JPH0263225B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for forming a multicolor image, and more particularly, the present invention relates to a method for forming a multicolor image, and in particular, by repeating an image forming process multiple times including at least the steps of charging, image exposure, toner development, and especially reversal development, the present invention relates to a multicolor image forming method. The present invention relates to a multicolor image forming method in which a plurality of toner images of different colors are superimposed on each other. [Prior art] As a multicolor image forming method as described above,
Methods described in Japanese Patent Application Laid-open No. 56-144452, Japanese Patent Application Laid-open No. 58-116553, and Japanese Patent Application Laid-open No. 58-116554 are known. In all of these methods, repeated image exposures are performed by separate devices,
This method requires shifting the subsequent image exposure position from the previous image exposure position so that they do not overlap, and the toner is charged to the same polarity as the electrostatic image whose potential is lower in the exposed area compared to the background area potential. This is a method using a development method that attaches. Therefore, when image exposure is performed using, for example, spot distribution exposure using a laser beam scanner to form a multicolor image such as a landscape painting, the spots of image exposure for each color are likely to be affected by the toner image that has already been formed. Since the positions are shifted so that they do not overlap each other, there is a problem that the density of the live spot distribution becomes coarse, and only a multicolor image that looks rough and faded can be formed.Furthermore, the recording device becomes larger and more expensive, and the image quality becomes worse. There is also the problem that the synchronization control of image exposure for the forming body is complicated because it is related to the position of the image exposure device. [Problems to be Solved by the Invention] The present invention enables multicolor images such as landscape paintings to be recorded with deep colors and fine details, and furthermore, the recording device can be configured to be small and low cost, and the synchronization control of image exposure can be easily controlled. The present invention provides a multicolor image forming method that can be performed in a variety of ways. In principle, the easiest way to obtain a multicolor image is to repeat the charging, image exposure, and development processes as many times as necessary to superimpose toner images of different colors on an electrostatographic photoreceptor (hereinafter simply referred to as photoreceptor). However, this is difficult in practice and one of the main reasons for having to use the above-mentioned complicated method is that the toner image previously formed on the photoreceptor is It blocks light during image exposure and prevents image formation at the image superimposed portion on the photoreceptor. The state is schematically shown in FIG. Figures 2A and 2B show the case of so-called regular development in which toner adheres to the unexposed charge residual area and gives a positive image upon exposure. Figures 2C and 2D show the charge of the developer and the bias during development. This shows a case of so-called reversal development in which toner adheres only to the portions of the photoreceptor where the charge has decreased due to exposure by changing the voltage, etc., and giving a negative image in response to exposure. In the figure, the position of the solid line indicates the potential E on the surface of the photoconductor, and the horizontal axis indicates the position on the photoconductor. In the case of regular development, the charge applied to the entire surface of the photoreceptor during the first charging (Fig. 2 A-1) is reduced by imagewise exposure, leaving unexposed areas b and d (Fig. 2 A-1).
2) By the first development, toner _T1 adheres to portions b and d, forming an image of the first color. Next, a charge is given to the entire surface again by the second charging (Fig. 2 A-4), and the second image exposure is performed at a, b,
When the electric potential is applied to the parts c, e, and g, in order to form a correct color image, the electric potential of all exposed parts must be lowered as shown in Figure 2 A-5, and the second electric potential must be lowered after development.
As shown in Figure A-6, even if images of different colors formed using toners T ₁ , T ₁ +T ₂ and T ₂ are to be formed on portions b, d and f, toners are already used.
If light is absorbed by the toner T ₁ layer in part b where an image is formed by T ₁ , no drop in potential occurs (Figure 2 B-5), and unexposed parts d and f
The toner T ₂ is attached to the b part as well as the b part by the second development (FIG. 2B-6). As a result, toner T ₁ is also applied to portion b where an image of only toner T ₁ is to be formed.
+T ₂ color image is formed. In addition, in the case of reversal development, when the second exposure is applied as shown in FIG. 2 C-5, the potential of the portion x where an image has already been formed by the first development and the toner T ₃ decreases, and the toner T ₄ After the second development, even if an image is obtained in which an image in which T ₃ and T ₄ are superimposed as shown in the x section of FIG. 2 C-6 is obtained, the toner T ₃
Due to _light absorption by 2, toner T ₃ ,
Only a monochrome image of T ₃ is formed in the x area where a mixed color image of T ₄ should be formed. In order to solve the above problems, the present inventors conducted research focusing on the spectral reflectance of toner, and as a result, they arrived at the present invention. [Means for solving the problem] This problem is solved by repeating the process of charging, image exposure with light of the same wavelength using a single exposure means, and reversal development using dry toner multiple times for each rotation of the photoreceptor. A multicolor image forming method in which a plurality of toner images of different colors are superimposed on the photoconductor and then transferred to a transfer material, the toner images already formed on the photoconductor being removed during repeated image exposure. A multicolor image forming method characterized in that the relationship between the constituent dry toner and the image exposure of the exposure means is set such that the spectral reflectance of the dry toner is 40% or more with respect to the image exposure of the exposure means. It will be resolved. [Function] As mentioned above, this problem basically lies in the blocking of light by the toner layer already formed on the surface of the photoreceptor at the time of exposure, but the layer formed by a light scattering material such as toner There are many difficulties in directly measuring the effective amount of transmitted light that reaches the photoreceptor directly under the photoreceptor, and the inventors' studies have revealed that the reflectance is the effective amount of light under the above-mentioned practical conditions, i.e. It has become clear that there is a correlation with the amount of effective transmitted light. Therefore, the reflectance of the toner layer referred to in the present invention can be understood to have the same meaning as its effective transmittance. In other words, the present invention uses light that is highly transparent to the toner layer already formed on the photoreceptor as the light used for exposure, thereby allowing the light to reach the photoreceptor covered with the toner layer and causing the superimposition. This allows a toner image to be formed. Each toner image is usually made up of one to two layers of toner particles, so the reflectance is a value measured using a sample in which toner particles are uniformly formed into almost one layer. Specifically, I sprinkled an appropriate amount of toner on the adhesive side of Maitatsu Label manufactured by Nichiban Co., Ltd. with a spoon, and smoothed out the toner with my fingers, removing the excess to create the desired toner attachment area on the adhesive side. removed from the area. Remove the label as necessary (due to the measuring instrument, this area is φ = 30
mm or more is required. ). The desired sample can then be obtained by gently rubbing the toner with the fingers in this manner until substantially no toner sticks to the fingers. The spectral reflectance of this sample is measured using a spectrophotometer 330 manufactured by Hitachi, Ltd. Although the method of the present invention can be applied to the formation of multicolor images by combining toners of arbitrary colors,
It can be particularly preferably used for forming so-called full-color images using yellow, magenta, and cyan toners. The exposure light used in the method of the present invention includes:
There is no particular restriction for the first exposure when no toner is present on the photoconductor, and for the second and subsequent exposures, each toner that makes up the toner image already formed on the photoconductor must be 40% or more. It is sufficient that the light has a spectral distribution maximum in a wavelength range showing a reflectance of . The light source is not particularly limited, but colored light obtained by using a white light source such as a laser or a monochromatic halogen lamp in combination with various filters is preferably used. Various methods can be used for color separation exposure, such as a method of inputting and recording images for each color in the form of electrical signals. The above method is a method used in color printers, etc., and the color of the exposure light can be selected independently of the color of the image to be recorded.The light source uses OFT (optical fiber tube), laser, LED, and liquid crystal shutter. etc. are preferably used. Hereinafter, the relationship between the exposure light and the spectral reflectance of the toner in the method of the present invention will be described in the case of forming a full-color image using the color separation method and monochromatic light. Figure 1 shows the spectral reflectance of full-color yellow Y, magenta M, and cyan C color toners used in the examples described below. , shows that cyan toner, on the contrary, strongly absorbs the long wavelength side of 550 nm or more. Further, this spectral reflectance is common for full-color toners. As the blue, green, and red outer filters mentioned above, commercially available glass filters and the like can be used, and these may be combined with a white light source such as a halogen lamp to form an exposure light source. It is also possible to use a combination of light sources having blue, green, and red wavelengths that satisfy the above conditions. If the three-color images are formed in any other order, the superimposition of the images will be hindered, as shown in Table 1, due to light absorption by the previously formed toner images, which is not preferable.

〔Example〕

Using the apparatus shown in FIG. 4, developing units 5 to 7 were filled with yellow, magenta, and cyan toners having the spectral absorptions shown in FIG. 1, respectively, and a full-color image forming test was conducted. A photoreceptor having a Se photosensitive layer was used, and its circumferential speed was 180 mm/sec. The surface of the image forming body 1 is charged to +500V by a charger 2 using a scorotron corona discharger, and 16 spots are placed on the charged surface by a laser beam scanner shown in FIG. 5 using a He-Ne laser with a wavelength of 632.8 nm. The first exposure was carried out at a density of /mm. The exposure intensity was set to 2 to 20 times the half-reduction exposure amount (the amount of exposure required to reduce the potential of the photoreceptor to 1/2) to sufficiently reduce the potential of the photoreceptor. As a result, the image forming body 1 has a background potential of +500 V.
In contrast, an electrostatic image with a potential of +30V at the exposed area was formed. This electrostatic image was subjected to first reversal development using a developing device 5 as shown in FIG. Developing unit 5 contains 50wt of magnetite in resin.
% dispersed content average particle size is 30μm, magnetization is
A carrier with a resistivity of 30emu/g and a resistivity of 10 ¹⁴ Ωcm or more,
Used under conditions where the toner ratio in the developer is 20 wt%, which is made of a non-magnetic toner with an average particle size of 10 μm, which is made by adding 15 parts by weight of a quinaphthalone pigment as a yellow pigment to a styrene-acrylic resin and other charge control agents. there was. Also, the outer diameter of the developing sleeve 22 is 30 mm.
mm, its rotation speed is 100 rpm, N, S of the magnet body 23
The magnetic flux density of the magnetic pole is 1000 Gauss, and the rotation speed is
1000 rpm, the thickness of the developer layer in the developing area is 0.7 mm, the gap between the developing sleeve 22 and the photoreceptor 1 is 0.8 mm, the developing sleeve 22 has a DC voltage of +400 V and 1.5 KHz,
Non-contact development conditions were used in which a superimposed voltage of 1000 V AC voltage was applied. While the electrostatic image was being developed by the developing unit 5, the other developing units 6 and 7, also shown in FIG. 3, were kept in a non-developing state. That is developing sleeve 2
2 from the power source 30 and placed in a floating state, or grounded, or actively apply a DC bias voltage to the developing sleeve 22 with a polarity opposite to that of the charging of the image forming member 1, that is, a polarity opposite to that of the charging of the toner. Among these, it is preferable to apply a DC bias voltage. Since the developing units 6 to 7 are also assumed to perform development under non-contact developing conditions like the developing unit 5, the developer layer on the developing sleeve 22 does not need to be particularly removed. This developing device 6 uses a developer in which the toner in the developing device 5 is changed to an azo reiki pigment as a magenta pigment instead of a yellow pigment, and the toner in the developing device 7 is also configured such that the toner is changed to an azo reiki pigment as a magenta pigment instead of a yellow pigment. A developer with a different composition was used. Of course, color toners containing other pigments or dyes may also be used. The pre-transfer exposure lamp 10 is applied to the surface of the photoreceptor 1 where the first development has been performed (this may be omitted), while the static eliminator 13 and the cleaning device 14 are not applied. After charging the rotation eye a second time to +500V with charger 2,
The same laser beam scanner again overlaps the spot positions and performs a second image exposure with the same spot density, and then the developer 6 exposes the second image of magenta toner.
I developed it twice. The third development of the cyan toner using the developing device 7 was repeated in the same manner. Regarding each of the above-mentioned developments, the amplitude, frequency, and frequency of the DC bias component and AC component of the voltage applied to the developing sleeve 22 are appropriately adjusted according to changes in the surface potential of the image forming body 1, development characteristics, color reproducibility, etc. The development density of each color can be adjusted by changing the selection time etc. of the time selection conversion. When the third development is performed and a three-color image is formed on the photoreceptor 1, the image is transferred to the pre-transfer charger 9.
The image was easily transferred using a pre-transfer exposure lamp 10, was transferred onto a recording medium P using a transfer device 11, and was fixed using a fixing device 12. The photoreceptor 1 to which the color image has been transferred is
The static electricity is removed by the static eliminator 13, residual toner is removed from the surface by contact with the cleaning blade or fur brush of the cleaning device 14, and the surface on which the color image has been formed is transferred to the cleaning device 1.
4, one cycle of multicolor image formation was completely completed. The color image recorded in the above manner had a high density of spot pixels and a delicately expressed pattern. The color mixture according to this embodiment is subtractive color mixture. On the other hand, additive color mixing is known in which the spot positions are shifted for each color. When using this method, extremely high writing position accuracy is required and it is difficult to achieve high density, but this method is also effective when used for additive color mixture. In this case, even if the writing position accuracy is insufficient and a subtractive color mixture part occurs during additive color mixture where some spots of different colors overlap, or an intermediate state between subtractive color mixture and additive color mixture is intentionally created to increase the density. Even if a toner image is created, it has the advantage that the toner images overlap, so that a good color balance can be maintained. [Effects of the Invention] According to the method of the present invention, a toner image for copying can be formed in a predetermined manner by using light with a spectral distribution that is less likely to be absorbed by the toner image already formed on the photoconductor for image exposure. It has now become possible to form superimposed lines. For this reason, it has become possible to increase the image spot density in recording devices such as laser printers, and it has become possible to record fine multicolor images. Excellent color images can also be recorded using ordinary color copying machines, and since the electrostatic images are formed by the same device, the recording device can be made compact and inexpensive. However, an excellent effect can be obtained in that synchronization control of image exposure for the image forming body can be easily performed. The present invention can also be applied to an image forming body in the form of a belt or a sheet, or an image forming body mounted on a substrate such as electrofax paper, and The color image formed by the toner may be fixed without being transferred. In addition to corona transfer, the transfer may be bias roller transfer, adhesive transfer, or pressure transfer via an intermediate transfer member.
Of course, fixing is not limited to heat roller fixing. That is, in the present invention, in the image forming process in which charging, exposure, and reversal development are repeated, exposure is performed using a common exposure means with light of the same wavelength. Thereby, registration in the main scanning direction and the sub-scanning direction between each monochromatic image formed on the photoreceptor can be easily and highly accurately ensured. And for that image exposure performed with light of the same wavelength,
The relationship between the dry toner and image exposure is set so that the spectral reflectance for the dry toner that makes up the toner image already formed on the photoreceptor is 40% or more, so whether the first image exposure or the photoreceptor It does not depend on repeated image exposures performed with a toner image already formed on the photoreceptor, nor does it depend on the color of the dry toner constituting the toner image already formed on the photoreceptor. The intensity and amount of image exposure applied to the photoreceptor are stable regardless of the number of image exposures, and the sensitivity of the photoreceptor is also the same in each image forming process, which is extremely convenient for color reproduction and color adjustment. is good. Further, in the present invention, in the repeated image forming process, charging is performed before exposure, and development is performed by a reversal development method, that is, a method in which development is performed using a toner having a charge of the same polarity as the charging. As a result, a latent image is formed and developed on the photoconductor, which has a uniform surface potential including the area to which toner is attached, so that sufficient image density is obtained and unnecessary color mixture is avoided. Prevented. Furthermore, a composite image on a photoreceptor can be easily transferred. Furthermore, in the present invention, exposure is performed with light of the same wavelength in each image forming step. When a color toner image is obtained by performing reversal development, a color image with good color reproducibility can be obtained by performing exposure with the same wavelength in this manner. That is, in reversal development, the density of the toner image obtained is closely related to the amount of reduction in the surface potential of the photoreceptor due to exposure, so in each image forming process, exposure is performed with light of the same wavelength, and during repeated image exposure The relationship between the dry toner constituting the toner image already formed on the photoreceptor and the image exposure of the exposure means is set such that the spectral reflectance of the dry toner is 40% or more with respect to the image exposure of the exposure means. Preventing fluctuations in the sensitivity of the photoreceptor by doing so is an extremely effective means for improving the color reproducibility of color images.

[Brief explanation of drawings]

FIG. 1 is a graph showing the spectral reflectance of yellow, magenta, and cyan toners and the spectral distribution of laser light used in the examples of the present invention, and FIG. 2 is a schematic diagram showing the state of superimposed formation of toner images. FIG. 3 is a sectional view of the developing device, FIG. 4 is a schematic diagram of the multicolor image forming apparatus, and FIG. 5 is a schematic diagram of the laser beam scanner. 1... Photoreceptor, 2... Charger, 4... Image exposure device, 5-7... Developer, 9... Pre-transfer charger, 1
0... Pre-transfer exposure lamp, 11... Transfer device, 12
... Fixing device, 13 ... Static eliminator, 14 ... Cleaning device, 15 ... Laser, 16 ... Acousto-optic modulator, 17 ... Mirror scanner, 18 ... F-θ lens for imaging, 19, 20 ... ...Miller, 21...
... Lens device, 22 ... Developing sleeve, 23 ...
Magnet body, 24... Layer thickness regulating blade, 25... Scraper blade, 26... Stirring rotor, 27...
...Developer reservoir, 28...Toner hopper, 29...
...Toner supply roller, 30...Power supply, 31...Protection resistor.

Claims (1)

[Claims] 1. A plurality of toner images of different colors are formed on the photoreceptor by repeating the steps of charging, image exposure with light of the same wavelength using a single exposure means, and reversal development with dry toner for each rotation of the photoreceptor. A multicolor image forming method in which images are superimposed and then transferred to a transfer material,
During repeated image exposure, the relationship between the dry toner constituting the toner image already formed on the photoreceptor and the image exposure of the exposure means is such that the spectral reflectance of the dry toner is 40% with respect to the image exposure of the exposure means.
A multicolor image forming method characterized by setting as described above.