JPS587989B2 - Carrier for dry copying machine - Google Patents

Description

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

In dry copying, ie, electrophotography, a two-component dry developer of toner and carrier is used to develop an electrostatically charged image formed on a photoreceptor by a magnetic brush method.

This developer is usually a mixture of a toner consisting of fine particles and a carrier consisting of relatively large particles.
~250 microns are used.

The toner is made of natural or synthetic resin, pigments such as carbon black, or dyes such as nigrosine dye, and if necessary, a charge control agent to impart the desired triboelectric charging properties, and an offset of the toner to the roller when it is fixedly attached to the heating roller. Particles having a particle diameter of 5 to 20 microns and containing a releasing agent or the like dispersed therein to prevent the phenomenon from occurring are generally used.

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, and to enhance the image area. The purpose is to develop the image to a high density and to remove the toner adhering to the non-image area by electrostatic attraction again, thereby forming a clear image.

If the charge of the toner is too low during development, 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 drawbacks such as large fog and 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 the disadvantage is that it is difficult to achieve density in image areas.

As described above, since the amount of charge on the toner affects 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 additives have been added to toner. Studies are being conducted on manufacturing conditions for uniformly dispersing the components in toner particles.

However, attempts to control the triboelectrification properties only from the toner side do not necessarily yield satisfactory results, so 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, and has excellent abrasion resistance.
A method has also been adopted in which the toner is coated with a resin having uniform and appropriate triboelectric charging properties.

Examples of such resins include ethyl cellulose,
Polyamide, polymethyl methacrylate, nitrocellulose, etc. are used.

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 affect images, 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 the developer is viewed from the carrier side, it is clear that the developer is required to have stable electrical resistance and triboelectric charging characteristics against toner due to repeated use.

However, as a result of a detailed study of the triboelectrification characteristics of carrier iron powder with toner by changing the phosphorus content or adhesion amount of iron powder, the inventors found that when iron powder containing or adhering to phosphorus is used as a carrier, toner The present inventors have discovered that the stability of triboelectric charging characteristics over time with phosphorus is significantly improved compared to conventional phosphorus-free materials, and have completed the present invention.

That is, an object of the present invention is to provide a carrier that can significantly improve the stability over time of triboelectric charging characteristics with a toner by using iron powder containing or adhering to phosphorus as a carrier.

Therefore, the developer comprising the carrier and toner according to the present invention has significantly improved durability.

The above purpose is to produce iron powder containing or adhering phosphorus to the iron powder or its surface, especially iron powder containing or adhering 0.1 to 2% by weight of phosphorus, with a particle size of 100 to 400 mesh, and an apparent particle diameter of 100 to 400 mesh. This is achieved by using iron powder, which has a density of 2.0 to 3.8 g/cm3 and whose surface is covered with an oxide film or resin, as a carrier.

The iron powder carrier according to the present invention is prepared by the following method.

Using phosphorus, its iron compound, or a mixture thereof as a phosphorus source, weigh it so that the composition is 0.1 to 2% by weight of phosphorus and the balance is iron, and then heat it in vacuum or under an inert gas such as nitrogen or argon. After melting, the molten metal is water-atomized to form iron powder, or the cast material is ground to 60 mesh or less using a grinder such as a ball mill, and the powder is crushed into a predetermined particle size range (for example, 100/200, 150/325 or 250 mesh). /400 etc.).

Further, iron powder to which phosphorus or its iron compound, or a mixture thereof is attached, is prepared by the following method.

A mixture of phosphorus or its iron compound or a mixture thereof and iron powder with a particle size of about 1 to 5μ weighed so that the phosphorus content is 0.1 to 2% by weight based on the iron powder is placed in an inert gas such as nitrogen or argon. The mixture is mixed and pulverized for a predetermined time using a pulverizer such as a ball mill, and particles having a predetermined particle size range are taken out as described above.

In either case, the iron materials used are pure iron powder such as reduced iron powder, atomized iron powder, electrolytic iron powder, and other relatively pure mild steel scrap iron.
Mention may be made of e3P, Fe2P and FeP.

Examples of the crusher that can be used include a ball mill, a roller mill, a vibration mill, and a hammer mill.

The iron powder containing phosphorus obtained by the above method, the iron powder to which phosphorus or its iron compound, or a mixture thereof is attached, has an apparent density of 2.0 to 3.89 within a predetermined particle size range.
/cm3.

The material thus prepared to have a predetermined apparent density and particle size is then subjected to oxidation treatment or resin coating to form a film on its outer surface.

The oxidation treatment is carried out by various methods, for example, by heating at 200 to 430°C for about 5 to 20 minutes in an inert gas such as nitrogen, argon, helium, etc. accompanied by water vapor, or in air. Oxidize until the amount is between 0.2 and 4.2% by weight, preferably between 0.5 and 3% by weight.

Resin coating can be achieved by immersing the iron powder in a resin solution dissolved in an appropriate solvent and then filtering and drying it, by spraying a resin emulsion onto the iron powder, or by causing a polymerization reaction on the iron powder. Although various methods can be used, it is desirable that the thickness of the coating is 5 μm or less.

The reason for this is that if it becomes thicker than 5μ, the effect of phosphorus will be weakened, and it is not economical to make it thicker unnecessarily.

A developer was prepared by mixing the phosphorus-containing carrier iron powder prepared by the above method with a toner at a constant toner specific concentration, and the changes over time in the triboelectric charging characteristics with the toner were investigated. As a result, the phosphorus content in the carrier iron powder was At 0.05% by weight or less, when stirring was continued in a magnetic brush developing device, the amount of triboelectric charge of the toner increased with time, and no significant difference was observed compared to a toner containing no phosphorus.

In the case of iron powder containing 0.05% by weight or more of phosphorus, the stability over time of the amount of triboelectric charge of the toner during agitation in a magnetic brush developer was extremely good.

When the phosphorus content exceeds 3% by weight, the stability of the triboelectric charge over time is good, or the magnetic force decreases because the metal Fe in the carrier iron powder decreases relatively due to the increase in the phosphorus content. , carrier scattering phenomenon from the magnetic brush developing device occurs, which is undesirable.

Therefore, in the carrier of the present invention, the phosphorus content is set at 0.1 to 2% by weight.The above also applies to the amount of adhesion.

Toners used in combination with the carrier iron powder according to the present invention are not particularly limited, and include those produced by dispersing various well-known dyes and pigments in a wide range of materials, including natural resins and modified materials that combine natural and synthetic resins. .

Further, the developer using the carrier iron powder 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 polyvinyl Rubazole, or an electrostatic image formed on an electrostatic recording sheet that is not photosensitive. It can be applied to any charge image.

Hereinafter, embodiments of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Example 1 Reduced iron powder containing 0.002% phosphorus as an iron material was vacuum melted and cast with varying amounts of phosphorus, and each product was ground separately in a ball mill to a size of 60 mesh or less to determine the phosphorus content. Six different types of powders A-F were obtained.

Analytical values for the phosphorus content of six types of powder (by spectrophotometric method, "Steel Rapid Analysis Method Continuation" p. 25).

1962 (Maruzen)) A: 0.002%, B: 0.0
5%, C; 0.11%, D; 0.92%, E; 2.0%
, F: 3.1%.

Particle size range 1 is obtained by sieving and classifying these powders from A to F.
Each of the 00/200 mesh pieces was taken out and heat treated in air at 370°C for 10 minutes.

The oxygen content of the produced carrier iron powder was analyzed using a steel oxygen analyzer (7-Romatic "0" manufactured by Kokusai Denki Co., Ltd.) and was found to be 0.8 to 0.9%.

Moreover, the apparent density according to JISZ-2504-1966 was 2.7 to 2.9.

To 1,000 parts each of the carrier iron powder A-F thus prepared, a commercially available magnetic brush toner (Toshiba BD-70) was used.
Weigh 30 parts of toner for 75r.68 into a 1L polyethylene bottle. p. m. A developer was prepared by stirring for 1 hour.

The amount of frictional charge at this time was taken as the initial charge amount, and the measurement was performed using a blow-off powder charge amount measuring device TB-200 manufactured by Toshiba Chemical.
It was done by mold.

Table 1 shows the relationship between the number of times of development and the amount of charge when an electrostatic latent image on a Se photoreceptor was developed using these developers.

When the phosphorus content in the carrier was 0.1 to 2.0% by weight, the amount of charge remained stable even when the number of times of development was increased, and the copied image was clear.

At 3.2%, transfer voids (white spots) due to carrier scattering were observed.

Example 2 Phosphorus-containing carrier iron powder D prepared in Example 1 (phosphorus:
A developer was prepared using 1,000 parts of 0.92%) and 30 parts of a commercially available magnetic brush toner (Sharp SF-725 toner) in the same manner as in Example 1, and the amount of charge was measured. It was 20.5μc/g.

As a result of developing the electrostatic latent image on the ZnO photoreceptor using this developer, a clear copy image was obtained, and even after 30,000 times of development, the amount of triboelectric charge of the toner was 21.2 μc/g, which is extremely stable. The copied image was clear.

In addition, with A (phosphorus; 0.002%), which has a low phosphorus content, a clear copy image was obtained at the initial stage of a similar test, but after 10,000 times of development, the image density was low and there was no fogging. The result was a blurry image.

Example 3 Mild steel scraps (phosphorus; 0.003%) were used as iron material and the amount of phosphorus added was varied, which was vacuum melted and cast. Each product was coarsely crushed in a rod mill and then crushed to 100 mesh or less in a vibrating mill. , four types of powders G to J with different phosphorus contents were obtained.

The phosphorus content of the four types of powder is G: 0.003%, H;
They were 0.12%, I: 0.55%, and J: 1.5%.

Particle size range 1 is obtained by sieving and classifying these powders from G to J.
Each of the 50/325 mesh pieces was taken out and heat treated in air at 400°C for 5 minutes.

The oxygen content of the carrier iron powder produced is 1.7 to 2.0
%Met.

Further, the apparent density was 2.9 to 3.1 g/cm3.

To 1,000 parts each of carrier iron powder G to J thus prepared, commercially available magnetic brush toner (U-Bi manufactured by Konishiroku Co., Ltd.)
A developer was prepared in the same manner as in Example 1 using 40 parts of xV toner).

Table 2 shows the relationship between the number of times of development and the amount of charge when an electrostatic latent image on a Se photoreceptor was developed using these developers.

With a phosphorus content of 0.12% or more, extremely clear copy images were obtained even after 50,000 times of development, but with a phosphorus content of 0.003%, the density decreased after 20,000 times. Fogging was observed.

Example 4 Mild steel scraps (phosphorus; 0.002%) were used as iron material, and after vacuum melting with varying amounts of phosphorus added, the molten metal was allowed to fall through the pores, and a high-pressure water stream was sprayed onto it to prepare water atomized iron powder. did.

These water-atomized iron powders with different amounts of phosphorus added were individually reduced at 850°C and crushed in a hammer mill to obtain iron powder of 100 mesh or less.

Four types of iron powder K with different phosphorus contents obtained in this way
The phosphorus content in N is K: 0.002%, L: 0.14%
, M: 0.37%, N: 1.0%.

Particle size range 1 is obtained by sieving and classifying these powders up to K-N.
Take out each 50/325 mesh and heat at 390°C.
Heat treatment was performed in air for 15 minutes.

The oxygen content of the carrier iron powder produced is 1.3 to 1.5.
%Met.

Moreover, the apparent density is 2.9 to 3. xg/c11l.

To 1,000 parts each of the carrier iron powder K-N thus prepared, a commercially available magnetic brush toner (BD-706 manufactured by Toshiba) was used.
A developer was prepared in the same manner as in Example 1 using 30 parts of S toner.

When an electrostatic latent image on a Se photoreceptor was developed using these developers, results were obtained in which the relationship between the number of times of development and the amount of charge corresponded to that of Example 1.

That is, for K with a low phosphorus content, the initial charge amount is 25 μc.
/g becomes 40μc after 30,000 times of development.
/g, and the copied image was also unclear.

On the other hand, L, M, and N have an initial charge amount of 25 to 26 μc.
/g, and even after 30,000 times of development, it is 26-27μ
It was stable at c/g, and the copied images were extremely clear.

Example 5 Electrolytic iron powder with an average particle size of 100μ and Fe3P with an average particle size of 5μ
5 with different amounts of phosphorus attached by mixing and pulverizing with a ball mill
A powder of type K~0 was obtained.

The results of analyzing the amount of phosphorus attached by the method shown in Example 1 are K: 0.05%, L: 0.10%, M: 0.5
0%, N: 1.8%, 0: 3.0% (all of the above are weight %).

These K~0 powders are sieved and classified to a particle size range of 150.
/325 mesh were each taken out and heat treated in air at 370°C for 10 minutes.

The oxygen content of the carrier iron powder produced is 0.8 to 0.9.
%, and the apparent density of the iron powder was 2.6 to 2.8.

To 1,000 parts each of the carrier iron powder K~0 thus prepared, a commercially available magnetic brush toner (Toshiba BD-70) was used.
A developer was prepared in the same manner as in Example 1 using 40 parts of 6S toner.

Table 3 shows the relationship between the development recovery and the amount of charge when an electrostatic latent image on a Se photoreceptor was developed using these developers.

Example 6 Reduced iron powder with an average particle size of 100 μm was mixed with red phosphorus powder and kneaded using a Henschel mixer to obtain five types of powders P to T with different amounts of phosphorus attached.

The results of analyzing the amount of phosphorus deposited by the method shown in Example 1 are: P: 0.08%, Q: 0.12%, R: 1.
3%, S: 2.0%, T: 3.5% (all of the above are weight %).

The particle size range is 150 by sieving and classifying these P-T powders.
/325 mesh was taken out and sprayed with a solution of vinyl chloride-vinyl acetate copolymer dissolved in methyl ethyl ketone-methanol mixed solvent (7:1), and carrier iron powder coated with vinyl chloride-vinyl acetate copolymer was applied. Obtained.

The thickness of this coating is 3 to 5μ, and the apparent density is 2.4 to 5μ.
It was 2.6.

The thus prepared carrier iron powder P-T was prepared as a developer in the same manner as in Example 3, and the performance tests were performed. Table 4 shows the results.
Shown below.

Claims (1)

[Scope of Claims] 1. Iron powder containing or adhering to phosphorus or an iron compound of phosphorus, or a mixture of two or more thereof, wherein the total phosphorus content or adhesion amount is 0 relative to the iron powder. .1~2
% by weight and whose outer surface is coated. 2 The coating treatment is an oxidation treatment or a resin coating treatment.The carrier 03 phosphorus iron compound according to claim 1 is Fe3P.2. Fe2P or Fe
The carrier according to claim 1, which is P or a mixture of two or more thereof.