Polymer compositions

Details Polymer compositions Polymer compositions

2000-12-12

2003-06-24

Tarazano, D Lawrence (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including grain, strips, or filamentary elements in...

C428S516000, C428S520000, C428S522000, C428S910000, C156S177000, C156S334000

Reexamination Certificate

active

06582795

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polymer compositions, such as polymer compositions obtainable by blending of two polyethylene components, and to polymer films blown from such polyethylenes and the use thereof for manufacturing films. In particular, the present invention concerns cross-laminated film materials and a method for the production of such materials.
2. Description of Related Art
There is a growing demand for tough films made without any reinforcements due to both environmental aspects and cost reductions.
Cross-laminated films are basically produced by the following two principles:
(1) Two or several single mono- and coextruded blended films are MD-oriented, annealed, precut at 45-60° angles and extrusion laminated together. The final films have a smooth surface without any physical structures.
(2) Two of several single, mono- and coextruded blended films, are precut at 45°-60° angles and laminated together by annealing, biaxially stretching and orientation. The final films have a longitudinal physical rib-structure.
Other related films, and processes are: (3) various reinforced films by PA and PET nets between two PE (LDPE) films, extrusion laminated together by LDPE. (4) Stretched tape from PP and HDPE extrusion laminated by LDPE or PP.
The two first mentioned alternatives are discussed in a number of patent applications and patents. Thus, cross-lamination of films is known from, e.g., GB 1 316 640, GB 1 084 550, U.S. Pat. Nos. 4,475,971, 4,439,260, 4,885,196, WO 89/12533 and WO 93/14928.
GB 1 316 640 presents a process for cross-lamination of two oriented polymer films together through a bonding film in such a manner that the directions of orientation cross each other. The publication discloses the use of high density polyethylene and polypropylene films in the process.
GB 1 084 550 discusses a packing material which is obtained by cross-lamination of at least two uniaxially oriented films of polyethylene or polypropylene in such a manner that the directions of orientation cross each other. The material is perforated so that free passage of air and vapours is allowed.
U.S. Pat. No. 4,475,971 discloses a method of forming a cross-laminated film. The film is a coextruded composite film containing a lower melting thermoplastic and a higher melting thermoplastic. The composite film is then fed through a pair of rollers to provide a bias oriented film and then laminating two such films together so that their directions of orientation are crossed. Both polyethylene and polypropylene are mentioned.
U.S. Pat. No. 4,439,260 discloses another method of forming cross-laminated films where the oriented film is slitted at a bias relative to the movement of the film. Two strips are then laminated together so that the directions of orientation are crossed. High density polyethylene and polypropylene are mentioned. Also a two-layer structure containing EVA, LDPE or another low-melting plastic as an outer layer is mentioned.
A three-layered composite film is disclosed in U.S. Pat. No. 4,885,196. The central layer consists of a foamed material, such as a foamed EVA copolymer. The structure has been obtained by cross-lamating two films together, where each films contains at least two layers, one of the outer layers being the foamed material which then forms a bonding layer between the films.
WO 89/12533 discloses a method of cutting the film and the cross-laminating two thus obtained strips to a cross-laminated film.
WO 93/14928 discloses a cross-laminate of at least two films. Each film is a three layer composite containing a surface layer acting as a release layer, another surface layer acting as a bonding layer and a main layer in the middle. In specific embodiments, the main layer contains 70% HDPE, 20% LLDPE and 10% PP. The release layer contains 70% LLDPE and 30% EPDM.
While the three-layer films presented in WO 93/14928 give good mechanical properties, they can only be produced in machines which allow for three-layer extrusion.
SUMMARY OF THE INVENTION
It is an object of the invention to eliminate the problems of the prior art and to provide a simple cross-laminated structure which still gives excellent properties to the cross-laminated film.
It is another object of the invention to provide a new polyethylene composition which can be useful for a number of everyday applications.
It is a third object of the invention to provide a method of manufacturing cross-laminated film materials.
It has now surprisingly been found that by using a composition containing a linear ethylene polymer together with a copolymer of ethylene and a (meth)acrylate monomer, good mechanical properties are obtained together with a good processability with a single-layer original structure. Films made from such compositions can be employed for cross-laminated film structures to provide tough products with good mechanical strength. The (meth)acrylate monomer will give the films adhesive properties when the films are warm, which removes or reduces the need for intermediate tie layers between the plies of a cross-laminate.
In particular, the cross-laminates are produced from preferred, novel compositions according to the invention, which comprise:
(I) 80-99 wt-% of an essentially linear polyethylene comprising
(i) a component having a relatively low MW and a relatively high density, and
(ii) a component having a relatively high MW and a relatively low density, said linear polyethylene having an MFR
2
of at least 5 g/10 min, a maximum MFR
2
of 6 g/10 min, a density of 915-945 kg/m
3
, and
(II) 1-20 wt-% of a branched copolymer of ethylene and a (meth)acrylate monomer containing 20-28 wt-% (meth)acrylate monomer units, said copolymer having an MFR
2
of 0.4 to 2.0 g/10 min.
Following the blending, the films are subjected to helical/biaxial cutting at a 45°-&agr;° angle to the machine direction and cross-lamination is achieved by superimposing two or several equal films/plies and binding them together by eating and pressing.
More specifically, the cross-laminate film materials comprise at least two oriented polymer film plies laminated together, each film being uniaxially oriented in a generally different direction with regard to each other, at least one of said polymer films comprising a polymer composition formed by
(I) 80-99 wt-% of an essentially linear polyethylene, which comprises
(i) a component having a relatively low MW and a relatively high density, and
(ii) a component having a relatively high MW and a relatively low density,
 said linear polyethylene having an MFR
21
of at least 5 g/10 min, a maximum MFR
2
of 6 g/10 min., a density of 915-945 kg/m
3
, and
(II) 1-20 wt-% of a branched copolymer of ethylene and an acrylate monomer containing 20-28 Wt-% acrylate monomer units, said copolymer having an MFR
2
of 0.4 to 2.0 g/10 min.
The method of producing the cross-laminates is characterized by a method comprising the steps of
providing a polymer composition consisting essentially of
(I) 80-99 wt-% of an essentially linear polyethylene, which comprises
(i) a component having a relatively low MW and a relatively high density, and
(ii) a component having a relatively high MW and a relatively low density,
said linear polyethylene having an MFR
21
of at least 5 g/10 min., a maximum MFR
2
of 6 g/10 min., a density of 915-945 kg/m
3
, and
(II) 1-20 wt-% of a branched copolymer of ethylene and an acrylate monomer containing 20-28 wt-% acrylate monomer units, said copolymer having an MFR
2
of 0.4 to 2.0 g/10 min
processing the polymer composition into a film,
subjecting the film to helical cutting to provide film bands having oblique orientation,
superimposing the film bands so that their directions of orientation are crossing; and
laminating the bands together to form a cross-laminated film structure.
By blending a limited amount of a copolymer of ethylene and a (meth)acrylate monomer, in particular an alkylated (meth)acrylate monomer into a linear polyethylene, such as a bimodal LLDPE, the right balance between final mechanical film strengt

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