Stock material or miscellaneous articles – Composite – Of polyamide
Patent
1998-12-11
2000-04-04
Pezzuto, Helen L.
Stock material or miscellaneous articles
Composite
Of polyamide
4284744, 4284749, 428500, B32B 2708
Patent
active
060459190
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a film for wrapping materials which diffuse volatile products. It is particularly useful for expandable polystyrene beads or granules which contain a flammable expansion agent such as pentane. The film of the invention has good barrier properties towards pentane. Furthermore, it is antistatic, which ensures that during its manufacture there will be no build-up of static electricity which can cause arcs that perforate the film, making it unsuitable for its use.
Furthermore, when it is used as a container, frictional contact with the wrapping cannot cause build-ups of static electricity and then arcs which could ignite the pentane.
The present invention relates to an antistatic film made of polyamide or of an alloy of polyamide and polyolefin. It is useful for wrapping materials which diffuse volatile products. The antistatic effect ensures that, during its manufacture, there will be no electric arcs caused by a build-up of static electricity, for example due to the frictional contact with the rollers of the manufacturing machines. Electric arcs can give rise to perforation of the film, which damages its leak tightness. They can also interfere with any printing of the film. The good barrier properties of the film make it possible to prevent the loss of volatile products. These products can be, for example, perfumes with which granules of a porous material have been impregnated, or water since it is necessary for certain materials to contain moisture, or because they naturally contain moisture and they should not become dehydrated. Generally, bags for materials which diffuse non-flammable volatile products are formed by hot-welding or by electronic sewing and if the bag is not antistatic, it is possible to have granules of material in the position of the weld for closing the bag, thereby making the closure of the bag non-leaktight. As regards wrapping which contains readily flammable volatile products, forming them by hot-welding is avoided, so a knot is made. On the other hand, the antistatic nature of the wrapping prevents electric arcs caused by build-up of static electricity, it being possible for these arcs to cause fires either during the filling of the bag or in the course of transportation and storage. The reason for this is that it is not possible to prevent some slight loss across the film, and a bag would thus cause a fire.
The invention also relates to wrapping comprising these films.
According to a first form, the film of the invention is made of polyamide or of an alloy of polyamide and of polyolefin, in which is dispersed an additive in order to make it antistatic. These additives can be various products, polymers or carbon black.
According to a second form, the film of the invention comprises at least one inner layer (A) made of polyamide or of an alloy of polyamide and of polyolefin, and on each side an antistatic outer layer (B) made of polyolefins, of polyamide or of an alloy of polyamide and of polyolefin, in which is dispersed an antistatic additive. Advantageously, the film according to this second form of the invention consists of 3 layers: B/A/B. A coextrusion binder can be placed between the layers (A) and (B) or alternatively the layers (B) or the layer (A) can contain products which improve the adhesion of the layers (A) and (B).
BACKGROUND OF THE INVENTION
The prior art has already described films made of an alloy of polyamide and of polyolefin, and in particular EP 506,515 describes such films for protecting polyesters before they are crosslinked in the SMC (sheet molding compound) process; these films are leaktight to the free styrene present in the polyesters to be crosslinked, and then, after shaping the polyester, this film is peeled off in order to recover the article made of polyester. These films are not antistatic.
U.S. Pat. No. 4,612,221 describes films consisting of a layer of polyamide between two layers of polypropylene containing a bonding agent. These films serve to protect food and must remain resistant in
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Alex Patrick
Bouilloux Alain
Elf Atochem S.A.
Pezzuto Helen L.
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