Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1999-03-24
2002-05-21
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S035800, C428S035900, C428S215000, C428S220000, C428S458000, C428S480000, C428S910000
Reexamination Certificate
active
06391410
ABSTRACT:
The invention relates to a transparent, biaxially oriented polyester film having a base layer at least 80% by weight of which is composed of a thermoplastic polyester, and having at least one outer layer. The invention also relates to the use of the film and to a process for its production.
BACKGROUND OF THE INVENTION
In many cases there is demand for food and drink packaging to have a high barrier effect with respect to gases, water vapor and flavors. For this reason, use is usually made of polypropylene films which are metallized or coated with polyvinylidene chloride (PVDC). However, metallized polypropylene films are not transparent and are therefore not used in cases where the view of the contents is likely to have added promotional effect. Although films coated with PVDC are transparent, the coating, like the metallizing, takes place in a second operation which makes the packaging markedly more expensive. Ethylene-vinyl alcohol copolymers (EVOH) likewise exhibit a strong barrier effect. However, films modified with EVOH are particularly highly sensitive to moisture, and this limits their range of application. In addition, because of their poor mechanical properties they have relatively high thickness or have to be laminated with other materials at high cost, and they are also difficult to dispose of after use. In addition to this, some raw materials are not approved by the authorities or are unsuitable for producing food and drink packaging.
It is therefore an object of the present invention to provide a transparent, biaxially oriented polyester film which presents a barrier to gases, such as water vapor, nitrogen, carbon dioxide and helium, and to flavors, and which has been improved over conventional polyester films and has the good physical properties of the known films and does not give rise to disposal problems.
DESCRIPTION OF THE INVENTION
The object is achieved by means of a biaxially oriented polyester film having a base layer at least 80% by weight of which is composed of (at least) one thermoplastic polyester, and having at least one outer layer, wherein the film has (an) outer layer(s) composed of a polymer or of a mixture of polymers which comprises at least 40% by weight of ethylene 2,6-naphthalate units and up to 40% by weight of ethylene terephthalate units and/or up to 60% of units from aliphatic, including cycloaliphatic, or aromatic diols and/or dicarboxylic acids, with the proviso that the glass transition temperature (T
g
2 value) of the polyester film is above the T
g
2 value of the base layer but below the T
g
2 value of the outer layer. As metallized film, this film has H
2
O permeability of less than 0.10 g/(m
2
·d), preferably less than 0.05 g/(m
2
d), particularly preferably less than 0.04 g/(m
2
·d).
Preference is given to a polyester film in which the polymers of the outer layer comprise at least 65% by weight of ethylene 2,6-naphthalate units and up to 35% by weight of ethylene terephthalate units. Among these, particular preference is then given to a polyester film of the type in which the polymers of the outer layer comprise at least 70% by weight of ethylene 2,6-naphthalate units and up to 30% by weight of ethylene terephthalate units. The outer layer may, however, also be composed completely of ethylene 2,6-naphthalate polymers.
Examples of suitable aliphatic diols are diethylene glycol, triethylene glycol, aliphatic glycols of the 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, and cycloaliphatic diols having one or more rings and if desired containing heteroatoms. Among the cycloaliphatic diols, mention may be made of cyclohexanediols (in particular 1,4-cyclohexanediol). Examples of suitable aromatic diols are those of the formula 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
—. Besides these, bisphenols of the formula HO—C
6
H
4
—C
6
H
4
—OH are also very suitable.
Preferred aromatic dicarboxylic acids are benzenedicarboxylic acids, naphthalenedicarboxylic acids (for example 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) or stilbene-x,x′-dicarboxylic acids. Among the cycloaliphatic dicarboxylic acids, mention may 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 present invention also provides a process for producing this film. It encompasses
a) producing a film from base and outer layer(s) by coextrusion,
b) biaxial orientation of the film and
c) heat-setting of the oriented film.
To produce the outer layer, it is expedient to feed granules of polyethylene terephthalate and polyethylene 2,6-naphthalate directly to the extruder in the desired mixing ratio. At about 300° C. and with a residence time of about 5 min, the two materials can be melted and can be extruded. Under these conditions, transesterification reactions can occur in the extruder and during these copolymers are formed from the homopolymers.
The polymers for the base layer are expediently fed in via another extruder. Any foreign bodies or contamination which may be present can be filtered off from the polymer melt before extrusion. The melts are then extruded through a coextrusion die to give flat melt films and are layered one upon the other. The coextruded film is then drawn off and solidified with the aid of a chill roll and other rolls if desired.
The biaxial orientation procedure is generally carried out sequentially or simultaneously. For the sequential stretching, it is preferable to orient firstly in a longitudinal direction (i.e. in the machine direction) and then in a transverse direction (i.e. perpendicularly to the machine direction). This causes an orientation of the molecular chains. The longitudinal orientation procedure may be carried out with the aid of two rolls running at different speeds corresponding to the stretching ratio to be achieved. For the transverse orientation procedure, use is generally made of an appropriate tenter frame. For the simultaneous stretching, the film is stretched in a tenter frame simultaneously in longitudinal and transverse directions.
The temperature at which the orientation procedure is carried out can vary over a relatively wide range and depends on the properties desired in the film. In general, the longitudinal stretching is carried out at from 80 to 1 30° C., and the transverse stretching at from 90 to 150° C. The longitudinal stretching ratio is generally in the range from 2.5:1 to 6:1, preferably from 3:1 to 5.5:1. The transverse stretching ratio is generally in the range from 3.0:1 to 5.0:1, preferably from 3.5:1 to 4.5:1. If desired, the transverse orientation procedure may be followed by another longitudinal orientation procedure and even a further transverse orientation procedure.
During the subsequent heat-setting, the film is held for from 0.1 to 10 s at a temperature of from 150 to 250° C. The film is then wound up in a conventional manner.
A great advantage of this process is that it is possible to feed the extruder with granules, which do not block the machine.
The base layer of the film is preferably composed to an extent of at least 90% by weight of the thermoplastic polyester. Polyesters suitable for this 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-bishydroxymethylcyclohexane and terephthalic acid (=poly-1,4-cyclohexanedimethylene terephthalate, PCDT), and also from ethylene glycol, naphthalene-2,6-dicarboxylic acid and bip
Bennett Cynthia
Crass Guenther
Hilkert Gottfried
Peiffer Herbert
Roth Werner
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Jackson Monique R.
Mitsubishi Polyester Film GmbH
Thibodeau Paul
LandOfFree
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