Interpolymer film pouch

Details Interpolymer film pouch Interpolymer film pouch

1998-08-17

2002-07-09

Pyon, Harold (Department: 1772)

Stock material or miscellaneous articles

Hollow or container type article

Nonself-supporting tubular film or bag

C428S035700, C428S036900, C428S200000, C428S220000, C428S347000, C428S500000, C428S515000, C428S516000, C428S517000, C428S521000

Reexamination Certificate

active

06416833

ABSTRACT:

FIELD OF THE INVENTION
Sealing properties of films are key to their effective use in many packaging applications, such as for example fluid containing disposable pouches that may be manufactured on form, fill and seal equipment employing either impulse or thermic sealing techniques; vacuum packages for irregular shaped products and for prepared meats, cheeses and the like; shrink wrapped poultry; and skin packaging. While this invention is directed to all forms of packaging, it is of particular value in the area of liquid packaging, namely for the manufacture of liquid containing pouches.
This invention relates to pouches for flowable materials made from films formed from a new class of ethylene-alpha-olefin interpolymers that demonstrate superior performance in pouches for foods, such as milk.
BACKGROUND OF THE INVENTION
Packaging machinery is being designed to operate at faster speeds all the time. Such machinery requires lower sealing temperatures and hence improved hot tack strength in films to be used to make packaging with such machines. While hot tack strength is often a good indicator of whether a film will produce an excellent pouch, other properties are proving to be of equal or greater significance, for example, melt strength.
Metallocene ethylene-octene or ethylene-hexene interpolymers are available commercially in the density range from 0.80 to 0.915 gm /cc. These densities are too low in modulus to be used alone to make pouches for flowable materials. They must be either blended with Zeigler-Natta interpolymers or used in co-extrusions to form liquid pouches. As a class of polymer they are much more expensive than conventional Zeigler-Natta linear low density polyethylene (LLDPE) and do not, on their own, possess the optimum balance of properties for liquid pouch applications.
The standard polymer of the liquid pouch industry is the copolymer of ethylene-octene polymerized with Zeigler-Natta catalysts. While these polymers offer acceptable performance there is room to reduce the incidence of field failure of pouches caused by punctures, or seal failure through property improvement.
There are now available a new class of polymers which are referred to as hybrid Zeigler-Natta/Metallocene catalyst interpolymers. These are formed of ethylene and C
4
to C
10
alpha-olefins produced by a polymerization process using multiple reactors (minimum of 2) in series or in parallel or both. The process uses both Zeigler-Natta and Metallocene catalysts, preferably in separate reactors to produce hybrid interpolymers with advantageous properties for liquid packaging. The catalysts are the known metallocene or single-site catalysts and the Zeigler-Natta catalysts, both of which are well documented in the catalyst art.
Hot tack strength is the ability of a film to seal under stress while still in a molten state. This property is one of the most critical in packaging applications where machines run at high speeds and sealing takes place between molten sealing components of a package, thereby placing the sealing components, and hence the seal under stress when the package is formed, filled and, sealed.
It should be noted that in the case of fluid containing pouches made on form, fill and seal equipment, there appears to be a correlation between seal leaker frequency and hot tack strength. This is supported by data gathered in the dairy industry.
As noted, the development of single site catalyst (SSC) or metallocene technology has brought about an improved class of polymers ranging from crystalline to elastomeric materials. These polymers have features such as improved impact strength and toughness, better melt characteristics, because of the control over molecular structure, and better clarity. Exxon and Dow have developed SSC or metallocene polymers and each has the benefit of a number of patents relating to these polymers. Exxon is said to use mono- and bis-cyclopentadienyl metallocenes, while Dow's focus is on titanium cyclopentadienyl metallocenes, which it calls “constrained geometry catalysts”.
In practice, Exxon produces ethylene-butene and ethylene-hexene polymers, while Dow makes ethylene-octene polymers of the metallocene or SSC type. Dow claims that its metallocene or SSC polymers are different as they have uniformly introduced comonomers and long chain branching that improve processability in otherwise linear polymers.
BACKGROUND ART
Examples of the non-hybrid polymers of Exxon are found in the following patents and applications, the disclosures of which are incorporated herein by reference: U.S. Pat. No. 5,382,630 issued Jan. 17, 1995 to Stehling et al and WO093/03093 published Feb. 18, 1993 to Meka et al. These resins are available commercially from Exxon under the Brand name EXACT™.
Examples of the non-hybrid polymers of Dow are found in the following U.S. patents, the disclosures of which are incorporated herein by reference: U.S. Pat. No. 5,508,051 issued Apr. 16, 1996 to Falla et al; U.S. Pat. No. 5,360,648 issued Nov. 1, 1994 to Falla et al; U.S. Pat No, 5,278,272 issued Jan. 11, 1994 to Lai et al; and U.S. Pat. No. 5,272,236 issued Dec. 21, 1993 to Lai et al. These resins are available commercially under the Brand name AFFINITY™.
In DUPONT CANADA INC.'s PCT International Publication WO 95/10566 published Apr. 20, 1995, the disclosure of which is incorporated herein by reference, there are disclosed pouches for flowable materials wherein the sealant film is made from a SSC linear copolymer of ethylene and at least one C
4
-C
10
alpha-olefin. Blends of these SSC interpolymers with at least one polymer selected from multi site catalyst linear interpolymers of ethylene and at least one C
4
-C
10
alpha-olefin, a high pressure polyethylene and blends thereof.
In DUPONT CANADA INC.'s PCT International Publication WO 95/21743 published Aug. 17, 1995, the disclosure of which is incorporated herein by reference, there is disclosed an ethylene copolymer film of improved stiffness for use in the manufacture of fluid containing pouches. Typically, the structure comprises an interposed layer of polyethylene having a thickness in the range of 5 to 20 microns and a density of at least 0.93 gm/cc and a melt index of from about 1 to 10 dg/minute, the at least one outer layer being a SSC or metallocene polyethylene/alpha-olefin film which may have a density in the range of 0.88 to 0.93 gm/cc. The only requirements placed on the stiffening interposed layer are that it be of a particular thickness and density. These properties are greater in the stiffening layer than in the metallocene or SSC layer(s). This application indicates that the stiffening layer is included in order for the fluid containing pouch to stand up properly so that fluid may be poured from it when the pouch is placed in a supporting container.
DUPONT CANADA INC.'s U.S. Pat. No. 4,503,102(Mollison) and U.S. Pat. No. 4,521,437(Storms), the disclosures of which are incorporated by reference, disclose a polyethylene film for use in a form, fill and seal process for the manufacture of a disposable pouch for liquids such as milk. U.S. Pat. No. 4,503,102 discloses pouches made from a blend of a linear ethylene copolymer of ethylene and a C
4
-C
10
&agr;-olefin and an ethylene-vinyl acetate polymer copolymerized from ethylene and vinyl acetate. The linear polyethylene copolymer has a density of from 0.916 to 0.930 g/cm
3
and a melt index of from 0.3 to 2.0 g/10 minutes. The ethylene-vinyl acetate polymer has a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10 g/10 minutes. The blend disclosed in Mollison U.S. Pat. No.4,503,102 has a weight ratio of linear low density polyethylene to ethylene-vinyl acetate polymer of from 1.2:1 to 24:1. U.S. Pat. No. 4,503,102 also discloses multi layer films having as a sealant film the aforementioned blend.
U.S. Pat. No. 4,521,437 (Storms) describes pouches made from a sealant film which is from 50 to 100 parts of a linear copolymer of ethylene and octene-1 having a density of from 0.916 to 0.930 g/cm
3
and a melt ind

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