Stock material or miscellaneous articles – Composite – Of polyester
Reexamination Certificate
2003-05-20
2004-09-21
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyester
C428S036600, C428S212000, C428S480000, C428S910000, C264S288400, C264S290200, C525S165000, C525S173000, C525S174000, C525S177000
Reexamination Certificate
active
06794051
ABSTRACT:
The invention relates to a multilayer, transparent, biaxially oriented polyester film which has a base layer B and at least one outer layer A. The film comprises cycloolefin copolymers (COCs) having a low glass transition temperature. The invention further relates to a process for producing the film, and to its use.
BACKGROUND OF THE INVENTION
Transparent biaxially oriented polyester films which feature enhanced barrier properties are prior art. In virtually all instances the films acquire their enhanced barrier properties offline, following actual production, by virtue of an additional processing step. Examples of such aftertreatments include extrusion coating, coating or lamination with barrier materials, coating in vacuum with metals or with ceramic substances, or plasma polymerization in conjunction with vacuum coating.
An exception to this is the process described in more detail in WO 99/62694, in which a multilayer, coextruded polyester film comprising at least one layer of EVOH (ethylene-vinyl alcohol) is simultaneously biaxially drawn. The resultant film features good mechanical properties and good barrier properties. Using the film, an oxygen transmission rate (OTR) of not less than 5 cm
3
/(m2·bar·d) is obtained. As far as the water vapor transmission rate (WVTR) obtained with the film is concerned, no information is forthcoming. A disadvantage of this process is that the reclaimed material obtained cannot be passed back to the production operation without the film without the film which then results losing its good optical properties.
U.S. Pat. No. 5,795,528 describes a coextruded film laminate with alternating layers of PEN and PET. The film laminate exhibits a heightened barrier to oxygen and water vapor, but tends toward delamination between the individual layers of PEN and PET. Between these layers there is virtually no adhesion. A laminate of this kind is therefore unsuitable for practical use.
U.S. Pat. No. 5,912,070 describes a coextruded film laminate which is resistant to temperature and impact, exhibits a barrier to water vapor, and can be torn by hand. The film is composed of one or more plies of a thermoplastic polyester base material (A), one or more plies of a resin based on cycloolefin polymers (C), and one or more intermediate layers of an adhesion promoter (B). The cycloolefin polymer of the layer (C) features a glass transition temperature of 60 to 120° C. and may have been prepared either by the ring-opening method or by way of metallocene catalysts. The adhesion promoter layer (B) is located between the two layers (A) and (C). The adhesion promoters specified include a range of known polymers, the preferred polymers listed including graft-modified random copolymers based on ethylene and a-olefins. The graft modification of these copolymers is carried out, for example, with unsaturated dicarboxylic acids or with derivatives thereof. In one preferred embodiment the film is biaxially oriented. Disadvantages of the film are its complex construction and the associated high level of technical complexity required for its production. These problems are particularly disadvantageous in the context of reusing the cut film scrap obtained. Because of the many different kinds of polymers for the three different layers, the cut film scrap can no longer be reused as reclaim, e.g., for the base layer (A), since it generally leads to an unduly high yellow coloration of the resultant film.
EP-A-1 068 949 relates to a white, biaxially oriented polyester film having at least one base layer, the characterizing features of which are that at least this base layer contains a cycloolefin copolymer (COC) in a concentration of from 2 to 60% by weight, based on the base layer, the glass transition temperature of the cycloolefin copolymer (COC) being in the range from 70 to 270° C. The glass transition temperature of the COC and the stretching temperatures are chosen so as to give an opaque-white film of low density. The film does not feature enhanced barrier values with respect to water vapor. For example, if a transparent, standard polyester film 23 mm thick and containing no COC has a WVTR of 21 g/(m
2
·d), a film according to EP-A-1 068 949, Example 1 (10% COC), is found to have a WVTR of about 27 g/(m
2
·d).
It is an object of the present invention, therefore, to provide a polyester film which is distinguished by enhanced barrier properties, particularly with respect to the passage of water vapor. Such a film should not have the disadvantages of the prior art films and should additionally be distinguished by the ensured possibility, during the production of the film, that the reclaim produced can be passed back to the extrusion operation without any notable adverse effect on the physical and optical properties of the resultant film, but particularly the barrier with respect to water vapor. Effective adhesion between the individual layers of a coextruded film must likewise be ensured for the purpose of their practical application.
At the same time, the other properties which characterize a polyester film should not suffer deterioration. These include, for example, the mechanical and the thermal properties, the winding characteristics, and the processing properties of the film, particularly in the case of subsequent printing, lamination, or coating with metallic or ceramic materials.
BRIEF DESCRIPTIONS OF THE INVENTION
This object is achieved by means of a multilayer, transparent, biaxially oriented polyester film which has a base layer B composed of at least 50% by weight of a thermoplastic polyester, and has at least one outer layer A, wherein
a) the base layer B comprises a fraction of from 0 to 30% by weight of a cycloolefin copolymer (COC),
b) the outer layer A comprises a fraction of from 20 to 100% by weight of a cycloolefin copolymer (COC),
c) the glass transition temperature T
g
of the cycloolefin copolymer (COC) is below 120° C., and
d) the permeation coefficient of the film for water vapor is smaller than 35 g[12 &mgr;m]/m
2
·d. d denotes day.
DETAILED DESCRIPTION OF THE INVENTION
The biaxially oriented, transparent polyester film according to the present invention has a water vapor transmission rate which is significantly reduced as compared with prior art films. At the same time, a minimum adhesion between the individual layers of the film of greater than 0.5 N/25 mm is ensured.
The abovementioned figures for composition and physical parameters are preferred figures, in the case of which the desired properties of the film of the invention are particularly pronounced.
The film of the invention is of at least two-layer construction. In that case it is composed of a base layer B and an outer layer A.
The percentages by weight are based in each case on the total weight of the layer in question.
The base layer of the film is composed preferably of at least 60% by weight, based on the weight of the base layer B, of a thermoplastic polyester. Examples of polyesters suitable for this purpose are those formed from ethylene glycol and terephthalic acid (i.e., polyethylene terephthalate, PET), from ethylene glycol and naphthalene-2,6-dicarboxylic acid (i.e., polyethylene 2,6-naphthalate, PEN), from 1,4-bishydroxymethylcyclohexane and terephthalic acid (i.e., poly-1,4-cyclohexanedimethylene terephthalate, PCDT), and from ethylene glycol, naphthalene-2,6-dicarboxylic acid, and biphenyl-4,4′-dicarboxylic acid (i.e., polyethylene 2,6-naphthalate bibenzoate, PENBB). Particularly preferred polyesters are those composed of at least 90 mol %, preferably at least 95 mol %, of ethylene glycol and terephthalic acid units or of ethylene glycol and naphthalene-2,6-dicarboxylic acid units. The remaining monomer units originate from other diols and/or dicarboxylic acids. Suitable thermoplastic polyesters for the base layer B can also be polyester copolymers or blends based on polyester, particularly those described in more detail as component II for the outer layer A.
Examples of suitable further aliphatic diols as polyester component include diethylene glycol, trieth
Hilkert Gottfried
Peiffer Herbert
Chen Vivian
Mitsubishi Polyester Film GmbH
ProPat L.L.C.
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