Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-04-07
2003-08-05
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S483000, C428S523000, C428S516000, C428S910000
Reexamination Certificate
active
06602609
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a multilayer polymeric film. More particularly, the present invention relates to a multilayer polymeric film with a skin layer having a non-migratory polydimethylsiloxane block copolymer.
BACKGROUND OF THE INVENTION
In the packaging of certain types of foods, such as snack foods including candies, potato chips, cookies and the like, it is common practice to employ a multi-layer film. Polypropylene films are widely used in the packaging industry due to their superior physical properties, such as, transparency, stiffness, moisture barrier characteristics and others. Despite these highly desirable properties, unmodified polypropylene film has the disadvantageous property of having a high inherent coefficient of friction and film-to-film destructive blocking on storage. This high film-to-film coefficient of friction makes polypropylene films, in their unmodified form, difficult to use in automatic packaging equipment.
Coefficient of friction characteristics of polypropylene and other thermoplastic films are beneficially modified by the inclusion of slip agents in the polymer. Most of these slip agents are migratory, such as polydiallyl siloxane or fatty amides, such as, erucamide and oleamide. Although they do reduce the coefficient of friction, their effectiveness depends upon the ability to migrate to the surface of the film. The development of the desired low coefficient of friction value is strongly dependent upon the type and amounts of amides, and time and temperature aging effects. Even the heat history of the film while in storage and shipping and during subsequent converter processes, significantly affects the coefficient of friction. In addition, the presence of these types of fatty acid amides on the film surface results in visible adverse appearance effects, manifested by an increase in haze, a decrease in gloss and the presence of streaks. These materials also adversely effect the wettability and adhesion of solvent and water-based inks, coatings and adhesives.
To overcome the problems associated with migratory slip agents, non-migratory systems were developed. A material described to be a non-migratory slip agent is a particulate crosslinked hydrocarbyl-substituted polysiloxane which is available worldwide from Toshiba Silicone Co., Ltd. and in the United States from General Electric Co. And marketed under the name TOSPEARL.
In PCT US94/14280 a film structure containing a non-migratory particulate crosslinked hydrocarbyl-substituted polysiloxane slip agent is described. The film structure includes at least one layer of an olefin homo-, co- or terpolymer having a surface-treated external surface which is printable, sealable and machinable The film has, as a combined slip agent and antiblock, a non-migratory particulate crosslinked hydrocarbyl-substituted polysiloxane, and/or liquid polydimethyl siloxane. Example 7 provides a polypropylene core layer having (a) an outer skin layer of high density polyethylene containing particulate crosslinked polymonoalkylsiloxane as a non-migratory combined antiblock and slip agent and low density polyethylene. On the other side of the core layer is (c) an outer layer resin which also contains the non-migratory combined antiblock and slip agent. The film is flame treated on one side to improve the wettability and printability and lamination strengths. The size of the particulate in terms of average diameter is about 4.5&mgr;. The target skin thickness of the (a) layer is three gauge units and four gauge units for the (c) layer The ratio of particle size in terms of average diameter to skin thickness is about 5.9 for the three gauge skin layer and about 4.42 for the four gauge skin layer. The film is described as having good coefficient of friction, on the treated side, and marginal machinability.
Additional descriptions of olefinic polymer films in which particulate siloxane resins are employed to provide improved films will be found in U.S. Pat. Nos. 4,966,933; 4,769,418; 4,652,618; and 4,594,134.
U.S. Pat. No. 4,966,933 describes a propylene polymer film containing 100 parts by weight of a propylene polymer, 0.01 to 0.5 parts by weight of a fine powder of a crosslinked silicone resin and 0.3 to 3.0 parts by weight of a hydroxy-fatty acid glyceride. In column 3, lines 6-20, the provided amounts of fine powder of silicone resin and hydroxy-fatty acid glyceride in the metallization layer are required for adaptability to vacuum deposition. Example 3 provides a two-layer coextruded film in which the fine powder of crosslinked silicone resin is compounded with polypropylene homopolymer to form a metallization layer (B) and the fine powder of crosslinked silicone resin is compounded with an ethylene/propylene/butene-1 copolymer to form a skin layer (A). The ratio of reported particle size to skin thickness is about 0.143 for skin layer (B) and about 1.29 for skin layer (A).
U.S. Pat. No. 4,734,317 to Bothe, et al. discloses a biaxially oriented multilayer polyolefin film which comprises a polypropylene base layer, a first polyolefin sealing layer positioned on one side of the base layer, and containing from about 0.5% to 3% by weight of incorporated polydialkylsiloxane, the first sealing layer not being subject to corona treatment, and a second polyolefin sealing layer positioned on the other side of the base layer and having a coating of the polydialkylsiloxane on its outer surface, the second sealing layer being subject to corona treatment, wherein the polydialkylsiloxane coating is formed by contact of the first and second layers.
U.S. Pat. No. 4,925,728 to Crass, et al. discloses a biaxially stretched multilayer film comprising a base layer essentially comprising polypropylene and at least one top layer, wherein the top layer essentially comprises (a) 98.5% to 99.6% by weight of a propylene homopolymer and (b) 0.4% to 1.5% by weight of a polydiorganosiloxane, relative to the top layer.
U.S. Pat. No. 5,482,780 to Wilkie, et al. discloses a polypropylene film with cold seal release and cold seal receptive surfaces, wherein a predominantly isotactic polypropylene homopolymer core has on one side thereof an ethylene-propylene random copolymer having a physically modified surface for reception of a cold seal cohesive composition and on the other side of the core there is a blend of an ethylene-butylene copolymer and an ethylene-propylene random copolymer containing a non-migratory slip agent. The preferred non-migratory slip agent is described as being a crosslinked silicone having a particle size of about 1 to 4.5 microns, such as that identified by TOSPEARL of Toshiba Company.
U.S. Pat. No. 5,489,473 to Wilkie discloses biaxially oriented polypropylene cold seal packaging films comprising at least one cold seal release layer and a cold seal receptive layer. The use of crosslinked silicone in the cold seal release skin layer is also disclosed.
U.S. Pat. No. 5,792,549 to Wilkie discloses a coextruded biaxially oriented polyolefin packaging film comprising a cold seal release layer, a core layer, and a cold seal receptive skin layer. The use of crosslinked silicone having a particle size of about 1 to about 4.5 microns such as that identified by TOSPEARL of Toshiba Company is also disclosed.
U.S. Pat. No. 5,798,174 to Wilkie discloses cold sealable films for heat sensitive packaging operations comprising, in order, a cold seal cohesive layer, a core layer, and a cold seal release layer comprising a mixture of about 1 to about 80% by weight butene-propylene copolymer and about 99 to 20% by weight butylene-ethylene copolymer.
U.S. Pat. No. 5,840,419 to Alder discloses a multilayer polyolefin film comprising a core layer of a propylene polymer and an outer polyolefin layer on the core layer, the outer polyolefin layer including a coefficient reducing amount of a particulate, partially crosslinked polysiloxane, which are preferably in the form of elastomeric particles including polysiloxane in the form of silicone oil. The patent states that the silicone oil is released when the particles
Bell Keith A.
ExxonMobil Oil Corporation
James Rick F.
Tarazano D. Lawrence
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