Method for manufacturing a composite using a degradable membrane

Abstract

A method for manufacturing a composite is provided herein, including laying at least one reinforcement layer onto the inner surface of a mold, positioning a degradable membrane onto the outermost reinforcement layer of the at least one reinforcement layer, applying suction between the inner surface of the mold and the degradable membrane to press the at least one reinforcement layer towards the inner surface of the mold, covering the degradable membrane with at least one vacuum film, generating a vacuum in the region between the vacuum film and the mold, injecting resin into this region by means of vacuum, and letting cure the resin, initiating a degradation of the degradable membrane by provoking a physical or chemical change of the membrane material after having generated a vacuum in the region between the vacuum film and the mold and before the resin has cured completely.

Claims

1. A method for manufacturing a composite comprising: laying at least one reinforcement layer onto the inner surface of a mould, positioning a degradable membrane onto an outermost reinforcement layer of the at least one reinforcement layer, wherein the degradable membrane is made of a material having a lower air permeability than the at least one reinforcement layer, applying suction between the inner surface of the mould and the degradable membrane to press the at least one reinforcement layer towards the inner surface of the mould, covering the degradable membrane at least partly with at least one vacuum film, generating a vacuum in the region between the vacuum film and the mould, injecting resin into the region between the vacuum film and the mould by means of vacuum, and letting the resin cure and initiating a degradation of the degradable membrane by provoking a physical or a chemical change of the degradable membrane material after having generated a vacuum in the region between the vacuum film and the mould and before the resin has cured completely.

2. The method according to claim 1, wherein the degradation of the degradable membrane is initiated by a decomposing agent introduced as a gas into the vacuum or as part of the resin.

3. The method according to claim 1, wherein the resin comprises a solvent and the degradable membrane comprises a material which is dissolvable into the solvent-comprising resin.

4. The method according to claim 1, wherein the resin comprises styrene and the degradable membrane comprises a material comprising polystyrene.

5. The method according to claim 1, wherein the resin comprises an acrylate, a methacrylate or a diluent and the degradable membrane comprises a material dissolvable in the respective resin.

6. The method according to claim 1, wherein the degradation of the degradable membrane is initiated by applying water to the degradable membrane and wherein the degradable membrane comprises a material dissolvable or degradable in water.

7. The method according to claim 1, wherein the degradation of the degradable membrane is initiated by exposure of the degradable membrane to a chemical substance other than a solvent.

8. The method according to claim 1, wherein the degradation of the degradable membrane is initiated by heating the degradable membrane to a temperature above a predetermined temperature.

9. The method according to claim 1, wherein the degradation of the degradable membrane is initiated by provoking a sublimation of the degradable membrane.

10. The method according to claim 1, wherein the degradation of the degradable membrane is initiated by a change of the vacuum conditions in the region between between the vacuum film and the mould.

11. The method according to claim 1, wherein the degradation of the degradable membrane is initiated by exposure of the degradable membrane to light or by a molecular degradation.

12. The method according to claim 1, wherein the degradable membrane is either completely impermeable or partially permeable at the time the degradable membrane is positioned onto the outermost reinforcement layer of the at least one reinforcement layer.

13. The method according to claim 1, wherein the degradable membrane is rigid, stretchable, attached to a carrier medium and/or produced directly on top of the outermost reinforcement layer or on top of a carrier medium.

14. The method of claim 3, wherein the resin comprises an unsaturated polyester material.

15. The method of claim 3, wherein the degradable membrane material comprises a synthetic plastic material.

16. The method of claim 12, wherein the partially permeable degradable membrane is perforated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings show preferred configurations and do not limit the scope of the invention. The same reference numerals are used in the drawings for elements having the same function.

(2) FIG. 1 shows schematically a sectional view of a part of a stack of reinforcement layers, a degradable membrane and the mould during manufacturing

(3) FIG. 2 shows schematically a sectional view of reinforcement layers and a degradable membrane positioned in a mould for manufacturing a wind turbine blade

(4) FIG. 3 shows schematically a sectional view of a part of the final composite before removing the mould.

DETAILED DESCRIPTION OF INVENTION

(5) As shown by the part of the layer stack in FIG. 1, the method for manufacturing a composite includes laying at least one reinforcement layer 2, 3, 4 onto the inner surface of a mould 6.

(6) Further, a degradable membrane 1 is positioned onto the outermost reinforcement layer 2 of the at least one reinforcement layer 2, 3, 4. The degradable membrane 1 is made of a material having a lower air permeability than the at least one reinforcement layer 2, 3, 4.

(7) The degradable membrane 1 is placed on top of the complete stack of fibre reinforcement layers 2, 3, 4 so as to form a barrier to air passage for the vacuum consolidation of the complete stack of fibre reinforcement layers 2, 3, 4 which may also include, core materials, etc.

(8) Then, suction is applied between the inner surface of the mould 6 and the degradable membrane 1 to press the at least one reinforcement layer 2, 3, 4 towards the inner surface of the mould 6. Suction may be applied by a vacuum pump 7 and may be distributed with or without a suction distributing layer 5.

(9) In case a suction distributing layer 5 is used, this layer is positioned between the inner surface of the mould 6 and the at least one reinforcement layer 2, 3, 4 and it becomes an integrated part of the final composite.

(10) The suction distributing layer 5 is for instance not necessary, if a vacuum tight degradable membrane is used during manufacturing. In case a degradable membrane with lower permeability than the glass fiber fabric is used, the suction distributing layer 5 may be of another type of reinforcement layer 2, 3, 4, e.g. glass fiber fabric, with a higher air permeability than the other reinforcement layers 2, 3, 4.

(11) Then, the degradable membrane 1 is covered at least partly with at least one vacuum film 9. This means that one or more the vacuum films 9 are positioned on top of the degradable membrane 1.

(12) After having placed the vacuum film 9, a vacuum is generated in the region between the vacuum film 9 and the mould 6.

(13) Following this, resin is injected into the region between the vacuum film 9 and the mould 6. The resin is injected under vacuum. Preferably, the resin is drawn into the region between the vacuum film 9 and the mould 6 by means of vacuum.

(14) Finally, the resin is cured and then, the mould 6 is removed.

(15) The method includes initiating a degradation of the degradable membrane 1 after having generated a vacuum in the region between the vacuum film 9 and the mould 6 and before the resin has cured completely.

(16) The degradation of the degradable membrane 1 is initiated by provoking a physical or chemical change of the membrane material 1.

(17) That means, the degradable membrane 1 is made of a material that can change its physical or chemical form so as to become open for diffusion at a controlled stage in the composite part production process, e.g. during the wetting of the fibres or during the curing of the laminate without impairing the quality of the final product.

(18) The initial properties of the degradable membrane 1 are changed no matter which process is used to change the physical or chemical form of the material.

(19) The degradable membrane 1 may be completely impermeable to air before initiating the degradation of the membrane 1. Alternatively, the degradable membrane 1 may be partially permeable, e.g. perforated, before degrading.

(20) That means, at the time the degradable membrane 1 is positioned onto the outermost reinforcement layer 2 of the at least one reinforcement layer 2, 3, 4, it may be either completely closed or partially opened so as to allow for a controlled air permeability.

(21) Further, the term membrane refers to a thin film or separation layer and degradable membrane may also be referred to as decomposable membrane.

(22) The degradable membrane 1 forms temporarily a surface film, wherein the thickness of the degradable membrane 1 is, preferably, below 0.1 mm. This ensures a fast degradation of the membrane and minimizes the amount of membrane material in the final composite part.

(23) In addition, the membrane material should be at least partly compatible with the resin, to ensure a strong interface bond between the remaining membrane material, if any after degradation, and the resin used in the manufacturing method in order not to affect the final composite properties negatively.

(24) In its original form, the degradable membrane 1 has sufficient mechanical properties to withstand the forces applied during use, e.g. layup and processing with vacuum. It is, for instance, fairly rigid in terms of its structure or stretchable.

(25) In relation to the resin used for the manufacturing method according to the invention, different groups of resin materials may be used, a solvent containing resin and a non-solvent containing resin. For each of these resins, different approaches can be used.

(26) For the solvent containing resins, a degradable membrane 1 made of a material which is soluble in the solvent of the resin may be applied. The degradation of the degradable membrane 1 is initiated by the solvent as decomposing agent.

(27) The degradable membrane 1 can be applied either as is or can be attached to a carrier medium, e.g. a fiberglass fabric, by a suitable adhesive, thermo bonding or stitching. Using the latter approach can protect the membrane during handling.

(28) The degradable membrane 1 may also be produced directly on top of the outermost reinforcement layer 2 or directly on top of the carrier medium, e.g. by coating the surface of the outermost reinforcement layer 2 or the carrier medium. Thereby, the surface of the said layer 2 or carrier medium is closed to form the degradable membrane 1.

(29) In case of using a solvent-comprising resin, the degradable membrane 1 stays intact until resin is injected into the appropriate region and comes into contact with the degradable membrane 1. The degradable membrane 1 is then dissolved and mixed with the resin and the materials previously separated by the membrane, e.g. different parts of the fibreglass structure, can merge and form the final laminate.

(30) In an embodiment of the invention, the resin includes styrene and the membrane is made of a material consisting of a polystyrene polymer.

(31) In another embodiment of the invention, the resin includes styrene and the degradable membrane 1 is made of a material comprising polystyrene, for example Acrylonitrile-Butadiene-Styrene polymer (ABS), Styrene-Acrylonitrile polymer (SAN) or Styrene-Butadiene rubber (SBR).

(32) As an alternative to the above-mentioned membrane 1 dissolvable in resins containing styrene, the degradable membrane 1 may comprise a material dissolvable in a resin containing other solvents, e.g. acrylates, methacrylates or diluents, used e.g. in epoxy resins, or even dissolvable in water. In this sense, a solvent is any material which has the ability to dissolve a solid or semi-solid material. The use of those non-styrene resins may have the advantage of a reduced impact on the working conditions and the environment.

(33) Furthermore, for resins not containing solvents, e.g. epoxy or polyurethane or biopolymer, other approaches are applicable. These approaches could, however, also be used for solvent containing resins.

(34) In order to make a degradable membrane 1 degrade using a non-solvent containing resin, the degradation must be triggered by another controlled event. This may be, for example, a change in temperature, a change in vacuum, an exposure to chemicals other than a solvent, an exposure to light or a combination of one or more of these factors.

(35) In an embodiment of the invention, the degradable membrane 1 is made of a synthetic plastic material which sublimates in high vacuum, e.g. in the range of 0-50 mbar absolute pressure, at room temperature or at a higher temperature which is below 100 Celsius. Thereby, sublimate refers to a phase transition of the membrane material into gas.

(36) In another embodiment of the invention, the degradable membrane 1 is made of a synthetic material that sublimates at temperatures between 50 C. and 300 C., preferably at a temperature below 100 C.

(37) Moreover, the degradable membrane 1 could be made of a synthetic material that melts at elevated temperatures, for instance at temperatures between 50 C. and 100 C., and thereafter is dissolved and/or absorbed into the matrix plastic material which forms part of the final composite.

(38) As mentioned before, the degradation of the degradable membrane 1 may be initiated by a change in vacuum, that means a change of the vacuum condition in the region between between the vacuum film and the mould. Such a change could, for instance, be a change of the direction of the pressure gradient over the degradable membrane 1, e.g. if on the upper side of the membrane the pressure is initially higher than on the lower side of the membrane, this is changed so that the pressure on the lower side becomes higher than that on the upper side. Here, the lower side is the side of the degradable membrane 1 facing the mould 6 or being directed towards the mould 6 and the upper side of the degradable membrane 1 is the side opposite to the lower side.

(39) Besides, as mentioned above, the degradation of the degradable membrane 1 may be initiated by exposure of the degradable membrane 1 to light, e.g. ultraviolet light, also referred to as ultraviolet radiation or infrared light. Moreover, the degradation of the degradable membrane 1 may be initiated by a molecular degradation.

(40) As shown in FIG. 2, the method for manufacturing a composite may be used to manufacture a wind turbine blade. For the manufacturing of a wind turbine blade, the mould 6 may comprise a lower mould part 6a and an upper mould part 6b. The vacuum film 9 may be a vacuum bag 9 which encloses a mould core 8a, 8b.

(41) As further shown in FIG. 2, a structural reinforcing part 10, e.g. in form of a shear web 10, may be placed on top of the degradable membrane 1 which in turn is placed on top of the at least one reinforcement layer 2, 3, 4. After the degradation of the degradable membrane 1 during the manufacturing process, this structural reinforcing part 10 is firmly connected to the composite of the wind turbine blade.

(42) FIG. 3 shows schematically a part of the composite which includes at least one reinforcement layer 2, 3, 4, wherein the at least one reinforcement layer 2, 3, 4 includes an outermost reinforcement layer 2 which was covered by a degradable membrane during manufacturing of the composite, wherein the constituent parts of the degraded degradable membrane 1 were either fused with the outermost reinforcement layer 2 or were removed.

(43) In case of fusioning of the degraded degradable membrane 1 with the outermost reinforcement layer 2 during manufacturing of the composite, the final composite includes constituent parts of the degraded degradable membrane 1.

(44) As shown in FIG. 3, at least one suction distributing layer 5 may, optionally, be comprised in the composite for distributing suction between the inner surface of the mould 6 and the degradable membrane 1 during manufacturing of the composite. If present, the suction distributing layer 5 is an integrated part of the final composite.

(45) The before-mentioned composite may be comprised in a wind turbine blade. In this case, the outermost reinforcement layer 2, which may become fused with the degraded degradable membrane 1 or freed from the degraded degradable membrane 1, is positioned at the inside of the wind turbine blade. Thus, structural reinforcing parts 10, like a shear web, may be firmly connected to the composite to form a wind turbine blade with enhanced structural properties.

(46) The addition of the degradable membrane 1 during manufacturing of the final composite may lead to a better quality of the final composite compared to what is possible by only using the usual reinforcement layers, such as fibreglass, carbon fibre or similar, which in general form part of the structure, because proper placement of the reinforcement materials is ensured throughout the manufacturing process.

(47) Moreover, the addition of the degradable membrane 1 can facilitate an independent layup and movement of separate composite parts and the joining of these composite parts before and during the resin injection to form a single composite part without the need for a subsequent bonding process, which also introduces weaknesses in the composite structure.