when microencapsulated fine particles using such polymer particles as child particles are used in specific applications, for example, as toners for developing electrostatic images in electrophotography and the like. In other words, this toner has insufficient charging properties, and also has high specific axial hygroscopicity, so toner properties such as charging properties tend to change over time. Therefore, when this toner is used repeatedly, the quality of the copied image may deteriorate. There is a problem in that image quality tends to deteriorate.

In addition, as a method for manufacturing microencapsulated fine particles that the present inventors have already proposed, there is a technique in which a coating layer of child particles is formed on the surface of the mother particles by stirring the mother particles and child particles at high speed under an air flow. (Special application No. 61-2554
No. 84 and Japanese Patent Application No. 6262-87727-1).

In this method, it is desired that the child particles have a particle size of about 0.3 μm or less, so it is necessary to use a larger amount of surfactant in the polymerization of the polymer particles used as the child particles. , therefore, the above-mentioned problem becomes even more pronounced.

Therefore, the purpose of the present invention is to polymerize polymer particles in the presence of a small amount of surfactant, and use these polymer particles as child particles to produce microencapsulated fine particles with good negative chargeability in a simple process. The object of the present invention is to provide a manufacturing method that can produce good results.

[Means for Solving the Problems] The above problems are based on base particles having a number average particle diameter of 1 to 200 μm, and base particles having a number average particle diameter of 115 μm, which is the number average particle diameter of the base particles.
A method for producing microencapsulated fine particles in which a coating layer of child particles is formed on the surface of a mother particle by subjecting the following child particles for forming a coating layer to a high-speed agitation treatment in an air flow, wherein the child particles are , Monomer composition 100 for forming child particles
In an aqueous medium containing 0.01 to 0.2 parts by weight of an anionic surfactant, 0.03 to 0.15 parts by weight
Polymerization is initiated in the presence of 1 part by weight of persulfate, and when the polymerization conversion reaches 65% or more, an additional 0.1 part of persulfate is added.
The problem is solved by a method for producing microencapsulated fine particles, which is characterized in that the particles are obtained by polymerizing the particles by adding 5 to 1.0 parts by weight.

That is, in the present invention, the electrolyte effect of the polymerization system is reduced by using a small amount of persulfate in the early stage of polymerization, thereby achieving good polymerization stability even in the presence of a small amount of anionic surfactant. In this state, polymer particles with a microparticle size can be formed. Further, by adding a persulfate at a late stage of polymerization, polymerization is promoted and the polymer particles are given chargeability. As a result, it is possible to obtain polymer particles that are extremely unaffected by surfactants, and by using these polymer particles as child particles, safe microencapsulation with excellent negative chargeability and little change in properties over time can be achieved. Fine particles can be obtained.

The present invention will be explained in detail below.

The number average particle diameter Sn of the base particles used in the present invention is
The thickness is 1 to 200 μm, preferably 1 to 100 μIn, and more preferably 2 to 50 μm. Number average particle diameter Sn is 1
If the diameter is less than μm, the collision energy generated by high-speed agitation of the particles is insufficient, making it difficult to form a coating layer, and the particles also aggregate, making it difficult to separate the particles and form a coating layer on their surfaces. It becomes difficult. On the other hand, if the number average particle diameter Sn exceeds 200 μm, the properties as fine particles will be lost.

As the base particles used in the present invention, both organic and inorganic substances can be used as long as they satisfy the above conditions, and can be selected as appropriate depending on the intended use of the microencapsulated fine particles as the final product. can. A typical example of the organic substance is a synthetic resin (polymer). In particular, vinyl polymers are preferred, and the vinyl monomers used in their production include aromatic vinyl monomers such as styrene, α-methylstyrene, halogenated styrene, and divinylbenzene, and vinyl monomers such as vinyl acetate and vinyl propionate. Esters, unsaturated nitriles such as acrylonitrile, methyl acrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl acrylate, lauryl methacrylate, ethylene glycol diacrylate, Examples include ethylenically unsaturated carboxylic acid alkyl esters such as ethylene glycol dimethacrylate.

This vinyl polymer may be a homopolymer or a copolymer consisting of two or more monomers selected from the vinyl mothmers mentioned above. In addition, the above vinyl monomers and conjugated diolefins such as butadiene and isoprene, acrylic acid, methacrylic acid, acrylamide, methacrylamide, glycidyl acrylate, glycidyl methacrylate, N-methylol acrylamide,
Copolymers with copolymerizable monomers such as N-methylolmethacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, diallyl phthalate, allyl acrylate, allyl methacrylate can also be used.

Polymer particles as the mother particles having a number average particle diameter within a specific range in the present invention can be easily obtained, for example, by emulsion polymerization or suspension polymerization of the above-mentioned vinyl monomers, or by crushing the polymer bulk.

In particular, when microencapsulated fine particles having a uniform particle size are required, base particles having a uniform particle size may be used.
The swelling polymerization method described in the publication, Journal of Polymer Science Polymer Letters Editorial (J, P
olym, Sci,, Polymer Lett
er Ed, ) or the polymerization method previously proposed by the present inventors (Japanese Patent Application Laid-Open No. 61-215602)
61-215603, 61-215604>. For example, the number average particle diameter Sn is 1 to 100 μm, preferably 1 to 25 μm,
When using fine particles having a particle size distribution such that particles having a particle size in the range of n±20% account for 70% by weight or more, preferably 80% or more, and more preferably 90% by weight or more of the total, uniform Microencapsulated fine particles suitable for applications requiring microencapsulated fine particles having a particle size can be obtained.

In addition to the above-mentioned polymer particles, the mother particles of the present invention include pharmaceuticals, agricultural chemicals, and agrochemicals having a number average particle diameter in the range of 1 to 200 μm.
Foods, fragrances, dyes, pigments, metal powders, etc. can also be used.

The child particle in the present invention is composed of a polymer, and the monomer for forming this polymer is selected from among the monomers used in polymerization of the polymer constituting the mother particle, depending on the intended use and use. Ru. However, the monomer for forming child particles (hereinafter referred to as
(referred to as "monomer composition for forming child particles"), 2
Those having a solubility in water at 5° C. of 0.5% by weight or less can be preferably used. Monomers with a solubility in water exceeding 0.5% by weight are used in an amount of less than 5 parts by weight, preferably 2 parts by weight or less, more preferably 1 part by weight or less, based on 100 parts by weight of the monomer composition for forming child particles. It is preferable. Monomer composition 1 for forming child particles contains a monomer having a solubility in water of more than 0.5% by weight.
If it is used in an amount exceeding 5 parts by weight per 00 parts by weight, the chargeability of the resulting polymer will be greatly reduced, which is undesirable.
Examples of poorly water-soluble monomers having a solubility in water of 0.5% by weight or less include styrene, n-butyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate, divinylbenzene, butadiene, and the like. .

Examples of water-soluble monomers having a solubility in water of more than 0.5% by weight include methyl acrylate, ethyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, itaconic acid, acrylonitrile, and vinyl acetate.

In the present invention, it is necessary to polymerize the polymer particles used as child particles in an aqueous medium in the presence of an anionic surfactant.

Examples of such anionic surfactants include dodecylbenzene sulfonate, lauryl sulfate, dialkyl sulfosuccinate, and alkylnaphthalene sulfonate (the counter ions of these salts are Na'', K'', and NH4'').
), etc.

The amount of anionic surfactant to be used is selected to be below the critical micelle concentration that does not adversely affect the chargeability of the obtained polymer particles, and is 0.01 to 0.00 parts by weight based on 100 parts by weight of the monomer composition for forming child particles. .2 weight and preferably 0.2 weight.
05 to 0.11 parts by weight. If the amount of anionic surfactant used is less than 0.01 parts by weight, polymerization stability will be insufficient;
If the amount exceeds 2 parts by weight, the charging performance of the resulting microencapsulated fine particles using polymer particles will be greatly reduced, causing problems in using them as toners.

In the present invention, the polymerization initiator used in the polymerization of polymer particles for child particles needs to be a persulfate salt from the viewpoint of polymerization stability and chargeability of the obtained polymer particles. Examples of persulfates include sodium persulfate,
Examples include potassium persulfate and ammonium persulfate.

In the present invention, the amount of persulfate used in the polymerization of polymer particles for child particles is most important.

That is, 0.03 to 0.15 parts by weight of persulfate is added to 100 parts by weight of the monomer composition for forming child particles at the start of polymerization, and when the polymerization conversion rate reaches 65% or more, further persulfate is added. It is necessary to perform polymerization by adding 0.15 to 1.0 parts by weight.

If the amount of persulfate used at the start of polymerization is less than 0.03 parts by weight, polymerization of the monomers will be insufficient. Also,
If the amount of persulfate used at the start of polymerization exceeds 0.15 parts by weight, the polymerization stability will be poor because the polymerization will be carried out under conditions where the concentration of surfactant is low, and the synthesis of polymer particles will actually be interrupted. It becomes difficult.

This finding is contrary to what is mentioned in the so-called soap-free polymerization (R, H, Fich; 5
Science and Technology of
Polymer Co11oidsp, 100 Ha
rtinus N1jhoff Publishers
(1983)). The reason for this difference is that while conventional soap-free polymerization is mainly carried out using relatively highly water-soluble monomers such as methyl methacrylate, in the polymerization of polymer particles for child particles in the present invention, This is thought to be due to the fact that monomers with relatively low water solubility are mainly used.

If the polymerization is carried out by adding persulfate only at the beginning of polymerization, the polymerization can be completed, but the resulting polymer particles have low negative chargeability, and they can be used as child particles to form microcapsules. Even if encapsulation is carried out, it is difficult to obtain encapsulated fine particles having sufficient negative chargeability. Therefore, in the present invention, the polymerization conversion rate is 65% or more, preferably 70-99%, more preferably 75-99%.
When reaching the 5% stage, add 0.15 to 1.0 parts of persulfate to the system per 100 parts by weight of the monomer composition for forming child particles.
weight and preferably 0.15 to 0.5 parts by weight to continue the polymerization. If persulfate is added before the polymerization conversion reaches 65%, new microparticles will be generated in the system, which will deteriorate the stability of the system and produce a large amount of coagulum to maintain the polymerization. become unable to do so.

If the amount of additional persulfate used is less than 0.15 parts by weight, the effect of increasing the amount of charge on the polymer particles will not be sufficient, and if it exceeds 1.0 parts by weight, the hydrophilicity of the polymer particles will increase, and As the amount of the hydrophilic oligomer increases, the charging property of the polymer particles decreases.

In the polymerization of polymer particles for child particles, the polymerization temperature is 50 to 100°C, preferably 60 to 90°C.

The child particles used in the present invention have a number average particle diameter of 175 or less, preferably 1/10 or less, more preferably 1720 or less of the number average particle diameter of the mother particle.

The number average particle diameter of the child particles is 175 the number average particle diameter of the mother particle.
If it exceeds 100%, it will not be possible to form a uniform and sufficiently thick coating layer on the surface of the base particles. The number average particle diameter and particle diameter distribution in the present invention were determined by randomly measuring the particle diameters of 1000 particles on an electron micrograph.

Further, in the present invention, powders such as pigments, dyes, magnetic substances, waxes, etc. can be used as child particles together with polymer particles for child particles depending on the purpose of modification.

Further, in order to form a thick coating layer by one encapsulation treatment, it is preferable to use mixed particles made of polymers from two or more companies as child particles. This is because a thick coating layer cannot be obtained due to electrostatic repulsion between child particles of the same type on the surface of the mother particle, whereas when child particles of different types are used, electrostatic repulsion between child particles as described above occurs. This is thought to be due to the reduction in In addition, if a particle consisting of a substance or composition different from that of the surface of the mother particle is used as a child particle, the child particle may adhere to the mother particle due to frictional electrification between the mother particle and the child particle. This is preferable because it facilitates the process of encapsulation, allows a thick coating layer to be formed by a single encapsulation process, and reduces the number of residual particles.

In addition, microencapsulated fine particles having a multilayer structure coating layer having a plurality of coating layers can be produced by carrying out microencapsulation multiple times using child particles of the same type or different types. In this case, if the type of child particles is changed for each coating layer, it becomes easier to adhere by triboelectric charging, and the formation of the coating layer becomes easier.

In order to form a coating layer of child particles on the surface of a mother particle by the method of the present invention, first the mother particles and child particles are mixed, and then these mother particles and child particles are placed in a container equipped with stirring blades in an air stream. Stir at high speed using a stirring blade. Due to this high-speed stirring, the particles collide with each other or with the stirring blade or the wall of the container, generating direct impact energy on the particle surface, and this energy melts the mother particle surface or child particles or stretches the child particles and coats them. In the method of the present invention, in which a layer is formed on the surface of the mother particles and microencapsulation is achieved, the mother particles and child particles are stirred at high speed in an air stream as described above. It is possible to prevent particles from coalescing and form a uniform coating layer on each surface of the base particles used. In addition, if a ball mill or an automatic mortar is used as in the conventional method, the degree of fusion of particles increases, which is not preferable.

The peripheral speed of the stirring blade in the method of the present invention is 15i1/sec or more, preferably 30m/sec or more, more preferably 40 m/sec or more.
~150m/sec. If the peripheral speed of the stirring blade is lower than 15 m/sec, sufficient energy cannot be obtained to form the coating layer. There is no particular limit to the upper limit of the circumferential speed of the stirring blade, but it is naturally determined based on the equipment to be used, energy efficiency, etc.

In the method of the present invention, if a large amount of the above-mentioned mother particles and child particles are introduced into a container equipped with stirring blades and stirred at high speed, collisions between the particles or with the stirring blades or the wall surface of the container will occur more than necessary. Since a coating layer cannot be formed or high-speed stirring becomes difficult, the total weight of the mother particles and child particles is 1! It is preferable to use it at a concentration of 10 to 1009 g, preferably 20 to 70 g. The total weight of the mother particles and child particles is 1 of the container internal volume!
When the weight is less than 10g, the frequency of collisions between particles is small;
The collision energy necessary for forming the coating layer cannot be obtained.

On the other hand, if the total weight of the mother particles and child particles exceeds 100 g, fusion of the mother particles will occur, making it impossible to obtain microencapsulated fine particles with a uniform particle size, and also causing adhesion of the particles to the inner wall of the device, which is not preferable. do not have.

Regarding the usage ratio of mother particles and child particles, the mother particles are 100
1 to 100 child particles per part by weight, preferably 5 to 100 parts by weight
It is preferable to use it in a proportion of 50 parts by weight.

If the amount of child particles used is less than 1 part by weight, the formation of a coating layer will be insufficient, while if it exceeds 100 parts by weight, fused particles of child particles will tend to be produced, which is not preferable.

One of the main uses of the microencapsulated fine particles obtained by the method of the present invention is as a toner for developing electrostatic images used in electrophotography. When producing this toner, particles having a number average particle size Sn of 1 to 30 μm, preferably 1 to 15 μm, and a particle size in the range of Sn ± 20% are
Polymer particles, usually selected from vinyl polymers, having a particle size distribution such that they account for 0% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more are used as mother particles, and as child particles. is a coloring particle such as carbon black and the polymer particle, and 0.1 to 100 weight of the polymer particle per 1 part by weight of the coloring particle,
It is preferable to use a mixture preferably in a proportion of 0.3 to 10 parts by weight. Also, as part of the child particle,
The performance of the toner can also be adjusted by mixing and using fine particles such as a charge control agent such as nigrosine or chromium-containing dye, a fixability control agent such as polyethylene wax or polypropylene wax, or a magnetism imparting agent such as magnetite.

[Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. In the following description, "parts" and "%" represent parts by weight and % by weight, respectively.

(Example 1) By the method described in Japanese Patent Publication No. 57-24369, the monomer composition was styrene/n-butyl acrylate = 7
0/30 polymer particles were produced.

The polymer particles had a number average particle diameter of 661 μm, 4.
Particles with a particle size in the range of 9 to 7.3 μm account for 9
The particles were extremely uniform in particle size and had a particle size distribution of 8% (standard deviation value of particle size was 4% of the number average particle size).

80 g of particles obtained by washing and drying the particles were used as base particles, and 10 g of carbon black #401 (manufactured by Mitsubishi Kasei Corporation) with a number average particle size of about 0.02 μm and 10 g of particles with a number average particle size of about 0.02 μm 0.15 μm polymethyl methacrylate powder IMP-1451J (manufactured by Soken Kagaku Co., Ltd.) 10 g
are mixed as child particles for forming a coating layer, and this mixture has an internal volume of 4! Hybridizer rNH8-1 type (manufactured by Nara Kikai Seisakusho Co., Ltd.) was used at room temperature for 8 minutes at a circumferential speed of stirring blades of 78 m/sec. A uniform coating layer was formed and encapsulated. In addition,
The temperature inside the hybridizer after treatment was about 80°C.

The thus obtained encapsulated fine particles were further used as base particles and subjected to high-speed stirring treatment with a hybridizer in the next coating layer forming step.

Styrene 14 parts n-butyl acrylate 6 parts Sodium dodecylbenzenesulfonate 0.1 part Potassium persulfate 0.1 part Water
Capacity 7 with cooler, temperature regulator and stirring device for more than 200 parts of substances! The mixture was placed in a flask for 4 days and reacted for 1 hour at 75°C under a nitrogen gas atmosphere, and then 56 parts of styrene and 24 parts of n-butyl acrylate were added over 3 hours to reach a polymerization conversion of 85%. At this point, add another 0.2 parts of potassium persulfate and continue to add 2 parts of potassium persulfate.
Following the time polymerization, a dispersion of polymer particles was obtained. The weight yield at this time was 99%, and the average particle diameter of the polymer particles was 0.15 μm. Furthermore, there was no deposit on the polymerization container or stirring blade, and when the obtained dispersion was filtered through a 200-mesh wire mesh, the amount of coagulated matter was as low as 0.05% by weight or less, indicating good stability. Ta.

Subsequently, a 1% calcium chloride solution was added to the obtained dispersion of polymer particles, stirred, and coagulated until it became a slurry, and then washed with water and dried to obtain polymer particles. This polymer particle is used as a child particle.

100 parts of the mother particles and 20 parts of the child particles obtained as described above
This mixture has an internal volume of 4! Using a hybridizer NMS-1 type, the circumferential speed of the stirring blade was 7 at room temperature.
High-speed stirring treatment was carried out at 8 m/sec for 8 minutes. As a result, microencapsulated fine particles were obtained in which a uniform polymer coating layer was formed on the surface of the base particles coated with carbon black.

Even when the obtained microencapsulated fine particles were sandwiched between slide glasses and rubbed, the coating layer did not fall off, indicating that the film formation was sufficient. Further, the microencapsulated fine particles were uniform particles with a number average particle diameter of 7 μm, and their electrical resistance was as high as 1.0 to ×10 16 Ωcm. Furthermore, when the amount of charge of this polymer particle was measured using a known blow-off method, the negative chargeability was as large as -52 μC/g, indicating that this polymer particle functions as a negatively chargeable toner.

We used these polymer particles as a toner and conducted a continuous copy test of 30,000 copies using a copying machine "Sanda DC313ZJ" (manufactured by Sanda Kogyo Co., Ltd.). A highly stable copy image was obtained. Furthermore, the copy image had a resolution of 12 lines/mm, confirming that it was of high quality.

(Examples 2 to 8. Comparative Examples 1 to 5) The polymerization conditions for polymer particles used as child particles were
Microencapsulated fine particles were obtained in the same manner as in Example 1 except for the changes shown in the table, and a copying test was conducted in the same manner as in Example 1 using the microencapsulated fine particles as a toner.

In Examples 2 to 6, microencapsulated fine particles were formed by variously changing the monomer composition of the polymer particles used as child particles. All of these microencapsulated fine particles have a blow-off charge amount of 150 μC/
In a copying test using these toners, as in Example 1, they had an excellent resolution of 12 lines/opening, and a clear and good copy image without fogging could be obtained. It was also confirmed that stable image quality was maintained up to 30,000 copies in a continuous copy test.

Examples 7 and 8 are examples in which a large amount of highly water-soluble monomers were used in the polymerization of polymer particles used as child particles. In this example, the polymerization stability of the system is poor, so the amount of coagulum is large;
In addition, the amount of charge of the microencapsulated fine particles obtained is -2
It is rather low at around 5 μC/g, which is inferior to Examples 1 to 6 for use as a negatively chargeable toner.

Comparative Example 1 is an example in which the amount of sodium dodecylbenzenesulfonate used as a surfactant during polymerization of polymer particles used as child particles was 063 parts, which was larger than the range of the present invention. The microencapsulated fine particles obtained in this example had a blow-off charge of 112 μC/g.
The negative chargeability was low, and the negative chargeability was insufficient. Also, this micro.

When we conducted a copying test using encapsulated fine particles as a toner, we found that the image density was low and a dusting phenomenon occurred after continuous copying of 10,000 sheets, making it impossible to obtain satisfactory copied images. .

Comparative Example 2 is an example in which the amount of potassium persulfate used as a polymerization initiator at the time of starting polymerization of polymer particles used as child particles is outside the range of the present invention. In this example, the polymerization stability of the system was worse than at the beginning of the polymerization, and the system gelled during the polymerization, making it impossible to continue the polymerization.

Comparative Example 3 is an example in which the timing of adding potassium persulfate in the latter stage of the polymerization of polymer particles used as child particles is outside the scope of the present invention, and the polymerization conversion rate is 5.
When the concentration reached 0%, potassium persulfate was added and polymerization was carried out. In this example, the polymerization stability of the system worsened after adding potassium persulfate, and the system gelled near the end of polymerization, making it impossible to obtain the desired polymer particles.

Comparative Example 4 is an example in which potassium persulfate, which should be added at a later stage of polymerization, is not added in the polymerization of polymer' particles used as child particles. The microencapsulated fine particles obtained in this example had a blow-off charge of 110μ.
C/g, and it was not possible to obtain sufficient negative chargeability. In addition, when we conducted a copying test using these microencapsulated fine particles as a toner, a good resolution of 12 lines/mm was obtained in the copied image, but in a continuous copying test, only 10,000 copies were printed. The image density decreased to 0.5, indicating that the toner deteriorated significantly over time.

Comparative Example 5 is an example in which the amount of potassium persulfate added in the latter stage of polymerization in the polymerization of polymer particles used as child particles is 0.1 part, which is less than the range of the present invention. The microencapsulated fine particles obtained in this example had a small charge amount of 117 μC/g, and had insufficient negative chargeability. In addition, when a copying test was conducted using these microencapsulated fine particles as a toner, as in Comparative Example 4, although the initial resolution of the copied image was good, in the continuous copying test of 10,000 sheets, the image density was 0. 7, indicating that deterioration over time is significant.

[Effects of the Invention] According to the present invention, polymer particles with a small particle size can be obtained in the presence of a trace amount of a surfactant, and by using these polymer particles as child particles, the negative chargeability is good and the friction Microencapsulated fine particles whose properties such as chargeability change little over time can be produced.

In addition, according to the present invention, microencapsulated fine particles having a capsule type structure whose surface is covered with a uniform polymer layer, having high mechanical strength, and being hard to break and are stable can be produced through a relatively simple process. Can be manufactured well.

The microencapsulated fine particles obtained by the present invention are
Can be used in many fields, including toner for electrostatic image development in electrophotography, electrostatic photography, etc., liquid crystal spacers, biochemical carriers, powder inks, ion exchange resins, catalyst carriers, adsorption It can be used as a filler for chromatography, display particles for electrophoresis or magnetic fluoride displays, etc. These microencapsulated fine particles can be effectively used as a toner having high resolution, little deterioration over time, and good durability, particularly in the fields of electrophotography and electrostatic photography.

Claims (2)

[Claims] (1) base particles having a number average particle diameter of 1 to 200 μm;
A coating layer of the child particles is formed on the surface of the mother particle by high-speed stirring treatment in an air stream with child particles for forming a coating layer whose number average particle diameter is 1/5 or less of the number average particle diameter of the mother particle. A method for producing microencapsulated fine particles, wherein the child particles are prepared in an aqueous medium containing 0.01 to 0.2 parts by weight of an anionic surfactant based on 100 parts by weight of a monomer composition for forming child particles. Polymerization is initiated in the presence of 0.03 to 0.15 parts by weight of persulfate, and when the polymerization conversion reaches 65% or more, an additional 0.15 parts by weight of persulfate is added.
A method for producing microencapsulated fine particles, characterized in that the polymer particles are obtained by polymerizing by adding ~1.0 part by weight. (2) In claim 1, the monomer composition for forming child particles comprises microencapsulated fine particles comprising 95% by weight or more of a monomer having a solubility in water of 0.5% by weight or less at 25°C. Production method.