JP3135139B2 - Additive-containing fine powder resin composition and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a crystalline resin having an inner core,
An outer shell whose surface is coated with an amorphous resin such as a styrene resin or an acrylic resin, or a polyester resin or the like. The present invention relates to a powdery resin composition and a method for producing the same. In particular, the additive-containing fine powder resin composition of the present invention is effective as a toner used in electrophotography, electrostatic recording, or the like, or as a cosmetic fine powder for absorbing or reflecting ultraviolet rays.

[0002]

2. Description of the Related Art Conventionally, various methods such as a mechanical pulverization method, a spray drying method, a microencapsulation method, and a polymerization method have been patented as a method for producing a toner used in electrophotography, electrostatic recording, and the like. In the literature. However, most of the currently commercially available methods for producing toners employ mechanical pulverization. The mechanical grinding method is safe, quality stable,
Although excellent in mass production, it has some potential problems. In the mechanical pulverization method, a matrix resin and additives such as a coloring agent, a magnetic agent, a charge control agent, and an abrasive are premixed, and then heated and kneaded with a kneader or a twin-screw extruder, and cooled, solidified, and coarsely crushed. After the process, a manufacturing process is performed in which the material is pulverized by a jet mill, a high-speed rotating mill, or the like, classified into coarse particles and fine particles, and then subjected to external addition and filling.

It is considered that a resin serving as a matrix has a certain degree of brittleness in order to increase production efficiency, and is preferably a resin which is easily crushed. However, if the brittleness is too high, excessive pulverization occurs in the pulverization step, and the amount of fine powder cut increases when obtaining a toner having an appropriate particle size distribution. In addition, while used as a developer in an electrostatic recording machine, etc., fine particles are generated by friction and impact between the carrier and the toner, and other members, causing trouble as spent toner. At present, it is necessary to use a strong resin. This hard resin is not only unfavorable for the pulverization efficiency but also has a high softening point, so that the fixing temperature is raised. For this reason, most heating and pressure fixing type electrostatic recording devices currently on the market require the fixing roll to be constantly heated to about 200 ° C. to be prepared for use, thus raising power costs.

[0004] The electrostatic recording industry has been continuously improving the apparatus aiming at high-quality copying, and there is a tendency for a spherical toner having a small particle diameter of about 5 to 8 μm having a good fluidity and a uniform charging property on the particle surface. It has become. However, the particle size distribution of the powder produced by the conventional mechanical grinding production method is wide,
A method is employed in which the coarse powder is returned to the grinder again. For this reason, in order to produce a toner having an average particle diameter of 10 μm or less, the pulverization efficiency is deteriorated and the amount of recirculation is significantly increased, so that as the particle diameter becomes finer, productivity sharply decreases and profitability is lost. There is a fatal defect such as. In addition, the powder has an irregular shape with many sharp corners, has poor fluidity, and has a disadvantage that it is difficult to obtain uniform charging characteristics as toner particles. It is extremely difficult to solve the above-described series of problems as long as the production method by such mechanical pulverization is employed.

On the other hand, using a suitable solvent, a resin is dissolved in a heated state, and a fine precipitate is precipitated by cooling or addition of a poor solvent, and the solvent is removed to obtain a powdered resin. ). Powders obtained by chemical methods are:
Its shape is closer to a sphere than the powder obtained by mechanical grinding,
Excellent particle size distribution and the like can be obtained. However, resins that can be powdered by this method are limited to resins having a high degree of crystallinity, such as polyethylene resins and some crystalline polyester resins, and amorphous resins such as styrene resins and acrylic resins. It is difficult to pulverize a low-crystalline polyester resin by a chemical pulverization method, and it is extremely difficult to industrially produce spherical fine particles having good fluidity. Also, currently, the particle size of resin powder produced industrially by a chemical grinding method is 60 μm.
In most cases, it is difficult to efficiently obtain resin powder having a particle size of about 10 μm required for toner.

[0006] After a crystalline resin such as polyethylene is heated and melted in a solvent according to a conventional method, the dissolved resin is precipitated by cooling or adding a poor solvent, and the resulting gel is observed under a microscope. It is observed that fine particles have already been formed while containing. The particles form fine particles (hereinafter referred to as primary particles) having a sharp particle size distribution of about 10 μm depending on the solvent / resin ratio, stirring conditions, and the like. Usually, a resin powder is produced by desolvation from this fine powder gel by a vacuum distillation method, but the finally obtained resin powder adheres to the solvent during desolvation and becomes large particles, as described above. The particle size will be from 60μ to 250μ. For this reason, a method of adding a poor solvent such as water during desolvation to prevent coalescence (blocking) of fine particles is generally used.
At present, it is still insufficient, and it is not possible to obtain resin fine powder as isolated primary particles.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a toner which solves the above-mentioned problems of the conventional mechanically ground toner. In other words, conventionally, if a hard and durable resin is used to prevent excessive pulverization in a copying machine, and if an attempt is made to increase the durability, the pulverization efficiency at the time of manufacture will be reduced, and the productivity will be lowered and the fixing temperature will not be raised at the same time. Must not,
It is an object of the present invention to provide a toner which solves a series of problems at once. In addition, it has a small particle size required for high-quality copying and a spherical particle shape with good fluidity, and additives such as a coloring agent, a magnetic agent, and a charge controlling agent are dispersed at a low energy cost and in a good state. An object of the present invention is to provide a toner and a method for producing the same.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the production of a toner using a chemical pulverization method, and as a result, have found the following method, which has led to the present invention. In other words, upon heating and dissolving the thermoplastic resin with a solvent,
(A) A crystalline resin and (B) an amorphous resin and / or a crystalline resin having a higher solubility in the solvent used than the component (A) are heated and dissolved in a solvent, and then cooled or mixed with a poor solvent. Thus, the granular component (A) is first precipitated, and then the solvent is removed at a temperature lower than the precipitation start temperature of the component (A), whereby the component (A) becomes the inner core and the component (B) becomes the outer shell. During the step of producing the finely divided resin composition having at least a two-layer structure, the method for producing an additive-containing finely divided resin composition having a step of blending an additive (C) results in adhesion during solvent removal. As a result, it was possible to obtain a fine powder having an extremely sharp particle size distribution of primary particles without increasing the particle size.

In the process of producing the fine resin powder according to the present invention, the components (A) and (B) in the molten state are reduced by the cooling or addition of a poor solvent to reduce the solvent power of the solvent. ) The components precipitate to form swollen primary particles. At this time, since the component (B) is still in a dissolved state, the component (A) particles are suspended in the component (B) solution. After that, if vacuum distillation is continued at low temperature,
The solvent in which the component (B) is dissolved and the solvent in the component (A) particles are gradually removed, and the component (B) starts to precipitate on the surface of the component (A) particles. The primary particles are covered with the component (B) without being united (blocked), and isolated fine particles having a two-layer structure are obtained.

The component (A) serving as the inner core in the present invention is a crystalline polyolefin-based polymer such as polyethylene, acid-modified polyethylene, polypropylene, poly (4-methylpentene-1), polybutene-1, and ethylene-
Vinyl acetate copolymer (hereinafter abbreviated as EVA), modified EV
A, ethylene-ethyl acrylate copolymer, ethylene-
Crystalline polyolefin copolymers such as acrylic acid copolymers, and modified products thereof, nylon-6, nylon-6.
6, crystalline polyamide resins such as nylon-12, epoxy resins, crystalline polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetals, and various synthetic or natural waxes.

The component (B) used as the outer shell in the present invention is a polystyrene, a styrene-acrylate copolymer, a styrene resin such as an ABS resin, a vinyl chloride resin, a vinyl acetate resin, a vinyl such as polyvinyl butyral. Examples of the resin include resins soluble in solvents such as a series resin, a cellulose resin such as ethyl cellulose and cellulose acetate, a methacryl resin, an acrylic resin, a polyamide resin, an epoxy resin, a polyester resin, polyethylene, EVA, modified EVA, and a rosin resin. In the present invention, a plurality of types of the component (A) may be used, and among the resins of the component (B),
If the solubility in the solvent to be used is higher than that of the component (A), it is possible to use a plurality of different resins as the outer shell.

The additive (C) used in the present invention includes:
It can be used for various types of products that have been used in the past, but is ideal for toner additives used in electrophotography and electrostatic recording, such as colorants, fillers, magnetic agents, lubricants, and charge control agents. It is. In addition, in order to improve the dispersibility in the resin, the use form of the component (C) is such that an additive previously dispersed in a solvent or a carrier resin is added to the component (A) and / or the component (B). This is preferred because it becomes easier. The addition of the component (C) is possible during any of the production steps of the present invention, for example, before the heating and dissolution of the thermoplastic resin with a solvent.
When the additives are mixed, a finely powdered resin composition containing the additives in both the inner core and the outer shell is obtained. In addition, granular (A)
When the component (C) is added in the course of removing the solvent immediately after the precipitation of the component (A) or at a temperature lower than or equal to the precipitation start temperature, the fine powder resin composition mainly containing the additive in the outer shell becomes can get.

The solvent may be removed by any method as long as the temperature is equal to or lower than the temperature at which the component (A) is precipitated, but the vacuum distillation method is most effective. When performing vacuum distillation, it is also possible to add another solvent for the purpose of azeotropic distillation, and after removing most of the good solvent, it is possible to raise the distillation temperature from the precipitation temperature of the component (A), which is effective. It is. Examples of the solvent used in the present invention include linear, branched or low molecular weight paraffins such as butane, pentane, heptane and octane, aromatic compounds such as benzene, toluene, xylene, tetralin and decalin or hydrogenated products thereof. Trichlorethylene,
Halogenated compounds such as perchlorethylene, chloroform, dichlorobenzene, trichlorobenzene and chloronaphthalene; phenols such as phenol, chlorinated phenol and cresol; alcohols such as isopropyl alcohol and glycerin; vinyls, acrylics and epoxy compounds , And other reactive monomers.

The amount of the solvent used with respect to the resin component used as the component (A) and the component (B) varies depending on the combination of the molecular weight of the resin, the ability to dissolve in the solvent, the dissolution, and the like. The solvent may be added in an amount of about 50 to 1000 parts by weight. The combination of the component (A) and the component (B) used in the present invention has a solubility in the solvent used (A).
Use the component (B) which is larger than the component. As a specific example, when a crystalline resin is used as the component (A) and an amorphous resin is used as the component (B), the component (A) / the component (B) / the solvent used can be expressed as polyethylene / polystyrene /
Xylene, polypropylene / polyacryl / perchloroethylene, EVA / polystyrene / toluene, polyamide / ethylcellulose / benzyl alcohol, polyethylene wax / rosin-modified phenol resin / xylene and the like. In addition, a crystalline resin may be used for both the component (A) and the component (B). In this case, it is necessary to combine the component (B) with one having a higher solubility in the solvent used than the component (A). Specific examples are polyethylene / polyester resin / xylene, polypropylene / E
VA / perchlorethylene, polypropylene / modified EV
There are combinations such as A / trichloroethylene. Hereinafter, Examples and Comparative Examples will be described.

[0015]

【Example】

Example 1 (A) Polyethylene (SHOLEX 5110)
(Showa Denko KK) 40 parts by weight, (B) 20 parts by weight of a styrene-acrylate copolymer resin (Priolite ACL Goodyear), (C) 20% carbon black based on polyethylene as an additive 40 parts by weight of the contained master batch and 2 parts by weight of the charge control agent were added together with 300 parts by weight of toluene in a reduced-pressure Henschel mixer to 100 parts.
After melting at 2 ° C. for 2 hours, the mixture was cooled to 40 ° C. Since the component (B) has good solubility in toluene, at 40 ° C., the polyethylene fine particles precipitated in the component (B) solution are in a suspended state. After adding 50 parts by weight of water to the suspension and removing most of the toluene by distillation under reduced pressure at 40 ° C. while crushing, the mixture was heated to 60 ° C. and sufficiently dried under reduced pressure. A black powder, which was a finely powdered resin composition, was obtained. Observation of this black powder with a microscope revealed that small particles of 8 to 13 μm were in an isolated or slightly aggregated state. In order to disintegrate the aggregates, they were pulverized through a jet mill under light pressure conditions (1 kg / cm ² ) to obtain a black powder with a sharp particle size distribution with an average particle size of 9.4μ without classification. Was. After adding the colloidal silica to this and using it with a carrier in a commercially available dry electrophotographic copying machine (Ricoh 4060), a clear copy image without background contamination was obtained.

[0016]

Example 2 70 parts by weight of EVA (Evaflex P-2505 manufactured by DuPont Mitsui Polychemicals) was used instead of (A) polyethylene in Example 1, and (C) kneaded with a ball mill instead of black master batch. A green toner was prepared in the same manner as in Example 1 except that 40 parts by weight of a fleshed cyanine green toluene dispersion (20% pigment concentration) was used. When this green toner was observed under a microscope, 8
It was found that small particles of 1515μ were in an isolated or slightly aggregated state. In order to dissolve the aggregates, the powder was subjected to crushing classification through a jet mill under light pressure conditions (1 kg / cm ² ) to obtain a green powder having an average particle size of 9.6 μm. After adding the colloidal silica to the mixture and using the carrier together with a carrier in a commercially available dry electrophotographic copying machine (Ricoh 4060), a clear copy image without background contamination was obtained.

[0017]

Example 3 (A) 60 parts by weight of polyethylene (Petrocene 180, a product of Tosoh Corporation), (B) 40 parts by weight of styrene-acrylate copolymer resin (Priolite ACL Goodyear), and xylene 300 parts by weight in an autoclave, 100 ° C., after heating and melting for 2 hours,
After cooling to 40 ° C., a suspension in which polyethylene was precipitated was obtained. To this suspension solution was added an additive dispersion in which cyanine green and 1 part by weight of a charge controlling agent were previously added to xylene as a component (C), and the mixture was thoroughly stirred.
When vacuum distillation was performed at ℃ to remove xylene,
The additive-containing fine powder resin composition of the present invention is obtained in which (A) polyethylene is used as an inner core, (B) a styrene-acrylate copolymer resin is used as an outer shell, and component (C) is present in the outer shell. Was done.

Observation of this green toner under a microscope revealed that small particles of 3 to 8 μm were in an isolated or slightly aggregated state. In order to dissolve the agglomerates, the particles were crushed and classified through a jet mill under light pressure conditions (1 kg / cm ² ), and a green powder having an average particle size of 5.8 μm and a sharp particle size distribution without classification was obtained. Obtained. After adding the colloidal silica thereto and using the carrier together with a carrier in a commercially available dry electrophotographic copying machine (Ricoh 4060), a clear copied image excellent in the same quality as in Example 1 and free of background stain was obtained.
Further, although the durability of the toner was the same as that of the general toner and no generation of spent toner was observed, the toner was sufficiently fixed at 140 ° C. lower than the conventional fixing temperature. The fine powder of the additive-containing fine powder resin composition of the present invention was prepared by FTIR.
(Fuerier transform infrared spectrophotometer)
A composite peak of polyethylene and styrene-acrylate copolymer resin was obtained. Further, when the fine powder obtained by thoroughly washing and drying the fine powder using xylene was again subjected to FTIR analysis, the peak of the styrene-acrylate copolymer resin was not recognized, and the peak of the polyethylene resin was not observed. There was only a peak.

[0019]

Example 4 (A) 75 parts by weight of EVA (Ultracene UE25, manufactured by Tosoh Corporation) and polypropylene wax (Viscol 550-P, manufactured by Sanyo Chemical Industries, Ltd.) (B) Polyester resin (Polyester HP-300 Nihon Gosei Co., Ltd.)
The mixture was heated and dissolved in an autoclave at 80 ° C. for 2 hours together with 20 parts by weight of toluene and 300 parts by weight of toluene, and then cooled to 40 ° C. to obtain a suspension. To this were added (C) 1 part by weight of a charge controlling agent as an additive, 40 parts by weight of a cyanine green / toluene dispersion (pigment concentration 20%), and 50 parts by weight of water, and the mixture was sufficiently stirred. Then, toluene was removed, and distillation under reduced pressure was continued at 60 ° C. to remove water, whereby a green powder was obtained. In order to dissolve the aggregates, the powder was subjected to crushing classification through a jet mill under light pressure conditions (1 kg / cm ² ). As a result, a green powder having an average particle size of 8.8 μm was obtained without classification. After adding the colloidal silica to the mixture and using the carrier together with a carrier in a commercially available dry electrophotographic copying machine (Ricoh 4060), a clear copy image without background contamination was obtained.

[0020]

Comparative Example 1 As a developer for electrophotography, 70 parts by weight of a crosslinked styrene-n-butyl acrylate copolymer, 25 parts by weight of magnetic powder, and 2 parts by weight of a gold-containing dye were mixed using a Henschel mill, and then roll milled. And melt kneading. After cooling, the mixture was pulverized by a hammer mill, and further pulverized by a supersonic jet pulverizer at 10 kg / Cm ² to obtain a resin powder. The obtained resin powder has a wide particle size distribution of 1 to 40μ, and a yield of 80% after classification.
A powder having a mean particle size of 14 μm was obtained. Observation with a microscope revealed that the powder was amorphous with sharp corners, had poor fluidity, and had an undesirable shape as an electrophotographic developer.

[0021]

Comparative Example 2 As a developer for electrophotography, 88 parts by weight of a polyester resin, 10 parts by weight of acicular ferrite, 3 parts by weight of carbon black and 3 parts by weight of an amine-based charge control agent were mixed at 110 ° C., 3
Kneading was performed using a kneader for 0 minutes. Cool this to 25 ° C,
After crushing, it was crushed by a conventional method using a jet mill. The resulting black powder has a wide particle size distribution of 1 to 50μ, and when observed with a microscope, becomes an irregular-shaped powder with sharp corners, poor fluidity, and an unfavorable shape as an electrophotographic developer. there were.

[0022]

The object of the present invention is to provide a finely powdered resin composition having a two-layer structure consisting of an inner core and an outer shell, wherein additives are added to the inner core and / or the outer shell as required. .
Since the present invention uses a method of precipitating resin fine particles from a resin solution, the stirring conditions can keep the precipitating conditions of the entire system constant. For this reason, it is characterized in that the diameter of the precipitated resin particles is constant and fine particles having a very sharp particle size distribution can be obtained. It is also possible to control the particle size by changing the resin / solvent ratio, selection of the solvent, temperature conditions, and stirring conditions. The feature of the present invention is that the precipitated fine particles become spherical due to surface tension, and the fluidity of the finally obtained powder is very good.

In the conventional chemical pulverization, during the desolvation step, the precipitated primary particles adhere to each other to form large particles. However, as the desolvation of the present invention proceeds, the component (B) precipitates. Since the component (A) adheres and deposits on the surface of the component (A), coalescence of the particles is prevented, and finally, it can be produced as a light aggregate of primary particles. When this aggregate is crushed with a light force, isolated fine powder can be efficiently obtained. If the additive is blended with the resin component from the beginning, it can be uniformly dispersed in both the inner core and the outer shell. However, when the additive is added after the component (A) serving as the inner core is precipitated, the additive is added only to the outer shell. Can be distributed and is effective in the following cases.

For example, a charge control agent is generally used in a toner to control charging characteristics. Only the charge control agent near the surface of the toner particles exhibits its effect, and the charge control agent inside the particle is meaningless. Therefore, the purpose can be achieved with a small amount by dispersing the charge control agent only in the outer shell, so that the charge control agent, which is by far the most expensive material in the toner, can be saved.
In other words, material costs can be greatly reduced. Further, by using an inexpensive polyolefin resin as the inner core component and using a conventionally used styrene-acrylate copolymer resin for the outer shell, the cost of the raw material resin can be reduced.

Hard toner is generally used because the toner may be excessively pulverized by friction or impact during use as a developer and cause trouble. In order to fix the toner made of the hard resin, a fixing roller at about 200 ° C. is currently used. Many patents relating to pressure-fixable toners have been filed in order to save the fixing energy, but most of them use wax or polyethylene as a matrix resin. However, in reality, it has not been put to practical use due to disadvantages such as brittleness, poor durability, poor adhesion to paper (fixability), difficulty in obtaining a desired particle size distribution and poor production efficiency. When manufacturing the toner according to the present invention, if the outer shell is made of a conventional hard resin and the inner core is made of a soft resin having a low softening point, such as polyethylene, the same durability against friction and impact as the current toner is exhibited, but the fixing is compared. Since the fixing roller temperature can be set lower by 50 to 60 ° C., the utility cost of the electrostatic recording apparatus can be reduced.

In general, commercially available colorants, magnetic materials,
Since additives such as a charge controlling agent are aggregated, it is necessary to sufficiently knead them with a strong kneader, a Banbury mixer, a twin screw extruder or the like to uniformly disperse them. These kneading machines make the resin into a molten state by heating, and apply a strong shearing force to each additive in an aggregated state to disperse the additive. Most of the large amount of energy used here is used for moving and stirring the high-viscosity resin in the molten state, rather than being used for loosening and dispersing the aggregated state of each additive, and is converted into thermal energy. Although a large amount of the generated thermal energy is partially used for melting the resin, at present, most of the heat energy is exchanged with cooling water for preventing overheating of the machine and is discarded. Durable resins conventionally used for toners are:
As a whole, the melt viscosity is high and high energy is required, resulting in an increase in production cost.

In the production method according to the present invention, not only the production of a masterbatch in which the additives are dispersed at a high concentration, but also the dispersion of the additives dissolved in a solvent or treated with a ball mill or a sand mill having high fine dispersion efficiency. Since it can be used as a liquid, the energy cost required for dispersion can be significantly reduced. A coloring agent that is finely dispersed in a liquid layer efficiently has a large coloring power and a high transparency, and thus is optimal for a toner for full-color copying.
As described above, the “additive-containing fine powder resin composition and the method for producing the same” according to the present invention has already reached the limit in the conventional mechanical pulverization method by using a completely new method for toner used in electrostatic recording and the like. Problems, for example, efficient productivity of fine powder toner of 10μ or less, production of spherical fine powder toner with good fluidity, reduction of material cost, uniform fine dispersion of additives, improvement of production yield, reduction of production energy cost Thus, the production of a toner for low-temperature fixing can be led to a solution at once.

Claims (10)

(57) [Claims] 1. When a thermoplastic resin is dissolved by heating in a solvent, (A) a crystalline resin and (B) an amorphous resin and / or a crystal having a higher solubility in a solvent to be used than the component (A). After heating and dissolving the conductive resin in a solvent, the particulate (A) component is first precipitated by cooling or adding a poor solvent, and then the solvent is removed at a temperature lower than the precipitation start temperature of the component (A). As a result, the component (A) becomes the inner core (B)
A method for producing an additive-containing fine powder resin composition, comprising the step of: (C) adding an additive during the step of producing a fine powder resin composition having at least a two-layer structure with the components as outer shells. 2. The method for producing an additive-containing fine powdery resin composition according to claim 1, wherein the step (C) of adding the additive is before the thermoplastic resin is dissolved by heating with a solvent. 3. The additive-containing fine powder according to claim 1, wherein the step (C) of adding the additive is in the process of removing the solvent immediately after the precipitation of the component (A) or at a temperature lower than the precipitation start temperature. A method for producing a resin composition. 4. When a thermoplastic resin is dissolved by heating in a solvent, (A) a crystalline resin and (B) an amorphous resin and / or a crystal having a higher solubility in the solvent to be used than the component (A). After heating and dissolving the conductive resin in a solvent, the particulate (A) component is first precipitated by cooling or adding a poor solvent, and then the solvent is removed at a temperature lower than the precipitation start temperature of the component (A). As a result, the component (A) becomes the inner core (B)
An additive-containing fine powder resin composition, wherein an additive is blended during a step of producing a fine powder resin composition having at least a two-layer structure with the components as outer shells. 5. A method for producing an additive-containing fine powdery resin composition, wherein the additive according to claim 1 is a colorant, a filler, a magnetic agent, a lubricant and / or a charge control agent. 6. An additive-containing fine powder resin composition wherein the additive according to claim 4 is a colorant, a filler, a magnetic agent, a lubricant and / or a charge control agent. 7. A process for producing a masterbatch, wherein the colorant according to claim 5 is finely dispersed in a thermoplastic resin using a kneader or a rudder. 8. A masterbatch wherein the additive according to claim 6 is obtained by finely dispersing a pigment and / or a dye in a thermoplastic resin using a kneader or a ruder. 9. A process for producing an ink-like colorant, wherein the colorant according to claim 5 is obtained by finely dispersing a pigment and / or dye in a solvent using a ball mill or a sand mill. 10. An ink-like colorant, wherein the colorant according to claim 6 is obtained by finely dispersing a pigment and / or a dye in a solvent using a ball mill or a sand mill.