Stock material or miscellaneous articles – Structurally defined web or sheet – Including variation in thickness
Patent
1994-06-16
1997-05-06
Loney, Donald
Stock material or miscellaneous articles
Structurally defined web or sheet
Including variation in thickness
428 357, 428 352, 428152, 428167, 428174, 428213, 428910, 264167, 264241, 2642888, 2642902, 156229, 156494, 156496, 425328, 425336, 425374, B32B 300, B32B 3100, A01J 2100, B29C 5500
Patent
active
056269447
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns an improved cross-laminate of oriented films of the general type defined in the preamble of claim 1 and improved processes and apparatus for manufacturing cross-laminates of this general type.
2. Description of Related Art
Processes for production cross-laminates of oriented films are known in particular from GB-A-1,526,722. In this known invention, the material is melt oriented in a generally uniaxial manner before cross lamination, and is biaxially oriented after cross lamination, preferably near room temperature. The melt orientation may be very weak, but is always combined with the use of blends of polymers, which are sufficiently incompatible for formation of a two- or multiphase grain of polymer under the influence of the melt-orientation, which grain has a very significant influence on the strength properties of the final cross-laminate. In order to enhance the tear-propagation resistance the bonding between the films is a generally weak bonding, but may be supplemented with a strong bonding in spots or lines.
The objective of this known invention is to provide for a film material which exhibits high strength properties in all respects. One of its important uses is for bags and similar packaging uses.
Further according to the above mentioned British Patent, the transverse stretching which is subsequent to the cross-sandwiching of the melt-oriented films (see the introduction to claims 12 and 24) is preferably carried out by passing the sandwich through several sets of mutually intermeshing grooved rollers, the grooves of which are as fine as practically possible. Also, the sandwich is normally (but not necessarily) stretched longitudinally in continuous manner between smooth rollers before, between or after said steps of grooved rollers stretching. (I distinguish between "sandwiching" which may involve, but needs not involve a bonding of the films to one another, and "laminating" which always involves such bonding). For obtaining optimum energy-absorbing properties (such as e.g. shock-tear propagation resistance) the different stretching steps, following the cross-sandwiching, are preferably carried out at temperatures very much below the melting ranges of the films, and may even be carried out at normal room temperature.
Further according to the above mentioned British Patent, the cross-lamination of films having a uniaxial or an unbalanced biaxial melt-orientation can be carried out already in the extrusion process under use of counterrotating dieparts, but can also be established on the basis of helical cutting of melt-oriented, tubular films. Thus the tubular films can be melt-oriented mainly in their longitudinal direction, helically cut e.g. under 45 degrees after solidification, and subsequently sandwiched in such manner that the said main directions criss-cross one another (i.e. become perpendicular to one another if the cutting angles all have been 45 degr.). In this connection, recent WIPO publication WO-A-89/12533 discloses particularly practical methods for spiral cutting of tubular film, and also discloses a suitable method to achieve a melt-orientation, which, if desired, can be perpendicular to the machine direction (i.e. the continous direction) of the film. The last mentioned method consists in first hauling-off the tubular film from the extrusion die in a screw-movement to give the tubular film a melt-orientation which forms an angle (e.g. 30 degrees) to the axis of the tube, and then helically cutting the tubular film (e.g. under 60 degrees) in the way which increases the angle between the machine direction and main direction of melt-orientation. Thus, using the above mentioned example that the "screwing" is under 30 degr. and the cutting under 60 degr., the melt orientation will become perpendicular to the machine direction after the helical cutting. This film can continuously be sandwiched with a film which is melt-oriented mainly in its longitudinal direction (the machine direction) to form a perpendi
REFERENCES:
patent: 4767488 (1988-08-01), Rasmussen
patent: 4874653 (1989-10-01), Rasmussen
Daniel William J.
Loney Donald
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