Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1999-12-16
2002-03-19
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S515000, C428S516000, C428S518000, C428S511000
Reexamination Certificate
active
06358622
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to improved packaging films which can be heat sealed and then easily opened when desired. More specifically, this invention relates to improved heat sealable packaging films prepared from (1) ionomers modified with polypropylene, ethylene vinyl acetate copolymer, and, optionally, polyethylene and (2) ethylene-carboxylic acid copolymers modified with polypropylene, ethylene vinyl acetate copolymer, and, optionally, polyethylene. The resulting films are heat sealable with a relatively low heat seal initiation temperature and with consistent seal strengths over a relatively broad heat sealing temperature range. The heat seal strength, which is retained over time, can be varied or adjusted to desired values by adjusting the composition of the modified ionomer and/or ethylene-carboxylic acid copolymer blends. When opened, the seal fails cohesively in a clean manner (i.e., not stringy). Since the seal whitens upon opening, the film of this invention allows for tamper evident packaging.
BACKGROUND OF THE INVENTION
Heat sealable and easily opening multilayer thermoplastic films are widely used in the packaging industry, especially for food products. These films are usually formed by coextrusion or coating equipment. An external layer of a heat sealable composition is used to form the heat seal with another layer of the heat sealable composition or another substrate material. Heat sealable, easy-opening packages made from polymeric materials are known in the art and are used in many packaging applications, including food packaging.
U.S. Pat. No. 4,279,344 (Jul. 21, 1981) provides a heat sealable, easy opening packaging compositions containing 15 to 35 percent ionomer with the balance being either polypropylene or a polypropylene-polyethylene copolymer (up to 5 percent polyethylene). These compositions required relatively high heat seal temperature (i.e., about 450° F.).
U.S. Pat. No. 4,346,196 (Aug. 24, 1982) and U.S. Pat. No. 4,469,754 (Sep. 4, 1984) provide heat seal compositions of 20 to 80 percent ionomer and 20 to 80 percent of a terpolymer (ethylene, vinyl alkanoate or ester, and ethylenically unsaturated monocarboxylic acid). U.S. Pat. No. 4,550,141 (Oct. 29, 1985) and U.S. Pat. No. 4,539,263 (Sep. 3, 1985) provide heat sealable and peelable compositions containing 80 to 93 percent ionomer and 7 to 20 percent of a propylene/&agr;-olefin copolymer. Polypropylene homopolymers did not form satisfactory heat sealable compositions when combined with ionomers.
U.S. Pat. No. 4,689,340 (Jul. 14, 1987) provides a heat sealable composition containing up to 40 percent of a first polymer with a melt flow index of less than 5 and 60 percent or more of a second polymer having a melt flow index of greater than 20. The first polymer may be an ionomer or an ethylene vinyl acetate copolymer. The second polymer is selected from the group consisting of low density polyethylene, ethylene/vinyl acetate copolymers, and modified ethylene/vinyl acetate copolymers. When the first polymer is an ethylene/vinyl acetate copolymer, the second polymer must be a low density polyethylene.
U.S. Pat. No. 4,859,514 (Aug. 22, 1989) provides a sealing system having first and second webs which are heat sealed together to form the seal. The first web is an ionomer or an ionomer-ethylene vinyl acetate copolymer blend. The second web is a blend of ethylene vinyl acetate copolymer, ethylene 1-butene copolymer, and polypropylene.
U.S. Pat. No. 5,023,121 (Jun. 11, 1991) also provides a sealing system having first and second webs which are heat sealed together to form the seal.
The first web includes a sealant layer which is a blend of polybutene and polypropylene and a third polymeric material selected from the group consisting of: (i) ethylene vinyl acetate copolymer; (ii) low density polyethylene; (iii) linear low density polyethylene; and (iv) ionomer. The second web includes a sealant layer consisting essentially of a polymeric material selected from the group consisting of ethylene vinyl acetate copolymer, low density polyethylene, linear low density polyethylene, ionomer, and mixtures thereof. An additional layer of polymeric adhesive can be placed adjacent to and bonded to the sealant layer of the first web.
U.S. Pat. No. 5,547,752 (Aug. 20, 1996) provides heat seal compositions having 15 to 50 percent of an isotactic nonelastomeric polybutylene and 50 to 85 percent ionomer. U.S. Statutory Invention Registration H1 727 (May 5, 1998) provides a heat sealable multiple layer film having an outer layer and an adjacent interior layer. The interior layer is a blend of polypropylene and a primary resin selected from the group ionomer, ethylene vinyl acetate, low density polyethylene, and linear low density polyethylene. The exterior layer is a blend of a polybutylene and a copolymer such as low density polyethylene, linear low density polyethylene, ethylene vinyl acetate, ethylene acrylic acid, or ionomer. U.S. Pat. No. 5,891,500 (Apr. 6, 1999) provides heat sealable compositions which are blends of ionomer and polybutylene.
U.S. Pat. No. 4,870,134 provides heat sealable films formed from blends of an ethylene-carboxylic acid copolymer, a butene-1 homopolymer or copolymer, and a propylene homopolymer or copolymer. U.S. Pat. No. 5,066,543 provides heat sealable films formed from blends of an ethylene-carboxylic acid copolymer, a butene-1 homopolymer or copolymer, and an ethylene homopolymer or an ethylene unsaturated ester copolymer.
There still remains a need for heat sealable, easy opening packaging systems having improved performance. Such a system would provide low heat seal initiation temperatures with consistent heat seal strengths over a relatively wide range of heat sealing temperatures. Ideally, such a system would allow for easily adjustment of the heat seal strength for specific applications and provide a heat seal strength that remains essentially unchanged over time. Such a system would also provide for an easy opening seal which opens smoothly and cleanly (i.e., not stringy) with a uniform peel force. It would also be beneficial if the packaging system could provide a built-in tamper evident feature that would allow the consumer to readily determine if the package had been previously opened. The present invention provides such an improved heat sealable, easy opening packaging system.
SUMMARY OF THE INVENTION
This invention generally relates to heat sealable films comprising ionomer resin, polypropylene, ethylene vinyl acetate copolymer, and, optionally, polyethylene and to heat sealable films comprising ethylene-carboxylic acid copolymers modified with polypropylene, ethylene vinyl acetate copolymer, and, optionally, polyethylene. More particularly, the heat sealable films of this invention are formed from blends of about 50 to about 99 percent ionomer resin, ethylene-carboxylic acid copolymers, or mixtures thereof; about 0.5 to about 25 percent polypropylene; about 0.5 to about 25 percent ethylene-vinyl acetate copolymer; and about 0 to about 25 percent polyethylene. More preferably, the heat sealable films of this invention are formed from blends of about 60 to about 95 percent ionomer resin, ethylene-carboxylic acid copolymers, or mixtures thereof; about 2.5 to about 20 percent polypropylene; about 2.5 to about 20 percent ethylene vinyl acetate copolymer; and about 0 to about 10 percent polyethylene. Preferably the polypropylene is a homopolymer. The heat sealable films of this invention are ideally suited for extrusion coating and/or coextrusion with other film materials to form heat sealable multilayer or composite films. In such multilayer films, the present heat sealable film may be heat sealed to itself or to another film material.
The heat sealable films of this invention are especially useful in food packaging applications. The heat seal strength can be varied and controlled over a relatively large range (i.e., about 0.5 to about 4 lbs/in or about 9 to about 71 g/mm). Moreover, the present films also exhibit low heat seal initiation temperatures
Machonis, Jr. John
Mueller Mark R.
Pucci Mark S.
Shida Mitsuzo
Fitch Even Tabin & Flannery
Jackson Monique R.
M.S.I. Technology L.L.C.
Thibodeau Paul
LandOfFree
Heat sealable films does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Heat sealable films, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat sealable films will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2888666