Method for manufacturing a composite/metal laminate, half-product for use in this method, and thus manufactured composite/metal laminate
The invention relates to a method for manufacturing a composite/metal laminate. The invention also relates to a metal plate which is a half -product during the method according to the invention and to a composite/metal laminate manufactured using this method.
A material which has favourable properties in respect of (bending) stiffness, resistance to impact energy and a low specific weight among others is composite/metal laminate (examples of such a laminate are: a fibre/metal laminate also referred to as Fibre Metal Laminate' or FML', and metal laminates incorporating a foam layer, a honeycomb- shaped layer or a plastic layer). A fibre/metal laminate with aluminium plate material is applied according to the prior art inter alia in transport means with the trade name "Glare". A drawback of such composite/metal laminate is that it is relatively expensive and is therefore only considered for high-grade applications such as in particular the aviation industry. For less advanced applications composite/metal laminate is for the moment not a very attractive alternative because of the price.
The material is expensive, among other reasons, because of the considerable production costs caused by the pre-treatment (cleaning) of the metal, the subsequent laminating of the metal and the composite material, and finally the curing of the laminate. In the pre- treatment existing layers of oxide are removed from the surface of metal plates and a new artificial oxide layer is then optionally applied (anodizing), whereafter the metal plates are protected with a primer layer which has anti -corrosive properties and forms a good adhesive layer for the resin in a fibre layer. During curing the composite (for instance the fibres) is impregnated and the adhesion of the impregnating agent (for instance glue or resin) to the metal also takes place. Since the metal plates in the laminate do not let through undesired fluid such as air, moisture and solvents, it is of great importance to evacuate the metal plates along the edges thereof. In practice an autoclave is found to be necessary for this purpose; only using a furnace, optionally in combination with a flatbed press, does not result in the desired quality of composite/metal laminate. The curing in an autoclave furthermore takes 3 to 4 hours. The curing also makes great demands of the combination of impregnating agent and
fibres. The impregnating agent must not only provide sufficient support to the composite in the laminate but must also provide a sufficient adhesion with the metal. In short, the separate production steps according to the prior art are relatively complex and require the use of expensive equipment (including a line of immersion baths with chemicals, a clean room and an autoclave). The raw materials required are also expensive.
The publication from database WPI, XP-002252914 describes a production method wherein a solid thermoplastic resin plate and a metal plate are connected by means of co-acting pressing rollers. For this purpose the metal plate is pre-heated and provided with an adhesive layer foil, whereafter the metal plate is carried between the pressing rollers. The adhesive layer is herein placed against the thermoplastic solid resin plate. Also described is the application of a pair of metal plates, of aluminium or iron, wherein the solid thermoplastic plate consists of polyethylene. The adhesive layer is formed by a composite plate of polyethylene and an activated polyethylene. Stated as an advantage of this invention is the great surface flatness.
The present invention has for its object to provide an improved method, as well as the means required therein, for manufacturing composite/metal laminate in inexpensive manner and with an improved result relative to the prior art.
For this purpose the invention provides a method for manufacturing a composite/metal laminate according to claim 1. Although it is an object to reduce the production costs, the present invention proposes to increase the number of processing steps; in the prior art processing step B) is in any case integrated with processing step D). By means of an extra processing step the individual processing steps become less critical and the demands made of the materials used become less heavy. This results in it being possible to considerably limit the costs of manufacturing composite/metal laminate with the method according to the present invention relative to the prior art. A clear example hereof is that the process parameters during laminating of the metal and the composite material according to the prior art must be tailored to impregnating of the fibres as well as to the adhesion of the impregnating agent to the metal. In addition, discharge of unwanted fluid must be ensured at the edges of the metal. According to the invention however, the adhesive layer can first be applied to the metal. During this process it is
only necessary to take into account the adhesion of -the adhesive layer to the metal, which allows much more freedom in setting the process parameters. Gases and moisture can moreover easily escape from the surface. The expensive use of an autoclave hereby becomes less urgently necessary. Partly as a result of the greater process freedom, there are increased options for the adhesive material to be applied, which increases the possibility of applying a less expensive material. The adhesive layer can consist preferably of a thermoplastic material layer, but it is also conceivable for a thermoset (not yet cured in the first instance) to be applied. This layer should not be confused with a primer. After being applied primers are cured (for instance in a furnace) before subsequent processing steps follow. After curing the primer can no longer be used as an adhesive layer in a subsequent processing step.
The pre-treatment of metal plate according to processing step A) preferably comprises of removing oxide and/or the arranging a primer layer having anti-corrosive properties. Other operations can however also be considered, optionally in combination, as the pre- treatment; for instance unpacking, making to size, unrolling, unstacking or degreasing. The pre-treatment is partly dependent on the applied metal and the eventual laminate for which it is intended. The primer ("prime coat") makes it possible to separate the processing steps A) and B) from each other in time. Instead of applying a primer, it is however also possible to envisage an adhesive layer, which also fulfills the function of primer, being applied directly to the metal.
During processing step B) the metal plate can be provided on one flat side with an adhesive layer, which will particularly be the case with metal plates forming the outside of the laminate for manufacturing. However, metal plates located on both flat sides inside the laminate for manufacture will normally (although not necessarily) be provided on both flat sides with an adhesive layer.
During processing step B) the metal plate can consist of a flat plate, which will particularly be the case in smaller-scale production. When production takes place on a larger scale it is more probable that the metal plate is unrolled from a roll ("coil") during processing step B), and rolled up again or divided into separate elements, as desired, after the adhesive layer has been applied. Processing step B) can be carried out by another party, on a different scale and at a different location than the subsequent
processing steps. Economies of scale can hereby be realized which can result in a decrease in the cost price of the final laminate.
If processing steps C) and D) are carried out on sufficiently large scale, it is possible that the metal plates are connected during the steps to metal plate wound onto a coil. The method can be performed both on very small scale (batch-wise processing of plate parts) and on very large scale (for instance in-line production with rollers).
The metal plates and the at least one layer of composite can be connected to each other in simple manner by supplying heat. Other connecting techniques can however also be envisaged (for instance by means of chemical activation of materials). In addition, the metal plates and the at least one layer of composite are preferably connected to each other while exerting pressure.
The invention also provides a metal plate according to claim 11. The adhesive layer can for instance be formed by a thermosetting adhesive, but on the other hand can also consist of a (not yet cured) thermoset. As already indicated above, this half-product can also be manufactured (and traded) separately. A further economic optimization of the production of the composite/metal laminate is possible by separating the production of the plate material and the follow-on process. The metal plate can herein be wound onto a coil.
The invention furthermore provides a composite/metal laminate manufactured with the described method which, owing to the greater freedom during production, can also possess properties which could not be realized in the traditional production methods. In the first instance the invention relates particularly to laminate containing fibre material between the metal plates, although the invention also expressly extends to other composite/metal laminates.
The invention will be further elucidated with reference to the block diagrams shown in the following figures. Herein: figure 1 is a schematic representation of the method for manufacturing composite/metal laminate according to the prior art, and
figure 2 is a schematic representation of the method for manufacturing composite/metal laminate according to the present invention.
Figure 1 is a block diagram showing a method for manufacturing composite/metal laminate according to the prior art. During a processing step A) the metal is pre-treated (for instance removal of oxide and application of a primer). The individual materials which are to form the laminate are subsequently brought together (stacked) in the correct order during a processing step C). After the correct order has been obtained, the whole stack is fused to form the final laminate in a single processing step E).
Figure 2 is a block diagram in which a method for manufacturing composite/metal laminate according to the present invention is shown schematically. Here too the metal is pre-treated (for instance removal of oxide and application of a primer) during a processing step A). However, an adhesive layer is now applied to the metal during a processing step B). In a known processing step C) the correct order is then arranged in the materials for assembling The difference with the processing step as shown in figure 1 is that in figure 2 the metal is already provided with an adhesive layer. After arranging the desired order, the metal plates and the at least one layer of composite are connected to each other (fused) in a processing step D). When the methods according to figures 1 and 2 are now compared to each other, it is apparent that processing steps A) and C) substantially correspond with each other. Processing step E) of figure 1 can however be deemed as being divided into two separate processing steps: B) and D).