JPH04340985A - Developing device - Google Patents

Abstract

PURPOSE:To prevent the scattering of toner having a fine grain diameter by specifying a gap between the image forming face of a photosensitive body and a shielding plate, and an electric field formed between the surface of a developer sleeve and the shielding plate. CONSTITUTION:An developing unit 3 opposite to the photosensitive body 1 has a shielding part 40 for preventing the scattering of the toner, and is installed so that the gap (d) of the face of the photosensitive body 1 and the top end parts of the shielding plates 11 and 21 provided on the upper and lower parts of the opening parts 24 of the developing unit is 0.2mm<=d<=0.8mm, desirably, 0.3mm<=d<=0.7mm. Further, for forming the electric field E for collecting a developer, among the shielding plates 11 and 21, and the developer sleeve 18, a dc power source 41 is connected and further, a dc power source 42 is connected, to obtain a developing bias. The electric filed E has the same strength of ¦100-10000¦V/cm, on both bottom and top end part sides of the shielding plates 11 and 21. Thus, negatively electrified toner is attracted to the shielding plates, and pollution inside a copying machine and a defect in an image can be prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in electrophotographic copying machines and the like.

0002

[Prior Art] In an electrophotographic copying machine based on the Carlson method, the surface of a photoreceptor is uniformly charged, and then the charge is erased imagewise by exposure to form an electrostatic latent image. Dry development is performed using toner, and then the toner image is transferred and fixed onto paper or the like.

Conventionally, in the dry developing method as described above, toner with a relatively large particle size was used.
No particular problems regarding toner scattering occurred.

However, in recent years, the demand for higher image quality has increased,
The practical use of toner having a particle size of, for example, 10 μm or less, particularly 7 μm or less, is being considered. It has been revealed that the amount of scattering of toner particles having a fine particle size rapidly increases as the particle size decreases. As the amount of toner scattering increases, the inside of the copying machine gets dirty, which causes defects in the copied images.

[0005] At present, methods for preventing toner scattering by improving the developer itself have not been sufficiently effective. For example, if an attempt is made to prevent scattering by increasing the amount of toner charge, the developing ability will decrease and sufficient image density will not be obtained. Further, even if an attempt is made to prevent toner scattering by mixing a small amount of magnetic powder into the toner, the developing ability similarly decreases, and it is difficult to prevent toner scattering using this method.

[0006] Techniques for preventing toner scattering, not by improving the developer itself, but by improving the developing device and its peripheral equipment, are disclosed in, for example, Japanese Patent Application Laid-open No. 120376/1982 and Japanese Patent Application Laid-open No. 60-120376.
-134263, 61-226772, 61-
No. 262767, No. 62-66282, No. 63-1
It is disclosed in each publication of No. 44373.

However, for example, the above-mentioned Japanese Patent Application Laid-open No. 1203-1983
In the case of each publication of No. 76 and No. 62-66282,
Toner is prevented from scattering by sealing the space between the upper end of the developing device and the photosensitive drum using an insulating brush or the like. That is, since members such as brushes are in contact with the photoreceptor,
The durability of the photoreceptor is reduced and the electrostatic latent image is disturbed. Furthermore, in the case of overlapping development, it disturbs the previously developed toner image, so it cannot be used for full color production in which the development process is repeated multiple times.

[0008] Furthermore, the techniques disclosed in the above-mentioned Japanese Patent Laid-Open Nos. 60-134263 and 63-144373 only take into consideration the prevention of scattering from the lower end of the opening of the developing device, and do not prevent scattering from the upper end. is not mentioned. For this reason,
Overall, the amount of toner scattering from around the developing device is not sufficiently reduced.

Further, in the above-mentioned Japanese Patent Laid-Open Nos. 61-226772 and 61-262767, conductive rollers or electrode plates capable of applying a bias voltage are provided at the tips of the upper and lower shields, and the generated electric field Although this is a technique for preventing toner scattering, it is difficult to effectively prevent toner particles having a fine particle size from scattering only by generating an electric field.

0010

OBJECTS OF THE INVENTION It is an object of the present invention to provide a developing device suitable for electrophotography using a dry developer provided with toner scattering prevention means that is particularly effective even for toner having a minute particle size.

[0011]

SUMMARY OF THE INVENTION The present invention provides a developing device using a dry developer, in which an image forming surface of a photoreceptor and shield portions provided at the upper and lower ends of an opening of a developing device opposite to this image forming surface are provided. The distance d is 0.2 mm≦d≦0.8 mm, and the voltage between the developer carrier (for example, the developing sleeve) in the developing device and the shield portion is |100 to 10,000|V/c.
The present invention relates to a developing device characterized in that it is provided with means for forming an electric field of m.

The developing device of the present invention can be used even if the developer is one-component or two-component, and magnetic or non-magnetic. Furthermore, it can be used for anything from monochrome to full color.

[0013] Furthermore, it is possible to use either so-called contact development, in which the photoreceptor contacts the developer on the developing sleeve provided in the developing device, or non-contact development. be able to.

[0014]

[Examples] Examples of the present invention will be described below.

First, the outline of the electrophotographic copying apparatus will be explained based on FIG. In this figure, a corotron corona charger is used.

Reference numeral 1 denotes a drum-shaped photoreceptor having a photoreceptor layer 1a and rotating in the direction of the arrow. 2 is an image exposure device, and 3 is a developing device.

As the photoreceptor material constituting the above-mentioned photosensitive layer, in the case of two-component development, an inorganic material such as selenium-tellurium is preferable, and in the case of one-component development, OPC (organic photoconductive material) is preferable. preferable. Among these, carrier generating substances (CGM) include, for example, anthrone-based compounds, and carrier transport substances (CTM) include:
For example, known compounds such as styryl compounds can be used.

Reference numeral 4 denotes a pre-transfer exposure lamp provided as necessary to facilitate the transfer of the toner image formed on the photoreceptor 1 onto the recording medium P, 5 a transfer device, and 6 a separation corona radiation. A fixing device 7 fixes the toner image transferred to the recording medium P. Reference numeral 8 denotes a static eliminator consisting of one or a combination of a static eliminator lamp and a corona discharger for static elimination, and 9 a cleaning device having a cleaning blade or a fur brush for removing residual toner on the surface of the photoreceptor 1 after the image has been transferred. It is a device.

The surface of the photoreceptor 1 is uniformly charged by a corotron corona charger 10.

Next, a first embodiment of the present invention will be explained based on FIG. 1. In addition, as a test copying machine, U-Bix
A modified 3042 aircraft was used.

The developing device 3 facing the photoreceptor 1 has a shield portion 40 to prevent toner scattering, and shield plates 11 and 2 are provided on the surface of the photoreceptor 1 and above and below the developer opening 24.
The distance d from the tip of 1 is 0.2mm ≦d≦0.8mm
, preferably 0.3 mm≦d≦0.7 mm. In this case, it is preferable that d related to the upper shield plate 11 and d related to the lower shield plate 21 be set to be equal.

Further, a DC power source 41 is connected so that an electric field E for developer collection (scattering prevention) is formed between the shield plates 11, 21 and the sleeve 18.
2 is connected to obtain the developing bias. The electric field E has the same magnitude on both the lower end side and the upper end side of the shield plates 11 and 21, and is |100 to 10,000|V/cm, preferably |500 to 6000|V/cm, and more preferably |1000| ~3000|V/cm. For example, negatively charged toner is attracted to the shield plate, which is a positive electrode, by the electric field E and is effectively collected.

When the above d is less than 0.2 mm, the toner formed on the photoreceptor 1 is generated due to the rotation of the developing sleeve and the air flow passing between the photoreceptor and the shield plate becomes too strong. The image may be disturbed, and if d exceeds 0.8 mm, the toner scattering prevention effect will be insufficient.

On the other hand, if the above E is less than |100 |V/cm, the toner collection effect is lost, and |10,000|V
/cm, there is a risk of disturbing the developing bias.

The angle θ1 between the lower shield plate 21 and the horizontal plane is important for returning the developer into the developing device after development, and preferably satisfies 30°≦θ1≦90°, and 50°≦θ1. ≦80° is more preferable, 60°≦
It is even more preferable that θ1≦70°.

The angle θ2 between the bottom slope 12 of the developing device main body following the shield plate 21 and the horizontal plane is 0≦θ2≦90.
The angle is preferably 10°≦θ2≦30°. However, it is preferable to set θ1 >θ2, and by doing so, it becomes possible to effectively return the toner attached to the shield plate 21 into the developing device.

The shield plates 11 and 21 are made of a conductive material, for example, a metal plate, and particularly have a resistance value of 1×10
-2 Ωcm or less is preferable.

Electrophotographic development using the developing device of this example was carried out as follows. That is, the developer is supplied from the hopper 13 storing the developer (not shown) to the supply amount adjusting roller 14.
is supplied to the main body of the developing device.

The developer used in this example has two components,
The magnetic carrier used had an average particle size of 43 μm, and the nonmagnetic toner used had a negatively charged average particle size of 6 μm.

The developer is then conveyed to the stirring plate 16 by the conveying roller 15, and the magnetic carrier and non-magnetic toner are thoroughly mixed. Thereafter, the developer is attached to a sleeve 18 containing a plurality of fixed or rotating magnets 17. The sleeve 18 rotates in the opposite direction to the rotation of the photoreceptor 1, and the circumferential speeds of both are adjusted to be the same.

While the developer adhering to the sleeve 18 moves on the fixed magnet 17 as the sleeve 18 rotates, the magnetic carrier particles join together and stand up on the sleeve 18, resulting in a so-called "stand-up" state. After the spiked developer is adjusted to a constant height by the blade 19, it is brought into contact with the surface of the photoreceptor 1, or development is performed without contacting the surface of the photoreceptor 1. In this example, contact development was performed.

In this example, an electrostatic image is formed by an electrostatic image forming method in which a positively charged photoreceptor is used, the exposed part of the image becomes the background part, and the non-exposed part becomes an electrostatic image, and development is performed to form the electrostatic image. An example of regular development performed by adhering toner charged to the opposite polarity was shown.

In addition to the above configuration, the following configuration was adopted in this example. That is, although the photoreceptor 1 has a photoreceptor layer provided on a cylindrical drum, there are portions on both ends of the drum in the direction along the rotation axis where the photoreceptor layer is not formed. In this example, a pad was used to set the distance between both end portions of the drum (non-image portion) on which the photoreceptor layer was not formed and the end surface of the developing device 3 to 0 (ie, a closed state). This makes it possible to further reduce leakage of toner from the developing device. Further, a developing bias voltage 41 was applied to the sleeve 18.

Using the above configuration, the above d, θ1
The amount of toner scattering, dirt inside the machine after copying 50,000 copies, and the presence or absence of image defects were examined by varying the values of and θ2. The results are shown in Table 1.

[0035] Details of each evaluation method are as follows.

(a) Amount of toner scattering: Tips of shield plates 11 and 21 of developing device 3 and photoreceptor 1
The sampling tube opening of a particle counter was installed at a location 1 cm away from both (two locations above and below), and the average value of the number of counts of particles with a particle size of 1 μm or more was measured as the amount of toner scattering (particles/l). Measurements were performed twice, immediately after the start of the experiment and after copying 50,000 copies.

(b) Contamination inside the copying machine After copying 50,000 copies, the contamination inside the copying machine was observed and judged as follows. ◎: No stains at all. ○: A small amount of scattered toner adheres to the outer wall of the developer container (0
．． 01mg/cm2), but it has no effect on the optical system or other internal parts of the machine. △: The amount of scattered toner attached to the outer wall of the developing unit is not that large (in the range of 0.1 mg/cm2 or less), but scattered toner was confirmed to be attached to various lamps (e.g. static elimination lamps) installed around the drum. Ru. There are still few problems with image formation, but we must be careful. There is a problem with reliability. ×: The amount of toner scattered on the outer wall of the developing device is large. (0.
(about 5mg/cm2) is also attached to various lamps,
This causes problems such as insufficient exposure light, which adversely affects image formation. XX: Scattered toner adheres to the entire interior of the machine. Optical system(
Cleaning is required mainly for image writing parts such as mirrors, various lamps, etc. This is a condition in which normal image formation cannot be performed.

(c) Image defects After copying 50,000 sheets, copying was continued and the state in which defects appeared in the images was ranked as follows. ○: Not occurring at all. Δ: A state in which black dot-like or meteor-like image defects appear at a rate of 1 out of every 10,000 copies made when A3 size copies are continued. ×: A state in which the above image defect appears at a rate of 1 in every 1000 to 2000 copies made when A3 size copies are continued. Unreliable. XX: A state in which A3 size copies are continued and the above image defects appear at a rate of 10 or more per 1000 copies. It cannot be used practically.

[0039]
Table-1A No.
1-1 1-2 1-3
1-4 1-5 1-6 ─
──────────────────────────
─────────d (mm)
0.15 0.2 0.5
0.8 0.85 1.0 E(V
/cm) 1100
1100 1100 1100 11
00 1100 θ1 (°)
50 50 50
50 50 50 θ2
(°) 20
20 20 20 2
0 20 Toner scattering amount (pcs/l) Top end at start 340
380 520 760
880 1730 After 50,000 pieces
710 750 9
20 1200 1500 287
0 Lower end at start 230
240 470 590
680 950 After 50,000 pieces
330 340 8
30 980 1030 166
0 Dirt inside the machine ◎
◎ ◎ ○
△ ×Image defect
△ ○ ○ ○
△ ×Remarks
Comparative example Example Example Example Comparative example Comparative example

[0040]
Table-1B No.
1-7 1-8 1-9
1-10 1-11 1-12─
──────────────────────────
─────────d (mm)
2.0 0.5 0.5
0.5 0.5 0.5E(V
/cm) 1100
55 93 120 11
00 9800θ1 (°)
50 50 50
50 50 50θ2
(°) 20
20 20 20 2
0 20 Toner scattering amount (pcs/l) Upper end At start 9820
920 790 680
520 470 After 50,000 sheets
14700 2390 17
60 1410 920 85
0 Lower end at start 2210
710 640 590
470 380 After 50,000 sheets
6740 1830 11
40 1020 830 69
0 Internal dirt ×
× △ ○
◎ ◎Image defects
× × △ ○
○ ○Notes
Comparative example Comparative example Comparative example Example Example Example

[0041]
Table-1C No.
1-13 1-14
1-15 1-16 1-17 ───
──────────────────────────
─────d (mm)
0.5 0.5 0.5
0.5 0.5 E (V/cm)
12000 2.1×10
5 1100 1100 1100
θ1 (°) 50
50 25
50 30 θ2 (°)
20 20
20 5 20 Toner scattering amount (pcs/l) Top end At start 350
320 580 520
530 After 50,000 sheets
810 570 8
90 950 940 Lower end at start 190
110 550 570
540 After 50,000 pieces
310 190 26
00 1700 890 Dirt inside the machine
◎ ◎
△ △ ○Image defect △
× × × ○
Remarks Comparative example
Comparative example Comparative example Comparative example Example

[0042]
Table-1D No.
1-18 1-19 1
-20 1-21 1-22 ────
──────────────────────────
─ d (mm)
0.5 0.5 0.5 0
．． 5 0.5 E (V/cm)
1100 1100 1
100 1100 1100 θ1
(°) 90
60 50 50
45 θ2 (°)
20 20 10
30 50 Amount of toner scattering (pcs/l) Top end At start 510
500 520 510
490 After 50,000 pieces
900 890 910
870 880 Lower end at start 520
480 550 490
500 After 50,000 sheets
800 740 980
790 780 Dirt inside the machine
○ ◎
○ ◎ ◎ Image defect
○ ○
○ ○ ○ Notes
Example Example Example Example Example Example

[0043] In Table 1, 1-1
In the experiment, it seems that because d was too small, the air flow became violent and the image was disturbed. Also, 1-5 to 1
It seems that in -7, d was too large, and in 1-8 and 1-9, the electric field E was too weak, causing the toner to scatter and smear the image. Furthermore, it is thought that the electric field E was too large in samples 1-13 and 1-14, resulting in a decrease in image density. Further, in cases 1-15 and 1-16, it is thought that the toner accumulated at the bottom of the developing device hit the spikes, causing the toner to scatter or spill, resulting in image stains.

On the other hand, in this embodiment, d=0.
2 to 0.8 mm, and the electric field E is |102 to 104
|V/cm and θ1 etc. are also appropriate, so toner scattering can be suppressed to a minimum and image defects can also be reduced. Also,
The amount of scattering at the bottom of the developing device is relatively small, but this is thought to be due to the formation of magnetic brushes due to contact development.

Next, a second embodiment of the present invention will be described. In this example, so-called non-contact development was performed in which developer spikes on the surface of the sleeve 18 were not brought into contact with the photoreceptor 1. Further, an AC developing bias was applied to the sleeve 18.

The configuration and operation other than the above were the same as in the first embodiment. The results are shown in Table 2.

[0047]
Table-2A No.
2-1 2-2 2-3
2-4 2-5 2-6 ─
──────────────────────────
─────────d (mm)
0.15 0.2 0.5
0.8 0.85 1.0E(V
/cm) 1100
1100 1100 1100 11
00 1100θ1 (°)
50 50 50
50 50 50θ2
(°) 20
20 20 20 20
20 Toner scattering amount (pcs/l) Top end at start 280
290 520 640
730 1000 After 50,000 sheets
380 400 8
80 1030 1090 171
0 Lower end at start 410
460 550 800
880 2120 After 50,000 sheets
820 890 9
80 1300 1630 325
0 Dirt inside the machine ◎
◎ ◎ ○
△ ×Image defect
△ ○ ○ ○
△ ×Remarks
Comparative example Example Example Example Comparative example Comparative example

[0048]
Table-2B No.
2-7 2-8 2-9
2-10 2-11 2-12─
──────────────────────────
─────────d (mm)
2.0 0.5 0.5
0.5 0.5 0.5E(V
/cm) 1100
55 93 120 11
00 9800θ1 (°)
50 50 50
50 50 50θ2
(°) 20
20 20 20 2
0 20 Toner scattering amount (pcs/l) Upper end At start 2260
760 690 640
520 430 After 50,000 sheets
6790 1880 11
90 1070 880 74
0 Lower end at start 12150
1080 840 680
550 510 After 50,000 sheets
18300 2720 15
80 1270 980 92
0 Internal dirt ×
× △ ○
◎ ◎Image defects
× × △ ○
○ ○Notes
Comparative example Comparative example Comparative example Example Example Example

[0049]
Table-2C No.
2-13 2-14
2-15 2-16 2-17 ─
──────────────────────────
──────── d (mm)
0.5 0.5 0
．． 5 0.5 0.5 E(V/c
m) 12000 2.
1×105 1100 1100 1
100 θ1 (°)
50 50 25
50 30 θ2 (°)
20 20
20 5 20
Amount of toner scattering (pieces/l) Top end at start 240
160 600 5
80 530 After 50,000 sheets
360 240
950 1010 920
Lower end at start 410
380 560 5
70 560 After 50,000 sheets
870 780
3200 2000 1000
Dirt inside the machine ◎
◎ △ △
○ Image defects
△ × ×
× ○ Notes
Comparative example Comparative example Comparative example Comparative example Example

[0050]
Table-2D No.
2-18 2-19
2-20 2-21 2-22
────────────────────────
──────── d (mm)
0.5 0.5 0.
5 0.5 0.5 E(V
/cm) 1100
1100 1100 1100 1
100 θ1 (°)
90 60 50
50 45 θ2 (°)
20 20
10 30 50
Amount of toner scattering (pcs/l) Top end At start 54
0 530 540 520
530 After 50,000 sheets
910 900 9
20 890 910
Lower end at start 54
0 500 560 570
580 After 50,000 sheets
910 890 11
00 970 960 Dirt inside the machine ○
◎ ○ ◎ ◎
Image defect ○
○ ○ ○ ○
Remarks Examples Examples Examples Examples Examples Examples

00
[51] In the experiment 2-1 in Table 2, it seems that d was too small, so the air flow became violent and the image was disturbed. Also, in 2-5 to 2-7, d is too large, so 2
-8 and 2-9, it seems that the electric field E was too weak, so the toner was scattered and the images were smudged. Furthermore, 2-
It is thought that in Nos. 13 and 2-14, the image density decreased because the electric field E was too large. Also, 2-15 and 2-
In No. 16, it is thought that the toner accumulated at the bottom of the developing device hit the spikes, causing the toner to scatter or spill, causing the image to become smudged. In contrast, in this example,
d=0.2 ~ 0.8 mm, electric field E is |102 ~
104 |V/cm and θ1 etc. are also appropriate, so toner scattering can be suppressed to a minimum and image defects can also be reduced.

In non-contact development as in this example, the amount of toner falling from the lower end is relatively large, but it is clear that this is sufficiently suppressed in the examples.

Next, a third embodiment of the present invention will be explained based on FIG. 2. In this example, the shield plate 11 of the first example,
21, conductive shield rollers 20 and 30 are used in the shield portion 40. This shield roller 2
0 and 30 rotate in the direction of the arrow in the figure so that the captured toner powder can be efficiently taken into the developing device 3. The rest is the same as the example of FIG. 1 described above.

Furthermore, a fourth embodiment of the present invention will be explained based on FIG. This example is full color (yellow, magenta,
This is an example in which the developing device of the present invention is used for electrophotography of (cyan). The individual developing devices 3 containing toners of different colors are similar to those of the first embodiment, but in order to keep the distance d between the photoreceptor 1 and the shield plates 11 and 21 constant, the outside of the developing device is The size has been adjusted. Further, a power source for forming an electric field E between each shield plate 11, 21 and sleeve 18 is installed in the same manner as described above (not shown).

When a plurality of developing units are used as in this example, the shield plates 11 and 21 and the photoreceptor 1 between each developing unit are
By setting the distance d from 0.2 mm≦d≦0.8 mm, color mixing (that is, toner from the upper developing device mixes into the lower developing device) can be prevented.

In the embodiment of the present invention, as described above, the conductive shield plates 11 and 21 or the conductive shield rollers 20 and 30 are used to form a constant electric field between the sleeve 18 and each shield portion. Since the distance d between the photoconductor 1 and the photoreceptor 1 is also set within a specific range, it is possible to effectively prevent toner scattering to the upper part in contact development and toner spilling to the lower part in non-contact development. In addition, by providing certain slopes of θ1 and θ2 at the bottom of the developing device, and by directing the rotation direction of the shield roller toward the inside of the developing device, toner scattering can be effectively prevented and captured toner can be effectively recycled. can be used.

Although the embodiments of the present invention have been described above, various modifications can be made to the embodiments described above based on the technical idea of the present invention. For example, the shape, structure, material, etc. of the shield portion, the method of forming the electric field E, etc. may be changed in various ways. In connection with the fourth embodiment, it is possible to use a plurality of developing devices such as twin color (two colors) or full color developing devices including black in addition to three colors. Further, between a plurality of developing devices, the shield portion may be common to both or may be integrated. In addition, as a method for forming an electrostatic latent image, it is also possible to use a digital exposure method using a semiconductor laser in addition to image exposure using reflected light from the original, and furthermore, in addition to the regular development described above, a reversal development method can be used. Alternatively, the charging polarity of the image carrier can be set to negative.

[0058]

Effects of the Invention As described above, the present invention defines the distance between the photoreceptor and the shield portion of the developing device, and further forms a constant electric field between the shield portion and the developer carrier. , it is possible to sufficiently capture toner that is about to scatter or fall and return it to the inside of the developing device. Therefore, it is possible to prevent the interior of the copying machine from being contaminated and also to prevent image defects.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a developing device according to an embodiment of the present invention.

FIG. 2 is a sectional view of a developing device according to another embodiment of the present invention.

FIG. 3 is a sectional view of a developing device according to yet another embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing an example of an electrophotographic copying apparatus.

[Explanation of symbols]

1 Photoreceptor 2 Image exposure 3 Developing device 10 Corotron corona charger 11, 21 Shield plate 12　　　　Developer body bottom slope 17 Magnet 18 Non-magnetic sleeve 19 Blade 20, 30 Shield roller 24 Opening 40 Shield part 41, 42 Power supply

Claims (1)

[Claims] Claim 1: In a developing device using a dry developer, the distance d between the image forming surface of the photoreceptor and the shield portions provided at the upper and lower ends of the opening of the developing device facing the image forming surface is 0. .2mm≦d≦0.8mm, and between the developer carrier in the developing device and the shield portion |100
A developing device characterized in that it is provided with means for forming an electric field of ~10,000 V/cm.