POLYMER FILMS AND THEIR PRODUCTION AND USE

Abstract

The invention provides a process to orient a high molecular weight polymer film, formed from molten, dispersed or dissolved state, characterised in that as a start of this orientation process the film becomes embossed in a pattern of closely spaced dots or thin short lines, 5 thereby becoming oriented within these embossments, whereafter the orientation process is continued in one or more steps by m.d. stretching, t.d. stretching, or combined m.d. and t.d. stretching, whereby the embossed and oriented dots or lines gradually grow and develop until essentially the entire film has become oriented.

Claims

1. A process to orient a high molecular weight polymer film, formed from molten, dispersed or dissolved state, characterised in that as a start of this orientation process the film becomes embossed in a pattern of closely spaced dots or thin short lines, thereby becoming oriented within these embossments, whereafter the orientation process is continued in one or more steps by m.d. stretching, t.d. stretching, or combined m.d. and t.d. stretching, whereby the embossed and oriented dots or lines gradually grow and develop until essentially the entire film has become oriented.

2. A process according to claim 1, characterised in that the high molecular weight polymer mainly consists of polyolefin, polyamide, polyester, polyvinylidene chloride, or a biodegradable polymer.

3. A process according to claim 1, characterised by at least two such steps of embossment.

4. A process according to claim 1, characterised in that as measured in slack state immediately prior to the continued stretching, the distance between any adjacent dots or short lines, is shorter than 50 mm.

5. A process according to claim 4, characterised in that these distances are shorter than 30 mm, preferably shorter than 10 mm.

6. A process according to claim 3, characterised in that there is formed a pattern of embossed lines, which cross each other, or form a zig-zag pattern.

7. A process according to claim 1, characterised in that two films become embossed simultaneously, while one is arranged on top of the other.

8. A process according to claim 1, characterised in that the process is carried out on a lay-flat tubular film.

9. A process according to claim 1, characterised in that the embossment is carried out, first from one outer surface, and then from the other outer surface.

10. A process according to claim 1, characterised in that the film originally was a tubular film extruded from a circular die, and during draw-down the molten or semi-molten tubular film is blown in a ratio no less than 1,1:1, preferably no less than 1,2:1, and more preferably no less than 1,3:1.

11. Any set of apparatus suitable for carrying out the process of claim 1.

12. Any polymer film product, including cross-laminates, manufactured under use of claim 1.

Description

[0016] In FIG. 1, the basically unoriented film (or assemblage of two, non-bonded films) becomes pleated in a low ratio while kept under m.d. tension. This step is optional, but preferable. In the next step, the film becomes embossed between a he-shaped and a she-shaped embossment roller. While the film leaves these rollers it is m.d. stretched in a low ratio. This stretching is also optional, but preferable. After this follows a process of deeper pleating by conventional means (known from conventional m.d. stretching processes) and final m.d. stretching, or alternatively (without any pleating) either t.d. or biaxial stretching. A biaxial stretching can take place in three different ways, namely a) first m.d. stretching, then t.d. stretching in a tenter-frame; b) opposite of a); and c) combined m.d. and t.d. stretching in a special tenter-frame. Finally, the oriented film is brought to relax and to some extent contract in an oven heated to a temperature near the melting range of the polymer, otherwise it will gradually shrink during storage and use.

[0017] In FIG. 2, the vertical direction represents the m.d. of the embossed and directly thereafter mildly stretched film. The dots have developed and formed lines, which in this experiment have become continuous. That is due to the short distance between the dots. Such fine and even pattern facilitates the final stretching, but makes the embossment rollers expensive, and as it appears from the main claim, the invention has a broader scope re the form and distribution of the embossments.