Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
1999-03-24
2001-03-13
Boykin, Terressa M. (Department: 1711)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C264S216000, C428S035700, C428S480000, C430S160000, C528S176000, C528S272000
Reexamination Certificate
active
06200511
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 food and drink packaging, there is frequently a demand for a high level of barrier with respect to gases, water vapor and flavors. Use is therefore usually made of polypropylene films which have been metalized or have been coated with polyvinylidene chloride (PVDC). Metalized polypropylene films, without special pretreatment, have a modest oxygen barrier, and they have poor adhesion between the metal layer and the polypropylene layer. The metal layer can therefore easily be damaged (scratched) with loss of barrier. Metalized polyester films generally have a significantly better barrier with respect to, for example, oxygen, and also somewhat better metal adhesion than untreated polypropylene films, but the danger of damage to the metal layer is also present with metalized polyester film. A PVDC layer also provides a barrier, but layers of this type have to be applied from a solution in a second operation, and this considerably increases the cost of the packaging. Ethylene-vinyl alcohol copolymers (EVOH) likewise exhibit a high barrier. However, films modified with EVOH have particularly severe moisture sensitivity, and this limits their scope of application. Due to their poor mechanical properties, they are also relatively thick or have to be laminated with other materials at high cost. They are, furthermore, 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 biaxially oriented polyester film which is simple and cost-effective to produce, has the good physical properties of the known films, has good adhesion to a layer applied by metalizing, 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 outer layer(s) of the film is/are composed of one or more copolyesters which is/are prepared from dicarboxylic acids and diols or derivatives of these, where the dicarboxylic acid component is composed of a mixture of at least 35 mol % of 2,6-naphthalate units, up to 44 mol % of terephthalate units, from 1 to 20 mol % of isophthalate units and from 0 to 20 mol % of an aromatic dicarboxylic acid which has been substituted with an alkali metal sulfo group. The film is preferably transparent.
In other preferred embodiments, the outer layer is composed of a copolymer or of a mixture of polymers which comprises at least 35 mol % of ethylene 2,6-naphthalate units, up to 44 mol % of ethylene terephthalate units, and from 1 to 20 mol % of ethylene isophthalate units, and also up to 20 mol % of a sulfo-substituted dicarboxylic acid and, if desired, up to 10 mol % of units from aliphatic, including cycloaliphatic, or aromatic diols and/or dicarboxylic acids (based in each case on the total content of dicarboxylic acid or diol).
Preference is given to a polyester film in which the polymers of the outer layer comprise at least 60 mol % of ethylene 2,6-naphthalate units, 1-10 mol % to isophthalate units and up to 30 mol % of ethylene terephthalate units. Among these, particular preference is in turn given to a polyester film of this type in which the polymers of the outer layer comprise at least 65% by weight of ethylene 2,6-naphthalate units and up to 25% by weight of ethylene terephthalate units. Preference is also given to films wherein the outer layer comprises at least 70 mol %, more preferably at least 75 mol %, of ethylene 2,6-naphthalate units.
Alkali-metal-sulfo-substituted dicarboxylic acids are understood to be monomers which correspond to the formula:
In this formula,
M is a monovalent cation of an alkali metal,
z is a trivalent aromatic radical, and
X and Y are carboxyl groups or polyester-forming equivalents.
Examples of monomers of this type are the sodium salts of sulfoterephthalic acid, of 5-sulfoisophthalic acid, of sulfophthalic acid, of 5-(p-sulfophenoxy)isophthalic acid, of 5-(sulfopropoxy)isophthalic acid and of similar monomers, and other examples are the derivatives of these which can form polyesters, for example as the dimethyl esters. M is preferably Na
+
, Li
+
or K
+
.
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 other components of the aromatic dicarboxylic acid mixture 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
)alkane-dioic acids, where the alkane moiety may be straight-chain or branched, are particularly suitable.
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(bne of them is modified with the required quantity of isophthalat) 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 trans-verse direction (i.e. perpendicularly to the machine direction). This causes an orientation of the molecular chains. The orientation procedure in a longitudinal direction 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 a longitudinal direction and in a transverse dir
Bennett Cynthia
Crass Guenther
Hilkert Gottfried
Peiffer Herbert
Roth Werner
Boykin Terressa M.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Mitsubishi Polyester Film GmbH
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