Amide functional ultraviolet light absorbers for fluoropolymers

Details Amide functional ultraviolet light absorbers for fluoropolymers Amide functional ultraviolet light absorbers for fluoropolymers

1999-08-03

2001-07-17

Acquah, Samuel A. (Department: 1711)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

C548S259000, C548S260000, C548S261000, C526S259000, C524S091000, C524S359000, C524S462000, C524S502000, C524S505000, C524S507000, C524S539000, C524S543000, C524S545000, C524S565000, C428S421000, C428S423100, C428S542600, C428S690000

Reexamination Certificate

active

06261676

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to ultraviolet light absorbing materials that comprise a fluoropolymer and an amide functional ultraviolet light absorbing compound. The invention also relates to films that incorporate such ultraviolet light absorbing materials and to articles that include such films.
BACKGROUND OF THE INVENTION
The effect of ultraviolet light on articles such as retroreflective sheetings for use on license plates or signage articles that are exposed to the sun or other sources of ultraviolet light are of great concern to the manufacturers of such articles. Over time, constant or repeated exposure to ultraviolet light can result in fading of the dyes and pigments used in such articles and in the degradation or breakdown of the adhesives, polymers, and other materials used in the construction of the articles. This fading and degradation shortens the useful life of the articles in question, making protection from ultraviolet light exposure an issue of great importance to the manufacturers of such articles.
Molecules that function as ultraviolet light absorbers are generally known in the art. For example, in U.S. Pat. No. 4,853,471 Rody et al. describe 2-(2-hydroxyphenyl)benzotriazole compounds that are useful as ultraviolet light absorbers. These compounds are described as useful in the stabilization of a wide variety of polymeric materials against ultraviolet light, particularly those that are used in the preparation of photographic materials.
Fluoropolymers are sometimes used as top films in multilayer constructions which are exposed to ultraviolet light. The incompatibility of known ultraviolet absorbing compounds with such fluoropolymers limits their long term usefulness in such constructions. The low solubility and/or high mobility of typical ultraviolet light absorbers in fluoropolymers results in an inability to maintain high levels of these compounds in fluoropolymeric films; the compounds tend to bloom or migrate out of the film, and the protective properties of the compounds are lost.
Therefore, a need exists for ultraviolet light absorbing materials that are compatible with and resist blooming out of fluoropolymers, and for products such as fluoropolymeric films and other articles that incorporate such a material.
SUMMARY OF THE INVENTION
The invention provides an ultraviolet light absorbing material made up of a fluoropolymer and an amide functional ultraviolet light absorbing compound, wherein the ultraviolet light absorbing compound is hydrogen bonded to the fluoropolymer and there is at least one hydrogen bonding site on the polymer per mole of ultraviolet light absorbing compound. For the sake of clarity, the invention will be described with reference to fluoropolymers (i.e., products containing a polymer which includes chain units of the formula
The invention also provides a polymeric film made up of a polymeric matrix and an ultraviolet light absorbing material, said ultraviolet light absorbing material made up of a fluoropolymer and an amide functional ultraviolet light absorbing compound, wherein the amide functional ultraviolet light absorbing compound is hydrogen bonded to the fluoropolymer and there is at least one hydrogen bonding site on the polymer per mole of ultraviolet light absorbing compound. By “polymeric matrix” is meant a matrix comprising one or more homopolymers, copolymers, polymer blends, or polymer alloys. The ultraviolet light absorbing material must be compatible with the polymeric matrix, i.e., it is miscible therein or can be blended therein.
The invention further provides a method of protecting a substrate from the effects of ultraviolet light, the method comprising applying a polymeric film to the substrate, said film comprising a polymeric matrix and an ultraviolet light absorbing material, said ultraviolet light absorbing material comprising a fluoropolymer and an amide functional ultraviolet light absorbing compound, wherein the ultraviolet light absorbing compound is hydrogen bonded to the fluoropolymer and there is at least one hydrogen bonding site on the polymer per mole of ultraviolet light absorbing compound.
In addition the invention provides products such as retroreflective sheetings, signage articles and conformable marking sheets that comprise the polymer films of the invention. In one such aspect the invention provides a conformable marking sheet comprising a top polymeric film layer having glass microspheres and skid resistant particles partially embedded therein, the film comprising a polymer matrix and an ultraviolet light absorbing material, the ultraviolet light absorbing material comprising a fluoropolymer and an amide functional light absorbing compound, wherein the amide functional ultraviolet light absorbing compound is hydrogen bonded to the fluoropolymer and there is at least one hydrogen bonding site on the polymer per mole of ultraviolet light absorbing compound; an optional base layer, e.g., comprising a deformable thermoplastic polymer and a nonreinforcing mineral particulate; an optional adhesive layer, e.g., pressure sensitive adhesive; and an optional release liner.
In another aspect of the invention is provided an enclosed-lens retroreflective sheeting, e.g., comprising a layer of lenses anchored in a binder layer, a specularly reflective layer underlying the lenses, and a top layer comprising a polymeric film, said film comprising a polymeric matrix and an ultraviolet light absorbing material, said ultraviolet light absorbing material comprising a fluoropolymer and an amide functional ultraviolet light absorbing compound, wherein the amide functional ultraviolet light absorbing compound is hydrogen-bonded to the fluoropolymer and there is at least 1 hydrogen bonding site on the polymer per molecule of ultraviolet light absorbing compound. Embedded-lens retroreflective sheetings and encapsulated-lens retroreflective sheetings may be made in accordance with the invention. Retroreflective signs and articles including such sheetings are also provided.
In another aspect, the invention provides a cube corner type retroreflective article comprising an overlay or cover layer with a layer of cube comer shaped elements on a side thereof wherein the overlay or cover layer comprises a film comprising a polymeric matrix and an ultraviolet light absorbing material, the ultraviolet light absorbing material comprising a fluoropolymer and an amide functional light absorbing compound, wherein the anide functional ultraviolet light absorbing compound is hydrogen bonded to the fluoropolymer and there is at least one hydrogen bonding site on the polymer per mole of ultraviolet light absorbing compound.
The term “polymer” is used herein to refer to compounds that have more than one occurrence of a given monomeric structural unit.
As used herein the term “amide functional ultraviolet light absorbing compound” refers to a compound that absorbs ultraviolet light and that contains at least one —CONH— moiety. The term “UVA” is used interchangeably with the term “amide functional ultraviolet light absorbing compound”.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION
Ultraviolet Light Absorbing Material
As described above, the ultraviolet light absorbing material of the invention is composed of an amide functional light absorbing compound and a fluoropolymer. In these materials there is at least one hydrogen bonding site present on the polymer per mole of ultraviolet light absorbing compound and the amide functional ultraviolet light absorbing compound is hydrogen bonded to the fluoropolymer.
In addition to absorbing ultraviolet light, the UVA's useful in the invention are preferably transparent to visible light. Useful classes of amide functional ultraviolet light absorbing compounds include amide containing 2-hydroxyphenylbenzotriazoles, 2-hydroxybenzophenones, phenylene-bis-benzoxazinones, diphenylcyanoacrylates, and triazines.
Any 2-hydroxyphenylbenzotriazole ultraviolet light absorbing compound that contains an amide group may be used in the material of the invention. Sui

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