JPH0616301A - Method for coating surface of roller for copying machine - Google Patents

Abstract

PURPOSE:To provide the method for coating the surface of a roller for copying machine, with which the surface of a roller main body can be coated safely and easily with a thin skin having a flat and smooth surface and a low of hardness and in which the soil of the material in contact with the skin, by the formed skin is not generated. CONSTITUTION:The method for coating the surface of a roller for copying machine comprises a process for coating the surface 3 of a roller main body 2 with terminal isocyanate prepolymer, which contains urethan bonding, and a process for hardening the coated surface 3 of the roller main body 2 in the high temperature and wet atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging roller, a transfer roller, a printer for electrophotography, electrostatic recording, etc.
The present invention relates to a surface coating method of a roller for a copying machine such as a conductive roller used for the purpose of electrically controlling an object by contacting a photoconductor such as a cleaning roller.

[0002]

2. Description of the Related Art Toner prepared in a conventional toner cartridge is supplied to a photosensitive member on which an electrostatic latent image is formed,
The electrophotographic process of transferring and fixing on paper is generally composed of charging, photosensing, developing, transferring, fixing, and neutralizing mechanisms, and each mechanism uses various rollers for precisely controlling static electricity. The required properties for the roller material are becoming more and more severe. In particular, the roller used in the developing mechanism including the roller for toner transportation, the charging roller, the transfer roller, and the roller used in the cleaning mechanism electrostatically control the contacted object, so that the material of the roller is not conductive. It is required that the level of non-charging is controlled within a narrow range (one digit at 5 ° C to 45 ° C, for example, 1 × 10 ⁹ Ω · cm to 1 × 10 ¹⁰ Ω · cm).
In addition, these rollers are made of a conductive elastic material for the purpose of preventing damage to the other party by contact with precision parts such as a photosensitive drum, or increasing the contact area of the roller for accurate gripping. In particular, the use of foam has been investigated because it can reduce the compression hardness. However, a roller made of foam generally sets a core metal on a block-shaped foam and grinds the surface of the roller to form a shape, so that the surface of the final product becomes porous and has a microscopic shape like a charging roller. When it was necessary to control static electricity in a part, there was a problem in the roughness of the cells of the foam exposed on the surface. In order to solve such a problem, Japanese Patent Laid-Open No. 61-150370 discloses a conventional technique in which a shaft is arranged at the center of a cylindrical molding die and a mixture of a polyol, an isocyanate, a foaming agent and the like is provided around the shaft. It has been proposed to use a technique of so-called integral skin foam, in which the leather-like skin and the elastic foam are simultaneously molded by injecting and then foaming. As another solution, there are proposed a method of coating a roller having a porous surface, a method of manufacturing a roller having a porous surface and then covering the same with a tubular surface layer, and a method of covering with a shrink tube. There is.

[0003]

In the method using the integral skin foam technique, the boundary of the surface skin with the internal foam part is not clear, and it is particularly noticeable in a roller for a printer having a small roller diameter. In order to obtain the desired roller surface, the entire surface is in a high-density skin state, and the effect of decreasing the hardness described above cannot be expected. In addition, such an integral skin foam technology injects a liquid foaming mixture into the mold to foam and form the skin at the mold temperature and mold pressure, so that the sealability of the mold with the shaft set is produced. The technique is difficult (there are many defects), and in the case of vertical foaming to prevent air entrapment, there is an inconvenience such as a density difference (hardness difference) between the upper side and the lower side. In addition, the method of coating on a porous surface has a drawback that the surface unevenness finally remains and the desired smoothness cannot be obtained. Furthermore, in the method of covering the tube, in addition to the complexity of creating a tube having a diameter that matches the roller diameter, the cost increases due to an increase in the steps of coating and bonding, and a tubular material that does not impair the hardness of the foam. It was difficult to select the material and thickness of the, and the tube and the roller material were easily separated as they were used.

Therefore, according to the present invention, the surface of the roller body can be safely and easily coated with a thin skin having a smooth surface, low hardness, and the formed skin contaminates the contacted object. It is an object of the present invention to provide a method for coating a surface of a roller for a copying machine, which does not have the above.

[0005]

To achieve the above object, the present invention comprises a step of coating a surface of a roller body with a terminal isocyanate prepolymer having a urethane bond, and a high temperature wetting of the coated surface of the roller body. And a step of curing in an atmosphere.

[0006]

In this invention, since the terminal isocyanate prepolymer is used and cured in a high temperature and humid atmosphere, a large amount of solvent is not used. Therefore, there is a risk of flame due to volatilization of the solvent, deterioration of working environment, high cost, etc. There is no problem. Further, the terminal isocyanate prepolymer does not cause a problem of pot life by controlling the moisture content. further,
A strong, non-staining epidermis is obtained which hardens in a high temperature and humid atmosphere in a short time.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

The roller for a copying machine shown in FIG.
A conductive elastic body, which is the roller main body 2, is stacked on the upper surface of the roller main body 2, and a skin 3 is formed on the surface of the roller main body 2.
The skin 3 is formed by coating the surface of the roller body 2 with a terminal isocyanate prepolymer having a urethane bond and curing the coated surface of the roller body 2 in a high temperature wet atmosphere.

In the terminal isocyanate prepolymer, a compound containing two or more active hydrogens (polyhydroxyl compound) and a compound having two or more isocyanate groups (polyisocyanate compound) are reacted stoichiometrically in excess of the polyisocyanate compound. As a polyhydroxyl compound, the polyhydroxyl compound used is a polyol used in the production of general flexible polyurethane foams and urethane elastomers, that is, a polyether polyol having a polyhydroxyl group at the terminal, a polyester polyol, and a polyether which is a copolymer of both. In addition to polyester polyols, general polyols such as so-called polymer polyols obtained by polymerizing ethylenically unsaturated monomers in polyols can be used, and the resistance value of the coating film depends on the environment such as temperature and humidity. Polyhydroxyl compounds having a fluorine-containing or silicon-containing compound or polybutadiene, polyisoprene or a hydrogenated backbone having two or more active hydrogen to reduce the sexual also useful. Further, as the polyisocyanate compound, a polyisocyanate commonly used for the production of flexible polyurethane foams and urethane elastomers can be used. That is, tolylene diisocyanate (TDI), crude TDI, 4,4-diphenylmethane diisocyanate (MDI), crude MD
I, an aliphatic polyisocyanate having 2 to 18 carbon atoms, an alicyclic polyisocyanate having 4 to 15 carbon atoms, and a mixture or modified product of these polyisocyanates are used. The mixing ratio of the polyhydroxyl compound and the polyisocyanate compound may be such that the polyisocyanate compound is reacted stoichiometrically in an excess amount, and the mixing ratio of the polyhydroxyl compound and the polyisocyanate compound depends on the viscosity (workability) of the resulting prepolymer, the physical properties at the time of curing, etc. It can be arbitrarily selected in consideration.

In order to impart conductivity, addition of conductive fillers and ionic substances and alkaline substances such as magnesium oxide and calcium oxide, and moisture such as ketimine to prevent generation of bubbles during moisture curing. It is also possible to add chemicals that react to produce substances that react with the prepolymer. Further, it is possible to add some solvent for the purpose of decreasing the viscosity.

As a coating means for the roller body 2, a general method such as dipping, spraying or roll coater is used, but the thickness of the coating film is preferably 200 μm or less in consideration of foaming due to moisture. In a moisture-curing atmosphere, the higher the temperature and humidity, the faster the curing speed, but considering productivity and economic efficiency, the temperature is 30 ° C to 100 ° C and the humidity is 40% to 100%.
%, Preferably 50% to 80% RH (50% R
If it is less than H, the curing time becomes long, and if it is more than 80% RH, bubbles are likely to enter during curing).

An example of the roller body 2 is a compound containing two or more active hydrogens (polyhydroxyl compound), a compound having two or more isocyanate groups (polyisocyanate compound), a catalyst, a foaming agent, and a foam stabilizer. Polyurethane foam obtained by foaming and curing by stirring and mixing with additives such as, and as the polyhydroxyl compound, a polyol used for producing a general flexible polyurethane foam or urethane elastomer, that is, a polyether polyol having a hydroxyl group at the terminal, In addition to polyester polyols and polyether polyester polyols which are copolymers of both, general polyols such as so-called polymer polyols obtained by polymerizing ethylenically unsaturated monomers in the polyols are used.
Further, as the polyisocyanate compound, a polyisocyanate commonly used for the production of flexible polyurethane foams and urethane elastomers can be used. That is, tolylene diisocyanate (TDI), crude TD
I, 4,4-diphenylmethane diisocyanate (MD
I), crude MDI, aliphatic polyisocyanate having 2 to 18 carbon atoms, alicyclic polyisocyanate having 4 to 15 carbon atoms, and mixtures and modified products of these polyisocyanates, for example, partially obtained by reacting with polyols. A prepolymer or the like is used. Furthermore, a catalyst, a foam stabilizer, a foaming agent, and other additives are stirred and mixed to foam, but the polyhydroxy component and the polyisocyanate component are mechanically stirred together with the catalyst and the foam stabilizer without using H ₂ O or an organic solvent. A so-called mechanical floss method, in which the material is foamed in advance and discharged, and heat-cured, is preferable as the foam material for the roller. If necessary, various fillers and conductivity-imparting substances can be added. To impart conductivity to the polyurethane foam used in the present invention, a generally known method such as addition of a conductive filler or an ionic substance is used.

The above-mentioned roller for a copying machine has a roller body 2 made of a conductive polyurethane foam mounted on a metal shaft 1 and is useful for a conductive roller used for charging, developing and transferring. In particular, the hardness of the conductive roller using a foam with a low hardness should not be so high by forming a coating (skin 3), and sufficient strength, elongation, elasticity, and abrasion resistance can be obtained only by forming a thin film. It is useful because of its excellent properties and the ease of controlling the conductivity of the film.

Example 1 Propylene oxide and ethylene oxide were added to glycerin as a compound containing two or more active hydrogens to give a molecular weight of 5000, and a polyether polyol (Asahi Glass Co., Ltd., Exenol 828) 100 parts, 1,4- Butanediol (manufactured by Toyo Soda Co., Ltd.) 7.5 parts, urethane-modified MD as a compound having two or more isocyanate groups
I (Sumitomo Bayern, Sumidur PF) 50 parts,
Silicon-based surfactant (Japan Unicar, SZ161
8) 1.5 parts, 1.8-diazabicyclo [5.4.0] undecene-7 as a catalyst, 0.5 part of toluenesulfonate and 0.0015 part of dibutyltin dilaurate, and Ketjen Black manufactured by Lion Akzo. 3 parts of EC was foamed with a foaming and pouring machine manufactured by MONDOMIX, and the foamed body was injected into the mold device shown in FIGS. 2 and 3 from the nozzle 9 to form a cylindrical roller. The inner diameter of the cylindrical mold 4 is 16 mm, the length is 23 cm, the metal shaft 1 is 8 mm in diameter, and the length is 2
A 5 cm one was used. By press-fitting the foam into the mold device, the air in the mold device is smoothly replaced with the foam, and after the foam is filled in the mold, 80
By curing at 10 ° C. for 10 minutes, an elongated cylindrical body having void-free fine cells could be molded with a smooth skin on the surface. A lid mold 5. is provided on both ends of the cylindrical mold 4.
6 is fitted, and a through hole 7.8 is formed at the center of the lid mold 5.6. In order to form the skin 3 on the roller body 2 molded in this way, as a material for forming the skin 3,
Tolylene diisocyanate (TDI80, manufactured by Mitsui Toatsu Co., Ltd.) is added to 100 parts of polyether polyol (Exasol 828, manufactured by Asahi Glass Co., Ltd.) having a molecular weight of 5,000 by adding propylene oxide and ethylene oxide to glycerin.
20 parts of them are mixed and reacted at 80 ° C. for 2 hours while stirring to obtain a terminal isocyanate prepolymer (isocyanate content 6.8%). And this prepolymer 100
Ketjen Black EC2.5 manufactured by Lion Akzo Co., Ltd.
Parts were added to obtain a conductive urethane prepolymer. Next, the molded product was immersed in this prepolymer and then pulled up to form a film having a constant thickness on the surface, which was then left in an atmosphere of 60 ° C. × 85% relative humidity for 20 minutes, and was found to have excellent elasticity and strength. A skin 3 having a smooth surface is obtained and its thickness is 8
It was 0 μm. The roller with the skin 3 had no problem of contamination on the photoconductor, and when used as a charging roller and a transfer roller, it was possible to obtain a good image for a long period of time.

Example 2 To Example 1, 30 parts of ethyl acetate was added in order to reduce the viscosity and coated on the surface of the roller body 2 in the same manner. A roller having a film thickness of 30 μm and improved nip with the photosensitive drum by maintaining flexibility of the roller and pressure bonding at a constant pressure, and having good performance for the same application were obtained.

In order to form the skin 3, a method in which an elastic resin such as thermoplastic urethane is dissolved in a solvent and coated and then dried and coated, and a polyol and an isocyanate as two components are mixed in a stoichiometric proportion and then coated. A method of heating and curing the coating film, a method of applying a water emulsion of an elastic resin, and the like can be considered. However, since the resin is generally of high molecular weight, a large amount of solvent (80% to 90%) is required to make a solution having a viscosity suitable for coating work, and the solvent selection range is small. Sometimes the adherend (roller body 2) is swollen, and as a result, a smooth surface cannot be obtained after drying and curing, or drying takes time and productivity is poor. Alternatively, since a large amount of solvent is volatilized, there are problems such as a danger of flame, deterioration of working environment, and high cost. Since the reactive materials are mixed and used, the mixture has a pot life, which is not suitable for continuous production. That is, the mixture thickens with time, and it becomes difficult to control the film thickness due to a change in viscosity, and the thickening progresses eventually to cure, making it unusable. The additive such as a surfactant used when preparing the water emulsion contaminates an object to be contacted such as a photoreceptor. The products obtained in Examples 1 and 2 of the present invention described above have solved all of these defects.

[0017]

As described above, according to the present invention, since a large amount of solvent is not used, safety is high, workability is improved, and the curing process is easy. Even when the conductive polyurethane foam is used for the roller body, the foam does not swell with the solvent. Furthermore, the adhesion to the surface of the roller body is good, the skin has elasticity and strength. Further, it is also excellent in non-staining property.

[Brief description of drawings]

FIG. 1 is a sectional view of a roller for a copying machine manufactured according to the present invention.

FIG. 2 is a perspective view showing a mold device for molding a roller body.

FIG. 3 is a perspective view showing a state in which a metal shaft is inserted into the mold device and a nozzle is inserted therein.

[Explanation of symbols]

 1 metal shaft 2 roller body 3 skin

Claims (5)

[Claims] 1. A surface coating of a roller for a copying machine, which comprises a step of coating a surface of a roller body with a terminal isocyanate prepolymer having a urethane bond, and a step of curing the coated surface of the roller body in a hot and humid atmosphere. Method. 2. The surface coating method of a roller for a copying machine according to claim 1, wherein conductive fine powder is mixed and dispersed in the isocyanate prepolymer. 3. The high temperature wet atmosphere in the curing step after coating is set to a temperature of 30 ° C. to 100 ° C. and a humidity of 40%.
The surface coating method of a roller for a copying machine according to claim 1, characterized in that the content is 100%, preferably 50% to 80%. 4. The method for coating a surface of a roller for a copying machine according to claim 1, wherein the roller main body is made of a conductive elastic body loaded on a metal shaft. 5. The method of coating a roller for a copying machine according to claim 4, wherein the conductive elastic body is a conductive polyurethane foam.