JPS6356980B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a carrier for a developer in an electrophotographic image forming system.

Traditionally, electrophotography has been subject to U.S. patents.
No. 2297691, Special Publication No. 23910, Special Publication No. 1977-
As described in Japanese Patent No. 24748, etc., the photoconductive layer is uniformly charged and exposed to a light image corresponding to the original, thereby eliminating the charge in the exposed area and forming a latent image. Development is carried out by depositing a finely powdered electrostatic substance, so-called toner, on the obtained electrostatic latent image. The toner is attracted to the electrostatic latent image depending on the amount of charge on the photoconductive layer, forming a toner image with shading. This toner image is transferred to a supporting surface such as paper or cloth as necessary, heated,
It is permanently fixed on the supporting surface by applying pressure or the like. Alternatively, if it is desired to omit the toner image transfer step, the toner image can be fixed to the photoconductor layer. In addition to the fixing method described above, it is also possible to use other means such as solvent treatment and overcoating treatment.

Many developing methods for electrophotography are known. Cascade development method described in US Pat. No. 2,618,552, magnetic brush method described in US Pat. No. 2,874,063,
Examples include the touch-down method described in US Pat. No. 2,895,847, a fur brush development method, and a jumping development method.

The cascade development method is when a developer in which fine powder toner particles are electrostatically attached to the surface of carrier particles cascades over the surface of a photoconductor bearing an electrostatic latent image. Development is carried out by selectively adhering only to portions and not adhering to uncharged portions.

Further, in the magnetic brush method, a developer consisting of toner particles and magnetic carrier particles is held by a magnet, and the developer is arranged in a brush shape by the magnetic field of the magnet. When this magnetic brush comes into contact with the surface of the electrostatic latent image on the photoconductor, only the toner particles are attracted from the brush to the electrostatic latent image by Coulomb force to effect development. Touch-down development is a method in which a support layer, such as a web or sheet, carries developer material to a latent image-bearing surface and develops the electrostatic latent image.

The present invention relates to a two-component developer in which toner particles and carrier particles coexist, and particularly to a method for producing a carrier applied to a magnetic brush development method. In the conventional magnetic brush development method, the mixture of toner particles (developer) and carrier particles suffers from pulverization of the toner, chipping of the carrier surface, or Toner adheres to the carrier surface,
A phenomenon of gradual accumulation and fusion occurs. These phenomena significantly impair the triboelectric generation function of the carrier, and therefore have an adverse effect on images. Therefore, in order to overcome the above-mentioned drawbacks, various studies have been conducted on coating materials forming the carrier surface. For example, Special Publication No. 47-19398, Special Publication No. 48-
As described in No. 8139 and Japanese Patent Publication No. 51-1430, triboelectric properties can be improved by coating with various resins, dispersing pigments or dyes in the resin, or enclosing the carrier surface with metal. Attempts have been made to control the hardness of the carrier envelope.

A commonly used magnetic brush developing device has a permanent magnet fixed therein so as not to rotate, and has a non-magnetic cylinder serving as a developer carrier (sleeve) on the outside. The developer is held on the sleeve surface and is transported along the cylindrical sleeve surface according to the magnitude of the magnetic field of the internal permanent magnet and the magnetic pole arrangement. Also,
When the toner is transferred to the electrostatic latent image on the photoconductor, the carrier is electrostatic force, and the dominant force is the magnetic field of the permanent magnet inside the developing device, and the developer in this area is At the magnetic pole position, the panicle grows up and grows as if it were elongating (hereinafter, this phenomenon is referred to as the "head standing" phenomenon). As a result, the surface of the electrostatic latent image comes into contact with the developer, the toner remains on the surface of the electrostatic latent image, and the carrier returns to the developing device, completing the development.

By covering the carrier as mentioned above,
Although it is possible to control the chargeability and carrier hardness, it is difficult to control the magnetic field. The present invention attempts to control the magnetic field by changing the specific surface area of the carrier by changing the surface shape of the coated carrier. In other words, by changing the unevenness of the surface of the coated carrier, the specific surface area can be changed appropriately, and the height and hardness of the spikes during development can be controlled.

That is, the gist of the present invention is to mix and contact magnetic carrier particles continuously coated with resin with non-magnetic abrasive hard fine powder, form irregularities on the surface of the resin layer by contact with the hard fine powder, and improve the carrier surface. A method for producing a carrier for electrophotographic development, characterized by increasing the specific surface area of the carrier.

The effect of spikes on the image during development is extremely large. If the spikes are too long, it becomes difficult to obtain uniform spikes, and as a result, the toner adheres unevenly to the electrostatic latent image, resulting in poor copied images with fading and unevenness. Furthermore, if the length is short, the image density will be low. If the panicle is hard, many white lines called shading will appear on the image, resulting in an extremely unsightly copy.

The present invention attempts to overcome the above-mentioned drawbacks by changing the surface shape of the coated carrier and changing the specific surface area without changing the magnetic field strength or the magnetic pole arrangement.

As the carrier core material applied to the present invention, magnetic particles are used to form a magnetic carrier, and are mainly reduced iron powder, electrolytic iron powder, and carbonyl iron powder having a diameter of several tens to several hundred microns. Particles can be mentioned.

Many materials can be used to coat the carrier core, including known materials. Examples include fluororesin, melamine resin, polyphenylene oxide resin, silicone resin, polyester resin, polyamide resin, and polystyrene resin. In particular, as carrier coating materials that give good results in the present invention, fluororesins such as polyvinyl fluoride, polyvinylidene fluoride, polytrifluoroethylene, polytrifluorochloroethylene, polytetrafluoroethylene, etc. Examples include copolymers of two or more of vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, hexafluoroethylene, and hexafluoropropylene. Moreover, all known methods can be used to coat the carrier core with the above-mentioned substance.

The hard fine powder used in the present invention has a size and hardness that can form the desired unevenness on the resin coating the carrier, and when magnetic force is applied when separating it from the carrier in a later process, it can be used as a non-magnetic powder. It is best to use hard fine powder. For example, natural abrasives such as diamond dust, corundum, emery, garnet, and silica stone, and artificial abrasives such as artificial diamond, boron nitride, boron carbide, silicon carbide, fused alumina, artificial emery, and fused zirconia can be used.

In carrying out the present invention, the above-mentioned hard fine powder and carrier are placed in a pulverizing device such as a ball mill, and are thoroughly mixed in contact with each other without adding iron or porcelain balls for pulverization. By changing the time of this contact mixing and the frictional force caused by the contact, the unevenness of the coated surface of the carrier can be freely changed. 1000g of coated carrier and super hard silicon carbide in ball mill
When 1000 g is added and mixed, the specific surface area increases with mixing time as shown in Figure 1. Figure 2 shows the change in specific surface area when a certain amount of coated carrier (1000 g) was added to a ball mill, the amount of silicon carbide charged was varied, and the mixture was mixed for a certain period of time (2 hours). In this case, the specific surface area shows a maximum value as the filling amount of silicon carbide increases. This is presumably because as the amount of silicon carbide increases, the frictional effect on the coated carrier increases, but on the other hand, the space for the two to freely mix in the ball mill decreases, resulting in the specific surface area reaching its maximum value.

The specific surface area can be measured using an air type specific surface area analyzer.
Nitrogen gas was adsorbed onto a sample other than silicon carbide using the BET adsorption method using Model 2100 (Shimadzu Corporation), and the specific surface area was determined from the number of adsorbed nitrogen gas molecules and the surface area of the adsorbed sample. .

Scanning electron microscope JSM-T200 type (manufactured by JEOL)
When observing the surface of the coated carrier by the method, a clear difference was observed between the carrier before and after the formation of irregularities on the surface, but the carrier after the experiment shown in Figures 1 and 2 It was difficult to recognize any difference in the shape of the unevenness between the two.
However, since there is a clear difference in specific surface area, it is inferred that the unevenness of the carrier coating surface is quite different. The mixture is placed in a strong magnetic field, and only diamond chips, carborundum, etc. are attracted from the side or above by a suction pump, and the coated carrier is separated. This is because the coated carrier overcomes the attraction force due to the action of the magnetic field and is held in place, but substances that are not affected by the magnetic field are attracted as they are.

The toner material used with the coated carrier of the present invention may be any known toner material. For example, copal rubber, rosin, coumaron indene resin,
Included are phenolic resins, methacrylic resins, polystyrene resins, polypropylene resins, epoxy resins, polyethylene resins, polyester resins, and copolymers or mixtures of two or more thereof.

As the colorant contained in the toner material, suitable dyes and pigments can also be used. For example, carbon black, nigrosine dye, aniline blue,
Calco oil blue, chrome yellow, quinolin blue,
There are Phthalocyanine Blue, Malachite Blue, Rose Bengal, Lamp Black, Sudan Black SM, Phthalocyanine Green, and mixtures thereof.

Next, examples will be shown regarding the present invention.

Example 1 250 to 400 meshes of reduced iron powder (Japanese iron powder) is washed with dichloromethane to degrease the surface of the iron powder.
The filtered and dried iron powder is added to the polyvinyl fluoride dispersion (20% solids content) and mixed for 20 minutes. Further, the solvent is removed while heating and stirring the mixture to form a thin, hard, continuous coating on the iron powder. This is used as a coated carrier.

1,000 g of the coated carrier and 1,000 g of silicon carbide (green carbon) of 500 to 300 microns were placed in a ball mill with an internal capacity of 1.5, and mixed for 2 hours. This mixture is then placed in a strong magnetic field, and only the silicon carbide is sucked in from above using a suction pump. In the magnetic field, only the coated carrier whose surface is uneven and whose specific surface area has changed remains.

After stirring 880 g of the above-mentioned coated carrier with a rough surface and 120 g of black toner made of styrene acrylic resin in a V-type mixer for 5 minutes, use a commercially available NP-5000 electronic copying machine (Canon When copying was carried out using a copying machine (manufactured by the Company), an excellent image with clearness and rich gradation was obtained.

Example 2 1000 g of coated carrier described in Example 1 and 100 ~
1000g of 200μ aluminum oxide was placed in a ball mill with an internal capacity of 1.5, and mixed for 3 hours. After mixing, only the coated carrier is taken out and mixed with toner made of styrene acrylic resin to form a developer (toner concentration 12%). When this developer was placed in an NP-5000 electronic copying machine (manufactured by Canon) and copies were made, good images with no blurring or unevenness were obtained.

Example 3 A coated carrier is produced in the same manner as in Example 1 using a polyvinylidene fluoride-chlorotrifluoroethylene dispersion (solid content 10%). This coated carrier
1000g and 100~200μ silicon carbide (green carbon) in a ball mill with an internal capacity of 1.5.
After mixing for a period of time, only the coated carrier is taken out and mixed with a toner made of styrene resin to form a developer. When copies were made using this developer using the same copying machine as in Example 1, the images were clear and good.

Comparative Example 1 A carrier coated in the same manner as in Example 1 was mixed with a toner made of styrene acrylic resin without any unevenness on the surface to prepare a developer. This developer was put into the copying machine used in Example 1, and when it was copied, the result was a poor image with shading. Incidentally, the hardness of the ears due to standing up in the developing device was considerably harder than in Examples 1 to 3.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between time and specific surface area when a resin-coated carrier and ultra-hard fine powder are mixed and contacted, and FIG. 2 is a diagram showing the relationship between filling amount and specific surface area.

Claims (1)

[Claims] 1. Mixing and contacting magnetic carrier particles continuously coated with resin with non-magnetic abrasive hard fine powder, forming irregularities on the surface of the resin layer by contact with the hard fine powder,
A method for producing a carrier for electrophotographic development, characterized by increasing the specific surface area of the carrier surface.