JPH0125059B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color printing method, in which an electrostatic latent image is developed and visualized using colored particles (toner) to obtain an image. The present invention relates to a color printing method that forms an image consisting of:

Many means and methods for recording and printing image information using electrostatic recording and electrophotographic techniques have been proposed, and in recent years,
Printing methods that print computer output have become widely used.

However, conventional techniques generally have the disadvantage that they can only be printed in one color, such as black, and although there is a demand for printing in two or three colors, such methods have problems with printing quality. There were problems such as inferiority and the need for a high-precision drive mechanism, high-voltage power supply, and high-voltage mechanism, which hindered its practical application.

The present invention improves printing quality by reducing toner image loss and color mixing in a color printing method in which two or more colors are developed sequentially using one drum and the two or more color toner images formed are transferred simultaneously. The purpose of this invention is to provide an excellent color printing method that does not require a high-precision drive mechanism, high-voltage power supply, or high-voltage mechanism.

A feature of the present invention according to the above is that a first latent image is formed by a first exposure on a photoconductive photoreceptor, this first latent image is reversely developed, and then a first latent image is formed on the photoconductive photoreceptor. A second latent image is formed by second exposure, and the process of reversing and developing this second latent image is repeated two or more times to create a toner image of two or more colors on the photoreceptor, and this is recorded. In a color printing method that creates images in two or more colors by simultaneously transferring them to paper, the first color is black, and non-magnetic toners with sequentially higher saturation and brightness are used for the second and subsequent colors, and at least the first color is black. For the second and subsequent colors, a high-resistance two-component magnetic brush development method using a high-resistance magnetic carrier of 10 ⁴ Ωcm or more is used.

Next, one embodiment of the present invention will be described based on the drawings.

The device according to the present invention uses an electrophotographic method for electrostatic recording and is particularly suitable for printing in two to three colors, but in order to make the explanation easier to understand, the following will be described.
Based on Examples, a method for obtaining two-color printing by electrophotography will be described.

Here, FIG. 1 shows 2 according to an embodiment of the present invention.
FIG. 2, which is a schematic configuration diagram of a printing device used for color printing electrophotography, is an enlarged explanatory diagram showing the state of toner adhesion after development.

In the figure, 1 is a photoconductive photoreceptor (hereinafter referred to as a photoconductive drum), 2 is a charger, 4 is a first developer, 6 is a second developer, 7 is a recording paper, 8 is a transfer device, and 9 is a cleaner. These constitute a printing device, and 3,5
shows the first and second light images.

Further, 10 is a first latent image, 11 is a second latent image, 12
13 is a first toner image, 13 is a second toner image, and 14 is a mixed color toner image.

First, general color printing using the above-mentioned configuration will be described below.

That is, the photoconductive drum 1 is uniformly charged by the charger 2, and then the first optical image 3 is irradiated to form a charge latent image. Then, this charge latent image is reversely developed by the first developing device 4.

Subsequently, portions of the photoconductive drum 1 that were not irradiated with the first light image 3 are irradiated with a second light image 5;
A second charge latent image is created and reversely developed by the second developer 6 to form a two-color toner image on the photoconductive drum 1.

The toner image created in this way is transferred to the recording paper 7.
The images are simultaneously transferred to and from the transfer device 8 in the presence of a transfer corona.

This transferred toner image is not shown, but
It is something that will eventually become established.

The toner image remaining on the photoconductive drum 1 is removed by a cleaner 9, and the same process is repeated again to continuously obtain a large number of images.

However, if you configure it as above,
Since toner images of two colors can be transferred simultaneously using one photoconductive drum, there is no reduction in printing speed or complication of the device.

FIG. 2 shows the state of a toner image formed on the photoconductive drum 1 by two successive developments in the above-described structure.

The illustrated V ₀ indicates the charge level on the photoconductive drum 1, and the first optical image 3 forms a first latent image 10, and the second optical image 5 forms a second latent image 11.

The first development by the first developing device 4 causes the first toner image 12 to be placed on the first latent image 10, and the second development by the second developing device 6 causes the second toner image 13 to be placed in the second location. A latent image 11 is formed at a certain location.

However, the potential V ₁ when the first latent image 10 is developed and the toner is attached is V ₁ <V ₀ , and since there is a potential of (V ₀ −V ₁ ) during the second development, this portion The second toner adheres to the toner, resulting in a mixed color toner image 14 as shown in the figure.

Another problem is that during the second development, the first
Toner is removed and enters the second developing device 6, and if this accumulates, the color of the second toner image 13 may deteriorate (staining of the second developer).

Therefore, in order to be able to obtain stable printing over a long period of time without mixed color images or stains of the second developer using such a system, it is necessary to do the following.

(1) The first toner image is not removed during the second development.

(2) Even if there is some loss, it is not accumulated and is immediately used in the second development, so that color deterioration does not increase.

(3) The overlapping of the second toner on the first toner image is minimized, and the color mixture is kept to an extent that does not cause any practical problems.

The present invention was developed focusing on the above points, and each embodiment thereof will be described next.

Example 1 A photoconductive drum 1 was positively charged to 500 to 1000 V and irradiated with a first optical image 3 to form a first latent image 10. The residual potential in the exposed area was 50V.

Next, a two-component magnetic developer with a weight ratio of 1 to 5% of a low resistance magnetic carrier of 10 ³ Ωcm or less and a positively charged black toner is prepared as a first developer.
A bias voltage of ⁺¹⁰⁰ to ⁺⁵⁰⁰ V was applied to the developing device 4, and the first latent image 10 was developed with a magnetic brush.

At this time, the developed image density is close to the saturation density,
It was 1.0 or more. When the potential after development was measured, it was found to be V ₁ 200V at the highest image density.

Next, a second optical image 5 was irradiated to create a second latent image 11.

A high-resistance magnetic carrier of 10 ⁴ Ωcm or more is used as the second developer, a two-component magnetic developer with a weight ratio of 1 to 5% is made from positively charged red toner, and a bias is applied to the second developer 6. I did magnetic brush development without doing anything.

The first and second toner images 1 developed in this way
When images 2 and 13 were transferred to recording paper 7 and thermally fixed, there were few mixed color toner images 14, and the first toner image 1
In No. 2, a black image with no practical problems was obtained. Further, even if the second toner image 13 is continuously printed, the second toner image 13
A red image with very little toner contamination was obtained.

In particular, the carrier resistance was good when it was 10 ⁶ Ωcm or more and the thickness of the magnetic brush was 2 to 6 mm, and stable carrier resistance was obtained when the carrier resistance was 10 ⁶ Ωcm. In addition, such a carrier is 50
It was obtained by creating an oxide film on the surface of iron powder with a diameter of ~500 μm.

On the other hand, when the second development was performed using the same magnetic carrier as the first development and applying approximately the same bias, approximately half of the first toner image 12 was removed, and the second development The toner adheres to almost the same extent as the first toner, resulting in only a black image with a strong red color.Furthermore, when printing continuously, black toner gets mixed into the second developer, resulting in a muddy red image. I'm getting old.

At this time, when a bias voltage having the same polarity as that of the first developing device 4 was applied to the second developing device 6,
Although the removal of the first toner image 12 during the second development is reduced and the above problems are improved, the second development is inferior to those using a high resistance magnetic carrier.
There remained some problems with stable printing.

As mentioned above, the reason why such good results can be obtained when using a high-resistance magnetic carrier is that the attraction force between the carrier and the toner (Coulomb force due to the charge on the toner) is small, and the force between the photoconductor surface and the magnetic brush is small. Since the electric field gradient formed is small and a reversal electric field is maintained, the first toner image 12 remains attracted to the photoconductor surface and the force removed by the carrier is small, and reversal development is possible even without bias. it is conceivable that.

As described above, according to the developing method of this embodiment in which the amount of the mixed color toner image 14 on the first toner image 12 is small, there is less color mixing on the first toner, there is no cloudiness in the second toner image 13, and the recording paper 1st transcribed in 7
In the image, since the chromatic toner is located below the black toner image, the influence of the mixed color toner image 14 is extremely reduced.

Example 2 In Example 1 above, the first development was performed using the same high resistance carrier as the second development, and similar to Example 1, good results were obtained.

At this time, the first developing bias voltage is 0 to
At 500V, good images were obtained even with non-bias (0V) development.

In order to reduce the mixed color toner image 14 in the second development, it is necessary to perform the first development sufficiently. 800 to 1000 Gauss or more), magnetization width is 10 to 30 to widen the development width.
It is preferable to set it to mm.

Example 3 In Examples 1 and 2 described above, when the second developing ability was made smaller than that of the first, the amount of the mixed color toner image 14 to the first toner image 12 was reduced, and black reproduction was improved. Although the image density of the second toner image 13 was slightly reduced, it was a value that caused no problem in practical use.

As a means of reducing the developing capacity, in order to reduce the contact between the photoconductive drum 1 and the magnetic brush, the gap between the photoconductive drum 1 and the first developing device 4 is made smaller than that of the first developing device 4.
Increased size by 0.1~0.5mm. Also, the magnetic force is 100~200
Gauss lower.

By doing this, the effect of removing the first toner image 12 during the second development was slightly reduced, but in the method of the present invention in Examples 1 and 2, this removal effect was originally small. There was no significant difference in practical effects.

Example 4 In Examples 1 to 3, when the charge amount of the toner of the second developer was made larger than that of the first developer, the mixed color toner image 14 was reduced in the first toner image 12, and the amount of the mixed color toner image 14 was reduced. The accumulation of the first toner in the second developing device 6 has been reduced.

The reason for this is that when the charge is large, the toner adsorption force to the carrier is large, and the ability to develop a certain (V ₀ -V ₁ ) latent image of the first toner image 12 is small; Even if the first toner gets mixed in,
It is thought that the first toner is easier to develop and therefore does not accumulate.

Example 5 In Examples 1 to 4, a low bias voltage of 50~ with the same polarity as the charging of the photoconductor was applied to the second developer 6.
When 200V was applied, the number of mixed color toner images 14 to the first toner image 12 decreased, and black reproduction improved. Although the density of the second toner image 13 was slightly reduced, there was no problem in practical use. In addition, the removal of the first toner image 12 by the second development and the addition of the first toner image to the second developer may also be performed.
Accumulation of toner caused no practical problems.

Although the bias voltage to be applied has a polarity that attracts the first toner, the problem of toner removal is small because this bias voltage is not very large (1/10 to 1/3 of V ₀ ), and the bias voltage is However, the force with which the first toner image 12 is attracted to the first latent image 10 is large, and the first toner is not attracted to the carrier, and the mixed color toner image 14 overlaps with each other slightly.

Example 6 In Examples 1 to 4, when an alternating current voltage was used for the bias voltage of the second developing device 6, the tone of the second image obtained by the second development could be softened, making adjustment easier. .

Further, in Example 5, when an alternating current component was superimposed on the bias voltage, a similar effect was obtained.

Example 7 In Example 1, the contact between the magnetic brush and the photoconductive drum 1 during the first development was made close so that the potential of the photoreceptor after development was reduced by 100 to 200 V. The mixed color toner image 14 was reduced, and black reproduction was improved.

This is because the developing ability in the second development is reduced by the amount of the potential drop, and the overlap of the second toner is reduced.

Example 8 In Examples 1 to 6, after development, the photoconductive drum 1 was uniformly exposed to weak light, and the surface potential was increased to 100~
When the voltage was lowered by 200V, the same effect as in Example 7 was obtained.

Example 9 In Examples 1 to 6, when the irradiation amount was adjusted and printed so that the residual voltage at the time of irradiation of the first optical image 3 was 100 to 300 V, color mixing of the second toner to the first toner image 12 was observed. The toner image 14 was reduced and black reproduction was improved.

This is because the developing ability in the second development becomes relatively low due to the presence of residual voltage.
It would have been better to apply a bias during the first development.

Example 10 In Examples 1, 3 to 6, 8, and 9, when the first development was cascade development and the second development was high resistance magnetic brush development as in each of the above examples, similar good images were obtained. was gotten.

Example 11 In Examples 1 to 4, the first latent image 10 is
When a bias is applied to the developing device 4 and the first development is sufficiently performed to increase the amount of toner in the first toner image 12, a portion of the first toner image 12 tends to be removed during the second development. Ta. At this time, during the second development, the contact between the photoconductive drum 1 and the magnetic brush is lightened to reduce the developing ability, and a bias voltage of 100 to 200 V with the same polarity as V ₀ is applied to develop the first image. When the second toner was made to slightly overlap the toner image 12, a portion of the first toner image 12 was almost never removed.

The color printing method disclosed in Japanese Patent Application Laid-open No. 55-83069 entitled "Non-impact printer" performs the second development using "high resistance magnetic toner developer". Developing is performed by forming a magnetic brush on a developing roll containing a built-in magnet.

However, the printing method described in the above publication was
The problems when used in color printers are: (1) The developer contains a large amount of black or low-brightness magnetic material, so the color cannot be freely selected. (2) The first color is a chromatic color. , when black magnetic toner is used for the second color, the first color is
If even a small amount of black magnetic toner gets mixed into the color image,
The coloring of the first color is significantly reduced. (3) When using a "high resistance magnetic toner developer," the gap between the photoconductive photoreceptor and the developing roll must be narrowed to about 0.5 mm, resulting in high accuracy. (4)Also,
When using a "high-resistance magnetic toner developer," in order to improve the developability, the bias voltage to be applied must be set to a large value (500 to
700V), which requires a high-voltage power supply and a high-withstand voltage mechanism.

On the other hand, in the present invention, the first color is black, and non-magnetic toners having sequentially higher saturation and brightness are used for the second and subsequent colors, and at least for the second and subsequent colors,
This is a high-resistance two-component magnetic brush development using ^{a high-resistance magnetic carrier of 10 4 Ωcm} or more. The superiority was described in Example 1 above.
Further, in the present invention, the above-mentioned Japanese Patent Application Publication No. 55-83069
Compared to the color printing method described in the publication, since a non-magnetic toner is used, any color can be printed without being limited to the colors specific to magnetic materials, such as the black of magnetite and ferrite, or the brown of maghemite. Furthermore, the gap between the photoconductive photoreceptor and the developing roll can be made large (as shown in Example 1, the optimal gap between the photoconductive photoreceptor and the developing roll is 2 to 6 mm). Therefore, not only does it not require a high-precision drive mechanism, but it also requires a low voltage bias, which is advantageous in terms of power supply and insulation structure. In addition, in the present invention, since the first development is black, even if other chromatic colors are mixed into the first development, the effect thereof can be practically ignored.

Furthermore, although the electrophotographic method has been described above, the present invention can be applied to an electrostatic recording method in which reversal development of a negative latent image is sequentially performed two or more times.

Furthermore, in the case shown in FIG. 1, it is effective to appropriately adopt a method of improving the transfer efficiency by uniformly irradiating the toner to eliminate static electricity, uniformly charging the toner, and recharging the toner before transfer. Furthermore, installing a magnetic carrier cleaner to remove unnecessary carrier that has adhered to the photoconductive drum after development is effective in preventing transfer omissions.

In summary, according to the present invention, in a color printing method in which two or more colors are sequentially developed using one drum and the formed toner images of two or more colors are simultaneously transferred, It can provide a color printing method that reduces toner image loss and color mixing, provides excellent print quality, and does not require a high-precision drive mechanism, high-voltage power supply, or high-voltage mechanism.
It can be said that this invention has excellent effects.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a printing device used for two-color printing electrophotography according to an embodiment of the present invention, and FIG. 2 is an enlarged explanatory diagram showing the state of toner adhesion after development. DESCRIPTION OF SYMBOLS 1... Photoconductive drum, 2... Charger, 3... First optical image, 4... First developing device, 5... Second optical image, 6
...Second developer, 7...Recording paper, 8...Transfer device,
9...Cleaner, 10...First latent image, 11...Second latent image, 12...First toner image, 13...Second toner image, 14...Mixed color toner image.

Claims (1)

[Scope of Claims] 1. A first latent image is formed on a photoconductive photoreceptor by a first exposure, this first latent image is reversely developed, and then a first latent image is formed on the photoconductive photoreceptor. A second latent image is formed by second exposure, and the process of reversing and developing this second latent image is repeated two or more times to create a toner image of two or more colors on the photoreceptor, and this is transferred to the recording paper. In a color printing method that creates an image of two or more colors by simultaneously transferring the image to a computer, the first color is black, and non-magnetic toners with sequentially higher saturation and brightness are used for the second and subsequent colors, and at least the second color is black. Color printing is a color printing method characterized by high-resistance two-component magnetic brush development using a high-resistance magnetic carrier of 10 ⁴ Ωcm or more. 2 In the invention described in claim 1,
The total development of multiple colors in sequence is 10 ⁴ Ωcm.
A color printing method that is high resistance two-component magnetic brush development using the above-mentioned high resistance magnetic carrier.