Reinforcement method of hinge part of resin molding and resin molding having hinge part

Abstract

To provide a reinforcement method of a hinge part of a resin molding capable of easily reinforcing the hinge part, and a resin molding having a hinge part with high toughness.SOLUTION: A reinforcement method of a hinge part of a resin molding includes a step A of molding a resin molding having a hinge part by injection molding and a step B of applying flexure stress or tensile stress to a hinge part of the resin molding at a temperature 5 to 20°C higher than a glass transformation temperature of a resin constituting the resin molding. A resin molding having a hinge part has, at the hinge part of the resin molding having the hinge part, between an alignment layer and a core layer, another layer having a birefringence different from those of the alignment layer and the core layer.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for strengthening a hinge portion of a resin molded product, and to a resin molded product having a hinge portion. [Background technology]

[0002] In recent years, resin molded products having hinges have been widely used in connector parts and the like. The hinges are joints or fulcrums between parts, and are important parts for opening and closing devices and the like. The hinges are usually formed thin-walled to obtain sufficient flexibility, so that their toughness tends to decrease. Therefore, the hinges may crack when they are repeatedly bent, such as during opening and closing operations. Various proposals have been made to prevent cracking of the hinges (see Patent Document 1). As a measure to prevent cracking of the hinges, in terms of shape, it has been proposed to increase the length of the bending part (hinge) or to make it thinner so that the generated distortion is not large. In terms of materials, it has been proposed to improve the elongation and fluidity of the material. Furthermore, in terms of molding conditions, it has been proposed to adjust the temperature, injection speed, or pressure dwell, or to reduce the residence time. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-8209 A Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, various conventional measures have been proposed to prevent cracking of the hinge portion in terms of shape, material, or molding conditions. However, these measures require changes or adjustments to the shape, material, or molding conditions, and it is difficult to say that the hinge portion can be strengthened easily.

[0005] The present invention has been made in consideration of the above-mentioned problems in the conventional art, and an object of the present invention is to provide a method for reinforcing a hinge portion of a resin molded product, which allows the hinge portion to be easily reinforced, and a resin molded product having a highly tough hinge portion. [Means for solving the problem]

[0006] One aspect of the present invention that solves the above problems is as follows. (1) a process A for molding a resin molded product having a hinge portion by injection molding; A step B of applying a bending stress or a tensile stress to the hinge portion of the resin molded product at a temperature 5 to 20° C. higher than the glass transition temperature of the resin constituting the resin molded product; A method for strengthening a hinge portion of a resin molded product, comprising:

[0007] (2) The method for strengthening a hinge portion of a resin molded product according to (1) above, wherein in the step B, the resin molded product is bent at least once around the hinge portion by 20 to 90 degrees for 0.5 to 2 seconds to impart a bending stress to the hinge portion of the resin molded product.

[0008] (3) The method for strengthening a hinge portion of a resin molded product according to (1) or (2), wherein the application of bending stress or tensile stress to the hinge portion of the resin molded product in the step B is carried out in the step A by a bending mechanism or a tensile mechanism provided in a mold.

[0009] (4) A resin molded product having a hinge portion, the hinge portion having a layer between an orientation layer and a core layer, the layer having a birefringence different from that of the orientation layer and the core layer. Effect of the Invention

[0010] According to the present invention, it is possible to provide a method for reinforcing a hinge portion of a resin molded product, which enables the hinge portion to be easily reinforced, and a resin molded product having a hinge portion with high toughness. [Brief description of the drawings]

[0011] [Figure 1] FIG. 4 is a diagram showing a hinge portion in a resin molded product. [Diagram 2] 1 is a photograph showing a layer structure in a thick-walled portion of a resin molded product. [Diagram 3] 1 is a photograph showing a layer structure in a thin-walled portion of a resin molded product. [Figure 4] 1A is a photograph showing the layer structure of a resin molded article before bending stress is applied, and FIG. 1B is a photograph showing the layer structure of a resin molded article after bending stress is applied. [Diagram 5] 1 is a graph showing the distribution of tensile strain versus perforation depth before and after bending of (A) a molded product to which no tensile stress has been applied, and (B) a molded product to which tensile stress has been applied. [Figure 6] FIG. 2 is a top view showing a dumbbell test piece used in a test for applying a tensile stress. [Figure 7] 1A and 1B are diagrams illustrating a bending test performed on molded products having a wall thickness at the hinge portion of (A) 0.3 mmt and (B) 0.5 mmt. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] <Method of strengthening hinge part of resin molded product> The method for reinforcing the hinge portion of a resin molded product of this embodiment includes step A of molding a resin molded product having a hinge portion by injection molding, and step B of applying bending stress or tensile stress to the hinge portion of the resin molded product at a temperature 5 to 20°C higher than the glass transition temperature of the resin that constitutes the resin molded product.

[0013] In the method for strengthening the hinge part of the resin molded product of this embodiment, bending stress or tensile stress is applied to the hinge part of the resin molded product under heating at a predetermined temperature, thereby strengthening the hinge part.The principle of how the toughness of the hinge part is improved by applying bending stress or tensile stress to the hinge part of the resin molded product is not clear.However, as described below, it is also considered that by applying bending stress or tensile stress to the hinge part, another new layer having a different birefringence from the orientation layer and the core layer is formed between the orientation layer and the core layer, and the new layer contributes to improving the toughness of the hinge part.

[0014] 1 shows an example of the shape of the hinge portion in a resin molded product 10. Hinge portion 12 is M-shaped, and hinge portion 14 is straight. In this embodiment, toughness can be improved regardless of the shape.

[0015] As shown in FIG. 2, the microstructure of a thermoplastic (crystalline) resin injection molded product generally consists of three layers, from the surface: a skin layer, an orientation layer, and a core layer. In FIG. 2, the skin layer and the orientation layer are located at A, and the core layer is located at B. It is known that in a thick-walled molded product, the core layer dominates the physical properties, while in a thin-walled molded product, the skin layer and the orientation layer dominate. This is clear from the fact that, as shown in FIG. 3, in a thin-walled molded product, the skin layer, the orientation layer, and the core layer are located within X, and the ratio of the core layer is small, unlike the thick-walled structure shown in FIG. 2. And, since the hinge part is thinner than other parts as shown in FIG. 1, the ratio of the skin layer and the orientation layer is larger than that of a normal thick product, so it is easily affected by the condition of the skin layer and the orientation layer. Therefore, it is useful as a measure against breakage to ensure that the microstructure of the skin layer and the orientation layer is formed without any disturbance, that is, to reduce internal defects. That is, in this embodiment, as described above, a new layer is present between the orientation layer and the core layer, and it is believed that the new layer reduces internal defects and improves toughness, thereby contributing to reducing breakage.

[0016] Each step in the method for reinforcing a hinge portion of a resin molded product according to this embodiment will be described below. Note that in this embodiment, step A and step B are not necessarily performed in that order. That is, step A may be performed first, followed by step B, or step B may be performed during step A.

[0017] [Process A] In step A, a resin molded product having a hinge portion is molded by injection molding. That is, a resin molded product having a hinge portion is injection molded according to a standard method. Examples of the resin include thermoplastic resins such as polyacetal resin, polybutylene terephthalate resin, and polyarylene sulfide resin. However, in this embodiment, since the purpose is to improve the toughness of the hinge portion of the resin molded product, a resin suitable for forming the hinge portion is preferable.

[0018] [Process B] In step B, bending stress or tensile stress is applied to the hinge portion of the resin molded product at a temperature 5 to 20° C. higher than the glass transition temperature of the resin constituting the resin molded product. By applying bending stress or tensile stress to the hinge portion of the resin molded product under such temperature conditions, it is possible to improve the toughness as described above.

[0019] In step B, when bending stress or tensile stress is applied to the hinge portion of the resin molded product, the temperature is set to be 5 to 20°C higher than the glass transition temperature of the resin constituting the resin molded product. If the temperature is outside the range of 5 to 20°C higher, the toughness of the hinge portion cannot be improved. The temperature is preferably 7 to 18°C ​​higher, more preferably 10 to 15°C higher than the glass transition temperature of the resin constituting the resin molded product. There is no particular limitation on the heating means for bringing the temperature to the above range. If the resin molded product is within the above range immediately after injection molding, it is sufficient to carry out step B at that temperature, and there is no need to heat it.

[0020] Fig. 4(A) shows the microstructure near the surface of the resin molded product before bending stress is applied to the hinge part of the resin molded product, and Fig. 4(B) shows the microstructure near the surface of the resin molded product after bending stress is applied. In Fig. 4(B), it can be seen that a new layer N separate from the orientation layer and the core layer is formed between the orientation layer and the core layer.

[0021] The bending stress or tensile stress applied to the hinge portion of the resin molded product is preferably 60 to 80% of the maximum stress, and more preferably 65 to 75%. By setting the bending stress or tensile stress to 60 to 80% of the maximum stress, a new layer N can be formed between the orientation layer and the core layer, separate from the orientation layer and the core layer. The thickness of the new layer N is less than 100 μm, and is 50 to 70 μm.

[0022] In step B, when bending stress is applied to the hinge portion of the resin molded product, the bending angle is preferably 20 to 90°. The bending time is preferably 0.5 to 2 seconds. The bending direction when applying bending stress to the resin molded product may be the same as the bending direction when the hinge portion is formed, or may be the opposite direction. The number of times that bending stress is applied to the hinge portion may be one or more than one bending, and it is preferable that the number of bending times is two to three.

[0023] The microstructure near the surface before and after applying bending stress to the hinge section is shown in Figure 4. When the hinge section is bent, a stress equivalent to a tensile stress is applied near the outer surface, so it is presumed that a layer similar to layer N in Figure 4(B) is formed near the outer surface even when tensile stress is applied to the hinge section.

[0024] When applying tensile stress to the hinge portion of the resin molded product, it is preferable to maintain the applied state of tensile stress for 0.5 to 2 seconds. Moreover, the application of tensile stress can be performed once or multiple times. When applying multiple times, it is preferable to apply the tensile stress 2 to 3 times.

[0025] On the other hand, the application of bending stress or tensile stress to the hinge portion of the resin molded product in step B can be configured to be performed by a bending mechanism or tension mechanism provided in the mold in step A. Such a bending mechanism or tension mechanism is preferably a rack and pinion mechanism. The rack can be driven by an electric motor or an air cylinder. Alternatively, the rack may be driven by an angular pin or a dog leg cam when the mold is opened, or an inclined slide core may be provided and the rack may be driven during ejection.

[0026] Here, the results of measuring the residual strain for a molded product in which step B was not performed and a molded product in which step B was performed are shown in FIG. 5. As the molded product, a dumbbell test piece (multipurpose test piece type A1) shown in FIG. 6 was used. In FIG. 6, L0 (initial length of measurement gauge): 50 ± 0.5 mm, L1 (length of parallel part): 80 ± 2 mm, L2 (distance between tab parts): 109.3 ± 3.2 mm, L3 (total length): 170 mm or more, b1 (width of central parallel part): 10 ± 0.2 mm, b2 (width of end part): 20 ± 0.2 mm, r (radius of shoulder part): 24 ± 1 mm, h (thickness): 4 ± 0.2 mm. Then, for both molded products (wall thickness h: 4 mmt), a drilling strain gauge was attached to the center, and the tensile strain distribution with respect to the depth of the drilling was measured. The measurement was performed according to the residual stress measurement method for resin molded products described in JP 2022-69103 A. Figure 5 shows the distribution of tensile strain versus perforation depth before and after bending for (A) a molded product to which no tensile stress was applied, and (B) a molded product to which tensile stress was applied. In Figure 5, ch1 is the longitudinal direction, ch2 is a direction inclined at 45° to the longitudinal direction, and ch3 is a direction perpendicular to the longitudinal direction. As shown in Figure 5(B), it can be seen that by applying tensile stress to a 4 mmt molded product, tensile strain remains from the surface layer to a depth of 0.2 mm.

[0027] In this embodiment, a resin molded product may be produced in step A, cooled once, and then the step B may be performed. That is, after a certain time has elapsed since the production of the resin molded product, the product may be heated to a predetermined temperature in step B to impart a tensile stress or bending stress to the hinge portion.

[0028] As described above, in this embodiment, it is possible to easily strengthen the hinge portion of a resin molded product without changing or adjusting the shape, material, or molding conditions.

[0029] <Resin molded product with hinge> The resin molded article having a hinge portion of the present embodiment has another layer between the orientation layer and the core layer in the hinge portion of the resin molded article having a hinge portion, the another layer having a birefringence different from that of the orientation layer and the core layer. The birefringence of the another layer is preferably different from that of the orientation layer and the core layer by 0.05 or more.

[0030] As explained in the method for reinforcing the hinge portion of the resin molded product of this embodiment above, it is presumed that the resin molded product having the hinge portion of this embodiment has high toughness because, in the hinge portion, between the orientation layer and the core layer, there is another layer having a different birefringence from the orientation layer and the core layer. Moreover, such a separate layer is formed by the method for reinforcing the hinge portion of the resin molded product of this embodiment described above, but may be formed by other methods.

[0031] In the resin molded product having the hinge portion of this embodiment, as described above, it is considered that the hinge portion is reinforced by the separate layer. This has been explained in the method for reinforcing the hinge portion of the resin molded product of this embodiment, so the explanation will be omitted here.

[0032] The thickness of the other layer present between the alignment layer and the core layer is less than 100 μm, and preferably 50 to 70 μm.

[0033] The resin molded product having a hinge portion of this embodiment can be applied to resin molded products having a hinge portion, as the name suggests. In addition, since the hinge portion has high toughness, it is unlikely to crack even if it is repeatedly bent, such as during opening and closing operations. EXAMPLES

[0034] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to the following examples.

[0035] [Example 1] A polybutylene terephthalate resin (DURANEX (registered trademark) 2002) manufactured by Polyplastics Co., Ltd. was used as the thermoplastic resin, and the molded product 1 shown in Fig. 7(A) was produced by injection molding. The thickness of the hinge part of the molded product 1 was 0.3 mmt, and the width of the hinge part area was 2 mm. In addition, immediately after injection molding (within 1 second after release from the mold), the hinge part was bent once by 90° (bending time: 0.5 seconds) at the mold temperature (80°C) (see Fig. 7(A)).

[0036] [Comparative Example 1] A molded article was obtained in the same manner as in Example 1, except that the bending operation immediately after injection molding was not carried out.

[0037] [Example 2] A molded article was obtained in the same manner as in Example 1, except that the thermoplastic resin was changed to a polybutylene terephthalate resin (Duranex (registered trademark) 2000) manufactured by Polyplastics Co., Ltd.

[0038] [Comparative Example 2] A molded article was obtained in the same manner as in Example 2, except that the bending operation immediately after injection molding was not carried out.

[0039] [Example 3] A molded article was obtained in the same manner as in Example 1, except that the thermoplastic resin was changed to a polyacetal resin (Duracon (registered trademark) M90-44) manufactured by Polyplastics Co., Ltd.

[0040] [Comparative Example 3] A molded article was obtained in the same manner as in Example 3, except that the bending operation immediately after injection molding was not carried out.

[0041] [Example 4] A molded article was obtained in the same manner as in Example 1, except that the molded article to be molded was molded article 2 shown in Fig. 7(B). Molded article 2 had a hinge thickness of 0.5 mmt and a width of the hinge region of 2 mm.

[0042] [Comparative Example 4] A molded article was obtained in the same manner as in Example 4, except that the bending operation immediately after injection molding was not carried out.

[0043] [Example 5] A molded article was obtained in the same manner as in Example 4, except that the thermoplastic resin was changed to a polybutylene terephthalate resin (Duranex (registered trademark) 2000) manufactured by Polyplastics Co., Ltd.

[0044] [Comparative Example 5] A molded article was obtained in the same manner as in Example 5, except that the bending operation immediately after injection molding was not carried out.

[0045] [Example 6] A molded article was obtained in the same manner as in Example 4, except that the thermoplastic resin was changed to a polyacetal resin (Duracon (registered trademark) M90-44) manufactured by Polyplastics Co., Ltd.

[0046] [Comparative Example 6] A molded article was obtained in the same manner as in Example 6, except that the bending operation immediately after injection molding was not carried out.

[0047] Crack evaluation The molded products produced in each Example and Comparative Example were subjected to a bending test 10 times around the hinge part, and were evaluated as ◯ if they were not broken and × if they were broken. The bending direction was the same as that immediately after injection molding. The evaluation results are shown in Table 1.

[0048] [Table 1]

[0049] As can be seen from Table 1, there was no breakage due to bending in any of Examples 1 to 6. In contrast, there was breakage at least once out of 10 times in Comparative Examples 1 to 6. This shows that the toughness of the hinge portion is improved by applying a bending stress to the hinge portion under a specified temperature condition. [Explanation of symbols]

[0050] 10 Resin molded products 12 14 Hinge part

Claims

1. A process A of molding a resin molded product having a hinge portion by injection molding; A step B of applying a bending stress or a tensile stress to the hinge portion of the resin molded product at a temperature 5 to 20° C. higher than the glass transition temperature of the resin constituting the resin molded product; A method for strengthening a hinge portion of a resin molded product, comprising:

2. 2. The method for reinforcing a hinge portion of a resin molded product according to claim 1, wherein in the step B, the resin molded product is bent at least once around the hinge portion by 20 to 90 degrees for 0.5 to 2 seconds to impart a bending stress to the hinge portion of the resin molded product.

3. 3. The method for strengthening a hinge portion of a resin molded product according to claim 1 or 2, wherein the application of bending stress or tensile stress to the hinge portion of the resin molded product in the step B is performed in the step A by a bending mechanism or a tensile mechanism provided in a mold.

4. A resin molded product having a hinge portion, the hinge portion having a layer between an orientation layer and a core layer, the layer having a birefringence different from that of the orientation layer and the core layer.

Images