Matte, coextruded polyester film, its use and process for...

Details Matte, coextruded polyester film, its use and process for... Matte, coextruded polyester film, its use and process for...

1999-07-26

2002-03-19

Chen, Vivian (Department: 1773)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Physical dimension specified

C428S423700, C428S430000, C428S446000, C428S458000, C428S480000, C428S483000, C428S910000, C525S437000

Reexamination Certificate

active

06358604

ABSTRACT:

The invention relates to a biaxially oriented polyester film with a base layer at least 80% by weight of which is composed of a thermoplastic polyester, and with at least one matte outer layer which comprises a mixture or a blend of two components I and II. The invention further relates to the use of the film and to a process for its production.
Component I of the mixture or of the blend is a polyethylene terephthalate homopolymer or polyethylene terephthalate copolymer or a mixture of polyethylene terephthalate homo- or copolymers.
Component II of the mixture or of the blend is a polyethylene isophthalate copolymer which is composed of the condensation product of the following monomers and/or of their derivatives capable of forming polyesters: isophthalic acid, aliphatic dicarboxylic acid, sulfomonomers which comprise a metal sulfonate group on the aromatic moiety of an aromatic dicarboxylic acid, and aliphatic or cycloaliphatic glycol.
The outer layer according to the invention has a characteristic matte surface and/or appearance and is highly suitable for use as a packaging film or for applications in the industrial sector.
BACKGROUND OF THE INVENTION
The packaging industry has a high requirement for transparent, high-gloss plastic films, such as biaxially oriented polypropylene films or biaxially oriented polyester films. There is also an increasing requirement for transparent films of this type with at least one surface layer which is not high-gloss but has a characteristically matte appearance and thus gives, for example, the packaging an appearance which is particularly attractive and therefore effective for sales promotion.
EP 346 647 describes a biaxially oriented polyester film which comprises at least one outer layer having a concentration of from 0.05 to 50% of a filler, where the diameter of this filler is in a particular ratio to the thickness of the outer layer. The outer layer moreover has a particular thickness and a particular degree of crystallinity, determined with the aid of Raman spectroscopy.
U.S. Pat. No. 4,399,179 describes a coextruded biaxially oriented polyester film which is composed of a transparent base layer and of at least one matte layer consisting essentially of a particular polyethylene terephthalate copolymer and also comprising a concentration of from 3 to 40% of inert particles with a diameter of from 0.3 to 20 &mgr;m. The specific copolymer is a processing aid which reduces the viscosity of the melt comprising the inert particles, allowing satisfactory extrusion of this layer. The matte quality of the film is achieved by adding the inert particles to the appropriate layer.
EP 0 144 878 describes a self-supporting oriented film which is composed of thermoplastic and at least one of the two surfaces of which carries a continuous polyester coating, which is applied in the form of an aqueous dispersion to the film before the final stretching step. The polyester coating is composed of a condensation product of various monomers or of their derivatives capable of forming polyesters, such as isophthalic acid, aliphatic dicarboxylic acid, sulfomonomers and aliphatic or cycloaliphatic glycols.
In the cases described there is no indication as to how the film can be made low-gloss on at least one of its surfaces while retaining high film transparency.
It is therefore an object of the present invention to provide a coextruded, biaxially oriented and transparent polyester film which has at least one matte outer layer, is simple and cost-effective to produce, has the good physical properties of the known films, and does not create disposal problems.
DESCRIPTION OF THE INVENTION
The object is achieved by means of a coextruded and biaxially oriented polyester film of the type described at the outset whose characterizing features are that the matte outer layer comprises a mixture or a blend of two components I and II.
Component I of the mixture or of the blend is a polyethylene terephthalate homopolymer or polyethylene terephthalate copolymer or a mixture of polyethylene terephthalate homo- or copolymers.
Component II of the copolymer or of the mixture or of the blend is a polyethylene isophthalate copolymer which is composed of the condensation product of the following monomers and/or of their derivatives capable of forming polyesters:
A) from 65 to 95 mol % of isophthalic acid;
B) from 0 to 30 mol % of at least one aliphatic dicarboxylic acid with the formula
HOOC(CH
2
)
n
COOH, where
n is from 1 to 11;
C) from 5 to 15 mol % of at least one sulfomonomer comprising an alkali metal sulfonate group on the aromatic moiety of a dicarboxylic acid;
D) a copolymerizable aliphatic or cycloaliphatic glycol having from 2 to 11 carbon atoms, in the stoichiometric amount necessary to form 100 mol % of condensate;
where each of the percentages given is based on the total amount of the monomers forming component II.
For the purposes of the present invention, mixtures are mechanical mixtures produced from the individual components. For this, the individual constituents are generally combined in the form of small-dimension compressed moldings, e.g. lenticular or bead-shaped pellets, and mixed with one another using a suitable agitator. Another way of producing the mixture is for each of the components I and II in pellet form to be fed separately to the extruder for the outer layer according to the invention and for mixing to take place in the extruder and/or in the downstream systems for transporting the melt,
For the purposes of the present invention a blend is an alloy-like composite of the individual components I and II which can no longer be separated into the initial constituents. A blend has properties like those of a homogeneous material and can therefore be characterized by appropriate parameters.
The subclaims give preferred embodiments of the invention, and these are also described below.
According to the invention the film has at least two layers. Its layers are then a layer B and the outer layer A according to the invention. In a preferred embodiment of the invention the film has a three-layer structure and has the outer layer A on one side of the layer B (=base layer) and another layer C on the other side of the layer B. In this case the two layers A and C form the outer layers A and C.
The base layer B of the film preferably comprises at least 90% by weight of a thermoplastic polyester. Polyesters suitable for this are those made from ethylene glycol and terephthalic acid (polyethylene terephthalate, PET), made from ethylene glycol and naphthalene-2,6-dicarboxylic acid (polyethylene 2,6-naphthalate, PEN), made from 1,4-bishydroxymethylcyclohexane and terephthalic acid [poly(1,4-cyclohexanedimethylene terephthalate), PCDT], and also those 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 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 derive from other aliphatic, cycloaliphatic or aromatic diols and, respectively, dicarboxylic acids, as may also be present in layer A (or layer C).
Examples of other suitable aliphatic diols are diethylene glycol, triethylene glycol and aliphatic glycols of the general 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 may be made of cyclohexanediols (in particular 1,4-cyclohexanediol). Other suitable aromatic diols have, for example, 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 highly suitable.
Other preferred aromatic dicarboxylic acids are benzenedicarboxylic acids, naphthalenedicarboxy

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