Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
2001-08-06
2004-09-07
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S215000, C428S216000, C428S480000, C428S446000, C428S458000, C428S910000, C264S288400, C264S290200
Reexamination Certificate
active
06787219
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a transparent, biaxially oriented polyester film with a base layer B which comprises at least 80% by weight of thermoplastic polyester, and with at least one intermediate layer Z, and with at least one outer layer A. The invention further relates to the use of the film and to a process for its production.
PRIOR ART
EP-A-0 878 297 describes a transparent, biaxially oriented polyester film with a base layer B, at least 80% by weight of which is composed of a thermoplastic polyester, and with at least one outer layer A which is composed of a mixture of polymers which contains at least 40% by weight of ethylene 2,6-naphthalate units (PEN) and up to 40% by weight of ethylene terephthalate units (PET) and/or up to 60% by weight of units derived from cycloaliphatic or aromatic diols and/or dicarboxylic acids.
If the outer layer A of the film of EP-A-0 878 297 contains high concentrations of ethylene 2,6-naphthalate units, the film has a tendency for delamination between the outer layer A and the base layer B. If, on the other hand, the outer layer A contains low concentrations of ethylene 2,6-naphthalate units, the thickness of this layer has to be raised in order to achieve the desired low oxygen permeation of not more than 80 cm
3
/(m
2
·bar·d).
In a film in Example 8 of EP-A-0 878 297 the outer layer A uses pure polyethylene 2,6-naphthalate (corresponding to 100% by weight of ethylene 2,6-naphthalate units). In this case there is no significant adhesion between the outer layer A and the base layer B. The film is unsuitable for industrial use (e.g. as a composite film), since the bond releases even when subjected to a low level of mechanical stress, due to the low adhesion between the outer layer A and the base layer B of the polyester film.
In a film in Example 11 of EP-A-0 878 297, the outer layer A contains 60% by weight of ethylene 2,6-naphthalate units. In order to achieve the low oxygen permeation demanded, below 80 cm
3
/(m
2
·bar·d), the thickness of the outer layer A has to be raised to 3 &mgr;m, and this is economically disadvantageous (high capital expenditure and high material costs).
U.S. Pat. No. 5,795,528 describes a coextruded film laminate which has alternating layers of PEN and PET. Like the film of EP-A-0 878 297, this film has a tendency toward delamination between the individual layers of PEN and PET. There is no significant adhesion between these layers. A laminate of this type is therefore again unsuitable for industrial use.
It was an object of the present invention, therefore, to provide a transparent, biaxially oriented polyester film which overcomes the disadvantage of the prior art films and in particular has improved adhesion between the individual layers. It should be simple and cost-effective to produce, have good barrier properties, and pose no problems of disposal.
SUMMARY OF THE INVENTION
The object is achieved by means of a transparent, biaxially oriented polyester film with a base layer B which comprises at least 80% by weight of thermoplastic polyester, with at least one intermediate layer Z, and with at least one outer layer A, the characterizing features of which are regarded as being that
the outer layer A is composed of a polymer, of a mixture of polymers/copolymers, or of a copolymer, which contains at least 85% by weight of ethylene 2,6-naphthalate units and up to 15% by weight of ethylene terephthalate units, and/or up to 15% by weight of units derived from cycloaliphatic or aromatic diols and/or dicarboxylic acids;
the intermediate layer Z is composed of a mixture of polymers/copolymers, or of a copolymer, which contains at least 3% by weight of ethylene 2,6-naphthalate units, and up to 97% by weight of ethylene terephthalate units, and/or up to 97% by weight of units derived from cycloaliphatic or aromatic diols and/or dicarboxylic acids, and
the T
g
2 value of the polyester film is above the T
g
2 value of the base layer B but below the T
g
2 value of the outer layer A.
The film of the invention has low oxygen permeation, below 85 cm
3
/(m
2
·bar·d), and minimum adhesion (between the individual layers) greater than 0.5 N/25 mm.
DETAILED DESCRIPTION OF THE INVENTION
The structure of the film of the invention has at least three layers, and is then composed of the outer layer A, of a base layer B, and of an intermediate layer Z located between the outer layer A and the base layer B.
Preference is given to a polyester film in which the polymers of the outer layer A contain at least 90% by weight of ethylene 2,6-naphthalate units and up to 10% by weight of ethylene terephthalate units. Among these, particular preference is in turn given to a polyester film in which the polymers of the outer layer A contain at least 92% by weight of ethylene 2,6-naphthalate units and up to 8% by weight of ethylene terephthalate units. However, the outer layer A may also be composed entirely of ethylene 2,6-naphthalate polymers.
Preference is also given to a polyester film in which the polymers of the intermediate layer Z contain at least 5% by weight of ethylene 2,6-naphthalate units and up to 95% by weight of ethylene terephthalate units. Among these, particular preference is in turn given to a polyester film in which the polymers of the intermediate layer Z contain at least 7% by weight of ethylene 2,6-naphthalate units and up to 93% by weight of ethylene terephthalate units.
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 other 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 base layer of the film is preferably composed 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 biphenyl-4,4′-dicarboxylic acid (=polyethylene 2,6-naphthalate bibenzoate, PENBB). Particular preference is given to polyesters which are composed of at least 90 mol %, preferably at least 95 mol %, of ethylene glycol units and terephthalic acid units or of ethylene glycol units and naphthalene-2,6-dicarboxylic acid units. The remaining monomer units are derived from other diols and/or dicarboxylic acids. Examples of suitable diol comonomers are diethylene glycol, triethylene glycol, aliphatic glycols of the formula HO—(CH
2
)
n
—OH, where n is an integer from 3 to 6, branched aliphatic glycols having up to 6 carbon atoms, aromatic diols of the formula
Hilkert Gottfried
Peiffer Herbert
Chen Vivian
Mitsubishi Polyester Film GmbH
ProPat L.L.C.
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