JPS6039230B2 - Image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming method in which an electrical latent image formed by electrophotography or electrostatic printing is developed using a carrier-free one-component magnetic developer.

Conventionally, as an electrophotographic method, U.S. Patent No. 2,297,69
Although many methods are known, as described in Japanese Patent Publication No. 42-2391, Japanese Patent Publication No. 43-124748, etc., they generally utilize a photoconductive substance and perform various methods. forming an electrical latent image on the photoreceptor by means of;
The latent image is then developed using toner, and if necessary, the toner image is transferred to a transfer material such as paper, and then fixed by pressure or solvent vapor 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. No. 2,618,552, and U.S. Pat.
A number of development methods are known, such as the powder cloud method described in No. 776, the fur brush development method, and the liquid development method.

Among these developing methods, the magnetic brush method using a developer mainly consisting of toner and carrier, the one-cascade method, the liquid developing method, and the like have been 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, in the developing section, a conductive path is formed by the toner particles between the recording medium surface and the sleeve surface, and through this conductive path, the sleeve conducts charges to the toner particles, causing a Coulomb force between the electrostatic image and the image area. The toner particles adhere to the image area 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, since the toner is conductive, the developed image can be transferred from the recording medium to plain paper, etc. It has the disadvantage that it is difficult to transfer electrostatically to the final 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 development method using high-resistance magnetic toner is to triboelectrically charge a single toner particle by friction between toner particles or friction between toner particles and a sleeve, etc.
A method is known in which the image is developed by contacting it with an electrostatic image holding member. 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 present applicant previously applied for the
In No. 3y', we proposed a new developing method that eliminated the above-mentioned drawbacks.

This is done by applying a very thin layer of magnetic toner onto the sleeve.
This is triboelectrically charged, and then under the action of a magnetic field, it is brought very close to the electrostatic image and opposed to it without contacting it to develop it. According to this method, by applying an extremely thin layer of magnetic toner onto the sleeve, the chances of contact between the sleeve and toner are increased, and sufficient frictional electrification is possible.The toner is supported by magnetic force, and the magnet and toner By moving the toner particles relative to each other, the toner particles are disaggregated and sufficiently rubbed against the sleeve, and the toner is supported by magnetic force and developed by facing the electrostatic image without coming into contact with it. Excellent images can be obtained by preventing soil blurring.

However, this has the disadvantage that, for example, when the fluidity of the toner is reduced, such as at high temperatures, the agglomeration of toner cannot be sufficiently dissolved by magnetic force, resulting in a decrease in image quality and image density. has.

Tokukan Sho 53-31136 proposes another developing method using a high-resistance magnetic toner.

This is because the electric charge is transferred to the toner from the conductor parts such as sleeves and blades.
U.S. Pat. No. 3,909,25 in that it is induced by
It is similar to No. 8, but due to the high resistance of the toner, the charge does not flow through the toner particles, and by disturbing the toner, the charged toner particles are transferred to the surface of the electrostatic image and developed. It is something. Although this method does not utilize triboelectric charging as described above, it sufficiently disturbs the toner particles, increases the chance of contact with the member that gives the toner particles a charge, and ensures the transfer of the charged toner. must be carried out. Therefore, the need for a means that can reliably disturb the toner particles even when the fluidity of the toner is reduced due to high temperatures is similar to the development method using triboelectric charging, and in this respect there are many points. have difficult problems.

In addition, the present applicant has previously proposed a new developing method using high-resistance magnetic toner.

This causes the magnetic toner, which has a conductive part and an insulating part on its surface, to be extremely disturbed, and when the conductive parts of the toner come into contact with each other near the image area of the electrostatic image, charges are generated between the toner particles. The images are transferred and developed.

In order to achieve sufficient development in this method, a much more severe state of toner agitation is required than in conventional developing methods using various single-component magnetic toners, and a large number of relatively large magnetic poles are required. It is necessary to rotate a powerful magnet at an extremely high speed. The present invention provides a developing method that solves the above-mentioned drawbacks, and also provides a carrier-free magnetic developer suitable for the developing method.

The present invention is a developing method that utilizes the transfer of charges caused by frictional charging, contact between a charge injection member and toner particles, contact between toner particles, etc., which has been proposed in the past, and which is extremely effective regardless of temperature, humidity, etc. The present invention provides a novel developing method that makes it possible to strongly disturb toner particles for stable and good development.

That is, a magnetic toner whose coercive force is extremely large compared to the magnetic toner conventionally used in these developing methods is used. Conventionally, in producing magnetic toner, magnetic powder having a relatively low coercive force has been widely used.

This is mainly due to the fact that magnetic powder with a small coercive force is relatively inexpensive and that most of the powders have a pure black color tone, making them suitable for producing black toner. According to a generally widely used method for producing magnetic powder, goethite (QFe2Q, ratio ○) is produced in an aqueous solution and then reduced to obtain magnetite (Fe304).

The magnetite obtained by this process has a relatively low coercive force and a pure black color. On the other hand, magnetic powder with a relatively large coercive force is mainly produced by applying some kind of post-treatment to the magnetite obtained through the above-mentioned process.
Or they are often manufactured using a separate process using expensive raw materials such as cobalt. All of these have a slightly reddish tinge compared to pure black magnetite, which has been conventionally widely used for magnetism, and are also slightly more expensive.

Among developing methods using magnetic toner, there is no particular need to bring the toner into a crushed state in the conventionally widely used methods using conductive magnetic toner or developing methods that utilize the polarization phenomenon within toner particles. It is considered important to reliably support the magnetic toner by magnetic force.

In that case, it is considered that high magnetic permeability or magnetization strength is important as a magnetic property. In that case, it would be appropriate to manufacture the magnetic toner by using as much as possible pure black magnetic powder, which is relatively inexpensive. Conventional conductive and magnetic toners generally contain a large amount of magnetic powder, approximately 60% of their weight. On the other hand, in the above-mentioned development method that utilizes frictional charging, contact between a charge injection part and toner particles, and transfer of charge due to contact between toner particles, toner particles and other members or each other may be disturbed. It is important to sufficiently repeat friction and contact, and in this case, it is effective to use a magnetic material with high holding power, as will be described later.

In addition, as will be described later, in these developing methods, if a magnetic material with high coercive force is used, it is possible to sufficiently achieve the purpose even with a relatively small amount of magnetic powder, and as a result, ,
This can compensate for the fact that magnetic powder with high coercive force is relatively expensive, and the color tone can also be improved by adding dyes and pigments such as carbon black without adversely affecting image fixability. It is. The present invention supplies a developer made of magnetic toner having a coercive force of at least 170 Oersteds to a developing device having a developer support member and a magnet that applies a magnetic field to the surface of the support member. The developing method is characterized in that an electric latent image is developed while moving at least one of the magnets and the magnetic toner relative to each other.

Furthermore, the present invention is directed to a magnetic developer comprising a magnetic toner having a coercive force of at least 170 Oe or more.

When considering the magnetic properties of magnetic toner and its influence on development, it is thought to be approximately as follows.

Sleeve 2 with magneto inside as shown in Figure 1
Consider the case where magnetic toner is supported on top.

The direction of internal magnetization of the toner particles 4 remote from the center 3 of one of the magnetic poles of the magneto will be approximately parallel to the sleeve surface as shown by the arrow. When the toner particles and the center 3 of the magnetic pole are moved relative to each other by rotating the sleeve or magnet, the direction of magnetization of each toner particle gradually rises as shown in 5, and when the toner particle is at the center 3 of the magnetic pole. , 6 will be approximately perpendicular to the sleeve surface. As the toner particles move away from the center 3 of the magnetic pole, the direction of magnetization begins to become parallel to the sleeve surface, but opposite to the initial direction, as shown at 7 and 8. In this manner, the direction of magnetization of the toner is reversed by 1/2 each time a toner particle passes in front of a magnetic pole. When a magnetic toner with a low coercive force is used, the direction of internal magnetization of the toner particles can take any direction with respect to the direction of the toner particles themselves, so the direction of magnetization is 1'
Even if the toner particles rotate twice, the toner particles themselves do not necessarily rotate. However, in the case of magnetic toner having a high coercive force, the direction of internal magnetization of the toner particles is substantially fixed relative to the toner particles themselves, and therefore is rotated strongly as the direction of internal magnetization rotates. However, when considering the movement of toner particles in the developing device of an actual electrophotographic apparatus, it is even more complicated than this. In other words, toner particles are subjected to complex external forces due to mutual collisions, etc., and as mentioned above, the direction of internal magnetization does not always match the direction of the magnetic field from the magnet, but instead faces in various directions. it is conceivable that. In this case, if the magnetic toner has a small coercive force, the direction of its internal magnetization will immediately match the direction of the magnetic field, and if the magnetic toner has a large coercive force, which causes almost no mechanical disturbance, the direction of the internal magnetization and the magnetic field caused by the magnet will match. It is thought that the toner particles themselves try to rotate in a direction that matches the direction of the toner particles, causing mechanical turbulence and further intensifying the turbulent state. Furthermore, it is thought that the toner or the like that has aggregated on the sleeve is similarly loosened due to the application of rotational force to the toner particles themselves. When the direction of magnetization of the toner particles does not match the direction of the magnetic field generated by the magnet, the rotational force acting on the toner particles is naturally not determined only by the coercive force. The rotational force acting on the toner particles is determined by the size of the magnetic field from the magnet, the size of the magnetization of the toner particles, and the angle between the direction of magnetization of the toner particles and the direction of the magnetic field from the magnet. This simply means that the direction of magnetization rarely coincides with the direction of the magnetic field without rotation of the toner particles. Therefore, as a parameter for the rotational force applied to the toner, rather than the coercive force, the maximum energy product (usually (B H) m cape x) would be more accurate. but,
When increasing the magnetic flux density in response to a certain external magnetic field among the magnetic properties of magnetic toner (that is, increasing the strength of magnetization in response to a certain external magnetic field), the disturbance effect of the toner's magnetic field becomes stronger, but at the same time, the magnetic flux between the toner and the magnet increases. This causes a problem in that the attractive force becomes stronger and the density of the developed image decreases. Generally, in order to increase the strength of magnetization, it is necessary to increase the amount of magnetic powder in the magnetic toner, which results in a relative decrease in the amount of resin. When fixing using heat, pressure, etc. after transferring to a paper, etc., a problem arises in that the fixing performance deteriorates. As is well known, the coercive force of a magnetic toner does not depend on the amount of magnetic powder in the magnetic toner, but is determined by the coercive force of the magnetic powder used in the magnetic toner.

Therefore, in order to increase the coercive force of the magnetic toner, there is no need to increase the amount of magnetic powder, and it is sufficient to simply use magnetic powder with a large coercive force. In general, by increasing the coercive force, the maximum energy product can be increased without increasing the magnitude of magnetization. Therefore, in the various developing methods described above, in order to obtain good images with high density, magnetic toner must be made using a relatively small amount of magnetic powder with high coercive force, and the magnets in the developing device must be strong. It is better to use

However, if the amount of magnetic powder is excessively reduced, there will be a drawback that soil burrs are likely to occur. Since the appropriate amount of magnetic powder is not necessarily constant depending on the configuration of the developing device, it is desirable to ultimately determine this through experiment. As mentioned above, it cannot be said that the coercive force necessarily corresponds accurately to the force of the disturbance action exerted on the toner particles, but when producing toner that can exert a sufficient disturbance action, it is necessary to maintain the magnetic powder. Selection based on magnetic force can be said to be the most effective means for determining toner formulation.

The toner used in the present invention contains a binder and magnetic powder as essential components, and materials conventionally used as binders for toners can be used as the binder.

For example, monomers of styrene and its substituted products such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene, styrene-p-chlorostyrene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene copolymers, Styrene-acrylic acid ester copolymer,
Styrene-methacrylate ester copolymer, styrene-Q-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, Styrenic copolymers such as styrene-vinylmethylketone copolymer, styrene-ptadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, polyvinyl chloride, phenolic resin , natural resin-modified phenolic resin, natural resin-modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester resin, polyurethane, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral, terbene resin, Coumarone indene resin, petroleum-based resin, etc. can be used.

Magnetic powders include ferromagnetic elements and alloys containing them;
Compounds, etc., which have a coercive force of at least 170 Oersted or more than materials conventionally known as magnetic materials such as magnetite, hematite, ferrite, alloys and compounds of iron, cobalt, nickel, manganese, and other ferromagnetic alloys. What you have is used. For example, the magnetic powder with high coercive force of the present invention is Q-Fe.
Acicular y-F produced by low-temperature oxidation in air of Fe304 obtained by dehydrating and reducing 00-day needle crystals in a hydrogen stream.
COO・F in e203, y-Fe203 and Fe304
The substance ESD (EIo) obtained by dissolving a small amount of e203
In the field of magnetic tapes, these are extremely common magnetic materials used as magnetic powders for magnetic tapes.

Specifically, M old D-BL, M old-BL manufactured by Titan Kogyo Co., Ltd.
, Kanto Denka Co., Ltd. CJ-300 female, CJ-300 female day, Tokyo Denki Kagaku Kogyo Co., Ltd. TD-4, TD-5, TD-6, T
M-1, TM-3, TP-3, MTA- manufactured by P Ichiyu Kogyo Co., Ltd.
740, CDX-650, etc. are available and are magnetic powders suitable for the present invention. These magnetic materials are added as a fine powder with an average particle height of about 0.1 to 5 microns, preferably 0.1 to 1 micron, in a proportion of about 10 to 8% by weight, preferably 20 to 5% by weight of the toner weight. You will get good results if you do this.

The toner particle size is generally about 0.5 to 100 microns, preferably about 1 to 40 microns. If necessary, the toner used in the present invention may contain colorants (dyes and pigments such as carbon black and phthalocyanine blue), charge control agents, and fixing aids that are conventionally used.

Further, a third substance (such as hydrophobic silica) that is not a carrier may be mixed in order to improve the fluidity of the toner and the prevention of coating formation on a photoreceptor, etc. When a magnetic toner having a coercive force of 170 Oersted or more is used as in the present invention, a stable and clear image can always be obtained, and in particular, no image deterioration is observed even at high temperatures, and the purpose of the present invention is fully achieved. was able to achieve this. Magnetic toners with a coercive force of 170 Oersted are widely used.

It has a coercive force approximately twice as high as that of a magnetic toner using magnetite that has not undergone any special treatment to increase its coercive force. Further, as will be clear from the examples shown later, if the coercive force of the magnetic toner is 300 Oe or more, the effect becomes extremely obvious.

In particular, images obtained with magnetic toners exceeding 400 oersteds were very good, and even in experiments at high temperatures, they were quite good. Further, it is generally preferable that the magnetic toner used in the developing method of the present invention has a volume resistivity of 1 to 20 or more.

In particular, when magnetic toner is charged by the friction of a developing support member, etc., the volume resistivity of magnetic toner is 1 to 3.
0. skin or higher, preferably 1 or 4 Q. or higher. In addition, when transferring electric charge between the magnetic toner and the developer support member, or when transferring the electric charge between magnetic toners, it is preferable to use a value of 1 to 20 cm or more, preferably 1 to 30 cm or more. . It goes without saying that the present invention is suitable not only for the development methods mentioned above but also for all development methods in which it is effective to exert a sufficient perturbation effect on the magnetic developer.

It is also considered effective to magnetize the magnetic toner in advance in order to fully utilize the effects of the magnetic toner with a high coercive force, but these are not included in the scope of the present invention. be. EXAMPLES The present invention will be specifically explained below with reference to Examples, but it is clear that these are not intended to limit the present invention in any way.

Example 1 5 parts by weight of epoxy resin (Araldite 6097, manufactured by Chibagaiki Co., Ltd.) and 50 parts by weight of magnetic powder (CJ-300 dish, manufactured by Kanto Denka Co., Ltd.) were mixed using a ball mill, and then melted and kneaded in a roll mill. .

After cooling, it is coarsely pulverized using a hammer mill and further finely pulverized using an ultrahigh-speed jet pulverizer. Obtained fine powder 1
0 parts by weight of carbon black and 1 part by weight of carbon black were mixed, and carbon black was adhered to the surface of the fine powder using the apparatus described in Samurai Seki 50-1140136 to obtain a toner.

The coercive force of the toner is 429 oersted, the volume resistivity is 1
The skin was 60%. Images were produced using this toner in the following manner. 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 coated with a corona discharge of 10 aKV at a linear surface speed of the drum of 168/sec. 7K is charged at the same time as the original image is irradiated.
After performing AC corona discharge of V, the entire surface is uniformly exposed to form an electrical latent image on the surface of the photoreceptor.

This latent image is created by rotating a magnet fixed to the sleeve with a sleeve diameter of 5 mm, sleeve surface magnetic flux density of 700 Gauss, number of magnetic poles of 12, and ear cutting blade sleeve surface distance of 0.6 mm as shown in Figure 2. 100 enemies in the same direction
A p/m) type developer is set at a distance of 0.4 degrees between the insulating layer surface and the sleeve surface, and the toner is used for development.Then, while irradiating a direct current corona of 17 KV from the back side of the transfer paper, the powder is The image was transferred and fixed by heating. An extremely good image with good pongee line reproduction was obtained.

Further, when images were produced in substantially the same manner at high temperatures (3000, 85%), good images were obtained. Second
In the figure, 9 is a photosensitive drum, and a conductive metal drum 1'' having an electrophotographic photosensitive member 1' on its circumferential surface is electrically grounded.

The drum 1 is rotated at a constant speed in the direction of the arrow. Reference numeral 11 denotes a cylindrical sleeve for carrying and conveying the developer, and in this example, it is fixed non-rotatably.

The cylinder 11 has a conductive non-magnetic metal cylinder 11' as a base, and a non-magnetic insulating layer 11'' is provided on a part of its circumferential surface. The area where the developer comes into contact with the photoreceptor 1', that is, the developing section, and the circumferential direction of the cylinder 11 are extended to both sides of the developing section, and the developer is in agitated movement in the developing section. is provided so that it does not come into contact with the conductive surface of the metal cylinder 11'. Reference numeral 12 denotes a container containing an insulating ridge component developer made of insulating magnetic toner, and is arranged so that the contained developer comes into contact with the metal surface of the cylinder 12. As a result, even if some toner is charged in the developing section and returns to the container 12 without being discharged anywhere, the discharge of the toner into the metal cylinder 11' can be promoted, and the developer can be This makes it possible to further stabilize the potential state of the film, making it possible to obtain a better developed image. 1
A blade 3 is made of an insulating material and is arranged at a small distance from the cylinder 11.

This blade 13 regulates the amount of developing agent moving on the cylinder 11 toward the developing section. 14 is multipolar (12 in the figure)
Jar) A magnetic roll is driven to rotate at high speed in the direction of the arrow shown by a motor (not shown).

By this rotation of the magnet roll 14, the developer made of magnetic toner is taken out from the container 12 along the circumferential surface of the cylinder 11 and moves in the opposite direction to the rotation direction of the roll 14.
Example 2 Example 1 except that y-Fe203 (TD-3, manufactured by Tokyo Denki Kagaku Kogyo Co., Ltd.) was used as the magnetic powder.
When carried out in the same manner as above, a good image was obtained.

The coercivity of the toner was 175 Oersteds. The volume resistivity was 1 and 60 skin. Example 3 A good image was obtained in the same manner as in Example 1 except that y-Fe203 (TD-5, manufactured by Tokyo Denki Kagaku Kogyo Co., Ltd.) was used as the magnetic powder.

The coercive force of the toner was 192 Oersted, and the volume resistivity was 1.60 Oersted. Example 4 The same procedure as in Example 1 was conducted except that y-Fe203 (TD-6, manufactured by Tokyo Denki Kagaku Kogyo Co., Ltd.) was used as the magnetic powder, and a very good image was obtained.

The coercive force of the toner was 250 Oersted, and the volume resistivity was 1.60 Oersted. Examples 5 to 8 The same procedure as in Example 1 was carried out except that the materials shown in Table 1 were used as the magnetic powder, and very good images with good string alignment and high density were obtained.

Examples 9 to 14 Weight ratio of epoxy resin and magnetic powder is 80/20, 75/2
5, 60/40, 40/60, 30/70, 20/80
When the same machine as in Example 1 was used except for changing to On the other hand, in areas where the amount of magnetic powder is large, the toner is strongly attracted to the magnet, so the image density tends to be low.

However, in all cases, good images with good pongee line reproduction were obtained. Examples 15 to 17 The same procedure as in Example 1 was performed except that polystyrene, polyester resin, or phenol resin was used instead of the epoxy resin, and almost the same results as in Example 1 were obtained.

Example 18 75 parts by weight of a polyester resin (ACRAC 382A, manufactured by Kao Atlas Co., Ltd.) and 25 parts by weight of magnetic powder (CJ-300 clothing, manufactured by Kanto Denka Co., Ltd.) are mixed using a ball mill, and then melt-kneaded using a roll mill.

After cooling, it is coarsely pulverized using a hammer mill and further finely pulverized using a supersonic jet pulverizer. The obtained fine powder was classified, and 1 to 20 particles were selected and used as a toner. The toner had a coercive force of 413 oersteds and a volume resistivity of 1 p60 oersteds. An electrically fused image formed in the same manner as in Example 1 was transferred to a magnetic fixed sleeve rotating type phenomenon device (sleeve diameter 5
The sleeve surface magnetic flux density is 800 gauss, the distance between the ear cutting blade and the sleeve surface is 100 gauss, the sleeve is in the opposite direction to the rotating drum and the circumferential speed is the same as the drum circumferential speed), and the distance between the sleeve surface and the insulating layer surface is 100 gauss. Develop the insulating layer using the toner so that the toner layer on the transfer paper does not come into contact with the insulating layer.
The powder image was transferred while being irradiated with V direct current corona and fixed by heating.

An extremely good image with good fine line reproduction and no background fog was obtained. When images were produced in substantially the same manner at a high temperature (30 oo, 85%), good image strength was obtained. Further, in the same manner as during development, a developing device and toner were set, a potential measuring probe was placed above the developing area of the developing sleeve, and the potential of the toner layer was measured with a surface electrometer.

The measured value was -20V, and the toner was clearly charged due to friction with the developer support member. Example 19 The same procedure as Example 18 was carried out except that TD-3 was used as the magnetic powder, and a good image without turn IJ was obtained.

The coercive force of the toner was 170 oersted. Example 20 The same procedure as in Example 18 was performed except that TD-5 was used as the magnetic powder, and a good image without fog was obtained.

The coercive force of the toner was 188 oersted. Example 21 The same procedure as in Example 18 was carried out except that TD-6 was used as the magnetic powder, and very good images without fog were obtained.

The coercive force of the toner was 245 elsted. Example
22-25 The same procedure as in Example 18 was carried out except that the materials shown in Table 1 were used as the magnetic powder, and very good images with no fog and good fine line reproducibility were obtained.

Examples 26-29 Weight ratio of polyester resin and magnetic powder is 90/10,80
/20, 50/50, 30/70 was carried out in the same manner as in Example 18, and it was found that where the amount of magnetic powder was small, the image density was high because the force to attract the toner to the magnet was weak. Although it is above the practical level, the reproduction of fine lines becomes somewhat unclear, and in areas where there is a large amount of magnetic powder, the toner is strongly attracted to the magnet, which tends to lower the image density, but in both cases, fogging is a problem. No good images were obtained.

Example 30 A latent image was formed in the same manner as in Example 1, and this latent image was formed with a sleeve diameter of 5 mm and a sleeve surface magnetic flux density of 70 mm.
0 gauss, number of magnetic poles 12, magnetic fixed sleeve rotation (25 pm in the opposite direction to the rotational direction of the drum) type developer (in Fig. 2, non-magnetic Set the distance between the insulation layer surface and the sleeve surface to 0.46 using a developing device (without insulation notification 11").
It was developed using the toner of Example 1, and a powder image was transferred while irradiating a direct current corona of 17 KV from the back side of the transfer paper, and then fixed by heating. A good image was obtained. High humidity (30q085%
), the image was produced in almost the same manner, and although it was inferior to Example 1, an image of a practical level was obtained. Examples 31 to 37 The same procedure as Example 30 was carried out using the toners of Examples 2 to 8, respectively.

Comparative Example 1 A comparatively good image was obtained in the same manner as in Example 1 except that BL-500 (manufactured by Titan Kogyo Co., Ltd.) was used as the magnetic powder.

Toner coercive force 82 Oersted volume resistivity 1 and 60
skin. When image formation was carried out at a high temperature (300085%), only very poor images with low density were obtained.
Comparative Example 2 A comparatively good image was obtained in the same manner as in Example 1 except that EPT-500 (manufactured by Toda Kogyo Co., Ltd.) was used as the magnetic powder.

The coercive force of the toner is 115 oersted, the volume resistivity is 1
and 60 arcs. When an image was formed at a high temperature (3:085%), a poor image with low density was obtained. Comparative Example 3 The same procedure as in Example 18 was carried out except that BL-500 (manufactured by Titanium Kogyo Co., Ltd.) was used as the magnetic powder.

The toner had a coercive force of 80 oersted, a volume resistivity of 1 and 60 arc, and a relatively good image was obtained at normal humidity, but a poor image was obtained at high temperature (30° C. 85%). Comparative Example 4 The same procedure as in Example 18 was conducted except that EPT-500 (manufactured by Toda Kogyo Co., Ltd.) was used as the magnetic powder.

The coercive force of the toner is 112 elsted, and the volume resistivity is 1.
Although relatively good images were obtained at room temperature with the
At high temperatures (30:085%) only poor images were obtained. Comparative Example 5 The magnetic toner of Comparative Example 1 was used in the same manner as in Example 30.

Comparative Example 6 The magnetic toner of Comparative Example 2 was used in the same manner as in Example 30.

The evaluation of each example is shown in Table 1 below.

Table 1 A: Very good high-density image with good reproducibility of mesh lines, good image quality in solid areas, and no fog.

B Good high density image with no fog. C Good image at a practical level.

D Thin image with poor image quality.

Image evaluation at high temperature (3000, 85%) is shown in Table 2.

Table 2 Measurement method {1' Coercive force Using a vibrating sample magnetometer (product name, VSM-3 type, manufactured by Toei Kogyo Co., Ltd.), the magnetization of toner placed in a magnetic field of up to 5000 Oe is measured and recorded. The coercive force was determined from the hysteresis curve drawn on paper.

[21 Volume Resistance] Volume resistivity was measured using an aluminum electrode with a measurement area of 100 skins x 10 ships. Using a measuring device with a structure in which a guard electrode is provided at a distance of approximately 5 mm from the electrode periphery, and the electrode is insulated with a Teflon material, the sample is filled between the electrodes by applying slight vibration.
The test was carried out by applying a voltage of 00 V/arc.

For measurement, YHP YHP4329A Hi heat Resi
A stance Meter was used.

[Brief explanation of drawings]

FIG. 1 is an explanatory view showing the state of magnetization of magnetic toner on a sleeve, and FIG. 2 is a schematic cross-sectional view showing an example of a developing device. 1...Magnet, 2...Sleeve, 3...Magnetic pole, 4,
5, 6, 7, 8... Magnetic powder toner, 9...
Photosensitive drum, 11...Sleeve, 13...
...Blade, 14. ．．・…Multi-polar magnet roll. *
Figure lFigure 2

Claims (1)

[Scope of Claims] 1. A developing device having a developer support member and a magnet that applies a magnetic field to the surface of the support member has a coercive force of at least 170 oersteds or more and a volume resistivity of 10^1^2 Ωcm or more. By supplying a developer containing no carrier particles made of magnetic toner and moving at least one of the developer support member and the magnet, the magnetic toner is moved while the magnet and the magnetic toner are relatively moved. By triboelectrically charging, by transferring charge between the magnetic toner and the developer support member, and/or by transferring charge between the magnetic toners on the developer support member, An image forming method characterized by developing a latent image and transferring the obtained toner image to a transfer material. 2. The image forming method according to claim 1, wherein the magnetic toner contains 20 to 50% by weight of magnetic material.