Slide part and surface processing method of the same

Abstract

A slide part has a surface structure in which there are at least two periodic structures among a first periodic structure with a period of 10 nm to 100 nm inclusive and a depth of 5 nm to 50 nm inclusive, a second periodic structure with a period of 100 nm to 1000 nm inclusive and a depth of 20 nm to 500 nm inclusive, and a third periodic structure with a period of 1000 nm to 10000 nm inclusive and a depth of 100 nm to 3000 nm inclusive, in which one of the at least two periodic structures is formed on the other periodic structure.

Claims

1. A slide part comprising at least one surface structure among a first surface structure in which a first periodic structure with a period of 10 nm to 100 nm inclusive and a depth of 5 nm to 50 nm inclusive is formed on a second periodic structure with a period of 100 nm to 1000 nm inclusive and a depth of 20 nm to 500 nm inclusive, a second surface structure in which the first periodic structure is formed on a third periodic structure with a period of 1000 nm to 10000 nm inclusive and a depth of 100 nm to 3000 nm inclusive, and a third surface structure in which the first periodic structure is formed on the second periodic structure and the second periodic structure is formed on the third periodic structure.

2. The slide part according to claim 1, wherein at least one of the second periodic structure and the third periodic structure is a ripple structure.

3. The slide part according to claim 2, wherein the ripple structure of the at least one of the second periodic structure and the third periodic structure is formed in a direction orthogonal to a slide direction of the slide part.

4. The slide part according to claim 1, wherein the at least one surface structure is formed at least on an edge of the slide part.

5. The slide part according to claim 2, wherein the at least one surface structure is formed at least on an edge of the slide part.

6. The slide part according to claim 3, wherein the at least one surface structure is formed at least on an edge of the slide part.

7. The slide part according to claim 1, wherein at least one of the second periodic structure and the third periodic structure is formed by irradiation of a gas cluster ion beam.

8. The slide part according to claim 2, wherein the at least one of the second periodic structure and the third periodic structure is formed by irradiation of a gas cluster ion beam.

9. The slide part according to claim 3, wherein the at least one of the second periodic structure and the third periodic structure is formed by irradiation of a gas cluster ion beam.

10. A method of processing a surface of a slide part using a gas cluster ion beam, comprising radiating the gas cluster ion beam to the surface of the slide part from a direction parallel to a slide direction of the slide part in order to form, on the surface of the slide part, at least one surface structure among a first surface structure in which a first periodic structure with a period of 10 nm to 100 nm inclusive and a depth of 5 nm to 50 nm inclusive is formed on a second periodic structure with a period of 100 nm to 1000 nm inclusive and a depth of 20 nm to 500 nm inclusive, a second surface structure in which the first periodic structure is formed on a third periodic structure with a period of 1000 nm to 10000 nm inclusive and a depth of 100 nm to 3000 nm inclusive, and a third surface structure in which the first periodic structure is formed on the second periodic structure and the second periodic structure is formed on the third periodic structure.

11. A method of processing a surface of a slide part using a gas cluster ion beam, the method comprising radiating the gas cluster ion beam to the surface of the slide part in order to form, on the surface of the slide part, at least one surface structure among a first surface structure in which a first periodic structure with a period of 10 nm to 100 nm inclusive and a depth of 5 nm to 50 nm inclusive is formed on a second periodic structure with a period of 100 nm to 1000 nm inclusive and a depth of 20 nm to 500 nm inclusive, a second surface structure in which the first periodic structure is formed on a third periodic structure with a period of 1000 nm to 10000 nm inclusive and a depth of 100 nm to 3000 nm inclusive, and a third surface structure in which the first periodic structure is formed on the second periodic structure and the second periodic structure is formed on the third periodic structure, with an angle formed by the gas cluster ion beam to be radiated and a line normal to the surface of the slide part being within a range from 30 degrees to 75 degrees inclusive.

12. A method of processing a surface of a slide part using a gas cluster ion beam, the method comprising radiating the gas cluster ion beam to the surface of the slide part from a direction parallel to a slide direction of the slide part and another gas cluster ion beam to the surface of the slide part from a direction opposite to the former direction in order to form, on the surface of the slide part, at least one surface structure among a first surface structure in which a first periodic structure with a period of 10 nm to 100 nm inclusive and a depth of 5 nm to 50 nm inclusive is formed on a second periodic structure with a period of 100 nm to 1000 nm inclusive and a depth of 20 nm to 500 nm inclusive, a second surface structure in which the first periodic structure is formed on a third periodic structure with a period of 1000 nm to 10000 nm inclusive and a depth of 100 nm to 3000 nm inclusive, and a third surface structure in which the first periodic structure is formed on the second periodic structure and the second periodic structure is formed on the third periodic structure.

13. A method of processing a surface of a slide part using a gas cluster ion beam, the method comprising radiating the gas cluster ion beam to the surface of the slide part in order to form, on the surface of the slide part, at least one surface structure among a first surface structure in which a first periodic structure with a period of 10 nm to 100 nm inclusive and a depth of 5 nm to 50 nm inclusive is formed on a second periodic structure with a period of 100 nm to 1000 nm inclusive and a depth of 20 nm to 500 nm inclusive, a second surface structure in which the first periodic structure is formed on a third periodic structure with a period of 1000 nm to 10000 nm inclusive and a depth of 100 nm to 3000 nm inclusive, and a third surface structure in which the first periodic structure is formed on the second periodic structure and the second periodic structure is formed on the third periodic structure, with an angle formed by the gas cluster ion beam to be radiated and a line normal to the surface of the slide part being within a range from 30 degrees to 75 degrees inclusive and with another gas cluster ion beam being irradiated to the surface of the slide part from a direction opposite to an irradiation direction of the former gas cluster ion beam.

14. The method according to any one of claims 10 to 13, wherein at least one of the second periodic structure and the third periodic structure is a ripple structure.

15. The method according to claim 14, wherein the ripple structure of the at least one of the second periodic structure and the third periodic structure is formed in a direction orthogonal to the slide direction of the slide part.

16. The method according to any one of claims 10 to 13, wherein the surface structure is formed at least on an edge of the slide part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows the occurrence of adhesion in press working (the prior art) even using a mold having a very flat surface, specifically, an illustration (a) in FIG. 1 shows the state before the press working and an illustration (b) in FIG. 1 shows the state after the press working;

(2) FIG. 2 shows transfer particles observed by a scanning electron microscope;

(3) FIG. 3 schematically shows the occurrence of adhesion in press working (the prior art) using a mold with periodic projections and depressions on its surface, specifically, an illustration (a) in FIG. 3 shows the state before the press working and an illustration (b) in FIG. 3 shows the state after the press working;

(4) FIG. 4 schematically shows the occurrence of adhesion in press working (the prior art) using a mold with irregular projections and depressions on its surface, specifically, an illustration (a) in FIG. 4 shows the state before the press working and an illustration (b) in FIG. 4 shows the state after the press working;

(5) FIG. 5 shows that no adhesion occurs in press working using the slide part (mold) according to the present invention, specifically, an illustration (a) in FIG. 5 shows the state before the press working and an illustration (b) in FIG. 5 shows the state after the press working;

(6) FIG. 6 shows a set of the images observed by an atomic force microscope and a schematic view, specifically, an image (a) in FIG. 6 shows an observational result of the shapes of the first to third periodic structures observed by the atomic force microscope; an image (b) in FIG. 6 shows an observational result of the shapes of the first and second periodic structures observed by the atomic force microscope, an image (c) in FIG. 6 is a schematic view of the section enclosed by the square in the image (b) in FIG. 6;

(7) FIG. 7 shows schematic views of the periodic structures, specifically, an illustration (d) in FIG. 7 is a schematic view of the first to third periodic structures in FIG. 6(a), and an illustration (e) in FIG. 7 is an enlarged view of the part indicated by the double-headed arrow in the illustration (d) in FIG. 7 and schematically shows the surface structure in which the first, second and third periodic structures are combined;

(8) FIG. 8 shows a schematic view of the mold and images observed by the scanning electron microscope, specifically, an illustration (a) in FIG. 8 is a schematic view of a punch mold, an image (b) in FIG. 8 shows an observational result of the section enclosed by the square in the illustration (a) in FIG. 8, and an illustration (c) in FIG. 8 is an enlarged view of the section enclosed by the circle in the image (b) in FIG. 8;

(9) FIG. 9 shows a procedure of a sliding test performed in examples and comparative examples, specifically, an illustration (a) in FIG. 9 shows a step in which a workpiece is set in a certain position, an illustration (b) in FIG. 9 shows a step in which the punch mold is pounded into the workpiece, an illustration (c) in FIG. 9 shows a step in which the punch mold is pulled out of the workpiece;

(10) FIG. 10A lists the results of the sliding test performed in examples 1 to 10;

(11) FIG. 10B lists the results of the sliding test performed in examples 11 to 20; and

(12) FIG. 10C lists the results of the sliding test performed in examples 21 to 25 and comparative examples.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(13) As described above, if small projections and depressions are formed on the surface of a slide part in advance, the lubricant applied to the slide part or its counterpart before processing is stored in the depressions (micro pools) on the surface. If there is no space to which the lubricant escapes when the slide part and its counterpart make contact each other, the lubricant is encapsulated in the micro pools and supplied to the friction interface with this state maintained.

(14) Even when a lubricant injection mechanism supplies a large amount of lubricant to the friction interface, however, a continuous fluid lubrication film is rarely formed over the entire friction interface. This is particularly true for, for example, press working. There are two types of contact states on the friction interface: a solid/solid contact state, in which the slide part and its counterpart make contact each other, and a solid/liquid contact state, in which the slide part and the lubricant in micro pools make contact each other. In the solid/solid contact state, boundary lubrication is dominant and metallic bonds also occur at the friction interface. On the other hand, in the solid/liquid contact state, a high hydrostatic fluid pressure is applied to the lubricant in micro pools and a state similar to fluid lubrication is achieved.

(15) For example, if a mold, which is a slide part 1, has a very flat surface, since a lubricant 2 escapes from the friction interface between the mold and a workpiece 3 as shown in FIG. 1, the workpiece 3 readily adheres to the mold. Reference numeral 4 indicates an adhesive portion (only one adhesive portion is indicated by the reference numeral to eliminate complexity of the drawing). FIG. 2 shows the adhesion of the workpiece 3 to the mold observed by a scanning electron microscope. Transfer particles (enclosed by the circles in the figure) are observed which are formed because parts of workpiece are left on the surface of the mold when the adhesive part 4 of the workpiece 3 and the mold is separated. It is found from the observation that many transfer particles have a diameter of hundreds of nanometers to one micrometer. When periodic projections and depressions 1a are formed on the surface of the mold as in the prior art, the solid/solid contact state is relieved and adhesion of the workpiece 3 is reduced because the lubricant 2 is supplied to the friction interface as shown in FIG. 3. In addition, when irregular projections and depressions 1b are formed on the surface of the mold as shown in FIG. 4, adhesion of the workpiece 3 is also reduced. In such conditions, however, it is impossible to prevent adhesion to the workpiece 3. This is because boundary lubrication is dominant in the solid/solid contact state as described above.

(16) There are projections and depressions, flaws, crystal grain boundaries, accumulated processing strain, etc. on the surface of the workpiece 3. Friction between these uneven portions (e.g. high projections) and the surface of the mold causes adhesion with a size of approximately 100 nm to 1 m. The inventors found that a significantly larger amount of lubricant could be supplied to the friction interface as compared with the prior art by forming at least two types of micro pools on the surface of the slide part 1 among micro pools with a diameter similar to the diameter (approximately from 100 nm to 1 m) of the adhesion, micro pools with a period (from 1 m to 10 m) larger than the size of the adhesion, and micro pools with a period (from 10 nm to 100 nm) smaller than the size of the adhesion. Specifically, the slide part according to the present invention has a surface structure including at least two periodic structures among a first periodic structure with a period of from 10 nm to 100 nm inclusive and a depth of from 5 nm to 50 nm inclusive, a second periodic structure with a period of from 100 nm to 1000 nm inclusive and a depth of from 20 nm to 500 nm inclusive, and a third periodic structure with a period of from 1000 nm to 10000 nm inclusive and a depth of from 100 nm to 3000 nm inclusive, in which one of the at least two periodic structures is formed on the other periodic structure.

(17) If the slide part 1 according to the present invention is used for press working or other processing, a continuous fluid lubrication film is formed all over the friction interface, thereby preventing adhesion of the workpiece 3 (see FIG. 5). The reason why fluid lubrication can be achieved by micro pools (with a period of 1 m to 10 m) having a larger diameter than that of a transfer particle is assumed to be that the lubricant is supplied to the friction interface in multiple stages through wedge effects in the order of a micrometer (see non-patent literature 1 for wedge effects). Accordingly, the surface structure of the slide part should be wedge-shaped. On the other hand, a mechanism for using micro pools (with a period of 10 nm to 100 nm) having a smaller diameter than that of a transfer particle to relieve the contact pressure of a micro solid contact caused in the liquid lubrication state at the friction interface is considered. Such effects can suppress the adhesion of the workpiece 3 to the surface of the slide part 1.

(18) The inventors also found that the surface structure could be formed on the slide part by radiating a gas cluster ion beam to the slide part. Processing by a gas cluster ion beam is a beam process, so a gas cluster ion beam can be radiated to a part of the slide part, which is, for example, an edge of the slide part. A fine ripple structure can be formed on the surface of the slide part by radiating a gas cluster ion beam so that the angle formed by the gas cluster ion bean and a line normal to the surface of the slide part becomes typically 30 degrees to 75 degrees inclusive. It is preferable that the lines of the ripple structure extend in a direction orthogonal to the slide direction for storing the lubricant in micro pools.

(19) The gas cluster ion beam apparatus disclosed by, for example, Japanese Patent No. 3994111 can be used to form the above surface structure on the surface of the slide part. Clusters are generated by injecting a source gas from a nozzle to a cluster generating chamber kept under vacuum to aggregate gas molecules. The clusters are lead to an ionization chamber as a gas cluster beam through a skimmer. In the ionization chamber, an ionizer radiates an electron beam such as thermal electrons to neutral clusters to ionize them. The ionized gas cluster beam is accelerated by an accelerating electrode. The incident gas cluster ion beam is adjusted by an aperture to have a predetermined beam diameter and radiated to the slide part. When, for example, the surface of the slide part made of electrical insulator is flattened, gas cluster ion may be neutralized in advance by electrons. It is possible to control the angle at which the gas cluster ion beam is radiated to the surface of the slide part by slanting the slide part. In addition, the gas cluster ion beam can be radiated in any direction by moving the slide part vertically or horizontally or rotating the slide part using an X-Y stage or rotation mechanism.

(20) There is a mechanism by which a hydrostatic fluid pressure is generated in the water stored in micro pools because moisture in the normal atmosphere adsorbed on the surfaces of the slide part or the counterpart functions as a lubricant and generates a hydraulic pressure even though a lubricant that causes a hydrostatic fluid pressure to generate in micro pools is not applied to the slide part or the counterpart. Accordingly, application of a lubricant is not necessarily be required in the present invention.

(21) Examples according to the present invention and comparative examples for confirming the effects of the examples will be described below.

EXAMPLE 1

(22) A punch mold, which is an example of the slide part 1, was created by grinding work. The punch mold is made of ultrahard material (Japanese Industrial Standards V20). The punch mold has a rectangular (1 mm2 mm) bottom. To a side of the punch mold, a gas cluster ion beam was radiated in parallel with a slide direction of the punch mold with respect to a workpiece 3 so that the angle formed by the normal line of the surface of the punch mold and the gas cluster ion beam was 60 degrees. The slide direction is indicated by the arrows in FIGS. 6(a) and 9(a) and 9(c). An argon gas was used as the source gas. The acceleration voltage was 20 kV and the radiation dose amount was 310.sup.18 ions/cm.sup.2. Upon completion of radiation, the punch mold was observed by a scanning electron microscope and atomic force microscope. Periodic structures were observed on the side and the edge of the punch mold. The shapes of the periodic structures observed by the atomic force microscope are shown in FIGS. 6 and 7. The periodic structures observed by the scanning electron microscope are shown in FIG. 8. Each of the periodic structures had a ripple structure in which lines extend in a direction orthogonal to the slide direction. In detailed observation, as shown in FIG. 7(e), three types of periodic structures were combined. The first periodic structure had a period of 20 nm to 70 nm and an average depth of 10 nm, the second periodic structure had a period of 200 nm to 500 nm and an average depth of 75 nm, and the third periodic structure had a period of 2000 nm to 3000 nm and an average depth of 320 nm. In addition, of these periodic structures, the first periodic structure had a particle structure (see FIG. 6(c)) and the second and third periodic structures had a ripple structure in which lines extend in a direction orthogonal to the slide direction (see FIG. 6(b) for the second periodic structure or FIG. 6(a) for the third periodic structure.).

(23) A sliding test was performed, in which a stainless steel (Japanese Industrial Standards SUS304) plate with a thickness of 0.1 mm to which a lubricant (naphthene series mineral oil) was applied was punched by the punch mold that was set in a press machine (see FIG. 9). The stainless steel (Japanese Industrial Standards SUS304) plate is equivalent to the workpiece 3. Reference numeral 7 indicates a die. Whether a transfer particle 5 was present on a side wall of the punch mold was observed by the scanning electron microscope every hundred thousands of shots and the composition of the particle was analyzed by energy dispersive X-ray analysis. No transfer particle 5 from the workpiece 3 (stainless steel plate) was observed until at least ten million shots (see FIG. 10A). In FIGS. 10A to 10C, EE indicates an example; CE indicates a comparative example; AccV indicates an acceleration voltage (kV), Dose indicates a dose amount (ions/cm.sup.2), IrrA indicates a radiation angle (degree); Prd indicates period (nm); Dpth indicates a depth (nm); S50 indicates five hundred thousand shots; S100 indicates one million shots; S200 indicates two million shots; S400 indicates four million shots; S1000 indicates ten million shots; symbol x indicates no generation of adhesion, and symbol indicates occurrence of adhesion.

EXAMPLES 2 to 21

(24) First to third periodic structures were formed on the surface of the punch mold by changing the radiation conditions of a gas cluster ion beam, and the same slide test as in example 1 was performed. The radiation conditions of the gas cluster ion beam, the periods and depths of the first to third periodic structures corresponding to the radiation conditions, and the presence or absence of a transfer particle 5 on the side wall of the punch mold are shown in FIGS. 10B and 10C.

(25) In examples 1 to 17, the radiation angle of the gas cluster ion beam was changed.

(26) In examples 1, 18, and 19, the acceleration voltage of the gas cluster ion beam was changed.

(27) In examples 1, 20 and 21, the dose amount of the gas cluster ion beam was changed.

EXAMPLES 22 to 24

(28) The material of the slide part was changed, but the other conditions were the same as in example 1. In example 22, the material of the punch mold was die steel SKD11 (Japanese Industrial Standards) and the material of the workpiece 3 was stainless steel SUS304 (Japanese Industrial Standards). In example 23, the material of the punch mold was die steel SKD11 (Japanese Industrial Standards) and the material of the workpiece 3 was phosphor bronze. In example 24, the material of the punch mold was superhard material (V20) and the material of the workpiece 3 was phosphor bronze. The same sliding test as in example 1 was performed. The radiation conditions of the gas cluster ion beam, the periods and depths of the first to third periodic structures corresponding to the radiation conditions, and the presence or absence of a transfer particle 5 on the side wall of the punch mold are shown in FIG. 10C.

EXAMPLE 25

(29) A punch mold was created by grinding work. The material of the punch mold was superhard material (V20). The punch mold had a rectangular (1 mm2 mm) bottom. A periodic structure was formed on a side of the punch mold by an ultraprecise five-axis working machine. The periodic structure is a line-and-space structure in which lines extend in a direction orthogonal to the slide direction. Then, the same slide test as in example 1 was performed. The periods and depths of the second and third periodic structures and the presence or absence of a transfer particle 5 on the side wall of the punch mold are shown in FIG. 10C.

COMPARATIVE EXAMPLE 1

(30) The radiation angle of the gas cluster ion beam was set to 0 degrees, at which the radiation direction matches the direction of a line normal to the side of the punch mold. The other conditions were the same as in example 1. In this processing, only the first periodic structure was formed on the side of the punch mold and the same slide test as in example 1 was performed. The radiation conditions of the gas cluster ion beam, the period and depth of the first periodic structure corresponding to the radiation conditions, and the presence or absence of a transfer particle 5 on the side wall of the punch mold are shown in FIG. 10C.

COMPARATIVE EXAMPLE 2

(31) Only the second periodic structure was formed on the side of the punch mold. The other conditions were the same as in example 25. The same slide test as in example 1 was performed. The period and depth of the second periodic structure and the presence or absence of a transfer particle 5 on the side wall of the punch mold are shown in FIG. 10C.

COMPARATIVE EXAMPLE 3

(32) Only the third periodic structure was formed on the side of the punch mold. The other conditions were the same as in example 25. The same slide test as in example 1 was performed. The period and depth of the third periodic structure and the presence or absence of a transfer particle 5 on the side wall of the punch mold are shown in FIG. 10C.

COMPARATIVE EXAMPLE 4

(33) A punch mold was created in the same conditions as in example 1 except that the radiation direction of the gas cluster ion bean was changed. The radiation direction of the gas cluster ion bean was changed so as to be parallel with the slide direction. The first to third periodic structures were formed so that the lines in the ripple structure, which were the second periodic structure, extended in a direction parallel with the slide direction. The same slide test as in example 1 was performed. The periods and depths of the first to third periodic structures and the presence or absence of a transfer particle 5 on the side wall of the punch mold are shown in FIG. 10C.

COMPARATIVE EXAMPLE 5

(34) A punch mold was created in the same conditions as in example 1 except that the radiation direction of the gas cluster ion bean was changed. The radiation direction of the gas cluster ion bean was changed so that the angle formed by the radiation direction and the slide direction becomes 45 degrees. The first to third periodic structures were formed so that the angle formed by the line in the ripple structure, which were the second periodic structure, and the slide direction became 45 degrees. The same slide test as in example 1 was performed. The periods and depths of the first to third periodic structures and the presence or absence of a transfer particle 5 on the side wall of the punch mold are shown in FIG. 10C.

(35) The results of examples 1 to 21 and comparative example 1, the following facts are found. When only the first periodic structure is formed, a transfer particle 5 adheres to the surface of the press mold even if the press count is as small as five hundred thousand shots. On the other hand, when at least two of the first, second, and third periodic structures are formed on the surface of the press mold, generation of a transfer particle 5 is significantly suppressed. When all of the first, second, and third periodic structures are formed as shown in examples 7 to 15, further significant effects can be obtained and no transfer particle 5 is generated until four million shots. It is sufficient to set the angle formed by the radiation direction of the gas cluster ion beam and the line normal to the side of the press mold to 30 degrees to 75 degrees inclusive in order to form all of the three periodic structures.

(36) The results of examples 1 and 22 to 24 show that the effects of the present invention do not depend on the material of the slide part.

(37) Consideration of example 25 and comparative examples 2 and 3 shows that no effects are obtained if only one of the three periodic structures is formed. At least two of the three periodic structures need to be formed on the punch mold to obtain effects.

(38) Consideration of example 1 and comparative examples 4 and 5 shows that adhesion can be prevented if the slide part has a ripple structure in which lines extend in a direction substantially orthogonal to the slide direction of the slide part.

(39) Besides the above examples, the gas cluster ion beam can also be radiated to ceramic or silicon materials to form at least two periodic structures for improvement of the sliding durability of the slide part. The present invention takes advantage of an essential phenomenon in which the gas cluster ion beam forms periodic structures such as ripples while flattening acute projections. Accordingly, it will be clear that various conditions such as the type of the gas cluster and acceleration energy, and the materials of the slide part and lubricant are not specially limited. In addition, the above surface structure does not need to be present on all slide areas and only needs to be present, for example, at an edge of the slide part.

(40) In the above examples, as shown in FIG. 7(e), the first periodic structure and/or the second periodic structure were formed on a part of the third periodic structure that faces the slide part 1 when the slide part 1 (punch mold) was inserted into the workpiece 3. This is because the gas cluster ion beam was radiated to the side of the slide part 1 from only one direction; if the gas cluster ion beam is radiated from the opposite direction to this direction under appropriate radiation conditions, the first periodic structure and/or the second periodic structure can be formed on the back of the above part of the third periodic structure. In consideration of the fact that the friction resistance when the slide part 1 is inserted into the workpiece 3 is larger than that when the slide part 1 is pulled out of the workpiece 3, the first periodic structure and/or the second periodic structure are preferably formed on the above portion of the third periodic structure and the first periodic structure and/or the second periodic structure are preferably also formed on the back of the above portion of the third periodic structure. This is also true when the first periodic structure and the second periodic structure are formed on the surface of the slide part 1.

(41) The foregoing description of the embodiments of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiment was chosen and described to provide the illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.