Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-01-07
2001-08-07
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S035800, C428S035900, C428S212000, C428S343000, C428S346000, C428S349000, C428S480000, C428S458000
Reexamination Certificate
active
06270888
ABSTRACT:
This invention relates to a polymeric film, and in particular to a heat-sealable film which comprises an ultra-violet (UV) light absorber, and to a metal sheet comprising said film.
Metal sheet, in coil or plate form, needs to be coated with protective layers in order for it to possess adequate corrosion resistance. Generally paint layers, or polymeric films such as polyvinyl chloride (PVC), or a combination of the two have been used to coat metal sheet. Polymeric films have certain advantages over paint layers, such as hardness, weatherability and aesthetic appearance. Unfortunately, polymeric films can be difficult to bond to the primer-coated or painted metal sheet. In addition, for certain applications of coated metal sheet, polymeric films may possess insufficient weatherability, particularly when metal sheet is exposed to sunlight, eg when used as external cladding for buildings.
Polyester films generally exhibit a lack of stability to UV radiation. This lack of stability manifests itself in a yellowing, hazing and cracking of the polyester film on exposure to sunlight, which has limited the potential uses of the film in an outdoor environment.
It is known to increase the stability of polymers, such as polyester to UV light by the incorporation therein of a UV absorbing material. A UV absorber has an extinction coefficient much higher than that of the relevant polymer such that most of the incident UV light is absorbed by the UV absorber instead of by the polymer. The UV absorber generally dissipates the absorbed energy as heat, ie does not result in degradation of the polymer chain, with consequent increase in the stability of the polymer to UV light.
Some UV absorbers are actually degraded by UV light which results in a reduction of effect over time. In addition, some UV absorbers have relatively high volatility and/or thermally degrade which can cause problems including reduction in effectiveness, particularly when incorporated into a polymer for making film.
We have now devised a polymeric film and a laminated metal sheet which reduces or overcomes at least one of the aforementioned problems.
SUMMARY OF INVENTION
Accordingly, the present invention provides a polymeric film comprising a polyester film substrate comprising in the range from 0.1% to 10% by weight, relative to the weight of the polyester, of at least one UV absorber, and a heat-sealable layer on a surface of the substrate.
The invention also provides a method of producing a polymeric film which comprises forming a substrate by extruding a layer of molten polyester comprising in the range from 0.1% to 10% by weight, relative to the weight of the polyester, of at least one UV absorber, quenching the extrudate, orienting the quenched extrudate in at least one direction, and forming a heat-sealable layer on a surface of the substrate.
The invention further provides a use of a polymeric film comprising a polyester film substrate comprising in the range from 0.1% to 10% by weight, relative to the weight of the polyester, of at least one UV absorber, and a heat-sealable layer on a surface of the substrate, as a protective coating layer on a metal sheet.
The invention still further provides a laminated metal sheet comprising (i) a metal sheet, (ii) an optional primer layer, (iii) a paint layer, and (iv) a polymeric film comprising a polyester film substrate comprising in the range from 0.1% to 10% by weight, relative to the weight of the polyester, of at least one UV absorber, and a heat-sealable layer on a surface of the substrate, the heat-sealable layer being in contact with the paint layer.
The polyester film substrate is a self-supporting film by which is meant a self-supporting structure capable of independent existence in the absence of a supporting base.
A polyester suitable for use in the formation of a substrate layer is preferably a synthetic linear polyester and may be obtained by condensing one or more dicarboxylic acids or their lower alkyl (up to 6 carbon atoms) diesters, eg terephthalic acid, isophthalic acid, phthalic acid, 2,5-, 2,6- or 2,7-naphthalenedicarboxylic acid, succinic acid, sebacic acid, adipic acid, azelaic acid, 4,4′-diphenyldicarboxylic acid, hexahydro-terephthalic acid or 1,2-bis-p-carboxyphenoxyethane (optionally with a monocarboxylic acid, such as pivalic acid) with one or more glycols, particularly an aliphatic or cycloaliphatic glycol, eg ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol and 1,4-cyclohexane dimethanol. A polyethylene terephthalate or polyethylene naphthalate film is preferred. A polyethylene terephthalate film is particularly preferred, especially such a film which has been biaxially oriented by sequential stretching in two mutually perpendicular directions, typically at a temperature in the range from 70 to 125° C., and preferably heat set, typically at a temperature in the range from 150 to 250° C., for example as described in GB-A-838708.
The polyester substrate may be unoriented, or preferably oriented, for example uniaxially oriented, or more preferably biaxially oriented by drawing in two mutually perpendicular directions in the plane of the film to achieve a satisfactory combination of mechanical and physical properties. Simultaneous biaxial orientation may be effected by extruding a thermoplastics polymeric tube which is subsequently quenched, reheated and then expanded by internal gas pressure to induce transverse orientation, and withdrawn at a rate which will induce longitudinal orientation. Sequential stretching may be effected in a stenter process by extruding the thermoplastics material as a flat extrudate which is subsequently stretched first in one direction and then in the other mutually perpendicular direction. Generally, it is preferred to stretch firstly in the longitudinal direction, ie the forward direction through the film stretching machine, and then in the transverse direction. A stretched substrate film may be, and preferably is, dimensionally stabilised by heat-setting under dimensional restraint at a temperature above the glass transition temperature thereof.
In principle, any organic or inorganic UV absorber suitable for use in polyester may be employed in the present invention. Suitable examples include the organic UV absorbers disclosed in Encyclopaedia of Chemical Technology, Kirk-Othmer, Third Edition, John Wiley & Sons, Volume 23, Pages 615 to 627. Particular examples of UV absorbers include benzophenones, benzotriazoles (U.S. Pat. Nos. 4,684,679, 4,812,498 and 4,681,905), benzoxazinones (U.S. Pat. Nos. 4,446,262, 5,251,064 and 5,264,539) and triazines (U.S. Pat. Nos. 3,244,708, 3,843,371, 4,619,956, 5,288,778 and WO 94/05645). The teaching of the aforementioned patent specifications is incorporated herein by reference.
In one embodiment of the invention, the UV absorber may be chemically incorporated in the polyester chain. Preferred UV stable polyesters are produced by incorporating benzophenones in to the polyester, for example as described in EP-A-0006686, EP-A-0031202, EP-A-0031203 and EP-A-0076582, the teaching of which is incorporated herein by reference.
Triazines are preferred UV absorbers, more preferably hydroxyphenyltriazines, and particularly hydroxyphenyltriazine compounds of Formula 1
wherein R is hydrogen, C
1
-C
18
alkyl, C
2
-C
6
alkyl substituted by halogen or by C
1
-C
12
alkoxy, or is benzyl and R′ is hydrogen or methyl. R is preferably C
1
-C
12
alkyl or benzyl, more preferably C
3
-C
6
alkyl, and particularly hexyl. R′ is preferably hydrogen. An especially preferred UV absorber is 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol, which is commercially available as Tinuvin 1577 FF from Ciba-Additives.
Suitable inorganic UV absorbers include metal oxide particles, such as zinc oxide or titanium dioxide, having a mean crystal size, as determined by electron microscopy, of less than 200 nm, more preferably in the range from 5 to 150 nm, particularly 10 to 100 nm, and especially 15 to 40 nm. Titanium dioxide particles are particularly preferred.
The titanium di
Lovatt Allan
Rutter Philip Mark
Chen Vivian
Dupont Teijin Films US Limited Partner
Golian Andrew G.
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