JPH01184034A - Production of microencapsulated fine particle - Google Patents

Abstract

PURPOSE:To produce positive chargeable microencapsulated fine particles by agitating both base particles having specified number average particle diameter and minor particles which have number average particle diameter not larger than 1/5 of particle diameter of the base particle and have been produced by a specified polymerization in an air flow at high velocity. CONSTITUTION:90wt.% or more of the monomer of a raw material consisting of both amino group-contg. vinyl monomer and the other copolymerizable monomer having solubility for water not larger than 0.5wt.% at 25 deg.C. Minor particles are produced by copolymerizing those monomers in an aqueous system while utilizing a water soluble azo compd. as a polymerization initiator. Both base particles having 1-200mum number average particle diameter and minor particles which have number average particle diameter not larger than 1/5 of particle diameter of the base particle and are utilized as the material for forming a coating layer are agitated in an air flow at high velocity and positive chargeable microencapsulated fine particles are obtained by forming the coating layer consisting of the material for forming it on the surfaces of the base particles being core substance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Fields of Application] The present invention is applicable to toners whose surfaces are covered with child particle polymers, which are used in many fields including toners for developing electrostatic images in electrophotography and the like. The present invention relates to a method for producing microencapsulated fine particles with high positive chargeability.

[Prior Art] So-called encapsulation methods for coating particle surfaces with other substances include chemical methods such as interfacial polymerization, 1n 51tu 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 an in-liquid drying method, and mechanical methods such as a fluidizing method and a spray drying method. However, these traditional encapsulation methods
Since it is difficult to uniformly coat individual particles and aggregates are likely to form, there have been problems such as the need for delicate control of reaction conditions when producing industrially.

Recently, methods have been proposed in which the surface of particles is modified using mechanochemical effects, or in which particles are microencapsulated as a core material (Kagaku-Shitsu, 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 using a ball mill, an automatic mortar, or high-speed stirring under an air flow. By embedding and immobilizing child particles in a mother particle, it is attempted to modify the particle surface or to achieve microencapsulation using the mother particle as a core substance.

The child particles that cover the particle surface are usually polymers obtained by aqueous polymerization, but whether they are produced by emulsion polymerization or suspension polymerization, a large amount of surfactant is required to maintain polymerization stability. Or use a suspending protectant during polymerization. For this reason, when capsule particles containing such child particles are used in toner, they are subject to changes over time due to the external environment due to their low chargeability and hygroscopicity, resulting in poor image quality during continuous copying with a copier. This is the cause of a decline in

Furthermore, if the amount of surfactant is minimized, it becomes extremely difficult to maintain polymerization stability. As described above, capsule particles using child particles produced by polymerization in an aqueous system have a problem in that it is difficult to maintain a balance between high chargeability and polymerization stability.

In addition, in the method carried out by the present inventors, in which a coating layer of child particles is formed on the surface of a mother particle by high-speed stirring under an air current, the particle size of the child particles is reduced to a microscopic size of about 0.3 μm or less. Therefore, polymerization of the child particles requires a large amount of surfactant, and it is also necessary to solve the above-mentioned problems.

Furthermore, when producing positively charged microencapsulated fine particles, the production of child particles is often carried out using an anionic surfactant and anionic polymerization initiator. It was difficult to make it positively chargeable.

[Problems to be Solved by the Invention] The present invention solves problems in the polymerization method of child particles that are polymerized by an aqueous polymerization method. Only capsule particles with low chargeability can be obtained from the particles; 2) If a surfactant is used in a small amount or not, polymerization stability becomes poor and it is difficult to synthesize child particles; 3) General anionic particles are difficult to synthesize. The present invention solves problems such as the inability to obtain positively chargeable particles through polymerization, synthesizes child particles with good stability, and thereby provides a method for producing microencapsulated fine particles with high positively chargeability. .

Means for Solving Problem E] The present inventors have made extensive studies to solve the above problems and have completed the present invention. That is, in the present invention, the number average particle diameter is 1 to 2.
A coating layer is formed on the surface of the base particles as a core material by stirring the base particles of 00 μm and the child particles of the coating layer forming material whose number average particle diameter is 115 or less of the number average particle diameter of the base particles in an air stream at high speed. In a method for forming a coating layer of a forming material, the child particles are a copolymer of an amino group-containing vinyl monomer and another copolymerizable monomer, and the amount is 90% by weight or more of the monomers as raw materials for the copolymer. The solubility in water at 25°C is 0.
The present invention provides a method for producing microencapsulated fine particles with high positive chargeability, characterized in that these monomers are polymerized in an aqueous system using a water-soluble azo compound as a polymerization initiator.

Here, the amino group-containing vinyl monomer is particularly preferably dimethylaminoethyl methacrylate, and the water-soluble azo compound is particularly selected from sodium salts, potassium salts, ammonium salts, and organic amine salts of azobiscyanovaleric acid. It is preferable that

The present invention will be explained in detail below.

The number average particle diameter Sn of the base particles used in microencapsulation in the present invention is 1 to 200 μm, preferably 1 to 100 μm.
μm1 More preferably, it is 2 to 50 μm. If the number average particle diameter Sn is less than 1 μm, the collision energy generated by high-speed agitation of the particles will be insufficient, making it difficult to form a coating layer, and the particles will aggregate, making the particles independent and forming a coating layer on their surfaces. It becomes difficult to form. On the other hand, if the number average particle diameter Sn exceeds 200 μm, the properties of fine particles will be lost. Here, the particle size distribution is Sn±2
Particles with a particle size in the range of 0% usually account for 70% of the total
The amount used is at least 80% by weight, more preferably at least 90% by weight.

As the base particles used in microencapsulation in the present invention, both organic and inorganic substances can be used as long as they satisfy the above conditions. It can be selected as appropriate.

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 types of monomers selected from the above vinyl monomers. 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-methylolacrylamide, N-methylolmethacrylamide, 2-hydroxyethyl acrylate, Copolymers with copolymerizable monomers such as 2-hydroxyethyl methacrylate, diallyl phthalate, acrylic acrylate, and acrylic methacrylate can also be used.

Polymer particles having a number average particle size within a specific range as the mother particles for microencapsulation of the present invention can also be obtained, for example, by suspension polymerization of the above-mentioned vinyl monomers, or by pulverization and classification of 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, or the polymerization method previously proposed by the present inventors (JP-A No. 61-215602, JP-A-61-215602)
215603, 6l-215604).

In addition to the above-mentioned polymer particles, the mother particles of the present invention include pharmaceuticals, agricultural chemicals, etc. 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.

Furthermore, naturally, the microencapsulated fine particles obtained in the present invention can be used as base particles.

In this way, microencapsulated fine particles having a multilayer structure can be easily obtained.

Although the monomer composition of the polymer particles for child particles in the present invention can be appropriately selected depending on the purpose, it is a mixture of an amino group-containing monomer and other copolymerizable monomers.

Examples of the amino group-containing monomer include aromatic amino monomers such as pyridine and amino group-containing (meth)acrylates.

The amino group-containing (meth)acrylate is represented by the following general formula (I), where R is H or CH3,
R1 and R2 have 1 to 8 carbon atoms, preferably 1 to 8 carbon atoms.
3 is a hydrocarbon group, and X is an alkylene group having 2 to 4 carbon atoms.

Specific examples of the acrylate of general formula CI) include dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dipropylaminoethyl methacrylate, methylethylaminoethyl methacrylate, dibutylaminoethyl methacrylate, dibutylaminopropyl methacrylate, diethylaminobutyl Methacrylate, diethylaminoethyl methacrylate, dioctylaminoethyl methacrylate, etc. are used.

Among these, preferred are dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dipropylaminoethyl methacrylate, methylethylaminoethyl methacrylate, etc., and a particularly preferred amino group-containing monomer is dimethylaminoethyl methacrylate.

Other copolymerizable monomers can be selected from those exemplified in the description of the synthesis of the base particles above, as long as they are copolymerizable.

The child particles in the present invention must be selected from among these monomers based on the condition of solubility in water.

That is, monomers having a solubility in water at 25° C. of 0.5% by weight or less must account for 90% by weight or more, preferably 95% or more of the total monomer composition. If the total monomer composition is less than 990% by weight of monomers with water solubility of 0.5% or less, a large amount of low polymerization degree substances with many hydrophilic groups will be produced during polymerization, which will affect the charging characteristics of the resulting child particles. Greatly damaged.

Examples of monomers having a water solubility of 0.5% by weight or less include styrene, α-methylstyrene, n-butyl methacrylate, n-butyl acrylate, 2-ethylhexyl acrylate, divinylbenzene, butadiene, and the like.

Examples of monomers with water solubility exceeding 0.5% by weight include:
Examples include methyl acrylate, ethyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, acrylonitrile, vinyl acetate, glycidyl methacrylate, acrylamide, hydroxyethyl acrylate, and many amino group-containing monomers such as dimethylaminoethyl methacrylate. included. Therefore, the amount of the amino group-containing monomer to be used is naturally determined by the water solubility of the monomer.

In the polymerization of the child particles of the present invention, a water-soluble azo compound is used as a polymerization initiator.

Examples of water-soluble azo compounds include azobisisobutyronitrile or azobiscyanovalerianic acid, as long as they are soluble in water, but especially sodium salts, potassium salts, lithium salts, ammonia Salts or organic amine salts are preferred.

In the polymerization of the child particles of the present invention, if a general anionic or nonionic water-soluble polymerization initiator is used instead of a water-soluble azo compound, the polymerization stability becomes poor and stable polymerization cannot be maintained.

The polymerization temperature for these is 50 to 100℃, and the pH of the system is neutral to
Preferably, it is alkaline.

Further, in the present invention, child particles such as pigments, dyes, magnetic fine particles, wax fine particles, etc. can be mixed and used together with the polymer particles for child particles described above.

For example, in toner applications, some of the child particles include carbon black as a pigment, chromium-containing dye as a charge control agent, etc.
It is possible to adjust the toner performance by using fine particle wax as a fixing performance adjusting agent and fine particle magnetite as a magnetism imparting agent.

[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, "part" and "%" represent parts by weight and percentage of polymerization, respectively.

Example 1 (Production of base fine particles) Styrene 70 parts Butyl acrylate 30 parts Water
200 parts Sodium lauryl sulfate 1.5 parts Benzoyl peroxide (dissolved in styrene) After mixing 2 parts with a stirrer, 3 parts with a 300W ultrasonic disperser.
Finely dispersed for 0 minutes, the maximum particle size of monomer droplets was 0.4 μm
A dispersion was prepared. The particle size was measured using a dynamic light scattering analyzer "Model N4" (manufactured by Coulter).

This dispersion was added to 300 parts of water and gently stirred at room temperature. 303.5 parts of the thus obtained fine dispersion of monomer (containing 100 parts of styrene/butyl acrylate, maximum particle size 0)
．． 4 μm) was mixed with 200 parts of a monodispersed polystyrene dispersion (containing 0.13 parts of polystyrene as a solid content) with a number average particle size of 0.70 μm produced by soap-free polymerization, and the mixture was slowly stirred for 6 hours to dissolve the monomer. A contact operation was performed to bring the droplets into contact with the seed particles.

After that, polyvinyl alcohol "GOHSENOL GH20"
When 100 parts of a 10% aqueous solution of J (manufactured by Nippon Gosei Kagaku ■) was added and the system was heated to 80°C to polymerize the monomers, the number average particle size was 6.1 μm, and the particle size was 4.9 μm to 7. .3μ
Particles with extremely uniform particle sizes were obtained, having a particle size distribution in which particles in the range m accounted for 98% by weight of the total (standard deviation of particle size was 4% of the number average particle size).

(Manufacture of mother particles) 80 g of particles obtained by washing and drying the particles produced as described above were used as mother particles, and the number average particle diameter was about 0.
．． 10 g of carbon black #404 (manufactured by Mitsubishi Kasei) of 0.02 μm and polymethyl methacrylate (p-MMA) powder (trade name MP-) with a number average particle size of 0.15 μm.
1451, manufactured by Soken Kagaku ■) as child particles for forming a coating layer, and this mixture was mixed at room temperature using a hybridizer NH8-1 type (manufactured by Nara Kikai Seisakusho) with an internal volume of 41 mm. When the blades (stirring blades) were treated for 8 minutes at a circumferential speed of 78 m/sec, a uniform coating layer of carbon black and p-MMA was formed on the surface of the mother particles and encapsulated (the hybridizer after treatment - the internal temperature was approximately 80°C).

This is used as a base particle for the second stage hybridizer in the next step.
It was used for surface coating film formation treatment.

(Manufacture of child particles) Dimethylaminoethyl methacrylate 3 parts styrene was added to a 72 polymerization vessel equipped with a cooler, a temperature controller, and a stirring device.
75 parts n-butyl acrylate 22 parts water
200 parts and 3 parts of ammonium salt of azobiscyanovaleric acid were added, and the mixture was reacted at 70° C. for 5 hours in a nitrogen gas atmosphere. The polymerization yield was 98%, the particle size was 0.21 μm,
It was a good latex with few aggregates.

A uniform polymer powder was obtained by washing and drying this with water in a conventional manner. The glass transition temperature of this child particle polymer was 62° C., making it optimal as a resin for toner.

(Manufacture of encapsulated fine particles) 20 parts of the obtained polymer particles for child particles are mixed with 100 parts of the mother particles that have undergone the first encapsulation as child particles for forming a coating layer. When this mixture was treated for 8 minutes at room temperature with a blade circumferential speed of 78 m/sec using a Hybridizer NH8-1 type with an internal volume of 4°C, a uniform polymer coating layer was formed on the surface of the carbon black-coated mother particles. Microencapsulated fine particles were obtained.

Even when the obtained microencapsulated particles were rubbed between slide glasses, the coating layer did not fall off, indicating that the coating layer was sufficiently formed.

In addition, these microencapsulated fine particles are uniform particles with a number average particle system of 7 μm and an electrical resistance of 1.0×10
It had a high resistance of 16Ω·cm.

When the charge amount of the particles was measured using a blow-off charge measuring device, it was found that the particles had a high positive charge of +27 μc/g, and could be used as a positively charged toner.

Using this toner, copying machine "Sharp 5F-751"
(manufactured by Sharp ■), a continuous copy test was performed on up to 30,000 copies, and stable, clear, fog-free and high-density copied images were obtained. For duplicate images, 12/
A resolution of mm was obtained and the image quality was high.

Examples 2 to 6, Comparative Examples 1 to 4 In the synthesis of surface coating child particles in Example 1, the child particles were synthesized in the same manner as in Example 1, except that the monomer composition was changed as shown in Table 1. Based on this, microencapsulated fine particles were obtained and designated as Examples 2 to 6 and Comparative Examples 1 to 4.

It can be seen that when the monomer having a solubility in water exceeding 0.5% by weight exceeds 10% by weight, the polymerization stability becomes poor and child particles cannot be stably obtained.

Examples 7 and 8, Comparative Examples 5 to 8 In the synthesis of surface coating particles in Example 1, the polymerization initiator was changed as shown in Table 2. This was used to obtain microcapsule particles, which were designated as Example 7.8 and Comparative Examples 5 to 8.

It can be seen that stable polymerization is possible only when polymerizing with azobiscyanovalerate.

[Effects of the Invention] According to the present invention, it has become possible to stably polymerize an amino group-containing vinyl monomer to obtain cationic child particles, and use this to easily obtain positively chargeable microencapsulated fine particles. .

The microencapsulated fine particles of the present invention are useful as positively chargeable electrophotographic toners.

These particles can also be used for a variety of purposes, such as liquid crystal spacers, bioparticles, powdered inks, ion exchange resins, catalyst supports, adsorbents, packing materials for chromatography, display particles for electrophoresis, or magnetic display displays. It is possible to do so.

Patent applicant: Japan Synthetic Rubber Co., Ltd.

Claims (1)

[Claims] (1) Mother particles with a number average particle diameter of 1 to 200 μm and child particles of a coating layer forming material whose number average particle diameter is 1/5 or less of the number average particle diameter of the mother particles are stirred at high speed in an air stream. , in a method of forming a coating layer of a coating layer-forming material on the surface of a mother particle as a core material, the child particle is a copolymer of an amino group-containing vinyl monomer and another copolymerizable monomer, and , 90% by weight or more of the monomers as raw materials for the copolymer are those whose solubility in water at 25°C is 0.5% by weight or less, and these monomers are polymerized in an aqueous system using a water-soluble azo compound as a polymerization initiator. A method for producing positively charged microencapsulated fine particles, characterized by: