Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
2001-07-18
2003-08-19
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S323000, C428S213000, C428S215000, C428S332000, C428S339000, C428S480000, C428S910000, C428S457000, C428S458000, C428S343000, C428S344000, C428S346000, C428S347000, C428S349000, C264S288400, C264S290200
Reexamination Certificate
active
06607815
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a coextruded, biaxially oriented polyester film with high metal adhesion, composed of a base layer B and of at least one outer layer A applied to the base layer. The invention also includes the use of the film and a process for its production.
EP-A-0 144 878 describes films with a copolyester coating, based on isophthalic acid, on aliphatic dicarboxylic acid and on sulfoisophthalic acid. The films do have good adhesion to metals, but this metal adhesion is unsatisfactory for certain applications.
EP-A-0 035 835 describes a polyester film which comprises a sealable outer layer based on isophthalate units. This outer layer has a high thickness, ≧2 &mgr;m, leading to cracking in the metallic layer after metallization, which is unacceptable since it leads to loss of barrier properties.
It was an object of the present invention to provide a biaxially oriented polyester film which has high metal adhesion and does not have the disadvantages of the prior art films mentioned and which, in addition, is cost-effective to produce and has good processability while its other optical properties are unchanged or improved. A particular object of the present invention was to improve the metal adhesion of the film without any occurrence of cracking in the metallic layer of the metallized film. In addition, the film should be capable of processing on high-speed machinery. It should also be ensured that during the production of the film (without the metallic layer) any cut material directly associated with film production should be capable of reintroduction as regrind into the extrusion process for film production in amounts of up to 60% by weight, based on the total weight of the film, without any resultant significant adverse effect on the physical properties of the film produced with this amount of regrind.
The film therefore has excellent suitability for use in flexible packaging, and specifically wherever high metal adhesion is particularly important. An example of a case of this type is also known as “bag-in-box packs”, which use a multilayer composite made from metallized PET film, laminated to both sides of which there is a polyethylene film.
SUMMARY OF THE INVENTION
According to the invention, the object is achieved by providing a coextruded, biaxially oriented polyester film with good metal adhesion, where the polyester film has at least one base layer B and at least one outer layer A, and where the outer layer A has
(a) a metal adhesion (after metallization) above or equal to 4 N/25 mm and
(b) a thickness below or equal to 1.6 &mgr;m.
The film of the present invention exhibits exceptionally high adhesion to metallic coatings and, surprisingly, no cracking in the metallic layer applied to the outer layer A.
DETAILED DESCRIPTION OF THE INVENTION
The film of the invention has at least two layers, and in this embodiment the layers present are the base layer B and the metal-adherent outer layer A. For the purposes of the present invention, an “metal-adherent” outer layer A is an outer layer composed of a plastic whose chemical makeup gives it a particularly high affinity for metal and which therefore has particularly good properties of metal adhesion.
However, the film of the invention particularly preferably has three layers and then also encompasses an additional outer layer C, which may be identical with or different from the metal-adherent outer layer A. The subclaims give preferred embodiments of the invention, and these are also described in more detail below.
At least 90% by weight of the base layer B of the film is preferably composed of a thermoplastic polyester. Polyesters suitable for this purpose 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), or else made 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 at least 90 mol %, in particular at least 95 mol %, of which is composed of ethylene glycol units and terephthalic acid units, or of ethylene glycol units and naphthalene-2,6-dicarboxylic acid units. The remaining monomer units derive from other aliphatic, cycloaliphatic or aromatic diols and, respectively, dicarboxylic acids, as may also occur in layer A (or in layer C).
Other 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) and branched aliphatic glycols having up to 6 carbon atoms. Among the cycloaliphatic diols, mention should be made of cyclohexanediols (in particular 1,4-cyclohexanediol). Examples of other suitable aromatic diols have 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
—. Bisphenols of the formula HO—C
6
H
4
—C
6
H
4
—OH are also very suitable.
Other aromatic dicarboxylic acids are preferably benzenedicarboxylic acids, naphthalene dicarboxylic 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) or 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
alkanediacids are particularly suitable, and the alkane moiety here may be straight-chain or branched.
One way of preparing the polyesters is the transesterification process. Here, the starting materials are dicarboxylic esters and diols, which are reacted using the customary transesterification catalysts, such as the salts of zinc, of calcium, of lithium, of magnesium or of manganese. The intermediates are then polycondensed in the presence of well-known polycondensation catalysts, such as antimony trioxide or titanium salts. Another equally good preparation method is the direct esterification process in the presence of polycondensation catalysts. This starts directly from the dicarboxylic acids and the diols.
Metal-adherent Outer Layer A
The metal adherent outer layer A preferably applied by coextrusion to the base layer B has been built up on the basis of copolyesters and essentially consists of copolyesters composed predominantly of isophthalic acid units and of terephthalic acid units and of ethylene glycol units. The remaining monomer units derive from other aliphatic, cycloaliphatic or aromatic diols and, respectively, dicarboxylic acids, as may also occur in the base layer. Preferred copolyesters which have the desired metal adhesion properties are those which have been built up from ethylene terephthalate units and from ethylene isophthalate units and from ethylene glycol units. The proportion of ethylene terephthalate is preferably from 40 to 99 mol %, and the corresponding proportion of ethylene isophthalate is preferably from 60 to 1 mol %. Particular preference is given to copolyesters in which the proportion of ethylene terephthalate is from 50 to 95 mol % and the corresponding proportion of ethylene isophthalate is from 50 to 5 mol %, and very particular preference is given to copolyesters in which the proportion of ethylene terephthalate is from 60 to 85 mol % and the corresponding proportion of ethylene isophthalate is from 40 to 15 mol %.
Non-metal-adherent Outer Layer C
For the other, non-metal-adherent outer layer C, or for any intermediate layers present, use may be made in principle of the polyesters described above for the base layer B. In addition to this, in one particular embodiment of the i
Bartsch Stefan
Peiffer Herbert
Mitsubishi Polyester Film GmbH
ProPat L.L.C.
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