JP2013057365A - Slide bearing for adaptive front-lighting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slide bearing which can be appropriately assembled in an adaptive front-lighting system.SOLUTION: The slide bearing (sintered bearing) 10 made of sintered metal is formed by sintering pressurized powder body of raw material powder mainly consisting of metal powder, and is equipped in the adaptive front-lighting system 1 to rotatably support shafts to be supported (a shaft part 4a and a shaft part 5a) in a non-oil-impregnated state. The raw material power for manufacturing the sintered bearing 10 is formed by adding Sn powder, C powder and Ni powder as fillers, to Cu powder as a primary raw material. The raw material powder contains no Fe powder. The ratios of the Sn powder, C powder and Ni powder in the total raw material powder are 7-11 wt.%, 3-7 wt.%, and 4-6 wt.%, respectively.

Description

  The present invention relates to a sliding bearing, and is particularly suitable for a variable light distribution headlamp device that can vary the light distribution angle of the headlamp in the vertical and horizontal directions among headlamp devices mounted on vehicles such as automobiles. The present invention relates to a slide bearing that can be incorporated.

  Vehicles such as automobiles are usually equipped with a headlight device that illuminates the front side of the vehicle in the traveling direction. As a conventional headlight device, the light distribution angle (optical axis) of the headlamp is set in the vertical direction. In general, those that can be changed only by (which can only switch between a low beam and a high beam) are common. However, such a headlamp device cannot sufficiently illuminate the front side in the turning direction, which is the direction most visible to the driver when the vehicle turns.

  Therefore, a variable light distribution headlamp device (abbreviated as “AFS”. “AFS” is a combination of an acronym of Adaptive Front-lighting System) has been developed and mounted on various vehicles. Has reached. This variable light distribution type headlamp device is configured to change the light distribution angle of the headlamp not only in the vertical direction but also in the horizontal direction in accordance with the steering angle of the steering wheel. At times, the light distribution is automatically directed to the front side in the turning direction, which can contribute to the improvement of safety particularly during night driving. The variable light distribution type headlamp device has a light source and a reflector as described in, for example, Patent Document 1 below, and includes an optical system that irradiates a light beam, a reflector according to a steering angle of a steering wheel, and the like. A light distribution variable means that rotates in the vertical and horizontal directions and a bearing that rotatably supports the rotating shaft of the reflector are provided as main components.

JP 2005-125851 A

  As described above, the variable light distribution headlight device is useful as it can improve safety during night driving and reduce the probability of traffic accidents. Compared with the conventional headlamp device that can be changed only in the direction, the structure (mechanism) becomes complicated and expensive. For this reason, the variable light distribution type headlamp device is only installed in some high-end cars, and it is difficult to say that it is widely used. Therefore, in order to promote the spread of the variable light distribution type headlamp device, it is urgent to reduce the cost.

  Therefore, the inventor of the present application, among the components of the variable light distribution type headlamp device, includes a plurality of members such as an inner ring, an outer ring, a cage, and a rolling element as a bearing that supports a rotating shaft such as a reflector. We considered replacing the rolling bearing with a plain bearing composed of a single cylindrical member. A plain bearing may be a solid metal material (melted material), but it is made of a plastic bearing in order to effectively enjoy the cost reduction effect of replacing a rolling bearing with a sliding bearing. We actively considered the adoption.

  However, since the inside of the headlamp device becomes hot when the light source is turned on, the resin bearing may be thermally deformed no matter how much resin having excellent heat resistance is used. Further, in the case of a resin bearing, the bearing surface may be deformed / damaged due to the influence of vibration during traveling. Therefore, when a resin bearing is used for rotating support of the components of the headlamp device, it is difficult to stably maintain a desired support capability, and the operability of the headlamp device is likely to be lowered.

  In view of such circumstances, an object of the present invention is to provide a plain bearing that can contribute to cost reduction without deteriorating basic performance including operability of a variable light distribution type headlamp device. It is in.

  In order to solve the above-described problems, the present invention provides a slide bearing provided in a variable light distribution type headlamp device in which the light distribution angle of the headlamp is variable in the vertical and horizontal directions, and the metal powder is used as a main raw material. A plain bearing is provided which is obtained by sintering a green compact of the raw material powder and supports the shaft to be supported so as to be rotatable in a non-oil-containing state.

  In this way, a slide bearing (hereinafter also referred to as a “sintered bearing”) obtained by sintering a green compact of a raw material powder containing metal powder as a main raw material has the same cost as a resin slide bearing. While mass production is possible, it has higher heat resistance and mechanical strength than resin-made plain bearings, and the bearing surface is less likely to be thermally deformed or damaged. Therefore, it is possible to accurately support the shafts of the components of the variable light distribution type headlamp apparatus, and it is possible to reduce the cost while stably maintaining the operability of the headlamp apparatus.

  Sintered bearings have a porous structure, and are generally used in a state where the internal pores are impregnated with lubricating oil (oil-impregnated state). However, even if the internal pores of the sintered bearing are impregnated with the lubricating oil, the inside of the headlamp device becomes hot when the light source is turned on, so the lubricating oil impregnated in the internal pores is likely to evaporate. Then, when the lubricating oil evaporates in the headlamp device, the evaporated lubricating oil component adheres to the lens inner surface and the light source surface of the headlamp device, and its transparency decreases, and the illuminance of the headlamp decreases. There is a possibility of causing a fatal problem as a lighting device. These problems can be solved by using a heat-resistant lubricating oil such as fluorine-based lubricating oil. However, since fluorine-based lubricating oil is very expensive, replace the rolling bearing with a sliding bearing. You will not be able to fully enjoy the cost merit. In this respect, since the sintered bearing according to the present invention is used in a non-oil-containing state, the basic function of the headlamp device for brightly illuminating the front side is not impaired.

  As raw material powder for sintered bearings, it is possible to use iron-based metal powder as the main raw material, but iron-based metal material has high hardness, so it should be used in a non-oil-impregnated state. Considering this, it is not preferable because the shaft to be supported may be damaged. Further, since iron-based metallic materials are easily rusted, there is a difficulty in terms of durability when considering use in a non-oil-impregnated state. Furthermore, since the iron-based metal powder has a high melting point, it is necessary to sufficiently increase the heating temperature when sintering the green compact of the raw material powder containing the iron-based metal powder. Restrictions tend to occur on the type of filler that is usually blended. Therefore, the sintered bearing according to the present invention is obtained by sintering a green compact of raw material powder containing Cu powder as a main raw material and not including Fe powder. In this way, it is possible to avoid as much as possible the various problems described above when using Fe powder.

  In the above configuration, as the raw material powder, a powder blended with Sn powder, C powder and Ni powder as a filler can be used. Since Sn (tin) has a considerably lower melting point than Cu (copper) (Cu melting point: about 1080 ° C., Sn melting point: about 230 ° C.), a green compact of raw material powder containing these fillers is used. When heated at a temperature at which the Cu powder as the main raw material can be sintered, the Sn powder melts and diffuses into the base material (copper), and the base material becomes an alloy (Cu-Sn alloy) to increase its hardness. . Thereby, the abrasion resistance of the bearing surface of a sintered bearing can be improved. In addition, if the mixing ratio of Sn powder in the raw material powder (whole raw material powder) is 7 to 11 wt%, copper can be completely alloyed. In addition, since Ni powder has higher hardness and higher melting point than Cu powder, Ni powder is distributed and arranged on the bearing surface of the sintered bearing while retaining its original shape. The wear resistance can be further improved. In particular, if the mixing ratio of the Ni powder in the raw material powder is 4 to 6 wt%, the wear resistance can be effectively increased without increasing the aggressiveness to the shaft to be supported.

  In addition, since C powder (graphite powder) is blended into the raw material powder, it is possible to improve the sliding performance of the bearing surface of the sintered bearing (to reduce the friction coefficient of the bearing surface and to improve the seizure resistance). Can) This is because the C powder functioning as a solid lubricant remains in its original form and is distributed on the bearing surface even after sintering because Cu powder is used as the main raw material. Here, the slidability increases as the blending ratio of the C powder is increased. However, if the blending ratio of the C powder is too high, the fluidity of the raw material powder is lowered and the filling property of the raw material powder into the molding die is lowered. In addition, the compressibility of the raw material powder is adversely affected, and it becomes difficult to form the green compact to a predetermined density, and it becomes difficult to obtain a green compact with a predetermined accuracy and a predetermined strength, and thus a sintered bearing. Therefore, in consideration of the balance between the merit and demerit of blending C powder, the blending ratio of C powder in the raw material powder is desirably 3 to 7 wt%.

  As described above, Sn powder melts and diffuses into the base material in the stage of obtaining a sintered body by heating the green compact. Holes will be formed at the site where Sn powder was dispersed in the stage. For this reason, if an Sn powder having an excessively large particle size is used, unreasonably large holes are formed in the sintered bearing, which is disadvantageous in terms of strength. Therefore, it is desirable to use Sn powder having an average particle size of 45 μm or less.

  In the above configuration, it is desirable to use Ni powder having an average particle diameter of 5 μm or less as the Ni powder to be blended with the raw material powder. This is because when the various powders are mixed to produce the raw material powder, the dispersibility of the Ni powder in the raw material powder is improved, and the wear resistance of the bearing surface is uniformly improved. That is, if a large Ni powder with an average particle size exceeding 5 μm is used, it will be difficult to uniformly disperse the Ni powder in the raw material powder, and the wear resistance may vary among the parts of the bearing surface. There is sex.

  In the above configuration, the C powder may contain 30 wt% or more of an average particle size of 60 to 110 μm with respect to the total amount. The particle size distribution of the C powder particularly affects the fluidity of the raw material powder. Therefore, if such a powder is used as the C powder, it is possible to further improve the fluidity of the raw material powder and achieve higher precision of the green compact and, consequently, the sintered bearing.

  As described above, according to the present invention, it is possible to contribute to the cost reduction without degrading the basic performance including the operability of the variable light distribution type headlamp device.

It is a figure which shows typically the principal part of one structural example of the variable light distribution type headlamp apparatus incorporating the sintered bearing which concerns on embodiment of this invention. It is an AA arrow directional cross-sectional view in FIG. It is a flowchart which shows the manufacturing process of a sintered bearing. It is a schematic perspective view of the test apparatus used for a wear resistance confirmation test. It is a figure which shows the composition of the sample used for the confirmation test of abrasion resistance. It is a figure which shows the confirmation test result of abrasion resistance.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows a main part of a configuration example of a variable light distribution headlamp device 1 including a sintered metal sliding bearing according to an embodiment of the present invention. The AA line arrow directional cross-sectional view is shown. The variable light distribution type headlamp device 1 includes a reflector 2, a light source 3 attached to a substantially central portion of the reflector 2, a reflector 2 and the light source 3 that hold the reflector 2 and the light source 3 and rotate (rotate) in the left-right direction. 1 rotation member 4, second rotation member 5 rotating (rotating) in the vertical direction, casing 6, drive means (not shown) for rotating the first and second rotation members 4, 5 With. Sintered metal slide bearings (hereinafter referred to as “sintered bearings”) 10 and 10 are fixedly attached to the casing 6, and these sintered bearings 10 and 10 project from the left and right sides of the second rotating member 5. The shaft portions 5a and 5a are rotatably supported. A sintered bearing 10 is also attached and fixed to the second rotating member 5, and a shaft portion 4 a protruding from the first rotating member 4 is rotatably supported by the sintered bearing 10.

  The sintered bearing 10 is formed of a sintered metal porous body that has copper (Cu) as a main component and does not contain iron (Fe), and is formed in a cylindrical shape having a constant diameter, and impregnated with lubricating oil in internal pores. It is assembled to the casing 6 and the second rotating member 5 in a non-oil-impregnated state. As shown in FIG. 3, the sintered bearing 10 is manufactured through a raw material powder production process P1, a compression molding process P2, a sintering process P3, and a correction process P4 in this order. Hereinafter, each process is explained in full detail.

(A) Raw material powder production process In this raw material powder production process P1, for example, appropriate amounts of copper (Cu) powder, tin (Sn) powder, graphite (C) powder and nickel (Ni) powder are respectively charged into a V-type mixer. The raw material powder for manufacturing the sintered bearing 10 is manufactured. This raw material powder does not contain any Fe powder. Here, Cu powder having an average particle size of 150 μm or less is used as a main raw material, and the mixing ratio of Sn powder, C powder and Ni powder as fillers to the raw material powder is 7 to 11 wt%, 3%, respectively. It mix | blends so that it may become -7 wt% and 4-6 wt%. Of these fillers, those having an average particle diameter of 5 μm or less are used as the Ni powder in order to improve the dispersibility of the Ni powder in the raw material powder. That is, the reason why the Ni powder is blended in the raw material powder is to improve the wear resistance of the bearing surface (inner peripheral surface) among the sintered bearings 10, but the average particle diameter of the Ni powder exceeds 5 μm. This is because the dispersibility in the raw material powder decreases and it becomes difficult to uniformly increase the wear resistance of the bearing surface of the sintered bearing 10 (the wear resistance tends to vary in each part of the bearing surface). .

(B) Compression molding process P2
In this compression molding step P2, the raw material powder produced in the raw material powder production step P1 is put into a cavity of a molding die (not shown) and compression-molded, and a cylindrical pressure approximating the sintered bearing 10 as a finished product. Obtain powder.

  By the way, as mentioned above, C powder is mix | blended with the raw material powder. The C powder functions as a solid lubricant, and if it is blended, the mold releasability of the green compact can be improved. Further, since the Cu powder is used as the main raw material, the C powder remains in its original form and is dispersedly arranged on the bearing surface even after the sintering process P3 described later. It is possible to effectively increase the slidability of the bearing surface (reducing the friction coefficient of the bearing surface and increasing the seizure resistance). Considering such advantages, it is desirable to increase the blending amount of C powder as much as possible (the blending ratio of C powder in the raw material powder is as high as possible), but graphite has a specific gravity higher than that of copper, tin and nickel. The smaller the C powder is, the lower the density than Cu powder, Sn powder and Ni powder. Mold filling property) and compression moldability are lowered, and it becomes difficult to obtain a green compact having a predetermined shape and a predetermined density.

  Therefore, in order to effectively enjoy the merits of improving the sliding performance of the bearing surface of the sintered bearing 10 and to minimize the demerit of lowering the compacting accuracy of the green compact, the mixing ratio of C powder to the raw material powder In addition, as the C powder, a powder containing an average particle size of 60 to 110 μm in an amount of 30 wt% or more is used as the C powder. That is, by setting the blending ratio of the C powder in the above range, it is possible to prevent the compression moldability from being lowered as much as possible, and the C powder having the above particle size distribution is used. This improves the fluidity.

  Since the raw material powder includes C powder that functions as a solid lubricant, as described above, when the green compact is released from the molding die, the green compact can be released smoothly. For this reason, it is possible to prevent the green compact from being partially lost as the mold is released, and to obtain a high-precision green compact.

(C) Sintering process P3
In the sintering process P3, the green compact obtained in the compression molding process P2 is heated within a temperature range of 700 to 800 ° C. for a predetermined time to obtain a sintered body formed by sintering and bonding Cu powders. Here, the green compact (raw material powder) contains Sn powder having a melting point lower than that of Cu (Cu melting point: about 1080 ° C., Sn melting point: about 230 ° C.). Is heated within the above temperature range, the Cu powders are sintered and bonded simultaneously, and at the same time, the Sn powder is melted and diffused into the base material (Cu), so that the base material (Cu) becomes an alloy (Cu-Sn alloy). ) To increase its hardness.

(D) Correction process P4
In this correction process P4, the sintered body obtained through the sintering process P3 is subjected to correction processing (sizing processing). Thereby, the shape and each part dimension of a sintered compact are finished with predetermined precision, and the sintered bearing 10 as a finished product is obtained.

  As described above, the sintered bearing 10 can be mass-produced at the same cost as a resin sliding bearing, but has higher heat resistance and mechanical strength than a resin sliding bearing, and has a bearing surface. Hard to be thermally deformed or damaged. Therefore, the shafts of the components of the variable light distribution type headlamp device 1 can be supported with high accuracy, and the cost can be reduced while the operability of the headlamp device 1 is stably maintained. . Further, since the sintered bearing 10 according to the present invention is used in an oil-free state, the most basic and maximum function of the headlamp device 1, that is, the function of brightly illuminating the front side is impaired. Disappears.

  As a raw material powder of the sintered bearing 10, it is possible to use a material containing an iron-based metal powder as a main raw material or a material containing an appropriate amount. However, since an iron-based metal material has high hardness, Considering the use in an oil-impregnated state, it is not preferable because the shafts (shaft portions 4a and 5a) to be supported may be damaged. The sintered bearing 10 according to the present invention is obtained by compacting and sintering a raw material powder containing Cu powder as a main raw material and not containing an Fe powder. Various problems can be avoided as much as possible.

  Moreover, since the sintered bearing 10 is manufactured using the raw material powder containing Sn powder and Ni powder, the wear resistance of the sintered bearing 10 (the bearing surface thereof) can be improved. That is, as described above, since Sn has a lower melting point than Cu, when a green compact containing Sn powder is heated in a temperature range in which the main raw material Cu powder can be sintered and bonded, Sn powder This is because the metal melts and diffuses into the base material (copper), and the base material is alloyed (Cu—Sn alloy) to increase its hardness and eventually wear resistance. Further, since Ni has higher hardness and higher melting point than Cu, Ni powder blended in the raw material powder is dispersedly arranged in each part of the sintered bearing 10 without melting, and the bearing of the sintered bearing 10 Contributes effectively to improved surface wear resistance. Therefore, it is possible to effectively ensure the wear resistance required for the bearing surface of the sintered bearing 10 which is difficult to ensure with Cu alone.

  However, if the proportion of Sn powder in the raw material powder is less than 7 wt%, it becomes difficult to completely alloy Cu. On the other hand, if the blending ratio exceeds 11 wt%, there is an excess of Sn that does not contribute to alloying, which is inefficient. Therefore, it is desirable that the blending ratio of the Sn powder in the raw material powder is in the range of 7 to 11 wt% as described above. As described above, since Sn powder melts and disappears in the process of obtaining a sintered body, Sn powder is dispersed (existing) in the green compact stage of the sintered body (sintered bearing 10). Holes will be formed at the sites. Therefore, if Sn powder having an excessively large particle size is used, unreasonably large holes are formed in the sintered bearing 10, which is disadvantageous in terms of strength. Therefore, it is desirable that the Sn powder blended in the raw material powder has an average particle size of 45 μm or less.

  Ni powder is useful for improving the wear resistance of the sintered bearing 10, but when the proportion of Ni powder in the raw material powder exceeds 6 wt%, the shaft to be supported (shaft portions 4a and 5a). The possibility of hurting is increased. On the other hand, if the blending ratio is less than 4 wt%, the effect of improving the wear resistance of the bearing surface of the sintered bearing 10 cannot be fully enjoyed. Therefore, the mixing ratio of Ni powder in the raw material powder is desirably in the range of 4 to 6 wt%. Thereby, the improvement effect of abrasion resistance can be acquired, without improving the aggressiveness with respect to the shaft which should be supported.

  As mentioned above, although one Embodiment of this invention was described, the sintered bearing 10 can give a various deformation | transformation in the range which does not deviate from the summary of this invention. For example, in the embodiment described above, the sintered bearing 10 is formed in a cylindrical shape with a constant diameter, but the outer peripheral surface of the sintered bearing 10 is a member to which the sintered bearing 10 is attached (FIGS. 1 and In the example shown in FIG. 2, it can be changed according to the shape of the mounting portion of the second rotating member 5 and the casing 6). Moreover, the form of the variable light distribution type headlamp device 1 to which the sintered bearing 10 according to the present invention is attached is not limited to that shown in FIGS. 1 and 2.

  In order to demonstrate the usefulness of the present invention, the sintered bearing 10 is formed using the raw material powder having the configuration of the present invention (Example) and sintered using the raw material powder not having the configuration of the present invention. To what extent the amount of wear is different from the case where the bearing 10 is formed (comparative example) was compared and verified using the testing machine 20 shown in FIG. The testing machine 20 shown in FIG. 4 includes a barbell 21 having a shaft portion 22 and a pair of ring portions 23, 23 provided on the outer periphery thereof, and a flat plate 24 on which the barbell 21 is placed. This is a so-called barbell plate testing machine. In the testing machine 20, a downward load is applied to the barbell 21, and the barbell 21 and the plate 24 are relatively rotated at a predetermined speed with the outer peripheral surfaces of the ring portions 23 and 23 pressed against the upper surface of the plate 24 (this test). Then, the plate 24 is rotated while the barbell 21 is stationary), and the amount of wear of the plate 24 after a predetermined time has elapsed is measured.

  In the confirmation test, the barbell 21 (the shaft portion 22 and the pair of ring portions 23, 23) is manufactured from a material (for example, stainless steel) corresponding to the shaft of the variable light distribution headlamp device 1, and the raw material according to the example is produced. Plates 24 were respectively made of the powder (Examples 1 and 2) and the raw material powders (Comparative Examples 1 to 4) according to the comparative example. In addition, the material composition of the plate 24 which concerns on Examples 1, 2 and Comparative Examples 1-4 is shown in FIG.

Further, the main test conditions of the wear test are as shown in the following (1) to (4), and the actual use conditions and use environment of the sintered bearing 10 according to the present invention are taken into consideration. No lubricant such as lubricating oil is interposed between the ring portion 23 and the plate 24.
(1) Load: 20N and 50N are switched every minute (2) Test time: 60 minutes (3) Rotational speed: 2.7 m / s
(4) Atmosphere: normal temperature and humidity

  The test result of the wear test is shown in FIG. As is clear from the test results shown in FIG. 6, in Example 1 and Example 2 using the raw material powder having the configuration of the present invention, comparison was made using the raw material powder mainly composed of Cu powder and Fe powder. The amount of wear was significantly less than in the examples (particularly Comparative Example 1 and Comparative Example 2). Moreover, from the comparison between Example 1 and Example 2 and the comparison between Comparative Examples 1 to 3, the wear amount decreases as the blending ratio of C powder in the raw material powder is increased, and the blending ratio of C powder is It is understood that the increase is effective for improving the wear resistance. In addition, when Example 1 and Comparative Example 3 are compared, it is considered that there is no great difference in the amount of wear, and equivalent wear resistance can be ensured, but the sample according to Comparative Example 3 is made from a raw material powder containing Fe powder. Since it was manufactured, many scratches were formed on the barbell 21 (ring portion 23) corresponding to the shaft to be supported. Therefore, the sintered bearing having the configuration of Comparative Example 3 is not suitable for a shaft support application in an oil-free state. In Comparative Example 4, Ni powder was omitted from the configuration of Example 1, and the blending ratio of Sn powder was increased by the omission, but compared with Example 1 in which Ni powder was blended, the amount of wear was lower. The result is increasing.

  The above test results demonstrate the usefulness of the present invention. That is, with the sintered bearing 10 according to the present invention, high wear resistance and slidability can be ensured on the bearing surface, so that it is incorporated into the variable light distribution type headlamp device 1 in an oil-free state. Even when used in the above, the rotating shafts of the components of the headlamp device 1 can be accurately supported over a long period of time. Thereby, it can contribute to the cost reduction, without impairing basic performance and functions including the operability of the variable light distribution headlamp device 1.

DESCRIPTION OF SYMBOLS 1 Light distribution variable type headlamp apparatus 2 Reflector 3 Light source 4a Shaft part (shaft which should be supported)
5a Shaft (shaft to be supported)
10 Sintered bearing (slide bearing)
20 Testing machine 21 Barbell 24 Plate

Claims (6)

  A slide bearing installed in a variable light distribution type headlight device that can change the light distribution angle of the headlight in the vertical and horizontal directions, and sinters the green compact of the raw material powder made mainly of metal powder. It is a plain bearing that supports the shaft to be supported in a non-oil-free state so that it can rotate freely.   2. A slide bearing for a variable light distribution headlamp device according to claim 1, wherein the green powder is made of a raw material powder containing Cu powder as a main raw material and containing no Fe powder.   As the raw material powder, a mixture of Sn powder, C powder and Ni powder as a filler is used, and the mixing ratio of Sn powder, C powder and Ni powder in the raw material powder is 7 to 11 wt%, 3 to 3, respectively. The slide bearing for a variable light distribution headlamp device according to claim 2, wherein the weight is 7 wt% and 4 to 6 wt%.   The sliding bearing for a variable light distribution type headlamp device according to claim 3, wherein the Sn powder has an average particle diameter of 45 µm or less.   5. The slide bearing for a variable light distribution headlamp device according to claim 3, wherein the Ni powder has an average particle size of 5 [mu] m or less.   6. The slide bearing for a variable light distribution headlamp device according to claim 3, wherein the C powder contains 30 wt% or more of an average particle size of 60 to 110 μm with respect to the total amount thereof.

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