Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1994-11-07
2001-09-18
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S332000, C428S447000, C428S448000, C428S476900, C428S516000
Reexamination Certificate
active
06291063
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to films, both monolayer films and multilayer films, and particularly to packaging films. The present invention also relates to packages, especially packages having one or more seals, as well as packaged products. The present invention is particularly related to films having a relatively low film-to-film coefficient of friction.
BACKGROUND OF THE INVENTION
For some time it has been known to provide a packaging film which contains silicone oil, in an outer film layer and/or an inner film layer. Silicone oil has been sprayed onto the surface of a film, as well as extruded in admixture with one or more polymers which make up the film, including polymer making up an outer layer of a multilayer film. The silicone oil has been used in combination with antiblocking agents, such as particulate silica, to provide a film having a desired coefficient of film-to-metal slip, as well as imparting desired antiblocking characteristics to the film.
It has been discovered that a film having two outer layers, each of which comprises 72.5 weight percent ethylene/propylene copolymer, 15 weight percent polybutylene, and 12.5 weight percent of a masterbatch comprising about 90 weight percent polypropylene (based on masterbatch weight), 4% inorganic antiblock, and 6% of a blend of fatty acid amides (hereinafter, “amides”), if used in a horizontal-form-fill-and-seal operation (“HFFS”), or vertical-form-fill-and-seal operation (“VFFS”), results in an unacceptable amides/antiblock buildup on the machine surface of the HFFS machine, or VFFS machine, because the amides/antiblock buildup sluffs off into the product, and/or hardens and damages the film. The amides/antiblock buildup is caused by the amides, which are extruded in admixture with the polymer of the surface layer, blooming to the surface of the film, in an amount thick enough to result in the buildup on machine surfaces. The antiblock particulates on the surface of the film also accumulate on the machine surfaces, together with the bloomed amides.
However, the fatty acid amides are present in order to provide the film with a desirable film-to-film coefficient of friction, so that packaged products slide freely when in contact with one another. This is desired in order to facilitate alignment of packaged products for the bulk packaging thereof, for example in boxes, as well as providing a desired low film-to-equipment coefficient of friction.
Thus, it would be desirable to provide a film which exhibits a low film-to-film coefficient of friction, as well as a low film-to-equipment/metal coefficient of friction, without buildup of fatty acid amides/antiblock on equipment/metal, and particularly without buildup and subsequent sluffing off into the product being packaged in the film. In order to accomplish this result, it would be desirable to reduce or eliminate the presence of fatty acid amides on the surface of the film, while providing a desired low film-to-equipment coefficient of friction, and while providing a desired low film-to-film coefficient of friction.
SUMMARY OF THE INVENTION
In an effort to produce a film having improved slip characteristics, polydimethylsiloxane, in an amount greater than 1100 parts per million, together with 1100 parts per million erucamide, was blended with a polyolefin, the resulting blend then being extruded to form the film. However, it was discovered that this particular formulation of polyolefin, polydimethylsiloxane, and erucamide, could not be extruded from a single screw extruder, in a manner which produced an acceptable film, because “surging” resulted. That is, during extrusion, the composition comprising polymer, erucamide, and polydimethylsiloxane, oscillated from periods of “slipping”, during which the mixture was not being forwarded in spite of the fact that the extruder screw was turning, to periods in which slipping did not occur. Due to the surging, the resulting film exhibited undesirable fluctuations in thickness and silicone oil concentration, and was of unacceptable quality for use as a heat-shrinkable packaging film.
However, it has been discovered that surging does not occur upon extrusion of a composition comprising propylene/ethylene random copolymer in an amount of 88 weight percent, based on total blend weight, together with 1.5 weight percent aluminum silicate antiblocking agent having an average particle size of 0.7 microns, and 0.5 weight percent polydimethysiloxane having a viscosity of 350 centistokes at 25° C. and a specific gravity of 0.973. The film produced using this formulation was discovered to be free of undesirable fluctuations in thickness and organosiloxane concentration, and to have acceptable quality for use as a heat-shrinkable packaging film.
It is believed that the relatively high level of aluminum silicate antiblocking agent prevents the presence of the relatively high level of orgaonsiloxane from causing the intermittent screw slippage which produces surging. Screw slippage and surging have been found to be higher in single screw extruders, as opposed to twin-screw extruders. At the same time that the antiblocking agent decreases screw slippage, the presence of the relatively high level of organosiloxane acts as a dispersant for the relatively high level of aluminum silicate antiblocking agent, thereby allowing the production of a film which is free of visible agglomerates of antiblocking agent. Thus, it is apparent that for the production of packaging films, the silicone oil and antiblocking agent act together to provide a plurality of advantages, each allowing the other to be used, to result in a film having desired coefficients of friction, as well as a uniformity of thickness and organosiloxane concentration, to provide a film of high quality for use as a heat-shrinkable packaging film.
Furthermore, it has been discovered that without the presence of the relatively high level of silicone oil, the relatively high level of the antiblocking agent would result in an undesirable head pressure in the extruder, thereby lowering the extrusion speed, as well as resulting in a higher melt temperature and a lower output rate from the extruder.
It has further been discovered that the above-described film, which comprises specified amounts of antiblocking agent and organosiloxane, can further comprise a relatively low level of fatty acid amide, in order to further enhance the frictional coefficients of the resulting film, as well as reducing the amount of organosiloxane needed to provide the desired film coefficients of friction. It is believed that this relatively low level of fatty acid amide, and reduced level of organosiloxane, in combination with the relatively high amounts of antiblocking agent, decreases the level of fatty acid amide/antiblocking agent buildup on machinery and fatty acid amide/antiblocking agent sluffing off into the product, because the migration rate of fatty acid amide to the film surface, i.e., fatty acid amide “blooming”, is directly related to the concentration of the fatty acid amide within the film layer.
As a first aspect, the present invention relates to a film comprising an outer layer. The outer layer comprises (A) polyolefin; (B) a member selected from the group consisting of:
i. antiblocking agent in an amount of from about 0.6 to 3 percent, based on the weight of the outer layer, wherein the antiblocking agent has an average particle size of from about 0.1 to 6 microns; and
ii. antiblocking agent in an amount of from about 0.4 to 0.59 percent, based on the weight of the outer layer, wherein the antiblocking agent has an average particle size of from about 2 to 4 microns; and
iii. antiblocking agent in an amount of from about 0.1 to 0.39 percent, based on the weight of the outer layer, wherein the antiblocking agent has an average particle size of from about 4.1 to 6 microns; and
(C) organosiloxane in an amount of from about 0.1 to 1.0 weight percent, based on the weight of the outer layer.
As a second aspect, the present invention pertains to a multilayer film comprising an
Hayes Gary Joseph
Shah Gautam Punshibhai
Cryovac Inc.
Hurley Jr. Rupert B.
Kiliman Leszek
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