Weldable thermoplastic composite

Abstract

The present invention relates to the use of a low Tg compatible resin as an adhesive layer for welding thermoplastic composite structures to thermoplastic or thermoset structures. The invention is particularly good for welding large parts, such as wind turbine half shells and spar caps. Useful thermoplastic composites are those formed by infusion of long fibers with a reactive acrylic liquid resin system, such as the ELIUM® resin system from Arkema and cured.

Description

Technical Field

[0001] This invention relates to the use of low-Tg compatible resins as adhesive layers for welding thermoplastic or thermosetting composite components to other thermoplastic or thermosetting components or to metal components. This invention is particularly useful for welding thermoplastic composite components to other thermoplastic components, especially for very large components, such as wind turbine blade sections. Background Technology

[0002] Mechanical or structural components that must absorb high stresses during use are widely made of composite materials. Composite materials are macroscopic combinations of two or more materials. Typically, composite materials comprise a matrix material that forms a continuous phase for structural cohesion, and reinforcing materials that provide various structural features for mechanical properties.

[0003] Composite materials are widely used in several industrial sectors, such as construction, automotive, aerospace, transportation, leisure, electronics, and sports. Compared to homogeneous materials with lower density, composite materials are generally considered to offer better mechanical properties (e.g., higher tensile strength, higher tensile modulus, higher fracture toughness, etc.).

[0004] On a commercial industrial scale, the most important class of composite materials by volume are those with an organic matrix, where the matrix material is a polymer. The main matrix or continuous phase of polymer composites is typically a thermoplastic or thermosetting polymer. In a typical example of producing polymer composites, a prepolymer is usually mixed with another component, such as glass beads or fibers, which is then wetted or impregnated by the prepolymer, followed by curing of the composition.

[0005] Thermosetting polymer matrices are rigid. Thermoplastic polymers can soften or become less viscous when heated, and can take on new shapes by applying heat and / or pressure.

[0006] Composite articles are typically manufactured as two or more parts or structures that must be assembled to form the final product. For example, a hollow wind turbine blade is formed by first forming the upper and lower sections of the blade, plus a spar cap extending between the top and bottom sections to provide mechanical stability and strength. These structures are then bonded together at their respective interfaces to form a robust final product. Currently, most bonding of composite parts is done using adhesives. Several welding methods have been used to join thermoset components, such as ultrasonic welding (US 2017,0355150) and resistance implantation welding (US 2018 / 0178457), including the use of smart sensors (US 2017 / 0165902).

[0007] question:

[0008] The goal is to bond large thermoplastic or thermoset composite materials together without using adhesives, thus avoiding the use of any different materials in the final product. Currently, large composite parts are bonded together using adhesives. For large parts, using an external energy source or heating the entire structure to heat only the interface materials is impractical. Furthermore, some welding methods, such as using heating plates between the surfaces to be joined, require a step of assembling the parts after heating, which presents a near-impossible challenge for very large parts.

[0009] Another problem with composite materials, including thermoplastic and thermoset composites, is that there is often not enough matrix material available to form a strong weld. This problem is amplified in thick materials, where surface tolerances are less tight and the gaps between parts are uneven, resulting in larger gaps at the interfaces for complete surface coverage.

[0010] Additional materials can be added as interlayers for welding. However, interlayers made solely of composite matrix resin have been found to be too brittle to be used effectively and are prone to failure.

[0011] Solution:

[0012] It has been found that low-Tg thermoplastic polymer compositions compatible with the structures to be welded can be used as sandwich layers in effective welding methods. This is particularly effective when welding composite structures to thermoplastic or thermoset structures or metal parts, and especially for thermoplastic composite structures.

[0013] Low-Tg sandwich thermoplastic compositions can be heated and will flow and bond into composite structures. This sandwich and welding method is particularly useful in forming wind turbine blades and other large composite structures. Summary of the Invention

[0014] In this specification, embodiments have been described in a manner that allows for a clear and concise description; however, it is intended and will be understood that embodiments may be combined or separated in various ways without departing from the invention. For example, it should be understood that all preferred features described herein apply to all aspects of the invention as described herein.

[0015] In a first aspect, the present invention relates to a sandwich polymer composition for welding a thermoplastic or thermosetting composite structure (1) to a thermoplastic or thermosetting structure or metal component (2), the sandwich comprising a thermoplastic polymer with a Tg of less than 100°C, preferably less than 95°C, more 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.

[0016] In a second aspect, the sandwich polymer composition of aspect 1 comprises (meth)acrylic polymers or copolymers, styrene, polyvinylidene fluoride, polyolefins, polyvinyl chloride (PVC), polyurethane (PU), polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polystyrene (including high-impact polystyrene (HIPS)), functionalized polyolefins, vinyl esters, poly(vinyl esters), polyesters, and mixtures thereof, and preferably comprises (meth)acrylic polymers or copolymers.

[0017] In a third aspect, the sandwich polymer composition of aspect 1 or 2 may further contain an impact modifier of 1 to 60% by weight, preferably 10 to 40% by weight, based on the total sandwich polymer composition.

[0018] In the fourth aspect, the sandwich polymer composition described above may contain one or more functional polymers, with the functional groups preferably selected from epoxy groups, carboxylic acids, and acid anhydrides.

[0019] In a fifth aspect, a composite structure is provided, which has, in sequence:

[0020] a) Structure 1, wherein structure 1 is a thermoplastic composite material or a thermosetting composite material.

[0021] b) A sandwich composition comprising a thermoplastic polymer with a Tg of less than 100°C, preferably less than 95°C, more preferably less than 90°C, more preferably less than 85°C, more preferably less than 80°C, less than 70°C, even less than 60°C, 50°C, and 40°C, and

[0022] c) Structure 2, wherein the external structure is a thermoplastic polymer or thermosetting polymer, or a metal component.

[0023] In the sixth aspect, the composite structure of aspect 5 has both structure 1 and structure 2 as thermoplastic composite materials.

[0024] A seventh aspect of the present invention relates to a method for welding a composite structure (1) to a thermoplastic or thermosetting structure (2), comprising the following steps:

[0025] a) Placing the thermoplastic sandwich composition directly between and in contact with the composite structure (1) and the thermoplastic or thermosetting structure or metal component (2), wherein the sandwich comprises a thermoplastic polymer with a Tg less than 95°C, preferably less than 90°C, more preferably less than 85°C, and even more preferably less than 80°C, and

[0026] b) Apply an effective amount of energy to the thermoplastic sandwich composition to melt the thermoplastic sandwich composition, and weld structure 1 to structure 2.

[0027] c) Remove the energy and allow the resulting welded product to cool.

[0028] In the eighth aspect, the welding methods of aspect 7 include welding methods selected from hot gas welding, hot wedge welding, extrusion welding, hot plate welding, infrared welding, laser welding, rotary welding, stir welding, vibration welding, ultrasonic welding, resistance / implantation / electrofusion welding, induction welding, dielectric welding and microwave welding.

[0029] In the ninth aspect, the welding methods of aspects 7 and 8 include the step of embedding a sensor within the sandwich composition before placing the sandwich between structure 1 and structure 2. Detailed Implementation

[0030] This invention relates to a low-Tg sandwich composition for welding two or more structures together, wherein at least one structure is a composite material, preferably at least one structure is a thermoplastic composite material. The invention also relates to a welding method using this novel low-Tg sandwich composition, and composite articles formed by welding at least two structures together using this novel sandwich composition, wherein at least one structure is a thermoplastic composite structure.

[0031] All references cited in this article are incorporated herein by reference. Unless otherwise stated, all molecular weights are weight-average molecular weights determined by gas permeation chromatography (GPC), and all percentages are weight percentages.

[0032] As used herein, the term "copolymer" refers to a polymer composed of two or more different monomer units, including two comonomers, terpolymers, and polymers having three or more different monomers. Copolymers can be random or block copolymers, multiphase or homogeneous copolymers, and can be synthesized by batch, semi-batch, or continuous methods.

[0033] As used in this article, "(meth)acrylates" or "(meth)acrylates" refers to acrylates and methacrylates.

[0034] The sandwich composition of the present invention comprises at least one low Tg thermoplastic polymer resin compatible with the structure to be welded together.

[0035] The low Tg used in this article refers to the glass transition temperature, which is measured in DSC in N2 at a heating rate of 10°C / min, wherein the Tg is less than 120°C, 110°C, preferably less than 95°C, more preferably less than 90°C, more preferably less than 85°C, more preferably less than 80°C, more preferably less than 75°C, even less than 70°C, less than 60°C, less than 50°C, and even less than 40°C. The Tg of the interlayer is less than the Tg of the matrix polymer of the thermoplastic composite, preferably at least 15°C less, more preferably at least 10°C less, and even less than 20°C.

[0036] The term "compatible polymer" as used in this article refers to polymers that are immiscible with each other but exhibit macroscopically uniform physical properties as blends. Macroscopically uniform properties are typically caused by sufficiently strong interactions between the component polymers.

[0037] As used in this article, “miscible polymers” refers to two or more polymers that form a homogeneous polymer blend, which is a single-phase structure with a single glass transition temperature.

[0038] Useful sandwich polymers for acrylate-based thermoplastic composite structures include, but are not limited to, (meth)acrylate polymers and copolymers (available from Arkema), styrene, polyvinylidene fluoride, polyolefins, polyvinyl chloride (PVC), polyurethane (PU), polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polystyrene (including high-impact polystyrene (HIPS)), functionalized polyolefins, vinyl esters, poly(vinyl esters), polyesters, and mixtures thereof.

[0039] As used herein, acrylic polymers include, but are not limited to, homopolymers, copolymers, and terpolymers comprising (meth)acrylate alkyl ester monomer units. The alkyl methacrylate monomer is preferably methyl methacrylate, which may comprise 30 to 95% by weight of the monomer mixture. 5-70% of other acrylates, methacrylates, and / or other vinyl monomers may also be present in the monomer mixture. Other methacrylates, acrylates, and other vinyl monomers that may be used in the monomer mixture include, but are not limited to, methyl acrylate, ethyl acrylate and ethyl methacrylate, butyl acrylate and butyl methacrylate, isooctyl methacrylate and isooctyl acrylate, lauryl acrylate and lauryl methacrylate, stearyl acrylate and stearyl methacrylate, isobornyl acrylate and isobornyl methacrylate, methoxyethyl acrylate and methoxyethyl methacrylate, 2-ethoxyethyl acrylate and 2-ethoxyethyl methacrylate, dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate, styrene and its derivatives.

[0040] The styrene polymers used herein 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 copolymers (SBS) and their partially or fully hydrogenated derivatives, styrene-isopropylene 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 styrene copolymers of the present invention have a styrene monomer content of at least 10% by weight, preferably at least 25% by weight.

[0041] Those skilled in the art can select the comonomer ratio to provide the desired low Tg copolymer.

[0042] The sandwich polymer matrix may also contain functional monomer units, which can be used to improve adhesive properties and provide crosslinking sites. Useful functional groups include, but are not limited to, epoxy groups, carboxylic acids, carboxylic esters, amines, siloxanes, silicones, urethanes, amides, and anhydride groups. Note that functional groups generally increase the Tg of copolymers or terpolymers; therefore, sufficient low-Tg monomers must be included to offset the Tg-increasing functional monomers. Low levels of crosslinking can provide better fatigue properties and thermal stability.

[0043] The sandwich composition requires a low Tg to provide fluidity between the structures to be welded and also to increase the ductility of the sandwich – resulting in better adhesion.

[0044] A low-Tg sandwich composition refers to the Tg of the entire sandwich composition—including the polymer and additives. Those skilled in the art will recognize that additives such as plasticizers can be incorporated into the polymer composition to provide a composition with a lower Tg. Furthermore, since a low Tg is desired to allow the polymer composition to flow into the interface between adjacent polymer structures, a low-Tg composition can be a compatible blend of a low-Tg polymer and a higher-Tg polymer, such as a blend of polylactic acid and polymethyl methacrylate—available under the trademark RNEW® from Arkema.

[0045] Typical additives present in polymer formulations can be incorporated into sandwich compositions at typical effective levels. These additives include, but are not limited to, stabilizers, plasticizers, fillers, antioxidants, antistatic agents, surfactants, colorants, UV stabilizers, and dispersants. Some of these additives, such as plasticizers, further contribute to improving the ductility of the sandwich composition.

[0046] Impact modifiers can be present at a level of 1 to 60% by weight, preferably 10 to 40% by weight, based on the total sandwich composition of the matrix polymer and all additives. Impact modifiers that can be used in this invention include, but are not limited to, core-shell particles (hard and soft cores), block copolymers, and graft copolymers. Impact modifiers can increase the ductility of the sandwich and improve weldability.

[0047] As used herein, core-shell impact modifiers are multi-level, sequentially prepared polymers having a core / shell particle structure with 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 between impact strength and high modulus, which is not achievable with core / shell modifiers having a soft core layer.

[0048] The interlayer exists with a thickness sufficient to effectively and completely contact the structures being welded together. If the thickness is insufficient, it will not be able to fill the gap between the structures to be welded. For large components, tolerances are variable, and the interlayer must be able to fill the entire gap for optimal adhesion. Typically, the thickness of the interlayer should be 0.1 to 10 mm, preferably 0.2 to 5 mm, and more preferably 0.25 to 3 mm.

[0049] In one embodiment, the sandwich polymer is a liquid acrylic polymer / monomer system combined with a polymerization initiator, similar to the composition of a matrix prepreg used to form an acrylic thermoplastic composite, as described below, which cures during the welding process.

[0050] structure

[0051] As used herein, “structure 1 and 2” refers to structures located directly on either side of the weld formed by the interlayer. Each layer of the structure in contact with the interlayer weld is referred to herein as the outer layer. Structure 1 and 2 can be single-layer or multi-layer structures.

[0052] At least one, preferably both, of structures 1 and 2 is a composite material. The preferred thermoplastic composite material is a fiber-reinforced thermoplastic, such as the cured ELIUM® resin system from Arkema. The ELIUM® resin system is a system having the following characteristics:

[0053] (a) A polymeric thermoplastic (meth)acrylic matrix comprising at least one acrylic copolymer, said acrylic copolymer comprising 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 degree of olefinic unsaturation capable of copolymerizing with methyl methacrylate;

[0054] (b) A fiber material as a reinforcing material comprising at least 30% by weight of the total weight of the polymer composite, wherein the fiber material comprises fibers with an aspect ratio of at least 1000, or the fiber material has a two-dimensional macrostructure, and

[0055] c) Initiator.

[0056] In a preferred embodiment, prior to polymerization, the fiber material is brought into contact with the polymeric thermoplastic (meth)acrylic matrix by wetting the fiber material in a closed, opaque mold with a liquid slurry containing monomers for forming the polymeric thermoplastic (meth)acrylic matrix, wherein the liquid slurry has a dynamic viscosity of 10 mPa*s to 10000 mPa*s at 25°C.

[0057] In a preferred embodiment, the welded composite article of the present invention comprises at least one structure of a thermoplastic polymer composite material. The second structure (2) of the welded article may be a thermoplastic, thermosetting, thermoplastic composite, thermosetting composite, or metal. The welding method provides a means of attaching a structure, such as a spar cap or auxiliary structure, to a thermoplastic composite structure. Typical thermosetting composite matrices include, but are not limited to, epoxy resins, vinyl esters, and polyurethanes.

[0058] In a preferred embodiment, both the first and second structures (1 and 2) are thermoplastic composites, which may be the same polymeric chemicals or different chemicals. The chemicals of structure 1 and structure 2 do not need to be compatible with each other, as long as each structure (matrix polymer) is compatible with the sandwich layer.

[0059] The preferred embodiment involves welding two thermoplastic composite materials having the same or nearly the same composition, such as welding the upper and lower halves of a wind turbine blade.

[0060] This invention is intended to use sandwich panels to weld the following structures:

[0061] a. Thermoplastic composites to thermoplastic composites.

[0062] b. Thermoplastic (non-composite) to thermoplastic composite.

[0063] c. From thermoplastic composites to thermosetting composites.

[0064] d. From thermoplastic composites to thermosetting non-composite materials.

[0065] e. From thermosetting composites to thermoplastic composites.

[0066] f. From thermosetting composites to thermosetting non-composite materials.

[0067] g. Thermosetting composites to thermoplastic non-composite materials.

[0068] h. Thermoplastic composites to metal parts.

[0069] i. Thermosetting composite materials to metal parts.

[0070] The matrix polymer for each of the above structures needs to be compatible with the sandwich polymer composition. Preferably, but not necessarily, the matrix polymers of the structures are compatible with each other.

[0071] Welding methods

[0072] Sandwiches are used to weld two or more dissimilar structures together. Several different welding methods can be used, and the choice of method can 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, rotary welding, stir welding, vibration welding, ultrasonic welding, resistance / implantation / electrofusion welding, induction welding, dielectric welding, and microwave welding. These methods enable the rapid joining of thermoplastic acrylic composites and provide a bond that meets desired mechanical properties.

[0073] In one embodiment, the welding method is a resistance or induction welding method powered by an external power source, which uses a sensor, such as a stainless steel mesh, to heat the interlayer and allow it to flow between the structures to be welded. Before insertion between the structures to be welded, the sensor can be encapsulated with an interlayer composition. Encapsulation can be performed by coating or melt lamination, or layers of the interlayer can be placed on either side of the sensor within the joint. In the case of a reactive liquid resin composition, the sensor can be infused with the liquid reactive resin composition and cured to create a single component at the mating interface.

[0074] In one implementation, a rubber strip may be placed on the side of the area to be welded to reduce interlayer flow beyond the desired joint.

[0075] Example:

[0076] In each embodiment, the lap shear bond test, ASTM D5868, was used.

[0077] Example 1: Two flat, 1 / 8-inch thick composite sheets were prepared by vacuum infusion using the ELIUM® 188O system and biaxial glass fibers. A 0.5 mm thick monolayer acrylic film, Solarkote® P600, with an HDT of 63°C, was sandwiched between these sheets. The sandwich was placed in a Carver press with the top platen heated to 197°C and the bottom platen heated to 99°C. The plates were closed without pressure. After 1 minute, the sandwich was removed from the hot press and transferred to a Carver press at ambient temperature, where a pressure of 1000 psi was applied for 2 minutes. The resulting 0.2595-inch thick sheet exhibited a fracture stress of 27 MPa in the lap shear test.

[0078] Example 2: Overlap Shear Test Using a Hot Plate. In this case, a composite sheet infused with the same ELIUM® resin system as used in Example 1 was placed on a hot plate with the same film in between. The hot plate was heated to 250°C, and the part temperature was recorded as 200°C. The stack was held together using a clamp and continuous pressure was applied. The part was heated for 2 minutes while clamped, and then cooled for 2 minutes. The overlap shear test resulted in a fracture stress of 46 MPa for the 0.217-inch thick sample.

Claims

1. A sandwich polymer composition for welding a thermoplastic composite structure (1) to a thermoplastic or thermosetting structure or metal part (2), comprising a thermoplastic polymer with a Tg less than 120°C, wherein the sandwich polymer composition is compatible with the thermoplastic composite structure (1) and the thermoplastic or thermosetting structure or metal part (2), wherein the Tg of the sandwich polymer composition is at least 10°C lower than the Tg of the matrix polymer of the thermoplastic composite structure (1).

2. The sandwich polymer composition according to claim 1, comprising a thermoplastic polymer with a Tg less than 80°C.

3. The sandwich polymer composition according to claim 1, comprising a thermoplastic polymer with a Tg less than 40°C.

4. The sandwich polymer composition according to claim 1, wherein the sandwich polymer composition comprises a matrix polymer selected from (meth)acrylic polymers, styrene polymers, polyvinylidene fluoride, polyolefins, polyvinyl chloride (PVC), polyurethane (PU), poly(vinyl ester), polyesters, and mixtures thereof.

5. The sandwich polymer composition according to claim 4, wherein the sandwich polymer composition comprises a matrix polymer selected from (meth)acrylic copolymers, polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polystyrene, functionalized polyolefins, and mixtures thereof.

6. The sandwich polymer composition of claim 1, wherein the sandwich polymer composition further comprises an impact modifier comprising 1 to 60% by weight of the total sandwich polymer composition.

7. The sandwich polymer composition of claim 1, wherein the sandwich polymer composition further comprises an impact modifier comprising 10 to 40% by weight of the total sandwich polymer composition.

8. The sandwich polymer composition of claim 1, wherein the sandwich polymer composition comprises one or more functional polymers.

9. The sandwich polymer composition according to claim 8, wherein the functional polymer comprises a functional group selected from epoxy groups, carboxylic acids, acid anhydrides, carboxylic esters, amines, siloxanes, urethanes, and amide groups.

10. The sandwich polymer composition of claim 1, wherein the sandwich polymer composition comprises a (meth)acrylic polymer as a matrix polymer.

11. The sandwich polymer composition of claim 1, wherein the sandwich polymer composition further comprises one or more additives selected from stabilizers, plasticizers, fillers, antioxidants, antistatic agents, surfactants, colorants, UV stabilizers and dispersants.

12. A composite structure, comprising, in sequence: a) Structure (1), wherein structure (1) is a thermoplastic composite material, b) The sandwich polymer composition according to any one of claims 1-11, and c) Structure (2), wherein the structure (2) is a thermoplastic polymer, thermosetting polymer or metal structure or component.

13. The composite structure according to claim 12, wherein the structure (2) is a thermoplastic composite material.

14. A method for welding a thermoplastic composite structure (1) to a thermoplastic or thermosetting structure or metal component (2), comprising the following steps: a) Placing and contacting the sandwiched polymer composition directly between and with the thermoplastic composite structure (1) and the thermoplastic or thermosetting structure or metal component (2), wherein the sandwiched polymer composition is the sandwiched polymer composition according to any one of claims 1-11. b) Apply an effective amount of energy to the sandwich polymer composition to melt the sandwich polymer composition and weld the thermoplastic composite structure (1) to the thermoplastic or thermosetting structure or metal component (2), and c) Remove the energy and allow the resulting welded product to cool.

15. The method of claim 14, wherein the welding is selected from hot gas welding, hot wedge welding, extrusion welding, hot plate welding, infrared welding, laser welding, rotary welding, stir welding, vibration welding, ultrasonic welding, resistance / implantation / electrofusion welding, induction welding, dielectric welding, and microwave welding.

16. The method of claim 15, wherein the welding is selected from resistance welding or induction welding and wherein the method includes the step of embedding a sensor within the sandwich polymer composition before placing the sandwich polymer composition between the thermoplastic composite structure (1) and the thermoplastic or thermosetting structure or metal part (2).