JP3092252B2 - Charging member and charging method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member for charging an object to be charged such as a photoreceptor used in an electrophotographic or electrostatic recording process in a printer or a copying machine.

[0002]

2. Description of the Related Art In an electrophotographic process in a copying machine, first, the surface of a photoreceptor is uniformly charged, and an image is projected on the photoreceptor from an optical system so that the photoreceptor is exposed to light. A method has been adopted in which a latent image is formed by erasing the electrification of a part, and furthermore, a toner is adhered and a toner image is transferred to paper to perform copying.

In this case, a corona discharge method is generally employed as an operation for charging the first photosensitive member. However, since this corona discharge method requires application of a high voltage of 5 to 10 kV, the degree of freedom of design of the entire device is limited, for example, a power supply unit is enlarged, and safety is also concerned. In addition, since ozone is generated during corona discharge, there is also an environmental problem.

Therefore, recently, there has been proposed a method of charging a member to be charged by bringing a charging member to which a voltage is applied into contact with a member to be charged such as a photosensitive member. However, in the conventional contact method, although the applied voltage tends to decrease due to the narrowing of the distance between the charging member and the member to be charged, the voltage is still low enough to be sufficiently satisfactory. No change has been made. In addition, the generation of ozone is also observed although it is smaller than in the corona discharge method.

According to the study of the present inventor, although charging is performed in a state in which the charging member and the member to be charged are in contact with each other, a minute amount of charge between the charging member and the member to be charged is precisely determined. This is an air discharging method in which charging is performed through a gap, and it is considered that the fundamental charging method is not different from the above-described corona discharging method.

The present invention has been made in view of the above circumstances, and it is possible to directly inject electric charges into an object to be charged, instead of air discharge, and to obtain a sufficient charging potential by applying a relatively low voltage. Further, an object of the present invention is to provide a charging member and a charging method capable of reliably preventing generation of ozone.

[0007]

In order to achieve the above object, the present inventor has constructed various charging members and tested their charging characteristics. The charging member was brought into contact with a member to be charged. When a voltage is applied between the charging member and the member to be charged, and when the applied voltage is gradually increased from a low voltage, a voltage at which the member to be charged starts charging, that is, a charging start voltage (charging threshold) is 500 V If it is less than or equal to, the charging threshold is 500
It has been found that an applied voltage that is much lower to obtain the same charging potential than that in the case of exceeding V and that ozone is almost completely eliminated has been completed, and the present invention has been completed.

Therefore, according to the present invention, an object is brought into contact with a member to be charged,
A charging member for charging the charged body by applying a voltage between the charged body and the charged body comprises only a conductive foam formed in a roller or plate shape, and has a threshold voltage of 500 V applied for charging. The following is a charging member characterized in that the member to be charged is charged substantially directly by charge injection without air discharge, and that ozone is not substantially generated during the charging operation, and In the charging method in which the charging member is brought into contact with the member to be charged and a voltage is applied between the charging member and the member to be charged, the member to be charged is charged to a predetermined potential. Using a roller-shaped or plate-shaped conductive foam having an applied voltage of 500 V or less, the charged object is charged substantially directly by charge injection without air discharge. Performing the charging without substantially generating ozone during the charging operation to provide a charging method comprising.

[0009] The reason why the charging member whose charging becomes possible has a threshold value of 500 V or less having the good charging characteristics as described above is not necessarily clear, but the charging by this charging member is not easy. It can be easily guessed that the reason is that the charge is directly injected into the member to be charged, not the medium discharge. That is, according to Passen's law regarding air discharge, the threshold value at which charging by air discharge is possible is 600 to 750 V,
Below this, charging by air discharge cannot occur. Therefore, the fact that the chargeable threshold value is equal to or lower than the applied voltage of 500 V surely indicates that the charge is caused by direct charge injection, not air discharge.

Hereinafter, the present invention will be described in more detail.
As described above, the charging member of the present invention has a chargeable threshold value of 500 V or less. For example, as shown in FIG. When the voltage is applied from the power supply 3 and the applied voltage is gradually increased from a low voltage, the applied voltage at which charging of the object to be charged is started is 500 V or less.
Note that the chargeable threshold value is set between the charging member 1 and the charged member 2.
Is the absolute value of the applied voltage at which charge starts to be accumulated in the charged body 2 when a voltage is applied between the two, and may be a negative value or a positive value.

Here, the preferable charging threshold of the charging member of the present invention is 400 V or less, more preferably 300 V or less, and ideally a value extremely close to 0 V. If the chargeable threshold exceeds 500 V, a high voltage equivalent to that of a conventional charging member is required to obtain sufficient charge, and ozone is generated.

Further, the charging member of the present invention is not limited in its material and can be made of various materials, as long as the charging threshold value is 500 V or less as described above. In addition,
Specific examples of suitable materials include polyurethane-based synthetic resins and various rubbers.

Here, for example, when the charging member of the present invention is made of polyurethane, the method for producing polyurethane is as follows.
Usually, a compound containing two or more active hydrogens, a compound having two or more isocyanate groups, and a catalyst are mixed and foamed, if necessary, and the mixture is molded and then heat-cured to form an elastomer or foam. A method of molding into a charging member made of

In this case, the compound containing two or more active hydrogens (polyhydroxyl compound) includes polyols used for producing general polyurethane elastomers and polyurethane foams, that is, polyols having a hydroxyl group at a terminal. It is possible to use general polyols such as ether polyols, polyester polyols and polyether polyester polyols which are copolymers of both, and so-called polymer polyols obtained by polymerizing ethylenically unsaturated monomers in the polyol. it can. In addition, the compounding quantity of these polyols can be made into a usual quantity.

As the compound having two or more isocyanate groups (polyisocyanate compound), polyisocyanate compounds used for producing general polyurethane elastomers and polyurethane foams can be used. Cyanate (TDI),
Crude TDI, 4,4'-diphenylmethane diisocyanate (MDI), crude MDI, aliphatic polyisocyanate having 2 to 18 carbon atoms, aromatic polyisocyanate having 6 to 15 carbon atoms, and mixtures or partially polyols of these polyisocyanates And a modified product such as a prepolymer obtained by reacting the same. The amount of these polyisocyanate compounds used can also be a usual amount.

The polyurethane may contain carbon black, carbon, graphite, metal,
Other additives such as various inorganic substances can be mixed. In this case, the volume resistivity of the polyurethane is 10 ⁴ to 10.
It is preferable to control to ¹² Ω · cm. Further, the shape of these additives may be any shape such as a spherical shape, a whisker shape, a phosphorous shape, and an amorphous shape.

Further, in the case of forming a foam, etc., a silicone-based foam stabilizer, a flame retardant, an organic filler, an inorganic filler, a pigment, a plasticizer, a freon,
An auxiliary blowing agent such as methylene chloride can be blended.

Further, as described above, the charging member of the present invention is configured to perform charging by a method other than air discharge, specifically, by a direct charge injection method, by setting the chargeable threshold value to an applied voltage of 500 V or less. However, a slight air discharge may be present. However, it is preferable to avoid such air discharge as much as possible, and it is preferable that the charging is performed substantially only by the direct charge injection method. Furthermore, in order to avoid the mixture of air discharge as much as possible, it is important that the charging member and the member to be charged surely contact each other during charging (when voltage is applied). It is preferable to configure the charging device such that the contact state with the body is always maintained during the charging process.

The shape of the charging member of the present invention is not limited to a roll shape as shown in FIG. 1, but may be a plate shape as long as the charging member can be securely brought into contact with the member to be charged. There may be.

[0020]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Example 1 100 parts of polyether polyol (parts by weight, the same applies hereinafter), 25 parts of urethane-modified 4,4′-diphenylmethane diisocyanate (MDI), 2.5 parts of 1,4-butanediol, silicon interface 1.5 parts of activator, 0.5 parts of nickel acetylacetonate and natural graphite 3
0 parts were thoroughly stirred for 2 minutes and cured at 80 ° C. for 10 minutes to prepare a polyurethane foam. Cut out this polyurethane foam into a 20 x 20 x 3 mm plate,
This was used as a charging member.

The charging performance of the charging member was evaluated by the following method. That is, a photoreceptor made of polyvinyl carbazole was used as a member to be charged, and the charging member was brought into contact with the surface of the member to be charged, and a voltage was applied between both members. At this time, the applied voltage was gradually increased from 0 V, and the charging potential of the member to be charged was measured. The results are shown in FIG.

As is clear from the results shown in FIG. 2, the chargeable threshold value of this charging member is about 200 V, which is much lower than 500 V, and -4 at an applied voltage of about 700 V.
The charge potential was as good as 00 V. In addition, when the current during the test was observed with an oscilloscope, no spark-like current specific to air discharge was observed. Further, no ozone was generated during the test.

Comparative Example A charging member similar to that of the example was constructed except that butadiene rubber containing 10 parts of carbon was used as a material, and a test similar to the example was performed. The results are shown in FIG.

As is apparent from the results shown in FIG. 2, the chargeable threshold value of this charging member is about 60
It is recognized that a considerably higher applied voltage than in the case of the embodiment is required in order to obtain a charging potential near 0 V and equivalent to the charging potential of the charging member of the above embodiment. In addition, when the current during the test was observed with an oscilloscope, a spark-like current characteristic of air discharge was observed. Further, ozone generation was observed during the test.

[0026]

As described above, according to the charging member of the present invention, it is possible to drastically reduce ozone which has been generated during the conventional charging process to almost zero, and to perform sufficient charging with a relatively low applied voltage. An electric potential can be obtained, so that the size of the power supply can be reduced, so that the degree of freedom in device design and the safety can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a state in which an object to be charged is subjected to a charging process using the charging member of the present invention.

FIG. 2 is a graph showing a relationship between an applied voltage and a charging potential in a charging test in Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charging member 2 Charged object 3 Power supply

Continuation of front page (56) References JP-A-2-40683 (JP, A) JP-A-63-153563 (JP, A) JP-A-61-63867 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) G03G 15/02 101 G03G 15/08 501 G03G 15/16 103 G03G 21/06

Claims (6)

(57) [Claims] 1. A charging member for charging a member to be charged by applying a voltage between the member and the member to be charged by contacting the member with a member to be charged. A charging threshold value is 500 V or less, and the object to be charged is substantially directly charged by charge injection without air discharge, and substantially generates ozone during the charging operation. A charging member characterized by no occurrence. 2. The charging member according to claim 1, wherein the conductive foam body is a conductive polyurethane foam. 3. The conductive foam body has a volume resistance of 1
The charging member according to claim 1, wherein the charging member has a density of 0 ⁴ to 10 ¹² Ωcm. 4. The method according to claim 1, wherein the threshold for enabling the charging is an applied voltage of 3.
The charging member according to any one of claims 1 to 3, which has a voltage of 00 V or less. 5. A charging method in which a charging member is brought into contact with a member to be charged and a voltage is applied between the charging member and the member to be charged, thereby charging the member to be charged to a predetermined potential. The threshold voltage at which charging is possible is applied voltage 500
Using a roller-shaped or plate-shaped conductive foam having a voltage of V or less, the charged object is charged by direct charge injection substantially without air discharge, and substantially generates ozone during the charging operation. A charging method characterized in that charging is performed without any charge. 6. The charging method according to claim 5, wherein the charging operation is performed at an applied voltage of not less than the chargeable threshold value and not more than 700 V.