Patent Application
20070287787
It is an object of the present invention, therefore, to provide a silane/epoxy hybrid adhesive which not only ensures high light transmittance but also combines a rheology suitable for vertical application with sufficient Shore A hardness and tensile strength.
This object is achieved by means of the hybrid adhesive of the invention.
The hybrid adhesive of the invention has a silane resin and an epoxy resin and further comprises
at least one nonaromatic, tertiary diamine or polyamine, selected in particular from the group consisting of aliphatic amines, cycloaliphatic amines, amidoamines, and mixtures thereof; and
at least one silane catalyst which is not an amine compound, being more particularly an organometallic compound, preferably selected from the group consisting of organotin compounds, an organozirconate compounds, organotitanate compounds, and mixtures thereof.
By a silane resin are meant here polymers whose backbone is formed from a polymer, in particular a polyurethane, silicone, polyether or polyolefin, which has been modified with siloxane groups. Particularly preferred on account of their reactivity are the methoxysilanes, which crosslink under the effect of moisture:
2(CH3O)m(CH3)nSi—R—Si(OCH3)m(CH3)n+H2O→(CH3O)m(CH3)nSi—R—Si(OCH3)m-1(CH3)n—O—Si(OCH3)m-1(CH3)n—O—Si(OCH3)m(CH3)n+2CH3OH
(where m=3, 2, 1; n=0, 1, 2; m+n=3)
Silane resins particularly preferred in the context of the present invention are silane-terminated polyurethanes (e.g., Baycoll® XP 2458, based on a polyether polyol) and reactants capable of forming a silane-terminated polyurethane. Suitable reactants are known to the skilled worker (examples being isocyanate-terminated polyether polyols and aminosilanes such as Dynasylan® DAMO-T, for example).
In customary practice the silane crosslinking is catalyzed in particular by organometallic catalysts, preferably tin catalysts, or by amines, which have been found outstandingly suitable; suitable in principle, however, are all Brønsted/Lewis acids and bases which are suitable for catalyzing the rate-determining step, the hydrolysis of the silane ester. In a silane/epoxy hybrid adhesive the use of an amine catalyst would be particularly preferable, since it also catalyzes the epoxide crosslinking:
The aromatic amines that are actually preferred on account of their higher reactivity, however, have the effect—intolerable in the present case—of giving rise to discolorations which disrupt the optical impression. In the present invention, therefore, nonaromatic amine catalysts are employed. A nonaromatic amine catalyst, however, has on its own not been found suitable for producing, in a thickened hybrid adhesive, such complete crosslinking that the desired Shore A hardness of ≧60, preferably of ≧65, more preferably of ≧70 is achieved in the cured state. It has been found that the inadequate Shore A hardness is attributable to incomplete crosslinking of the silane fraction. In the present invention, therefore, a further silane catalyst is employed which is not an amine compound. Particularly preferred silane catalysts are organotin compounds.
A further aspect of the present invention relates to achieving a firmness such that, following application in a thickness of approximately 1 mm, preferably approximately 2 mm, more preferably approximately 3 mm to a vertical surface of HVG-DGG (Hüttentechnische Vereinigung der deutschen Glas-industrie e.V., Deutsche Glastechnische Gesellschaft e.V.) standard glass I, the hybrid adhesive does not run. It would easily be possible to add a multiplicity of fillers if the only consideration was that of achieving such a firmness. However, it was necessary to find a filler that did not significantly hinder the transparency or light transmittance.
A component which emerged as being particularly advantageous was a hydrophobic fumed silica, more particularly a hexamethyldisilazane-modified fumed silica, which has a specific surface area (BET) of ≧160 m2/g, preferably of ≧200 m2/g, more preferably of ≧240 m2/g. Products of this kind are available commercially, for example under the trade name Aerosil® R 812 (Degussa AG).
In particularly preferred embodiments a hybrid adhesive of this kind exhibits substantially no discoloration and/or clouding of the adhesive when stored under air ingress conditions at 70° C. for 24 hours.
Suitable nonaromatic polyamines are familiar to the skilled worker. Particularly preferred for use as constituent (a) is a nonaromatic polyamine selected from the group consisting of DABCO (1,4-diaza-bicyclo[2.2.2]octane), DBU (1,8-diazabicyclo[5.4.0]-undec-7-ene, DBN (1,5-diazabicyclo[4.3.0]non-5-ene), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,2,2,6,6-pentamethylpiperidine, N,N-diisopropyl-3-pentylamine, N-ethyldiisopropylamine, 2-tert-butyl-1,1,3,3-tetra-methylguanidine, N,N′-dimethylpiperazine, 1,8-diaza-bicyclo[5.4.0]under-7-ene, and mixtures thereof.
Particularly preferred as constituent (a) is 1,8-diazabicyclo[5.4.0]-undec-7-ene, available under the trade name Lupragen N700 (BASF):
Particularly preferred embodiments use as constituent (b) an organotin compound selected from the group consisting of dioctyltin di(2-ethylhexanoate) solution, dioctyltin dilaurate, dioctyltin oxide, dibutyltin dilaurate, dibutyltin dicarboxylate, butyl-tin tris (2-ethylhexanoate), dibutyltin dineodecanoate, laurylstannoxane, dibutyltin diketanoate, dioctyltin oxide, dibutyltin diacetate, dibutyltin maleate, dibutyltin dichloride, dibutyltin sulfide, dibutyltin oxide, butyltin dihydroxychloride, butyltin oxide, dibutyltin dioctylmaleate, tetrabutyltin, zinc ricinoleate, zinc octoate, zinc acetylacetonate, zinc oxalate, and mixtures thereof.
The organozirconate or organotitanate compounds which can be employed alternatively or supplementarily are familiar to the skilled worker and are available, for example, from DuPont under the brand name Tyzor®.
Used with particular preference as constituent (b) is laurylstannoxane, [(C4H9)2Sn(OOCC11H23)]2O, which is available commercially (Tegokat® 225, Goldschmidt TIB GmbH, Mannheim, Germany).
In particularly preferred embodiments the hybrid adhesive of the invention in the cured state has a tensile strength to DIN 53455 (aluminum) of ≧7 MPa, preferably of ≧8 MPa, more preferably of ≧9 MPa. In the prior art, silane-terminated polyurethane resins and silane-terminated polyethers are considered equivalent in their usefulness. Now, however, it has been found that silane-terminated polyurethane resins, particularly those based on polyether polyols, are able in the context of the present invention to ensure a tensile strength which is superior to that obtained using silane-terminated straight polyethers.
The present hybrid adhesive is preferably a 2-component adhesive, which may be offered, for example, in typical dual cartridges or suitable tubular pouches. In these cases the nonaromatic polyamine and the silane catalyst will be present preferably in separate components. Given appropriate deactivation or encapsulation of one reactive constituent, the epoxide for example, however, the presentation of the hybrid adhesive of the invention in a 1K (1-component) form is also conceivable.
As set out above, there should be very little adverse effect on the transparency of the adhesive. With particular preference, the hybrid adhesive of the invention in the cured state, along a path length of 1 mm, backed with a BaSO4 background (Ulbricht sphere), has a light transmittance in the visible region of ≧30%, preferably of ≧40%, more preferably of ≧50%.
A further aspect of the invention therefore relates to the use of a catalyst combination comprising
at least one nonaromatic tertiary diamine or polyamine selected in particular from the group consisting of aliphatic amines, cycloaliphatic amines, amidoamines and mixtures thereof; and
at least one silane catalyst which is not an amine compound, being more particularly an organometallic compound, preferably selected from the group consisting of organotin compounds, organozirconate compounds, organotitanate compounds, and mixtures thereof; to avoid discoloration and/or clouding in adhesives, particularly in the hybrid adhesives described above.
The invention is illustrated below with reference to a specific exemplary embodiment, without any intention that the invention should be restricted to this embodiment. An exemplary 2-component hybrid adhesive has the following composition:
The Aerosil® as well was selected in particular in the above example to have a suitability such that it was possible to meet the requirements in terms both of light transmittance and of firmness: whereas it was not possible to achieve satisfactory results with Aerosils R 202, R 972, and R 8200, the aforementioned objectives were met using Aerosil R 812.
The above components A and B were mixed in an A/B ratio of 2/1 to form a hybrid adhesive of the invention and were cured (using routine measures typical in the art it is also possible to adjust the hybrid adhesive, if desired, to any other mixing ratio, for example in the range from 1:1 to 10:1 or else from 1:1-1:10). Even after 24 hours at 70° C. under air ingress conditions, no yellowing or clouding of the adhesive whatsoever was observed. The firmness of the composition is such that, following application in a thickness of approximately 1 mm to a vertical surface of HVG-DGG (Hüttentechnische Vereinigung der deutschen Glasindustrie e.V., Deutsche Glastechnische Gesellschaft e.V.) standard glass I, it does not run. The desired Shore A hardness can be set with ease in the context of the invention, by the skilled worker, in routine experiments on the selection and the amount of the catalysts, in particular of the nonaromatic diamine or polyamine.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06115326.8 | Jun 2006 | EP | regional |
