Method for the treating films
A method for treating a film by providing a structure including a substrate and an array of upstanding projections each of which includes multiple contact points. The structure is pressed against the surface of a polymeric film to cause deformation or rupture of the film. The film may then be pressed to partially reseal the perforations. The structure can be produced by electroplating a mould which includes an array of elements of dimensions corresponding to the projections of the desired structure.
1. A method for treating a film, comprising:
providing a web of polymeric film having a front face and a reverse face,
providing a structure including a substrate and an array of upstanding projections having an average width dimension of less than 200 μm, each projection including multiple contact points that are positioned to produce a non-uniform pressure distribution when film is stretched between the contact points of a projection,
providing a backing form made from a resilient material of appropriate stiffness to enable the projections to penetrate into or through the surface of the film, and
pressing the film between the projection-bearing surface of the structure and the backing form a sufficient distance to fix the film against the contact points and creating a non-uniform pressure distribution across the film in the region between the separate contact points in a projection and causing rupture of the film between the separate contact points in the projection while the film is fixed without heating the structure or the film during the pressing step.
2. A method for treating a film according to claim 1 , comprising rupturing the film to form perforations in the film having a size such that at least 80% of the perforations formed in the film have an effective aperture of less than or equal to 25 μm measured using the MOCON oxygen transmission tester calibrated against a film of the defined size.
3. The method of claim 2 , wherein the perforations create a line of weakness in the film.
4. The method of claim 2 , wherein the perforations create a controlled tearing film.
5. The method of claim 2 , wherein the width of the perforations formed by the perforation forming step are smaller than the width dimension of the projections.
6. A method for treating a film according to claim 2 , wherein at least 80% of the perforations formed in the film have an effective aperture of less than or equal to 10 μm.
7. A method for treating a film according to claim 1 , wherein the pressing step involves pressing the structure into the polymeric film a sufficient distance to create perforations in the film in a line, to thereby form a line of weakness in the film.
8. A method for treating a film according to claim 1 , wherein the backing form has an outer surface that is between 40 and 100 as measured by the Shore A hardness test.
9. A method for treating a film according to claim 1 , wherein the structure is mounted onto, or is in the form of, a roller or a platen, and the pressing step is conducted as a continuous process.
10. A method for treating a film according to claim 9 , wherein structure is mounted onto or in the form of a roller and the pressing step involves passing the film between the roller form of the structure and a backing roller.
11. A method for treating a film according to claim 10 , wherein the roller form of the structure and the backing roller are indexed relative to one another to reduce the spacing therebetween, or to increase the pressure of application of the film against the structure, as the projections are worn down over time.
12. A method for treating a film according to claim 1 , wherein the projections of the structure have an average height of between 5 μm and 250 μm.
13. A method for treating a film according to claim 12 , wherein the projections of the structure have an average height of between 10 μm and 200 μm.
14. A method for treating a film according to claim 12 , wherein the projections of the structure have an average height of between 10 μm and 100 μm.
15. A method for treating a film according to claim 1 , wherein the average maximum width dimension of the projections is less than 150 μm.
16. A method for treating a film according to claim 1 , wherein the average maximum width dimension of the projections is less than 100 μm.
17. A method for treating a film according to claim 1 , wherein the projections of the structure include a rime or margin that is greater height than the central part of the projection inside the rim or margin.
18. The method of claim 1 , wherein the projections of the structure pressed into the polymeric film are separated by a distance that is equivalent to or greater than the width of the projection.
19. The method of claim 1 , wherein each projection is cross-shaped.
20. The method of claim 1 , wherein each projection is of a height between 100 μm and 300 μm and has a maximum width of between 50 μm and 150 μm.
21. The method of claim 20 , wherein each projection has a height that is greater than its maximum width.
22. The method of claim 1 , wherein the projections contain cut-away regions between the contact points down which the polymeric material can be drawn to create uneven pressure distribution between the contact points and rupture between the contact points.
23. A method for treating a film according to claim 1 , wherein the web of polymeric film is a laminated film.
24. A method for treating a film according to claim 1 , wherein the web of polymeric film comprises a layer of a laminated film.