Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
2001-01-09
2003-06-24
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S523000, C428S476100, C428S518000, C428S515000, C426S395000, C426S396000, C426S398000, C426S415000
Reexamination Certificate
active
06582828
ABSTRACT:
BACKGROUND OF THE INVENTION
The surface slip of thermoformable films is becoming increasingly important. For economic reasons, automatic insert-placing machines (robots) are used to insert products packaged in film into cartons. An essential prerequisite for insertion by machines is a film with good surface slip. In the case of thermoformable films, the surface slip in the thermoformed regions is critical. If the surface slip of the shaped parts is inadequate, then the carton cannot be filled with the intended number of packages. In addition, product protection by the packaging is an important factor. This means that the film has to have high mechanical load-bearing capacity, in particular towards sharp-edged packaged goods.
To simplify the description of the prior art and the invention, the polymers which are used for films in the area of the present invention and the abbreviations used for these polymers is explained in more detail in the following, in order to simplify the rest of the description. If specific polymers are mentioned here, then these are suitable for the corresponding layers in the film according to the invention.
Polyolefins are referred to as “PO”. Examples of polyolefins are low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), polypropylene (PP), polyisobutylene, polybutylene and all other polymers which are prepared from olefins. Furthermore, PO here also includes olefin copolymers consisting of olefins and other monomers, wherein the olefins predominate in the composition. These are, for example, ethylene copolymers with unsaturated esters (e.g. vinyl acetate) and ethylene copolymers with unsaturated carboxylic acids or their salts.
Polyamides (abbreviated to “PA”) are understood in the widest sense to be polymeric compounds which are linked together by the acid amide group R—NH—CO—R′. Two groups of polyamides are differentiated: those built up from one parent substance by polycondensation of co-aminocarboxylic acids or polymerisation of their lactams to give polyamide-6 type compounds and those which are produced from two parent substances, diamines and dicarboxylic acids by polycondensation to give polyamide-66 type compounds. In addition, copolyamides are also known, these being a combination of the types of polyamide mentioned.
“PP” is used for polypropylene, no matter what the spatial arrangement of the methyl side-groups. “EPC” is used for copolymers of propylene with 1-10 mol. % of ethylene, wherein the ethylene is randomly distributed in the molecule.
“LDPE” is used for low density polyethylene which has a density in the range 0.86 to 0.93 g/cm
3
. LDPE molecules are characterised by a high degree of branching.
“LLDPEs” are linear low density polyethylenes which contain, apart from ethylene, one or more &agr;-olefins with more than 3 carbon atoms as comonomers. The following are mentioned here as representative of &agr;-olefins: butene-1, hexene-1,4-methylpentene-1 and octene-1. By polymerisation of the substances mentioned, the typical molecular structure of LLDPEs is produced, which is characterised by a linear main chain with side chains attached thereto. The density varies between 0.86 and 0.935 g/cm
3
. The melt flow index MFI is normally between 0.3 and 8 g/10 min. In some publications, linear ethylene/&agr;-olefin copolymers are subdivided into VLDPEs and ULDPEs, in accordance with the density. Since, however, according to GNAUCK/FRÜNDT (Einsteig in die Kunststoffechemie Hanser-Verlag 1991, p. 58), the properties, processing and use of these copolymers corresponds largely to those of ethylene homopolymers, the more precise differentiation is not used here.
“HDPE” is used to describe linear polyethylenes of high density which have only a small degree of branching in the molecular chain. The density of HDPE may be between 0.9 g/cm
3
and 0.97 g(cm
3
.
“mPE” is used here to describe an ethylene copolymer which was polymerised using metallocene catalysts. An &agr;-olefin with four or more carbon atoms is preferably used as a comonomer. The polymers prepared using conventional Ziegler-Natta catalysts frequently contain higher concentrations of the &agr;-olefins in the lower molecular weight fractions. As a result of the very uniform catalytic effect of metallocene centres, narrow distributions of molecular weights are found and, during fractionation, very uniform incorporation of the &agr;-olefins in both the high and also the low molecular weight fractions. The density is preferably between 0.900 and 0.930 g/cm
3
. The molecular weight distribution M
w
/M
n
is less than 3.5, preferably less than 3.
“EAA” is used for copolymers consisting of ethylene and acrylic acid and “EMAA” for copolymers consisting of ethylene and methacrylic acid. The ethylene content is preferably between 60 and 99 mol. %.
“I” is used to describe olefin-based copolymers in which the molecules are cross-linked via ionic bonding. Ionic cross-linking is reversible, which results in breaking up of the ionic cross-linking at conventional processing temperatures (180° C.-290° C.) and fresh formation in the cooling phase. Copolymers of ethylene and acrylic acid, which are cross-linked with sodium or zinc ions, are normally used as polymers.
“EVA” is used for a copolymer consisting of ethylene and vinyl acetate. The ethylene content is preferably between 60 and 99 mol. %.
“HV” is used for coextrudable, adhesion-promoting polymers (bonding agents). In contrast, adhesives are understood to be non-metallic materials, including polymers, which can bond two layers of film due to surface adhesion and internal strength without substantially altering the structure of the bonded film layers. In contrast to bonding agents, adhesives are not coextrudable, but have to be applied separately by surface application (e.g. lamination) or liquid application. Bonding agents are preferably modified polyolefins such as e.g. LDPE, LLDPE, mPE, EVA, EAA, EMAA, PP, EPC which are grafted with at least one monomer from the group of &agr;,&bgr;-monounsaturated dicarboxylic acids such as, for example, maleic acid, fumaric acid, itaconic acid or their acid anhydrides, acid esters, acid amides or acid imides. Other extrudable bonding agents which may be used are also copolymers of ethylene with &agr;,&bgr;-monounsaturated dicarboxylic acids such as acrylic acid, methacrylic acid and/or their metal salts with zinc or sodium and/or their C
1
-C
4
-alkyl esters, which may also be grafted with at least one monomer from the group of &agr;,&bgr;-monounsaturated dicarboxylic acids such as, for example, maleic acid, fumaric acid, itaconic acid or their acid anhydrides, acid esters, acid amides or acid imides. In addition, polyolefins such as e.g. polyethylene, polypropylene, ethylene/propylene copolymers or ethylene/&agr;-olefin copolymers which are grafted with copolymers of ethylene with &agr;,&bgr;-monounsaturated dicarboxylic acids such as acrylic acid, methacrylic acid and/or their metal salts with zinc or sodium and/or their C
1
-C
4
-alkyl esters, may be used. Particularly suitable bonding agents are polyolefins, in particular ethylene/&agr;-olefin copolymers with grafted &agr;,&bgr;-monounsaturated dicarboxylic anhydrides, in particular maleic anhydride. HVs may also contain an ethylene/vinyl acetate copolymer, preferably with a vinyl acetate content of at least 10wt. %.
Different layers in a film are separated in the following by “/”. Mixtures of polymers in a layer are signified by round brackets and linked by a “+”. Thus the film structure “ . . . /LLDPE/(mPE+LDPE)” describes a multi-layered film, wherein the outer layer contains a mixture of mnPE and LDPE. The inner layer consists of LLDPE. The other layers in the film are indicated by “ . . . ”.
The following documents are regarded as the relevant prior art for the present invention:
EP 0 236 099 describes a 7-layered, coextruded film with a fully symmetric structure. It includes a core layer made of an ethylene/vinyl alcohol copolymer, two outer layers which each contain polymeric
Bissett Melanie
Norris & McLaughlin & Marcus
Seidleck James J.
Wolff Walsrode AG
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