MULTI-LAYER SYSTEM OF AT LEAST 3 LAYERS OF POLYESTER, ITS PRODUCTION AND USE

Abstract

The present invention relates to a multi-layer system of at least 3 layers of polyester, to its production and use for the production of packaging, protective films, adhesive films, solar cells or medical materials, and to solar cells produced from the same.

Description

MULTI-LAYER SYSTEM OF AT LEAST 3 LAYERS OF POLYESTER, ITS PRODUCTION AND USE The present invention relates to a multi-layer system of at least 3 layers of polyester, its production and use for the production of packaging, protective films, adhesive films, solar cells or medical materials, as well as solar cells produced from the same. Polyester films have numerous applications, including in solar cells. Their lack of stability against hydrolysis is often problematic in this case (document WO2010113920). Several carbodiimides have proven effective as hydrolysis protection agents for thermoplastics. However, these have the drawback of emitting gases of health concern during processing. The film spreading stage is particularly problematic in this regard, as effective suction separation devices cannot be used at this stage. The emission of partially gaseous isocyanates during the polymer sheet production process is harmful to health and therefore requires the installation of bulky and expensive suction separation devices, which are not technically feasible in some cases (EPA document 0 838 500). Polyester films with epoxidized vegetable oils as a stabilizer have been described in documents EP-A-1 634 914 and EP-A-1 842 871. In this case, the typical toxic degradation products of carbodiimides are not produced, incorporation into the polyester matrix is ​​good with the appropriate selection of oils, and protection against hydrolysis of the film is achieved. However, this protection can only be obtained at high concentrations of the epoxide, with poorer long-term stabilization compared to the use of carbodiimides. Additional drawbacks in this application include recurring production intervals with an extreme tendency for gel formation. When the gel level becomes too high, damage occurs, and film production becomes temporarily impossible. Production must then be stopped, and the extrusion line must be cleaned. frpunn / Lznz / e / YiAi Therefore, there is a need for a polyester layering system, particularly for sheets, in which the emission of isocyanates is clearly reduced during processing and which provides very good long-term protection against hydrolysis. Surprisingly, a multi-layer system of at least 3 polyester layers, in which the inner polyester layer contains carbodiimides, and which is wrapped on the top and bottom sides by other polyester layers, at least one of which contains epoxide, has now been found to be stable against hydrolysis and exhibits a markedly reduced isocyanate emission during processing. The object of the present invention is a multi-layer system of at least 3 layers of polyester, which have the following structure: - at least one polyester layer (I) containing at least one carbodiimide, - at least one layer of polyester (II) over the top side of the polyester layer (I) and - at least one polyester (III) layer on the underside of the polyester (I) layer, wherein at least one of these polyester (II) or (III) layers contains at least one epoxide. In the case of carbodiimides, they are preferably compounds of formula (I) Ri-R2.(-N=C=N-R2-)n-R1(I), in which n corresponds to an integer from 1 to 500, preferably from 3 to 20, most preferably from 4 to 20, R1 represents a residue of the series of -NCO, -NCNR3-NHCONHR3, -NHCONR3R4 or -NHCOOR5, R3 and R4 being equal or different and in each case independently representing a residue of the series of C1-C12 alkyl, C6-C12 cycloalkyl, C7-C18 aralkyl or Ce-C-is aryl residue and R5 represents a residue of the series of C1-C22 alkyl, C6-C12 cycloalkyl, Ce-Cis aryl or C7-C18 aralkyl residue, as well as representing an unsaturated alkyl residue with 2 - 22 carbon atoms or representing an alkoxypolyoxyalkylene residue, R2 represents Ce-Cis arylenes substituted with C1-C12 alkyl, Ce-Cis arylenes substituted with C7-C18 alkyl, and, where applicable, represents frrunn / Lznz / e / YiAi arylenes bridged with C1-C12 alkyl via Ci-Cs alkylene groups, having a total of 7 to 30 carbon atoms, as well as arylene, preferably frpunn / Lznz / e / YiAi in which R6, R7 and R8 in each case independently represent methyl or ethyl, each benzene ring having only one methyl group. The particularly preferred carbodiimides are compounds of formula (H), R6R6R6 wherein R1 is selected from the group -NCO, -NHCONHR3, -NHCONR3R4 or -NHCOOR5, R3 and R4 being the same or different and representing a C1-C12 alkyl, C6-C12 cycloalkyl, C7-C18 aralkyl or Ce-Cis aryl residue, R5 corresponding to a C1-C22 alkyl, C6-C12 cycloalkyl, CeC18 aryl or C7-C18 aralkyl residue, as well as to an unsaturated alkyl residue with 2-22 carbon atoms, preferably 12-20 carbon atoms, most preferably 16-18 carbon atoms, or to an alkoxypolyoxyalkylene residue, and R6, R7 and R8 in each case independently represent methyl or ethyl, with each benzene ring having only one methyl group and meaning n = 1 to 20. The carbodiimide content (NCN content, measured by titration with oxalic acid) of the carbodiimides used according to the invention of formula (I), preferably of formula (II) is preferably 2-16% by weight, preferably 4-13% by weight, especially preferably 6-12% by weight. The carbodiimides used according to the invention of formula (I), preferably of formula (II), further preferably have an average molar mass (Mw) to be determined by CPG viscometry of 1000 - 20000 g / mol, preferably 1500 - 10000 g / mol, especially preferably 2000 - 5000 g / mol. The physical, mechanical, and rheological properties are frequently determined by polymolecularity (the ratio of weight average to number average). This ratio is also called polydispersity and is a measure of the width of a molar mass distribution (MMV). According to the invention, carbodiimides of formula (II) are preferred, exhibiting a polydispersity D, determined by gel permeation chromatography (GPC), of Mw / Mn in the range of 1.2 to 2.2, and particularly preferably in the range of 1.4 to 1.8. In the case of the carbodiimides used according to the invention, these are commercially available compounds, such as, for example, the polymeric carbodiimides under the name Stabaxol® from Lanxess Deutschland GmbH. These can also be produced, for example, according to the processes described in document EP-A-3018124. In the case of polyester caps (I), (II) and / or (III) it is preferably thermoplastic polyester caps. The polyesters preferred in the context of the invention are preferably poly(alcohol terephthalates), preferably poly(ethylene terephthalates) (PET), poly(butylene terephthalates) (PBT), poly(adipato-butylene terephthalates) (PBAT), poly(trimethylene terephthalates) (PTT), as above copolyester, thermoplastic polyester elastómeros (TPE E), ethylene vinyl acetate (EVA), poly(lactic acid) (PLA) and / or derivatives of PLA, poly(butylene succinate) (PBS), polyhydroxialkanoates (PHA), as well as distinct combinations and / or thermoplastic polyurethanes based on polyester (TPU). Poly(alkyl terephthalates), such as particularly preferably poly(ethylene terephthalate), poly(butylene terephthalate), or poly(butylene adipate terephthalates), and polylactic acid (PLA) and their copolyesters, are used as polyester layers (I), (II), and (III) independently of each other. The polyester layers (I), (II), and (III) in the multilayer system may be made up of the same polyester or, however, of different polyesters. In the case of epoxides, these are preferably compounds based on molecules with two or more epoxide groups per molecule. Preferably, this includes at least one epoxidized natural oil, or at least one epoxidized grade acid ester, or at least one synthetic epoxidized compound. Most preferably, the epoxides to be used according to the invention have at least one terminal epoxide group and, in total, at least two epoxide groups per molecule. epoxides are also preferably made from epoxidized natural oils or epoxidized fatty acid esters. The preferred epoxidized natural oils are based on at least one oil from the group of olive oil, linseed oil, peanut oil, palm oil, soybean oil, and cod liver oil. Linseed oil or soybean oil are especially preferred, with linseed oil being particularly preferred. Epoxidized natural oils are generally prepared according to methods familiar to the expert, as this is known for example by Angew. Chem. 2000, 112, 2292 - 2310. Preferably epoxidized fatty acid esters are obtained from unsaturated aliphatic carboxylic acids with 10 to 40 C atoms, preferably with 16 to 22 C atoms, by reaction with saturated aliphatic alcohols with 2 to 40 C atoms, preferably 2 to 6 C atoms and subsequent reaction with peroxides, preferably hydrogen peroxide. Epoxidized fatty acid esters are preferably prepared by reacting mono- or diunsaturated carboxylic acids with saturated aliphatic alcohols. Particularly preferred is the use of at least one carboxylic acid from the following groups: pelargonic acid, palmitic acid, lauric acid, margaric acid, dodecanedioic acid, behenic acid, stearic acid, capric acid, montanic acid, linoleic acid, linolenic acid, and oleic acid, followed by reaction with peroxides, preferably hydrogen peroxide. The saturated aliphatic alcohols to be used are preferably 1- to 4-hydroxylated alcohols, selected from the n-butanol, n-octanol, stearyl alcohol, ethylene glycol, propylene glycol, neopentyl glycol, pentaerythritol, and glycerol groups. Glycerol is particularly preferred. frpunn / Lznz / e / YiAi Mixtures of different epoxidized fatty acid esters and / or epoxidized natural oils can also be used. However, synthetic epoxidized compounds can also be used, such as aromatic epoxidized polymers or condensation products. These are prepared, for example, by reacting aromatic alcohols with formaldehyde, which are then reacted with peroxides. Mononuclear or polynuclear phenols can be used as aromatic alcohols. The preferred mononuclear phenols are resorcinol or hydroquinone. The preferred polynuclear phenols are bis-(4-hydroxyphenyl)-methane, 2,2bis-(4-hydroxyphenyl)-propane, 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane or 4,4'-dihydroxydiphenylsulfone. The preferred condensation products of phenols with formaldehyde are phenolic novolacs. In another preferred embodiment of the invention, aromatic epoxy compounds with two terminal epoxide groups are used. These compounds are preferably oligomeric reactions of bisphenol A with epichlorohydrin, having an average molecular weight determined according to EN ISO 10927 of 900 to 1200 g / mol and an epoxy index determined according to ISO 3001 of 450 to 600 grams per equivalent. Particularly preferred for this purpose is the reaction product of formula (III) from the reaction of bisphenol A with epichlorohydrin. frpunn / Lznz / e / YiAi in which a represents an average number from 0 to 10, preferably from 1 to 8, especially preferably from 1 to 6, most especially preferably from 2 to 3. The epoxides are preferably prepared according to a procedure in accordance with document US2002 / 0128428 A1 and then have, in accordance with EN ISO 10927, an average molecular weight of 900 to 1200 g / mol, which corresponds in formula (III) to an a in the range of 2 to 3, with an epoxy index determined according to ISO 3001 of 450 to 600 grams per equivalent. Synthetic epoxy compounds are preferably used with a Mettler softening point, according to DIN 51920, in the range of 0 to 150 °C, particularly preferably from 50 °C to 120 °C, most preferably from 60 °C to 110 °C, and especially from 75 °C to 95 °C. The Mettler softening point is the temperature at which the sample flows from a cylindrical fitting with a discharge opening of 6.35 mm in diameter, interrupting a light barrier located 19 mm below. For this purpose, the sample is heated in air under constant conditions. Preferably, synthetic epoxy compounds are used, which have an average epoxide equivalent weight (EEW, grams of resin containing one mole of epoxy-bonded oxygen) by titration according to DIN 16945 of 160 to 2000 g / eq, preferably 250 to 1200 g / eq, especially preferably 350 to 1000 g / eq and particularly preferably in the range of 450 to 800 g / eq. In particular, a poly(bisphenol A-co-epichlorohydrin) [n.eCAS 25068-38-6] is preferably used as the compound of formula (III), preferably with a number-averaged molecular weight (Mn) in the range of 600 to 1800 g / mol to be determined by MALDITOF mass spectrometry using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry in accordance with EN ISO 10927, to refer to Epilox® of Leuna Harze GmbH, Leuna. Other preferred epoxy compounds with at least 2 epoxide functions are commercially available under the name Joncryl® from BASF AG, in particular Joncryl® 4368, which contains the following units in discretionary combination frpunn / Lznz / e / YiAi In the units represented, R9 and R10 each independently represent H or Ci-Cs alkyl, R11 represents Ci-Cs alkyl, x and y independently represent an average number from 1 to 20, and yz represents an average number from 2 to 20. The chain closure is formed by terminal groups R* which independently represent H or alkyl. Ci-C8. Preferably, the epoxide corresponds to formula (IV) (IV) wherein R9, R10 in each case independently of each other represent H or Ci-Cs alkyl, R11 represents Ci-Cs alkyl, xey independently of each other represent an average number from 1 to 20 and yz represents an average number from 2 to 20, the terminal groups R* independently of each other representing H or Ci-Cs alkyl. In a preferred or alternative embodiment, epoxidized fatty acid esters of glycerol, particularly epoxidized vegetable oils, are used as epoxides. These are obtained by epoxidation of the reactive olefin groups of unsaturated fatty acid triglycerides. The preparation of epoxidized fatty acid esters of glycerol can be carried out starting from unsaturated fatty acid esters of glycerol, preferably from vegetable oils, and organic peroxycarboxylic acids (Prileschajew reaction). Procedures for the preparation of epoxidized natural oils have been described, for example, in Smith, March, March's Advanced Organic Chemistry, 5th edition, Wiley-Interscience, New York, 2001. The preferred epoxidized fatty acid esters of glycerol are epoxidized natural oils, most preferably epoxidized soybean oil [CAS 8013-07-8]. The proportion of the polyester layer (I) in the multi-layer system according to the invention is generally between 10% by weight and 99% by weight, preferably between 30% by weight and 90% by weight, and most preferably between 50% by weight and 70% by weight, with respect to the total weight of the multi-layer system. Preferably, the polyester layers (II) and (III) contain an epoxide. It is also preferred that the polyester layers (II) and (III) do not contain carbodiimide. In a preferred embodiment of the invention, the amount of carbodiimide in the polyester layer (I) is from 0.2 to 3% by weight, preferably from 0.5 to 1.5% by weight, with respect to the polyester layer (I). In another preferred embodiment of the invention, the amount of epoxides in at least one of the polyester sheets (II) and / or (III) is from 0.1 to 6% by weight, preferably from 0.5 to 4% by weight, with respect to the polyester layer (II) or polyester layer (III). In a preferred embodiment of the invention, the weight of the polyester layer (I) containing carbodiimide ranges from 70% to 95% by weight, with respect to the total weight of the multi-layer system. In another preferred embodiment of the invention, the thickness of the polyester layer is preferably between 11 and 500 micrometers and especially preferably between 24 and 300 micrometers. In multi-layer embodiments of the carbodiimide-containing layer, the sum of the thicknesses of the carbodiimide-containing layers is usually greater than 10 micrometers and less than 500 micrometers, and most preferably greater than 40 micrometers and less than 300 micrometers. The polyester (II) and / or polyester (III) layers are preferably made thin to minimize alteration of the overall sheet's hydrolysis stability; that is, these layers are preferably thinner than 5 micrometers, especially thinner than 3 micrometers, and ideally thinner than 0.8 micrometers. However, it has proven advantageous when the polyester (II) and / or polyester (III) layers are no thinner than 0.1 micrometers. Another object of the present invention is further a process for producing the multi-layer system, characterized in that the polyester layer (I) containing carbodiimide, the polyester layers (II) and (III) if and when containing epoxide are co-extruded to give a multi-layer system. Coextrusion processes are known in the prior art. Therefore, the temperatures and pressures commonly used in coextrusion can also be used in the production process of the multi-layer system according to the invention. The temperatures are preferably between 200 and 300 °C. Preferably, this procedure is carried out in such a way that from the polyester layer (I) and polyester layer (II) and (III), by means of co-extrusion with the use of at least two extrusion presses, if applicable, with the addition of adhesive agents, the multi-layer system is produced in accordance with the invention frpunn / Lznz / e / YiAi. In particular, during the extrusion of the polyester layer (I), isocyanates may form through the decomposition of carbodiimide. In this process, a wide-slot nozzle is preferably used in the extrusion for preparing the polyester layer. In a preferred variant of the production process according to the invention, suction separation devices are placed in the wide-slot nozzle. For the production of the polyester layer (I), the polyester is mixed with carbodiimide and extruded. For the production of polyester layers (II) and (III), the epoxide is added to at least one of the polyesters during extrusion. Conventional dosing systems can be used for this purpose. The polyester layer (I) is then extruded with polyester layers (II) and (III) so that the polyester layer (I) is surrounded by polyester layers (II) and (III) on the opposite side. In the process for producing the layers of the multi-layer system according to the invention, the corresponding polyester melts, modified with carbodiimide of formula (I) for polyester layer (I) or modified with epoxide for polyester layers (II) and / or (III), are preferably extruded through a flat nozzle. The resulting layer is then withdrawn for solidification onto one or more rollers, preferably a cooling roller, as a largely amorphous pre-layer, and is rapidly cooled. Optionally, the layer is then reheated, and preferably biaxially stretched (oriented) and heat-set. This preferably results in a sheet form. In the extrusion zone, it has proven advantageous in this respect to maintain temperatures below 295 °C. It is especially favorable when the nozzle area, and particularly the nozzle edge area and its immediate vicinity, is no hotter than 290 °C, preferably no hotter than 285 °C, and most preferably no hotter than 275 °C. The higher the temperature, the greater the thermal stress on the stabilizers and the greater the tendency for gel formation. Biaxial stretching is generally performed sequentially. In this regard, stretching is preferably carried out first in the longitudinal direction (i.e., in the machine direction = MD direction) and then in the transverse direction (i.e., perpendicular to the machine direction = TD direction). This leads to an orientation of the molecular chains. The longitudinal stretching can be performed using two rapidly rotating rollers at different speeds, corresponding to the desired stretching ratio. The stretching temperature can vary over a relatively large range and depends on the desired properties of the layer. Generally, both longitudinal and transverse stretching are performed at Tg + 10°C to Tg + 60°C (Tg = glass transition temperature of the layer). The longitudinal stretching ratio is generally between 2.0:1 and 6:1, preferably between 3:1 and 4.5:1. The transverse stretching ratio is generally between 2:1 and 5:1, preferably between 3:1 and 4.5:1, and the second longitudinal and transverse stretching ratio, if applicable, is between 1.1:1 and 5:1. Longitudinal extension can, in some cases, be performed simultaneously with transverse extension (simultaneous extension). This has proven advantageous when the ratio of extension in the longitudinal to transverse directions is greater than 3.0 in each case. In the subsequent heat setting, the layer is preferably held for approximately 0.1 to 10 seconds at a temperature of 150 to 260 °C, preferably 200 to 245 °C. Following, or at the beginning of, heat setting, the layer is relaxed by 0 to 15%, preferably 1.5 to 8%, in the transverse direction and, if necessary, also in the longitudinal direction, and then cooled and rolled in the usual manner. Another object of the present invention is the use of the multi-layer system according to the invention for the manufacture of containers, protective films, preferably for solar cells or in the medical field, or for the production of adhesive films. The multi-layer system according to the invention is preferably used for the production of protective films for solar cells. Therefore, the present invention also comprises solar cells containing the multi-layer system. frpunn / Lznz / e / YiAi In the present invention, the multi-layer system according to the invention is used in solar cells as a back-side film. In this respect, the multi-layer system according to the invention can be used for all solar cells known in the prior art. In this respect, the production of the solar cell is carried out according to the procedures described in the state of the art, starting from the standard procedures for the production of silicon by casting procedures, the Bridgman procedure, the EFG procedure (edge-defined film-fed growth) or the Czochralski procedure and the subsequent production of Si wafers and the lamination of the aforementioned material layers, using the multi-layer system according to the invention instead of the back-side film used in a standard manner. The scope of the invention encompasses all definitions of remains, indices, parameters, and general explanations found above and explained below or mentioned in preferred intervals, including in the respective intervals and preferred intervals in any combination. Using the multi-layer system according to the invention, a multi-layer system of polyester stabilized against hydrolysis can be provided for the first time. The following examples serve to explain the invention, without being limiting in this respect. Examples Example 1 They were tested: 1) carbodiimide A: a polymeric carbodiimide with an NCN content of approx. 11.8% by weight, D = approx. 1.8 and Mw = 2300 g / mol of formula (II) with n = approx. 3 - 4, R6, R7, R8 in each case independently represent methyl or ethyl, each benzene ring having only one methyl group and R1= -NHCOOR5 and R5= cyclohexyl. 2) Basic mixture of carbodiimide B: Poly(ethylene terephthalate) (PET), which can be obtained from Invista Deutschland GmbH with an intrinsic viscosity of 0.8, which is mixed with 10% by weight of carbodiimide A and extruded. frpunn / Lznz / e / YiAi 3) Stabilizer C: Epoxide of formula (III) with n = in the range of 2 - 3 with an equivalent weight of epoxide (DIN 16945) of 500 to 700 g / eq and a softening point (Mettler, DIN 51920) between 75 and 90 °C. [n.sCAS 2506838-6], 4) Poly(ethylene terephthalate) (PET), which can be obtained by the company Invista Deutschland GmbH with an intrinsic viscosity of 0.8. The multilayer systems shown in Table 1 were produced using an extruder for the inner polyester layer (I) and a co-extruder for the outer polyester layers (II) and (III), with polyethylene terephthalate (PET) as the polyester. A suction separation device was positioned next to the wide-slot nozzle. Table 1 summarizes the quantities used, as well as the results of qualitative emission measurements in the spread area using standardized indicator tubes for isocyanates (measurement time approx. 30 min.) and the hydrolysis stability of the multilayer PET sheets. Hydrolysis stability measurement For the hydrolysis test, the layers were stored in steam at a temperature of 120 °C for 24 hours, and their elongation at break was measured after 0 and 24 hours. The values ​​shown in Table 1 for stability against hydrolysis result from the following calculation: Elongation at break [%] = (elongation at break after 24 hours / elongation at break after 0 hours) x 100. Table 1: frpunn / Lznz / e / YiAi Polyester layer composition (1) Polyester layer composition (II) and (III) Isocyanate test Hydrolysis stability (elongation at break in %) Comparative example 100% PET 100% PET negative 38 Comparative example in analogy to document EP0838500 15% by weight of basic carbodiimide B mixture / 85% by weight of PET 15% by weight of basic carbodiimide B mixture / 85% by weight of positive PET 95 Comparative example in analogy to document EP1634914 4% of stabilizer C, 96% of PET 4% of stabilizer C, 96% of negative PET 36 Example according to the invention 15% by weight of basic carbodiimide B mixture / 85% by weight of PET 0.5% by weight of stabilizer C, 99.5% by weight of negative PET 91 Comparative example 15% by weight of basic carbodiimide B mixture / 85% by weight of PET 100% of positive PET Test values ​​very dispersed, The example according to the invention shows the positive effect of the multi-layer system according to the invention, since it does not show any kind of isocyanate gas release with good stability against hydrolysis.

Claims

1. A multi-layer system of at least 3 polyester layers, having the following structure: - at least one polyester layer (I) containing at least one carbodiimide, - at least one polyester layer (II) on the upper side of the polyester layer (I) and - at least one polyester layer (III) on the lower side of the polyester layer (I), characterized in that at least one of these polyester layers (II) or (III) contains at least one epoxide, the amount of carbodiimide in the polyester layer (I) being from 0.2 to 3% by weight, with respect to the polyester layer (I).

2. A multi-layer system according to claim 1, characterized in that the carbodiimide is a compound of formula (I) Ri-R2.(-N=C=N-R2-)n-R1 (I), wherein n corresponds to an integer from 1 to 500, preferably from 3 to 20, most preferably from 4 to 20, R1 represents a residue of the series -NCO, -NCNR3, -NHCONHR3, NHCONR3R4 or -NHCOOR5, R3 and R4 being the same or different and in each case independently representing a residue of the series of C1-C12 alkyl, C6-C12 cycloalkyl, C7-C18 aralkyl or Ce-Cis aryl, and R5 represents a residue of the series of C1-C22 alkyl, C6-C12 cycloalkyl, Ce-Os aryl or aralkyl C7-C18, as well as representing an unsaturated alkyl residue with 2-22 carbon atoms or representing an alkoxypolyoxyalkylene residue, R2 represents Ce-Cw alkyl-substituted anlenes C1-C12,Ce-Cw adienes substituted with C7-C18 alkylaryl as well as, where applicable, representing C1-C12 alkyl substituted arylenes bridged through Ci-Cs alkylene groups, having a total of 7 to 30 carbon atoms, as well as arylene, preferably frpunn / Lznz / e / YiAi frpunn / Lznz / e / YiAi in which R6, R7 and R8 in each case independently represent methyl or ethyl, each benzene ring having only one methyl group.

3. A multi-layered system according to claim 1, characterized in that, in the case of carbodiimides, it is a compound of formula (II), wherein R1 is selected from the group -NCO, -NHCONHR3, -NHCONR3R4 or NHCOOR5, R3 and R4 being the same or different and representing a C1-C12 alkyl, C6-C12 cycloalkyl, C7-C18 aralkyl or Ce-C1e aryl group, R5 corresponding to a C1-C22 alkyl, C6-C12 cycloalkyl, CeC18 aryl or C7-C18 aralkyl group, as well as to an unsaturated alkyl group with 2-22 carbon atoms, preferably 12-20 carbon atoms, most preferably 16-18 carbon atoms, or to an alkoxypolyoxyalkylene group, and R6, R7 and R8 in each case independently of each other they represent methyl or ethyl, each benzene ring having only one methyl group and meaning n = 1 to 20.

4. Multi-layer system according to at least one of claims 1 to 3, characterized in that in the case of the polyester layer (I), (II) and / or (III) it is thermoplastic polyester.

5. Multi-layer system according to at least one of claims 1 to 4, characterized in that the polyester is poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(butylene adipate terephthalate) (PBAT), poly(trimethylene terephthalate) (PTT), as well as copolyesters, thermoplastic polyester elastomers. (TPE E), ethylene-vinyl acetate (EVA), poly(lactic acid) (PLA) and / or PLA derivatives, poly(butylene succinates) (PBS), polyhydroxyalkanoates (PHA), as well as different combinations and / or polyester-based thermoplastic polyurethanes.

6. Multi-layer system according to at least one of claims 1 to 5, characterized in that in the case of epoxides, it is a compound based on molecules with two or more epoxide groups per molecule.

7. Multilayer system according to at least one of claims 1 to 6, characterized in that in the case of epoxides it is a compound of formula (IV) frpunn / Lznz / e / YiAi wherein R9, R10 in each case independently of each other represent H or Ci-Cs alkyl, R11 represents Ci-Cs alkyl, xey independently of each other represent an average number from 1 to 20 and yz represents an average number from 2 to 20, the terminal groups R* independently of each other representing H or Ci-Cs alkyl.

8. Multi-layer system according to at least one of claims 1 to 7, characterized in that the amount of carbodiimide in the polyester layer (I) is from 0.5 to 1.5% by weight, with respect to the polyester layer (I).

9. Multi-layer system according to at least one of claims 1 to 7, characterized in that the amount of epoxides in at least one of the polyester layers (II) or (III) ranges from 0.1 to 6% by weight, with respect to the polyester layer (II) or (III).

10. Multi-layer system according to at least one of claims 1 to 8, characterized in that the amount by weight of the polyester layer (I) containing carbodiimide is from 70% by weight to 90% by weight, with respect to the total weight of the multi-layer system.

11. A method for producing a multi-layer system according to any one of claims 1 to 10, characterized in that the polyester layer (I) containing carbodiimide, and the polyester layers (II) and (III) if and when containing epoxide are co-extruded to give a multi-layer system.

12. Method according to claim 11, characterized in that the polyester layer (I) is extruded and around this polyester layer (I) the polyester layers (II) and (III) are extruded by coextrusion.

13. Use of the multi-layer system according to any one of claims 1 to 10 for the production of packaging, protective films, adhesive films, solar cells or medical materials.

14. Solar cell, comprising at least one multi-layer system according to any one of claims 1 to 10.