Stock material or miscellaneous articles – Composite – Of epoxy ether
Patent
1996-07-11
1999-03-09
Nakarani, D. S.
Stock material or miscellaneous articles
Composite
Of epoxy ether
4284258, 428624, 428626, 428650, 428684, 156 60, 156325, 156327, 156330, 1563317, B32B 1508
Patent
active
058798102
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of International application PCT/ GB94/ 02750, filed Dec. 16, 1994.
This invention relates to composite articles and more particularly to composite articles comprising at least two substrates bonded together by means of an intermediate layer of adhesive.
The adhesive bonding of substrates to form composite articles is a technology of increasing importance. By appropriate selection of adhesive, all solid substrates can be bonded although pretreatment of the substrate surfaces may be necessary in some cases.
Substrates which are commonly given a pretreatment include metals, the most frequently bonded metals being aluminium and steel. The pretreatments developed for metals generally have the effect not only of removing surface contaminants, for example lubricants, and oxide layers which may be intrinsically weak or may adhere poorly to the underlying metal, leading to weak joints in either case but also of providing a new oxide layer which is strong and which firmly adheres to the underlying metal. Established pretreatments include etching for steel and etching and/or anodising for aluminium.
In addition to the difficulties that can be experienced in attaining an acceptable initial bond strength, a significant problem associated with the use of adhesives on metal surfaces is the deterioration in bond strength that can occur over a period of time. This deterioration is exacerbated by high humidity and high temperatures.
Another method of improving the durability of adhesive bonded metal joints is to apply a primer to the metal surface and a number of primers have been proposed. In Adhesives Age, June 1977, pp 30-34, Brockmann describes the application of 8-hydroxyquinoline and 2',3,4',5, 7-pentahydroxyflavone as primers on aluminium that has been either etched or etched and anodised and reports their effect on the ageing behaviour of bonds provided by phenolic and nitrile-epoxy adhesives. In all cases, it is said, the additional application of the primer increases the water-stability of the adhesive bond above that obtained by etching and anodising alone.
It has now been found that a similar improvement in the stability of the adhesive bond can be achieved when 2',3,4',5,7-pentahydroxyflavone is applied as a primer to aluminium that has been neither etched nor anodised and this is not only economically advantageous but also surprising in view of the difficulties hitherto experienced in achieving acceptable bond strength between adhesive compositions and untreated aluminium. Galvanised steel can also be successfully treated. Furthermore, it has been found that similar effects can be obtained by merely incorporating pentahydroxyflavone as an additive in an adhesive resin, thus avoiding the extra step of applying it as a primer.
Thus, according to the invention, there is provided a composite article which comprises a first substrate comprising a body of metal containing aluminium or galvanised steel, a second substrate and, interposed between said first and second substrates whereby to provide adhesive bonding between said substrates, an adhesive and 2',3,4',5,7- pentahydroxyflavone with the proviso that when either substrate is etched or anodised aluminium, the pentahydroxyflavone is not present thereon as a primer coat.
The first and second substrates may have any shape or configuration provided that each has at least one surface suitable for being adhesively bonded to a surface of the other.
The metal constituting the first substrate may be aluminium in any of its known forms or galvanised steel in any of its known forms or an alloy of either metal. Suitable forms of aluminium include bare aluminium (having had no surface treatment), clad aluminium or aluminium that has been etched and/or anodised so long as the above proviso is observed. It is preferred, however, to avoid the use of etched or anodised aluminium because of the environmental hazards presented by etching and anodising processes. Suitable forms of galvanised steel include hot dipped or electrogalvanised grades.
The
REFERENCES:
patent: 4855001 (1989-08-01), Damico et al.
patent: 5079094 (1992-01-01), Kimball
patent: 5162156 (1992-11-01), Troughton, Jr. et al.
Brockmann: "Interface Reactions and Their Influrence on the Long-Term Properties of Metal Bonds"; Adhesives Age, vol. 20, No. 6, Jun. 1977, pp. 30-34; cited in the application see p. 33, middle column, line 6-page 34, middle column, line 31.
Ellwood Michael
Leeming Stephen William
Nakarani D. S.
Rickman Holly C.
Zeneca Limited
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