JP3139653B2 - Contact charging device - 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 device used in an electrophotographic image forming apparatus, and more particularly, to a charging device of a contact type in which a charging member is brought into contact with a surface of an object to be charged to perform a charging process (including a static elimination process). About.

[0002]

2. Description of the Related Art In recent years, contact charging devices for directly contacting an electrophotographic photosensitive member have been proposed. (For example, JP
This system has the advantages that a lower applied voltage can be used and that the amount of generated ozone is smaller than that of a conventionally used corona charging system.

In this contact charging device, as shown in FIG. 1, for example, a charging roller 2 serving as a charging member is contact-driven by an electrophotographic photosensitive drum 1 serving as an object to be charged, and a DC voltage or an AC voltage and a DC voltage are applied. Is applied from the power supply 3 to uniformly charge the surface of the photosensitive drum 1.

As understood from the above description, the charging roller 2 needs to maintain conductivity and uniformly contact the photosensitive drum. Conventionally, a conductive elastic layer 201b is formed around a conductive core 2a. What was used is used.

Further, a pinhole on the surface of the photosensitive drum 1
To prevent charge leakage due to surface defects such as scratches,
A charging roller 2 is used in which a high-resistance surface layer 202b is coated on a conductive elastic layer 201b.

[0006]

In the case of the above construction, the resistance value of the surface layer fluctuates under the influence of the use environment conditions, especially humidity. If the resistance of the surface layer increases at low temperature and low humidity,
Poor charging occurs in which uniform charging of the surface of the photosensitive drum is not obtained, and so-called "sand fog", which is a black spot on the image, occurs. Also, when the resistance value of the surface layer becomes low due to high temperature and high humidity, if there is a pinhole in the photosensitive drum, a leak occurs in which a current is concentrated at one point from the contact charging member at the pinhole portion, and the power supply output is As a result, poor charging occurs at pinholes on the photosensitive drum.

Accordingly, an object of the present invention is to provide a contact charging device which does not cause the above-mentioned environmental fluctuation of the resistance value.

[0008]

That is, the present invention relates to a contact charging device for charging a surface of a member to be charged by pressing a member against the surface of the member to be charged and relatively moving the member.
The charging member comprises a cored bar, a conductive elastic layer on the cored bar, and a surface layer on the elastic layer, wherein the surface layer has different OH equivalents of the polyol compound (I) and the polyol compound (I).
I) and a reaction product containing a polyisocyanate compound as an essential raw material component, the polyol compound (I) is a polyol compound having an OH equivalent of 500 or more and having 2 to 60 OH groups per molecule, A contact charging device, wherein the polyol compound (II) is a polyol compound having an OH equivalent of 300 or less.

[0009] Further, there is provided a contact charging device wherein the surface layer contains conductive particles.

In the present invention, the OH equivalent is JIS K00.
It is the reciprocal (g / eg-OH) of the hydroxyl value determined in accordance with 70 "Test method for chemical product acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable matter".

First, the polyol (I) used in the present invention will be described.

The polyol compound (I) used in the present invention is a polyol compound having an OH equivalent of 500 or more and containing 2 to 6 OH groups per molecule.
In addition, for example, an alkylene oxide having 2 to 10 carbon atoms is homopolymerized or a copolymer of two or more thereof in the presence of a catalyst in an active hydrogen compound, and the product is then ion-exchanged and neutralized filtration. Alternatively, it is a polyol compound obtained after removing the catalyst by treating with a generally known purification method such as an adsorption method. Further, a part of the polyol may be substituted with another group, and examples of the substituent include a halogen atom such as fluorine, chlorine and iodine, and an aryl group such as phenyl and naphthyl.

As such active hydrogen compounds, compounds having two or more active hydrogen groups in one molecule, among which polyhydric alcohols such as ethylene glycol, propylene glycol, 1,4-butanediol, glycerin, trimethylolpropane, Sorbitol and the like; amines such as
Monoethanolamine, ethylenediamine, diethylenetriamine, 2-ethylhexylamine, hexamethylenediamine, etc .; bisphenol A, bisphenol F,
Examples thereof include polyhydric phenolic active hydrogen compounds such as 1,1-bis (hydroxyphenyl) ethane, bisphenol AP, acetophenone, and hydroquinone.

Examples of the alkylene oxide having 2 to 10 carbon atoms include ethylene oxide, propylene oxide, butylene oxide, hexene oxide,
It is an alkylene oxide such as cyclohexene oxide and nonene oxide.

As the catalyst, a basic catalyst such as sodium methoxide, sodium hydroxide, potassium hydroxide, lithium carbonate and triethylamine is generally used, but a Lewis acid catalyst such as boron trifluoride is also used. Can be used.

Examples of the polyol compound (I) used in the present invention are shown below.

[0017]

[Table 1]

* 1 Number of carbon atoms 2 ... Ethylene oxide 3 ... Propylene oxide 4 ... Butylene oxide 6 ... Cyclohexene oxide 9 ... Nonene oxide * 2 Numerical values are weight% of added alkylene oxide. * 3 Block * 4 Random * 5 Tri Methylol propane * 6 Ethylene glycol * 7 1,4-butanediol * 8 Pentaerythritol The polyol compound (II) used in the present invention has an OH equivalent of 300 or less and is a compound other than a compound having two or more hydroxyl groups in one molecule. The following are included. That is, the alkylene oxide having 2 to 10 carbon atoms is homopolymerized in a compound having two or more hydroxyl groups in the presence of the catalyst or two or more alkylene oxides are copolymerized, and the product is then ion-exchanged and neutralized. It is a polyol compound obtained after removing the catalyst by treating with a generally known purification method such as a filtration method and an adsorption method.

Examples of such compounds having two or more hydroxyl groups in one molecule include polyhydric alcohols such as ethylene glycol, propylene glycol, 1,4-butanediol, glycerin, trimethylolpropane, sorbitol, and sucrose; Hydrogen compounds include phenolic active hydrogen compounds such as bisphenol A, bisphenol F, 1,1-bis (4-hydroxyphenyl) ethane, bisphenol AP, bisphenol Z and hydroquinone.

Examples of the polyol compound (II) used in the present invention are shown below.

[0021]

[Table 2]

* 1 Number of carbon atoms 2: ethylene oxide 3: propylene oxide 4: butylene oxide 9: nonene oxide Examples of the polyisocyanate compound used in the present invention include 2,4-toluene diisocyanate,
2,6-toluene diisocyanate (trade name TDI-1)
00), 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HMD)
I), isophorone diisocyanate, mixtures thereof and adducts (adducts).

The above-mentioned polyisocyanate compound is
It can be used in the form of a blocked isocyanate (a terminal isocyanate group protected).

Examples of the blocking agent (terminal treating agent) include methyl ethyl ketoxime (MEKO), phenol, caprolactam, ethyl acetoacetate, methanol,
And sodium hydrogen sulfite.

Blocking is performed by adding the above-mentioned blocking agent to the polyisocyanate compound, and heating at 30 to 90 ° C. for 0.5 to 0.5.
The reaction can be performed by reacting for 2 hours.

As a method for forming an intermediate layer containing a reaction product of a polyol compound and a polyisocyanate compound used in the present invention, a mixture containing the aforementioned polyol compounds (I) and (II) and a polyisocyanate compound is applied. Even after heating and curing after the process, a polymer containing the above-mentioned polyol compounds (I), (II) and the polyisocyanate compound is synthesized in advance, dissolved in an appropriate solvent, dried after application, and formed. You may.

Also, a polyoxyalkylene segment-containing polyisocyanate compound obtained by reacting a polyol compound with a polyisocyanate compound, a polyisocyanate compound in which the isocyanate group terminal of the polyisocyanate compound is converted into a blocked isocyanate with a blocking agent, A compound in which a polyol such as a polyoxyalkylene polyol is added to the terminal of the isocyanate group or the like is synthesized in advance, and a coating layer containing this compound is applied and heated and cured to form a coating layer.

In the reaction between the polyol compound and the polyisocyanate compound, a catalyst can be used to promote the reaction. Examples of the reaction promoting catalyst include amine catalysts such as triethylamine, dimethylethanolamine,
Triethylenediamine and the like; metal salt catalysts such as zinc octylate, tin octylate, dibutyltin dilaurate and the like.

Further, the reaction ratio between the polyol and the polyisocyanate used in the present invention is such that the ratio of NCO group / OH group is 1.
The range of 0 to 2.0 is preferred.

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

FIG. 1 schematically shows a contact charging device according to an embodiment of the present invention. (A) is a side view, and (B) is a sectional view. Reference numeral 1 denotes an electrophotographic photosensitive member (hereinafter abbreviated as a photosensitive drum) which is a member to be charged. The photosensitive drum 1 is driven to rotate at a predetermined process speed (peripheral speed) in the direction of the arrow (clockwise). Reference numeral 2 denotes a charging roller (rotating roller body) serving as a contact charging member, which is formed on a conductive core 2a, a conductive elastic layer 202b having a low volume resistance integrally formed on the outer periphery thereof, and an outer periphery of the elastic layer. It comprises a roller section 2b composed of a surface layer 201b.

Then, both ends of the cored bar 2a are rotatably supported by bearings 4a, and the roller length is adjusted to the length of the photosensitive drum 1a.
The charging roller 2 is pressed against the photosensitive drum 1 by a predetermined force by urging the bearings at both ends of the roller 4a toward the photosensitive drum by pressing springs 4b so as to be substantially parallel to the generatrix direction. It is contacted with. The charging roller 2 is driven by the rotation of the photosensitive drum 1.

At this time, the bearing on one side of the bearing 4a is a conductive bearing 4a ', and the pressing spring of the conductive bearing is a conductive pressing spring 4b'.

Reference numeral 3 denotes a power supply for applying a bias voltage to the charging roller 2. The power supply applies a conductive pressing spring 4 b ′, a conductive bearing 4 a ′, and a conductive core to the charging roller 2. For example, a predetermined superposition of a DC voltage or an AC voltage of, for example, about 1 to 2 kV, and an AC voltage having a peak-to-peak voltage that is twice or more the charging start voltage of the photosensitive drum when the DC voltage is applied to the charging roller. A bias voltage such as a voltage is applied.

As a result, the surface of the rotating photosensitive drum 1 is contact-charged to a predetermined polarity and potential.

The surface layer 201b of the contact charging member of the contact charging device of the present invention is used for stabilizing the resistance value of the reaction product of the polyol compound (I), the polyol compound (II) and the polyisocyanate compound. It is preferable to disperse conductive particles in the resin.

As described above, the surface layer 201b may have a volume resistivity of 1 × 10 ⁸ Ω · cm or more in order to prevent leakage due to surface defects such as pinholes and scratches on the surface of the photosensitive drum 1. is necessary. If the volume resistivity of the surface layer is 1 × 10 ¹¹ Ω · cm or more, the applied voltage causes a voltage drop and uniform charging is not performed.

The conductive particles used in the present invention include powders of carbon black, carbon graphite, conductive titanium oxide, conductive zinc oxide, conductive tin oxide, conductive potassium titanate, nickel, aluminum, copper, silver and the like. Alternatively, it is preferable to use glass fiber, brass fiber, aluminum fiber, or the like whose surface is subjected to metal plating.

As the material of the conductive elastic layer 202b under the surface layer, synthetic rubber such as EPDM, SBR, NBR, CR, epichlorohydrin rubber, silicon rubber, olefin, styrene, urethane, polyester,
A thermoplastic elastomer such as polyamide can be used. Then, carbon black, carbon graphite, conductive titanium oxide, conductive zinc oxide, conductive tin oxide, nickel, silver, copper, aluminum, or the like can be added and kneaded as the conductive particles.

As the conductive core 2a, a metal round bar of iron, copper, stainless steel or the like may be used as it is, or a surface treatment such as chemical nickel plating may be applied to the surface for rust prevention. It is necessary not to impair the conductivity.

[0041]

The present invention will be described below with reference to examples.

Example 1 EPDM (Mooney viscosity at 100 ° C. 20) 100 parts Conductive carbon black (Lion, Ketjen Black EC) 6 parts Paraffin oil 15 parts sufficiently mixed on a two-roll mill EPDM compound A
It was created.

Raw rubber was prepared by mixing 50 parts of EPDM compound A, 100 parts of silicone rubber, and 3 parts of dicumyl peroxide on two rolls.

As the conductive core metal, a stainless steel round bar having a length of 245 mm and an outer diameter of 6 mm was used.
It was vulcanized at 60 ° C. for 15 minutes to prepare a conductive roller.
(Rubber outer diameter 12 mm, rubber portion longitudinal length 226 mm) The resistance value of each portion of the conductive roller along the length of the roller portion was measured by the method shown in FIG. Specifically, a 10 mm-wide aluminum foil 5 (thickness: 50 μm) is tightly wound around the outer circumference of the rubber portion, and a voltage of 250 V is applied between the cored bar and the aluminum foil to make a tester (resistance meter) 6 ( Hioki 3116
(DEGITAL MΩ Hi TESTER), the resistivity was 8 × 10 ⁴ Ω. (Measurement Environment Temperature 23 ° C., Relative Humidity 63%) Next, the outer surface of the roller portion of the conductive rubber roller was coated with a paint having the following formulation by a dipping method.

Polyol (I) 1 (Table 1) 13.3 parts Polyol (II) D (Table 2) 3.3 parts Hexamethylene diisocyanate (HMDI) 3.4 parts Dibutyltin laurylate (DBTL) 0.02 parts Methyl ethyl ketone (MEK) 90 parts Methoxypropanol 10 parts Conductive titanium oxide (manufactured by Ishihara Sangyo, Taipaek ET-500W) 30 parts The above materials were dispersed at room temperature using a sand mill to form a coating. When the viscosity of the obtained paint was measured by a B-type viscometer, it was 106 cps.

After coating the conductive rubber roller, 15
After drying at 0 ° C. for 1 hour, a surface layer having a thickness of 20 μm was obtained.
The volume resistivity of the surface layer was measured according to JIS K6911 after coating on an aluminum foil (thickness: 50 μm). The measurement was performed using Mitsubishi Yuka Hiresta IP and Hiresta J-BOX. The measurement was conducted at a temperature of 23 ° C and a relative humidity of 6 ° C.
When performed at 3%, the volume resistivity was 6 × 10 ¹⁰ Ω · cm.
Met.

The charging roller of Example 1 was manufactured by the above method.

Next, image evaluation was performed using this charging roller. For image evaluation, use a laser printer (Canon L
BP-A404) and a process cartridge were used. The charging roller was disposed at the primary charger position of the process cartridge, and was brought into contact with the photosensitive drum at a contact pressure of 500 g for one side of the metal core.

A DC voltage of -550 V AC peak-to-peak voltage of 1800 V and a bias of AC frequency of 150 Hz were applied to the core of the charging roller from an external power supply to perform primary charging of the photosensitive drum.

The image evaluation was performed at low temperature and low humidity (temperature 15 ° C., relative humidity 10%), normal temperature and normal humidity (temperature 23 ° C., relative humidity 63
%) And high temperature and high humidity (temperature 32 ° C., relative humidity 85%).

As a result, in all three environments, good images were obtained after the initial 300 sheets and 3,000 sheets of images were output.

Example 2 A conductive rubber roller having the same structure as in Example 1 was used, and a coating having the following formulation was used as the surface layer to form a surface layer having a thickness of 20 μm.

Polyol (I) 3 (Table 1) 11.9 parts Polyol (II) E (Table 2) 5.1 parts Hexamethylene diisocyanate (HMDI) 3 parts Dibutyltin laurylate (DBTL) 0.02 parts Methyl ethyl ketone (MEK) 90 parts Methoxypropanol 10 parts Conductive titanium oxide (manufactured by Ishihara Sangyo Corp., Taipaek ET-500W) 30 parts When the volume resistivity of the surface layer was measured in the same manner as in Example 1, 2.5 × 10 ¹⁰ Ω · cm.

Further, image evaluation was performed in the same manner as in Example 1.

As a result, in all three environments, good images were obtained after the initial 300 sheets and 3,000 sheets of images were output.

Example 3 A surface layer having a thickness of 20 μm was formed using a conductive rubber roller having the same structure as in Example 1 and a coating material having the following formulation as the surface layer.

Polyol (I) 3 (Table 1) 11.9 parts Polyol (II) E (Table 2) 5.1 parts Hexamethylene diisocyanate (HMDI) 3 parts Dibutyltin laurylate (DBTL) 0.02 parts Methyl ethyl ketone (MEK) 90 parts Methoxypropanol 10 parts Conductive carbon black 1.2 parts (Lion, Ketjen Black EC) The volume resistivity of the surface layer was measured in the same manner as in Example 1 to be 5.8.
× 10 ⁹ Ω · cm.

Further, image evaluation was performed in the same manner as in Example 1.

As a result, in all three environments, good images were obtained after the initial 300 sheets and 3,000 sheets of the images were output.

Comparative Example 1 A conductive rubber roller having the same structure as in Example 1 was used, and a coating having the following formulation was used as the surface layer to form a surface layer having a thickness of 20 μm.

Alcohol-soluble copolymerized nylon 100 parts (Toray Co., Ltd., Amilan CM-8000) Conductive carbon black 4 parts (Lion Co., Ltd., Ketjen Black EC) Methanol 425 parts Toluene 142 parts Surface layer in the same manner as in Example 1. The measured volume resistivity was 3 × 10 ¹⁰ Ω · cm.

Further, image evaluation was performed in the same manner as in Example 1.

As a result, good images were obtained for the initial 300 sheets in all three environments. However, under the conditions of high temperature and high humidity, after 700 images were output, the leak image caused by the pinhole of the photosensitive drum (the horizontal side of the drum cycle Black streaks) occurred. A possible cause of the leak is a decrease in the resistance value due to moisture absorption of the surface layer. Under normal temperature and normal humidity and low temperature and low humidity conditions, a good image was obtained even after 3,000 sheets of paper were durable.

Comparative Example 2 A surface layer having a thickness of 20 μm was formed using a conductive rubber roller having the same structure as in Example 1 and a coating material having the following formulation as the surface layer.

Polyurethane resin solution (solid content 30%) 100 parts (Sanpreka Chemical Industries, Samprene MW-010) Conductive carbon black 2.1 parts (Lion, Ketjen Black EC) methyl ethyl ketone 60 parts Toluene 40 parts Examples When the volume resistivity of the surface layer was measured by the same method as in Example 1, it was 5.2 × 10 ¹⁰ Ω · cm.

Further, image evaluation was performed in the same manner as in Example 1.

As a result, good images were obtained in the initial 300 sheets in all three environments, but under low-temperature and low-humidity conditions, after 1200 images were formed, sand fogging occurred. (Black dot image on white background)
A possible cause of sand fog is considered to be an increase in the resistance of the surface layer.

Under normal temperature and normal humidity and high temperature and high humidity conditions, 3000
Good images were obtained even after the durability test.

Comparative Example 3 A conductive rubber roller having the same structure as in Example 1 was used, and a coating having the following formulation was used as the surface layer to form a surface layer having a thickness of 20 μm.

Polyurethane resin solution (solid content 30%) 100 parts (manufactured by Sanyo Chemical Industries, Samprene MW-010) Conductive titanium oxide 48 parts (manufactured by Lion, Ketjen Black EC) methyl ethyl ketone 60 parts toluene 40 parts Example 1 and When the volume resistivity of the surface layer was measured by the same method, it was 4.2 × 10 ¹⁰ Ω · cm.

Further, image evaluation was performed in the same manner as in Example 1.

As a result, good images were obtained for the initial 300 sheets in all three environments, but under low-temperature and low-humidity conditions, after 500 images were output, fogging in the sand occurred. (Image of black spots on a white background) An increase in the resistance of the surface layer is considered to be a cause of the occurrence of the sand fog.

Table 3 shows the image evaluation results of the examples and comparative examples.
Shown in

[0074]

Table 4 shows the volume resistivity of the surface layer materials used in Examples and Comparative Examples.

The volume resistivity was measured in each environment according to JIS K691.
Measured according to 1.

[0077]

[0078]

In the contact charging device, the surface layer of the charging roller contains a reaction product containing polyol compounds (I), polyol compounds (II) and polyisocyanate compounds having different OH equivalents as essential raw material components. The polyol compound (I) has an OH equivalent of 500 or more,
A polyol compound having 2 to 60 OH groups per molecule, wherein the polyol compound (II) has an OH equivalent of 30.
Since the composition is a polyol compound of 0 or less,
The resistance value does not fluctuate due to the environment, good images can be obtained in each environment, and the durability is excellent.

Further, since the surface layer having the above structure contains conductive particles, a predetermined resistance value can be obtained stably.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a contact charging device of the present invention;
(A) is a schematic side view, and (B) is a schematic sectional view.

FIG. 2 is a diagram showing a procedure for measuring the resistance of a conductive roller.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 2 charging roller 2a conductive core 2b roller part 201b surface layer elastic layer 202b conductive elastic layer 3 power supply 4a bearing 4a 'conductive bearing 4b pressure spring 4b' conductive pressure spring 5 aluminum foil 6 resistance meter

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Eiji Funabashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-3-38663 (JP, A) JP-A-2 -230267 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/02 101 G03G 15/08 501 G03G 15/106 103 G03G 21/06

Claims (2)

(57) [Claims] 1. A contact charging device for charging a surface of an object to be charged by pressing the member against the surface of the object to be charged and relatively moving the member, wherein the charging member comprises a core, a conductive elastic layer on the core, and a conductive elastic layer on the core. A surface layer on the elastic layer, the surface layer containing a reaction product containing polyol compound (I), polyol compound (II) and polyisocyanate compound having different OH equivalents as essential raw material components, I) is a polyol compound having an OH equivalent of 500 or more and having 2 to 60 OH groups per molecule,
A contact charging device, wherein the polyol compound (II) is a polyol compound having an OH equivalent of 300 or less. 2. The contact charging device according to claim 1, wherein the surface layer contains conductive particles.