Patent Publication Number: US-2016221254-A1

Title: Bonded body and bonding method

Description:
TECHNICAL FIELD 
     The present invention relates to a bonded body in which a first member, and a second member formed of a material different from that of the first member are bonded to each other, and a bonding method thereof. 
     BACKGROUND ART 
     Hitherto, as a method of bonding metal to a resin, there is a bonding method described in Patent Literature 1. This bonding method is a manufacturing method of inserting a laser bonding sheet formed of a polymer between a first member formed of metal and a second member formed of a resin and melting the laser bonding sheet through laser light irradiation, thereby bonding the first member and the second member to each other. Accordingly, a bonded body in which the first member and the second member are bonded to each other with the laser bonding sheet interposed therebetween can be obtained. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent No. 4771387 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, when the first member formed of metal and the second member formed of a resin are welded to each other by laser welding, the material of the laser bonding sheet does not infiltrate into gaps such as pores formed on the surface of the first member formed of metal, and voids remain in the gaps. Therefore, there is a possibility that sufficient bonding strength of the first member and the second member may not be obtained. 
     In addition, in the bonding method described in Patent Literature 1, since the laser bonding sheet has a flat sheet shape, a case in which bonding surfaces of the first member and the second member have three-dimensional shapes cannot be coped with, and the degree of freedom of shape is extremely low. Furthermore, since the laser bonding sheet is simply interposed between the first member and the second member, the laser welding sheet has low position holding properties, and has a limitation on the enhancement of quality stability. Moreover, the laser bonding sheet needs to be manufactured to match the shape of the bonding surfaces of the first member and the second member. Therefore, a large amount of waste materials are generated during the manufacturing of the laser bonding sheet, and processing costs for the laser bonding sheet are required. 
     Here, an object of the present invention is to provide a bonded body capable of achieving the enhancement of bonding strength, and a bonding method. 
     Solution to Problem 
     In a bonded body according to the present invention, a first member, and a second member formed of a material different from that of the first member are bonded to each other via a bonding layer interposed therebetween, and in a range of 13 μm in a cross-section of a bonding interface between the first member and the bonding layer, the number of air bubbles having a void area of 1.5×10 −3  μm 2  or greater is 100 or less. 
     In the bonded body according to the present invention, since the number of air bubbles having a void area of 1.5×10 −3  μm 2  or greater in a range of 13 μm in the cross-section of the bonding interface between the first member  2  and the bonding layer  4  is 100 or less, the enhancement of the bonding strength of the first member and the second member can be achieved. 
     In this case, the bonding layer may have a tensile elastic modulus of 800 MPa or higher and 2400 MPa or lower in an absolute dry state as a water absorption state at 23° C. Furthermore, the bonding layer may have a tensile elastic modulus of 1200 MPa or higher and 2000 MPa or lower in the absolute dry state as the water absorption state at 23° C. When the tensile elastic modulus of the bonding layer in the absolute dry state as the water absorption state at 23° C. is lower than 800 MPa, the bonding strength of the first member and the bonding layer is low. When the tensile elastic modulus of the bonding layer in the absolute dry state as the water absorption state at 23° C. is higher than 2400 MPa, the linear expansion relaxation effect of the bonding layer is decreased. Therefore, by allowing the tensile elastic modulus of the bonding layer at 23° C. to be 800 MPa or higher and 2400 MPa or lower, the linear expansion relaxation effect of the bonding layer can be increased while increasing the bonding strength of the first member and the bonding layer. 
     In addition, the bonding layer may contain an elastomer component in an amount of 5 wt % or more and 75 wt % or less. When the amount of the elastomer component is less than 5 wt %, the linear expansion relaxation effect of the bonding layer is decreased. When the amount of the elastomer component is more than 75 wt %, the bonding strength of the first member and the bonding layer is decreased. Therefore, by allowing the amount of the elastomer component of the bonding layer to be 5 wt % or more and 75 wt % or less, the linear expansion relaxation effect of the bonding layer can be increased while increasing the bonding strength of the first member and the bonding layer. 
     In addition, the elastomer may have a tensile elastic modulus of 50 MPa or higher and 1000 MPa or lower in the absolute dry state as the water absorption state at 23° C. Accordingly, the linear expansion relaxation effect of the bonding layer can be further increased while further increasing the bonding strength of the first member and the bonding layer. In this case, examples of the elastomer may include a styrene-based elastomer, an olefin-based elastomer, an engineering plastic-based elastomer, and a polyester-based elastomer. 
     A bonding method according to the present invention is a bonding method of bonding a first member to a second member which is formed of a material different from that of the first member, the method including: an injection molding process of integrally laminating a bonding layer for bonding the first member and the second member to each other, on a bonding surface of the first member, which is to be bonded to the second member, through injection molding; and a bonding process of bonding the second member to the bonding layer after the injection molding process. 
     According to the bonding method according to the present invention, since the bonding layer is integrally laminated on the bonding surface of the first member through the injection molding of the bonding layer, compared to a case where the first member and the bonding layer are bonded to each other by laser welding, the bonding layer more easily infiltrates into gaps such as pores formed in the surface of the first member, and the gaps are less likely to remain. As a result, the number of air bubbles generated in the bonding interface between the first member and the bonding layer can be reduced. Therefore, in the bonded body in which the first member and the second member are bonded to each other via the bonding layer interposed therebetween, the enhancement of the bonding strength of the first member and the second member can be achieved. Furthermore, since the bonding layer is integrally laminated on the first member through injection molding in the injection molding process, even when the bonding surfaces of the first member and the second member have three-dimensional shapes, the bonding layer can be formed on the bonding surface of the first member, which is to be bonded to the second member. Accordingly, the first member and the second member can be appropriately bonded to each other in the bonding process. In addition, the injection-molded bonding layer does not deviate from the first member unlike the laser bonding sheet of Patent Literature 1 and thus achieves bonding quality stability. Moreover, the bonding layer can be formed only in a necessary portion. Therefore, waste materials from the laser bonding sheet or processing costs are not generated unlike in Patent Literature 1, and thus a reduction in costs can be achieved. 
     In this case, in the bonding process, the second member may be bonded to the bonding layer through welding. Accordingly, the first member and the second member can be appropriately bonded to each other. Examples of the welding may include laser welding, hot plate welding, vibration welding, and ultrasonic welding, and among these, laser welding is preferable. 
     In addition, the injection molding process may further include a surface treatment process of forming pores on the bonding surface of the first member. Accordingly, the bonding strength of the bonding layer to the first member is enhanced. Particularly, in the injection molding process, since the bonding layer infiltrates into the pores formed in the bonding surface in a state of being melted through injection molding, the bonding strength of the bonding layer to the first member is further enhanced. 
     In addition, the first member may be formed of any one of metal and glass, and the second member may be formed of a resin. Accordingly, the resin can be appropriately bonded to the metal or the glass. Moreover, although the bonding layer is less likely to be bonded to the metal or the glass than the resin, the bonding layer can be firmly bonded to the metal or the glass by injection-molding the bonding layer onto the metal or the glass. 
     Advantageous Effects of Invention 
     According to the present invention, the enhancement of bonding strength can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a flowchart illustrating a bonding method according to an embodiment. 
         FIG. 2  is a perspective view illustrating the relationship among a first member, a second member, and a bonding layer. 
         FIG. 3  is a sectional view illustrating an insert-molded state in an injection molding process. 
         FIG. 4  is a perspective view illustrating a shape example of a bonding surface. 
         FIG. 5  is a schematic view illustrating a bonded body according to the embodiment. 
         FIG. 6  is a sectional view illustrating a bonded body of Examples 1 to 11 and Comparative Examples 1 and 2. 
         FIG. 7  is a view showing laser welding conditions. 
         FIG. 8  is a view showing test results of Examples 1 to 11 and Comparative Examples 1 and 2. 
         FIG. 9  is a sectional view illustrating a bonded body of Examples 12 to 14. 
         FIG. 10  is a view showing test results of Examples 12 to 14. 
         FIG. 11  is a schematic view illustrating a method of counting the number of air bubbles. 
         FIG. 12  is an enlarged view of a portion of  FIG. 11 . 
         FIG. 13  is a schematic view illustrating a method of conducting a heat shock test. 
         FIG. 14  is a view showing test results of Reference Example 1 and Comparative Example 3. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a preferred exemplary embodiment of a bonded body and a bonding method according to the present invention will be described in detail with reference to the drawings. The bonded body according to the embodiment is a bonded body in which a first member, and a second member formed of a material different from that of the first member are bonded to each other via a bonding layer interposed therebetween. The bonding method according to the embodiment is a method which manufactures the bonded body according to the embodiment and in which a first member, and a second member formed of a material different from that of the first member are bonded by a bonding layer. In addition, in all of the figures, like elements that are the same or similar are denoted by like reference numerals. 
       FIG. 1  is a flowchart illustrating the bonding method according to the embodiment. As illustrated in  FIG. 1 , in the bonding method according to the embodiment, first, an injection molding process (Step  1 ) of integrally laminating a bonding layer for bonding the first member and the second member to each other, on a bonding surface of the first member, which is to be bonded to the second member, through injection molding is performed. An injection molding method performed in the injection molding process (Step  1 ) is not particularly limited, and for example, in a case where the first member is formed of metal, glass, or ceramic, insert molding may be employed. In a case where the first member is formed of a resin, two-color molding may be employed. The injection molding method is not limited thereto, and various injection molding methods may be employed. Typically, the bonding surface of the first member, which is to be bonded to the second member, is not a completely flat surface, and has fine gaps formed therein. In a case where the first member is formed of metal, glass, or ceramic, it is preferable that pores be formed on the bonding surface of the first member which is to be bonded to the second member. The pores are formed to form the gaps in the bonding surface of the first member, which is to be bonded to the second member, and to further increase bonding strength of the first member (bonding surface) and the bonding layer. The formation of the pores may be performed through any treatment, and for example, may be performed through an alumite treatment or laser irradiation. In addition, a body formed by injection-molding the bonding layer onto the bonding surface in the injection molding process (Step S 1 ) is referred to as a bonding layer formed body. 
     Next, a bonding process (Step S 2 ) of bonding the second member to the bonding layer is performed. In addition, a body in which the second member is bonded to the bonding layer in the bonding process (Step S 2 ) is referred to as a bonded body. The bonding method performed in the bonding process (Step S 2 ) is not particularly limited, and for example, welding may be employed. Examples of the welding may include laser welding, hot plate welding, vibration welding, and ultrasonic welding, and among these, laser welding is preferable. In this case, for example, in a case where the second member is formed of metal, glass, or ceramic, the bonding layer can be formed on the second member by melting the bonding layer. In a case where the second member is formed of a resin, the second member may be bonded to the bonding layer by melting any of the bonding layer and the second member, or the second member may be bonded to the bonding layer by melting both of the bonding layer and the second member. Here, the bonding method is not limited to welding, and various bonding methods may be employed. In addition, in a case where the second member is formed of metal, glass, or ceramic, it is preferable that pores be formed on a bonding surface of the second member, which is to be bonded to the bonding layer. The pores are formed to increase the bonding strength of the second member (bonding surface) and the bonding layer. The formation of the pores may be performed through any treatment, and for example, may be performed through an alumite treatment or laser irradiation. A body in which the first member and the second member are bonded to each other via the bonding layer interposed therebetween in the bonding process (Step S 2 ) is referred to as a bonded body. 
       FIG. 5  is a schematic view illustrating the bonded body according to the embodiment. As illustrated in  FIG. 5 , a bonded body  1  according to the embodiment is a bonded body in which a first member  2 , and a second member  3  formed of a material different from that of the first member  2  are bonded to each other via a bonding layer  4  interposed therebetween. Specifically, in the bonded body  1 , the bonding layer  4  is integrally laminated on a bonding surface  2   a  of the first member  2 , which is to be bonded to the second member  3 , through injection molding, and the second member  3  is bonded to the bonding layer  4 . The bonding layer  4  and the second member  3  are bonded to each other by welding. 
     In addition, in a range of 13 μm in the cross-section of the bonding interface between the first member  2  and the bonding layer  4 , the number of air bubbles having a void area of 1.5×10 −3  μm 2  or greater is 100 or less. In this case, the number of air bubbles is preferably 80 or less, more preferably 60 or less, and even more preferably 40 or less. 
     Here, a method of calculating the number of air bubbles will be described. First, broad ion beam processing is performed on the bonded body  1  in each layer direction using IM4000 manufactured by Hitachi High-Technologies Corporation, thereby producing a cross-sectional sample in a bonding direction α of the first member  2  and the second member  3 . In addition, the cross-sectional sample is observed by a scanning electron microscope (SEM). For example, observation conditions include S-4700 manufactured by Hitachi High-Technologies Corporation with an accelerating voltage of 2.0 kV and a photographic magnification of 10.0 k. Next, from an SEM image (picture), a range of 13 μm in the cross-section of the bonding interface between the first member  2  and the bonding layer  4  is extracted. Next, the number of air bubbles having a void area of 1.5×10 −3  μm 2  or greater in the extracted range is counted. In addition, the size of a void that can be recognized in the case of being magnified under conditions of an accelerating voltage of 2.0 kV and a photographic magnification of 10.0 k using the SEM is 1.5×10 −3  μm 2  or greater. In the bonded body  1  according to the embodiment, the number of air bubbles that are bounded is 100 or less. The bonded body  1  according to the embodiment can be manufactured, for example, by the above-described bonding method. 
     The material of the first member  2  is not particularly limited, and various materials such as metal, glass, ceramic, and resins may be used. For example, in a case where the bonding layer  4  and the second member  3  are laser-welded to each other by emitting laser light from the first member  2  side in the bonding process (Step S 2 ), a material having a property of transmitting the laser light is preferably used for the first member  2 . 
     The material of the second member  3  is not particularly limited as long as the material is different from that of the first member  2 , and various materials such as metal, glass, ceramic, and resins may be used. For example, in a case where the bonding layer  4  and the second member  3  are laser-welded to each other by emitting laser light from the second member  3  side in the bonding process (Step S 2 ), a material having a property of transmitting the laser light is preferably used for the second member  3 . 
     The material (also referred to as “bonding layer material”) of the bonding layer  4  is not particularly limited as long as the material can bond the first member and the second member to each other, and various bonding materials may be used. For example, in a case where the bonding layer  4  and the second member  3  are laser-welded to each other in the bonding process (Step S 2 ), a material that is melted by laser irradiation is preferably used for the bonding layer  4 . 
     For example, the bonding layer  4  may contain an elastomer component in an amount of 5 wt % or more and 75 wt % or less. In this case, the elastomer component is preferably in an amount of 10 wt % or more and 70 wt % or less, more preferably in an amount of 15 wt % or more and 65 wt % or less, and even more preferably in an amount of 20 wt % or more and 60 wt % or less. When the amount of the elastomer component is more than 75 wt % (when the rubber content is too high), the fluidity is decreased, and the elastomer component is less likely to infiltrate into the pores (gaps) of the first member  2 , resulting in a decrease in the bonding strength of the first member and the bonding layer. Therefore, by allowing the amount of the elastomer component of the bonding layer to be 75 wt % or less, the fluidity is increased, and the elastomer component easily infiltrates into the pores (gaps) of the first member  2 . Accordingly, the bonding strength of the first member and the bonding layer can be increased. On the other hand, when the amount of the elastomer component is less than 5 wt % (when the rubber content is too low), the linear expansion relaxation effect of the bonding layer is decreased. Therefore, by allowing the amount of the elastomer component of the bonding layer to be 5 wt % or more, the linear expansion relaxation effect of the bonding layer can be increased. 
     The elastomer contained in the bonding layer  4  may be, for example, an elastomer having a tensile elastic modulus of 50 MPa or higher and 1000 MPa or lower in an absolute dry state as a water absorption state at 23° C. Here, the absolute dry state as the water absorption state means a state in which the moisture content is 0.1% or less. Accordingly, the linear expansion relaxation effect of the bonding layer can be further increased while further increasing the bonding strength of the first member and the bonding layer. In this case, examples of the elastomer contained in the bonding layer  4  include a styrene-based elastomer, an olefin-based elastomer, an engineering plastic-based elastomer, and a polyester-based elastomer. 
     In addition, from the viewpoint of maintaining high bonding strength, the tensile elastic modulus of the bonding layer  4  in the absolute dry state as the water absorption state at 23° C. may be 800 MPa or higher and 2400 MPa or lower. In this case, the tensile elastic modulus of the bonding layer  4  in the absolute dry state as the water absorption state at 23° C. is preferably 1200 MPa or higher and 2000 MPa or lower, and more preferably 1600 MPa or higher and 1900 MPa or lower. When the tensile elastic modulus of the bonding layer  4  in the absolute dry state as the water absorption state at 23° C. is lower than 800 MPa, the bonding strength of the first member and the bonding layer is low. When the tensile elastic modulus of the bonding layer in the absolute dry state as the water absorption state at 23° C. is higher than 2400 MPa, the linear expansion relaxation effect of the bonding layer is decreased. 
     Next, as a specific example of the bonded body and the bonding method according to the embodiment, the case of manufacturing a bonded body  11  in which a square metal container  12  and a resin cover  13  are bonded to each other via a bonding layer  14  interposed therebetween will be described with reference to  FIGS. 2 and 3 . 
       FIG. 2  is a perspective view illustrating the relationship among the first member, the second member, and the bonding layer.  FIG. 3  is a sectional view illustrating an insert-molded state in the injection molding process. 
     First, the square metal container  12  which is open upward is prepared (see  FIG. 2( a ) ), and a large number of pores are formed on an upper end surface  12   a  of the metal container  12  through an alumite treatment, laser irradiation, or the like. 
     Next, as illustrated in  FIG. 3 , a mold  16  which accommodates the metal container  12  and has a bonding layer formation space  15  for forming the bonding layer  14  on the upper end surface  12   a  of the metal container  12  is prepared. In addition, the metal container  12  is set in the mold  16  (see  FIG. 3( a ) ), and the bonding layer material for forming the bonding layer is heated, melted, and poured into the bonding layer formation space  15  (see  FIG. 3( b ) ). In addition, by allowing the bonding layer material to be cooled and solidified, the bonding layer  14  is laminated on the upper end surface  12   a  of the metal container  12 . At this time, the melted bonding layer material infiltrates into the large number of pores formed in the upper end surface  12   a  of the metal container  12 . Therefore, as the bonding layer material is cooled and solidified, the bonding strength of the bonding layer  14  to the upper end surface  12   a  is further increased by the anchoring effect. Accordingly, a bonding layer formed body in which the bonding layer  14  is injection-molded onto the upper end surface  12   a  can be formed (see  FIG. 2( b ) ). 
     Next, the resin cover  13  to be bonded to the metal container  12  is prepared (see  FIG. 2( c ) ), and the resin cover  13  is welded to the bonding layer  14  of the bonding layer formed body by laser welding. Accordingly, the bonded body  11  in which the metal container  12  and the resin cover  13  are firmly bonded to each other via the bonding layer  14  interposed therebetween can be formed (see  FIG. 2( d ) . 
     As described above, according to the bonded body  1  according to the embodiment, since the number of air bubbles having a void area of 1.5×10 −3  μm 2  or greater in a range of 13 μm in the cross-section of the bonding interface between the first member  2  and the bonding layer  4  in the cross-section of the bonding layer  4  in the bonding direction α, of the first member  2  and the second member  3  is 100 or less, the enhancement of the bonding strength of the first member  2  and the second member  3  can be achieved. 
     In addition, by allowing the tensile elastic modulus of the bonding layer  4  in the absolute dry state as the water absorption state at 23° C. to be 800 MPa or higher and 2400 MPa or lower, the linear expansion relaxation effect of the bonding layer can be increased while increasing the bonding strength of the first member and the bonding layer. 
     In addition, by allowing the amount of the elastomer component in the bonding layer to be 5 wt % or more and 75 wt % or less, the linear expansion relaxation effect of the bonding layer can be increased while increasing the bonding strength of the first member and the bonding layer. 
     In addition, by allowing the tensile elastic modulus of the elastomer in the absolute dry state as the water absorption state at 23° C. to be 50 MPa or higher and 1000 MPa or lower, the linear expansion relaxation effect of the bonding layer  4  can be further increased while further increasing the bonding strength of the first member  2  and the bonding layer  4 . 
     According to the bonding method according to the embodiment, since the bonding layer is integrally laminated on the bonding surface of the first member through the injection molding of the bonding layer, compared to a case where the first member and the bonding layer are bonded to each other by laser welding, the bonding layer more easily infiltrates into the gaps such as the pores formed in the surface of the first member, and the gaps are less likely to remain. As a result, the number of air bubbles generated in the bonding interface between the first member and the bonding layer can be reduced. Therefore, in the bonded body in which the first member and the second member are bonded to each other via the bonding layer interposed therebetween, the enhancement of the bonding strength of the first member and the second member can be achieved. Furthermore, since the bonding layer is injection-molded onto the first member in the injection molding process (Step S 1 ), even when the bonding surfaces of the first member and the second member have three-dimensional shapes, the bonding layer can be formed on the bonding surface of the first member, which is to be bonded to the second member. Accordingly, the first member and the second member can be appropriately bonded to each other in the bonding process (Step S 2 ). For example, as in a bonded body  21  illustrated in  FIG. 4 , even when bonding surfaces of a first member  22  and the second member  23  are formed in a three-dimensional stepped shape, a bonding layer  24  can be easily formed on a bonding surface  22   a  of the first member  22 , and thus the first member  22  and the second member  23  can be appropriately bonded to each other. 
     In addition, the injection-molded bonding layer does not deviate from the first member unlike the laser bonding sheet of Patent Literature 1 and thus achieves bonding quality stability. Moreover, the bonding layer can be formed only in a necessary portion. Therefore, waste materials from the laser bonding sheet or processing costs are not generated unlike in Patent Literature 1, and thus a reduction in costs can be achieved. 
     In addition, in a case where the first member is formed of metal, glass, or ceramic, by forming the pores in the first member, the bonding strength of the bonding layer to the first member is enhanced. In the injection molding process (Step S 1 ), since the bonding layer infiltrates into the pores formed in the bonding surface in a state of being melted through injection molding, the bonding strength of the bonding layer to the first member is further enhanced. Similarly, in a case where the second member is formed of metal, glass, or ceramic, by forming the pores in the second member, the bonding strength of the bonding layer to the second member is enhanced. In the case of melting the bonding layer in the bonding process (Step S 2 ), since the bonding layer infiltrates into the pores formed in the bonding surface in a state of being melted, the bonding strength of the bonding layer to the second member is further enhanced. 
     In addition, the bonding layer is less likely to be bonded to metal than a resin. However, by injection-molding the bonding layer onto the first member made of metal, the bonding layer can be firmly bonded to the first member made of metal. 
     While the exemplary embodiment of the present invention has been described above, the present invention is not limited to the embodiment. 
     For example, in the detailed description of the embodiment, the first member is formed of metal and the second member is formed of a resin. However, the first member and the second member are not limited to these materials, and may employ various materials. For example, the first member may be formed of glass. Otherwise, the first member may be formed of a resin while the second member is formed of metal. In the case of forming the first member of the resin, the bonding layer may be formed on the first member through two-color molding or the like. 
     In addition, in the description of the embodiment, the surface treatment process is performed before the injection molding process. However, when the connection strength of the bonding layer to the bonding surface of the first member causes no problem, such a surface treatment process is not necessarily needed. 
     EXAMPLES 
     Next, Examples of the present invention will be described. The present invention is not limited to the following Examples. 
     Examples 1 to 11 
     As a first member, a metal flat plate was used. As the material of the first member, aluminum (AL5052) and aluminum (ADC12) were used. 
     As the material of a bonding layer, the following materials were used. A polyamide resin composite material (hereinafter, referred to as “bonding material A”) obtained by melting and kneading 80 mass % of PA 66 (trade name: Leona 1200, manufactured by Asahi Kasei Chemicals Corporation) and 20 mass % of an elastomer (trade name: Tuftec M1918, manufactured by Asahi Kasei Chemicals Corporation) using a twin screw extruder (trade name: TEM35, manufactured by Toshiba Machine Co., Ltd.) set to a barrel temperature of 290° C., diluting the obtained thermoplastic material 100 times with a Leona resin (trade name: 2300LA33295, manufactured by Asahi Kasei Chemicals Corporation), and mixing the resultant, and a polyamide resin composite material (hereinafter, referred to as “bonding material B”) obtained by melting and kneading 80 mass % of PA 66 (trade name: Leona 1200, manufactured by Asahi Kasei Chemicals Corporation) and 20 mass % of an elastomer (trade name: Tuftec M1918, manufactured by Asahi Kasei Chemicals Corporation) using a twin screw extruder (trade name: TEM35, manufactured by Toshiba Machine Co., Ltd.) set to a barrel temperature of 290° C., were used. 
     As a second member, a cup-shaped container formed of a resin was used. As the material of the second member, the following materials were used. 3 mass % of potassium iodide and 0.1 mass % of copper iodide were added to an aqueous solution of a 40% AH salt (an equimolar salt of adipic acid, hexamethylenediamine, or the like) in a 400 L autoclave, and the resultant was heated and melted under an increased pressure of 1.8 MPa so as to be polymerized. 67 parts by mass of polyamide 66 obtained by allowing the obtained polymer to be subjected to cooling, solidification, and granulation, and 33 parts by mass of glass fiber (trade name: T275H, manufactured by Asahi Kasei Chemicals Corporation) were melted and kneaded using a twin screw extruder (trade name: TEM35, manufactured by Toshiba Machine Co., Ltd.) set to a barrel temperature of 290° C., thereby obtaining a thermoplastic material (hereinafter, referred to as “resin material A”). 3 mass % of potassium iodide and 0.1 mass % of copper iodide were added to an aqueous solution of a 40% AH salt (an equimolar salt of adipic acid, hexamethylenediamine, or the like) in a 400 L autoclave, and the resultant was heated and melted under an increased pressure of 1.8 MPa so as to be polymerized. 64.5 parts by mass of polyamide 66 obtained by allowing the obtained polymer to be subjected to cooling, solidification, and granulation, 33 parts by mass of glass fiber (trade name: T275H, manufactured by Asahi Kasei Chemicals Corporation), and 2.5 parts by mass of a color masterbatch for laser welding (trade name: eBIND ACW-9871, manufactured by Orient Chemical Industries Co., Ltd.) were melted and kneaded using a twin screw extruder (trade name: TEM35, manufactured by Toshiba Machine Co., Ltd.) set to a barrel temperature of 290° C., thereby obtaining a thermoplastic material (hereinafter, referred to as “resin material B”). The resin material A and the resin material B obtained as described above were used as the material of the second member. 
     In addition, pores were formed on a bonding surface of the first member, which was to be bonded to the second member, through an alumite treatment, the bonding layer was integrally laminated on the bonding surface of the first member through injection molding, and the second member and the bonding layer were laser-welded to each other, thereby producing a bonded body illustrated in  FIG. 6 . An opening through which water was injected into the bonded body was formed in the first member. 
     The alumite treatment is a treatment of forming an oxide film on the surface of metal at an appropriate current density and allowing the obtained film coated with the oxide to form pores. 
     The laser welding conditions were as shown in A to C fields of  FIG. 7 . In  FIG. 7 , WD represents the distance from an optical system to the bonding surface of the first member. 
     A destructive test was conducted on the bonded body. In destructive inspection, the bonded body was attached to the destructive test tool, water was injected through the inflow port of the destructive test tool, and a pressure at which breaking of the bonded body occurred or water leakage occurred was measured as a burst strength. As a result of the test, a burst pressure of 1 MPa or higher was evaluated as {dot over (•)}, a burst pressure of 0.1 MPa or higher and lower than 1 MPa was evaluated as ◯, 0 MPa, which was measured because there were unwelded portions and leakage occurred although the portions were bonded in an external view, was evaluated as Δ, and non-welding was evaluated as ×. The test results are shown in  FIG. 8 . 
     Comparative Examples 1 and 2 
     As a first member, a metal flat plate was used. As the material of the first member, aluminum (AL5052) and aluminum (ADC12) were used. 
     As a bonding layer, a cup-shaped container formed of a resin was used. As the material of the bonding layer, the bonding material A and the bonding material B were used. 
     A second member was formed of a resin. As the material of the second member, the resin material A and the resin material B were used. 
     In addition, pores were formed on a bonding surface of the first member, which was to be bonded to the second member, through an alumite treatment, the bonding layer was placed on the bonding surface of the first member, and the first member, the second member, and the bonding layer were laser-welded to each other, thereby producing a bonded body illustrated in  FIG. 6 . An opening through which water was injected into the bonded body was formed in the first member. 
     The laser welding conditions were as shown in A to C fields of  FIG. 7 . 
     A destructive test was conducted on the bonded body. In destructive inspection, the bonded body was attached to a destructive test tool, water was injected through an inflow port of the destructive test tool, and a pressure at which breaking of the bonded body occurred or water leakage occurred was measured as a burst strength. As a result of the test, a burst pressure of 1 MPa or higher was evaluated as {dot over (•)}, a burst pressure of 0.1 MPa or higher and lower than 1 MPa was evaluated as ◯, 0 MPa, which was measured because there were unwelded portions and leakage occurred although the portions were bonded in an external view, was evaluated as Δ, and non-welding was evaluated as ×. The test results are shown in  FIG. 8 . 
     As shown in  FIG. 8 , in both of Comparative Examples 1 and 2, the first member and the second member were peeled and separated from each other before a burst test. However, in Examples 1 to 11, the first member and the second member were not peeled or separated from each other at an internal pressure of the burst test, and were not peeled or separated from each other as long as they were not forcibly pulled to be separated from each other. 
     Examples 12 to 14 
     As a first member, a cup-shaped container formed of a resin was used. As the material of the first member, the resin material A was used. 
     A bonding layer was formed of a resin. As the material of the bonding layer, the bonding material A was used. 
     As a second member, a metal flat plate was used. As the material of the second member, aluminum (AL5052) was used. 
     In addition, the first member and the bonding layer were integrally laminated by two-color molding, pores were formed on a bonding surface of the second member, which was to be bonded to the first member, through an alumite treatment, and the second member and the bonding layer were laser-welded to each other, thereby producing a bonded body illustrated in  FIG. 9 . An opening through which water was injected into the bonded body was formed in the second member. 
     The alumite treatment is a treatment of forming an oxide film on the surface of metal at an appropriate current density and allowing the obtained film coated with the oxide to form pores. 
     The laser welding conditions were as shown in A to C fields of  FIG. 7 . 
     A destructive test was conducted on the bonded body. In destructive inspection, the bonded body was attached to the destructive test tool, water was injected through the inflow port of the destructive test tool, and a pressure at which breaking of the bonded body occurred or water leakage occurred was measured as a burst strength. As a result of the test, a burst pressure of 1 MPa or higher was evaluated as {dot over (•)}, a burst pressure of 0.1 MPa or higher and lower than 1 MPa was evaluated as ◯, 0 MPa, which was measured because there were unwelded portions and leakage occurred although the portions were bonded in an external view, was evaluated as Δ, and non-welding was evaluated as ×. The test results are shown in  FIG. 10 . 
     As illustrated in  FIG. 10 , in all of Examples 12 to 14, the first member and the second member were not peeled or separated from each other at an internal pressure of the burst test, and were not peeled or separated from each other as long as they were not forcibly pulled to be separated from each other. 
     (Evaluation of Number of Air Bubbles) 
     The bonded body of Example 1 and the bonded body of Comparative Example 1 were prepared. Each of the bonded bodies was cut in the bonding direction of the first member and the second member, and the cut surface was observed through SEM.  FIG. 11  is a schematic view illustrating a method of counting the number of air bubbles.  FIG. 12  is an enlarged view of a portion of  FIG. 11 . As illustrated in  FIGS. 11 and 12 , from an SEM image (picture), a range of 13 μm in the cross-section of the bonding interface between the first member  2  and the bonding layer  4  was extracted, and the number of air bubbles having a void area of 1.5×10 −3  μm 2  or greater in the extracted range was counted. 
     As a result, the number of air bubbles in the bonded body of Comparative Example 1 was 134, while the number of air bubbles in the bonded body of Example 1 was 31. As described above, it was presumed that since the number of air bubbles in the bonding layer in the bonded body of Example 1 was significantly reduced compared to that in the bonded body of Comparative Example 1, the bonding strength of the first member and the second member was high. 
     Reference Example 1 
     In Reference Example 1, as a bonded body, a body in which a bonding member was integrally laminated onto a first member through injection molding was used. That is, in the bonded body of Reference Example 1, a second member was not provided, and the bonding member was used as a bonding layer. 
     As illustrated in  FIG. 13 , as the first member, a long, thin, and flat plate formed of metal was used, and an end surface thereof, which was to be bonded to the bonding layer, was formed in a stepped shape having two steps. The stepped end surface had a step width of 10 mm and a step height of 3 mm. As the material of the first member, aluminum (AL5052) was used. As the material of the bonding layer, the bonding material B having an elastic modulus of 1900 MPa was used. In addition, the bonding layer was integrally laminated onto the stepped end surface of the first member through injection molding, thereby obtaining a bonded body having a long, thin, and flat plate shape as the overall shape. 
     Thereafter, a heat shock test was conducted. In the heat shock test, first, the bonded body of Reference Example 1 was fixed to metal (SUS) having low linear expansion in order to forcibly hold the linear expansion of the first member and the connection member. Next, assuming −35±5° C.×2 hours and 130±5° C.×2 hours as 1 cycle, 50 cycles, 100 cycles, and 150 cycles were conducted, and the tensile strength retention ratio at this time was measured. The tensile strength retention ratio was expressed as a percentage when the tensile strength retention ratio at 0 cycle (a state before the experiment) is set to 100%. The test results are shown in  FIG. 14 . 
     Comparative Example 3 
     In Comparative Example 3, as a bonded body, a body in which a bonding member was integrally laminated onto a first member through injection molding was used. That is, in the bonded body of Comparative Example 3, a second member was not provided, and the bonding member was used as a bonding layer. 
     As illustrated in  FIG. 13 , as the first member, a long, thin, and flat plate formed of metal was used, and an end surface thereof, which was to be bonded to the bonding layer, was formed in a stepped shape having two steps. The stepped end surface had a step width of 10 mm and a step height of 3 mm. As the material of the first member, aluminum (AL5052) was used. As the material of the bonding layer, the resin material B having an elastic modulus of 9800 MPa was used. In addition, the bonding layer was integrally laminated onto the stepped end surface of the first member through injection molding, thereby obtaining a bonded body having a long, thin, and flat plate shape as the overall shape. 
     Thereafter, a heat shock test was conducted. In the heat shock test, first, the bonded body of Comparative Example 3 was fixed to metal (SUS) having low linear expansion in order to forcibly hold the linear expansion of the first member and the connection member. Next, assuming −35±5° C.×2 hours and 130±5° C.×2 hours as 1 cycle, 50 cycles, 100 cycles, and 150 cycles were conducted, and the tensile strength retention ratio at this time was measured. The tensile strength retention ratio was expressed as a percentage when the tensile strength retention ratio at 0 cycle (a state before the experiment) is set to 100%. The test results are shown in  FIG. 14 . 
     As illustrated in  FIG. 14 , in Comparative Example 3, after 50 cycles had passed, the tensile strength retention ratio was already 0%, that is, the first member and the connection member were in a broken state. However, in Reference Example 1, even when 150 cycles had passed, the tensile strength retention ratio was 4.3, that is, the first member and the connection member were in a state of not being broken. From the results, in the present invention, it was found that by using the bonding member having a low elastic modulus as the bonding layer, the tensile strength retention ratio between the first member and the bonding layer could be maintained even under harsh temperature cycle conditions. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  bonded body 
               2  first member 
               2   a  bonding surface 
               3  second member 
               4  bonding layer 
               11  bonded body 
               12  metal container (first member) 
               12   a  upper end surface 
               13  resin cover (second member) 
               14  bonding layer 
               15  bonding layer formation space 
               16  mold 
               21  bonded body 
               22  first member 
               22   a  bonding surface 
               23  second member 
               24  bonding layer 
             α bonding direction