News Column

Researchers Submit Patent Application, "Self-Healing Transparent Coatings Containing Mineral Conductive Colloids", for Approval

February 27, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventor Zheng, Haipeng (St. Petersburg, FL), filed on July 30, 2013, was made available online on February 13, 2014.

The patent's assignee is Essilor International (Compagnie Generale D'Optique).

News editors obtained the following quote from the background information supplied by the inventors: "The development of optical elements, including ophthalmic lenses, manufactured from plastic materials has also required the development of protective coatings providing good abrasion resistance and/or scratch resistance.

"In the optical field there is still considerable endeavor and research for improving the known hard-coatings to make them ever more abrasion and scratch resistant.

"A rather new and very interesting route for solving the problem of scratches and/or abrasion of organic glasses is to protect the lenses with coating layers able to repair themselves, i.e. coatings which would be able, when submitted to a simple physical treatment, to revert completely or partially to the initial non-scratched condition. The use of such self-healing coatings as clear top coats in the automotive industry has been described for example in US 2009/06453 and WO 2009/029641.

"Cornerstone Research Group Inc. has marketed two transparent shape memory polymers, Veriflex.RTM. (a polystyrene base resin) and Veriflex.RTM. E (a two-part epoxy-based resin), showing interesting self-healing performances. Preliminary experimental tests carried out by the inventors have however shown that these coatings suffer either from excessive initial haze and/or from very poor scratch resistance."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "Provided is an optical article comprising (a) a transparent optical substrate and (b) a transparent coating, said transparent coating being the outermost coating of the optical article and consisting essentially of a polythiol-ene matrix obtained by curing a liquid monomer mixture comprising at least one polyfunctional thiol and at least one polyfunctional allyl monomer, said cured polythiol-ene matrix having a glass transition temperature comprised in the range of from 40.degree. C. to 70.degree. C., and from 0.5 to 7% by weight of conductive mineral colloids homogeneously dispersed therein.

"Also provided is a method for preparing an optical article and a method for suppressing scratches on an optical article.

DETAILED DESCRIPTION

"The present invention is based on the discovery that a class of known thermocured or photocured resins obtained by thiol-ene reactions and used heretofore as UV-curable adhesives, display interesting transparency and a shape memory effect with transition temperature in the range of 45 to 65.degree. C. These resins are the Norland Optical Adhesives (NOA) marketed by Norland Products Inc. When tested as protective coatings on ophthalmic lenses, these resins showed healing levels similar to the Veriflex.RTM. coatings in the Manual Brass Brush test (described hereafter), but turned out to display lower healing levels for some deeper scratches (up to 3 .mu.m depth) generated by the Automated Steel Wool test (described hereafter).

"The Applicants therefore have tried to improve the healing performance of said thiol-ene resins by incorporating colloidal particles into the monomer mixture before curing.

"A large number of colloids have been tested, most of which turned out to be 'non-compatible' with the liquid monomer mixture, in other words it has not been possible to prepare a homogenous, clear and stable suspension of the particles in the monomer mixture.

"The Applicants, after having selected a few colloids compatible with the monomer mixture, have further observed that non-conductive colloids, such as silica, desirably improved the healing performances of the final cured resin coatings. This effect was however undesirably counteracted by lower scratch resistance, eventually leading to a much higher haze value.

"It was only when incorporating conductive colloids such as Sb.sub.2O.sub.5 or SnO.sub.2 into the known thiol-ene resins that the Applicants obtained cured coatings having both of significantly increased healing levels and lower final haze values.

"In its first aspect, the present invention is therefore drawn to an optical article comprising (a) a transparent optical substrate, and (b) a transparent coating, said transparent coating being the outermost coating of the optical article and consisting essentially of a polythiol-ene matrix obtained by curing a liquid monomer mixture comprising at least one polyfunctional thiol and at least one polyfunctional allyl monomer, said cured polythiol-ene matrix having a glass transition temperature comprised in the range of from 40.degree. C. to 70.degree. C., preferably in the range of from 45.degree. C. to 65.degree. C., and from 0.5 to 7% by weight of conductive mineral colloids homogeneously dispersed therein.

"The optical substrate may be any organic glass commonly known and used in the optical field. It may be a thermoplastic resin such as thermoplastic polycarbonate, or a thermoset or photo-cured resin such as CR 39.RTM., polyurethane or polythiourethane. Its selection is not critical to the present invention.

"The transparent self-healing coating is not necessarily in contact with the underlying optical substrate and there may be one or more intermediate layers, such as a primer layer, a polarizing layer, anti-reflection layers, etc. Each of these intermediate layers should be also transparent.

"The final cured coating of the optical article is a composite of a polymer matrix based on a thiol-ene resin, and conductive mineral colloids homogeneously dispersed in said polymer matrix.

"The cured coating is thus essentially free of any other component which is not part of the polymer matrix or the colloids, such as solvents, non-colloidal mineral fillers, fibres, organic fillers, etc.

"This however does not mean that the polythiol-ene matrix is the only polymer component of the self-healing coating of the present invention. There may be a minor amount of another oligomer or polymer component, said component being either covalently bound to the polythiol-ene matrix or homogeneously incorporated therein. This additional oligomer or polymer component must be sufficiently compatible with both of the liquid monomer mixture and the cured resin to prevent any phase separation during or after the curing procedure which would inevitably lead to excessive haze of the final coating. The amount of the additional oligomer or polymer component in the polymer matrix preferably is not higher than about 30% by weight, preferably not higher than 20% by weight, and most preferably not higher than 10% by weight.

"In a preferred embodiment of the present invention the polyfunctional thiol in the liquid monomer mixture is a tetrathiol of formula (1)

"##STR00001##

"This tetrathiol preferably is reacted with triallyl isocyanurate as the polyfunctional allyl monomer. The weight ratio of the polyfunctional thiol to the polyfunctional allyl monomer is preferably comprised in the range of from 55/45 to 57/43.

"As explained above, the polyfunctional thiol and the polyfunctional allyl monomer are the major components of the liquid monomer mixture. They preferably comprise at least 70% by weight, more preferably at least 80% by weight, and even more preferably at least 90% by weight of the liquid monomer mixture. In a particularly preferred embodiment, the liquid monomer mixture essentially consists of polyfunctional thiols, polyfunctional allyl monomers, and/or of a suitable amount of photo-initiators or catalysts.

"Liquid UV curable monomer mixtures comprising or consisting essentially of a polyfunctional thiol and a polyfunctional allyl monomer as defined hereabove are marketed under the reference NOA 61, NOA 63, NOA 65 and NOA 68 by Norland Products Inc. NOA 61 and NOA 63 lead to very low haze values of finally healed coatings and therefore are the most preferred curable monomer mixtures. NOA 61 essentially consists of 55-57 weight % of tetrathiol of formula (1) and 43-45 weight % of triallyl isocyanurate. NOA 63 contains about 70-75 weight % of NOA 61 and about 25-30 weight % of a urethane component.

"The conductive colloids used in the present invention have an average particle size comprised in the range of 5 to 25 nm. They may be selected from the group consisting of Sb.sub.2O.sub.5, SnO.sub.2, ATO (SnO.sub.2/Sb.sub.2O.sub.5), PTO (SnO.sub.2/P.sub.2O.sub.5).

"As will be apparent from the examples, the Applicants have observed that colloidal nanoparticles Sb.sub.2O.sub.5 and SnO.sub.2, when added in a sufficient but not too high amount, significantly increase the self-healing performance of polythiol-ene matrices as defined above and also are satisfactory both with regard to the initial haze of the coating and with regard to the haze after a self-healing step. These conductive metallic oxides therefore are particularly preferred in the present invention.

"The mineral conductive colloids are present in the final cured coating in an amount from 0.5 to 7% by weight, preferably from 1 to 6% by weight. At lower concentrations, the self-healing performance of the final coating is not significantly increased. When the concentration of the conductive colloid is too high, i.e. above 7%, the scratch resistance, the haze value after healing, and the healing performance of the final coating are surprisingly reduced with respect to lower concentrations.

"There is no particular limitation as to the thickness of the self-healing coating of the present invention. The coating should be sufficiently thick to efficiently protect the underlying substrate and optional functional layers. Excessive coating thickness could however be detrimental to transparency of the final optical article.

"The self-healing coatings consequently have a thickness similar to known abrasion resistant coatings which is typically comprised in the range of 2 .mu.m to 50 .mu.m, preferably of 5 .mu.m to 20 .mu.m.

"The optical article preferably is a lens, such as an ophthalmic lens, sunglass lens or other optical lens, and most preferably is an ophthalmic lens. As mentioned above, it may contain functional layers such as polarizing layers, anti-reflective coatings, visible light and UV absorbing coatings, anti-choc coatings, photochromic coatings, all of which are familiar to the skilled person.

"The present invention is also drawn to a method for manufacturing an optical article having a self-healing component according to the present invention. Such a manufacturing method comprises: homogeneously dispersing a conductive mineral colloid, in an amount comprised in the range of 0.5 to 7% by weight relative to the total dry weight of the dispersion, in a liquid monomer mixture comprising at least one polyfunctional thiol and at least one polyfunctional allyl monomer, coating the resulting dispersion onto a transparent optical substrate, and curing the resulting layer by submitting the coated substrate to UV light and/or heat.

"The conductive mineral colloid may first be dispersed in an organic solvent, such as a lower alkanol or a glycol alkyl ether, for example Dowanol PM (propyleneglycol methyl ether).

"A wetting agent (surfactant) may also be added to the coating composition, preferably in an amount not exceeding about 0.2% by weight of the total coating composition. A preferred wetting agent is EFKA.RTM.-3034, a fluorocarbon-modified polysiloxane sold by Ciba Specialty Chemicals.

"The liquid monomer mixture with the conductive colloid dispersed therein is then coated onto the optical substrate, or a functional layer overlaying the optical substrate. The dispersion may be coated by any suitable coating method such as dip-coating, bar coating, spray coating, or spin coating. Spin coating is most preferred.

"The coated substrate may be submitted to a drying step at room temperature or at elevated temperature for example at a temperature ranging from 30 to 120.degree. C., in order to evaporate the solvent used for dispersing the conductive colloid.

"The optionally dried coating is then submitted to UV irradiation, preferably with a UV radiation dosage ranging from 0.150 J/cm.sup.2 to 1.20 J/cm.sup.2 in the UV-C range (290 nm-100 nm).

"The present invention is also drawn to a method for suppressing scratches on an optical article according to the present invention. Said method comprises heating the optical article with the cured and scratched self-healing coating to a temperature at least equal to the glass transition temperature of the polythiol-ene matrix. The coating may be heated by conduction or convection. The heating medium may be a gas, for example warm or hot air. In a preferred embodiment, the heating is carried out by contacting the outermost scratched coating of the optical article with a warm or hot liquid, preferably warm or hot water. The heating is preferably maintained for a duration comprised in the range of 1 to 60 minutes, preferably of 10 to 30 minutes.

"The self-healing performance, or 'healing level', of the coatings is assessed using two different scratch/abrasion tests, generating scratches with different depths.

"Manual Brass Brush Test (MBB Test):

"Initial haze (Haze.sub.0) of a coated lens is measured using a Haze Guard XL-211 plus meter using the standard method ASTM D 1003-00. The convex side of the lens is first rubbed with a brass brush (Weiler 44189, Block size L.times.W: 7.5 inches.times.0.5 inch, Bristle rows: 3.times.7, Trim length: 0.5 inche) for ten forward strokes. The haze of the scratched lens (Haze.sub.s) is then measured under the same conditions as the initial haze. The scratches made by this method are analyzed by profilometer and confirmed to be in the range from 0 to 1 .mu.m in depth, most scratches being less than 0.6 .mu.m in depth, except some larger scratches having a depth higher than 1 .mu.m on Veriflex.RTM. coatings.

"Automated Steel Wool Test (ASW Test):

"Initial haze (Haze.sub.0) of a coated lens is measured using a Haze Guard XL-211 plus meter using the standard method ASTM D 1003-00. The convex side of the lens is first rubbed with steel wool (000 grade) for 5 cycles (1 cycle=1 forward and 1 backward motion) under 1200 g of load using the automated steel wool machine. The haze of the scratched lens (Haze.sub.s) is then measured under the same conditions as the initial haze. The scratches made by this method are analyzed by profilometer and confirmed to be in the range of from 0 to 3 .mu.m in depth, except some larger scratches having a depth higher than 3 .mu.m on Veriflex.RTM. coatings.

"The lenses submitted to the MBB test or ASW test are subsequently immersed in warm water at 60.degree. C. for 15 minutes and are taken out from the water to cool down at room temperature. The haze (Haze.sub.h) of a lens after this healing process is measured with a Haze Guard XL-211 plus meter using the standard method ASTM D 1003-00.

"The healing level is then calculated as follows:

"Healing level ( % ) = Haze s - Haze h Haze s .times. 100. ##EQU00001##

"Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined in the appended claims. The present invention will be further illustrated in the following Examples which are given for illustration purposes only and are not intended to limit the invention in any way."

For additional information on this patent application, see: Zheng, Haipeng. Self-Healing Transparent Coatings Containing Mineral Conductive Colloids. Filed July 30, 2013 and posted February 13, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4868&p=98&f=G&l=50&d=PG01&S1=20140206.PD.&OS=PD/20140206&RS=PD/20140206

Keywords for this news article include: Essilor International (Compagnie Generale D'Optique).

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Politics & Government Week


Story Tools