Process for preparing a binder resin useful in electrophotograph

Details Process for preparing a binder resin useful in electrophotograph Process for preparing a binder resin useful in electrophotograph

1994-02-04

1995-05-16

Buttner, David

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

525301, 430109, 430138, C08F26706, C08F26708, C08F 622, G03G 9087

Patent

active

054161665

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a process for preparing a binder resin useful for a dry toner which is used in the dry development of a latent electrostatic image in electrophotography. More particularly, the present invention relates to a process for preparing a resin which is partially cross-linked and has a low cross-link density and high gel content.


BACKGROUND OF THE INVENTION

Most of copy machines useful in office work employ an electrophotographic copy system. A typical mechanism of such electrophotographic system may be represented as follows: A photoconductive layer is photosensitized by being charged with a surface potential; through an exposure to light a latent electrostatic image of an original image is formed on the photoconductive layer; subsequently, a toner is charged with a potential having a charge opposite to that of the potential of the latent image; the charged toner is transferred onto the latent image and then transferred again onto a plain paper by electrostatic force, on which the toner image is fixed to provide a desired printed image.
In electrophotography, a hot roll fixing method has been generally used to fix a toner image on a plain paper. The hot roll fixing method comprises transferring a toner image from the surface of a photoconductive drum in an electrophotographic copying machine to a plain paper and fixing permanently the toner image on the paper using a hot roller at a temperature ranging from 120.degree. to 180.degree. C.
Toners which can be suitably used in the hot roll fixing method are required to soften at relatively low temperatures and adhere easily to the paper(to meet the fixability requirement) and not to adhere to the hot rollers even when the temperature of the hot rollers is relatively high(to have the non-offset property). The above-mentioned properties of toners are mainly dictated by the binder resins used for the preparation of the toners.
In general, if the melt viscosity of a binder resin used in a toner decreases, the fixability of the toner upon hot fixing becomes better while the non-offset property of the toner becomes deteriorated and vice versa. Therefore, many attempts have been made to develop a binder resin capable of satisfactorily meeting the above requirements for both fixability and non-offset property.
U.S. Pat. No. 4,486,524 discloses a method which comprises: producing each of a low molecular weight polymer which imparts the fixability to a toner and a high molecular weight polymer which gives the non-offset property to the toner separately; and mixing the polymers so produced. This method improves the fixability of the toner; but has the defect that the toner has poor non-offset property; and, further, a long period of time is required to produce the high molecular weight polymer, and the cost of production is high. U.S. Pat. No. 4,652,511 discloses a process for producing a resin composition which comprises suspension-polymerizing at least one vinyl monomer in aqueous medium in the presence of a dispersing agent and a high molecular weight vinyl polymer obtained by emulsion polymerization. This process requires short periods of time to produce a toner resin but the non-offset property still remains inferior.
Japanese Laid Open Patent Publication No. 134,248/1985 proposes a two-step polymerization which produces a polymer of partially cross-linked structure, that is, having both a cross-linked structure and a linear structure of low molecular weight. However, in this method, non-offset property and fixability are also liable to betray each other depending upon the cross-link density of the polymer. That is, when the cross-link density of the polymer is low, the proper gel content can not be maintained and the non-offset property of toner is poor although the fixability is adequate. On the other hand, when the cross-link density of the polymer is high, the non-offset property becomes acceptable while the toner's fixability becomes inferior.
Further, European Patent Publication No. 412,712 discloses a meth

REFERENCES:
patent: 4983681 (1991-01-01), Mori
patent: 5219946 (1993-06-01), Tanikawa

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