JPS63139366A - Production of developer for electrophotography - Google Patents

Abstract

PURPOSE:To obtain a developer not causing fogging due to filming when a developer for electrophotography contg. fine silicic acid powder is produced, by removing fine silicic acid powder not stuck to a toner. CONSTITUTION:A mixture of 100pts. styrene-2-ethylhexyl acrylate-divinylbenzene copolymer with 4pts. nigrosine and 50pts. magnetite having 8m<2>/g BET specific surface area is melted at 100 deg.C, mixed, cooled, crushed, pulverized and pneumatically classified to obtain black powder of about 11mum volume average particle size. The black powder is mixed with 0.5wt% fine silicic acid powder and the mixture is pneumatically classified to remove fine silicic acid powder not stuck to the black powder and to obtain a developer contg. 0.4wt% fine silicic acid powder. When the developer is used, a high density clear image is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a developer for developing electrostatically charged images in electrophotography, electrostatic recording, static printing, etc.

[Prior Art] Conventionally, as an electrophotographic method, U.S. Patent No. 2.297°89
Although a number of methods are known, such as in the specification of No. 1, in general, an electrical latent image is formed on a photoreceptor by various means using a photoconductive substance, and then the latent image is transferred to a developing powder ( After the toner image is transferred to a transfer material such as paper as necessary, it is fixed by heat, pressure, solvent vapor, etc. to obtain a copy. Further, when a step of transferring a toner image is included, a step for removing residual toner on the photoreceptor is usually provided.

Examples of methods for visualizing electrical latent images using toner include the magnetic brush method described in U.S. Pat. No. 2,874,083, and the cascade method described in U.S. Pat. No. 2,818,552. Development method and 2,221°776
The powder cloud method described in US Pat. No. 3.9
A method using a conductive magnetic toner described in Japanese Patent Publication No. 09.258, a method using various insulating magnetic toners described in Japanese Patent Publication No. 41-9475, etc. are known.

As toners applied to these developing methods, fine powders in which dyes and pigments are dispersed in natural or synthetic resins have conventionally been used. For example, particles obtained by dispersing a colorant in a binder resin such as polystyrene and pulverizing the particles to about 1 to 30 layers are used as toner. As the magnetic toner, one containing magnetic particles such as magnetite is used. In the case of a system using a so-called two-component developer, the toner is usually mixed with carrier particles such as glass beads and iron powder.

Examples of adding silicic acid fine powder called colloidal silica to conventional toners are well known, and it is recognized that the addition has the effect of imparting fluidity to toners and furthermore uniformizing the chargeability of the toners. . However, with conventional toner containing fine silicic acid powder, as copying continues, the fine silicic acid powder on the photoreceptor cannot be completely cleaned and gradually adheres to the photoreceptor, resulting in filming on the photoreceptor. As a result, there were problems in that the contrast deteriorated and the background portion of the print became significantly fogged.

As a result of studies to solve the above-mentioned problems, the present inventors found that among the silicic acid fine powders contained in the toner, the silicic acid fine powders (hereinafter referred to as ``M-release silica'') that are not attached to the toner cause filming. It was determined that this was the cause.

In other words, to explain this, when we investigated the silicic acid content in the toner scraped off by the photoreceptor cleaner after transfer, we found that it had increased compared to that in the toner before development. When observed under a microscope, many particles that could be recognized as aggregates of fine silicic acid powder were observed to exist without adhering to the toner particles. Further, when the location on the photoreceptor where filming occurred was analyzed, it was found that silicic acid and transfer paper powder were the main components.

Based on these results, the present inventors have found that the above-mentioned problems can be solved by removing free silica in the toner.

An example of a developing process to which the present invention can be applied will be explained.

FIG. 1 shows a cross-sectional view of one 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 in the developing section so as to move in the same direction as the surface of the electrostatic image carrier. A multipolar permanent magnet 3 is arranged inside the nonmagnetic cylinder 2 so as not to rotate. The one-component insulating magnetic developer 6 sent from the developer container 4 is applied onto the non-magnetic cylindrical surface, and the friction between the cylindrical surface and the toner particles imparts a charge of opposite polarity to the electrostatic image charge to the toner particles. give. Furthermore, an iron doctor blade 5 is placed close to the cylindrical surface (at intervals of 50μ11 to 500μ).
+*), by arranging it to face one magnetic pole (the S pole in the figure) of the multipolar permanent magnet 3, thereby regulating the thickness of one layer of the toner to be thin (30 gm to 300 g+*) and uniform.

By adjusting the rotational speed of the cylinder 2, the surface speed and preferably the internal speed of the developer layer are made to be substantially equal to or close to the speed of the electrostatic image holding surface. A permanent magnet may be used instead of iron as the doctor blade 5 to form opposing magnetic poles, and an alternating current bias may be applied between the developer carrier and the electrostatic image holding surface in the developing section. AC bias f is 200~4
000Hz and Vpp of 500 to 3000V are sufficient.

As described above, in this developing step, the non-magnetic cylinder 2 containing the multipolar permanent magnet 3 was used in order to stably hold the one-component magnetic developer on the developer carrier. In addition, in order to form a thin and uniform developer layer, a doctor blade 5 made of a magnetic thin plate or a permanent magnet was placed close to the surface of the cylinder 2. Using a magnetic doctor blade like this.

Opposing magnetic poles are formed between the magnetic poles of the permanent magnet contained in the developer carrier, and the toner particles are forcibly raised between the doctor blade and the developer carrier, causing the toner particles to stand up on other parts of the developer carrier. This is advantageous, for example, in controlling the thickness of the developer layer in the development area facing the electrostatic image surface. Further, by imparting such forced movement 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 wide, there is an effect of preventing the destruction of toner particles and agglomeration. When the toner particles are transferred in the developing area, they are transferred to the electrostatic image side due to the attraction action of the electrostatic image or the action of an alternating current bias.

In the development process, the electrostatic latent image on the photosensitive drum, which is an electrostatic image holder, is turned into a visible image.
In order to prevent excess toner from adhering to the photosensitive drum and causing fog, a constant DC bias VOC higher than the bright area potential VL of the photosensitive drum is applied to the developing sleeve.

Furthermore, in order to erase the image of finger and toe divisions for multiplex/multicolor copying, etc., a strong light such as an LED or a fuse lamp is applied to prevent the tram potential from decreasing further, and the bright area potential VSt is applied to the photoreceptor. give.

However, when filming occurs on the photoreceptor,
The original amount of light does not hit the photoreceptor, resulting in decreased contrast and fog.

It is necessary to eliminate such a phenomenon, and the present inventors have discovered a method that is extremely effective for this purpose.

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

That is, an object of the present invention is to provide 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 that eliminates excessive silica accumulation on a portion of a photoreceptor cleaner and prevents damage to the photoreceptor.

Another object of the present invention is to provide a method for producing a developer that does not cause mixing of colors 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 operation for solving problem C] In the present invention, in an electrophotographic developer to which fine silicic acid powder is added, the above object is achieved by removing fine silicic acid powder that is not attached to the toner. It is something.

The silicic acid fine powder used in the present invention is a fine powder having a 5i-0-Si bond, and includes both those manufactured by a dry method and those manufactured by a wet method.

Various conventionally known methods can be applied to produce the silicic acid fine powder used in the present invention by a wet method. For example, the decomposition of sodium silicate with an acid can be expressed by the general reaction formula (the reaction formula is omitted below): Na20-xsi02+Hci)+H20+ 5i
02-nH20 Nac #Other decomposition of sodium silicate with ammonia salts or alkali salts, after producing alkaline earth metal silicate from sodium silicate.

A method of decomposing with an acid to form silicic acid, and a method of converting a sodium silicate solution to silicic acid using an ion exchange resin.

There are methods that use natural silicic acid or silicates.

In addition to anhydrous silicon oxide (silica), silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, and zinc silicate can be used as the silicic acid fine powder here. In addition, these silicic acid fine powders are effective when applied in an amount of 0.01 to 6% by weight, preferably 0.02 to 3% by weight, particularly preferably 0.05 to 6% by weight, based on the weight of the developer. A preferred form of addition that exhibits excellent stability when added at 1% by weight is 0.01 to 0.01% by weight of the developer! It is preferable that % by weight of the fine silicic acid powder be attached to the surface of the toner particles.

The most effective method for removing free silica is to remove free silica by classification using air classification a or the like.

The toner used in the present invention may be a toner that has undergone a pulverization process, a micro-encapsulated toner, or a toner formed by 1 ftm suspension. It is preferable that silica is externally added by mixing the classified toner and the warp force after classification to an average particle size of 1 to 20 gm, and then free silica is removed by classification.

As the binder resin of the toner used in the present invention, monopolymers of styrene and its substituted products such as polystyrene, polyP-chlorostyrene, and polyvinyltoluene;
-Chlorstyrene 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-functional tylhexyl copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer,
Styrene-butyl methacrylate copolymer, styrene-
α-chloromethyl methacrylate copolymer, styrene-acrylonitrile co-ffi copolymer, styrene-vinyl methyl ether copolymer, styrene-vinylethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer , styrene-based copolymers such as styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, and styrene-maleic acid ester copolymer; polymethyl methacrylate, polybutyl methacrylate, polychloride Vinyl, 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 resins, chlorinated paraffin, paraffin wax, caruna wax, etc. can be used alone or in combination.

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

Furthermore, the toner of the present invention may optionally contain lubricants, conductivity imparting agents, fixing aids, etc., such as polytetrafluoroethylene powder, polyvinylidene fluoride powder, metal salts of higher fatty acids, carbon black, and conductive agents. Tin oxide, etc. may be added.

Further, the toner of the present invention has a volume resistivity of lQi 000
It is preferably 11 or more, particularly 10]2 Ωca+ or more.

The volume resistivity mentioned here is 100 kg/c of toner.
It is defined as the value calculated from the current value after 1 minute has elapsed after molding with a pressure of m2 and applying an electric field of 100 V/c+s.

The toner of the present invention can also be mixed with carrier particles such as iron powder, glass beads, nickel powder, ferrite powder, etc., if necessary, and used as a developer for electrical latent images.

Furthermore, the present invention may contain magnetic powder if necessary. The magnetic powder is a substance that is magnetized when placed in a magnetic field, and is made of ferromagnetic metals such as iron, cobalt, and nickel. Powder or magnetite, γ-Fe+03. There are alloys and compounds such as ferrite.

In particular, in order to exhibit the above-mentioned effects, magnetic powder with a BET specific surface density of 2 to 20 m2/g, particularly 2.5 to 12 II2/g, determined by the nitrogen adsorption method is preferred.

The content of this magnetic powder is preferably 10 to 70% by weight based on the weight of the toner.

[Example] The basic structure and features of the present invention have been described above, and the method of the present invention will be specifically explained based on Examples below. However, this does not limit the embodiments of the present invention in any way. 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 rrr27 g were mixed and melt-kneaded at 160°C in a roll mill. After cooling, the mixture is coarsely pulverized using a hammer mill, and then finely pulverized using a pulverizer. Next, it was classified using an air classifier to obtain a black powder having a volume average diameter of approximately 11 μm.

Adding 0.5% by weight of silicic acid fine powder to this black powder,
A developer having a silicic acid fine powder content of 0.4% by weight was obtained by mixing with a Henschel mixer and removing unattached fine silicic acid powder using an air classifier.

Next, a negative electrostatic image was formed on the OPC photoreceptor, and the image was developed using the above-mentioned developer and transferred and fixed using the method described above. Even after copying 30,000 copies, the resulting image had a density of 1.22. and there is no fog due to filming.
A clear image was obtained.

Example 2 After adding 0.7% by weight of silicic acid fine powder to the black powder of Example 1, a developer was obtained in the same manner as in Example 1.

When a test was conducted in the same manner as in Example 1, the concentration was 1.
20, and there was no fog due to filming at all.

Comparative Example 1 0.4% by weight of silicic acid fine powder was added to the black powder of Example 1, mixed in a Henschel mixer, and developed without performing classification to remove unattached silicic acid fine powder. It was used as a drug.

When this was tested in the same manner as in Example 1, 2
After copying 1,000 copies, filming occurred on the photoreceptor, resulting in fogging.

[Effects of the Invention] As described above, since the electrophotographic developer obtained by the production method of the present invention does not substantially contain M-releasing silica, it is free from filming caused by adhesion of MFLl silica onto the photoreceptor. In addition, there is no excessive silica accumulation on the photoconductor cleaner area, which prevents damage to the photoconductor, and the photoconductor has good durability, resulting in good images over a long period of time. is obtained. Furthermore, even in multicolor/multiple copies, colors do not mix, and toner consumption is reduced.

[Brief explanation of the drawing]

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

Claims (1)

[Claims] A method for producing an electrophotographic developer to which fine silicic acid powder is added, the method comprising removing the fine silicic acid powder not attached to the toner.