RETROREFLECTIVE TRAFFIC SIGNS

Abstract: Traffic or roadway signs comprising retroreflective sheeting (12) attached to a support substrate (16) comprising polymeric fiber-reinforced castable cementitious compositions. The support substrate is comprised of one or more dispersible primary packages maintained in a close-packed alignment in a dispersible containment means.

Description: RETROREFLECITVE TRAFFIC SIGNS Field of the Invention The present invention relates to retroreflective roadway traffic signs. More particularly, this invention relates to traffic signs comprised of retroreflective sheeting attached to a support substrate comprising primary packages of reinforcing elements for castable compositions. Background of the Invention Retroreflective materials have the property of redirecting incident light back towards its originating source. This advantageous property has led to the widespread use of retroreflective sheetings on a variety of articles. Often the retroreflective sheetings are used on flat articles, for example, traffic signs and barriers. Retroreflective traffic or road signs are used worldwide to direct travelers using roadways. Generally, a sign is constructed by attaching retroreflective sheeting to a substrate which provides support for the sheeting. Typical support substrates include aluminum and steel, although wood and steel-reinforced concrete materials have also been used. Aluminum support substrates are useful because they are lightweight as compared to steel or steel-reinforced concrete. In addition, aluminum is less susceptible to corrosion than steel. Often, a protective coating, such as a chromate coating, is applied to prevent oxidation. Steel support substrates are tough and rigid, but tend to be heavy and susceptible to corrosion. A protective coating must be applied to prevent moisture and elements from corroding or degrading the steel. In some localities, the aluminum or steel support substrates used for traffic signs are vandalized or even stolen to utilize these metals for other purposes such as cooking utensils and building materials. Wooden support substrates are not as tough or rigid as aluminum or steel and also tend to have weathering problems. Steel-reinforced concrete is useful as a support substrate material because it is rigid, tough, and castable. However, these substrates tend to be relatively thick in order to protect the steel-reinforcements from water and elements which will corrode or degrade the steel and in turn break apart the support substrate. Generally, the steel-reinforcements are covered with at least 2 inches (5 centimeters (cm)) of concrete to passivate the steel surface. Thus, the need exists for a support substrate material which has adequate strength, weather-resistance, sufficient longevity, is relatively inexpensive, and which does not contain metals which can be readily converted into another use. Summary of the Invention The present invention provides traffic or roadway signs comprising retroreflective sheeting attached to a support substrate comprising polymeric fiber-reinforced castable cementitous compositions. These fiber-reinforced cementitous compositions, or more particularly Portland cement-based compositions, are particularly suitable materials for support substrates. The support substrates comprised of this material are relatively lightweight because thinner substrates are possible (e.g., 0.25 inch (0.64 cm) thick). In addition, the fiber-reinforced cementitous substrate is tough, ductile, corrosion-resistant, and weather-resistant. The polymeric fibers help control failure due to crack propagation. These substrates can be constructed without welding, cutting, or waste. Further, the polymeric iϊber- reinforced substrate of the present invention is drillable, for example, bolt holes may be drilled to fasten the sign to another substrate or pole if desired. The material costs tend to be lower than aluminum, steel, or steel- reinforced concrete. Further advantages include the ease of handling and the variety of shapes and sizes afforded castable materials. The support substrate of the present invention is comprised of one or more dispersible primary packages each comprising a plurality of high aspect ratio polymeric fibers maintained in a substantially aligned arrangement introduced into a castable composition under dispersion conditions, wherein each of the primary packages is controllably disrupted to release fibers into the castable composition in a substantially unentangled manner. Preferably the fibers are maintained in a substantially aligned arrangement by means of a perimeter wrap prior to dispersion. The support substrate preferably has one surface which is substantially flat such that the retroreflective sheeting (which tends to be flat and often inflexible) may be effectively attached to the substrate (e.g., with adhesive, mechanical fasteners, insert molding). The two common types of retroreflective sheeting, microsphere-based sheeting and cube corner sheeting, are suitable for the present invention. Enclosed-lens sheetings are particularly suitable for the present invention. The retroreflective sheeting generally has at least two major surfaces. Typically, the first major surface is substantially flat and the second major surface is reflective. Typically, the first major surface (i.e., the substantially flat surface) of the retroreflective sheeting is attached to the substantially flat surface of the support substrate with an adhesive. A variety of adhesives are suitable to attach the sheeting to the support substrate. Preferably, the adhesive is a pressure- sensitive adhesive. For example, suitable pressure-sensitive adhesives include hydrocarbon-based elastomers combined with a large amount of tackifier and acrylic adhesives known in the art for adhering sheeting to metal substrates. Optionally, a primer may be used prior to attaching the sheeting to the support substrate with an adhesive to enhance the bonding of the retroreflective sheeting to the support substrate. Other embodiments include retroreflective sheeting attached to the support substrate with mechanical fasteners such as staples, anchors, rivets, screws, nails, etc. Further, the sheeting may be insert molded to the support substrate. The traffic signs of the present invention typically are at least 0.70 centimeter thick, but the thickness varies with the physical properties required for the particular application. Brief Description of the Drawings Figure 1 is a cross-sectional illustration of a traffic sign wherein an adhesive layer (14) is used to attach retroreflective sheeting (12) to a fiber- reinforced cementitous support substrate (16). Figure 2 is an illustration of a package of elongate reinforcing elements (22), including a primary containment means (24). These figures, which are idealized and not to scale, are intended to be merely illustrative and non-limiting. PeflnUions As used herein: "castable composition" means flowable compositions that can be cast as such or can be applied to surfaces by alternative techniques such as shotcrete process used with cementitous compositions; "cast face" means the support substrate surface (preferably where the sheeting material is attached) which is in contact with the mold during casting; "dispersing agent" means the water contained in the castable composition which serves to release fibers from the bundles; and "exposed face" means the support substrate surface which is open to the air during casting. Detailed Description of Illustrative Embodiments Support Substrate The support substrate of the present invention may be cast into a variety of shapes and sizes depending on the desired use of the traffic sign. For example, the substrate may be a polygon, circle, triangle, etc. Preferably, the substrate has two major surfaces where at least one of the major surfaces is substantially flat such that the adhesion to the retroreflective sheeting is enhanced. The support substrate may have essentially any thickness, but is typically at least 0.125 inch (.32 cm) thick. Preferably the support substrate is between 0.25 in (.64 cm) and 1.5 inches (3.8 cm) thick, more preferably, the support substrate is 0.50 inch (1.27 cm) to 1 inch (2.54 cm) thick. This thickness range decreases the material costs while still providing sufficient strength, toughness, ductility, and impact strength. The performance of castable compositions can be improved by the incorporation of reinforcing elements. For example, reinforcing elements are incorporated into cementitous compositions such as grout, mortar and concrete to improve strength or to reduce surface cracking tendencies. Reinforcing elements encompass a broad range of shapes, but typically share an elongate structure (i.e., the dimension of a major axis is significantly larger than the dimension of the minor axis). These elongate structures include rod-like filaments having substantially round cross-sections, flat strips having a helically twisted structure or made with a varying cross-section to reduce pull-out tendencies, or cable-like constructions based on twisted constructions of rod-like filaments. Materials used as reinforcing elements include metals, synthetic polymeric materials, and naturally occurring materials. In cementitous compositions (i.e., grout, mortar or concrete), the impact strength, flexural strength and toughness of the material improves with increasing percentages of the reinforcing elements in the composition. There is, however, a practical limit to the level of reinforcing elements that can be introduced as above this limit, the reinforcing elements tend to entangle with each other, forming balls or other undesirable conglomerates. Proper selection of criteria relating to the length and diameter (e.g., aspect ratio) of the reinforcing elements can help reduce the tendency to agglomerate. Achieving improved mixability by this technique is difficult, however, as these types of changes negatively impact the reinforcing capabilities of the elements. The method of delivering reinforcing elements into cementitous compositions also plays a major role in realizing high incorporation levels of reinforcing elements. For example, high aspect ratio reinforcing elements must be introduced into cementitous compositions as substantially individual fibers and in very low concentrations over an extended period of time with very good mixing if high volume concentrations of reinforcing elements are desired. Rod shaped reinforcing elements can become entangled and/or agglomerated in their shipping containers as a result of the vibration and jostling encountered during shipping. Agglomerated elements are not readily pourable from their shipping containers and cannot be added to cementitous compositions until the agglomerates have been broken up into individual elements. Various mechanical and pneumatic techniques have been employed to break-up the agglomerated masses and introduce the individual elements into the cementitous mix as a rain of elements. Reinforcing elements for castable compositions, and particularly for cementitous compositions, frequently have a much higher aspect ratio than the typical components of cementitous compositions. This disparity in aspect ratio makes uniform incorporation of reinforcing elements into cementitous compositions, particularly at high volume percentages of reinforcing elements, difficult. The present invention utilizes a primary package of elongate reinforcing elements that allows the addition of high volume percentages of reinforcing fibers to cementitous compositions in a single step while producing a substantially uniform incorporation of the individual reinforcing elements throughout the cementitous composition without "balling" or similar undesirable agglomeration formation. Preferably the reinforcing elements are polyolefin, polyester, poryamide, polyimide, or polysulfone polymeric fibers. Preferably each fiber has a diameter ranging from about 0.01 centimeters to about 0.02 centimeters. The volume percent of reinforced fibers typically ranges from zero to about 8 percent, preferably at least 1.5 volume percent. The volume percent of fibers varies with physical property requirements. One embodiment of the present invention comprises a plurality of primary packages contained in a secondary package. The secondary package may be another perimeter wrap, a bag, a box, or other suitable containment means. The secondary package comprises a dispersible packaging means, the dispersion of which is effected by the combined action of (1) a dispersing agent (i.e., water) present in the castable composition and (2) the substantially concurrent mechanical mixing of the castable composition and the secondary package. The secondary packaging means consolidates a multiplicity of primary packages of reinforcing elements. The primary packages of reinforcing elements 20 of Figure 2 comprise a plurality of elongate reinforcing elements 22 maintained in a close-packed, side- by-side alignment by a primary dispersible containment means 24. The primary containment means preferably comprises a perimeter wrap comprising compositions whose continuity can be disrupted, at least in part, so as to release the contents of the primary package, by the combined action of the water present in the cementitous composition and substantially concurrent mechanical mixing action. Disruption of the continuity of the primary containment means releases the elongate reinforcing elements and allows uniform mixing of the elements into the castable composition. Compositions suitable for use in aqueous cementitous compositions include, but are not limited to cellulose based papers, cellulose based papers saturated with water swellable or water dispersible binders, and water dispersible PSA tape constructions. Suitable water swellable or water dispersible binders that can be used in conjunction with the water dispersible containment means include, but are not limited to polysaccharides, gelatin, and poly(meth)acrylic acid. The water swellable or water dispersible binders can be applied to the water dispersible containment means by any of several techniques commonly used to apply binders to paper-like webs constructions, including, but not limited to roll coating, squeeze roll saturation, knife coating, and gravure coating processes. The dispersibility, or time required to disrupt the continuity of the primary containment means sufficiently to cause the release the reinforcing elements, can be controlled by the basis weight of the water dispersible packaging means, the type of binder and the binder incorporation level. Cylindrical primary packages of fibrous reinforcing elements 20 can be readily fabricated from a fiber tow or a hank by wrapping the tow or hank with a strip of primary containment means material in a spiral overlap manner to form a core of reinforcing elements 22 with a perimeter wrap of a water dispersible containment means and cutting the tow or hank to produce reinforcing elements of the desired length. The dispersion of the primary packages of reinforcing elements 20 can be extended by utilizing a higher basis weight primary containment means, by utilizing a primary containment means having a higher binder add-on, or simply by increasing the amount of overlap or the number of overlapping layers of the primary containment means 24. The primary containment means may exhibit sufficient cohesive attraction to itself to keep the terminal end of the top overlapping strip from unwinding after the fiber tow or hank has been cut to produce primary packages of reinforcing elements. If there is insufficient cohesive attraction between adjacent layers, an optional dispersible adhesive may be applied across the width of the outer face of primary containment means as, for example, a strip of a dispersible hot melt adhesive, a strip of a dispersible transfer adhesive, or a coating of water-soluble adhesive, as primary containment means is being wrapped around reinforcing elements. Dispersible adhesive preferably is selected so that it is dispersible by the water used to disperse primary containment means. A dispersible shrink wrap material may possibly be utilized for the perimeter wrap for the primary containment means. In addition to providing the shrink wrap capability, suitable materials would also have to exhibit substantially similar dispersibility performance to the materials described above. Regardless of the shape or design of the primary package of reinforcing elements, the perimeter wrap around each primary package is preferably maintained under sufficient tension to substantially restrict the lateral movement of the elongate reinforcing elements relative to one another. This restriction of lateral movement of reinforcing elements relative to one another prevents premature release of the reinforcing elements, either during shipping or during addition to castable compositions. In addition to providing a convenient and organized manner of introducing the reinforcing elements into castable compositions by effecting a significant reduction in the volume of reinforcing elements introduced into cementitous compositions at a critical mixing point, the packaging provides a distinct shipping advantage because it maintains the reinforcing elements in a configuration that will not permit agglomeration during shipping. Additionally, the primary package is significantly more dense than a comparable volume of unconsolidated elements, thereby allowing a significantly greater weight of elements to be shipped in the same volume occupied by the unconsolidated elements. Cylindrical packages of reinforcing elements can range in height from about 0.25 cm to about 20 cm, preferably from about 1.0 cm to 10 cm, and from about 0.25 cm to about 20 cm, preferably from about 1.0 cm to 10 cm in diameter. Even though this size range can result in primary packages having a significant disparity in size and shape relative to other components of typical cementitous compositions, the primary packages of reinforcing elements are readily mixed into the cementitous compositions in a substantially uniform manner. Upon disruption of the continuity of the perimeter wrap and the resulting tension it has maintained on the reinforcing elements, the elements are rapidly dispersed into the cementitous mixture with minimal, if any agglomeration. While not being bound by any theory, it is presumed that this lack of agglomeration is due, in part, to the fact that the reinforcing elements are maintained in a organized, substantially parallel arrangement on release. On being released, the elements continue to act in an aligned fashion, further enhancing substantially uniform macro-distribution of the elements throughout the cementitous composition until the individual elements are wetted and dispersed. Even though the perimeter wraps are substantially identical on each primary package of reinforcing elements, they exhibit a range of dispersing times. This range in dispersion times allows the addition of a high concentration of reinforcing elements, in the form of the primary package of reinforcing elements, to cementitous compositions as a single charge. Reinforcing elements are subsequently released from the primary packages in a controlled manner such that there is minimal, if any, agglomeration and the reinforcing elements are distributed throughout the cementitous compositions in a substantially uniform manner. Typically, essentially all of the fibers within an individual primary package are released substantially simultaneously in the form of individual fibers upon disruption of said primary package. This proposed incorporation mechanism stands in contrast to the introduction of individual elements into cementitous compositions in a totally random orientation that would allow inter-fiber interactions and subsequent agglomeration of the elements. Preferably the primary packages of reinforcing elements are free from binders that bind individual reinforcing elements together (i.e. inter-fiber binders). The absence of inter-element binders facilitates a more rapid dispersion of the elements as the binder does not have to dissolve to allow release of the individual elements. The elongate reinforcing elements may be incorporated using the following method: a) preparing a mixture of ingredient materials for the castable composition; b) introducing at least one primary package of elongate reinforcing elements into the mixture, the primary package of reinforcing elements comprising a plurality of elongate reinforcing elements maintained in a close- packed, side-by-side alignment by a primary dispersible containment means, the primary dispersible containment means comprising a perimeter wrap maintained under sufficient tension to restrict lateral movement of said elongate reinforcing elements relative to one another. The continuity of the primary dispersible containment means is capable of being controllably disrupted by dispersion of at least a portion thereof, the dispersion of the primary dispersible containment means being affected by the combined action of the water present in the castable composition and substantially concurrent mechanical mixing of the at least one primary package of reinforcing elements; c) mixing the castable composition and the at least one primary package of reinforcing elements to distribute substantially uniformly the at least one primary package of reinforcing elements into the castable material and to subsequently disrupt the continuity of the primary dispersible containment means, thus releasing the elongate reinforcing elements into the castable composition; and d) continuing to mix the castable composition and the elongate reinforcing elements mixture until the elongate reinforcing elements are distributed substantially uniformly throughout the castable composition. This process contemplates the introduction of one or more primary packages of reinforcing elements into a castable composition, depending on the level of reinforcing elements required for the composition. A mixture of sizes of reinforcing elements can be introduced into the composition by a) incorporating primary packages each of which contains a plurality of reinforcing element sizes, or b) by utilizing primary packages containing only one size of reinforcing elements each, but adding primary packages containing different sized elements in the appropriate ratio to achieve the desired final composition. As another embodiment, one or more secondary packages may be included in a similar manner. The water (i.e., dispersing agent) may be present in the mix of components of the castable composition prior to the addition of the primary package of reinforcing elements, or alternatively, the water may be added to the castable composition subsequent to the addition of the primary package of reinforcing elements. Addition of the water subsequent to the addition of the primary package can afford a longer time for the primary packages to be substantially uniformly incorporated into the castable composition before initiating the disruption of the dispersible packaging means and the perimeter wrap material. In either case, mechanical mixing action supplied by mixing the primary package and the castable composition mixture substantially concunent with the presence of the water is required to achieve dispersion the primary containment means materials. If a secondary packaging means is used, preferably the dispersion time of the perimeter wrap is controlled such that the disruption of its continuity does not occur prior to the disruption of the continuity of the secondary packaging means. Premature release of the reinforcing elements while they are still contained within the secondary package may result in undesirable agglomeration of the reinforcing elements. Retroreflective Sheeting The two common types of retroreflective sheeting suitable for use in the present invention are microsphere-based sheeting and cube corner sheeting. Microsphere-based sheeting, sometimes referred to as "beaded" sheeting, is well known in the art and employs a multitude of microspheres, typically at least partially embedded in a binder layer and having associated specular or diffuse reflecting materials (e.g., pigment particles, metal flakes, or vapor coats, etc.) to retroreflect incident light. Illustrative examples of such suitable retroreflectors are disclosed in U.S. Patent Nos. 3,190,178 (McKenzie), 4,025,159 (McGrath), and 5,066,098 (Kult). Cube corner sheeting, on the other hand, typically employs a multitude of cube corner elements to retroreflect incident light. Cube corner retroreflectors typically comprise a sheet having a generally planar front surface and an array of cube corner elements protruding from the back surface. Cube corner reflecting elements comprise generally trihedral structures which have three approximately mutually perpendicular lateral faces meeting in a single corner, i.e., cube corner. In use, the retroreflector is arranged with the front surface disposed generally toward the anticipated location of intended observers. Light incident to the front surface enters the sheet, passes through the body of the sheet to be internally reflected by the faces of the elements so as to exit the front surface in a direction substantially toward the light source, i.e., retroreflection. The light rays are typically reflected at the cube faces due to either total internal reflection, or reflective coatings such as a vapor-deposited aluminum film. Illustrative examples of cube corner type reflectors are disclosed in U.S. Patent Nos. 3,712,706 (Stamm), 4,025,159 (McGrath), 4,202,600 (Burke et al.), 4,243,618 (Van Arnam), 4,349,598 (White), 4,576,850 (Martens), 4,588,258 (Hoopman), 4,775,219 (Appeldorn et al.), and 4,895,428 (Nelson et al.). Encapsulated-lens sheeting may be particularly suitable for the traffic signs of the present invention because of the likelihood of exposure to moisture, e.g., outdoors or in high humidity. Illustrated examples of encapsulated-lens sheeting are disclosed in U.S. Patent Nos. 3,190,178 (McKenzie), 4,025,159 (McGrath), 4,896,943 (Tolliver et al.), 5,064,272 (Bailey et al.) and 5,066,098 (Kult). Conformable retroreflective sheeting may also be useful in the present invention. Typically, such sheeting has a conformable layer, such as aluminum, behind the sheeting which enhances application to rougher surfaces. An illustrative example of a commercially available conformable sheeting is Scotchlite™ High Intensity Conformable Series available from Minnesota Mining and Manufacturing Co. ("3M"), St. Paul, MN. Illustrative examples of commercially available retroreflective sheetings that may be used herein include Scotchlite™ High Intensity Retroreflective Sheeting (microsphere-based) and Scotchlite™ Diamond Grade Retroreflective Sheeting (cube-corner) both available from 3M, St. Paul, MN. Adhesive Laver To secure the retroreflective sheeting to the support substrate, an adhesive or a combination of an adhesive and primer is typically used. An adhesive layer may already be present on the retroreflective sheeting if commercial sheeting is used (e.g., Scotchlite™ Reflective Sheeting Engineer Grade Series 3200, Scotchlite™ Reflective Sheeting High Intensity Grade Series 3800, and Scotchlite™ Reflective Sheeting Diamond Grade VIP Series 3990, all available from 3M, St. Paul, MN). Additional adhesive may be necessary to achieve sufficient bonding to the support substrate or a primer may be required. For sheeting without an adhesive layer, the adhesive, and when necessary the primer, may be applied to the sheeting and/or the support substrate when the traffic sign is formed using a conventional method (e.g., roll-coating). Preferably, the adhesive is a pressure-sensitive adhesive ("PSA"). Suitable pressure-sensitive adhesives include hydrocarbon-based elastomers (e.g., polybutadiene, cis-polyisoprene) and acrylic adhesives as known in the art. An illustrative example of such a hydrocarbon-based PSA is disclosed in U.S. Patent No. 5,453,320 (Harper et al.). Harper et al. discloses an adhesive comprising rubber having a Tg (glass transition temperature) between -120°C and about - 50°C and about 125 to about 225 parts by weight of a tackifier having a ring and ball softening point of between about 70°C and about 140°C. For the present invention, the adhesive thickness preferably is at least 40 grain weight (grains per 4-inch by 6-inch (about 170 grams per square meter (gsm))). Preferably the adhesive thickness is 100 grain weight (425 gsm) or less. Other suitable adhesives may be readily selected by one skilled in the art, such as epoxy resin and silicone resin adhesives. The adhesive may be prepared using any suitable conventional method as known in the art. Adhesives of the invention may be crosslinked via chemical crosslinkers, or actinic radiation, e.g., electron beam or ultraviolet exposure. The adhesive preferably is crosslinked sufficiently to resist long-term shear while not inhibiting bond-building to a substrate. Primers A primer composition such as a contact cement may be applied to the surface of the support substrate to which the retroreflective sheeting of the invention is to be adhered. When the retroreflective sheeting is adhered to the casting face surface, a primer is not necessary. Sufficient bonding may be achieved using the exposed face surface. Although the bonding may be enhanced by "cleaning" the surface (i.e., power washing; brushing away debris) and/or using a primer. Primers improve the bond making performance of the adhesive, and in some instances may be necessary to attain a bond, such as where the adhesive 5 PC17US96/16590 - 15 - contains particularly high tackifier loadings and/or is very highly crosslinked. Primers useful with this invention preferably form hard coatings. For instance, a preferred class of primers are neoprene-based contact cements which form hard, water-resistant coatings. The surface of the support substrate to which the retroreflective sheeting and primer, if any, is applied is preferably substantially dry to ensure effective bonding. If used, a primer is preferably applied thick enough to provide an essentially continuous coating over the support substrate surface, and more preferably, thick enough to provide a somewhat more planar surface to increase the degree of contact with the surface of the adhesive layer. The adhesive or the retroreflective sheeting, having an adhesive layer, is preferably applied to the primed surface during the open time of the primer. Process for Manufacturing Traffic Signs The traffic signs of the present invention may be constructed using the following method. Typically, the support substrate 16 is wet cast, although it is foreseeable to use a dry cast method. The components are mixed together in a concrete mixer using a conventional method (i.e., ready-mix truck, rotary pan mixer) until a homogeneous mixture is obtained. The polymeric fibers are added in this mixture in a single charge, as described above. Typically, the mix time is 3 to 5 minutes for a rotary pan mixer. The fiber-containing mixture is then poured into a mold open on the top side of desired size and shape. The exposed face surface is then finished to the desired texture. After approximately 12 hours, the substrate is de-molded and allowed to cure for at least 7 days (although 28 days may be desirable). The surface of the substrate is then prepared using a power-washer or brush. If commercial retroreflective sheeting is used which has an adhesive layer, the release liner is removed from the adhesive side and the sheeting is then applied adhesive-side down to preferably the cast face surface of the support 5 PC17US96/16590 - 16 - substrate. Note if desired, a primer may first be applied to the support surface. During the primer's open time, the sheeting is then applied. If the sheeting 12 does not have an adhesive layer 14, or if additional adhesive is desired, the adhesive is first applied to preferably the cast face surface of the support substrate using a conventional method. Then, the sheeting 12 is applied over the adhesive layer 14 (and if desired, the primer applied prior to application of the adhesive layer). The next step is to laminate the sheeting down on the substrate. Any conventional method may be used (e.g., a squeeze roller). As alternative embodiments, mechanical fasteners (e.g., screws, nails, rivets, anchors, staples, and the like) may be used to attach the sheeting to the concrete substrate. In addition, insert molding may be used to secure the sheeting to the support substrate. When insert molding, the sheeting may first be placed in the mold with the reflective surface contacting the bottom surface of the mold. The fiber-reinforced castable composition is then poured into the mold and allowed to cure in situ against the back of the retroreflective sheeting so as to form a good bond thereto. Examples The following examples illustrate various specific features, advantages, and other details of the invention. The particular materials and amounts recited in these examples, as well as other conditions and details, should not be construed in a manner that would unduly limit the scope of this invention. Example l Traffic signs were prepared using the following method. A 30.5 cm x 30.5 cm x 0.635 cm support substrate was prepared by mixing together in a Hobart (A-200T) mixer (available from Hobart Corp., Troy, OH): 4720 grams 40/30 sand 1568 grams 3/8 inch (0.95 cm) gravel 1680 grams Type 1 Portland Cement 1680 grams water 80 grams fibers (2 volume percent of 3M Polyolefin Fiber Type 25/38) - 15 mil (381 μm) x 2.54 cm fibers wrapped with kraft paper held together by a water-dispersible adhesive system (density of fiber is 0.91) until a homogeneous mixture was obtained. The mixing process was as follows: 1. Charge sand, gravel, and half of the water 2. Mix for 1 minute 3. Charge cement and rest of water 4. Mix for 4 minutes 5. Rest for 1 minute 6. Mix for 3 minutes while adding fibers 7. Mix for 2 to 3 minutes. The mixture was then poured into the mold. The mix in the mold was then vibrated (Syntron (VP51 DI) vibrating table available from FMC Corp., Homer City, PA.) for 30 seconds while screeding the concrete. A trowell was used to smooth the mix in the mold. Then, the mold was placed on a level table and covered with plastic after 1 hour. After about 12 hours, the mixture was de-molded and moisture cured for 14 days prior to air drying. Example 1A. To the cast face surface of the support substrate, a layer of hydrocarbon-based elastomer adhesive was laminated. The adhesive was prepared early by mixing together the following with high sheer rubber compounding equipment: 100 parts Natural Rubber - cis-polyisoprene CV-60 125 parts PICCOLYTE S155 (beta-pinene), available from Hercules, Inc., Wilmington, DE 1 part IRGANOX 1010, available from Ciba-Geigy Corporation, Ardsley, NY The adhesive was then coated onto a release liner and dried to yield a 80 grain weight (341 gsm) thick film of adhesive on the liner. The adhesive was then irradiated with an electron beam. The adhesive was laminated onto the cast side of the support substrate. Retroreflective sheeting (3M Scotchlite™ Reflective Sheeting High Intensity Grade Series 3800, 3M Co., St. Paul, MN) without an adhesive layer was laminated to the adhesive side of the support substrate using a hand-roller. The sign was evaluated for adhesion failure by trying to separate the sheeting from the support substrate. Cohesive failure occurred before any adhesive failure. Two hours later, the adhesion improved, indicating adhesion build-up over time. Example IB. Retroreflective sheeting (3M™ Scotchlite™ Reflective Sheeting High Intensity Grade Series 3800, 3M Co., St. Paul, MN) having an adhesive layer (acrylic-type adhesive) was laminated to the cast face side of the support substrate using a hand-roller. As in Example 1 A, the sign was evaluated for adhesion failure. Cohesive failure occurred before any adhesive failure. After two hours, the adhesion appeared to improve. Example 2 Traffic signs were prepared using the following method. Using the method of Example 1, a mortar mix comprising 6000 grams sand 2000 grams Type 1 Portland cement 1400 grams water 76 grams fibers (2 volume percent of 3M Polyolefin Fiber Type 50/63) - 25 mil (635 μm) x 5.08 cm fibers wrapped with kraft paper held together by a water- dispersible adhesive system was mixed in a Hobart (A-200T) mixer. The mixture was poured into two 10.16 cm x 15.24 cm x 0.64 cm molds (Examples 2A and 2B). The adhesive/sheeting systems of Examples 1 A and IB were likewise applied to the cast side of this support substrate. As in Examples 1A and IB, the sheeting tore rather than delaminate, indicating cohesive failure prior to adhesive failure. Example 3 Traffic signs were prepared using the following method. Two support substrates were prepared using the mixture and method of Example 1. The mixture was poured into two 0.16 cm x 15.24 cm x 0.64 cm molds. Example 3A. Conformable retroreflective sheeting (3M™ Scotchlite™ High Intensity Conformable 6800 Series, available from 3M, St. Paul, MN) having an adhesive layer (acrylic-type adhesive) was laminated to the cast face surface of the support substrate using a hand-roller. The sheeting was peeled cleanly off the surface indicating adhesive failure prior to cohesive failure. Note, this type of sheeting is removable. Example 3B. The support substrate cast face surface was first brushed and dusted with a dry towel to remove dust and other debris. A light coat of Scotchlite™ 4448 Primer, a polychloroprene-based primer, (available from 3M. St. Paul, MN) was brushed onto the cast face surface of the support substrate. The primer was allowed to dry for about 10 minutes until it was tacky. Then, conformable retroreflective sheeting (3M™ Scotchlite™ High Intensity Conformable 6800 Series, available from 3M, St. Paul, MN) having an adhesive layer (acrylic-type adhesive) was laminated to the cast face surface of the support substrate using a hand-roller. The sheeting was more difficult to peel away from the surface than Example 3A. After 1 hour, the adhesion improved and the sign appeared to have cohesive failure prior to adhesive failure. Various modifications and alterations will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein.

Claims: What is claimed is: 1. A retroreflective sign comprising: (a) a support substrate comprising: one or more dispersible primary packages each comprising a plurality of high aspect ratio polymeric fibers maintained in a substantially aligned arrangement introduced into a castable composition under dispersion conditions wherein each of said packages is controllably disrupted to release fibers into said castable composition in a substantially unentangled manner; and (b) a retroreflective sheet attached to said substrate. 2. The support substrate according to claim 1 wherein said primary packages comprise polyolefin fibers. 3. The support substrate according to claim 1 wherein said polymeric fibers are maintained in a substantially aligned arrangement by means of a perimeter wrap. 4. The support substrate according to claim 1 wherein said castable composition comprises a cementitous composition. 5. The support substrate according to claim 1 wherein said fibers comprise at least 1.5 volume percent of the total volume of the castable composition. 6. The support substrate according to claim 1 wherein said primary packages are substantially free of inter-fiber binding. 7. The support substrate according to claim 1 wherein each of the fibers has a diameter ranging from about 0.01 centimeters to about 0.02 centimeters. 8. The support substrate according to claim 1 wherein each of said packages has a height ranging from about 0.25 centimeters to about 20 centimeters, and a diameter ranging from about 1.0 centimeter to about 10 centimeters. 9. The support substrate according to claim 1 wherein said dispersion conditions comprise water incorporated in said castable composition. 10. The support substrate according to claim 1 wherein essentially all of the fibers within an individual primary package are released substantially simultaneously in the form of individual fibers upon disruption of said primary package. 11. The support substrate of claim 1 wherein said primary packages are further contained in secondary packages. 12. The traffic sign according to claim 1 wherein said retroreflective sheeting is selected from the group consisting of microsphere-based sheeting and cube-corner sheeting. 13. The traffic sign according to claim 1 wherein said retroreflective sheeting is conformable. 14. The traffic sign according to claim 1 wherein said retroreflective sheeting is attached to said support substrate with an adhesive. 15. The traffic sign according to claim 14 wherein said adhesive is selected from the group consisting of a hydrocarbon-based elastomer adhesive and an acrylic adhesive. 16. The traffic sign according to claim 15 further comprising a primer on the portion of said support substrate to which said retroreflective sheeting is adhered. 17. The traffic sign according to claim 1 wherein said retroreflective sheeting is attached to said support substrate with a mechanical fastener. 18. The traffic sign according to claim 17 wherein said mechanical fastener is selected from the group consisting of screws, nails, rivets, anchors, or staples. 19. The traffic sign according to claim 1 wherein said retroreflective sheeting is attached to said support substrate with insert molding. 20. The traffic sign according to claim 1 wherein said sign is at least 0.70 centimeter thick. 21. The traffic sign according to claim 1 wherein said support substrate is at least 0.32 centimeter thick. 22. A retroreflective sign comprising: (a) a support substrate comprising a fiber-reinforced castable cementitous composition, and (b) a retroreflective sheet attached to said substrate.

Inventors: ERICKSON RANDALL L, HURLOCKER L MAX, RICH LARRY D, ERICKSON, RANDALL, L., HURLOCKER, L., MAX, RICH, LARRY, D.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1996
Main classification: E01F9
IPC codes: C04B28, E01F9