JPH01288866A - Carrier for electrophotographic developer - Google Patents

Abstract

PURPOSE:To enhance the electrostatic chargeability of a negative electrostatic charge type carrier and to prevent sticking thereof to a photosensitive body as well as to prolong the life of the carrier by incorporating fine fluoroplastic powder and acicular magnetic particles into the carrier. CONSTITUTION:This carrier is the negative electrostatic charge type carrier essentially consisting of a binder resin (e.g. styrene/acryl copolymer) and the magnetic powder (e.g. granular magnetite) and is further added with the fine fluoroplastic powder (A) and is also added with the acicular magnetic particles (B) as a part of the magnetic powder. The amt. of the component A (e.g. polyvinylidene fluoride) to be added is preferably >=3wt.% of the total weight of the carrier and the amt. of the component B (e.g. acicular magnetite) to be added is preferably >=5wt.% of the total weight of the magnetic powder. The average grain size of the carrier is preferably >=50mum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a component of a two-component developer for developing an electrostatic latent image or a magnetic latent image in electrophotography, electrostatic recording, electrostatic printing, etc. More specifically, the present invention relates to a magnetic particle-dispersed negatively charged carrier.

Conventional technology In electrophotography, a photoconductive substance such as selenium is used as a photoreceptor, an electrical latent image is formed using various means, and this latent image is developed using a magnetic brush development method or the like. Generally, a method is adopted in which toner is attached to the image and visualized.

In this development process, a two-component developer that uses carrier particles called chytria is most often used in order to impart an appropriate amount of positive or negative electricity to the toner.

Various types of developer carriers have been developed and put into practical use.

There are various properties required for carriers, but particularly important properties include appropriate charging properties, impact resistance, abrasion resistance,
It can improve developability, developer life, etc.

By the way, conventionally used carriers still have problems to be improved and cannot fully satisfy the above-mentioned characteristics.

For example, conductive carriers such as iron oxide powder have poor solid developability, but are inferior in fine line recyclability, and in order to extend the life of the toner, it is recommended to include a special charge control agent in the toner. It has disadvantages such as not being necessary. In order to improve these drawbacks, a small particle size carrier in which magnetic fine particles are dispersed in a resin, a so-called carrier for microtoning, has been proposed and put into practical use. (Refer to JP-A-54-68134 and JP-A-58-220146).

It has also been proposed to use acicular magnetic powder as magnetic fine particles (Japanese Unexamined Patent Publication No. 59-223458).Problems to be Solved by the InventionHowever, conventionally proposed carriers do not adhere to the photoreceptor or surface. There are disadvantages such as changes in the amount of charge at high and low humidity caused by magnetic particles liberated in the air, and difficulty in surface treatment, which makes it difficult to dramatically extend the service life. It wasn't completely satisfying. For example, the one described in Japanese Patent Application Laid-Open No. 59-223458,
When used for a long period of time, contamination inside the machine and background fog occur, and the lifespan of the developer is extremely short.

On the other hand, the present inventors previously proposed a carrier made of magnetic powder and resin containing a fluorine resin (Japanese Patent Application No. 61-173559), but from the beginning of the copying operation, the carrier and The toner adheres to the background area, resulting in a copied image with fog in the background area, and no matter what innovations are made to the developing machine or how the particle size of chitria is adjusted, this problem cannot be resolved. I couldn't.

The present invention has been made in view of the above-mentioned problems in the prior art.

Therefore, an object of the present invention is to provide a negatively charged carrier for magnetic brush development, which is used for developing electrostatic latent images in electrophotography and electrostatic recording.

Another object of the present invention is to provide a negatively charged carrier for magnetic brush development that has a long developer life, is excellent in environmental stability, and does not cause toner fog in the background or carrier fog in the background.

Means for Solving the Problems The present inventors have conducted various studies and examinations to improve the drawbacks of the conventional carriers, and as a result, they have developed a carrier that contains a specific fine resin powder and uses a specific magnetic powder. The present inventors have discovered that the use of a magnetic fine particle dispersed carrier is effective in improving the various required characteristics of the carrier, and have completed the present invention.

That is, the negatively charged carrier for electrophotographic developer of the present invention contains a binder resin and magnetic powder as essential components,
It is characterized in that a carrier contains fine fluororesin powder, and a portion of the magnetic powder consists of acicular magnetic particles.

As the binder resin used as an essential component of the negatively charged carrier of the present invention, any resin generally known as a thermoplastic resin can be used. Specifically, styrenes such as styrene and chlorostyrene; monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoonate, and vinyl butyrate; methyl acrylic and acrylic acid. α-methylene aliphatic monocarboxylic acid esters such as ethyl, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate; vinyl methyl ether;
Vinyl ethers such as vinyl ethyl ether and vinyl butyl ether; homopolymers or copolymers of vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and vinyl isopropenyl ketone can be used.

Particularly typical binder resins include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, and styrene-maleic anhydride copolymer. Polymers can be mentioned. Further examples include polyester, polyurethane, epoxy resin, polyamide, modified rosin, paraffin, and wax.

The magnetic powder used in the present invention is partially composed of acicular magnetic particles.

The acicular magnetic particles have an average particle size of 0.1 to 3 mm, a long axis/
The short axis ratio is 2 or more, and fine powders such as acicular magnetite, acicular ferrite, and γ-F8203 can be used. These acicular magnetic particles are preferably used in an amount of 5% by weight or more based on the total amount of magnetic powder, and more preferably 20% by weight or more based on the total amount of magnetic powder.
-50% by weight, and better results can be obtained when blending in this range. If the amount is less than 5% by weight, carrier and toner will adhere to the background area.

As the magnetic fine particles used together with the above-mentioned acicular magnetic fine particles, any commonly used ferromagnetic fine particles can be used. Examples include powders of ferrite, chromium oxide, and various metals. In addition, the particle size of these is usually 5#.
1 or less, especially 2 or less is used.

The content of the magnetic powder, a part of which is composed of acicular magnetic particles, is usually about 50 to 90% by weight, preferably 65 to 85% by weight, based on the total amount of Kyrelia, giving good results.

In the present invention, examples of the fluororesin contained in the carrier in the form of fine powder include the following. That is, polymers containing fluorine in the main chain, such as homopolymers such as tetrafluoroethylene, trifluoroethylene, vinylidene fluoride, monofluoroethylene, hexafluoropropylene, or the above monomers and ethylene, propylene,
Examples include copolymers with butylene, vinyl chloride, vinylidene chloride, trifluoroethylene, and other copolymerizable unsaturated bond-containing monomers.

These fluororesins are dispersed in the carrier in the form of fine powder (-order particles), and the average particle size is suitably a submigron number.

The proportion of the fluororesin fine powder varies depending on its type, but is used in an amount of 3% by weight or more, preferably 3 to 20% by weight, based on the total amount of carrier. If the proportion of the fluororesin fine powder is less than 3% by weight, it will not be possible to impart a sufficient amount of charge to the carrier, and the effect of extending the life of the developer will be poor. Moreover, if it exceeds 20% by weight, depending on the toner used, the amount of charge may increase too much, resulting in low density images.

In addition to the binder resin, magnetic powder, and fluororesin fine powder, the negatively charged carrier of the present invention may contain resins, charge control agents, Coupling agents, fillers, other fine powders, etc. can also be added inside the carrier.

The carrier of the present invention can be prepared by various methods such as binding resin,
Fine fluororesin powder and magnetic powder are kneaded, Banbury,
It can be produced by pulverization, classification, etc. using a heating melt mixing device such as an extruder.

The particle size of the carrier of the present invention is determined from an average particle size of 3.
0~2001II! i, more preferably 50 to 100. That is, when the average particle size of the carrier is 5ON1 or more, when mixed with the toner,
This is preferable because it is possible to produce 1q copy images without carrier or toner adhesion in the background area without making any modifications to the developing machine.

The negatively charged carrier of the present invention thus obtained is mixed with a toner and used as a magnetic brush developer for developing electrostatic latent images.

As the toner, any toner can be used as long as it has a colorant dispersed in a binder resin and is commonly used in electrophotography. In particular, when used in combination with a toner containing a metal oxide such as aluminum oxide, titanium oxide, silicon oxide, or tin oxide as an external additive, a remarkable effect is obtained.

The negatively charged carrier according to the present invention has the above-mentioned structure, but the fluororesin fine powder dispersed in the binder resin imparts a high charge amount to the toner, which shortens the life of the carrier and, therefore, shortens the development process. It is presumed that this works to prolong the life of the agent and to reduce its environmental dependence. Further, it is presumed that the acicular magnetic fine particles used as part of the magnetic powder act to extremely reduce adhesion of the carrier and toner to the background area.

EXAMPLES Hereinafter, the present invention will be briefly and concretely explained using examples and comparative examples. However, the present invention is not limited to this example.

In addition, in the following examples, "parts" represent "parts by weight".

Example 1 Granular magnetite (particle size 0.5) 45 parts Magnetite acicular powder (long axis diameter 0.5 ua, short axis diameter 0.05) 25 parts Styrene-acrylic copolymer 24 parts Polyvinylidene fluoride (KYNAR) .

Penn Wait, USA! 6 parts The above ingredients were melt-kneaded using a pressure kneader, and further crushed and classified using a turbo mill and a classifier to obtain an average particle size of 70p.
I got a career of m.

Example 2 Granular magnetite (particle size 0.5 μm) 50 parts Magnetite acicular powder (long axis diameter 0.5 μm, short axis diameter 0.05 μm)
a> 20 parts Styrene-acrylic copolymer 24 parts Polytetrafluoroethylene (trade name: Lublon, manufactured by Daikin Industries, Ltd.) 6 parts Using the above components, cross-mixing, crushing and classification were carried out in the same manner as in Example 1, A carrier having an average particle size of 70 μm was obtained.

Comparative Example 1 Granular magnetite (particle size 0.5M> 45 parts magnetite acicular powder (long axis diameter 0.5 μs, short axis diameter 0.057
m> 25 parts Styrene-acrylic copolymer 30 parts Using the above components, cross-mixing, pulverization, and classification were carried out in the same manner as in Example 1, and the average particle size was 7.
0 Immediate career (qta.

Comparative Example 2 Magnetite (EPT 1000° manufactured by Toda Kogyo viJ) 70 parts Styrene-acrylic copolymer 24 parts Polyvinylidene fluoride (KYNAR).

Manufactured by PerinWa l in the USA) 6
Using the above components, mixing, pulverization, and classification were carried out in the same manner as in Example 1 to obtain a carrier having an average particle size of 70 iun.

The carriers obtained in Examples 1 and 2 and Comparative Examples 1 and 2 above were mixed with the following toners to form a developer of 1.2%, respectively.
．． 1q of 3 and 4. That is, the toner used was a toner made of styrene-acrylic resin and watching red with an average particle size of 12 mm, using 2 parts by weight of titanium oxide P-25 (manufactured by Nippon Aerosil) as an external additive, and the toner concentration was 5 parts by weight. % to obtain a developer.

For these developers, the photoreceptor speed is 150 rrm/
sec and developing magnetic roll (sleeve) speed 410 m
/sec, an initial image quality test and a lifespan test were conducted using a bench machine for evaluation fli.

In the initial image quality test, developers 1, 2 and 3 had no carrier or toner adhesion to the background area, and showed excellent performance even when the bias voltage applied to the developing sleeve was increased and even in a low temperature and low humidity environment. I was able to obtain high quality images. However, with developer 4, carrier and toner adhesion to the background area occurred significantly.

Next, we performed a lifespan test on Developers 1, 2, and 3 while replenishing toner, and found that in the case of Developer 3, contamination inside the machine was significant after 10,000 copies, and image quality problems appeared; In the cases of Nos. 1 and 2, even after 50,000 copies were made, images with excellent gradation, without any internal contamination, and without fogging or loss of density, could be obtained.

Further, a test was conducted in the same manner as above except that a toner containing copper phthalocyanine as a coloring agent instead of watching red was used, and the same results as above were obtained.

Effects of the Invention Since the negatively charged carrier of the present invention is made of a binder resin in which fine fluororesin powder and magnetic powder partially consisting of acicular magnetic particles are dispersed, the chargeability of the carrier can be controlled. In addition to extending the life of the carrier and, ultimately, the life of the developer, the chargeability of the carrier can be increased and controlled to be negative, the adhesion of the carrier to the photoreceptor can be prevented, and the background It becomes possible to obtain a copy image without adhesion of toner or carrier to the area.

In addition, especially when the average particle diameter of the carrier is set to 50 pm or more, when mixed with toner, a copy image is formed without carrier and toner adhesion in the background area, without any modification to the developing machine. becomes possible.

Patent applicant Fuji Xerox Co., Ltd. Agent
Patent attorney Tsuyoshi Seibe

Claims (4)

[Claims] (1) In a negatively charged carrier for an electrophotographic developer in which magnetic particles are dispersed and which has a binder resin and magnetic powder as essential components, a fine fluorine-based resin powder is contained in the carrier, and a part of the magnetic powder is A negatively charged carrier for an electrophotographic developer characterized by comprising acicular magnetic particles. (2) The amount of fluororesin fine powder is 3% relative to the total amount of carrier.
The negatively charged carrier for an electrophotographic developer according to claim 1, wherein the carrier is contained in an amount of % by weight or more. (3) Acicular magnetic particles are 5% by weight based on the total amount of magnetic powder
The negatively charged carrier for an electrophotographic developer according to claim 1 or 2, characterized in that the carrier is as follows. (4) The negatively charged carrier for an electrophotographic developer according to claim 1, (2) or (3), wherein the average particle size of the carrier is 50 μm or more.