JP7613207B2 - Method and structure for joining metal and resin members - Google Patents

Description

The present invention relates to a method and structure for joining metal and resin members.

Conventionally, weight reduction has been demanded in the fields of automobiles, railway vehicles, aircraft, etc. For example, in the field of automobiles, the use of high-tensile steel has led to the use of thin steel plates, aluminum alloy materials have been used as a substitute for steel materials, and the use of resin materials has also progressed. In such fields, the development of joining techniques between metal members and resin members is important not only from the perspective of simply reducing the weight of the car body, but also from the perspective of realizing high strength and high rigidity of the joining members and improved productivity. So far, a so-called friction stir welding (FSW) method has been proposed as a method for joining metal members and resin members. As an example of the friction stir welding method, as shown in FIG. 10, a metal member 211 and a resin member 212 are overlapped, and a rotating tool 216 is rotated while being pressed against the metal member 211 to generate frictional heat, and the resin member 212 is melted by this frictional heat and then solidified to join the metal member 211 and the resin member 212 (for example, Patent Document 1). For example, when the resin member is a thermosetting resin member, a method for joining a metal member and a thermosetting resin member is known in which a thermoplastic resin is interposed between the metal member and the thermosetting resin member (Patent Document 2).

In thermocompression joining methods, including friction stir joining, solidification is usually achieved by natural cooling from the standpoint of manufacturing costs.

Meanwhile, as a method for joining metal and resin members, in addition to friction stir welding, thermocompression joining methods that apply heat while applying pressure, such as resistance heating joining (electrical heating joining), induction heating joining, and ultrasonic heating joining, are also known.

JP 2016-68465 A JP 2017-177465 A

However, the inventors of the present application have discovered that in conventional friction stir welding methods, when the molten resin is solidified using conventional cooling methods, including natural cooling by leaving it at room temperature, sufficient joint strength cannot be obtained.

The inventors of the present application also discovered that in conventional friction stir welding methods, when the molten resin is solidified by conventional cooling methods, including natural cooling by leaving it at room temperature, the insufficient joint strength is due to the degree of crystallinity of the molten and solidified part at the joint interface. Therefore, they attempted to improve the joint strength by reducing the degree of crystallinity through forced cooling, but a new problem arose in that the process management for forced cooling became complicated.

In thermocompression joining methods other than friction stir welding, when the molten resin is solidified by conventional cooling methods, including natural cooling by leaving it at room temperature, sufficient joint strength cannot be obtained. For this reason, attempts were made to improve joint strength by reducing the degree of crystallinity through forced cooling, as in the case of friction stir welding, but a new problem arose in that the process management for forced cooling became complicated.

The present invention aims to provide a method and structure for joining a metal member and a resin member that achieves a sufficient strength of the bond between the resin member and the metal member without the need for complicated processes such as forced cooling.

The present invention relates to
A method for joining a metal member and a resin member by a thermocompression joining method, comprising overlapping a metal member and a resin member with an intervening member therebetween, applying heat and pressure to the metal member by a pressing member to soften and melt the intervening member and then solidifying the intervening member,
The present invention relates to a method for joining a metal member and a resin member, wherein the interposing member contains 40% by mass or more of a crystallization retarder and a thermoplastic base resin with respect to the total amount of the interposing member.

The present invention also provides
A joining structure of a metal member and a resin member, in which a metal member and a resin member are joined with an interposition member therebetween,
The intermediate member relates to a joint structure between a metal member and a resin member, and contains a crystallization retarder and a thermoplastic base resin in an amount of 40 mass % or more relative to the total amount of the intermediate member.

The joining method and joining structure of the present invention can achieve a joining between a resin member and a metal member with sufficient strength.

1 is a schematic diagram showing an example of a part of a friction stir welding apparatus suitable for a method for joining a metal member and a resin member according to the present invention. FIG. 4 is an enlarged view of a tip portion of an example of a rotation tool as a pressing member used in the joining method of the present invention. FIG. FIG. 2 is a schematic cross-sectional view for explaining an example of a preheating step of the present invention. FIG. 2 is a schematic cross-sectional view for explaining an example of the thrust stirring step and the stirring maintaining step of the present invention. 1 is a schematic diagram showing an example of a joint structure between a metal member and a resin member according to the present invention; 1 is a schematic diagram showing a surface state of a resin member when the metal member is forcibly peeled off from an example of a joint structure between a metal member and a resin member according to the present invention and the metal member side surface of the resin member is observed. FIG. FIG. 2 is a schematic diagram for explaining a method for measuring a bonding strength in the examples. 1 is a graph showing the bonding strength of the bonded structures obtained in Examples A1 and A2, Comparative Examples A1 and A2, and Reference Examples A1 and A2. 1 is a graph showing the bonding strength of the bonded structures obtained in Examples B1 and B2, Comparative Examples B1 and B2, and Reference Examples B1 and B2. 1 is a schematic diagram for explaining a method for joining a metal member and a resin member in a conventional technique.

[Joining method]
The joining method of the present invention is a thermocompression joining method in which a metal member and a resin member are overlapped with an intervening member interposed therebetween, and heat and pressure are applied by pressing from the metal member side with a pressing member, the intervening member is softened and melted, and then solidified to join the metal member and the resin member. The heat and pressure are preferably applied locally. The joining method adopted in the joining method of the present invention is not particularly limited as long as it is a method in which heat and pressure are applied by a pressing member, and may be, for example, a friction stir welding method, an ultrasonic heating joining method, a laser heating joining method, a resistance heating joining method, an induction heating joining method, etc. Preferably, it is a method in which heat and pressure are applied locally from the metal member side by a pressing member, and more preferably, a friction stir welding method is adopted.

As described in detail below, the friction stir welding method involves overlapping a metal member and a resin member, rotating a rotating tool as a pressing member and pressing it against the metal member to generate frictional heat, which softens and melts the resin member, and then solidifies it to join the metal member and the resin member.

The ultrasonic heating bonding method involves overlapping a metal member and a resin member, applying pressure to the resin member with a pressing member while ultrasonic vibrations are generated in the pressing member and the resin member, and the resin member is softened and melted by frictional heat between the resin member and the metal member generated by the vibrations, and then solidified to bond the metal member and the resin member.

The laser heating joining method is a method in which a metal member and a resin member are overlapped and restrained, and then a laser is irradiated onto the metal member to generate heat, which softens and melts the resin member, and then solidifies it to join the metal member and the resin member. The laser used may be a YAG laser, a fiber laser, or a semiconductor laser.

The resistance heating joining method is a method in which a metal member and a resin member are overlapped and restrained, and then joined using the heat generated by passing an electric current directly through the metal member.

The induction heating joining method involves overlapping and restraining a metal member and a resin member, generating an induced current in the metal member through electromagnetic induction, and joining the members using the heat generated by the current.

The joining method of the present invention, which employs the friction stir welding method, will be explained in detail below with reference to the drawings. However, it is clear that the effects of the present invention can be obtained even if other joining methods as mentioned above are used, so long as the joining is performed by interposing an interposing member between the metal member and the resin member. In these drawings, common symbols indicate the same members, parts, dimensions, or areas.

[Method for joining metal member and resin member by friction stir welding method]
The joining method (friction stir joining method) of the present invention will be specifically described with reference to Figs.

(1) Welding Apparatus Fig. 1 is a schematic diagram showing an example of a part of a friction stir welding apparatus suitable for carrying out the welding method of the present invention. The friction stir welding apparatus 1 shown in Fig. 1 is configured as an apparatus for friction stir welding a metal member 11 and a resin member 12, and includes a cylindrical rotating tool 16 as a pressing member.

As shown in the figure, the rotating tool 16 rotates around the central axis X (see FIG. 2) of the rotating tool 16 as indicated by arrow A1 while moving downward as indicated by arrow A2 by a driving source (not shown) with respect to the workpiece 10, which is stacked so that the metal member 11 is on top and the resin member 12 is on the bottom. At this time, the rotating tool 16 applies pressure to a pressing area P (area to be pressed) on the surface of the metal member 11. The pressing of the rotating tool 16 generates frictional heat, which is conducted to the intermediate member (see FIGS. 3 and 4) (and the resin member 12, if desired) to soften and melt at least the intermediate member, and then the molten resin solidifies. As a result, the metal member 11 and the resin member 12 are joined.

2 is an enlarged view of the tip of the rotary tool 16. In FIG. 2, the right half shows the appearance of the rotary tool 16, and the left half shows a cross section. As shown in FIG. 2, the cylindrical rotary tool 16 has a pin portion 16a and a shoulder portion 16b at the tip (lower end portion in FIG. 2). The shoulder portion 16b is a portion of the tip of the rotary tool 16 that includes the circular tip surface of the rotary tool 16. The pin portion 16a is a cylindrical portion that protrudes outward (downward in FIG. 2) from the circular tip surface of the rotary tool 16 on the central axis X of the rotary tool 16 and has a smaller diameter than the shoulder portion 16b. That is, the rotary tool 16 has, at the tip, a shoulder portion that includes the circular tip surface of the rotary tool, and a cylindrical pin portion that protrudes outward from the circular tip surface of the rotary tool and has a smaller diameter than the shoulder portion. The pin portion 16a is used to position the rotating tool 16 when the rotating tool 16 first comes into contact with and presses against the workpiece 10.

The material of the rotary tool 16 and the dimensions of each part are set mainly according to the type of metal of the metal member 11 pressed by the rotary tool 16. For example, when the metal member 11 is made of an aluminum alloy, the rotary tool 16 is made of tool steel (e.g., SKD61, etc.), and the diameter D1 of the shoulder portion 16b is set to 10 mm, the diameter D2 of the pin portion 16a is set to 2 mm, and the protruding length h of the pin portion 16a is set to 0.3 to 0.5 mm. Also, when the metal member 11 is made of steel, the rotary tool 16 is made of silicon nitride or PCBN (cubic boron nitride sintered body), etc., and the diameter D1 of the shoulder portion 16b is set to 10 mm, the diameter D2 of the pin portion 16a is set to 3 mm, and the protruding length h of the pin portion 16a is set to 0.3 to 0.5 mm. However, it goes without saying that these are merely examples and are not limited to these. For example, the diameter D1 of the shoulder portion 16b is usually 5 to 30 mm, preferably 5 to 15 mm, but is not limited to this.

Below the rotating tool 16, a cylindrical receiver 17 having the same diameter as the rotating tool 16 or a larger diameter than the rotating tool 16 is arranged coaxially with the rotating tool 16. The receiver 17 is moved upward with respect to the workpiece 10 as indicated by the arrow A3 by a driving source not shown. The upper end surface of the receiver 17 abuts against the lower surface of the workpiece 10 (more specifically, the lower surface of the resin member 12) at the latest before the rotating tool 16 starts pressing the workpiece 10. The receiver 17 sandwiches the workpiece 10 between itself and the rotating tool 16, and supports the workpiece 10 from below against the pressing force during the pressing period by the rotating tool 16, that is, during friction stir welding. Note that the receiver 17 does not necessarily need to be moved in the direction of the arrow A3, and a method of moving the rotating tool 16 in the direction of the arrow A2 after the workpiece 10 is placed on the receiver 17 can also be adopted.

The friction stir welding apparatus 1 is attached to a drive control device (not shown) that is an articulated robot or the like. The coordinate positions of the rotating tool 16 and the receiving tool 17, the rotation speed (rpm) of the rotating tool 16, the moving speed (mm/min), the pressure (N), the pressure time (sec), etc. are appropriately controlled by the drive control device. Although not shown in FIG. 1, the friction stir welding apparatus 1 is equipped with jigs such as spacers and clamps for fixing the workpiece 10 in advance and preventing the metal member 11 from lifting up when the rotating tool 16 is pressed.

(2) Metal Member In Fig. 1 and other figures, the metal member 11 has an approximately flat plate shape as a whole, but is not limited thereto, and may have any shape as long as the metal member and the resin member can be sufficiently pressed by the pressing member. For example, only the portion of the metal member 11 that is to be overlapped with the resin member 12 for joining may have at least an approximately flat plate shape.

The thickness T (thickness before joining; see Figure 3) of the approximately flat plate-shaped portion of the metal member 11 that overlaps with the resin member 12 is usually 0.5 to 4 mm, but is not limited to this.

There are no particular limitations on the metal constituting the metal member 11, and any metal can be used. Among them, the following metals and alloys used in the automotive field are preferably used:
aluminum;
Aluminum alloys such as 5000 series and 6000 series;
steel;
Magnesium and its alloys;
Titanium and its alloys.

Aluminum or an aluminum alloy is preferably used as the metal constituting the metal member 11 from the viewpoints of weight reduction, improved productivity, and cost reduction.

(3) Resin Member The resin member 12 may be a thermoplastic resin member or a thermosetting resin member. From the viewpoint of combination with the thermocompression bonding method, the resin member 12 is preferably a thermoplastic resin member.

The thermoplastic resin member contains a thermoplastic resin and may further contain reinforcing fibers.

As the thermoplastic resin constituting the thermoplastic resin member, any polymer having thermoplastic properties can be used. Among them, thermoplastic resins used in the field of automobiles are preferably used. Specific examples of such thermoplastic resins include the following polymers and mixtures thereof:
Polyolefin resins such as polyethylene and polypropylene (PP) and acid-modified products thereof;
Polyester-based resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), and polylactic acid (PLA);
Polyacrylate resins such as polymethyl methacrylate resin (PMMA);
Polyether-based resins such as polyether ether ketone (PEEK) and polyphenylene ether (PPE);
Polyacetal resin (POM);
Acrylonitrile-butadiene-styrene copolymer resin (ABS);
Polyphenylene sulfide resin (PPS);
Polyamide resins (PA) such as PA6, PA66, PA11, PA12, PA6T, PA9T, and MXD6;
Polycarbonate resin (PC);
Polyurethane resin;
Fluoropolymer-based resins; and Liquid Crystal Polymers (LCPs).

As the thermoplastic resin constituting the thermoplastic resin member, from the viewpoint of being an inexpensive polymer with excellent mechanical properties, one or more polymers selected from the group consisting of polyphenylene sulfide-based resins, polyamide-based resins, and polyolefin-based resins (particularly polypropylene) are preferably used.

The melting point Mpy (°C) of the thermoplastic resin constituting the thermoplastic resin member is not particularly limited and may be, for example, 100 to 400°C, particularly 150 to 350°C.

The melting point Mpy (℃) of the thermoplastic resin is measured according to JIS 7172.

The weight average molecular weight Ky of the thermoplastic resin constituting the thermoplastic resin member is not particularly limited, and may be, for example, 1×10 ¹ to 1×10 ⁷ (Mw), particularly 1×10 ² to 1×10 ⁶ (Mw).

The weight average molecular weight Ky of the thermoplastic resin is measured according to JIS 7252.

The reinforcing fibers contained in thermoplastic resin members are fibers contained in polymers to improve strength in the field of polymer-containing composite materials. Reinforcing fibers are generally broadly divided into continuous fibers and discontinuous fibers, but in the present invention, the reinforcing fibers may be either continuous fibers or discontinuous fibers.

The reinforcing fibers constituting the thermoplastic resin member are usually contained in the resin member in a randomly oriented form, and the average fiber length is usually 50 mm or less, particularly 0.1 to 50 mm, and preferably 1 to 50 mm. There are no particular limitations on the average fiber diameter of the reinforcing fibers, and it is, for example, 2 to 20 μm, and preferably 6 to 15 μm.

The type of reinforcing fiber that constitutes the thermoplastic resin member is not particularly limited, and examples include carbon fiber, glass fiber, etc.

The content of reinforcing fibers constituting the thermoplastic resin member is usually 1% by weight or more, particularly 10 to 50% by weight, preferably 20 to 50% by weight, and more preferably 30 to 50% by weight, based on the total weight of the resin member.

The content of reinforcing fibers that make up a thermoplastic resin member can be a value based on the amount of each material used when manufacturing the resin member, or a value measured by the following method can be used. First, the resin member is heated in an electric furnace or the like at a temperature above the decomposition temperature of the thermoplastic resin (or thermosetting resin) and below the decomposition temperature of the reinforcing fibers, thereby removing the thermoplastic resin (or thermosetting resin) and extracting only the reinforcing fibers. By measuring the weight before and after heating, the content of reinforcing fibers can be calculated as a percentage of the weight before heating. Alternatively, the content can also be measured by measuring the specific gravity.

Thermoplastic resin components may further contain additives other than reinforcing fibers, such as stabilizers, flame retardants, colorants, and foaming agents.

Thermoplastic resin parts can be manufactured by subjecting a mixture containing a thermoplastic resin and optionally contained reinforcing fibers and additives to a molding method such as injection molding or press molding.

Thermosetting resin members contain thermosetting resin and may further contain reinforcing fibers. Thermosetting resin members are thermosetting resin members that have been hardened by heat, that is, they are hardened products made of thermosetting resin. Hardening refers to the formation of a three-dimensional network structure. Thermosetting resin refers to resin that has the property of being hardened by heat.

Any polymer having thermosetting properties can be used as the thermosetting resin constituting the thermosetting resin member. Examples of the thermosetting resin constituting the thermosetting resin member include thermosetting epoxy resin, thermosetting phenolic resin, thermosetting melamine resin, and thermosetting urea resin. From the viewpoint of further improving the bonding strength, the preferred thermosetting resin is thermosetting epoxy resin.

The thermosetting epoxy resin includes an epoxy resin and a hardener.
The epoxy resin is not particularly limited as long as it is a compound having two or more epoxy groups. Examples of the epoxy resin include bifunctional glycidyl ether type epoxy resins such as epoxy compounds having a bisphenyl group, such as bisphenol A type, bisphenol F type, brominated bisphenol A type, hydrogenated bisphenol A type, bisphenol S type, bisphenol AF type, and biphenyl type, polyalkylene glycol type, alkylene glycol type epoxy compounds, epoxy compounds having a naphthalene ring, and epoxy compounds having a fluorene group; polyfunctional glycidyl ether type epoxy resins such as phenol novolac type, orthocresol novolac type, trishydroxyphenylmethane type, and tetraphenylolethane type. ether type epoxy resins; glycidyl ester type epoxy resins of synthetic fatty acids such as dimer acid; aromatic epoxy resins having glycidylamino groups such as N,N,N',N'-tetraglycidyldiaminodiphenylmethane (TGDDM), tetraglycidyl-m-xylylenediamine, triglycidyl-p-aminophenol, and N,N-diglycidylaniline; epoxy compounds having a tricyclodecane ring (for example, epoxy compounds obtained by a manufacturing method in which dicyclopentadiene and cresols such as m-cresol or phenols are polymerized and then reacted with epichlorohydrin). In addition, epoxy resins having sulfur atoms in the epoxy resin main chain, such as FLEP 10 manufactured by Toray Fine Chemicals Co., Ltd., can be used. Each of the epoxy resins can be used alone or in combination of two or more kinds. Among these, bisphenol A type and/or bisphenol F type are preferred. The amount of the bisphenol A type epoxy resin and/or the bisphenol F type epoxy resin in the epoxy resin is preferably more than 0 parts by mass and not more than 100 parts by mass, more preferably more than 0 parts by mass and not more than 70 parts by mass. In the present invention, the contents of the bisphenol A type epoxy resin and the bisphenol F type epoxy resin are defined as the added amounts.

Examples of curing agents that may be contained with the epoxy resin include polyamines, acid anhydrides, and mixtures thereof. The polyamines are not particularly limited, and examples thereof include aromatic polyamines such as o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, m-xylylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, and diaminodiethyldiphenylmethane; aliphatic polyamines such as ethylenediamine, propylenediamine, butylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexamethylenediamine, trimethylhexamethylenediamine, 1,2-propanediamine, iminobispropylamine, methyliminobispropylamine, and MPMD (a product of DuPont Japan); and polyamines having an ether bond in the main chain such as N-aminoethylpiperazine and 3-butoxyisopropylamine. Specific examples of such diamines include monoamines having a polyether skeleton, such as a monoamine such as JEFFAMINE EDR148 manufactured by Sun Techno Chemical Co., Ltd.; alicyclic polyamines such as isophorone diamine, 1,3-bisaminomethylcyclohexane, 1-cyclohexylamino-3-aminopropane, and 3-aminomethyl-3,3,5-trimethylcyclohexylamine; diamines having a norbornane skeleton, such as NBDA manufactured by Mitsui Chemicals; polyamideamines having amino groups at the molecular terminals of polyamides, such as 2,5-dimethyl-2,5-hexamethylenediamine, menthene diamine, 1,4-bis(2-amino-2-methylpropyl)piperazine, and JEFFAMINE D230 and JEFFAMINE D400 manufactured by Sun Techno Chemical Co., Ltd., which have a polypropylene glycol (PPG) skeleton. Examples of acid anhydrides include trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, nadic anhydride, methylnadic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and dodecenylsuccinic anhydride (DSA).

Thermosetting phenolic resins contain phenol and/or its derivatives, and formaldehyde.
Thermosetting melamine resins contain melamine and/or its derivatives, and formaldehyde.
The thermosetting urea resin contains urea and/or its derivatives, and formaldehyde.

The reinforcing fibers contained in the thermosetting resin member may be the same as the reinforcing fibers contained in the thermoplastic resin member, and may be continuous or discontinuous fibers.

The average fiber length of the reinforcing fibers constituting the thermosetting resin member may be the same as the average fiber length of the reinforcing fibers contained in the thermoplastic resin member.

The type of reinforcing fiber that constitutes the thermosetting resin member may be the same as the type of reinforcing fiber that constitutes the thermoplastic resin member.

The content of reinforcing fibers constituting the thermosetting resin member may be the same as the content of reinforcing fibers constituting the thermoplastic resin member.

The content of reinforcing fibers constituting the thermosetting resin member can be measured in the same manner as the content of reinforcing fibers constituting the thermoplastic resin member.

As with thermoplastic resin components, thermosetting resin components may further contain additives other than reinforcing fibers, such as stabilizers, flame retardants, colorants, and foaming agents.

The thermosetting resin member can be obtained by a molding method such as an autoclave method, a hand lay-up method, an RTM (Resin Transfer Molding) method, or a filament winding method.
The thermosetting resin part can also be obtained by subjecting a mixture containing a thermosetting resin and desired additives to a molding method such as injection molding or press molding, and then maintaining the mixture at a high temperature to sufficiently harden it.

In FIG. 1 etc., the resin member 12 has an overall shape that is generally flat, but is not limited thereto and may have any shape as long as the pressing member can apply sufficient pressure to the metal member and the resin member. For example, only the portion of the resin member 12 that overlaps with the metal member 11 for joining may have a generally flat shape. Both sides of the portion of the resin member 12 directly below the metal member 11 may usually be made of flat surfaces.

The thickness t (thickness before joining; see Figure 3) of the portion of the resin member 12 directly below the metal member 11 is usually 2 to 10 mm, and in particular 2 to 5 mm, but is not limited to this.

(4) Intervening member The intervening member 50 includes a crystallization retarder and a thermoplastic matrix resin. The thermoplastic matrix resin means a thermoplastic resin as a matrix contained in the intervening member, and is a polymer that can also be called a "thermoplastic intervening member matrix resin". As shown in FIG. 3, the intervening member 50 is a so-called intermediate adhesive member (e.g., an intermediate adhesive layer) that is disposed between the metal member 11 and the resin member 12 and achieves bonding between the metal member 11 and the resin member 12. The intervening member 50 softens and melts due to the applied heat, and then solidifies by cooling, resulting in bonding between the metal member 11 and the resin member 12. The intervening member 50 contains a predetermined amount of a crystallization retarder, so that the crystallization of the thermoplastic matrix resin is delayed during solidification. In addition, when the resin member 12 is a thermoplastic resin member, the crystallization of the melt-solidified portion of the resin member 12 is also delayed. As a result, the crystallization degree is sufficiently reduced in the melt-solidified portion described later, so that the bonding strength can be sufficiently increased.

The crystallization retarder is a crystallization retarder for at least the thermoplastic matrix resin contained in the intermediate member.
More specifically, for example, when the resin member 12 is a thermosetting resin member, the crystallization retarder is a crystallization retarder for the thermoplastic base resin contained in the interposed member. The crystallization retarder for the thermoplastic base resin contained in the interposed member means a crystallization retarder for the thermoplastic base resin, and is a compound for delaying the crystallization of the thermoplastic base resin.
Also, for example, when the resin member 12 is a thermoplastic resin member, the crystallization retarder may be a crystallization retarder for only the thermoplastic base resin contained in the interposed member. In a similar case, from the viewpoint of further improving the bonding strength, the crystallization retarder is preferably a crystallization retarder for both the thermoplastic base resin contained in the interposed member and the thermoplastic resin contained in the thermoplastic resin member. The crystallization retarder for both the thermoplastic base resin contained in the interposed member and the thermoplastic resin contained in the thermoplastic resin means a crystallization retarder for the thermoplastic base resin contained in the interposed member and a crystallization retarder for the thermoplastic resin contained in the thermoplastic resin, and is a compound that delays the crystallization of both the thermoplastic base resin contained in the interposed member and the thermoplastic resin contained in the thermoplastic resin.

When the crystallization retarder is a crystallization retarder for a thermoplastic matrix resin contained in an interposed member, the crystallization retarder is a thermoplastic resin having the following melting point Mp and weight average molecular weight Ka, where Mpx (° C.) and Kx are the melting point and weight average molecular weight of the thermoplastic matrix resin contained in the interposed member, respectively:
The melting point Mp is 0.4 x Mpx to 0.7 x Mpx, and from the viewpoint of further improving the bonding strength, preferably 0.4 x Mpx to 0.6 x Mpx;
The weight average molecular weight Ka is 0.01×Kx to 0.5×Kx, and from the viewpoint of further improving the bonding strength, it is preferably 0.01×Kx to 0.4×Kx, more preferably 0.01×Kx to 0.3×Kx, and particularly preferably 0.01×Kx to 0.2×Kx.

In this case, the thermoplastic matrix resin and the crystallization retarder contained in the interposed member are selected from the group consisting of polymers similar to the polymers exemplified as the thermoplastic resin contained in the thermoplastic resin member.
When a thermoplastic resin member is used for the resin member, the bonding strength is ensured mainly by the characteristics of the resin type of the thermoplastic resin member and additives, so there is no limitation on the polymer used, and the thermoplastic base resin and crystallization retarder contained in the interposed member and the thermoplastic resin of the thermoplastic resin member may be the same type of polymer. For example, the thermoplastic base resin and crystallization retarder contained in the interposed member and the thermoplastic resin of the thermoplastic resin member are preferably the same type of polymer selected from the group consisting of polyolefin resins (particularly polypropylene) and polyamide resins from the viewpoint of bonding and productivity, but are not limited thereto.
In addition, when a thermosetting resin member or the like is used for the resin member and does not melt due to heat and pressure during bonding, it is preferable that the interposed member has adhesiveness to ensure bonding strength. In this case, the thermoplastic base resin and the crystallization retarder contained in the interposed member are preferably the same type of polymer selected from a group of polymers that contain functional groups and have adhesiveness, such as polyamide-based resins, but adhesiveness may be provided by an additive contained in the interposed member, and are not limited thereto.

In the case where a thermoplastic resin member is used as the resin member and the crystallization retarder is a crystallization retarder for both the thermoplastic matrix resin contained in the interposed member and the thermoplastic resin contained in the thermoplastic resin member, when the melting point and weight average molecular weight of the thermoplastic matrix resin contained in the interposed member are Mpx (°C) and Kx, respectively, the crystallization retarder is a thermoplastic resin having the above-mentioned melting point Mp and weight average molecular weight Ka, while the thermoplastic resin contained in the thermoplastic resin member is a thermoplastic resin having the following melting point Mpy (°C) and weight average molecular weight Ky:
The melting point Mpy is 0.8 x Mpx to 1.2 x Mpx, and from the viewpoint of further improving the bonding strength, is preferably 0.9 x Mpx to 1.1 x Mpx, more preferably 0.95 x Mpx to 1.05 x Mpx, and even more preferably equal to Mpx;
The weight average molecular weight Ky is 0.8×Kx to 1.2×Kx, and from the viewpoint of further improving the bonding strength, it is preferably 0.9×Kx to 1.1×Kx, more preferably 0.95×Kx to 1.05×Kx, and even more preferably equal to Kx.

When the crystallization retarder is polypropylene, it is preferable that the crystallization retarder is polypropylene synthesized using a metallocene catalyst from the viewpoint of further improving the bonding strength. Polypropylene synthesized using a metallocene catalyst is a material in which the stereoregularity of polypropylene is controlled to a low level by the metallocene catalyst, and is a so-called low-crystalline and soft polypropylene having a stereorandom structure.

The content of the crystallization retarder in the interposed member is 40% by mass or more relative to the total amount of the interposed member, and from the viewpoint of further improving the bonding strength, it is preferably 50% by mass or more, and from the viewpoint of obtaining a more stable bonding strength, it is preferably 60% by mass or more, and more preferably 70% by mass or more. If the content of the crystallization retarder in the interposed member is too small, the crystallization degree of the melt-solidified portion of the interposed member (or the interposed member and the thermoplastic resin member) increases, and as a result, sufficient bonding strength cannot be obtained. There is no particular limit to the upper limit of the content of the crystallization retarder in the interposed member, and the content is usually 90% by mass or less.

The melting point (°C) of the thermoplastic resin used as the crystallization retarder is not particularly limited as long as it satisfies the above-mentioned melting point Mp, and may be, for example, 50 to 300°C, particularly 70 to 250°C, and is usually the melting point of the thermoplastic resin used as the crystallization retarder selected based on the resin type and melting point of the thermoplastic matrix resin contained in the interposed member.

The melting point (°C) of the thermoplastic resin used as the crystallization retarder is a value measured using a method similar to that used to measure the melting point Mpy (°C) of the thermoplastic resin that constitutes the thermoplastic resin component.

The weight average molecular weight of the thermoplastic resin as the crystallization retarder is not particularly limited as long as it satisfies the above-mentioned weight average molecular weight Ka, and may be, for example, 1×10 ¹ to 1×10 ⁷ (Mw), particularly 5×10 ¹ to 5×10 ⁵ (Mw), and is usually the weight average molecular weight of the thermoplastic resin as the crystallization retarder selected depending on the resin type and weight average molecular weight of the thermoplastic matrix resin contained in the interposed member.

The weight average molecular weight of the thermoplastic resin used as the crystallization retarder is a value measured using a method similar to the method for measuring the weight average molecular weight Ky of the thermoplastic resin constituting the thermoplastic resin member.

The melting point Mpx (°C) of the thermoplastic matrix resin contained in the intermediate member is not particularly limited and may be, for example, 100 to 400°C, particularly 150 to 350°C.

The melting point Mpx (°C) of the thermoplastic base resin contained in the interposed member is a value measured using a method similar to that used to measure the melting point Mpy (°C) of the thermoplastic resin that constitutes the thermoplastic resin member.

The weight average molecular weight Kx of the thermoplastic matrix resin contained in the interposed member is not particularly limited, and may be, for example, 1×10 ¹ to 1×10 ⁷ (Mw), particularly 1×10 ² to 1×10 ⁶ (Mw).

The weight average molecular weight Kx (°C) of the thermoplastic base resin contained in the interposed member is measured using a method similar to that used to measure the weight average molecular weight Ky of the thermoplastic resin that constitutes the thermoplastic resin member.

The intervening member 50 may have any form as long as it is disposed between the metal member 11 and the resin member 12. More specifically, the intervening member 50 may have the form of a film (or sheet) that can be handled independently of the metal member 11 and the resin member 12, may have the form of a coating formed on the surface of the metal member 11, may have the form of a coating formed on the surface of the resin member 12, or may have a composite form of these. In addition, the intervening member does not need to be in the form of a thin membrane such as a film, and may be in the form of a pellet or other lump (e.g., a lump) as long as it spreads sufficiently in the joining region of the joining interface due to heat and/or pressure before and during joining.

A film (or sheet) form refers to a thin plate shape that is not attached to either a metal or resin member and can be traded independently. An intervening member in the form of a film (or sheet) can be formed by hot pressing a specified material.

The form of the film formed on the surface of a metal member or a resin member refers to a thin film formed by adhering to the surface of a metal member or a resin member. An intervening member having the form of a film formed on the surface of a metal member or a resin member can be formed by applying a solution or dispersion of a specified material to the surface and drying it.

The intervening member having a composite form means that the intervening member has two or more of the above forms and is interposed between the metal member 11 and the resin member 12. Figure 3 is a schematic cross-sectional view for explaining an example of the preheating process described below, and is a cross-sectional view of the X-X cross section in Figure 1 as viewed in the direction of the arrows.

The thickness of the interposing member is not particularly limited, even when it is used in any of the above forms. From the viewpoint of productivity and fully exerting the effect of the interposing member, it is preferable that the interposing member is interposed between the metal member 11 and the resin member 12 with a thickness of 10 to 1000 μm, and particularly 100 to 500 μm, before bonding. When the interposing member is used in a composite form among the above forms, the total thickness of the interposing member may be within the above range.

The arrangement and dimensions of the intervening member are not particularly limited as long as the joining of the metal member and the resin member is achieved, and usually, after joining, the intervening member 50 needs to be present in the joining region between the metal member 11 and the resin member 12. For example, when the friction stir welding method is used as the spot joining and a sheet-like intervening member is used, the arrangement and dimensions (dimensions other than thickness) of the intervening member 50 usually need to be arranged and sized so that the intervening member 50 covers at least the immediate area 112 on the metal member side surface 120 of the resin member 12, as shown in FIG. 3. Specifically, when the diameter of the rotating tool 16 is D1, the intervening member 50 needs to be a square (or circular) sheet having one side (or diameter) of at least 1×D1 or more, preferably 1.5×D1 or more, arranged in the immediate area 112 per joining point.

In a joined structure where joining is completed, the composition of the interposed member 50 (e.g., the type and content of the crystallization retarder and the type and content of the thermoplastic base resin) can be easily detected in any of the following: the unmelted remaining portion of the interposed member, the melted and solidified portion of the interposed member, or, when a thermoplastic resin member is used, the melted and solidified portion where the interposed member and the resin member are compatible with each other.

(5) Joining Method The method for joining a metal member and a resin member by the friction stir welding method according to the present invention includes at least the following steps:
a first step of overlapping the metal member 11 and the resin member 12 with the interposing member 50 therebetween; and a second step of pressing the rotating tool 16 against the metal member 11 while rotating the rotating tool 16 to generate frictional heat, softening and melting at least the interposing member 50 by the frictional heat, and then solidifying the interposing member 50 to join the metal member 11 and the resin member 12.
It includes.

First step:
In the first step, as shown in FIG. 3, the metal member 11 and the resin member 12 are overlapped at a desired joining portion, and the interposing member 50 is disposed therebetween.

Second step:
In the present invention, in the second step, while rotating the rotary tool 16, at least the interposed member 50 is softened and melted by pressing it against the surface of the metal member 11, and then solidified. Softening and melting at least the interposed member 50 means that, when the resin member is a thermoplastic resin member, at least the interposed member 50 is softened and melted, and preferably the interposed member 50 and the resin member 12 (particularly its surface on the metal member 11 side) are softened and melted. When the resin member is a thermosetting resin member, only the interposed member 50 is softened and melted.

In the second step, it is preferable to at least perform a pushing and stirring process C2 before the solidification process, in which the rotating tool 16 is pushed into the metal member 11 to a depth that does not reach the joint boundary surface 13 (or the intervening member 50) between the metal member 11 and the resin member 12.

In the second step, it is preferable to perform a preheating step C1 before the pushing and stirring step, in which the rotating tool 16 is rotated with only the tip of the rotating tool 16 in contact with the surface of the metal member 11, but this is not necessarily required.

In the second step, after the pushing stirring process and before the solidification process, it is preferable to perform a stirring maintenance process C3 in which the rotating tool 16 continues to rotate at a position where the rotating tool 16 has penetrated to a depth not reaching the joining boundary surface (or the interposed member 50), but this process does not necessarily have to be performed.

Each step in this embodiment may be performed by a pressure control method that controls the pressing force (pressure) and pressing time of the rotating tool, or by a position control method that controls the insertion amount in the pressing direction of the rotating tool (the amount of insertion into the metal member after contacting the metal member) and the insertion speed, and the movement time (joining time) determined by these two, or by a combination of these.

These steps are explained in detail below.

(Preheating process C1)
The preheating step C1 is a step in which the rotating tool 16 and the receiver 17 are brought close to each other, and the rotating tool 16 is rotated in a state in which only the tip of the rotating tool 16 is in contact with the surface portion of the metal member 11 (the upper surface portion in the illustrated example) as shown in Fig. 3. More specifically, the rotating tool is rotated in a state in which only the pin portion at the tip of the rotating tool, or only the pin portion and the shoulder portion surface, are in contact with the surface portion of the metal member.

Specifically, in the preheating process C1, frictional heat is generated on the surface of the metal member 11 (the upper surface in the illustrated example) due to the pressure of the rotating tool 16. The frictional heat is transmitted to the inside of the metal member 11, and the range of the pressing area of the metal member 11 (the area pressed by the rotating tool 16) and the area adjacent to the pressing area are preheated. At the same time, the axial center of the rotating tool is positioned. This makes it easier to press the rotating tool 16 into the metal member 11 in the next pressing and stirring process C2.

When this process is performed using a position control method, the tool insertion amount and insertion speed, or insertion time in the preheating process C1 is not particularly limited as long as the rotating tool 16 can be rotated with only the tip of the rotating tool 16 in contact with the surface of the metal member 11.

When this process is performed by the pressure control method, the pressure (i.e., the first pressure) and pressure time (i.e., the first pressure time) in the preheating process C1 are set from the viewpoint of ease of pressing the rotary tool 16 and from the viewpoint of productivity, and the values vary depending on, for example, the rotation speed of the rotary tool 16, the thickness of the metal member 11, and the type of material. For example, when using an aluminum alloy metal member 11 with a thickness of 1 mm or more and 2 mm or less, the first pressure in the preheating process C1 is preferably a value of 500 N or more and less than 1000 N. The first pressure time is preferably a value of 0.1 seconds or more and less than 3.0 seconds. The rotation speed of the rotary tool is preferably a value of 2000 rpm or more and 4000 rpm or less.

(Intrusion stirring process C2)
In the thrust stirring step C2, the rotary tool 16 and the receiver 17 are brought close to each other, so that the rotary tool 16 is thrust into the metal member 11, as shown in FIG. 4. When the thrust stirring step C2 is performed following the preheating step C1, the rotary tool 16 and the receiver 17 are brought even closer to each other, so that the rotary tool 16 is thrust into the metal member 11, as shown in FIG. 4. This allows the rotary tool 16 to advance to a depth that does not reach the joint boundary surface 13 (or the interposed member 50) between the metal member 11 and the resin member 12. In this step, although not shown, the part of the metal member 11 directly below the rotary tool may be deformed to protrude toward the resin member 12. FIG. 4 is a schematic cross-sectional view for explaining an example of the thrust stirring step and the stirring maintaining step of the present invention.

In this process, it is preferable to soften and melt at least the interposed member 50 by heat, and to cause the molten material to flow from the area directly below the rotating tool to its outer peripheral area by pressure, thereby expanding the contact area between the interposed member 50 and the metal member 11 and the resin member 12.

For example, if the resin member 12 is a thermosetting resin member, only the interposed member 50 softens and melts due to heat, and the molten material flows from the area directly below the rotating tool to its outer peripheral area due to pressure, expanding the contact area between the interposed member 50 and the metal member 11 and resin member 12. Therefore, the melted and solidified portion formed in the solidification process described below is a melted and solidified portion of only the interposed member.

For example, when the resin member 12 is a thermoplastic resin member, the interposed member 50 is softened and melted by heat, and it is preferable that the surface portion of the thermoplastic resin member on the metal member 11 side (particularly the area directly below the rotating tool) is also softened and melted by heat. Therefore, in this case, the interposed member 50 and the surface portion of the thermoplastic resin member on the metal member 11 side (particularly the area directly below the rotating tool) are softened and melted by heat, and the molten material flows from the area directly below the rotating tool to its outer peripheral area due to pressure, expanding the contact area between the interposed member 50 and the metal member 11 and the resin member 12. Therefore, the melted and solidified portion formed in the solidification process described below is the melted and solidified portion of the interposed member and the thermoplastic resin member.

In this process, when the molten material flows from the area directly below the rotating tool to its outer periphery due to pressure, excessive melting may occur and/or the pressure may be too high, resulting in an excessively small amount of molten material or no molten material in the area directly below the rotating tool. In this case, as long as sufficient strength is obtained, the molten material of the intermediate member does not need to remain in the area directly below the rotating tool, and may remain over the entire melted and solidified area, or may remain only on the outer periphery of the melted and solidified area.

The insertion amount of the rotary tool 16 may be close to T, where T (mm) is the thickness of the metal member 11, and from the viewpoint of further improving the joining strength, is preferably T-0.5 (mm) or more and less than T (mm). In this specification, the insertion amount of the rotary tool 16 refers to the insertion amount of the pin portion 16a of the rotary tool 16 from the outer periphery of the metal member surface in the thickness direction. The insertion amount of the rotary tool 16 can be controlled more precisely by using a rotary tool position (insertion amount) control device.

When this process is performed using a position control method, the tool insertion amount and insertion speed, or insertion time, in the thrust mixing process C2, may be controlled so that the above insertion amount is achieved.

When this process is performed by the pressure control method, in the pushing-in stirring process C2, the rotating tool 16 is rotated at a predetermined rotation speed with a second pressure force for a second pressurizing time. The second pressure force and the second pressurizing time in the pushing-in stirring process C2 may be controlled so that the above-mentioned insertion amount is achieved in this method as well. The second pressure force and the second pressurizing time are set, for example, from the viewpoint of penetrating the rotating tool 16 to the interface 13 between the metal member 11 and the resin member 12, and in the pushing-in stirring process C2, the rotating tool 16 is rotated at a predetermined rotation speed (for example, 3000 rpm) with a second pressure force (for example, 1500 N) greater than the first pressure force and for a second pressurizing time (for example, 0.25 seconds) shorter than the first pressurizing time. For example, when using an aluminum alloy metal member 11 having a thickness of 1 mm or more and 2 mm or less, the second pressure force in the pushing-in stirring process C2 is preferably a value of 1200 N or more and less than 1800 N. The second pressurization time is preferably 0.1 seconds or more and less than 3 seconds. The rotation speed of the rotating tool is preferably 2000 rpm or more and 4000 rpm or less.

(Stirring maintenance step C3)
The stirring maintaining step C3 is a step of stopping the mutual approach of the rotating tool 16 and the receiving tool 17, and continuing the rotational operation of the rotating tool 16 at a position (called the "reference position") where the rotating tool 16 has penetrated to a depth not reaching the weld boundary surface 13 (or the interposed member 50), as shown in FIG. 4. In this step, frictional heat is further generated, and most of the generated frictional heat moves to the interposed member 50 and the resin member 12. Therefore, the molten resin in at least the region directly below the rotating tool in the interposed member 50 and the resin member 12 flows further beyond the region directly below the rotating tool to the outer peripheral region. The molten resin spreads in a substantially circular shape centered on the region directly below the rotating tool.

When this process is performed using a position control method, the amount and speed of tool insertion, or the insertion time, during the stirring maintenance process C3 are not particularly limited as long as the rotation operation continues at the above position.

When this process is performed by the pressure control method, in the stirring maintenance process C3, the rotating tool 16 is rotated at a predetermined rotation speed (e.g., 3000 rpm) with a third pressure force (e.g., 500 N) smaller than the first pressure force and for a third pressure time (e.g., 6.75 seconds) longer than the first pressure time. The third pressure force and the third pressure time are set from the viewpoint of sufficient softening and melting over a wide range of the resin member 12 and productivity, and the values vary depending on, for example, the rotation speed of the rotating tool 16, the thickness of the metal member 11, the type of material, etc. For example, when using an aluminum alloy metal member 11 with a thickness of 1 mm or more and 2 mm or less, the third pressure force in the stirring maintenance process C3 is preferably a value of 100 N or more and less than 700 N. The third pressure time is preferably a value of 3.0 seconds or more and 10 seconds or less. The rotation speed of the rotating tool is preferably a value of 2000 rpm or more and 4000 rpm or less.

(Solidification process)
In the solidification step, the rotary tool 16 is separated from the metal member 11 and left to cool. In the present invention, it is not necessary to separate the rotary tool 16 from the metal member 11, and the rotary tool may be left to cool while being in contact with the metal member 11. From the viewpoint of further improving the bonding strength, it is preferable to separate the rotary tool 16 from the metal member 11 and leave it to cool. The term "left to cool" refers to cooling by leaving it at an ambient temperature (e.g., 25°C). As a result, a melt-solidified portion containing at least the constituent material of the interposed member is formed. In detail, when the resin member 12 is a thermosetting resin member, the melt-solidified portion contains only the constituent material of the interposed member 50. Also, for example, when the resin member 12 is a thermoplastic resin member, the melt-solidified portion may contain only the constituent material of the interposed member 50, but from the viewpoint of further improving the bonding strength, it preferably contains the constituent material of the interposed member 50 and the surface portion of the thermoplastic resin member on the metal member 11 side (particularly the area directly below the rotary tool).

The present invention does not preclude forced cooling (i.e., rapid cooling) in the solidification process, but sufficient bonding strength can be obtained without forced cooling by simply interposing the interposing member 50 between the metal member 11 and the resin member 12 and bonding them. For this reason, in the present invention, from the viewpoint of simple bonding, it is preferable to leave the members to cool.

In this specification, forced cooling (or rapid cooling) means forcibly cooling the "pressed area pressed by the metal member 11" at a faster cooling rate than the cooling rate when the area is left to cool at the ambient temperature (e.g., 25°C).

The above describes the case where the metal member and the resin member are joined at points without moving the rotary tool in the planar direction on the contact surface of the metal members (point joining). However, it is clear that the effects of the present invention can also be obtained when the metal member and the resin member are joined in a line while moving the rotary tool in the planar direction (linear joining or continuous joining), as long as the joining is performed by interposing the interposing member 50 between the metal member 11 and the resin member 12.

[Joint structure]
The joint structure according to the present invention is a structure in which a metal member 11 and a resin member 12 are joined to each other, as shown in Fig. 5, for example. Although not shown in Fig. 5, the metal member 11 and the resin member 12 are joined to each other with an intervening member interposed therebetween. In Fig. 5, the joint structure is a structure obtained by a friction stir welding method, and therefore has a pressing mark W by a pressing member, but may not have the pressing mark W depending on the joining method. Fig. 5 is a schematic diagram showing an example of the joint structure of a metal member and a resin member according to the present invention.

In the joining structure according to the present invention, more specifically, the metal member 11 and the resin member 12 are joined at least by the melted and solidified portions 60, 61 of the interposed member. In other words, the resin member 12 is joined to the metal member 11 at its metal member side surface 120 by at least the melted and solidified portions 60, 61 of the interposed member. More specifically, when the metal member 11 is forcibly peeled off from the joining structure, the metal member side surface 120 of the resin member 12 can be observed, for example, as shown in FIG. 6. In the metal member side surface 120 of the resin member 12, melted and solidified portions are formed in the region 60 directly below the rotating tool (hatched region) and in its outer peripheral region 61 (lattice region), and joining is achieved by such melted and solidified portions. The melted and solidified portion needs to be formed at least in the region 60 (hatched region) directly below the rotating tool, and does not necessarily have to be formed in the peripheral region 61 (lattice region). However, from the viewpoint of further improving the joining strength, it is preferable that the melted and solidified portion is formed in the region 60 (hatched region) directly below the rotating tool and in the peripheral region 61 (lattice region). Figure 6 is a schematic diagram showing the surface state of the resin member when the metal member is forcibly peeled off from an example of the joining structure between a metal member and a resin member according to the present invention, and the surface of the resin member on the metal member side is observed.

As shown in FIG. 6, the melted and solidified portions 60 (hatched area) and 61 (grid area) refer to the portions where the intervening member melts and solidifies during joining, and if the resin member 12 is a thermoplastic resin member, it may further contain a constituent material of the thermoplastic resin member (e.g., thermoplastic resin). The intervening member does not have to be entirely melted and solidified, and there may be unmelted portions (not shown) between the metal member 11 and the resin member 12.

The melted and solidified portions 60 (hatched areas) and 61 (lattice areas) are areas on the metal member side surface 120 of the resin member 12 where no melting of the resin member 12 has occurred, and on the periphery of the melted and solidified portions there is a visually distinguishable step (a step of several microns). The melted and solidified portions 60 and 61 may have the surface of the corresponding area on the metal member transferred thereto, or may have an exposed cohesive failure surface caused by part of the resin material of the melted and solidified portion adhering to the metal material surface.

For example, when the resin member is a thermosetting resin member, the melt-solidified portions 60, 61 are clearly distinguishable from each other by visual observation at the interface between them on the surface of the thermosetting resin member.
Furthermore, for example, when the resin members are thermoplastic resin members, the melted and solidified portions 60, 61 can be clearly distinguished visually from the original resin base material that does not melt during joining by, for example, observing a cross section of the joined members.
Therefore, the melt-solidified portion can also be called a "molten and solidified resin layer". The thickness of the melt-solidified portion is not particularly limited, and is preferably 0.50 mm or less, more preferably 0.10 mm or less. The lower limit of the thickness of the melt-solidified portion is not particularly limited, and the thickness of the melt-solidified portion is usually 0.01 mm or more. The thickness of the melt-solidified portion is, for example, the average value of measurements taken at any five points on a circular line 62 (dashed line) of diameter 1.5 x D1 concentric with the region 60 directly below the pressing member (diameter D1 (mm)).

In the present invention, the joining is performed using the intermediate member 50, and since the crystallization is delayed during solidification, the melted and solidified portion has a crystallinity (maximum crystallinity ratio) of 80% or less. If the crystallinity (maximum crystallinity ratio) of the melted and solidified portion exceeds 80%, the joining strength decreases. The crystallinity (maximum crystallinity ratio) is the ratio of the "actual crystallinity analyzed and calculated by DSC (differential scanning calorimetry)" to the "maximum crystallinity". Since the maximum crystallinity differs depending on the type of resin, this indicator is used in the present invention. Therefore, in the present invention, the melted and solidified portion is characterized by having a relatively low crystallinity (maximum crystallinity ratio). In this way, the melted and solidified portion has a relatively low crystallinity (maximum crystallinity ratio), which sufficiently improves the joining strength. Although the details of such a phenomenon are not clear, it is thought to be based on the following mechanism. For example, the low crystallinity (maximum crystallinity ratio) reduces the physical properties of the molten and solidified resin in contact with the metal components, resulting in improved adhesion, improved bonding strength due to the anchor effect, and reduced residual stress between the bonded components.

The crystallinity (maximum crystallinity ratio) of the melt-solidified portion is usually 40% or more (particularly 40 to 80%), and from the viewpoint of further improving the bonding strength, it is preferably 40 to 76%, and more preferably 40 to 72%. The crystallinity (maximum crystallinity ratio) may be, for example, 50% or more.

The crystallinity (maximum crystallinity ratio) of the melted and solidified portion is the average value of values measured at any five points on a circular line 62 (dashed line) of diameter 1.5×D1 concentric with the region 60 (diameter D1 (mm)) directly under the pressing member, as shown in Fig. 6. In detail, 6 g (not including resin weight, fibers, etc.) of the melted and solidified portion sampled from a specified position on the resin-side fracture surface is used, and the crystallinity is analyzed and calculated by the following method using a DSC (differential scanning calorimetry) device.
Equipment used: DSC (differential scanning calorimetry) Equipment temperature cycle: 23°C → freezing point + 70°C → 23°C
Temperature increase rate: 10℃/min Temperature decrease rate: 10℃/min
Analysis method: Investigate the endothermic peak heat quantity and exothermic peak heat quantity when applying heat to the sample. Calculation method: Calculate using the following method and formula based on various peak heat quantities.
The peak heat quantity (during temperature rise) of the exothermic heat associated with the crystal formation is represented as x.
The endothermic peak heat quantity accompanying crystal melting is represented as y.
The heat quantity of 100% crystal melting peak (resin specific value) is defined as z.
Examples of z: PPS: 146.2 J/g, PP: 209.0 J/g, PA6: 229.7 J/g.
In the case of resin types for which x can be observed (e.g. PPS, etc.), "actual degree of crystallinity" = (y-x)/z x 100
・"Maximum crystallinity" = y/z x 100
In the case of resin types where x cannot be measured (e.g. PP, PA, etc.), "actual crystallinity" = y (first cycle) / z x 100
"Maximum crystallinity" = y (2nd cycle) / z x 100
Using the "actual crystallinity" and "maximum crystallinity" calculated using the above formula, the crystallinity (maximum crystallinity ratio) used in the present invention is calculated by the following formula.
"Crystallization degree (maximum crystallinity ratio)" = "actual crystallinity degree" / "maximum crystallinity degree" x 100

The dimension (e.g., diameter) R (mm) of the molten and solidified portions (60, 61) usually satisfies the following relationship when the dimension of the pressing member (e.g., diameter of the rotating tool) is D1 (mm):
1.2≦R/D1≦5;
Preferably, 2≦R/D1≦5;
More preferably, 3≦R/D1≦5.
If R/D1 is too small, the bonding strength is insufficient.

The dimension (e.g., diameter) R (mm) of the melted and solidified portion (60, 61) can be easily measured based on the step on the outer periphery of the melted and solidified area on the metal member side surface 120 of the resin member 12. The dimension R is the maximum dimension of the melted and solidified area (60, 61).

<Experimental Example A>
[Resin member]
A resin member 12 having dimensions of 100 mm length x 30 mm width x 3 mm thickness was manufactured by injection molding using polypropylene pellets containing 40% by weight of carbon fiber (PP-CF40%; manufactured by Daicel Corporation). The melting point of the polypropylene in the resin member was about 160°C, and the weight average molecular weight (Mw) was about 5.0 x ¹⁰⁵ .

[Interposition member film]
A film was produced by hot pressing using polypropylene pellets (manufactured by Daicel Corporation) and a crystallization retarder (L-MODU (Idemitsu)).
Four types of films were produced as the spacer film, each having a crystallization retarder content of 0 mass %, 25 mass %, 50 mass % or 75 mass % relative to the total mass.
The melting point of the polypropylene pellets in the spacer film was about 160° C., and the weight average molecular weight (Mw) was about 5.0×10 ⁵ .
The crystallization retarder in the interposer film was polypropylene, and the polypropylene had a melting point of about 90 and a weight average molecular weight (Mw) of about 5.0×10 ⁴ .
The interposing member film had dimensions of 20 mm length x 20 mm width x 0.2 mm thickness, and was used so that its center was positioned on the axis of the rotating tool.

[Metal Members]
The metal member used was a flat plate member (thickness 1.2 mm) made of a 5000 series aluminum alloy.
[Rotate Tool]
The rotary tool used was made of tool steel and had dimensions of D1=10 mm, D2=2 mm, and h=0.35 mm as shown in FIG.

[Example A1]
(Joining method)
A bonded structure of a metal member 11 and a resin member 12 was manufactured by the following method using a position control system: A spacer film containing 50% by mass of a crystallization retarder was used.
First step:
The metal member 11 and the resin member 12 were laminated together with the interposing member film 50 interposed therebetween as shown in FIG.

Second step:
4, without performing the preheating step C1, the rotating tool 16 was pressed into the metal member 11 to a depth not reaching the joining boundary surface 13 between the metal member 11 and the resin member 12. Pressing and stirring step C2: insertion amount 1.0 mm, insertion speed 12 mm/min, tool rotation speed 3000 rpm.
Next, the rotary tool 16 was removed from the bonded structure, and the bonded structure was left to cool (solidification step).

[Example A2]
A bonded structure was obtained in the same manner as in Example A1, except that a spacer film having a crystallization retarder content of 75% by mass was used.

[Comparative Example A1]
A bonded structure was obtained in the same manner as in Example A1, except that a spacer film containing 0% by mass of the crystallization retarder was used.

[Comparative Example A2]
A bonded structure was obtained in the same manner as in Example A1, except that a spacer film having a crystallization retarder content of 25% by mass was used.

[Reference Example A1]
A bonded structure was obtained in the same manner as in Example A1, except that no interposing member film was used.

[Reference Example A2]
A bonded structure was obtained in the same manner as in Example A1, except that no interposing member film was used, and that the following forced cooling (i.e., rapid cooling) was carried out instead of leaving it to cool.

After the rotating tool 16 was removed from the joint structure, the pressing area of the metal member 11 pressed by the rotating tool 16 and the surrounding area were forced to cool (solidification process). More specifically, a 15°C air flow was blown from a nozzle at a flow rate of 400 L/min onto the pressing area to perform forced cooling, and a joint structure was obtained.

[Bonding strength]
As shown in Fig. 7, a joint structure of a metal member 11 and a resin member 12 was placed in a jig 100. The jig 100 was configured so that a downward force was applied to the upper end of the resin member 12 by pulling the jig 100 downward. By fixing the jig 100 and pulling the metal member 11 upward, a downward force was applied to the upper end of the resin member 12, and the shear strength TS of the joint was measured without being affected by the base material strength of the resin member 12. Fig. 7 is a schematic diagram for explaining a method for measuring the joint strength in the examples.
Three bonded structures were manufactured, and the bond strength of the three bonded structures was measured. The measurement results are shown in FIG.

(Crystallinity (maximum crystallinity ratio))
The metal member 11 was forcibly peeled off from the resulting joined structure. The surface 120 of the resin member 12 on the side of the metal member was observed, and the melted and solidified portion of the intermediate member [particularly, the portion immediately below the rotating tool as shown in FIG. 6 ] was observed. A sample was scraped off at any five points on a circular line 62 (dashed line) of diameter 1.5×D1 concentric with the region 60 (diameter D1 (mm)), and the sample was measured by a DSC (differential scanning calorimetry) device according to the above-mentioned method. The crystallinity (maximum crystallinity ratio) was measured and calculated according to the following.
Three bonded structures were produced, and the crystallinity of each of the three bonded structures was measured. The average value of the measurement results is shown in Table 1.

The numbers in the table indicate the maximum crystallinity ratio.
The area to be investigated was a position 7.5 mm from the center of the joint on the resin side fracture surface after the shear strength evaluation, and was investigated using the specified method.

<Experimental Example B>
[Resin member]
A resin member 12 having dimensions of 100 mm length × 30 mm width × 3 mm thickness was manufactured by injection molding using polyamide pellets containing 40% by weight of carbon fiber (PA-CF40%; manufactured by Daicel Corporation). The melting point of the polyamide in the resin member was about 230°C, and the weight average molecular weight was about 5.0 × ¹⁰⁵ .

[Interposition member film]
A film was produced by hot pressing using polyamide pellets (PA6; Daicel Corporation) and a crystallization retarder ( ^{TechnylStar®} (Solvay, star-shaped polyamide)).
Four types of films were produced as the spacer film, each having a crystallization retarder content of 0 mass %, 25 mass %, 50 mass % or 75 mass % relative to the total mass.
The melting point of the polyamide pellets in the spacer film was about 230° C., and the weight average molecular weight was about 5.0×10 ⁵ .
The crystallization retarder in the interposer film was polyamide, and the polyamide had a melting point of about 130° C. and a weight average molecular weight of about 5.0×10 ⁴ .
The interposing member film had dimensions of 20 mm length x 20 mm width x 0.2 mm thickness, and was used so that its center was positioned on the axis of the rotating tool.

[Metal Members]
The same metal member as in Experimental Example A was used.
[Rotate Tool]
A rotary tool similar to that in Example A was used.

[Example B1]
(Joining method)
A bonded structure of a metal member 11 and a resin member 12 was manufactured by the following method using a position control system: A spacer film containing 50% by mass of a crystallization retarder was used.
First step:
The metal member 11 and the resin member 12 were laminated together with the interposing member film 50 interposed therebetween as shown in FIG.

Second step:
4, without performing the preheating step C1, the rotating tool 16 was pressed into the metal member 11 to a depth not reaching the joining boundary surface 13 between the metal member 11 and the resin member 12. Pressing and stirring step C2: insertion amount 1.0 mm, insertion speed 12 mm/min, tool rotation speed 3000 rpm.
Next, the rotary tool 16 was removed from the bonded structure, and the bonded structure was left to cool (solidification step).

[Example B2]
A bonded structure was obtained in the same manner as in Example B1, except that a spacer film having a crystallization retarder content of 75% by mass was used.

[Comparative Example B1]
A bonded structure was obtained in the same manner as in Example B1, except that a spacer film containing 0% by mass of the crystallization retarder was used.

[Comparative Example B2]
A bonded structure was obtained in the same manner as in Example B1, except that a spacer film containing 25% by mass of the crystallization retarder was used.

[Reference Example B1]
A bonded structure was obtained in the same manner as in Example B1, except that no interposing member film was used.

[Reference Example B2]
A bonded structure was obtained in the same manner as in Example B1, except that no interposing member film was used, and that the following forced cooling (i.e., rapid cooling) was carried out instead of leaving it to cool.

After the rotating tool 16 was removed from the joint structure, the pressing area of the metal member 11 pressed by the rotating tool 16 and the surrounding area were forced to cool (solidification process). More specifically, a 15°C air flow was blown from a nozzle at a flow rate of 400 L/min onto the pressing area to perform forced cooling, and a joint structure was obtained.

[Bonding strength]
The shear strength TS of the joint was measured by the same method as that used for measuring the joint strength in Experimental Example A.
Three bonded structures were manufactured, and the bond strength of the three bonded structures was measured. The measurement results are shown in FIG.

[Crystallinity (maximum crystallinity ratio)]
The crystallinity of the molten and solidified portion of the intermediate member was measured by the same method as that used in Experimental Example A.
Three bonded structures were produced, and the crystallinity of each of the three bonded structures was measured. The average value of the measurement results is shown in Table 2.

According to the joining method and joining structure of the present invention, simply by interposing a specific interposing member between the metal member and the resin member, it is possible to obtain a joining strength equivalent to that obtained when forced cooling (i.e., quenching) is performed without performing forced cooling (i.e., rapid cooling).

The joining structure and joining method of the present invention are useful for joining metal members and resin members in fields such as automobiles, railway vehicles, aircraft, and home appliances.

1: Friction stir welding apparatus 10: Work 11: Metal member 12: Resin member 13: Welding interface between metal member and resin member 16: Rotating tool 17: Receiving tool 50: Interposed member 100: Jig for measuring welding strength P: Pressing area (area to be pressed)

Claims (19)

A method for joining a metal member and a resin member by a thermocompression joining method, comprising overlapping a metal member and a resin member with an intervening member therebetween, applying heat and pressure to the metal member by a pressing member to soften and melt the intervening member and then solidifying the intervening member,
the resin member is a thermoplastic resin member,
The intermediate member contains a crystallization retarder in an amount of 50 % by mass or more relative to the total amount of the intermediate member , and further contains a thermoplastic matrix resin,
The crystallization retarder is a thermoplastic resin having the following melting point Mp and weight average molecular weight Ka, where Mpx (°C) and Kx are the melting point and weight average molecular weight of the thermoplastic base resin contained in the intermediate member, respectively:
The method for joining a metal member and a resin member, wherein the thermoplastic base resin contained in the interposing member, the thermoplastic resin as the crystallization retarder, and the thermoplastic resin contained in the thermoplastic resin member are all polyolefin-based resins or polyamide-based resins (PA) :
The melting point Mp is between 0.4×Mpx and 0.7×Mpx;
The weight average molecular weight Ka is 0.01×Kx to 0.5×Kx . The method for joining a metal member and a resin member according to claim 1, wherein the crystallization retarder is a crystallization retarder for at least the thermoplastic base resin contained in the intermediate member. 3. The method for joining a metal member and a resin member according to claim 1 or 2, wherein the crystallization retarder is a crystallization retarder for both the thermoplastic base resin contained in the intermediate member and the thermoplastic resin contained in the thermoplastic resin member. The method for joining a metal member and a resin member according to any one of claims 1 to 3 , wherein the thermoplastic resin contained in the thermoplastic resin member has the following melting point Mpy (°C) and weight average molecular weight Ky:
The melting point Mpy is between 0.8 x Mpx and 1.2 x Mpx;
The weight average molecular weight Ky is 0.8×Kx to 1.2×Kx. the thermoplastic matrix resin contained in the intermediate member and the thermoplastic resin contained in the thermoplastic resin member are polypropylene;
5. The method for joining a metal member and a resin member according to claim 1 , wherein the thermoplastic resin serving as the crystallization retarder is polypropylene synthesized using a metallocene catalyst. The method for joining a metal member and a resin member according to any one of claims 1 to 5 , wherein the intervening member has a form of a film, a form of a coating formed on the surface of the metal member, a form of a coating formed on the surface of the resin member, or a combination thereof. 7. The method for joining a metal member and a resin member according to claim 1 , wherein the molten and solidified portion of the interposed member formed in the solidification step has a crystallinity (maximum crystallinity ratio) of 80% or less. The method for joining a metal member and a resin member according to any one of claims 1 to 7 , wherein cooling is carried out in the solidification step. The thermocompression bonding method comprises:
9. The method for joining a metal member and a resin member according to claim 1, comprising: a first step of overlapping the metal member and the resin member with the intervening member interposed therebetween; and a second step of pressing the metal member against a rotating tool as a pressing member while rotating the rotating tool to generate frictional heat, softening and melting the intervening member by the frictional heat, and then solidifying the intervening member to join the metal member and the resin member. 10. The method for joining a metal member and a resin member according to claim 9, wherein the second step includes a pushing and stirring process of pushing the rotating tool into the metal member to a depth not reaching a joining boundary surface between the metal member and the resin member before the solidification process . The method for joining a metal member and a resin member according to claim 10, wherein the second step further includes a preheating step of rotating the rotary tool with only a tip portion of the rotary tool in contact with a surface portion of the metal member before the thrust stirring step . 12. The method for joining a metal member and a resin member according to claim 10 or 11, wherein the second step further includes a stirring maintenance step of continuing the rotation operation of the rotation tool at a position after the thrust stirring step and before the solidification step , where the rotation tool has penetrated to a depth not reaching the joining boundary surface. The method for joining a metal member and a resin member according to any one of claims 1 to 12 , wherein the metal constituting the metal member is one or more metals selected from the group consisting of aluminum, an aluminum alloy, steel, magnesium and its alloy, and titanium and its alloy. A joining structure of a metal member and a resin member, in which a metal member and a resin member are joined with an interposition member therebetween,
the resin member is a thermoplastic resin member,
The intermediate member contains a crystallization retarder in an amount of 50 % by mass or more relative to the total amount of the intermediate member, and further contains a thermoplastic matrix resin,
The crystallization retarder is a thermoplastic resin having the following melting point Mp and weight average molecular weight Ka, where Mpx (°C) and Kx are the melting point and weight average molecular weight of the thermoplastic base resin contained in the intermediate member, respectively:
A joining structure between a metal member and a resin member, wherein the thermoplastic base resin contained in the intermediate member, the thermoplastic resin as the crystallization retarder, and the thermoplastic resin contained in the thermoplastic resin member are all polyolefin-based resins or polyamide-based resins (PA) :
The melting point Mp is between 0.4×Mpx and 0.7×Mpx;
The weight average molecular weight Ka is 0.01×Kx to 0.5×Kx . The joint structure between a metal member and a resin member according to claim 14 , wherein the crystallization retarder is a crystallization retarder for at least the thermoplastic matrix resin contained in the intermediate member. The joining structure between a metal member and a resin member according to claim 14 or 15, wherein the crystallization retarder is a crystallization retarder for both the thermoplastic base resin contained in the intermediate member and the thermoplastic resin contained in the thermoplastic resin member. The thermoplastic resin contained in the thermoplastic resin member has the following melting point Mpy (° C ) and weight average molecular weight Ky:
The melting point Mpy is between 0.8 x Mpx and 1.2 x Mpx;
The weight average molecular weight Ky is 0.8×Kx to 1.2×Kx. the thermoplastic matrix resin contained in the intermediate member and the thermoplastic resin contained in the thermoplastic resin member are polypropylene,
The joint structure between a metal member and a resin member according to any one of claims 14 to 17 , wherein the thermoplastic resin as the crystallization retarder is polypropylene . the resin member is joined to the metal member by the melt-solidified portion of the intermediate member on the surface of the resin member facing the metal member,
The joining structure between a metal member and a resin member according to any one of claims 14 to 18 , wherein the melt-solidified portion has a crystallinity (maximum crystallinity ratio) of 80% or less.

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