JPS62291672A - Formation of outline image - Google Patents

Abstract

PURPOSE:To develop the positive image of an outline image by forming a developing process for inversely developing an electrostatic latent image formed through a 2nd electrostatic charging process for executing recharging while impressing voltage having the same polarity as that of a 1st charging process by charged toner having the same polarity as that of the 1st charging process. CONSTITUTION:After exposing a negative image to the surface 1 of an electrostatic sensitive body to which the charge of fixed potential is applied by an electrostatic charger 2, a grid 42 is recharged while impressing voltage lower than the surface potential of the non-image part of an electrostatic latent image formed by an exposure process 3 and having the same polarity as the charger 2 by a scorotron charger 4 to which DC voltage or alternate voltage having the same polarity as the charger 2 is impressed. The surface potential of the electrostatic latent image part other than the outline part of the image part is raised up to almost the grid voltage and then the electrostatic latent image formed through the scorotron charger 4 is inversely developed by the charged toner having the same polarity as the electrostatic charger. Consequently, the charged toner is stuck to the outline part of the electrostatic latent image part with low potential and the outline image is turned to a positive image.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Field of Application The present invention relates to a contour image forming method as one of electrophotographic image forming methods, and in particular to a method for forming a contour image using a negative original image, a laser, an LED, etc. The present invention relates to a method for forming a contour image corresponding to the inner circumferential portion of a contour of a negative image formed by et al.

BACKGROUND OF THE INVENTION Conventional techniques and their problems In general, contour lines are a part of an image that contains a lot of information, and at the same time sufficiently express the characteristics of the image, and thus play an important role in the image. Furthermore, an image that has been converted into a binary graphic with contour lines is easier to identify than a normal A-light image.

Extremely easy to handle in various 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 and enhancement, bandwidth compression, and the like. Also, for example, you can repeat copying twice and add a colored outline around the black pattern ;+'i'1 to make it easier to hitch, or you can color one pattern by coloring it in different colors)'4 It is also useful when preparing a so-called coloring book-like pattern in order to create a pattern that looks like a coloring book.

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 A method characterized by extracting a contour line of an electrostatic latent image on a member to be developed by applying a DC bias having a polarity opposite to that of the electrostatic latent image charge between the member to be developed and a conductive toner carrier. (Refer to Japanese Patent Application Laid-open 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, a fully developed image can only be obtained as a negative image. Normally, the required contour image is a positive image (black, image), so in order to make a positive image, the negative contour image obtained by this method must be copied again using reversal development. There are problems.

In order to solve the above problems, the contour image forming method according to the present invention includes: (i) a first charging step of applying a constant electric charge to the surface of an electrophotographic photoreceptor; (i) the first charging step; (i) exposing the surface of the electrophotographic photoreceptor that has undergone the exposure process to a negative image; (■) a second charging step of recharging while applying a voltage lower than the surface potential of the non-image area and having the same polarity as the first charging step; and (■) static electricity formed through the second charging step. It is characterized by comprising a developing step of reversing developing the electrostatic latent image with a charged toner having the same polarity as the first charging step.

In other words, a negative image is exposed on the surface of the electrophotographic photoreceptor that has been charged with a constant potential in the first charging step (see (a) in FIGS. 3 and 6), and then in the second charging step. A scorotron charger to which a DC voltage or an alternating voltage of the same polarity as that of the first charging step is applied is applied to the first charging step, which is lower than the surface potential of the non-image area of the electrostatic latent image formed on the grid in the exposure step.
Recharging is performed while applying a voltage of the same polarity as the charging process.

As a result, the surface potential of the electrostatic latent image image area increases to approximately the grid voltage, leaving the outline of the image area [see Fig. 3 (
In particular, when an alternating voltage is applied to the scorotron charger, the surface potential of the non-image area also decreases slightly to around the grid voltage, leaving the area near the contour area [see (b) in Figure 6] .

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 blank image [see FIGS. 3 and 6 (C)].

Embodiment [First embodiment, see FIGS. 1 to 3] FIG. 1 schematically shows an electrophotographic copying apparatus for carrying out the first embodiment, in which the electrophotographic photosensitive drum (1) is It is a well-known device having a photoconductive layer on its surface, and can be rotated in the direction of arrow (a), and around it are the following members,
Equipment is installed.

The charging charge-r (2) is for performing first charging to apply a constant electric charge to the surface of the photoreceptor drum (1), and 71JX (21) is connected to the charge wire.

The exposure device (3) is a device that forms an electrostatic latent image corresponding to a negative original image on the surface of the photoreceptor drum (1) using the well-known slit exposure method, and uses an exposure lamp, mirror, lens, etc. As the exposure device (3), as long as it can form a negative electrostatic latent image, a scanning exposure method using electric signals such as a laser or LED may be used. good.

The scorotron charger (4) is connected to the exposure device (3).
) is used to perform a second charge on the surface of the photoreceptor drum (1) on which an electrostatic latent image has been formed. ) is connected to a power source (43).A DC voltage of the same polarity as (2) is applied from the power source (41) to the charged charge to the charge wire, and the grid (42) is connected to the power source (43).
), a voltage lower than the surface potential of the non-image area of the electrostatic latent image and having the same polarity as the charger (2) is applied. Note that the voltage applied to the grid (42) needs to be higher than the surface potential of the electrostatic latent image area whose potential has decreased in the exposure device (3>).

The developing device (5) is a well-known magnetic brush type device that includes a developing sleeve (51) that includes a built-in magnetic roller (52) with N and S poles magnetized around its periphery, and also functions as a developing electrode. A power source (53) for developing bias is not connected to the developing sleeve (51). The developer is made of a mixture of a magnetic 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, the developing sleeve (
51), a developing bias which is slightly lower than the surface potential of the electrostatic latent image area raised in the second charging process and has the same polarity as the charger (2) is applied from the power supply (53). ing. The insulating toner may have magnetism, and a bias voltage slightly higher than the surface potential of the electrostatic latent image area raised in the second charging step is not applied to the developing sleeve (51). Also good. Further, a developing bias in which an alternating current voltage is superimposed can also be applied. If the toner has magnetism, it is possible to use only insulating toner.

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 for transferring the formed toner image onto the copy paper (10), and the wire has 'W1. ! (6
From 1), a pressure of 1" of polarity opposite to that of the insulating toner can be applied.

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 a power source (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 the first embodiment will be shown.

[1] When using non-magnetic insulating toner, charge the power supply (21) positive polarity +5.5kV Scorotron Chihe-sha [1lJX (4t)] positive polarity +5.5kV grid [power supply (43)] ] Positive polarity +500v Grid-photosensitive drum distance (dg) 1.5mm Developing bias [power supply (53) positive polarity +400■ Transfer chiller [power supply (61)] Negative polarity -6, OkV Non-magnetic insulating toner positive pole [1] When using magnetic insulating toner Charger [power supply (21)] Positive polarity +5.5kV Scorotron charger ['Cff1 (41)] Positive polarity +5.5kV Grid [power supply (43>)] Positive polarity +500v Grid-photosensitive drum distance (dg) 1.5mm Development bias [power supply (53) positive polarity (DC) +530V (AC) 350Vrms, 1kHz Development start potential +450v boron insulating toner positive polarity Note that these polarities Regarding, everything may be reversed,
Of course, the voltage value is only an example.

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

(1) First Charging Step In the charging step 2), a constant electric charge is applied to the surface of the photoreceptor drum (1). As a result, in the first embodiment, the surface potential of the photoreceptor drum (1) is +600V.

(i) Exposure step A negative original image is exposed to slit light on the surface of the photosensitive drum (1) charged to a potential of +600V to form a negative electrostatic latent image. In this case, as shown in (a) in Figure 3,
The potential of the portions corresponding to the image areas (A) and (B) decreases to about +100V by light irradiation, and the potential of the portions corresponding to the non-image areas remains at +600V.

(i) Second charging step The photosensitive drum (1
) is recharged by applying a charge of the same polarity as the electrostatic latent image using a scorotron charger (4).

At this time, a voltage of +500 V is applied to the grid (42) from 'FLm (43) when non-magnetic insulating toner and magnetic insulating toner are used. The voltage applied to the scorotron charger (4) has the same polarity as the first charging step, and the voltage applied to the grid (42) is lower than the surface potential (+600V) of the non-image area of the electrostatic latent image and It has the same polarity as the first charging step. Note that the voltage applied to the grid (42) is equal to the surface potential (+100
V) Higher.

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

The positive polarity ions generated from the charge wire are subjected to a transport force along the lines of electric force. In this case, the electric lines of force that direct positive ions toward the surface of the photoreceptor drum (1) near the grid (42) occur only in the central part of the surface image area (A), excluding the inside of the contour. . Therefore, as shown by the arrow →, the positive ions reach only the central part of the surface image area (A) excluding the inside of the outline, and the area they reach is recharged to a potential close to approximately equal to the grid voltage (Vg). raise.

That is, in terms of the surface potential of the photoreceptor drum (1), as shown in FIG. almost + toov
The surface potential of the non-image area is also left as a high potential area of approximately +600V, which is the initial surface potential, and the center part of the surface image area (A) is approximately near the grid voltage (Vg). rises to.

Specifically, if the insulating toner has no magnetism or if it has magnetism, +5.5 kV to the scorotron charger power supply (41), grid electric m (43)
When voltage is applied to +500V (7), the voltage increases to around +500V.

Note that although the surface potential of the line image portion (B) hardly increases, the width of the low potential portion is slightly narrowed.

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

(iv) Developing step In the second charging step, the electrostatic latent image formed as a negative image of the outline is developed by a developing device (5). If the insulating toner does not have magnetism, the developing sleeve (51
) can be applied with a developing bias of +400V. This developing bias voltage (Vb) is set in order to prevent toner from adhering to the central part of the electrostatic latent image area (of course also in the non-image area) where the surface potential has increased in the second charging process. This potential increase is slightly lower than the central part of the image area (+500V) and has the same polarity as the first charging step.

On the other hand, when the insulating toner has magnetism, the developing sleeve (51) has AC350V, 1kHz and DC+53V.
A developing bias of 0V is applied. The developing bias voltage (vb) is higher than the potential (+500 V) at the center of the electrostatic latent image area, which has risen to a value approximately equal to the grid voltage (Vg). However, when an insulating toner having magnetism is used, there is a threshold value due to magnetic binding force, so development starts when the surface potential is around +450V. For this reason, the static 7 that rose in the second charging process
rL't! ! When the toner is applied to the central part of the image area (and of course to the non-image area), there is no chance of it being covered.

In this way, the positively charged insulating toner is transferred to the low potential areas of the photo drum (1), that is, the image areas (A) and (B).
), or so to speak, a toner image of an "inner edging pad" 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 via a fixing device (not shown).

By the way, the reason why the grid voltage (Vg) is made sufficiently higher than the surface potential (+100V) of the electrostatic latent image area is that the surface potential of the central part of the electrostatic latent image area is raised to the original surface in the second charging step. This is to raise the potential sufficiently.

[1[I] An example in which the conditions of the scorotron charger (4) in the second charging step are changed when the non-magnetic insulating toner of the first embodiment is used will be shown. In this case, when using a non-magnetic insulating toner, the above [I
] Among the conditions, change the following items.

Scorotron charger ['jff, source (41)] positive polarity +6.5 kV Grid [power source (43) positive polarity +400■ Grid-photosensitive drum distance (dg) 1, Omm Developing bias [power source (53) positive polarity +430 ■ In this modification, the charging ability of the scorotron charger (4〉) is high, so the potential at the center of the surface image area (A) is slightly higher than the grid voltage (Vg) +450
It rises to around V. Then, the developing bias potential (v
b) is set to +430v, which is higher than the grid voltage (Vg) of +400v, but the raised surface potential +
Since the voltage is lower than 450V, there is no possibility that toner will adhere to the central part of the electrostatic latent image surface image area (A) and cover it.

In the first embodiment described above, the distance ill (dg) between the surface of the photoreceptor drum (1) and the grid (42)
(See No. 213!!l) is set to 1.5 mm or 1.0 mm.

This value is larger than the setting of the scorotron charge conventionally used in this type of electrophotographic copying machine. This is to increase the degree to which the electric lines of force are directed toward the surface of the photoreceptor in the edge portion (contour) of the plane image portion (A) or the line image portion (B), and to obtain a good contour image. The state of the electric lines of force changes depending on the pressure 11t (dg). That is, by changing the distance FJ (dg), it is possible to arbitrarily change the width of the contour line obtained as an image, and as the distance i1t (dg) increases, the width tends to increase as well.

Note that this point also applies to the second embodiment described below.

[Second Embodiment, see Figures 4 to 6] This second embodiment differs from the first embodiment in that an alternating voltage is applied from the power supply (41') to the scorotron charger (4) that performs the second charging. 4 is different from Fig. 1, Fig. 5 is similar to Fig. 2, and Fig. 6 is similar to Fig. 3. Corresponds to each. Therefore, the differences will be explained below.

The scorotron chihe-ja (4) is the exposure device (3)
This is to perform a second charge on the surface of the photographic photosensitive 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). An alternating voltage is applied to the charge wire from the power supply (41'), and the power supply (41') is applied to the grid (42) as in the first embodiment.
3), a voltage lower than the surface potential of the non-image area of the electrostatic latent image and having the same polarity as the charger (2) is applied. In addition, the voltage that can be applied to the grid (42) is
It is necessary that the surface potential is higher than the surface potential of the electrostatic latent image area whose potential has decreased in the exposure device (3).

In addition, the polarity and voltage of each charge in the second embodiment are the same as those shown in the first embodiment, but the voltage of the power supply (41°) of the scorotron charger (4) is When using non-magnetic insulating toner, AC±f7. OKV, even when using insulating toner with i-character, AC±6. It is OkV.

Next, the contour image forming method will be explained step by step.

(1) First Charging Step A charging chiller (2) applies a constant electric charge to the surface of the photoreceptor drum (1). In the second embodiment as well, the surface potential of the photosensitive drum (1) is +600V, which is 9.

N) Exposure step The surface of the photosensitive drum (1) charged to a potential of +600V is irradiated with a laser to form a negative electrostatic latent image. In this case, as shown in FIG. 6 (a), the image areas (A) and (B
) is reduced to about +100V by laser irradiation, and the potential of the part corresponding to the non-image area remains at +600V.

(i) Second charging step The negative static 1! Photosensitive drum (1) on which a latent image is formed
The surface of the sample is recharged by a scorotron charger (4) to which an alternating voltage is applied from 71<4t'). At this time, the grid (42) is connected to the power source (43) by +5oov if non-magnetic insulating toner is used.
+500V even when using magnetic insulating toner
voltage is applied. The voltage applied to this grid (42) is the surface potential (+600V) of the non-image area of the electrostatic latent image.
It is lower and has the same polarity as the first charging step.

Electric lines of force shown by arrows in FIG. 5 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 electric lines of force that direct positive ions toward the surface of the photoreceptor drum (1) near the grid (42) occur only in the central part of the surface image area (A), excluding the inside of the contour. . Therefore, as in the first embodiment, the positive ions reach only the central part of the image area (A) excluding the inner side of the outline, as shown by the arrow →, and recharge the reached part to the grid voltage ( Vg). In addition, as shown by the arrow →, the negative ions reach only the background area excluding the outside of the outline of the image areas (A) and (B), and remove the charge in the area they reach, increasing the grid voltage (Vg).
The potential is lowered to approximately the same potential as .

That is, to describe the surface potential of the photosensitive drum (1), as shown in FIG. 6(b), the inner side of the outline of the surface image area (A) and the line image g+! (B) is approximately + to with a certain width
In addition to remaining as a low potential part of ov, the non-image areas near the image areas (A) and (B) also have an initial surface potential of approximately +6
The surface potential of the non-image area is left as a high potential area of 00V, and the surface potential of the non-image area decreases slightly to approximately the grid voltage (Vg) except for the outer edge of the image area (A) and (B), and the surface potential of the surface image area ( The surface potential of the central portion of A) increases to approximately the grid voltage (Vg), leaving the inside of the contour.

Specifically, if the insulating toner does not have magnetism, the scorotron charge ~7 [m (to 4n (7) ±6
．． okV, grid power supply (43) He (7) + 50
When a voltage of 0V (7) is applied, the surface potential of the central portion of the image area (A) and the surface potential of the non-image area are +50
It rises and falls to around 0V. Also, if the insulating toner has magnetism, the scorotron charger? If
±6. to source (41'). OkV, grid electric, Hara (43
), similarly, by applying a voltage of +500V to
Itching and drops to around 0V.

In other words, even in the second embodiment, the contours of the image areas (A) and (B) are formed as negative electrostatic latent images in the second charging step.

(iv) Developing step In the second charging step, the electrostatic latent image formed as a negative image of the outline is developed by a developing device (5). The development conditions and development mechanism here are the same as those in the first embodiment, but in the case of the second embodiment, the potential of the non-image area of the electrostatic latent image is lowered to the grid voltage in the second charging step. Even if the voltage drops to approximately equal to (Vg), the toner will not expand and cover the tube.

[Other Examples] By the way, since the development by the development device (5) is based on the reversal development method, the scorotron charger (
If the second charging step (4) is not performed, the negative electrostatic latent image formed in the exposure step can be developed as a normal reversal development to obtain a positive image. This can be easily controlled by switching the scorotron charger (4) on and off.

As is clear from the above explanation, according to the present invention, as the second charging step, the surface of the electrophotographic photoreceptor that has undergone the negative image exposure step is exposed to the grid using a scorotron charger. While applying a voltage lower than the surface potential of the non-image area of the electrostatic latent image formed in the step and having the same polarity as the first charging step,
Since the electrophotographic photoreceptor is recharged, a negative electrostatic latent image is formed on the surface of the electrophotographic photoreceptor in which the outline of the original image area remains as a low potential area. Because reversal development is performed using charged toner with the same polarity as in the charging process, toner is attached to the contour of the negative original image, which is the low potential part of the electrostatic latent image, and the toner is removed. A contour image without fog can be obtained as a positive image.

[Brief explanation of the drawing]

1 to 3 are for explaining a first embodiment of the present invention, and FIG. 1 is a schematic configuration diagram of an electrophotographic copying apparatus;
FIG. 2 is a schematic diagram of the lines of electric force in the second charging step, and FIG. 3 is a graph showing the potential of the electrostatic latent image in each step. 4 to 6 are for explaining the second embodiment of the present invention. FIG. 4 is a schematic configuration diagram of a sub-photocopying apparatus, and FIG. 5 is a diagram showing the electric force in the second charging process. The schematic diagram of the line, FIG. 6, is a graph showing the static M and the potential of the latent image in each step. (1)... Electrophotographic photosensitive drum, (2)... Charger, (21)... Power supply, (3)... Exposure device, <4)... Scorotron charge ~, ( 41>
, (41')...power supply, (42)...grid, (
43)...'Ff, source, (5)...developing device, 5
1)...Developing sleeve.

Claims (1)

[Scope of Claims] 1. A first charging step of applying a constant electric charge to the surface of the electrophotographic photoreceptor; and an exposure step of exposing a negative image to the surface of the electrophotographic photoreceptor that has undergone the first charging step. The surface of the electrophotographic photoreceptor that has undergone the exposure step is subjected to a voltage lower than the surface potential of the non-image area of the electrostatic latent image formed in the exposure step on the grid by a scorotron charger and of the same polarity as that of the first charging step. a second charging step in which the electrostatic latent image formed through the second charging step is re-charged while applying an electric current; and a developing step in which the electrostatic latent image formed through the second charging step is reversely developed with a charged toner having the same polarity as that in the first charging step. A contour image forming method comprising the following steps.