Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-02-12
2003-09-30
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S100000, C428S318400, C428S319300, C428S480000, C428S903300, C428S910000
Reexamination Certificate
active
06627695
ABSTRACT:
The present invention relates to a white, biaxially oriented, UV-resistant polyester film comprising at least one layer which comprises a polyester and a cycloolefin copolymer (COC). The invention further relates to the use of the polyester film, and to a process for its production.
BACKGROUND OF THE INVENTION
White, biaxially oriented polyester films are known from the prior art. These known prior art films are either easy to produce, have good optical properties or have acceptable processing performance.
DE-A 2 353 347 describes a process for producing milky polyester film having one or more layers, which comprises preparing a mixture from particles of a linear polyester with from 3 to 27% by weight of a homopolymer or copolymer of ethylene or propylene, extruding the mixture as a film, quenching the film and biaxially orienting the film via orientation in directions running perpendicular to one another, and heat-setting the film. A disadvantage of this process is that regrind which arises during production of the film (essentially a mixture of polyester and ethylene or propylene copolymer) cannot be reused without yellowing the film. However, this makes the process uneconomic, but the film produced with regrind would not gain acceptance in the market. In addition, the roughness of the film is much too high, and this gives the film a very matt appearance (very low gloss), undesirable for many applications.
EP-A 0 300 060 describes a single-layer polyester film which comprises, besides polyethylene terephthalate, from 3 to 40% by weight of a crystalline propylene polymer and from 0.001 to 3% by weight of a surface-active substance. The effect of the surface-active substance is to increase the number of vacuoles in the film and at the same time to reduce their size to the desired extent. This gives the film greater opacity and lower density. A residual disadvantage of the film is that regrind which arises during production of the film (essentially a mixture of polyester and propylene homopolymer) cannot be reused without yellowing the film. However, this makes the film uneconomic, but the film produced with regrind would not gain acceptance in the market. In addition, the roughness of the film is much too high, giving it a very matt appearance (very low gloss), undesirable for many applications.
EP-A 0 360 201 describes a polyester film having at least two layers and comprising a base layer with fine vacuoles, with a density of from 0.4 to 1.3 kg/dm
3
, and having at least one outer layer whose density is above 1.3 kg/dm
3
. The vacuoles are achieved by adding from 4 to 30% by weight of a crystalline propylene polymer, followed by biaxial stretching of the film. The additional outer layer improves the ease of production of the film (no streaking on the film surface), and the surface tension is increased and the roughness of the laminated surface can be reduced. A residual disadvantage is that regrind arising during production of the film (essentially a mixture of polyester and propylene homopolymer) cannot be reused without yellowing the film. However, this makes the process uneconomic, but the film produced with regrind would not gain acceptance in the market. In addition, the roughnesses of the films listed in the examples are still too high, giving the films a matt appearance (low gloss), undesirable for many applications.
EP-A 0 795 399 describes a polyester film having at least two layers and comprising a base layer with fine vacuoles, the density of which is from 0.4 to 1.3 kg/dm
3
, and having at least one outer layer, the density of which is greater than 1.3 kg/dm
3
. The vacuoles are achieved by adding from 5 to 45% by weight of a thermoplastic polymer to the polyester in the base, followed by biaxial stretching of the film. The thermoplastic polymers used are, inter alia, polypropylene, polyethylene, polymethylpentene, polystyrene or polycarbonate, and the preferred thermoplastic polymer is polypropylene. As a result of adding the outer layer, ease of production of the film is improved (no streaking on the film surface), the surface tension is increased and the roughness of the laminated surface can be matched to prevailing requirements. Further modification of the film in the base layer and/or in the outer layers, using white pigments (generally TiO
2
) and/or using optical brighteners permits the properties of the film to be matched to the prevailing requirements of the application. A residual disadvantage is that regrind which arises during production of the film (essentially a mixture of polyester and the added polymer) cannot be reused without undefined and highly undesirable changes in the color of the film. This makes the process uneconomic, but the film produced with regrind would not gain acceptance in the market. In addition, the films listed in the examples continue to have excessive roughness values, giving them a matt appearance (low gloss), undesirable for many applications.
DE-A 195 40 277 describes a polyester film having one or more layers and comprising a base layer with fine vacuoles, with a density of from 0.6 to 1.3 kg/dm
3
, and having planar birefringence of from −0.02 to 0.04. The vacuoles are achieved by adding from 3 to 40% by weight of a thermoplastic resin to the polyester in the base, followed by biaxial stretching of the film. The thermoplastic resins used are, inter alia, polypropylene, polyethylene, polymethylpentene, cyclic olefin polymers, polyacrylic resins, polystyrene or polycarbonate, preferred polymers being polypropylene and polystyrene. By maintaining the stated limits for the birefringence of the film, the film claimed has in particular superior tear strength and superior isotropy properties. However, a residual disadvantage is that regrind arising during production of the film cannot be reused without undefined discoloration of the film arising, and this is highly undesirable. This makes the process uneconomic, but the film produced with regrind would not gain acceptance in the market. In addition, the roughnesses of the films listed in the examples are still too high, giving them a matt appearance (low gloss), undesirable for many applications.
The object of the present invention was to provide a white, biaxially oriented polyester film which has high gloss and improved ease of production, i.e. low production costs, and which moreover has high UV resistance. In particular, it should be possible for cut material (regrind) directly associated with the production process to be reused in the production process at a concentration of from 10 to 70% by weight, based on the total weight of the film, without any significant resultant adverse effect on the physical or optical properties of the film produced with regrind. In particular, addition of regrind should not cause any significant yellowing of the film.
High UV resistance means that the film is damaged only slightly or not at all by sunlight or other UV radiation, and therefore that the films are suitable for outdoor applications and/or critical indoor applications. In particular, during outdoor use over a period of some years, the films should not yellow, embrittle or show surface-cracking, nor exhibit any impairment of mechanical properties. High UV resistance therefore means that the film absorbs UV light and does not begin to transmit light until the visible region has been reached.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, the object is achieved by means of a white, biaxially oriented and UV-resistant polyester film with at least one base layer made from polyester, the characterizing features of which are that at least the base layer also comprises, based on the weight of the base layer, from 2 to 60% by weight of a cycloolefin copolymer (COC), where the glass transition temperature of the cycloolefin copolymer (COC) is within the range from 70 to 270 C., and that the base layer comprises at least one UV stabilizer as light stabilizer.
The white, biaxially oriented polyester film as defined in the present invention is a film of this type who
Davis Richard Lee
Hilkert Gottfried
Murschall Ursula
Peiffer Herbert
Mitsubishi Polyester Film GmbH
ProPat L.L.C.
Szekely Peter
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