JP2005107377A - Image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method adopting a trickle developing process and capable of forming stable good images free from fogging, etc., over a prolonged period of time. <P>SOLUTION: A carrier having a lower electric resistance and a larger charge amount than carrier in a start developer is used as carrier in a two-component developer used for replenishment in the trickle developing process, and a toner having a smaller particle diameter than toner in the start developer is used as toner in the two-component developer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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.

  However, when image formation is repeated, new toner is supplied each time. However, the same carrier is used repeatedly over a long period of time, so the performance gradually deteriorates. End up. The main causes are so-called spent in which finely pulverized toner or the like adheres to the surface of the carrier, and conversely, so-called scraping in which the resin covering the carrier surface falls off.

  Therefore, in recent years, a trickle developing method has been proposed in which two-component developer is replenished as needed to suppress the deterioration of the carrier, and image formation is performed while collecting the two-component developer that has become excessive due to this replenishment. . Then, it was thought that a maintenance-free image forming apparatus could be constructed over a long period of time by combining this trickle development method with a long-life amorphous silicon photoconductor.

However, since the amorphous silicon photoconductor has a low charging potential, there is a problem that the toner tends to be selectively developed and the carrier is likely to deteriorate.
In order to form a stable image over a long period of time even if the replenishment amount of the two-component developer is reduced, in Patent Document 1, as a carrier in the two-component developer for replenishment, a carrier in the start developer is used. It has also been proposed to use a material having a large charge amount and an equal or low electrical resistance value.
JP 11-202630 A (Claim 1, columns 0012 to 0014)

  However, until the two-component developer is completely replaced, the old carrier remaining in the system is spent, and the ability to charge the toner is reduced. Even when a new two-component developer containing a low-resistance carrier is added, the toner charged by the old carrier is less charged than the toner charged by the new carrier, and the toner is likely to scatter. There has been a problem that fogging is likely to occur in the blank portion of the formed image.

In addition, the added carrier may cause a similar problem due to the progress of spent when the next new two-component developer is added. Further, since the additional carrier has a low resistance, there is a problem that the image density is excessively high.
An object of the present invention is to provide a novel image forming method that employs a trickle development method and can form a stable and good image free from fogging for a longer period of time.

  According to the first aspect of the present invention, the two-component developer containing the carrier and the toner is replenished as needed, and the electrostatic latent image on the image carrier is recovered while collecting the two-component developer that has become excessive due to the replenishment. Is an image forming method including a step of developing a toner image using the two-component developer, wherein the electric resistance value is lower than that of the carrier in the start developer first used for image formation and the charge amount is An image forming method characterized in that a two-component developer comprising a combination of a large carrier and a toner having a smaller volume-based center particle diameter than toner in the start developer is used for the replenishment. It is.

  According to the first aspect of the present invention, since a carrier having a higher charge is used for the two-component developer for replenishment than that used for the start developer, the amount of the two-component developer for replenishment is smaller than before. By simply replenishing, the charge amount of the two-component developer as a whole can be stably maintained in response to a decrease in charging ability accompanying the deterioration of the carrier. In addition, the carrier has a low resistance despite the high charge, a good circulation of toner, and a high development performance, so that the occurrence of spent or charge-up can be suppressed.

  In addition, the above-mentioned carrier is combined with a toner having a toner particle size smaller than that used for the start developer, and such a small particle size toner can be well charged even by an old carrier with a high spent. . In addition, since the toner with a small particle size has a good balance of development performance such as excellent adhesion to the carrier, these effects suppress the occurrence of toner scattering and ensure that fog and the like occur more than ever before. Can be prevented.

  Therefore, according to the first aspect of the present invention, it is possible to form a stable and good image free from fogging by using the trickle development method and for a longer period than before.

The present invention will be described below.
<Image forming method>
FIG. 1 is a schematic cross-sectional view showing an example of developing means used for carrying out the image forming method of the present invention.
As shown in the figure, the developing means of this example includes an apparatus main body 2 for accommodating a two-component developer D1, which incorporates a magnetic roll 1 incorporating a magnet, which is opposed to an image carrier EP of the image forming apparatus. A developer container 3 for supplying the two-component developer D2 for replenishment to the apparatus main body 2, and a collection container 4 for recovering the two-component developer D1 in the apparatus main body 2 that has become excessive due to the replenishment. It has. The apparatus main body 2 initially stores a predetermined amount of start developer as the two-component developer D1.

  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 21 and 22 are provided. Further, in the vicinity of the magnetic roll 1 of the apparatus main body 2, a regulating blade 23 for regulating the height of the head of the magnetic brush formed on the surface of the magnetic roll 1 is provided.

  The connecting portion between the apparatus main body 2 and the developer container 3 is provided with a stirring conveyance spiral 31 for supplying the two-component developer D2 for supply to the apparatus main body 2 while stirring. Furthermore, the apparatus main body 2 and the collection container 4 are connected by a cylindrical body 41 in which an upper end provided with an opening 41 a is protruded to a position of a predetermined height in the apparatus main body 2. Then, the excess two-component developer D1 exceeding the opening 41a is recovered in the recovery container 4 through the cylindrical body 41.

In order to carry out the image forming method of the present invention using the developing means described above, a predetermined amount of start developer is first stored in the apparatus main body 2 as the two-component developer D1, and a predetermined amount is stored in the developer container 3. Contains a two-component developer D2 for replenishment.
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 21 and 22 are rotated so that the two-component developer D1 in the apparatus main body 2 is directed in the direction of the magnetic roll 1. The image formation is started while being conveyed. Then, the ears of the magnetic brush formed on the surface of the magnetic roll 1 and adjusted to a predetermined height by the regulating blade 23 come into contact with the surface of the image carrier EP, and the static formed on the surface of the image carrier. Image formation is performed by developing the electrostatic latent image into a toner image.

When the image formation proceeds and the toner in the two-component developer D1 is consumed and the toner density is reduced to a predetermined value, the image formation is temporarily stopped and the agitating and conveying spiral 31 is rotated to After supplying a predetermined amount of supply developer D2 into the apparatus main body 2, image formation is resumed.
When the amount of the two-component developer D1 in the apparatus main body 2 becomes excessive due to the supply of the two-component developer D2 for replenishment, the excess two-component developer D1 exceeding the opening 41a is automatically Then, it is collected in the collection container 4 through the cylinder 41.

When image formation is performed while repeating the above operations, the two-component developer D1 in the apparatus main body 2 can always maintain a new state.
<< two-component developer >>
In the image forming method according to the present invention, among the above, as the two-component developer D2 for replenishment supplied from the developer container 3 to the apparatus main body 2, the apparatus main body 2 of the developing means is initially used as the two-component developer D1. A combination of a carrier having a lower electrical resistance value and a larger charge amount than the carrier in the start developer to be accommodated and a toner having a smaller volume-based center particle size of toner particles than the toner in the start developer. Must be used.

<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. The electric resistance value of the carrier is preferably 10 ⁶ to 10 ¹³ Ω · cm.

  The electric resistance value of the carrier used for the two-component developer for replenishment needs to be lower than the electric resistance value of the carrier used for the start developer within the above range. For this purpose, for example, the carrier is coated. What is necessary is just to change the kind of coating resin to perform, or to add electrically conductive agents, such as carbon black, in coating resin. Further, the charge amount of the carrier used for the two-component developer for replenishment needs to be larger than the charge amount of the carrier used for the start developer. For this purpose, for example, the type of the coating resin is changed, What is necessary is just to increase the coating amount of the coating resin, increase the baking temperature when the carrier is manufactured by baking the magnetic material, or reduce the volume-based center particle diameter of the carrier.

Here, the ratio (R ₁ / R ₂ ) of the electric resistance value (R ₁ ) of the carrier used for the start developer to the electric resistance value (R ₂ ) of the carrier used for the two-component developer for replenishment is It is preferable that 5 ≦ R ₁ / R ₂ ≦ 200, particularly 10 ≦ R ₁ / R ₂ ≦ 100. The ratio (Q ₂ / Q ₁ ) of the charge amount (Q ₂ ) of the carrier used for the two-component developer for replenishment to the charge amount (Q ₁ ) of the carrier used for the start developer is 1 <Q _It is preferable that ₂ / Q ₁ ≦ 10, particularly 3 ≦ Q ₂ / Q ₁ ≦ 5.

  Further, as the carrier used for the two-component developer for replenishment, a carrier having a larger volume-based center particle diameter and a larger bulk density than the carrier used for the starting developer is used, particularly within the above range. Is preferred. Thereby, the fall of the fluidity | liquidity of the developer by a spent can be suppressed. In order to make the bulk density of the carrier used for the two-component developer for replenishment larger than the bulk density of the carrier used for the start developer, for example, the surface condition of the carrier surface, specifically the number of irregularities on the carrier surface, What is necessary is just to change the coating amount of resin, when the size etc. are different, or the center particle diameter of a volume reference | standard is different, or when using the type which coat | covered the surface of the magnetic body particle | grains with resin.

  Specifically, the bulk density can be increased as the number of irregularities on the carrier surface is reduced and the size is reduced. Further, the bulk density can be increased as the volume-based center particle size is increased. Furthermore, the bulk density can be increased as the coating amount of the resin is decreased. The values of carrier electrical resistance, charge amount, bulk density, volume-based center particle diameter, resin coating amount, etc. 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. The toner particles preferably have a volume-based center particle size of 4 to 12 μm.

In the toner used for the two-component developer for replenishment, it is necessary that the volume-based center particle diameter of the toner particles be smaller than the toner in the start developer within the above range. More specifically, the volume-based center particle diameter (D ₁ ) of the toner used for the start developer and the volume-based center particle diameter (D ₂ ) of the toner used for the two-component developer for replenishment. the difference _D 1 -D _2, wherein:
0.5 ≦ D ₁ −D ₂ ≦ 2
It is preferable to be within the range. The toner used for the start developer has a volume-based center particle diameter (D ₁ ) of 6 to 12 μm, and the toner used for the two-component developer for replenishment has a volume-based center particle diameter (D ₂ ) of 4. It is preferable to set it as 10 micrometers.

Further, as such a toner, the toner particles, the median particle size D _V volume basis, the ratio D _{V /} D _N between the average particle diameter D _N of the number basis is not more than 1.15, sharp particle size distribution Is preferably used. As a result, the content ratio of the fine powder toner having a volume-based center particle size of 5 μm or less can be reduced to improve the development performance and suppress the occurrence of spent.

In order to adjust the volume-based center particle size and particle size distribution of the toner particles within the above ranges, for example, when the toner particles are produced by a pulverization method in which the following components are melt-kneaded and then pulverized, What is necessary is just to adjust the classification | category conditions of a later toner particle.
The toner used for the two-component developer for replenishment preferably has the same charge amount as the toner in the start developer, or about 0.8 to 0.9 times smaller. As described above, the replenishing toner having a small volume-based center particle size has a large adhesion force to the carrier and tends to be difficult to develop. However, by reducing the charge amount as described above, sufficient development performance can be obtained. Can be secured.

(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 phenolic 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, Rizor 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.

(External additive)
Examples of the external additive externally added to the toner particles include ultrafine silica particles (colloidal silica, hydrophobic silica, etc.) and titanium oxide for improving the fluidity of the toner and maintaining the storage stability. And so on. 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.

<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.
<Toner 1>
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 a charge control agent (FCA201PS manufactured by Fujikura Kasei Co., Ltd.) 3.5 7 parts by weight of polyethylene wax (Yumex (registered trademark) 100TS manufactured by Sanyo Chemical Co., Ltd.) as an offset preventive agent is added, premixed using a Henschel mixer, and then using a twin-screw kneading extruder After melting, kneading and cooling, toner particles having a volume-based center particle size of 9.0 μm and a ratio D _V / _DN of 1.2 were produced through coarse pulverization, fine pulverization, and classification steps. .

Then, 0.5 part by weight of hydrophobic silica was added to 100 parts by weight of the toner particles and mixed using a Henschel mixer to produce toner 1.
<Toner 2>
Toner particles having a volume-based center particle size of 8.0 μm and a ratio D _V / _DN of 1.2 were prepared by changing the amount of the charge control agent to 5 parts by weight and adjusting the classification conditions. Toner 2 was produced in the same manner as Toner 1 except that it was used.

<Toner 3>
Toner 3 was prepared in the same manner as Toner 1 except that toner particles having a volume-based center particle size of 8.0 μm and the ratio D _V / _DN of 1.15 were prepared by adjusting the classification conditions. Manufactured.
<Carrier 1>
The carrier 1 has a volume-based center particle size of 60 μm, in which the surface of Mn—Mg magnetic particles is coated with 20 parts by weight of a fluorine-silicone resin with respect to 100 parts by weight of the magnetic particles. A thing was used. The carrier 1 had an electric resistance value of 10 ¹² Ω · cm, a charge amount of 16.5 μC / g, and a bulk density of 2.02 g / cm ³ .

<Carrier 2>
The carrier 2 has a volume-based center particle size of 80 μm, in which the surface of Mn—Mg 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. A thing was used. The carrier 2 had an electric resistance value of 10 ¹¹ Ω · cm, a charge amount of 18.5 μC / g, and a bulk density of 2.10 g / cm ³ .

Examples 1 and 2 and Comparative Examples 1 and 2
The toners 1 to 3 and the carriers 1 and 2 produced as described above were combined as shown in Table 1 to prepare a start developer and a two-component developer for replenishment. In both cases, the toner concentration was 5%.
These starting developer and replenishment two-component developer are used in a laser printer (model number FS-8000C modified machine manufactured by Kyocera Mita Co., Ltd.) whose developing means is modified as shown in FIG. Images with a density of 4% were continuously formed. That is, in the developing device of FIG. 1, the start developer D <b> 1 is accommodated in the apparatus main body 2, and the replenishment two-component developer D <b> 2 is accommodated in the developer container 3. 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, when the toner concentration measured by a magnetic permeability sensor (not shown) was reduced to 4.0% by weight, an operation of supplying the two-component developer D2 for supply in the developer container 3 to the apparatus main body 2 was performed. The one-time supply amount of the two-component developer D2 was 5.0 g.
After continuous image formation of 200,000 sheets while repeating the above operation, the image density ID of the first image formation image, the 50,000th image formation image, and the 200,000th image formation image and the fog density FD of the blank portion are obtained. It was measured.

  The results are shown in Table 1.

From the table, in Comparative Example 1 in which the same carrier 1 and toner 1 are used for the start developer and the two-component developer for replenishment, the image density ID is significantly increased by performing 200,000 continuous image forming properties. The fog density FD was also significantly increased.
Further, although the carrier is different between the start developer and the two-component developer for replenishment in the same manner as in Examples 1 and 2 described below, in Comparative Example 2 using the same toner 1 as in Comparative Example 1, Comparative Example 1 is the same. However, it was found that the image density ID is increased and the fog density FD is also increased by performing continuous image forming of 200,000 sheets.

  On the other hand, as the carrier for the two-component developer for replenishment, the carrier 2 having a lower electrical resistance value and a larger charge amount than the carrier 1 used for the start developer is used, and the two-component developer for replenishment is used. In Examples 1 and 2 in which the toner 2 having a smaller particle diameter than the toner 1 used in the start developer is used as the toner of the developer, the image density ID is the same even when 200,000 sheets are continuously formed. It was found that the fog density FD was constant at a low level that was not different from that of the first sheet.

Further, when Examples 1 and 2 are compared, Example 2 using the toner 3 having the ratio D _V / _DN of 1.15 as the toner of the two-component developer for replenishment has a ratio D _V / D _N of It was found that the image density ID can be further stabilized when 200,000 continuous image forming properties are performed as compared with Example 1 using the toner 2 of 1.2.

It is a schematic sectional drawing which shows an example of the image development means used in order to implement the image forming method of this invention.

Explanation of symbols

D1 Two-component developer (start developer)
D2 Two-component developer for replenishment EP Image carrier

Claims (1)

  The two-component developer containing the carrier and the toner is replenished as needed, and the two-component developer that has become excessive due to the replenishment is collected while the electrostatic latent image on the image carrier is removed from the two-component developer. An image forming method including a step of developing into a toner image using a carrier having a lower electrical resistance value and a higher charge amount than a carrier in a start developer first used for image formation, and the start developer An image forming method comprising using a two-component developer in combination with a toner having a smaller volume-based center particle size than toner in the toner for replenishment.

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