JPH01229266A - Dry type two component developer for electrophotography - Google Patents

Abstract

PURPOSE:To prolong the life of a developer to be used for the development in a high speed copying machine by specifying a resistivity of a carrier resin- coated on the surface, and a particle size and resistivity of semiconductor particles to be deposited on the surface of a toner, and specifying also the polarity and electric charge of the carrier, toner, and semiconductor particles to each other. CONSTITUTION:The surface of a carrier is coated with a synthetic resin such as silicone resin, etc,. and the resistivity of the carrier is arranged to 10<10>-10<16>OMEGA.cm. Fine semiconductor particles consisting of magnetic powder such as electroconductive silicon carbide, electroconductive ZnO, electroconductive SnO2, Fe3O4, gamma-Fe2O3, CrO2, Ni-2 ferrite, etc., and having 10<2>-10<9>OMEGA.cm resistivity, are deposited to the surface of a toner. The electric charge of fine semiconductor particles is arranged to be reverse in polarity to the polarity of the toner, or to be in the midway between the electric charge of the toner and the carrier. Thus, frictional electric charge is made uniform, fog and scattering of the toner are reduced, and the life of a developer is prolonged.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is an improvement of a dry developer comprising a carrier and a toner used for developing electrostatic images formed by electrophotography, electrostatic recording, etc. Regarding.

<Prior Art><Problems to be Solved by the Invention> In electrophotography, an electrostatic image formed on a photoreceptor is developed with a developer and then transferred and fixed onto a transfer sheet. As this developer, a dry two-component developer for electrophotography consisting of toner and carrier is known.

In recent years, high-speed copying machines with a copying speed of 50 to 60 sheets per minute have been required, and the developer used in these high-speed copying machines requires a carrier that always maintains the desired polarity and sufficient amount of toner during long-term use. The amount of charge must be triboelectrically charged.

However, in conventional developers, a toner film is formed on the surface of the carrier due to the mechanical impact caused by collisions between particles or collisions between particles and the developing machine, or the heat generated by these, resulting in the so-called spent phenomenon, which deteriorates the charging characteristics of the carrier. Decreases with usage time,
The supplied toner is developed without being sufficiently charged, resulting in poor images due to fogging, etc., and there is also a lot of toner scattering, contaminating the interior of the copying machine, making it necessary to replace the entire developer.

In order to prevent such a spent phenomenon, it has been known to coat the surface of the carrier with various resins to increase the insulation properties of the carrier and prevent toner from fusing due to repeated use.

For example, a developer using a carrier whose surface is coated with a silicone resin and a toner containing a metal-containing monoadz dye (
Special Publication No. 60-61948) and magnetic powder.

Toner containing conductive fine particles (JP-A-58-1052)
36, Japanese Patent Publication No. 58-118632. Japanese Patent Publication No. 59-736
9) is known and aims to create a long-life developer.
At most, it is 100,000 to 300,000 pieces, which is still not enough.

The present invention provides a toner with improved toner properties for use in high-speed copying machines. The first objective of the present invention is to provide a long-life developer for high-speed copying machines, the second objective is to provide a toner with low running costs, and the third objective is to provide a toner with low running costs. Another object of the present invention is to provide a developer with stable image quality.

Means for Solving the Problems> The present invention controls the amount of charge on the toner by specifying the relationship between the resistivity of a carrier whose surface is coated with a resin and the particle size and resistivity of semiconductive particles attached to the outside of the toner surface. In addition, by specifying the polarity and charge of the carrier, toner, and semiconductive particles, it was discovered that when continuous high-speed copying is performed, the amount of charge does not decrease even when stirred for a long time in the developer tank. This led to the invention.

That is, in the dry two-component developer for electrophotography of the present invention, the surface of the gear is coated with a synthetic resin and has a resistivity of 1010 to 1016 Ωcm, and the surface of the toner has a resistivity of 102 to 10q0cm. Semiconductive fine powder particles are attached, and the triboelectric charging of the l-na and the tribo-charging of the carrier are opposite in polarity. This is a dry two-component developer for electrophotography, which is characterized by being on the side opposite to the toner when centered on the toner.

Generally, an electrostatic latent image formed on a photoreceptor of a copying machine is developed with toner to become a visible image. In this case, toner particles that are triboelectrically charged to a polarity opposite to that of carrier particles such as synthetic resin-coated iron powder or glass beads are held on the surface of carrier particles larger than the particle diameter; Upon contact with the photoreceptor surface during development, electrostatic forces in the latent image area of the photoreceptor overcome the bonding forces between the carrier particles and toner particles and the toner particles adhere to the latent image to form a toner visible image. Therefore, in order to sufficiently charge the toner, it is preferable that the materials for the toner and the gear have high resistance. However, if the developer consisting of toner and carrier has a high resistance, a so-called edge effect occurs in which only the periphery of the formed print becomes clear and the central part of the print becomes thinner.

On the other hand, in order to prolong the life of the developer used and to prevent spent development, a method has been adopted in which the surface of the carrier is coated with a synthetic resin, but when coated with a resin,
The carrier appears to have a high resistance, and the charge remains in the carrier forever, resulting in a problem that the toner attached to the carrier cannot be sufficiently charged.

Therefore, as a developer, it is desirable that the toner and carrier have high resistance in order to improve charging properties, and since the charged toner can easily move to the location of the electrostatic latent image, the developer is In order for the developer to work effectively, it is necessary to have a certain degree of chargeability, and the developer must have these contradictory properties.

For this reason, it is necessary to maintain the developer in a state where there is no spent phenomenon and the replenished toner can be sufficiently charged even when used for a long time. The present invention was achieved by selecting a developer based on a combination of resistivities, and improving a developer that has low toner consumption, good image quality, and less fog.

The toner constituting the developer of the present invention contains 100% by weight of synthetic resin such as polystyrene, styrene-acrylic copolymer, unsaturated polyester, polyvinyl chloride, polyvinyl acetate, phenol resin, and epoxy resin, carbon black, and chromium. Mixing 1 dispersion, kneading,
These are colored fine particles produced by pulverization and first classification.

To this toner, semiconductive particles having a particle size smaller than that of the toner and having a resistivity of 102 to 109 Ωcm are added to the toner in an amount of 0.1 to 2.0% by weight, preferably 0.3 to 0.
．． A 5% by weight toner is used in the present invention.

Here, semiconductive fine particles have a particle shape of 0.1 to 0.5
μm conductive silicon carbide, conductive zinc oxide, conductive tin oxide, Fe, Oa, r-Fe203. Examples include magnetic powders such as CrO□ and nickel-2 ferrite.
Among them, magnetic powder is most suitable.

On the other hand, the carrier used in the present invention has silicone resin, fluororesin, methyl acrylate, ethyl acrylate, isobutyl acrylate, etc. Coated with resin such as acrylic esters such as methyl methacrylate and butyl methacrylate, vinyl ethers such as acrylonitrile, acrylamide, and vinyl isobutyl ether, and has a resistivity of 1010 to 10.
A resin coated carrier with I6Ω CIN is used.

As the resin used in the present invention, silicone resin is effective in extending the life of the developer.

Also, if the resistivity of the carrier is less than 1010 Ωcm, the resistivity will be low and the amount of toner consumed will increase.
If it exceeds 6 Ωcm, the amount of toner consumed increases despite the high resistivity due to the edge effect, so the above range is appropriate.

To coat the surface of the core material with various resins, for example, a dispersicon liquid (containing 1 to 5%) containing vinylidene fluoride polymer particles is dropped onto the powder of the core material, and the whole is stirred or sprayed. Attach dispersion particles to the material.

Next, the toner (T), carrier (C), and semiconductive fine powder particles (P) constituting the electrophotographic dry two-component developer of the present invention must have the following triboelectrification series.

In other words, when the toner (T) has a negative polarity with respect to the carrier (C), the semiconductive fine powder particles (P) have the same polarity (negative polarity) as (T) as shown in Figure 1 (A). (charged polarity), it is necessary to have a relationship of P<T, or to have a polarity opposite to T as shown in Figure 1 (b), and in particular in the present invention, the relationship as shown in Figure 1 (b) is required. It is preferable.

On the other hand, when the toner (T) is in a positively charged polarity relationship with the carrier (C), the semiconductive fine powder particles (P) are
It is necessary to have the same polarity as T (positively charged polarity) and the relationship P<T as shown in Figure 2 (a), or to have the opposite polarity to T as shown in Figure 2 (b). In this case as well, it is preferable that the relationship shown in FIG. 2(b) holds true.

The present invention will be explained below using examples.

<Example-1> Silicone resin was coated on iron oxide powder having an average particle size of about 150 μm using a fluidized bed coating device, and the material was placed in an electric furnace and fired at 250° C. for 2 hours to obtain a carrier. The carrier resistivity was 10'5 Ωcm.

On the other hand, 100 parts by weight of styrene-acrylic copolymer resin, 1 part by weight of chromium-containing metal dye, and 5 parts by weight of carbon black were melted in a roll mill for 20 minutes, kneaded, cooled, coarsely pulverized in a mill, and then further heated using a supersonic jet. The powder was finely pulverized in a mill to obtain a toner having an average particle size of 5 to 7 μm. For this toner, semiconductive silicon carbide (
1.5% by weight of SiC) was added and mixed for 1 minute using a Henschel mixer. Furthermore, a toner is mixed with the carrier iron powder at a ratio of 5% by weight, and the electrophotographic dryer of the present invention is used.
A two-component developer was prepared.

Put this developer into a high-speed continuous copying machine (60 sheets/minute) and
When a continuous copying durability test of 00,000 sheets was performed, the image density (1,0,) measured by Macbeth reflection densitometer was approximately 1.35, and the background dirt (B, G,) in the non-image area was found to be approximately 1.35.
is approximately 0.4 to 0.6, and the amount of triboelectric charge (Q/M) is 35μc
/g, both were stable, and there was no toner scattering and toner consumption was small.

The resistivity of the carrier and semiconductive particles was measured using a multi-insulation type super insulation resistance meter (TERAOHMMET) manufactured by Kawaguchi Electric Co., Ltd.
ERVE-30 model), the electrical resistance of the powder was measured between electrodes with an electrode area of 5 cJ under a load of 2 kg, and the resistance was calculated.

Next, Table 1 shows the results of the continuous copy durability test for this example and each of the comparative examples and examples shown below. <Comparative Example-1> Example-1 except that semiconductive particles were not attached to the outside
When a continuous copying durability test was conducted for 100,000 sheets under the same conditions as , the initial 0.68 of B and G exceeded 1.0, and after 200,000 sheets, it exceeded 2.0, and the amount of charge was also 100,000 sheets. When the number of sheets exceeded 10,000 sheets, the performance decreased, and the toner consumption amount increased and deterioration of the toner was observed.

<Example 2> A continuous copy durability test of 500,000 copies was conducted under the same conditions as in Example 1, except that the semiconductive particles were replaced with tin oxide (resistivity 3 x 102 Ωcm). The amount of triboelectric charge was also stable without any decrease.

<Example 3> A continuous copy durability test of 500,000 copies was conducted under the same conditions as Example 1, except that the semiconductive particles were replaced with magnetic powder (resistivity 8 x 1011 Ωcm). There was no ground drop and the amount of triboelectric charge was stable.

(Note) The resistivity of Examples and Comparative Examples was measured by putting toner in a cylindrical body, compressing it from the top under a load of 2 kg, and applying electricity from the upper and lower electrodes.

Table 1 High-speed copying durability test (width Image density (1, D,), hack ground (B, G,) in Table 1
This is the value measured using the Maghes scale.

The unit of triboelectric charge 1t (Q/M) is (μC/g),
T: toner, C: resin-coated carrier, P: semiconductive fine powder, toner consumption is the amount of toner replenished when copying 10,000 sheets at each time point of 100,000 sheets, 200,000 sheets, and 500,000 sheets ( g).

(Effects of the Invention) According to the present invention, since the supplied toner is sufficiently charged and then consumed, the image density is high from the initial stage to after 500,000 copies have been copied, the huck ground is small, and the amount of frictional charging is unbiased. As a result, fog was reduced, toner scattering was improved, and the life of the developer was dramatically extended.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams showing the triboelectrification series of components used in the present invention.

Claims (1)

[Claims] In a dry two-component developer for electrophotography consisting of a carrier and a toner, the surface of the carrier is coated with a synthetic resin, and its resistivity is 10^1^0 to 10^1^6.
Ωcm, and the resistivity of the toner surface is 10^2
Semiconductive fine powder particles of ~10^9Ωcm are attached, and the triboelectric charge of the toner and the triboelectric charge of the carrier are opposite in polarity, and the electric charge of the semiconductive fine powder is the same as that of the toner and the carrier. A dry two-component developer for electrophotography, characterized in that the charge is in the middle of the charge or on the side opposite to the charge of the toner when the charge of the carrier is centered.