Coating processes – Optical element produced – Polarizer – windshield – optical fiber – projection screen – or...
Reexamination Certificate
2002-04-26
2003-06-24
Seidleck, James J. (Department: 1711)
Coating processes
Optical element produced
Polarizer, windshield, optical fiber, projection screen, or...
C427S163400, C428S423100, C428S426000, C428S475200, C428S480000, C428S704000
Reexamination Certificate
active
06582759
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical elements comprising fluorochemical surface treatments. The invention further relates to materials such as retroreflective sheetings, pavement markings and beaded projection screens comprising a binder and the surface treated optical elements. The fluorochemical surface treatment comprises at least two linkages selected from urethane linkages, ester linkages or phosphate linkages; and at least one perfluorinated group.
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. No. 2,662,835 (Dec. 15, 1953) and U.S. Pat. No. 2,809,990 (Oct. 15, 1957) and U.S. Pat. No. 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 fluoroctyl sulphonyl-containing compound.
SUMMARY OF THE INVENTION
The present invention relates to fluorochemicals suitable for use as a surface treatment to induce float of optical elements. The fluorochemicals comprise the reaction product of at least one hydroxyl group containing material and a coreactant including polyisocyanates, polycarboxylic acids and derivatives thereof, or (poly)phosphoric acid derivatives. At least one reactant or coreactant comprises a fluorinated group. Preferably, at least one reactant or coreactant comprises a water-solubilizing group or silane group. Preferred fluorinated groups include perfluoroalkyl and perfluoroheteroalkyl, preferably having 2 to 6 and more preferably no more than 4 carbon atoms. The hydroxyl group containing material may be a fluorinated monoalcohol, fluorinated polyol or mixture thereof. Alternatively a non-fluorinated polyol may be employed as the hydroxyl containing material, preferably in combination with a fluorinated monoalcohol. The hydroxyl group containing material and/or the coreactant may be substituted with a water-solubilizing group and/or a silane group. Further, the reaction product may further comprise a long chain hydrocarbon monoalcohol, a monofunctional fluorochemical, a water-solubilizing group containing ingredient, a silane group containing ingredient or mixture thereof.
The invention further relates to optical elements comprising a fluorochemical surface treatment wherein the fluorochemical comprises at least two linkages selected from urethane linkages, ester linkages or phosphate linkages; and at least one perfluorinated group with the provision that wherein the linkages are urethane the fluorochemical surface treatment is free of oxygen in the backbone.
In another embodiment, the invention relates to a method of coating optical elements comprising the steps of providing a surface treatment composition comprising a solvent and the previously described fluorochemical surface treatment, coating optical elements with the composition; and drying the composition. The solvent is preferably water, optionally comprising from 0 to about 30 wt-% of a cosolvent.
In other embodiments, the invention relates to a pavement marking, a reflective sheeting, and a rear projection screen comprising a binder and a multitude of the surface treated optical elements. The optical elements are embedded in the binder at a depth of about 40-70% of their diameters.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to optical elements such as glass beads coated with a fluorochemical surface treatment. The terminology “optical element” refers to a material having a particle size ranging from about 25 to 1000 microns and having a refractive index ranging from about 1.5 to about 2.3 and higher.
The optical elements have at least one dimension that is no larger than 2 millimeters and preferably no larger than 250 microns. The optical elements may be in the form of any shape such as granules, flakes and fibers. However, spheroidal glass elements, denoted as “glass beads”, “beads” and “microspheres” hereinafter are preferred for materials such as retroreflective articles (e.g. retroreflective sheetings, pavement markings and beaded projection screens).
During the manufacture of retroreflective materials, optical elements are fixed in place by means of a liquid binder. Optical elements have a density or specific gravity several times that of the liquid binder, causing the optical elements to sink into the liquid binder layer, rather than float on the surface.
Preferred properties of optical elements will be described herein with respect to glass beads. Ordinary glass beads typically have a density of about 2.5 and a refractive index of about 1.5. “High index” beads refers to beads having a density of about 3.5 and a refractive index of about 1.9, whereas “super high index” typically refers to beads having a density of about 5 and a refractive index of about 2.3 or higher. The diameter of the glass beads typically ranges from a few microns to approximately 2500 microns and is preferably from about 25 to 1000 microns.
In addition to having the desired particle size and refractive index, the glass beads are typically transparent. The term transparent means that when viewed under an optical micros
Jing Naiyong
Qiu Zai-Ming
3M Innovative Properties Company
Fischer Carolyn A.
Ribar Travis B.
Seidleck James J.
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