Abstract:
An injection mold includes a sliding member having a partial cavity surface which forms part of a cavity surface, and an adjacent member having a partial cavity surface which forms part of the cavity surface. A sliding surface of the sliding member is guided by a sliding surface of the adjacent member and is linearly movable by a relative sliding distance. A portion from the partial cavity surface to the sliding surface of at least one of the sliding member and adjacent member is continuously coated with a heat insulating coat, and a range over which the sliding surface is coated with the heat insulating coat is so set as to exceed an end of the relative sliding distance, where an edge of the partial cavity surface of the adjacent member contacts with the sliding surface of the sliding member.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an injection mold in which at least a portion of the cavity surface is coated with a heat insulating coat, and which is used in plastic injection molding. 
   BACKGROUND OF THE INVENTION 
   As an injection mold having improved cavity surface transfer properties, an injection mold having a heat insulating structure (Japanese Patent Laid-Open No. 53-86754) is conventionally known. The surface transfer properties of this injection mold are improved by interposing a heat insulating material layer between a thin metal layer forming the cavity surface and a backing material, thereby decreasing the cooling rate of an injection-molded product during injection molding. 
   Unfortunately, the above prior art has the following unsolved problem. 
   An injection mold uses sliding members, such as an ejector pin, slide core, and inclined core, having partial cavity surfaces which form portions of the cavity surface. Each of these sliding members is slidably guided by the sliding surface of an adjacent member which is adjacent to this sliding member, and protruded into the cavity or retracted into the adjacent member, i.e., linearly moved. This linear motion is repeated for each molding cycle. Consequently, a load such as the frictional force is repetitively exerted on the edge of a heat insulating coat with which the sliding member or adjacent member is coated. This causes easy peeling of the heat insulating coat. 
   The edge of the heat insulating coat with which the sliding member or adjacent member is coated is formed by masking or machining. Therefore, the adhesion of the edge is lowered by a load generated when the masking material is peeled or when machining is performed. This presumably further promotes .peeling. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in consideration of the unsolved problem of the above-mentioned prior art, and has as its object to provide an injection mold having high durability because a heat insulating coat with which at least one of a sliding member and adjacent member is coated has a high peeling resistance. 
   To achieve the above object, according to a first aspect of the present invention, there is provided an injection mold comprising a sliding member having a partial cavity surface which forms part of a cavity surface, and an adjacent member having a partial cavity surface which forms part of the cavity surface, a sliding surface of the sliding member being guided by a sliding surface of the adjacent member and linearly movable by a relative sliding distance, wherein a portion from the partial cavity surface to the sliding surface of at least one of the sliding member and adjacent member is continuously coated with a heat insulating coat, and a range over which the sliding surface is coated with the heat insulating coat is so set as to exceed the relative sliding distance. 
   According to a second aspect of the present invention, there is provided an injection mold comprising a sliding member having a partial cavity surface which forms part of a cavity surface, and an adjacent member having a partial cavity surface which forms part of the cavity surface, a sliding surface of the sliding member being guided by a sliding surface of the adjacent member and linearly movable by a relative sliding distance, wherein a portion from the partial cavity surface to the sliding surface of at least one of the sliding member and adjacent member is continuously coated with a heat insulating coat, a range over which the sliding surface is coated with the heat insulating coat is so set as to exceed the relative sliding distance, and an entire region from the heat insulating coat to the sliding surface is continuously coated with a protective coat. 
   According to a third aspect of the present invention, there is provided an injection mold comprising a sliding member having a partial cavity surface which forms part of a cavity surface, and an adjacent member having a partial cavity surface which forms part of the cavity surface, a sliding surface of the sliding member being guided by a sliding surface of the adjacent member and linearly movable by a relative sliding distance, wherein a portion from the partial cavity surface to the sliding surface of at least one of the sliding member and adjacent member is continuously coated with a heat insulating coat, and an entire region from the heat insulating coat to the sliding surface is continuously coated with a protective coat. 
   According to a fourth aspect of the present invention, there is provided an injection mold comprising a sliding member having a partial cavity surface which forms part of a cavity surface, and an adjacent member having a partial cavity surface which forms part of the cavity surface, a sliding surface of the sliding member being guided by a sliding surface of the adjacent member and linearly movable by a relative sliding distance, wherein at least a portion of the partial cavity surface of at least one of the sliding member and adjacent member is continuously coated with a heat insulating coat, and an entire region from the heat insulating coat to the sliding surface is continuously coated with a protective coat. 
   In the present invention having the above arrangements, even when the sliding member is repetitively linearly moved as it is guided by the adjacent member, a load such as the frictional force is not applied on the edge of the heat insulating coat with which at least one of the sliding member and adjacent member is coated. Since this increases the peeling resistance of the heat insulating coat, the durability of the injection mold improves. 
   Further objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  illustrate an injection mold according to the first embodiment, in which  FIG. 1A  is a schematic partial sectional view showing the state in which a sliding member and adjacent member form a cavity surface, and  FIG. 1B  is a schematic partial sectional view showing the state in which the sliding member protrudes into the cavity by a relative sliding distance; 
       FIGS. 2A and 2B  illustrate a modification of the injection mold according to the first embodiment, in which  FIG. 2A  is a schematic partial sectional view showing the state in which a sliding member and adjacent member form a cavity surface, and  FIG. 2B  is a schematic partial sectional view showing the state in which the sliding member is retracted into the adjacent member by a relative sliding distance; 
       FIGS. 3A and 3B  illustrate another modification of the injection mold according to the first embodiment, in which  FIG. 3A  is a schematic partial sectional view showing the state in which a sliding member and adjacent member form a cavity surface, and  FIG. 3B  is a schematic partial sectional view showing the state in which the sliding member protrudes into the cavity by a relative sliding distance; 
       FIG. 4  is a schematic partial sectional view showing a sliding member of an injection mold according to the second embodiment; 
       FIG. 5  is a schematic partial sectional view showing a sliding member of an injection mold according to the third embodiment; 
       FIG. 6  is a schematic partial sectional view showing a sliding member of an injection mold according to the fourth embodiment; 
       FIG. 7  is a schematic partial sectional view showing a sliding member of an injection mold according to the fifth embodiment; 
       FIG. 8  is a schematic partial sectional view showing a sliding member of an injection mold according to the sixth embodiment; 
       FIG. 9  is a schematic partial sectional view showing a sliding member of an injection mold according to the seventh embodiment; 
       FIG. 10  is a schematic partial sectional view showing a sliding member of an injection mold according to the eighth embodiment; 
       FIG. 11  is a schematic partial sectional view showing a sliding member of an injection mold according to the ninth embodiment; 
       FIG. 12  is a schematic partial sectional view showing an injection mold used in Comparative Example 1; 
       FIG. 13  is a schematic partial sectional view showing an injection mold used in Comparative Example 2; 
       FIG. 14  is a view showing the number of times of injection molding before peeling occurred in each example; 
       FIG. 15  is a view showing the number of times of injection molding before peeling occurred in each example; and 
       FIG. 16  is a view showing the number of times of injection molding before peeling occurred in each example. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
     FIGS. 1A and 1B  illustrate an injection mold according to the first embodiment, in which  FIG. 1A  is a schematic partial sectional view showing the state in which a sliding member and adjacent member form a cavity surface, and  FIG. 1B  is a schematic partial sectional view showing the state in which the sliding member protrudes into the cavity by a relative sliding distance. 
   As shown in  FIGS. 1A and 1B , the injection mold according to this embodiment has an adjacent member  1  and sliding member  2  adjacent to each other. A sliding surface  2   b  of the sliding member  2  is slidably guided by a sliding surface  1   b  of the adjacent member  1  such that a partial cavity surface  2   a  of the sliding member  2  protrudes into the cavity by a relative sliding distance e from the state in which the partial cavity surface  2   a  is leveled with that partial cavity surface  1   a  of the adjacent member  1 , which forms a portion of the cavity surface. 
   A portion from the partial cavity surface  2   a  to the sliding surface  2   b  of the sliding member  2  is continuously coated with a heat insulating coat  3 . The range over which the sliding surface  2   b  is coated with the heat insulating coat  3  is so set as to exceed the relative sliding distance e. 
   In this embodiment, in the state in which the sliding member  2  protrudes into the cavity by the relative sliding distance e, a corner  1   c  between the partial cavity surface  1   a  and sliding surface  1   b  of the adjacent member  1  does not contact an edge  3   a  of the heat insulating coat  3  on the sliding surface  2   b  of the sliding member  2 , so no overload is exerted on the edge  3   a . This improves the peeling resistance of the heat insulating coat  3 . 
     FIGS. 2A and 2B  illustrate a modification of the injection mold according to the first embodiment, in which  FIG. 2A  is a schematic partial sectional view showing the state in which a sliding member and adjacent member form a cavity surface, and  FIG. 2B  is a schematic partial sectional view showing the state in which the sliding member is retracted into the mold body by a relative sliding distance. 
   As shown in  FIGS. 2A and 2B , the injection mold according to this modification has an adjacent member  11  and sliding member  12  adjacent to each other. A sliding surface  12   b  of the sliding member  12  is slidably guided by a sliding surface  11   b  of the adjacent member  11  such that a partial cavity surface  12   a  of the sliding member  12  is retracted into the adjacent member by a relative sliding distance e from the state in which the partial cavity surface  12   a  is leveled with that partial cavity surface  11   a  of the adjacent member  11 , which forms a portion of the cavity surface. 
   A portion from the partial cavity surface  11   a  to the sliding surface  11   b  of the adjacent member  11  is continuously coated with a heat insulating coat  13 . The range over which the sliding surface  11   b  is coated with the heat insulating coat  13  is so set as to exceed the relative sliding distance e. 
   In this modification, in the state in which the sliding member  12  is retracted into the adjacent member by the relative sliding distance e, a corner  12   c  between the partial cavity surface  12   a  and sliding surface  12   b  of the sliding member  12  does not contact an edge  13   a  of the heat insulating coat  13  of the adjacent member  11 , so no overload is exerted on the edge  13   a . This improves the peeling resistance of the heat insulating coat  13 . 
     FIGS. 3A and 3B  illustrate another modification of the injection mold according to the first embodiment, in which  FIG. 3A  is a schematic partial sectional view showing the state in which a sliding member and adjacent member form a cavity surface, and  FIG. 3B  is a schematic partial sectional view showing the state in which the sliding member protrudes into the cavity by a relative sliding distance. 
   As shown in  FIGS. 3A and 3B , the injection mold according to this embodiment has an adjacent member  21  and sliding member  22  adjacent to each other. A sliding surface  22   b  of the sliding member  22  is slidably guided by a sliding surface  21   b  of the adjacent member  21  such that a partial cavity surface  22   a  of the sliding member  22  protrudes into the cavity by a relative sliding distance e from the state in which the partial cavity surface  22   a  is leveled with that partial cavity surface  21   a  of the adjacent member  21 , which forms a portion of the cavity surface. 
   A portion from the partial cavity surface  22   a  to the sliding surface  22   b  of the sliding member  22  is continuously coated with a heat insulating coat  23 . The range over which the sliding surface  22   b  is coated with the heat insulating coat  23  is so set as to exceed the relative sliding distance e. Also, a portion from the partial cavity surface  21   a  to the sliding surface  21   b  of the adjacent member  21  is continuously coated with a heat insulating coat  24 . The range over which the sliding surface  21   b  is coated with the heat insulating coat  24  is so set as to exceed the relative sliding distance e. 
   In this modification, in the state in which the sliding member  22  protrudes into the cavity by the relative sliding distance e, a corner  21   c  between the partial cavity surface  21   a  and sliding surface  21   b  of the adjacent member  21  does not contact an edge  23   a  of the heat insulating coat  23  on the sliding surface  22   b  of the sliding member  22 , so no overload is exerted on the edge  23   a . This improves the peeling resistance of the heat insulating coat  23 . 
   Note that the injection mold of this modification can also be so constructed that the sliding member  22  is retracted into the adjacent member as shown in  FIGS. 2A and 2B . Even in this injection mold, in the state in which the sliding member  22  is retracted into the adjacent member by the relative sliding distance e, a corner  22   c  between the partial cavity surface  22   a  and sliding surface  22   b  of the sliding member  22  does not contact an edge  24   a  of the heat insulating coat  24  of the adjacent member  21 , so no overload is exerted on the edge  24   a.    
   Injection molds of other embodiments will be explained below by taking a sliding member as an example. 
     FIG. 4  is a schematic partial sectional view of a sliding member of an injection mold according to the second embodiment. In the injection mold according to this embodiment, a portion from a partial cavity surface  32   a  to a sliding surface  32   b  of a sliding member  32  is continuously coated with a heat insulating coat  33 . The range over which the sliding surface  32   b  is coated with the heat insulating coat  33  is so set as to exceed a relative sliding distance e. In addition, an entire region from the partial cavity surface  32   a  to the sliding surface  32   b  is continuously coated with a protective coat  34 . 
   In this embodiment, a load such as the frictional force is not directly applied on the heat insulating coat  33 . This makes the peeling resistance and durability higher than those of the injection mold according to the first embodiment. 
     FIG. 5  is a schematic partial sectional view of a sliding member of an injection mold according to the third embodiment. In the injection mold according to this embodiment, a portion from a partial cavity surface  42   a  to a sliding surface  42   b  of a sliding member  42  is continuously coated with a heat insulating coat  43 . In addition, an entire region from the partial cavity surface  42   a  to the sliding surface  42   b  is continuously coated with a protective coat  44 . 
     FIG. 6  is a schematic partial sectional view of a sliding member of an injection mold according to the fourth embodiment. In the injection mold according to this embodiment, a partial cavity surface  52   a  of a sliding member  52  is continuously coated with a heat insulating coat  53 . In addition, an entire region from the partial cavity surface  52   a  to a sliding surface  52   b  is continuously coated with a protective coat  54 . 
     FIG. 7  is a schematic partial sectional view of a sliding member of an injection mold according to the fifth embodiment. In the injection mold according to this embodiment, a partial cavity surface  62   a  except for a portion h near a sliding surface  62   b  of a sliding member  62  is continuously coated with a heat insulating coat  63 . In addition, an entire region from the partial cavity surface  62   a  to the sliding surface  62   b  is continuously coated with a protective coat  64 . 
     FIG. 8  is a schematic partial sectional view of a sliding member of an injection mold according to the sixth embodiment. In the injection mold according to this embodiment, a portion from a partial cavity surface  72   a  to a sliding surface  72   b  of a sliding member  72  is continuously coated with a heat insulating coat  73 . The range over which the sliding surface  72   b  is coated with the heat insulating coat  73  is so set as to exceed a relative sliding distance e ( FIG. 1B ). In addition, a jagged portion  75  is formed on that surface of the heat insulating coat, which opposes the sliding surface  72   b . The sliding member  72  is strongly connected via the jagged portion  75 . 
     FIG. 9  is a schematic partial sectional view of a sliding member of an injection mold according to the seventh embodiment. In the injection mold according to this embodiment, a sliding member  82  is continuously coated with a heat insulating coat  83  similar to that shown in  FIG. 8 . In addition, an entire region from a partial cavity surface  82   a  to a sliding surface  82   b  is continuously coated with a protective coat  84 . 
     FIG. 10  is a schematic partial sectional view of a sliding member of an injection mold according to the eighth embodiment. In the injection mold according to this embodiment, a portion from a partial cavity surface  92   a  to a sliding surface  92   b  of a sliding member  92  is continuously coated with a heat insulating coat  93 . A jagged portion  95  is formed on that surface of the heat insulating coat  93 , which opposes the sliding surface  92   b . The heat insulating coat  93  is strongly connected to the sliding member  92  via the jagged portion  95 . In addition, an entire region from the partial cavity surface  92   a  to the sliding surface  92   b  is continuously coated with a protective coat  94 . 
     FIG. 11  is a schematic partial sectional view of a sliding member of an injection mold according to the ninth embodiment. In the injection mold according to this embodiment, a partial cavity surface  102   a  except for a portion h near a sliding surface  102   b  of a sliding member  102  is continuously coated with a heat insulating coat  103 . A jagged portion  103   a  is formed on that surface of the heat insulating coat  103 , which opposes the sliding surface  102   b . In addition, an entire region from the partial cavity surface  102   a  to the sliding surface  102   b  is continuously coated with a protective coat  104 . 
   The above second to ninth embodiments are explained by taking the sliding member as an example. The adjacent member or the sliding member and adjacent member are similar to those shown in  FIGS. 2A and 2B  and  FIGS. 3A and 3B  as modifications of the first embodiment, so a detailed description thereof will be omitted. 
   In the present invention, a heat-resistant polymer material is preferably used as the heat insulating coat. 
   Also, the protective coat is preferably a single-layered coat or multilayered coat made of, e.g., a metal such as Ni, Ti, Cr, Zr, or Si, ceramics such as an oxide, carbide, or nitride of any of these metals, or diamond. 
   Experiments were conducted to confirm the effects of the injection molds according to the present invention. The results of these experiments will be explained below. 
   EXPERIMENTAL EXAMPLE 1 
   An injection mold having an ejector pin as a sliding member was used in injection molding an injection molding product by changing the combination of the arrangement of the ejector pin and the arrangement of an adjacent member, and the number of times of injection molding before a heat insulating coat peeled was checked. The results are shown in  FIGS. 14 and 15 . 
   Note that as the arrangement of the sliding member and the arrangement of the adjacent member in Examples 1 to 35 shown in  FIG. 14 , the arrangements of the sliding members shown in  FIGS. 1 ,  4 ,  5 ,  6 ,  7 , and  10  were used. 
   Note also that in each of Examples 1 to 35, a 0.1 mm thick polyimide vacuum deposited polymerized coat (manufactured by VACUUM METALLURGICAL CO., LTD.) was used as the heat insulating coat, and a 0.001 mm thick CrN coat was used as the protective coat. 
     FIG. 12  is a schematic partial sectional view of an injection mold used in Comparative Example 1. The injection mold of this comparative example has an adjacent member  201  and sliding member  202  adjacent to each other. A sliding surface  202   b  of the sliding member  202  is slidably guided by a sliding surface  201   b  of the adjacent member  201  such that a cavity surface  202   a  of the sliding member  202  protrudes into the cavity by a relative sliding distance from the state in which the cavity surface  202   a  is leveled with a cavity surface  201   a  of the adjacent member  201 . 
   A portion from the cavity surface  202   a  to the sliding surface  202   b  of the sliding member  202  is continuously coated with a heat insulating coat  203 . The range over which the sliding surface  202   b  is coated with the heat insulating coat  203  is so set as not to exceed the relative sliding distance. In addition, the heat insulating coat  203  extending from the cavity surface  202   a  to the sliding surface  202   b  is coated with a protective coat  204 . 
     FIG. 13  is a schematic partial sectional view of an injection mold used in Comparative Example 2. The injection mold of this comparative example has an adjacent member  301  and sliding member  302  adjacent to each other. A sliding surface  302   b  of the sliding member  302  is slidably guided by a sliding surface  301   b  of the adjacent member  301  such that a cavity surface  302   a  of the sliding member  302  protrudes into the cavity by a relative sliding distance from the state in which the cavity surface  302   a  is leveled with a cavity surface  301   a  of the adjacent member  301 . 
   The cavity surface  302   a  of the sliding member  302  is coated with a heat insulating member  303 . The heat insulating member  303  is also coated with a protective coat  304 . 
   In each of Comparative Examples 1 and 2, the number of times of injection molding before the heat insulating coat peeled was checked following the same procedure as in Examples 1 to 35. The results are shown in  FIG. 15 . 
   As shown in  FIGS. 14 and 15 , in each of Examples 1 to 35, 10,000 times or more of injection molding were necessary before the heat insulating coat peeled, indicating high durability. In contrast, the heat insulating coats peeled when the numbers of times of injection molding were  13  and  122  in Comparative Examples 1 and 2, respectively. 
   EXPERIMENTAL EXAMPLE 2 
   The combination of the sliding member ( FIG. 8 ) and the adjacent member ( FIG. 1 ) in Example 11 described above was used to check the number of times of injection molding before the heat insulating coat peeled by changing the material of the protective coat. The results are shown in  FIG. 16 . Note that electroless plating, physical vapor deposition, and chemical vapor deposition were used as coat formation methods, and thickness of the protective coat was set to 1 μm. As shown in  FIG. 16 , in each of Examples 37 to 44, 10,000 times or more of injection molding were necessary before the heat insulating coat peeled, indicating high durability. 
   In each of the above embodiments as described above, the peeling resistance of the heat insulating coat is high, and this improves the durability. Therefore, high-quality injection molded products having excellent outer appearance can be stably molded. 
   The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to apprise the public of the scope of the present invention the following claims are made.