JP7824366B2 - Method for manufacturing resin molded body - Google Patents

Description

The present invention relates to a method for manufacturing a resin molded product.

Resin molded products containing natural fibers such as cellulose fibers are used in a wide range of fields, including everyday items, home appliance housings, building materials, and automotive parts. Increasing the natural fiber content in resin molded products can reduce the use of petroleum-derived materials.

Resin molded articles containing natural fibers can be formed by injection molding (see, for example, Patent Document 1).

Patent No. 6839570

When a resin composition containing natural fibers is injection molded, a resin molded product with a unique pattern is obtained, but there is an issue in that the pattern appears throughout the entire resin molded product.

The present invention was made in consideration of the above circumstances, and aims to provide a method for manufacturing a resin molded product that can produce patterns derived from natural fibers at any location.

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 body 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.

The present invention provides a method for producing a resin molded product that can produce patterns derived from natural fibers at any location.

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. In an experimental example, 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. In an experimental example, 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. In an experimental example, photographs are shown 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, 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. 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. 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. 1 is a microscope image of the surface of a resin molded body in an experimental example in which the temperature of the main mold was 15° C. and the temperature of the insert was 45° C.

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.

[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.

The method for manufacturing a resin molded body of this embodiment uses a resin composition containing a thermoplastic resin and natural fibers.

Examples of thermoplastic resins include olefin-based resins, styrene-based resins, acrylic-based resins, polycarbonate-based resins, etc.

Examples of natural fibers include cellulose fiber, jute fiber, bamboo fiber, and kenaf fiber.

The natural fiber content relative to the total mass (100% by mass) of the resin composition is preferably 35% by mass or more and 55% by mass or less, more preferably 40% by mass or more and 50% by mass or less, and even more preferably 45% by mass or more and 48% by mass or less. If the natural fiber content is above the lower limit, a distinctive pattern derived from the natural fibers will develop. If the natural fiber content exceeds the upper limit, it will be difficult to perform injection molding with a resin molded product containing natural fibers.

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 Figure 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 portion where the insert 20 is not placed becomes a portion 10A that has a low temperature during molding, and the portion where the insert 20 is placed becomes a portion 10B that has a high temperature during molding.

In the method for manufacturing 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 within 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 pipe 30. Because the heat-insulating space 20A is provided in the high-temperature portion 10B, the cooling effect of the water pipe 30 is suppressed, and the high-temperature portion 10B becomes hotter than the low-temperature portion 10A.

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

In the method for manufacturing 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. If the temperature is above the lower limit, injection molding can be performed on a resin molded product containing natural fibers. If the temperature exceeds the upper limit, it becomes difficult to produce the unique patterns derived from natural fibers.

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

In the method for manufacturing a resin molded body of this embodiment, in the low-temperature portion 10A of the main mold 10, a portion (first portion) 100A is set where the 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, is 1.8 mm, and a portion (second portion) 100B is set where the 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, is 2.2 mm. As a result of verifying the occurrence of a pattern (marble pattern) in the first portion 100A and the second portion 100B, it was found that the likelihood of a pattern occurring differs between the first portion 100A and the second portion 100B. That is, the first portion 100A is a portion where the occurrence of a pattern is limited and where the pattern is unlikely to occur. The second portion 100B is a portion where the pattern occurs and where the pattern is likely to occur. 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 that a skin layer will form. Therefore, molding is completed before the pattern appears, making it difficult for the pattern to appear. On the other hand, in the portion where the height of the flow path 11 is large (second portion 100B), the injection speed of the resin composition is reduced, 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.
The high-temperature portion 10B of the main mold 10 is a portion where the generation of a pattern is suppressed (third portion 100C).

According to the method for manufacturing a resin molded body of this embodiment, by providing high-temperature portions 10B and low-temperature portions 10A within the mold 1, it is possible to suppress the development of patterns derived from natural fibers in the high-temperature portions 10B and promote the development of patterns derived from natural fibers in the low-temperature portions 10A. This makes it possible to develop patterns derived from natural fibers at any location on the resin molded body.

The present invention will be explained in more detail below using experimental examples, but the present invention is not limited to these examples.

[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.

As shown in Figures 2 and 3, when water whose temperature has been adjusted by a temperature regulator is run through the water pipe and the temperature of the mold is set to 31°C, the marble pattern becomes less noticeable on the surface of the resin molded body (top of Figure 2, top of Figure 3). Furthermore, when water whose temperature has been adjusted by a temperature regulator is run through the water pipe and the temperature of the mold is set to 29°C, the marble pattern appears on the surface of the resin molded body (bottom of Figure 2, bottom of Figure 3).

As shown in Figures 4 and 5, when the temperature of the main mold was 15°C and the temperature of the insert mold was 35°C, a marbled pattern was generated in the area that had been in contact with the main mold, and a slight marbled pattern was generated in the area that had been in contact with the insert mold (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 mold was 45°C, a marbled pattern was generated in the area that was in contact with the main mold, while the generation of a marbled pattern was suppressed in the area that was in contact with the insert mold (bottom of Figure 4, Figure 6).

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 was 45°C. A Keyence microscope was used. As shown in Figure 7, in the part that came into contact with the master mold, irregularities with a marbled pattern were formed, while in the part that came into contact with the insert, no irregularities were formed.

1 Mold 10 Main mold 10A Low temperature part 10B High temperature part 11, 12 Flow path 20 Insert 20A Heat insulating space 30 Water pipe 100A First part 100B Second part 100C Third part

Claims (2)

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