Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2000-11-10
2002-12-10
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S340000, C428S3550EN, C428S3550RA, C428S516000, C428S520000, C150S168000, C156S327000
Reexamination Certificate
active
06492017
ABSTRACT:
The invention relates to a protective film whose high transparency and reliable adhesion make it particularly suitable for the temporary protection of automobile glass and also other sensitive surfaces such as metals, plastics and surface coatings.
On the long journey traveled by export vehicles in particular from the manufacturing plant to the end user, starting with the assembly of the vehicle and continuing by way of its loading onto railcars, transportation by rail or road, unloading from the railcar, loading onto ships, the ship journey, unloading from the ship, transportation to the central storage facility, and transportation through to the local dealer, the new vehicle is exposed to diverse harmful influences. Repairs to paint and windows, especially the windshield, are the order of the day, since the customer demands a flawless new vehicle. This is a considerable cost factor for the manufacturers, and there is a great interest in reducing this expense.
Whereas minor paint damage can generally be removed by means of a small refinish, making good a scratch on an automobile window necessitates its complete replacement.
The replacement of a windshield is particularly expensive. In the case of a windshield installed by bonding with a water-reactive PU adhesive, the technique now used almost universally, the windshield is removed using a wire which cuts through the adhesive film. In the course of this operation, the windshield frame paint is often damaged, necessitating additional repairs. For the manufacturer, accordingly, there arise costs for the replacement windshield, for its removal and installation, and, possibly, for the repair of the paint damage caused during its replacement. In some cases, additionally, the delivery times are prolonged significantly, and customers are unhappy.
For a number of years already, paint surfaces of new vehicles, especially exposed surfaces, such as trunk lids, roof and engine hood, in particular, have been effectively masked off using self-adhesive films. They protect the finishes against slight injuries and soiling by media such as battery acid or fuel, fly rust and bird excrement. These films generally comprise unoriented polyolefin films of polyethylene, polypropylene or propylene-ethylene copolymers, and also mixtures of these, filled with TiO
2
to improve the long-term stability. The adhesive composition used frequently comprises polyisobutylene or polyethylene-vinyl acetate.
The former are disclosed in EP 0 519 278 A2, where the adhesive composition is applied to a film which in turn is used to protect automobiles. The pressure-sensitive adhesive is based on polyisobutylene rubber, having a dynamic modulus of elasticity of from 2×10
5
to 7×10
6
dyn/cm
2
, corresponding in SI units to a figure of from 2×10
4
to 70×10
4
Pa, at 60° C. In addition, the adhesive may have been blended with a silicone oil or with a low molecular mass acrylic polymer.
DE 196 35 704 A1 describes a self-adhesive surface protection film made from polyolefins with an adhesive comprising polyethylene-vinyl acetate (EVA) with a vinyl acetate content of from 40 to 80 mol %, especially 70 mol %, and with a loss angle tan &dgr; of from 0.6 to 1.0, measured at a temperature of 60° C. and a frequency of 10
−2
Hz, and from 0.4 to 0.7, measured at a temperature of 60° C. and a frequency of 10 Hz. EVA in the claimed form possesses good initial bond strength to paint and good paint compatibility. The high ultimate bond strength to paints and glass surfaces, although it permits highly reliable bonding, nevertheless necessitates a disproportionately great effort when removing the film, which may adversely affect the health of persons for whom the demasking is a daily task. Moreover, because of the high bond strength, tearing during the demasking operation is a frequent occurrence, and means that the film cannot be removed in one piece.
Those nontransparent, white films specified in the prior art, however, cannot be used for window protection, since the masked vehicles must be moved and arranged a number of times in the course of their distribution, and an unobstructed view through the windows is vital.
There have been numerous descriptions of window films, which alter the properties of the windows to which they are stuck—they do this, for example, by darkening shading, IR absorption for heat insulation, or as antireflection coatings. U.S. Pat. No. 5,925,453, for example, describes a window film which is light-reflecting and IR-absorbing and can be stuck to the inside of curved auto windows. Preferred candidates as backing materials, which may also be blended with the IR absorbent, include polyolefins such as polyethylene and polypropylene, polyvinyl chloride and polyesters such as polyethylene terephthalate and polybutylene terephthalate. Possible adhesive compositions cited are self-adhesive compositions, including synthetic rubbers such as styrene-butadiene rubber, polyisobutylene, styrene block copolymers and polyethylene-vinyl acetate, and also heat- and moisture-activable compositions. The film described, however, has no protective function, especially since it is applied from the inside to the concave glass surfaces. Articles of this kind are normally conceived for permanent bonding and must therefore meet different key requirements.
In the case of a protective film for automobile glass, particular value must be placed not only on outstanding transparency but also on easy, fold-free and rapid applicability and on a balanced bond strength—i.e., a bond strength which is not so weak that the film is detached under the influence of wind or slipstream, or even detaches by itself, but also not so strong that it is impossible to remove the film again without excessive effort or even tearing. Moreover, the film must withstand outdoor weathering periods, typical for its application, of approximately 6 months without becoming brittle, becoming dull, or leaving residues of adhesive composition on removal. The abovementioned requirements place stringent demands on film and adhesive composition and on the tailoring of the two components to one another.
Beiersdorf A G, Hamburg, Germany, has for many years sold as Article 4604 PV1 a transparent protective film which is used, inter alia, for window protection but which in many respects does not meet customer requirements of transparency, weathering stability and bonding reliability for this utility. The aforementioned article comprises a polyethylene backing and is coated with an acrylate self-adhesive composition. The film is slightly cloudy, which manifests itself as highly disruptive especially when light is incident from the sides. After a few weeks or outdoor weathering, the film becomes brittle under the effect of UV light, so that it can no longer be removed in one piece and the adhesive composition remains extensively on the glass. Furthermore, the film loses its adhesion properties at temperatures above 60° C., which are easily achieved under insolation, whereupon shrinkage-related folds are produced.
It is an object of the invention to provide a surface protection film for automobile glass, especially windshields, and other sensitive surfaces which does not exhibit the above-described disadvantages of the prior art, or not to the same extent. In particular, the surface protection film should possess not only a pronounced initial bond strength but also a balanced ultimate bond strength and an extremely high transparency, and also weathering stability.
This object is achieved by means of a surface protection film as laid down in the main claim. The subclaims relate to advantageous developments of the surface protection film.
The invention accordingly provides the construction of a surface protection film comprising a transparent backing of polypropylene or propylene-ethylene copolymer, which comprises a light stabilizer, and a self-adhesive composition of polyethylene-vinyl acetate (EVA) having a VA fraction of from 40 to 80% by weight and a melt index MFI in accordance with ISO 1133 (A/
Böhm Nicolai
Klemp Jobst-Waldemar
Ströh Horst-Günther
Morris McLaughlin & Marcus
Tarazano D. Lawrence
tesa AG
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