Thermoforming system for masked polymers

Abstract

In a thermoforming system for masked polymer substrate sheets, a temperature resistant, non-stick coating is applied to a sheet of a polymer substrate material. The coated sheet is positioned on a flexible platen positioned over a mold having a predetermined shape. Heat is applied until the polymer reaches a thermoforming temperature and softens, whereupon the platen is lowered to stretch over and cover the mold. When the sheet begins to conform to the mold, the heat is withdrawn and a second platen is lowered over the sheet to urge it into conformance with the mold. The temperature resistant coating can be applied over an existing polymer film masking, and rapidly cures to form a non-stick surface which prevents adhesion of the masked polymer sheet to the platen surfaces.

Description

BACKGROUND OF INVENTION [0001] 1. Field of the Invention [0002] The present invention is concerned with a system for thermoforming masked polymer substrates. [0003] 2. Description of the Related Art [0004] Transparent and selectively transparent thermoformable polymeric synthetic resin compositions are employed to form a variety of products such as lenses, windows, housings and a wide-variety of containers and coverings. These polymer compositions are particularly well-suited for automotive use because they provide glass-like optical clarity yet are substantially lighter in weight and offer greater crash safety. High polymer thermoplastic compositions such as polycarbonate, present a superior substrate for molded windshields and windows for vehicles of all types, for example, racing cars, motorcycles, all terrain vehicles, automobiles, heavy equipment, boats and aircraft, as well as for skylights and windows used in conventional housing and mobile homes. [0005] The clear polymer sub...

AI Technical Summary

Benefits of technology

[0011] The present invention provides a thermoforming system for masked polymer substrates which is energy efficient, minimizes thermoforming temperatures and produces a product with superior optical clarity. A temperature resistant, non-stick coating is applied to a sheet of a thermoformable polymer substrate material. The coated sheet is positioned on a flexible platen positioned over a mold having a predetermined shape. Heat is applied until the polymer reaches a thermoforming temperature and softens, whereupon the platen is lowered to stretch over and cover the mold. When the sheet begins to conform to the mold, the heat is withdrawn and a second platen is lowered over the sheet to urge it into conformance with the mold. The temperature resistant coating can be applied over an existing polymer film masking, and rapidly cures to form a non-stick surface which prevents adhesion of the masked polymer sheet to the platen surfaces.

Problems solved by technology

Thermoformable polymers are not abrasion resistant.

Such masking is difficult to apply and an adhesive composition must be employed to bond the paper to the polymer sheet.

Adhesive bonding agents are incompatible with many polymer compositions and may chemically interact with the polymer, altering the surface of the sheet, for example, with pitting or blistering.

Adhesive bonding agents may be also be difficult to remove completely from the substrate surface when the masking is removed.

Adhesively bonded protective masking is not suitable for use during thermoforming and must be removed prior to the application of heat to the polymer substrate in order to avoid melting the adhesive into the substrate.

Once the protective masking is removed, the surfaces of the polymer sheet are exposed to damage from abrasion and scratching inflicted by the hard surfaces of the mold during thermoforming.

In addition, static electricity may cause the unmasked polymer surfaces to become contaminated with dust and grit during thermoforming and incidental handling.

Images