Stock material or miscellaneous articles – Structurally defined web or sheet – Including variation in thickness
Reexamination Certificate
1999-12-30
2002-10-29
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including variation in thickness
C428S143000, C428S522000, C359S515000, C359S529000, C359S534000, C524S090000, C524S102000, C524S567000
Reexamination Certificate
active
06472050
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to polymeric articles containing fluorescent dyes. More particularly, the invention concerns dye-stabilized polyvinyl chloride compositions, and articles therefrom, useful for making flexible retroreflective sheeting that has superior fluorescence durability and improved retention of retroreflectivity.
BACKGROUND OF THE INVENTION
In the highway construction industry, fluorescent orange warning signs are used to alert drivers of on-going construction activity. The bright color and/or the fluorescent material attracts the driver's eye to the sign. Typically, these signs are fabricated by adhesive lamination of retroreflective sheeting to a rigid aluminum or wood sign substrate. However, such a rigid construction has two primary problems. First, the wood or aluminum substrate makes these signs bulky and awkward to move, especially for temporary highway construction activities. Second, such signs can present a potentially deadly hazard to construction zone workers. When hit by a vehicle moving at high speeds, these rigid signs become projectiles capable of severely injuring a worker. Hence the need for soft, flexible signs which can easily be rolled-up and moved, and which do not present a projectile hazard.
Fluorescent roll-up signs fabricated from flexible polyvinyl chloride (“PVC”) are known in the art. Unfortunately, when used to manufacture microprismatic retroreflective films, flexible PVC suffers from two serious drawbacks: loss of retroreflectivity, and loss of fluorescence. Loss of retroreflectivity is due in part to the fact that PVC is a soft, flexible material. Unlike polymethyl methacrylate or polycarbonate microprisms (used in traditional sheeting materials) which are rigid and inflexible, microprisms formed in plasticized PVC are subject to deformation when the sheeting material is exposed to high tension or pressure as is typically the case under the stress conditions encountered in the production, handling and ultimate roadway use of such sheetings. Typically, if the microprism cube corner angles change by more than about 0.01°, the retroreflective levels will be significantly reduced.
Losses in retroreflectivity can further be attributed to the use of plasticizer compounds in the manufacture of PVC film. Plasticizers are typically added to PVC resin to make the resin more flexible. However, most plasticizers will eventually migrate from the PVC film. When the flexible PVC is used for retroreflective applications, such migration can result in retroreflectivity losses due to slight disfiguration of the microprisms as the plasticizer exudes from the film and changes the film's overall material composition. This phenomenon is particularly noticeable in outdoor applications where the material may be exposed to elevated temperatures during the summer months. The plasticizers commonly used in PVC retroreflective film are low molecular weight monomeric plasticizers (typically <700 grams/mole) and often from the phthalate family, such as dioctyl phthalate or diisononyl phthalate. Given the problems noted above, there is presently a need to provide PVC reflective sheeting capable of retaining more of its retroreflectivity over time.
A further problem in fluorescent PVC roll up signs is that ultraviolet exposure causes the fluorescence to fade very quickly, typically in two to three months. To circumvent this problem, many manufacturers create fluorescent orange PVC roll-up sheets by combining two different layers of PVC. A top (outer) layer of the flexible PVC is colored with a fluorescent pink colorant. A lower layer having reflective elements is colored with a non-fluorescent orange colorant. The combination of these two layers produces a brilliant fluorescent orange color. After the pink flourescent layer fades (which typically occurs in 2-3 months of outdoor exposure), a non-fluorescent orange sign will remain. Although this approach for extending the useful life of flexible highway signs has met with some acceptance, it still does not address the fundamental problem of how to achieve a more stable (and therefore longer-lived) fluorescence in retroreflective PVC roll-up films when fluorescent dyes are incorporated directly into the retroreflective PVC layer.
SUMMARY OF THE INVENTION
The present invention provides a fluorescence-stabilized polymeric composition comprising: polyvinyl chloride resin; a fluorescent dye selected from the group consisting of perylene imide fluorescent dyes; an ultraviolet absorbing compound selected from the group consisting of benzophenone ultraviolet absorbers; and a light stabilizing compound selected from the group consisting of polymeric hindered amine light stabilizer compounds having molecular weight greater than about 1500. The combination of benzophenone UV absorbers and polymeric HALS lends surprising stability to the perylene imide dyes.
The invention is further directed to a polymeric film suitable for fabricating retroreflective sheeting, comprising polyvinyl chloride resin and a polymeric plasticizer having molecular weight greater than about 1000, and preferably in the range of about 2000 to about 8000. Particularly preferred are polymeric plasticizers having molecular weight in the range of about 2500 to about 5000. It has been discovered that the use of a polymeric plasticizer can substantially minimize the retroreflectivity losses which flexible PVC signs typically exhibit over time.
In still a further aspect the invention is directed to a flexible road sign capable of being manually rolled and unrolled by a user, wherein the sign comprises a fluorescent, retroreflective polymeric sheet. The retroreflective sheet comprises a polyvinyl chloride resin having an intrinsic viscosity in the range of about 1.02 to about 1.14; a polymeric plasticizer having molecular weight in the range of about 2000 to about 8000; a fluorescent perylene imide dye; an ultraviolet absorbing benzophenone compound; a polymeric hindered amine light stabilizing compound having molecular weight greater than about 2000; and further comprising a plurality of retroreflective elements.
In a particularly preferred embodiment the invention is a flexible, rollable fluorescence-stabilized retroreflective road sign comprising a retroreflective, flourescent sheet, where the retroreflective sheet comprises; (i) polyvinyl chloride resin having an intrinsic viscosity in the range of about 1.08 to about 1.10; (a) a plasticizer mixture comprising (1) a polymeric plasticizer selected from polyester glutarate, adipate or sebacate plasticizers having molecular weight in the range of about 2500 to about 4200, and (b) a monomeric plasticizer selected from phthalate plasticizers having molecular weight less than about 1000; wherein the polyester plasticizer constitutes about 25 to about 45 percent by weight of the plasticizer mixture; and the plasticizer mixture is present in the polymeric sheet in an amount ranging from about 30 to about 35 parts per hundred by weight of said polyvinyl resin in the sheet; (iii) a mixture of perylene imide fluorescent dyes comprising BASF Lumogen F Red 300 and BASF Lumogen F Orange 240, wherein the dye mixture constitutes about 0.05 to about 0.5 percent by weight of the sheet; (iv) an ultraviolet absorbing compound comprising 2-hydroxy-4-n-octoxybenzophenone present in an amount constituting about 0.2 to about 4 percent by weight of the sheet; (v) a polymeric hindered amine light stabilizing compound comprising the polymerization product of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine and having molecular weight greater than about 2000, wherein the light stabilizing compound constitutes about 0.1 to about 3 percent by weight of the sheet; and (vi) a plurality of cube-corner retroreflective elements.
In still a further embodiment, the invention provides a polymeric retroreflective film comprising polyvinyl chloride resin and a plurality of retroreflective elements in the form of corner-cube microprisms, wherein the film exhibits an “Average Perc
Avery Dennison Corporation
Jones Day Reavis & Pogue
Watkins III William P.
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