Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Patent
1996-08-28
1998-11-24
Yamnitzky, Marie
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
428323, 428402, 4284111, 428447, 428500, 428515, 428516, 4283044, 4283211, 428 357, B32B 516
Patent
active
058404198
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns polymeric films having good slip properties.
2. Description of Related Art
Many proposals have been made hitherto for improving the slip properties of polymeric films, and those of polyolefin films in particular. In the case of polypropylene based films, for example, it has been proposed to incorporate migratory slip additives such as fatty acid amides into the films so that with time the slip additive migrates to the surface of the film, thereby improving the slip properties of the film.
One problem encountered with migratory slip additives is that the slip properties of films containing them tend to increase with time, due to progressively more of the slip additive accumulating on the film surface. Such increases in slip properties can cause the film to have poor performance when used in high speed packaging machinery because the films have become too slippery. In addition, accumulating migratory slip additive on the film surface tends to reduce the optical characteristics of the films, for example leading to increased haze and reduced gloss.
As an alternative to the use of migratory slip additives, it has been proposed to use silicone oil as a slip agent, the silicone oil either being compounded into an outer layer or layers of the films or coated onto at least one surface of the films. Silicone oil is apparently essentially non-migratory since the slip properties of films including it in compounded form remain substantially constant with time, that is, silicone oil within the film apparently remains there and the slip properties of the films are a function of the amount of silicone at or on the surface of the film when it is made. However, silicone on one surface of a film has been found to transfer to the opposite surface of the film when the film is wound up, whether or not the silicone present on that surface has been put there by compounding or by coating. Thus when silicone oil is used as a slip agent, it need only be coated on or compounded with one surface of the film since transfer in the roll causes silicone to become present on both film surfaces.
Although the use of silicone oil as a slip agent for polyolefin films has advantages over the use of migratory slip additives such as fatty acid amides, it does have disadvantages. One major disadvantage is that treatments of the surfaces of films to increase their surface energy, for example with the objective of increasing the printability of the films, have not been possible with film surfaces having silicone compounded into or coated on them since other properties of the films, for example heat sealability, can be adversely affected. However, it is possible to increase the printability of such films if the surface which is treated, for example by flame or corona discharge treatment, does not include compounded silicone oil and does not have a surface coating of silicone oil thereon at the time of the treatment. Silicone oil on the other surface of the film, whether there as a result of coating or compounding, can then transfer to the treated surface of the film when the film is in the roll, and at least some of the benefits of the surface treatment remain without the loss of properties which would have resulted if the silicone oil had been present at the time of the treatment.
Despite this ability to avoid the problems with treating film surfaces having a surface layer of silicone oil, by transferring silicone oil to the surface after treatment rather than before, there are problems with such films, notably in that the amount of silicone oil transferred from the surface of a film in which the silicone oil is compounded is often insufficient to provide the surface to which it is transferred with desired levels of slip. Coating a film surface with silicone oil followed by transfer to the treated surface in the roll can reduce this problem, but the amount of silicone oil which has to be coated onto the film for this to occur tends to be sufficiently high that the effect
REFERENCES:
patent: 4595625 (1986-06-01), Crass et al.
patent: 4966933 (1990-10-01), Kawakami et al.
patent: 4983447 (1991-01-01), Crass et al.
patent: 5691043 (1997-11-01), Keller et al.
Hoechst Trespaphan GmbH
Yamnitzky Marie
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