Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-02-27
2001-12-04
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S165000, C428S212000
Reexamination Certificate
active
06326431
ABSTRACT:
The present invention relates to a milkily translucent, biaxially oriented polyester film which comprises at least one layer which comprises a polyester and a cycloolefin copolymer (COC). The invention further relates to the use of the film and to a process for its production.
BACKGROUND OF THE INVENTION
Milky biaxially oriented polyester films are known from the prior art. These known prior art films have good optical properties, but are difficult to produce.
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 by stretching 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 raw material and ethylene copolymer or propylene copolymer) cannot be reused without yellowing the film. This makes the process uneconomic, but the film produced with regrind would not gain acceptance in the market. If the amount of copolymer in the polyester is increased, the film loses its milky character and turns white with high opacity.
The object of the present invention was to provide a milkily translucent, biaxially oriented polyester film which has improved ease of production, i.e. low production cost. In particular, it should be possible for the cut material (regrind) directly associated with the production process, in an amount of from 10 to 70% by weight based on the total weight of the film, to be reused for the production process without any significant adverse effect on the physical or optical properties of the film produced using regrind. In particular, the addition of regrind should not cause any significant yellow coloration in the film.
SUMMARY OF THE INVENTION
According to the invention, this object is achieved by means of a milkily translucent, biaxially oriented polyester film with at least a base layer made from polyester, the characterizing features of which are that at least the base layer also comprises an amount of not more than 5% by weight of cycloolefin copolymer (COC), based on the weight of the base layer.
DETAILED DESCRIPTION OF THE INVENTION
The COC incorporated according to the invention into the film is preferably a COC whose glass transition temperature T
g
is within the range from 70 to 270° C.
For the purposes of the present invention, a milkily translucent film is a film whose whiteness is within the range from 15 to 110%, preferably from 20 to 100%, particularly preferably from 25 to 90%. The opacity of the milkily translucent film here should be within the range from 5 to 55%, preferably from 10 to 50%, particularly preferably from 15 to 45%. At the same time, the film should have a transparency within the range from 45 to 95%, preferably from 47 to 93%, particularly preferably from 49 to 91%.
Depending on the production conditions, the film of the invention may have a lustrous (metallic-look) surface or a pearlescent (matt- or satin-look) surface. The gloss values for the film of the invention therefore extend over a wide range from 10 to 200, preferably from 12 to 195, particularly preferably from 15 to 190.
To achieve the acquired whiteness, the desired opacity and the desired transparency of the film of the invention, the amount of COC in the base layer should not be above 5% by weight, otherwise the whiteness is above 110%, the opacity is above 55%, and the transparency falls below 45%.
It is also advantageous if the glass transition temperature of the COC used is above 70° C. Otherwise, if the glass transition temperature T
g
of the COC used is below 70° C., the polymer mixture is difficult to process, since it becomes difficult to extrude. The desired whiteness is lost and use of regrind gives a film with a tendency toward increased yellowness. On the other hand, if the glass transition temperature T
g
of the COC selected is above 270° C. the homogenization of the polymer mixture in the extruder will no longer be sufficient. This then gives a film with undesirably inhomogeneous properties.
In the preferred embodiment of the film of the invention, the glass transition temperature T
g
of the COCs used is within the range from 90 to 250° C., and in the particularly preferred embodiment it is within the range from 110 to 220° C.
Surprisingly, it has been found that a milkily translucent film can be produced by adding a COC in the manner described above.
The whiteness, the opacity and the transparency of the film can be adjusted with precision and adapted to particular requirements by varying the amount and nature of the COC added. This means that the use of other milkiness-producing additives can be dispensed with. It was quite sensational to find that the regrind exhibits no tendency toward yellowing, as is observed with the use of conventional polymeric additives as opacifiers in the prior art.
None of the features described was foreseeable. This was particularly the case since COCs are evidently substantially incompatible with polyethylene terephthalate but are known to require stretching ratios and stretching temperatures similar to those for polyethylene terephthalate. Under these circumstances the skilled worker would not have expected that a milkily translucent film could be produced under these production conditions.
In the preferred and particularly preferred embodiments, the film of the invention has high/particularly high metallic or pearlescent luster, while addition of regrind causes extremely little change in the color of the film.
The film of the invention has one or more layers. Single-layer embodiments have the structure identical with that of the COC-containing layer described below. Multilayer embodiments have at least two layers and always comprise the COC-containing layer and at least one other layer, where the COC-containing layer is the base layer but may also form the intermediate layer or the outer layer of a film having more than one layer. In one preferred embodiment, the COC-containing layer forms the base layer of the film with at least one outer layer, preferably with outer layers on both sides, and an intermediate layer or intermediate layers may, if desired, be present on one side or on both sides. In another embodiment, the COC-containing layer also forms an intermediate layer of a multilayer film. Other embodiments with COC-containing intermediate layers have a five-layer structure and, alongside the COC-containing base layer, have COC-containing intermediate layers on both sides. In another embodiment, the COC-containing layer can form, in addition to the base layer, and on one or both sides, an outer layer or outer layers on the base layer or on the intermediate layer. For the purposes of the present invention, the base layer is that layer which makes up 50%-100%, preferably 70-90%, of the total thickness of the film. The outer layers are the layers which form the outermost layers of the film.
Each embodiment of the invention is a milkily translucent film. For the purposes of the present invention, milkily translucent films are films whose light transmittance to ASTM-D 1003-77 is within the range from 45 to 95%, preferably from 47 to 93%, particularly preferably from 49 to 91%.
The COC-containing layer (the base layer) of the film of the invention comprises a polyester, preferably a polyester homopolymer, a COC, and also, if desired, other additives, in each case in effective amounts. This layer generally comprises at least 20% by weight, preferably from 40 to 98% by weight, in particular from 70 to 96% by weight, of polyester, based on the weight of the layer.
The base layer of the film comprises a thermoplastic polyester. Polyesters suitable here are those made from ethylene glycol and terephthalic acid (=polyethylene terephthalate, PET), from ethylene glycol and naphthalene-2,6-
Hilkert Gottfried
Janssens Bart
Peiffer Herbert
Cain Edward J.
Mitsubishi Polyester Film GmbH
ProPat L.L.C.
LandOfFree
Biaxially oriented polyester film comprising a cycloolefin... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Biaxially oriented polyester film comprising a cycloolefin..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Biaxially oriented polyester film comprising a cycloolefin... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2598643