JPH0327054A - Electrophotographic carrier and binary developer - Google Patents

Abstract

PURPOSE:To reduce production of a spent toner and tendency of charging up of a toner and to stabilize chargeability characteristics at the time of repeated uses by coating the core material of the carrier with a coating material comprising a specified vinyl copolymer and a fluororesin. CONSTITUTION:This carrier to be used is formed by coating the core material, such as ferrite particles, with the coating material containing the vinyl copolymer having a hydroxyl value of 1 - 100, such as a styrene.2-hydroxyethyl methacrylate.methyl methacrylate copolymer., and the fluororesin, such as a vinylidene fluoride-tetrafluoroethylene copolymer, and fine conductive particles of <=1.0 mum particle diameter, such as carbon black, dispersed into both resins. It is preferred to use the binary developer comprising the positively chargeable toner and the carrier.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a carrier and a two-component developer that together with a toner constitute a developer for C electrostatic charge image development. Patent No. 2,297,891, Japanese Patent Publication No. 42-23910 and Japanese Patent Publication No. 43-2
Various methods are described in Japanese Patent No. 4748, etc., but in all of these methods, an electrostatic latent image is formed by irradiating the photoconductive layer with a light image corresponding to the original, and then the electrostatic latent image is formed. The electrostatic latent image is developed by attaching colored fine powder called toner having the opposite polarity onto the latent image, and if necessary, after transferring the toner image to a transfer material such as paper, heat, Copies are obtained by fixing using pressure or solvent vapor. In the process of developing the electrostatic latent image, toner particles charged to the opposite polarity to that of the latent image are attracted by electrostatic attraction and attached to the electrostatic latent image (in the case of reversal development, (using a toner with a triboelectric charge of the same polarity as the charge of the latent image).Generally speaking, methods for developing electrostatic latent images using toner can be roughly divided into so-called two-component methods in which a small amount of toner is dispersed in a medium called a carrier. There are two methods: one uses a developer, and the other uses a so-called one-component developer, which uses toner alone without using a carrier. In general, carriers used in such two-component type developers are broadly classified into conductive carriers and insulating carriers. Oxidized or unoxidized iron powder is usually used as a conductive carrier, but developers using this iron powder carrier have unstable triboelectric charging properties with respect to toner, and There is a problem that fog occurs in the visible image. In other words, with the use of developer,
As the toner particles adhere to the surface of the iron powder carrier particles, the electrical resistance of the carrier particles increases and the bias current decreases, and the triboelectric charging properties become unstable, resulting in a decrease in the image density of the visible image formed. and fog increases.

Insulating carriers are generally iron and nickel. A typical example is a carrier in which the surface of a carrier core material made of a ferromagnetic material such as ferrite is uniformly coated with an insulating resin. Developers using this carrier have significantly fewer toner particles fused onto the carrier surface than those using conductive carriers, and are particularly suitable for high-speed electronic copying machines due to their excellent durability and long service life. It has the advantage of being suitable.

However, in this insulating carrier, the coating layer covering the surface of the carrier core material must have sufficient abrasion resistance and strong adhesion to the core material (durability), and the coating layer that covers the surface of the carrier core material must have sufficient abrasion resistance and strong adhesion to the core material (durability). The coating layer must have good adhesion prevention properties (toner venting properties) so that the film body does not become deformed, and the desired charge value and polarity can be obtained by friction with the specific toner used with the carrier. (Chargeability) is required. That is, the carrier is rubbed against other carrier particles and toner particles in the developing device, but when toner adheres to the surface of the carrier coating layer and a film is formed, the charging characteristics become unstable.

Conventionally, as a technique for solving this problem, a coated carrier coated with a fluorine-containing polymer or fluorine-containing resin having a low critical surface tension has been proposed in U.S. Pat. No. 3,922,382. In terms of technology, carriers coated only with fluorine-containing polymers have poor film-forming properties, can only partially coat the carrier surface, and have a strong tendency to have unstable charging characteristics.

On the other hand, carriers coated with vinyl resins such as styrene/methacrylate copolymers have good film-forming properties, strong adhesion to the carrier core material, and excellent wear resistance. However, since this vinyl resin has a relatively high critical surface tension, toner tends to vent when used repeatedly, causing some problems in the lifespan of the developer.
In addition, positively chargeable toners often have problems if they have low charge imparting ability.Furthermore, due to their good film-forming properties, carriers tend to have an excessively high resistance, and as a result, toner Charge-up tends to make toner difficult to separate from the carrier.

Also, Japanese Patent Application Laid-Open No. 110839/1983 (US Pat
entNo. In order to improve the film-forming properties of fluorine-containing polymers, a carrier coated with a polymer mixed with relatively good film-forming properties has been proposed in 4297427).
If the film resistance improves, the resistance will inevitably increase, and the above-mentioned toner charge-up (due to toner separation from the carrier) will become worse.

Furthermore, if development is continued for a long time in a state where the toner is difficult to separate from the carrier, the above-mentioned sventing of the carrier by the toner will be further promoted, which is undesirable. Furthermore, if the resistance of the carrier is too high, the image density may decrease, the reproducibility of halftones in the evening area may deteriorate, or the carrier may be developed onto the photoreceptor, causing damage to the photoreceptor.
Carrier may adhere to the image.

In this way, it is extremely important, yet difficult, to control the resistance of the carrier surface without damaging the coating properties of the coating material. In order to solve these problems, attempts have been made to control the resistance by dispersing conductive fine particles in carrier coating resin. For example, in Japanese Patent Publication No. 53-6535,
It has been shown that conductive fine particles of 0.1 μm or less are added, and many other applications such as Japanese Patent Laid-Open No. 7343/1983 have been filed.

However, a common problem with these proposed methods is that when a sufficient amount of conductive powder is added to reduce the surface resistance of the carrier to a desirable value, the adhesion between the core material and the coating resin decreases. This will impair the durability of the carrier as described above, and furthermore, a film may not be formed even in the process of coating the carrier surface with the coating material. In addition, another problem arises in that the ability to charge the toner decreases, especially under high humidity conditions. [Problems to be Solved by the Invention] In view of the current problems as described above, the purpose of the present invention is to solve the following points. The first object of the present invention is to provide a resin-coated carrier that causes less spent toner. A second object of the present invention is to provide a resin-coated carrier that is difficult to charge up.

A third object of the present invention is to provide a resin-coated carrier that has stable charging characteristics even when used repeatedly.

A fourth object of the present invention is to provide a resin-coated carrier with excellent abrasion resistance.

[Means and effects for solving the problems] The present invention provides a mixed resin containing a vinyl copolymer and a fluororesin in which conductive fine particles having a particle size of 1.0 μ1 or less are dispersed and having a hydroxyl value of 1 to 100. The present invention relates to an electrophotographic carrier characterized in that it is coated with a carrier core material, and a developer comprising the carrier and a positively chargeable toner. As a result of intensive research by the present inventors, vinyl resins containing hydroxyl groups have excellent binding properties with carrier core materials, and have a strong tendency to selectively adhere to carrier core materials. It has been found that there appears to be a tendency for the mixture to be exposed on the carrier coated surface. The present invention takes advantage of this characteristic by actively exposing the fluororesin, which has a high ability to impart positive charge to positively chargeable toner, on the surface of the carrier coating, and also to prevent the surface from becoming too high in resistance. By exposing the conductive fine particles on the surface of the carrier in a similar manner, a carrier having excellent durability, preventing charge-up, and having a high ability to impart a positive charge can be obtained.

The vinyl resin containing a hydroxyl group used in the present invention is a copolymer of a vinyl monomer having a hydroxyl group and another vinyl monomer.

Vinyl monomers having hydroxyl groups include 2-hydroxyethyl acrylate, 2-hydroxybrobyl acrylate, 2-hydroxybutyl acrylate, 2-hydroxy-3-phenyloxyprobyl acrylate, 2-hydroxyethyl methacrylate, and methacrylate. 2-hydroxybrobyl acid, 2-hydroxybutyl methacrylate,
Examples include methacryl RL & 2-hydroxy-3-phenyloxyprobyl. These monomers have a copolymer hydroxyl value of 1 to 100 (KOHmg/g), more preferably 5 to 70, and even more preferably 10 to So
(Koumg/g). If this value is small, the adhesion between the carrier core material and the coating layer will be insufficient, and the coating will be easily destroyed by impact, friction, etc., and furthermore, the exposure of the fluorine-containing resin to the carrier surface, which is the main objective of the present invention, will be reduced. The effect is insufficient, and the carrier's ability to impart positive charge decreases. On the other hand, if it is too large, the hygroscopicity will increase and the f-electrode stability will be lost under high temperature and high humidity conditions.

Other vinyl monomers to be copolymerized with these vinyl monomers having hydroxyl groups include styrene. α−
Styrene derivatives such as methylstyrene, p-methylstyrene, p-t-butylstyrene, p-chlorostyrene;
Methyl methacrylate. Ethyl methacrylate, probyl methacrylate. Butyl methacrylate, bentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, nonyl methacrylate. Decyl methacrylate. Undecyl methacrylate, dodecyl methacrylate. Glycidyl methacrylate, methoxyethyl methacrylate, broboxyethyl methacrylate. Butoxyethyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate. Methyl acrylate, ethyl acrylate, probyl acrylate, butyl acrylate. Bentyl acrylate, hexyl acrylate, hebutyl acrylate.
Octyl acrylate. Nonyl acrylate, decyl acrylate. Mention may be made of vinyl monomers.

Among these other vinyl monomers, vinyl monomers having one vinyl group in one molecule include styrene, styrene derivatives, methacrylic acid esters. Acrylic acid esters are preferred, and alkyl esters of methacrylic acid or acrylic acid having 1 to 5 carbon atoms in the alkyl group are particularly preferred.

Among these vinyl monomers, vinyl monomers having a hydroxyl group have a copolymer with a hydroxyl value of 1 to 1.
100 (1 g/g of KOH).

These vinyl monomers are produced using suspension polymerization. It is copolymerized using methods such as emulsion polymerization and solution polymerization. Further, this copolymer may be crosslinked with melamine aldehyde or isocyanate. In addition, in this invention, a hydroxyl number refers to the value measured based on JIS-KOO70.

On the other hand, examples of the fluororesin to be mixed with the vinyl resin containing hydroxyl groups include polyvinyl fluoride, polyvinylidene fluoride, halofluorobolymers such as polytrifluoroethylene and polytrifluorochloroethylene, polytetrafluoroethylene, Polyvar fluoropropylene,
Copolymer of vinylidene fluoride and acrylic monomer, copolymer of vinylidene fluoride and trifluorochloroethylene,
A copolymer of tetrafluoroethylene and hexafluoropropylene, a copolymer of vinyl fluoride and vinylidene fluoride, a copolymer of vinylidene fluoride and tetrafluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene, A copolymer of tetrafluoroethylene, vinylidene fluoride, and a fluoroturbopolymer such as a nonfluorinated monomer is preferably used.

The mixing ratio of these fluororesins and the vinyl resin having a hydroxyl group can be applied within a wide range due to the above-mentioned characteristic effects of the vinyl resin having a hydroxyl group. Specifically, in C, the ratio of the fluororesin to the vinyl resin having a hydroxyl group (Ii quantitative ratio) is 3:9.
7 to 95:5, more preferably 5:95 to 90:1
0, more preferably 80:20 to 20:80. If the content of the fluororesin is less than 3% by weight, the effect of adding the fluororesin tends to be insufficient. On the other hand, if the content of the fluororesin exceeds 95% by weight, vinyl having hydroxyl groups Since the amount of the system resin decreases, the adhesion of the resin coating layer to the core material tends to decrease.

The amount of the above-mentioned coating resin to be treated is generally 0.1 to 30% by weight based on the carrier core material in total, considering the film formability and durability of the coating material.
(preferably 0.5 to 20% by weight). Coverage amount is 0
．． If it is less than 1% by weight, the effects of coating tend to be insufficient, and if it exceeds 30% by weight, it becomes difficult to form a coating layer with a uniform thickness.

As the conductive fine particles added to these coating resins, 1
A suitable inorganic particulate material having a volume resistivity of less than 0 Ω·cm, preferably less than 1 Ω·cm is used.

Specifically, carbon black powder, graphite powder, Cu. Zn, Sn. ^2, Ti, Sb, etc. alone, alloys, or oxides are used. The particle size is
The thickness to be exposed to the surface of the carrier coating film, which is the object of the present invention, is 1.0 ttm or less, preferably 0.5 μm or less, more preferably 0.1 μm or less. The amount of conductive fine powder added to the coat resin is 0.1 to the resin.
wt% to 20 wt%, preferably 0.2 wt% to 1
If it is less than 0 wt% or 0.1 at%, the effect of the present invention will not be significant, and if it exceeds 20 wt%, the coating properties of the coating film, which is one of the characteristics of the present invention, will not be sufficiently good. As the carrier core material used in the present invention, general materials such as iron powder and ferrite are used, and the particle size thereof is l(1
-10007zm, preferably 20-200μm is suitable. In order to coat the surface of the carrier core material with the resin to which the conductive fine particles have been added, the resin is dissolved or suspended in a solvent, the conductive fine particles are further added, and the resin is placed in a dispersion machine. It can be sufficiently dispersed and applied by a general method such as spraying. The binder resin of the toner used in the two-component developer in combination with the carrier of the present invention includes monomers of styrene and its substituted products such as polystyrene and polyvinyltoluene; styrene-brobylene copolymer; Vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl axolate copolymer , styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-acrylic-aminoacrylic copolymer, styrene-aminoacrylic copolymer, styrene- Acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isobrene copolymer, styrene- acrylonitrile-indene copolymer,
Styrenic copolymers such as styrene-maleic acid copolymers and styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide, epoxy resin, polyvinyl Butyral, polyacrylic acid resin, terpene resin,
Phenol resins, aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, paraffin waxes, etc. can be used alone or in combination of two or more as necessary. Any suitable pigment or dye can be used as a colorant in the above toner, such as Rikibon Black.
Iron black, phthalocyanine blue, ultramarine. Dyes or pigments such as quinacridone and benzidine yellow are used. In addition, as positive charge control agents, amino compounds, quaternary ammonium compounds, organic dyes, especially basic dyes and their salts, penzyldimethyl-hexadecyl ammonium chloride. Desyltrimethylammonium chloride. Nigrosine base, nigrosine hydrochloride, safranin gamma and crystal violet. etc. may be added. In combination with the carrier of the present invention, positively charged toners are preferred because they provide good triboelectric charge. The above-described toner structure may be used for a toner produced by the commonly used mixing and pulverizing method, and may also be used for the wall material, the core material, or both of the microcapsule toner. In the present invention, toner may mean colored resin particles to which colloidal silica is externally added, or may mean colored resin particles themselves. In the present invention, positively charged silica refers to silica that has a positive triboelectric charge relative to an iron powder carrier or a stainless steel carrier when measured by a blow-off method. As the silicone oil having a nitrogen atom in the side chain used in the treatment of the silica powder, a silicone oil having at least a partial structure represented by the following formula can be used.

(In the formula, R represents hydrogen, an alkyl group, an aryl group, or an alkoxy group, R2 represents an alkylene group or a phenylene group, R, and R4 represent hydrogen, an alkyl group, or an aryl group, and R represents a The above alkyl group, aryl group, alkylene group, and phenylene group (representing a nitrogen heterocyclic group) may have an organo group having a nitrogen atom, or may have a substituent such as a halogen to the extent that the chargeability is not impaired. You may have one. Further, the nitrogen-containing silane cobbling agent used in the present invention generally has a structure represented by the following formula.

R. -St-Yn (R represents an alkoxy group or halogen, Y represents an amino group or an organo group having at least one nitrogen atom, m and n are integers of 1 to 3, and m+n is 4) .) Examples of the organo group having at least one nitrogen atom include a main group having an organic group as a substituent, a nitrogen-containing heterocyclic group, or a group having a nitrogen-containing heterocyclic group. Examples of the nitrogen-containing heterocyclic group include unsaturated heterocyclic groups and saturated heterocyclic groups, and publicly known ones can be used. Examples of the unsaturated heterocyclic group include the following.

Examples of the saturated heterocyclic group include the following.

The heterocyclic group used in the present invention is preferably a five-membered or six-membered ring in terms of stability. Examples of such treatment agents include nobrobyltrimethoxysilane, aminobrobyltriethoxysilane, dimethylaminobrobyltrimethoxysilane, and diethylaminobrobyltrimethoxysilane. Dibropyrua-based nobrobil trimethoxysilane, dibutylaminobrobyl trimethoxysilane, monobutylar-based nobrobil trimethoxysilane. Dioctylaminopropyltrimethoxysilane, dibutyl-nobrobil dimethoxysilane, dibutyl-nobrovir monomethoxysilane. Dimethylaminophenyltriethoxysilane. There are trimethoxysilyl-γ-propylphenylamine, trimethoxysilyl-Y-propylbenzylamine, etc. Furthermore, as the nitrogen-containing heterocyclic group, those having the above structure can be used, and examples of such compounds are , trimethoxysilyl-γ-brobylbiberidine. Examples include trimethoxysilyl-γ-propylmorpholine, trimethoxysilyl-γ-brobyl-dazole, and the like.

The typical amount of these treated positively charged silica fine powders is:
Positively charged toner 100 [[0.01 to 100 parts]
The effect is exhibited when the amount is 8 parts by weight, particularly preferably 0.1
-Exhibits positive chargeability with excellent stability when a certain amount of Sl is added. A preferred form of addition is 0.1 to 3 parts by weight per 100 parts by weight of positively charged toner.
It is preferable that the weight part of the treated silicate fine powder is attached to the surface of the toner particles. Furthermore, the silica fine powder used in the present invention may be treated with a treatment agent such as a silane coupling agent or an organosilicon compound for the purpose of hydrophobization, if necessary, to react with or physically adsorb to the silica fine powder. Treated with the above processing agent.
Examples of such treatment agents include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane,
Allyl phenyldichlorosilane, benzyldimethylchlorosilane, prommethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercabutane, trimethylsilylmercabutane, triorganosilyl Acrylate, vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane,
Hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane,! ．． Examples include 3-diphenyltetramethyldisiloxane, and dimethylpolysiloxane, which has 2 to 12 siloxane units per molecule and each unit located at the end contains one hydroxyl group bonded to Si. These 1f! It is used as lI or as a mixture of two or more types.

A commonly used mixing method can be used to mix the carrier and toner (and silica fine powder) of the present invention, but the toner concentration is 100% of the developer (carrier + toner).
It is preferable that the toner contains 0.5 to 20 parts by weight (more preferably 1 to 10 parts by weight) in the parts by weight.

This will be explained in detail in Examples below. "r part" shown in the following examples.
is parts by weight. [Example] Spherical ferrite particles with an average particle size of 69 μm were prepared as the core material of Oiwatari Ucarrier.

The above copolymer (10 parts in total) was dissolved in 90 parts of a mixed solvent of acetone and methyl ethyl ketone (mixed weight ratio = 1 + 1) to prepare a solution with a 10% concentration. This solution 100
conductive carbon black (average particle size = 0.02
pm, specific electrical resistance = 0. A coating solution was prepared by adding 0.1 part of 12Ω-cm) and dispersing it for 24 hours using a Pall Mill Bot.

The prepared coating solution was applied to the ferrite particles using a coating machine (Subira Coater manufactured by Okada Seiko Co., Ltd.). After removing the solvent, it was dried at a temperature of 90° C. for 1 hour to produce a resin coated carrier A1.

The ferrite particles were coated with about 0.8% by weight of the copolymer, calculated from the weight change before and after coating.

On the other hand, the above composition is mixed, melt-kneaded, pulverized, and classified,
Cyan resin fine particles having a volume average particle diameter of 12 gm were produced. Positively charged hydrophobic colloidal silicone treated with 100 parts of cyan resin particles and amino-modified silicone oil with a strength of 0.8
% by weight using a Henschel mixer to prepare a cyan toner.

The toner and carrier A were mixed at a weight ratio of 7:93 using a V-blender to obtain a two-component developer.

When the obtained two-component developer was applied to a Canon Co., Ltd. copier NP-4835 and an image formation test (image production) was performed in various environments, the image reflection density was
℃, 60% RH). 25. Low temperature and low humidity (15℃,
io%RH) under 1.27, high temperature (35℃, 90%
RH) and a high value of 1.30, a clear image without fogging was obtained.

Furthermore, the above developer was put into the developing device of NP-4835, and an external idle rotator that rotates only the sleeve without image formation was used to run idle for 4 hours at room temperature to prevent charge-up and carrier deterioration. The durability was simulated. When an image was produced using NP-4835 using the developing device containing the developer after idling, a high-quality image with a density of 1.20, which was almost the same as the initial image, was obtained. It was found that it was possible to prevent the toner from blowing up, and there was no substantial deterioration such as toner venting of the carrier.

In place of the mixed resin of Example 1 (mixing ratio = 1:1),
Styrene - 2-hydroxymethyl methacrylate - methyl methacrylate - ethyl methacrylate (monomer composition weight ratio = 57: 20: 13: 10, hydroxyl value =
40) 3.5 parts of methyl etherified melamine formaldehyde resin and vinylidene fluoride-tetrafluoroethylene copolymer (monomer composition weight ratio +-75:
25) Dissolve 5 parts of methyl ethyl ketone solution C to 10%
A solution of the same concentration was prepared. Conductive Zn was added to 100 parts of this solution.
A coating solution was prepared in the same manner as in Example 1 by adding 0.2 parts of O powder (average particle size -0.1 um), and then a coated carrier was prepared. On the other hand, the above components were mixed, melt-kneaded, crushed, and classified to obtain black fine particles with a volume average particle diameter of 11 μm. The positively charged hydrophobic colloidal silica used in Example 1 was added to these characteristic particles. A toner was prepared by mixing 31% by weight of C.s with a Henschel mixer. The toner and the carrier are mixed in a weight ratio of 2:98.
- A two-component developer was obtained by mixing using a blender.

When this developer was applied to a Canon NP-5000 copier that had been modified for use in black toner development and evaluated in the same manner as in Example 1, images of high density and high quality were obtained in each environment. Furthermore, as in Example 1, even after idling only this developing device for 4 hours, a high-quality image that was almost the same as the initial image was obtained. [Effects of the Invention] The present invention provides that vinyl resins containing hydroxyl groups have excellent binding properties with carrier core materials, have a strong tendency to selectively adhere to carrier core materials, and as a result, can be mixed with other mixtures. This takes advantage of the characteristic that C1 tends to be exposed on the surface of the carrier coating. Conductive fine particles to prevent excessive resistance are likewise actively exposed on the carrier surface, resulting in a carrier with excellent durability and high ability to impart positive charge that prevents charge-up.

Claims (2)

[Claims] (1) The carrier core material is coated with a mixed resin containing a vinyl copolymer and a fluororesin having a hydroxyl value of 1 to 100 and in which conductive fine particles with a particle size of 1.0 μm or less are dispersed. Characteristic carrier for electrophotography. (2) A two-component developer comprising a positively chargeable toner and the carrier according to claim (1).