Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-08-24
2003-05-27
Goodrow, John (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, C430S137180
Reexamination Certificate
active
06569590
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a master batch pigment and a toner including the master batch pigment as well as a method for manufacturing the toner.
2. Discussion of the Background
A toner used for a dry developing method is mainly formed from a thermoplastic resin (i.e., a binder resin), a pigment (i.e. a colorant) and a release agent. Optionally, an additive such as a magnetic powder, a charge controlling agent or a fluidity improving agent is added thereto. As disclosed in Japanese Laid-Open Patent Publication No. 1-304467, a typical manufacturing method for such a toner is as follows:
(1) all the constituents for such a toner are mixed together and the mixture is heated (i.e., melted) and dispersed by a kneading machine to a uniform composition; and
(2) the composition is cooled, pulverized and classified into toner having a volume average diameter of from about 6 to about 10 &mgr;m.
Particularly, a color toner for electrophotography, which is used to form a colored image, is typically formed from a binder resin, in which various coloring dyes or pigments are dispersed. Requisites for such a color toner are more severe than that for a black toner. Namely, a color toner is required to have color reproducibility and optical transmittance (i.e., transparency) when used for an over head projector (OHP) in addition to mechanical and electrical stability.
Specific examples of dyes for use as a colorant of a toner include those disclosed in Japanese Laid-Open Patent Publications Nos. 57-130043 and 57-130044. When a dye is used as a colorant, the resultant image has good transparency and coloring ability, and it is possible to form a clear color image.
However, a problem which occurs is that the image has poor light resistance and the color of an image is changed or faded when it is left under direct light.
On the other hand, specific examples of pigments for use as a colorant include those disclosed in Japanese Laid-Open Patent Publications Nos. 49-46951 and 52-17023. However, although a pigment type color toner has good light resistance, the toner has poor coloring ability and transparency because the pigment has poor dispersibility in a binder resin.
As a method for improving dispersiblity of a pigment in a binder resin, the following technology is disclosed in Japanese Laid-Open Patent Publication No. 62-280755:
(1) a polyester resin (resin A) is used as a binder resin; (2) a pigment is covered by a polyester resin having a higher molecular weight (resin B) than the resin A; and (3) the covered pigment is dispersed in the resin A to form a color toner.
In addition, the following color toner is disclosed in Japanese Laid-Open Patent Publication No. 2-66561:
a processed pigment obtained by melting and kneading a pigment and a resin for the pigment is dispersed in a binder resin, wherein the average molecular weight of the resin for the pigment is lower than the average molecular weight of the binder resin and the average molecular weight of the binder resin is not less than 100,000.
Another technology to obtain a color toner is also disclosed in Japanese Laid-Open Patent Publication No. 9-101632:
(1) a binder resin and a pigment are mixed with an organic solvent at a lower temperature than the melting point of the binder resin in the first stage; and
(2) the binder resin and a charge controlling agent are further added into the mixture prepared in the first stage and kneaded while heating in the second stage.
Further, a toner including a colorant made of a binder resin having an average molecular weight of not greater than 40,000 and a flushed pigment using the binder resin is disclosed in Japanese Laid-Open Patent Publication No. 4-39671.
In addition, the following technology is disclosed in Japanese Laid-Open Patent Publication No. 4-230770:
(1) a solvent, a first binder resin soluble in the solvent and a colorant insoluble in the solvent are mixed;
(2) the colorant is dispersed in the binder resin at from 50 to 100° C. while applying a shearing stress thereto;
(3) the solvent is removed to obtain a colorant/binder resin composition, in which the particles of the colorant are dispersed in the binder resin; and then,
(4) the binder resin and a charge controlling agent are further added into the composition, which is kneaded upon application of heat in the second stage to obtain a toner.
However, a toner in which a pigment is well dispersed cannot be prepared by any one of the methods of above-mentioned Japanese Laid-Open Patent Publications Nos. 62-280755 and 2-6651, and coloring stability and transparency of the resultant toners are poor.
In addition, the present inventors recently discovered that in any methods of above-mentioned Japanese Laid-Open Patent Publications Nos. 9-101632, 4-39671 and 4-230770, a small amount of the solvent remains in the resultant toner even if the removal of the solvent is attempted. In addition, the remaining solvent deteriorates chargeability of the resultant toner particularly in a high temperature environment, resulting in a problem wherein the toner scatters at a developing section.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a master batch pigment for a toner capable of producing a toner which does not cause the above-mentioned problems, and which has a good combination of coloring ability, transparency and chargeability.
Another object of the present invention is to provide a toner using the master batch pigment.
Yet another object of the present invention is to provide a method for manufacturing the toner.
Briefly these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by a method for manufacturing a master batch pigment for a toner, including the steps of mixing a dry pigment powder, a binder and water; and kneading the mixture upon application of heat to prepare the master batch pigment, wherein the master batch pigment has a weight loss of from 0.01 to 1.0% when heated at 110° C. for 2 hrs.
In another aspect of the present invention, a method for manufacturing a color toner is provided, which includes the steps of preparing the master batch pigment mentioned above; kneading a binder resin, which may be the same as or different from the binder resin included in the master batch pigment, with the master batch pigment such that the concentration of the pigment is less than the concentration of the pigment in the master batch pigment; and pulverizing the mixture.
In addition, the above-mentioned objects can be attained by a master batch pigment characterized in that the weight loss is from 0.01 to 1.0% when heated at 110° C. for 2 hrs. and not greater than 0.05% at 70° C. for 2 hrs.
Further, the above-mentioned objects can be attained by a color toner prepared by the method mentioned above. Namely the master batch pigment is further mixed with a binder resin which is the same as or different from the binder resin included in the master batch pigment until the concentration of the pigment in the mixture reaches the target concentration for the toner, and then the mixture is pulverized.
Still, the above-mentioned objects can be attained by a method for manufacturing the above-mentioned color toner.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Generally, the present invention provides a master batch pigment in which a pigment is well dispersed in a binder resin, wherein the weight loss is from 0.01 to 1.0% when heated at 110° C. for 2 hrs. and not greater than 0.05% when heated at a relatively low temperature of 70° C. for 2 hrs.
When such a master batch pigment is used for a toner, the dispersion of the pigment in the resin can be significantly improved.
In addition, the present invention provides a toner using the master batch pigment including a pigment, wherein the toner (i.e., a color to
Kuroda Noboru
Sugiyama Shoichi
Goodrow John
Ricoh Company Limited
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