Double bubble process for making strong, thin films

• US 5,674,607 A
• Filed: 03/23/1995
• Issued: 10/07/1997
• Est. Priority Date: 07/28/1989
• Status: Expired due to Fees

• Current Assignee: Cryovac Incorporated (Sealed Air)
• Original Assignee: W R Grace & Company - CONN (WR Grace & Company)
• Inventors: Schirmer, Henry G.
• Primary Examiner(s): Buffalow, Edith
• Application Number:
  US08/409,224
• Time in Patent Office: 929 Days
• Field of Search: 428/336, 428/500, 428/910, 428/509
• US Class Current: 428/336
• CPC Class Codes: B29C 55/28 of blown tubular films, e.g. by inflation extrusion moulding of tubular films B29C48/03
• CPC Class Codes: B29K 2023/06 PE, i.e. polyethylene
• CPC Class Codes: B29K 2023/083 EVA, i.e. ethylene vinyl acetate copolymer
• CPC Class Codes: B29K 2025/00 Use of polymers of vinyl-aromatic compounds or derivatives thereof as moulding material
• CPC Class Codes: B32B 27/322 comprising halogenated polyolefins, e.g. PTFE
• CPC Class Codes: B32B 27/36 comprising polyesters
• CPC Class Codes: Y10S 264/905 having plural, distinct differential fluid pressure shaping steps
• CPC Class Codes: Y10S 428/91 Product with molecular orientation
• CPC Class Codes: Y10T 428/1379 Contains vapor or gas barrier, polymer derived from vinyl chloride or vinylidene chloride, or polymer containing a vinyl alcohol unit
• CPC Class Codes: Y10T 428/265 1 mil or less
• CPC Class Codes: Y10T 428/31794 Of cross-linked polyester
• CPC Class Codes: Y10T 428/31855 Of addition polymer from unsaturated monomers
• CPC Class Codes: Y10T 428/31888 Addition polymer of hydrocarbon[s] only
• CPC Class Codes: Y10T 428/31913 Monoolefin polymer

Abstract

Polymeric, thin oriented films can be made by use of a combination of a hot blown process and a blown bubble process, i.e. a double bubble process. The resulting film has use in replacing PVC for in store stretch wrap applications. Very low density polyethylene, VLDPE, is an especially preferred material for this process. It may be used as a monolayer, or as one layer of a multilayer structure. In practicing the invention, the polymer is extruded and hot blown, and heated to a temperature above its orientation temperature. This heating can be accomplished by the use of a heated liquid reservoir or sock disposed at the lower end of the primary bubble, inside the bubble. The hot blown heated film is then passed through a first set of pinch rolls, re-inflated into a blown bubble, and collapsed at a second set of pinch rolls. Thin, tough and elastic packaging materials are obtained by this process.

Claims

1. A biaxially oriented packaging film having a thickness of less than about 0.10 mils comprising a layer of polystyrene.

2. The film of claim 1 wherein the film is cross-linked.