Hydrolysis-resistant, transparent, amorphous film made from a crystallizable thermoplastic and process for its production

The invention relates to a monolayer or multilayer, transparent, amorphous film containing as main component at least one crystallizable thermoplastic. It further relates to a process for producing the film and its use.

Transparent amorphous as well as partially crystalline films of crystallizable thermoplastics, in particular of crystallizable polyesters, are known and described in numerous ways. In addition, functionalized films of this type are known. The functionalization can be achieved by incorporating additives into the film. The additives increase, for example, their flame retardancy and / or their UV stability. It is also possible to coat the film or to modify its surface by chemical pretreatment, corona discharge or flame treatment, for example to make them sealable, printable, writable, antistatic, metallizable or sterilizable

In EP-A 620 245 biaxially oriented polyester films are disclosed which exhibit improved thermal stability. They contain antioxidants that scavenge radicals formed in the film or degrade formed peroxides. As radical scavengers, hindered phenols, secondary aromatic amines and sterically hindered amines are disclosed, as peroxide-degrading agents compounds of trivalent phosphorus, in particular phosphonites or phosphites. However, the UV stability of the films is generally insufficient.

In DE-A 198 23 991 amorphous (= non-crystalline), unstretched and non-oriented plates are described with a thickness of 0.1 to 20 mm, containing as the main component of a bibenzolmodifiziertes polyalkylene terephthalate and / or a bibenzolmodifiziertes polyalkylene naphthalate. The plates are characterized by particularly good properties in a wide temperature range. This means in particular that in the determination of the Charpy impact strength (determined according to ISO 179 / 1D) no break occurs and that the Izod impact strength (ISO 180) at -40 ° C preferably in the range of 10 to 120 kJ / m² lies. The plates are made by means of calendering calenders, the amorphous state being frozen by rapidly cooling the polymers to a temperature below the glass transition temperature.

EP-A-035 835 discloses a biaxially stretched and heat-set multilayer polyester film comprising a layer of highly crystalline polyester and, associated therewith, a sealable layer of a substantially amorphous linear polyester. The latter layer contains finely divided particles, wherein the mean diameter of the particles is greater than the layer thickness. The particles form surface protrusions which prevent unwanted blocking and sticking to rollers or guides. The film can be wound up and processed better. By choosing particles with a larger diameter than the sealing layer and the concentrations given in the examples, the sealing behavior of the film is deteriorated. The seal seam strength of the sealed film at 140 ° C is in the range of 63 to 120 N / m (0.97 N / 15 mm to 1.8 N / 15 mm film width).

EP-A 432 886 describes a coextruded film having a polyester base layer, a top layer of a sealable polyester and a backside polyacrylate coating. The sealable overcoat may consist of a copolyester having units of isophthalic acid and terephthalic acid. The back coating gives the film improved processing behavior. The seal seam strength is measured at 140 ° C. For a 11 μm thick sealing layer, a seal seam strength of 761.5 N / m (11.4 N / 15 mm) is specified. A disadvantage of the back acrylate coating is that this side no longer seals against the sealable top layer. The film is therefore very limited use.

A coextruded, multilayer, sealable polyester film is further described in EP-A 515 096. The sealable layer additionally contains pigmentation particles, preferably silica gel particles. The particles can also be applied to the already extruded film, for example by coating with an aqueous silica gel dispersion. As a result, the film should retain its good sealing properties and be easy to process. The backside contains very few particles, which mainly get into this layer via the regranulate. The seal seam strength is measured at 140 ° C and is more than 200 N / m (3 N / 15 mm). For a 3 μm thick sealing layer, a seal seam strength of 275 N / m (4.125 N / 15 mm) is specified.

The coextruded multilayer polyester film known from WO 98/06575 comprises a sealable top layer and a non-sealable base layer. The base layer may be composed of one or more layers, wherein the inner layer is in contact with the sealable layer. The other (outer) layer then forms the second, non-sealable cover layer. The sealable outer layer may also consist of copolyesters with units of isophthalic acid and terephthalic acid. However, the topcoat does not contain antiblock particles. The film also contains at least one UV absorber, which is contained in the base layer in a proportion of 0.1 to 10 wt .-%. Zinc oxide or titanium dioxide particles having an average diameter of less than 200 nm, but preferably triazines, for example ®Tinuvin 1577 of the Fa. Ciba, used. The base layer is equipped with conventional anti-blocking agents. The film is characterized by a good sealability, but does not have the desired processing behavior and also has deficits in the optical properties.

Layers of copolyester can also be produced by applying a corresponding aqueous dispersion. Thus, EP-A 144 978 describes a polyester film which carries on at least one side a continuous coating of the copolyester. The dispersion is applied to the film before stretching or applied before the last stretching step. The polyester coating consists of a condensation product of various monomers capable of forming polyesters, such as isophthalic acid, aliphatic dicarboxylic acids, sulfomonomers, and aliphatic or cycloaliphatic glycols.

DE-A 23 46 787 discloses, among other things, flame-retardant films of linear polyesters which have been modified with carboxyphosphinic acids. However, the production of these films involves a number of problems. So the raw material is very susceptible to hydrolysis and must be very well pre-dried. When drying the raw material with dryers, which correspond to the prior art, it sticks, so that only under the most difficult conditions, a film can be produced. The films produced under extreme, uneconomic conditions also become brittle when exposed to temperature. The mechanical properties go back so much that the film is useless. Already after 48 hours of temperature stress, this embrittlement occurs.

However, the films mentioned are generally not sufficiently resistant to the action of aqueous media, so that they or the articles produced therefrom are not suitable for applications in which they come into contact with moisture or water. In this case, the mechanical properties deteriorate so that the films can become completely unusable. Most of the known film are also stretched and thus semi-crystalline.

It is an object of the present invention to provide a transparent, amorphous film which has good mechanical and optical properties, exhibits no embrittlement upon exposure to heat, is economical to produce and is resistant to hydrolysis. Resistant to hydrolysis is a film which has an impact strength of more than 100 mJ / mm in the climate test (moisture long-term test) after 1,000 hours at 60 ° C. and 95% relative atmospheric humidity² in the longitudinal and transverse directions (determined according to DIN 53448). The film should also be easily thermoformable. This means that the film can be deep-drawn or thermoformed on conventional thermoforming machines without uneconomical predrying to form complex and large-area moldings.

This problem was solved by incorporating at least one hydrolysis stabilizer. Losses in the optical and mechanical properties of the film surprisingly do not occur.

The present invention accordingly provides a mono- or multilayer, transparent, amorphous film which contains as main constituent at least one crystallizable thermoplastic and is characterized in that it contains at least one hydrolysis stabilizer.

As hydrolysis stabilizers are effective compounds that suppress or slow down the hydrolysis of ester bonds. These are, for example, phenolic stabilizers, in particular those having a molecular weight of more than 500. These include sterically hindered phenols, thiobisphenols, Alkylidenbisphenole, alkylphenols, hydroxybenzyl compounds, acylaminophenols and hydroxyphenylpropionates (in particular (3,5-di<i>-tert</i>.-butyl-4-hydroxy-phenyl) -propionic acid ester of pentaerythritol or 1-octadecanol, available under the name Irganox from Ciba Specialty Chemicals). These compounds are described for example in the monograph 3Plastic Additive "by Gächter and Müller, 2. Ed., Carl Hanser Verlag. The proportion of phenolic stabilizers is generally 0.1 to 5.0 wt .-%, preferably 0.2 to 3.0 wt .-%, each based on the weight of the film or the layer provided therewith (in the case of the multilayer film).

The said phenolic stabilizers are preferably combined with organic phosphites, in particular with triaryl phosphites (obtainable, for example, under the name ® Irgafos 168 from Ciba Specialty Chemicals). These are able to break down peroxides and thus act as secondary stabilizers. The weight ratio of phenolic stabilizers to organic phosphites is generally 10:90 to 90:10. Mixtures of primary and secondary hydrolysis stabilizers are also commercially available, for example under the names ® Irganox B 561 or ® Irganox B 225.

On the other hand, compounds which are able to restore bonds broken by hydrolysis are effective as hydrolysis stabilizers. In order to produce an ester bond from a hydroxy and a carboxy group, are monomeric or polymeric carbodiimides, especially dicyclohexylcarbodiimide or aromatic polymeric carbodiimides, whereof of the polymeric carbodiimides are those having a molecular weight of 2,000 to 50,000 and a melting range of 60 to 210 ° C. (obtainable, for example, under the names ® Stabaxol P from Rhein Chemie GmbH, Mannheim, or P17 from Raschig GmbH, Ludwigshafen) are particularly suitable besides also oxazolines. The proportion of these compounds is generally 0.1 to 5.0 wt .-%, preferably 0.2 to 3.0 wt .-%, each based on the weight of the single-layer film or the so-equipped layer of the multilayer film.

A preferred film according to the invention contains both compounds which reduce the rate of hydrolysis and compounds which can restore ester bonds. It is particularly resistant to moisture or water. In a preferred embodiment, the film accordingly contains 0.1 to 5 wt .-% of polymeric aromatic carbodiimides and 0.1 to 5 wt .-% of a blend of 30 to 90 wt .-% of an organic phosphite (in particular a triaryl phosphite) and 70 to 10 wt .-% of a hydroxyphenylpropionate.

The proportion of all hydrolysis stabilizers together is generally 0.2 to 16.0 wt .-%, preferably 0.5 to 14.0 wt .-%, each based on the weight of the film or the relevant layer of the multilayer film.

Unlike UV stabilizers, the hydrolysis stabilizers show virtually no or only a relatively low absorption at a wavelength of 380 to 400 nm.

By hydrolysis stabilizers, the film of the invention is very resistant to moisture. This means that they have a tensile strength of more than 100 N / mm in the climate test (humidity long-term test) after 1,000 hours at 85 ° C. and 95% relative humidity² in the longitudinal and transverse direction.

The good optical properties of the film include in particular a high light transmission L (determined according to ASTM D 1003) of more than 80%, preferably more than 82%, and a low yellowness YID (determined according to DIN 6167) of less than 15, preferably less than 12, which is surprisingly good given the high hydrolytic stability.

It can also be produced economically. Thus, the raw materials or the raw material components that are required for the production of the film can be dried with conventional industrial dryers, such as vacuum dryers, fluidized bed dryers, fluidized bed dryers or fixed bed dryers (shaft dryers) without the raw materials sticking together or being thermally degraded.

The film does not become brittle when exposed to temperature. This means that the mechanical properties of the film deteriorate only insignificantly even after 1,000 hours annealing at 60 ° C in a convection oven. Amorphous polyethylene terephthalate films without hydrolysis stabilizers, however, do not meet these requirements.

The film according to the invention contains as main component a crystallizable thermoplastic, in particular a crystallizable polyester or copolyester. Suitable crystallizable or semicrystalline (co) polyesters are, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), bibenzo-modified polyethylene terephthalate (PETBB), bibenzo-modified polybutylene terephthalate (PBTBB) and bibenzo-modified polyethylene naphthalate (PENBB), and mixtures thereof, wherein polyethylene terephthalate (PET) and bibenzo-modified polyethylene terephthalate (PETBB) are preferred.

For the purposes of the present invention, "crystallizable thermoplastics" are understood to mean crystallizable homopolymers, crystallizable copolymers, crystallizable compounds, crystallizable recyclates or other variants of crystallizable thermoplastics.

For the preparation of crystallizable, thermoplastic (co) polyesters, in addition to the main monomers, such as dimethyl terephthalate (DMT), ethylene glycol (EG), propylene glycol (PG), butane-1,4-diol, terephthalic acid (TA), benzenedicarboxylic acid and / or naphthalene 2,6-dicarboxylic acid (NDA), also isophthalic acid (IPA) and / or <i>cis</i> and or <i>trans</i>-1,4-cyclohexane-dimethanol (<i>c</i>-CHDM, <i>t</i>-CHDM or c / t-CHDM).

The standard viscosity SV (DCE) of the polyethylene terephthalate is generally between 800 and 1,400, preferably between 900 and 1,300.

Preferred starting materials for the production of the film according to the invention are crystallizable thermoplastics having a crystalline melting temperature Tm of from 180 to 365 ° C. and more, preferably from 180 to 310 ° C, a crystallization temperature range Tc between 75 and 280 ° C, a glass transition temperature Tg of 65 to 130 ° C (determined by differential scanning calorimetry (DSC) at a heating rate of 20 ° C / min), with a density of 1.10 to 1.45 (determined according to DIN 53479) and a crystallinity of 5 to 65%, preferably from 20 to 65%.

In the context of the present invention, amorphous films are to be understood as meaning those which are not crystalline, although a crystallizable thermoplastic having a crystallinity of from 5 to 65%, preferably from 20 to 65%, is used. Non-crystalline (= amorphous) means that the degree of crystallinity is less than 3%, preferably less than 1%. Such a film is generally not oriented.

Films with a particularly good thermoformability contain crystallizable thermoplastics which have a proportion of diethylene glycol units of from 1.0 to 12% by weight, preferably from 1.2 to 11% by weight, particularly preferably from 1.3 to 10% by weight. , and / or a proportion of polyethylene glycol units of 1.0 to 12 wt .-%, preferably 1.2 to 11 wt .-%, particularly preferably 1.3 wt .-% to 10 wt .-%, and / / or have a content of isophthalic acid units of 3.0 to 10 wt .-%.

The bulk density (determined according to DIN 53466) is between 0.75 and 1.0 kg / dm³, preferably between 0.80 and 0.90 kg / dm³,

The polydispersity (= Mw to Mn ratio) of the thermoplastic, as measured by gel permeation chromatography (GPC), is preferably between 1.5 and 4.0, more preferably between 2.0 and 3.5.

"Main constituent" means that the proportion of the at least one semicrystalline (crystallisable) thermoplastic is preferably between 50 and 99 wt .-%, particularly preferably between 75 and 95 wt .-%, in each case based on the total weight of the film or the total weight the layer in the foil. In addition to the hydrolysis stabilizer, the remaining fractions may comprise further additives customary for biaxially oriented, transparent films.

The amorphous film according to the invention generally has a thickness of from 30 to 1000 .mu.m, preferably from 50 to 500 .mu.m, particularly preferably from 75 to 300 .mu.m. It can be both single-layered and multi-layered. In the multilayered embodiment, the film is made up of at least one core layer, at least one cover layer and optionally at least one intermediate layer, wherein in particular a three-layered ABA or ABC structure is preferred. For this embodiment, it is essential that the polyethylene terephthalate of the core layer has a similar standard viscosity as the polyethylene terephthalate of the cover layer (s) adjacent to the core layer.

In a particular embodiment, the outer layers and / or the intermediate layers of the multilayer film can also consist of a polyethylene naphthalate homopolymer or of polyethylene terephthalate / polyethylene naphthalate copolymers or a compound. In this embodiment, the thermoplastics of the overcoats also have similar standard viscosities to the polyethylene terephthalate of the core layer.

In the multi-layered embodiment, the hydrolysis stabilizer (s) are preferably contained in the base layer. However, if desired, the top layers and / or any intermediate layers present may also be provided with hydrolysis stabilizers at the concentration specified for the monofilm. Here, unlike the single-layer embodiment, the concentration of stabilizers refers to the weight of the finished layer.

With the film of the invention can be combined with another, single or multilayer film to form a composite film. The further film is, for example, a standard PET film or a polyolefin film, in particular a polyethylene or polypropylene film. It is also possible to combine two films according to the invention. Optionally, the film according to the invention is previously coated, for example with an ethylene / vinyl alcohol copolymer (EVOH), a polyvinyl alcohol or a polyvinylidene dichloride. The further film may, like the film according to the invention, be amorphous, ie be unoriented. It can also have a sealing layer. Their thickness is generally 30 to 500 microns. Optionally, an adhesive layer can be arranged between the individual films. It can be produced by applying an appropriate solution or dispersion which may contain water or an organic solvent. To an adhesive layer with a coating weight of 1 to 10 g / m² To prepare, the proportion of the adhesion promoter is suitably 5 to 40 wt .-%, based on the total weight of the coating solution. Particularly suitable adhesion promoters are adhesives consisting of thermoplastic resins, such as cellulose esters and ethers, alkyl and acrylic esters, polyamides, polyurethanes, polyesters, thermosetting resins (in particular epoxy resins, urea / formaldehyde resins, phenyl / formaldehyde resins or melamine / Formaldehyde resins) or synthetic rubbers. Suitable organic solvents for the coating solutions or dispersions are hydrocarbons (such as ligroin and toluene), esters (such as ethyl acetate) or ketones (such as acetone or butanone).

The composite film can be produced by lamination or laminating. The films are usually passed through rollers, which are heated to 30 to 90 ° C. The further film can also be produced directly on the first film by in-line coating (melt extrusion onto an existing film).

The film according to the invention may additionally contain one or more optical brighteners. The proportion of brightener (s) is generally 10 to 50,000 ppm, preferably 20 to 30,000 ppm, more preferably 50 to 25,000 ppm, each based on the weight of the crystallizable thermoplastic. The optical brightener is preferably added in the form of a masterbatch directly during film production. It is capable of absorbing UV radiation in the wavelength range of 360 to 380 nm and emitting it as longer-wavelength, visible, blue-violet light. Particularly suitable as brighteners are benzoxazole derivatives, triazines, phenylcoumarins and bis-styrylphenols, obtainable, for example, under the names ®Tinopal (Ciba Specialty Chemicals, Basel, Switzerland), ®Hostalux KS (Clariant GmbH, Germany) or ®Eastobrite OB-1 ( Eastman, USA).

Optionally, in addition to the optical brightener also soluble in the thermoplastic blue dyes may be added. For example, ultramarine blue and anthraquinone dyes, in particular Sudan blue 2 (BASF AG, Ludwigshafen, Germany), are suitable for this purpose. The proportion of blue dye is generally 10 to 10,000 ppm, preferably 20 to 5,000 ppm, particularly preferably 50 to 1,000 ppm, in each case based on the weight of the crystallizable thermoplastic.

Furthermore, the film according to the invention is recyclable without polluting the environment, wherein the film produced from the recyclate shows virtually no deterioration in the optical properties (in particular the yellowness value) or the mechanical properties compared to a product prepared from new starting materials.

Base layer and / or cover layer (s) can contain, in addition to the hydrolysis stabilizer (s) and the additives described hitherto, further conventional additives, such as fillers and antiblocking agents. Examples of inorganic blocking agents are silica, alumina, titania, barium sulfate, calcium carbonate and kaolin. The anti-blocking agents are advantageously added to the polymer or the polymer mixture before melting.

As additives it is also possible to choose mixtures of two or more different antiblocking agents or mixtures of antiblocking agents of the same composition but different particle size. The particles can the individual layers in the usual proportions, eg as a glycolic dispersion, during polycondensation or via masterbatches during extrusion. Pigment proportions of from 0.0001 to 10.0% by weight, based on the weight of the outer layers, have proven particularly suitable.

For certain applications, it may be appropriate to chemically pretreat the surface of the film by treatment with acids. Particularly suitable for this so-called Ätzhaftvermittlung trichloroacetic acid, dichloroacetic acid or hydrofluoric acid, which act on the surface for a short time (between 5 and 120 seconds) and then removed again, for example with a so-called air knife. This gives the film a very reactive, amorphous surface.

The film of the invention may have one or more other functionalities. The additional functionality is preferably that the film is stabilized against UV radiation, flame-retardant, coated on one or both sides, sealable and / or corona-treated or flame-treated.

Thus, the film of the invention may be coated on one or both sides. The coating generally has a thickness of 5 to 100 nm, preferably 20 to 70 nm, in particular 30 to 50 nm, on the finished film. It is preferably applied in-line, ie during the film manufacturing process. Particularly preferred is the application by means of the "reverse gravure-roll coating" process, in which the coating can be applied very homogeneously in said layer thickness. The coatings are applied as - preferably aqueous - solutions, suspensions or dispersions to give the film surface additional functionalities of the type mentioned. Examples of fabrics or compositions which impart additional functionality are acrylates (see WO 94/13476), ethylvinyl alcohols, PVDC, water glass (Na₂SiO₄), hydrophilic polyesters (5-Na-sulfoisophthalic acid-containing PET / IPA polyesters as mentioned in EP-A 144 878 or US Pat. No. 4,252,885), copolymers with vinyl acetate units (see WO 94/13481), polyvinyl acetates, polyurethanes, Alkali or alkaline earth salts of (C₁₀-C₁₈) Fatty acids, copolymers with units of butadiene and acrylonitrile, methyl methacrylate, methacrylic acid and / or acrylic acid and / or their esters. The substances or compositions conferring the additional functionality may contain the usual additives, such as antiblocking agents and / or pH stabilizers, in amounts of from 0.05 to 5% by weight, preferably from 0.1 to 3% by weight, based on the substances or compositions imparting the additional functionality.

The substances or compositions mentioned are applied to one or both sides of the film as a dilute, preferably aqueous solution, emulsion or dispersion. Subsequently, the solvent is removed.

The film may be vapor-coated on one or both sides, in particular with ethylene / vinyl alcohol copolymers, polyvinyl alcohol or polyvinylidene dichloride.

The film according to the invention can also be UV stabilized. Light, in particular the ultraviolet portion of solar radiation, d. H. The wavelength range of 280 to 400 nm, induced in thermoplastics degradation processes, as a result, not only the visual appearance by color change occurring or Yellowing changes, but by the extremely adverse effects on the mechanical properties of the thermoplastic films. The suppression of these photooxidative degradation processes is of considerable technical and economic importance, since otherwise the applications of numerous thermoplastics are drastically limited. For example, polyethylene terephthalates begin to absorb UV light below 360 nm, their absorption increases significantly below 320 nm, and is very pronounced below 300 nm. The maximum absorption is in the range between 280 and 300 nm. In the presence of oxygen, chain scissions are mainly observed, but no crosslinks. Carbon monoxide, carbon dioxide and carboxylic acids represent the quantitatively predominant photo-oxidation products. In addition to the direct photolysis of the ester groups, oxidation reactions must also be considered, which also lead to the formation of carbon dioxide via peroxide radicals. The photooxidation of polyethylene terephthalates can also lead to hydrogen splitting in α-position of the ester groups to hydroperoxides and their decomposition products and to associated chain cleavage (H. Day, D. M. Wiles, <i>J. Appl. Polym. Sci.</i><b>16</b> [1972] p. 203).

UV stabilizers, ie UV absorbers as light stabilizers, are chemical compounds that interfere with the physical and chemical processes of light-induced degradation. Soot and other pigments can partially cause a sunscreen. However, these substances are unsuitable for transparent films because they lead to discoloration or color change. Suitable UV stabilizers as light stabilizers are UV stabilizers which absorb at least 70%, preferably at least 80%, particularly preferably at least 90%, of the UV light in the wavelength range from 180 nm to 380 nm, preferably 280 to 350 nm. Particularly suitable UV stabilizers are also thermally stable in the temperature range of 260 to 300 ° C, ie they do not decompose into fission products and do not gase. Examples of suitable UV stabilizers as light stabilizers are 2-hydroxybenzophenones, 2-hydroxybenzotriazoles, organo-nickel compounds, salicylic acid esters, cinnamic acid ester derivatives, resorcinol monobenzoates, oxalic anilides, hydroxybenzoic acid esters, benzoxazinones, sterically hindered amines and triazines Hydroxy benzotriazoles which are benzoxazinones and the triazines are preferred. It was completely surprising to the experts that the use of UV stabilizers in combination with hydrolysis stabilizers leads to useful films with excellent properties. From the literature, UV stabilizers are known which absorb UV radiation and thus provide protection. The skilled person would then have probably used one of these known and commercially available UV stabilizers, but found that the UV stabilizer has a lack of thermal stability and decomposes at temperatures between 200 and 240 ° C or outgassed. In order not to damage the film, he would have large quantities (approx. 10 up to 15% by weight) of UV stabilizer must be incorporated so that it really effectively absorbs the UV light. At these high concentrations, however, the film yellows in a short time after production. The mechanical properties are also negatively affected. In addition, stabilizer on the nozzles or Rollers deposit, resulting in profile fluctuations or to the impairment of the optical properties (high turbidity, adhesive defect, inhomogeneous surface) leads.

In a very particularly preferred embodiment, the film according to the invention contains as UV stabilizer 0.1 to 5.0% by weight of 2- (4,6-diphenyl- [1,3,5] triazin-2-yl) -5- hexyloxyphenol of the formula<chemistry id="chem0001" num="0001"><img file="EP1297948A2_D0001.tif" /></chemistry> or 0.1 to 5.0% by weight of 2,2'-methylenebis [6-benzotriazol-2-yl-4- (1,1,2,2-tetramethyl-propyl) -phenol] of the formula<chemistry id="chem0002" num="0002"><img file="EP1297948A2_D0002.tif" /></chemistry> or 0.1 to 5.0% by weight of 2,2 '- (1,4-phenylene) -bis - ([3,1] benzoxazin-4-one) of the formula<chemistry id="chem0003" num="0003"><img file="EP1297948A2_D0003.tif" /></chemistry> In a further embodiment, it is also possible to use mixtures of these UV stabilizers or mixtures of at least one of these UV stabilizers with other UV stabilizers, the total concentration of light stabilizer preferably being between 0.1 and 5.0% by weight, particularly preferably Range of 0.5 to 3.0 wt .-%, based on the weight of the finished layer.

Surprisingly, even a small proportion of the abovementioned UV stabilizers is sufficient to give the film according to the invention excellent UV protection. The film according to the invention has an excellent appearance, an excellent profile and an excellent flatness. It can thus be procedurally safe and economically viable manufacture. Furthermore, it is very surprising that the regenerate can be used again without negatively affecting the yellowness of the film. Also, compared to a non-finished film, the yellowness is not negatively changed within the measurement accuracy.

In another embodiment, the film according to the invention is flame-retardant. Flame retardant means that the film meets the conditions of 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 the building material class B 2 and in particular B1 of flame retardant substances. Furthermore, the optionally flame-retardant film is to pass the UL Test 94 "Burning Test for Flammability of Plastic Material" so that it can be classified in Class 94 VTM-0. The film accordingly contains a flame retardant, which is metered in via the so-called masterbatch technology directly during film production, the proportion of the flame retardant in the range of 0.2 to 30.0 wt .-%, preferably 0.5 to 25 wt. %, more preferably from 1.0 to 20.0 wt .-%, based on the weight of the layer of crystallizable thermoplastic. In the masterbatch, the proportion of the flame retardant is generally 5 to 60 wt .-%, preferably 10 to 50 wt .-%, each based on the total weight of the masterbatch. Suitable flame retardants are, for example, bromine compounds, chloroparaffins and other chlorine compounds, antimony trioxide and aluminum trihydrate. The halogen compounds, however, have the disadvantage that halogen-containing by-products may be formed. In case of fire arise in particular hydrogen halides. Another disadvantage is the low light resistance of a thus equipped film. Further suitable flameproofing agents are, for example, organic phosphorus compounds such as carboxyphosphinic acids, their anhydrides and alkanephosphonic acid esters, the organic phosphorus compound being preferably polymerized into the PET chain. It is essential that the organic phosphorus compound is soluble in the thermoplastic, since otherwise the required optical properties are not met.

Quite 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 quite sufficient to equip the 0.5 to 2 μm thick outer 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, ie contain a so-called basic equipment.

In addition, measurements showed that even the flame-resistant film according to the invention does not become brittle during long-term exposure to heat (1,000 hours at 60 ° C.).

Where a very good sealability is required and where this property can not be achieved via an on-line coating, the film according to the invention is at least three-layered and then comprises in a particular embodiment the base layer B, a sealable top layer A and an optionally sealable top layer C. If the cover layer C is also sealable, then the two cover layers are preferably identical.

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

In principle, the same polymers which are also used in the base layer can be used for the optionally sealable outer layer C and for any intermediate layers.

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 top layer and the topographies of the sealable top layer A and the optionally sealable top layer C.

The sealing initiation temperature of 110 ° C. and the seal seam strength of at least 0.6 N / 15 mm is achieved if the copolymers described in more detail above are used for the sealable outer layer A. The best sealing properties of the film are obtained if the copolymer no further additives, in particular no inorganic or organic fillers are added. For this case, given a given copolyester, the lowest seal initiation temperature and highest seal seam strengths are obtained.

However, in this case, the handling of the film is poor, since the surface of the sealable cover layer A is prone to blocking. The film is difficult to wrap and is not suitable for further processing on high-speed packaging machines. To improve the handling of the film and the processability, it is necessary to modify the sealable top layer A. This is best done with the help of suitable antiblocking agents of a selected size, which are added in a certain concentration of the sealing layer in such a way that on the one hand minimizes blocking and on the other hand, the sealing properties are only slightly deteriorated.

Optionally, an intermediate layer may be present between the base layer and the cover layer (s). It may consist of the polymers described for the base layer. In a particularly preferred embodiment, it consists of the polyester used for the base layer. In addition to the hydrolysis stabilizer (s), it may also contain other customary additives. The thickness of the intermediate layer is generally greater than 0.3 μm and is preferably in the range of 0.5 to 15 μm, in particular 1.0 to 10 μm.

The thickness of the cover layer / s is generally greater than 0.1 .mu.m and is preferably in the range of 0.2 to 5 .mu.m, in particular 0.2 to 4 .mu.m, wherein the cover layers may be the same or different thickness.

The total thickness of the polyester film according to the invention can vary within wide limits and depends on the intended use. It is preferably 1 to 500 .mu.m, in particular 5 to 350 .mu.m, preferably 100 to 300 .mu.m, wherein the base layer has a proportion of preferably about 40 to 90% of the total thickness.

To set other desired properties, the film may also be corona or flame treated. The treatment is usually carried out so that the surface tension of the film is thereafter generally above 45 mN / m.

The present invention also provides a process for producing the film. In general, the production takes place by an extrusion or coextrusion process, for example on an extrusion line. It has proved to be particularly advantageous to add the at least one hydrolysis stabilizer in the form of a predried or pre-crystallized masterbatch prior to extrusion or coextrusion. The proportion of hydrolysis stabilizer (s) in the masterbatch is generally 5 to 50 wt .-%, preferably 6 to 30 wt .-%, each based on the total weight of the masterbatch. The or the hydrolysis stabilizer (s) are dispersed in a carrier material. As a carrier material of the thermoplastic itself, z. B. Polyethylene terephthalate or other polymers which are compatible with the thermoplastic, in question.

Preferred in the masterbatch technology is that the grain size and the bulk density of the masterbatches is similar to the grain size and the bulk density of the thermoplastic, so that a homogeneous distribution is obtained, resulting in the homogeneous properties.

The polyester films can be prepared by known methods from a polyester raw material, optionally other raw materials, at least one hydrolysis stabilizer and optionally further customary additives (the latter in the usual amount of from 0.1 to 30% by weight, based on the weight of the film) both as a monofilm and as multilayered - optionally coextruded - films are prepared with the same or differently shaped surfaces, for example, one surface contains particles and the other does not or all layers contain particles. Likewise, one or both surfaces of the film may be provided with a functional coating by known methods.

Masterbatches containing the hydrolysis stabilizer (s) should be pre-crystallized or predried. The same applies to masterbatches containing flame retardants or UV stabilizer (s). This predrying involves a gradual heating of the masterbatches under reduced pressure (20 to 80 mbar, preferably 30 to 60 mbar, in particular 40 to 50 mbar) and stirring and optionally drying at a constant, elevated temperature (also under reduced pressure). The masterbatches are preferably at room temperature from a dosing in the desired blend together with the polymers of the base and / or outer layers and optionally other raw material components in batches in a vacuum dryer, which in the course of drying or Residence a temperature range of 10 to 160 ° C, preferably 20 to 150 ° C, in particular 30 to 130 ° C passes through, filled. During the approximately 6-hour, preferably 5-hour, in particular 4-hour, residence time, the raw material mixture is stirred at 10 to 70 rpm, preferably 15 to 65 rpm, in particular 20 to 60 rpm. The thus pre-crystallized or Pre-dried raw material mixture is in a downstream also evacuated container at 90 to 180 ° C, preferably 100 to 170 ° C, in particular 110 to 160 ° C, for 2 to 8 hours, preferably 3 to 7 hours, in particular 4 to 6 hours, after-dried.

The polymers or the raw material mixtures are then fed to the extruder, in the production of multilayer film corresponding to several extruders. Any foreign bodies or impurities present can be filtered off from the polymer melt prior to extrusion. The melt (s) are then with the aid of a monodis or a multi-layer nozzle to a flat melt film or formed into a plurality of flat melt films stacked on top of each other. Subsequently, the one or multilayered film quenched on a chill roll and considered largely amorphous, ie solidified unoriented film. Subsequently, the film is lined and wrapped.

It was surprising that masterbatch technology, combined with suitable predrying and / or pre-crystallization, and the use of hydrolysis stabilizers produce a hydrolysis- and high-temperature-stable film with the required property profile without technical problems (such as adhesions in the dryer).

It was also unexpected that the foil according to the invention also exists in the flame-resistant embodiment of the environmental test and does not become brittle.

Weathering tests have shown that the film according to the invention in the UV-stabilized embodiment, even after about 5 to 7 years of outdoor use, shows virtually no yellowing, embrittlement, no loss of gloss and no cracking on the surface and no deterioration in the mechanical properties.

The combination of their properties makes the films of the invention suitable for a variety of applications, for example, indoors and outdoors, in the construction sector and in exhibition construction, in shop and shelf construction, in the electronics and lighting sectors, for greenhouses, Interior decoration, Trade fair and promotional items, as displays, for signs, Illuminated advertising profiles, Protective glazing of machines and vehicles, laminating medium, for credit and debit cards as well as in the refrigerated and frozen area, as composite foil, as a furniture film, especially in the thermoforming sector and in the automotive sector.

The thermoforming process usually includes the steps of predrying, heating, molding, cooling, demolding and tempering. Surprisingly, the film according to the invention can be deep-drawn even without predrying. Thus, the film can also be supplied as a roll to the thermoforming process. This is an essential, in particular an economic advantage over thermoformable polycarbonate or polymethyl methacrylate films. Depending on their thickness, these predrying times require 10 to 15 hours at temperatures of 100 to 120 ° C. Surprising was also the exact reproduction of details of the moldings produced with the film according to the invention.

For the thermoforming of the film of the invention, it has proved to be particularly useful when the mold has a temperature of 100 to 140 ° C, the heating time per 10 .mu.m film thickness is less than 5 seconds and the film temperature during molding in the range of 100 to 160 ° C is. The draw factor is generally 1.5 to 4.0, the shrinkage (shrinkage) less than 1.5%.

Correspondingly functionalized film according to the invention are also suitable for outdoor applications, for example for greenhouses, roofs, covers, exterior cladding, applications in the construction sector, in the cooling and deep-freezing areas, for advertising profiles and for credit, due to their good UV stability, flame resistance and low temperature resistance. Telephone or other customer cards.

The invention will be explained in more detail below with reference to embodiments, without being limited thereto. The film properties were tested as follows:

Climate test (humidity long-term test)

In this test, the film is stored for 1,000 h at 60 ° C and 95% relative humidity in an autoclave under atmospheric pressure. After storage, the impact resistance in the longitudinal and transverse directions is determined according to DIN 53448. It must be more than 100 mJ / mm² to meet the requirements.

temperature strength

The temperature resistance is determined after 1000 h tempering at 60 ° C in a convection oven. After this tempering, the impact strength according to DIN 53448 must be more than 100 mJ / mm² to meet the requirements.

DEG content / PEG content / PA content

The DEG, PEG or PA content is determined by gas chromatography after saponification with methanolic KOH and neutralization with aqueous hydrochloric acid.

Light transmission (transparency)

Under the light transmission is the ratio of the total transmitted light to the amount of incident light to understand. The light transmission was determined using the device ®HAZEGARD plus from Byk Gardener, Germany, according to ASTM D 1003.

yellowness

The yellow value (YID) is the deviation from the colorlessness in the direction "yellow" and was measured according to DIN 6167. Yellowness values ​​(YID) of less than 6 are not visible to the naked eye.

surface defects

The surface defects were determined visually.

Standard viscosity (SV) and intrinsic viscosity (IV)

The standard viscosity SV was - based on DIN 53726 - measured as a 1% solution in dichloroacetic acid (DCE) at 25 ° C. SV (DCE) = (η_rel-1) x 1000. The intrinsic viscosity (IV) is calculated from the standard viscosity (SV) as follows:<maths id="math0001" num=""><math display="block"><mrow><msup><mrow><mtext>IV = [η] = 6.907 x 10</mtext></mrow><mrow><mtext>-4</mtext></mrow></msup><mtext> SV (DCE) + 0.063096 [dl / g]</mtext></mrow></math><img file="EP1297948A2_D0004.tif" /></maths>

Weathering (two-sided), UV stability

The UV stability was tested according to the test specification ISO 4892 as follows: <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">tester</entry><entry namest="col2" nameend="col2" align="left">Atlas Ci 65 Weather Ometer</entry></row><row><entry namest="col1" nameend="col1" align="left">test conditions</entry><entry namest="col2" nameend="col2" align="left">according to ISO 4892, ie artificial weathering</entry></row><row><entry namest="col1" nameend="col1" align="left">exposure time</entry><entry namest="col2" nameend="col2" align="left">1000 Hours (per page)</entry></row><row><entry namest="col1" nameend="col1" align="left">radiotherapy</entry><entry namest="col2" nameend="col2" align="left">0.5 W / m², 340 nm</entry></row><row><entry namest="col1" nameend="col1" align="left">temperature</entry><entry namest="col2" nameend="col2" align="left">63 ° C</entry></row><row><entry namest="col1" nameend="col1" align="left">Relative humidity</entry><entry namest="col2" nameend="col2" align="left">50 %</entry></row><row><entry namest="col1" nameend="col1" align="left">Xenon lamp</entry><entry namest="col2" nameend="col2" align="left">inner and outer filter made of borosilicate</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">irradiation cycles</entry><entry namest="col2" nameend="col2" align="left">102 Minutes of UV light, then 18 minutes of UV light with water spraying of the samples then again 102 minutes of UV light, etc.</entry></row></tbody></tgroup></table></tables>

fire behavior

The fire behavior was 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 the UL-test 94.

Determination of the sealing temperature (minimum sealing temperature)

Heat-sealed samples (sealing seam 20 mm x 100 mm) were produced using the sealing device HSG / ET from Brugger, the film being sealed at different temperatures with the aid of two heated sealing jaws at a sealing pressure of 2 bar and a sealing time of 0.5 s. Test strips of 15 mm width were cut from the sealed samples. The T-seal strength was measured as in the determination of the seal strength. The seal initiation temperature is the temperature at which a seal strength of at least 0.5 N / 15 mm is achieved.

Seal strength

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

Examples

The following Examples and Comparative Examples are each single-layered or multi-layered transparent films of different thicknesses produced on an extrusion line. Percentages are by weight, unless stated otherwise.

The polyethylene terephthalate (clearstock) from which the transparent films were made had a standard viscosity SV (DCE) of 1110, which corresponds to an intrinsic viscosity IV (DCE) of 0.83 dl / g (polyethylene terephthalate T94 V from KoSa, Germany).

The additives for achieving the hydrolysis protection and the additional functionalities were added in the form of different masterbatches:

Masterbatch MB1:

<ul id="ul0001" list-style="none" compact="compact"><li>6 % By weight of a phenolic hydrolysis stabilizer (Irganox B561, a blend of 80% by weight of Irgafos® 168 and 20% by weight of Irganox 1010, Ciba Specialty Chemicals, Basel, Switzerland),</li><li>94 % By weight of polyethylene terephthalate (hereinafter referred to as PET)</li><li>Bulk weight: 750 kg / m³</li></ul>

Masterbatch MB2

:

<ul id="ul0002" list-style="none" compact="compact"><li>20 % By weight of an aromatic polymeric carbodiimide (®Stabaxol P from Rhein Chemie, Mannheim, Germany),</li><li>80 Weight% PET</li><li>Bulk weight: 750 kg / m³</li></ul>

The following masterbatch was used to prepare UV-stabilized films:

Masterbatch MB3

:

<ul id="ul0003" list-style="none" compact="compact"><li>20 Wt .-% 2- (4,6-diphenyl- [1,3,5] triazin-2-yl) -5-hexyloxy-phenol (®Tinuvin 1577 from Ciba Specialty Chemicals) and</li><li>80 Weight% PET</li></ul>

To improve the slip properties, the following masterbatch was used:

Masterbatch MB4

:

In addition to PET, it contained 10,000 ppm ® Sylobloc 44H (Grace, Germany).

The following masterbatch was used to prepare a flame-retardant film:

Masterbatch MB5

:

<ul id="ul0004" list-style="none" compact="compact"><li>25 % By weight of methanephosphonic acid bis (5-ethyl-2-methyl-2-oxo-2λ⁵- [1,3,2] dioxaphosphinan-5-ylmethyl ester) (® Amgard P1045 from Albright &amp; Wilson Americas, USA) and</li><li>75 Weight% PET</li></ul>

Example 1:

A 150 μm thick, transparent, amorphous monofilm was produced containing 51% PET, 10% MB2 (the film accordingly contained 2% hydrolysis stabilizer) and 4% MB4 as antiblocking agent. In addition, the film contained 35% immanent accumulating Regenerat.

The mixture of the individual components was filled at room temperature from separate dosing into a vacuum drier, which went through from the filling time to the end of the residence time, a temperature range of 25 to 130 ° C. During the approximately 4-hour residence time, the raw material mixture was stirred at 61 revolutions per minute.

The pre-crystallized or predried raw material mixture was post-dried in the downstream, also under vacuum hopper at 140 ° C for 4 hours. The raw material mixture was then fed to extruders where it was melted and then extruded into the film described.

Example 2:

As described in Example 1, a 150 micron thick monofilm was prepared. In contrast to Example 1, the film contained in addition to the PET (T94 V), the 10% MB2 and the 4% MB4 additionally 2% MB1.

Example 3:

Example 1 was repeated with the modification that the film was now coated on both sides. For this purpose, the film was coated on both sides after extrusion by means of a "reverse gravure-roll coating" process with an aqueous dispersion. The dispersion contained next to water<dl id="dl0001" compact="compact"><dt>4.2%</dt><dd>a hydrophilic polyester (5-Na-sulfoisophthalic acid containing PET / IPA polyester, SP41 from Ticona, USA),</dd><dt>0.15%</dt><dd>colloidal silica (®Nalco 1060 from Deutsche Nalco Chemie) and</dd><dt>0.15%</dt><dd>Ammonium carbonate as pH buffer.</dd></dl>

The wet application weight was 1 g / m² per page. The calculated thickness of the dried coating was 80 nm.

Example 4:

Coextrusion was used to produce a 150 μm thick, hydrolysis-stable and UV-stable three-layer PET film with the sequence of layers ABA, B representing the core layer and A the covering layers. The thickness of the core layer was 145 microns, the two outer layers each 2.5 microns.

The core layer was made from a mixture of 52% PET (T94 V), 10% MB2, 3% MB3 and 35% inherent regenerate. For the cover layers, a mixture of 93% PET (T94 V) and 7% MB4 was used.

Example 5:

By coextrusion, a 400 micron thick sealable film with the layer sequence ABC was prepared, wherein the base layer B had a thickness of 396 microns, while the cover layers A and C each had a thickness of 2 microns.

For the base layer B, a mixture of 55% PET (T94 V), 10% MB2 and 35% inherent regenerate was used.

For the sealable outer layer A, a copolyester of 78 mol% of ethylene terephthalate and 22 mol% of ethylene isophthalate was used as the thermoplastic (prepared by transesterification in the presence of a manganese catalyst - Mn concentration: 100 ppm). In addition to the thermoplastic, the topcoat contained 3% MB4 as antiblocking agent.

For the non-sealable overcoat C, a mixture of 93% PET (T94V) and 7% MB4 was used.

Example 6:

As described in Example 5, a 400 micron thick, amorphous, hydrolysis-stable, sealable film was produced with the layer sequence ABC. In contrast to Example 5, the non-sealable outer layer C was coated after extrusion by "reverse gravure-roll coating" with an aqueous dispersion of the composition mentioned in Example 3. The wet application weight was 1 g / m², The calculated thickness of the dried coating was 80 nm.

Example 7:

As described in Example 1, a 150 micron thick monofilm was prepared. In contrast to Example 1, the film additionally contained 3% MB5.

Example 8:

As described in Example 1, a 150 micron thick monofilm was prepared. In contrast to Example 1, the film additionally contained 3% MB5 and 3% MB3.

Example 9:

As described in Example 4, a 150 micron thick, hydrolysis and UV-stable film was produced with the layer sequence ABA. The film was then corona treated on one side. After the treatment, the surface tension of the film was 48 mN / m.

Comparative Example 1

As described in Example 7, a 150 micron thick monofilm was prepared with the only difference that the film did not contain a hydrolysis stabilizer.

Comparative Example 2:

Comparative Example 1 was repeated, but this time also the flame retardant was omitted.

The properties of the films prepared according to the examples are summarized in the following table.<tables id="tabl0002" num="0002"><img file="EP1297948A2_D0005.tif" /></tables>