Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
2000-09-21
2003-10-14
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C264S173130, C264S173160, C264S173190
Reexamination Certificate
active
06632383
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing improved polymeric films. More particularly, this invention relates to a method for producing oriented polymeric films having improved gauge uniformity.
BACKGROUND OF THE INVENTION
Polymeric films having a polyolefin core layer, e.g., of an oriented isotactic polypropylene (OPP), have been widely used in food and non-food packaging applications, because such films have desirable properties, such as resistance to transmission of moisture, air, deleterious flavors, and the like, as well as outstanding mechanical properties.
However, during the production of, for example, an opaque polymeric film, uneven distribution of polymer flow through the die often occurs, and as a result, film products having inferior gauge (i.e., thickness) uniformity are obtained. In these conventional production processes, a significant percentage (e.g., 22%) of mill rolls of white opaque film often fails to achieve “superprime” quality classification. Further, in cases where polybutylene terephthalate (PBT) is used as the cavitating agent, PBT may degrade and build up in the film production equipment, forming deposits which further affect the flow patterns of molten polymer in the die.
We have now discovered that the addition of a relatively small amount of a fluoropolymer to a resin allows a more even distribution of polymer flow through a die, which in turn leads to improved gauge uniformity. In particular, the addition of a relatively small amount of a fluoropolymer to a resin leads to improved gauge uniformity by providing (i) better distribution and control of the base material and (ii) a better interfacial relationship between the base layer and any tie or skin layer material. In addition to this unexpected benefit, such a use of a relatively small amount of a fluoropolymer in the core layer reduces the build-up of degraded PBT and deposits therefrom.
U.S. Pat. No. 4,753,995 to Chu, et al. discloses that the extrudability of linear resins of ethylene into thin films is improved by adding small amounts (e.g., 0.02 to 2 weight percent) of polyvinylidene fluoride for reducing melt fracture and head pressure, and for providing films having reduced blocking.
U.S. Pat. No. 4,829,116 to Piesold discloses a polyolefin molding composition which contains a fluorine-containing polymer together with a wax. The patent states that the composition has a broad processing range in which no surface defects occur, and that the throughput on extrusion is greatly increased.
U.S. Pat. No. 4,904,735 to Chapman, Jr., et al. discloses a processing aid composition for difficultly melt-processable polymers, wherein the processing aid composition consists essentially of specific amounts of a particular fluorocarbon copolymer and specific amounts of a tetrafluoroethylene homopolymer or copolymer.
U.S. Pat. No. 4,931,499 to Sakai, et al. discloses a rubber composition obtained by subjecting a mixture of (I) 35-95 parts by weight of a fluoroelastomer and (II) 65-5 parts by weight of an ethylene-&agr;-olefin copolymer rubber and a crosslinking agent for the copolymer rubber (III) to reaction while imparting shearing deformation to the mixture.
U.S. Pat. Nos. 5,010,130, 5,013,792, and 5,057,575 to Chapman, Jr., et al. disclose polymer blend compositions comprising (a) a major portion of difficultly-processable polymer and (b) a minor portion of (1) at least an effective amount of a particular fluorocarbon copolymer and (2) at least an effective amount of at least one tetrafluoroethylene homopolymer or copolymer.
U.S. Pat. No. 5,106,911 to Chapman, Jr., et al. discloses a polymer blend composition comprising: (a) a major portion of a difficultly-melt-processable hydrocarbon polymer; and (b) a minor portion of: (1) at least an effective amount of an elastomeric fluorocarbon copolymer; and (2)at least an effective amount of crystalline vinylidene fluoride polymer.
U.S. Pat. No. 5,132,368 to Chapman, Jr., et al. discloses a composition comprising a difficultly-melt-processable polymer and 0.002-0.5 wt % of one or more fluoropolymer process aids, wherein the fluoropolymer has a fluorine to carbon ratio of at least 1:2, is capable of forming a die-coating film under the prevailing conditions of extrusion temperature and pressure, and contains an effective amount of specific polar groups.
U.S. Pat. No. 5,266,639 to Chapman, Jr., et al. discloses tetrafluoroethylene/hexafluoropropylene (TFE/HFP) copolymers having a HFP index within a specifically selected range and having utility as processing aids in polyolefins and as solutions in highly-fluorinated solvents.
U.S. Pat. No. 5,374,683 to Morgan and U.S. Pat. No. 5,464,904 to Chapman, Jr., et al. disclose copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) having a high HFP content and an end-of-melting temperature as low as 200° C.
U.S. Pat. No. 5,587,429 to Priester discloses a processing aid system composition containing a fluoropolymer processing aid, a polar-side-group-containing extrusion adjuvant, and a poly(oxyalkylene) polymer to enhance extrusion of polyolefins.
U.S. Pat. No. 5,707,569 to Priester, et al. discloses polar-side-group-containing extrusion adjuvants that counteract the deleterious effect of certain additives used in polyolefins on the effectiveness of fluoropolymer processing aids in polyolefins.
U.S. Pat. No. 5,827,615 to Touhsaent, et al. discloses a metallized film substrate in which about 1 wt % of a fluoropolymer is used in a surface skin layer.
None of these patents, however, disclose a method for producing a polymeric film involving the addition of a relatively small amount of a fluoropolymer to a resin to provide a more even distribution of polymer flow through a die, which in turn leads to improved film gauge uniformity.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a more even flow of polymer through a die.
It is another object of the present invention to provide a method for producing a polymeric film having improved gauge uniformity.
It is yet another object of the present invention to provide a method for producing an opaque polymeric film having improved gauge uniformity, in which the build-up of degraded polybutylene terephthalate (PBT) is reduced.
In a first embodiment of the present invention, there is provided a method for producing a coextruded polymeric film comprising:
(a) coextruding (i) a base layer comprising a polymeric matrix; and (ii) at least one additional layer on at least one side of the base layer;
(b) cooling the coextruded multi-layer film; and then
(c) orienting the film in at least the machine direction (MD);
wherein at least said base layer contains a fluoropolymer and said base layer does not contain a cavitating agent.
In a second embodiment of the present invention, there is provided a method for producing a coextruded, opaque polymeric film comprising:
(a) coextruding (i) a base layer comprising a polymeric matrix and at least one cavitating agent and (ii) at least one additional layer on at least one side of the base layer;
(b) cooling the coextruded multi-layer film; and then
(c) orienting the film in at least the machine direction (MD);
wherein at least said base layer contains a fluoropolymer.
DETAILED DESCRIPTION OF THE INVENTION
The fluoropolymer used in the present invention may be any fluoropolymer which meets the objects of the present invention. Useful fluoropolymers include, but are not limited to, FX 9613, made by Dyneon, which is identified as a copolymer of vinylidene fluoride and hexafluoropropylene, and VITON A, made by E. I. Dupont de Nemours & Co., Inc.
Although the amount of fluoropolymer used may vary depending on the type of resin being modified, it is preferably used in an amount effective to provide a more even distribution of polymer flow through a die so as to provide an extruded web having improved gauge uniformity. Typically, such amounts can range from about 0.005 to about 3 weight percent, more preferably 0.01 to about 0.1 weight percent, based on the entire weight of t
Eashoo Mark
ExxonMobil Oil Corporation
James Rick F.
LandOfFree
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