WO2001053092A1

WO2001053092A1 - Amorphous, white, heat-sealable, uv-stable, flame-retardant, thermoformable polyester film, a method for the production thereof and the use of the same

Info

Publication number: WO2001053092A1
Application number: PCT/EP2001/000215
Authority: WO
Inventors: Ursula Murschall; Wolfgang Dietz; Günther Crass; Herbert Peiffer
Original assignee: Mitsubishi Polyester Film Gmbh
Priority date: 2000-01-20
Filing date: 2001-01-10
Publication date: 2001-07-26
Also published as: DE10002150A1

Abstract

The invention relates to a co-extruded polyester film with a thickness ranging between 30 and 2000 νm, which consists of at least a base layer B and outer layers A and C that are applied to both sides of said base layer. The film also contains at least one UV-stabiliser as a light-protection agent and a flame-retardant agent. The heat-sealable outer layer A has a seal kick-off temperature of 110 °C, a seal weld strength of at least 1.3 N/15 mm, a surface roughness, expressed as the Ra value, of < 30 nm and a measured value for the gaseous flux which ranges between 500 and 4000 s. The outer layer C, which cannot be heat-sealed, has a frictional constant of this layer in relation to itself, expressed as a COF value, of < 0.5, a surface roughness, expressed as an Ra value, ranging between 40 nm and 100 nm, a measured value of the gaseous flux of < 120 s and a number of elevations N per mm2 of film surface which are correlated using the respective height h by means of the following equations: A¿C1? - BC1 . log h/νm < NC/mm?2 < A¿C2 - BC2 . log h/νm with 0.01 νm < h < 10 νm and AC1 = 0.29; BC1 = 3.30; AC2 = 1.84; und BC2 = 2.70. The invention also relates to the production of the film and the use thereof.

Description

Amorphous, white, sealable, UV-stabilized, flame-retardant, thermoformable polyester film, process for its production and its use

The invention relates to an amorphous, white, UV-stabilized, flame-retardant, sealable, coextruded polyester film whose thickness is in the range from 30 to 2000 μm, consisting of at least one base layer B and cover layers A and C applied to this base layer on both sides. The film contains additionally at least one UV stabilizer as a light stabilizer and one flame retardant. The invention further includes a method for making the film and using it.

The films and articles made from them are particularly suitable for outdoor applications, such as. B. for greenhouses and canopies. The films are also very suitable for covering and thus for protecting metallic surfaces on which the films are heat-sealed. In outdoor applications, films that do not contain UV-absorbing materials show a deterioration and deterioration of the mechanical properties after a short time due to photooxidative degradation by sunlight. In addition, the films and articles made from them are particularly suitable for applications where fire protection or flame retardancy is required. The films can be thermoformed economically on commercially available deep-drawing systems. The molded body produced has good detail rendition.

Sealable, biaxially oriented polyester films are known in the prior art. Sealable, biaxially oriented polyester films which are equipped with one or more UV absorbers are also known. This according to the state of the

Technically known films are either characterized by good sealing behavior, good optics or an acceptable processing behavior. The known films can also have an opaque appearance.

GB-A 1 465 973 describes a co-extruded, two-layer polyester film, one layer of which contains isophthalic acid-containing and terephthalic acid-containing copolyesters and the other layer of polyethylene terephthalate. There is no usable information in the script about the sealing behavior of the film. Due to the lack of pigmentation, the film cannot be produced reliably (film cannot be wound) and can only be processed to a limited extent.

EP 0035835 describes a coextruded, sealable polyester film in which, in order to improve the winding and processing behavior, particles are added to the sealing layer, the average particle size of which exceeds the layer thickness of the sealing layer. The particulate additives form surface protrusions that prevent unwanted blocking and sticking to rollers or guides. No further details regarding the incorporation of antiblocking agents are given about the other, non-sealable layer of the film. It remains open whether this layer contains antiblocking agents. The choice of particles with a larger diameter than the sealing layer and the concentrations given in the examples deteriorate the sealing behavior of the film. The script does not give any information on the sealing temperature range of the film. The seal seam strength is measured at 140 ° C and is in a range from 63 to 120 N / m (0.97 N / 15 mm to 1.8 N / 15 mm film width).

EP 0432886 describes a coextruded multilayer polyester film which has a first surface on which a sealable layer is arranged and a second surface on which an acrylate layer is arranged. Here, too, the sealable cover layer can consist of copolyesters containing isophthalic acid and terephthalic acid. The film on the back has improved processing properties. Information on the sealing area of the film are not made in scripture. The seal seam strength is measured at 140 ° C. A seal seam strength of 761.5 N / m (11.4 N / 15 mm) is specified for an 11 μm thick sealing layer. A disadvantage of the acrylic coating on the back is that this side no longer seals against the sealable top layer. The film can therefore only be used to a very limited extent.

EP 0515096 describes a coextruded, multilayer sealable polyester film which contains an additional additive on the sealable layer. The additive can e.g. contain inorganic particles and is preferably applied in an aqueous layer to the film during its manufacture. As a result, the film should maintain the good sealing properties and be easy to process. The back contains very few particles that get into this layer mainly through the regranulate. No information is given in this document on the sealing temperature range of the film. The seal seam strength is measured at 140 ° C and is more than 200 N / m (3 N / 15 mm). A seal seam strength of 275 N / m (4.125 N / 15 mm) is given for a 3 μm thick sealing layer.

WO 98/06575 describes a coextruded multilayer polyester film which contains a sealable cover layer and a non-sealable base layer. The base layer can be constructed from one or more layers, the interior of the layers being in contact with the sealable layer. The other (outer) layer then forms the second non-sealable cover layer. Here too, the sealable cover layer can consist of copolyesters containing isophthalic acid and terephthalic acid, which, however, contain no antiblocking particles. The film also contains at least one UV absorber, which is added to the base layer in a weight ratio of 0.1 to 10%. Triazines, for example ^® Tinuvin 1577 from Ciba, are preferably used as UV absorbers. The base layer is equipped with common antiblocking agents. The film is characterized by a good sealability, but does not have the desired processing behavior and exhibits also deficits in the optical properties (gloss and cloudiness). The film is not thermoformable and is not flame retardant.

A flame-retardant raw material is described in DE AS 2346787. In addition to the raw material, the use of the raw material for films and fibers is also claimed. The following deficits emerged in the production of film with this claimed phospholane-modified raw material

The raw material mentioned is sensitive to hydrolysis and must be pre-dried very well. When drying the raw material with dryers which correspond to the prior art, the raw material sticks together, so that a film can only be produced under the most difficult conditions.

The films produced under uneconomical conditions become brittle when exposed to temperature, i.e. the mechanical properties decrease sharply due to embrittlement, making the film unusable. This embrittlement occurs after 48 hours of exposure to heat.

No reference can be found whether and how the foils can be thermoformed. The films described are all oriented and are therefore crystalline, the crystallinity depending on the degree of orientation being between 35% and 50%.

The object of the present invention was to provide an amorphous, white, UV-stabilized, flame-retardant, sealable and thermoformable polyester film which does not have the disadvantages of the films mentioned according to the prior art and, in particular, is economical to produce due to its very good sealability , features improved processability and improved optical properties. Above all, it should have a flame-retardant effect and no embrittlement after exposure to temperature. Furthermore it should be thermoformable on complex deep-drawing systems to form complex shaped bodies.

It was an object of the present invention to expand the sealing area of the film to low temperatures, to increase the sealing seam strength of the film and at the same time to provide improved handling of the film than is known in the prior art. In addition, it must be ensured that the film can also be processed on high-speed processing machines. In the production of the film, it is intended that regenerated material which is produced in a concentration of up to 60% by weight, based on the total weight of the film, should be able to be fed to the extrusion without the properties of the film being adversely affected.

Since the film is intended in particular for outdoor use and / or critical indoor use, it should have a high UV stability. A high UV stability means that the films are not or only extremely little damaged by sunlight or other UV radiation. In particular, the films should not yellow over several years of external use, should not show embrittlement or cracking of the surface, and should also not show any deterioration in the mechanical properties. High UV stability means that the film absorbs the UV light and only lets light through in the visible range.

The standard viscosity SV (DCE) of the crystallized thermoplastic, measured in dichloroacetic acid according to DIN 53728, is 600 to 1000, preferably 700 to 900.

A flame-retardant effect means that the white film meets the conditions according to DIN 4102 Part 2 and in particular the conditions according to DIN 4102 Part 1 in a so-called fire protection test and can be classified in building material class B 2 and in particular B1 of the flame-retardant materials. Furthermore, the film should pass the UL test 94 "Vertical Burning Test for Flammability of Plastic Material", so that it can be classified in class 94VTM-0. This means that the film no longer burns 10 seconds after the burner has been removed, that no glow is observed after 30 seconds and that no dripping is detected.

Economic production includes the fact that the raw materials or the raw material components that are required to produce the flame-retardant film can be dried with industrial dryers that meet the standard of technology. It is essential that the raw materials do not stick together and are not thermally broken down. These state of the art industrial dryers include vacuum dryers, fluidized bed dryers, fluid bed dryers, fixed bed dryers (shaft dryers). These dryers operate at temperatures between 100 and 170 ° C, where the flame-retardant raw materials stick together and have to be mined so that film production is not possible.

In the most gently drying vacuum dryer, the raw material goes through a temperature range of approx. 30 to 130 ° C with a vacuum of approx. 50 mbar. Afterwards, a so-called drying in a hopper at temperatures of 100 to 130 ° C and a residence time of 3 to 6 hours is required. Even here, this raw material sticks extremely.

No embrittlement at short temperatures means that after 100 hours of tempering at 100 ° C in a convection oven, the film shows no embrittlement and no bad mechanical properties.

Good thermoformability means that the film can be thermoformed or thermoformed on commercially available thermoforming machines without economical predrying, the thermoformed molded body having good detail rendering. The object is achieved according to the invention by providing an amorphous, white, coextruded, UV-stabilized and flame-retardant, thermoformable, sealable polyester film with at least one base layer B, a sealable cover layer A and a further, non-sealable cover layer C, the sealable cover layer A being one Seal starting temperature of 110 ° C and a seal seam strength of at least 1.3 N / 15 mm, the distinguishing features of which can be seen in the fact that the sealable cover layer A has a surface roughness, expressed as R _a value, of <30 nm and a measured value of the gas flow in the range from 500 to 4000 s and that the non-sealable cover layer C has a coefficient of friction of this layer against itself, expressed as a COF value, of <0.5, a surface roughness, expressed as R _a value, in the range of 40 nm up to 100 nm, a measurement of the gas flow of <120 s and a number of elevations N per mm ^{2 of} film surface, which are correlated with the respective height h using the following equations:

A _d - At '' ° 9 h / μm <N _c / mm ² <Ac ₂ - B _G2 ^• log h / μm with 0.01 μm <h <10 μm; A _C1 = 0.29; B _C1 = 3.30; A _C2 = 1.84; and B _C2 = 2.70.

The UV stabilizer (s) is (are) expediently metered in directly as masterbatch (s) in film production, the concentration of the UV stabilizer (s) within a layer preferably being between 0.01 and 5 wt .-%, based on the weight of the respective layer of the polyester used, lies.

The film according to the invention contains at least one flame retardant which is metered in directly during film production using the so-called 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 wt .-%, based on the weight of the layer of crystallizable thermoplastic, is. During the production of the masterbatch, generally maintained a ratio of flame retardant to thermoplastic in the range of 60 to 40 wt .-% to 10 to 90 wt .-%.

Typical flame retardants include bromine compounds, chlorinated paraffins and other chlorine compounds, antimony trioxide, aluminum trihydrates, the halogen compounds being disadvantageous because of the halogen-containing by-products formed. Furthermore, the low light resistance of a film equipped with it, in addition to the development of hydrogen halide in the event of fire, is extremely disadvantageous.

Suitable flame retardants which are used according to the invention are, for example, organic phosphorus compounds such as carboxyphosphinic acids, their anhydrides and dimethyl methylphosphonate. It is essential to the invention that the organic phosphorus compound is soluble in the thermoplastic, since otherwise the required optical properties are not met.

Since the flame retardants generally have a certain sensitivity to hydrolysis, the additional use of a hydrolysis stabilizer can be useful.

Phenolic stabilizers, alkali / alkaline earth stearates and / or alkali / alkaline earth carbonates are generally used as hydrolysis stabilizers in amounts of 0.01 to 1.0% by weight. Phenolic stabilizers are preferred in an amount of 0.05 to 0.6% by weight, in particular 0.15 to 0.3% by weight and with a molar mass of more than 500 g / mol. Pentaerythrityl tetrakis 3- (3,5-di-tertiary-butyl-4-hydroxyphenyl) propionate or 1,3,5-trimethyl-2,4,6-tris (3,5-di-tertiary-butyl-4-hydroxybenzyl) benzene are particularly advantageous.

According to the invention, the film has at least three layers and then comprises as layers the base layer B, the sealable cover layer A and the non-sealable cover layer C. The base layer B of the film preferably consists of at least 70% by weight of a thermoplastic polyester. Polyesters of ethylene glycol and terephthalic acid (= polyethylene terephthalate, PET), of ethylene glycol and naphthalene-2,6-dicarboxylic acid (= polyethylene-2,6-naphthalate, PEN), of 1,4-bis-hydroxymethylcyclohexane and terephthalic acid are suitable for this (= Poly-1, 4-cyclohexanedimethylene terephthalate, PCDT) as well as from ethylene glycol, naphthalene-2,6-dicarboxylic acid and biphenyl-4,4'-dicarboxylic acid (= polyethylene-2,6-naphthalate bibenzoate, PENBB). Particularly preferred are polyesters which consist of at least 90 mol%, preferably at least 95 mol%, of ethylene glycol and terephthalic acid units or of ethylene glycol and naphthalene-2,6-dicarboxylic acid units. The remaining monomer units originate from other suitable aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids, as can also occur in layer A or layer C.

The thermoplastic is e.g. characterized in that the diethylene glycol content (DEG content) and / or polyethylene glycol content (PEG content) is greater than / equal to 1.0% by weight, in particular greater than / equal to 1.2% by weight. In a particularly preferred embodiment, the DEG content and / or PEG content is in the range from 1.3% by weight to 5% by weight. In addition or instead of DEG and / or PEG, it can also contain isophthalic acid (IPA) in a concentration of 3% by weight to 10% by weight.

It was more than surprising that the films can be thermoformed economically on commercially available thermoforming machines and deliver excellent detail reproduction due to the higher diethylene glycol content and / or polyethylene glycol content and / or IPA content compared to standard thermoplastics.

Suitable other aliphatic diols are, for example, diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO- (CH ₂ ) _n -OH, where n is a whole

Represents the number from 3 to 6 (in particular propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol and hexane-1,6-diol) or branched aliphatic glycols with up to 6 carbon atoms Atoms. Of the suitable cycloaliphatic diols, cyclohexanediols (in particular cyclohexane-1,4-diol) should be mentioned in particular. Suitable other aromatic diols correspond, for example, to the formula HO-C ₆ H ₄ -XC ₆ H ₄ -OH, where X is -CH ₂ -, -C (CH ₃ ) ₂ -, -C (CF ₃ ) ₂ -, -O -, -S- or -SO ₂ - stands. In addition, bisphenols of the formula HO-C ₆ H ₄ -C ₆ H ₄ -OH are also very suitable.

Suitable aromatic dicarboxylic acids are preferably benzenedicarboxylic acids, naphthalene dicarboxylic acids (for example naphthalene-1, 4- or 1,6-dicarboxylic acid), biphenyl-x, x '-dicarboxylic acids (in particular biphenyl-4,4'-dicarboxylic acid), diphenylacetylene-x, x' -dicarboxylic acids (especially diphenylacetylene-4,4'-dicarboxylic acid) or stilbene-x.x'-dicarboxylic acids. Of the cycloaliphatic dicarboxylic acids, cyclohexanedicarboxylic acids (in particular cyclohexane-1,4-dicarboxylic acid) should be mentioned. Of the aliphatic dicarboxylic acids, the (C ₃ -C ₁₉ ) alkanedioic acids are particularly suitable, the alkane fraction being straight-chain or branched.

The production of the polyesters can e.g. according to the transesterification process. The starting point is dicarboxylic acid esters and diols, which are reacted with the usual transesterification catalysts, such as zinc, calcium, lithium, magnesium and manganese salts. The intermediates are then polycondensed in the presence of generally customary polycondensation catalysts, such as antimony trioxide or titanium salts. It can also be produced by the direct esterification process in the presence of polycondensation catalysts. Here one starts directly from the dicarboxylic acids and the diols.

The sealable outer layer A applied to the base layer B by coextrusion is based on polyester copolymers and essentially consists of copolyesters which are composed predominantly of isophthalic and terephthalic acid units and of ethylene glycol units. The remaining monomer units come from other aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids, as can also occur in the base layer. The preferred Copolyesters which provide the desired sealing properties are those which are composed of ethylene terephthalate and ethylene isophthalate units and of ethylene glycol units. The proportion of ethylene terephthalate is 40 to 95 mol% and the corresponding proportion of ethylene isophthalate is 60 to 5 mol%. Preferred are copolyesters in which the proportion of ethylene terephthalate is 50 to 90 mol% and the corresponding proportion of ethylene isophthalate is 50 to 10 mol% and very preferred are copolyesters in which the proportion of ethylene terephthalate is 60 to 85 mol% and the corresponding The proportion of ethylene isophthalate is 40 to 15 mol%.

In principle, the same polymers as described above for the base layer B can be used for the other, non-sealable top layer C or for any intermediate layers that are present.

The desired sealing and processing properties of the film according to the invention are obtained from the combination of the properties of the copolyester used for the sealable cover layer and the topographies of the sealable cover layer A and the non-sealable cover layer C.

The seal initiation temperature of 110 ° C and the seal seam strength of at least 1.3 N / 15 mm is achieved if the copolymers described in more detail above are used for the sealable cover layer A. The best sealing properties of the

Film is obtained if no further additives, in particular no inorganic or organic fillers, are added to the copolymers. In this case, the lowest seal starting temperature and the highest seal seam strengths are obtained for a given copolyester. However, the handling of the film is poor in this case, since the surface of the sealable cover layer A tends to block. The film can hardly be wrapped and is practically not suitable for further processing on high-speed packaging machines. In order to improve the handling of the film and the processability, it is necessary to modify the sealable cover layer A. This is best done with the help of suitable ones Antiblocking agents of a selected size, which are added to the sealing layer in a specific concentration in such a way that on the one hand the blocking is minimized and on the other hand the sealing properties are only marginally impaired. This desired combination of properties can be achieved if the topography of the sealable outer layer A is characterized by the following set of parameters:

The roughness of the sealable top layer, expressed by the R _a value, should be less than 30 nm. In the other case, the sealing properties are negatively influenced in the sense of the present invention.

The measured value of the gas flow should be in the range from 500 to 4000 s. At values below 500 s, the sealing properties are negatively influenced in the sense of the present invention, and at values above 4000 s, the handling of the film becomes poor.

In order to further improve the processing behavior of the sealable film, the topography of the non-sealable cover layer C should be characterized by the following set of parameters:

The coefficient of friction (COF) of this side against itself should be less than 0.5. Otherwise the winding behavior and further processing of the film are unsatisfactory.

The roughness of the non-sealable top layer, expressed by the R _a value, should be greater than 40 nm and less than 100 nm. Values smaller than 40 nm have negative effects on the winding and processing behavior of the film and values larger than 100 nm impair the optical properties (gloss, haze) of the film. The measured value of the gas flow should be in the range below 120 s. At values above 120, the winding and processing behavior of the film is negatively affected.

The number of elevations N per mm ^{2 of} film surface is correlated with the respective height h using the following equation:

0.29 - 3.30 ^• log h / μm <log N / mm ² <1.84 - 2.70 ^• log h / μm with 0.01 μm <h <10 μm.

If the values for N are smaller than the left side of the equation, the winding and processing behavior of the film is adversely affected. If the values for N are larger than the right side of the equation, the gloss and haze become the film negatively affected.

In principle, all organic and inorganic UV stabilizers which are suitable for incorporation into polyesters can be selected for the film according to the invention. Such suitable UV stabilizers are known in the art and e.g. described in more detail in WO 98/065575, in EP-A-0 006 686, in EP-A-0 031 202, EP-A-0 031 203 or in EP-A-0 076 582.

Light, in particular the ultraviolet portion of solar radiation, ie the wavelength range from 280 to 400 nm, initiates degradation processes in thermoplastics, as a result of which not only the visual appearance changes as a result of color change or yellowing, but also negatively influences the mechanical-physical properties become. The inhibition of these photooxidative degradation processes is of considerable technical and economic importance, since otherwise the application possibilities of numerous thermoplastics are drastically restricted.

Polyethylene terephthalates, for example, begin to absorb UV light below 360 nm, their absorption increases considerably below 320 nm and is very pronounced below 300 nm. The maximum absorption is between 280 and 300 nm.

In the presence of oxygen, mainly chain cleavages are observed, but no cross-links. Carbon monoxide, carbon dioxide and carboxylic acids are the predominant quantities of photooxidation products. In addition to the direct photolysis of the ester groups, oxidation reactions must also be considered, which also result in the formation of carbon dioxide via peroxide radicals.

The photooxidation of polyethylene terephthalates can also lead to hydroperoxides and their decomposition products and the associated chain cleavages via elimination of hydrogen in the position of the ester groups (H. Day, D. M. Wiles: J. Appl. Polym. Sei 16, 1972, page 203).

UV stabilizers or UV absorbers as light stabilizers are chemical compounds that can intervene in the physical and chemical processes of light-induced degradation. Soot and other pigments can partially protect against light. However, these substances are unsuitable for transparent films because they lead to discoloration or color change. For transparent, matt films, only organic and organometallic compounds are suitable which give the thermoplastic to be stabilized no or only an extremely slight color or color change, ie which are soluble in the thermoplastic. UV stabilizers suitable as light stabilizers for the purposes of the present invention are UV stabilizers which absorb at least 70%, preferably 80%, particularly preferably 90%, of the UV light in the wavelength range from 180 nm to 380 nm, preferably 280 to 350 nm. These are particularly suitable if they are thermally stable in the temperature range from 260 to 300 ° C, ie they do not decompose and do not lead to outgassing. Suitable UV stabilizers as light stabilizers are, for example, 2-hydroxybenzophenones, 2-hydroxybenzotriazoles, organo-nickel compounds, salicylic acid esters, cinnamic acid ester derivatives, resorcinol monobenzoates, oxalic acid anilides, hydroxybenzoic acid esters, sterically hindered amines and triazines, the 2-hydroxybenzotriazoles being preferred.

In a very particularly preferred embodiment, the film according to the invention contains 0.01% by weight to 5.0% by weight of 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5- ( hexyl) oxyphenol of the formula

or 0.01% by weight to 5.0% by weight of 2,2-methylene-bis (6- (2H-benzotriazol-2-yl) -4- (1, 1, 2,2-tetramethylpropyl) - phenol of the formula

In a preferred embodiment, mixtures of these two UV stabilizers or mixtures of at least one of these two UV stabilizers with other UV stabilizers can also be used, the total concentration of light stabilizer preferably being between 0.01% by weight and 5.0% by weight. -%, based on the weight of crystallizable polyethylene terephthalate.

The UV stabilizer or stabilizers are preferably contained in the cover layer (s). If necessary, the core layer can also be equipped with a UV stabilizer.

It was completely surprising that the use of the above-mentioned UV stabilizers in films led to the desired result. The person skilled in the art would probably have initially tried to achieve a certain UV stability by means of an antioxidant, but would have found in weathering that the film quickly turns yellow.

In view of the fact that UV stabilizers absorb the UV light and thus offer protection, the person skilled in the art would have used commercially available stabilizers. He would have noticed that the UV stabilizer lacks thermal stability and decomposes and outgasses at temperatures between 200 ° C and 240 ° C; - He has to incorporate large amounts (approx. 10 to 15% by weight) of UV stabilizer so that the UV light is absorbed and so that the film is not damaged.

At these high concentrations, he would have found that the film was already yellow after production, with differences in yellowness index (YID) around 25. Furthermore, he would have found that the mechanical properties are negatively affected.

It was therefore more than surprising that excellent UV protection was achieved even with low concentrations of the UV stabilizer. It was very surprising that this excellent UV protection the yellowness index of the film does not change compared to a non-stabilized film within the scope of the measurement accuracy; there were no outgassings, no nozzle deposits, no evaporation, which gives the film an excellent appearance and an excellent profile and flatness;

Surprisingly, weathering tests according to the test specification ISO 4892 with the Atlas CI65 Weather Ometer have shown that in the case of the aforementioned three-layer film, it is quite sufficient to equip the 0.3 μm to 2.5 μm thick cover layers with UV stabilizers in order to improve UV -To achieve stability.

Weathering tests have shown that the films stabilized according to the invention, even in weathering tests after an extrapolated 5 to 7 years of outdoor use, generally have no yellowing, no embrittlement, no loss of gloss on the surface, no cracking on the surface and no deterioration in the mechanical properties.

The light stabilizer can be metered in at the thermoplastic raw material manufacturer or metered into the extruder during film production.

The addition of the light stabilizer via masterbatch technology is particularly preferred. The light stabilizer is fully dispersed in a solid carrier material. Suitable carrier materials are the polyethylene terephthalate itself or also other polymers which are sufficiently compatible with the thermoplastic.

It is important with masterbatch technology that the grain size and bulk density of the masterbatch is similar to the grain size and bulk density of the thermoplastic, so that homogeneous distribution and thus homogeneous UV stabilization can take place. It was therefore more than surprising for the person skilled in the art that a flame-retardant film with the required property profile can be produced economically and without adhesion in the dryer using masterbatch technology, suitable predrying or pre-crystallization and the use of small amounts of a hydrolysis stabilizer, and that the film after exposure to temperature of up to 100 ° C over a longer period of time, it does not even become brittle.

It was also very surprising that with this excellent result and the required flame retardancy, the yellowness index of the film compared to a film that was not equipped was not negatively influenced within the scope of the measurement accuracy, that no outgassing and no nozzle deposits occurred, which gives the film an excellent appearance and has an excellent profile and flatness.

This means that such a film is also economically viable for your manufacturer.

In addition, it is very surprising that the regrind can also be used again in the production process without negatively affecting the yellowness index of the film. This makes it suitable, for example, for use as short-lived advertising signs, for trade fair construction and for other promotional items where fire protection is required and required.

It is essential to the invention that the crystallizable thermoplastic has a diethylene glycol content of> 1.0% by weight, preferably ≥1.2% by weight, in particular ≥1.3% by weight and / or a polyethylene glycol content of> 1.0% by weight, preferably > 1.2% by weight, in particular> 1.3% by weight and / or an isophthalic acid content of 3% by weight to 10% by weight.

In a preferred embodiment, the white, flame-retardant film according to the invention contains, as the main constituent, a crystallizable polyethylene terephthalate, 1 to 20 wt .-% of an organic phosphorus compound soluble in polyethylene terephthalate as a flame retardant and 0.1 to 1, 0 wt .-% of a hydrolysis stabilizer.

In the three-layer embodiment of the film according to the invention, like the UV absorber, the flame retardant is preferably contained in the non-sealable cover layer C. However, the base layer B or the sealable cover layer A can also be equipped with flame retardants as required. The concentration of the flame retardant (s) relates to the weight of the thermoplastics in the layer equipped with flame retardants.

Surprisingly, fire protection tests according to DIN 4102 and the UL test have shown that in the case of a three-layer film, it is sufficient to equip the 0.5 to 10 μm thick top layers with flame retardants in order to achieve improved flame retardancy. If required and with high fire protection requirements, the core layer can also be equipped with flame retardants, i.e. include so-called basic equipment.

As a result, the flame-retardant, multi-layer films produced with the known coextrusion technology become economically very interesting for production in comparison to the monofilms which are completely finished in high concentrations, since significantly less flame retardants and significantly less UV absorbers are required.

In addition, measurements showed that the film according to the invention does not become brittle at a temperature load of 100 ° C. over a longer period of time, which is more than surprising. This result is due to the synergistic effect of suitable pre-crystallization, pre-drying, masterbatch technology and hydrolysis stabilizer. Surprisingly, films according to the invention in the thickness range from 30 to 2000 μm already meet the building material classes B2 and B1 according to DIN 4102 and UL test 94.

According to the invention, the flame retardant is added using masterbatch technology. The flame retardant is fully dispersed in a carrier material. Polyethylene terephthalate or other polymers which are compatible with the polyethylene terephthalate are suitable as the carrier material.

It is important with the masterbatch technology that the grain size and the bulk density of the masterbatch is similar to the grain size and the bulk density of the thermoplastic, so that a homogeneous distribution and thus a homogeneous flame resistance can take place.

It is essential to the invention that the masterbatch, which contains the flame retardant and optionally the hydrolysis stabilizer, is pre-crystallized or pre-dried. This predrying involves gradual heating of the masterbatch under reduced pressure (20 to 80 mbar, preferably 30 to 60 mbar, in particular 40 to 50 mbar) and with stirring and optionally post-drying at a constant, elevated temperature, likewise under reduced pressure. The masterbatch is preferably batchwise at room temperature from a metering container in the desired mixture together with the polymers of the base and / or outer layers and possibly other raw material components in a vacuum dryer, which has a temperature range from 10 ° C to during the drying or dwell time 160 ° C, preferably 20 ° C to 150 ° C, in particular 30 ° C to 130 ° C passes. During the approx. 6-hour, preferably 5-hour, in particular 4-hour dwell time, the raw material mixture is stirred at 10 to 70 rpm, preferably 15 to 65 rpm, in particular 20 to 60 rpm. The raw material mixture pre-crystallized or pre-dried in this way is in a downstream likewise evacuated container at 90 ° to 180 ° C., preferably 100 ° C. to 170 ° C., in particular 110 ° C. to 160 ° C. for 2 to 8 hours, preferably 3 to 7 hours , especially after 4 to 6 hours The base layer B can additionally contain conventional additives, such as, for example, stabilizers and / or antiblocking agents. The other two layers A and C additionally contain conventional additives, such as stabilizers and / or antiblocking agents. They are expediently added to the polymer or the polymer mixture before the melting. For example, phosphorus compounds such as phosphoric acid or phosphoric acid esters are used as stabilizers.

Typical antiblocking agents (also referred to as pigments in this context) are inorganic and / or organic particles, for example calcium carbonate, amorphous silica, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, LiF, calcium, barium , Zinc or manganese salts of the dicarboxylic acids used, carbon black, titanium dioxide, kaolin or crosslinked polystyrene or acrylate particles.

Mixtures of two or more different antiblocking agents or mixtures of antiblocking agents of the same composition but different particle size can also be selected as antiblocking agents. The particles can the individual layers in the respective advantageous concentrations, e.g. as a glycolic dispersion during polycondensation or via masterbatches during extrusion.

Preferred particles are SiO ₂ in colloidal and in chain-like form. These particles are very well integrated into the polymer matrix and only slightly generate vacuoles. Vacuoles generally cause turbidity and should therefore be avoided. In principle, the particle diameters of the particles used are not restricted. To achieve the object, however, it has proven to be expedient to use particles with an average primary particle diameter of less than 100 nm, preferably less than 60 nm and particularly preferably less than 50 nm and / or particles with an average primary particle diameter of greater than 1 μm, preferably larger than 1.5 μm and particularly preferably larger than 2 μm. However, these particles described last should not have an average particle diameter that is greater than 5 μm.

To achieve the aforementioned properties of the sealable film, in particular the desired degree of whiteness, the base layer contains the pigmentation necessary for this. It has proven particularly advantageous here to use barium sulfate as an additional additive with an average grain size in the range from 0.3 to 0.8 μm, preferably from 0.4 to 0.7 μm. This gives the film a brilliant white appearance without being yellowish. In order to achieve a degree of whiteness of 70 or more (according to Berger), the base layer must be filled up. The particle concentration of barium sulfate is then above 12% by weight, preferably above 14% by weight and very particularly preferably even above 16% by weight.

In the advantageous form of use, the film consists of three layers, the base layer B and cover layers A and C applied to both sides of this base layer, the cover layer A being sealable against itself and against the cover layer C.

In order to achieve the stated property profile of the film, the top layer C has more pigments (i.e. higher pigment concentration) than the top layer A. The pigment concentration in this second cover layer C is between 0.1 and 1.0%, advantageously between 0.12 and 0.8% and in particular between 0.15 and 0.6%. The other sealable cover layer A, which is opposite the cover layer C, is less filled with inert pigments. The concentration of the inert particles in layer A is between 0.01 and 0.2% by weight, preferably between 0.015 and 0.15% by weight and in particular between 0.02 and 0.1% by weight.

There may also be an intermediate layer between the base layer and the cover layers. This can in turn consist of those for the base layers described polymers exist. In a particularly preferred embodiment, it consists of the polyester used for the base layer. It can also contain the usual additives described. The thickness of the intermediate layer is generally greater than 0.3 μm and is preferably in the range from 0.5 to 5 μm, in particular in the range from 1.0 to 20 μm and very particularly preferably in the range from 1.0 to 15 μm.

In the particularly advantageous three-layer embodiment of the film according to the invention, the thickness of the cover layers A and C is generally greater than 0.5 μm and is generally in the range from 0.5 to 10 μm, it being possible for the cover layers A and C to be of the same or different thickness ,

The total thickness of the polyester film according to the invention can vary within certain limits. It is 30 to 2000 μm, in particular 50 to 1800 μm, preferably 100 to 1500 μm.

production method

The invention further relates to a process for producing the polyester film according to the invention by the coextrusion process known per se.

For this purpose, the polymeric raw materials for the film are first pre-crystallized or pre-dried. Predrying involves gradually heating the raw materials under reduced pressure and with stirring and, if appropriate, post-drying at a constant, elevated temperature, likewise under reduced pressure. The polymeric raw materials are preferably batchwise at room temperature from a metering container in the desired mixture together with any other raw material components in a vacuum dryer which has a temperature range of 10 to 160 ° C., preferably 20 to 130 ° C. in the course of the drying or dwell time. passes through, filled. During the approx. 4-hour, preferably approx. 6-hour, dwell time, the raw material mixture is stirred at 10 to 70 rpm. The pre-crystallized or Predried raw material mixture is subsequently dried in a downstream likewise evacuated container at a temperature in the range from 90 to 180 ° C., preferably from 100 to 170 ° C., over a period of 2 to 8 hours, preferably 3 to 6 hours.

Thereafter, in the coextrusion process, the polymers or the polymer mixtures for the individual layers are compressed and liquefied in their own extruders, and the additives which may have been added may already be present in the polymer or in the polymer mixture. Any foreign bodies or impurities that may be present can be separated from the polymer melt by suitable filters before extrusion. The melts are then pressed simultaneously through a flat die (slot die), and the pressed multilayer film is drawn off on one or more take-off rolls, where it cools and solidifies. The solidified film is then optionally corona or flame treated on the surface layer intended for the treatment.

After solidification, one or both surface (s) of the film can be coated in-line by the known methods. The in-line coating can serve, for example, to improve the adhesion of the metal layer or a possibly applied printing ink, but also to improve the antistatic behavior or the processing behavior.

To set other desired properties, the film can also be coated. Typical coatings are adhesion-promoting, antistatic, slip-improving or adhesive layers. It is advisable to apply these additional layers to the film by means of inline coating using aqueous dispersions after the solidification.

The thermoforming process usually includes the steps of predrying, heating, molding, cooling, demolding and tempering. During the thermoforming process Surprisingly, it was found that the film according to the invention can be deep-drawn without prior predrying. This advantage compared to thermoformable polycarbonate and polymethyl methacrylate films, which require drying times of 10 to 15 hours depending on the thickness at temperatures of 100 to 120 ° C, drastically reduces the costs of the forming process.

The following process parameters were surprisingly found for thermoforming.

Process step film according to the invention

Predrying Not necessary

Mold temperature ° C 100 - 140

Heating up time <5 sec per 10 μm thickness

Film temperature during forming ° C 100 - 160 Possible stretch factor 1, 5 -4.0

Detail rendition Excellent

Shrinkage (shrinkage)% <1, 5

Advantages of the Invention The film according to the invention is notable for excellent sealability, very good stability against UV light, very good handling and very good processing behavior. In the case of the film, the sealable cover layer A seals not only against itself (fin sealing) but also against the non-sealable cover layer C (lab sealing). With the lab sealing method, the sealing start temperature is only shifted upwards by approx. 10 K, while the sealing seam strength is not deteriorated by more than 0.3 N / 15.

The film absorbs 100% of the short-wave, aggressive UV light in the wavelength range of less than 380 nm, while non-UV-treated amorphous films allow the UV light to pass through at a wavelength of greater than 280 nm. Furthermore, the film fulfills the fire tests according to DIN 4102 part 1 and part 2 and thus the building material classes B2 and B1 and can be classified in the group of flame-retardant materials. UL test 94 is also passed.

In any case, the film shows no embrittlement after tempering for 200 hours in an air drying cabinet at a temperature of 100 ° C.

Furthermore, the film can be used on commercially available thermoforming machines, e.g. B. from Illig / Heilbronn, thermoformed to complex molded articles economically without predrying. The detail reproduction of the molded bodies is excellent with a homogeneous surface.

In addition, the film impresses with an excellent degree of whiteness, which also gives the film a very attractive, effective advertising appearance. During the production of the film, it is ensured that the regenerate can be fed back into the extrusion in a concentration of 20 to 60% by weight, based on the total weight of the film, without the physical properties of the film being adversely affected.

Due to its excellent sealing properties, its very good handling and its very good processing properties, the film is particularly suitable for processing on high-speed machines.

In addition, due to its excellent combination of properties, the film is suitable for a variety of different applications, for example for interior cladding, for trade fair construction and trade fair items, as displays, for signs, for protective glazing of machines and vehicles, in the lighting sector, in shop and shelf construction, as promotional items, laminating media and for thermoforming applications of all kinds. Due to the good UV stability and flame retardancy, the transparent film according to the invention is also suitable for outdoor applications, such as, for example, for greenhouses, roofing, external cladding, covering materials, such as steel sheets, applications in the construction sector and illuminated advertising profiles, shadow mats, electrical applications.

The table below (Table 1) summarizes the most important film properties according to the invention at a glance.

Table 1

Top layer A

Top layer C

further film properties

The films were weathered according to the test specification ISO 4892 for 1000 hours with the Atlas Ci 65 Weather Ometer from Atlas and then tested for mechanical properties, discoloration, surface defects, haze and gloss.

The following measured values were used to characterize the raw materials and the foils:

measurement methods

DEG content PEG content / IPA content

The DEG / PEG / IPA content is determined by gas chromatography after saponification in methanolic KOH and neutralization with aqueous HCl.

SV (DCE), IV (DVE)

The standard viscosity SV (DCE) is measured based on DIN 53726 in dichloroacetic acid.

The intrinsic viscosity (IV) is calculated from the standard viscosity as follows

IV (DCE) = 6.67-10 ^"4 SV (DCE) + 0.18

Determination of the sealing initiation temperature (minimum sealing temperature) The sealing device HSG / ET from Brugger is used to produce heat-sealed samples (sealing seam 20 mm x 100 mm) , 5 s is sealed. Test strips 15 mm wide were cut from the sealed samples. The T-seal strength was measured as in the determination of the seal strength. The seal start temperature is the temperature at which a seal seam strength of at least 0.5 N / 15 mm is achieved.

Seal strength

To determine the seal seam strength, two 15 mm wide strips of film were placed on top of each other and sealed at 130 ° C, a sealing time of 0.5 s and a sealing pressure of 2 bar (device: Brugger type NDS, one-sided heated sealing jaw). The seal seam strength was determined by the T-Peel method. friction

The friction was determined according to DIN 53 375. The sliding friction number was measured 14 days after production.

surface tension

The surface tension was determined using the so-called ink method (DIN 53364).

Degree of whiteness The degree of whiteness according to Berger was determined with the Spectrogard Color System according to ASTM E 313. First, the colorimetric measures were determined, which were then converted into a single value, the degree of whiteness according to Berger, W _B , whereby the following applies:

W _B = R _y + 3 (R _Z - R _x ) with R _x , R _y and R _z = spectral reflection values.

shine

The gloss was determined in accordance with DIN 67 530. The reflector value was measured as an optical parameter for the surface of a film. Based on the standards ASTM-D 523-78 and ISO 2813, the angle of incidence was set at 20 °. A light beam hits the flat test surface at the set angle of incidence and is reflected or scattered by it. The light rays striking the photoelectronic receiver are displayed as a proportional electrical quantity. The measured value is dimensionless and must be specified with the angle of incidence.

Determination of the grain sizes on film surfaces

The size distribution of elevations on film surfaces is determined using a scanning electron microscope and an image analysis system. The scanning electron microscope XL30 CP from Philips is used with an integrated image analysis program AnalySIS from Soft-Imaging System. For these measurements, foil samples are placed flat on a sample holder. Then they are vapor deposited at an angle α with a thin metal layer (eg made of silver). Here α is the angle between the sample surface and the direction of propagation of the metal vapor. This oblique vaporization creates a shadow behind the elevation. Since the shadows are not yet electrically conductive, the sample is then vapor-deposited or sputtered with a second metal (for example gold), the second coating hitting the sample surface perpendicularly and therefore no shadows being produced in the second coating.

The sample surfaces prepared in this way are imaged in a scanning electron microscope (SEM). The shadows of the elevations are visible due to the material contrast of the metals. The sample is oriented in the SEM so that the shadows run parallel to an image edge. The following conditions are set on the SEM for image acquisition: secondary electron detector, working rod distance 10 mm, acceleration voltage 10 kV and spot 4.5. The brightness and contrast are set so that all image information is shown as gray values and the intensity of the background noise is so low that it is not detected as a shadow. The length of the shadows is measured with the image analysis. The threshold value for shadow detection is placed at the point where the 2nd derivative of the gray value distribution of the image crosses the zero point. Before the shadow detection, the image is smoothed with an NxN filter (size 3, 1 iteration). The setting of a frame ("frame") ensures that elevations that are not fully represented in the image are not measured. The magnification, the frame size and the number of evaluated images are selected so that a total of 0.36 mm ² film surface is evaluated.

The height of the individual elevations is calculated from the individual shadow lengths using the following relationship: h = (tan α) ^• L where h is the height of the elevation, α is the vaporization angle and L is the shadow length. The surveys determined in this way are divided into classes in order to arrive at a frequency distribution. The division is made into 0.05 mm wide classes between 0 and 1 mm, whereby the smallest class (0 to 0.05 mm) is not used for further evaluations. The diameters (spread perpendicular to the direction of the shadow) of the elevations are similarly 0.2 mm wide

Classes from 0 to 10 mm, whereby the smallest class is used for further evaluation.

Surface gas flow time

The principle of the measuring method is based on the air flow between a film side and a smooth silicon wafer plate. The air flows from the environment into an evacuated room, the interface between the film and the silicon wafer plate serving as flow resistance.

A round film sample is placed on a silicon wafer plate, in the middle of which a hole ensures the connection to the recipient. The recipient is evacuated to a pressure less than 0.1 mbar. The time in seconds that the air needs to cause a pressure increase of 56 mbar in the recipient is determined.

Measurement conditions:

Measuring area 45.1 cm2

Contact weight 1276 g air temperature 23 ° C

Air humidity 50% relative humidity

Gas collection volume 1, 2 cm ³

Pressure interval 56 mbar surface defects

The surface defects are determined visually.

Mechanical properties

The modulus of elasticity, tensile strength and elongation at break are measured in the longitudinal and transverse directions according to ISO 527-1-2.

Weathering (both sides), UV stability

The UV stability is tested according to the test specification ISO 4892 as follows:

Test device: Atlas Ci 65 Weather Ometer

Test conditions: ISO 4892, i.e. H. artificial weathering

Irradiation time: 1000 hours (per side)

Irradiation: 0.5 W / m2, 340 nm

Temperature: 63 ° C

Relative humidity: 50%

Xenon lamp: inner and outer filter made of borosilicate

Irradiation cycles: 102 minutes of UV light, then 18 minutes of UV light: with water spraying the samples again

102 minutes of UV light ^" etc.

yellowness

The yellowness index (YID) is the deviation from the colorlessness in the "yellow" direction and is measured in accordance with DIN 6167. Yellowness index (YID) values of <5 are not visible to the naked eye.

fire behavior

The fire behavior is determined according to DIN 4102 part 2, building material class B2 and according to DIN 4102 part 1, building material class B1 as well as according to UL test 94. example 1

Polyethylene terephthalate chips (produced via the transesterification process with Mn as the transesterification catalyst, Mn concentration: 100 ppm) with a DEG content of 1.4% by weight were dried at 150 ° C. to a residual moisture content of below 100 ppm and used for the extruder the base layer B supplied. Chips of polyethylene terephthalate and a filler were also fed to the extruder for the non-sealable top layer C.

In addition, chips were made from a linear polyester consisting of an amorphous copolyester with 78 mol% ethylene terephthalate and 22 mol% ethylene isophthalate (produced by the transesterification process with Mn as the transesterification catalyst, Mn concentration: 100 ppm). The copolyester was dried at a temperature of 100 ° C. to a residual moisture content of below 200 ppm and fed to the extruder for the sealable outer layer A.

The UV stabilizer 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5- (hexyl) ~ oxyphenol ( ^® Tinuvin 1577) is metered in in the form of masterbatches. The masterbatches consist of 5% by weight of Tinuvin 1577 as an active ingredient and 95% by weight of polyethylene terephthalate (for the top layer C) or 95% by weight of polyethylene isophthalate (for the top layer A). The 5% by weight Tinuvin 1577 masterbatches are only added to the two thick top layers with 20% by weight using the masterbatch technology.

The hydrolysis stabilizer and the flame retardant are added in the form of a master batch. The masterbatch is composed of 20% by weight of flame retardant, 1% by weight of hydrolysis stabilizer and 79% by weight of polyethylene terephthalate. The hydrolysis stabilizer is pentaerylthrityl tetrakis 3- (3,5-di-tertiary-butyl-4-hydroxylphenyl) propionate and the flame retardant is dimethyl methyl phosphonate (Armgard P 1045). The masterbatch has a bulk density of 750 kg / m ³ and a softening point of 69 ° C. 10% by weight of the masterbatch is added to the base layer B and 20% by weight of the masterbatch to the non-sealable top layer C.

A white three-layer film with ABC structure and a total thickness of 300 μm was produced by coextrusion, subsequent cooling and solidification. The thickness of the respective cover layers is shown in Table 2.

Top layer A, mixture of:

20.0% by weight UV masterbatch based on polyethylene isophthalate with 5% by weight Tinuvin 1577

77.0% by weight of copolyester with an SV value of 800 3.0% by weight of masterbatch of 97.75% by weight of copolyester (SV value of 800) and 1.0% by weight of ^® Sylobloc 44 H (synthetic SiO ₂ from Grace) and 1.25% by weight ^® Aerosil TT600 (pyrogenic SiO ₂ from Degussa)

Base layer B:

70.0 wt .-% polyethylene terephthalate with an SV value of 800 and

DEG content of 1.4% by weight 20.0% by weight barium sulfate with an average grain size of 0.5 μm

10.0% by weight of masterbatch, which contains flame retardant and hydrolysis stabilizer

Cover layer C, mixture of: 20.0% by weight of masterbatch, which contains flame retardant and hydrolysis stabilizer

20.0% by weight of UV masterbatch based on polyethylene terephthalate with 5

Wt% Tinuvin 1577

48% by weight of polyethylene terephthalate with an SV value of 800 12 wt .-% master batch of 97.75 wt .-% copolyester (SV value of 800) and 1.0 wt .-% Sylobloc ^® 44 H (synthetic SiO ₂ from. Grace) and 1, 25 parts by weight % ^® Aerosil TT 600 (chain-like SiO ₂ from Degussa)

The film had the required good sealing properties, the desired degree of whiteness and shows the desired handling and processing behavior. The film structure and the properties achieved in films produced in this way are shown in Tables 2 and 3.

The film in this and in all the following examples was weathered for 1000 hours with the Atlas Ci 65 Weather Ometer from Atlas in accordance with the test specification ISO 4892 and then tested for discoloration, surface defects and gloss. The film complies with building material classes B2 and B1 according to DIN 4102, part 2 and part 1. The film passes UL test 94.

Example 2

In comparison to Example 1, the cover layer thickness of the sealable layer A was increased from 4 to 6.0 μm. The sealing properties have improved as a result, in particular the seal seam strength has become significantly greater.

Example 3

In comparison to Example 1, a 500 μm thick film was now produced. The cover layer thickness of the sealable layer A was 6.0 μm and that of the non-sealable layer C was 3.0 μm.

Example 4

Compared to Example 3, the copolymer for the sealable outer layer A was changed. Instead of the amorphous copolyester with 78 mol% polyethylene terephthalate and 22 mol% ethylene terephthalate, an amorphous copolyester with 70 mol% Polyethylene terephthalate and 30 mol% ethylene terephthalate are used. The raw material was processed on a twin-screw extruder with degassing without it having to be pre-dried. The cover layer thickness of the sealable layer A was again 6.0 μm and that of the non-sealable layer C was 3.0 μm.

Comparative Example 1

Example 1 is repeated. However, the sealable top layer is not pigmented. The

The film contains no UV absorber, no flame retardant and no white pigment.

After 1000 hours of weathering, the film shows severe cracking, embrittlement and a visible yellowing. The film allows UV radiation from 280 nm.

The film does not meet the fire tests according to DIN 4102 TeiH and part 2 and the UL test 94.

The handling behavior and the processing behavior have become unacceptably worse.

Table 2

Table 3

C i

Explanation of symbols for winding behavior, handling and processing behavior of the films: ++: no tendency to stick to rollers or other mechanical parts, no block problems during winding and processing on packaging machines, low manufacturing costs +: average manufacturing costs

-: tendency to stick to rollers or other mechanical parts, block problems during winding and during

Processing on packaging machines, high manufacturing costs due to complex handling of the film in the machines

Fire behavior

The films from Examples 1 to 4 meet building material classes B1 and B2 according to DIN 4102 Part 1 and Part 2. The foils can therefore be classified in the building material class of flame-retardant materials. The films meet UL test 94.

brittleness

The films from Examples 1 to 4 show no embrittlement after 200 hours of tempering at 100 ° C. in an air drying cabinet. The foils do not break when folded, i.e. the mechanical properties are essentially retained after the tempering.

weathering

After 1000 hours of weathering with the Atlas CI 65 Weather Ometer, the films from Examples 1 to 4 show no crack formation on the surface and no signs of embrittlement. The optical properties of gloss and haze are almost unchanged. The yellowness index is less than 4.

UV-absorption

The films from Examples 1 to 4 absorb 100% of the aggressive short-wave UV light in the wavelength range less than 380 nm.

thermoformability

The films from Examples 1 to 4 can be thermoformed on complex thermoforming machines from Illig / Heilbronn, without predrying, to form complex moldings. The detail reproduction of the molded bodies is excellent with a homogeneous surface.

Claims

claims

1. Amorphous, white, UV-absorbing, flame-retardant, sealable, coextruded polyester film whose thickness is in the range from 30 to 2000 μm, consisting of at least one base layer B and cover layers A and C applied to both sides of this base layer and additionally containing at least one UV Stabilizer as a light stabilizer and a flame retardant, the sealable cover layer A having a seal starting temperature of 110 ° C. and a seal seam strength of at least 1.3 N / 15 mm, characterized in that the sealable cover layer A has a surface roughness, expressed as R _a - Value, of <30 nm and a measured value of

Gas flow in the range of 500 to 4000 s and that the non-sealable cover layer C has a coefficient of friction of this layer against itself, expressed as a COF value of <0.5, a surface roughness, expressed as R _a value, in the range of 40 nm up to 100 nm, a measurement of the gas flow of <120 s and a number of elevations N per mm ²

Has film surface, which are correlated with the respective height h using the following equations:

A _C ι - B _C1 ^• log h / μm <N _c / mm ² <A _C2 - B _C2 ^• log h / μm with 0.01 μm <h <10 μm; A _c1 = 0.29; B _G1 = 3.30; A _C2 = 1.84; and B _C2 = 2.70.

2. Film according to claim 1, characterized in that the concentration of UV stabilizer within a layer in the range between 0.01 and 5 wt .-%, based on the weight of the polyester used for the respective layer.

3. Film according to claim 1, characterized in that the concentration of flame retardant within a layer between 0.5 and 30 wt .-%, preferably between 1 and 20 wt .-%, based on the weight of the polyester used for the respective layer , lies.

4. Film according to one of claims 1 to 3, characterized in that the base layer B of the film at least 70 wt .-% of a thermoplastic polyester made of ethylene glycol and terephthalic acid (= polyethylene terephthalate, PET), or of ethylene glycol and 2,6-naphthalene -dicarboxylic acid (= polyethylene-2,6-naphthalate, PEN), or from 1,4-bis-hydroximethyl-cyclohexane and

Contains terephthalic acid (= poly-1,4-cyclohexanedimethylene terephthalate, PCDT) or from ethylene glycol, naphthalene-2,6-dicarboxylic acid and biphenyl 4,4'-dicarboxylic acid (= polyethylene-2,6-naphthalate bibenzoate, PENBB), preferably at least 90 % By weight, preferably at least 95% by weight, and that the remaining monomer units are selected from other suitable aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids.

5. Film according to claim 4, characterized in that suitable other aliphatic diols diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO- (CH ₂ ) _n -OH, where n represents an integer from 3 to 6, in particular propane-1, 3-diol, butane-1, 4-diol, pentane-1, 5-diol and hexane-1, 6-diol, or branched aliphatic glycols with up to 6 carbon atoms are suitable cycloaliphatic diols are cyclohexanediols, especially cyclohexane -1,4-diol, that other suitable aromatic diols are diols corresponding to the formula HO-C ₆ H ₄ -XC ₆ H ₄ -OH, where X represents -CH ₂ -, -

C (CH ₃ ) ₂ -, -C (CF ₃ ) ₂ - -O-, -S- or -SO ₂ -, or bisphenols of the formula HO-C ₆ H ₄ -C ₆ H ₄ -OH and that suitable aromatic dicarboxylic acids benzene-dicarboxylic acids, naphthalene-dicarboxylic acids, preferably naphthalene-1,4- or 1,6-dicarboxylic acids, biphenyl-x, x '-dicarboxylic acids, in particular biphenyl-4,4'- are dicarboxylic acid, diphenylacetylene-x, x'-dicarboxylic acids, in particular diphenylacetylene-4,4'-dicarboxylic acid or stilbene-x, x'-dicarboxylic acids.

6. Film according to claim 4 or 5, characterized in that the diethylene glycol content of the thermoplastic polyester is greater than 1.0 and less than 5.0

% By weight, preferably greater than 1, 2 and less than 4.5% by weight and in particular greater than 1, 3 and less than 4.0% by weight.

7. Film according to claim 4 or 5, characterized in that the isophthalic acid content is in the range between 3% by weight and 10% by weight.

8. Film according to one of claims 1 to 7, characterized in that the sealable cover layer A consists essentially of copolyesters which are predominantly composed of isophthalic and terephthalic acid units and of ethylene glycol units, the remaining monomer units being composed of other aliphatic, Cycloaliphatic or aromatic diols or dicarboxylic acids, as they can also occur in the base layer, are selected, the proportion of ethylene terephthalate being 40 to 95 mol% and the corresponding proportion of ethylene isophthalate being 60 to 5 mol%.

9. Film according to one of claims 1 to 8, characterized in that the non-sealable cover layer C and any intermediate layers present contain the same polymers as the base layer B.

10. Film according to one of claims 1 to 9, characterized in that the base layer B white pigment in an amount of at least 12 wt .-%, based on the weight of the polyester for the base layer, preferably barium sulfate in an amount of at least 14 wt. -%, and that the average grain size of the white pigment is in the range of 0.3 to 0.8 μm.

11. A method for producing a film according to any one of claims 1 to 10 by coextrusion, wherein the polymers or the polymer mixtures for the individual layers are compressed and liquefied in their own extruders, and the additives which may have been added already contain in the polymer or in the polymer mixture can be characterized in that the

Melt is simultaneously pressed through a flat die, and the pressed multilayer film is drawn off on one or more take-off rolls, where it cools and solidifies, and that the solidified film is then optionally corona or flame treated on the surface layer intended for treatment.

12. The method according to claim 11, characterized in that the film after the solidification on one surface or on both surfaces is coated with an adhesion-promoting, antistatic, slip-improving or dehesively acting layer which is applied to the film by means of “inline coating” by means of aqueous dispersions is applied.

13. Use of a film according to one of claims 1 to 10 for interior paneling, for trade fair construction and trade fair articles, as displays, for signs, for protective glazing of machines and vehicles, in the lighting sector, in shop and shelf construction, as a promotional article, as a lamination medium , for thermoforming on all types of twists.

14. Use of a film according to one of claims 1 to 10 for outdoor applications, such as for greenhouses, roofing, external cladding,

Covers of materials, such as sheet steel, for applications in the construction sector and illuminated advertising profiles, shadow mats or electrical applications.