Unilaterally mat, sealable, UV-stabilized, flame-resistant,...

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Reexamination Certificate

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C428S346000, C428S347000, C428S349000, C428S480000, C428S910000, C264S288400, C264S290200, C106S015050, C106S018140, C106S018180, C106S018310

Reexamination Certificate

active

06709731

ABSTRACT:

The invention relates to a sealable, UV-resistant and flame-retardant, coextruded, biaxially oriented polyester film with one matt side and composed of at least one base layer B and of, applied to the two sides of this base layer, a sealable outer layer A and matt outer layer C. The film also comprises at least one light stabilizer which is a UV stabilizer, and comprises a flame retardant. The invention also includes the use of the film and a process for its production.
BACKGROUND OF THE INVENTION
GB-A 1 465 973 describes a coextruded polyester film having two layers, one layer of which consists of copolyesters containing isophthalic acid and terephthalic acid, and the other layer of which consists of polyethylene terephthalate. The patent gives no useful indication of the sealing performance of the film. The lack of pigmentation means that the film cannot be produced by a reliable process (cannot be wound up) and that the possibilities for further processing of the film are limited.
EP-A 0 035 835 describes a coextruded, sealable polyester film where, in the sealable layer, particles whose average size exceeds the sealable layer thickness are present in order to improve winding and processing performance. The particulate additives form surface protrusions which prevent undesired blocking and sticking of the film to rolls or guides. No further details are given concerning the incorporation of antiblocking agents in relation to the other, nonsealable layer of the film. It is uncertain whether this layer comprises antiblocking agents. The choice of particles having diameters greater than the sealable layer thickness, at the concentrations given in the examples, impairs the sealing performance of the film. The patent does not give any indication of the sealing temperature range of the film. The seal seam strength is measured at 140° C. and is in the range from 63 to 120 N/m (from 0.97 N/15 mm to 1.8 N/15 mm of film width).
EP-A 0 432 886 describes a coextruded multilayer polyester film which has a first surface on which has been arranged a sealable layer, and has a second surface on which has been arranged an acrylate layer. The sealable outer layer here may also be composed of isophthalic-acid-containing and terephthalic-acid-containing copolyesters. The coating on the reverse side gives the film improved processing performance. The patent gives no indication of the sealing range of the film. The seal seam strength is measured at 140 C. For a sealable layer thickness of 11 &mgr;m the seal seam strength given is 761.5 N/m (11.4 N/15 mm). A disadvantage of the reverse-side acrylate coating is that this side is now not sealable with respect to the sealable outer layer, and the film therefore has only very restricted use. EP-A 0 515 096 describes a coextruded, multilayer sealable polyester film which comprises a further additive in the sealable layer. The additive may is comprise inorganic particles, for example, and is preferably distributed in an aqueous layer onto the film during its production. Using this method, the film is claimed to retain its good sealing properties and to be easy to process. The reverse side comprises only very few particles, most of which pass into this layer via the recycled material. This patent again gives no indication of the sealing temperature range of the film. The seal seam strength is measured at 140° C. and is above 200 N/m (3 N/15 mm). For a sealable layer of 3 &mgr;m thickness the seal seam strength given is 275 N/m (4.125 N/15 mm).
WO 98/06575 describes a coextruded, multilayer polyester film which comprises a sealable outer layer and a nonsealable base layer. The base layer here may have been built up from one or more layers, and the inner layer of these layers is in contact with the sealable layer. The other (outward-facing) layer then forms the second nonsealable outer layer. Here, too, the sealable outer layer may be composed of isophthalic-acid-containing and terephthalic-acid-containing copolyesters, but these comprise no antiblocking particles. The film also comprises at least one UV absorber, which is added to the base layer in a weight ratio of from 0.1 to 10%. The base layer has been provided with conventional antiblocking agents. The film has good sealability, but does not have the desired processing performance and also has shortcomings in optical properties. The film may also have one matt surface, but then has high haze, which is undesirable.
DE-A 23 46 787 describes a flame-retardant polymer. Besides the polymer, its use to give films and fibers is also described. The following shortcomings were apparent during production of film using this claimed phospholane-modified polymer
The polymer mentioned is susceptible to hydrolysis and has to be very effectively predried. When the polymer is dried using prior-art dryers it cakes, and production of a film is possible only under very difficult conditions.
The films produced under uneconomic conditions also embrittle at high temperatures, i.e. mechanical properties decline sharply as a result of embrittlement, making the film unusable. This embrittlement arises after as little as 48 hours at high temperature.
Films which comprise no UV-absorbing materials exhibit yellowing and impairment of mechanical properties after even a short time in outdoor applications, due to photo oxidative degradation by sunlight.
Good mechanical properties include high modulus of elasticity (E
MD
>3200 N/mm
2
; E
TD
>3500 N/mm
2
) and also good values for tensile stress at break (in MD>100 N/mm
2
; in TD>130 N/mm
2
).
It was an object of the present invention to eliminate the disadvantages of the prior art.
BRIEF DESCRIPTION OF THE INVENTION
The invention provides a sealable, UV-resistant, flame-retardant, coextruded, biaxially oriented polyester film with one matt side and with at least one base layer B, and one sealable outer layer A, and another, matt, outer layer C, where at least one layer comprises a UV absorber and a flame retardant, and where the sealable outer layer A has a minimum sealing temperature of 110° C. and a seal seam strength of at least 1.3 N/15 mm, and the topographies of the two outer layers A and C have the following features:
Sealable outer layer A:
R
a
value<30 nm
Value measured for gas flow from 500 to 4000 s
Nonsealable, matt outer layer C:
200 nm<R
a
<1000 nm
Value measured for gas flow<50 s.
The invention also provides the use of the film and a process for its production.
DETAILED DESCRIPTION OF THE INVENTION
The sealable, transparent, UV-resistant, flame-retardant, coextruded, and biaxially oriented polyester film provided, with one matt side, does not therefore have the disadvantages of the prior-art films mentioned and in particular has good sealability, is cost-effective to produce, has improved processability, and has improved optical properties. In particular it has flame-retardant action and does not embrittle at high temperature.
The sealing range of the film has been extended to low temperatures, and the seal seam strength of the film has been increased, and at the same time the handling of the film has been improved over the prior art. It has also been ensured that the processability of the film extends to high-speed processing machinery. Directly-arising regrind can be reintroduced to the extrusion process during film production at a concentration of up to 60% by weight, based on the total weight of the film, without any significant resultant adverse effect on the physical properties of the film.
Since the film of the invention is intended in particular for outdoor applications and/or critical indoor applications, it is to have high UV resistance. High UV resistance means that sunlight or other UV radiation causes no, or only extremely little, damage to the films. In particular, when used outdoors for a period of some years the films should not yellow or exhibit any embrittlement or surface cracking, nor show any impairment of mechanical properties. High UV resistance therefore means that the film absorbs UV light and does not transmit light u

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