JPS6345098B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an insulating magnetic developer applied to electrophotography. Conventionally, as an electrophotographic method, U.S. Patent No. 2297691
Specification of No. 42-23910 and Special Publication No. 1973
Many methods are known, as described in Japanese Patent No. 24748, etc., but in general, a photoconductive substance is used to form an electrical latent image on a photoreceptor by various means, and then the A latent image is developed using toner, and 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. Various methods are also known for visualizing electrical latent images using toner. For example, the magnetic brush method described in U.S. Pat. No. 2,874,063, the cascade development method described in U.S. Pat. Many developing methods are known, such as the developing method. Among these developing methods, in particular, a magnetic brush method using a developer mainly consisting of toner and carrier,
Cascade method, liquid development method, etc. are widely put into practical use. All of these methods are excellent methods in which good images can be obtained relatively stably, but on the other hand, they have common drawbacks associated with two-component developers, such as deterioration of the carrier and fluctuations in the mixing ratio of toner and carrier. In order to avoid such drawbacks, various development methods using a one-component developer made only of toner have been proposed, among which many methods are superior to methods using a developer made of magnetic toner particles. US Pat. No. 3,909,258 proposes a developing method using an electrically conductive magnetic toner. In this system, a conductive magnetic developer is supported on a cylindrical conductive sleeve having magnetism inside, and is brought into contact with an electrostatic image to develop it. At this time, a conductive path is formed between the recording body surface and the sleeve surface by toner particles in the developing section.
An electric charge is applied to the toner particles from the sleeve through this conductive path, and the toner particles adhere to the image area due to the Coulomb force between the sleeve and the image area of the electrostatic image and are developed. This developing method using conductive magnetic toner is an excellent method that avoids the problems associated with conventional two-component developing methods, but on the other hand, because the toner is conductive, the developed image can be transferred from the recording medium to the final product such as plain paper. It has the disadvantage that it is difficult to electrostatically transfer it to a permanent support member. As a developing method using a high-resistance magnetic toner that can be electrostatically transferred, JP-A-52-94140 discloses a developing method that utilizes dielectric polarization of toner particles. However, such a method has drawbacks such as an inherently slow development speed and an inability to obtain a developed image with sufficient density, making it difficult in practice. Another developing method using high-resistance magnetic toner is a method in which the toner particles are triboelectrified by friction between the toner particles or friction between the toner particles and a sleeve, etc., and the toner particles are brought into contact with an electrostatic image holding member for development. It has been known. However, these methods have drawbacks such as the small number of times the toner particles come into contact with the friction member, which tends to result in insufficient triboelectric charging, and the Coulomb force between the charged toner particles and the sleeve increases, making them apt to aggregate on the sleeve. This was difficult in practice. The one-component developing method that has been put into practical use to date is the method described in the above-mentioned US Pat. No. 3,909,258 or a method similar thereto. The practical characteristics of this method are that the toner is electrically conductive and that the toner contains 50 wt % or more of magnetic material. These two characteristics are advantages in the developing process, but the former is a major disadvantage in the transfer process, and the latter is a major disadvantage in the fixing process. That is, since the toner is conductive, electrostatic transfer is difficult as described above, and even if the resistance is well adjusted, the transfer efficiency will drop significantly at high humidity. Furthermore, since the toner contains 50 wt % or more of magnetic material, a large amount of energy is required when fixing with a heating pressure roller or a pressure roller. In other words, if a large amount of non-meltable matter is contained in the toner, the adhesion between toner particles or between toner particles and a toner image supporting member such as paper becomes poor during fixing, requiring a large amount of thermal energy or pressure. That is to say. SUMMARY OF THE INVENTION An object of the present invention is to provide an insulating magnetic developer applicable to a developing method that improves the above-mentioned drawbacks. That is, an object of the present invention is to provide an insulating magnetic developer that can be applied to a developing method with high fidelity and stable image quality. Another object of the present invention is to provide an insulating magnetic developer that can be applied to a developing method that eliminates the background fog phenomenon and provides a high-resolution image that is uniform and has sufficient density in the image area. That is, in the present invention, an electrostatic image holder that holds an electrostatic image on its surface and a developer carrier that includes a magnet that supports an insulating magnetic developer containing magnetic toner on its surface are separated by a certain gap. The insulating magnetic developer is triboelectrically charged, and the insulating magnetic developer having the triboelectric charge is supported by a magnetizable limiting member or a magnetic member disposed close to the developer carrier. The insulating magnetic developer is supported on a body to a thickness thinner than the gap, and the insulating magnetic developer is transferred to the electrostatic image holder under the action of a magnetic field for development. The agent is a one-component insulating magnetic developer capable of electrostatic transfer, and the magnetic toner contains 10 to 50% by weight of magnetic powder, and the magnetic toner is a crosslinked styrene copolymer as a binding substance. An insulating magnetic developer characterized by containing: A developing method to which the one-component insulating magnetic developer of the present invention is applied will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an example of a copying device or a recording device to which the developing method according to the present invention can be applied, but the present invention is not limited thereto. Reference numeral 1 corresponds to an electrostatic image carrier, and is a photosensitive drum containing a photoelectrostatic layer, and any type with or without an insulating layer on the surface can be used. A belt-shaped one is also possible. Reference numeral 2 represents a known photosensitive charging device, and 3 represents a light image irradiation device that projects an original image, a light image, or a light beam modulated by an image signal. As a result, an electrostatic image is formed on the photoreceptor 1. A developing device 4 has a developer carrier 4a, and forms a toner particle visual image in accordance with the electrostatic image on the photoreceptor 1. 5 is a device for transferring the toner image onto a transfer material 6. In order to improve transferability, the image line may be charged in advance by corona discharge or the like before transfer. Furthermore, it is possible to adopt a so-called electrostatic image transfer method in which the electrostatic image on the photoreceptor 1 is temporarily transferred to another image carrier and then converted into a visible image by the developing device 4. 7, the toner image is transferred to a member 6;
This is a fixing device for fixing images on a paper, and is composed of at least two rollers having pressure or heating pressure means. Reference numeral 8 denotes a cleaning device for cleaning and removing residual toner on the photoreceptor 1 after transfer, so that the photoreceptor 1 can be reused. Each step of the electrophotographic method to which the one-component insulating magnetic developer of the present invention is applied will be described below. First, the process of forming an electrical latent image will be described. Electrophotographic photoreceptors have various configurations in order to obtain predetermined characteristics or depending on the type of electrophotographic process to which they are applied. 2. Description of the Related Art As typical electrophotographic photoreceptors, there are photoreceptors having a photoconductive layer formed on a support and photoreceptors having an insulating layer on the surface, which are widely used. The photoreceptor, which is composed of a support and a photoconductive layer, is produced by the most common electrophotographic process. That is, it is used for charging, image exposure, development, and, if necessary, image formation by transfer. In addition, for photoreceptors equipped with an insulating layer, this insulating layer protects the photoconductive layer, improves the mechanical strength of the photoreceptor, improves dark decay characteristics, or
It is provided for the purpose of application to a specific electrophotographic process (furthermore, to eliminate pollution). Examples of such a photoreceptor having an insulating layer or an electrophotographic process using a photoreceptor having an insulating layer are disclosed in U.S. Pat.
They are described in Japanese Patent Publication No. 41-16429, Japanese Patent Publication No. 38-15446, Japanese Patent Publication No. 3713-1971, Japanese Patent Publication No. 19747-1974, Japanese Patent Publication No. 4121-1974, and the like. In particular, typical specific electrophotographic processes include:
Examples include a process that utilizes injecting charges from the support side during charging and moving the charges between the insulating layer and the photoconductive layer. Such a process is described in Japanese Patent Publication No. 42-23910 and Japanese Patent Publication No. 42-23910
As disclosed in Publication No. 24748, etc., an electrostatic image is created by secondary charging with a polarity opposite to that of the primary charging, or by AC neutralization, simultaneous image exposure, and full-face exposure (full-face exposure may be omitted as necessary). It is the process of forming Also, Tokuko Sho No. 42-19748, Tokuko Sho
As disclosed in Japanese Patent Publication No. 44-13437 and Japanese Patent Publication No. 49-44902, image exposure may be performed before or after secondary charging or AC neutralization in the above process. A predetermined electrophotographic process is applied to the electrophotographic photoreceptor to form an electrostatic image, and this electrostatic image is developed and made visible. Some typical other image holding members are those used in the following electrophotographic process. (1) As described in Japanese Patent Publication No. 32-7115, Japanese Patent Publication No. 8204, and Japanese Patent Publication No. 43-1559, the electrophotographic The electrostatic image formed on the body is transferred to another holding member for development, and then the toner image is transferred to the transfer member. (2) Or as another electrophotographic process in which an electrostatic image is formed on another image holding member in correspondence with the electrostatic image formed on the electrophotographic photoreceptor, for example, Japanese Patent Publication No. 45-30320,
As described in Japanese Patent Application Laid-open No. 43-5063 and Japanese Patent Application Laid-Open No. 51-341, an electrostatic image is formed on a screen-shaped electrophotographic photoreceptor having many minute openings by a predetermined electrophotographic process. This electrostatic image is then used to perform corona charging on another image holding member, thereby modulating the ion flow of the corona to form an electrostatic image on the other image holding member, which is then developed with toner. Examples include a process of transferring the image to a transfer member to form a final image. (3) Also, according to other electrophotographic processes, it is possible to apply electrical signals to (multiple) needle electrodes and form an electrostatic image on the surface of the image holding member according to the electrical signals. Image holding members used in electrophotographic processes such as (1) to (3) need only have an insulating electrostatic holding surface and do not require a photoconductive layer. As described above, various types of surface insulating members are generally used as image holding members on which electrostatic images are formed, including electrophotographic photoreceptors. Next, the developing process used in the present invention will be explained. FIG. 2 shows a cross-sectional view of one embodiment of the developing process used in the present invention. In the figure, when the electrostatic image holding surface 1 moves in the direction of the arrow, the multipolar permanent magnet 9 is fixed so as not to rotate. By rotating in the direction, the one-component insulating magnetic developer 11 sent from the developer container 12 is coated on the non-magnetic cylindrical surface, and the friction between the cylindrical surface and the toner particles causes electrostatic charge to be applied to the toner particles. Gives a charge of opposite polarity to the image charge. Furthermore, by arranging the iron doctor blade 10 close to the cylindrical surface (with an interval of 50 μm to 500 μm) and facing one magnetic pole (S pole in the figure) of the multipolar permanent magnet 9, the thickness of the toner layer can be reduced. Regulate thinly (30μ to 300μ) and uniformly. This cylinder 4
By adjusting the rotational speed of b, 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. Instead of iron as the doctor blade 10, a magnetic limiting member such as a permanent magnet may be used to form the opposing magnetic poles. Further, in the developing section, an alternating current bias may be applied between the developer carrier and the electrostatic image holding surface. As mentioned above, in this development process, in order to stably hold the one-component magnetic developer on the developer carrier,
A nonmagnetic cylinder 4b containing a multipolar permanent magnet 9 was used. In addition, in order to form a thin and uniform developer layer,
A doctor blade 10 made of a magnetic thin plate or a permanent magnet was placed close to the surface of the cylinder 4b. Using a magnetic doctor blade in this way,
Opposing magnetic poles are formed between the magnetic poles of the permanent magnet contained in the developer carrier, and the toner particle chains are forcibly raised between the doctor blade and the developer carrier, causing other particles on the developer carrier to stand up. It is advantageous to keep the developer layer thin in that area, for example in the area facing the electrostatic image surface. Further, by imparting such forced movement to the developer, the developer layer becomes more uniform, thereby achieving a thin and uniform toner layer formation that could not be achieved with a non-magnetic doctor blade. As mentioned above, the method described in U.S. Pat. No. 3,909,258, which has been put into practical use up to now, is based only on the magnetic binding force between the toner particles and the permanent magnet in the developing device. In order to retain the magnetic powder on the surface and transport it to the developing section, the amount of magnetic powder in the toner had to be 50 wt% or more. Alternatively, it is possible to reduce the amount of magnetic powder in the toner by making the magnetic field of the permanent magnet extremely strong, but this would require a larger developing device.
In addition, the cost would be high, making it practically impossible. However, in the method of the present invention, the toner is held and transported by the magnetic binding force acting between the toner particles and the permanent magnet in the developing device and the electric attraction force based on the friction between the toner particles and the sleeve surface. It is possible to reduce the amount of magnetic material in the toner. On the other hand, in the method of the present invention, the amount of charge possessed by toner particles is
In order to be smaller than the method described in No. 3909258, in the range where the sleeve surface magnetic flux density that is commonly used is about 600 to 1300 Gauss, the amount of magnetic powder in the toner is 10 to 50% by weight, preferably 15 If it is less than 35% by weight, when the developer layer approaches the electrostatic image, it will not be able to overcome the magnetic force that holds the toner particles and transfer them to the latent image surface. The development phenomenon according to the present invention is such that in the non-image area of the electrostatic image holding surface, the developer layer is maintained in a non-contact manner, and in the image area, the developer layer is maintained in such a way that the developer is transferred to the electrostatic image holding surface. is formed and developed using it. The image area of the electrostatic image holding surface referred to herein refers to the area to which toner particles should adhere during development, and the non-image area refers to other areas to which toner particles should not adhere. During the transfer, the developer layer corresponding to the image area increases in thickness in the direction of the electric field due to the attraction of the electric field, and as a result of the action of the magnetic field, the toner in this area grows upright at the magnetic pole position, like an elongated spike. This phenomenon is hereinafter referred to as the "toner elongation" phenomenon. Therefore, when the surface layer of the developer layer and the electrostatic image holding surface are close to each other, this toner elongated portion directly contacts the image area of the electrostatic image holding surface. When the developer carrier and the electrostatic image holding surface are separated from each other, the toner remains on the electrostatic image holding surface and development is completed. Unlike the so-called contact development method or conventional jumping development, this method substantially avoids developer contact in non-image areas under a magnetic field during development, and the above-mentioned toner elongation occurs in image areas. It is thought that development is carried out by the phenomenon of contact. If the gap between the surface layer of the developer layer and the electrostatic image holding surface is larger than the above, in addition to the development state due to the phenomenon of toner elongation as described above, there is also a problem that the electrostatic image holding surface will not be able to reach the electrostatic image holding surface even though it is elongated. It is thought that a developing state occurs in which the toner that is not in contact also stands up in the electric field and flies as if the tips of its spikes are torn off and reaches the electrostatic image holding surface. Of course, the present invention can carry out the above-described toner elongation development and development in which the toner flying phenomenon is added thereto, depending on the gap between the electrostatic image carrier surface and the developer carrier. In this way, by utilizing the toner elongation phenomenon in which the developer layer stands up and grows in the image area of the electrostatic image holding surface and develops by directly contacting the electrostatic image holding surface,
By reducing the amount of toner flying through the development gap, the influence of the airflow flowing through the gap, the gravity of the toner itself, and vibrations of the electrostatic image holding surface and developer carrier can be minimized. , it is possible to obtain an excellent image quality with faithful image reproducibility and no background fog, and it is good if the gap size of each part is set to meet this condition. In order to ensure sufficient toner expansion in this way,
The purpose is to suppress the gap between the developer surface layer (in the non-image area where no upright growth occurs) and the electrostatic image holding surface to 3 times or less the thickness of the developer layer. Further, as an acceptable condition for development which mainly involves the above-mentioned toner elongation and also allows toner flying, the above-mentioned gap should be 10 times or less the thickness of the developer layer. According to experiments and theoretical analysis including the above-mentioned considerations, the gap D in the developing section between the developer carrier and the electrostatic image holding surface is preferably 50μ≦D≦500μ. The upper limit value is a value determined to develop fine characters (100μ) printed with the smallest commercially available typeface with good resolution, and the lower limit is an appropriate value determined in relation to the thickness of the developer layer. According to experiments, the thickness a of the developer layer supported on the developer carrier is 30μ≦a≦
A thin layer of about 300μ was preferred. During development, the developer layer stands up due to the intervention of a magnetic field, and as mentioned above, the height of the developer layer is thought to be about three times the thickness of the developer layer, so the surface layer of the developer is placed on the electrostatic image holding surface. To achieve this, the gap b between the developer surface layer and the electrostatic image holding surface must be set to b≦300μ.
In general, good results were obtained when b≧a/5. As explained above, in the developing process in the electrophotographic method according to the present invention, it is necessary for the toner to generate an appropriate frictional charge with the sleeve surface and to have an appropriate magnetic component. That is, when the toner is thinly applied to the sleeve surface and then conveyed under the electric field of the electrostatic latent image, if it does not have sufficient triboelectric charge, the developed density will decrease and the magnetic medium will not be properly applied. If it does not have this, it may cause ground fog. Incidentally, although the details will be described later, toners with varying magnetic powder content between 0 and 70 wt% are produced,
The results of testing the amount of frictional charge and image density are shown in FIGS. 3 and 4. In Fig. 4, _L1 is the maximum density, and _L2 is the curve showing the fog density. As is clear from FIG. 3, when the content of magnetic powder exceeds 50 wt%, the triboelectric charge decreases significantly, and at this time, the image density also decreases below a practical level. This is presumably because the electrical resistance of the magnetic powder (magnetite) used is low, which inhibits the generation of appropriate frictional charges.
Also, as can be seen from Figure 4, the content of magnetic powder is
At 10 wt% or less, the magnetic binding force of the toner in the sleeve magnetic field is small, and the magnetic brush elongates irregularly, causing the toner to fly even to non-image surfaces, resulting in an unclear image with large background fog. Regarding the process of transferring the powder image to the transferred member,
An electrostatic transfer method is preferable, and a corona transfer method, a roller transfer method, etc. can be used. Further, for the step of fixing the transferred powder image, heat fixing, pressure fixing, etc. are used. The developer used in the present invention consists of a binding substance, magnetic powder, and additives. As the binding substance, when using a pressure heating roller fixing device that applies oil as described below, any known binding substance for toner can be used, such as polystyrene, poly-p-chlorostyrene, etc. , monopolymers of styrene and its substituted products such as polyvinyltoluene, styrene-p-chlorostyrene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene copolymers,
Styrene-acrylic ester copolymer, styrene-methacrylic ester copolymer, styrene-
α-Methyl chlormethacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer Coalescence, styrene-isoprene copolymer, styrene-
Styrenic copolymers such as acrylonitrile-indene copolymers, polyvinyl chloride, phenolic resins, natural resin-modified phenolic resins, natural resin-modified maleic acid resins, acrylic resins, methacrylic resins, polyvinyl acetate, silicone resins, polyester resins, Polyurethane, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, coumaron indene resin, petroleum resin, etc. can be used. In the fixing method using a heated pressure roller without applying oil, there are important issues such as transfer of a part of the toner image on the toner image support member to the roller, offset development, and adhesion of the toner to the toner image support member. be. Toners that are fixed with less thermal energy usually tend to block or cake during storage or in a developing device, so these problems must also be taken into consideration. The physical properties of the binding substance in the toner are most responsible for these phenomena, but according to research by the present inventors, reducing the content of magnetic material in the toner improves toner image support during fixing as described above. Although the adhesion of the toner to the member is improved, offset is more likely to occur, and blocking or caking is also more likely to occur. Therefore, when using the heated pressure roller fixing method without applying oil in the present invention, the selection of the binding substance is more important. Preferred binding materials include crosslinked styrenic copolymers. Examples of comonomers for this styrenic copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate,
Monocarboxylic acids having double bonds such as phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, etc., or substituted products thereof, such as maleic acid , dicarboxylic acids with double bonds such as butyl maleate, methyl maleate, dimethyl maleate, etc., and substituted products thereof, vinyl esters such as vinyl chloride, vinyl acetate, vinyl benzoate, etc., e.g. ethylene, propylene. , vinyl monomers such as ethylene olefins such as butylene, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, etc., vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether, etc. may be used singly or in combination. As the crosslinking agent, compounds having two or more polymerizable double bonds are mainly used, such as aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene, such as ethylene glycol diacrylate and ethylene glycol dimethacrylate. ,
Divinyl compounds such as carboxylic acid ester divinylaniline, divinyl ether, divinyl sulfide, and divinyl sulfone having two double bonds, such as 1.3-butanediol dimethacrylate, and compounds containing three or more vinyl groups are used alone. Or used as a mixture. In addition, when using a pressure fixing method, it is possible to use known binder resins for pressure fixable toners, such as polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-acetic acid. Examples include vinyl copolymers, ionomer resins, styrene-butadiene copolymers, styrene-isoprene copolymers, and linear saturated polyesters. The magnetic powder used in the present invention includes ferromagnetic elements and alloys and compounds containing these, such as iron such as magnetite, hematite, and ferrite, alloys and compounds of cobalt, nickel, and manganese, and other ferromagnetic alloys. There are some materials that have been known as magnetic materials. The average particle size of the magnetic powder usually used is 0.1 to 5 μm, preferably 0.1 to 1 μm. Furthermore, the additives used in the present invention are added for the purpose of controlling charge, coloring, toning, imparting fluidity, etc., and include carbon black, various dyes and pigments, hydrophobic colloidal silica fine powder, plasticizers, etc. There is. The particle size distribution of the toner particles used here is 5
Mainly toner with particle size of ~20μ, with 10 to 50% by weight (more preferably 10 to 50% by weight) of toner with particle size of 20 to 35μ
35% by weight), 1% by weight or less (more preferably 0.5% by weight or less) of toner particles with a particle size of 5μ or less, and 10% by weight or less (more preferably 6% by weight or less) of toner particles with a size exceeding 35μ. It's good to do that. By setting the particle size distribution in this way, stable and good images can be obtained despite changes in humidity, and the particle size distribution of toner particles can be kept constant even when making many copies, allowing stable development. can be done.
In order to obtain such a particle size distribution, pulverization and classification may be controlled during the toner particle manufacturing process. The method described in US Pat. No. 3,909,258 is
A latent image is formed using ZnO paper, and it is developed using conductive toner. Since conductive toner is used, no transfer is performed, and the fixing process uses ZnO paper, so a pressure fixing method is used. It was put into practical use by adopting a system that uses This was successful because it created a complete system that takes advantage of the advantages of developing and compensates for the disadvantages in each process. In contrast, the method of the present invention obtains a developed image with no fog and high resolution by applying an extremely thin layer of insulating magnetic toner onto the sleeve and developing the toner with a triboelectric charge. Due to its insulating properties, electrostatic transfer is possible, and the developing process of the present invention can reduce the amount of magnetic material in the toner compared to conventional methods, thereby making it possible to transfer materials such as plain paper. This makes it possible to fix the film with a roller. It is clear from the above explanation that it is appropriate to limit the content of magnetic powder in the toner to 10 to 50 wt% in the electrophotographic method of the present invention. It is. Example 1 70 parts by weight of crosslinked styrene-butyl acrylate copolymer, magnetic powder (magnetite, average particle size
0.25μ) and 2 parts by weight of a metal-containing dye (trade name, Zapon First Black B, manufactured by BASF) were mixed using a ball mill, and the mixture was melt-kneaded using a roll mill. After cooling, it is coarsely pulverized using a hammer mill, and then finely pulverized using a supersonic jet pulverizer. The obtained powder was classified and 1 to 40 microns were used as toner. At this time, the particle size distribution is approximately 0.2% by weight of particles of 5μ or less, 20~
Approximately 20% by weight of particles of 35μ, approximately 3% of particles larger than 35μ
It was hot. 0.3 parts by weight of hydrophobic colloidal silica was added to 100 parts by weight of this toner to prepare a developer. Image formation was performed using this developer. The surface of the insulating layer of the photosensitive drum, which consists of three layers: an insulating layer made of polyester resin, a photosensitive layer made of CdS and acrylic resin, and a conductive substrate, is uniformly charged by +6 KV corona discharge at a linear surface speed of 168 mm/sec of the drum. and then at the same time as the original image irradiation.
After performing a 7KV alternating current corona discharge, the entire surface is uniformly exposed to form a latent image on the surface of the photoreceptor. As shown in Fig. 2, a developer with a sleeve diameter of 50 mm, a sleeve surface magnetic flux density of 700 Gauss, and a distance between the iron ear cutting blade and the aluminum sleeve of 0.1 mm was used, and the distance between the insulating layer surface and the sleeve surface was set at 0.15 mm. Develop with a dye and then apply + from the back of the transfer paper.
Transfer the powder image while irradiating with 7KV DC corona,
When fusing was performed using the fuser of a commercially available dry type electrophotographic copying machine NP5000 (silicon rubber heated roller fuser without applying silicone oil to the surface), a high resolution image with no fogging was obtained, and no offset was observed. Ta. The thickness of the toner layer on the sleeve was approximately 70μ. Example 2 The same procedure as in Example 1 was carried out except that the iron blade was replaced with a magnet, and almost the same results as in Example 1 were obtained. Example 3 75 parts by weight of polystyrene, magnetic powder (ferrite)
The use of a toner consisting of 25 parts by weight (average particle size 0.53μ) and 2 parts by weight of a metal-containing dye, and the fixing device of a commercially available dry-type electrophotographic copying machine NP-5500 (a silicone rubber heated roller whose surface is coated with silicone oil). The same procedure as in Example 1 was performed except that fixing was performed using a fixing device (fixing device), and almost the same results as in Example 1 were obtained. Example 4 40 parts by weight of polyethylene, 25 parts by weight of styrene-butadiene copolymer, magnetic powder (acicular magnetite.
Example 1 except that a toner consisting of 35 parts by weight (average particle size: 0.35μ, axial ratio 8/1) was used, and fixing was performed using a fixing device consisting of two metallic rollers at a pressure of 25 kg/cm. I did it almost the same way. A clear image without fogging was obtained. Furthermore, the fixing properties were also excellent. Example 5 Almost the same as Example 1 except that the distance between the sleeve surface and the blade was 200μ, the distance between the sleeve surface and the photosensitive drum surface was 300μ, and an AC bias of 200Hz and 500V was applied to the sleeve surface of the developing section. As a result, the same results as in Example 1 were obtained. The thickness of the toner layer was approximately 120μ. Example 6 When Example 1 was repeated using 80 parts by weight of the styrene/butyl acrylate copolymer and 20 parts by weight of magnetic powder, the same results as in Example 1 were obtained. Example 7 As shown in Table 1, toners with different amounts of magnetic powder (Magnetite Toda Kogyo EPT-1000) added were prepared in the same manner as in Example 1.

[Table] The amount of triboelectric charge of each toner was measured by mixing it with iron powder and using a blow-off method. In addition, each toner was developed and fixed using the same method as in Example 1, and the results of examining the image density, fog density, and fixing temperature were reported in the second example.
This is shown in the table, FIGS. 3 and 4.

[Table] From the above results, the content of magnetic powder that can be applied to the present invention is 10 to 50 wt% (Toner No. CD
E). Content below this (Toner No.A,
B) results in an unclear image with large background fog.
Further, if the content is higher than this (toner Nos. F and G), the toner will have a low maximum density and lack fixing properties.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an example of a copying device or a recording device to which a developing method according to the present invention can be applied. FIG. 2 is a sectional view of one embodiment of the developing process used in the present invention. FIG. 3 is a graph showing the relationship between magnetic powder content and amount of frictional charge. FIG. 4 is a graph showing the relationship between magnetic powder content and image density. 1...Photosensitive drum. 4...Developing device. 4a...
...Developer carrier. 4b...Nonmagnetic cylinder. 9... Magnet Troll. 10...Doctor Blade. 1
1...Insulating magnetic developer. L ₁ ... Maximum concentration curve.
L ₂ ...Fog density curve.

Claims (1)

[Claims] 1. An electrostatic image carrier that holds an electrostatic image on its surface and a developer carrier that includes a magnet that supports an insulating magnetic developer containing magnetic toner on its surface for a certain period of time.
the insulating magnetic developer is triboelectrically charged, and the insulating magnetic developer having the triboelectric charge is developed by a magnetizable limiting member or a magnetic member disposed close to the developer carrier. In the insulating magnetic developer for developing by supporting the insulating magnetic developer on the agent carrier to a thickness thinner than the above distance, and transferring the insulating magnetic developer to the electrostatic image holder under the action of a magnetic field, The magnetic developer is a one-component insulating magnetic developer capable of electrostatic transfer, and the magnetic toner contains 10 to 50% by weight of magnetic powder, and the magnetic toner is a styrene-based copolymer crosslinked as a binding substance. An insulating magnetic developer characterized by containing. 2. The insulating magnetic developer according to claim 1, wherein the insulating magnetic developer contains hydrophobic colloidal silica. 3. The insulating magnetic developer according to claim 1 or 2, wherein the magnetic toner is a magnetic toner for a heating and pressure roller fixing method.