JPH04340984A - Developing device - Google Patents

Abstract

PURPOSE:To prevent the scattering of toner having a fine grain diameter and pollution inside a copying machine and a defect in an image by specifying a gap between the image forming face of a photosensitive body and a shielding plate, and the angle of the shielding plate with respect to a horizontal surface. CONSTITUTION:A 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 part 24 of the developing unit is 0.2mm<=d<=0.88mm, desirably, 0.3mm<=d<=0.7mm. On the other hand, an angle theta1 formed by the lower part shielding plate 21 and the horizontal surface is set at 30 deg.<=theta1<=90 deg., desirably, 50 deg.<=theta1<=80 deg.. Further, an angle theta2 formed by the bottom part slope 12 of developing unit main body adjoining to the shielding plate 21 and the horizontal surface is set at 0<=theta2<=90 deg., desirably, 10 deg.<=theta2<=30 deg.. Thus, dropping or scattering toner can be sufficiently captured and returned to the inside of the developing unit.

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.

[0003] Conventionally, in the dry developing method as described above, while toner having a relatively large particle size was used, no particular problem 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.

For example, in the case of the above-mentioned Japanese Patent Laid-Open Nos. 60-120376 and 62-66282, scattering of toner is prevented by sealing the space between the upper end of the developing device and the photosensitive drum using an insulating brush or the like. Preventing. However, 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 reduction in the amount of toner scattering from around the developing device is insufficient.

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 angle θ1 that the shield part makes with respect to the horizontal plane is 3
The present invention relates to a developing device characterized in that 0°≦θ1≦90°.

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. Can be done.

[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.

The angle θ1 between the lower shield plate 21 and the horizontal plane is very important for returning the developer into the developing device after development, and is within the range of 30°≦θ1≦90°, preferably 50°≦θ1. ≦80°, more preferably 60°≦
θ1 ≦70°.

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, when θ1 is less than 30°, the toner continues to accumulate on the shield plate and does not return to the inside of the developing section, so that the accumulated toner comes into contact with the developer ears on the developing sleeve. This results in toner scattering. Furthermore, if the angle exceeds 90 degrees, toner will accumulate at the intersection between the shield plate and the bottom of the developing device main body, resulting in toner scattering as described above. Furthermore, if a plurality of developing devices are installed around the drums, it becomes inefficient in terms of space, and the effects of the present invention cannot be exhibited in either case.

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≦9.
The angle is set to 0°, preferably 10°≦θ2≦30°. However, it is preferable that θ>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 may be made of any rigid member, but plastic is particularly preferred from the viewpoint of cost.

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 (indicated by a black dot) to the supply amount adjusting roller 1.
4 to the developing unit main body.

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 transport 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 attached 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 "stiffing" 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. After development, the developer moves on the shield plate 21 as the sleeve 18 rotates and is returned into the container. 22 in the figure is a scraping plate.

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, the developing bias voltage 2 is applied to the sleeve 18.
3 was applied.

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 θ1
(°) 50
50 50 50 5
0 50 θ2 (°)
20 20 20
20 20 20 Toner scattering amount (pcs/l) Top end At start 550
700 800 950
1500 3700 After 50,000 sheets
600 750 8
50 1000 1900 400
0 Lower end at start 510
620 740 920
980 2000 After 50,000 pieces
550 660 7
90 950 1050 250
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 0.5θ1
(°) 50
25 50 30 9
0 20θ2 (°)
20 20 5
20 20 20 Toner scattering amount (pcs/l) Upper end At start 120,000
830 770 810
830 820 After 50,000 sheets
130,890 780
870 880 900
Lower end 9500 at start
760 750 750
760 770 After 50,000 pieces
10000 5100 28
00 940 850 860
0 Dirt inside the machine ××
△ △ ○ ○
×Image defect
× × × ○
○ ×Remarks
Comparative example Comparative example Comparative example Example Example Comparative 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 θ1
(°) 100
60 50 50
45 θ2 (°)
20 20 10
30 50 Amount of toner scattering (pcs/l) Top end At start 83
0 790 810 800
780 After 50,000 sheets
910 820 8
40 850 820
Lower end at start 77
0 730 780 750
740 After 50,000 pieces
3200 770 10
00 810 810 Dirt inside the machine ×
◎ ○ ◎ ◎
Image defect ×
○ ○ ○ ○
Remarks Comparative Example Example Example Example Example Example

00
42] In the experiment 1-1 in Table 1, it seems that d was too small, so the air flow became violent and the image was disturbed. In addition, in experiments 1-8 and 1-9, 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. Moreover, if the setting of θ1 is incorrect, problems such as increased scattering occur as shown in 1-12 and 1-13. On the other hand, in this embodiment, d=0.2 to 0.8 mm and θ1 etc. are appropriate, so that toner scattering can be suppressed to a minimum and image defects can be reduced. Furthermore, 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.

[0045]
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 1.0θ1
(°) 50
50 50 50 50
50θ2 (°)
20 20 20
20 20 20 Toner scattering amount (pcs/l) Top end At start 470
510 570 710
850 2200 After 50,000 sheets
510 550 6
00 820 970 23
70 Lower end at start 630
660 880 1040
1730 19400 After 50,000 pieces
660 690 9
00 1100 1820 210
00 In-flight dirt ◎
◎ ◎ ○
△ ×Image defect
△ ○ ○ ○
△ ×Remarks
Comparative example Example Example Example Comparative example Comparative example

[0046]
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 0.5θ1
(°) 50
25 50 30 9
0 20θ2 (°)
20 20 5
20 20 20 Toner scattering amount (pcs/l) Top end At start 53000
830 850 590
600 610 After 50,000 sheets
62000 860 8
70 650 660 67
0 Lower end At start 201000
950 1030 900
910 920 After 50,000 sheets
215000 10700 78
00 910 890 1280
0 Dirt inside the machine ××
△ △ ○ ○
×Image defect
×× × × ○
○ ×Remarks
Comparative example Example Example Example Example Comparative example

[0047]
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 θ1
(°) 100
60 50 50
45 θ2 (°)
20 20 10
30 50 Toner scattering amount (pcs/l) Top end At start 59
0 550 580 570
560 After 50,000 sheets
660 570 6
10 600 590
Lower end at start 90
0 860 950 880
890 After 50,000 pieces
9500 890 11
50 900 910 Dirt inside the machine ×
◎ ○ ◎ ◎
Image defect ×
○ ○ ○ ○
Remarks Comparative Example Example Example Example Example Example

00
48] 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. In addition, in experiments 2-8 and 2-9, 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. If θ1 is improperly set, problems such as increased scattering will occur as shown in 2-12 and 2-13. On the other hand, in this example, d=0.2 to 0.8 mm and θ1 etc. are appropriate, so toner scattering can be suppressed to a minimum.
Image defects can also be reduced. In the case of non-contact development as in this example, toner falls from the lower end relatively often, but this is sufficiently suppressed within the scope of the example.

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, a shield roller 20 is attached to the shield portion 40.
, 30 are used. This shield roller 20, 30
is rotated in the direction of the arrow in the figure so that the captured toner powder can be taken into the developing device 3 efficiently. The rest is the same as the example of FIG. 1 described above.

Further, a fourth embodiment of the present invention will be explained based on FIG. 3. In this example, the developing device of the present invention is used for full-color (yellow, magenta, cyan) electrophotography. individual developing devices 3A containing toners of different colors;
3B and 3C are similar to those of the first example, but
The outer dimensions of the developing device are adjusted to keep the distance d between the photoreceptor 1 and the shield plates 11 and 21 constant. Note that developer particles are omitted in the figure.

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, the angle θ1 between the shield portion and the horizontal plane is adjusted by using the insulating shield plates 11, 21 or the insulating shield rollers 20, 30 as described above
is set within a specific range, and the distance d between each shield member and the photoreceptor 1 is also set within a specific range, which is particularly effective in preventing toner scattering to the upper part in contact development and toner spilling to the lower part in non-contact development. can be prevented. 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 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. Furthermore, between a plurality of developing devices, the shield portion may be common to both or may be integrated.

[0054] 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. It is also possible to use a method or to set the charging polarity of the image carrier to be negative.

[0055]

Effects of the Invention As described above, the present invention prevents toner from scattering or falling by defining the distance between the photoreceptor and the shield portion of the developing device and further defining the angle of the shield portion. Enough can be captured and returned 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

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 the angle θ1 that the shield part makes with respect to the horizontal plane is 30°≦θ
1. A developing device characterized in that the angle is ≦90°.