JPH09152749A - Carrier for electrostatic latent image developer, electrostatic latent image developer and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the increase of the resistance of a developer, to considerably improve the reproducibility of a halftone image, to improve durability and to prolong service life by using electrically conductive powder which is inorg. fine powder having shape anisotropy. SOLUTION: This carrier has a coating layer consisting of a resin and electrically conductive powder which is inorg. fine powder having shape anisotropy on each of magnetic substance particles or a core material. The magnetic substance is, e.g. a magnetic metal such as iron, steel, Ni or Co or a magnetic oxide such as ferrite or magnetite. The core material is, e.g. glass beads. This carrier is preferably a magnetic carrier from the viewpoint of the use of a magnetic brush. The average particle diameter of the magnetic substance particles is 0.05-1μm and that of the core material is 10-500μm, preferably 30-150μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for an electrostatic latent image developer used for an electrostatic latent image in an electrophotographic method or an electrostatic recording method, an electrostatic latent image developer and an image forming method. .

[0002]

2. Description of the Related Art Conventionally, in electrophotography, an electrostatic latent image is formed on a photoconductor or an electrostatic recording medium by various means, and electroscopic fine particles called toner are attached to the electrostatic latent image. The method of developing an electrostatic latent image is generally used.

In this phenomenon, carrier particles called carriers are mixed with toner particles, and both particles are triboelectrically charged with each other to give an appropriate amount of positive or negative charge to the toner. Carriers are generally classified into a coated carrier having a coating layer on the surface and an uncoated carrier having no coating layer on the surface. However, considering the life of the developer, the coated carrier is superior. , Various types of coated carriers have been developed and put into practical use. Although there are various characteristics required of the coated carrier, it is possible to impart appropriate chargeability (charge amount and charge distribution) to the toner and maintain appropriate chargeability of the toner for a long period of time. For this reason, it is especially important not to change the chargeability of the toner against impact resistance, abrasion resistance, and environmental changes such as humidity and temperature, and various coated carriers have been proposed. There is.

[0004]

In order to solve such problems, a copolymer of a nitrogen-containing fluorinated alkyl (meth) acrylate and a vinyl monomer, or a fluorinated alkyl (meth) acrylate and a nitrogen-containing vinyl. A relatively long-life coated carrier has been proposed in which a surface of a carrier core material is coated with a copolymer with a base monomer (Japanese Patent Laid-Open No. 61-8).
No. 0161, JP-A-61-80162, JP-A-61-80163), the carrier is insulated due to the resin coating, and it becomes difficult to act as a developing electrode during development. As a result, the reproducibility of the solid is deteriorated, such as an edge effect occurring in the solid black portion. When the subject is a halftone image like a photograph, the image has very poor reproducibility.

On the other hand, for the purpose of improving the reproducibility of solids, there has been proposed a carrier in which conductive fine powder such as carbon black, metal or inorganic oxide is dispersed in a coat film (Japanese Patent Laid-Open No. 1-101560). Japanese Laid-Open Patent Publication No. 1-1052
No. 64). However, the conductive fine powder and the coating resin are
Generally, they are not compatible and the interaction between the interfaces between them is small, so the coating film in which the conductive material is dispersed has low film strength,
Easily worn or peeled from the core carrier. When this type of carrier is used, when the copying machine is repeatedly used, background fog or image density fluctuation occurs, and stable quality cannot be maintained.

In order to improve this phenomenon, it has been proposed to treat the surface of the conductive material with a silane coupling agent to enhance the interaction at the interface between the two (Japanese Patent Laid-Open No. 5-303238). However, it cannot be said that it has been improved sufficiently. In recent years, color copiers have become widespread, and the required level of image quality is increasing. In this color image quality, solid reproducibility is indispensable, and a developer having good reproducibility for a long time is required.

The present invention solves the above problems and allows the conductive material in the coat resin film to act efficiently,
Carrier for electrostatic latent image developer and electrostatic latent image developer that suppresses increase in resistance of developer, greatly improves reproducibility of halftone image, and improves durability. And an image forming method.

[0008]

The present invention has made it possible to provide a carrier having the above-mentioned characteristics by adopting the following constitution, thus completing the present invention. (1) A carrier for an electrostatic latent image developer having a coating layer made of a resin and a conductive powder, wherein the conductive powder is an inorganic fine powder having shape anisotropy, for the electrostatic latent image developer Career. (2) The carrier for electrostatic latent image developer according to (1) above, wherein the shape anisotropy is a dendritic shape branched in at least three directions.

(3) The carrier for electrostatic latent image developer according to the above (1) or (2), wherein the inorganic fine powder is surface-treated with a coupling agent and / or silicone oil. (4) The above resin (1), wherein the resin contains at least a fluorine resin and / or a silicone resin.
The carrier for electrostatic latent image developer according to any one of (3).

(5) Toner comprising a binder resin and a colorant,
An electrostatic latent image developer comprising a carrier having a coating layer made of a resin and a conductive powder, wherein the conductive powder is an inorganic fine powder having shape anisotropy. (6) The electrostatic latent image developer according to (5) above, wherein the toner is a color toner.

(7) a step of forming a latent image on the latent image carrier,
In the image forming method, the image forming method includes a step of developing the latent image with a developer, a step of transferring the developed toner image onto a transfer body, and a fixing step of heating and fixing the toner image on the transfer body. An image forming method comprising using the electrostatic latent image developer according to the above (5) or (6) as an agent.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have made earnest studies on a carrier for developing an electrostatic latent image in order to improve the above problems, and as a result, have found that a conductive inorganic powder having a shape anisotropy in a coat resin of the carrier. Providing a carrier for electrostatic latent image development that suppresses an increase in the resistance of the developer, greatly improves the reproducibility of halftone images, and improves durability by blending Made possible.

The form of the carrier used in the present invention may be a so-called magnetic substance-dispersed carrier in which a magnetic substance is dispersed in a resin, or a resin-coated carrier having a core material surface coated with a resin. The effects of the invention can be sufficiently exhibited.

Examples of the magnetic particles or core material used in the carrier of the present invention include magnetic metals such as iron, steel, nickel and cobalt, magnetic oxides such as ferrite and magnetite, and glass beads. From the viewpoint of using, a magnetic carrier is preferable.

The magnetic particles for the magnetic substance dispersion type carrier are
An average particle size of 0.05 to 1 mμ is used, preferably 0.1 to 0.6 mμ. The carrier core material having an average particle size of 10 to 500 mμ is used, preferably 30 to 150 mμ.

The conductive inorganic powder used in the present invention includes metals such as gold, silver and copper, carbon black, semiconductive oxides such as titanium oxide and zinc oxide, titanium oxide and zinc oxide, Examples thereof include barium sulfate, aluminum borate, potassium titanate powder and the like whose surface is coated with tin oxide, carbon black, metal or the like.

In the present invention, the shape anisotropy means, for example,
It refers to a dendritic form in which lines or fibers are branched in three or more directions. As a conductive material having this shape anisotropy, a conductive material “H1-2” manufactured by Ishihara Sangyo Co., Ltd. and the like are commercially available.

When the conductive inorganic powder having shape anisotropy as described above is dispersed in the coating film, the conductive inorganic powder contacts the resin in a branched state in three or more directions in the resin coat. It can have stronger adhesion to the coating resin than needle-like or fibrous conductive inorganic powder. In addition, since the conductive inorganic powder such as needle-like, fibrous, and dendritic particles easily forms a continuous conductive path in the dispersed resin, the addition amount thereof can be smaller than that of the spherical conductive inorganic powder. Among them, the dendritic conductive inorganic powder has a remarkable tendency.

Further, the conductive inorganic powder is usually laid down and dispersed along the tangential direction of the carrier core, but when the needle-like or fibrous conductive inorganic powder is exposed on the surface of the coating film,
The main body of the carrier may be exposed to a large extent, and is easily dropped from the carrier, which makes the characteristics of the carrier unstable. On the other hand, in the case of a conductive material having a dendritic shape anisotropy, the conductive paths can be provided in the coating resin while being branched in three directions, so that the conductive paths can be formed in a three-dimensional mesh shape. In addition, even if it is almost buried in the coat film, a part of the coat film is exposed on the surface of the coat film, which can surely contribute to the control of the electric resistance. Further, the conductive inorganic powder having shape anisotropy exposed on the surface of the coating film acts to suppress abrasion of the coating film.

Therefore, when the conductive inorganic powder having shape anisotropy is used, the amount of the conductive inorganic powder added to the coating film can be reduced, and as a result, the reduction of the strength of the coating film can be suppressed. It is possible to improve wear resistance at the same time. The major axis of the conductive material having shape anisotropy is 0.1 to 20 mμ, preferably 0.2 to 10 mμ. The diameter of the minor axis is 0.002 to 2 μm, preferably 0.02 to 0.5 μm. The shape anisotropy is branched in at least three directions, and the number of branches is preferably 8 or less. The conductive inorganic powder having shape anisotropy is preferably added in an amount of 3 to 50 wt%, particularly 5 to 25 wt% based on the total coating film material.

The conductive inorganic powder may be surface-treated with a coupling agent and / or silicone oil, if necessary, in order to improve the dispersibility in the coating film and the adhesion. As the coupling agent used for the surface treatment of the electrically conductive inorganic powder, a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, a zirconium coupling agent or the like which reacts with a hydroxyl group is suitable.

Among them, the silane coupling agent represented by the following formula is preferably used. R _4-x Si (NCO) _x R _4-x Si (OR ₁ ) _x R _4-x SiCl _x (x is an integer of 1 to 3, R is an alkyl group having 1 to 16 carbon atoms or a perfluoroalkyl group) , R ₁ represents an alkoxy group such as a methoxy group or an ethoxy group) Specifically, (CH ₃ ) ₂ Si (NCO) ₂ , CH ₃ S
i (NCO) ₃ , C ₁₀ H ₂₁ Si (OCH ₃ ) ₃ , CF ₃
Although Si (OCH ₃ ) _{3 and the} like can be mentioned, x = 3 in the above formula is particularly excellent in that the dispersibility is improved.

As the silicone oil used for the surface treatment of the conductive inorganic powder, modified silicone oil can be used in addition to dimethyl, methylphenyl and methylhydrogen silicone oils. For the surface treatment of the conductive inorganic powder, the above coupling agent or silicone oil may be used alone or in combination. The surface treatment amount of the conductive inorganic powder is in the range of 2 to 50%, preferably 5 to 30%.

Examples of the coating resin used in the present invention include polyolefin resins such as polyethylene and polypropylene; polyvinyl and polyvinylidene resins such as polystyrene, acrylic resins, polyacrylonitrile, and the like.
Polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether and polyvinyl ketone; vinyl chloride / vinyl acetate copolymers; styrene / acrylic acid copolymers; straight silicone resins composed of organosiloxane bonds or modifications thereof Examples thereof include fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene; polyesters, polyurethanes, polycarbonates, amino resins such as urea / formaldehyde resins, epoxy resins and the like.

In the carrier of the present invention, a release resin such as a resin containing fluorine and / or a silicone resin, which is a low surface energy material, can be mixed in order to suppress contamination of the carrier surface.

In the present invention, the method for forming the coating resin film on the surface of the carrier core material is a dipping method in which the powder of the carrier core material is immersed in a coating layer forming solution, and the solution is the surface of the powder of the carrier core material. Spraying method, a fluidized bed method of spraying the solution in a state where the carrier core material is suspended in fluidized air, a kneader coater method of removing the solvent by mixing the carrier core material and the solution in a kneader coater The kneader coater method is particularly preferably used in the present invention.

As the solvent used for the coating layer forming solution,
It is not particularly limited as long as it dissolves the coating resin, and for example, aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, and ethers such as tetrahydrofuran and dioxane can be used. it can.

The thickness of the coating layer of the carrier used in the present invention is in the range of 0.1 to 10 μm, preferably 0.4 to 4 μm. The film thickness L can be easily obtained from the following formula from the carrier specific gravity ρ _D , the average particle diameter D of the carrier, the specific gravity ρ _{c of the} coating resin and the total coating amount W _c (wt%). L = [(amount of coating material per carrier) / (surface area per carrier)] / (specific gravity of coating material) = [((4π / 3) (D / 2) ³ ρ _D W _c ) / 4π (D / 2) ² ] ÷ ρ _c = Dρ _D W _c / 6ρ _c

As the binder resin of the toner used in the present invention, styrenes such as styrene and chlorostyrene; monoolefins such as ethylene, propylene, butylene and isoprene; vinyl acetate, vinyl propionate, vinyl benzoate, etc. Vinyl esters of α-methylene such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, dodecyl (meth) acrylate, octyl (meth) acrylate, and phenyl (meth) acrylate. Aliphatic monocarboxylic acid esters; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl butyl ether; homopolymers of vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, vinyl isopropenyl ketone, etc., or their copolymers. Polymers can be mentioned, Examples of typical binder resins include polystyrene, styrene / alkyl (meth) acrylate copolymer, styrene / acrylonitrile copolymer, styrene / butadiene copolymer, styrene / maleic anhydride copolymer, polyethylene, polypropylene. Can be mentioned. Furthermore, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin, and wax can be exemplified. Among them, it is particularly effective when polyester is used as the binder resin. For example, a linear polyester resin comprising a polycondensate containing bisphenol A and a polyvalent aromatic carboxylic acid as main monomer components can be preferably used.

The binder resin has a softening point of 90 to 1
50 ° C., glass transition point is 50 to 70 ° C., number average molecular weight is 2,000 to 6,000, and weight average molecular weight is 8,000 to 15,
000, an acid value of 5 to 30, and a hydroxyl value of 5 to 40 are particularly preferably used. Furthermore, these toner particles may optionally contain known additives such as a charge control agent and a fixing aid.

The colorant used in the toner of the present invention includes:
Carbon Black, Nigrosine, Aniline Blue, Calcoil Blue, Chrome Yellow, Ultramarine Blue, DuPont Oil Red, Quinoline Yellow, Methylene Blue Chloride, Phthalocyanine Blue, Malachite Green Oxalate, Lamp Black, Rose Bengal, CI Pigment Red 48: 1 , CI Pigment
Red 122, CI Pigment Red 57: 1, CI Pigment Yellow 97, CI Pigment Yellow 12, CI
Pigment Blue 15: 1, CI Pigment Blue 15: 3
And the like can be exemplified as typical ones.

[0032]

【Example】

[Production of Carrier] (Example 1) Cu-Zn ferrite particles (average diameter 50 µm) 100 parts by weight Toluene 14 parts by weight Styrene / methacrylate copolymer (copolymerization ratio = 20:80) 2.0 parts by weight Conductive oxidation Titanium (manufactured by Ishihara Sangyo Co., Ltd., H1-2, long axis 0.2 to 0.3 μm, short axis 0.04 to 0.07 μm, maximum number of branches 4) 0.5 parts by weight Sand milling the above components except ferrite particles For 5 minutes to prepare a coating layer forming solution, and then the coating layer forming solution and ferrite particles are put into a vacuum degassing type kneader and stirred at a temperature of 60 ° C. for 10 minutes, and then the pressure is reduced to distill toluene. After that, a coating layer was formed to obtain a carrier A.

(Example 2) Cu-Zn ferrite particles (average diameter 50 μ) 100 parts by weight Toluene 14 parts by weight Styrene / methacrylate copolymer (copolymerization ratio = 20: 80) 1.6 parts by weight Conductive titanium oxide ( Ishihara Sangyo Co., Ltd., H1-2, long axis 0.2 to 0.3 μm, short axis 0.04 to 0.07 μm, branch number 4) 1 part by weight Disperse the above components in a sand mill for 5 minutes excluding ferrite particles. Then, the coating layer forming liquid is prepared, and then the coating layer forming liquid and the ferrite particles are put in a vacuum degassing kneader,
After stirring at a temperature of 60 ° C. for 30 minutes, the pressure was reduced and toluene was distilled off to form a coating layer, and a carrier B was obtained.

(Comparative Example 1) In Example 2, needle-shaped titanium oxide (manufactured by Ishihara Sangyo Co., Ltd., FT-1000, long axis 1.6) was used instead of conductive titanium oxide (manufactured by Ishihara Sangyo Co., Ltd., H1-2).
Carrier C was obtained in the same manner as in Example 2 except that 8 μm and minor axis 0.13 μm) were used.

(Comparative Example 2) A carrier D was obtained in the same manner as in Example 2, except that the conductive titanium oxide (H1-2 manufactured by Ishihara Sangyo Co., Ltd.) was omitted.

Comparative Example 3 Cu-Zn ferrite particles (average diameter 50 μ) 100 parts by weight Toluene 14 parts by weight Styrene / methacrylate copolymer (copolymerization ratio = 20: 80) 0.5 parts by weight Excluding ferrite particles, The above components are dispersed in a sand mill for 10 minutes to prepare a coating layer forming solution, and then this solution and ferrite particles are put into a vacuum degassing kneader and stirred at a temperature of 60 ° C. for 10 minutes, and then decompressed to remove toluene. A coating layer was formed by evaporation to obtain a carrier E.

[Production of Toner] Linear polyester resin 100% by weight (terephthalic acid / bisphenol A ethylene oxide adduct / cyclohexane dimethanol copolymer Tg = 62 ° C., Mn = 4000, Mw = 12000, acid value = 12, Hydroxyl value = 25) Magenta pigment (CI Pigment Red 57) 3% by weight The above mixture was kneaded with an extruder, pulverized with a jet mill, and then dispersed with an air classifier to obtain a magenta toner A having d ₅₀ = 8 μm. Obtained.

(Evaluation) 100 parts by weight of each of the carriers obtained in Examples 1 and 2 and Comparative Examples 1 to 3 was mixed with 6 parts by weight of the magenta toner, and Examples 1 and 2 and Comparative Examples 1 to 1 were mixed.
An evaluation developer corresponding to carrier No. 3 was prepared. An electrophotographic copying machine (A-Color 630, manufactured by Fuji Xerox Co., Ltd.) was used for these developers, and the evaluation environment was adjusted to a temperature of 22 ° C. and a humidity of 55%, and a copy test was performed.
The results are shown in Table 1. The charge amount in Table 1 is C
It is a value obtained by image analysis of GS (charge spectrograph method). The image density is shown in Table 2.

[0039]

[Table 1]

[0040]

[Table 2]

As is clear from Table 1, the developers of Examples 1 and 2 were able to obtain excellent images having no edge effect. Further, the image density was stable at 1 to 1.2, and the toner charge amount was stable even after the number of copies exceeded 10,000.

On the other hand, with the developer of Comparative Example 1, an image having no edge effect was obtained at the initial stage, but when the number of copies exceeded 1,000, a slight edge effect was recognized.
When the number of copies exceeds 10,000, the edge effect was clearly recognized. The edge effect of the developer of Comparative Example 2 was clearly recognized from the initial stage. With the developer of Comparative Example 3, the edge effect was not recognized even when the number of copies exceeded 10,000, but when the number of copies exceeded 10,000, the toner charge amount was significantly reduced. In Comparative Example 2, the resistance is high and the edge effect occurs, but the charging life is long.
Had low resistance and no edge effect, but had a poor charging life.

[0043]

According to the present invention, by adopting the above-mentioned constitution, even if a coat film is provided on a carrier, the resistance does not become high, an image having excellent halftone reproducibility can be obtained, and the image can be reproduced for a long time. It has become possible to provide a carrier which maintains a good charge imparting ability even when continuously used.

Claims (3)

[Claims] 1. A carrier for an electrostatic latent image developer having a coating layer made of resin and conductive powder, wherein the conductive powder is an inorganic fine powder having shape anisotropy. Drug carrier. 2. An electrostatic latent image developer comprising a toner comprising a binder resin and a colorant and a carrier having a coating layer comprising resin and conductive powder, wherein the conductive powder is an inorganic fine particle having shape anisotropy. An electrostatic latent image developer characterized by being a powder. 3. A step of forming a latent image on a latent image carrier, a step of developing the latent image with a developer, a step of transferring the developed toner image onto a transfer body, and a transfer body. 3. The image forming method having a fixing step of heating and fixing the toner image according to claim 2, wherein the electrostatic latent image developer according to claim 2 is used as the developer.