Patent Application
20160252876
1. Field of the Invention
The present invention relates to a sliding member including diamond like carbon (DLC) on a sliding surface thereof, and a sliding device including the sliding member.
2. Description of the Related Art
Materials of low friction that are self-lubricating without using oils or greases are known. Among these, DLC, which is a hard material, does not damage a sliding counterpart.
DLC is amorphous carbon having a diamond structure (sp3 mixture) and a graphite structure (sp2 mixture) mixed therein. DLC is a material having characteristics of highly hard diamond and characteristics of low-shearing graphite.
Japanese Patent Laid-Open No. 2013-53340 discloses segmenting DLC film and forming the segmented DLC film on a substrate to increase wear-resistance of a frictional contact surface.
Adhesiveness between DLC and the substrate is low. Japanese Patent Laid-Open No. 2013-53340 is proposed to increase wear-resistance on the frictional contact surface. If DLC is segmented, the DLC segments are arranged with spaces therebetween. Therefore, planar pressure between DLC and a sliding counterpart in contact with DLC is higher than that when DLC is not segmented. If the DLC segments are arranged with spaces therebetween, DLC is easily worn out or easily removed from the substrate.
The present invention provides a sliding member with reduced planar pressure on DLC of a sliding surface even if DLC is provided on the sliding surface as the sliding member.
The present invention provides a sliding member provided with a sliding surface, wherein the sliding surface has a first sliding surface and a second sliding surface, the first sliding surface comprises diamond like carbon, the second sliding surface comprises a material of which frictional coefficient is higher than that of the diamond like carbon at a temperature of 25° C. and a humidity of 45%, and the frictional coefficient of the sliding member is 0.12 or less.
The present invention provides a sliding member in which, even if the DLC segments are separated on the sliding surface, not only DLC but another member are not removed from the substrate by providing another member between the separated DLC segments while keeping the low friction property of the sliding member.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
A first embodiment according to the present invention relates to a sliding member in which the first sliding surface is made of diamond like carbon and, the second sliding surface is made of a material of which frictional coefficient is higher than that of diamond like carbon at a temperature of 25° C. and a humidity of 45%.
The sliding member has a first sliding surface and a second sliding surface.
The second sliding surface is disposed on a substrate in a region where the first sliding surface is not disposed.
Sliding herein refers to a relative movement between two members in contact with each other. In the present embodiment, the sliding member performs both a sliding movement in which the sliding member itself moves, and a sliding movement in which the sliding movement itself does not move but the sliding counterpart moves (that is, a sliding movement in sliding contact with the sliding counterpart).
In the first embodiment, a plurality of first sliding surfaces exist and a second sliding surface is disposed in a region where the first sliding surfaces are separated from one another.
In the left-hand diagram of
In the right-hand diagram of
In
The member included in the second sliding surface has a frictional coefficient that is higher than that of DLC. For example, the frictional coefficient of DLC included in the first sliding surfaces is equal to or greater than 0.12 to equal to or lower than 0.20.
The frictional coefficient is a value at a temperature of 25° C. and a humidity of 45%. For example, the frictional coefficient may be measured by applying a probe to a surface of the sliding member illustrated in
The frictional coefficient of each sliding surface may be calculated in the following manner. At a temperature of 25° C. and a humidity of 45%, a probe with a ball of 10 mmφ made of SUS304 fixed at the tip thereof is moved at a rate of 600 mm/min in contact with each of the sliding surfaces with the load N of 100 g. Resistance F at this time is monitored and the frictional coefficient μ may be obtained based on F=μN.
The frictional coefficient of the sliding member according to the present embodiment is 0.12 or lower at a temperature of 25° C. and a humidity of 45% and may be calculated by, for example, the following method.
The sliding counterpart is prepared as a rotary member and the torque is measured by pressing the sliding member against the sliding counterpart so that load is applied thereto. The load to be applied is measured simultaneously in a load cell. Resistance of the sliding member is obtained from the measured torque and the diameter of the shaft, and the frictional coefficient μ is calculated from Expression F=μN based on the load measured by the load cell.
The shape and existence of the first sliding surfaces or the second sliding surface may be confirmed by observing the sliding surfaces of the sliding member with an optical microscope, a laser microscope, and a scanning electron microscope (SEM).
As described above, in the sliding member according to the present embodiment, since the second sliding surface is disposed in the region on the substrate where the first sliding surfaces are not provided, DLC is not removed from the substrate even if the entire surface of the substrate is not covered with DLC. Further, even if the material included in the second sliding surface has a frictional coefficient higher than that of DLC, the frictional coefficient of the sliding member is 0.12 or less, which means that the sliding member keeps its low friction property.
Further, if a plurality of first sliding surfaces are provided, and a second sliding surface is provided in a region in which the first sliding surfaces are separated, since the material of the second sliding surface is disposed in contact with DLC, removal of DLC from the substrate may be controlled more reliably.
A ratio of the first sliding surfaces and the second sliding surface may be suitably determined so as not to cause removal of DLC from the substrate. For example, the ratio of the first sliding surfaces is desirably equal to or greater than 20% to equal to or less than 90% of the entire area of the sliding surface. More desirably, the first sliding surfaces are distributed uniformly on the entire sliding surface as a plurality of regions.
Regarding a separation distance (pitch interval) of adjacent first sliding surfaces, it is only necessary to consider the separation distance from a contact area between the sliding counterpart and the sliding member, and an amount of deformation of the sliding member not to cause the deformation of the sliding member during sliding and not to cause the removal of DLC. For example, the pitch interval is equal to or greater than 1 μm to equal to or smaller than 1 mm, the upper limit is 1 mm or less, and more preferably 500 μm or less. If the sliding surface has a periodical shape, the pitch means the period.
The thickness of DLC of the first sliding surfaces is, for example, equal to or greater than 0.1 μm to equal to or less than 10 μm. More preferably, the thickness is equal to or greater than 0.5 μm to equal to or less than 5 μm. The roughness (unevenness) of the substrate is desirably smaller than the thickness of DLC.
The separation distance between the adjacent first sliding surfaces is desirably inside the contact surface of the sliding member with the sliding counterpart. This is because the first sliding surfaces and the second sliding surface exist inside the contact surface.
The material included in the second sliding surface is a self-lubricating material. For example, at least one of MoS2, WS2, and BN which are known as solid lubricants may be used. At least one of resins, such as PTFE, polyacetal (POM), polyethylene (PE), and polyphenylenesulfide (PPS) may also be used. Therefore, the material included in the second sliding surface includes, for example, at least one of MoS2, WS2, BN, PTFE, POM, PE, and PPS.
The material included in the second sliding surface may be disposed with no space left or disposed as grains when disposed between a plurality of first sliding surfaces. The latter is more desirable. It is considered that, if the material included in the second sliding surface is disposed as grains, the material may easily enter the roughness in the thickness direction of DLC (for example, 1/10 or less of the size of the second sliding surface, i.e., the separation distance between adjacent first sliding surfaces), and may follow the deformation (film deformation) of the entire sliding member.
As will be described as an unexpected effect in Example, the sliding member according to the present embodiment has a frictional coefficient lower than that of a sliding member of which entire sliding surface is formed by DLC. This is significant when the second sliding surface is formed by at least one of MoS2 and WS2. Although details are unknown, it is considered that these materials are lamellar crystals, and a conforming layer is easily formed when DLC-derived graphite and the lamellar crystals slide against each other.
DLC is disposed directly on the substrate. The substrate may be formed by any materials. Examples of materials used in the known DLC manufacturing process may include metals, such as SUS, aluminum, copper, nickel, tungsten, chromium, titanium, gold, silver, and platinum. Engineering plastics, such as polyetheretherketone (PEEK) may also be used. If engineering plastics are used, DLC may be formed by a low temperature process.
In the sliding member, another substrate may be provided on the side opposite to the side on which DLC is disposed.
DLC may be provided on the substrate by, for example, plasma CVD, ionization vapor deposition, arc ion plating, and sputtering. The sliding surface of arbitrary pattern or arbitrary shape may be obtained by using a mask or by etching.
The material included in the second sliding surface may be disposed on the substrate by coating or by printing. Alternatively, the material may be embedded between the first sliding surfaces using a roller (roller burnishing), or surface-formation of DLC may be conducted after the first sliding surfaces and the space formed between the first sliding surfaces are coated uniformly with a granular material. Alternatively, after forming the second sliding surfaces, the first sliding surfaces may be formed between adjacent second sliding surfaces.
In disposing a material included in the second sliding surface, a granular material may be used. A granular material may be included in, for example, resin which may be coated by drying at a normal temperature, curing at a normal temperature, thermally setting, and other methods.
The sliding member according to the present embodiment which is cylindrical column or cylindrical in shape may be obtained by rolling up, together with the substrate, the flat, i.e., sheet-shaped sliding member having the first sliding surfaces and the second sliding surface.
In the foregoing description, the DLC segments are disposed in the dot pattern in the sliding member according to the present embodiment. The shape of the dot may be round, rectangular, rhombus, polygon, or a plurality of these shapes may be selected.
A sliding member according to a second embodiment of the present invention relates to a sliding member provided with a flat substrate and a sliding surface which is also flat. Other configurations are the same as those of the first embodiment.
In the case of
A sliding member according to a third embodiment slides relatively against a sliding counterpart by reciprocating or rotating. Other configurations are the same as those of the first and the second embodiments.
The sliding counterpart may be made of, for example, SUS, SUJ2, and a member of which sliding surface is nickel-plated. The sliding counterpart may be a rod, such as a shaft, a plate, or a sphere.
The sliding member moves relative to the sliding counterpart while being in contact with the sliding body on a sliding surface. The relative movement refers to the movement of at least one of the sliding member and the sliding counterpart. The movement is, for example, reciprocation or rotation. Rotation may be conducted in, for example, the sliding surface, or may be conducted as illustrated in
The present invention is used desirably in a case where, for example, a cylindrical sliding member as illustrated in the right-hand diagrams of
At least one of the sliding member and the sliding counterpart may be provided with a driving unit which causes a sliding movement (for example, at least one of reciprocation and rotation. The sliding member may be driven by the driving unit. Alternatively, a sliding device may have the sliding member, the sliding counterpart, and the driving unit which drives at least one of the sliding member and the sliding counterpart.
The sliding device may be provided in an electrophotographic image forming apparatus. The sliding device may be disposed at a conveyance unit which conveys a recording medium, such as paper, on which an image is recorded. If load is applied to a roller rotating in the conveyance unit, removal of DLC is controllable with low friction and the recording medium may be conveyed smoothly by employing the sliding device of the present invention. The sliding device of the present embodiment is applicable to an apparatus provided with a conveying mechanism, such as a 2D printer and a 3D printer. As an example, a configuration of an electrophotographic 3D printer 4 is schematically illustrated in
Evaluation on Friction in Sliding Portions
The frictional coefficient is measured with a friction measuring apparatus designed by CANON KABUSHIKI KAISHA. A shaft of SUS303 as a rotary member is rotated at a constant rotational speed by a motor. A member on which a solid lubricating film made in Example is formed is pressed against the shaft so that certain specific load is applied. Then, the torque is measured. Since load is applied, a contact portion is not linear but planar in shape. The load to be applied is measured simultaneously in a load cell. The frictional coefficient is calculated from the measured torque, the diameter of the shaft, the rotational speed, and the load.
The measurement conditions are as follows:
Material of shaft: SUS303
Rotational speed of shaft: 100 rpm
Diameter of shaft: 14 mm
Load: 20N
Atmosphere: atmospheric air
Temperature: room temperature
Contact length between sliding portion and shaft: 5 mm
DLC segments are formed on a flat SUS 440 substrate. The segment is 200-μm square. DLC is formed to the thickness of 1 μm by CVD using a mask with a gap of 50 μm. Then, WS2 (Tungmic B: manufactured by Japanese Lubricant Corporation) of an average particle diameter of 0.2 m is coated to the gap, and the entire surface is pressurized to cause WS2 to be held in the gap. WS2 on DLC is removed with a squeegee. It is confirmed with a laser microscope that WS2 is disposed between a plurality of surfaces (DLC) and a plurality of surfaces.
DLC is formed on the entire surface of a substrate made of SUS440. Other procedures are the same as those of Example 1.
Segmented DLC is formed on a substrate made of SUS440 in the same manner as in Example 1. The segmented DLC is 200-μm square. The segments are arranged at intervals of 50 μm with nothing formed therebetween.
Only WS2 is provided on a substrate made of SUS440. A substrate with roughened surface of SUS440 is used and WS2 is pressurized against the substrate so that WS2 is held thereon.
Results of evaluation on friction in the sliding portions of Example 1 and Comparative Examples 1 to 3 are shown in
In Comparative Example 1, the frictional coefficient increases rapidly in a range between 3000 seconds and 4000 seconds. This is because the film has been removed.
In Comparative Example 2, time until the frictional coefficient increases (in the middle of 1000 seconds and 2000 seconds) is short. This is because the film has been worn out.
The frictional coefficient in Example 1 is lower than those in Comparative Examples 1 and 2 by 30%, which means that sliding portion of Example 1 can be slid for a longer time than those of Comparative Examples 1 and 2.
The frictional coefficient in Comparative Example 3 is originally high, and the film is worn out before 1000 seconds.
Surprisingly, although Example 1 has a member of which frictional coefficient is higher than that of DLC on the sliding surface, the frictional coefficient on the sliding surface is lower than that of Comparative Example 1 in which only DLC is provided.
As described above with reference to the embodiment and Examples, the sliding member according to the present invention in which the first sliding surfaces have DLC and the second sliding surface has a material having a frictional coefficient higher than that of DLC at a temperature of 25° C. and a humidity of 45%, removal of DLC from the substrate is controllable. The sliding member of the present invention may be used as an oilless sliding member without using oil and grease.
Although details are unknown, if the humidity is lower than 45% at a temperature of 25° C., the frictional coefficient of the material included in the second sliding surface can be lower than that of DLC. It is considered that, the humidity on the sliding surface becomes lower as the sliding time becomes longer, and the frictional coefficient of DLC becomes higher when the humidity becomes lower, but in the present invention, the member included in the second sliding surface lowers the frictional coefficient to compensate for the increase in the frictional coefficient of DLC. As a result, a desirable low friction sliding member may be provided.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2015-039401, filed Feb. 27, 2015 which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-039401 | Feb 2015 | JP | national |
