Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1999-07-08
2002-10-01
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S518000, C428S910000
Reexamination Certificate
active
06458470
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a high barrier multilayer film, and more particularly to a high barrier multilayer film having polymer layers produced from Ziegler-Natta and metallocene catalysts.
Polymeric films are widely used in many industrial applications. One particularly important application is the food packaging industry. Films employed in the food packaging industry are chosen to provide barrier characteristics necessary for proper food containment. Such barrier characteristics include water vapor barrier, oxygen and gas barrier, as well as flavor and aroma barrier properties.
Polypropylene is a polymer commonly employed in films used in the food packaging industry. In the case of multilayer films, polypropylene may be used in the base or core layer, or may be used in layers intermediate between the core and skin layers. Often, the polypropylene layers are modified to vary the barrier characteristics from those exhibited in the unmodified state. For example, a resinous modifier, additive, and/or second polymer, may be blended with the polypropylene.
Attempts to vary the characteristics of polypropylene are often directed toward the improvement of the moisture barrier properties and machinability provided by the films formed of such polymer.
U.S. Pat. No. 5,620,803, issued Apr. 15, 1997 to Oyama et al., discloses a heat shrinkable polypropylene laminate film having two surface layers of isotactic polypropylene and an intermediate layer of syndiotactic polypropylene.
U.S. Pat. No. 5,500,282, issued Mar. 19, 1996 to Heffelfinger et al, is directed to a high moisture barrier oriented polypropylene film containing a high crystallinity polypropylene and a terpene polymer.
U.S. Pat. No. 5,451,455, issued Sep. 19, 1995 to Peiffer, discloses a biaxially oriented polypropylene film consisting of a base layer of propylene polymer and a low molecular weight resin and at least one additional layer on the base layer, in which the additional layer is readily subjected to corona treatment. The propylene polymer has a melting point of at least 140° C., a melt flow index in the range of about 0.5 g/10 min., and an n-heptane-soluble fraction of less than about 15% by weight.
U.S. Pat. No. 5,595,827, issued Jan. 21, 1997 to Yamada et al., relates to a polypropylene resin composition consisting of a crystalline polypropylene having a high stereoregularity, and terpene and petroleum resins having no polar group. The crystalline polypropylene has a melt flow rate at 230° C. under a load of 2.16 kg in the range of 0.1 to 500 g/10 min. and a crystallinity as determined by the components insoluble in boiling heptane of at least 60%.
Despite these advances in the art, the conventional films in the art are not without disadvantages. Particularly, polypropylene suffers a significant decrease in dimensional stability when blended with certain materials. This in turn hinders the machinability and processability of the resultant films, resulting in increased manufacturing costs and/or films of inferior quality. Certain polypropylene materials, for example, polypropylenes synthesized with metallocene catalysts have narrow molecular weight distribution, and thus would not be expected to provide as good operability in the production of oriented polypropylene films as resins with broad molecular weight distribution, but having all other resin characteristics essentially the same.
There exists a continuing need for multilayer films having improved barrier properties, while maintaining machinability and processability.
It is therefore an object of the present invention to provide a polypropylene multilayer film which exhibits improved barrier properties.
It is also an object of the present invention to provide a polypropylene multilayer film which exhibits increased machinability and processability.
It is also another object of the present invention to make these improvements at improved economics.
For better understanding of the present invention, reference is made to the following description and examples, the scope of which is pointed out in the appended claims.
SUMMARY OF THE PRESENT INVENTION
The present invention is a high barrier multilayer film particularly suitable for packaging. The high barrier multilayer film is a film including (a) a core substrate layer having an isotactic polypropylene produced from Ziegler-Natta catalysts, and (b) an adjacent layer on at least one surface of the core substrate layer, wherein the adjacent layer (b) comprises an isotactic polypropylene produced from metallocene catalysts; or the high barrier multilayer film includes (a′) a core substrate layer having an isotactic polypropylene produced from metallocene catalysts, and (b′) an adjacent layer on at least one surface of the core substrate layer, wherein the adjacent layer (b′) comprises an isotactic polypropylene produced from Ziegler-Natta catalysts.
In one preferred embodiment, the high barrier multilayer film further includes a resinous component blended into the Ziegler-Natta catalyzed layer. The resinous component can be based on natural or synthetic sources. Examples of the resinous component include, but are not limited to, hydrocarbon resins such as petroleum resins, styrene resins, cyclopentadiene resins, alicyclic hydrocarbon resins, terpene resins and mixtures thereof Preferred resinous components are alicyclic hydrocarbon resins and terpene resins. In general, these resinous components are typically 2-4 times as expensive as the polypropylene they are replacing in the blends. It is therefore preferred to keep the amount of the resinous component in the overall structure to a comparatively low level of about 1 to about 15%. This can be accomplished by incorporating them in chosen layers where they are particularly beneficial.
In another preferred embodiment, the high barrier multilayer film further includes at least one coating layer adhered to the outer surface of the topmost contiguous layer. The coating layer consists of ethylene methyl acrylate polymers, ethylene acrylic acid polymers, mixtures thereof, as well as other acrylic and vinyl polymers.
The core, intermediate, skin, and coating layers can optionally include conventional additives. Examples of the additives include, but are not limited to, antiblocking agents, antistatic agents, and slip agents.
As a result, the present invention advantageously provides a multilayer film exhibiting improved moisture barrier properties. Additionally, the multilayer film of the present invention exhibits increased dimensional stability in the resultant film. The resultant film also has a high degree of machinability and processability, resulting in better quality film and reduced manufacturing costs.
For a better understanding of the present invention, together with other and further objects, reference is made to the following description and its scope will be pointed out in the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a high barrier multilayer film, which includes (a) a core substrate layer having an isotactic polypropylene produced from Ziegler-Natta catalysts; and (b) an adjacent layer on at least one surface of the core substrate layer, wherein the adjacent layer (b) is an isotactic polypropylene produced from metallocene catalysts. Alternatively, the high barrier multilayer film can include (a′) a core substrate layer comprising an isotactic polypropylene produced from metallocene catalysts and (b′) at least one adjacent layer (b′), comprising an isotactic polypropylene produced from Ziegler-Natta catalysts.
The Ziegler-Natta catalyzed isotactic polypropylene of the core substrate layer is commercially available from the stereo regular polymerization of propylene based on the use of Ziegler-Natta catalysts. Such catalysts generally are reaction products of an organometallic compound belonging to Groups IA to IIIA with a compound of a transition metal of Groups IVB to VIII, as described in greater detail by G. Crespi and L. Luciani in “Olefin P
DeLisio John P.
Peet Robert G.
ExxonMobil Oil Corporation
James Rick F.
Santini Dennis P.
Tarazano D. Lawrence
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