JP2003207985A - Contact type electrostatic charging member and contact type electrostatic charging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contact type electrostatic charging member which is excellent in the uniformity of electrostatic charging and does not give rise to the image defect, etc., by the electric discharge dielectric breakdown of a photoreceptor and a contact type electrostatic charging device using the same. <P>SOLUTION: The contact type electrostatic charging member has a conductive substrate, a conductive elastic layer and a surface layer containing a polyurethane resin, in which the polyurethane resin of the surface is 0.3≤NCO/OH<1.0 in the molar ratio of the hydroxyl group (OH) and isocyanate group (NCO) of polyurethane raw materials and 5 to 100 KOHmg/g in hydroxyl value. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact type charging member and a contact type charging device mainly used in an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as an electrophotographic copying machine, an electrophotographic printer, an electrostatic recording device, etc., a primary charging means for charging an image carrier and a developer on the image carrier are attracted to a material to be printed. It includes means for uniformly charging the body to be charged, such as transfer means. As a charging method used at that time, a contact type charging method, which produces a significantly smaller amount of ozone than the conventional corona charging method, has been studied, and recently, it has been partially put into practical use.

The contact charging method is a method in which a charging member to which a voltage is applied is brought into contact with a member to be charged to charge the member to be charged, but the discharge phenomenon that occurs in a minute gap near the contact portion is used. It is common to charge the body to be charged by means of A number of techniques relating to the contact charging method have been proposed (Japanese Patent Laid-Open No. 57-57157).
-178267, JP-A-56-104351, JP-A-58-40566, and JP-A-58-13.
9156, JP-A-58-150975, etc.).

Further, the charging member has its original purpose of maintaining the charged body at a predetermined potential, and for that purpose, proper design of the surface layer is particularly important. For example, in Japanese Patent Application Laid-Open No. 06-248174, a polymer composition containing a polyol containing a polyether polyol or a polyester polyol and a polyisocyanate, and containing a conductive material, the conductive material is an alkali metal salt, and Disclosed is a roll in which a layer composed of a polymer composition is formed on the surface of a cored bar, wherein the OH / NCO ratio of the molecular composition is 0.7 or more and less than 1. With this structure, the polyurethane polymer composition is characterized in that it has no variation in electric resistance and no precipitation of an alkali metal salt as a conductive material is observed.

However, although many proposals have been made regarding the contact charging method and the charging member, the conventional charging member is brought into contact with the member to be charged and a voltage, particularly a DC voltage is applied to charge the member to be charged. In this case, streak images are likely to be generated due to non-uniformity of charging, and pinholes are generated due to discharge dielectric breakdown of the photoreceptor due to direct voltage application. The drawback that the entire axial direction may not be charged due to the electric current flowing through the pinhole has not yet been solved.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and to provide a contact type charging member which is excellent in charging uniformity and which does not cause image defects due to discharge dielectric breakdown of a photoreceptor. And to provide a contact type charging device using the same.

[0007]

Means for Solving the Problems As a result of diligent studies made by the present inventors on the above-mentioned problems (charging uniformity and leak property) of a charging member, (1) the minimum required for a binder resin having a low volume resistivity value. The above two problems can be solved at the same time by forming the surface layer with a material whose resistance is adjusted by dispersing the conductive material of (2). (2) The volume resistivity of a material having a hydroxyl group in the binder resin is There is a good correlation with the absolute amount, in particular, the polyurethane resin is a suitable material because the amount of hydroxyl groups can be controlled relatively freely by appropriately adjusting the ratio of the polyol compound and the isocyanate compound that are the raw materials, Heading The present invention has been reached.

That is, the present invention is as follows. (1) A contact-type charging member having a conductive substrate, a conductive elastic layer provided on the conductive substrate, and a surface layer containing a polyurethane resin, wherein the polyurethane resin of the surface layer is polyurethane. The molar ratio of the hydroxyl group (OH) and the isocyanate group (NCO) of the raw material is 0.3 ≦ NCO / OH
<1.0 and hydroxyl value is 5 KOHmg / g or more 10
A contact-type charging member characterized by being 0 KOHmg / g or less. (2) The contact type charging member according to (1), wherein the surface layer contains a conductive material. (3) The content of the conductive material is the polyurethane resin 1
The contact type charging member according to (2), which is 30 to 200 parts by mass with respect to 00 parts by mass. (4) The surface layer has a volume resistivity value of 10 ⁶ to 10 ¹⁴
Ωcm, The contact type charging member according to any one of (1) to (3). (5) The contact type charging member according to any one of (1) to (4), wherein the volume resistivity of the surface layer is larger than the volume resistivity of the conductive elastic layer. (6) In a contact charging device having a charging member, which charges the member to be charged by bringing the charging member into contact with the member to be charged and applying a voltage, the charging member is one of (1) to (5). A contact-type charging device, which is any one of the contact-type charging members. (7) The contact type charging device according to (5), wherein the voltage is only a DC voltage.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.

The charging member of the present invention has a conductive substrate, a conductive elastic layer provided on the conductive substrate, and a surface layer containing a polyurethane resin, and the polyurethane resin of the surface layer is The molar ratio of the hydroxyl group (OH) and the isocyanate group (NCO) of the polyurethane raw material is 0.3 ≦ NCO / O
H <1.0 and a hydroxyl value of 5 KOHmg / g or more 1
It is a contact type charging member having a content of 00 KOHmg / g or less.

An embodiment of the contact type charging member of the present invention is shown in FIG.

The contact type charging member of the present invention comprises a core metal 2a which is a conductive substrate to which a voltage is applied, a conductive elastic layer 2b which imparts elasticity, and a surface layer 2d which is a coating layer which comes in contact with a body to be charged. The resistance control layer 2c for controlling the resistance of the charging member may be provided outside the conductive elastic layer 2b as required.

The core metal 2a, which is a conductive substrate used in the present invention shown in FIG. 2, is a stainless steel column. In addition to the materials constituting the conductive substrate, for example, metals such as iron, aluminum, titanium, copper and nickel, alloys containing these metals such as stainless steel, duralumin, brass and bronze, carbon black and carbon fibers are used as plastics. It is also possible to use a known material that is rigid and conductive, such as a composite material hardened by. Further, the shape may be a cylindrical shape having a hollow central portion, in addition to the cylindrical shape. In the present invention, first, the conductive elastic layer 2b is formed on the outer periphery of the conductive substrate 2a.

The conductive elastic layer is made of a metal-based powder or fiber such as aluminum, palladium, iron or copper; polyacetylene,
Conductive polymer powder such as polypyrrole and polythiophene;
Carbon black; metal oxides such as titanium oxide, tin oxide and zinc oxide, metal compound powders such as copper sulfide and zinc sulfide,
Or tin oxide, antimony oxide,
Indium oxide, molybdenum oxide, zinc, aluminum, gold, silver, copper, chromium, cobalt, iron, lead, platinum, rhodium are electrolytically treated, spray-coated, powdered by mixing and shaking, acetylene black, Ketjen Examples thereof include a layer made of rubber or insulating resin in which a conductive material such as black is dispersed and subjected to a conductive treatment. Alternatively, a rubber or insulating resin having a surface laminated or coated with a metal or another conductive substance can be used.

As the rubber used for the conductive elastic layer,
EPM (ethylene / propylene rubber), EPDM (ethylene / propylene rubber), norbornene rubber, NBR
(Nitrile rubber), chloroprene rubber, natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chlorosulphonated polyethylene, hydrin rubber,
Urethane rubber, silicone rubber and the like can be mentioned, and examples of the insulating resin include polycarbonate, polyester and the like.

The conductive elastic layer has a volume resistivity value of 10 ¹ to
10 ¹¹ Ωcm is preferable, especially 10 ² to 10 ¹⁰ Ωcm
Is preferred. The volume resistivity value may be adjusted by adjusting the amount of conductive material such as carbon black, conductive metal oxide, metal powder or conductive polymer powder added to the rubber or insulating resin. The compounding amount thereof is 0.5 to 300 parts by mass, preferably 3 to 10 parts by mass with respect to 100 parts by mass of rubber or insulating resin.
It is 0 part by mass.

The thickness of the conductive elastic layer is 0.5 to 10 mm,
Particularly, the range of 1 to 6 mm is preferable.

In order to set the thickness of the conductive elastic layer within the above range, when the conductive elastic layer is molded, for example, when the film thickness is controlled by injection molding, the elasticity after vulcanization and after vulcanization is controlled. There are methods such as designing (die, shape) the die in consideration of thermal deformation of the layer material, and adjusting the polishing conditions of the polishing machine when controlling the film thickness by polishing after extrusion molding. .

Examples of the method for molding the conductive elastic layer include known methods such as extrusion molding, injection molding, compression molding, etc. by mixing the above-mentioned raw materials for the conductive elastic layer. The conductive elastic layer may be formed by directly molding the conductive elastic layer on the conductive substrate, or the conductive substrate may be formed into a tube shape. Note that the surface may be polished to adjust the shape after the conductive elastic layer is formed.

After the conductive elastic layer is completed, a surface layer containing a polyurethane resin is provided as a coating layer for the conductive elastic layer.

As the raw material for the polymer of the polyurethane resin for the surface layer, there are the following polyol compounds and isocyanate compounds.

As an example of the polyol compound, an oil-free polyester polyol using a dibasic acid such as phthalic acid or adipic acid, or an alcohol such as TMP, ethylene glycol, hexanediol or neopentyl glycol as a raw material; Polyester polyols such as soybean oil, castor oil and coconut oil; propylene oxide,
Polyether polyol using alkylene oxide such as ethylene oxide as a raw material; acrylic polyol which is a copolymer of acrylic acid ester, methacrylic acid ester, hydroxyethyl methacrylate (HEMA), styrene, acrylic acid and the like; OH group in the polymer chain Fluorine polyol which is an introduced organic fluorine compound; epoxy polyol having an epoxy group; polytetramethylene glycol by polymerization of THF; polycarbonate polyol; compounds having a terminal hydroxyl group such as polybutadiene polyol made from butadiene, and mixtures thereof. To be

As the isocyanate compound, tolylene diisocyanate, metaxylylene diisocyanate,
Aromatic isocyanate compounds such as diphenylmethane isocyanate and polymethylene polyphenyl isocyanate, water addition of the above isocyanates, aliphatic isocyanate compounds such as hexamethylene diisocyanate, and isocyanate groups of these isocyanate compounds are phenol, ketoxime, aromatic secondary amines. , A tertiary isocyanate, an amide, a lactam, a heterocyclic compound, a blocked isocyanate compound blocked with a sulfite, and the like.

Since the above-mentioned polyol compound and isocyanate compound can be dissolved in a solvent such as benzene, toluene, nitrobenzene, dibutyl ether, methyl ethyl ketone, dioxane, and acetonitrile, the lower conductive elastic layer can be removed during molding. It is possible to use a coating method that does not exist.

Polyurethane and elastomer are N-
It is also possible to dissolve it in methylpyrrolidone, dimethylacetamide, DMF, pyridine, benzyl alcohol, etc. and remold it.

As the catalyst for promoting the formation of the polymer, naphthenates such as magnesium naphthenate and cobalt naphthenate, organic tin compounds such as dibutyltin dilaurate and dimethyltin dilaurate, N-methylmorpholine, N, N, N ', An amine compound such as N'-tetramethylpolymethylenediamine may be added. The addition amount of the catalyst is preferably in the range of 0.001 to 5 mass% with respect to the polymer.

The polyurethane resin used in the surface layer of the present invention has a molar ratio of hydroxyl groups (OH) to isocyanate groups (NCO) of the above polyurethane polymerization raw material of 0.3≤NCO.
/OH<1.0. NCO / OH is preferably 0.
4 to 0.99. When NCO / OH is less than 0.3, the strength of the material is insufficient due to the small degree of cross-linking. Therefore, when the surface layer is formed from such a material, the surface layer may be cracked during use and cause poor charging. There is a tendency that image defects occur. When NCO / OH is 1.0 or more, there are few hydroxyl groups in the polyurethane resin, and it is difficult to adjust the volume resistivity value of the polyurethane resin itself to a desired value.

The hydroxyl value of the polyurethane resin of the present invention is 5 KOHmg / g or more and 100 KOHmg / g or less, preferably 10 KOHmg / g or more and 50 KOHm.
It is g / g or less.

When the hydroxyl value is lower than 5 KOHmg / g, the volume resistivity of the polyurethane resin itself becomes high, and in order to control within the above-mentioned desirable resistance range of the surface layer,
It is necessary to add and disperse a large amount of conductive material. According to the study of the present inventors, such a material has a large voltage dependence of resistance even if the resistance is adjusted under a certain voltage, and the resistance tends to be extremely lowered under the application of a high voltage. . In order to improve the charging uniformity, it is necessary to reduce the resistance of the surface layer under the application of a low voltage, but the leak property deteriorates for the above reason. On the contrary, if the resistance at the time of applying a high voltage is increased, the leak property is good, but the charging uniformity is deteriorated, so that the charging uniformity and the leak property cannot both be achieved. Further, when a large amount of a conductive material is added and dispersed, microscopic resistance unevenness of the surface layer increases, and the charging uniformity tends to deteriorate.

When the hydroxyl value is higher than 100 KOHmg / g, the volume resistivity of the polyurethane resin itself is lowered, and the resistance can be adjusted by adding and dispersing a small amount of a conductive material.
A surface layer with good charging uniformity (low resistance of the surface layer) and good leak property can be obtained, but the tackiness of the material (especially under high temperature and high humidity) becomes large. In the middle of use, a developer, paper powder, or the like tends to adhere to cause image defects due to poor charging.

The hydroxyl value of polyurethane is 50 KOHmg
/ G or more and 100 KOHmg / g or less, the ratio of the raw material polyol compound and isocyanate compound may be appropriately adjusted.

As the conductive material contained in the surface layer, there are conductive materials made of metal oxides such as titanium oxide, tin oxide, zinc oxide, etc., conductive materials made of carbon black and spherical carbon materials, etc., either alone or in 2 You may use it in combination of 2 or more types.

Blending of these conductive materials in addition to the surface resin
The amount is such that the volume resistivity of the resin of the surface layer is 10⁶-10¹⁴
It is preferable to determine it to be Ωcm. In addition, special application
As shown in Japanese Patent Laid-Open No. 62-230334,
Volume resistivity is the volume resistivity of the lower layer in contact with the surface layer
It is preferably larger. In the present invention, "in the surface layer
The "lower layer in contact" is mainly a conductive elastic layer. Specifically
Has a surface layer volume resistivity of 10⁶-10¹⁴Ω cm
And the volume resistivity value of the conductive elastic layer is 10¹-10 ¹¹Ω
It is preferably cm.

The specific content of the conductive material used in the surface layer is 30 to 100 parts by mass of the polyurethane resin.
200 parts by mass is preferred. When the volume specific resistance value of the surface layer is smaller than the volume specific resistance value of the conductive elastic layer, the resistance of the charging member is likely to decrease under the application of high voltage, and the leak property becomes poor.

The volume specific resistance value is measured by a resistance value measuring device (trade name: Hiresta UP, J-Box, manufactured by Mitsubishi Chemical Corporation).
Is measured using a sheet sample of the conductive elastic layer and the surface layer material. The measurement is performed under the condition that a DC voltage of 100 V is applied for 30 seconds. The thickness of the surface layer is 1 to 500 μm, especially 2
The range of ˜200 μm is preferable.

In order to control the thickness of the surface layer within the above range, it is controlled by adjusting the solid content, viscosity, etc. of the resin coating material for forming the surface layer to an appropriate range according to the molding method when molding the surface layer. To do. The film thickness is measured by the following method. 1) A sample is cut out with a knife from 9 locations of the charging member (in the case of a roller shape, 10 mm positions from both ends, and 3 locations in the center, and 3 locations in the circumferential direction (individual locations are 120 ° intervals)) . 2) Observe the cross section of each sample with an optical microscope (about 400 times) to determine the film thickness of the surface layer. The arithmetic average of 9 points is taken as the surface layer thickness.

As the method for molding the surface layer, the materials for forming the surface layer are sand mill, paint shaker,
Dynomill, pearl mill, etc. by using a conventionally known dispersing device using beads, it is dispersed by a known method, the resulting resin coating for surface layer formation, by dipping method or spray coating method, the surface of the charging member, In the invention, it is applied on the conductive elastic layer.

The resistance control layer 2c may be provided between the elastic layer and the surface layer as necessary for the purpose of eliminating partial resistance unevenness of the charging member and improving the uniformity of resistance.

As the shape of the charging member, a roller, a brush,
Any shape such as a blade or a belt may be adopted and can be selected according to the specifications and form of the electrophotographic apparatus. Of these, the roller shape is preferable.

<2> Contact Charging Device of the Present Invention FIG. 1 is a schematic configuration diagram of an image forming apparatus (copier) incorporating the contact charging device using the contact charging member of the present invention.

In the contact type charging member 2 of the present invention, an oscillating voltage such as a DC voltage or a superimposed voltage of a DC voltage and an AC voltage is applied to the conductive substrate from the power source 3.

In the contact type charging device of the present invention, by using the contact type charging member of the present invention as the charging member, the resistance of the charging member is stable from (1) low voltage to high voltage as described above. That is, the voltage dependence of the resistance is small. (2) Since the surface resistance can be controlled stably by adding a small amount of conductive material,
Since the effect of the charging member itself such as the microscopic resistance unevenness of the surface layer is brought about, the charging device using the charging member is
It is possible to configure the one having “excellent charging uniformity and no occurrence of image defects due to discharge dielectric breakdown of the photoconductor”. The voltage applied to the conductive substrate may be either a DC voltage or an oscillating voltage such as a superimposed voltage of an AC voltage and a DC voltage. In either case, the excellent effect of the present invention can be exhibited. In particular, the effect is remarkable when only the DC voltage without the AC power supply is used.

In the conventional charging member, when the photosensitive member is charged by applying only a DC voltage, charging unevenness is likely to occur due to microscopic resistance unevenness of the surface layer, and when an AC voltage is superimposed. However, the charging member of the present invention significantly improves the uniform charging property and the leak resistance of the surface of the photoconductor, so that the charging process can be performed only with the DC voltage. became. The DC voltage is preferably 800 to 2000V.

In the contact type charging member 2 of the present invention, an oscillating voltage such as a DC voltage or a superimposed voltage of a DC voltage and an AC voltage is applied from a power source 3 to a core metal 2a which is a conductive substrate.

The contact type charging member 2 is brought into contact with the photoreceptor 1 which is the member to be charged with a predetermined contact force by a pressing means (not shown). The contact force is preferably a contact force of 100 to 800 g on one side and a load of 200 to 1600 g on both sides.

In the image forming apparatus shown in FIG. 1, the contact type charging member 2 and the photoconductor 1 rotate in the directions of the respective arrows, and the photoconductive layer of the photoconductor which the contact type charging member 2 abuts by the voltage applied by the power source 3. 1b is charged, an electrostatic latent image is formed by the exposure unit 4, the electrostatic latent image is developed by the developing unit 5, a toner image is formed on the photosensitive layer 1b, and the toner image is formed on the printing material 7 by the transfer unit 6. And a permanent image is formed. The transfer residual toner that has not been transferred is collected by the cleaning unit 8.

[0047]

EXAMPLES The contact type charging member and the contact type charging device of the present invention will be described in detail below with reference to examples.

[0048]

[Example 1] (1) Preparation of conductive elastic layer 100 parts by mass of silicone rubber, 5 parts by mass of zinc oxide, 7 parts by mass of conductive carbon black and industrial paraffin 20
After sufficiently mixing and kneading parts by mass using a closed mixer, 2 parts by mass of dicumyl peroxide was added with an open roll to prepare a compound for a conductive elastic layer.
The compound for conductive elastic layer was heated and vulcanized at 150 ° C. for 15 minutes on a stainless steel core having a diameter of 6 mm to prepare a silicone rubber roller having a conductive elastic layer having a thickness of 3 mm.

At the same time, a vulcanized sheet (2 mm thick) was prepared and the volume resistivity value was measured (23 ° C./60%, 100 V applied, 30 seconds) using Mitsubishi Chemical Hiresta UP, which was 2 × 10 ^7. It was Ωcm.

(2) Preparation of surface layer Lactone-modified acrylic polyol (OH number 90 KOHm
g / g) 71 parts by mass, 129 parts by mass of methyl ethyl ketone, and 50 parts by mass of conductive tin oxide were dispersed using a small bead mill, and then hexamethylene diisocyanate 1
4.3 parts by mass were added and dissolved to prepare a surface layer forming resin coating material. (NCO / OH = 0.70) The resin coating material for forming the surface layer was applied onto the silicone rubber roller by dipping and dried at 150 ° C. for 1 hour to obtain a charging member having a surface layer with a thickness of 20 μm. The OH number in the polyurethane resin was 27.3 KOHmg / g. At the same time, a film having a thickness of 40 μm was produced, and the volume resistivity value was measured using Mitsubishi Chemical Hiresta UP (100 V applied, 30 seconds), 5 × 10 ¹² Ωc
It was m.

(3) Evaluation of Charging Member The above charging member was attached to the position of the primary charger of the cartridge used in the laser beam printer (laser jet 4si Hewlett Packard), and the DC voltage -116.
A bias of 0 V was applied and an initial image evaluation, a leak test and a durability test of 8000 sheets were performed in an environment of 23 ° C./60%. The results are shown in Table 1.

<1> Image uniformity Horizontal stripes appearing in a horizontal halftone image of 1 dot and 2 spaces were evaluated. The evaluation criteria are as follows. ◯: No horizontal stripe △: Small horizontal stripe ×: Large horizontal stripe

<2> Durability After the stain resistance of the surface layer, the uneven density appearing in the horizontal halftone image of 1 dot and 2 spaces was evaluated. The evaluation criteria are as follows. ◯: Good density unevenness Δ: Slight density unevenness ×: Significant density unevenness The surface of the charging roller after the surface was cracked was observed with an optical microscope, and the degree of cracking was evaluated based on the following criteria. ◯: Only minor cracks are observed Δ: Partial cracks are observed ×: Significant cracks are observed

<3> Pinhole Leakage Test Using a photosensitive drum having a pinhole, a horizontal hole (horizontal black streak) caused by a pinhole appearing in a horizontal halftone image of one dot and two spaces was evaluated (DC voltage- 1160
V). The evaluation criteria are as follows. ○: No side-through △: Slight side-through x: Significant side-through

[0055]

[Table 1]

[0056]

Example 2 (1) Preparation of Conductive Elastic Layer The same procedure as in Example 1 was performed. (2) Preparation of surface layer Example 1 except that the amount of conductive tin oxide was 55 parts by mass and the amount of hexamethylene diisocyanate was 17.8 parts by mass.
A resin coating material for forming a surface layer was prepared in the same manner as in. (NC
O / OH = 0.87) A charging member having a surface layer with a thickness of 21 μm was obtained in the same manner as in Example 1 using the obtained resin coating material for forming a surface layer. OH number in polyurethane resin is 11.7KOHm
It was g / g.

At the same time, a 40 μm thick film was prepared,
When the volume resistivity value was measured, it was 6 × 10 ¹² Ωcm. (3) Evaluation of charging member The above charging member was evaluated for initial image under the same conditions as in Example 1,
A durability test and a leak test were conducted. The results are shown in Table 1.

[0058]

Example 3 (1) Preparation of Conductive Elastic Layer The same procedure as in Example 1 was carried out. (2) Preparation of surface layer A resin coating material for forming a surface layer was prepared in the same manner as in Example 1 except that the amount of conductive tin oxide was 45 parts by mass and the amount of hexamethylene diisocyanate was 8.9 parts by mass. (NCO
/OH=0.44) A charging member having a surface layer with a thickness of 19 μm was obtained in the same manner as in Example 1 using the obtained resin coating for forming a surface layer. The OH number in polyurethane resin is
It was 50.8 KOHmg / g. At the same time, a film having a thickness of 40 μm was prepared and the volume resistivity value was measured and found to be 4 × 10 ¹² Ωcm.

(3) Evaluation of Charging Member The above charging member was evaluated for initial image under the same conditions as in Example 1.
A durability test and a leak test were conducted. The results are shown in Table 1.

[0060]

Example 4 (1) Preparation of Conductive Elastic Layer The same procedure as in Example 1 was carried out. (2) Preparation of surface layer Example 1 except that the amount of conductive tin oxide was 60 parts by mass and the amount of hexamethylene diisocyanate was 19.3 parts by mass.
A resin coating material for forming a surface layer was prepared in the same manner as in. (NC
O / OH = 0.94) Using the obtained surface layer coating material in the same manner as in Example 1,
A charging member having a surface layer having a thickness of 22 μm was obtained. The OH number in the polyurethane resin was 5.42 KOHmg / g. At the same time, a film having a thickness of 40 μm was prepared, and the volume resistivity value was measured and found to be 5.5 × 10 ¹² Ωcm. (3) Evaluation of charging member The above charging member was evaluated for initial image under the same conditions as in Example 1,
A durability test and a leak test were conducted. The results are shown in Table 1.

[0061]

Example 5 (1) Preparation of Conductive Elastic Layer The same procedure as in Example 1 was carried out. (2) Preparation of surface layer Polyester polyol (OH number 150 KOHmg /
g) 71 parts by mass, 129 parts by mass of methyl ethyl ketone, and 40 parts by mass of conductive tin oxide are dispersed using a small bead mill, and then 11.4 parts by mass of hexamethylene diisocyanate is added and dissolved to form a resin coating for forming a surface layer. Was prepared.
(NCO / OH = 0.33) Using the obtained resin coating for surface layer formation, a charging member having a surface layer with a thickness of 20 μm was obtained in the same manner as in Example 1. OH number in polyurethane resin is 99.9KOHm
It was g / g. At the same time, a film having a thickness of 40 μm was produced and the volume resistivity value was measured to be 4.5 × 10 ¹²
It was Ωcm.

(3) Evaluation of Charging Member The above charging member was evaluated for initial image under the same conditions as in Example 1,
A durability test and a leak test were conducted. The results are shown in Table 1.

[0063]

Comparative Example 1 (1) Preparation of Conductive Elastic Layer The same procedure as in Example 1 was performed. (2) Preparation of surface layer A resin coating material for forming a surface layer was prepared in the same manner as in Example 1 except that the amount of conductive tin oxide was 70 parts by mass and the amount of hexamethylene diisocyanate was 20 parts by mass. (NCO /
OH = 0.97) A charging member having a surface layer with a thickness of 18 μm was obtained in the same manner as in Example 1 using the obtained surface layer-forming resin coating material. OH number in polyurethane resin is 2.30KOHm
It was g / g. At the same time, a film having a thickness of 40 μm was produced and the volume resistivity value was measured to be 6.0 × 10 ¹²
It was Ωcm.

(3) Evaluation of Charging Member The above charging member was subjected to initial image evaluation under the same conditions as in Example 1,
A durability test and a leak test were conducted. The results are shown in Table 1.

[0065]

Comparative Example 2 (1) Preparation of Conductive Elastic Layer The same procedure as in Example 1 was performed. (2) Preparation of surface layer A resin coating material for forming a surface layer was prepared in the same manner as in Comparative Example 1 except that the amount of conductive tin oxide was 50 parts by mass. (NCO
/OH=0.97) A charging member having a surface layer with a thickness of 18 μm was obtained in the same manner as in Example 1 by using the obtained resin coating material for forming a surface layer. The OH number in polyurethane resin is
It was 2.30 KOHmg / g. At the same time, a film having a thickness of 40 μm was prepared and the volume resistivity value was measured and found to be 2.0 × 10 ¹⁴ Ωcm.

(3) Evaluation of Charging Member The above charging member was subjected to initial image evaluation under the same conditions as in Example 1,
A durability test and a leak test were conducted. The results are shown in Table 1.

[0067]

Comparative Example 3 (1) Preparation of Conductive Elastic Layer The same procedure as in Example 1 was performed. (2) Preparation of surface layer Polyester polyol (OH number 225 KOHmg /
g) 71 parts by mass, 129 parts by mass of methyl ethyl ketone, and 30 parts by mass of conductive tin oxide were dispersed using a small bead mill, and then 21.4 parts by mass of hexamethylene diisocyanate was added and dissolved to form a resin coating for forming a surface layer. Prepared.
(NCO / OH = 0.42) A charging member having a surface layer with a thickness of 22 μm was obtained in the same manner as in Example 1 by using the obtained resin coating material for forming a surface layer. O in polyurethane resin
The H value was 131 KOHmg / g. At the same time 40
When a film having a thickness of μm was prepared and the volume resistivity value was measured, it was 0.9 × 10 ¹² Ωcm.

(3) Evaluation of charging member The above charging member was evaluated for initial image under the same conditions as in Example 1,
A durability test and a leak test were conducted. The results are shown in Table 1.

[0069]

According to the present invention, it is possible to provide a contact type charging member which is excellent in charging uniformity and does not cause image defects due to discharge dielectric breakdown of a photoconductor, and a contact type charging device using the same. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus using a contact type charging device of the present invention.

FIG. 2 is a sectional view showing an example of a contact type charging member of the present invention.

[Explanation of symbols]

1 Photoconductor (charged body) 1a conductive substrate 1b Photosensitive layer 2 Contact type charging member 2a conductive substrate 2b conductive elastic layer 2c Resistance control layer 2d surface layer 3 power supplies 4 Exposure means 5 Developing means 6 Transfer means 7 Printed material 8 Cleaning means

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Inoue             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Naoki Fueki             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Satoshi Taniguchi             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H200 FA02 FA13 FA16 GA23 GA33                       GA44 GB12 HA02 HA28 HB12                       HB22 HB45 HB46 HB47 HB48                       JA02 MA03 MA04 MA12 MA13                       MA14 MA17 MA20 MB04 MC01                       NA02 NA09                 4J002 CK031 CK041 CK051 DA016                       DA036 DE096 DE106 DE136                       FD116 GF00 GM00 GQ02                 4J034 BA03 DA01 DB03 DB07 DD07                       DF01 DF02 DF16 DF20 DF22                       DG03 DG04 DG06 DK02 DP03                       DP13 DP18 GA06 GA33 HA01                       HA06 HA07 HC03 HC12 HC17                       HC22 HC46 HC53 HC61 HC63                       HC64 HC67 HC71 HC73 HD03                       HD04 HD05 HD07 HD12 HD13                       KA01 KB02 KC07 KC17 KC35                       KD02 KD12 KE02 QA02 QA03                       QB07 RA05 RA07 RA14

Claims (7)

[Claims] 1. A contact type charging member having a conductive base, a conductive elastic layer provided on the conductive base, and a surface layer containing a polyurethane resin, wherein the polyurethane resin of the surface layer is , Hydroxyl group (OH) of polyurethane raw material
And the isocyanate group (NCO) molar ratio is 0.3 ≦ NC
O / OH <1.0 and hydroxyl value is 5 KOHmg / g
A contact type charging member characterized by being 100 KOHmg / g or less. 2. The contact type charging member according to claim 1, wherein the surface layer contains a conductive material. 3. The contact type charging member according to claim 2, wherein the content of the conductive material is 30 to 200 parts by mass with respect to 100 parts by mass of the polyurethane resin. 4. The surface layer has a volume resistivity value of 10 ⁶
The contact type charging member according to claim 1, wherein the contact type charging member has a resistance of about 10 ¹⁴ Ωcm. 5. The contact type charging member according to claim 1, wherein the volume resistivity of the surface layer is larger than the volume resistivity of the conductive elastic layer. . 6. A contact charging device having a charging member, wherein the charging member is brought into contact with a member to be charged and a voltage is applied to charge the member to be charged, wherein the charging member is a charging unit.
5. A contact type charging device, which is the contact type charging member according to any one of items 1 to 5. 7. The contact type charging device according to claim 6, wherein the voltage is only a DC voltage.