Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-05-31
2003-04-01
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, C430S108400, C430S108800, C430S137180
Reexamination Certificate
active
06541173
ABSTRACT:
This application is based on application No. 156521/1999 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color toner for developing electrostatic image suitably used in full color image-forming apparatuses such as a full color electrostatic copying machine, a full color laser beam printer and the like.
2. Description of the Related Art
In a full color image-forming method in electrophotography, the most significant properties required for toners were to have sharply melting properties so that toner layers of. various colors are instantaneously melted by heat, mixed and develop color in a fixing process in order to form full color images by laminating toner images of a magenta toner, a cyan toner, an yellow toner and a black toner (U.S. Pat. Nos. 4,142,982, 4,590,139 etc.). However, such toners had high viscosity, extremely low elasticity, and small intermolecular coagulation force when toners melted by heat, causing a problem of offset onto a heat roller (particularly, offset at higher temperatures). Such a problem was remarkable, particularly when a roller is deteriorated due to repeated use, and when images such as full color images (for example, photographic image) having a large toner-adhered area and having a large toner amount on a toner support member (such as paper and the like) are copied.
For the purpose of preventing offset phenomenon by improving the releasing properties from a roller, it has been known to use a material excellent in surface releasability and having lower surface energy as the surface material of a roller, and to apply a large amount of oil on the surface of a roller. When a full color toner having high viscosity is used in such an apparatus constitution, there were a lot of problems. Though prevention of offset is possible to a certain extent, a large amount of oil has to be applied for complete prevention of offset. Consequently, toner support members (paper etc.) are stained with the oil, the cost increases, further, accommodation and application of oil cause increase in size of a fixing apparatus, and the like. There was a further problem that when oil is applied on a fixing roller, the oil adheres to the surface of the resulted image to cause brilliance of copied images.
Therefore, there has been desired a color toner having constitution by which offset is not caused even if a large amount of oil is not applied. As trial for obtaining what is called an oil-less toner requiring no oil application onto a fixing roller, addition and inclusion of wax are known. However, in the case of a color toner, since the elasticity of the toner was too small relatively, ooze of wax in fairly large amount was necessary, and complete prevention of offset was impossible. Further, there as been tried to achieve sufficient offset-resistance with the addition of a small amount of wax, by allowing a color toner to have toner constitution showing relatively high viscosity and high elasticity as general monochrome toners. However, in such toner constitution, the toner can not be fully melted at relatively lower temperatures, causing big problems in fixing ability at low temperature, color-developing properties and color-mixing properties.
On the other hand, with the prevalence of color printers and copying machines having high image-quality, output pieces of color images increases dramatically, and further high speed is required. Under such recent conditions, toners giving small change of image gloss in continuous copying are in need. If change of image gloss is significant, appearances, namely, color and color reproducibility are felt changing significantly by person.
However, when a conventional toner of which sharply melting properties is emphasized is used, there is a problem that image gloss changes significantly in continuous copying. This problem becomes more remarkable by speedup of the copying. Such a gloss change is believed to be derived from lowering of fixing roller temperature due to gradual deprivation of heat on the surface of the fixing roller by paper. Further, when continuous copying is conducted using A4 paper at longitudinal direction before copying using A4 paper at transverse direction, change of gloss occurs on one piece of image paper, problematically. Specifically, when A4 paper is used at longitudinal direction, both end portions of a fixing roller are not used for fixing, whereas, when A4 paper is used at transverse direction, also both end portions of a fixing roller are used for fixing as well as center portions, therefore, temperature difference between the center portions and both end portions of a fixing roller occurs in copying at longitudinal direction of A4 paper, and when copying is conducted at longitudinal direction of A4 paper, high gloss portions and low gloss portions appear on copied images. The problems of gloss change by continuous copying and gloss change on copied images (hereinafter, simply referred to gloss change) as described above are particularly remarkable in cold regions and directly after switch on.
SUMMARY OF THE INVENTION
The present invention is to provide a color toner for developing electrostatic image excellent in offset-resistance, which can suppress offset without applying oil to a fixing roller.
Another object of the present invention is to provide a color toner for developing electrostatic image, which can suppress change of gloss due to change of fixing temperature, and has excellent offset-resistance and fixing properties at lower temperature.
The present invention relates to a toner for developing electrostatic image, comprising:
a coloring agent;
a binder resin comprising a first binder resin and a second binder resin, the first binder resin being composed of a linear polyester resin having a number-average molecular weight (Mn) of from 2,500 to 7,000, a weight-average molecular weight (Mw) of from 8,000 to 25,000, and a Mw/Mn ratio of 2 to 4, the second binder resin being composed of a non-linear polyester resin having a number-average molecular weight (Mn) of from 3,500 to 11,000, a weight-average molecular weight (Mw) of from 40,000 to 250,000, and a Mw/Mn ratio of 10 to 35, and a ratio of the first binder resin to the second binder resin (the first binder resin:the second binder resin) being 15:85 to 85:15 by weight,
a first releasing agent having a softening point of 55 to 110° C., and
a second releasing agent having a softening point of 110 to 160° C.
DETAILED DESCRIPTION OF THE INVENTION
The toner of the present invention comprises, at least, a binder resin, a coloring agent and a releasing agent, and uses two kinds of resins having different molecular weight (first binder resin; lower molecular weight, second binder resin; higher molecular weight,) as the binder resin.
The first binder resin is a linear polyester having a number-average molecular weight (in this specification, referred to as Mn) from 2,500 to 7,000, preferably from 2,500 to 6,000, more preferably from 2,800 to 6,000, a weight-average molecular weight (in this specification, referred to as Mw) from 8,000 to 25,000, preferably from 8,000 to 22,000, and a Mw/Mn ratio from 2.0 to 4.0, preferably from 2.1 to 3.9.
In the first binder resin, when Mn is less than 2,500 or Mw is less than 8,000, an effect for suppressing gloss change against change of fixing temperature is not obtained, and an effect to prevent offset at higher temperatures is not obtained. Further, lowering of Tg is caused, and toner storing properties (blocking-resistance) under high temperature deteriorates, in addition, the resin becomes too fragile, and in stirring in a developing vessel, a toner becomes a fine particles, deteriorating durability. When Mn is over 7,000 or Mw is over 25,000, heat-melting properties is inferior, fixing strength at relatively lower temperatures becomes weak, in addition, an image having appropriate gloss can not be obtained at relatively lower fixing temperatures. Further, resin becomes too hard, and pulverizing pro
Aoki Megumi
Arai Takeshi
Hagi Masayuki
Kido Kenichi
Mikuriya Yoshihiro
Dote Janis L.
Minolta Co. , Ltd.
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