JPH07248662A - Color image forming method - Google Patents

Abstract

PURPOSE:To smooth the surface of a toner regardless of the gray level of an image by converting the toner stuck quantity in response to the document density, and adding a transparent toner so that the total toner stuck quantity becomes a fixed value or above. CONSTITUTION:Developing units 36T, 36Y, 36M, 36C, 36BK are provided, the developing unit 36T storing a transparent toner T is arranged at the most upstream section on the peripheral edge of a photo drum 30, and a developing unit 36BK storing a black toner BK is arranged at the most downstream section. A transparent constituent extraction section calculates the equation t=Z-(y+ m+c+bk) based on the Y, M, C image signals (y, m, c) corrected by a masking section and the black constituent signal (bk) extracted by a black constituent extraction section via backing picture removal (UCK) to extract the transparent constituent signal (t), where Z is a value for making the toner stuck quantity a fixed value within the range of 0.5-1.5mg/cm<2> based on the signals (y), (m), (c), (bk). A transparent toner section is formed based on the signal (t) for the transparent toner section, and the transparent toner section is added on the photosensitive drum 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises an image reading unit for reading an original image of an electrophotographic copying machine or the like by a device such as a CCD and outputting the image, and a toner image on a recording medium such as paper or an overhead projector (OHP). And a color image forming method capable of forming a clear color image.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine, means for monitoring the toner concentration of a developer and automatically replenishing the toner is provided to keep the developing condition constant, or the average density of an original document. There is known a device in which the developing conditions are measured according to the measurement result and the developing conditions are changed to obtain a copy which is as faithful to the original as possible and is easy to read. But,
A color image forming method capable of completely reproducing the glossiness of the low density image portion of the original image has not yet been realized.

[0003]

In the conventional image forming apparatus, since the toner adhesion amount is small in the portion where the original density is low,
There is a problem that the unevenness of the fibers of the transfer material is picked up, and the toner is not completely united at the time of fixing and does not become smooth, so that the glossiness is lowered and the saturation is lowered in the color copy.

Also, in an image recorded on a transparent sheet used for an overhead projector or the like, when the toner adhesion amount is small, the toner does not completely coalesce at the time of fixing and does not become smooth, so that diffuse reflection of transmitted light occurs. However, there is a problem in that a clear and highly saturated projection image cannot be obtained.

The present invention solves the above-mentioned problems and makes a copy image on a transfer material a glossy image even in a portion having a low image density,
Alternatively, in the case of an OHP sheet, it is an object of the present invention to provide a color image forming method which can be recorded as a projected image having a color developability and has good saturation.

[0006]

In the color image forming method for forming a color image with toner on a recording medium, the toner adhesion amount is converted according to the original density,
This is achieved by a color image forming method characterized by adding transparent toner so that the total amount of adhered toner becomes a certain value or more.

The constant value is a constant value within the range of 0.5 to 1.5 mg / cm ² , and when the total amount of adhered colored toner is less than the constant value, the transparent toner corresponding to the insufficient amount is superposed, The above-described color image forming method is characterized in that the transparent toners are not superposed when the total amount of the adhered colored toners is a certain value or more.

[0008]

First, the image processing method of the present invention will be described.

In the image processing method of the present invention, the total amount of colored toner adhered is calculated from the image data obtained by scanning (prescanning) the entire original image in advance, and the required amount of transparent toner is calculated. Calculate the magnitude of the signal that attaches.

The basic configuration of the image signal processing performed by the present invention is roughly the calculation of the amount of transparent toner adhesion based on the image reading system, the memory for storing the image data, and the image data stored by the prescan. It is composed of a CPU that performs a process of storing again in the memory.

The image data is taken into the memory during the prescan. The CPU calculates the toner adhesion amount based on this data, and returns the result to the memory again. Since this calculation is completed within a few seconds, it can be executed without waiting for the main scan. Further, because of such a configuration, it is possible to provide a system that does not require special hardware other than the CPU, has a simple mechanism, and can easily change algorithms and parameters. Note that the scanner and the control CPU may also serve as the CPU even if the CPU has an independent configuration.

The glossiness of the copy image is related to the toner adhesion amount. If the toner adhesion amount is small, the toner surface will not be sufficiently compressed during fixing and the toner surface will not be smooth and the glossiness will be low. As a result of the experiment, as shown in FIG. 5, when the toner adhesion amount is small, the glossiness is low, and when the toner adhesion amount is 1 mg / cm ² , the copy glossiness is 50 and the image has high gloss.
It was found that even if the toner adhesion amount is further increased, the increase in glossiness becomes slow and saturated. As for the OHP sheet, when the toner adhesion amount is small as shown in FIG. 6, the transmittance is low, and when the toner adhesion amount is 1 mg / cm ^{2, the} transmittance is 75.
It can be said that the projected image also has sufficient coloring. This allows
It has been found that the toner adhesion amount needs to be 1 mg / cm ² or more to satisfy both. However, this value is an experimental value, and varies depending on the toner particle size, the viscoelastic property of the toner, and the fixing conditions.
It has been clarified that the condition of 50 is a constant value of the total toner adhesion amount of 0.5 to 1.5 mg / cm ² . Further, when the total toner adhesion amount is 1.5 mg / cm ² or more, offset occurs, which is not preferable for another reason.

(Embodiment 1) FIG. 1 is a sectional view showing an example of an image forming apparatus to which the present invention is applied so that a copy having gloss can be obtained. This image forming apparatus comprises an image reading system A, a laser writing system B, an image forming section H and the like.

An original table made of a transparent glass plate or the like is provided above the image forming apparatus, and an original document D placed on the original table.
There is a document placing section 11 composed of a document cover or the like for covering the first mirror unit below the document table and inside the apparatus main body.
12, second mirror unit 13, main lens 20, color CCD
An image reading system A composed of 23 etc. is provided. The first mirror unit 12 includes an illumination lamp 14 and a first mirror 15,
It is mounted parallel to the document table and linearly movable in the horizontal direction in the drawing, and optically scans the entire surface of the document D.
The second mirror unit 13 includes a second mirror 16 and a third mirror 17.
To be integrated, and to always maintain a predetermined optical path length
It moves linearly in the same direction to the left and right at a speed half that of the mirror unit 12. Of course, the movement of the second mirror unit 13 is the same as that of the first
Like the mirror unit 12, it is parallel to the document table.
Original D on the platen illuminated by the illumination lamp 14
Image of the first mirror 15 and the second mirror 1 by the main lens 20.
6. The image is formed on the color CCD 23 through the third mirror 17. After scanning, the first mirror unit
The 12 and the second mirror unit 13 return to their original positions and stand by until the next copy.

Image data obtained from the color CCD 23 by the above scanning is processed by the image signal processing unit 60 shown in FIG. 2, and is output to the laser writing system B as an image signal through the reading unit 68.

The image signal processor 60 includes an A / D converter 61, a shading corrector 62, a complementary color converter 63, and a black component extractor 6.
4. It is composed of a masking unit 65, a transparent component extracting unit 66, and a memory unit 67.

The A / D converter 61 receives blue (B), green (G) and red (R) from the color CCD 23.
Color image data consisting of image data of
The gradation digital signal is converted into image digital, and the shading correction unit 62 corrects the gradation improvement, and then outputs it to the complementary color conversion unit 63 described later.

The complementary color conversion unit 63 performs complementary color conversion on the digital signal of the color image data converted by the A / D conversion unit 61 and corrected by the shading correction unit 62 to obtain yellow (Y), magenta (M), cyan (C). ) Image data (y, m, c)
To get

The black component extraction unit 64 removes the undercolor, for example, to obtain black (BK) image data (Y, M, C) image data (y, m, C) obtained by the complementary color conversion unit 63. bk) is extracted.

The masking portion 65 is for removing Y, M, and
Correct the image data of C.

The transparent component extraction unit 66 extracts the Y, M and C image signals (y, m, c) corrected by the masking unit 65 and the black component signal (black) extracted by the black component extraction unit 64 (UCR). The following equation is calculated from bk) and the transparent component signal t is extracted.

[0022] t = Z- (y + m + c + bk) where, Z is the signal y, m, c, a constant value, for example 1 mg / cm ² within the toner adhesion amount of 0.5 to 1.5 mg / cm ² by bk
Is the value. As a result, the toner layer shown in FIG. 3 is formed on the image forming body in the copying process described later, and the total thickness of the toner layers can be set to a constant value, for example, 1 mg / cm ² . When the total thickness of the color toners Tc is a constant value, for example, 1 mg / cm ² or more, the signal t = 0 of the transparent toner T.
Therefore, the transparent toner T does not adhere (FIG. 3).

The memory section 67 includes Y, M, and C image data (y, m, c) color-corrected by the masking section 65, and BK image data (bk) extracted by the black component extracting section 64. Color image data including the data (t) of the transparent toner T extracted by the transparent component extraction unit 66 is stored. In addition,
It goes without saying that the image processing process up to this point may be substituted by a computer or the like. Further, the memory unit 67 can be omitted by scanning the reading scan for each color.

The stored image data may be color or monochrome image data stored in the memory unit 67 created by a computer or the like.

The image forming unit H includes a charging device 35, an image exposing unit 50, developing devices 36T, 36Y, 36M, 36C, 36BK, a transfer device 37, which are arranged on the periphery of a photosensitive drum 30 which is an image forming body. Separator
38, a cleaning device 39, a conveyor belt 44, a fixing device 45 and the like.

The developing devices 36T, 36Y, 36M, 36C, 36B
K is provided with a developing device 36T containing a transparent toner T in the most upstream part of the peripheral edge of the photosensitive drum 30, and a developing device 36BK containing a black toner BK in the most downstream part. Developing device 36Y, 36
Well-known color toners are used as the color toners contained in the M, 36C, and 36BK, and the description thereof will be omitted. However, as the black toner BK, a toner having infrared transmissivity is used, and thus a toner not restricted by the order of image formation is selected.

Transparent toner T contained in the developing device 36T
Means that almost all light in the visible wavelength range is transmitted and does not contribute to the image density of the obtained color image. The toner T is obtained by removing a colorant or a dye from an ordinary color toner, and for example, a styrene monomer such as styrene and an acrylic ester monomer such as butyl acrylate and / or a methacrylic acid ester such as methyl methacrylate. A thermoplastic resin such as a styrene-acrylic copolymer resin obtained by copolymerization with a similar monomer or a polyester resin is used. Therefore, the electrical characteristics and the particle size are almost the same as those of the normal toner. Transparent toner T
The specific resistance is 10 ¹⁰ Ω · cm or more, and the particle size is 5 to 15
The one with μm is preferably used.

Next, the copy process of the image forming section H will be described.

When the copy button is pressed in the operation section (not shown), the image signal from the image reading system A is transmitted by the control of the control section (not shown) to the drive motor 31, the rotary polygon mirror 32, the semiconductor laser (not shown), and fθ. It is input to the laser writing system B including a lens, a correction lens and the like to start the copy operation. That is, the photosensitive drum 30 rotates in the clockwise direction as shown by the arrow, is uniformly charged by the charger 35, and the yellow (Y) image corresponding to the image of the document D is written in the image exposure unit 55. The electrostatic latent image of the Y image is formed by the laser beam from the laser writing system B.
The electrostatic latent image on the photosensitive drum 30 is transferred to the developing device 36.
Reversal development with Y toner is performed by Y to form a visible Y toner image. That is, a DC or further AC bias voltage is applied to the developing sleeve of the developing device 36Y having a built-in magnet roll, and non-contact development is performed by a two-component developer which is a developing means to form a Y toner image. . The photoconductor drum 30 on which the Y toner image is formed passes under the retracted cleaning device 39, and subsequently, charging by the charging device 35 and laser beam writing of a magenta (M) image by the laser writing system B are performed. , An electrostatic latent image of a magenta (M) image is formed on the Y toner image. This latent image is subjected to reversal development by a developing device 36M containing magenta toner and M
It becomes a toner image. Then, similarly, a cyan (C) toner image,
A black (BK) toner image is formed. Finally, a transparent toner T portion is superimposed on the transparent toner portion T by the signal t, and a multicolored color toner image to which the transparent toner T portion is added is formed on the photosensitive drum 30.

When the original D is a single-color magenta image, only the developing device 36M and the developing device 36T are operated and the magenta toner M
A transparent toner T is added to the toner image to form a toner image.

Next, the transfer paper P fed out by the paper feed roller 41 one by one from the paper feed cassette 40 containing the white transfer paper P which is the transfer material is synchronized with the toner image on the photosensitive drum 30. Then, it is sent onto the photosensitive drum 30 by the registration roller 42 which operates in the same manner. This transfer paper P has a transfer device
By the action of 37, the color toner image including the transparent toner T portion on the photoconductor drum 30 is transferred, separated from the photoconductor drum 30 by the separator 38, and then sent to the fixing device 45 by the transport belt 44, It is nipped and pressed by a heat fixing roller and a pressure roller to perform gloss fixing with the transparent toner T portion as a lower layer, and then is ejected to a tray outside the apparatus by a paper ejection roller 46.

On the other hand, the photosensitive drum 30 continues to rotate,
The toner remaining on the surface without being transferred is collected and cleaned by the cleaning device 39 having the cleaning blade 39A that has been retreated, and stands by for the next copy.

As described above, the color toner T of the image is
A toner image having a sufficient thickness such that the sum of c and the thickness of the transparent toner T is a fixed value, for example, 1 mg / cm ² or more is formed. Therefore, at the time of fixing, the toner layer is sufficiently compressed and coalesced so that the unevenness of the toner surface is eliminated and a copy having high glossiness can be obtained.

In the present invention, the transparent toner T is basically added only on the color toner Tc as shown in FIG. 3 to make the white background matte, but as shown in FIG. It is also possible to form a transparent toner T having an adhesion amount of 1 mg / cm ² so that the entire surface has gloss. Further, in the image forming process, a glossy image or a projected image having a color forming property can be obtained by adding transparent toner to the process of forming a color toner image by superposing toner on paper.

[0035]

As described above, according to the present invention, the total amount of toner adhered is set to a certain amount or more, so that the toner surface can be smoothed regardless of the density of the image.
Therefore, even if a general transfer paper is used, it is possible to obtain a color copy without unevenness with excellent saturation and gloss in the image area. Furthermore, even when a transparency sheet is used as the transfer material, all image areas can be obtained. It is possible to provide a method in which an excellent copy having good transparency and no irregular reflection, capable of projecting a clear and highly saturated image can be obtained, and the transparent toner is kept to a minimum necessary amount and is not wasted.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a color image forming apparatus to which the present invention is applied.

FIG. 2 is a block diagram showing an example of an image signal processing unit according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing an example of a toner layer structure formed by the present invention.

FIG. 4 is a cross-sectional view showing another toner layer structure formed according to the present invention.

FIG. 5 is a graph showing the relationship between toner adhesion amount and copy glossiness.

FIG. 6 is a graph showing the relationship between the toner adhesion amount and the transmittance of the transparency sheet.

[Explanation of symbols]

 30 Photosensitive drum 35 Charging device 36T, 36Y, 36M, 36C, 36BK Developing device 37 Transfer device 38 Separator 39 Cleaning device 40 Paper feed cassette 44 Conveyor belt 45 Fixing device 46 Discharging roller 60 Image signal processing unit 66 Transparent component extraction Part A Image reading system B Laser writing system BK Black toner C Cyan toner H Image forming part M Magenta toner P Transfer paper T Transparent toner Tc Color toner Y Yellow toner

Claims (2)

[Claims] 1. A color image forming method for forming a color image with toner on a recording medium, wherein a toner adhesion amount is converted according to a document density, and a transparent toner is used so that the total toner adhesion amount becomes a certain value or more. A method for forming a color image, which comprises adding. 2. The constant value is a constant value within a range of 0.5 to 1.5 mg / cm ² , and when the total amount of colored toner adhered is less than a constant value, the transparent toner corresponding to the insufficient amount is overlapped, 2. The color image forming method according to claim 1, wherein the transparent toners are not superposed when the total amount of the adhered colored toners is a predetermined value or more.