Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2001-07-12
2002-08-20
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S108800, C430S111400, C430S137140
Reexamination Certificate
active
06436599
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner used in an electrostatic photographic process or the like, a method of producing the toner, and an image forming method using the toner.
2. Description of the Related Art
Various methods have been known as an electrophotographic method as described in U.S. Pat. No. 2,297,691, Japanese Patent Application Publication (JP-B) No.42-23910 (U.S. Pat. No. 3,666,363), and the like. The electrophotographic method generally comprises fundamental steps including an exposure step of forming a latent image by exposure means on a photorecepter using a photo-electroconductive material, a step of developing the latent image using a toner (forming a toner image), a step of transferring the toner image to a recording material such as paper, a step of fixing the transferred toner image by means of heating and/or pressure or solvent vapor, and a step of removing a residual toner from the photorecepter.
In recent years, there have been a demand for inexpensive and miniaturized copiers and printers using an electrophotographic method. In order to design such a copier or a printer, it is important to fix a toner image at low consumption electronic power in a simple manner. As a means of fixing the toner image to paper at present, a method comprising a step of melting and fixing the toner image using a heat-roll is generally used.
In copiers and printers used for forming a monochromatic image, a system (hereinafter called “oilless fixing”) in which no oil is supplied to a heat roll is generally adopted. In copiers and the like used for forming a color image, a means of supplying oil is still essential for the purpose of preventing an offset to a heat roll. This is an obstacle to achievements of copiers used for forming a color image with a miniaturized and inexpensive system.
Particularly, it is necessary to melt under heat each color toner layer sufficiently in case of a system of forming multi-color images with vivid color by a subtractive color mixing method using cyan, yellow, and magenta toners. It is therefore necessary to fix color images by use of the heat roll at a higher temperature than in case of the monochromatic copiers and the like. As a consequence, an offset phenomenon tends to occur, which necessitates the supply of oil to the heat roll.
When a resin of which fusion curve is sharp is used as a binder resin for the toner in the case of forming a multi-color image, an image surface can be smooth, which is desirable. As such a resin, a polyester is frequently used which exhibits sufficient plasticity even if its molecular weight is lowered. However, if a polyester resin which has low internal cohesion is used for a color toner, the toner can be peeled off from the heat roll with difficulty after it is melted. It is therefore difficult to fix toner images using the oilless fixing method.
In order to solve such a problem, the methods are proposed in which a releasing agent, e.g. wax, is added to the toner to help the toner to peel off the roll as described in, for example, Japanese Patent Application Publication (JP-B) Nos. 52-3304, 52-3305, Japanese Patent Application Laid-Open (JP-A) Nos. 57-52574, 61-138259, 56-87051, 63-188158, and the like. When the releasing agent is internally added, the separation of the toner from the heat roll is improved. However, the other characteristics of the toner are sometimes worse by internally adding the releasing agent.
For example, when the toner is produced by a conventional melt mixing/pulverizing method, an addition of the releasing agent in an amount as small as 1 to 3% by weight impairs the fluidity and thermal cohesiveness of toner powder. This is caused by a large leakage of the releasing agent together with a pigment to the surface of the toner which is a crushed breaking surface. Furthermore, in process steps, toner particles collides with each other in a crasher or classifier, or with the wall of the apparatus to cause frictional heat, by which the releasing agent which exists on the surface of the toner is partially melted and spread. There is the case that the toner further covers the surface of the toner. On the surface of a melt mixed/pulverized toner to which 1 to 10% by weight of a releasing agent is added, a releasing agent generally exists in a proportion as high as 30 to 50% by weight. As a consequence, a blocking phenomenon (a condition in which the toner is coagulated into a solid) is caused while using the toner and further the releasing agent contaminates the surfaces of a photorecepter and carrier thereby inducing variations in the developing characteristics.
Furthermore, the addition of the releasing agent to the toner causes an increase in the adhesion of the toner to an intermediate transfermember and the transfer efficiency of the toner hence tends to be lowered. As a result, there is the case that the image is disordered when a color image which requires multiple transfer steps is formed.
In addition, a sufficient shear is not sometimes applied to the toner containing the releasing agent and the dispersibility of the releasing agent is often deteriorated, resulting in formation of a dull or dark image, imparting a problem when especially an OHP color image with high transmittance is formed.
In order to solve such a problem of the toner produced by the melt mixing/pulverizing method, a so-called in-liquid drying method is proposed in which an oil-phase solution in which a toner component is dissolved is treated in a water-phase containing a water-soluble resin to form particles of the solutions, followed by removing a solvent to form powder as described in JP-A Nos. 50-120632, 63-25664, 5-127422, and 8-179556. As a method similar to the in-liquid drying method, there is a method for producing a toner (methods such as described in Japanese Patent Application Publication (JP-B) No. 36-10231 and the like) utilizing a suspension-polymerization method. In these conventional suspension polymerization methods, however, a polymerizable monomer composition to be a binder resin for the toner is limited to those which can be polymerized in a solution (for example, styrene or its derivatives and &agr;-methylene fatty acid monocarboxylates). On the contrary, the in- liquid drying method has the advantage that there is not such a limitation and a polyester can be used as the resin for the toner. A method and the like are proposed in JP-A No. 7-152202 in which polyester is dissolved to prepare a solution, which is then treated in a water-phase containing an inorganic dispersant to form particles of the solution. Also, the use of tricalcium phosphate or hydroxyapatite with a grain size of 0.7 to 5 &mgr;m is proposed as the inorganic dispersant to be used as described in JP-A Nos. 7-168395 and 7-271099.
In above mentioned publications in which these in-liquid drying methods are proposed, however, there are no descriptions with regard to a novel invention including addition of a releasing agent such as wax to the toner and any limitation in the chemical structure and configuration of a polyester resin to keep each of the oil-less fixing capability, developing characteristics, and transfer characteristics of the toner at a high level.
Furthermore, in recent years, there has been the requirement to allow a thermal fixing roll to secure the oil-less fixing capability sufficiently not only in the case of using a soft roll such as a conventional silicon roll but also even in the case of using a hard roll such as a Teflon roll. In order to satisfy such a requirement, a low-melting point wax should be added to a toner particles in a high content. When the above-proposed toner resin is used in combination with the low-melting point wax, however, there is the case that only insufficient offset resistance to rolls composed of a highly hard material can be obtained.
The above in-liquid drying method cannot prevent the low-melting wax from oozing out to the surface of the toner. Toners prepared in this method are deteriorated with time in the developing cha
Lee Jong Won
Matsuoka Hirotaka
Suzuki Isamu
Dote Janis L.
Fuji 'Xerox Co., Ltd.
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