Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-02-26
2004-11-23
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...
C430S109400, C430S110300, C430S111400, C430S137140, C430S137190
Reexamination Certificate
active
06821697
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner for electrostatic image development which is preferably employed in electrophotographic copying machines, printers, and facsimiles, and is also employed in TONER JET type printers.
2. Description of the Related Art
In electrophotographic copying machines, printers, and facsimiles, the following needs for the toner have recently been enhanced for cost reduction and size reduction of the machines as well as power saving and resource saving, including a further improvement in the quality of the printed image. The needs include:
(1) improvement in the definition and gradation of the printed image, reduction in the thickness of the toner layer, reduction in the amount of wasted toner, reduction in the particle diameter and spheroidizing of the toner for reducing the amount of the toner consumed per page,
(2) decrease in the fixation temperature for reduction in power consumed,
(3) oilless fixation for simplification of the machines;
(4) improvement in the hue, transparency and gloss in full-color images,
(5) reduction in VOCs (volatile organic compounds) during fixation which are likely to exert an adverse effect on human health and the like.
A reduction in the particle diameter of the powdered toner prepared by a pulverization method, which has been employed for a long time, can be basically carried out. However, with the reduction in particle size, the following problems arise: (1) it becomes difficult to control the charge because of an increase in the amount of colorants and waxes exposed on the surface of the toner particles, (2) the fluidity of the powder is lowered by the unfixed shape of the toner particles, and (3) the energy cost required for production increases, thus, in actuality, it is difficult to sufficiently satisfy the needs described above using a toner having an unfixed shape prepared by employing the pulverization method.
Therefore, development of a spherical toner having a small particle diameter has been intensively carried out by the polymerization method or the emulsification/dispersion method. Although various methods are known for producing a toner employing the polymerization method, the suspension polymerization method has been widely employed which comprises: uniformly dissolving and dispersing a monomer, a polymerization initiator, a colorant, and a charge control agent; adding the mixture to an aqueous medium containing a dispersion stabilizer while stirring to form oil droplets; and heating, thereby causing the polymerization reaction to produce toner particles. Although the reduction in particle diameter and spheroidizing can be satisfactorily conducted by the polymerization method, a principal component of the binder resin is limited to a radically-polymerizable vinyl polymer, and toner particles made of a polyester resin or epoxy resin suited for use as a color toner cannot be produced by the polymerization method. It is difficult to reduce VOCs (volatile organic compounds made of an unreacted monomer) by the polymerization method, and improvements are required.
As is disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 5-66600 and Japanese Unexamined Patent Application, First Publication No. Hei 8-211655, the method of producing a toner employing the emulsification/dispersion method comprises mixing a mixture of a binder resin and a colorant with an aqueous medium and emulsifying them to obtain toner particles, and has the following advantages: (1) possible binder resins can be widely selected, (2) the reduction of VOCs is easy to realize, and (3) the concentration of the colorant is easy to change optionally within a range of low to high values, as compared with the polymerization method, in addition to the advantage that it is easy to cope with the reduction in particle diameter and spheroidizing of the toner similar to the polymerization method.
It is generally known that a polyester resin is more preferable than a styrene-acrylic resin as a binder resin for toner, which can reduce the fixing temperature and forms a smooth image surface by melting rapidly during fixation, and a polyester resin having e:xcellent pliability is particularly preferably employed in the color toner.
As described above, toner particles containing a polyester resin as the principal component cannot be produced by the polymerization method as described above. Therefore, a spherical or generally spherical toner having a small particle diameter containing a polyester resin as the binder resin obtained by the emulsification/dispersion method has attracted special interest recently.
However, in the spherical toner obtained by the emulsification/dispersion method, reduction of the fixation temperature and widening of the anti-offset temperature range are not necessarily sufficiently realized. Therefore, a fixing drum is coated with silicone oil to prevent the toner from adhering to the fixing drum during fixation. An improvement in the thermal properties of the spherical toner makes it possible to obtain an oilless toner having high anti- offset properties while utilizing its high image quality.
Techniques are disclosed in Japanese Unexamined Patent Application, First Publication Nos. Hei 9-311502, Hei 5-66600, Hei 8-211655, Hei 6-332224, Hei 6-332225, and Hei 10-319639 as methods for producing a toner containing a polyester resin as a binder resin, for example. However, not all of the problems to be solved by the present invention can be solved using these methods.
Japanese Unexamined Patent Application, First Publication No. Hei 5-66600 discloses a method of providing a mixture of a binder resin, a colorant, and an organic solvent having self-water dispersibility and/or water solubility by neutralizing the binder resin, thereby dispersing the mixture in an aqueous medium. However, this technique is intended exclusively for a styrene-acrylic resin as the binder resin and is not necessarily suited for fixation at low temperatures and a color toner. Furthermore, the publication does not make any reference to the composition of the binder resin in the toner employing a polyester resin which makes fixation at low temperatures and oilless fixation possible.
Japanese Unexamined Patent Application, First Publication Nos. Hei 6-332224 and Hei 6-332225 each disclose a method of dispersing a mixture of a polyester resin, a colorant, an organic solvent and a specific dispersion stabilizer in an aqueous medium. According to this technique, the polyester resin is dispersed in the aqueous medium by only an action of the dispersion stabilizer because the polyester resin itself has no self-water dispersibility. According to the system of dispersing employing the dispersion stabilizer, dispersion is hardly performed at low shear, and, therefore, dispersion must be performed at high shear employing a homomixer or the like. As a result, coarse particles and microparticles tend to occur, resulting in large classification loss. This publication does not make any reference to a composition which can provide the fixation at low temperatures and oilless fixation. A toner containing a high-molecular weight component or a tetrahydrofuran-insoluble fraction has a wide particle size distribution, and, therefore, there is a limit in manufacturing.
Japanese Unexamined Patent Application, First Publication No. Hei 9-311502 discloses a method of mechanically dispersing a mixture of a polyester resin and a colorant in an aqueous medium by reducing the viscosity due to melting with heating without employing a solvent. According to this method, there is a limit in molecular weight of a usable resin and those containing a large amount of a high-molecular weight component result in the breakage of the molecular chain, thus making it impossible to raise the hot offset temperature. As a result, it is impossible to attain a good fixing range in the oilless fixation system, which is the problem to be solved by the present invention.
Japanese Unexamined Patent Application, First Publication No
Hashizume Toyomi
Hirabayashi Kenichi
Ito Takashi
Takayanagi Hitoshi
Armstrong Kratz Quintos Hanson & Brooks, LLP
Dainippon Ink and Chemicals Inc.
Dote Janis L.
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