JPH04268573A - Carrier for electrostatic image development - Google Patents

Abstract

PURPOSE:To improve strength, toner contamination resistance, fluidity and environmental stability of a coating layer by applying on a nucleus particle with a specific coating resin. CONSTITUTION:When the nucleus particle is applied with the coating resin, a particulate of a silicone rubber and/or a particulate of an insoluble and infusible silicone is allowed to contain in the coating resin. The particulate of the insoluble and infusible silicone is a particulate of silicone resin three- dimensionally cross-linked by executing dehydrating reaction or dealcoholating reaction with SiOH group, and does not have m.p., does not dissolve in organic solvent. And the particulate of silicone rubber obtained by substituting a part of CH3 group of chain crude rubber with -C6H5, -CH2-CH2CF3, -(CH2)2CN or the like, or cross-linking by organic peroxide, aliphatic azo compound to make rubber is used.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic image developing carrier used when electrostatic images formed by electrophotography, electrostatic recording, etc. are developed with a two-component developer.

0002

2. Description of the Related Art Methods for visualizing image information through electrostatic images, such as electrophotography, are currently used in various fields. In electrophotography, an electrostatic latent image is formed on a photoreceptor through charging and exposure steps, developed with a developer containing toner, and visualized through transfer and fixing steps. There are two types of developers used here: two-component developers consisting of toner and carrier, and one-component developers such as magnetic toner that use toner alone. Because it shares functions such as transport and charging, and is functionally separated as a developer, it has characteristics such as good controllability, and is currently widely used. In particular, a developer using a resin-coated carrier has excellent charge controllability, and it is relatively easy to improve environmental dependence and stability over time. Also,
As a developing method, a cascade method and the like were used in the past, but now the mainstream is a magnetic brush method that uses a magnetic roll as a sole developer conveyor.

The magnetic brush method using a two-component developer includes:
There are problems such as a decrease in image density due to charging deterioration of the developer, significant staining of the background area, image roughness and carrier consumption due to carrier adhesion to the image, and uneven image density. The adhesion mechanism of the carrier to the image is
When the resistance of the carrier decreases, induced charges are injected into the image area and the carrier adheres to the image area, or the upper limit control of the charge amount of the carrier is insufficient and the charge amount of the carrier becomes excessive after development. It is thought that carriers adhere to the edge portions.

In recent years, negatively charged organic photoreceptors have become widespread, and even in the case of inorganic photoreceptors, a reversal development method in which an electrostatic charge image is recorded using a laser or the like has come into widespread use. Needless to say, there is a high demand for high-quality developers for positively charged toner as well. As carriers for this positively charged toner, those in which core particles are coated with a negative polarity resin are widely used.

[0005] Resin-coated carriers do not have a decrease in carrier resistance due to abrasion or peeling of the coating layer, and can freely control the amount of triboelectric charge of the toner by selecting and adjusting the coating resin to obtain sufficient image density and image quality. There are demands for obtaining stable images over a long period of time by preventing deterioration in chargeability due to toner contamination on the carrier surface, and research has been conducted on coating resins that meet these required characteristics.

[0006] In recent years, among such coating resins, fluororesins and silicone resins have been actively studied.
When these resins are used alone, there are problems in the adhesion between the core particles and the coating layer and in the abrasion resistance.

[0007] In JP-A-54-110839 and JP-A-56-113146, in order to improve the adhesion between the core particles and the fluororesin, a second compound having excellent compatibility with the fluororesin is disclosed. It is described that a resin such as methyl methacrylate copolymer is mixed and coated. However, this mixed system impairs the excellent properties of the fluororesin, such as solid lubricity and low tackiness, making it difficult to dramatically improve surface stain resistance.

[0008] JP-A-57-96355 discloses that by laminating a silicone resin layer on the core particles, even if the surface layer silicone resin is worn out, the lower layer silicone resin appears and restores the chargeability of the carrier. It is stated that Although this method can ensure charging stability over time, as the coating layer becomes thinner, the resistance value of the carrier decreases, causing defects in image quality.

Furthermore, Japanese Patent Application Laid-Open No. 57-78552 discloses that an intermediate layer made of an elastic material is provided on the core particles, and a silicone resin layer is provided on the intermediate layer to improve the strength against stress applied to the carrier. However,
The effect of improving strength against shear stress is small and it is not possible to prevent wear of the surface silicone resin itself.

[0010] Furthermore, Japanese Patent Application Laid-Open No. 60-46567-465
Publication No. 69 describes that the silicone resin layer contains fine particles such as asbestos, kaolin, talc, etc. to improve mechanical strength, but in these systems there are fine particles exposed on the carrier surface. Problems such as changes in carrier characteristics due to the environment and damage to the photoreceptor arise.

Therefore, the present invention aims to solve the above-mentioned problems and provide a carrier for an electrostatic image developer having excellent coating layer strength, toner stain resistance, fluidity, environmental stability, etc. Another object of the present invention is to provide a carrier that has excellent charge maintenance properties, can suppress carrier adhesion and carrier consumption, and can form stable image quality.

0012

[Means for Solving the Problems] The present invention provides an electrostatic image developing carrier in which core particles are coated with a coating resin.
This carrier for developing an electrostatic image is characterized in that the coating resin contains silicone rubber fine particles and/or insoluble and infusible silicone fine particles.

The insoluble and infusible silicone fine particles used in the present invention are fine particles of silicone resin in which SiOH groups are three-dimensionally crosslinked by dehydration or dealcoholization, and have no melting point and are resistant to organic solvents. It also does not dissolve. In addition, silicone rubber fine particles may be any known silicone rubber fine particles, but the general formula

[Chemical 1] A part of the CH3 group of chain raw rubber represented by -C6H5
, -CH2CH2CF3, -(CH2)2CN, etc., or silicone rubber fine particles crosslinked with an organic peroxide, an aliphatic azo compound, etc. to form a rubber are preferred.

[0014]

[Function] By coating the core particles with a coating resin containing silicone rubber fine particles and insoluble and infusible silicone fine particles, the coating layer becomes smaller than that of a resin-coated carrier that does not contain the fine particles. Strength, toner stain resistance, fluidity, and environmental stability can be improved. The improvement in the strength of the coating layer is due to the effect of the fine particles as a filler, and the toner contamination resistance and fluidity are due to the low surface energy, thermal stability, and low coefficient of friction of the silicone particles, which are environmentally friendly. The improved stability is thought to be due to the water repellency of silicone. In particular, silicone rubber fine particles and/or insoluble and infusible silicone fine particles have similar functional effects, but the latter can be coated with a solution using an organic solvent, mixed in a dry state, heated, melted, and cooled. While it is applicable to both dry coating methods, the former is different in that it often swells in organic solvents, and the effect of the present invention is mainly exhibited in the dry coating method. Therefore, it is preferable to select the silicone material of the present invention in accordance with the carrier manufacturing method.

[0015] As the coating resin of the present invention, any resin can be used regardless of whether it has a positive or negative charge polarity. In this manner, the positively chargeable carrier of the present invention can be obtained. As negative polarity resin, fluororesin,
Specifically, examples include homopolymers or copolymers of vinyl fluorine-containing monomers such as vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, monochlorotrifluoroethylene, monochloroethylene, and trifluoroethylene. , but not limited to these. Further, specific examples of positive polar resins include styrenes such as styrene, chlorostyrene, and methylstyrene;
α-Methylene aliphatic monocarboxylic acids such as methyl methacrylate, methyl acrylate, propyl acrylate, lauryl acrylate, lauryl methacrylate, methacrylic acid, acrylic acid, butyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate; acrylonitrile, methacrylonitrile Homopolymers or copolymers of vinylpyridines such as 2-vinylpyridine and 4-vinylpyridine can be used, but are not limited thereto. The blending amount of the coating resin is about 0.2 to 10% by weight, preferably 0.5 to 10% by weight based on the carrier.
A range of 3% by weight is suitable.

The blending amount of the fine particles of the present invention is about 0.5 to 80% by weight, preferably 2 to 50% by weight, based on the amount of coating resin.
A range of weight percent is suitable. The fine particles may be uniformly dispersed within the coating layer, or may be exposed and uniformly arranged on the surface of the coating layer. The particle size of the fine particles is preferably such that they do not separate from the coating layer, and specifically, it is preferably at most twice the size of the coating layer and at most 5 μm.

The nuclear particles used in the present invention include ferrite, magnetite, metals or alloys exhibiting ferromagnetism such as iron, cobalt, and nickel, compounds containing these elements, or elements exhibiting ferromagnetism. Alloys that do not contain ferromagnetism but become ferromagnetic through heat treatment, such as manganese-copper-aluminum, manganese-
Examples include Heusler alloy containing manganese and tin such as copper-tin, chromium dioxide, etc., and the particle size is usually 10~
A material having a diameter of about 500μ, preferably 40 to 150μ is used.

When the carrier of the present invention is produced by a solution coating method, the fine particles of the present invention are dispersed in a coating resin solution by a known method such as a ball mill, and then the fine particles of the present invention are dispersed using a fluidized bed device, a spray dryer, etc. When using the dry coating method, which includes dry mixing, heating, melting, and cooling steps, a kneader, Henschel mixer, attritor, etc. equipped with heating equipment using a heating medium is used.
A Radige mixer, a UM mixer, a planetary mixer, etc. can be used, and depending on the blending ratio such as the amount of resin, a heated fluidized rolling bed, a heated kiln, etc., which are less susceptible to blade shearing, can also be used. However, it is not limited to these.

The toner constituting the two-component developer used in the present invention has toner components such as a colorant dispersed in a binder resin, and the binder resin used here includes styrene, parachloro, etc. Styrenes such as styrene and α-methylstyrene; methyl acrylate, ethyl acrylate, n-propyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, methacrylate α-methylene aliphatic monocarboxylic acid esters such as lauryl acid and 2-ethylhexyl methacrylate; vinyl nitriles such as acrylonitrile and methacrylonitrile; 2-
Vinylpyridines such as vinylpyridine and 4-vinylpyridine; Vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, and methyl isopropenyl ketone; Ethylene, propylene, isoprene, butadiene, etc. and copolymers obtained by combining two or more of these monomers, and Mixtures of these resins, as well as vinyl condensation resins such as rosin-modified phenol-formalin resins, epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, and polyether resins, or mixtures of these and the vinyl resins can be mentioned. Can be done. As the coloring agent, for example,
carbon black, nigrosine dye, aniline blue,
Mention may be made of calco oil blue, chrome yellow, ultramarine blue, methylene blue, rose bengal, phthalocyanine blue, or mixtures thereof. Toner components other than colorants include charge control agents, anti-offset agents, fluidity improvers, and transfer aids, and magnetic powder may be included if necessary.

[0020]

[Examples] The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto. (Example 1) Frozen pulverized product of St/MMA copolymer with a softening point of 120°C (DSC measurement peak value) (average particle size 5 μm)
(BR52 manufactured by Mitsubishi Rayon Co., Ltd.) 20 parts by weight, average particle size 3
2 parts by weight of micron silicone rubber particles (Silicone E500 manufactured by Dow Corning Toray Industries, Inc.) and an average particle size of 80 μm.
m Cu-Zn ferrite core (manufactured by Powder Tech)
1000 parts by weight were mixed in a 5L small kneader for 5 minutes, then the heating medium temperature was set at 195° C., and after stirring and kneading for 40 minutes, the heater was turned off and the mixture was allowed to cool for 50 minutes while stirring. Thereafter, sieving was performed using a 177 μm sieve to obtain a carrier. In addition, binder resin (styrene-n-butyl methacrylate) 85% by weight, carbon black (Cabot B
PL) 10% by weight, charge control agent (Hodogaya Chemical TRH)
A toner having an average particle size of 10 μm was obtained by kneading and pulverizing using 1% by weight of polyethylene wax (400P manufactured by Mitsui Petrochemicals) and 4% by weight of polyethylene wax (400P manufactured by Mitsui Petrochemicals). And toner density 4
A developer was prepared by mixing toner and carrier so that the amount of When we conducted an image quality maintenance test on this developer using a Fuji Xerox copying machine (FX5039), we found that the images were clear after 100,000 copies, with no fogging or stains, and no unevenness in the images. There were no occurrences of this phenomenon, and excellent image quality could be obtained. Further, carrier consumption was also small. In addition, the temperature and humidity environment is 10℃20%RH,
When the initial image quality was evaluated by changing the temperature to 30° C. and 80% RH, almost no change in image quality was observed.

(Comparative Example 1) A carrier was produced in the same manner as in Example 1 except that silicone rubber fine particles (silicone E500 manufactured by Dow Corning Toray Industries, Inc.) were removed from the raw material for the carrier in Example 1. A developer was prepared by mixing in the same manner as above. When this developer was subjected to an image quality maintenance test in the same manner as in Example 1, the image density decreased significantly after 30,000 copies were made, and fogging occurred over the entire surface, so the test was discontinued. After the toner was removed from the developer by a blow-off method, the surface of the carrier was observed using an SEM, and it was observed that the toner was adhered to the entire surface of the carrier. In addition, the temperature and humidity environment was set to 10°C, 20% RH, and 30°C, 80% RH.
When we evaluated the initial image quality by varying the temperature, fogging was significant in high temperature and high humidity environments.

(Example 2) After dissolving 25 parts by weight of St/MMA copolymer (BR50 manufactured by Mitsubishi Rayon Co., Ltd.) with a softening point of 120°C (DSC measurement peak value) in 50 parts by weight of toluene, the average particle size was determined using a ball mill. 0.5 μm three-dimensional crosslinked silicone fine particles (Silicone R manufactured by Dow Corning Toray)
925) was dispersed, and this dispersion was applied to 1000 parts by weight of Cu-Zn ferrite core (manufactured by TDK) with an average particle size of 50 μm using a fluidized bed device, and the solvent was removed to form a film. did. Thereafter, sieving was performed using a 149 μm sieve to obtain a carrier. Then, using the toner of Example 1, a developer was prepared by mixing the toner and carrier so that the toner concentration was 4%. When this developer was subjected to an image quality maintenance test in the same manner as in Example 1, the images after 100,000 copies were clear, there was no fogging, and there was no occurrence of image unevenness, indicating excellent image quality. I was able to get Further, carrier consumption was also small. In addition, the temperature and humidity environment was set to 10°C, 20% RH, and 30°C, 80% RH.
When the initial image quality was evaluated by varying the %RH, almost no change in image quality was observed.

(Comparative Example 2) A carrier was produced in the same manner as in Example 2, except that the three-dimensionally crosslinked silicone fine particles (Silicone R925 manufactured by Dow Corning Toray Industries, Inc.) were removed from the raw materials for the carrier in Example 2. A developer was prepared by mixing in the same manner as toner No. 2. When this developer was subjected to an image quality maintenance test in the same manner as in Example 2, the test was discontinued because the image density decreased significantly after 50,000 copies were made, fogging occurred on the entire surface, and the inside of the machine was heavily contaminated. After removing the toner from the developer using a blow-off method, the carrier surface was examined using an SEM.
When observed, it was observed that toner was adhered to the entire surface of the carrier. In addition, the temperature and humidity environment is 10℃20%RH.
, and 30° C. and 80% RH. When the initial image quality was evaluated, fogging was significant in a high temperature and high humidity environment, and carrier adhesion to the background area was observed in a low temperature and low humidity environment.

(Example 3) Vinylidene fluoride-tetrafluoroethylene copolymer (KYNAR7201 manufactured by Pennwalt) 1 with a softening point of 121° C. (DSC measurement peak value)
5 parts by weight was dissolved in 100 parts by weight of DMF, and the average particle size was 1.
After dispersing 3 parts by weight of 0 μm silicone fine particles (Silicone R930 manufactured by Dow Corning Toray Industries, Inc.) in a ball mill, this dispersion and 1000 parts by weight of Cu-Zn ferrite cores (manufactured by TDK) with an average particle size of 80 μm were placed in a small vacuum kneader. A film was formed by vacuum drying while stirring and mixing. Thereafter, the mixture was sieved using a 149μ sieve to obtain a carrier. In addition, 84% by weight of a binder resin (styrene-n-butyl methacrylate), 10% by weight of carbon black (BPL manufactured by Cabot Corporation), 2% by weight of a charge control agent (Bontron N04 manufactured by Orient Corporation), and polyethylene wax (Mitsui Petrochemical Co., Ltd.) A toner having an average particle size of 11 μm was obtained by kneading and pulverizing 4% by weight of 400P (manufactured by Co., Ltd.). and,
A developer was prepared by mixing toner and carrier so that the toner concentration was 4%. When we conducted an image quality maintenance test on this developer using a modified machine for organic photoreceptors (FX5017) manufactured by Fuji Xerox, the images were clear even after 100,000 copies were made, and there was no fogging or staining. Excellent image quality was obtained without any unevenness. Further, carrier consumption was also small.

(Comparative Example 3) A carrier was produced in the same manner as in Example 3 except that silicone fine particles (Silicone R930 manufactured by Dow Corning Toray Industries, Inc.) were removed from the raw material for the carrier in Example 3. A developer was prepared by mixing in the same manner. When this developer was subjected to an image quality maintenance test in the same manner as in Example 3, image density unevenness occurred after 60,000 copies were made, so the test was discontinued. After removing the toner from the developer using the blow-off method, the carrier surface is subjected to SE.
When observed with M, peeling of the coating layer of the carrier was observed, and about 30% of the entire surface of the carrier was exposed.

(Example 4) 30 parts by weight of polyvinylidene fluoride (KYNAR201 manufactured by Pennwalt Co., Ltd.) with a softening point of 178° C. (DSC measurement peak value), silicone rubber fine particles with an average particle size of 1.5 μm (Silicone E730S manufactured by Dow Corning Toray Co., Ltd.) ) 10 parts by weight, and average particle size 100μ
1,000 parts by weight of iron powder (TSRYV manufactured by Powder Tech) were mixed in a 5L small kneader for 5 minutes, then the heating medium temperature was set to 195°C, and after stirring and kneading for 40 minutes, the heater was turned off and the mixture was mixed for 50 minutes while stirring. Cooled. After that, 2
A carrier was obtained by sieving with a 50 μm sieve. and,
Using the toner of Example 3, a developer was prepared by mixing the toner and carrier so that the toner concentration was 4%. When we conducted an image quality maintenance test on this developer using a modified Fuji Xerox inorganic photoreceptor reversal developer machine (FX6790), the images were clear even after 200,000 copies were made, and there was no fogging or staining. It was possible to obtain excellent image quality without any occurrence of image unevenness. Further, carrier consumption was also small.

(Comparative Example 4) A carrier was produced in the same manner as in Example 4 except that silicone rubber fine particles (silicone E730S manufactured by Dow Corning Toray Industries, Inc.) were removed from the raw material for the carrier in Example 4, and the toner of Example 4 was A developer was prepared by mixing in the same manner as above. When this developer was subjected to an image quality maintenance test in the same manner as in Example 4, image density unevenness occurred after 80,000 sheets were copied, and carrier adhesion to the solid image area became severe, so the test was carried out. Canceled. After the toner was removed from the developer by a blow-off method, the surface of the carrier was observed using a SEM, and peeling of the coating layer of the carrier was observed, and about 50% of the entire surface of the carrier was exposed to the core surface.

[0028]

[Effects of the Invention] By adopting the above configuration, the present invention can improve the charge retention of the carrier.
This prevents carrier from adhering to the image, making it possible to obtain stable image quality without fog or unevenness.

Claims (1)

[Claims] 1. A carrier for electrostatic image development in which core particles are coated with a coating resin, characterized in that the coating resin contains silicone rubber fine particles and/or insoluble and infusible silicone fine particles. A carrier for developing electrostatic images.