Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-06-26
2003-05-20
Chapman, Mark A. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108800
Reexamination Certificate
active
06566026
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image prepared by an image forming method such as electrophotography, electrostatic recording and electrostatic printing. In addition, the present invention relates to a toner container, and to an image forming method and apparatus using the toner.
2. Discussion of the Related Art
A typical image forming method using electrophotography is as follows:
(1) forming an electrostatic latent image on an image bearing member such as photoreceptors;
(2) developing the latent image with charge toner particles to form a toner image on the image bearing member;
(3) transferring the toner image on a receiving material such as paper; and
(4) fixing the toner image on the receiving material, resulting in output of a recorded image.
Recently, demands for color copiers and color printers are increasing more and more.
In color image forming methods using electrophotography, the processes mentioned above are typically repeated plural times using three primary color toners (i.e., a yellow toner, a magenta toner and a cyan toner) and a black toner to form a full color image in which the color toner images are overlaid.
In order to form a full color image having good color reproducibility and sharpness, the surface of a fixed color toner image should be smoothed to some extent to reduce light scattering. For such a reason, the color images produced by conventional full color copiers typically have a medium to high gloss of from 10 to 50%.
In general, as the fixing method for fixing a dry toner image on a receiving material, contact fixing methods in which a toner image is pressed by a heated roller or belt having a smooth surface have been typically used. These methods have an advantage such that the methods have high heat efficiency so that high speed fixing can be performed. In addition, the methods also have an advantage such that the resultant color toner image has a high gloss and a high transparency. However, the methods have a drawback such that an image offset problem tends to occur in which a part of a toner image adheres to the surface of a fixing roller and the part of the image is re-transferred onto other part of the receiving material and/or another receiving material having an image.
In attempting to solve this offset problem, a fixing roller whose surface is coated with a silicone rubber or a fluorine-containing resin and to which a releasing oil such as silicone oils is applied have been typically used for image forming apparatus. This method is effective to avoid the offset problem, but has drawbacks in that an oil applicator must be provided in the image forming apparatus, and thereby the image forming apparatus become large in size and have manufacturing high costs.
Therefore, in monochrome image forming apparatus a method a toner including a binder resin having a controlled molecular weight distribution and having high melt viscoelasticity has been used so as not to cause internal fracture when melted is typically used. In addition, a release agent such as waxes is typically included in the toner in order not to use an oil applicator or in order to use an oil applicator which applies a small amount of an oil to a fixing roller (hereinafter referred to as a small-amount-oil applicator).
However, as mentioned above, color images should be smoothed so as to have good color reproducibility, and therefore color toners have to have a relatively low melt viscoelasticity. Accordingly, color toners tend to cause the offset problem more frequently than monochrome toners having a relatively low gloss compared to color toners. Therefore, it is hard not to use an oil applicator or to use a small-amount-oil applicator. In addition, when a release agent is included in a toner, the following problems tend to occur:
(1) transferability of the toner to receiving materials deteriorates because the adhesion of the toner increases, resulting in increase of cohesive force of the toner or deterioration of fluidity of the toner; and
(2) the carrier which is mixed with the toner to charge the toner is contaminated with the release agent, resulting in deterioration of the charging ability of the carrier, and thereby the life of the developer shortens.
Conventionally, low molecular weight polyester resins and epoxy resins have been typically used as a binder resin for color toners because images having a high gloss can be easily produced. However, since these resins have a hydrophilic group such as a hydroxyl group, the resins have a drawback in that the charge quantity of the resultant toner largely changes as the humidity changes. In addition, currently the particle diameter of toner particles becomes smaller and smaller to produce high quality images. When a low molecular weight polyester resin or an epoxy resin is used as a toner constituent, it is relatively hard to pulverize the kneaded toner constituents compared to monochrome toners typically including a styrene type resin (i.e., such resins have poor pulverizability). Therefore such toners including a polyester resin or an epoxy resin have low productivity.
In view of such situations, Japanese Laid-Open Patent Publication No. (hereinafter JOP) 8-220808 discloses a toner including a linear polyester resin having a softening point of from 90 to 120° C. and carnauba wax. JOP 9-106105 discloses a toner including a resin and a wax, wherein they are compatible with each other and have different softening points. JOP 9-304964 discloses a toner including a polyester resin and a wax, wherein the melt viscosities of the resin and wax are specified. JOP 10-293425 discloses a toner including a polyester resin having a softening point of from 90 to 120° C., rice wax, carnauba wax and a silicone oil. JOP 5-61242 discloses a polymerized toner including a wax therein.
However, there is no toner having all the following advantages:
(1) capable of producing images having a proper gloss and good color reproducibility;
(2) not causing the offset problem even when an oil applicator is not used or a small-amount-oil applicator is used;
(3) having good transferability and durability;
(4) having good charge stability even when humidity changes; and
(5) having good pulverizability.
Because of these reasons, a need exists for a color toner having a combination of such advantages mentioned above.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a color toner which has good transferability, durability, charge stability and pulverizability and which can produce a toner image having a proper gloss and good color reproducibility without causing the offset problem even when an oil applicator is not used or a small-amount-oil applicator is used.
Another object of the present invention is to provide an image forming method and apparatus in which a toner image having a proper gloss and good color reproducibility can be produced without causing the offset problem even when an oil applicator is not used for the fixing device or a small-amount-oil applicator is used.
To achieve such objects, the present invention contemplates the provision of a toner including mother toner particles including at least two resins A and B and a wax and an external additive including at least one of a particulate inorganic material and a particulate resin, wherein the resins A and B and the wax form a phase separation structure (i.e., a sea-island structure) in which the resin B is present like islands in a sea of the resin A and the wax is substantially present in the resin B while dispersed therein, and wherein the resin A does not include a component insoluble in tetrahydrofuran and has a weight average molecular weight of from 10,000 to 90,000 when measured by a gel permeation chromatography (GPC) method.
It is preferable that the resins A and B and the wax have different solubility parameters, SPa, SPb and SPw, respectively, wherein SPa is greater than SPb and SPb is greater than SPw.
In addition, it is preferable that SPa is
Katoh Kohki
Saito Takuya
Sawada Toyoshi
Shiraishi Keiko
Suzuki Masanori
Chapman Mark A.
Cooper & Dunham LLP
Ricoh Company,. Ltd.
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