JP5204953B2 - Developing roller and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a developing roller and an image forming apparatus including the developing roller. Particularly, the developing roller does not contaminate a photosensitive drum or deteriorate toner, and further has a developing roller having a small compression set and the developing roller. The present invention relates to an image forming apparatus capable of forming a clear image.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, as a developing method for visualizing a latent image by supplying toner to a photosensitive drum holding a latent image and attaching the toner to the latent image on the photosensitive drum. A pressure development method is known. In the pressure development method, for example, after the photosensitive drum is charged to a constant potential, an electrostatic latent image is formed on the photosensitive drum by an exposure machine, and further, a developing roller carrying toner is placed on the electrostatic latent image. Development is performed by bringing the toner into contact with the latent image on the photosensitive drum in contact with the held photosensitive drum.

  In the above pressure development method, the developing roller must rotate while securely holding the photosensitive drum, so that polyurethane, silicone rubber, acrylonitrile is placed on the outer periphery of the shaft made of a highly conductive material such as metal. -Semiconductive elastic body in which carbon black or metal powder is dispersed in an elastomer such as butadiene rubber (NBR), ethylene-propylene-diene rubber (EPDM), epichlorohydrin rubber (ECO), or a foam obtained by foaming these. It has a structure in which a semiconductive elastic layer made of is formed. In some cases, a surface coating layer is further formed on the surface of the elastic layer for the purpose of controlling the chargeability and adhesion to the toner and preventing the photosensitive drum from being contaminated by the elastic layer.

  On the other hand, in recent years, with the increase in color, high speed, high image quality, and energy saving of image forming apparatuses, the number of image forming apparatuses using low-melting toner is increasing. Here, when using a low-melting toner, the low-melting toner is damaged by repeated compression or friction between the components, and the toner is aggregated and fused, and thus, such as fogging. Image defects are likely to occur. That is, since the toner deteriorates at the end of the life of the toner cartridge and the chargeability becomes non-uniform, there is a problem that an image defect occurs or the life is shortened. Therefore, there is a demand for a developing roller having a low hardness that hardly damages the toner.

  On the other hand, when a low-hardness developing roller is used in the image forming apparatus, there is a problem that pressure contact marks due to a photosensitive drum, a blade, a supply roller, and the like are easily generated on the surface of the developing roller. Therefore, in recent years, there is a demand for a developing roller having a low compression set in addition to a low hardness. However, since materials with low hardness tend to have large compression set, it has been very difficult to balance both hardness and compression set sufficiently low (see Patent Documents 1 to 3).

JP-A-8-190263 JP 2001-75354 A JP 2004-67726 A

  Accordingly, an object of the present invention is to provide a developing roller that solves the above-mentioned problems of the prior art, and that does not contaminate the photosensitive drum or deteriorate the toner, and further has a small compression set. Another object of the present invention is to provide an image forming apparatus that includes such a developing roller and that can stably form a good image without causing image defects such as fogging. .

As a result of diligent studies to achieve the above object, the present inventor, as a result, in a developing roller having a surface coating layer, a urethane obtained by crosslinking a lactone-modified polyol having a weight average molecular weight of 500 or more to the surface coating layer with a polyisocyanate. By using a resin, the hardness and compression set of the developing roller can be made sufficiently small to make it difficult for the toner to deteriorate. Furthermore, by incorporating the developing roller into the image forming apparatus, a good image can be stabilized. As a result, the present invention was completed.

That is, the developing roller of the present invention is a developing roller comprising a shaft, an elastic layer formed on the outer periphery of the shaft, and a surface coating layer formed on the outer peripheral surface of the elastic layer.
The surface coating layer includes a urethane resin obtained by crosslinking a lactone-modified polyol having a weight average molecular weight of 500 or more with a polyisocyanate.

  In a preferred example of the developing roller of the present invention, the urethane resin is obtained by crosslinking the lactone-modified polyol with two or more polyisocyanates.

  In another preferred embodiment of the developing roller of the present invention, the elastic layer is made of polyurethane.

  In another preferred embodiment of the developing roller of the present invention, the elastic layer is made of a foam. Here, when the said elastic layer consists of a foam, it is still more preferable that the bubble of this foam is a closed cell.

  In another preferred embodiment of the developing roller of the present invention, the surface coating layer further contains a conductive agent. In this case, the conductivity of the surface coating layer can be easily controlled.

  The developing roller of the present invention preferably has a surface JIS 10-point average roughness (Rz) of 10 μm or less. In this case, a sufficient toner charge amount can be secured to prevent the occurrence of background fogging or gradation failure in the image.

  The image forming apparatus of the present invention includes the developing roller.

According to the present invention, a urethane resin obtained by crosslinking a lactone-modified polyol having a weight average molecular weight of 500 or more with a polyisocyanate is used for the surface coating layer, the photosensitive drum is not contaminated, the toner is not deteriorated, and the permanent compression is used. A developing roller with small distortion can be provided. Further, it is possible to provide an image forming apparatus that includes the developing roller and can stably form a good image.

<Developing roller>
Hereinafter, the developing roller of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of an example of the developing roller of the present invention. The developing roller 1 in the illustrated example includes a shaft 2, an elastic layer 3 formed on the outer periphery of the shaft 2, and a surface coating layer 4 formed on the outer peripheral surface of the elastic layer 3. In the figure, the surface coating layer 4 is composed of one layer, but the surface coating layer 4 of the developing roller of the present invention may be composed of two or more layers. In the developing roller of the present invention, since the surface coating layer 4 is disposed on the outer peripheral surface of the elastic layer 3, it is possible to sufficiently prevent the contaminants oozing out from the elastic layer 3 from contaminating the photosensitive drum. it can.

The developing roller of the present invention is characterized in that the surface coating layer 4 includes a urethane resin obtained by crosslinking a lactone-modified polyol having a weight average molecular weight of 500 or more with a polyisocyanate. By including the urethane resin in the surface coating layer 4, the hardness of the developing roller is lowered and the toner is not damaged, and further, the compression set of the developing roller is reduced, and a good image is formed. Is possible.

  The shaft 2 of the developing roller of the present invention is not particularly limited as long as it has good electrical conductivity. For example, a metal core made of a metal such as iron, stainless steel, or aluminum, or a hollow interior is hollowed out. A metal shaft such as a metal cylinder or a highly conductive plastic shaft can be used.

The elastic layer 3 of the developing roller of the present invention is formed from an elastomer, and may contain other components such as a conductive agent as necessary. Examples of the elastomer used for the elastic layer 3 include polyurethane, silicone rubber, ethylene-propylene-diene rubber (EPDM), acrylonitrile-butadiene rubber (NBR), natural rubber, styrene-butadiene rubber (SBR), butadiene rubber, isoprene rubber, poly Examples include norbornene rubber, butyl rubber, chloroprene rubber, acrylic rubber, epichlorohydrin rubber (ECO), ethylene-vinyl acetate copolymer (EVA), and mixtures thereof. Among these, polyurethane is preferable. The elastomer may be used as the non-foamed material for the elastic layer 3, but the elastomer is chemically foamed using a foaming agent, or air is mechanically entrained and foamed like a polyurethane foam. And it is preferable to use the said elastomer as a foam. Here, when the elastic layer 3 is made of a foam, the expansion ratio is preferably 1.5 to 50 times, and the density is preferably 0.05 to 0.9 g / cm ³ .

  In addition, it is preferable to use the elastomer foam for the elastic layer 3, and further, by making the foam bubbles into closed cells, the compression set performance is improved, so that the bubbles in the foam are independent. Air bubbles are preferred. Here, in order to make the bubbles of the foam into closed cells, a technique in which the above-mentioned elastomer raw material is foamed by mechanical stirring is suitably employed.

  Examples of the conductive agent that can be used for the elastic layer 3 include an electronic conductive agent and an ionic conductive agent. Electronic conductive agents include conductive carbon such as ketjen black and acetylene black, carbon black for rubber such as SAF, ISAF, HAF, FEF, GPF, SRF, FT and MT, and carbon black for color subjected to oxidation treatment. , Pyrolytic carbon black, natural graphite, artificial graphite, antimony-doped tin oxide, ITO, tin oxide, titanium oxide, zinc oxide and other metal oxides, nickel, copper, silver, germanium and other metals, polyaniline, polypyrrole, polyacetylene, etc. Conductive whiskers such as conductive polymer, carbon whisker, graphite whisker, titanium carbide whisker, conductive potassium titanate whisker, conductive barium titanate whisker, conductive titanium oxide whisker, and conductive zinc oxide whisker. The blending amount of the electronic conductive agent is preferably in the range of 1 to 50 parts by mass, more preferably in the range of 5 to 40 parts by mass with respect to 100 parts by mass of the elastomer.

  Examples of the ionic conductive agent include tetraethylammonium, tetrabutylammonium, dodecyltrimethylammonium, hexadecyltrimethylammonium, benzyltrimethylammonium, modified fatty acid dimethylethylammonium, perchlorate, chlorate, hydrochloride, bromate, and the like. Ammonium salts such as salts, iodates, borofluorides, sulfates, ethyl sulfates, carboxylates, sulfonates; alkaline metals such as lithium, sodium, potassium, calcium, magnesium, alkaline earth metals Examples include perchlorate, chlorate, hydrochloride, bromate, iodate, borofluoride, sulfate, trifluoromethyl sulfate, and sulfonate. The compounding amount of the ionic conductive agent is preferably in the range of 0.01 to 10 parts by mass, more preferably in the range of 0.05 to 5 parts by mass with respect to 100 parts by mass of the elastomer. The said electrically conductive agent may be used individually by 1 type, may be used in combination of 2 or more type, and may combine an electronic conductive agent and an ionic conductive agent.

The elastic layer 3 preferably has a resistance value of 10 ³ to 10 ¹⁰ Ωcm, more preferably 10 ⁴ to 10 ⁸ Ωcm, depending on the blending of the conductive agent. If the resistance value of the elastic layer 3 is less than 10 ³ Ωcm, electric charges may leak to the photosensitive drum or the developing roller itself may be damaged by voltage, and if it exceeds 10 ¹⁰ Ωcm, ground fog is likely to occur.

  The elastic layer 3 may contain a crosslinking agent such as an organic peroxide and a vulcanizing agent such as sulfur in order to make the elastomer into a rubbery material as necessary. Sulfur accelerators, vulcanization accelerators, vulcanization retarders, and the like may be included. The elastic layer 3 is further used for rubber such as a filler, a peptizer, a foaming agent, a plasticizer, a softener, a tackifier, an anti-tacking agent, a separating agent, a release agent, an extender, and a coloring agent. You may contain a compounding agent.

The surface coating layer 4 of the developing roller of the present invention mainly contains a urethane resin obtained by crosslinking a lactone-modified polyol with polyisocyanate, and if necessary, contains other components such as a conductive agent. The lactone-modified polyol can be produced by modifying the end of the polyol with a lactone such as ε-caprolactone, and a commercially available product can also be used. Further, the lactone-modified polyol is the weight average molecular weight (Mw) of 500 or more, and preferably 1000 or more.

  Polyols modified with the above lactone include polyether polyols obtained by addition polymerization of alkylene oxides such as ethylene oxide and propylene oxide on glycerin, polytetramethylene glycol, glycerin, ethylene glycol, propylene glycol, butanediol, pentanediol, hexane Examples include diol, octanediol, polybutadiene polyol, polyisoprene polyol, and polyester polyol.

  Polyisocyanates that crosslink the lactone-modified polyol include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), crude diphenylmethane diisocyanate (crude MDI), isophorone diisocyanate (IPDI), hydrogenated diphenylmethane diisocyanate, hydrogenated tolylene diene. Examples include isocyanate and hexamethylene diisocyanate (HDI). These polyisocyanates may be used alone or in combination of two or more.

  The surface coating layer 4 can further contain a catalyst for promoting a crosslinking reaction between the lactone-modified polyol and the polyisocyanate. Examples of the catalyst include organic tin compounds such as dibutyltin dilaurate, dibutyltin diacetate, dibutyltin thiocarboxylate, dibutyltin dimaleate, dioctyltin thiocarboxylate, tin octenoate; organic lead compounds such as lead octenoate; triethylamine, Monoamines such as dimethylcyclohexylamine; diamines such as tetramethylethylenediamine, tetramethylpropanediamine, tetramethylhexanediamine; triamines such as pentamethyldiethylenetriamine, pentamethyldipropylenetriamine, tetramethylguanidine; triethylenediamine, dimethylpiperazine, Cyclic amines such as methylethylpiperazine, methylmorpholine, dimethylaminoethylmorpholine, dimethylimidazole Alcohol amines such as dimethylaminoethanol, dimethylaminoethoxyethanol, trimethylaminoethylethanolamine, methylhydroxyethylpiperazine, and hydroxyethylmorpholine; ether amines such as bis (dimethylaminoethyl) ether and ethylene glycol bis (dimethyl) aminopropyl ether And the like. Of these catalysts, organotin compounds are preferred. These catalysts may be used individually by 1 type, and may be used in combination of 2 or more type. The amount of the catalyst used is preferably in the range of 0.001 to 2.0 parts by mass with respect to 100 parts by mass of the lactone-modified polyol.

The surface coating layer 4 can be blended with a conductive agent for the purpose of controlling its conductivity, and examples of the conductive agent are the same as those exemplified as the conductive agent used for the elastic layer 3. can do. Here, in the case of an ionic conductive agent, the blending amount of the conductive agent in the surface coating layer 4 is preferably 20 parts by mass or less with respect to 100 parts by mass of the urethane resin constituting the surface coating layer 4, and 0.01 to 20 parts by mass In the case of an electronic conductive agent, the range of 1 to 70 parts by mass with respect to 100 parts by mass of the urethane resin constituting the surface coating layer 4 is more preferable. Is preferable, and the range of 5 to 50 parts by mass is more preferable. The surface coating layer 4 is preferably adjusted to have a volume resistance in the range of 10 ³ to 10 ¹⁰ Ω · cm by adding the conductive agent, and in the range of 10 ⁴ to 10 ⁸ Ω · cm. It is more preferable to adjust so that it becomes.

  The thickness of the surface coating layer 4 is not particularly limited, but is preferably 30 μm or less, and more preferably in the range of 1 to 15 μm. If the thickness of the surface coating layer 4 exceeds 30 μm, the surface coating layer 4 may become hard and the flexibility may be impaired, and durability may be reduced, cracking may occur due to use, or toner may be damaged. There is a possibility that the toner adheres to the photosensitive drum or the stratified blade, resulting in an image defect.

  The method for forming the surface coating layer 4 is not particularly limited. A coating material containing each component constituting the surface coating layer 4 is prepared, and the coating material is applied by a dipping method, a spray method, or a roll coating method. A drying method is preferably used.

  As for the surface roughness of the developing roller of the present invention, the JIS 10-point average roughness (Rz) is preferably 10 μm or less. When the JIS 10-point average roughness (Rz) of the developing roller exceeds 10 μm, the toner conveyance amount tends to increase, but the toner charge amount is insufficient, causing background fogging and poor gradation in the image. .

The resistance value of the developing roller of the present invention is not particularly limited, but in order to obtain a good image, the electric resistance is preferably 10 ³ to 10 ¹⁰ Ω, and 10 ⁴ to 10 ⁸ Ω. Is more preferable. If the resistance value of the developing roller is less than 10 ³ Ω, gradation control is extremely difficult, and bias leakage may occur if the photosensitive drum is defective. On the other hand, if the resistance value exceeds 10 ¹⁰ Ω, for example, when developing toner on a photosensitive drum, the developing bias causes a voltage drop due to the high resistance of the developing roller itself, and a sufficient developing bias for development cannot be secured. Thus, a sufficient image density cannot be obtained. The resistance value is measured, for example, by pressing the outer peripheral surface of the developing roller against a flat plate or cylindrical counter electrode with a predetermined pressure, applying a voltage of 100 V between the shaft and the counter electrode, and obtaining from the current value at that time. be able to. In this way, by appropriately and uniformly controlling the resistance value of the developing roller, the electric field strength for moving the toner can be kept appropriate and uniform.

  The developing roller of the present invention preferably has an Asker C hardness of 60 ° or less. If it is a low-hardness developing roller with Asker C hardness of 60 ° or less, the toner will be damaged between the developing roller and the photosensitive drum, blade, toner supply roller and the like when incorporated in the image forming apparatus. And a sufficiently good image can be formed.

<Image forming apparatus>
The image forming apparatus of the present invention includes the above-described developing roller that does not contaminate the photosensitive drum, does not deteriorate the toner, and has a small compression set, and does not cause image defects such as fogging. A good image can be formed stably. The image forming apparatus of the present invention is not particularly limited except that the developing roller is used, and can be manufactured by a known method.

  The image forming apparatus of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a partial cross-sectional view of an example of the image forming apparatus of the present invention. The image forming apparatus of the illustrated example includes a toner supply roller 6 for supplying toner 5, a photosensitive drum 7 that holds an electrostatic latent image, and the above-described toner disposed between the toner supply roller 6 and the photosensitive drum 7. The developing roller 1, the stratified blade 8 provided in the vicinity of the developing roller 1 (upper part in the figure), the charging roller 9 located in the vicinity of the photosensitive drum 7 (upper in the figure), and the vicinity of the photosensitive drum 7 (in the figure) A transfer roller 10 positioned on the lower side and a cleaning unit 11 provided adjacent to the photosensitive drum 7. The image forming apparatus of the present invention can further include a known component (not shown) that is usually used in the image layer forming apparatus.

  In the image forming apparatus of the illustrated example, after the photosensitive drum 7 is charged to a constant potential by the charging roller 9, an electrostatic latent image is formed on the photosensitive drum 7 by an exposure machine (not shown). Next, the toner supply roller 6, the developing roller 1, and the photosensitive drum 7 rotate in the direction of the arrow in the drawing, so that the toner 5 on the toner supply roller 6 is sent to the photosensitive drum 7 through the developing roller 1. It is done. The toner 5 on the developing roller 1 is adjusted to a uniform thin layer by the stratifying blade 8, and the toner 5 is transferred from the developing roller 1 to the photosensitive drum 7 by rotating while the developing roller 1 and the photosensitive drum 7 are in contact with each other. It adheres to the electrostatic latent image and the latent image becomes visible. The toner 5 attached to the latent image is transferred onto a recording medium such as paper by the transfer roller 10, and the toner 5 remaining on the photosensitive drum 7 after the transfer is removed by the cleaning blade 12 of the cleaning unit 11. Here, in the image forming apparatus of the present invention, it is preferable that the developing roller 1 does not contaminate the above-described photosensitive drum, does not deteriorate the toner, and has a small compression set. It is possible to form a stable image.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(Production of roller body)
100 parts by mass of urethane prepolymer synthesized from tolylene diisocyanate (TDI) and polyether polyol and 2 parts by mass of acetylene black are mixed to prepare a urethane prepolymer in which acetylene black is dispersed. did. On the other hand, 30 parts by mass of polyether polyol and 0.1 part by mass of sodium perchlorate (NaClO ₄ ) were mixed while heating to 70 ° C., and 4.5 parts by mass of polyether-modified silicone oil (foam stabilizer), dibutyltin dilaurate (Catalyst) 0.2 parts by mass was mixed to prepare a mixture, which was used as component B. Next, the A component and the B component are foamed by a mechanical floss method, and further injected into a cylindrical mold set with a core metal, and a roller body having an elastic layer made of foamed polyurethane is formed by RIM molding. Produced.

Example 1
100 parts by mass of caprolactone-modified polyol [Daicel Chemical Industries: PCL205, molecular weight 500], 35 parts by mass of carbon black, and 50 parts by mass of nurate-modified HDI [manufactured by Nippon Polyurethane: Coronate HX] in 300 parts by mass of methyl ethyl ketone (MEK) A paint for surface coating was prepared by dispersing. The obtained coating material was applied to the outer periphery of a roller body having an elastic layer made of the above polyurethane foam to form a surface coating layer, thereby producing a developing roller. Next, the roller resistance, JIS 10-point average roughness (Rz), Asker C hardness, and toner chargeability of the obtained developing roller are evaluated by known methods, and the developing roller is attached to a laser printer for printing. And image characteristics were evaluated. Further, the obtained developing roller was assembled in a cartridge and stored in an environment of 50 ° C. and 90% RH for one week, and then the presence or absence of contamination of the photosensitive drum and the presence or absence of blade pressure contact marks on the surface of the developing roller were examined. The results are shown in Table 1.

(Example 2)
100 parts by mass of caprolactone-modified polyol [manufactured by Daicel Chemical Industries: PCL210N, molecular weight 1000], 35 parts by mass of carbon black, and 50 parts by mass of nurate-modified HDI [manufactured by Nippon Polyurethane: Coronate HX] are dispersed in 300 parts by mass of MEK. A paint for surface coating was prepared. A developing roller was prepared and evaluated using the coating material thus obtained in place of the coating material prepared in Example 1. The results are shown in Table 1.

(Example 3)
100 parts by mass of caprolactone-modified polyol [manufactured by Daicel Chemical Industries: PCL220, molecular weight 2000], 35 parts by mass of carbon black, and 50 parts by mass of nurate-modified HDI [manufactured by Nippon Polyurethane: Coronate HX] are dispersed in 300 parts by mass of MEK. A paint for surface coating was prepared. A developing roller was prepared and evaluated using the coating material thus obtained in place of the coating material prepared in Example 1. The results are shown in Table 1.

Example 4
100 parts by mass of caprolactone-modified polyol [manufactured by Daicel Chemical Industries: PCL 312, molecular weight 1200], 35 parts by mass of carbon black, and 50 parts by mass of nurate-modified HDI [manufactured by Nippon Polyurethane: Coronate HX] are dispersed in 300 parts by mass of MEK. A paint for surface coating was prepared. A developing roller was prepared and evaluated using the coating material thus obtained in place of the coating material prepared in Example 1. The results are shown in Table 1.

(Comparative Example 1)
Polycarbonate diol-modified polyurethane paint [Nippon Polyurethane Industry: N5196] 100 parts by mass, carbon black 35 parts by mass, and nurate-modified HDI [Nippon Polyurethane: Coronate HX] 50 parts by mass are dispersed in 300 parts by mass of MEK. A coating for coating was prepared. A developing roller was prepared and evaluated using the coating material thus obtained in place of the coating material prepared in Example 1. The results are shown in Table 1.

(Comparative Example 2)
Adipic acid-modified polyurethane paint [Nippon Polyurethane Industry: N3126] 100 parts by mass, carbon black 35 parts by mass, and nurate-modified HDI [Nippon Polyurethane: Coronate HX] 50 parts by mass are dispersed in MEK 300 parts by mass. A coating for coating was prepared. A developing roller was prepared and evaluated using the coating material thus obtained in place of the coating material prepared in Example 1. The results are shown in Table 1.

  As is apparent from Table 1, the developing roller of the embodiment according to the present invention does not contaminate the photosensitive drum, and since the compression set is small, there is no pressure contact mark of the blade, and the damage to the toner is small. Therefore, a good image could be stably formed.

It is sectional drawing of an example of the developing roller of this invention. 1 is a partial cross-sectional view of an example of an image forming apparatus of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing roller 2 Shaft 3 Elastic layer 4 Surface coating layer 5 Toner 6 Toner supply roller 7 Photosensitive drum 8 Layering blade 9 Charging roller 10 Transfer roller 11 Cleaning part 12 Cleaning blade

Claims (8)

In a developing roller comprising a shaft, an elastic layer formed on the outer periphery of the shaft, and a surface coating layer formed on the outer peripheral surface of the elastic layer,
The developing roller , wherein the surface coating layer includes a urethane resin obtained by crosslinking a lactone-modified polyol having a weight average molecular weight of 500 or more with a polyisocyanate.   The developing roller according to claim 1, wherein the urethane resin is obtained by crosslinking the lactone-modified polyol with two or more polyisocyanates.   The developing roller according to claim 1, wherein the elastic layer is made of polyurethane.   The developing roller according to claim 1, wherein the elastic layer is made of a foam.   The developing roller according to claim 4, wherein the bubbles of the foam are closed cells.   The developing roller according to claim 1, wherein the surface coating layer further contains a conductive agent.   The developing roller according to claim 1, wherein the surface has a JIS 10-point average roughness (Rz) of 10 μm or less. An image forming apparatus having a developing roller according to any one of claims 1-7.

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