MXPA06007614A - Color shifting retroreflector and method of making same - Google Patents

Abstract

Color shifting retroreflective articles can provide features such as decorative effects, evidence of tampering, security authentication or positional information. In some embodiments, the color shifting retroreflective article includes a layer of microspheres (14), and a reflective coating that is disposed in optical association with the layer of microspheres. The reflective coating includes a spacer layer (24) disposed between a semitransparent first reflective layer (22) and a second reflective layer (26). The first reflective layer includes a reflective layer disposed adjacent the layer of microspheres (t1, t2). At least one layer of the reflective coating includes a non-uniform thickness associated with each of a plurality of microspheres such that light incident on the article from a first direction is retroreflected at a first color and light incident on the article from a second direction is retroreflected at a second color visibly different from the first color.

Description

RETRORREFLECTOR OF CHANGE OF COLOR AND METHOD OF ELABORATION OF THE SAME BACKGROUND OF THE INVENTION Retroreflective articles have the ability to redirect incident light obliquely back to the light source. This unique ability has led to the wide-spread use of retroreflective articles in various substrates. For example, retroreflective articles can be used on flat inflexible substrates, such as signs and obstacles on streets or highways; on uneven surfaces, such as corrugated metal truck trailers, license plates and traffic barriers; and on flexible substrates, such as in the safety vests worn by highway workers, in shoes of the person practicing field sports, signs of upward movement and in trucks with side awnings. A type of retroreflective article includes pearls. These pearl articles typically use a plurality of glass or ceramic microspheres to retroreflect incident light. Normally, the microspheres are partially embedded in a support film, and a specular reflection material is provided between the microsphere layer and the support film. The Ref.:174252 reflection material may be a metal layer (eg, an aluminum coating such as is described in U.S. Patent Nos. 3,700,478 (Bingham 478) and 4,648,932 ( Bailey), an inorganic dielectric mirror consisting of multiple layers of inorganic materials having different refractive indexes (for example, as described in U.S. Patent Nos. 3, 700,305 (Bingham? 305) and 4,763,985 (Bingham 985 )) or an organic reflective coating consisting of multiple layers of polymer having different refractive indices (for example, as described in U.S. Patent No. 6, 172,810 Bl (Fleming et al., '810)). Categories of pearl retroreflective articles include types of exposed lens, enclosed lens and encapsulated lens.Exposed lens pearl articles have a layer of microspheres, the front sides of which are exposed to the medium The articles of encased lens beads have a protective layer, such as a transparent polymer resin that contacts and surrounds the front side of the microspheres. The encapsulated lens articles have an air gap surrounding the front side of the microspheres and a transparent film sealed in a sealing film in order to protect the microspheres from water, dust and other environmental elements.

Other references involving optical articles include U.S. Patent Nos. 5,877,895 (S aw et al., 895) and 6,083,628 (Yializis). SUMMARY OF THE INVENTION When a retroreflective article not inked at observation angles perpendicular or almost perpendicular to white light is observed, the retroreflective image is usually also white. When viewed at highly oblique angles almost at the angular boundary of the article due to retroreflectivity, the image may exhibit some color distortion or color alteration, an effect that is normally considered undesirable. However, if the retroreflective article was made to exhibit a perceptible color change at viewing angles less than the angular limit of the article due to retroreflectivity, the resulting effects of color may provide useful features that include decorative effects, the evidence of the manipulation, security authentication or position information. For example, the visibility and clarity of an object can be improved not only by the reflection light returning to its source, but also by retro-reflecting light color according to the information about the object, such as its orientation to the light source and the object's color change properties.

In one aspect, the present disclosure provides a retroreflective color change article that includes a layer of microspheres, and a reflective coating located in optical association with the layer of microspheres. The reflective coating includes at least one partially transparent spacer layer that is located between a first semitransparent reflective layer and a second reflective layer. The first reflective layer could be located, for example, adjacent to and between the microsphere layer and the spacer layer. The second reflective layer could be semitransparent or opaque and could be placed, for example, adjacent to the spacer layer. At least one layer of the reflective coating includes a non-uniform thickness associated with each of the plurality of microspheres, so that the light incident on the article coming from a first direction is retroreflected in a first color and the light incident on the article that comes from a second direction is retroreflected in a second color visibly different from the first color. In another aspect, the present disclosure provides a retroreflective color change article that includes a layer of microspheres, and a reflective coating that is placed in optical association with the layer of microspheres. The reflective coating includes a first semitransparent reflective layer adjacent to the microsphere layer. The reflective coating also includes an at least partially transparent spacer layer adjacent to the first reflective layer, and a second reflective layer adjacent to the spacer layer, so that the spacer layer is between the first and second reflective layers. The reflective coating reflects the visible light without uniformity, and a first predetermined area of the reflective coating associated with each microsphere of at least a plurality of microspheres includes a first thickness and a second predetermined area of the reflective coating associated with each microsphere at least a plurality of microspheres includes a second thickness different from the first thickness. In one aspect, the present disclosure provides a retroreflective color change article that exhibits a visually perceptible change in the color of retroreflected light at viewing angles that are not close to the angular limit of the article due to retroreflectivity. In another aspect, the present disclosure provides a method of making a retroreflective color change article that includes providing a layer of microspheres, and forming a reflective coating in optical association with the microsphere layer. The formation of the reflective coating includes the deposition of a first semitransparent reflective layer adjacent to the microsphere layer. The formation of the reflective coating further includes deposition in a spacer layer at least partially transparent on the first reflective layer, and deposition of a second reflective layer on the spacer layer. The reflective coating is formed so as to provide for each of the plurality of microspheres, a non-uniform thickness in at least one of the respective layers of the reflective coating, so that the light incident on the article coming from a first direction is retroreflected in a first color and the incident light on the article coming from a second direction is retroreflected in a second color visibly different from the first color. In another aspect, the present disclosure provides a method of making a retroreflective color change article that includes providing a layer of microspheres, and forming a reflective coating in optical association with the microsphere layer. The formation of the reflective coating includes the deposition of a first semitransparent reflective layer adjacent to the microsphere layer. The formation of the reflective coating further includes the deposition of an at least partially transparent spacer layer on the first reflective layer, and deposition in a second reflective layer on the spacer layer, so that the spacer layer is between the first and second reflective layers. The reflective coating reflects the visible light without uniformity, wherein a first predetermined area of the reflective coating associated with each microsphere of at least a plurality of microspheres includes a first thickness and a second predetermined area of the reflective coating associated with each microsphere of at least one The plurality of microspheres includes a second thickness different from the first thickness. The above summaries are not intended to explain each described modality or each implementation of the present invention. The Figures and the Detailed Description that follow exemplify, more particularly, the illustrative modalities. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a schematic cross-sectional diagram of one embodiment of a portion of a retroreflective article of color change. Figure 2 is an enlarged schematic view of a portion of a microsphere taken from region 2 of Figure 1. Figure 3 is a schematic diagram of one embodiment of a coating apparatus.

Figure 4 is a chromaticity diagram using the CIÉ x-y chromaticity coordinates for the retroreflective color change article of the Example. Figure 5 is a photograph of a portion of the color change retroreflective article of the Example taken using a scanning electron microscope. DETAILED DESCRIPTION OF THE INVENTION Figure 1 is a schematic cross-sectional diagram of a portion of an embodiment of a retroreflective article of beads 10. The retroreflective article 10 includes optical elements in the form of a layer of microspheres 12 partially embedded in a layer of binder 30. A reflective coating 20 is located between the layer of microspheres 12 and the layer of binder 30, so that the reflective coating 20 is in optical association with the layer of microspheres 12. As used herein, the The term "optical association" refers to the reflective coating 20 that is positioned relative to the layer of microspheres 12, so that a significant portion of light transmitted through each microsphere 14 may collide or impinge on the reflective coating 20 and be reflected back to the microsphere 14. The optional substrate layer 40 can be used to add support and structural The retroreflective article of beads 10 as illustrated in Figure 1 is commonly referred to as a retroreflective article of "exposed lens" beads. A retroreflective article of "exposed lens" beads is one in which the optical elements, in this case the microspheres 14, are exposed to the ambient environment, namely air. Optionally, a cover layer (not shown) could be located on at least one portion of the microsphere layer 12 opposite the reflective coating 20, so as to cover or encapsulate the exposed portions of the microspheres 14 to make the articles retroreflective "encased lens" beads or "encapsulated lens." Examples of exposed lens articles are described, for example, in Bingham? 478; Bingham? 85 and in United States Patent No. 5, 812,317 (Billingsley et al.) Examples of encapsulated lens products are described, for example, in U.S. Patent Nos. 4, 896,943 (Tolliver et al.); 5, 066,098 (Rult et al.) and 5,784,198 (Nagaoka) Preferably, the microspheres 14 used in a pearl product of the disclosure are of a substantially spherical shape in order to provide a uniform and efficient retroreflection.Preferably, the microspheres 14 are also highly transparent to minimize the absorption of light, so that a large percentage of incident light is retroreflected. Often, the microspheres 14 are substantially colorless although they may be inked or colored in some other way. The microspheres 14 could be made from a glass or non-vitreous ceramic composition, or a synthetic resin. In general, glass and ceramic microspheres are preferred because they tend to be harder and more durable than microspheres made from synthetic resins. Examples of microspheres that could be useful are described in U.S. Patent Nos. 1, 175, 224 (Bleeker); 2, 461, 011 (Taylor et al.); 2, 726,161 (Beck et al.,? 161); 2, 842, 446 (Beck et al., 446); 2, 853,393 (Beck et al.,? 393) 2, 870, 030 (Stradley et al.); 2,939,797 (Rindone); 2, 965,921 (Bland); 2, 992, 1222 (Beck et al., 122); 3, 468,681 (Jaupain); 3, 946, 130 (Tung et al., 130); 4, 192.576 (Tung et al., V576); 4, 367, 919 (Tung et al.,? 919); 4, 564,556 (Lange '556); 4, 758,469 (Lange 69; 4, 772, 511 (Wood et al.,? 511) and 4, 931, 444 (Wood et al., 414) Commonly, microspheres 14 have an average diameter of approximately 10 to 500 μm. that the microspheres have an average diameter of approximately 20 to 250 μm.Smaller microspheres than those with these ranges tend to provide lower levels of retroreflection, and larger microspheres having these ranges could impart an undesirable rough texture to the retroreflective article 10 or could undesirably decrease their flexibility in embodiments in which flexibility is a desired property. Microspheres 14 used in the present disclosure typically have a refractive index of approximately 1.2 to 3.0. It could be preferred that the microspheres 14 have a refractive index of about 1.6 to 2.7. It may be more preferred that the microspheres 14 have a refractive index of about 1.7 to 2.5. The layer of microspheres 12 is partially embedded in a layer of binder 30, so that the binder layer 30 is adjacent to the reflective liner 20. The binder layer 30 could include any suitable material or materials, for example, polymers such as acrylics, urethanes, epoxies, rubber, olefins, polyvinyl chloride, copolymers or polyesters of ethylene vinyl acetate. The binder layer 30 could be formed using any suitable technique, as described further, for example, in Billingsley et al.,? 317. In some embodiments, the reflective liner 20 or one of the layers of the reflective liner 20 could act as the binder layer, so that a separate layer of binder 30 is not included in the article 10. Figure 2 shows an enlarged view of a portion of the microsphere 14 indicated by the region 2 in Figure 1. The reflective coating 20 includes a first reflective layer 22, a second reflective layer 26 and a transparent spacer layer 24 located between the first reflective layer 22 and the second reflective layer 26. The first reflective layer 22 could be made, for example, from one or more metals in one or more layers and is thin enough to be transparent. As used herein, the term "semitransparent" when used with respect to a reflective layer, refers to a layer that is partially reflective and partially transmissive to visible light. As used herein, the term "metal" refers to elemental metals and metal alloys. Examples of suitable metals include aluminum, chromium, nickel, nickel-chromium alloy, stainless steel, silver. The first reflective layer 22 could also be a stack of layers, each of which contains one or more inorganic or organic materials, with two or more of these layers having refractive indices that differ sufficiently to reflect the light. As used herein, the phrase "organic materials" refers to monomers, oligomers and polymers of organic or organometallic materials. Examples of suitable inorganic materials are described, for example, in Bingham? 305 and Bingham? 985. Examples of suitable organic materials are described, for example, in Bingham 305 and Bingham? 985 and in Fleming et al., '810. In this way, in some embodiments the first reflective layer 22 is a single layer of metal; in other embodiments, the first reflective layer 22 may include multiple layers. In some embodiments, the first reflective layer 22 is at least 25% transparent. In some embodiments, the first reflective layer 22 is approximately 50% transparent and 50% reflective. In some embodiments, the first reflective layer 22 has a thickness that is at least about 3 nm. In some embodiments, the first reflective layer 22 has a thickness that is less than about 200 nm. Although Figure 2 illustrates the first reflective layer 22 which is located and is in contact with the microsphere 14, one or more additional layers could be located between the first reflective layer 22 and the microsphere layer 12. For example, a layer or intermediate layers could be included between the layer of microspheres 12 and the first reflective layer 22 of the reflective coating 20. These intermediate layers are described, for example, in Billingsley et al., '317. These intermediate layers could be used in retroreflective articles to improve retroreflective optical devices. Depending on the refractive index of the microspheres 14, and if the article is an exposed lens retroreflector or an encapsulated lens retroreflector, these intermediate layers are of the order of 10 μm in thickness and can be used to place the reflective coating 20 in the focal point of the microsphere 14. The second reflective layer 26 could be placed on the spacer layer 24 opposite the first reflective layer 22. Although Figure 2 illustrates the second reflective layer 26 which is located and is in contact with the spacer layer 24, one or more additional layers could be located between the second reflective layer 26 and the spacer layer 24. The second reflective layer 26 could also include any suitable metal or metals, for example, aluminum, chromium, nickel, nickel-chromium alloy , stainless steel, silver, and could also be formed from a stack of layers, each of which contains one or more non-metallic materials. organic or organic, with two or more of these layers that have refractive indices that differ enough to reflect light. Thus, in some embodiments, the second reflective layer 26 includes a single layer; in other embodiments, the second reflective layer 26 could include multiple layers. In some embodiments, the second reflective layer 26 is substantially opaque. In some embodiments, the second reflective layer 26 has a thickness that is at least about 20 nm. In some embodiments, the second reflective layer 26 has a thickness that is less than about 200 nm. In some embodiments, the second reflective layer 26 could also be the binder layer 30. The first reflective layer 22 and the second reflective layer 26 could be formed or deposited using any suitable technique, for example, vacuum metallization, sputter coating. , evaporation, chemical vapor deposition (CVD) and improved plasma CVD. These and other convenient techniques will be known to those skilled in the art. In some embodiments, the retroreflective color change article 10 could include one or more additional layers. For example, an adhesion promoter could be provided between the layer of microspheres 12 and the reflective coating 20 as is further described herein. Additional exemplary layers may contain silane coupling agents for adhesion promotion as described, for example, in U.S. Patent No. 5,976,669 (Fleming). Located between the first reflective layer 22 and the second reflective layer 26 is the spacer layer 24. The spacer layer 24 could include any suitable material or materials at least partially transparent, for example, inorganic dielectric materials such as metal oxides, nitrides, oxynitrides, carbides, fluorides and borides; or solid organic materials including molecules, oligomers and polymers. In some embodiments, the spacer layer 24 may include a dielectric material. In some embodiments, the spacer layer 24 may include a monolithic acrylate polymer. The spacer layer 24 could include one or more layers. In the embodiment illustrated in Figure 2, the spacer layer 24 has a non-uniform thickness associated with one or more microspheres 14 in the microsphere layer 12. The average thickness of the spacer layer 24 can be, for example, at least 70 nm. In some embodiments, the spacer layer 24 can have an average thickness that is less than about 1000 nm. The spacer layer 24 could be formed using any convenient technique, for example, evaporation, plasma deposition, solution coating, extrusion coating, gravure coating or spray coating. These and other suitable techniques will be familiar to those skilled in the art. In some modalities, the spacer layer 24 is formed using a vacuum evaporation as further described herein. In some embodiments, at least one layer of the reflective liner 20 includes a non-uniform thickness associated with each microsphere 14 of a plurality of microspheres of the microsphere layer 12. This non-uniform thickness allows light incident on the retroreflective article to change from color 10 coming from a first direction is retroreflected in a first color and the light incident on the article 10 coming from a second direction is retroreflected in a second color visibly different from the first color. For example, as shown in Figure 1, the incident light I entering a microsphere 14 from a first direction (which in this case is approximately perpendicular to the layer 12) can be refracted towards the center of the microsphere 14, reflected outside the reflective coating 20 behind the microsphere 14, and redirected out of the microsphere 14 in the general direction of the incident light, as indicated by the reflected light beam R. When the incident light I finds the front of the coating reflective 20, a portion of the light is reflected by the first reflective layer 22, and another portion passes through the first reflective layer 22 and towards the spacer layer 24. At least a portion of the transmitted light is then reflected by the second reflective layer 26 and is retransmitted through the spacer layer 24. At least a portion of the retransmitted light passes through the first reflective layer 22, where it could interfere, onstructively or destructively, with the portion of the light that was reflected by the first reflective layer 22. As also shown in Figure 1, the incident light I 'entering the microsphere 14 from a second direction (which in this case is oblique with respect to the layer 12 but not close to the angular limit due to retroreflectivity) can be refracted towards the center of the microsphere 14, reflected outside the reflective coating 20 behind the microsphere 14 and redirected out of the microsphere 14 in the general direction of the incident light, as indicated by the reflected light beam R '. The incident light I and the reflected beam R move through a different thickness in the reflective coating 20 compared to the incident light I 'and the reflected beam R', whereby the color of the reflected beam R 'is caused to differ Visibly from the color of the reflected beam R. This color effect can be visually perceived at viewing angles less than the angular limit due to retroreflectivity, for example, by changing the viewing angle from the I direction to the I 'direction. In the embodiment illustrated in Figures 1-2, the spacer layer 24 includes a non-uniform thickness. In some embodiments, the first reflective layer 22 or the second reflective layer 26 could include a non-uniform thickness. In these embodiments, the article could present not only a change of color in angular function but also a change of intensity in angular function of retroreflected light. In other embodiments, more than one reflective coating layer 20 could include a non-uniform thickness. For example, as shown in Figure 2, the reflective liner 20 could include a first area 28 wherein the spacer layer 24 has an average thickness ti that is measured along the radius from almost the center of the microsphere 14. In a second area 29 of the reflective liner 20, the spacer layer 24 could have an average thickness t2. In the embodiment shown in Figure 2, the thickness t2 is larger than the thickness ti. The thickness of one or more of the layers of the reflective coating 20 could vary in any suitable manner in order to produce a non-uniform thickness. For example, the thickness could follow a thickness gradient. In the modality shown in Figure 2, the spacer layer 24 has a non-uniform thickness variation having a cross-sectional configuration in increasing shape behind the microsphere 14. The thickness of the spacer layer 24 could be a small multiple of a quarter wavelength of light due to constructive interference (allowing the refractive index of the dielectric material). When light is retroreflected through the spacer layer, light with the appropriate wavelength could have the beams reflected and transmitted in phase due to constructive interference. Light of other colors could have at least a partial destructive interference. When an article 10 with this spacer layer 24 is observed at a fixed angle in the white light, the article 10 could reflect a strong characteristic color, for example, blue or green. The spacer layer 24 could also have a thickness, so that the article 10 will retroreflect a colored light when illuminated at an incidence perpendicular to the white light. This combination of retroreflection and color could be easier to perceive the article, and when combined with the described change of color can make the item and its position or condition much clearer than if the item simply merged as a diffuse or specular white reflector or of color. The color reflected from article 10 may be a function of the length of the optical path of the light passing through the microsphere 14 and its respective reflective coating 20. When the article 10 is observed with a light at an incidence substantially perpendicular (ie, substantially perpendicular to the layer of the microspheres 12 of Figure 1), a certain color, e.g., green, would be observed. As described herein, a portion of the incident light of a shape substantially perpendicular to the layer of the microspheres 12 of article 10 will pass through the first reflective layer 22 and will pass through the spacer layer 24 next to the second area 29 of the Article 10. In the second area 29, the spacer layer has an average thickness t2. Therefore, the light will travel approximately twice the thickness t2 before a portion passes back through the first reflective layer 22 and the microsphere 14. When the angle of incidence and reflection of article 10 is oblique rather than perpendicular, the The total length of the optical path through the reflective liner 20 is shorter in the embodiment illustrated in Figure 2, because at least a portion of the light entering an oblique angle traverses a small region of the thickness of the spacer layer 24, such as the region near the first area 28 where the spacer layer 24 has an average thickness ti that is less than the thickness t2. Therefore, when the article 10 is observed at an oblique angle, a shorter wavelength color may be seen, for example, a blue color. In other words, the light incident on the article 10 coming from a first direction is reflected in a first color and the light incident on the article 10 coming from a second direction is retroreflected in a second color which can be visually different from the first color. Therefore, the retroreflective article of color change 10 reflects light without uniformity. It may be preferred that the first direction be substantially perpendicular to the layer of the microspheres 12. In addition, it may be preferred that the first and second directions differ by at least 10 °. It may be more preferred that the first and second directions differ by at least 30 °. In general, the color can be measured using the CIÉ 1931 Calorimetric Standard System. This system uses a two-dimensional diagram that includes the points specified by the chromaticity coordinates (x, y), which represent the chromaticities of the color stimuli in the CIÉ color matching system. The color of an article or region of an article can be specified by a point (x, y) or a region (expressed in terms of more than one chromaticity coordinate (x, y)) on the CIÉ chromaticity diagram (see example, Figure 4). The first and second colors reflected by the retroreflective color change article 10 can be characterized by the CIÉ chromaticity coordinates (xi, yi), (x2, y2), respectively. It might be preferred that the larger coordinates of) x2-x? | and | y2-y? | are at least 0.05. It could be more preferred than the larger coordinates of | x2-x? | Y | y2-y? | be at least 0.015. See, for example, J. A.

Dobrowolski et al., "Research on thin film anticounterfeiting coatings at the National Research Council of Canada" Applied Optical Devices, 28 (14): 2702-2717 (1989); Shaw et al. , '895.

The layers used in the reflective coating 20 to form the spacer layer 24 can be placed in optical association with the layer of microspheres 12 using the techniques now known or subsequently developed which are suitable for the deposition of layers of materials having desired thicknesses. These techniques can include solvent-loaded coating techniques, liquid reagent coating techniques, extrusion coating techniques, gravure coating techniques, physical and chemical vapor deposition techniques, plasma deposition techniques , film lamination techniques, and the like. Exemplary techniques of coating polymer layers include the pre-polymer vapor deposition methods taught in U.S. Patent No. 6, 503,564 (Fleming et al.,? 564). In short, these methods involve the condensation of a prepolymer vapor on a structured substrate, and the curing of the material on the substrate. These methods can be used to form polymer coatings having a controlled chemical composition and which preserve the fundamental profile of the structured substrate. Multiple coatings of the same or different material may be applied in this manner to form a spacer layer in a reflective coating.

Preferred methods of making reflective coatings in optical association with the microsphere layer of the color change retroreflective articles of the present disclosure may include aspects of the coating process shown in Figure 3. The process may be carried out at atmospheric pressure, optionally, enclosing the coating region in a chamber 118 (eg, to provide a clean environment, to provide an inert atmosphere or for other reasons), or at a reduced pressure where the chamber 118 is a vacuum chamber . As shown in Figure 3, the retroreflective color change article 112 is provided in the chamber 118. The color change retroreflective article 112 could include any retroreflective color change article suitable as described herein.

The retroreflective color change article 112 could include a layer of microspheres linked with a carrier film as described, for example, in U.S. Patent No. 6,355,302 (Vandenberg et al.). The microsphere layer could include the microspheres 111. In some embodiments, the article 112 could include a first reflective layer (e.g., the first reflective layer 22 of the Figure 2) formed prior to the placement of the color change retroreflective article 112 in chamber 118. Alternately, an optional deposition station 130 (eg, a metallization station) could be included in the chamber 118 to deposit a first reflective layer adjacent to the microsphere layer using any convenient technique, for example, vacuum metallization, bombardment ions, evaporation, chemical vapor deposition (CVD) and improved plasma CVD. Prior to deposition of the first reflective layer, the microsphere layer could be treated to promote adhesion of the first reflective layer in the microsphere layer. Any suitable technique could be used to treat the microsphere layer, for example, plasma treatment, corona treatment, flame treatment, UV / ozone treatment. In addition, one or more intermediate layers could be formed on the microsphere layer before the deposition of the first reflective layer as further described herein. A spacer layer (eg, the spacer layer 24 of Figure 2) is then deposited on the first reflective layer using the coating material 100. The coating material 100, supplied in the form of a monomer or liquid pre-polymer can be metered into the evaporator 102 by means of the pump 104. As described in detail herein, the coating material 100 can be evaporated by one of several techniques, including vacuum evaporation and vaporization of carrier gas collision. It may be preferred that the coating material 100 be atomized into fine droplets through an optional nozzle 122, the droplets being subsequently vaporized into the interior of the evaporator 102. Optionally, a carrier gas 106 can be used to atomize the coating material 100 and to direct the droplets through the nozzle 122 to the evaporator 102. The vaporization of the liquid coating material 100, or the droplets of the liquid coating material 100, can be effected by contacting the hot walls of the evaporator 102, also by contact with the optional carrier gas 106 (to which optionally, the temperature is increased by the heater 108) or by contact with some other hot surface. Any convenient operation for vaporization of the liquid coating material 100 is contemplated for use in this description. After vaporization, the coating material 100 can be directed through a coating matrix 110 and onto the first reflective layer of the retroreflective color change article 112. A mask (not shown) can optionally be placed between the matrix of coating 110 and the retroreflective color change article 112 to coat the selected portions of the first reflective layer. Optionally, the surface of the first reflective layer can be pre-treated using an electric discharge source 120, such as a light discharge source, a silent discharge source, a corona discharge source, or the like. The pretreatment step is optionally performed in order to modify the surface chemistry, for example, to improve the adhesion of the coating material 100 in the first reflective layer, or for other such purposes. In addition, the microsphere layer, the surface of the first reflective layer or both, can be pre-treated, optionally, with an adhesion promoter, as discussed herein. It may be preferred that the retroreflective color change article 112 be maintained at a temperature at or below the condensation temperature of the monomer vapor or pre-polymer leaving the coating matrix 110. The retroreflective color change article 112 the surface of the cylinder 114. may be placed on, or otherwise located in a temporal relationship. The cylinder 114 allows the retroreflective article 112 to be moved through the coating matrix 110 at a selected rate to control the thickness of the layer .

The cylinder 114 can also be maintained at a suitable forming temperature to maintain the retroreflective article 112 at or below the condensation temperature of the pre-polymer vapor. After condensation of the curing material 100 on the article 112, the liquid monomer or pre-polymer layer can be cured to form the spacer layer. In general, the curing of the material involves the irradiation of the material on the substrate using visible light, ultraviolet radiation, electron beam radiation, ion radiation or free radicals (from a plasma), or heat or any other technique convenient. When the article 112 is mounted on a rotatable cylinder 114, it is preferred that the radiation source 116 be located downstream from the monomer or pre-polymer vapor source, so that the coating material 100 can be applied and cured continuously on the surface of the first reflective layer. An amount of multiple revolutions or passes of the substrate can be employed to successively deposit and cure the monomer vapor on the layers that were deposited and cured during the previous revolutions. In some embodiments, the spacer layer could be cured once the second reflective layer is deposited on the spacer layer as further described herein. Once the coating material 100 is cured by the radiation source 116 to form the spacer layer, the retroreflective color change article 112 passes an optional deposition station 140 (e.g., a metallization station) where it could be a second reflective layer (eg, the second reflective layer 26 of Figure 2) is deposited on the sparger layer using any suitable technique, eg, vacuum metallization, sputtering, evaporation, chemical vapor deposition (CVD) and enhanced CVD of plasma. In alternate form, the second reflective layer could be deposited by inverting the cylinder 114 and using the deposition station 130. The second reflective layer could also be deposited after the retroreflective color change article 112 has been removed from the chamber 118. After the deposition of the second reflective layer, a binder layer or a substrate could be formed on the reflective coating opposite the microsphere layer as further described herein. Those skilled in the art will appreciate that the apparatus shown in Figure 3 could be modified to apply the first or second reflective layers or a stack of layers, each of which contains one or more inorganic or organic materials, with two or more of these layers that have refractive indices that differ enough to reflect light. Those skilled in the art will also appreciate that the apparatus shown in Figure 3 could be modified to apply additional coating materials, as desired. For example, inorganic, organometallic or non-polymeric layers could be deposited using convenient methods, now known or subsequently developed, which include ion bombardment, chemical vapor deposition, electro-deposition, condensation of a solvent, and other such methods These additional layers could be deposited directly onto the layer of the microspheres before the first reflective layer is deposited, after the first reflective layer is deposited or after the spacer layer is deposited. In some embodiments, an adhesion promoter may be coated between the microsphere layer and the reflective coating or between the first reflective layer and the spacer layer. Adhesion promoters can be selected to improve adhesion between layers, for example, between the reflective coating and the microsphere layer or between the first reflective layer and the spacer layer. For example, a silane coupling agent can be used in a manner that promotes adhesion between the polymer layers of the multilayer reflective coatings of the present disclosure and the optical elements which can be, for example, glass or glass microspheres. ceramics. Exemplary silane coupling agents include aminopropyltriethoxysilane, glycidoxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane. Also, the titanate coupling agents can be employed as adhesion promoters, examples of which include isopropyl tri (dioctyl) phosphate dimethacryloxymethylene titanate, and titanium (tetraisopropoxide). Silazanes such as hexamethyldisilazane can also be used as adhesion promoters. Examples of silane coupling agents are described in U.S. Patent No. 5,200,262 (Li).

Apparatus suitable for carrying out various aspects of the method illustrated in Figure 3 are described, for example, in Fleming et al '564 and in U.S. Patent Nos. 6, 012,647 (Lyons et al.,' 647); 6, 045,864 (Lyons et al., '864); 4, 722, 515 (Ham); 4, 842, 893 (Yializis et al., '893); 4, 954,371 (Yializis' 371); 5, 097,800 (Shaw et al., '800) and 5, 395,644 (Finite Af). The apparatuses and portions of apparatuses that could be convenient for effecting these and other aspects of the method illustrated in Figure 3 are described in greater detail in the cited documents. Exemplary monomers and oligomers that are suitable for use in the process shown in Figure 3 include acrylates, methacrylates, acrylamides, methacrylamides, vinyl ethers, maleates, cinnamates, styrenes, olefins, vinyls, epoxides, silanes, melanins, functional monomers of hydroxy and amino functional monomers. Suitable monomers and oligomers may have more than one reactive group, and these reactive groups may be of different chemistries in the same molecule. The prepolymers can be mixed to achieve a wide range of optical properties such as the desired refractive index in one or more layers of the reflective coating. It may also be useful to coat reactive materials from the vapor phase on the substrate that already has chemically reactive species on its surface, examples of these reactive species include monomers, oligomers, initiators, catalysts, water or reactive groups such as hydroxy , carboxylic acid, isocyanate, acrylate, methacrylate, vinyl, epoxy, silyl, styryl, amino, melamines and aldehydes. These reactions can be initiated in thermal form or by radiation curing with initiators and catalysts as appropriate for chemistry or, in some cases, without initiators or catalysts. When more than one pre-polymer starting material is used, the constituents could be vaporized and deposited together, or they can be vaporized from separate sources of evaporation. The deposited pre-polymer materials may be applied in a substantially uniform manner, in a substantially continuous mode or they may be applied in a batch mode, for example, as islands covering only the selected portion or portions of the optical elements. Discontinuous applications may be provided in the form of characters, numbers or other indicia or marks by using, for example, a mask or other suitable technique, including the subsequent removal of unwanted portions. The vapor deposition of the pre-polymer is particularly useful for the formation of thin films having a thickness of approximately 0.01 to 50 μm. Thicker layers can be formed by increasing the exposure time of the substrate to the vapor, increasing the flow rate of the fluid composition in the atomizer or exposing the substrate to the coating material through multiple passes. The increase of the exposure time of the retroreflective article to steam can be achieved if multiple sources of steam are added to the system or if the speed at which the article is moved through the system is decreased. Coatings of layers of different materials may be formed by sequential depositions of coating using a different coating material with each deposition, or by simultaneously depositing materials from different sources displaced from each other along the travel path of the substrate. In addition, a variety of techniques could be employed to produce a spacer layer including a non-uniform thickness for each of the various microspheres of the color change articles described herein. An example technique is to condense different amounts of monomer in different thicknesses directly. These techniques are described, for example, in Shaw et al., '895. Alternatively, a uniform monomer thickness could be deposited in all areas and subsequently, the thickness of the spacer layer could be contracted to different reaches in different areas for each microsphere. By controlling the degree of polymerization of the spacer layer, the thickness of the spacer layer could also be controlled. These techniques are also further described, for example, in Shaw et al., '895. Table I lists a few examples of polymer and pre-polymer materials that can be deposited to form the spacer layer using various methods. - The known refractive index of the monomer or polymer made from the monomer is given for each material. Different refractive indexes can be achieved by choosing these or other starting materials that have either a desired refractive index or that can be mixed with one or more other materials to obtain the desired refractive index. Other polymers that could be convenient are described, for example, in Fleming et al '564. Table I Table I (Continued) The described color change retroreflective articles could be used in a variety of applications. For example, articles may provide decorative effects for use in vehicle identity plates, advertising or graphics or designs. Items may be posted on substrates such as passports, driver's licenses or identification cards to provide evidence of tampering or security authentication. The articles may provide the position information based on the color of the retroreflected light. The articles may have other uses that will be apparent to those skilled in the art each time a visually perceptible change in the color of the retroreflected light is desired for the information or for other purposes. Next, the invention will be described with reference to the following non-limiting example, in which all parts and percentages are by weight unless otherwise indicated. Example Glass beads with a high refractive index were partially embedded having a refractive index of 1.93 and a nominal diameter of 60 μm in a polyethylene layer on a polyester film carrier forming a bead coating carrier having a layer of microspheres. A reflective coating was formed on the microsphere layer in three separate passes of coating. Between each coating pass the chamber was opened towards the atmosphere. The bead coating carrier was loaded in a vacuum chamber and the pressure was reduced to 2.7xl0-5 torr. The pearl coating was first treated with plasma with a nitrogen plasma at a power of 100 watts, subsequently, a chromium layer of 4 nm (target thickness) was coated with ion bombardment using a power of 12,250 watts with an argon gas to form a first semitransparent reflective metallic layer. The target linear velocity was approximately 15 meters / minute (50 feet / minute), and the current velocity was approximately 12 meters / minute (40 feet / minute) due to apparent spill-over. The vacuum chamber was opened to allow inspection of the bead coating carrier with a first chromium reflective metallic layer. Next, the carrier was charged once more into the vacuum chamber and the pressure was reduced to 3. 5xl0 ~ 6 torr. A 600 nm acrylate spacer layer was deposited at a web speed of 15 meters / minute (50 feet / minute). The acrylate spacer layer was formed from a mixture containing 48.5% cyclic diacrylate SRR-214 from UCB Chemicals, 48.5% lauryl acrylate and 3% an acrylated acrylic compound EBECRYL ™ from UCB Chemicals. In a third pass, 30 nm of aluminum was deposited by steam from evaporative containers heated in resistive form to form the second reflective metal layer. A layer of polyurethane adhesive binder was applied in the retroreflective color change article located on the pearl coating carrier. The adhesive binder layer was made by mixing 10.6 grams of a CAPA ™ 720 block copolymer (now, CAPA 72 OIA) of epsilon-caprolactone and poly (1,4-butylene glycol) from Solvay Chemicals; 18 0 grams of 8009 SYN FAC ™ alkoxylate from Milliken Corporation; 3 . 4 grams of PERSONALP ™ TP30 acrylic polyol from Perstop Inc; 3 drops of dibutyltin dilaurate; 60.4 grams of a polyurethane prepolymer made by the reaction of diphenylmethane diisocyanate ML MONDUR ™ from Bayer Corp., with a CAPA 720 block copolymer in a mole ratio of 4: 1; and 4.6 grams of a silane adhesion promoter. The silane adhesion promoter was made from a mixture of 2.44 grams of diethyloxy silane synthesized by the reaction of 3.05 parts of aminopropylmethyl diethoxy silane from Witco Corp., and 1. 625 parts of propylene carbonate and 2.46 grams of triethoxy silane synthesized by the reaction of 3.63 parts of aminopropyl triethoxy silane A1100 from Witco Corp., and 1. 675 parts of propylene carbonate. The resulting mixture of reactive polyurethane was coated with a set of notch bar coater at a separation of 0.15 nm (6 mil) and cured for 3 minutes at a temperature of 66 ° C, subsequently, a polyester woven substrate was applied over the semi-cured adhesive and cured for 10 minutes at 104 ° C. After 4 weeks, the substrate of the polyester film was stripped to produce the retroreflective article of exposed lens color change. The material had a gray-blue-green appearance according to ambient light conditions. During retroreflection, the material appeared blue or green and changed to green or blue as the orientation of the sample changed. The coefficient of retroreflection (Ra) was 214 at an angle of observation of 0 .2 ° and with an angle of entry of -4o. After 25 cycles of domestic washing, this sample retained more than 50% of its original Ra. Figure 4 is a chromaticity diagram using the CIÉ x-y chromaticity coordinates for the color change retroreflective article of the Example. An approximately 21 by 24 cm area of the retroreflective color change article was examined using the CIÉ 2 o observer and the light source A. The observation angle was set at 0 .33 °, which is the usual value for color measurements at night time, and the angle of entry was changed in stages of 2 or from 0 to 60 °. The resulting coordinates of CIÉ color for the color at night time vary in a smooth, spiral-shaped curve of the colors yellow-green, green, blue, violet, purple, pink, orange and finally white. These values are actually averages of several color changes due to the variation across the area of the sample that was examined at the same time. Figure 5 is a photograph of a portion of the retroreflective article of color change of the example taken using the scanning electron microscope. A cross section of the glass-coated microspheres was examined with the scanning electron microscope. Figure 5 shows the reflective coating formed on the microsphere layer. The coating is very thin, it contours the structure of the surface of the beads, and approaches the target thickness. As can be seen in Figure 5, the reflective coating includes a non-uniform thickness associated with each microsphere. All references cited herein are incorporated herein by reference in their entirety in this disclosure. Illustrative embodiments of this description are discussed and reference has been made to possible variations within the scope of this description. These and other variations and modifications in the description will be apparent to those skilled in the art without departing from the scope of the description, and it should be understood that this description is not limited to the illustrative embodiments set forth herein. Accordingly, the invention will not be limited only by the claims provided below. It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (10)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A retroreflective article of color change, characterized in that it comprises: a layer of microspheres; and a reflective coating located in optical association with the microsphere layer, wherein the reflective coating includes at least one partially transparent spacer layer that is located between a first semitransparent reflective layer and a second reflective layer, and at least one layer of the coating The reflective includes a non-uniform thickness associated with each of the plurality of microspheres, so that the light incident on the article coming from a first direction is retroreflected in a first color and the light incident on the article coming from a second direction. be retroreflected in a second color visibly different from the first color.
2. 2. The article according to claim 1, characterized in that the spacer layer comprises the non-uniform thickness.
3. 3. The article according to claim 1, characterized in that the first color and the second color are characterized by the CIÉ chromaticity coordinates. (xi / yi) / (X2 / Y2) respectively, where the first and second directions differ by at least 30 °, and also where the largest coordinates of | x2-x? | and | y-y? | are at least 0.05.
4. 4. The article according to claim 3, characterized in that the first direction is substantially normal to the microsphere layer.
5. 5. A retroreflective article of color change, characterized in that it comprises: a layer of microspheres; and a reflective coating that is located in optical association with the microsphere layer, wherein the reflective coating is comprised of: a first semitransparent reflective layer adjacent to the microsphere layer; and an at least partially transparent spacer layer adjacent to the first reflective layer; and a second reflective layer adjacent to the spacer layer, so that the spacer layer is between the first and second reflective layers; wherein the reflective coating reflects visible light without uniformity, and a first predetermined area of the reflective coating associated with each microsphere of at least a plurality of microspheres includes a first thickness and a second predetermined area of the reflective coating associated with each microsphere at least of a plurality of microspheres includes a second thickness different from the first thickness.
6. 6. A method of making a retroreflective color change article, characterized in that it comprises: providing a layer of microspheres; and forming a reflective coating in optical association with the microsphere layer, wherein the formation of the reflective coating includes: depositing a first semitransparent reflective layer adjacent to the microspheres layer; depositing an at least partially transparent spacer layer on the first reflective layer; and depositing a second reflective layer on the spacer layer; wherein the reflective coating is formed in order to provide for each of the plurality of microspheres, a non-uniform thickness in at least one of the respective layers of the reflective coating, so that the light incident on the article that comes from a first The direction is retroreflected in a first color and the incident light on the article coming from a second direction is retroreflected in a second color visibly different from the first color.
7. 7. The method according to claim 6, characterized in that the deposition of the spacer layer comprises: condensing a pre-polymer vapor on the first reflective layer; and curing condensed pre-polymer vapor.
8. 8. The method according to claim 7, characterized in that the deposition of the spacer layer further comprises vaporizing a liquid composition containing a monomer or an oligomer to form the pre-polymer vapor. The method according to claim 7, characterized in that the curing of the pre-polymer vapor occurs simultaneously with the condensation of the pre-polymer vapor. The method according to claim 6, further characterized in that it comprises forming a layer of binder on the reflective coating opposite the microsphere layer.