DE19913982A1 - Transparent biaxially-oriented thin crystallisable thermoplastic films containing UV stabilizer and optical brightener to impart sufficient UV stability to allow outdoor uses - Google Patents

Abstract

A transparent biaxially-oriented 1-500 mu m film based mainly on a crystallisable thermoplast also contains a UV stabilizer and an optical brightener. An Independent claim is also included for production of the film by melt extrusion of the composition onto a cooled roll, followed by biaxial stretching and winding up.

Description

The invention relates to a, transparent, UV-stabilized film from a crystallizable thermoplastic, whose thickness is in the range of 1 to 500 microns. The foil contains at least one UV stabilizer as a light stabilizer and is characterized by good stretchability due to very good optical and mechanical properties out. The invention further relates to a method for producing this film and its Use.

Transparent films made of crystallizable thermoplastics with a thickness between 1 and 500 µm are well known.

These films contain no UV stabilizers as light stabilizers, so that neither the foils nor the articles made from them are suitable for outdoor use. In outdoor applications, these films show yellowing after a short time and deterioration in mechanical properties due to photooxidative degradation by sunlight.

In EP-A-0 620 245 foils are described with regard to their thermal Stability are improved. These films contain antioxidants which are suitable are to trap radicals formed in the film and to break down the peroxide formed. This document suggests how the UV stability of such films should be improved however not to be inferred.

The object of the present invention was to provide a transparent film with a thickness of To provide 1 to 500 microns, which in addition to good stretchability, good mechanical and optical properties, especially high UV stability having.  

High UV stability means that the films are exposed to sunlight or other UV Radiation are not damaged or only extremely little, so that the foils are suitable for Outdoor applications and / or critical indoor applications are suitable. In particular the films should not yellow when used for several years, no embrittlement or surface cracking and no deterioration of the surface have mechanical properties. High UV stability means that the film absorbs UV light and only lets light through in the visible range.

Good optical properties include, for example, high light transmission (≧ 84%), a high surface gloss (<120), an extremely low haze (<20%) and a low yellow number (YID <10).

The good mechanical properties include a high modulus of elasticity (E _MD <3800 N / mm ² ; E _TD <5000 N / mm ² ) and good tensile strength values (in MD <130 N / mm ² ; in TD <180 N) / mm ² ) and good elongation at break values in the longitudinal and transverse directions (in MD <120%; in TD <70%).

Good stretchability means that the film can be produced both in Can be oriented longitudinally as well as transversely and without tears.

In addition, the film according to the invention should be recyclable, in particular without Loss of optical and mechanical properties, as well as flame-retardant, so that they can also be used for indoor applications and trade fair construction, for example can be.

This task is solved by a transparent film with a thickness in the range of 1 to 500 µm, which contains a crystallizable thermoplastic as the main component, which is characterized in that the film as at least one UV stabilizer Contains light stabilizers, the UV stabilizer expediently as Masterbatch is metered directly in the film production.  

The main component of the transparent film is a crystallizable one Thermoplastics. Suitable crystallizable or partially crystalline thermoplastics are for example polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, with polyethylene terephthalate being preferred.

According to the invention, crystallizable thermoplastics are understood

• Crystallizable homopolymers,
• - crystallizable copolymers,
• - crystallizable compounds,
• - Crystallizable recyclate and
• - other variations of crystallizable thermoplastics.

The transparent film can be either single-layer or multi-layer. The transparent film can also be used with various copolyesters or adhesion promoters be coated.

The transparent film contains at least one UV stabilizer as a light stabilizer, which is expediently provided by the so-called masterbatch technology Film production is metered in, the concentration of the UV stabilizer preferably between 0.01 wt .-% and 5 wt .-%, based on the weight of the Layer of the crystallizable thermoplastic, lies.

Light, especially the ultraviolet portion of solar radiation, i.e. H. the Wavelength range from 280 to 400 nm, initiates degradation processes with thermoplastics, as a result not only the visual appearance due to color change or yellowing changes, but also the mechanical-physical properties be adversely affected.  

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, start below 360 nm UV To absorb light, 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 there are mainly chain cleavages, but none Networking observed. Carbon monoxide, carbon dioxide and carboxylic acids are the quantitatively predominant photo-oxidation products. In addition to the direct Photolysis of the ester groups still need to consider oxidation reactions that also lead to the formation of carbon dioxide via peroxide radicals to have.

The photooxidation of polyethylene terephthalates can also be done via hydrogen cleavage in the α-position of the ester groups to hydroperoxides and their Decomposition products and the associated chain cleavages (H. Day, D. M. Wiles: J. Appl. Polym. Sci 16, 1972, page 203).

UV stabilizers, d. H. UV absorbers as light stabilizers are chemical Compounds involved in the physical and chemical processes of light-induced Degradation can intervene. Soot and other pigments can partially Effect sun protection. However, these substances are for transparent films unsuitable as they lead to discoloration or color change. For transparent films only organic and organometallic compounds that are suitable for this stabilizing thermoplastics no or only an extremely low color or Give color change.  

Suitable UV stabilizers as light stabilizers are UV stabilizers which 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 absorb. These are particularly suitable if they are in the temperature range of 260 to 300 ° C are thermally stable, d. H. do not decompose and not outgas to lead. Suitable UV stabilizers as light stabilizers are, for example, 2- Hydroxybenzophenones, 2-hydroxybenzotriazoles, nickel-organic compounds, Salicylic acid esters, cinnamic acid ester derivatives, resorcinol monobenzoates, oxalic acid anilides, Hydroxybenzoic acid esters, sterically hindered amines and triazines, the 2- Hydroxybenzotriazoles and the triazines are preferred.

It was completely surprising that the use of the above UV stabilizers in Slides led to the desired result. The specialist would probably have initially tried to achieve a certain UV stability via an antioxidant, but would have after weathering found that the film quickly turns yellow.

In view of the fact that UV stabilizers which absorb the UV light and thus offer protection, the person skilled in the art would have used commercially available UV stabilizers. He would have noticed that

• - The UV stabilizer has a lack of thermal stability and at Temperatures between 200 ° C and 240 ° C decomposed or outgassed
• - He has to incorporate large amounts (approx. 10 to 15% by weight) of UV stabilizer so that the UV light is absorbed and therefore the film is not damaged.

At these high concentrations, he would have found that the film was yellow as soon as it was produced, and the yellowness index difference (YID) would be around 25. Furthermore, he would have found that the mechanical properties are negatively affected. He would have had unusual problems with stretching like

• - Demolition due to lack of strength, d. H. E-module
• - Nozzle deposits, which leads to profile fluctuations  
• - Roller deposits from the UV stabilizer, which affects the optical properties (poor cloudiness, adhesive defect, inhomogeneous Surface).
• - Deposits in stretching and fixing frames that drip onto the film.

It was therefore more than surprising that excellent UV protection was achieved even at low concentrations of the UV stabilizer according to the invention. It was very surprising that this excellent UV protection

• - The yellowness index of the film compared to a non-stabilized film in the frame the measurement accuracy does not change;
• - no outgassing, no nozzle deposits, no frame evaporation set, which gives the film an excellent appearance and a has an excellent profile and flatness;
• - The UV-stabilized film has excellent stretchability distinguished so that they are reliable and stable on high speed film lines up to can be produced reliably at speeds of 420 m / min. This means that the film is also economically viable.

Furthermore, it is very surprising that the regrind can also be used again, without negatively affecting the yellowness index of the film.

In a particularly preferred embodiment, the transparent film according to the invention contains, as the main constituent, a crystallizable polyethylene terephthalate and 0.01% by weight to 5.0% by weight of 2- (4,6-diphenyl-1,3,5-triazine-2 -yl) -5- (hexyl) oxy-phenol (structure in Fig. 1a) or 0.01% to 5.0% by weight of 2,2'-methylenebis (6- (2H-benzotriazol-2 -yl) -4- (1,1,3,3-tetramethylbutyl) phenol (structure in Fig. 1b) In a preferred embodiment, mixtures of these two UV stabilizers or mixtures of at least one of these two UV stabilizers can also be used other UV stabilizers are 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 surface gloss, measured according to DIN 67530 (measuring angle 20 °), is greater than 120, preferably greater than 140, the light transmission L *, measured in accordance with ASTM D 1003, is more than 84%, preferably more than 86% and the haze of the film, measured according to ASTM D 1003, is less than 20%, preferably less than 15%, which is surprisingly good for the UV stability achieved.

The standard viscosity SV (DCE) of the polyethylene terephthalate, measured in Dichloroacetic acid according to DIN 53728, is between 600 and 1000, preferably between 700 and 900.

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

IV (DCE) = 6.67.10 ^-4 SV (DCE) + 0.118

The transparent polyethylene terephthalate film, which has at least one UV stabilizer contains, can be both single-layer and multi-layer.

In the multilayer embodiment, the film is composed of at least one core layer and built up at least one top layer, in particular a three-layer A-B-A or A-B-C structure is preferred.

For this embodiment it is essential that the polyethylene terephthalate Core layer has a similar standard viscosity as the polyethylene terephthalate the top layer (s) that are adjacent to the core layer.  

In a special embodiment, the cover layers can also consist of one Polyethylene naphthalate - homopolymers or from a polyethylene terephthalate - Polyethylene naphthalate copolymers or compound exist.

In this embodiment, the thermoplastics also have the cover layers Standard viscosity similar to the polyethylene terephthalate of the core layer.

In the multilayer embodiment, the UV stabilizer is preferably in the or the top layers. However, the core layer can also be used as required UV stabilizers.

In contrast to the single-layer embodiment, the concentration relates here of the stabilizer or stabilizers on the weight of the thermoplastics in the with UV Stabilizer (s) equipped layer.

Surprisingly, weathering tests according to the test specification ISO 4892 have with the Atlas CI65 Weather Ometer demonstrated that in the case of a three-layer Foil is sufficient, the 0.5 µm to 2 µm thick cover layers with UV Equip stabilizers to achieve improved UV stability.

As a result, the UV produced with the known coextrusion technology stabilized, multilayer films compared to the completely UV stabilized Monofilms economically interesting, since significantly less UV stabilizer at one comparable UV stability are required.

The film can also be coated on at least one side with a scratch-resistant coating Copolyester or be provided with an adhesion promoter.

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

During the production of the film it was found that the UV-stabilized film excellent orientation in the longitudinal and transverse directions without tears. Furthermore no outgassing of the UV stabilizer was found in the production process, which is essential to the invention, since most UV stabilizers Extrusion temperatures above 260 ° C show annoying, unpleasant outgassing and are unsuitable.

In addition, measurements showed that the film according to the invention was difficult to combust and is flame retardant, so that it can be used, for example, for indoor applications suitable for stand construction. Surprisingly, films according to the invention already fulfill Building material class B2 in the thickness range from 350 to 500 µm. 350 to 500 µm thick Surprisingly, films also meet the S4 fire class according to DIN 5510, Smoke development SR2, dripability ST1.

Furthermore, the film according to the invention is without environmental pollution and without loss the mechanical properties can be easily recycled, which makes them unique for example for use as short-lived advertising signs or others Promotional items are suitable.

The transparent, UV-stabilized film according to the invention can be produced for example by an extrusion process in an extrusion line.

According to the invention, the light stabilizer can already be used in the thermoplastic Raw material manufacturers are metered in or in the film production in the extruder be dosed.  

The addition of the light stabilizer via is particularly preferred Master batch technology. The light stabilizer is full in a solid carrier material dispersed. The carrier materials are the thermoplastic itself, such as. B. that Polyethylene terephthalate or other polymers with the thermoplastic are sufficiently tolerated.

It is important with the masterbatch technology that the grain size and the bulk weight of the masterbatch similar to the grain size and bulk density of the thermoplastic is so that a homogeneous distribution and thus a homogeneous UV stabilization can be done.

The polyester films can be made from a polyester raw material by known methods optionally other raw materials and the UV stabilizer and / or other conventional additives in the usual amount of 0.1 to a maximum of 10% by weight both as monofilms and as multilayer, possibly coextruded films with the same or different trained surfaces are produced, one surface for example is pigmented and the other surface contains no pigment. Likewise, one or both surfaces of the film according to known methods with a conventional one functional coating.

In the preferred extrusion process for producing the polyester film, the melted polyester material is extruded through a slot die and quenched as a largely amorphous pre-film on a cooling roll. This film is then heated again and stretched in the longitudinal and transverse directions or in the transverse and in the longitudinal direction or in the longitudinal, in the transverse and again in the longitudinal direction and / or transverse direction. The stretching temperatures are generally T _g + 10 ° C to T _g + 60 ° C (T _g = glass temperature), the stretching ratio of the longitudinal stretching is usually 2 to 6, in particular 3 to 4, 5, that of the transverse stretching is 2 to 5, in particular in the case of 3 to 4, 5, and that of the second longitudinal stretching which may be carried out at 1.1 to 3. The first longitudinal stretching can, if appropriate, be carried out simultaneously with the transverse stretching (simultaneous stretching). This is followed by heat setting of the film at oven temperatures of 200 to 260 ° C, especially at 220 to 250 ° C. The film is then cooled and wound up.

Due to the surprising combination of excellent properties, the transparent film of the invention excellent for a variety of different Applications, for example for interior cladding, 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 promotional items, Lamination medium.

Because of the good UV stability, the transparent film according to the invention is suitable also for outdoor applications, such as B. for greenhouses, canopies, Exterior cladding, covers, applications in the construction sector and Illuminated advertising profiles.

The invention is explained in more detail below on the basis of exemplary embodiments.

The individual properties are measured in accordance with the following standards or procedure.

Measurement methods Surface gloss

The surface gloss is measured at a measuring angle of 20 ° according to DIN 67530.

Light transmission

Below the light transmission is the ratio of the total transmitted light to understand the amount of incident light.  

The light transmission is carried out using the "Hazegard plus" measuring device in accordance with ASTM D 1003 measured.

Cloudiness

Haze is the percentage of light that passes through the radiated light beam deviates by more than 2.5 ° on average. The sharpness will determined at an angle less than 2.5 °.

The haze is measured using the "Hazegard plus" measuring device in accordance with ASTM D 1003.

Surface defects

The surface defects are determined visually.

Mechanical properties

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

SV (DCE), IV (DCE)

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

The intrinsic viscosity (IV) is calculated as follows from the standard viscosity (SV) IV (DCE) = 6.67.10 ^-4 SV (DCE) + 0.118

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, ie artificial weathering
Irradiation time: 1000 hours (per side)
Irradiation: 0.5 W / m ² , 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, then again 102 minutes of UV light, etc.

Color change

The color change of the samples after artificial weathering is carried out with a Spectrophotometer measured according to DIN 5033.

The following applies:
ΔL: difference in brightness
+ ΔL: The sample is lighter than the standard
-ΔL: The sample is darker than the standard
ΔA: difference in the red-green area
+ ΔA: The sample is redder than the standard
-ΔA: The sample is greener than the standard
ΔB: difference in the blue-yellow range
+ ΔB: The sample is more yellow than the standard
-ΔB: The sample is bluer than the standard
ΔE: total color change
ΔE = ΔL ² + ΔA ² + ΔB ²

The greater the numerical deviation from the standard, the greater the Color difference.  

Numerical values of ≦ 0.3 are negligible and mean that none significant color change is present.

Yellowness index

The yellowness index G is the deviation from the colorlessness in the "yellow" direction and will measured according to DIN 6167. Yellow value G values of-5 are not visually visible.

The following examples and comparative examples are each single-layer, transparent films of different thickness, which are described on the Extrusion line to be manufactured.

All foils were processed on both sides per 1000 hours per the test specification ISO 4892 Weathered side with the Atlas Ci 65 Weather Ometer from Atlas and then in terms of mechanical properties, discoloration, surface defects, of turbidity and gloss checked.

example 1

A 50 µm thick, transparent film is produced, which is the main component Polyethylene terephthalate 0.3% by weight of Sylobloc and 1.0% by weight of UV stabilizer 2- (4,6-Diphenyl-1,3,5-triazin-2-yl) -5- (hexyl) oxyphenol (®Tinuvin 1577 from Ciba Geigy) contains.

Tinuvin 1577 has a melting point of 149 ° C and is thermally stable up to approx. 330 ° C.

For the purpose of homogeneous distribution, 0.3% by weight of Sylobloc and 1.0% by weight of the UV Stabilizer incorporated into the polyethylene terephthalate.

The polyethylene terephthalate from which the transparent film is made has one Standard viscosity SV (DCE) of 810, indicating an intrinsic viscosity IV (DCE) of Corresponds to 0.658 dl / g.  

The transparent PET film produced has the following property profile:

• - Thickness: 50 µm
• - Surface gloss 1st page: 155
  (Measuring angle 20 °) 2nd side: 152
• - Light transmission: 91%
• - turbidity: 4.0%
• - Surface defects per m ² : none
• - E-module lengthways: 4300 N / mm ²
• - E-module across: 5800 N / mm ²
• Longitudinal tensile strength: 190 N / mm ²
• - Tear strength across: 280 N / mm ²
• - Elongation at break along: 170%
• - Elongation at break across: 85%
• - Yellow number (YID): 3.1

After 1000 hours of weathering per side with Atlas Ci 65 Weather Ometer, the PET film shows the following properties:

• - Thickness: 50 µm
• - Surface gloss 1st page: 145
  (Measuring angle 20 °) 2nd side: 141
• - Light transmission: 90.1%
• - turbidity: 4.5%
• - Total discoloration ΔE: 0.22
• - Dark discoloration ΔL: -0.18
• - Red-green discoloration ΔA: -0.08
• - Blue-yellow discoloration ΔB: 0.10
• - Surface defects: none
  (Cracks, embrittlement)
• - Yellow number (YID): 3.6
• - E-module lengthways: 4150 N / mm ²
• - E-module across: 5600 N / mm ²
• Longitudinal tensile strength: 170 N / mm ²
• - transverse tensile strength: 250 N / mm ²
• - Elongation at break: 150%
• - Elongation at break across. 70%

Example 2

A transparent film is produced analogously to Example 1, the UV stabilizer 2- (4,6-Diphenyl-1,3,5-triazin-2-yl) -5- (hexyl) -oxyphenol (®Tinuvin 1577) in the form of a Masterbatches is metered. The masterbatch consists of 5% by weight ®Tinuvin 1577 as active ingredient and 95% by weight of the polyethylene terephthalate from Example 1 together.

Before the extrusion, 90% by weight of the polyethylene terephthalate from Example 1 are added 10% by weight of the masterbatch dried at 170 ° C. for 5 hours. The extrusion and Foil production takes place analogously to example 1.

The transparent PET film produced has the following property profile:

• - Thickness: 50 µm
• - Surface gloss 1st side: 160
  (Measuring angle 20 °) 2nd side: 157
• - Light transmission: 91.3%
• - turbidity: 3.8%
• - Surface defects: none
  (Specks, orange peel, blisters, etc.)
• - E-module lengthways: 4200 N / mm ²
• - E-module across: 5650 N / mm ²
• Longitudinal tensile strength: 160 N / mm ²
• - transverse tensile strength: 250 N / mm ²
• - Elongation at break along: 160%
• - Elongation at break across: 75%
• - Yellow number (YID): 3.4

After 1000 hours of weathering per side with Atlas Ci 65 Weather Ometer, the PET film shows the following properties:

• - Thickness: 50 µm
• - Surface gloss 1st page: 148
  (Measuring angle 20 °) 2nd side: 146
• - Light transmission: 89.9%
• - turbidity: 4.1%
• - Total discoloration ΔE: 0.24
• - Dark discoloration ΔL: -0.19
• - Red-green discoloration ΔA: -0.08
• - Blue-yellow discoloration ΔB: 0.12
• - Surface defects: none
  (Cracks, embrittlement)
• - Yellow number (YID): 4.3
• - E-module lengthways: 4050 N / mm ²
• - E-module across: 5500 N / mm ²
• Longitudinal tensile strength: 151 N / mm ²
• - Tear strength across: 238 N / mm ²
• - Elongation at break: 152%
• - Elongation at break across: 68%

Example 3

Analogously to example 2, a transparent 350 μm thick film is produced.  

The PET film produced has the following property profile:

• - Thickness: 350 µm
• - Surface gloss 1st page: 149
  (Measuring angle 20 °) 2nd side: 144
• - Light transmission: 84.1%
• - turbidity: 13.1%
• - Surface defects per m ² : none
  (Specks, orange peel, blisters, etc.)
• - Yellow number: 4.5
• - E-module lengthways: 3600 N / mm ²
• - E-module across: 4200 N / mm ²
• Longitudinal tensile strength: 180 N / mm ²
• - transverse tensile strength: 200 N / mm ²
• - Elongation at break: 220%
• - Elongation at break across: 190%

After 1000 hours of weathering per side with Atlas Ci 65 Weather Ometer, the PET film shows the following properties:

• - Thickness: 350 µm
• - Surface gloss 1st page: 136
  (Measuring angle 20 °) 2nd side: 131
• - Light transmission: 84.3%
• - Turbidity: 14.0%
• - Total discoloration ΔE: 0.47
• - Dark discoloration ΔL: -0.18
• - Red-green discoloration ΔA: -0.09
• - Blue-yellow discoloration ΔB: +0.42
• - Surface defects: none
  (Cracks, embrittlement)
• - Yellow number (YID): 5.4
• - E-module lengthways: 3500 N / mm ²
• - E-module transverse: 4050 N / mm ²
• Longitudinal tensile strength: 165 N / mm ²
• - Tear resistance across: 185 N / mm ²
• - Elongation at break: 200%
• - Elongation at break across: 170%

Example 4

According to the coextrusion technology, a 50 µm thick multilayer PET film is used the order of layers A-B-A, where B is the core layer and A the Represent top layers. The core layer B is 48 µm thick and the two Cover layers that cover the core layer are each 1 µm thick.

The polyethylene terephthalate used for the core layer B is identical to that from example 2, but contains no sylobloc. The polyethylene terephthalate Cover layers A is identical to the polyethylene terephthalate from Example 2, i. H. the Top layer raw material is equipped with 0.3% by weight of Sylobloc.

Analogously to Example 2, the 5% by weight ®Tinuvin 1577 masterbatch is used, where but only the 1 mm thick cover layers 20% by weight of the masterbatch over the Masterbatch technology can be added.

The transparent, multilayer PET film that is UV-stabilized in the outer layers has the following property profile:

• - Layer structure: A-B-A
• - Total thickness: 50 µm
• - Surface gloss 1st page: 164  
• - (measuring angle 20 °) 2nd side. 159
• - Light transmission: 94.2%
• - turbidity: 2.1%
• - Surface defects: none
  (Specks, orgone skin, blisters, etc.)
• - E-module lengthways: 4300 N / mm ²
• - E-module transverse: 5720 N / mm ²
• Longitudinal tensile strength: 180 N / mm ²
• - Tear resistance across: 265 N / mm ²
• - Elongation at break: 165%
• - Elongation at break across: 85%
• - Yellow number (YID): 2.9

After 1000 hours of weathering per side with Atlas CI 65 Weather Ometer, the multilayer film shows the following properties:

• - Layer structure: A-B-A
• - Total thickness: 50 µm
• - Surface gloss 1st page: 152
• - (measuring angle 20 °) 2nd side: 150
• - Light transmission: 92.3%
• - turbidity: 3.0%
• - Total discoloration ΔE: 0.25
• - Dark discoloration ΔL: -0.20
• - Red-green discoloration ΔA: -0.09
• - Blue-yellow discoloration AB: 0.13
• - Surface defects: none
  (Specks, orange peel, blisters, etc.)
• - E-module lengthways: 4175 N / mm ²
• - E-module across: 5650 N / mm ²
• Longitudinal tensile strength: 165 N / mm ²
• - transverse tensile strength: 250 N / mm ²
• - Elongation at break: 155%
• - Elongation at break across: 75%
• - Yellow number (YID): 3.0

The examples according to the invention show that the optical and mechanical Properties of the films meet the high requirements, whereby at the same time the UV stability is significantly increased.

Comparative Example 1

Analogously to Example 1, a 50 µm thick PET monofilm is produced. In contrast to Example 1 contains no UV stabilizer in the film.

The manufactured, unstabilized, transparent film has the following property profile:

• - Thickness: 50 µm
• - Surface gloss 1st side: 160
• - (measuring angle 20 °) 2nd side: 155
• - Light transmission: 91.8%
• - turbidity: 3.6%
• - Surface defects: none
  (Specks, orange peel, blisters, etc.)
• - E-module lengthways: 4350 N / mm ²
• - E-module across: 5800 N / mm ²
• Longitudinal tensile strength: 185 N / mm ²
• - transverse tensile strength: 270 N / mm ²
• - Elongation at break along: 160%
• - Elongation at break across: 80%
• - Yellow number (YID): 2.7

After 1000 hours of weathering per side with Atlas CI 65 Weather Ometer, the Foil on the surfaces cracks and embrittlement. A precise one Property profile - especially the mechanical properties - can therefore not can be measured more. The film also shows a visually visible yellow color.

Claims (27)

1. Transparent biaxially oriented film, with a thickness in the range of 1 to 500 microns, which contains a crystallizable thermoplastic as the main component, characterized in that it contains at least one UV stabilizer. 2. Film according to claim 1, characterized in that the concentration of UV stabilizer in the range of 0.01 to 5 wt .-%, based on the weight of the crystallizable thermoplastic. 3. Film according to claim 1 or 2, characterized in that the UV Stabilizer is selected from 2-hydroxybenzotriazoles and / or triazines. 4. Film according to claim 3, characterized in that the UV stabilizer 2- (4,6-Diphenyl-1,3,5-triazin-2-yl) -5- (hexyl) oxyphenol and / or 2,2'-methylene bis (6- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol. 5. Film according to one of claims 1 to 4, characterized in that the Surface gloss, measured according to DIN 67530 (measuring angle 20 °), greater than 120 is. 6. Film according to one of claims 1 to 5, characterized in that the Light transmission, measured according to ASTM D 1003, is more than 84%. 7. Film according to one of claims 1 to 6, characterized in that the Turbidity, measured according to ASTM D 1003, is less than 20.   8. Film according to one of claims 1 to 7, characterized in that the crystallizable thermoplastic has a crystallinity ranging from 5 to 65% lies. 9. Film according to one of claims 1 to 8, characterized in that the crystallizable thermoplastic is selected from polyethylene terephthalate, Polybutylene terephthalate and polyethylene naphthalate and mixtures of one or more of these thermoplastics. 10. Film according to claim 9, characterized in that as crystallizable Thermoplastic polyethylene terephthalate is used. 11. A film according to claim 10, characterized in that the Polyethylene terephthalate contains polyethylene terephthalate recyclate. 12. Film according to one of claims 1 to 4, characterized in that it has a single-layer structure. 13. Film according to one of claims 1 to 12, characterized in that the A multilayer structure with at least one top layer and has at least one core layer. 14. Film according to claim 13, characterized in that the multilayer Structure two cover layers and one between the cover layers Has core layer. 15. A film according to claim 13 or 14, characterized in that the at least a UV stabilizer is contained in the top layers. 16. Film according to one of claims 1 to 15, characterized in that the Film has an adhesion promoter on at least one surface.   17. Film according to one of claims 1 to 16, characterized in that the Film has a copolyester on at least one surface. 18. Film according to one of claims 1 to 17, characterized in that the Film has a scratch-resistant coating on at least one surface. 19. Film according to one of claims 10 or 11, characterized in that the polyethylene terephthalate had a crystallite melting point as measured by DSC with a heating rate of 10 ° C / min., in the range of 220 ° to 280 ° C. 20. Film according to one of claims 10 or 11, characterized in that the polyethylene terephthalate has a crystallization temperature as measured by DSC with a heating rate of 10 ° C / min., In the range from 75 ° to 280 ° C. 21. Film according to one of claims 10 or 11, characterized in that the polyethylene terephthalate used has a standard viscosity SV (DCE), measured in dichloroacetic acid according to DIN 53728, which in the range of 600 to 1000 lies. 22. Film according to one of claims 13 to 15, characterized in that the Cover layers contain polyethylene terephthalate. 23. Film according to one of claims 13 to 15, characterized in that the Cover layers contain polyethylene naphthalate. 24. Film according to one of claims 13 to 15, characterized in that the Copers or compounds made of polyethylene terephthalate and Contain polyethylene naphthalate.   25. A method for producing a transparent film according to one of the Claims 1 to 24, characterized in that a crystallizable Thermoplastic in an extruder together with at least one UV stabilizer melts, extruded onto a chill roll, biaxially oriented, fixed and rolled up. 26. The method according to claim 25, characterized in that the crystallizable Thermoplastic is dried in the extruder before melting. 27. The method according to any one of claims 25 and 26, characterized in that that the addition of the UV stabilizer via the masterbatch technology is carried out.