Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-11-14
2003-02-04
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S404000, C525S523000
Reexamination Certificate
active
06515045
ABSTRACT:
This invention relates to an adhesive composition and a method for temporarily bonding a removable flexible substrate to a rigid permanent substrate.
Construction of composite parts in which two or more parts are bonded with an adhesive to produce the final article, continues to be important, demanding development of higher performance composite materials and adhesives to bond these new composite materials.
Within this area, there is special need arising to remove selectively one of the adhered parts including total removal of the adhesive, such that the remaining part can be re-adhered to a fresh cover. Increasingly such type of cleanly strippable articles are important for specialist applications such as in aircraft interiors (where the strippable cover has additional features of high fire retardancy, low inflammability, low smoke emission etc.), or for construction of temporary signs where a rigid permanent support is covered with renewable signs output from various digital imaging devices (i.e. ink jet images for use on trucks and lorries, billboards etc.). Another area is in removal windscreens from automobile or other parts in the automobile applications where increasingly, bonded structures/articles are being incorporated.
Most important is that the bonded structures should have on the one hand significant peel resistance, yet the temporary (bonded) cover should still be removable with the simultaneous removal of the adhesive without damaging the remaining fixed part. This is especially important for aerospace application, where any damage to the fixed part can result in fracture points, deleterious to the aeroplane.
A mode of removing the adhered article involves the use of heating, be it from a hot air gun or other means.
Strippable adhesives are known, e.g. in the wall-paper area, where a combination of heat gun use and scrapping actions are used to removal haphazardly the wall paper. Clean strippability is not readily acheived.
Hot melt adhesives have been used, again not giving very clean separation between the adhered parts.
Two layer mechanisms have been suggested to achieve clean selective separation of adhered parts: U.S. Pat. No. 5,620,794, for example, discloses a two layer mechanism involving an adhesive and a heat active layer to separate a car windscreen from the car (metal) body.
U.S. Pat. No. 3,909,497 describes the heat decomposition of solid resins into flowing resins which could be the basis of T
g
reduction and loss of adherence, however, clean separation in this mode is difficult.
Mixtures of acrylic adhesives with blowing agents having decomposition temperatures of 50-250° C. are disclosed in JP-A 62-022874. On heating these compounds decompose forcing the adhering bonds to break. A clean selective removal of the adhesive cannot be achieved by this process.
It has now been found that an adhesive composition containing a linear epoxy resin, an amine hardener and an acetylene is suitable for bonding non-flexible parts (metal or non-metalic rigid supports) to flexible removable covers under mild curing conditions to achieve useful peel strengths, but on aggressive heating continues to bond preferentially to the removable part, such that substantially clean removal of the adhesive and the flexible removable part is effected.
Accordingly, the present invention relates to an adhesive composition comprising
(a) an epoxy resin having a substantially linear structure,
(b) an amine hardener, and
(c) a non-ionic surfactant.
Epoxy resins having a substantially linear structure can be prepared by an advancement reaction, i.e. by polymerizing a difunctional epoxy resin having two epoxy groups per molecule and a dihydric phenol being used in quantities which provide a ratio of phenolic hydroxyl groups to epoxy groups of from 1:0.8 to 1:1.2. Suitable starting materials and reaction conditions for the advancement reaction are well-known in the art.
Examples for suitable difunctional epoxy resins are diglycidyl ethers or diglycidyl esters like bisphenol-A-diglycidylether, bisphenol-F-diglycidylether, hydrogenated bisphenol-A-diglycidylether, hydrogenated bisphenol-F-diglycidylether and diglycidyl esters of phthalic, isophthalic or terephthalic acid.
Difunctional cycloaliphatic epoxy resins like 3,4epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate can also be applied.
Bisphenol-A-diglycidyl ether and bisphenol-F-diglycidyl ether are particularly preferred.
Examples for dihydric phenols which can be used for the advancement reaction of difunctional epoxy resins are 4,4′-dihydroxybiphenyl, bisphenol A, bisphenol F, bisphenol S and 4,4′-dihydroxydiphenyl ketone.
Bisphenol A is the preferred dihydric phenol.
Amine hardeners which can be used as component (b) in the compositions according to the invention are preferably aliphatic and cycloaliphatic amines.
The aliphatic amine may be alkylene diamines such as ethylene or propylene diamine, triethylene diamine, piperazine-N-ethylamine, polyoxyalkylene diamines, such as polyoxyethylene diamine or polyoxypropylene diamine and the like. Cycloaliphatic amines may be used as cyclohexane diamine, isophorone diamine and the like.
Tertiary amines and imidazoles are preferably employed as curing catalysts. Suitable examples are benzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, 1-methylimidazole, 2-methylimidazole and 2,4-diethylimidazole.
Basically, every non-ionic surfactant can be applied as component (c). Suitable surfactants are, for instance, fluorosurfactants like derivatives of non-ionic perfluorinated polyalkylenes and polyoxyalkylenes, alkoxylated, in particular ethoxylated, perfluorinated fattic acid derivatives, polyglycidylethers of castor oil, melamine derivatives, like hexamethoxymethylmelamine, or compounds of formula I,
R
1
—C≡C—R
2
(I)
wherein R
1
and R
2
independently from one another denote hydroxy or an unsubstituted or hydroxy or halogen-substituted organic radical selected from the group consisting of C
1
-C
20
alkyl, C
1
-C
20
alkoxy, C
5
-C
20
aryl, C
5
-C
20
aryloxy, C
6
-C
20
aralkyl, C
5
-C
12
cycloalkyl, C
5
-C
12
cycloalkoxy and C
2
-C
20
-alkoxyalkyl.
The compositions according to the invention may further contain stabilizers known in the art. The stabilizers may be for protection during the life of the finished product against, for example, oxygen, ozone, and UV radiation.
Compounds of formula I wherein R
1
and R
2
denote Ethoxy are especially preferred.
Environmental standards nowadays require to minimize the use of organic solvents in adhesive compositions and therefore there is a special need for water-based adhesives. The compositions according to the invention are highly water dispersible and sprayable and accordingly is particularly suitable for adhering low energy (composite) surfaces to rigid metal or non-metal composite surfaces or parts.
The invention therefore further relates to an aqueous dispersion containing an adhesive composition containing an epoxy resin having a substantially linear structure, an amine hardener and a non-ionic surfactant.
The adhesive composition is used as a two-component composition, i.e. the epoxy resin (Part A) and the amine hardener (Part B) are stored separately and mixed a short time prior to application. The non-ionic surfactant can be added either to the epoxy or to the hardener component. Water can be added as well to either part of the composition to adjust the viscosity.
The adhesive compositions have almost no or only a very mild odor. The viscosities of Part A and Part B are low and similar thus allowing easy mixing. The formulation can be applied to part using any type of spray equipment or roller coat; no slumping, sagging or mottling of adhesive appears during application. The water in the formulation evaporates quickly; the adhesive is milky white when sprayed on the substrate and turns opaque when water has flashed off thus visually telling the operator that the sides can be bonded together.
The adhesive can be used in high humidity environments as well as in low and high temperature e
Neuman, Esq. Kristin H.
Proskauer Rose LLP
Sellers Robert E. L.
Vantico Inc.
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