JP2002304035A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus for preventing such a sensor of incompatibility that an image on the opposite side is seen through the paper, the images on both sides are seen in an overlaid state, and also, the hue of the image is changed when the images are formed on both sides by a both-side image forming apparatus. SOLUTION: A means for forming a surface side image and a means for forming a backside image are constituted of a means for forming a color toner image by color toner and a means for forming a white toner image by white toner, and the white toner image is formed on the surface side or rear side of a transfer material as an under layer for the color toner image, and in the case of forming the images on both sides of the transfer material, the quantity of the sticking white toner in an area where the area of the surface side image and the area of the rear side image overlap each other is made differ from that in an area where the area of the surface side image and the area of the backside image never overlap each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to copying in which a charging means, an image writing means and a developing means are arranged around an image carrier to transfer and fix a toner image formed on the image carrier onto a transfer material. More particularly, the present invention relates to an image forming apparatus that forms an image on both sides of a transfer material, such as a machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art Conventionally, in double-sided image formation, an image on one side formed on an image carrier is transferred and fixed on a transfer material, and this is temporarily stored in a two-sided reversing transport device, and is again returned to the image carrier. A method has been adopted in which a transfer material is fed from a double-sided reversing conveyance device at the same time as an image formed thereon, and an image on the other surface is transferred and fixed onto the transfer material.

On the other hand, conventionally, as a method of forming a multi-color image, an image carrier having the same number of colors as the required image is provided, and charging means, image writing means, and developing means are provided around the image carrier. A device in which a single-color toner image formed on each image carrier is superimposed to form a color image, or charging, image exposure (image writing), and development for each color are repeated by rotating one image forming body a plurality of times. A device for forming a color image superimposed on an image carrier, and repeating charging, image exposure (image writing) and development for each color on one image carrier,
2. Description of the Related Art An apparatus for forming a superimposed color image on an image carrier during one rotation of the image carrier is known. Fixing and double-sided color image formation by batch fixing are performed. Of course, using these image forming apparatuses, double-sided image formation using only a single color monochrome image is also performed.

[0004]

However, in the double-sided image forming apparatus which performs two-sided fixing using the above-described color image forming apparatus and two-sided color image formation by batch fixing using the above-described reversal conveyance apparatus, If thin paper or highly transparent paper is used as the material, the image on the opposite side will be transparent when output with double-sided copying, and the images on both sides will appear overlapping, or the color of the image will change, There is a problem that a sense of incongruity occurs.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and provides an image forming apparatus for forming a double-sided image when forming a double-sided image.
It is an object of the present invention to provide an image forming apparatus that prevents an uncomfortable feeling that an image on the opposite side is transmitted and the images on both sides appear to be overlapped or the color of the image is changed.

[0006]

An object of the present invention is to provide an image forming apparatus comprising: means for forming a front surface image on the front surface of a transfer material; and means for forming a back surface image on the back surface of the transfer material. The means for forming and the means for forming the back side image are constituted by means for forming a color toner image by color toner and means for forming a white toner image by white toner, and are formed on the front surface or the back surface of the transfer material. A white toner image is formed as a lower layer of the color toner image, and when images are formed on both surfaces of the transfer material, an area where the area of the front image and the area of the rear image overlap, This is achieved by an image forming apparatus (first invention), wherein the amount of the attached white toner is changed between a region and a region where the back surface image does not overlap.

The object of the present invention is to provide an image forming apparatus having means for forming a front image on the front surface of a transfer material and means for forming a back image on the back surface of the transfer material. A means for forming a color toner image using a color toner and a means for forming a white toner image using a white toner, wherein the means for forming the backside image includes a white toner image on the front surface or the back surface of the transfer material. Formed as a lower layer of the color toner image, in the case of forming an image on both sides of the transfer material, in a region where the area of the front image and the area of the back image do not overlap, the front or back of the transfer material An image characterized in that the amount of adhesion of the white toner is changed between a region having an image on one of the surfaces and a region having no image on either the front surface or the back surface of the transfer material. It is accomplished by forming device (second invention).

The object of the present invention is to provide an image forming apparatus for forming a color image by superimposing a white toner image of a white toner and a color toner image of a color toner on a transfer material. This is achieved by an image forming apparatus (third invention) in which a toner image is formed as a lower layer of a color toner image, and the white toner contains a fluorescent whitening agent.

[0009]

Embodiments of the present invention will be described below. Note that the description in this column does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope. In the following description of the embodiment, the surface of the transfer material supported and conveyed by the intermediate transfer member, the surface on the side facing the image carrier is the front surface, and the other surface, that is, the surface on the side facing the intermediate transfer member is the back surface. That is, an image transferred to the front surface of the transfer material is called a front image, and an image transferred to the back surface of the transfer material is called a back image.

An image forming process and each mechanism of an embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of a double-sided image forming apparatus according to the present invention, FIG. 2 is a diagram showing an example of a document image reading unit, and FIG. FIG. 4 is a block diagram of an image processing system. FIG. 4 is a diagram showing an area where white toner is used. FIG. 5 is a diagram showing the formation of a white toner image for preventing discomfort due to an image on the opposite surface during double-sided image formation. FIG. 6 is a diagram illustrating a first example of a state, and FIG. 6 is a diagram illustrating a second example of a state of forming a white toner image for preventing discomfort due to an image on the opposite surface during double-sided image formation.

According to FIGS. 2 to 4, as shown in FIG. 2, a document image reading device 500 as document image reading means is provided.
Are provided with a reading device main body 501, a document storage tray 505 for storing the document D, a document sending roller 502, a transparent plate 503 made of, for example, a glass member, a document conveying roller 504, a document discharge plate 506, and a transparent plate 503 interposed therebetween. It is composed of linear original image reading sensors PS1 and PS2 using, for example, a solid-state image sensor (CCD sensor) for reading color original images on both sides of the original D from above and below, and is incorporated in an external device or a color image forming apparatus described later. Is connected to the control unit by the signal line.

When the original D sent by the original sending roller 502 passes through the transparent plate 503, the original D is converted to a single-sided original by original image reading sensors PS1 and PS2 provided above and below the transparent plate 503. Discrimination as to whether the document is a double-sided document (single-sided or double-sided) and reading of image data on both sides of the document D are performed. Depending on whether the document is a single-sided document or a double-sided document, image formation on only one side or double-sided image is performed in an image forming apparatus described later.

In the present embodiment, one-sided and two-sided discrimination and image data reading are performed by one set of upper and lower sensors. However, a plurality of sensors corresponding to image data reading and one-sided and two-sided discrimination may be provided. For example, image data may be read after a single-sided or double-sided discrimination is performed using a plurality of corresponding sensors. Original image reading sensor P
Image data of one bundle of originals PS is read by S1 or PS2, and stored in the RAM of the storage unit of the image forming apparatus main body through a control unit (not shown).

As shown in FIG. 3, an original image is read by an image reading means using a solid-state image pickup device such as the above-mentioned CCD (F1), and the read original image is amplified by the output from the CCD. Analog image signal is 8 ~
A / D conversion is performed on a 10-bit digital signal, and shading correction and subsequent image processing (1) such as color space conversion, logarithmic conversion, black generation, and color correction are performed. The image data may be read from the stored memory and subjected to the same processing.

The image data obtained in the image processing (1) is
Image data (F) for yellow (Y), magenta (M), cyan (C), and black (K) based on the image determination result (F3) as to whether the image is a halftone image or a character image.
5) is created.

The obtained image data (F5) is subjected to γ correction for the toner of each color (F6), MTF correction (F7), and PWM modulation (F8). The image data of each color subjected to the PWM modulation is subjected to image exposure on the photosensitive drum 10 by a Y, M, C and K exposure optical system 12 for forming Y, M, C and K color toner images. Image writing) is performed (F9).

In the present embodiment, the image data obtained in the image processing (1) is converted into an intermediate image such as a photograph or picture by checking the density distribution of the data and the density difference between adjacent dots. It is determined whether the image is a toned image or a character image such as a character or a line drawing (F3). Further, the use area of the white toner is determined based on the image discrimination (F3) such as the halftone image and the character image (F13), and the white (W) toner image forming W is formed based on the use area determination of the white toner. The image exposure (image writing) on the photosensitive drum 10 is performed by the exposure optical system 12 (F14). As will be described in detail later, image exposure (image writing) on the photosensitive drum 10 is performed on the use area of the white toner by the exposure optical system 12 of W, and the recording paper as the transfer material shown in FIG. A white toner image is formed on the area where the white toner is used on P.

According to FIG. 1, the color image forming apparatus shown in FIG. 1 is a tandem type color image forming apparatus using an intermediate transfer member, and an intermediate transfer belt 14 which is an intermediate transfer member.
A five-color image formation consisting of white (W), black (K), cyan (C), magenta (M), and yellow (Y) is formed on the peripheral edge of a from the upstream side in the rotation direction of the intermediate transfer belt 14a. Unit 100, which is an image forming process unit (a unit for forming a front surface image on the front surface of the transfer material or a unit for forming a back surface image on the back surface of the transfer material), is provided with white (W) as necessary. In the process unit 100), a white toner image (white toner image) using white toner is formed, and further, K, C, M, and Y
Process unit 100 forms color toner images of K, C, M, and Y color toner images on a white toner image formed as needed, and each toner image is an intermediate transfer member as an intermediate transfer member. After being transferred onto the recording paper P, which is a transfer material conveyed on the belt 14a, the charge removing electrode 1
The sheet is separated from the intermediate transfer belt 14a by 4m, is conveyed to the fixing device 17, is fixed by the fixing device 17, and is discharged outside the apparatus. The K, C, M, and Y process units 100 are units for forming a color toner image, and the W process unit 100 is a white unit for preventing a feeling of strangeness due to transmission of the color toner image formed on the opposite surface of the transfer material. (W) means for forming a toner image (white toner image).

Photosensitive drums 1 each serving as an image carrier
0, a scorotron charger 11 as a charging unit, an exposure optical system 12 as an image writing unit, and a developing unit 13 as a developing unit
The five process units 100 of W, K, C, M, and Y, each including the photoconductor cleaning device 19 serving as an image carrier cleaning unit, have a common structure, and only one of them will be described.

The photoreceptor drum 10 as an image carrier has a photoconductive layer of a conductive layer and an organic photoconductive layer (OPC) formed on the outer periphery of a cylindrical base.

The photosensitive drum 10 is rotated clockwise as indicated by an arrow with the conductive layer grounded by power from a driving source (not shown) or driven by the intermediate transfer belt 14a.

Reference numeral 11 denotes a scorotron charger as a charging means, which is attached to the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10 so as to face and be close to the photosensitive drum 10.
Same polarity as toner (minus polarity in this embodiment)
A uniform potential is applied to the photosensitive drum 10 by the corona discharge of

Reference numeral 12 denotes W, K, C,
An exposure optical system as an image writing unit that performs M and Y image exposure (image writing), and is a scanning optical system that performs scanning in parallel with the rotation axis of the photosensitive drum 10 using, for example, a polygon mirror. A latent image is formed on the uniformly charged photosensitive drum 10 by performing image exposure (image writing) by the exposure optical system 12.

A developing device as a developing means is provided around the periphery of the photosensitive drum 10 with a built-in one-component conductive toner charged negatively (negative polarity) or a two-component developer composed of a conductive toner and a magnetic carrier. 13, a developing sleeve 1 having a built-in magnet body and rotating while holding a developer.
Reverse development is performed by 3a.

A one-component developer consisting only of toner or a two-component developer obtained by mixing toner and a carrier having ferrite as a core and an insulating resin coated around the core is provided on the developing sleeve 13a in a range of 0.1 to 0.1. 6mm
And transported to the developing zone. White (W) for preventing discomfort of the image on the front side of the transfer material (surface image of the transfer material) due to transmission of the color toner image (for example, the color toner image of the back surface image) formed on the opposite surface of the transfer material. The white toner for forming the toner image (white toner image) can be produced in the same manner as the Y, M, and C toners.
O _2, ZnO, those with white pigment incorporated therein such as MgO is used.

The gap between the developing sleeve 13a and the photosensitive drum 10 in the developing area is larger than the layer thickness of the developer.
As 2～1.0Mm, applies an AC bias voltage obtained by superposing an AC voltage V _AC to a DC voltage V _DC between the developing sleeve 13a and the photosensitive drum 10. Since charging of the toner is a DC voltage V _DC with the same polarity (negative polarity), the toner given the opportunity to leave from the carrier by the AC voltage V _AC, the high absolute value of the potential from the DC voltage V _DC V
_The toner does not adhere to the _H portion, and the toner amount corresponding to the potential difference adheres to the _VL portion where the absolute value of the potential is low, and is visualized (reversal development). Further, the developing sleeve 13a and the photosensitive drum 1
Between 0 and 0, only the DC voltage _VDC may be applied. The development may be contact development.

A photoconductor cleaning device 19, which is an image carrier cleaning means, is provided downstream of the transfer position of the toner image on the photoconductor drum 10 onto the recording paper P in the rotation direction of the photoconductor drum 10, and is provided for cleaning. The transfer residual toner on the photosensitive drum 10 is cleaned by a blade (no symbol).

The intermediate transfer belt 14a, which is a belt-shaped intermediate transfer member in which five process units 100 of W, K, C, M and Y face in parallel, has a volume resistivity of 10 ¹⁰ -1.
It is an endless belt having a resistance of 0 ¹⁵ Ω · cm and a surface resistivity of 10 ¹⁰ to 10 ¹⁵ Ω / □. For example, engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, and nylon alloy Conductive material dispersed in the thickness of 0.1 to
This is a seamless belt having a two-layer structure in which a 1.0 mm semiconductive film substrate is coated with a fluorine coating having a thickness of 5 to 50 μm, preferably as a toner filming preventing layer. In addition, as the base of the intermediate transfer belt 14a, a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber or urethane rubber or the like can be used. The intermediate transfer belt 14a is
It is stretched around a drive roller 14d, a driven roller 14e, a tension roller 14i, and a fixed roller 14k. During image formation, the drive roller 14d is rotated by a drive motor (not shown), and a transfer position for each color is formed. Then, the intermediate transfer belt 14a is pressed against the photosensitive drum 10 by the transfer roller 14c, and the intermediate transfer belt 14a is rotated in the direction indicated by the arrow in the figure.

A transfer roller 14c, which is a transfer means for W, K, C, M and Y, is provided to face each photosensitive drum 10 with the intermediate transfer belt 14a interposed therebetween. Each transfer area (no reference numeral) is formed between the transfer area and the body drum 10. A DC voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied to each transfer roller 14c, and a transfer electric field is formed in a transfer area, thereby forming a W photosensitive drum as required. The toner image of W on 10 and the toner images of K, C, M and Y on the photosensitive drum 10 are transferred onto the recording paper P.

The static eliminator 14n, which is a means for neutralizing W, K, C, M and Y, is preferably constituted by a corona discharger, and neutralizes the intermediate transfer belt 14a charged by the transfer roller 14c.

Upon start of image recording, a photosensitive drum driving motor (not shown) is started to rotate the photosensitive drum 10 of the white (W) process unit 100 in the direction shown by the arrow in FIG. The application of a potential to the W photosensitive drum 10 is started by the charging action.

After an electric potential is applied to the W photosensitive drum 10, the W exposure optical system 12 starts image writing by a color signal for white toner, that is, an electric signal corresponding to W image data, and An electrostatic latent image corresponding to the W image of the original image is formed on the surface of the photosensitive drum 10.

The W latent image is subjected to reversal development in a contact or non-contact state by a W developing device 13 and the W toner on the W photosensitive drum 10 according to the rotation of the W photosensitive drum 10. A white toner image is formed.

On the other hand, with the formation of the white toner image on the photosensitive drum 10 of W, the recording paper P as the transfer material is sent out from the paper feed cassette 15 as the transfer material storage means by the feed roller 15a, and is conveyed. The toner is conveyed to a timing roller 16 as a transfer material feeding unit through a roller 15b, and the timing roller 16 is driven to synchronize with a white toner image formed on the photosensitive drum 10 of W and transfer the image to a transfer area (unsigned). ).

A W toner image (white toner image) composed of white toner formed on the W photoreceptor drum 10 is transferred onto the recording paper P by the W transfer roller 14c in the W transfer area (no symbol). Transferred to the surface.

Next, the recording paper P is synchronized with the K toner image, and the black (K) process unit 100 causes
The K toner image corresponding to the K image data based on the first color signal formed on the photosensitive drum 10 is transferred by the K transfer roller 14c in the K transfer area (no sign). The toner image is formed so as to overlap the surface of the recording paper P from above the toner image.

By the same process, the C and W superimposed toner images are synchronized, and the C (C) based on the second color signal formed on the C photoconductor drum 10 by the cyan (C) process unit 100. The toner image of C corresponding to the image data of No. is formed by being superimposed on the surface of the recording paper P from the above-described toner image of W and K by the transfer roller 14c of C in the transfer area of C (no symbol). Then, the M image is formed on the M photoconductor drum 10 by the magenta (M) process unit 100 in synchronization with the superposed toner images of W, K, and C, and the M image is formed by the third color signal. An M toner image corresponding to the data is formed by being superimposed on the surface of the recording paper P from above the W, K, and C toner images by the transfer roller 14c in the M transfer area (no symbol). To W, K, C, toner images synchronized superimposition of M is taken by the process unit 100 for yellow (Y) is formed on the photosensitive drum 10 of the Y,
The Y toner image corresponding to the Y image data based on the fourth color signal is transferred onto the above-described W, K, C, and M toner images by the Y transfer roller 14c in the Y transfer area (no sign). And a superimposed toner image (a superimposed toner image of the surface image) is formed on the surface of the recording paper P by superposing the white toner image and the color toner image in that order. .

The untransferred toner remaining on the peripheral surface of each photoconductor drum 10 after the transfer is cleaned by a photoconductor cleaning device 19 as each image carrier cleaning means.

A superposed toner image (a superposed toner image of a surface image) is formed on the surface of the recording paper P by superposing a white toner image and a color toner image in that order.
m, is separated from the intermediate transfer belt 14a, is conveyed to a fixing device 17 as a fixing unit, and has a first fixing roller 17a and a second fixing roller each having a halogen lamp (no symbol) as a heating unit inside. 1
7b, the heat and the pressure are added in the nip portion N, so that the toner image of the surface image on the recording paper P is fixed. When single-sided image formation is selected in the color image forming apparatus of the present embodiment, the recording paper P after fixing is transported straight and conveyed, and is discharged to a tray (not shown) outside the apparatus through the discharge rollers 18. .

The toner remaining on the peripheral surface of the intermediate transfer belt 14a after the transfer is cleaned by an intermediate transfer body cleaning device 19a which is an intermediate transfer body cleaning means.

When the double-sided image formation is selected in the color image forming apparatus of the present embodiment, the toner image (the surface image of the surface image) is overlaid by fixing the white toner image and the color toner image on the surface in that order. The recording paper P having the superposed toner image) is switched by the transport switching lever 41 and is not transported to the transport roller 18 without being transported by the reverse transport path 4.
0 and is conveyed to the reversing conveyance roller 44 through the reversing path conveyance roller 42. The reversing transport roller 44 is configured to switch between the forward and reverse rotation directions.
Is detected, the transport switching lever 43 switches the transport path, the reverse transport roller 44 turns reverse, the recording paper P is reversed, and the timing roller 16 is again passed through the reverse path transport roller 42 of the reverse transport path 40. Transported to

K, C, M and Y process units 10
0 and a W (white) processing unit 100 for preventing the image on the front surface of the transfer material from being unnatural due to transmission of the color toner image formed on the opposite surface of the transfer material. W), the toner image of the back surface image on the photosensitive drum 10 of each color formed by using a plurality of image forming process means using the means for forming the toner image (white toner image) 10 is transferred from the timing roller 16 in synchronization with the toner image of the back surface image on the recording paper P, and is sequentially transferred onto the recording paper P conveyed on the intermediate transfer belt 14a. A superimposed toner image (a superimposed toner image of the backside image) is formed in the order of the images. The recording paper P having the superposed toner image of the fixed front image and the superposed toner image of the unfixed back image on the front and back is transported to the fixing device 17 again, and the superposed toner image of the back image is formed. Is fixed, and the recording paper P on which the front and rear sides have been fixed is straightly conveyed and discharged through a discharge roller 18 to a tray (not shown) outside the apparatus.

According to the above-described image forming method, a white toner image for preventing a sense of incongruity due to transmission of an image from the opposite surface is formed as a lower layer of the color toner image on the recording paper P as a transfer material. A toner image in which a color toner image and a white toner image are superimposed on both sides is formed. When forming a double-sided image, as shown in FIG. Layer thickness (thickness)
Is tha, for example, the layer thickness tha is 0.8 to 1.5 mg.
/ Cm ² , where the color toner image of the front side image and the color toner image of the back side image overlap each other on the front and back sides of the recording paper P, the color toner image of the front side image having a large area width The thickness (thickness) thb of the lower white toner image is equal to the thickness tha (thb = th
a) or thinner, for example 0.5-1.2 mg / cm
^A white toner image is formed with about ² (thb <tha), and the layer thickness (thickness) thc of the white toner image below the color toner image of the back image whose area width is smaller than that of the front image is calculated as The white toner image is formed with a thickness smaller than the thickness thb, for example, about 0.1 to 1.0 mg / cm ² (thc <thb), and the area of the color toner image of the front image and the area of the color toner image of the rear image are formed. The amount of the adhered white toner of the white toner image is changed between an area where the image overlaps and an area where the image does not overlap. By setting the layer thickness (thickness) thc of the white toner image as the lower layer of the color toner image of the rear surface image having a small area width to 0 (zero), a white toner image is formed only on one surface of the front surface image, The white toner image below the toner image may not be provided. Further, as shown in FIG. 5B, the same applies to the back side image as described above, and the color toner image of the back side image and the color toner image of the front side image overlap and exist on the front and back of the recording paper P, and the back side image In a portion where the area width of the color toner image is larger than the area width of the color toner image of the front image, the layer thickness (thickness) thc of the white toner image below the color toner image of the front image is changed to the thickness of the color toner image of the rear image. Thicker (thc <th) than the layer thickness (thickness) thb of the lower white toner image
b) a white toner image is formed, and the adhesion amount of the white toner image of the white toner image is determined in a region where the color toner image region of the front image and the color toner image region of the rear image overlap. To be changed. Also in this case, the layer thickness (thickness) of the white toner image as the lower layer of the color toner image on the front and back sides is usually tha, and thb = tha or tb.
A white toner image is formed with hb <tha. Further, the layer thickness (thickness) thc of the white toner image under the color toner image of the front surface image having a small area width is set to 0 (zero), and a white toner image is formed only on one surface of the rear surface image. The white toner image of the lower layer of the color toner image may not be provided.

As described above, when forming a two-sided image in the two-sided image forming apparatus, the image on the opposite side is transmitted, and the two-sided image appears to be overlapped or the color of the image is changed. Thus, it is possible to provide an image forming apparatus in which an unpleasant sensation is prevented. Further, the consumption of the white toner is small.

Further, according to the above-described image forming method, a white toner image for preventing a sense of incongruity due to transmission of an image from the opposite surface is formed as a lower layer of the color toner image on the recording paper P as a transfer material. A color toner image and a white toner image are superimposed on both sides to form a superimposed toner image. When forming a double-sided image, as shown in FIG. Is set to tha, for example, the layer thickness tha is set to 0.8 to 1.5.
mg / cm ² , a white toner image is formed, and even in a region where the color toner image region of the front image and the color toner image region of the rear image do not overlap, as shown by the dotted line in FIG. The layer thickness (thickness) is set to th on the surface of the recording paper P.
A white toner image d is formed to prevent a sense of incompatibility with the surroundings. At this time, the layer thickness (thickness) of the white toner image
thd is, for example, 0.1, which is smaller than the layer thickness tha, for example.
About 1.0 mg / cm ² (thd <tha) to form a white toner image. In a region where the color toner image region of the front image and the color toner image region of the rear image do not overlap, the recording paper P The amount of the adhered white toner is changed between an area having an image on the surface of the recording paper P and an area having no image on the surface of the recording paper P. The same applies to the back side image, and a white toner image having a layer thickness (thickness) of thd is formed on the back side of the recording paper P to prevent discomfort from the surroundings, as shown by a dashed line in FIG. To do it. At this time, the layer thickness (thickness) thd of the white toner image is set to, for example, 0.1 to 1.0 mg / cm, which is smaller than the layer thickness tha.
^A white toner image is formed with about ² (thd <tha), and an image is formed on the back surface of the recording paper P in a region where the color toner image region of the back image and the color toner image region of the front image do not overlap. The amount of the adhered white toner is changed between an area and an area having no image on the back surface of the recording paper P. Further, as shown in FIG. 6B, a white toner image of a portion where the color toner image of the back image exists is formed on the surface of the recording paper P, and a white toner image is formed only on one surface of the recording paper P. You may do so. The same applies to the case where a white toner image is formed on the back side image.
And a white toner image is formed only on one surface of the recording paper P (not shown).

As described above, when forming a two-sided image in the two-sided image forming apparatus, the image on the opposite side is transmitted, and the two-sided image appears to be overlapped or the color of the image is changed. Thus, it is possible to provide an image forming apparatus in which an unpleasant sensation is prevented. Further, the consumption of the white toner is small.

However, by providing a white toner image on the transfer material as in the above-described image forming apparatus, an effect of concealing the base color (color of the transfer material) can be obtained, but the paper (transfer) having a large color difference from the white paper can be obtained. Material),
It is difficult to completely hide that color.

In order to solve this, it is possible to form an image in the image forming apparatus described above with reference to FIG. 1 by mixing a fluorescent whitening agent described below into a white toner and using the white toner produced. This is preferable because the effect of concealing the underlying color (color of the transfer material) by the white toner image can be improved, and an image having a clear and excellent contrast can be obtained.

An image is formed by the same image forming method as described above with reference to FIG. 1, and a white toner image for preventing discomfort due to transmission of an image from the opposite surface is formed on a recording paper P as a transfer material. The layer thickness (thickness) of the white toner image, which is the lower layer of the color toner image and the lower layer of the color toner image, is set to, for example, about 0.8 to 1.5 mg / cm ^2. A color toner image and a white toner image are superimposed to form a toner image. As a white toner for forming a white (W) toner image (white toner image), as described above, Y, M, C toner and can be prepared in the same manner as the toner.
iO _2, ZnO, those with white pigment incorporated therein such as MgO is used. Examples of the fluorescent whitening agent mixed into the white toner include coumarin derivatives represented by bis-benzoxazole, triazine-phenylcoumarin and the like;
(Styryl) biphenyl derivatives and the like are used, and acrylic resin, alkyd resin, polyester, vinyl resin and the like are used as a resin material for forming the protective film,
It is preferable that about 0.5 to 5% of a fluorescent whitening agent is contained in the resin material.

As described above, when the white toner contains the fluorescent whitening agent, the effect of concealing the undercolor (color of the transfer material) by the white toner image in the above-described image formation in the image forming apparatus is increased, and the image is sharp. Further, it is possible to provide an image forming apparatus capable of obtaining an image having good contrast.

Further, it is preferable to use white toner composed of flat toner in order to improve the effect of transferability and fixability in the image forming process. The white toner composed of flat toner will be described with reference to FIG. 7 or FIG. I do. FIG. 7 is a diagram showing the shape of the white toner made of flat toner, and FIG. 8 is a diagram showing a white toner image made of flat toner on the image forming body or the transfer material.

According to FIG. 7 or FIG. 8, as described above, the base of the white toner is a mixture of a binder resin and a white pigment such as TiO ₂ , ZnO or MgO as a colorant. It is preferable that a toner in which a fluorescent whitening agent is mixed is used as a white toner, and it is more preferable that the white toner has a flat shape as shown in FIG.

As shown in FIG. 7, as a flat white toner forming a white toner image, the circle equivalent diameter d of the flat white toner when viewed from the direction in which the projected area is maximized.
Is 5 to 15 (μm), the thickness t of the flat white toner is 1 to 4 (μm), the ratio of the circle equivalent diameter d to the thickness t, and the flatness of the flat white toner represented by t / d is 0.2 or more,
It is preferably 0.7 or less, more preferably 0.4 or more and 0.5 or less. As shown in FIG. A white toner image made of flat toner is formed on the upper surface of the photosensitive drum 10 so as to be thinner and flattered, and the transferability is improved without toner disturbance, and as shown in FIG. Even on the recording paper P to which the upper color toner image is transferred, the lower flat toner, which is in close contact with the recording paper P, is thinned and flattened, and has good fixability without toner disturbance. And a superposed color toner image are formed.

As described above, by using the white toner composed of the flat toner, the unevenness of the surface of the white toner image is reduced in the image forming apparatus described above with reference to FIG. In both the image area and the non-image area formed by the white toner image, uneven gloss is reduced, and a good image is obtained. In addition, since the flat toner is thin, it is difficult to adhere to the transfer material without following the unevenness of the transfer material. However, by imparting an undercoat to the white toner image, disturbance during transfer and uneven fixing are reduced. Further, the total toner layer thickness of the white toner and the color toner is reduced, and transferability is improved.

In the above description of the image forming apparatus shown in FIG. 1, the means for forming the surface image on the surface of the transfer material and the means for forming the surface image on the surface of the transfer material have been described as the same. According to the invention, as shown in FIG. 9, a schematic configuration diagram of another example of the image forming apparatus, a unit for forming a surface image on the surface of a transfer material and a unit for forming a surface image on the surface of the transfer material are separated. , Two belt-like intermediate transfer members are provided above and below,
A plurality of the image forming process means described above with reference to FIG. 1 are arranged around each intermediate transfer body, and a color toner image for superimposing the front image and a color toner image for superimposing the back image are arranged on each intermediate transfer body. A color toner image formed and superimposed on the front surface image on one intermediate transfer member is transferred to the front surface of the transfer material by first transfer means using, for example, a corona charger, and the back surface image on the other intermediate transfer member is formed. Is transferred to the back surface of the transfer material by a second transfer unit also using a corona charger, and then the front and back sides are overlapped by a fixing unit including a pair of fixing roller members each having a heating unit inside. The present invention is also applied to an image forming apparatus having a configuration in which the combined toner images are fixed collectively.

[0056]

According to the first to fourth aspects of the present invention, the image on the opposite side of the image forming apparatus for forming a double-sided image is transmitted when the double-sided image is formed, so that the two-sided image appears to be overlapped. It is possible to provide an image forming apparatus capable of preventing an unpleasant sensation that the color of the image changes. Further, the consumption of the white toner is small.

According to the fifth aspect, by incorporating a fluorescent whitening agent into the white toner, the effect of concealing the undercolor (color of the transfer material) by the white toner image is increased, and an image having a clear and good contrast is obtained. Can be provided.

In particular, by using flat toner as the white toner, the unevenness of the surface of the white toner image is reduced, and the image area of the color toner image having the white toner image as the lower layer or the white toner is used. Gloss unevenness is reduced in both non-image areas formed by an image, and a good image is obtained. Further, since the flat toner is thin, it does not follow the unevenness of the transfer material and is difficult to adhere to it. However, by imparting an undercoat to the white toner image, disturbance during transfer and uneven fixing are reduced. Further, the total toner layer thickness of the white toner and the color toner is reduced, and transferability is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of a double-sided image forming apparatus according to the present invention.

FIG. 2 illustrates an example of a document image reading unit.

FIG. 3 is a block diagram of an image processing system.

FIG. 4 is a diagram illustrating a use area of a white toner.

FIG. 5 is a diagram illustrating a first example of a state of forming a white toner image for preventing discomfort due to an image on the opposite surface during double-sided image formation.

FIG. 6 is a diagram illustrating a second example of a state of forming a white toner image for preventing discomfort due to an image on the opposite surface during double-sided image formation.

FIG. 7 is a diagram illustrating a shape of a white toner composed of flat toner.

FIG. 8 is a diagram illustrating a white toner image formed of flat toner on an image forming body or a transfer material.

FIG. 9 is a schematic configuration diagram illustrating another example of the image forming apparatus.

[Explanation of symbols]

 Reference Signs List 10 photoconductor drum 11 scorotron charger 12 exposure optical system 13 developing device 14a intermediate transfer belt 14c transfer roller 17 fixing device 100 process unit P recording paper

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tetsu Haneda 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation F-term (reference) 2H005 AA15 AA21 EA10 2H027 DC02 DE02 DE07 DE10 EB04 EB06 EC11 EC12 ED06 FA12 FA13 2H030 AB02 AD01 AD16 BB02 BB23 BB42

Claims (7)

[Claims] 1. An image forming apparatus comprising: means for forming a front surface image on a front surface of a transfer material; and means for forming a back surface image on a back surface of the transfer material, wherein: the means for forming the front surface image; Means for forming a color toner image by a color toner and means for forming a white toner image by a white toner, wherein the white toner image is formed on the front or back surface of the transfer material by a color toner image. Formed as a lower layer, when forming images on both sides of the transfer material, the area of the front image area and the area of the back image overlap, the area of the front image and the area of the back image An image forming apparatus, wherein the amount of the adhered white toner is changed in an area where the white toner does not overlap. 2. The image forming apparatus according to claim 1, wherein the white toner image is formed on only one surface of the transfer material. 3. An image forming apparatus comprising: means for forming a front image on a front surface of a transfer material; and means for forming a back image on the back surface of the transfer material. Means for forming a color toner image by a color toner and means for forming a white toner image by a white toner, wherein the white toner image is formed on the front or back surface of the transfer material by a color toner image. Formed as a lower layer, in the case where images are formed on both surfaces of the transfer material, in a region where the region of the front image and the region of the back image do not overlap, on either the front surface or the back surface of the transfer material An image forming apparatus, wherein an amount of the white toner adhered is changed between an area having an image and an area having no image on either the front surface or the back surface of the transfer material. 4. The image forming apparatus according to claim 3, wherein the white toner image is formed only on one surface of the transfer material. 5. An image forming apparatus for forming a color image by superimposing a white toner image made of white toner and a color toner image made of color toner on a transfer material, wherein the white toner image is colored on the front surface or the back surface of the transfer material. An image forming apparatus formed as a lower layer of a toner image, wherein the white toner contains a fluorescent whitening agent. 6. The image forming apparatus according to claim 5, wherein flat toner is used as the white toner. 7. The flat toner according to claim 6, wherein the circle-equivalent diameter of the flat toner when viewed from the direction in which the projected area is maximized is d.
(Μm), and when the thickness is t (μm), the ratio of the equivalent circle diameter d to the thickness t, that is, t / d, is 0.2 to 0.7. Image forming device.