KR960015101B1 - Roller apparatus - Google Patents

Abstract

None.

Description

Image Forming Device

1 is a cross-sectional view of a conventional charging roller.

2 is a schematic cross-sectional view of a testing apparatus based on an electrophotographic process used to determine the characteristics of a charging roller.

3 is a graph showing the relationship between the DC voltage applied to the charging roller and the charging potential of the photosensitive drum.

4 is a graph showing irregularities of the charging potential when measured in the direction in which the drum operates.

5 shows a non-uniform pattern of a particular charge.

6 is a graph comparing ozone concentration.

7 is a contrast table for the characteristics of the three types of rollers produced for testing.

8A-8E are cross-sectional views illustrating preferred embodiments of the present invention.

9 is a schematic view of an image forming apparatus according to the present invention.

10a-10c show improvements over the prior art of the present invention.

11 is a graph showing the relationship between the surface temperature of the charging roller, the resistance of the thermistor and the output of the power supply.

12, 13 and 14 are schematic diagrams showing another embodiment of the image forming apparatus according to the present invention.

15 is a schematic cross-sectional view showing three types of charging rollers according to the present invention.

FIG. 16 is a table showing the relationship between uniform charging and charging characteristics of the thickness of epichlorohydrin rubber.

17 is a graph showing the charging characteristics of the charging roller under various conditions.

18 is a table comparing the ozone concentration.

19A and 19B are schematic views showing another embodiment of the image forming apparatus according to the present invention.

20A and 20B are schematic diagrams showing specific test apparatus applied to the present invention.

21A and 21B are graphs showing the temperature dependence of various characteristics of the charging roller according to the present invention.

22A and 22B are graphs showing the humidity dependence of various characteristics of the charging roller according to the present invention.

24, 24 and 25 are schematic diagrams showing yet another embodiment of the chemical forming apparatus according to the present invention.

Fig. 26 is a graph showing the relationship between the surface temperature of the charging roller, the resistance of the thermistor and the voltage applied to the roller.

27 is a schematic cross-sectional view of another embodiment showing another charging roller according to the present invention.

Fig. 28 is a schematic diagram illustrating an image forming apparatus having a charging roller according to the present invention.

29 is a graph showing the charging characteristics of the charging roller under various conditions.

30 is a table showing the amount and electrical resistance of lithium perchlorate salt added to the urethane rubber.

Figure 31 is a schematic diagram of a particular test apparatus applicable to a charging roller according to the present invention.

32a and 32b are graphs showing test results performed with the device of FIG.

33 is a graph showing I-Vs characteristics and Vs-Va characteristics of a charging roller according to the present invention when measured at 25 ° C. temperature and 50% humidity.

34 is a schematic diagram showing how a conventional charging roller is used.

35 is a schematic diagram showing a conventional charging device mounted with an image forming apparatus.

36 is a graph showing the relationship between the voltage applied to the charging roller observed under various conditions and the charging potential of the photosensitive drum.

* Explanation of symbols for main parts of the drawings

100: charging roller 908: CPU

101: Core 909: cleaning member

102: elastic layer 912: exhaust fan

103: surface layer 1902: transfer roller

208: ozone monitor 2301: charging roller

209: electrometer 2401: charging roller

902: charging roller 2501: charging roller

907: thermistor 2302: anti-heat heater

2402: cleaning member 2502: DC power

TECHNICAL FIELD The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and the like, and more particularly, to an image forming apparatus in the form of using a charging roller to uniformly charge the photosensitive element or the image carrier surface during image formation.

In the image forming apparatus of this type, it is common to use a corona discharger as a charging means for uniformly charging the photosensitive element surface. The corona discharger uniformly and effectively charges the surface of the photoconductor element to a predetermined potential. The problem, however, is that the corona discharger needs a high voltage power source and generates ozone during discharge. Ozone generated in large quantities not only pollutes the environment but also causes deterioration of the photosensitive drum element and the charging member.

In view of the above, a charging device using a charging roller instead of a corona discharger has been proposed. The charging device has a charging roller which is driven in connection with the photosensitive drum. This charging roller has a metal core. When a voltage is applied from the power supply to the core of the charging roller, the charging roller charges the metal surface. It is possible to lower the voltage required by the charging roller and thus reduce the amount of ozone generated by charging.

In addition, the charging roller prevents the electrostatic deposition of dust particles on the corona wire and eliminates the need for a high voltage power supply. However, the problem with this type of charger is that not only the charging distribution is uneven, but also the charging potential is extremely sensitive to the environment. In fact, such a charger is worse than a charger of the type using a corona discharger in terms of uniformity of charge distribution.

In fact, the present inventors found spots in the background of images copied in the early winter mornings with a laser printer having a charging roller. It is assumed that the charging roller left at low temperature during the night increases the electrical resistance, and thus the reverse phenomenon occurs because the charging potential of the photosensitive drum is about 200V away from the normal temperature and humidity.

According to Japanese Patent Publication No. 149668/1988 (hereinafter referred to as 'Document 1') when an AC voltage having a peak-peak voltage that is twice or more the charging start voltage V _TH in the case of DC voltage application is superimposed. It is said that the charging uniformity is remarkably improved.

Japanese Patent Laid-Open No. 132356/1981 (hereinafter referred to as "Document 2") discloses applying a voltage to a charging roller from a constant current power source in order to reduce the charge roller being sensitive to ambient conditions.

Japanese Patent Publication No. 156476/1990 (hereinafter referred to as "Document 3") discloses an arrangement in which an AC-overlapping DC voltage is applied to a charging roller to ensure stable charging regardless of the surrounding environment.

In addition, Japanese Patent Laid-Open No. 288174/1990 (hereinafter referred to as Document 4) discloses a means for heating a charging roller in order to eliminate the roller from being affected by the surrounding environment.

However, according to the document 1, in order to superimpose the AC voltage on the DC voltage, not only the DC power but also the AC power supply has a drawback in that the cost of equipment is increased, and moreover, a problem that many AC currents do not contribute to the charging potential of the photosensitive element is wasted. There is also. This not only increases the operating cost of the device but also generates a large amount of ozone, which causes the important problem mentioned above.

In Document 4, although the current is constant, the charging potential of the photoreceptor element can be kept constant irrespective of the electrical resistance of the charging roller, but the leakage current change cannot be ignored as the ambient conditions, especially the humidity, change.

According to Document 3, uneven charging can be reduced, but the installation cost is increased due to AC power, and Document 4 has a problem that the size and cost of the device are increased because the heating means heats the entire charging roller.

Accordingly, an object of the present invention is to provide an image forming apparatus that can reduce the cost of the device itself and the cost of power, and can prevent deterioration of charging members and photoreceptor elements and prevent environmental pollution by reducing ozone generation. .

It is another object of the present invention to provide an image forming apparatus which is not only simple in structure but can always provide clear images regardless of changes in the surrounding environment.

According to the present invention, in a charging roller having at least one elastic layer and a surface layer covering the surface of the elastic layer, the surface layer contains a material forming the elastic layer. Further, according to the present invention, in the image forming apparatus having a charging roller having at least one elastic layer and a surface layer covering the surface of the elastic layer, each of the surface layers produces a plurality of solutions of rubber and resin in a specific mixing ratio, It is produced by applying the solution in turn to the elastic layer.

In addition, the image forming apparatus according to the present invention includes a photosensitive drum, a charging roller which is in contact with the photosensitive drum and rotated by the photosensitive drum, and a light emitting part for emitting the surface of the photosensitive drum charged by the charging roller, the light emitting part. A developing unit which forms an electrostatic latent image electrostatically formed on the photosensitive drum by means, a temperature sensor for detecting a temperature around the charging roller, and a voltage and a developing means applied to the charging roller based on the temperature detected by the temperature sensor. And a controller for controlling at least one of the applied development bias voltages. Further, according to the present invention, an image forming apparatus having a charging mechanism for uniformly charging the surface of the photosensitive drum by applying a voltage to the charging roller which is rotated in contact with the photosensitive drum, wherein the ambient temperature of the charging roller is detected. The thermistor is installed in the DC power supply circuit which applies the DC voltage to the charging roller.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The charging device shown in FIG. 34 has a charging roller 3400 in contact with the photosensitive drum 3401. The charging roller 3400 has a metal core 3402. As voltage is applied from the power source 3403 to the core 3402 of the charging roller 3400, the roller 3400 charges the surface of the drum 3401. The charging roller 3400 can lower the required voltage of the power supply 3403 and reduce the amount of ozone caused by charging. The charging roller 3400 also prevents dust particles from being electrostatically deposited on the corona wire and eliminates the need for a high voltage power supply. However, the problem with this type of charger is that the charging distribution tends to be uneven and the charging potential is severely affected by the ambient conditions.

In fact, such a charger is much inferior to a charger using a corona discharger in terms of nonuniformity of charge distribution. 35 shows another conventional charging mechanism of another type using a charging roller.

As shown, the photosensitive drum 3501 consists of a metal drum 3501a and a photosensitive member layer 3501b covering the drum 3501. The charging roller 3502 is composed of a metal core 3502a, a conductive rubber layer 3502b, and a resistance layer 3502a forming the surface of the roller 3502.

As shown in the figure, as the drum 3501 is rotated in the clockwise direction, the charging roller 3502 is rotated by the drum 3501 in the counterclockwise direction. A DC power supply 3503 is connected between the drum 3501 and the charging roller 3502. Electrometer 3504 is installed close to the drum 3501 to measure the charge potential.

Three different kinds of environments, for example, a high temperature and humidity environment with a temperature of 30 ° C. and a humidity of 90%, a normal environment with a temperature of 25 ° C. and a 52% humidity, and a low temperature with a temperature of 10 ° C. and a humidity of 15%. Let's simulate a conditional environment.

These are correlated with the voltage Va (-kV) and the charge potential Vs (-kV) applied in each environment as shown in FIG. If a constant DC power is set in the high voltage power source 3503 and the charge voltage Vs is set to -800V, the voltage Va is -1.5kV as shown in FIG. As the ambient environment changes to high temperature and high humidity, the charge potential Vs becomes -900V; When the surrounding environment is changed to low temperature drying, the charge potential Vs changes to -600V. Here, the charge potential changes over the 300V range, causing actual use to cause various problems. Several methods have been proposed to solve this problem, but none of them are satisfactory.

Hereinafter, the present invention will be described in detail.

1 shows the structure of a conventional charging roller 100. The charging roller 100 covers the 8φ metal core 101, the core 101, and has a thickness of about 4 mm and a conductive elastic layer 102 (10 ³ Ω · cm) made of carbon-dispersed silicone rubber, and a 50 탆 thickness covering the elastic layer 102. Has a surface layer of 103.

FIG. 2 shows an image forming apparatus used to test the charging characteristics and the charge distribution uniformity of the charging roller of FIG.

As shown, the apparatus has a photosensitive drum 201 and a charging roller 100 in contact with the drum 201. The developing unit 202 develops an electrostatic latent image formed on the drum 201 charged with the charging roller 100 with toner. Transfer charger 203 transfers the resultant toner image from drum 201 to copy paper or other recording medium. The separation charger 204 discharges the paper to separate the paper from the drum 201 after the transfer. The cleaning blade 205 removes the toner remaining on the drum 201 after the transfer. The discharge lamp 206 scatters the charge still present on the drum 201 after the transfer. The power source 207 applies a voltage to the discharge roller 100. The developing unit 202 has a developing sleeve 202a, which transfers toner to the drum 201. A bias voltage is applied to the developing sleeve 202a to control the amount of toner deposited on the drum 201. Reference numeral 208 denotes an ozone monitor for monitoring ozone due to the operation of the charging roller 100, and 209 denotes an electrometer directed toward the center of the drum 201 in front of the developing unit 202.

In operation, the drum 201 is rotated at a linear speed of? Mm / sec by a drive line not shown. The charging roller 100 charges the drum 201 surface with a negative polarity as voltage is applied from the power source 207. As the charged drum 201 surface is turned into furnace, the charge on the drum 201 is selectively erased (spread) according to the brightness. As a result, a latent image is electrostatically formed on the drum 201. The developing unit 202 develops the latent image by inverse phenomenon to convert the electrostatic latent image into a toner image. The transfer charger 203 transfers the toner image from the drum 201 to the paper supplied through the conveying means. The separation charger 204 separates the paper having this toner image from the drum 201. Toner and charges remaining on the drum 201 after image transfer are respectively removed by the cleaning braid 205 and the discharge lamp. This is the end of one imaging cycle.

3 and 4 show uniformity of charging characteristics and charge distribution measured by the electrometer 209, respectively. That is, FIG. 3 shows the relationship between the DC voltage Va (-kV) applied to the charging roller 100 and the charging potential Vs (-V) deposited on the drum 201.

4 shows the nonuniformity of the electric potential Vs in the drum 201 measured by the electrometer 209 in the direction in which the drum 201 moves. As shown, I: DC (-1200 V) and II: DC + AC (DC: -600 V, AC: V _pp = 2.0 kV / f = 1.0 kHz) are applied to the charging roller 100. The range of non-uniformity of the charge potential Vs is | Vs _(MAX) -Vs _(MIN) | = 80V under the condition I, and about 10V under the condition II.

Regarding the potential potential Vs (about -600V), the inversion effect is affected by the developing bias voltages (-550V, -600V, -650V). Then, the potential Vs is charged toner is deposited in the lower portion than the bias voltage V _B as shown in FIG. 5, that is, it is non-uniform throughout the area the charge distribution of the entire charge. As a result, under the condition I, the background is contaminated in the cycle of the charging roller 100. This is considered to be a nonuniformity of the charge distribution due to the nonuniform electrical characteristics of the roller layer.

On the other hand, under condition II, the toner is lightly deposited over the entire area, that is, the nonuniformity of the charge distribution is not noticeable. 6 is ozone (O ₃ ) concentration (ppm) measured by placing the inlet of the ozone monitor 208 on the outlet side of the site where the charging roller 100 and the drum 201 contact under conditions I and II. As shown in FIG. 6, AC current increases ozone generation. This means that the ozone can be reduced if only the DC voltage is applied to the charging roller 100, i.e., if it does not overlap the AC voltage.

Further studies on the nonuniformity of charging caused when DC voltage is applied to the charging roller 100 revealed that the conductive elastic layer 102 is composed of carbon and silicon rubber dispersion. This was found when the conductive elastic layer 102 used a charging roller (nylon / epichlorohydrin rubber) made of epichlorohydrin rubber. More specifically, this nonuniformity arises from the nonuniform electrical properties of layer 102, and the nonuniform electrical properties of layer 102 are the result of incomplete dispersion of carbon and silicone rubber. This dispersion eliminates non-uniformity when replaced with non-analytic epichlorohydrin rubber.

The nylon surface layer 103 of the charge roller 100 is very sensitive to the environment. To improve this point, as shown in FIG. 7, the present inventors manufacture the charging rollers 100 (a), (b) and (c) of a specific material and then charge characteristics and charge uniformity for each of them. Sex was evaluated.

As shown in FIG. 7, in order to obtain a uniform charging distribution using only the DC voltage, the elastic layer (2 mm to 20 mm thickness) of the charging roller 100 should be electrically uniform.

In this respect, even if a single layer (roller (a), FIG. 7) made of non-disperse and low resistance rubber (epichlorohydrin rubber) is optimal, the surface arrangement obtainable here is undesirable and uniform in charge distribution. Deteriorates the sex. In order to improve the surface arrangement, the roller b shown in FIG. 7 is provided with a resin surface layer of 30 탆 thickness. However, in this case, since the surface layer made of fluorine resin has high resistance, charging characteristics and charging uniformity are lowered. In order to improve the surface arrangement without affecting the charging characteristics, a surface layer having a thickness of 10 µm to 100 µm can be formed of a low resistance rubber and a resin dispersion, which also has an elastic layer. The roller of FIG. 7 has such a surface layer.

More preferably, the resin concentration of this surface layer should increase gradually toward the surface while the rubber concentration should increase gradually toward the elastic layer. Such a surface layer can be formed if a solution, each having a specific mixing ratio of resin and rubber, is applied in turn. As the elastic layer, epichlorohydrin rubber, nitrile rubber, urethane rubber, acrylic rubber or chloropretan rubber can be used. As for the surface layer, fluororesins, silicone resins or the like are most preferred.

As described above, the charging rollers of the present invention arranged to obtain a uniform charge distribution only by the DC voltage and the conventional charging rollers that depend on the AC voltage to obtain a uniform charge distribution have a charge characteristic (R, C) and a layer structure. It's a completely different thing. In particular, a conventional charging roller has a conductive elastic layer (carbon dispersed rubber) and a surface (resistance) layer. In this type of roller, the surface layer acts as a capacitor, so the capacitance C is large, which plays a large role in uniform charge distribution. do. On the other hand, since the charging roller of the present invention serves as a resistor (less capacitance C), even if AC is superimposed on DC, charging uniformity will not be greatly improved.

Hereinafter, the present invention will be described in detail according to the embodiment.

Example 1

As shown in FIG. 8A, in Example 1, the elastic layer 102 of the charging roller 100 is molded by adding epichlorohydrin rubber to the 6φ core so that the roller outer diameter is 12φ. The electrical resistance of the elastic layer 102 is 3 × 10 ⁸ Pa · cm. 100 parts of epichlorohydrin rubber solution (2.5 wt% solids) and 40 parts of fluororesin solution (solid 10.8 wt%) soluble in a solvent are applied to the elastic layer 102 to form a film or surface layer having a thickness of 30 μm when dried. . The electrical resistance of the surface layer 103 is 3 x 10 ¹⁰ Pa · cm. The charging characteristics of the charging roller 100 are Vs = -580V with respect to Va (DC) -1200V, and the nonuniformity range of the charging potential Vs is 12V, and it forms a uniform charging distribution.

Example 2

As shown in FIG. 8B, the elastic layer 102 was formed by forming nitrile rubber (NBR) on the 8φ core 101 so that the roller outer diameter became 16φ. The elastic layer 102 has an electrical resistance of 8 × 10 ⁶ Pa · cm. 100 parts of the nitrile rubber solution (2.5 wt% solids) and 40 parts of the fluorine resin solution (solids 10.8 wt%) soluble in the solvent were applied to the elastic layer 102 to form a film or surface layer 103 having a thickness of 50 μm when dried. The electrical resistance of the surface layer 103 is 8x10 <^10> Pa * cm. The charging characteristic of the charging roller 100 is Vs = -570V with respect to Va (DC) -1200V, and it has a charging potential Vs nonuniformity in the range of 15V and shows uniform charging distribution as in the first embodiment.

Example 3

As shown in FIG. 8C, epichlorohydrin was formed on the 8φ core 101 such that the roller outer diameter became 16φ, thereby forming an elastic layer 102. Epichlorohydrin rubber solution (solid content of 2.5wt%) and soluble fluorine resin solution (solid content of 10.8wt%) are mixed and applied to the elastic layer 102 while changing the mixing ratio, each having a thickness of 30㎛ Two films were formed. That is, a mixture consisting of 100 parts of epichlorohydrin rubber solution and 20 parts of fluorine resin solution (electrical resistance 2 × 10 ⁸ Ω · cm) is applied first, followed by a mixture of 100 parts of epichlorohydrin rubber solution and 60 parts of fluororesin. (Electrical resistance 2 × 10 ¹¹ Pa · cm) was applied. Due to the high fluorine resin concentration, the charging roller 100 had a flat surface. The charging characteristics were Vs-580V for Va (DC) -1200V, and the charge potential Vs nonuniformity was in the range of 100V and has a uniform charge distribution.

Example 4

As shown in FIG. 8D, the urethane rubber was molded to the 6φ metal core 101 to have a roller outer diameter of 12φ to form an elastic layer 102. The electrical resistance value of the elastic layer 102 is 8x10 ⁹ Pa · cm. 100 parts of urethane rubber solution (25.wt% solids), 50 parts of silicone resin solution soluble in a solvent (7.5 wt% solids), and 2 parts of carbon are added to the elastomer 102 to form a film or surface layer 103 having a thickness of 40 탆 upon drying. It was. The electrical resistance value of the surface layer 103 is 2 x 10 ⁹ Pa · cm. The charging characteristics of the charging roller are Vs-560V with respect to Va (DC) 1200V, and the charging potential Vs nonuniformity in the range of 18V shows uniform charging distribution.

Example 5

As shown in FIG. 8E, this example is the same as Example 4 except that the thickness of the surface layer 103 is 60 mu m using chloroproren rubber instead of urethane rubber. The charging characteristics of the charging roller 100 are Vs = -590V with respect to Va (DC) -1200V. The nonuniformity of the charging potential Vs is in the range of 15V and shows a uniform charging distribution.

As described above, the charging roller according to the present invention has a smooth surface without deteriorating charging characteristics by the surface layer being composed of a mixture of polar synthetic rubber and non-adhesive resin. Since the resin concentration gradually increases toward the surface of the surface layer, the surface arrangement is preferable and the durability of the roller is also enhanced. Furthermore, since the electrical resistance of this synthetic resin (non-dispersible) is 10 ⁶ Pa · cm to 10 ¹⁰ Pa · cm and is non-dispersible, even if the surface layer comes into contact with the pinhole portion of the photoconductor, it does not cause electrification breakdown.

Example 6

9 shows a laser printer or similar image forming apparatus to which Embodiment 6 of the present invention is applied.

As shown, this image forming apparatus has, for example, a photosensitive drum 901 having a diameter of 60 mm and a charging roller 902 rotating in contact with the drum 901 with a diameter of 15 mm. The charging roller 902 is connected to a high voltage power supply 903 '. The charging roller 902 is, for example, a metal core 902a having a diameter of 10 mm, a conductive rubber layer 902b having a thickness of 5 mm, and a surface resistance layer 902a having a thickness of 50 µm. The developing unit 905 for the inversion phenomenon attaches the dry toner to the electrostatic latent image formed on the drum 901 by the laser beam L. The bias voltage Vb is applied to the developing unit 905 from the power supply 906. At least one of the bias power supply 906 and the high voltage power supply 903 'is controlled via a CPU (Central Processing Unit) 908 by a thermistor 907 which is sensitive to a temperature around the charging roller 902.

According to the experiment, the surface linear velocity ν of the drum 901 is 120 mm / sec, the ambient temperature T of the charging roller 902 when measured by the thermistor 907 is 25 ° C., and the voltage applied to the charging roller 902 is -1.54 kV. A preferable image is obtained when the charging voltage Vs is -800V and the developing bias voltage Vb is -600V.

For example, under the usual conditions of winter early morning T = 10 ° C. and neither of the power supplies 903 'and 906 are controlled by the CPU 908, Vs was measured at 590 V as shown in FIG. 10 and the background was contaminated. If the thermistor is detected and applied to the CPU 908 as T = 10 ° C, when the bias voltage V'b is controlled to -500V as shown in FIG. 10B, or the voltage V'a for the charging roller 902 is set to 10c. As shown in the figure, when controlled to -1.6 kV (V's = -650 V), a good improvement was obtained in which the background was not contaminated. 11 shows the surface temperature T of the charging roller 902, the resistance R of the thermistor 907, the DC power output Vb, when the terminator 907 is used in the DC power supply circuit for developing bias voltage Vb and the DC power supply circuit for charging roller application voltage Va. TR-Va characteristics showing the relationship with Va.

Example 7

The embodiment in which the bias voltage Vb applied to the developing unit 905, FIG. 9 is controlled in accordance with the T-R-Vb characteristic of FIG.

As shown, the thermistor 907 disposed around the charging roller 902 is provided in the bias DC power supply 906 so as to apply an appropriate bias voltage Vb regardless of the surrounding environment. This is successful in obtaining the necessary image without contaminating the background. When T = 16 ° C., R = 14 kPa, Vb = -560V and Vs = -740V under these conditions, a preferable image can be obtained.

Example 8

FIG. 13 shows Example 8, wherein the voltage Va for the charging rollers 902 and 9 is controlled according to the T-R-Va characteristic of FIG.

The terminator 907 installed around the charging roller 902 is connected to the DC power supply circuit 903 'and outputs the optimum voltage Va regardless of the surrounding conditions.

The charging voltage Vs for the drum 901 is always kept constant.

In this embodiment, the cleaning member 909 contacts the charging roller 902 to clean the roller 902 surface. At the same time, the cleaning member 909 improves charging characteristics by playing a role of rapidly increasing the surface temperature of the charging roller 902 by friction even when the ambient temperature is low.

In fact, when the temperature T was 12 ° C., Vs = -760V at R = 1.65kPa, Va = -16.5kV, and kept constant at Vb = -600V, and a good image was obtained.

Example 9

According to the embodiments described so far, a good image can be obtained in a very short period even when the ambient temperature is low, while the ninth embodiment of FIG. 14 can further reduce the waiting time.

As shown in FIG. 14, the image forming apparatus includes a chemical transfer means 910, a fixing unit 911 using a heating roller, an exhaust fan 912, drum cleaning means 913 attached to a photosensitive drum 901, a charging roller 902, and the like. It has a developing unit 905.

In this embodiment, carbon is dispersed in the conductive rubber layer 902b of the charging roller 902 or a small amount of carbon is added to the surface resistance layer 902a of the roller 902. This blackens the surface of the charging roller 902 to improve the absorption of radiant heat. Before using this apparatus, the drum 901 and the charging roller 902 are idling, the exhaust fan 912 is rotated in the reverse direction, and the heater of the fixing unit 911 is operated. Then, the heat generated in the fixing unit 911 goes to the charging roller 902 to raise the surface temperature of the roller 902. As the temperature of the charging roller 902 reaches the predetermined temperature detected by the thermistor 907, the exhaust fan 912 rotates in the exhaust direction. In this condition, the image forming apparatus starts the image forming operation.

In this way, even if the image forming apparatus has been kept at a low temperature for a long time, the surface temperature of the charging roller 902 can be raised within a very short time, thereby making it possible to produce an image without contaminating the background. If necessary, the bias control means and / or charge roller voltage control means described in connection with the seventh and eighth embodiments may be used in this embodiment to further shorten the waiting time.

The nonuniformity of the charge distribution caused when a DC voltage is applied to a normal charging roller (having a resin layer covering the conductive elastic layer) will be described below. This charging nonuniformity is caused when the conductive elastic layer is a dispersion system of carbon and silicone rubber. This was found when using a charging roller (overcoating the resin on the epichlorohydrin rubber elastic layer) made of the epichlorohydrin rubber.

That is, the charging nonuniformity of the conventional charging roller is caused by the electrical nonuniformity of the conductive elastic layer due to the dispersion of the carbon / silicon rubber, and the charging nonuniformity is eliminated by using epichlorohydrin rubber of non-dispersion type.

FIG. 15 shows three charge rollers that can achieve a uniform charge distribution when only a DC voltage is applied, that is, when the AC voltage is not superimposed on the DC voltage.

That is, roller A is a single layer of epichlorohydrin rubber (1 to 5 mm thickness), and roller B is composed of an epichlorohydrin rubber elastic layer (1 mm to 5 mm thickness) and a fluororesin surface layer (1 μm to 10 μm thickness). do.

Similarly, the roller C is composed of an epichlorohydrin rubber layer (1 mm to 5 mm thickness), a fluororesin and an epichlorohydrin dispersion layer (10 to 100 µm). If necessary, in a single layer of epichlorohydrin rubber (1 to 5 mm thick), the fluororesin may be configured to concentrate in a single layer surface portion of epichlorohydrin rubber.

The thickness of the epichlorohydrin rubber layer is 1 to 5 mm. The reason for this is that the thickness of the epichlorohydrin rubber layer is less than 1 mm, and the function of the elastic body is insufficient. If the thickness is 5 mm or more, the electrical resistance is high, or the thermal conductivity when the heater is heated. There is a problem with this drop (ie, reduced resistance). FIG. 16 shows experimental results regarding the thickness of the epichlorohydrin rubber layer (1 to 5 mm).

Example 10

The elastic layer (3 mm thickness) of epichlorohydrin rubber was shape | molded on the 8phi metal core 1501 so that the roller outer diameter might be 14phi. 100 parts of epichlorohydrin rubber solution (2.5 wt% solids) and 40 parts of solvent-soluble fluororesin solution (solids 10.8 wt%) are dried and plotted on an elastic layer so that the film thickness is 30 μm. The resulting charging roller (Fig. 15, roller C) has a charging characteristic of Vs = -720V for Va = -1400V, and a nonuniformity range of charging potential is in the range of 10V and has a uniform charging distribution.

When DC + AC is applied to the charging roller as in the conventional apparatus, even if the latent image potential remains on the photoconductor or there is some residual toner on the photoconductor, a uniform charging distribution can be obtained by the AC superposition effect. In order to obtain a uniform charging distribution, not only the charging roller (non-dispersion type, epichlorohydrin elastic roller) of the present invention is used, but also the surface of the photoconductor drum subjected to converter light with QL (Quenching Lamp) first. It is necessary to pass the charging step and then put it in the charging process from the photoreceptor surface from which the residual toner on the surface of the photoreceptor drum is completely removed with a cleaning braid.

In this case, a uniform charge distribution as shown by II of FIG. 17 was obtained. In the absence of QL, the charge potential becomes nonuniform, as indicated by 17 degrees I by adding the residual potential. In addition, when the cleaning is insufficient, the toner remaining on the drum is transferred to the roller surface at the time of bonding with the charging roller, thereby causing charging irregularity in the roller cycle (III in FIG. 17).

Example 11

If an image transfer device is used as contact transfer instead of normal corona transfer, the amount of ozone generated can be greatly reduced. 18 shows a comparison of ozone concentrations. 19A and 19B show a schematic structure of the image forming apparatus embodying this embodiment. In general, in the case of the small diameter photosensitive drum (or belt photosensitive member) 1901a to which the curvature separation method is applied to the separation of the transfer paper, the transfer is performed by the roller 1902 (Fig. 19a), and in the case of the photosensitive drum 1901b having a diameter of 50φ or more. Transcription by 1903 (degree 19b) is applied.

In the image forming apparatus which performs roller charging / roller transfer only by applying DC voltage, roller charge / roller transfer in which the amount of ions generated is superimposed on AC at 1/800 to 1/1000 and DC is applied compared to corona charging / corona transfer. It is also reduced to 1/30 ~ 1/40 compared to the chemical forming apparatus of.

The charging roller (FIG. 15, roller A) was manufactured by shape | molding the elastic layer of epichlorohydrin (4 mm thickness) on the 8phi metal core 1501 so that a roller outer diameter might be 16phi. The charging rollers were evaluated for the temperature and humidity dependence of the I-Va characteristics and the Vs-Va characteristics using the test apparatus shown in FIGS. 20a and 20b (FIGS. 21a and 21b, 22a and 22b). ).

As shown, the resistance of the epichlorohydrin rubber layer (= Va / 2) greatly depends on the temperature (Fig. 21a), but is not significantly affected by humidity (Fig. 22a).

The charge characteristics (charge potential Vs and uniform charge distribution) of this layer are greatly influenced by temperature (FIG. 21), that is, both Vs and uniformity are lowered at a temperature of 10 DEG C or lower. However, the charging characteristic is not significantly affected by the humidity (Figs. 22a and 22b).

Despite the use of the charging roller having the epichlorohydrin rubber layer as described above, in order to uniformly charge the photoreceptor element and obtain a uniform distribution, the charging roller should be used at a temperature of 10 ° C. or higher.

In addition, the roller temperature is detected by the thermistor, and the output correction of the charge roller applied voltage to the temperature change is necessary.

Example 12

As shown in FIG. 23, the charging roller 2301 is a 4mm thick elastic roller made of epichlorohydrin rubber, and a heater 2302 (heat sink of 30 × 200 mm ² , 200V, 18W) is installed on the charging roller 2301. Defrost is eliminated. In the winter night, the heater 2302 is turned on to prevent the internal temperature of the apparatus from dropping below 5 ° C.

For this reason, since the roller temperature becomes 10 degreeC or more at the time of image formation in winter and early morning, an image with a favorable charging characteristic is obtained by DC application.

In addition, since condensation of the optical system and the photoconductive drum 2303 is also prevented by the frost condensation prevention heater 2302, occurrence of an abnormal image can be prevented.

Example 13

As shown in FIG. 24, the charging roller 2401 has an epichlorohydrin rubber layer or elastic layer having a thickness of 3 mm and an overcoat layer having a thickness of 1 to 3 탆 on the elastic layer. When the roller rotates while the cleaning member 2402 for cleaning the roller surface is compressed, the cleaning blade 2402 not only cleans the roller 2401 but also raises the surface temperature of the roller 2401 due to friction.

In winter or early morning, the drum 2403 can be idled before image formation to raise the surface temperature of the charging roller 2401 to 10 ° C or more, thereby restoring the charging characteristic to a normal state.

The cleaning member 2402 may be always in contact with the charging roller 2401 or may be in contact with the roller 2401 only when idling the imaged drum 2403.

Example 14

25 shows a roller charging apparatus using a charging roller 2501 such as the charging roller of the tenth embodiment.

FIG. 26 shows the relationship between the roller surface temperature T (° C.), thermistor resistance R (kΩ) and the roller voltage Va (kV) from the temperature characteristics of the charging roller 2501. The 25 degree power supply 2502 is provided with the control circuit so that the applied voltage corresponding to the instantaneous roller temperature may be obtained based on the T-R-V characteristic.

In this embodiment, even when the charging roller is temperature dependent, a constant charging potential can always be obtained because a voltage is output in accordance with the roller temperature.

Next, the nonuniform charging distribution caused when DC voltage is applied to the conventional charging roller (a structure having a resin overcoat layer on the conductive elastic layer surface) will be described.

The nonuniform charge distribution is caused by the conductive elastic layer being a dispersion system of synthetic rubber and carbon. This was proved by testing the conductive elastic layer (synthetic rubber and carbon dispersion system) of the conventional charging roller using a charging roller made of urethane which does not contain carbon or urethane rubber containing a small amount of alkali metal salt.

That is, the charging nonuniformity of the conventional charging roller is caused by the electrical nonuniformity of the conductive elastic layer due to the dispersion defect of carbon / synthetic rubber, and the charging nonuniformity is eliminated by using a non-dispersed urethane rubber.

FIG. 27 shows a configuration of a charging roller capable of uniform charging even when only a DC voltage is applied, that is, when the AC voltage is not superimposed on the DC voltage. As shown, roller D is composed of a metal core 2701 and an elastic layer 2702 in which an alkali metal salt is contained in a urethane or urethane rubber having a thickness of 1 to 5 mm. The roller E has the surface layer 2703 of 1-30 micrometers thickness which consists of a non-adhesive resin in the elastic layer 2702.

Here, since the elastic layer 2702 is urethane rubber having an electrical resistance of 10 ⁶ to 10 ¹⁰ Pa · cm alone or a urethane rubber containing an alkali metal salt without depending on dispersion of conductive particles such as carbon, the voltage resistance is good and the entire elastic layer is electrically Uniform.

Also, since urethane rubber has adequate hardness and surface property, it has sufficient performance for roller D, but when a higher performance electrified roller is required, the roller has a surface layer 2703 made of non-adhesive resin (for example, fluorocarbon resin or silicone resin). You can use E.

Example 15

An elastic layer 2702 made of urethane rubber (3 mm thick) was formed on the 8φ metal core 2701 so that the outer diameter of the roller was 14φ (roller D, Fig. 27). The electrical resistance of this elastic layer 2702 is 3 × 10 ⁹ Pa · cm (at 20 ° C temperature and 50% humidity).

28 is a partial schematic view of an image forming apparatus using the charging roller 2800 of this embodiment. As shown, the apparatus has a photosensitive drum 2801 having a photosensitive layer having a thickness of 30 μm.

The power supply 2803 applies a DC voltage Va. The quenching lamp (QL) 2804 is tight emitting diodes (LEDs), and the cleaning unit 2805 removes toner remaining on the drum 2801. The charging roller 2800 has charging characteristics Vs = -800V with respect to Va = -1500V, and the nonuniformity of the charging potential Vs ranges from about 15V and shows a uniform charging distribution. When AC-overlapped DC is applied to the charging roller as in a conventional apparatus, a uniform charging distribution is obtained by the AC superposition effect even if there is a residual power supply at the photoreceptor temperature or some toner remains in the photoreceptor element.

On the other hand, in order to obtain a uniform charging distribution with only DC voltage, using a charging roller having an elastic layer having an electrical resistance of 10 ⁶ Pa · cm to 10 ¹⁰ Pa · cm made of urethane rubber containing urethane rubber or alkali metal salt In addition, it is necessary to first allow the photosensitive element portion subjected to converter light by QL first to undergo a charging process, and secondly, a surface portion of the element from which residual toner is completely removed by the cleaning braid first.

Under this condition, a uniform charge distribution can be obtained as in FIG. 29 II. In addition, when the cleaning is not sufficient, the toner remaining on the photoreceptor element is transferred to the charging roller, causing uneven charging in subsequent roller cycles (Fig. 29 III).

Example 16

An elastic layer 270 2 (4 mm thick) made of urethane rubber was formed on the 8φ metal core 2701 so that the roller outer diameter was 16φ. Since the elastic layer 2702 contains 05 wt% lithium perchlorate, its electrical resistance is 3 × 10 ⁸ Pa · cm (temperature 20 ° C., humidity 50%). A solvent-soluble fluorine resin solution (solid content of 10.8 wt%) was applied on the elastic layer 2702 so that the film thickness after drying was 5 µm to form a surface layer 2703. (Roller E, Fig. 27).

The charging roller was replaced with the charging roller (roller D) in Example 15, whereupon an experiment similar to that of Example 1 was obtained. Among various synthetic rubbers, urethane rubber is an excellent elastomer in terms of low hardness, friction resistance, compressive stress resistance and strength. Therefore, urethane rubber is the most suitable as an elastic layer of the charging roller in terms of strength and hardness.

However, the problem was that urethane rubber was very sensitive to the environment because of its high electrical resistance. The resistance of urethane rubber can be reduced by introducing alkali metal salts into urethane rubber. In this case, there is no resistance unevenness as in the case of dispersion of conductive particles such as carbon (Japanese Patent Laid-Open No. 189876/1988). Suitable alkali metal salts are perhalogenous oxyacids.

30 shows the amount of lithium perchlorate added to the urethane rubber and its electrical resistance.

Next, environmental change measures of the electrical resistance of urethane rubber will be described. Roller D ', FIG. 27, and roller D' with 0.05 wt% lithium perchlorate salt were used for the experiment. For each of rollers D and D ', two different environments, one in temperature and humidity of 25 ° C. and 80%, respectively, and the other in temperature and humidity of 15 ° C. and 30%, respectively, are shown in FIG. 31. Vs-Va characteristics were measured by the test apparatus. 32a and 32b show the measured Vs-Va properties of rollers D and D ', respectively. The charging characteristics of both the rollers D and D 'change in the above environment because the electrical resistance of each roller changes depending on the environment.

In Fig. 31, the current I to be measured is a power supply current with respect to the applied voltage Va and a charge current for charging the photosensitive member Vs. Therefore, even if the electrical resistance of the charging roller changes, if the current I can be maintained as one, the photosensitive member charge potential Vs can be made one.

33 shows I-Vs and Vs-Va characteristics measured at 25 ° C. temperature and 50% humidity of roller D (solid line) and roller D '(dashed line). When a constant current DC power supply is used for the applied voltage power supply, the applied voltage ΔVa fluctuates so that the current I = 30 mA in any of the rollers D and D 'having different resistances, thereby obtaining Vs = 800V. This method is applied to the environmental variation of the electrical resistance of each roller.

Example 17

The rollers D and D 'were used in two environments: temperature 15 ° C. and humidity 30% and temperature 25 ° C. and humidity 80%.

When the power supply of the apparatus shown in FIG. 28 was a constant current DC power supply, the charging potential Vs of the photosensitive drum was measured at 800 ± 25V for the constant current I = 30 ± 1 mA. Since the use of a constant current power supply means that a constant charge is always supplied to the photoconductor, there is no residual potential on the surface of the photoconductor before charging, and the absolute condition is that the current toner is completely removed.

As described above, according to the present invention, charging efficiency is enhanced and uniform charging distribution can be achieved using only DC voltage. This is to increase the equipment cost of the device, increase the power cost and suppress the generation of large amounts of ozone. As a result, the deterioration of the charging member and the photosensitive member member can be prevented, and the concern of environmental pollution can be eliminated at the same time.

According to the image forming apparatus according to the present invention, at least one of the charging roller applied voltage and the developing bias voltage is controlled based on the temperature around the charging roller to obtain a stable image without contamination of the background regardless of the change in the environment. To be able. The thermistor responding to the charge roller ambient temperature is provided in the developing bias power supply circuit, so that the image forming apparatus is very simple in its structure.

In addition, since the heat generated from the fixing means is supplied to the charging roller, the surface temperature of the roller can be increased, and thus, good image quality can be obtained even at a low temperature without a separate heating means.

In addition, by blackening the surface of the charging roller, the heat absorption rate is increased to stabilize the image in a short time.

Further, according to the present invention, since the thermistor sensitive to the temperature around the charging roller is installed in the DC voltage power supply circuit for applying the voltage to the charging roller, it becomes a constant voltage power supply, thereby reducing the charging unevenness and breaking current due to voltage fluctuation. Can be removed.

In addition, since no AC power is used, not only ozone is suppressed, but also the cost is reduced. In addition, since the cleaning member is in contact with the charging roller, the friction may increase the roller temperature in a short time. This is particularly desirable when operating the image forming apparatus in winter or early morning.

As the present invention discloses, those skilled in the art will be able to make modifications without departing from the present invention.

Claims (14)

Photosensitive drum 901; A charging roller 902 rotated by the photosensitive drum 901 and in contact with the photosensitive drum 901; Light emitting means for emitting a surface of the photosensitive drum 901 charged by the charging roller 902; Developing means 905 for developing a latent image electrostatically formed on said photosensitive drum 901 by said light emitting means; Temperature detecting means 907 for detecting a temperature around the charging roller 902; And control means 908 for controlling at least one of an applied voltage applied to the charging roller 902 and a developing bias voltage applied to the developing means based on the temperature detected by the temperature detecting means 907. Photosensitive drum 901; A charging roller 902 rotated by the photosensitive drum 901 and in contact with the photosensitive drum 901; Light emitting means for emitting a surface of the photosensitive drum 901 charged by the charging roller 902; Developing means 905 for developing a latent image electrostatically formed on said photosensitive drum 901 by said light emitting means; A bias power supply circuit 906 'for applying a bias voltage to the developing means 905; And a thermistor 907 disposed in the bias power supply circuit 906 'for detecting a temperature around the charging roller 902. Photosensitive drum 901; A charging roller 902 rotated by the photosensitive drum 901 and in contact with the photosensitive drum 901; Light emitting means for emitting a surface of the photosensitive drum 901 charged by the charging roller 902; Developing means 905 for developing a latent image electrostatically formed on the photosensitive drum by the light emitting means to form a visible image; Transfer means 910 for transferring the visible image to a recording medium; Fixing means 911 for fixing the visible image transferred to the recording medium by heat; And heat inducing means 912 for controlling the surface temperature of the charging roller 902 by inducing heat generated by the fixing means 911 to the charging roller 902. 4. The image forming apparatus as claimed in claim 3, wherein the charging roller 902 has a black surface. An image forming apparatus having a charging device for uniformly charging the surface of a photosensitive drum 901 by applying a voltage to a charging roller 902 contacted and rotated by a photosensitive drum 901, wherein the thermistor 907 for detecting a temperature around the charging roller 902 is And a DC voltage power supply circuit 903 'for applying a DC voltage to the charging roller 902. The image forming apparatus of claim 5, wherein a cleaning member 909 is installed in contact with the surface of the charging roller 902. An image forming apparatus having a charging device, comprising: a DC to a charging roller of the charging device in which an elastic layer made of a polar rubber having an intermediate resistance value is formed between the core and the surface layer so as to uniformly charge the surface of the photoconductor element which has been cleaned. An image forming apparatus characterized by applying a voltage Va. Charging means for applying a DC voltage to the charging roller of the charging device in which an elastic layer of polar rubber is formed with an intermediate resistance value between the core and the surface layer to uniformly charge the surface of the photoconductor element after the cleaning process; And transfer means for applying a DC voltage having a polarity opposite to that of the toner adhered to the photoconductor to the roller 1902 or belt 1903 pressed against the rear surface of the recording medium for transferring the image. An image forming apparatus having a charging device, comprising: a charging roller of the charging device having an elastic layer made of a polar rubber having an intermediate resistance value between the core and the surface in order to uniformly charge the surface of the photoconductor element after cleaning. And a constant current type power supply. The image forming apparatus according to claim 9, wherein the polar rubber is selected from the group consisting of epichlorohydrin rubber, nitrile rubber, urethane rubber, acrylic rubber and chloropretan rubber. An image forming apparatus having a charging device, comprising: a heater 2302 for preventing dew condensation around a charging roller 2301 having an elastic layer made of epichlorohydrin rubber in order to maintain the surface of the charging roller 2301 at an appropriate temperature. An image forming apparatus. In an image forming apparatus having a charging device, in order to maintain the surface of the charging roller 2401 at an appropriate temperature, the cleaning member 2402 is brought into contact with the charging roller 2401 having an elastic layer made of epichlorohydrin rubber, and the cleaning is performed before actual image formation. And rotate the member 2402. 13. An image forming apparatus according to claim 12, wherein said suitable temperature is at least 10 &lt; 0 &gt; C. An image forming apparatus having a charging device, comprising: a temperature detecting means 907 provided around a charging roller having an elastic layer 1502 made of epichlorohydrin rubber, and the DC controlled in accordance with the temperature detected by the temperature detecting means 907; And applying a voltage to the charging roller.