Multiple-pack system comprising a sealable polyester film

Details Multiple-pack system comprising a sealable polyester film Multiple-pack system comprising a sealable polyester film

2000-05-25

2002-03-19

Chen, Vivian (Department: 1773)

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

C428S216000, C428S335000, C428S346000, C428S347000, C428S349000, C428S3550RA, C428S480000, C428S483000, C528S302000, C528S305000, C528S308000, C528S308600

Reexamination Certificate

active

06358579

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a multiple-pack system, composed of a combined pack made from individual packages, where the individual packaging takes place in a biaxially stretch-oriented polypropylene film with modified polyolefinic outer layers and the combined-pack film is composed of a sealable polyester film with sealable layers based on polyester copolymers.
DESCRIPTION OF THE RELATED ART
Individual packages are generally brought together to form combined multiple packs. A known example of this is the packaging of blocks of cigarette packets.
The film usually used for wrapping cigarette packets has predominantly polyolefinic outer layers (sealable layers), but these seal undesirably to any combined-pack wrap made from a plastic which is also sealable. Besides the polyolefinic outer layers, therefore, sealable layers made from PVDC or from (poly)acrylates have been used for plastic films in the application sector described. Although these plastic films have had better usability overall for multiple-packaging systems, their relatively high price has prevented them from achieving importance in the market.
DE-A-3 635 928 describes a multiple-pack system composed of a combined pack made from individual packages, where the individual packaging takes place in a biaxially stretch-oriented polypropylene film with modified polyolefinic sealable layers. The characterizing features of the multiple-pack system are that the combined-pack film is composed of a sealable, biaxially stretch-oriented coextruded polypropylene film having a symmetrical structure and more than one layer, where the outer layers comprise a low-molecular-weight hydrocarbon resin as additive and have been corona-treated. However, the film for the combined pack has the technical disadvantage of a relatively high sealing temperature when compared with PVDC-coated or acrylate-coated films. If this temperature is applied to the combined-pack film this shrinks, as does the film for the individual packaging. This results in creases in both films, and these which have an adverse effect on the appearance of the packaging.
When blocks of cigarette packets are packaged it has therefore been necessary to continue using paper wrapping, and it has been possible to use film only for the cigarette-packet wrap for the individual pack.
Experiments have also been carried out in rendering the base layer of a plastic film sealable by incorporating certain hydrocarbon resins, as an alternative to the sealable materials in specific sealable layers.
DE-C-2 045 115 obtains a hot-sealable monofilm starting from a stereoregular polypropylene by adding from 5 to 40% by weight of at least one 50%-hydrogenated vinylaromatic hydrocarbon resin, in particular a styrene resin, with a molecular weight of more than 500 and a drop softening point of from 70 to 170° C.
DE-A-0 065 367 describes polypropylene films which comprise a low-density polyethylene, besides the components present previously in DE-C-2 045 115. This specific composition is said to improve the extrudability of the polypropylene film.
DE-A-2 362 049 describes a transparent, self-sealable film which is composed of from 90 to 99.95% by weight of a copolymer of ethylene and vinyl ester or a hydrocarbyl-substituted vinyl ester and from 0.05 to 10% by weight of a hydrocarbon resin, also combined with from 0.05 to 5% by weight of polyisobutylene or polybutylene, in order to give the film high tackiness and exceptional elasticity.
Especially the polyolefinic raw materials in the sealable layer of the self-supporting polypropylene films, but also the self-sealing polypropylene films, have excellent bonding properties. However, packaging films intended for the multiple-packaging system are to have adequate sealability to themselves on the one hand but on the other hand are not to seal to the packaging films of the individual packages present within the combined pack. Such films known hitherto do not meet this very important requirement, or meet it only at very high cost.
SUMMARY OF THE INVENTION
It was therefore an object of the present invention to develop a multiple-pack system for combined-pack packaging, where the combined-pack film in the multiple-pack system does not seal to the film of the individual package.
This object is achieved via a multiple-pack system composed of a combined pack made from individual packages, where the individual packaging takes place in a biaxially stretch-oriented polypropylene film with modified polyolefinic sealable layers. The characterizing features of the multiple-pack system are that the combined-pack film is composed of a sealable, biaxially stretch-oriented coextruded polyester film whose structure may or may not be symmetrical and which has more than one layer, where the structure(s) of the sealable layer(s) has/have been based on modified polyester copolymers.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, the combined-pack film has at least two layers, and its layers are then a base layer B and the sealable outer layer A. In a preferred embodiment, the combined-pack film has sealable outer layers A and C on both sides of its base layer B.
The base layer B of the film is preferably composed of at least 90% by weight of a thermoplastic polyester. Polyesters suitable here are those made from ethylene glycol and terephthalic acid (=polyethylene terephthalate, PET), from ethylene glycol and naphthalene-2,6-dicarboxylic acid (=polyethylene 2,6-naphthalate, PEN), from 1,4-bishydroxymethylcyclo-hexane and terephthalic acid (=poly-1,4-cyclohexane-dimethylene terephthalate, PCDT) or else made from ethylene glycol, naphthalene-2,6-dicarboxylic acid and biphenyl-4,4′-dicarboxylic acid (=polyethylene 2,6-naphthalate bibenzoate, PENBB). Preference is given to polyesters composed of at least 90 mol %, particularly preferably at least 95 mol %, of ethylene glycol units and terephthalic acid units or ethylene glycol units and napthalene-2,6-dicarboxylic acid units. The remaining monomer units are derived from other aliphatic, cycloaliphatic or aromatic diols and, respectively, dicarboxylic acids, as may also be present in layer A (or in layer C).
Examples of other suitable aliphatic diols are diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO—(CH
2
)
n
—OH, where n is an integer from 3 to 6 (in particular 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol) or branched aliphatic glycols having up to 6 carbon atoms. Among the cycloaliphatic diols, mention should be made of cyclohexanediols (in particular 1,4-cyclo-hexanediol). Examples of other suitable aromatic diols are HO—C
6
H
4
—X—C
6
H
4
—OH, where X is —CH
2
—, —C(CH
3
)
2
—, —C(CF
3
)
2
—, —O—, —S—or —SO
2
—. Bisphenols of the formula HO—C
6
H
4
—C
6
H
4
—OH are also highly suitable.
Other preferred aromatic dicarboxylic acids are benzenedicarboxylic acids, naphthalenedicarboxylic acids (such as naphthalene-1,4- or -1,6-dicarboxylic acid), biphenyl-x,x′-dicarboxylic acids (in particular biphenyl-4,4′-dicarboxylic acid), diphenylacetylene-x,x′-dicarboxylic acids (in particular diphenylacetylene-4,4′-dicarboxylic acid) and stilbene-x,x′-dicarboxylic acids. Among the cycloaliphatic dicarboxylic acids, mention should be made of cyclohexanedicarboxylic acids (in particular cyclohexane-1,4-dicarboxylic acid). Among the aliphatic dicarboxylic acids, the (C
3
-C
19
) alkanedioic acids are particularly suitable, where the alkane moiety may be straight-chain or branched.
The polyesters may, for example, be prepared by the transesterification process. The starting materials here are dicarboxylic esters and diols, and these are reacted using the usual transesterification catalysts, such as salts of zinc, of calcium, of lithium, of magnesium or of manganese. The intermediates are then polycondensed in the presence of typical polycondensation catalysts, such as antimony trioxide or titanium salts. They may equally well be prepared by direct esterification in the presence

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