JPH11338185A - Powdery toner for forming image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a powdery toner capable of forming a high quality stable image because the toner particles are uniformly charged by using nearly spherical toner base particles having a specified dispersity of particle diameter and an electrically conductive fine powder added to the surfaces of the toner base particles. SOLUTION: An electrically conductive fine powder is added to the surfaces of nearly spherical toner base particles to obtain the objective powdery toner. By the addition of the electrically conductive fine powder, appropriate electric conductivity is imparted to the toner particles so that the quantity of electric charges on the toner particles is made uniform. The particle diameter of the toner matrix particles is preferably 3-12 μm, further preferably 5-10 μm in consideration of the handleability of the toner and the resolution of an image. In order to ensure uniformity in the quantity of electric charges, the dispersibility of the toner base particles is preferably <=1.2. The toner base particles are formed by synthesizing polymer particles from a monomer and a polymn. initiator and coloring the polymer particles with a colorant. The particle diameter can be regulated by controlling the polymn. conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming powder toner for developing an electrostatic latent image.

[0002]

2. Description of the Related Art Conventionally, when a powder toner for forming an image by developing an electrostatic latent image is manufactured, a binder resin, a coloring agent, a charge control agent, and a release agent are heated and mixed. In general, a so-called pulverizing method is used in which a solidified product obtained by cooling and solidifying this is pulverized into fine particles. In this case, the particles obtained by mixing and solidifying the above-mentioned materials have a wide particle size distribution, and therefore, when producing a toner using a pulverization method, the particles are classified after the pulverization. A classification step to narrow the particle size distribution is required.

However, when the particle size distribution is relied on the classification process as described above, the particle size distribution is defined by the performance of the classification device, and there is a limit in making the particle size uniform. Further, if the uniformity of the particle size is to be improved, the yield in the classification step is reduced, which is inefficient. Further, the minimum particle size obtained by pulverization is about 7 μm, and it is impossible to produce a toner having a smaller particle size by a pulverization method. Therefore, high resolution by reducing the toner particle size cannot be expected. .

In order to solve the above problem of the pulverization method, it is desirable to produce the toner by a polymerization method.
According to the polymerization method, a toner having a narrow particle size distribution and a small particle diameter can be obtained without classification. Examples of the polymerization method include a method by dispersion polymerization, a method by suspension polymerization, and a method by agglomerating emulsion-polymerized particles. Among them, the method by dispersion polymerization can obtain a toner having the narrowest particle size distribution. .

[0005] As an image forming toner produced by a dispersion polymerization method, there is, for example, one disclosed in Japanese Patent Application Laid-Open No. 3-121466. The toner produced by the dispersion polymerization method has an essential feature that since the particle size distribution is narrow, the charge amount of each particle tends to be uniform, and the phenomenon of selective development hardly occurs. For this reason, even if the toner is consumed after printing, the particle size distribution and the charge amount of the remaining toner hardly change, so that stable printing can be performed continuously for a long time. In addition, there are advantages such as high development efficiency and improvement in transfer efficiency. Further, high resolution can be achieved because the particle diameter can be reduced.

Further, in order to impart more uniform charging ability to toner particles produced by a dispersion polymerization method, Japanese Patent Application Laid-Open No. 4-308858 discloses a method in which a charge control agent is dyed on polymer particles. As a technique for adsorption, Japanese Patent Application Laid-Open No. 4-39673 discloses a technique for driving a charge control agent into the surface of polymer particles.

[0007]

However, since particles produced by a polymerization method such as a dispersion polymerization method are spherical, when compared with particles produced by the pulverization method, the surface area of the particles is the same as that of particles produced by the pulverization method. Even if the charge control agent is dyed, adsorbed, or driven and coated as described above, the amount of the charge control agent that can be applied is reduced. For this reason, the effect of the charge control agent for equalizing the charge amount is weakened,
The essential feature of the above-mentioned polymerization method that the charge amount of each particle tends to be uniform cannot be fully utilized. Further, the frictional force applied to the toner in the developing device varies, and the charge amount of the toner tends to be non-uniform.

In the toner produced by the polymerization method, since the charge control agent cannot be sufficiently applied, the charge amount of the toner particles is uneven due to the influence of the variation in the triboelectric charge generated in the developing device. When fogging occurs due to development where no electrostatic latent image exists on the photoreceptor, or when only toner particles having a charge amount suitable for development are selectively developed and print density is insufficient. There is a problem that there is.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming powder toner in which toner particles are uniformly charged, so that a high quality and stable image can be formed.

[0010]

According to the first aspect of the present invention, there is provided a toner base particle having a substantially spherical particle shape and a degree of dispersion of a particle diameter of 1.2 or less, and a surface of the toner base particle. And a conductive fine powder externally added to the above.

The invention according to claim 2 comprises toner base particles formed by a dispersion polymerization method and conductive fine powder externally added to the surface of the toner base particles.

According to a third aspect of the present invention, in the image forming powder toner according to the second aspect, the degree of dispersion of the particle diameter of the toner base particles is 1.2 or less.

According to a fourth aspect of the present invention, there is provided a powdery toner for forming an image according to any one of the first to third aspects, wherein
A conductive titanium oxide is used as the conductive fine powder.

According to a fifth aspect of the present invention, there is provided a powdery toner for forming an image according to any one of the first to fourth aspects, wherein
A charge control agent is added.

To facilitate understanding of the present invention, reference numerals in the accompanying drawings are appended in parentheses, but the present invention is not limited to the illustrated embodiment.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the powder toner for image formation according to the present invention will be described below.

The powder toner according to the present invention is obtained by externally adding conductive fine powder to the surface of substantially spherical toner base particles. By externally adding the conductive fine powder, appropriate conductivity is imparted to the toner particles, and the charge amount of the toner particles can be made uniform.

In consideration of the handling of the toner and the resolution of the image, the particle size of the toner base particles is preferably 3 to 12 μm.
m, more preferably 5 to 10 μm. Further, from the viewpoint of ensuring the uniformity of the charge amount, the degree of dispersion of the toner base particles is preferably 1.2 or less. In general, the degree of dispersion of the particle size is

## EQU1 ## The degree of dispersion is defined by the formula: dispersion degree = volume average particle diameter / number average particle diameter. The smaller the value (closer to 1), the narrower the particle size distribution, that is, the more uniform the particle diameter.

The toner base particles are formed by synthesizing polymer particles from a monomer and a polymerization initiator, and coloring the polymer particles with a colorant. When such a polymerization method is used, the particle size can be adjusted by controlling the polymerization conditions. Further, according to the polymerization method, it is possible to form toner base particles having a small particle diameter, and it is possible to form a high-resolution image.

The polymerization method for forming the toner base particles includes:
In addition to a method based on dispersion polymerization and a method based on suspension polymerization, there is a method in which fine particles formed by emulsion polymerization are aggregated to form toner base particles, and any of them can be applied to the present invention.

However, among the above polymerization methods, a method by dispersion polymerization is most preferred. The dispersion polymerization method is a method in which a monomer is polymerized in a solvent having a property that a monomer dissolves but a polymer formed by a polymerization reaction of the monomer does not dissolve. Thus, toner base particles having a degree of dispersion of 1.2 or less can be obtained relatively easily. Further, according to the dispersion polymer, the formed toner base particles have a substantially spherical and uniform shape.

On the other hand, when the suspension polymerization method is used, the particle size distribution of the particles obtained as a result of the polymerization reaction becomes broad.
Therefore, for example, if it is desired to obtain toner base particles having a degree of dispersion of 1.2 or less, a classification step is usually required. Further, when the toner base particles are formed by aggregating the fine particles formed by emulsion polymerization, it is difficult to obtain an aggregate having a uniform size, and the particle size distribution of the toner base particles after the aggregation is also broad. Prone.

Next, a method for preparing toner base particles using a dispersion polymerization method will be described. In the dispersion polymerization method, at least a monomer (monomer) and an initiator are dissolved in a solvent having the above properties, and a polymer (polymer) is generated by a polymerization reaction. Since the polymer does not dissolve in a solvent when the polymer is formed, the produced polymer becomes spherical polymer particles and can be collected by filtration.

Specific examples of the monomer include aromatic vinyls such as styrene, vinyltoluene and α-methylstyrene;
Methacrylates such as methyl methacrylate, ethyl methacrylate, diethylhexyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate,
Acrylates such as ethylhexyl acrylate,
Vinyl esters such as vinyl formate, vinyl acetate, and vinyl propionate; vinyl methyl ether;
Vinyl ethers such as vinyl ethyl ether, methacrylic acid, acrylic acid, maleic anhydride and metal salts thereof, monomers having a functional group such as diethylaminoethyl methacrylate, diethylaminoethyl acrylate, trifluoroethyl methacrylate, methacrylic acid Examples include fluorine-containing monomers such as tetrafluoropropyl. These monomers are polymerized singly or two or more are copolymerized to prepare toner base particles.

In general, it is desirable to use a material having high transparency as the material of the toner base particles, because the material is suitable for forming an image on an overhead projector (OHP) sheet. Further, in order to obtain a good developed image, it is necessary that the insulating property is high. Furthermore, while having sufficient mechanical strength at room temperature,
In forming an image, it is desirable that the material is softened and fixed to the object to be drawn without using a large amount of energy. Therefore, it is necessary to set the glass transition point in an appropriate range.

From the viewpoint that the above conditions are satisfied, the material of the toner mother particles is a copolymer obtained by blending a styrene monomer with one or more monomers of acrylates or methacrylates. Coalescing is particularly preferred.

In the reaction of dispersion polymerization, examples of the organic solvent that dissolves the above-listed monomers include methanol, ethanol, isopropyl alcohol, n-butanol, s-butanol, t-butanol, n-amyl alcohol, and the like. s-amyl alcohol, t-amyl alcohol, isoamyl alcohol, isobutyl alcohol, isopropyl alcohol, 2-ethylbutanol, 2-ethylhexanol, 2-octal, n-octal,
n-decanol, cyclohexanol, n-hexanol, 2-heptanol, 3-heptanol, 3-pentanol, methylcyclohexanol, 2-methyl-2-
One of alcohols such as butanol, 3-methyl-2-butanol, 3-methyl-1-butyn-3-ol, 4-methyl-2-pentanol, and 3-methyl-1-pentyn-3-ol , Or a mixture of two or more types.

Further, examples of the organic solvent used by mixing with these alcohols and adjusting the SP value of the alcohol include hexane, toluene, cyclohexane, and the like.
Hydrocarbon solvents such as benzene and xylene, ethyl benzyl ether, dibutyl ether, dipropyl ether, dibenzyl ether, dimethyl ether, tetrahydrofuran, ethers such as vinyl methyl ether and vinyl ethyl ether, acetaldehyde, acetone, acetophenone, diisobutyl ketone, diisopropyl Ketone,
Ketones such as cyclohexanone; esters such as ethyl formate, ethyl acetate, methyl acetate, ethyl stearate, and methyl salicylate; and water.

Examples of the polymerization initiator to be mixed in the solvent together with the above monomers include azobisisobutyronitrile, dimethyl 2,2-azobis (isobutyrate), benzoyl peroxide and the like.

Further, as a crosslinking agent, divinylbenzene,
Ethylene glycol di (meth) acrylate, butanediol di (meth) acrylate, trimethylolpropane (tri) methacrylate, pentaerythritol tri (meth) acrylate, or the like may be added.

As described above, there is an appropriate range for the particle size of the toner base particles. Therefore, the particle size of the polymer particles is preferably 3 to 12 μm, more preferably 5 to 1 μm.
0 μm. If the particle diameter is too large, the printing resolution will be reduced, and it is difficult to produce particles having a diameter of 15 μm or more by a dispersion polymerization method. On the other hand, it is possible to produce particles having a smaller particle size, for example, particles of about 1 μm by using a dispersion polymerization method. However, if the particle size is too small, there arises a problem that handling of the toner becomes difficult.

Next, the polymer particles are colored. A method for coloring the polymer particles is described in JP-A-3-121466.
As described in the publication, a method of dispersing and dissolving the dye in an organic solvent in which the polymer particles do not dissolve, and then dispersing the polymer particles, heating while maintaining the temperature at or below the glass transition point, and stirring are mentioned. Can be Also, Japanese Patent Application Laid-Open No.
As described in Japanese Patent No. 9365, upon dyeing, ultrasonic waves may be applied to promote dispersion and dissolution of the dye and prevent aggregation of the polymer particles. As the solvent at the time of dyeing, the same solvent as that in which the monomer was dissolved during the polymerization may be used.

Dyes used for coloring include disperse dyes, oil-soluble dyes,
Any dyes such as sublimable dyes, basic dyes and acid dyes can be used. A dyeing experiment may be performed in advance, and a dye having good coloring efficiency may be selected.

After dyeing the polymer particles with a dye, washing may be performed to remove the dye deposited on the surface of the polymer particles. As a solvent used for this washing, water or an alcohol, an organic solvent that dissolves the dye but does not dissolve the polymer particles, or a mixture thereof is used.

Subsequently, if necessary, a charge controlling agent is added to the polymer particles to prepare toner base particles. For example, the charge control agent may be driven into the surface of the polymer particles by mixing the polymer particles and the charge control agent and applying a somewhat high shear force.

As the charge control agent, metal-containing azo compounds,
Salicylic acid-based metal complexes, nigrosine, triphenylmethane, quaternary ammonium salts and the like can be mentioned.

Finally, a conductive fine powder is externally added to the surface of the toner base particles produced by the above method. As conductive fine powder, conductive titanium oxide, carbon black,
Metal oxide or fine metal powder such as alumina powder and nickel powder can be mentioned, but a material having conductivity sufficient to improve the uniformity of the charge amount without unnecessarily reducing the absolute value of the charge amount is selected. It is desirable to do.
In that respect, conductive titanium is particularly preferred. The conductive titanium has a specific resistance of 1 to 50 Ωcm, which is an appropriate value for making the charge amount of the toner uniform without significantly lowering it.

As the conductive titanium oxide suitable for the present invention, ECT-100 (manufactured by Titanium Co., Ltd.), ECT-62
(Titanium Industry Co., Ltd.), ECTR-72 (Titanium Industry Co., Ltd.), ECTT-1 (Titanium Industry Co., Ltd.) and the like.

The conductive fine powder is externally added by stirring and mixing with the toner base particles. External addition amount is 0.01-5
Weight percent is preferred, with 0.05 to 3 weight percent being particularly preferred. When the amount of the externally added conductive fine powder is too small, the effect of making the charge amount of the toner uniform is insufficient, so that the print density becomes low or the print density becomes uneven (unevenness).
Or fogging. On the other hand, if the external addition amount of the conductive fine powder is too large, the conductivity becomes excessive and the absolute value of the charge amount becomes insufficient. For this reason, fogging may occur or development may be difficult.

For externally adding the conductive fine powder, a mixing device such as a Henschel mixer (manufactured by Mitsui Mining) and a mechanomill (manufactured by Okada Seiko) can be used. If necessary, fine particles of hydrophobic silica, carbon black, tin oxide or the like, or fine particles of a lubricant such as higher fatty acid or metal soap may be externally added together with the conductive fine powder. The external addition of a lubricant improves the fluidity of the toner, improves the replenishability of the toner during printing, and has the effect of preventing aggregation of the toner.

In the present embodiment, since the toner is manufactured using a polymerization method, the degree of dispersion of the toner particle diameter can be reduced, and the conductive fine powder is externally added to the toner base particles. The charge amount of the toner particles becomes uniform, and an image of good quality can be formed. In addition, despite the fact that the toner base particles are spherical and only a relatively small amount of the charge control agent can be applied as compared with the case where the toner is manufactured by a pulverization method, the effect of the charge control agent is provided by the conductive fine powder. Therefore, in this embodiment, the charge amount of the toner particles can be made uniform.

In this embodiment, the charge controlling agent is used and the conductive fine powder is externally added to the toner base particles. However, the present invention is also applicable to a case where the charge controlling agent is not added to the toner base particles. It is possible.

In the above-described embodiment, the case where the toner base particles are formed by using the polymerization method has been described. However, the present invention can be applied to the case where other methods for forming substantially spherical toner base particles are used. It is.

[0044]

Next, examples of the powder toner according to the present invention will be described in comparison with comparative examples.

Example First, polymer particles serving as base particles were prepared by a dispersion polymerization method. Stirrer, condenser, thermometer,
A gas inlet tube was attached, methanol and 2-propanol as organic solvents, polyvinylpyrrolidone K-30 as a dispersant, styrene and n-butyl acrylate as monomers, and α, α'-azobis as a polymerization initiator. Isobutyronitrile was placed in a reaction vessel in the weight ratio shown in Table 1 and stirred.

[0046]

[Table 1]

Stirring was performed at a rotation speed of 100 rpm, and the polymerization reaction was performed by heating to 60 ° C. while purging nitrogen gas from a gas inlet tube. After polymerization for 13 hours, the mixture was cooled to 20 ° C. in an ice-water bath for 15 minutes, and polymer particles produced by the polymerization reaction were collected by filtration. Further, the collected polymer particles were washed with methanol and left at room temperature for 48 hours to dry them.

When the polymer particles thus obtained were observed with a scanning electron microscope, it was found that the polymer particles were formed in a substantially spherical shape, and the particle size was measured using a Coulter counter (Multisizer 2 manufactured by Coulter, Inc.). As a result, the volume average particle diameter was 7.5 μm, and the degree of dispersion of the particle diameter was 1.1.

Next, the polymer particles were converted to toner. First, Kayalon Polyster B is used as a dye.
5 g of a saturated methanol solution of lac S200 (manufactured by Nippon Kayaku Co., Ltd.) was mixed with spherical polymer particles 1
The parts by weight were added and dispersed while stirring, and stirring was continued at a temperature of 30 ° C. for 1 hour to dye spherical polymer particles. After the dyed polymer particles were collected by filtration, they were air-dried to obtain dyed spherical polymer particles.

2 parts by weight of the charge control agent Spiron Black T-77 per 1000 parts by weight of the dyed spherical polymer particles
(Hodogaya Chemical Co., Ltd.) was added, and the mixture was treated with a hybridization system (manufactured by Nara Machinery Co., Ltd.) at a rotation speed of 13000 rpm for 5 minutes.

Next, 1 part by weight of conductive titanium oxide (ECTT-1 manufactured by Titanium Industry Co., Ltd.) and hydrophobic silica (HDK H-200 manufactured by Wacker Inc.) were added to 100 parts by weight of the toner base particles.
0) 1 part by weight is 275 with a mechano mill (manufactured by Okada Seiko)
The mixture was stirred and mixed at a rotation speed of 0 rpm for 3 minutes and externally added to obtain a black toner.

When the above-described black toner was filled in a toner cartridge of a laser printer using a negatively charged toner and printing was attempted, a sufficient printing density of 2.3 was obtained with good transmission density and no fog or toner scattering. Image quality was obtained. Also, when the solid printing was performed, the change in the printing density on the printing surface was not noticeable. At this time, the toner charge amount on the developing roller is −24 μC / g,
The charge amount of the toner on the developed photoreceptor was −24 μC / g, and it was found that there was almost no difference between the charge amounts of the two and that selective development did not occur.

Comparative Example To the toner base particles produced by the same method as in the example, only the above-mentioned hydrophobic silica was externally added by the same method as in the example without externally adding the conductive titanium oxide. To obtain a black toner.

When this toner was filled in the toner cartridge of the laser printer described above and printing was attempted, only an image having a transmission density of 1.5 and an insufficient density was obtained. At this time, the toner charge amount on the developing roller is-
41 μC / g, the toner charge amount on the developed photoreceptor is −
24 μC / g, and there was a great difference between the two. From this, it was found that so-called selective development occurred in which the excessively charged toner was not developed, and stable printing could not be performed.

[0055]

According to the first aspect of the present invention, toner base particles having a substantially spherical particle shape and a degree of dispersion of the particle diameter of 1.2 or less, and externally added to the surface of the base particles. Since the toner particles are made of the conductive fine powder thus obtained, the conductivity of the toner particles is optimized and the charge amount becomes uniform, so that a high-quality image can be formed.

According to the second aspect of the present invention, since the toner base particles formed by the dispersion polymerization method and the conductive fine powder externally added to the surface of the base particles, the conductivity of the toner particles is reduced. This makes the charge amount uniform and makes it possible to obtain a high-quality image.

According to the third aspect of the present invention, the degree of dispersion of the particle diameter of the toner base particles is 1.2 or less, so that the charge amount is made more uniform.

According to the fourth aspect of the present invention, the conductive titanium oxide having an appropriate specific resistance value is used as the conductive fine powder, so that the charge amount of the toner particles can be reduced while suppressing the decrease in the charge amount. Uniformity can be ensured.

According to the fifth aspect of the present invention, since the charge control agent is added, the uniformity of the charge amount can be further improved.

Claims (5)

[Claims] 1. A toner base particle having a substantially spherical particle shape and a degree of particle diameter dispersion of 1.2 or less, and a conductive fine powder externally added to the surface of the toner base particle. A powder toner for image formation, comprising: 2. An image forming powder toner comprising: toner base particles formed by a dispersion polymerization method; and conductive fine powder externally added to the surface of the toner base particles. 3. The image forming powder toner according to claim 2, wherein the degree of dispersion of the particle diameter of the toner base particles is 1.2 or less. 4. The method according to claim 1, wherein conductive titanium oxide is used as said conductive fine powder.
Item 10. The powder toner for image formation according to item 8. 5. The image forming powder toner according to claim 1, further comprising a charge control agent.