JPS63300257A - Two-color printer - Google Patents

Abstract

PURPOSE:To prevent an image from having color contamination by setting the two-dimensional light intensity distribution of the laser beam of a laser optical system positioned at least on the upstream side in an image forming process so that specific requirements are satisfied. CONSTITUTION:The spot shape of the laser beam emitted by the 1st optical system 3 of a two-color printer is so set that the two-dimensional light intensity distribution satisfies a condition a=x2/x1<=2.5. Here, x1 is radius width, and x2 is width at a position where light intensity is 1/e<2> as large as that in the center. Consequently, the potential distribution of an electrostatic latent image becomes relatively sharp at the boundary between an image part and a background part, the attractive force of toner at an edge part is relatively strong, and no toner is fetched into the developer of a 2nd developing device 7, so the color contaminating of the image is precluded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application 'J'F) The present invention relates to a two-color printer using a laser optical system.

(Prior Art) Conventionally, two sets of reversal development image forming process and transfer devices each consisting of a charging means, a laser optical system, and a developing device are arranged around a photoconductor drum along the rotational direction of the photoconductor drum. Two color printers are provided.

In this two-color printer, as shown in FIG.
In the first image forming process, the first charge uniformly charges (W
The surface of the photoreceptor drum subjected to the above process is subjected to first exposure from a laser optical system to form a negative electrostatic latent image, and then a first image of the electrostatic latent image is formed by first development. The toner of the first color is supplied to the portion (1, X charge erasing portion) to form a first toner image (T1).

Next, in the second copying process, second charging, second exposure, and second development are performed in the same manner as in the first copying process, and the second color toner is applied to the second image area (■,). is supplied to form a second toner image ('rt).

The 1st and 2nd toner images ('r +
) and ('r t) are transferred all at once to a transfer paper (not shown) in a transfer process.

(Problems to be Solved by the Invention) However, in the two-color printer, the first image portion (1
1), the toner of the first toner image (eighth) attached to the second toner image
When passing in front of the developing device, it often gets mixed into the second developing device, and this is supplied to the second image section ([,) along with the second color toner, resulting in color mixing in the image. .

Therefore, as a result of examining the cause, the present inventor found that
We found that the sharpness of the laser beam emitted from the laser optical system has an important effect on color mixture.

To explain this point in detail, since the Gaussian beam (Rg) having the light intensity of the Gaussian distribution shown in FIG. 13 is sharp, when the photoreceptor drum is irradiated with it,
As shown by the solid line in the figure, the potential distribution of the electrostatic latent image (V
g) is the image area (charge erased area) and the background area (charge remaining i'i
) becomes relatively sharp. Therefore, as shown in FIG. 15, the toner image (To) of the image area irradiated with the light of the Gaussian beam (Rg) has a clear outline.
The adhesion force of l.ner is relatively strong.

However, as shown by the dotted line in FIG. 13, when the photoreceptor is irradiated with a laser beam (R) in which the flare part (F) has a wider spread than the Gaussian beam (Rg), the light in the flare part (F) The potential decreases from the irradiated part, and the potential distribution (V) of the electrostatic latent image is less sharp than that of the Gaussian beam.

Therefore, in the case of the laser beam (R), as shown in FIG. 16, toner adheres not only to the original image area but also to the edge area irradiated with the light of the flare area (Fo).

However, the adhesion of the toner ('ro') at the edge portion is weak, and therefore, when it comes into contact with the developer in the second developing device when passing through the area facing the second developing device, it easily damages the photoreceptor. It peels off from the surface of the drum and is incorporated into the developer of the second developing device.

In particular, when a semiconductor laser is used in the laser optical system, it has been experienced that the laser light emitted from the semiconductor laser, unlike laser light such as a gas laser, has a very large flare area and a large degree of color mixing. It was done.

(Means for Solving the Problems) The present invention has been made based on the above-mentioned findings, and includes a charging means, a laser optical Two toner images formed in different colors on the surface of the electrostatic latent image carrier are simultaneously formed on transfer paper using the image forming process. In a two-color printer that transfers,
In the image forming process, the two-dimensional light intensity distribution of the laser beam of the laser optical system located at least on the upstream side is α-X, /X, ≦2.5. It is set so as to satisfy the condition that the width at the position becomes 1/e''.

(Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a schematic configuration of a two-color printer, in which a photosensitive drum (1) rotating in the direction of arrow (a) is surrounded by a first charging charger (2), a first optical system (3), a first Developing device (4
), the second charger (
5), a second image forming process consisting of a second optical system (6), a second developing device (7), a transfer roller (8), a cleaning device (9), and an eraser lamp (10).

From the above configuration, in a two-color printer, the photoreceptor drum (1)
is rotating in the direction of arrow (a), first, in the first image forming process, a first charge is applied to the surface of the photoreceptor drum (1), which is uniformly charged by the first charging charge (2). A laser beam is irradiated from the first optical system (3) to form an electrostatic latent image, and the image area where the charge has disappeared by being irradiated with the laser beam is exposed to the first color toner from the first developing device (4). The toner image is supplied to form a first toner image.

Next, in a second image forming process, similarly to the first image forming process, a second optical system (6) is applied to the surface of the photoreceptor drum (+) charged by the second charging charger (5). The laser beam is irradiated, and then the second phenomenon device (7)
Colored toner is supplied to form a second toner image.

When the transfer charger (8) reaches the development area facing the photoreceptor drum (1), the 1.2 toner image formed in this way is transferred to the development area due to the discharge of the transfer charger (8). The image is transferred all at once onto a transfer paper conveyed from the direction of arrow (P).

After residual toner is removed from the surface of the photosensitive drum (1) onto which the toner image has been transferred by a cleaning device (9), residual charges are removed by an eraser lamp (10) in preparation for the next image formation.

By the way, in the two-color printer, as described above, there is a possibility that the first toner may get mixed into the second developing device (7).

Therefore, in the two-color printer according to this embodiment, based on the study results described below, the spot shape of the laser beam emitted from the first optical system (3) has a two-dimensional light intensity distribution of α"X 1 / It is set so as to satisfy the condition that X 1≦2.5 x, −half width x,; the width of the position where the light intensity becomes I/e2 of the center.

The details of the study will be explained below.

Figure 2 shows five types of laser beams (G) and (A).

The light intensity distributions of (I3), (C), and (D) are shown, and the laser beam (G) is a Gaussian beam.

Note that the ratio between the half-width (xl) of each beam and the width (X, ) at a position where the light intensity corresponds to 1/e1 of the center.

The α value (α-Xt/XI) is shown in the table below.

Next, the potential distribution of the electrostatic latent image when the surface of the photosensitive drum (1) is irradiated with each beam is calculated based on the following equation, and the results are shown in FIGS. 3 to 12. In addition, the charger (2
), (5), the surface of the photoreceptor drum (1) is 500
Assume that it is charged to V.

v-v. -e-E ■ Two surface potentials o: Initial surface potential E; light intensity (E = Eo-e-') In Figs. 3 to 12, Eo'' is 3°0 and E. -4
The case of 0 is also shown.

As a result, the laser beam (
G) (Gaussian beam), the electrostatic latent image shows a very sharp shape. Also, as shown in Figures 5 to IO, the laser beams (A), (I3), and (C) are relatively sharp, but as shown in Figure 11.12, the laser beam (D) When this happens, the image lacks sharpness.

Next, 1 If I laser beam (G), (A) to (D)
was irradiated onto the surface of the photoreceptor drum (1), and the degree of color mixing was investigated. The results are shown in the table below.

As shown in Table 2, if the α value of the laser beam is about 2.0, a clear image can be obtained with almost no color mixture. However, when the α value is about 2.4, some color mixture occurs.

Therefore, it can be seen that if the α value is 2.5 or less, there is no extreme color mixture, the color mixture does not appear so clearly on the image, and it is suitable for use.

Therefore, in the two-color printer, the toner of the toner image formed in the first image forming process is scraped off by the second developing device (7), and is further supplied to the surface of the photoreceptor drum (1). There will be no color mixing in the image.

Although not shown in the above table, it was confirmed that color mixture increases when the light intensity distribution contains many components with peak values of 1710 or less.

Therefore, by using a laser beam with less of the above-mentioned components (components with a peak value of 1710 or less), images can be made clearer and free from color mixture.

Further, in the above embodiment, only the laser beam of the first optical system (3) is set to have an α value of 2.5 or less. The laser beam may also be set up accordingly.

(Effects of the Invention) As is clear from the above description, in the two-color printer according to the present invention, the two-dimensional light intensity distribution of the laser beam of the laser optical system located at least on the upstream side of the two image forming processes is , α-Xt/XI≦2.5 It is set to satisfy the condition that x is the half-width X: the width of the position where the light intensity is 1/e'' of the center.

Therefore, since the toner of the first toner image formed in the first image forming process is strongly attracted to the surface of the electrostatic latent image carrier even at the edge portion, when it passes through the opposing portion of the second developing device, Even if it comes into contact with the second developer, it will not be easily peeled off and will not be mixed into the second developer. Therefore, the image formed by the first developing device is sharp, and there is no color mixture in the image formed by the second developing device, and the image quality is the same. , Figure 2 is a diagram showing the light intensity distribution of the laser beam, Figures 3 to 12 are potential distribution diagrams on the surface of the photoreceptor drum irradiated with the laser beam, Figure 13 is a diagram showing the light intensity distribution of the laser beam, and Figure 14. 15 and 16 are diagrams showing the potential distribution of an electrostatic latent image, FIGS. 15 and 16 are diagrams showing the state of toner adhesion to the photosensitive drum, and FIG. 17 is a diagram showing the image forming process.

1... Photosensitive drum, 2... First charging charger,
3... First optical system, 4... First developing device, 5...
2nd charging charger, 6...2nd optical system, 7...2nd developing device, 2nd...transfer charger, G, A, ~, D
...Laser beam (G Ni Gauss beam).

Figure 1 Figure 9 Figure 10 Figure 11 Figure 12 χ
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Claims (1)

[Claims] (1) Two sets of reversal development image forming processes consisting of a charging means, a laser optical system, and a developing device are arranged around the electrostatic latent image carrier along the moving direction of the electrostatic latent image carrier, and the image forming process is In a two-color printer that simultaneously transfers two toner images formed in different colors on the surface of the electrostatic latent image carrier onto transfer paper using an image process, the printer is located at least on the upstream side of the image forming process. The two-dimensional light intensity distribution of the laser beam of the laser optical system satisfies the following conditions: α=x_2/x_1≦2.5 x_1: Half width x_2: Width at the position where the light intensity is 1/e^2 of the center A two-color printer characterized by being set to