Electrophotography – Control of electrophotography process – Control of exposure
Reexamination Certificate
2001-04-02
2002-12-24
Braun, Fred L (Department: 2852)
Electrophotography
Control of electrophotography process
Control of exposure
C399S302000
Reexamination Certificate
active
06498910
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus for conducting image forming by the use of toner in an electrophotographic method, and in particular, to an image forming apparatus and a color image forming apparatus for conducting image forming by developing with two toner types represented by light colored toner and dark colored toner both in the similar color hue.
In an image forming apparatus employing an electrophotographic method, uniform charging is conducted by a charging means on an image forming body which is then subjected to image-wise exposure so that a latent image is formed. The latent image section is then subjected to reversal development by the succeeding developing means, and a toner image is formed. In an image forming apparatus of a digital mode, image-wise exposure is made by dots modulated in terms of a pulse width, for example, and there is conducted reversal development wherein toner is stuck to a section of dots. An amount of toner adhering to the section of dots is determined depending on an area of a dot section on an image forming body, a state of potential, a developing bias for the state of potential and a state of electric charges on toner.
With regard to a section of a high density image recorded by an image exposure means on an image forming body, the number of dots per a unit of area is large, a size of one dot is great, and electric potential falls greatly. On the other hand, With regard to a section of a high density image recorded by an image exposure means on an image forming body, the number of dots per unit area is large, a size of one dot is great, and electric potential falls greatly. With regard to a section of a low density image, on the other hand, the number of dots per unit area is small, a size of one dot is small, and electric potential falls less. Owing to the foregoing, a toner adhesion amount on the section of a high density image on the image forming body after development is large and a toner adhesion amount on the section of a low density image is small. A difference between high image density and low image density on a recorded image is represented by whether the amount of tone per unit area adhering to the image forming body after development is large or small.
However, it is difficult for toner of a single type to form images with excellent gradation. On the highlight section (low density part), in particular, adhesion of toner in extremely small amount per unit area is unstable because of a small size of a dot, thus, image unevenness tends to be caused easily and it is difficult to obtain stable gradation. On the high density part, toner is in the excessive toner adhesion, and image density tends to be saturated, and gradation in a broad area is not obtained. Even if dark colored toner and light colored toner are simply used, a medium density part turns out to be discontinuous or unstable.
SUMMARY OF THE INVENTION
The invention is represented by an image forming apparatus that performs development by using two toner types of light colored toner and dark colored toner in the similar color (for example, either one of cyan (C), magenta (m), yellow (Y) and black (K)), and is applied to a monochromatic image forming apparatus and a color image forming apparatus. Further, the invention is represented by an image forming apparatus wherein reversal development by dark colored toner and reversal development by light colored toner are conducted for one image-wise exposure so that smooth gradation may be obtained without a formation of deviation between a light colored toner image and a dark colored toner image, and thereby image forming is carried out by using dark colored toner and light colored toner.
(1) In the apparatus stated above, the first object of the invention is to provide a monochromatic image forming apparatus employing dark colored toner and light colored toner, wherein there is stipulated characteristic relationship between dark colored toner and light colored toner which can maintain gradation and can obtain stably excellent images.
(2) In the apparatus stated above, the second object of the invention is to provide a color image forming apparatus employing dark colored toner and light colored toner for 4 colors of Y, M, C and K, wherein there is stipulated characteristic relationship between dark colored toner and light colored toner which holds color reproducibility, maintains gradation and can obtain stably excellent color images.
(3) In the apparatus stated above, the third object of the invention is to provide a color image forming apparatus employs transparent toner and white toner in addition to dark colored toner and light colored toner for 4 colors of Y, M, C and K and is capable of obtaining images with higher image quality, wherein there is stipulated characteristic relationship for light colored toner, transparent toner and white toner which makes it possible to obtain excellent color images.
Further, the invention is represented by an image forming apparatus that performs development by using two toner types of light colored toner and dark colored toner in the similar color (for example, either one of cyan (C), magenta (M), yellow (Y) and black (K)), and is applied to a monochromatic image forming apparatus and a color image forming apparatus. Further, the invention is represented by an image forming apparatus wherein reversal development by dark colored toner and reversal development by light colored toner are conducted for one image-wise exposure so that smooth gradation may be obtained without a formation of deviation between a light colored toner image and a dark colored toner image, and thereby image forming is carried out by using dark colored toner and light colored toner.
(4) In the apparatus stated above, the fourth object of the invention is to provide an image forming apparatus wherein stability of gradation on a highlight portion and improvement of gradation on a high density part are attained by combining processing of image density data and usage of image data for light colored toner and dark colored toner.
(5) In the apparatus stated above, the fifth object of the invention is to provide an image forming apparatus wherein there is provided the most desirable relationship in terms of recorded density between light colored toner and dark colored toner that heightens the effect when forming images with excellent gradation by using light colored toner and dark colored toner.
(6) When forming color images by using light colored toner and dark colored toner, it is necessary to provide developing means respectively for 4 colors of Y, M, C and K each housing therein light colored toner and dark colored toner, resulting in 8 sets of developing units provided to face an image forming body. There may be an image forming apparatus wherein 8 sets of developing units are provided to face an image forming body, and toner images respectively for 4 colors and respectively for light colored toner and dark colored toner are superimposed on an image forming body for image forming, or an image forming apparatus wherein 8 sets of developing units are provided to face respectively 8 image forming bodies, and one toner image for one color for light colored toner and dark colored toner is formed on each image forming body to be superimposed on a transfer sheet. In the apparatus stated above, the sixth object of the invention is to provide an image forming apparatus wherein the size is smaller than that of the aforesaid image forming apparatus and colors can be superposed easily.
(7) In the apparatus stated above, the seventh object of the invention is to provide an image forming apparatus wherein a reproduction area is broadened by using light colored toner and dark colored toner, and further, image quality is improved by reducing splash of dark colored toner on a highlight section which easily stands out conspicuous.
Further, the invention is represented by an image forming apparatus that performs development by using two toner types of light colored toner and dark col
Braun Fred L
Frishauf Holtz Goodman & Chick P.C.
Konica Corporation
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