Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
1999-10-26
2002-04-09
Woodward, Ana (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamide
C525S184000
Reexamination Certificate
active
06368723
ABSTRACT:
The present invention relates in general to films comprising metallocene polyethylene and polyamide and uses thereof. The film may be a monolayer film or a multilayer film.
The present invention comprises a mono- or multilayer film comprising metallocene polyethylene, at least one layer (A) of a mixture of polyamide and polyethylene, and optionally a layer (B) of polyethylene, in which film the metallocene polyethylene is in the layer (A) and/or in the layer (B).
In other words, this invention comprises a film comprising at least one layer (A) of a mixture of polyamide and polyethylene, and optionally a layer (B) of polyethylene, such that if the polyethylene of the layer (A) is not a metallocene polyethylene, then the presence of the layer (B) is necessary and this layer essentially consists of metallocene polyethylene.
Film Embodiments
In a first embodiment, the film of the invention comprises at least one layer (A) of a mixture of polyamide and metallocene polyethylene.
In a second embodiment, the film of the invention comprises the above mentioned layer (A) and at least one layer (B) of polyethylene. This layer (B) is advantageously composed of metallocene polyethylene.
In a third embodiment, the film of the invention comprises a layer (A) of a mixture of polyamide and metallocene polyethylene between two layers (B) of polyethylene, where one or both may be composed of metallocene polyethylene.
In a fourth embodiment, the film of the invention comprises a layer (B) of polyethylene between two layers (A) of a mixture of polyamide and metallocene polyethylene, where the central layer (B) may be composed of metallocene polyethylene.
In a fifth embodiment, the film of the invention comprises at least one layer (A) of a mixture of polyamide and polyethylene which is not metallocene polyethylene, and at least one layer (B) of metallocene polyethylene.
In an advantageous form of this fifth embodiment of the invention, the layer (A) is arranged between two layers (B) of the metallocene polyethylene.
In another advantageous form of this fifth embodiment of the invention, the layer (A) is arranged between a layer (B) of metallocene polyethylene and another layer (B) of non-metallocene polyethylene.
In another advantageous form of this fifth embodiment, the central layer (B) of metallocene polyethylene is arranged between two layers (A).
SMC Embodiment
The films of the invention are used in SMC (sheet moulding compound) technology.
SMC is used in the manufacture of processed parts, both in the automotive sector (bumpers, hatchback doors . . . ) and in the sectors of water sports (boat hulls) and electronics (casings).
SMC is generally composed of a crosslinkable polymeric resin, in particular an unsaturated polyester, reinforcing fillers such as glass fibres, and also subordinate amounts of various other additives.
SMC is usually produced by laying down fibres on a layer of unsaturated polyester resin, this layer itself being supported on a mobile film generally composed of polyethylene or polyamide.
Another film of the same type is then laid down on the system comprising resin/reinforcing filler, to form a composite material composed of a sandwich between two films. The sandwich then traverses a series of kneading and compacting rolls and is generally wound up in the form of large rolls.
It is then stored until subsequent processing. During the period of storage the polyester resin partially crosslinks, increasing the viscosity of the SMC, until the consistency reached makes it suitable for moulding.
The users of SMCs, generally molders, cut a piece of appropriate dimensions from the roll, peel off the support film and place the SMC into a heated mold for processing and at the same time complete curing. SMC sandwich composite materials are then readily employed in procedures for compression molding.
Three properties relating to the sandwich film are of prime importance for manufacturers and users of SMCs.
The first property has regard to the permeability to styrene of the peelable film. The peelable film has to have very low permeability to styrene in order to avoid the loss of styrene monomer which acts as crosslinking agent in the SMC. This loss of styrene monomer is also harmful to the health of personnel during operations of manufacturing or storing SMC.
The second property relates to the ease of peeling this film from the polyester structure, in order that no film residues remain on the structure and in order to avoid risks associated with tearing of this film during the operations of manufacturing and processing the SMC.
Finally, the moisture uptake of these peelable films, and their permeability to water, have to be very low, so that the quality of the polyester resin, which is very sensitive to water, does not become impaired during the operations of manufacturing the SMC, of storing the polyester or of processing the SMC.
Prior Art
The prior art has described SMC films composed of blends of polyamide and polypropylene in European Patent EP 0 506 515.
The use of metallocene polyethylene is not described therein.
The films of the invention are also useful for soil fumigation. This technique consists in treating soils by injecting gas to a depth of about 0.5 or 1 m. The soil to be treated is covered with a film, so that the gas remains in the soil for a longer period, and this makes it possible to reduce the quantities of gas to be used. The prior art has described such films in EP 0 766 913.
The use of metallocene polyethylene is not described therein.
Packaging Embodiment
The films of the invention are also used for the manufacture of packaging.
The applicant has discovered that the use of metallocene polyethylene, either in the polyamide/polyethylene mixture or in the optional layer of polyethylene in a film which comprises, in addition, a layer of a mixture of polyamide and polyethylene, makes it possible to obtain good resistance to tearing and to the DART test (i.e. resistance to perforation).
The present invention also relates to packaging consisting of the films of the invention or comprising the films of the invention.
Detailed Description
The thickness of the layer (A) may be between 5 and 150 &mgr;m.
The term metallocene polyethylene denotes polymers obtained by copolymerizing ethylene and an alpha-olefin, such as propylene, butene, hexene or octene, in the presence of a monosite catalyst generally consisting of an atom of a metal which may, for example, be zirconium or titanium, and of two cyclic alkyl molecules bonded to the metal. More specifically, the metallocene catalysts are usually composed of two cyclopentadiene-type rings bonded to the metal. These catalysts are often used with aluminoxanes as cocatalysts or activators, preferably methylaluminoxane (MAO). Hafnium may also be used as a metal to which the cyclopentadiene is bound. Other metallocenes may include transition metals of groups IV A, V A and VI A. Metals of the lanthanide series may also be used.
These metallocene polyethylenes may also be characterized by their M
w
/M
n
ratio of <3, preferably <2.
The term polyamide means a condensation product:
of one or more amino acids, such as aminocaproic acids, 7-aminoheptanoic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid or of one or more lactams, such as caprolactam, enantholactam or laurolactam;
of one or more salts or mixtures of diamines, such as hexamethylenediamine, dodecamethylenediamine, m-xylylenediamine, bis(p-aminocyclohexyl)methane or trimethylhexamethylenediamine, with diacids, such as isophthalic, terephthalic, adipic, azelaic, suberic, sebacic or dodecanedicarboxylic acid;
or of mixtures of one or more of these monomers, giving copolyamides.
Examples which may be mentioned are polycaprolactam (nylon-6), polylaurolactam (nylon-12) and polyhexamethyleneadipamide (nylon-6,6). Mention may be also made of copolyamides, such as nylon-6/12, derived from the condensation of caprolactam and laurolactam, and nylon-6/6,6, derived from the condensation of caprolactam, hexamethylenediamine and adipic acid. The copolyamides are of int
Andre Jean-Marc
Bouilloux Alain
Teze Laurent
AtoFina
Millen White Zelano & Branigan P.C.
Woodward Ana
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