JPS6013170B2 - Strongly negatively charged carrier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carrier in a developer for electrophotography, etc.
In particular, the present invention relates to a strongly negatively chargeable carrier that reduces wear of latent image forming media and is useful as a carrier for negatively triboelectrically chargeable latent image forming media.

Conventionally, iron powder, surface oxidized iron powder, glass beads, etc. have been used in two-component powder developers.

These are called carriers and are used in combination with powdered resin ink called toner. During this mixing, the toner causes frictional electrification with the carrier,
The toner and carrier are charged with equal amounts of electrostatic charges of opposite signs, and the Coulomb force acting between the electrostatic charges causes the toner to adhere to the carrier surface. This two-component mixture of toner and carrier is a developer. When this developer rubs against the latent image medium, which has formed a latent image potential pattern of the opposite sign to that of the toner, the toner is separated from the carrier surface and transferred onto the latent image medium, thereby making the latent image visible and forming a powder image. becomes. In such processes, the biggest problem is that the latent image forming medium is rubbed by the hard carrier, causing surface roughness due to abrasion or scratches, especially when the latent image forming medium is a photoconductor. The characteristics of the latent image deteriorate, making it impossible to form a normal latent image.
Further, triboelectric charging of the latent image medium by the developer during development causes a reduction in the strength of the latent image. These two losses become more noticeable as the operating speed of the device increases, and the shortening of the operating life due to the former cause in particular requires frequent maintenance, which affects the operating characteristics of the entire device. This is a determining factor. It is known to coat the carrier with a resin (eg, Teflon) to reduce wear on the latent image forming medium. On the other hand, in the developing process, the latent image forming medium and the carrier come into strong contact,
Since they are frictionally charged and electrostatically attracted to each other, there is a phenomenon in which the frictional force between them increases and the amount of wear increases.

Therefore, in order to prevent wear of the latent image forming medium, it is necessary not only to simply coat the carrier with a resin, but also to select a resin whose frictional potential during friction is close to that of the fusion medium.

Here, the solution forming medium is an inorganic photoconductive material such as CdS, Z core, SeTe, etc. or DEASP (1-phenyl-3-3-(P-diethylaminostyryl)-5-(P-diethylaminophenyl)-pyrazoline), etc. A negative triboelectric latent image forming medium such as a binder-based photoconductor containing an organic pigment or a photoconductor coated with a polyethylene terephthalate film, or an acrylic master drum in which a latent image is formed by pin discharge. When performing positive development using a chargeable toner, a strongly chargeable carrier charges the toner highly positively, and a negatively charged latent image forming medium consists of a mixture of a positively charged toner and a carrier that exhibits strong negative chargeability. Since the latent image is rubbed by the static developer, development can be performed without substantially deteriorating the strength of the negatively charged latent image. Furthermore, since this frictional potential affects the latent image potential of the latent image forming medium, it is necessary to consider the selection of the resin so as to minimize this effect as much as possible and prevent deterioration of print density.

That is, it is assumed that the latent image forming medium has the latent image intensity shown in FIG. 1. In the figure, V is the background potential, V2 is the latent image potential, and V
o is the limit potential. In the developing process, when the latent image forming medium is rubbed by the developer, V, becomes V as shown in Figure 2.
,', the potential level of V2 changes to V2'.

Typically, the difference between V,' and V, and V2' and V2 is between 500 and 1000 volts. However, the amount exceeding the inherent limit potential Vo of the latent image forming medium is discharged, and as shown in FIG.
drops to V,″, resulting in V,″−V2
′ becomes the potential difference.

Therefore, it is desirable that the frictional potential be such that the potential difference V,''-V2' is as close to the potential difference (V,-V2) at the time of image formation as possible. The main purpose of this invention is to reduce wear and prevent deterioration of print density, and particularly to provide a strongly negatively chargeable carrier suitable as a carrier for a negatively triboelectrically chargeable latent image forming medium.

From the above-mentioned viewpoint, the present invention is characterized in that ABS is selected as the base resin to be coated on the carrier.

This selected resin needs to be uniformly coated on a solid surface such as carrier iron powder, but it can be dissolved in a solvent (such as methyl ethyl ketone) suitable for the rotary drying method to achieve uniform coating. becomes.

Polyacrylonitrile is dissolved in the solvent trichloroethylene, A spots are dissolved in the solvent chloroform, and a rotary drying method can be applied.

The rotary dry method is used to completely and uniformly coat hard surfaces such as iron or glass with resin.
The operation and equipment are easy, and in this method, a cylindrical pot that rotates in the circumferential direction is filled with the required amount of coating resin, and is dissolved in an amount of organic solvent that is sufficient to soak the entire carrier material.

After confirming that it has completely dissolved, a predetermined amount of carrier base material is added, and the pot is rotated across the ocean, and the organic solvent that evaporates at this time is taken out with a suction tube attached to the rotating shaft of the pot, and the condenser is cooled with solid carbonic acid. Recover by. The material dried in this pot to a smooth state is taken out into a vat, and the base materials that have stuck to each other with resin are sieved out, and the properly coated material is heated in a direct temperature bath to ensure complete drying. Here, the coating film thickness is estimated from the specific surface area of the carrier substrate and the amount of coating resin, and the surface condition can be confirmed by SEM observation.

In addition, ABS can be negatively charged by friction, and the triboelectric potential of each material included in the developing system depends on the type of substance that is the subject of friction, but It shall be expressed by the charging property when it rubs against the surface treatment carrier iron powder. This potential change was measured by a surface electrometer. Furthermore, wear of the latent image forming medium by the developer consists of uniform film wear and scratches, and among these, uniform film wear is determined by measuring the dielectric constant of the latent image medium in advance.
The capacitance due to wear was measured and estimated from these two values by changing the thickness of the latent image medium. In addition, the number of scratches and the number of scratches were determined by microscopic observation of printing defects and the surface of the latent image medium. The incidence of scars was also reduced by 60%. Furthermore, it has been found that the preferred coating film thickness ranges from the critical film thickness of 0.1 at which the anti-friction effect appears, to the range of 1.5 mm at which the occurrence of associated carriers in which carriers bind together during coating increases. Ta.

Examples of the present invention will be described below. Generally A, which is a copolymer of acrylonitrile with styrene and putadiene.
It has also been found that a carrier coating having similar printing characteristics can be made using a resin called BS.

Kanease S-10 manufactured by Kanebuchi Chemical Industry ■ among commercially available A mother (
(product name) was used. This resin was placed in a polyethylene tank for 150 minutes and then 2000 cc of chloroform was added thereto to dissolve it. To this, Nippon Iron Powder EFVIOO/200 (product name)
, put in 15k9 and do a rotating hawk worship. The solvent that evaporates while rotating the pot is collected by a suction pump.
This operation is continued for 1 hour to completely dry the coated carrier to obtain the desired coated carrier. This is 1100
It was dried in a temperature bath of 0 for 1 hour. The carrier thus prepared developed the electrostatic latent image of 6 C' on the Mylar film to a level of 0.0.1.2. The following experiment was conducted to compare the coated carrier obtained according to the present invention with a conventionally used carrier.

First, positively charged toner TP-6 (trade name) containing epoxy black dye manufactured by Dainippon Ink was added to each of the coated carrier obtained in the example and the oxidized surface-treated iron powder DSP-12 solution (trade name) manufactured by Dowa Iron Powder. A developer was prepared by adding % of the developer, and each was called developer C and D in that order. When these developers were subjected to a development test using a high-speed impact printer equipped with an acrylic resin master drum as a latent image forming medium, at an initial effective latent image strength of 250V, developer C had a latent image potential of 170y for development. It worked effectively against.

On the other hand, in developer D, liOV only acted effectively. As a result, the print density obtained was 0. D.I. 1 was obtained, which is 0.00.
Compared to 85, the sharpness could be sufficiently improved. As described above, according to the present invention, the wear of the latent image forming medium is reduced by approximately 60%, the after-effect rate is also reduced by approximately 60%, and the wear life of the molten image forming medium is doubled. Furthermore, the printing density is improved, and it is an extremely useful developer and can be used.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the latent image potential during latent image formation, FIG. 2 is an explanatory diagram of the latent image potential due to frictional potential in the developing step, and FIG. 3 is an explanatory diagram of the latent image potential in the developing step. Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. A strongly negatively chargeable carrier comprising magnetic powder coated with ABS resin. 2. The strongly negatively chargeable carrier according to claim 1, wherein the resin coating has a thickness of 0.1 to 1.5 μm.