Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-06-23
2003-08-26
Rodee, Christopher (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, C430S108400, C430S108800, C430S110100, C430S110300, C430S137140, C430S109300
Reexamination Certificate
active
06610453
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a toner for the development of an electrostatic image for use in electrophotographic process copying machines and printers. More particularly, the present invention relates to a toner for the development of an electrostatic image having excellent fixability, offset resistance and blocking resistance which can provide an image with a good OHP transparency.
BACKGROUND OF THE INVENTION
A toner for the development of an electrostatic image which has heretofore been widely used in electrophotography is prepared by a process which comprises melt-kneading a mixture of a styrene-acrylate copolymer, a colorant such as carbon black and pigment, a charge control agent and/or a magnetic material through an extruder, crushing the material, and then classifying the powder. However, the conventional toner obtained by the foregoing melt-kneading/crushing process is disadvantageous in that the controllability of the particle diameter of the toner is limited, making it difficult to prepare a toner substantially having an average particle diameter of not more than 10 &mgr;m, particularly not more than 8 &mgr;m in a good yield. Thus, the conventional toner cannot be considered good enough to realize a high resolution which will be required in the future electrophotography.
Further, from the standpoint of reduction of energy required, it has been desired to provide a toner having a good low temperature fixability. To this end, an approach involving the blend of a low softening wax in a toner during kneading has been proposed. In the kneading/crushing process, however, the amount of such a wax to be blended in 100 parts of the resin is limited to about 4 to 5parts. Thus, toners having a sufficient low temperature fixability cannot be obtained.
In an attempt to eliminate these difficulties, JP-A-60-220358 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”) and JP-A-60-225170 propose a process for the preparation of a particulate toner which involves emulsion polymerization in the presence of a colorant, followed by salting out of the emulsion polymer solution under predetermined conditions. Further, JP-A-2-616650 proposes a process which involves the mixing of an emulsion polymer solution with a dispersion of colorant, followed by coagulation of particles by salting out. According to these processes, the particles obtained at the agglomeration step have a particle diameter of not more than 25 &mgr;m and thus can provide a particulate toner without passing through crushing step. However, these processes leave something to be desired in the control over the particle diameter distribution. Thus, a classification step is indispensable. Further, these processes are disadvantageous in that the yield of a toner having a desired particle diameter is poor.
In an attempt to overcome the forgoing difficulty in controlling the particle diameter and particle diameter distribution and hence realize a high resolution, JP-A-63-186253 proposes a process for the preparation of a toner involving emulsion polymerization/two-stage agglomeration process. However, this process, too, is limited in the amount of a wax to be introduced into the agglomeration step. Thus, this process leaves something to be desired in the improvement in low temperature fixability.
A process disclosed in JP-A-6-329947 involves the addition of an organic solvent infinitely soluble in water at the same time with a flocculating agent at the agglomeration step which allows the formation of aggregates having a narrow particle diameter distribution. However, this process is disadvantageous in that it has many factors to be controlled and hence shows a poor reproducibility. This process is also disadvantageous in that it gives a great burden of disposal of waste water.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to overcome the difficulties of the conventional toner for the development of an electrostatic image and hence provide a process for the preparation of a novel toner satisfying a high resolution, a low temperature fixability and a high offset resistance at a low cost.
The object of the present invention will become more apparent from the following detailed description and examples.
The inventors made extensive studies of the foregoing objects. As a result, it was found that the use of primary polymer particles obtained by the emulsion polymerization of monomers in the presence of a wax emulsion as a seed makes it possible to solve the foregoing problems. The present invention has thus been worked out.
The essence of the present invention lies in a toner for the development of an electrostatic image comprising an agglomerate of particles containing at least primary polymer particles, wherein said primary polymer particles substantially comprise a wax encapsulated therein and a process for the preparation of a toner for the development of an electrostatic image which comprises a first step of subjecting a monomer mixture containing a monomer having an acidic or basic polar group to seeded emulsion polymerization in the presence of a particulate wax as a seed, a second step of mixing a dispersion of primary polymer particles thus obtained with a dispersion of particulate colorant, and a third step of causing the mixture of dispersions to be agglomerated to form aggregates.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be further described hereinafter.
As the wax to be used as a seed there may be any known wax. Examples of such a wax include olefinic wax such as low molecular weight polyethylene, low molecular weight polypropylene and polyethylene copolymer, paraffin wax, ester-based wax having long-chain aliphatic group such as behenyl behenate, montanic acid ester and stearyl stearate, vegetable wax such as hydrogenated castor oil carbanauba wax, ketone having long-chain alkyl group such as distearyl ketone, silicone having alkyl side group, higher fatty acid such as stearic acid, long-chain fatty acid alcohol, long-chain fatty acid-based polyvalent alcohol such as pentaerythritol, partial esterification product thereof, and higher fatty acid amide such as oleic acid amide and stearic acid amide.
Among these waxes, those having a melting point of not higher than 100° C., preferably from 40° C. to 90° C., particularly from 50° C. to 80° C., are preferably used to improve the fixability of the toner. If the melting point of the wax exceeds 100° C., the resulting effect of lowering the fixing temperature of the toner is poor.
The particulate wax employable herein can be obtained by the emulsification of the foregoing wax in the presence of at least an emulsifying agent selected from the group consisting of known cationic surface active agents, anionic surface active agents and nonionic surface active agents. Two or more of these surface active agents may be used in combination.
Specific examples of the cationic surface active agent employable herein include dodecyl ammonium chloride, dodecyl ammonium bromide, dodecyl trimethyl ammonium bromide, dodecyl pyridinium chloride, dodecyl pyridinium bromide, and hexadecyl trimethyl ammonium bromide.
Specific examples of the anionic surface active agent employable herein include fatty acid soap such as sodium stearate and sodium dodecanate, sodium dodecylsulfate, sodium dodecylbenzene sulfonate, and lauryl sodium sulfate.
Specific examples of the nonionic surface active agent employable herein include dodecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether, nonylphenyl polyoxyethylene ether, lauryl polyoxyethylene ether, sorbitan mono-oleate polyoxyethylene ether, and monodecanoylsuccrose.
In the present invention, these waxes are dispersed in the presence of an emulsifying agent to produce an emulsion which is then used for the seeded polymerization of resin. The average particle diameter of the wax emulsion is preferably from 0.01 &mgr;m to 3 &mgr;m, more preferably from 0.03 &mgr;m to 1 &mgr;m, particularly from 0.05 to 0.8 &mgr;m. For the measurement
Akai Hideko
Jo Usei
Kokubo Takashi
Maruyama Kazunori
Nukui Masahiro
Mitsubishi Chemical Corporation
Rodee Christopher
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