Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-12-01
2002-07-09
Rodee, Christopher (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S109400, C430S109500, C430S110300, C430S111400
Reexamination Certificate
active
06416917
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a dry toner suitable for use in electrophotography, electrostatic recording, electrostatic printing or the like.
BACKGROUND ART
As a dry toner for electrophotograpy, electrostatic recording, electrostatic printing or the like, those prepared by melting and kneading a toner binder such as styrene resin or polyester with a colorant and then pulverizing the resulting mass have been employed conventionally.
Such a dry toner is developed and transferred to a substrate such as paper and then fixed by hot melting using a heat roll. Upon hot melting, when the heat roll temperature is too high, there occurs a problem that the toner is excessively molten and sticks to the heat roll (hot offset). When the heat roll temperature is too low, there occurs a problem that the toner is not molten sufficiently and fixation is insufficient. From the viewpoints of energy saving and size reduction of apparatuses such as copying machine, there is a demand for the development of a toner having a higher hot offset occurring temperature (anti-hot offset property) and a low fixing temperature (low temperature fixing property).
In addition, a toner is required to have heat storage stability enough for preventing blocking of the toner particles during storage or at the atmospheric temperature in the apparatus.
Since the toner must have a melt viscosity as low as possible particularly in a full color copying machine or full color printer because of the necessity of good gloss and sufficient color mixing property for the formation of its image, a polyester toner binder having a sharp melt characteristic has mainly been employed. Such a toner tends to cause hot offset so that application of a silicone oil or the like onto a heat roll has been conducted in a full color copying or printing machine.
Application of a silicone oil onto a heat roll however needs an oil tank and oil coating apparatus, making the whole equipment complex and large-scale. In addition, it deteriorates the heat roll, which needs maintenance at certain intervals. Furthermore, it inevitably causes adhesion of an oil to a copying paper, OHP (overhead projector) film or the like and particularly in OHP, the color tone of an OHP film is deteriorated by the adhered oil.
In recent years, there is a strong demand for a reduction in the particle size of a toner for higher image quality and improvement in resolution. The conventional toner obtained by kneading and pulverization has not a uniform shape so that a reduction in its particle size deteriorates powder flowability, causing problems such as difficulty in feeding of the resulting toner to a developing apparatus and worsening of transferability.
As a toner having heat storage stability, low-temperature fixing property and anti-hot offset property, thereby overcoming some of the above-described problems, proposed are (1) that [JP-A-57-109825 (the term “JP-A” as used herein means an “unexamined published Japanese patent application)] using, as a toner binder, a polyester which has been partially crosslinked using a polyfunctional monomer and (2) that [JP-B-7-101318 (the term “JP-B” as used herein means an “examined published Japanese patent publication”)] using, as a toner, binder, an urethane-modified polyester.
As a toner for full color printing or copying which is reduced in an oil application amount to a heat roll, proposed is (3) that (JP-A-7-56390) obtained by granulating polyester fine particles and wax fine particles.
As a toner having a reduced particle size, but being improved in powder flowability and transferability, proposed are (4) a toner (JP-A-9-43909) obtained by dispersing a vinyl monomer composition containing a colorant, a polar resin and a releasing agent in water and then subjecting the resulting dispersion to suspension polymerization and (5) a toner (JP-9-34167) comprising spherical particles which is obtained by treating the toner made of a polyester resin with a solvent in an aqueous medium.
Owing to insufficient powder flowability and transferability, however, the toner disclosed in any one of (1) to (3) cannot attain high image quality when reduced in its particle size.
The toner disclosed in (1) or (2) does not attain heat storage stability and low temperature fixing property simultaneously, and in addition, is not suited for use in a full color printing or copying machine because it does not exhibit gloss.
The toner disclosed in (3) is not satisfactory in hot offset property upon oil-less fixation as well as in low temperature fixing property.
The toner disclosed in (4) is improved in powder flowability and transferability, but owing to insufficient low-temperature fixing property, it needs much energy for fixation. Particularly in a toner for full color image, this problem is marked.
The toner disclosed in (5) is improved in powder flowability and transferability. It is superior to that of (4) in low temperature fixing property, but owing to insufficient anti-hot offset property, oil application to a heat roll cannot be omitted when used for the formation of a full color image.
An object of the present invention is to provide a dry toner having excellent powder flowability and transferability when reduced in its particle size.
Another object of the present invention is to provide a dry toner excellent in any one of heat storage stability, low temperature fixing property and anti-hot offset property.
A further object of the present invention is to provide a dry toner having excellent gloss exhibition when an image is formed by a full color copying machine or the like.
A still further object of the present invention is to provide a dry toner which does not need oil application to a heat roll.
DISCLOSURE OF THE INVENTION
Extensive investigation with a view to attaining the above-described objects has lead to the present invention.
Described specifically, the present invention provides a dry toner comprising a toner binder and a colorant, characterized in that the toner has a Wadell's practical sphericity of 0.90 to 1.00, the toner binder contains a high molecular weight condensation resin (A) and a low molecular weight condensation resin (B), a ratio (MnA/MnB) of the number average molecular weight (MnA) of the resin (A) to the number average molecular weight (MnB) of the resin (B) is at least 1.6 and a ratio (MwA/MwB) of the weight average molecular weight of the resin (A) to the weight average molecular weight of the resin (B) is at least 2.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will hereinafter be described more specifically.
The term “Wadell's practical sphericity” as used herein means a quotient resulting from (the diameter of a circle equivalent to the projected area of a particle)÷(the diameter of the minimum circumcircle with the projected image of the particle) and it can be measured by electron microscopic observation of toner particles.
The Wadell's practical sphericity is usually 0.90 to 1.00, preferably 0.95 to 1.00, more preferably 0.98 to 1.00. In the present invention, the practical sphericity of all the toner particles does not necessarily fall within the above-described range, but average may fall within the above-described range. The average is obtained from the practical sphericity of about 20 particles taken out at random from the toner particles produced.
As the particle size of the toner, the median diameter (d
50
) is usually 2 to 20 &mgr;m, preferably 3 to 10 &mgr;m.
Examples of the high-molecular-weight condensation resin (A) and low-molecular-weight condensation resin (B), each constituting the toner binder, include polyester, polyurethane, polyurea, polyamide and epoxy resins, of which the polyester, polyurethane and epoxy resins are preferred, with the polyester resin being particularly preferred.
As the polyester resin, polycondensates between a polyol (1) and a polycarboxylic acid (2) can be given as examples.
Examples of the polyol (1) include diols (1-1) and polyols (1-2) having at least 3 functional groups. Among the
Fukushima Hajime
Nakanishi Hideo
Morgan & Lewis & Bockius, LLP
Rodee Christopher
Sanyo Chemical Industries Ltd.
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