JP4190444B2 - Electrophotographic carrier - Google Patents

Description

  The present invention relates to an electrophotographic carrier, and more particularly to a carrier used in a two-component dry developer for electrophotography.

  Conventionally, as a method for forming an image, a method of charging a toner for visualizing a toner, a so-called two-component development method using frictional charging by stirring and mixing the toner and a carrier, and a charge to the toner without using a carrier It is roughly divided into a so-called one-component development system in which the application is performed. Among these, the two-component development tends to be frequently used in a copying machine or a multi-function machine that requires high speed and high image quality.

  The carrier used in the two-component development is held on the surface by an electric force generated by friction of fine toner particles, and the toner particles are generated by an electric field formed by the electrostatic latent image when approaching the electrostatic latent image. The electrostatic latent image is visualized by overcoming the binding force with the carrier and attracting and adhering onto the electrostatic latent image. The toner consumed by development is repeatedly used while being replenished each time. Accordingly, the carrier must always be triboelectrically charged to a sufficient charge amount with the desired polarity of the toner particles during long-term use. However, in the conventional carrier, a toner film is formed on the surface of the carrier due to a collision with toner particles or carrier particles, a mechanical collision such as a collision with a developing machine, or heat generated by these, and so-called toner spending occurs. Since the charging characteristics of the carrier decrease with use time, the carrier must be replaced.

  One technique that has been proposed to prevent such spent is a resin-coated carrier. Examples of the resin used for the resin-coated carrier include resins such as styrene / methacrylate copolymer, styrene polymer, and silicone resin. However, styrene / methacrylate copolymers and styrene polymer coated carriers have a relatively high surface energy, and may become spent due to long-term use.

  On the other hand, silicone resin-coated carriers have low surface energy and are difficult to be spent. However, there are generally drawbacks in that the adhesion to the core material is weak and the coating layer is easily peeled off.

  Thus, Patent Document 1 describes that a resin coating layer in which resin fine particles and conductive powder are dispersed and contained in a matrix resin is provided to prevent spent by the toner. Therefore, whether or not the function of preventing spenting can be sufficiently obtained will ultimately depend on the matrix resin, and is uncertain.

  Patent Document 2 discloses a technique for preventing peeling of the resin coating by containing an elemental silicon in the core material and applying an electrochemical adhesive force in addition to a physical adhesive force by resin coating. Proposed. However, depending on the strength of the resin itself, wear may occur during long-term use, and the toner may become spent without being peeled off.

As described above, in two-component development, the toner and the carrier are agitated and charged, and a sufficient charge amount is imparted to the toner particles, while maintaining the mechanical durability and preventing the adhesion of the toner. It is still insufficient to form a coat layer on the surface of the carrier.
JP-A-9-269614 JP-A-8-62902

  The object of the present invention is to prevent the spent toner from being used for a long period of time and to improve the adhesion and mechanical strength between the core surface of the carrier and the coating layer, and to peel off the coating layer in view of the conventional technology as described above. An object of the present invention is to provide a carrier that can maintain stable performance.

  The above object is achieved by the electrophotographic carrier according to the present invention. That is, the carrier for electrophotography of the present invention comprises the following constitution or means, and solves the above problems. (1) A coat layer made of a composite plating film containing a resin is provided on the surface of the core material of the carrier. (2) The resin in the composite plating film is composed of fluororesin fine particles. (3) After the composite plating film is formed on the surface, heat treatment is performed.

That is, the present invention provides an electrophotographic carrier in which a coat layer is provided on the surface of a core material of a carrier, wherein the coat layer is composed of a composite plating film containing a resin, and the resin in the composite plating film is a fluororesin The carrier for electrophotography, which is made of fine particles, is heat-treated after the composite plating film is formed on the surface, and the temperature of the heat treatment is 370 ° C to 380 ° C.

By forming a composite plating film containing resin on the surface of the core material of the carrier, the adhesion between the coating layer and the core material is increased, and the mechanical strength is increased, so that the coating layer will not peel off due to long-term use. , Can maintain stable performance. By including the resin, it is possible to prevent the spent phenomenon of bets toner. In addition, the composite plating film contains a fluorine resin having good releasability with respect to the toner, thereby preventing the toner from becoming spent. Further, since these resins are composed of fine particles, the resin component can be uniformly dispersed in the plating solution forming the composite plating film, and the characteristics of the coating layer can be stabilized. The composite plating film subjected to the heat treatment is excellent in hardness and water repellency and is effective in preventing toner spent and preventing the coat layer of the carrier from peeling off.

  According to the present invention, it is possible to obtain an electrophotographic carrier having high developing ability, effectively preventing toner spent on the carrier surface, and having excellent charging ability over a long period of time.

The best mode for carrying out the present invention will be described.
Hereinafter, preferred embodiments of the electrophotographic carrier according to the present invention will be described in detail. FIG. 1 is a schematic sectional view of an electrophotographic carrier according to an embodiment of the present invention. The carrier is formed by forming a composite plating film 2 on the surface of the core material 3, and the composite plating film 2 has a structure in which resin fine particles 22 are dispersed and contained in a matrix metal 21.

  The core material is not particularly limited within the scope of the present invention, and conventionally known materials can be used, for example, metals such as iron, cobalt and nickel, and alloys and compounds such as magnetite, hematite and ferrite. Can be mentioned. The average particle diameter of the carrier core material is generally 10 to 300 μm, preferably 30 to 150 μm.

  The following method is illustrated as a method of forming a composite plating film on the core material. The plating process is usually completed by degreasing the base material, washing with acid and then water, performing the plating process, washing with water again and drying. In the case of performing the heat treatment, the heating is performed for a certain time thereafter.

  In general, the fluororesin contained in the composite plating film includes polytetrafluoroethylene (hereinafter referred to as “PTFE”), tetrafluoroethylene-hexafluoropropylene copolymer (hereinafter referred to as “FEP”), tetrafluoroethylene-perfluoro. There are alkyl vinyl ether copolymers (hereinafter referred to as “PFA”), polychlorotrifluoroethylene (hereinafter referred to as “PCTFE”), tetrafluoroethylene-ethylene copolymers (hereinafter referred to as “ETFE”) and the like. Features such as excellent lubricity, slidability (low friction), non-adhesiveness and the like can be obtained.

  Among these, as the fluororesin contained in the plating layer used in the present invention, PTFE is preferable from the viewpoint of toner releasability and non-adhesiveness.

  All of the fluororesins used in the present invention are known substances, and the raw materials, production methods, and the like are not particularly limited. In the present invention, the above fluororesins may be used alone or in combination of two or more. Even when two or more kinds of fluororesins are used in combination, the mixing ratio thereof is not particularly limited and can be arbitrarily selected.

  By depositing these fluororesin fine particles together with the metal on the surface of the base material to form a composite plating film, the releasability with respect to the toner is good and the wear of the sliding surface can be reduced.

  For the matrix in the composite plating film of the present invention, for example, nickel, silver, copper, iron, zinc, tin, lead, cadmium, palladium, noble metals and the like are used. Moreover, nonmetallic elements, such as phosphorus and boron, may be contained.

  When the matrix contains one or more kinds of metals or nonmetals, the content of other metals or nonmetals in the composite plating is not particularly limited as long as the effect of the present invention can be obtained. Based on the total weight of the matrix in the composite plating film, it is usually 10% by weight or less, preferably about 5% by weight or less.

  In the formation of the composite plating film in the present invention, a known electroless plating method and electrolytic plating method capable of precipitating a matrix metal on the surface of the substrate can be employed. It is preferable in terms of easy formation and low cost. In addition, as for the plating solution to be used, various types of plating solutions containing a metal as a matrix and other metals or non-metals as required are known. Can also be used.

  In the present invention, the particle size of the fine particles of the fluororesin added to the plating solution for forming the composite plating film (hereinafter referred to as “composite plating solution”) is not particularly limited, but the film of the entire composite plating film If the thickness is smaller than the thickness, particles are less likely to be detached from the plating surface due to friction or the like, so it is desirable to use fine particles smaller than the layer thickness of the composite plating film.

  Although the film thickness of the composite plating film by this invention can be suitably set according to the material, shape, etc. of a base material, it is 0.1 micrometer-5 micrometers normally, Preferably it is 0.3 micrometer-3 micrometers. If the thickness is less than 0.1 μm, the composite plating film is fragile, so that it is easily worn or peeled off by friction with the toner. Further, when the thickness of the composite plating film is greater than 5 μm, it may be difficult to maintain the carrier characteristics.

  Accordingly, the particle diameter of the fluororesin fine particles contained in the composite plating film may be determined in consideration of the thickness of the composite plating film, but usually 0.1 μm to 5 μm and 0.2 μm to 1 μm are more preferable. If the particles are less than 0.1 μm, the particles are likely to aggregate in the plating solution, and uniform dispersion is difficult. On the other hand, when particles larger than 5 μm are used, there arises a problem that the particles are detached from the plating surface of the fine particles in the plating solution.

  The addition amount of the fluororesin fine particles in the composite plating film is not particularly limited, and varies depending on the desired resistance of the carrier, resistance of the core material used, resistance of the toner, and the like. In addition, the above-described resistance value varies depending not only on the addition amount but also on the thickness of the composite plating film and the size of the resin fine particles.

  Since the composite plating solution for forming the composite plating film according to the present invention is required to uniformly disperse the fluororesin fine particles having very high water repellency in the plating solution and make it completely wet, A surfactant is used. As the surfactant, for example, a water-soluble cationic system, a non-ionic system, and a double-sided surfactant exhibiting cationicity at the pH value of the plating solution can be used.

  The plating conditions may be appropriately determined according to the material of the core material used as the base material and the type of the composite plating solution to be used, etc., and generally the same liquid temperature, pH value as employed in the normal composite plating method, What is necessary is just to select from current density etc.

  In addition, in order that the composite plating film in this invention may improve adhesiveness with the core material used as a base material, after forming a well-known base plating layer on a core material, a composite plating film is formed.

  The method for producing an electrophotographic carrier of the present invention is to coat the surface of the core material of the carrier with the composite plating solution. Specifically, the spin spray method of spraying the plating solution onto the surface of the core material, Immersion method in which the carrier core is floated by flowing air, fluidized bed method in which the plating solution is sprayed, a reactor method in which the carrier core surface and the plating solution are reacted in a reaction vessel, and the reaction solution is an ultrasonic horn Examples include an ultrasonic excitation method that stirs and disperses in a wet coating method such as a kneader coater method in which a carrier core material and a solution for forming a film layer are mixed in a kneader coater, and a solvent is removed. However, other means than the above may be used.

  Another embodiment of the present invention includes heat-treating the composite plating film formed as described above. The heat treatment is preferably performed at 150 ° C. to 400 ° C., more preferably 200 ° C. to 400 ° C. If the temperature of the heat treatment is less than 150 ° C., it must be heated for a long time in order to obtain the effect, and if it is higher than 400 ° C., the characteristics of the fluororesin may be affected.

  The heat treatment time is not particularly limited, but is usually about 10 minutes to 1.5 hours, preferably about 1 hour.

  Hereinafter, the results of image formation using the above-described electrophotographic carrier will be described in detail with reference to examples.

  Example 1 will be described. The surface of the ferrite particles (average volume particle diameter = 50 μm, manufactured by Powdertech Co., Ltd.) is subjected to a base treatment, and a nickel-phosphorus plating containing 30 vol% of 0.2 μm PTFE particles is used to form a core surface film thickness of 1 μm. Then, a plating process was performed to obtain an electrophotographic carrier.

  A second embodiment will be described. The carrier produced in Example 1 was heat-treated at 380 ° C. for 30 minutes to obtain an electrophotographic carrier.

  A third embodiment will be described. The surface of the magnetite particles (average volume particle diameter = 60 μm, manufactured by Kanto Denka Kogyo Co., Ltd.) was subjected to a ground treatment, and then the coating thickness of the core surface by a nickel-phosphorus plating containing 25 vol% of 0.5 μm PTFE particles. Was plated to give an electrophotographic carrier.

  Example 4 will be described. The carrier manufactured in Example 3 was heat-treated at 370 ° C. for 40 minutes to obtain an electrophotographic carrier.

  Comparative Example 1 will be described. The ferrite particles used in Example 1 were used as carriers without being coated.

  Comparative example 2 will be described. The ferrite particles used in Example 1 were coated with a resin composed of toluene, a perfluoroacrylate copolymer, a copolymer of methacrylate and dimethylaminoethyl methacrylate by a kneader coater method, and the film thickness on the core surface was 0. An 8 μm electrophotographic carrier was obtained.

  Comparative Example 3 will be described. The magnetite particles of Example 3 were coated with a film made of toluene and silicone resin using a fluid coating apparatus, and then heat treated at 150 ° C. for 2 hours to obtain an electrophotographic carrier having a core surface film thickness of 1 μm.

  Using the various carriers in Examples 1 to 4 and Comparative Examples 1 to 3 and a magenta toner (average volume particle diameter = 6.4 μm) mainly composed of a polyester resin, images and carriers are evaluated by the following means. It was.

  As an image forming method, a toner is introduced into a developing device of a process cartridge for a laser beam printer (trade name: AR-270, manufactured by Sharp Corporation), and the process cartridge is attached to the laser beam printer. 30,000 image drawing tests were performed at room temperature of 25 ° C. and humidity of 50%.

  The evaluation method was as follows.

Initial image A 1-dot toner image was formed under image forming conditions capable of forming 600 dot images per inch, and the toner image was enlarged and visually evaluated. A case where the dot shape is good is indicated by “◯”, a case where the dot shape is not a problem is indicated by “Δ”, and a case where the toner is scattered or the shape is bad is indicated by “X”.

The difference in whiteness before and after fog printing was measured using a whiteness meter (Hunter whiteness meter, manufactured by Nippon Denshoku Industries Co., Ltd.), and the value at which the difference was maximum was shown. In the fog density measurement method, whiteness of A4 size white paper is measured in advance with a whiteness meter (Hunter Whiteness Meter, manufactured by Nippon Denshoku Industries Co., Ltd.), and this value is taken as the first measurement value. Next, three copies are made using a manuscript including a white circle having a diameter of 55 mm, and the white portion of the obtained image sample is measured with the above-mentioned whiteness meter, and this value is set as a second measurement value. A value obtained by subtracting the value of the second measurement value from the first measurement value is set as the fog value. When this value was less than 0.4, “◯” was evaluated, “0.4” when 0.4 or more and less than 1.0, and “×” when 1.0 or more.

Charging rise characteristics Developers replenished with new toner are agitated and mixed in the developing machine, and the charge application speed for the replenished toner is obtained from the charge amount fluctuation value during the agitation time, and ranking is performed. evaluated. “◎” when the rise of the charge is very good, “◯” when the level is satisfactory, “△” when the level is practically usable, and “X” when the level is not usable. It was.

Adhesion of toner component Each developer after 30,000 continuous image drawing tests are collected, and the toner adhering to the surface is removed by air blow, and then a certain amount of the remaining carrier is dispersed in toluene. The supernatant was collected and the amount of the eluted toner component was evaluated. For the evaluation of the adhered matter, an unused carrier was used as a comparison, and the difference between the visible light transmittance in the supernatant liquid collected by the same method and the visible light transmittance of the collected sample was calculated as the amount of the toner component adhered to the surface. Each sample was evaluated as a relative difference. In addition, a spectrophotometer U-3310 (manufactured by Hitachi High-Technologies Corporation) was used for measuring the transmittance.

Detachment of the film on the carrier surface Collect the developer after the completion of the 30,000 continuous image printing test, remove the toner adhering to the surface by air blow, and observe the remaining carrier surface with a scanning electron microscope. The coated film was examined for wear or peeling. The observation was performed using a scanning electron microscope S-2500 (manufactured by Hitachi High-Technologies Corporation). “○” indicates that the film on the carrier surface is hardly worn or peeled off, “△” indicates that the streaks are conspicuous but not peeled, and “×” indicates that the core material of the carrier is seen due to peeling. did.

  The evaluation results (A) to (E) and the overall evaluation results are shown in FIG. The electrophotographic carriers of Examples 1 to 4 all had good characteristics and good overall evaluation with respect to initial images, fogging, rising of charge, adhesion of toner components, and peeling of the film on the carrier surface. On the other hand, the characteristics of the carriers of Comparative Examples 1 to 3 were normal or bad, and the overall evaluation was normal or poor.

  As described in the above embodiments, the present invention forms a film with a composite plating containing a resin on the surface of the carrier, thereby providing high image quality, excellent chargeability for toner, and preventing toner spent over a long period of time. In addition, a durable electrophotographic carrier can be obtained.

Sectional drawing of the carrier for electrophotography of this invention. The figure explaining the characteristic of the carrier of an Example and a comparative example.

Explanation of symbols

2 Composite plating film 21 Matrix metal 22 Resin fine particles 3 Core material

Claims (1)

In the carrier for electrophotography in which a coat layer is provided on the surface of the core material of the carrier,
The coating layer is made of a composite plating film containing a resin, and the resin in the composite plating film is made of fluorine resin fine particles, and after the composite plating film is formed on the surface, the heat treatment is performed. The temperature for the electrophotographic carrier is 370 ° C. to 380 ° C.

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