Abstract:
Provided is a resin laminates in which the depth of concave ribs provided to a back side sheet can be made uniform, even when a convex region and flat regions are present on an front side sheet of the resin laminate. The resin laminate is provided with the front side sheet and the back side sheet, which overlap with a hollow interposed therebetween. The back side sheet is recessed into the hollow, and a large number of concave ribs are provided. The bottoms of the concave ribs are fused to the front side sheet. The front side sheet is provided with front side flat region configured from a flat surface and a front side convex region protruding away from the hollow. The back side sheet is provided with back side flat region configured from a flat surface and a back side concave region recessed into the hollow.

Description:
TECHNICAL FIELD 
     The present invention relates to a resin laminate. 
     BACKGROUND ART 
     So-called resin laminates are conventionally employed for interior materials of automobiles, building materials, and materials for logistics and packaging. Such resin laminate has a front surface material made of a resin and a back surface material made of a resin. The back surface material is provided with concave ribs having tip ends to be abutted on the internal surface of the front surface material. For a method of manufacturing such resin laminate, various methods have been employed conventionally. 
     For example, PTL 1 discloses a method as follows. 
     That is, using a split mold in which a cavity in one piece of the split mold is provided with a plurality of projections projecting towards the other piece of the split mold, two sheet materials made of a thermoplastic resin in a molten state is positioned between the pair of split mold pieces. Then, after an enclosed space is formed between one of the sheet materials and the cavity in the one piece of the split mold, the air in the enclosed space is sucked from the side of the one piece of the split mold. By the suction action, a plurality of concave ribs are formed in the sheet material at the plurality of projections. By closing the pair of split mold pieces, the bottom of the concave ribs is welded to the other sheet material to obtain a resin laminate having a hollow structure reinforced by the plurality of ribs. 
     Use of such manufacturing technique enables maximum thinning of the respective thicknesses of the two sheet materials, thereby enabling reduction in weight and thickness while securing the manufacturing efficiency and the product quality. 
     CITATION LIST 
     Patent Literature 
     PLT 1: Japanese Unexamined Patent Application Publication No. 2013-10273 
     SUMMARY OF INVENTION 
     Technical Problem 
     In PTL 1, a resin laminate having a flat surface of a front side sheet is assumed, where a back side sheet is provided with a step to form a thick plate area and a thin plate area in the resin laminate. The concave ribs having the back side sheet recessed towards the front side sheet have the depth in the thick plate area deeper than the depth in the thin plate area. 
     As illustrated in  FIG. 6 , a front side sheet  3  of a resin laminate  1  is sometimes provided with a convex region  3   a  and flat regions  3   b . In such a case, concave ribs  7   a  with a back side sheet  5  recessed towards the front side sheet  3  in a manner same as that in PTL 1 have the depth in the convex region  3   a  deeper than the depth in the flat regions  3   b . The concave ribs  7   a  formed in the convex region  3   a , therefore, have a thickness thinner than the thickness of concave ribs  7   b  formed in the flat regions  3   b . When the thicknesses of the concave ribs  7   a  and  7   b  are different in such a manner, the entire thickness has to be thicker to prevent pinholes in the thinnest area, leading to increase in weight of the resin laminate. 
     The present invention has been made in view of such circumstances and provides a resin laminate that is capable of equalizing the depth of concave ribs provided in a back side sheet even when there are flat regions and a convex region in a front side sheet of the resin laminate. 
     Solution to Problem 
     According to the present invention, a resin laminate is provided that includes: a front side sheet; and a back side sheet, both stacked across a hollow, the back side sheet being recessed into the hollow to provide a large number of concave ribs and a bottom of the large number of concave ribs welded to the front side sheet to couple the front side sheet to the back side sheet by the large number of concave ribs, wherein the front side sheet is provided with a front side flat region configured with a flat surface and a front side convex region projecting to an opposite side of the hollow, the back side sheet is provided with a back side flat region configured with a flat surface and a back side concave region recessed into the hollow, the front side convex region and the back side concave region are provided in a position facing each other, and at least one of the concave ribs is provided for each of the front side convex region and the front side flat region. 
     The present inventors have made various investigations to achieve the above object. As a result, they have come up with an idea of providing a concave region in a back side sheet so as to face a convex region of a front side sheet. Then, by providing a concave region in this position, it is possible to reduce a difference between the depth of the concave ribs in the convex region of the front side sheet and the depth of the concave ribs in the flat regions of the front side sheet, and thus they have come to complete the present invention. In addition, by equalizing the depth of the concave ribs, the thickness of the concave ribs is equalized. Then, by equalizing the thickness of the concave ribs, pinholes do not easily occur even when the back side sheet is thinned, thereby enabling reduction in thickness, that is, reduction in weight of the back side sheet. 
     Various embodiments of the present invention are exemplified below. The embodiments shown below may be combined with each other. 
     It is preferred that the front side convex region has a length in a height direction substantially equal to a length in a depth direction of the back side concave region. 
     It is preferred that the front side convex region has a shape fitting into the back side concave region. 
     It is preferred that the large number of concave ribs are arranged to substantially form an equilateral triangle with a line connecting centers of adjacent three of the concave ribs. 
     It is preferred that the adjacent three of the concave ribs at a border between the back side concave region and the back side flat region include the concave ribs provided in the back side concave region and the concave ribs provided in the back side flat region. 
     It is preferred that a border line between the back side concave region and the back side flat region is provided between the concave ribs provided in the back side concave region and the concave ribs provided in the back side flat region. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrate a configuration of a resin laminate  1  in a first embodiment of the present invention, where (a) is a plan view taken from a front side sheet  3  side, (c) is a bottom view taken from a back side sheet  5  side, and (b) is an A-A cross-sectional view of (c). 
         FIGS. 2( a ) and ( b )  are cross-sectional views corresponding to  FIG. 1( b ) , where (a) illustrates a state of vertically arranging two resin laminates  1  in  FIG. 1  in alignment and (b) illustrates a state of stacking two resin laminates  1 . 
         FIG. 3  illustrates a step of closely adhering melted resin sheets  13  and  14  to molds  11  and  12  in a procedure of manufacturing the resin laminate  1  in  FIG. 1 . 
         FIG. 4  is a diagram illustrating the procedure of manufacturing the resin laminate  1  following  FIG. 3  and illustrates a state after closing the molds. 
         FIG. 5( a )  is a cross-sectional view of a resin laminate  1  in a second embodiment of the present invention corresponding to  FIGS. 1( b ), and 5( b )  illustrates a state of vertically stacking two resin laminates  1  in  5 ( a ). 
         FIG. 6  is a reference drawing to illustrate the problems for the present invention and is a cross-sectional view corresponding to  FIG. 1( b ) . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     With reference to the drawings, embodiments of the present invention are described below. 
     1. First Embodiment 
     As illustrated in  FIG. 1 , a resin laminate  1  in the first embodiment of the present invention is provided with a front side sheet  3  and a back side sheet  5  that are stacked across a hollow  2 . In the back side sheet  5 , a large number of concave ribs  7   a  and  7   b  are formed by causing the back side sheet  5  recessed into the hollow  2 . The bottom of the respective concave ribs  7   a  and  7   b  is welded to the front side sheet  3 , thereby coupling the front side sheet  3  to the back side sheet  5  by the large number of concave ribs  7   a  and  7   b . The front side sheet  3  is provided with front side flat regions  3   b  configured with a flat surface and a front side convex region  3   a  projecting to the opposite side of the hollow  2 . The back side sheet  5  is provided with back side flat regions  5   b  configured with a flat surface and a back side concave region  5   a  recessed into the hollow  2 . The front side convex region  3   a  and the back side concave region  5   a  are provided in a position facing each other. The large number of concave ribs  7   a  are formed in the front side convex region  3   a , and the large number of concave ribs  7   b  are formed in the front side flat regions  3   b.    
     As described above, in a mode where the back side concave region  5   a  is not formed in the back side sheet  5  as illustrated in  FIG. 6 , there used to be a problem that the concave ribs  7   a  provided in the front side convex region  3   a  have a depth deeper than the depth of the concave ribs  7   b  provided in the front side flat regions  3   b  and the thickness becomes thinner accordingly. In the present embodiment, the back side concave region  5   a  is provided to face the front side convex region  3   a , and thus deepening of the concave ribs in the front side convex region  3   a  may be suppressed. In the embodiment illustrated in  FIG. 1 , the front side convex region  3   a  has a length in the height direction substantially equal to the length in the depth direction of the back side concave region  5   a , and thus the concave ribs  7   a  have a depth substantially identical to the depth of the concave ribs  7   b . The length in the height direction of the front side convex region  3   a , however, does not have to match the length in the depth direction of the back side concave region  5   a , and there may be a difference in the lengths. In this case, the depth of the concave ribs  7   a  and the depth of the concave ribs  7   b  do not become completely same but the difference in the depth is less than that in the mode illustrated in  FIG. 6 . The effect of the present invention to equalize the depth of the concave ribs is thus obtained. 
     In the embodiment illustrated in  FIG. 1 , the front side convex region  3   a  has a shape fitting into the back side concave region  5   a . As illustrated in  FIGS. 2( a ) and 2( b ) , when a plurality of resin laminates  1  are stacked, such shape allows volume reduction by having the front side convex region  3   a  entering the back side concave region  5   a . In the state of the front side convex region  3   a  entering the back side concave region  5   a , the plurality of stacked resin laminates  1  are suppressed from horizontal movement to each other, which may cause flaws on the surface of the resin laminates  1 . 
     Then, with reference to  FIG. 1( c ) , distribution of the concave ribs  7   a  and  7   b  viewed from the back side sheet  5  side is described. The concave ribs  7   a  and  7   b  are arranged to substantially form an equilateral triangle with a line connecting centers of adjacent three of the concave ribs. Specifically, as illustrated in  FIG. 1( c ) , the back side concave region  5   a  is provided with the large number of concave ribs  7   a , and the concave ribs  7   a  are arranged to form an equilateral triangle Ta with a line connecting the centers of adjacent three of the concave ribs  7   a . The back side flat regions  5   b  are provided with the large number of concave ribs  7   b , and the concave ribs  7   b  are arranged to form an equilateral triangle Tb with a line connecting the centers of adjacent three of the concave ribs  7   b.    
     Further, at a border BB between the back side concave region  5   a  and the back side flat regions  5   b , the concave ribs  7   a  and  7   b  are arranged to form an equilateral triangle Tab with a line connecting the centers of adjacent three of the concave ribs including  7   a  and  7   b . In such a manner, the large number of concave ribs are uniformly arranged at an identical pitch over the back side concave region  5   a  and the back side flat regions  5   b . The border BB between the back side concave region  5   a  and the back side flat regions  5   b  is provided in zigzag to weave between the concave ribs  7   a  and  7   b . By providing the border BB in such a manner, the border BB may avoid overlap with the concave ribs, and thus mold design is facilitated. Meanwhile, there is no concave rib in the front surface side. A border FB between the front side convex region  3   a  and the front side flat regions  3   b  may thus be freely designed. It may be, as illustrated in  FIG. 1( a )  for example, linear. One of the points of the present invention is to avoid complex mold design by differentiating the shapes of the borders BB and FB in such a manner. 
     Then, a method of manufacturing the resin laminate  1  in the present embodiment is described. To manufacture the resin laminate  1  in the present embodiment, as illustrated in  FIG. 3 , a pair of molds  11  and  12  in accordance with the shape of the resin laminate  1  are prepared. By sucking the melted resin sheets (parisons)  13  and  14  from the mold  11  and  12  sides, the melted resin sheets  13  and  14  are closely adhered to the molds  11  and  12 . 
     Then, as illustrated in  FIG. 4 , the molds  11  and  12  are closed to sandwich the melted resin sheets  13  and  14 . The molds  11  and  12  are provided with pinch-offs  11   b  and  12   b  to surround a cavity  15  formed inside the molds  11  and  12 . The melted resin sheets  13  and  14  are pinched and crushed by the pinch-offs  11   b  and  12   b . In the melted resin sheets  13  and  14 , the areas outside the cavity  15  become burrs  16  and the areas pinched by the pinch-offs  11   b  and  12   b  become cut-off lines for the burrs  16 . After mold closing, air may be optionally blown in the cavity  15 . 
     Then, the molds  11  and  12  are opened to remove the molded product and the burrs  16  are cut on the cut-off lines formed in the molded product by the pinch-offs  11   b  and  12   b  and eliminated. 
     By the above steps, the resin laminate  1  illustrated in  FIG. 1  is formed. 
     2. Second Embodiment 
     Then, with reference to  FIG. 5 , the second embodiment of the present invention is described. The resin laminate  1  in the present embodiment is similar to that in the first embodiment, and the configuration of the front side convex region  3   a  and the back side concave region  5   a  is mainly different. The following description is given mainly to such points. 
     In the first embodiment, the front side convex region  3   a  has a size substantially identical to that of the back side concave region  5   a . As illustrated in  FIG. 2( b ) , in a state of inserting the front side convex region  3   a  into the back side concave region  5   a , the plurality of stacked resin laminates  1  is almost unmovable horizontally. Meanwhile, in the present embodiment, the back side concave region  5   a  is larger than the front side convex region  3   a . The plurality of stacked resin laminates  1  is thus relatively movable horizontally within the range illustrated with arrows D in  FIG. 5( b )  even in the state of inserting the front side convex region  3   a  into the back side concave region  5   a . The resin laminate  1  in the present embodiment is allowed to relatively move slightly in the horizontal direction when stacked, and thus the effect of suppressing flaws in the resin laminate  1  may be worse than that in the first embodiment. Instead, the front side convex region  3   a  is easily inserted into the back side concave region  5   a  and there is an advantage of easy stacking of a plurality of resin laminates  1 . 
     In the first embodiment, the front side convex region  3   a  and the back side concave region  5   a  occupy a substantially same region, and thus there are the concave ribs  7   a  provided in the front side convex region  3   a  and the concave ribs  7   b  provided in the front side flat regions  3   b . In the present embodiment, the back side concave region  5   a  is wider than the front side convex region  3   a , and thus in addition to the concave ribs  7   a  and  7   b , concave ribs  7   c  shallower than the concave ribs  7   a  are provided in the regions where the back side concave region  5   a  overlaps with the front side flat regions  3   b.    
     In the first embodiment, as illustrated in  FIG. 1( b ) , the borders FB and BB have a substantially identical angle of inclination. In the present embodiment, the border FB has an angle of inclination less than that of the border BB. The borders FB and BB may thus have different angles of inclination. Although the borders FB and BB are inclined surfaces in the first and second embodiments, these borders may be surfaces substantially vertical to the front surface or the back surface of the resin laminate  1 . 
     REFERENCE SIGNS LIST 
       1 : Resin Laminate,  2 : Hollow,  3 : Front Side Sheet,  5 : Back Side Sheet,  11 ,  12 : Mold,  13 ,  14 : Melted Resin Sheet