MXPA97010362A - Retrorreflejante article of elevated inlet angle, with refracc spherical elements - Google Patents

Abstract

A retroreflective article (80) is provided which provides effective retroreflective brilliance with very high entry angles as well as low entry angles and under wet conditions. The article comprises spherical refractive elements (60) having a refractive index greater than 1.35 and less than 1.75, which adhere to cover a film (66) of a retroreflective base sheet with embedded lenses.

Description

ARÍcai RETRQRREFLEJM ?? TITANIUM TITLE REFERENCES FIELD OF INVENTION The present invention relates to a retroreflective article exhibiting high retroreflective brilliance at high entry angles and low entry angles, and under wet conditions, and a method of making such an article. The article is suitable for use as a pavement marking or as a vertical barrier or a delineation mark.

Pavement markings, such as the center line and the edges of a road, are important to provide a visual guide for motor vehicle drivers. Pavement marking materials are used in traffic control markings for various uses, such as a short distance line strip, stop bars and pavement markings for pedestrians at intersections. A common form of pavement markings is a tape with adhesive backing that is applied to the road surface in position and REF: 26424 desired length; The upper surface of the tape has a selected color and typically retroreflective features. Currently, many pavement markings are based on an optical system of exposed lenses made up of transparent microspheres partially embedded in a binder layer containing pigment particles, eg, titanium dioxide (Ti02) or lead chromate (PbCr04), as reflective. In use, light from a vehicle headlight enters the microsphere and is reflected to impact the reflecting pigment particles. A certain portion of the light generally returns along the original entry path in the vehicle direction so that it is visible to the driver. The amount of refraction and the amount of light reaching these microspheres depends in part on maintaining a low refractive index at the interface with the air on the exposed portion of the microsphere. During periods of rain, the microspheres are moistened with water which reduces their ability to refract light, resulting in a very low retroreflective performance. A solution to this problem is the enhanced pavement markings in which the retroreflective ones appear in slightly vertical configurations. U.S. Patent Nos. 4,388,359 (Ethen et al.), 4,988,555 (Hedblom) and 4,988,541 (Hedblom) describe pavement markings with protruding portions that carry retroreflective elements with lenses exposed on the sides thereof. The use of retroreflective structures with lenses embedded on pavement markings is also known. These structures are typically used as point guides which are augmented with continuous painting or tape markings. See, for example, U.S. Patent Nos. 5,277,513 (Flanagan et al.) And 5,340,231 (Steere et al.). Retro-reflective laminates with lenses included with flat roof films (sometimes also referred to as roof sheets, top sheets, top films, etc.,) have been constructed as a means to improve wet retroreflectivity. See, for example, U.S. Patent No. 4,025,159 (McGrath) which describes retroreflective articles with encapsulated lenses and U.S. Patent Nos. 4,505,967 (Bailey) and 4,664,966 (Bailey et al.) Which describe retroreflective articles with embedded lenses. U.S. Patent No. 4,145,112 (Crone) discloses an article comprising a retroreflective layer with an underlying base and a layer for directing the light constituted of a longitudinally extending series of short transparent projections which each have a part front and rear (defined in relation to the expected origin of light to be retroreflected) upwards, which extends towards the surfaces of the edge. The surfaces of the leading edge are exposed through (ie, relatively perpendicular to) the expected path of the light at the high angle of incidence, so they transmit, instead of reflecting a high percentage of the incident light of the approaching motor vehicles. The surface of the trailing edge is positioned so as to reflect the light transmitted through the surface of the leading edge to a path within a predetermined angular range for retroreflection by the retroreflective elements, and to reflect light retroreflected by the retroreflective elements back to through the surface of the leading edge, towards its source. In order to retain the proper retroreflectivity, a precise configurational relationship of the front and rear upward part extending from the edge surfaces of each projection must be established and maintained. In addition, the longitudinally extending projections tend to return to such less flexible laminates. U.S. Patent No. 4,236,788 (Wyckoff) discloses a related type of pavement marking tape in which both sides of the transverse prisms are adjusted to provide internal reflection downwardly within the base sheet from one side and refraction to the space between successive prisms in the base sheet from the other side. As with the article described in U.S. Patent No. 4,145,112, it is critical to maintain an accurate configurational relationship between the two vertical faces of the prisms. U.S. Patent No. 3,920,346 (Wyckoff) discloses a sawtooth-like marker strip made up of protruding portions with curved edges and having retroreflective members placed therein, embedded therein. The disturbed edges of the raised protruding parts are said to reduce the loss of incident light so that the marker is bright over a wide range of angles of light incident on the marker strip. In addition, the incorporation of retroreflective members placed upwards in the projecting portions results in a narrower angle of incidence or entry of light from the approaching motor vehicles, which allows a more effective retroreflection by the article. U.S. Patent No. 4,072,403 (Eigenmann) discloses a retroreflective assembly that is particularly useful for situations in which retroreflection is required in rainy conditions. The assembly described in that document comprises a transparent globule with a transparent microsphere monolayer on certain portions of the globule and a retroreflective layer placed behind the microspheres. Retroreflective assemblies, sometimes referred to as "retroreflective globule / microsphere assemblies", are placed on the upper surface of a pavement marking where they provide enhanced retroreflectivity to light at high angles of incidence. U.S. Patent No. 5,268,789 (Bradshaw) discloses an improved retroreflective globule / microsphere assembly and an improved method for manufacturing such an assembly. EP patent number 385746 Bl (Kobayashi et al.) Discloses a pavement marking comprising a layer of large glass microspheres embedded in the upper part of a retroreflective embedded lens type base laminate. It is said that the brand for retroreflective pavement is. Particularly useful in rainy conditions because the larger glass microspheres are partially exposed to air. However, the pavement marking described is limited to using microspheres as a light-activating source. In addition, it is said that the pavement marker only increases the retroreflectivity of its base laminate at the entry angles between 60 ° and 80 °. It is known in the art that high entry angles, greater than about 85 °, are more common for pavement marking applications. further, the reference discloses that large glass microspheres have a refractive index of less than 1.75 which may not be suitable for the invention. The pavement markings currently available provide an effective retroreflective response for only a narrower range of entry angles than is sometimes desired. In addition, currently available pavement markings are not as effective reflectors as desired for some applications. For example, current commercial flat pavement markings are based on microspheres partially embedded in layers containing pigment particles, which are more easily observed at distances of approximately 80 meters and less. At greater distances than this, the retroreflective brightness declines due to the relatively larger entrance angles of the incident light and limited retroreflective efficiency. In addition to the generally low retroreflectivity at high angles of incidence, flat pavement markings are particularly difficult to observe under rainy conditions. Enhanced pavement markings have better reflectivity in number because rain is removed from the enhanced portions. However, snow removal is often a problem on roads that have raised pavement markings, because snow shovels have a tendency to trap the raised protruding parts and detach the markings from the road surface. There is a need for low profile retroreflective articles that exhibit high retroreflective brilliance in a continuous line even at high incident angles and which retain an effective retroreflective brilliance at high angles of incidence even when wet. As used herein, "low profile" refers to an article low enough to sustain impacts of a snow shovel after the winter season with minimal damage to the article. In addition, there is a need for retroreflective articles that show effective retroreflective responses over a wide range of entry angles for application to vertical surfaces such as rail protections, Jersey barriers, etc.

BRIEF DESCRIPTION OF THE ^ VENTTION The present invention provides novel retroreflective articles, preferably low profile, which provide a non-obvious combination of improved retroreflectivity at very high (88 ° or greater) entry angles such as those seen in pavement markings, bright retroreflectivity to low entry angles and much higher retroreflectivity under wet conditions compared to typical pavement markings. The invention also provides a novel method for marking such retroreflective articles. In summary, an article of the invention comprises a retroreflective base sheet with included or embedded lenses and an array of spherical reflective elements on the front surface of the base sheet. The base sheet comprises an array of retroreflective elements beneath a continuous superimposed transparent cover layer. The spherical reflective elements are placed in relation to the retroreflective base sheet so that the incident light in the array of spherical refractive elements at a high input angle is refracted so that it is transmitted to the base sheet and is retroreflected by the base sheet . Unlike the refractive elements in the articles described in the North American patents numbers 4, 145, 112 and 4, 236, 788, the front and rear sides of the spherical refractive elements of the articles of the invention do not have a precise configuration in relation one with the other in order to obtain an effective retroreflection. Unlike EP patent number 385746 Bl, the refractive elements are not limited to glass microspheres with a refractive index of 1.75 to 2. As a result, the retroreflective articles of the invention can be processed easily and inexpensively. The retroreflective articles of the invention utilize the refraction on the front surface of the spherical refractive elements to direct incident light at high entry angles within the base laminate. As a result, the articles of the invention provide a surprisingly bright retroreflection and are surprisingly durable. Retroreflective articles of the invention are particularly suitable for applications in which light affects high entry angles greater than about 85 °, for example, in pavement marking geometries. Such applications include pavement markings and applications in which incident light can come from any direction, such as horizontal signs. Illustrative examples of such horizontal signs include legends and symbols usually placed on the pavement in parking lots to indicate handicapped parking area, and arrows and markings on the lines placed on the pavement at the intersection. In addition, the retroreflective articles of the invention are also suitable for use on vertical surfaces, particularly those that are observed with high incidence angles such as railroad crossing protection or warnings, building walls along tunnels, Jersey barriers, etc. . An advantage of the retroreflective articles of the invention is that in addition to exhibiting improved retroreflective brilliance with improved incident angles, they also exhibit high retroreflective brilliance at lower entry angles, for example, within 30 ° to 40 ° of normal, at which signs are often observed. This makes the articles of the invention especially suitable for use in walls and barriers along motorways and other applications in which the vehicle can approach the structure from a wide range of angles in which effective retroreflective brilliance is desired. For example, a first road may have a vertical barrier placed substantially parallel to a portion thereof and a second road may intercept the first road. If the barrier has an article of the present invention on the surface thereof, will provide effective retroreflection to vehicles that approach the barrier from either side, thereby increasing safety. The retroreflective articles of the invention can be used in curved formats, for example, wound around cones and traffic barrels, or curved guardrails, etc., which provide excellent retroreflective brilliance throughout essentially the entire visible portion due to the exceptional entry angles of the articles. Unlike the reflective laminate with exposed lenses that does not retroreflect when wet, the retroreflective articles of the invention are wet reflective. That is, the article of the invention produces retroreflection under rainy conditions, when the rain has subsided but the article has not yet dried, and in the early hours of the morning when dew is collected on the article, or under similar conditions. In addition, in a pavement marking application, the spherical refraction elements provide raised surfaces that also increase the retention of the wet reflectivity article by facilitating water shifting. However, the relatively low profile of the raised surfaces allows the retroreflective article to maintain its usefulness even in areas where snow shovels are used. In summary, the method of the invention comprises: (1) providing a retroreflective base sheet comprising an array of retroreflective elements and a cover layer; and (2) adhering an array of spherical refractive elements as described herein on the cover layer, the spherical refractive elements are placed in relation to the base sheet so that the incident light to the array is refracted so that it is transmitted in the base sheet, retroreflected by the base sheet and further refracted by the spherical refractive elements so that it is retroreflected by the article. The manufacturing process of the retroreflective article of the invention is much simpler in relation to the previous processes for manufacturing retroreflective articles comprising a light direction layer and a retroreflective base sheet. With prior retroreflective articles such as those described in U.S. Patent Nos. 4,145,112 and 4,236,788, the light direction layer must be carefully configured. In contrast, the spherical refraction elements of the invention can be randomly placed on the retroreflective base web if desired. In addition, the impacts and abrasion of traffic on the road which tend to distort the light direction layer of the previous retroreflective articles will have a much smaller effect on the spherical refractive elements of the invention because it is not critical to maintain an accurate configuration for get retroreflection. Finally, because the maintenance of precise geometries is not critical, more comfortable soft materials can be chosen, so that the ability of the pavement markings of the invention to stay on the road is improved.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further explained with reference to the drawings in which: Figure 1 is a plan view of the previously known pavement markings with a layer for directing the light placed above a retroreflective base layer; Figure 2 is a sectional view of the pavement marking shown in Figure 1; Figure 3 is a plan view of a retroreflective article illustrating the invention; and Figure 4 is a sectional view of an illustrative retroreflective article. These figures, which are idealized and not to scale, are intended to illustrate only and are not limiting.

DETAILED DESCRIPTION OF THE MODALITIES ILUSTRA.TTVA5 E THE INVENTION The retroreflective article of the invention has a novel optical system that increases the retroreflective capacity of a base laminate with high entrance angles without significantly compromising the retroreflectivity at all other entrance angles. As used herein, "high entry angles" means angles greater than about 85 ° (a glossary of terms is provided at the end of this specification). Because the article of the invention is capable of retroreflecting light at high entrance angles, it is useful for horizontal applications, such as pavement markings. Because the laminate of the invention has good angularity and also good retroreflective brilliance, it is useful for vertical applications such as delineators and barrier markers. "Front" brightness indicates low entry angles, typically from 0 ° to approximately 30 ° to 40 °. Figures 1 and 2 show a previously known retroreflective article such as that described in U.S. Patent No. 4,145,112 wherein article 10 comprises a light direction layer 12 with internally reflecting projections 16 and a laminate 14 of underlying retroreflective base and an underlying optional adaptation layer 18. Typically, such articles would further comprise an adhesive layer (not shown) on the underside of the shaping layer 18 by means of which the article would be attached to a desired surface, eg, the surface of a road or road (not shown). ). As described above, the projections 16 use internal reflection to direct light with a high entry angle towards the laminate 14 of the base and then use the internal reflection to redirect the retroreflected light through the return base laminate 14. towards the source. The layer 12 is shown adhered to the base laminate 14 with an intermediate adhesive layer 13. The base laminate 14 comprises an array of cube corner retroreflective elements 20 on the back side of its main layer 22 and a seal film 24 sealed to the main layer 22 with a network of interconnecting junctions 26 to provide the interface of the cube corner elements 20 required for retroreflection.

J_ General Structure of the Article of the Inv ^ n ^ n An illustrative retroreflective article of the invention, in this case a pavement marking, is shown in Figure 3. The pavement marking 30 comprises a retroreflective base laminate 32 with an arrangement of spherical light refractive elements 34 on the upper surface of the same, and optionally a shaping layer 36 underlying the base laminate 32 and a layer 38 of functional adhesive underlying the shaping layer 36. Different types of retroreflective laminate can be used as the base laminate 32. Retroreflective base laminates typically, by themselves, do not provide sufficient retroreflectivity at extremely high entrance angles, for example, at angles of 85 ° to 89 °. However, when these laminates are used in a composite article of the invention, good retroreflective performance is obtained at both high input angles and low input angles. The spherical refraction elements 34 adhere to the relatively flat front face of the retroreflective base laminate, for example, and are partially embedded in it. Due to their placement, these spherical refraction elements capture the light that would usually be reflected in a specular manner with high entrance angles. The captured light is refracted by the spherical refractive elements so that it enters the base laminate 32, is retroreflected by the base laminate 32 and is refracted so that it is directed towards the light source. A retroreflective article of the invention may contain colorants in at least a portion thereof, for example in the spherical refraction elements and / or in one or more components of the base laminate. Illustrative examples of common dyes include white, yellow and red, although other dyes may be used as desired. In addition, a thin coating can be applied to provide high abrasion resistance and / or dust resistance on the upper surface of the retroreflective article to protect it from traffic wear and dust accumulation. Preferably, the coating will be light transmitting and will not reduce the slip resistance of the article. In Figure 4 another retroreflective article illustrating the invention is shown. The pavement marking 80 comprises spherical refractive elements 60, slip-preventing particles 62, laminate 82 of high-angularity retro-reflective base, optional shaping layer 74, optional adhesive layer 76, and optional coating 78. The base laminate 82 further comprises retroreflective elements 68 embedded in the transparent polymer matrix 65, a specular coating 70, an adhesive layer 72 and a cover layer 66 from which the spherical refraction elements 60 protrude.

II. Laminates of Base Retrorrefle antea The retroreflective base laminates used in the invention preferably have good angularity, that is, the retroreflectivity of the base laminates is still substantial at relatively high entry angles of about 80 ° or more. All the component layers of the retroreflective base laminate are preferably adhered together in all types of environmental conditions, including under repeated impact and shear stress resulting from road traffic passing over the laminate in the case of applications of marks for the pavement. In addition, the base laminates used in the invention are inherently wet reflecting due to the important components of the optical systems which are included within the laminate and are not exposed to water.

The retroreflective base laminates used herein comprise a relatively flat cover layer on the front surface thereof. The cover layer projects the underlying components of the base laminate and can be a single layer or multiple layers. The cover layers are typically polymers but may be other light transmitting materials, if desired. They can be selected to separately optimize different characteristics of the laminate. The spherical refractive elements can adhere to the base laminate by being embedded in the cover layer or in an additional layer that adheres to the front of the cover layer. Different types of retroreflective base laminate can be used for the present invention. Illustrative examples of retroreflective base laminates that can be used of the invention include, but are not limited to, retroreflective laminates of embedded lenses and retroreflective laminates of encapsulated lenses (ie, both microsphere type and cube corner type). ). Illustrative encapsulated lens laminates include retroreflective laminates based on microspheres that comprise a monolayer of transparent microspheres partially embedded in a binder layer with a reflective layer in the back (i.e., embedded) portions thereof. An area interface is provided by a cover layer positioned at the front of the microspheres. Alternatively, a cube corner type laminate comprising a monolayer of cube corner retroreflective elements having an air interface protected by a sealing layer may also be used. The cube corner type laminate in which the cube corner elements have been covered with a specular reflective metal layer, can also be used. In a cube corner type laminate, the cover layer may be an integral part of the cube corner formations or may be an independent film. U.S. Patent No. 4,025,159 (McGrath) discloses certain retroreflective laminates of the encapsulated lens of the microsphere type and cube corner type that may be used herein. Illustrative embedded lens laminates include microsphere-based retroreflective laminates comprising: (1) a monolayer of transparent microspheres whose front and back surfaces are embedded in a transparent matrix, and (2) a reflective layer positioned from the back surface of the microspheres at a selected distance. U.S. Patent No. 4,505,967 (Bailey) discloses a retroreflective embedded lens laminate that is particularly suitable and preferred for use herein. An illustrative example of the. Embedded lens, cube corner laminate comprises a monolayer of cube corners whose front and rear reading surfaces are embedded in polymer matrices and a reflective layer coated specularly or metallized on the surface of the cube corners. It is known in the art that the metallization of a cube-corner laminate increases the angularity of the laminate's entrance. Retroreflective laminates of embedded lenses are typically preferred over encapsulated lens retroreflective laminates when used as pavement markings. It is believed that the solid construction of the embedded lens laminate will be more durable when subjected to traffic conditions because it has no internal voids such as the encapsulated lens laminate. Inlaid retroreflective lens laminates are available in commercial forms that are very durable and flexible. They are available in embodiments that provide retroreflective performance of effective brightness at higher entrance angles than many encapsulated lens systems are capable of. further, the reflective layer in many laminates of encrusted lenses is aluminum and the aluminum forming layers are commonly used in pavement marking materials. This similarity can minimize any possible corrosion problems that may arise in different metals when they are used. The optical systems of included or embedded lenses based on microspheres use light coverage effect and focus of the microspheres to refract light in a reflector member which is reflected and then refracted back to its origin. The degree of refraction and therefore the optimal placement of the specular reflector depends on the relative refractive indices of the cover layer above the microspheres, the microspheres and the separation layer between the microspheres and the reflector member in as in case if there is. For example, when used with a cover layer and separation layer materials having refractive indices of approximately 1.5, a microsphere with a refractive index of 2.25 will focus a light behind a distance of approximately 0.44 times its radius. The thickness of the separation layer preferably approaches this so that the light is focused on the specular reflector. Any deviation away from these precise optical relationships will tend to result in retroreflectivity losses of the base laminate. Therefore, the cover layer preferably remains firmly attached to the microsphere layer, the microspheres are preferably stably placed in the matrix, and all the capable through which the light must pass to be retroreflected they are preferably transparent and free from distortion. In addition, the specular reflector, aluminum typically deposited by steam, preferably remains as a substantially continuous distortion-free layer without fractures or corrosion. The interphase of the separation layer-specular layer preferably remains smooth and free of chips. Very small changes in these optical relationships tend to result in degradation of the retroreflective performance of the base laminate and therefore any reflected article using such a base laminate. Although extremely small changes do not change a loss of objectionable brightness, slight changes can severely alter precise relationships. It is surprising that any retroreflective laminate manufactured using these precise optical ratios can withstand the repeated impact of traffic and stresses necessarily in combination with other effects of sunlight, rain, oil on the road, sand on the road, salt on the road and vehicle emissions. When light enters a retroreflective lens laminate embedded at high incidence angles and passes through the microsphere, it tends to be focused on the side of the microsphere instead of on the back side as it happens when light strikes a shape more perpendicular at low incidence angles. Therefore, it is important to maintain the correct separation between the microspheres and the reflective layer. As will be understood by those familiar with the art, the thickness of the space coating layer can be partially controlled by manufacturing methods. When the separation layer tends to be semi-spherical, that is, concentrically to the rear side of the microspheres, an optimum separation of a plurality of input angles can be obtained. U.S. Patent No. 4,505,967 (Bailey) describes a retroreflective lens laminate suitable for use herein and describes in detail the relationship between the configuration of the separation layer and the retroreflective response of the laminate. The 3M SCOTCHLITE No. 3750 reflective license plate laminate is an illustrative example of a commercial retroreflective laminate that can be used in the invention. It is important that the light-transmitting cover layer placed at the front of the retroreflective elements be durable because the pavement marking, in some applications, will be exposed to high volumes of traffic. The cover layer is preferably substantially continuous. The compositions of the cover layer must be selected so as to provide a strong bond to the spherical refractive elements. Preferably, the cover plate is a thermoplastic polymer. Illustrative examples of thermoplastic polymers suitable for use in the invention include polyurethanes, polyethylene acid copolymer consisting of ethylene-methacrylic acid (EMAA), ethylene-acrylic acid (EAA), EMAA or ionically cross-linked EAA. A preferred material is an aliphatic polyurethane because of its high impact resistance, low temperature flexibility, color clarity, abrasion resistance and good bond to preferred base laminates. The cover layer is also preferably resistant to the accumulation of transparent powder, flexible enough to adapt to the surface of the roads, binds to inorganic particles against slippage and does not noticeably change color during use. If desired, the spherical refractive elements can be treated with materials to further increase their attachment to a cover layer.

TTT. Spherical Reflective Elements In accordance with the present invention, an array of spherical refractive elements adhere to the cover layer of the retroreflective base laminate. As used herein, "array" means a plurality of spherical refractory elements, whether or not elements are arranged in an orderly or random pattern. The desired properties of the spherical refractory elements include a high degree of clarity or transparency, a scratch-resistant, shiny surface. The clarity of the elements is important so that the incident light is transmitted to the element with minimal loss so that most of the light will be retroreflected back to the source. The surface of the element is preferably scratch resistant so that it will still remain bright, and the light will not scatter through the cracks. The elements are preferably of sufficient hardness to withstand the effects of flattening of traffic and should not appreciably soften at temperatures below 75 ° C (170 ° F). In addition, the elements should not be fractured by the impact of traffic at temperatures from -40 ° C to 75 ° C (-40 ° F to -170 ° F). Preferably, the elements will adhere well to retroreflective base laminate and preferably will be oil resistant, dust resistant and moisture resistant. Other desirable or preferred properties of the elements include low color and low cost. The refractory serum elements applied to the retroreflective base laminate according to the invention may be any of glass, ceramic, thermosetting polymer or thermoplastic polymers. The selection will be based in part on the desired properties of the resulting article, for example abrasion resistance, wear resistance, etc. Illustrative examples of. thermoset or thermoplastic polymers for use as spherical refractive elements include polycarbonates, acrylics, polyurethanes, polyvinyl chloride and polyolefin copolymers such as polyethylene acid copolymer consisting of ethylene-methacrylic acid (EMAA), ethylenacrylic acid (EAA), EMAA or ionically crosslinked EAA. A material is an aliphatic polyurethane because of its high impact resistance, low temperature flexibility, color, clarity, abrasion resistance and bond strength to a preferred base laminate coating layer. The spherical refractive elements preferably have a refractive index greater than 1.35 and less than 1.75, more preferably between 1.4 and 1.7. Unlike EP patent number 385746 Bl (Kobayashi et al.), Higher refractive indices are not necessary to carry out this invention because the retroreflective base laminate has good angularity; that is, the retroreflectivity of the base laminates is still substantial at relatively high entry angles of about 80 ° or greater. In general, large glass microspheres (for example, those approaching 2 millimeters in diameter) with higher refractive indices (greater than about 2) are difficult and expensive to manufacture. Typically, a portion of each refractive element will be exposed above the cover layer with the remaining portion embedded in the cover layer. For example, typically from about 10 to 70 percent of the diameter of the element is embedded. Preferably, about 30 to 70 percent of the diameter of each spherical refractive element will be exposed. More preferably, about 40 to 60 percent of each diameter of the spherical refractory element will be embedded. Preferably, the spherical refractory elements are embedded such that a major portion of the incident light in the article between about 70 ° and 90 ° is refracted so as to enter the retroreflective base sheet. According to the invention, the retroreflective brilliance of an article of the invention at entrance angles greater than 89 °, and typically greater than 85 °, is greater than the retroreflective brightness of the base sheet alone. Typically, it is preferred that the spherical refractive elements be in the range of from about 0.5 to about 4.0 millimeters, and more preferably to about 1 and about 2 millimeters in diameter. The elements described in U.S. Patent Nos. 4,145,112 (Crone) and 4,236,788 (Wyckoff) require that the second face of the element be oriented in conjunction with the first face such that the quality of light reflected between the base laminate. In contrast, the spherical refractory elements of the invention are based on refraction, typically on a single face (i.e., the front). This eliminates the need to configure the first and second faces to obtain retroreflection outside the second face, and also eliminates the need for the second face to be of a reflective quality, for example, polished. The quality required for reflection is typically more restricted than that required for refraction. In addition, articles described in these references are known to have base sheets used that are capable of retroreflecting light at a high angle of incidence so that they are preferred for use in the present invention. The separation between the spherical refraction elements can be uniform, or the elements can be placed randomly. A less than optimal separation of the elements can be used in those applications where optimum brightness is not required. This random placement feature allows a simplified and less expensive manufacturing. However, in the present invention, uniform placement in a specific pattern can be advantageous because the elements can be placed in specific positions in such a relationship to each other that each element does not overshadow the other elements. In this way, most of the incident light will be captured by the elements so as to optimize the retroreflective brilliance in pavement marking geometry. For example, the spherical refractory elements can be placed spaced such that the shadows of adjacent elements are minimized at anticipated entry angles and to allow greater surface contact of the vehicle tires with the spaces between the light spherical refractory elements which can contain protruding slipper particles. Preferably, the surface area occupied by the spherical reflec- tion elements is less than 50 percent of the base sheet in order to allow a maximum adaptation of the article of the invention, for example, on the way, a protection or crossing warning of rail, or other structure. More preferably, the surface area covered by the spherical refractory elements is less than 25 percent. The entire article of the invention, which includes the spherical refractory elements, can be protected, for example by a protective coating. Such a coating has the advantages of providing abrasion and / or dust resistance. Illustrative examples of protective coating compositions include, but are not limited to, Ceramer coatings or cross-linked, water-based polyurethane coatings. As used herein, "Ceramer" refers to a noise comprising colloidal silica particles that modify the surface, dispersed in an organic liquid polymerizable by free radicals. The advantages of the coating include the ability to withstand outdoor conditions with excellent resistance to moisture, light and heat; abrasion resistance; resistance to chemical attack and change of coloration by automobile motor oil and carbon black (for example carbon black from tires); desirable optical properties such as transparency; good adhesion to spherical refractory elements; and good flexibility. In a first step, a Ceramer precursor coating composition is applied to the surface of the retroreflective article, preferably including the top surface of the spherical refractory elements and portions of the base sheet not covered by the spherical refractory elements. The coating composition comprises about 20 weight percent (weight%) to about 80 weight% of ethylenically unsaturated monomers; about 10% by weight to about 50% by weight of colloidal silica functionalized with acrylate; and about 5% by weight to about 40% by weight of N, N-disubstituted acrylamide monomer or substituted N-vinylamide N monomer; wherein the percentages are per hundred by weight of the total weight of coating. Subsequently, the composition is cured to form a retroreflective article having a Ceramer coating that transmits light, resistant to abrasion. The Ceramer composition can be applied by any of several methods known in the art, including spraying, rolling, dip coating or blade type coating. The pending U.S. patent application of the assignee, serial number 08/444076 (filed May 19, 1995, and incorporated herein by reference in its entirety) discloses the use of a Ceramer in pavement markings and retroreflective coatings. An illustrative example of a cross-linked water-based polyurethane protective coating suitable for use in the invention comprises the NEOREZ R-960 polyurethane resin crosslinked with the CX100 brand crosslinking agent (both available from ICI Resins, Wilmington, Massachusetts). As will be understood by those familiar with the art, other water-based systems and cross-linking agents can be used for the formulation of a protective coating.

IV. Manufacturing Methods A method of the invention comprises: (1) providing a retroreflective base sheet comprising an array of reflective elements and a cover layer and (2) adhering an array of spherical refractory elements onto the cover layer, the spherical refractory elements being placed in relation to the base sheet so that the light incident to the arrangement with a high input angle is refracted so that it is transmitted to the base sheet, retroreflected by the base sheet and subsequently refracted by the spherical refractive elements so that it is retroreflected by the article. In a typical manufacturing process for making pavement markings, a base sheet (for example, the SCOTHCLITE 3M reflective license plate, number 3750) is applied to an aluminum forming plate. Subsequently, spherical refraction elements can be adhered to cover the layer of the base sheet by embedding them in the cover layer or to an additional layer thereon. Typically, the more deeply the spherical refractory elements are embedded, the more resistant they are to detachment. In addition, if embedded at least 50 or more in diameter, they tend to be less subject to dust and debris collection (which would otherwise reduce the retroreflective performance of the article) than if they were embedded in a more superficial manner. In the manufacturing process, it is typical to add particles that prevent slippage, if used, at the same time that the spherical refractory elements are bonded to this sheet. In addition, dyes, for example dyes and / or pigments, can be introduced at an appropriate time during the manufacturing process, based on whether a dye is to be added to the article.

The components of the article of the invention that lie below the retroreflective base sheet are preferably selected to suit the desired application. For example, a diffusing gauze adhesive (i.e., a polymeric diffusing gauze that has been saturated with an adhesive) imparts additional strength as well as selected adhesive characteristics to the retroreflective article. Suitable conformation layers, adhesive layers, reinforcement layers, etc., can be easily selected by those familiar with the art.

V. Colorants Numerous methods can be used to add colorants to selected portions of the entire retroreflective article. In pavement marking applications, illustrative examples of desirable dyes include, among others, white, yellow, red and blue. The dyes can be light transmitters or opaque, as desired. Typically, if the colorant is placed within the optical path, preferably it should be a light transmitter in a manner that does not undesirably reduce retroreflective performance. However, it will be appreciated that in some cases it may be desirable to use a disperse opaque dye in a position that reduces the retroreflective brilliance and at the same time provides other desired defects, for example a brighter overall color or appearance. The dyes that transmit light can improve both the daytime and nighttime color of the article of the invention. In applications to mark pavement, as well as in others, it is important that drivers distinguish well color markers, for example between yellow and white markers. One way to obtain colors that are observed in the dark involves placing a material with color transmitter of light in the optical path. In one approach, the color is obtained using a colored base laminate. For example, in Figure 4, the light transmitting matrix 65 can be manufactured with the desired color, for example yellow. In a cube corner base laminate with encapsulated lenses, the cube corners themselves can be colored. Another approach is to use a layer with colored cover. For example, an article of the invention can be manufactured with a cover layer of yellow, red or blue color, transmitting light. In addition, spherical refractory elements with color can be used. When a cover layer with light-transmitting color is used together with color spherical refractory elements, light transmitters, a retroreflective article of very strong colors is obtained. Alternatively, a plate with light transmitting color may be applied on top of the base laminate. A colorless cover layer can be applied over the top of the base sheet with color. This approach has the advantage of protecting the layer with color and thus improving its durability. In addition, multiple color layers in a pattern can be applied to form desired symbols or legends. Opaque dyes are typically used primarily to improve the daytime color of the article of the invention and preferably leave the exterior of the optical path so that they do not reduce the retroreflectivity performance. Therefore, a base laminate which is initially gray in color, due to the aluminum reflective layer, can change to the desired color by the addition of an opaque dye. For example, one way to produce an article with color would be to apply white opaque segments on top of the article of the invention or to use opaque spherical refraction elements. Although these particular segments and opaque elements do not retroreflect incident light, they increase the true color of the laminate when used in small quantities. Alternatively, between the spherical refractory elements, the granules or the white pigmented resin can be applied to the cover layer and can be heated so as to cause it to melt and adhere to it. In addition, desired color segments can be applied to some portions of the spherical refraction elements as well as to the base laminate, although with some reduction in retroreflective response. For example, a method for producing a retroreflective article with color comprises the following steps: (1) providing a retroreflective base laminate comprising an array of retroreflective elements and a cover layer, (2) laminating a conformal layer to the part bottom of the base sheet, (3) adhere an array of spherical refractory elements to the cover layer of the base canvas, (4) degrease the spherical refractory elements to provide a relatively flat top surface, (5) apply a layer of color on top surface; and (6) etching the base sheet so that the spherical refractory elements protrude from the base sheet. As used herein, "de-engraving" refers to the reverse of engraving, that is, making a textured surface that is relatively flat. The spherical refractory elements that originally protrude from the upper surface of the base sheet are pushed down so that they are relatively level with the base sheet. One way of degreasing involves supplying the base sheet with its bonded conformation layer and the spherical refractory elements through a set of rollers. For example, the spherical refractory elements can make contact with a steel roll while the forming layer would contact a rubber roll that can be formed under the rolling pressure. Pressure is applied to push the spherical refractive elements down into the shaping layer. After gravure, it is not necessary that the upper surface of the laminate be perfectly smooth. Some surface topography is allowed. Preferably, the resulting surface of the base laminate is almost in the same plane as the spherical refractory elements as possible. After gravure, a layer of color is applied to the portions of the base sheet, portions of the spherical refractory elements and to the anti-slip particles, if any, by any convenient technique. An opaque color layer can also be transferred onto the selected portions of the base sheet before adding spherical reflection elements the. For example, a method for rendering a color oreflective article comprises the following steps: (1) providing a oreflective base comprising an array of reflective elements and a thermoplastic cover layer, (2) providing a discontinuous thermosetting polymer on the layer of cover in a regular pattern to provide a partially printed base sheet, (3) heat the partially printed base sheet to soften the cover layer (4) deposit spherical refraction elements on the partially printed base sheet while the cover layer The cover is softened so that the spherical refractive elements can selectively adhere the, and (5) cool. The portions of the thermoset polymer may contain a colorant, as desired. For example, in one embodiment, the entire area of the base laminate may be printed with a thermoset color layer except for the regions below the spherical refractive elements, when attached to the cover sheet. In another embodiment, a light transmissive thermoset polymer may be printed to encompass the spherical refractory elements at a defined radius. The rest of the laminate can be printed with another thermoset polymer, for example white. The regions immediately below the spherical refractive elements may be unprinted. Because it is possible for a beam of light to enter the base laminate outside of the spherical refractive elements, the region of the transmitter polymer encompassing the spherical refractive elements may still allow the beam of light to enter the laminate. base and be oreflected by the base laminate. This same method has the advantage of placing the spherical refractive elements in an orderly manner and therefore increasing the optical efficiency of the article and at the same time minimizing the amount of spherical refraction elements used for cost effectiveness. The composition of the color layer, if it exists, would be resistance to solvents, wear by traffic and ultraviolet light. An example of a dye solution comprises 78 percent by weight (% by weight) of water-based uane resin NEOREZ "* R960 (from Zeneca Resins, Wilmington, Massachusetts), 19% by weight of titanium dioxide dispersion brand WW3000 (from Heucotech Ltd., Fairless Hills, Pennsylvania) and 3% by weight of CX100 crosslinker (from Zeneca Resins, Wilmington, Mass.) It will be apparent to those familiar with the art that other color layer compositions can be used.

It will be evident to those familiar with the technique to use a combination of light-transmitting and opaque dyes. For example, spherical colored light-transmitting refractory elements that are in the optical path can be used with an opaque color-coats coating out of the optical path. In this way, an item can have effective colors for day and night. Therefore, any of the above compositions of light transmitting and opaque color systems can be used.

VT Particles that prevent slippage Anti-slip particles are a common component of many pavement marking articles to increase slip resistance of the pavement marking and have been widely used in the art. They can be placed anywhere on the surface of the article when they are in contact with the tires of the vehicles. Typically, the anti-slip particles can be randomly dispersed on a cover film or the base sheet while in a softened state. It has been found that the anti-slip particles can be placed preferentially close to the zenith of the spherical refractive elements. For example, a web of base laminate with spherical refraction elements thereon can be coated by contact with a binder composition. Contact coating refers to a coating method in which the composition is desirably coated only in the upper portions of the spherical refractive elements; that is, the solution is allowed to "touch" the upper parts of the spherical refractive elements only. This process is carried out when controlling the. spaces between the coating rolls and maintaining the network so that only the upper portions of the spherical refractive elements are allowed to make contact with the coating composition. To the extent that the composition remains wet, copious amounts of anti-slip particles are dispersed over the network. Because the rest of the base laminate is dry, the particles only adhere to the wet areas. The excess particles against slippage are eliminated by vibration of the network. Subsequently, the network is sent to a series of ovens for drying, curing or solidifying the wet binder composition. As a result, the anti-slip particles are selectively fixed in the upper regions of the spherical refractive elements so they provide resistance against slippage. vile. Applications The retroreflective articles of the present invention can be used advantageously in different applications, particularly in wet conditions and when light strikes at high entry angles. In particular, the articles are suitable for use in pavement markings or horizontal signs. Due to their high retroreflectivity at both high and low entry angles, the articles are also suitable for vertical applications, such as the use of Jersey barricades or protection bars; for applications on curved surfaces such as traffic barrels, tubes and cones; for vehicle surfaces; and for other applications where an exceptional effective input angularity of the article will be advantageous. For example, because many embodiments of the laminate of the invention can provide effective retroreflection over all entry angles from 0 ° to almost 90 °. As a result, when the laminate is wrapped around an object such as a telephone pole or barrel, the entire surface of the laminate that is within the line of sight can provide effective retroreflection including portions on the surface of the article that they are curved away from the observer. This increases the retroreflective effective area, provides more visible marking and therefore improves safety. In addition, a unique mark such as a strip on a protection bar, a Jersey barrier or a wall that is parallel to a first path and perpendicular to a second path that intercepts the first path on the opposite side of the first path from the second path it can provide an effective retro-reflective visible response for vehicle drivers in both the first and second way. Another advantage of the present invention is due to the fact that the retroreflective article is visible from many orientations. This omnidirectional feature renders the invention particularly suitable for applications of horizontal sign placement, intercept markings, etc., where vehicles can be approached from various angles. The ease of color change of these laminates also makes horizontal signs particularly useful. Transparent color layers can be applied over the laminate in a graphic pattern so that the retroreflected light has almost the same color and pattern as that observed during the day. This is especially useful if the ink is applied underneath the cover layer so that it is protected from abrasion of both, the elements and the solid transparent cover that overlaps continuously. This feature is particularly important as the commonly used inks are thin, and therefore can be quickly worn by road traffic when exposed. The material of the invention can be wound on itself in a roll. The projections fabricated from the spherical refractive elements are not substantial enough to interfere with winding.

VIII. Examples The invention will be further explained by the following illustrative examples which are considered as non-limiting.

Retrorrctivity in Humid The wet retrorctivity of the rctive laminates is measured using an LTL 2000 (available from Delta Light & Optics, Lyngly, Denmark) which measures the retrorctive brightness at 88.76 ° angle of entry and 1.05 ° angle of observation. Such a configuration is similar to what would be experienced by an average car driver 30 meters away from the rctive mark on the pavement. The laminate is first placed horizontally in the test area and then moistened with a solution of tap water and 0.1 percent by weight of AJAX brand dishwashing soap. The solution is allowed to run and brightness measurements are made in the next approximately 10 seconds. Soap is added to the water to increase the wetness of the surface of the laminate. The soap also simulates the effect of rain after the rctive markings on the pavement are on the floor for a certain time, when they have been subjected to wetting capacity and increased due to the action of the sun, abrasive cries and sand and accumulations of dust.

Example l A thermoplastic polyethylene-methacrylic acid copolymer resin (NUCREL brand 699, available from DuPont) is extruded onto a polyethylene terephthalate (PET) carrier to provide an EMAA cover film of 0.25 millimeters (0.0098 inches) in thickness.

A high angularity base laminate is prepared in the following manner (3M SCOTCHLITE rctive license plate laminate number 3750"laminate 3750"). It is prepared with a water-based polyethylene acrylic acid solution (ADCOTE brand 50T4983, available from Morton Chemical Co., Seabrook, New Hampshire) under common etch coating techniques using a 150-row square-gravure pattern. The solution is applied on the front surface, ie, on the rcting side of laminate 3750, and dried in a forced air convection oven for one minute at 93 ° C (200 ° F) to provide the primed 3750 laminate. The cover film EMAA is hot-rolled to laminate 3750 primed by a nip generated by a hot can and a rubber roll under the following conditions. The PET carrier of the cover film EMAA is allowed to make contact with the hot can heated to 150 ° C (300 ° F); the EMAA film is exposed to the atmosphere. The primed laminate, with the exposed rctive side, is allowed to contact the rubber roller. Two films that make contact with each other in the narrowing, so the EMAA film is laminated onto the 3750 laminate primed to provide a composite laminate. Both the hot can and the rubber roll rotate at a surface velocity of 6.1 meters / minute (20 retrorctive feet / minute). In the composite laminate, the PET carrier is separated from the EMAA film. The coating of the 3750 laminate is also removed by exposing the "PSA" pressure sensitive adhesive that comes with 3750. A 0.075 millimeter (0.003 inch) thin aluminum sheet is laminated onto the PSA (thin sheet rolled in only number 1145-0 of AJ Oster Foils, Inc.). Glass microspheres are dispersed with an average diameter of approximately 1.5 millimeters and a refractive index of 1.5 (glass spheres A135, available from Potters Bros.), on the laminated laminate composite sheet. The entire article is heated in an oven at 205 ° C (400 ° F) for two minutes. No fusion of the glass microspheres is observed. The microspheres are embedded in themselves in the EMAA cover layer by means of the gravitational effect. In addition, the EMAA resin adheres by capillarity around the microspheres due to capillary action. Approximately 83,000 spheres per square meter of laminate are used. The retrorctive wet brilliance is measured in milicandelas / lux / meter2 as described above under "wet retrorctivity". For this example, the retrorctivity between 700 and 800 milicandelas / lux / meter2 is determined. When dry, the sample has a retrorctive brilliance of 840 to 960 milicandelas / lux / meter2.

Glossary The following definitions are used in the present when the geometry of retroreflection is discussed: The term "reference axis" is the normal line to the retroreflective article at the point where light falls on it. The term "axis of incidence" is the axis defined by the trajectory of the incident light on the light source, for example, the headlight of a motor vehicle, at the point of incidence in the article. The term "entry angle" (sometimes referred to as "incidence angle" or "incidence angle" also indicated as ß) is the angle between the reference axis and the incidence axis. The term "observation axis" is the axis defined by the path of the retroreflected light from the point of incidence of the article to the observation point, for example, the eyes of the driver of the motor vehicle.

The term "observation angle" (sometimes referred to as a) is the angle between the input axes and the observation axis. The term "entry plane" is the plane defined by the reference axis and the axis of incidence. The term "observation plane" is the plane defined by the observation axis and the axis of incidence. Various modifications and alterations of this invention will become apparent to those familiar with the art without departing from the scope and spirit of this invention. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following:

Claims (35)

1. A retroreflective article, characterized in that it comprises: (a) a retroreflective base sheet comprising an array of retroreflective elements having a cover layer; and (b) an array of refractory elements or serum refractors adhered to the front surface of the base sheet so that part of the incident light in the array of spherical refractive elements is refracted so that it is transmitted within the base sheet retroreflected by the base sheet and further refracted by the spherical refractive elements so that it is retroreflected by the article, the spherical refractive elements have a refractive index greater than 1.35 and less than 1.75.

2. The article according to claim 1, characterized in that the base sheet comprises at least one of the group consisting of retroreflective laminate of embedded lens or retroreflective laminate of encapsulated lens.

3. The article according to claim 1, characterized in that the cover layer comprises thermoplastic polymers.

4. The article according to claim 1, characterized in that the retroreflective brilliance of the article in the entry angle greater than 85 ° C is greater than the retroreflective brilliance of the article without the arrangement of the spherical refraction elements.

5. The article according to claim 1, characterized in that it additionally comprises particles against slippage.

6. The article according to claim 1, characterized in that at least part of the spherical refractive elements comprise material that is selected from the group consisting of glass, ceramic and polymeric material.

7. The article according to claim 1, characterized in that at least part of the spherical refractive elements comprise polymeric material which is selected from the group consisting of fluoropolymer, polycarbonate, acrylic, polyester, polyurethane, polyvinyl chloride, polyolefin copolymers and mixtures thereof.

8. The article according to claim 1, characterized in that at least part of the spherical refraction elements comprise thermoplastic material.

9. The article according to claim 1, characterized in that at least part of the spherical refraction elements comprise thermoset material.

10. The article according to claim 1, characterized in that the spherical refraction elements have an average diameter between approximately 0.5 and 4 millimeters.

11. The article according to claim 1, characterized in that the spherical refraction elements have an average diameter between approximately 1 and 2 millimeters.

12. The article according to claim 1, characterized in that the spherical refractive elements have a refractive index of between about 1.4 and 1.7.

13. The article according to claim 1, characterized in that a portion of the spherical refraction elements are embedded or embedded in the cover layer.

14. The article according to claim 13, characterized in that the portion is between about 30 and 70 percent of the diameter of the spherical refractive elements.

15. The article according to claim 13, characterized in that the portion is between about 40 and 60 percent of the diameter of the spherical refractive elements.

16. The article according to claim 1, characterized in that the spherical refractive elements are in contact with less than 50 percent of the surface area of the retroreflective base sheet.

17. The article according to claim 1, characterized in that the spherical refraction elements are in contact with less than 25 percent of the surface area of the retroreflective base sheet.

18. The article according to claim 1, characterized in that the spherical refraction elements are arranged randomly on the front surface of the base sheet.

19. The article according to claim 1, characterized in that the spherical refraction elements are uniformly arranged on the front surface of the base sheet.

20. The article according to claim 1, characterized in that the spherical refraction elements are placed in a regular pattern on the front surface of the base sheet.

21. The article according to claim 1, characterized in that the base sheet comprises a retroreflective laminate of encrusted lens comprising a monolayer of transparent microspheres, a transparent matrix in which the front surfaces of the microspheres are embedded, a reflective medium associated behind of the microspheres and a cover layer placed at the front of the transparent matrix, the spherical refractive elements are attached to the cover layer.

22. The article according to claim 21, characterized in that it additionally comprises a colorant in at least one group consisting of the spherical refractive elements, the cover layer and the transparent matrix.

23. The article according to claim 1, characterized in that the base sheet comprises a monolayer of retroreflective elements in the form of a cube corner.

24. The article according to claim 1, characterized in that it additionally comprises a layer containing discontinuous dye covering the upper portions of at least part of the spherical refractive elements and portions of the cover layer between the spherical refractive elements .

25. The article according to claim 1, characterized in that it is applied to a surface on which the motor vehicles travel.

26. The article according to claim 1, applied to a vertically placed surface that is selected from the group consisting of protection bars, Jersey barriers, building wall, fence, installation pole, traffic cone and vehicle side.

27. The article according to claim 25, characterized in that at least a portion of the surface is curved.

28. A method for producing a retroreflective article, characterized in that it comprises: (a) providing a retroreflective base comprising an array of retroreflective elements and a cover layer; (b) Adhere an array of spherical refractive elements that have a refractive index greater than 1.35 and less than 1.75 on the front surface of the cover layer so that part of the light incident on the arrangement of the refractive elements Spherical is refracted so that it is transmitted to the base sheet, retroreflected by the base sheet and further refracted by the spherical refractive elements so that it is retroreflected by the article.

29. The article according to claim 28, characterized in that it additionally comprises at least one group consisting of incorporating at least one dye in the spherical refractive elements, incorporating at least one dye in the cover layer, or incorporating at least one colorant in a lid formed on the cover layer.

30. A method for producing a retroreflective article with color, characterized in that it comprises: (a) providing a retroreflective base sheet having a main surface comprising an array of retroreflective elements and a cover layer; (b) applying a conformation layer to the main surface of the base sheet; (c) adhering an array of spherical refractive elements that have a refractive index greater than 1.35 and less than 1.75 in the cover layer; (d) deburring the spherical refraction elements to provide a relatively flat top surface; subsequently (e) apply a layer of color on the upper surface; and (f) etching the base sheet so that the spherical refraction elements protrude from the base sheet.

31. The method according to claim 30, characterized in that the dye comprises polymers resistant to solvents, wear by traffic and ultraviolet light.

32. The method according to claim 30, characterized in that the colored layer comprises an opaque dye.

33. A method for producing a retroreflective article with heat, characterized in that it comprises: (a) providing a retroreflective base sheet comprising an array of reflective elements and a thermoplastic cover layer; (b) applying a layer of thermoset polymer to some portion of the cover layer; (c) heating the cover layer so as to soften it; (d) placing spherical refractive elements having a refractive index greater than 1.35 and less than 1.75 to selectively adhere the softened cover layer; and (e) cooling the cover layer so that it hardens.

34. The method according to claim 33, characterized in that the thermosetting polymer layer is light transmitting.

35. The method according to claim 33, characterized in that the thermosetting polymer comprises colorants that are selected from the group consisting of dyes that transmit light and dyes-opaque. A retroreflective article (80) is provided which provides effective retroreflective brilliance with very high entry angles as well as low entry angles and under wet conditions. The article comprises spherical refractive elements (60) having a refractive index greater than 1.35 and less than 1.75, which adhere to cover a film (66) of a retroreflective base sheet with embedded lenses.