JP2892150B2 - Image forming method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming method including a step of developing an electrostatic image formed in an electrophotographic method, an electrostatic printing method, or the like using a magnetic toner.

[Description of Prior Art]

Conventionally, electrophotography has been disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910 (U.S. Pat.No. 3,666,363) and Japanese Patent Publication No. 43-24748 (U.S. Pat.
Many methods are known as described in US Pat. No. 1,361, and the like. Generally, a photoconductive substance is used to form an electrostatic latent image on a photoreceptor by various means. The latent image is developed using toner, and if necessary, a toner image is transferred to a transfer material such as paper, and then fixed by heating, pressure, or solvent vapor to obtain a copy.

The present applicant has proposed a novel developing method using a one-component magnetic toner for developing these electrostatic latent images (for example,
55-18656 and JP-A-55-18659). In this method, an insulating magnetic toner is uniformly coated on a cylindrical toner carrier having a magnet therein, and the toner is developed without contacting the latent image holding member without contact.

According to this method, during development, a low-frequency alternating voltage is applied between the toner carrier and the substrate conductor of the latent image holder, and the toner is reciprocated between the toner carrier and the latent image holder. , Excellent in reproduction of gradation without background fogging and good development without thinning of image edges. In this developing method, electrostatic transfer is easy because toner is an insulator. It is.

Also, photoconductive materials known to be used as electrophotographic photoconductors include Se, CdS, OPC (organic photoconductor), and amorphous silicon (hereinafter referred to as a-Si).
Etc.

Se-based photoconductors are traditional photoconductors that have been used since the earliest days of electrophotographic technology, and because of their good sensitivity and durability as characteristics, many applications in practical use have been made. At present, SeTe, which has higher color sensitivity and higher photosensitivity than pure selenium, is mainly used, but still, the Se photoreceptor inherently possesses heat resistance, abrasion resistance, mechanical It has problems in strength and stability over time. That is, crystallization is liable to occur due to touch with hands, blowing of breath, increase in temperature, and frictional contact by the cleaning device, and performance is likely to deteriorate.

Although the OPC system has been put into practical use due to the discovery of excellent sensitizers and the development of sensitization methods, it has decisive disadvantages in abrasion resistance and durability, so measures must be taken to address it. It is urgently needed. As described above, photoconductors that are currently in practical use and applied to electronic copiers have sensitivity, durability, image quality,
There is no one that satisfies all aspects such as non-pollutability, and the current situation is that the electronic copying machine is marketed as a product by compensating for the disadvantages of each photoreceptor with toner or process.

In recent years, as electronic copiers have been diversified into color, personalized, intelligent, and maintenance-free, photoconductors with new characteristics, high stability and low cost have been desired, and development is proceeding. Have been. Among them, a-Si has been attracting attention as a material to be replaced with an existing photoconductor.

Since a-Si has a high photosensitivity over the entire visible region, it can be used for semiconductor lasers and colors. In addition, high surface hardness, long life can be expected, Vickers hardness is 15
It has a printing durability of 200 to 500,000 sheets, which is several times that of the CdS photoreceptor, which is said to have the most durability and abrasion resistance at present. With respect to heat resistance, it can be used sufficiently within the practical level of an electronic copying machine.

However, the a-Si photoreceptor has problems in cost reduction and mass production on the contrary to such advantages.

It is generally said that the surface dark potential of the a-Si photoconductor corresponds to the film thickness. At present, the surface dark potential of photoconductors practically used is at least 500 V for CdS type, Se type, OPC
The system requires 600-800V. In order to achieve this potential with a-Si, it is necessary to increase the film thickness, and it is necessary to provide a film thickness in consideration of a change in various characteristics and a decrease in sensitivity due to a difference in environment. For this reason, in order to obtain the film thickness, an increase in a-Si manufacturing cost and a decrease in production capacity are unavoidable problems. In addition, an increase in the film thickness tends to cause abnormal growth of the a-Si film during the manufacturing process, and a partially non-uniform a-Si film is formed, making the film practically unusable.

To cope with such a problem, it has been proposed to reduce the thickness of the a-Si photoreceptor so as to satisfy both mass productivity, cost, and performance. However, in this method, a toner that can be developed at a low potential must be selected. This is because the thinning of the a-Si film requires cost and production capacity,
Despite satisfying the photosensitive characteristics, the decisive drawbacks are that the surface potential drops significantly, and that impurities adhere to the drum surface under high humidity, deteriorating the photosensitive characteristics and causing image deletion in image quality. It is easy to do. That is,
For practical a-Si films, the surface dark potential is at most
At around 400V, the potential that can be used stably is about 300V. Therefore, in order to be able to use the a-Si photoconductor practically, it is necessary to use a toner that can be developed at a low potential and has a high developing ability.

On the other hand, the a-Si photoreceptor holding a negative electrostatic image has a charge characteristic, a dark decay, and an electrophotographic characteristic such as a charge memory, but the a-Si photoreceptor holding a positive electrostatic image is not clear. Is better than. This is because the characteristics of the a-Si photoreceptor holding a negative electrostatic image depend on the mobility of electrons of the generated photocarriers, but in the a-Si photoreceptor, electrons are larger than holes. It is thought to be.

In the charging step for forming an electrostatic latent image,
Generally, corona charging is used, and ozone and ozone products (such as nitrogen oxides) are generated simultaneously with charging. The amount of the generated ozone is proportional to the amount of current supplied to the charger, and ozone is generally generated 5 to 10 times more in the case of the negative charge than in the case of the positive charge. Further, impurities adhere to the drum under high humidity due to ozone products and the like, causing image deletion. Therefore, a-Si which holds a negative electrostatic charge image having excellent electrophotographic characteristics
In order to use the photoreceptor, it is necessary to reduce the current value supplied to the charger in order to suppress the generation of ozone. As a result, the surface potential cannot be too high,
A-Si that has a positive electrostatic image because of its excellent chargeability
It is practically impossible to provide a surface potential higher than that of the photoconductor, but it is preferable to reduce the current value.

For the above reasons, in an image forming method using an a-Si photoreceptor that holds a negative electrostatic image, a sufficient development is performed with a low potential difference, and a positive chargeability that can be developed with good gradation properties faithfully according to the potential difference. Magnetic toner is required.

In general, a developing method using a one-component magnetic toner includes:
A sleeve ghost (image defect due to toner carrier memory) may occur. The reason is not clear,
Positively chargeable toner is lighter in degree and causes less problem.

Here, the phenomenon of carrier memory means a phenomenon in which an image is formed as shown in part 4 of FIG. 1c in the attached drawings.

For example, when developing the wide image 2 shown in FIG. 1b after developing the image 1 shown in FIG. 1a, the image 1 is developed with toner on a toner carrier such as a sleeve corresponding to a white background outside the area of the image 1. As shown in FIG. 1c, the portion 4 of the image 2 has a lower image density than the other image regions. When the toner carrier makes one rotation to develop the image 2, the toner corresponding to the width b on the toner carrier is consumed, so that the portion 3 after one rotation (after the length l) has an image density of Make uniform.

According to the experiments and considerations of the present inventors, the mechanism of the formation of the toner carrier memory is deeply related to the fine powder layer formed on the toner carrier. That is, the particle size distribution of the toner in the lowermost layer of the toner layer on the toner carrier has a clear difference between the toner consuming portion and the non-consuming portion, and a fine powder layer is formed in the toner consuming lowermost portion. The fine powder has a large surface area per volume, so that the triboelectric charge per unit weight is larger than that of the particles having a large particle size. Be strongly restrained. As a result, the toner in the upper layer of the portion where the fine powder amount is formed is not sufficiently triboelectrically charged by the developer carrier, so that the amount of triboelectric charge is reduced. As a result, the toner carrier memory (partial image density Thin).

In the case of the positively chargeable toner, the amount of triboelectric charge of the fine powder in the toner does not increase, so that the toner carrier memory hardly occurs. The reason is that the binder resin used in the toner is negatively charged, so that in the case of a negatively chargeable toner, the fine powder in the toner has a larger frictional charge amount, and the above-described toner carrier memory is generated. On the other hand, in the case of a positively chargeable toner, on the other hand, since the resin is controlled to have the opposite polarity, it is considered that charge neutralization works to prevent the fine powder in the toner from being excessively charged.

[Object of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and to provide a-
An object of the present invention is to provide an image forming method using a developing method using a positively chargeable one-component magnetic toner for visualizing a negative electrostatic latent image formed on a Si photoreceptor.

Further, an object of the present invention is to provide a drum ghost (an image defect due to a charged memory, a latent image formed in a previous process remains,
It is an object of the present invention to provide an image forming method capable of high-speed development using an a-Si photoreceptor excellent in electrophotographic characteristics without causing a phenomenon of visualization.

Furthermore, an object of the present invention is to provide a high image density, fog,
An object of the present invention is to provide an image forming method capable of obtaining an image without a sleeve ghost and excellent in fine line reproducibility and gradation.

It is a further object of the present invention to provide an image forming method that does not change its performance over a long period of use.

Furthermore, an object of the present invention is to provide a low surface dark potential a
An object of the present invention is to provide an image forming method capable of obtaining a good image density using a Si photoreceptor.

Still another object of the present invention is to provide an image forming method capable of obtaining image quality without image deletion under high temperature and high humidity.

It is a further object of the present invention to provide an image forming method in which the performance does not change due to environmental changes.

Another object of the present invention is to provide an image forming method having excellent transferability.

Another object of the present invention is to provide an image forming method capable of obtaining a high image density with a small consumption.

[Configuration of the invention]

The present invention provides an amorphous silicon photoreceptor for holding a negative electrostatic charge image, in which the surface dark area potential is negative and the absolute value is 400 V.
A negative electrostatic charge image is formed on the surface of the charged amorphous silicon photoconductor, and the amorphous photoconductor and a toner carrier for supporting a positively chargeable magnetic toner on the surface are developed by the developing unit. The positively-charged magnetic toner is conveyed to the developing unit while regulating the thickness of the positively-chargeable magnetic toner to a thickness smaller than the gap on the toner carrier. Applying a developing bias to the developer carrier to develop a negative electrostatic image held on the amorphous silicon photoreceptor with the positively chargeable magnetic toner, the image forming method comprising: The toner uses magnetic toner particles having a particle size of 5 μm or less.
It contains 12 to 60% by number, contains 1 to 33% by number of toner particles having a particle size of 8 to 12.7 μm, contains toner particles having a particle size of 16 μm or more at 2.0% by volume or less, and has a volume average particle size of 4%. ~ 10μm
An image forming method characterized by having a particle size distribution of

One feature of the present invention is that a photosensitive member having an a-Si photosensitive layer on a conductive substrate is used as a negative electrostatic image holding member.

In the present invention, a lower charge injection preventing layer may be provided below the photosensitive layer as a constitution of the a-Si photoreceptor to prevent intrusion of charges from the substrate. If necessary, a charge injection blocking layer, a light absorbing layer for preventing an interference phenomenon, and a surface protective layer can be provided above or below the photosensitive layer.

The a-Si photoreceptor used in the present invention has a hydrogen atom,
Boron, aluminum, gallium and other group III atoms of the periodic table, germanium, tin and other group IV atoms, nitrogen, phosphorus, arsenic and other group V atoms, oxygen, sulfur, A or a compound of a halogen atom such as fluorine, chlorine, bromine, etc.
Introducing at the time of -Si formation, each characteristic of each layer can be controlled, and a negative electrostatic charge image holding member can be formed by the a-Si photosensitive member in which the characteristics of each layer are controlled. For example, if the photosensitive layer is provided with hydrogenated a-Si, the phosphorus-doped hydrogenated a-Si is provided on the lower charge injection preventing layer and the boron-doped hydrogenated a-Si is provided on the upper charge injection preventing layer, the negative charge can be obtained. Photosensitive drum holding the electrostatic image of the present invention.

An a-Si photosensitive drum holding such a negative electrostatic image is an a-Si photosensitive drum holding a positive electrostatic image formed in a similar manner.
Compared with photosensitive drums, it has better charging ability (that is, it can have a higher surface potential with a smaller current value), dark decay,
It has excellent characteristics such as a charged memory (drum ghost).

Further, in general, a-Si photoreceptors are excellent in heat resistance and abrasion resistance, and are excellent in durability. Therefore, the image forming method of the present invention has an advantage in speeding up a copying machine. .

In the present invention, the magnetic toner particles having a particle size of 5 μm or less
It contains 60% by number, contains 1 to 33% by number of magnetic toner particles having a particle size of 8 to 12.7 μm, contains 2.0% by volume or less of magnetic toner particles having a particle size of 16 μm or more, and has a volume average particle size of the magnetic toner. Another feature is to use a positively-chargeable magnetic toner having a particle size distribution with a diameter of 4 to 10 μm, and a toner carrier that carries the magnetic toner on the surface is arranged at a certain gap in the developing unit, The magnetic toner is regulated on the toner carrier to a thickness smaller than the gap and transported to the developing unit,
This is an image forming method to be developed. By this method, the above-described negative electrostatic image is faithfully visualized, and a high-density image without fog can be provided.

That is, the magnetic toner having the particle size distribution characteristic of the present invention can faithfully reproduce the fine lines of the latent image formed on the photoreceptor, An image that is excellent in reproduction and excellent in halftone gradation and line resolution is provided. Furthermore, high image quality can be maintained even when copying is continued, and good development can be performed with less toner consumption than conventional magnetic toners even for high-density images. This has an advantage in reducing the size of the main body.

The reason why such an effect is obtained in the magnetic toner used in the present invention is not necessarily clear, but is presumed as follows.

That is, in the magnetic toner used in the present invention, 5
One feature is that magnetic toner particles having a particle size of μm or less are 12 to 60% by number. Conventionally, magnetic toner particles having a particle size of 5 μm or less have difficulty in controlling the charge amount or impair the fluidity of the magnetic toner.
It has been considered that it is necessary to aggressively reduce the toner as a component that scatters toner and stains the machine, and further as a component that causes image fogging.

However, studies by the present inventors have revealed that magnetic toner particles having a size of 5 μm or less are essential components for forming high-quality images.

For example, using a magnetic toner having a particle size distribution ranging from 0.5 to 30 μm, the surface potential on the photoreceptor is changed, and a large development potential contrast from which a large number of toner particles are easily developed to a halftone, and further, a very small number of toner particles A negative electrostatic image with a changed surface potential on the photoreceptor was developed to a small development potential contrast that could only be developed, the developed toner particles on the photoreceptor were collected, and the toner particle size distribution was measured. It has been found that there are many magnetic toner particles, especially magnetic toner particles of 5 μm or less. That is, when magnetic toner particles having a particle size of 5 μm or less, which are most suitable for development, are smoothly supplied to the development of the negative electrostatic image on the photoreceptor, the magnetic toner particles are faithful to the negative electrostatic image and protrude from the negative electrostatic image. Therefore, an image having truly excellent reproducibility can be obtained.

Further, in the magnetic toner used in the present invention, 8 to 1
One feature is that particles in the range of 2.7 μm are 1 to 33% by number. This is related to the necessity of the magnetic toner particles having a particle size of 5 μm or less as described above.
The magnetic toner particles having a particle size of m or less strictly cover the negative electrostatic image and have the ability to faithfully reproduce, but in the negative electrostatic image itself, the electric field strength of the peripheral edge portion is higher than that of the central portion. Therefore, the amount of toner particles inside the negative electrostatic charge image becomes thinner than the edge portion, and the image density may appear to be light. In particular, magnetic toner particles of 5 μm or less have a strong tendency. However, the present inventors have solved this problem by including 1 to 33% by number of toner particles in the range of 8 to 12.7 μm, and have found that the toner particles can be further sharpened. That is, it is considered that the toner particles having a particle size in the range of 8 to 12.7 μm have a moderately controlled charge amount with respect to the magnetic toner particles having a particle size of 5 μm or less.
The negative electrostatic charge image is supplied to the inner side where the electric field intensity is smaller than the edge portion, thereby compensating for the small amount of toner particles inside the edge portion, thereby forming a uniform developed image, and as a result, the resolution is high. This provides a sharp image with excellent characteristics and gradation.

Further, for magnetic toner particles having a particle size of 16 μm or more, the content is preferably set to 2.0% by volume or less, and as small as possible.

Thus, the magnetic toner used in the present invention solves the conventional problems and can withstand the recent severe demands for high image quality, based on a completely different concept from the conventional viewpoint.

The magnetic toner used in the present invention will be described in more detail.

Magnetic toner particles having a particle size of 5 μm or less have a total particle number of 12 to
It is preferably 60% by number, more preferably 25 to 50% by number, and even more preferably 30 to 50% by number. When the number of magnetic toner particles having a particle size of 5 μm or less is less than 12% by number, the amount of magnetic toner particles that are effective for high image quality is small, and the effective magnetic toner particle component is reduced particularly as the toner is used by continuing copying. Therefore, the balance of the particle size distribution of the magnetic toner as shown in the present invention is deteriorated, and the image quality is gradually reduced. On the other hand, when the content is 60% by number or more, the magnetic toner particles tend to aggregate with each other, and the toner particles become larger than the original particle size, resulting in rough image quality, reduced resolution, or negative electrostatic image. The density difference between the edge portion and the inside becomes large, and the image tends to be slightly hollow.

The particle size in the range of 8 to 12.7 μm is preferably 1 to 33% by number, and more preferably 8 to 20% by number. If the content is more than 33% by number, the image quality is deteriorated, and the development is performed more than necessary, that is, the toner is excessively applied, which causes an increase in toner consumption. On the other hand, if it is less than 1% by number, it becomes difficult to obtain a high image density.

The content of the magnetic toner particles having a particle diameter of 16 μm or more is preferably 2.0% by volume or less, more preferably 1.0% by volume.
Or less, more preferably 0.5% by volume or less.
When the content is more than 2.0% by volume, not only does it hinder the reproduction of fine lines, but also in the transfer, coarse toner particles of 16 μm or more protrude from the thin layer surface of the toner particles developed on the photoreceptor. The delicate state of contact between the photoreceptor and the transfer paper via the layer is made irregular, causing fluctuations in the transfer conditions and causing poor transfer images. The volume average particle diameter of the magnetic toner is 4 to 10 μm, preferably 4 to 9 μm, and this value cannot be considered separately from the above-mentioned components. When the volume average particle diameter is 4 μm or less, in applications where the image area ratio of graphic images and the like is high, the problem that the amount of applied toner on transfer paper is small and the image density is low tends to occur. This corresponds to the edge portion in the negative electrostatic image described above.
This is probably due to the same reason that the internal concentration was reduced. If the volume average particle size is 10 μm or more, the resolution is not good,
At the beginning of copying, image quality is liable to be deteriorated if the user keeps using it at best.

FIG. 5 shows the gradient of the image density with respect to the surface potential obtained by the developing method using a magnetic toner having a specific particle size distribution, which is a feature of the present invention.

As is apparent from FIG. 5, since the negative electrostatic charge image has a proper inclination, the negative electrostatic charge image is faithfully visualized according to the potential, so that an image having halftone reproduction and gradation can be obtained. Further, the cut from the white image portion to the halftone image portion is good, and no fogging occurs. The cut from the halftone image portion to the black image portion is good, and a sufficient image density can be obtained even with a low potential difference, and no density unevenness occurs. As will be described later, the magnetic toner having a specific particle size distribution as in the present invention has a good adhesion to a negative electrostatic image, and a uniform magnetic toner can be developed evenly according to the potential of the negative electrostatic image. Therefore, since the change from white to halftone and from halftone to black is good, it is possible to obtain an image having no fog, high image density, and excellent halftone gradation reproducibility. .

Although the particle size distribution of the toner can be measured by various methods, in the present invention, the measurement was performed using a Coulter counter.

In other words, the Coulter Counter TA is used as a measuring device.
-Type II (manufactured by Coulter, Inc.) was connected to an interface (manufactured by Nikkaki) for outputting the number distribution and volume distribution and a CX-1 personal computer (manufactured by Canon). Prepare a% NaCl aqueous solution. As a measuring method, 0.1 to 5 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the aqueous electrolytic solution, and 2 to 20 mg of a measurement sample is further added. The electrolyte in which the sample was suspended was treated with an ultrasonic
After a dispersion treatment for minutes, the Coulter Counter TA-II
According to the mold, the particle size distribution of particles of 2 to 40 μ was measured on the basis of the number, using a 100 μ aperture as the aperture, and then the value according to the present invention was determined.

As the binder resin used in the magnetic toner used in the present invention, when a heating / pressing roller fixing device having an apparatus for applying oil is used, the following binder resins for toner can be used.

For example, polystyrene, poly-p-chlorostyrene,
Styrene such as polyvinyltoluene and its substituted homopolymer; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, styrene -Methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone Styrene-based copolymers such as copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-acrylonitrile-indene copolymers; polyvinyl chloride, phenolic resins, naturally-modified phenolic resins, and natural-resin-modified malees Acid resin, acrylic tree , Methacrylic resins, polyvinyl acetate, silicone resins, polyester resins, polyurethane, polyamide resins, furan resins, epoxy resins, xylene resins, polyvinyl butyral, terpene resin, coumarone-indene resin, petroleum resin, or the like can be used.

In the heat and pressure roller fixing method in which almost no oil is applied, the so-called offset phenomenon in which a part of the toner image on the toner image support member is transferred to the roller and the adhesion of the toner to the toner image support member are important issues. is there. These problems must be considered at the same time because toners that fix with less heat energy tend to block or casing during storage or in a developer. The physical properties of the binder resin in the toner are most involved in these phenomena, but according to the study of the present inventors, when the content of the magnetic substance in the toner is reduced,
At the time of fixing, the adhesion of the toner to the toner image supporting member is improved, but offset tends to occur, and blocking or caking tends to occur. Therefore, when using a heat and pressure roller fixing method in which almost no oil is applied in the present invention, selection of a binder resin is more important. Preferred binders include crosslinked styrenic copolymers or crosslinked polyesters.

Examples of the comonomer for the styrene monomer of the styrene copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, and methacrylic. Acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, a monocarboxylic acid having a double bond such as acrylamide or a substituted product thereof; for example, maleic acid, butyl maleate, Dicarboxylic acids having a double bond such as methyl maleate, dimethyl maleate and the like, and substituted products thereof; vinyl esters such as vinyl chloride, vinyl acetate, vinyl benzoate, etc .; Vinyl monomers such as ethylene-based olefins such as ethylene; vinyl ketones such as vinyl methyl ketone and vinyl hexyl ketone; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether; Are used alone or in combination of two or more.

Here, as the cross-linking agent, a compound having two or more polymerizable double bonds is mainly used, for example, an aromatic divinyl compound such as divinylbenzene, divinylnaphthalene or the like; for example, ethylene glycol diacrylate,
Carboxylic acid esters having two double bonds such as ethylene glycol dimethacrylate and 1,3-butanediol dimethacrylate; divinyl compounds such as divinylaniline, vidinyl ether, divinyl sulfide and divinyl sulfone; and three or more Compounds having a vinyl group are used alone or as a mixture.

When a pressure fixing method is used, a binder resin for a pressure fixing toner can be used. For example, polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer can be used. Coalescent, ionomer resin, styrene-butadiene copolymer, styrene-isoprene copolymer, linear saturated polyester, paraffin and the like.

In the magnetic toner used in the present invention, it is preferable to use a charge control agent mixed (internally added) with toner particles or mixed (externally added) with toner particles. Depending on the charge control agent,
It is possible to control the amount of charge optimally according to the developing system, and in particular, it is possible to further stabilize the balance between the particle size distribution and the charge. Examples of positive charge control agents include denatured products such as nigrosine and fatty acid metal salts; quaternary ammonium salts such as tributylbenzylammonium-1-hydroxy-4-naphthosulfonate and tetrabutylammonium tetrafluoroborate; dibutyltin oxide and dioctyltin Oxides, diorganotin oxides such as dicyclohexyltin oxide;
Diorganotin borates such as dibutyl tin borate, dioctyl tin borate and dicyclohexyl tin borate can be used alone or in combination of two or more. Among these, charge control agents such as nigrosine and quaternary ammonium salts are particularly preferably used.

Also, the general formula [In the formula, R ₁ represents H or CH ₃ , and R ₂ and R ₃ represent a substituted or unsubstituted alkyl group (preferably, C ₁ -C ₄ ). ] Or a copolymer with a polymerizable monomer such as styrene, acrylate or methacrylate as described above can be used as the positive charge control agent. The charge control agent is
It also has the function as (all or part of) the binder resin.

The above-mentioned charge control agent (having no action as a binder resin) is preferably used in the form of fine particles. In this case, the number average particle size of the charge control agent is specifically preferably 4 μm or less (more preferably 3 μm or less).

When internally added to the toner, such a charge control agent is used in an amount of 0.1 to 20 parts by weight (more preferably 0.2 to 10 parts by weight) based on 100 parts by weight of the binder resin.
Parts by weight).

In the magnetic toner used in the present invention, various additives may be added internally or externally as necessary. As the coloring agent, conventionally known dyes and pigments can be used,
Usually, 0.5 to 20 parts by weight may be used with respect to 100 parts by weight of the binder resin. Other additives include, for example, a lubricant such as zinc stearate; an abrasive such as cerium oxide and silicon carbide; a fluidity imparting agent or an anti-caking agent such as colloidal silica and aluminum oxide; There is a conductivity imparting agent.

Further, for the purpose of improving the releasability at the time of heat roll fixing, a wax-like substance such as low-molecular-weight polyethylene, low-molecular-weight polypropylene, microcrystalline wax, carnauba wax, sasol wax, paraffin wax, etc. Addition of about 5 wt% to the magnetic toner is also a preferred embodiment of the present invention.

Further, the magnetic toner used in the present invention may also serve as a colorant, but contains a magnetic material. Examples of the magnetic material contained in the magnetic toner used in the present invention include iron oxides such as magnetite, γ-iron oxide, ferrite, and iron-rich ferrite; metals such as iron, cobalt, and nickel; , Cobalt, copper,
Examples include alloys with metals such as lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, and vanadium, and mixtures thereof.

These ferromagnetic materials preferably have an average particle size of 0.1 to 1 μm, preferably about 0.1 to 0.5 μm, and the amount contained in the magnetic toner is 60 to 1 part by weight per 100 parts by weight of the resin component.
50 parts by weight, preferably 65 to 120 parts by weight per 100 parts by weight of the resin component
Parts by weight.

The positively chargeable magnetic toner used in the present invention comprises a magnetic powder, a vinyl-based or non-vinyl-based thermoplastic resin, a pigment or a dye as a colorant, if necessary, a charge control agent, and other additives, such as a ball mill. After thoroughly mixing with a mixer, the mixture is melted, kneaded, and kneaded using a hot kneader such as a heating roll, kneader, or extruder to disperse or disperse the pigment or dye in the resin in which the resins are mutually compatible. , After cooling and solidifying, and then crushing and strict classification.

Another method is to obtain a toner by dispersing the constituent materials in a binder resin solution and then spray-drying the mixture; or mixing a predetermined material with a monomer to constitute the binder resin to obtain an emulsion suspension. And then polymerizing the toner to obtain a toner; or a method in which a core material, a shell material, or both of them include a predetermined material in a so-called microcapsule toner comprising a core material and a shell material; Method can be applied.

The true density of the magnetic toner used in the present invention is 1.45 to 1.
Is preferably 80 g / cm ^3, more preferably 1.50
1.71.70 g / cm ³ . Within this range, the magnetic toner having the above-mentioned specific particle size distribution is most effective in terms of high image quality and durability stability. If the true density of the magnetic toner is less than 1.45, the magnetic toner particles themselves are too light in weight, so that fine lines are crushed and scattered due to reverse fogging and excessive toner particles, and the resolution is likely to be deteriorated. Also, if the true density of the magnetic toner is greater than 1.80, the image density is low, resulting in an image lacking sharpness such as breaks in thin lines,
Further, since the magnetic force is relatively large, the ears of the toner are likely to be long or branched, and in this case, when the negative electrostatic image is developed, the image quality is disturbed and the image tends to be rough.

The true density of the magnetic toner can be measured by several methods. In the present invention, the following method is employed as an accurate and simple method for measuring fine powder.

A stainless steel cylinder with an inner diameter of 10 mm and a length of about 5 cm, a disk with an outer diameter of about 10 mm and a height of 5 mm (A) that can be closely inserted into it, and a piston with an outer diameter of about 10 mm and a length of about 8 cm (B)
Prepare The disk (A) is placed at the bottom of the cylinder, then about 1 g of the measurement sample is placed, and the piston (B) is gently pushed. A force of 400 kg / cm ² is applied to this with a hydraulic press, and the product is compressed for 5 minutes and taken out. The weight of the compressed sample is weighed (wg), the diameter (Dcm) and the height (Lcm) of the compressed sample are measured with a micrometer, and the true density is calculated by the following equation.

In order to obtain better development characteristics, the magnetic toner used in the present invention has a residual magnetization σ _{r of 1} to 10 emu / g, preferably 2 to 5.0 emu / g, and a saturation magnetization σ _s of 20 to 80 emu / g. , preferably 20~40emu / g, coercive force Hc of 40 to 200 Esuteddo _(e), preferably is preferable to satisfy the magnetic properties of 40~100emu / g (both determined magnetic field is 1K _e) .

The magnetic toner used in the present invention may be internally or externally mixed with silica fine powder, but is more preferably externally mixed. A magnetic toner having a particle size distribution as a feature of the present invention has a larger specific surface area than conventional toners. When magnetic toner particles are brought into contact with the surface of a cylindrical conductive sleeve having a magnetic field generating means inside due to triboelectric charging, the number of times of contact between the surface of the toner particles and the sleeve increases compared to conventional magnetic toner, and the toner Particle wear is likely to occur. When the magnetic toner used in the present invention is combined with silica fine powder, wear is significantly reduced because the silica fine powder is interposed between the toner particles and the sleeve surface. As a result, the life of the magnetic toner can be prolonged, and stable chargeability can be maintained, and a developer having a magnetic toner that is more excellent for long-term use can be obtained.

As the silica fine powder, both silica fine powder produced by a dry method and a wet method can be used, but from the viewpoint of filming resistance and durability, it is preferable to use a silica fine powder obtained by a dry method.

Here, the dry method is a method for producing silica fine powder generated by vapor phase oxidation of a silicon halide. For example, in a method utilizing the thermal decomposition oxidation reaction of silicon tetrachloride gas in oxygen-hydrogen, the basic reaction formula is as follows.

SiCl ₄ + 2H ₂ + O ₂ → SiO ₂ + 4HCl Also, in this manufacturing process, a composite fine powder of silica and another metal oxide is obtained by using another metal halide such as aluminum chloride or titanium chloride together with a silicon halide. It is also possible and encompasses them.

Commercially available silica fine powder produced by the vapor phase oxidation of a silicon halide used in the present invention includes, for example, those commercially available under the following trade names.

AEROSIL 130 (Nippon Aerosil) 200 300 380 OX50 TT600 MOX80 MOX170 COK84 Ca-O-SiL M-5 (CABOTO Co.) MS-7 MS-75 HS-5 EH-5 Wacker HDK N 20 V15 (WACKER-CHEMIE GMBH) N20E T30 T40 D-C Fine Silica (Down Corning Co.) Fransol (Fransil) On the other hand, the method of producing the silica fine powder used in the present invention by a wet method includes various conventionally known methods. Applicable. For example, the decomposition of sodium silicate with an acid is represented by the following general reaction formula.

Na ₂ O ・ XSiO ₂ + HCl + H ₂ O → SiO ₂・ nH ₂ O + NaCl In addition, decomposition of sodium silicate with ammonium salts or alkali salts, formation of alkaline earth metal silicate from sodium silicate, and decomposition with acid Silicate, a method of converting a sodium silicate solution into silicic acid with an ion exchange resin, a method of using natural silicate or silicate, and the like.

Silica such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, zinc silicate and the like can be applied to the silica fine powder here, in addition to anhydrous silicon dioxide (silica).

Commercially available fine silica powder synthesized by the wet method includes, for example, those commercially available under the following trade names.

Carplex Shionogi Pharmaceutical Niepseal Nippon Silica Tokusil, Fine Seal Tokuyama Soda Vita Seal Titagi Hito Shilton, Shirunex Mizusawa Chemical Starsil Kamijima Chemical Himezil Ehime Pharmaceutical Syloid Fuji Devison Chemical Hi-sil Pittsburgh Plate Glass.Co Durosil (Durosill) Ultorasil (Ultraseal) Fiillstoff-Gesellschaft Marquart (Fürstoff-Gesershaft Marquart) Manosil (Manosil) Hardes and Holden (Headsmann and Holden) Hoesch (Hesche) Chemische Fabrik Hoesch KG (Hemische Fabhesheche) ) Sil-Stone (Sil-Stone) Stoner Rubber Co. (Stoner Rubber) Nalco (Narco) Nalco Chem. Co. (Narco Chemical) Quso (Kuso) Philadelphia Quartz Co. Radelphia Quartz Imsil Illinois Minerals Co. Calcium Silikat Calcium Silikat Chemische Fabrik Hoesch.K-G Calmille ) Fortafil Imperial Chemical Industries.Ltd. (Imperial Chemical Industries) Microcal Joseph Crosfiels & Sons.Ltd. (Joseph Crossfield and Sands) Vulkasil (Vurkazir) Farbenfabriken Bryer, A.-G. (Farben Fabryken) (Baya) Tufknit (Tuffnit) Durham Chemicals, Ltd. (Durham Chemicals) Silmos Shiraishi Kogyo Star Rex Kamishima Chemical Fricosyl Polywood fertilizer Of the above silica fine powder, BET method The specific surface area by measuring nitrogen adsorption 30 m ² / g or more (especially 50 to 400 m ² / g)
Those within the range give good results. Magnetic toner 100
It is preferable to use 0.01 to 8 parts by weight, preferably 0.1 to 5 parts by weight of silica fine powder based on parts by weight.

Further, when used as a positively charged magnetic toner such as the magnetic toner used in the present invention, the silica fine powder to be added to prevent wear of the toner may be more positively charged than finely charged silica fine powder. The use of a body is preferred without impairing the charging stability.

As a method of obtaining the positively chargeable silica fine powder, a method of treating the untreated fine silica powder with a silicon oil having an organo group having at least one nitrogen atom in a side chain, or a nitrogen-containing silane cup There is a method of treating with a ring agent or a method of treating with both.

In the present invention, the positively chargeable silica refers to a silica having a positive triboelectric charge with respect to an iron powder carrier when measured by a blow-off method.

Used for processing silica fine powder. As the silicone oil having a nitrogen atom in the side chain, a silicone oil having at least a partial structure represented by the following formula can be used.

(Wherein, R ₁ represents hydrogen, an alkyl group, an aryl group or an alkoxy group, R ₂ represents an alkylene group or a phenylene group, R ₃ and R ₄ represents hydrogen, an alkyl group, or aryl group, R ₅ Represents a nitrogen-containing heterocyclic group.) The alkyl group, the aryl group, the alkylene group, and the phenylene group may have an organo group having a nitrogen atom, and halogen may be used as long as the chargeability is not impaired. And the like.

Further, the nitrogen-containing silane coupling agent used in the present invention generally has a structure represented by the following formula.

Rm-Si-Yn (R represents an alkoxy group or halogen, Y represents an amino group or an organo group having at least one nitrogen atom, m and n are integers of 1 to 3, and m + n = 4. Examples of the organo group having at least one nitrogen atom include an amino group having an organic group as a substituent, a nitrogen-containing heterocyclic group, or a group having a nitrogen-containing heterocyclic group.
As the nitrogen-containing heterocyclic group, there is an unsaturated heterocyclic group or a saturated heterocyclic group, and each of them is applicable. Examples of the unsaturated heterocyclic group include the following.

Examples of the saturated heterocyclic group include the following.

The heterocyclic group used in the present invention is preferably a 5- or 6-membered ring in consideration of stability.

Examples of such treating agents include aminopropyltrimethoxysilane, aminopropyltriethoxysilane,
Dimethylaminopropyltrimethoxysilane, diethylaminopropyltrimethoxysilane, dipropylaminopropyltrimethoxysilane, dibutylaminopropyltrimethoxysilane, monobutylaminopropyltrimethoxysilane, dioctylaminopropyltrimethoxysilane, dibutylaminopropyldimethoxysilane, dibutyl Aminopropyl monomethoxysilane, dimethylaminophenyltriethoxysilane, trimethoxysilyl-γ-propylphenylamine, trimethoxysilyl-
γ-propylbenzylamine and the like. Further, as the nitrogen-containing heterocycle, those having the above-mentioned structures can be used. Examples of such compounds include trimethoxysilyl-γ-propylpiperidine, trimethoxysilyl-γ-propyl Morpholine, trimethoxysilyl-γ-propylimidazole and the like.

The applied amount of these treated positively charged silica fine powders is effective when it is 0.01 to 8 parts by weight, particularly preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the positively charged magnetic toner. Positive chargeability with sometimes excellent stability. In a preferred embodiment, the addition form is such that 0.1 to 3 parts by weight of the treated silica fine powder is attached to the surface of the toner particles based on 100 parts by weight of the positively charged magnetic toner. . The untreated silica fine powder described above can be used in the same application amount.

Further, the silica fine powder used in the present invention may be treated with a silane coupling agent, if necessary, with a treating agent such as silicon oil or an organosilicon compound for the purpose of hydrophobizing, or with various treating agents. It may be treated with the treating agent that reacts or physically adsorbs with the silica fine powder. Examples of such a treating agent include hexamethyldisilazane, trimethylsilane, tritylchlorosilane,
Trimethylethoxysilane, dimethyldichlorosilane,
Methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α
-Chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane,
Triorganosilyl mercaptan, trimethylsilyl mercaptan, triorganosilyl acrylate, vinyldimethylacetoxysilane, dimethylethoxysilane,
Dimethyldimethoxysilane, diphenylethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane, and 2 to 12 siloxane units per molecule; 1 each to the unit located in
And a dimethylpolysiloxane having a hydroxyl group bonded thereto.

The silicone oil is generally represented by the following formula.

Preferred silicone oils are those having a viscosity of about 5 to 5000 centistokes at 25 ° C., such as methyl silicone oil, dimethyl silicone oil, phenylmethyl silicone oil, chlorophenylmethyl silicone oil, alkyl-modified silicone oil, and fatty acid-modified silicone oil. Silicone oil and polyoxyalkylene-modified silicone oil are preferred. These are used alone or as a mixture of two or more.

In the magnetic toner used in the present invention, a fine powder of a fluorine-containing polymer may be added internally or externally.
Examples of the fluorine-containing polymer fine powder include, for example, fine powder of polytetrafluoroethylene, polyvinylidene fluoride, and the like, and fine powder of tetrafluoroethylene-vinylidene fluoride copolymer.In particular, the fine powder of polyvinylidene fluoride flows. It is preferable in terms of polishing properties and polishing properties. Addition amount to toner is 0.01-2.0wt%, especially 0.02-1.0wt%
Is preferred.

In particular, in the magnetic toner mixed and externally added with the fine silica powder and the fine powder, the reason is not clear,
Stabilizes the presence of silica adhering to the toner. For example, the silica adhering to the toner is not separated from the toner and the effect on toner abrasion and sleeve fouling is not reduced, and charging stability is further increased. It is possible to

FIG. 3 shows an example of a specific apparatus that can be used to carry out the image forming method of the present invention, but this does not limit the present invention in any way.

In the present invention, the magnetic toner is preferably applied to a method of developing a negative electrostatic image while flying the toner from a toner carrier such as a cylindrical sleeve to a negative electrostatic image holder such as a photoconductor. That is, the magnetic toner is provided with a triboelectric charge mainly by contact with the sleeve surface, and is applied in a thin layer on the sleeve surface. The thickness of the thin layer of the magnetic toner is formed to be smaller than the gap between the photosensitive member and the sleeve in the developing area. When developing a negative electrostatic image on the photoreceptor,
It is preferable that the magnetic toner having the triboelectric charge is caused to fly from the sleeve to the photosensitive member while applying an alternating electric field between the photosensitive member and the sleeve.

Examples of the alternating electric field include a pulse electric field, an AC bias, and a synergistic AC and DC bias.

In the developing device shown in FIG. 3, for example, a non-magnetic non-magnetic sleeve 12 as a toner carrier used in the present invention has a diameter of 32 m / m.
m stainless steel sleeve (SUS304), the magnetic pole of magnet 14 in the sleeve N ₁ = 850 gauss, N ₂ = 500 gauss,
S ₁ = 650 gauss, S ₂ = 500 gauss, the blade 11a is made of magnetic iron, the blade 11a and the non-magnetic sleeve 1
The gap of 2 is 250μ, the toner 10 is a magnetic toner according to the present invention,
As the bias power supply 11, a device in which DC is superimposed on AC is used, and an apparatus in which V _pp = 1400V, f = 2000 (Hz), and DC = + 100V is used. The sleeve 12 and the negative electrostatic image holder 9
With the shortest distance set to 300 μm.

In the image forming method of the present invention, in the toner carrier carrying the magnetic toner on the surface thereof, the surface of the toner carrier is subjected to sandblasting with irregular-shaped particles, so that a surface having a rough surface with specific irregularities is used. A good toner coating state can be maintained for a long period of time without any uniform unevenness on the surface of the toner carrier.
The intended surface is an embodiment in which the surface of the toner carrier is formed with countless fine cuts or projections in random directions over the entire area.

However, in a developing device using a toner carrier having such a specific surface state, depending on the magnetic toner to be applied, toner or a component in the toner adheres to the surface, causing contamination on the surface of the toner carrier. As a result, the density of the initial image may decrease.

This is because the components in the toner adhere to the slopes and the concave portions of the convex portions on the surface of the toner carrier, so that poor charging of the magnetic toner particles occurs and the charge amount of the toner layer decreases.

As a method of preventing or reducing the contamination of the magnetic toner carrier, a method of making the surface of the toner carrier smoother is preferable.

In the magnetic toner carrier of the developing method according to the present invention, when the surface has specific irregularities formed by a plurality of spherical trace dents, it becomes difficult for toner components to adhere to the surface, and contamination over a long period of time. It was able to prevent or reduce it, and was excellent in performance of uniformly coating the toner carrier with the magnetic toner.

The toner carrier having such a surface shape also has excellent triboelectric charging ability, and can sufficiently draw out the triboelectric charging ability of the magnetic toner according to the present invention to stabilize the charging property.

Therefore, the follow-up property to the potential of the negative electrostatic image is further improved, the gradation property for halftone is excellent, and a moist image can be obtained. In addition, the potential-density curve of the white image portion is sharply cut, which is more effective for fogging.

 The toner carrier is hereinafter referred to as a sleeve.

As a method for obtaining the surface state of the sleeve having a surface having irregularities formed by a plurality of spherical trace depressions, a blasting method using fixed particles can be used. As regular shaped particles,
For example, various hard spheres made of metal such as stainless steel, aluminum, steel, nickel, and brass having a specific particle size, or various hard spheres such as ceramic, plastic, and glass beads can be used. By blasting the surface of the sleeve with the regular particles having a specific particle diameter, a plurality of spherical trace depressions having substantially the same diameter R can be formed.

Also, the diameter R of the plurality of spherical trace depressions on the sleeve surface is
When the diameter R is less than 20 μm, contamination due to components in the magnetic toner tends to increase. Conversely, when the diameter R is more than 250 μm, the uniformity of the toner coat on the sleeve decreases. Tend to. Therefore,
Shaped particles used when blasting the sleeve surface are also
Those having a diameter of 20 to 250 μm are preferred. Further, the pitch P and the surface roughness d of the unevenness of the sleeve surface are measured by using a fine surface roughness meter (manufacturer, Taylor Hopson, Kosaka Laboratory, etc.) on the surface of the sleeve. It is based on JIS 10-point average roughness (RZ) "JIS B 0601".

That is, as shown in FIG.
A straight line parallel to the average line of the extracted portion passes through the third highest peak from the highest and passes through the third valley bottom from the deepest. The interval between the two straight lines is expressed in micrometers (μm). , The reference length 1 = 0.25 mm. Further, the pitch P is obtained by counting the peaks having a height of 0.1 μ or more with respect to the concave portions on both sides as one peak, and calculating the number of peaks within the reference length of 0.25 mm as follows. is there.

[250 (μ)] / [number of peaks (μ) included in 250 (μ)] The pitch P of the irregularities on the sleeve surface is preferably 2 to 100 μm. If P is less than 2 μm, the component in the magnetic toner When P exceeds 100 μ, the uniformity of the toner coat on the sleeve tends to decrease. The surface roughness d of the irregularities on the sleeve surface is preferably from 0.1 to 5 μm. If d is more than 5 μm, an alternating voltage is applied between the sleeve and the negative electrostatic image carrier to form a negative electrostatic image from the sleeve side. In the system in which the magnetic toner flies to the surface to perform development, the electric field tends to concentrate on the uneven portion and the image tends to be disturbed, and conversely, d is 0.
If it is less than 1 μm, the uniformity of the toner coat on the sleeve tends to decrease.

〔Example〕

Hereinafter, the present invention will be described specifically with reference to Examples, but this does not limit the present invention in any way. All parts in the following formulations are parts by weight.

Example 1 First, a used a-Si photosensitive drum will be described.

The a-Si photosensitive drum uses a high-frequency plasma CVD apparatus, and uses gases such as SiH ₄ , H ₂ , CH ₄ , PH ₃ , B ₂ H ₆ , and GeH ₄ .
It was produced by a glow discharge method.

A lower charge injection blocking layer of hydrogen-doped a-Si doped with phosphorus is provided on a substrate which is an aluminum cylinder of 108φ / 360 mm, and a hydrogenated
A photosensitive layer of -Si was provided.

Next, an upper charge injection blocking layer of hydrogenated a-Si doped with boron was provided.

Next, an amorphous film (hydrogenated a-SiC) made of silicon, carbon, and hydrogen was provided on the uppermost portion as a surface protective layer.

The thus obtained a-Si photosensitive drum was mounted on a commercially available electrophotographic copying machine NP-8570 (manufactured by Canon Inc.), and was modified so that a positively chargeable toner could be used. Further, the current value of the primary charger and the amount of light irradiated on the original were adjusted so that the potential of the surface dark portion was -400 V and the potential of the light surface portion was -50 V.

The developing conditions were applied by synergistically applying an AC bias of 2000 Hz / 1400 V _pp and a DC bias of -100 V.

The sleeve of the toner carrier has a surface of a stainless steel sleeve (SUS304) with a diameter of 80% or more as regular particles.
Spray nozzle system 7 using 53-62 μm glass beads
Blasting is performed under the conditions of φ distance of 100 mm, air pressure of 4 kg / cm ² and 2 minutes, and the diameter R of the plurality of spherical trace depressions is 53 to 62.
One having irregularities of μm was used. The pitch P of the irregularities on the sleeve surface is 33 μ, and the surface roughness d is
2.0μ.

 Hereinafter, an image evaluation method according to the present invention will be described.

The fine line reproducibility was measured by the following method. In other words, an image obtained by copying an original original of a fine line accurately having a width of 100 μm under appropriate copying conditions is used as a measurement sample, and a Luzex 450 particle analyzer is used as a measuring device. Perform the measurement. At this time, since the line width measurement position has irregularities in the width direction of the thin line image of the toner, the average line width of the irregularities is used as the measurement point. From this, the value (%) of the fine line reproducibility is calculated by the following equation.

The resolution was measured by the following method. That is, a pattern consisting of five thin lines having the same line width and interval, 1 mm
Create an original image drawn between 2.8, 3.2, 3.6, 4.0, 4.5, 5.0, 5.6, 6.3, 7.1 or 8.0 lines. this
An image obtained by copying an original document having 10 types of line images under appropriate copying conditions is observed with a magnifying glass, and the number of images (lines / mm) in which fine lines are clearly separated is defined as the value of the resolution.

 The larger this number is, the higher the resolution is.

 On the other hand, the magnetic toner was prepared as follows.

After the above materials were mixed well in a blender, they were kneaded with a biaxial kneading extruder set at 150 ° C. The obtained kneaded material was cooled, coarsely pulverized by a cutter mill, and then finely pulverized using a fine pulverizer using a jet stream, and the obtained finely pulverized powder was classified by a fixed wall type air classifier. A classified powder was produced. Furthermore, the obtained classified powder is strictly classified and removed simultaneously with a multi-division classifier (elbow jet classifier manufactured by Nittetsu Mining Co., Ltd.) utilizing the Coanda effect to remove black fine powder (magnetic toner). Obtained. Table 1 shows the particle size distribution of the magnetic toner.

0.6 part of positively charged hydrophobic dry silica (BET specific surface area: 200 m ^{2 /} g) was added to 100 parts of the magnetic toner of the obtained black fine powder,
Mix with a Henschel mixer.

This magnetic toner externally added to silica was charged into the above-described modified NP-8570, and an image output test was performed. Table 2 shows the results of repeating this test 20,000 times.

As is clear from this table, an image having excellent line reproduction and halftone dot reproduction, high image density, and no fog was obtained. Further, the image density of the large area was high (1.39), the halftone was reproduced with gradation, and no drum ghost or sleeve ghost was observed. Further copying was repeated 30,000 times, but no deterioration was observed in the image.

FIG. 2 shows the relationship between the surface potential of the drum and the image density.
In this method, the illuminance of a halogen lamp is adjusted using a gray scale, various electric charges are placed on a drum, and the surface potential of the portion is measured. Each potential was developed to determine the image density.

When a copying test was conducted under a high temperature and a high humidity of 32.5 ° C. and 85% RH, good results were obtained, and no image deletion occurred. Further, even when the temperature of the drum heater was lowered, no image deletion occurred. Further, the same results were obtained even at a low temperature and a low humidity of 150 ° C. and 10% RHF.

Examples 2 and 3 Instead of the magnetic toner used in Example 1, a magnetic toner having a particle size distribution as shown in Table 1 was used by changing the addition amount of the magnetic substance and controlling the pulverization and classification conditions. .

The toner carrier is a stainless steel sleeve (SUS304)
Using # 300 carborundum as irregular shaped particles, spray nozzle diameter 7φ distance 100mm, air pressure 4kg / c
The blast treatment was performed under the conditions of m ² and 2 minutes.

A copy test was performed in the same manner as in Example 1 except for the above. As shown in Table 2, clear images without drum ghosts and sleeve ghosts were obtained. Also, 3
No image deletion occurred even at 2.5 ° C. and 85% RH.

Example 4 Table 1 shows the particle size distribution of the magnetic toner obtained in the same manner as in Example 1 using the above materials.

 Further, the same external addition as in Example 1 was performed.

The same copying test was carried out using the silica externally added magnetic toner obtained above in the developing device used in Example 2. The results are shown in Table 2. As a result, there was no fog or ghost and the image quality was excellent.

Examples 5 and 6 Using the raw materials used in Example 4 and controlling the amount of the magnetic substance and the conditions of the fine pulverization and classification, a magnetic toner having a particle size distribution as shown in Table 1 was obtained. Then, as shown in Table 1, a silica externally added magnetic toner having an external silica addition amount of 0.8% by weight was obtained. Table 2 shows the results of a similar copy test performed using the silica externally added magnetic toner obtained above in the developing device used in Example 1. As is clear from this table, a high-quality image having high density, excellent halftone gradation reproduction, and no fog and ghost was obtained.

Comparative Example 1 In the magnetic toner used in Example 1, the amount of magnetic iron oxide was 60%.
A magnetic toner having the particle size distribution shown in Table 1 was obtained in the same manner using the same materials except for the parts. In addition, 100 parts of this magnetic toner is coated with positively charged hydrophobic dry silica (BET200m ² / g)
Was added and mixed with a Henschel mixer. Table 2 shows the results of the same image forming test as in Example 2 performed on the silica externally added magnetic toner.

Inferior in line expression, halftone dot reproduction and resolution, slight fog was seen, and halftone was rough. The concentration was slightly lighter (1.25), especially the solid part was lighter (1.18). Here, the primary charging current value is increased, and the photosensitive drum surface dark potential is reduced by -55.
When the voltage was set to 0 V, the image density increased (1.35), but when the front door of the copier was opened, the ozone odor increased.

Comparative Examples 2 to 4 Comparative Examples 1 to 4 were carried out using the crushed products obtained in Examples 1 to 6 and using toner having a particle size distribution as shown in Table 1 by controlling the conditions of fine pulverization and classification. A similar image-drawing test was performed. Table 2 shows the results.

In Comparative Example 2, a good image could not be obtained due to halftone roughening and fog after durability, Comparative Example 3 due to lines and halftone dots collapsed due to excessive glue, and Comparative Example 4 due to fog.

Comparative Example 5 A similar test was performed in the test of Example 1 except that the current value of the charger was increased and the potential of the surface dark portion of the photosensitive drum was -550 V. As a result, no change was observed in image quality. However, when the front door of the copier was opened, the ozone odor was higher than in Example 1.

Further, when the temperature of the drum heater was lowered in a copy test at 32.5 ° C. and 85% RH, image deletion occurred.

[Summary of Effects of the Invention] The present invention is an image forming method comprising a specific developing method using a positively chargeable magnetic toner having a specific particle size distribution and an a-Si photoconductor holding a negative electrostatic image. The following excellent effects are exhibited.

(1) a-Si with excellent electrophotographic properties such as drum ghost
High-speed copying can be performed using a photoconductor.

(2) An image having a high image density, no fog, sleeves and ghosts, and excellent in fine line reproducibility, halftone dot reproducibility and halftone gradation can be obtained.

(3) An image can be formed without a change in performance over a long period of use.

(4) Using an a-Si photoreceptor having a low surface dark potential,
Good image density is obtained.

(5) Image quality without image deletion can be obtained under high temperature and high humidity.

(6) Ozone generation can be reduced.

(7) High image density can be obtained with a small amount of consumption.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a carrier memory, FIG. 2 is an explanatory diagram of a relationship between image density and a potential of a photosensitive member surface, and FIG.
FIG. 1 is a schematic explanatory view of a developing device suitable for carrying out the image forming method of the present invention, FIG. 4 is a definition explanatory view of surface roughness and pitch, and FIG. 4 is a graph plotting the relationship between the image density and the surface potential of the photosensitive drum obtained in the image forming method. 11a: magnetic blade, 12: sleeve, 13: applied magnetic toner, 14: fixed magnet roller, 17: developing container, 19
... photosensitive drum, 20 ... magnetic toner, 21 ... alternating voltage power supply.

Continuation of front page (56) References JP-A-1-112253 (JP, A) JP-A 1-219757 (JP, A) JP-A 1-214876 (JP, A) JP-A-2-990 (JP, A) , A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 9/08 G03G 5/08 G03G 15/08

Claims (4)

(57) [Claims] An amorphous silicon photoreceptor for holding a negative electrostatic image has a negative potential of 400 V on a surface with a dark potential.
A negative electrostatic charge image is formed on the surface of the charged amorphous silicon photoconductor, and the amorphous photoconductor and a toner carrier for supporting a positively chargeable magnetic toner on the surface are developed by the developing unit. The positively-charged magnetic toner is conveyed to the developing unit while regulating the thickness of the positively-chargeable magnetic toner to a thickness smaller than the gap on the toner carrier. Applying a developing bias having the following formula to the developer carrier, and developing the negative electrostatic image held on the amorphous silicon photoreceptor with the positively chargeable magnetic toner. Means that magnetic toner particles having a particle size of 5 μm or less
1 to 33% by number of toner particles having a particle size of 8 to 12.7 μm, and toner particles having a particle size of 16 μm or more.
An image forming method characterized by having a particle size distribution of not more than 2.0% by volume and a volume average particle size of 4 to 10 μm. 2. The toner carrier has a cylindrical non-magnetic sleeve. The surface of the non-magnetic sleeve has a diameter.
2. The image forming method according to claim 1, wherein a plurality of spherical trace depressions of 20 to 250 [mu] m are formed. 3. The toner carrier according to claim 1, wherein the toner carrier has a cylindrical non-magnetic sleeve, and the surface of the non-magnetic sleeve is formed with irregularities having a pitch of 2 to 100 μm. 2. The image forming method according to 1., 4. The toner carrier has a cylindrical non-magnetic sleeve, and the surface of the non-magnetic sleeve is formed with irregularities having a surface roughness (Rz) of 0.1 to 5 μm. The image forming method according to claim 1, wherein