JPS5911104B2 - Dry developer for electrophotography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic developer, that is, a two-component dry developer consisting of toner and carrier.

In electrophotography, the dry developer used to develop an electrostatic image formed on a photoreceptor by a magnetic brush method is a two-component system consisting of toner and carrier.

This developer is usually a mixture of a toner consisting of fine particles and a carrier consisting of relatively large particles. Diameter 30
~250 microns are used. The toner is made of natural or synthetic resin, a pigment such as carbon black, or a dye such as nigrosine dye, and if necessary, a charge control agent to impart desired triboelectric charging properties, and an offset phenomenon of the toner to the roller during fixation with a heating roller. Generally, particles having a particle size of 5 to 20 microns are used, and contain a releasing agent or the like dispersed therein to prevent the formation of such particles. The role of the carrier in the developer is to impart accurate triboelectric polarity and appropriate charge to the toner so that the toner is preferentially and selectively attracted to the electrostatic charge image formed on the photoreceptor, thereby creating a high density image area. The object of this invention is to form a clear image by forming a 25-image image and electrostatically attracting and removing the toner adhering to the non-image area again.

If the charge of the toner during development is too low, the density of the resulting image area will be high, but at the same time the density of the non-image area will also be high, resulting in the disadvantages of a large so-called force 30 blur and a low resolution. On the other hand, if the charge of the toner is too high during development, the fog in non-image areas will be small and the resolution will be high, but there will be a drawback that it will be difficult to achieve density in image areas. As described above, since the amount of charge on the toner has a great influence on the image obtained, controlling it to a desired value is extremely important for development. Conventionally, in order to control the charge amount of toner to a desired value, the types and amounts of components (dyes, pigments, etc.) added to toner have been adjusted, resin components have been improved, or resin components have been added to toner. Studies have been made on manufacturing conditions for uniformly dispersing components into toner particles.

However, attempts to control triboelectric charging properties only from the toner side do not necessarily yield satisfactory results, and attempts have also been made to improve the characteristics of the carrier. For example, a method of forming an oxide film within a specific range on the surface of the carrier, a method that has adhesiveness on the surface of the carrier, is as non-adhesive to toner as possible, has excellent abrasion resistance, and is uniform and resistant to toner. A method of coating with a resin having appropriate triboelectric charging properties has been adopted. Examples of such resins used include ethyl cellulose, polyamide, polymethyl methacrylate, and nitrocellulose. However, when these carriers formed with oxide films and carriers coated with resin are used as developers mixed with toner, they are not necessarily satisfactory in terms of developer life and durability.

This is because the electrical resistance of the carrier changes when the surface of the carrier is contaminated with toner, and the triboelectric charging characteristics of the toner, which influences the image, change due to changes in the surface condition of the carrier. Such deterioration of the developer due to repeated use significantly deteriorates copy quality, specifically resulting in a loss of image density and increased fog in non-image areas. When looking at the developer from the carrier side, it is clear that stability in electrical resistance and triboelectric charging characteristics against toner is required through repeated use. However, in most conventional developer compositions, the amount of charge on the toner increases or decreases over time, and they do not necessarily have a satisfactory lifespan as a developer. Nakatsuta.

As a result of studying a developer composition with excellent stability over time, the present inventors found that by adding fine iron phosphide powder to a two-component dry developer consisting of toner and carrier, the amount of charge on the toner could be reduced. It was found that the stability over time was significantly improved, and the present invention was completed based on this knowledge. The iron phosphide used in the present invention includes Fe3p,
There are Fe2p and FeP, and one or a mixture of two or more of these can be used. Particularly preferred is Fe3
It is p. Further, the finer the particle size, the better, but a particle size of 5 μm or less is sufficient. The amount of iron phosphide added is 0.05 to 10% by weight, preferably 0.1% by weight based on the carrier.
~5% by weight; if the amount is less than this range, the effect of addition will be insufficient, and if the amount exceeds this range, the effect will be reduced. The addition method may be such that the carrier iron powder and the toner are mixed in a blender or a mixer to prepare the developer, or the carrier iron powder may be added and mixed in the process of manufacturing the carrier iron powder. The toner used in the present invention is not particularly limited, and can be a positively charged toner manufactured by dispersing various well-known dyes and pigments in a wide range of materials, including natural resins, synthetic resins, and modifiers that combine them. and negatively charged toner can be used, and as carriers, ordinary oxidized iron and resin-coated metal powders such as iron, nickel, and cobalt, alloy powders thereof, glass beads, etc. can be used. There are no particular limitations on the mixing ratio of these toners and carriers, and they can be used within the usual mixing range.

Further, the developer according to the present invention is an electrostatic image formed on a photoconductive photoreceptor using a known photoconductor such as selenium, zinc oxide, cadmium sulfide, or polyvinylcarbazole, or an electrostatic record that does not have photosensitivity. Any electrostatic charge image formed on a sheet can be applied.

The present invention will be explained below with reference to Examples.

Example 1 Reduced iron powder (particle size of 100 mesh or less) was processed in a ball mill for 2.5 hours in batches, and then sieved to obtain particles in the particle size range of 15.
Take out the 0-325 mesh and 325℃ in the air.
, heat treated for 5 minutes.

The oxygen content of the treated iron powder was analyzed using a steel oxygen analyzer (Kokusai Denki Coulomatic 502) and was found to be 1.36% by weight.
It was hot. Further, the apparent density of the iron powder measured in accordance with JIS Z25O4396O was 2.67y/Crl. 1000 parts of the above carrier iron powder, 50 parts of a commercially available magnetic brush developing toner (Toner for SF-725 manufactured by Sharp), and 10 parts of iron phosphide of 5 microns or less were mixed using a polyethylene pin with an internal volume of 11 to 80 R. p. m. A developer was prepared by stirring and mixing for 1 hour.

The toner charge amount of this developer was measured using a powder charge amount measuring device manufactured by Toshiba Chemical Co., Ltd., and found to be 18.4 μc/F7. For comparison, a sample without iron phosphide was similarly investigated, and as a result, the amount of charge was 19.2 μc/y. As a result of developing the electrostatic charge image on the ZnO photoreceptor using these two developers, clear copy images were obtained in both cases at the initial stage, but the developer without iron phosphide added
After 000 times of development, the image density decreased and fog increased.

The amount of charge at this time was 28.2 μc/y. On the other hand, the developer containing iron phosphide was able to produce clear copy images even after 30,000 times of development. Further, the amount of charge at this time was 19.1 μc/7. Example 2 After processing atomized iron powder with a particle size of 60 mesh or less in a vibration mill, it is sieved and the particle size range is 100 to 30.
The one with 0 mesh was taken out and heated in air at 400°C for 5 minutes.

The oxygen content of the treated iron powder was 0.92% by weight, and the apparent density was 3.617/Cli. Above carrier iron powder 10
00 copies and commercially available magnetic brush developing toner (Toshiba BD-
Toner for 706S) 30 parts and 5 parts of iron phosphide of 5 microns or less with an internal volume of 11? ．． 80r with polyethylene pin
．． p. m. A developer was prepared by stirring and mixing for 1 hour.

For comparison, a developer containing no iron phosphide was also prepared in the same manner. As a result of developing the electrostatic latent image on the Se photoreceptor using these two developers, initially clear copy images were obtained with either developer, but the one without the addition of iron phosphide The developer showed a decrease in density and fog after 5,000 times of development.

The initial charge amount of the toner is 50 for 15.6 μc/y.
After 00 cycles, it was 29.2 μc/y. On the contrary,
With the developer containing iron phosphide, there was no significant change in the copy image even after 20,000 times of development, and the toner charge amount was 15.1 μc/7 at the initial stage, and it remained 1 even after 20,000 times of development.
It was extremely stable at 6.3μc/7. Example 3 In the process of manufacturing the carrier iron powder of Example 2, after sieving and taking out 100 to 300 meshes, 0.5% by weight of iron phosphide was added based on the iron powder and mixed. Example 2
Similarly to Example 2, the effect of adding iron phosphide was observed in the same oxidation treatment as in Example 2.

Example 4 8% by weight of iron phosphide (based on iron powder) was added to atomized iron powder with a particle size of 60 mesh or less, and the powder was processed in a ball mill for 5 hours in batches and then sieved to obtain particles with a particle size range of 100 to 100 mesh. 3
Take out the 00 mesh and store it in the air at 380℃ for 10 minutes.
Heat treated for minutes.

The oxygen content of the treated iron powder was 0.81% by weight, and the apparent density was 2.867/Cd. In addition, the iron phosphide content is 2
．． It was 5% by weight. 1000 parts of the above carrier iron powder and commercially available magnetic brush developing toner (Toshiba BD-706S)
A developer was prepared using 30 parts of toner) in the same manner as in Example 2.

For comparison, a developer was also prepared using carrier iron powder that was subjected to the same treatment without adding iron phosphide. As a result of developing the electrostatic latent image on the Se photoreceptor using these two developers, initially, no matter which developer was used, the image density was high and clear copy images without fog were obtained. In the case of the developer to which no iron phosphide was added, the image density decreased after 6,000 times of development, and fogging was observed.

The initial charge amount of the toner is 60 compared to 16.7μc/y.
After 00 times of development, it was 33.0 μc/7. On the other hand, with the developer containing iron phosphide, there was no major change in the copy image even after 20,000 times of development, and the toner charge amount was 16.3 μc/7 at the initial stage, and 16.3 μc/7 even after 20,000 times of development. It was extremely stable at .8μc/y. Example 5 Carrier iron powder prepared in Example 1 (particle size range 150
~325 mesh, apparent density 2.677/Cd, oxygen content 1.36% by weight) was fluidized while spraying a solution of silicone modified epoxy resin to coat the surface of the iron powder with resin.

The coating amount was 1.2% by weight based on iron powder. Next, this material was heat-treated at 180° C. for 30 minutes while stirring to obtain a coated carrier. Commercially available magnetic brush developing toner (Toshiba BD-706) was applied to 1000 parts of the above coated carrier.
A developer was prepared in the same manner as in Example 1 by adding 35 parts of S toner) and 10 parts of iron phosphide having a particle size of 5 microns or less.

For comparison, a developer was also prepared without containing iron phosphide. As a result of developing the electrostatic latent image on the Se photoreceptor using these two developers, a clear copy image was obtained in both cases at the initial stage, but the developer without iron phosphide was used for 10,000 cycles. After development, the image density decreased and fogging was observed.

Claims (1)

[Scope of Claims] 1. A dry developer for electrophotography, comprising a mixture of a toner, a carrier, and iron phosphide, and containing iron phosphide in an amount of 0.05 to 10% by weight based on the carrier. 2 Iron phosphide is Fe_3P, Fe_2P or FeP
The developer according to claim 1, which is a mixture of two or more thereof.