Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1994-08-17
2001-09-11
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S063000, C525S166000, C525S169000
Reexamination Certificate
active
06288166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a binder resin for a toner and also to a positively chargeable toner containing such a binder resin, wherein the toner is used for developing latent images in electrophotography, electrostatic recording, electrostatic printing, etc.
2. Discussion of the Related Art
As disclosed in U.S. Pat Nos. 2,297,691, 2,357,809, and other publications, conventional electrophotography comprises the steps of forming an electrostatic latent image by evenly charging a photoconductive insulating layer and subsequently exposing the layer to eliminate the charge on the exposed portion, and visualizing the formed image by adhering a colored charged fine powder known as a toner to the latent image (a developing process); transferring the obtained visible image to an image-receiving sheet such as a transfer paper (a transfer process); and permanently fixing the transferred image by heating, pressure application or other appropriate means of fixing (a fixing process).
As indicated above, a toner must meet the requirements not only in the development process but also in the transfer process and fixing process.
In general, in order to obtain a positively chargeable toner, an binder resin used therefor is a styrene-acrylic resin which can be easily positively charged. However, the styrene-acrylic resin has low mechanical properties, so that the resulting toner is less durable for continuous printing. Also, when a resin having a relatively high molecular weight is used in order to solve this problem, the fixing ability of the toner becomes extremely poor. Further, although a polyester resin having excellent mechanical properties can provide both good fixing ability and stability upon continuous printing, its negative chargeability is too strong, making it difficult to provide positive chargeability.
In order to solve the above problems, the following methods for blending polyester resins having excellent fixing ability with styrene-acrylic resins having a small change in the triboelectric charge under the high-temperature, high-humidity conditions when compared with that under normal-temperature, normal-humidity conditions have been known. For instance, examples of such methods include:
(1) Methods for blending polyester resins with styrene-acrylic resins (see Japanese Patent Laid-Open Nos. 49-6931, 54-114245, 57-70523, and 2-161464);
(2) Methods for chemically linking polyester resins with styrene-acrylic resins (see Japanese Patent Laid-Open No. 56-116043);
(3) Methods for copolymerizing unsaturated polyesters with vinyl monomers (see Japanese Patent Laid-Open Nos. 57-60339, 63-279265, 1-156759, and 2-5073);
(4) Methods for copolymerizing polyester resins having a (meth)acryloyl group with vinyl monomers (see Japanese Patent Laid-Open No. 59-45453);
(5) Methods for copolymerizing reactive polyesters with vinyl monomers in the presence of polyester resins (see Japanese Patent Laid-Open No. 2-29664); and
(6) Methods for forming a block copolymer by linking polyester resins and vinyl resins with an ester bond (see Japanese Patent Laid-Open No. 2-881).
However, since the polyester resins have inherently poor compatibility with the styrene-acrylic resins, mere mechanical blending of the components may result in poor dispersion of the resins and the internal additives such as a carbon black at the time of production of the toner in certain blending ratios. This may in turn cause unevenness in the triboelectric charge of the toner, thereby causing problems such as background in the formed images. Further, when the two types of resins have different molecular weights, the differences in their melt viscosities are likely to take place, thereby making it difficult to make the grain size of the resin for the dispersed domain fine. In such a case, when a toner is produced with such resins, the dispersion of the internal additives such as a carbon black becomes extremely poor, so that such a problem arises that the resulting toner results in poor image quality. Moreover, in the case where the vinyl monomers are copolymerized with the reactive polyesters, it is applicable only in a restricted compositional range in order not to allow gelation to take place.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a binder resin for a toner which can give good even chargeability and a high charging-up speed for the toner.
Another object of the present invention is to provide a positively chargeable toner having good even chargeability and a high charging-up speed with a small proportion of a reversely charged toner by using the binder resin mentioned above.
As a result of intense research in view of the above problems, the present inventors have found a positively chargeable toner having excellent low-temperature fixing ability and offset resistance which maintains good stability under severe conditions in triboelectric charge and image quality can be obtained by using a particular combination of binder resins, and thus providing excellent durability in the obtained developer. The present invention has been completed based on this finding.
Specifically, the present invention is concerned with the following:
(1) A binder resin for a toner comprising:
a resin (1) capable of forming a matrix in the toner, the resin (1) being a hybrid resin of a polyester resin and a vinyl resin; and
a resin (2) capable of forming a domain dispersed in the matrix formed by the resin (1), the resin (2) being a vinyl resin having a positive charge functional group; and
(2) A positively chargeable toner comprising the binder resin described in (1) above and a coloring agent. The present invention is also concerned with a positively chargeable toner further containing a compound having the following general formula (I) and/or (II):
wherein R
1
, R
2
, R
3
, and R
4
, which may be identical or different, independently represent an alkyl group, an alkoxy group, an aryl group, or an allyl group, each of which may form a ring; and A
−
represents an anion.
A positively chargeable toner containing the binder resin of the present invention has a good evenness of chargeability and high charging-up speed with a small proportion of a reversely charged toner upon triboelectric charging. Moreover, in a heat roller fixing method, fixing at a low temperature can be performed without using an offset inhibiting liquid.
DETAILED DESCRIPTION OF THE INVENTION
The binder resin of the present invention is a binder resin for a toner comprising a resin (1) capable of forming a matrix in the toner and a resin (2) capable of forming a domain dispersed in the matrix formed by the resin (1). The resin (1) is a hybrid resin of a polyester resin and a vinyl resin, and the resin (2) is a vinyl resin having a positive charge functional group.
First, the preferred embodiment of the resin (1) will be explained in detail below.
The resin (1) is a hybrid resin of a polyester resin and a vinyl resin, the polyester resin and the vinyl resin being chemically linked with each other. The resin (1) can be produced using monomers of a polyester resin, monomers of a vinyl resin, and a compound reacting with both monomers.
As for the monomers of polyester resins, alcohols such as a dihydric alcohol or a trihydric or higher polyhydric alcohol, and carboxylic acid components such as a dicarboxylic acid or a tricarboxylic or higher polycarboxylic acid, an acid anhydride thereof or an ester thereof are used.
Examples of the dihydric alcohols include bisphenol A alkylene oxide adducts such as polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(3.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(2.0)-polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, and polyoxypropylene(6)-2,2-bis(4-hydroxyphenyl)propane; ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexane
Aoki Katsutoshi
Hidaka Yasuhiro
Kawaji Hiroyuki
Maruta Masayuki
Sata Shin-ichi
Birch & Stewart Kolasch & Birch, LLP
Kao Corporation
Short Patricia A.
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