Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-02-24
2001-02-06
Martin, Roland (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111400
Reexamination Certificate
active
06183924
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel two-component developer suitable for use in the development of electrostatic image in electrophotographic process copying machines or printers.
BACKGROUND OF THE INVENTION
The state-of-the-art electrophotographic process copying machines or printers are far inferior to lithography or silver salt system photography in image quality. In an attempt to improve the image quality of electrophotographic process copying machines or printers, various efforts have been made to improve toners and carriers constituting the developer, image-forming apparatus, etc.
For the part of toner, it has recently been necessary more and more to reduce the particle diameter of particulate toner in order to improve image quality such as resolution.
Various technical developments have been made. However, most of powder toners for development of electrostatic image commercially available at present have a volume-average particle diameter of from about 8 to 13 &mgr;m. Powder toners having the smallest particle diameter have a volume-average particle diameter of about 7 &mgr;m (as measured by Coulter Multisizer). Thus, the smallest allowable volume-average particle diameter of particulate toners extremely useful for the enhancement of image resolution is about 7 &mgr;m at present. No particulate toners having far smaller particle diameters are commercially produced. Little or no developing machines using such a small particle size toner have been developed.
A powder toner is prepared by a dry process such as pulverization process or a wet process such as polymerization process and so-called phase inversion emulsification method as described in JP-A-5-66600 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”) and JP-A-09-311502. It is said that the smallest allowable particle diameter of toners produced by a pulverization process using the present crushing machine on an industrial basis is about 6 to 7 &mgr;m. Of course, small particle diameter toners having a particle diameter of about 5 &mgr;m can be produced. However, these toners cannot hardly be considered practical because they add to cost and exhibit deteriorated triboelectricity or powder fluidity caused by the reduction of the particle diameter thereof.
The wet process such as polymerization process and emulsification process is said to be essentially free from difficulty for the reduction of the particle diameter of powder toners. However, the prior art wet process toner is mainly intended in the stage of development or production to replace the foregoing pulverization process toner having an ordinary volume-average particle diameter range (about 7 to 13 &mgr;m). Electrostatic image developers comprising small particle diameter toners having a volume-average particle diameter of about 6 &mgr;m or less have been so far little studied. No practical formulations have been known.
SUMMARY OF THE INVENTION
The inventors made extensive studies of two-component developer for use in the development of electrostatic image which can provide an printed image excellent in density, resolution, tone reproduction, etc. As a result, it was found that the use of a spherically particulate toner having a small particle diameter and a high pigment concentration as a two-component developer in combination with a carrier having a predetermined range of particle diameter makes it possible to provide an excellent image quality and drastically reduce the amount of toner to be consumed per sheet of printing paper. The inventors further found a specific emulsion or polymerization process suitable for use in the preparation of a particulate toner to be used as such a two-component developer.
The present invention provides the following inventions:
1. An electrostatic image developer comprising a spherically particulate black toner containing a binder resin and a colorant and a resin-coated carrier, characterized in that said spherically particulate toner has a volume-average particle diameter of from 1 to 6 &mgr;m, said colorant is carbon black, the content of which is from 8 to 20% by weight based on the sum of the weight of said binder resin and said colorant and said carrier has a volume-average particle diameter of from 20 to 150 &mgr;m.
2. The electrostatic image developer according to Clause 1, wherein said colorant is encapsulated in said binder resin and said spherically particulate toner has an average circularity of not less than 0.97.
3. The electrostatic image developer according to Clause 1 or 2, wherein said spherically particulate toner has a particle size distribution such that the ratio of 50%-volume particle diameter/50%-number particle diameter is not more than 1.25 and the square root of the ratio of 84%-volume particle diameter/16%-volume particle diameter is not more than 1.25.
4. The electrostatic image developer according to Clause 1 or 2, wherein said binder resin for said spherically particulate toner is a polyester resin.
5. The electrostatic image developer according to Clause 1 or 2, wherein said spherically particulate toner is a negatively polar toner comprising a hydrophobic silica and a hydrophobic titanium oxide externally added thereto.
6. The electrostatic image developer according to Clause 1 or 2, wherein said spherically particulate toner is a particulate toner obtained by a process which comprises mixing a mixture comprising a colorant and a water-insoluble binder resin as essential components and an aqueous medium, emulsifying the mixture to form spherical colored particles, and then withdrawing the said particles dispersed in the liquid medium in the form of dried powder.
7. The electrostatic image developer according to Clause 1 or 2, wherein said spherically particulate is a particulate toner obtained by a process which comprises allowing a polymerizable monomer having a colorant dispersed therein to undergo polymerization in a liquid medium to form spherical colored particles, and then withdrawing the said particles dispersed in the liquid medium in the form of dried powder.
8. An electrostatic image developer comprising a spherically particulate color toner containing a binder resin and a colorant and a resin-coated carrier, characterized in that said spherically particulate toner has a volume-average particle diameter of from 1 to 6 &mgr;m, said colorant is an organic pigment, the content of which is from 3 to 20% by weight based on the sum of the weight of said binder resin and said colorant and said carrier has a volume-average particle diameter of from 20 to 150 &mgr;m.
9. The electrostatic image developer according to Clause 8, wherein said colorant is encapsulated in said binder resin and said spherically particulate toner has an average circularity of not less than 0.97.
10. The electrostatic image developer according to Clause 8 or 9, wherein said spherically particulate toner has a particle size distribution such that the ratio of 50%-volume particle diameter/50%-number particle diameter is not more than 1.25 and the square root of the ratio of 84%-volume particle diameter/16%-volume particle diameter is not more than 1.25.
11. The electrostatic image developer according to Clause 8 or 9, wherein said binder resin for said spherically particulate toner is a polyester resin.
12. The electrostatic image developer according to Clause 8 or 9, wherein said spherically particulate toner is a negatively polar toner comprising a hydrophobic silica and a hydrophobic titanium oxide externally added thereto.
13. The electrostatic image developer according to Clause 8 or 9, wherein said spherically particulate toner is a particulate toner obtained by a process which comprises mixing a mixture comprising a colorant and a water-insoluble binder resin as essential components and an aqueous medium, emulsifying the mixture to form spherical colored particles, and then withdrawing the said particles dispersed in the liquid medium in the form of dried-powder.
14. The electrostatic image developer according to Clause 8 or 9, wherein said
Ito Takashi
Itoya Kazuo
Nomura Minoru
Takayanagi Hitoshi
Armstrong, Westerman Hattori, McLeland & Naughton
Daimippon Ink and Chemicals, Inc.
Martin Roland
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