Resin composition for welding, molded article containing resin composition for welding, and method for producing molded article

Abstract

Provided are a resin composition for welding, a molded body including the resin composition for welding, and a method for producing the molded body.SOLUTION: The resin composition for welding contains a thermoplastic resin containing polypropylene, a glass fiber, and an antioxidant, and has an oxidation induction time at 230 °C of 30 minutes or more.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a resin composition for welding, a molded article containing the resin composition for welding, and a method for producing the molded article. [Background technology]

[0002] BACKGROUND ART Conventionally, resin compositions have been known in which strength and heat resistance have been improved by adding glass fibers and antioxidants to thermoplastic resins (see, for example, Patent Document 1).

[0003] Patent Document 1 describes a molded article made of a resin composition in which glass fiber and an antioxidant are added to a thermoplastic resin such as polyamide. The molded article is formed by joining molded members made of the resin composition together by stamping using a press. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-177117 Summary of the Invention [Problem to be solved by the invention]

[0005] Although the molded article described in Patent Document 1 has improved heat resistance, there is no mention of creep life, etc. Therefore, when molded members made of a resin composition such as that described in Patent Document 1 are heat-welded to each other, there is a problem that the strength and creep life of the welded part are reduced due to thermal deterioration of the welded surface and the vicinity of the welded surface.

[0006] Therefore, there is a demand for a resin composition for welding that is resistant to deterioration even when subjected to a thermal load. [Means for solving the problem]

[0007] The resin composition for welding according to the present invention is characterized in that it contains a thermoplastic resin containing polypropylene, glass fiber, and an antioxidant, and has an oxidation induction time at 230°C of 30 minutes or more.

[0008] According to this configuration, the glass fiber improves the strength of the resin composition for welding, and the antioxidant suppresses oxidative degradation of the resin composition for welding. Furthermore, since the oxidation induction time at 230°C is 30 minutes or longer, even if the resin composition for welding is placed in a high-temperature environment and subjected to a thermal load, the strength and creep life are unlikely to decrease. Therefore, it is possible to provide a resin composition for welding that is resistant to degradation even when subjected to a thermal load. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is an exploded perspective view of the cooling module. [Figure 2] FIG. 2 is a cross-sectional view of a cooling module. [Figure 3] 1 shows the results of thermal scanning analysis at 210° C. for Examples and Comparative Examples. [Figure 4] 1 shows the results of thermal scanning analysis at 230° C. for Examples and Comparative Examples. [Figure 5] 1 shows the results of thermal scanning analysis at 250° C. for Examples and Comparative Examples. [Figure 6] 1 is a graph showing measurement temperatures and oxidation induction times according to examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the resin composition for welding, the molded article containing the resin composition for welding, and the method for manufacturing the molded article according to the present invention will be described with reference to the drawings. In this embodiment, a cooling module will be used as an example of a molded article containing the resin composition for welding (hereinafter referred to as the resin composition). However, the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the present invention.

[0011] [Resin composition] The resin composition according to the present invention contains a thermoplastic resin including polypropylene. The resin composition may contain resins other than polypropylene, such as polyethylene, polyester, or polyamide. The thermoplastic resin may be a new resin derived from petroleum, a recycled resin obtained from waste materials, or a mixture thereof. Examples of waste materials include waste plastics such as defectively molded products, or waste plastics collected from the market. By using waste materials as the thermoplastic resin, the production cost of the resin composition can be reduced, and environmental impact can also be reduced. The mixing ratio of new resin to recycled resin can be set to any value, but from the perspective of reducing environmental impact, the higher the mixing ratio of recycled resin, the better. It is most preferable that the thermoplastic resin be recycled resin.

[0012] The resin composition according to the present invention also contains glass fibers. The type of glass fiber is not particularly limited, and any glass fiber made of E glass, A glass, or C glass can be used. A mixture of these may also be used. The glass fiber in the present invention is not particularly limited, but the average fiber diameter of the glass fiber is preferably 1 μm to 50 μm, more preferably 5 μm to 20 μm.

[0013] The resin composition preferably contains 15% to 55% of glass fiber, and more preferably 20% to 40% of glass fiber. The inclusion of glass fiber in the resin composition can improve the mechanical strength of the resin composition.

[0014] The resin composition according to the present invention also contains an antioxidant. Examples of the antioxidant that can be used include a hindered phenol-based antioxidant, a phosphorus-based process stabilizer, and a metal deactivator. Although a mixture of these antioxidants may be used, it is preferable that the resin composition contains at least a hindered phenol-based antioxidant and a phosphorus-based process stabilizer.

[0015] The antioxidant is contained in a predetermined amount in the resin composition so that the oxidation induction time at 230°C described below is at least a predetermined time. For example, the antioxidant may be contained in the resin composition in an amount of 0.1% to 2.0%. The inclusion of an antioxidant in the resin composition suppresses oxidative degradation of the thermoplastic resin and extends the oxidation induction time. Furthermore, the use of a metal deactivator as an antioxidant can inactivate catalysts and the like contained in the thermoplastic resin. When recycled resin is used as the thermoplastic resin, the recycled resin may contain an antioxidant. When such recycled resin is used, the amount of antioxidant added may be adjusted so that the antioxidant content in the resin composition is a predetermined value.

[0016] The oxidation induction time is an index used to evaluate the thermal stability of a resin composition. The oxidation induction time refers to the time from when a sample first comes into contact with oxygen until exothermic decomposition begins at an isothermal temperature. The oxidation induction time relatively indicates the sample's stability against oxidation, and a longer oxidation induction time indicates higher antioxidant properties and improved durability. The oxidation induction time can be measured using thermal analysis methods such as differential thermal analysis (DTA) and thermal scanning calorimetry (DSC), as described in JIS K 6774.

[0017] The oxidation induction time of the resin composition according to the present invention at 230°C is 30 minutes or more, preferably 30 to 200 minutes. That is, even when exposed to an oxidizing atmosphere at 230°C, the resin composition according to the present invention is thermally stable until an oxidation induction time of 30 minutes or more (preferably 30 to 200 minutes) has elapsed. Therefore, the resin composition according to the present invention is unlikely to experience a decrease in strength or creep life even when subjected to a thermal load for a certain period of time (e.g., 30 minutes) in a high-temperature (e.g., approximately 230°C) environment. For this reason, the resin composition according to the present invention can be suitably used as a material for parts that undergo a thermal load treatment in a high-temperature environment around 230°C. Specifically, the resin composition can be suitably used as a material for part or all of parts that undergo a heat welding treatment. Examples of such parts include automotive parts. When the resin composition of the present invention is used as a material for on-vehicle parts, even if heat welding is performed during production, the strength and creep life of the welded parts and the joints W between the welded parts (see FIG. 2) are prevented from decreasing, and high durability performance (e.g., 100,000 km in 5 years) can be achieved. In other words, the resin composition of the present invention is particularly suitable for use as a material for on-vehicle molded products having joints formed by heat welding of welded parts of members using the resin composition.

[0018] As a result of extensive research, the inventors of the present application have confirmed through experiments that even when only recycled resins are used as the thermoplastic resin, a resin composition having an oxidation induction time of 30 minutes or more at 230°C can be realized. In other words, even when only recycled resins are used as the thermoplastic resin, the resin composition according to the present invention can be suitably used as a material for molded articles for vehicles.

[0019] [Molded body] Next, a molded body 1 according to the present invention will be described with reference to Fig. 1. In this embodiment, the molded body 1 will be described as a housing 10 of an on-vehicle cooling module M. The cooling module M includes a flow path, pump, valves, etc. for a coolant to cool devices such as the motor and battery of the automobile.

[0020] As shown in FIG. 1 or 2, the housing 10 is composed of an upper housing 10a (an example of a molded member) having a first joint S1 (an example of a welded portion) and a lower housing 10b (an example of a molded member) having a second joint S2 (an example of a welded portion). The upper housing 10a and the lower housing 10b are each a housing having an internal space for accommodating a coolant flow path, a valve, and the like. In this embodiment, the upper housing 10a and the lower housing 10b, including the first joint S1 and the second joint S2, are each formed from a resin composition according to the present invention. The upper housing 10a and the lower housing 10b may each be formed into a predetermined shape by injection molding or the like.

[0021] The housing 10 is formed by heat welding the first joint S1 and the second joint S2 at the joint W. The entire housing 10 may be formed from a resin composition, or only the first joint S1 and the second joint S2 of the housing 10 may be formed from the resin composition. By forming the joint W between the upper housing 10a and the lower housing 10b from the resin composition according to the present invention, even if a thermal load due to heat welding occurs at the first joint S1 and the second joint S2, a decrease in the strength and creep life of the first joint S1, the second joint S2, and the joint W is suppressed. This makes it possible to suppress deterioration of the housing 10, thereby achieving a housing 10 with high durability.

[0022] [Method for producing molded body] The manufacturing method of the housing 10 includes a molding step of molding the upper housing 10a having the first joint portion S1 and the lower housing 10b having the second joint portion S2, and a welding step of thermally welding the first joint portion S1 and the second joint portion S2. The molding step may be performed by a known method. In this embodiment, the upper housing 10a and the lower housing 10b including the first joint portion S1 and the second joint portion S2 are formed using the resin composition according to the present invention.

[0023] After the upper housing 10a and the lower housing 10b are formed in the molding process, the first joint S1 and the second joint S2 are heat-welded together in the welding process. In this embodiment, the welding process is performed by hot plate welding, IR welding, or vibration welding. For example, IR welding can be performed by applying IR light for 5 to 30 seconds to heat the surface to a temperature of 175°C to 250°C. Therefore, if the oxidation induction time at 230°C of the resin composition constituting the first joint S1 and the second joint S2 is 30 minutes or longer, deterioration in the strength and creep life of the first joint S1, the second joint S2, and the joint W thereof during heat welding is suppressed. This makes it possible to manufacture a housing 10 that is durable and resistant to deterioration.

[0024] [Example] Examples of the present invention will be described below, but the present invention is not limited to the descriptions of these examples.

[0025] (Example) The resin composition of the present example was obtained by adding glass fiber and an antioxidant to polypropylene, a recycled resin made from waste materials such as food containers. These were added so that the glass fiber content in the resin composition was 30% and the antioxidant content was 0.3%. The antioxidants added included a hindered phenol-based antioxidant, a phosphorus-based processing stabilizer, and a metal deactivator.

[0026] (Comparative Example) A resin composition according to the comparative example was obtained by adding glass fiber and an antioxidant to a new polypropylene resin. The glass fiber content and the antioxidant content in the resin composition were adjusted to 30% and 0.05%, respectively.

[0027] For each of the examples and comparative examples, the oxidation induction time at 210°C, 230°C, and 250°C was determined by differential scanning calorimetry (DSC). In the differential scanning calorimetry, the sample was heated to a predetermined temperature in a nitrogen atmosphere, then switched from the nitrogen atmosphere to an air atmosphere, and the time from the time of switching to the time when an exothermic peak occurred due to oxygen absorption by the sample was measured. The time when the heat flow of the sample reached 0.5 mW was defined as the time when the exothermic peak occurred.

[0028] 3 to 5 show the results of thermal scanning analysis. For the example, the oxidation induction time at 210°C was 203.4 minutes, the oxidation induction time at 230°C was 40.0 minutes, and the oxidation induction time at 250°C was 1.6 minutes. This shows that the resin composition according to the example is less likely to deteriorate even when subjected to a thermal load at 230°C. On the other hand, for the resin composition according to the comparative example, the oxidation induction time at 210°C was 12.2 minutes, the oxidation induction time at 230°C was 1.6 minutes, and the oxidation induction time at 250°C was 0.4 minutes. This shows that the resin composition according to the comparative example is more likely to deteriorate in a high-temperature environment.

[0029] Figure 6 is a graph plotting the logarithm of the oxidation induction time against each test temperature. As shown in Figure 6, there is a correlation between the test temperature and the oxidation induction time for the same material, and an approximation formula can be calculated from the oxidation induction time values ​​at each test temperature. Therefore, the resin compositions according to the present invention also include those for which the oxidation induction time at 230°C calculated using the approximation formula is 30 minutes or more and 200 minutes or less.

[0030] Furthermore, a molded part having a welded portion was formed using the resin composition of the example, and the welded portion was IR-welded to obtain a molded article. The IR welding was performed by irradiating the welded portion with IR light for 20 seconds to heat the surface of the welded portion to 230°C. A molded article was also obtained in the same manner using the resin composition of the comparative example.

[0031] A pressure resistance durability test at 80°C was carried out on each of the molded articles according to the Examples and Comparative Examples. The pressure resistance durability test was carried out by holding the articles under an internal pressure of 300 kPa. The durability of the molded article according to the Examples was 340 hours, and the durability of the molded article according to the Comparative Examples was 100 hours, demonstrating that the welded parts made of the resin compositions according to the Examples exhibit high durability.

[0032] In the above-described embodiment, the following configurations are envisioned. (1) A resin composition for welding, which comprises a thermoplastic resin containing polypropylene, glass fiber, and an antioxidant, and has an oxidation induction time at 230°C of 30 minutes or more.

[0033] According to this configuration, the glass fiber improves the strength of the resin composition, and the antioxidant suppresses oxidative degradation of the resin composition for welding. Furthermore, since the oxidation induction time at 230°C is 30 minutes or longer, even if the resin composition for welding is placed in a high-temperature environment and subjected to a thermal load, the strength and creep life are unlikely to decrease. Therefore, it is possible to provide a resin composition for welding that is resistant to degradation even when subjected to a thermal load.

[0034] (2) In the resin composition for welding of (1), the thermoplastic resin is preferably a recycled material obtained from waste materials.

[0035] According to this configuration, the resin composition for welding can be obtained by material recycling, so that it is possible to reduce the manufacturing cost and also reduce the environmental load.

[0036] (3) In a molded body (housing 10) formed by thermally welding together the welded portions of two or more molded members (upper housing 10a, lower housing 10b) having welded portions (first joint S1, second joint S2), it is preferable that the welded portions are made of the welding resin composition of (1) or (2).

[0037] According to this configuration, the welded portions (first joint S1, second joint S2) of the molded body (housing 10) formed by thermal welding are made of a welding resin composition, so oxidation deterioration due to thermal welding is less likely to occur, and the durability of the molded body (housing 10) can be improved.

[0038] (4) The manufacturing method of the molded body (housing 10) of (3) includes a molding process of molding molded members (upper housing 10a, lower housing 10b) having welding portions (first joint portion S1, second joint portion S2), and a welding process of thermally welding the welding portions (first joint portion S1, second joint portion S2) of the molded members (upper housing 10a, lower housing 10b) to each other, and the welding process is preferably performed by hot plate welding, IR welding, or vibration welding.

[0039] According to this configuration, the welding process can be performed by hot plate welding, IR welding, or vibration welding, and therefore, by thermally welding the welding portions (first joint S1, second joint S2) of the molded parts (upper housing 10a, lower housing 10b) having a welding resin composition together, a highly durable molded body (housing 10) can be obtained in a simple manner.

[0040] Other Embodiments (a) In the above embodiment, the entire upper housing 10a and the lower housing 10b are formed from the resin composition according to the present invention. However, the present invention is not limited to this. The first joint portion S1 of the upper housing 10a and the second joint portion S2 of the lower housing 10b may be formed from a resin composition, and other portions of each housing 10a, 10b may be formed from a material other than the resin composition according to the present invention. In other words, it is sufficient that each welded portion of the upper housing 10a and the lower housing 10b is formed from the resin composition according to the present invention.

[0041] (b) In the above embodiment, the welding process for manufacturing the housing 10 is performed by any one of hot plate welding, IR welding, and vibration welding, but the present invention is not limited to these. The welding process may be performed by a method other than those described above. [Industrial Applicability]

[0042] INDUSTRIAL APPLICABILITY The present invention is applicable to a resin composition containing a thermoplastic resin including polypropylene, glass fiber, and an antioxidant, a molded article containing the resin composition, and a method for producing a molded article. [Explanation of symbols]

[0043] 10: Housing (molded body), 10a: Upper housing (molded member), 10b: Lower housing (molded member), S1: First joint S1 (welded portion), S2: Second joint S2 (welded portion)

Claims

1. The thermoplastic resin includes polypropylene, glass fiber, and an antioxidant, A resin composition for welding having an oxidation induction time of 30 minutes or more at 230°C.

2. 2. The resin composition for welding according to claim 1, wherein the thermoplastic resin is a recycled material obtained from waste materials.

3. A molded body formed by thermally welding two or more molded members having welded portions to each other, The welded portion is a molded article made of the resin composition for welding according to claim 1 or 2.

4. A method for producing the molded body according to claim 3, comprising: a molding step of molding the molded member having the welded portion; a welding step of thermally welding the welding portions of the molded members together, The method for producing a molded body, wherein the welding step is performed by hot plate welding, IR welding, or vibration welding.

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