JPS6350698B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in magnetic developers, and more specifically, it can be easily applied to high-speed copying, that is, high-speed development, and is capable of forming copied images with excellent density, color tone, sharpness (cuts), and resolution even during high-speed copying. , and a composite magnetic developer for electrophotography that has excellent halftone reproducibility. Conventionally, when developing electrostatic latent images, a so-called magnetic developer containing powder of a magnetic material in developer particles has been widely known as a developer capable of developing a latent image without using a special carrier. ing. As one type of this one-component magnetic developer, developer particles contain fine powder of magnetic material to impart magnetic attraction properties, and conductive agents such as conductive carbon black are added to the surface of the particles. So-called conductive magnetic developers are also known, which are made to have conductivity by distributing them (for example, as disclosed in US Pat.
3639245 and 3965022). When this conductive magnetic developer, in the form of a so-called magnetic brush, is brought into contact with the electrostatic latent image supporting substrate to develop the latent image,
Although it provides an excellent visible image free of so-called edge effects and fog, it is also known that quite serious problems arise when the image of this developer is transferred from the substrate onto ordinary transfer paper. That is, Japanese Patent Application Publication No. 1973
-As stated in Publication No. 117435, the specific electrical resistance of the transfer paper used is 3×13 ¹³ Ω, like plain paper.
If it is lower than -cm, there is a tendency for outline broadening and transfer efficiency to decrease due to scattering of developer particles during transfer. This tendency is caused by the use of high electrical resistance resin,
Even if some improvement can be achieved by applying wax or oil, such improvement effect is relatively small under high humidity conditions, and the application of resin etc. increases the cost of the transfer paper and further reduces the texture. It cannot escape the drawbacks such as As another type of one-component magnetic developer, a one-component non-conductive magnetic developer consisting of a granular mixture of fine powder of magnetic material and an electroscopic binder is already known. For example, U.S. Pat. No. 3,645,770 discloses that a magnetic brush (layer) of the non-conductive magnetic developer described above is charged by a corona discharge with a charge opposite in polarity to the electrostatic latent image to be developed, and this charged An electrostatographic reproduction process is disclosed which comprises contacting a latent electrostatic image-bearing substrate with a developer to develop the latent image, and then transferring the formed developer image to a transfer paper. This electrophotographic copying method has the advantage of being able to form a transferred image on transfer paper made of so-called plain paper, but it is also difficult to uniformly charge the deep part of the magnetic brush of the non-conductive magnetic developer. In general, it is difficult to form images with sufficiently high density, and furthermore, since a corona discharge mechanism must be provided in the developing device, there are disadvantages such as the complexity of the device. Recently, a method for developing an electrostatic latent image using charging of the developer caused by friction between a non-conductive magnetic developer and the surface of the electrostatic latent image supporting substrate (Japanese Unexamined Patent Application Publication No. 1989-1989) has been developed.
62638), and a method of developing using dielectric polarization of a non-conductive magnetic developer (Japanese Patent Application Laid-open No. 1983-
133026) has already been proposed, but in the former method, the developing conditions must be strictly controlled, otherwise fog in non-image areas (between the photoreceptor surface and magnetic toner particles) may occur. This is particularly likely to occur when there is strong mutual contact with the tips of the ears)
This causes the occurrence of magnetic toner particles, adhesion of magnetic toner particles onto the developing sleeve, and blocking, which becomes an important problem especially when continuous copying is performed. Also,
In the latter case, fogging is not a problem, but because a developing charge is obtained by the dielectric polarization effect induced in the magnetic toner against the electrostatic latent image and a visible image is formed, it is disadvantageous for the low-potential latent image area. It becomes a state. Therefore, in the resulting copy, it is difficult to copy the low-density portions of the original, and it is difficult to reproduce halftones in the copy. Furthermore, the copies obtained by both methods lack sharpness, and when a P-type photoreceptor such as selenium is used as a photosensitive plate and a positively charged image is developed, no matter which method is used, It is difficult to form an image with sufficiently high density. Furthermore, U.S. Pat. No. 4,102,305 describes a one-component magnetic developer whose electrical resistance changes depending on the electric field strength, i.e., one component that is substantially conductive in high electric fields, while having high electrical resistance in low electric fields. Using a component-based magnetic developer, development is performed under conditions where a high voltage is applied between the magnetic brush forming sleeve and the photosensitive plate to make the developer particles conductive, while the developer particles are transferred to copy paper. It is disclosed that excellent reproduced images can be formed by performing the transfer in a low electric field or no electric field. This specification also states that the above-mentioned developer whose electrical resistance is highly dependent on the electric field is composed of 50% by weight of magnetite coated with stearate and 50% by weight of styrene-n-butyl methacrylate copolymer.
It is disclosed that it can be obtained by spray granulation of % by weight. Although this method is excellent in terms of the above idea, it has the disadvantage that it requires a special high-voltage device for development, and although the formed image is certainly high in density, the sharpness of the image is still insufficient. It's not satisfactory. Furthermore, US Pat. No. 4,121,931 states:
Using an electrically insulating one-component magnetic developer, a magnetic brush-forming sleeve is used as an electrode, and a voltage is applied between this electrode and the photosensitive plate, giving intense turbulent agitation to the developer on the sleeve for development. Uniform charging of agent particles is disclosed. This invention also
This method not only requires a high-voltage device in the developing device, but also requires special measures to agitate the developer particles on the sleeve. In this way, past research on one-component magnetic developers and development methods using them has focused on the developer composition,
The current situation is that research has focused exclusively on the developer manufacturing method, the charging method of developer particles, etc., and there has been almost no research on the characteristics of the magnetite itself contained in the developer. Generally, when a magnetic brush of a one-component magnetic developer is brought into contact with the surface of a substrate supporting an electrostatic latent image,
Both the electrostatic attraction force (Coulomb force) between the developer particles and the electrostatic latent image and the magnetic attraction force between them and the magnet for forming the magnetic brush act on each developer particle.
Thus, developer particles with a greater Coulomb force will be attracted toward the electrostatic latent image, while developer particles with a greater magnetic attraction will be attracted toward the developer sleeve and will be attracted to the electrostatic latent image on the substrate. Development will be performed depending on the image. Thus, a one-component magnetic developer requires a certain balance between magnetic properties and charging properties during development. Thus, it will be understood that in a one-component magnetic developer, the characteristics of the magnetic material powder used also have an important effect on the characteristics of the image formed. According to the present invention, (A) a non-friable agglomerate which is an aggregate of cubic particles of magnetite that does not substantially change its particle size distribution even when subjected to a ball milling process for 5 hours; (B) a number average particle size of 0.1 to 0.7 μm and a particle diameter of 0.45 g/ml or more; A second granule having an average particle size of 5 to 30 microns, comprising magnetite particles having a hanging density and a shape anisotropy defined as the ratio of the longest dimension to the shortest dimension of 1.0 to 5.5, dispersed in a binding resin medium. , wherein the agglomerates in the first granules (A) have a number average particle size of 1 to 10 microns as measured by an electron microscope;
0.5 to 1.5 g/ml measured by JIS K-5101 method
, a saturation magnetization of 75 to 88 emu/g, a residual magnetization of 3 to 12 emu/g, and a coercive force of 40 to 150 oersteds, and Granular matter (B) is A/ on a weight basis.
A composite magnetic developer for electrophotography is provided, characterized in that B is present in a ratio of B=95/5 to 10/90. As mentioned above, the characteristics of the magnetic developer of the present invention are as follows.
The purpose is to use two types of granular materials (resin-magnetic material granular molded products, hereinafter sometimes referred to as granular molded products) containing mutually different types of magnetic material powder in the form of a dry blend. Therefore, when the above-mentioned non-friable agglomerate particles are used as the magnetite of one of the developer particle components, compared to the conventional one-component magnetic developer using acicular crystal, cubic crystal, or amorphous magnetite. , it is possible to significantly improve the sharpness (notch) and resolution of images, and it is also possible to improve the reproducibility of intermediate tones. Moreover, in addition to this first developer component (granular molded product), the aforementioned particle size is 0.1 to 0.7 μm.
Although within the range of , the apparent density is 0.45g/
A composite magnetic developer with new characteristics that can be easily applied to high-speed development and therefore high-speed copying by blending a second developer component (granular molded product) containing fine magnetite particles of ml or more in a specific ratio. Furthermore, compared to the case where any of these developer particle components is used alone, image density can be significantly improved during high-speed development, and the color tone of the image can be improved to a pure black tone or pure black tone. It can be made close to. The magnetic material powder used for the first developer component in the present invention is shown in the electron micrograph of FIG.
As shown in the X-ray diffraction image in the figure, it is magnetite consisting of non-crushable agglomerates of cubic particles. In this specification, non-friable agglomerates are those in which fine particles are densely aggregated, as is clear from FIG. Refers to aggregates that do not substantially change the particle size distribution. This non-fragile agglomerate magnetite has a number average particle size of 1 to 10 as measured by an electron microscope.
microns, especially in the range of 2 to 7 microns,
It has a coarser particle size than normal magnetite particles. The magnetic material particles used for the first developer component have the above-mentioned dense agglomerated structure and are relatively coarse in particle size, and are therefore conventionally used in one-component magnetic developers. It has a characteristic that the volume per unit weight, that is, the bulk, is small compared to needle crystal, cubic crystal, or irregularly shaped magnetite particles.
Thus, in the first magnetic developer component, the resin/magnetite volume ratio is set to a much larger value than that of the conventional one-component magnetic developer, when comparing the magnetite blending weight ratio at a constant value. It will be appreciated that this can provide the first magnetic developer component with more of the charging characteristics inherent in the resin. It has been known that polymer materials with higher dielectric constants are more likely to be positively charged due to triboelectric charging (The Society of Photographic Scientists and
Eegineers 2nd Int. Conf. 1974, pp. 95-100).
In addition, the present inventors have found that even in a magnetic developer formed by dispersing magnetic material powder in a fixing medium, if the dielectric constant of the magnetic developer is small, it is likely to be negatively charged, and if it is large, it is likely to be triboelectrically charged positively. It was discovered by In fact, developer particles containing 55% by weight of magnetite, which is conventionally used in styrenic resin, exhibit a dielectric constant of 3.85 to 4.05, whereas the non-fragile agglomerate magnetite mentioned above shows a dielectric constant of 3.85 to 4.05. It was confirmed that when the same amount was mixed, the dielectric constant was 3.79, and the material was more likely to be negatively charged. As described above, the magnetic material powder used as the first component in the present invention has a smaller bulk, that is, a larger apparent density than ordinary magnetite, and has, for example, JIS
It has an apparent density of 0.5 to 1.5 g/ml, in particular 0.7 to 1.3 g/ml, measured by the method K5101. Furthermore, the magnetite, which is composed of non-fragile agglomerates of cubic particles, has magnetic properties such as a saturation magnetization of 75 to 88 emu/g, a remanent magnetization of 3 to 12 emu/g, and a coercive force of 40 to 150 oersteds. The magnetite made of non-friable agglomerates of cubic particles 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
In steps 9 to 9, pressurized hydrothermal treatment is performed to transform the pseudoglue-like precipitate of iron hydroxide into fine cubic α-Fe ₂ O ₃ (Hematite). That is, in this case, 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 easily agglomerated are generated. By aging for a long time of 50 hours or more, α-iron sesquioxide in the form specified in the present invention can be obtained. Obtained α-
Triiron tetroxide (Fe ₃ O ₄ ) in the form described above is obtained by reducing iron sesquioxide under conditions known per se, for example, with hydrogen in a reduction furnace at a temperature of 400°C. The reduction treatment is performed so that the atomic ratio of F ₂ ²⁺ /Fe ³⁺ in triiron tetroxide is generally from 0.9/1.0 to 1.1/1.0 to obtain triiron tetroxide having the above-mentioned microstructure. It was confirmed that the X-ray diffraction image of the agglomerate type magnetite used in the present invention is the same as that of normal cubic magnetite, and there is no particular difference in crystallinity from the height of the diffraction peak. Ta. The fixing medium in which the non-friable agglomerate magnetite particles are dispersed is a resin, wax-like substance or rubber that exhibits fixing properties under the application of heat or pressure. These fixing media are
These fixing media may be used alone or in combination of two or more types, but it is desirable that these fixing media have a volume resistivity of 1×10 ¹⁵ Ω-cm or more when measured without containing magnetite. As the fixing medium, various mono- or diethylene-based saturated monomers are used, especially homopolymers and copolymers of (a) vinyl aromatic monomers, and (b) acrylic monomers. . The vinyl aromatic monomer has the following formula: In the formula, R ₁ is a hydrogen atom, lower (having 4 or less carbon atoms)
is an alkyl group or a halogen atom, R ₂ is a substituent such as a lower alkyl group or a halogen atom, and n is an integer of 2 or less including zero, such as styrene, vinyltoluene, Examples include α-methylstyrene, α-chlorostyrene, vinylxylene, and vinylnaphthalene. Among these, styrene,
Vinyltoluene is 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. Methacrylic 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-diethylamino Examples include propyl acrylate and acrylamide. 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. In the present invention, the above-mentioned agglomerate is used in an amount of 35 to 35 per the total amount of the fixing medium and magnetic material powder.
Preferably used in an amount of 75% by weight, particularly 45 to 65% by weight, the magnetite is homogeneously and uniformly kneaded into the fusing medium and then granulated to form the first magnetic developer component. 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. For molding, the above-mentioned kneaded fine product is cooled, then pulverized and, if necessary, sieved. Of course, there is no particular problem in performing rapid mechanical stirring in order to round off irregularly shaped particles. 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 type magnetite. According to the present invention, a developer made of amorphous particles formed by kneading and pulverization achieves a further increase in transfer efficiency and the formation of sharp images. In the present invention, the first magnetic developer component (A) containing the above-mentioned agglomerate type magnetite
and a second magnetic developer component (B) containing fine magnetite particles having a number average particle size in the range of 0.1 to 0.7 μm and an apparent density of 0.45 g/ml or more, A:B=95 :5 to 10:90, especially in combination at a weight ratio of 90:10 to 20:80. That is, when these two components are used in combination in the above-mentioned ratio as magnetic developer components, a magnetic developer that can be easily applied to high-speed development and therefore high-speed copying can be obtained, and it is also possible to use either component alone. A significant increase in image density during high-speed development is obtained compared to the case where the image density is developed at high speed, and this increase in image density is achieved without sacrificing the advantages of developer particles containing non-friable agglomerate magnetite. be done. Developer components containing magnetite, a non-friable agglomerate, are particularly suited for the purpose of improving image sharpness (cuts), resolution, and midtone reproducibility; There is still room for improvement in that it is easy to provide images with a dark tone, and when high-speed development is performed, the image density is lower than in the case of low-speed development. According to the present invention, by combining the developer component containing this agglomerate magnetite with the developer component containing fine-grained magnetite, the color tone of the image can be made pure black or close to pure black. In addition, image density during high-speed development can be significantly improved. In the present invention, the magnetite used for the second developer particle component has a number average particle size of 0.1 to 0.7 microns, as described above, and an apparent density of 0.45 g/ml or more. We use magnetite, which has a high apparent density. In other words, in normal magnetite, as the particle size becomes finer, the apparent density tends to decrease. When used in combination with the first developer particles containing the agglomerate magnetite particles described above, it is suitable for the purpose of making the image tone pure black or close to pure black. However,
The objective of improving image density during high-speed development is still not fully satisfied. In contrast, according to the present invention, magnetite having the unique characteristics of having a fine particle size and a relatively large apparent density is selected and contained in the second developer component, and the magnetite is added to the agglomerate described above. By combining this with a second developer component containing a form of magnetite, the image density during high-speed development was successfully improved significantly. Moreover,
This composite developer has the advantage that both components are consumed in a blended composition and there is no fluctuation in the composition. The fine magnetite particles 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. is in the range of 1.0 to 5.5, preferably 1 to 3. Fine magnetite having the above characteristics is produced by the following method, although it is not limited thereto. That is, an aqueous solution of caustic soda is added to an aqueous solution of iron sulfate () to form a precipitate of iron hydroxide (). This precipitate is subjected to pressurized hydrothermal treatment with the mother liquor having a bulk of 4 to 11, thereby converting the pseudoglue-like precipitate of iron hydroxide into cubic α-Fe ₂ O ₃ (Hematite). The details of the manufacturing conditions for this cubic α-iron sesquioxide are as follows:
For example, Nobuoka et al., Koka Journal, Vol. 66, p. 412 (1963)
It is stated in At this time, the hydrothermal treatment
It can be carried out at a temperature of 230℃ for 10 to 100 hours, and the particle size generally tends to increase as the pH of the mother liquor increases, and by changing the treatment temperature and treatment time, it is possible to obtain a predetermined particle size. α-Iron sesquioxide is obtained. The obtained α-iron sesquioxide is reduced under conditions known per se, for example, with hydrogen in a reduction furnace at a temperature of 400°C, to form cubic or slightly rounded amorphous trioxide. Iron (Fe ₃ O ₄ ) is obtained. F ₂ ²⁺ / in triiron tetroxide
Reduction treatment is performed so that the atomic ratio of F ₂ ³⁺ is generally 0.9/1.0 to 1.1/1.0, and magnetite (triiron tetroxide) having the above-mentioned characteristics is obtained. When producing the aforementioned α-iron sesquioxide precursor,
When the hydrothermal treatment is carried out under relatively low pH conditions, magnetite with a cubic crystal shape with rounded corners or a slightly rounded shape is obtained, but such particles can also be used in the present invention in the same way as cubic crystal particles. May be used for any purpose. The second developer component (B) containing fine magnetite particles is prepared in the same manner as the first developer component (A) containing agglomerate magnetite particles. That is, as the fixing medium and other compounding agents, those exemplified above can be used in the same manner, and the compounding ratio thereof can also be within the range described above. However, when preparing the second developer component (B), the type or blending ratio of the resin may be changed from that of the first developer component (A), for example, even within the above-mentioned range. Furthermore, it is also free to exclude the ingredients blended in the first component (A) or to blend ingredients that are not blended in the first component (A). Furthermore, the particle size of the second developer component (B) is in a smaller range than the particle size of the first developer component (A), generally in the range of 5 to 30 microns. The product of the invention is obtained by blending the first developer component (A) and the second developer component (B) by dry blending means known per se. 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, a developer hopper is filled with the one-component magnetic developer described above. 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 on the sleeve, and after this brush layer is cut to an appropriate length with a cutting board, a selenium drum rotating in the same direction as the sleeve is inserted. 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, flush 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 photosensitive plates. Although conventional triboelectric one-component magnetic developers can generally be used to develop photosensitive plates with negatively charged latent images, they cannot be used to develop positively charged latent images on p-type photosensitive plates as described above. It only shows extremely unsatisfactory results. On the other hand, according to the present invention, excellent effects can be achieved in developing and transferring such a positive charge latent image. Moreover, this composite developer has the advantage that both components are consumed in the same ratio during development, and the composition does not change. The invention is illustrated by the following example. Example 1 55 parts by weight (hereinafter referred to as parts) of agglomerate magnetite (Fe ₃ O ₄ ) shown in Table 1, 37 parts of styrene/butyl methacrylate copolymer (weight average molecular weight 27000), low molecular weight polypropylene (average molecular weight 4000) and 0.5 parts of zinc stearate were kneaded and melted at 140℃ for 35 minutes using a two-roll mill, and after cooling, coarsely ground with a cutting mill to obtain 0.5 parts of zinc stearate.
Make it ~2mm in size. Next, the powder was finely ground using a jet mill and classified using a zigzag classifier.
Obtain magnetic toner with a particle size range of ~35μ. The classification was performed so that the lower limit of this particle size range was at least twice the particle size of magnetite.

[Table] The magnetic properties in the table were measured using a magnetic property measuring instrument manufactured by Toei Kogyo (Model VSMP-1 type, magnetic field 5K Oersted). Next, 55 parts of magnetite with a coercive force of 2130e, an apparent density of 0.55 g/ml, and a particle size of 0.4 to 0.5 μ is added to a thermoplastic resin.
41.5 parts (vinyltoluene/butadiene copolymer,
average weight molecular weight 78000), negative charge control agent 0.675 part (Hodogaya Chemical, Spiron Black BHH), zinc stearate 0.45 part and low molecular weight polypropylene
3.5 parts were kneaded and melted in the same manner and ground. 5
After classification, 0.2 wt % of hydrophobic silica (R-972, manufactured by Nippon Aerosil Co., Ltd.) is mixed into a particle size range of ~25 μ to obtain magnetic toner e. The weight ratio of the four types of magnetic toners (a', b', c' and d') is 70:
This magnetic toner (e) is dry-blended so that the magnetic toner has a total particle size of 30, and composite magnetic toners (referred to as a″, b″, c″, and d″) are prepared. 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. The above magnetic toner was deposited on a developing roller of a so-called double-rotation system 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 30 A4 size copies per minute. High-quality paper with a thickness of 80 μm was used as the transfer paper. The copy test results are shown in Table 2. The image density was determined by measuring solid black areas using a commercially available reflection densitometer (manufactured by Konishiroku Photo Industry). The copy test chart uses a commercially available test pattern from Dataquest, and the gradation and resolution are judged from the copy, the sharpness is judged from the line image in the copy, and the notches are judged from the line image in the copy. The good ones were classified as excellent. In addition, the volume resistivity of the magnetic toners a', b', c', and d' is in the range of 1.2 to 4.6×10 ¹⁴ Ωcm, and the magnetic toner e is 1.5×10 ¹⁴ Ωcm, and the distance between the electrodes is 0.65 mm. The dielectric constant of the four types of magnetic toners measured under the conditions of a cross-sectional area of 1.43 cm ² and an interelectrode load of 105 g/cm ² was 3.59.
The range was 3.79 to 3.79, and e was 3.97.

[Table] By using the composite magnetic toner of the present invention, clear images with high image density and high blackness can be obtained without compromising halftones or resolution even at a copying speed of 30 pages per minute (A4). It was done. Example 2 Agglomerate magnetite (apparent density 0.785
g/ml, number average particle size 2.8μ, coercive force 580e, saturation magnetization
87.2emu/g, residual magnetization 5.1emu/g), thermoplastic resin (styrene/acrylic copolymer, weight average molecular weight 71000), zinc stearate and high density polyethylene (average molecular weight 4000) in the composition ratios shown in Table 8. A magnetic toner (particle size distribution 6~
20μ) was prepared.

[Table] Similarly, 55 parts of each of the five types of magnetite in Table 4 and vinyltoluene/2-ethylhexyl acrylate copolymer (weight average molecular weight
139000), 0.5 parts of calcium stearate, 0.6 parts of a negative charge control agent, and 3.5 parts of high-density polyethylene wax were melt-kneaded, and after pulverization and classification (5 to 20μ), 0.2% of hydrophobic silica was mixed with the total weight. .
A composite magnetic toner (No. 5
A copying test was conducted in the same manner as in Example 1 using f', g', h', i' and j') listed in the table. The results are shown in Table 5. Image density was measured at solid black areas.

【table】

[Table] I made 10,000 continuous copies using i' composite magnetic toner, and the image density was 1.52 or higher, and I made copies until the toner in the hopper ran out without any fogging or decrease in density. However, since this is consumed according to the mixing ratio of i and l toner,
It was shown that there was no change in composition. Furthermore, by using a composite magnetic toner, even at high copying speeds, images with higher density, less fog, and overall sharpness were obtained than when using a single component.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph of magnetite composed of non-fragile agglomerates of cubic particles used in the present invention, and FIG. 2 is an X-ray diffraction image of the agglomerates of FIG.

Claims (1)

[Scope of Claims] 1 (A) A non-friable aggregate of cubic magnetite particles that does not substantially change the particle size distribution even when subjected to a ball milling process for 5 hours. (B) a number average particle size of 0.1 to 0.7 μm and a particle size of 0.45 g/ml or more; A second particle having an average particle size of 5 to 30 microns is formed by dispersing magnetite particles in a binding resin medium with an apparent density and a shape anisotropy defined as the ratio of longest dimension to shortest dimension of 1.0 to 5.5. A composite magnetic developer comprising a mixture of granules, wherein the agglomerates in the first granules (A) have a number average particle size of 1 to 10 microns as measured by an electron microscope;
0.5 to 1.5 g/ml measured by JIS K-5101 method
, a saturation magnetization of 75 to 88 emu/g, a residual magnetization of 3 to 12 emu/g, and a coercive force of 40 to 150 oersteds, and Granular matter (B) is A/ on a weight basis.
A composite magnetic developer for electrophotography, characterized in that B is present in a ratio of 95/5 to 10/90. 2. A patent claim in which the magnetite in the first granular material (A) and the second granular material (B) are each blended in a proportion of 35 to 75% by weight based on the total amount of the binding resin medium and magnetite. Composite magnetic developer according to item 1.