Sheet-like semi-finished product with a plastic matrix

Abstract

This invention provides a sheet-like semi-finished product having a plastic matrix. The invention relates to a sheet-like semi-finished product comprising a matrix having at least one potentially reactive plastic composition, said plastic composition being curable to obtain an elastomer, particularly a thermoplastic elastomer, and fibers embedded in the matrix. The invention also relates to a method for preparing the sheet-like semi-finished product.

Description

[0001] This application is a divisional application of the invention patent application PCT / EP2018 / 066509, filed on June 21, 2018, entitled "Sheet-shaped semi-finished product with plastic matrix", which entered the Chinese national phase on December 19, 2019, with application number 201880041107.7. Technical Field

[0002] This invention relates to sheet-like semi-finished products according to the preamble of the independent claims, methods for preparing sheet-like semi-finished products, and uses of sheet-like semi-finished products. Background Technology

[0003] Fiber-reinforced plastics are becoming increasingly important in the fabrication of structural components. These components are particularly suitable for manufacturing racing cars, spacecraft, rail vehicles, and aircraft. For example, for the same performance, these components are lighter than conventional components made of steel, aluminum, or wood, resulting in savings in energy and fuel consumption.

[0004] Fiber-reinforced plastics can be prepared, for example, by embedding fibers into a polymer matrix and subsequently curing the latter. Thermosetting resin systems primarily serve as the polymer matrix. Alternatively, fibers and resins can be combined with suitable hardeners and stored in an uncured state. Crosslinking to form fiber-reinforced plastics then occurs only at a later point in time. Epoxy resins are typically used as the resin. However, due to the presence of hardeners and accelerators in the resin matrix, they are only stable for a limited time during storage. To avoid premature crosslinking, such reaction systems are stored at low temperatures (approximately -20°C) and must be thawed before further processing.

[0005] WO 2015 / 097097 A1 describes a storage-stable prepreg based on epoxy resin, which is cured by a crosslinking agent to form a thermosetting material. Here, storage stability is achieved by physically separating the reactive resin and crosslinking agent after drying. The components can then be mixed by increasing the temperature so that all compounds are present in a molten state. However, these potentially reactive epoxy resins result in relatively long pressing times at relatively high temperatures during prepreg processing. Longer pressing times and higher processing temperatures also affect the types of fibers that can be used. Low-melting-point fiber types such as polyamide, polyethylene, or polyester cannot be used. Furthermore, it is possible to cure only to produce a thermosetting material. However, a disadvantage of thermosetting materials is that they tend to fracture and crack under high transient mechanical stress, leading to material weakening.

[0006] WO 99 / 29755 describes a method for preparing storage-stable, potentially reactive layers and powders of dispersions or aqueous solutions of surface-deactivated solid polyisocyanates and isocyanate reactive polymers that can be used as adhesives and coatings.

[0007] WO 2013 / 139704 discloses storage-stable prepregs (prepreg fibers) based on low-viscosity polyurethane systems and flat fiber composite parts (molded articles, composite parts) prepared therefrom, which are obtained by impregnation methods for fiber-reinforced materials such as woven fabrics and nonwoven fabrics.

[0008] Potential reactive polymer compositions based on isocyanates and / or polyurethanes are also disclosed in WO 03 / 016374, WO 2016 / 205254 and WO 2016 / 205255.

[0009] However, existing technologies lack sheet-like semi-finished products that can be stored for long periods and have high stiffness and strength values, which can be ensured, for example, by using continuous fibers. Summary of the Invention

[0010] Therefore, one object of the present invention is to overcome the shortcomings of the prior art. In particular, one object of the present invention is to provide a sheet-like semi-finished product that exhibits a shortened curing processing time and is resistant to high transient mechanical forces after curing. The semi-finished product should be stable for storage over a relatively long period. Another object of the present invention is to provide a method for preparing such a sheet-like semi-finished product and the use of such a product.

[0011] This objective is achieved by the apparatus, method, and use as defined in the independent claims. Further embodiments can be derived from the dependent claims.

[0012] This invention provides a sheet-like semi-finished product, comprising:

[0013] - A matrix comprising at least one potentially reactive polymer composition, said polymer composition comprising polyurethane and a potentially reactive isocyanate, particularly encapsulated, surface-deactivated or blocked isocyanate, said polymer composition being curable to obtain an elastomer, particularly a thermoplastic elastomer;

[0014] - Continuous fibers embedded in a matrix, wherein the fibers are preferably unidirectionally oriented.

[0015] Here, "embedded" is interpreted as a macroscopic view, i.e., a view from the outside. "Embedded" specifically refers to impregnation. The fiber is wrapped in a matrix. Wrapping can be achieved, for example, by spraying the matrix or by pulling the fiber through a matrix solution.

[0016] The semi-finished product of the present invention has the advantage that the fibers are completely impregnated, i.e., surrounded by a polymer matrix. The semi-finished product can be stored at room temperature for a long time before further processing (i.e., molding and curing).

[0017] Furthermore, the semi-finished product of the present invention is suitable for preparing fiber composite material parts with high resistance to mechanical forces.

[0018] The resistance to mechanical forces comes from the use of continuous fibers. These fibers increase the stiffness and strength of the composite material.

[0019] For the purposes of this patent application, continuous fiber refers to all fibers with a length ≥ 50 mm.

[0020] The fibers are preferably unidirectional. Here, "unidirectional" means that the longitudinal axes of a single fiber extend substantially parallel to each other. For the purposes of this invention, "substantially parallel" means that the angle between the longitudinal axes of the fibers is no greater than ±25°. The angle between the longitudinal axes of the fibers is preferably less than ±10°.

[0021] The advantage of unidirectional semi-finished products is that they can be layered in a targeted manner along the direction of force. When multiple sheet-like semi-finished products with unidirectionally oriented fibers in each case are placed on top of each other in a rotating manner, particularly good resistance to mechanical forces from all sides is achieved.

[0022] Fibers can be based on proteins, cellulose, synthetic polymers, or inorganic substances.

[0023] Protein-based fibers can be selected from: wool, silk, Angolan goat hair, cashmere, casein, collagen, ardein, and zein.

[0024] Cellulose fibers can be cotton and bast fibers such as cotton, flax, hemp, or jute. Cellulose fibers can also be wood-based, such as viscose, modal, lyocell, cuprammonium, and acetate.

[0025] Fibers composed of synthetic polymers can be selected from: polyethylene, polyester; polyamide; aromatic polyamide; polypropylene; polyurethane (Elastan); acrylic acid; polytetrafluoroethylene; polyphenylene-2,6-benzodioxazole; liquid crystal polymers (LCP), especially poly(p-hydroxybenzoic acid-co-hydroxy-6-naphthoic acid).

[0026] Fibers composed of inorganic materials include carbon, ceramics, glass, silicon dioxide, and metals.

[0027] Fibers can be embedded in a matrix as single fibers, or they can be pre-spun to obtain yarn and embedded as yarn. Similarly, fibers can be processed to obtain yarn, and then a woven fabric is obtained, in which the fibers are embedded. Filaments can also be embedded. Here, filaments are synthetic fibers of any length. Combinations of different fibers can also be conceived.

[0028] The ability to use various types of fibers opens up a wide range of applications. The properties of the product can be optimally matched to its intended use.

[0029] The polymer composition comprises polyurethane and a potentially active isocyanate. The isocyanate is preferably encapsulated, surface-deactivated, or blocked. Radiation-crosslinkable isocyanates are also conceivable. The ratio of polyurethane to isocyanate can be varied. For example, for surface-deactivated isocyanates, the following composition is conceivable: for 100 parts by weight (pbw) of polyurethane, 5 to 10 pbw of toluene 2,4-diisocyanate dimer (TDI dimer) can be added. Alternatively, 15 pbw of isophorone diisocyanate trimer (IPDI trimer) can be added to 100 pbw of polyurethane to prevent yellowing of the material. Blocked isocyanates can also be used. For example, 2 to 15 pbw of (dimethylpyrazole)-blocked hexamethylene 4,6-diisocyanate (HDI) trimer can be added to 100 parts by weight of polyurethane.

[0030] Potentially reactive isocyanates prevent the free OH groups of isocyanates and polyurethanes from reacting at room temperature. The sheet-like semi-finished product can be stored for extended periods at room temperature without difficulty. The reaction process, i.e., the reaction with surface-deactivated isocyanates, can be achieved by brief initiation at low temperatures (<120°C). However, blocked isocyanates, which are only activated at higher temperatures, such as above 120°C, can also be used. Molding operations (e.g., pressing, vacuum bagging, or autoclave) can be kept short. Short cycle times can be used, which has a positive impact on the fibers that can be used. Therefore, low-melting-point fiber types, such as polyamide, polyethylene, or polyester, can also be used.

[0031] The polymer composition is preferably in the form of an aqueous dispersion. The polymer composition may also be in the form of a powder or melt. The dispersion can be applied, for example, by spraying, doctor blade coating, impregnation, injection, and / or vacuum injection. However, fibers can also be drawn through the dispersion and spread in the process.

[0032] Dispersion promotes fiber spreading. This increases wettability, leading to optimal fiber incorporation and a high proportion of fibers in the matrix.

[0033] The polymer composition is essentially free of VOCs (volatile organic compounds). This improves occupational health when handling the polymer composition.

[0034] Surprisingly, it was discovered that a fabric-like feel could be obtained from unfolded fibers impregnated with a potentially reactive polymer composition using a vacuum bag method.

[0035] The cured semi-finished or final product, i.e., fiber composite component, can acquire other properties by adding other functional additives such as flame retardants, antimicrobial agents, adhesives, fluorescent agents or UV protectants, such as adhesives that increase affinity for metals or rubber or similar materials.

[0036] The fibers are arranged primarily longitudinally relative to the main area of ​​the semi-finished product.

[0037] The advantage of unidirectional semi-finished products is that they can be placed on top of each other in a targeted manner along the direction of force. After further processing (pressing, curing), strong and durable fiber composite parts can thus be obtained.

[0038] The fibers of the sheet-like semi-finished product are preferably unfolded.

[0039] Unfurled fibers are easier to wet, and fiber incorporation and therefore the proportion of fibers increase. A higher proportion of fibers improves the performance of fiber composite components.

[0040] Fiber unfolding also makes it possible to use different types of fibers in the semi-finished product. It is also conceivable to use different polymer compositions in the semi-finished product. Therefore, a variety of properties can be combined in the material.

[0041] Another aspect of the invention relates to a method for preparing a sheet-like semi-finished product, the sheet-like semi-finished product comprising a matrix, particularly a matrix as described above. The method includes the step of embedding fibers into the matrix. The matrix comprises at least one potentially reactive polymer composition, the polymer composition being curable to obtain an elastomer, particularly a thermoplastic elastomer.

[0042] The semi-finished products prepared in this way can be stored at room temperature for extended periods. In particular, the use of potentially reactive, encapsulated, surface-deactivated, or blocked isocyanates makes it possible to trigger activation only at high temperatures. This contrasts with two-component systems, where reactivity depends on the activation state of the catalyst. Such systems are typically reactive even at temperatures below 100°C, thus achieving only short-term storage stability.

[0043] The potentially reactive polymer composition can be cured at a temperature of 60 to 180°C, preferably 100 to 140°C.

[0044] Curing can occur after molding. For this purpose, the semi-finished product is optionally cut to size and introduced into molding tools, such as a press. Curing can occur simultaneously during the molding operation.

[0045] Compared to conventional methods, the reactivation temperature can be lower, thus making it possible to use low-melting-point fibers.

[0046] Fiber composite parts can then be removed from the molding tool and subjected to post-processing if necessary.

[0047] As summarized above, fibers can be based on proteins, cellulose, synthetic polymers, or inorganic substances. Combinations of various fibers in semi-finished products are also conceivable.

[0048] The properties of semi-finished products and fiber composite components can be controlled by the selection of fibers.

[0049] The polymer composition preferably comprises a polyurethane and a potentially reactive isocyanate. The isocyanate may be encapsulated, surface-deactivated, or blocked.

[0050] Potentially reactive isocyanates remain unreacted for extended periods at room temperature. Therefore, the resulting semi-finished product can be stored for months without difficulty before further processing. Reactivation can be carried out at relatively lower temperatures compared to conventional methods, reducing processing time and energy input.

[0051] Curing of this polymer composition yields an elastomer, particularly a thermoplastic elastomer, with both soft and hard segments. The resulting fiber composite component exhibits high final properties, such as cohesion, tensile strength, toughness, fatigue, and aging resistance. Compared to other fiber composites, the component is essentially stress-free.

[0052] The polymer composition is preferably an aqueous dispersion. However, powders and melts are also possible.

[0053] The dispersion allows for complete fiber impregnation. Drying the semi-finished product before storage releases virtually no environmentally polluting solvents.

[0054] The fibers are arranged longitudinally relative to the main area of ​​the semi-finished product.

[0055] Unidirectional semi-finished products can be layered on top of each other along the direction of force, resulting in good mechanical properties.

[0056] The fibers are preferably spread out, especially during the embedding process.

[0057] Different fibers can be spread out adjacent to each other, thus combining the properties of different fibers in a single semi-finished product. This further increases the ability to obtain a variety of fiber composite materials.

[0058] Furthermore, the increased fiber wettability is achieved through unfolding. Fiber incorporation is optimized. Individual fibers can also be coated with different polymer compositions. This allows for the combination of other properties in the semi-finished product.

[0059] In principle, unidirectional semi-finished products with a thickness of 1 to 100 μm, preferably 15 to 80 μm, and very particularly preferably 20 to 50 μm, can be prepared by the method described above. For example, such semi-finished products can be used to manufacture vehicles and vehicle parts, toys and sporting goods or tools, where low weight and / or ease of stretching are valued.

[0060] However, the present invention also provides a method for preparing a semi-finished product with a thickness of 100 μm to 1 mm, preferably 150 μm to 700 μm, and very particularly preferably 300 μm to 500 μm. This semi-finished product can be used to prepare components with high stability and robustness.

[0061] The fiber volume ratio of the unidirectional semi-finished product can be 1 to 99%, preferably 40 to 80%, and very particularly preferably 55 to 65%.

[0062] Another aspect of the present invention relates to sheet-like semi-finished products, particularly sheet-like semi-finished products that can be prepared or have been prepared as described above.

[0063] Sheet-shaped semi-finished products can consist of the same type of fibers embedded in a polymer matrix, different fibers embedded in a polymer matrix, the same type of fibers embedded in different polymer matrices, or different fibers embedded in different polymer matrices.

[0064] The properties of the semi-finished product can be adjusted according to its intended use. This semi-finished product is suitable for preparing various fiber composite material components. These components exhibit high resistance and long service life.

[0065] Another aspect of the invention relates to the use of the sheet-like semi-finished product described above in the manufacture of protective equipment, vehicle parts, sports and leisure products, tools, cases, machine parts, clothing and jewelry.

[0066] For example, protective equipment could be heat-resistant equipment for emergency services such as fire departments, or military clothing and equipment.

[0067] The semi-finished products of this invention are suitable for vehicle components in aerospace, as well as for automotive construction, rail vehicles, or ships. For example, the semi-finished products can be used to manufacture tires, hoses, clothing, and body parts, or as vehicle armor. Sheet-like semi-finished products containing a polymer matrix can, for example, be further used in textiles, such as sails.

[0068] Sports and leisure products include, for example, helmets, tennis rackets, harnesses, climbing harnesses, hockey sticks, skis, shoes, ski boots, bicycle racks, tents, stand-up paddleboards, and boards.

[0069] Other items that can be thought of include tool handles, grinding belts, conveyor belts and drive belts, toothed belts and drive straps, tensioning elements on cranes, ropes, suitcases, bags, and items such as jewelry, watches, and shoes made of multi-layered composite materials of gold and carbon fiber. Detailed Implementation

[0070] Two embodiments of the present invention are illustrated by the following examples.

[0071] Example 1

[0072] Composition of the dispersion:

[0073] Dispercoll® U XP 2702 (from Covestro AG) is an aqueous anionic dispersion of aliphatic polyurethane. Combined with an aqueous suspension of deactivated solid isocyanate Desmodur® LP BUEJ 471 (IPDI trimer from Covestro AG), a potentially reactive system is obtained with approximately 60% polyurethane and isocyanate content and approximately 40% water content.

[0074] Fibers are spread out to obtain sheet-like semi-finished products:

[0075] High-performance fibers are spread and impregnated using this dispersion, resulting in a unidirectional high-performance tape after drying at 45°C. The matrix material embedding the fibers remains potentially reactive at this point. High-strength and high-stiffness polyethylene fibers, such as Dyneema SK75 1760 dtex, are spread and impregnated at a speed of 5 m / min. After drying, one layer of this sheet-like semi-finished product has a density of approximately 15 g / m³. 2 The mass load is 60% fiber and 40% matrix.

[0076] Lamination to obtain textiles:

[0077] These semi-finished products can be laid into, for example, a four-layer laminate. The layer structure is preferably symmetrical with a fiber orientation of 90° / 0° / 0° / 90° (referred to as a cross-laminated layer). These laminates are cured in a vacuum bag at 100 mbar and 110°C for 10 minutes to obtain the composite material. During this process, the matrix is ​​activated to cure. The textile exhibits a mass load of approximately 60 g / m². 2 .

[0078] test:

[0079] The routine tests for this type of textile include:

[0080] (1) Tear propagation test (referred to as “trouser test”) using the method based on DIN EN ISO 13937-2, and (2) T-peel test using the method based on DIN EN ISO 11339. After sample preparation, the tests were conducted for 24 hours, and the samples were stored at 20°C and 65% relative humidity.

[0081] (1) Tear extension test:

[0082] A 75 mm longitudinal cut was made along the centerline of the 150 mm × 50 mm specimen. These specimens were then stretched at a test speed of 10 mm / min in a general-purpose testing machine. The textiles failed due to delamination under a maximum force of 146 (+ / - 10) N (sample number = 3).

[0083] (2) T-peel test:

[0084] Specimens with a length of approximately 150 mm and a width of 20 mm were cut to size. The initial crack was located between two layers with a fiber orientation of 0°. These specimens were further peeled in a general-purpose testing machine at a test speed of 50 mm / min. The T-peel force value of the above textiles was 1.7 (+ / -0.6) N / mm (sample number = 5).

[0085] For reference, comparable textiles were prepared using the dispersion composition according to the introductory section of Example 1, but without the addition of deactivated solid isocyanate. The maximum force obtained in the tear propagation test under the conditions described in Section (1) above was 81 (+ / -4) N (sample number = 3). The T-peel force was 1.0 (+ / -0.4) N / mm (sample number = 5) under the conditions described in Section (2) above.

[0086] Example 2

[0087] Composition of the dispersion:

[0088] An anionic aqueous polyurethane dispersion, Dispercoll® U XP 2702 (from Covestro AG), was formulated with a water-dispersible blocked isocyanate, Trixene Aqua B 201 (a (dimethylpyrazole) blocked hexamethylene 1,6-diisocyanate trimer from Lanxess), to obtain a potentially reactive system.

[0089] Fiber impregnation to obtain sheet-like semi-finished products:

[0090] Unidirectional carbon fiber tape (50 g / m²) was impregnated with this dispersion using a scraper. 2 (From TK-Industries). After drying, one layer of this sheet-like semi-finished product has approximately 85 g / m³. 2 The mass load is 50% fiber and 50% matrix.

[0091] Lamination to obtain textiles:

[0092] These semi-finished products can be laid into, for example, a 4-layer laminate. The layer structure is preferably symmetrical with a fiber orientation of 90° / 0° / 0° / 90° (referred to as a cross-layer). These laminates are cured in a vacuum bag at 100 mbar and 160°C for 30 minutes to obtain the composite material. During this process, the matrix is ​​activated to cure. The mass load of this textile is approximately 340 g / m². 2 .

[0093] test:

[0094] After sample preparation, testing was conducted for 24 hours, and the samples were stored at 20°C and 65% relative humidity. Tear propagation and T-peel tests were performed under the conditions shown in Example 1.

[0095] (1) Tear extension test:

[0096] The textile of Example 2 failed to delaminate under a maximum force of 52 (+ / -2) N (sample number = 3).

[0097] (2) T-peel test:

[0098] The textiles in Example 2 showed a T-peel force value of 2.7 (+ / -0.7) N / mm (sample number = 5).

[0099] For comparison, textiles were prepared using the dispersion composition from the introduction of Example 2, but without the addition of blocked isocyanate. The maximum force obtained in the tear propagation test under the conditions described in Section (1) above was 41 (+ / - 2) N (sample number = 3). Under the conditions described in Section (2) above, the T-peel force was 1.6 (+ / - 0.2) N / mm (sample number = 5).

Claims

1. A sheet-like semi-finished product, comprising: A matrix comprising at least one potentially reactive polymer composition, said polymer composition comprising a polyurethane and a potentially reactive isocyanate, said polymer composition being an aqueous dispersion and curable to obtain an elastomer; and Continuous fibers embedded in the matrix.

2. The sheet-like semi-finished product according to claim 1, wherein the fiber is based on protein, cellulose, synthetic polymer or inorganic substance.

3. The sheet-like semi-finished product according to claim 1, wherein the fibers are arranged substantially longitudinally relative to the main region of the semi-finished product.

4. The sheet-like semi-finished product according to claim 1, wherein the fibers are unfolded.

5. A method for preparing a sheet-like semi-finished product comprising a matrix, comprising the following steps: Continuous fibers are embedded in a matrix comprising at least one potentially reactive polymer composition, the polymer composition comprising polyurethane and a potentially reactive isocyanate, the polymer composition being an aqueous dispersion and curable to obtain an elastomer.

6. The method of claim 5, wherein the potentially reactive polymer composition is cured at a temperature of 60 to 180°C.

7. The method of claim 5, wherein the fiber is based on protein, cellulose, synthetic polymer or inorganic substance.

8. The method of claim 5, wherein the fibers are arranged longitudinally relative to the main region of the sheet-like semi-finished product.

9. The method of claim 5, wherein the fibers are unfolded.

10. The sheet-like semi-finished product of claim 1, wherein the potentially reactive isocyanate is encapsulated, surface-deactivated, or blocked.

11. The sheet-like semi-finished product according to claim 1, wherein the polymer composition can be cured to obtain a thermoplastic elastomer.

12. The sheet-like semi-finished product according to claim 1, wherein the continuous fibers embedded in the matrix are unidirectionally oriented.

13. The method of claim 5, wherein the at least one potentially reactive polymer composition is cured to obtain a thermoplastic elastomer.

14. The method of claim 5, wherein the potentially reactive polymer composition is cured at a temperature of 100 to 140°C.