POLYESTER-FREE LAMINATED ADHESIVE COMPOSITION

Description

[0001] The present invention relates to a 2-component polyurethane adhesive for laminating films, as defined in the appended claim 1, wherein the PU adhesive contains, based on the total weight of the laminating adhesive composition, (a) as resin component at least one NCO-terminated polyurethane prepolymer having a content, based on the total weight of the resin component, of at least 40 wt.% diphenylmethane diisocyanate (MDI), wherein the MDI is 4,4'-diphenylmethane diisocyanate or a mixture thereof with 2,4'-diphenylmethane diisocyanate, and 2 to 20 wt.% polyglycol and (b) as hardener component a polyol mixture comprising at least three different polyols and is free of polyesters.The present invention further relates to the use of the adhesive for bonding films as defined in appended claim 7, to processes for producing composite films as defined in appended claim 8, and to composite films bonded with the described adhesive as defined in appended claim 10.

[0002] Laminating adhesives are well known in the industry. They are solvent-based or solvent-free, cross-linking or physically curing adhesives used to bond thin, flat substrates, such as plastic films, metal foils, paper, or cardboard. It is essential that the bonding only slightly reduces the flexibility of the thin individual layers while still achieving sufficient adhesion. By selecting the individual film layers, it is possible to influence certain properties of these multilayer films, particularly permeability to water and other liquids, chemical resistance, and permeability to oxygen or other gases.Such multilayer films are used to produce, for example, packaging for food in solid, pasty, or liquid form, plastic cutlery, medical materials, chemical products, cosmetics, cleaning agents, and other objects. Furthermore, such laminates are used for technical products such as flexible conductors, electrical insulation materials, sails, and photovoltaic components.

[0003] The above-mentioned areas of application for food products mean that these multilayer films must not contain any substances that could migrate from the packaging into the packaged goods in quantities that are harmful to health. Finally, it is also desirable for the multilayer films to have an appealing visual appearance. In the prior art, two-component systems are particularly well-known as adhesives for such applications. These are mixed before use and then applied to one of the films to be bonded in quantities of typically around 1-5 g / m². By laminating the second film to the adhesive-coated side of the first film, composite films can be obtained after curing. These are used as packaging material, in particular for food products, but also for the other applications mentioned above. Such adhesive systems are usually transparent.

[0004] The systems commonly used in the state of the art consist of NCO-terminated prepolymers with a polyether-polyester-based hardener component. Polyester polyols result in good adhesion to various surfaces, such as metallic layers, especially aluminum-based layers. An unavoidable component in polyester-containing formulations is cyclic esters, which can migrate from the packaging into the packaged food. These are generally, but not always, harmless to humans but can be detected in the human digestive tract. Formulations free of polyester polyols are intended for use in simple laminate structures without metallic layers and as packaging for non-aggressive foods such as olive oil. However, such packaging is not suitable for heating, for example, during pasteurization.WO2014 / 031846, WO2014 / 184270 and WO2016 / 001265 disclose laminating adhesive compositions.

[0005] There is still a need for adhesive systems for composite films that do not contain polyester and are nevertheless stable to heat (e.g. pasteurization temperatures of 90-95 °C for a period of 30 to 45 minutes) and aggressive foodstuffs.

[0006] This object is achieved by a 2-component polyurethane-based laminating adhesive system as defined in the appended claim 1.

[0007] The systems described herein are characterized by good adhesion to metallic layers and low viscosities.

[0008] In a first aspect, the invention therefore relates to a 2-component polyurethane-based laminating adhesive composition containing, based on the total weight of the laminating adhesive composition, (a) as resin component, at least one NCO-terminated polyurethane prepolymer having a content, based on the total weight of the resin component, of at least 40 wt.% diphenylmethane diisocyanate (MDI), wherein the MDI is 4,4'-diphenylmethane diisocyanate or a mixture thereof with 2,4'-diphenylmethane diisocyanate, and 2 to 20 wt.% polyglycol, wherein the polyglycol is polypropylene glycol having a molecular weight of 400 to 700 g / mol, or polyethylene glycol having a molecular weight of 400 to 700 g / mol; and (b) as hardener component, a polyol mixture comprising at least three different polyols, as defined in claim 1, The laminating adhesive composition is free of polyesters.

[0009] In a further aspect, the invention relates to a method for producing composite films according to claim 8, in which at least two identical or different plastic films are bonded using a laminating adhesive composition as described herein, and composite films produced accordingly.

[0010] The invention also covers the use of composite films produced in this way as packaging, in particular for packaging medicines or foodstuffs.

[0011] In yet another aspect, the invention relates to the use according to claim 7 of the laminating adhesive compositions described herein for bonding films.

[0012] Unless otherwise stated, the molecular weights given in this text refer to the number-average molecular weight (Mn). The molecular weight Mn can be determined based on end-group analysis (hydroxyl number according to DIN 53240-1:2013-06) or by gel permeation chromatography (GPC) according to DIN 55672-1:2007-08 using THF as the eluent. Unless otherwise stated, the molecular weights listed are those determined by hydroxyl number. The weight-average molecular weight Mw can also be determined by GPC, as stated above.

[0013] When referring to an ingredient, "at least one" refers to the type of ingredient and not to the absolute number of molecules. "At least one polyol" thus means, for example, at least one type of polyol, meaning that one type of polyol or a mixture of several different polyols may be used. When used in conjunction with weight specifications, the statement refers to all compounds of the specified type contained in the composition / mixture, meaning that the composition contains no further compounds of this type beyond the specified amount of the corresponding compounds.

[0014] Unless explicitly stated otherwise, all percentages given in connection with the compositions described herein refer to % by weight, in each case based on the mixture in question.

[0015] "Approximately" or "ca.", as used herein in connection with a numerical value, refers to the numerical value ±10%, preferably ±5%.

[0016] "Free from," as used herein with reference to polyester, means that the corresponding composition does not contain the stated ingredient or does not contain it as a deliberately added ingredient. The amount of the ingredient in the respective composition is therefore preferably less than 1 wt.%, more preferably less than 0.5 wt.%, even more preferably less than 0.1 wt.%, most preferably less than 0.01 wt.% or below the detection limit.

[0017] Polyurethane adhesives are generally known. They are also used for laminating multilayer films. The adhesives suitable according to the invention are two-component polyurethane adhesives. The adhesives are preferably liquid. The adhesives may contain solvents, but are preferably solvent-free. The crosslinking of the polyurethane adhesives suitable according to the invention is based on the reaction of reactive NCO groups with H-acidic functional groups, for example, OH groups, amino groups, or carboxyl groups. An alternative crosslinking method involves the NCO groups reacting with moisture from the applied adhesive, the substrate, or the environment to form urea groups. These crosslinking reactions are known and can also occur concurrently.To accelerate such reactions, catalysts can be introduced into the adhesive, for example amine, titanium or tin catalysts.

[0018] Surprisingly, it has been shown that the polyester-free two-component (2K) formulations described herein do not reduce the bond strength of selected systems, but in some cases even increase it. This means that the formulations described herein can improve the performance of the adhesives. The mechanical properties can also be improved. It has been found that completely eliminating polyester from the adhesive composition results in low viscosities, which enable rapid passage through application machines. Furthermore, the fogging typical of polyester-containing adhesive compositions, which usually occurs when polyester-containing adhesive compositions pass through the application machine, is prevented.The speed of build-up of bond strength of the formulations described herein is also comparable to or faster than systems known in the prior art.

[0019] The adhesive according to the invention is a two-component (2K) polyurethane adhesive. According to the invention, the adhesive contains at least one NCO-terminated polyurethane prepolymer as the resin component and at least one polyol mixture as the hardener component. The adhesive composition according to the present invention does not contain any polyesters.

[0020] The isocyanate (NCO)-terminated PU prepolymers of the resin component are obtained by reacting a polyol or polyol mixture with a stoichiometric excess of polyisocyanate. The polyols used in the preparation of the prepolymer can be any polyol commonly used for polyurethane synthesis, especially polyether polyols. However, no polyester polyols are used, since the adhesive compositions, as described herein, are free of polyester components.

[0021] Polyether polyols can be prepared from a variety of alcohols containing one or more primary or secondary alcohol groups. Examples of starters used for the preparation of the polyethers include the following compounds or mixtures of these compounds: water, ethylene glycol, propylene glycol, glycerin, butanediol, butanetriol, trimethylolethane, pentaerythritol, hexanediol, 3-hydroxyphenol, hexanetriol, trimethylolpropane, octanediol, neopentyl glycol, 1,4-hydroxymethylcyclohexane, bis(4-hydroxyphenyl)dimethylmethane, and sorbitol. Ethylene glycol, propylene glycol, glycerin, and trimethylolpropane are preferably used, particularly preferably ethylene glycol and propylene glycol, and in a particularly preferred embodiment, propylene glycol is used.

[0022] Suitable cyclic ethers for the preparation of the polyethers described above are alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, styrene oxide, or tetrahydrofuran, or mixtures of these alkylene oxides. Propylene oxide, ethylene oxide, or tetrahydrofuran, or mixtures thereof, are preferably used. Particular preference is given to using propylene oxide or ethylene oxide, or mixtures thereof. Propylene oxide is very particularly preferred.

[0023] The molecular weight of the polyols used to synthesize the prepolymer is preferably in the range of 100 to 20,000 g / mol, especially 330 to 4,500 g / mol. The average functionality can be in the range of 2 to 4.5. The PU prepolymer preferably has a polyether backbone.

[0024] The stoichiometric excess of polyisocyanate in the PU prepolymer, based on the molar ratio of NCO to OH groups, is in particular 1:1 to 1.8:1, preferably 1:1 to 1.6:1 and particularly preferably 1.05:1 to 1.5:1.

[0025] The well-known paint or adhesive polyisocyanates can be used, which are polyisocyanates with two or more isocyanate groups.Suitable polyisocyanates are, for example, 1,5-naphthylene diisocyanate (NDI), 2,4- or 4,4'-diphenylmethane diisocyanate (MDI), hydrogenated MDI (H12MDI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), di- and tetraalkylenediphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,3- or 1,4-phenylene diisocyanate, tolylene diisocyanate (TDI), 1-methyl-2,4-diisocyanato-cyclohexane, 1,6-diisocyanato-2,2,4-trimethylhexane, 1,6-diisocyanato-2,4,4-trimethylhexane, 1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane (IPDI), tetramethoxybutane-1,4-diisocyanate, butane-1,4-diisocyanate, Hexane-1,6-diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane-1,4-diisocyanate, ethylene diisocyanate, methylenetriphenyl triisocyanate (MIT), phthalic acid bis-isocyanatoethyl ester, trimethylhexamethylene diisocyanate, 1,4-diisocyanatobutane, 1,12-diisocyanatododecane and dimer fatty acid diisocyanate.

[0026] Suitable isocyanates with at least trifunctionality are polyisocyanates formed by trimerization or oligomerization of diisocyanates or by the reaction of diisocyanates with low-molecular-weight, polyfunctional compounds containing hydroxyl or amino groups. Commercially available examples include trimerization products of the isocyanates HDI, MDI, or IPDI, or adducts of diisocyanates and low-molecular-weight triols, such as trimethylolpropane or glycerol. Further examples are isocyanurates of hexamethylene diisocyanate (HDI) and isocyanurates of isophorone diisocyanate (IPDI).

[0027] In principle, aliphatic, cycloaliphatic, or aromatic isocyanates can be used, but aromatic diisocyanates are particularly suitable. A particularly preferred aromatic diisocyanate is 4,4-methylenediphenyl diisocyanate, which can be used either alone or in a mixture with 2,4-methylenediphenyl diisocyanate. The PU adhesives according to the invention can contain the isocyanates reacted as PU prepolymers or they can contain at least a proportion of low-molecular-weight, optionally oligomeric, isocyanates.

[0028] PU prepolymers can be produced from the above-mentioned polyols and polyisocyanates in a known manner. An NCO-containing prepolymer can be produced from the polyols and isocyanates. Examples of such prepolymers are described in EP-A951493, EP-A1341832, EP-A 150444, EP-A 1456265, and WO 2005 / 097861.

[0029] The at least one NCO-terminated PU prepolymer is preferably an aromatic isocyanate-terminated, more preferably MDI-terminated polyurethane prepolymer made from one or more polyether polyol(s) and an aromatic diisocyanate, such as MDI.

[0030] According to the present invention, the resin component of the adhesive composition has a content of at least 40 wt.% based on the total weight of the resin component

[0031] Diphenylmethane diisocyanate (MDI) and 2 to 20 wt.% polyglycol. The MDI is 4,4'-diphenylmethane diisocyanate or a mixture thereof with 2,4'-diphenylmethane diisocyanate. 2,2'-Diphenylmethane diisocyanate is preferably not present or is present only in comparatively small amounts, i.e., less than 2 wt.%, preferably less than 1 wt.%, based on the total weight of the resin component.

[0032] The polyglycol in the resin component is polypropylene glycol with a molecular weight of 400 to 700 g / mol, or is polyethylene glycol with a molecular weight of 400 to 700 g / mol.

[0033] The corresponding prepolymers typically have an NCO content of 5-20 wt.% (determined according to Spiegelberger, DIN EN ISO 11909:2007-05) and an average NCO functionality of 2 to 3.

[0034] Due to the excess of isocyanate used, the NCO-terminated PU prepolymers usually contain certain amounts of isocyanate monomers, ie in particular aromatic polyisocyanate monomers, such as MDI, typically in amounts of 0.1 to 25 wt.% based on the total weight of prepolymers and monomers.

[0035] The molecular weight (Mn) of the prepolymer is in the range from 1500 g / mol to 100,000 g / mol, particularly preferably from 2000 g / mol to 50,000 g / mol.

[0036] In addition to the resin component, the binder system according to the invention contains a hardener component. According to the present invention, the hardener component comprises at least three different polyols.

[0037] Suitable polyols are aliphatic and / or aromatic alcohols with 2 to 6, preferably 2 to 4, OH groups per molecule. The OH groups can be primary or secondary.

[0038] Suitable aliphatic alcohols include, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, and their higher homologues or isomers. Higher-functional alcohols such as glycerol, trimethylolpropane, pentaerythritol, and oligomeric ethers of the above-mentioned substances are also suitable. The polyol components used are preferably reaction products of low-molecular-weight polyfunctional alcohols with alkylene oxides. The alkylene oxides preferably have 2 to 4 carbon atoms. Suitable examples are the reaction products of ethylene glycol, propylene glycol, the isomeric butanediols, hexanediols, or 4,4'-dihydroxydiphenylpropane with ethylene oxide, propylene oxide, or butylene oxide, or mixtures of two or more thereof.Furthermore, the reaction products of polyfunctional alcohols, such as glycerol, trimethylolethane or trimethylolpropane, pentaerythritol or sugar alcohols, or mixtures of two or more thereof, with the aforementioned alkylene oxides to form polyether polyols are also suitable. Other polyols commonly used in the invention are formed by polymerizing tetrahydrofuran (poly-THF). Polyethers modified with vinyl polymers are also suitable for use as polyol components. Such products are obtainable, for example, by polymerizing styrene or acrylonitrile, or a mixture thereof, in the presence of polyethers.

[0039] Polyacetals are also suitable as polyol components. Polyacetals are understood to be compounds obtainable from glycols, for example, diethylene glycol or hexanediol, or their mixtures with formaldehyde. Polyacetals usable in the context of the invention can also be obtained by the polymerization of cyclic acetals.

[0040] Another group of polyols can be OH-functional polyurethane polyols, for example OH-terminated polyurethane prepolymers.

[0041] The hardener component contains a triol, in particular based on glycerol or trimethylolpropane (TMP), to which alkylene oxide (AO), in particular propylene oxide (PO), is added and which has a molecular weight M w of less than 700 g / mol, preferably 400 to <700 g / mol, more preferably 450 to <700 g / mol. In some embodiments, the hardener component of the composition according to the invention comprises 5 to 90 wt. %, preferably 15 to 60 wt. %, in particular 25 to 40 wt. % of at least one such triol. According to some embodiments, this at least one triol can in particular be a propylene oxide (PO)-based triol, such as a glycerol- or TMP-initiated molecule to which propylene oxide is added. According to preferred embodiments, the at least one triol is a propylene oxide-based triol having a molecular weight M w of at least 400, in particular at least 450 to <700 g / mol.

[0042] The hardener component additionally contains an aliphatic di- or polyhydric, preferably di- to tetrahydric, alcohol, preferably with a molecular weight <150 g / mol and / or preferably with a hydroxyl number of 700-2000 mgKOH / g, more preferably 1200-1900 mgKOH / g. In some embodiments, the hardener component of the composition according to the invention comprises 0.5 to 10 wt. %, preferably 2 to 8 wt. %, in particular 3 to 7 wt. % of at least one such aliphatic alcohol. According to some embodiments, this at least one aliphatic alcohol can be an aliphatic alcohol selected from the group consisting of ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, glycerin, trimethylolpropane, and pentaerythritol. In some embodiments, the at least one aliphatic alcohol is in particular trimethylolpropane.

[0043] The hardener component additionally contains higher molecular weight AO-based triols, which are defined as above but have a molecular weight M w of more than 700 g / mol, preferably >700 to 1200 g / mol, or castor oil. In some embodiments, the hardener component of the composition according to the invention comprises 5 to 80 wt. %, preferably 15 to 70 wt. %, in particular 20 to 65 wt. % of such triols or castor oil.

[0044] The hardener component contains all three of the aforementioned polyols, i.e. (1) at least one triol, in particular based on glycerol or trimethylolpropane (TMP), to which alkylene oxide (AO), in particular propylene oxide (PO), is added and which has a molecular weight M w of less than 700 g / mol, preferably 400 to <700 g / mol, more preferably 450 to <700 g / mol; (2) at least one aliphatic di- or polyhydric, preferably 2- to 4-hydric, preferably monomeric alcohol; and (3) at least one triol, in particular based on glycerol or trimethylolpropane (TMP), to which alkylene oxide (AO), in particular propylene oxide (PO), is added and which has a molecular weight M w of more than 700 g / mol, preferably >700 to 1200 g / mol, or castor oil. Such triols are commercially available as Voranol ®< CP 755 or CP 1055 (Dow Chemical).

[0045] In some embodiments, the NCO:OH ratio of resin component to hardener component is less than 1.4, preferably less than 1.3, in particular less than 1.25, more preferably 1.0 to 1.2.

[0046] In various embodiments, the binder system described herein may further comprise at least one catalyst, in particular selected from metal catalysts based on Sn or Ti or amine catalysts. Suitable catalysts are known in the art. The catalyst is preferably present in the curing component, ie, in the systems preferred according to the invention, in the hydroxy-functionalized component.

[0047] Furthermore, the adhesive according to the invention may contain the usual additives. Other components include, for example, resins (tackifiers), stabilizers, crosslinking agents or viscosity regulators, pigments, plasticizers, or antioxidants.

[0048] The polyurethane adhesives of the invention are liquid at application temperatures. It is preferred that the PU adhesives of the invention be liquid at room temperature. The compositions described herein, in various embodiments, have a viscosity of 500 to 5000, in particular 600 to 900 mPas, at a temperature of 40°C, determined according to DIN ISO 2555 (Brookfield RVT viscometer, spindle no. 4, 25°C; 5 rpm).

[0049] The adhesives described herein may contain solvents or be solvent-free. In principle, all solvents known to the person skilled in the art can be used as solvents, in particular esters, ketones, halogenated hydrocarbons, alkanes, alkenes, and aromatic hydrocarbons. Examples of such solvents are methylene chloride, trichloroethylene, toluene, xylene, butyl acetate, amyl acetate, isobutyl acetate, methyl isobutyl ketone, methoxybutyl acetate, cyclohexane, cyclohexanone, dichlorobenzene, diethyl ketone, diisobutyl ketone, dioxane, ethyl acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monoethyl acetate, 2-ethylhexyl acetate, glycol diacetate, heptane, hexane, isobutyl acetate, isooctane, isopropyl acetate, methyl ethyl ketone, tetrahydrofuran, or tetrachloroethylene, or mixtures of two or more of the solvents mentioned.

[0050] However, in preferred embodiments, the adhesive compositions described herein are substantially free of organic solvents.

[0051] The adhesives are applied to the substrates to be bonded, especially films, using conventional equipment and all common application methods, for example, by spraying, doctor blade coating, 3-4-roller applicators in the case of a solvent-free system, or 2-roller applicators in the case of a solvent-based system. After application, the substrates to be bonded are bonded together in a known manner. It is advisable to use elevated temperatures if necessary to achieve better application and faster crosslinking. However, the adhesives of the invention exhibit very good curing even at room temperature or only slightly elevated temperatures, such as 40°C.

[0052] The polyurethane adhesives according to the invention are particularly suitable as laminating adhesives for films. They can be used in a process in which known films based on polymers such as PP, PE, OPA, polyamide, PET, polyester, or metal foils are bonded together. The adhesive according to the invention is applied to a possibly pretreated or printed film. The application rate is typically 1-5 g / m². This can take place at elevated temperature to achieve a thin and uniform coating. A second film of the same or a different material is then laminated on under pressure. The film can be heated, the adhesive crosslinks, and a multilayer film is created. This can optionally consist of more than two layers.

[0053] Typically, the films are stored after production. During this time, the adhesives of the invention may continue to crosslink.

[0054] By using the liquid or hot melt adhesives according to the invention as laminating adhesives, it is possible to obtain laminated two- or multi-layer films that meet the high requirements for suitability for food or medical packaging.

[0055] All embodiments disclosed herein in connection with the PU adhesive are of course also applicable to the described uses and methods and vice versa.

[0056] The invention will be explained in more detail below using a few examples. The amounts given are percentages by weight unless otherwise stated. Examples Example 1 (according to the invention) Resin base:

[0057] NCO-terminated MDI prepolymer with an NCO content of 13-15 wt.% and an NCO:OH ratio of 4.3:1, consisting of 50 wt.% 4,4'-diphenylmethane diisocyanate (MDI); 15 wt.% polypropylene glycol (PPG) with Mw=400 g / mol; 25 wt.% polypropylene glycol (PPG) with Mw=1000 g / mol; 10 wt.% hexane-1,6-diisocyanate (HDI) trimer. Hardener:

[0058] Polyol mixture with an OH value of 210-250 mgKOH / g and a functionality f=3, consisting of 30 wt.% trifunctional polypropylene glycol (PPG) with Mw=450 g / mol; 70 wt.% castor oil. Resin:hardener mixing ratio 100:70 parts by weight. Example 2 (according to the invention) Resin base:

[0059] NCO-terminated MDI prepolymer with an NCO content of 13-15 wt.% and an NCO:OH ratio of 4.0:1, consisting of 50 wt.% 4,4'-diphenylmethane diisocyanate (MDI); 10 wt.% polypropylene glycol (PPG) with Mw=400 g / mol; 30 wt.% polypropylene glycol (PPG) with Mw=1000 g / mol; 10 wt.% toluene diisocyanate (TDI) prepolymer*. Hardener:

[0060] Polyol mixture with an OH value of 330-370 mgKOH / g and a functionality f=3, consisting of 5 wt% trimethylolpropane; 70 wt% trifunctional polypropylene glycol (PPG) with Mw=450 g / mol; 25 wt% castor oil.

[0061] *TDI prepolymer: reaction product of 2,4'-TDI with a polyetherdiol with Mw=400...1000, demonomerized. Mixing ratio resin:hardener 100:35 parts by weight Example 3 (according to the invention) Resin base:

[0062] NCO-terminated MDI prepolymer with an NCO content of 12-14 wt% and an NCO:OH ratio of 3.9:1, consisting of 50 wt% 4,4'-diphenylmethane diisocyanate (MDI); 5 wt% polypropylene glycol (PPG) with Mw=400 g / mol; 25 wt% polypropylene glycol (PPG) with Mw=1000 g / mol; 10 wt% polypropylene glycol (PPG) with Mw=2000 g / mol; 10 wt% hexane-1,6-diisocyanate (HDI) trimer. Hardener:

[0063] Polyol mixture with an OH value of 330-370 mgKOH / g and a functionality f=3, consisting of 5 wt% trimethylolpropane; 70 wt% trifunctional polypropylene glycol (PPG) with Mw=450 g / mol; 25 wt% castor oil. Mixing ratio resin:hardener 100:40 parts by weight Example 4 (according to the invention) Resin base:

[0064] NCO-terminated MDI prepolymer with an NCO content of 11-13 wt.% and an NCO:OH ratio of 4.3:1, consisting of 55 wt.% 4,4'-diphenylmethane diisocyanate (MDI); 5 wt.% polypropylene glycol (PPG) with Mw=400 g / mol; 30 wt.% polypropylene glycol (PPG) with Mw=1000 g / mol; and 10 wt.% polypropylene glycol (PPG) with Mw=2000 g / mol. Hardener:

[0065] Polyol mixture with an OH value of 330-370 mgKOH / g and a functionality f=3, consisting of 5 wt% trimethylolpropane; 70 wt% trifunctional polypropylene glycol (PPG) with Mw=450 g / mol; 25 wt% castor oil. Mixing ratio resin:hardener 100:38 parts by weight Example 5 (comparison example) Resin base:

[0066] NCO-terminated MDI prepolymer with an NCO content of 11-13 wt.% and an NCO:OH ratio of 4.3:1, consisting of 50 wt.% 4,4'-diphenylmethane diisocyanate (MDI); 10 wt.% hexane-1,6-diisocyanate (HDI) trimer; 20 wt.% polypropylene glycol (PPG) with Mw=1000 g / mol; and 20 wt.% polypropylene glycol (PPG) with Mw=2000 g / mol. Hardener:

[0067] Polyol mixture with an OH value of 210-250 mgKOH / g and a functionality f=3, consisting of 30 wt% trifunctional polypropylene glycol (PPG) with Mw=450 g / mol; 70 wt% castor oil. Mixing ratio resin:hardener 100:60 parts by weight Example 6 (comparison example) Resin base:

[0068] NCO-terminated MDI prepolymer with an NCO content of 12-14 wt.% and an NCO:OH ratio of 3.4:1, consisting of 55 wt.% 4,4'-diphenylmethane diisocyanate (MDI); 15 wt.% polypropylene glycol (PPG) with Mw=1000 g / mol; 15 wt.% polypropylene glycol (PPG) with Mw=400 g / mol; 15 wt.% bifunctional polyester*. Hardener:

[0069] Polyol mixture with an OH value of 200-230 mgKOH / g and a functionality of f~2.3, consisting of 75 wt% bifunctional polyester*; 22 wt% polypropylene glycol (PPG) triol with Mw=450 g / mol; 3 wt% trimethylolpropane. Mixing ratio resin:hardener 100:60 parts by weight

[0070] *Polyester based on isophthalic acid, adipic acid, 1,2-propanediol, diethylene glycol. Example 7 (comparison example) Resin base:

[0071] NCO-terminated MDI prepolymer with an NCO content of 13-15 wt.% and an NCO:OH ratio of 3.7:1, consisting of 51 wt.% 4,4'-diphenylmethane diisocyanate (MDI); 10 wt.% hexane-1,6-diisocyanate (HDI) trimer; 13 wt.% polypropylene glycol (PPG) with Mw=1000 g / mol; 13 wt.% polypropylene glycol (PPG) with Mw=400 g / mol; 13 wt.% bifunctional polyester*. Hardener:

[0072] Polyester blend with an OH value of 200-230 mgKOH / g and a functionality of f~2.3, consisting of 75 wt% bifunctional polyester*; 22 wt% polypropylene glycol (PPG) triol with Mw=450 g / mol; 3 wt% trimethylolpropane.

[0073] *Polyester based on isophthalic acid, adipic acid, 1,2-propanediol, diethylene glycol. Mixing ratio resin:hardener 100:65 parts by weight Composite film:

[0074] The composite films are produced, for example, using a Super Combi 2000 laminator. The adhesive composition is applied at a rate of approximately 2 g / m² to one of the films to be bonded (OPA or metOPP), and this film is then laminated to the second film (PE or OPP) under pressure. The effective roller pressure of the laminator corresponds to a force of up to 200 N (20 kg). Joint liability:

[0075] The bond strength is determined in accordance with DIN 53357 after 14 days of curing at room temperature using an Instron tensile testing machine (Instron 4301). Sample strips of the composite film (sample width: 15 mm) are clamped between clamping jaws and then pulled apart at a peel speed of 100 m / min, a peel angle of 90°, and a peel length of 5 to 10 cm. The average value of a triplicate determination of the maximum force applied is reported, based on the sample width of 15 mm. Composite materials:

[0076] OPA: oriented polyamide PE: polyethylene PET: polyethylene terephthalate OPP: oriented polypropylene metOPP: metallized OPP (OPP coated with aluminum) Al: aluminum foil CPP: cast polypropylene Table 1: Experimental parameters parameter Widest range Narrowest area 1 Adhesion spectrum: Bond strength on PET / AI / PE >3 N / 15 mm after 14 days 3-9 N / 15mm after 14 days PET...Al > 3 N / 15 mm 3-4 N / 15 mm AI...PE >2 N / 15 mm 2-6 N / 15 mm PET / AI / CPP >4 N / 15mm after 14 days 4-6 N / 15mm after 14 days 2 Duration: a. Pot life curve (viscosity increase vs. time) a. Initial mixed viscosity <1000 mPas at 40 °C a. 600-900 mPas at 40 °C b. V = 300-350 m / min b. Experimental test: on lamination equipment 9 b. Super Combi machine >300 m / min without fogging 3 Bond strength after thermal treatment: OPA pr 14µ / PE 50µ >3 N / 15mm without any delamination after pasteurization 30 min 90 °C 3-5 N / 15mm without any delamination after pasteurization 30 min 90 °C 4 Filling material resistance: bond strength on PET / AI / PE Bubble bath: > 1 N / 15mm after 14d / 40 °C in chambers, olive oil: > 2 N / 15mm after 14d / 40 °C in chambers Bubble bath: 1-3 N / 15mm Olive oil: 2-5 N / 15mm

Claims

1. A polyurethane-based 2-component laminating adhesive composition containing, based on the total weight of the laminating adhesive composition, (a) as a resin component, at least one NCO-terminated polyurethane prepolymer having a content, based on the total weight of the resin component, of at least 40 wt.% diphenylmethane diisocyanate (MDI), the MDI being 4,4'-diphenylmethane diisocyanate or a mixture thereof with 2,4'-diphenylmethane diisocyanate, and 2 to 20 wt.% polyglycol, the polyglycol being polypropylene glycol having a molecular weight of 400 to 700 g / mol or polyethylene glycol having a molecular weight of 400 to 700 g / mol; and (b) as a curing component, a polyol mixture comprising at least three different polyols, the laminating adhesive composition being free of polyesters, characterized in that the curing component contains: (1) at least one triol to which alkylene oxide (AO) is added and which has a molecular weight Mw of less than 700 g / mol; (2) at least one aliphatic di- or polyhydric alcohol; and (3) at least one triol to which alkylene oxide (AO) is added and which has a molecular weight Mw of more than 700 g / mol, or castor oil.

2. The laminating adhesive composition according to claim 1, characterized in that one of the at least three different polyols of the curing component is a triol to which alkylene oxide (AO) is added and which has a molecular weight Mw of less than 700 g / mol, which is contained in the curing component at 5 to 90 wt.%.

3. The laminating adhesive composition according to at least one of claims 1 to 2, characterized in that one of the at least three different polyols of the curing component is an aliphatic, di- or polyhydric alcohol which is contained in the curing component at 0.5 to 10 wt.%.

4. The laminating adhesive composition according to at least one of claims 1 to 3, characterized in that one of the at least three different polyols of the curing component is a triol to which alkylene oxide (AO) is added and which has a molecular weight Mw of 700 to 1200 g / mol, or is castor oil, which is contained in the curing component at 5 to 80 wt.%.

5. The laminating adhesive composition according to one of claims 1 to 4, characterized in that the NCO:OH ratio of resin component to curing component is less than 1.4.

6. The laminating adhesive composition according to at least one of claims 1 to 5, characterized in that (a) the composition further contains at least one catalyst and / or (b) the composition has a viscosity of 500 to 5000 mPas at a temperature of 40 °C, determined in accordance with DIN ISO 2555; and / or (c) the composition is free of organic solvents.

7. The use of the laminating adhesive composition according to at least one of claims 1 to 6 for bonding films.

8. A method for producing composite films, characterized in that at least two identical or different plastics films are bonded over part or all of the surface using a laminating adhesive composition according to one or more of claims 1 to 6.

9. The method according to claim 8, characterized in that the laminating adhesive composition is applied to at least one of the surfaces to be adhesively bonded of the films to be adhesively bonded in an amount of 1 to 5 g / m2.

10. A composite film produced by the method according to at least one of claims 8 to 9.

11. The use of a composite film according to claim 10 as packaging.