Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2002-07-19
2004-02-10
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S480000, C428S910000, C428S403000, C428S404000, C264S288400, C264S290200, C106S015050, C106S018140, C106S018180, C106S018310, C106S400000, C106S436000
Reexamination Certificate
active
06689454
ABSTRACT:
The invention relates to a white, flame-retardant, UV-resistant, thermoformable, oriented film made from a crystallizable thermoplastic, the thickness of the film being in the range from 10 to 350 &mgr;m. The film comprises at least one white pigment and one flame retardant and one UV absorber and has good orientability and thermoformability, and very good optical and mechanical properties, and can be produced cost-effectively. The invention further relates to the use of this film and to a process for its production.
BACKGROUND OF THE INVENTION
White, oriented films made from crystallizable thermoplastics with a thickness of from 10 to 350 &mgr;m are well known.
These films do not comprise UV absorbers of any kind as light stabilizers and do not comprise flame retardants of any kind, and therefore neither the films nor the items produced from them are suitable for outdoor applications which demand fire protection or flame retardancy. The films do not pass the fire tests to DIN 4102 Part 2 and Part 1, or the UL 94 test. The films have inadequate thermoformability.
Even after a short time in outdoor applications, these films yellow and exhibit impairment of mechanical properties due to photooxidative degradation by sunlight.
EP-A-0 620 245 describes films with improved heat resistance. These films comprise antioxidants which are suitable for scavenging free radicals formed in the film and degrading any peroxide formed. However, that specification gives no proposal as to how the UV resistance of these films might be improved.
DE-A 2346 787 describes a flame-retardant polymer. Alongside the polymer, the use of the polymer is also claimed for producing films or fibers.
The following shortcomings were apparent during production of films from this phospholane-modified polymer:
The polymer is very susceptible to hydrolysis and has to be very thoroughly predried. The polymer cakes during its drying by prior-art dryers, and it is impossible to produce a film except under the most difficult of conditions.
The films produced under extreme and uneconomic conditions embrittle on exposure to heat, i.e. the mechanical properties are severely impaired due to substantial embrittlement, making the film unusable. This embrittlement occurs after as little as 48 hours of exposure to heat.
It was an object of the present invention to provide a white, flame-retardant, UV-resistant, thermoformable, oriented film with a thickness of from 10-350 &mgr;m which not only can be produced cost-effectively and has good orientability and good mechanical and optical properties, but in particular is flame retardant, does not embrittle on exposure to heat, is thermoformable, and has high UV resistance.
Flame retardancy means that in a fire test the white film complies with the conditions of DIN 4102 Part 2 and in particular the conditions of DIN 4102 Part 1, and can be allocated to construction materials class B 2 and in particular B1 for low-flammability materials.
The film is also intended to pass the UL 94 test “Vertical Burning Test for Flammability of Plastic Material”, permitting its classification in class 94 VTM-0. This means that 10 seconds after removal of the Bunsen burner the film has ceased to burn, and after 30 seconds no glowing is observed, and no drips are found to occur.
High UV resistance means that sunlight or other UV radiation causes no, or only extremely little, damage to the films, so that the films are suitable for outdoor applications and/or critical indoor applications. In particular, after a number of years in outdoor applications the films are intended not to yellow, nor to exhibit any embrittlement or surface cracking, nor to exhibit any impairment of mechanical properties. High UV resistance therefore means that the film absorbs UV light and does not transmit light until the visible region has been reached.
Thermoformability means that the film can be thermoformed to give complex and large-surface-area moldings on commercially available thermoforming machinery, without uneconomic predrying.
Examples of good optical properties include uniform coloration, high surface gloss (>15), low light transmission (<70%), and also a Yellowness Index unchanged from that of the flame-retardant and UV-modified film.
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
).
Good orientability includes the capability of the film to give excellent orientation, both in a longitudinal direction and I transverse direction during its production, without break-offs.
Cost-effective production includes the capability of the raw materials or raw material components needed to produce the flame-retardant film to be dried using industrial-standard dryers. It is important that the raw materials neither cake nor become thermally degraded. These prior-art industrial dryers include vacuum dryers, fluidized-bed dryers, fixed-bed dryers (tower dryers). These dryers operate at temperatures of from 100 to 170° C., at which the flame-retardent polymers cake and have to be dug out, making film production impossible.
In the case of the vacuum dryer, which provides the mildest drying conditions, the raw material traverses a temperature range from about 30 to 130° C., under a vacuum of 50 mbar. Post-drying is then needed in a hopper at temperatures from 100 to 130° C. with a residence time of from 3 to 6 hours. Here, too, this polymer cakes to an extreme extent.
BRIEF DESCRIPTION OF THE INVENTION
This object is achieved by means of a white thermoformable film with a thickness in the range from 10 to 350 &mgr;m, which comprises a crystallizable thermoplastic principal constituent, and comprises at least one white pigment, at least one UV absorber, and at least one flame retardant, where expediently the UV absorber and according to invention the flame retardant are fed directly as masterbatch during the production of the film.
DETAILED DESCRIPTION OF THE INVENTION
The white, flame-retardant, UV-resistant, thermoformable, oriented film comprises, as principal constituent, a crystallizable thermoplastic. Examples of suitable crystallizable or semicrystalline thermoplastics are polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, preferably polyethylene terephthalate.
According to the invention, crystallizable thermoplastics are crystallizable homopolymers, crystallizable copolymers, crystallizable compounded materials (mixtures), crystallizable recycled material, and other types of crystallizable thermoplastics.
The white film may be either a single-layer or a multilayer film. The film may also have a coating of various copolyesters or adhesion promoters.
According to the invention, the white film comprises a UV absorber and a flame retardant. The UV absorber is expediently fed directly during the production of the film by way of masterbatch technology, the concentration of the UV stabilizer preferably being from 0.01 to 5% by weight, based on the weight of the layer of the crystallizable thermoplastic.
No embrittlement on brief exposure to heat means that after 100 hours of a heat-conditioning procedure at 100° C. in a circulating-air oven the film or the molding exhibits no embrittlement nor any poor mechanical properties.
The film of the invention comprises at least one flame retardant, fed directly during the production of the film by way of masterbatch technology, the concentration of the flame retardant being in the range from 0.5 to 30.0% by weight, preferably from 1.0 to 20.0% by weight, based on the weight of the layer of the crystallizable thermoplastic. The ratio of flame retardant to thermoplastic maintained during production of the masterbatch is generally in the range from 60:40% by weight to 10:90% by weight.
Typical flame retardants include bromine compounds, chloroparaffins, and 10 other chlorine compounds, antimony trioxide, aluminum trihydrates, the halogen compounds being disadvantageous due to the halogen-containing by-products
Crass Guenther
Kern Ulrich
Murschall Ursula
Oberlaender Klaus
Chen Vivian
Mitsubishi Polyester Film GmbH
ProPat L.L.C.
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