JPS6033267B2 - Positively chargeable 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 positively chargeable carriers that reduce wear of latent image forming media and are useful as carriers for negatively triboelectrically chargeable latent image forming media.

In two-component powder development, iron powder whose surface has been oxidized or glass beads have conventionally been used.

These are called carriers and are used in combination with powdered resin ink called toner. During this mixing, the toner and the carrier cause frictional electrification, and the toner and carrier are charged with equal and opposite electrostatic charges.
The Coulomb force acting between these 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 a process, the biggest problem is that the surface of the latent image forming medium is rubbed by the hard carrier, resulting in friction or scratches and roughening of the surface, especially when the latent image forming medium is a photoconductor. The characteristics deteriorate and normal latent image formation becomes impossible.

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 equipment increases, and the shortened operating life due to the former cause requires frequent maintenance, which affects the operating characteristics of the entire equipment. This is a deciding factor. It is known to coat the carrier with a resin (eg, Teflon) to reduce wear on the latent image forming medium. However, in the case of conventional copying machines, where the development speed is slow and the printing quality is low, it is sufficient to simply coat the carrier with resin, but in recent years, with the advent of laser printers using electrophotography, There is a demand for fast development speed and high print quality, and the influence of the frictional potential between the developer and the latent image forming medium has become impossible to ignore.

That is, it is assumed that the latent image forming medium has the latent image strength shown in FIG.

In the figure, V is the background potential, V2 is the latent image potential, and Vo is the limit potential. In the developing process, when the latent image forming medium is rubbed by the developer, the potential level changes from V to V2 and from V2 to V2' as shown in FIG.

Generally V. ' and V, and the difference between V2' and V2 is 500 to 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 is such that the potential difference V,''-V2' is as close as possible to the potential difference during latent image formation (V. - V2).On the other hand, if the latent image forming medium is CdS, Zn
○, inorganic photoconductive materials such as SeTe or DEASP
(1-phenyl-3-(P-diethylaminostyryl)
A binder-based photoconductor containing an organic pigment such as (P-diethylaminophenyl)-pyrazoline) or a photoconductor coated with a polyethylene terephthalate film, or an acrylic master drum on which a latent image is formed by pin discharge. Negative triboelectric materials such as triboelectric materials have come to be widely used.

An object of the present invention is to provide a positively chargeable carrier that can reduce the wear of the latent image forming medium and prevent deterioration of the latent image strength of the negatively triboelectrically chargeable latent image forming medium.

In order to achieve this objective, the positively chargeable carrier of the present invention is characterized by being made of magnetic powder having a resin coating made of polyamideimide. Polyamideimide is a polyimide with an amide bond introduced into its main chain, and is a type of modified imide resin that has improved processability at the expense of some heat resistance. In the present invention, when a negatively chargeable toner is used in the above-mentioned negatively triboelectrically chargeable latent image forming medium and positive development is performed using a uniformly positively charged corona, the positively chargeable carrier charges the toner negatively, and the latent image forming medium discovered that development is possible with almost no deterioration in the strength of the latent image because it is rubbed by a slightly negatively charged developer consisting of a mixture of a negatively charged toner and a positively chargeable carrier.

This selected resin needs to be uniformly coated on solid surfaces such as carrier iron powder in order to improve the anti-wear effect, but it is dissolved in a solvent (such as toluene) that is passed through a rotary drying method to achieve a uniform coating. This enables uniform coating.

Polyamideimide is dissolved in toluene, a solvent that is passed through a rotary drying method. The rotary drying method uses a rotary drying method that is easy to operate and use in order to completely and uniformly coat hard surfaces such as iron or glass with resin.

In this method, a cylindrical pot that rotates in the circumferential direction is filled with the required amount of resin to be coated, and the resin 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 the carrier base material is added and the pot is rotated, 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 is cooled with solid carbonic acid and condensed. Collect by container. After drying in this pot to a smooth state, take it out into a vat and sift out the glue that has stuck to each other with resin, and heat the properly coated one in a heating tank to completely dry it. Now. Here, the coating film thickness was estimated from the specific surface area of the carrier base material and the amount of coating resin, and the surface condition was confirmed by SEM observation.

Moreover, polyamideimide can be positively charged by friction.

The triboelectric potential of each material contained in the developing system depends on the type of substance to be rubbed, but below, when it rubs with the oxidized surface-treated carrier iron powder, shall be expressed by the chargeability of This potential change was measured by a surface electrometer. Furthermore, wear of the latent image forming medium by the developing agent consists of uniform film wear and scratches.

Among these, uniform film wear was estimated by measuring the dielectric constant of the latent image medium in advance, measuring the capacitance accompanying wear, and using these two values as a change in the film thickness of the latent image medium. In addition, scratches can be detected by microscopic observation of printing defects and the surface of the latent image medium.
It was measured as the number of scratches. The amount of wear of the latent image medium by the carrier coated with this carrier is 1/2 that of the case with the uncoated iron powder carrier.
As a result, the incidence of scratches was reduced by 40%, and the wear life of the latent image soot body was extended by 1.30%.

Furthermore, since the frictional charging voltage with the latent image medium is controlled, shrinkage and deterioration of the latent image during development is reduced, print density is improved, and background stains such as tailing and fogging are reduced.

It has been found that the coating film thickness is preferably 1.5 mm, which increases the generation of associated carriers in which carriers are bound to each other during coating, from the critical thickness of 0.1 mm at which the effect of reducing friction is exhibited.

Examples of the present invention will be described below. [Example 1] This example relates to the coating of a carrier made of polyamideimide.

The carrier iron coating is RHONE-POULE.
Rhodeftal 101 (trade name) polyamideimide varnish manufactured by NC Company was used. This varnish was diluted to 5M% with toluene, and
(Product name) Resin solid content 1.1k per iron powder 100k9
9, then fill it into a rotary dryer and mix thoroughly. Here, put the dryer pot at 9
000 and evaporate the solvent while rotating, and the solvent that comes out is condensed using a dry ice trap. The coated carrier obtained here is classified using 100 mesh to remove the associated carriers, spread on a stainless steel vat, and cured in a constant flooding tank for 250 q02 hours. Since the carrier obtained by this method has less toner stickiness, it exhibits good electron imparting properties and is stable when negative type epoxy toner is used as a carrier for a laser printer using a urethane photocontainer with Z pigment added. Achieve development over a long period of time. The following experiment was conducted to compare the coated carrier obtained according to the present invention with a conventionally used carrier.

First, each of the cord carrier obtained in Example 1 and the oxidized surface-treated iron powder EFVIOO/200 (trade name) manufactured by Nippon Steel Powder was combined with a negatively charged toner containing styrene acrylic black dye FN-803 (trade name) manufactured by Dainippon Ink. Developers were prepared by adding fine t% and were called developers A and D, respectively. When these developers were subjected to a development test using a high-speed non-nicto printer (printing speed 10.00/min) equipped with our company's DEASP-containing polyester photoreceptor sheet as a latent image forming medium, the initial effective latent image strength was Compared to 260V, developer A developed a latent image potential of 170V.

On the other hand, in developer ○, 140V only acted effectively. As a result, the obtained print density was 0. D.I. 1 to 1.2, compared to 0.01.0 obtained in the case of D, it was possible to improve the print density, and development such as fogging did not occur, and it was confirmed that the operating margin was expanded. . As described above, according to the present invention, the wear of the latent image forming medium is reduced by about 3/4, the scratch occurrence rate is also reduced by about 40%, and the wear life of the latent image forming medium is extended by 1.5 times. This effect is obtained, and the print density is further improved, so that it can be used as an extremely useful developer.

[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 positively chargeable carrier comprising magnetic powder coated with polyamide-imide resin. 2. The positively chargeable carrier according to claim 1, wherein the resin coating has a thickness of 0.1 to 1.5 μm. 3. The positively chargeable carrier according to claim 1 or 2, wherein the positively chargeable carrier is used as a development carrier for a negatively triboelectrically chargeable latent image forming medium.