Electrolysis: processes – compositions used therein – and methods – Electroforming or composition therefor – Mold – mask – or masterform
Patent
1998-01-28
2000-01-04
Mayekar, Kishor
Electrolysis: processes, compositions used therein, and methods
Electroforming or composition therefor
Mold, mask, or masterform
264 25, 264 19, 425808, C25D 110
Patent
active
060106093
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of making a microprism master mold for use in the production of cube-corner retroreflectors (i.e., articles reflecting most of the incident light back toward the light source). In particular, it relates to a method of making a microprism master mold which is suitable for use in the production of retroreflective elements useful in signs such as road signs and construction signs, license plates for vehicles such as automobiles and motorcycles, safety products such as safety clothing and life-saving devices, markings such as signboards, reflectors for visible light or laser light reflection sensors, and the like, as well as retroreflective sheeting composed of such retroreflective elements.
BACKGROUND ART
Conventionally, retroreflective sheeting capable of reflecting incident light back toward the light source have been well known, and such sheeting is widely used in the above-described fields of application due to its retroreflectivity. Among others, retroreflective sheeting utilizing the retroreflection principle of prisms, such as cube-corner retroreflective sheeting, has markedly higher optical retroreflection efficiency than conventional retroreflective sheeting using micro glass beads, and the range of its use is expanding every year because of its excellent retroreflection performance.
On the basis of their principle of reflection, cube-corner retroreflective elements exhibit high retroreflectivity, so long as the angle between the optical axis [i.e., an axis lying at an equal distance from three mutually perpendicular faces constituting the prismatic reflective elements (sometimes referred to simply as "prismatic element")] of a prismatic element and incident light (i.e., the entrance angle) is narrow. However, cube-corner retroreflective elements have the disadvantage that, as entrance angle increases, their retroreflection efficiency is reduced. Moreover, when rays of light are incident on a lateral face at an angle greater than the critical angle satisfying the conditions for total internal reflection which are determined according to the ratio of the refractive index of the transparent medium constituting the retroreflective element to the refractive index of air, most of them do not undergo total reflection at the interfaces of the prismatic element but pass to the back side of the prism. Thus, they have the additional disadvantage that the range of entrance angle which permits retroreflection is limited.
In order to overcome these disadvantages, various attempts have been made to improve the method of making a mold used for the formation of prisms. Some typical methods of making a prism mold which have been proposed in prior arts are described below.
(1) Bundled pin method (U.S. Pat. Nos. 1,591,572, 3,922,065 and 2,029,375):
This is a method in which a large number of metallic pins having a prism formed at the tip thereof are bundled to form an array of prisms. This method is characterized in that the design of the prism formed at the tip of each pin may be arbitrarily modified and is suitable for the production of relatively large prisms. However, it is not practical when the formation of, for example, more than 2,000 microprisms per square centimeter is required as dictated by the object of the present invention.
(2) Plate method (U.S. Pat. Nos. 1,591,572, 3,069,721 and 4,073,568):
This is a method of making a microprism mold of the hexagonal prism type which comprises stacking a plurality of flat sheets having two mutually parallel major surfaces, cutting therein V-shaped grooves in a direction perpendicular to the major surfaces and at a fixed pitch to form a series of successive roof-shaped projections having a vertical angle of about 90.degree., and then shifting the flat sheets so that the vertices of the roof-shaped projections formed on each flat sheet meet the bottoms of the V-shaped grooves formed on an adjacent flat sheet. This method is characterized by a relatively better design freedom, though it is lower than that of the bund
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Adachi Keiji
Mimura Ikuo
Mayekar Kishor
Nippon Carside Kogyo Kabushiki Kaisha
Tran Thao
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