JPH083651B2 - Method for producing electrophotographic developer - Google Patents

Description

The present invention relates to a method for producing a developer for developing an electrostatically charged image in electrophotography, electrostatic recording, electrostatic printing and the like.

[Prior Art] Conventionally, a number of methods such as US Pat. No. 2,297,691 are known as electrophotographic methods, but generally, a photoconductive material is used, and various methods are used to form an electrophotographic image on a photoreceptor. Latent image is formed, then the latent image is developed using developing powder (hereinafter referred to as toner), and the toner image is transferred to a transfer material such as paper, if necessary, and then heating, pressure, solvent vapor, etc. To fix and obtain a copy. When the method has a step of transferring a toner image, it usually has a step for removing the residual toner on the photoconductor.

A method of visualizing an electric latent image using toner is, for example, a magnetic brush method described in U.S. Pat.No. 2,874,063, a cascade developing method described in U.S. Pat. No. 2,618,552 and 2,221,776. Powder cloud method described in U.S. Pat. No. 3,909,258, and a method using a conductive magnetic toner described in U.S. Pat. No. 3,909,258, JP-B-41-947.
A method of using various insulating magnetic toners described in Japanese Patent No. 5 and the like is known.

As a toner applied to these developing methods, a fine powder in which a dye or a pigment is dispersed in a natural or synthetic resin is conventionally used. For example, particles in which a colorant is dispersed in a binder resin such as polystyrene and finely pulverized to about 1 to 30 μm are used as toners. As the magnetic toner, a magnetic toner containing magnetic particles such as magnetite, which also serves as a colorant, is used.
In the case of using a so-called two-component developer, the toner is usually mixed with carrier particles such as glass beads and iron powder before use.

It is known that an example of adding fine powder of silicic acid called colloidal silica to a conventional toner is known to have the effect of imparting fluidity to the toner and further making the chargeability of the toner uniform. . However, with the toner containing the conventional silicic acid fine powder, as the copying is continued, the silicic acid fine powder on the photoreceptor cannot be completely cleaned,
It gradually adheres and filming occurs on the photoconductor.
Therefore, there is a problem that the contrast is lowered and the fog on the printed background portion becomes remarkable.

As a result of studies to solve the above-mentioned problems, the present inventors have found that, in the silicic acid fine powder contained in the toner, the silicic acid fine powder not adhered to the toner (hereinafter referred to as free silica) causes filming. I found out that it was the cause.

That is, to explain this, when the content of silicic acid in the toner scraped off by the photoreceptor cleaner after transfer was examined, it was found to be higher than that of the toner before development. When observed under a microscope, it was found that many particles that could be recognized as aggregates of fine powder of silicic acid existed without adhering to the toner particles. In addition, when the filming on the photoconductor was analyzed, it was found that silicic acid and transfer paper powder were the main components.

The present inventors have found from this result that the above-mentioned problems can be solved by removing the agglomerates of fine silicic acid powder that are free from the toner particles in the developer.

An example of the developing process to which the present invention can be applied will be described. FIG. 1 is a sectional view showing an embodiment of the developing process. In the figure, the electrostatic image holder 1 moves in the direction of the arrow. The non-magnetic cylinder 2, which is a developer carrier, rotates so as to move in the same direction as the surface of the electrostatic image carrier in the developing section. Inside the non-magnetic cylinder 2, a multi-pole permanent magnet 3 is arranged so as not to rotate. The one-component insulating magnetic developer 6 sent from the developer container 4 is applied on the non-magnetic cylindrical surface, and the friction between the cylindrical surface and the toner particles causes the toner particles to be charged with a polarity opposite to the electrostatic image charge. give. Further, by arranging an iron doctor blade 5 close to the cylindrical surface (interval 50 μm to 500 μm) and facing one magnetic pole (S pole in the figure) position of the multi-pole permanent magnet 3, the thickness of the toner layer can be increased. Is regulated to be thin (30 μm to 300 μm) and uniform. By adjusting the rotation speed of the cylinder 2, the surface speed and preferably the internal speed of the developer layer is made substantially equal to or close to the speed of the electrostatic image holding surface. Instead of iron as the doctor blade 5, a permanent magnet may be used to form the opposing magnetic poles. Further, an AC bias may be applied between the developer carrier and the electrostatic image holding surface in the developing section. This AC bias may be f at 200 to 4000 Hz and Vpp at 500 to 3000 V.

As described above, in this developing step, the non-magnetic cylinder 2 containing the multi-pole permanent magnet 3 was used in order to stably hold the one-component magnetic developer on the developer carrier. Further, in order to form the developer layer thinly and uniformly, a doctor blade 5 made of a magnetic thin plate or a permanent magnet was arranged close to the surface of the cylinder 2. When the magnetic doctor blade is used in this way, an opposing magnetic pole is formed between the magnetic pole of the permanent magnet contained in the developer carrier, and the toner particle chains are forced to rise between the doctor blade and the developer carrier. And then
It is advantageous to thinly regulate the developer layer on other portions of the developer carrier, for example, the developing portion facing the electrostatic image surface. Furthermore, by giving such a forced motion to the developer, the developer layer becomes more uniform, and a thin and uniform toner layer formation is achieved. Moreover, since the distance between the doctor blade and the sleeve can be set wider, there is an effect of preventing the destruction and aggregation of the toner particles. When the toner particles are transferred in the developing portion, they are transferred to the electrostatic image side by the action of attracting the electrostatic image or the action of AC bias.

In the development process that makes the electrostatic latent image on the photosensitive drum, which is the electrostatic image holder, into a visible image, excess toner adheres to the bright part (the part exposed to light) of the photosensitive member, causing fog. to prevent a light portion potential V _L of the photosensitive drum to the developing sleeve
A higher constant DC bias V _DC is applied.

Furthermore, in order to erase images in designated sections for multiplex, multicolor copying, etc., the LED, fuse lamp, etc. are irradiated with strong light so that the drum potential does not drop any further, and the bright part potential V _{SL is applied} to the photoconductor. give.

However, when filming occurs on the photoconductor, the original amount of light does not reach the photoconductor, the contrast is lowered, and fog occurs.

It is necessary to eliminate such development, and the present inventors have found a method that is extremely effective for it.

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for producing a developer that solves the above problems.

That is, an object of the present invention is to provide a method for producing a developer that is free from fog due to filming.

A further object of the present invention is to provide a method for producing a developer, which prevents excessive silica accumulation in the photoconductor cleaner section and prevents damage to the photoconductor.

Another object of the present invention is to provide a method for producing a developer in which color mixing does not occur even in multicolor / multiple copying.

Another object of the present invention is to provide a method for producing a developer that consumes less toner.

[Means and Actions for Solving Problems] Specifically, the present invention provides a method for producing an electrophotographic developer having a toner and a fine powder of silicic acid, wherein (a) at least a binder resin and a colorant are used. The colored powder for producing the contained toner is classified to produce a toner having a predetermined particle size, and (b) the toner having a predetermined particle size is mixed with the silicic acid fine powder to adhere the silicic acid fine powder to the toner particle surface. The present invention relates to a method for producing a developer for electrophotography, comprising: (c) removing an aggregate of fine silicic acid powder not adhering to toner particles from the prepared developer by classification.

The silicic acid fine powder used in the present invention is a fine powder having a Si—O—Si bond, and includes both those produced by a dry method and those produced by a wet method.

Various conventionally known methods can be applied to the method for producing the fine silica powder used in the present invention by a wet method. For example, if sodium silicate is decomposed by an acid, and if it is shown by a general reaction formula (the following reaction formula is abbreviated), Na ₂ O ・ xSiO ₂ + HCl + H ₂ O → SiO ₂・ nH ₂ O + NaCl, other ammonium salts of sodium silicate or alkali Decomposition by salts, method of generating alkaline earth metal silicate from sodium silicate, then decomposing with acid to silicic acid, method of converting sodium silicate solution into silicic acid by ion exchange resin, natural silicic acid or There is a method of using silicate.

The silicic acid fine powder referred to here includes, in addition to anhydrous silicon dioxide (silica), aluminum silicate, sodium silicate,
Any silicate such as potassium silicate, magnesium silicate, or zinc silicate can be applied. Further, when the applied amount of these fine silicic acid powders is 0.01 to 6% by weight based on the weight of the developer, the effect is exhibited, preferably 0.02 to 3% by weight, particularly preferably 0.05 to 1% by weight. Shows excellent stability. To describe a preferable mode of addition, it is preferable that 0.01 to 1% by weight of the fine silica powder is attached to the toner particle surface with respect to the weight of the developer.

As a method for removing the agglomerates of fine silicic acid powder released from the toner particles, it is possible to remove the agglomerates of fine silicic acid powder released from the toner particles by classification using an air classifier or the like. This is the most effective method.

The toner used in the present invention may be a toner that has been subjected to a pulverization process, a microcapsulated toner, or a toner formed by suspension polymerization. In the toner that has undergone the pulverization step, after classifying the toner to a predetermined particle size (for example, a volume average particle size of 1 to 20 μm), the classified toner and the silicic acid fine powder are mixed to remove the silicic acid fine powder on the toner particle surface. It is preferable that the particles are additionally attached and then classified to remove the agglomerates of fine silicic acid powder released from the toner particles.

As the binder resin of the toner used in the present invention, a homopolymer of styrene such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene, or a substitution product thereof; styrene-
p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer,
Styrene-butyl acrylate copolymer, styrene-acrylic acid / 2-ethylhexyl copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene -Butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ketone copolymer, styrene-vinyl methyl Ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer,
Styrene-maleic acid copolymers, styrene-based copolymers such as styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide, Epoxy resin, polyvinyl butyral, polyamide, polyacrylic acid resin, rosin, modified rosin, terpene resin,
Phenolic resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, carnauba wax and the like can be used alone or in combination.

If necessary, conventionally known carbon black, copper phthalocyanine iron black, etc. can be used as the colorant used in the toner used in the present invention, and the conventionally known positive or negative charge control agent is used in the present invention.

Further, in the toner of the present invention, if necessary, for example, a lubricant, a conductivity-imparting agent, a fixing aid, etc., such as polytetrafluoroethylene powder, polyvinylidene fluoride powder, metal salt of higher fatty acid, carbon black, conductive oxidation Tin, etc. may be added.

Further, the toner of the present invention preferably has a volume resistivity of 10 ¹⁰ Ωcm or more, particularly 10 ¹² Ωcm or more. The volume resistivity here means that the toner is molded at a pressure of 100 kg / cm ² and
It is defined as a value converted from a current value after 1 minute has passed after applying an electric field of 00 V / cm.

The toner of the present invention may be mixed with carrier particles such as iron powder, glass beads, nickel powder, and ferrite powder, if necessary, and used as a developer for an electric latent image.

When the toner used in the present invention is a magnetic toner,
The toner contains a magnetic powder that also serves as a colorant. As the magnetic powder, substances that are magnetized by being placed in a magnetic field are used, and there are powders of ferromagnetic metals such as iron, cobalt and nickel, or alloys and compounds such as magnetite, γ-Fe ₂ O ₃ and ferrite. .

In particular, in order to exert the above-mentioned effect, the BET specific surface area by the nitrogen adsorption method is preferably ² to 20 m ² / g, particularly 2.5 to 12
Magnetic powder of m ² / g is preferred. The content of the magnetic powder is preferably 10 to 70% by weight based on the weight of the toner.

[Example] The basic configuration and features of the present invention have been described above.
Hereinafter, the method of the present invention will be specifically described based on Examples. However, this does not limit the embodiments of the present invention in any way. The numbers of parts in the examples are parts by weight.

Example 1 100 parts of styrene-2 ethylhexyl acrylate-divinylbenzene copolymer, 4 parts of nigrosine, and 50 parts of magnetite having a BET specific surface area of 8 m ² / g were mixed, and the mixture was rolled.
Melt kneading at 160 ° C. After cooling, with a hammer mill,
After coarse pulverization, fine pulverization was performed with a jet pulverizer to obtain a black powder. Then classify the black powder using an air classifier,
A black magnetic toner having a volume average diameter of about 11 μm was obtained.

99.5% by weight of this black magnetic toner and 0.
5% by weight is mixed with a Henschel mixer to adhere fine silicic acid powder to the surface of the magnetic toner particles to prepare a developer,
Then, an aggregate of silicic acid fine powder not adhering to the magnetic toner particles was removed from the developer by using an air classifier to obtain a developer having a silicic acid fine powder content of 0.4% by weight.

Then, a negative electrostatic image was formed on the OPC photoconductor, and the above developer was used to develop, transfer, and fix the image by the method described above. The image obtained after 30,000 copies had a high density of 1.22. A clear image was obtained without fogging due to filming.

Example 2 A developer was obtained in the same manner as in Example 1 after adding 0.7% by weight of fine silicic acid powder to the magnetic toner of Example 1.

When tested in the same manner as in Example 1, the concentration was 1.
It was as high as 20, and there was no fog caused by filming.

Comparative Example 1 0.4% by weight of fine powder of silicic acid was added to the magnetic toner of Example 1.
After the addition, the mixture was mixed with a Henschel mixer to obtain a developer without performing classification for removing aggregates of silicic acid fine powder not adhering to the magnetic toner particles.

When this was tested in the same manner as in Example 1,
Filming occurred on the photoconductor after copying 2,000 sheets, and fogging occurred due to the filming.

[Advantages of the Invention] As described above, since the electrophotographic developer obtained by the production method of the present invention does not substantially contain free silica, filming caused by adhesion of the free silica onto the photoreceptor is prevented. The image can be prevented and a fog-free image can be obtained.Because there is no excessive silica accumulation in the photoconductor cleaner part, it is possible to prevent damage to the photoconductor, and the durability of the photoconductor is good, and a good image can be obtained for a long time. can get. In addition, colors do not mix even in multi-color / multi-copy. Further, the toner consumption amount is also reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of a developing process to which the present invention can be applied. 1: Electrostatic image carrier 2: Developer carrier 3: Permanent magnet 4: Developer container 5: Doctor blade 6: Developer

Front Page Continuation (72) Inventor Shigeo Urawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-53-58244 (JP, A)

Claims (1)

[Claims] 1. A method for producing an electrophotographic developer having a toner and a fine powder of silicic acid, wherein (a) a colored powder for producing a toner containing at least a binder resin and a colorant is classified and predetermined. A toner having a particle size is produced, (b) a toner having a predetermined particle size is mixed with a silicic acid fine powder to adhere the silicic acid fine powder to the toner particle surface to prepare a developer, and (c) the prepared developer A method for producing an electrophotographic developer, characterized in that agglomerates of fine silicic acid powder not attached to toner particles are removed by classification.