JP7263621B2 - Joining method - Google Patents

Description

The present disclosure relates to methods for joining fiber reinforced thermoplastics (FRTP).

As a method for joining members to be joined made of FRTP, bolting, fusion and adhesion (see Patent Document 1) are known.

In bolt connection, members to be joined are fixed with bolts and nuts. In fusion bonding, members to be joined are joined together by melting the base material (thermoplastic resin) of FRTP. In adhesion, members to be joined are joined together using an adhesive.

JP 2016-175331 A

However, the above joining methods each have their own problems.

Bolted joints have a low bolted joint strength, and it is necessary to increase the plate thickness of the members to be joined. Moreover, when drilling, bolting, and sealing operations are performed at many locations, the number of assembling man-hours increases and the weight of the product increases. Furthermore, in the use of bolts and nuts, there is concern about electrolytic corrosion when using carbon fibers as reinforcing fibers.

In fusion bonding, since the base material of FRTP is once melted, it is difficult to control the plate thickness and shape. In addition, the melting of the base material may cause the reinforcing fibers contained in the members to be joined to undulate.

In adhesion, since a material different from the adherend is used as an adhesive, there are problems such as deterioration of the adhesion interface and additional costs. Thermosetting resins are mainly used as structural adhesives. Thermosetting resins used as structural adhesives include epoxy resins. Epoxy resin loses strength due to moisture absorption, and its heat resistance and toughness may differ greatly from those of the adherend (base material).

As a method for joining members to be joined made of FRTP, joining using plasma treatment is being considered as an alternative method. When a member to be joined made of FRTP is irradiated with plasma, the surface of the member is activated and a functional group such as a hydroxyl group is introduced. When the surfaces to which the functional groups have been introduced are brought together and heated and pressurized, adjacent functional groups are chemically reacted and bonded. Since the heating in the method using plasma treatment is performed at a temperature below the melting point of the base material of FRTP, the base material is not melted. Therefore, the plate thickness and shape do not change due to melting, and the reinforcing fibers do not undulate.

However, even in the method using plasma treatment, further improvement in bonding strength is required.

The present disclosure has been made in view of such circumstances, and an object thereof is to provide a bonding method capable of improving the bonding strength in bonding between FRTPs by activating the surfaces to be bonded.

In order to solve the above problems, the joining method of the present disclosure employs the following means.
The present disclosure relates to a joining method for joining members to be joined that are made of a fiber-reinforced thermoplastic whose base material is a thermoplastic resin, wherein the surfaces of the members to be joined are smoothed and smoothed. activating the surface that has been treated to introduce an active functional group capable of causing a chemical bond , and superimposing the two members to be joined with the surfaces that have been activated so that they face each other, and the temperature of the base material is Provided is a bonding method for bonding by chemical bonding by heating and pressurizing the members to be bonded in a superimposed state so as to maintain the temperature below the melting point.

According to the joining method according to the present disclosure, since members to be joined are joined by activation treatment, there is no concern about weight increase and electrolytic corrosion. By performing heating and pressurization so that the temperature of the base material is maintained below the melting point, it becomes easier to control the plate thickness and shape, and the waviness of the reinforcing fibers can be suppressed. By smoothing the surfaces of the members to be joined before the activation treatment, the joining strength can be improved.

It is a figure explaining superposition concerning a 1st embodiment. FIG. 2 is an exploded view taken along the line AA of FIG. 1; FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1; It is a figure which illustrates the cross section of the to-be-joined member which overlap|superposed without planarization processing by the conventional method. It is a figure explaining superposition concerning a 2nd embodiment. It is a cross-sectional view showing an example of a joint portion.

The joining method according to the present disclosure is suitable for joining components of an aircraft. For example, it can be applied to the joining of the skins of the fuselage or wings of an aircraft and the stringers that reinforce them as members to be joined.

[First Embodiment]
A method of joining members to be joined together will be described.

(Member to be joined)
The members to be joined are made of fiber reinforced thermoplastic (FRTP). The member to be joined may be composed of a single layer of FRTP, or may be composed of a plurality of layers of FRTP. In this embodiment, the members to be joined are those after molding the FRTP.

FRTP includes a thermoplastic resin and reinforcing fibers. Thermoplastic resin is the base material (matrix) of FRTP.

Thermoplastic resins are not particularly limited, but may be super-engineered plastics such as polyaryletherketone (PAEK), polyphenylene sulfide (PPS), polyetherimide (PEI), and liquid crystal polymer (LCP). PAEK is, for example, polyetheretherketone ( PEEK ), polyetherketoneketone (PEKK), low melting point PAEK (LM PAEK).

The reinforcing fibers may be inorganic fibers or organic fibers. Inorganic fibers include carbon fibers, glass fibers, silicon carbide fibers, and the like. Organic fibers include aramid fibers, polyparaphenylene-benzobis-oxazole (PBO) fibers, polyarylate fibers, and PEEK fibers. The reinforcing fibers may be in the form of unidirectionally oriented fiber bundles, wovens and nonwovens.

The thermoplastic resins contained in the two members to be joined may be the same or different. The reinforcing fibers contained in the two joined members to be joined may be of the same type or of different types. The forms of reinforcing fibers contained in the two members to be joined may be the same or different.

The joining method according to this embodiment includes the following steps.
(S1) Smoothing process (S2) Activation process (S3) Superposition (S4) Joining

(S1) Smoothing Treatment First, the surfaces of the members to be joined are smoothed.
In the smoothing treatment, the surfaces of part or all of the members to be joined are polished by known mechanical polishing means such as sanding and blasting to improve the smoothness of the surfaces. In the smoothing treatment, it is desirable to bring the surfaces to be joined closer to a mirror surface within the practicable range. A "smooth surface" allows the presence of irregularities of at least nm order.

Conditions for the smoothing treatment are appropriately set according to the materials of the members to be joined.
For example, when the members to be joined contain hard and brittle reinforcing fibers such as SiC fibers, the surface of the members to be joined may be polished using diamond as an abrasive. Even if the member to be joined contains SiC fibers, if the outermost surface is a resin layer (a layer that does not contain SiC fibers) or if the amount of SiC fibers contained in the outermost layer is small, it should be polished by other methods. good too.

(S2) Activation treatment The smooth surface (surface to be joined) of the member to be joined is activated. By "activated" is meant the introduction of active functional groups that cause chemical bonding. Activation can be performed by methods such as plasma treatment, ultraviolet (UV) treatment, vacuum ultraviolet (VUV) treatment, flame treatment, and chemical solution treatment. In the present embodiment, the following description is based on the assumption that the surfaces to be bonded are activated by plasma processing.

A plasma irradiation apparatus using a known plasma generation technique can be used for plasma irradiation. Plasma irradiation to large parts (members) is desirably carried out by an atmospheric pressure plasma irradiation apparatus. Plasma irradiation to the small member may be carried out by a low-pressure plasma irradiation apparatus.

A plasma can be formed by any gas. The plasma can be formed from at least one substance that is gaseous at room temperature, such as air, oxygen, nitrogen, carbon dioxide, water vapor, helium, neon, argon, and the like.

Conditions for plasma irradiation may be appropriately selected according to the type of plasma irradiation device, materials of the resin layer and members to be joined, required joining strength, condition of the surfaces to be joined, and the like.

By irradiating the surfaces to be bonded with plasma, the molecules on the surfaces to be bonded are activated to generate active functional groups (hereinafter referred to as functional groups). A hydroxyl group, a carboxy group, a carbonyl group, and the like are functional groups that can be generated by irradiation with oxygen-containing plasma. The same type of functional groups or different types of functional groups may be generated on the surfaces to be bonded between the members to be bonded. By selecting the type of plasma to be irradiated, the type of functional groups generated can be controlled.

(S3) Overlapping After the activation process, as shown in FIG. 1, the member to be joined 1 and the member to be joined 2 are overlapped. FIG. 2 is an exploded view taken along the line AA of FIG. The members to be joined 1 and 2 are arranged such that the smooth surfaces (surfaces to be joined S ₁ and S ₂ to be joined) after being irradiated with plasma face each other.

As shown in FIG. 2, in smoothed area F, contaminant C and release agent R have been removed. Contaminant C is, for example, oil, silicone, or the like. The release agent R is, for example, silicone, fluororesin, or the like.

(S4) Joining As shown in FIG. 3, the member to be joined 1 and the member to be joined 2 are pressed while being heated while being superimposed. As a result, the functional groups on the surface to be bonded _S1 and the functional groups (not shown) on the surface to be bonded _S2 are chemically reacted and bonded. As a result, the member to be joined 1 and the member to be joined 2 are joined.

Heating and pressing are not particularly limited, but can be carried out, for example, with a hot press machine, rollers, or the like. It should be noted that the heating and pressurization may be a combination of mechanisms. For example, it can be pressurized with a transparent block and heated with a laser, sandwiched between blocks and energized, and the like.

Heating and pressing are performed under the condition that the temperature of the base material of the members to be joined 1 and 2 does not exceed the melting point (the temperature can be maintained below the melting point). Here, "the temperature of the base material does not reach the melting point or higher" is synonymous with "the base material is not melted." When an amorphous thermoplastic resin is used as the base material of FRTP, "the base material is not melted" means "the glass transition temperature of the base material is exceeded, the elastic modulus is significantly reduced, and shape retention becomes impossible. It is synonymous with "not reaching the temperature".

Heating and pressurization are performed under conditions that allow chemical reaction between functional groups that are within a reactable distance. The heating and pressurizing conditions under which the functional groups can chemically react with each other are based on the activation energy of the chemical reaction that occurs between the functional groups introduced to the surfaces to be joined, and the chemical reaction proceeds beyond the activation energy. can be set by calculating a sufficient temperature for

The above conditions are preferably acquired in advance by preliminary tests or the like.

For reference, FIG. 4 illustrates cross sections of members to be joined 3 and 4 that are superimposed without being flattened.

Due to manufacturing reasons, the release agent R and other contaminants C may remain on the surfaces of the FRTP members to be joined. Further, when the surfaces of the members to be joined 3 and 4 on which the release agent R and the contaminant C are present are irradiated with plasma, the surfaces of the contaminant C and the release agent R are activated and hidden beneath them. Therefore, the surfaces of the members 3 and 4 to be joined cannot be sufficiently activated. This is considered to be a factor that hinders the improvement of the bonding strength.

Furthermore, the surfaces of the members 3 and 4 to be joined made of FRTP have irregularities and are not flat. When the non-flat surfaces are brought together, a gap G is created between the surface to be bonded _S3 and the surface to be bonded _S4 . In the gap G portion, since the surfaces cannot be joined together, the joining force becomes weak.

According to this embodiment, the release agent R and the contaminant C can be removed from the treated region by performing the smoothing treatment before the activation treatment. As a result, the surfaces to be bonded can be sufficiently activated without being inhibited by the release agent R and the contaminant C, so that the bonding strength is improved.

According to this embodiment, the smoothing process is performed before the activation process, so that the gap between the members to be joined can be reduced. This increases the probability that adjacent functional groups on the facing surfaces meet each other, thereby improving the bonding strength.

[Second embodiment]
This embodiment differs from the first embodiment in that a resin film is interposed between members to be joined.

The resin film is made of thermoplastic resin. The resin film has heat resistance equivalent to that of the base material of the member to be joined. Equivalent heat resistance means that the strength and function of the base material are not substantially affected at the operating environmental temperature of the product in which the members to be joined are joined. For example, when the base material is PEEK, PEEK and PAEK such as PEKK can be used as the thermoplastic resin of the resin film.

The thermoplastic resin used for the resin film is the same material as the base material of the member to be joined, a material with a lower melting point than the base material of the member to be joined, or a material with the same or slightly higher melting point than the base material of the member to be joined. It's okay.

The thermoplastic resin used for the resin film preferably has a lower melting point than the base material of the member to be joined. The thermoplastic resin has a lower glass transition temperature than the base material of the member to be joined. Molecular motion of such a thermoplastic resin can be activated in a temperature range in which the base material does not melt. This makes it easier for the resin film to conform to the irregularities of the member to be joined.

The thickness of the resin film is preferably equal to or larger than the radius of the reinforcing fibers included in the members to be joined. As a result, even if the reinforcing fibers are exposed on one surface of the member to be joined, the gaps between the fiber bundles can be filled.

The joining method according to this embodiment includes the following steps.
(S11) smoothing process (S12) activation process (S13) superposition (S14) joining

(S11) Smoothing Treatment Similar to the first embodiment, a part or all of the surfaces of the members to be joined are smoothed to form a smooth surface. In the smoothing treatment, it is desirable to bring the surfaces to be joined closer to a mirror surface within the practicable range. A "smooth surface" allows the presence of unevenness on the order of nm.

(S12) Activation Treatment The surfaces of the members to be bonded and both surfaces of the resin film are activated. In the present embodiment, the following description is based on the assumption that the surfaces to be bonded are activated by plasma processing.

Plasma is applied to the surface of the member to be joined and both surfaces of the resin film. Irradiation may be performed one surface at a time, or may be performed collectively. Active functional groups (hereinafter referred to as functional groups) are introduced into the plasma-irradiated surface.

A plasma irradiation apparatus using a known plasma generation technique can be used for plasma irradiation. Plasma irradiation to large parts (members) is desirably carried out by an atmospheric pressure plasma irradiation apparatus. Plasma irradiation to the small member may be carried out by a low-pressure plasma irradiation apparatus.

Conditions for plasma irradiation may be appropriately selected according to the type of plasma irradiation apparatus, the materials of the resin film and the member to be joined, the required joining strength, the state of one surface of the member to be joined, and the like.

The plasma irradiation is preferably carried out under the condition that the temperature of the object to be irradiated (base material or resin film of the member to be joined) exceeds the glass transition temperature (Tg). By doing so, it is possible to suppress subsequent penetration of the functional groups generated on the surface of the object to be irradiated.

(S13) Overlapping After the activation process, as shown in FIG. 5, the member to be joined 11, the resin film 12, and the member to be joined 13 are overlapped in order. The members to be joined 11 and 13 are arranged so that their smooth surfaces (surfaces to be joined S ₁₁ and S ₁₃ ) after being irradiated with plasma face each other.

(S14) Bonding The member to be bonded 11, the resin film 12, and the member to be bonded 13 are pressed while being heated while being superimposed. As a result, the functional groups (not shown) on the surface to be joined _S11 and the functional groups (not shown) on one surface _S12a of the resin film, and the functional groups (not shown) on the surface to be joined _S13 and the resin film are chemically bonded to the functional groups (not shown) on the other surface S _12b . As a result, the member to be joined 11 and the member to be joined 13 are joined. FIG. 6 shows a cross section of the joined members 11 and 13 joined together.

Heating and pressing are not particularly limited, but can be carried out, for example, with a hot press machine, rollers, or the like. It should be noted that the heating and pressurization may be a combination of mechanisms. For example, it can be pressurized with a transparent block and heated with a laser, sandwiched between blocks and energized, and the like.

Heating and pressing are performed under the condition that the temperature of the base material of the members to be joined 11 and 13 does not exceed the melting point (the temperature can be maintained below the melting point). Heating and pressurization are carried out under conditions in which adjacent functional groups on surfaces S ₁₁ and S ₁₃ to be bonded and both surfaces S _12a and S _12b of the resin film can chemically react with each other. Heating and pressing are preferably performed under the condition that the resin film 12 exceeds the glass transition temperature.

When the glass transition temperature is exceeded, the molecular motion of the resin film 12 becomes active and the rigidity is lowered. The resin film 12 having a temperature higher than the glass transition temperature is in a state where it easily conforms to the irregularities of the member to be joined. As a result, as shown in FIG. 6, the gap between the member to be joined 11 and the member to be joined 13 can be filled during heating and pressurization, thereby improving the strength of the joint.

In addition, although the procedure of joining in one batch is described above, the joining in the joining method according to the present embodiment may be performed stepwise. In this case, after the resin film 12 is overlaid on the smooth surface of the member to be joined 11 and heated and pressed, the member to be joined 13 is overlaid on the resin film 12 with the smooth surface facing the resin film 12, and then heated and pressed. pressurize.

[Third Embodiment]
This embodiment differs from the second embodiment in that a resin material is interposed between the members to be joined instead of the resin film. Other configurations are the same as those of the second embodiment.

The resin material is made of thermoplastic resin. The resin material has heat resistance equivalent to that of the base material of the member to be joined. The resin material may contain reinforcing fibers.

As the resin material, two or more kinds of materials may be combined. For example, a material with a melting point lower than that of the base material is combined with the same material as the base material. In this case, the resin material should preferably have a three-layer structure (a structure in which two resin materials made of a material having a lower melting point than the base material sandwich a resin material made of the same material as the base material).

The thermoplastic resin used for the resin material is preferably made of the same material as the base material.

The resin material has a surface (imitation surface) that imitates the shape of the surface to be joined of the member to be joined in which the resin material is to be interposed. The simulated surface can be formed by measuring the surface to be bonded of the member to be bonded after the smoothing process using a mold using a resin material or the like or by using a three-dimensional scanner or the like, and by simulating the surface based on the measurement result.

For large members such as skin-stringers, it is difficult to obtain the precision of individual parts. If the precision of the part is not good, there is a concern that even if the resin film is interposed and the heat and pressure are applied, a gap that cannot be completely filled will remain. In this embodiment, a resin material having a surface shape that follows the gap between the members to be joined is used, and the resin material is arranged so as to match the shape of the surfaces to be joined. As a result, the gap generated between the surfaces to be joined can be more reliably filled, thereby improving the joining strength.

Note that the heating in the first to third embodiments may be performed by applying ultrasonic vibrations.

When pressure and ultrasonic vibration are applied to the superimposed members to be joined, frictional heat is generated at a portion (joining portion) where the surfaces to be joined are in contact with each other. Due to this frictional heat, the chemical reaction between the functional groups progresses, and the members to be joined are joined together.

The pressure and ultrasonic vibration are applied under conditions that do not melt the thermoplastic resin contained in the members to be joined due to frictional heat. Therefore, changes in the plate thickness and shape of the members to be joined can be suppressed.

In addition, by applying pressure and ultrasonic vibration, the surfaces to be joined become more familiar with each other, and stronger joining can be expected. By blending the surfaces to be bonded together, even when the surfaces to be bonded have irregularities, the gap generated between the surfaces to be bonded can be reduced. The smaller the gap, the closer the distance between the functional groups, creating an environment that facilitates chemical reactions. In addition, since ultrasonic vibration activates the molecular motion of functional groups, the probability of encountering a reaction partner increases.

<Appendix>
For example, the joining method described in each embodiment described above is grasped as follows.

The present disclosure relates to a joining method for joining members to be joined (1, 2, 11, 13) made of a fiber-reinforced thermoplastic whose base material is a thermoplastic resin. In the joining method according to the present disclosure, (S1, S11) smoothing the surface of the member to be joined, (S2, S12) activating the smoothed surface, and (S3, S13) activating. (S4, S14) heating and pressurizing the superimposed members to be joined so that the temperature of the base material is maintained below the melting point; , are joined by chemical bonding.

In one aspect of the above disclosure, the smoothing treatment can be performed by polishing.

The surfaces of the members to be joined that have undergone the activation treatment are activated, and functional groups are generated on the surfaces. By matching the surfaces on which the functional groups are generated and applying heat and pressure, adjacent functional groups are bonded by chemical reaction. Thereby, the members to be joined are joined together.

In the above disclosure, by smoothing the surfaces of the members to be joined (surfaces to be joined), it is possible to eliminate or reduce the gap that occurs between the surfaces to be joined when they are overlapped. Eliminating the gap increases the area where the opposing surfaces can contact each other. Further, when the gap is small, the functional groups on the facing surfaces are close to each other so that they can chemically react with each other, increasing the probability of encountering a reaction partner. The bonding strength between the surfaces to be bonded is improved by increasing the chemical bonds between the functional groups on the facing surfaces.

In the smoothing treatment, not only the unevenness of the surfaces to be joined but also the contaminants adhering to the surfaces can be removed. As a result, inhibition of the activation process by contaminants can be reduced, so that the surfaces to be joined can be sufficiently activated. By aligning the activated surfaces to be joined and joining them together, stronger joining can be realized.

Since the heating and pressurization disclosed above are performed so that the temperature of the base material does not exceed the melting point, the base material of the members to be joined does not melt. As a result, changes in plate thickness and shape can be suppressed, and the occurrence of waviness in the fibers can also be reduced.

In the above disclosure, since members to be joined are joined together by chemical bonding without using an adhesive, material costs can be reduced.

In one aspect of the above disclosure, both surfaces of the thermoplastic resin film (12) are activated, and the activated resin film is interposed between the two members to be joined (11, 13). , the member to be joined may be joined.

Heating and pressurizing the resin film made of thermoplastic resin activates the molecular motion and reduces the rigidity. Therefore, the resin film interposed between the members to be joined can enter recesses on the surfaces of the members to be joined by heating and pressurizing. When the gap between the members to be joined is filled, the contact area increases and the gap becomes smaller, thereby increasing the joint strength.

Since both surfaces of the resin film are activated, the resin film can be chemically bonded to the member to be joined in contact therewith.

In one aspect of the above disclosure, both surfaces of a resin material made of a thermoplastic resin having a simulated surface that follows the shape of the surface of the member to be joined are activated, and the shape of the surface of the member to be joined and the shape of the surface of the member are activated. The members to be joined may be joined by interposing the resin material subjected to the activation treatment between the two members to be joined by aligning the surfaces so that the shapes of the surfaces of the resin materials match.

Thereby, the gap can be more reliably filled and the bonding strength can be improved.

1, 2, 3, 4, 11, 13 member to be joined 12 resin film

Claims (4)

A joining method for joining members to be joined, wherein the members to be joined are made of a fiber-reinforced thermoplastic whose base material is a thermoplastic resin,
Smoothing the surface of the member to be joined,
activating the smoothed surface to introduce active functional groups capable of causing chemical bonding ;
overlapping the two members to be joined with the activated surfaces facing each other;
heating and pressurizing the members to be joined in a state of being overlapped so that the temperature of the base material is maintained below the melting point;
A joining method that joins by chemical bonding. The joining method according to claim 1, wherein the smoothing treatment is performed by polishing. Both sides of the resin film made of thermoplastic resin are subjected to the activation treatment,
interposing the activated resin film between the two members to be joined;
3. The joining method according to claim 1, wherein the members to be joined are joined. Both surfaces of a resin material made of a thermoplastic resin having a simulated surface that follows the shape of the surface of the member to be joined is subjected to the activation treatment,
Aligning the shape of the surface of the member to be joined with the shape of the surface of the resin material so that the shape of the surface of the resin material is aligned, interposing the activated resin material between the two members to be joined;
3. The joining method according to claim 1, wherein the members to be joined are joined.

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