Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1999-08-11
2001-05-22
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S195100, C428S203000, C428S204000
Reexamination Certificate
active
06235375
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to oligomers that contain ultraviolet light absorbing compounds (UVAs) covalently bound to the oligomeric backbone. The invention also relates to stabilization of polymers or other substrates against photochemical degradation by use of the oligomers.
BACKGROUND OF THE INVENTION
Many plastics tend to degrade when exposed to sunlight or other sources of ultraviolet (UV) light. This exposure results in, for example, loss of tensile strength, embrittlement, and discoloration. To help prevent such degradation, ultraviolet light stabilizers are often incorporated into a polymer composition, which is used as a protective top layer for underlying materials. These uv light stabilizers perform well but are often not stable in or compatible with the polymer, which results in the stabilizer leaving the polymer by leaching, migration, vaporization, or other means. When the uv stabilizer levels are lowered in this manner, their protective effect is diminished, leading to degradation of the polymer and the underlying materials.
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. Other classes of ultraviolet light absorbers include the 2-hydroxybenzophenones and the diphenylcyanoacrylates.
While such compounds are known to absorb ultraviolet light, their incompatibility with the polyolefins often used as the top film in multilayer sheetings has limited their usefulness in such constructions. The low solubility and high mobility of typical ultraviolet light absorbers in polyolefins results in an inability to maintain high levels of these compounds in polyolefin films; the compounds tend to bloom or migrate out of the film, and the protective properties of the compounds are lost.
Much effort has been directed to the development of methods of maintaining the uv stabilizer compound in a selected polymeric matrix. Ultraviolet light stabilizers have been developed that have polymerizable functionalities. The polymerizable stabilizer is then incorporated into the polymer as a co-monomer or copolymerized with another monomer to form a stabilizing polymer that can be added to the desired polymer. Because the stabilizing compound is then part of the polymer backbone, it remains in the polymer composition and the stabilizing benefits are retained for a longer period of time. Examples of incorporation of a stabilizing monomer into a polymer backbone may be found in, for example, Vogl et al., POLYMER, Vol. 26, p. 1288 (1985); U.S. Pat. No. 3,313,866 (Horton et al.), U.S. Pat. No. 4,128,536 (Brodsky et al.), and U.S. Pat. No. 4,528,311 (Beard et al.).
There has also been development in the area of “attaching” the ultraviolet light absorbing compound to a polymer backbone by selecting UV light absorbers with groups that react with various functionalities present on the polymer. Fu et al., in U.S. Pat. No. 4,413,096, describe &agr;-olefin copolymers wherein hindered amine light stabilizers are pendant to the polymer backbone. The Fu copolymers may be prepared by transesterification of the polymer with the hindered amine light stabilizing compound.
There is a continuing need in the art for a method of stabilizing polymers such as polyolefins with ultraviolet light absorbing compounds that provides lasting protection both to the polyolefin and to articles that incorporate the polyolefin.
SUMMARY OF THE INVENTION
We have found that hydroxy or amine functional ultraviolet light absorbing compounds may be covalently bound to a carboxyl functional oligomer. This covalent bonding allows us to deliver a compatible non-fugitive uv absorber to polyolefin type polymers. Accordingly, the invention provides an ultraviolet light absorbing oligomer made up of an ultraviolet light absorbing oligomer comprising the reaction product of a carboxyl functional oligomer and a hydroxy or amine functional ultraviolet light absorbing compound, wherein the ultraviolet light absorbing compound is a group of formula (I), (II), (III), or (IV):
wherein each R1 is independently halogen, hydroxy, straight-chain or branched C
1-12
alkyl, straight-chain or branched C
2-12
alkenyl, straight-chain or branched C
1-12
alkoxy, straight-chain or branched C
2-12
alkenyloxy, straight-chain or branched C
1-12
alkanol, amino, straight-chain or branched C
1-12
alkylamino, or straight-chain or branched C
1-12
dialkylamino; Y is a C
1-18
alkylene or C
2-18
alkenylene group which may be straight-chain or branched and which may be interrupted by one or more
wherein each R2 is independently H or C
1-6
alkyl that may be straight-chain or branched; and Z is —OH or —NH
2
.
The invention also provides polymer compositions that contain the UV light absorbing oligomer and a polyolefin, and articles such as retroreflective sheetings, conformable pavement markers, and signs that contain films made of the polymer composition.
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 polyolefin and the ultraviolet light absorbing oligomer of the invention; a base layer comprising a deformable thermoplastic polymer and a nonreinforcing mineral particulate; a pressure sensitive adhesive layer; and a release liner.
In another aspect of the invention is provided an enclosed-lens retroreflective sheeting 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 polyolefin and the ultraviolet light absorbing oligomer of the invention.
All percentages are weight percentages based on total composition weight unless otherwise specified.
DETAILED DESCRIPTION OF THE INVENTION
The UV light absorbing oligomers of the invention are generally prepared by reacting a carboxyl bearing oligomer with a hydroxy or amine functional ultraviolet light absorbing compound. The carboxyl functional oligomer contains at least one monomer having a pendant carboxyl (—COOH) group. Carboxyl functional oligomers useful in the formation of the UV light absorbing oligomers of the invention typically have a weight average molecular weight of about 100 to 10,000, preferably about 1000 to 3500. The acid number (mg KOH required to neutralize 1 gram of the oligomer) of the oligomer is generally about 40 to 180.
Monomers useful in the formation of the carboxyl functional oligomer include ethylenically unsaturated carboxylic acids. The carboxyl functional oligomer may be a homopolymer or copolymer of such carboxy bearing monomers. The copolymer may contain different carboxy bearing monomers, or may contain a carboxy bearing monomer and a non-carboxy bearing monomer. Examples of useful types of non-carboxy bearing monomers include ethylenically unsaturated carboxylic acid esters, olefins, vinyl compounds, and the like.
Suitable ethylenically unsaturated carboxylic acids include alkenoic and aralkenoic mono- di- and tri-carboxylic acids having up to 20 carbon atoms as well as acids having higher numbers of carboxyl groups. Examples of such acids include acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid, itaconic acid and cinnamic acid. Of these, acrylic acid and methacrylic acid are preferred.
Comonomers that may be used in the preparation of the carboxyl functional polymer include olefins such as ethylene, propylene, and butylene; ethylenically unsaturated aromatic monomers that contain up to 20 carbon atoms such as styrene and vinyl tolulene; ethylenically unsaturated esters of carboxylic acids that contain a total of up to 20 carbon atoms such as vinyl acetate; and the
Burns David M.
Olson David B.
3M Innovative Properties Company
Ahmad Nasser
Gwin Doreen S. L.
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