JPH081524B2 - Carrier for electrophotography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a structure of carrier powder having improved deterioration due to spent toner and improved solid printing characteristics.

[Conventional technology]

Although electrophotographic technology is widely used in copying machines, it is also widely used in information equipment such as printers and facsimiles.

Here, as the printing process of the electrophotographic printer,
After the surface of the photocondrum coated with photoconductive insulator is uniformly charged by corona discharge, etc., the photoconductive insulator is irradiated with light that is turned on and off according to an electric signal, and electrostatically charged. A latent image is formed and toner is attached to the latent image to form a visible image.

Here, the toner is colored fine particles having a particle size of 5 to 30 μm in which a colorant is dispersed in a synthetic resin, and is supplied to a magnetic roll together with magnetic powder having a particle size of 30 to 300 μm called a carrier, and the carrier is magnetically adsorbed. To form a magnetic brush, the carrier and toner rub against each other at the stage of rotation to generate charging, and the toner carried by the carrier to the latent image adheres to the latent image by electrostatic force to form a visible image. To be

Next, the toner image thus created is electrostatically transferred onto the recording paper by applying an electric field from the back side of the recording paper at the transfer section, and then heat and pressure are applied to the toner image by the fixing device. The recording is completed by fusing the recording paper.

Development and fixing are performed by the above method,
Although such a developing method is extremely practical and widely used, the following problems have been pointed out.

If the mixing ratio of the toner and the carrier is constantly kept constant, a stable developing effect cannot be expected, and the allowable range of the mixing ratio is relatively narrow.

When the developer is used for a long time, a phenomenon called toner filming occurs in which a toner called a spent toner that does not contribute to the development is fused on the surface of the carrier, resulting in deterioration of image quality.

A phenomenon called an edge effect occurs in which the inside of the solid printing portion becomes thinner than the surroundings, which deteriorates the printing quality.

Conventionally, as a measure against this, a plate-shaped carrier is used to increase the specific surface area, thereby expanding the allowable range of the toner concentration.

With respect to (1), a resin that is non-adhesive to the toner is coated on the surface of the carrier to reduce the fusion of the spent toner to the carrier.

With respect to, the edge effect is reduced by using a plate-shaped carrier or lowering the electric resistance of the developer.

Although the problems have been solved by these methods, they are insufficient, and it cannot be said that they have been solved.

[Problems to be solved by the invention]

As described above, the problems are that the allowable range of the toner density is expanded, and the toner filming and the edge effect are eliminated.

[Means for solving problems]

The above problem is caused by coating a plate-like magnetic powder with a resin as a carrier used as a carrier for a two-component magnetic brush developer for electrophotography, and associating it with a porosity of 60% or more and measuring an average particle size increase rate with a mesh. The problem can be solved by using a product that is 10% or larger in size.

[Action]

As a result of studying and researching a method for solving the above-mentioned problems, the inventors have found that it is only necessary to associate resin-coated plate-shaped carriers with each other so as to have a sufficiently high porosity.

In other words, the cause of the deterioration of image quality with use is that the insulating toner adheres to the surface of the carrier to increase the electrical resistance and that the spent toner covers the surface of the carrier to cause frictional charging with the toner. This is because you will not be lost.

The inventors of the present invention have found that the toner used as the spent toner does not suddenly stick to the surface of the carrier, and probably has a large specific charge, so that it does not contribute to the development and latently remains on the surface of the carrier for a long time. It is moving around, and if it happens that a large pressure or stress is applied, it will stick to the surface of the carrier, but at this time, if there is a recess on the surface, I think that it must enter here.

From this point of view, it suffices to use a carrier containing a large number of concave portions, but it is difficult to manufacture such a carrier from spherical iron powder or ferrite particles.

Therefore, the inventors have realized this condition by making a carrier having a large porosity by associating a plurality of carriers at the stage of coating a plate-shaped carrier with a resin.

Then, a two-component developer was prepared by changing the degree of association and shape of the carrier, printing was performed using this, and the relationship between the number of printed sheets and the electric resistance of the carrier and the influence of the edge effect in solid black printing were investigated.

As a result, as for the degree of carrier association, it was confirmed that good results were obtained when the average particle size increase rate was 10% or more when measuring the average particle size with a mesh, and when the porosity was 60% or more. did.

〔Example〕

In order to prove the effectiveness of the present invention, iron powder having a spherical shape, a potato shape and the plate shape according to the present invention was used, and the same resin coating was applied to the iron powder to make a carrier.

 The names of the materials used here are as follows.

Iron powder (spherical) ... TSS-20C (Nippon Iron Powder Co., Ltd.) Iron powder (potato) TSS-200R (Nippon Iron Powder Co., Ltd.) Iron powder (plate) ... EF-250 (Nippon Iron Powder ( Co., Ltd.) Resin… 1,2 Polybutadiene magnetite… FPF500 (Toda Kogyo Co., Ltd.) Curing agent… Dicumyl peroxide coating solvent… Trichloroethylene Prototype example 1: Spherical iron powder 8Kg, resin 24g, magnetite 96g, curing agent A polybutadiene coating layer consisting of 0.24 g was formed by a rotary dry method and heated at 180 ° C. for 2 hours, and then 120
The powder was dispensed with a mesh sieve to remove coarse powder and used as a carrier.

Prototype example 2: 8 kg of potato-like iron powder, 37 g resin, 1 magnetite
A polybutadiene coating layer composed of 49 g and a curing agent of 0.37 g was formed by a rotary dry method, heated at 180 ° C. for 2 hours, and then classified with a 120 mesh sieve to remove coarse powder to obtain a carrier.

Trial Production Example 3: A polybutadiene coating layer consisting of 65 g of resin, 260 g of magnetite, and 0.65 g of a curing agent was formed by a rotary dry method on 7 kg of plate-shaped iron powder, and heated at 180 ° C. for 2 hours.
The powder was classified with a mesh sieve and the coarse powder was removed to obtain a carrier.

The above three types of carriers and an epoxy-based toner having a melting point of 97 ° C. were combined under the condition that the toner concentration was 2.5 to 3.5% by weight, and the life characteristics were compared using FACOM-6715D laser sub-printer manufactured by Fujitsu.

The measurement results of the porosity of the carrier and the increase rate of the average particle diameter are as follows.

Next, the toner in the developer was removed with a vacuum cleaner and the electric resistance of the carrier was measured to examine the change in the resistance value as a guide for knowing the degree of deterioration of the developer.

In the graph, the horizontal axis represents the number of printed sheets and the vertical axis represents the change in the resistance value of the carrier.

In the figure, the characteristic 1 is the embodiment 1 and the characteristic 2 is the embodiment 2
And characteristic 3 corresponds to the third embodiment.

As is clear from this figure, the spherical and potato-like carriers have a linearly increased resistance value due to toner filming as the number of printed sheets increases, but the carrier embodying the present invention has a moderate increase in resistance value. .

This indicates that toner filming is less likely to occur, but this is clear from observation with a scanning microscope (SEM) .Spent toner shows recesses and boundaries caused by the association of multiple carriers during operation. It is possible to observe the state of preferentially entering a part or the like.

〔The invention's effect〕

According to the present invention, the toner which does not contribute to the development can be dropped into the concave portion formed by the association of the carrier particles during the operation, so that the toner filming is suppressed, and the life of the carrier can be extended.

[Brief description of drawings]

The figure shows the relationship between the number of printed sheets and the electric resistance of the carrier, which shows the effect of the present invention. In the figure, the characteristics 1 and 2 are conventional carriers, and the characteristic 3 is the carrier in which the invention is implemented.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location G03G 9/10 351 (72) Inventor Katsuji Hu 1015 Uedotachu, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited (56) References JP-A-58-59456 (JP, A) JP-A-59-216153 (JP, A) JP-A-59-216152 (JP, A) JP-A-59-216155 (JP, A) JP-A-59-216154 (JP, A)

Claims (2)

[Claims] 1. A carrier for electrophotography, characterized in that a carrier used for a two-component magnetic brush developer for electrophotography comprises a plate-like magnetic powder coated with a resin and associated with the resin. 2. The porosity of the carrier is 60% or more,
The electrophotographic carrier according to claim 1, wherein the average particle size increase rate is 10% or more.