Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2001-02-15
2003-02-11
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S343000, C428S354000, C428S3550BL
Reexamination Certificate
active
06517937
ABSTRACT:
The invention relates to a protective film whose great weathering stability and adhesion reliability make it especially suitable for temporarily protecting fresh automobile finishes from soiling and damage, as well as for other sensitive surfaces such as metals, plastics and glazing.
The preservation and protection of motor vehicles in the course of transportation from manufacturer to dealer has long been common practice.
The conventional method of preserving automobiles is 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, such as the hood, roof and trunk lid, a thin and usually nonuniform layer of this nature does not afford adequate protection against external influences, such as the corrosive effect of bird droppings, for example.
A considerable disadvantage of sealing with paraffin wax is the need to remove the preservative using a steam jet, surfactants or solvents. Environmentally sound recovery and disposal of the residues are the cause of great complexity in terms of apparatus, and of very high costs.
A current development in the field of automotive transit protection is the use of covers which go over the entire vehicle and are shrunk on to fit by exposure to heat. Cover solutions of this kind are very costly and involve a great deal of effort in applying the cover, effecting shrinkage, and especially when climbing into the masked automobile. For that particular purpose, zip fastener openings are provided, whose necessary opening and reclosing is time-consuming. Visibility when parking is severely impaired, and there are areas of dulling on the finish as a result of enclosed dirt and unavoidable scuffing. This solution cannot become widespread.
Instead, increasing use is being made of temporarily applied self-adhesive surface protective films. These are specifically intended for the mechanical and chemical protection of fresh motor vehicle finishes, have a protective action which is much better than that of the waxes, and have the advantage over the covers of being more cost effective and significantly quicker to apply.
A key requirement of a surface protective film is its weathering stability over a period of more than six months. Accordingly, even after six months of intense sunlight exposure, such a film must be removable in one piece and must not leave any residues of adhesive composition on the finish. Moreover, it must have a sufficient initial tack, so as not to detach of itself prematurely in situations of difficult bonding geometry, but at the same time must not have too great an ultimate bond strength to the finish, so that the film can be removed without substantial force being applied and certainly without tearing.
In accordance with the prior art, therefore, film materials used are generally polyolefins or mixtures thereof which are normally blended with light stabilizers and titanium dioxide.
A diversity of systems are used as self-adhesive compositions, but are without exception hampered by weaknesses.
Self-adhesive compositions based on natural rubber possess relatively good initial adhesion and can be removed again without residue. Even on short-term exposure to UV radiation, however, these compositions are not stable to aging. Following realistic weathering exposures over a period of several months, this leads to severe greasy residues or hardened paintlike residues on the finish.
U.S. Pat. No. 5,612,136 mentions a protective film having an acrylate-based self-adhesive composition. Polyacrylate compositions are indeed highly UV-stable. If, however, uncrosslinked polyacrylate compositions are stored under alternating climatic conditions, their compatibility with paint surfaces is good only in some cases. Compatibility denotes that the paint surface shows no deformation whatsoever after the adhesive tape is removed. Moreover, these compositions exhibit an undesirable level of peel increase. Where these compositions are strongly crosslinked chemically or by radiation, they are indeed easier to remove but on the other hand cause increased incidence of permanent deformations of the paint surface which are clearly visible.
Self-adhesive compositions based on polyisobutylene (polyisobutylene homopolymer or butyl rubber) exhibit little adhesion to finishes customary in the automotive industry following storage under alternating climatic conditions. Under jerky stresses, such as on flapping in the slipstream, the adhesion is so low that the bond strength required in the art is not always present to a sufficient extent. Under the influence of moisture, in particular, the adhesion is often reduced to such an extent that the film detaches from the protected vehicles in the course of transit, resulting firstly in a loss of protection and secondly in a safety risk if it drifts onto the windshield of following vehicles. Furthermore, these adhesives are not very cohesive and therefore produce residues of composition when the film is removed, especially in the edge region after UV aging. Moreover, this self-adhesive composition is not compatible with the 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 remain on the rubber. Adhesive articles of this kind are described in EP 0 519 278, JP 95-325285 and U.S. Pat. No. 5,601,917.
Substantially more UV-stable than polyisobutylenes are adhesives produced from hydrogenated styrene-diene block copolymers, whose use is described in JP 827 444. An important disadvantage of such block copolymers is their thermally reversible crosslinking by way of the styrene domains. If an adhesive film produced from them is removed in the summer from a vehicle which has become hot in the sun, the adhesive largely remains adhering to the finish, since the cohesion of the adhesive compositions is lower than the adhesion to the finish. Heating always leads to the shrinkage of the protective film, and so the adhesive, soft in the heat, smears onto the metal at the retreating edges of the adhesive film.
The adhesive film described in DE 195 32 220 A1, comprising ethylene-vinyl acetate (EVAc) adhesive, is significantly superior in adhesion to the systems described above. With the exception of one-component PU systems, there is no effect on the finishes to be protected. During removal after use, however, this adhesive film has a bond strength which is much too high, as a result of which it is in many cases impossible to remove the adhesive film without tearing. This increase in bond strength when the adhesive composite is stored, referred to by the skilled worker as peel increase, is caused by interactions of the adhesive, especially polar forces, with the finish. On the other hand, polar comonomers such as acrylate or vinyl acetate give rise to the desired high initial adhesion.
WO 96/37568A1 describes the use of polyhexene and/or polyoctene for a nonpolar pressure-sensitive adhesive. Because of the low cohesion, the polymers described in the examples do in fact exhibit little peel increase, but these polymers, owing to the low molecular weight of commercial polymers of this kind, likewise lead to residues, which it is attempted to avoid by adding other polymers, referred to therein as “cold flow restricting agents”. For practical purposes, nevertheless, these adhesives are of inadequate cohesion, which leads to residues after weathering, especially if the adhesive tape shrinks under the effect of heat. A similar phenomenon is displayed by ethylene-propylene-diene copolymers (EPDM) as specified in DE 197 42 805. These, furthermore, exhibit very limited initial adhesion.
It is an object of the invention to provide a self-adhesive protective film, especially for fresh automobile finishes, which does not have (or not to the same extent) the above-described disadvantages of the prior art. In particular, the self-adhesive protective film should possess not only a pronounced initial bond strength but also a balanced (not too strong) ult
Böhm Nicolai
Klemp Jobst Waldemar
Schütz Ingolf
Dawson Robert
Keehan Christopher M.
Norris & McLaughlin & Marcus
tesa AG
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