MXPA01006937A - Cube corner cavity based retroreflectors and methods for making same - Google Patents

Abstract

Retroreflective sheeting includes a body layer (12) having a structured surface with recessed faces (22) and top surfaces (20), the recessed faces forming cube corner cavities. The recessed faces have a high specular reflectivity, while the top surfaces have a low specular reflectivity. In some embodiments, a substantially continuous film of reflective material covers the structured surface, and a masking substance is provided over the reflective material at the top surfaces. Alternatively, the top surfaces are given a non-smooth surface finish so that the film of reflective material on those portions has a diffuse reflectivity. In other embodiments the film of reflective material is discontinuous, disposed selectively on the recessed faces and not on the top surfaces. A cover layer (16) is also provided, and can bond at least to the top surfaces. Keeping the top surfaces substantially free of reflective material inhibits corrosion and can enhance the bond integrity. The top surfaces are preferably flat, and diffusely reflective to enhance the daytime whiteness of the sheeting.

Description

RETRORREFLECTORS BASED ON TRIEDRIC CAVITIES AND METHODS TO MAKE THEMSELVES FIELD OF THE INVENTION The present refers, in general, to retroreflective articles such as laminates. More particularly, the invention relates to those articles or laminates in which the retroreflective elements comprise reflecting faces arranged to form a cavity.

BACKGROUND OF THE INVENTION The user is asked to consult the glossary at the end of the specification, as a guide for the meaning of certain terms used herein. Tricyclic retroreflective laminates can generally be categorized as those that use a back surface body layer and those that use a front surface body layer. Commercially available tri -hedral retroreflective laminates are of the above type, in which a thin transparent body layer has a front surface REF .: 131455 substantially planar and a rear structured surface containing a plurality of geometric structures of pyramidal shape, some or all of which include three reflecting faces configured as a trihedral element. Light impinges on the flat front surface, passes through the thickness of the body layer, and is retroreflected by the trihedral elements, backward and across the front surface. In some cases, a reflective coating such as aluminum is applied to the rear structured surface, followed by a layer of adhesive that covers and molds to some degree to the shape of the structured surface. However, in general, a reflector coating is not required as long as a clean air interface can be maintained on the structured surface, in which case reflection occurs through total internal reflection. Some known tricyclic retroreflective laminate structures use a front surface body layer, wherein the body layer has a front structured surface. See, for example, U.S. Patent Nos. 3,712,706 (Stamm), 4,127,693 (Lemelson), and 4,656,072 (Coburn, Jr. et al.), And PCT publication WO 89/06811 (Johnson et al.). The front structured surface comprises a plurality of reflecting faces arranged to form trihedral chambers. For this reason, said retroreflective laminate is referred to herein as a retroreflective laminate based on trihedral cavities. A thin metallic film is commonly applied to the structured surface to improve the reflectivity of the faces. The incident light does not penetrate through the body layer but on the contrary is reflected by the faces that form the trihedral cavities. In some embodiments a cover layer that does not transmit the incident light is provided on top of the structured surface, to protect the cavities from dirt or other degradation, where portions of the cover layer extend within the trihedral cavities, -from the structured surface, and fill them. In other embodiments, a cover layer is sealed or adhered to the structured surface by a color-sensitive pressure or heat-sensitive adhesive that cancels, removes or obliterates the retroreflectivity of the structured surface. Some geometries of structured surfaces define both trihedral pyramids and trihedral cavities. An example is a structured surface having a plurality of contiguous square faces, each of which is mutually oriented perpendicular to its adjacent faces, and each group of three adjacent faces has a hexagonal outline seen in a top plan view. Trihedral trino-retroreflective laminate is commonly produced by first making a master mold having a structured surface, that structured surface corresponds either to the geometry of the trihedral element, desired, in the finished laminate or in a negative (inverted) copy thereof, depending on whether the finished laminate is going to have three-dimensional pyramids or trihedral (or both) cavities. The mold is then duplicated using any suitable technique such as nickel electroconformation, conventional, chemical vapor deposition, or physical vapor deposition, to produce tools for forming trihedral retroreflective laminates, by processes such as stamping, extrusion or casting and curing. U.S. Patent No. 5,156,863 (Pricone et al) provides a general illustrative review of a process for forming tools used in the manufacture of a trihedral retroreflective laminate. Known methods for manufacturing the master mold include bolt pressing techniques, rolling techniques and direct machining techniques. Each of these techniques has its own benefits and limitations. Several advantages can be understood when manufacturing retroreflective laminates based on trihedral cavities. An advantage is the ability to use a much wider variety of material compositions for the body layer than would otherwise be possible. This is because the body layer does not need to be optically clear, in fact it can even be opaque, unlike the structure of the body layer of the back surface. Another advantage is the ability to form certain types of structured surfaces, in the body layer, more quickly than the time it takes to form a negative copy of those structured surfaces in back surface body layer structures. This is because the molds used to form the structured surface of a front surface body layer may have grooves that are essentially not joined in the direction of the groove. In contrast, the molds used to form the structured surface of a back surface body layer typically have an array of closed (trihedral) cavities joined by a plurality of inverted slots, i.e. rims. Unbonded slots, of the preceding molds, are easier to fill with the material of the body layer, than the arrangement of closed cavities provided on the last molds. The retroreflective laminate based on trihedral cavities, however, has certain disadvantages. One of these is the grayish appearance, known as gray casting of the laminate, when an aluminum vapor coating is used as the reflecting film on the faces of the cavities. Gray cast iron is not advantageous in signaling applications, due to its effect on the perceived color of the signal, most notably the reduction in apparent retroreflectivity during daylight. This problem can be alleviated a bit by replacing materials with higher reflectivity, such as silver, instead of aluminum. A second disadvantage is corrosion or other type of degradation of the reflective film. Unfortunately, silver is more susceptible to degradation than aluminum. Although a cover layer can provide a certain amount of protection, the harmful agents present on the exposed edges of the laminate can migrate along the reflective film, steadily advancing towards the laminate, starting from the edges. The discontinuous coatings with steam, applied to the structured surface of the trihedral laminate, are known (See, for example, U.S. Patents No. 5,734,501 (Smith) and 5,657,162 (Nilsen et al)). However, those discontinuous coatings have been described only in relation to laminates of the layer type with backsheet body, and are used to address issues other than those of interest in the present. Retroreflective laminates that incorporate the advantages of laminations based on trihedral grids, while eliminating or reducing the disadvantages referred to above, they would have a wide applicability.

BRIEF SUMMARY OF THE INVENTION According to one aspect of the invention, a trihedral retroreflective laminate is provided, with a body layer having a structured surface comprising recessed faces and upper surfaces, the recessed faces forming trihedral cavities. The recessed faces have a high specular reflectivity to allow efficient retroreflection of incident light. However, the upper surfaces have a low or reduced specular reflectivity, to provide the desired optical or mechanical properties. A film of reflective material is placed at least on the recessed faces, to provide high specular reflectivity. The film can be continuous on the structured surface, covering both the recessed faces and the top surfaces, or it can be discontinuous, covering only the recessed faces and being substantially absent from the top surfaces. In several described embodiments, the film is selectively exposed on the recessed faces. The upper surfaces of the structured surface preferably comprise flat areas that are diffusely reflecting, contributing to the apparent retroreflectivity of the laminate, and circumscribing a whole number of trihedral spaces. The diffuse reflectivity of the upper surfaces can be provided by the material of the body layer itself, by a separate layer, such as paint, or by a non-smooth surface finish. A cover layer may also be provided to protect the trihedral cavities from contamination and to provide improved weather resistance. Also disclosed are methods for manufacturing a trihedral article in which a body layer having a structured surface as described above is provided, and a reflective film is formed on at least the recessed faces. The structured surface is treated to impart a low specular reflectivity, selectively, to the upper surfaces. In some embodiments, the reflective film is applied substantially continuously to the structured surface. In that case the treatment step may include: removing the upper portions of the structured surface, together with any reflective film that is on it, to form upper surfaces, or modified upper surfaces, that are free of any reflective material; applying a masking material such as a paint, selectively, to the top surfaces; or roughening, selectively, the upper surfaces, to provide a smooth surface finish, either by abrasion of the body layer itself or by abrasion of a mold that is used directly or indirectly in the production of the body layer . In other embodiments, the reflective film is applied discontinuously to the structured surface. In that case the treatment step may include applying an adhesion resistant material, selectively, to the upper surfaces, before the reflective film is applied. The adhesion resistant material, such as an oil, prevents the subsequently applied reflective material from adhering to the treated areas.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a retroreflector, wherein a top cover layer thereof, is shown only partially, laminated to the body layer, to reveal the three-dimensional cavities, formed in the body layer; Figure 2 is a sectional view of a portion of the body layer of Figure 1, taken along line 2-2; Figures 3A-3H are a series of drawings showing the sequence of how a retroreflector can be manufactured such as that shown in Figure 1, wherein Figures 3A-3C depict a sequence showing the formation of a mold capable of producing a body layer having flat top surfaces, Figures 3D-3G represent a sequence showing that body layer and various coatings applied thereto, and Figure 3H shows the finished body layer, in combination with a layer of protective cover; Figures 4A-4C are a series of drawings showing a sequence which, if substituted for the Figures 3E-3H, produces an alternative modality of the one shown in Figure 3H; Figure 5 represents an alternative form for producing a body layer based on trihedral cavities, with flat upper surfaces, and a discontinuous reflective film, using a grinding wheel; Figures 6A, 6B are sectional views showing how a continuous reflective layer can be used, in combination with a non-smooth surface finish, on top surfaces of the structured surface; Figure 7 is a top plan view of a portion of a structured surface for a body layer that can be used with the invention; and Figure 8 is a schematic view of a portion of an array used to measure the specular reflectivity of the top surfaces of samples based on trihedral chambers. In the drawings, the same reference symbol is used, for convenience, to indicate elements that are the same or that perform the same function or a similar function.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE MODALITIES In Figure 1 a portion of a retroreflective laminate 10 is shown enlarged. The laminate 10 comprises a body layer 12 having a structured surface 14 and a transparent cover layer. The structured surface 14 includes a plurality of recessed faces 18 and upper surfaces 20. The recessed faces 18, shown shaded in Figure 1 by visual effect, form a plurality of trihedral cavities 22. The structured surface 14 can be described as consisting essentially of three sets of inverted parallel grooves or ridges, intersecting, each flange having a flat upper surface bounded by opposite, inclined recess faces 18. Three recessed, adjacent faces meet at a vertex of the cavity and approximately mutually perpendicular to each other. The faces can be configured as optically opposed trihedral elements as shown in Figures 1 and 2, where the elements can be grouped in pairs where one element is rotated 180 degrees relative to the other, although other configurations are also possible. The trihedral elements may also have a chamfered configuration, wherein their optical axes or axes of symmetry are inclined relative to a direction perpendicular to the structured surface. Such a chamfer is described for trihedral pyramids, for example in U.S. Patent Nos. 4,588,258 (Hoopman), 5,822,121 (Smith et al.), And 5,812,315 (Smith et al.). Tricyclic elements can also be used in which the non-dihedral edges of each trihedral element are not all coplanar (sometimes referred to as complete triad elements or truncated triad elements). A structured surface containing these complete or non-truncated trihedral elements would not only consist of sets of parallel flanges intersecting. A film 24 of retroreflective material is provided on the recessed faces to impart a high specular reflectivity to these faces, such that the trihedral bends efficiently retroreflect the incident light which impinges on the article from above, ie, through the layer 16. The film 24 may comprise metals such as aluminum, silver, nickel, tin, copper or gold, or may comprise non-metals such as a multilayer dielectric stacking. These films can be applied through known physical or chemical deposition techniques, such as vacuum evaporation, cathodic sputtering, chemical vapor deposition ("CVD") or plasma enhanced CVD, deposition without electric current, and the like, depending on of the type of film desired. A given film can include multiple layers, including layers that promote adhesion to the body layer, barrier layers and topcoat layers. A suitable film for body layers based on polycarbonate, comprises a layer of titanium dioxide with a thickness of approximately 1 nm, formed by the sputtering of titanium on the body layer, followed by a layer of evaporated aluminum with a thickness of 100 nm. The titanium dioxide layer acts as both an adhesion promoter and a barrier layer to counteract the small holes typically present in the aluminum vapor coating. The film 24 shown in Figure 2 is discontinuous because it substantially covers all the recessed faces 18, and substantially does not have top surfaces 20. The top surfaces 20 are preferably substantially flat to provide an excellent base for bonding the body layer 12 to cover layer 16. Flat top surfaces can improve surface contact with cover layer 16, or with a layer of intermediate filler material, and can provide good visibility as compared to a convex or concave shape , although these other forms can be advantageous for other purposes. Flat top surfaces do not need to have a smooth surface finish, as discussed below. The joining of the body layer 12 to the cover layer 16 can comprise the conventional thermal seal, or adhesive layers or other tie layers, applied to the cover layer 16, to the top surfaces 20 or both. In some cases, not using reflective film 24 on the upper surfaces 20 can make the bond between the body layer 12 and the cover layer 16 more reliable, since failure situations involving a bond failure are less likely. between the film 24 and the body layer 12, or between the film 24 and the cover layer 16 or an intermediate layer of filling material. Indeed, even reflective materials having a relatively poor adhesion to the body layer 12 can be used, with little or no negative impact on the integrity of the bond between the body layer 12 and the cover layer 16. Significantly, where the upper surfaces 20 are interconnected and circumscribe one or more trihedral cavities, the discontinuity of the film 24 provides a barrier to corrosion, such that the corrosive agents or other harmful agents acting along the film 24 will be stopped at a short distance, preferably to no more than 1 or 2 trihedral elements, from the edge of the laminate. The body and cover layers, composed of compatible materials, or even of the same material or similar material, can improve adhesion between them. Where the number of circumscribed trihedral cavities is small, preferably not more than 1 or 2, wherein each trihedral chamber has a characteristic opening size of less than 1 mm and more typically of the order of approximately 25 to 250 μm (from 1 to 10 mils), the laminate can be cut to produce any desired shape, such as letters or symbols, while maintaining good optical quality even near the edge, without having to seal the laminate edges. In this context, the opening size of a trihedral cavity refers to its maximum width in the plane of the structured surface. Dirt, water, contamination or corrosion, are unable to penetrate significantly into the laminate, due to the discontinuous nature of the film 24 and the network of closely spaced junctions between the top surfaces and the cover layer. The upper surfaces 20 can be used to improve apparent retroreflectivity during the day (referred to in the art as cap Y) of the article, by virtue of being diffusely reflective. This diffuse reflectivity may be provided by the material of the body layer itself, or by a masking agent selectively applied to the upper separation surfaces, discussed below. The diffuse reflectivity can also be provided by imparting a non-smooth surface finish to the surfaces 20, and optionally coating the rough portions with the reflective film 24, or with other substances. In yet another embodiment, the diffuse reflectivity can be provided by upper, substantially transparent surfaces, 20 and the body layer 12 together with a diffusely reflecting upper surface of the body layer 12. For most of the embodiments it is anticipated that the upper surfaces, as seen from a top plan view of the structured surface, comprise at least about 5% of the area of the structured surface. To achieve maximum effect on apparent retroreflectivity, substantially all of the top surfaces of the structured surface are diffusely reflective. In other cases it may be desirable to impart diffuse reflectivity (or low specular reflectivity) only to certain areas of the upper surfaces, for example, in order to define a particular pattern, symbol, or other signals. Figures 3A-C are side sectional views showing a manner of producing an appropriate mold to form a laminate based on trihedral grooves, with superior, flat separation surfaces. Briefly, sets of parallel grooves are formed in an initial substrate (not shown) by milling with polished, scratched, milled diamond tool, or the like, to create in it a structured surface, of trihedral pyramids. A replica 30 is then made by electroplating with nickel or any other appropriate process, wherein the replica 30 has a structured surface 32 of inverted ridges or ridges, which define recessed faces 34 that form three-dimensional cavities 36. The replica 30 is a negative copy of the initial machined substrate. The upper portions of the structured surface 32 may or may not include top surfaces, depending on the type of tool used to mark the initial substrate. Then a milling operation is carried out, removing by shaving a certain thickness from the upper part of the replica 30 in order to produce flat surfaces 38 which are flat and which each circumscribe a trihedral cavity 36. In one embodiment of the modified replica 30, a perspective view substantially the same as the body layer 12 in Figure 1 can be observed. A further replica 40 is then fabricated, by electroplating with nickel or otherwise, the structured, modified surface , 32a. The replica 40 has a structured surface 42 characterized by sets of parallel flat-bottom grooves (one of those sets is marked with 44) defining separate, three-dimensional pyramids 46. The replica 40 is thus a positive, slightly modified copy of the initial machined substrate. Alternatively, the structured surface 42 can be manufactured by machining flat-bottomed grooves, directly onto an initially flat substrate, with a flat-tipped diamond tool. An advantage of this approach is to avoid at least two stages of replication. Another advantage is the additional flexibility of the design: slots having different flat-bottom widths, can be mixed and matched, to produce a non-uniform pattern of flat surfaces, and variable height and aperture trihedral elements (see Figure 7 below) . Finally, this technique can more easily produce upper surfaces that have a smooth surface finish, if desired. One disadvantage is the increased number of passes of the cutting tool, required, if a width greater than the flat tip of the cutting tool is desired. Regardless of how the structured surface 42 is prepared, this (or a positive replica thereof) is then used as a mold, to produce the laminate as illustrated in the sectional views of Figures 3D-H. In Figure 3D, there is shown a body layer 50 which can be used in a retroreflective laminate, having a structured surface 52 formed by stamping, by casting a thermoplastic or thermosetting, melted material, or by casting and curing a material that cures with radiation, using the structured surface 42. The structured surface 52 is substantially the same as the surface 32a discussed above, and includes recessed faces 54 and flat upper surfaces 56, wherein the recessed faces define trihedral cavities 58. On a printing machine in which a drum or band has a set of slots such as 44, which extend through its structured surface, the material of the body layer can be forced more easily into those grooves than inside the machine. the closed cavities, such as the trihedral cavities 36, shown in Figure 3B. This ease of replication allows for increased speeds in the line, and lower manufacturing costs. The body layer 50 is shown as a unitary layer, but may also comprise two or more different layers to provide improved mechanical flexibility or other desired properties. Since the layer 50 does not need to be optically clear or even transparent, the materials of the body layer are preferably selected for their ability to keep the faces trihedral, accurate, in optical tolerances, for weather resistance, for hardness , ease in manufacturing, low cost, or other characteristics. A preferred material is polycarbonate, but other thermoplastic, thermosetting or radiation curing materials may also be used. Additives can be used to provide the desired properties. For example, colorants may be used to give the exposed portions of the layer 50 a diffuse white or other color appearance. Titanium dioxide is an example of a diffuse white additive. Dyes and fluorescent and / or luminescent pigments can also be used. In one embodiment, the body layer can be light transmissive and fluorescent, with a diffuse white layer applied on the opposite side of the structured surface 52. Alternatively, light absorbing additives can be used, if a dark or dark appearance is desired. black during the day. For retroreflective lamination, the body layer 50 is made sufficiently thin and flexible so as to conform to a target substrate, despite the presence of foreseeable imperfections or deviations from the flat. In Figure 3E, a thin film of oil 58 has been applied as a roller coating on the upper surfaces 56 of the structured surface 52. Subsequently the entire structured surface is vapor coated to form a thin film 60 of aluminum, silver or other reflective material, as shown in Figure 3F. Significantly, the vapor coating is unable to adhere to the surfaces treated with the oil. Therefore the vapor coating adheres only to the untreated portions of the structured surface, especially the recessed faces 54. In this manner, a discontinuous reflective film 60 is selectively formed on the recessed faces 54. and is substantially absent from the upper surfaces 56. This is most clearly seen in Figure 3G which represents the body layer 50 after removing the oil film 58. In a subsequent step, a transparent cover layer 62 is formed in the form of a cover layer. laminates to the body layer 50 to maintain the cavities 58 free of foreign substances that could diminish its operation. Thermal sealing techniques can be used, conventional, for attaching the cover layer 62 directly to the top surface 56. Alternatively, a layer of adhesive or bonding may be provided, as described below. Preferably, the cover layer 62 comprises thermoplastic or thermosetting polymers, or combinations thereof, in a single layer or in multiple layers. Acrylics, vinyl chloride, urethanes, copolymers of ethylene and acrylic acid, polyesters, and fluoropolymers, including polyvinylidene fluoride, are preferred for weather resistance. Dyes, dyes, UV absorbers or other type of absorbers, and similar additives are also contemplated. The cover layer may have graphics, symbols or other markings, such that the laminate formed by the combination of the body layer and the cover layer conveys useful information. Although Figure 3H represents the cavities 58 filled under vacuum or with air, filling the cavities with a clear substance has the advantage of improving the angularity at the entrance to the laminate. That is, the light striking the laminate, with certain large entry angles, will not be retroreflected for air-filled cavities but will be retroreflected for cavities filled with a filler material. The higher the refractive index of the filler material, the more the material will refract the light rays that enter very obliquely, towards the axis of symmetry of a trihedral cavity, and the greater the angularity at the entrance, of the laminate. The preferred materials are described in the co-pending US Patent Application, to which reference was made above. Briefly, the preferred fillers are acrylic polymers which may be pressure sensitive adhesives, at room temperature, or thermally activated adhesives, which are substantially non-tacky at room temperature but which become tacky at higher temperatures. The relatively low viscosity, pressure and temperature associated with the replication of typical materials that cure with radiation, allows for fairly easy filling of the cavities. In a preferred embodiment the filling material is an optically clear pressure sensitive adhesive, sandwiched between the body layer and the cover layer, and preferably in a continuous layer covering both the recessed faces and the top surfaces. In other embodiments, the cover layer can serve as the filler material by itself, if it is molded to extend within the cavities. A wide variety of other fillers can also be used, such as appropriate epoxy resins, hot melt adhesives, high melt index thermoplastic polymers, and thermosetting polymers that cure by radiation. Although not preferred due to reduced retroreflectivity, structures in which only a portion of the cavities remain filled with a filler material are possible. Also shown in Figure 3H (not to scale) is a pressure sensitive or thermally activated adhesive 59 and a release liner 59a. These would typically be applied to the back surface of the body layer 50 to allow easy application of laminate to a target substrate. Figures 4A-C show a laminate of an alternative embodiment, which uses a substantially continuous reflective film, which remains on the structured surface. However, as with the embodiment of Figure 3H, the upper surfaces of the structured surface have a reduced specular reflectivity, due to the presence of a masking material such as a pigmented paint. Figure 4A depicts the body layer 50 of Figure 3D after the application of a continuous reflective film 64. The film 64 covers both the recessed faces 54 and the top surface 56. Subsequently a masking material 66 is applied discontinuously, as shown in Figure 4B, by roller coating, thermal transfer printing or a similar process. The material 66 thus covers the film 64 selectively on the upper surfaces 56, leaving the remainder of the film 64 exposed. The film 64 is thus selectively exposed on the recessed faces of the structured surface of the body layer, such as the films 60 (Figures 3G, 3H) and 24 (Figure 2), described above. Depending on the desired characteristics of the laminate, the material 66 is selected to impart those characteristics. If it is desired to make a retroreflective laminate with cap Y, then a highly diffuse, reflective white paint is selected. It may also be desirable to produce a laminate with a color for the day or a fluorescent effect that differs from the appearance in the retroreflected light, in which case a diffuse color paint or a phosphor pigment is selected. In addition it may be desirable to make a laminate that is retroreflective at night but discreet or even dark during the day, in which case a black absorbing paint is selected. These masking materials can also be printed on the laminate face, to form patterns or symbols. Figure 4C shows the laminate after the application of the cover layer 62, previously described. The filler material can occupy cavities 58 as discussed above to increase the angularity at the entrance. Since the upper surfaces reduce the retroreflective characteristics of the laminate, it is desirable in most cases, to make them as small as necessary to achieve the desired effect, and to cover them completely with masking material 66. However in some cases such as where the material 66 forms a graphic image, it may be desired to cover less than all the upper surfaces with the masking material. Likewise, it may be desirable to remove the reflective material from less than all of the upper surfaces, in previously analyzed modalities. Figure 5 depicts another method for producing a front surface body layer, with a discontinuous reflective film. A body layer 70 is fed along the direction 75 and is guided by a roller 74 that rotates as shown through a grinding wheel 76 that rotates in an opposite direction. Prior to making contact with the grinding wheel, the body layer 70 has a front structured surface 78 which includes recessed faces 80 which form three-dimensional cavities, and narrow upper surfaces 82. The structured surface 78 may consist, essentially, of faces. recessed 80 and not having upper surfaces in their upper portions. A substantially continuous reflective film covers both the recessed faces 80 and the top surfaces 82. The emery 76 removes by grinding a predetermined thickness of the structured surface 78, thereby removing the reflective film, along with a certain amount of the material of the body layer, selectively from the upper portions. The residues collected in the cavities can be removed in a • cleaning stage. The processed body layer 70 has modified upper surfaces 82a, substantially free of reflective material. The reflective material is selectively exposed on the recessed faces. The process depicted in Figure 5 can also be used to form an initial body layer having flat top surfaces, such as the body layer 50 shown in Figure 3D. In this way, instead of building a specialized mold, as described in relation to Figures 3A-C, a more conventional mold is used (for example a simple negative copy of the surface shown in Figure 3A) and the laminate is process by putting it in contact with the grinder. Subsequently, a reflective, continuous or discontinuous film can be applied, as desired, to the modified structured surface. Figures 6A and 6B show still another embodiment of a lamination based on trihedral cubicles, in which the upper surfaces of a structured surface receive a reduced specular reflectivity, relative to the recessed trihedral faces. A polymeric body layer 84 is produced in the same manner as that of the body layer 50 of Figure 3D, except that the body layer 84 has flat upper surfaces 86 treated to provide a non-smooth surface finish. The non-smooth, or rough, surface finish may be the result of replication of the body layer, using a mold having corresponding rough surfaces, or roughening the selected portions of the body layer after fabrication. Roughness can be achieved by laser wear, chemical etching, selective abrasion, or even stamping. Figure 6B shows how a thin reflective film 88 is deposited, continuously, on the structured surface and provides high specular reflectivity on the recessed, smooth trihedral faces, but provides a more diffuse and lower specular reflectivity on the upper surfaces, due to the surface finish not smooth. The principles of Figures 6A and 6B can alternatively be applied to tri -hedral retroreflective laminates, which use a body layer with a back surface. In this case a mold having a structured surface with rough upper surfaces substantially equal to the body layer 84 in Figure 6A is used to stamp, cast, or otherwise form a body layer with a back surface, either directly or using a series of stages of replication with mold. The back surface body layer has a structured surface substantially the same as the surface 42 in Figure 3C, except that the flat intermediate surfaces between the trihedral elements 46 are not smooth or rough. Subsequently, a continuous film of reflective material is applied to the structured surface of the body layer. The portion of the reflective film on the layers of the tricyclic pyramids supports retroreflection and the portion of the reflective film on the rough intermediate surfaces receives diffuse reflectivity, resulting in improved, perceived retroreflectivity. Subsequently a layer of adhesive would be applied to the reflective film. One advantage of the embodiments associated with Figures 6A, 6B is the simplicity of construction. Additional process steps and materials associated with the production of a discontinuous reflective film or with the selective application of a masking material can be avoided. However, if desired, one or both of those characteristics may be used. In any case, the increased surface area of the upper surfaces, due to the non-smooth finish, can also help the adhesion between the reflective film and the body layer, or between the body layer and the cover layer or any intermediate layer .

In Figure 7 is shown the plan view of a body layer, which represents another possible configuration of structured surface. Only a portion of the repeat pattern is shown. The structured surface 90 is csed of recessed faces (shown unshaded) and upper portions including upper (non-shaded) surfaces arranged to define three sets of inverted, parallel grooves or ridges. The set of flanges 92 includes parallel flanges 92a, 92b, the flange assembly 94 includes parallel flanges 94a, 94b, 94c, and the flange assembly 96 includes parallel flanges 96a, 96b, 96c. As shown, the flanges within each set of flanges have upper portions of different transverse dimensions, ie of different widths when measured in the plane of the structured surface perpendicular to the flange axis in question. Such a configuration is possible using a mold made according to the technique described above, wherein diamond tools (at least one of which has a flat tip) are used to form grooves having different widths at the bottom of the groove. When the body layer is applied from that mold, the grooves in the mold produce ridges in the body layer. In another approach the same configuration can result from a sharp-edged tool that cuts grooves at different depths, and then fabricates a negative copy and machining the upper portions of the structured surface to a common height. As shown, not all flanges are provided with top surfaces: flanges 92a, 94a, 96a have none. However, the illustrated interconnection network of upper surfaces circumscribes individual trihedral elements and groups of one, two, three and six elements. The different types of flanges are preferably arranged in repeating patterns to produce a variety of different types of trihedral cavities. For example, the sequences of tricyclic cavities 98a, 98b, 98c demonstrate a decreasing aperture size, as do the optically opposite three-dimensional cavities, 100a, 100b, 100c respectively. For tricyclic cavities, which have an aperture size of approximately 0.25 mm or less, the effects of diffraction begin to become noticeable. The trihedral cavities, interspersed, of different size of opening, on the same structured surface, helps to average those effects, producing better uniformity and a profile of divergence that varies more smoothly. As shown, the structured surface 90 consists essentially of trihedral faces, recesses, and top surfaces. Note that some of the geometric structures on the surface 90 have an additional, recessed face 101. The faces 101 are artifacts that arise during cutting of the master mold, due to the arrangement of the trihedral elements of different sizes. The faces 101 have a small or negligible effect on the optical characteristics. Each pair of flange assemblies 92, 94, 96 mutually intersect with an angle between the sides of 60 degrees, forming non-bevelled three-dimensional cavities. Arrangements are also contemplated where the cavities are chamfered, including the case where only a pair of the flange assemblies intersect each other at an angle less than 60 degrees, and the case where only the pair of the flange assemblies intersect each other at an angle greater than 60 degrees. The chamfering of the trihedral cavities is useful if an enlarged angularity at the entrance is desired for the lamination, and can be used together with the filling of the trihedral cavities, with a transparent filler material. Structured surfaces having only two intersecting flange assemblies, having more than three sets of intersecting flanges, are also contemplated., or that do not have sets of edges that intersect, but instead have trihedral elements, not truncated. The flanges within a set of defined flanges and the flanges of different sets of flanges, may have different heights. The structured surface may comprise cavities having one or more non-optical faces, in addition to the three mutually perpendicular three-sided faces. See, for example, U.S. Patent Nos. 5,557,836 (Smith et al) and No. 5,831,767 (Benson et al) for structured tricyclic pyramidal surfaces, the negative copies of which may be used with the body layers described herein.

Examples 1-4 Four body layers were stamped, with a mold, to impart a structured surface similar to that shown in Figure 1. The mold had a structured surface consisting of three sets of flat bottom grooves, and was the negative replica of a previous mold whose upper portions had been ground with an abrasive to make them flat. The stamped body layers were made of polycarbonate. The body layers for Examples 1 and 2 had a thickness of approximately approximately 1.1 millimeters (43 mils) and included sufficient Ti02 filler material to render them opaque with a diffuse white surface appearance. Those for examples 3 and 4 had a thickness of approximately 0.46 millimeters (18 mils) and included a red dye to give a diffuse red surface appearance. The structured surface of each body layer consisted essentially of three sets of parallel ridges that intersected. Two of these assemblies, referred to as "secondary" flange assemblies, had uniform shoulder spacings of approximately 408 μm (16 mils) and intersecting each other at an angle between the sides of approximately 70 degrees. The other set of parallel ridges, referred to as a set of "primary" flanges, had a uniform spacing of approximately 356 μm (14 mils) and intersected each of the secondary flange assemblies, at an angle between the sides, about 55 degrees. This produced matching pairs of trihedral, chamfered cavities with an angle of approximately 9.18 degrees. All flanges had substantially flat upper surfaces whose transverse dimension was 89 μm (3.5 mils) for the primary grooves and approximately 56 μm (2.2 mils) for the secondary grooves. The upper surfaces were all not smooth as a result of the abrasive action in the original mold analyzed above, transferred to the body layers through the stages of replication. The trihedral elements had a cube depth below the top surfaces, approximately 131 μm (5.17 mils). A silver film was vacuum deposited on the structured surface of each sample, to a thickness sufficient to render the film opaque but highly reflective. For examples 2 and 4, the portion of the silver film deposited on the upper surfaces was removed by the light application of an abrasive. The silver film for examples 1 and 3 was left undisturbed and continuous. A radiation curable composition was prepared by combining (by weight) 74% Ebecryl 270 (a urethane acrylate available from Radcure), 25% Photomer 4127 (propoxylated neopentyl glycol diacrylate, available from Henkel) and 1% Daracure 1173 ( a photoinitiator available from Ciba-Geigy). Subsequently this composition was applied as a flow coating, on the structured surface of all the samples, at room temperature, to a sufficient thickness to fill the three-dimensional cavities and to cover the upper surfaces. The composition was fluid and had a viscosity of about 2 Pa-s (2000 centipoise) during filling. The samples were degassed at room temperature in a small vacuum chamber. Subsequently, when no bubbles remained in the composition, the samples were removed from the chamber and covered with a sheet with a thickness of 178 μm (7 mils) of photographic grade PET laminate to remove oxygen during curing. subsequent. A quartz plate, heavy, which had good transparency in the UV was placed on the PET laminate and later the curing was carried out through the quartz plate and the PET laminate with ultraviolet light of a mercury lamp, for approximately two minutes. The composition of the filling material had a sufficiently low shrinkage, so that it hardened and bonded to the vapor-coated body layer. The composition was not bonded to the PET laminate, which was subsequently removed. The curing composition was substantially clear and smooth but not permanently sticky. The laminates thus constructed exhibited all retroreflectivity. The coefficient of retroreflection was measured with an input angle of -4 degrees, an orientation angle of 0 degrees, with observation angles of both 0.2 and 0.5 degrees, and had not been adjusted to take into account the proportion of the surface structured really occupied by the trihedral elements: These measurements show that the silver film imparts a high specular reflectivity for the recessed faces. Samples 2 and 4, with the silver film selectively exposed on the recessed faces, exhibited a noticeable color during the day (white or red) as a result of the exposed body layer on the upper surfaces. The specular reflectivity of the top surfaces for samples 1 and 2 was also measured. For this purpose, a UV / Vis / NIR spectrometer from Perkin-Elmer Lambda 900 (Perkin-Elmer Corp., Norwalk, Conn.) Was used with an accessory. for the PELA-1029 absolute specular reflectance test (Labsphere Inc., North Sutton, NH). This test fixture used an angle of incidence of 7.5 degrees, and had a "V" optical geometry for reference purposes and an "W" optical geometry with the sample in place. See Figure 8, where S is the sample, Ml and M3 are fixed mirrors, and M2 is a moving mirror that has a reference position M2a and another position M2b when the sample is installed. The absolute reflectance of each sample was determined by dividing the measurement of the sample between the corresponding reference measurement, thus canceling the characteristics of all the optical components different from the sample. Data were taken from 400 to 700 nm in 10nm increments, and averaged. The square root of the original reflectance value was calculated, in the test equipment described, the light is reflected from the sample twice. Then the value thus obtained was corrected to eliminate the contribution of reflected light from the air / filler interface to the front surface of the filling material. This contribution can be calculated using simplified Fresnel equations for perpendicular or near-perpendicular incidence, in an air environment, Reflectance * It is known that the refractive index n of the composition of the filler material is approximately 1.5 in the visible spectrum, producing a contribution of approximately 4%. Finally, after subtracting this contribution, the value obtained is divided between the fractional area of the sample occupied by the upper surfaces, which for the geometry described above was determined to have a value of approximately 45.5%. This calculated final value is taken as the specular reflectivity of the upper surfaces. Using this procedure a specular reflectivity of approximately 9% was calculated for sample 1, and calculated as approximately 3% for sample 2.

Examples 5-8 Samples were produced to better quantify the concept of roughness. Four polycarbonate body layers having a structured surface similar to that of Figure 1 were produced with three sets of intersecting parallel flanges, each set of flanges having a uniform spacing of approximately 216 μm (8.5 mils) and each set intersected the other two sets at 60 °, thus forming trihedral, non-chamfered cavities. Each flange had a flat upper surface of approximately 42 μm (1.65 mils) in the transverse dimension, such that the upper surfaces represented approximately 50% of the structured surface area in a plan view. A flat-tipped diamond tool had been used to form a master mold from which the body layers would replicate, and as a result, the top surfaces were initially optically smooth. The upper surfaces of the samples were then made, selectively, rough, by lightly rubbing the structured surface side of the body layer, with different abrasives. Subsequently, the modified structured surfaces were vacuum coated with a continuous aluminum vapor coating of approximately 100 nm in thickness. A resin layer of acid and ethylene copolymer of the brand Nucrel (type 699), a thermally activated adhesive available from E.l. du Pont de Nemours and Company) was then applied as a filler, to a thickness of approximately 76 μm (3 mils) as measured from the upper surfaces of the body layer) at approximately 130 degrees C on the structured surface, which hardened on cooling. The roughness of the upper surfaces and the value of the cap Y of the samples were measured after filling with the resin composition. For the rugosity measurements, a Leica brand TCS4D Confocal Laser Scan microscope was used, equipped with a 20x objective, 0.45 NA, using light at 488 nm. A topographic image of an area of 0.5 mm by 0.5 mm was generated on the structured surface, from a series of 20 images taken in different axial positions, and a macro for roughness TCS supplied by Leica was used to measure the roughness. The roughness was characterized in terms of the average deviation of a plane ("Ra", expressed in units of μm). The Y cap of the samples was also measured using a LabScan 6000 0 ° / 45 ° spectrocolorimeter from Hunter Lab. To perform a full job, the specular reflectivity of the upper surfaces was measured using the same procedure outlined above in relation to the samples 1 and 2 (subtracting a calculated 4% reflectivity from the air / filler interface and dividing it by 0.50), and the coefficient of retroreflectivity was measured with standard equipment with an input angle of -4 degrees and an angle of observation of 0.2 degrees. The results are given in the following table, where the listed retroreflectivity coefficient has also been divided by 0.5 to take into account the proportion of the structured surface actually occupied by the trihedral cubes: The table shows that the fact of making the upper surfaces rough or not smooth, can substantially reduce the specular reflectivity and increase the apparent retroreflectivity of the laminate, even with a continuous reflective film covering the entire structured surface. A roughness value of at least about 0.15 μm, and preferably at least about 0.2 μm, is desirable to make appreciable changes to the apparent retroreflectivity of the Y cap seen. Similarly, it is desirable to impart to the upper surfaces a specular reflectivity of less than about 60%, preferably less than 40%, and more preferably less than about 20%.

Analysis The tricyclic cavities described herein may be custom-made, individually, in order to distribute the retroreflected light for the articles, in a desired pattern or divergence profile, in a manner analogous to that described by US Patent No. 4,775,219 (Appledorn et al). The faces constituting the trihedral cavities can be arranged in a pattern of repetition of orientations, which differs by small amounts, such as by a few minutes of arc, from the orientation that would have produced the mutual orthogonality with the other surfaces of the trihedral element. Typically, deviations from orthogonality are less than ± 20 arc minutes and often less than ± 5 arc minutes. The body layer for the retroreflective laminate, as described herein, can be manufactured as an integral material, for example by stamping a preformed sheet, with an arrangement of trihedral elements as described above, or by casting a fluid material in a cast. Alternatively, the body layer can be manufactured as a layer product, by casting a defining layer. the structured surface against a flat, preformed film, analogous to the descriptions of PCT publication No. WO 95/11464 (Benson, Jr. et al) and US Patent No. 3,684,348 (Rowland), or by lamination of a preformed film to produce a preformed layer having trihedral grooves. The materials useful for the body layer are those that are dimensionally stable, durable, weather resistant, and that can be easily formed to the desired configuration. Examples include acrylic compounds such as Plexiglas brand resin from Rohm and Haas, thermosetting acrylates and epoxy acrylates, preferably radiation cured; the polycarbonates; polystyrenes; polyolefins; the polyethylene-based ionomers (marketed under the name "SURLYN"); Polyesters; and the cellulose acetate butyrates. In general, any material that can be formed can be used, typically under heat and pressure. The laminate may also include colorants, dyes, UV absorbers, or other additives, as desired. The mold substrates used to make the initial structured surface, a negative copy of which is employed in the body layer, can comprise any material suitable for forming grooves or sets of grooves, directly machined. Appropriate materials should machine cleanly without bumping, and maintain dimensional accuracy after groove formation. A variety of materials such as plastics or metals that can be machined can be used. Suitable materials comprise thermoplastic or thermoset materials, such as acrylics. Suitable metals include aluminum, brass, copper, (soft or hard) and nickel (electroformed or without electric current). Copies of the machined master mold can be produced, through any appropriate process, for example by nickel electrolytic deposition, to produce duplicate, positive or negative templates. Duplicate molds, composed of metal, plastic, or other suitable materials, can be used to stamp, cast or otherwise form the mold pattern to produce a body layer.

Glossary of selected terms The "body layer" of a retroreflective sheet or article that uses a structured surface, for retroreflection, is the layer (or layers) that has (n) the structured surface and mainly responsible for maintaining the integrity of that structured surface. "Trihedral chamber" means a cavity limited at least in part by three faces arranged as a trihedral element. "Trihedral element" means a set of three faces that cooperate to retroreflect the light or to otherwise direct the light to a desired location. "Trihedral element" also includes a set of three faces that by themselves do not retroreflect light or otherwise direct light to a desired location, but if it is copied (either positively or negatively) onto an appropriate substrate, It forms a set of three faces that do retroreflect light or otherwise direct light to a desired location. "Trihedral pyramid" means a mass of material that has at least three lateral faces arranged as a trihedral element. "Cube height" or "cube depth" means, with respect to a triadic element formed or that can be formed on a substrate, the maximum spacing along an axis perpendicular to the substrate, between portions of the trihedral element. "Diffusely reflective", "diffuse reflectivity", and related terms thereof, means the property of reflecting a collimated incident light beam, in a plurality of reflected light beams. The surfaces that are diffusely reflecting, also have a low specular reflectivity. "Dihedral edge" of a trihedral element is an edge of one of the three faces of the trihedral element that joins one of the two different faces of the same trihedral element. "Geometric structure" means a protuberance or cavity having a plurality of faces. "Groove" means an elongated cavity along a groove axis and limited at least in part by two opposite side faces of the groove. "Side surface of the slot" means a surface or series of surfaces, capable (capable) of being formed by passing one or more cutting tools through a substrate with a substantially continuous linear motion. That movement includes milling techniques with polished diamond tools wherein the cutting tool has a rotary movement as it proceeds along a substantially linear path. "Non-Dihedral Edge" of a trihedral element is an edge of one of the three faces of the trihedral element that is not a dihedral edge of that trihedral element. "Retruereflector" means that it has the characteristic by which the obliquely incident light is reflected in a non-parallel direction with respect to the incident, or nearly equal, direction such that an observer near the source of light , can detect the reflected light. "Specularly reflective", "specular reflectance", and terms thereof, refer to the property of reflecting an incident light beam striking a surface, with an angle of entry? in relation to the perpendicular surface, substantially in a single beam of reflected light, directed along an axis (which is referred to as "specular axis") staying in the plane of incidence and making an equal but opposite angle -? with the perpendicular surface. A recessed face (or a reflective film on that face) is said to have a high specular reflectivity if a plurality of those faces can be configured on a structured surface to produce a retroreflection coefficient of at least about 5 cd / lux / m2 with an angle of entry ß = -4 degrees and with an angle of observation a = 0.2 degrees, that coefficient of retroreflection takes into account the proportion of the structured surface actually occupied by the trihedral elements. The upper surfaces (or films or other substrates on them) are said to have a low specular reflectivity if they reflect less than about 60% of the light incident on them., along the specular axis, taking into account the proportion of the structured surface actually occupied by the upper surfaces. In the measurement of the high and low specular reflectivity, both the recessed faces and the surfaces are typically illuminated; the contribution to the upper surfaces is typically negligible in the preceding case and the contribution of the recessed faces (along the specular axis) is arranged to be negligible in the latter case by appropriate selection of the test geometry. "Structured" when used in relation to a surface means a surface composed of a plurality of different faces arranged in various orientations. "Axis of symmetry" when used in relation to a trihedral element, refers to the axis that extends through the vertex of the trihedral and forms an equal angle with the three faces of the trihedral element. Sometimes it is also referred to as the optical axis of the trihedral element. "Top surfaces" of a structured surface containing also recessed faces, refers to surfaces that are different from recessed faces and that have a minimum width in a plan view, of at least about 2.5 μm (0.0001 inches). Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes in shape and detail can be made without departing from the spirit and scope of the invention.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (51)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A trihedral article, characterized in that it comprises: a body layer having a structured surface comprising recessed faces and upper surfaces, the recessed faces defining three-dimensional cavities; and a film of reflective material selectively exposed on the recessed faces of the structured surface.

2. The article according to claim 1, characterized in that the film is substantially continuous.

3. The article according to claim 2, characterized in that it further comprises: a masking material selectively placed on the upper surfaces and covering the film.

4. The article according to claim 3, characterized in that the masking material is diffusely reflective.

5. The article according to claim 4, characterized in that the masking material is substantially white.

6. The article according to claim 3, characterized in that the masking material is substantially opaque.

7. The article according to claim 1, characterized in that the film is discontinuous.

8. The article according to claim 7, characterized in that the film is substantially absent from at least some of the upper surfaces.

9. The article according to claim 8, characterized in that the film is substantially absent from all the top surfaces, and the structured surface essentially consists of recessed faces and the top surfaces.

10. The article according to claim 8, characterized in that the body layer is exposed on at least some of the upper surfaces, the body layer comprises a diffusely reflecting material.

11. The article according to claim 7, characterized in that the body layer is transparent.

12. The article according to claim 7, characterized in that the reflector material comprises silver.

13. The article according to claim 1, characterized in that the structured surface comprises sets of parallel flanges that intersect.

The article according to claim 13, characterized in that the ridges inside at least one of the parallel flange assemblies, have upper portions with different transverse dimensions.

15. The article according to claim 14, characterized in that the upper portions of the flanges, for at least two of the sets of parallel flanges, have different transverse dimensions.

16. The article according to claim 1, characterized in that the three-dimensional cavities comprise three-dimensional cavities of different opening size.

17. The article according to claim 1, characterized in that it further comprises: a substantially transparent cover layer covering the structured surface.

18. The article according to claim 1, characterized in that it further comprises: an adhesive applied to a rear surface of the body layer.

19. A trihedral article, characterized in that it comprises: a body layer having a structured surface comprising recessed faces and upper surfaces, the recessed faces defining three-dimensional cavities; wherein the recessed faces have a high specular reflectivity and at least some of the upper surfaces have a low specular reflectivity.

20. The article according to claim 19, characterized in that substantially all of the top surfaces have a low specular reflectivity, and that the structured surface consists essentially of the recessed faces and of the top surfaces.

21. The article according to claim 19, characterized in that the high specular reflectivity is provided by a film of reflective material placed on the recessed faces.

22. The article according to claim 21, characterized in that the film is discontinuous and is selectively placed on the recessed faces.

23. The article according to claim 21, characterized in that the reflective material film covers both the recessed faces and at least some of the upper surfaces, at least some of the upper surfaces have a non-smooth surface finish.

24. The article according to claim 23, characterized in that at least some of the upper surfaces have an average roughness of at least about 0.15 μm.

25. The article according to claim 19, characterized in that at least some of the upper surfaces have an average roughness of at least about 0.15 μm.

26. The article according to claim 19, characterized in that the upper surfaces comprise substantially planar areas.

27. The article according to claim 26, characterized in that the planar areas circumscribe an integer number of trihedral cavities.

28. The article according to claim 27, characterized in that the integer is one.

29. The article according to claim 19, characterized in that at least one of the upper surfaces has a specular reflectivity of less than about 60%.

30. The article according to claim 29, characterized in that at least some of the upper surfaces have a specular reflectivity of less than about 40%.

31. The article according to claim 30, characterized in that at least some of the upper surfaces have a specular reflectivity of less than about 20%.

32. A method for manufacturing a trihedral article, characterized in that it comprises: providing a body layer having a structured surface that includes recessed faces and upper surfaces, the recessed faces define three-dimensional cavities; forming a reflective film on at least the recessed faces of the structured surface; and treating the structured surface to selectively expose the reflective film on the recessed faces.

33. The method according to claim 32, characterized in that the treatment step is initiated before the formation step.

34. The method according to claim 33, characterized in that the treatment step comprises applying a material resistant to adhesion, selectively to the upper surface.

35. The method according to claim 32, characterized in that the treatment step starts after the forming step.

36. The method according to claim 35, characterized in that the treatment step comprises removing the reflecting layer from the upper portions of the structured surface.

37. The method according to claim 35, characterized in that the treatment step comprises applying a masking material, selectively, to the upper surfaces.

38. A method for manufacturing a trihedral article, characterized by: providing a body layer having a structured surface including recessed faces and upper surfaces, the recessed faces defining three-dimensional cavities. forming a reflective film on at least the recessed faces of the structured surface; and treating the structured surface to impart a low specular reflectivity, selectively, to the upper surfaces.

39. The method according to claim 38, characterized in that the step of forming comprises: applying the reflective film in a substantially continuous manner to the structured surface.

40. The method according to claim 39, characterized in that the treatment step comprises removing the upper portions of the structured surface to form the upper surfaces.

41. The method according to claim 40, characterized in that the removal step comprises placing the structured surface in contact with an abrasive.

42. The method according to claim 39, characterized in that the treatment step comprises: applying a masking material, selectively, to the upper surfaces.

43. The method according to claim 42, characterized in that the masking material is applied on the portions of the reflective film.

44. The method according to claim 39, characterized in that the treatment step comprises: roughening, selectively, the upper surfaces, to provide a surface finish not smooth thereon.

45. The method according to claim 44, characterized in that the provision stage comprises preparing a mold used directly or indirectly to form the structured surface, the step of selectively making the roughness, comprising roughly, selectively, portions of the mold that correspond to the upper surfaces.

46. The method according to claim 44, characterized in that the step of selectively causing the roughness comprises contacting the upper surfaces with an abrasive agent.

47. The method according to claim 38, characterized in that the forming step comprises: applying the reflective film, in a discontinuous manner, to the structured surface.

48. The method according to claim 47, characterized in that the treatment step comprises: applying a resistive material to the adhesion, selectively, to the upper surfaces, before the application of the reflective film stage.

49. A method for manufacturing a trihedral article, characterized in that it comprises: providing a mold having recessed faces and upper surfaces, the upper surfaces are not smooth; forming a body layer, directly or indirectly, from the mold, the body layer has a structured surface of faces arranged to form trihedral elements and intermediate surfaces between the trihedral elements, and form a reflective film on the trihedral elements and the surfaces intermediate of the structured surface.

50. The method according to claim 49, characterized in that the forming step forms a front surface body layer, and in that the faces are recessed to form trihedral cavities.

51. The method according to claim 49, characterized in that the forming step forms a back surface body layer, and in that the faces are arranged to form three-dimensional pyramids.