Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
2001-04-10
2003-09-30
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S474400, C428S474700, C428S474900, C428S446000, C428S448000, C428S454000, C524S104000, C524S105000, C525S432000
Reexamination Certificate
active
06627324
ABSTRACT:
The present invention relates to a flexible single or multi-layer film having a layer containing partially aromatic polyamide compositions or compositions having aliphatic copolyamide, which contains between 10 and 2000 ppm of a nanodisperse filling material.
Polyamide-containing films are widely used for packaging foodstuffs.
The material polyamide has the advantage of having high mechanical strength, being a good barrier to oxygen, carbondioxide and other apolar gases, and having high resistance to high and low temperatures and scratch resistance. In addition, polyamide-containing unstretched films can be thermally formed, that is to say thermoformed into a form suitable for receiving a product to be contained. Polyamide films are flexible and are consequently able to conform to the contours of the product to be contained. This is important in the case of vacuum packs, for example.
Multi-layer films having polyamide as a strength-imparting layer are always used for packaging. Further layers are in particular a sealing layer to seal the pack securely, possibly a layer providing an extreme oxygen barrier as well as coupling layers between the other named functional layers.
Important properties of such films are attractive appearance, that is to say high gloss as well as low turbidity; in addition high mechanical resistance, in particular in the form of high resistance to destruction by buckling and creasing, termed hereinbelow resistance to fracture by buckling, are required.
For many applications a soft behaviour of the film is additionally desirable. This is the case, for example, when a number of packs made from a film are bundled in one transport outer. In the case of rigid films the corners of one pack may, under such circumstances, puncture adjacent packs.
The requirements for high resistance to fracture by buckling as well as low rigidity can be summarised as a desire for the material to behave in a tough-ductile manner. A suitable measuring method for its quantitative determination is described in the context of the Examples.
Polyamide firms may be produced by the flat or blown film extrusion process. The blown film extrusion process is preferred in many cases because it enables thick and thin regions to be staggered without incurring cutting losses, by rotation of the film bubble relative to the wind-up station of this film. Thus a wind-up quality superior to that of flat film can be achieved, which experience has taught is associated with better straight-through delivery and better film flatness.
A substantial disadvantage of producing films by the blown film extrusion process is the restriction to soft films. For films which are excessively rigid crease when the film bubble which has been formed in the round die and has then solidified is collapsed, leading to unsatisfactory film quality as well as-an inefficient production cycle.
Polyamide-containing film structures are documented, for example, in The Wiley Encyclopedia of Packaging Technology (published by M. Bakker, D. Eckroth; John Wiley & Sons, 1986) as well as in Nentwig (Joachim Nentwig: Kunststoff-Folien, Carl Hanser Verlag 1994, Munich).
Unless otherwise indicated, the convention of letter symbols for plastics in accordance with DIN 7728 or ISO 1043-1987 (E) is adopted in order to describe such polyamide-containing films and the polymers contained in the individual layers. The abbreviation HV denotes “coupling agent” and designates a polymer or polymer mixture which serves primarily to bond two adjacent layers.
In the case of multi-layer structures the layer sequence is reproduced by forming a string of the letter symbols of the polymers of the corresponding layers or of otherwise explained symbols, separated from one another by double forward slashes. Here, the sealing layer side is always on the right. It is also possible here for only a part of the complete layer sequence which makes up the film to be indicated. In these cases the sealing layer side is likewise always on the right, and layers or layer combinations which are not stated are indicated by three dots, . . . Mixtures of different polymers are indicated by the sign + as well as the bracketing together of the components, ( ). Optionally information as to the percentage composition may additionally be given here. Unless otherwise indicated, in such cases these are always percentages by weight which relate to the total weight of the mixture. Thus, for example, the expression . . . //PA//EVOH// . . . //(PE-LD+PE-LLD)//d describes a structure having an unspecified exterior layer or exterior layer sequence, followed by a layer substantially consisting of polyamide, followed by a layer substantially consisting of ethylene/vinyl alcohol copolymer (EVOH), followed by an unspecified layer or layer sequence, followed by a layer which contains a mixture of low-density polyethylene (PE-LD) and an ethylene/&agr;-olefin-copolymer (PE-LLD), as well as a layer following on the sealing side, as d, to be specified in greater detail.
Polyamide is a partially crystalline thermoplastic polymer. Here, the polyamide structure which adjusts in a film is to a large extent dependent on the processing conditions as well as on the composition of the polyamide. The lower the cooling rate of the polyamide, the larger the crystalline structures which can form by crystallisation. Low-crystalline systems can be obtained by the use of copolyamides as a result of sterically hindered molecules. The latter may be purely aliphatic systems such as, for instance, PA 6/66 or copolymers of aliphatic elements with aromatic constituents such as, for example, PA 6/6I or PA 6/6T.
The rate of nucleus formation in the crystallisation process can be increased by nucleation. Even when cooling is rapid due to the accelerated crystallisation during cooling from the melt the major part of the crystallisation process within the film is thus concluded by the time extrusion takes place. In non-nucleated systems, on the other hand, a metastable state can arise which leads to post-crystallisation of the polyamide over a protracted period after production, because of the cooling which, in relation to the rate of crystallisation, is excessively rapid. As a result of the reduction in the specific volume of the polyamide, which is associated with crystallisation, post-shrinkage of such a film thus occurs on the roll. This is fundamentally undesirable. Substantial disadvantages which accrue from this are poor film flatness due to non-uniform shrinkage, as well as fluctuating film width, which becomes more pronounced the greater the distance from the core of the roll.
When cooling rates are very low, such as, for example, in the blown film extrusion process, according to the prior art copolyamides are used in order to obtain adequate optical properties with PA on the exterior. Because they have a low rate of crystallisation the post-shrinkage problem is also very significant for blown films despite cooling rates which are lower than those of flat films.
The prior art currently fails to meet the need for copolyamides which are nucleated such that the transparency of the film is not impaired by the nucleation, while the nucleation nevertheless effectively prevents post-crystallisation by accelerating the crystallisation process during solidification.
The use of conventional nucleating systems, in particular in the form of dispersed finely divided inorganic solid particles, is prior art. In this context WO 8802763 names in particular talc, mica, kaolin and, in the second instance, substances such as asbestos, aluminium, silicates, silver bromide, graphite, molybdenum disulfide, lithium fluoride, sodium phenylphosphinate, magnesium oxide, mercury bromide, mercury chloride, cadmium acetate, lead acetate, silver chloride, diatomaceous earth, and the like. Named systems are admixed at concentrations of between 0.001 and 1.0 per cent, in relation to the total weight of the nucleated polymer.
The addition of solid particles in the size region of less than one micrometer to polymeric matrices and specifical
Brandt Rainer
Eggers Holger
Eilers Bernd
Gasse Andreas
Kaschel Gregor
Norris & McLaughlin & Marcus
Ribar Travis B
Seidleck James J.
Wolff Walsrode AG
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