Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-09-24
2004-05-11
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S172000, C523S205000, C524S805000, C526S247000, C428S407000, C428S421000, C359S453000
Reexamination Certificate
active
06734227
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical elements comprising fluorochemical surface treatments. The invention further relates to articles such as retroreflective sheetings, pavement markings and beaded projection screens comprising a binder and the surface treated optical elements. The surface treatment comprises at least one fluoropolymer selected from a) fluoropolymers comprising a fluorinated hydrocarbon backbone and side chains comprising at least one of fluoroalkyl, fluoroether alkyl, fluoroalkoxy and mixtures thereof; and b) fluoropolymers comprising a hydrocarbon backbone and side chains comprising at least one of fluoroether alkyl, fluoroalkoxy and mixtures thereof.
BACKGROUND OF THE INVENTION
Beaded projection display screens, retroreflective sheeting used in the manufacture of roadway signs, and retroreflective paints typically include optical elements adhered through the use of a binder. In the case of beaded projection display materials, the optical elements are microscopic glass beads that act as lenses to collect projected light from the rear of the screen and focus it to relatively small spots, near the surfaces of the microspheres. The foci are approximately in the areas where the optical elements contact a front support layer. In other retroreflective materials, the optical elements act as lenses which focus the light onto a reflector (metal mirror of diffusely reflecting pigment) and once the light has been reflected off the reflector the microspheres again act as lenses to resend the light back toward the incoming light source. In order to contribute the desired retroreflective property, however, it is important that a layer of glass microspheres be present on the surface of the binder layer.
As discussed in U.S. Pat. No. 3,222,204, ordinary glass beads tend to sink into the uncured liquid binder layer. In instances wherein the individual beads are not entirely submerged, the optical properties of the bead can also be impaired by the binder wetting out the bead surface and spreading on the exposed bead surface. To address this problem, U.S. Pat. No. 3,222,204 teaches coating the glass beads with a thin surface coating of an oleophobic fluorocarbon-sizing agent. At column 5, lines 61-75, this reference states that, “Aqueous treating solutions of fluorocarbon chromium coordination complexes are preferred and are described in U.S. Pat. Nos. 2,662,835 (Dec. 15, 1953) and 2,809,990 (Oct. 15, 1957) and 2,934,450 (Apr. 26, 1960). The complex may be made by reacting chromyl chloride with a fluorocarbon monocarboxylic acid (having a highly fluorinated terminal chain or tail containing 4 to 10 carbon atoms) in an isopropanol vehicle that serves as both a solvent and reducing agent, the chromium to acid mole ratio being in the range of 2:1 to 5:1. The resultant green-colored isopropanol solution of the complex is diluted with water at the time of use. The fluorocarbon acid preferably has 6 to 8 fully fluorinated (perfluorinated) carbon atoms in the terminal fluorocarbon chain or tail.” Specific working examples include chromium coordination complexes of perfluorooctanoic acid and N-ethyl-N-perfluorooctanesulfonyl glycine.
U.S. Pat. No. 4,713,295 teaches coating glass beads with a mixture of substances. The mixture comprises a first substance, which if used alone would tend to make the beads hydrophobic while leaving them oleophilic, and a second substance, which if used alone would tend to make the beads both hydrophobic and oleophobic. “For the best results, it is preferred to use a second substance which is an anionic fluorocarbon compound, and optimally, said second substance is a fluoro-alkyl-sulphonate, for example a fluoro-alkyl-sulphonate in which the alkyl has a long chain (C14 to C18).” (See Column 4, lines 8-13). The exemplified hydrophobic and oleophobic substance is a potassium fluoroalkyl-sulphonate (for example FC129 from 3M). (See column 5, lines 50-52) FC129 is a potassium fluorooctyl sulphonyl-containing compound.
SUMMARY OF THE INVENTION
The present invention relates to optical elements having a surface treatment comprising at least one fluoropolymer selected from:
a) fluoropolymers comprising a fluorinated hydrocarbon backbone and side chains comprising at least one of fluoroalkyl, fluoroether alkyl, fluoroalkoxy and mixtures thereof; and
b) fluoropolymers comprising a hydrocarbon backbone and side chains comprising at least one of fluoroether alkyl, fluoroalkoxy and mixtures thereof.
The backbone of the fluoropolymer surface treatment is preferably free of oxygen atoms. The fluoropolymer is preferably perfluorinated. The surface treatment is substantially free of perfluoroalkyl side chains or end groups having 6 or more carbon atoms, and more preferably substantially free of perfluoroalkyl side chains or end groups having more than 4 carbon atoms.
In one aspect, the fluoropolymer is prepared from at least one fluorovinyl ether monomer and at least one comonomer having a polymerizable double bond. The fluorovinyl ether monomer is preferably selected from CF
2
═CF—O—CF
3
(PMVE), CF
2
═CF—O—CF
2
CF
2
CF
3
(PPVE), CF
2
═CF—O—CF
2
CF(CF
3
)—O—CF
2
CF
2
CF
3
(PPVE-2) and mixtures thereof. For embodiments wherein PMVE is the sole fluorovinyl ether monomer, the fluoropolymer preferably comprises at least about 30 mole % of repeat units derived from PMVE. It is surmised, however, that lower concentrations of repeat units derived from PMVE would also be suitable provided that the fluoropolymer has a molecular weight of less than about 30,000 g/mole. For embodiments wherein PPVE is the sole fluorovinyl ether monomer, the fluoropolymer preferably comprises from about 10 to about 20 mole % of repeat units derived from PPVE. For embodiments wherein PPVE-2 is the sole fluorovinyl ether monomer, the fluoropolymer preferably comprises from about 1 to about 10 mole % of repeat units derived from PPVE-2. The comonomer is preferably tetrafluoroethylene (TFE) employed alone or in combination with vinylidene fluoride (VDF). The fluoropolymer preferably comprises about 10 to about 30 mole % of repeat units derived from TFE and about 50 to about 80 mole % of repeat units derived from VDF. Other suitable comonomers include alkyl (meth)acrylates, substituted alkyl (meth)acrylates, (meth)acrylic acid, (meth)acrylamides, alkenes, styrenes, vinyl halides, vinyl esters, and mixtures thereof.
In another aspect, the fluoropolymer is a homopolymer or copolymer prepared from at least one monomer selected from fluoroalkyl ether acrylate, fluoroalkoxy acrylate, and mixtures thereof. The copolymer further comprises repeat unit derived from at least one of alkyl (meth)acrylates, substituted alkyl (meth)acrylates, (meth)acrylic acid, (meth)acrylamides, fluorinated alkenes, styrenes, vinyl halides, malaic anhydride, vinyl esters, and mixtures thereof
The surface treatment may further comprise a second polymer blended therewith. The percent float in heptane of the surface treated optical elements is preferably at least about 90%. The fluoropolymer surface treatment is preferably present at an amount of less than about 300 ppm and more preferably at an amount of about 50 ppm or less.
In another aspect, the invention provides a method of coating optical elements comprising the steps of:
a) providing at least one surface treatment comprising:
i) fluoropolymers comprising a fluorinated hydrocarbon backbone and side chains comprising at least one of fluoroalkyl, fluoroether alkyl, fluoroalkoxy and mixtures thereof, and/or
ii) fluoropolymers comprising a hydrocarbon backbone and side chains comprising at least one of fluoroether alkyl, fluoroalkoxy and mixtures thereof;
b) coating optical elements with said composition; and
c) drying said composition.
The surface treatment is preferably an aqueous composition, yet may optionally comprise up to about 30 wt-% of a cosolvent, with respect to the total weight of the surface treatment solution.
In another aspect, the present invention relates to a pavement marking article comprising a liquid binder and a mult
Pellerite Mark J.
Tiers George Van Dyke
Fischer Carolyn A.
Yoon Tae H.
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