Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Utilizing plasma – electric – electromagnetic – particulate – or...
Reexamination Certificate
1998-10-30
2001-10-16
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Utilizing plasma, electric, electromagnetic, particulate, or...
C264S001900, C264S002700, C264S571000, C264SDIG007
Reexamination Certificate
active
06303058
ABSTRACT:
FIELD OF INVENTION
The present invention relates to methods of making profiled retroreflective articles having a retroreflective base sheet formed to have first portions arranged in an upwardly contoured profile and second portions in a substantially planar position.
BACKGROUND
Retroreflective articles have the ability to redirect substantial quantities of incident light, which otherwise would be reflected elsewhere, back towards the incident light source. This ability has led to widespread use of retroreflective articles in a variety of applications relating to traffic safety. Retroreflective sheetings are particularly useful to guide motorists under poor lighting conditions, such as, for example, under nighttime driving or under inclement weather. Examples of uses of retroreflective sheeting include, but are not limited to traffic signs, cones, and barricades.
Some skilled in the art have developed various methods of making profiled retroreflective articles using retroreflective base sheets. By “profiled,” it is meant that some portion of the retroreflective base sheet is elevated from the body of the article so as to create a vertical component.
For example, Assignee's pending U.S. patent application Ser. No. 08/895,384, filed on Jul. 16, 1997, discloses a retroreflective sheeting that has a continuous, longitudinal extending retroreflective portion and pleated retroreflective portions. Each pleated portion extends generally perpendicular to and is spaced along the longitudinal portions. As defined in the application, “pleated” means that a portion of the sheeting is doubled upon itself and bonded together by, for example, an adhesive or ultrasonic bonding. The pleats elevate a portion of the retroreflective sheet so that incident light at high entrance angles strikes the pleated portion and is retroreflected by the pleated portion. The sheeting is very useful for application on traffic barricades, such as jersey barriers or guard railings.
Publication No. WO 93/21388 discloses a method and device for producing light-reflecting surfaces, particularly for road markings. The markings have ridge-like stripes containing reflecting components, the stripes applied perpendicularly or at an angle to the traffic direction. The marking can be applied directly onto a road surface or prefabricated onto a carrier web and applied to a road surface. When a marker is made directly on the road, the method includes applying a thin coating onto a road surface, applying ridge-like profile markings across the longitudinal direction of the coating, applying light reflecting materials, such as glass beads, into the surfaces of the coating and ridge-like material while the surfaces are still soft to yield a pavement marking.
A need exists for streamlined methods to make profiled retroreflective articles for use in vertical or horizontal applications.
SUMMARY OF INVENTION
The present invention provides methods of making articles using retroreflective base sheets and a novel approach of elevating portions of the base sheet. The inventive articles exhibit surprisingly effective retroreflective properties, especially at very high entrance angles (e.g., 85° or more) as well as at low entrance angles. They are well suited for use on vertical and horizontal surfaces.
In brief summary, a method of the invention comprises: (a) providing a substantially continuous, longitudinally extending retroreflective base sheet comprising a cover layer and a plurality of retroreflective elements, the base sheet having a retroreflective top surface and a bottom surface; (b) creating a plurality of cavities on the bottom surface of the base sheet without substantially stretching it to yield (i) first portions extending generally perpendicular to the base sheet, the first portions having retroreflective elements arranged in an upwardly contoured profile, and (ii) second portions having retroreflective elements arranged in a substantially planar position; and (c) applying a filling material into the cavities to retain the first portions.
Typically the inventive methods generates a plurality of first portions and second portions in a continuous sheet. Base sheets can be cube-corner based or microsphere based and are typically provided in a substantially continuous, longitudinally extending form, such as, for example, in a roll. The base sheet can be an enclosed-lens or an exposed-lens sheet. An advantage of using an enclosed-lens retroreflective sheet is that the resultant article is inherently wet retroreflective. That is, the inventive article will retroreflect under wet conditions, occurring, for example, during rainy conditions, during conditions when the rain has subsided but the article has not yet dried, or during the early morning hours when dew has collected on the inventive article. Some enclosed-lens base sheets are flexible and many can be made in desired colors. They are low profile and conform to road surfaces. They are resistant to damage from traffic and withstand exposure to water, salt, oils, ultraviolet radiation, sand abrasion, high temperatures, making them well suited for use on road surfaces. An enclosed-lens base sheet typically exhibits higher retroreflective performance compared to an exposed-lens base sheet using diffuse reflectors in the environments stated above.
The inventive methods produce articles that are particularly well suited for applications where incident light strikes at entrance angles greater than about 85°. In this document, “entrance angle” has the same definition as that defined in the United States Federal Test Method 370. In general, two axes define the entrance angle. The first axis is an axis of incident light, which is a line along which incident light travels from a light source to an indicia mark on a retroreflective base sheet. The second axis is a reference axis, which is a line perpendicular to the plane of the sheet extending from the indicia mark. Entrance angles range from −90° to 0° to +90°. A 0° entrance angle occurs when the reference axis is superimposed on the axis of incident light. This situation is typically termed as “head on” because the light source is nearly perpendicular to the sample at the indicia mark. An entrance angle of 85° and above is referred to as a “high entrance angle.”
High entrance angle applications include pavement markings and applications where the incident light may be from any direction, such as horizontal signs. Illustrative examples of such horizontal signs include the legends and symbols commonly placed on pavement in parking lots to denote handicapped parking, and the arrows and lane markings placed on the pavement at an intersection.
In addition, retroreflective articles of the invention are also well suited for use on vertical surfaces, particularly those that are observed at high entrance angles, such as, but not limited to, guard rails, building walls along alleys, Jersey barriers, bridge abutments, posts, and traffic barrels. An advantage of inventive articles is that they also have the ability to retroreflect incident light nearly the full spectrum of entrance angles. This ability makes the inventive article especially well suited for use on walls and barriers along highways and other applications where a vehicle may approach the structure from a wide range of angles at which effective retroreflective brightness is desired. The inventive articles can be used on curved substrates, e.g., wrapped around traffic cones and barrels, and on curved guardrails, providing excellent retroreflective brightness along essentially the entire visible portion of the substrate.
DEFINITIONS
As used in this document:
“base sheet” is a substantially continuous, longitudinally extending retroreflective sheeting having (a) a top retroreflective surface and a bottom surface, and (b) a cover layer and a plurality of retroreflective elements in the form of cube-corner elements, optionally having a specular reflector on the cube-corner elements faces, or in the form of microspheres with a reflector in optical association with the mic
Bailey Terry
Frank John W.
Haunschild Dale H.
Kelley Michele H.
Nakayama Naoki
3M Innovative Properties Company
Hofmann, Jr. Rudolph P.
Vargot Mathieu D.
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