Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1995-06-06
2002-07-02
Yamnitzky, Marie (Department: 1774)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C427S533000, C427S536000, C264S448000
Reexamination Certificate
active
06413333
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to thermoplastic films and more particularly to films of oriented high density polyethylene (HDPE) which have good dead-fold characteristics, twistability, printability and receptivity of water-based coatings.
BACKGROUND OF THE INVENTION
Blown films of HDPE having an ethylene-vinyl acetate heat seal coating are used for food packaging but such films must have a thickness of about two mils to meet the water vapor transmission (WVTR) requirements for packaging suitable for dry foods such as cereals. Moreover, blown HDPE films do not exhibit the dead-fold properties desirable in food packages particularly of the bag-in-box type.
U.S. Pat. Nos. 4,870,122 and 4,916,025 (Lu) describe HDPE films which have good WVTR properties at film thicknesses of about one mil. The films are produced from high density polyethylene (HDPE) having a density of 0.96 or higher and are biaxially oriented in an imbalanced manner to a degree of about 1.25:1 to about 2:1 in the machine direction (MD) and to a degree of about 6:1 to about 12:1 in the transverse direction (TD). These films have reduced water vapor transmission (WVTR), improved dead-fold characteristics and other physical characteristics which are markedly better than blown HDPE films which can be further improved by the addition of microcrystalline wax. When provided with a heat seal layer by co-extrusion or coating, the films are particularly well suited for use in packaging foods in bag-in-box operations conducted on vertical, form, fill and seal (VFFS) machinery. While the imbalanced orientation confers the desired overall combination of properties on the film, the high degree of orientation in the transverse direction tends to make the film weak in this direction so that it tears relatively easily.
U.S. Pat. Nos. 4,343,852, 4,400,428, 4,419,411, 4,502,263, 4,692,379, and 4,734,317, all of which are incorporated herein by reference, disclose films having a base layer of polypropylene polymers and sealable skin layers on one or more sides of the base layer. However, these structures do not comprise HDPE base layer and typically lack good deadfold properties while having higher water vapor transmission rates associated with polypropylene. Given the differences between polypropylene and HDPE, e.g., in melting point (348° F. for PP, 279° F. for HDPE), processing polypropylene films requires different extrusion temperature, extruder screw design, die design draw down ratio, machine direction orientation temperature and percent, as well as transverse direction orientation temperature and rate.
SUMMARY OF THE INVENTION
The present invention relates to providing a film having good dead fold properties, optical clarity, good slip properties, and good receptivity to water based coatings, including water based inks, water based adhesives and other common water based coatings such as polyvinylidene chloride (PVDC), and acrylics.
The present invention relates to a film of high density polyethylene (HDPE) that has coextruded skin resins, laminated film or coatings on both sides of the HDPE base layer. Up to three layers of skin resins can be on each side of the base layer and can include heat sealable or non heat sealable type skins. For present purposes heat sealable skin resins are those which seal at a minimum seal temperature below the distortion temperature of HDPE base layer film.
More particularly, the present invention relates to an oriented polymer film which comprises:
a) a treated upper skin layer (a) capable of receiving a water base coating, said layer (a) having a surface coextensively adherent to the upper surface of a core layer (b), and an exposed surface, said upper layer (a) being formed from at least one polymer selected from the group consisting of ethylene-propylene-butene-1 terpolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, isotactic polypropylene, low density polyethylene (LDPE), very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), polyvinylidene chloride (PVDC), polyvinyl alcohol (PVOH) and acrylic, said upper layer (a) being substantially devoid of silicone oil, the exposed surface of upper layer (a) containing a coefficient of friction-reducing amount of silicone oil transferred to said surface of (a) by contact with a silicone oil present upon the exposed surface of a lower skin layer (c);
b) a base layer (b) derived from HDPE, having an upper surface and lower surface,
c) a lower skin layer (c) having a surface adherent to said lower surface of base layer (b), and an exposed surface, said layer (c) containing at least one polymer selected from the group consisting of ethylene-propylene-butene-1 terpolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, isotactic polypropylene, low density polyethylene (LDPE), very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), said polymer being compounded with i) an effective amount of a particulate cross-linked hydrocarbyl-substituted polysiloxane anti-blocking agent and ii) a quantity of silicone oil such that a coefficient of friction-reducing amount is present on the exposed surface of layer (c) as well as the exposed surface of layer (a) after mutual contact of said surfaces.
In another aspect, the present invention relates to a method of making a film which comprises:
(1) providing the upper major surface of the above-described core layer (b) derived from a high density polyethylene with a coextensive water-based coating receiving upper skin layer (a) formed from at least one polymer selected from the group consisting of ethylene-propylene-butene-1 terpolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, isotactic polypropylene, low density polyethylene (LDPE), very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), polyvinylidene chloride (PVDC), polyvinyl alcohol (PVOH) and acrylic, said upper skin layer (a) being substantially devoid of silicone oil;
(2) providing the lower major surface of core layer (b) with a coextensive surface lower skin layer (c) formed from at least one polymer selected from the group consisting of ethylene-propylene-butene-1 terpolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, isotactic polypropylene, low density polyethylene (LDPE), very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), said lower skin layer (c) being compounded with i) an effective amount of a particulate cross-linked hydrocarbyl-substituted polysiloxane anti-blocking agent and ii) a quantity of silicone oil such that a coefficient of friction-reducing amount will be present on the exposed surface of layer (c) as well as the exposed surface of layer (a) after mutual contact of said surfaces; and
(3) contacting the exposed surface of layer (c) with the exposed surface of layer (a) such that a coefficient of friction reducing amount of silicone oil is transferred from the exposed surface of layer (c) to the exposed surface of layer (a).
The film composition of the present invention can comprise a biaxially oriented high density base layer of at least 50 weight percent of a high density polyethylene having a density of 0.96 or higher. The skin layers are used with HDPE films which have been biaxially oriented to provide product having good WVTR properties as well as other characteristics, e.g., barrier properties for gases such as oxygen, which are desirable in packaging films.
Those embodiments wherein a skin layer consists essentially of PVDC, PVOH or acrylic exhibit reduced water vapor transmission rate and oxygen transmission rate.
The skin layers help provide a film which is readily castable while maintaining the desirable properties of HDPE including dead fold, twist retention, TD tear and moisture barrier. The films can be cast, and oriented in the solid state up to about two
Bader Michael John
O'Brien Jeffrey James
ExxonMobil Oil Corporation
James Rick F.
Santini Dennis P.
Yamnitzky Marie
LandOfFree
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