JPS60239769A - Color image forming device - Google Patents

Abstract

PURPOSE:To take a sufficient time from preexposure for ghost image erasing to primary charging to obtain pictures of good quality having a sufficient picture density, by providing an exposure means, which gives uniform exposure of near infrared rays to a photosensitive body, between a transfer means and a cleaning means. CONSTITUTION:When a preexposure light source 2 is arranged between a transfer means 9 and a cleaning means 7 as shown by a solid line, a sufficient time can be taken from preexposure to primary charging in comparison with the case where the light source 2 is arranged in a position 2' indicated by a dotted line in a device, and potential reduction after primary charging is held down to a minimum even if necessary uniform exposure is given by the preexposure light source 2. Since near infrared rays are used as the light of the preexposure light source 2, the difference of the quantity of light between a toner sticking part and a part where a toner is not stuck is reduced considerably in case of a black toner, and this difference is reduced in case of a cyan toner, a magenta toner, and a yellow toner also. Consequently, the occurrence of ghost images which are apt to occur when uniform exposure to a remaining toner image after transfer is performed is prevented effectively.

Description

Detailed Description of the Invention A. Purpose of the Invention [Field of Industrial Application] This invention is for making multicolor copies by electrophotography, and is particularly directed to photosensitive drum-type transfer type color copying devices or color copies. -Relating to laser beam printers, etc.

[Conventional technology]

The process of forming color-separated latent images on an electrophotographic photoreceptor, developing them with developers of corresponding colors, and transferring the resulting developed images to a transfer material is repeated multiple times to form a multicolor image on the transfer material. Color image forming apparatuses have been put into practical use.

However, in order to obtain a full color image in the color image forming apparatus described in (a), it was necessary to increase the diameter of the photosensitive drum in order to securely arrange the developing devices around the photosensitive drum for three to four colors.

Therefore, a color image forming apparatus was proposed in which developing units for three to four colors are hung like a gondola and are of a rotationally movable type, and the developing unit corresponding to the latent image is moved to the developing position during development (#
(Refer to Publication No. 50-93437), the diameter of the photosensitive drum can be reduced, and the device has the great advantage of making the device more compact and making the photosensitive drum more versatile (-common use with photosensitive drums for black-in-the-shell image forming devices). be.

[Problem that the invention seeks to solve]

By adopting the rotary developing device as described in L, it has become possible to reduce the diameter of the photosensitive drum to, for example, 150 mmφ or less. However, the distance between the pre-exposure position for eliminating ghost images and the primary charger inevitably becomes close. Therefore, especially when the circumferential speed of the photosensitive drum is high, if the fog light amount of the pre-exposure required to erase the ghost image is increased by 1J-, a large number of photocarriers generated by the pre-exposure remain until the primary charging, and the photosensitive drum is As a result of lowering the dark resistance of the body, only a low charging potential can be obtained when primary charging is performed.

Figure 2 shows the time t from pre-exposure to reaching the primary charger position.
It shows the characteristics of the surface potential vS of the photoreceptor due to the primary charging against . When the amount of fog light necessary to obtain the pre-exposure effect is applied, ■ is 0.3 seconds or less.

In this case, Vs tends to drop significantly.

Therefore, in order to compensate for the potential drop after primary charging as described in L,
When the voltage applied to the primary charger is reduced, pinholes are generated in the photosensitive drum, which significantly reduces the durability of the photosensitive drum. Therefore, it is necessary to reduce the number of pre-exposure light stars, but if this is done, the ghost image on the original document will not be erased sufficiently.6Especially in full-color image formation, the ghost image of one color separation latent image will appear in the next color separation latent image. If it appears during formation, the image will be observed as a one-tone difference, making it easy to stand out and making it impossible to put it into practical use.

The present invention aims to solve the problems listed in L.

1. Structure of the invention [Means for solving the problems] A latent image formed on a drum-type electrophotographic photoluminescent body is exposed to light having a wavelength of approximately 700 nm or more (near infrared light) using a rotationally moving developing device. Developed with a transparent toner.

In a color image forming apparatus equipped with a cleaning means for transferring the developed images onto a transfer material and cleaning residual toner on the photoreceptor, near-infrared light is uniformly applied to the photoreceptor between the transfer means and the cleaning means. This is a color image forming apparatus characterized by being provided with an exposure means for applying light.

[Effect]

According to the configuration of item L, as will be described later, sufficient time can be taken from pre-exposure for ghost image erasing to completion of primary charging, and the above-mentioned problem can be solved.

〔Example〕

FIG. 1 is an explanatory diagram of the apparatus of the present invention. 1 is a photosensitive drum using a photosensitive material such as amorphous silicon (hereinafter abbreviated as ^-3i), the surface of which is given a positive electrostatic charge by a primary charger 3; 4 forms a color separation latent image in an image exposure path.

Reference numeral 5 denotes a rotationally movable multicolor developing device group, in which developing devices containing negative polarity toners of yellow 5Y, magenta 5M, cyan 5C, and black 5B are suspended from a photoreceptor in a gondola shape, and the color separations shown in L are carried out. The developing device of the color corresponding to the latent image moves to the developing position and stops F to develop the color separated latent image 6. The developing devices are transferred and charged to the transfer material PI-, held on the surface of the mesh screen transfer drum 6. The image is transferred by the positive polarity corona current of the device (transfer means) 9. The toner remaining on the surface of the photosensitive drum 1 without being transferred is cleaned by a cleaner (cleaning means) 7 that does not require a blade, for example.

Rolling: After the four colors of developed images are aligned and transferred onto the material P, the transfer material P is separated by the separation claw 8 and guided to a fixing device (not shown) where it is fixed to obtain a full color image.

No. L is a known device, and conventionally, a pre-exposure light source for erasing ghost images is placed at position 2 indicated by the dotted line, that is, immediately before the primary charger 3, so it has the above-mentioned problems. Ta.

Note that it; i Wa is a uniform exposure of light with a wavelength of about 700 nm or more, and I.na is transparent to light of that wavelength.

In the present invention, the pre-exposure light source 2 described in I- is arranged between the transfer element 13) 9 and the cleaning means 7'- as shown by the solid line 1. It's ours.

With this configuration, it is possible to take sufficient time (for example, three times as long) to complete the primary charging after the pre-exposure compared to the 11 exposures shown in dotted line 2 in the device arrangement. Even if sufficient uniform exposure is achieved using light source 2, the problem of potential drop after primary charging can be minimized. , 1-5 is a method of applying uniform white light to the surface of the photoreceptor in order to assist in cleaning and remove the trapped charge of residual toner after transfer. Since there is an extreme difference in the amount of exposure that the photoreceptor receives between the part and the part that is not adhered, even if strong exposure is given for the purpose of removing ghosts, the result is that the ghosts are increased.

The present invention solves the above problems by providing uniform exposure to near-infrared light using a pre-exposure light source 2 in a color image forming apparatus using color toner or black toner that transmits near-infrared light. This is what I did.

The exposure light source 2 may include a plurality of bulbs of halogen lamps or tungsten lamps arranged in the axial direction of the photosensitive drum, and a filter having visible light cutting and near-infrared light transmission properties provided between the photosensitive drum and the bulbs, or Alternatively, it is preferable to arrange a large number of LEDs or the like having an emission wavelength of about 700 nm or more in the axial direction of the photosensitive drum.

FIG. 3 shows the spectral transmittance T of each color toner image transferred to a transparent transfer material, and each characteristic curve shows that the transmission density of the image after fixing is cyan=1. Ei, magenta = 1.4
, yellow=1.0. This is about a toner image with black=1.2.

Regarding the spectral transmittance of the cyan, magenta, and yellow toners shown in FIG. 3, similar characteristics can be obtained if the toner uses general dyes and pigments as colorants. However, regarding black toner, toner (B) that uses general carbon black pigment as a colorant and toner (A) that uses black dye (for example, manufactured by Nippon Kayaku Co., Ltd. (Kayaset, Black 822, etc.) as a colorant) This shows two characteristics of .

As shown in the characteristics in Figure 3, the four color toners of cyan, magenta, yellow, and black (A) all have a particle diameter of approximately 700 nm.
It has high transmission characteristics for the following wavelengths, and uniform exposure by the exposure light source 2 can be carried out through those toners to a photoreceptor (such as A-5i photoreceptor) sensitive to this wavelength range. The residual latent image charge corresponding to the residual toner image after transfer can be effectively removed.

Figures 4 and 1 are cyan, Figures 4 and 2 are magenta, fJtJ
Figure 4113 shows the characteristics of yellow toner, and Figure 404 shows the characteristics of black toner.White light from a halogen lamp light source (dotted chain line) for one undetermined 7I toner image on transparent transfer material H, and 50% cut by the halogen lamp light source. wavelength is 7
It shows the transmittance T of near-infrared light (solid line) provided with a near-infrared light transmission filter that cuts visible light of 40 nm. The horizontal axis indicates the transmission density DT after the unfixed toner image is fixed (transmission density through a complementary color filter for cyan, magenta, and yellow images).

The broken lines in each figure are calculated values, and the characteristics of the black (B) toner (double-dashed line) in FIGS. 4 and 4 are characteristics due to near-infrared light and white light, and almost match the calculated values.

As shown in Figures 4.1 to 4.4, for cyan, magenta, yellow, and blurred (A) toners, near-infrared light (solid line) is higher than white light (dotted chain line). Indicates transmittance. Furthermore, the near-infrared light transmittance of the black (A) toner is much higher than that of the black (B) toner.

By the way, the maximum developed image density of photosensitive drum ■: is usually 2.
．． It is around 0. Also, the transfer rate of the first color is usually 70 to 80.
%, but when multiple transfer is performed in a color image forming apparatus, the transfer rate of the third or fourth color may drop to about 60% in a low humidity environment.

Therefore, the maximum residual toner image density after transfer is 0.8 compared to the above image density on the photosensitive drum of 2.0 (
(at a transfer rate of 60%). In Figures 4.1 to 4, when the transmission density DT = 0-8, the transmittance of near-infrared light is cyan = 62%, magenta = 66%, yellow 26%.
9 times, black (A) = 57%. Also, D = 0.
Transmittance by white light at 8 is cyan - 39%, magenta = 47%, yellow = 53%, blank (B) = 1
It will be 5%.

Therefore, when uniform exposure is given to a photoconductor having a black toner image, the amount of exposure received by the photoconductor surface in the area to which toner is not attached is as follows:
The case where white light is applied to black (B) toner is xoo/
15': 8.7 times, and 100757 to 1.8 times when near infrared light is applied to black (A) toner.

As described above, according to the present invention, in the case of Blur 7 toner, it is possible to significantly reduce the difference in light amount between the toner-adhered area and the non-adhered area, and it is also possible to reduce the difference in light amount between cyan, magenta, and yellow. Therefore, it is extremely effective in preventing the generation of ghost images that are likely to occur when a residual toner image after transfer is uniformly exposed.

The reason why the transmittance of uniform exposure to near-infrared light of the present invention is higher than that of white light is due to the transmission characteristics of the toner itself, as well as the fact that short wavelength light generally has a higher refractive index. be.

When light is irradiated onto fine particles, such as in a single unfixed toner image, refraction occurs between the particles and the air layer.
It is thought that near-infrared light, which has a small refractive index, has the effect of reducing light refraction and the resulting light scattering, thereby increasing transmittance6. Pre-exposure may be performed using a pre-exposure light source 2 shown by dotted lines in FIG. In this case, the pre-exposed portion of the light ff12 can be reduced, and the drop in charging potential after primary charging can be suppressed, which is more effective in preventing the generation of ghost images.

C. Effects of the invention As mentioned above, compared to the case where the pre-exposure light source is provided immediately before the primary charger, it provides a necessary and sufficient amount of light, and also minimizes the potential drop after the primary charging, while maintaining image density. images of sufficient high quality can be obtained.

Furthermore, since it is not necessary to increase the single charge potential, the durability of the photosensitive drum can be improved without causing pinholes in the photosensitive member.

In addition, uniform exposure to near-infrared light has the effect of neutralizing the latent image charge on the photoreceptor corresponding to the residual toner image after transfer, and furthermore, it is possible to suppress the generation of ghost images that are likely to occur at that time.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the color image forming apparatus of the present invention, FIG. 2 is a characteristic diagram showing the relationship between charging time and photoreceptor potential, FIG. 3 is a spectral transmittance curve diagram of color toner and black toner, and FIG.・Figures 1 to 4 are transmittance curve diagrams of unfixed toner images. l is a photosensitive drum, 2 is a pre-exposure light source, 3 is a primary charger, 4
5 is an image exposure optical path, 5 is a rotationally movable developing device, 6 is a transfer drum, Pi running transfer material, 7 is a 7h sweeping means, and 9 is a transfer means. Patent applicant Canon Co., Ltd. Figure 3 Figure 1

Claims (1)

[Claims] (1) A latent image formed on a drum-type electrophotographic photoreceptor is developed with a toner that is transparent to near-infrared light using a rotary moving type developer, and the developed images are transferred to a transfer material and placed on the photoreceptor. In a color image forming apparatus equipped with a process means for cleaning residual toner, an exposure means for uniformly exposing the photoreceptor to near-infrared light is provided between the transfer means and the cleaning means. A color image forming apparatus with v characteristics.