Method for manufacturing resin molded body

Abstract

To provide a method for manufacturing a resin molded body capable of generating a pattern derived from a natural fiber at an arbitrary place.SOLUTION: A method for producing a resin molded article, comprising injecting a resin composition containing a thermoplastic resin and a natural fiber into a mold to obtain a resin molded article made of the resin composition, wherein a high-temperature portion and a low-temperature portion are provided in the mold.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a resin molded article. [Background technology]

[0002] Resin molded products containing natural fibers such as cellulose fibers are used in a wide range of fields, including daily necessities, housings for home appliances, building materials, and automotive parts. Increasing the natural fiber content in resin molded products can reduce the use of petroleum-derived materials.

[0003] Resin molded articles containing natural fibers can be formed by injection molding (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6839570 Summary of the Invention [Problem to be solved by the invention]

[0005] When a resin composition containing natural fibers is injection molded, a resin molded article having a unique pattern can be obtained, but there is a problem in that the pattern appears over the entire resin molded article.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a method for manufacturing a resin molded article that can generate a pattern derived from natural fibers at any desired location. [Means for solving the problem]

[0007] The present invention has the following aspects. [1] A method for producing a resin molded article, comprising injecting a resin composition containing a thermoplastic resin and natural fibers into a mold to obtain a resin molded article made of the resin composition, A method for manufacturing a resin molded article, wherein a high temperature portion and a low temperature portion are provided within the mold. [2] The method for producing a resin molded article according to [1], wherein the temperature of the low temperature portion is 10°C or higher and 30°C or lower, and the temperature of the high temperature portion is 40°C or higher. [3] The method for producing a resin molded body described in [1], wherein the height of the flow path of the resin composition corresponding to the thickness direction of the resin molded body in the mold is 1.8 mm or less or 2.2 mm or more. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing a resin molded article that can produce a pattern derived from natural fibers at any desired location. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view showing an example of a mold used in the method for producing a resin molded body according to the present embodiment. [Figure 2] In an experimental example, these photographs show the surface of a resin molded body when water whose temperature has been adjusted by a temperature regulator is flowed through the water pipe to set the temperature of the mold to 31°C, and the surface of a resin molded body when water whose temperature has been adjusted by a temperature regulator is flowed through the water pipe to set the temperature of the mold to 29°C. [Figure 3] In an experimental example, these photographs show the surface of a resin molded body when water whose temperature has been adjusted by a temperature regulator is flowed through the water pipe to set the temperature of the mold to 31°C, and the surface of a resin molded body when water whose temperature has been adjusted by a temperature regulator is flowed through the water pipe to set the temperature of the mold to 29°C. [Figure 4] These are photographs showing the surface of a resin molded body when the temperature of the main mold is 15°C and the temperature of the insert is 35°C in an experimental example, and the surface of a resin molded body when the temperature of the main mold is 15°C and the temperature of the insert is 45°C. [Figure 5] 10 is a photograph showing the surface of a resin molded body in an experimental example when the temperature of the main mold is 15° C. and the temperature of the insert is 35° C. [Figure 6]10 is a photograph showing the surface of a resin molded body in an experimental example when the temperature of the main mold is 15° C. and the temperature of the insert is 45° C. [Figure 7] This is a microscope image of the surface of a resin molded body in an experimental example when the temperature of the main mold was 15°C and the temperature of the insert was 45°C. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the method for producing a resin molded article of the present invention will be described. It should be noted that the present embodiment is specifically described to allow a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0011] [Method of manufacturing resin molded body] A method for manufacturing a resin molded body according to one embodiment of the present invention is a method for manufacturing a resin molded body in which a resin composition containing a thermoplastic resin and natural fibers is injected into a mold to obtain a resin molded body made of the resin composition, and high-temperature areas and low-temperature areas are provided within the mold.

[0012] In the method for producing a resin molded article of this embodiment, a resin composition containing a thermoplastic resin and natural fibers is used.

[0013] Examples of thermoplastic resins include olefin-based resins, styrene-based resins, acrylic-based resins, and polycarbonate-based resins.

[0014] Examples of natural fibers include cellulose fibers, jute fibers, bamboo fibers, and kenaf fibers.

[0015] The content of natural fibers relative to the total mass (100 mass%) of the resin composition is preferably 35% by mass to 55% by mass, more preferably 40% by mass to 50% by mass, and even more preferably 45% by mass to 48% by mass. If the content of natural fibers is above the lower limit, a unique pattern derived from the natural fibers will occur. If the content of natural fibers exceeds the upper limit, it becomes difficult to perform injection molding of a resin molded product containing natural fibers.

[0016] FIG. 1 is a cross-sectional view showing an example of a mold used in the method for producing a resin molded article according to this embodiment. As shown in FIG. 1, the mold 1 has a main mold 10, a insert 20, and a water pipe 30. The water pipe 30 is provided inside the main mold 10. Water flows through the water pipe 30. The insert 20 is fitted into the main mold 10 when in use. The insert 20 has a space (heat insulating space) 20A that is not in contact with the main mold 10 on a part of the surface that contacts the main mold 10. In the main mold 10, the part where the insert 20 is not placed becomes a part 10A that has a low temperature during molding, and the part where the insert 20 is placed becomes a part 10B that has a high temperature during molding.

[0017] In the method for producing a resin molded body of this embodiment, when the resin composition is injected into the mold 1, a high-temperature portion 10B and a low-temperature portion 10A are provided in the main mold 10. The main mold 10 is heated by a heater, but the temperature can be lowered by running water through the water pipes 30. In the high-temperature portion 10B, the cooling effect of the water pipes 30 is suppressed due to the provision of the heat-insulating space 20A, and the temperature becomes higher than that of the low-temperature portion 10A.

[0018] In the method for producing a resin molded product of this embodiment, the temperature difference between the high-temperature portion 10B and the low-temperature portion 10A is preferably 20° C. or more and 30° C. or less. When the temperature difference is equal to or more than the lower limit, a pattern derived from natural fibers can be generated at any location.

[0019] In the method for producing a resin molded product of this embodiment, the temperature of the low-temperature portion 10A is preferably 10°C or higher and 30°C or lower, and more preferably 15°C or higher and 19°C or lower. When the temperature is equal to or higher than the lower limit, injection molding can be performed on a resin molded product containing natural fibers. When the temperature exceeds the upper limit, it becomes difficult to produce the characteristic pattern derived from natural fibers.

[0020] The pressure when injecting (introducing) the resin composition into the mold 1 is preferably 120 MPa or more and 170 MPa or less.

[0021] In the method for manufacturing a resin molded body of this embodiment, a portion (first portion) 100A in the low-temperature portion 10A of the main mold 10 has a height d1 (height in the thickness direction of the mold 1) of the resin composition flow path 11, which corresponds to the thickness direction of the resulting resin molded body, of 1.8 mm, and a portion (second portion) 100B has a height d2 (height in the thickness direction of the mold 1) of the resin composition flow path 11, which corresponds to the thickness direction of the resulting resin molded body, of 2.2 mm. As a result of examining the occurrence of patterns (marble patterns) in the first portion 100A and the second portion 100B, it was found that the likelihood of pattern occurrence differs between the first portion 100A and the second portion 100B. That is, the first portion 100A is a portion where pattern occurrence is limited and where pattern occurrence is difficult. The second portion 100B is a portion where pattern occurrence is likely and where pattern occurrence is easy. In the portion (first portion 100A) where the height of the flow path 11 is small, the injection speed of the resin composition increases, and the resin molded body becomes thinner, making it more likely to form a skin layer. Therefore, molding is completed before the pattern appears, making it difficult for the pattern to appear. On the other hand, in the part where the height of the flow path 11 is large (second part 100B), the injection speed of the resin composition is slower, and the resin molding becomes thicker, making it difficult for a skin layer to form, and it is thought that the resin is slowly reflected in the design surface, resulting in the pattern being formed. The high temperature portion 10B of the main mold 10 is a portion where the generation of a pattern is suppressed (third portion 100C).

[0022] According to the method for producing a resin molded body of this embodiment, by providing high-temperature portion 10B and low-temperature portion 10A in mold 1, it is possible to suppress the generation of patterns derived from natural fibers in high-temperature portion 10B and promote the generation of patterns derived from natural fibers in low-temperature portion 10A. This makes it possible to generate patterns derived from natural fibers at any location on the resin molded body. [Example]

[0023] The present invention will be explained in more detail below by way of experimental examples, but the present invention is not limited to the following experimental examples.

[0024] [Experimental Example] Under the conditions shown in Table 1, a resin molded body was formed by injection molding. As the thermoplastic resin, polypropylene was used.

[0025] As shown in Figures 2 and 3, when the temperature of the mold is raised to 31°C by running water whose temperature is regulated by a temperature regulator through the water pipe, the marble pattern becomes less noticeable on the surface of the resin molded body (upper side of Figure 2, upper side of Figure 3). On the other hand, when the temperature of the mold is raised to 29°C by running water whose temperature is regulated by a temperature regulator through the water pipe, the marble pattern appears on the surface of the resin molded body (lower side of Figure 2, lower side of Figure 3).

[0026] As shown in Figures 4 and 5, when the temperature of the main mold was 15°C and the temperature of the insert was 35°C, a marbled pattern occurred in the area that had been in contact with the main mold, and a slight marbled pattern occurred in the area that had been in contact with the insert (upper side of Figure 4, Figure 5). Furthermore, as shown in Figures 4 and 6, when the temperature of the main mold was 15°C and the temperature of the insert was 45°C, the marble pattern appeared in the area that was in contact with the main mold, while the marble pattern was suppressed in the area that was in contact with the insert (bottom of Figure 4, Figure 6).

[0027] Figure 7 shows a microscope image of the surface of a resin molded body when the temperature of the master mold was 15°C and the temperature of the insert mold was 45°C. A Keyence microscope was used. As shown in Figure 7, in the part that had been in contact with the master mold, irregularities with a marbled pattern were formed, while no irregularities were formed in the part that had been in contact with the insert mold.

[0028] [Table 1] [Explanation of symbols]

[0029] 1. Mold 10 Main Type 10A Low temperature part 10B High temperature area 11,12 Flow path 20 Nesting 20A Insulation space 30 water tube 100A First Part 100B Second Part 100C Third Part

Claims

1. A method for producing a resin molded article, comprising injecting a resin composition containing a thermoplastic resin and natural fibers into a mold to obtain a resin molded article made of the resin composition, the method comprising: A high temperature portion and a low temperature portion are provided in the mold, the temperature difference between the high temperature portion and the low temperature portion is 20°C or more and 30°C or less; The method for producing a resin molded body, wherein the temperature of the low temperature portion is 10°C or higher and 30°C or lower, and the temperature of the high temperature portion is 40°C or higher.

2. The method for producing a resin molded article according to claim 1, wherein a height of the flow path of the resin composition in the mold corresponding to a thickness direction of the resin molded article is 1.8 mm or less or 2.2 mm or more.

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