1. Field of the Invention
The object of the invention appears from the title. By textile properties there is primarily meant a soft and warm handle. In particular the invention concerns very low weight film materials, and embodiments of the invention are directed to film material which additionally exhibits through-going porosity and/or high strength such as tear propagation resistance, tensile strength and puncture strength.
2. Description of the Related Art
During the last 40-50 years there have been presented a number of proposals and a few industrial processes for manufacture of film materials formed of thermoplastic polymer material exhibiting textile properties, but due to complications in the manufacturing process and/or relatively high machine costs, these technologies have in general not been competitive with non-woven technologies based on spun filaments. In particular this has been a difficulty for materials with low weight per area. The object of the present invention can be further specified as aiming at relatively low machine costs, and simplicity in the carrying out of the process.
WO 06/072604 and WO 06/120238, both concerning inventions which have been developed in the laboratory of the inventors, disclose stretching of monoaxially oriented film in a direction transverse to the original orientation, by passage between intermeshing grooved rollers on which the crests are generally flat and have sharp edges. There is hereby formed a fine pattern of thicker linear “bosses” and intervening thinner “webs”, and due to the sharp edges on the crests of the grooved rollers there is a distinct separation between the two regions in the pattern.
In both inventions this stretching is a step in the manufacture of crosslaminates. In the first mentioned patent the produced pattern of thickness differences serves to form an internal micro-channel system in the crosslaminate, channels which in connection with mutually displaced perforations in the two films form an advantageous type of through-going porosity.
In the second mentioned invention the purpose of the introduction of the fine pattern of “webs” which have become biaxially oriented, is to improve the tear propagation resistance.
As it appears from both of the above-mentioned WO publications, the stretching between the intermeshing grooved rollers with crests having sharp edges is carried out in such a way that the original direction of orientation is parallel or practically parallel with the grooves. However, in trials preceding the present invention the inventors used their grooved-roller machine, designed for the abovementioned two inventions, in a different way, namely to stretch a 20 micron thick coextruded uniaxially melt-oriented HDPE film under an angle of about 45° to the melt orientation and with an engagement between the crests of the grooved rollers which was deeper than tried before. This produced a film of unique structure, namely the structure which appears from the microphoto FIG. 1. This structure gave the film a surprising soft and warm feel. It became 15 clear that such film in itself, or in form of an assembly of several films, is very suited for several textile applications. As it will appear from the following, this film structure and an assembly of such films can be manufactured by an uncomplicated process and using relatively inexpensive and safely working machinery, the key machinery being the grooved rollers with sharp-edged crests and industrially well established, uncomplicated machinery designed to make a uniaxial orientation extend under an acute angle to the continuous direction of a film web.