Cast film made from metallocene-catalyzed polypropylene

Details Cast film made from metallocene-catalyzed polypropylene Cast film made from metallocene-catalyzed polypropylene

1999-07-08

2002-05-21

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Composite

Of addition polymer from unsaturated monomers

C428S409000, C264S211120, C264S211170, C264S212000, C526S351000, C526S941000

Reexamination Certificate

active

06391467

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a single or multi-layer cast film which contains a layer of metallocene-catalyzed substantially syndiotactic propylene polymer.
BACKGROUND OF THE INVENTION
Metallocene catalyzed propylene polymers are known to have a low melting temperature, relative to conventional propylene polymers. For this reason, metallocene-catalyzed propylene polymers have been described as useful as the outer layer heat sealable material of biaxially oriented multi-layer films in U.S. Pat. No. 5,468,440 (column 6, lines 32 to 41). Other multi-layer films in which the advantage of an outer layer of metallocene-catalyzed propylene polymers are described are found in U.S. Pat. Nos. 5,529,843 and 5,462,807. Although these patents describe multi-layer films in which an outer layer is made from a metallocene-catalyzed propylene polymer, the patents are silent on the use of metallocene-catalyzed propylene polymers in the core layer of a multi-layer film.
U.S. Pat. No. 5,254,394 to Bothe, et al., discloses a polyolefin film for packaging comprising isotactic polypropylene base layer and a top layer of syndiotactic polypropylene which has high sealed-seam strength and excellent optical properties. The top layer can contain lubricant additives, such as waxes at levels of up to 2 wt. % relative to each other.
U.S. Pat. No. 5,212,246 discloses a cast film material of a heterophasic olefin polymer composition and a random copolymer of propylene and ethylene which is formed into a film by a cast film process.
Typically, in the food-packaging area, the use of cast or nonoriented polypropylene is limited because such cast films tend to be brittle at below-freezing temperatures and are not generally used for heavy, sharp or dense products without lamination to more puncture-resistant materials.
SUMMARY OF THE INVENTION
The invention is directed to a cast film which comprises a metallocene-catalyzed substantially syndiotactic propylene polymer which has been found to overcome the problems associated with conventional cast polypropylene. Optionally, the film includes one or more coextruded additional layers. The invention is also directed to a process for making cast films.
DETAILED DESCRIPTION OF THE INVENTION
The film of this invention is a cast film which comprises a metallocene-catalyzed substantially syndiotactic propylene polymer. The cast film is produced by pouring, spreading or extruding a fluid thermoplastic material onto a temporary carrier, solidifying the material by any suitable means, and removing it from the carrier. The film may be solidified by cooling, curing, or heating or a combination of these steps appropriate to the material being processed. The cast film is not stretched in the manner of oriented films. Generally, the cast films are made by the well-known chill roll cast process, but other known methods can be used.
An essential feature of the present invention is a metallocene-catalyzed substantially syndiotactic propylene polymer. By “substantially syndiotactic propylene polymer,” it is meant that the polymer generally possesses a syndiotacticty of at least 60% based on racemic pentads, typically greater than 70%, as measured by C
13
NMR spectroscopy. Useful substantially syndiotactic propylene polymers and methods of making them are found in U.S. Pat. Nos. 5,162,278; 5,158,920; 5,155,080; 5,036,034; 4,975,403; 4,892,851; and 4,794,096, which are incorporated herein by reference.
Metallocene-catalyzed syndiotactic polypropylene resins are available under the product name FINACENE by Fina, one example being FINACENE EOD 95-01.
The propylene polymer is predominantly comprised of propylene (at least 85% by weight) and has a melting point of about 135° C. or higher. The melt flow rate usually ranges from about 0.5 g/10 min to about 15 g/10 min at 230° C., more typically about 1.5 g/10 min to about 8 g/10 min at 230° C. The melt flow rate is measured in accordance with the standard ASTM D1238 method for propylene polymers.
The film can be fabricated with one or more outer layers. If outer layers are used, they may be any one of the coextrudable, film-forming resins known in the art. Such materials include isotactic polypropylene, propylene copolymers with a second monomer such as ethylene or butene-1, and propylene terpolymers which include additional monomers such as ethylene, butene-1, pentene-1, etc. Typical copolymers are ethylene-propylene copolymers and ethylene-butene-1 copolymers. Typical terpolymers are ethylene-propylene-butene-1 terpolymers. Blends of any of the foregoing homopolymers, copolymers and terpolymers are contemplated. The outer layer can be isotactic polypropylene, as discussed above.
Ethylene-propylene-butene-1 random terpolymers appropriate for use in the outer layer of the present invention include those containing 1-5 weight percent random ethylene and 10-35 weight percent random butene-1 with the balance being made up of propylene. The amounts of the random ethylene and butene-1 components in these terpolymers are typically in the range of 10 to 25 weight percent (ethylene plus butene-1) based on the total amount of the copolymer.
The copolymers and terpolymers typically have a melt flow rate in the range of about 5 to 10 with a density of about 0.9 and a melting point in the range of about 100 to about 130° C.
The polymers of the outermost layers of the film can also be fabricated from any polymers, copolymers or terpolymers or blends of homopolymers and blends of copolymer(s) and homopolymer(s) which have heat seal properties. Several of the materials identified above are illustrative of heat sealable copolymers which can be used in the present invention.
In one aspect of the invention the outer layer is derived from polyethylene. The polyethylene can be low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE) or high density polyethylene (HDPE). These ethylene polymers typically have a melt index ranging from about 1 to about 15 g/10 min. The low density polyethylenes should have a density of about 0.88 to about 0.93 g/cm
3
. Linear low density materials may have a density as high as 0.94 g/cm
3
, often ranging from 0.90 to 0.94 g/cm
3
, with a melt index of about 1 to about 10. The linear low density polyethylenes may be derived from ethylene together with other higher comonomers such as butene-1, hexene-1, or octene-1. HDPE has a density of greater than about 0.95 g/cm
3
, typically from about 0.95 to about 0.965 g/cm
3
. High density polyethylene suitable for use as the outer layer is described in Bakker, Ed. “The Wiley Encyclopedia of Packaging Technology,” pp. 514 to 523 (1986).
There can be more than one outer layer on one or both sides of the core. That is, one or more layers can be applied to the exposed surface of the outer layer. Films having such a multi-layer structure are represented, in simplified form, as having a structure “ABCBA” where “C” represents a core layer, “B” represents an intermediate layer adjacent to the core layer and “A” represents a further outer layer or skin layer applied to the outer surface of intermediate layer “B.” In such a film structure, the intermediate layer “B” can be referred to as a “tie-layer.” Layers “A” and “B” can be the same or different. Additionally, structures containing more than five layers are contemplated, e.g., seven, nine, or more layers.
In order to improve or enhance certain properties of the cast films of the invention for specific end-uses, it is possible for one or more of the layers to contain appropriate additives in effective amounts. Preferred additives include antistatic agents, antiblocking agents, lubricants, stabilizers and/or alicyclic hydrocarbon resins. Such additives are further described in U.S. Pat. No. 5,254,394, which is incorporated herein by reference. It is useful to incorporate additives such as wax, finely divided inorganic antiblock particles, silicone oil, and silicone spheres, such as non-migratory particulate crosslinked hydrocarbyl substituted polysiloxane slip agent, one such m

Affiliated with

Also associated with

Rating

Cast film made from metallocene-catalyzed polypropylene does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Cast film made from metallocene-catalyzed polypropylene, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cast film made from metallocene-catalyzed polypropylene will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2871727