JP2002049205A - Image-forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image-forming device capable of improving resolution performance and image quality by making toner scattering at an image edge part inconspicuous. SOLUTION: In this electrophotographic image forming device, the surface of an electrified electrostatic latent image carrier is irradiated with light by an optical write means, so that an electrostatic latent image may be formed, and color toner T is supplied to visualize the electrostatic latent image by developing bias applied between the electrostatic latent image carrier and a developing means; then the color toner T on the surface of the electrostatic latent image carrier is transferred to transfer paper or an intermediate transfer body, whereby a color image or a monochrome image is formed. Based on inputted image data, the area of the image is separated. When an area adjacent to the image decided as a text part is the ground color of the transfer paper, white toner TW is printed in the prescribed area of the adjacent area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic high-quality image forming apparatus using white toner.

[0002]

2. Description of the Related Art As an electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of a charged electrostatic latent image carrier by an optical writing unit, and toner is supplied to the electrostatic latent image by a developing unit. There is known an image forming apparatus which visualizes and transfers a toner on the surface of the electrostatic latent image carrier to a transfer paper or an intermediate transfer body by a transfer means to form a color image or a monochrome image.

[0003] As a transfer means, there is a charger type for transferring toner by electrostatic force. In this case, the surface of the electrostatic latent image carrier is not in contact with the transfer paper or the intermediate transfer body. The toner flies in the space and adheres to the transfer paper or the intermediate transfer body.

[0004]

When the toner on the surface of the electrostatic latent image carrier is transferred to the transfer paper by using a charger type transfer means, the toner is transferred between the surface of the electrostatic latent image carrier and the transfer paper. In addition to the fact that the spread of the transfer electric field cannot be ignored, the spread of the discharge charge from the charger opening causes the charge to be applied to the upstream side of the transfer paper, so that the toner is scattered. For this reason, compared to the image on the surface of the electrostatic latent image carrier, scattering occurs in the toner image after transfer, and a solid image,
At the edges of characters and fine lines, toner may adhere to portions of the transfer paper where there is no image due to scattering of toner, and the image quality may be degraded. In particular, as the resolution of the image forming apparatus increases, the toner scatters around characters and thin lines, and the resolution is significantly reduced. However, there is a big problem as the resolution is increased.

[0005] Since scattering of toner at an image edge portion occurs at the time of transfer, as a countermeasure, a transfer roller,
Using a contact type transfer means such as a transfer drum, narrowing the opening of the transfer charger to prevent toner from scattering on the upstream side of the opening, and reducing the resistance value and charge amount of the transfer paper and the intermediate transfer body. Control and the like are employed.

However, it is still impossible to obtain a high-resolution high-quality image by eliminating all toner scattering due to poor charging of the toner, charging of the opposite characteristics, and deterioration of the environment and aging of each member.

[0007] The same applies to the case where the toner on the surface of the electrostatic latent image carrier is transferred to the intermediate transfer body using a charger type transfer means.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of improving the resolution performance and the image quality by making the scattering of the toner at the image edge portion inconspicuous.

[0009]

The image forming apparatus according to the present invention forms an electrostatic latent image by irradiating a charged electrostatic latent image carrier surface with light by an optical writing means, A colored toner is supplied to the electrostatic latent image by a developing bias applied between the electrostatic latent image carrier and the developing means to visualize the electrostatic latent image, and the colored toner on the surface of the electrostatic latent image carrier is transferred to a transfer paper or an intermediate transfer member. In an electrophotographic image forming apparatus that forms a color image or a monochrome image by transferring the image to an area, the area of the image is separated based on the input image data, and the area adjacent to the image determined to be a text part is transferred. In the case of paper ground color, white toner is printed in a predetermined area of the adjacent area.

In general, a black toner is used in a monochrome image forming apparatus, and three chromatic toners of cyan (C), magenta (M) and yellow (Y) are used in a color image forming apparatus. When using these and these 3
Color chromatic toner and black toner may be used.

The present invention can be applied to both a monochrome image forming apparatus and a color image forming apparatus.
In addition to the above toner, a white toner is used.

In the present specification, toners other than white toner, that is, chromatic toner and black toner are collectively referred to as colored toner.

According to the present invention, the white toner is printed in a predetermined area adjacent to the text image. Therefore, at the edge of the text image, the scattering of the toner at the time of transfer becomes inconspicuous, and the resolution of the text image is improved. It is possible to reproduce a high-quality image with high sharpness.

In the image forming apparatus of the present invention, for example, an area where white toner is printed in the adjacent area is
When the image resolution is D (dpi), this is an area corresponding to the number of pixels of a value N obtained by rounding up the decimal point of the value X calculated by the following equation.

X = 50 ° (25400 ° D) The area where the colored toner scatters at the edge of the image is about 50 μm from the edge regardless of the image resolution.
Therefore, by performing the above, white toner can be printed in an area where toner scattering is likely to occur, so that toner scattering can be made inconspicuous.

In the above image forming apparatus, for example,
If there is color print data within the number of pixels corresponding to the value N obtained as described above, white toner is printed only in an area where there is no color print data.

Even when there is colored print data to be printed with colored toner within the number of pixels corresponding to the value N, if white toner is printed over the entire number of pixels corresponding to the value N, the original colored print data Are hidden by the white toner. However, as described above, white toner is printed only in areas where there is no colored print data, and white toner is not printed in areas where there is colored data, so that the original colored print data is hidden by the white toner. It will not be done.

In the image forming apparatus of the present invention, for example, a white toner is printed after a colored toner is printed on transfer paper or an intermediate transfer member.

At the edge of an image after printing of a color image or a monochrome image with colored toner, scattered toner exists at the edge portion, and this toner causes a reduction in resolution. As described above, by printing the white toner on the edge portion of the text image after the color toner printing, the scattered color toner can be covered, and the resolution is improved, and a high-quality image with high sharpness can be reproduced.

However, after forming the color toner image corresponding to the image data and the white toner image at the edge portion of the text image on the surface of the electrostatic latent image carrier, the color toner image and the white toner image are simultaneously transferred to a transfer paper or You may make it transfer (print) to an intermediate transfer body.

In the image forming apparatus of the present invention, for example, when the color difference ΔE between the transfer paper and the white toner is less than 15, white toner is printed in a predetermined area of the adjacent area, and when the color difference ΔE is 15 or more, white is printed. Do not print toner.

Generally, when the color difference ΔE between white colors is 15 or more, the color difference can be identified by eyes. Therefore, even when the color difference ΔE between the transfer paper and the white toner is 15 or more, the edge of the text image is not affected. When white toner printing is performed on the portion, scattering of toner can be made inconspicuous, but on the contrary, the printed white toner becomes conspicuous, the effect of resolution improvement disappears, and the image quality rather deteriorates. On the other hand, when the color difference ΔE between the white colors is less than 15, the color difference is hardly discernible by eyes. Therefore, when the color difference ΔE between the transfer paper and the white toner is less than 15, the white toner is added to the edge of the text image. Is printed, the scattering of the toner can be made inconspicuous, and the white toner is not conspicuous, and a high-resolution and high-quality image can be obtained. Therefore, as described above, when the color difference ΔE between the transfer paper and the white toner is less than 15, the white toner is printed in a predetermined area in the adjacent area, and when the color difference ΔE is 15 or more, the white toner is printed in the predetermined area in the adjacent area. By not printing, it is possible to obtain a high-quality image in which scattering of toner is not conspicuous and white toner is not conspicuous.

In the image forming apparatus of the present invention, for example, the height in the thickness direction of the white toner printed on the predetermined area of the adjacent portion is substantially equal to the height of the color toner of the adjacent image in the thickness direction.

If the height of the white toner is different from the height of the colored toner adjacent thereto, in the case of the contact fixing method, the higher toner is placed above the lower toner between the toners having different heights during compression fixing. The image is disturbed at the edge portion of the text image because the text image is covered or scattered. In particular, in the case of the non-contact fixing method, non-uniformity of heat transfer occurs at the time of fixing, and the fixing strength is reduced, thereby deteriorating the image quality. On the other hand, when the heights of the white toner and the adjacent colored toner are substantially equal, the above-described problem does not occur, and excellent image reproduction can be achieved.

In the image forming apparatus of the present invention, for example, the particle size of the white toner is smaller than the particle size of the color toner.

By making the particle size of the white toner smaller than that of the color toner, the effect of hiding the color toner scattered at the edge portion by the white toner is further improved.

In the above image forming apparatus, for example,
The particle size of the white toner is 5 μm or less.

At present, the particle size of the color toner is 6 to 10 μm.
When m is a standard value and the toner scatters around the edge portion, the concealing effect is reduced with toner having the same particle size, but the concealing effect is further improved by using the small particle size toner. Therefore, the particle size of the white toner is 5 μm
By doing so, the particle size of the white toner can be made smaller than the particle size of the color toner, and the effect of hiding the color toner scattered at the edge by the white toner can be further improved.

In the above image forming apparatus, for example,
The white toner is manufactured by a polymerization method.

The method for producing the toner is roughly classified into a pulverization method and a polymerization method. Generally, it is difficult to produce a toner having a small particle diameter by the pulverization method, and the particle diameter is limited to about 6 μm. On the other hand, according to the polymerization method, it is possible to reliably produce a toner having a small particle diameter having a uniform particle diameter.

In the image forming apparatus of the present invention, for example, the resin component of the white toner is styrene acrylic.

Since styrene acrylic resin is translucent, by using a white toner containing it as a component,
The effect of hiding the colored toner scattered near the edge of the text image can be enhanced.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment in which the present invention is applied to a monochrome image forming apparatus for printing a monochrome image, and schematically shows an image forming section (printing section).

In FIG. 1, the image forming section is provided with a drum-shaped photosensitive member (1) constituting an electrostatic latent image carrier. The photoconductor (1) rotates in the direction of the arrow (clockwise) in the figure,
Around the photoreceptor (1), in the direction of rotation, a first charger (2) constituting black (Bk) charging means, and a first optical writing unit (3) constituting black optical writing means. ), A first developing device (4) as a developing means containing the black toner (T),
A second charger (5) constituting a charging means for white (W), a second optical writing unit constituting an optical writing means for white
(6), a second developing device (7) as a developing device containing white toner (TW), a transfer device (8) forming a transfer device, and a cleaning unit (9) forming a cleaning device are arranged in this order. ing. Then, the transfer paper (P) is moved between the photoreceptor (1) and the transfer unit (8) in the direction of the arrow in the figure (from right to left) by a transport device (not shown). Photoconductor (1)
With respect to the transfer device (8), a transfer paper detection sensor (10) is provided on the upstream side of the movement path of the transfer paper (P), and a fixing device (11) constituting a fixing unit is provided on the downstream side. ing.

As the chargers (2) and (5), for example, a contact type or a charger type is used. The optical writing units (3) and (6) use, for example, a laser light source or an LED light source. As the transfer device (8), for example,
A contact transfer device such as a non-contact charger transfer device or a roller transfer device is used. As the fixing device (10), for example, a non-contact type or a contact type is used.

In the image forming section, first, in order to print the image data with the black toner (T), the first charger (2)
The surface of the photoreceptor (1) is uniformly charged by the first optical writing unit (3), and writing is performed on the uniformly charged photoreceptor (1) based on the image data. A corresponding electrostatic latent image is formed, and the first developing device (4) visualizes (visualizes) the electrostatic latent image corresponding to the image data on the photoconductor (1) using the black toner (T). Is done. afterwards,
Photoreceptor (1) on which a black toner image of image data is formed in order to print white toner (TW) to prevent scattering of black toner (T) at the edge of the text image
The surface of is uniformly charged again, and the second optical writing unit (6) writes on the uniformly charged photoconductor (1) based on white toner print data to be described later. An electrostatic latent image corresponding to the print data is formed in an overlapping manner, and the second developer (7) visualizes the electrostatic latent image corresponding to the white print data.

The white toner print data will be described in detail later. This is data for printing white toner (TW) in a predetermined area adjacent to the text image at the edge of the text image in the image. is there.

By performing the above-described processing, the toner image obtained by combining the black toner image corresponding to the image data and the white toner image formed at the edge of the text image in the black toner image is formed on the photosensitive member. (1) formed on Then, the toner image is transferred to the transfer paper (P) by the transfer device (8). Then, the toner (T) (TW) remaining on the photoconductor (1)
Is collected by the cleaning unit (9). Further, when the transfer paper (P) passes through the fixing device (11), the toners (T) and (TW) on the transfer paper (P) are fixed on the transfer paper (P).

When the black toner image and the white toner image on the surface of the photoreceptor (1) are transferred to the transfer paper (P) as described above, the white toner adjoins the edge of the black toner (T) of the text image. (TW), black toner (T)
And the height in the thickness direction of the white toner (TW) are made substantially equal, so that the black toner (T) at the boundary between the black toner (T) and the white toner (TW), that is, at the edge of the text image
Also, scattering of white toner (TW) is prevented. For this reason, the edge portion of the text image is not disturbed, and the sharpness (resolution) is improved. White toner (TW) is transfer paper (P)
Is not conspicuous, so that there is no problem even if it is printed at the edge of the text image. The white toner (TW) scatters at the edge opposite to the text image, but the scattered white toner (TW) also
There is no problem because (P) is inconspicuous.

FIG. 2 shows a second embodiment in which the present invention is applied to a monochrome image forming apparatus, and schematically shows an image forming section thereof. In the second embodiment, portions corresponding to those of the first embodiment are denoted by the same reference numerals.

This image forming apparatus is of a tandem type, and the image forming section is provided with two photosensitive members (1a) and (1b) in the moving direction of the transfer paper (P). Around the first photoconductor (1a) on the upstream side of the transfer paper (P) moving direction,
First charger (2) and first optical writing unit (3) similar to the above.
And a first developing unit (4), and a first transfer unit (8a) forming a transfer unit of the black toner (T) and a first cleaning unit (9) forming a cleaning unit of the black toner (T).
a) are arranged in order. Around the second photoreceptor (1b) on the downstream side in the transfer paper (P) moving direction, the second charger (5), the second optical writing unit (6) and the second developing A unit (7), a second transfer unit (8b) constituting a transfer unit of the white toner (TW), and a second cleaning unit (9b) constituting a cleaning unit of the white toner (TW) are sequentially arranged.

In the image forming section, first, the transfer paper
In order to print image data on (P) with black toner (T), the surface of the first photoconductor (1a) is uniformly charged by the first charger (2), and the first optical writing unit (3) Writing is performed on the uniformly charged first photoconductor (1a) based on the image data, an electrostatic latent image corresponding to the image data is formed, and the first developing device (4) performs black toner First using (T)
An electrostatic latent image corresponding to the image data on the photoconductor (1a) is visualized.

By performing the above-described processing, a black toner image corresponding to the image data is formed on the first photosensitive member (1a). Then, this black toner image is transferred to the first transfer unit (8
Transferred to transfer paper (P) by a). Then, the first photoconductor
The black toner (T) remaining on (1a) is collected by the first cleaning unit (9a).

During the transfer by the first transfer unit (8a), the black toner (T) scatters at the edge of the black toner (T) of the image.

On the other hand, the black toner scattered at the edge of the text image printed on the transfer paper (P) as described above.
In order to print the white toner (TW) for concealing (T), the surface of the second photoconductor (1b) is uniformly charged by the second charger (5), and the second optical writing unit (6 ), Writing is performed on the uniformly charged second photoconductor (1b) based on the white toner print data, an electrostatic latent image corresponding to the white toner print data is formed, and the second developer ( According to 7), the electrostatic latent image corresponding to the white toner print data on the second photoconductor (1b) is visualized using the white toner (TW).

By performing the above processing, the white toner image corresponding to the white toner print data is transferred to the second photosensitive member.
(1b). Then, the white toner image is transferred by the second transfer unit (8b) on the transfer paper (P) on which the black toner image has been printed as described above. Thereafter, the white toner (TW) remaining on the second photoconductor (1b) is collected by the second cleaning unit (9b). Further, when the transfer paper (P) passes through the fixing device (11), the transfer paper (P)
The upper toner (T) (TW) is fixed on the transfer paper (P).

At the time of the transfer by the second transfer unit (8b), the black toner by the first transfer unit (8a) is transferred onto the transfer paper (P).
The black toner (T) at the edge of the text image scattered during the transfer of (T) is hidden by the white toner (TW) transferred by the second transfer unit (8b). At this time, as described later, by setting the height in the thickness direction of the white toner (TW) substantially equal to that of the black toner (T), the boundary between the black toner (T) and the white toner (TW), that is, the text image is The scattering of the white toner (TW) at the edge portion is prevented, and the edge portion of the text image is not disturbed by the white toner (TW).

In the first and second embodiments, two examples of the monochrome image forming apparatus to which the present invention is applied have been described. However, the present invention can be applied to a monochrome image forming apparatus having a configuration other than the above. .

FIG. 3 shows a third embodiment in which the present invention is applied to a color image forming apparatus for printing a color image, and schematically shows an image forming section thereof. In addition,
In the third embodiment, portions corresponding to those in the first embodiment or the second embodiment are denoted by the same reference numerals.

This image forming apparatus uses an intermediate transfer member (12), and is an endless endless member that rotates and moves in a direction indicated by an arrow in the figure between a photosensitive member (1) and a transfer sheet (P). Intermediate transfer member (1
2) is located. Around the photoreceptor (1), in the direction of rotation thereof, a charger (13), an optical writing unit (14), a first developing device (15) containing cyan toner, and a second developing device (15) containing magenta toner. Developing device (16), third developing device (17) containing yellow toner, fourth developing device containing black toner
(18), a fifth developing device (19) containing white toner (TW), a first transfer device (20), and a cleaning unit (21) are arranged in this order, and the photoconductor (1) and the first transfer device are arranged. A part of the intermediate transfer member (12) is passed between the containers (20). In addition, the intermediate transfer member (1
Around 2), in addition to the first transfer device (20), a second transfer device
The transfer paper (P) is passed between the intermediate transfer body (12) and the second transfer unit (22). Note that the cyan toner, magenta toner, yellow toner, and black toner are collectively referred to as colored toner (T).

In the image forming section, first, a white toner (TW) is printed to prevent the colored toner (T) from scattering at the edge of the text image or to conceal the scattered colored toner (T). Then, the surface of the photoconductor (1) is uniformly charged by the charger (13), and writing is performed on the uniformly charged photoconductor (1) based on the white toner print data by the optical writing unit (14). Then, an electrostatic latent image corresponding to the white toner print data is formed, and the fifth developer (19) uses the white toner (TW) to correspond to the white toner print data on the photoconductor (1). The electrostatic latent image is visualized. As a result, a white toner image corresponding to the white toner print data is formed on the photoreceptor (1), and the white toner image is transferred to the intermediate transfer body (12) by the first transfer unit (20). As a result, a white toner image corresponding to the white toner print data is printed on the intermediate transfer body (12). Then, the white toner (TW) remaining on the photoconductor (1) is collected by the cleaning unit (21).

Next, in order to print the cyan toner, the surface of the photosensitive member (1) is uniformly charged by the charger (13), and the photosensitive member uniformly charged by the optical writing unit (14).
(1) On the basis of the cyan toner image data, writing is performed, an electrostatic latent image corresponding to the cyan toner image data is formed, and the first developing device (15) uses the photosensitive member ( 1) An electrostatic latent image corresponding to the above cyan toner image data is visualized. As a result, a cyan toner image corresponding to the cyan toner image data is formed on the photoconductor (1), and the cyan toner image is printed by the first transfer unit (20) with the white toner (TW) as described above. The cyan toner remaining on the photoreceptor (1) is transferred by being superimposed on the intermediate transfer body (12) after the completion of the above operation, and is collected by the cleaning unit (21). Thereafter, the same operation is repeated, and a magenta toner image corresponding to the magenta toner image data, a yellow toner image corresponding to the yellow toner image data, and a black toner corresponding to the black toner image data are formed on the intermediate transfer member (12). The images are printed one on top of the other. As a result, an image is printed on the intermediate transfer member (12) using the white toner (TW) and the four colored toners (T).

When the five color toners (T) and (TW) are transferred onto the intermediate transfer member (12) as described above, these toners (T)
(TW) is transferred to the transfer paper (P) by the second transfer device (22). Then, the toner (T) (TW) on the transfer paper (P) is fixed to the transfer paper (P) by passing the transfer paper (P) through the fixing device (11).

When the color toner (T) is transferred onto the intermediate transfer body (12) by the first transfer unit (20) as described above, the white toner (TW) is already printed adjacent to the edge of the text image. Therefore, scattering of the color toner (T) is prevented.
Even if the colored toner (T) scatters on the white toner (TW), the first printed white toner (TW) is on the lowermost layer on the intermediate transfer body (12), and the transfer paper ( When printed on (P), the colored toner scatters because it is on the top layer.
(T) is concealed by the white toner (TW). Further, when the toner image on the intermediate transfer body (12) is transferred to the transfer paper (P) as described above, similarly to the first embodiment, the toner image adjacent to the edge of the color toner (T) of the text image is transferred. White toner (T
W), the color toner (T) and the white toner (TW) have substantially the same height in the thickness direction as described below, so that
The scattering of the colored toner (T) and the white toner (TW) at the boundary between the colored toner (T) and the white toner (TW), that is, at the edge of the text image is prevented.

In the third embodiment, one example of the color image forming apparatus to which the present invention is applied has been described.
The present invention can be applied to a color image forming apparatus having a configuration other than the above.

In the above-described image forming apparatus, printing of white toner is performed, for example, as follows.

First, image area separation is performed based on the input image data. If the area adjacent to the image determined to be a text part is the ground color of the transfer paper (the background area where nothing is printed). The white toner is printed in a predetermined area of the adjacent area. However, even if the adjacent area of the text image is the ground color of the transfer paper, the color difference ΔE
Is not large, the white toner is not printed. For example, when the color difference ΔE is less than 15, white toner is printed, and when the color difference ΔE is 15 or more, white toner is printed.

The area where the white toner is to be printed in the adjacent area between the text image and the ground color portion of the transfer paper is calculated by the following equation (100) when the image resolution is D (dpi), for example. This is an area corresponding to the number of pixels of the value N obtained by rounding up the decimal point of the value X. X = 50 ° (25400 ° D) (100) However, if there is colored print data within the number of pixels corresponding to the value N obtained as described above, only the area where there is no colored print data is white. Print toner. After printing the color toner, finally, the white toner is printed. Further, the height of the white toner in the thickness direction is substantially equal to the height of the adjacent color toner in the thickness direction.

The particle size of the white toner is smaller than the particle size of the color toner and is not more than 5 μm. Further, the white toner is manufactured by a polymerization method. Further, the resin component of the white toner is styrene acrylic.

FIG. 4 shows an outline of the processing of the image processing section in the image forming apparatus of the third embodiment. The image processing unit processes the input image data and outputs the processed image data to the image forming unit. For example, when used as a copying machine, the image data is input from a solid-state image sensor such as a CCD sensor of a document reading device (not shown), and when used as a printer, external data connected to the image forming apparatus. From a personal computer or the like.

Next, image processing in the image processing section, particularly generation of white toner print data, will be described with reference to FIG.

The image data input to the image processing unit is converted into a text image area and a photographic image by an area separation unit in order to improve the reproducibility of an area such as a black character, a color character or a figure in an original in which characters and photographs are mixed. An area is extracted and separated into these two image areas. For the area determined to be a text image in the area separation unit,
It is determined whether the area adjacent to the edge of the image area is the color of the transfer paper, that is, whether the area of the transfer paper is the ground color where nothing is printed. The calculation of the color difference ΔE of the toner is performed. If the color difference ΔE is less than 15, white toner print data is created in which a predetermined area at the edge of the text image is a white toner print area, and thereafter, normal image processing is performed on the image data. In other cases, white print data is not created, and normal image processing is performed on the image data.

In the case of a color image determined to be a text image, black generation processing for generating a Bk signal from the C, M, and Y signals based on the spectral characteristics of each color material is performed. After that, the enhancement amount of the high frequency band is increased by the sharpness enhancement processing in the spatial filter processing unit. After that, in the output gradation correction section and the halftone generation gradation reproduction processing section, binarization or multi-value processing is performed on a high-resolution screen suitable for reproduction of a high frequency band.

On the other hand, the same black generation processing as described above is performed on the color image area determined to be a photographic image, and thereafter, a low-pass filter processing suitable for the photographic image is performed in the spatial filter processing unit, and smoothing is performed. Processing is performed so as to enable accurate image reproduction. After that, an output gradation correction unit,
In the halftone generation tone reproduction processing section, binarization or multi-value processing is performed on a screen that emphasizes tone reproduction.

After such image processing is performed, C,
The print data of M, Y, Bk, W is sent to the image processing unit,
The printing operation as described above is performed.

The image processing method for a color image has been described above. In the case of a monochrome image, the black generation processing is omitted, and the other points are the same as above.

Next, the white toner printing area will be described with reference to FIGS.

FIG. 5A shows a text image made of colored toner and the colored toner (T) scattered at the edge thereof, and FIG. 5B shows the text image and white toner (TW) printed on the edge thereof. Is shown. FIG. 6 shows a text image made of colored toner and another colored printing portion printed adjacent to the edge portion thereof.

As shown in FIG. 5A, generally, the area where the toner scatters at the edge of the image is about 50 μm regardless of the image resolution. Therefore, at the edge of the text image, the above equation (1)
5B, the area corresponding to the number of pixels of the value N obtained based on the white toner printing area is printed as shown in FIG. 5B. T) can be hidden.

For example, when the resolution is 1200 dpi,
In the above expression (100), X is 2.36, and N obtained by rounding up the decimal point is 3. Thus, three pixels from the edge of the text image are set as the white toner print area. However,
Depending on the image data, as shown in FIG. 6, there is a case where a colored print portion of another colored print data exists within three pixels from the edge portion of the text image. In the case of FIG. 6, there is another colored print portion at a position separated by two pixels from the edge of the text image. In such a case, when the white toner is printed on the entire white toner print area for three pixels, a part of another original color print portion is hidden by the white toner. Therefore, in such a case, as shown in FIG. 6, the white toner is printed only in the area of two pixels where there is no other color printing part in the white toner print area of three pixels, and Some other colored printing parts are not hidden.

FIG. 7 shows a cross section perpendicular to the transfer paper (P) in FIG. 5B.

Next, referring to FIG. 7 and FIG.
The printing order of the white toner will be described.

In the second embodiment, the transfer paper
After printing the colored toner (T) on (P), the white toner (T
W) is printed. Therefore, as shown in FIG. 5B and FIG. 7, the colored toner (T) scattered during the transfer of the colored toner (T) can be covered by the white toner (TW) to be printed last.

However, after forming the color toner image corresponding to the image data and the white toner image at the edge of the text image on the surface of the photoreceptor (1) as in the first embodiment, the color toner image is formed. And white toner image at once on transfer paper
(P) You may make it print.

Next, the color difference between the white toner (TW) and the transfer paper (P) will be described.

When the color difference between the transfer paper (P) and the white toner (TW) is large, when the white toner (TW) is printed on the edge of the text image, the white toner (TW) printed on the transfer paper (P) is printed.
W) is conspicuous, and instead of increasing the resolution, the image quality may be degraded. Therefore, if the color difference between the transfer paper (P) and the white toner (TW) is 15 or more, it is easy to identify the colors of both, so that printing of the white toner (TW) is not performed, and the color difference is reduced. If less than 15, transfer paper
Since the color difference between (P) and the white toner (TW) is hardly distinguishable, white toner (TW) is printed on the edge portion of the text image to perform processing for improving the resolution. By doing so, the image quality can be more efficiently improved.

The color difference ΔE between the two colors is obtained using the brightness L * and the hues a * and b * of each color as follows.

When each of the two colors is measured by a colorimeter, three values of color brightness L * and hues a * and b * are calculated. The color difference between the two colors is the difference ΔL *, Δ between L *, a *, and b * of each color.
It is calculated by the following equation (101) using a * and Δb *.

ΔE = (ΔL * ² + Δa * ² + Δb * ² ) ^1/2 (101) In the case of the image forming apparatus, L *, a of white toner (TW)
* And b * are determined in advance and the transfer paper to be printed
The color (P) is measured before printing, and its L *, a *, and b * are obtained. And the difference ΔL *, Δa *
And Δb * are calculated, and the color difference ΔE is calculated using the above equation (101).

Next, referring to FIGS. 8, 9 and 10, the heights of the color toner (T) and the white toner (TW) in the thickness direction will be described.

FIGS. 8 (a) and 9 (a) show the color toner (T) and white toner (TW) before fixing, which have been transferred to the transfer paper (P). b) Color toner (T) and white toner after fixing using pressure (contact) fixing device
(TW). 8 shows the case where the height of the color toner (T) and the white toner (TW) transferred to the transfer paper (P) are different, and FIG. 9 shows the case where the heights are almost equal.

As shown in FIG. 8A, when the height of the color toner (T) and the height of the white toner (TW) are different from each other, fixing is performed using a pressure fixing device. As shown in the figure, the higher toner (color toner (T)) covers the lower toner (white toner (TW)), and the image is disturbed in portions having different heights, and the image quality is degraded. For this reason, as shown in FIG. 9A, it is desirable that the height of the white toner (TW) transferred to the transfer paper (P) is substantially equal to the height of the color toner (T).
Since the height of the color toner (T) varies depending on the number of colors, that is, the number of the color toners (T) to be superimposed, the height of the white toner (T) is changed accordingly. When the height of the color toner (T) is substantially equal to the height of the white toner (TW), even if the fixing is performed using a pressure fixing device, FIG.
As shown in (b), no movement occurs between the toners (T) and (TW).

FIG. 10 shows a state in which the color toner (T) and the white toner (TW) transferred to the transfer paper (P) are heat-fixed in a non-contact manner, and FIG. FIG. 3B shows a case where the height of the white toner (TW) is different from the height of the white toner (TW), and FIG.

As shown in FIG. 9A, when the height of the color toner (T) and the height of the white toner (TW) are different, the heat transfer rate at the time of heating and fixing is the same for both toners (T) and (TW). In some cases, sufficient fixing strength cannot be secured. On the other hand, as shown in FIG. 9 (b), when the height of the color toner (T) and the height of the white toner (TW) are substantially equal, the heat transfer rate at the time of heating and fixing is the same for both toners (T). (TW), so that sufficient fixing strength can be secured.

Next, referring to FIG. 11, the color toner (T)
And the particle size of the white toner (TW) will be described.

FIG. 11 shows the colored toner (T) scattered at the edge of the text image and the white toner (TW) printed by one layer to conceal it.
(a) shows the case where the particle size of the white toner (TW) is substantially equal to the particle size of the color toner (T), and (b) shows the case where the particle size of the white toner (TW) is the particle size of the color toner (TW). It shows the case where it is smaller.

FIG. 11 shows that the smaller the particle size of the white toner (TW), the larger the concealment ratio of the color toner (T).
If white toner (TW) is printed in multiple layers, the white toner
Regardless of the particle size of (TW), the color toner (T) can be hidden, but it is desirable to adjust the height of the white toner (TW) to the height of the color toner (T) as described above. Therefore, it is desirable that the color toner (T) can be efficiently concealed by the white toner (TW) having a layer as thin as possible, and it is understood that a smaller particle size of the white toner (TW) is advantageous for that purpose.
Currently, the color toner (T) generally has a particle size of about 10 to 6 μm, so that the white toner (TW) has a particle size of 5 μm or less is more effective. Generally, it is said that it is difficult to handle a toner having a small particle size of 5 μm or less at the time of development. However, this is a case where four color toners are handled at a time, and only one color is consumed. Since the amount of the white toner is small, the burden is much less than when the colored toner is handled. Also,
Since only the white toner reduces the particle size, there is no significant cost increase.

Next, a method for producing a white toner will be described.

The method for producing the toner is roughly classified into a polymerization method and a pulverization method. The pulverization method is a method in which carbon, a resin binder, and other additives are hot-kneaded, cooled, and then crushed, finely crushed, and classified to obtain a toner. However, this method is not suitable for reducing the particle size because the method for pulverizing is pulverization, and currently, the limit is about 6 μm.
On the other hand, the polymerization method is a method for producing a toner by polymerizing while dispersing a colorant or an additive and a monomer in an aqueous medium.
According to this method, the shape of the toner is spherical and the particle size can be reduced, and a toner having a small particle size of 5 μm or less can be manufactured.

Next, the material of the white toner (TW) will be described.

As base materials of the toner, there are styrene acrylic type and polyester type. Generally, polyester-based resins are used when aiming at image quality with high color reproducibility, such as color images, because the transparency of the resin is high. On the other hand, since styrene acrylic is milky white, the permeability is reduced. Since the white toner is used for concealing the scattered colored toner, it is preferable that the white toner has an effect of preventing the transmission of the undercolor. In other words, a styrene acrylic material is suitable as a base material for the shell.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part of an image forming apparatus according to a first exemplary embodiment of the present invention.

FIG. 2 is a configuration diagram of a main part of an image forming apparatus according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a main part of an image forming apparatus according to a third embodiment of the present invention.

FIG. 4 is a flowchart illustrating an example of a process in an image processing unit of the image forming apparatus in FIG. 3;

FIG. 5 is an explanatory diagram illustrating a white toner printing area at an edge of a text image.

FIG. 6 is an explanatory diagram illustrating a text image, a colored printing portion adjacent to the text image, and a white toner printing portion therebetween.

FIG. 7 is an explanatory diagram illustrating a color toner printed on transfer paper and a white toner printed thereafter.

FIG. 8 is an explanatory diagram illustrating a state of both toners before fixing and a state of both toners after pressure fixing when the heights of the color toner and the white toner in the thickness direction are different.

FIG. 9 is an explanatory diagram illustrating a state of both toners before fixing and a state of both toners after pressure fixing when the heights of the color toner and the white toner in the thickness direction are substantially equal.

FIG. 10 is an explanatory diagram illustrating a color toner and a white toner before fixing, and a state of both toners after heat fixing.

FIG. 11 is an explanatory diagram showing a text image, colored toner particles scattered at an edge portion thereof, and white toner particles printed for concealing the colored toner;

[Explanation of symbols]

 (1) (1a) (1b) Photoconductor (2) (5) (13) Charger (3) (6) (14) Optical writing unit (4) (7) (15) (16) (17) ( 18) (19) Developing unit (8) (8a) (8b) (20) (22) Transfer unit (12) Intermediate transfer body (P) Transfer paper (T) Colored toner (TW) White toner

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Claims (10)

[Claims] An electrostatic latent image is formed by irradiating a charged electrostatic latent image carrier surface with light by an optical writing means,
A colored toner is supplied to the electrostatic latent image by a developing bias applied between the electrostatic latent image carrier and the developing means to visualize the electrostatic latent image, and the colored toner on the surface of the electrostatic latent image carrier is transferred to a transfer paper or an intermediate transfer member. In an electrophotographic image forming apparatus that forms a color image or a monochrome image by transferring the image to an area, the image area is separated based on the input image data, and the area adjacent to the image determined to be a text portion is transferred. An image forming apparatus, wherein a white toner is printed in a predetermined area of the adjacent area when the ground color of paper is used. 2. The image forming apparatus according to claim 1, wherein an area where white toner is to be printed in the adjacent area is a pixel number of a value N obtained by rounding up a decimal part of a value X calculated by the following equation when an image resolution is D (dpi). 2. An area corresponding to the following:
Image forming apparatus. X = 50 ° (25400 ° D) 3. The image forming apparatus according to claim 2, wherein when there is color print data within the number of pixels corresponding to the value N obtained by the method according to claim 2, white toner is printed only in an area where there is no color print data. . 4. The image forming apparatus according to claim 1, wherein a white toner is printed after the color toner is printed on the transfer paper or the intermediate transfer body. 5. The method according to claim 1, wherein a white toner is printed in a predetermined area of the adjacent area when the color difference ΔE between the transfer paper and the white toner is less than 15, and the white toner is not printed when the color difference ΔE is 15 or more. The image forming apparatus according to claim 1. 6. The apparatus according to claim 1, wherein the height in the thickness direction of the white toner printed on the predetermined area of the adjacent portion is substantially equal to the height in the thickness direction of the color toner of the adjacent image. The image forming apparatus according to any one of the preceding claims. 7. The image forming apparatus according to claim 1, wherein the particle size of the white toner is smaller than the particle size of the color toner. 8. The image forming apparatus according to claim 7, wherein the particle size of the white toner is 5 μm or less. 9. The image forming apparatus according to claim 8, wherein the white toner is produced by a polymerization method. 10. The image forming apparatus according to claim 1, wherein the resin component of the white toner is styrene acrylic.