JPH05204188A - Carrier for developing electrostatic charge image - Google Patents

Abstract

PURPOSE:To form uniform continuous films on magnetic core particles when a carrier for developing an electrostatic charge image is produced by dry coating and to provide a carrier which sticks hardly to an image area, reduces consumption and can form an image free from fog and unevenness in density while suppressing aggregation during production. CONSTITUTION:Resin particles used for coating are made of a resin having <=30 deg.C difference between the intersections T1 and T2 of a base line and an inclined line forming a heat absorption peak when the quantity of heat is measured by differential scanning.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic charge image developing carrier used for developing an electrostatic latent image formed by electrophotography, electrostatic recording or the like with a two-component developer.

[0002]

2. Description of the Related Art A method of visualizing image information through an electrostatic latent image such as electrophotography is currently used in various fields. In the electrophotographic method, an electrostatic latent image formed on a photoconductor by a charging and exposing process is developed with a developer containing toner, and then visualized through a transferring and fixing process. Developers used for development include a two-component developer composed of a toner and a carrier, and a one-component developer such as a magnetic toner which is used alone as a toner. In the two-component developer, the carrier is a developer. Functions such as stirring, conveyance, and charging are shared,
It is widely used at present because of its features such as good controllability because it is functionally separated as a developer. In particular, a developer using a carrier coated with a resin has excellent charge controllability, and it is relatively easy to improve environmental dependency and stability over time. Further, as a developing method, a cascade method or the like has been used in the old days, but at present, a magnetic brush method using a magnetic roll as a developer transporting unit is mainly used.

In recent years, negatively charged type organic photoconductors have been remarkably spread, and in the case of inorganic photoconductors, a reversal development method for recording an electrostatic charge image by using a laser may be used.
A high-quality developer is required not only in the developing method using the negatively charged toner in the image method but also in the developing method using the positively charged toner. Therefore, it is desirable that the charging performance of the carrier can be freely controlled according to the charging polarity and charging strength of the toner. Furthermore, with the recent trend toward downsizing and speeding up of copiers and printers, downsizing of the developing machine itself and high-speed driving are required, and demands for improvement such as improvement in mechanical strength and stability over time of carriers are increasing. .. As carriers satisfying these required characteristics, in recent years, resin-coated carriers have been extensively studied, and as the selection of coating resins has become diversified, the coating method also dissolves the coating resin in a solvent to form core particles. A method of forming a coating by mixing and removing a solvent, a method of dry-mixing core particles and a coating resin, and then heating to melt the coating resin to form a coating have been proposed.

Among these resin coating methods, the dry coating method can use a material having poor solvent solubility as a coating resin, and is excellent in safety since it does not use an organic solvent. Has been actively studied,
It still has many drawbacks. For example, a method of forming a coating layer by heating a powder mixture consisting of core particles and a coating resin to a temperature not lower than the melting point of the coating resin in a stationary state (JP-A-54-3).
No. 5735) was proposed, but the formation of this coating layer largely depends on the melt flow behavior of the coating resin, and it is very difficult to use a resin exhibiting a high viscosity during melting. Further, since it is a coating treatment in a stationary state, it is unavoidable to agglomerate the carrier and requires post-treatment such as crushing, resulting in poor production efficiency and difficulty in forming a continuous smooth coating layer. ..

Further, a method of mixing core particles and coating resin particles in a dry state, heating and melting in a fluidized bath or a rotary furnace, and cooling (JP-A-55-118047 and JP-A-60-17).
No. 0865 and JP-A No. 62-106475) have been proposed, but since the mixing of the core particles and the coating resin depends on the self-weight shearing of the mixture, the coating resin particles are softened by heat, In the region where the viscosity of the mixture is high,
In some cases, the shearing force acting between the core particles and the coating resin particles is insufficient and sufficient mixing cannot be performed, so that a uniform coating layer cannot be formed on the carrier. In particular,
If the particle size of the core particles is small, the specific gravity is small, the shape is irregular, or the coating resin amount is large,
There is a problem similar to the above-mentioned Japanese Patent Laid-Open No. 54-35735.

Further, the mixture of the core particles and the coating resin particles is repeatedly impacted to spread the coating resin,
Method for forming coating layer (Japanese Patent Laid-Open No. 2-87167)
Japanese Unexamined Patent Publication (Kokai) No. 2-87168), this method requires the coating resin to be fine particles of 1 μm or less, and a resin obtained by emulsion polymerization or soap-free polymerization is used, or ultrafine pulverization is performed. Must be used.

[0007]

Therefore, the present invention is intended to provide a carrier for developing an electrostatic charge image in which the above problems are solved, and the purpose thereof is as follows. Easy to form a carrier film without using an organic solvent,
In addition, it should be possible to manufacture carriers safely and at low cost. There is no restriction on solvent solubility, molecular weight, softening point, etc. of the coating resin, and the coating resin amount can be selected relatively freely,
As a result, it is possible to arbitrarily control characteristics such as chargeability and electric resistance of the carrier. To be able to manufacture a carrier that is excellent in mechanical strength, stability over time, and environmental stability, suppresses carrier adhesion and carrier consumption, and can obtain good image quality.

[0008]

The present invention relates to a carrier for developing an electrostatic charge image produced by a dry coating method, wherein as coating resin particles, a tilt line and a baseline forming an endothermic peak by a differential scanning calorimetry method are used. The difference between the intersection points T ₁ and T ₂ is 30
A carrier for developing an electrostatic charge image, which is characterized by using a resin having a temperature of not higher than ° C.

[0009]

The present inventors, while considering the dry coating method,
Depending on the temperature change in the dry mixing, heating, melting, and cooling processes, the glass region changes to the rubber region, the molten liquid state, and then the rubber region and the glass region again, and the film is formed in the molten liquid state. It was found that mixing in the temperature range where the rubber state is reached accelerates the interfacial destruction between the coating and the surface of the core particles, causing the coating to become rough, and the endothermic peak shape near the softening point of the differential scanning calorimetry (DSC). We succeeded in preventing the above-mentioned interfacial destruction by shortening the mixing time in the rubber state by using a resin having a sharp temperature and a small temperature range in which it becomes a rubber state.

That is, the present invention is based on the differential scanning calorimetry (D
(SC) by using a coating resin having a difference of 30 ° C. or less between the intersection points T ₁ and T ₂ of the inclined line forming the endothermic peak and the baseline, dry-mixing and heating the core particles and the coating resin particles, Through the melting and cooling steps, a carrier for electrostatic image development having a smooth and continuous strong film on the surface can be obtained, and the required characteristics of the carrier such as charging property over time, environmental stability and mechanical strength are secured. Made it possible. When the endothermic peak is a single peak, the intersection points T ₁ and T ₂ are determined as shown in FIG. 1, but when the endothermic peak is a multiple peak, the intersection point is obtained from the slope of the peak closest to the baseline as shown in FIG. , T ₁ and T ₂ are determined. Above intersections T ₁ and T
_{If a} resin having a difference of ₂ is larger than 30 ° C., it will be mixed for a long time in the rubber state having the highest viscosity in the heating and cooling steps, which hinders uniform mixing and causes a large variation in film thickness of the coating film. Roughness of the coat is likely to occur. As a result, it becomes difficult to control the electric resistance of the carrier, and there arises a disadvantage that the change of the charge amount becomes large with the passage of time and environmental changes.

Examples of the core particles used in the present invention include, but are not limited to, iron powder, ferrite particles, and granulated magnetite. The average particle size is usually 10 to 500 μm, preferably 20 to 200 μm.
The thing of about m is used.

The coating resin used in the present invention is T
_As long as the coating resin has a difference between ₁ and T ₂ of 30 ° C. or less, various resins can be used regardless of their types, regardless of whether the triboelectricity polarity is positive or negative. In particular, in order to improve heating / melting / cooling efficiency, it is preferable to use a resin having a softening point of 150 ° C. or lower. Further, the present invention is particularly effective when using a fluororesin that is difficult to dissolve in an organic solvent.

Further, since the difference between T ₁ and T ₂ is 30 ° C. or less, when the resin is a crystalline polymer, it is preferable that there is no mixed crystal that does not cause crystal transition upon heating. Is a high density polyethylene which is a symmetric polymer having a high degree of crystallinity, specifically, Marlex (trade name: manufactured by Philips), PE130 (trade name: manufactured by Hoechst).
Or vinylidene fluoride / trifluoroethylene copolymer, specifically KF1500 (trade name: Kureha Chemical Co., Ltd.), vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, specifically KYNA
R9301 (trade name: manufactured by Penwalt), Hosta
Examples include flon TFB7100 (trade name: manufactured by Hoechst), but are not limited thereto. Polystyrene having a short side chain even with an amorphous polymer, specifically Microgel E-5001 (trade name: manufactured by Nippon Paint Co., Ltd.) or polymethylmethacrylate, specifically MP1000 (trade name: Soken Kagaku) Manufactured by the company) or the like can be used.

Examples of the fluorine-based resin include homopolymers or copolymers of vinyl-based fluorine-containing monomers such as vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene and monochlorotrifluoroethylene. Further, other resins such as acrylic resins include homopolymers of α-methylene aliphatic monocarboxylic acids such as lauryl acrylate, lauryl methacrylate, acrylic acid, methacrylic acid, butyl methacrylate, 2-ethylhexyl acrylate and ethyl methacrylate. , Or copolymers, styrene, for these acrylic monomers,
Styrenes such as methyl styrene and acrylonitrile,
Nitriles such as methacrylonitrile; vinyl pyridines such as 2-vinyl pyridine and 4-vinyl pyridine; vinyl ethers; vinyl ketones; olefins; silicones such as methyl silicone and methyl phenyl silicone copolymerized It is also possible to do so. These coating resins may be used alone, or a plurality of types of resins may be mixed and used in order to further increase the degree of freedom of charge adjustment in combination with the toner. The particle size of the coating resin is 1/3 or less, preferably 1/5 or less of that of the core particles. If it is larger than 1/3, it takes a long time for the coating resin to melt and spread to form a continuous film, resulting in poor production efficiency.

Further, for the purpose of adjusting the conductivity of the coating layer and improving the fluidity of the copolymer, it is possible to use fine particles such as an inorganic substance or carbon black in the coating resin. In the case of the conventional solution coating method, a step of previously dispersing the fine particles in a resin solution using a ball mill or the like is required, but in the present invention, the fine particles, the coating resin particles, and the core particles are simultaneously added and mixed. By doing so, it becomes possible to disperse the fine particles in the coating resin layer during the film formation process during heating and melting, so that the production efficiency is not adversely affected. The amount of the coating resin blended is about 0.2 to 10% by weight, preferably 0.5 to 3% by weight, based on the weight of the carrier, either alone or in combination with the resin. Further, when the above-mentioned fine particles are added, the compounding amount thereof is 0.
5 to 80% by weight, preferably 2 to 50% by weight are suitable.

The mixer used in the present invention may be of any kind as long as it has heating and cooling means, but as a means for allowing a wider selection of the coating resin amount, a forced shearing force is applied to the mixture. Those equipped with a stirring blade such as a rotary blade and a scraper that can be applied are suitable, and specific examples thereof include a batch kneader, a ribbon blender, and a pony mixer. Examples of means for heating the mixture include a method in which a jacket is attached to the mixing tank to heat transfer heat by circulating steam, a heating medium, and a direct heating method in which hot air is blown into the mixing tank. Not limited. Further, as the cooling means for the mixture, a method of switching from a heat medium to a refrigerant and a method of blowing cold air into the mixing tank can be mentioned, but are not limited thereto.

The carrier of the present invention is mixed with a toner and used as a two-component developer. The toner is a binder resin in which a colorant or the like is dispersed. The binder resin used in the toner includes styrenes such as styrene and chlorostyrene; vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate. And other vinyl esters; methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate,
Α-methylene aliphatic monocarboxylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate; vinyl methyl ether,
Vinyl ethers such as vinyl ethyl ether and vinyl butyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone; homopolymers and copolymers such as olefins. As the resin, polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyethylene, Examples thereof include polypropylene. Furthermore, polyester resin, polyurethane resin, epoxy resin, silicone resin, polyamide resin, modified rosin, and paraffin wax can be mentioned.

The colorant used in the toner is carbon black, aniline blue, chalco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate,
Typical examples include lamp black and rose bengal. The average particle size of the toner is about 30
It is suitable to be not more than μm, preferably 3 to 20 μm. The toner may be a magnetic toner containing a magnetic material or a capsule toner. In addition, various additives may be added to the toner, if necessary, and specifically, a salicylic acid metal salt, a metal-containing azo compound, a charge control agent such as nigrosine or a quaternary ammonium salt, and a low molecular weight Examples of the anti-offset agent include propylene, low molecular weight polyethylene and wax. Further, a fluidizing agent such as silica, titania, or alumina, or an external additive such as a cleaning aid or a transfer aid such as polystyrene fine particles, polymethylmethacrylate fine particles, or polyvinylidene fluoride fine particles can be used.

The developer composition thus obtained is used for developing the electrostatic latent image formed on the photoreceptor or the electrostatic recording material. That is, an electrostatic latent image is electrophotographically formed on a photoreceptor made of an inorganic photoconductive material such as selenium, zinc oxide, cadmium sulfide, or amorphous silicon, or an organic photoconductive material such as a phthalocyanine pigment or a bisazo pigment. Alternatively, an electrostatic latent image is formed on the electrostatic recording material having a dielectric material such as polyethylene terephthalate by a needle electrode or the like,
The developer composition is brought close to or in contact with the electrostatic latent image by a developing method such as a magnetic brush method or a touchdown method to form a toner image. This toner image is transferred to a transfer material such as paper and then fixed to obtain a copy or a printed matter. Further, the toner remaining on the surface of the photoconductor or the like is cleaned.

[0020]

[Example 1]

 (Manufacture of carrier) Vinylidene fluor with a softening point of 120 ° C
Loride-tetrafluoroethylene copolymer (Daikin
Kogyo Co., Ltd .: Finely pulverized resin particles having an average particle size of 9 μm,
T₁And T₂Difference of 15 ° C) 1.0 part by weight, softening point of 81 ° C
Styrene / methyl methacrylate / butyl methacrylate
Tocopolymer (manufactured by Soken Chemical Industry Co., Ltd .: average particle size 0.4 μm, T₁
And T ₂Difference of 19 ° C) 0.3 parts by weight and spherical Cu-Z
n-ferrite (manufactured by TDK: average particle size 80 μm) 100
Part by weight is a batch type with a jacket and a capacity of 50 L.
Mix for 10 minutes in a mixer and warm the mixture while stirring.
And stirred at a temperature of 120 ° C or higher for 20 minutes
Then, cool and stir until the temperature of the mixture reaches 60 ° C.
It started. Then, sieve with a 177 μm sieve and
I got a aria. (Production of toner) Binder resin: Styrene-n-butyl methacrylate resin 86% by weight Carbon black (R330 manufactured by Cabot) 8% by weight Charge control agent: Nigrosine (Bondron N04 manufactured by Hodogaya Chemical Co., Ltd.) 2% by weight Polypropylene wax (Sanyo) Chemical compound 330P) 4% by weight or more of material is melt-kneaded and finely pulverized to obtain an average particle size of 11μ.
Toner was obtained. (Preparation of developer) 100 parts by weight of the carrier and the toner described above.
-5 parts by weight were mixed with a V blender to obtain a developer.

Example 2 (Production of Carrier) Vinylidene fluorolide / trifluoroethylene copolymer having a softening point of 148 ° C. (Kureha Chemical Co., Ltd .: resin particles having an average particle size of 7 μm by fine pulverization, T ₁
And T ₂ of 22 ° C.) 1.3 parts by weight and spherical Zn ferrite (manufactured by TDK: average particle size 60 μm) 100 parts by weight,
Mix in a ribbon blender with a capacity of 30 L equipped with a jacket for 10 minutes, raise the temperature of the mixture while stirring, stir at a temperature of 150 ° C or higher for 20 minutes, and then cool and stir until the temperature of the mixture reaches 70 ° C. Done and then taken out. Then, sieving was performed with a 149 μm sieve to obtain a carrier. (Preparation of developer) 100 parts by weight of the above carrier and Example 1
5 parts by weight of the toner used in 1 above was mixed with a V blender to obtain a developer.

Example 3 (Production of Carrier) Styrene / methyl methacrylate copolymer having a softening point of 110 ° C. (manufactured by Soken Chemical Co., Ltd .: average particle size:
4 parts, 0.8 parts by weight of T ₁ and T ₂ (13 ° C. difference between T ₁ and T ₂ ) and 100 parts by weight of spherical Cu—Zn ferrite (manufactured by Powder Tech Co., Ltd .: average particle size 120 μm), batch kneader with jacket and capacity of 50 L. The mixture was mixed for 10 minutes, the temperature of the mixture was raised with stirring, the mixture was stirred at a temperature of 110 ° C. or higher for 20 minutes, cooled and stirred until the temperature of the mixture reached 60 ° C., and taken out. Then 210 μm
The carrier was obtained by sieving with a No. 1 sieve. (Production of toner) Binder resin: Styrene-n-butyl methacrylate resin 88% by weight Carbon black (BPL manufactured by Cabot Corporation) 6% by weight Charge control agent: Chromium-containing dye (TRH manufactured by Hodogaya Chemical Co., Ltd.) 2% by weight Polypropylene wax ( 330P manufactured by Sanyo Kasei Co., Ltd. 4 wt% or more of the material was melt-kneaded to obtain a toner having an average particle diameter of 11 μ. (Preparation of Developer) 100 parts by weight of the carrier and 5 parts by weight of the toner were mixed with a V blender to obtain a developer.

Comparative Example 1 (Production of Carrier) Fluorine-containing acrylic polymer having a softening point of 70 ° C. (manufactured by Dainippon Ink and Chemicals, Inc .: resin particles having an average particle size of 11 μm by fine pulverization, difference between T ₁ and T ₂ 36 ° C)
1.3 parts by weight and 100 parts by weight of spherical Cu—Zn ferrite (manufactured by TDK: average particle size 80 μm) were mixed in a ribbon blender with a capacity of 30 L equipped with a jacket for 10 minutes, and the temperature of the mixture was stirred while stirring. Increase to 70 ℃
After stirring for 20 minutes at the above temperature, the temperature of the mixture is 30
The mixture was cooled and stirred until the temperature reached ℃, and then taken out. Then, sieving was performed with a 177 μm sieve to obtain a carrier. (Preparation of developer) 100 parts by weight of the above carrier and Example 1
5 parts by weight of the toner used in 1 above was mixed with a V blender to obtain a developer.

Comparative Example 2 (Production of Carrier) Polymethylphenyl silicone having a softening point of 93 ° C. (manufactured by Toray Dow Corning Co., Ltd .: resin particles having an average particle size of 9 μm by fine pulverization, difference between T ₁ and T ₂ ) 33
C.) 2.0 parts by weight and 100 parts by weight of spherical Cu—Zn ferrite (manufactured by Powder Tech Co., Ltd .: average particle size 80 μm).
Mix for 10 minutes in a batch kneader with a capacity of 50 L equipped with a jacket, raise the temperature of the mixture with stirring, stir for 20 minutes at a temperature of 95 ° C or higher, and then cool and stir until the temperature of the mixture reaches 50 ° C. And then removed. Then, sieving was performed with a 177 μm sieve to obtain a carrier. (Preparation of developer) 100 parts by weight of the above carrier and Example 3
5 parts by weight of the toner used in 1 above was mixed with a V blender to obtain a developer.

[Image Quality Maintainability Test] The developers of Examples 1 and 2 and Comparative Example 1 were replaced with VIVACE500 manufactured by Fuji Xerox Co., Ltd.
The image quality retention test was conducted using the above, and the image quality retention test was conducted on the developers of Example 3 and Comparative Example 2 using FX5039 manufactured by Fuji Xerox Co., Ltd. The results of the test are shown in Table 1.

[0026]

[Table 1]

[0027]

According to the present invention, by adopting the above-mentioned constitution, it is possible to form a uniform continuous film with respect to the magnetic core particles, the carrier aggregation at the time of production is small, and the carrier adhesion to the image area is small. Low, low carrier consumption, and
It has made it possible to manufacture a carrier that can provide excellent copy image quality without fog or density unevenness at a high yield.

[Brief description of drawings]

FIG. 1 shows the intersection points T ₁ and T when the endothermic peak is a single peak.
It is a graph for explaining how to make the determination of ₂ .

FIG. 2 shows an intersection T ₁ , when the endothermic peak is a multiple peak.
6 is a graph for explaining how to determine T ₂ .

Claims (2)

[Claims] 1. A carrier for developing an electrostatic charge image produced by a dry coating method, wherein as coating resin particles, the difference between the intersection points T ₁ and T ₂ of a tilt line and a baseline forming an endothermic peak by a differential scanning calorimetry method. A carrier for developing an electrostatic charge image, which comprises a resin having a temperature of 30 ° C. or lower. _2. The difference between the intersection points T ₁ and T ₂ of the inclined line forming the endothermic peak and the baseline in the differential scanning calorimetry is 30.
2. The carrier for developing an electrostatic charge image according to claim 1, further comprising a step of heating and cooling while mixing the resin particles having a temperature of not more than 0 ° C. and the carrier core material to coat the resin on the carrier core material.