Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-08-08
2002-11-05
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108100, C430S110100, C430S111400
Reexamination Certificate
active
06475690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a toner for developing an electrostatic image which may be employed in printers and copying machines wherein an electrophotographic mode, an electrostatic printing mode and the like are adopted.
2. Description of the Related Art
The toner for developing an electrostatic image is generally prepared by a grinding method from a viewpoint of easy preparation. The grinding method is a method wherein at least a binder resin and a colorant are melted, kneaded, cooled, coarsely ground, finely ground and then classified if necessary to obtain toner particles having desired particle size. However, it has been difficult to efficiently prepare small-size toner particles by employing said grinding method in order to satisfy the requirement of recent tendencies of a full-colorization and a high image quality. Although it has been known that a grindability of a toner composition is increased when what is called a grinding agent (a resin which is more brittle than the binder resin) is added to the toner composition before grinding, there is a problem that said grinding agent exerts a bad influence upon basic properties of the toner, such as electrification, heat resistance, fixability and the like.
Accordingly various techniques have been disclosed, such as a technique wherein C
7
-C
10
aromatic petroleum resin is added to binder resins, such as styrene-butadiene resin and the like (Japanese Patent Publication (KOKAI) No. 257868/1992), a technique wherein a hydrogenated petroleum resin whose hydrogenation degree is not less than 50% is added to binder resins (U.S. Pat. No. 5,614,347), a technique wherein a copolymer comprising styrene monomer and indene monomer is added to binder resins (U.S. Pat. No. 5,972,547) and a technique wherein a copolymer comprising aliphatic hydrocarbon and aromatic hydrocarbon having carbon atoms of not less than 9 is added to binder resins (U.S. Pat. No. 5,958,642).
However, the aforementioned techniques could not sufficiently prevent the decrease of the aforesaid basic properties of the toner. Particularly, when the toners according to the aforementioned techniques are employed, an electrification stability is remarkably decreased because toner particles are broken at the time of wearing, and pieces of the broken particles are adhered to the various members and stuck to carriers. Furthermore, although the toner compositions according to the aforementioned techniques are easy to grind, there is a problem of productivity (yield) of the toner that it is difficult to effectively obtain the toner particles having a desired particle size since fine particles and large-size particles are easy to form.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned situation. The object of the present invention is to provide a toner for developing an electrostatic image which has excellent rising property of electrification, electrification stability, maintenance of heat resistance, fixability, image quality and productivity.
Another object of the present invention is to provide a toner for developing an electrostatic image which has relatively high roundness and uniform shape, said toner being applied to full-color image formation, cleanerless system and toner-recycling system.
The present invention relates to a toner for developing an electrostatic image characterized in that it comprises toner particles containing a binder resin (A), a polymer (B) and colorant, the polymer (B) having a weight-average molecular weight of 1000-3000 and having a ratio of weight-average molecular weight
umber-average molecular weight being not more than 2.0, wherein the polymer (B) particles exists on surfaces of the toner particles.
DETAILED DESCRIPTION OF THE INVENTION
In the toner particles which constitute the toner of the present invention, at least the colorant and the polymer (B) are dispersed into the binder resin (A). Particularly, the toner particles have a construction wherein the polymer (B) is more densely dispersed in surface regions of said particles in comparison with central parts of said particles. Preferably, the polymer (B) is exposed on the surfaces of the toner particles.
In the present invention, the productivity of the toner can be increased without decreasing the basic properties, such as rising property of electrification, electrification stability, maintenance of heat resistance, fixability, image quality and the like by realizing the aforesaid construction of the toner particles.
The effect of the present invention cannot be obtained when the polymer (B) is not densely dispersed in the surface regions of the toner particles in comparison with the central parts of said particles, i.e. when the polymer (B) is uniformly dispersed in the toner particles or is densely dispersed in the central parts of said particles. That is to say, if the toner particles have these constructions, it is difficult to obtain a desired electrification amount from an early stage and a fogging occurs remarkably at the time of wearing since the toner particles are easy to break to form their broken pieces which stick to various kinds of blades and carriers. Furthermore, these toner particles have a bad grindability during their preparation process and a large amount of energy is required to obtain the toner particles having a desired particle size. On this occasion, a portion of the toner particles is overground to increase fine particles having smaller particle size than the desired particle size, and on the contrary, large-size particles are easy to mix with the desired toner particles. Consequently, a particle size distribution of the ground toner particles becomes broad, and a yield of the toner is decreased.
The fact that the toner particles which constitute the toner of the present invention have the construction wherein the polymer (B) is more densely dispersed in the surface regions of the toner particles in comparison with the central parts of the toner particles can easily be understood by the following knowledges:
(1) When a slice of the obtained toner particles was observed by means of TEM (transmission electron microscopy; 10000 magnifications), the polymer (B) was more densely dispersed in the surface regions of the toner particles in comparison with the central parts of the toner particles.
(2) Even if the glass transition point (Tg) of the binder resin (A) to be used is relatively low, a decrease of the maintenance of heat resistance was effectively suppressed when the polymer (B) having a relatively high Tg was employed.
The toner having the aforementioned construction of the present invention can be prepared by dispersing a suitable amount of the polymer (B) having a suitable particle size and higher grindability than the binder resin (A) in said binder resin. More particularly, the toner according to the present invention can be obtained by employing a grinding method and by controlling the grindabilities of the binder resin (A) and polymer (B) as well as the dispersed state of the polymer (B) in the kneaded mixture which is obtained by cooling the molten kneaded mixture.
As regards the polymer (B) employed in the present invention, a weight-average molecular weight (Mw) is 1000-3000, preferably 1000-2800, and a ratio of Mw/Mn (wherein Mn is a number-average molecular weight) is not more than 2.0, preferably not more than 1.9. When Mw of the polymer (B) is less than 1000, not only the toner particles cannot be obtained wherein the polymer (B) is densely dispersed in the surface regions of the toner particles, but also the maintenance of heat resistance becomes worse when the toner is left at relatively high temperature and a practical use becomes difficult since the glass transition temperature of the polymer (B) is decreased. In addition, volatile components, such as acetone, benzene, monomers and the like are apt to remain in said polymer, and the problems concerning a security and an offensive smell are brought about since said volatile components are
Anno Masahiro
Fukuda Hiroyuki
Kido Kenichi
Sano Tetsuo
Dote Janis L.
Minolta Co. , Ltd.
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