JPS6261632A - Preparation of colored polymer particles - Google Patents

Abstract

PURPOSE:To obtain colored polymer particles having a uniform particle size, by polymerizing a vinyl monomer in the presence of colored particles, which were prepared by adhering a colorant to the surfaces of core particles, in an aqueous medium using an oil-soluble polymerization initiator to form a shell layer to the surface of each colored particle. CONSTITUTION:100pts.wt. of core particles with an average particle size of 0.5-100mum obtained by polymerizing a vinyl monomer (e.g., styrene) are mechanically mixed with 1-30pts.wt. of a colorant (e.g., titanium oxide) with a particle size 1/5 or less that of the core particles to obtain colored particles each having a colorant layer 2. Subsequently, 100pts.wt. of the colored particles and 100-4,000pts.wt. of water are stirred in the presence of a dispersion stabilizer to prepare a dispersion and 10-1,000pts.wt. of a vinyl monomer is added to said dispersion and polymerized in the pressure of an oil-soluble polymerization initiator (e.g., benzoyl peroxide) to obtain a colored polymer wherein a shell layer 3 was formed to each colored particles.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a capsule type product whose surface is covered with a polymer, which is used in many fields including toner for electrostatic image development in electrophotography, etc. The present invention relates to a method for producing colored polymer particles.

[Conventional technology]

A typical method that has been proposed or practiced in the past as a method for producing colored polymer particles used for developing electrostatic images in electrophotography, etc. is to add a coloring agent to an adhesive resin and the necessary amount depending on the application. There is a method in which the mixture is melt-kneaded together with various additives in a Nigu machine, cooled, coarsely pulverized in a Zig crusher, and then finely pulverized in a jet mill or the like.

However, the colored polymer particles obtained by this method have a wide particle size distribution and require classification, and their morphology is amorphous, requiring spheronization treatment if necessary. Requires a process.

In addition, with this method, it is extremely difficult to uniformly disperse the colorant and additives in the adhesive resin, and problems arising from the unevenness of the dispersion state of the colorant, etc., include uneven optical properties and electrical properties. One example is the unevenness of physical characteristics.

For colored polymer particles produced by these pulverization methods, for example, JP-A-54-84730, JP-A-54-84731, JP-A-57-83756, JP-A-57-81217. Publication, JP-A-58-76
As described in Japanese Patent Application Laid-open No. 46 and Japanese Patent Application Laid-Open No. 58-80650, a method of producing colored polymer particles by a suspension polymerization method has been proposed. In these methods, a mixture of a vinyl monomer, a polymerization initiator, a colorant, etc. is suspended in water and polymerized to directly produce colored polymer particles. In these suspension polymerization methods, spherical colored polymer particles containing a colorant inside the particles can be obtained, but -
1G has the disadvantage that it has a very wide particle size distribution.

If the particle size distribution of the toner is wide, not only the resolution of the obtained image will be significantly reduced, but also problems such as low gradation of the image will occur.

In general, in order to produce colored polymer particles with a uniform particle size within the particle size range of 1 to several tens of micrometers, which is the particle size range of colored polymer particles used in toner, it is necessary to
No. 9 discloses a method of carrying out swelling polymerization using seed particles of uniform particle size. In this method, the colorant cannot be encapsulated within the polymer particles if the polymer is in a non-crosslinked state, and in order to encapsulate the colorant into the polymer particles, the polymer particles must be highly crosslinked to create a porous state. particles. However, when polymer particles are made into particles in a porous state in this way, the melting point of the polymer becomes high, so there is a problem that it is difficult to satisfy one of the most important performances required for a toner. be.

Furthermore, Japanese Patent Laid-Open Nos. 58-106554 and 60-3647 propose a method of uniformly coating the surfaces of polymer particles with a mixture of a colorant and a polymer solution in a fluidized bed. However, in this method, a sophisticated technique is required to perform coating without particles fused together, and the productivity is considered to be low.

In addition, in Japanese Patent Application No. 60-29293, a coloring agent is attached to the surface of polymer particles of uniform particle size, and the surface is further covered with a capsule layer composed of an aggregate of many small-sized polymer particles. Capsule particles are disclosed. However, when this capsule particle is used, for example, as a toner, its durability is somewhat insufficient.

[Problem that the invention seeks to solve]

The present invention solves problems in conventional methods of producing colored polymer particles using pulverization methods, suspension polymerization methods, etc. (a) the dispersion state of colorants, etc. in the particles is not uniform, and (b) the shape of the particles is non-uniform. (C) wide particle size distribution, etc., and it is possible to easily produce colored polymer particles with high productivity that have high mechanical strength, are hard to break, and have a uniform particle size. The purpose is to provide a manufacturing method that can.

[Means for solving problems]

The above problem can be solved by polymerizing a vinyl monomer using an oil-soluble polymerization initiator in the presence of colored particles made by adhering a coloring agent to the surface of a core particle in an aqueous medium, and forming a shell on the surface of the colored particle. The problem is solved by a method for producing colored polymer particles, which is characterized in that they form a layer.

That is, in the present invention, colored particles formed by attaching a coloring agent to the surface of core particles are dispersed in an aqueous medium,
In this dispersion, a vinyl monomer is polymerized in the presence of an oil-soluble polymerization initiator to form a shell layer made of a polymer on the surface of the colored particles, thereby producing capsule-type colored polymer particles. have

The colored polymer particles obtained by this method consist of three layers in which a coloring agent layer 2 and a shell Ji3 having a substantially uniform thickness are stacked in order on the surface of a core particle L, as schematically shown in FIG. It is a perfectly spherical particle with a structure.

The present invention will be explained in detail below.

The core particles in the present invention usually have an average particle size of 0.
Polymer particles of 5 to 100 μm, preferably 1 to 50 μm are used. Preferred vinyl monomers that can be used to produce the core particles include aromatic vinyl monomers such as styrene, α-methylstyrene, p-methylstyrene, halogenated styrene, and divinylbenzene, vinyl acetate, vinyl propionate, and the like. vinyl esters, unsaturated nitriles such as acrylonitrile, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl acrylate, lauryl methacrylate, Examples include ethylenically unsaturated carboxylic acid alkyl esters such as ethylene glycol diacrylate and ethylene glycol dimethacrylate. In addition, conjugated diolefins such as butadiene and isoprene, acrylamide, methacrylamide, glycidyl acrylate, glycidyl methacrylate, N-methylol acrylamide, N-methylol methacrylamide, 2-hydroxyethyl acrylate,
-Hydroxyethyl methacrylate, diallyl phthalate, allyl acrylate, allyl methacrylate, etc. can also be used depending on the purpose.

The core particles can be easily produced by polymerizing the above-mentioned vinyl monomers by commonly used suspension polymerization or emulsion polymerization. In addition, the swelling polymerization method disclosed in Japanese Patent Publication No. 57-24369 or the Journal of Polymer Science
,Sci,, Polymer Letter Ed
The polymerization method described in , ) 21937 (1983) can also be employed, and this method is advantageous in that it is possible to obtain colored polymer particles having a uniform particle size.

As the colorant in the present invention, various substances can be selected depending on the intended use and use of the colored polymer particles, including pigments and dyes that are generally used as colorants. Specific examples of colorants that can be used include carbon blank, magnetite, hematite, nigrosine, activated carbon, titanium oxide, red iron oxide, quinacridine, and the like.

The particle size of the colorant is preferably 115 or less, particularly 1/10 or less of the particle size of the core particles. If the particle size of the colorant is larger than 115 of the particle size of the core particles, the colorant and the core particles This causes a problem in that the particles tend to break easily when polymerizing a vinyl monomer or using colored polymer particles to form a shell layer. Further, the thickness of the coloring agent layer varies depending on the use of the colored polymer particles, but is usually about 0.01 to 0.5 μm.

Although the method of producing colored particles by attaching a coloring agent to the surface of the core particles is not particularly limited, the mechanical mixing method described below can be preferably used.

In this mechanical mixing method, core particles and a colorant having an average particle size of 115 or less of the average particle size of the polymer particles are mixed in a dry environment such as in air or a nitrogen atmosphere.
The coloring agent is attached to the surface of the core particles by mechanically rubbing and mixing while keeping the temperature of the entire system lower than the glass transition point of the polymer constituting the core particles, thereby forming colored particles. Here, the ratio of the core particles to the colorant varies depending on the size of the core particles and colorant to be combined or the properties required for the colored polymer particles, but usually 1 part of the colorant is added to 100 parts by weight of the core particles.
It is preferable to use up to 30 parts by weight.

In the above mechanical mixing method, it is preferable that the glass transition point of the polymer constituting the core particles is 40°C or higher.If the glass transition point of the polymer is lower than 40°C, the core particles and the colorant may be mixed together. Mechanical frictional mixing is difficult to be carried out smoothly, and even if mixing is carried out across the two, the core particles will be crushed and fused together, producing so-called propionic acid, which is not preferable.

Further, the colored particles can also be obtained by a wet method of mixing core particles and a colorant in a slurry state. This wet method is suitable for attaching a coloring agent when the particle size of the core particles is as small as 2 μm or less. in this case,
It is preferable to treat the surface of the core particles or colorant with a silane coupling agent, a titanium coupling agent, a surfactant, an organic amine compound, etc., since this improves the adhesion efficiency.

In addition, in the present invention, it is also possible to use various additives together with the colorant depending on the use of the colored polymer particles. For example, the colored polymer particles can be used as a toner for electrostatic image development in electrophotography, etc. In some cases, a charge control agent such as nigrosine or chromium-containing dye may be added together with the colorant.

The colored particles thus obtained are subjected to a polymerization step detailed below to form colored polymer particles of the present invention.

First, add 1 part by weight of colored particles to 100 parts by weight of the colored particles.
00-4,000 parts by weight, preferably 300-3.0
The dispersion is prepared by stirring the system in the presence of 00 parts by weight of water plus a dispersion stabilizer.

Examples of the dispersion stabilizer include polyvinyl alcohol, protective colloids such as methyl cellulose, surfactants such as sodium lauryl sulfate and polyoxyethylene nonylphenyl ether, and dispersants such as sodium polyacrylate.

Then, 10 to 1 vinyl monomers were added to the above dispersion,
000 parts by weight, preferably 30 to 300 parts by weight,
In the presence of an oil-soluble polymerization initiator, the temperature of the system is usually 50°C.
Polymerization is carried out by increasing the temperature to ~90°C.

The vinyl monomer can be selected from monomers used for polymerization of the polymer constituting the core particles described above.

In addition, when using colored polymer particles as a toner for electrostatic image development in electrophotography, etc., the polymer constituting the shell layer has a glass transition temperature of 40 to 110°C,
In particular, the temperature is preferably 50 to 90°C.

The oil-soluble polymerization initiator used in the polymerization of the present invention is
It is not particularly limited as long as it is soluble in the vinyl monomer and has a solubility in water of 0.5% by weight or less, preferably 0.1% by weight or less.

Specific examples of the oil-soluble polymerization initiator include lauroyl peroxide, benzoyl peroxide, di-tar-butyl peroxide, and ter-butyl peroxy-2-hexanoate. These oil-soluble polymerization initiators may be added after being dissolved in the vinyl monomer, or may be added alone to the dispersion.

The amount of the oil-soluble polymerization initiator used is not particularly limited, but is 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, per 100 parts by weight of the vinyl monomer.

In order to increase the uniformity of the particle size of the colored polymer particles obtained by polymerization, the polymerization of the vinyl monomer is preferentially carried out on the surface of the colored particles, and new polymer particles are formed independently of the colored particles. It is necessary to suppress the occurrence. An effective method for this purpose is to use vinyl monomers with a particle size of 5 μm or less in order to promote adsorption or absorption of vinyl monomers onto colored particles.
It is preferable to use it in a finely dispersed state in water so that the particle size is preferably 2 μm or less. In order to finely disperse the vinyl monomer in this way, in the presence of a small amount of surfactant, use a homomixer or an ultrasonic homogenizer. Conventional fine dispersion means can be used, such as a high pressure piston homogenizer. Furthermore, in order to suppress the generation of new polymer particles, a water-soluble polymerization inhibitor such as ferric chloride, potassium dichromate, sodium nitrite, etc. may be added to the reaction system.

Note that if the absorption capacity of the core particles for vinyl monomers is too high, most of the vinyl monomers will be absorbed by the core particles, and if polymerization is carried out in this state, the colorant will not be reliably covered with the polymer and will not be completely covered with the polymer. becomes exposed. Such colored polymer particles are undesirable when used for purposes such as toners for developing electrostatic images. In order to prevent this, the following methods (a) and (b) can be used.

(a) The solvent-insoluble content of the polymer constituting the core particles is 95% by weight or more.

Here, the solvent-insoluble content of the polymer.

Cut 1 g of polymer into small pieces, soak it in 100 g of a good solvent for the polymer, leave it at 20°C for 24 hours, and then calculate the weight ratio of the solids that remain undissolved in the solvent to the total amount of the polymer. Although the above-mentioned good solubility table differs depending on the IJmer, for example, toluene, methyl ethyl ketone, xylene, cyclohexane, acetone, chloroform, or a combination thereof can be used.

In order to increase the amount of solvent-insoluble content of the polymer constituting the core particle, for example, a functional vinyl monomer may be used as part of the vinyl monomer used to polymerize the core particle. There is a method of using polymer as a binding structure.

(b) A monomer having a nitrile group as a part of the monomer used for polymerization of the polymer constituting the core particle.

20% by weight or more of mer. According to this method 1', the vinyl monomer absorption capacity can be lowered without forming the polymer constituting the core particle into a crosslinked structure.

As the above-mentioned hexamer having a nitrile group, aj
Examples include crylonitrile and methacrylonitrile.

Methods (a) and (b) above are each simple
Can be used alone or in combination.

In addition, colored polymer particles 1 obtained by the present invention
When using the polymer as a toner for electrostatic image development, a polymer made by copolymerizing a monomer having a nitrile group with another vinyl monomer is used as the core particle since crosslinking does not adversely affect fixing properties. It is preferable to use r.

9 In addition, in the polymerization of the present invention, known surfactants, suspension protectants, dispersants, etc. can be used, and it is particularly preferable to polymerize in the presence of a suspension protectant.

The above-mentioned suspending protectants include organic ones such as polyvinyl alcohol, methyl cellulose, polyvinyl pyrrolidone, magnesium, barium or calcium phosphates, calcium carbonate, zinc white, aluminum oxide, hydroxide, etc. Examples include inorganic materials such as aluminum.

When a surfactant is used in combination, the dispersion stability of the dispersion improves. As the surfactant, a nonionic surfactant is preferable, and when an anionic surfactant is used, the concentration must be below the critical micelle concentration.

In the polymerization of the present invention, additives can be added to the vinyl monomer depending on the use of the colored polymer particles. For example, when using the colored polymer particles as a toner for electrostatic image development, the vinyl monomer An electrostatic modifier such as nigrosine or chromium-containing dye can be added to the monomer.

C Example] 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, "1 part" represents part by weight.

Example 1 Polymer particles having a monomer composition ratio of styrene/acrylonitrile/butyl acrylate -53/30/17 and a glass transition temperature of 70°C were produced by the method disclosed in Japanese Patent Publication No. 57-24369. This particle is
The particles were extremely uniform in size, with an average particle size of 5 μm and a standard deviation of 4% of the average particle size.

Next, 90 parts of the dried particles were used as core particles, and 10 parts of carbon black "Color Blank #40J (manufactured by Mitsubishi Kasei) was stirred with a Henschel mixer for 15 minutes. Colored particles were obtained in which carbon black was uniformly adhered to the surface of the particles to a thickness of about 0.1 μm.It should be noted that most of the carbon blank was completely adhered to the surface of the core particles and did not adhere to the core particles. No residual carbon black particles were observed.The electrical resistance of these colored particles was 4X.
It was as low as 10'Ω.

100 parts of the colored particles thus obtained were added to 700 parts of water in which 3 parts of polyvinyl alcohol had been dissolved, with stirring, and uniformly dispersed to obtain a dispersion of colored particles.

Next, 83 parts of styrene and 17 parts of butyl acrylate (glass transition temperature 60°C) as monomers, and 4 parts of ter-butyl peroxy-2-hexanoate "Perbutyl OJ (manufactured by NOF) as a polymerization initiator were mixed. The mixture was finely dispersed in 200 parts of water in which 1 part of sodium lauryl sulfate was dissolved using an ultrasonic disperser to obtain a monomer dispersion.

At this time, the particle size of the monomer droplets was 2 μm or less. This monomer dispersion was added to the above-mentioned colored particle dispersion and stirred. After stirring for 30 minutes, optical aaL
When observed with *, almost all of the monomer was precipitated on the surface of the colored particles, and no single monomer droplet was present.

To the thus obtained dispersion, 50 parts of a 1% aqueous solution of ferric chloride was added to prevent the generation of unnecessary new powder, and the temperature was raised to 80°C for 6 hours. , colored polymer particles were obtained with a polymerization yield of 95%. The colored polymer particles had a uniform particle size with an average particle size of 6.2 μm and a standard deviation of 5% per particle size.

When the electrical resistance value of the powder particles obtained by drying the colored polymer particles was measured, it was found to have a high resistance of 4.2 XIO"Ω.

Furthermore, when this particle powder was stirred at high speed for 15 minutes using a Henschel mixer and then observed under an optical microscope, no broken particles were found, and it was found that the particles were sufficiently strong mechanically.

Furthermore, to 100 parts of this particle powder, a solution of 1 part of chromium-containing dye "Pontron S-34J (manufactured by Orient Chemical ■), dissolved in 200 parts of methanol, as an electricity regulating agent, was added and thoroughly sprinkled, and dried. , charge amount -12μ
A negatively chargeable toner of c/H was obtained.

Using this toner, copy machine r FD-4045J
(manufactured by Ricoh ■), a copying image had a resolution of 10 lines/dragon and good gradation.

Example 2 Dispersion 80 of colored particles similar to that described in Example 1
3 parts, 83 parts of styrene, 17 parts of butyl acrylate,
4 parts of ter-butylperoxy-2-hexaphate and 200 parts of water were added without fine dispersion, and after stirring at 20°C for 60 minutes to absorb or adhere the monomer to the colored particles, 1% of ferric chloride was added. Add 50 parts of aqueous solution to 8
When polymerization was carried out at 0°C for 6 hours, the polymerization yield was 97%.
colored polymer particles were obtained.

The colored polymer particles had a particle size of 6.3 μm and a standard deviation of 1094, and had a slightly wider particle size distribution than the colored polymer particles obtained in Example 1, but were more or less uniform in particle size.

Comparative Example 1 In place of 4 parts of oil-soluble polymerization initiator ter-butylperoxy-2-hexanoate in Example 2, 2 parts of potassium persulfate, which is a water-soluble polymerization initiator, was used, and no ferric chloride solution was added. Other than that, polymerization was carried out in the same manner as in Example 2, and colored polymer particles were obtained with a polymerization yield of 96%.

These colored polymer particles have a uniform particle size of 6.0 μm and a standard deviation of 8%, but the particle surface has many zero particles.
．． It was covered with small diameter polymer particles of 1-0.3 μm.

When the electrical resistance value of the powder particles obtained by drying the colored polymer particles was measured, it was found to be txio"Ω. In addition, after stirring the powder particles at high speed for 15 minutes with a Henschel mixer, an optical microscope was used to measure the electrical resistance value of the powder particles. Upon observation, some of the small particles on the surface came off, exposing the internal carbon blank and core particles.

Furthermore, when a toner was prepared using this particle powder in the same manner as described in Example 1 and a copying test was conducted, the initial copying performance was good, but after continuous copying of about 3,000 sheets. From this point on, the charging performance deteriorated, and a copied image with low image density was obtained.

Examples 3 to 10 Eight types of colored polymer particles were obtained in the same manner as in Example 2 except that core particles having the conditions shown in Table 1 were used.

The average particle size, standard deviation of particle size, and electrical resistance value of the colored polymer particles of each example obtained are also shown in Table 1.

As is clear from the results in Table 1, the colored polymer particles obtained in Examples 3 to 10 all had a standard deviation of less than 10% and were highly monodisperse. Furthermore, the electrical resistance values of the colored polymer particles obtained in Examples 3, 4.5, and 7 were smaller than those of the colored polymer particles obtained in Examples 6.8.9 and 10. Ta. This is Example 3. 4. In the colored polymer particles obtained in steps 5 and 7, polymerization is performed in a swollen state in which the core particles absorb a lot of particles during polymerization, and for this reason, carbon blanks are present on or near the surface of the colored polymer particles. This is thought to be because of this.

Example 3. 4. The colored polymer particles obtained in Examples 5 and 7 were not very suitable for use as a toner because of their low electrical resistance, but could be suitably used as a spacer for a colored liquid crystal cell.

The colored polymer particles obtained in Examples 6, 8.9 and 1O were used to produce two-layer toners in the same manner as in Example 1.
The toner passed the 00-sheet continuous copying test.

Example 11 Using potassium persulfate as a polymerization initiator, soap-free polymerization was performed to obtain a composition ratio of styrene/2-ethylhexyl acrylate/acrylonitrile/methacrylic acid-15150/3015, an average particle size of 0.72 μm, and a particle size of Polymer particles for core particles with a very narrow particle size distribution with a standard deviation of 3% and a glass transition temperature of 2° C. were obtained.

Next, we introduced the hydrophilic carbon blank “Color Black MA”.
Disperse 5 parts of -100J (manufactured by Mitsubishi Kasei ■) in 50-1 ethanol, and while stirring, add 1 part of a silane camping agent (epoxycyclohexylethyltriethoxysilane, manufactured by Nippon Unicar Co., Ltd.) dropwise. , carbon black surface treatment was performed.

To this, 1000 parts of the dispersion containing 100 parts of the core particles was added, and the mixture was heated at a rotation speed of 5000 rpm using a homomixer.
Stirring was carried out at m for 15 minutes to obtain a dispersion of colored particles in which carbon black was uniformly adhered to the surface of the core particles.

Add 10% polyvinyl alcohol water to this dispersion as a dispersion stabilizer. (110 parts, 1 part of polyoxymethylene nonylphenyl ether and 100 parts of water were added, and further 90 parts of styrene as monomers, 10 parts of n-butyl methacrylate, and 3.5.5- as a polymerization initiator)
Trimethylhexanoyl peroxide [Perloyl 35
5J (NOF■!!ri) Add a mixture of 2 parts and make 30
The mixture was stirred at ℃ for 1 hour. Thereafter, polymerization was carried out at 70° C. for 6 hours to obtain black colored polymer particles with a yield of 93%.

The colored polymer particles were highly monodisperse with an average particle size of 0.90 μm and a 45 standard deviation of particle size of 7%. [Effects of the Invention] According to the present invention, polymer particles with a uniform surface One layer (Shell IW
A production method that can easily produce colored polymer particles with high productivity that have a capsule-type structure covered with can be provided.

Further, according to the present invention, colored polymer particles with high rti dispersibility can be easily obtained by using polymer particles having a uniform particle size as core particles.

The colored polymer particles of the present invention can be used in many fields, such as toners for developing electrostatic images in electrophotography, electrostatic photography, etc., liquid crystal spacers, bioparticles, powder inks, and ion exchange resins. It can be used as a catalyst support, an adsorbent, a packing material for chromatography, display particles for electrophoresis or magnetic display, etc.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing the structure of colored polymer particles obtained by the method of the present invention. l... Core particle 2... Colorant layer 3.
・Shell layer

Claims (1)

[Claims] 1) In an aqueous medium, a vinyl monomer is polymerized using an oil-soluble polymerization initiator in the presence of colored particles formed by adhering a coloring agent to the surface of a core particle, and the colored particles are polymerized using an oil-soluble polymerization initiator. A method for producing colored polymer particles, characterized by forming a shell layer on the surface. 2) The colored polymer particles according to claim 1, wherein the core particles are composed of a polymer having a solvent-insoluble content of 95% by weight or more. 3) The colored polymer particles according to claim 1 or 2, wherein the core particles are composed of a polymer obtained by polymerizing a monomer composition containing 20% by weight or more of a monomer having a nitrile group.