Patent Publication Number: US-2023160219-A1

Title: Molded body and method for producing molded body

Description:
TECHNICAL FIELD 
     The present invention relates to a molded body and a method for producing the molded body. 
     BACKGROUND ART 
     For example, among resin molded bodies that are one type of molded bodies, there is known a resin molded body in which a marked surface is formed on a portion of a surface thereof. The marked surface is visually different from the rest of the surface of the resin molded body. In such a resin molded body, a marked surface including a text or a figure is formed by performing laser processing on a portion of the surface (see Patent Literature (PTL) 1, for example). 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Unexamined Patent Application Publication No. 2001-283669 
     SUMMARY OF INVENTION 
     Technical Problem 
     When a resin molded body is disposed in an environment exposed to water, a marked surface is covered with water and the visibility of the marked surface deteriorates. 
     An object of the present invention is to provide a molded body and the like of which visibility does not easily deteriorate even when the molded body gets wet. 
     Solution to Problem 
      In order to achieve the above-described object, a molded body according to an aspect of the present invention includes a marked surface provided on a portion of a surface of the molded body, the marked surface including a plurality of recesses and a plurality of projections that are alternately arranged at a predetermined pitch in a predetermined direction in a planar form, wherein the marked surface has a light absorption rate higher than a light absorption rate of an area of the molded body other than the marked surface and is a water-repellent surface having a water contact angle of at least 120 degrees or a hydrophilic surface having a water contact angle of at most 60 degrees. 
     A method for producing a molded body according to an aspect of the present invention includes forming a marked surface by performing laser processing on a portion of a surface of a base material to form a plurality of recesses and a plurality of projections that are alternately arranged at a predetermined pitch in a predetermined direction in a planar form, wherein the marked surface has a light absorption rate higher than a light absorption rate of an area of the base material other than the marked surface and is a water-repellent surface having a water contact angle of at least 120 degrees or a hydrophilic surface having a water contact angle of at most 60 degrees. 
     Advantageous Effects of Invention 
     The present invention can provide a molded body and the like of which visibility does not easily deteriorate even when the molded body gets wet. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view illustrating a bathroom in which a resin molded body according to Embodiment 1 is used. 
         FIG.  2    is a descriptive diagram illustrating a portion of a floor according to Embodiment 1. 
         FIG.  3    is an enlarged cross-sectional view of a marked surface according to Embodiment 1. 
         FIG.  4    is an enlarged cross-sectional view of a marked surface according to Embodiment 2. 
         FIG.  5    is a plan view illustrating an uneven structure according to Embodiment 3. 
         FIG.  6    is a plan view illustrating a signboard in which a resin molded body according to Embodiment 4 is used. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a resin molded body according to embodiments of the present invention will be described in detail with reference to the Drawings. It should be noted that each of the embodiments described below shows a specific example of the present invention. Accordingly, the numerical values, shapes, materials, constituent elements, the arrangement and connection of the constituent elements, steps, the order of the steps, etc., in the following embodiments are mere examples, and therefore are not intended to limit the present invention. Therefore, among the constituent elements in the following embodiments, constituent elements not recited in any of the independent claims are described as optional constituent elements. 
     It should be noted that the respective figures are schematic diagrams and are not necessarily precise illustrations. Accordingly, for example, the scaling, etc., depicted in the figures is not necessarily accurate. Additionally, in the figures, elements that are substantially the same are given the same reference signs, and overlapping descriptions thereof are omitted or simplified. 
     Additionally, in the present Description, terms indicating relations between elements, such as ‘parallel’ or ‘orthogonal’; terms indicating shapes of elements, such as ‘square’ or ‘rectangle’; and numerical ranges are not strictly defined and include a substantially same range or a margin of error of a few percent. 
     Embodiment 1 
     Molded Body 
     First, an example of an application of resin molded body  1  that is a molded body according to Embodiment 1 will be described with reference to  FIG.  1   .  FIG.  1    is a perspective view illustrating bathroom  100  in which resin molded body  1  according to Embodiment 1 is used. 
     As shown in  FIG.  1   , bathroom  100  includes floor  101  including drain outlet  102 , wall  103 , and bathtub  104 . Although it is sufficient that at least one of floor  101 , wall  103 , or bathtub  104  is formed using resin molded body  1 , the present embodiment describes, as an example, a case where floor  101  is formed using resin molded body  1 . 
       FIG.  2    is a descriptive diagram illustrating a portion of floor  101  according to Embodiment 1. Specifically, (a) in  FIG.  2    is a plan view illustrating a front surface of floor  101 . (b) in  FIG.  2    is a cross-sectional view of floor  101 . (c) in  FIG.  2    is a plan view illustrating a back surface of floor  101 . Each of the front surface and the back surface of floor  101  is an entirely exposed surface of resin molded body  1  which is a base material. In other words, no coating layer or the like is laminated on the surface of resin molded body  1 . 
     As shown in (a) and (b) in  FIG.  2   , the front surface of floor  101  includes boundary part  10  which is in the shape of grooves and a plurality of planar parts  20  defined by boundary part  10 . 
      Boundary part  10  consists of grooves formed in a lattice shape on the front surface of floor  101 . Boundary part  10  consists of grooves for draining water. Boundary part  10  consists of, for example, through grooves (i.e., linear grooves). Width W of each groove forming boundary part  10  is of millimeter order and uniform. 
     The plurality of planar parts  20  are each formed in a square shape in a plan view and are arranged in a matrix. Label  21  is provided on a front surface of at least one planar part  20  of the plurality of planar parts  20 . Various information (e.g., the manufacturer’s name, the brand name, a caution) is indicated on label  21 . 
     Fine uneven structure  30  is formed on front surfaces of boundary part  10  and planar parts  20 . (a) in  FIG.  2    illustrates an enlarged view of uneven structure  30  on each of the front surface of boundary part  10  and the front surface of planar part  20 . Although the present embodiment describes, as an example, a case where uneven structure  30  on the front surface of boundary part  10  and uneven structure  30  on the front surface of planar part  20  are same structure, they may be different from each other. It should be noted that, here, the front surface of boundary part  10  consists of bottom surfaces of the grooves forming boundary part  10 . Specifically, marked surface  39  is not formed on side surfaces of the grooves (i.e., side surfaces of planar parts  20 ). It should be noted that when a cross-sectional shape of each of the grooves is a trapezoidal shape widening upward, marked surface  39  can also be formed on the side surfaces of the grooves. 
     Uneven structure  30  includes a plurality of recesses  31  arranged in a matrix in a plan view. Each of recesses  31  is substantially square in a plan view. The portions between the plurality of recesses  31  in a predetermined direction form projections  32 . Although it can be said that there is a single projection  32  because projection  32  is in a lattice shape and continuous as a whole, it can also be said that there are a plurality of projections  32  because projection  32  is separated by recesses  31  when viewed only in the predetermined direction. In other words, the plurality of recesses  31  and the plurality of projections  32  are alternately arranged at a predetermined pitch in both a lengthwise direction and a crosswise direction. A face including such a fine uneven structure  30  is referred to as marked surface  39 . 
     As shown in (c) in  FIG.  2   , the back surface of floor  101  does not include marked surface  39  and is flat as a whole. In short, the front surface of floor  101  has a high light absorption rate compared to the back surface of floor  101  because the front surface of floor  101  includes marked surface  39  on the front surfaces of boundary part  10  and each planar part  20 . 
     Hereinafter, marked surface  39  will be described in detail.  FIG.  3    is an enlarged cross-sectional view of marked surface  39  according to Embodiment 1. Specifically,  FIG.  3    is a cross-sectional view taken along line III-III in (a) in  FIG.  2   . 
     As shown in  FIG.  3   , the sum of width w2 of projection  32  and width w1 of recess  31  in the predetermined direction is the predetermined pitch (p=w1+w2). Marked surface  39  can be made into a water-repellent surface by setting predetermined pitch p, width w1, and width w2 so as to satisfy a specific relation. Specifically, the water contact angle on marked surface  39  can be set to at least 120°. 
     For example, by assuming width w2/width w1 &lt; 0.5 and setting predetermined pitch p to be between 200 nm and 300 µm, inclusive, the water contact angle on marked surface  39  can be set to at least 120°. It is preferable that predetermined pitch p be between 200 nm and 100 µm, inclusive. It is more preferable that predetermined pitch p be between 200 nm and 50 µm, inclusive. Predetermined pitch p is smaller than width W of each groove of boundary part  10 . 
     As long as the relation is satisfied, uneven structure  30  may be non-uniform in marked surface  39 . Specifically, portions having different light absorption properties can be formed in marked surface  39  by forming a dense portion and a sparse portion in uneven structure  30 . For example, in (a) in  FIG.  2   , uneven structure  30  in label  21  is denser than that in the rest of marked surface  39 . Accordingly, in label  21 , the light absorption property is enhanced and thus visibility different from the rest of marked surface  39  is manifested. In other words, in marked surface  39 , various information can be indicated without using paint or the like. 
     Furthermore, when depth d of recess  31  and width w2 satisfy a relation of depth d/width w2 ≤ 1, the strength of projection  32  can be enhanced and thus damage to projection  32  can be reduced. 
     Next, a method for producing resin molded body  1  will be described. 
     First, a base material in a board-like shape is prepared. The base material can be formed from any resin, as long as laser processing can be performed thereon. Examples of resin on which laser processing can be performed include thermoplastic resins. Examples of the thermoplastic resins include: polyolefin resins; polyamide resins; elastomer resins, such as styrene resins, olefin resins, polyvinyl chloride (PVC) resins, urethane resins, ester resins, and amide resins; polyester resins; engineering plastics; polyethylene; polypropylene; nylon resins; acrylonitrile butadiene styrene (ABS) resins; acrylic resins; ethylene acrylate resins; ethylene-vinyl acetate resins; polystyrene resins; polyphenylene sulfide resins; polycarbonate resins; polyester elastomer resins; polyamide elastomer resins; liquid crystal polymers; polybutylene terephthalate resins; cellulose acetates; and polyvinyl acetates. One of the above-described resins may be used alone or a mixture of a plurality of resins that includes, as a main component, one of the above-described resins may be used. 
     Furthermore, the base material may include a thermosetting resin. Examples of the thermosetting resin include epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, urethane resins, melamine resins, urea resins, maleimide resins, cyanate ester resins, alkyd resins, addition-curable polyimide resins, and thermosetting acrylic resins. The thermosetting resin may include one of the above-described resins or a mixture of a plurality of resins that includes, as a main component, one of the above-described resins. Accordingly, the heat resistance of resin molded body  1  can be enhanced. In particular, the base material may include at least one of filler, glass fiber, carbon fiber, or colorant. 
     Next, pressing is performed on the base material to form boundary part  10  and the plurality of planar parts  20  on the front surface of the base material. 
     Subsequently, laser processing is performed on the front surface of the base material to form marked surface  39 . Specifically, marked surface  39  is formed by performing laser processing on a portion (front surfaces of boundary part  10  and the plurality of planar parts  20 ) of the front surface of the base material to form the plurality of recesses  31  and the plurality of projections  32  that are alternately arranged at predetermined pitch p in the predetermined direction in a planar form. The front surface of the base material is irradiated with a short pulse laser from a laser emitter that emits a laser. The pulse width of the short pulse laser is preferably less than or equal to a nanosecond. 
     When marked surface  39  is formed by laser irradiation, the light absorption rate of marked surface  39  is enhanced compared to an area (back surface or side surface) of the base material other than marked surface  39 . This is considered to be due to the various factors described below. For example, 1) the front surface of the base material is carbonized by laser irradiation and turns into a dark color. 2) The molecular density of the front surface of the base material is increased and concentrated by laser irradiation, and thus the front surface of the base material turns into a dark color. 3) A level of impurity of metallic oxide is formed on the front surface of the base material by laser irradiation, and thus the front surface of the base material turns into a dark color. Although it is currently uncertain which factor is reliable, laser processing consequently causes marked surface  39  to have a dark color and a high light absorption rate compared to other area of the base material. 
     Here, when the base material includes at least one additive such as filler, glass fiber, carbon fiber, or colorant, laser irradiation causes the additive to undergo chemical reaction, and thus the light absorption rate can be further enhanced. 
     The above-described process produces resin molded body  1  that includes marked surface  39  that is a water-repellent surface having a water contact angle of at least 120° and has a high light absorption rate compared to other area of the resin molded body  1 . It should be noted that analysis of marked surface  39  can confirm that marked surface  39  was formed by laser processing. 
     Advantageous Effects, Etc. 
     As described above, marked surface  39  of resin molded body  1  is a water-repellent surface having a water contact angle of at least 120° and has a high light absorption rate compared to an area of resin molded body  1  other than marked surface  39 . Specifically, marked surface  39  demonstrates the above-described properties because of uneven structure  30 . Uneven structure  30  is engraved on the front surface of resin molded body  1 . Therefore, uneven structure  30  is likely to remain even when it gets wet. For example, it is also possible to demonstrate a certain level of water repellency even with a structure in which a sheet provided with an uneven structure is attached on a front surface of a resin molded body or with a structure in which a fluorine layer is applied on a front surface of a resin molded body. However, there is a risk that the sheet or the fluorine layer may peel off from the resin molded body with prolonged use. Whereas, in the present embodiment, the water repellency of marked surface  39  is achieved by uneven structure  30  engraved on the front surface of resin molded body  1 , and thus the properties of marked surface  39  can be maintained stably for a long time. 
     Especially, since marked surface  39  is a water-repellent surface having a water contact angle of at least 120°, it easily repels water. Accordingly, the visibility of marked surface  39  can be prevented from deteriorating due to getting wet. 
     Consequently, it is possible to provide resin molded body  1  of which visibility does not easily deteriorate even when it gets wet. 
     Furthermore, since the plurality of recesses  31  and the plurality of projections  32  are alternately arranged at predetermined pitch p, uneven structure  30  interferes with and disperses reflected light, and thus structural color appears on at least a portion of marked surface  39 . In other words, the peak wavelength of the reflection spectrum becomes angle dependent at a portion of marked surface  39 . Accordingly, in marked surface  39 , the color changes depending on the viewing angle, and thus the visibility of marked surface  39  is further enhanced. 
     Furthermore, because depth d of recess  31  and width w2 of projection  32  satisfy the relation of depth d/width w2 ≤ 1, the strength of projection  32  can be enhanced and thus damage to projection  32  can be reduced. 
      Furthermore, the grooves (grooves forming boundary part  10 ) each having width W greater than or equal to predetermined pitch p are formed on the front surface of resin molded body  1 , and marked surface  39  is formed on the inside of the grooves. Accordingly, the visibility of the inside of the grooves can be enhanced. Furthermore, the water repellency of the grooves can be maintained for a long time. 
     Furthermore, since the molded body is resin molded body  1 , it is suitable for laser processing. 
     Furthermore, since resin molded body  1  includes a thermosetting resin, the heat resistance of resin molded body  1  can be enhanced. 
     Furthermore, since resin molded body  1  includes at least one of filler, glass fiber, carbon fiber, or colorant, the strength of resin molded body  1  can be enhanced. Accordingly, the shape of uneven structure  30  can be maintained for a longer time. Furthermore, since the additives undergo chemical reaction due to laser irradiation, the light absorption rate can be further enhanced. 
     Furthermore, since marked surface  39  is formed by laser processing, uneven structure  30  can be formed without using organic material or the like that tends to have an impact on the environment. 
     Embodiment 2 
     In Embodiment 1, a case where marked surface  39  is a water-repellent surface is described as an example. In Embodiment 2, a case where marked surface  39   a  is a hydrophilic surface will be described.  FIG.  4    is an enlarged cross-sectional view of marked surface  39   a  according to Embodiment 2. Specifically,  FIG.  4    is a diagram corresponding to  FIG.  3   . It should be noted that, hereinafter, parts equivalent to the parts in Embodiment 1 are given the same reference signs and descriptions thereof may be omitted. 
     As shown in  FIG.  4   , a fine uneven structure  30  in which a plurality of recesses  31  and a plurality of projections  32  are arranged at a predetermined pitch in a planar form is formed in marked surface  39   a . The sum of width w2 of projection  32  and width w1 of recess  31  in a predetermined direction is the predetermined pitch (p=w1+w2). Marked surface  39   a  can be made into a hydrophilic surface by setting predetermined pitch p, width w1, and width w2 so as to satisfy a specific relation. Specifically, the water contact angle on marked surface  39   a  can be set to at most 60°. 
     For example, by assuming width w2/width w1 ≥ 0.5 and setting predetermined pitch p to be between 1 µm and 1000 µm, inclusive, the water contact angle on marked surface  39   a  can be set to at most 60°. In this case as well, predetermined pitch p is smaller than width W of each groove of boundary part  10 . 
     Furthermore, when depth d of recess  31  and width w2 satisfy a relation of depth d/width w2 ≤ 1, the strength of projection  32  can be enhanced and thus damage to projection  32  can be reduced. 
     In this way, marked surface  39   a  of resin molded body 1A is a hydrophilic surface having a water contact angle of at most 60° and has a high light absorption rate compared to an area of resin molded body 1A other than marked surface  39   a . In other words, marked surface  39   a  demonstrates the above-described properties because of uneven structure  30 . Uneven structure  30  is engraved on a front surface of resin molded body 1A. Therefore, uneven structure  30  is likely to remain even when it gets wet, and thus the properties of marked surface  39   a  can be maintained stably for a long time. 
     In particular, since marked surface  39   a  is a hydrophilic surface having a water contact angle of at most 60°, water does not form a droplet but spreads over marked surface  39   a . Accordingly, the visibility of marked surface  39   a  can be prevented from deteriorating. 
     Consequently, it is possible to provide resin molded body 1A of which visibility does not easily deteriorate even when it gets wet. 
     Embodiment 3 
     In Embodiment 1, uneven structure  30  in which a plurality of recesses  31  are arranged in a matrix is described as an example. In Embodiment 3, uneven structure  30   b  in which a plurality of recesses  31   b  are arranged in stripes will be described as an example.  FIG.  5    is a plan view illustrating uneven structure  30   b  according to Embodiment 3. Specifically,  FIG.  5    is a diagram corresponding to (a) in  FIG.  2   . As shown in  FIG.  5   , each of recesses  31   b  and each of projections  32   b  are formed in a linear shape. The plurality of recesses  31   b  and the plurality of projections  32   b  are alternately arranged at a predetermined pitch. In this case, marked surface  39   b  can be made into a water-repellent surface or a hydrophilic surface, as long as the above-described condition is satisfied. 
     It should be noted that recesses and projections may be formed in any shape in a plan view, as long as they are alternately arranged at a predetermined pitch. Furthermore, a plurality of marked surfaces may be provided in a single surface. Furthermore, a plurality of marked surfaces each having recesses and projections in a layout different from the layout in another marked surface can be formed overlapping with one another. In this case, the above-described factors 1) to 3) become more prominent, and thus a portion where the plurality of marked surfaces overlap with one another has a high light absorption rate compared to the rest of a molded body. Furthermore, the layout, shape, and size of the recesses and projections may vary in a single marked surface. 
     Embodiment 4 
     Furthermore, in Embodiment 1, a case where resin molded body  1  is applied to bathroom  100  is described as an example. However, resin molded body  1  is applicable to any structure that may get wet. Other structures to which resin molded body  1  is applied include a surface material of a lighting fixture that is disposed outdoors, such as a street light or a neon sign, a lighting device for a fountain or a swimming pool, a headlight of a vehicle, digital signage, a television installed outdoors, a traffic sign, and a signboard. 
     For example, in  FIG.  6   , a case where resin molded body  1  according to Embodiment 4 is applied to signboard  200 C is illustrated. As shown in  FIG.  6   , a front surface of signboard  200 C includes a plurality of marked surfaces  39   c  and area  39   d  other than marked surfaces  39   c . Because of an uneven structure not shown in the figure, the plurality of marked surfaces  39   c  have a higher light absorption rate than area  39   d . On the other hand, no uneven structure is formed on area  39   d . Specifically, each of marked surfaces  39   c  forms a letter ‘A’. In this case as well, even when marked surface  39   c  gets wet, marked surface  39   c  is not easily obstructed by water since marked surface  39   c  is a water-repellent surface or a hydrophilic surface. Accordingly, the visibility of a content displayed on signboard  200 A can be maintained. 
     Other Embodiments 
     Although wet-area components according to the present invention have been described thus far based on the foregoing embodiments, the present invention is not limited to the foregoing embodiments. 
     For example, the top view shape of each planar part  20  need not be a quadrilateral shape, such as a square, a rectangle, a parallelogram, or a rhombus. The top view shape of each planar part  20  may be a polygonal shape, such as a triangle or a hexagon, or an asymmetrical shape at least partially including a curve. For example, the top view shapes of planar parts  20  may be asymmetrical shapes different from one another. 
      Furthermore, in the above embodiments, a case where planar part  20  only includes marked surface  39  having water repellency is described as an example. However, there may be both a marked surface having water repellency and a marked surface having hydrophilicity on a same surface of a planar part. For example, when a marked surface having water repellency and a marked surface having hydrophilicity are alternately arranged on a same surface of a planar part (resulting in non-uniform uneven structures  30  on the same surface), the Marangoni effect causes water droplets to roll out from the same surface of the planar part even when it is a level surface, and thus an effect of enhancing visibility is exerted. 
     Furthermore, although a case where resin molded body  1  includes grooves forming boundary part  10  is described as an example in the foregoing embodiments, elements of the present invention can also be applied to a resin molded body that includes no groove. 
     Furthermore, although resin molded body  1  is given as an example of a molded body in the above-described embodiments, the molded body can be formed of any material on which laser processing can be performed. Example of the material includes metal or the like. 
     Additionally, various modifications of the embodiments conceivable by those skilled in the art as well as forms resulting from arbitrary combinations of constituent elements and functions in the embodiments which do not depart from the essence of the present invention are intended to be included within the scope of the present invention. 
     
       
         
           
               
               
               
               
             
               
                 Reference Signs List 
               
             
            
               
                 
                   1 
                 
                 resin molded body (molded body) 
               
               
                 
                   10 
                 
                 boundary part (grooves) 
               
               
                   31 , 31   b   
                 recess 
               
               
                   32 , 32   b   
                 projection 
               
               
                   39 , 39   a , 39   b , 39   c   
                 marked surface 
               
               
                 
                   39 
                   d 
                 
                 area 
               
               
                 p 
                 predetermined pitch 
               
               
                 W,w1,w2 
                 width 
               
            
           
         
       
     
     F