JPS63301069A - Method for exposing image of colored electrophotography - Google Patents

Abstract

PURPOSE:To obtain an image with favorable color balance without necessitating a complicated correcting means and adjustment by illuminating an original with fluorescent lamp obtained by mixing plural kinds of phosphors whose light emission peak lengths are different respectively at the time of separating the color of original. CONSTITUTION:By illuminating the original 1 with the fluorescent lamp 3 obtained by mixing plural kinds of phosphors whose light emission peak wavelengths are different respectively, at the time of separating the color of the original, the color difference between the original and a copied matter obtained by copying the original can be made small. Then, a complicated adjusting mechanism for adjusting the color balance is not necessitated and a trouble that the color balance should be adjusted while seeing copied result can be saved. Since the light emission peak wavelength of the light source itself is selected, the loss of light quantity can be made extremely small and the power consumption in the case of color separation can be suppressed low. Thus, the color balance of the image can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image exposure method for color electrophotography, and in particular,
The present invention relates to a color separation image exposure method for forming a latent image on a sensitive material in color electrophotography.

[Conventional technology]

As one of the color image recording methods, a method is known in which monochrome electrophotography is repeated as many times as necessary. for example,
Using yellow, magenta, and cyan toners, processes such as exposure and development are repeated three times to obtain a color image. According to this electrophotographic method, color images can be obtained more easily and in a shorter time than with printing methods or color photography methods. However, the image quality is generally inferior to that of printing methods and color photography methods.

The reason for this is that there is not enough contrast between the necessary and unnecessary colors during the latent image formation stage, and color correction (also known as masking, which is widely used in printing, etc.) cannot be performed easily. can be mentioned.

The conventional color electrophotographic method will be explained below with reference to FIGS. 5 to 7.

FIG. 5 shows the image forming process of a conventional color electrophotographic method using a powder development method.

The sensitive material is first uniformly charged by a charger.

Next, the color original image is irradiated with a fluorescent lamp and separated into colors by a color separation filter having transmission characteristics as shown in FIG. 6, and the sensitive material is exposed to light using this color separation image to form a color latent image . In addition, Figure 6 Nioite, 10B, LOG
, IORIt show the characteristics of blue, n-color, and red color separation filters, respectively.

Next, this color latent image is developed with toner of a complementary color to the color of the color separation filter, and then a toner image on the sensitive material is formed on paper in a transfer process.

The above-mentioned series of cycles is repeated a number of times for the necessary colors to transfer the necessary engraving onto the paper, and then fix the toner on the paper. Usually, the number of repetitions is red separation/cyan toner development, edge separation/magenta toner development.

There are three times: blue separation and yellow toner development, and black toner development may be added depending on the case.

At this time, the following points become a problem.

For example, considering the case where a printed matter becomes an original image, FIG. 7(a) shows the reflection characteristics of process ink during each color separation.

Shown in (b) and (C).

In Fig. 7(a), IIC, IIYM are the reflection characteristics of the overlapping part of cyan ink, yellow ink, and magenta ink during red separation, and in Fig. 7(b), IIM, IIYM are
CY is the reflection characteristic of the overlapping part of magenta ink, cyan ink, and yellow ink during edge separation, and in the same figure (C), ll
MC, IIY indicates the overlapping part of magenta ink and cyan ink during blue separation and the reflection characteristics of yellow ink.

In FIG. 7, the two reflection characteristics in each color separation indicate the color that should be developed in each color separation, that is, the necessary color, and the color that should not be developed, that is, unnecessary color. For example, when red is separated, the line becomes a necessary color, and yellow and magenta become unnecessary colors.

During color separation, the three color filters having the characteristics shown in FIG. 6 are sequentially exposed to light, so that the photosensitive material is illuminated with an amount of light corresponding to the average reflectance of the original image in the transmission range of each filter. Decrease the potential on the sensitive material. Therefore, the post-exposure potential on the photosensitive material is determined for the necessary color and unnecessary color from the above steps, and the potential difference becomes the contrast.

In the developing step, the developing bias in the developing device is set between the necessary color potential and unnecessary color potential so that the necessary color portion is developed with toner and the unnecessary color portion is not developed with toner.

At this time, if the contrast on the photosensitive material is not sufficient, the latitude of the development bias setting will be narrow, and changes in development characteristics due to fluctuations in temperature, humidity, etc. will easily appear in the image quality.

Therefore, there is a problem that stability of image quality is impaired.

Now, if we think about red resolution exposure, we can see Figure 6.

According to FIG. 7(a), the necessary color is cyan, and the unnecessary colors are yellow and magenta, that is, red, and the difference in average reflectance between the two during red separation exposure is relatively large. At this time, for example, a wavelength of 570 nm or more is transmitted, but if this wavelength is set on the long wavelength side, this difference becomes even larger.

However, during green separation exposure and blue separation exposure, as shown in FIGS. 7(b) and 7(C), the process ink becomes green.

The unnecessary absorption of blue is large, and the transmission band of the filter during color separation is 50 nm' at half value of green exposure and 1 at half value of blue exposure.
Due to the wide range of 00rv, the difference in average reflectance between necessary colors and unnecessary colors is small, and sufficient contrast cannot be obtained.

This unbalanced contrast between red, green, and blue separation causes unbalanced color reproduction, and especially the amount of cyan and magenta for important colors called memory colors such as skin tone, grass green, and sky blue. Errors will occur in the amount and quantity.

The following two methods are known as methods for improving this error.

One is a masking method used during color separation in printing and the like. This is to perform color conversion by, for example, IJ Fuchs calculation, taking into account unnecessary absorption of color materials used for image reproduction. Even when recording color images using color electrophotography, this masking method is employed in digital laser printers and digital copying machines, and is effective in correcting imbalance during color reproduction.

The other method is to optimize the optical system response according to the output color material, as is done in photography. In this case, optical adjustment is performed so that the unbalance of the reproduced image is corrected.

[Problem that the invention seeks to solve]

However, when employing the above masking method, the image must be first converted into an electrical signal and processed, so it is difficult to apply it to anything other than a so-called digital image output device. A binarization processing circuit or the like is required, which increases costs.

Optimization methods for optical system responses can also be adopted in color electrophotography, but in order to achieve strict optimization, it is necessary to apply a desired filter to a white light source such as a halogen that emits spectrally smooth light. It is necessary to apply However, with this method, the spectral light utilization rate is low, an excessive amount of light is required from the light source, the lamp power consumption increases, and the power consumption of the entire copier increases. A problem arises in that a commercial power source with sufficient power capacity cannot be used.

To deal with this, in the past, an adjustment unit was provided that could adjust the exposure amount, developing bias, etc. according to the characteristics of the original image, and the operator could match the image according to a certain adjustment procedure and be satisfied to some extent. The method is to adjust even the image quality.

However, such a method not only requires a complicated adjustment mechanism but also requires a dedicated operator for adjustment. That is, it is difficult for general customers to obtain satisfactory image quality with simple adjustments. Also,
Without sufficient contrast between necessary and unnecessary colors,
Since color correction is performed in the entire adjustment section, it has the disadvantage that it is difficult to maintain stability in image quality.

In view of the drawbacks of the prior art described above, the present invention aims to perform image exposure so as to obtain an image with good color balance without using complicated correction means or requiring complicated adjustment. shall be.

[Means for solving problems]

In the image exposure method for color electrophotography of the present invention, during color separation of the original, the original is illuminated with a fluorescent lamp containing a mixture of multiple types of phosphors each having a different emission peak wavelength, thereby copying the original and the original. It is characterized by reducing the color difference between it and the copy obtained by the process.

The plurality of types of phosphors can be used for blue exposure, edge exposure, and red exposure, respectively, and their emission peak wavelengths can be set to the following wavelengths.

For blue exposure 445±10nm For green exposure 515±10nm For red exposure 650±10nm In addition, 3.5Mg O.
It is desirable to use Q, 5MgFz-GeO,:Mn.

[Effect]

The present invention basically adopts the optical system response optimization method described above, but instead of selecting the band characteristics of the color filter, the optical system is adapted to the color characteristics of the toner used for electrophotographic recording. Calculate the response and color this optical response in blue.

This is achieved using a phosphor that is a mixture of green and red phosphors.

Below, the procedure for calculating the optical response will be explained.

Figures 2(a), 2), and 2(C) show the color characteristics of typical cyan, magenta, and yellow toners used in electrophotography. Calculate the optical system response.

Now, using the Macbeth Color Checker 24-color patch manufactured by Macbeth Co. as a manuscript, the optical system response to minimize the color difference between the manuscript and the copy was calculated using a multivariate analysis method. For example, the color difference is calculated by calculating the color difference between both the input document and the output spectral characteristics, and the system response is changed so that the average color difference in the 24 colors of the Macbeth color checker is minimized. When changing this system response, first red, I! , blue is varied to find the optimal value, and then this is fixed to find the system response for the next color.

The results obtained in this manner are shown in FIG.

In the figure, the horizontal axis is the wavelength, and the vertical axis is the NBS color difference ΔE by the CIELAB display system in a 2° field of view.
Shown in units.

At this time, the gradation characteristics due to the system parameters of electrophotography are involved at the same time, so the gradation characteristics differ from each other (in the figure,
The analysis was performed assuming the following conditions: (indicated by ○, ×, △). As a result, as shown in Figure 1, the wavelength that minimizes the color difference between the original and the copy obtained by copying this original does not depend on the gradation characteristics, and it is necessary to have the following peak wavelength. It turns out that there is something.

Blue resolution: 440nm Green resolution: 540nm Red resolution: around 650nm Therefore, phosphors having the above-mentioned peak wavelength as the peak of their emission band are mixed, and they are used to determine the spectral transmission characteristics of the optical system, the spectral sensitivity of the sensitive material, the dark potential of the sensitive material, and the spectral sensitivity of the optical system. By blending in a balance according to the contrast between bright potentials, it becomes possible to perform image exposure with excellent color balance without increasing power consumption.

〔Example〕

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, features of the present invention will be specifically described based on examples with reference to the drawings.

FIG. 3 shows an embodiment of the present invention.

The document 1 placed on the platen glass 2 is irradiated with direct light from the fluorescent lamp 3 and indirect light via the reflector 6 . The reflected light from the original 1 is filtered through the color separation filter 7.
8.7G and 7H, for example, is exposed to light on a sensitive material (not shown) through a blue color separation filter 7B and a lens (not shown) to form an electrostatic latent image. The fluorescent lamp 3 is equipped with a lamp heater 4 to stabilize the light output. A heat sink 5 is provided, and the mercury vapor pressure is controlled by a temperature control device (not shown).

The inner wall of the fluorescent lamp 3 is coated with a phosphor, and in this embodiment, a mixture of the following three types of phosphors at a certain ratio is used.

Blue Ba! Jg2AQ 1s○2. ;εu (4
45nm peak) Green Mg+41)++○l 9:C
e, Tb (545nm peak) red 3.5Mg
0 ・0.5MgF2:GeO,:Mn(658
nm peak) The mixing ratio is determined from the spectral transmittance of the optical system, the spectral sensitivity of the sensitive material, the white paper reflectance, and the dark potential/bright potential contrast of the sensitive material. It is specified as a ratio.

Blue: Green; Red = 0.17: 1: 0. '79 That is, the amount of each phosphor is selected so as to obtain the above ratio.

In addition, each of the above-mentioned phosphors has the ideal blue, green, and red wavelengths of 440 nm and 540 nm from among manually available phosphors.
, those having an emission peak wavelength close to 650 nm are selected.

FIG. 4 shows a system response curve obtained by multiplying the spectral transmittance of the fluorescent lamp and optical system thus obtained and the spectral sensitivity of the sensitive material. This curve is normalized and displayed with the peak luminescence value of each color as 100%. Note that the numbers in parentheses indicate the ratio of the peak luminescence amount of each color phosphor.

At this time, the filter 108 in FIG. IOG
.

10R was used, but since the phosphor itself emits light in a specific wavelength band, the filter has less influence on color separation than when using a white light source such as a halogen lamp. Therefore, the present invention is not necessarily limited to the filter having the characteristics shown in FIG.

In addition, in this embodiment, rather than applying a narrow band color separation filter to the halogen lamp, the emission peak wavelength of the fluorescent lamp 3 itself is selected, so that the amount of light emission that does not contribute to color separation is extremely small. There is less attenuation in the filter.

Therefore, there is no need to increase the amount of light from the fluorescent lamp 3, and power consumption during color separation can be kept low.

Next, the results of imagewise exposure according to the embodiments of the present invention will be explained in comparison with the results of imagewise exposure according to the conventional method.

The dark potential of ah was set to 1200 V for red, green, and blue, and the bright potential was set to 150 V for red, green, and blue. Take a 24-color copy of
The results obtained in E are shown.

This example: R, M, S, ΔE = 21 (L"a"
b"ΔE) Conventional example: RIM, S, ΔE=28 (
L"a"b"ΔE) Here, the conventional example has a color temperature of 3000
This is the case where the color filter shown in FIG. 6 is used for the K/% O) The factors involved in the system response are all the same.

As can be seen from the comparison results, according to this example, the color difference with the original was smaller and the color balance was improved than when a halogen lamp was used. Moreover, the lamp power consumption required in this case has been significantly reduced as shown below.

Near 0 W of this embodiment Conventional example: 400 W As described above, in this embodiment, in the color electrophotography method for obtaining one color copy by multiple copying processes, multiple types of light sources are used to illuminate the original to be copied. Fluorescent lamps are made of a mixture of phosphors. This phosphor is for blue, green, and red, and its emission peak wavelength is 445±10 nm.
By setting the wavelengths to 515±10 nm and 650±10 nm, an image exposure method with excellent color balance can be provided with low power consumption. Especially 3.5 as a red phosphor! , 1g○・0.5
When MgFz.GeO, +Mn is used, the emission peak wavelength is 658 nm, which satisfies the above conditions, and also has high energy conversion efficiency and little deterioration of light quantity over time, so it is preferable as a light source for copying.

〔Effect of the invention〕

As described above, in the present invention, the document is illuminated with a fluorescent lamp made of a mixture of multiple types of phosphors each having a different emission peak wavelength, taking into account the color characteristics of the toner that reproduces the image. , the color difference between the original and the copy is minimized. That is, the overall optical system response is set so that the color balance of the image obtained by copying is improved.

Therefore, there is no need for a complicated adjustment mechanism for adjusting the color balance, and there is no need to adjust the color balance while checking the copy result. Furthermore, in the present invention,
Since the emission peak wavelength of the light source itself is selected, compared to the method of applying a narrow band color separation filter to a halogen lamp,
Loss of light amount is extremely small, and power consumption during color separation can be kept low.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between optical system response and color balance, FIG. 2 is a graph showing the spectral characteristics of typical toners used in color electrophotography, and FIG. 3 is a configuration diagram showing an embodiment of the present invention. Fig. 4 is a graph showing the optical response in an example of the present invention, Fig. 5 is an explanatory diagram showing the color electrophotographic process, Fig. 6 is a graph showing the spectral transmission characteristics of the color separation filter, and Fig. 7 is the process. It is a graph explaining unnecessary colors and necessary colors in ink. 1: Original 2 Nibraten glass 3: Fluorescent lamp 4: Lamp heater 5/heat sink
6: Reflectors 7B, 7G, 7R: Color separation filter patent applicant Masu Kobori, agent of Fuji Xerox Co., Ltd.
(and 2 others) No. 1 Wavelength (nm) Figure 3 Figure 4 Wavelength (nm) Figure 5 Figure 56 Wavelength (nm)

Claims (1)

[Claims] 1. During color separation of the original, the original is illuminated with a fluorescent lamp containing a mixture of multiple types of phosphors each having a different emission peak wavelength, thereby obtaining a copy of the original and the original. An image exposure method for color electrophotography characterized by reducing the color difference between a copy and a copy. 2. The plurality of types of phosphors are for blue exposure, green exposure,
2. The image exposure method for color electrophotography according to claim 1, which is for red exposure and has a peak emission wavelength as shown below. For blue exposure 445±10nm For green exposure 515±10nm For red exposure 650±10nm 3. As the phosphor for red exposure, 3.5MgO・0.
The image exposure method for color electrophotography according to claim 2, characterized in that 5MgF_2.GeO_2:Mn is used.