Developing roller

Abstract

To provide a developing roller which offers good chargeability and high durability.SOLUTION: The present invention relates to a developing roller 1 comprising a shaft 2, an elastic layer 3 provided on an outer peripheral surface of the shaft 2, and a coating layer 4 provided on the outer side of the elastic layer 3, the coating layer 4 containing a urethane resin and two types of particles with different average particle diameters and having a slip angle of 35 degrees or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a developing roller. [Background technology]

[0002] Developing rollers used in electrophotographic image forming devices such as copiers, printers, and facsimiles have the function of imparting a uniform frictional charge to toner and stably transporting a predetermined amount of toner to a development area. In recent years, efforts have been made to lower the melting points of toner used in electrophotographic copiers in order to reduce power consumption and achieve high-speed printing.

[0003] However, such low-melting-point toner is easily melted by frictional heat caused by the pressure of the developing roller and other regulating members, and the melted toner is likely to adhere to the developing roller, which is known as filming. Furthermore, in a high-temperature, high-humidity environment, the chargeability of the toner itself tends to decrease due to the influence of moisture, and at the end of its life, a phenomenon known as fogging occurs, in which insufficiently charged toner adheres to the white area (background) of the image.

[0004] Patent Document 1 proposes a conductive roller that has an elastic layer formed on the outer surface of a shaft and a urethane coating layer formed on the outer surface of the elastic layer, in order to form high-quality images that are free from reduction in image density and unevenness in density due to toner filming, and the urethane coating layer contains urethane resin and 5 to 35 parts by mass of the same type of particles with different average particle sizes per 100 parts by mass of the urethane resin. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-174512 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in order to meet the demands for faster image forming devices and higher resolution, it is required to further reduce toner stress, have high durability, and provide sufficient charging properties to provide high-quality images, compared to the inventions described in the above patent documents. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a developing roller that can impart good charging properties and has high durability. [Means for solving the problem]

[0007] The present invention is a developing roller comprising a shaft, an elastic layer provided on the outer surface of the shaft, and a coating layer provided outside the elastic layer, wherein the coating layer contains a urethane resin and two types of particles with different average particle sizes, and the sliding angle of the surface of the coating layer is 35 degrees or less.

[0008] The developed area ratio Sdr of the interface of the coating layer is preferably 0.2 or more and 1.2 or less.

[0009] Of the two types of particles, it is preferable that one of the particles has an average particle size of 1.5 μm or more and 3 μm or less, and the other particle has an average particle size of 5 μm or more and 15 μm or less.

[0010] The hardness of the other particle is preferably higher than the hardness of the one particle, and the modulus of elasticity of the other particle is preferably 18 MPa or more and 40 MPa or less.

[0011] The coating layer is formed from a resin composition for forming a coating layer, and the total content of the two types of particles in the resin composition for forming a coating layer is preferably 35 parts by mass or more and 70 parts by mass or less per 100 parts by mass of the urethane resin, and the mass blending ratio of one type of particle to the other type of particle is preferably 25:75 or more and 90:10 or less.

[0012] It is preferable that one of the particles is a silicone rubber particle and the other is a urethane resin particle. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a developing roller that can be imparted with good chargeability and has high durability. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view illustrating an embodiment of a developing roller of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Developing roller] As shown in FIG. 1, the developing roller 1 of the present invention comprises a shaft 2, an elastic layer 3 provided on the outer peripheral surface of the shaft 2, and a coating layer 4 provided outside the elastic layer 3, wherein the coating layer 4 contains a urethane resin and two types of particles with different average particle sizes, and the sliding angle of the surface of the coating layer 4 is 35 degrees or less. Each component will be described in detail below.

[0016] <Shaft> The shaft 2 can preferably be a conductive shaft used in a conventionally known developing roller. The shaft 2 is preferably made of at least one metal selected from the group consisting of iron, aluminum, stainless steel, and brass. Such a shaft 2 is also generally known as a "core metal."

[0017] The shaft 2 may contain an insulating resin. The insulating resin may be, for example, a thermoplastic resin or a thermosetting resin. The shaft 2 may include, for example, a core made of an insulating resin and a plating layer provided on the core. Such a shaft 2 can be obtained, for example, by plating the core made of an insulating resin to make it conductive. The shaft 2 is preferably a cored bar in order to obtain good electrical conductivity.

[0018] The shape of the shaft 2 is preferably, for example, rod-like or tubular. The cross-sectional shape of the shaft 2 may be, for example, circular or elliptical, or may be non-circular such as polygonal. The outer peripheral surface of the shaft 2 may be subjected to treatment such as cleaning, degreasing, or primer treatment.

[0019] The axial length of the shaft 2 is not particularly limited and may be adjusted appropriately depending on the type of the image forming apparatus in which it is installed. The diameter of the shaft 2 (diameter of the circumscribing circle) is also not particularly limited and may be adjusted appropriately depending on the type of the image forming apparatus in which it is installed.

[0020] <Elastic layer> The elastic layer 3 is provided to impart hardness and elasticity to the developing roller 1 so that it can press against the photosensitive member with an appropriate nip width and nip pressure, so that toner can be supplied to the electrostatic latent image formed on the surface of the photosensitive member without excess or deficiency. The elastic layer 3 contains silicone rubber. Silicone rubber has the advantage of being less susceptible to compressive stress distortion due to pressing. Examples of silicone rubber include polydimethylsiloxane, polymethyltrifluoropropylsiloxane, polymethylvinylsiloxane, polyphenylvinylsiloxane, and copolymers of these siloxanes.

[0021] The conductivity of the elastic layer 3 can be adjusted appropriately by adding a conductivity imparting agent such as an electronically conductive substance or an ionic conductive substance. Examples of electronically conductive substances include conductive carbons such as Ketjen Black EC and acetylene black; rubber carbons such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, and MT; oxidized carbons for color (ink) applications; and metals and their oxides such as copper, silver, and germanium. Among these, carbon black (conductive carbon, rubber carbon, and color (ink) carbon) is preferred because it is easy to control conductivity with a small amount. Examples of ionic conductive substances include inorganic ionic conductive substances such as sodium perchlorate, lithium perchlorate, calcium perchlorate, lithium chloride, lithium bisimide, and potassium bisimide; and organic ionic conductive substances such as modified aliphatic dimethylammonium ethosulfate and stearylammonium acetate. Reactive ether-modified silicone oil may also be added to the elastic layer 3.

[0022] <Coating layer> The coating layer 4 contains a urethane resin and two types of particles with different average particle sizes. The coating layer 4 can be formed, for example, by curing a resin composition for forming a coating layer, which contains (A) a polyol and (B) an isocyanate compound that constitute the urethane resin, and (C) two types of particles with different average particle sizes.

[0023] (A) Polyol The polyol component is not particularly limited, but polyether polyol, polyester polyol, polycarbonate polyol, polybutadiene polyol, polyisoprene polyol, acrylic polyol, silicone-modified polyol, and fluorine-modified polyol can be used.

[0024] (B) Isocyanate compounds As the isocyanate compound for curing the polyol, various isocyanate compounds that are commonly used in the preparation of polyurethanes, such as aromatic isocyanate compounds, aliphatic isocyanate compounds, and alicyclic isocyanate compounds, can be used. Examples of aromatic isocyanate compounds include 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 1,4-phenylene diisocyanate, polymethylene polyphenylene polyisocyanate, tolidine diisocyanate (TODI), 1,5-naphthalene diisocyanate (NDI), and 3,3'-dimethylbiphenyl-4,4'-diisocyanate. Examples of aliphatic isocyanate compounds include hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMHDI), lysine diisocyanate, norbornene diisocyanate methyl (NBDI), xylylene diisocyanate (XDI), and tetramethylxylylene diisocyanate (TMXDI). Furthermore, examples of alicyclic isocyanate compounds include transcyclohexane-1,4-diisocyanate, isophorone diisocyanate (IPDI), H6XDI (hydrogenated XDI), H12MDI (hydrogenated MDI), and 4,4'-dicyclohexylmethane diisocyanate.

[0025] In the present invention, the amount of the isocyanate compound used in the composition used to form the coating layer 4 is preferably used so that the reaction rate of the isocyanate compound is 80% or more and 126% or less, preferably 95% or more and 112% or less.

[0026] (C) Two types of particles with different average particle sizes The developing roller 1 of this embodiment contains two types of particles with different average particle diameters. Of the two types of particles, the average particle diameter of one of the particles (hereinafter referred to as "small particles") is preferably 1.5 μm or more and 3 μm or less, and more preferably 2 μm or more and 3 μm or less. The other type of particles (hereinafter referred to as "large particles") preferably have an average particle size of 5 μm or more and 15 μm or less, and more preferably 7 μm or more and 11 μm or less. The average particle size of the particles can be measured as a median diameter using a particle size distribution measuring device based on a laser diffraction / scattering method.

[0027] The small particles are preferably at least one type selected from silicone rubber particles, urethane resin particles, and acrylic resin particles, and are more preferably silicone rubber particles because this stabilizes the amount of toner transport. The large particles are preferably at least one type selected from silicone rubber particles, silicone resin particles, urethane resin particles, and acrylic resin particles, and are more preferably urethane resin particles from the viewpoints of excellent adhesion to the urethane resin of the coating layer and less occurrence of uneven charging of the toner.

[0028] (elastic modulus of particle) Of the two types of particles, the hardness of the large particles is preferably higher than that of the small particles, and the elastic modulus of the large particles is more preferably 18 MPa or more and 40 MPa or less. The elastic modulus of the large particles is a value measured using a nanoindenter as described in the examples below.

[0029] The developing roller 1 of this embodiment contains two types of particles with different average particle sizes, which allows unevenness to be formed on the surface of the coating layer 4. The convex portions allow point contact between the developing roller 1 and the regulating blade to be maintained, reducing toner stress. Furthermore, by containing small particles, the difference in surface area between the small particles and the large particles forms concave portions on the surface of the coating layer 4, ensuring contact with the toner on the surface of the concave portions. This allows for sufficient charging properties to be obtained, enabling the formation of high-quality images. Furthermore, the hardness of the large particles is greater than that of the small particles, which allows for more reliable point contact, thereby providing a high quality image.

[0030] The total content of the two types of particles in the resin composition for forming a coating layer is preferably 35 to 70 parts by mass, and more preferably 50 to 65 parts by mass, per 100 parts by mass of the resin composition for forming a coating layer. The mass blending ratio of the small particles to the large particles is preferably 25:75 to 90:10, and more preferably 50:50 to 75:25. By setting the total content and blending amount of the two types of particles within the above ranges, it is possible to obtain good point contact between the developing roller 1 and the regulating blade at the convex portions while obtaining sufficient charging properties at the concave portions, thereby forming high-quality images.

[0031] The thickness of the coating layer 4 is preferably 5 μm or more and 13 μm or less, and more preferably 6 μm or more and 11 μm or less.

[0032] (Other ingredients) In addition to the above components, the resin composition for forming a coating layer may contain a solvent such as n-butyl acetate, and an auxiliary agent typically used in the reaction between the (A) polyol and the (B) isocyanate compound, such as a chain extender, a crosslinking agent, etc. Examples of the chain extender and crosslinking agent include glycols, hexanetriol, trimethylolpropane, and amines.

[0033] <Other configurations> The developing roller 1 of the present invention may have adhesive layers between the shaft 2 and the elastic layer 3, and between the elastic layer 3 and the covering layer 4. The surface of the elastic layer 3 may be modified by irradiating it with UV light or the like, or an adhesive layer may be provided between the elastic layer 3 and the covering layer 4 by primer treatment. Alternatively, the surface may be modified and an adhesive layer may be provided simultaneously by plasma coating.

[0034] <Developed area ratio Sdr of the coating layer interface> The developed interface area ratio Sdr of the coating layer 4 is preferably 0.2 or more and 1.2 or less, and more preferably 0.4 or more and 1.0 or less. By setting the developed interface area ratio Sdr to 0.2 or more, fogging in a high-temperature, high-humidity environment can be effectively prevented. Furthermore, by setting the developed interface area ratio Sdr to 1.2 or less, ghosting in a low-temperature, low-humidity environment can be effectively prevented. In this specification, the developed area ratio Sdr is measured by the method described in the Examples below.

[0035] <MD-1 hardness of coating layer> The MD-1 hardness of the coating layer 4 is more preferably 20° or more and 60° or less, and even more preferably 30° or more and 50° or less. By adjusting the MD-1 hardness of the coating layer 4 within the above range, it is possible to reduce the load on the developer while maintaining the amount of developer transport. The MD-1 hardness can be measured using an MD-1 hardness tester ("Micro Rubber Hardness Tester MD-1" manufactured by Kobunshi Keiki Co., Ltd.). In the present invention, the MD-1 hardness is determined by pressing the indenter type A of the MD-1 hardness tester against the roller surface, reading it in peak hold mode after a hold time of 3 seconds, and using it as the MD-1 hardness. In principle, the MD-1 hardness tester conforms to the type A durometer specified in JIS K6253.

[0036] <Slip angle> The sliding angle of the surface of the coating layer 4 is 35 degrees or less. The sliding angle is preferably 10 degrees or more and 35 degrees or less. In this specification, the term "slip angle" means an angle determined as follows. First, a base covered with a PET (polyethylene terephthalate) film is placed horizontally (0 degree angle with the horizontal plane), and the developing roller is placed on the base so that the longitudinal direction of the base is parallel to the axial direction of the developing roller. Next, with one longitudinal end of the base fixed, the other end is raised to gradually tilt the base, and the angle between the base and the horizontal plane is measured when the developing roller begins to slide toward one end.

[0037] By keeping the sliding angle of the developing roller surface at 35 degrees or less, the developing roller can properly carry and transport the developer to the photoconductor, and the developer can easily detach from the developing roller after adhering to it, allowing the developer to be supplied in a predetermined amount according to the image data. Furthermore, the frictional force on the toner when it comes into contact with the developing roller surface is reduced, suppressing toner damage during long-term printing. In other words, by keeping the sliding angle at 35 degrees or less, the developer can be properly carried and transported, maintaining high-quality images.

[0038] The sliding angle can be adjusted appropriately by changing the types, contents, etc. of the two particles having different average particle sizes. [Example]

[0039] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the examples shown below.

[0040] [Example 1] The developing roller of Example 1 was produced by the following procedure.

[0041] (Formation of primer layer) An electroless nickel-plated shaft (made of SUM22, diameter 7.5 mm, length 274.1 mm) was washed with ethanol, and its surface was coated with a silicone primer (product name "Primer No. 16", manufactured by Shin-Etsu Chemical Co., Ltd.). The primer-treated shaft was baked in a gear oven at 150°C for 10 minutes and then cooled at room temperature for at least 30 minutes, forming a primer layer on the outer surface of the shaft.

[0042] (Formation of elastic layer) An elastic body made of rubber material was molded on the outer circumferential surface of the shaft by extrusion molding using a rubber composition made of silicone rubber. In the extrusion molding, the rubber composition made of silicone rubber was heated at 360°C for 5 minutes using an infrared heating furnace (IR furnace), and then further heated at 200°C for 4 hours using a gear oven to harden it. This formed an elastic layer made of a cured product of the rubber composition on the outer circumferential surface of the primer-treated shaft. The elastic layer was a solid layer and had a thickness of 4.25 mm.

[0043] (Formation of coating layer) -Preparation of resin composition for forming coating layer- (A) Polyol: Product name "Kuraray Polyol P-2010" (manufactured by Kuraray Co., Ltd.) (B) Isocyanurate: Trade name "Duranate TPA-100" (manufactured by Asahi Kasei Corporation) (C) Two types of particles with different average particle sizes (1) Small particles: Silicone rubber particles (trade name "DOWSIL EP-2601 TM Powder, average particle size 2 μm, manufactured by Dow Toray Industries, Inc. (2) Large particles: urethane resin particles (product name "U-600T", average particle size 10 μm, manufactured by Negami Chemical Industrial Co., Ltd.) (D) n-Butyl acetate

[0044] Next, the outer peripheral surface of the elastic layer was UV-treated. Then, a coating layer-forming composition was applied to the UV-treated elastic layer by spray coating. The applied composition was heated at 150°C to 160°C for 30 minutes to obtain a developing roller. The thickness of the coating layer after drying was 9 μm.

[0045] [Examples 2 to 8 and Comparative Examples 1 to 6] A developing roller was produced in the same manner as in Example 1, except that the average particle diameters and compounding ratios of the small particles and the large particles were changed as shown in Tables 1 and 2.

[0046] [evaluation] The following evaluations were carried out on the above Examples and Comparative Examples. The evaluation results are shown in Tables 1 and 2.

[0047] (Measurement of average particle size) The particle dispersion in n-butyl acetate was measured using a particle size distribution analyzer (product name: LS 13 320; manufactured by Beckman Coulter, Inc.) to determine the volume average particle diameter. The optical model used a dispersion medium refractive index of 1.394 and particle refractive indexes determined for each particle, and the particle size distribution was calculated.

[0048] (Measurement of particle elastic modulus) The elastic modulus of the particles was measured using a nanoindenter measuring device (trade name: Hysitron TI Premier; manufactured by Bruker Japan Co., Ltd.) For the surface layer of the developing roller, measurements were taken at five points on each of the particle convex portions, and the average value of the calculated composite elastic modulus was taken as the elastic modulus of the particles. Measurement indenter: Berkovich indenter, diamond, Young's modulus 1140 GPa, Poisson's ratio 0.07 Measurement environment: Temperature 23°C, relative humidity 50%RH Loading speed: 1μm / 5 seconds Maximum load holding time: 5 seconds Unloading speed: 1μm / 5 seconds

[0049] (slip angle) The sliding angle was measured by the method described above.

[0050] (Interface development area ratio Sdr) For the developing rollers produced in the above examples and comparative examples, the coating layer at the center in the longitudinal direction of the roller was photographed at a magnification of 1200x using a non-contact laser microscope "VK-X1000" manufactured by Keyence Corporation. Next, quadratic curve correction was performed on the geometric data obtained from the photograph using Version 3.8.0.0 of the multi-file analysis application "VK-H1XA" manufactured by Keyence Corporation, and based on the obtained data, the cutoff values ​​λs and λc were set to "none" in the photographed field of view, and the developed area ratio Sdr was calculated.

[0051] <Image evaluation> The developing rollers of the above Examples and Comparative Examples were mounted on a contact-type monochrome image forming apparatus (product name "HL-L2360DN", manufactured by Brother Industries, Ltd.) and the following image evaluation was carried out. The developer and developer regulating member used were the developer, developer seal member, and developer regulating member that came with this contact-type monochrome image forming apparatus.

[0052] (Vertical streaks in durable printing) In a high temperature and humidity environment (32°C, 80% RH), two solid white sheets and one solid black sheet were printed for every 500 sheets printed at 0.3% duty, and the printed image was visually inspected to see if there were any vertical white streaks (vertical streaks). This process was repeated six times and the results were evaluated according to the following criteria. ○: No vertical streaks were found in the printed image △: Very slight vertical streaks were observed in the printed image, but this does not affect use. ×: When a large number of vertical streaks that cause problems in use are found in the printed image

[0053] (HH (high temperature and humidity) fogging during durable printing) In a high temperature and humidity environment (32°C, 80%RH), 1,500 sheets were printed at 0.3% duty, and the solid white printing was stopped instantly, tape was attached to the photosensitive drum, and the image was transferred onto a white piece of paper. Tape was attached to a reference paper, and the color difference ΔE between the reference value and the transferred part was measured. ◎: ΔE is less than 0.5 ○: ΔE is 0.5 or more and less than 1.0 △: ΔE is 1.0 or more and less than 1.5 ×: ΔE is 1.5 or more

[0054] [Table 1]

[0055] [Table 2]

[0056] As shown in Tables 1 and 2, the examples in which small particles and large particles are contained in the coating layer and the sliding angle of the coating layer is 35 degrees or less are excellent in the evaluation of vertical streaks in durable printing and fogging under high temperature and high humidity conditions, and it can be confirmed that they are endowed with high durability against toner stress and good charging properties. Comparative Examples 1 to 3, which contained only large particles and no small particles, were inferior in the evaluation of fogging under high-temperature, high-humidity conditions. Comparative Example 4, which contained only small particles, was poorly evaluated for vertical streaks in durable printing. Furthermore, Comparative Examples 5 to 7, which contain both small and large particles but have a sliding angle of more than 35, were inferior in either or both of the vertical streaks and fogging evaluations in durable printing. [Explanation of symbols]

[0057] 1 Developing roller 2-axis body 3 Elastic layer 4 Covering layer

Claims

1. A developing roller comprising a shaft, an elastic layer provided on an outer peripheral surface of the shaft, and a coating layer provided outside the elastic layer, the coating layer contains a urethane resin and two types of particles having different average particle sizes, The developing roller has a surface sliding angle of 35 degrees or less.

2. 2. The developing roller according to claim 1, wherein the coating layer has an interface developed area ratio Sdr of 0.2 or more and 1.2 or less.

3. 2. The developing roller according to claim 1, wherein one of said two types of particles has an average particle size of 1.5 [mu]m or more and 3 [mu]m or less, and the other has an average particle size of 5 [mu]m or more and 15 [mu]m or less.

4. 4. The developing roller according to claim 3, wherein the hardness of said other particles is higher than the hardness of said one particles, and the modulus of elasticity of said other particles is 18 MPa or more and 40 MPa or less.

5. the coating layer is formed from a resin composition for forming a coating layer, the total content of the two types of particles in the resin composition for forming a coating layer is 35 parts by mass or more and 70 parts by mass or less relative to 100 parts by mass of the urethane resin, 5. The developing roller according to claim 4, wherein the mass ratio of said one type of particles to said other type of particles is 25:75 or more and 90:10 or less.

6. the one particle is a silicone rubber particle, 5. The developing roller according to claim 3, wherein the other particles are urethane resin particles.

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