MXPA97008685A - A retrorreflejante coating with an abrasive resistant ceramer cover - Google Patents

Abstract

A retroreflective coating having an abrasion-resistant ceramer coating that is prepared from about 20% to about 80% ethylenically unsaturated monomers, about 10% to about 50% acrylate-functionalized colloidal silica; and about 40% N, N-disustiumide or N-substituted N-vinyl-amide monomers having a molecular weight between 99 and 500 atomic units, wherein said percentage is by weight hundreds of the total weight of the coating. A method of a retroreflective coating coated with a cured ceramer layer of abrasion resistance is also described.

Description

A RETRORREFLEJANTE COATING WITH AN ABRASION RESISTANT CERAMER COAT FIELD OF THE INVENTION The present invention relates to a retroreflective coating having an abrasion resistant coating and a method for preparing the same. More specifically, the invention relates to a retroreflective coating having a ceramer coating comprising an organic resin and silica particles.

BACKGROUND OF THE INVENTION For many applications of retroreflective cladding and especially for retroreflective cladding on raised pavement markers, abrasion resistance and weather durability are essential properties for a long life. The retroreflective coating on the raised pavement markers is impacted by tires, and often sand, mud or stones are REF: 25965 imprisoned between the retroreflective coating and the tire. Frequently the surface of the retroreflective coating can not withstand these abrasive forces and, as a result, the reflectivity of the pavement marker is decreased.

In many raised pavement markers, the surface of the retroreflector is protected by joining a sheet of glass to the surface of the retroreflector. Examples of retroreflective coating having a glass plate attached to the surface are disclosed in Heenan et al., In U.S. Patent No. 4,596,662 and Johnson et al., In U.S. Patent No. 4,340,319.

The use of a glass plate as an abrasion resistant coating has disadvantages due to the increased production cost and occasional breakage of the glass plate caused by the impact during use. Apart from using a glass plate, researchers in the retroreflective technique have made other proposals to protect the retroreflective coating. For example, various efforts have been made to protect the retroreflective coating by applying the coating to the surface of the coating. In U.S. Patent Nos. 4,753,548 and 4,797,024, Forrer applied a hard coating to the retroreflective coating made by means of UV curing a composition comprising dipentaerythritol hydroxypentacrylate, 1,6-hexanediol diacrylate, methyl ethyl ketone and isobutyl isobutyrate together with stabilizers , a surfactant and a photoinitiator. Huang in U.S. Patent Nos. 4,755,425, 4,844,976 and 5,073,404, applied an abrasion-resistant coating by treating the retroreflective coating with a colloidal silica dispersion in polyurethane. It was found that this protective coating has good adhesion to the retroreflective coating with an upper layer of polyurethane, however, for the coating with a top layer of polyacrylate, it was found convenient to pretreat the coating with a corona treatment to improve the adhesion.

A variety of coatings containing abrasion resistant silica particles for general thermoplastic substrates (as opposed to those specifically adapted to the retroreflective coating) were also disclosed. Katsa beris in U.S. Patent No. 5,258,225 discloses a coating composition containing: multifunctional acrylate ester monomers, colloidal silica functionalized with acrylate; multifunctional aliphatic acrylate urethanes, a UV absorber, and a photoinitiator that can be applied to thermoplastic substrates, especially polycarbonate substrates. Cottington et al., In U.S. Patent No. 5,368,941 and EP 424,007 A2 disclose an abrasion resistant coating composition containing: multifunctional acrylate monomers; an aminofunctional silane; colloidal silica and a polyalkylene oxide terminated by acrylate or an acrylate ester monomer. Wright in U.S. Patent No. 5,374,483 discloses a UV curable composition containing a multifunctional acrylate monomer, an amino-organo-functional silane and colloidal silica. A UV curable abrasion resistant coating with improved polycarbonate adhesion is described in J. Of Appl. Polymer Sciences 42, 1551-1556 (1991). Bilkadi in U.S. Patent Nos. 4,885,332 and 5,104,929, discloses coating compositions containing colloidal silica and polyacryloyl monomers.

Humphrey, in U.S. Patent No. 4,188,451, discloses a coating composition for polycarbonate substrates which uses: a first layer of a polyfunctional acrylic ester monomer and organosilane and a top layer of organopolysiloxane filled with silica. Schmidt, in J. Non-cryst. Solids, 100, 57-64 (1988), reports the incorporation of organic substances in an inorganic matrix formed by sol-gel processing. Bilkadi, in U.S. Patent No. 4,906,523, discloses the addition of silica sol to polymers in azeotropic solvents to impart adhesion to inorganic oxide surfaces such as concrete.

UV curable coatings without silica particles have also been applied to thermoplastic substrates. For example, Bilkadi in the co-pending US patent application Serial No. 08 / 426,495 (filed April 20, 1995, incorporated herein by reference) discloses the use of multifunctional acrylates and N, N-dialkylacrylamines as protective coatings in aircraft windows. Miller in U.S. Patent No. 4,908,230 discloses a method of coating polycarbonate substrates at low temperatures (about 40 ° F) which is reported to have a good tack without cloudiness. Lake in WO 92/17337, discloses a UV curable composition comprising multifunctional acrylate and acrylated aliphatic urethanes. Siol et al. in U.S. Patent Nos. 4,814,207 and 5,053,177 disclose abrasion-resistant acrylate coatings and a method for applying the coatings to the coating in a continuous manner.

DESCRIPTION OF THE INVENTION In a first step, a ceramer precursor coating composition is applied to the surface of the retroreflective coating. The coating composition comprises approx. 20% to approx. 80% ethylenically unsaturated monomers; approx. 10% to approx. 50% colloidal silica functionalized with acrylate; and approx. 5% to approx. 40% N, N-disubstituted acrylamide monomer, or N-substituted N-vinyl amide monomer, wherein said percentages are percentages by total weight of said coating. The coating is then cured to form a retroreflective coating having a light-transmissive, abrasion-resistant coating of ceramer.

The amide monomer must be an N, N-disubstituted acrylamide monomer or an N-substituted N-vinyl amide monomer. It has been found that the use of an acrylic acid or acrylic ester in place of the N, N-disubstituted acrylamide or N-substituted N-vinyl-amide monomer gives coatings that adhere poorly to the polycarbonate surfaces and do not resist well to the interperience. It was also surprisingly found that the use of acrylated urethanes in place of the N, N-disubstituted acrylamide monomer or N-substituted N-vinyl amide resulted in compositions that can not be handled.

The N, N-disubstituted acrylamide monomer or N-substituted N-vinyl amide monomer must also have a molecular weight between 99 (the molecular weight of N, N-dimethylacrylamide) and 500 atomic units. This molecular weight range is necessary to stabilize the silica particles and for the proper functioning of the coating.

In the present invention, the term "ceramer" is used to identify a fluid comprising surface modified colloidal silica particles dispersed in an organic polymerizable free radical liquid. The term "cured ceramer" is used to identify a material comprising inorganic particles (specifically silica) attached or connected by means of covalent bonds to a degraded organic matrix. The term "acrylate" as used herein, comprises acrylates and methacrylates. The term "disubstituted nitrogen" means that the acrylamide nitrogen atom, in addition to being the nitrogen of the acrylamide, has two substituents covalently attached to the nitrogen.The term "ceramer coating transmissive to light" means that the coating Ceramer has a light transmission, measured according to ASTM D1003, of at least 75% preferably at least 85% and more preferably at least 95%.

The ceramer composition can be coated on the retroreflective coating by methods known in the art, including: spraying, flow, lamination, dip coating or knife coating. In many applications, especially applications where the retroreflective cladding has cube corner elements having an air interface, it is convenient to coat the cladding without allowing the cladder to flow over the back side of the retroreflective cladding as this may diminish its optical characteristics . After the composition is coated on the coating, it is cured to form the abrasion-resistant wax coating. Since the retroreflective coating has an anterior surface made of a thermoplastic material, it is important in many cases that the curing takes place at a temperature below that at which the thermoplastic material is deformed, and is preferably irradiated by UV light at room temperature. in an atmosphere of air.

The ceramer coating of the present invention provides numerous advantages for coating the retroreflective coating, especially retroreflective coating on raised pavement markers. Due to the inorganic / organic nature of the ceramer coatings, the coatings of the present invention can provide excellent abrasion resistance and good flexibility. The coatings of the present invention also adhere well to the retroreflective coating, especially the polycarbonate coating, without fogging, turbidity or the addition of primers.

Additional advantages of the retroreflective coating coating of the present invention include: the ability to withstand outdoor conditions with excellent resistance to moisture, light and heat; resistance to cracking and detachment; suitable optical properties such as transparency; and resistance to chemical attack and coloration by automobile motor oil and carbon black (such as carbon black from tires).

In addition, coatings can be formulated, applied and cured more easily, and can be used without a primer layer because of their ability to attach directly to the surface of the retroreflective coating. The curing of the coatings can be carried out in air at room temperature.

The drawing illustrates a cross section of a preferred embodiment of the present invention. The retroreflective coating 2 having a reflection interface 4 and a surface 6 is made abrasion resistant by attaching a wax coating 8 to the surface 6. In a preferred embodiment, the interface 4 is an air interface that is protected by an airtight seal. In another embodiment, interface 4 is coated (typically by vapor deposition) with a metal layer.

The ceramer coatings of the present invention are applicable to the retroreflective coating having a thermoplastic surface.

Suitable retroreflective coating includes the descriptive lenses in US Pat. Nos. 3. 712,706 of Stamm and 4,895,428 of Nelson et al .; U.S. Patent No. 3,924,929 to Holmen, U.S. Patent No. 4,349,598 to White, U.S. Patent No. 4,726,706 to Attar, U.S. Patent No. 4,682,852 to Weber, and U.S. Patent No. 4,588 .258 of Hoopman, which are incorporated here as a reference. The retroreflective coating is preferably of the cube corner type as taught by the Nelson patents mentioned above. The lenses can be incorporated into a raised pavement marker as taught in U.S. Patent No. 4,875,798 to May, incorporated herein by reference. Preferably the coating is formed from a sheet of polycarbonate resin. The ceramer coating compositions of the present invention are especially effective for use in polycarbonate coating. These coating compositions also work well on polyacrylics and light polystyrene. The coatings adhere to polyester under laboratory conditions but tend to lose adhesion under weather conditions. It has been discovered that coatings of the present invention adhere better to hard coatings. Preferred retroreflective coatings have a thermoplastic surface having a Knoop hardness of at least 20 kg / mm2.

The ethylenically unsaturated monomer is preferably a multifunctional ethylenically unsaturated ester of (meth) acrylic acid selected from the group consisting of a difunctional ethylenically unsaturated ester of acrylic or methacrylic acid, a trifunctional ethylenically unsaturated ester of acrylic or methacrylic acid, a ethylenically unsaturated tetrafunctional ester of acrylic or methacrylic acid, and combinations thereof. Of these, the ethylenically unsaturated trifunctional and tetrafunctional esters of (meth) acrylic acid are more preferred.

Particularly preferred ethylenically unsaturated monomers have the formula: Or ii (H, C = C-CO.A- Y "I Rl wherein R 1 represents an element selected from the group consisting of hydrogen, halogen, and lower alkyl group, preferably having from one to four carbon atoms, more preferably hydrogen or methyl, R2 represents an organic polyvalent group having a molecular weight of from 14 to 1000 and a valence of m + n; m represents an integer indicating the number of acrylic or methacrylic groups or both in the ester, preferably from 2 to 9 , more preferably from 2 to 5, and wherein a mixture of acrylic or methacrylic monomers is used, preferably having an average value of 1.05 to 5; n represents an integer having a value of 1 to 5; and Y is selected between the group consisting of hydrogen, C1-C5 lower alkyl groups and protic functional groups, preferably selected from the group consisting of -OH, -COOH, -SO3H, -SO (OH) 2, -PO (OH) 2 and oxazolidone. The polyvalent organic group R2 can be cyclical or linear, branched, aromatic, aliphatic or heterocyclic having nitrogen, oxygen, non-peroxide, sulfur, or phosphorus atoms. The acrylate ester monomers are used in the coating from 20% to 80% by weight, more preferably from 30% to 70%.

Examples of suitable multifunctional ethylenically unsaturated esters of (meth) acrylic acid are the polyacrylic or polymethacrylic acid esters of polyhydric alcohols including, for example, the diacrylic acid ester and dimethylacrylic acid of aliphatic diols such as ethylene glycol, triethylene glycol, 2,2 -dimethyl-1,3-propanediol, 1,3-cyclopentanediol, 1-ethoxy-2,3-propanediol, 2-methyl-2, 4-? entanediol, 1,4-cyclohexanediol, 1,6-hexamethylene-diol, 1,2-cyclohexanediol, 1,6-cyclohexanedimethanol; the esters of triacrylic acid and trimetacrylic acid of aliphatic triols such as glycerin, 1,2,3-propanetrimethanol, 1,2,4-butanetriol, 1, 2, 5-pentanotriol, 1,3,6-hexanetriol and 1, 5, 10-decanotriol; the esters of triacrylic acid and trimethacrylic acid of tris (hydroxyethyl) -isocyanurate; the esters of the tetraacrylic and tetrametacrylic acids of aliphatic tetroles, such as 1, 2, 3, 4-butanotetrol, 1, 1, 2, 2-tetrathioletane, 1, 1, 3, 3-tetramethylolpropane, and pentaerythritol tetraacrylic; the esters of pentaacrylic acid and pentamethacrylic acid of aliphatic pentoles such as adonitol; the esters of hexaacrylic acid and hexametacrylic acid of hexanols such as sorbitol and dipentaerythritol; the esters of diacrylic acid and dimethacrylic acid of aromatic diols such as resorcinol, pyrocatechol, bisphenol A, and bis (2-hydroxyethyl) phthalate; the trimethacrylic acid ester of aromatic triols such as pyrogallol, phloroglucinol and 2-phenyl-2,2-methylol ethanol; and the esters of hexaacrylic acid and hexametacrylic acid of dihydroethylhydantoin, and mixtures thereof.

Preferably, for a good acid resistance, the ethylenically unsaturated multifunctional ester of (meth) acrylic acid is an unsaturated ethylenically unsaturated non-polyester ester of (meth) acrylic acid. More preferably, the ethylenically unsaturated multifunctional ester of (meth) acrylic acid is selected from the group consisting of pentaerythritol triacrylate, pentaerythritol tri- methacrylate, pentaerythritol pentacrylate, and a combination thereof. More preferably, the ethylenically unsaturated multifunctional ester of (meth) acrylic acid is pentaerythritol triacrylate.

The silica sols useful for preparing ceramers can be prepared by methods well known in the art. Colloidal silicas dispersed as sols in aqueous solutions can also be obtained commercially under such trademarks as "LUDOX" (EI Dupont de Nemours &Co., Inc. Wilmington, Delaware), "NYACOL" (nyacol Co., Ashland, Massachusetts ), and "NALCO" (Nalco Chemical Co., Oak Brook, Illinois). Nonaqueous silica sols (also referred to as silica organosols) can also be obtained commercially under such trademarks as "NALCO 1057" (a silica sol in 2-propoxyethanol, Nalco Chemical Co., Oak Brook, Illinois), and "MA -ST "," IP-ST "and" EG-ST ", (Nissan Chemical Industries, Tokyo, Japan). The silica particles preferably have an average particle diameter of from 5 to approx. lOOOnm, more preferably 10 to 50 nm. The average particle size can be measured using transmission electron microscopy to count the number of particles of a given diameter. Additional examples of suitable colloidal silicas are described in U.S. Patent No. 5,126,394 incorporated herein by reference.

For use in the present invention, the silica particles have to be functionalized by acrylate. The term "functionalized by acrylate" means that the silica particles are functionalized with an acrylate or an alkyl acrylate. The functionalized particles bind intimately and isotropically with the organic matrix. Typically the silica particles are functionalized by adding a silylacrylate to aqueous colloidal silica. Examples of colloidal silica functionalized with acrylate are described in U.S. Patent Nos. 4,491,508 and 4,455,205 to Olsen et al .; U.S. Patent Nos. 5,258,225 to Katsamberis, which are incorporated herein by reference.

It is especially preferred that the colloidal silica particles of the ceramer coating are derived from a sol instead of a colloidal silica powder. The use of colloidal silica powder results in a non-manipulable mass that is unsuitable for coating as an aqueous sol. The addition of additives, such as high molecular weight polymers, can cause the compositions derived from the colloidal silica powder to be molded onto thermoplastic substrates; however, it is believed that the use of compositions containing colloidal silica powder will result in coatings having relatively poor optical clarity and / or increased production costs and the use of such compositions is clearly not preferred in the coatings and methods of the invention. present invention.

The colloidal silica particles are used in the coating from 10% to 50% by weight, and more preferably from 25% to 40% by weight and even more preferably from approx. 30% to 33% by weight.

Within the above-described limitations of molecular weight and composition, the N, N-disubstituted and / or N-substituted N-vinyl-amide acrylamide monomers can independently contain the following substituents including (but not limited to): Ci alkyl -Ca, C2-C8 alkylene, and can be straight chain, for example, methyl, ethyl, propyl, butyl, or branched, for example, isopropyl, isobutyl, cycloalkane, for example, cyclopentane, cycloalkene, for example. ., cyclopentadiene, aryl, for example, phenyl. The N-substituents can be covalently bound such as in N-vinylpyrrolidone. The N-substituents may also be substituted with heteroatoms such as halide, for example, fluoromethyl, chloromethyl, 1,2-dichloroethyl, oxygen, for example, furfuryl, alkyl-alkoxy, such as ethyl-methoxide, nitrogen, for example. , nitrobenzyl, and sulfur, for example ethylthiomethyl.

In one embodiment, the preferred substituents on the N-vinyl-N-substituted amide or N, N-disubstituted acrylamine monomers are independently a (Cj-Cß) alkyl group optionally having hydroxy, halide functionalities , carbonyl and amino, a (C2-Cs) alkylene group optionally having carbonyl and amido functionalities, a (C? -C4) alkoxymethyl group, a (C? -Cio) aryl group, a (C1-C3) alk group (C6) -C? O) aryl and a (C6-C10) heteroaryl group. In a preferred embodiment. Both substituents of the N, N-disubstituted acrylamide are (C? -C) alkyl groups.

In a preferred embodiment, the N, N-disubstituted acrylamide has the formula H2CC (R3) C (O) (R1) (R2) wherein: R1 and Rz are each independently a (Ci-Ca) alkyl group optionally having hydroxy, halide, carbonyl and oxo functionalities, a (C2-C8) alkylene group optionally having carbonyl and oxo functionalities, a (Cx-C4) alkoxymethyl group, a (C6-C18) aryl group, a (Ci-Ca) alk group (C6-C? 8) aryl and a (C6-C? A) heteroaryl group; and R3 is hydrogen, halogen or methyl group.

Preferred N, N-disubstituted and / or N-substituted N-vinyl-amide acrylamide monomers are N, N-dimethylacrylamide and N-vinyl pyrrolidone and N, N-disubstituted or N-substituted N-vinylamide monomers which they are functional equivalents, for example when they are used in the composition of the present invention they produce coatings on retroreflective coatings which after curing exhibit satisfactory dry adhesion; wet adhesion and resistance to high temperature; resistance to abrasion and weathering, when these properties are measured according to the methods described here in test procedures I-IV. More preferred functional equivalents also exhibit resistance to engine oil and carbon black as described herein in test procedures V and VI.

It is believed that the N, N-disubstituted acrylamide and N-substituted N-vinylamide monomers are able to penetrate the surface of the retroreflective coating, especially polycarbonate coating and thus provide good adhesion. The N, N-disubstituted and / or N-substituted N-vinylamide monomers are of relatively low molecular weight to stabilize the sol; Larger molecules can lead to precipitation. Due to their relatively low toxicity, N, N-dimethylacrylamide, N, N-diethylacrylamide and N-vinyl pyrrolidone are sometimes preferred. Preferably, the molecular weight of the N, N-disubstituted acrylamide monomer or N-substituted N-vinylamide monomer is between 99 and 200 atomic units. It was found that adding acrylated urethanes to the wax compositions of the present invention resulted in flocculation and precipitation of the silica particles. Therefore, it is preferred that the ceramer compositions contain no acrylated urethane.

The N, N-disubstituted acrylamide monomer is preferably present in the coating with 5 and 40 percent of the total weight of the coating, more preferably 10 to 30 percent by weight and even more preferably 10 to 15 percent by weight.

Other additives such as photoinitiators, UV stabilizers and antioxidants can be added to the compositions of the invention. Sources of energy for curing include, but are not limited to: heat, untraviolet light or visible light, X-rays and electron beam. A polymerization initiator may be added to the composition to aid in curing (although X-ray and electron beam curing processes typically do not require an added initiator). Examples of initiators that may be suitable include organic peroxides, azo compounds, quinones, nitroso compounds, acyl halides, hydrazones, mercapto compounds, pyrilyl compounds, imidazoles, chlorotriazines, benzoin, benzoin alkyl ethers, diketones, phenones, and mixtures thereof. same. Other examples of suitable photoinitiators can be alluded to in U.S. Patent No. 4,735,632 incorporated herein by reference.

Optionally, the compositions may contain photosensing or photoinitiating systems that affect polymerization in both air and in an inert atmosphere such as nitrogen. These photoinitiators include compounds having carbonyl groups, tertiary amino groups and mixtures thereof. Among the preferred compounds having carbonyl groups are benzophenone, acetophenone, benzyl, benzaldehyde, or chlorobenzaldehyde, xanthone, thioxanthone, 9,10-anthraquinone, and other aromatic ketones which can act as photosensors. Among the preferred tertiary amines are methyldiethanolamine and dimethylaminobenzoate. In general, the amount of photoinitiator can vary from approx. 0.01 to 10% by weight, more preferably 0.25 to 4.0% by weight, based on the weight of the waxer. A preferred photoinitiator is 1-hydroxycyclohexylphenyl ketone.

In a preferred method, the ceramer coating composition is placed in a glass syringe equipped with a Gelman Glass Acrodisc ™ 1.0 micron filter. Then the composition is pushed through the filter and coated with flow over the retroreflective polycarbonate coating. The pavement marker coated with uncured ceramer is then placed in a convection oven set at 60C for 2.5 minutes and transferred to the curing station. Filtering large particles helps improve optical transparency by minimizing light scattering. Preferably, the ceramer composition has a viscosity below 2400 centipoise.

The coating can be cured by methods recognized by the art including electron beam, UV radiation, visible light and heat. Preferably the curing is performed at a temperature below the temperature at which the retroreflective coating is deformed. Preferably, the composition is cured by UV irradiation in ambient air at room temperature. Low-temperature curing procedures prevent damage to lens optics and reduce processing costs.

The cured ceramer coating should be between 1 and 100 micrometers in thickness. Preferably, the film should be between 2 and 50 micrometers and more preferably between 2 and 25 micrometers thick. Particles between 4 and 9 micrometers thick have convenient properties such as good adhesion and abrasion resistance. Films that are too thin may not provide resistance to abrasion and films that are too thick tend to crack.

EXAMPLES The following non-limiting examples further illustrate the invention. All the parts, percentages, relationships, etc. in the examples they are by weight unless otherwise indicated. The following abbreviations and trademarks are used: NNDMA N, N-dimethylacrylamide, which can be obtained from Aldrich Chemical Co., Milwaukee, Wisconsin.

PETA Pentaerythritol Acrylate, obtainable from Aldrich Chemical Co., Milwaukee, Wisconsin.

TMPTA Trimethylol propane triacrylate, obtainable from Aldrich Chemical Co., Milwaukee, Wisconsin. Z6030 3- (trimethoxysilyl) propyl methacrylate, which can be obtained from Dow Corning Co., Midland, Michigan.

OX-50 Colloidal silica particles, which have an average surface area of 50 m2 / gram, which can be obtained commercially from Degussa Corp., Ridgefield Park, New Jersey.

HHA hydantoin hexaxacrylate, which can be obtained from 3M Co., St. Paul, Minnesota.

GDMA Glycerol dimethacrylate, obtainable from Akzo Co., Chicago, Illinois.

HEA Hydroxyethyl Acrylate, obtainable from Rohm and Hass, Philadelphia, Pennsylvania, under the trade name "Rocryl 420".

HEMA Hydroxyethyl Dimethacrylate, available from Rohm and Hass, Philadelphia, Pennsylvania, under the trade name "Rocryl 400". Trinuvin 292 Methyl 1, 2,2,6,6-pentamethyl-4-piperidinyl sebacate, available from Ciba Geigy Corp. Hawthorne, New York.

Irgacure 184 1-hydroxycyclohexyl ketone. It can be obtained from Ciba-Geigy.

Nalco 2327 An aqueous dispersion (40% solids) of colloidal silica particles having an average particle diameter of 20 nanometers, obtainable from Nalco Chemical Co., Chicago, Illinois.

Nalco 1042 An aqueous dispersion (30% solids) of colloidal silica particles having an average particle diameter of 20 nanometers, which can be obtained from Nalco Chemical Co., Chicago, Illinois.

NVP N-vinyl pyrrolidone, which can be obtained from Aldrich Chemical Co., Milwaukee, Wisconsin.

The following test procedures were used to evaluate the protective coatings of the present invention.

PROOF PROCEDURE I; DRY ADHERENCE This test was performed in accordance with the ASTM test procedure D-3359-93 (standard test methods for measuring adhesion by tape test), whose disclosure was incorporated here as a reference. ASTM is a grid adhesion test that determines how well the abrasion resistant coating adheres to the substrate. The test was performed using a multi-blade cutter commercially available from BYK / Gardner Inc of Silver Spring, Maryland, as BYK / Gardner 1MM, DIN / ISO. The cutter had six parallel blades spaced 1 mm (0.04 inches) apart. The test specimen was cut in a grid pattern according to Figure 1 of ASTM D3359-93. After the cuts were made, the surface was lightly brushed to remove surface residues. The adhesion of the coating was tested by applying a 2.5 cm wide piece of adhesive tape (clear Scotch tape No. 600, commercially available from 3M Co., St. Paul, MN) to the surface, and then removing the tape at a 90-degree angle quickly. The grid was examined using an illuminated magnifier and classified according to the classification indicated in ASTM D3359-93. In order to provide an effective protective coating for a particular thermoplastic substrate, the degraded protective coating of this invention must have an adhesion value of G + 0 / 5B on the Gardner scale, which represents no delamination. That is to say, the edges of the cuts are completely smooth and none of the squares of the grid detached. A value of G + 0 / 5B is required to pass this test.

TEST PROCEDURE II: ADHERENCE UNDER HUMID CONDITIONS AND HIGH TEMPERATURE This test evaluates the adhesion between the protective coating and the thermoplastic substrate after having been immersed in water. A 2.5 cm coated substrate sample was immersed in a water bath that was continuously heated at 82 ° C for 24 hours. At the end of 24 hours, the sample was removed and examined for delamination. To approve this test the coating should not show any delamination.

TEST PROCEDURE III: RESISTANCE TO ABRASION This test measures the Taber abrasion of the coating made in accordance with ASTM D1044-94 (Standard method for the resistance of transparent plastics to surface abrasion) and ASTM D1003-92 (approved again in 1988, Standard test method for turbidity and transmittance luminous of transparent plastics), whose revelations are incorporated here as a reference. Briefly, the test method involved which measures as a reference point the initial turbidity value of a sample in the test device HAZEGARD1"PLUS (Gardner Co., Silver Springs, Maryland) that complies with ASTM D1003-61. then subjected to abrasion on a TABER HAZE test device for 500 cycles using a 500 gram load with a CS-10F wheel, the sample was evaluated again on the HAZEGARD PLUS test device.The test results are reported as the change percent turbidity Preferably, the percent change in turbidity for the degraded protective coating of this invention is less than 15%, more preferably less than about 10%, and more preferably less than about 5% after 500 abrasion cycles As described above, to pass this test, the change% turbidity must be less than 15%.

TEST PROCEDURE IV: ALTERABILITY AT THE WEATHER This test evaluates the ability of the protective coating on the thermoplastic substrate to withstand weather conditions (eg, sunlight). The test was performed according to ASTM Standard test G-26-90, type B, BH (standard practice for apparatus that operates on exposure to light (xenon arc type) with and without water for exposure of non-metallic materials), the disclosure of which is incorporated herein by reference. Briefly, a sample was exposed to a xenon burner filter of 6500 Watt indoor and outdoor borosilicate filters at 0.35 w / m2 in a 65 XWWR water-cooled xenon arc weathering chamber, obtainable from Atlas Electric Devices Co. (Chicago, Illinois) for repetitive cycles of 102 minutes at 63 ° C followed by 18 minutes with a water sprayer. In order to provide an effective abrasion-resistant protective coating for a particular thermoplastic substrate (and thus to approve this test), the degraded protective coating of the present invention must be able to withstand at least 1000 hours of exposure under these conditions without becoming yellowish. , white or other significant discoloration.

TEST PROCEDURE V: CHEMICAL RESISTANCE TO ENGINE OIL This test evaluates the ability of the protective coating to resist degradation and discoloration after prolonged exposure to automobile engine oil. The test involved completely immersing retroreflective lenses coated with ceramer in motor oil SAE 10W-30 (Valvoline) for 10 hours at 20 ° C. After each immersion period the coated lenses were washed with detergent water and visually inspected for discoloration. The coated lenses were then rubbed at least 3 times with 0000 grade steel wool to evaluate their abrasion resistance. Finally, the coated lenses were subjected to the grid adhesion test described in the test procedure I. In order to provide a satisfactory coating for the retroreflective lens the ceramer coatings of the present invention have to present after the above-mentioned dips in oil. automobiles: 1. No visually observable discoloration, cracking or cracking; 2. It must resist any scratching after rubbing with grade 0000 steel wool; and 3. It must not exhibit delamination or loss of adhesion as determined by test procedure I.

TEST PROCEDURE VI: CHEMICAL RESISTANCE TO ENGINE OIL / CARBON BLACK This test evaluates the ability of the protective coating to resist degradation and discoloration after exposure to a hot suspension of carbon black in motor vehicle oil. This suspension was prepared by vigorously mixing 4 parts of carbon black with 90 parts of Valvoline SAE 10W-30 engine oil and heating the suspension to 75 ° C. The test involved the complete immersion of retroreflective lenses coated with ceramer for 15 minutes in the heated suspension. After each immersion period the coated lenses were washed with detergent water and visually inspected to determine any discoloration. The coated lenses were then rubbed at least 3 times with 0000 grade steel wool to evaluate their abrasion resistance. Finally, the coated lenses were then subjected to the grid adhesion test described in the Test procedure I. In order to provide a satisfactory coating for the retroreflective lens, the cured ceramer coatings of the present invention have to present after immersion above indicated in the dispersion of carbon black / car oil: 1. No visually observable discoloration, cracking or cracking; 2. It has to resist scratching after rubbing with grade 0000 steel wool; and 3. You do not have to present delamination or loss of adhesion according to Test Procedure I.

Preparation 1: The following materials were loaded into a 10 liter round base flask: 1195 grams (g) of Nalco 2327, 118 g of NNDMA, 60 g of Z6030 and 761 g of PETA. The flask was then placed in a rotary evaporator R152 from Bucchi (which can be obtained from Bucchi Laboratory AG, Flanil, Switzerland) with the bath temperature set at 55 ° C. A refrigerated 50% deionized water / 50% antifreeze mixture (Texaco) was recirculated through the cooling coils. The volatile components were removed at a reduced pressure of approx. 25 Torr until the distillation flow was reduced to less than 5 drops per minute (approximately 2 hours). The resulting material (1464 g) was a clear liquid, containing less than 1% water (determined by Cari Fisher titration) and comprising 54.2% of PETA, 8.4% of NNDMA, and 38.8% of acrylated silica. This material is called CER1.

Preparation 2: Preparation 1 was repeated except that the amount of Z6030 was 120 g. The resulting CER2 comprised 39.6% acrylated silica, 8.1% NNDMA and 52.3% PETA.

Preparation 3: In a glass round bottom flask were mixed 100 g of Nalco 1042 silica sol, 8.4 g of Z6030 and 34 g of NVP. The round base flask was attached to a Bucchi rotary evaporator and heated in the 65 ° C water bath. The volatile components were removed at a reduced pressure of approx. 25 Torr. Until the distillation flow was reduced to less than 5 drops per minute (approximately 25 minutes). The resulting material (74.9 g) was a perfectly clear liquid with a very slight purple hue. To this clear material were added by vigorously mixing 15 g of PETA, 0.88 g of Irgacure 184 and 0.07 g of Tinuvin 292. The resulting material is called CER3 and comprised 45% acrylated silica, 16.5% PETA, 37.4% NVP, 1% Irgacure 184 and 0.1% Tin292.

Example 1: 29.8 parts of CER1 were mixed with 0.2 part of Tinuvin 292, 70 parts of isopropanol and 1.2 parts of Irgacure 184. The mixture was filtered through a 1.0 micron polypropylene filter (Gelman Glass Acrodisc ( R ', which can be obtained from Fisher Scientific, Chicago, Illinois) and then flow coated in the retroreflective polycarbonate lenses of raised two-way pavement markers (Model 280-2W obtainable from 3M Company, St. Paul , Minnesota) Immediately after the flow coating operation was completed (approximately 30 seconds) each of the coated pavement markers was then placed for 2 days., 5 minutes in a forced air convection oven where the temperature was maintained at 60 ° C. This ensures that substantially all of the isopropanol solvent was ignited. The coated pavement marker was then placed on a UV processor conveyor belt model QC1202 (available from PPG Industries, Plainfield, Illinois) equipped with a high pressure mercury lamp. The following procedure parameters were used for curing the coated raised pavement marker: line speed 55 feet / minute; voltage 410 volts; energy 90mJ / cm2,; atmosphere-air. The resulting cured protective coating on the retroreflective polycarbonate lens was perfectly clear and adhered to the polycarbonate retroreflective lens. The resulting coating approved test procedures I, II, III, IV, V and VI.

Example 2: 29.8 parts of CER2 were mixed with 0.2 part of Tinuvin 292, 70 parts of isopropanol and 1.2 parts of Irgacure 184 photoinitiator. This clear liquid was flow coated and cured on the retroreflective polycarbonate lenses of 15 markers of raised pavements (model 280-2W obtainable from 3M) using the same procedures described in Example 1. The resulting cured protective coating on the retroreflective polycarbonate lens was clear and adhered to the retroreflective polycarbonate lens. The coating approved test procedures I, II, III, IV, V and VI.

Example 3: A 30% solution of CER3 in isopropanol was coated with a # 12 wire wrapped bar (RD Specialties, Rochester, New York) on a series of thermoplastic substrates made of polyethylene terephthalate, polycarbonate and polymethyl methacrylate. The coated sheets were cured as described in Example 1. The resulting protective coatings on the coated sheets approved test procedures I, II, III, IV, V and VI.

Comparative preparation 1: This composition contains only acrylated silica and NNDMA, but not ethylenically unsaturated monomers. The following materials were mixed in a 1 liter round base flask: 100 g of Nalco 2327, 8.2 g of Z6030 and 40 g of NNDMA. The round base flask was attached to a Bucchi rotary evaporator and heated in the water bath to 55 ° C. After approx. Five minutes of heating, the mixture began to thicken and then gelled. Approximately 40 g of isopropanol were added to redissolve the gel. The volatile components were removed at a reduced pressure of approx. 25 Torr until the distillation flow was reduced to less than 5 drops per minute (approximately 25 minutes). The resulting clear liquid (86.7 g) is designated COMP1 and nominally comprises 53.9% acrylated silica and 46.1% NNDMA. Comparative example ÍA: A mixed coating solution was prepared 29.8 parts of COMP1 with 0.2 part of Tinuvin 292, 70 parts of isopropyl alcohol and 1.2 parts of Irgacure 184. The coating solution was coated with a wire wrapped bar # 12 (RD Specialties, Rochester, New York) on various sheets of polymethyl methacrylate (Acrylite GP sheets _ obtained from Cyro Industries, Milford, Connecticut). After baking the coated sheets during the volatile solvent (isopropanol), the coated sheets were passed under high pressure mercury lamps installed in an RPC ultraviolet light curing station (manufactured by PPG Industtries, Fairfield, Illinois). It was found that when the coated sheets were passed under the UV curing lamps in an ambient atmosphere, the protective coating did not cure and remained tacky and soft. When the atmosphere in the curing chamber was saturated with nitrogen gas, the coating cured but did not pass any of the test procedures listed above. The hardened coating was water soluble and completely disintegrated with the test II procedure.

Comparative example 1 B: The coating solution of Comparative Example 1A was coated on several polycarbonate sheets (thickness 125 microns, obtained from Tekra Corp., New Berlin, Wisconsin) using a # 12 wire wrapped bar (RD Specialties, Rochester, New York) . Immediately after the coating solution was applied, the polycarbonate became opaque and its surface cracked and cracked, indicating that the coating solution was corrosive to the polycarbonate and therefore unsuitable as a protective coating for retroreflective coating made of thermoplastic polycarbonate .

Comparative Preparation 2 Preparation 1 was repeated, except that N-substituted N-vinyl-amides or N-acrylamides were not used., N-disubstituted. The following materials were loaded into a 10 liter round base flask: 1195 g of Nalco 2327, 60 g of Z6030 and 761 g of PETA. Because the PETA was not soluble in the aqueous dispersion, a white precipitate formed at the base of the flask. The white precipitate was not redispersed when the mixture was heated to 55 ° C. When the inhomogeneous mixture was subjected to vacuum in the rotary evaporator R152 of Bucchi with the temperature of the bath set at 55 ° C, the white precipitate solidified and became non-manipulable as the volatile materials were removed by distillation. Under these circumstances it was not possible to obtain a homogeneous liquid dispersion to coat the retroreflective coating.

Comparative Example 3: This composition does not contain monomers of N-substituted N-vinyl amide or N, N-disubstituted acrylamide. Instead it contains a monoethylenically unsaturated ester of acrylic acid called HEA which has a molecular weight of 116. The example shows that the use of small molecules (molecular weight 100-200) instead of the appropriate acrylamides or NVP, does not form a Optically transparent protective coating for the retroreflective coating.

The following materials were mixed together in a round-bottomed flask: 85 g of Nalco 2327, 8.2 g of Z6030, 34 g of HEA and 74.1 g of TEGDA. The round base flask was attached to a Bucchi rotary evaporator and heated in the 65 ° C water bath. The volatile components were removed at a reduced pressure to ca. 25 Torr until the distillation flow was reduced to less than 5 drops per minute (approximately 25 minutes). The resulting material was a clear liquid. However, when 0.07 g of Tinuvin 292 was added to the mixture, it spontaneously became a milky white gel. The coatings of this white gel were not optically transparent and therefore were not useful as protective coatings for retroreflective coating.

Comparative Example 4: This example demonstrates that the use of commercially available colloidal silica powder (OX-50) instead of silica sol (Nalco 2327) is not suitable for preparing clear protective coatings for thermoplastic substrates when prepared in a similar manner to Example 1. Preparation 1 was repeated but instead of 1195 g of Nalco 2327 (which are 40% monodispersed silica particles) an equivalent amount of OX-50 and bidistilled water was used. Into a 10 liter round base flask were mixed 478 g of OX-50, 717 g of distilled water, 118 g of NNDMA, 60 g of Z6030 and 761 g of PETA. The flask was then placed in a rotary evaporator R152 from Bucchi with the bath temperature set at 55 ° C. A cooled mixture of 50% deionized water / 50% antifreeze (Texaco) recirculated through the cooling coils. The volatile components were removed at a reduced pressure of approx. From Torr until the distillation flow was reduced to less than 5 drops per minute (approximately 2 hours). The resulting material (1405 g) was a free-flowing white powder that was not re-dispersed in water or isopropanol or methyl ethyl ketone and therefore was not suitable for providing solutions that can be coated. Comparative Example 5: This example demonstrates that the use of a urethane acrylate in place of N-substituted N-vinyl-amide or N, N-disubstituted acrylamide is not suitable for preparing clear protective coatings for retroreflective coating. Preparation 1 was repeated, except that a urethane acrylate was used instead of NNDMA. The following materials were loaded into a 1 liter round base flask: 119.5 g of Nalco 2327, 11.8 g of Photomer 6160 (an aliphatic urethane acrylate from Henkel, Ahbler, Pennsylvania), 12 g of Z6030 and 76 , 1 g of PETA. A white precipitate formed which did not dissolve even after vigorous mixing and heating at 55 ° C. The inhomogeneous mixture was subjected to vacuum in the Bucchi rotary evaporator with the temperature bath set at 55 ° C. The white presipitate became denser and became unmanageable. It was not possible under these circumstances to obtain a homogeneous liquid dispersion suitable for coating a retroreflective coating.

Modifications and variations of the embodiments described above of the present invention are possible, as will be appreciated by those skilled in the art in light of the teachings indicated above. For example, the colloidal silica particles can be functionalized before mixing with the acrylate monomers. Therefore, it should be understood that within the scope of the appended claims and their equivalents, the invention may be practiced in a manner other than that specifically described.

Claims (11)

1. - A retroreflective abrasion-resistant coating, characterized in that it comprises a retroreflective coating having a thermoplastic surface and having a cured, light-transmissive wax coating disposed on the thermoplastic substrate; the cured ceramer coating being prepared from a mixture comprising 20% to 80% ethylenically unsaturated monomers; 10% to 50% of colloidal silica functionalized with acrylate; and 5% to 40% of an amide monomer selected from the group consisting of N, N-disubstituted acrylamide monomers and N-substituted N-vinyl amide monomer, wherein said amide monomer has a molecular weight of between and 500 atomic units; and in that said percentages are percentages by weight of the total weight of said coating.

2. - A retroreflective abrasion resistant coating according to claim 1, characterized in that the coating has a thickness of 2 micrometers to 25 micrometers.

3. - A retroreflective abrasion resistant coating according to claims 1-2, characterized in that it also comprises a UV stabilizer.

4. A retroreflective abrasion resistant coating according to claims 1-3, characterized in that the surface comprises polycarbonate and the amide monomer is selected from the group consisting of N, N-dimethylacrylamide, N, N-diethylacrylamide and N-vinyl pyrrolidone.

5. - A retroreflective abrasion resistant coating according to claims 1-4, characterized in that the ethylenically unsaturated monomer is a multifunctional acrylated ester and that said amide monomer has a molecular weight of 99 to 200 atomic units.

6. - A retroreflective coating resistant to abrasion according to claims 1-5, characterized in that said coating has: dry adhesion; wet adhesion and high temperature resistance; abrasion resistance and interoperability, satisfactory, according to these properties are measured according to Test Procedures I-IV.

7. - A retroreflective abrasion resistant coating according to claims 1-6, characterized in that said coating has a light transmission of at least 85% as measured by ASTM D1003.

8. - A retroreflective abrasion resistant coating according to claims 1-7, characterized in that the ethylenically unsaturated monomer is selected from the group consisting of an ethylenically trifunctional unsaturated ester of acrylic or methacrylic acid, an unsaturated ethylenically tetrafunctional ester of acrylic or methacrylic acid, and a combination thereof.

9. A retroreflective abrasion resistant coating according to claims 1-8, characterized in that the ethylenically unsaturated monomer comprises a radically curable free monomer having the formula: or il (H, C = C -CO] .Ra-Y "I R ' wherein R1 represents an element selected from the group consisting of hydrogen, halogen, C1-C5 alkyl; R2 represents an organic polyvalent group having a molecular weight of 14 to 1000 and valence of m + n; m represents an integer indicating the number of acrylic or methacrylic groups or both in the ester; n represents an integer having a value of 1 to 5; and Y is selected from the group consisting of hydrogen, C1-C5 lower alkyl group and protic functional groups.

10. A retroreflective abrasion resistant coating according to claims 1-9, characterized in that the surface comprises polycarbonate and the amide monomer is selected from the group consisting of N, N-dimethylacrylamide, N, N-diethylacrylamide and N-vinyl pyrrolidone.

11. A raised, retroreflective pavement marker characterized in that it comprises a retroreflective abrasion resistant coating according to claims 1-10.