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

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

2002-07-26

2004-09-28

Chen, Vivian (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Continuous and nonuniform or irregular surface on layer or...

C428S212000, C428S347000, C428S349000, C428S3550RA, C428S480000, C428S910000, C264S288400, C264S290200

Reexamination Certificate

active

06797358

ABSTRACT:

The invention relates to a sealable, UV-resistant, co-extruded, biaxially oriented polyester film which has one matt side and is 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 a matt outer layer C. The film also comprises at least one UV stabilizer as light stabilizer. 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 that of the sealable layer, 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 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 temperature 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 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 ratio of from 0.1 to 10% by weight. The base layer has 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 a matt surface, but then has high haze, which is undesirable.
Films in which no UV-absorbing materials are present exhibit yellowing and impairment of mechanical properties after even a short period in outdoor applications, due to photooxidative degradation by sunlight.
Good mechanical properties include a high modulus of elasticity (E
MD
>3200 N/mm
2
; E
TD
>3500 N/mm
2
) and 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 UV-resistant, sealable, coextruded, biaxially oriented polyester film with one matt side and with at least one base layer B, and with a sealable outer layer A, and with another, matt, outer layer C, where at least one layer comprises a UV absorber 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 are characterized by the following features: sealable outer layer A:
R
a
value <30 nm
value measured for gas flow 500-4000 s nonsealable, matt outer layer C:
200 nm<R
a
<1000 nm
value measured for gas flow <50 s.
The invention further relates to the use of the film and to a process for its production.
DETAILED DESCRIPTION OF THE INVENTION
A transparent, UV-resistant, sealable, and biaxially oriented polyester film with one matt side is therefore provided and in particular has very good sealability, is cost-effective to produce, has improved processability, and has improved optical properties.
The invention permits the sealing range of the film to be extended to low temperatures, the seal seam strength of the film to be increased, and at the same time better handling of the film to be provided than in the prior art. It has also been ensured that the film is capable of processing even on high-speed machinery. Regrind arising directly during production of the film can be reintroduced to the extrusion process 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 particularly intended 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 number of years films should show no yellowing, embrittlement, or surface-cracking, and should have unimpaired mechanical properties. High UV resistance means that the film absorbs UV light and does not begin to transmit light until the visible region has been reached.
The UV stabilizer(s) is/are advantageously fed directly in the form of masterbatch(es) during film production, the concentration of the UV stabilizer(s) preferably being in the range from 0.01 to 5.0% by weight, with preference from 0.1 to 3.0% by weight, based on the weight of the respective layer of the polyester used.
The film of the invention generally has at least three layers, the layers encompassed then being the base layer B, the sealable outer layer A, and the matt outer layer C.
At least 90% by weight of the base layer B of the film is generally 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),

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