JPH07114247A - Contact electrifier - Google Patents

Abstract

PURPOSE:To provide a contact electrifier capable of stably electrifying a body to be electrified with respect to dispersion in manufacturing of the resistance of an electrifying member and variation by environment. CONSTITUTION:In the electrifying member, as a conductive member 12, a film supported by a conductive substrate 11 on both ends and sagged is used. The conductive substrate 11 is fixed so that the sagged part surely comes into contact with a photoreceptor drum 50. Moreover, the conductive substrate 11 of the electrifying member 10 is grounded via a switch 18 and an external power source 22. In such a contact electrifier, the resistance R (OMEGA) when a current required for the electrification of the electrifying member 10 is made to flow is 6<= log (R)<=7.5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device used in an image forming apparatus adopting an electrophotographic system such as a printer, a video printer, a facsimile, a copying machine and a display. The present invention relates to a contact charging device for charging or discharging an object to be charged by bringing a charging member applied with a voltage into contact with the object to be charged.

[0002]

2. Description of the Related Art A conventional contact charging device is configured such that a charging member such as a conductive brush, a conductive elastic roller, or a conductive blade, to which a voltage is applied from the outside, is brought into contact with the surface of a photoreceptor, which is a member to be charged, It was configured to charge the surface of the photoreceptor to a desired potential.

As a charging mechanism that occurs in this contact charging device, for example, the Electrophotographic Society of Japan, VOL.27, NO.4,1988, p59-6.
As described in 3, it is considered that a) charging by charge injection (direct charge transfer), b) charging by discharge, and c) charging by friction. Particularly, in the cases of a) and b), the surface potential Vs of the charged body after charging is

[0004]

[Equation 1]

Is given by Where Va is the voltage applied to the charging member, t is the contact time between the charging member and the member to be charged, r is the resistance of the charging member, and c is the capacitance of the member to be charged.
cg is the capacitance of the gap between the charging member and the body to be charged, Vt
Is a charging start voltage that can be derived from Paschen's law, and Vs, Va, and Vt in Equation (2) have the same sign.

When the thickness of the body to be charged is d (μm) and the relative permittivity is ε, the charging start voltage Vt (V) is

[0007]

[Equation 2]

Is given by

Then, using this type of contact charging device,
The conditions for stably and uniformly charging the body to be charged are described in, for example, JP-A-3-217871.

In this conventional example, the volume resistivity and the surface resistivity of the charging member are specified when the charging is performed by rubbing the charging member against the body to be charged. The volume resistivity of the member for use is 10 ⁹ (Ωcm) or less,
The surface resistivity of the contact surface is 5 × 10 ⁷ (Ω / □) or more,
The upper limit of the volume resistivity of the charging member is the charging efficiency, and the lower limit of the surface resistivity is the condition that pinholes do not occur in the photoreceptor, which is the member to be charged.

[0011]

However, even if a charging member having a volume resistivity and a surface resistivity within the range defined by the conventional technique is simply used, a desired surface potential of the body to be charged can be obtained. In some cases, on the contrary, the desired surface potential of the body to be charged may be obtained even with a charging member having a volume resistivity or surface resistivity outside the specified range. However, it was difficult to control the charging only by specifying the surface resistivity.

Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to set the resistance of the charging member, which regulates the electric current, within a predetermined range to thereby make the charging member. Another object of the present invention is to provide a contact charging device capable of stably charging an object to be charged with respect to the manufacturing variation of the resistance and the variation due to the environment.

[0013]

The contact charging device of the present invention is a contact charging device for charging or discharging an object to be charged by applying a voltage to the charging member from the outside, wherein the charging member is a conductive substrate. The conductive member is supported by the conductive base and is made of a conductive member that rubs against the charged body,
Further, the resistance R (Ω) when a current required for charging is applied to the charging member is 6 ≦ log (R) ≦ 7.5.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings.

First, FIG. 1 shows a schematic sectional view of a contact charging device according to the present invention.

An undercoat layer 52 is formed on the surface of a grounded conductive cylindrical substrate 51, and a photosensitive drum 50 on which a photosensitive layer 53 whose resistance decreases when exposed to light is formed is covered. Used as a charged body. In this embodiment, as the photosensitive drum 50, a 60 (mmφ) cylindrical aluminum substrate 51 is formed on the surface of an alumite undercoat layer 52 having a thickness of 7 (μm).
m) and the photosensitive layer 53 having a relative dielectric constant of 3.3 was used. The organic photoreceptor of this embodiment is a general one having a structure in which the charge transport layer is laminated on the charge generation layer as the photosensitive layer 53. However, the present invention is not limited to this.

The charging member 10 is a conductive member 12 in which a film is adhered / bonded to a conductive substrate 11. Specifically, both ends of the film are supported by the conductive substrate 11 so that the film has a flexible portion. Then, the conductive substrate 11 is fixed so that the bent portion surely contacts the photosensitive drum 50, and
The conductive substrate 11 of the charging member 10 is grounded via the switch 18 and the external power source 22.

In this state, the photosensitive drum 50 starts to rotate in the direction of arrow a by a driving means (not shown),
Simultaneously with or immediately after that, by closing the switch 18, a voltage (or a current) is supplied to the charging member 10, and the charge moves from the surface of the charging member 10 to the surface of the photoconductor drum 50, and the photoconductor drum 50. 50 can be charged.

Here, the conductive substrate 11 is made of a metal such as iron, aluminum, stainless steel or brass, an alloy, a carbon dispersed resin, a metal particle dispersed resin or the like. Conductive member 12
Is composed of, for example, nylon resin, olefin resin, polyethylene terephthalate resin in which carbon black is dispersed. The film may have a multi-layered structure, or may have a structure in which only one end of the film is supported.
Further, the conductive member 12 may have a blade shape or a brush made of conductive fibers.

In this embodiment, as the charging member, a film having the structure and material shown below, in which the resistance was changed by changing the amount of the conductive agent added to the conductive member, was used.

The effective length of the conductive member 12 is 225 (m
The charging member 10 is configured by using the film of m) and sandwiching and fixing both ends of the film with the aluminum plates that are the conductive bases 11. In particular, the conductive member 12 has three types shown in Table 1 below. Was used.

[0022]

[Table 1]

Next, using the contact charging device having the above-mentioned structure, the member to be charged was charged by the charging members having different resistances R, and the charging characteristics of the charging member were examined. However, in the present invention, the resistance R is a resistance when a current required for charging is applied. The experimental conditions were as shown in Table 2 below.

[0024]

[Table 2]

The charging characteristics of the charging member of this embodiment are shown in FIG. In FIG. 2, the horizontal axis represents the resistance R of the charging member.
Is the logarithmic value log (R) (Ω), and the vertical axis is the absolute value | Vs | (V) of the surface potential of the charged body. The symbols in the figure represent the measurement environment, NN environment (20 ° C, 50% RH), HH environment (35 ° C, 65% RH), LL environment (10 ° C, 15% R).
H).

As shown in FIG. 2, by setting the resistance R (Ω) of the charging member to the range of 10 ^{6 to} 3 × 10 ⁷ with respect to the change of the environment, it is shown by the above-mentioned formula (2). Charging can be performed by such discharge, and a stable surface potential of the charged body can be obtained.

However, when the resistance R (Ω) is 10 ⁶ or less, charging is performed by the charge injection as shown in the above formula (1), so that the surface potential of the charged body depends on the resistance. If the resistance changes by one digit, the surface potential will be 200 (V)
Will also change. On the other hand, when the resistance R (Ω) is 10 ⁸ or more, the current supply required for charging cannot be supplied in time, so-called a time constant delay, which reduces charging efficiency, and the surface potential of the body to be charged depends on the resistance. When the resistance changes by one digit, the surface potential changes by 400 (V).

Generally, the manufacturing variation of the resistance of the charging member is about one digit, and it is difficult to suppress it to 0.5 digit even if thorough management is performed. Therefore, the resistance R (Ω) is 10
^In the range of ^{6 to} 3 × 10 ^7, a stable surface potential of the member to be charged can be obtained with respect to the resistance fluctuation of the charging member, so that the allowable range of manufacturing variation of the resistance of the charging member can be widened, and the manufacturing can be relatively performed. It becomes easy and the cost can be reduced. However, if the resistance R (Ω) is 10 ⁶ or less and 3 × 10 ⁷ or more, the surface potential of the body to be charged is not stable depending on the resistance variation of the charging member, so that a charging member having a uniform resistance is used. Therefore, it becomes very difficult to manufacture the charging member.

When the charging member is made of a film or a brush, it is possible to make stable contact with the movement of the body to be charged and to perform charging by stable discharge. Stable contact will be explained in detail here. Even if the fibers of the film or brush are pulled by the charged body and move, the flexure of the fiber keeps the film or brush in contact with the charged body at all times. That is. Furthermore, since the film or brush can make uniform contact with the charged body with a low pressing force, and the frictional force with the charged body can be reduced, wear deterioration of the charging member and the photoconductor drum can be prevented. can do. Also,
When the charging member is composed of a blade, the Asker C hardness of the blade is 20 to 90 (°), the pressing force of the blade on the charged object is a linear load of 10 to 100 (g / cm), the blade and the charged object. By always setting the friction coefficient between the blades to be 0.7 or less, the contact between the blade and the body to be charged becomes more reliable, and stable discharge can be performed without causing stick-slip.

Now, a method of measuring the surface potential Vs of the charged body shown in FIG. 2 will be described.

Using the contact charging device shown in FIG. 1, a surface potential measuring means (not shown) (eg, surface electrometer model 344, manufactured by Trek) is provided downstream of the charging member 10 in the direction of arrow a.
By installing the surface potential V of the photosensitive drum 50
s was measured. The surface potential of the photoconductor drum is initialized (surface potential to 0 V) by static elimination light emitted from a light source (not shown) installed upstream of the charging member 10 in the direction opposite to the arrow a. Further, the surface potential measuring means or the light source was installed so that the angle between each position, the center of the photosensitive drum 50 and the charging member 10 was 30 °.

Now, a method of measuring the resistance of the charging member shown in FIG. 2 will be described.

In the contact charging device shown in FIG. 1, except that the photosensitive drum 50 is replaced with a conductive cylindrical electrode having the same shape, the surface moving speed of the cylindrical electrode, the pressing force of the charging member 10 against the cylindrical electrode, etc. 1 is the same as the experimental conditions described above and the charging member 10 when the same current as the current required to charge the photosensitive drum 50 to a predetermined surface potential is applied to the charging member 10. The resistance of the charging member was determined by measuring the voltage with the cylindrical electrode. The most important point of this measuring method is to flow the current required for charging through the charging member 10 to obtain the resistance of the charging member.

The current required for charging is obtained by actually measuring the current value at the time of charging or by the following equation (4).

I = εεLVpVs / d (4) where I (μA) is the current necessary to charge to a predetermined surface potential Vs (V), and L (cm) is the charge Effective length of the working member 10, d (μm) is the thickness of the photosensitive layer 53, ε is the photosensitive layer 53
Relative dielectric constant, vp (cm / sec) of the photosensitive drum 50
The surface moving speed, εo (F / cm), is the dielectric constant of vacuum. Incidentally, in this embodiment, the current required to charge the photosensitive drum to the surface potential Vs = −600 (V) was I = −6 (μA).

As is apparent from the above, the resistance of the charging member in the present invention reflects the actual state at the time of charging, and is different from the simple volume resistivity of the charging member.

More specifically, the resistance of the charging member depends on the current, and generally, when the current changes by one digit, the resistance changes by 0.7 digits. Furthermore, since the charging member is in contact with the body to be charged, the resistance of the charging member during actual charging includes electrical contact resistance, and the contact area between the charging member and the body to be charged is , And the degree of deformation of the charging member. For example, when the moving speed of the member to be charged is doubled to change the contact state between the charging member and the member to be charged and the deformation degree of the charging member, the resistance changes by 0.5 to 1 digit. Therefore, a current necessary for charging is applied to the charging member,
In addition, the resistance measured when the contact state between the charging member and the electrode is the same as that of the member to be charged reflects the actual state at the time of charging.

Next, experimental examples will show that the object to be charged can be uniformly charged by performing stable charging using the contact charging device of the present invention.

(Experimental Example) The contact charging device of the present invention was incorporated into an electrophotographic image forming apparatus to form an image, and image density, image unevenness, and white background stain were evaluated, thereby uniformly charging an object to be charged. I checked if it could be done. In addition,
The white background stain means that a small amount of toner particles adhere to the non-image portion of the recording sheet on which an image has been formed and stain it.

Table 3 shows the resistance R (Ω) of each film and the absolute value of the surface potential | Vs | (V), the image density, the image unevenness, and the white background stain under each environment.

[0041]

[Table 3]

The image forming conditions will be described below.

The environment examined is the NN environment (20 ° C., 50% R
H), HH environment (35 ° C, 65% RH), LL environment (1
3 levels of 0 ° C and 15% RH). The conditions of the film prepared as a charging member and the contact charging device are the same as those shown in FIG.

The image forming method will be described. In the schematic sectional view of the image forming apparatus shown in FIG. 3, the photosensitive drum 50 starts to rotate in the direction of arrow c in response to the image forming start signal, and the contact charging device 30 causes the photosensitive drum 50 to start rotating. Charged to a predetermined potential,
An electrostatic latent image is drawn by emitting light 31 from an exposing unit (not shown), and a toner image corresponding to the electrostatic latent image is formed on the photosensitive drum 50 by the developing unit 32. The toner image on the photosensitive drum 50 is transferred by the transfer unit 34.
Accordingly, the recording paper 33 transferred to the recording paper 33 sent in the direction of the arrow d by the conveying means (not shown) and having the toner image transferred thereto is sent to the fixing means (not shown) to be fixed, and a desired image is formed. Get the image. On the other hand, the residual toner on the photosensitive drum 50 after the transfer is collected by the cleaning unit 35, and then the residual charge on the photosensitive drum 50 is removed by the static eliminating unit 36, and the series of operations of the image forming apparatus is completed. As the developing means 32, a one-component pressure contact developing type developing device was used.

Table 3 was obtained under the above image forming conditions.

As shown in Table 3, the resistance R (Ω) to environmental changes is 5 × 10 ^{5 to} 10 ⁸ , preferably 10 ⁶
By using the charging member in the range of 3 × 10 ^{7 to} 3, it is possible to obtain good image density without image unevenness. Also, the resistance R (Ω) against environmental changes is 4 × 1.
By using the charging member in the range of 0 ^{5 to} 10 ⁸ , preferably 5 × 10 ^{5 to} 10 ^8, an image free from white background stain can be obtained. Therefore, for example, the films A-2 and A
-3, C-2, and C-3, the resistance R (Ω) against environmental changes is 5 × 10 ^{5 to} 10 ⁸ , preferably 10 ⁶
By using the charging member within the range of from 3 to 10 ⁷ it is possible to obtain an image having no unevenness, good image density, and no white background stain.

However, the resistance R (Ω) of the charging member is
If it is 10 ⁶ or less, the surface potential of the member to be charged becomes higher than desired, so that the image density becomes low, and if it is 5 × 10 ⁵ or less, it becomes unpractical. On the other hand, when the density is 3 × 10 ⁷ or more, the surface potential of the member to be charged becomes lower than the desired value, so that the image density becomes high, and when it is 10 ⁸ or more, it becomes unpractical. Furthermore, the resistance R
When (Ω) is 10 ⁶ or less, or 3 × 10 ⁷ or more,
Since the surface potential of the body to be charged depends on the resistance of the charging member, image unevenness occurs due to the resistance unevenness of the conductive elastic body of the charging member, and it is not practical when it is 5 × 10 ⁵ or less, or 10 ⁸ or more. Become. Also, through 10 ⁸ and resistance R (Ω) are 4
× is 10 ⁵ or less by the surface potential of the member to be charged is desired above, the toner is easily adhered to the oppositely charged to the surface potential smearing is increased, a practical impossible with 10 ⁵ or less Become. Further, by comprising the surface potential of the member to be charged is a desired or less than 10 ⁸ or more, the toner is easily adhered, smearing is increased, a practical impossible with 2 × 10 ⁸ or more.

The contact charging device of the present invention can obtain the same effect even if the surface speed of the member to be charged is changed. The same effect can be obtained by applying to the charging member a charging member in which a DC voltage is superimposed with an AC voltage is applied. However, the resistance R in that case is measured by applying the average value of the current required for charging to the charging member.

[0049]

As described above, according to the present invention, in the contact charging device for charging or discharging a charged member by applying a voltage to the charging member from the outside, the charging member is a conductive substrate. The electroconductive member is supported by the electroconductive substrate and is rubbed against the member to be charged, and
Resistance R when a current required for charging is applied to the charging member
Since (Ω) is set to 6 ≦ log (R) ≦ 7.5, it is possible to provide a contact charging device capable of stably charging the charged body against manufacturing variations in resistance of the charging member and environmental changes. It was

Further, since the allowable range of the unevenness and variation of the resistance of the charging member can be widened and the charging member can be constituted by a relatively easy manufacture, a low-cost contact charging device can be provided.

Further, by mounting the contact charging device of the present invention on the image forming apparatus, it is possible to provide an image forming apparatus capable of obtaining a good image quality against environmental changes.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a contact charging device according to the present invention.

FIG. 2 is a diagram showing the relationship between the resistance of the charging member and the surface potential of the body to be charged in the example of the present invention.

FIG. 3 is a schematic sectional view of an image forming apparatus equipped with a contact charging device according to the present invention.

[Explanation of symbols]

 10 ... Charging member 11 ... Conductive substrate 12 ... Conductive member 17 ... Pressing means 18 ... Switch 22 ... External power supply 50 ... Photosensitive drum 51 ... Cylindrical substrate 52 ... Undercoat layer 53 ... Photosensitive layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takehiko Okamura 3-5-3 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (2)

[Claims] 1. A contact charging device for charging or discharging an object to be charged by applying a voltage to the charging member from the outside,
The charging member is composed of a conductive substrate and a conductive member that is supported by the conductive substrate and rubs against the body to be charged, and a current necessary for charging is applied to the charging member. The contact charging device is characterized in that the resistance R (Ω) at time is 6 ≦ log (R) ≦ 7.5. 2. The contact charging device according to claim 1, wherein the conductive member of the charging member is a film, a blade or a brush.