Patent Publication Number: US-2021188018-A1

Title: Tire

Description:
TECHNICAL FIELD 
     The present disclosure relates to a tire having projections formed on an outer surface. 
     BACKGROUND ART 
     Conventionally, a pattern region having contrast has been formed through forming of fine projections on a side portion of a tire. For example, International Publication No. 2012/131089 discloses a technique that provides large contrast on the side portion of a tire with a plurality of projections formed all over the pattern region. 
     SUMMARY OF INVENTION 
     Technical Problem 
     The decorative portion of the side portion of the tire has one region in which projections are formed. Since the projections control reflection of light, the brightness of this one region is low compared with the brightness of another region in which the light is reflected as it is. However, when the brightness of the entire one region in which the projections are formed is lowered to the same degree, a range of expression of the decorative portion in which the projections are formed in the tire is limited. 
     An object of the present disclosure is to broaden the range of expression of the decorative portion having a region in which the projections are formed in the tire. 
     Solution to Problem 
     A tire according to a first aspect is a tire including: a decorative portion that is formed on an outer surface of the tire and has a base surface; and a pattern region that is provided at the decorative portion and that includes a plurality of projections projecting from the base surface and formed at an interval of from more than 0.1 mm to 1.0 mm, the plurality of projections having a height of from 0.1 mm to 1.0 mm, in which the pattern region is provided with a gradual decrease region in which a height of projections disposed adjacent to each other gradually decreases. 
     According to this tire, a pattern region is formed in the decorative portion on the outer surface of the tire. In this pattern region, a plurality of projections projecting from the base surface and having a height of from 0.1 mm to 1.0 mm is formed at an interval of from more than 0.1 mm to 1.0 mm. 
     Accordingly, light that enters the pattern region declines while being repeatedly reflected on side surfaces, of the projections, facing each other and is reflected to the outer side. Therefore, the brightness of the pattern region is low compared with the brightness of the other region (flat surface) in which the projections are not formed on the outer surface of the tire. 
     The pattern region is provided with a gradual decrease region in which the height of the projections disposed adjacent to each other gradually decreases. As described above, the light that enters the pattern region declines while being repeatedly reflected on the side surfaces, of the projections, facing each other. However, when the height of the projections is low, the decline of the light decreases and the amount of light reflected to the outer side of the tire increases, whereby the brightness increases. 
     Since the height of the projections gradually decreases in the gradual decrease region, the amount of light reflected to the outer side of the tire increases from a portion including higher projections to a portion including lower projections, whereby the brightness gradually increases. This means that a gradation is added to the brightness in the gradual decrease region, and as compared with a case where the brightness is constant, the range of expression of the decorative portion having a region in which the projections are formed in the tire can be broadened. 
     A second aspect provides the tire according to the first aspect, in which the gradual decrease region includes projections having a constant height from the base surface and a bottom raising portion including a gradual increase portion having a height from the base surface that gradually increases across the projections, so that a height from the bottom raising portion to tops of the projections gradually decreases. 
     In this tire, the projections have a constant height from the base surface and a bottom raising portion includes a gradual increase portion having a height from the base surface that gradually increases across the projections. As a result, a configuration can be achieved in which a height from the bottom raising portion to the tops of the projections is gradually decreased. 
     A third aspect provides the tire according to the second aspect, in which the bottom raising portion includes two gradual increase portions connected in mutually opposite directions. 
     In this tire, the bottom raising portion includes two gradual increase portions connected in mutually opposite directions. Therefore, the height of the bottom raising portion gradually increases from one side to the other side, exceeds the peak of the height of the bottom raising portion, and then gradually decreases. 
     Therefore, in a portion in which this bottom raising portion is disposed, the light reflected to the outer side of the tire gradually increases and then gradually decreases. In other words, the range of expression of the decorative portion can be further broadened as compared with only a case where the brightness gradually increases, gradually decreases, and gradually increases, and then black color suddenly appears. 
     A fourth aspect provides the tire according to the second or the third aspect, in which a portion in which a height of the bottom raising portion changes is formed with a curve that projects toward the base surface. 
     The portion in which the height of the bottom raising portion changes is formed with a curved surface that projects toward the base surface. Therefore, an inclination angle of the bottom raising portion (curved surface portion) with respect to the base surface gradually increases toward the top from a foot portion, and thus a change in the amount of light reflected to the outer side of the tire is relatively small in the foot portion and relatively large around the top. 
     Consequently, as compared with a case where the portion in which the height of the bottom raising portion changes is formed with a curved surface that recesses toward a base portion or a plane surface, it is possible to make a portion in which the height of the bottom raising portion is maximum appear to be bright and clear. In other words, a change in the brightness is small around the foot portion of the bottom raising portion and the change in the brightness is large around the top. Therefore, the portion in which the height of the bottom raising portion is maximum stands out. In this way, the range of expression of the decorative portion can be further broadened. 
     A fifth aspect provides the tire according to any one of the second to the fourth aspects, in which the base surface is a bottom of a recess formed toward an inner side of the tire with respect to the outer surface, and the bottom raising portion is formed such that a top of the bottom raising portion does not project toward an outer side of the tire from the outer surface. 
     In this tire, the top of the bottom raising portion is formed so as not to project toward the outer side of the tire from the outer surface of the tire. Therefore, the bottom raising portion hardly comes into contact with a flow of air flowing along a tire surface during traveling, and thus the aerodynamic effect can be improved. 
     A sixth aspect provides the tire according to any one of the second to the fourth aspects, in which the base surface is a bottom of a recess formed toward an inner side of the tire with respect to the outer surface, and the projections are formed such that tops of the projections do not project toward an outer side of the tire from the outer surface. 
     In this tire, the tops of the projections are formed so as not to project toward the outer side of the tire from the outer surface of the tire. Therefore, the projections hardly come into contact with a flow of air flowing along the tire surface during traveling, and thus the aerodynamic effect can be improved. 
     A seventh aspect provides the tire according to any one of the first to the sixth aspects, in which in the gradual decrease region, the height of the projections measured from the base surface is constant. 
     Since the height of the projections measured from the base surface is made constant, processing depths of recesses to be formed in a mold for forming the projections can be made constant, and constant blackness of the pattern region other than the gradual decrease region can be maintained. 
     An eighth aspect provides the tire according to the second aspect, in which the gradual decrease region is provided with three or more kinds of the projections and heights of each of the three or more kinds of projections from the bottom raising portion is different. 
     In the tire provided with the bottom raising portion projecting from the base surface in the gradual decrease region, three or more kinds of the projections are provided different in height from the bottom raising portion. As a result, a smooth gradation can be obtained. 
     In a case where the height of the projections is made different through provision of the bottom raising portion, when two kinds of the projections different in height are provided, a change in height of the bottom raising portion per length unit becomes too large, and a large level difference where stress is easily concentrated is generated in the gradual decrease region, whereby a crack may occur from the level difference. On the other hand, when three or more kinds of the projections different in height are provided, in the gradual decrease region, a change in height of the bottom raising portion per length unit becomes small, and stress concentration is relieved, whereby a crack hardly occurs. 
     Advantageous Effects of Invention 
     According to the present disclosure, a range of expression of a decorative portion in which projections are formed in a tire can be broadened. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a side view of a tire according to a first embodiment of the present invention,  FIG. 1B  is an explanatory view showing a relationship between a bottom raising projection of a gradation region provided in a low brightness region of a decorative portion and brightness, and  FIG. 1C  is a perspective view of the bottom raising projection. 
         FIG. 2  is a plan view showing the low brightness region of the decorative portion of the tire according to the first embodiment of the invention. 
         FIG. 3  is an enlarged plan view showing projections formed in the low brightness region of the decorative portion of the tire according to the first embodiment of the invention. 
         FIG. 4A  is a sectional view showing first asterisk projections formed in the low brightness region of the decorative portion of the tire according to the first embodiment of the invention, and  FIG. 4A  is a sectional view showing second asterisk projections formed in the low brightness region. 
         FIG. 5  is a plan view showing a low brightness region of a decorative portion of a tire according to a second embodiment of the invention. 
         FIG. 6A  is a sectional view showing the low brightness region of the decorative portion of the tire according to the second embodiment of the invention, and  FIG. 6B  is a sectional view of rib projections formed in the low brightness region. 
         FIGS. 7A to 7C  are sectional views of a bottom raising projection according to other embodiments. 
         FIG. 8  is a perspective view of a tread showing a decorative portion of a tire according to a third embodiment of the invention. 
         FIG. 9  is a sectional view of a low brightness region of a tire according to another embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     One example of a tire according to a first embodiment of the present invention will be described with reference to  FIGS. 1 to 5 . Arrow C shown in the drawings indicates a tire circumferential direction and arrow R indicates a tire radial direction. 
     As shown in  FIG. 1A , a decorative portion  14  is formed in a tire side portion  12  of a tire  10 . When seen from an axial direction of the tire  10 , the decorative portion  14  of the embodiment has an arc shape, but may have an annular shape that extends continuously in the circumferential direction. 
     In the decorative portion  14 , a flat base surface  30  (see  FIG. 4 ) is formed that recesses by a constant dimension with respect to another region  20  in which projections described later or the like are not formed in regions other than the decorative portion  14  in the tire side portion  12 . In the embodiment, the base surface  30  is recessed by  0 . 45  mm with respect to the other region  20  of the tire side portion  12  (see  FIG. 4 ). The base surface  30  of the embodiment has the same surface roughness as that of the other region  20 . 
     A low brightness region  18  whose brightness is lower than the other region  20  and that appears to be black color is formed all over the decorative portion  14 . The low brightness region  18  is an example of the pattern region. 
     In a mold (metal mold) for forming the tire  10 , irregularities are provided in a portion corresponding to the low brightness region  18  to form the low brightness region  18 . The low brightness region  18  is preferably disposed in the tire side portion  12  from the perspective of visibility when the tire  10  is mounted to a vehicle. 
     (Low Brightness Region  18 ) 
     As shown in  FIGS. 2 to 3 , the low brightness region  18  includes a plurality of first asterisk projections  34  and a plurality of second asterisk projections  36  projecting from the base surface  30 . The first asterisk projections  34  and the second asterisk projections  36  are alternately disposed in the tire circumferential direction and the tire radial direction. The first asterisk projections  34  and the second asterisk projections  36  are examples of the projection. 
     [First Asterisk Projection  34 ] 
     As shown in  FIG. 3 , each of the first asterisk projections  34  is constituted of first extending portions  35 A- 1  and  35 A- 2 , second extending portions  35 B- 1  and  35 B- 2 , and third extending portions  35 C- 1  and  35 C- 2 , each of which extends in a different direction from a center O 1  serving as a base point when seen from a direction orthogonal to the base surface  30  (direction of a rotation axis of the tire  10 ). Hereinafter, these six extending portions are collectively referred to as “extending portion  34 E”. One extending portion  34 E and another extending portion  34 E (excluding extending portions extending in mutually reverse directions from the center O 1 ) constitute a line shape bent at the center O 1 . 
     The first extending portion  35 A- 1  and the first extending portion  35 A- 2  extend in mutually reverse directions from the center O 1 , and the first extending portion  35 A- 1  and the first extending portion  35 A- 2  constitute a shape that continuously extend in a straight line. The first extending portion  35 A- 1  extends to the outer side in the tire radial direction from the center O 1 , and the first extending portion  35 A- 2  extends to the inner side in the tire radial direction from the center O 1 . The first extending portion  35 A- 1  and the first extending portion  35 A- 2  have the same length. Hereinafter, the first extending portion  35 A- 1  and the first extending portion  35 A- 2  are collectively referred to as “first extending portion  35 A”. 
     The second extending portion  35 B- 1  and the second extending portion  35 B- 2  extend in mutually reverse directions from the center O 1 , and the second extending portion  35 B- 1  and the second extending portion  35 B- 2  constitute a shape that continuously extend in a straight line. The second extending portion  35 B- 1  and the second extending portion  35 B- 2  are inclined with respect to the tire circumferential direction so that an end on one side (left side of the drawing) in the tire circumferential direction is located outer side in the tire radial direction as compared with an end on the other side (right side in the drawing). 
     The second extending portion  35 B- 1  extends to the one side in the tire circumferential direction from the center O 1 , and the second extending portion  35 B- 2  extends to the other side in the tire circumferential direction from the center O 1 . The second extending portion  35 B- 1  is longer than the second extending portion  35 B- 2 . A portion on a tip side of the second extending portion  35 B- 2  is curved to the inner side in the tire radial direction. Hereinafter, the second extending portion  35 B- 1  and the second extending portion  35 B- 2  are collectively referred to as “second extending portion  35 B”. 
     The third extending portion  35 C- 1  and the third extending portion  35 C- 2  extend in mutually reverse directions from the center O 1 , and the third extending portion  35 C- 1  and the third extending portion  35 C- 2  constitute a shape that continuously extend in a straight line. The third extending portion  35 C- 1  and the third extending portion  35 C- 2  are inclined with respect to the tire circumferential direction so that an end on the one side (left side of the drawing) in the tire circumferential direction is located inner side in the tire radial direction as compared with an end on the other side (right side in the drawing). 
     The third extending portion  35 C- 1  extends to the other side in the tire circumferential direction from the center O 1 , and the third extending portion  35 C- 2  extends to the one side in the tire circumferential direction from the center O 1 . The third extending portion  35 C- 1  is shorter than the third extending portion  35 C- 2 . Hereinafter, the third extending portion  35 C- 1  and the third extending portion  35 C- 2  are collectively referred to as “third extending portion  35 C”. 
     Six extending portions  34 E each form an angle of 60° together with an adjacent extending portion  34 E. In other words, the first asterisk projections  34  each have a shape in which six extending portions  34 E extend radially from the center O 1 . 
     As shown in  FIG. 4A , in each of the extending portions  34 E of the first asterisk projections  34 , the cross section in the direction orthogonal to the extending direction has a substantially isosceles triangle shape having a flat top surface  34 C. This means that the first asterisk projections  34  include the top surface  34 C and a pair of side surfaces  34 D. In the embodiment, the width of the top surface  34 C (W 1  in the drawing) is  0 . 02  mm, and an apex angle (D 1  in the drawing) of the first asterisk projections  34  is 26 [° ]. The height (H 1  in the drawing) of the first asterisk projections  34  measured from the base surface  30  is set to one predetermined value of from 0.1 mm to 1.0 mm. When the height of the projections (projecting height) is less than 0.1 mm, it is difficult to form a projection, and the brightness may not be lowered to such a degree that the low brightness region  18  appears to be black color through causing of the incident light to decline (details will be described later). Since the height of the projections is set to 1.0 mm or less, a difference between the rigidity of projection portions and the rigidity of portions around the projections is reduced so that local concentration of stress is suppressed. 
     The height of the projections in the embodiment and a dimension of an interval (pitch) or the like between the projections described later can be measured using, for example, VR-3000 One-Shot 3D Measuring Macroscope by KEYENCE CORPORATION. 
     [Second Asterisk Projection  36 ] 
     As shown in  FIG. 3 , second asterisk projections  36  each have a shape similar to the shape of the first asterisk projections  34 . Specifically, second asterisk projections  36  each have a shape of the first asterisk projections  34  vertically inverted after being rotated by 90 [° ] clockwise around the center O 1  when seen from the direction orthogonal to the base surface  30 . 
     In the second asterisk projections  36 , portions corresponding to the first extending portions  35 A- 1  and  35 A- 2 , the second extending portions  35 B- 1  and  35 B- 2 , the third extending portions  35 C- 1  and  35 C- 2 , and the center O 1  of the first asterisk projections  34  are referred to as first extending portions  37 A- 1  and  37 A- 2 , second extending portion  37 B- 1  and  37 B- 2 , third extending portion  37 C- 1  and  37 C- 2 , and a center O 2 , respectively. Hereinafter, these six extending portions are collectively referred to as “extending portion  36 E”. 
     As shown in  FIG. 4B , in the second asterisk projections  36 , a portion corresponding to the top surface  34 C of the first asterisk projections  34  is referred to as a top surface  36 C. In the second asterisk projections  36 , portions corresponding to the side surfaces  34 D of the first asterisk projections  34  are referred to as side surfaces  36 D. A height H 1  and an apex angle D 1  of the second asterisk projections  36  are specified in the same manner as the height H 1  and the apex angle D 1  of the first asterisk projections  34 . 
     [Others] 
     As shown in  FIGS. 2 and 3 , the first asterisk projections  34  and the second asterisk projections  36  are alternately disposed in the tire circumferential direction and the tire radial direction and fill the entire low brightness region  18 . 
     The tip of each of the first extending portions  35 A- 1  and  35 A- 2  of the first asterisk projections  34  is inserted into each of areas between the second extending portion  37 B- 2  and the third extending portion  37 C- 1 , and between the second extending portion  37 B- 1  and the third extending portion  37 C- 2  of the adjacent second asterisk projections  36  in the tire radial direction. The tip of each of the first extending portions  37 A- 1  and  37 A- 2  of the second asterisk projections  36  is inserted into each of areas between the second extending portion  35 B- 1  and the third extending portion  35 C- 2 , and between the second extending portion  35 B- 2  and the third extending portion  35 C- 1  of the adjacent first asterisk projections  34  in the tire circumferential direction. 
     The tip of the third extending portion  35 C- 1  of the first asterisk projections  34  is connected with the tip of the second extending portion  37 B- 1  of the second asterisk projections  36  disposed outer side in the tire radial direction with respect to the first asterisk projections  34 . In this way, a connecting portion  34 A is formed. The tip of the second extending portion  35 B- 1  of the first asterisk projections  34  is connected with the tip of the third extending portion  37 C- 1  of the second asterisk projections  36  disposed on the one side in the tire circumferential direction with respect to the first asterisk projections  34 . In this way, a connecting portion  34 B is formed. 
     In this configuration, the first asterisk projections  34  and the second asterisk projections  36  are connected with each other from the inner side toward the outer side in the tire radial direction through the connecting portions  34 A and  34 B in a step shape. 
     In the first asterisk projections  34  and the second asterisk projections  36  adjacent to each other in the tire radial direction and the tire circumferential direction, the interval (hereinafter, referred to as “interval Pl”) between the center O 1  and the center O 2  is set to one predetermined value of from 0.1 mm to 1.0 mm. When the interval P 1  is less than 0.1 mm, it is difficult to form a projection. When the interval P 1  is more than 1.0 mm, the brightness may not be lowered to such a degree that the low brightness region  18  appears to be black color through causing of the incident light to decline as compared with the other region  20  other than the decorative portion  14  in the tire side portion  12  (details will be described later). 
     As shown in  FIG. 4 , the height H 1  of the first asterisk projections  34  and the height H 1  of the second asterisk projections  36  each are preferably smaller than a depth dimension D (dimension from the surface of the other region  20  of the tire side portion  12  to the base surface  30 ) of the decorative portion  14 . In other words, the first asterisk projections  34  and the second asterisk projections  36  preferably do not project from the surface of the other region  20  of the tire side portion  12 . 
     [Gradation Region  48 ] 
     In the decorative portion  14  of the embodiment, the brightness of the entire low brightness region  18  is not equally lowered (that is, the value of the brightness is not set to a constant value). In order to broaden the range of expression of the decorative portion, a gradation of the brightness is added so that the brightness gradually increases from black color. Hereinafter, in the low brightness region  18 , a region to which the gradation is added is referred to as a gradation region  48 . As shown in  FIG. 1 , the decorative portion  14  of the embodiment is provided with four long narrow strips of the gradation region  48  extending in an inclined manner with respect to the tire circumferential direction. 
     As shown in  FIG. 1B , the low brightness region  18  of the embodiment is provided with a bottom raising projection  50  having a rib shape on the base surface  30  so as to provide the gradation region  48 . The bottom raising projection  50  is an example of the bottom raising portion. A sectional shape of the bottom raising projection  50  perpendicular to a longitudinal direction has a height that gradually decreases from a ridge  50 A which is the highest at the center toward both sides in the width direction. In other words, the height of the bottom raising projection  50  gradually increases from both ends (foot portions)  50 C in the width direction toward the ridge  50 A. In this bottom raising projection  50 , one side of the ridge  50 A (half portion in the width direction) is an example of the gradual increase region. An inclined surface  50 B located on both sides of the ridge  50 A is formed into a substantially arc shape that has a center of curvature in the outer side of the tire and projects toward the base surface  30 . In other words, the inclination angle of the inclined surface  50 B with respect to the base surface  30  gradually increases from the ends (foot portions)  50 C in the width direction toward the ridge  50 A. 
     In the sectional view of the bottom raising projection  50  perpendicular to the longitudinal direction shown on the left side of  FIG. 1B  and the enlarged plan view showing the brightness of the gradation region  48  of the low brightness region  18  on the right side of  FIG. 1B , the first asterisk projections  34  and the second asterisk projections  36  are omitted, and the plan view on the right side only shows a change in the brightness. 
     A height H 3  of the bottom raising projection  50  is preferably smaller than the depth dimension D (see  FIG. 4A ) of the decorative portion  14 , and smaller than the height H 1  of the first asterisk projections  34  and the height H 1  of the second asterisk projections  36  (see  FIG. 4 ). The height H 3  of the bottom raising projection  50  of the embodiment is constant in the longitudinal direction of the bottom raising projection  50 . A width W of the bottom raising projection  50  is not particularly specified, and as shown in  FIG. 2 , the plurality of first asterisk projections  34  and second asterisk projections  36  may be disposed in the width direction (direction in which the height changes) in a half region  48 A, which is a half of the gradation region  48  in the width direction (half the width W of the bottom raising projection  50 ). The half region  48 A is an example of the gradual decrease region. 
     Here, in the base surface  30  of the gradation region  48  of the embodiment, a region from the ridge  50 A to each of the ends (foot portions)  50 C in the width direction, in which the inclined surface  50 B is provided, in other words, the half region  48 A, which is a half of the gradation region  48  in the width direction corresponds to the gradual decrease region as an example in the disclosure. Through provision of the inclined surface  50 B on the base surface  30 , in the first asterisk projections  34  and the second asterisk projections  36 , a height (apparent height) Hf measured from the surface (surface of the inclined surface  50 B) of the bottom raising projection  50  is gradually decreased along the inclined surface  50 B from the ridge  50 A to the ends (foot portions)  50 C in the width direction. 
     Here, with respect to the low brightness region  18  that appears to be black color described in the embodiment, the value of brightness L measured using a handy spectrophotometer manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD is, for example, in a range below  10 . However, the value of the brightness L need not be below  10  as long as the low brightness region  18  appears to be blacker than the other region  20  other than the decorative portion  14 . 
     On the other hand, with respect to the other region  20  other than the decorative portion  14  in the tire side portion  12  (region in which the first asterisk projections  34  and the second asterisk projections  36  are not formed), the value of the brightness L measured using an handy spectrophotometer manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD is, for example, in a range larger than  20 , but the brightness L may be  20  or less. This means that the low brightness region  18  that appears to be black color is a region whose brightness is relatively low compared with the brightness of the surrounding part on the outer surface of the tire  10 . 
     (Function and Effect) 
     Next, the function and the effect of the tire  10  according to the embodiment will be described. 
     In the other region  20  of the tire side portion  12  in which the first asterisk projections  34  and the second asterisk projections  36  are not formed, incident light is reflected to the outer side by the outer surface that constitutes the other region  20 . 
     On the other hand, in the low brightness region  18  provided at the decorative portion  14  of the tire side portion  12 , light that enters the first asterisk projections  34  and the second asterisk projections  36  formed in the low brightness region  18  strikes the side surfaces  34 D shown in  FIG. 4A . The incident light declines while being repeatedly reflected between the side surfaces  34 D facing each other, and then is reflected to the outer side. 
     Therefore, the amount of light reflected to the outer side in the low brightness region  18  is smaller than the amount of light reflected to the outer side in the other region  20  in which the first asterisk projections  34  and the second asterisk projections  36  are not formed, and thus the low brightness region  18  appears to be relatively black color compared with the other region  20 . 
     As shown in  FIGS. 1 and 4 , the low brightness region  18  is provided with the gradation region  48  that changes the height Hf of the plurality of first asterisk projections  34  and second asterisk projections  36  measured from the surface of the bottom raising projection  50 . In the gradation region  48 , in a portion including the first asterisk projections  34  and the second asterisk projections  36  whose height Hf is relatively high, the amount of light reflected to the outer side is small and the portion appears to be relatively black color, and in a portion including the first asterisk projections  34  and the second asterisk projections  36  whose height Hf is relatively low, the amount of light reflected to the outer side is relatively large and the portion appears to be relatively bright. 
     In the gradation region  48 , the height of the bottom raising projection  50  gradually changes. Therefore, the brightness increases from the lower portion to the higher portion of the bottom raising projection  50 . This means that a smooth gradation is added to the brightness in the gradation region  48 . Therefore, as compared with a case where the brightness is set constant, the range of expression of the decorative portion  14  can be broadened (range of technique can be broadened). In the low brightness region  18 , the area around the ridge  50 A of the bottom raising projection  50  is relatively bright and stands out. 
     As shown in  FIG. 3 , each of the extending portions  34 E of the first asterisk projections  34  extends in a different direction, and each of the extending portions  36 E of the second asterisk projections  36  extends in a different direction. In this way, even when the low brightness region  18  is seen after the angle for seeing the low brightness region  18  is changed, a difference in appearance can be suppressed. 
     In addition, the first asterisk projections  34  and the second asterisk projections  36  are connected with each other through the connecting portions  34 A and  34 B in a step shape. In this way, the first asterisk projections  34  and the second asterisk projections  36  support each other through the connecting portions  34 A and  34 B and falling of the first asterisk projections  34  and the second asterisk projections  36  can be suppressed, whereby the durability can be improved. 
     Second Embodiment 
     Next, one example of a tire according to a second embodiment of the present invention will be described with reference to  FIGS. 5 and 6 . Note that the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. 
     As shown in  FIGS. 5 and 6 , the base surface  30  of the decorative portion  14  of the embodiment is provided with a plurality of rib projections  52  instead of the first asterisk projections  34  and the second asterisk projections  36  of the first embodiment. As shown in  FIG. 5 , the rib projections  52  are formed in a zigzag shape in plan view of the decorative portion  14 . The rib projections  52  are examples of the projection. 
     As shown in  FIG. 6 , in each of the rib projections  52 , the cross section in a direction orthogonal to an extending direction has a substantially isosceles triangle shape having a flat top surface  52 C. This means that the rib projections  52  each include the top surface  52 C and a pair of side surfaces  52 D. In the embodiment, the width of the top surface  52 C (Wa in the drawing) is 0.02 mm, and an apex angle (Da in the drawing) of the rib projections  52  is 26 [°]. The height (Ha in the drawing) of the rib projections  52  measured from the base surface  30  is set to one predetermined value of from 0.1 mm to 1.0 mm. 
     In the rib projections  52  adjacent to each other, the interval (hereinafter, referred to as “interval Pa”) between the center of one of the rib projections  52  and the center of the other one of the rib projection  52  is set to one predetermined value of from 0.1 mm to 1.0 mm. 
     The rib projections  52  provided in the low brightness region  18  of the decorative portion  14  of the embodiment are different in shape from the first asterisk projections  34  and the second asterisk projections  36  of the first embodiment. However, by the same principle as the first embodiment, light that enters the rib projections  52  declines while being repeatedly reflected between the side surfaces  52 D facing each other, and then is reflected to the outer side. In this way, the amount of light reflected to the outer side in the low brightness region  18  of the embodiment is smaller than the amount of light reflected to the outer side in the other region  20  in which the rib projections  52  are not formed, and thus the low brightness region  18  appears to be relatively black color compared with the other region  20 . 
     The low brightness region  18  of the embodiment is provided with the gradation region  48  that gradually decreases the height of the rib projections  52  measured from the surface of the bottom raising projection  50 . Therefore, in the gradation region  48 , in a portion including the rib projections  52  whose height is relatively high, the amount of light reflected to the outer side is small and the portion appears to be relatively black color, and in a portion including the rib projections  52  whose height is relatively low, the amount of light reflected to the outer side is relatively large and the portion appears to be relatively bright. 
     Accordingly, in the low brightness region  18  of the embodiment provided with the rib projections  52  that are different in shape from the first asterisk projections  34  and the second asterisk projections  36 , a smooth gradation can be added to the brightness in the gradation region  48 . Therefore, as compared with the case where the brightness is made constant, the range of expression of the decorative portion  14  can be broadened (range of technique can be broadened). 
     Other Embodiments 
     The present invention has been described in detail with respect to specific embodiments. However, the present invention is not limited to the above embodiments, and it is apparent to those skilled in the art that various other embodiments are possible within the scope of the present invention. 
     For example, in the above embodiments, the inclination angle of the inclined surface  50 B of the bottom raising projection  50  gradually increases toward the ridge  50 A from both ends. Alternatively, as shown in  FIG. 7A , the inclined surface  50 B may be a plane surface whose inclination angle is constant, and as shown in  FIG. 7B , the inclined surface  50 B may be a curved surface whose inclination angle gradually decreases toward the ridge  50 A from both ends and that recesses toward the base surface  30 . As shown in  FIG. 1C , the shape of the inclined surface  50 B is formed into a substantially arc shape that has a center of curvature in an outer side of the tire and projects toward the base surface  30 . As a result, as compared with the cases of the shapes shown in  FIGS. 7A and 7B , it is possible to make the ridge  50 A in which the height of the bottom raising projection  50  is maximum appear to be clear. 
     The bottom raising projection  50  of the embodiments described above is provided with the inclined surface  50 B at both sides of the ridge  50 A. Alternatively, as shown in  FIG. 7C , the bottom raising projection  50  may have the inclined surface  50 B on one side and a vertical surface perpendicular to the base surface  30  on the other side. 
     In the above embodiments, the height H 3  of the bottom raising projection  50  is constant in the longitudinal direction of the bottom raising projection  50 . Alternatively, the height H 3  may change in the longitudinal direction. In this way, in the gradation region  48 , a gradation can be added in the longitudinal direction of the bottom raising projection  50 , and the range of expression of the decorative portion  14  can be further broadened. 
     In the above embodiments, the width W of the bottom raising projection  50  is constant in the longitudinal direction of the bottom raising projection  50 . Alternatively, the width W may change in the longitudinal direction. In this way, in the gradation region  48 , a gradation can be added in the longitudinal direction of the bottom raising projection  50 , and the range of expression of the decorative portion  14  can be further broadened. 
     In the above embodiments, the bottom raising projection  50  continuously extends in a rib shape. Alternatively, the bottom raising projection  50  may be intermittently formed. 
     In the above embodiments, the bottom raising projection  50  is formed in a rib shape that extends in one direction. However, the present invention is not limited to this, and the bottom raising projections  50  may be formed into a cone shape. In this way, it is possible to make the gradation region  48  appear to be a circular shape in plan view. Additionally, it is possible to make the central part of the circle appear to be the brightest and make the brightness appear to be gradually decreased toward the radial outer side from the central part. 
     The shape of the gradation region  48  in plan view is not limited to an arc shape, and may be another shape such as a linear shape, and may be a character, a brand logo, a mark, or the like. 
     In the above embodiments, the entire decorative portion  14  is defined as the low brightness region  18 , but only a part of the decorative portion  14  may be defined as the low brightness region  18  (the rest is the base surface  30  only). The shape of the low brightness region  18  in plan view is not limited to an arc shape, and may be another shape such as a linear shape, and may be a character, a brand logo, a mark, or the like. 
     In the embodiments described above, the decorative portion  14  including the low brightness region  18  is provided on the tire side portion  12  of the tire  10 . Alternatively, although not shown, the decorative portion  14  may be provided in a bead portion. For example, as shown in  FIG. 8 , the low brightness region  18  including the gradation region  48  may be provided at a groove bottom of a groove  56  that is formed in a tread  54  so that the groove bottom serves as a decorative portion. Although not shown, the low brightness region  18  may be provided on a groove side surface of the groove  56  so that the groove side surface serves as a decorative portion. The part in which the decorative portion  14  is provided is not limited as long as the decorative portion  14  is provided on the outer surface of tire  10 . 
     For example, in the low brightness region  18  of the first embodiment, since a part of the low brightness region  18  serves as the gradation region  48 , the bottom raising projection  50  is provided and a depth of a valley between projections is changed so as to change the height Hf of the first asterisk projections  34  and the second asterisk projections  36  from the bottom raising projection  50 . However, as shown in  FIG. 9 , a region in which the height of the first asterisk projections  34  and the second asterisk projections  36  from the base surface  30  are gradually changed is defined as the gradation region  48  so that a smooth gradation is added to the brightness, whereby the range of expression of the decorative portion  14  can be broadened (technique can be broadened) 
     The disclosure of Japanese Patent Application No. 2017-238588 filed on Dec. 13, 2017 is incorporated herein by reference in its entirety. 
     All documents, patent applications, and technical standards mentioned in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated herein by reference.