Patent Publication Number: US-2023150023-A1

Title: Sliding member

Description:
FIELD 
     The present invention relates to a sliding member. 
     BACKGROUND 
     Conventionally, a configuration in which a porous layer is provided between the resin layer and the base material of a sliding member is known. 
     For example, as the porous layer, a configuration in which a plurality of granular inorganic fillers are stacked and a configuration in which a plurality of metal grains are bonded with a brazing material are disclosed. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 2002/327750 A 
         Patent Literature 2: JP 2016/108600 A 
       
    
     SUMMARY 
     Technical Problem 
     In the conventional techniques, however, it has been difficult to achieve both ease of impregnation of the resin layer into the porous layer and improvement in the resistance to peeling of the resin layer from the base material. 
     An object of the present invention is to provide a sliding member capable of achieving both ease of impregnation of the resin layer into the porous sintered layer and improvement in the resistance to peeling of the resin layer from the base material. 
     Solution to Problem 
     In order to solve the above problem and achieve the object, a sliding member according to the present invention includes a base material; a porous sintered layer provided on the base material; and a resin layer impregnated into the porous sintered layer and provided on the porous sintered layer, wherein in the porous sintered layer, a porosity decreases from a second surface opposite to a first surface closer to the base material, toward the first surface, the first surface and the second surface each being one of end surfaces in a thickness direction, and a decrease rate of the porosity in the thickness direction in a first region occupying 50% or more of thickness of the porous sintered layer from the second surface toward the first surface is larger than a decrease rate of the porosity in the thickness direction in a second region other than the first region of the porous sintered layer. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to achieve both ease of impregnation of the resin layer into the porous sintered layer and improvement in the resistance to peeling of the resin layer from the base material. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic diagram illustrating an example of a sliding member according to an embodiment. 
         FIG.  2    is a graph illustrating an example of the relationship between the porosity and the position in the thickness direction of a porous sintered layer of the embodiment. 
         FIG.  3    is a graph illustrating a measurement result of the relationship between the porosity and the position in the thickness direction of a comparative porous layer. 
         FIG.  4    is a graph illustrating a measurement result of the relationship between the porosity and the position in the thickness direction of a comparative porous layer. 
         FIG.  5    is a diagram illustrating a cross section on the observation side of a sample. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of a sliding member according to the present invention will be described in detail with reference to the accompanying drawings. 
     The sliding member of the present embodiment includes a base material, a porous sintered layer provided on the base material, and a resin layer impregnated into the porous sintered layer and provided on the porous sintered layer. In the porous sintered layer, a porosity decreases from a second surface opposite to the first surface closer to the base material, toward the first surface, the first surface and the second surface each being one of end surfaces in a thickness direction, and a decrease rate of the porosity in the thickness direction of a first region occupying 50% or more of the thickness of the porous sintered layer from the second surface toward the first surface is larger than a decrease rate of the porosity in the thickness direction of a second region other than the first region of the porous sintered layer. 
     Thereby, the sliding member of the present embodiment can achieve both ease of impregnation of the resin layer into the porous sintered layer and improvement in the resistance to peeling of the resin layer from the base material. 
     The reason why the above effect is exhibited is not clear, but it is presumed as follows. However, the present invention is not limited by the following presumption. 
     In the porous sintered layer of the sliding member of the present embodiment, the porosity decreases from the second surface opposite to the first surface closer to the base material, toward the first surface, the first surface and the second surface each being one of the end surfaces in the thickness direction. Thereby, it is presumed that pores of the porous sintered layer are effectively impregnated with a resin material when the resin layer is formed by impregnating the porous sintered layer with the resin material constituting the resin layer. In addition, it is presumed that pores of the porous sintered layer are effectively impregnated with the resin layer regardless of the magnitude of the viscosity of the resin material. 
     In addition, in the porous sintered layer of the sliding member of the present embodiment, a decrease rate of the porosity in the thickness direction of the first region occupying 50% or more of the thickness of the porous sintered layer from the second surface to the first surface is larger than a decrease rate of the porosity in the thickness direction of the second region other than the first region of the porous sintered layer. Thereby, it is presumed that improvement in the adhesion force between the entire porous sintered layer and the resin layer and reduction of variation in the adhesion force to the resin layer in the porous sintered layer can be achieved as compared with the case where a decrease rate of the porosity does not satisfy the above relationship. Therefore, it is presumed that the resin layer is firmly held to the base material by the porous sintered layer, and the resistance to peeling of the resin layer from the base material can be improved. 
     Hereinafter, the sliding member of the present embodiment will be described in detail. 
       FIG.  1    is a schematic diagram illustrating an example of a sliding member  10  according to the present embodiment.  FIG.  1    schematically illustrates an example of a cross-sectional structure of the sliding member  10 . 
     The sliding member  10  includes a base material  12 , a porous sintered layer  14 , and a resin layer  16 . The sliding member  10  is a laminate of the base material  12 , the porous sintered layer  14  formed on the base material  12 , and the resin layer  16  impregnated into the porous sintered layer  14  and provided on the porous sintered layer  14 . 
     The base material  12  is a layer for providing mechanical strength to the sliding member  10 . The base material  12  is sometimes referred to as a back metal or a back metal layer. As the base material  12 , for example, a metal plate such as an Fe alloy, Cu, or a Cu alloy can be used. 
     The porous sintered layer  14  is a porous layer produced by sintering. 
     The porosity decreases in the thickness direction Z (specifically, the direction of the arrow Z 1 ) from the second surface S 2  opposite to the first surface S 1  loser to the base material  12 , toward the first surface S 1 , the first surface and the second surface being end surfaces in the thickness direction Z (the first surface S 1  and the second surface S 2 ), in the porous sintered layer  14  of the present embodiment. In other words, in the porous sintered layer  14 , the porosity of the second surface S 2  farthest from the base material  12  is the highest, the porosity decreases toward the base material  12 , and the porosity of the first surface S 1  closest to the base material  12  is the lowest. 
     In addition, in the porous sintered layer  14 , a decrease rate of the porosity in the thickness direction Z (specifically, the direction of the arrow Z 1 ) of a first region E 1  is larger than a decrease rate of the porosity in the thickness direction Z (specifically, the direction of the arrow Z 1 ) of a second region E 2 . 
     The thickness direction Z is the thickness direction of the layer of the porous sintered layer  14 , and coincides with the lamination direction of the base material  12 , the porous sintered layer  14 , and the resin layer  16 . 
     The porosity refers to a proportion of a total area of pores to the total area of the cross section of the porous sintered layer  14 . Specifically, the porosity is measured by the following method. First, the sliding member  10  is cut in a direction orthogonal to the thickness direction Z of the sliding member  10 . Then, a photographed image is obtained by photographing the cut surface at an arbitrary magnification (e.g., 100 magnifications) using an electron microscope. Then, this photographed image is binarized using a known image analysis method, and regions of pores of the porous sintered layer  14  are specified. Then, the proportion of the total area of the regions of the pores to the total area of the cross section shown in the photographed image may be calculated as a porosity. Then, porosities at positions in the thickness direction Z may be measured by changing the cutting position in the thickness direction Z of the sliding member  10  and calculating porosities from cut surfaces at cutting positions by the above method. 
     In the porous sintered layer  14  having end surfaces in the thickness direction Z, the first surface S 1  is an end surface on the base material  12  side. The first surface S 1  is specifically a surface contacting with the base material  12  of the porous sintered layer  14 . 
     The second surface S 2  is an end surface opposite to the first surface S 1  and is an end surface opposite to the base material  12  among the end surfaces in the thickness direction Z. The second surface S 2  specifically includes a point farthest from the base material  12  on the surface of one or more inorganic particles  18  present at a position farthest from the base material  12  in the porous sintered layer  14  and is a surface parallel to a surface of the base material  12 . The surface of the base material  12  having end surfaces in the thickness direction Z of the base material  12  is an end surface on the side of the porous sintered layer  14  and resin layer  16 . 
     The thickness of the porous sintered layer  14  is the length of the porous sintered layer  14  in the thickness direction Z. Specifically, the thickness of the porous sintered layer  14  is a distance between the first surface S 1  and the second surface S 2  of the porous sintered layer  14  (see a distance L 1  in  FIG.  1   ). 
     The porosity of the porous sintered layer  14  only needs to decrease from the second surface S 2  toward the first surface S 1  along the thickness direction Z (that is, along the direction of the arrow Z 1 ), and the porosity decrease may be either a stepwise decrease or a continuous decrease. 
     The first region E 1  is a region having a thickness of 50% or more of the thickness of the porous sintered layer  14  from the second surface S 2  toward the first surface S 1  (the direction of the arrow Z 1 ). In other words, the first region E 1  is a region including the second surface S 2  and having a thickness of 50% or more of the thickness of the porous sintered layer  14  from the second surface S 2  toward the first surface S 1  in the porous sintered layer  14 . 
     Incidentally, the first region E 1  may be a region having a thickness of 50% or more of the porous sintered layer  14  from the second surface S 2  toward the first surface S 1 , but is preferably a region having 50% or more and 70% or less, and more preferably a region having 55% or more and 65% or less. 
     When the first region E 1  is a region within the above range in the porous sintered layer  14 , the resistance to peeling of the resin layer  16  from the base material  12  can be effectively improved. 
     The second region E 2  is a region other than the first region E 1  in the porous sintered layer  14 . Specifically, the second region E 2  is a region from the end surface on the base material  12  side of the first region E 1  to the first surface S 1  in the porous sintered layer  14 . 
     As described above, a decrease rate of the porosity in the thickness direction Z of the first region E 1  is larger than a decrease rate of the porosity in the thickness direction Z of the second region E 2 . The decrease rate of the porosity refers to a decrease rate of the porosity in the thickness direction Z from the second surface S 2  toward the second surface S 2  (specifically, the direction of the arrow Z 1 ) with respect to the unit thickness of the porous sintered layer  14 . 
     When the decrease rate of the porosity in the thickness direction Z of the first region E 1  is larger than the decrease rate of the porosity in the thickness direction Z of the second region E 2 , it is possible to attain ease of impregnation of the resin layer  16  into the porous sintered layer  14  while maintaining the resistance to peeling of the resin layer  16  from the base material  12 . 
       FIG.  2    is a graph illustrating an example of the relationship between the porosity and the position in the thickness direction Z of the porous sintered layer  14  in the sliding member  10  of the present embodiment. In  FIG.  2   , the vertical axis shows the porosity of the porous sintered layer  14 . The horizontal axis shows the position in the thickness direction Z of the porous sintered layer  14 . In addition, the position in the thickness direction on the horizontal axis, on which the thickness of the porous sintered layer  14  is 150 μm, is shown with the position of the second surface S 2  as 0 μm and the position of the first surface S 1  as 150 μm. 
     In the case of the example shown in  FIG.  2   , change in the porosity of the porous sintered layer  14  is represented by, for example, a line graph  40 . The line graph  40  is expressed with a line graph  40 A and a line graph  40 B having different decrease rates of the porosity. A decrease rate of the porosity represented by the line graph  40 A is larger than a decrease rate of the porosity represented by the line graph  40 B. Therefore, in the example shown in  FIG.  2   , the first region E 1  is a region having a thickness to a position of a thickness of about 80 μm from the second surface S 2  toward the first surface S 1  in the porous sintered layer  14 . The second region E 2  is a region having a thickness from the position of a thickness of about 80 μm to a position of 150 μm as the first surface S 1  from the second surface S 2  toward the first surface S 1  in the porous sintered layer  14 . 
     Returning to  FIG.  1   , the description will be continued. The porosity of a central part P in the thickness direction Z of the porous sintered layer  14  is preferably 30% or more and less than 50%. 
     The porosity of the central part P in the thickness direction Z of the porous sintered layer  14  refers to a porosity of a cut surface obtained by cutting the porous sintered layer  14  along a line passing through the center of the porous sintered layer  14  in the thickness direction Z. 
     The porosity of the central part P in the thickness direction Z of the porous sintered layer  14  is preferably 30% or more and less than 50%, and more preferably 35% or more and 45% or less. 
     In addition, the porosity of the second surface S 2  of the porous sintered layer  14  is higher than that of the central part P. Specifically, the porosity of the second surface S 2  is preferably 30% or more. 
     In addition, the porosity of the first surface S 1  of the porous sintered layer  14  is lower than that of the central part P. Specifically, the porosity of the first surface S 1  is preferably 15% or more and 40% or less, and more preferably 20% or more and 35% or less. 
     When the porosities of the central part P, the first surface S 1 , and the second surface S 2  in the thickness direction Z of the porous sintered layer  14  fall within the above-mentioned ranges, it is possible to attain ease of impregnation of the resin layer  16  into the porous sintered layer  14  while maintaining the resistance to peeling of the resin layer  16  from the base material  12 . 
     The porous sintered layer  14  only needs to satisfy the above-mentioned relationship of the porosities, and the constituent material thereof is not limited. For example, the porous sintered layer  14  may include a sintered layer of a plurality of inorganic particles  18 . 
     The porous sintered layer  14  is produced by, for example, sintering a plurality of the inorganic particles  18 . The inorganic particles  18  may be any particles capable of forming the porous sintered layer  14  by being sintered, and the constituent material of the inorganic particles  18  is not limited. The inorganic particles  18  are a copper-based alloy. The inorganic particles  18  are, for example, pure copper, a Cu alloy such as bronze, lead bronze, or phosphor bronze, or a composite material obtained by dispersing a powder such as FeP or Al 2 O 3  in the pure copper or the copper alloy. 
     The average particle diameter of the inorganic particles  18  is preferably 75 μm or more and 150 μm or less, and more preferably 80 μm or more and 125 μm or less. 
     The average particle diameter of the inorganic particles  18  indicates a volume average particle diameter. Specifically, the average particle diameter of the inorganic particles  18  refers to a value measured using a laser diffraction/scattering type particle diameter distribution measuring apparatus (LS Particle Size Analyzer: LS13 320, manufactured by BECKMAN COULTER, Inc.). With respect to particle diameter ranges (channels) obtained by dividing an obtained particle diameter distribution, a volume cumulative distribution is subtracted from the small particle diameter side, and a particle diameter at which the cumulative 50% is obtained is defined as an average particle diameter (volume average particle diameter) D 50v  of the inorganic particles  18 . 
     In addition, in the porous sintered layer  14 , it is preferable that the average particle diameter of the inorganic particles  18  constituting the porous sintered layer  14  is in the above-mentioned range, and that the ratio of the thickness of the porous sintered layer  14  to the average particle diameter of the inorganic particles  18  is preferably 1.1 times or more and 2.2 times or less. 
     Incidentally, the ratio of the thickness of the porous sintered layer  14  to the inorganic particles  18  in the range of the above-mentioned average particle diameter is preferably 1.1 times or more and 2.2 times or less, and more preferably 1.3 times or more and 1.8 times or less. 
     When the ratio of the thickness of the porous sintered layer  14  to the inorganic particles  18  in the range of the above-mentioned average particle diameter is in the above range, it is possible to more effectively attain both improvement in the resistance to peeling of the resin layer  16  from the base material  12  and ease of impregnation of the resin layer  16  into the porous sintered layer  14 . 
     In addition, the porous sintered layer  14  is preferably a laminate obtained by stacking 1.1 layers or more and 2.2 layers or less of the inorganic particles  18 , and more preferably a laminate obtained by stacking 1.3 layers or more and 1.8 layers or less. 
     When the lamination state of the inorganic particles  18  in the porous sintered layer  14  is the above state, it is possible to more effectively attain both improvement in the resistance to peeling of the resin layer  16  from the base material  12  and ease of impregnation of the resin layer  16  into the porous sintered layer  14 . 
     The inorganic particles  18  constituting the porous sintered layer  14  may have substantially the same size (particle diameter) or different sizes. The term “substantially the same” means that the particle diameter of one particle with respect to the particle diameter of the other particle is within a range of ±10%. Incidentally, the inorganic particles  18  constituting the porous sintered layer  14  preferably have substantially the same size. 
     The shape of each of the inorganic particles  18  is not limited. The shape of each of the inorganic particles  18  may be any of a spherical shape, a substantially spherical shape without a sharp edge, and other deformed shapes (such as flaky, dendritic, chain-like, scalenohedral shapes). 
     All the inorganic particles  18  constituting the porous sintered layer  14  may have the same shape, or a particle having a different shape may be mixed. 
     When the porous sintered layer  14  has a form in which the inorganic particles  18  having different shapes are mixed, the proportion of the inorganic particles  18  having a minor axis/major axis ratio in the range of 0.2 or more and 0.7 or less in all the inorganic particles  18  constituting the porous sintered layer  14  is preferably 50% or more, and more preferably 70% or more. In addition, the proportion of the inorganic particles  18  having a minor axis/major axis ratio in the range of 0.2 or less in all the inorganic particles  18  constituting the porous sintered layer  14  is preferably 30% or less, and more preferably 10% or less. 
     Incidentally, the thickness of the porous sintered layer  14  is preferably 0.11 mm or more and 0.22 mm or less, and more preferably 1.3 mm or more and 1.8 mm or less, specifically. 
     Next, the resin layer  16  will be described. The resin layer  16  is a layer including a resin material. The resin material includes a synthetic resin and an additive dispersed in the synthetic resin. 
     As the synthetic resin, polytetrafluoroethylene (PTFE) is mainly used. Furthermore, tetrafluoroethylene/perfluoroalkoxyethylene copolymer (PFA), perfluoroethylene propene copolymer (FEP), low molecular weight PTFE, or the like can be added. 
     The synthetic resin may be a synthetic resin containing not only PTFE but also one or more selected from polyimide (PI), polyamideimide (PAI), polybenzimidazole (PBI), polyamide (PA), a phenol resin, an epoxy resin, polyacetal (POM), polyetheretherketone (PEEK), polyethylene (PE), polyphenylene sulfide (PPS), and polyetherimide (PEI). 
     For reducing the friction coefficient of the synthetic resin and stabilizing the friction, an additive can be added. As such an additive, for example, an additive selected from solid lubricants such as graphite, molybdenum disulfide, tungsten disulfide, CF 2 , CaF 2 , and BN, and soft metals such as Pb, Bi, and Sn may be added. 
     In addition, an additive can be added to improve the abrasion resistance of the synthetic resin. As such an additive, one or more additives selected from salts such as BaSO 4 , CaSO 4 , calcium phosphate, magnesium phosphate, and magnesium silicate, resins such as aromatic polyester, polyimide, and PEEK, oxides such as Al 2 O 3 , FeO 3 , and TiO 2 , sulfides such as ZnS, carbides such as TiC, glass fibers, carbon fibers, carbon, and the like can be added. 
     EXAMPLES 
     Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. 
     Test pieces each having a porous sintered layer  14  or a comparative porous layer described below and a resin layer  16  were prepared, and these test pieces were evaluated for ease of impregnation of the resin layer  16  into each of the porous sintered layer  14  and the comparative porous layer and for the peeling resistance of the resin layer  16 . 
     Preparation of Test Pieces 
     Step 1: A steel plate (SPCC (JIS)) having a thickness of 1.32 mm was prepared as a base material  12 . 
     Step 2: A powder of phosphor bronze (Cu, 6% Sn, and 0.1% P) was sprayed on the base material  12 . 
     Step 3: The powder of the step 2 was sintered at 900° C. to 950° C. to produce a porous sintered layer. 
     Step 4: Next, a PTFE powder and an additive were mixed, and an auxiliary agent was added to prepare a mixed powder. 
     Step 5: The synthetic resin that is the above mixed powder was impregnated into the porous sintered layer with a roll. 
     Step 6: The impregnated material obtained in the step 5 was dried at 150° C. to 200° C. for about 10 minutes. 
     Step 7: Then, firing was performed at 380° C. to 400° C. for about 10 minutes. 
     Test pieces each having a porous sintered layer of Example 1, 2, or 3 and test pieces each having a comparative porous layer of Comparative Example 1 or 2 were prepared by the above Steps 1 to 7. Incidentally, the porosity of the porous sintered layer was adjusted by adjusting the particle diameter of the powder sprayed in Step 2. 
       FIG.  2    is a graph illustrating a measurement result of the relationship between the porosity and the position in the thickness direction Z of the porous sintered layer  14  in the test piece of Example 1. In  FIG.  2   , the vertical axis shows the porosity of the porous sintered layer  14 . The horizontal axis shows the position in the thickness direction Z of the porous sintered layer  14 . In addition, as for the thickness direction on the horizontal axis, the thickness of the porous sintered layer  14  is 150 μm, and the position of the second surface S 2  is shown as 0 μm and the position of the first surface S 1  as 150 μm. 
     As shown in  FIG.  2   , in Example 1, change in the porosity of the porous sintered layer  14  was represented by a line graph  40 . The line graph  40  was expressed with a line graph  40 A and a line graph  40 B. The line graph  40 A shows a decrease rate of the porosity of the first region E 1 , and a line graph  40 B shows a decrease rate of the porosity of the second region E 2 . As shown in  FIG.  2   , the first region E 1  of the porous sintered layer  14  of Example 1 was a region occupying 80% of the thickness of the porous sintered layer  14  from the second surface S 2 . In addition, the decrease rate of the porosity of the first region E 1  was larger than the decrease rate of the porosity of the second region E 2 . In addition, the porosity of the central part P of the porous sintered layer  14  was 40%. 
       FIG.  3    is a graph illustrating a measurement result of the relationship between the porosity and the position in the thickness direction Z of the comparative porous layer in the test piece of Comparative Example 1. In  FIG.  3   , the vertical axis shows the porosity of the comparative porous layer. The horizontal axis shows the position in the thickness direction Z of the comparative porous layer. In addition, the position in the thickness direction on the horizontal axis, on which the thickness of the comparative porous layer is 250 μm, is shown with the position of the second surface S 2  as 0 μm and the position of the first surface S 1  as 250 μm. 
     As shown in  FIG.  3   , in Comparative Example 1, change in the porosity of the comparative porous layer was represented by a line graph  42 . The line graph  42  was expressed with a line graph  42 A and a line graph  42 B. The line graph  42 A shows a decrease rate of the porosity of the first region E 1 , and a line graph  42 B shows a decrease rate of the porosity of the second region E 2 . As shown in  FIG.  3   , the first region E 1  of the comparative porous layer of Comparative Example 1 was a region occupying 20% of the thickness of the comparative porous layer from the second surface S 2 . In addition, the decrease rate of the porosity of the first region E 1  was larger than the decrease rate of the porosity of the second region E 2 . In addition, the porosity of the central part P of the comparative porous layer was 25%. 
       FIG.  4    is a graph illustrating a measurement result of the relationship between the porosity and the position in the thickness direction Z of the comparative porous layer in the test piece of Comparative Example 2. In  FIG.  4   , the vertical axis shows the porosity of the comparative porous layer. The horizontal axis shows the position in the thickness direction Z of the comparative porous layer. In addition, the position in the thickness direction on the horizontal axis, on which the thickness of the comparative porous layer is 150 μm, is shown with the position of the second surface S 2  as 0 μm and the position of the first surface S 1  as 150 μm. 
     As shown in  FIG.  4   , in Comparative Example 2, change in the porosity of the comparative porous layer was represented by a line graph  44 . The line graph  44  was expressed with a line graph  44 A and a line graph  44 B. The line graph  44 A shows a decrease rate of the porosity of a first region E 1 . On the other hand, as shown in the line graph  44 B, the line graph  44 B shows that the porosity is substantially constant. Therefore, in Comparative Example 2, the second region E 2  did not exist. No decrease in the porosity was shown. 
     In addition, the first region E 1  of the comparative porous layer of Comparative Example 2 was a region occupying 40% of the thickness of the comparative porous layer from the second surface S 2 . Further, the porosity of the central part P of the comparative porous layer was 50%. 
     Evaluation 
     Ease of Impregnation into Porous Sintered Layer (or Comparative Porous Layer) 
     Impregnation defects of the resin material described above in the porous sintered layer  14  and the comparative porous layer at the time of preparing test pieces of Examples and Comparative Examples were evaluated, and the evaluation results are shown in Table 1. In Table 1, the smaller the value shown in the column of “Difficulty in occurrence of impregnation defect” is, the more the occurrence of the impregnation defect is. In addition, in Table 1, the larger the value shown in the column of “Difficulty in occurrence of impregnation defect” is, the less the occurrence of the impregnation defect is. In Table 1, when the value shown in the column of “Difficulty in occurrence of impregnation defect” is “1”, it means that an impregnation defect has occurred, when the value is“2”, it means that impregnation defects have partly occurred, and when the value is “3”, it means that an impregnation defect hardly occurs. 
     The occurrence of the impregnation defect can be seen by observing the cross section of the samples. However, for a material of PTFE, the material was carefully polished due to generation of resin flow at the time of polishing the cross section, then subjected to cross section polisher processing, and observed with an electron microscope (see  FIG.  5   ). 
     Peeling Resistance of Resin Layer 
     The peeling resistance of each resin layer  16  in the test pieces of Examples and Comparative Examples was evaluated. 
     For the peeling resistance, the base material  12  was fixed, a load was applied in the thickness direction Z in such a way that the end part along the axis orthogonal to the thickness direction Z of the resin layer  16  is toward the side away from the base material  12  with respect to the base material  12 , and the load when a tear occurred was measured as a peeling strength. The measurement results are shown in Table 1. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                   
                 Test result 
               
            
           
           
               
               
               
               
            
               
                   
                 Material component (wt %) 
                 Abrasion 
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Magnesium 
                 Barium 
                 Molybdenum 
                 Calcined 
                 loss 
                 Friction 
               
               
                   
                 PTFE 
                 phosphate 
                 sulfate 
                 disulfide 
                 clay 
                 (μm) 
                 coefficient 
               
               
                   
               
               
                 Example 1 
                 Balance 
                 15.6 
                 13.0 
                 6.0 
                 3.1 
                 5 
                 0.09 
               
               
                 Example 2 
                 Balance 
                 12.5 
                 16.1 
                 4.1 
                 1.3 
                 9 
                 0.07 
               
               
                 Example 3 
                 Balance 
                 13.3 
                 16.9 
                 4.7 
                 2.1 
                 7 
                 0.07 
               
               
                 Example 4 
                 Balance 
                 14.0 
                 17.7 
                 5.4 
                 2.9 
                 9 
                 0.06 
               
               
                 Example 5 
                 Balance 
                 14.8 
                 18.5 
                 6.0 
                 3.6 
                 8 
                 0.06 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, in Examples in which the porosity decreases from the second surface toward the first surface S 1 , and the decrease rate of the porosity from the second surface S 2  toward the first surface S 1  in the thickness direction Z of the first region E 1  occupying 50% or more of the thickness of the porous sintered layer  14  is larger than the decrease rate of the porosity in the thickness direction Z of the second region E 2 , the porous sintered layer  14  was easily impregnated with the resin layer  16 , and the peeling resistance of the resin layer  16  was high as compared with Comparative Examples not satisfying the conditions. 
     On the other hand, in Comparative Examples, the results were obtained that at least one of ease of impregnation of the resin layer  16  into the comparative porous layer and the peeling resistance of the resin layer  16  was lower than those in Examples. 
     Thus, when the porous sintered layer  14  shown in Examples was used, the evaluation result was obtained that both ease of impregnation of the resin layer  16  into the porous sintered layer  14  and improvement in the resistance to peeling of the resin layer  16  from the base material  12  can be achieved as compared with Comparative Examples. 
     It should be noted that various materials and compositions thereof used in the above-described Examples are merely examples, and the present invention is not limited thereto. The resin layer  16  according to the present invention may contain inevitable impurities. The specific structure of the sliding member  10  is not limited to that exemplified in  FIG.  1   . 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  SLIDING MEMBER 
               12  BASE MATERIAL 
               14  POROUS SINTERED LAYER 
               16  RESIN LAYER 
               18  INORGANIC PARTICLE 
             S 1  FIRST SURFACE 
             S 2  SECOND SURFACE