Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-07-27
2001-02-27
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S104000, C524S167000, C524S287000, C524S299000, C524S359000, C524S464000
Reexamination Certificate
active
06194499
ABSTRACT:
The present invention relates to an adhesive composition for the hot bonding of substrates and to a process enabling its use.
The adhesive composition of the invention enables substrates to be bonded, in particular polymer matrix composite substrates or metal substrates, for example aluminium alloy, without restricting their characteristics. It can be applied to very great advantage in the making of laminates and aeronautical quality foam or honeycomb core sandwich structures with a toughened polymer material coating, for use in rotor blades, or in mechanical parts of the rotor hub, particularly of helicopters and also for use in the interior furnishings of aircraft, public transport, etc. Such structures offer very attractive performance in terms of cost, mass, physical and mechanical characteristics.
Furthermore, the adhesive composition of the invention can be used at temperatures lower than the temperatures usually used for the bonding of toughened polymer materials, and thus gives rise to a reduction in manufacturing costs. This composition also enables the bonding of substrates of different, often incompatible, types.
Currently, in aeronautics, sandwich structures are widely used on account of their performance/mass saving ratio. Their development is however limited by their temperature performance which is difficult to improve without an increase in structure mass.
Indeed, for reasons of technical knowledge, sandwich structures are constituted, for the coating, by composite materials with an epoxy thermosetting matrix which is possibly auto-adhesive and, for the core, by honeycomb of the aromatic polyamide sheet type such as polyaramide marketed under the NOMEX® brand or metal sheets assembled with phenolic or polyimide resins. It would be very advantageous to replace the possibly auto-adhesive epoxy matrices by other modified epoxy matrices, bismaleimides (BMI) or thermoplastics such as polyetheretherketone (PEEK) or polyetherimide (PEI). Indeed, this would enable an improvement in durability at higher operating temperatures and in certain types of performance, for example damage tolerance and fire resistance.
However, to obtain good adhesion to the honeycomb core, such a modification would require:
a significant supply of adhesive,
an adhesive appropriate to the coating,
the use of another honeycomb with temperature limits compatible with those of the bonding agents,
which would entail a considerable increase in costs and/or in mass.
Furthermore, it is also advantageous to be able to make materials constituted by the assembling of substrates with a thermosetting or thermoplastic matrix.
Currently, thermoplastic matrix composites can be assembled:
by standard bonding with a thermosetting adhesive,
or by local melting of the matrix, which enables the two substrates to weld together.
However, these two processes have two types of limitation. On the one hand, with regard to mechanical strength which is directly affected by the compatibility of the matrices of substrates and the films of adhesive and by the surface treatment. For example, making honeycomb core sandwich structures of the aramid/phenol type and with a bismaleimide matrix coating (BMI) is not possible with these processes on account of the chemical incompatibility of BMI with the core materials. And on the other hand, the temperature required to ensure the co-consolidation of interfaces is difficult to control and may give rise to deformations in neighbouring areas. Thus, it is difficult to make sandwich structures with a polyetheretherketone (PEEK) coating and with an aramid/phenol honeycomb core given that the melting temperature of the PEEK is 400° C., a temperature which honeycombs cannot resist.
So as to minimise these drawbacks, a process also called Thermabond is used. This process is both a bonding, since another resin film is added, and a co-consolidation since this film is taken to its melting temperature. For example, if it is required to assemble a PEEK matrix substrate with a PEI matrix substrate, a PEI film is interposed and the whole is heated to a temperature of about 300° C. which ensures the melting of the PEI. This high temperature is not appropriate for the making of all the substrates that it might be required to use. In particular, it is not appropriate for the making of honeycomb core sandwich structures of the aramid/phenol type.
There is therefore a pressing need for an adhesive composition appropriate for the manufacture of laminate materials which does not reduce the performance of the resulting laminate materials during use and which can be used at a temperature which is not economically prohibitive and which is also low enough to ensure that the substrates to be bonded do not deteriorate.
It is to the credit of the inventors that they have found a composition for the hot bonding of substrates comprising:
at least one polymer material,
at least one plasticiser and wetting agent,
and possibly at least one solvent, characterised in that it provides an operating temperature lower than the temperature at which the substrates degrade and lower than the melting temperature of the polymer material.
The preferred temperature for using the adhesive composition of the invention is lower than the temperature at which the substrates deform and lower than the melting temperature of the polymer material.
Thus the use of the composition of the invention enables substrate structures to be obtained which have lost none of their mechanical characteristics during assembly and for which the adhesive composition does not constitute a factor limiting their possible uses.
This operating temperature is clearly a function of the nature of the substrates to be bonded and of the polymer material of the adhesive composition. It is between 50 and 250° C., preferably between 70 and 240° C. and even more preferentially between 100 and 200° C.
The polymer material of this adhesive composition comprises at least one polymer or copolymer having different or identical repetitive patterns with the general formula
—Ar—X—
in which:
Ar is a mono- or polycyclic substituted or non-substituted aromatic radical,
and X is an atom of nitrogen, oxygen or sulphur or an OCO, O—CO—O, CO, NHCO, N(CO
2
), SO
2
, O—SO
2
, N(SO
2
), C═NH function or a saturated or unsaturated alkyl group bearing an atom of nitrogen, oxygen or sulphur or an OCO, O—CO—O, CO, NHCO, N(CO
2
), SO
2
, O—SO
2
, N(SO
2
), C═NH function
This polymer is selected as a function of the nature of the substrates to be assembled. This polymer should preferably have a chemical structure close to that of the substrate when the latter is a polymer substrate.
Examples of polymer material that can be mentioned for use in the composition of the invention, are polyetherimides (PEI), polyethersulphones, polyimides, polysulphones, polyphenylene sulphides, polyarylene oxides, aromatic polyamides, polyamideimides, aromatic polyesters, aromatic polycarbons, polyethetetherketones (PEEK).
The preferred polymer material is a polyetherimide (PEI).
The plasticiser and wetting agent is an aromatic compound bearing at least one functional group selected from ketones, such as propiophenone, benzophenone, from sulphones, such as diphenylsulphone, ditolysulphone, from esters such as phenyl benzoate or benzyl benzoate and from alcohols such as phenol.
By plasticiser and wetting agent is understood any material capable of lowering the melting temperature, the glass transition temperature and the viscosity of a polymer and of facilitating wettability, by reversible transformation of the polymer. This plasticiser and wetting agent presents a boiling or melting point comparable to that of the polymer material of the adhesive composition.
This plasticiser may be volatile at the temperature at which the adhesive composition is used or else may not be volatile at this temperature, in which case clearly it must be selected so as not to adversely affect the characteristics of the formed assembly in which it subsists.
The possible solvent is selected from chlorinated solvents such as dic
Berthier Jean-Marc
Magnin Georges
Sibois Hélène
Eurocopter
Henderson & Sturm LLP
Michl Paul R.
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