Patent Publication Number: US-2023133229-A1

Title: Surface-Colored Glass Cloth and Fiber-Reinforced Resin Molded Product

Description:
TECHNICAL FIELD 
     The present invention relates to a surface-colored glass cloth and a fiber-reinforced resin molded product. 
     BACKGROUND ART 
     A strain distribution of a fiber-reinforced resin molded product needs to be measured in order to understand its fatigue state and life. Therefore, for example, a method of testing a fatigue state of a carbon fiber-reinforced resin molded product using a characteristic in which an electric resistance of a carbon fiber increases when the carbon fiber is distorted due to bending or the like has been proposed (Patent Literature 1). A method for measuring a strain distribution by image analysis of a two-dimensional lattice image of a material has also been proposed (Patent Literature 2). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Publication No. H05-269874 
     Patent Literature 2: International Publication WO 2016/001986 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the fiber-reinforced resin molded product containing a glass cloth as a reinforced fiber, since the glass fiber has an electrical insulation property and a clear two-dimensional lattice image thereof cannot be easily acquired, it has been difficult to measure a strain distribution with high accuracy in a conventional method. 
     Here, the present invention provides a surface-colored glass cloth capable of measuring a strain distribution of a fiber-reinforced resin molded product with high accuracy by image analysis. 
     Solution to Problem 
     An aspect of the present invention is to provide a surface-colored glass cloth including: a glass cloth which includes a warp and a weft and in which the warp and the weft respectively contain a plurality of bundled glass filaments; and a plurality of colored portions which are attached to a surface of the glass cloth. 
     One colored portion is disposed in each area including one colored point and a plurality of the colored points are arranged on a surface of the glass cloth so that a plurality of rows are formed along a predetermined direction. An average distance D between the adjacent colored points is 0.50 to 10.00 mm. When one colored point is a reference colored point and an area around the reference colored point is equally divided into eight areas by four lines extending in directions of 22.5°, 67.5°, 112.5°, and 157.5° in a clockwise manner with respect to the predetermined direction through the reference colored point, D is an average value of distances between the reference colored point and eight colored points adjacent to the reference colored point in each of the eight areas. The reference colored point is selected from the colored points in which the adjacent colored points exist in each of the eight areas. 
     When the number of warp rows is St, a warp widening degree is Et, the number of weft rows is Sy, and a weft widening degree is Ey in the glass cloth, D, St, Et, Sy, and Ey satisfy the following formula: 
       3.3≤100 ×D   1/2 ×( Et×Ey )/( St×Sy )≤25.0.
 
     Each of the number of warp rows and the warp widening degree is calculated by the following formulae: 
       number of warp rows=(width of glass filament constituting warp)×(number of glass filaments constituting warp)/(width of warp);
 
       and 
       warp widening degree=(width of warp)/{25000 μm/(weaving density of warp)}.
 
     Each of the number of weft rows and the weft widening degree is calculated by the following formulae: 
       number of weft rows=(width of glass filament constituting weft)×(number of glass filaments constituting weft)/(width of weft); and
 
       weft widening degree=(width of weft)/{25000 μm/(weaving density of weft)}.
 
     The weaving density is the number of the warps or wefts per each width of 25 mm of the glass cloth. St and Sy are 0.8 to 8.0 and Et and Ey are 0.30 to 1.20. The width of the glass filament constituting the warp or weft is 3.0 to 11.0 μm. The number of the glass filaments constituting one warp or one weft is 30 to 600. The width of the warp and the weft is 100 to 800 μm. The weaving density of the warp and the weft is 30 to 120/25 mm. 
     Another aspect of the present invention is to provide a fiber-reinforced resin molded product containing the surface-colored glass cloth and resin impregnated in the surface-colored glass cloth. 
     A still another aspect of the present invention relates to a fiber-reinforced resin molded product including: a main body which is a fiber-reinforced resin; and an inspection fiber-reinforced resin layer which is provided on a surface of the main body. The inspection fiber-reinforced resin layer contains the surface-colored glass cloth and transparent resin impregnated in the surface-colored glass cloth. 
     Advantageous Effects of Invention 
     According to an aspect of the present invention, a surface-colored glass cloth capable of measuring a strain distribution of a fiber-reinforced resin molded product with high accuracy by image analysis is provided. According to another aspect of the present invention, a fiber-reinforced resin molded product capable of measuring a strain distribution by image analysis is provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a plan view showing an embodiment of a surface-colored glass cloth. 
         FIG.  2    is a schematic diagram showing an example of an arrangement pattern of a colored portion and a colored point. 
         FIG.  3    is a plan view showing an embodiment of a surface-colored glass cloth. 
         FIG.  4    is a schematic diagram showing an example of an arrangement pattern of a colored portion and a colored point. 
         FIG.  5    is a cross-sectional view showing an embodiment of a glass cloth. 
         FIG.  6    is a cross-sectional view showing an embodiment of a fiber-reinforced resin molded product. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, some embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. 
       FIG.  1    is a plan view showing an embodiment of a surface-colored glass cloth. A surface-colored glass cloth  1  shown in  FIG.  1    includes a glass cloth  3  and a plurality of colored portions  5  attached to the surface of the glass cloth  3 . The glass cloth  3  is a woven fabric formed of a plurality of warps aligned in the X direction and a plurality of wefts aligned in the Y direction perpendicular to the X direction and may include a void portion in which the warp and the weft do not exist in the woven fabric although not shown in the drawings. Each of the warp and the weft contains a plurality of bundled glass filaments. 
     The color of the colored portion  5  is not particularly limited as long as the glass cloth  3  has a color and contrast. Since the uncolored glass cloth  3  is usually white, the colored portion  5  may be black, for example. The colored portion  5  is formed of, for example, resin ink. One colored portion  5  is disposed in each area including one colored point  10 . The colored point  10  is usually located at the center of the colored portion  5 . The center of the smallest rectangle circumscribing the colored portion  5  may be the colored point  10 . The plurality of colored points  10  are arranged on the surface of the glass cloth  3  so that a plurality of rows  10 L are formed along a predetermined direction (the X direction). Each row  10 L is composed of the plurality of colored points  10  arranged at substantially equal intervals. In the adjacent rows  10 L, the colored points  10  are arranged alternately so that the positions in the X direction do not overlap. Examples of the color of the colored portion  5  include red, blue, green, yellow, gray, and white in addition to black. 
     The glass cloth  3  is typically not colored, but may be colored. For example, the entire glass cloth  3  may be colored black, and the colored portion  5  may be white or the like. The entire glass cloth  3  may be colored white, and the colored portion  5  may be black or the like. 
     An average distance D between the adjacent colored points  10  is 0.50 to 10.00 mm.  FIG.  2    is a schematic diagram showing an arrangement pattern of the colored points of the surface-colored glass cloth of  FIG.  1   . A method of determining the average distance D will be described with reference to  FIG.  2   . Any one colored point is selected as a reference colored point  10 R. An area around the reference colored point  10 R is equally divided or divided into eight areas A 1 , A 2 , A 3 , A 4 , A 5 , A 6 , A 7 , and A 8 . These eight areas are areas in which an area around the reference colored point  10 R is equally divided by four lines L 22 . 5 , L 67 . 5 , L 112 . 5 , and L 157 . 5  passing through the reference colored point  10 R. A line L 0  is a line extending in the X direction and the lines L 22 . 5 , L 67 . 5 , L 112 . 5 , and L 157 . 5  are respectively lines extending in the directions of 22.5°, 67.5°, 112.5°, and 157.5° in a clockwise manner with respect to the X direction. A colored point  11  and a colored point  15  located on both sides of the reference colored point  10 R are respectively arranged in the areas A 1  and A 5  on the line L 0  extending in the X direction through the reference colored point  10 R. A colored point  12  and a colored point  16  located on both sides of the reference colored point  10 R are respectively arranged in the areas A 1  and A 6  on a line L 45  extending in the direction of 45° with respect to the X direction through the reference colored point  10 R. A colored point  13  and a colored point  17  located on both sides of the reference colored point  10 R are respectively located in the areas A 3  and A 7  on a line L 90  extending in the direction of 90° with respect to the X direction through the reference colored point  10 R. A colored point  14  and a colored point  18  located on both sides of the reference colored point  10 R are respectively arranged in the areas A 4  and A 8  on a line L 135  extending in the direction of 135° with respect to the X direction through the reference colored point  10 R. An average value of the distances between the reference colored point  10 R and eight colored points  11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  17 , and  18  adjacent to the reference colored point  10 R in each of the eight areas A 1  to A 8  is an average distance D. Eight colored points  11  to  18  are colored points closest to the reference colored point  10 R in each of the eight areas A 1  to A 8 . The reference colored point  10 R is selected from the colored points in which adjacent colored points exist in each of the eight areas A 1  to A 8 . The average distance D may be constant or may vary to some extent at the plurality of colored points that can be selected as the reference colored point. The average distance D may vary within ±10% over the entire colored points arranged on the surface of the glass cloth. 
     The colored portions  5  arranged as shown in  FIGS.  1  and  2    can be formed, for example, by printing in which a rectangular (or square) area shown around the colored point is set as a print area. 
       FIG.  3    is a plan view showing another embodiment of the surface-colored glass cloth and  FIG.  4    is a schematic diagram showing an arrangement pattern of the colored points of the surface-colored glass cloth of  FIG.  3   . In the case of the embodiments of  FIGS.  3  and  4   , the plurality of colored points  10  are arranged within the surface of the glass cloth  3  so that the plurality of rows  10 L are formed along a predetermined direction (the X direction) and the positions of the colored point  10  in the X direction are the same in the adjacent rows  10 L. As shown in  FIG.  4   , the average distance D between the adjacent colored points  10  is an average value of the distances between the reference colored point  10 R and the colored points  11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  17 , and  18  adjacent to the reference colored point  10 R in each of eight areas A 1 , A 2 , A 3 , A 4 , A 5 , A 6 , A 7 , and A 8  around the arbitrarily selected reference colored point  10 R. 
     In the embodiments shown in  FIGS.  1  to  4   , the average distance D is 0.50 to 10.00 mm. The average distance D may be 1.00 mm, 1.50 mm or more, 3.00 mm or more, 8.00 mm or less, 6.00 mm or less, or 5.00 mm or less. In these embodiments, the direction of each row  10 L matches the warp direction. However, the arrangement direction of the row  10 L of the colored point may be a direction other than the warp direction. 
       FIG.  5    is a cross-sectional view showing an embodiment of the glass cloth constituting the surface-colored glass cloth.  FIG.  5    is a cross-sectional view in which the glass cloth  3  is cut in the weft direction. The glass cloth  3  shown in  FIG.  5    includes a warp  30  and a weft  40 . The warp  30  includes a plurality of glass filaments  31 . A width  31 W (a maximum width in the cross-section perpendicular to the longitudinal direction) of the glass filament  31  may be 3.0 to 11.0 μm or 3.5 to 9.5 μm. When the glass filament  31  has a circular cross-section, the width  31 W is a diameter of the circular cross-section. The number of the glass filaments contained in one warp  30  is 30 to 600 and may be 40 to 450. A width  30 W (a maximum width in the cross-section perpendicular to the longitudinal direction) of the warp  30  is 100 to 800 μm and may be 120 to 600 μm. The weaving density of the warp, that is, the number of the warps  30  per each width of 25 mm of the glass cloth in the direction perpendicular to the longitudinal direction of the warp is 30 to 120/25 mm and may be 32 to 100/25 mm. The weft  40  also includes a plurality of glass filaments similarly to the warp  30 . The width and number of the glass filaments, the width of the weft, and the weaving density of the weft can be the same as those in the warp. The weaving density of the weft is the number of the wefts  40  per each width of 25 mm of the glass cloth in the direction perpendicular to the longitudinal direction of the weft. The width of the glass filament (the diameter of the glass filament) can be an average value of 50 measured values when the width of the glass filament is measured with a scanning electronic microscope for each of 50 cross-sections of the warp or weft. The number of the glass filaments can be an average value of 50 measured values when the number of the glass filaments constituting the warp or weft is measured with a scanning electronic microscope for each of 50 warps or wefts. The width of the warp and the weft can be an average value of 30 measured values when three samples of 60 mm×100 mm were cut out from the glass cloth and the thread width was measured with a microscope for 30 warp (weft) threads for each sample. The weaving density can be determined by measuring the number of warp rows or wefts per each width of 25 mm of the glass cloth using a textile decomposition mirror in accordance with JIS R 3420: 2013. The glass composition of the glass filament constituting the glass cloth  3  is not particularly limited, and may be E glass, T glass, S glass, NE glass, or L glass. From the viewpoint of excellent versatility, the glass composition of the glass filament constituting the glass cloth  3  may be E glass. The weaving structure of the glass cloth  3  is not particularly limited, and may be a plain weave, a twill weave, or a stain weave. The glass cloth  3  may be a plain weave from the viewpoint of reducing the anisotropy of deformation between the warp direction and the weft direction. An organic substance other than the colored portion  5  such as a silane coupling agent and a surfactant may be attached to the surface of the glass cloth  3 . 
     In the glass cloth  3 , the number of warp rows is St, the warp widening degree is Et, the number of weft rows is Sy, and the weft widening degree is Ey. Each of the number of warp rows and the warp widening degree can be calculated by the following formulae: 
       Number of warp rows=(width of glass filament constituting warp)×(number of glass filaments constituting warp)/(width of warp);
 
       and 
       Warp widening degree=(width of warp)/{25000 μm/(weaving density of warp)}
 
     Each of the number of weft rows and the weft widening degree is calculated by the following formulae: 
       Number of weft rows=(width of glass filament constituting weft)×(number of glass filaments constituting weft)/(width of weft); and
 
       Weft widening degree=(width of weft)/{25000 μm/(weaving density of weft)}
 
     St and Sy may be 0.8 to 8.0. St and Sy may be 1.0 or more, 2.0 or more, 3.0 or more, 7.0 or less, or 5.0 or less. Et and Ey may be 0.30 to 1.20. Et and Ey may be 0.60 or more, 0.70 or more, 0.80 or more, 1.10 or less, or 1.00 or less. 
     D, St, Et, Sy, and Ey satisfy the following formula (1): 
       3.3≤100 ×D   1/2 ×( Et×Ey )/( St×Sy )≤25.0   (1)
 
     The fiber-reinforced resin molded product capable of measuring the strain distribution with high accuracy by image analysis when the composition of the glass cloth and the average distance D are selected so that D, St, Et, Sy, and Ey satisfy this formula. Et and Ey correlate with the size of the void between the warps or wefts. The large Et and Ey mean that the voids between the warps or wefts are small St and Sy correlate with the size of surface irregularities that may occur on the surface of the warp or weft and the thickness of the warp or weft. The small St and Sy mean that the size of surface irregularities that may occur on the surface of the warp or weft is small and the thickness of the warp or weft is thin Here, the small void between the warps or wefts and the small irregularities that may occur on the surface of the warp or weft contributes to the improvement of the accuracy when the colored portion  5  is provided and further contributes to the improvement of the accuracy of the strain distribution measurement. On the other hand, the thin thickness of the warp or weft affects the work accuracy of the coloring process when the colored portion  5  is provided, which leads to a decrease in the accuracy of the colored portion  5 . The average distance D correlates with the work accuracy of the coloring process. The value of 100×D 1/2 ×(Et×Ey)/(St×Sy) reflects such various elements and indicates the accuracy when the colored portion  5  is provided. 
     From the above-described viewpoint, D, St, Et, Sy, and Ey may satisfy the following formula (2) or (3): 
       6.0≤100 ×D   1/2 ×( Et×Ey )/( St×Sy )≤17.0   (2)
 
       9.5≤100 ×D   1/2 ×( Et×Ey )/( St×Sy )≤16.0   (3)
 
     The fiber-reinforced resin molded product can be obtained from the surface-colored glass cloth and the resin according to the above-described embodiment. Here, the resin may be a curable resin or a thermoplastic resin. When the resin is the curable resin, the fiber-reinforced resin molded product can be obtained in such a manner that the surface-colored glass cloth according to the above-described embodiment is impregnated with the curable resin by using a press molding method, a hand lay-up molding method, an infusion molding method, an RTM molding method, or the like and the curable resin is cured or semi-cured by heat or light. The fiber-reinforced resin molded product can be also obtained by using a press molding method for a fiber-reinforced resin molded product (prepreg) in which a curable resin is semi-cured. Further, when the resin is the thermoplastic resin, the fiber-reinforced resin molded product can be obtained by using a press molding method, a double belt type continuous press molding method, or the like for one in which a thermoplastic resin film and the surface-colored glass cloth according to the above-described embodiment are alternately laminated. 
     Examples of the curable resin used as the resin include epoxy resin, unsaturated polyester resin, vinyl ester resin, polyisocyanate resin, polyimide resin, melamine resin, phenol resin, urethane resin, and polyisocyanurate resin. Examples of the thermoplastic resin used as the resin include polystyrene resin, acrylonitrile/butadiene/styrene (ABS) resin, methacrylic resin, polyacetal resin, polyethylene terephthalate (PET) resin, polycarbonate resin, polyallylate (PAR) resin, polyethylene resin, polypropylene resin, vinyl chloride resin, polyamide resin, polybutylene terephthalate (PBT) resin, polyphenylene sulfide (PPS) resin, polyether ether ketone (PEEK) resin, liquid crystal polymer (LCP) resin, fluororesin, polyetherimide (PEI) resin, polysulfon (PSF) resin, polyether sulfone (PES) resin, and polyamideimide (PAI) resin. The resin may be a resin composition containing additives other than the curable resin and the thermoplastic resin, for example, a low shrinkage agent, a flame retardant agent, a defoaming agent, and the like. 
     The resin may be transparent resin in order to ensure the visibility of the colored portion  5 . The transparent resin means resin having a total light transmittance of 90% or more measured in accordance with JIS-K7375. The transparent resin may be, for example, a curable resin such as an epoxy resin, an unsaturated polyester resin, a vinyl ester resin, a polyisocyanate resin, and a polyimide resin or a thermoplastic resin such as a polystyrene resin, an acrylonitrile/butadiene/styrene (ABS) resin, a methacrylic resin, a polyacetal resin, a polyethylene terephthalate (PET) resin, a polycarbonate resin, and a polyallylate (PAR) resin. 
     In the above-described fiber-reinforced resin molded product, the ratio of the surface-colored glass cloth to the total amount thereof may be 5 to 70% by mass or 10 to 50% by mass. 
     The fiber-reinforced resin molded product including the inspection fiber-reinforced resin layer for inspecting strain distribution can be obtained by using the surface-colored glass cloth according to the above-described embodiment.  FIG.  6    is a cross-sectional view showing an embodiment of the fiber-reinforced resin molded product. A fiber-reinforced resin molded product  100  shown in  FIG.  6    includes a main body  50  and an inspection fiber-reinforced resin layer  60  provided on the surface of the main body  50 . 
     The main body  50  is a fiber-reinforced resin containing a reinforced fiber and a resin layer impregnated in the reinforced fiber. The main body  50  may be a product which includes a plurality of fiber-reinforced resin layers including a sheet-shaped reinforced fiber and a resin layer and in which these are laminated. The reinforced fiber constituting the main body  50  is not particularly limited, but may be, for example, a glass fiber, a carbon fiber, an aramid fiber, or a combination thereof. The reinforced fiber may be a non-woven fabric or a woven fabric. 
     The inspection fiber-reinforced resin layer  60  may be the above-described fiber-reinforced resin molded product including one or more surface-colored glass cloths according to the above-described embodiment and transparent resin impregnated in the surface-colored glass cloth. The surface-colored glass cloth is disposed in a direction in which the colored portion is located on the outer surface side of the fiber-reinforced resin molded product  100 . The inspection fiber-reinforced resin layer  60  can be formed by using, for example, a prepreg including a surface-colored glass cloth and transparent resin which is a curable resin impregnated in the surface-colored glass cloth. The transparent resin constituting the inspection fiber-reinforced resin layer  60  may be the same as or different from the resin layer constituting the main body  50 . The thickness of the inspection fiber-reinforced resin layer  60  may be, for example, 0.01 to 1.5 mm or 0.05 to 0.5 mm. In the inspection fiber-reinforced resin layer  60 , the ratio of the surface-colored glass cloth may be 25 to 80% by mass or 50 to 70% by mass based on the mass of the inspection fiber-reinforced resin layer  60 . The inspection fiber-reinforced resin layer  60  does not need to cover the entire surface of the main body  50 , but may be provided to cover a portion of the surface of the main body  50  required for inspection. When the transparent resin constituting the inspection fiber-reinforced resin layer  60  and the main body  50  is the same, the boundary between the inspection fiber-reinforced resin layer  60  and the main body  50 , that is, the surface of the main body  50  may not be visually clear. In that case, for example, the surface of the smallest rectangular body containing the entire reinforced fiber constituting the main body  50  can be regarded as the surface of the main body  50 . 
     By detecting a change in the position of the colored portion and the like by image analysis of the surface of the inspection fiber-reinforced resin layer  60 , it is possible to measure the strain distribution of the fiber-reinforced resin molded product  100  with high accuracy. 
     EXAMPLES 
     Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. 
     1. Manufacturing of Surface-Colored Glass Cloth 
     Three types of glass cloths A, B, and C having the configurations shown in Table 1 were prepared. The glass cloths A, B, and C are all plain weave. The glass composition of the glass filaments constituting the glass cloths A, B, and C is E glass. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Glass 
                 Glass 
                 Glass 
               
               
                   
                 cloth A 
                 cloth B 
                 cloth C 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Warp 
                 Width of glass 
                 7.0 
                 9.0 
                 4.0 
               
               
                   
                   
                 filament 
               
               
                   
                   
                 [μm] 
               
               
                   
                   
                 Number of glass 
                 200 
                 400 
                 50 
               
               
                   
                   
                 filaments 
               
               
                   
                   
                 Weaving density 
                 60 
                 44 
                 95 
               
               
                   
                   
                 [number/25 mm] 
               
               
                   
                   
                 Width [μm] 
                 346 
                 592 
                 132 
               
               
                   
                   
                 Number of warp 
                 4.0 
                 6.1 
                 1.5 
               
               
                   
                   
                 rows St 
               
               
                   
                   
                 Warp widening 
                 0.83 
                 1.04 
                 0.50 
               
               
                   
                   
                 degree Et 
               
               
                   
                 Weft 
                 Width of glass 
                 7.0 
                 9.0 
                 4.0 
               
               
                   
                   
                 filament 
               
               
                   
                   
                 [μm] 
               
               
                   
                   
                 Number of glass 
                 200 
                 400 
                 50 
               
               
                   
                   
                 filaments 
               
               
                   
                   
                 Weaving density 
                 58 
                 32 
                 95 
               
               
                   
                   
                 [number/25 mm] 
               
               
                   
                   
                 Width [μm] 
                 399 
                 565 
                 200 
               
               
                   
                   
                 Number of weft 
                 3.5 
                 6.4 
                 1.0 
               
               
                   
                   
                 rows Sy 
               
               
                   
                   
                 Weft widening 
                 0.93 
                 0.72 
                 0.76 
               
               
                   
                   
                 degree Ey 
               
               
                   
                   
               
            
           
         
       
     
     On the surface of each glass cloth, a square print area centered on colored points arranged at regular intervals was set in the same arrangement pattern as in  FIG.  1  or  3    in which a plurality of rows were formed along the warp direction. The interval between the adjacent colored points in the warp and weft directions and the area of the print area were set as shown in Table 2. Table 2 also shows the average distance D between adjacent colored points. Each print area on the surface of the glass cloth is printed with black resin ink using a printing station type gravure printing tester (manufactured by Kumagai Riki Kogyo Co., Ltd.) and a surface-colored glass cloth having a plurality of black colored portions arranged at regular intervals in the warp and weft directions was obtained. In the case of Comparative Example 2, when the resin ink was printed, the glass cloth was misaligned and the ink was missing. As a result, it was difficult to perform a normal printing operation. 
     2. Evaluation of Coloring Accuracy 
     At least 10 colored portions of the surface-colored glass cloth were photographed while approximating a square using a measurement tool of a digital microscope (KH-8700 manufactured by Hirox Co., Ltd.). 
     A black portion in the captured image was detected using image processing software, and the area was taken as the area of the colored portion. The black portion is the color portion of Mansell N1 to N5 specified in the 2011 F version paint standard color (pocket version) of the Japan Paint Industry Association. The ratio of the print area in which the average value of the area of each colored portion was set was calculated as the coloring accuracy (%). 
     3. Manufacturing of Fiber-Reinforced Resin Molded Product 
     Eight carbon cloths (CO6343 manufactured by Toray) were laminated, and one surface-colored glass cloth was laminated on top of them. A laminate composed of the carbon cloth and the surface-colored glass cloth was impregnated with a transparent epoxy resin using an impregnating roll. This laminate was press-molded at 85° C. for 4 hours to prepare a fiber-reinforced resin molded product with a thickness of 2 mm having a fiber-reinforced resin layer including a surface-colored glass cloth on an outermost layer (corresponding to the inspection fiber-reinforced resin layer  60 ) and the other layer composed of a fiber-reinforced resin layer (corresponding to the main body  50 ) including a carbon cloth. The ratio of the fiber reinforced material (the carbon cloth and the surface-colored glass cloth) in the fiber-reinforced resin molded product was 60% by mass with respect to the total mass of the fiber reinforced material and the transparent epoxy resin. Further, the ratio of the surface-colored glass cloth in the fiber-reinforced resin layer (corresponding to the inspection fiber-reinforced resin layer  60 ) including the surface-colored glass cloth was 70% by mass. 
     4. Strain Measurement Suitability Evaluation Method 
     A tensile test was performed in which tensile stress was applied to the fiber-reinforced resin molded product in the biaxial directions of X and Y An image was taken with 600×600 pixels when the amount of tensile strain was 3% in both the X and Y directions. The dimensions of the printed and non-printed areas in the area of 300×300 pixels in the center of the captured image in the X and Y directions were measured and the fluctuation rate (standard deviation/average×100) was calculated from the average and standard deviation of the measured strain (%; ideally 3%). The strain measurement suitability was “A” when the calculated fluctuation rate was 1.0% or less, the strain measurement suitability was “B” when the calculated fluctuation rate was more than 1.0% and 3.0% or less, and the strain measurement suitability was “C” when the calculated fluctuation rate was more than 3.0%. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Examples 
                 Com. Examples 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 1 
                 2 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Glass cloth 
                 A 
                 A 
                 A 
                 A 
                 B 
                 B 
                 B 
                 C 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Colored point 
                 Warp direction 
                 2 
                 2 
                 1 
                 1 
                 2 
                 2 
                 1 
                 1 
               
               
                 interval [mm] 
                 Weft direction 
                 2 
                 2 
                 1 
                 1 
                 2 
                 2 
                 1 
                 1 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Average distance D between colored points 
                 4.83 
                 3.41 
                 2.41 
                 1.71 
                 4.83 
                 3.41 
                 2.41 
                 2.41 
               
               
                 [mm] 
               
               
                 100 × D 1/2  × (Et × Ey)/(St × Sy) 
                 12.1 
                 10.2 
                 8.6 
                 7.2 
                 4.2 
                 3.5 
                 3.0 
                 39.3 
               
               
                 Area of print area [mm 2 ] 
                 4 
                 4 
                 1 
                 1 
                 4 
                 4 
                 1 
                 Difficult 
               
               
                 Area of colored portion [mm 2 ] 
                 3.02 
                 2.86 
                 0.67 
                 0.63 
                 1.75 
                 1.92 
                 0.39 
                 printing 
               
               
                 Coloring accuracy [%] 
                 75.5 
                 71.5 
                 66.9 
                 63.3 
                 43.7 
                 48.0 
                 39.2 
               
               
                 Strain measurement suitability 
                 A 
                 A 
                 B 
                 B 
                 B 
                 B 
                 C 
                 — 
               
               
                   
               
            
           
         
       
     
     REFERENCE SIGNS LIST 
       1 : surface-colored glass cloth,  3 : glass cloth,  5 : colored portion,  10 ,  11 ,  12 ,  13 ,  14 ,  15 ,  16 ,  17 : colored point,  10 L: row of colored points,  10 R: reference colored point,  30 : warp,  30 W: width of warp,  31 : glass filament,  31 W: width of glass filament,  40 : weft,  50 : main body,  60 : inspection fiber-reinforced resin layer,  100 : fiber-reinforced resin molded product, A 1 , A 2 , A 3 , A 4 , A 5 , A 6 , A 7 , A 8 : area, L 22 . 5 , L 67 . 5 , L 112 . 5 , L 157 . 5 : lines extending in directions of 22.5°, 67.5°, 112.5°, and 157.5° in a clockwise manner with respect to predetermined direction through reference colored point.