Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-05-03
2002-07-23
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S500000, C428S515000, C428S520000, C428S910000
Reexamination Certificate
active
06423421
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to oriented, heat shrinkable thermoplastic film.
BACKGROUND OF THE INVENTION
For many years, the heat shrinkable films industry has endeavored to reduce film gauge while maintaining performance in response to initiatives associated with source reduction. Lower gauges also allow for increased footage on rolls, which benefits the customer by reducing downtime (changeover time).
However, prior strategies involving films having single resin layers or conventional melt blends of resins, especially linear low density polyethylene (LLDPE), typically resulted in performance concessions. For instance, some improvement in optical quality and percent free shrink may have been seen, but with an undesirable degradation in impact strength. In the case of other blend compositions, good impact resistance and abrasion resistance could be obtained, but with an accompanying degradation in free shrink and clarity.
Thus, the technical challenge remained to design display films with higher impact resistance than LLDPE, but with optical and shrink properties comparable to LLDPE. The inventors have found that the use of a multicomponent ethylene/alpha-olefin interpenetrating network resin (herein “IPN resin”) permits property tailoring without compromising clarity, impact resistance, free shrink, or resistance to tear propagation. The result is a stronger, more abuse resistant film having the shrink and optical properties presently provided by LLDPE. These inventive films result in lower failures at a processor's packaging machine, or during distribution of contents. The tensile strength of this film is superior to many conventional films, thereby permitting downgauging. A down-gauged film with performance properties comparable to prior LLDPE formulations at their previous gauge can account for less downtime and changeovers at the customer's plant owing to the above mentioned greater roll footage. The ability to deliver higher value heat shrinkable film without a significant cast premium is a distinct advantage of the films of this invention. Other resins recognized for providing certain performance features (i.e. clarity, seal initiation temperature, low temperature shrink) such as metallocene resins, or blends, cannot provide abrasion resistance, nor deliver low temperature and low haze performance without a substantial cost penalty. The inventors have found that the use of an IPN resin in the skin layer or layers of a multilayer film can result in reduced levels of required antiblocking agent via removal of, or reduction in, the need for ethylene/vinyl acetate copolymer (EVA) in the skin layers. Additive reduction is advantageous because of reduced abrasive damage from inorganic particles, reduced accumulation of wax onto machine and package contents due to transfer from film to contact surfaces, together with better gloss and clarity.
The use of IPN resins thus provides superior mechanical strength properties while preserving excellent optical and shrink values comparable to e.g. D955™ film. These performance attributes can lead to higher performance films at comparable thickness relative to current LLDPE films or to thinner films.
An improved packaging film in accordance with the present invention can thus provide adequate resistance to tear propagation; excellent free shrink; good optics, including haze, clarity, and gloss values; high impact resistance; and high tensile strength.
SUMMARY OF THE INVENTION
In a first aspect, a multilayer oriented heat shrinkable film comprises an internal layer comprising a multicomponent ethylene/alpha-olefin interpenetrating network resin having a melt index less than 1.4, the resin comprising a homogeneous component having a melt index of less than 1, and a density of at least 0.91 grams/cubic centimeter, and a heterogeneous component having a melt index of between 1.5 and 20; and outer layers comprising a polymeric resin; wherein the film has a haze value (ASTM D 1003-95) less than or equal to 5, a peak load/mil value (ASTM D 3763-95a) of at least 155 newtons/mil, and a free shrink (ASTM D 2732-83) at a temperature of 200° F. of at least 8% in either or both of the longitudinal and transverse directions.
In a second aspect, a multilayer oriented heat shrinkable film comprises an internal layer comprising polymeric resin; first and second intermediate layers, each disposed on a respective opposite side of the internal layer, comprising multicomponent ethylene/alpha-olefin interpenetrating network resin having a melt index less than 1.4, the resin comprising a homogeneous component having a melt index of less than 1, and a density of at least 0.91 grams/cubic centimeter, and a heterogeneous component having a melt index of between 1.5 and 20; and first and second outer layers, disposed on the first and second intermediate layers respectively, comprising a polymeric resin; wherein the film has a haze value (ASTM D 1003-95) less than or equal to 5, a peak load/mil value (ASTM D 3763-95a) of at least 155 newtons/mil, and a free shrink (ASTM D 2732-83) at a temperature of 200° F. of at least 8% in either or both of the longitudinal and transverse directions.
In a third aspect, a solid state oriented heat shrinkable film comprises between 50 and 100 percent, by volume of the total film, of a multicomponent ethylene/alpha-olefin interpenetrating network resin having a melt index less than 1.4, the resin comprising a homogeneous component having a melt index of less than 1, and a density of at least 0.91 grams/cubic centimeter, and a heterogeneous component having a melt index of between 1.5 and 20; and between 0 and 50 percent, by volume of the total film, of a polymeric resin; wherein the film has a haze value (ASTM D 1003-95) less than or equal to 5, a peak load/mil value (ASTM D 3763-95a) of at least 155 newtons/mil, and a free shrink (ASTM D 2732-83) at a temperature of 200° F. of at least 8% in either or both of the longitudinal and transverse directions.
In a fourth aspect, a multilayer oriented heat shrinkable film comprises an internal layer comprising a blend of a multicomponent ethylene/alpha-olefin interpenetrating network resin having a melt index less than 1.4, and ethylene polymer or copolymer having a density of at least 0.935 grams/cubic centimeter, wherein the multicomponent ethylene/alpha-olefin interpenetrating network resin having a melt index less than 1.4 comprises a homogeneous component having a melt index of less than 1, and a density of at least 0.91 grams/cubic centimeter, and a heterogeneous component with a melt index of between about 1.0 and 20; and outer layers comprising a polymeric resin; wherein the film has a haze value (ASTM D 1003-95) less than or equal to 5, a peak load/mil value (ASTM D 3763-95a) of at least 155 newtons/mil, and a free shrink (ASTM D 2732-83) at a temperature of 200° F. of at least 8% in either or both of the longitudinal and transverse directions.
Definitions
“Acrylic” herein refers to acrylic or to methacrylic.
“Composite free shrink” herein refers to a value determined by summing the percent free shrink in the longitudinal direction with the percentage free shrink in the transverse direction. For example, Example 1 in Table 3 displays the following values at 200° F.: 17% free shrink in the longitudinal direction, and 19% free shrink in the transverse direction. The composite free shrink would then be 17% +19%, or a value of 36%.
“CRYSTAF” herein refers to an analytical technique which can be used to characterize the composition of a polymer by means of a fractionation scheme based on crystallization isolation. Samples were analyzed by Polymer Char (Valencia Parc Tecnologic, PO Box 176 E-46980, Paterna, Spain). The technique generates results equivalent to that provided from TREF. (see Monrabal (1994) J. Applied Poly. Sci. 52, 491; Soares et al., SPE Polyolefins XI p287-312).
“Ethylene/alpha-olefin copolymer” (EAO) herein refers to copolymers of ethylene with one or more comonomers selected from C
3
to C
10
alpha-olefins such as propene, b
Banaszak Cheryl M.
Buccolo Adam D.
Childress Blaine C.
Nakarani D. S.
Quatt Mark B.
Sealed Air Corporation
LandOfFree
Heat shrinkable film with multicomponent interpenetrating... 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 shrinkable film with multicomponent interpenetrating..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat shrinkable film with multicomponent interpenetrating... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2866487