JP4386701B2 - Image forming method and developing device for implementing the same - Google Patents

Description

  The present invention relates to an image forming method using electrophotography and a developing device for carrying out the image forming method.

  In an image forming apparatus such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine, or a composite machine of these, first, the surface of the image carrier is uniformly charged by a charging means, and then exposed by an exposure means. After forming the electrostatic latent image, the electrostatic latent image is developed into a toner image by developing means. Next, the toner image is transferred onto the surface of a printing material such as paper by a transfer unit and then fixed by a fixing unit, thereby completing a series of image forming steps. Among these, as a developing method for developing the electrostatic latent image into a toner image in the developing means, a dry two-component developing method using a two-component developer containing a toner and a carrier is most common.

  Further, in the dry two-component development method, the carrier is connected in a spike shape on the magnetic roll by bringing the two-component developer into contact with a magnetic roll incorporating a magnet arranged facing the drum-shaped image carrier. By forming a magnetic brush with toner attached on the surface and bringing the magnetic brush into contact with the electrostatic latent image on the image carrier, the toner is selectively attached to the image carrier and electrostatic latent Developing the image into a toner image is performed.

  In order to achieve oil-less fixing means, the monochrome toner constituting the two-component developer generally contains an offset preventive agent such as wax. In recent years, attempts have been made to include such an anti-offset agent in full-color toners that have not previously contained an anti-offset agent because the light transmittance is reduced and color mixing properties are reduced.

In order to achieve complete oilless fixing, it is necessary to consider the type and amount of the offset inhibitor, the dispersion state in the toner particles, and the like. However, as the amount of the anti-offset agent increases, the anti-offset agent exposed on the surface of the toner particles decreases the fluidity of the toner, and the adhesion to the toners or other members may increase, causing various problems. There is. Therefore, in order to improve the fluidity of the toner and reduce the adhesion, it has been proposed to externally add a fatty acid metal salt that functions as a lubricant such as zinc stearate to the toner (see, for example, Patent Document 1). .
JP 2000-19773 A (Claim 1, columns 0008 to 0009)

  However, when image formation is repeatedly performed using a two-component developer containing a toner externally added with a fatty acid metal salt, the two-component developer is transported particularly in the axial direction of the magnetic roll and in the width direction of the magnetic roll intersecting therewith. However, in the developing means using the method of supplying to the magnetic roll, a sufficient magnetic brush is not formed on a part of the magnetic roll in the width direction, for example, both ends, and a part of the image forming area is not formed accordingly. The problem that occurred.

  The cause of this problem is that when image formation is performed over a long period of time, the fatty acid metal salt is detached from the toner surface and stays in the developing means, and adheres to the surface of the carrier or lubricates the two-component developer. Or act as an agent. When such a phenomenon occurs, the flow characteristics of the two-component developer change, and the developer transport balance in the developing unit is lost. Therefore, the developer is biased, and as described above, A sufficient amount of the two-component developer is not supplied to a part in the width direction. For this reason, a sufficient magnetic brush is not formed on a part of the magnetic brush, and accordingly, an image defect occurs in which an image is not formed on a part of the image forming area.

  The object of the present invention is to prevent the phenomenon that a sufficient magnetic brush is not formed in a part of the magnetic roll because the flow characteristics of the two-component developer do not change even after image formation over a long period of time. It is an object of the present invention to provide a novel image forming method and a developing device for carrying out the method.

The invention according to claim 1 includes the step of developing the electrostatic latent image on the image carrier into a toner image using a two-component developer including a carrier and a toner externally added with a fatty acid metal salt. a method, additional comprising bulk density than the carrier of the start developer to be first used for image formation 0.05 g / cm ³ or more, and a small carrier at 0.2 g / cm ³ or less in the range, a toner The image forming method is characterized in that an image is formed while adding the two-component developer as needed.

  According to a second aspect of the present invention, there is provided a developing device for carrying out the image forming method according to the first aspect, wherein the main body for containing the start developer and the replenishment toner are supplied to the main body. A developing device comprising a toner container and a developer container for supplying an additional two-component developer to the apparatus main body.

According to the first aspect of the present invention, the two-component developer in the developing unit, in which fatty acid metal salts tend to accumulate due to repeated image formation and the fluidity tends to increase, has a bulk density of 0. 05G / cm ³ or more, including a small carrier at 0.2 g / cm ³ or less in the range from time to time the fluidity low additional two-component developer, by adding, as a whole fluidity of the two-component developer The fluidity can be maintained within a suitable range by suppressing the amount from becoming too high.

Therefore, according to the image forming method of the first aspect of the present invention, the flow characteristics of the two-component developer do not change even when image formation is performed over a long period of time, so that a sufficient magnetic brush is not formed with a part of the magnetic roll. Can be prevented.
According to the second aspect of the present invention, the replenishment toner from the toner container and the additional two-component developer from the developer container are separately supplied to the apparatus main body containing the start developer, at any time point. Therefore, the image forming method of the present invention can be carried out efficiently.

The present invention will be described below.
<Image forming method>
The image forming method of the present invention is a method for forming an image using the two-component developer containing the carrier and the toner as described above, and has a bulk density higher than that of the carrier in the start developer used for the image formation first. There 0.05 g / cm ³ or more, and a small carrier at 0.2 g / cm ³ or less in the range, from time to time additional 2-component developer containing a toner, and is characterized in adding.

  The additional two-component developer is preferably added according to the number of images formed, the amount of toner consumed, and the like. Specifically, for example, every time the number of image formations counted by the counter of the apparatus reaches a predetermined value (for example, 1000 sheets) set in advance, a predetermined amount of additional two-component developer is added. Count how many times the operation of replenishing a predetermined amount of toner for replenishment with a decrease in toner density is performed, and each time the number of times reaches a predetermined value, a predetermined amount of additional two-component developer is added. It is preferable to perform an operation such as.

  The total amount of the additional two-component developer is preferably 1/5 or less (weight ratio) of the amount of the start developer supplied to the image forming apparatus first. Further, the additional amount for each time is preferably a value obtained by dividing the additional total amount evenly, and differs depending on the interval at which the additional two-component developer is added. In addition, when the image is added every 1000 sheets, the added amount is set to 1/500 or less (weight ratio) of the amount of the start developer supplied to the image forming apparatus first, even within the above range. Is particularly preferred.

The toner concentration in the start developer and the additional two-component developer varies depending on, for example, the type of image forming apparatus used, but is preferably about 2 to 15% by weight.
<Carrier>
As the carrier used for the two-component developer, those having various conventionally known structures can be used. That is, as the carrier, for example, glass beads, oxidized or non-oxidized iron powder, ferrite, Co-based, Mn-Mg-based, Cu-Zn-based, Li-based magnetic particles, or the surface thereof is made of synthetic resin (acrylic). , Fluorine-based, silicone-based, and polyester-based resins). The carrier preferably has a volume-based center particle size of 35 to 100 μm, particularly 40 to 65 μm.

  In order to make the bulk density of the carrier used for the additional two-component developer smaller than the bulk density of the carrier used for the start developer, for example, the surface state of the carrier surface, more specifically, the number and size of irregularities on the carrier surface. Etc., the average particle size of the carrier (= center particle size based on volume) is different, or the amount of resin coating is different when using the type with magnetic particles coated with resin. do it. Specifically, the bulk density can be reduced as the number of irregularities on the carrier surface is increased and the size is increased. Further, the bulk density can be reduced as the average particle size is reduced. Furthermore, the bulk density can be reduced as the coating amount of the resin is increased.

The bulk density of the carrier to be used for additional two-component developer, from 0.05 g / cm ³ or more bulk density of the carrier to be used for starting developer, by reducing by 0.2 g / cm ³ or less in the range of above The effect of this invention can be exhibited more efficiently. In particular, the bulk density of both carriers is preferably set so that the difference between the bulk densities of both carriers is 0.1 g / cm ³ or more. However, the bulk density since the carrier is 1.8 g / cm ³ or less is difficult to produce, the difference in the bulk density of the two carriers, are 0.2 g / cm ³ or less as described above.

  In addition, the charge amount of the additional two-component developer containing such a carrier is preferably larger than the charge amount of the start developer in order to maintain good charging characteristics. In order to increase the charge amount of the additional two-component developer, the average particle size of the carrier used in the additional two-component developer is made smaller than the average particle size of the carrier used in the start developer, What is necessary is just to change the kind of resin to coat | cover when using the type which coat | covered the surface of magnetic body particle | grains with resin.

The values such as the carrier bulk density, average particle diameter, resin coating amount, and charge amount of the two-component developer are all comparisons with initial values before use in image formation.
<toner>
As the toner, toner containing toner particles having various conventionally known configurations for a two-component developer can be used. Specifically, a toner obtained by externally adding an external additive such as silica to a toner particle having a structure in which a colorant and other additives are dispersed in a fixing resin as in the prior art is preferable.

(Fixing resin)
Examples of fixing resins include styrene polymers, acrylic polymers, styrene-acrylic polymers, olefin polymers such as chlorinated polystyrene, polypropylene, and ionomers, polyvinyl chloride, polyester resins, polyamides, and polyurethanes. , Epoxy resin, diallyl phthalate resin, silicone resin, ketone resin, polyvinyl butyral resin, phenol resin, rosin modified phenol resin, xylene resin, rosin modified maleic acid resin, rosin ester, etc. Styrene-acrylic polymers and polyester resins are preferred. Of these, examples of the styrene polymer and styrene-acrylic polymer include styrene homopolymers and copolymers of the styrene and other monomers.

  Examples of other monomers copolymerizable with styrene include p-chlorostyrene; vinyl naphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl chloride, vinyl bromide, vinyl fluoride, and the like. Vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate, etc .; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-acrylate -(Meth) acrylic esters such as octyl, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; acrylonitrile, methacrylonitrile, acrylamide, etc. Acrylic acid derivatives of: vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N -N-vinyl compounds such as vinylpyrrolidene can be mentioned. These copolymerization monomers can be copolymerized with styrene either alone or in combination of two or more.

  As the polyester resin, for example, a resin obtained by polycondensation of a polyvalent carboxylic acid component and a polyhydric alcohol component can be used. Among these, as the polyvalent carboxylic acid component, for example, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, Divalent carboxylic acids such as azelaic acid and malonic acid; n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n-octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n -Alkyl or alkenyl esters of divalent carboxylic acids such as dodecenyl succinic acid, isododecyl succinic acid, isododecenyl succinic acid; 1,2,4-benzene tricarboxylic acid (trimellitic acid), 1,2,5- Zentricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphtha Talentricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohe Examples thereof include trivalent or higher carboxylic acids such as xanthricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empole trimer acid. Also, anhydrides of these polyvalent carboxylic acids can be used.

  On the other hand, examples of the polyhydric alcohol component include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4- In addition to diols such as butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, Bisphenols such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, penta Lithritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2, Examples thereof include polyols having a triol or higher such as 4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

(Coloring agent)
As the colorant, a colorant of each color that matches the color of the toner particles can be used. Suitable examples are as follows.
Black pigment Carbon black, acetylene black, lamp black, aniline black.

Yellow pigment Yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, naples yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow G, benzidine yellow GR, quinoline yellow lake , Permanent yellow NCG, tartrage rake.

Orange pigment Red-yellow chrome lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, indanthrene brilliant orange GK.
Red Pigment Bengala, Cadmium Red, Red Plum, Mercury Cadmium, Permanent Red 4R, Risor Red, Pyrazolone Red, Watching Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B.

Purple pigment Manganese purple, fast violet B, methyl violet lake.
Blue pigments Bitumen, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, first sky blue, indanthrene blue BC.

Green pigment Chrome green, chromium oxide, pigment green B, malachite green lake, final yellow green G.
White pigment Zinc flower, titanium oxide, antimony white, zinc sulfide.

Body pigments Barite powder, barium carbonate, clay, silica, white carbon, talc, alumina white.
The addition amount of the colorant is preferably 1 to 20 parts by weight, and more preferably 2 to 8 parts by weight with respect to 100 parts by weight of the fixing resin.

(Other additives)
Representative examples of additives other than the colorant include charge control agents and offset preventing agents.
The charge control agent is for controlling the triboelectric charging characteristics of the toner, and a charge control agent for positive charge control and / or negative charge control is used according to the charge polarity of the toner. Among these, as a charge control agent for positive charge control, organic compounds having a basic nitrogen atom, such as basic dyes, aminopyrines, pyrimidine compounds, polynuclear polyamino compounds, aminosilanes, etc. An agent etc. can be mentioned.

  Examples of charge control agents for controlling negative charge include oil-soluble dyes such as nigrosine base (CI5045), oil black (CI26150), Bontron S, and spiron black; charge control resins such as styrene-styrenesulfonic acid copolymer A compound containing a carboxy group (for example, an alkyl salicylic acid metal chelate), a metal complex dye, a fatty acid metal soap, a resin acid soap, a naphthenic acid metal salt, and the like. The addition amount of the charge control agent is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of the fixing resin.

  The offset preventive agent is blended in order to impart an offset preventing effect to the toner. Examples of the offset preventive agent include aliphatic hydrocarbons, aliphatic metal salts, higher fatty acids, fatty acid esters or partially saponified products thereof, silicone oil, and various waxes. Among these, aliphatic hydrocarbons having a weight average molecular weight of about 1000 to 10,000 are preferable. Specifically, one or a combination of two or more of low molecular weight polypropylene, low molecular weight polyethylene, paraffin wax, a low molecular weight olefin polymer composed of olefin units having 4 or more carbon atoms, silicone oil and the like are suitable. The addition amount of the offset preventing agent is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of the fixing resin. In addition, you may mix | blend various additives, such as a stabilizer, in a suitable ratio.

The volume-based center particle diameter of the toner particles is preferably 4 to 12 μm, and particularly preferably 6 to 10 μm.
(External additive)
As an external additive externally added to the toner particles, fatty acid metal salts are mainly used as described above, and for example, ultrafine particles for improving the fluidity of the toner and maintaining the storage stability. Silica (colloidal silica, hydrophobic silica, etc.) or titanium oxide can also be used. Further, for example, titanium oxide or alumina having a number average diameter of about 0.1 to 2 μm as abrasive particles for polishing the surface of the amorphous silicon photoreceptor may be externally added.

(Fatty acid metal salt)
As the fatty acid metal salt, for example, a metal salt of a higher fatty acid having 15 or more carbon atoms such as stearic acid (eg, zinc salt, calcium salt) is preferable, and zinc stearate is most preferable.
The fatty acid metal salt is preferably in the form of granules having a number-based average particle size of 0.1 to 10.0 μm. When the average particle size is less than 0.1 μm or exceeds 10 μm, in any of these cases, the function of the fatty acid metal salt may be insufficient.

The amount of the fatty acid metal salt added to 100 parts by weight of the toner is preferably 0.5 parts by weight or less.
<Developing device>
An example of the developing device of the present invention used as the developing means of the image forming apparatus in order to carry out the image forming method of the present invention is shown in FIG.

  As shown in the figure, the developing device of this example includes a magnetic roll 1 incorporating a magnet and facing an image carrier EP of the image forming apparatus, and an apparatus main body 2 for containing a two-component developer D1. A toner container 3 for supplying replenishing toner T to the apparatus main body 2 and a developer container 4 for supplying additional two-component developer D2 to the apparatus main body 2 are provided. The apparatus main body 2 initially stores a predetermined amount of start developer as the two-component developer D1. Of the above, the toner container 3 is preferably detachable from the apparatus main body 2.

  Further, in the apparatus main body 2, two agitators are supplied to the magnetic roll 1 while being fed in the axial direction of the magnetic roll 1 and the width direction intersecting with the two-component developer D <b> 1 while stirring. Conveying spirals 5 and 6 and a magnetic permeability sensor 7 for measuring the toner concentration of the two-component developer D1 are provided. Further, in the developer container 4, a stirring conveyance spiral 8 for supplying the additional two-component developer D2 to the apparatus main body 2 while stirring is disposed.

In order to carry out the image forming method of the present invention using the above developing apparatus, a predetermined amount of start developer is accommodated in the apparatus main body 2 as the two-component developer D1 as described above, and the layer value main body 2 In addition, a toner container 3 filled with replenishing toner T is mounted, and a predetermined amount of an additional two-component developer D2 is accommodated in the developer container 4.
In this state, the magnetic roll 1 is rotated in accordance with the rotation of the image carrier EP, and the agitating and conveying spirals 5 and 6 are rotated so that the two-component developer D1 in the apparatus main body 2 is directed to the magnetic roll 1. When the image formation is started while being conveyed, the toner in the two-component developer D1 is consumed for the image formation and the toner concentration gradually decreases. This is detected by the magnetic permeability sensor 7, and the toner concentration is a predetermined value. The image formation is temporarily stopped at the time when the pressure drops to a level, and a replenishing means (not shown) is operated to supply a predetermined amount of replenishing toner T in the toner container 3 into the apparatus main body 2 and then resume image formation. .

  Up to this point, the image forming method is the same as the normal image forming method. However, in the present invention, as described above, the number of formed images counted by the counter of the image forming apparatus reaches a predetermined value set in advance, or the replenishing toner T The number of times the operation of replenishing the toner is counted, and when the number of times reaches a predetermined value set in advance, the image formation is temporarily stopped and the stirring and conveying spiral 8 is rotated so that the inside of the developer container 4 After the predetermined amount of the additional two-component developer D2 is supplied into the apparatus main body 2, image formation is resumed.

Thereby, as described above, various problems caused by accumulation of the fatty acid metal salt in the apparatus main body 2 can be solved.
<Image carrier>
As the image carrier EP used in the image forming method of the present invention, an amorphous silicon photoreceptor having a high surface hardness and a long lifetime is preferable. Further, as the amorphous silicon photoconductor, for example, photoconductors having various known structures in which an amorphous silicon photoconductive layer is provided on the surface of a conductive substrate formed in a predetermined shape such as a drum shape can be used. .

  In addition, the amorphous silicon-based photosensitive layer can be formed by a vapor phase growth method such as a glow discharge decomposition method, a sputtering method, an ECR method, or a vapor deposition method. In forming the amorphous photosensitive layer, H or a halogen element may be included. it can. Further, in order to adjust the characteristics of the photoreceptor, elements such as C, N, and O may be included, or a group 13 element or a group 15 element in the periodic table (long period type) may be included.

Specifically, the photosensitive layer can be formed of various photoconductive materials such as a-SiC, amorphous silicon-based materials such as a-SiC, a-SiO, and a-SiON.
In particular, it is preferable to use a-SiC. In that case, the value of x of Si _1-x C _x should be set to 0 <x ≦ 0.5, preferably 0.05 ≦ x ≦ 0.45. Within this range, the a-SiC layer can have a higher resistance than the a-Si layer while maintaining good carrier transport, and the photosensitivity characteristics of the photoreceptor can be improved.

As group 13 elements and group 15 elements, B and P are desirable in that they are excellent in covalent bonding properties, can change semiconductor characteristics sensitively, and can provide excellent photosensitivity.
Furthermore, when the amorphous silicon-based photosensitive layer is formed by laminating a layer region (photoexcitation layer region) having an enhanced function of generating photocarriers and a layer region (carrier transporting layer region) having a function of transporting carriers, Both the photosensitivity and withstand voltage characteristics of the photoreceptor can be enhanced.

At this time, in order to increase the generation efficiency of the photocarrier in the photoexcitation layer region, among the film formation conditions, (1) the film formation rate is set low, (2) the dilution ratio of the film forming component with H ₂ or He (3) It is preferable to form the film while taking measures such as increasing the amount of the element to be doped to be larger than that of the carrier transport layer region.
The carrier transport layer region mainly has a role of increasing the pressure resistance of the photosensitive layer and smoothly transporting carriers injected from the photoexcitation layer region to the conductive substrate. This layer region also transmits through the photoexcitation layer region. Since the carrier generation is performed by the generated light, it contributes to the improvement of the photosensitivity of the photoreceptor.

The thickness of the amorphous silicon-based photosensitive layer is preferably a thickness obtained by adding 0.1 to 2.0 μm to the depth of light absorption determined from the absorption coefficient of this layer with respect to light having an exposure wavelength.
When the photosensitive layer is formed by laminating the photoexcitation layer region and the carrier transport layer region as described above, it is preferable to set the thickness of the photoexcitation layer region substantially equal to the light absorption depth.

A carrier blocking layer is preferably interposed between the photosensitive layer and the conductive substrate.
The carrier blocking layer prevents the injection of carriers from the conductive substrate to the photosensitive layer when the surface of the photosensitive member is in contact with the toner while a bias voltage is applied during development, so that the exposed portion and the non-exposed portion are separated. It has a function of increasing electrostatic contrast to improve image density and reducing background fog.

  As the carrier blocking layer, inorganic insulating layers formed of a-SiC, a-SiO, a-SiN, a-SiON, a-SiCON, etc., which are insulating, or polyethylene terephthalate, Parylene (registered trademark), It is preferable to use an organic insulating layer formed of polytetrafluoroethylene, polyimide, polyfluoroethylenepropylene, polyurethane, epoxy resin, polyester, polycarbonate, cellulose acetate resin, or the like.

In addition, the carrier blocking layer is required to have insulating properties, good adhesion to the conductive substrate and the amorphous silicon-based photosensitive layer, and characteristics that do not cause significant alteration during heating or the like when forming the photosensitive layer.
Considering such characteristics, the carrier blocking layer is preferably formed of a-SiC.
In order to make the a-SiC forming the carrier blocking layer insulative, the amount of C contained in the carrier blocking layer may be increased as compared with the photosensitive layer.

The thickness of the carrier blocking layer is preferably from 0.01 to 5 [mu] m, more preferably from 0.1 to 3 [mu] m.
The surface of the photosensitive layer is preferably covered and protected by a surface protective layer made of an organic or inorganic insulating material. Thereby, it is possible to prevent the surface of the photosensitive layer from being oxidized during discharge by a charging means or the like and forming an oxide film that easily adsorbs discharge products and water molecules. In addition, the withstand voltage can be improved, and the wear resistance when repeatedly used can be improved.

In particular, it is preferable to use a layer made of an a-Si insulating material such as a-SiC, a-SiN, a-SiO, a-SiCO, or a-SiNO, which is formed by a thin film forming method similar to that for the photosensitive layer. can do.
In particular, it is preferable to use a-SiC. When a-SiC is used for the surface protective layer, the amount of C contained in the surface protective layer may be increased as compared with the photosensitive layer, as in the case of the carrier blocking layer.

Specifically, the x value of Si _1-x C _x is preferably 0.3 ≦ x <1.0, particularly 0.5 ≦ x ≦ 0.95.
Further, it is preferable that the dark resistivity of the surface protective layer is 10 ¹³ Ω · cm or more by adjusting the x value of C.
When the dark resistivity is 10 ¹³ Ω · cm or more, the photosensitive member has a high ability to maintain an electrostatic latent image because of less potential flow in the surface direction of the surface protective layer, and also has excellent moisture resistance. The effect of suppressing the occurrence of image flow due to water absorption is excellent.

In addition, such a high-resistance surface protective layer prevents the injection of charge due to bias through the toner, enhances the potential contrast between the exposed area and the non-exposed area, and attracts more toner to the surface to attract the toner image. It also has a function of increasing the image density and sufficiently increasing the image density. Moreover, background fogging can also be suppressed. Furthermore, the withstand voltage of the photoreceptor can be increased.
In addition, in the surface protective layer formed of an insulating material other than a-SiC, photocarriers continue to be trapped even after image formation, and there is a possibility that the residual potential cannot be erased reliably in a normal charge removal process. However, the surface protective layer formed of a-SiC effectively blocks positive charges from the surface, but has the property that negative charges from the conductive substrate are relatively easy to pass through. Therefore, the residual potential after image formation is reduced. Further, there is an advantage that the image can be erased effectively by a normal static elimination process and images can be continuously formed.

In addition, the surface protective layer formed of a-SiC has good adhesion to an amorphous silicon-based photosensitive layer such as a-SiC, and also has excellent wear resistance, environmental resistance, etc. There is also an advantage that stable image formation can be performed.
The surface protective layer formed of a-SiC may form a gradient in the thickness direction in the amount of C in the layer, or may contain elements such as N, O, Ge and the like together with C to provide moisture resistance. It can be further increased.

  The thickness of the surface protective layer is preferably 0.05 to 5 μm, and more preferably 0.1 to 3 μm. If the thickness is less than 0.05 μm, the effect of preventing the above-described oxide film formation, the effect of improving the withstand voltage, or the effect of improving the wear resistance when repeatedly used may not be sufficiently obtained. is there. Further, there is a possibility that the optical carrier cannot be effectively trapped to contribute to the formation of the toner image.

  On the other hand, when the thickness exceeds 5 μm, when a fine charge pattern is formed, the electric field (electric field lines) spreads in the film surface direction in the surface protective layer, resulting in a decrease in resolution, resulting in sufficient resolution. May not be obtained. In addition, since the electric charge remaining on the surface increases and the residual potential becomes high, there is a possibility that problems such as a decrease in image density, background fogging, or a change in image density in repeated use may occur.

Hereinafter, the present invention will be described in more detail based on examples and comparative examples.
<Manufacture of toner>
100 parts by weight of a polyester resin as a fixing resin, 5 parts by weight of carbon black (MA-100 manufactured by Mitsubishi Chemical Corporation) as a colorant, and 5 parts by weight of a charge control agent (FCA201PS manufactured by Fujikura Chemical Co., Ltd.) , And 7 parts by weight of polyethylene wax (Yomex (registered trademark) 100TS manufactured by Sanyo Chemical Co., Ltd.) as an offset preventive agent, premixed using a Henschel mixer, and then melted using a twin-screw kneading extruder After kneading and cooling, toner particles having a volume-based center particle size of 9.0 μm were prepared through steps of coarse pulverization, fine pulverization, and classification.

To 100 parts by weight of the toner particles, 0.5 parts by weight of hydrophobic silica and 0.2 parts by weight of zinc stearate were added and mixed using a Henschel mixer to produce a toner.
<Preparation of start developer>
As a carrier, the surface of Mn—Mg based magnetic particles is coated with 10 parts by weight of a fluorine-silicone resin with respect to 100 parts by weight of the magnetic particles, and the volume-based center particle size is 80 μm. Was used. The bulk density AD of such a carrier was 2.025 g / cm ³ .

The carrier and the toner were mixed so that the toner concentration T / D was 5% by weight to prepare a start developer. The charge amount Q / M of the start developer was 16.8 μC / g.
<Preparation of additional two-component developer>
As the carrier, the surface of Mn-Mg based magnetic particles is coated with 30 parts by weight of a fluorine-silicone resin with respect to 100 parts by weight of the magnetic particles, and the volume-based center particle diameter is 60 μm. Was used. The bulk density AD of such a carrier was 1.921 g / cm ³ .

The carrier and the toner were mixed so that the toner concentration T / D was 5% by weight to prepare an additional two-component developer. The charge amount Q / M of the additional two-component developer was 20.5 μC / g.
Example 1
A laser printer having a developing device modified as shown in FIG. 1 with the start developer, the additional two-component developer, and toner manufactured as described above (model number FS-8000C manufactured by Kyocera Mita Co., Ltd.) The image having a document density of 4% was continuously formed. That is, the starter D1 is accommodated in the apparatus main body 2 of the developing device of FIG. 1, the toner is accommodated in the toner container 3 as the replenishing toner T, and the additional two-component developer is accommodated in the developer container 4. D2 was accommodated. The amount of the start developer D1 accommodated in the apparatus main body 2 at the start of use of the apparatus was 500 g.

Then, the stirring conveyance spiral 8 was rotated for a predetermined time for every 1000 sheets of image formation, and an operation of supplying the additional two-component developer D2 in the developer container 4 to the apparatus main body 2 while stirring was performed. The supply amount of the additional two-component developer at one time was about 0.8 g.
Separately from this, when the toner concentration measured by the magnetic permeability sensor 7 decreased to 4.0% by weight, an operation of supplying the toner T in the toner container 3 to the apparatus main body 2 was performed. The replenishment amount of toner T at one time was 5.0 g.

When 50,000 continuous images were formed while repeating the above operation, a stable image could always be formed without causing a problem that a part of the image forming area was not formed.
Further, after the continuous image formation of 50,000 sheets, the carrier was separated from the two-component developer D1 in the apparatus main body 2 and the bulk density AD was measured to be 2.068 g / cm ^3. It was almost the same as the density. The charge amount Q / M of the two-component developer was measured and found to be 15.1 μC / g, which was close to the charge amount of the start developer.

Comparative Example 1
When 50,000 continuous images were formed in the same manner as above without adding any additional two-component developer, there was a problem that a part of the image forming area was not formed.
Further, after the continuous image formation of 50,000 sheets, the carrier was separated from the two-component developer D1 in the apparatus main body 2 and the bulk density AD was measured to be 2.181 g / cm ^3, which was the carrier volume in the start developer. It turned out to be much larger than the density. Further, the charge amount Q / M of the two-component developer was measured and found to be 12.5 μC / g, which was greatly reduced from the charge amount of the start developer.

It is a schematic sectional drawing which shows an example of the image development apparatus of this invention for enforcing the image forming method of this invention.

Explanation of symbols

2 Device body 3 Toner container 4 Developer container D1 Two-component developer (start developer)
D2 Additional two-component developer T Toner

Claims (2)

An image forming method comprising a step of developing an electrostatic latent image on an image carrier into a toner image using a two-component developer containing a carrier and a toner externally added with a fatty acid metal salt. first bulk density than the carrier in the starting developer to be used is 0.05 g / cm ³ or more, and a small carrier at 0.2 g / cm ³ or less in the range, the additional two-component developer containing toner needed, An image forming method comprising forming an image while adding.   A developing device for carrying out the image forming method according to claim 1, wherein the device main body contains a start developer, a toner container for supplying replenishment toner to the device main body, and an addition to the device main body. And a developer container for supplying the two-component developer.

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