JPH0445821B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a one-component electroscopic magnetic developer,
More specifically, it is a one-component electrodetector consisting of powder particles of a kneaded composition in which ferromagnetic powder such as magnetite and red iron are dispersed in an electrically insulating resin binder at a weight ratio of 95:5 to 50:50. This invention relates to a magnetic developer. Conventionally, when developing an electrostatic latent image, a so-called one-component magnetic developer containing powder of a ferromagnetic material in developer particles has been used as a developer capable of developing a latent image without using a special carrier. widely known. Magnetite is mainly used as this ferromagnetic material due to its magnetic properties and black coloring. When developing an electrostatic latent image using a one-component magnetic developer, each developer particle has an electrostatic attraction force (Coulomb force) between it and the electrostatic latent image and a magnet for forming a magnetic brush. The magnetic attraction force between the particles acts simultaneously, and particles on which the Coulomb force acts more strongly are attracted to the electrostatic latent image, while particles on which the magnetic attraction force acts more strongly remain on the developing sleeve. Development is performed according to the electrostatic latent image on the substrate. However, known one-component electroscopic magnetic developers are still not satisfactory for the purpose of stably forming images of sufficiently high density over a long period of time. In other words, in a one-component magnetic developer, since there is no carrier, the developer particles must be charged by friction between the particles, but charging due to self-friction is not possible in a two-component developer. Compared to electrification, it is inferior in potential height and stability. In addition, in single-component developers, there is a considerable distribution in the magnitude of the magnetic attraction of individual particles, and particle components with large magnetic attraction remain and accumulate on the development sleep, resulting in long-term During use, the amount of fresh developer supplied onto the sleeper gradually decreases, resulting in a significant reduction in the amount of developer that can migrate to the electrostatic latent image side, resulting in the disadvantage that image density is reduced. This is believed to be because the developer particles are classified by air classification, and as a result, the developer contains fine particles with a significantly high concentration of magnetite. In order to prevent such drawbacks, it may be possible to reduce the concentration of magnetite in the kneaded composition for forming the developer, but in this case, the electrodetectability of the final developer particles, that is, the friction between the particles, may be reduced. There is a problem in that the charging property is significantly reduced due to the electrification, and the image density is reduced. The present inventors kneaded ferromagnetic powder such as magnetite and red iron in an electrically insulating resin binder at a certain ratio, and then used this kneaded composition in the form of powder particles to produce a one-component electrodetecting magnetic material. When used as a developer, the distribution of magnetic attraction of individual particles can be relatively uniform, while maintaining the triboelectric properties of the developer particles at an excellent level, and the distribution of particle components onto the developer sleeve can be improved. It has been found that the tendency of residual accumulation can be significantly prevented and images with high density can be stably formed over long periods of copying work. The present invention shows that when a red to brown pigment mainly composed of red iron oxide (iron oxide) is blended into a resin binder in combination with a ferromagnetic powder such as magnetite, the triboelectric charging properties of developer particles are significantly improved. It is based on new knowledge that will be obtained. That is,
Red iron has a tendency to be triboelectrically charged more positively than magnetite, and is also more insulating than magnetite. In this way, when powder particles made of red iron and magnetite dispersed in a resin are rubbed against each other, the exposed areas of red iron on the surface of the particles become positively charged, and the exposed areas of magnetite become negatively charged. It is recognized that the powder particles as a whole remain strongly negatively charged because the charge retention is large. As already mentioned above, when the concentration of magnetite in the developer composition is reduced, the potential due to triboelectric charging tends to decrease, but in the present invention, part of the magnetite can be replaced with red iron. This makes it possible to charge the powder particles rather strongly. The red iron used in the present invention is mainly composed of α-Fe203 (hematite), which is a non-magnetic material that is considerably weaker than magnetite, whereas the true specific gravity of magnetite is 5.2. Its true specific gravity is 5.1 to 5.2, and its properties are very similar to magnetite. Thus, when magnetite and red iron are dispersed in the electrically insulating resin binder, both are dispersed in the binder in a relatively uniform composition ratio. Thus, cooling such a kneaded composition,
Even when crushed and further classified to obtain developer particles, each developer particle contains magnetite, which is a magnetic material, and iron red iron, which is a non-magnetic material, in an almost constant composition ratio. This makes it possible to significantly suppress the possibility of producing powder particles with a significantly high concentration of magnetite. For the above reasons, it will be understood that when the one-component electroscopic magnetic developer of the present invention is used, high-density images can be stably formed throughout long-term copying operations. In the developer of the present invention, it is also important to use ferromagnetic powder such as magnetite and red iron in a weight ratio of 95:5 to 50:50, sometimes 95:5 to 70:30. That is, if the weight ratio of red iron is less than the above range, it will be inconvenient for the purpose of the present invention, which is to prevent the generation of particle components with an abnormally high magnetite concentration and to increase the amount of triboelectrification of the particles. If the amount ratio exceeds the above range, the magnetically attracted properties of the particles will be weakened, the particles will become more conductive, and the hue will be closer to red or brown, which is characteristic of red red iron. Undesirable. In the present invention, the electrically insulating resin binder is preferably used in an amount of 230 to 40 parts by weight, particularly 190 to 50 parts by weight, per 100 parts by weight of the total amount of magnetite and red iron. That is, if the amount of resin is less than the above range, it tends to be unsatisfactory in terms of triboelectricity, while if it is used in an amount greater than the above range, the chargeability and magnetic properties will also be poor. Furthermore, it tends to be unsatisfactory in terms of triboelectric charging properties. In the present invention, red iron oxide having any particle shape and particle size can be used, but for the purpose of the present invention, it is composed of non-crushable agglomerates of cubic particles and has a particle size of 1 to 10 microns, particularly Red iron in the range of 1.5 to 5 microns is preferably used. The red iron oxide made of cubic particles of relatively friable acromerate preferably used in the present invention is produced by the following method, although it is not limited thereto.
That is, a weak alkaline aqueous solution such as aqueous ammonia is added to an aqueous solution of iron sulfate (2) to form a precipitate of iron hydroxide (2). This precipitate, the pH of the mother liquor is 3
As ~9, the pseudoglue-like precipitate of iron hydroxide is transformed into fine cubic hematite by pressurized hydrothermal treatment.
change to That is, at this time, by using the above-mentioned weak alkali and bringing the pH of the mother liquor close to the acidic side, fine cubic particles that are easy to aggregate are generated,
In addition, by performing hydrothermal treatment at a temperature of 150 to 230° C. for a long time of 50 hours or more, and roasting if necessary, the above-mentioned red iron granules can be obtained. On the other hand, the magnetite (Fe ₃ O ₄ ) used in combination with red iron oxide may have any particle shape and size, but the number average particle size is less than 1 micron, especially 0.1 to 0.7 micron. It is particularly desirable to use magnetite which is extremely fine and has a high apparent density of 0.45 g/ml or more. The fine magnetite particles preferably used in the present invention generally have the morphology of cubic particles or slightly rounded amorphous particles, and also have shape anisotropy defined as the ratio of longest dimension/shortest dimension. It is desirable that the gender is in the range of 1.0 to 5.5, preferably 1 to 3. In addition to the above-mentioned magnetite, the ferromagnetic powder may include various ferrites, such as
Synthetic ferrites such as ZnFe ₂ O ₄ can also be used. According to a preferred embodiment of the present invention, by using a combination of red iron oxide and magnetite having such particle size characteristics, an electroscopic magnetic developer is obtained which is particularly suitable for the above-mentioned purpose of the present invention. That is, by using the aforementioned coarse red iron particles, there is a greater tendency for the red iron particles to be exposed on the surface of the molded developer particles, and the frictional electrification between the developer particles is effectively performed, thereby increasing the image density. There will be a noticeable improvement. Furthermore, by using fine particles as magnetite, it is possible to reliably contain magnetite in each developer particle, and it is possible to further ensure charging due to mutual friction between the two. In addition, by using coarse grains of red to brown red iron oxide and fine grains of black magnetite, the hue of the developer as a whole can be made close to pure black. As the electrically insulating resin binder, any developer resin binder having an electrical resistance of 5×10 ¹³ Ω-cm or more when measured alone is used, and generally various mono- or diethylene resin binders are used. Systemically unsaturated monomers, particularly homopolymers and copolymers of (a) vinyl aromatic monomers and (b) acrylic monomers, are used. The vinyl aromatic monomer has the following formula: In the formula, R ₁ is a hydrogen atom, lower (having 4 or less carbon atoms)
The monomer represented by is an alkyl group or a halogen atom, _R2 is a substituent such as a lower alkyl group or a halogen atom, and n is an integer of 2 or less including zero. , α-methylstyrene, α-chlorostyrene, vinylxylene, and vinylnaphthalene. Among these, styrene and vinyltoluene are preferred. As an acrylic monomer, the following formula In the formula, R ₃ is a hydrogen atom or a lower alkyl group, and R ₄ is a hydroxyl group, an alkoxy group, a hydroxyalkoxy group, an amino group or an aminoalkoxy group. Acid, ethyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 3-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 3-aminopropyl acrylate, 3-N,N-diethylaminopropyl Examples include acrylate, acrylamide, and the like. Examples of other monomers used alone or in combination with these monomers (a) or (b) include those of the following formula: In the formula, R ₅ is a hydrogen atom, a lower alkyl group, or a chlorine atom.Conjugated diolefin monomers represented by, for example, butadiene, isoprene, chloroprene, etc.Other examples include maleic anhydride, fumaric acid, crotonic acid, and itacon. Other ethylenically unsaturated carboxylic acids such as acids or their esters, vinyl esters such as vinyl acetate, vinylpyridine, vinylpyrrolidone,
Vinyl ethers, acrylonitrile, vinyl chloride, vinylidene chloride and the like can also be mentioned. The molecular weight of these vinyl polymers is 3000 or
300,000, preferably in the range of 5,000 to 200,000. The developer of the present invention can be obtained by kneading the resin binder magnetite and red iron oxide described above under conditions in which the resin binder is melted, cooling and pulverizing the kneaded composition, and classifying the pulverized product. Prior to kneading and granulating the developer components, auxiliary components of the developer that are known per se may be blended according to a recipe that is known per se. For example, to improve the color tone of the developer, pigments such as carbon black,
Dyes such as acid violet alone or in combination of two or more, 0.5 to 5% by weight of the total
Can be used in amounts of In addition, for the purpose of increasing the volume, fillers such as calcium carbonate and finely powdered silicic acid are added to the total volume.
It can be incorporated in amounts up to 20% by weight. In the method of fixing the developer with a heated roll, an offset preventing agent such as silicone oil, low molecular weight olefin resins, various waxes, etc. can be used in an amount of 2 to 15% by weight based on the total amount. Further, in applications where the developer is fixed with a pressure roll, a pressure fixing agent such as paraffin wax, various animal/vegetable waxes, fatty acid amide, etc. may be used in an amount of 5 to 30% by weight based on the total amount. Furthermore, in order to prevent mutual agglomeration of developer particles and improve its fluidity, a fluidity improver such as polytetrafluoroethylene fine powder or fine powder silica is added in an amount of 0.1 to 1.5% by weight based on the total amount. May be blended. Although the particle size of the developer particles is related to resolution and other factors, it is generally in the range of 5 to 35 microns, and preferably has a particle size that is at least twice the particle size of the agglomerate red red iron. In the electrostatographic copying method using the developer of the present invention, the formation of the electrostatic latent image can be carried out in any manner known per se, for example after uniformly charging the photoconductive layer on the conductive substrate. , an electrostatic latent image can be formed by imagewise exposure. The surface of the substrate having this electrostatic latent image is brought into contact with the magnetic brush of the magnetic developer described above to form a visible image of the developer. To develop an electrostatic latent image using the developer of the present invention, the developer hopper is filled with the above-described one-component diameter magnetic developer. A non-magnetic sleeve is rotatably provided at the lower end opening of the hopper, and a magnet is provided inside the sleeve so as to be rotatable in a direction opposite to the sleeve. In this way, when the sleeve and magnet are rotated, a brush layer of magnetic developer is formed in the shape of a sleeve, and after this brush layer is cut into an appropriate length with a cutting board, a selenium drum and a selenium drum rotating in the same direction as the sleeve are cut. With light contact, the electrostatic image on the selenium drum is developed with a magnetic developer. Next, the developer image on the substrate is brought into contact with the transfer paper, and corona charging with the same polarity as the electrostatic latent image described above is performed from the back side of the transfer paper to transfer the developer image onto the transfer paper. In the present invention, the transferred image can be fixed by any method such as heat roller fixing, flash lamp fixing, or pressure roller fixing, depending on the type of developer. The developer of the present invention is particularly useful for developing p-type photosensitive plates having a positive latent image, such as selenium photosensitive plates and organic photoconductor light plates. Although conventional triboelectric one-component magnetic developers can generally be used for developing photosensitive plates with negatively charged latent images,
- type photosensitive plates show extremely unsatisfactory results in developing positively charged latent images. On the other hand, according to the present invention, excellent effects can be achieved in developing and transferring such a positive charge latent image. The invention is illustrated by the following example. Example 1 A mixture of the compositions shown in Table 1 was kneaded and melted at 145° C. for 30 minutes using a three-roll mill, and after cooling, the mixture was coarsely ground using a cutting mill to a size of 0.5 to 2 mm. Next, the powder is finely pulverized using a jet mill, and then classified using a zigzag classifier to obtain magnetic toners (A, B, C, D, E, F, G, H) of 8 to 25 microns.
Furthermore, in order to improve fluidity, 0.3% of hydrophobic silica (R-972, manufactured by Nippon Aerosil Co., Ltd.) was mixed to perform surface treatment. The following copying test was conducted using these prepared magnetic toners. In a copying machine that uses a selenium drum (outer diameter 150 mm) as a photoconductor, the strength of the magnetic field on the developing sleeve (outer diameter 33 mm) containing a built-in magnet is set to about 900 Gauss through a non-magnetic member, and the magnet and The above magnetic toner was deposited on a developing roller of a so-called double-rotation type in which the sleeves could be rotated independently and individually, with a spacing of 0.3 mm between the cutting board and the sleeve.
The magnetic toner was arranged so that it could be supplied from the hopper to the developing roller, and the distance between the surface of the photoreceptor and the developing roller was 0.5 mm. Under rotating conditions in which the developing sleeve and photoreceptor rotate in the same direction and the magnet rotates in the opposite direction, charging (+6.7KV),
Exposure, development, transfer (+6.3KV), heater roller fixing, and fur brush cleaning were performed.
However, the copying speed was set to 25 A4 size copies per minute. High-quality paper with a thickness of 80 μm was used as the transfer paper. FIG. 2 shows the image density of the copy as a result of the copying test. The image density was determined by measuring solid black areas using a commercially available reflection densitometer (manufactured by Konishiroku Photo Industry).

[Table] According to the results, magnetite and red iron 95:
Magnetic toner dispersed in an electrically insulating resin binder in a weight ratio of 5 to 50:50 gave copies with higher image density than magnetic toner with magnetite alone. Also, for reference, when the frictional charge amount of the magnetic toner was measured using a commercially available blow-off powder charge measuring device (manufactured by Toshiba Chemical), it was 22.5 μc/g for the A toner and -25.8 μc/g for the E toner. , h toner is -
It showed 20.2μc/g. Example 2 Average particle size 0.7μ, apparent density 0.53g/ml magnetite 40% by weight (hereinafter expressed as %), average particle size 15μ
A magnetic toner having a composition of 5% red iron oxide and 55% styrene/acrylic copolymer resin is prepared in the same manner as in Example 1. The following continuous copying test was conducted using this prepared magnetic toner. In a copying machine using an organic semiconductor drum as a photoreceptor, the magnetic toner described above is deposited on a developing roller with a built-in magnet via a non-magnetic member, with a spacing of 0.3 mm between the cutting plate and the developing roller, and Charging,
Exposure, development, transfer fixing and fur brush cleaning were performed. After making 30,000 copies, there was no toner accumulation on the developing roller, and the image density remained stable from 1.40.
I was able to get a copy of 1.51.

[Brief explanation of drawings]

FIG. 1 is a microscopic photograph of Red Red Garlic used in Example 1 of the present invention, and FIG. 2 is a graph showing the image density of a copy corresponding to the mixing ratio of Red Red Garlic.

Claims (1)

[Claims] 1. A compound comprising powder particles of a kneaded composition in which ferromagnetic powder such as magnetite and red iron are dispersed in an electrically insulating resin binder at a weight ratio of 95:5 to 50:50. Component-based electroscopic magnetic developer. 2. The developer according to claim 1, wherein the resin binder is present in an amount of 40 to 230 parts by weight per 100 parts by weight of the ferromagnetic powder and red red iron. 3. The developer according to claim 1, wherein the red red iron consists of non-friable agglomerates of cubic particles and has a particle size of 1 to 10 microns. 4. The developer according to claim 1, wherein the ferromagnetic powder has a particle size of 0.1 to 1.0 microns.