JPS62260168A - Contour image forming method - Google Patents

Abstract

PURPOSE:To obtain a contour image free from photographic fog due to a toner as a positive image by subjecting an electrostatic latent image, which is formed in the second electrifying process with the charged toner having the same polarity as the first electrifying process, to reversal development to stick the toner to the outline part of an original image in the low-potential part of the electrostatic latent image. CONSTITUTION:The first electrifying process where the electric charge of a certain potential is applied to the surface of an electrostatic latent image carrier and the exposure process where a positive is exposed on the surface of the electrostatic latent image carrier which passes the first electrifying process are provided. In the second electrifying process, the surface of the electrostatic latent image carrier is electrified again while applying a voltage, which is lower than the surface potential of an electrostatic latent image part formed on a grid in the exposure process and is higher than that of a non-image part and has the same polarity as the first electrifying process, by a scotron charger to which an alternating voltage is applied; and the development process is provided where the electrostatic latent image formed in the second electrifying process is subjected to reversal development with the charged toner having the same polarity as the first electrifying process.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a contour image forming method as one of electrophotographic image forming methods, and particularly to a method of forming a contour image corresponding to the outer peripheral portion of a contour of a document image.

In general, in an image, contour lines contain a lot of information, and at the same time fully express the characteristics of the image, and play an important role in the image. Furthermore, images that have been converted into binary figures by drawing contour lines are easier to identify than ordinary grayscale images.

Extremely easy to handle in multiple processes such as determination and transmission,
Converting an image into a binary figure by drawing a contour line is extremely effective in terms of image pattern recognition, image correction/enhancement, bandwidth compression, and the like. Also, for example, by repeating two copies and adding a colored outline around a black pattern to make it more noticeable, or by painting one pattern in different colors to create patterns with different colors, so-called coloring books can be used. It is also useful when preparing a specific pattern.

By the way, conventional methods for forming contour images of this type include:
The present applicant has already developed a one-component toner developing method in which an electrostatic latent image is developed with a conductive toner, which has a potential intermediate between the maximum and minimum surface potentials of the member to be developed, and Shizuka 1! We propose a method characterized by extracting the outline of an electrostatic latent image on a member to be developed by applying a DC bias having a polarity opposite to that of the latent image charge between the member to be developed and a conductive toner carrier. (Refer to Japanese Unexamined Patent Publication No. 134635/1983).

However, in this method, the contour formed as an electrostatic latent image is a negative image, and the conductive toner adheres to areas with a large potential difference based on the potential difference on the surface of the electrostatic latent image carrier, that is, areas other than the contour line. Therefore, the developed image is obtained only as a negative image. Normally, the required contour image is a positive image (black image), so the problem is that in order to make a positive image, the negative contour image obtained by this method must be copied again using reversal development. have.

Means for Solving the Problems In order to solve the above problems, the contour image forming method according to the present invention includes: (1) a first charging step of applying a constant electric charge to the surface of the electrostatic latent image carrier; (i) an exposure step of positively exposing the surface of the electrostatic latent image carrier that has undergone the first charging step, and (i) a scorotron in which an alternating voltage is applied to the surface of the electrostatic latent image carrier that has undergone the exposure step.・The charger applies a voltage that is lower than the surface potential of the electrostatic latent image image area formed in the exposure process to the grid, higher than the surface potential of the non-image area, and has the same polarity as the first charging process, while recharging the grid. (iv) a developing step of reversing and developing the electrostatic latent image formed through the second charging step with a charged toner having the same polarity as that of the first charging step; It is characterized by having

1-In other words, after exposing the surface of the electrostatic latent image carrier to which a constant electric charge is applied in the first charging step (see (a) in FIG. 3), a positive image is exposed in the second charging step. A scorotron charger to which a voltage is applied applies a voltage to the grid that is lower than the surface potential of the electrostatic latent image image area formed in the exposure process, higher than the surface potential of the non-image area, and has the same polarity as the first charging process. while recharging. As a result, the surface potential of the non-image area of the electrostatic latent image increases to approximately the grid voltage, leaving the outline of the image area, and the surface potential of the image area decreases slightly to around the grid voltage, leaving the outline of the image area. (See (b) in Figure 3).

Next, the electrostatic latent image formed through the second charging step is reversely developed using charged toner having the same polarity as the first charging step. As a result, the charged toner adheres to the contour of the electrostatic latent image portion left at a low potential, and the contour image is developed as a positive image (see (c) in FIG. 3).

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the contour image forming method according to the present invention will be described below.

FIG. 1 schematically shows an electrophotographic copying machine for carrying out the present invention, in which the photosensitive drum (1) is a well-known type having a photoconductive layer on its outer peripheral surface, and can be driven to rotate in the direction of the arrow (,). The following members and equipment have been installed around it.

Charging (2) is for performing a first charging to apply a constant electric charge to the surface of the photoreceptor drum (1), and a power source (21) is connected to the charging wire.

The exposure device (3) is for forming an electrostatic latent image corresponding to the original image on the surface of the photoreceptor drum (1) using the well-known slit exposure method, and is composed of an exposure lamp, a mirror, a lens, etc. has been done.

The scorotron charger (4) is connected to the exposure device (3).
) to perform a second charge on the surface of the photoreceptor drum (1) on which an electrostatic latent image has been formed.The charge wire is connected to a power source (41), and the grid (42) is connected to a power source. (43) is connected. What about the charge wire? [F
An alternating voltage is applied from t (41), and the grid (42)
From the electric charge fA (43>), the electrostatic latent image has a surface potential lower than the surface potential of the image area and higher than the surface potential of the non-image area, and an electrostatic charge ~(
A voltage of the same polarity as 2) is applied.

Developing equipment! (5) is a developing sleeve (51) that has a built-in magnet roller (52) with Nai and S poles on its periphery.
4ii! The developing sleeve (51), which also functions as a developing electrode, is equipped with 1! for developing bias. source (53) is connected. The developer is composed of a mixture of a sensitive carrier and an insulating toner, which are charged to opposite polarities by frictional charging, and the insulating toner is charged to the same polarity as the charger (2).

Here, if the insulating toner does not have magnetism, a developing bias slightly lower than the grid voltage and having the same polarity as the charger (2) is applied from the power source (53) to the developing sleeve (51). It looks like this. On the other hand, when the insulating toner has magnetism, a developing bias that is higher than the grid voltage and on which an alternating current voltage is superimposed is applied to the developing sleeve (51). However, in this case, only insulating toner can be used.

The transfer charger (6) applies an electric field from the back side to the copy paper (10) being conveyed in the direction of arrow (b), and the developing device (5) applies an electric field to the surface of the photoreceptor drum (1). It is used to transfer the formed toner image onto the copy paper (10), and its charge wire has 1! A voltage having a polarity opposite to that of the insulating toner is applied from a source (61).

The separation charger (7) applies an alternating current electric field to the copy paper immediately after transfer to remove static electricity from the copy paper (10) and separate it from the surface of the photoreceptor drum (1). An alternating current voltage is applied to the wire from an electric current tA (71).

The cleaning device (8) uses a blade method to remove toner remaining on the surface of the photoreceptor drum (1).

The eraser lamp (9) is used to remove charges remaining on the surface of the photoreceptor drum (1) by irradiating light in preparation for the next copying process.

Here, the polarity and voltage of each charger etc. in this example will be shown.

[I] When using insulating non-magnetic toner Charger [power supply (21) positive polarity +5.5kV Scorotron charger ['Kfi (41)] alternating voltage ±6. OkV Grid [Power supply (43)] Positive polarity +500v Developing bias [Electric! <53)] Positive polarity +400v Transfer charge ~ [Electricity m (61)] Negative polarity -6, OkV Insulating non-magnetic toner Positive polarity [II] When using insulating magnetic toner Charger [Power supply (21) positive pole +5.5kV Scorotron charge ~ [mEa (4t)] Alternating voltage ±6. OkV Grid [power supply (43)] Positive polarity +500■ Development bias [power supply (53)] Positive polarity (DC) +530■ (AC>350Vrms, 1kllz development start potential
+450 ■ Insulating magnetic toner Positive polarity Note that all of these polarities may be reversed,
Of course, the voltage value is only an example.

The outline image forming method using the copying machine described above will be explained step by step.

(1) First charging step A charger (2) applies a constant electric charge to the surface of the photoreceptor drum (1). As a result, in this example, the surface potential of the photoreceptor drum (1) is +600V.

(i) Exposure step The original image is exposed to slit light on the surface of the photoreceptor drum (1) fully charged to a potential of +600V to form an electrostatic latent image. In this case, as shown in FIG. 3 (a), the image area (A)
, (B) remains as a potential of +600■, and the charge of the part corresponding to the non-image area decreases to about +100■ upon irradiation with light. Note that a positive original image is used.

(i) Second charging step The surface of the photoreceptor drum (1) on which the electrostatic latent image is formed is recharged using a scorotron charger <4) to which an alternating voltage is applied from a power source (41). At this time, a voltage of +500V is applied from the power supply (43) to the grid (42).The voltage ξ applied to this grid (42) is the surface potential ( +600V
), higher than the surface potential (+100V) of the non-image area, and the same polarity as the first charging step.

Electric lines of force shown by arrows in FIG. 2 are formed between the surface of the photosensitive drum (1) and the grid (42).

Ions of negative and positive polarity generated from the charge wire to which an alternating voltage is applied are subjected to a transport force along the lines of electric force. In this case, the lines of electric force that direct positive ions toward the surface of the photoreceptor drum (1) in the vicinity of the grid (42) are It only occurs in some areas.

Therefore, positive ions are located in the image area (A) as indicated by the arrow →.

It reaches only the background part excluding the outside of the outline part in (B), and raises the potential of the reached part to a potential approximately equal to the grid voltage (+500V).

In addition, as shown by the arrow →, the negative ions reach only the central part of the image area (A) excluding the inner part of the outline, and remove the charge in the reached part, near the potential approximately equal to the grid voltage (+500V). It drops to . That is, the photosensitive drum (1
), as shown in FIG. 3(b), the surface potential of the non-image area of the electrostatic latent image is equal to
The grid voltage (Vg: +
500V), and the outside of the contour remains with a constant width as a low potential portion of approximately +100V.

In other words, in this second charging step, the image area (A),
This means that the outline in (B) is formed as a negative electrostatic latent image.

(~) Developing Step In the second charging step, the static latent image formed as a negative image of the contour portion is developed by the developing device (5). If the insulating toner does not have magnetism, the developing sleeve (5
1>, a developing bias of +400v is applied. The voltage (vb) of this developing bias is 1! In order to prevent toner from adhering to the non-image area of the latent image (and of course the image area), the voltage is raised to a value that is slightly lower than the grid voltage (Vg: +500V) and approximately equal to the grid voltage (Vg). It is lower than the potential of the background portion and has the same polarity as the first charging step.

On the other hand, if the insulating toner has magnetism, the developing step
7-B (51) has AC350V, 1kHz and DC
A developing bias of +530V is applied. The developing bias voltage (Vb) is the grid voltage (Vg: 50
0V) and higher than the potential of the background area, which has risen to approximately the same value as the grid voltage (Vg). However, when using magnetic toner, there is a threshold due to magnetic binding force, so developing starts when the surface potential is around 450V. Therefore, toner does not adhere to and cover the non-image area of the electrostatic latent image (of course, the image area) that has risen in the second charging step.

In this way, the positively charged insulating toner is applied to the low potential areas of the photoreceptor drum (1), that is, to the contour areas of the image areas (A) and (B), or so to speak, to form an "outer edge." A toner image is formed by reversal development.

This toner image is then transferred onto the copy paper (10) by negative discharge from the transfer charger (6), and is formed as a copy image by passing through a fixing device (not shown).

Furthermore, in this embodiment, the distance Pi (dg) between the surface of the photoreceptor drum (1) and the grid (42) (see FIG. 2)
is said to be 1.5 mm. This value is large compared to the settings of the scorotron charger conventionally used in this type of electrophotographic copying machine. This is the surface image part (A)
This is to increase the extent to which the lines of electric force are directed toward the surface of the photoreceptor in the edge portion (contour) or line image portion (B), thereby obtaining a good contour image.

The state of the electric lines of force changes depending on the distance ai (dg). That is, by changing the distance (dg), it is possible to arbitrarily change the width of the contour line obtained as an image, and as the distance (dg) increases, the width tends to increase as well.

Effects of the Invention As is clear from the above explanation, according to the present invention, as a second charging step, the surface of the electrostatic latent image carrier that has undergone the exposure step is charged onto a grid using a scorotron charger to which an alternating voltage is applied. The surface potential of the electrostatic latent image carrier is lower than the surface potential of the image area, higher than the surface potential of the non-image area, and is recharged while applying a voltage of the same polarity as the first charging step. A negative electrostatic latent image is formed in which the outline of the image area remains as a low potential area, and in a further development process, the electrostatic latent image is reversely developed using a charged toner having the same polarity as that in the first charging process. Therefore, in this reversal development, toner adheres to the contour portion of the document image, which is the low potential portion of the electrostatic latent image, and a contour image without toner fog can be obtained as a positive image.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an electrophotographic copying machine for carrying out the contour image forming method according to the present invention, FIG. 2 is a schematic diagram of electric lines of force in the second charging step, and FIG. It is a graph showing the potential of an electrostatic latent image. (1) Photoreceptor drum, (2) Charger, (3) 15 light'A position, (4) Scorotron charger, (42) Grid, (5) Developing device, (51)...Developing sleeve.

Claims (1)

[Claims] 1. A first method for applying a constant electric charge to the surface of the electrostatic latent image carrier.
a charging step, an exposure step of exposing a positive image on the surface of the electrostatic latent image carrier that has undergone the first charging step, and a scorotron in which an alternating voltage is applied to the surface of the electrostatic latent image carrier that has undergone the exposure step. The charger applies a voltage that is lower than the surface potential of the electrostatic latent image area formed in the exposure process to the grid, higher than the surface potential of the non-image area, and has the same polarity as the first charging process, while recharging the grid. a second charging step; and a developing step of reversing and developing the electrostatic latent image formed through the second charging step with a charged toner having the same polarity as that of the first charging step. Characteristic contour image forming method.