JP2984697B2 - Electrophotographic copying machine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying machine (including an electrostatic copying machine), and more particularly, to a photoconductor (including an electrostatic recording body) after transferring a toner image onto plain paper or the like. The present invention relates to an electrophotographic copying apparatus in which a magnetic brush cleaning device is provided in a cleaning section for removing residual toner on the surface.

(Prior art)

As shown in FIG. 1, the electrophotographic copying apparatus roughly includes an organic or inorganic photoreceptor 1 (which may be a belt-shaped member instead of a drum-shaped member) and a charger 2 and an optical system 3 around the photosensitive member. , A developing unit 4, a transfer charger 5, a separation charger 6, and a cleaning unit 7. The transfer charger 5 is used to transfer the toner image on the photoconductor 1 to transfer paper 8 such as plain paper, and the separation charger 6 transfers the transfer paper 8 having the toner image to the photoconductor 1.
It is provided to separate from the surface. In the drawing, reference numeral 9 denotes a separating claw.

Either a dry developing method or a wet developing method (including a semi-dry developing method) is employed for visualizing an electrostatic charge image. The former is advantageous in that a copy can be obtained in a dry state. Therefore, the dry development method is now mainstream.

Dry development systems are broadly classified into those using a one-component type developer (composed of only toner) and those using two-component type developer (composed of carrier and toner). In any case, it is desirable that all the toner images visualized by such a developer are ideally transferred to transfer paper, but actually, toner that cannot be completely transferred to transfer paper remains on the photoconductor. For,
This residual toner must be removed by a cleaning device.

Methods for cleaning residual toner (untransferred toner) include (1) fur brush, (2) blade, and (3)
It is common to use a magnetic brush or the like. But
The fur brush method requires a large cleaning device,
There is a dislike that filming easily occurs on the photoconductor. In addition, the blade method has a defect that the photosensitive member is easily damaged. On the other hand, the cleaning by the magnetic brush method has been studied in, for example, Japanese Patent Application Laid-Open No. 58-102273. However, there is a disadvantage that long-term cleaning is not guaranteed.

〔Purpose〕

A first object of the present invention is to provide a magnetic brush cleaning unit using a two-component dry type developer, in which residual toner on a photoreceptor can be removed satisfactorily and cleaning can be performed for a long time. An electrophotographic copying apparatus is provided. A second object of the present invention is to provide an electrophotographic copying apparatus capable of obtaining a large number of high quality copies over a long period of time.

[Constitution] The present invention forms an electrostatic charge image on a photoreceptor, visualizes it with a two-component developer, transfers this toner image to a transfer device, and removes the toner remaining on the photoreceptor surface. In an electrophotographic copying machine to be removed by a magnetic brush cleaning unit, the cleaning carrier housed in the magnetic brush cleaning unit has a particle size of 48 to 78 μm, and has a specific resistance of 50 V / cm by a filled cell electric resistance measurement method. It shows a value of 1.5 × 10 ^{7 to} 1.4 × 10 ¹⁵ Ωcm when applying a DC electric field of 2.5 × 10 ^{8 to} 1.2 × when a DC electric field of 500 V / cm is applied.
It is characterized by showing a value of 10 ¹⁵ Ωcm.
To define the content of the “filled cell electric resistance measurement method” in the present invention, two electrodes are opposed to each other in a longitudinal direction in an insulating rectangular container, and a carrier is charged into the space. After that, a DC voltage is applied between the electrodes after the carrier is densely filled in the container by tapping, and the electric resistance is measured.

Incidentally, the present inventors set the specific resistance value and the particle size of the carrier (cleaning agent) in the cleaning section of the electrophotographic copying apparatus using the two-component dry developer as described above, so that the residual toner is magnetically separated. It is easy to transfer to the carrier (cleaning carrier) of the brush cleaning unit, and the residual toner once attached to the cleaning carrier is easily separated from the cleaning carrier in the magnetic brush cleaning unit.
We have confirmed that long-term cleaning can be performed. The present invention has been made based on such a thing.

In the following, the device according to the invention will be explained in more detail in connection with the copying process with reference to the accompanying drawings.

First, as shown in FIG. 1, positive or negative charging is uniformly applied to the surface of a photoconductor (inorganic photoconductor, organic photoconductor) 1 by a charging charger 2. Positive charging or negative charging is selected depending on the type (property) of the photoreceptor 1. For example, if the photoreceptor is a Se-based photoreceptor, positive charging is performed. The image is exposed to the light by the optical system 3 to form an electrostatic image, and the electrostatic image is visualized by the developing unit 4.

The developing unit 4 contains a two-component developer composed of a carrier (magnetic carrier) and a toner (developed toner). The developer is held on a developing sleeve 41 containing a magnet 411 and develops an electrostatic image on the photoconductor 1. Since only the developing toner is consumed each time the developing is performed, the sensor 42 detects the toner density of the developer and new developing toner is supplied so that the toner density always becomes constant. Reference numeral 43 denotes a paddle wheel for stirring the developer. Note that a bias may be applied to the developing sleeve 41 as needed.

The visible image (toner image) is transferred to the transfer paper 8 by the transfer charger 5, and the transfer paper 8 is separated from the photoreceptor 1 by the separation charger 6 and the separation claw 9 and sent to the fixing process.

As mentioned above, all of the toner that forms a visible image on the photoconductor 1 at the time of transfer is not transferred to the transfer paper 8, and part of the toner remains on the photoconductor 1. The residual toner is removed by the cleaning unit 7.

The cleaning unit 7 in the apparatus of the present invention employs a magnetic brush cleaning method, in which a magnetic carrier (cleaning carrier) as a cleaning agent is stored. A positive or negative bias of about 100 to 500 V is applied to the cleaning roller 71 having a magnet (not shown) built therein, and a cleaning agent is held on the cleaning roller 71 by the magnet. here,
The polarity of the bias applied to the cleaning roller 71 is opposite to the polarity of the toner in the two-component developer.

The residual toner is electrostatically attracted to a cleaning agent (cleaning carrier) and is transferred to the pumping rollers 72 to 73 together with the cleaning agent. A residual toner collecting roller 74 to which a bias having the same polarity as that of the cleaning roller 71 is applied is disposed behind the pumping roller 73, and only the residual toner is transferred to the collecting roller 74. The bias applied to the collection roller 74 is desirably relatively higher than the bias applied to the cleaning roller, and is suitably about 200 to 800 V.

Immediately after the residual toner is transferred from the pickup roller 73 to the collection roller 74, the cleaning carrier
The cleaning scraper 75 is scraped off by the cleaning scraper 75 and is returned to the surface of the cleaning roller 71 again. on the other hand,
The residual toner transferred to the collecting roller 74 is scraped off by a collecting blade 76 in contact with the collecting roller 74, taken out of the cleaning unit 7 by a discharge screw 77, and, if necessary, as a two-component developer toner. used. The collecting roller 74 cleaned by the collecting blade 76 is used for collecting the next remaining toner. The cleaning agent (cleaning carrier) that falls on the cleaning roller 71 and circulates again to contribute to the recovery of the residual toner is inevitably containing some residual toner. Is in the range of at most 2% by weight.

In the apparatus of the present invention, such a cycle of a series of copying and cleaning steps is repeated, but when the photoconductor 1 is uniformly charged by the charging charger 2, residual toner is present on the surface of the photoconductor. Therefore, uniform charging of the photoconductor 1 is assured.

FIG. 2 shows a cleaning section in which the pumping rollers 72 and 73 in FIG. 1 are removed, and this can also be used as the apparatus of the present invention.

In the apparatus according to the present invention, a means for achieving good cleaning performance by defining the specific resistance of the carrier (cleaning carrier) housed in the cleaning unit 7 is adopted.

Generally, the toner remaining on the photoreceptor 1 without being transferred onto the transfer paper 8 has a very low or high charge amount (hereinafter referred to as “Q / M”), and the transfer is not performed smoothly. Therefore, in the cleaning section 7, it is necessary to reduce the carrier resistance and increase the cleaning electric field as much as possible.
However, on the other hand, if the resistance of the cleaning carrier is too small, the carrier adheres to the photoconductor 1. Further, the bias applied to the collecting roller 74 is likely to leak, and the toner does not transfer to the collecting roller 74 (when the bias is applied to the roller 71, a cleaning failure due to the leak occurs). Therefore, the toner concentration of the cleaning agent in the cleaning unit 7 becomes too high, and as a result, the photoconductor 1 is not sufficiently cleaned. Conversely, if the resistance of the cleaning carrier is increased, the cleaning electric field is reduced, and it becomes impossible to clean toner having a low or high Q / M. Further, the toner is not sufficiently transferred to the collection roller 74. Therefore, when the bias of the collection roller 74 is increased, the carrier is transferred to the collection roller 74, and the cleaning is not sufficiently performed.

The apparatus according to the present invention can solve the above-mentioned problem by defining the resistance of the cleaning carrier, so that the photoconductor 1 can be satisfied.
Cleaning has been achieved. The good cleaning carrier has a specific resistance of 1.5 × 10 ⁷ to 1.4 when a DC electric field of 50 V / cm is applied, as measured by the filled cell electric resistance measurement method of the present invention.
× 10 ¹⁵ Ωcm, and (b) When a DC electric field of 500 V / cm is applied, 2.5 × 10 ^{8 to} 1.2
× 10 ¹⁵ Ωcm.

Here, the method of measuring the specific resistance in the present invention, that is, the method of measuring the electric resistance of the packed cell will be described in detail as follows. That is, as shown in FIG. 3, first, the sample was allowed to flow into a cell formed by facing two electrode plates having an area of 10 cm ² (length 4 cm, width 2.5 cm) at an interval of 2 mm so that the sample overflowed. Thereafter, in this state, a tapping operation of dropping the sample from a position having a height of 15 mm onto a flat plate is repeated 30 times, and the sample is densely filled in the cell. Next, after removing the excess sample on the cell, 50 V / cm and 50 V / cm were applied to the electrode plates in an environment of 20 ° C. and 60% RH, respectively.
A DC electric field of 500 V / cm is applied.
Part) to determine the specific resistance. In the figure, S is the cell, E ₁ and E ₂ are both represent electrode plates.

The cleaning carrier is desirably made by coating a carrier core material with a release resin. The provision of this coating layer is also advantageous from the viewpoint of preventing toner from adhering to the carrier (spenting) and extending the life.

As the carrier core material (cleaning carrier core material), non-metals such as sand, cobalt, iron, copper, nickel, zinc, aluminum, brass, glass, and the like having an average particle diameter of 20 to 1000 μm, preferably 50 to 500 μm, and metals. Conventionally used materials such as alloys are widely used.

Examples of the releasing resin for coating include polyolefin resins such as polyethylene, polypropylene, chlorinated polyethylene, and chlorosulfonated polyethylene; polyvinyl and polyvinylidene resins such as polystyrene, acrylic resins (eg, polymethyl methacrylate), polyacrylonitrile, and polyvinyl acetate. Polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether and polyvinyl ketone; vinyl chloride-vinyl acetate copolymer; styrene-acrylic acid copolymer; silicone resin such as straight silicone resin comprising organosiloxane bond; Modified products (for example, modified products of alkyd resin, polyester, epoxy resin, polyurethane, etc.); fluorine resin such as polytetrafur Roechiren, polyvinyl fluoride, polyvinylidene fluoride Biniden, polychlorotrifluoroethylene; polyamides; polyesters such as polyethylene terephthalate; polyurethanes; polycarbonates; amino resins such as urea - formaldehyde resins, epoxy resins and the like. Above all, acrylic resin, silicone resin or its modified product, fluorine resin and the like are preferable in terms of preventing the spent toner from adhering to the carrier, and silicon resin or its modified product is sometimes preferable. The commercially available silicone resin (straight silicone resin) is KR271, KR255, KR251 manufactured by Shin-Etsu Chemical Co., Ltd., SR manufactured by Toray Silicon Co., Ltd.
2400, SR2406, etc., and as modified silicone resin, KR206 (modified alkyd resin), KR3093 manufactured by Shin-Etsu Chemical Co., Ltd.
(Modified acrylic resin), ES1001N (modified epoxy resin), Toray Silicon SR2115 (modified epoxy resin), SR2110 (modified alkyd resin), and the like.

The thickness of the coating layer may be about 0.1 to 2.5 μm. If necessary, a pigment such as phthalocyanine, a quaternary ammonium salt, silica, a dye, a resin, or the like may be added to the coating layer as a conductive substance or a charge-imparting material.

As the conductive carbon, any carbon black having conductivity can be used. For example, furnace black (a commercially available product such as Black Pearls 2000, manufactured by Cabot Corporation, C
arbolacl; Lion Akzo Ketchen Black EC-D
J500, Ketjen Black EC-DJ 600, etc.), and acetylene black (as commercial products, Denka Black granules and decane black powder, manufactured by Denki Kagaku Kogyo Co., Ltd .; Anaman, etc., manufactured by Postman Co., Ltd.). Particle size is 0.5-50
0 μm, preferably about 1 to 100 μm is appropriate.

On the other hand, examples of the white conductive agent include TiO ₂ , SnO ₂ , Zn0, and the like, and a mixture thereof. The particle size is suitably about 0.01 to 3 μm, preferably about 0.05 to 2.0 μm. Commercially available white conductive agents include the following. All percentages here are percentages by weight.

Products of Titanium Industry: ECT 52 (Anatase type titanium oxide with TiO ₂ content of 56-58%) KV 400 (Anatase type titanium oxide with TiO ₂ content of 58-62%) ECR 72 (TiO ₂ content of 80-85%) Rutile type titanium oxide) Ishihara Sangyo Co., Ltd. product: 500W (titanium oxide-tin oxide mixed system) 300W (titanium oxide-tin oxide mixed system) S-1 (titanium oxide) Mitsubishi Metals product: W-1 (titanium oxide- Antimony oxide-doped tin oxide mixture) Hakusui Chemical's product: 23 K (zinc oxide) Honjo Chemical's product: conductive zinc white No.1 (zinc oxide content 99%) conductive zinc white No.2 (zinc oxide Next, examples will be described. All parts here are by weight.

Example 1 An average particle diameter of about 100 μm as a two-component developing carrier
Steel beads (Micro Shot SF-
100) was prepared.

On the other hand, a mixture having the following formulation was kneaded under heating on a two-roll mill, cooled, and then pulverized and classified to prepare a two-component developer toner having a particle size of 5 to 20 μm.

100 parts of polystyrene (D-125, manufactured by Esso) 100 parts of metal-containing dye (Spilon Black BH, manufactured by Hodogaya Chemical Co., Ltd.) 5 parts 10 parts of carbon black (# 44 manufactured by Mitsubishi Kasei Corporation) 100 parts of these carriers and 3.0 parts of toner are mixed. Thus, a two-component developer was prepared. The charge amount (Q / M) of the toner in this developer by a blow-off method was −24 μc / g.

Further, a coated carrier was obtained for the cleaning carrier by changing the amount of added carbon according to the following formulation.

500 parts of silicone resin solution (KR250 manufactured by Shin-Etsu Chemical Co., Ltd.) Ketcheng Black (EC-DJ 6 manufactured by Lion Akzo)
00) Part X Toluene 1500 parts The mixture consisting of the following was dispersed with a homomixer for 30 minutes to prepare a coating layer forming solution, and the surface of 5000 parts of irregular shaped iron powder (TEFV 200/300) having a particle size distribution of 46 to 76 μm (average particle size 60 μm) was prepared. The coating was applied to a thickness of about 0.9 μm using a fluidized bed type coating apparatus to form a coating layer. The coating layer was used as a cleaning carrier to obtain the following four types of cleaning carriers.

To the carrier, 1.0 part of the toner was mixed to prepare a cleaning agent.

Subsequently, the two-component developer and the cleaning agent are uniformly charged so that the surface potential of the photoreceptor 1 becomes +800 V using a selenium-based photoreceptor as shown in FIG. + 250V bias to the cleaning roller 71,
(A bias of +300 V was applied to the collection roller 74) to obtain 30 copies per minute and to replenish the toner consumed by the developing unit 4. Table 1 summarizes the results of the running test and the carrier resistance.

In Table 1, the copy image density is measured by a Macbeth densitometer (RD514). In the column of dirt on the photoreceptor, ○ means no dirt and X means dirt (the same applies hereinafter).

From Table 1, cleaning can be performed satisfactorily if the carrier resistance is No. 2 and No. 3. On the other hand, if the carrier resistance deviates from the specified value (No. 1 and No. 4), cleaning cannot be performed at all. As a result, the image density becomes extremely low.

Examples 2 to 6 As a two-component developing carrier, an average particle diameter of about 100 μm
Steel beads (Micro Shot SF-
100) was prepared.

On the other hand, a mixture having the following formulation was kneaded under heating on a two-roll mill, cooled, and then pulverized and classified to prepare a two-component developer toner having a particle size of 5 to 20 μm.

100 parts of polystyrene (D-125, manufactured by Esso) 100 parts of metal-containing dye (Spilon Black BH, manufactured by Hodogaya Chemical Co., Ltd.) 5 parts 10 parts of carbon black (# 44 manufactured by Mitsubishi Kasei Corporation) 100 parts of these carriers and 3.0 parts of toner are mixed Thus, a two-component developer was prepared. The charge amount (Q / M) of the toner in this developer by a blow-off method was −24 μc / g.

The cleaning carrier is as follows: Silicone resin solution (KR250 manufactured by Shin-Etsu Chemical Co., Ltd.) 500 parts Conductive material and / or charge imparting material 5 parts Toluene 1500 parts The mixture consisting of the following was dispersed with a homomixer for 30 minutes to prepare a coating layer forming solution, and the surface of 5000 parts of irregular shaped iron powder (TEFV 200/300) having a particle size distribution of 46 to 76 μm (average particle size 60 μm) was prepared. The coating was applied to a thickness of about 0.9 μm using a fluidized bed type coating apparatus to form a coating layer, which was used as a cleaning carrier to obtain five types of cleaning carriers.

The copying machine shown in FIG. 1 (using a selenium-based photoreceptor,
Uniformly charged so that the surface potential of the photoconductor 1 becomes +800 V;
A bias of +250 V is applied to the cleaning roller 71 and a bias of +300 V is applied to the collection roller 74).
Copies were obtained at a rate of 30 sheets per minute, and toner consumed in the developing unit 4 was supplied. Table 2 summarizes the results of the running test and the carrier resistance.

Examples 7 to 11 The carrier of Example 1 (steel beads having an average particle diameter of about 100 μm) was prepared as a two-component developing carrier. On the other hand, a mixture having the following formulation was kneaded under heating on two roll mills, cooled and then pulverized and classified to prepare a toner for a two-component developer having a particle size of 5 to 20 μm.

Polystyrene (D-125 manufactured by Esso) 100 parts Dye (Special Black SB manufactured by Orient Chemical) 5 parts Carbon black (# 44 manufactured by Mitsubishi Kasei) 100 parts 100 parts of these carriers and 3.0 parts of toner are mixed to form a two-component system. A developer was prepared. In addition, Q / M in this developer
Was 20 μc / g.

On the other hand, as in the case of the coat carriers of Examples 2 to 6, the cleaning carrier is a silicone resin solution 500
Parts and 1,500 parts of toluene were added with 5 parts of each of the following conductive materials and / or charge-imparting materials to obtain five types.

The two-component developer and the cleaning agent are uniformly charged so that the surface potential of the photoreceptor 1 becomes -800 V by using an organic photoreceptor and a cleaning roller as shown in FIG. -71V bias at 71, collection roller 74
, A bias of -300 V was applied), 30 copies per minute were obtained, and the toner consumed in the developing unit 4 was supplied. Table 3 summarizes the results of the running test and the carrier resistance.

Next, in order to examine the influence of the cleaning agent on the environment and the cleaning agent, those subjected to various tests in a low-temperature and low-humidity environment are shown below as Examples 12 to 14, and Comparative Examples 15 to 16. .

Example 12 A developer and a cleaning agent were prepared in exactly the same manner as in Examples 1 to 3 described above, and a test was conducted in the same manner as in Example 1 above in a low-temperature and low-humidity environment at a temperature of 10 ° C. and a humidity of 15%. The results in Table 4 were obtained.

Example 13 A test was performed in the same manner as in Example 1 except that the average particle diameter of only the cleaning carrier particles in Example 1 was changed to 90 μm, and the same result as that in Example 12 was obtained.

Example 14 A test was performed in the same manner as in Example 1 except that only the cleaning carrier particles of Example 1 were changed to an average particle diameter of 30 μm, and the same results as in Example 12 were obtained.

Comparative Example 15 A test was conducted in the same manner as in Example 12 except that only the cleaning carrier particles of Example 12 were changed to an average particle diameter of 100 μm. As a result, cleaning failure occurred from the start to the entire surface. Therefore, further tests were stopped.

Comparative Example 16 A test was performed in the same manner as in Example 12 except that only the cleaning carrier particles of Example 12 were changed to an average particle diameter of 20 μm, and carrier adhesion and carrier scattering were remarkable from the start. Stopped.

As a result of the various tests described above, it has been found that the cleaning agent and the copying machine can cope with various use environments by defining the cleaning carrier resistance and the particle size of the cleaning agent. For example, the aforementioned low temperature and low humidity of 10 ° C and humidity of 15% or less, or high temperature and high humidity of 30
The environment is below 90 ° C and 90% humidity. In a low-temperature and low-humidity environment, the amount of water is low, so that the Q / M tends to be low.
Accompanying this, at low temperature and low humidity, the fluidity of the cleaning agent deteriorates, and the clogging of the cleaning agent in the developing sleeve 41 tends to be coarse (a state in which the air layer increases). The degree of tight packing is not sufficient (it is likely to be rough), and the carrier resistance (cleaning agent resistance) is increased (out of the range of the carrier resistance in the present application). This particle size becomes remarkable when it is 90 μm or more. On the other hand, when the thickness is 30 μm or less, there is no problem of clogging of the cleaning agent.

〔effect〕

As is apparent from the description of the embodiment, according to the copying apparatus of the present invention, a high-quality copy can be obtained without image contamination even when copying 100,000 sheets. Further, it was found that the surface of the photoreceptor after cleaning was very clean visually. Further, it was recognized that the cleaning agent and the copying apparatus could be used in a wide range of environments from a low-temperature low-humidity region to a high-temperature high-humidity region.

[Brief description of the drawings]

FIG. 1 is a schematic view of an electrophotographic copying apparatus according to the present invention. FIG. 2 is a schematic view of another example of the cleaning unit slightly different from that shown in FIG. FIG. 3 is a view for explaining a method of measuring the specific resistance of the cleaning carrier. DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Charger 3 ... Optical system 4, Developing part 5 ... Transfer charger, 6 ... Separation charger 7 ... Cleaning part, 8 ... Transfer paper 9 ... Separation nail, 41 Development sleeve 411 Magnet 42 Sensor 43 Paddle wheel 71 Cleaning roller 72, 73 Pumping roller 74 Collection roller 75 Cleaning scraper 76 Collection blade 77 … Discharge screw

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kayo Makita 1-3-6 Nakamagome, Ota-ku, Tokyo, Japan Ricoh Co., Ltd.Jury, Yoshifumi Muramoto Judge Mikio Kinoshita Judge Yoshinori Hirai (56) Reference JP-A-60-12568 (JP, A) JP-A-59-30573 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 21/00 316

Claims (1)

(57) [Claims] An electrostatic charge image is formed on a photoreceptor, visualized with a two-component developer, the toner image is transferred to a transfer member, and the toner remaining on the photoreceptor surface is removed by a magnetic brush. In the electrophotographic copying machine to be removed by the cleaning unit, the cleaning carrier housed in the magnetic brush cleaning unit has a particle diameter of 48 to 78 μm, and has a specific resistance of 50 V / cm according to a filled cell electric resistance measuring method. It shows a value of 1.5 × 10 ^{7 to} 1.4 × 10 ¹⁵ Ωcm when a field is applied, and 2.5 × 10 ^{8 to} 1.2 × when a DC electric field of 500 V / cm is applied.
An electrophotographic copying apparatus having a value of 10 ¹⁵ Ωcm.