JPH08160711A - Electrifying device - Google Patents

Abstract

PURPOSE: To realize an inexpensive electrifier capable of mechanically setting each gap in the electrifier to an allowable distance, decreasing ozone producing amount by decreasing a discharge current and realizing uniform electrification. CONSTITUTION: A discharge electrode is constituted by arranging many needle electrodes 4 at fixed pitch (p). A rubber sheet 15 having middle resistance is allowed to intervene between the discharge electrode and the electrode of a power source. A grid electrode 7 is set between the discharge electrode and a body to be electrified. In the case the gap between the tip of the discharge electrode and the grid electrode is set (g), the electrodes are constituted so as to satisfy g<=0.5p+1p<=2mm and g<=pp>=2mm, and the gap between the tip of the discharge electrode and the grid electrode is set to >=0.5mm and <=4mm. The film thickness of a rubber layer is set within the range of >=1mm and <=10mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for a recording device such as a copying machine, a printer or a facsimile which uses an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art Most of electrophotographic copying machines which have been put into practical use conventionally employ a corotron or scorotron charger by non-contact corona discharge. In particular,
Even if the discharge source (corona wire) has uneven discharge, the scorotron charger automatically eliminates uneven charge potential because corona ions selectively move between the grid and the body to be charged to a location with low potential. It has very excellent characteristics.

However, these chargers have a problem that a large amount of ozone is generated. Therefore, recently, a contact charging method using an electrode such as a roller, a brush, or a blade that contacts an object to be charged has been proposed. In this contact charging method, the air discharge (corona discharge) in the air gap, the charge injection in the contact portion, and the frictional charge are combined to generate the charge, but the air discharge (corona) discharge is dominant in practice. .

The contact charging method produces less ozone.
The applied voltage for corona discharge is 5-8 KV, but the applied voltage for the contact charging method may be 1-2 KV. However, the structure of the contact charging type charger is more complicated and costly than that of the corona charger. Further, a charging roller made by dispersing conductive carbon black in high resistance rubber is used as an electrode, but since the conductivity of the charging roller is partially different,
The charging potential becomes uneven, and the resistance of the charging roller changes with environmental changes (humidity changes), which changes the charging characteristics. Furthermore, since the body to be charged and the charging roller are in contact with each other,
The residual toner after cleaning stains the charging roller, causing uneven charging. As a countermeasure, it is necessary to clean the charging roller. In addition, when there is a pinhole on the photoconductor drum, an overcurrent flows there, so that the image does not appear in a horizontal line or the image becomes completely black. Further, there is a problem that a part of the rubber roller flies and is damaged.

Therefore, several new techniques have been proposed in order to avoid the problems associated with contact and to reduce the amount of ozone generated.

For example, Japanese Unexamined Patent Publication No. 5-107866 proposes a system in which a semiconductive flat plate electrode is brought close to a photosensitive member and a corona discharge is performed. Since this method is non-contact like the conventional corona discharge, it has an advantage that it is not affected by poor cleaning or pinholes of the photoconductor.

However, unlike the corona discharge in which the gap between the electrode and the photoconductor is 10 mm and the contact charging in which the gap is 0 mm, the gap of 0.2 mm must be accurately maintained. For example, in corona discharge or contact charging, there is no problem even if the gap between the centers is deviated by 0.1 mm. However, when the technique of Japanese Patent Laid-Open No. 5-107866 is adopted, a slight difference in the gap is immediately large. This leads to uneven charging potential and eventually uneven density in the recorded image. For example, if 2kV is applied at 0.2mm, about 600V
It becomes charged, but if it becomes 0.1 mm, it becomes 900 V,
If it becomes 0.3 mm, it will be 100 V.

In order to improve this problem, the gap may be widened from the beginning, for example, 1.0
If it is expanded to mm, the required applied voltage will be 10
It becomes very high with KV.

Further, in Japanese Unexamined Patent Publication No. 5-204226, discharge electrodes whose electric field concentrates are arranged at a fine pitch on the tip thereof so as to be close to the member to be charged, and a low voltage is applied to the discharge electrode to cause corona discharge. Proposing technology. This technique will be specifically described with reference to FIG. In FIG. 1, reference numeral 16 is a photosensitive drum composed of a conductor 12 and a photosensitive member 14, 10 is a charger composed of an electrode 21 and a high resistance body 18, 23 is a voltage generator, and 25 is a needle-shaped protrusion. . The high-resistor 18 is made of titanium oxide or tantalum nitride having a film thickness of 1 μm or less, and the distance between the high-resistor 18 and the photoconductor 14 is 0.3-.
It is placed at 1.0 mm. The applied voltage required for corona discharge is about -1.5 kV.

In this technique, it is considered that the ozone generation amount is significantly reduced as compared with the applied voltage (-5 to -9 kV) of a general scorotron. Further, the reason why the gap was 1 mm or less, which was significantly smaller than that in the case of a general scorotron, is considered that the discharge electrode was formed of a high resistance material.

However, in the technique disclosed in Japanese Patent Laid-Open No. 5-204226, it is considered that the charging potential is uneven. Since the pitch between the protrusions is not described in the publication, it cannot be accurately grasped, but the results of our experiments using the same charger revealed that the pitch between the protrusions was sufficiently smaller than the gap with the photoconductor, even under the same conditions. Even if it happens, there is a protrusion that happens to start discharging and a protrusion around it that does not discharge, and streaky uneven charging occurs. Also, when the pitch and the gap are about the same, there is a degree of difference due to the pitch between the electrodes and the gap with the photoconductor, but the potential immediately below the electrodes inevitably increases,
The electric potential between the electrodes becomes low, and the stripes become uneven. Further, since titanium oxide or tantalum nitride is etched to form the discharge electrode, it is inevitable that the cost becomes high.

[0012] Instead of regularly arranging the protrusions in the above technique, it is also proposed to place a conductive fiber nonwoven fabric. However, even in this case, it is unavoidable that uneven charging occurs because it is determined by chance which of the densely planted conductive fibers is discharged.

Japanese Patent Laid-Open No. 60-80870 proposes to use a grid in combination with a needle-shaped discharge electrode array. This technique is shown in FIG. In FIG. 2, 12
Is a needle discharge electrode array (hereinafter referred to as pin electrode), 11 is a pin support, 10 is a grounded metal plate (shield case), 13
Is the grid electrode. The distance between the pin electrodes is 2 mm, the radius of curvature of the tip of the pin is 30 μm, the distance from the tip to the grid is 12 mm, the distance from the grid to the body to be charged is 3 mm, the grid is parallel to the pin electrode, and the distance is 2 mm.
Is.

According to Japanese Patent Laid-Open No. 60-80870,
The following points are pointed out. The applied voltage to the pin electrode is -9
As a result of setting the kV and the grid voltage to 0 V, uniform discharge could be performed regardless of the position of the pin electrode. At that time, the discharge current was about -2.6 μA / cm for the grounded metal member to be charged. Further, when the current value was made uniform and the ozone concentration was compared with that of the conventional corotron, it was reduced to about 1/5.

A technique similar to this is disclosed in Japanese Patent Laid-Open No. 6-119.
The technique disclosed in Japanese Patent No. 46 is proposed. The structure of the charger of this technique is shown in FIG. 3, and its explanatory view is shown in FIG. In FIG. 3, 22 is a saw-toothed electrode, 21 is a conductive shield case, 23 is a grid electrode, and 24 and 25 are insulating holding members. The pitch of the sawtooth electrodes is 2 mm,
It does not disclose the gap to the photoreceptor.

Different voltages are applied to the electrodes 22, the shield case 21, and the grid 23 from independent power sources. In a laser printer having a process speed of 50 mm / sec, -3.4 kV is applied to the electrode 22, -500 V is applied to the grid 23 to change the applied voltage of the shield case 21 to 0 to -1.5 kV, and the current flowing in the grid. Ig
The current Ic flowing in the shield case and the shield case was measured, and at the same time, the uniformity of charging at that time was evaluated by a printed image.
It is reported that uniform charging was achieved when Ig and Ic were almost equal, as shown in FIG.

The shield case voltage at this time is -60.
0 V, Ig and Ic are −145 μA each, the drum current Id flowing through the photoconductor is −10 μA, and the total current It discharged from the pin electrode is −300 μA. Also,
In the case of a copying machine of 200 mm / sec, the applied voltage is -4.
2 kV, It = -700 μA, Ig = Ic = -340 μ
A, Id = -20 μA. It does not disclose ozone concentration.

[0018]

As described above, according to the conventional technique, uniform charging and sufficient ozone are carried out while the gap (for example, 1 mm) between the electrode of the charger and the member to be charged is stable in terms of the apparatus. It is not possible to achieve both reduction of generation (that is, reduction of discharge current).

In particular, in a normal scorotron in which a wire is used as a discharge electrode and three sides are grounded by a shield case, a large amount of useless current flows in the shield case, which is larger than the current used for charging. The amount of ozone generated is large. In the technique of the above-mentioned JP-A-60-80870, it is proposed to use a needle electrode in which a current flowing through the shield case is relatively small and combine a grid electrode to make the charging potential uniform. .

In Japanese Patent Laid-Open No. 60-80870, the distance between the needle electrode and the grid is set to 12 mm, but if the distance is made closer, the current is further reduced,
The generation of ozone can be further suppressed. Therefore, in order to achieve a further reduction in the amount of ozone generated, the present inventor has disclosed in Japanese Patent Laid-Open No.
A charger having the same structure as that of JP-A-0-80870 was prepared, and an experiment was tried by changing only the distance between the needle electrode and the grid.
As a result, it was found that when the distance between the needle electrode and the grid was 4 mm or less, the charging potential was uneven.

According to the present invention, each gap in the charger is set to a mechanically acceptable interval, the discharge current is reduced to reduce the ozone generation amount, and uniform charging is realized. The challenge is to achieve it.

[0022]

In order to solve the above-mentioned problems, the charging device of the present invention comprises a large number of discharge electrodes (4) arranged in a predetermined axial direction at a substantially constant pitch; High-voltage power supply (5) for applying a voltage equal to or higher than a voltage; a resistor (15) installed between the output electrode of the high-voltage power supply and the plurality of discharge electrodes; A grid electrode (7) installed at a position between the charged body and a grid power source (8) for applying a grid voltage to the grid electrode.

In the second aspect, when the pitch between the discharge electrodes is p (mm) and the gap between the tip of the discharge electrode and the grid electrode is g (mm), g ≦ g
It is configured so that the relationship of 0.5p + 1 (p ≦ 2 mm) and g ≦ p (p ≧ 2 mm) is satisfied.

In the third aspect, the gap between the tip of the discharge electrode and the grid electrode is 0.5 mm or more.

According to the present invention, the gap between the tip of the discharge electrode and the grid electrode is 4 mm or less.

According to a fifth aspect, the volume resistivity is 10 ⁴
A material of Ωcm or more and 10 ¹⁰ Ωcm or less is used as the resistor.

In the sixth aspect, the resistor is made of rubber.

According to a seventh aspect of the present invention, the rubber layer of the resistor has a thickness of 1 mm or more and 10 mm or less.

In the eighth aspect, the resistor is pressed against the end of each of the discharge electrodes on the non-discharge side so that the resistor and each of the discharge electrodes come into direct contact with each other.

According to a ninth aspect of the present invention, the discharge electrode is composed of an insulating support having a large number of holes formed at equal intervals, and a large number of needle-shaped electrodes inserted and fixed in the holes. .

According to a tenth aspect of the present invention, the power supply voltage applied to the discharge electrode is greater than ± 1.5 kV and ± 4.5 kV.
It is smaller than V.

In the eleventh aspect, the pitch between the discharge electrodes is p (mm), and the pitch between the grid electrodes is λ.
(Mm), the relationship of λ ≦ p is satisfied.

According to a twelfth aspect, the line width (w) of the grid electrode is 0.1 mm or more.

In the thirteenth aspect, the grid electrode has an aperture ratio of 50% or more and 93% or less.

In the fourteenth aspect, when the gap between the tip of the discharge electrode and the grid electrode is g (mm), the effective width (d) of the grid electrode is more than twice g. To configure.

According to a fifteenth aspect, the minimum value of the effective width (d) of the grid electrode is set to 2 mm or more.

In the sixteenth aspect, the gap between the grid electrode and the body to be charged is set to 1 mm or more and 3 mm or less.

The symbols shown in parentheses above are the reference numerals of the corresponding elements in the examples described later, but each component of the present invention is a specific element in the examples. It is not limited to only.

[0039]

It is known that the amount of ozone generated is proportional to the discharge current. Of course, there are some conditions in which the amount of ozone generated differs even if the discharge current is the same, and the reason for this has been clarified, but here we will assume that the amount of ozone generated is proportional to the discharge current. Therefore, one of the objects of the present invention, ozone reduction, can be achieved by reducing the discharge current.

The reduction of the discharge current can be achieved by eliminating the shield to make the shield current zero and reducing the gap between the discharge electrode and the photosensitive member to reduce the applied voltage. At that time, in order to eliminate the risk of sparking between the discharge electrode and the photoconductor, the electrode may be made of a high resistance material. However, it is costly to finely process the high resistance element by etching. The present inventor has confirmed by experiments that sparks can be similarly prevented by inserting an appropriate resistance between the conductive discharge electrode and the power source instead of using the high resistance body. Therefore, such a low-cost discharge electrode was created.

The charging unevenness that occurs when using this type of charger can be eliminated by providing a grid electrode between the discharge electrode and the photosensitive member.

That is, the problem can be solved by disposing a needle-shaped discharge electrode close to the photosensitive member, disposing a grid between them, and inserting an appropriate resistance between the discharge electrode and the power supply.

It should be noted that ideal uniform charging is achieved under a charging condition where a regular discharge pattern can be formed without a grid.

A regular discharge pattern means, for example, when the latent image (charged charge image) is subjected to cascade development with toner (particularly developing a portion having a potential difference), a black stone is placed on a board to have the same radius. It means that the polka dot pattern spreads in a certain cycle. A polka dot may be connected in the traveling direction or in a direction perpendicular thereto to form a stripe pattern of a certain width. Of course, it would be good if everything was uniformly black, but it would be impossible without the grid. In the conventional charger without a grid, a black and white pattern with various widths was formed on both the wire and the needle row.

When the grid is operated in such a state that a regular discharge pattern is generated, the variation in the charging potential is within ± 5V. By the way, it is within ± 30V in the conventional scorotron.

In such a regular discharge pattern, the relationship between the gap from the discharge point to the photosensitive member and the pitch between the discharge points is set within the range of claim 2, and an appropriate high resistance is inserted between the discharge electrode and the power supply. Can be achieved by things. That is, the needle-shaped discharge electrodes are arranged close to the photoconductor, and grids are arranged between them so that the relationship between the pitch between discharge electrodes and the distance between the discharge electrodes and the grid satisfies claim 2. The problem can be solved more effectively by inserting an appropriate resistor between the power supply and the power supply.

That is, according to the present invention, the following effects can be obtained.

Since the discharge current is small, ozone generation can be suppressed low.

Since the discharge is originally regular without the grid, very uniform charging can be performed by controlling the grid.

The discharge electrode can be produced at low cost.

As a result of various experiments by changing the shape and position of the grid, the present inventor was able to create a charging device capable of making the charging potential uniform even when the discharge electrode was in close proximity to the grid. .

[0052]

EXAMPLE FIG. 5 shows the configuration of the charging experimental apparatus used in the experiment for determining the structure of the charger of the example. This will be described with reference to FIG. The charging body 1 is a polyester film having a thickness of 25 μm, and aluminum is vapor-deposited on the back surface.
The carrier stage 2 moves at a constant speed with the charged body 1 placed thereon. The traveling direction is defined as the X direction, and the direction perpendicular thereto is defined as the Y direction. For the stage, an insulator (Bakelite, thickness 5 mm) is placed on a metal support, and the thickness is 2 m.
It is constructed by pasting m aluminum plates. Therefore, the current flowing through the back electrode of the charged body 1 due to the corona discharge can be measured by the ammeter 3. Hereinafter, this current is referred to as a plate current and is represented by Ip.

Reference numeral 4 is a needle array for corona discharge, and reference numeral 5 is its power source. The current flowing through the needle 4 is measured by the ammeter 6. This current is called a total current (discharge current) and will be referred to as It hereinafter. 7 is a grid and 8 is its power supply. The current flowing through the grid 7 is measured by the ammeter 9.
This current is called a grid current and is hereinafter referred to as Ig. The surface potential of the charged body 1 after charging is measured by the probe 10 of the surface electrometer 11. A recorder 12 is connected to the surface electrometer 11. The surface electrometer 11 used is Model 360 from Trek Japan. Reference numeral 17 is a suction nozzle port for measuring the ozone concentration near the charger, 18 is an ozone concentration meter, and 19 is a recorder. The ozone concentration meter used is EB2001R from Ebara Jitsugyo.

In this experimental example, the charging width is 210 mm,
The moving speed of the stage is 100 mm / sec. The charged body 1 after charging is removed from the stage and set in the cascade developing device shown in FIG.

In FIG. 6, 1 is a charged body, 22 is a hopper, 23 is a developer, and 24 is an open / close valve. When the valve is opened, the developer cascades on the charged body 1, and the toner adheres to the latent image (charge pattern) on the charged body 1 to convert it into a visible image. In cascade development, toner adheres only to the areas with a potential difference.Therefore, even if there is a slight potential difference, that is, there is unevenness in the potential, toner adheres to the areas with a high potential, and toner adheres to the adjacent areas with a relatively low potential. Is not attached, and the potential distribution is emphasized and visualized. However, when there is no potential difference, the toner does not adhere even if it is charged to 1000V. That is, ideal uniform charging is a state in which development is not performed by cascade development. The toner used has a positive charging polarity and the color is black.

[Embodiment 1] FIG. 7 shows a front view of a charger according to an embodiment. In FIG. 7, 4 is a needle row, 7 is a grid,
13 and 14 are polyester spacers, 15 is a medium resistance rubber layer, and 16 is a metal electrode for voltage application.

A side view of the charger shown in FIG. 7 is shown in FIG. FIG.
In FIG. 1, 1 is a charged body, 4 is a needle row, 5 is a discharge power source, 7 is a grid power source, 8 is a grid power source, 13 and 14 are polyester spacers, 15 is a medium resistance rubber layer, and 16 is a metal electrode for voltage application. Is. The other part is an insulating support member.

When observing the charging pattern without the grid, the grid 7 and the spacer 13 were removed and an experiment was conducted. In this state, the gap between the needle tip and the charged body is 2
mm. When changing the gap between them, the thickness of the spacer 14 was changed.

FIG. 9 shows an enlarged view of the tip of the needle 4 used in the charger of the embodiment.

As shown in FIG. 7, a tungsten needle 4 (precision probe needle W26-10-01 manufactured by Japan Micronics) having a length of 12.5 mm, a diameter of 0.66 mm, and a tip radius of 5 μm is made of boat-shaped polycarbonate insulation. Of a flexible support into a through hole having a diameter of 0.7 mm and a pitch of 3 mm, the height from the surface of the support to the tip of the needle is adjusted to 3 mm, fixed with an insulating adhesive, and then discharged. The electrode was created.

With this manufacturing method, the needle electrode array can be manufactured accurately and at low cost. The precision probe needle used is expensive because it has a different purpose, but it can be replaced with an inexpensive record needle or the like.

The grid 7 and the spacer 13 shown in FIG. 7 were not used, and a spacer 14 having a thickness of 5 mm was inserted to make the gap between the tip of the needle 4 and the charged body 1 2 mm. A rubber sheet 15 having a volume resistivity of 10 ⁸ Ωcm and a thickness of 2 mm,
The electrode 16 was placed on the back side of the discharge electrode needle, and the electrode 16 was overlapped and crimped with a screw (not shown).

With this configuration, Japanese Unexamined Patent Publication No. 5-204226
It was possible to produce a discharge electrode for proximity charging at a low cost without producing an expensive material as shown in No. 10 at a high cost such as sputtering or etching. Further, by pressing and pressing the rubber layer in this way, it was possible to electrically connect a large number of discharge electrodes to the power supply evenly.

This charging device was set in the experimental device shown in FIG. 5, charged with a discharge voltage of −2100V, and then developed by the cascade developing device shown in FIG. The patterns were continuously arranged in both XY directions. The surface potential at this time is -890 ± in both XY directions.
It was 30V.

In this state, the grid 7 and the spacer 13 having a thickness of 2 mm were inserted. The gap between the needle tip and the grid was 3 mm. The grid 7 is 0.1 mm thick S
It was prepared by etching a US plate. The grid 7 has a line width of 0.3 mm, a pitch of 0.6 mm (aperture ratio of 50%), and an angle of 45 degrees.

The grid voltage is -800 V and the discharge voltage is-
After setting to 3000V, charging and developing,
No toner adhered.

The surface potential at this time is -77 in both XY directions.
It was 5 ± 1V. That is, ideal uniform charging was realized by this charger.

The applied voltage (-3 kV) at this time is significantly lower than the applied voltage (-9 kV) of the needle-grid charger (gap 12 mm) of JP-A-60-80870.

Regarding the total discharge current, the saw-toothed electrode-grid charger of Japanese Patent Laid-Open No. 6-11946 discloses It = -300 μA (50 mm / sec),
-700 μA (200 mm / sec),
In the embodiment, it is reduced by almost one digit at It = -60 μA (however, in this embodiment, 100 mm / sec). This is mainly an effect that the applied voltage can be lowered by narrowing the gap.

As a result, the ozone concentration could be greatly reduced. When the ozone concentration in the vicinity of the charger of the example was measured, it was 1.0 ppm.

On the other hand, the ozone concentration was similarly measured for a scorotron of a commercially available copying machine manufactured by Rico-Co., In which the applied voltage and the grid voltage were adjusted so that the same surface potential was obtained at the same charging speed. It was 0.0 ppm. The total current It at that time was −500 μA. That is, as a result of the discharge current being greatly reduced by the charger of the example, the ozone concentration could be reduced by one digit.

Although only the case of negative charging will be described below, the same effect can be obtained in the case of positive charging.

[Example II] With respect to the configuration of Example I,
The film thickness of the spacer 14 is changed to 4, 5, 6 and 7 mm, respectively, and the gap between the needle tip and the charged body 1 (25 μm backside aluminum vapor-deposited polyester film) is set to 1, 2,
An experiment similar to the above was performed by changing the length to 3, 4 mm. When the grid is added, the gaps between the needle tip and the grid are 1, 2, 3, 4 mm, respectively. In addition, when the grid is added, the gap between the grid and the body to be charged is fixed at 2 mm while the pitch between the electrodes remains 3 mm.

The applied voltage has a surface potential after charging of −850 ±
I changed it to 50V. -1.8 kV, -2.2 k for gaps 1, 2, 3, and 4 mm, respectively
It was set to V, -2.5 kV, and -3.0 kV. When the grid was added, −0.8 kV was added to each.

Before the grid was attached, when the gap was 1 mm, black circles having a diameter of about 1 mm were regularly arranged.
When the gap was 2 mm, it changed into a row of large black circles having a diameter of about 2 mm and a row of black circles having a diameter of 1 mm or less. It was a regular pattern overall, but partly a disordered pattern. When the gap became 3 mm and became equal to the pitch between the electrodes, black bands with a width of 3 mm were seen at a pitch of 6 mm. This phenomenon can be interpreted as that even-numbered electrodes are strongly discharged and odd-numbered electrodes are weakly or not discharged. When the gap became 4 mm and became wider than the pitch between the electrodes, the pattern became more and more disordered, and a black band of about 4 mm and a region between which no toner adhered were observed.

In this state, a grid was attached to measure the surface potential variation in the Y direction (direction perpendicular to the stage moving direction).
± 1V at m, ± 5V at 2mm, ± 30V at 3mm, 4m
It was ± 70 V in m.

When the surface potential variation is ± 30 V or more, uneven electric potential appears as uneven density in the low-density (gray) portion of the copy or print image, making it unusable. Therefore, from this result, it is understood that when the inter-electrode pitch is 3 mm, the allowable gap is 3 mm or less.

[Example III] With respect to the structure of Example II described above, an experiment similar to the above was conducted by changing the pitch between the discharge electrodes from 3 mm to 2 mm.

When the gap is 1 mm, black circles having a diameter of slightly more than 1 mm are regularly arranged in both XY directions. However, at 2 mm, the size and pitch of the black circles are subtly disturbed. The pattern was not disturbed, and the variation in the potential when the grid was added was ± 50V and ± 70V. From this result, it is understood that when the inter-electrode pitch is 2 mm, the allowable gap is 2 mm or less.

Example IV An experiment similar to the above was conducted with the configuration of Example II described above, except that the pitch between the discharge electrodes was changed from 3 mm to 1.2 mm.

A regular pattern was obtained when the gap was 1.2 mm, but at 1.5 mm the size and pitch of the black circles were slightly disturbed, at 1.8 mm it was further disturbed, and at 2.0 mm some electrodes did not discharge much. Appeared. The variation in potential when a grid is added is 1.8 mm
Up to ± 30V, but at 2.0mm ± 40V
It has become V. From this result, it is found that when the electrode pitch is 1.2 mm, the allowable gap is 1.8 mm or less.

[Example V] In the structure of Example I, the thickness of the spacer 14 was changed to 4 mm, the gap between the tip of the needle and the member to be charged or the grid was fixed to 1 mm, and the electrode was replaced. Inter-pitch 1.2mm, 2mm, 3mm
The same experiment was conducted for each of the above.

When the electrode pitch is 3 mm, the diameter is about 1
Black circles of a little over mm were connected in the X direction, and were regularly seen in the Y direction at a pitch of 3 mm. At a pitch of 2 mm, the diameter is about 1
Black circles of a little over mm were seen at a pitch of 2 mm in both X and Y directions. With a pitch of 1.2 mm, a width of 1 m connected in the Y direction
It became a black belt with a m strength and a pitch (X direction) of 2 mm.

When a grid was attached and the surface potential variation was measured, it was ± 1 V at pitches of 3 mm and 2 mm, and ± 10 V at a pitch of 1.2 mm.

From the results of the four experimental examples, the allowable gap width g (mm) is the electrode pitch p (mm).
It is estimated that the following relation must be satisfied.

G ≦ 0.5p + 1 (p ≦ 2 mm) (1) g ≦ p (p ≧ 2 mm) (2) [Example VI] In the configuration of Example I, between the electrodes When electrodes with a pitch of 4 mm are used, the thickness of the spacer 14 is set to 7 mm and the gap between the needle tip and the charged body is set to 4 mm. When electrodes with an inter-electrode pitch of 5 mm are used, the thickness of the spacer 14 is Was set to 8 mm, the gap between the needle tip and the charged body was set to 5 mm, and the same experiment as above was performed for each configuration. When the grid is added, the gap between the needle tip and the grid is 4 mm and 5 mm, respectively.
become. When the grid is added, the gap between the grid and the charged body is fixed at 2 mm.

The applied voltage has a surface potential of −850 after charging.
It was changed to ± 50V. Gap 4 mm and 5
-3.5 kV and -3.9 k, respectively for mm
V. When a grid is added, each −
0.8kV plus -4.4kV and -4.8kV
Set to V.

Before the grid is attached, when the gap is 4 mm, the black circles having a diameter of about 4 mm are almost regularly arranged, but at 5 mm, there are large black circle rows having a diameter of 5 mm or more and black circle rows having a diameter of 5 mm or less. It changed. It was a regular pattern overall, but partly a disordered pattern.

In this state, a grid was attached to measure the variation of the surface potential in the Y direction (direction perpendicular to the stage moving direction), and it was ± 30 V at 4 mm and ± 40 at 5 mm.
It was V.

From the above results, even when the above relational expressions (1) and (2) are satisfied, uniform charging cannot be realized when the gap is 5 mm, and the upper limit of the gap is 4 m.
It turns out that it is m.

Further, since the applied voltage becomes −4.5 kV or less by suppressing the upper limit of the gap to 4 mm, the discharge current is reduced, and as a result, the ozone generation amount can be lowered.

[Embodiment VII] With respect to the structure of the embodiment I, the thickness of the spacer 14 is 3.5, 3.3, 3.1 mm.
The gap between the needle tip and the charged body to 0.5, 0.3,
The same experiment was performed by changing to 0.1 mm. When the grid is added, the gap between the needle tip and the grid becomes 0.5, 0.3, and 0.1 mm, respectively. In addition, when the grid is added, the gap between the grid and the charged body is fixed to 2 mm while the pitch between the electrodes remains 3 mm.

The applied voltage has a surface potential of −850 after charging.
It was changed to ± 50V. Gap 0.5,0.
-1.4 kV, -for 3,0.1 mm
It is 1.1 kV and -0.9 kV. When the grid was added, the voltage was increased by −0.8 kV.

-1.7 k when the gap is 0.1 mm
When a voltage of V was applied, a current exceeding the limit current flowed and the power supply was automatically turned off. The cause is that the grid is attracted to the discharge electrode by electrostatic attraction and comes into direct contact. When the gap was 0.3 mm, such a leak phenomenon did not occur, but it was found that the grid current Ig fluctuated finely. The grid seems to be pulled by the discharge electrode and vibrating.

From this result, considering the mechanical tolerance, the lower limit of the gap is determined to be 0.5 mm. The applied voltage required at this time is at least −1.5 kV (depending on the surface potential).

Example VIII The same experiment as in Example III was conducted by changing the tip R (radius of curvature) of the discharge electrode needle from 5.0 μm to 12.7 μm and 2.5 μm, but exactly the same results were obtained. Was given. From these results, as the needle of the discharge electrode,
It can be seen that the tip R can be made of a record needle, a sewing needle, or the like, which is inexpensive but large in cost.

Example IX With respect to the structure of Example I, the same experiment was conducted by changing the volume specific resistance value of the resistor rubber layer 15 inserted between the discharge electrode and the power supply. The thickness of the rubber layer was 2 mm, the pitch between the electrodes was 3 mm, and the gap between the electrode tip and the member to be charged (or grid) was 1 mm.

When the conductive rubber was used, the size of the black circles was uneven and the size was from 1 mm or less to 3 mm or more. In addition, when the grid was attached later, sparks were generated between the discharge electrode needles and the grid, and a part of the grid melted.

When rubber of 10 ⁴ Ωcm is used,
It became a regular pattern of almost uniform black circles. Also, 1
In the case of the 0 ⁸ Ωcm it has become a beautiful black circle pattern. When these medium resistance rubber sheets were used, sparks did not occur even when discharged under various conditions for a long period of time. These medium resistance rubbers were made by kneading an appropriate amount of carbon black into a high resistance rubber material.

In the case of carbon blackless high resistance rubber of 10 ¹² Ωcm or more, no discharge was generated even when the applied voltage was increased to -5.0 kV. It seems that the voltage drop in the rubber layer of the resistor was too large and the potential at the tip of the needle did not rise to the firing voltage.

The variation of the surface potential when the grid was attached was within ± 40 V for the conductive rubber and within ± 10 V for the medium resistance rubber.

From the above experimental results, it is considered appropriate that the volume resistivity of the resistor inserted between the discharge electrode and the power source is 10 ⁴ Ωcm or more and 10 ¹⁰ Ωcm or less.

[Example X] In the configuration of Example IX, the thickness of the resistor rubber layer 15 inserted between the discharge electrode and the power source was changed to 0.5 mm, 1 mm, 2 mm, 4 mm, 8 mm, The same experiment was carried out for each. Resistor rubber layer 1
For 5, a rubber sheet having a volume resistivity of 10 ⁸ Ωcm was used.

When the film thickness of the medium resistance rubber sheet is 0.5 mm, the pattern becomes a disordered pattern close to that of conductive rubber and is 1 m.
Even in the case of m, there was a regular variation in the size of the black circles.

The most regular pattern was obtained when the film thickness was 2 mm. As the thickness increased to 4 mm and 8 mm, the black circles became slightly triangular, and the discharge intervals in the X direction showed some variation.

However, when a grid is added, 0.
Except for the film thickness of 5 mm, the potential variation is ± 30 in each case.
It was within V.

If the film thickness is too thin, the effect of resistance does not contribute much, and if it is too thick, it seems that even if pressure was applied to the rubber electrode against the rear end of the discharge electrode, it was difficult to achieve uniform adhesion. Be done.

From the above results, it is considered appropriate that the thickness of the medium resistance rubber sheet placed between the discharge electrode and the power source is 1 mm or more and 10 mm or less.

Symbols showing the shapes and arrangements of the electrodes and grids of the charger in the respective embodiments described below are shown in FIGS. 10 and 11. FIG. 10 shows a front view of the charger, and FIG. 11 shows a state in which the grid is viewed from directly above. FIG.
At 0, p is the pitch between the discharge electrodes, λ is the pitch of the grid electrodes, w is the line width of the grid electrodes, g (g) is the gap between the discharge electrode tip and the grid, and g (p) is the grid electrode and the covered area. The gap with the charged body, t is the thickness of the grid. The aperture ratio was calculated by the following formula (3).

Aperture ratio = (λ−w) / λ × 100 (%) (3) Further, in FIG. 11, p, λ, and w are the same as in FIG. 10, and d is the effective grid electrode. The width, θ is an angle formed by the grid electrode and the X direction.

[Example XI] A tungsten needle 4 having a length of 12.5 mm, a diameter of 0.66 mm, and a tip radius of 5 μm.
(Precision probe needle W26-10 manufactured by Nippon Micronics
No. 01) is inserted into a through hole having a diameter of 0.7 mm and a pitch of 3 mm at the bottom of a boat-shaped insulating support made of polycarbonate, as shown in FIG. The height was adjusted to 3 mm and fixed with an insulating adhesive to form a discharge electrode.

A spacer 14 having a thickness of 5 mm, a grid shown below, and a spacer 13 having a thickness of 2 mm were stacked and fixed on the needle electrode. The gap between the needle tip and the grid is 2 mm. A rubber sheet 15 having a volume resistivity of 10 ⁸ Ωcm and a thickness of 2 mm was applied to the back side of the discharge electrode needle, and the electrode 16 was overlapped and crimped with a screw (not shown).

The grid was formed by etching a SUS plate having a thickness t of 0.1 mm. The line width w of the grid is 0.
3 ± 0.03mm, pitch λ is 1.0 ± 0.02m
m, effective width d is 24 mm, angle θ is 45 degrees, and aperture ratio is 7
It is 0%.

The parts not described are the same as those in the embodiment I.

This charger was attached to an experimental apparatus as shown in FIG. 5, and the grid voltage was -800 V and the discharge voltage was -3.
When charging was carried out by setting each to 000 V and development was carried out by the cascade developing device shown in FIG. 6, no toner adhered. The surface potential at this time is -775 ± in both XY directions.
It was 1V. That is, with this grid shape and arrangement,
Ideal uniform charging is realized. The ozone concentration was about 1/10 of that of the conventional scorotron charger.

[Embodiment XII] With respect to the structure of Embodiment XI, the grid pitch λ is 0.2 mm in steps of 0.
A similar experiment was conducted by changing from 6 mm to 4.2 mm. As a result, when the pitch λ is 3.2 mm or more,
After development, uneven density occurs and the surface potential varies ± 30.
It became V or more.

If the variation of the surface potential is ± 30 V or more, the unevenness of the potential appears in the low density (gray) portion of the copy image or the printed image as the uneven density, which makes it unusable. Therefore, from this result, it is understood that when the pitch p between the discharge electrodes is 3 mm, the allowable grid electrode pitch λ is 3.0 mm or less.

[Embodiment XIII] With respect to the structure of the above-mentioned Embodiment XI, the pitch p between discharge electrodes is 4 mm, 2 mm, 1.
The experiment similar to the above was conducted about each, changing to 2 mm. As a result, when the pitch p between the discharge electrodes was 4 mm, no unevenness was observed until the grid electrode pitch λ was 4.0 mm, and the potential variation was within ± 30 V.

When the discharge electrode pitch p is 2 mm, the upper limit of the allowable grid electrode pitch λ is 2.0 mm, and when the discharge electrode pitch p is 1.2 mm, the allowable grid pitch is λ. The upper limit of the interelectrode pitch λ is 1.2 mm.

That is, by setting the upper limits of the pitch p between the discharge electrodes and the pitch λ between the grid electrodes so that the relational expression "λ≤p" is satisfied, preferable results are obtained.

[Example XIV] With respect to the structure of Example XI, the grid pitch λ was changed to 1.4 mm, and the line width w of the grid electrode was 0.07 mm. 0.1 mm, 0.2
mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 m
m, 0.7 mm, 0.8 mm, 0.9 mm, and 1.0
Instead of mm, the same experiment as above was performed under each condition. The aperture ratios are 95%, 93% and 86, respectively.
%, 79%, 71%, 64%, 57%, 50%, 43
%, 36%, and 29%.

As a result of this experiment, striped shading unevenness occurred when the line width w of the grid electrode was 0.07 mm, and similar unevenness also occurred when it was 0.8 mm or more. When the line width w of the grid electrode is 0.07 mm, the potential control force between the grid electrodes is weak, and when it is 0.8 mm or more, the grid current Ig is too large, and the current I flowing through the charged body is large.
Since p is small, the surface potential of the member to be charged did not rise to the grid potential (-800 V) at the linear velocity in this example, and it seems that the grid function for making the potential uniform did not work yet.

From this result, the line width w of the grid electrode is 0.1 mm or more, the aperture ratio of the grid is 50% or more, 93
% Or less is judged to be good.

[Embodiment XV] The effective width d of the grid is 20 mm, 16 m with respect to the configuration of the embodiment XI.
m, 12 mm, 8 mm, 4 mm, 3 mm, and 2 mm were changed, and the same experiment as above was performed under each condition. As a result, the effective width d of the grid is 3 mm and 2 mm.
When the effective width d of the grid was 4 mm or more, the vertical unevenness corresponding to the pitch of the needles appeared in each case.
The unevenness did not occur, and the variation in the electric potential was within ± 30V.

[Embodiment XVI] With respect to the structure of Embodiment XI, the thickness of the spacer 14 is changed to 4 mm, the gap from the tip of the needle to the grid is changed to 1 mm, and at the same time the grid is effective. Width d is 20mm, 16m
m, 12 mm, 8 mm, 4 mm, 3 mm, and 2 mm were changed, and the same experiment as above was performed under each condition. As a result, even when the effective width d of the grid was 2 mm, the unevenness did not occur and the variation in the potential was within ± 30 V.

From the results of Examples XV and XVI, it can be judged that good results can be obtained if the effective width d of the grid is at least twice the gap between the discharge electrode and the grid. That is, if it is configured to satisfy this condition, the width of the charger can be narrowed from about 20 mm of the conventional charger to about 4 mm.

[Embodiment XVII] With respect to the structure of the embodiment XI, the thickness of the spacer 14 is changed to 4.5 mm, and the gap g (g) from the tip of the needle to the grid is 1.
Change to 5mm, and at the same time, change the effective width d of the grid to 4m.
Experiments similar to the above were performed under the respective conditions by changing m, 3 mm, 2 mm, and 1 mm. As a result, when the gap from the tip of the needle to the grid is 2 mm or more, uneven density does not occur and the potential variation is ± 3.
It fell within 0V. In addition, when the gap from the tip of the needle to the grid is 1 mm, the potential variation is ±
The voltage became 30 V or more, and the density unevenness increased.

From the results of this experiment, the effective width d of the grid has a minimum value as a condition for obtaining preferable charging characteristics, and even if the effective width d is more than twice the gap g (g) between the discharge electrode and the grid. However, it can be seen that when the effective width d is 1 mm, a preferable result cannot be obtained.

[Embodiment XVIII] The gap g from the grid to the aluminum vapor deposition mylar is changed by changing the thickness of the spacer 13 from 2 mm to 5.0 mm in 0.5 mm steps with respect to the configuration of the above Embodiment XI. (p) is 2m
From m to 5.0 mm, for each condition,
An experiment similar to the above was performed.

As a result, when the gap g (p) is within 3 mm, uneven density does not occur and the potential variation is ± 30.
Although it was within V, when the gap g (p) was 3.5 mm, the potential varied more than ± 30 V, and the density unevenness also occurred.

From this experimental result, it is understood that if the gap between the grid and the member to be charged is too wide, the ability to make the potential uniform is weakened, and the gap g (p) is preferably 3 mm or less.

[Embodiment XIX] With respect to the structure of Embodiment XI, the spacers 13 have thicknesses of 1.5 mm and 1.0.
Gap from the grid to the aluminum evaporated mylar by changing to mm, 0.7 mm, and 0.5 mm
(p) is 1.5 mm, 1.0 mm, 0.7 mm, and 0.
An experiment similar to the above was performed under each condition while changing to 5 mm.

As a result, the density unevenness did not occur under all conditions, and the potential variation was within ± 30 V. However, when the gap g (p) is 0.7 mm and 0.5 mm
In the case of, a small spark discharge was observed between the grid and the aluminum surface of the charged body.

From this experimental result, it is understood that the gap g (p) between the grid and the member to be charged is preferably 1 mm or more in order to prevent abnormal discharge therebetween.

[0135]

According to the first aspect of the present invention, the amount of ozone generated can be significantly reduced and uniform charging can be performed.

According to the second aspect, more uniform charging becomes possible.

According to the third aspect, the main charger can be manufactured within a practical mechanical tolerance.

According to claim 4, the discharge voltage can be lowered to reduce the ozone generation amount, and the height of the charger can be lowered.

According to the fifth aspect, the risk of sparking can be eliminated and at the same time more uniform charging can be performed.

According to the sixth, seventh and eighth aspects, the resistor can be brought into uniform contact with each discharge electrode.

According to the ninth aspect, a large number of needle-shaped discharge electrodes can be easily and uniformly arranged and fixed at low cost.

According to the tenth aspect, safe charging with a small amount of generated ozone is realized.

According to the eleventh to sixteenth aspects, more uniform charging is realized. Further, in the sixteenth aspect, it is possible to reliably prevent abnormal discharge from occurring between the grid and the body to be charged.

[Brief description of drawings]

FIG. 1 is a front view showing one conventional example of a charger.

FIG. 2 is a perspective view showing one conventional example of a charger.

FIG. 3 is an exploded perspective view showing one conventional example of a charger.

FIG. 4 is a graph showing characteristics of the charger of FIG.

FIG. 5 is a block diagram showing the configuration of an experimental device incorporating the charger of the embodiment.

FIG. 6 is a front view showing a cascade developing device used in an experiment.

FIG. 7 is a front view showing the configuration of the charger of the embodiment.

FIG. 8 is a cross-sectional view of the charger of FIG. 7 as seen from a side surface.

9 is an enlarged front view of a tip portion of a needle 4 used in the charger of FIG.

FIG. 10 is a front view showing the configuration of the charger of the embodiment.

11 is a plan view of the grid of the charger shown in FIG. 10 as seen from directly above.

[Explanation of symbols]

1: Charged body (25 μm thick backside aluminum vapor-deposited polyester film) 2: Conveying stage 3: Ammeter (for plate current measurement) 4: Discharge electrode 5: High voltage power supply 6: Ammeter (for total current measurement) 7: Grid 8: Power supply for grid 9: Ammeter (for grid current measurement) 10: Surface electrometer probe 11: Surface electrometer 12: Recorder 13: Lower grid spacer 14: Upper grid spacer 15: Resistor (medium resistance rubber sheet) 16: Metal electrode for voltage application of discharge electrode 17: Inhalation nozzle for ozone concentration measurement 18: Ozone concentration meter 19: Recorder 22: Hopper 23: Developer 24: Open / close valve

Claims (16)

[Claims] 1. A large number of discharge electrodes arranged in a predetermined axial direction at a substantially constant pitch; a high voltage power supply for applying a voltage higher than a discharge start voltage to the discharge electrodes; an output electrode of the high voltage power supply and the large number. A resistor disposed between the discharge electrode and a discharge electrode; a grid electrode disposed close to the discharge electrode and located between the discharge electrode and a body to be charged; and a grid voltage applied to the grid electrode. A charging device having a grid power supply. 2. When the pitch between the discharge electrodes is p (mm) and the gap between the tip of the discharge electrode and the grid electrode is g (mm), g ≦ 0.5p + 1 (p ≦ The charging device according to claim 1, wherein the relationship of 2 mm) g ≦ p (p ≧ 2 mm) is satisfied. 3. The charging device according to claim 2, wherein a gap between the tip of the discharge electrode and the grid electrode is 0.5 mm or more. 4. The charging device according to claim 2, wherein the gap between the tip of the discharge electrode and the grid electrode is 4 mm or less. 5. The volume resistivity of the resistor is 10 ⁴ Ωc
The charging device according to claim 1, wherein the charging device has a m or more and 10 ¹⁰ Ωcm or less. 6. The charging device according to claim 5, wherein the resistor is made of rubber. 7. The charging device according to claim 6, wherein the rubber layer of the resistor has a thickness of 1 mm or more and 10 mm or less. 8. The charging device according to claim 1, wherein the resistor is pressed against an end of each of the discharge electrodes on a non-discharge side, and the resistor and each of the discharge electrodes are in direct contact with each other. . 9. The discharge electrode is composed of an insulating support having a large number of holes formed at equal intervals, and a plurality of needle-shaped electrodes inserted and fixed in the holes, respectively. 1. The charging device according to 1. 10. The power supply voltage applied to the discharge electrode is:
The charging device according to claim 1, wherein the charging device is larger than ± 1.5 kV and smaller than ± 4.5 kV. 11. The relationship of λ ≦ p is satisfied when the pitch between the discharge electrodes is p (mm) and the pitch between the grid electrodes is λ (mm).
The charging device described. 12. The line width (w) of the grid electrode is 0.
The charging device according to claim 11, which is 1 mm or more. 13. The charging device according to claim 11, wherein an aperture ratio of the grid electrode is 50% or more and 93% or less. 14. The effective width (d) of the grid electrode is twice or more of g when the gap between the tip of the discharge electrode and the grid electrode is g (mm). 11. The charging device according to item 11. 15. The charging device according to claim 14, wherein the minimum value of the effective width (d) of the grid electrode is 2 mm or more. 16. The gap between the grid electrode and the body to be charged is 1 mm or more and 3 mm or less.
The charging device described.