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

Abstract

The invention provides a resin composition for welding, a molded body containing the resin composition for welding, and a method for manufacturing the molded body. The resin composition for welding contains a thermoplastic resin containing polypropylene, glass fibers, and an antioxidant, and the oxidation induction time of the resin composition for welding at 230 DEG C is 30 minutes or more.

Description

TECHNICAL FIELD

[0001] The present application relates to a resin composition for welding, a molded body containing the resin composition for welding, and a method for producing the molded body. BACKGROUND

[0002] In the past, a resin composition in which a glass fiber and an antioxidant are added to a thermoplastic resin to improve strength and heat resistance has been known (for example, refer to Patent Literature 1).

[0003] A molded body formed of a resin composition in which a glass fiber and an antioxidant are added to a thermoplastic resin such as polyamide is described in Patent Literature 1. In this molded body, joining of molded parts formed of the resin composition to each other is achieved by press molding using a press machine. PATENT LITERATURE

[0004] Patent Literature 1: Japanese Patent Application Laid-Open No. 2014-177117 SUMMARY

[0005] The molded body described in Patent Literature 1 seeks to improve heat resistance, but does not mention creep life and the like. Therefore, when molded parts formed of a resin composition as described in Patent Literature 1 are heat-welded to each other, there is a problem that the strength and the creep life of the welded portion are reduced due to thermal aging occurring at the welding surface and the vicinity thereof.

[0006] Therefore, there is a need for a resin composition for welding that is not easily aged even when subjected to a thermal load.

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

[0008] According to the present structure, the strength of the resin composition for welding is improved by the glass fiber, and the oxidative aging of the resin composition for welding is suppressed by the antioxidant. Furthermore, since the oxidation induction time at 230°C is 30 minutes or more, even when the resin composition for welding is placed in a high-temperature environment and subjected to a thermal load, reduction in strength and creep life does not easily occur. Therefore, it is possible to provide a resin composition for welding that is not easily aged even when subjected to a thermal load. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is an exploded perspective view of the cooling module. Figure 2 is a cross-sectional view of the cooling module. Figure 3 is a result of differential scanning calorimetry analysis at 210°C relating to the examples and the comparative examples. Figure 4 Results of differential scanning calorimetry at 230°C of the examples and comparative examples. Figure 5 Results of differential scanning calorimetry at 250°C of the examples and comparative examples. Figure 6 Graph showing the measured temperature and oxidation induction time of the examples and comparative examples. DETAILED DESCRIPTION

[0010] Hereinafter, embodiments of the resin composition for welding, the molded body containing the resin composition for welding, and the manufacturing method of the molded body according to the present application will be described based on the drawings. In the present embodiments, as one example of the molded body containing the resin composition for welding (hereinafter referred to as the resin composition), a cooling module will be described. However, the present application is not limited to the following embodiments, and various modifications can be made within the scope of the gist thereof.

[0011] [Resin composition] The resin composition according to the present application contains a thermoplastic resin containing polypropylene. The resin composition can contain, in addition to the polypropylene, a resin such as polyethylene, polyester, polyamide, or the like. The thermoplastic resin can be a virgin resin derived from petroleum, can be a recycled resin obtained from waste materials, or can be a mixture of both. The waste materials are, for example, waste plastics such as molding rejects, or waste plastics recovered from the market. By forming the thermoplastic resin from the waste materials, the manufacturing cost of the resin composition can be reduced, and the environmental load can be reduced. The mixing ratio of the virgin resin to the recycled resin can be set to an arbitrary value, but from the viewpoint of reducing the environmental load, it is preferable that the mixing ratio of the recycled resin be as high as possible, and it is most preferable that the thermoplastic resin be a recycled resin.

[0012] In addition, the resin composition according to the present application contains glass fibers. The type of the glass fibers is not particularly limited, and any one of glass fibers formed of E glass, A glass, or C glass can be used, or they can be used in a mixture. The glass fibers in the present application are not particularly limited, but the average fiber diameter of the glass fibers is preferably 1 μm to 50 μm, and more preferably 5 μm to 20 μm.

[0013] The content of the glass fibers in the resin composition is preferably 15% or more and 55% or less, and more preferably 20% or more and 40% or less. By containing the glass fibers in the resin composition, the mechanical strength of the resin composition can be improved.

[0014] In addition, the resin composition according to the present application contains an antioxidant. As the antioxidant, for example, a hindered phenol antioxidant, a phosphorus-based processing stabilizer, a metal deactivator, or the like can be used. As the antioxidant, a mixture of the above-mentioned substances can be used, but it is preferable that at least a hindered phenol antioxidant and a phosphorus-based processing stabilizer be contained.

[0015] The content of the antioxidant in the resin composition is a specified amount so that the oxidation induction time at 230°C described later reaches a specified time or more. For example, the content of the antioxidant in the resin composition is preferably 0.1% or more and 2.0% or less. By containing the antioxidant in the resin composition, the oxidative aging of the thermoplastic resin can be inhibited, and the oxidation induction time can be extended. In addition, by using a metal deactivator as the antioxidant, a catalyst or the like contained in the thermoplastic resin can be deactivated. Note that, when a recycled resin is used as the thermoplastic resin, the antioxidant can be contained in the recycled resin. In the case where such a recycled resin is used, the amount of the antioxidant added is preferably adjusted so that the content of the antioxidant in the resin composition reaches a specified value.

[0016] As an index for evaluating the heat stability of the resin composition, there is an oxidation induction time. The oxidation induction time refers to the time from when a test sample initially contacts oxygen to when it starts to thermally decompose at an isothermal temperature. The oxidation induction time is an index that relatively shows the stability of the test sample to oxidation, and the longer the oxidation induction time, the higher the oxidation resistance and the durability are improved. As described in JIS K 6774, the oxidation induction time can be measured using a thermal analysis method such as differential thermal analysis (DTA) or differential scanning calorimetry (DSC).

[0017] The resin composition according to the present application has an oxidation induction time of 30 minutes or more at 230°C, preferably 30 minutes or more and 200 minutes or less. That is, the resin composition according to the present application maintains thermal stability before the oxidation induction time of 30 minutes or more (preferably 30 minutes or more and 200 minutes or less) even when exposed to an oxidizing atmosphere at 230°C. Therefore, the resin composition according to the present application is less likely to undergo a decrease in strength and creep life even when a thermal load is applied for a certain period of time (e.g., 30 minutes) in a high-temperature (e.g., around 230°C) environment. Thus, the resin composition according to the present application can be favorably used as a material for a member subjected to a process in which a thermal load is applied in a high-temperature environment around 230°C. Specifically, it can be favorably used as a material for a part or the entirety of a member subjected to a heat welding process. As such a member, for example, a member for a vehicle can be mentioned. If the resin composition according to the present application is used as a material for a member for a vehicle, a decrease in strength and creep life of a welded portion and a joint portion W (see Figure 2 ) between welded portions can be suppressed even when a heat welding process is performed at the time of manufacture, thereby achieving high durability (e.g., 100,000 km for 5 years). That is, the resin composition according to the present application can be favorably used as a material for a molded article for a vehicle, which has a joint portion formed by heat welding welded portions of members each of which is made of the resin composition.

[0018] Further, the present inventors have conducted intensive studies repeatedly, and as a result, it has been confirmed through experiments that a resin composition having an oxidation induction time of 30 minutes or more at 230°C can be achieved even when only a recycled resin is used in a thermoplastic resin. That is, the resin composition according to the present application can be favorably used as a material for a molded article for a vehicle even when only a recycled resin is used in a thermoplastic resin.

[0019] [Shaped article] Next, the use of the resin composition according to the present application will be described. Figure 1 The shaped article according to the present application will be described. In the present embodiment, the shaped article 1 will be described as a case 10 of a cooling module M for a vehicle. The cooling module M has a flow path for a coolant for cooling an electric motor, a battery, and the like of a vehicle, a pump, a valve, and the like.

[0020] As described above, the resin composition according to the present application can be favorably used as a material for a member for a vehicle. Figure 1 or Figure 2As shown, the housing 10 is composed of an upper housing 10a (an example of a molded member) having a first joint portion S1 (an example of a weld portion) and a lower housing 10b (an example of a molded member) having a second joint portion S2 (an example of a weld portion). The upper housing 10a and the lower housing 10b are each a case having a flow path of a coolant, a housing space of a valve, and the like in the inside. In the present embodiment, the upper housing 10a and the lower housing 10b including the first joint portion S1 and the second joint portion S2 are each formed of the resin composition according to the present application. The upper housing 10a and the lower housing 10b are each preferably formed into a prescribed shape by injection molding or the like.

[0021] The housing 10 is formed by heat welding the first joint portion S1 and the second joint portion S2 at a joint portion W. The housing 10 can be formed entirely of the resin composition, or only the first joint portion S1 and the second joint portion S2 of the housing 10 can be formed of the resin composition. Since the joint portion W of the first joint portion S1 and the second joint portion S2 is formed of the resin composition according to the present application, even if thermal stress due to heat welding occurs in the first joint portion S1 and the second joint portion S2, the reduction in the strength and the creep life of the first joint portion S1, the second joint portion S2, and the joint portion W can be suppressed. Thus, the aging of the housing 10 can be suppressed, and a housing 10 having high durability can be achieved.

[0022] [Method for manufacturing molded member] The method for manufacturing 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 heat welding the first joint portion S1 and the second joint portion S2. The molding step is preferably performed by a publicly known method. In the present 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 application.

[0023] After the upper housing 10a and the lower housing 10b are formed in the molding step, the first joint portion S1 and the second joint portion S2 are heat welded by the welding step. In the present embodiment, the welding step is performed by hot plate welding, IR (Infrared) welding, or vibration welding. For example, in the case of IR welding, the welding is performed by irradiating IR light for 5 to 30 seconds to heat so that the surface temperature reaches 175°C to 250°C. Thus, if the oxidation induction time of the resin composition constituting the first joint portion S1 and the second joint portion S2 at 230°C is 30 minutes or more, the reduction in the strength and the creep life of the first joint portion S1, the second joint portion S2, and the joint portion W thereof at the time of heat welding will be suppressed. Thus, a housing 10 that has been suppressed from aging and has durability can be manufactured.

[0024] [Example] Embodiments of the present application will be described below, but the present application is not limited to the description of these embodiments.

[0025] [Example] A resin composition according to the example was obtained by adding glass fiber and an antioxidant to polypropylene which is a recycled resin formed from waste materials such as food containers. The above components were added so that the content of the glass fiber in the resin composition would be 30% and the content of the antioxidant would be 0.3%. As the antioxidant, a hindered phenol antioxidant, a phosphorus-based processing stabilizer, and a metal deactivator were added.

[0026] [Comparative Example] A resin composition according to the comparative example was obtained by adding glass fiber and an antioxidant to polypropylene which is a virgin resin. The above components were added so that the content of the glass fiber in the resin composition would be 30% and the content of the antioxidant would be 0.05%.

[0027] For the example and the comparative example, the oxidation induction time at 210°C, 230°C, and 250°C was obtained by differential scanning calorimetry (DSC). In the differential scanning calorimetry, after the sample was warmed to the specified temperature under a nitrogen atmosphere, the atmosphere was switched from the nitrogen atmosphere to the atmospheric air, and the time from the switching time until the exothermic peak caused by the absorption of oxygen by the sample was measured. Note that the time at which the heat flow of the sample reached 0.5 mW was taken as the time at which the exothermic peak was generated.

[0028] Figures 3 to 5 The results of the differential scanning calorimetry are shown. The oxidation induction time of the example 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. From this, it was found that the resin composition according to the example was not easily aged even when a thermal load was applied at 230°C. On the other hand, the oxidation induction time of the resin composition according to the comparative example 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. From this, it was found that the resin composition according to the comparative example was easily aged in a high-temperature environment.

[0029] Figure 6 is a graph in which the logarithm of the oxidation induction time corresponding to each test temperature is plotted. As shown in Figure 6As shown, there is a correlation between the test temperature and the oxidation induction time of the same material, and an approximate formula can be calculated from the value of the oxidation induction time at each test temperature. Therefore, the resin composition according to the present application also includes a substance having an oxidation induction time of 30 minutes or more and 200 minutes or less at 230°C calculated using the approximate formula.

[0030] In addition, a molded member having a weld portion was formed using the resin composition according to the example, and a molded body was obtained by IR welding the weld portions to each other. The IR welding was performed by heating to a surface temperature of 230°C by irradiation of IR light for 20 seconds. Also for the resin composition according to the comparative example, a molded body was obtained in the same manner.

[0031] The molded bodies according to the example and the comparative example were subjected to a pressure resistance durability test at 80°C, respectively. The pressure resistance durability test was performed by maintaining at an internal pressure of 300 kPa. The durability time of the molded body according to the example was 340 hours, and the durability time of the molded body according to the comparative example was 100 hours, and thus it was found that the weld portion formed using the resin composition according to the example exhibited high durability.

[0032] In the above-described embodiment, the following structures can be conceived. (1) A resin composition for welding containing a thermoplastic resin containing polypropylene, glass fibers, and an antioxidant, having an oxidation induction time of 30 minutes or more at 230°C.

[0033] According to the present structure, the strength of the resin composition is improved by the glass fibers, and the oxidation aging of the resin composition for welding is suppressed by the antioxidant. In addition, since the oxidation induction time at 230°C is 30 minutes or more, even if the resin composition for welding is placed in a high-temperature environment and subjected to a heat load, a decrease in strength and creep life is less likely to occur. Therefore, it is possible to provide a resin composition for welding that is less likely to age even if subjected to a heat load.

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

[0035] According to the present structure, it is possible to obtain a resin composition for welding by material recycling, and thus it is possible to reduce environmental load while reducing manufacturing costs.

[0036] (3) In a molded body (housing 10) formed by thermally welding the weld portions of two or more molded members (upper housing 10a, lower housing 10b) having weld portions (first joint portion S2, second joint portion S2) to each other, the weld portions are preferably formed of the resin composition for welding of (1) or (2).

[0037] According to the present structure, since the welded portions (first joint portion S1, second joint portion S2) of the molded body (housing 10) formed by thermal welding are formed of the resin composition for welding, oxidation aging caused by thermal welding is less likely to occur, and the durability of the molded body (housing 10) can be improved.

[0038] (4) The production method of the molded body (housing 10) of (3) includes a molding step of molding a molded member (upper housing 10a, lower housing 10b) having a welded portion (first joint portion S1, second joint portion S2), and a welding step of thermally welding the welded 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 step is preferably performed by hot plate welding, IR welding, or vibration welding.

[0039] According to the present structure, the welding step can be performed by hot plate welding, IR welding, or vibration welding, and thus, by thermally welding the welded portions (first joint portion S1, second joint portion S2) of the molded members (upper housing 10a, lower housing 10b) having the welded portions to each other, a molded body (housing 10) having high durability can be obtained in a simple manner.

[0040] [Other Embodiments] (a) In the above embodiment, the configuration in which the entire upper housing 10a and lower housing 10b are formed of the resin composition according to the present application is described, but the present application is not limited to this configuration. The first joint portion S1 of the upper housing 10a and the second joint portion S2 of the lower housing 10b can be formed of the resin composition, and the other portions of each housing 10a, 10b can be formed of a material other than the resin composition according to the present application. That is, as long as each welded portion of the upper housing 10a and lower housing 10b is formed of the resin composition according to the present application.

[0041] ( b) In the above embodiment, the configuration in which the welding step is performed by any one of hot plate welding, IR welding, and vibration welding when the housing 10 is produced is described, but the present application is not limited to this configuration. The welding step can be performed by a method other than the above-described methods.

[0042] [Industrial Applicability] The present application can be applied to a resin composition containing a thermoplastic resin containing polypropylene, glass fibers, and an antioxidant, a molded body containing the resin composition, and a production method of the molded body. Glossary of symbols 10: housing (molded body), 10a: upper housing (molded part), 10b: lower housing (molded part), S1: first joint S1 (welded portion), S2: second joint S2 (welded portion).

Claims

1. A resin composition for welding, comprising: a thermoplastic resin containing polypropylene; glass fibers; and an antioxidant, the resin composition for welding having an oxidation induction time of 30 minutes or more at 230°C.

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 the welding portions of two or more molded parts having the welding portions to each other, wherein the welding portions are formed from the resin composition for welding according to claim 1 or 2.

4. A method for manufacturing a molded body, which is a method for manufacturing the molded body according to claim 3, comprising: a molding step of molding the molded parts having the welding portions; and a welding step of thermally welding the welding portions of the molded parts to each other, the welding step being performed by hot plate welding, IR welding, or vibration welding. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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