JP2002108038A - Image forming device and color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device provided with an image of good quality where glossiness is controlled by enlarging a range of color reproduction by utilizing dark and light toners. SOLUTION: In the image forming device where a toner image is formed by carrying out a repetition of developing by high concentration toner and developing by low concentration toner on a latent image formed on an image carrier by carrying out electrification and image exposure, the image forming device has a relationship between glossiness GH of the toner image by the high concentration toner and glossiness GL of the toner image by the low concentration toner on transfer material is GL>GH.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image using toner by electrophotography,
More particularly, the present invention relates to an image forming apparatus and a color image forming apparatus that develop an image by using two types of toners, a light color toner and a dark color toner, for the same color to form an image.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic method, an image forming body is uniformly charged by a charging means and then exposed to an image to form a latent image. The latent image portion is subjected to reversal development by the subsequent developing means to form a toner image. In a digital image forming apparatus, image exposure is performed by, for example, dots that have been subjected to pulse width modulation, and reversal development in which toner adheres to the dot portions is performed. The amount of toner adhering to the dot portion is determined by the area and potential state of the dot portion on the image forming body, the developing bias for the dot portion, the state of the charge of the toner, and the like.

A high-density image portion recorded on an image forming body by an image exposure means has a large number of dots per area,
The size of the dot is large and the drop in potential is large. On the other hand, in the low-density image portion, the number of dots per area is small, the size of one dot is small, and the decrease in potential is small. Thus, after development, the amount of toner adhered to the high density image portion on the image forming body is large, and the amount of toner adhered to the low density image portion is small. The difference in the density of the recorded image is expressed by the amount of toner adhering to the area of the image formed on the image forming body by development.

[0004]

However, it is difficult to form an image with good gradation with one type of toner. Particularly in a highlight portion (low-density portion), the attachment of a very small amount of toner per area is unstable due to the small size of the dot, so that image unevenness is likely to occur and it is difficult to obtain stable gradation. In the high-density portion, the toner is in an excessively toner-adhered state, and the image density is likely to be saturated, and the gradation property in a wide area is not obtained. Also, even if the dark and light toners are simply used together, the intermediate density becomes discontinuous,
It becomes unstable.

The present invention is applied to a monochrome or color image forming apparatus, and includes two kinds of toners of the same color, a light color and a dark color (for example, cyan (C), magenta (M), yellow (Y), The present invention is directed to an image forming apparatus that performs development using any of black (K), so that a light toner image and a dark toner image are formed without being shifted from each other so that a smooth gradation can be obtained. A first object of the present invention is to provide an image forming apparatus which performs reversal development using a dark toner and reversal development using a light toner for one image exposure to form an image using dark and light toners. For a monochrome or color image forming apparatus using dark and light toners, the gradation is maintained, the gloss is controlled, and a stable and good image with an appropriate gloss is obtained. It is to provide a device.

A second object of the present invention is to provide Y, M, C, K
For a color image forming apparatus in which a transparent toner and a white toner are added in addition to the four color dark and light color toners, and the image quality is further improved, the white toner sufficiently shields the base and the glossiness Is to provide a color image forming apparatus capable of stably obtaining good color images with appropriate glossiness.

[0007]

SUMMARY OF THE INVENTION A first object of the present invention is to:
A latent image formed by performing charging and image exposure on an image forming body is repeatedly subjected to development using a dark toner and development using a light toner to form a toner image. An image forming apparatus wherein the glossiness _GH of the toner image formed by the dark toner and the glossiness _GL of the toner image formed by the light toner have a relationship of _GL > _GH.
Invention).

[0008] A second object of the present invention is to form a plurality of image forming members by repeatedly performing development with dark and light toners for each color, and repeatedly performing development with a transparent toner and white color. In a color image forming apparatus that forms a toner image on a transfer material by superimposing the same, the gloss G _T of the toner image due to the transparent toner on the transfer material and the gloss G _S of the toner image due to the white toner are G _T> G color image forming apparatus, characterized in that a relation of _S (invention of claim 2) and, for each of the plurality of image forming body, dark for each color is performed by repeating the development with light toner, In a color image forming apparatus which repeatedly performs development with a transparent toner and a white color to form a formed toner image on a transfer material, the gloss G _T of the toner image by the transparent toner on the transfer material, the light toner By The toner image glossiness G _L
In between, G _T> G _L, or G _T ≒ color image forming apparatus, characterized in that a relation of G _L (invention of claim 3) and, for each of the plurality of image forming body, each color In a color image forming apparatus that repeats development with dark and light toners, repeats development with transparent toner and white color, and forms a formed toner image on a transfer material, a glossiness G _H of the toner image by the toner, the glossiness G _S of the toner image by the white toner
In between it is achieved by a color image forming apparatus characterized by a relationship of G _H> G _S (invention of claim 4).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In any of the image forming apparatuses of the present invention, a latent image is formed on an image forming body by image exposure based on image data, and the formed latent image contains dark toner of the same hue. Developing is performed by a developing device (H) and a developing device (L) containing light toner, and the same
This is an image forming apparatus in which a development region is widened by performing development using light toner, and an image with excellent gradation is formed. Since the monochrome image forming apparatus is configured to form an image using only the dark and light toners for only one color of the color image forming apparatus, a preferable small-sized image forming apparatus that forms a color image using the dark and light toners is used here. The configuration of the color image forming apparatus will be described.

(1) In the present embodiment, as shown in the cross-sectional view of FIG. 1, the dark and light toner images are superimposed on the image forming body by repeating charging, image exposure and development using dark and light toners. An image forming apparatus that forms an image together, and particularly a color image forming apparatus that forms a color image by superimposing dark and light toner images of Y, M, C, and K colors in a tandem system, and has a small shape. It is characterized by.

The color image forming apparatus shown in FIG. 1 is a tandem type color image forming apparatus using an intermediate transfer member, and a yellow (Y), magenta (M) ), Cyan (C), and black (K) are provided, and each process unit 100 forms Y, M, C, and K toner images using dark and light toners. Then, the toner image is superimposed and transferred on the transfer belt 14a,
The transferred color toner image is collectively transferred onto a recording sheet as a transfer material, fixed, and discharged outside the apparatus.

Since the four process units 100 all have a common structure, only one of them will be described. The photoconductor drum 10, which is an image forming body, has a photoconductor layer of a conductive layer and an organic photoconductor layer (OPC) formed on the outer periphery of a cylindrical substrate.

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

Reference numeral 11 denotes a scorotron charger as 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.
The photosensitive drum 1 is driven by corona discharge having the same polarity as the toner.
A uniform potential is given to 0.

Reference numeral 12 denotes an exposure optical system that performs image exposure based on image data, 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. Exposure optical system 1 on photoreceptor drum 10 uniformly charged
The latent image is formed by performing the image exposure by the method 2.

Reference numeral 13 denotes a developing device. A developing device 13 (H) containing dark toner on the upstream side in the rotation direction of the photosensitive drum 10 is
On the downstream side, a developing device 13 (L) containing light toner is arranged. A developing sleeve 13 is provided in the developing device 13 (H).
1 (H), the rotating developing sleeve 131
(H) The dark toner held above is conveyed to the opposing portion of the photosensitive drum 10. A developing bias potential V _H having the same polarity as the toner is applied to the developing sleeve 131 (H), and reversal development is performed on the latent image with the dark toner in a contact or non-contact state, preferably in a contact state. Similarly, the developing device 13
The developing bias potential _VL having the same polarity as that of the toner is also applied to the developing sleeve 131 (L) of (L), and the reversal development with the light toner is performed on the toner image of the dark toner. Although soft contact development is possible, non-contact development is desirable from the viewpoint of preventing destruction of the toner image and color mixing. It is preferable to perform non-contact development by superimposing an AC component on the applied developing bias. The developing bias potential V _H applied here has the same polarity as the developing bias potential _VL, and the relationship of | (1/2) V ₀ | <| V _H | <| V _L | <| V ₀ | Is set. This toner image is transferred onto a transfer belt 14a described later at a transfer position.
The transfer residual toner remaining on the drum after the transfer is cleaned by a cleaning device 19 that electrostatically collects the toner.

Process unit 1 for four colors of Y, M, C and K
The transfer belt 14a in which 00 is opposed in parallel has a volume resistivity of 10 ¹⁰ to 10 ¹⁵ Ω · cm and a surface resistivity of 10 ¹⁰ to 10 ¹⁵ Ω.
/ □, for example, a conductive material dispersed in engineering plastic such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, nylon alloy, etc., having a thickness of 0.1 to 1.0 mm Outside the semiconductive film substrate of
Preferably, the toner filming preventing layer has a thickness of 5 to 5
This is a seamless belt having a two-layer structure and a fluorine coating of 0 μm. In addition, as the base of the 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 can be used. Transfer belt 14a
Is stretched in contact with a driving roller 14d, a driven roller 14e, a tension roller 14k, and a backup roller 14j. At the time of image formation, the driving roller 14d is rotated by a driving motor (not shown) to rotate the driving roller 14d. At the transfer position, the transfer belt 14a is pressed against the photosensitive drum 10 by the primary transfer device 14c, and the transfer belt 14a is rotated in the direction indicated by the arrow in the drawing.

A primary transfer device 14c, which is a transfer roller for each color, is provided to face the photosensitive drum 10 for each color with the transfer belt 14a interposed therebetween, and the transfer belt 14a and the photosensitive member for each color are provided. A transfer area (no reference numeral) for each color is formed between the transfer area and the drum 10. Primary transfer unit 14 for each color
By applying a DC voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) to c, and forming a transfer electric field in the transfer area, the toner image on the photosensitive drum 10 for each color is transferred onto the transfer belt 14a. Transfer to

The static eliminator 14n, which is a static eliminator for each color, comprises:
Preferably, the primary transfer unit 1 is constituted by a corona discharger.
The transfer belt 14a charged by 4c is neutralized.

The process unit 1 of black (K) is started by starting a photoconductor drive motor (not shown) when image recording is started.
The photoconductor drum 10 is rotated in the direction indicated by the arrow in the figure, and at the same time, the application of a potential to the K photoconductor drum 10 is started by the charging action of the K scorotron charger 11.

After a potential is applied to the K photosensitive drum 10, image writing is started by the K exposure optical system 12 using a first color signal, that is, an electrical signal corresponding to K image data. K of the original image on the surface of the body drum 10
An electrostatic latent image corresponding to the image is formed.

The K latent image is subjected to reversal development in a non-contact state by a developing device 13 (H) for K dark toner, and a toner image is formed by K dark toner in accordance with the rotation of the K photosensitive drum 10. Is done. Subsequently, a developing device 13 (L) for light toner
As a result, a toner image of K light toner is formed on the previously formed toner image of K dark toner.

The K toner image formed of the dark and light toners formed on the K photoreceptor drum 10 as the image forming body by the above-described image forming process is the first toner image in the K transfer area (no sign). The image is transferred onto the transfer belt 14a by a K primary transfer device 14c as a transfer unit.

Next, the transfer belt 14a is synchronized with the C toner image, and the cyan (C) process unit 10
0 indicates that a toner image composed of C dark and light toner corresponding to C image data based on the second color signal formed on the C photoconductor drum 10 in the C transfer area (no sign). The toner image composed of the dark and light C toners is superposed on the toner image composed of the dark and light K toners by the C primary transfer device 14c as the transfer means.

By the same process, the image is synchronized with the superposed toner images of K and C, and is formed on the photosensitive drum 10 of M by the process unit 100 of magenta (M). M corresponding to the image data of
The toner image composed of the dark and light toners in the M transfer area (no symbol) is transferred from the top of the K and C toner images by the M primary transfer device 14c as the first transfer means. A toner image composed of dark and light toners is formed by being superimposed, synchronized with the superposed toner images of K, C, and M.
The toner image formed of the dark and light toners of Y corresponding to the image data of Y by the fourth color signal formed on the photosensitive drum 10 of the first color is transferred in the Y transfer area (no sign). By the Y primary transfer device 14c, a toner image composed of Y dark and light toners is superimposed on the K, C and M toner images, and the transfer belt 14a
A superimposed color toner image of K, C, M and Y is formed thereon.

The transfer residual toner remaining on the peripheral surface of the photosensitive drum 10 for each color after the transfer is cleaned by a cleaning device 19 which is a cleaning means of the image forming body for each color.

In synchronization with the formation of the superimposed color toner images on the transfer belt 14a, the recording paper P is transferred from the paper feed cassette 15 as the transfer material storage means via the timing roller 16 as the transfer material feed means to the second paper. The superimposed color toner image on the transfer belt 14a is conveyed to a transfer area (no symbol) of a secondary transfer device 14g, which is a transfer unit, and to which a DC voltage having a polarity opposite to that of the toner is applied. The images are collectively transferred onto the recording paper P.

The recording paper P on which the color toner image has been transferred is
The charge is removed by a charge removing electrode 16b, which is a separating means formed of a sawtooth electrode plate, conveyed to the fixing device 17, and heat and pressure are applied between the fixing roller 17a and the pressure roller 17b, so that the recording paper P After the toner image is fixed,
It is discharged to a tray outside the device.

The untransferred toner remaining on the peripheral surface of the transfer belt 14a after the transfer is cleaned by a cleaning device 19a which is a transfer belt cleaning means provided opposite to the driven roller 14e with the transfer belt 14a interposed therebetween. .

In the present embodiment, as will be described later in detail, the photosensitive drum 1 of the process unit 100
On the latent image portion formed by image exposure on 0, first, the developing unit 13 (H) containing the dark toner selectively performs development on a high density portion of the latent image, and then, The developing unit 13 (L) containing the light toner develops the low density portion of the latent image. Using such dark and light toners, the color reproduction range is expanded by selectively performing development using the light toner for the low-density parts, and using the dark toner for the high-density parts. By selectively performing development, the dynamic range is expanded, and a high-quality image is obtained.

In the present embodiment, Y, M,
Although the C, K, and four colors are developed with the dark and light toners, the Y, M, and C colors are developed with the dark toner only, and only K is developed with the dark and light toners. Thus, the excellent effects of the present invention can be obtained. In this case, the developing device is an image forming apparatus provided with five sets.

As described above, a small-sized image forming apparatus in which color reproduction is easily performed by enlarging a reproduction area using dark and light toners is shown in FIG.
Explained by. FIG. 2 is a cross-sectional view of a color image forming apparatus showing another embodiment having the same effect. Although the process units 100 for forming Y, M, C, and K toner images using dark and light toners are arranged in parallel as in FIG. 1, in the present embodiment, an intermediate transfer member is used. The toner image is superimposed on the transfer material without any intervention. Only the differences from FIG. 1 will be described. In the image formation, the recording paper P discharged from the paper supply cassette 15 passes through the timing roller 16 in synchronization with the toner image formation on the process unit 100, and is conveyed to the transport belt 14. Transported to

The transported recording paper P is charged to the same polarity as the toner by the paper charger 14m, and the rotating transport belt 1 is rotated.
The toner image formed of the dark and light Y toner formed on the process unit 100Y is transferred onto the recording paper P by the primary transfer unit 14c, and the process units 100M and 100C are transferred onto the recording paper P. , 100K, M, C, and K toner images formed of dark and light toners are superimposed and transferred to form a color toner image.

The recording paper P carrying the color toner image is neutralized by the separation electrode 14n, separated from the transport belt 14 and transported to the fixing device 17, and after the color toner image on the recording paper P is fixed, the recording paper P is fixed. Discharge to an external tray.

(2) FIG. 2 is an explanatory diagram showing a potential state and a toner adhering state of a high density portion and a low density portion of an electrostatic latent image.
Normally 500 to 100 depending on the scorotron charger 11
The photosensitive layer of the photosensitive drum 10 uniformly charged to a charging potential V ₀ of ₀ V is subjected to image exposure by an exposure optical system 12, and latent images of a high-density portion, a medium-density portion, and a low-density portion having different potentials Is formed. In the maximum high concentration part, the residual potential is usually several tens of volts.
It remains but drops to approximately 0V.

In Step 1, the first reversal development is performed by the developing unit 13 (H) in which the dark toner is stored and the developing bias potential V _H is applied. Since the absolute value of the developing bias potential V _H applied here is set to a potential equal to or higher than V _0/2 and lower than the potential of the latent image in the low-density part, When the latent image on the photosensitive drum 10 moves, a developing electric field is formed between the developing sleeve 131 (H) in the high-density part and the medium-density part, and the developing electric field is formed in the high-density part and the medium-density part. The first development is performed with the toner electrostatically attached. However, in the low-density portion, no developing electric field is formed between the developing sleeve 131 (H) and the high-density toner. Development bias potential V _H
Is (0.5-0.8) V _{0 with} respect to the charged potential V ₀ of the photoconductor.
It is desirable that Note that an AC bias may be superimposed on this. By doing so, the dark toner can be made to adhere to the medium-density portion, so that the adhesion boundary with the light toner can be left to a low density. As a result, it is possible to realize a gradation property having a smooth density change from a low density portion by the light toner. In addition, since the coexistence region of the dark and light toners is wide, the image is stable and image noise is hardly perceived.

In Step 2, the latent image portion of the high to medium density portion is
The photosensitive drum 10 to which the dark toner adheres collects the light toner.
Capacitance developing bias potential V_LDeveloping device 13 to which
(L) reaches a position facing the developing sleeve 131 (L).
Upon reaching, the second development with the light toner is performed. developing
Bias potential V_LIs V₀/ 2 or more and developing bias potential
V _HAnd the charged potential V of the photoconductor₀Is set to a potential between
Therefore, in the low density portion, the developing sleeve 131 (L)
A developing electric field is formed between
Adheres electrostatically. Also, the dark toner is electrostatically attached.
Most of the latent image potential (70 to 90%) remains in high to medium density areas.
The toner on the dark toner in the high to medium density areas.
Is electrostatically attached. Development bias potential V_LIs the photoconductor
Charging potential V₀For V_HHigher and (0.7-0.
9) V₀It is desirable that The AC via
May be superimposed.

FIG. 2 also shows the adhesion state of the dark and light toners. However, in order to obtain a high-quality toner image, the total amount of toner adhesion of the dark and light toners is limited, and in the low-density portion. Indicates that a large amount of light toner is electrostatically adhered, dark and light toners are attached together in the middle density part, and the gradation changes smoothly, and a large amount of dark toner is attached in the high density part. Requires that the amount of adhesion be limited,
In order to satisfy such toner adhesion conditions, the following means will be taken.

In the case of the same potential contrast, in the low potential contrast portion, the amount of light toner adhered is larger than the amount of dark toner adhered. That is, a setting is made to enhance the developability of the light toner as described later. On the other hand, in the high-potential contrast section, it is preferable to perform control so that the maximum amount of light toner adhered is smaller than the amount of dark toner adhered. Specifically, for example, when the developing device 13 (H) and the developing device 13 (L) have the same shape, the rotation speed of the developing sleeve 131 (L) is changed to the rotation speed of the developing sleeve 131 (H). It is set lower to limit the supply amount of the light toner to the development area during development. Thus, when the potential contrast is small, the amount of light toner adhering is increased, and when the potential contrast is high, the amount of light toner adhering is limited. Thus, the relationship between the potential contrast and the amount of toner adhering in FIG. As shown in the graph, even in the high-density part, the amount of light toner adhering is limited to a small amount, and the total amount of toner adhering to the high-density part is also restricted.

In the case of the same potential contrast, control is performed so that the γ characteristic of the light toner is higher than the γ characteristic of the dark toner. Since the γ characteristic (potential contrast-image density) of the dark and light toners also changes depending on the developing characteristics of the dark and light toners and the developing bias potential, it is necessary to perform γ correction during development. The potential contrast of FIG. 4 (= developing bias−
By setting the gamma characteristic of the light toner higher than the gamma characteristic of the dark toner, as shown in the graph showing the relationship between the latent image potential and the image density, a sufficient amount of light is obtained for the low density part. The toner adheres and the color reproduction range is expanded.

In this embodiment, an appropriate amount of toner adheres to the low-density portion, dark and light toner adhere to the medium-density portion, and excess toner adheres to the high-density portion. Does not adhere, the toner uniformly adheres to the latent image portion, and the transfer of the toner image is performed well. Also, since light toner adheres to the upper layer of dark toner,
Even if transfer unevenness occurs, it is hardly recognized since it occurs in the portion where the light toner adheres.

The developing machine 13 in which the above-mentioned means is adopted
The latent image potential, the image density, and the toner adhesion amount obtained as a result of the development using the dark toner in (H) and the subsequent development using the light toner in the developing unit 13 (L) are performed. FIG. 5 shows the relationship.

(3) In the present invention, Y, M, C, K
After image processing is performed on the image density data of each color, the exposure optical system 12 performs image exposure on the photosensitive drum 10.

FIG. 6 is a block diagram of the image processing system according to the present embodiment. An original image is read by an image reading means using a solid-state imaging device such as a CCD (F1). B amplified output from CCD,
The G and R analog image information is A / D-converted into digital signals of 8 to 10 bits for each pixel, and shading correction and the luminance information after shading correction are converted to 256-level density information (F2).

Subsequently, in image processing (2), masking, U
Color processing such as CR and color correction is performed (F3). Generally, linear masking is used as masking, or non-linear masking or masking using a look-up table is used when performing advanced color correction. In UCR, Y,
An operation of removing the gray component from the three color components of M and C and replacing it with black (K) is performed, and a process of improving the reproducibility of the shadow portion and the character portion is performed.

Subsequently, the obtained image data is subjected to γ correction for each toner (F4), subjected to multi-value processing (F5), and then output to the exposure optical system 12 to be output to the printer for image processing. The formation is performed (F6).

In the present embodiment, the image data obtained in the image processing (1) is checked for the density distribution of the data and the density difference between adjacent dots, so that the image of the original is intermediate between a photograph and a picture. It is determined whether the image is a toned image or a character image such as a character or a line drawing (F11). Further, when the output mode is instructed to the image mode of characters, photographs, or pictures, the usage ratio of the dark and light toners is determined based on the instruction (F12).

When it is determined that the image is a halftone image, the dark toner
To reduce the amount of toner used and increase the amount of light toner used
Perform control. That is, the developing bias voltage of the developing device 13 (H) is
Rank V _HLower the absolute value of
In the developing direction of the developing unit 13 (L).
Potential V_LSet the absolute value of
Control in the direction to increase.

When it is determined that the image is a character image, control is performed to increase the amount of dark toner used and decrease the amount of light toner used. That is, set high absolute value of the developing bias potential V _H of the developing device 13 (H), and controls the direction to increase the supply amount of the dark toner, the absolute of the developing bias potential V _L of the developing unit 13 (L) The value is set low, and control is performed to reduce the supply amount of the light toner (F13).

In addition to the determination of the use ratio of the dark and light toners at the time of the development, the image processing is controlled by switching the UCR, the γ correction, and the multi-value processing as follows.

The UCR amount is set as low as 10 to 15% for a halftone image and as high as 40 to 10% for a character image.
Set to 0%.

With regard to the γ correction, the setting is switched low for a halftone image and high for a character image according to the usage ratio of dark and light toners.

Switching between multi-value processing is performed by two-pixel PWM to increase the gradation of a halftone image, and performed by one pixel PWM to emphasize the resolving power of a character image. Make settings.

As described above, the usage ratio of the dark and light toners is changed based on the determination as to whether the image is a halftone image or a character image, and the image processing is also changed. As for the image, the dynamic range is expanded, and for the character image, a sharp and clear good image suitable for each image can be obtained.

(4) For an image forming apparatus using a light toner and a dark toner, in order to obtain a sufficient effect according to the present invention, for example, the toner adhesion amount shown in FIG. It is desirable to have a relationship of concentration. The difference in density between the dark and light toners is caused by a difference in the amount of pigment contained in the toner particles. Further, the amount of toner adhered at the time of saturation depends on the toner particle size. For example, for a dark toner, the amount of toner adhering to white paper is 1 mg / c.
The recording density becomes saturated at about m ² . It is necessary that the saturated concentration value _Dmax (H) in the saturated state be 1.7 to 2.5. As shown in FIG. 7, the density value at the point of substantially saturation is defined as D _max (H). To be exact, the concentration gradually increases as shown by the broken line.

On the other hand, the density of the light toner does not reach a saturated state when the amount of toner attached to white paper is 1 mg / cm ² , for example. When the light toner has the same toner adhesion amount as the dark toner reaching the saturation density value, that is, the recording density D of the light toner when the dark toner concentration is saturated.
It is necessary that (L) is between 0.3 and 0.8.
The recording density D _S (L) and the dark toner when the light toner is used when the toner adhesion amount to the white paper reaches the saturation density value, for example, when the toner adhesion amount is 0.5 mg / cm ² . recording density D _S (L) and a ratio, i.e. a light recording density of the toner and the dark toner tilt ratio D _S (L) / D of
_S (H) needs to be between 0.2 and 0.5.

The recording density needs to have the above relationship between the dark toner and the light toner, but the toner particle diameter and the charge amount may be the same for the dark and light toners. preferable. For toner particle size,
Because both dark and light toners ensure image quality and developability,
It is preferable that the volume average particle size is between 3 and 10 μm, and even if there is a difference, it is ± 20% or less. The charge amount is between 5 and 30 μC / g for both the dark and light toners. In particular, when the toner particle size is small, a high charge amount is required. Preferably, there is. By satisfying these conditions,
A similar γ characteristic can be obtained between the dark and light toners, and the design can be made so that the sum of the adhesion amounts of the light toner and the dark toner in the middle to high density areas is substantially the same, and the change in the recording density is linear. It will be easier.

Note that the gradation characteristics shown in FIG. 7 also vary depending on the toner particle size and the contained coloring material. In the case of a toner having a small particle diameter, the toner may saturate even with a smaller amount of adhesion of 0.5 mg / cm ² , but is important in designing a toner having a high saturation density and a low slope ratio. (5) Next, the gloss between the dark toner and the light toner will be described.

In this embodiment, the relationship of G _L > _GH is established between the gloss G _H of the toner image formed by the dark toner on the recording paper as the transfer material and the gloss G _L of the toner image formed by the light toner. Set as in.

In this embodiment, as shown in FIG. 8, only the light toner adheres to the low density portion, and the light toner adheres to the high density portion together with the dark toner. Since the light toner has a high gloss even in a small amount, and has a gloss in a form where the light toner adheres and is pressed even in a high density portion, the observed gloss is almost uniform in the dark and light portions. It is preferable that a business character image is non-glossy, so for example, a non-glossy mode selection button is set on the operation panel, and when the non-glossy mode is selected, a process program for developing with only dark toner is used. It is also possible to form

[0061] Preferred glossiness of the dark toner and the light toner, as shown in FIG. 9, a light gloss G _L of the toner 25 °
It is preferable that the glossiness G _H of the dark toner is 10 ° to 20 °, and the gloss difference is between 5 ° to 35 °. Here, the measurement of the glossiness is performed after fixing the solid image adhered on the recording paper with the toner in close contact with the second and third layers. Since the gloss and non-gloss of the toner image vary depending on the fixing unit to be applied, it is difficult to strictly define the gloss, but the evaluation is performed by the image forming apparatus to be applied. The light toner has a glass transition temperature of 5 ° to 25 ° C. as compared with the dark toner.
When the toner is required to be low, and the toner is manufactured by the emulsion polymerization association method described below, a difference occurs in the glass transition temperature, for example, by changing the addition ratio of a styrene monomer and an acrylic monomer.

By setting the above gloss relationship for the dark and light toners, it is possible to obtain a good image with gloss and rich gradation, and to obtain a non-gloss and easy-to-read image for business documents. It will be.

(6) Next, a method for producing a developer having the above characteristics used in the image forming apparatus of the present invention will be described.

Both the dark and light color toners are spherical toners having a weight average particle diameter of 3 to 10 μm, and polymerized toners by an emulsion polymerization association method are used. In the method for producing a polymerized toner by the emulsion polymerization association method, first, a colorant is dispersed in water using a surfactant. On the other hand, a surfactant, an emulsion polymerization initiator, a styrene monomer and an acrylic monomer are added to water, and a resin emulsion is formed by emulsion polymerization. Next, the colorant dispersion and the resin emulsion are mixed and slowly aggregated while balancing the repulsive force of the particle surface generated by pH adjustment and the cohesive force due to the addition of the electrolyte. At the same time, by heating and stirring, fusion and shape control between the fine particles are performed.
The stirring at this time is performed by heating and stirring using a stirring tank designed to be stirred in a laminar flow state without turbulence, thereby performing fusion and shape control between the fine particles, and filtering, washing, and filtering the obtained particles.
By drying, a spherical toner having a desired particle diameter having a weight average particle diameter of 3 to 10 μm can be obtained.

The toner obtained by the emulsion polymerization association method thus obtained has a sharp particle size distribution and a small amount of fine powder, reduces toner contamination of the carrier, so-called toner spent, improves the durability of the developer, and improves the charge amount distribution. Is uniform, and a high quality image can be obtained as compared with a conventional pulverized toner.

The carrier used is formed by forming a spherical ferrite particle having an average particle diameter of 40 μm and a styrene resin coating layer having a thickness of 0.5 μm, and the toner is mixed in an amount of 5 to 10% by mass with respect to the carrier. At the same time, 0.5% by mass of hydrophobic silica is added to form a developer.

(7) According to the present invention, a color image having gradation and excellent reproducibility can be obtained. The color image forming apparatus to be described next uses a transparent (T) toner and a white (S) toner in the color image forming apparatus described above, and forms a white toner layer between the transfer material surface and the color toner image. By providing a transparent toner layer portion and providing a white toner layer, the surface condition of the transfer material does not affect image quality, and by providing a transparent toner layer below the color toner image, a clear hue and high image quality can be obtained. A color image is obtained.

FIG. 10 is a sectional view showing an embodiment of such a color image forming apparatus. 4 arranged in parallel with the transfer belt 14a of the color image forming apparatus shown in FIG.
Color process units 100K, 100C, 100M,
A new process unit 100TS downstream of 100Y
Is provided. The process unit 100TS includes a developing device 13 using a white (S) toner and a transparent (T) toner.
(S) and 13 (T) are provided on the periphery of the photosensitive drum 10 and the photosensitive drum 10 is exposed by the exposure optical system 12 (TS).
The latent image formed above is first developed by a developing unit 13 (S) with white toner, and then the developing unit 13
The development using the transparent toner is performed by (T).

In the color image forming apparatus having such a configuration, a white toner image is formed on the lowermost layer on the recording paper P and a transparent toner image is formed thereon on the recording paper P by a transfer process in which the image is once transferred onto the transfer belt 14a and then transferred onto the recording paper. A color toner image using dark and light toners is transferred and formed thereon.

The process of forming a color toner image is the same as that in the color image forming apparatus shown in FIG. 1, and therefore the description is omitted, and the white (S) toner layer serving as the base of the color toner image and the color toner image formed thereon are formed. Transparent (T)
The process of forming the T and S toner layers with toner will be described.

In forming the T and S toner layers, FIG.
According to the block diagram shown in FIG. 7, a region for forming the T and S toner layers is designated, and a white (S) toner layer is provided as a lower layer in the designated region, and a transparent (T) toner layer is provided as an upper layer.

Prior to image formation, by pressing a T, S toner layer area setting button on an operation panel (not shown),
The mode is the S toner area designation mode. To specify the area,
Placed at a designated position on the editor F shown in FIG.
For example, a range (X1Y1, X2Y2, X3Y) indicated by oblique lines
3, X4Y4) using the light pen LP (F2
1), the T, S toner layer formation range indicated by the designated oblique line is temporarily stored in the RAM in the T, S image formation range setting (F22) circuit.

By pressing the copy button, the image formation is started in the manner already described, and the exposure optical system 12TS of the process unit 100TS sets the toner layer formation range of (X1Y1, X2Y2, X3Y3, X4Y4) called from the RAM. Exposure is performed. The exposed latent image portion is subjected to reversal development by a developing unit 13S and a subsequent developing unit 13T, transferred, and a toner layer is formed in a range of (X1Y1, X2Y2, X3Y3, X4Y4) on the recording paper P. You.

Here, T, S in the T, S toner layer forming range.
The S toner layer is executed by a program provided in advance. That is, as shown in the enlarged cross-sectional view of FIG. 12, the exposure optical system 12TS is configured such that the white toner layer and the transparent toner layer each have a uniform thickness in the T and S toner layer formation ranges.
Is performed under the exposure condition (F23) set in advance. For the latent image thus formed, the developing bias of the developing units 13S and 13T is set according to the preset developing condition (F24), and the developing unit 1
3S developing white toner layer, and developing device 13
A transparent toner layer is formed by development of T. The thicknesses of the white toner layer and the transparent toner layer formed on the recording paper are preferably between 3 and 20 μm.

By providing a color toner layer on the T and S toner layers, light is reflected on the matt white toner surface,
The light transmitted through the transparent toner layer and the color image on the transparent toner layer is observed in addition to the direct reflection light on the surface of the color image, and a high-quality image with a clear hue is obtained.

(8) In the color image forming apparatus of the present embodiment, G _T > G between the gloss G _T of the toner image by the transparent toner on the transfer material and the gloss G _S of the toner image by the white toner. Set so as to have a relationship of G _S.

The white toner has a function of blocking irregularities on the surface of the transfer material and a colored base, and the transparent toner has a function of providing transparency to a color image formed thereon to prevent color mixing. I do. The white toner adheres to the base but does not penetrate, and the transparent toner is sufficiently melted and brought into close contact with the white toner.

The glossiness of the transparent toner and the glossiness of the white toner are preferably such that the glossiness G _T of the transparent toner is 25 ° to 60 ° and the glossiness G _S of the white toner is 5 ° to 15 °. The difference is preferably between 20 ° and 45 °.

By maintaining the above-mentioned gloss relationship between the transparent toner and the white toner, a good image with a high gradation can be obtained in which the color is more transparent and a deep color image can be obtained. .

In the color image forming apparatus of this embodiment,
The gloss G _T of the toner image due to the transparent toner on the transfer material,
The relationship between the glossiness G _L of the toner image due to the light toner and G _T >
_GL or G _T ≒ _GL is set.

[0081] From the relationship pale toner image on a transparent toner layer is formed, that a glossiness in a relation of approximately the same (G _T ≒ G _L) is, since it is observed as a natural glossy image preferred. On the other hand, in the transparent toner is not used, the glossiness G _L of the light toner that may correspond to a non-glossy image, it is preferred to be lower than the gloss of the transparent toner (G _T> G _L) configuration.

Since the gloss _GH of the dark toner is set lower ( _GL > _GH ) than the gloss _GL of the light toner, it is required that the character image for business use is non-glossy. In some cases, a non-glossy character image can be obtained by separately providing a process of developing with only the dark toner.

The glossiness of the transparent toner and the light toner is preferably such that the gloss G _T of the transparent toner is 25 ° to 60 ° and the gloss G _L of the light toner is 25 ° to 50 °. The difference is preferably between 0 and 20 °.

By maintaining the above-described gloss relationship between the transparent toner and the light toner, a good image with rich gradation can be obtained as a color image having a more natural gloss and transparency. Becomes

In the color image forming apparatus of this embodiment,
Between the gloss G _H of the toner image due to the dark toner on the transfer material and the gloss G _S of the toner image due to the white toner, G _H >
Set so as to have a relationship of G _S.

Since the white toner is used to shield unevenness and a colored base of the transfer material, the softening temperature tends to be high and does not sufficiently fuse with the color toner. Its glossiness of the white toner for G _S is lower than the gloss G _H of dark toner (G _H> G _S) to set. For business character images, use neither dark toner nor transparent toner, develop only dark toner on the white toner layer,
It is also possible to obtain a non-glossy character image.

The glossiness of the dark toner and the white toner is preferably such that the glossiness _GH of the dark toner is 10 ° to 20 ° and the glossiness _GL of the white toner is 5 ° to 15 °. The difference is preferably between 5 ° and 20 °.

By maintaining the above-mentioned gloss relationship between the dark toner and the white toner, a good image with rich gradation can be obtained as a deeper color image.

FIG. 9 is a graph summarizing the preferable glossiness of each toner described in the above.
It is.

[0090]

According to the first aspect of the invention, in an image forming apparatus having dark and light toners, the gradation is maintained, the gloss is controlled, and a high-quality image having an appropriate gloss is obtained. It was obtained.

According to the second to fourth aspects, the background is sufficiently shielded by the white toner, the gloss is controlled, and a high-quality color image having an appropriate gloss is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus according to an embodiment.

FIG. 2 is an explanatory diagram illustrating a state where toner adheres to a latent image portion.

FIG. 3 is a graph showing a relationship between a potential contrast and a toner adhesion amount.

FIG. 4 is a graph showing a relationship between potential contrast and image density.

FIG. 5 is a graph showing a relationship between a latent image potential, an image density, and a toner adhesion amount.

FIG. 6 is a block diagram of an image processing system.

FIG. 7 is a graph showing a relationship between a charge amount and transferability.

FIG. 8 is an explanatory diagram showing the state of toner adhesion.

FIG. 9 is a graph showing the glossiness of a toner.

FIG. 10 is a cross-sectional configuration diagram of a color image forming apparatus according to another embodiment.

FIG. 11 is an explanatory diagram showing an operation on an editor.

FIG. 12 is an enlarged cross-sectional view of a toner image on recording paper.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 photoconductor drum 11 scorotron charger 12 exposure optical system 13 (L), 13 (H), 13 (T), 13 (S) developing device 14 transport belt 14 a transfer belt 14 c primary transfer device 14 g secondary transfer device 15 Paper cassette 16 Timing roller 17 Fixing device 100 (Y, M, C, K, TS) Process unit

Claims (4)

[Claims] 1. An image forming apparatus for forming a toner image by repeating development using a dark toner and development using a light toner on a latent image formed by performing charging and image exposure on the image forming body. An image forming apparatus, wherein a relationship of G _L > _GH is established between the gloss G _H of the toner image formed by the dark toner on the transfer material and the gloss G _L of the toner image formed by the light toner. . 2. A method according to claim 1, further comprising the step of repeatedly performing development with dark and light toners for each of the plurality of image forming bodies, repeatedly performing development with the transparent toner and white color, and forming the formed toner image on a transfer material. In a color image forming apparatus that is formed by superimposing the toner images, the relationship G _T > G _S is established between the gloss G _T of the toner image formed by the transparent toner on the transfer material and the gloss G _S of the toner image formed by the white toner. A color image forming apparatus, comprising: 3. A method of repeatedly developing a plurality of image forming bodies with dark and light toners for each color, repeatedly developing a transparent toner and a white color, and forming the formed toner image on a transfer material. In a color image forming apparatus which is formed by superimposing the toner images, G _T > _GL or G between the gloss G _T of the toner image by the transparent toner on the transfer material and the gloss G _L of the toner image by the light toner. color image forming apparatus, characterized in that a relation of _T ≒ G _L. 4. A method for repeatedly developing a plurality of image forming bodies using dark and light toners for each color, repeatedly developing a transparent toner and a white color, and forming the formed toner image on a transfer material. In a color image forming apparatus that is formed by superimposing the toners, the relationship of G _H > G _S is established between the gloss G _H of the toner image formed by the dark toner on the transfer material and the gloss G _S of the toner image formed by the white toner. A color image forming apparatus, comprising: