Method for compression molding of retroreflective sheeting and sheeting produced thereby

• US 4,332,847 A
• Filed: 08/18/1980
• Issued: 06/01/1982
• Est. Priority Date: 09/20/1979
• Status: Expired due to Term

• Current Assignee: Relfexite Corporation
• Original Assignee: Relfexite Corporation
• Inventors: Rowland, William P.
• Primary Examiner(s): Lowe, James B.
• Application Number:
  US06/178,842
• Time in Patent Office: 652 Days
• Field of Search: 264/284, 264/293, 264/1.6, 264/1.9, 264/2.7, 425/89, 425/143, 425/193, 425/335, 425/339, 425/384, 425/411, 425/808, 428/156, 428/164, 428/913
• US Class Current: 428/156
• CPC Class Codes: B29C 59/02 by mechanical means, e.g. pressing B29C59/007 takes precedence; embossing expanded porous articles B29C44/5627
• CPC Class Codes: B29D 11/00605 Production of reflex reflectors
• CPC Class Codes: B29L 2011/0091 Reflex reflectors
• CPC Class Codes: Y10S 428/913 Material designed to be responsive to temperature, light, moisture
• CPC Class Codes: Y10T 428/24479 including variation in thickness
• CPC Class Codes: Y10T 428/24545 Containing metal or metal compound

Abstract

There are disclosed an apparatus to perform a method for continuously embossing synthetic plastic sheet material with precisely formed embossments in patterns repeating along the length thereof. The apparatus includes a movable polished belt upon which the sheet material is carried, and a series of molds are placed on the sheet material. As the sheet material and molds are advanced in steps through the apparatus, presses clamp the molds and belt against opposite surfaces of the sheet material and raise the temperature of the assembly to embossing temperature for the resin to cause the resin to flow into the mold cavities, and volatiles at the interface are dissolved in the resin. After the embossing step, the clamping pressure is released and this permits limited shrinkage of the mold and sheet material. At subsequent stations, controlled temperature reduction is effected, and limited shrinkage is permitted after the clamping pressure is released at each station and as the material and molds move to the next station. Mold distortion is thus avoided and the embossments remain precisely formed.

Claims

1. In a method for embossing synthetic plastic sheet material to generate precisely formed embossments on one surface thereof, the steps comprising:

A. disposing one surface of an elongated strip of synthetic thermoplastic sheet material on an elongated member movable in a path providing a series of stations therealong;

B. placing on the other surface of said synthetic plastic sheet material a series of embossing molds having the desired embossing pattern in their adjacent surfaces, said molds being closely spaced along the length of said sheet material;

C. moving a clamping member against the first of said series of molds to apply clamping force to said first of said series of molds and said elongated member at the first of said series of stations to deform said sheet material therebetween and cause said synthetic plastic thereof to flow into said embossing pattern of said mold to effect embossment thereof;

D. moving said clamping member away from said first of said series of molds to release said clamping force on said first of said series of molds and elongated member;

E. advancing said first mold and the cooperating portions of said elongated member and sheet material to a second station and a second mold and cooperating portions of said elongated member and sheet material to said first station;

F. moving a second clamping member against said first mold to apply a clamping force to said first mold and elongated member at said second station while simultaneously moving said first mentioned clamping member against said second mold at said first station to apply a clamping force to said second mold and said elongated member at the first station to effect embossment of said sheet material thereat;

G. moving said clamping members away from said first and second molds to release said clamping force at said first and second stations and advancing the first and second molds and the cooperating portions of said elongated member and sheet material to the next stations while advancing a third mold into registry with said first station;

H. moving said first and second clamping members against said molds registering therewith to apply a clamping force to said molds and elongated member at each of said stations;

I. repeating the foregoing series of steps to advance said molds, elongated member and sheet material through said series of stations;

J. controlling the temperature of said molds at at least some of said stations so that said synthetic resin of said sheet material is readily deformed into the embossing pattern of the mold at said first station and is cooled in its mold in subsequent stations; and

K. stripping said embossed sheet material from said molds and elongated member after it has advanced through said series of stations.

2. The embossing method of claim 1 wherein said synthetic resin of said sheet material is a thermoplastic resin substantially free from solvents and materials volatile at the embossing temperature.

3. The embossing method of claim 1 wherein said step of controlling temperature of said molds includes the heating of said sheet material to a semifluid condition for embossing in the first station(s) of said series of stations and the cooling of said sheet material to a temperature below its heat distortion temperature in the stations subsequent to said embossing thereof.

4. The embossing method of claim 1 wherein there is included the step of removing said molds from said elongated member and said sheet material subsequent to passage through said series of stations and returning them to a point prior to said first of said series of stations for repetition of the several steps.

5. The embossing method of claim 1 wherein said elongated member has a polished surface and provides a polished opposite surface on said embossed sheet material.

6. The embossing method of claim 5 wherein said embossing pattern of said molds provides microprism cavities and the embossed sheet material has closely spaced microprism formations thereon.

7. An elongated strip of embossed synthetic thermoplastic resin sheet material having a series of closely spaced repeating patterns of precisely formed embossments on one surface along substantially the entire length thereof, said embossments being microprisms having a vertical height of not more than 0.008 inch, the deviation in the embossments for the first pattern in the series on said strip from that of the last pattern in the series being less than one percent, said strip being produced in accordance with the method of claim 1.

8. The elongated strip of claim 7 wherein said resin is a thermoplastic, wherein the other surface thereof is highly polished, and wherein said embossments are precisely formed microprisms.