JP2009282209A - Coated carrier, developer, developing device, image forming apparatus, and method for manufacturing the coated carrier - Google Patents

Abstract

The present invention provides a coated carrier that can suppress a decrease in transport amount due to a change in carrier shape over time and can maintain high-quality output over a long period of time.
A carrier 1 of the present invention is a coated carrier having a wearable carrier core material 6 and a coating layer 7 covering the carrier core material 6, and a surface of the carrier core material 6 is partially exposed. . Then, the shape factor (SF-2) of the carrier core material 6 is set as the first shape factor, the shape factor (SF-2) of the initial carrier 1 is set as the second shape factor, and the carrier core material of the initial carrier 1 is set. When the shape factor (SF-2) of the coated carrier changed by the wear of the coating layer 7 and the coating layer 7 is the third shape factor, the first shape factor is 120 or more and 150 or less, and the second shape factor The ratio of the third shape factor to is 90% or more. As a result, the wear balance of the resin-coated portion that forms the recess can be optimized and the shape factor over time can be prevented from decreasing, so that the decrease in developer transport amount can be suppressed.
[Selection] Figure 1

Description

  The present invention relates to a coated carrier, a developer, a developing device, an image forming apparatus, and a method for producing a coated carrier. More specifically, the present invention relates to an electron that develops and visualizes an electrostatic latent image formed on an image carrier. The present invention relates to a carrier used in a photographic system, a developer using the carrier, a developing device, an image forming apparatus, and a method for manufacturing a coated carrier.

  In an image forming apparatus using electrophotographic technology such as a printer or a copying machine, a developer for developing an electrostatic latent image formed on an image carrier and forming a visible image is used. . Conventionally, a two-component developer composed of toner and carrier and a one-component developer composed of toner alone are used as the developer. Among these developers, the magnetic brush development method using a two-component developer is widely used because it is superior in image quality and capable of high-speed printing as compared with other development methods.

  By the way, an image forming apparatus using a magnetic brush developing system includes a developer carrier that carries a two-component developer and an image carrier that forms an electrostatic latent image. The developer carrier is configured to include a cylindrical metal sleeve and a magnet roller provided therein. Note that permanent magnets, which are magnetic field generating means, are arranged on the magnet roller so that the north and south poles are alternately arranged.

  In such an image forming apparatus, a visible image is formed by the following method. First, the two-component developer is carried on the surface of the metal sleeve of the developer carrying member, and only the metal sleeve is rotated while the magnet roller is fixed. As a result, the two-component developer can be transported to the development area that is the area facing the image carrier. Thereafter, only a charged toner is electrostatically attached to the image carrier by a developing electric field applied between the developer carrier and the image carrier, so that a visible image is formed.

  The metal sleeve of the developer carrying member for carrying the developer is intended to assist the carrying force due to the magnetic attraction force of the magnet roller and to apply a mechanical carrying force that realizes securing and stabilizing the necessary carrying amount. . As a metal sleeve that requires such an object, for example, a configuration in which irregularities are formed by sandblasting the surface, or a configuration in which grooves are formed at an equal pitch in the sleeve axial direction is generally used. Is. Here, sufficient development performance is realized by appropriately setting the surface roughness of the sandblasting surface, groove opening width, groove depth, groove pitch, etc. according to the carrier particle size, particle shape, particle size distribution, etc. Developer transportability can be obtained.

  However, even if a sufficient transport amount can be obtained in the initial state, in the development unit, a regulation that regulates the friction between the metal sleeve and the developer, the friction between the developer particles, and the layer thickness of the developer on the metal sleeve. Mechanical agitation stress such as friction between the blade and the developer occurs. For this reason, the metal sleeve and the developer (carrier) are deteriorated, and the conveyance amount is reduced with time. Further, since the amount of toner transport used for development is relatively reduced, there is a problem that image resolution is lowered, image density is lowered, and image density unevenness is caused.

  In order to solve the above problems, attempts have been made to improve the surface shape of the metal sleeve and prevent the developer transport amount from changing with time. For example, in Patent Document 1, a plurality of grooves having a V-shaped cross section extending in a direction orthogonal to the movement direction are provided on the surface of the developer carrying member, and the inner wall surface of each groove is positioned on the upstream side in the movement direction of the surface. A technique is disclosed in which an inclination angle formed between the upstream slope and the virtual plane passing through the apex of the groove and perpendicular to the moving direction of the surface is 45 ° or more and 60 ° or less. Patent Document 2 discloses a technique in which a large number of elliptical concave portions are randomly provided on the outer surface of a developer carrier.

  In addition, the decrease in the developer conveyance amount due to the deterioration of the developer (carrier) described above is due to the change in the shape of the carrier over time. The mechanical conveying force that is generated is reduced. The change in the particle shape accompanying the use over time depends on the change over time in the irregularities formed on the surface of the carrier particles in the initial state, and the shape is determined by the progress of wear deterioration of the convex portions and the concave portions. Therefore, maintaining the surface shape of the carrier at the initial stage and the surface unevenness with respect to the increase in the number of printed sheets is extremely important in order to suppress the change (decrease) in the developer conveyance amount with time.

  The shape of a particle such as a carrier is mainly defined by a shape factor, and is quantified using (SF-1) calculated by Formula 1 and (SF-2) calculated by Formula 2.

  (SF-1) indicates the degree of roundness of the particles, and (SF-2) indicates the degree of unevenness of the particles.

Accordingly, here, the initial value of (SF-2) and the change over time are treated in order to pay attention to the change over time of the unevenness of the particles as a factor governing the change in the developer transport amount. As a prior art that defines (SF-2), for example, in Patent Document 3, the carrier core material is a ferrite carrier coated with a resin, and the shape factor (SF-2) is 120 to 150, and A technique is disclosed in which the resin amount is 0.01 to 10.0% by weight with respect to the carrier core material. In Patent Document 4, the shape factor (SF-2) of the carrier core material is 1.15 to 1.70, and the shape factor (SF-2) of the carrier particles after the resin coating layer is formed is 1.05 to 1.70. 30 is disclosed (however, (SF-2) dealt with in this document is a value that is not multiplied by 100 in Equation 2 above), and values based on Equation 2 are 115 to 170, respectively. And 105 to 170.)
JP 2004-21043 A (published January 22, 2004) JP 2007-86091 A (published April 5, 2007) JP 2007-148452 A (published on June 14, 2007) JP-A-8-292607 (published on November 5, 1996)

  As described above, a two-component developer held on the surface of the developer carrying member to prevent a decrease in image resolution, a decrease in image density, uneven image density, etc. and maintain a high-quality image output over a long period of time It is a very important issue to stabilize the transport amount.

  However, with the technique disclosed in Patent Document 1, a sufficient initial conveyance amount can be secured, and a decrease in the conveyance amount due to toner fixation in the V-shaped groove can be prevented. However, it is impossible to prevent a decrease in the conveyance amount due to a change in the shape of the carrier.

  Further, in the technique disclosed in Patent Document 2, although the decrease in the transport amount due to wear of the dent formed on the surface of the developing sleeve can be prevented, the transport accompanying the change in the shape of the carrier as in Patent Document 1 described above. It is not possible to prevent a decrease in the amount.

  Further, in the technique disclosed in Patent Document 3, the toner particles are prevented from scattering and the high image density is realized by ensuring sufficient toner charging performance by reducing the resistance, high specific surface area, and specific gravity of the carrier particles. Yes. However, no countermeasure has been taken against changes with time in the carrier particle shape, and it is impossible to prevent a decrease in the conveyance amount due to the shape change. Further, when estimated from (SF-2) after resin coating and the amount of resin coating, a carrier whose SF-2 of the carrier core exceeds 150 is included. With such a carrier, there is a concern that a decrease in the initial transport amount accompanying a decrease in bulk density and a scratch on the surface of the photoreceptor may be caused. Further, when the amount of the coating resin is relatively small, the resin coating layer is thin, so that the refreshing effect of the charging site using the resin layer scraping is lost with time, and the toner charging ability is lowered. For this reason, there is a concern that the image quality deteriorates. On the other hand, when the amount of the coating resin is relatively large, since the resin coating layer is thick, the resin film is not scraped off, and the toner charging ability is lowered due to the influence of toner spent or external additive contamination. As a result, as with the case where the amount of the coating resin is relatively small, there is a concern that the image quality is degraded.

  Further, in the technique disclosed in Patent Document 4, on the side where the shape factor of the carrier core material is relatively large, there is a risk of causing a decrease in the conveyance amount and generation of scratches on the photosensitive member, as in Patent Document 3. Moreover, in the coated carrier set to the shape factor disclosed in Patent Document 4, the thickness of the coated resin layer tends to increase. For this reason, similarly to the above-mentioned Patent Document 3, the resin layer is not scraped, and the charging ability of the toner is reduced. In addition, no measures are taken against changes with time in the particle shape, and there is a possibility that the transport amount may deteriorate with time.

  The present invention has been made in view of the above-described problems, and its object is to suppress a decrease in the conveyance amount due to a change in the shape of a carrier over time and to reduce a toner charge amount over time and a photoreceptor. An object of the present invention is to provide a coated carrier, a developer, a developing device, an image forming apparatus, and a method for producing a coated carrier that can maintain high-quality output over a long period of time by preventing generation of scratches on the surface.

  As a result of intensive studies, the present inventor has been effective in suppressing the decrease in the carrier shape factor (SF-2) in order to maintain the developer transport amount when the carrier is used over time. It has been found that it is effective to expose a part of the surface and maintain a balance between the degree of wear of the exposed part of the core material and the degree of abrasion of the resin layer by the exposed part of the core material. And in order to achieve optimization of film shaving, it discovered that it was important to set the film thickness (resin amount) of a coating resin layer in an appropriate range.

  That is, in order to solve the above problems, the coated carrier according to the present invention has a wearable carrier core material and a coating layer covering the carrier core material, and a part of the surface of the carrier core material is exposed. In the coated carrier, the carrier core material shape factor (SF-2) is the first shape factor, the initial coated carrier shape factor (SF-2) is the second shape factor, and the initial coated carrier carrier. When the shape factor (SF-2) of the coated carrier changed by the wear of the core material and the coating layer is the third shape factor, the first shape factor is 120 or more and 150 or less, and the second shape factor The ratio of the third shape factor to is 90% or more. Here, “abrasion” means “a property of being abraded by agitation stress in the developing device”.

  According to the above configuration, by partially exposing the carrier core material, the effect of scraping off the coating layer and refreshing the toner spent or toner external additive adhering to the coating layer can be obtained, and the charging ability for the toner can be maintained. Can be planned. Further, according to the above configuration, since the ratio of the third shape factor to the second shape factor is 90% or more, surface smoothing caused by uniform wear of the carrier core material and the coating layer Can be prevented. This prevention action can suppress a decrease in the developer conveyance amount. That is, since the progress of film scraping of the coating layer can be optimized, the unevenness of the carrier surface can be maintained, and a decrease in developer transport amount with time can be prevented. Further, according to the above configuration, since the first shape factor is 120 or more and 150 or less, the initial developer conveyance amount can be secured.

  Therefore, according to the above configuration, it is possible to realize a coated carrier that suppresses a decrease in the conveyance amount due to a change in shape of the carrier over time and prevents a decrease in toner charge amount over time and generation of scratches on the surface of the photoreceptor. be able to. Furthermore, this makes it possible to maintain high image quality output over a long period of time.

  In the coated carrier according to the present invention, the coating layer is made of a coating resin composition, and the coating amount of the coating resin composition on the carrier core material is 0.5 to 100 parts by weight with respect to 100 parts by weight of the carrier core material. The amount is preferably 1.5 parts by weight.

  When the coating amount of the coating resin composition is 0.5 parts by weight or less, the shaving margin of the coating layer is small, and when the number of printed sheets exceeds the specified amount, the effect of refreshing the toner spent or toner external additive adhesion is lost. At the same time, the coating layer forming the recess is lost. For this reason, only the carrier core material which forms a convex part is worn out, and unevenness | corrugation is no longer maintained. Therefore, the conveyance amount decreases with time.

  On the other hand, when the coating amount of the coating resin composition is 1.5 parts by weight or more, the elasticity of the coating layer appears remarkably, and the progress of shaving is slowed down. For this reason, the exposed portion of the carrier core material that forms the convex portion is worn, while the coating layer that forms the concave portion is not scraped. Therefore, the unevenness of the carrier surface layer is lost over time, and the transport amount of the developer is reduced.

  Therefore, as described above, by setting the coating amount of the coating resin composition on the carrier core material to 0.5 to 1.5 parts by weight with respect to 100 parts by weight of the carrier core material, unevenness on the surface of the carrier Can be maintained, and a decrease in the developer transport amount with time can be prevented.

  In the coated carrier according to the present invention, the coating resin composition preferably contains a silicone resin.

  According to said structure, since the coating layer formed in the carrier core material surface can be equalize | homogenized, the distribution of the shape factor of each carrier becomes sharp, and the conveyance unevenness of a developer can be prevented. Further, since the wear of the coating layer accompanying the increase in the number of printed sheets can be made uniform, the spread of the shape factor distribution over time can be suppressed, and the unevenness of the conveyance amount can be prevented.

  In the coated carrier according to the present invention, the content of the silane coupling agent is preferably 2 to 5 parts by weight with respect to 100 parts by weight of the coating resin composition.

  As in the above configuration, the coating layer can be made uniform by optimizing the content of the silane coupling agent. When the content of the silane coupling agent is 2 parts by weight or less, the aggregation of the resins becomes remarkable, the film thickness of the coating layer becomes thin, and the coating layer becomes non-uniform. On the other hand, when the content of the silane coupling agent is 5 parts by weight or more, the added silane coupling agent becomes excessive, and during the resin coating, the carrier core material and the coating resin composition solution are mixed. The coating resin composition adheres to the wall surface of the container used for stirring. For this reason, the malfunction that sufficient covering amount cannot be obtained with respect to a carrier core material generate | occur | produces.

  Moreover, in the coated carrier which concerns on this invention, it is preferable that the average particle diameter of a coated carrier is 35 micrometers or more and 55 micrometers or less.

  According to the above configuration, by setting the average particle diameter to 35 μm or more, a uniform coating layer can be formed and the toner charge amount distribution becomes sharp, so that high image quality can be achieved. Further, since a sufficient magnetic restraining force acts, it is possible to prevent carrier adhesion to the photoreceptor. Further, by setting the average particle size to 55 μm or less, a sufficient amount of toner can be secured on the surface and a sufficient toner conveyance amount can be obtained, so that high-resolution image formation is possible.

  The developer according to the present invention is characterized by containing a toner and the above-described coated carrier.

  As a result, it is possible to realize a developer that suppresses a decrease in the conveyance amount due to a change in the shape of the carrier over time, and prevents a decrease in toner charge amount over time and generation of scratches on the surface of the photoreceptor. Furthermore, this makes it possible to maintain high image quality output over a long period of time.

  In order to solve the above-described problems, a developing device according to the present invention has a developing unit that stores a developer, and development that visualizes an electrostatic latent image formed on an image carrier with toner contained in the developer. An apparatus is characterized in that the developer is stored in the developing unit.

  By using the developer, it is possible to realize a developing device that can maintain a high-quality image output over a long period of time.

  An image forming apparatus according to the present invention is characterized in that the developing device is mounted in order to solve the above-described problems.

  As a result, it is possible to realize an image forming apparatus that can maintain high-quality output over a long period of time.

  Moreover, in order to solve said subject, the manufacturing method of the coated carrier which concerns on this invention has a carrier core on the surface of the abradable carrier core material whose 1st shape factor (SF-1) is 120-150. It is characterized in that a wearable coating layer is formed so that a part of the surface of the material is exposed.

  As a result, it is possible to realize a coated carrier that suppresses a decrease in the conveyance amount due to a change in the shape of the carrier over time, and prevents a decrease in toner charge amount over time and generation of scratches on the surface of the photoreceptor.

  In the method for producing a coated carrier according to the present invention, the coating layer may be formed by coating 0.5 to 1.5 parts by weight of the coating resin composition with respect to 100 parts by weight of the carrier core material. preferable. Thereby, the unevenness | corrugation of the carrier surface manufactured can be maintained, and the fall of the developer conveyance amount with time can be prevented. In particular, when the coating layer is formed by an immersion method, the unevenness of the carrier surface can be kept high.

  As described above, the coated carrier according to the present invention uses the shape factor (SF-2) of the carrier core material as the first shape factor, and the shape factor (SF-2) of the initial coated carrier as the second shape. When the shape factor (SF-2) of the coated carrier changed by the wear of the carrier core material and the coating layer of the initial coated carrier is the third shape factor, the first shape factor is 120 or more and 150. This is a configuration in which the ratio of the third shape factor to the second shape factor is 90% or more.

  Further, the developer according to the present invention is configured to contain the toner and the coated carrier as described above.

  In addition, the developing device according to the present invention has a configuration in which the developer is stored in the developing unit as described above.

  In addition, the image forming apparatus according to the present invention is configured to include the developing device as described above.

  Moreover, the manufacturing method of the coated carrier which concerns on this invention is the surface of a carrier core material on the surface of the abradable carrier core material whose 1st shape factor (SF-1) is 120-150, as mentioned above. This is a configuration in which a wearable coating layer is formed so that a part of the surface is exposed.

  Therefore, high-quality output can be achieved over a long period of time by suppressing a decrease in the conveyance amount due to a change in the shape of the carrier over time, and preventing a decrease in the charge amount of the toner over time and scratches on the surface of the photoreceptor. Can be maintained.

  One embodiment of the present invention will be described below with reference to FIGS. In addition, this shows one embodiment, and the present invention is not limited to this. The developer according to this embodiment is a two-component developer 3 including a coated carrier 1 and a toner 2 coated with a silicone resin. Hereinafter, toner, carrier, and developer will be described in this order. In the following description, unless it is described as particles, it refers to the entire toner and the entire carrier.

(Toner 2)
The toner 2 shown in FIG. 1 forms an image by adhering to a medium such as paper, and includes a binder resin and a colorant as essential ingredients. In addition, the toner 2 may contain a charge control agent, a release agent, a fluidity improver, and the like in addition to the essential components. Further, two or more types of external additives 5 having different particle diameters are added to the toner core 4 serving as a base material.

  The binder resin is not particularly limited, and a known binder resin for black toner or color toner can be used. Examples thereof include polyester resins, polystyrene, styrene resins such as styrene-acrylic acid ester copolymer resins, acrylic resins such as polymethyl methacrylate, polyolefin resins such as polyethylene, polyurethane, and epoxy resins. Moreover, you may use resin obtained by mixing a raw material monomer mixture with a mold release agent and performing a polymerization reaction. Binder resin may be used individually by 1 type, and may use 2 or more types together.

  Here, when a polyester resin is used as the binder resin, examples of the aromatic alcohol component for obtaining the polyester resin include bisphenol A, polyoxyethylene- (2.2) -2,2-bis (4- Hydroxyphenyl) propane, polyoxyethylene- (2.0) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene- (2.0) -2,2-bis (4-hydroxyphenyl) propane , Polyoxypropylene- (2.2) -polyoxyethylene- (2.0) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene- (6) -2,2-bis (4- Hydroxyphenyl) propane, polyoxypropylene- (2.2) -2,2-bis (4-hydroxyphenyl) propane, polyoxyp Examples include pyrene- (2.4) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene- (3.3) -2,2-bis (4-hydroxyphenyl) propane, and derivatives thereof. It is done.

  The polybasic acid component of the polyester resin includes succinic acid, adipic acid, sebacic acid, azelaic acid, dodecenyl succinic acid, n-dodecyl succinic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic Acid, cyclohexanedicarboxylic acid, orthophthalic acid, isophthalic acid, terephthalic acid and other dibasic acids, trimellitic acid, trimethic acid, pyromellitic acid and other acids and their anhydrides and lower alkyl esters From the viewpoint of heat-resistant aggregation, terephthalic acid or its lower alkyl ester is preferred.

  Here, the acid value of the polyester resin constituting the toner 2 is preferably in the range of 5 to 30 mgKOH / g. When the acid value is less than 5 mgKOH / g, the charging characteristics of the resin are lowered, and the charge control agent is hardly dispersed in the polyester resin as described later. This may adversely affect the charge amount stability of repeated development due to rising of the charge amount or continuous use of the electrophotographic toner 3. On the other hand, when the acid value exceeds 30 mgKOH / g, the environmental stability of the charge amount is deteriorated, and the decrease in the charge amount becomes remarkable particularly in a high temperature and high humidity environment.

  As the colorant, various colorants can be used depending on the desired color. For example, a colorant for yellow toner, a colorant for magenta toner, a colorant for cyan toner, a colorant for black toner, and the like. Can be mentioned.

  Specifically, examples of the colorant for yellow toner include C.I. I. Pigment yellow 1, C.I. I. Pigment yellow 5, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 15, C.I. I. Azo pigments such as CI Pigment Yellow 17; inorganic pigments such as yellow iron oxide and ocher; I. Nitro dyes such as Acid Yellow 1, C.I. I. Solvent Yellow 2, C.I. I. Solvent Yellow 6, C.I. I. Solvent Yellow 14, C.I. I. Solvent Yellow 15, C.I. I. Solvent Yellow 19, C.I. I. Examples thereof include oil-soluble dyes such as Solvent Yellow 21.

  Examples of the colorant for magenta toner include C.I. I. Pigment red 49, C.I. I. Pigment red 57, C.I. I. Pigment red 81, C.I. I. Pigment red 122, C.I. I. Solvent Red 19, C.I. I. Solvent Red 49, C.I. I. Solvent Red 52, C.I. I. Basic Red 10, C.I. I. Disperse Red 15 etc. are mentioned.

  Examples of the colorant for cyan toner include C.I. I. Pigment blue 15, C.I. I. Pigment blue 16, C.I. I. Solvent Blue 55, C.I. I. Solvent Blue 70, C.I. I. Direct Blue 25, C.I. I. Direct Blue 86 and the like can be mentioned.

  Examples of the colorant for black toner include carbon black such as channel black, roller black, disk black, gas furnace black, oil furnace black, thermal black, and acetylene black. From these various types of carbon black, an appropriate carbon black may be appropriately selected according to the design characteristics of the toner to be obtained.

  As the colorant, in addition to these pigments, a red pigment, a green pigment, or the like may be used. A coloring agent may be used individually by 1 type, and may use 2 or more types together. Two or more of the same color can be used, and one or more of the different colors can also be used.

  The form of the colorant is not limited as long as it can be colored. For example, it is used in the form of a masterbatch. The master batch of the colorant can be produced in the same manner as a general master batch. For example, it can be produced by kneading a melt of a synthetic resin and a colorant to uniformly disperse the colorant in the synthetic resin, and then granulating the resulting melt-kneaded product. As the synthetic resin, the same kind as that of the toner binder resin or one having good compatibility with the toner binder resin is used. At this time, the use ratio of the synthetic resin and the colorant is not particularly limited, but is preferably 30 to 100 parts by weight with respect to 100 parts by weight of the synthetic resin. The master batch is granulated to a particle size of about 2 to 3 mm.

  The amount of the colorant used is not particularly limited, but is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the binder resin. This is not the amount of the master batch but the amount of the colorant itself contained in the master batch. By using the colorant in this range, an image having a high image density and a very good image quality can be formed without impairing various physical properties of the toner.

  The release agent is for improving the peelability between the paper and the fixing roller when the toner is fixed on the paper. As such a release agent, those commonly used in this field can be used, for example, petroleum wax such as paraffin wax and derivatives thereof, microcrystalline wax and derivatives thereof, Fischer-Tropsch wax and derivatives thereof, polyolefin wax and Derivatives thereof, low molecular weight polypropylene wax and derivatives thereof, hydrocarbon-based synthetic waxes such as polyolefin polymer waxes (such as low molecular weight polyethylene wax) and derivatives thereof, carnauba wax and derivatives thereof, rice wax and derivatives thereof, candelilla wax And their derivatives, plant waxes such as wood wax, animal waxes such as beeswax and spermaceti, synthetic fat waxes such as fatty acid amides and phenol fatty acid esters, long chain carboxylic acids and Derivatives, long chain alcohols and derivatives thereof, silicone polymers, such as higher fatty acids. Derivatives include oxides, block copolymers of vinyl monomers and waxes, graft modified products of vinyl monomers and waxes, and the like. The amount of the release agent used is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

  As the external additive 5 of the toner base material 4, those commonly used in this field can be used, and examples thereof include silicon oxide, titanium oxide, silicon carbide, aluminum oxide, and barium titanate. In the present embodiment, two or more kinds of external additives having different particle diameters are used in combination, and at least one kind of primary particle diameter is 0.1 μm or more. When an external additive having at least one kind of primary particle diameter of 0.1 μm or more is used, particularly in a color toner, transferability is improved, and charging due to adhesion of the external additive to the carrier surface is reduced. The toner 2 can be charged for a long time and stably without causing it. The amount of external additive 5 used is not particularly limited, but is preferably 0.1 to 3.0 parts by weight with respect to 100 parts by weight of toner 2.

  The raw materials of the toner base material 4 are mixed by a mixer such as a Henschel mixer, a super mixer, a mechano mill, and a Q-type mixer, excluding external additives, and a raw material mixture obtained is a twin-screw kneader, a single-screw kneader, After being melt-kneaded at a temperature of about 70 to 180 ° C. by a kneader such as a continuous two-roll kneader, the mixture is cooled and solidified. The melt-kneaded material of the raw material of the toner 2 after cooling and solidification is roughly pulverized by a cutter mill, a feather mill or the like. The resulting coarsely pulverized product is finely pulverized. For fine pulverization, a jet mill, a fluidized bed type jet pulverizer, or the like is used. These pulverizers pulverize the toner particles by causing the toner particles to collide with each other by colliding the air flow containing the toner particles from a plurality of directions. Thereby, a non-magnetic toner having a specific particle size distribution can be produced. The particle diameter of the toner base material 4 is not particularly limited, but the average particle diameter is preferably in the range of 5 to 7 μm. Furthermore, particle size adjustment such as classification may be performed as necessary. The external additive 5 is added to the toner base material 4 thus manufactured by a known method. The manufacturing method of the toner 2 is not limited to the above.

(Carrier 1)
In the carrier 1 of this embodiment, the first shape factor (SF-2) of the carrier core material 6 is 120 or more and 150 or less in order to secure a necessary amount of the initial amount of developer held on the surface of the developer carrier. It is said.

  When the first shape factor (SF-2) is less than 120, the unevenness of the carrier surface is reduced and the mechanical transportability of the developer is lowered, so that a sufficient initial transport amount cannot be obtained. In addition, since the carrier core material 6 has few convex portions, the resin coating film cannot be sufficiently refreshed, and the surface is smoothed due to accumulation of toner spent and external attachment to the concave portions. The amount will decrease.

  On the other hand, when the first shape factor (SF-2) exceeds 150, the shape of the carrier core material 6 becomes extremely needle-like, and the particles become brittle. For this reason, the particles cannot withstand the particle agitation stress at the time of image formation, causing problems such as cracking and breaking. In addition, since the bulk density of the particles is reduced, there arises a problem that a sufficient transport amount cannot be obtained.

  Hereinafter, the relationship between the first shape factor (SF-2) of the carrier core material 6 and the initial transport amount of the two-component developer 3 will be further described in detail. FIG. 2 is a diagram showing the relationship between the shape factor (SF-2) of the carrier core material 6 and the initial transport amount.

  The “allowable limit” shown in FIG. 2 defines a conveyance amount necessary for obtaining a sufficient image density and image resolution and preventing image density unevenness from occurring. More specifically, with respect to image density, image resolution, and density unevenness measured based on examples described later, an image quality of 1.4 or more, image resolution of less than 5 μm, and density unevenness of less than 0.05 is allowed. It is the limit value to do. Further, the “target value” means an initial transport amount of the developer that is a target in the initial stage of the development process in order to obtain a developer transport amount of an allowable limit value. If an initial transport amount equal to or greater than the target value is obtained for the developer, the transport amount exceeding the allowable limit can be realized even if the carrier is used over time (continuous use).

Note that the target value of the conveyance amount differs depending on the process configuration (for example, toner adhesion to the carrier, development conditions, transfer efficiency, fixability, etc.) used for image output. In FIG. 2, a carrier core material 6 having a plurality of different shape factors is used as the carrier 1, and 1.5 parts by weight of resin is coated on 100 parts by weight of each carrier core material. Further, the target value is set to 55 mg / cm ² and the allowable limit is set to 45 mg / cm ² .

As can be seen from FIG. 2, for the developer 3, 55 mg / cm ² is required as a target value for the initial transport amount in order to obtain a transport amount that exceeds the allowable limit of 45 mg / cm ² after the carrier 1 is used over time. And in order to exceed the target value 55 mg / cm < ² > of initial conveyance amount, it is necessary to set (SF-2) of the carrier core material 6 to 120 or more and 150 or less.

  Further, the carrier 1 of the present embodiment uses the initial shape factor (SF-2) of the initial carrier 1 as the second shape factor in order to suppress a decrease in the transport amount of the developer 3 due to continuous use. The ratio of the third shape factor to the second shape factor when the shape factor (SF-2) of the carrier 1 changed by the wear of the carrier core material 1 and the coating layer 7 is the third shape factor. Is 90% or more.

  “Initial carrier 1” refers to the carrier 1 immediately after the coating layer 7 is formed on the carrier core material 6. When the coating layer 7 is formed on the carrier core material 6, the shape factor (SF-2) of the carrier 1 is different from the first shape factor (SF-2) of the carrier core material 6. In the present embodiment, the surface of the carrier core material 6 is partially exposed in the initial carrier 1. The second shape factor is the shape factor (SF-2) of the “initial carrier 1”.

  When such an initial carrier 1 is used over time, the carrier core material 6 and the coating layer 7 are worn, and the shape of the carrier 1 changes. The third shape factor is the shape factor (SF-2) of the carrier 1 whose shape has changed.

  The ratio of the third shape factor to the second shape factor is preferably 90% or more, and the higher the better. This ratio means that the unevenness on the surface of the carrier 1 is maintained as the ratio is large, and the unevenness on the surface of the carrier 1 is lost and the smoothing is advanced as the ratio is small. Since the ratio of the third shape factor to the second shape factor is 90% or more, the wear balance between the exposed portion of the carrier core material 6 that forms the convex portion and the coating layer 7 that forms the concave portion is maintained. It is. Thereby, the fall of the conveyance amount of the developer 3 resulting from continuous use can be suppressed. On the other hand, when the ratio of the third shape factor to the second shape factor is less than 90%, the wear balance between the exposed portion of the carrier core material 6 that forms the convex portion and the coating layer 7 that forms the concave portion is maintained. Therefore, the exposed portion of the carrier core material 6 is worn relatively much, which is not preferable.

  Here, a method for measuring the shape factor (SF-2) will be described. The shape factor (SF-2) is expressed by the following mathematical formula 2.

  The shape factor (SF-2) can be calculated by measuring the projected perimeter and the projected area of each particle, as shown in Formula 2, and is widely used as a value expressing the degree of unevenness of the particle. It is an evaluation value.

  The shape factor (SF-2) of the carrier 1 in the present embodiment is a coefficient calculated based on an image analysis method for quantitatively analyzing the projection area and the projection perimeter of a particle image photographed by a scanning electron microscope with high accuracy. is there. More specifically, a particle image observed with an electron microscope (product model number: VE-9800, manufactured by Keyence Corporation) was image-analyzed and measured by an image measurement application (VE-H2A: manufactured by Keyence Corporation). The projection perimeter and the projection area of each particle were derived by applying Equation 2. In addition, the average value of the shape factor (SF-2) of 300 particles is applied to the shape factor (SF-2) handled in this embodiment.

  As the carrier core material 6, those commonly used in this field can be used, and examples thereof include magnetic metals such as iron, copper, nickel and cobalt, and magnetic metal oxides such as ferrite and magnetite. When the carrier core material 6 is a magnetic material as described above, the carrier 1 suitable for a developer used in the magnetic brush development method can be obtained. The average particle diameter of the carrier core material 6 is preferably in the range of 25 to 70 μm.

  Moreover, the manufacturing method of the carrier core material 6 which implement | achieves the said 1st shape factor will not be specifically limited if it is a conventionally well-known method. For example, the manufacturing method demonstrated below is mentioned.

  First, the magnetic metal or magnetic metal oxide which is a component of the carrier core material 6 is finely pulverized (a fine pulverization step). Water, a binder resin, and a dispersant are added to the pulverized product to form a slurry. Thereafter, the slurry is wet-pulverized and dried to obtain a granulated product. In the process so far, the shape factor largely reflects the first stage fine pulverization process, which determines the size of the agglomerates which are the minimum units constituting the granulated product.

  Next, the obtained granulated material is calcined and finely pulverized again to form a slurry similar to the above. Then, the particles of the carrier core material 6 are obtained by performing the crushing process through the main granulation and the main baking.

  Here, the particle size of the carrier core material 6 is determined by the degree of crushing in the crushing step. Further, the surface shape of the core material can be manipulated from a complete spherical shape to an indeterminate shape by changing the size of the agglomerates and the conditions for the main firing.

  The resin of the coating resin composition constituting the coating layer 7 on the surface of the carrier core material 6 contains conductive fine particles. There is no limitation in particular as resin contained in the resin composition for coating | cover, A well-known thing can be used. Use of a silicone resin leads to better results from the point that both the releasability with the toner 2 and the adhesion with the carrier core material 6 can be achieved.

  The silicone resin is not particularly limited, and a silicone resin commonly used in this field can be used, but a cross-linked silicone resin is preferable. The cross-linked silicone resin is a known silicone resin that is cured by crosslinking between hydroxyl groups bonded to Si atoms or a hydroxyl group and a group -OX by a heat dehydration reaction, a room temperature curing reaction, or the like, as shown in the following chemical formula.

  As the crosslinkable silicone resin, either a heat curable silicone resin or a room temperature curable silicone resin can be used. In order to crosslink the thermosetting silicone resin, it is necessary to heat the resin to about 200 to 250 ° C. Heating is not necessary to cure the room temperature curable silicone resin, but it is preferable to heat at 150 to 280 ° C. in order to shorten the curing time.

  Among the cross-linked silicone resins, those in which the monovalent organic group represented by R is a methyl group are preferable. Since the cross-linked silicone resin in which R is a methyl group has a dense cross-linked structure, when the coating layer 25 is formed using the cross-linked silicone resin, a carrier 1 having good water repellency and moisture resistance can be obtained. . However, if the cross-linked structure becomes too dense, the coating layer 7 tends to become brittle, so selection of the molecular weight of the cross-linked silicone resin is important.

  Moreover, it is preferable that the weight ratio (Si / C) of silicon and carbon in the crosslinkable silicone resin is 0.3 to 2.2. If Si / C is less than 0.3, the hardness of the coating layer 7 may decrease, and the carrier life and the like may decrease. On the other hand, when Si / C exceeds 2.2, the charge imparting property of the carrier 1 to the toner 2 is easily affected by the temperature change, and the coating layer 7 may become brittle.

  When a crosslinkable silicone resin is used for the coating resin composition, a commercially available product can be used. Examples of commercially available cross-linked silicone resins include SR2400, SR2410, SR2411, SR2510, SR2405, 840RESIN, 804RESIN (all trade names, manufactured by Toray Dow Corning Co., Ltd.), KR271, KR272, KR274, KR216, KR280, KR282. , KR261, KR260, KR255, KR266, KR251, KR240, KR155, KR152, KR214, KR220, X-4040-171, KR201, KR5202, KR3093 (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.), etc. . One type of cross-linked silicone resin may be used alone, or two or more types may be used in combination.

  As the conductive fine particles, for example, fine particles such as conductive carbon black and conductive titanium oxide are used. Carbon black is suitable for developing conductivity with a small addition amount, but for color toners, there is concern about the detachment of carbon particles from the surface of the resin-coated carrier. As a result, the quality of the developed image is degraded. In such a case, conductive titanium oxide doped with antimony is useful.

  Further, the carrier 1 may contain a silane coupling agent for the purpose of adjusting the charge amount to the toner 2 and making the coating layer 7 uniform. More specifically, a silane coupling agent having an electron donating functional group is preferably used. Specific examples of the silane coupling agent include amino group-containing silane coupling agents. A well-known thing can be used as an amino group containing silane coupling agent, For example, what is represented by the following General formula (1) can be used.

(Y) nSi (R) m (1)
(In the formula, m R represents the same or different alkyl group, alkoxy group or chlorine atom. N Y represents a hydrocarbon group containing the same or different amino group. M and n are 1 to 3 respectively. (Where m + n = 4).
In the general formula (1), examples of the alkyl group represented by R include a straight chain having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group. Examples thereof include a chain or branched alkyl group. Among these, a methyl group, an ethyl group, etc. are preferable. Examples of the alkoxy group include linear or branched alkoxy groups having 1 to 4 carbon atoms such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, and a tert-butoxy group. . Among these, a methoxy group, an ethoxy group, etc. are preferable. Examples of the hydrocarbon group containing an amino group represented by Y include the following formulas:
- _(CH 2) a-X
(Wherein, X represents an amino group, an aminocarbonylamino group, an aminoalkylamino group, a phenylamino group or a dialkylamino group, and a represents an integer of 1 to 4),
-Ph-X
(Wherein, X is the same as described above, and -Ph- represents a phenylene group).

  Specific examples of the amino group-containing silane coupling agent include the following.

H ₂ N (H ₂ C) ₃ Si (OCH ₃ ) _3,
H ₂ N (H ₂ C) ₃ Si (OC ₂ H ₅ ) _{3,
H 2 N (H 2 C)} 3 Si (CH 3) (OCH 3) 2,
_{H 2 N (H 2 C)} 2 HN (H 2 C) 3 Si (CH 3) (OCH 3) 2,
H ₂ NOCHN (H ₂ C) ₃ Si (OC ₂ H ₅ ) _3,
H ₂ N (H ₂ C) ₂ HN (H ₂ C) ₃ Si (OCH ₃ ) _{3,
H 2 N-Ph-Si (} OCH 3) 3 ( wherein -Ph- indicates a p- phenylene group),
Ph-HN (H ₂ C) ₃ Si (OCH ₃ ) ₃ (wherein Ph- represents a phenyl group),
(H ₉ C ₄ ) ₂ N (H ₂ C) ₃ Si (OCH ₃ ) ₃
An amino group containing silane coupling agent may be used individually by 1 type, or may use 2 or more types together. The amount of the amino group-containing silane coupling agent used is appropriately selected from a range in which sufficient charge is imparted to the toner 2, the coating layer 7 can be made uniform, and the mechanical strength is not significantly reduced. The amount is preferably 10 parts by weight or less, more preferably 2 to 5 parts by weight, based on 100 parts by weight of the resin contained in the coating resin composition.

  The coating resin composition can contain other resins together with the silicone resin as long as the preferable properties of the coating layer formed of the silicone resin (particularly, the cross-linked silicone resin) are not impaired. Examples of other resins include epoxy resins, urethane resins, phenol resins, acrylic resins, styrene resins, polyamides, polyesters, acetal resins, polycarbonates, vinyl chloride resins, vinyl acetate resins, cellulose resins, polyolefins, and copolymers thereof. Examples thereof include resins and compounded resins.

  The coating resin composition may contain a bifunctional silicone oil in order to further improve the moisture resistance, releasability, and the like of a coating layer formed of a silicone resin (particularly a cross-linked silicone resin).

  The coating resin composition can be produced by mixing predetermined amounts of a silicone resin and an aminosilane coupling agent and the like, and if necessary, an appropriate amount of a resin other than the silicone resin and an additive such as a bifunctional silicone oil. As one form of the resin composition for coating, a form of a solution in which the above components are dissolved in an organic solvent can be mentioned. The organic solvent is not particularly limited as long as it can dissolve the silicone resin. For example, aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, and higher alcohols. And a mixed solvent of two or more of these.

  If this solution resin composition for coating (hereinafter referred to as “coat resin solution”) is used, a coating layer can be easily formed on the surface of the carrier core which is the core material of the carrier. For example, a coating resin solution is applied to the surface of the carrier core to form a coating layer, and the organic solvent is volatilized and removed from the coating layer by heating or decompression and a combination thereof, and the coating layer is heat cured or simply cured during or after drying. By doing so, a coating layer is formed, and a resin-coated carrier is manufactured.

  Examples of methods for applying the coating resin liquid onto the carrier core surface include an immersion method in which the carrier core is impregnated with the coating resin liquid, a spray method in which the coating resin liquid is sprayed on the carrier core, and a carrier core that is in a floating state by a flowing air current. Examples thereof include a fluidized bed method in which a coating resin solution is sprayed. Among these, the dipping method is preferable because film formation can be easily performed.

  Here, in order to suitably apply the resin to the surface of the carrier core, it is necessary to balance both the precipitation of the resin caused by solvent evaporation and the curing of the silicone resin and the incorporation of the additive into the resin. is there. These vary greatly depending on the heating temperature, the amount of reduced pressure, and the like, but a certain amount of time is required for that purpose. Therefore, a curing accelerator may be used for drying the coating resin solution. Organic compound catalysts such as tin compounds, aluminum compounds, and titanium compounds, which have high capabilities as curing accelerators for silicone resins, can be used. However, if a tin compound is used in the resin coating, the coating resin solution cures too fast, making it difficult to form a uniform coating film, and also causing the added fine particles to be deposited outside the coating resin. End up. In addition, since the resin coating becomes extremely hard compared to the case where other curing catalysts are used, the effective coating effect of the coating film due to the friction between the particles of the resin-coated carrier Cannot be obtained. In order to balance the precipitation of such additives and the curing of the resin, it is desirable to use an aluminum compound or titanium compound curing catalyst that does not react too quickly. These curing catalysts are preferably contained in an amount of 0.2 to 5 parts by weight with respect to 100 parts by weight of the coating resin solution.

  Thermosetting of the coating layer applied after coating is performed while selecting a heating temperature according to the type of silicone resin. For example, it is preferable to carry out by heating to about 150 to 280 ° C. Of course, when the silicone resin is a room temperature curable silicone resin, heating is not necessary, but for the purpose of improving the mechanical strength of the resin coating layer to be formed, shortening the curing time, and the like. You may heat to about degreeC. However, in order not to impair the homogenizing effect of the resin coating layer 25 possessed by the aminosilane coupling agent, it is more preferable that the heating temperature be equal to or lower than the boiling point of the aminosilane coupling agent to be used.

  The coating amount of the coating resin is based on 100 parts by weight of the carrier core material in consideration of ensuring the refreshing effect of the resin coating layer, preventing the carrier surface from being smoothed, and ensuring the film scraping performance of the coating layer. It may be adjusted to 0.5 to 1.5 parts by weight, preferably 0.5 to 1.0 parts by weight, and it is desirable that the surface of the core material is partially exposed.

  The average particle size of the carrier 2 thus obtained is preferably 45 μm or less. The carrier 2 preferably has a high electrical resistance and a spherical shape, but the effect of the present invention is not lost even if it is conductive or non-spherical.

(Developer)
The developer 3 is manufactured by mixing the carrier 1 and the toner 2. The mixing ratio of the toner 2 and the carrier 1 is not particularly limited. However, considering that the two-component developer 1 is used in a high-speed image forming apparatus (40 sheets / minute or more for an A4 size image), the mixing ratio of the toner 2 and the carrier 1 may be adjusted as follows. That's fine. That is, in the developer 3 in which the volume average particle diameter of the carrier 1 / the volume average particle diameter of the toner 2 is 5 or more, the total projected area of the toner 2 relative to the total surface area of the carrier 1 (total surface area of all carrier particles) The ratio (total projected area of toner particles) (total projected area of toner / total surface area of carrier × 100) may be adjusted to be 30 to 70%.

  As a result, the toner 2 is stably maintained in a state where the chargeability is sufficiently good. Therefore, the developer 3 containing such toner 2 can form a high-quality image stably and for a long time even in a high-speed image forming apparatus. For example, for the developer 3 in which the volume average particle diameter of the toner 2 is 6.5 μm and the volume average particle diameter of the carrier 1 is 90 μm, the ratio of the total projected area of the toner 2 to the total surface area of the carrier 1 is 30 to 70%. At this time, the mixing ratio of the toner 2 and the carrier 3 in the developer 3 is a ratio that the toner 2 includes about 2.2 to 5.3 parts by weight with respect to 100 parts by weight of the carrier 3. When high-speed development is performed using such a developer 3, the amount of toner 2 transported and the amount of toner 2 supplied to the developing tank of the developing device in accordance with the amount of toner 2 consumed are maximized. However, the supply and demand balance of the toner 2 is not impaired. When the amount of the carrier 1 in the developer 3 is larger than 2.2 to 5.3 parts by weight, the charge amount tends to be lower. Therefore, not only the desired development characteristics cannot be obtained, but also the consumption amount of the toner 2 is larger than the supply amount of the toner 2, so that a sufficient charge cannot be applied to the toner 2 and the image quality is deteriorated. On the other hand, when the amount of the carrier 1 is small, the charge amount tends to be high, and it becomes difficult to separate the toner 2 from the carrier 1 due to the electric field, resulting in degradation of image quality.

  In this embodiment, the total projected area of the toner 2 is calculated as follows. The specific gravity of the toner 2 is set to 1.0, and calculation is performed based on the volume average particle diameter obtained with a Coulter counter (trade name: Coulter Counter Multisizer II, manufactured by Beckman Coulter, Inc.). That is, the number of toners with respect to the weight of the toner 2 to be mixed is calculated, and the number of toners × the toner area (calculated assuming a circle) is defined as the total toner projected area. Similarly, the surface area of the carrier 1 is calculated from the weight of the carrier 1 to be mixed based on the particle diameter obtained from Microtrac (trade name: Microtrac MT3000, manufactured by Nikkiso Co., Ltd.). The specific gravity of the carrier 1 at this time is 4.7. The mixing ratio is calculated by the total toner projected total area / carrier total surface area × 100 obtained above.

(Developing device 30 and image forming apparatus)
The developing device 30 of this embodiment performs development using the developer 3 of this embodiment described above. As shown in FIG. 3, the developing device 30 includes a developing unit 31 that stores the developer 3, and a developer carrier (developer carrying carrier) 32 that conveys the developer 3 to the image carrier 35.

  In the developing unit 31, a developer 3 composed of a carrier 1 and a toner 2 is put in advance. The developer 3 is stirred and charged by the stirring screw 34. Inside the developer carrier 32, magnetic field generating means is disposed. The developer 3 is transported to the developer carrier 32 by the magnetic field generated from the magnetic field generating means, and is held on the surface of the developer carrier 32. In this way, the developer 3 held on the surface of the developer carrier 32 is regulated to a constant layer thickness by the developer regulating member 33, and the adjacent region between the developer carrier 32 and the electrostatic latent image carrier 35. Is conveyed to the development area formed in the step. An electric field due to a developing bias is formed between the developer carrier 32 and the image carrier 35. This electric field is an oscillating electric field formed by applying an AC bias voltage. By this electric field, the toner 2 of the developer 3 on the developer carrier 32 is electrically attached to the electrostatic latent image pattern on the image carrier 35. Thereby, the electrostatic latent image pattern on the electrostatic latent image carrier 35 is visualized (reversal development method).

  Further, consumption of the toner 2 is detected by the toner density sensor 36. When the toner 2 is consumed by development, the toner 2 is replenished from the toner hopper 37 by the consumed amount. The toner density sensor 36 detects that the toner density in the developing unit 31 has reached a predetermined specified toner density. The replenishment of the toner 2 from the toner hopper 37 is performed until the toner density sensor 36 detects that the specified toner density is reached. In this way, the concentration of the toner 2 contained in the developer 3 in the developing unit 31 is kept substantially constant so as to be a predetermined specified toner concentration.

  The image forming apparatus of this embodiment includes the developing device 30. For other configurations, a known electrophotographic image forming apparatus can be used. For example, an image carrier having a photosensitive layer capable of forming an electrostatic image on the surface, and charging for charging the surface of the image carrier to a predetermined potential. From the developing device 30, an exposure unit that irradiates the surface of the image carrier with signal light corresponding to the image information to form an electrostatic charge image (electrostatic latent image) on the surface of the image carrier. A transfer means for transferring the toner image on the surface of the image carrier developed by supplying the toner 2 to the intermediate transfer body and then transferring it to the recording medium; a fixing means for fixing the toner image on the surface of the recording medium to the recording medium; A cleaning unit that removes toner, paper dust, and the like remaining on the surface of the image carrier after the transfer of the toner image to the recording medium, and a cleaning unit that removes excess toner adhered to the intermediate transfer member. .

  When developing an electrostatic charge image, a developing process for developing the electrostatic charge image on the image carrier 35 by reversal development is performed for each toner color, and a plurality of toners having different colors are formed on the intermediate transfer member. A multicolor toner image is formed by superimposing the images. In this embodiment, an intermediate transfer method using an intermediate transfer member is employed, but a configuration in which a toner image is directly transferred from an image carrier to a recording medium may be used.

  By using the image forming apparatus of this embodiment, it is possible to stably maintain the charge amount of the toner and to output a high-quality image over a long period of time.

  Examples and comparative examples according to the present invention will be described below. The present invention is not limited to this example unless it exceeds the gist.

(Development of developer)
First, a developer (two-component developer) obtained by mixing the toner and the carrier used in this example and the comparative example will be described.

The toner was manufactured as follows. Using polyester as the main resin, a pigment, a release agent, and a charge control agent (manufacturer: Nippon Carlit Co., Ltd., product name: LR-147) are melt-kneaded, pulverized and classified, and then subjected to a volume average particle size of 100 nm and 12 nm. A magenta toner (non-magnetic magenta toner) having a negative charge property with a volume average particle diameter of 6.7 μm and externally added two types of hydrophobized silica was prepared. The charge control agent LR-147 used here has the substance name “Boro bis (1.1-diphenyl-1-oxo-acetyl) potassium salt”, and the chemical formula is represented by C ₂₈ H ₂₀ BKO ₆ .

  On the other hand, the carrier was manufactured as follows. Mn-Mg based ferrite (Manufacturer: DOWA IP Creation Co., Ltd., saturation magnetization 65 emu / g, average particle size φ43 μm, shape factor (SF-2) 120 to 150) is used as a carrier core material (core material), and this is electrically conductive Particles (conductive agent) (manufacturer: Fuji Dye Co., Ltd., product name: 9-19-1), aminosilane coupling agent (manufacturer: Toray Dow Corning Co., Ltd., product name: AY43-059) are internally added and dispersed. Silicone Resin A (Manufacturer: Shin-Etsu Chemical Co., Ltd., product name: KR-240) and Silicone Resin B (Manufacturer: Shin-Etsu Chemical Co., Ltd., product name: KR-251) are equal in amount and 100 parts by weight of carrier core material A total of 0.25 to 2.0 parts by weight with respect to the carrier core material was coated by the dipping method. Thereafter, after a curing process with a curing temperature of 200 ° C. and a curing time of 1 hour, the carrier (magnetic carrier) was produced by sieving with a sieve having an opening of 150 μm. The carrier core material has a partial surface exposed portion 40 as shown in FIG. 4 in order to have an effect of refreshing the toner spent and the toner external additive adhesion to the resin coating layer. While maintaining the charging ability, it is possible to suppress a decrease in the transport amount of the developer by preventing the surface from being smoothed.

Incidentally, each density of each particle, the carrier 4.7 g / cm ^3, the toner is 1.0 g / cm ^3. The coating method is not limited to the dipping method, and other coating methods such as a spray method and a fluidized bed method may of course be used.

  For comparison, a plurality of resin-coated carriers shown in Table 1 were prepared using a plurality of carrier core materials having different shape factors and different coating resin amounts. Each carrier shown in Table 1 contains 2 parts by weight of the aminosilane coupling agent in 100 parts by weight of the silicone resin in the coating resin.

  In addition, a core material having a shape factor (SF-2) = 121 and a carrier with a resin coating amount of 2.0 parts by weight were produced together. However, the aggregation of the carriers was remarkably significant, and the coating resin layer Since the thickness was extremely uneven, it was excluded from the evaluation and comparison.

  Furthermore, in order to examine the influence of the content of the aminosilane coupling agent contained in the coating resin, the carriers shown in Table 2 were also produced. Here, the shape factor (SF-2) of the core material was 133, and the coating resin amount was 1.0 part by weight. The exposure rate of the core material in Table 2 means that the surface area of the particles after the silicone resin is coated on the surface of the carrier core material is S1, and the total area of the background of the core material exposed on the particle surface is S2. It is a value derived by S2 / S1 × 100. The measurement method of the exposure rate of the core material will be described in detail. A particle image taken with a scanning electron microscope (product model number: VE-9800, manufactured by Keyence Corporation) is image analysis software (product name: A image-kun, Asahi Kasei). By detecting the core exposed parts scattered on the particle surface and measuring the individual areas using Engineering Co., Ltd., and calculating the ratio of the total to the projected area of the particles, the individual core material exposure rate Asked. In addition, the average value of the exposure rate of 100 particle | grains is applied to the exposure rate handled in a present Example.

  As shown in Table 2, this time, the amount of the aminosilane coupling agent contained in the coating resin was set to 0 to 10.0 parts by weight with respect to 100 parts by weight of the coating resin. Even if it is too much, it can be seen that the exposure rate of the core material is increased, the covering state of the resin layer is deteriorated, and the surface exposure of the core material background becomes remarkable. When the content is too small, the aggregation of the resins becomes remarkable, the film thickness of the resin coating layer becomes thin, and the coating layer becomes non-uniform. On the other hand, if the content is too large, it will be excessively added, and the resin will adhere to the wall surface of the iron-based container used for mixing / stirring the carrier core material and the coating resin solution during resin coating. This is because a sufficient resin coating amount cannot be obtained. For this reason, in the use of an amine coupling agent for the purpose of stably forming the coating resin layer, it is extremely important to optimize the content.

  In the two-component developer obtained by mixing the toner and the carrier, the toner weight mixing ratio (hereinafter referred to as toner concentration) in the total weight of the developer is set to 8 wt%, and the resin cylindrical container is filled with the above-described toner. After adding the toner and the carrier, the mixture was stirred by mixing on a biaxially driven polybottle rotating base at 200 rpm for 1 hour.

(Evaluation of developer transport amount)
Next, using a plurality of two-component developers produced under the above-described conditions, the test conditions and measurement conditions of the continuous printing test performed when confirming the change over time of the developer transport amount on the developer carrier are described. To do.

  Using a plurality of types of two-component developers produced under the above-described conditions, an aging test was conducted by continuous image printing using a digital multifunction machine with a printing rate of 5%. For the test, a digital full color multifunction machine MX-7001N (printing speed: <color> 50 ppm, <monochrome> 70 ppm) manufactured by Sharp Corporation was used. In this apparatus, in the developing unit that stores the developer 3, the developer 3 is stirred and charged by the stirring screw 34 as shown in FIG. 3. The developer 3 is transported to the developer carrier 32 having a magnet roller serving as a magnetic field generating means disposed therein, so that the developer 3 is held on the surface of the developer carrier 32 by a magnetic restraining force and a mechanical restraining force. The Next, the two-component developer 3 held on the surface of the developer carrying member 32 is regulated to a constant layer thickness by the developer regulating member 33, and a magnetic brush is formed at the opposing portion between the developer carrying member 32 and the image carrying member 35. And a bias voltage obtained by superimposing the DC bias voltage on the AC bias voltage is applied to the developer carrier 32, so that an electrostatic latent image formed on the surface of the image carrier 35 by a charging unit and an exposure unit (not shown). A visible image is formed by attaching only toner to the toner. In this apparatus, the surface of the image carrier 35 is charged to a negative potential by the charging unit, and exposure is performed only in the region where the toner is adhered by the exposure unit.

  Here, the DC bias value of the bias voltage applied to the developer carrying member 32 in the aging test is appropriately changed according to the charge amount of the toner in each developer, so that the image density of the solid image becomes a specified value. It was adjusted. The potential difference between the non-image area potential on the image carrier 35 and the developer carrier 32 was 200V.

  The toner consumption due to the visible image formation is detected by the toner density sensor 36 as a change in toner density, which is a toner weight ratio with respect to the developer weight, and the consumed amount has reached a predetermined specified toner density. This is replenished from the toner hopper 37 until the toner concentration sensor 36 detects that the toner concentration in the two-component developer 3 inside the developing unit 30 is kept substantially constant. In this apparatus, the gap between the developer carrier 32 and the developer regulating member 33 is 0.65 [mm], and the gap between the developer carrier 32 and the image carrier 35 in the development region is 0.4 [mm]. ] Was set. Of course, it is not limited to this value. The developer carrier 32 is an aluminum cylindrical sleeve provided with a plurality of V-shaped grooves in the surface axis direction. The diameter is 25 mm, and the number of V-shaped grooves is 50.

The developer carrying amount on the surface of the developer carrying member 32 is measured by measuring the developer weight in a specified area at a total of three locations with respect to the axial direction of the developer carrying member 32, and calculating the average value for each carrying amount. Defined. In addition, the measurement area per location at this time was 2.3 cm ² .

(Career comparison)
When an aging test with a printing rate of 5% under the above conditions is performed, the evaluation results of the characteristics of the developer using each carrier described above and the shape factor (SF) after the test in the idling deterioration test for each carrier alone Table 3 shows the ratio of -2) to the shape factor before the test.

  Here, the evaluation criteria for each characteristic were defined as follows.

(1) Image density: Evaluated by an average value measured at a plurality of solid images using a spectral densitometer X-Rite 939 (manufactured by X-Rite).
◎: 1.6 or more ○: 1.5 or more and less than 1.6 Δ: 1.4 or more and less than 1.5 ×: less than 1.4 (2) Density unevenness: Measurement at a plurality of solid images by a spectral densitometer X-Rite 939 Evaluation is based on the standard deviation σ of the value.
A: 0.025 or less B: 0.025 or more and less than 0.05 Δ: 0.05 or more and less than 0.1 ×: 0.1 or more (3) Image resolution (thin line reproducibility): Personal image quality evaluation system PIAS- Evaluated by standard deviation σ of multiple measured values of line width according to II (QEA). (Evaluated with a line of about 40 μm width corresponding to an image resolution of 600 dpi.)
A: 3 μm or less B: 3 μm or more and less than 5 μm Δ: 5 μm or more and less than 7 μm x: 7 μm or more (4) Overall image quality evaluation ◎: No deterioration in image quality from the beginning.
○: Image quality is slightly inferior to the initial level, but acceptable level.
Δ: Image quality deterioration exceeds an allowable level.
X: Image quality is significantly deteriorated and cannot be used.

  In any case, since the carry amount has been stable since the aging number of 20k (20,000) regardless of the carrier used, any measurement value other than the shape factor and the evaluation are at the end of aging of the 20k sheet. Results are shown. Moreover, even when any of the carriers in Examples 1 to 9 and Comparative Examples 1 to 5 was used, both the transport amount and the image quality exceeded the target level in the initial stage.

As shown in Table 3, the ratio of the shape factor (SF-2) after the test in the idling deterioration test to the shape factor before the test is 90% or more in the examples, and 90% or more in the comparative examples. It becomes. The larger the ratio is, the more the unevenness of the carrier surface is maintained, and the smaller the ratio is, the more the unevenness is lost and the smoothing of the surface is progressing. Therefore, in the example, the wear balance of the carrier core material exposed part forming the convex part and the resin coating part forming the concave part is maintained, and in the comparative example, the carrier core material exposed part forming the convex part is maintained. It can be said that wear is dominant. As shown in Table 3, in the comparative example, the image quality is lower than 45 mg / cm ² which is the allowable limit value of the conveyance amount shown in FIG. It can be seen that the image quality can be maintained.

  As described above, by using a carrier in which the ratio of the shape factor (SF-2) after the test in the carrier idling deterioration test to the shape factor before the test is 90% or more, the developer conveyance amount is decreased with respect to the increase in the number of printed sheets. It can be seen that the image quality can be suppressed and the deterioration of the image quality can be prevented.

  This time, the coating amount of the resin covering the surface of the carrier core material is set to 0.25 to 2.0 parts by weight with respect to 100 parts by weight of the core material, and any resin amount exceeds the allowable image quality even after the number of printed sheets is increased. It was confirmed. However, as the results of Comparative Example 1 (0.25 parts by weight), Comparative Example 3 (0.25 parts by weight), and Comparative Example 5 (2.0 parts by weight) show, 0.25 parts by weight and 2.0 parts by weight. In some cases, depending on the combination with the shape factor (SF-2) of the carrier core material, there may be a condition below the allowable image quality level. Therefore, as shown in Table 4, 0.5 to 1.5 parts by weight that are not affected by the shape factor (SF-2) of the carrier core material is more preferable as the coating resin amount.

  Next, Table 5 shows the results of examining the influence of the content of the aminosilane coupling agent contained in the coating resin using a plurality of carriers shown in Table 2. In this evaluation as well, any measurement value other than the shape factor and the evaluation show the results at the end of 20k sheet aging. In the initial stage, except for Comparative Example 6, both the transport amount and the image quality exceeded the target level. In Comparative Example 6, the image density exceeded the target level, but the coating resin layer was not uniform. Therefore, the density unevenness and the image resolution were below the target level.

  As shown in Table 5, in Comparative Examples 6 to 8, the transport amount is insufficient and sufficient image quality is not obtained. This is because the surface of the carrier core material is much exposed and the film thickness of the resin coating layer is thin, so the wear speed of the resin coating part that forms the recesses is increased while the wear of the core material exposed part that forms the protrusions progresses. This is because the unevenness is lost over time and the carrier surface is smoothed. In particular, in Comparative Example 6 that does not contain an aminosilane coupling agent, the image quality is particularly deteriorated, and considering the image quality failure in the initial state described above, the inclusion of the aminosilane coupling agent results from the stable formation of the coating resin layer. It can be said that it is essential to maintain image quality. On the other hand, in Example 5 (2 parts by weight of coupling agent) and Example 10 (5 parts by weight of the same), it can be seen that a sufficient transport amount is obtained and high image quality can be maintained. Here, the coating resin amount of the carrier was 1.0 part by weight, but the same tendency was obtained even when the coating resin amount was 0.5 parts by weight and 1.5 parts by weight. As mentioned above, it is necessary to contain an aminosilane coupling agent in the coating resin layer of a carrier, Preferably, the content is 2-5 weight part with respect to 100 weight part of coating resin.

  The carrier core material used in the above has an average particle diameter of 43 μm, but it is preferable that the average particle diameter is not less than 35 μm and not more than 55 μm in view of improving image quality. This is because when a particle having a small particle size of 35 μm or less is used, the so-called carrier adhesion occurs in which the magnetic binding force on the surface of the developer carrier proportional to the cube of the particle diameter is insufficient and the carrier is attracted to the image carrier. This is because image defects are caused. Further, since the fluidity of the carrier particles decreases, the resin does not spread evenly on the surface of the carrier particles during resin coating, and the resin coating layer becomes non-uniform, resulting in a broad toner charge amount distribution, image unevenness and image It causes fogging. Further, when the particle diameter is 55 μm or more, the total surface area per unit weight is smaller than that of a carrier having a small particle diameter, so that the amount of toner transport is relatively reduced, and the image resolution is lowered. This is because reproducibility is lowered.

  Table 6 shows the results of quantitative evaluation of the tendencies explained above. Here, regarding the carrier adhesion, the number of carriers adhered in a fixed area (297 mm × 24 mm) in the non-image portion on the image carrier was measured. As a result of the evaluation, the case where the number of adhered particles was 20 or less was evaluated as “◯”, the case where the number was 20 to 40 was evaluated as “Δ”, and the case where the number was 40 or more was evaluated as “X”. For image fogging, the image density in the non-image area is measured with a spectral densitometer X-Rite 939, and the measured value is 0.05 or less, and the one with 0.05 to 0.06. “Δ”, 0.06 or more was evaluated as “x”. The image unevenness and fine line reproducibility were the same as the evaluation method described above.

  As shown in Table 6, the average particle size is preferably 35 μm or more and 55 μm or less, and more preferably 35 μm or more and 45 μm or less.

  The coated carrier according to the present invention can be expressed as follows.

  That is, the coated carrier according to the present invention has a coating layer made of a silicone-based resin on the surface, and the carrier core material is partially exposed after the silicone resin coating. In the coated carrier that wears the coating layer, the shape factor (SF-2) of the carrier core material is 120 or more and 150 or less, and the coating amount of the silicone resin on the carrier core material is 0. 0 parts by weight with respect to 100 parts by weight of the carrier core material. It can be expressed as 5 to 1.5 parts by weight.

  As a result, as the number of printed sheets increases, the wear balance between the exposed portion of the carrier core material that forms the convex portion of the carrier surface and the resin-coated portion that forms the concave portion can be optimized, and the shape factor over time can be reduced. Since it can prevent, the fall of a developer conveyance amount can be suppressed. Therefore, it is possible to prevent a decrease in image resolution, a decrease in image density, uneven image density, and the like over a long period of time, and maintain a high-quality image output.

  The present invention can be widely applied to an image forming apparatus to which an electrophotographic image forming system using a two-component developer including a magnetic carrier is applied, for example, a laser printer, a copying machine, a multifunction machine, and a fax machine.

It is a cross-sectional schematic diagram of the developer comprising the resin-coated carrier and toner of the present invention. It is the figure which showed the correlation between the shape factor (SF-2) of the carrier used for the resin coating carrier, and the conveyance amount of the developer in an initial state. It is a schematic block diagram of the image development apparatus which forms a visible image with the developing agent using the resin coating carrier of this invention. It is the figure which showed the surface state of the resin coating carrier of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Resin coated carrier 2 Toner 3 Two-component developer 6 Carrier core material 7 Cover resin layer 30 Developing device 31 Developing unit 32 Developer carrier 33 Developer regulating member 34 Stir screw 35 Image carrier 36 Toner density sensor 37 Toner hopper 40 Surface exposed part

Claims (12)

In a coated carrier having an abrasion property, a carrier core material and a coating layer covering the carrier core material, the surface of the carrier core material being partially exposed,
The carrier core material of the initial coated carrier and the coating are formed with the shape factor (SF-2) of the carrier core material as the first shape factor and the shape factor (SF-2) of the initial coated carrier as the second shape factor. When the shape factor (SF-2) of the coated carrier that has changed due to wear of the layer is the third shape factor,
The first shape factor is 120 or more and 150 or less,
A coated carrier, wherein the ratio of the third shape factor to the second shape factor is 90% or more. The coating layer is made of a coating resin composition,
The coated carrier according to claim 1, wherein the coating amount of the coating resin composition on the carrier core material is 0.5 to 1.5 parts by weight with respect to 100 parts by weight of the carrier core material.   The coated carrier according to claim 2, wherein the coating resin composition contains a silicone resin.   The coated carrier according to claim 2, wherein the coating resin composition contains a silane coupling agent.   The coated carrier according to claim 4, wherein the content of the silane coupling agent is 2 to 5 parts by weight with respect to 100 parts by weight of the coating resin composition.   The coated carrier according to any one of claims 1 to 5, wherein an average particle size of the coated carrier is 35 µm or more and 55 µm or less. Toner and
A developer comprising the coated carrier according to any one of claims 1 to 6. A developing device that has a developing unit for storing a developer and visualizes an electrostatic latent image formed on an image carrier with toner contained in the developer,
The developing device according to claim 7, wherein the developer according to claim 7 is stored in the developing unit.   An image forming apparatus comprising the developing device according to claim 8.   Forming a wearable coating layer on the surface of the wearable carrier core material having a first shape factor (SF-1) of 120 or more and 150 or less so that a part of the surface of the carrier core material is exposed; A method for producing a coated carrier, which is characterized.   11. The coated carrier according to claim 10, wherein the coating layer is formed by coating 0.5 to 1.5 parts by weight of the coating resin composition with respect to 100 parts by weight of the carrier core material. Method.   The method for producing a coated carrier according to claim 11, wherein the coating layer is formed by a dipping method.

Images