Method of making a retroreflective article and a retroreflective article having an aluminum reflector

#Retroreflective articles have the ability to return substantial quantities of incident light, which otherwise would be reflected elsewhere, back towards the light source. This unique ability has led to widespread use of retroreflective articles in a variety of applications relating to traffic and personal safety. For example, in the personal safety area, retroreflective articles have been used on clothing, primarily to enhance a pedestrian's visibility to motor vehicle operators after dusk or under other low visibility conditions. They also have been attached to book-bags and backpacks for the same purpose. Retroreflective articles can be made from cube-corner structures, such as cube-corner elements and cube-corner shaped cavities.

#Cube-corner elements are structures that resemble the corner of a room—that is, they contain three generally perpendicular faces that meet at a point or an apex. Cube-corner cavities, on the other hand, are structures that are defined by a recessed area bounded by three generally perpendicular faces that meet at a point in a valley. In general, the cube-corner formation process, whether forming cube-corner elements or cube-corner shaped cavities, is referred to as “replication.” Numerous methods exist for making cube-corner retroreflective articles. For example, U.S. Pat. No 5,450,235 to Smith et al. discloses an extrusion method, where a stream of polymer melt is extruded into a microstructured mold containing a multitude of cube-corner shaped cavities. The resulting product is a microstructured article that has a plurality of cube-corner elements arranged in an array. U.S. Pat. No. 5,691,846 to Benson, Jr. et al. discloses another method, where a curable resin solution is applied to a mold having a multitude of cube-corner shaped cavities. An overlay film is allowed to contact the resin. The resin solution is cured using actinic radiation to form a composite sheeting that has an array of cube-corner elements bonded to the overlay film.

#Cube-corner shaped cavities have been made by various methods. Such methods, however, typically have separated the process of making a retroreflective article from the process of process of metalizing the article—that is, the process of applying a reflective layer onto the article.

#The invention is further explained with reference to the drawings, wherein:

#FIG. 1 is a top view of a known array 50 of cube-corner elements 2;

#FIG. 2 is a cross-sectional view of a retroreflective article 10 in accordance with the invention;

#The following examples are provided to illustrate different embodiments and details of the invention. Although the examples serve this purpose, the particular ingredients and amounts used, as well as other conditions and details, are not to be construed in a manner that would unduly limit the scope of the invention. Unless specified otherwise, all percentages are weight percentages.

#Brightness Measurements

#Measurements of the coefficient of retroreflection (brightness measurements), RA, were taken of the samples below using standard photometric equipment and techniques as generally described in ASTM E 808-94. The actual test method used to obtain RA values reported in the Examples are traceable back to ASTM E 808-94. The observation angle was set at 0.2 degree, the entrance angle was set at −4 degree, and the rotation angle of the sample was set at 0 degree, all of the angles being defined as in the test method.