JPH0527539A - Image forming device and method - Google Patents

Abstract

PURPOSE:To provide the color image forming method by which bright projected images having high saturation are obtd. CONSTITUTION:The product of the height h of the color toner image structure and space frequency 1/lambda is specified to <=0.036 in the image forming method consisting in forming the color toner images 41 on a transparent film 42 for an overhead projector. The height of the color toner image structure is set by changing the toner weight per unit area on the transparent film 42 and the space frequency of the image structure may be set by changing resolution. The transparent film 42 for the overhead projector may be constituted of a 1st transparent resin layer formed of a transparent film 42 having heat resistance and a 2nd transparent resin layer which has compatibility with toners and has the thickness of 1/2 to 2 times the height of the color toner image structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and method for forming a color toner image on paper or a transparent film for an overhead projector (OHP) by an electrophotographic method.

[0002]

2. Description of the Related Art Conventionally, an image is formed on a transparent film using a color toner by an electrophotographic method, and the image is OH
Screen projection is performed with P or the like, but when the image is projected, a low-density portion and a halftone portion of the image become an unclear blackened image, so that a pseudo contour may occur. In this phenomenon, the toner image surface forming the image is sufficiently smoothed by the fixing device in the high density portion of the image, but the unevenness of the toner image surface remains in the low density portion of the image, and the unevenness of light caused by the unevenness It is considered that the cause is that the image portion is adversely affected by the scattering. However, the exact cause was unknown.

In order to prevent scattering of transmitted light, a method has been proposed in which a lacquer or the like is spray-coated on the toner image surface to smooth the image surface. Also, JP-A-63-80273
As described in Japanese Patent Laid-Open Publication No. JP-A-2003-264, the toner particles forming an image are deformed, and at the same time, the toner particles are adhered so as to be integrated with each other to eliminate particle gaps and steps, and the toner layer surface is a sufficiently smooth surface. There is also a method of forming.

Further, in the conventional electrophotographic system, since the refraction of the incident light generated at the boundary surface between the toner and the air is large, only a dark image can be obtained as the projected image because of low saturation. In order to solve this problem, JP-A-63-80
Japanese Patent No. 273 proposes a method of fixing at a temperature at which the toner melts sufficiently. In addition, the surface roughness of the color toner image is the 10-point average roughness based on JIS B0601-1982.
A method of applying a treatment of 0.8Z is disclosed in JP-A-60-5286.
It is proposed in Japanese Patent No.

[0005]

In the method of spraying a lacquer or the like on the toner image surface to make the image surface smooth,
In addition to dissolution of the toner forming an image by the solvent and deterioration of the sharpness of the image, uneven color or contamination of the non-image area, there is a problem in workability. Further, in the method of deforming the toner particles forming the image and simultaneously adhering the toner particles so as to be integrated with each other to eliminate the particle gaps and steps, the toner layer surface is formed to be a sufficiently smooth surface. In order to fix the toner at a temperature at which the toner melts sufficiently, the set temperature of the fixing device needs to be set higher than that of paper, and there is a problem that a waiting time or the like occurs when the type of paper changes. To polish the fixed image surface,
There is a problem that a polishing mechanism must be separately provided.

In the roller fixing method at high temperature as described in Japanese Patent Laid-Open No. 63-80273, when it is attempted to sufficiently smooth the portion with a small amount of toner in the halftone portion, the offset is applied to the portion with a large amount of toner. There is a problem that it easily occurs. Therefore, in this method, the surface of the toner image on which the image is formed is sufficiently smoothed in the high-density portion, but the unevenness of the toner image surface remains in the halftone portion, so that the incident light is scattered and a natural image is formed. There is a case where a pseudo contour occurs in the halftone part of.

Particularly in a digital color copying machine, density control of each color is performed by changing the area of a minute dot or line, and unevenness due to the image structure of the dot or line in the halftone portion exists. In the process of improving the image quality of the OHP projected image in the analog color copying machine due to the unevenness of the toner image surface in the halftone portion, a pseudo contour is likely to occur.

In the embodiment of the method proposed in Japanese Patent Laid-Open No. 60-52861, the height of the image structure in the case of the unevenness of the image structure having a specific spatial frequency such as an analog color copying machine is determined. It is not clear if it should be below a certain level. The object of the present invention is to solve the above-mentioned problems of the prior art and to reduce the apparent resolution when forming an image on a transparent film for HP without lowering the apparent resolution.
An object of the present invention is to provide an image recording device in which a pseudo contour does not occur on a P transparent film.

An object of the present invention is to solve the above problems of the prior art and to provide a color image forming method capable of obtaining a bright projected image with high saturation. Another object of the present invention is to provide a color image forming method in which a pseudo contour does not occur in a projected image of a natural image.

[0010]

According to the present invention, based on a pulsed image signal corresponding to the image density, the beam scanning unit repeats turning on and off the beam to perform beam scanning on the photosensitive member, and various kinds of papers. In an image recording apparatus for recording an image on a sheet, a reference generating means for generating a reference signal for determining an image density, a means for detecting a sheet type, and a cycle of the reference signal based on a detection result of the detecting means. The beam scanning unit is provided with a reference signal period changing unit and a pulse width modulating unit for generating a signal obtained by pulse-width modulating the reference signal changed by the reference signal period changing unit with an image signal. An image recording device characterized by being driven is provided.

Since the image density is determined by the screen ruling, changing the period of the reference signal means changing the screen ruling. Therefore, according to the present invention, the screen ruling is changed according to the type of paper. In order to prevent the occurrence of false contours, it is considered that the image density should be reduced, but the reduction in image density is accompanied by the reduction in resolution.
However, in order to improve the image quality, it is more important to prevent the occurrence of the pseudo contour than to reduce the resolution.

Therefore, for example, when an image is formed on a transparent film for OHP, the unevenness of the toner image on the transparent film for OHP is reduced by reducing the number of screen lines as compared with the case of paper, and pseudo contours are formed. Try to get a projection image that does not occur. Since the paper detection circuit is provided, in the case of paper, image processing is performed with a normal screen ruling, and the resolution is not reduced.

According to the present invention, in the image forming method for forming a color toner image on a transparent film for an overhead projector, the product of the height of the color toner image structure and the spatial frequency is 0.036 or less. An image forming method is provided. That is, the feature of the color image forming method of the present invention is that the height of the image structure of the color toner formed on the transparent film and the spatial frequency are simultaneously taken into consideration, and the product of the height of the image structure and the spatial frequency is calculated. The process is to set the value to 0.036 or less. When an image is formed on an OHP film by using a digital color copying machine, as shown in FIG. 1, regular unevenness having the height h of the image structure 41 and the spatial frequency 1 / λ appears. As a result of research by the present inventor, if the product h / λ of the height h of the image structure and the spatial frequency 1 / λ is 0.036 or less,
Even if refraction of incident light occurs due to unevenness of the toner image, OH
Since it can be projected on the screen by the optical system of P, it is concluded that the projected image has sufficient brightness and saturation, and pseudo contour does not occur.

As a method for setting h / λ of the color toner image structure formed on the transparent film 42 to 0.036 or less, there are roughly two methods. One is a method in which h is changed by changing the toner weight per unit area on the transparent film, and 1 / λ is changed by further changing the resolution. The other is as shown in FIG. A first transparent resin layer 43 formed of a transparent film and a second transparent resin layer 43 which is compatible with the toner and whose thickness is 1/2 to 2 times the height of the color toner image 44.
There is a method that can be realized by using an OHP film having a transparent resin layer 45 to reduce the height of the image structure after fixing.

The present invention may be implemented by any of the above methods.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in more detail with reference to the accompanying drawings with reference to the accompanying drawings. FIG. 1 schematically shows an image processing configuration of an electrophotographic copying machine which is a typical example of an image recording apparatus as an embodiment of the present invention.
As shown in FIG. 1, the signals of the triangular wave generation circuit 1 used when forming an image on paper and the triangular wave generation circuit 2 used when forming an image on a transparent film for OHP are the same as those of the paper detection circuit 3. The signal is selected by the multiplexer 4. Triangular wave signal 20 selected according to the type of paper
Is compared with the image signal 21 by the comparator 5 to generate a pulse width modulated laser drive signal 22.

In this embodiment, the triangular wave generating circuits 1, 2,
The paper detection circuit 3 and the multiplexer 4 respectively constitute the reference signal generating means, the paper type detecting means, and the reference signal cycle changing means for changing the cycle of the reference signal of the present invention. The triangular wave generation circuit 2 is the triangular wave generation circuit 1
It generates a triangular wave signal with a longer cycle than. These two triangular wave signals having different periods correspond to the reference signal of the present invention, and the multiplexer 4 selects one triangular wave signal 20 according to the input signal of the paper detection circuit 3,
The period of the reference signal is substantially changed.

FIG. 2 shows the triangular wave signal 20 and the image signal 21 input to the comparator 5, and the laser drive signal 22 output from the comparator. The laser drive signal 22 is a pulse signal in which the triangular wave signal 20 is amplitude-modulated by the image signal 21. Since the frequency of the triangular wave signal 20 corresponds to the screen ruling of the image, the frequency of the triangle wave signal 20 may be lowered to reduce the screen ruling. In other words, the cycle of the triangular wave signal 20 may be lengthened.

FIG. 3 shows an optical system for image formation. As shown in FIG. 3, the laser drive signal 22 drives the laser 31 through the laser drive signal line 30, whereby the laser beam is scanned by the polygon mirror 32 in the main scanning direction, and passes through the f-θ lens 33 to be exposed. The drum 34 is exposed. Then, an image is formed according to a usual electrophotographic process.

In this embodiment, when forming an image on paper, the frequency of the triangular wave is selected so that the number of screen lines is 200 lines per inch, and when the image is formed on the OHP transparent film. The frequency of the triangular wave was selected so that the number of screen lines was 141 lines per inch. In this example, when a natural image of a person or the like was formed on a transparent film for OHP and projected by FXOHPZ1 (trademark of Fuji Xerox Co., Ltd.), no pseudo contour was generated, but the same 200 per 1 inch as paper. When a natural image was formed on the OHP transparent film with the number of lines, a pseudo contour was generated.

In order to prevent the occurrence of false contours, the height of the color toner image structure formed on the transparent film and the spatial frequency are simultaneously taken into consideration, and the product of the height of the image structure and the spatial frequency is set to 0. It is preferably 0.036 or less. When an image is formed on an OHP film using a digital color copying machine, regular unevenness having a height h of an image structure and a spatial frequency 1 / λ appears as shown in FIG. As a result of research by the inventor of the present application, if the product h / λ of the height h of the image structure and the spatial frequency 1 / λ is 0.036 or less,
Even if refraction of incident light occurs due to unevenness of the toner image, OH
Since it can be projected on the screen by the P optical system, it is concluded that the projected image has sufficient brightness and saturation, and that no pseudo contour occurs.

There are roughly two methods for controlling the h / λ of the image structure of the color toner formed on the transparent film to 0.036 or less. One is a method in which h is changed by changing the toner weight per unit area on the transparent film, and 1 / λ is changed by further changing the resolution. The other is
As shown in FIG. 5, a first transparent resin layer 43 formed of a transparent film and a second transparent resin compatible with the toner and having a thickness of 1/2 to 2 times the height of the color toner image 44. There is a way to do this by using an OHP film with layer 45 to reduce the height of the image structure after fixing.

FIG. 6 schematically shows the structure of the color image forming apparatus. As shown in FIG. 6, the photosensitive drum 46
Is charged by a corona charger 47, and the laser light modulated by the image information signal is converted into a laser scanner optical device 48.
Thus, the photosensitive drum 46 is horizontally scanned to form an electrostatic latent image. Next, any one of the black developing device 49, the yellow developing device 50, the magenta developing device 51, and the cyan developing device 52 controls the photosensitive drum 46 on which the electrostatic latent image is formed by an image information signal forming the latent image. A developing device of a specified color is contacted with the developing device for development. Next, the visible image is sent from the paper tray 53 to the transfer drum 55 by the paper feeding device 54, and is further transferred to the wound transfer paper (OHP film) by the corona charger 56 from the back side to apply corona discharge. It When a multicolor image is to be obtained, the transfer paper is repeatedly contacted with the photosensitive drum 46 two to four times, and a plurality of or all visible images of cyan, magenta, yellow, and black are superposed and transferred. is there. Next, the transfer paper holding the transferred visible image is sent to the fixing device 57, where the toner image is heated and melted and fixed to the transfer paper, whereby a color image is obtained. On the other hand, the photosensitive drum 46 is cleaned by the cleaning device 58 and is ready for reuse.

Next, a method of changing the height h and the spatial frequency 1 / λ of the color toner image structure will be described. First, the height h of the image structure can be changed by changing the toner weight per unit area on the transparent film. The toner weight is adjusted by adjusting the toner density,
Adjustment of the toner charge amount, adjustment of the potential contrast that contributes to development, adjustment of the facing distance between the electrostatic latent image and the developer carrier,
It can be performed by adjusting the developing bias voltage and frequency. The spatial frequency 1 / λ of the image structure can then be changed by changing the resolution.

FIG. 7 shows the experimental results when the height h of the color toner image and the spatial frequency 1 / λ are changed. Here, all h / λ of the solid portion were 0.036 or less, and had sufficient transparency, but as shown in FIG.
Has a maximum value in the halftone portion, and FIG. 7 shows the value of h / λ at the maximum value of h. As shown in FIG.
It can be seen that if the value of / λ is 0.036 or less, sufficient transparency is obtained even in the halftone portion, so that no pseudo contour is generated.

Here, when the height h of the image structure is reduced, the color components absorbed in the toner layer are reduced,
The saturation of the projected color is reduced, and the resolution of the projected image is reduced in order to reduce the spatial frequency 1 / λ. Therefore, when the value of h / λ is 0.036 or less, the resolution is lowered when the saturation of the projection color is emphasized, and the height h of the image structure is reduced when the resolution of the projected image is emphasized. good.

The color image forming apparatus shown in FIG. 6 and FIG.
A color image was formed using the first transparent resin layer formed of the heat-resistant transparent film shown in 1 and the OHP film having the second transparent resin layer compatible with the toner. Here, polyethylene phthalate (PET) having heat resistance was used as the first transparent resin layer, and a polyester resin similar to the binder resin of the toner was used as the second transparent resin layer. If the binder resin of the toner is a styrene resin, a styrene resin of the same type may be used.

When a color image was formed by using a screen generator having 200 lines per inch as a resolution, the saturation and brightness of the halftone portion may vary depending on the thickness of the second transparent resin layer as shown in FIG. It fell and a false contour occurred. Here, the vertical axis of FIG. 9 represents the pseudo contour grade, the larger the value, the more clearly the pseudo contour can be seen, and the zero indicates that the pseudo contour is completely invisible, and the horizontal axis shows the second transparent resin layer. The ratio with respect to the height h of the image structure when there is no symbol.

FIG. 10 shows the change in the height h of the image structure after fixing depending on the thickness of the second transparent resin layer. As shown in FIGS. 9 and 10, the thickness of the second resin layer is the height h of the image structure.
If it is less than 1/2, a pseudo contour occurs because a region where h / λ is 0.036 or more is generated in the halftone portion, but if the thickness of the second transparent resin layer is 1/2 or more of h, In the entire image, h / λ was 0.036 or less, and no pseudo contour was generated. Further, if the thickness of the second transparent resin layer is more than twice the h, not only the cost will increase, but also the transparency will decrease and the image will be cracked due to bending. Therefore, the second
The thickness of the transparent resin layer is preferably 1/2 to 2 times the height of the image structure of the color toner.

According to such a method, when an image is formed on the transparent film for OHP, it is possible to obtain a projected image having high saturation and brightness and having no pseudo contour in a natural image.

[0031]

According to the present invention, since the screen ruling is changed by changing the period of the reference signal according to the type of paper, the optimum image quality can be obtained according to the paper. . For example, when an image is formed on a transparent film for OHP, the number of screen lines is reduced as compared with the case of paper, so that the unevenness of the toner image on the transparent film for OHP is reduced, and pseudo contours are not generated, and transparent images are not generated. It is possible to obtain a projected image with high lightness and good color tone.
Further, since the paper detection circuit is provided, in the case of paper, image processing is performed with a normal screen ruling, and the resolution is not reduced. Further, there is no need to apply a solvent or the like on the toner image or polish the image surface or the like unlike the conventional method.

Further, according to the present invention, when an image is formed on a transparent film for OHP, the saturation is high, the brightness is high,
Moreover, it is possible to obtain a projected image in which a pseudo contour does not occur in the natural image. In particular, an OHP composed of a first transparent resin layer formed of a transparent film and a second transparent resin layer which is compatible with the toner and whose thickness is 1/2 to 2 times the height of the color toner image. When using a film,
It is possible to obtain a projected image with high saturation, brightness, and no pseudo contours, without sacrificing the saturation of the projected color and the resolution of the projected image.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing a configuration of image processing of an image recording apparatus of the present invention.

FIG. 2 is a signal waveform diagram showing an input signal and an output signal of the comparator of FIG.

FIG. 3 is a schematic view showing an optical system according to the image recording apparatus of the present invention.

FIG. 4 is a sectional view showing an image structure of color toner.

FIG. 5 is a cross-sectional view showing an image structure when the OHP film of the present invention is used.

FIG. 6 is a schematic diagram showing a configuration of a color image forming apparatus used in the present invention.

FIG. 7 is a table showing generation of pseudo contours when the color toner image height h and the spatial frequency 1 / λ are changed.

FIG. 8 is a graph showing a relationship between an input halftone dot area ratio and a height h of an image structure.

FIG. 9 is a graph showing the relationship of pseudo contour with respect to the thickness of the second transparent resin layer of the OHP film of the present invention.

FIG. 10 is a graph showing changes in the height h of the image structure after fixing with respect to the thickness of the second transparent resin layer. 1, 2 triangular wave generation circuit 3 paper detection circuit 4 multiplexer 5 comparator 20 triangular wave signal 21 image signal 22 laser drive signal 30 laser drive line 31 laser 32 polygon mirror 33 f-θ lens 34 photosensitive drum 41 toner image 42 OHP film 43 1 Transparent Resin Layer 44 Color Toner Image 45 Second Transparent Resin Layer 46 Photosensitive Drum 47 Corona Charger 48 Laser Scanner Optical Device 49 Black Developer 50 Yellow Developer 51 Magenta Developer 52 Cyan Developer 53 Paper Tray 54 Paper Feeder 55 transfer drum 56 corona charger 57 fixing device 58 cleaning device

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Claims (4)

[Claims] 1. An image recording apparatus for recording an image on various kinds of paper by performing beam scanning on a photosensitive member by repeating lighting or extinction of a beam of a beam scanning unit based on a pulsed image signal corresponding to image density. Reference signal generating means for generating a reference signal for determining the image density, means for detecting the type of paper, reference signal cycle changing means for changing the cycle of the reference signal based on the detection result of the detecting means, and the reference A pulse width modulation means for generating a signal in which the reference signal changed by the signal period changing means is pulse width modulated with an image signal, and the beam scanning unit is driven by the pulse width modulation signal. apparatus. 2. An image forming method for forming a color toner image on a transparent film for an overhead projector, wherein the product of the height of the color toner image structure and the spatial frequency is 0.036 or less. 3. The height of the color toner image structure is set by changing the toner weight per unit area on the transparent film, and the spatial frequency of the image structure is set by changing the resolution. The image forming method according to claim 2. 4. The transparent film for an overhead projector is compatible with a first transparent resin layer formed of a transparent film having heat resistance, and has a thickness that is equal to a height of an image structure of a color toner. The image forming method according to claim 2 or 3, wherein the image forming method is configured by a second transparent resin layer having a ratio of / 2 to 2 times.