Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1997-05-22
2001-11-06
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
Reexamination Certificate
active
06312788
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile apparatus and the like, and to an image receiving sheet to be applied to the foregoing apparatus. More particularly, the present invention relates to an image forming apparatus capable of outputting a multi-color image and an image receiving sheet to be applied to the foregoing apparatus.
2. Description of the Prior Art
In recent years, a high quality color image has been required to perform a presentation or the like. Also research and development of the electrophotography has a requirement for improving the quality of the image including the color reproducibility and image density. In order to improve the saturation, image density and luster of the color image, an image receiving sheet, such as glossy paper, can be available as exclusive paper. The image receiving sheet is structured to embed toner into a resin layer on the sheet in order to prevent deformation and shift of dots when toner is fixed with heat and attain luster of the surface of the image. Since the image receiving sheet is required to have luster, light resistance and water resistance equivalent to the silver salt photography, toner must be deeply embedded into the resin layer by fixing and smoothness of the surface of the image must be realized. An image receiving sheet of a type to embed the toner uses a transparent sheet as the base thereof so as to be applied as a sheet for an over head projector (OHP). If the image receiving sheet is used as the OHP sheet, the difference in the smoothness of the surface determines the color development characteristic of the projected image. Accordingly, the image receiving sheet for electrophotography must have smoothness on the surface of the fixed image and therefore embedding of the toner into the resin layer is a critical factor.
To satisfy the above-mentioned requirements, Japanese Patent Publication No. Hei. 4-125567 has a structure in which an image receiving layer is formed which contains thermoplastic resin having a softening point lower than that of the color toner and a print in which the toner has been embedded in the image receiving layer and thus irregularity is prevented is obtained so as to solve the above-mentioned problem.
If a resin layer having a low softening point as disclosed in Japanese Patent Publication No. Hei. 4-125567 is applied to the surface of the image receiving sheet, the weak coagulation force of the melted resin results in that offset of the toner layer and the image receiving layer to the fixing roller easily takes place. When the image is stored, there arises a problem of fusion of the image receiving sheet due to blocking or the like.
By the way, the foregoing suggestion for forming the image receiving layer on the surface of the base sheet has been performed to be adaptable to an image receiving sheet for forming a monochrome image and an image forming apparatus arranged to use the foregoing image receiving sheet. An object of the foregoing suggestion is to improve the fixing characteristic in order to realize strength sufficient to prevent separation of toner from the image receiving sheet and to improve the conveyance easiness to prevent jamming of the image receiving sheet.
However, the image forming apparatus for outputting a color image and the image receiving sheet to be adapted to the foregoing apparatus must form toner images fixed on the image receiving sheet and having excellent color development characteristic and transparency in order to obtain a high quality color image in a manner different from the image forming apparatus for outputting a monochrome image.
To obtain an image having excellent color development characteristic and transparency, it is an important fact that the fixed toner image does not scatter light.
To prevent light scattering caused by the fixed image, the surface of the fixed image must satisfactorily be smoothed and the fixed image must be free from generation of an interface between toner particles. To realize his, a method has generally been employed in which the toner is sufficiently melted when the image is fixed. In U.S. Pat. No. 4,549,803, a structure has been disclosed which employs the foregoing method and in which the fixing speed and the fixing temperature can be varied to be adaptable to the type of the image receiving sheet, for example, whether the sheet is plain paper or a transparent sheet for OHP (Over Head Projector). However, the foregoing structure suffers from a problem in that the structure of the image forming apparatus becomes too complicated to switch the fixing speed and the fixing temperature.
As another method of sufficiently melting toner when fixing is performed, a method has been suggested which uses so-called sharp melt toner having a low melting point, or having the melting viscosity which is rapidly lowered when the heated toner reaches the melting toner. However, simple use of the sharp melt toner is insufficient to form an excellent image. The reason for this is that a color image is formed by generally using toners in three colors, that is, cyan, yellow and magenta. Moreover, black toner is frequently used to remove the undercolor and to form a high contrast black characters. Therefore, the toner is, in the form of a multiplicity of layers, allowed to adhere to the surface of the image receiving sheet. Thus, the thickness of the toner image is enlarged as compared with a monochrome image. Therefore, by lowering the melting viscosity of the toner when fixing is performed is insufficient to attain the effect of smoothing the surface of the fixed image. In this case, the surface becomes irregular excessively and thus considerable irregular reflection takes place on the surface. Thus, the transparency is lowered and there arises a problem in that only a dark image can be formed. Since the thickness of the toner image is large, heat conductivity from the fixing means becomes insufficient or non-uniform when fixing is performed. As a result, toner cannot sufficiently be melted and thus a satisfactory effect of removing the interface between toner particles cannot be obtained. Therefore, color reproducibility deteriorates and there arises a problem in that a sharp color image cannot be formed. In general, the fixing means is a fixing means, for example, a known heat roller fixing means which is structured to heat and press a toner image to the image receiving sheet when fixing is performed. However, there arises a problem in that a so-called offset phenomenon takes place in which a portion of the toner is allowed to adhere to the fixing means in place of adhesion to the image receiving sheet. Moreover, in a case where the sharp melt toner is fixed to a recording medium (so-called rough paper), such as bond paper or regenerated paper, having coarse fibers and great irregularity on the surface of the paper, toner melted when fixing is performed and thus having a low viscosity is introduced into concave portions of the paper. Thus, there arises a problem in that convex portions in the regions which must be image portions and in which the surface of the paper must be covered with the toner are exposed in the image portions and thus the quality of the image deteriorates. What is worse, resin in the toner permeates fibers in the paper and thus luster becomes non-uniform along the fibers in the paper. As a result, there arises a problem of deterioration in the quality of the formed image.
To prevent the foregoing problems attributable to the thickness of the toner image, a structure in which the thickness of the toner image is reduced has been considered. However, the color development characteristic must be improved while reducing the thickness of the toner image because the image must have sufficiently high image density in order to obtain visibility of the image and practical image quality. In recent years, toner having significant coloring power has been investigated. Even if toner of the foregoing type is empl
Ishiwatari Tahei
Kunugi Masanao
Mohri Shuhei
Grendzynski Michael E.
Hess Bruce H.
Seiko Epson Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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