WO1998024859A1

WO1998024859A1 - Pavement marking article

Info

Publication number: WO1998024859A1
Application number: PCT/US1997/005261
Authority: WO
Inventors: Gina M. Buccellato; Cristina U. Thomas; Bimal V. Thakkar; Gregg S. Bennett
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1996-12-04
Filing date: 1997-04-02
Publication date: 1998-06-11
Also published as: AU2428897A

Abstract

A pavement marking article that has an adhesive composition for adhering the article to a pavement substrate, where the adhesive composition includes a reaction product of an acrylic acid ester of a monohydric alcohol whose homopolymer has a Tg less than 0 °C, a non-polar ethylenically unsaturated monomer, and 0-10 parts by weight of a polar ethylenically unsaturated monomer. Preferably the amount of the acrylic acid ester is about 60-90 parts by weight, and the amount of the non-polar ethylenically unsaturated monomer is about 10-40 parts by weight.

Description

PAVEMENT MARKING ARTICLE

Background The invention relates to adhering an article to a substrate such as a pavement substrate.

Pavement markings convey information to motorists and pedestrians and assist in controlling motor vehicle, bicycle, and pedestrian traffic. Pavement markings have been attached to pavement substrates using adhesives e.g., pressure- sensitive adhesives, to prevent the markings from becoming dislodged. Road surfaces present a considerable challenge for adhesive attachment because they vary widely in terms of surface properties, i.e., the underlying material may be asphalt or cement concrete and may vary in aggregate type, age, temperature, moisture content and oil content. Although a variety of adhesives have been used in pavement marking applications, acrylic adhesives generally have not been used because they are moisture sensitive and tend to fail in the presence of water, and also generally do not adhere well to pavement substrates.

Summary of the Invention In a first aspect, the invention features a pavement marking article that has a first major surface that would be displayed when the article is positioned on a pavement substrate and a second major surface that has an adhesive composition for adhering the article to the pavement substrate. The adhesive composition includes a reaction product of an acrylic acid ester monomer of a monohydric alcohol whose homopolymer has a Tg less than 0°C, a non-polar ethylenically unsaturated monomer, and 0-10 parts by weight of a polar ethylenically unsaturated monomer. Preferably the homopolymer of the non-polar ethylenically unsaturated monomer has a solubility parameter of no greater than 10.50 and a Tg greater than 15°C, and the homopolymer of the polar ethylenically unsaturated monomer has a solubility parameter of greater than 10.50 and preferably a Tg greater than 15°C. Preferably the amount of the acrylic acid ester is about 55-90 parts by weight (more preferably about 60-85 parts by weight), and the amount of the non- polar ethylenically unsaturated monomer is about 10-45 parts by weight (more preferably about 15-40 parts by weight), and the amount of the polar ethylenically unsaturated monomer is about 0-10 parts by weight.

Examples of suitable acrylic acid esters include isooctyl acrylate, 2- ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, decyl acrylate, lauryl acrylate, hexyl acrylate, butyl acrylate, octadecyl acrylate, and combinations thereof.

Preferred acrylic acid esters are isooctyl acrylate, 2-ethylhexyl acrylate, and butyl acrylate.

Examples of suitable non-polar ethylenically unsaturated monomers include 3,3,5 trimethylcyclohexyl acrylate, cyclohexyl acrylate, isobornyl acrylate,

N-octyl acrylamide, t-butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, and combinations thereof. A preferred non-polar ethylenically unsaturated monomer is isobornyl acrylate.

Examples of suitable polar ethylenically unsaturated monomers include acrylic acid, itaconic acid, N,N dimethylacrylamide, N-vinyl-2-pyrolidone, N-vinyl caprolactam, acrylonitrile, tetrahydrofuryl acrylate, glycidyl acrylate, 2- phenoxyethylacrylate, benzylacrylate, and combinations thereof. A preferred polar ethylenically unsaturated monomer includes acrylic acid.

In one preferred embodiment, the pavement marking article includes an adhesive composition including the reaction product of an acrylic acid ester, a non- polar ethylenically unsaturated monomer, a polar ethylenically unsaturated monomer, and a crosslinking agent. Preferably the amount of crosslinking agent is about 0.01 to about 0.50 parts (more preferably about 0.05 to about 0.3 parts) per 100 parts of acrylic acid ester, non-polar ethylenically unsaturated monomer, and polar ethylenically unsaturated monomer.

In one embodiment the adhesive composition also includes a tackifier that is miscible in the adhesive composition. Preferably the tackifier is present in an amount ranging from about 1-50 parts per 100 parts acrylate containing polymer.

Preferred adhesive compositions have a Tg ranging from between about -25°C to about +10°C. Preferred articles include those in the form of a tape and those that are retroreflective.

The invention further features a method of marking a pavement substrate by affixing the above-described pavement marking article to a pavement substrate, or by applying the above-described adhesive composition to the pavement substrate and affixing the pavement marking article to the adhesive composition. In both cases, the adhesive composition may directly contact the pavement substrate (i.e., the pavement substrate does not require pre-treatment with a primer). This avoids the negative environmental impact caused by the volatile organic compounds that may be emitted by some primer compositions.

The invention also features a retroreflective article that has a surface provided with the above-described adhesive composition.

The pavement marking articles of this invention display good adhesion to oily substrates, and, in particular, to pavement substrates such as asphalt and cement concrete. The articles have properties that include good adhesion to damp surfaces, good oily surface adhesion, good low energy surface adhesion, hydrophobicity, and high tack. The articles also have good low temperature application properties. The articles are also able to remain adhered to a pavement substrate when subjected to the shear forces typically exerted on transverse pavement marking applications, e.g., vehicle stops, starts and turns. Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.

Brief Description of the Drawing Fig. 1 is a cross-sectional view of a pavement marking article in accordance with the present invention.

Description of Preferred Embodiments Fig. 1 is a representative example of a pavement marking article 10 having (i) a top or first major surface 12 for providing visual or tactile indicia to pedestrians and motorists, and to make portions of a roadway more visible, and (ii) a bottom or second major surface 14 that is provided with an adhesive composition 16 for adhering the marking article to a pavement substrate. The pavement marking article may take the form of essentially any traffic control article that utilizes adhesive compositions such as, signs; pavement marking tapes for cross-walks, stop bars, lane and shoulder delineations, and skips; and marking tapes for berms, barriers, curbs, and the like. The article may also be a raised pavement marker such as those having a body housing with a slanted top surface and a retroreflective lens positioned thereon, or those that are arcuately shaped. Raised pavement marking articles are described, e.g., in U.S. Patent Nos. 4,875,798 and 4,626,127. Pavement marking articles are generally described, e.g., in U.S. Patent Nos. 5,453,320 (Harper et al.) and 4,490,432 (Jordan). Removable pavement marking articles are described, e.g., in U.S. Patent Nos. 4,299,874 and 5,536,569.

The pavement marking article on its exposed top or first surface 12 typically provides visual or tactile indicia to a motorist and may have reflective, skid-resistant and visibility enhancing properties that are often furnished by optical elements 18, skid-resistant particles 20, and pigments and/or dyes, respectively. Surfaces having reflective elements and skid-resistant particles are well known in the art and are taught, for example, in U.S. Patent Nos. 5,453,320 (Harper), 5,227,221 (Hedblom) and 5,194,113 (Lasch). One example of a visibility enhancing surface is a surface having retroreflective properties. An article that has retroreflective properties is one that returns substantial quantities of incident light, which otherwise would be reflected elsewhere, back towards the light source. Often a surface with retroreflective properties will have a monolayer of retroreflective elements in a binder see, for example, U.S. Patent No. 5,227,221 (Hedblom). Common retroreflective elements include microspheres, typically glass or ceramic, with reflectors thereon. Well known reflectors include dielectric reflectors, metal layers (e.g. aluminum or silver), or nacreous pigment flakes. U.S. Patent No. 3,700,305 (Bingham) discloses retroreflective constructions comprising microspheres with dielectric reflectors. U.S. Patent No. 3,758,192 discloses retroreflective constructions comprising nacreous pigment flakes. The reflective layer may also comprise a cube-corner retroreflective sheeting see, for example, U.S. Patent Nos. 4,938,563 (Nelson), 5,450,235 (Smith) and 4,025,159 (McGrath).

The pavement marking article may include a base sheet to provide additional conformability and strength to the pavement marking article. Suitable materials for the base sheet include, e.g., rubbers, aluminum foil, polyolefins, woven scrims (e.g., durable netting) and non-woven scrims. Suitable base sheets are also described, e.g., in U.S. Patent Nos. 4,490,432 (Jordan), 4,117,192 (Jorgenson), 5,194,113 (Lasch et al.), and 5,082,715 (Lasch et al.).

The adhesive composition is formulated to adhere the pavement marking article to a pavement substrate. Preferred adhesive compositions are capable of wetting a pavement substrate during application. Examples of suitable adhesive compositions are disclosed in U.S. Patent Application Serial Nos. 08/150,426 (filed September 9, 1995), entitled, "Pressure Sensitive Adhesives with Good Oily Surface Adhesion," and 08/537,034 (filed September 9, 1995), entitled, "Pressure Sensitive Adhesives with Good Low Energy Surface Adhesion. "

The adhesive compositions are also capable of maintaining adhesion with the pavement substrate under the shear forces typically exerted on pavement substrates. The adhesive composition can remain adhered to the pavement substrate upon the application of transverse shear forces, i.e., the forces exerted on transverse marking article applications (e.g., cross-walks) when vehicles start, stop and turn. One measure of the adhesive's ability to withstand shear forces is its loss shear modulus and its storage shear modulus. The adhesive composition preferably has a high loss shear modulus and a high storage shear modulus under impact conditions, i.e., the temperature and frequency conditions that exist when a tire impacts the pavement marking article.

The adhesive composition also preferably maintains adhesion with the pavement substrate under the environmental conditions that pavement typically encounters. These conditions include wind, water (including standing water, rain, freezing rain, snow and ice), temperature extremes, deicing and anti-icing materials, automobile fluids (e.g., gasolines, oils and antifreeze), dirt, sand, and the like. The rheological character of the adhesive composition can be partially but usefully described by the glass transition temperature (Tg) as measured by the 1 radian/second tan delta maximum temperature. The Tg of adhesive compositions useful in the present invention is preferably in the range of about -25°C to about +10°C, more preferably about -20°C to about +5°C, most preferably about -15°C to about 0°C at one radian/second. If the Tg is too low, the adhesive composition may become too soft and may move under impact conditions. If Tg is too high, the adhesive composition's cold temperature performance may be impaired, i.e., the adhesive composition may not adhere well to the pavement substrate and may break away from the substrate upon impact.

Preferred adhesive compositions include the reaction product of 55-90 parts (more preferably 60-85 parts) of an acrylic acid ester monomer whose homopolymer has a Tg less than 0°C, 10-45 parts (more preferably 15-40 parts) of a non-polar ethylenically unsaturated monomer whose homopolymer has a solubility parameter of no greater than 10.50 and a Tg greater than 15°C, and 0-10 parts (more preferably 0-5 parts) of a polar ethylenically unsaturated monomer whose homopolymer has a solubility parameter of greater than 10.50 and a Tg preferably greater than 15°C. The resulting reaction product is an acrylate containing polymer. Preferably the reaction product has a weight average molecular weight of at least about 50,000, more preferably greater than 300,000 and most preferably between about 500,000 and 1.5 million.

The preferred acrylic acid ester is a monofunctional acrylic ester of a monohydric alcohol having from about 4 to about 18 carbon atoms in the alcohol moiety whose homopolymer has a Tg less than 0°C. Included in this class of acrylic acid esters are isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, decyl acrylate, lauryl acrylate, hexyl acrylate, butyl acrylate, octadecyl acrylate, and combinations thereof. In the case of octadecyl acrylate, the amount is chosen such that side chain crystallization does not occur at room temperature. The preferred acrylic acid esters are isooctyl acrylate, 2-ethylhexyl acrylate, and butyl acrylate. Preferred non-polar ethylenically-unsaturated monomers include those whose homopolymer has a solubility parameter as measured by the Fedors method of not greater than 10.50 and a Tg greater than 15°C. The non-polar nature of this monomer in combination with the other monomers, it is believed, helps improve the low surface energy adhesion, imparts hydrophobicity, oily adhesion and helps control the overall polarity of the composition. It is also believed that it improves the structural properties of the adhesive composition (e.g., cohesive strength) relative to a homopolymer of the acrylic acid ester described above. Examples of suitable non-polar monomers include 3,3,5 trimethylcyclohexyl acrylate, cyclohexyl acrylate, isobornyl acrylate, N-octyl acrylamide, t-butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, and combinations thereof. A preferred non-polar monomer is isobornyl acrylate.

The adhesive composition may contain a limited quantity (e.g., no more than 10 parts) of a polar ethylenically unsaturated monomer whose homopolymer has a solubility parameter as measured by the Fedors method of greater than 10.50 and preferably a Tg greater than 15°C to improve structural properties (e.g., cohesive strength). The polar monomer can add strength and stiffness to the adhesive composition but it also can be somewhat moisture sensitive. It is not desirable to include more than 10 parts of the polar monomer because the polar monomer impairs oily surface adhesion and adhesion in the presence of water. Examples of suitable polar monomers include acrylic acid, itaconic acid, certain substituted acrylamides such as N,N dimethylacrylamide, N-vinyl-2-pyrolidone, N- vinyl caprolactam, acrylonitrile, tetrahydrofuryl acrylate, glycidyl acrylate, 2- phenoxyethylacrylate, benzylacrylate, b-carboxyethyl acrylate, and combinations thereof. The preferred polar monomer is acrylic acid.

The monomer mixture can be polymerized by various conventional free radical polymerization methods, whether thermally or radiation initiated, including, e.g., solution polymerization, and bulk polymerization. Photoinitated bulk polymerization involves adding an initiator to aid in polymerization of the monomers. The type of initiator used depends on the polymerization process. Photoinitiators that are useful for polymerizing the acrylate monomers include benzoin ethers such as benzoin methyl ether or benzoin isopropyl ether, substituted benzoin ethers such as 2-methyl-2-hydroxylpropiophenone, aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride, and photoactive oxides such as 1- phenyl-l,l-propanedione-2-(o-ethoxycarbonyl)oxime. An example of a commercially available photoinitiator is Irgacure™ 651 available from Ciba-Geigy Corporation, believed to be 2,2-dimethoxy-l,2-diphenylethane-l-one. Generally, the photoinitiator is present in an amount of about 0.005 to 1% by weight based on the weight of the monomers. Examples of suitable thermal initiators include azobisisobutyronitrile and peroxides, e.g., benzoyl peroxide and cyclohexanone peroxide.

Solution polymerization involves combining the acrylate ester component, the non-polar ethylenically unsaturated monomer component, and the polar ethylenically unsaturated monomer component along with a suitable inert organic solvent and a free radically copolymerizable crosslinker in a reaction vessel. After the monomer mixture is charged into the reaction vessel, a concentrated thermal free radical initiator solution is added. The reaction vessel is then purged with nitrogen to create an inert atmosphere. Once purged, the solution within the vessel is heated to the activation temperature of the initiator, the initiator is added, and the mixture is stirred during the course of the polymerization reaction. Another polymerization method is a two step free radical polymerization of a 100% solids monomer mixture. In the first step, the low viscosity monomers are mixed at the appropriate ratios and an initiator is added to the mixture. The mixture is purged with nitrogen to remove dissolved oxygen. The solution is partially polymerized to produce a syrup with moderate viscosity that can be coated easily. Further initiator and crosslinker are added to the syrup. The syrup is then coated (while excluding oxygen) at a desired thickness, usually about 0.5 to 20 mils (about 0.01 to about 0.25 mm). During the coating process the syrup is further exposed to energy to complete the polymerization and crosslink the adhesive composition. The free radical polymerization is preferably preformed by thermal or UV catalysts and the preferred energy sources are thermal or UV. An alternative to the above two step polymerization method involves use of an extruder. In this method, a packaging material e.g., a pouch, that will not substantially adversely affect the adhesive properties of the adhesive composition when the pre-adhesive composition and packaging material are melted and mixed together, is filled with monomers and initiators, and optionally with the addition of chain transfer agents to keep the molecular weight low enough after polymerization so that the polymer can be extruded. The filled pouch is exposed to UV radiation, which produces the polymerized composition inside the pouch. The pouch and contents can then be fed to the extruder and the resulting molten composition hot melt coated onto a release liner, to yield a composition comprising a high molecular weight adhesive composition having a small percentage of pouch plastic polymer material therein, typically 3% by weight or less after which it is exposed again to low intensity UV radiation or electron beam radiation to crosslink the adhesive composition. Alternatively, the adhesive composition can be removed from the pouch, coated onto a substrate, and exposed to radiation to crosslink the adhesive. Suitable pouch materials include, e.g., ethylene- vinylacetate, ethylene acrylic acid, polypropylene, polyethylene, and ionomeric films.

The mixture of the polymerizable monomers may contain a crosslinking agent, or a combination of crosslinking agents, to increase the shear strength of the adhesive composition. Suitable crosslinking agents include, e.g., thermal, photosensitive, and radical initiating crosslinking agents.

Thermal crosslinking agents such as a multifunctional aziridine, e.g., l, -(l,3-phenylenedicarbonyl)-bis-(2-methylaziridine) (CAS No. 7652-64-4), can be incorporated into the adhesive composition and activated by heat during oven drying of the coated adhesive.

Crosslinkers that rely on free radicals to carry out the crosslinking reaction can also be employed. Reagents such as, for example, peroxides serve as precursor sources of free radicals. When heated sufficiently, these precursors will generate free radicals that cause crosslinking reactions in polymer chains. A common free radical generating agent is benzoyl peroxide. Suitable photosensitive crosslinking agents, i.e., crosslinkers that are activated by ultraviolet (UV) light, include substituted triazines such as 2,4,- bis(trichloromethyl)-6-(4-methoxyphenyl)-s-triazine, 2,4-bis(trichloromethyl)-6- (3,4-dimethoxyphenyl)-s-triazine, and the chromophore-substituted halo-s-triazines disclosed in U.S. Patent Nos. 4,329,384 and 4,330,590 (Vesley) incorporated herein by reference. Additional useful crosslinking agents include hydrogen abstraction type photocrosslinkers such as those based on benzophenones, e.g., 4- acryloxybenzophenone, acetophenones, and anthraquinones. Other useful crosslinking agents include multifunctional alkyl acrylate monomers such as trimethylpropane triacrylate, pentaerythritol tetra-acrylate, 1,2 ethylene glycol diacrylate, 1,4 butanediol diacrylate, 1,6 hexanediol diacrylate, and 1,12 dodecanol diacrylate. Copolymerizable a-cleavage type photoinitiators such as acrylamido- functional disubstituted acetyl aryl ketones can also be employed. Various other crosslinking agents with different molecular weights between (meth)acrylate functionality would also be useful. These crosslinkers are activated by UV light generated by artificial sources such as medium pressure mercury lamps and UV black light.

Generally, when a crosslinker is used, the crosslinker is present in an amount of about 0.01 to about 0.50 parts, preferably about 0.05 to about 0.30 parts crosslinker per 100 parts of the acrylic acid ester, the non-polar ethylenically unsaturated monomer, and the polar ethylenically unsaturated monomer.

Crosslinking may also be achieved using high energy electromagnetic radiation such as gamma or electron beam radiation, in which case the addition of a crosslinking agent is not necessary. Preferably the adhesive composition is about 20% to about 98%, more preferably about 40% to about 80% crosslinked.

The adhesive composition may also include a tackifier. The tackifier is preferably miscible with the acrylate containing polymer, i.e., macroscopic phase separation does not occur, in order to improve the properties of the adhesive composition. Preferably, the adhesive composition is free of microscopic phase separation as well. The total amount of tackifier is preferably about 1 to about 50 parts per 100 parts of the acrylate containing polymer. The particular amount of tackifier depends on the composition of the acrylate containing polymer and is generally selected to maximize adhesion as well as wetting of the substrate without compromising desired shear strength and low temperature performance.

A wide variety of tackifiers may be used. The most commonly used tackifiers in acrylic pressure-sensitive adhesives include terpenes (e.g., Zonarez A- 100, Piccolyte 5115 (commercially available from Hercules, Wilmington, DE), Piccolyte A-115 (Hercules), Piccolyte A- 135 (Hercules) and Piccofyn A- 135 (Hercules)), phenolics, rosins, rosin esters (e.g., Hercoflex 400 (Hercules), Permalyn 85), esters of hydrogenated rosins (e.g., Foral 85 and RegalRite 355 (Hercules)), synthetic hydrocarbon resins, hydrogenated C5 resins (e.g., Escorez 5340, 5300, and 5380 (commercially available from Exxon, Baton Rouge, LA)), hydrogenated C₉ resins (e.g., Regalrez resins 1085, 1094, 1128, 6108 and 3102 (Hercules), and Arkon P90 and PI 15 (commercially available form Arkawa, Japan)), C₅ hydrocarbons (e.g., Hercotac RT110, 100S, and RT400 (Hercules), Escorez 1310 (Exxon), hydrogenated aromatics (e.g., Exxon FCJ-90-019 (Exxon) and combinations thereof. In cases where the amount of polar ethylenically unsaturated monomer is small, the class of hydrogenated Cg resin tackifiers known under the tradename "Regalrez" resins are preferred. These tackifiers are produced by polymerization and hydrogenation of pure monomer hydrocarbon feed stock and include Regalrez™ resins 1085, 1094, 1128, 6108 and 3102, with 6108 being preferred.

The adhesive composition is preferably in the form of a coating applied to the surface of the pavement marking article. The adhesive coating may be continuous or discontinuous, e.g., a dot or stripe pattern. The thickness of the adhesive coating on the pavement marking article is preferably sufficient to permit the article to adhere to a pavement substrate. The thickness of the adhesive coating may vary depending on the application, i.e., the pavement substrate and the article substrate. The adhesive coating thickness is generally about 127 μm (5 mils) to about 508 μm (20 mils), more generally about 254 μm (10 mils). The adhesive composition may be coated onto a release-treated surface and then laminated to a surface of a pavement marking substrate. Alternatively, the adhesive composition may be applied directly to a surface of the pavement marking article, and optionally a release-treated surface can then be laminated to the adhesive composition.

Methods for marking pavement substrates include affixing the adhesive coated surface of the pavement marking article to the pavement substrate, and, alternatively, applying the adhesive composition to the pavement substrate and then affixing the pavement marking article to the adhesive. Examples of suitable methods for affixing raised pavement marking articles to a pavement substrate are described in U.S. Patent No. 4,974,990. Preferably the pavement marking article is affixed directly to the pavement substrate, i.e., a substrate that has not been primed. The article may, however, be affixed to a pavement substrate that has been first primed with a primer composition suitable for use in pavement marking applications. For environmental reasons, the primer composition preferably contains no volatile organic components. Primer compositions are well known in the art and are described, for example, in U.S. Patent Nos. 4,906,523 (Bilkadi et al.), and 5,468,795 (Guder et al.). Additional examples of primer compositions include, Stamark® E-44, Stamark® E-44T and P-46, Stamark® SP-44 sprayable adhesive, Scotch-Lane pavement Preparation Adhesive P-40 (available from Minnesota Mining and Manufacturing, St. Paul, MN), #BL 33 and #BL 52 (Brite-Line, Bedford, MA), ATM primer and ATM contact cement (Advanced Traffic Markings, Roanoke Rapids, NC).

The invention is further described in the following examples. It is to be understood, however, that while the examples serve this purpose, the particular ingredients and amounts used, as well as other details, are not to be construed to limit the invention's scope and may be varied.

EXAMPLES

Test Procedures Test procedures used in the examples include the following. Impact Shear Resistance Test

Impact shear resistance is determined using a vehicle wear simulator designed to simulate shear and wear conditions experienced by a pavement marking located near an intersection. The simulator has a test area consisting of a horizontal annular ring about 6 feet (1.8 meters) in diameter and about 1 foot (0.3 meter) in width having an unprimed concrete surface. Samples of pavement marking material are cut into 2 by 6 inch (5 by 15 centimeter) rectangles and mounted in the annular ring with the long axis of the sample being aligned with the radial axis of the ring. Each sample is then rolled by hand with a rubber roller to provide good contact to the unprimed pavement surface and its initial position noted. Two tires, B.F.

Goodrich P165/80R13 steel belted radials with an inflation pressure of 30 pounds/inch ι (2.1x105 Pascals), are positioned vertically above the test area at opposite ends of a rigid connecting frame. Downward pressure is applied to the connecting frame pneumatically to provide a load of between about 420 and about 440 pounds (about 190 and about 200 kilograms) on each tire. The frame is rotated, driving the tires across the surface of the test area at 5 revolutions/minute which is equivalent to a linear tire speed of about 1 mile/hour (2 kilometers/hour), simulating the high impact shear and abrasion forces encountered at high temperature. Impact Shear resistance is evaluated as the lateral movement of the sample on the substrate following a specified number of tire hits.

Method of Measuring Glass Transition Temperature Tg

The glass transition temperature, Tg, of the adhesive composition can be measured by first determining its storage (G') and loss shear moduli (G"). Storage and loss shear moduli can be measured by placing a 0.5 to 2 mm sample of adhesive composition on parallel plates 1 inch (2.54 cm) in diameter. A first set of measurements is taken at 25°C. Using liquid nitrogen, measurements are taken starting at 10°C down to -40°C at 10° increments. There is roughly a 15 minute interval between measurements at different temperatures to allow the adhesive sample to relax and attain equilibrium at the set temperature. The frequency sweeps range from 0.063 to 63 radians per second at each temperature. The normal force is held constant and the torque is about 20 gm-cm. G' and G" are obtained at each temperature for each sample. The ratio of G7G', a unitless parameter typically denoted "tan d", is plotted versus temperature. The maximum point (point where the slope is zero) in the transition region between the glassy region and the rubbery region of the tan d curve, if well defined, determines the Tg of the adhesive composition at that particular frequency.

Method of Measuring Gel Fraction

Gel fraction is measured by placing an adhesive sample weighing about 0.3 grams on a stainless steel fine mesh wire screen. The screen is folded and immersed in about 100 ml of tetrahydrofuran for 3 days at room temperature. On removal from the solvent, the adhesive samples are dried at about 93 °C (200°F) for 30 minutes and re- weighed. The uncrosslinked portions of the adhesive are extracted by the solvent. The gel fraction is the ratio of the final adhesive weight to its original weight.

Adhesive Preparation EXAMPLE 1

100 parts by weight of iso-octyl acrylate (IOA), isobornyl acrylate (IB A) and acrylic acid (AA) with a monomer ratio of 76/23/1 (IOA LBA/AA) were blended with 0.04 parts of benzildimethylketal (KB-1, commercially available from Sartomer, Weschester, Pennsylvania) photoinitiator, purged with nitrogen, and partially photopolymerized under an ultraviolet (UV) light source to yield an acrylate syrup having a viscosity of about 4000 centipoise (cPs). 0.16 parts of additional benzildimethylketal photoinitiator, 0.15 parts of 2,4-bis(tricholormethyl)- 6-(4-methoxyphenyl), and 20 parts Regalrez™ 6108 tackifier resin were added to the acrylate syrup and mixed thoroughly until all of the components had completely dissolved. After mixing, the blend was knife-coated at a 254 μm (10 mils) thickness onto a silicone-treated polyethylene-coated paper release liner. The composite was then exposed to ultraviolet radiation having a spectral output from 300-400 nanometers (nm) with a maximum at 351 nm in a nitrogen rich environment (<200 ppm oxygen). The average intensity was about 2.07 milliwatts per square centimeter (mW/cm²) resulting in a total energy of 646 mJ/cm². The adhesive composition was then laminated to a Stamark® N420 backing (available from Minnesota Mining and Manufacturing). Four 1 by 12 foot samples were then placed directly on a pavement substrate in an intersection. After twelve months, three of the samples remained intact on the substrate with no visible damage or movement and one sample showed approximately 40% loss.

EXAMPLE 2

A portion of the adhesive composition of Example 1 was laminated to a Stamark® 5760 backing (available from Minnesota Mining and Manufacturing). 4" x 10' samples of the adhesive coated backing were installed transverse to traffic on an unprimed asphalt substrate. Thirteen months later the samples were still intact.

EXAMPLE 3

An adhesive composition was prepared and applied to a Stamark® N420 backing according to the method described in Example 1 with the exception that the ratio of IOA/TOA/AA was 76/22/2 (IOA/IBA/AA). The adhesive coated backing was partitioned into three samples.

The three samples were subjected to the above described impact shear resistance test, except that the tires were driven across the surface of the test area at 8 revolutions/minute with 15 pounds per square inch (psi); 105 KPascals, downward pressure for the first 1000 hits after which the speed was ramped up to 60 revolutions/minute with 20 psi of downward pressure, which is equivalent to a linear tire speed of about 35 miles per hour. After 300,000 hits two of the three samples remained intact and undamaged. One of the three samples showed slight damage on the leading edge of the sample. EXAMPLE 4

100 parts by weight of iso-octyl acrylate (IOA), isobornyl acrylate (IB A) and acrylic acid (AA) with a monomer ratio of 80/17/3 (IOA/TBA/AA) were mixed together in a jar under a constant nitrogen purge and transferred to a plastic pouch (ethylene-vinyl acetate). The filled pouch was exposed to a UV blacklight to completely polymerize the adhesive. The pouch and contents were then fed to a counter-rotating twin-screw extruder (Leistritz, Sumerset, NJ.) at 149°C (300°F) and hot melt coated onto a release liner. The extruded coating was exposed to a 4 megarad electron beam to crosslink the adhesive composition. The gel fraction was 71. The adhesive coated liner was then laminated to a Stamark® 5760 backing and cut into four 2 by 6 inch (5.1 x 15.2 cm) sections.

EXAMPLE 5

An adhesive composition was prepared, extruded onto a release liner, and laminated onto a Stamark® 5760 backing according to the method described in

Example 4, with the exception that the ratio of IOA/IBA/AA was 75/22/3 and the extruded coating was subjected to a 5 megarad electron beam instead of a 4 megarad beam. The gel fraction was 71. The backing was then cut into four 2 by 6 inch (5.1 x 15.2 cm) sections.

EXAMPLE 6

Example 4, with the exception that the ratio of IOA/LBA/AA was 67/30/3 and the extruded coating was subjected to a 2 megarad electron beam instead of a 4 megarad beam. The gel fraction was 51. The backing was then cut into four 2 by 6 inch (5.1 x 15.2 cm) sections.

EXAMPLE 7 An adhesive composition was prepared, extruded onto a release liner, and laminated onto a Stamark® 5760 backing according to the method described in Example 4, with the exception that the ratio of IOA/LBA/AA was 67/30/3. The gel fraction was 59. The backing was then cut into four 2 by 6 inch (5.1 x 15.2 cm) sections.

EXAMPLE 8

An adhesive composition was prepared as in Example 4, with the exception that the ratio of IOA IBA/AA was 67/30/3 and the extruded coating was subjected to a 6 megarad electron beam instead of a 4 megarad beam. The gel fraction was 71. The backing was then cut into four 2 by 6 inch (5.1 x 15.2 cm) sections.

Each of the four samples of Examples 4-8 was tested pursuant to the above-described impact shear resistance test procedure. After 18,000 hits the samples were soaked in water and then subjected to 4,000 hits under a constant spray of water. The resulting average impact shear data are shown in Table I (movement in millimeters).

TABLE I

* Three of the four samples had no movement, one sample failed.

The data in Table I demonstrate that the samples passed the impact shear test.

The glass transition temperature of each of the adhesive compositions from Examples 1-8 was measured according to the above-described method. The resulting Tg data are reported in Table II (°C). The gel fraction of the adhesive compositions from Examples 4-8 was measured according to the above-described method. The resulting data are reported in Table II (% Gel).

TABLE π

The data in Table JJ show the glass transition temperature and percent gel or crosslinking of the adhesive composition.

Other embodiments are within the following claims. For example, the pavement marking articles can be applied to cover or obliterate existing pavement markings. It is further contemplated that the surface of the pavement marking articles on which the acrylate adhesive composition is provided may include an adhesive that is different from the acrylate adhesive, i.e., the acrylate adhesive may be provided on a coating of adhesive, e.g., polybutadiene adhesive. All of the patents and patent applications cited above are wholly incorporated by reference into this document.

Claims

CLAIMS:

1. A pavement marking article comprising a first exposed surface and a second surface that has disposed thereon an adhesive composition for adhering the article to a pavement substrate, the adhesive composition comprising the reaction product of: an acrylic acid ester of a monohydric alcohol whose homopolymer has a Tg less than 0°C; a non-polar ethylenically unsaturated monomer; and

0-10 parts by weight of a polar ethylenically unsaturated monomer.

2. The pavement marking article of claim 1, wherein the non-polar ethylenically unsaturated monomer comprises a homopolymer having a solubility parameter of no greater than 10.50 and a Tg greater than 15°C.

3. The pavement marking article of claims 1-2, wherein the polar ethylenically unsaturated monomer comprises a homopolymer having a solubility parameter of greater than 10.50 and a Tg greater than 15°C.

4. The pavement marking article of claims 1-3, wherein the amount of the acrylic acid ester is about 55-90 parts by weight and the amount of the non- polar ethylenically unsaturated monomer is about 10-45 parts by weight.

5. The pavement marking article of claims 1-4, wherein the amount of the acrylic acid ester is about 60-85 parts by weight, and wherein the amount of the non-polar ethylenically unsaturated monomer is about 15-40 parts by weight.

6. The pavement marking article of claims 1-5, wherein the acrylic acid ester comprises isooctyl acrylate, or 2-ethylhexyl acrylate.

7. The pavement marking article of claims 1-6, wherein the non- polar ethylenically unsaturated monomer comprises isobornyl acrylate.

8. The pavement marking article of claims 1-7, wherein the polar ethylenically unsaturated monomer comprises acrylic acid.

9. The pavement marking article of claim 1, wherein the adhesive composition comprises a tackifier in an amount ranging from about 1-50 parts per 100 parts acrylate containing polymer.

10. The pavement marking article of claims 1-9, wherein the first surface of the article includes a retroreflective element.