MXPA98008962A - Material in layers composed of retrorreflector cube corners, ultraflexible, conformed with optical objective properties and a method for the manufacture of the - Google Patents

Abstract

A layered, retroreflective material having a multiplicity of discrete cube corners elements cured in situ on a superimposed, polymeric, transparent film deformed into a three dimensional structure so that the base edges of a plurality of cube corner elements they are not flat with respect to each other. The retroreflective article preferably has at least one objective optical property. The present invention also relates to a method for deforming the layered, retroreflective material for forming the layered, retroreflective material to form a retroreflective article in which the base edges of a plurality of cube corner elements are not flat with respect one of the ot

Description

MATERIAL IN LAYERS, COMPOSED OF CUBE CORNERS, RETRORREFLECTOR, ULTRAFLEXIBLE, CONFORMED WITH OPTICAL OBJECTIVE PROPERTIES AND A METHOD FOR MANUFACTURE OF THE SAME FIELD OF THE INVENTION The present invention relates to a layered, retroreflective, flexible material deformed to produce objective optical properties and to a process for deforming a layered, retroreflective material in a three-dimensional article with such optical properties.

BACKGROUND OF THE INVENTION The cube corner retroreflectors typically comprise a layered material having a generally flat front face and an array of cube corner elements protruding from the back surface. The reflection elements of cube corners comprise generally trihedral structures that have three approximate and mutually perpendicular side faces that meet in a corner REF: 028653 individual, that is, a cube corner. The incident of the light to the front surface penetrates the layer, passes through the body of the layer to be reflected internally by the faces of the elements in order to exit to the front surface in a direction substantially towards the light source. The light rays are typically reflected on the faces of the cubes due to either a total internal reflection ("T.I.R." for its acronym in English), or reflective coatings such as an aluminum film deposited with steam. The use of a metallized aluminum coating on the cube corner elements tends to produce a gray coloration for an observer under conditions of ambient light or natural light, and thus is considered aesthetically undesirable for some applications. A very common retroreflective, layered material uses a set of cube corner elements to retroreflect light. Figures 1 and 2 illustrate an example of such a retroreflective layered material, generally observed by the number 10. The set of cube corner elements 12 projects from a first or a rear side of a portion of the body 14 that includes a body layer 18 (also referred to in the art as a superimposed layer) and may also include a layer of floor 16. The light illustrated as the arrows 23 penetrates the material in cube corner layers 10 through the front surface 21; it then passes through the body portion 14 and hits the flat faces 22 of the cube corner elements 12 to return in the direction from which it came. Figure 2 shows the back side of the cube corner elements 12, where each cube corners element 12 is in the form of a trihedral prism having three flat, exposed faces 22. The cube corner elements 12 in the Known assemblies are typically defined by three series of v-shaped notches, parallels 25, 26 and 27. The flat, adjacent faces 22 in the adjacent, cube corner elements 12 in each notch form a dihedral, external angle (an angle dihedral is the angle formed by two intersecting planes). This dihedral, external angle is constant along each indentation in the set. This has been the case for the variety of cube corner sets, previously produced.

The planar faces 22 defining each individual cube corner element 12 are generally substantially perpendicular to each other, as in the corner of a room. The dihedral, internal angle - that is, the angle between the faces 22 in each cube corner element, individual in the set - is typically 90 °. However, this internal angle can deviate slightly from 90 ° as is well known in the art; see, for example, U.S. Patent No. 4,775,219 issued to Appeldorn et al. Although the apex 24 of each cube corner element 12 can be aligned vertically with the center of its base (see, for example, US Patent No. 3)., 684,348) the apex may also be offset or tilted from the center of the base as published in U.S. Patent No. 4,588,258 issued to Hoopman. Other configurations of cube corners are published in US Patents Nos. 5,138,488, 4,066,331, 3,923,378, 3,541,606, and Re 29, 396, 3,712,706 (Stamm), 4,025,159 (McGrath), 4,202,600 (Burke et al.), 4,243,618 (Van Arnam). , 4,349,598 (White), 4,576,850 (Martens), 4,588,258 (Hoopman), 4,775,219 (Appeldorn et al.), And 4,895,428 (Nelson et al.). Where the material layered, retroreflector, cube corners to be used probably in an environment where it could be exposed to moisture or other elements, for example, outside or in high humidity, it may be preferred that the elements of cube corners they are encapsulated with a conformable sealing film. U.S. Patent No. 4,025,159, mentioned above, publishes the encapsulation of the cube corner elements using a sealing film. The basic cube corner elements have a low angularity such that the retroreflective element only brilliantly collides with light within a narrow angular range that centers approximately on its optical axis. The optical axis is the trisectoral of the internal space defined by the faces of the element. The impact light that slopes substantially away from the optical axis of the element strikes a face at an angle less than its critical angles, because of that it passes through the face before it is reflected.

Figure 3 is a graph in polar coordinates of the optical profile of a retroreflective layer, cube corner, basic, having a maximum of six and a minimum of six at azimuth intervals of 30 ° C. The retroreflective beam intensity of a retroreflective, cube cornered layer material is larger when the incident beam has an angle of incidence of 0 ° (normal for the plane of the layered material). At the highest incidence angles (approximately greater than 30 °) the brightness of the retroreflected beam is a function of the angle with respect to an axis normal to the layer called the azimuth angle. When the angle of incidence of a light beam is kept constant at a value of, for example, 60 ° from normal, and the azimuth angle of the incident beam varies from 0 ° to 360 °, the intensity of the retroreflected beam varies as it is illustrated in Figure 3. There are a number of applications for the layered, retroreflector, cube corner material with non-standard or custom optical profiles. For example, a more uniform retroreflectivity or a wider retroreflectivity angularity than that shown in Figure 3 is often required. For some applications it may be desirable to limit retroreflectivity to a narrow band of angularity and / or along a specific segment. of the azimuthal angle. One method for changing the optical profile of the cube corner elements is to cut the original or mold formed therein into pieces and reassemble the pieces in a pattern that produces different orientation zones in the layered, retroreflective material. For example, an optical profile with a wide retroreflection angularity in multiple viewing planes can be achieved by rotating the adjacent parts of the original mold or 30 ° or 90 ° with respect to an axis normal to the plane of the elements (the rotation of the parts at 60 ° or any multiple thereof does not effect a net change in the orientation of the cube corner elements). However, reassembling the mold or original parts with the necessary precision takes time and is expensive. A method for reassembling a master mold is published in U.S. Patent Application Serial No. 08 / 587,719, filed January 19, 1996. Another method for changing the optical profile of the cube corner elements is to tilt or tilt. the optical axes of the corner elements of the -cube with respect to each other. Figure 4 illustrates a cube corner element 30 with three mutually perpendicular faces 31a, 31b, and 31c that meet at the apex of the hub 34. The base edges of the hub 35 are generally linear and generally consist of a plane individual defining the base plane 36 of the element '30. The cube corner element 30 also has a central or optical axis 37, which is the trisectoral of the internal angles defined by the side faces 31a, 31b, and 31c. The optical axis may be placed perpendicular to the base plane 36, or it may be tilted as described in U.S. Patent No. 4,588,258 issued to Hoopna and in U.S. Patent No. 5,138,488 issued to Szczech. The necessary cost of producing the tooling to practice Hoopman's invention is relatively high. On the other hand, this technique does not lend itself to a rapid prototype of angularity or customized optical profiles. Therefore, what is necessary is a method to create retroreflective articles with a prototype or objective optical properties without the need for expensive tooling.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a layered, retroreflective, flexible material deformed to produce objective optical properties. The present invention is also directed to a process for deforming a retroreflective, layered material in a three-dimensional article having such optical properties. The layered material, retroreflector includes a multiplicity of cube corner elements, discrete cured in situ in a superimposed, polymeric, transparent film. The retroreflective, layered material is deformed into a three dimensional structure so that the base edges of a plurality of cube corner elements are not planar with respect to each other to produce at least one objective optical property. The objective optical properties can be a desired optical profile, angularity, three-dimensional appearance, whiteness, gloss effect, or combinations thereof. The retroreflective, layered material is preferably a single, unitary layer. The base edges of a plurality of adjacent cube corner elements can not be flat or inclined with respect to each other. The base edges of one or more cube corner elements are preferably not parallel to a front surface of the superimposed film. The cube corner elements may have a variable density through a portion of the retroreflective article. The cube corner elements, adjacent through a portion of the retroreflective article may have a variable spacing. The superposed film can have a thickness that varies through a portion of the retroreflective article. The present retroreflective article can be used as an original to produce a tool for forming additional retroreflective articles. The three-dimensional structure may have one or more stamped symbols. The retroreflective, layered material may optionally include a specular reflector coated on the cube corner elements. The retroreflective, layered material may optionally include a sealing film that extends substantially through the cube corner elements opposite the superimposed film. The metallized cube corner elements can be padded or optionally upside down with a coating, such as a polymeric material, resin or adhesive. In one embodiment, the coating may be applied uniformly or in a pattern, such as printing symbols in one or more colors. The polymer superimposed film preferably has a first coefficient of elasticity and the cube corner elements preferably have a second coefficient of elasticity greater than the first coefficient of elasticity. The cube corner elements are preferably manufactured from a thermoset polymer. The polymeric superimposed film is preferably manufactured from a thermoformable polymer. The superimposed film can be selected from the group consisting of the following: ionomeric ethylene copolymers, plasticized vinyl halide polymers, functional acid ethylene copolymers, aliphatic polyurethanes, aromatic polyurethanes, other light transmitting elastomers, and combinations thereof. The cube corner elements can be selected from the group consisting of monofunctional, difunctional and polyfunctional acrylates or combinations thereof. The present invention is also directed to a method for forming a retroreflective article having at least one objective optical property. A layered, retroreflective, cube corner material is prepared having a multiplicity of discrete cube corner elements cured in situ in a polymeric, transparent overlay film. The retroreflective, flexible, layered material is deformed into a three-dimensional configuration so that the base edges of a plurality of cube corner elements are not planar with respect to each other. The deformation step may include tilting the base edges of the plurality of cube corner elements, adjacent to one another. The deformation step is preferably selected from the group consisting of thermoforming, vacuum molding, stamping, and combinations thereof. The deformation step may include forming a three-dimensional symbol in the layered, retroreflective material, altering the density and / or spacing of at least a portion of the cube corner elements, or stretching the material in layers, retroreflective in at least one direction. The stretch step may include stretching uniformly (or non-uniformly) or biaxially stretching the retroreflective, layered material. The deformation step may include altering the base edges of one or more cube corners so that they are not parallel to a front surface of the superimposed film. The cube corner elements can optionally be covered with a spectral reflector. Optionally, a sealing film can be joined substantially through an exposed surface of the cube corner elements either before or after the deformation step of the layered, retroreflective material. In an alternative embodiment, a mold is formed of the cube corner elements of the retroreflective article, deformed. A polymeric material is applied to the mold and the polymeric material is at least partially cured. The polymeric material is then removed from the mold so that a second retroreflective article is produced. As used in the present: Deformation refers to thermoforming, vacuum molding, embossing, molding, embossing, elastic or inelastic stretching, uniform or non-uniform stretching or combinations thereof. Symbol refers to any alphanumeric character, logo, stamp, geometric model or combinations thereof. "Objective optical properties" refers to a desired optical profile, angularity, three-dimensional appearance, whiteness, gloss effect, or combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is further explained with reference to the drawing, wherein: Figure 1 is a sectional view of a layered, retroreflective, cube corner material of the prior art; Figure 2 is a bottom view of the retroreflective, layered material of Figure 1; Figure 3 is a graph in polar coordinates of the optical profile of a cube corner element having a maximum of six and a minimum of six at azimuthal intervals of 30 °; Figure 4 is an isometric view of a cube corner element that can be used in a retroreflective, layered material of the invention; Figure 5 is a bottom view of a retroreflective article according to the present invention; Figure 6 is a sectional view of a retroreflective article taken along lines 6-6 of Figure 5; Figure 7 is a sectional view of the retroreflective article taken along lines 7-7 of Figure 6; Figure 8 is a sectional view of a retroreflective article having a sealing film secured to the back side of the retroreflective, layered material; Figure 9 is a schematic illustration of a method for preparing a retroreflective, layered material; Figure 10 is a schematic illustration of an alternative method for preparing a layered, retroreflective material; Figure 11 is a schematic illustration of a method for preparing a retroreflective article; Figure 12 is a schematic illustration of an alternative method for preparing a retroreflective article; Figure 13 is a photograph of an exemplary retroreflective article; Figure 14 is a photomicrograph of a depression in the retroreflective article of Figure 13; Figure 15 is a photomicrograph of a depression in the retroreflective article of Figure 13; Figure 16 is a photograph of an exemplary retroreflective article; Figure 17 is a photomicrograph of a profusion in the retroreflective article of Figure 16; Figure 18 is a photomicrograph of a profusion in the retroreflective article of Figure 16; Figure 19 is a photograph of an exemplary retroreflective article containing a symbol; Figure 20 is a photograph of a plurality of exemplary retroreflective article; Figure 21 is a photomicrograph of a retroreflective article containing a symbol®; Figure 22A is a graph of the angle of entry against brightness for various models; Figure 22B is a graph of the observation angle against brightness for the models of Figure 22A; Figure 23A is a graph of the angle of entry against brightness for various models; Figure 23B is a graph of the observation angle against brightness for the models of Figure 23A; Figure 23C is a bar graph of the change in whiteness of several models after deformation; Figure 24A is a graph of the angle of entry against brightness for various models; Figure 24B is a graph of the observation angle against brightness for the models of Figure 24A; Figure 25A is a graph of the angle of entry against brightness for various models; Figure 25B is a graph of the observation angle against brightness for the models of Figure 25A; Figure 26A is a graph of the angle of entry against brightness for various models; and Figure 26B is a graph of the observation angle against brightness for the models of Figure 26A; Figure 27A is a graph of the angle of entry against brightness for various models; Figure 27B is a graph of the observation angle against brightness for the models of Figure 27A; Figure 27C is a graph of the angle of entry against brightness for various commercial reflectors; and Figure 27D is a graph of the observation angle against brightness for the commercial reflectors of Figure 27C.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The present invention relates to a retroreflective article formed of a layered material, retroreflective, flexible to produce objective optical properties and to a process for deforming a layered, retroreflective material in a three-dimensional article. The layered, retroreflective material has a set of discrete cube corner elements, cured in situ on a superimposed, polymeric, transparent film. The assembly is deformed into a three-dimensional structure so that the base edges of a plurality of cube corner elements do not reside in the same plane when the layered material is laid flat. The retroreflective article of the present invention has the ability to reflect substantial amounts of incident light back to the light source while exhibiting objective optical properties. The present retroreflective article is suitable for being incorporated into a variety of products, such as clothing, shoes, vehicular circulation permits, signs, vehicle markings, conical casings and barrels covers. The manufacturing methods of retroreflective, glossy articles are published in the following related applications filed the same day with the present: "Method of Making Glittering Retroreflective Sheeting" now U.S. Patent No. 5,770,124); "Mold for Producing Glittering Cube-Corner Retroreflective Sheeting" attorney's license No. 52471USA5A, Serial No. 08 / 640,383; and "Glittering Cube-Corner Retroreflective Sheeting" attorney's license No. 52373USA3A, Serial No. 8 / 640,326. Figure 5 shows the back side of a unitary, cube corner, layer material that has been deformed to produce at least one objective optical property. The cube corner elements 30 are similar to those shown in Figure 4. Each cube corner element 30 is attached, but not necessarily connected to, a cube corner element, adjacent to a base edge 35. set includes three series of parallel notches 45, 46, and 47. The dihedral, external angles (designated as a in Figure 6) between the faces 31 of the adjacent cube corner elements 30 vary along the notches 45 -47 in the set. The base edges 35 of the cube corner elements in the set do not reside in the same plane. Accordingly, the apex 34 of a cube, such as the hub 30a can be relatively close to another apex such as the hub 30b, but then the apex of the hub 30b may be further away from the other adjacent apex such as the apex of the hub 30c . Figure 6 is an exemplary illustration of the distances the base edges 35 are offset or inclined with respect to each other, or with respect to the front surface 51. For the cube corner elements that are approximately 50 to 200 micrometers high, the variation in height between the base, adjacent edges is typically from about 0 to 50 micrometers. It will be understood that the present retroreflective article can be deformed at a micro or macro level. As will be discussed in the Examples, the retroreflective, layered material can be deformed onto a coated, abrasive paper containing abrasive grains with diameters of about 100 to 550 microns. Abrasive grains of this size have radii of curvature of approximately 50 to 225 micrometers. The retroreflective, layered material can be deformed into smaller structures, in the range of about 10 to 50 micrometers, although the change in optical properties can be minimal. It is believed that the change in the optical properties of the retroreflective, layered material when deformed on microstructures in the range of about 250 to 10 microns is a function of the size of the cube corner elements and the thickness of the superimposed film. For example, the elements of smaller cube corners and / or a thinner superimposed film may be more susceptible to deformation on the microstructures within this range. Figure 6 is a sectional view of the cube corner layer material 60 of Figure 5 showing the position of an apex of one cube relative to another. Additionally, Figure 5 shows the inclination or deviation of the base edges 35 relative to each other and relative to the front surface 51. The base edge 35 of a hub can be placed closer or more distant from the front surface 51. of the superimposed film 58 that of the base edges of the other cube corner elements, adjacent due to the deformation of the superimposed film 58. If the layer, cube corner, unit 60 material possesses a layer of soil 56 it is also not uniformly separated from the front surface 51. The layered material of cube corners 60 preferably does not have a floor area 56, such that each cube corner element 30 is a discrete entity. When the cube corner elements are tilted, the base edges 35 of many of the cube corner elements 30 do not reside in the same plane when the layer material is laid flat as shown in Figure 6. Additionally, the edges 35 of one or more cube corner elements 30 are not parallel to the front surface 51. Any surface of the superimposed film 58 may optionally contain symbols printed on or formed therein. Figure 6 also shows the dihedral, external angle, a, which defines the angle between the carcases 31 of the adjacent cube corner elements 30. The angle a can vary along all the notches in a series of Parallel, individual notches may vary along all the notches in two series of parallel notches, or may vary along the notches in all three series of notches in the assembly. In a set of randomly inclined cube corner elements, the angle a varies randomly between the adjacent faces of the cube corner elements, adjacent essentially throughout the whole.

The superimposed film 58 in a portion of the body 54 typically has an average thickness of about 20 to 1200 microns, and is preferably about 50 to 400 microns. The cube corner elements typically have an average height of about 20 to 500 micrometers, more typically about 25 to 200 micrometers. The optional floor layer 56 is preferably maintained at a minimum thickness of 0 to 150 micrometers, and is preferably as close to zero as possible so that the stress generated during deformation does not propagate laterally through the area of soil. A coating can optionally be applied to the exposed, metallized hub corner elements 30 to provide deformations of the retroreflective article 60 with additional structural support. For some applications, it may be desirable for the retroreflective article to be a self-supporting, self-supporting structure. In one embodiment, the coating is a polymeric material, resin or an adhesive. The coating may optionally contain a pigment or dye of one or more colors. Additionally, the coating can be applied uniformly or in a pattern containing symbols using a variety of printing techniques. The layered, retroreflective, metallized material generally maintains a higher brightness after deformation because the T.I.R. tends to fail in unsealed layered material. Figure 7 shows the elements of cube corners inter-connected by a plane that is parallel to the front surface 51. As illustrated, the plane does not interconnect each cube to produce a triangle 62 of the same cross-sectional area. A cube can be tilted or decentered from the front surface 51 to such a degree that the inter-contacting plane only passes through a tip of the hub, resulting in a small, triangular cross-section - whereas, a cube that remains straight it can be interceded such that the triangle resulting from the cross section is relatively large. In this way, although the cube corner elements in the set can be of a similar size, they can produce triangles of random sizes when intercepted as described due to the manner in which the cubes are tilted or decentered with respect to a reference plane. It will be understood that the spacing between the cube corner elements 30 may vary, as will be discussed later, although retroreflectivity tends to decrease as the spacing increases. Figure 8 shows a retroreflective article 61 having a sealing film 63 positioned on the back side of the cube corner elements 30, as published in US Patent No. 4,025,159. The sealing film 63 is attached to the body portion of the layered material through the cube corner elements 30 by a plurality of sealing lines 64. The bonding pattern produces a plurality of hermetically sealed chambers 65 which prevent the Contact of moisture and dust with the back side of the cube corner elements. The cameras 65 allow the cube-air interface to be maintained to prevent the loss of retroreflectivity. The cube corner elements 30 may optionally be coated with a reflective material on the surface 67, such as vapor deposition or chemical deposition of a metal such as aluminum, silver, nickel, tin, copper or dielectric materials as are known in the technique of retroreflective articles, cube corners. It will be understood that the retroreflector 61 layer material will typically have a metal layer on the surface 67 or a sealing film 63, but not both. Preferably, the sealing layer comprises a thermoplastic material with a low coefficient of elasticity, similar as the superimposed film 68. Illustrative examples include the ionomeric ethylene copolymers, plasticized vinyl halide polymers, acid-functional polyethylene copolymers, aliphatic polyurethanes, aromatic polyurethanes and combinations thereof. In certain applications, the optional seal layer 63 can provide significant protection for the bucket corner elements of the composite from the environmental effects, as well as maintain a sealing air layer around the bucket corner elements. which is essential to create the differential refractive index necessary for internal, total reflection. Because of the decoupling of the cube corner elements 30, the sealing layer 63 can optionally adhere, at least in part, directly to the superimposed film 68 between the independent cube corner elements. The sealing film can be attached to the cube corner elements in the body portion of the layered material using known techniques; see, for example, US Patent No. 4,025,159. Examples of the sealing technique include radiofrequency welding, thermal fusion, conductive thermal sealing, ultrasonic welding, and reactive welding. When a sealing film is applied to the back side of a retroreflective, layered material, considerable attention must be paid to the composition and physical properties of the sealing film. The sealing film should be able to firmly attach to the back side of the material in cube corner layers and should not contain components that could adversely affect the retroreflectivity or appearance of the retroreflective product. For example, the sealing film will not contain components that could be leached (for example, dyes) and make contact with the back side of the cube corner elements. The sealing film typically comprises a thermoplastic material because such materials lend themselves well to fuse through relatively simple and commonly available thermal bonding techniques. Figure 9 is a schematic illustration of an apparatus 120 for molding and curing the retroreflective, layered material suitable for use in the present invention. The superimposed film 121 is stretched along a guide cylinder 122 or a loading roller of the material to a press roll 123, for example, a rubber covered roller, where the overlay 121 contacts the resin formulations, suitable 124 previously applied to a molding tool roll 125 through a coating nozzle 126. Excess resin extending over the hub corner element forming the cavities 127 of the tool 125 is decreased by adjusting the press roller 123 to an aperture setting that is effectively less than the height of the cube corners forming elements of the tool 125. It will be understood that the aperture adjustment can be achieved by applying pressure to the pinch roller 123. In this way, the mechanical forces at the interface between the press roller 123 and the tool 125 ensure that a minimum amount of resin 124 is spread over the cavities 127 of the tool 125. Depending on the flexibility of the overlay 121, the film 121 can optionally be supported with a suitable carrier film 128 which provides structural and mechanical durability to the overlay 121 during molding and curing. The carrier film 128 can be removed from the superimposed film 121 after the layered material is removed from the tool 125 or left intact for further processing of the retroreflective, layered material. The use of such a carrier film is particularly preferred for superposed low coefficient films. The resin composition forming the retroreflective assembly of the cube corner elements can be cured in one or more steps. The radiation sources 129 expose the resin to actinic radiation, for example, ultraviolet light, visible light, etc. depending on the nature of the resin in a primary healing step through the superimposed film. As can be appreciated by one of skill in the art, the superimposed, selected film need not be completely or 100 percent transparent for all possible wavelengths of the actinic radiation that can be used in the curing of the resin. Alternatively, the cure can be performed by irradiation through a transparent tool 125, such as is disclosed in U.S. Patent No. 5,435,816. The tool 125 has a molding surface having a plurality of cavities that open thereon which have the proper shape and size to form the desired cube corner elements. The cavities, and thus the resulting cube corner elements, can be pyramids of three sides having a cube corner each, for example, as they are published in US Patent No. 4,588,258, they can have a rectangular base with two rectangular sides and two triangular sides such that each element has two cubic corners each, for example, as published in US Patent No. 4,938,563 (Nelson et al.), or may be otherwise desired, having at least a cubic corner each, for example, as they are published in the North American Patent No. 4,895,428 (Nelson et al.). It will be understood by those skilled in the art that any cube corner element can be used in accordance with the present invention. The tool 125 should be such that the cavities will not deform undesirably during the manufacture of the composite article, and such that the set of cube corner elements can be separated therefrom after curing. The materials useful in the formation of the tool 125 preferably a clean machine without the formation of flash, exhibit a low docility and a low granularity, and maintain a dimensional accuracy after the formation of the notch. The tool can be made of polymeric, metallic, composite or ceramic materials. In some modalities, the healing of the resin will be done by applying radiation through the tool. In such cases, the tool will be sufficiently transparent to allow irradiation of the resin therethrough. Illustrative examples of the materials of which the tools for such embodiments can be manufactured include polyolefins and polycarbonates. However, metal tools are typically preferred, as they can be formed into desired shapes and provide excellent optical surfaces to increase the retroreflective performance of a given cube corner element configuration. Primary healing can completely or partially cure the cube corner elements. A second source of radiation 130 can be provided to cure the resin after the layered material 131 has been removed from the tool 125. The extension of the second healing step is dependent on a number of variables, among them the speed of the feeding materials, the. composition of the resin, the nature of the crosslinking initiators used in the resin formulation, and the geometry of the tool. Illustrative examples include exposure to the electron beam and actinic radiation, for example, ultraviolet radiation, visible light radiation, and infrared radiation. The removal of the layered, retro-reflective material 131 from the tool 125 typically generates sufficient mechanical stresses to fracture the minimum floor area between the cube corner elements, if any, which exist between the individual cube corner elements. Layered material The independent, uncoupled nature of the discrete cube corner elements and the sturdy bond of each independent element to the superimposed film gives the substantial flexibility of the retroreflective, layered material, while maintaining high levels of retroreflectivity performance after being subjected to the tensions of the mechanical deformation. The heat treatment of the layered material 131 can optionally be carried out after it is removed from the tool. The heat serves to relax the tensions that could have developed in the superimposed film or cube corner elements, and remove the unreacted portions and byproducts from the reaction. Typically, the treatment involves heating the material in layers at an elevated temperature, for example, above the glass transition temperature of the target resin. Typically, a layered material will exhibit an increase in retroreflectivity brightness after such treatment.

Figure 10 illustrates an alternative apparatus for molding and curing the retroreflective, layered material suitable for making the present retroreflective article. The resin composition 124 is molded directly into the superimposed film 121. The resin-film combination is then contacted with the tool roller, model 125 with a pressure that is applied through an appropriate adjustment of the press roller 123. As in the configuration illustrated in Figure 9, the press roller 123 serves to decrease the amount of resin that extends over the cavities forming bucket corners 127 of the tool 125. The resin can then be cured by exposing it to an actinic radiation of a first source of radiation 129, and a second source of radiation, optional 130. The actinic radiation of the first source of radiation 129 must first pass through the superimposed film of the layered material before hitting the resin . The elements of individual or discrete cube corners are essentially and completely uncoupled from one another, providing the ultra-flexible character of the layered, retroreflective, composite material. Bucket corner elements, decoupled, are no longer mechanically forced by the effect of any area of the floor, reducing mechanical stresses that could tend to deform them and lead to degradation of retroreflective performance. The cube corner elements, discrete of the layered, retroreflective material retain a high degree of retroreflectivity brightness after they are deformed. The retroreflective layer material prepared according to the above method exhibits a retroreflectivity brightness, ie, a coefficient of retroreflection, of greater than about 50, preferably greater than about 250, and more preferably greater than about 500, candela / lux / square meter, measured at an input angle of -4o and an observation angle of -0.2 °, when the layered material is in a non-deformed, flat configuration. By the way, this means that the layered material lends itself to being laid flat and not deformed, this means that the layered material has not been mechanically stretched after the decoupling of the cube corner elements. The resin composition and the superimposed film are preferably such that when the resin composition makes contact with the superimposed film it penetrates the superimposed film so that after the primary cure treatment an interpenetration network is formed between the material of the films. elements of cube corners and the material of the superimposed film. The set of cube corner elements preferably comprises a material that is thermoset or extensively crosslinked, and the superimposed film preferably comprises a thermoplastic material. The superior chemical and mechanical properties of the thermoset materials produce cube corner elements optimally capable of maintaining the desired retroreflectivity. A decisive criterion in the selection of these components is the relative elasticity coefficient for each component. The term "coefficient of elasticity" as used herein means the coefficient of elasticity determined according to ASTM D882-75b using a Static Weight Method A with an initial setting of the fixator of 12.5 centimeters (5 inches), a width of the sample of 2.5 centimeters (1 inch), and a proportion of the fixative separation of 2.5 centimeters / minute (1 an inch / minute). Alternatively, the coefficient of elasticity can be determined according to the ASTM D882-75b standardized test using a Static Weight Method A with an initial fixation of 12.5 centimeters (five inches), a sample width of 2.5 centimeters (one inch), a fixation separation ratio of. centimeter per minute (inch per minute). Under some circumstances, the polymer can be very hard and brittle which is difficult to use in this test to accurately assess the value of the module (although it would be easily known that it is greater than a certain value). If the ASTM method is not very suitable, another test, known as the "Nanoindentation Technique", can be used. This test can be carried out using a microindentation device such as a UMIS 2000 available from CSIRO Division of Applied Physics Institute of Industrial Technologies of Lindfield, New South Wales, Australia. Using this kind of device, the penetration depth of a Berkovich pyramidal diamond penetrator having an included conical angle of 65 ° is measured as the function of the applied force up to the maximum load. After the maximum load has been applied, the material is allowed to relax in an elastic manner against the penetrator. It is usually assumed that the gradient of the upper portion of the discharge data is found to be linearly proportional to the force. The Sneddon analysis provides a relationship between the penetration force and the plastic and elastic components of the depth of penetration (Sneddon I.N. Int. J. Eng. Sci. 3, pp. 47-57 (1965)). From an examination of the Sneddon equation, the elasticity coefficient can be recovered in the form E / (l-v2). The calculation uses the equation: E / (l-v2) = (dF / dhe) Fmaxl / (3.3hpmaxtan (?)) where: v is the Poisson's ratio of the sample being tested; (dF / dhe) is the gradient of the upper part of the discharge curve; Fmax is the maximum force applied; hpmax is the depth of penetration of the plastic, maximum; ? is the semi-included conical angle of the Berkovich pyramidal penetrator; and E is the coefficient of elasticity. The values obtained under the nanoindentation technique may have to be correlated again to ASTM D 882-75b. As discussed above in relation to the fundamental principles behind the optical properties of the cube corner elements, even a slight distortion of the geometry of the cube corner elements can result in a substantial degradation of the optical properties of the cube corners. cube corner elements. In this way, higher coefficient of elasticity materials are preferable for cube corner elements due to their increased resistance to distortion. The superimposed film of the layered, retroreflective, composite material is preferably a polymeric material with a slightly lower coefficient of elasticity. During the curing of the cube corner component, depending on the composition of the cube corner material, the individual cube corner elements may experience a certain degree of contraction. If the coefficient of elasticity of the superimposed film is very high, torsional stresses can be applied to the cube corner elements if they shrink during curing. If the stresses are high enough, then the cube corner elements can become distorted with a resulting degradation in optical performance. When the coefficient of elasticity of the superimposed film is sufficiently lower than the coefficient of the material of cube corner elements, the superimposed film can deform together with the contraction of the cube corner elements without exerting such deformational functions on the elements of the cube. Cube corners that lead to undesirable degradation of optical characteristics. The coefficient differential between the superimposed film and the cube corner elements will be in the order of 1.0 to 1.5 x 107 pascals or more. As the height of the cube corner elements decreases, it is possible for this coefficient differential to reach the low end in the range given immediately before. However, it will be kept in mind that there is a lower, practical limit for material coefficients of the cube corner element. Below a certain level, generally in the order of approximately 2.0 to 2.5 x 108 pascals for the cube corner elements of approximately 175 microns (0.007 inches) in height, smaller for the smaller cube corner elements, the elements of cube corners become very flexible and do not possess sufficient mechanical rigidity to fracture properly with the application of tension. The cube corner elements preferably have a coefficient of elasticity greater than about 25 x 108 pascals. After curing, the thickness of the floor area, ie, the thickness of the material of the cube corner set opposite the plane defined by the bases of the cube corner elements, is preferably less than 10 percent of the height of the cube corner elements, and more preferably less than 1 percent thereof. Preferably, the resin will shrink at least 5 percent by volume when cured, more preferably between 5 and 20 percent by volume, when cured. It has been found that when using resin compositions of this type, the sets of cube corners with a minimum floor area thickness or without it can be more easily shaped, because of this high flexibility is achieved. For example, resin compositions that contract when cured will tend to retract into the cavity in the form of cube corners, tending to leave a floor area that contacts only the adjacent cavities and therefore adjacent cubic corners with a narrow portion if applied to the tool in appropriate quantities. The narrow portion is easily broken resulting in a decoupling of the individual corner-corner elements as discussed below. The layered material can be formed in theory essentially without a floor area making contact with adjacent cube corner elements, however, in typical high volume manufacturing arrangements, a minimum floor area will be formed that has a thickness of up to 10 percent of the height of the cubes, preferably in the order of 1 to 5 percent. Resins selected for use in the set of cube corner elements include the crosslinked acrylate such as mono- or multifunctional acrylates or acrylated epoxies, acrylated polyesters, and acrylated urethanes mixed with mono- and multifunctional monomers are typically preferred. Those polymers are typically preferred for one or more of the following reasons: high thermal stability, environmental stability, and clarity, excellent release of the tooling or mold, and high receptivity to receiving a reflective coating. Examples of suitable materials for forming the set of cube corner elements are reactive resin systems capable of being crosslinked by a mechanism of free radical polymerization by exposure to actinic radiation, eg, electron beam, ultraviolet light , or visible light. Additionally, those materials can be polymerized by thermal means with the addition of a thermal initiator such as benzoyl peroxide. It is also possible to use cationically polymerizable resins initiated with radiation. Reactive resins suitable for forming the set of cube corner elements can be mixtures of a photoinitiator and at least one compound bearing an acrylate group. Preferably, the resin mixture contains a monofunctional, a difunctional or a polyfunctional compound to ensure the formation of a polymer network, crosslinked with the irradiation. Illustrative examples of the resins that are capable of being polymerized by a free radical mechanism that can be used herein include acrylic based resins derived from epoxies, polyesters, polyethers, and urethanes, ethylenically unsaturated compounds, aminoplast derivatives having at least one suspended acrylate group, isocyanate derivatives having at least one suspended acrylate group, epoxy resins other than acrylated epoxides, and mixtures and combinations thereof. The term acrylate is used herein to encompass both acrylates and methacrylates. U.S. Patent No. 4,576,850 (Martens) publishes examples of the crosslinked resins that can be used in the cube corner element assemblies. Ethylenically unsaturated resins include both monomeric and polymeric compounds containing carbon, hydrogen and oxygen atoms, optionally nitrogen, sulfur, and halogens can be used herein. Oxygen or nitrogen atoms, or both, are generally present in the ether, ester, urethane, amide and urea groups. The ethylenically unsaturated compounds preferably have a molecular weight less than about 4,000 and are preferably esters made from the reaction of the compounds containing aliphatic monohydroxide groups, aliphatic polyhydroxide groups, and unsaturated carboxylic acids, such as acrylic acid, methacrylic acid , itaconic acid, crotonic acid, isocrotonic acid, maleic acid and the like. Such materials are typical and readily commercially available and can be easily crosslinked. Some illustrative examples of the compounds having an acrylic or methacrylic group which are suitable for use in the invention are listed below: (1) Monofunctional compounds: ethylacrylate, n-butylacrylate, isobutylacrylate, 2-ethylhexylacrylate, n-hexylacrylate, n-octyl acrylate, isooctyl acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, 2-phenoxyethyl acrylate, and N, N-dimethylacrylamide; (2) Difunctional compounds: 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, ethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, and diethylene glycol diacrylate; and (3) Polyfunctional compounds: trimethylolpropane triacrylate, pentaerythritol glycerol triacrylate, pentaerythritol tetraacrylate, and tris (2-acryloyloxyethyl) isocyanurate. Monofunctional compounds typically tend to provide faster penetration of the superimposed film material and difunctional and polyfunctional compounds typically tend to provide stronger, more crosslinked bonds within and between the cube corner elements and the superimposed film. Some representative examples of other ethylenically unsaturated compounds and resins include styrene, divinylbenzene, vinyl toluene, N-vinyl formamide, N-vinyl pyrrolidone, N-vinyl caprolactam, monoallyl, polyallyl, and polymethallyl esters such as diallyl phthalate and diallyl adipate. , and carboxylic acid amides such as N, N-diallyladipamide. Illustrative examples of the photopolymerization initiators that can be mixed with acrylic compounds in the cube corner assemblies include the following: benzyl, methyl o-benzoate, benzoin, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether , etc., benzophenone / tertiary amine, acetophenones such as 2,2-diethoxyacetophenone, benzyl methyl ketal, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-l-one, 2-benzyl-2-N, N-dimethylamino-1- (4-morpholinophenyl) -1-butanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2 -methyl-l-4 (methylthio), phenyl-2-morpholino-1-propanone, bis (2,6-dimethoxybenzoyl) (2,4,4-trimethylpentyl) phosphine oxide, etc. The compounds can be used individually or in combination. The cationically polymerizable materials which include but are not limited to materials containing epoxy and vinyl ether functional groups can be used herein. These systems are photoinitiated by onium salt initiators, such as triarylsulfonium salts, and diaryliodonium. Preferably, the superimposed film used is a polymeric material selected from the group consisting of ionomeric ethylene copolymers, plasticized vinyl halide polymers, acid-functional polyethylene copolymers, aliphatic polyurethanes, aromatic polyurethanes, other light-transmitting elastomer and combinations of the same. Such materials typically provide superimposed films imparted with desired durability and flexibility to the resulting retroreflective, layered material while allowing the preferred penetration desired by the resin composition of the cube corner elements.

The superimposed film preferably comprises a low modulus of elasticity polymer, for example, less than about 13 x 108 pascals, to impart easy bending, bending, bending, shaping or stretching to the resulting retroreflective composite. In general, the overlay comprises a polymer having a glass transition temperature of less than about 50 ° C. The polymer is preferably such that the superimposed film retains its physical integrity under the conditions that it is exposed so that the resultant layered, retroreflective, composite material is formed. The polymer desirably has a Vicat softening temperature that is greater than 50 ° C. The linear mold shrinkage of the polymer is desirably less than 1 percent, although certain combinations of polymeric materials for the cube corner elements and the superposed layer will tolerate a greater degree of shrinkage of the polymer.

»Superimposed layer material. Preferred polymeric materials used in the overlay are resistant to radiation degradation of UV light such that the retroreflective, layered material can be used for long-term outdoor applications. The superimposed film will transmit light and is preferably substantially transparent. The superimposed film can be either an individual layer or a multilayer component as desired. Any surface of the superimposed film may contain printed or shaped symbols (such as embossed or embossed). If it is multi-layered, the layer to which the set of the cube corner elements is attached will have the properties described herein so useful in that respect with other layers not in contact with the set of cube corner elements having characteristics. selected as necessary to impart desired characteristics to the layered, retroreflective, composite, resulting material. An alternative overlay is published in US Patent Application Serial No. 08 / 516,165 filed August 17, 1995. The overlay film will be sufficiently extensible to achieve decoupling of the cube corner elements as discussed herein. . It can be elastomeric, that is, it tends to recover at least some degree after being elongated, or it may not have substantially a tendency to recover after being elongated, as desired. Illustrative examples of the polymers that may be employed in overlaying films herein include: (1) Fluorinated polymers such as: poly (chlorotrifluoroethylene), for example, KEL-F800 Brand available from Minnesota Mining and Manufacturing, St. Paul, Minnesota; poly (tetrafluoroethylene-co-hexafluropropylene), for example EXAC FEP Brand available from Norton Performance, Brampton, Massachusetts; poly (tetrafluoroethylene-co-perfluoro (alkyl) vinyl ether), for example EXAC PEA Brand also available from Norton Performance; and poly (vinylidene fluoride-co-hexafluoropropylene), for example, KYNAR FLEX-2800 Brand available from Pennwalt Corporation, Philadelphia, Pennsylvania; (2) Ionomeric ethylene copolymers such as: poly (ethylene-co-methacrylic acid) with sodium or zinc ions such as SURLYN-8920 Brand and SURLYN-9910 Brand available from E.l. duPont Nemours, Wilmington, Delaware; (3) Low density polyethylenes such as: low density polyethylene; linear low density polyethylene; and very low density polyethylene; (4) Plasticized vinyl halide polymers such as plasticized poly (vinylchloride); 10 (5) Polyethylene copolymers including: acid-functional polymers such as poly (ethylene-co-acrylic acid) and poly (ethylene-co-metracrylic acid), poly (ethylene-co-maleic acid), and Poly (ethylene-co-fumaric acid); acrylic-functional polymers such as poly (ethylene-co-alkyl acrylates) where the alkyl group is methyl, ethyl, propyl, butyl, etc., or CH3 (CH2) n- where n is 0 to 12, and poly (ethylene-co-vinylacetate); and (6) Aliphatic and aromatic polyurethanes derived from the following monomers (1) - (3): (1) diisocyanates such as dicyclohexylmethane-4, -diisocyanate-diisocyanate, isophorone diisocyanate, 1,6-hexamethylene diisocyanate, cyclohexyl diisocyanate, diphenylmethane diisocyanate, and combinations of those diisocyanates, (2) polydioles such as polyethylene dipate glycol, polytetramethylene glycol ether, polycaprolactone diol, poly-1,2-butylene glycol oxide and combinations of those polydioles, and (3) expanders of chain such as butanediol and hexanediol. Commercially available urethane polymers include: PN-04, or 3429 from Morton International Inc. Seabrook, New Hampshire, or X-4107 from B. F. Goodrich Company, Cleveland, Ohio. The combinations of the above polymers can also be used in the superimposed film. Preferred polymers for the superimposed film include: ethylene copolymers containing carboxylic groups or carboxylic acid ester units such as poly (ethylene-co-acrylic acid), poly (ethylene-co-methacrylic acid), poly (ethylene) -co-vinylacetate); the ionomeric ethylene copolymers; plasticized poly (vinylchloride); and the aliphatic urethanes. These polymers are preferred for one or more of the following reasons: suitable mechanical properties, good adhesions to the cube corner layer, clarity and environmental stability. Dyes, ultraviolet absorbents ("UV"), light stabilizers, scavengers or free radical antioxidants, processing aids such as antiblocking agents, release agents, lubricants and other additives can be added to one or both of the retroreflective layer and the superimposed film if you want, either uniformly in the configuration of a symbol. The particular dye, selected depends on the desired color; dyes are typically added at about 0.01 to 1.5 weight percent for a given layer. UV absorbers are typically added at about 0.5 to 2.0 weight percent. Illustrative examples of suitable UV absorbers include benzotriazole derivatives such as TINUVIN Brand 327, 328, 900, 1130, TINUVIN-P Brand, available from Ciba-Geigy Corporation, Ardsley, New York; benzophenone chemical derivatives such as UVINUL Brand M40, 408, D-50, available from BASF Corporation, Clifton, New Jersey; SYNTASE Brand 230, 800, 1200 available from Neville-Synthese Organics. Inc., Pittsburgh, Pennsylvania; or chemical derivatives of diphenyl acrylate such as UVINUL Brand N35, 539, also available from BASF Corporation of Clifton, New Jersey. Light stabilizers that can be used include hindered amines, which are typically used in about 0.5 to 2.0 weight percent. Examples of hindered amine light stabilizers include TINUVIN Brand 144, 292, 622, 770, and CHIMASSORB Brand 944 all available from Ciba-Geigy Corp., Ardsley, New York. The hindered, alternative amines are published in U.S. Patent No. 5,387,458. Free radical scavengers or antioxidants can be used, typically, at about 0.01 to 0.5 percent by weight. Suitable antioxidants include hindered phenolic resins such as IRGANOX Brand 1010, 1076, 1035, or MD-1024, or IRGAFOS Brand 168, available from Ciba-Geigy Corp., Ardsley, New York. Small amounts of other processing aids, typically not more than one weight percent of the polymer resins, can be added to improve the processability of the resin. Processing aids, useful include fatty acid esters, or fatty acid amides available from Glyco Inc., Norwalk, Connecticut, metal stearates available from Henkel Corp., Hoboken, New Jersey, or WAX E Brand available from Hoechst Celanese Corporation, Somerville, New Jersey. The present retroreflective article can be manufactured according to two different techniques. In the first technique, a retroreflective article is manufactured by providing a first layer material of cube corners having the cubes arranged in a conventional configuration, i.e., a non-random orientation, and the deformation of this material in layers under heat and / or pressure. In the second technique, the retroreflective, deformed article can be used to create a tooling. The tooling can be used as a mold to mold or shape additional retroreflective articles. In one embodiment, the retroreflective article of the present invention is fabricated by thermoforming the retroreflective, cube-corner material on a three-dimensional, structured surface of a mold, as illustrated in Figures 11 and 12. In the Figure 11, the cube corner elements 150 are placed on the structured surface of a mold 152. The superimposed film 154 is located opposite an insulation fabric 156 to prevent the overlay 154 being molded or adhered to the diaphragm 158. Alternatively, the diaphragm 158 may have release properties that perform the function of the insulation cloth 156. The heat and / or pressure is applied to the layered, retroreflector 160 material through the thermoforming diaphragm 158. The three-dimensional shape of the molle 152 may also be Include a variety of embossed symbols. In an alternative embodiment illustrated in Figure 12, the superimposed film 170 is placed on the structured surface of a mold 172. The cube corner elements 174 are located opposite an insulation fabric 176. The heat and / or pressure are applied to the layered, retroreflector 180 material through the diaphragm 178. A suitable apparatus for thermoforming the layered, retroreflective material to form the present retroreflective article is available under the designation of manufactured Scotchlite ™ Heat Lamp Vacuum Applicator available from Dayco Industries, Inc Of Niles, MI or PM Black Co. Of Stillwater, M. The important variables of the thermoforming process that can determine the nature of the retroreflective article created include temperature, pressure, duration of each, thickness and thermal characteristics of the thermoforming diaphragm and the nature of the surface structured in the mold. The size, uniformity and rigidity of the mold can also alter the processing specifications of the thermoforming process as well as whether the mold has an optical or non-optical model. The manufacture of the layered, retroreflective material, such as the thickness, the softening temperature and the extensibility of the superimposed film, the size of the cube corner elements, the presence or absence of a vapor coating, whether a film of Sealing is present and the optical design of the material in layers, retroreflector can also determine the processing variables of the thermoforming. The vacuum forming produces a retroreflective article in which the superimposed film becomes thinner in proportion to the distance that the layer travels to make contact with the molding surface. Accordingly, the spacing gradient between the adjacent cube corner elements increases from the top of a projection in the mold towards the bottom of the depression. The increased spacing generally produces a lower retroreflectivity. Additionally, if the material in layers, retroreflector includes a sealing film, the film is visible through the space between the cube corner elements. The sealing film can be applied either before or after the deformation of the layered material, "cube corners.The sealing film can include one or more colors that would be visible during the observation during the day. which elements of cube corners of the layered material, retroreflector are covered with a specular reflector, a subsequent, colored coating can be visible through the separations between the elements of cube corners. A subsequent, colored coating or an adhesive serves to soften or alter the color and reduces the "gray color" of the specular reflector layer. Alternatively, the specular reflector may be a "non-silvery" color, such as copper. In an alternative embodiment, the retroreflective, layered material can be deformed by falling or draping. The thickness distribution of the superposed film using the falling or draping formation is opposite to the vacuum formation, so that the spacing gradient between the cube corner elements is increased along the upper part of protrusions during the formation, while the spacing between the cube corner elements along the bottom of a depression generally remains the same. Layered, retroreflective material can also be stretched in one or more directions before or during deformation. Stretching increases the space between adjacent cube corner elements and thus reduces retroreflectivity. Reduced retroreflectivity may be desirable for some applications. In an alternative embodiment of the present invention, the retroreflective article of the present invention can be used to prepare an original tooling which in turn can be used to prepare additional retroreflective articles. Layered, retroreflective material can be prepared directly from the tooling. The use of such originals produces the material in layers that is capable of retroreflecting the light and exhibits the objective optical properties of the original retroreflective article from which the tooling was prepared. You can also duplicate printed images, deposited, or shaped directly on the back side, exposed from the cube corner elements by various techniques in the mold manufacturing process.

Angularity Angularity refers to the concept of how retroreflectivity varies as the input angle varies. The retroreflectivity varies according to the angle of entry and the angle of observation. The angle of entry is the angle between a lighting axis of a light source and a normal retroreflective axis to the surface of the retroreflective article. The entrance angle is usually no larger than 90 °. Angularity is typically described in terms of a retroreflectivity diagram on the vertical axis versus the input angle on the horizontal axis. When the illumination axis, the observation axis and the retroreflector axis are in the same plane, the entry angle can be considered negative when the retroreflective axis and the observational axis are on opposite sides of the illuminating axis. The angle of observation is the angle between the axis of illumination of the light source and the axis of observation. The angle of observation is always positive and is typically an acute, small angle.

Optical Profile The optical profile refers to the concept of the rotational and orientational symmetry of a retroreflective article. The rotational and orientational symmetry refers to how the retroreflective light varies as the retroreflective article is rotated with respect to a perpendicular normal to the retroreflective surface. The diagrams of the symmetry of the rotation indicate how the retroreflective performance of an article will vary when it is oriented in different directions with respect to this axis. Figure 3 is an example of a diagram of an optical profile.

EXAMPLES The features and advantages of this invention are further explained in the following illustrative examples. For the purposes of these Examples, the retroreflective, layered material includes cube corner elements with optical axes inclined relative to one another, as generally shown in US Patent No. 4,588,258 issued to Hoopman.

Brightness Test of Retrorref lectivity The retroreflectivity coefficient, Rñ, was measured according to the standardized test ASTM E 810-93b. The values of RA are expressed in candelas per lux per square meter (cd »lx_1« m ~ 2). For the observation angle scans, the other test parameters were kept constant at: input angle = -4.0 degrees orientation angle = 0.0 degrees presentation angle = 0.0 • For the input angle scans, the other test parameters they were constant at: angle of orientation = 0.0 degrees observation angle = 0.2 degrees presentation angle = 0.0 Example 1- Preparation of a retroreflective layer, flexible A percentage by weight of Darocur Brand 4265 (50:50 mixture of 2-hydroxy-2-methyl-1-phenylpropan-1-one and 2,4,6-trimethylbenzoyldiphenylphosphine oxide, available from Ciba-Geigy Corp., Hawthorne, NY) was added to a mixture of 40 weight percent resin of Photomer Brand 4035 (phenoxyethyl acrylate available from Henkel Corp. Of Ambler, PA) and 60 weight percent of Photomer Brand 3016 (bis-phenol A epoxy acrylate available from Henkel Corp. Of Ambler , PA), and 1 weight percent Darocur 1173 (2-hydroxy-2-methyl-1-phenylpropan-1-one, available from Ciba-Geigy Corp., Hawthorne, NY). The resulting solution was used as a resin composition to form the cube corner elements. The resin composition was molded into a 0.152 mm (0.006 inch) thin aliphatic polyurethane superimposed film (MORTHANE Brand 3429 urethane from Morton International, Inc., Seabrook, NH) in a polyethylene terephthalate (PET) carrier film. The coated film was passed between a polyurethane press roll and the nickel electro-formed tool to create cube corner elements of 62.5 microns (0.0025 inches) high at 57 ° C (135 ° F). The space between the durometer 90 polyurethane rubber press roller and the nickel tool was adjusted to decrease the resin in the cavities. The resin was cured through both the superimposed film and the carrier film with an AETEK medium pressure mercury lamp (available from AETEK International of Plainfield, IL) adjusted to 160 watts / cm (400 W / inch). The feed rate of the material through the curing station was 1,524 meters / minute (5 fpm). With the termination of the micro-duplication process and the removal of the tool, the compound side with the cube corner elements was subsequently cured by irradiating it with a medium pressure mercury lamp (AETEK International) operating at 80 watts / cm (200 w / inch).

Example 2 - Retrorref Readers Articles Vacuum Formed The retroreflective, layered material of Example 1 was placed in a fixation structure with the flat side (superimposed film) of the film facing up in a vacuum forming machine Type Comet, Jr. , Model 10X10 from Comet Industries, Inc., of Sanford, FL. After heating the film to approximately 150 ° C using the resistance heater in the vacuum former, the film began to soften (approximately 20 seconds). The softened composite film was quickly lowered in a porous molding that carried a rectangular set of depressions of ~ 1.59 cm (0.625 inches) in diameter, hemispherical, 90 (9 x 10) while a vacuum was applied to the mold. The softened film formed a retroreflective layer with retroreflective hemispherical recesses or depressions, shown both in a planar view and a perspective view in Figure 13. Figure 16 illustrates an alternative retroreflective article with hemispherical protrusions formed using the process of the present Example .

Figure 14 is a photomicrograph (50X) taken from the cubic side of the retroreflective, layered material deformed at the bottom of a vacuum formed depression of Figure 13. Figure 15 is a photomicrograph (50X) taken from a depression formed by vacuum on the side of the superimposed layer. The elements of cube corners are shown in dark and the separations between them are blank. The photomicrograph illustrates a relationship of the base edge of the cube corner elements to the separations between them being in the range of about 0.5: 1 to 2: 1. The cube corner elements are nominally adjacent to one another before deformation. However, as is clear from Figures 14 and 15, the vacuum forming process stretches and thins the superimposed surface film and increases the separation of the cube corner elements at the bottom of a depression. The overall uniform spacing between the cube corner elements is increased by heating the layered, retroreflective material to soften the superposed film prior to vacuum forming.

Example 3 The retroreflective layer material of Example 1 was placed in a fixing structure with the flat side of the film facing downwards. The film was heated using the method of Example 2 until the film began to soften (approximately 10-15 seconds). The softened composite film is quickly lowered into a porous mold bearing a rectangular set of hemispherical depressions of 90 (9 x 10) (~ 1.90 cm in diameter (~ 0.75 inches)), as illustrated in Figure 13, while that a vacuum was applied to the mold. The softened film formed a reflecting sheet with hemispherical, retroreflective projections. Figure 17 is a photomicrograph (50X) taken from the cubic side of the layered, retroreflective material deformed at the top of the projection formed by vacuum. Figure 18 is a photomicrograph (50X) taken from a projection formed by a vacuum on the side of the superimposed layer. The cube corner elements are shown in dark and the separations between them are blank. The cube corner elements are nominally adjacent to each other. However, as is clear from Figures 17 and 18, the vacuum forming process stretches and thins the superimposed film and increases the spacing of the cube corner elements on the top of a projection. The separations between the cube corner elements are random due to non-uniform heating and stretching, mainly a function of the shortened heating cycle. Some elements of cube corners are grouped together, others are isolated. The random separation of the cube corner elements created a bright visual appearance. It will be understood that the spacing between the cube corner elements can be further altered by controlling the stretch ratio of the film superimposed on the mold. The present photomicrographs of the material in layers, retroreflector with increased brightness showed a substantially larger degree of reorientation and separation of the cube corner elements, which is present in a layered, retro-reflective material without deforming. It is believed that the increased gloss effect refers to the additional, reflective paths available for the light incident in adjacent cube corner elements. Accordingly, there is a general range of bright image shaping abilities of the retroreflective article of the invention that can be achieved by changing the processing variables.

Example 4 - Article Retrorreflector, shaped, filled Layered material, retroreflector of the Example 1 was metallized by vapor deposition of the aluminum metal in the cube corner elements. The layered, retroreflective, metallized material was vacuum formed with the flat side of the film in contact with a mold to form a series of letters that spelled the word "VIPER" like that sample in Figure 19. While the formed film still in the mold, a two-part polyurethane was emptied into the cavity to fill the cube corner elements and thermally cured. The individual letters were cut and adhered to a steel plate with a black enamel coating. Layered, retroreflective material is generally flat, except along the transitional edges of the letters. The retroreflective article exhibited normal retroreflectivity along the flat surface. Some brightness effect was observed, located along the transition edges of the letters.

Example 5 - Preparation of a Layered, Retroreflective, Flexible Material A mixture of 1 percent by weight of Darocur Brand 4265 (50:50 mixture of 2-hydroxy-2-methyl-1-phenylpropan-1-one and oxide) of 2,4,6-trimethylbenzoyldiphenylphosphine, available from Ciba-Geigy Corp., Hawthorne, NY) was added to a 19 weight percent resin blend of PHOTOMER Brand 3016 (epoxy bisphenol A diacrylate, available from Henkel Corp. , Ambler, PA), 49.5 weight percent of TMPTA (trimethylolpropane triacrylate) and 30.5% of Sartomer 285 (THFA is tetrahydrofurfuryl acrylate, available from Sartomer Corp.). This resin composition was molded at 57 ° C (135 ° F) between a tool with 85 micron (0.0034 inch) high cube corner elements and a 0.114 mm (0.0045 inch) thick superimposed aliphatic polyurethane film ( MORTHANE Brand 3429 urethane from Morton International, Inc., Seabrook, NH) on a 0.65 mm (0.002 inch) thick polyethylene terephthalate (PET) carrier film. The space of the rubber press roller was adjusted to decrease the amount of the resin composition on the cavities of the tool. The resin was cured through both the superimposed film and the carrier film with an AETEK medium pressure mercury lamp (available from AETEK International of Plainfield, Illinois) was adjusted to 160 watts / cm (400 watts / inch). The rate of feed of the material through the curing station was controlled to reach the desired degree of cure (exposed from 100 to 1000 milij oules / cm2). After the microduplication process was finished, the side of the cube corners of the composite material was cured again by irradiating it with a medium pressure mercury lamp (AETEK International) operated at 80 watts / cm (200 W / inch).

Example 6 - Layered Material, Retroreflector, Sealing The layered, retroreflector material of Example 5 was thermally sealed to a white polyurethane sealing film as follows. A laminated sample of the layered material, retroreflector and the sealing film was prepared by first protecting it with 0.025 mm (0.001 inch) polyester teraphthalate film. This fabrication was then fed into a nip between a heated steel relief roller and a durometer 85 rubber roller. The sealing film was an aliphatic polyester urethane, pigmented (Ti2), 0.05 mm white (0.002 mm). inches) thick (MORTHANE Brand PN03 supplied by Morton International, Seabrook, New Hampshire). The relief model was of a chain link configuration and the surface of the relief roller was at 220 ° C (410 ° F). The surface temperature of the rubber roller was 63 ° C (145 ° F). The rollers were turned at a surface velocity of 6.09 meters / minute (20 feet / minute), and the contact line force was maintained at 114 Newtons / centimeter (65 pounds / inch). The protective layers of polyester teraphthalate were removed from the samples before further use.

Example 7 - Preparation of the License Plate A 152.4 x 304.8 mm (6"x 12") piece of the layered, retroreflector material with a sealing film was prepared as described in Example 6. The layered material of cubes, then sealed was laminated to a sensitive adhesive to pressure with a protective coating number 467 MP available from Minnesota Mining and Manufacturing Company of St. Paul, M. The protective coating was removed and the layered material was laminated to a white, flat license plate blank. The resulting article was stamped using conventional license plate stamping techniques. The sample was stamped very well and did not extend over the letters. In view of that, the sample was noticeably brighter and white than the material in layers of license plates, spheres, conventional. The measure candela / lux / square meter was 200 in the horizontal direction and 300 in the vertical direction.

Example 8 - Layered material, retroreflector, Flexible stamped on a Wire Cloth The retroreflective, layered material of Example 6 using a pressure sensitive adhesive is run on five samples of small-screen industrial wire cloth, as shown in Figure 20. Thermal lamination of the retroreflective, layered material is preferable, because it helps shape the material in layers, retroreflector for the fundamental metal network. The industrial metallic net of Figure 20, observed from left to right, was sold under the product designations: NO 888 Regent-nylon 6.35 mm (0.25 inches) square; NO 916 Nylon delta 1.3 cm (0.5 inch) hexagonal; 504-nylon 1.3 cm (0.5 inch) square; PE-101 polyester 1.59 cm (0.625 inch) hexagonal; and the horizontally oriented specimen - NO 61339 3.175 mm (0.125 inch) hexagonal polyester, all available from Sterling Net Co. of Montclair, NJ. The metal net changed both the angularity of the cube corner elements and acted as a filler or a cushion for the layered, retroreflective, stamping material. The portion of the material in layers, retroreflector deformed by the metal net is shown in white and the space between the metal net is shown in black. A localized brightness effect was visible along the precise transition regions in the layered, retroreflective material deformed onto the metallic lattice. It will be understood that a layered, retroreflective, metallized material with a suitable adhesive can be stamped alternately on the metal net. One possible use could be in the provisional pavement markings, which need a different angularity of the material in layers, retroreflective, normal, as well as a damping when running on a car.

Example 9 The retroreflective, layered material of Example 1 was formed by vacuum in a mold bearing a ® symbol approximately 6.35 mm in diameter. Figure 21 is a photomicrograph (50X) taken from the side of the superimposed layer of the retroreflective, layered material. The elements of cube corners are shown in black and the separations in white. The asymmetry of the ® symbol prevented a uniform pattern, which results in a substantial randomization of the cube corner elements.

Example 10 A retroreflective, unsealed, layered material according to Example 5 with 0.086 mm (0.0034 inch) high cube corner elements was thermoformed onto an abrasive paper coated with 60, 100, 150 and 220 granules available of Minnesota Mining and Manufacturing Company of St. Paul, MN using the Scotchlite ™ Heat Lamp Vacuum Apllicator discussed above. The cube corner elements were placed opposite the coated abrasive paper. The baking cycle included heating the applicator to about 118 ° C and baking for about 1.5-2.5 minutes. The lamp bench was lifted at the end of the baking cycle to cool the retroreflective items. Figure 22A is a diagram of the relative brightness against the entry angle for the resulting retroreflective articles. Figure 22B is a diagram of the relative brightness against the viewing angle. The control diagram is the layered material, retroreflector, without deforming. The retroreflective article has a glossy appearance probably due to the high level of randomization of the base edges of the cube corner elements.

Example 11 A retroreflective, unsealed layer material according to Example 5 with 0.086 mm (0.0034 inch) high cube corner elements was metallized by vapor deposition of aluminum metal onto the corner elements of Cube. The metallized, retroreflective, layered material was thermoformed onto an abrasive paper coated with granules of 60, 100, 150 and 220 according to the method of Example 10. The granule designations refer to abrasive particles with diameters no larger than 551 microns , 336 microns, 169 microns and 100 microns, respectively. The cube corner elements were placed opposite the coated abrasive paper. Figure 23A is a diagram of the relative brightness against the entry angle for the resulting retroreflective articles. Figure 23B is a diagram of the relative brightness against the observation angle. The control diagram is the material layered, retroreflective, metallized, without deforming. The retroreflective article has a glossy appearance probably due to the high level of randomization of the base edges of the cube corner elements. The retroreflective, layered material was also thermoformed onto a spheres pavement marker available under the product designation of the Scotchlane ™ 5160 Aluminum Reinforced Tape from the Minnesota Mining and Manufacturing Company of St. Paul, MN according to the method of Example 10. Figure 23 is a bar graph showing the increase in whiteness of the. layered material, retro-reflective after the thermoforming process for the four models of coated abrasive paper and the pavement marker of spheres. Whiteness is measured using a spectrophotometer with an optical measurement system, bidirectional according to ASTM E 1349-90. The whiteness is believed to be an approximate measure of the glossy appearance of the layered, retroreflective material. The level of whiteness for the thermoformed retroreflective article on the abrasive paper covered with granules 100 is believed to be a function of the size of the cube corner elements relative to the granules of the coated abrasive paper. That is, the abrasive paper coated with granules 100 provided the highest level of randomization of the base edges of the 0.086 mm high cube corner elements.

Example 12 A retroreflective, unsealed, layered material according to Example 5 with 0.086 mm (0.0034 inch) tall cube corner elements was thermoformed onto a series of specimens using the method of Example 10. The specimen included a marker spheres pavement available under the product designation of Scotchlane ™ 5160 aluminum reinforced tape and an elevated pavement marker available under the product designation of a Stamark ™ A381 high performance tape, both from Minnesota Mining and Manufacturing Company of St Paul, MN; a tool for the manufacture of layered material, retroreflector with cube corner elements of 0.178 mm (0.007 inches) high; and a light diffuser available under the product designation Clear Prismatic from Plaskolite, Inc. of Columbus, OH. The elements of cube corners were placed opposite the specimens. Figure 24A is a diagram of the relative brightness against the entry angle for the resulting retroreflective articles. Figure 24B is a diagram of the relative brightness against the observation angle. The control diagram is the material in layers, retroreflective, without deforming. The variation in the glossy appearance of the retroreflective articles was presumably due to the various levels of randomization of the base edges of the cube corner elements.

Example 13 A retroreflective, unsealed, layered material according to Example 5 with 0.086 mm (0.0034 inch) high cube corner elements was metallized by vapor deposition of the aluminum metal on the cube corner elements. The layered material, retroreflector, metallized was thermoformed onto the pavement marker of spheres, the raised pavement marker and the light diffuser of Example 12 using the method of Example 10. The cube corner elements were placed opposite the specimens. Figure 25A is a diagram of the relative brightness against the entry angle for the resulting retroreflective articles. Figure 25B is a diagram of the relative brightness against the viewing angle. The control diagram is the layered, retro-reflective material without deforming.

Example 14 A retroreflective, layered material according to Example 5 with 0.086 mm (0.0034 inch) high cube corner elements was metallized by vapor deposition of the aluminum metal on the cube corner elements. The retroreflective, metallized, layered material was thermoformed using the method of Example 10 on an industrial propylene weft screen with a 1.27 cm (0.5 inch) hexagonal pattern, sold under the product designation N0916 by Sterling Net Co. of Montclair, NJ. The wire mesh softened during the thermoforming process and thus remained attached to the layered, retroreflective material. The elements of cube corners were placed opposite the specimens. Figure 26A is a diagram of the relative brightness against the entry angle for the resulting retroreflective articles. Figure 26B is a diagram of the relative brightness against the observation angle. The control diagram is the material in layers, retroreflective, without deforming.

EXAMPLE 15 Three samples of the retroreflective, unsealed, layered material according to Example 5 with the cube corner elements of different sizes were thermoformed onto an available pavement marker-low or the designation of the product of the reinforced tape. 5160 Scotchlane ™ Aluminum from Minnesota Mining and Manufacturing Company of St. Paul, M. The elements of cube corners were 0.0625 mm (0.0025 inches); 0.086 mm (0.0034 inches) and 0.178 mm (0.007 inches) in height, respectively. The largest gloss effect was visible in the layered material, thermoformed retroreflector over the 0.178 mm cubes. At least one amount of the gloss effect was visible on the layered, thermoformed retroreflector material on the .0625 cubes.

Example 16 A retroreflective, unsealed, layered material according to Example 5 with 0.086 mm (0.0034 inch) high cube corner elements was metallized by vapor deposition of the aluminum metal on the cube corner elements. The layered, retroreflective, metallized material was thermoformed on the cube corner side of three commercial reflectors. Reflector A was a 3-inch circumferential reflector divided into 6 cube-corner triangular prisms, sold as Model V472R from Peterson Manufacturing of Grandview, MO. Reflector B was a 7.62 cm (3 inch) circular reflector that has approximately 20 diamond-shaped models of 1.27 X 2.54 cm (0.5 X 1.0 inches) containing the cube corner elements, sold as Sate-Lite Model. 30 from KyKu Products of Bedford Heights, OH. The 6.35 X 7.62 mm (2.5 X 3.0 inch) rectangular reflector tube two vertical rows of the offset corner elements of one of the other, sold as Model PEC 4200C from The Refractory of Newburgh, NY. Figure 27A is a diagram of the relative brightness against the entry angle for the resulting retroreflective articles. Figure 27B is a diagram of the relative brightness against the observation angle. The control diagram is the material layered, retroreflective, metallized, without deforming. Figure 27C is a diagram of the relative brightness against the entry angle for the commercial reflectors illustrated in Figures 27A and 27B. Figure 27D is a diagram of the relative brightness against the viewing angle for commercial reflectors. All of the patents and patent applications mentioned above are incorporated in their entirety by reference in this document. The present invention has now been described with reference to various embodiments thereof. It will be apparent to those skilled in the art that many changes can be made in the described embodiments without departing from the scope of the invention. Thus, the scope of the present invention should not be limited to the structures described herein, but preferably by the structures described by the language of the claims, and the equivalents of those structures.

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.

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

Claims (1)

1. .3. The article according to claims 1-2, characterized in that the cube corner elements have a variable density through a portion of the retroreflective article, wherein the cube corner elements, adjacent through a portion of the retroreflective article they are variablely spaced, and wherein the superimposed film has a thickness that varies through a portion of the retroreflective article. 4. The article according to claims 1-3, characterized in that the cube corner elements of the retroreflective article are placed on the back side of the material in layers and filled with a coating. 5. The article according to claim 4, characterized in that the coating contains one or more colors. 6. The article according to claims 1-5, characterized in that the retroreflective layered material has its cube corner elements arranged such that an angle a between the faces of the adjacent cube corner elements varies between them along the Layered material 7. A method of forming a retroreflective article with at least one objective optical property, characterized in that it comprises the steps of: preparing a layered, retroreflector, cube corner material including a set of cube corner elements, discrete, having base edges, the set of cube corner elements is cured in situ on an overlay, polymeric, transparent film to form an interpenetration network between a thermoset material of the cube corner elements and the polymer superimposed film; and deforming the assembly such that the base edges of a plurality of cube corner elements reside in the same plane when the layered material is laid flat. 8. The method according to claim 7, characterized in that the deformation step results in the base edges of the plurality of adjacent cube corner elements being inclined with respect to each other. 9. The method according to claims 7-8, characterized in that the deformation step is selected from the group consisting of thermoforming, vacuum forming, stamping and combinations thereof. 10. The method according to claims 7-9, characterized in that the deformation step produces a three-dimensional symbol in the retroreflective, layered material.