Method of making a microprism master mold

• US 6,010,609 A
• Filed: 01/28/1998
• Issued: 01/04/2000
• Est. Priority Date: 07/28/1995
• Status: Expired due to Term

• Current Assignee: Nippon Carbide Kogyo Kabushiki Kaisha (Nippon Carbide Industries Company Incorporated)
• Original Assignee: Nippon Carbide Kogyo Kabushiki Kaisha (Nippon Carbide Industries Company Incorporated)
• Inventors: Mimura, Ikuo, Adachi, Keiji
• Primary Examiner(s): Mayekar, Kishor
• Assistant Examiner(s): TRAN, THAO T
• Application Number:
  US09/011,405
• Time in Patent Office: 706 Days
• Field of Search: 264/2.5, 264/1.9, 425/808, 205/70
• US Class Current: 205/70
• CPC Class Codes: B29C 2033/385 by laminating a plurality of layers moulds built up by stacking mould elements, e.g. plates, blocks, rods, in general B29C33/301, tyre moulds made of a plurality of laminations B29D2030/0609
• CPC Class Codes: B29C 33/302 Assembling a large number of mould elements to constitute one cavity
• CPC Class Codes: B29C 33/3857 by making impressions of one or more parts of models, e.g. shaped articles and including possible subsequent assembly of the parts
• CPC Class Codes: B29C 33/40 Plastics, e.g. foam or rubber
• CPC Class Codes: B29L 2011/0091 Reflex reflectors
• CPC Class Codes: G02B 5/045 Prism arrays
• CPC Class Codes: G02B 5/124 plural reflecting elements forming part of a unitary plate or sheet
• CPC Class Codes: Y10S 425/808 Lens mold

Abstract

This invention relates to a method of making a microprism master mold which is suitable for use in the production of cube-corner retroreflectors, especially in the form of thin retroreflective sheeting, and permits the formation of hexagonal prism type microprisms having both high reflectivity and excellent angularity. This method is characterized in that, in making a cube-corner microprism master mold by stacking a plurality of flat sheets having two mutually parallel major surfaces, cutting V-shaped grooves on one lateral surface of the resulting flat sheet stack 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°, 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. The flat sheets having a thickness of 50 to 500 μm and made of a synthetic resin having a Rockwell hardness of not less than 70 are used.

Claims

1. A method of making a cube-corner microprism master mold which comprises stacking a plurality of flat sheets having two mutually parallel major surfaces, cutting V-shaped grooves on one lateral surface of the resulting flat sheet stack 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°

, 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, characterized in that the flat sheets used have a thickness of 50 to 500 μ

m and in that the flat sheets are made of a synthetic resin having a Rockwell hardness of not less than 70.

2. A method as claimed in claim 1 wherein the flat sheets have a thickness of 60 to 200 μ

m.

3. A method as claimed in claim 1 wherein the synthetic resin is one having a glass transition point of 150°

C. or above.

4. A method as claimed in claim 1 wherein the synthetic resin is selected from the group consisting of polyethylene terephthalate resin, polybutylene terephthalate resin, polycarbonate resins, polymethyl methacrylate resin, polyimide resins, polyarylate resins, polyethersulfone resins, polyetherimide resins and cellulose triacetate resin.

5. A method of making a cube-corner microprism mold which comprises, after optionally imparting electrical conductivity to a cube-corner microprism master mold made by the method of claim 1, subjecting the master mold to a surface treatment for electroforming and an electroforming process, and stripping the resulting electroformed mold from the master mold.