Weldable thermoplastic synthetic composite

Abstract

To disclose use of a low Tg compatible resin as an adhesive layer for welding a thermoplastic composite structure to a thermoplastic or thermoset structure.SOLUTION: The present invention is especially suitable for welding large parts such as wind turbine halves and spar caps. A useful thermoplastic composite is one formed by infusion and curing of long fibers by a reactive acrylic liquid resin-based material such as an ELIUM (R) resin-based material from Arkema.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to the use of low Tg compatible resins as adhesive layers for welding thermoplastic or thermoset composite parts to other thermoplastic or thermoset parts, or to metal parts. The invention is particularly useful for welding thermoplastic composite parts to other thermoplastic parts, especially very large parts such as wind turbine blade sections. [Background technology]

[0002] Mechanical or structural components that must absorb high stresses during use are widely manufactured from composite materials. Composite materials are macroscopic combinations of two or more materials. Typically, composites contain a matrix material that forms the continuous phase for structural cohesion and reinforcement materials with varying structures for mechanical properties.

[0003] Composite materials are widely used in several industrial sectors, such as construction, automotive, aerospace, transportation, leisure, electronics, and sports. Composite materials are often thought to offer better mechanical performance (e.g., higher tensile strength, higher tensile modulus, higher fracture toughness, etc.) compared to less dense homogeneous materials.

[0004] On a commercial industrial scale, the most important class of composites by volume are composites with organic matrices, where the matrix material is a polymer. The primary matrix or continuous phase of a polymer composite is typically either a thermoplastic or a thermosetting polymer. In a typical example of polymer composite production, a prepolymer is typically mixed with another component, such as glass beads or fibers, which are wetted or impregnated with the prepolymer, and then the composition is post-cured.

[0005] A thermoset polymer matrix is ​​rigid. A thermoplastic polymer softens or loses viscosity when heated and can assume a new shape through the application of heat and / or pressure.

[0006] Composite articles are often manufactured from two or more parts or structures that must be combined together to form the final article. For example, a hollow wind turbine blade is first formed by forming the top and bottom of the wind turbine blade, as well as a spar cap that runs between the top and bottom pieces to provide mechanical stability and strength. These structures are then bonded together at their respective interfaces to form a strong final article. Currently, the majority of bonding of composite pieces is done using adhesives. Several welding methods have been used to join thermoset components, including the use of smart susceptors (U.S. Patent Application Publication No. 2017 / 0165902), ultrasonic welding (U.S. Patent Application Publication No. 2017 / 0355150), and resistance implant welding (U.S. Patent Application Publication No. 2018 / 0178457).

[0007] assignment It would be desirable to bond large thermoplastic or thermoset composite pieces together without the use of adhesives to avoid the use of dissimilar materials in the final article. Currently, large composite pieces are bonded together by adhesives. With large pieces, it is impractical to use an external energy source or to heat the entire structure simply to heat the interface materials. Furthermore, some welding methods, such as using heated plates between the surfaces to be joined, require a step of fitting the pieces together after heating, a nearly impossible challenge for very large pieces.

[0008] Another problem with composite materials, including thermoplastic and thermoset composites, is that there is generally not enough matrix material available to form a strong weld. This problem is amplified in thicker materials where surface area tolerances are less stringent and gaps between pieces are uneven, leaving areas of the interface with larger gaps to fill for complete surface coverage.

[0009] Extra material may be added as an interlayer for welding, however, it has been found that interlayers made solely from composite matrix resins are often too brittle to function as effective interlayers and are prone to fracture.

[0010] solution It has now been discovered that low Tg thermoplastic polymer compositions that are compatible with the structures being welded together can be used as an interlayer in an effective welding process, which is particularly effective when welding composite structures to thermoplastic or thermoset structures, or metal components, especially thermoplastic composite structures.

[0011] The compatible low Tg interlayer thermoplastic composition can be heated to flow and bond the composite structure, making this interlayer and welding method particularly useful for forming wind turbine blades and other large composite structures. Summary of the Invention

[0012] While embodiments have been described herein in a manner that enables a clear and concise specification to be written, it is intended, and will be understood, that the embodiments can be combined or separated in various ways without departing from the invention. For example, it will be understood that all preferred features described herein are applicable to all aspects of the invention described herein.

[0013] In a first aspect, the present invention relates to an interlayer polymer composition for welding a thermoplastic or thermoset composite structure (1) to a thermoplastic or thermoset structure, or to a metal part (2), wherein the interlayer comprises a thermoplastic polymer having a Tg of less than 100°C, preferably less than 95°C, preferably less than 90°C, more preferably less than 85°C, more preferably less than 80°C, less than 75°C, or even less than 70°C.

[0014] In a second embodiment, the intermediate layer polymer composition of embodiment 1 comprises a (meth)acrylic polymer or copolymer, a styrenic, polyvinylidene fluoride, a polyolefin, polyvinyl chloride (PVC), polyurethane (PU) polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), a polystyrenic (including high impact polystyrene (HIPS)), a functionalized polyolefin, a vinyl ester, a poly(vinyl ester) polyester, and mixtures thereof, preferably a (meth)acrylic polymer or copolymer.

[0015] In a third embodiment, the interlayer polymer composition of embodiment 1 or 2 may further contain from 1 to 60 weight percent, preferably from 10 to 40 weight percent, of an impact modifier based on the total interlayer polymer composition.

[0016] In a fourth embodiment, the interlayer polymer composition of the previous embodiment may contain one or more functional polymers, the functionality preferably being selected from the group consisting of epoxy, carboxylic acid, and anhydride.

[0017] In a fifth aspect, a composite structure is provided, the composite structure comprising: a) a structure 1 that is a thermoplastic or thermoset composite; b) an intermediate layer composition comprising a thermoplastic polymer having a Tg of less than 100°C, preferably less than 95°C, preferably less than 90°C, more preferably less than 85°C, more preferably less than 80°C, less than 70°C, and even less than 60°C, 50°C, and 40°C; c) Structure 2, in turn, wherein the outer structure is a thermoplastic or thermosetting polymer, or a metal part.

[0018] In a sixth embodiment, the composite structure of embodiment 5 has both Structure 1 and Structure 2 as thermoplastic composites.

[0019] A seventh aspect of the invention is a method for welding a composite structure (1) to a thermoplastic or thermoset structure (2), comprising: a) placing a thermoplastic interlayer composition between and in direct contact with a composite structure (1) and a thermoplastic or thermoset structure or metal part (2), said interlayer comprising a thermoplastic polymer having a Tg of less than 95°C, preferably less than 90°C, more preferably less than 85°C, more preferably less than 80°C; b) applying energy to an effective amount of the thermoplastic interlayer composition to melt the thermoplastic interlayer composition and weld Structure 1 to Structure 2; c) removing the energy and allowing the resulting welded article to cool.

[0020] In an eighth aspect, the welding method of aspect 7 includes a welding method selected from hot gas welding, hot wedge welding, extrusion welding, hot plate welding, infrared welding, laser welding, spin welding, stir welding, vibration welding, ultrasonic welding, resistance / implant / electrofusion welding, induction welding, dielectric welding, and microwave welding.

[0021] In a ninth embodiment, the welding method of embodiments 7 and 8 includes embedding a susceptor in the interlayer composition prior to disposing the interlayer between structure 1 and structure 2. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention relates to low Tg interlayer compositions used to weld together two or more structures, at least one of which is a composite material, preferably a thermoplastic composite. The present invention also relates to a welding method using the novel interlayer low Tg compositions, and to a composite article formed by welding together at least two structures, at least one of which is a thermoplastic composite structure, using the novel interlayer compositions.

[0023] All references cited herein are incorporated by reference. Unless otherwise specified, all molecular weights are weight average molecular weights as determined by gas permeation chromatography (GPC) and all percentages are weight percent.

[0024] The term "copolymer" as used herein refers to polymers composed of two or more different monomer units, including two comonomers, terpolymers, and polymers having three or more different monomers. Copolymers may be random or block, heterogeneous or homogeneous, and may be synthesized by batch, semi-batch, or continuous processes.

[0025] As used herein, "(meth)acrylic" or "(meth)acrylate" refers to both acrylate and methacrylate.

[0026] The interlayer compositions of the present invention contain at least one low Tg thermoplastic polymer resin that is compatible with the structures that are intended to be welded together.

[0027] Low Tg, as used herein, means a glass transition temperature as measured by DSC in N2 at a heating rate of 10°C / min, where Tg is less than 120°C, 110°C, preferably less than 95°C, preferably less than 90°C, more preferably less than 85°C, more preferably less than 80°C, preferably less than 75°C, even less than 70°C, less than 60°C, less than 50°C, or even less than 40°C. The Tg of the interlayer is lower than the Tg of the matrix polymer of the thermoplastic composite, preferably by at least 15°C, more preferably by at least 10°C, or even less than 20°C.

[0028] As used herein, "compatible polymers" refers to polymers that are immiscible with each other but that, as a blend, exhibit macroscopically uniform physical properties. The macroscopically uniform properties are generally caused by sufficiently strong interactions between the component polymers.

[0029] As used herein, "miscible polymer" refers to two or more polymers that form a homogeneous polymer blend that is a single-phase structure with a single glass transition temperature.

[0030] Useful interlayer polymers for use with acrylate-based thermoplastic composite structures include, but are not limited to, (meth)acrylate polymers and copolymers (available from Arkema), styrenics, polyvinylidene fluoride, polyolefins, polyvinyl chloride (PVC), polyurethane (PU) polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polystyrenics (including high impact polystyrene (HIPS)), functionalized polyolefins, vinyl esters, poly(vinyl esters), polyesters, and mixtures thereof.

[0031] As used herein, acrylic polymers include, but are not limited to, homopolymers, copolymers, and terpolymers containing alkyl (meth)acrylate monomer units. The alkyl methacrylate monomer is preferably methyl methacrylate, which may comprise 30 to 95 weight percent of the monomer mixture. 5 to 70% of other acrylates, methacrylates, and / or other vinyl monomers may also be present in the monomer mixture. Other methacrylates, acrylates, and other vinyl monomers useful in the monomer mixture include, but are not limited to, methyl acrylate, ethyl acrylate and methacrylate, butyl acrylate and methacrylate, isooctyl methacrylate and acrylate, lauryl acrylate and methacrylate, stearyl acrylate and methacrylate, isobornyl acrylate and methacrylate, methoxyethyl acrylate and methacrylate, 2-ethoxyethyl acrylate and methacrylate, dimethylaminoethyl acrylate and methacrylate monomers, styrene and its derivatives.

[0032] As used herein, styrenic polymers include, but are not limited to, polystyrene, high impact polystyrene (HIPS), acrylonitrile-butadiene-styrene (ABS) copolymers, acrylonitrile-styrene-acrylate (ASA) copolymers, styrene-acrylonitrile (SAN) copolymers, methacrylate-acrylonitrile-butadiene-styrene (MABS) copolymers, styrene-butadiene copolymers (SB), styrene-butadiene-styrene block (SBS) copolymers and their partially or fully hydrogenated derivatives, styrene-isopropene copolymers, styrene-isoprene-styrene (SIS) block copolymers and their partially or fully hydrogenated derivatives, styrene-(meth)acrylate copolymers, such as styrene-methyl methacrylate copolymers (S / MMA), and mixtures thereof. The styrenic copolymers of the present invention have a styrene monomer content of at least 10% by weight, preferably at least 25% by weight.

[0033] One skilled in the art can select the comonomer ratio to provide the desired low Tg copolymer.

[0034] The interlayer polymer matrix may also contain some functional monomer units that can be used to improve adhesive properties and provide crosslinking sites. Useful functional groups include, but are not limited to, epoxy, carboxylic acid, carboxylate, amine, siloxane, silicone, urethane, amide, and anhydride groups. Note that functional groups generally increase the Tg of the copolymer or terpolymer, so monomers with sufficiently low Tg must be included to offset the Tg-increasing functional monomers. A low level of crosslinking can provide better fatigue resistance and thermal stability.

[0035] The interlayer composition needs a low Tg to provide flowability of the interlayer composition between the structures being welded and to increase the ductility of the interlayer, which results in better adhesion.

[0036] A low Tg interlayer composition refers to the Tg of the entire interlayer composition, including the polymer and additives. Those skilled in the art will recognize that additives, such as plasticizers, are added to polymer compositions to provide a lower Tg for the composition. Furthermore, because a low Tg is desirable to allow the polymer composition to flow into the interface between adjacent polymer structures, the low Tg composition may be a compatible blend of a low Tg polymer with a higher Tg polymer, such as a blend of polylactic acid and polymethyl methacrylate, available from Arkema under the trademark RNEW®.

[0037] Typical additives present in polymer formulations can be added to the intermediate layer composition at typical effective levels. These additives include, but are not limited to, stabilizers, plasticizers, fillers, antioxidants, antistatic agents, surfactants, colorants, UV stabilizers, and dispersing aids. Some of these additives, such as plasticizers, further help improve the ductility of the intermediate layer composition.

[0038] The impact modifier may be present at a level of 1 to 60 weight percent, preferably 10 to 40 weight percent, based on the total of the interlayer composition of the matrix polymer and all additives. Impact modifiers useful in the present invention include, but are not limited to, core-shell particles (both hard-core and soft-core), block copolymers, and graft copolymers. Impact modifiers can increase the ductility of the interlayer and improve welding performance.

[0039] As used herein, a core-shell impact modifier is a multi-stage, continuously produced polymer having a core / shell particle structure of at least two layers. Preferably, the core-shell modifier comprises three layers: a hard core layer, one or more intermediate elastomer layers, and a hard shell layer. The presence of the hard core layer provides a desirable balance of good impact strength and high modulus, which is not achieved with core / shell modifiers having a soft core layer.

[0040] The interlayer must be thick enough to fully contact the structures being welded. If it is not thick enough, it will not fill the gap between the structures being welded. For large parts, tolerances vary, and the interlayer must be able to fill the entire gap for best adhesion. Generally, the interlayer should be between 0.1 and 10 mm thick, preferably 0.2 to 5 mm, and more preferably 0.25 to 3 mm.

[0041] In one embodiment, the interlayer polymer is a liquid acrylic polymer / monomer system mixed with a polymerization initiator, similar to the composition of the matrix prepreg used to form the acrylic thermoplastic composite, as described below, and cures during the welding process.

[0042] structure As used herein, "Structures 1 and 2" refer to the structures directly adjacent either side of the weld formed by the interlayer. The layer of each structure that contacts the interlayer weld is referred to herein as the outer layer. Structures 1 and 2 may be single-layer or multi-layer structures.

[0043] At least one, and preferably both, of Structures 1 and 2 are composites. A preferred thermoplastic composite is a fiber-reinforced thermoplastic, such as the cured ELIUM® resin system manufactured by Arkema. The ELIUM® resin system is (a) a polymeric thermoplastic (meth)acrylic matrix consisting of at least one acrylic copolymer containing at least 70% by weight of methyl methacrylate monomer units and 0.3 to 30% by weight of at least one monomer having at least one ethylenic unsaturation copolymerizable with methyl methacrylate; (b) at least 30 weight percent of a fibrous material as a reinforcement, based on the total weight of the polymer composite, the fibrous material comprising fibers having an aspect ratio of at least 1000 or having a two-dimensional macroscopic structure; and c) an initiator.

[0044] In a preferred embodiment, the fibrous material and the polymeric thermoplastic (meth)acrylic matrix are contacted prior to polymerization by wetting the fibrous material with a liquid syrup containing the monomers for forming the polymeric thermoplastic (meth)acrylic matrix, the liquid syrup having a kinematic viscosity at 25°C in a closed, opaque mold of 10 mPa*s to 10,000 mPa*s.

[0045] In a preferred embodiment, the welded composite article of the present invention includes at least one structure that is a thermoplastic polymer composite. The second structure (2) of the welded article may be a thermoplastic, a thermoset, a thermoplastic composite, a thermoset composite, or a metal. The welding method provides a means for attaching structures such as spar caps or auxiliary structures to the thermoplastic composite structure. Typical thermoset composite matrices include, but are not limited to, epoxies, vinyl esters, and polyurethanes.

[0046] In a preferred embodiment, both the first and second structures (1 and 2) are thermoplastic composites that can be of the same polymer chemistry or different chemistries. The chemistries of Structure 1 and Structure 2 do not have to be compatible with each other, provided that each structure (matrix polymer) is compatible with the intermediate layer.

[0047] The most preferred embodiment involves welding two thermoplastic composites of the same or nearly the same composition together, for example, the top and bottom halves of a wind blade.

[0048] The present invention contemplates the use of the interlayer to weld the following structures: a. Thermoplastic composite to thermoplastic composite b. Thermoplastic (non-composite) to thermoplastic composite c. Thermoplastic composites to thermoset composites d. Thermoplastic composites to thermoset non-composites e. Thermosetting composites to thermoplastic composites f. Thermoset composite to thermoset non-composite g. Thermosetting composites to thermoplastic non-composites h. Thermoplastic composites to metal parts i. Thermosetting composites to metal parts

[0049] The matrix polymer of each of the above structures must be compatible with the intermediate layer polymer composition. Compatibility between the matrix polymers of the structures is preferred, but not required.

[0050] Welding method An interlayer is used to weld two or more different structures together. Several different welding methods can be used, and the choice of welding method may depend on the size of the structure, available equipment, and other considerations. Some useful methods include, but are not limited to, hot gas welding, hot wedge welding, extrusion welding, hot plate welding, infrared welding, laser welding, spin welding, stir welding, vibration welding, ultrasonic welding, resistance / implant / electrofusion welding, induction welding, dielectric welding, and microwave welding. These methods can quickly join thermoplastic acrylic composites and provide bonds that meet desired mechanical performance.

[0051] In one embodiment, the welding method is a resistance or induction welding method that uses a susceptor, such as a stainless steel mesh powered by an external power source, to heat the interlayer and allow it to flow between the structures to be welded. The susceptor may be encapsulated in the interlayer composition before being inserted between the structures to be welded. The encapsulation may be by coating or fusion lamination, or layers of the interlayer may be placed on either side of the susceptor within the joint. In the case of a reactive liquid resin composition, the susceptor may be infused with the liquid reactive resin composition and cured to produce a single component at the mating contact surfaces.

[0052] In one embodiment, rubber strips can be placed on the sides of the welded area to reduce flow of the interlayer outside of the desired joint. [Example]

[0053] In each example, the Lap Shear Adhesion Test, ASTM D5868, is used.

[0054] Example 1 Two flat, 1 / 8-inch-thick composite sheets were fabricated by vacuum infusion using ELIUM® 188O system and biax glass fiber. The sheets were sandwiched together between a single layer of 0.5 mm acrylic film, Solarkote® P600, at an HDT of 63°C. The sandwich was placed in a Carver press with the upper platen heated to 197°C and the lower platen heated to 99°C. The platens were closed without applying pressure. After 1 minute, the sandwich was removed from the heated press and transferred to a cold Carver press where 1000 pounds of pressure was applied for 2 minutes. Lap shear testing of the resulting 0.2595-inch-thick panel resulted in a 27 MPA stress at break.

[0055] Example 2 Lap shear specimens were welded using a hot plate. In this case, the same ELIUM® resin-based infusion composite sheet used in Example 1 was placed on the hot plate with the same film sandwiched between them. The hot plate was heated to 250°C and a part temperature of 200°C was recorded. Clamps were used to hold the stack together and apply continuous pressure. The parts were heated for 2 minutes and then cooled for 2 minutes while clamped. Lap shear testing results showed a stress at break of 46 MPA for a 0.217 inch thick specimen.

Claims

1. 1. An interlayer polymer composition for welding a thermoplastic composite structure (1) to a thermoplastic or thermoset structure or to a metal part (2), comprising a thermoplastic polymer having a Tg of less than 120°C, 110°C, preferably less than 95°C, preferably less than 90°C, more preferably less than 85°C, more preferably less than 80°C, less than 75°C, even less than 70°C, less than 60°C, less than 50°C, or even less than 40°C, and which is compatible with said structures (1) and (2).

2. 10. The interlayer polymer composition of claim 1, wherein the interlayer comprises a primary polymer selected from the group consisting of (meth)acrylic polymers or copolymers, styrenics, polyvinylidene fluoride, polyolefins, polyvinyl chloride (PVC), polyurethane (PU), polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polystyrenics, high impact polystyrene (HIPS), functionalized polyolefins, vinyl esters, poly(vinyl esters), polyesters, and mixtures thereof.

3. 10. The interlayer polymer composition of claim 1 further comprising 1 to 60 weight percent, preferably 10 to 40 weight percent, of an impact modifier based on the total interlayer polymer composition.

4. The interlayer polymer composition of claim 1 comprising one or more functionalized polymers.

5. The interlayer polymer composition of claim 4 , wherein the functionality is selected from the group consisting of epoxy, carboxylic acid, anhydride, carboxylate, amine, siloxane, silicone, urethane, and amide groups.

6. The interlayer polymer composition of claim 1 , wherein the composition comprises a (meth)acrylic polymer or copolymer as the primary matrix polymer.

7. 10. The interlayer polymer composition of claim 1, wherein the composition further comprises one or more additives selected from the group consisting of stabilizers, plasticizers, fillers, antioxidants, antistatic agents, surfactants, colorants, UV stabilizers, and dispersing aids.

8. A composite structure comprising: a) Structure 1, which is a composite material; b) an intermediate layer composition comprising a thermoplastic polymer having a Tg of less than 120°C, 110°C, preferably less than 95°C, preferably less than 90°C, more preferably less than 85°C, more preferably less than 80°C, and less than 70°C; c) Structure 2, which is a thermoplastic polymer, a thermosetting polymer, or a metal structure or part; A composite structure that contains, in turn,

9. The composite structure of claim 8 , wherein both Structure 1 and Structure 2 are thermoplastic composites.

10. A method for welding a composite structure (1) to a thermoplastic or thermoset structure (2), comprising the steps of: a) placing a thermoplastic interlayer composition between and in direct contact with a thermoplastic composite structure (1) and a thermoplastic structure, a thermoset structure, or a metal component (2), said interlayer comprising a thermoplastic polymer having a Tg of less than 120°C, 110°C, preferably less than 95°C, preferably less than 90°C, more preferably less than 85°C, more preferably less than 80°C; b) applying energy to an effective amount of said thermoplastic interlayer composition to melt said thermoplastic interlayer composition and weld Structure 1 to Structure 2; c) removing said energy and allowing the resulting welded article to cool; A method comprising:

11. 11. The welding method of claim 10, wherein the welding method is selected from the group consisting of hot gas welding, hot wedge welding, extrusion welding, hot plate welding, infrared welding, laser welding, spin welding, stir welding, vibration welding, ultrasonic welding, resistance / implant / electrofusion welding, induction welding, dielectric welding, and microwave welding.

12. The welding method of claim 11 , selected from resistance welding or induction welding, including embedding a susceptor in the interlayer composition prior to placing the interlayer between structure 1 and structure 2.

13. The welding method of claim 12 , wherein the susceptor is embedded within the interlayer composition.