Retortable solvent-free lamination adhesive

Abstract

The present invention relates to a solventless two-component adhesive kit comprising an isocyanate-functionalized aliphatic polyurethane prepolymer and a polyol crosslinker. The present invention also relates to a laminating adhesive comprising the components of the adhesive kit of the present invention, and a retort pouch containing the same.

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority from EP Application 22209746.1, the contents of which are incorporated herein by reference.

[0002] This invention relates to a solvent-free two-component adhesive and the use of the adhesive in providing laminates for retort applications. [Background technology]

[0003] Retort processing is a well-known process in the packaging industry, in which a sealed bag containing moist food is treated at temperatures typically exceeding 100°C to both cook and sterilize the food.

[0004] Solvent-based adhesives are used in retort applications because they provide adhesive strength between layers of packaging laminates under retort conditions, ensuring the integrity of the laminates without delamination defects. In particular, solvent-based adhesives have high resistance to thermal degradation, partly because they allow the use of high-molecular-weight starting materials that construct a stronger network less prone to forming mobile low-molecular-weight species during thermal decomposition. The solvent maintains the appropriate viscosity of the composition used for lamination, which would otherwise increase as a result of incorporating high-molecular-weight materials.

[0005] Therefore, it is desirable to provide alternative solvent-free adhesives for retort applications in order to eliminate the need to handle volatile solvents such as ethyl acetate and methyl ethyl ketone (MEK). Furthermore, using solvent-free adhesives can achieve higher lamination press speeds.

[0006] Solvent-free adhesives are known in the art. However, the absence of solvents necessitates limiting the molecular weight of the constituent elements to provide compositions with a viscosity suitable for lamination. While low molecular weight species can provide low viscosity compositions, they may migrate through the composition and potentially contaminate food they come into contact with.

[0007] One method for providing lower viscosity adhesive compositions and reducing the amount of migratory species present in the adhesive is to remove residual isocyanate monomers using, for example, evaporation techniques. EP3176196 relates to a one-component laminating adhesive comprising an aromatic isocyanate polyurethane prepolymer, wherein the amount of free diisocyanate monomers in the polyurethane prepolymer is reduced to less than 0.1% (w / w) using a thin-film evaporator. Residual diisocyanate monomers are removed at 140°C under a pressure of 0.1 mbar or less. However, EP3176196 does not disclose two-component adhesives having different requirements than one-component adhesives, such as the adhesive according to the present invention comprising an aliphatic polyurethane prepolymer. Furthermore, EP3176196 does not disclose that these adhesive compositions are suitable for preparing flexible packaging laminates for the manufacture of retort pouches.

[0008] US5202001 discloses the use of a thin-film evaporator to remove aromatic diisocyanate (TDI-toluene diisocyanate) from isocyanate-functionalized polyurethane prepolymers. The use of aromatic isocyanates in the production of polyurethane prepolymers is undesirable due to the risks associated with the formation of potentially harmful primary aromatic amines that may occur under retort conditions. Furthermore, US5202001 does not relate to adhesive compositions and does not disclose adhesives according to the present invention that include aliphatic polyurethane prepolymers. Furthermore, US5202001 does not disclose the use of adhesives in the preparation of retortable laminates.

[0009] Numerous prior art documents describe reducing the amount of residual diisocyanate monomers present in polyurethane prepolymers by distillation in the presence of a solvent called an "inert solvent." In this regard, US20030065124 discloses the removal of free diphenylmethane diisocyanate (MDI) by vacuum distillation using a wipe-type membrane evaporator. In this process, dimethyl phthalate, which has a boiling point lower than that of MDI, is used as the "inert solvent." Similarly, WO2018013688 relates to a polyurethane prepolymer prepared from aromatic paraphenylenediisocyanate (PPDI), in which free monomers are also removed using a wipe-type membrane evaporator. In this case, dimethyl adipate is used as the "inert solvent."

[0010] Neither US20030065124 nor WO2018013688 relate to adhesive compositions and therefore do not disclose the two-component adhesive according to the present invention that includes an aliphatic polyurethane prepolymer. Furthermore, these documents do not disclose the use of such adhesives in the preparation of laminates suitable for retort applications. Moreover, in contrast to the aliphatic polyurethane isocyanate-functionalized prepolymer of the present invention, the polyurethane prepolymers of US20030065124 and WO2018013688 are prepared using solvents; i.e., they are not solvent-free.

[0011] CN110922929 relates to a one-component isocyanate-functionalized polyurethane prepolymer adhesive that can be used in the manufacture of flexible laminates. CN110922929 does not relate to a two-component adhesive and does not disclose reducing the amount of free isocyanate monomer to less than 0.1% (w / w) of the polyurethane prepolymer component. Furthermore, there is no teaching on a method for maintaining the viscosity of the disclosed composition at a level suitable for use in a laminating machine while removing residual isocyanate monomer. CN110922929 does not disclose the use of a wipe-type film evaporator. Furthermore, CN110922929 does not teach that a laminate adhesive with improved adhesive strength under retort conditions can be obtained by using an aliphatic polyurethane precursor. Furthermore, the one-component CN110922929 composition contains a large amount of catalyst to function, resulting in a significantly reduced pot life and making it unsuitable for use in a two-component adhesive kit.

[0012] CN102604583B relates to a solvent-free two-component adhesive that can be used in the manufacture of flexible laminates that can withstand boiling. However, CN102604583B does not disclose reducing the amount of free isocyanate monomer to less than 0.1% (w / w) of the polyurethane prepolymer component, nor does it teach a method for maintaining the viscosity of the disclosed composition at a level suitable for use in a laminating machine while also removing residual isocyanate monomer. Furthermore, CN102604583B does not disclose the use of a wipe-type film evaporator. In addition, a reactive silane is an essential component of the CN102604583B adhesive. Finally, CN102604583B does not evaluate the disclosed adhesive under retort conditions. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] EP3176196 [Patent Document 2] US5202001 [Patent Document 3] US20030065124 [Patent Document 4] WO2018013688 [Patent Document 5] CN110922929 [Patent Document 6] CN102604583B [Overview of the project] [Problems that the invention aims to solve]

[0014] To the best of our knowledge, no successful use of a solvent-free two-component lamination adhesive suitable for retort applications, comprising an aliphatic polyurethane prepolymer containing less than 0.1% (w / w) of free isocyanate monomers, has been disclosed. Therefore, the solvent-free lamination adhesive kit of the present invention is advantageous in at least this respect. Further advantages related to the solvent-free lamination adhesive kit of the present invention are described herein. [Means for solving the problem]

[0015] The present invention provides a solvent-free lamination adhesive kit comprising an isocyanate-functionalized aliphatic polyurethane prepolymer containing monomer units derived from an aliphatic isocyanate monomer, and a polyol crosslinking agent. The amount of free isocyanate monomer present in the polyurethane prepolymer is 0.1% (w / w) or less of the prepolymer. The aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, methylene dicyclohexyl diisocyanate, xylylene diisocyanate, tetramethyl xylylene diisocyanate, pentamethylene diisocyanate, and combinations thereof.

[0016] The adhesive kit of the present invention is a two-component adhesive kit, that is, it contains an isocyanate-functionalized prepolymer in addition to a polyol crosslinking agent.

[0017] The present invention further provides a laminated adhesive comprising components of the solventless laminated adhesive kit of the present invention mixed in a single composition. The present invention further provides a retort pouch comprising a laminated adhesive formed from components of the kit of the present invention.

[0018] The present invention further provides a method for providing a multi-layered structure, comprising forming a laminated adhesive from components of the kit of the present invention and applying this composition onto a flexible film.

[0019] The present invention further provides a method for manufacturing the kit of the present invention, comprising: a) reacting an aliphatic isocyanate with a polyester and / or a polyether polyol to obtain an isocyanate-functionalized aliphatic polyurethane prepolymer containing monomer units derived from the aliphatic isocyanate monomer; b) reducing the residual isocyanate monomer present in the prepolymer to less than 0.1% (w / w) of the prepolymer; and c) introducing a polyol crosslinking agent into the kit.

[0020] The present invention further provides the use of the kit of the present invention for forming a laminated adhesive. The present invention further provides the use of the kit of the present invention for improving the adhesion strength under retort conditions of a multi-layered structure formed from a flexible film and a laminated adhesive formed from the kit of the present invention. This improvement is compared with a multi-layered structure formed from the same flexible film and a laminated adhesive that is not formed from the kit of the present invention. The adhesion strength is the strength required to separate at least two layers of the multi-layered structure joined by the adhesive, and is measured at room temperature (25 °C) and 100 mm / min.

Embodiments for Carrying out the Invention

[0021] Definitions Aromatic monomer = a monomer in which a polymerizable functional group is directly bonded to an aromatic group. Aliphatic monomer = a monomer in which the polymerizable functional group(s) is not directly bonded to an aromatic group. Aromatic isocyanates = Isocyanates containing at least one isocyanate group (-NCO) directly bonded to an aromatic ring. Aliphatic isocyanates are isocyanates in which the isocyanate group (-NCO)(or more) is not directly bonded to an aromatic ring. Aliphatic isocyanates include alicyclic isocyanates. Therefore, aliphatic isocyanates can contain an aromatic ring as long as the isocyanate group(s)(or more) is not directly bonded to the aromatic ring. For example, xylylene diisocyanate. Aromatic polyurethane = polyurethane formed from aromatic isocyanates. Those skilled in the art will understand that the properties of a polyurethane, whether aliphatic or aromatic, are determined solely by the characteristics of the isocyanate (whether aliphatic or aromatic). For the purposes of this invention, an aliphatic polyurethane prepolymer is derived from 95 mol% or more of aliphatic isocyanate monomers relative to the total number of moles of isocyanate monomers incorporated into the prepolymer. Aliphatic polyurethane = polyurethane formed from aliphatic isocyanates. Those skilled in the art will understand that the properties of a polyurethane, whether aliphatic or aromatic, are determined solely by the characteristics of the isocyanate (whether aliphatic or aromatic). For the purposes of the present invention, an aliphatic polyurethane prepolymer is derived from 95 mol% or more of aliphatic isocyanate monomers relative to the total number of moles of isocyanate monomers incorporated into the prepolymer. Aromatic-aliphatic polyurethane = polyurethane formed from aromatic isocyanates and aliphatic isocyanates. For the purposes of the present invention, the aromatic-aliphatic polyurethane prepolymer contains, with respect to the total number of moles of isocyanate monomers incorporated into the prepolymer, more than 5 mol% and less than 95 mol% of aromatic isocyanate monomers, and more than 5 mol% of aromatic isocyanate monomers. It is derived from aliphatic isocyanate monomers in an amount of less than 95 mol%. Aromatic carboxylic acid = A carboxylic acid containing at least one acid (-COOH) group directly bonded to an aromatic ring. Aliphatic carboxylic acids are carboxylic acids in which the carboxylic acid group (-COOH) (or more) is not directly bonded to an aromatic ring. Aliphatic carboxylic acids include alicyclic carboxylic acids. Therefore, an aliphatic carboxylic acid can contain an aromatic ring as long as the carboxylic acid group (or more) is not directly bonded to the aromatic ring. Free isocyanate monomers are isocyanate monomer species that have not undergone reaction with comonomers, such as polyols. For example, unreacted starting materials from polymerization reactions used to form polyurethane prepolymers. Solvent-free = Contains any solvent at a concentration of 5 wt% or less. Retort pouch = A type of food packaging material made from laminated flexible plastic. Retort conditions = A method for cooking and sterilizing retort-packaged foods. Typically, this requires heating at a rising temperature, for example, 115-125°C, for a certain period of time, for example, 20-60 minutes. A two-part adhesive is an adhesive composition containing two components, in which one component induces crosslinking of the other component. A one-component adhesive is an adhesive product containing a single component, and crosslinking usually occurs through a reaction with residual moisture. PET = Polyethylene terephthalate PE = Polyethylene ALU = Aluminum CPP = Cast Polypropylene OPA = Nylon AlOx = Aluminum Oxide SiOx = silicon dioxide OPP = Oriented Polypropylene OPE = Oriented polyethylene LDPE = Low-density polyethylene LLDPE = Linear Low-Density Polyethylene VM-PET = Vacuum-deposited polyethylene terephthalate Methylenedicyclohexyl diisocyanate includes isomers, 1-isocyanato-1-[(1-isocyanatocyclohexyl)methyl]cyclohexane, and 4,4-diisocyanatodicyclohexylmethane. Xylylene diisocyanate includes its positional isomers.

[0022] Unless otherwise specified, all ranges include their respective endpoints. For example, the range from 3 to 9 includes endpoints 3 and 9. However, if an endpoint is defined as being "greater than" one value and / or "less than" another, the range does not include those endpoints.

[0023] Unless otherwise specified, wt%(w / w) refers to the mass of that component relative to the total mass of all components present in the composition.

[0024] The wt% (w / w) of the free isocyanate monomer is the mass of the species relative to the total mass of the polyurethane prepolymer derived from the monomer.

[0025] This invention The present invention provides an improved two-component, solvent-free lamination adhesive kit comprising an aliphatic polyurethane prepolymer. The adhesive kit of the present invention is suitable for preparing flexible packaging laminates that may be used in retort applications.

[0026] To the best of our knowledge, this invention is the first reported example of using a solvent-free aliphatic two-component laminating adhesive to prepare flexible multilayer laminates for retort applications, in which the laminate can withstand heat treatment temperatures of 100°C or higher.

[0027] The two-component solvent-free lamination adhesive kit of the present invention comprises an aliphatic isocyanate-functionalized polyurethane prepolymer, which is produced from an aliphatic isocyanate monomer such as diisocyanate. The amount of residual monomer in the polyurethane prepolymer for use in the present invention is less than 0.1% (w / w) of the prepolymer. The amount of residual monomer can be reduced by using an evaporator (e.g., a wipe-type film evaporator). The adhesive of the present invention is particularly suitable for preparing flexible packaging laminates used in the manufacture of retortable, pasteurizable, and boilable pouches.

[0028] Therefore, the kit of the present invention can be used to improve the adhesive strength under retort conditions of a multi-layer structure formed from a flexible film and a laminating adhesive formed from the components of the kit of the present invention. The improved adhesive strength relates to improved peel resistance of the laminate structure compared to a comparative laminate structure formed from the same flexible film and laminating adhesive but not from the components of the kit of the present invention.

[0029] Retorting conditions include heating at a temperature of 100°C or higher for 20 minutes, for example, heating at 120°C for 30 minutes, or heating at 135°C for 20 minutes. Retorting conditions can create a pressure difference between the pressure inside the retort packaging and atmospheric pressure, potentially putting stress on the adhesive used to seal the retort packaging. For example, a low-retort test may involve heating the retort pouch in an autoclave at approximately 120°C for at least 30 minutes, in which case the autoclave pressure is approximately 1.5 bar. A high-retort test may involve heating the retort pouch in an autoclave at approximately 135°C for at least 20 minutes, in which case the autoclave pressure is approximately 2.6 bar.

[0030] Advantages associated with the present invention The inventors have found that by incorporating an aliphatic polyurethane prepolymer, for use in the present invention, which contains monomer units derived from aliphatic isocyanate monomers, into a solvent-free lamination adhesive, an adhesive with improved adhesion under retort conditions can be obtained. This improvement is observed compared to a comparative adhesive containing an aromatic polyurethane prepolymer containing monomer units derived from aromatic isocyanate monomers.

[0031] The adhesive kit of the present invention is also improved compared to a comparative adhesive kit containing a polyurethane prepolymer with a residual isocyanate monomer content greater than that required by the present invention.

[0032] The aliphatic two-component solvent-free lamination adhesive kit of the present invention is suitable for preparing flexible packaging laminates that can withstand retort conditions of 100°C or higher for 10 minutes or more (i.e., form seals that do not break under such conditions). To date, two-component solvent-free lamination adhesives have been widely used in less demanding applications, but have failed in retort applications.

[0033] Furthermore, the importance of using aliphatic isocyanate monomers in the preparation of adhesives for use in the present invention lies in the elimination of the risk associated with the formation of harmful primary aromatic amines. Such aromatic amines can be formed when adhesives containing polyurethane prepolymers formed from aromatic diisocyanates are subjected to retort conditions. Using aliphatic isocyanate-based adhesives reduces the risk of primary aromatic amine formation under retort conditions.

[0034] A further advantage is that the amount of free diisocyanate monomer in the polyurethane prepolymer component of the two-component adhesive kit of the present invention is less than 0.1% (w / w) based on the weight of the polyurethane prepolymer. This is important with respect to the hazards associated with the prepolymer. In particular, keeping the free diisocyanate monomer content in the polyurethane prepolymer below 0.1% (w / w) ensures that the prepolymer can be treated to such an extent that there is no indication of hazards associated with free diisocyanate monomers under the current Classification, Labelling and Packaging of Substances and Mixtures (CLP) Guidelines. This is advantageous in that the adhesive kit of the present invention is easier to handle compared to conventional two-component laminate adhesive kits / compositions that contain large amounts of residual isocyanates. It has not been previously reported that the amount of free monomer isocyanates, such as xylylene diisocyanate, present in the adhesive can be reduced, for example, by using a wipe-type film evaporator.

[0035] Furthermore, even when aliphatic isocyanate monomers are used and primary aliphatic amines are generated under retort conditions, reducing the amount of free isocyanate monomers to less than 0.1% (w / w) minimizes the risks associated with the presence of migratory species in the adhesive composition.

[0036] Solvent-free lamination adhesives do not contain organic solvents or water in order to reduce the viscosity of the material to a level that allows it to be applied in a lamination machine at temperatures below 90°C, for example, below 80°C. However, as a result of the above advantages, the inventors have found a method for producing a solvent-free adhesive that can achieve the viscosity required for use in a lamination machine at the aforementioned temperature by controlling the molecular weight of the components and without the problems typically associated with the presence of migratory low molecular weight / small molecular weight components.

[0037] The solvent-free lamination adhesive kit of the present invention contains 5 wt% or less of any solvent. Preferably, the solvent-free lamination adhesive kit of the present invention contains 3 wt% or less of any solvent, and more preferably, contains 1 wt% or less of any solvent. Even more preferably, the solvent-free lamination adhesive kit of the present invention is substantially solvent-free.

[0038] Furthermore, the inventors have discovered that incorporating a polyester polyol containing monomer units derived from a mixture of aromatic monomers and aliphatic monomers into the polyurethane prepolymer used in the present invention improves its mechanical properties.

[0039] The two-component adhesive kit of the present invention provides an adhesive that offers further advantages compared to similar one-component adhesive compositions, including stronger adhesion, better chemical resistance, and faster curing. One-component adhesives cure using only moisture present in / on the substrate and in the air. Generally, one-component adhesives work well with paper substrates laminated to paper or film. However, in the case of laminates of films, for example, or laminates of film and aluminum, the reaction and development of adhesive strength of one-component adhesives can be very slow because there is little available moisture and / or moisture does not easily reach the isocyanate.

[0040] Furthermore, to compensate for the slower curing rate by making the isocyanate groups more reactive / moisture-sensitive, catalysts (e.g., ethylmorpholine, DMDEE=2,2-dimorpholinodiethyl ether, or other tertiary amine-containing compounds, or metal salts) are typically added to one-component adhesives. Two-component adhesives do not require catalysts, allowing for an even greater reduction in the amount of migratory chemical species compared to the comparable one-component adhesive. Instead, the isocyanate groups in two-component adhesives react with polyols that are closely mixed with the polyurethane prepolymer, providing readily available reaction sites. However, the isocyanate groups in the polyurethane prepolymer of two-component adhesives can also react with residual moisture.

[0041] Aliphatic polyurethane prepolymer Polyurethanes having NCO-terminated groups are typically obtained by reacting polyfunctionalized alcohols with an excess of polyisocyanate monomers. Generally, diisocyanates are used at temperatures of 80-90°C to obtain prepolymers with molecular weights and viscosities suitable for use in lamination machines. This is because diisocyanates do not form crosslinks, as they react with only two types of polyols (in contrast to more functionalized isocyanates).

[0042] The polyurethane prepolymer used in the present invention is characterized by having a viscosity at 80°C of 800 mPas to 20,000 mPas, preferably 1,000 mPas to 10,000 mPas, or more preferably 2,000 mPas to 7,000 mPas.

[0043] The polyurethane prepolymer used in the present invention preferably has a reactive isocyanate group content (%NCO) of 3% to 16%, or more preferably 5% to 10%.

[0044] Those skilled in the art will understand that the advantages associated with the present invention derive from the use of an aliphatic polyurethane precursor containing monomer units derived from aliphatic isocyanates, but this does not preclude the presence of small amounts of non-aliphatic isocyanates in the prepolymer, as long as such amounts do not affect these advantageous properties. Accordingly, for the purposes of the present invention, the “aliphatic polyurethane prepolymer” is derived from 95 mol% or more of aliphatic isocyanate monomers relative to the total number of moles of isocyanate monomers incorporated into the prepolymer. Preferably, the aliphatic polyurethane prepolymer for use in the present invention is derived from 98 mol% or more, more preferably 99 mol% or more of aliphatic isocyanate monomers relative to the total number of moles of isocyanate monomers incorporated into the prepolymer. Most preferably, the isocyanate monomers incorporated into the aliphatic polyurethane prepolymer for use in the present invention are aliphatic isocyanate monomers only.

[0045] A certain amount of residual diisocyanate monomer (due to the use of a stoichiometric excess) remains in the reaction mixture at the end of the reaction, regardless of the reaction time. The aliphatic polyurethane prepolymer for use in the present invention is isocyanate-functionalized such that a reactive NCO group is bonded to the prepolymer. The aliphatic polyurethane prepolymer for use in the present invention contains at least two isocyanate groups per prepolymer. The aliphatic polyurethane prepolymer for use in the present invention is preferably bifunctionalized with isocyanate groups, for example, the aliphatic polyurethane prepolymer for use in the present invention is linear and contains an isocyanate group at one of its ends.

[0046] The polyurethane prepolymer used in the present invention may contain three or more isocyanate groups per prepolymer, for example, four or more, or five or more isocyanate groups.

[0047] Polyurethane prepolymers are preferably linear. For the purposes of the present invention, "linear" polyurethane prepolymers are typically derived from difunctionalized isocyanates and difunctionalized polyols such that each isocyanate derivative is covalently bonded to up to two polyols, and each polyol derivative is covalently bonded to up to two isocyanates. Linear polyurethane prepolymers may contain branched monomer components, such as branched glycols.

[0048] The aliphatic polyurethane prepolymer used in the present invention is preferably derived from a polyester polyol, and more preferably from a polyester polyol containing monomer units derived from aromatic monomers such as aromatic dicarboxylic acids.

[0049] In the production of the polyurethane prepolymer for use in the present invention, it is preferable that at least 50 wt%, for example, at least 60 wt%, at least 70 wt%, more preferably at least 80 wt%, or at least 90 wt%, of the polyol components used is polyester polyol. It is even more preferable that all polyols used in the production of the polyurethane prepolymer for use in the present invention are polyester polyols. The inventors have found that polyester polyols provide desirable high-temperature mechanical properties to the polyurethane prepolymer for use in the present invention.

[0050] The molar ratio of NCO groups of the aliphatic isocyanate monomer used to produce the polyurethane prepolymer for use in the present invention to the HO groups of the polyol used to produce the polyurethane prepolymer for use in the present invention may be 5:1 to 2:1. Preferably, the molar ratio of NCO groups of the aliphatic isocyanate monomer used to produce the polyurethane prepolymer for use in the present invention to the HO groups of the polyol used to produce the polyurethane prepolymer for use in the present invention is 4:1 to 2:1, for example, 3:1 to 2:1.

[0051] The NCO:OH ratio of the isocyanate and polyol used to produce the prepolymer for use in the two-component adhesive kit of the present invention can be lower than the ratio required for a one-component adhesive, which depends on the amount of residual moisture for curing. While we do not wish to be bound by theory, a lower NCO:OH ratio can be used when producing polyurethane prepolymers for use in two-component adhesives. A lower ratio results in a polyurethane prepolymer with a higher molecular weight and higher viscosity, which can function effectively when combined with a polyol crosslinking agent. In contrast, a higher NCO:OH ratio is necessary when producing a polyurethane prepolymer for use in a one-component adhesive. Excess NCO results in a polyurethane prepolymer with a lower molecular weight, and therefore a viscosity low enough for use in one-component adhesive applications. Excess isocyanate monomers must be removed from the one-component adhesive after use.

[0052] Reduction of free isocyanate monomer content Diisocyanates such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), and diphenylmethane diisocyanate (MDI) have considerable vapor pressure even at room temperature. This poses a serious health risk during application, as these chemical species are toxic due to their sensitizing and irritating effects. Users are legally required to implement special measures to protect workers during use, which include significant additional equipment designed to keep the air breathable and / or to maintain these substances below the maximum permissible concentration in the workplace. Therefore, users must install expensive protective equipment for workers exposed to vapors and / or aerosols of such products generated by dynamic application conditions on rotating machinery.

[0053] These types of reagents are regulated under laws concerning hazardous materials and are required to be labeled as hazardous materials. This labeling requirement involves special packaging and transportation measures.

[0054] Many polyurethane adhesives in this art contain more than 0.1% (w / w) of residual isocyanate monomers (typically volatile diisocyanates such as free TDI, MDI, or other isocyanate monomers) (the threshold specified by the CLP regulations; below this level, the product is not considered hazardous). In particular, when using isocyanate functional groups in molar excess relative to the hydroxyl functional groups of polyols, excess free isocyanate monomers will remain in the reaction mixture after the formation of the polyurethane prepolymer. Unless additional processing steps are taken to remove this excess free monomer, more than 0.1% (w / w) of free isocyanate monomers will remain in the prepolymer, requiring the aforementioned safety precautions. Furthermore, if a prepolymer containing more than 0.1% (w / w) of free isocyanate monomers is used as an adhesive for food packaging, food contamination by migratory isocyanate monomers may occur.

[0055] The solvent-free lamination adhesive kit of the present invention comprises an isocyanate-functionalized aliphatic polyurethane component having a free isocyanate monomer content of 0.1% (w / w) or less relative to the prepolymer. For example, the isocyanate-functionalized polyurethane component preferably contains 0.1% (w / w) or less, or 0.08% (w / w) or less, of free isocyanate monomers. The polyurethane prepolymer is subjected to additional processing steps outlined herein to reduce the amount of free isocyanate monomers to the amount required by the present invention.

[0056] The low amount of free monomer isocyanate monomer required by the present invention may be achieved by stripping unreacted isocyanate monomer from a polyurethane prepolymer using an evaporator (e.g., a wipe-type film evaporator). The evaporator may be used at a temperature of 100 to 250°C, preferably 120 to 200°C, and more preferably 140 to 180°C. The evaporator may be operated under a pressure of less than 5 mbar, preferably less than 0.5 mbar, and more preferably less than 0.1 mbar. The evaporator may be operated for a total contact time of less than 30 minutes, preferably less than 15 minutes, and more preferably less than 5 minutes. The evaporator may be operated at a pressure of 0.1 mbar or less and a temperature of 140°C to 180°C.

[0057] Production of polyurethane prepolymers for use in the present invention Polyurethane prepolymers for use in the present invention may be obtained by a process comprising the following protocol: a) Aliphatic diisocyanates, i. Optionally, use a catalyst, and ii. Optionally, use an acid compound, A polyester polyol and / or polyether polyol having a number-average molecular weight (Mn) of ≤1000 g / mol is reacted with an NCO:OH molar ratio greater than 2.0:1.0 to obtain an NCO-terminated prepolymer, and b) The NCO-terminated prepolymer obtained in step a) is subjected to one or more stripping steps using a series of one or more wipe-type film evaporators and / or short-path evaporators.

[0058] Steps a) and b) are carried out according to known procedures and operating conditions.

[0059] The final polyurethane prepolymer obtained in this way, after the removal of free isocyanate monomers, has the following properties: -%NCO, over 7% Viscosity at -50°C: less than 30,000 mPas - wt% of free diisocyanate monomer, less than 0.1%.

[0060] The method for producing polyurethane prepolymers for use in the present invention preferably does not require a solvent. In other words, polyurethane prepolymers for use in the present invention may be formed using only reagents that are themselves incorporated into the prepolymer.

[0061] Aliphatic isocyanates for use in the manufacture of polyurethane prepolymers Aliphatic isocyanates for use in the preparation of isocyanate-functionalized aliphatic polyurethane prepolymers for use in the present invention are selected from the group including hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), methane dicyclohexyl diisocyanate, xylylene diisocyanate (XDI), tetramethyl xylylene diisocyanate (TMXDI), pentamethylene diisocyanate (PDI), and any combination thereof.

[0062] Preferably, the aliphatic isocyanate monomer for use in the present invention is a diisocyanate selected from the group including isophorone diisocyanate (IPDI) and mixtures thereof, 1,6-hexane diisocyanate (HDI), xylylene diisocyanate (XDI), and combinations thereof. More preferably, the aliphatic isocyanate monomer for use in the present invention is xylylene diisocyanate (XDI).

[0063] The aliphatic isocyanates used in the present invention contain isocyanate groups that are not directly bonded to an aromatic ring. Therefore, the aliphatic isocyanates used in the present invention may contain aromatic groups only if the isocyanate groups are not directly bonded to them.

[0064] Polyol for producing polyurethane prepolymers for use in the present invention The polyol used in the production of the isocyanate-functionalized aliphatic polyurethane prepolymer for use in the present invention may be selected from the group including polyester polyols, polyether polyols, and combinations thereof. The polyol used in the present invention is preferably a polyester polyol, and more preferably a polyester polyol containing monomer units derived from aromatic monomers.

[0065] The polyester polyols used in this invention were selected to provide a desirable combination of properties. In particular, the polyols were selected such that, when incorporated into the polyurethane prepolymer for use in this invention, the polyurethane prepolymer would have desirable mechanical properties at high temperatures and a final viscosity suitable for use in a laminating machine at 80-90°C.

[0066] The inventors have found that polyester polyols particularly preferred for use in the present invention are characterized as follows: 1. A mixture of aromatic dicarboxylic acids and aliphatic dicarboxylic acids, and / or 2. A mixture of linear and branched short-chain glycols, and / or 3. Having an OH value in the range of 110 to 400 mg KOH / g, and / or It has a viscosity in the range of 500 to 10,000 mPas at 4.23℃.

[0067] The polyester polyol used in the present invention may contain other components such as a polyether moiety, but it is preferable that at least 50 mol% of the present monomer units are polyester monomer units, for example, at least 60 mol%, at least 70 mol%, preferably at least 80 mol%, or more preferably at least 90 mol% of the present monomer units are polyester monomer units. The polyester polyol used in the present invention may contain only polyester monomer units.

[0068] The inventors have found that polyurethane prepolymers made from a polyester polyol backbone are advantageous when used to formulate the lamination adhesive of the present invention, as the resulting polyurethane prepolymer exhibits improved mechanical properties (e.g., tear strength) at typical temperatures used in retort processing (100-135°C).

[0069] The polyesters and / or polyether polyols for use in the present invention are preferably linear. In the context of the present invention, "linear" polyester polyols are derived from difunctionalized monomers (and optionally from monofunctionalized monomers) such that each monomer unit can react with up to two other monomers. In other words, the maximum functionalization of a monomer is two. For example, dicarboxylic acids and diols make linear polyesters.

[0070] Aromatic and aliphatic monomers When used to formulate polyurethane prepolymers for use in the present invention, polyester polyols containing at least 10 wt% monomer units derived from aromatic monomers are preferred. More preferably, at least 20 wt% of the monomer units of the polyester polyol are derived from aromatic monomers. This is because, generally, polyurethane prepolymers derived from such polyols exhibit improved mechanical properties at typical temperatures for retort processing, particularly improved adhesive strength under retort conditions. While we do not wish to be bound by theory, the inventors believe this improvement leads to higher hydrolysis resistance and higher glass transition temperature (T) of these polyester polyols. g I suspect it concerns )

[0071] Polyurethanes with a polyester polyol backbone generally have higher viscosity than polyurethanes with a polyether backbone, and polyester polyols containing aromatic rings in their backbone have even higher viscosity than pure aliphatic polyester polyols. The inventors have found that by incorporating a mixture of aliphatic and aromatic groups into the polyester polyol used in the present invention, a polyurethane prepolymer with improved mechanical properties and viscosity, suitable for use in adhesive laminate applications, can be obtained.

[0072] The polyester polyol used in the present invention may be derived from 10 to 55 wt%, preferably 15 to 45 wt%, and more preferably 15 to 35 wt%, for example 20 to 30 wt%, of aromatic monomers relative to the total wt% of the polyester polyol. The aromatic monomer is preferably an aromatic dicarboxylic acid, such as isophthalic acid.

[0073] The polyester polyol used in the present invention may be derived from an aliphatic monomer in an amount of 45 wt% to 90 wt%, preferably 55 wt% to 85 wt%, and more preferably 65 wt% to 85 wt%, relative to the total wt% of the polyester polyol. The aliphatic monomer is preferably an aliphatic dicarboxylic acid, such as sebacic acid. The aliphatic monomer is also preferably an aliphatic polyol, such as an aliphatic glycol and an aliphatic diol.

[0074] Polyols used in the manufacture of polyester polyols The polyol used to produce polyester polyols is preferably a glycol and / or a diol. The glycol and diol used to produce polyester polyols are preferably selected from the group consisting of neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, monoethylene glycol, and combinations thereof.

[0075] The polyester polyol used in the present invention may contain 15-35% monomer units derived from aromatic dicarboxylic acids, and 65-85 wt% monomer units derived from aliphatic dicarboxylic acids, aliphatic glycols, and aliphatic diols.

[0076] The polyester polyols used in the present invention may be formed from 10 to 55 wt% of aromatic monomers, preferably 15 to 45 wt%, and more preferably 15 to 35 wt%, for example 20 to 30 wt%, of aromatic dicarboxylic acids relative to the total amount of monomers used to form the polyester polyol. The polyester polyols used in the present invention may be formed from 45 to 90 wt% of aliphatic dicarboxylic acids, aliphatic glycols, and aliphatic diols, preferably 55 to 85 wt%, and more preferably 65 to 85 wt%, of aliphatic dicarboxylic acids, aliphatic glycols, and aliphatic diols relative to the total amount of monomers used to form the polyester polyol.

[0077] The aromatic dicarboxylic acid used in the preparation of polyester polyols is preferably selected from a list consisting of terephthalic acid, isophthalic acid, phthalic anhydride, and combinations thereof. The aliphatic dicarboxylic acid used in the preparation of polyester polyols is preferably a linear C2-C 14 A linear C2-C dicarboxylic acid selected from the group consisting of dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid, and combinations thereof. 14 It is a dicarboxylic acid.

[0078] The weight ratio of aromatic dicarboxylic acid to aliphatic dicarboxylic acid incorporated into the polyol may be 10:1 to 1:10, preferably 4:1 to 1:4, and more preferably 2:1 to 1:2. For use in the present invention, the weight ratio of aromatic dicarboxylic acid to aliphatic dicarboxylic acid incorporated into the polyol may be 1.5:1 to 1:1.5, such as being incorporated in substantially equal wt% amounts.

[0079] Short-chain glycols Short-chain glycols suitable for preparing polyester polyols for use in the present invention include, but are not limited to, linear C1-C6 diols, such as 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and combinations thereof. Short-chain glycols containing alkyl substituents are also suitable for preparing polyester polyols for use in the present invention and are preferably selected from C1-C6 diols, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, neopentyl glycol, 1,3-methylpentanediol, 2-methyl-1,3-propanediol, and combinations thereof.

[0080] The glycol used in this invention is preferably 500 gmol. -1 Less than, for example, 300 gmol -1 Less than, and preferably 200 gmol -1 It has a molecular weight of less than [amount missing].

[0081] The weight percentage ratio of straight-chain to branched short-chain glycols incorporated into the polyol for use in the present invention may be 10:1 to 1:10, preferably 4:1 to 1:4, and more preferably 2:1 to 1:2. The weight ratio of straight-chain to branched short-chain glycol dicarboxylic acids incorporated into the polyol for use in the present invention may be 1.5:1 to 1:1.5, such as being incorporated in substantially equal wt% amounts.

[0082] Polyurethane prepolymer additives The polyurethane prepolymer for use in the present invention can be used "as is" (i.e., in the form obtained by the method described above) or after the addition of additives such as adhesion promoters, viscosity and rheology modifiers, moisture scavengers, anti-skinning agents, and anti-foaming agents.

[0083] In particular, the use of adhesion promoters, such as silanes containing groups that react with isocyanate groups (e.g., 3-aminopropyltriethoxysilane), is advantageous when the adhesive system is used on metal or metallized substrates such as aluminum. Such adhesion promoters can also be incorporated into polyol crosslinking agents. However, such components are not essential to the adhesive kit of the present invention. The inventors have found that the adhesive of the present invention functions well under retort conditions even without silane additives that react with isocyanates. Therefore, the polyol functionalized crosslinking agent for use in the present invention may not contain silane compounds that can react with isocyanates.

[0084] Any additional aliphatic polyisocyanates (multiple) The polyurethane prepolymer for use in the present invention may also be formulated with one or more additional aliphatic polyisocyanates to further reduce the viscosity of the final system. That is, additional aliphatic polyisocyanates may be incorporated into part a) of the kit of the present invention. The additional aliphatic polyisocyanates for use in the present invention may have low viscosity. That is, the additional aliphatic polyisocyanates for use in the present invention may have a viscosity of 3,000 mPas or less, preferably 2,000 mPas or less, for example, 1,000 or less, or 500 or less at 23°C.

[0085] The additional aliphatic polyisocyanates are preferably selected from the group consisting of aliphatic polyisocyanate trimers (i.e., isocyanurates), aliphatic polyisocyanate allophanates, aliphatic polyisocyanate oligomers, aliphatic polyisocyanate biuretes, aliphatic polyisocyanate urelegions, and combinations thereof.

[0086] Specific examples of these compounds include hexamethylene diisocyanate (HDI) trimers (e.g., Wanhua's POLURENE MT100, POLURENE MT100LV, POLURENE MT100LLV, Wannate HT100, and Wannatye HT600), hexamethylene diisocyanate (HDI) allophanate, hexamethylene diisocyanate biuret, urezion / allophanate-modified HDI oligomers, and HDI oligomers (e.g., Polurgreen MT100 01, Polurgreen MT100LV 01, Polurgreen MT100LLV 01, Tolonate HDT, Tolonate HDT LV, Tolonate HDT LV2, Tolonate XFLO100, Basonat HI, Basonat HI-2000, Basonat HA3000, Desmodur ULTRA) Examples include N3300, Desmodur ULTRA N3600, Desmodur ULTRA N3900, and Desmodur XP2860. Allophanates are isocyanate dimers.

[0087] More preferably, the additional aliphatic polyisocyanate(or additional) is selected from the group consisting of aliphatic polyisocyanate trimers such as HDI trimers, aliphatic polyisocyanate allophanates such as HDI allophanate, and combinations thereof. Even more preferably, the additional aliphatic polyisocyanate(or additional) is an aliphatic polyisocyanate trimer such as HDI trimer.

[0088] The aliphatic polyurethane prepolymer for use in the present invention may be incorporated into a composition comprising additional polyisocyanates for use in the present invention. The wt% ratio of the polyurethane prepolymer for use in the present invention to the additional polyisocyanates for use in the present invention may be 8:1 to 1:1, more preferably 5:1 to 2:1, and even more preferably 3:1 to 2:1.

[0089] catalyst If desired, the urethane reaction can be accelerated by adding a suitable catalyst during the preparation stage. Suitable catalysts for the urethane reaction are known and include amines and organometallic compounds. However, such components are not essential for the adhesive kit of the present invention. The inventors have found that the adhesive of the present invention functions well under retort conditions even without a catalyst. Therefore, the polyurethane prepolymer used in the present invention (and the kit of the present invention) may not contain a catalyst.

[0090] Examples of catalysts suitable for use in the present invention include triethylamine, tributylamine, dimethylbenzylamine, dicyclohexylmethylamine, dimethylcyclohexylamine, N,N,N',N',N-tetramethyldiamine methyl ether, bis(dimethylaminopropyl)urea, N-methyl or N-ethylmorpholine, N,N'-dimorpholinodiethyl ether (DMDEE), N-cyclohexylmorpholine, N,N,N',N'-tetramethyl ethyl Diendiamine, N,N,N',N'-tetramethylbutylenediamine, N,N,N',N'-tetramethyl-1,6-hexanediamine, pentamethyldiethylenetriamine, dimethylpiperazine, N-dimethylaminoethylpiperidine, 1,2-dimethylimidazole, N-hydroxypropylimidazole, 1-azabicyclo-[2,2,0]-octane, 1,4-diazabicyclo-[2,2,2]octane (DABCO), triethanolamine, triisopropyl Examples include alkanolamines such as panolamine, N-methyl and N-ethyldiethanolamine, N,N',N-tris-(dialkylaminoalkyl)-hexahydrothiadin such as dimethylaminoethanol, 2-(N,N'-dimethylaminoethoxy)ethanol, and N,N',N-tris-(dimethylaminopropyl)-s-hexahydrothiadin, tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, alkaline hydroxides such as sodium hydroxide, alkaline alkoxides such as sodium methoxide, alkali salts of long-chain fatty acids, iron(II) chloride, zinc chloride, lead octyolate, tin dioctanoate, tin diethylhexanoate, butyltin dilaurate, dibutyldilauryl tin mercaptide, and other tin salts, titanium compounds such as titanium(IV) butyrate, organometallic compounds of tin, lead, iron, titanium, bismuth, and zirconium, tin oxides and sulfides, and bismuth carboxylate.

[0091] The polyurethane prepolymer adhesive obtained as described above is characterized by having less than 0.1% by weight of free monomers ("free monomers"), is completely safe for users, and does not require hazard labeling because it does not contain substances (primary aromatic amines and cyclic esters) that are easily transferred from the packaging to food, even when the packaged product has a long shelf life.

[0092] Polyol crosslinking agent The polyol crosslinking agent for use in the kit of the present invention may be a polyol suitable for curing the isocyanate-functionalized aliphatic polyurethane prepolymer for use in the present invention.

[0093] The polyol crosslinking agent for use in the kit of the present invention may be selected from linear or branched polyethers and / or linear or branched polyester polyols. The polyol crosslinking agent for use in the present invention may be a mixture of polyester polyol and polyether polyol. The polyol crosslinking agent for use in the present invention is preferably a polyester polyol.

[0094] The polyol crosslinking agent used in the present invention may be a polyester polyol formed from a glycol and a dicarboxylic acid. The glycol may be selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, neopentyl glycol, tetramethylene glycol, polyethylene glycol (including its methyl ether), polypropylene glycol (including its methyl ether), and polybutylene glycol (including its methyl ether). The dicarboxylic acid may be selected from the group consisting of aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, methylsuccinic acid, aspartic acid, malic acid, and aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid. The polyester polyol may also be derived from a non-glycol polyol containing trimethylolpropane.

[0095] The polyol crosslinking agent used in this invention may be a polyester polyol containing a tertiary amine group in its backbone.

[0096] The polyol crosslinking agent used in the present invention, such as a polyester polyol, may have a number average molecular weight of 200 to 10,000 Da, preferably 400 to 5,000 Da, and more preferably 500 to 2,000 Da.

[0097] The polyol crosslinking agent for use in the present invention may be incorporated into a crosslinking composition further comprising a polyether monool (i.e., a polypropylene glycol monoalkyl ether containing a single hydroxyl substituent) (as part b). The polyether monool is preferably selected from the list consisting of polyethylene glycol monoalkyl ether, polypropylene glycol monoalkyl ether, polybutylene glycol monoalkyl ether, and combinations thereof. For example, the polyol crosslinking agent for use in part b) of the present invention may be incorporated into a crosslinking composition further comprising polypropylene glycol monomethyl ether.

[0098] Polyether monools may have a number-average molecular weight of 200 to 2000 Da, for example, 200 to 1000 Da, or 200 to 500 Da.

[0099] If present, polyether monools (e.g., polypropylene glycol monoalkyl ethers) may be incorporated into the polyol crosslinker composition of part b) in amounts up to 50 wt%, e.g., up to 40 wt%, relative to the total weight of both the polyol crosslinker and the polyether monool. In other words, the wt% ratio of the polyol crosslinker of part b) to the polyether monool (if present) may be 100:0 to 50:50, e.g., 80:20 to 50:50, or 70:30 to 60:40, e.g., about 60:40.

[0100] The kit of the present invention comprises an aliphatic polyurethane prepolymer and optionally additional polyisocyanates as part a), and a polyol crosslinking agent as part b). The wt% ratio of part a) to part b) may be 5:1 to 1:2, preferably 4:1 to 1:1, and more preferably 3:1 to 1:1.

[0101] Laminates The market for adhesively molded multilayer structures for retort applications is large. Typical structures include the following substrate combinations: PET / CPP, PET / Al / CPP, PET / Al / OPA / CPP, PET-SiOx / CPP, PET-AlOx / CPP, OPA / CPP, OPA / LDPE, PET / Al / LDPE, VM-PET, AlOx-PET, SiOx-PET, AlOx-OPP, SiOx-OPP, AlOx-OPE, SiOx-OPE, AlOx-OPA, SiOx-OPA, PET / OPA / Al / CPP , OPA / VM-PET / LLDPE, PET / OPA / CPP, PET / OPA-SiOx / CPP, PET / OPA-AlOx / CPP, PET-SiOx / OPA / CPP, PET-AlOx / OPA / CPP, OPP / CP P, OPP-SiOx / OPA / CPP, OPP-AlOx / OPA / CPP, OPE-SiOx / OPA / CPP, OPE-AlOx / OPA / CPP, OPA-SiOx / OPA / CPP, OPA-AlOx / OPA / CPP.

[0102] The adhesive kit of the present invention can be used with any of the above-mentioned substrates to form a laminate.

[0103] Retort conditions The lamination adhesive kit of the present invention provides laminates with improved adhesive strength under retort conditions compared to comparative laminates. Retort conditions require placing a sealed retort package at a temperature for a certain period of time. For example, retort conditions may require heating the package at 115°C to 150°C for 10 to 60 minutes, or heating the package at 120°C to 140°C for 20 to 35 minutes. Retort conditions may require a pressure of 1.5 to 4 bar, for example, 1.5 to 3 bar. Retort conditions may require heating at 1.5 bar at 120°C for 30 minutes, or heating at 2.6 bar at 135°C for 20 minutes. [Examples]

[0104] The present invention is defined by the following non-limiting embodiments. These embodiments further illustrate the present invention and are not intended to limit, nor should they be construed as limiting, the scope of the invention.

[0105] Test method - Free diisocyanate monomer content (e.g., %HDI, %XDI): Determined by gas chromatography using an internal standard according to ASTM D3432. Expressed as wt% relative to the total amount of polyurethane prepolymer. - Reactive NCO group content (%NCO): Determined by back titration with excess n-butylamine acid according to ASTM D2572. - Viscosity: Measured using a Brookfield rotational viscometer Mod. LVDVII, according to ASTM D1084, at the specified temperature. Unless otherwise specified, viscosity is measured at 23°C. -Hydroxyl value (OH value): The number of milligrams of potassium hydroxide required to neutralize the acetic acid incorporated when acetylating 1 gram of a chemical substance containing free hydroxyl groups. The standard procedure specified in ISO 4629-1:2016(E) is used to measure the hydroxyl value. -Molecular weight: a) The molecular weight of a nonpolymer or oligomeric compound (i.e., a defined monomer species) is defined and calculated by the molecular structure of the compound. This is usually listed in the technical data sheet of the monomer supplier or can be found on the European Chemical Agency (ECHA) website. b) Oligomer and polymer species typically include a distribution of chain length, and therefore a distribution of molecular weight. Therefore, unless otherwise specified, the molecular weight of oligomer and polymer species (as well as components existing as mixtures of species with molecular weights greater than 500 Da (and thus having a distribution)—e.g., vegetable oils) is measured using a Hewlett-Packard 1050 series HPLC system with two GPC Ultrastyragel columns, 103 Å and 104 Å (5 μm mixed, 300 mm × 19 mm, Waters Millipore Corporation, Milford, MA, USA), with THF as the mobile phase. The column temperature is 40°C. Molecular weight is calculated by comparison with a polystyrene standard. Those skilled in the art will understand that this definition of molecular weight generally applies to polymer materials having a molecular weight distribution. Unless otherwise specified, the molecular weights of oligomers and polymers reported herein are number-average molecular weights. - Adhesion strength refers to the strength required to separate a multilayer structure formed from a flexible film and a laminated adhesive formed from the components of an adhesive kit. The multilayer structure includes at least two layers joined by the laminated adhesive. Adhesion strength was measured at room temperature (25°C) and 100 mm / min. Other parameters conform to ASTM D3330-F (90° peel test).

[0106] The improved adhesive strength relates to the increased peel resistance of a laminated structure made from a flexible film and a laminated adhesive formed from the components of the kit of the present invention, compared to a comparative laminated structure made from the same flexible film but using a laminated adhesive that is not formed from the components of the kit of the present invention.

[0107] Example 1: Synthesis of polyester polyols The polyester polyol of Example 1 is prepared by mixing the following diol and dicarboxylic acid and reacting them by typical condensation polymerization using an esterification reactor and well-known esterification conditions. [Table 1]

[0108] Example 1 is a typical polyester polyol obtained from the reagents formulated in the above amounts, and has the following characteristics: OH value = 265 mgKOH / g Viscosity at 23°C = 3,000 mPas

[0109] Example 2: Synthesis of NCO-terminated polyurethane prepolymer 550 parts of xylylene diisocyanate (XDI) are added to a 1-liter reaction flask equipped with a stirrer and reflux condenser while continuously supplying nitrogen. The mixture is heated to 50°C, and 450 parts of polyester polyol A of Example 1 (having two functional groups, number average M) are added. w Add 420 g / mol of OH-terminated polyester polyol dropwise over 240 minutes while stirring, monitoring the temperature of the reaction mixture and adjusting the polyol addition rate so that it never exceeds 60°C.

[0110] After the addition is complete, heat the mixture to 80°C and continue heating for 2 hours until the %NCO content reaches approximately 15.5%.

[0111] The resulting product is distilled in a thin-layer evaporator at a pressure of approximately 0.1 mbar and a temperature of 140°C to remove unreacted monomers. 760 parts of a colorless, transparent liquid with the following properties are obtained: %NCO=7.6% Viscosity at 50°C = 18,700 mPas %XDI=0.04wt%

[0112] Example 3: Preparation of solvent-free aliphatic isocyanate prepolymer with residual monomer levels of less than 0.1% 700 parts of Example 2 were mixed with 300 parts of a low-viscosity HDI trimer (Polurgreen MT100 LV01) with a residual HDI content of <0.1%, to obtain 1000 parts of a colorless, transparent liquid having the following properties: %NCO=12.3% Viscosity at 40°C = 11,000 mPas %XDI=0.04% %HDI=0.04%

[0113] Example 3 is a solvent-free aliphatic isocyanate prepolymer with a residual monomer level of less than 0.1% by weight, prepared according to the method described above. Its performance was evaluated in comparison with a solvent-free aromatic adhesive in a three-layer structure of PET (12 μm) / aluminum (8 μm) / cast polypropylene (CPP) (60 μm). Laminates using the adhesives listed in Table 2 below were manufactured using a Nordmeccanica Group Labo Combi 400 laminating machine under the following conditions: Coating weight: 2.5 gsm / dry; Adhesive roller speed: 80; Adhesive roller temperature: 50℃; Coating roller temperature: 50℃; Tension winding machine A:23N; Tension winding machine B: 20N; Tension winding machine (laminated material): 28N; Coating head pressure: 3 bar; Nip pressure: 3 bar; Nip temperature: 50℃; The laminate was cured at 20°C for 20 days.

[0114] [Table 2]

[0115] Sunlam NS-4158A (polyurethane polyisocyanate) / HA-328 (polyester polyol) is a two-component, solvent-free, partially aromatic laminated adhesive that can be processed at 50°C. The polyurethane prepolymer (NS-4158A) is aromatic, meaning the polyurethane contains monomer units derived from aromatic isocyanates.

[0116] Sunlam ZA-1000 (polyurethane polyisocyanate) / ZB-301 (a polyester polyol based on trimethylolpropane bonded to propylene glycol and adipic acid, containing a small amount of tetraol with a tertiary amine backbone) is a commercially available two-component, aromatic, solvent-free, ultra-low isocyanate monomer (<0.1 wt%) laminating adhesive that can be processed at 50-55°C. The polyurethane (ZA-1000) is aromatic, meaning it contains monomer units derived from aromatic isocyanates.

[0117] MP40 is a 60 / 40 mixture of DIC Dry HA930 (polyester polyol, DIC Graphics Corporation) and Smack MP-40 (Kao Corporation). Smack MP-40 is a polypropylene glycol monomethyl ether with a molecular weight of approximately 260 Da.

[0118] MP70 is a 60 / 40 mixture of DIC Dry HA930 (polyester polyol, DIC Graphics Corporation) and Smack MP-70 (Kao Corporation). Smack MP-70 is a polypropylene glycol monomethyl ether with a molecular weight of approximately 450 Da.

[0119] Sunlam HA450B is a commercially available solvent-free polyester polyol based on trimethylolpropane bonded with monoethylene glycol, neopentyl glycol, isophthalic acid, and adipic acid, and is typically used in combination with aromatic isocyanate-functionalized prepolymers.

[0120] ZB301 is a solvent-free polyester polyol.

[0121] The adhesive strength (expressed as N / 15mm) between aluminum and CPP was measured at room temperature at 100 mm / min and recorded after various heat treatments. The results are shown in the table below.

[0122] [Table 3]

[0123] Comparative examples (Samples 1 and 2) prepared using aromatic polyisocyanate prepolymers containing standard or very low levels of free monomers failed the high retort test and also failed the low retort test almost completely. Laminates that withstood the low retort process maintained their appearance and did not show delamination, but they had little adhesive strength and were therefore unsuitable for use in retort applications.

[0124] Four samples based on Example 3 of the Invention (i.e., samples 3, 4, 5, and 6) were cured using various polyol crosslinking agents and withstood both low-retort and high-retort processes, maintaining their appearance and integrity while exhibiting sufficient adhesive strength.

[0125] The present invention has been described in detail, including its various embodiments. However, those skilled in the art will understand that, taking this disclosure into consideration, modifications and / or improvements to the present invention may fall within the scope and spirit of the invention.

[0126] Numbered Embodiments of the Invention The present invention is defined by the following numbered embodiments, which constitute part of this specification.

[0127] 1. Solvent-free lamination adhesive kit, a) an isocyanate-functionalized aliphatic polyurethane prepolymer containing monomer units derived from aliphatic isocyanate monomers, and b) Polyol crosslinking agent, The solvent-free lamination adhesive kit comprises, wherein the amount of free isocyanate monomer present in the polyurethane prepolymer is 0.1% (w / w) or less of the prepolymer.

[0128] 2. The kit according to Embodiment 1, wherein the aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, methylene dicyclohexyl diisocyanate, xylylene diisocyanate, tetramethyl xylylene diisocyanate, pentamethylene diisocyanate, and combinations thereof, and optionally, the aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of isophorone diisocyanate, 1,6-hexane diisocyanate, xylylene diisocyanate, and combinations thereof.

[0129] 3. The kit according to any of the preceding embodiments, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is difunctionalized with isocyanate groups, and optionally, the isocyanate-functionalized aliphatic polyurethane prepolymer is linear and isocyanate-functionalized at each end.

[0130] 4.i) The isocyanate-functionalized aliphatic polyurethane prepolymer has a viscosity between 800 mPa and 20,000 mPas at 80°C, for example between 1,000 mPas and 10,000 mPas, or between 2,000 mPas and 7,000 mPas (where the viscosity is measured according to the method described herein), and / or ii) The isocyanate-functionalized aliphatic polyurethane prepolymer has an isocyanate group content (%NCO) between 3% and 16%, for example between 5% and 10%, and / or iii) The isocyanate-functionalized aliphatic polyurethane prepolymer is derived from more than 80 mol% of aliphatic isocyanates, for example more than 90 mol% or more than 95 mol% of aliphatic isocyanates, and / or d) A kit according to any of the preceding embodiments, wherein the isocyanate incorporated into said isocyanate-functionalized aliphatic polyurethane prepolymer is only aliphatic isocyanate.

[0131] 5. A kit according to any of the preceding embodiments, wherein said isocyanate-functionalized aliphatic polyurethane prepolymer is derived from a polyester polyol and / or a polyether polyol, and optionally, said isocyanate-functionalized aliphatic polyurethane prepolymer is derived from a polyester polyol containing monomer units derived from aromatic monomers.

[0132] 6. i) said isocyanate-functionalized aliphatic polyurethane prepolymer is derived from at least 50 wt% polyester polyol based on the total amount of polyol incorporated into said prepolymer, and / or ii) said polyester polyol contains monomer units derived from a mixture of an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid, and / or iii) said polyester polyol contains 10 - 55 wt%, such as 15 - 45 wt%, or 15 - 35 wt% monomer units derived from aromatic monomers, a kit according to embodiment 5.

[0133] 7. i) said polyester polyol contains monomer units derived from 45 wt% - 90 wt% aliphatic monomers, such as 55 wt% - 85 wt%, or 65 wt% - 85 wt% aliphatic monomers, and / or said polyester polyol contains monomer units derived from a mixture of a linear glycol and a branched glycol, and optionally, said linear glycol and said branched glycol have a molecular weight of less than 500 gmol -1 less than, such as less than 200 gmol -1 less than, and / or ii) said polyester polyol and / or said polyether polyol each have a number average molecular weight of less than 1000 g / mol, and / or iii) The kit according to Embodiment 5 or 6, wherein the polyester polyol and / or the polyether polyol is linear.

[0134] 8.i) The polyol crosslinking agent does not contain a silane compound that can react with isocyanates such as aminosilane, and / or ii) The polyurethane prepolymer is incorporated into a composition further comprising an additional polyisocyanate, optionally, The kit according to any of the preceding embodiments, wherein the additional polyisocyanate is selected from the group consisting of hexamethylene diisocyanate trimers, hexamethylene diisocyanate allophanates, or combinations thereof.

[0135] 9. A lamination adhesive comprising the components of a solvent-free lamination adhesive kit described in any of the preceding embodiments, mixed in a single composition.

[0136] 10. A retort pouch containing the lamination adhesive described in Embodiment 9.

[0137] 11. A method for providing a multi-layered structure, i) Forming a laminated adhesive from the components of the kit described in any one of Embodiments 1 to 8, or providing the laminated adhesive of Embodiment 9, and ii) The method comprising applying a lamination adhesive to a flexible film.

[0138] 12.i) The flexible film is selected from the group consisting of polyethylene terephthalate, nylon, aluminum, oriented polypropylene, cast polypropylene, low-density polyethylene, linear low-density polyethylene, vacuum-modified polyethylene terephthalate, aluminum oxide-polyethylene terephthalate, silicon oxide-polyethylene terephthalate, aluminum oxide-oriented polypropylene, silicon oxide-coated oriented polypropylene, aluminum oxide-oriented polyethylene, silicon oxide-oriented polyethylene, aluminum oxide-nylon, and silicon oxide-nylon, and coating films thereof, and / or ii) The method according to Embodiment 11, further comprising applying the adhesive at a press speed of more than 50 m / min or more than 100 m / min.

[0139] 13. A method for manufacturing a kit described in any of the prior embodiments, a) Reacting an aliphatic isocyanate with a polyester and / or polyether polyol to obtain an isocyanate-functionalized aliphatic polyurethane prepolymer containing monomer units derived from an aliphatic isocyanate monomer. b) Reduce the residual isocyanate monomer present in the prepolymer to less than 0.1% (w / w) of the prepolymer. c) Introduce a polyol crosslinking agent into the kit. The method comprising the step.

[0140] 14.i) The aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, methylene dicyclohexyl diisocyanate, xylylene diisocyanate, tetramethyl xylene diisocyanate, pentamethylene diisocyanate, and / or combinations thereof. ii) The aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of isophorone diisocyanate, 1,6-hexane diisocyanate, xylylene diisocyanate, and / or combinations thereof, and / or iii) The amount of the isocyanate monomer is reduced by stripping the prepolymer using a series of one or more thin-layer evaporators and / or molecular evaporators. The method according to Embodiment 13.

[0141] 15.i) The isocyanate-functionalized aliphatic polyurethane prepolymer is the isocyanate-functionalized aliphatic polyurethane prepolymer described in any one of Embodiments 3 to 6, and / or ii) step a) comprises reacting the aliphatic isocyanate with a polyester polyol, wherein optionally the polyester polyol is the polyester polyol described in Embodiment 6 or 7, and / or iii) Prior to step a), the method further comprises the step of reacting a mixture of aromatic dicarboxylic acids and aliphatic dicarboxylic acids with at least one polyol to form a polyester polymer, optionally Here, the at least one polyol is a mixture of a linear glycol and a branched glycol, and optionally, the linear glycol and the branched glycol are present in 500 gmol portions. -1 Less than, for example, 200 gmol -1 The method according to embodiment 13 or 14, having a molecular weight of less than .

[0142] 16. The method according to any one of Embodiments 13 to 15, which does not contain a solvent.

[0143] 17. Use of a kit according to any of the preceding embodiments for forming a laminated adhesive, wherein the laminated adhesive optionally forms part of a retort package such as a pouch.

[0144] 18. Use of the kit according to any of the preceding embodiments for improving the adhesive strength under retort conditions of a multilayer structure formed from a flexible film and a lamination adhesive formed from the components of the kit, wherein the retort conditions optionally include heating at 100°C or higher for 20 minutes, for example, heating at 120°C for 30 minutes or 135°C for 20 minutes.

Claims

1. This is a solvent-free lamination adhesive kit. a) i) an isocyanate-functionalized aliphatic polyurethane prepolymer comprising monomer units derived from an aliphatic isocyanate monomer, wherein the aliphatic polyurethane prepolymer is formed from an aliphatic isocyanate monomer, and the aliphatic isocyanate monomer is one in which the isocyanate group(s) is not directly bonded to an aromatic ring, and the aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, methylene dicyclohexyl diisocyanate, xylylene diisocyanate, tetramethyl xylylene diisocyanate, pentamethylene diisocyanate, and combinations thereof. The isocyanate-functionalized aliphatic polyurethane prepolymer is derived from polyester polyols and / or polyether polyols. The isocyanate-functionalized aliphatic polyurethane prepolymer, wherein the molar ratio of the NCO group of the aliphatic isocyanate monomer to the HO group of the polyol derived from the isocyanate-functionalized aliphatic polyurethane prepolymer is 5:1 to 2:1, and ii) A composition comprising an additional aliphatic polyisocyanate selected from the group consisting of aliphatic polyisocyanate trimers, aliphatic polyisocyanate allophanates, aliphatic polyisocyanate biuretes, aliphatic polyisocyanate oligomers, aliphatic polyisocyanate urelegions, and combinations thereof, b) A solvent-free lamination adhesive kit comprising a polyol crosslinking agent, wherein the polyol crosslinking agent is a linear or branched polyether polyol and / or a linear or branched polyester polyol, wherein the amount of free isocyanate monomer present in the polyurethane prepolymer is 0.1% (w / w) or less of the prepolymer, the amount of free isocyanate monomer is determined by gas chromatography using an internal standard in accordance with ASTM D3432 and expressed as wt% of the total amount of the polyurethane prepolymer, and the polyol crosslinking agent does not contain a silane additive that can react with isocyanate.

2. The kit according to claim 1, wherein the aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of isophorone diisocyanate, 1,6-hexane diisocyanate, xylylene diisocyanate, and combinations thereof.

3. The kit according to claim 2, wherein the aliphatic isocyanate monomer is xylylene diisocyanate.

4. The kit according to claim 1, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is difunctionalized with isocyanate groups, and optionally, the isocyanate-functionalized aliphatic polyurethane prepolymer is linear and isocyanate-functionalized at each end.

5. The kit according to claim 1, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer has a viscosity between 800 mPa and 20,000 mPas at 80°C, where the viscosity is measured at 23°C using a Brookfield rotational viscometer Mod. LVDVII according to ASTM D1084.

6. The kit according to claim 1, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer has an isocyanate group content (%NCO) between 3% and 16%.

7. The kit according to claim 1, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is derived from 95 mol% or more of aliphatic isocyanate monomers with respect to the total isocyanate monomers incorporated into the prepolymer.

8. The kit according to claim 1, wherein the isocyanate incorporated into the isocyanate-functionalized aliphatic polyurethane prepolymer is solely an aliphatic isocyanate monomer.

9. The kit according to claim 1, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is derived from a polyester polyol containing monomer units derived from an aromatic monomer.

10. The kit according to claim 1, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is derived from at least 50 wt% polyester polyol relative to the total amount of polyol incorporated into the prepolymer.

11. The kit according to claim 1, wherein the polyester polyol derived from the isocyanate-functionalized aliphatic polyurethane prepolymer comprises monomer units derived from aromatic dicarboxylic acids and monomer units derived from aliphatic dicarboxylic acids.

12. The kit according to claim 1, wherein the polyester polyol derived from the isocyanate-functionalized aliphatic polyurethane prepolymer comprises monomer units derived from 10 to 55 wt% aromatic dicarboxylic acid.

13. The kit according to claim 1, wherein the polyester polyol derived from the isocyanate-functionalized aliphatic polyurethane prepolymer comprises monomer units derived from 45 wt% to 90 wt% aliphatic dicarboxylic acid.

14. The polyester polyol derived from the isocyanate-functionalized aliphatic polyurethane prepolymer comprises monomer units derived from a mixture of linear glycol and branched glycol, optionally comprising 500 gmol of the linear glycol and branched glycol. －１ The kit according to claim 1, having a molecular weight of less than 1.

15. The kit according to claim 1, wherein the polyester polyol and / or polyether polyol derived from the isocyanate-functionalized aliphatic polyurethane prepolymer each has a number average molecular weight of 1000 g / mol or less.

16. The kit according to claim 1, wherein the polyester polyol and / or polyether polyol derived from the isocyanate-functionalized aliphatic polyurethane prepolymer is linear.

17. The kit according to claim 1, wherein the molar ratio of the NCO group of the aliphatic isocyanate monomer to the HO group of the polyol derived from the isocyanate-functionalized aliphatic polyurethane prepolymer is 4:1 to 2:1, or 3:1 to 2:

1.

18. i) the polyol crosslinking agent is a linear or branched polyester polyol, or ii) the polyol crosslinking agent is a mixture of at least one linear or branched polyester polyol and at least one linear or branched polyether polyol, according to claim 1.

19. The kit according to claim 1, wherein the polyol crosslinking agent is a polyester polyol formed from one or more glycols and one or more dicarboxylic acids.

20. The kit according to claim 19, wherein one or more glycols are selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, neopentyl glycol, tetramethylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, methyl ether derivatives of any of the above glycols, and combinations thereof.

21. The kit according to claim 19, wherein the dicarboxylic acid is selected from the group consisting of aliphatic dicarboxylic acids, namely malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, methylsuccinic acid, aspartic acid, malic acid, and aromatic dicarboxylic acids, namely terephthalic acid, isophthalic acid, and combinations thereof.

22. The kit according to claim 19, wherein the polyester polyol of the polyol crosslinking agent is derived from a non-glycol polyol.

23. The kit according to claim 1, wherein the polyol crosslinking agent is a polyester polyol containing a tertiary amine group in its skeleton.

24. The kit according to claim 1, wherein the additional aliphatic polyisocyanate has a viscosity of 3,000 mPas or less at 23°C.

25. The kit according to claim 1, wherein the additional aliphatic polyisocyanate is selected from the group consisting of hexamethylene diisocyanate trimers, hexamethylene diisocyanate allophanates, hexamethylene diisocyanate biuret, and combinations thereof.

26. The kit according to claim 1, wherein the wt% ratio of the polyurethane prepolymer to the additional polyisocyanate in the composition comprising the additional aliphatic polyisocyanate is 8:1 to 1:

1.

27. A laminating adhesive comprising the components of the solvent-free laminating adhesive kit described in claim 1, mixed in a single composition.

28. A retort pouch containing the lamination adhesive described in claim 27.

29. A method for providing a multi-layered structure, a) Forming a laminated adhesive from the components of a kit according to any one of claims 1 to 26, or providing a laminated adhesive according to claim 27, and b) The method comprising applying the lamination adhesive to a flexible film.

30. The method according to claim 29, wherein the flexible film is selected from the group consisting of polyethylene terephthalate, nylon, aluminum, oriented polypropylene, cast polypropylene, low-density polyethylene, linear low-density polyethylene, vacuum-modified polyethylene terephthalate, aluminum oxide-polyethylene terephthalate, silicon oxide-polyethylene terephthalate, aluminum oxide-oriented polypropylene, silicon oxide-coated oriented polypropylene, aluminum oxide-oriented polyethylene, silicon oxide-oriented polyethylene, aluminum oxide-nylon, and silicon oxide-nylon, as well as coating films thereof.

31. The method according to claim 29, comprising applying the adhesive at a press speed of more than 50 m / min or more than 100 m / min.

32. A method for manufacturing a kit according to any one of claims 1 to 26, a) A step of reacting an aliphatic isocyanate monomer with a polyester polyol and / or polyether polyol to obtain an isocyanate-functionalized aliphatic polyurethane prepolymer containing monomer units derived from the aliphatic isocyanate monomer, Aliphatic polyurethane prepolymers are formed from aliphatic isocyanates, and aliphatic isocyanates are those in which the isocyanate group(s) are not directly bonded to an aromatic ring. The aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, methylene dicyclohexyl diisocyanate, xylylene diisocyanate, tetramethyl xylylene diisocyanate, pentamethylene diisocyanate, and combinations thereof. The molar ratio of the NCO group of the aliphatic isocyanate monomer to the HO group of the polyol derived from the isocyanate-functionalized aliphatic polyurethane prepolymer is 5:1 to 2:1, in the step, b) A step of reducing the residual isocyanate monomer present in the aliphatic polyurethane prepolymer to less than 0.1% (w / w) of the prepolymer. c) Introducing an additional aliphatic polyisocyanate selected from the group consisting of aliphatic polyisocyanate trimers, aliphatic polyisocyanate allophanates, aliphatic polyisocyanate biuretes, aliphatic polyisocyanate oligomers, aliphatic polyisocyanate urelegions, and combinations thereof, and d) The method comprising the step of introducing a polyol crosslinking agent into the kit, wherein the polyol crosslinking agent is a linear or branched polyether polyol and / or a linear or branched polyester polyol, and the polyol crosslinking agent does not contain a silane additive that can react with an isocyanate.

33. The method according to claim 32, wherein the aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of isophorone diisocyanate, 1,6-hexane diisocyanate, xylylene diisocyanate, and combinations thereof.

34. The method according to claim 32, wherein the amount of isocyanate monomer is reduced by stripping the prepolymer using a series of one or more wipe-type film evaporators and / or short-path evaporators.

35. The method according to claim 32, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is difunctionalized with isocyanate groups, and optionally, the isocyanate-functionalized aliphatic polyurethane prepolymer is linear and isocyanate-functionalized at each end.

36. The method according to claim 32, wherein step a) comprises reacting the aliphatic isocyanate with a polyester polyol.

37. The method according to claim 36, wherein the polyester polyol derived from the isocyanate-functionalized aliphatic polyurethane prepolymer comprises monomer units derived from aromatic dicarboxylic acids and monomer units derived from aliphatic dicarboxylic acids.

38. The method according to claim 32, wherein, prior to step a), the method further comprises the step of reacting a mixture of aromatic dicarboxylic acid and aliphatic dicarboxylic acid with at least one polyol to form the polyester polyol.

39. The method according to claim 38, wherein at least one polyol according to claim 38 is selected from the group consisting of neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, monoethylene glycol, and combinations thereof.

40. The method according to claim 32, wherein the kit does not contain a solvent.

41. Use of the kit according to any one of claims 1 to 26 for forming a laminated adhesive.

42. The use according to claim 41, wherein the laminated adhesive forms part of the retort packaging.

43. The use according to claim 42, wherein the retort packaging is a pouch.

44. A use of the kit according to any one of claims 1 to 26 for improving the adhesive strength under retort conditions of a multilayer structure formed from a flexible film and a laminating adhesive formed from the kit, compared to a multilayer structure formed from a flexible film and a laminating adhesive not formed from the kit of the present invention, wherein the adhesive strength is such that it is necessary to separate at least two layers of the multilayer structure bonded with the adhesive, and is measured at 100 mm / min at room temperature (25°C).

45. The use according to claim 44, wherein the retort conditions include heating at 100°C or higher for 20 minutes.

46. The use according to claim 44, wherein the retorting conditions include placing the multilayer structure in an autoclave with an internal pressure of 1.5 bar to 3 bar.

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