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PROTECTIVE FILMS
This application is a National Stage Application of International Application No. PCT/US02/33487, filed Oct. 22, 2002, which claims priority to GB 0125319.4, filed Oct. 22, 5 2001.
The present invention relates to protective films and in particular to protective films that can be used to protect the surfaces of smooth articles such as glass or other transparent materials, electrical goods, displays and especially automo- 10 biles particularly during transportation and storage.
Thermoplastic films which may be applied to the automobile body for protection during transportation from manufacture to point of sale and during storage are known. In some instances, wax coatings are used. Where thermo- 15 plastic films are used, the film typically comprises a multi layer film comprising an adhering layer and a protective backing layer. The adhering layer ensures that the film will stick to an article such as an automobile under transportation and storage conditions; the protective backing layer provides 20 the bulk of the protection and easy handling of the film when applied to the surface.
An additional requirement of the adhering layer is that the film can be readily removed from the surfaces and that removal leaves no residues. 25
The film must also have good strength and puncture resistance and be as thin as possible. Furthermore, the materials from which the films are made must be such that economic manufacturing techniques such as blown and cast films, either mono- or co-extrusion, which requires adequate 30 melt strength, may be employed.
Increasingly automobiles are made from a variety of materials. Furthermore, different finishes, particularly paints, are used with different materials. For example, an automobile may contain metal body panels, rubber sealants 35 and plastic components, such as bumpers. Metal panels are typically painted with solvent-based paint systems and plastic components with water-based paint systems. The adhesive properties of the surfaces of these materials and the paints that are used thereon differ. Accordingly, there is a 40 need for protective films which have adequate adhesion to the various surfaces without leaving undesirable deposits on any of the surfaces after removal.
Protective films currently used consist of a polyolefin, usually polyethylene or polypropylene as backing layer and 45 an adhering layer consisting of polyethylene or an ethylene vinyl acetate copolymer containing polyisobutylene. Whilst these films have adequate adhesion to the automobile, they cannot be removed from the automobile without leaving undesirable deposits on the surface. 50
A further requirement for protective films is that they may be applied at room temperature and the necessary adhesion to the surface be achieved simply by pressing the film against the surface to be protected. It will be apparent that the need to, for instance, heat the film to achieve adequate 55 adhesion will be inconvenient when applying film to complex three-dimensional articles such as automobiles. Although films in which the adhering layer contains polyisobutylene as an adhesion enhancer can be applied at room temperature, these films tend to leave residues on the car 60 surface when they are removed. This is thought to be due to the migration of the polyisobutylene within the polymer film.
It has been proposed in PCT Publication WO 91/06609, French Certificate of Utility 2600981, European Patent 65 281694 and European Patent 592913 that laminar films comprising a polyolefin backing layer and an ethylene,
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unsaturated ester copolymer, particularly an ethylene vinyl acetate copolymer layer as the adhering layer may be used as protective films. We have found, however, that if the vinyl acetate content of the adhering layer is sufficiently high to provide the required adhesion, the film is too weak, blocks too much, cannot be readily extruded and sticks on the reel. Furthermore, the protective films of these patents need to be applied under heat to ensure adequate adhesion.
It has been proposed in Japanese Patent publication 54-160482 that a laminated film consisting of a polyethylene base layer having a thickness up to 18 um and an ethylene base copolymer layer having a thickness of at least 10 um may be used to protect metal sheets such as aluminium sheets and stainless steels sheets. A petroleum resin may be incorporated in the ethylene vinyl acetate copolymer adhesive layer and an example shows an ethylene vinyl acetate copolymer layer containing 2 parts by weight of a petroleum resin. The film is used for the protection of aluminium to which it is laminated at 70° C. GB 2277479 is concerned with protective films particularly for plastic sheeting which is subsequently moulded comprising a laminated film consisting of a polyethylene base layer and an ethylene vinyl acetate copolymer adhering layer which may contain an adhesion enhancing resin.
U.S. Pat. No. 5,154,981 is primarily concerned with stretch cling films and is concerned with the multilayer films comprising a cling layer of an ethylene unsaturated ester copolymer containing a tackifier and a polyolefin backing layer. The unsaturated ester is preferably methyl acrylate although vinyl acetate may be used. When a hydrocarbon resin tackifier is used it should have a softening point from 10° C. to 25° C. Although U.S. Pat. No. 5,154,981 states that its films may be used for surface protection applications, the use of a hydrocarbon resin tackifier of such a low softening point renders the film too soft for ready processing and effective surface protection.
Japanese Patent Publication JP 04239081 is concerned with films for the protection of chemically coloured stainless steel. The films are laminar films which may consist of a polyolefin backing layer and a polyolefin or ethylene vinyl acetate copolymer adhering layer. The ethylene vinyl acetate copolymer layer may contain a hydrocarbon resin. In Example 3, which relates to such a film, the ethylene vinyl acetate copolymer contains 6% vinyl acetate. The films are thick and are applied using heat to obtain the desired adhesion.
None of the films of these patents have been commercially successful for the protection of automobiles during transport. Accordingly, there remains a need for a film, which is easily manufactured, preferably by blown or cast co-extrusion, can be reeled and unreeled, which can be applied at room temperature and which achieves sufficient adhesion to all types of surfaces. The film and its adhesion to the surface must be able to withstand the storage and transportation conditions to which it may be subjected. The film must have adequate strength, stiffness and puncture resistance, and the film must be able to be removed from the various types of surfaces without leaving undesirable deposits on the protected surface.
The present invention provides such a film.
SUMMARY OF THE INVENTION
The present invention relates to protective films and in particular to protective films that can be used to protect the surfaces of smooth articles such as glass or other transparent
