JPH1078701A - Developing device and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device provided with a developer carrier having a developing sleeve being capable of stabilizing the chargeability of toner and the formation of a layer and uniform in resistivity by using resin incorporating conductive inorganic powder having a specific polymer, as a coating layer for the developer carrier. SOLUTION: As the developer carrier, one provided with a coating layer incorporating the conductive inorganic powder whose polymers are grafted, in the resin is used, so that a thin layer of a developer is formed on the developer carrier, to attain development. For instance, in an image forming device, a photoreceptor drum 1 is electrified by a roll electrifier 2 and then exposed with laser light to form an electrostatic latent image. Further, in a developing device 8, the toner is carried onto the surface of a developing roll 3 to which a voltage is applied by a developer supplying roll 4 to which the voltage is applied and the thin layer of the toner is formed by a blade 5 abutted on the developing roll 3 with fixed linear pressure. Thus, the electrostatic latent image is developed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing an electrostatic latent image using a developer in an electrophotographic method, and an image forming method for copying using the same.

[0002]

2. Description of the Related Art At present, two-component developing methods using a carrier such as toner and iron powder and one-component toner developing methods using no carrier are known as dry developing methods in various electrostatic copying methods that are currently in practical use. Have been.

[0003] In the two-component developing method, the developer is deteriorated due to the toner particles adhering to the carrier surface, and only the toner is consumed and the concentration ratio of the toner in the developer is reduced. An adjusting device or the like for keeping the mixing ratio with the carrier constant must be provided. For this reason, the two-component developing method has a disadvantage that the developing device becomes large, but the one-component developing method has no such a problem and is suitable for downsizing of the device. Is becoming mainstream. The one-component toner development method includes a magnetic one-component development method in which an electrostatic latent image formed on the surface of a photoconductor drum used as an electrostatic latent image carrier is visualized by a magnetic toner, and a non-magnetic toner in the same manner. It is classified into the non-magnetic one-component developing system used. Among them, the magnetic one-component developing method holds and develops a magnetic toner using a developer carrying member provided with a magnetic field generating means such as a magnet inside, and has recently been used in many small printers. Have been. As a developing device of this type, while applying a charge of the opposite polarity to the electrostatic latent image to the magnetic toner by friction between the magnetic toner particles and friction between the developing sleeve used as a developer carrier and the magnetic toner particles, It is known that this magnetic toner is formed as a thin layer on a developing sleeve, which is conveyed to a developing area, where the magnetic toner flies by the action of a magnetic field by a magnet in the developing area to visualize the toner.

[0004] However, in the above-described developing devices, it is necessary to form a uniform thin layer of toner on the developing sleeve. This thin layer is formed by environmental conditions such as temperature and humidity.
Since it is easily influenced by the physical properties of the toner, the state of the surface of the developing sleeve, and the like, it is difficult to obtain a uniform toner layer. Also, when the number of copies is increased using this developing device, the toner is repeatedly rubbed with the developing sleeve,
Additives that improve the fluidity of the toner accumulate on the developing sleeve, or the binder resin of the toner forms a film on the developing sleeve, changing the surface condition of the developing sleeve. The transfer state of the toner to the area becomes uneven.

In order to prevent such deterioration of the surface condition of the developing sleeve, a film containing an inorganic polymer fluorinated carbon is formed on the surface of the developing sleeve (Japanese Patent Laid-Open Publication No. Sho.
No. 7-66443) or a resin forming a resin having good releasability in which silica is dispersed (Japanese Patent Laid-Open No. 58-178).
No. 380) has been proposed. However, although these are effective to some extent in suppressing the deterioration of the surface state, they are easily worn and are insufficient in durability.

On the other hand, in the developing area, a potential difference (bias) is provided between the photosensitive drum and the developing sleeve for the purpose of controlling the amount of toner development and suppressing the development of the background portion having no electrostatic latent image. Further, in order to perform uniform development, it is necessary that the surface of the developing sleeve is not only uniform in material but also uniform in specific resistance. As a device for controlling the resistance of the developing sleeve, a device which forms a film containing conductive fine particles (Japanese Patent Laid-Open No. 3-252679) and a device which forms a film containing conductive carbon fiber (Japanese Patent Application Laid-Open No. 2-1090075) Japanese Patent Application Laid-Open No. Hei 2-50188), and a method in which a coating is formed by partially using a semiconductive resin such as polypyrrole. However, all of these have a problem that unevenness occurs in the formed copy image because the specific resistance of the surface of the developing sleeve is not uniform.

As described above, the developing device used in the one-component developing system still has problems to be solved in terms of stable charging of toner, formation of a toner layer, and preparation of a uniform copied image.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems in view of the above-mentioned circumstances in the prior art. That is, the object of the present invention is:
An object of the present invention is to provide a developing device provided with a developer carrying member having a developing sleeve having stable toner chargeability and layer formation and uniform resistivity. Another object of the present invention is to
Even if used repeatedly over a long period, the image density is stable,
An object of the present invention is to provide an image forming method in which density unevenness and ghost hardly occur.

[0009]

In order to solve the above-mentioned problems, the present inventors have conducted various studies on a developer carrier used in the above-mentioned developing device. It was found that it was necessary to keep the specific resistance of the sample uniformly. This variation in specific resistance is
When forming a resin coating layer having an inorganic powder provided as a conductive path on the surface of the developing sleeve, in the applying step or the drying step, due to the occurrence of ubiquitization and aggregation of the inorganic powder. I found out. In other words, depending on factors such as the affinity between the inorganic powder, the resin and the solvent for dissolution used for forming the coating layer, the specific gravity of the material itself, and the evaporation rate, the inorganic powder may be ubiquitous or may be agglomerated. It has been found that the above object can be achieved by using a resin containing a conductive inorganic powder having a specific polymer as the coating layer of the developer carrier for the developer carrier. Was completed.

That is, the developing device of the present invention forms a developer layer on the surface of a developer carrier and transfers the developer from the surface of the developer carrier to the surface of the electrostatic latent image holding member to form an electrostatic latent image. A developing device to be exposed, and as a developer carrying member thereof,
A developer carrier having a coating layer containing a conductive inorganic powder in which a polymer is grafted in a resin is provided.

Further, the image forming method of the present invention is an image forming method comprising a step of forming a latent image on a latent image carrier and a step of developing using a developer on the developer carrier. Using a developer carrier having a coating layer containing a conductive inorganic powder with a polymer grafted in a resin, forming a thin layer of developer on the developer carrier and performing development It is characterized by. The coating layer of the developer carrier preferably contains 10 to 80% by weight of the conductive inorganic powder to which the polymer is grafted.

[0012]

Embodiments of the present invention will be described below in detail. The developing device of the present invention includes a latent image forming step of forming a latent image on a latent image holding member, and developing the latent image on the latent image holding member using a thin layer-formed developer on a developer carrying member. This is used in an image forming method including a developing step of transferring a toner image on the latent image holding member to a transfer member, and a fixing step of thermally fixing the toner image on the transfer member. A magnetic toner is usually used as a toner that makes the latent image visible, but the toner is not limited to this. A non-magnetic full-color toner using four color toners of yellow, magenta, cyan, and black may also be used. it can.

In the latent image forming step, a conventionally known method can be applied, and a latent image carrier (hereinafter, referred to as a "photosensitive drum") such as a photosensitive layer or a dielectric layer is formed by an electrophotographic method or an electrostatic recording method. ) To form an electrostatic latent image thereon. As the photosensitive layer of the photosensitive drum used in the present invention, a known photosensitive material such as organic or amorphous silicon can be used. Further, as the photoreceptor drum, a drum obtained by a known manufacturing method such as extruding aluminum or an aluminum alloy and processing the surface thereof can be used.

In the developing step, the toner supplied by the toner supply roll is formed into a thin layer by an elastic blade or the like on a rotating cylindrical body used as a developer carrier (hereinafter, referred to as “development roll”). This is transported to the developing nip, and the developing roll and the photosensitive drum holding the electrostatic latent image are brought into contact with each other in the developing section, or are arranged with a certain gap, and are disposed between the developing roll and the photosensitive drum. The electrostatic latent image is developed with toner while applying a bias.

As the developing roll of the present invention, a specific conductive inorganic powder is coated on the surface of a metal substrate made of aluminum, SUS stainless steel, etc., which has been subjected to surface treatment such as polishing and blasting, for example, on the surface of a developing sleeve. A resin provided with a coating layer formed by coating a resin containing the same is used. This developing roll has the following configuration in order to have a developing sleeve having a uniform specific resistance. As the resin used for forming the coating layer of the developing roll, any resin can be used as long as it is soluble in a solvent.In particular, from the viewpoint of productivity and coating strength, phenol resin, epoxy resin, polymethyl Methacrylate (PMMA) resin, polycarbonate resin and the like are preferable.

In the present invention, the conductive inorganic powder to which a polymer dispersed in a resin is grafted refers to a resin obtained by graft-polymerizing a resin using a functional group present on the surface of the conductive inorganic particles. . That is, it can be said that the surface of the inorganic particles and the resin having a certain molecular weight are chemically bonded to each other. There are various methods for causing the polymer to undergo a graft polymerization reaction on the surface of the inorganic particles. For example, the following three methods are mentioned. 1. 1. A method in which a vinyl monomer is polymerized using a polymerization initiator in the presence of inorganic particles, and a growing polymer generated in the reaction system is terminated by a functional group on the particle surface. 2. a method of growing a graft chain from a polymerization initiation group introduced on the surface of the inorganic particles; A method by a polymer reaction between a functional group on the surface of the inorganic particles and a functional group at the terminal of the polymer.

In the present invention, the polymer graft-bonded to the surface of the conductive inorganic powder includes polyolefin resins such as polyethylene and polypropylene;
Examples of the polyvinyl and polyvinylidene resins include, for example, polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether or polyvinyl ketone; vinyl chloride-vinyl acetate copolymer; Styrene-acrylic acid copolymer; straight silicone resin composed of an organosiloxane bond or a modified product thereof; as a fluororesin, for example, polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene; polyester; polyurethane; Polycarbonate; phenolic resin; amino resin, for example,
A urea-formaldehyde resin, a melamine resin, a benzoguanamine resin, a urea resin, a polyamide resin; an epoxy resin and the like are used, but other known resins can also be used.

In the coating layer of the developing roll, the content of the conductive inorganic powder to which the polymer contained in the coating layer is grafted is preferably in the range of 10 to 80% by weight, more preferably 10 to 40% by weight. %. If the content is less than 10% by weight, the effect of controlling electric resistance is not sufficient, while if it is more than 80% by weight, adhesion between the grafted inorganic particles becomes insufficient and the strength of the coating film is greatly reduced.

Examples of the conductive inorganic powder used in the present invention include metals such as gold, silver and copper, carbon black, semiconductive oxides such as titanium oxide and zinc oxide, titanium oxide, zinc oxide, barium sulfate, and the like. The surface of aluminum borate, potassium titanate powder, etc. is coated with tin oxide or carbon black,
Examples thereof include those covered with a metal, and among them, carbon black having relatively high conductivity is preferable. These particles preferably have an average particle diameter in the range of 0.005 to 3 μm, and particularly preferably 0.005 to 0.5 μm. The coating layer may be added with other inorganic powders if necessary.For example, as a solid lubricant, molybdenum disulfide, boron nitride, graphite, etc. It can be used as appropriate while taking into account the balance. The thickness of the coating layer in the present invention is in the range of 1 to 100 μm, preferably 3 to 30 μm.
It is in the range of μm.

The method for producing the developing roll used in the present invention is as follows. A solid lubricant or the like is dispersed in a solution in which a resin and conductive inorganic particles grafted with a polymer are dissolved in a solvent in advance, and then this coating solution is dispersed. The coating is performed by applying the composition on the surface of the substrate by a known coating method such as spraying or dipping, and then drying or curing as necessary. In order to form a toner layer on the developing roll, a regulating member such as an elastic blade is brought into contact with the surface of the developing sleeve. As the elastic blade, a rubber elastic body such as silicone rubber or urethane rubber is preferably used, and an organic or inorganic substance is added to the elastic body to control the toner charge amount,
They may be dispersed.

As a method of developing a four-color toner, four developing machines are arranged around an electrostatic latent image holding member (photosensitive drum), and charging, exposure and development steps are performed for each toner in four steps. A cycle repetition method is used in which charging, exposure, and development of the four-color toner are performed in one cycle. Also, 4
As a method of superimposing the color toners, a method of transferring the toner image formed on the photosensitive drum one by one onto a transfer drum around which a transfer paper is wound and superimposing the toner images, and a method of superimposing the toner image formed on the photosensitive drum. A method of transferring images onto a transfer body and superimposing the color toner images on the transfer body and then transferring them collectively on transfer paper, a method of transferring the color toner images on the photoconductor drum and then transferring them collectively on transfer paper, etc. Is used. As a transfer unit, a known unit such as a contact type in which a transfer roller is pressed against a latent image holding member or a non-contact type using a corotron can be used.

In the cleaning step, the toner remaining on the latent image holding member without being used for the transfer in the transfer step is removed by a cleaner, and the cleaning means in the present invention includes blade cleaning or roller cleaning. Known blades are used, and as the blade cleaning, an elastic rubber such as silicone rubber or urethane rubber is used. The fixing step is to fix the toner image transferred to the transfer body using a fixing device. As a fixing unit of the present invention, a heat fixing method using a heat roll is preferable, and to improve gloss and OHP image quality. In addition, roller fixing with oil applied, oilless fixing with a release agent added to the toner for downsizing the apparatus, and the like can be applied.

It is considered that the present invention has the following advantages. That is, since the grafted polymer exists at the interface between the conductive inorganic powder and the other resin, the affinity of the interface is the same as the affinity of the interface between the conductive inorganic powder and the other resin in the conventional technology. As a result, aggregation of the conductive inorganic powders and ubiquity of the conductive inorganic powders can be significantly suppressed, and therefore, the storage stability as a lacquer for forming a resin layer is also improved. Also,
Since the interaction at the interface between the grafted conductive inorganic powder and the other resin is larger than that at the conventional interface, the mechanical strength of the formed resin layer itself is also improved.

It is known that a sleeve ghost, which is a history of a printed pattern, occurs in the toner layer on the developing sleeve and appears as a defect on an image. The mechanism of the occurrence of the ghost is caused by the fact that the toner has a particle size distribution and the charge opposite to the charge held by the toner remains on the surface of the developing sleeve. According to the configuration of the present invention, since the volume resistivity of the developer carrying member is in the range of 10 ³ to 10 ¹² Ω · cm, the charge on the developing sleeve surface is leaked to some extent, thereby suppressing the occurrence of sleeve ghost. can do.

FIG. 1 is a schematic diagram showing an example of a main part of an image forming apparatus used for forming a copied image in the present invention. In FIG. 1, a photoconductor drum 1 and a developing roll 3 are arranged so as to have a constant gap. The photoconductor drum 1 is charged by a roll charger 2 and then exposed to laser light and statically charged. An electrostatic latent image is formed. In the developing device 8, the toner is conveyed onto the surface of the developing roll 3 to which the voltage is applied by the developer supply roll 4 to which the voltage is applied, and is brought into contact with the developing roll 3 at a constant linear pressure. 5 forms a thin layer of toner, whereby the electrostatic latent image is developed. Reference numeral 6 denotes a roll transfer device, and reference numeral 7 denotes a blade type cleaner.

[0026]

The present invention will be specifically described below with reference to examples. [Conductive Inorganic Powder Grafted with Polymer] Production of Grafted Inorganic Particles (a) 4,4-azobis (4-cyanopentanoic acid) and diamine-type polydimethylsiloxane (Mw = 4.2 × 10 ³ ) are superposed. An azo polymer was synthesized by a condensation reaction. Next, 3
In a 00 ml flask, 1 g of carbon black (Neospectra II, average particle size: 0.013 μm; manufactured by Columbia Carbon Co., Ltd.), 10 g of the azo polymer and 60 ml of toluene were added, and the mixture was stirred at 100 ° C. under a nitrogen atmosphere with a magnetic stirrer. Was reacted. After 1 hour, the reaction system was diluted by adding about 60 ml of toluene,
The reaction was stopped by cooling to room temperature. By centrifuging the toluene solution of the reaction product, the carbon black is completely precipitated, and the carbon black is heated and dried, and then subjected to Soxhlet extraction using tetrahydrofuran as a solvent to remove the non-grafted polymer. Grafted carbon black was obtained and used as graft inorganic particles (a). The content of carbon black in the obtained graft inorganic particles (a) was 20.3% by weight, and the weight average molecular weight of the grafted polymer was 8.2 × 10 ³ .

Production of Grafted Inorganic Particles (b) In a 300 ml flask, 1 g of carbon black (Neospectra II, average particle diameter: 0.011 μm; manufactured by Columbia Carbon Co., Ltd.) and styrene-containing glycidyl groups were introduced.
10 g of an acrylic copolymer (Mw = 5.5 × 10 ³ ) and 60 ml of toluene were added and reacted at 100 ° C. while stirring with a magnetic stirrer under a nitrogen atmosphere. 1
After a lapse of time, about 60 ml of toluene was added to the reaction system for dilution, and the reaction was stopped by cooling to room temperature. By centrifuging the toluene solution of the reaction product, the carbon black is completely precipitated, and the carbon black is heated and dried, and then subjected to Soxhlet extraction using tetrahydrofuran as a solvent to remove the non-grafted polymer. Grafted carbon black was obtained and used as graft inorganic particles (b).
The content of carbon black in the obtained graft inorganic particles (b) was 15.5% by weight, and the weight average molecular weight of the grafted polymer was 7.6 × 10 ³ .

Example 1 <Developing Roll A> A resin solution obtained by ultrasonically dispersing grafted inorganic particles having the following composition on an aluminum substrate blasted to a surface roughness (Ra) of 0.4 μm was used. Apply with a push-up coater to a thickness of 10 μm.
The developing roll A having a coating layer was obtained by drying at 20 ° C. for 1 hour. Resin: PMMA resin 10 parts by weight Grafted inorganic particles (a) 15 parts by weight Solvent: methyl ethyl ketone 30 parts by weight

Example 2 <Developing Roll B> A resin in which grafted inorganic particles having the following composition and a solid lubricant were ultrasonically dispersed on an aluminum substrate blasted to a surface roughness (Ra) of 0.4 μm. The solution was applied by a push-up applicator so as to have a film thickness of 10 μm, and dried at 120 ° C. for 1 hour to obtain a developing roll B having a coating layer. Resin: PMMA resin 10 parts by weight Grafted inorganic particles (a) 10 parts by weight Solvent: methyl ethyl ketone 30 parts by weight Solid lubricant: molybdenum disulfide (average particle size: 0.5 μm) 10 parts by weight

Example 3 <Developing Roll C> A resin in which grafted inorganic particles having the following composition and a solid lubricant were ultrasonically dispersed on an aluminum substrate blasted to a surface roughness (Ra) of 0.4 μm. The solution was applied by a push-up applicator so as to have a film thickness of 10 μm, and dried at 120 ° C. for 1 hour to obtain a developing roll C having a coating layer. Resin: PMMA resin 10 parts by weight Grafted inorganic particles (b) 20 parts by weight Solid lubricant: molybdenum disulfide (average particle size: 0.5 μm) 10 parts by weight Solvent: methyl ethyl ketone 30 parts by weight

Comparative Example 1 <Developing Roll D> A developing roll D was obtained in the same manner as in Example 1 except that the graft inorganic particles (a) were not used in the resin solution. Comparative Example 2 <Developing Roll E> A resin solution obtained by ultrasonically dispersing grafted inorganic particles having the following composition on an aluminum substrate blasted to a surface roughness (Ra) of 0.3 μm has a film thickness of 10 μm. By a push-up coating machine
By drying at 20 ° C. for 1 hour, a developing roll E having a coating layer was obtained. Resin: 15 parts by weight of PMMA resin 5 parts by weight of carbon black (BPL, average particle size: 0.024 μm; manufactured by Cabot Corporation) Solvent: 30 parts by weight of methyl ethyl ketone

In the image forming apparatus shown in FIG. 1, the above-mentioned developing rolls A to E are used as developing devices, magnetic toner is put therein, and the environment is maintained at a temperature of 22 ° C./humidity of 55% RH.
Image quality and the like were evaluated by performing a print test on one sheet. The magnetic toner includes negatively charged magnetic toner particles (average particle diameter: 9 μm) obtained by internally adding 50 parts by weight of magnetite and 2 parts by weight of a metal-containing complex as a charge controlling agent to a styrene-acryl copolymer, and silica. (R972;
0.7 parts by weight of Nippon Aerosil Co., Ltd.) was used. Table 1 shows the obtained results. For the solid density, a sample after fixing was measured using a spectrophotometer (X-lite40).
4: X-rite).

[0033]

[Table 1] In Table 1, the evaluation of “density unevenness” was evaluated as follows: ○ when the density difference was less than 0.1, Δ when the density difference was 0.1 to 0.2, and × when the density difference was more than 0.2. And “Fog” was evaluated as ○ when no fog occurred, Δ when slightly fluctuated, and x when there were many problems.

Using the developing rolls A to E, the volume resistance in the film thickness direction of the coating layer was measured in an environment of a temperature of 22 ° C. and a humidity of 55% RH, and the variation width of the volume resistance was determined. As shown in FIG. 2, the measurement of the volume resistance was obtained by calculating from the current value measured for a constant voltage on the developing roll 3, the thickness of the coating layer on the developing roll, and the area of the electrode. . The measurement points are the four points shown in FIG.
The area of the electrode is 0.25 cm ² . Table 2 shows the obtained results.

[0035]

[Table 2] As can be seen from Table 2, it is considered that variations in the resistance appeared on the developing rolls D and E, and this result was detected as the density unevenness shown in Table 1.

[0036]

Since the developing device of the present invention uses a developing roll having a specific coating layer, the variation in the specific resistance of the developing roll can be reduced.
In image formation using the developing device, there is no density unevenness in the image density of the solid portion, and even when used continuously, the image density is stable for a long period of time, and there is no ghost, no excellent developability. A high quality image can be obtained, and an excellent effect that there is no fog, in-machine dirt, and the like can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a main part of an image forming apparatus used for forming a copy image in the present invention.

FIG. 2 is a schematic configuration diagram used for measuring a volume resistance value of a developing roll.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 2 ... Roll charger, 3 ... Developing roll, 4 ... Developer supply roll, 5 ... Blade, 6 ... Roll transfer device, 7 ... Blade cleaner, 8 ... Developing device.

Claims (4)

[Claims] 1. A developing device for forming a developer layer on a surface of a developer carrying member, and transferring the developer from the surface of the developer carrying member to a surface of the electrostatic latent image holding member to make an electrostatic latent image visible,
A developing device comprising a developer carrier having a coating layer containing a conductive inorganic powder in which a polymer is grafted in a resin, as the developer carrier. 2. The developing device according to claim 1, wherein the coating layer of the developer carrier contains 10 to 80% by weight of a conductive inorganic powder to which a polymer is grafted. 3. An image forming method comprising: a step of forming a latent image on a latent image carrier; and a step of performing development using a developer on the developer carrier. An image forming method, comprising: using a developer having a coating layer containing a conductive inorganic powder to which a polymer is grafted, forming a thin layer of a developer on the developer carrier, and performing development. 4. The image forming method according to claim 3, wherein the coating layer of the developer carrier contains 10 to 80% by weight of the polymer-grafted conductive inorganic powder.