JP2002108092A - Electrically conductive roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrically conductive roller which is easily controlled to have electric resistance within a fixed range in an electrically conductive region of 103 to 1010 Ωwhen manufactured and is excellent in the property of withstanding voltage. SOLUTION: An electrically conductive elastic layer 3 of this electrically conductive roller 1 is formed by using carbon black having a few functional group on the surface as an electrical conductivity imparting material, dispersing the carbon black in polyol so that the particle size of the carbon black is 5-50 μm when dispersion degree is evaluated according to JIS K5400-1990, reacting the polyol thus prepared with polyisocyanate to be polyurethane and curing it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive roller used in an electrophotographic apparatus, and more particularly to a conductive roller suitably used for a developing roller, a charging roller, a transfer roller and the like.

[0002]

2. Description of the Related Art A conductive roller used in an electrophotographic apparatus is required to be able to easily control resistance in a semiconductive region and to have excellent withstand voltage. Here, the conductivity of the conductive roller means a semiconductive region of about 10 ³ to 10 ¹⁰ Ω · cm. To impart conductivity to the roller and control the resistance, the rubber material that forms the conductive elastic layer of the roller contains carbon black, metal such as aluminum and stainless steel, and fine powder such as metal oxide such as tin oxide and titanium oxide. Is performed by dispersing. Above all, carbon black is often used.

As carbon black used for imparting conductivity, ketjen black and carbon black for paint are known. When Ketjen Black is used, it is possible to impart conductivity to the roller with a small amount of addition, but since the required resistance range in the semiconductive region is small, it is necessary to control the resistance of the roller to that range. Is difficult. In addition, since there are few conductive paths in the conductive elastic layer, there is a disadvantage that charge leakage easily occurs, that is, the withstand voltage is poor. In the case of carbon black for coatings, the resistance in the semiconductive region can be controlled relatively easily by controlling the amount of addition, but the structure of carbon black, that is, the diameter of the aggregate of carbon black particles is reduced. Since it is not uniform, there is a drawback that the bias of the conductive path occurs and charge leakage easily occurs.

In order to uniformly charge the surface of the conductive roller, conductive carbon black must be uniformly dispersed in the conductive elastic layer. In the case of a conductive roller using polyurethane as a conductive elastic layer,
In order to uniformly disperse carbon black, a method has conventionally been adopted in which the carbon black is dispersed in a polyol which is a raw material of polyurethane by kneading with three rolls. However, there is no prior art which examined the relationship between the degree of dispersion of carbon in the polyol and the electrical characteristics of the obtained roller.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a conductive roller in an area of 10 ³ Ω to 10 ¹⁰ Ω.
An object of the present invention is to provide a conductive roller for an electrophotographic apparatus which can easily control the electric resistance within a range of 2 to 3 digits required according to the use of the conductive roller and has excellent withstand voltage. .

[0006]

SUMMARY OF THE INVENTION The present invention relates to a conductive roller comprising a shaft having conductivity, a conductive elastic layer and a surface layer concentrically laminated on the outer peripheral surface of the shaft. The elastic layer is made of carbon black having a total amount of surface functional groups of 0.5 mmol / g or less according to JIS K5400-19.
The particle size is 5 to 50 μm in the evaluation of the degree of dispersion using a particle gauge of 90.
a conductive roller comprising a cured product of a polyisocyanate and a polyol dispersed so as to have a m value.

[0007] The present invention also relates to the present invention, wherein the content of the carbon black in the carbon-dispersed polyol is 1 to 5 wt%.
It is characterized by being.

According to the present invention, carbon black having a small number of surface functional groups is added to a polyol according to JIS K5400-
By using a polyol dispersed so that the particle diameter of carbon black when the degree of dispersion is evaluated in 1990 to be 5 to 50 μm and reacting with a polyisocyanate to form a polyurethane, the electric resistance of the conductive elastic layer is reduced. A conductive roller which can be easily controlled and has excellent withstand voltage can be provided.

Further, the present invention provides a method for preparing a carbon black
BP oil absorption is 150 to 190 ml / 100 g,
And a BET specific surface area of 40 to 70 m ² / g.

According to the present invention, when carbon black having a small specific surface area and a large value of DBP (n-dibutyl phthalate) oil absorption is used, the resistance can be easily controlled.
Further, it is possible to provide a conductive roller having a conductive elastic layer having excellent withstand voltage.

Further, the present invention is characterized in that the polyol is a polyolefin-based polyol which is liquid at normal temperature.

According to the present invention, when a polyol which is liquid at room temperature is used, it is easy to control the dispersibility when carbon black is dispersed in the polyol using a three-roll mill or the like. Further, since the polyolefin-based polyol has a hydrophobic property, the polyurethane obtained by reacting with the polyisocyanate has a hydrophobic property. That is, since polyurethane is hydrophobic,
A conductive roller which is hardly affected by temperature and humidity and which is excellent in environmental stability by using this as a base material can be provided.

Further, according to the present invention, while rotating a metal roller having a diameter of 30 mmφ at 0.48 rpm, a load of 500 g is applied to both ends of the shaft body and pressed against each other, and a resistance value when a voltage of −400 V is applied is obtained. , 10 ⁶ to 10 ⁸ Ω, and −
It is characterized in that charge leakage does not occur up to 1.5 kV.

According to the present invention, the carbon black having a small number of surface functional groups and having a well-developed structure can
By using the roll and using a polyol dispersed in the conductive elastic layer by averaging the structure particle diameter so that the particle diameter becomes 5 to 50 μm in the dispersion degree evaluation according to JIS K5400-1990, the electric resistance is reduced. 10 ⁶
It is possible to provide a conductive roller which can be controlled to 810 ⁸ Ω and has many conductive paths and is excellent in withstand voltage.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a conductive roller for an electrophotographic apparatus according to the present invention will be described with reference to the drawings. FIG.
1 is a perspective view of a conductive roller 1 for an electrophotographic apparatus according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view perpendicular to the axis of the conductive roller 1 of FIG. The conductive roller 1 is
It has a multilayer structure including a conductive shaft 2, a conductive elastic layer 3 formed on the outer peripheral surface of the shaft 2, and a surface layer 4 laminated on the outer peripheral surface of the conductive elastic layer 3. The shaft body 2 is a slender right circular column shape whose both ends are precision-machined for supporting both ends and fitting driving components, and a metal, for example, iron, aluminum alloy, stainless steel, or the like is suitably used.

The conductive elastic layer 3 of the conductive roller 1 is made of polyurethane in which carbon black for imparting conductivity is dispersed. The carbon black is
The total amount of the surface functional groups is 0 to 0.5 mmol / g. If so-called graphite-like carbon black having a small number of surface functional groups is used, the carbon black hardly aggregates when the carbon black is dispersed in the polyol, and can be uniformly dispersed. When the polyol in which the carbon black is uniformly dispersed is reacted and cured with a polyisocyanate to form a polyurethane, the carbon black is uniformly dispersed in the polyurethane. Can control.

The carbon black having a small number of surface functional groups and having a well-developed structure is prepared according to JIS K540.
The particle diameter was 5 in the evaluation of the degree of dispersion using a particle gauge of 0 to 1990.
When kneaded with three rolls or the like until it reaches ~ 50 μm and dispersed in polyol, it has an aggregate or structure in which carbon black is appropriately bonded,
The particle size is averaged and uniformly dispersed, and in the conductive elastic layer 3 formed using this polyol, an electron conductive mechanism by a tunnel effect or the like is easily formed, and the number of conductive paths increases. As a result, it is possible to provide the conductive roller 1 which is easy to control the electric resistance in a narrow range and does not cause charge leakage and has excellent withstand voltage.

As a carbon black having a small surface functional group and a high structure, the specific surface area is small and D
Carbon black having a large BP (n-dibutyl phthalate) oil absorption corresponds to this. Generally, the DBP oil absorption is 118
A carbon black of ml / 100 g or more is called a high structure, and a carbon black of 90 ml / 100 g or less is called a low structure.

The carbon black used in the present invention is B
ET specific surface area of 40 to 70 m ² / g and DBP
The oil absorption is preferably 150 to 190 ml / 100 g.

In forming the conductive elastic layer 3 according to an embodiment of the present invention, first, carbon black is kneaded and dispersed in a polyol by using three rolls.
React with polyisocyanate to form polyurethane.

In this case, the carbon black is a JI
It is necessary to disperse in a polyol so that the particle diameter is in the range of 5 to 50 μm in the evaluation of the degree of dispersion using a particle gauge of SK5400-1990.

When the degree of dispersion of the dispersed carbon black is 5 μm or less in particle size, the dispersibility is good, but the viscosity of the polyol becomes extremely high and the surface of the carbon black is covered with the polyol. It is difficult to form, and the electrical conductivity is reduced. When the degree of dispersion of the carbon black exceeds 50 μm in particle size, the aggregation of the carbon black increases and the conductive paths are biased, so that the electric conductivity is improved, but when a high voltage is applied, charge leakage occurs. I do.

Specific examples of the carbon black include Ensaco 250 (manufactured by MMM) and CF9 (manufactured by Mitsubishi Chemical Corporation).

The content of the carbon black is preferably 1 to 5% by weight based on the polyol. If it is less than 1%, an appropriate conductivity cannot be obtained, and if it exceeds 5%, the withstand voltage decreases.

As the polyol, any of the conventionally known polyols can be used, but those which are liquid at room temperature and are polyolefin-based are preferred. In the case of dispersing carbon black with a three-roll mill or a bead mill, it is easy to control the dispersibility of a polyol that is liquid at room temperature. When the polyol is solid at room temperature, it is necessary to heat and dissolve the polyol and also to heat the disperser to control the temperature, which complicates the production process and increases the cost.

Polyolefin polyols having a hydrophobic structure retain their hydrophobicity even when they are reacted with polyisocyanate to form polyurethane, so that they are not easily affected by temperature and humidity and have excellent environmental stability. This is more preferable because it can provide a conductive roller that has a high conductivity.

Examples of the polyol which is liquid at normal temperature include polyether polyol, modified polyester polyol, and modified polycarbonate polyol.

Examples of the polyolefin-based polyol include poly-IP, poly-BD15HT, and poly-BD45HT (all manufactured by Idemitsu Petrochemical Co., Ltd.). These compounds may be used singly or in combination.
It may be used in combination of more than one kind.

Examples of the polyisocyanate include conventionally known 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, and 1,5.
-Naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3
-Dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate,
3,3-dimethylphenylene diisocyanate, 4,4
-Diisocyanates such as biphenylene diisocyanate, 1,6-hexane diisocyanate and isophorone diisocyanate, and triisocyanates such as triphenylmethane triisocyanate.

Specifically, Coronate T80, T100
And Millionate MTL (all manufactured by Nippon Polyurethane Industry). These isocyanates may be used alone or in combination of two or more.

The conductive elastic layer 3 is formed as described above.
Using this roll, a reaction solution comprising a polyol in which the carbon black is dispersed and a polyisocyanate is poured into a cylindrical mold, and crosslinked and cured by a conventionally known method to form a polyurethane.

The mixing ratio of each component constituting the polyurethane of the conductive elastic layer is 100 parts by weight of polyol.
Parts are preferably in a range of 1 to 5 parts of carbon black, 5 to 25 parts of polyisocyanate and 0 to 1.0 part of a curing agent.

The thickness of the conductive elastic layer varies depending on the purpose of use of the conductive roller, but is preferably about 1 to 15 mm, more preferably about 2 to 10 mm.

A conductive roller 1 according to an embodiment of the present invention
The surface layer 4 is provided on the outer peripheral surface of the conductive elastic layer 3 for the purpose of protecting the roller surface, preventing contamination, adjusting resistance, and the like. As a base polymer constituting the surface layer 4,
Conventionally known thermoplastic resins and thermosetting resins can be used. Further, additives such as an antioxidant and a leveling agent may be added to the surface layer 4. The layer thickness of the surface layer 4 is preferably about 20 to 100 μm.

The conductive roller 1 can be suitably used as a charging roller 1, a developing roller 26, a transfer roller and the like in FIG.

FIG. 3 is a side view showing the structure of an electrophotographic apparatus provided with the conductive roller 1 of FIG. 1 as a charging roller 1. The charging roller 1 of the present invention uniformly applies, for example, a negative charge to the surface of the photoreceptor 11 having a right cylindrical shape. The charged photoconductor 11 is driven to rotate in the direction of arrow 16 to reach the exposure area 12, where the image is exposed by the laser beam from the exposure means 22, and the charge in the exposed portion is neutralized and the static electricity is reduced. An electrostatic latent image is formed.

The photoreceptor 11 is further driven to rotate and reaches the developing area 13, where the electrostatic latent image is developed with toner. The toner is negatively charged by frictional contact with each other by the stirring means 24 in the developing device 23. The charged toner is supplied to a developing roller 26 via a supply roller 25, and excess toner is regulated by a regulating blade 27, and an optimal amount of toner is supplied from the developing roller 26 to the photosensitive member 1.
1 is supplied to the portion of the neutralized electrostatic latent image, and is developed as a toner image.

The photoreceptor 11 is further rotated to reach the transfer area 14, where the toner image is transferred onto a recording medium such as a paper 28 supplied between the photoreceptor 11 and the transfer and conveyance belt 17. The transfer conveyance belt 17 includes two rollers 4
It is stretched around 1, 42 and driven in the direction of arrow 40.

The driven roller 41 close to the photoreceptor 11 has a shaft 43 connected to the positive electrode of a high-voltage power supply 45, and a positive charge of the transfer / transport belt 17 is given through a conductive elastic layer 44 around the shaft 43. The toner on the photoconductor 11 negatively charged by the positive charge of the transfer conveyance belt 17 is sucked, and the paper 28 conveyed between the photoconductor 11 and the transfer conveyance belt 17 is sucked.
The toner image on the photoconductor 11 is transferred to the photoconductor 11. The other drive roller 42 is connected to a drive source such as a motor (not shown). The photoconductor 11 is further driven to rotate, reaches the cleaning area 15, and is cleaned by the cleaning blade 29.
1 is cleaned, and the remaining charge is removed by the charge removing means 30.

The paper 28 is supplied between the photosensitive member 11 and the transfer / conveyance belt 17 by two paper feed rollers 46, and after the toner image is transferred, is conveyed to a fixing device 47 where the toner image is fixed. Is done.

Hereinafter, the conductive roller for an electrophotographic apparatus of the present invention will be specifically described with reference to examples. In the following, all the parts indicating each component represent parts by weight.

(Example 1) Polyolefin liquid at room temperature
Poly IP (hydroxyl group content 0.88m)
ol / kg, manufactured by Idemitsu Petrochemical Co.) 100 parts with conductivity
Ensaco 250 (DBP oil absorption)
190ml / 100g, specific surface area 65m ^Two/ G, M.P.
M. M company) (2.5 parts), kneading with 3 rolls
Dispersion evaluation according to JIS K5400-1990
Dispersion was performed until the particle size became 5 to 10 μm in terms of valency. Profit
The obtained carbon black-dispersed polyol liquid is heated at 80 ° C.
Vacuum degassing was performed for 24 hours. Then, carbon black
For 100 parts of the dispersed polyol liquid, the NCO group / OH group
The 2,4-tolylene diisocyanate is selected so that the ratio becomes 1.05.
80 / of anate and 2,6-tolylene diisocyanate
20 mixture, Coronate T80 (Nippon Polyure
7.84 parts) and TOYOCA as a catalyst
0.213 g of T-NP (manufactured by Tosoh Corporation) was added, and 3 minutes
The mixture is mixed so as not to form air bubbles, and the undiluted solution 34 for the conductive elastic layer is mixed.
Was prepared.

Next, as shown in FIG.
Then, a stock solution 34 for a conductive elastic layer was poured into a mold heated to 130 ° C. with the upper mold 38 removed. The inner diameter of the middle mold 37 is about 8mmφ
And the length is about 250 mm. Next, one end of the shaft body 2 is inserted from above as shown in FIG.
The solution was inserted through a stock solution into a recess 39 provided at the center of the lower mold 36. The other end of the shaft body 2 was assembled so as to enter a recess 33 provided at the center of the upper mold 38 as shown in FIG. The shaft 2 used was a steel rod (free-cutting steel: SUM22B) having an outer diameter of 5 mm and a length of 250 mm and electroless nickel plating with a thickness of about 10 μm.

The assembled mold 35 is heated at 100 ° C. for 1 hour to cure and cure the stock solution 34, remove the mold, and grind the outer peripheral surface to an outer diameter of 7 mmφ with a grinder to form a shaft 1. The conductive roller shown in FIG. 4 (4) having a conductive elastic layer of 0 mm was obtained.

Example 2 A conductive roller was obtained in the same manner as in Example 1 except that the degree of dispersion of carbon black in the polyol was kneaded and dispersed to a level of 20 to 30 μm in particle diameter.

Example 3 A conductive roller was obtained in the same manner as in Example 1, except that the degree of dispersion of carbon black in the polyol was kneaded and dispersed to a level of 40 to 50 μm in particle diameter.

Comparative Example 1 A conductive roller was obtained in the same manner as in Example 1, except that the degree of dispersion of carbon black in the polyol was kneaded and dispersed to a level of less than 5 μm in particle diameter.

(Comparative Example 2) A conductive roller was obtained in the same manner as in Example 1, except that the degree of dispersion of carbon black in the polyol was kneaded and dispersed to a level larger than 50 μm in particle diameter.

Comparative Example 3 Ketjen Black (DBP oil absorption: 360 ml /
100 g, specific surface area 800 m ² / g)
A conductive roller was obtained in the same manner as in Example 1 except that 0.1 part was added to 00 parts.

(Evaluation) Using the conductive rollers obtained in Examples and Comparative Examples, the electric resistance and the withstand voltage of the rollers were evaluated. The evaluation was performed using the apparatus shown in FIG. The electric resistance was measured by rotating a metal roller 50 having a diameter of 30 mmφ and a length of about 300 mm with F
₁ , a load of F ₂ = 500 g was pressed against the conductive roller, and a voltage of −400 V was applied so that the entire surface of the conductive roller 1 could be uniformly charged.

Further, the withstand voltage can be measured by using the same apparatus.
The evaluation was performed based on whether or not charge leakage occurred when a voltage was applied to 1.5 kV. Table 1 shows the results of the evaluation.

[0052]

[Table 1]

From Table 1, it was found that all of the conductive rollers obtained in Examples 1 to 3 had an electric resistance of 10 ⁶ to 10 ⁸ and also had good withstand voltage. On the other hand, the degree of dispersion (particle size) of carbon black by the particle gauge is
In Comparative Example 1 using a polyol of less than 5 μm,
The withstand voltage was good, but the electric resistance was as high as 10 ¹⁰ or more. In Comparative Example 2 in which the degree of dispersion (particle diameter) of carbon black by the particle gauge is greater than 50 μm and in Comparative Example 3 in which Ketjen Black is used, the electrical resistance of the conductive roller is good, but both are resistant. It turned out that the voltage property was bad.

[0054]

As described above, according to the present invention, carbon black having a small number of surface functional groups is contained in the conductive elastic layer of the conductive roller by the evaluation of the degree of dispersion according to JIS K5400-1990 to have a particle size of 5%. By uniformly dispersing so as to have a thickness of 50 to 50 μm, 10 ³ to 10 ¹⁰
In the region of Ω, the electric resistance can be controlled within a range of 2-3 digits,
An electrophotographic conductive roller having excellent withstand voltage can be provided. Further, by using a polyolefin polyol as a component of the polyurethane constituting the conductive elastic layer, it is possible to provide a conductive roller which is less affected by temperature and humidity and has excellent environmental stability.

[Brief description of the drawings]

FIG. 1 is a perspective view of a conductive roller 1 according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the conductive roller 1 of FIG.

FIG. 3 is a side view illustrating a configuration of an electrophotographic apparatus including the conductive roller 1 of FIG. 1 as a charging roller 1.

FIG. 4 is a cross-sectional view for explaining a step of forming a conductive elastic layer 3 of the conductive roller 1.

FIG. 5 is a conceptual diagram of an apparatus for measuring the electric resistance and the withstand voltage of the conductive roller 1.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 conductive roller (charging roller) 2 shaft 3 conductive elastic layer 4 surface layer 11 photoconductor 23 developing device 26 developing roller 28 paper (recording medium) 47 fixing device 50 metal roller

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) G03G 15/16 103 G03G 15/16 103 (72) Inventor Izumi Hiroshi 3-chome Meiwadori, Hyogo-ku, Kobe City, Hyogo Prefecture No. 2-15 Bando Chemical Co., Ltd. F term (reference) 2H003 BB11 CC05 2H032 AA05 BA23 2H077 AD06 AD13 AE05 FA13 FA27 3J103 AA02 AA14 AA23 AA33 AA51 BA41 FA06 FA14 FA18 GA02 GA52 GA74 HA03 HA04 HA05 HA12 HA33 HA33 HA33 HA33 HA33 HA33 HA52 4J002 CK021 CK041 DA036 GQ00 GT00

Claims (5)

[Claims] 1. A conductive roller comprising a shaft having conductivity, a conductive elastic layer and a surface layer concentrically laminated on an outer peripheral surface of the shaft, wherein the conductive elastic layer has a surface functional group. Total amount is 0.5 mmol / g
The following carbon black was used according to JIS K5400-
The particle size was 5 to 5 in the evaluation of the degree of dispersion by a particle gauge of 1990.
A conductive roller comprising a cured product of a polyisocyanate and a polyol dispersed so as to have a thickness of 0 μm. 2. The conductive roller according to claim 1, wherein the content of the carbon black in the carbon-dispersed polyol is 1 to 5 wt%. 3. The carbon black has a DBP oil absorption of 150 to 190 ml / 100 g and a BET
The conductive roller according to claim 1, wherein the specific surface area is 40 to 70 m ² g. 4. The conductive roller according to claim 1, wherein the polyol is a polyolefin-based polyol that is liquid at room temperature. 5. A metal roller having a diameter of 30 mmφ
While rotating at 8 rpm, the shaft body was pressed against each end with a load of 500 g applied to both ends, and the resistance value when a voltage of -400 V was applied was 10 ⁶ to 10 ⁸ Ω, and the electric charge was reduced to -1.5 kV. 2. A leak does not occur.
5. The conductive roller according to any one of 4.