JPH04329563A - Color image recording method - Google Patents

Abstract

PURPOSE:To efficiently obtain a color image having sufficient image density without the mixture of color and irregularities in an image, and also to prevent the occurrence of soil by toner caused by toner cloud by preventing a toner image formed at a 1st developing process from generating irregularities at the 2nd and subsequent developing processes. CONSTITUTION:This method is constituted of a latent image forming process for forming an electrostatic latent image on latent image carrier, a developing process for developing the formed electrostatic latent image by two or more different colored toner and a transfer process, and this method is a color image recording method for transferring a developed color toner image to a transfer material after repeating at least the developing process plural times out of the latent image forming process and the developing process, and as to the plural developing processes, the surface moving velocity of each developing roll is set within the extent of 1/2-2 times as compared with the surface moving velocity of the latent image carrier, and also, on at least the 2nd and subsequent developing processes, two-components developer which is obtained by mixing toner and magnetic carrier whose density is <=4.0g/cm<3> is used.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method of recording a color image using an electrostatic latent image, and in particular to a method of recording a color image by developing a toner image already formed on a latent image carrier without disturbing it. The present invention relates to a color image recording method for obtaining a toner image.

0002

2. Description of the Related Art Conventionally, various color recording methods using electrophotography have been known, one of which is the overlapping development method. In the superimposed development method, two
After forming a value or ternary electrostatic latent image and developing the first latent image on the photoconductor having these binary or ternary latent images with a first developing machine, the second latent image on the photoconductor is subsequently developed. 2 latent image as the second
A color image is obtained by developing the toner image with a developing machine and transferring the finally formed toner image all at once. This method is effective because the device is compact and the copying speed is extremely high. In such an overlapping development method, in the second development step, the photoreceptor on which the toner image has already been carried in the first development step is rubbed again with the developer, so that the first development step The toner image being formed by the process will be significantly disturbed by the second development step. As a result, the finally obtained color image has the drawback of being a significantly distorted color image. Therefore, in the image forming method using the overlapping development method, it is extremely important to determine how to perform the subsequent development without disturbing the toner image in the previous stage.

[0003] Methods for developing the toner image on the photoreceptor without disturbing it include (1) non-contact development (see Japanese Patent Application Laid-open No. 144452/1983), (2) increasing the amount of rubbing force in the subsequent development step. Weakened magnetic brush development method (Japanese Patent Application Laid-Open No. 55-36889
No. 57-79970, No. 60-126665) may be used.

0004

[Problem to be developed by the invention] In the method (1) above, when a non-contact AC flying method is adopted in the second developing step, as disclosed for example in Japanese Patent Application Laid-Open No. 56-144452, AC of already developed toner
Considering the flying phenomenon caused by the electric field, this is not a good idea in terms of mixing the second developer into the first toner image. Further, in the method (2), there is a problem that it is difficult to develop a sufficient image density because it is used in a state where the developing efficiency or developing ability of the second developing step is reduced.

[0005] Conventionally, in the developing process, the surface speed of the developing roll is 2 to 4 times higher than the surface speed of the photoreceptor.
Developing is performed by rotating at a ratio of about twice that, but at such rotation speeds, toner clouds are likely to occur.
It is not preferable if a charger, an exposure device, etc. are present between the first developing means and the second developing means, since they will be contaminated. Therefore, it is desirable to suppress the surface speed of the developing roll to less than twice the surface speed of the photoreceptor. However, satisfactory results have not been obtained due to insufficient development efficiency. The present invention has been made in view of the above problems.

Therefore, an object of the present invention is to prevent the toner image formed in the first development step from being disturbed in the second and subsequent development steps, and therefore to achieve sufficient image density without color mixture and image disturbance. An object of the present invention is to provide a color image recording method that can efficiently obtain a color image. Another object of the present invention is to provide a highly reliable color recording method that does not cause toner stains due to toner clouds.

[0007]

[Means for Solving the Problems] The present inventors have previously discovered that when forming a color image by an overlapping development method, in at least the second and subsequent development steps of a plurality of development steps, the density is 4. It was proposed to use a carrier of .0 g/cm3 or less (Japanese Patent Application No. 1983-272790).
As a result of further studies, it was discovered that development could be carried out more effectively if the moving speed of the developing roll was set within a specific range, and the present invention was completed. That is, the present invention includes a latent image forming step of forming an electrostatic latent image on a latent image carrier by a latent image forming means, and making the formed electrostatic latent image visible using two or more different toner colors. A color image recording method comprising a developing step and a transfer step, in which at least the developing step of the latent image forming step and the developing step is repeated multiple times, and then the developed color toner image is transferred to a transfer material. In the multiple development steps, the surface movement speed (vR) of each developing roll and the surface movement speed (vR) of the latent image carrier are
R ), and the developer used in at least the second and subsequent development steps is
It is characterized by being a two-component developer comprising a mixture of toner and a magnetic carrier having a density of 4.0 g/cm3 or less. In the present invention, it is preferable to use a developing roll having a main developing pole formed by magnetic poles of the same polarity adjacent to each other in at least the second and subsequent developing steps.

The present invention will be explained below with reference to the drawings. FIG. 1 shows an example of a color image recording apparatus used to carry out the present invention, in which a color image is formed by forming a binary latent image. Further, FIG. 3 is a diagram illustrating the surface potential of the photoreceptor and the state of development when the color image recording apparatus of FIG. 1 is operated. In Figure 1, 1a
1 is a first charger, 2a is a first exposure means, 3a is a first development means, 1b is a second charger, 2b is a second exposure means, 3b is a second development means, 4 is a transfer corotron, and 5 is a static elimination corotron. , 6 is a cleaner, 7 is a photostatic eliminator, 8 is a recording paper, 9 is a pre-transfer corotron, 10 is a photosensitive drum, and 10a is a photosensitive layer. The photosensitive drum 10 is rotating in the direction of the arrow. First, the photosensitive layer 10a on the surface of the photosensitive drum 10 is uniformly charged by the first charger 1a (FIG. 2(a)).
.

Next, the first exposure means 2a irradiates light according to image information corresponding to the first color, and an electrostatic latent image corresponding to the first color is formed on the photoreceptor. Note that any exposure means can be selected. Next, the photosensitive layer 1 having the first electrostatic latent image formed by the first exposure means
Toner corresponding to the first color is supplied to 0a by the first developing means 3a to visualize the image (FIG. 2(b)). Note that the color of the toner may be different from the first color. 1st
Any developing means can be used. On this occasion,
The developing bias is selected depending on whether regular development or reversal development is performed.

Next, the photosensitive layer 10a is uniformly charged again by the second charger 1b (FIG. 2(c)). Note that this second charger 1b may be omitted depending on the image forming process. For example, it can be omitted when negative writing is performed in the first exposure section and positive writing is performed in the second exposure section. Subsequently, the second exposure means 2
By b, light irradiation is performed according to image information corresponding to the second color, and an electrostatic latent image corresponding to the second color is formed on the photosensitive layer 10a. The exposure means and writing method are arbitrary. Next, the second developing means 3b supplies toner corresponding to the second color to the photosensitive layer 10a having the second electrostatic latent image formed by the second exposing means to visualize it (see FIG. 2). d)). Also in this case, the color of the toner may be different from the second color. At this time, the developing bias can also be selected arbitrarily.

The pre-transfer corotron 9 is used to align the polarities of the first toner and the second toner carried on the photoreceptor before transfer, but this can also be omitted in certain processes. The first toner image and the second toner image are transferred onto the recording paper 8 by the transfer corotron 4, but may be transferred using means other than electrostatic transfer. The recording paper is then fixed in a fixing section (not shown). Further, the photoreceptor that has passed through the transfer section is cleaned by a static eliminator 5, a cleaner 6, and an optical static eliminator 7 for reuse.

The first and second exposure means may include a light illumination means, an original scanning means, and an imaging optical system as used in a normal copying machine, or may be light modulated in accordance with image information. Any optical writing device, such as a laser writing device, a liquid crystal light valve consisting of a uniform light source and a liquid crystal microshutter, an LED array, an optical fiber, etc., can be used depending on the purpose.

In the developing step of the present invention, any two-component developing device can be used, but it is preferable to use the most common magnetic brush developing device. A magnetic brush developing device carries a two-component developer on a developing roll consisting of a magnet roll having a plurality of magnetic poles and a non-magnetic cylindrical sleeve provided on the circumferential surface of the magnetic roll. A magnetic brush is formed by adjusting the vertical length, and the latent image is formed by moving the magnetic brush by relative movement between the magnet roll and the sleeve and rubbing the surface of the photoconductor placed opposite to the magnetic brush. Toner is applied to the image and developed. In this case, from the viewpoint of preventing image disturbance, it is preferable to fix the magnet roll and rotate the sleeve.

In the present invention, the developing roll used in the first developing step and the developing roll used in the second and subsequent developing steps all have their surface movement speeds (VR).
is 1/with respect to the surface movement speed (vP) of the latent image carrier.
It is necessary to be in the range of 2 to 2 times. When the surface movement speed of each developing roll is within the above range, the toner image formed in the first development process is within an acceptable range for development to be disturbed by the second and subsequent development processes, but outside the above range. When this happens, image distortion becomes significant.

Further, in the present invention, two types of developers having different hues are used as the developer, but in at least the second and subsequent development steps among the plurality of development steps,
It is necessary to use a two-component developer consisting of a mixture of toner and a magnetic carrier having a density of 4.0 g/cm 3 or less. The carrier used in the present invention has a density of 4.
Any material can be used as long as it is 0 g/cm3 or less, but specific examples include carriers with porous surfaces, ferrite carriers, and carriers made by dispersing magnetic powder in a binder resin. Density is 4.0g/
It is necessary that it is below cm3. Among these, a carrier formed by dispersing magnetic powder in a binder resin is preferable because the density can be easily controlled by controlling the magnetic powder content. From the experimental results, image disturbance and carryover phenomena are within an acceptable range if the density ρ is in the range of 1.7 to 4.0 g/cm3, preferably 1.7 to 3.0 g/cm3. It has been found. It is presumed that this is because the density of the individual carriers is low, so that the formed spikes become soft.

[0016] Although the particle size of such low-density carrier particles in the present invention is arbitrary, from the results of experiments, it is preferable to have an average particle size in the range of 25 to 50 μm, particularly those having an average particle size of around 30 μm. is optimal. This is because, if the average particle diameter falls outside the above range, it becomes difficult to simultaneously prevent the carryover phenomenon and the image disturbance phenomenon.

The density of the carrier of the present invention is defined as the density determined by the true specific gravity measured by the following measuring method. Completely replace the voids in the powder with liquid and apply the relationship between its weight and volume to the formula below to find the true specific gravity.
Using the so-called pycnometer method (true specific gravity bottle method), the true specific gravity is determined from the following formula using a measuring device that automates the pycnometer method: Auto Truedenser MAT-5000 (manufactured by Seishin Enterprise Co., Ltd.).

[0018]

[Formula 1] (where, Pd: true specific gravity, Ld: specific gravity of liquid, Wa: cell tare (empty cell) (g), Wb: cell tare + powder (g),
Wc: Cell tare + powder + liquid (after determining the liquid level) (g), W
d: Cell tare + liquid (after liquid level determination) (g))

0019
]

EXAMPLES Example 1 A two-component developer used in the present invention was produced as follows. Carrier styrene-n-butyl methacrylate copolymer (density 1
．． 1g/cm3) and cubic magnetite (density 4
．． 8 g/cm3) at the following ratio, melted and kneaded, and then finely pulverized to obtain carriers shown in Table 1 below.

[0020]

[Table 1]

Toner 92 parts by weight of a resin obtained by graft polymerizing a low molecular weight polyolefin to a styrene-butyl methacrylate copolymer and a red pigment: Lysol Scult (trade name, BASF)
8 parts by weight were melt-kneaded and finely pulverized to give an average particle size of 9.8μ.
m toner was obtained.

Two-component developer A developer was obtained by mixing 90 parts by weight of the above carrier and 10 parts by weight of toner.

A test was conducted using a color image recording apparatus as shown in FIG. 1 above. A Se-based photoreceptor was used. The first charging was performed, and the charging potential was uniformly charged to 900V. Exposure was performed using a laser light source as the first exposure means. The exposed area of the photoreceptor in the first exposure was 200V. Next, develop bias 300V
Under this, first development is performed using a two-component magnetic brush method,
A black toner image was formed. Then, second charging was performed. The surface potential of the photoreceptor was 900V. developing bias 8
A second development was performed under 00V by a two-component magnetic brush method to form a red toner image. In this case, the developing roll in the first developing means and the developing roll in the second developing means are both composed of a non-magnetic developing sleeve and an 8-pole magnet roll, and the surface movement speed is the same as that of the photosensitive layer. I set it so that

In the above method, almost no image disturbance occurred in the toner image formed by the first developing means by the second developing means. When the surface movement speeds of the developing rolls in the first developing means and the second developing means were varied, the results shown in FIG. 3 were obtained. Figure 3 shows the second
This is a graph showing the state of disturbance of the first toner image due to the developing step, and the vertical axis represents the ratio of the line width of the toner image after the second developing step to the line width of the toner image formed by the first developing step. The width is the surface movement speed (vP) of the latent image carrier.
) to the surface moving speed (vR) of the developing roll. As shown in FIG. 3, when the surface movement speed of the developing roll is in the range of 1/2 to 2 times the surface movement speed of the latent image carrier, the toner image formed in the first development step is It can be seen that the degree of disturbance caused by 2 development is extremely low.

Example 2 Copying was carried out in the same manner as in Example 1, except that a magnetic roll having main developing poles with magnetic poles of the same polarity adjacent to each other was used as the developing roll in the second developing step. performed the operation. When the surface movement speed of the developing roll in the first developing means and the second developing means was varied, the results shown in FIG. 4 were obtained. In FIG. 4, the vertical axis represents the image density of the copy image, the horizontal axis represents the ratio of vR to vP (vR/vP), and curve A has a main developing pole formed by adjacent magnetic poles of the same polarity. Curve B means the case where a developing roll having a magnet roll is used, and the curve B means the case where the main developing pole does not form a repulsive magnetic field. As is clear from this figure, when using a magnet roll having main developing poles with magnetic poles of the same polarity adjacent to each other,
It can be seen that the image density increases significantly when the surface movement speed of the developing roll is in the range of 1/2 to 2 times the surface movement speed of the latent image carrier.

Embodiment 3 In the color image recording apparatus shown in FIG. 1, the first exposure means is an exposure lamp and the second exposure means is an LED array.
The procedure was the same as in . The copying operation was repeated with the surface moving speeds of the developing roll of the first developing means and the developing roll of the second developing means both set to 1 or 3 relative to the moving speed of the photosensitive layer. The stains on the lenses of the LED array were measured by transferring them to adhesive tape. The results are shown in Figure 5. In FIG. 5, the vertical axis represents the density of toner transferred onto the adhesive tape, the horizontal axis represents the number of copies, and curve A represents vR/
vP=1, and curve B shows the case where vR/vP=3. From this figure, it can be seen that in the case of the present invention, toner cloud is less generated by the first developing means.

[0027]

According to the present invention, the toner image formed in the first development step is not disturbed in the second and subsequent development steps, and therefore, a color having sufficient image density without color mixing and image disturbance can be obtained. Images can be formed efficiently. Further, there is no occurrence of toner stains due to toner clouds, and color image recording can be performed with high reliability. Therefore, the color image obtained by the present invention has excellent image quality without image disturbance.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an example of a color image recording device used to carry out the present invention.

FIG. 2 is an explanatory diagram illustrating the surface potential of a photoreceptor and the state of development when the color image recording apparatus of FIG. 1 is operated.

FIG. 3 is a graph showing the state of disturbance of the first toner image due to the second developing step.

FIG. 4 is a graph illustrating image density when the developing roll has main developing poles in which magnetic poles of the same polarity are adjacent to each other.

FIG. 5 is a graph illustrating the state of occurrence of toner cloud.

[Explanation of symbols]

1a...first charger, 1b...second charger, 2a...first exposure means, 2b...second exposure means, 3a...first development means, 3b
...Second developing means, 4...Transfer corotron, 5...Static charge removal corotron, 6...Cleaner, 7...Optical charge remover, 8...Recording paper, 9
...Corotron before transfer, 10...Photosensitive drum, 10a...Photosensitive layer.

Claims (2)

[Claims] 1. A latent image forming step in which an electrostatic latent image is formed on a latent image carrier by a latent image forming means, and a development step in which the formed electrostatic latent image is visualized with two or more different toner colors. A color image recording method comprising a step and a transfer step, in which at least the developing step of the latent image forming step and the developing step is repeated multiple times, and then the developed color toner image is transferred to a transfer material. , in the plurality of development steps, the surface movement speed of each developing roll is in the range of 1/2 to 2 times the surface movement speed of the latent image carrier, and at least 2 times the surface movement speed of the latent image carrier.
A color image recording method characterized in that the developer used in the subsequent development steps is a two-component developer prepared by mixing toner and a magnetic carrier having a density of 4.0 g/cm 3 or less. 2. The color image recording method according to claim 1, wherein in at least the second and subsequent development steps, a developing roll having a main developing pole formed by adjacent magnetic poles of the same polarity is used.