Abstract:
A method of producing a die for forming an interior component of a vehicle includes: setting a temperature of a plating bath in a range from 25 to 40° C.; immersing at least a forming surface on a base for the die in the plating bath; and feeding a current to the base with a current density in a range from 20 to 80 A/dm 2  until a metal layer is formed on the forming surface.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Japanese Patent Application No. 2016-078084 filed on Apr. 8, 2016. The entire contents of the priority application are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a method of producing a die, a die, and an interior component of a vehicle. 
       BACKGROUND 
       [0003]    A forming apparatus for forming an interior component of a vehicle using a set of dies is known (see Patent Document 1). The forming apparatus includes the set of dies that can be opened and closed. When the dies are closed, a forming cavity for forming the interior component is provided. 
         [0004]    It may be preferable to tinge the interior component with black from the aspect of design. To deepen the blackness of the interior component, black paint may be applied to a surface of the interior component after the interior component is formed with the set of dies. Use of the paint requires application and drying, that is, the larger number of steps is required for producing the interior component. 
       SUMMARY 
       [0005]    The present invention was made in view of the foregoing circumstances. An object is to deepen color of an interior component of a vehicle without using paint. 
         [0006]    A method of producing a die for forming an interior component of a vehicle includes: setting a temperature of a plating bath in a range from 25 to 40° C.; immersing at least a forming surface on a base for the die in the plating bath; and feeding a current to the forming surface with a current density in a range from 20 to 80 A/dm 2  until a metal layer is formed on the forming surface. 
         [0007]    According to a technology described herein, the color of the interior component deepens without using paint. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a cross-sectional view of a forming apparatus according to a first embodiment. 
           [0009]      FIG. 2  is a cross-sectional view of a die with recesses formed in an emboss pattern forming process. 
           [0010]      FIG. 3  is a cross-sectional view of the die with recesses formed in a sandblasting process. 
           [0011]      FIG. 4  is a cross-sectional view of a metal layer formed on the forming surface of the die by plating. 
           [0012]      FIG. 5  is a magnified cross-sectional view of a design surface of an interior component of an automobile. 
           [0013]      FIG. 6  is a cross-sectional view illustrating the emboss pattern forming process. 
           [0014]      FIG. 7  is a schematic view illustrating the sandblasting process. 
           [0015]      FIG. 8  is a schematic view illustrating an electroetching process. 
           [0016]      FIG. 9  is a schematic view illustrating a plating process. 
           [0017]      FIG. 10  is a picture of the forming surface before the etching process. 
           [0018]      FIG. 11  is a picture of the forming surface after the etching process. 
           [0019]      FIG. 12  is a table including results of brightness measurement. 
           [0020]      FIG. 13  is a picture of a surface of the metal layer. 
           [0021]      FIG. 14  is a picture of a surface of a metal layer of a comparative example. 
           [0022]      FIG. 15  is a schematic view illustrating a chemical etching process according to a second embodiment. 
       
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
       [0023]    A first embodiment will be described with reference to  FIGS. 1 to 14 . A forming apparatus for producing an interior component  50  for an automobile (an interior component for a vehicle) will be described. The interior component  50  is made of synthetic resin (e.g., thermoplastic resin including polypropylene) and in black. The interior component  50  may be a trim board included in a door trim for an automobile (e.g., an upper trim board, a lower trim board). 
         [0024]    As illustrated in  FIG. 1 , a forming apparatus  10  includes an injector  15  and a forming die set including a first die  11  and a second die  20 . The first die  11  and the second die  20  can be opened and closed. The first die  11  includes a forming surface  11 A for forming a back surface of the interior component  50 . The second die  20  includes a forming surface  21  for forming a design surface  51  of the interior component  50  (a surface to face an interior of a cabin). When the first die  11  and the second die  20  are closed, a forming cavity S 1  is created between the forming surface  11 A and the forming surface  21  that are opposed to each other. A contour of the forming cavity S 1  is along a contour of the interior component  50 . A runner  12  is provided inside the first die  11 . Molten plastic injected from the injector  15  run into the forming cavity S 1  via the runner  12 . 
         [0025]    As illustrated in  FIGS. 2 and 3 , the forming surface  21  of the second die  20  includes three types of recesses including first recesses  23 , second recesses  24 , and third recesses  25  formed by different forming methods. The recesses  23  to  25  are formed over an entire area of the forming surface  21 . As illustrated in  FIG. 4 , a metal layer  31  is formed to cover the forming surface  21  including the recesses  23 ,  24 , and  25 . The metal layer  31  includes grains with a mean grain size D 1  of 5 μm or smaller. 
         [0026]    The first recesses  23  are for forming an emboss pattern on the interior component  50  with chemical etching. The second recesses  24  are smaller than the first recesses  23 . The second recesses  24  are formed by sandblasting. The third recesses  25  are smaller than the second recesses  24 . The third recesses  25  are formed by electroetching. Methods of forming the recesses  23  to  25  and the metal layer  31  will be described later. Sizes of the recesses  23  to  25  described above are only an example and not limited thereto. In  FIGS. 2 and 3 , solid lines indicate the recesses larger than the other and two-dot chain lines indicate the recesses smaller than the other. 
         [0027]    As illustrated in  FIG. 5 , the design surface  51  of the interior component  50  includes a pattern transferred from the forming surface  21 . A first irregular pattern  52  in  FIG. 5  is formed with protrusions in the metal layer  31 . A second irregular pattern  53  that is coarser than the first irregular pattern  52  is formed with the third recesses  25  in the forming surface  21 . 
         [0028]    Next, a method of producing the second die  20  will be described. The method of producing the second die  20  includes a cutting process, an emboss pattern forming process, a sandblasting process, an etching process, and a plating process. The cutting process is for cutting a steel block (a base of the second die  20 ) to create a base surface that is a base for the forming surface  21 . The emboss pattern forming process is for forming the first recesses  23 . The sandblasting process is for forming the second recesses  24 . The etching process is form forming the third recesses  25 . The plating process is for forming the metal layer  31 . The steel of the second die  20  may contain iron as a main ingredient. The steel may further contain carbon, silicon, manganese, phosphorus, and sulfur. 
         [0029]    Emboss Pattern Forming Process 
         [0030]    In the emboss pattern forming process, the first recesses  23  are formed by etching. The etching uses an acid solution and an acid-resistant ink  41 . The acid solution is for corroding metal in the base of the second die  20 . The acid-resistant ink  41  is for blocking the acid solution, for example, a nitric acid solution. The base of the second die  20  is cleaned and portions of the base other than the base surface for the forming surface  21  are masked off with a masking tape. As illustrated in  FIG. 6 , the emboss pattern is transferred to the base surface with the acid-resistant ink  41 . The base surface is subject to the acid solution. Portions of the base surface covered with the acid-resistant ink  41  are not corroded with the acid solution and other portions of the base surface not covered with the acid-resistant ink  41  are corroded with the acid solution to form recesses. Through the process, the first recesses  23  are formed in the base surface. 
         [0031]    Sandblasting Process 
         [0032]    The sandblasting process is performed after the emboss pattern forming process. In the sandblasting process, the second recesses  24  are formed by sandblasting. As illustrated in  FIG. 7 , an abrasive is sprayed onto the base surface including the first recesses  23  via a nozzle  43  using compressed air generated by a compressor  42 . The base surface is scraped by the abrasive and the second recesses  24  are formed (see  FIG. 2 ). The abrasive may have a grit size in a range from #80 to #150 in Japanese Industrial Standards. In comparison to an abrasive having a smaller grit size (e.g., in a range from #150 to #250 in Japanese Industrial Standards), diameters of grains in the abrasive are larger and thus larger impact is applied to the base surface. Therefore, the second recesses  24  are easily formed. 
         [0033]    Etching Process 
         [0034]    The etching process is performed after the sandblasting process. In the etching process, the third recesses  25  are formed by etching. As illustrated in  FIG. 8 , the base of the second die  20  is immersed in a plating bath  61  (a chrome plating bath, a Sergeant bath) including chrome acid and sulfuric acid as the main ingredients and connected to a power source  63 . The base is connected to as a positive terminal of the power source  63  and an electrode  62  in the plating bath  61  is connected to a negative terminal of the power source  63 . Using the base of the second die  20  as a positive electrode and the electrode  62  as a negative electrode, electroetching is performed. The electroetching causes corrosion of an iron component included in the base and the third recesses  25  are formed in the base surface. 
         [0035]    It is preferable to perform the electroetching with a current density in a range from 15 to 20 A/dm 2  and with process time in a range from 1 to 20 minutes. Under the condition, the third recesses  25  having certain sizes (e.g., diameters of 10 μm or larger) are properly formed. Through the emboss pattern forming process, the sandblasting process, and the etching process, the forming surface  21  is prepared. 
         [0036]    Plating Process 
         [0037]    The plating process is performed after the etching process. In the plating process, the metal layer  31  is formed by electrodeposition. As illustrated in  FIG. 9 , the base of the second die  20  including the forming surface  21  in the plating bath  61  is connected to the negative terminal of the power source  63  and the electrode  62  is connected to the positive terminal of the power source  63 . Using the base as a negative electrode and the electrode  62  as a positive electrode, the electrodeposition is performed. Chrome ions in the plating bath  61  are reduced and deposited on the forming surface  21 . As a result, the metal layer  31  with a thickness of 5 μm or larger is formed. The plating is used in this embodiment is hard chrome plating to form the metal layer  31  with the thickness of 5 μm or larger but the plating is not limited to the hard chrome plating. 
         [0038]    The design surface  51  of the interior component  50  includes a pattern transferred from a surface of the metal layer  31 . By increasing the fineness of the pattern in the design surface  51  formed with the protrusions on the surface of the metal layer  31  in a reduced size, light reaching the design surface  51  is more likely to be scattered and thus the brightness of color of the design surface  51  decreases. The size of the protrusions on the surface of the metal layer  31  can be altered by adjusting the current density and a plating bath temperature of the plating bath  61 . When the electroplating is performed with the current density in a range from 20 to 80 A/dm 2  and the plating bath temperature in a range from 25 to 40° C., the metal layer  31  with the surface having a mean grain size of 5 μm or smaller is formed. With such a metal layer  31 , the brightness of color of the design surface  51  is reduced. 
         [0039]    The picture in  FIG. 13  shows an image of a surface of a metal layer formed with the electroplating under a condition that the current density is 60 A/dm 2  and the plating bath temperature is 37° C., which is within the condition of this embodiment. The picture in  FIG. 14  shows an image of a surface of a metal layer formed with the electroplating under a condition that the current density is 85 A/dm 2  and the plating bath temperature is 60° C., which is outside the condition of this embodiment. According to  FIGS. 13 and 14 , when the electroplating was performed under the condition of this embodiment, the mean grain size of the surface of the metal layer  31  was smaller, that is, the pattern was smaller. When the current density is set in a range from 30 to 60 A/dm 2  and the plating bath temperature is set in a range from 30 to 37° C., the finer pattern can be formed on the surface of the metal layer in comparison to a condition including the current density and the plating bath temperature outside the above ranges. Therefore, the brightness of color of the design surface  51  can be reduced. 
         [0040]    The brightness of color of the design surface  51  of this embodiment and the brightness of color of the design surface of a comparative example formed with the forming surface including the metal layer formed by the electroplating under the condition outside the condition of this embodiment were measured with a spectrophotometer (lightness in a Lab color space). The measurements are presented in  FIG. 12 . According to  FIG. 12 , the brightness of color of the design surface  51  of this embodiment is lower than the brightness of color of the comparative example. 
         [0041]    A method of producing the interior component  50  by the forming apparatus  10  will be described. As illustrated in  FIG. 1 , the first die  11  and the second die  20  are closed. The forming cavity S 1  is formed between the forming surface  11 A of the first die  11  and the forming surface  21  of the second die  20 . The forming cavity S 1  has a contour along the contour of the interior component  50 . A black molten resin is injected from the injector  15  into the forming cavity S 1  via the runner  12 . The black molten resin in the forming cavity S 1  is cooled down and the interior component  50  is formed (a forming process). The first die  11  and the second die  20  are opened and the interior component  50  is removed. This completes the production of the interior component  50 . 
         [0042]    The effects of this embodiment will be described. The design surface  51  of the interior component  50  is formed using the second die  20 . The patterns of the forming surface  21  and the pattern of the metal layer  31  form the pattern of the design surface  51  of the interior component  50 . The surface of the metal layer  31  includes the protrusions formed from grains in the metal layer  31 . The. By performing the electroplating with the plating bath temperature in the range from 25 to 40 c and the current density in a range from 20 to 80 A/dm 2 , the mean grain size can be reduced. Namely, the surface that is more likely to scatter light is formed. In comparison to a surface formed with a forming surface that is not plated or a surface formed with a forming surface that is plated under a condition other than the condition described above, the pattern of the design surface  51  formed using the pattern of the metal layer  31  is more likely to scatter light. According to the configuration, light reflectivity of the design surface  51  decreases and thus the brightness of color of the design surface  51  decreases. Therefore, the design surface  51  appears to be tinged with deeper black (a deep black tone). By reducing the brightness of color of the interior component  50 , the color of the interior component  50  may better match colors of components around the interior component  50 . 
         [0043]    In the etching process, the fine third recesses  25  are formed in the base surface. Then, the metal layer  31  is formed on the forming surface  21  including the third recesses  25  by plating. A combination of the pattern formed from the third recesses  25  formed in the etching process and the pattern formed from the protrusions of the metal layer  31  formed in the plating process creates a complicated irregular pattern. Therefore, the design surface  51  of the interior component  50  including the pattern formed using the complicated irregular pattern of the forming surface  21  is more likely to scatter light and thus the design surface  51  appears to be tinged with deeper black. Because the third recesses  25  are formed by etching in the etching process, the strength of the forming surface  21  may decrease. However, the metal layer  31  is formed on the forming surface  21  and thus a proper level of the strength is maintained. 
         [0044]    The electroetching and the electroplating are performed in the same plating bath with the polarities of the electrodes altered between the electroetching and the electroplating. Namely, separate facilities are not required for the electroetching and the electroplating as long as the electroetching and the electroplating are consecutively performed. Therefore, the facility cost can be reduced. Furthermore, it is not necessary to move the second die  20  between facilities, that is, the number of steps can be reduced. 
         [0045]    Because the sandblasting process is performed before the plating surface forming process, the fine second recesses  24  are formed in the base surface. Then, the metal layer  31  is formed on the forming surface  21  including the second recesses  24  by plating. A combination of the pattern formed from the second recesses  24  formed in the sandblasting process and the pattern formed from the protrusions of the metal layer  31  creates a complicated irregular pattern. Therefore, the design surface  51  of the interior component  50  including the pattern formed using the complicated irregular pattern of the forming surface  21  is more likely to scatter light and thus the design surface  51  appears to be tinged with deeper black. The sizes of the second recesses  24  can be easily adjusted by altering the sizes of grains in the abrasive used in the sandblasting. Therefore, darkness of the design surface  51  is easily adjustable. 
         [0046]    The chrome contained in the metal layer  31  has higher thermal conductivity in comparison to iron. Therefore, a partial cooldown of the forming surface  21  is less likely to occur and thus forming defects (e.g., weld line, uneven gloss) can be reduced. The chrome is harder than the iron that is the main ingredient of the second die  20 , that is, highly resistant to abrasion. The chrome is suitable for the metal layer  31  formed on the forming surface  21 . 
       Second Embodiment 
       [0047]    A second embodiment will be described with reference to  FIG. 15 . In this embodiment, a chemical etching is used in an etching process. As illustrated in  FIG. 15 , the etching process of this embodiment includes etching a base surface for a forming surface  121  of a second die  120  with an etching solution to form second recesses  125 . The etching solution may be an alkaline solution (e.g., sodium hydroxide, sodium carbonate). The alkaline solution causes corrosion of an iron component included in the second die  120 . It is preferable to set etching time in a range from 0.5 to 24 hours. The etching solution is not limited to the alkaline solution. An acid solution (e.g., nitric acid) may be used. 
       Other Embodiments 
       [0048]    The technology described herein is not limited to the above embodiments described above and the drawings. The following embodiments may be included in the technical scope of the present invention. 
         [0049]    (1) The forming die set is not limited to the injection molding die set as long as the forming surface of the die includes a pattern to be transferred onto a surface of a forming component. A press forming die for press forming and a vacuum forming die for vacuum forming may be included in the scope of the present invention. 
         [0050]    (2) The metal layer may be made of metal other than chrome (e.g., nickel, copper). 
         [0051]    (3) The interior component  50  is not limited to the upper trim or the lower trim. Onboard components having design surfaces, for example, synthetic resin skins, instrumental panels, and assist grips may be included in the scope of the present invention. The synthetic resin skins may be made of thermoplastic elastomer olefin. The interior component  50  may include multiple layers. 
         [0052]    (4) The interior component  50  may be tinged with color other than black. Even if the interior component  50  is tinged with color other than black, the brightness of color of the interior component  50  can be reduced according to the technology described herein, 
         [0053]    (5) The forming surface  21  of the second die  20  may not include the recesses  23  to  25  and the second die  20  may include only the metal layer  31  on the forming surface  21 . Furthermore, the forming surface  21  of the second die  20  may include one or two of the recesses  23  to  25 . 
         [0054]    (6) The plating bath is not limited to the configuration described earlier. A fluorosilicic acid bath including chrome acid, sulfuric acid, and fluorosilicic acid as the main ingredients may be used. 
         [0055]    (7) The technology described herein may be applied to an interior component installed in a vehicle other than the automobile.