Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2002-03-06
2004-10-12
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550RA, C428S3550EN, C428S515000, C428S516000, C428S520000, C428S522000, C156S241000
Reexamination Certificate
active
06803101
ABSTRACT:
The invention relates to a weathering-stable self-adhesive protective film with high adhesion for protecting surfaces such as glass, ceramic, stainless steel, polycarbonate glass of acrylic glass, especially painted surfaces. The protective films of the invention are particularly suitable for protecting the fresh finish of vehicles such as automobiles and for protecting freshly painted vehicle parts against soiling and damage during assembly, transit and storage.
For surface protection on unpainted areas there are numerous products. Painted areas have to date been covered little with self-adhesive protective films, and virtually not at all in the fresh state without being fully cured. When conventional protective films are used on fresh paint, numerous deficiencies arise, such as adhesive residues, instances of discoloration, severe peel increase (increase in bond strength following storage in the bonded state), tearing on removal, shrinking on storage, weak initial adhesion or low stretchability (especially on uneven bond substrates).
After prolonged periods, particularly after weathering, such effects become intensified. Application on vehicles (automobiles) and vehicle parts (bumpers for example) where the surface is to be protected during assembly or transit is therefore a challenging problem. The preservation and protection of motor vehicles during transit from manufacturer to dealer has long been common practice.
For the preservation of automobiles it is known to apply paraffin waxes in a thickness of from 5 to 20 &mgr;m. However, it has been found that, especially on horizontal areas of the vehicles, a thin and usually non-uniform layer of this kind does not afford adequate protection against external influences, such as the corrosive effect of bird droppings, for example.
A considerable disadvantage of paraffin wax sealing is the need to remove the preservative using a steam jet, surfactants or solvents. Environmentally sound recovery and disposal of the residues are a cause of great complexity in terms of apparatus and of very high costs.
Reversibly adhering self-adhesive films for protecting the automobile during transit have likewise been known for some time but have so far been used only to a small extent. In many cases the films in question are permanently adhering protective and decorative films, such as an anti-stonechip film, for example. These self-adhesive films remain permanently on the vehicle after they have been mounted.
Adhesive tapes or protective films with self-adhesive compositions based on natural rubber possess relatively good initial adhesion and may be removed again without residue. Even on short-term exposure to UV radiation, however, these compositions are not stable to aging. Following extreme weathering exposure over a prolonged period (three to six months), this leads to severe greasy residues or hardened paint-like residues on the painted metal.
Polyacrylate compositions, on the other hand, are very UV-stable. If uncrosslinked polyacrylate compositions are subjected to storage under alternating climatic conditions, their compatibility with paint surfaces is good only in some cases. Compatibility means that there are no defects visible on the surface after the adhesive tape has been removed. On the other hand, however, these compositions exhibit severe peel increase, so that when the film is difficult to peel off they leave significant residues of the adhesive composition on the substrate If these compositions are strongly crosslinked chemically or by radiation, they may in some cases be removed without residue but on the other hand cause permanent deformations on the paint surface and, furthermore, in some cases exhibit inadequate adhesion when bonded to curved painted areas.
JP 02 199 184 discloses a radiation-crosslinkable pressure-sensitive adhesive in which for protective application on paint films it is necessary to formulate a low glass transition temperature in order to prevent permanent deformations of the paint film. Here, problems arise owing to inadequate bond strength of the self-adhesive film to the motor vehicles during application and transit.
The same applies to acrylates as described in U.S. Pat. No. 5,612,136. Moreover, the method of irradiation disclosed therein damages the film, thereby reducing its weathering stability if irradiation is continued to the point where the residual monomers have abated completely as a result of polymerization. At relatively low irradiation doses, the residual monomer content is so high that these monomers migrate into the vehicle finish and, as a result, cause it to swell. A further disadvantage is the migration of photoinitiators into the paint, where they lower its UV stability.
Self-adhesive compositions based on polyisobutylene (polyisobutylene homopolymer or butyl rubber) exhibit easy removal in the bonding test in which they are applied to painted metal panels and then undergo storage under alternating climatic conditions. The initial adhesion, however, is low, so that critical edges have to be fastened using a more strongly adhering adhesive tape (a so-called edge securing tape). Under the influence of moisture, in particular the bond strength of the film is frequently reduced to such an extent that the film detaches from the protected vehicles in the course of transit, with the consequence that the protective effect is no longer there. Moreover, these adhesives are soft (not very cohesive) and therefore produce residues of composition when the film is removed, especially in the edge region after UV aging. Furthermore, this self-adhesive composition is not compatible with the rubber seals (sealing profiles) customary in automobile construction or with the plasticizers they contain; when the protective film is removed from window profiles, residues of the adhesive coating remain on the rubber. Adhesive tapes and films of this kind are described in EP 0 519 278, JP 95-325285 and U.S. Pat. No. 5,601,917.
EP 0 592 913 describes a surface protection film for the transit of automobiles which consists of an EVAc copolymer having a vinyl acetate content of 33%. With (his protective film, the application of an adhesive layer does not take place. Admittedly, a film of this kind has a simple structure, but exhibits distinct disadvantages in use, Owing to the high crystalline fraction the bond strength is very low; this deficiency is said to be eliminated by heating on application. Additionally these films, unless provided with a release cover (silicone paper, for example), lead to blocking on storage, as taught by EP 0 768 356. The films described exhibit severe paint deformation and are very difficult to remove following use. A reason for the latter phenomenon is that the EVAc described in the examples, with 33% (w/w) vinyl acetate has sealing properties (it is commonly employed for sealing applications). From 40% (w/w) vinyl acetate on, the crystalline fraction is so low that this defect does not occur; therefore, the protective film of the invention also preferably comprises an adhesive having a high vinyl acetate content.
The adhesive sheet set out in DE 195 32 220, comprising EVAc adhesive, is significantly superior in adhesion to the products described. With the exception of one-component PU systems, there is no effect on the finishes that are to be protected, During removal after use, however, this adhesive sheet has a high bond strength, and so cannot be removed without tearing. This increase in bond strength when the adhesive assembly is stored, which the skilled worker calls peel increase, is caused by interactions of the adhesive, especially polar forces, with the paint. On the other hand, polar comonomers such as acrylate or vinyl acetate give rise to the desired high initial adhesion.
Significantly more stable to UV than polyisobutylenes are adhesives comprising hydrogenated styrene-diene block copolymers, whose use is described in the utility model DE 296 04 473. A substantial disadvantage of such block copolymers is their thermally reversible crosslinking by way of the styrene d
Böhm Nicolai
Hirsch Ralf
Klemp Jobst-Waldemar
Meyer Robert
Müssig Bernhard
Norris McLaughlin & Marcus PA
Tarazano D. Lawrence
tesa AG
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