JP2518684B2 - Developer for reversal development - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is a reversal development comprising a carrier and a toner used for developing an electrostatic image formed by an electrophotographic method, an electrostatic recording method, an electrostatic printing method or the like. For developer.

[Conventional technology]

Generally, in an electrophotographic copying machine, a normal development method is used which forms the same image as a document image on a photoconductor. However, in recent years, a reversal development method has also been used in which a reversal image, which is the reversal of the original image, is formed on the photoconductor, and this method is mainly used in printers.

Generally, the developer for negative polarity toner using the reversal development method is developed as follows. First, the main charger is used to uniformly charge the surface of the photoconductor to a negative polarity, and the photoconductor surface is irradiated with laser light or the like in an imagewise manner to remove the electric charge in the irradiated part, and the potential is lowered to the latent image lower part potential. Lower. In this way, a latent image of a well potential is formed, and by applying a negative development bias to the developing device, the negative toner is developed on the exposed well potential latent image portion.

In the reversal printer based on such a principle, when the electric resistance of the developer is high, the developing bias is likely to be applied, the toner adhesion to the non-latent image part is small, and the increase of the toner consumption is suppressed. However, there is a problem that the image quality is deteriorated because the image density is reduced and the leading edge and trailing edge of the image area are chipped due to the edge effect. On the contrary, when the electric resistance of the developer is low, the image density is likely to be obtained, but the developing bias is less likely to be applied, and there is a problem that the toner consumption is increased due to the toner adhesion to the non-linear image portion.

Therefore, it is necessary for the reversal developing agent for a printer to have the above-mentioned contradictory properties, and as a means for that purpose, in the prior art, a method of using a high resistance carrier with a small carrier particle diameter is generally used. According to this method, by using the high resistance carrier, the toner adhesion to the non-latent image portion is eliminated, and the increase of the toner consumption amount is suppressed. Further, by using a carrier having a small particle diameter, the toner density in the developer is increased, and the image density is increased to suppress the occurrence of line rear end chipping in the image area due to the edge effect. However, in such a conventional method, the carrier is likely to adhere to the transfer paper (hereinafter referred to as carrier rise), and the toner density is further increased, so that toner scattering around the developing device and background fog occur. There was a problem.

[Problems to be Solved by the Invention]

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a novel developer for reversal development with clear image quality, less background fog, and less toner consumption.

[Means for solving the problem]

The gist of the present invention is to provide a ferrite carrier containing 5 to 15 mol% of magnesium oxide and having an electric resistance of 2 × 10 ^{8 to} 3 × 10 ⁹ Ω · cm, and an electric resistance of 9 × 10 ¹⁰ Ω · cm or more. It is a developer for reversal development, which is composed of a certain toner.

 The present invention will be described in detail below.

The ferrite carrier constituting the developer of the present invention is MO
In an iron oxide having a composition of Fe ₂ O ₃ (where M is a divalent metal ion), magnesium oxide (MgO) is added in an amount of 5 to 1
The content is 5 mol%, and other than MgO and Fe ₂ O ₃ , other metal oxides, that is, NiO, BaO, MnO, CuO, CoO, ZnO and the like are appropriately contained.

The ferrite carrier is manufactured as follows, for example. That is, ferric oxide and magnesium oxide and other metal oxides are mixed in a predetermined ratio, and 800 to 100
It is calcined at 0 ° C. for several hours, then pulverized, and the pulverized powder is spray-dried in a heating atmosphere by adding a binder such as polyvinyl alcohol, if necessary, to obtain spherical particles. A ferrite carrier can be obtained by firing the spherical particles at a temperature of 1100-1300 ° C. and then classifying them.

When the content of magnesium oxide in the ferrite carrier is less than 5 mol%, the electric resistance of the developer becomes unnecessarily high, so that the image density is lowered and leading and trailing edges are chipped. On the other hand, when the content of magnesium oxide exceeds 15 mol%, the electric resistance becomes too low and the toner consumption increases and the occurrence of background fog is observed. Further, if the content of magnesium oxide exceeds 15 mol%, it is necessary to raise the firing temperature during the production of the ferrite carrier, and therefore, the firing furnace must be made of a material capable of withstanding high temperatures. Therefore, it has a drawback that the manufacturing cost of the ferrite carrier is increased.

The electric resistance of the ferrite carrier constituting the present invention must be in the range of 2 × 10 ^{8 to} 3 × 10 ⁹ Ω · cm,
If it is less than 2 × 10 ⁸ Ω · cm, the carrier is likely to rise on the transfer paper, and if it exceeds 3 × 10 ⁹ Ω · cm, the image density is lowered.

The electric resistance of the ferrite carrier in the present invention is measured as follows. That is, the ferrite carrier is left for 15 minutes in an environmental condition of a temperature of 22 to 25 ° C. and a humidity of 50 to 54% RH, then the carrier is filled in a cell, and a DC voltage of 250 V is applied to obtain an electric resistance.

The ferrite carrier referred to in the present invention is used in combination with the toner having the specific composition and electric resistance value as described above in combination with the high resistance toner described below. Can be used as a carrier.

 The toner constituting the present invention will be described in detail below.

The toner constituting the present invention must have an electric resistance of 9 × 10 ¹⁰ Ω · cm or more, and the electric resistance of the toner is 9 × 10 ¹⁰
If it is less than Ω · cm, there is a problem that background fog and toner consumption increase. The electric resistance of the toner in this case is measured as follows. That is, the toner is formed into a pellet, and a voltage is applied to the pellet to obtain the conductance of the pellet. From the conductance, the electric resistance is calculated by the following equation.

In the present invention, the electric resistance of the toner is 9 × 10 ¹⁰ Ω · cm.
The above technical means can be achieved, for example, by reducing the amount of carbon black contained in the toner, or by preparing the toner using carbon black or a binder resin having high electric resistance.

Further, the toner in the present invention is mixed with a binder resin, a charge control agent, a colorant and, if necessary, other additives,
As a result of melt-kneading, it is obtained by cooling, solidifying, and pulverizing and classifying.

The materials used for the toner in the present invention will be described in detail below. First, as the binder resin, those generally used as a binder for toner can be used. Examples thereof include a styrene resin, a polyacrylic acid ester resin, a styrene-acrylic acid ester copolymer resin, a polyvinyl chloride resin, a polyvinyl acetate resin, a polyvinyl chloride resin, a phenol resin, an epoxy resin, and a polyester resin. Further, these resins are not limited to one type, but can be used as a mixture of two or more types depending on the purpose.

As the charge control agent, nigrosine dyes, quaternary ammonium salts, metal complex dyes, titanates or carbonates such as Ca and Ba, alkoxylated amines, various polyamide resins such as nylon, condensation polymers containing amino groups, etc. A polyamine resin or the like is appropriately selected and used according to the desired charging polarity of the toner.

Any appropriate pigment or dye can be used as the colorant. Examples thereof include carbon black, nigrosine dye, aniline blue, alkoyl blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue, phthalocyanine blue, malachite blue, and dyes containing transition metals such as copper or chromium.

Other additives that may be added to the toner as necessary include, for example, polytetrafluoroethylene powder such as lubricants, abrasives, and fixing agents, metal salts of higher fatty acids, cerium oxide, low molecular weight polyethylene, low molecular weight. Examples include polypropylene.

〔Example〕

Next, the present invention will be specifically described with reference to examples. In addition,
The present invention is not limited to the following examples unless it exceeds the gist.

(Examples 1 to 3 and Comparative Examples 1 to 3) The materials of the above composition are mixed, melt-kneaded in a roll mill, cooled, coarsely crushed in a hammer mill, finely crushed in a supersonic jet mill, and then classified to have an average particle diameter of 12 μm and an electric resistance of 9 × 10. A toner of ¹¹ Ω · cm was obtained.

Next, with respect to 6 parts by weight of the toner obtained above, each ferrite carrier having the composition shown in Table 1 was used.
100 parts by weight were mixed to prepare a developer according to the present invention and a comparative developer.

(Comparative example 4) The materials of the above composition are mixed, melted and kneaded in a roll mill, cooled, coarsely pulverized in a hammer mill, finely pulverized in a supersonic jet mill, and then classified to have an average particle diameter of 12 μm and an electric resistance of 3 × 10. A toner of ¹⁰ Ω · cm was obtained.

Next, 6 parts by weight of the toner obtained above was mixed with 100 parts by weight of a ferrite carrier having an average particle size of 50 μm and an electric resistance of 2.4 × 10 ⁸ having the following composition to prepare a comparative developer. did.

The two-component developer described in each of Examples 1 to 3 and Comparative Examples 1 to 4 was set in a reversing printer (A4 size, copy speed 8 sheets / min) using a reversal developing method, and up to 20,000 sheets were printed. A continuous copying durability test was conducted. Table 2 shows the image quality after 20,000 sheets,
The evaluation results regarding the background fog and the toner consumption amount are shown. Here, the image quality was evaluated by visually observing the transferred image. The background fog was evaluated by measuring the fog density in the non-image area with a photovoltmeter manufactured by Tokyo Denshoku Co., Ltd. The detailed evaluation criteria are as follows.

i) Image quality ◯: No chipping of the tip due to the edge effect was observed.

Δ: A slight chipping of the tip due to the edge effect was observed.

X: The tip chipping due to the edge effect was remarkably observed.

ii) Ground fog O: The density of the non-image area was less than 0.01.

X: The density of the non-image area was 0.01 or more.

iii) Toner consumption amount ○; The toner consumption amount is 6% in the black area in the entire area.
Was less than 50 (mg / sheet) in A4 manuscript.

×: Toner consumption is 6% of black area in the entire area
Was 50 (mg / sheet) or more in the A4 manuscript.

As is clear from Table 2, the developer for reversal development of the present invention was confirmed to have good image quality, background fog, and toner consumption.

(Comparative Example 5) The electric resistance obtained was the same as that of the ferrite carrier used in Example 2 except that the manufacturing conditions were changed.
A developer for comparison was prepared by mixing 100 parts by weight of a ferrite carrier having a particle diameter of 50 (μm) with 8.2 × 10 ⁷ (Ω · cm) and 6 parts by weight of the toner obtained in Example 1.

Next, when the above-mentioned developer was installed in a reversal printer using the reversal development method and an initial image was taken, the charge amount was 20.3
(Μc / g), the background fog was 0.005, but the continuous copying durability test was not conducted because the carrier was raised on the transfer paper.

〔The invention's effect〕

Since the present invention is composed of the ferrite carrier containing a specific amount of magnesium oxide and the toner having a specific electrical resistance as described above, the leading edge and trailing edge of the image area due to the edge effect do not occur in continuous copying, which is excellent. It has excellent practical characteristics such as high image quality, low background fog, and low toner consumption. Further, as a remarkable effect of the present invention, it is possible to provide a developer for reversal development which can endure continuous copying of a large number of sheets without applying an expensive resin coating on the surface of the carrier.

Claims (1)

(57) [Claims] 1. Containing 5 to 15 mol% of magnesium oxide,
A developer for reversal development comprising a ferrite carrier having an electric resistance of 2 × 10 ^{8 to} 3 × 10 ⁹ Ω · cm and a toner having an electric resistance of 9 × 10 ¹⁰ Ω · cm or more.