Method for continuously forming an array of optical elements and

Details Method for continuously forming an array of optical elements and Method for continuously forming an array of optical elements and

1997-06-24

1999-08-31

Vargot, Mathieu D.

Plastic and nonmetallic article shaping or treating: processes

Optical article shaping or treating

Continuous or indefinite length

264 19, 264 27, 264284, 425373, 425385, B29D 1100

Patent

active

059450428

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a method for continuously forming an array of optical elements such as cube-corner prisms, linear prisms, lenticular lenses, refractive lenses, Fresnel lenses, linear Fresnel lenses or hologram patterns, on sheeting such as synthetic resin sheeting, and apparatus therefor. More particularly, it relates to a method for continuously forming an array of cube-corner type microprisms which is useful in the production of cube-corner type retroreflectors (i.e., articles reflecting most of the incident light back toward the light source), and apparatus therefor.


BACKGROUND ART

Conventionally, many propositions have been made with respect to the production of synthetic resin optical sheeting comprising synthetic resin sheeting provided on a surface thereof with an array of various optical elements as described above.
In the production of such synthetic resin optical sheeting, highly precise processing is required because the shape accuracy of the optical elements determines its optical performance, as contrasted with general processing techniques for synthetic resins, such as so-called embossing, graining and satinizing. For example, in the case of so-called microprism type retroreflective sheeting comprising synthetic resin sheeting provided with an array of cube corners, the angular divergence of the bundle of retroreflected light will become too great for practical purposes even if the three mutually perpendicular faces constituting each prism is deviated during forming, for example, by about 1.degree..
In order to overcome this disadvantage, various attempts have been made to improve the method of forming an array of optical elements on a surface of synthetic resin sheeting. Several patents disclosing techniques for the production of synthetic resin optical sheeting are described below.
In Rowland U.S. Pat. No. 3,689,346, there is described a method for continuously producing cube-corner type retroreflective sheeting. According to this method, retroreflective sheeting is produced by depositing a curable molding material upon a cube-corner mold and applying a transparent, flexible film material over the molding material, after which the molding material is cured and bonded to the film material. However, the resins specifically described in this patent for use as molding materials are substantially limited to crosslinkable resins such as plastisol type vinyl chloride resin containing a crosslinking acrylic ester monomer. Although it is suggested that some resins in a molten state can be used, no specific description is given of the melt viscosity conditions, heating conditions and cooling conditions under which such a resin can be embossed to obtain a product having high shape accuracy.
In Rowland U.S. Pat. No. 4,244,683 (corresponding to Japanese Patent Publication No. 51320/'81), there is disclosed an apparatus and method (i.e., a so-called progressive pressure forming method) for semi-continuously embossing thermoplastic synthetic resin sheeting to form cube-corner prisms on one surface thereof. In this patent, it is described that prism elements are formed by placing a series of flat embossing molds on one surface of synthetic resin sheeting traveling on an endless belt having a smooth surface, and pressure-forming the sheeting successively in three types of press stations (i.e., a preheating station, a thermoforming station, and a plurality of cooling stations). However, the prism sheeting produced by this method shows seams distinctly owing to the use of juxtaposed flat molds, resulting in a poor appearance of the product. Moreover, this method has the additional disadvantage of being inferior in productivity.
In Pricone et al. U.S. Pat. No. 4,486,363 (corresponding to Japanese Patent Laid-Open No. 140021/ '84) and Pricone et al. U.S. Pat. No. 4,601,861 (corresponding to Japanese Patent Laid-Open No. 47237/'86), there are disclosed apparatus and methods for continuously embossing cube-corner prisms on one surface of thermoplastic synthetic resin sheeting. Accord

REFERENCES:
patent: 3146492 (1964-09-01), Lemelson
patent: 4332847 (1982-06-01), Rowland
patent: 4576850 (1986-03-01), Martens
patent: 4601861 (1986-07-01), Pricone et al.
patent: 5656209 (1997-08-01), Benz et al.

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