Retortable, solvent-free laminating 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 TO RELATED APPLICATIONS This application claims priority from EP application 22209746.1, the contents of which are incorporated herein by reference.

[0002] The present invention relates to solventless two-part adhesives and their use in providing laminates for retort applications. [Background technology]

[0003] Retorting is a process well known in the packaging industry in which sealed bags containing moist food are subjected to elevated temperatures, usually above 100°C, to both cook and sterilise the food.

[0004] Solvent-based adhesives are used in retort applications because they provide the adhesive strength between layers of packaging laminates under the conditions of the retort process, necessary to ensure the integrity of the laminate without delamination failure. In particular, solvent-based adhesives are highly resistant to thermal degradation, in part because they allow the use of higher molecular weight starting materials that build stronger networks that are less likely to form mobile low molecular weight species upon thermal degradation. The solvent maintains the appropriate viscosity of the composition used for lamination, which would otherwise increase in viscosity as a result of incorporating high molecular weight materials.

[0005] Therefore, it would be desirable to provide an alternative solvent-free adhesive for retort applications to eliminate the need to remove and handle volatile solvents such as ethyl acetate and methyl ethyl ketone (MEK). Additionally, higher lamination press speeds can be achieved using solvent-free adhesives.

[0006] Solvent-free adhesives are known in the art. However, in the absence of solvent, the molecular weight of the components must be limited to provide a composition with a viscosity suitable for use in lamination. Also, while low molecular weight species can provide a low viscosity composition, they can also migrate through the composition and contaminate food products that come into contact with it.

[0007] One way to provide a lower viscosity adhesive composition and reduce the amount of migratory species present in the adhesive is to remove residual isocyanate monomers, for example, using evaporation techniques. EP 3176196 relates to a one-component laminating adhesive containing an aromatic isocyanate polyurethane prepolymer, in which the amount of free diisocyanate monomer in the polyurethane prepolymer is reduced to less than 0.1% (w / w) using a thin-film evaporator. The residual diisocyanate monomer is removed at 140°C under a pressure of 0.1 mbar or less. However, EP 3176196 does not disclose two-component adhesives, such as the adhesives according to the present invention containing aliphatic polyurethane prepolymers, which have different requirements from one-component adhesives. Furthermore, EP 3176196 does not disclose that these adhesive compositions are suitable for preparing flexible packaging laminates for the production of retort pouches.

[0008] US 5,202,001 discloses the use of a thin-film evaporator to remove aromatic diisocyanates (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 can form under retort conditions. Furthermore, US 5,202,001 does not relate to adhesive compositions, nor does it disclose adhesives according to the present invention that include aliphatic polyurethane prepolymers. Furthermore, US 5,202,001 does not disclose the use of adhesives in the preparation of retortable laminates.

[0009] There are many prior art documents related to reducing the amount of residual diisocyanate monomer present in polyurethane prepolymers by distillation in the presence of a solvent known as an "inert solvent." In this regard, US20030065124 discloses the removal of free diphenylmethane diisocyanate (MDI) by vacuum distillation using a wiped film 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 polyurethane prepolymers prepared from aromatic paraphenylene diisocyanate (PPDI), in which the free monomer is also removed using a wiped film evaporator. In this case, dimethyl adipate is used as the "inert solvent."

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

[0011] CN110922929 relates to a one-component isocyanate-functionalized polyurethane prepolymer-based adhesive that can be used to produce flexible laminates. CN110922929 does not relate to two-component adhesives, nor does it disclose reducing the amount of free isocyanate monomer to less than 0.1% (w / w) of the polyurethane prepolymer component. Furthermore, it does not teach how to remove residual isocyanate monomer while maintaining the viscosity of the disclosed composition at a level suitable for use in a laminator. CN110922929 does not disclose the use of a wiped film evaporator. Furthermore, CN110922929 does not teach that the use of an aliphatic polyurethane precursor can result in a lamination adhesive with improved adhesive strength under retort conditions. Furthermore, the one-component CN110922929 composition requires a large amount of catalyst to function, resulting in a significantly reduced pot life and making it unsuitable for use in two-component adhesive kits.

[0012] CN102604583B relates to a solventless, two-component adhesive that can be used to produce 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 components, nor does it teach how to remove residual isocyanate monomer while maintaining the viscosity of the disclosed composition at a level suitable for use in a laminator. Furthermore, CN102604583B does not disclose the use of a wiped film evaporator. Furthermore, 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 Summary of the Invention [Problem to be solved by the invention]

[0014] To the inventors' knowledge, the successful use of a solventless two-component lamination adhesive suitable for retort applications, comprising an aliphatic polyurethane prepolymer containing less than 0.1% (w / w) free isocyanate monomer content, has not been disclosed. Thus, the solventless lamination adhesive kit of the present invention is advantageous in at least this respect. Further advantages associated with the solventless lamination adhesive kit of the present invention are described herein. [Means for solving the problem]

[0015] The present invention provides a solventless lamination adhesive kit comprising an isocyanate-functionalized aliphatic polyurethane prepolymer containing monomer units derived from an aliphatic isocyanate monomer and a polyol crosslinker. 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, tetramethylxylylene diisocyanate, pentamethylene diisocyanate, and combinations thereof.

[0016] The adhesive kit of the present invention is a two-part adhesive kit, i.e., it includes an isocyanate-functionalized prepolymer in addition to a polyol crosslinker.

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

[0018] The present invention further provides a method of providing a multi-laminate structure comprising forming a laminating adhesive from the 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 preparing the kit of the present invention, comprising the steps of: a) reacting an aliphatic isocyanate with a polyester and / or polyether polyol to obtain an isocyanate-functionalized aliphatic polyurethane prepolymer comprising monomer units derived from aliphatic isocyanate monomers; 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 crosslinker to the kit.

[0020] The present invention further provides the use of the kit of the present invention to form a laminating adhesive. The present invention further provides the use of the kit of the present invention to improve the adhesive strength under retort conditions of a multilaminate structure formed from a flexible film and a laminating adhesive formed from the kit of the present invention. This improvement is compared to a multilaminate structure formed from the same flexible film and laminating adhesive not formed from the kit of the present invention. The adhesive strength is the strength required to separate at least two layers of the adhesively bonded multilaminate structure, measured at room temperature (25°C) and 100 mm / min. DETAILED DESCRIPTION OF THE INVENTION

[0021] definition 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 attached to an aromatic group. Aromatic isocyanate = an isocyanate containing at least one isocyanate group (-NCO) directly attached to an aromatic ring. Aliphatic isocyanate = an isocyanate in which the isocyanate group(s) (-NCO) are not directly attached to an aromatic ring. Aliphatic isocyanates include cycloaliphatic isocyanates. Thus, an aliphatic isocyanate can contain an aromatic ring as long as the isocyanate group(s) are not directly attached to the aromatic ring. For example, xylylene diisocyanate. Aromatic polyurethane = polyurethane formed from aromatic isocyanates. Those skilled in the art will understand that it is only the identity of the isocyanate (either aliphatic or aromatic) that determines the nature of the polyurethane as either aliphatic or aromatic. For purposes of this invention, an aliphatic polyurethane prepolymer is derived from 95 mole % or more aliphatic isocyanate monomers, based on the total moles of isocyanate monomers incorporated into the prepolymer. Aliphatic polyurethane = polyurethane formed from aliphatic isocyanates. Those skilled in the art will understand that it is only the identity of the isocyanate (either aliphatic or aromatic) that determines the nature of the polyurethane as either aliphatic or aromatic. For purposes of this invention, an aliphatic polyurethane prepolymer is derived from 95 mole % or more aliphatic isocyanate monomers, based on the total moles of isocyanate monomers incorporated into the prepolymer. Aromatic-aliphatic polyurethane = a polyurethane formed from an aromatic isocyanate and an aliphatic isocyanate. For purposes of this invention, an aromatic-aliphatic polyurethane prepolymer is one that contains more than 5 mol% and less than 95 mol% aromatic isocyanate monomers, and more than 5 mol% Derived from less than 95 mol % aliphatic isocyanate monomers. Aromatic carboxylic acid = a carboxylic acid containing at least one acid (-COOH) group directly attached to an aromatic ring. Aliphatic carboxylic acid = a carboxylic acid in which the carboxylic acid group(s) (-COOH) are not directly attached to an aromatic ring. Aliphatic carboxylic acids include alicyclic carboxylic acids. Thus, an aliphatic carboxylic acid can contain an aromatic ring as long as the carboxylic acid group(s) are not directly attached to the aromatic ring. Free isocyanate monomer = an isocyanate monomer species that has not undergone reaction with a comonomer, e.g., a polyol. For example, the unreacted starting material from a polymerization reaction used to form a polyurethane prepolymer. Solvent-free = Contains up to 5 wt% of any solvent. Retort pouch = A type of food packaging material made from a flexible plastic laminate. Retort conditions = cooking and sterilization method for retort-packaged foods. Usually, it requires heating at an elevated temperature, for example, 115 to 125°C, for a certain period of time, for example, 20 to 60 minutes. Two-part adhesive = an adhesive composition containing two components, one of which induces crosslinking of the other component. One-component adhesive = adhesive composition containing one component, which usually crosslinks by reaction with residual moisture. PET = polyethylene terephthalate PE = polyethylene ALU = Aluminum CPP = Cast Polypropylene OPA = nylon AlOx = aluminum oxide SiOx = silicon oxide OPP = Oriented Polypropylene OPE = oriented polyethylene LDPE = low density polyethylene LLDPE = Linear low density polyethylene VM-PET = Vacuum-deposited polyethylene terephthalate Methylenedicyclohexyl diisocyanate includes the 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 endpoints. For example, the range from 3 to 9 includes the endpoints 3 and 9. However, when the endpoints are defined as "greater than" one value and / or "less than" another value, the range does not include each endpoint.

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

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

[0025] The present invention The present invention provides an improved two-component solventless laminating adhesive kit comprising an aliphatic polyurethane prepolymer, which is suitable for preparing flexible packaging laminates that may be used in retort applications.

[0026] To the best of our knowledge, this is the first reported example of the use of a solvent-free, aliphatic, two-part laminating adhesive for the preparation of flexible multi-layer laminates for retort applications, where the laminates can withstand heat processing temperatures of 100°C or greater.

[0027] The two-component solventless laminating adhesive kit of the present invention comprises an aliphatic isocyanate-functionalized polyurethane prepolymer prepared from an aliphatic isocyanate monomer, such as a 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 wiped film evaporator). The adhesive of the present invention is particularly suitable for preparing flexible packaging laminates used in the production of retortable, pasteurizable, and boilable pouches.

[0028] Thus, the kits of the present invention can be used to improve the adhesive strength under retort conditions of multi-laminate structures formed from flexible films and laminating adhesives formed from components of the kits of the present invention, the improved adhesive strength being related to increased peel resistance of the laminate structure compared to a comparative laminate structure formed from the same flexible film and laminating adhesive that is not formed from components of the kits of the present invention.

[0029] Retort conditions include heating at temperatures above 100°C for 20 minutes, such as 120°C for 30 minutes or 135°C for 20 minutes. Retort conditions create a pressure differential between the pressure inside the retort package and atmospheric pressure, which can strain adhesives used to seal the retort package. For example, a low retort test may involve heating the retort pouch in an autoclave at approximately 120°C for at least 30 minutes, where 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, where 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 an aliphatic isocyanate monomer, into a solventless laminating adhesive, the adhesive exhibits improved adhesion under retort conditions, and this improvement is observed compared to a comparative adhesive containing an aromatic polyurethane prepolymer containing monomer units derived from an aromatic isocyanate monomer.

[0031] The adhesive kits of the present invention are also improved over comparative adhesive kits that contain polyurethane prepolymers with residual isocyanate monomer content greater than that required by the present invention.

[0032] The aliphatic, two-part, solventless laminating adhesive kit of the present invention is suitable for preparing flexible packaging laminates that can withstand (i.e., form unbroken seals under) retort conditions at 100° C. or higher for 10 minutes or more. To date, two-part, solventless laminating 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 preparing adhesives for use in the present invention is that it eliminates the risk associated with the formation of harmful primary aromatic amines, which can be formed when adhesives containing polyurethane prepolymers formed from aromatic diisocyanates are subjected to retort conditions. The use of an aliphatic isocyanate-based adhesive 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, having a free diisocyanate monomer content of less than 0.1% (w / w) in the polyurethane prepolymer ensures that the hazards associated with monomeric isocyanates can be mitigated to the extent that the prepolymer does not carry any labeling for hazards associated with free diisocyanate monomers under the current Classification, Labeling and Packaging of Substances and Mixtures (CLP) Guidelines. This advantageously facilitates handling of the adhesive kit of the present invention compared to conventional two-component laminating adhesive kits / compositions that contain large amounts of residual isocyanate. Reducing the amount of free monomeric isocyanate, such as xylylene diisocyanate, present in an adhesive using, for example, a wiped film evaporator, has not previously been reported.

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

[0036] Solventless laminating adhesives do not contain organic solvents or water in order to reduce the viscosity to a level that allows the material to be applied in a laminator at temperatures below 90° C., for example below 80° C. However, as a result of the above advantages, the inventors have discovered a method of making solventless adhesives that, by controlling the molecular weight of the components, can achieve the viscosity required for use in a laminator at said temperatures, without the problems typically associated with the presence of migratory low molecular weight / small molecule components.

[0037] The solventless lamination adhesive kits of the present invention contain no more than 5 wt% of any solvent. Preferably, the solventless lamination adhesive kits of the present invention contain no more than 3 wt% of any solvent, more preferably no more than 1 wt% of any solvent. Even more preferably, the solventless lamination adhesive kits of the present invention are substantially solvent-free.

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

[0039] The two-component adhesive kit of the present invention provides an adhesive with the additional advantages of stronger adhesion, better chemical resistance, and faster cure compared to similar one-component adhesive compositions. One-component adhesives cure using only moisture present in / on the substrate and in the air. Generally, one-component adhesives are compatible with paper or paper substrates laminated to a film. However, in the case of, for example, a film-to-film laminate or a film-to-aluminum laminate, the reaction and bond strength development of the one-component adhesive may be very slow due to low available moisture and / or poor access of moisture to the isocyanate.

[0040] Additionally, 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 to compensate for the slower cure rate by making the isocyanate groups more reactive / sensitive to moisture. Because two-component adhesives do not require a catalyst, the amount of migrating species can be further reduced compared to comparable one-component adhesives. Instead, the isocyanate groups in two-component adhesives react with polyols, which are intimately mixed into the polyurethane prepolymer and provide readily available reactive sites. However, the isocyanate groups in the polyurethane prepolymer of two-component adhesives can also react with residual moisture.

[0041] Aliphatic Polyurethane Prepolymer Polyurethanes with NCO end groups are usually obtained by reacting polyfunctional alcohols with an excess of polyisocyanate monomers. Diisocyanates are generally used at temperatures of 80-90°C to obtain prepolymers with molecular weights and viscosities suitable for use in laminators. This is because diisocyanates (as opposed to more highly functionalized isocyanates) only react with two polyols and therefore do not form crosslinks.

[0042] The polyurethane prepolymers for use in the present invention are characterized by a viscosity at 80°C of from 800 mPas to 20,000 mPas, or preferably from 1,000 mPas to 10,000 mPas, or more preferably from 2,000 mPas to 7,000 mPas.

[0043] Polyurethane prepolymers for use in the present invention preferably have 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 while the advantages associated with the present invention derive from the use of aliphatic polyurethane precursors containing monomer units derived from aliphatic isocyanates, this does not preclude the presence of minor amounts of non-aliphatic isocyanates in the prepolymer, so long as such amounts do not affect these advantageous properties. Accordingly, for purposes of the present invention, an "aliphatic polyurethane prepolymer" is one derived from 95 mol% or more of aliphatic isocyanate monomers, based on the total number of moles of isocyanate monomers incorporated into the prepolymer. Preferably, aliphatic polyurethane prepolymers for use in the present invention are derived from 98 mol% or more, and more preferably 99 mol% or more, of aliphatic isocyanate monomers, based on the total number of moles of isocyanate monomers incorporated into the prepolymer. Most preferably, the isocyanate monomers incorporated into aliphatic polyurethane prepolymers for use in the present invention are exclusively aliphatic isocyanate monomers.

[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 prepolymers for use in the present invention are isocyanate-functionalized, such that reactive NCO groups are attached to the prepolymer. The aliphatic polyurethane prepolymers for use in the present invention contain at least two isocyanate groups per prepolymer. The aliphatic polyurethane prepolymers for use in the present invention are preferably difunctionalized with isocyanate groups, e.g., the aliphatic polyurethane prepolymers for use in the present invention are linear and contain isocyanate groups at either end.

[0046] Polyurethane prepolymers for use in the present invention may contain three or more isocyanate groups per prepolymer, such as four or more, or five or more isocyanate groups.

[0047] The polyurethane prepolymer is preferably linear. For purposes of this invention, a "linear" polyurethane prepolymer is typically one derived from a difunctionalized isocyanate and a difunctionalized polyol, such that each isocyanate-derived moiety is covalently bonded to up to two polyols and each polyol-derived moiety is covalently bonded to up to two isocyanates. Linear polyurethane prepolymers may contain monomeric components that are themselves branched, such as branched glycols.

[0048] Aliphatic polyurethane prepolymers for use in the present invention are preferably derived from polyester polyols, more preferably polyester polyols that include monomer units derived from aromatic monomers such as aromatic dicarboxylic acids.

[0049] Of the polyol components used to prepare the polyurethane prepolymers for use in the present invention, it is preferred 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% be polyester polyols. It is even more preferred that all polyols used to prepare the polyurethane prepolymers for use in the present invention be polyester polyols. The inventors have found that polyester polyols impart desirable high-temperature mechanical properties to the polyurethane prepolymers for use in the present invention.

[0050] The molar ratio of the NCO groups of the aliphatic isocyanate monomers used to prepare the polyurethane prepolymers for use in the present invention to the HO groups of the polyols used to prepare the polyurethane prepolymers for use in the present invention can be from 5:1 to 2:1. Preferably, the molar ratio of the NCO groups of the aliphatic isocyanate monomers used to prepare the polyurethane prepolymers for use in the present invention to the HO groups of the polyols used to prepare the polyurethane prepolymers for use in the present invention is from 4:1 to 2:1, for example, from 3:1 to 2:1.

[0051] The NCO:OH ratio of the isocyanate and polyol used to prepare prepolymers for use in the two-component adhesive kits of the present invention can be lower than that required for one-component adhesives, which rely on residual moisture for curing. Without wishing to be bound by theory, lower NCO:OH ratios can be used when preparing polyurethane prepolymers for use in two-component adhesives. Lower ratios result in polyurethane prepolymers with higher molecular weights and higher viscosities, which can function effectively when combined with polyol crosslinkers. In contrast, when preparing polyurethane prepolymers for use in one-component adhesives, higher NCO:OH ratios are required. Excess NCO results in polyurethane prepolymers with lower molecular weights and therefore lower viscosities sufficient for one-component adhesive applications. Excess isocyanate monomer 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 significant vapor pressures even at room temperature. This poses serious health risks during application because these species are toxic due to their sensitizing and irritating properties. Users are required by law to implement special measures to protect workers during use, including significant additional equipment designed to keep the air breathable and / or maintain these substances below maximum concentrations permitted in the workplace. Consequently, users must install expensive protective equipment for workers exposed to the vapors and / or aerosols of these products generated by the dynamic application conditions of rotating machinery.

[0053] These types of reagents are regulated under hazardous substances legislation and must be labelled as hazardous, which entails special packaging and transport measures.

[0054] Many polyurethane adhesives in the art contain more than 0.1% (w / w) residual isocyanate monomer (usually volatile diisocyanates such as free TDI, MDI, or other isocyanate monomers) (the threshold established by the CLP regulation, below which the product is not considered hazardous). In particular, when a molar excess of isocyanate functional groups relative to the hydroxyl functional groups of the polyol is used, excess free isocyanate monomer remains in the reaction mixture after the polyurethane prepolymer is formed. Unless additional processing steps are performed to remove this excess free monomer, more than 0.1% (w / w) free isocyanate monomer remains in the prepolymer, necessitating the safety precautions mentioned above. Furthermore, when prepolymers containing more than 0.1% (w / w) free isocyanate monomer are used as food packaging adhesives, food contamination by migrating isocyanate monomer may also occur.

[0055] The solventless lamination adhesive kit of the present invention includes 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 monomer. The polyurethane prepolymer is subjected to additional processing steps outlined herein to reduce the amount of free isocyanate monomer to the level required by the present invention.

[0056] The low amount of free monomeric isocyanate monomer required by the present invention may be achieved by stripping unreacted isocyanate monomer from the polyurethane prepolymer using an evaporator (e.g., a wiped 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 to 180°C.

[0057] Preparation of Polyurethane Prepolymers for Use in the Present Invention The polyurethane prepolymers for use in the present invention may be obtained by a process comprising the following protocol: a) an aliphatic diisocyanate, i. optionally using a catalyst, and ii. optionally using an acid compound, with a polyester polyol and / or a polyether polyol, each having a number average molecular weight (Mn) of ≦1000 g / mol, in an NCO:OH molar ratio of 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 stages using a series of one or more wiped 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 thus obtained, after removal of the free isocyanate monomer, 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 process for making polyurethane prepolymers for use in the present invention preferably does not require solvents, 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 preparation of polyurethane prepolymers The aliphatic isocyanate for use in preparing the isocyanate-functionalized aliphatic polyurethane prepolymer for use in the present invention is 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 of the foregoing.

[0062] Preferably, the aliphatic isocyanate monomer for use in the present invention is a diisocyanate selected from the group consisting of isophorone diisocyanate (IPDI) and isomeric 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] Aliphatic isocyanates for use in the present invention contain isocyanate groups that are not directly attached to an aromatic ring, and therefore may contain aromatic groups, so long as the isocyanate groups are not directly attached.

[0064] Polyols for preparing polyurethane prepolymers for use in the present invention The polyol for use in preparing 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 for use in the present invention is preferably a polyester polyol, more preferably a polyester polyol comprising monomer units derived from aromatic monomers.

[0065] The polyester polyols for use in the present invention are selected to provide a desirable combination of properties. In particular, the polyols are selected so that when incorporated into the polyurethane prepolymers for use in the present invention, the polyurethane prepolymers have desirable mechanical properties at elevated temperatures and a final viscosity suitable for use in laminators at 80-90°C.

[0066] The inventors have found that particularly preferred polyester polyols for use in the present invention can be characterized as follows: 1. containing a mixture of aromatic and aliphatic dicarboxylic acids, and / or 2. Contains a mixture of linear and branched short chain glycols, and / or 3. Having an OH number in the range of 110 to 400 mg KOH / g, and / or 4. It has a viscosity in the range of 500 to 10,000 mPas at 23°C.

[0067] Although polyester polyols for use in the present invention may contain other components such as polyether moieties, it is preferred that at least 50 mol % of the monomer units present 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 monomer units present are polyester monomer units. Polyester polyols for use in the present invention may contain only polyester monomer units.

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

[0069] The polyester 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 (and optionally monofunctionalized) monomers, such that each monomer unit can react with a maximum of two other monomers. In other words, the maximum functionality of the monomer is two. For example, dicarboxylic acids and diols produce 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% of 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 polyurethane prepolymers derived from such polyols generally exhibit improved mechanical properties at temperatures typical for retort processing, particularly improved adhesive strength under retort conditions. Without wishing to be bound by theory, the inventors believe that this improvement is due to the higher hydrolysis resistance and higher glass transition temperature (T) of these polyester polyols. g ) is speculated to be related to

[0071] Polyurethanes based on polyester polyols are generally more viscous than polyurethanes based on polyethers, and polyester polyols containing aromatic rings in the backbone are even more viscous than pure aliphatic polyester polyols. The present inventors have found that by incorporating a mixture of aliphatic and aromatic groups into the polyester polyols for use in the present invention, polyurethane prepolymers with improved mechanical properties and viscosity suitable for use in adhesive laminate applications can be obtained.

[0072] The polyester polyols for use 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 an aromatic monomer, based on the total wt% of the polyester polyol. The aromatic monomer is preferably an aromatic dicarboxylic acid, such as isophthalic acid.

[0073] The polyester polyols for use in the present invention may be derived from 45 wt% to 90 wt%, preferably 55 wt% to 85 wt%, and more preferably 65 wt% to 85 wt% of aliphatic monomers, based on the total wt% of the polyester polyol. The aliphatic monomers are preferably aliphatic dicarboxylic acids, such as sebacic acid. The aliphatic monomers are also preferably aliphatic polyols, such as aliphatic glycols and aliphatic diols.

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

[0075] Polyester polyols for use in the present invention may contain 15 to 35% monomer units derived from aromatic dicarboxylic acids and 65 to 85 wt % monomer units derived from aliphatic dicarboxylic acids and aliphatic glycols and aliphatic diols.

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

[0077] The aromatic dicarboxylic acid used in the preparation of the polyester polyol is preferably selected from the list consisting of terephthalic acid, isophthalic acid, phthalic anhydride, and combinations thereof. The aliphatic dicarboxylic acid used in the preparation of the polyester polyol is preferably a linear C2-C 14 Dicarboxylic acids, such as linear C2-C6 dicarboxylic acids selected from the group consisting of 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 can be from 10:1 to 1:10, preferably from 4:1 to 1:4, and more preferably from 2:1 to 1:2. The weight ratio of aromatic dicarboxylic acid to aliphatic dicarboxylic acid incorporated into the polyol for use in the present invention can be from 1.5:1 to 1:1.5, such as incorporated at substantially equal wt%.

[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 glycols for use in the present invention are preferably 500 gmol -1 Less than, for example, 300 gmol -1 Less than, and preferably less than 200 gmol -1 has a molecular weight of less than

[0081] The weight percent ratio of linear to branched short chain glycols incorporated into polyols for use in the present invention can be from 10:1 to 1:10, preferably from 4:1 to 1:4, and more preferably from 2:1 to 1:2. The weight ratio of linear to branched short chain glycol dicarboxylic acids incorporated into polyols for use in the present invention can be from 1.5:1 to 1:1.5, such as incorporated at substantially equal wt %.

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

[0083] In particular, the use of an adhesion promoter, such as a silane containing a group reactive with isocyanate groups (e.g., 3-aminopropyltriethoxysilane), is advantageous when the adhesive system is used on metal or metallized substrates, such as aluminum. Such an adhesion promoter can also be incorporated into the polyol crosslinker. However, such a component is not required for the adhesive kit of the present invention. The inventors have found that the adhesive of the present invention performs well under retort conditions even without an isocyanate-reactive silane additive. Therefore, the polyol-functionalized crosslinker for use in the present invention may not contain a silane compound capable of reacting with isocyanates.

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

[0085] The additional aliphatic polyisocyanate(s) are preferably selected from the group consisting of aliphatic polyisocyanate trimers (i.e., isocyanurates), aliphatic polyisocyanate allophanates, aliphatic polyisocyanate oligomers, aliphatic polyisocyanate biurets, aliphatic polyisocyanate uredione, 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) allophanates, hexamethylene diisocyanate biurets, uredione / 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 of allophanates include Desmodur Ultra N3300, Desmodur Ultra N3600, Desmodur Ultra N3900, and Desmodur XP2860. Allophanates are isocyanate dimers.

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

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

[0089] catalyst If desired, the urethanization reaction can be accelerated by adding a suitable catalyst during the preparation stage. Suitable catalysts for the urethanization 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 for use in the present invention (and the kit of the present invention) may be catalyst-free.

[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'-tetramethylethyl Diamine, 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 of suitable organic solvents include alkanolamines such as diethanolamine, N-methyl- and N-ethyldiethanolamine, dimethylaminoethanol, 2-(N,N'-dimethylaminoethoxy)ethanol, N,N',N-tris-(dialkylaminoalkyl)-hexahydrothiazines such as N,N',N-tris-(dimethylaminopropyl)-s-hexahydrothiazine, 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, tin salts such as iron(II) chloride, zinc chloride, lead octoate, tin dioctoate, tin diethylhexanoate, butyltin dilaurate, and dibutyldilauryltin mercaptide, titanium compounds such as titanium(IV) butyrate, organometallic compounds of tin, lead, iron, titanium, bismuth, and zirconium, tin oxides and sulfides, and bismuth carboxylates.

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

[0092] Polyol Crosslinker The polyol crosslinker for use in the kits of the present invention may be a polyol suitable for curing the isocyanate-functionalized aliphatic polyurethane prepolymers for use in the present invention.

[0093] The polyol crosslinker 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 crosslinker for use in the present invention may be a mixture of polyester polyols and polyether polyols. The polyol crosslinker for use in the present invention is preferably a polyester polyol.

[0094] The polyol crosslinker for use 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 ethers), polypropylene glycol (including its methyl ethers), and polybutylene glycol (including its methyl ethers). 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, and 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, including trimethylolpropane.

[0095] Polyol crosslinkers for use in the present invention may be polyester polyols containing tertiary amine groups in the backbone.

[0096] Polyol crosslinkers for use in the present invention, such as polyester polyols, 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 crosslinker for use in the present invention may be incorporated into a crosslinking composition further comprising a polyether monol (i.e., containing a single hydroxyl substituent, e.g., polypropylene glycol monoalkyl ether) (as part b). The polyether monol 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 crosslinker for use as part b) in the present invention may be incorporated into a crosslinking composition further comprising polypropylene glycol monomethyl ether.

[0098] The polyether monol 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, the polyether monol (e.g., polypropylene glycol monoalkyl ether) may be incorporated into the part b) polyol crosslinker composition in an amount of up to 50 wt %, e.g., up to 40 wt %, based on the total weight of both the polyol crosslinker and the polyether monol. In other words, the wt % ratio of part b) polyol crosslinker to polyether monol (if present) may be from 100:0 to 50:50, e.g., from 80:20 to 50:50, or from 70:30 to 60:40, e.g., about 60:40.

[0100] The kit of the present invention comprises an aliphatic polyurethane prepolymer and optionally an additional polyisocyanate as part a) and a polyol crosslinker as part b), the weight percent ratio of part a) to part b) can be 5:1 to 1:2, preferably 4:1 to 1:1, and more preferably 3:1 to 1:1.

[0101] laminate There is a large market for adhesively molded multilaminates for retort applications. Typical constructions 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 substrates to form a laminate.

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

[0104] The present invention is defined by the following non-limiting examples, which further illustrate the invention and are not intended to, and should not 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. LVD VII, in accordance with ASTM D1084 at the specified temperatures. Unless otherwise specified, viscosity is measured at 23°C. -Hydroxyl number (OH number): The number of milligrams of potassium hydroxide required to neutralize the acetic acid incorporated during the acetylation of one gram of a chemical containing free hydroxyl groups. The hydroxyl number is measured using the standard procedure specified in ISO 4629-1:2016(E). -Molecular weight: a) The molecular weight of a non-polymeric or oligomeric compound (i.e., a defined monomeric species) is defined and calculated according to the molecular structure of the compound. This is usually found in the technical data sheet of the monomer supplier or can be found on the European Chemical Agency (ECHA) webpage. b) Oligomeric and polymeric species typically contain a distribution of chain lengths and therefore a distribution of molecular weights. Therefore, unless otherwise specified, the molecular weights of oligomeric and polymeric species (as well as components present as a mixture (and therefore distributed) of species with molecular weights greater than 500 Da—e.g., vegetable oils)—are measured using a Hewlett-Packard 1050 series HPLC system equipped with two GPC Ultrastyragel columns, 103 Å and 104 Å (5 μm mixed, 300 mm × 19 mm, Waters Millipore Corporation, Milford, MA, USA), using THF as the mobile phase. The column temperature is 40°C. Molecular weights are calculated by comparison with polystyrene standards. Those skilled in the art will understand that this definition of molecular weight generally applies to polymeric materials with a molecular weight distribution. Unless otherwise specified, the molecular weights of oligomeric and polymeric species reported herein are number average molecular weights. - Adhesion strength refers to the strength required to separate a multi-laminate structure formed from a flexible film and a laminating adhesive formed from the components of the adhesive kit. The multi-laminate structure includes at least two layers bonded with a laminating adhesive. Adhesion strength was measured at room temperature (25°C) at 100 mm / min. Other parameters comply with ASTM D3330-F (90° peel test).

[0106] Improved adhesive strength refers to increased peel resistance of a laminated structure from a flexible film and a laminating adhesive formed from a component of the kit of the present invention compared to a comparative laminated structure formed from the same flexible film but using a laminating adhesive not formed from a component of the kit of the present invention.

[0107] Example 1: Synthesis of polyester polyol The polyester polyol of Example 1 is prepared by combining the following diols and dicarboxylic acids and reacting them in a 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 combined in the amounts described above, and has the following characteristics: OH value = 265 mg KOH / 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 a reflux condenser under a continuous nitrogen flow. The mixture is heated to 50°C and 450 parts of Polyester Polyol A of Example 1 (having a functionality of 2 and a number average M w C. An OH-terminated polyester polyol having a molecular weight of 420 g / mol is added dropwise over 240 minutes under stirring, monitoring the temperature of the reaction mixture and adjusting the rate of polyol addition so that it never exceeds 60.degree.

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

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

[0112] Example 3: Preparation of a solvent-free aliphatic isocyanate prepolymer with residual monomer levels 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 give 1000 parts of a clear, colorless liquid with 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 wt% 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 produced using a Nordmeccanica Group Labo Combi 400 laminator under the following conditions: Coating weight: 2.5gsm / dry; Adhesion roller speed: 80; Adhesive roller temperature: 50℃; Application roller temperature: 50℃; Tension unwinder A: 23N; Tension unwinder B: 20N; Tension winder (laminate): 28N; Coating head pressure: 3bar; Nip pressure: 3bar; 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 laminating adhesive that can be processed at 50°C. The polyurethane prepolymer (NS-4158A) is aromatic, i.e., the polyurethane contains monomer units derived from aromatic isocyanates.

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

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

[0118] MP70 is a 60 / 40 blend of DIC Dry HA930 (a polyester polyol, DIC Graphics Corporation) and Smack MP-70 (Kao Corporation), which 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 combined with monoethylene glycol, neopentyl glycol, isophthalic acid, and adipic acid, typically used in combination with an aromatic isocyanate-functionalized prepolymer.

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

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

[0122] [Table 3]

[0123] Comparative examples (Samples 1 and 2) prepared with aromatic polyisocyanate prepolymers containing standard or very low levels of free monomer failed the high retort test and nearly failed the low retort test. The laminates that survived the low retort process maintained their appearance and showed no delamination, but had little adhesive strength and were therefore unsuitable for use in retort applications.

[0124] Four samples according to inventive Example 3 (i.e., Samples 3, 4, 5, and 6) were cured with various polyol crosslinkers and survived both low and high retort processes, maintaining their appearance and integrity while exhibiting sufficient adhesive strength.

[0125] Although the present invention has been described in detail, including various embodiments thereof, it will be appreciated that those skilled in the art, upon consideration of this disclosure, may make modifications and / or improvements to the present invention which are within the scope and spirit of the present invention.

[0126] Numbered Embodiments of the Invention The present invention is defined by the following numbered embodiments, which form a part hereof.

[0127] 1. A solventless laminating adhesive kit comprising: a) an isocyanate-functionalized aliphatic polyurethane prepolymer comprising monomer units derived from an aliphatic isocyanate monomer; and b) a polyol crosslinker; wherein the amount of free isocyanate monomer present in said polyurethane prepolymer is 0.1% (w / w) or less of said prepolymer.

[0128] 2. The kit of 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, tetramethylxylene diisocyanate, pentamethylene diisocyanate, and combinations thereof; 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 of 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 at 80°C of between 800 mPa and 20,000 mPas, e.g., between 1,000 mPas and 10,000 mPas, or between 2,000 mPas and 7,000 mPas, where viscosity is measured according to the methods 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 greater than 80 mol % aliphatic isocyanate, e.g., greater than 90 mol %, or greater than 95 mol % aliphatic isocyanate, based on the total number of moles of isocyanate incorporated in the prepolymer; and / or d) The kit of any of the preceding embodiments, wherein the only isocyanates incorporated into said isocyanate-functionalized aliphatic polyurethane prepolymer are aliphatic isocyanates.

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

[0132] 6.i) the isocyanate-functionalized aliphatic polyurethane prepolymer is derived from at least 50 wt. % polyester polyol, based on the total amount of polyol incorporated into the prepolymer; and / or ii) the polyester polyol comprises monomer units derived from a mixture of aromatic and aliphatic dicarboxylic acids; and / or iii) The kit of embodiment 5, wherein the polyester polyol comprises 10 to 55 wt %, for example 15 to 45 wt %, or 15 to 35 wt % of monomer units derived from aromatic monomers.

[0133] 7.i) the polyester polyol comprises 45 wt% to 90 wt% of monomer units derived from aliphatic monomers, for example 55 wt% to 85 wt%, or 65 wt% to 85 wt% of monomer units derived from aliphatic monomers, and / or the polyester polyol comprises monomer units derived from a mixture of linear glycols and branched glycols, optionally wherein the linear glycols and the branched glycols are in an amount of 500 gmol -1 Less than, for example, 200 gmol -1 and / or has a molecular weight of less than ii) the polyester polyol and / or the 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 crosslinker does not contain silane compounds capable of reacting with isocyanates, such as aminosilanes, and / or ii) the polyurethane prepolymer is incorporated into a composition further comprising an additional polyisocyanate, and optionally The kit of any of the preceding embodiments, wherein the additional polyisocyanate is selected from the group consisting of hexamethylene diisocyanate trimer, hexamethylene diisocyanate allophanate, or a combination thereof.

[0135] 9. A lamination adhesive comprising the components of the solventless lamination adhesive kit according to any of the preceding embodiments mixed into a single composition.

[0136] 10. A retort pouch comprising the lamination adhesive of embodiment 9.

[0137] 11. A method for providing a multi-laminate structure, comprising: i) forming a lamination adhesive from the components of the kit according to any one of embodiments 1 to 8, or providing a lamination adhesive according to embodiment 9; and ii) applying a lamination adhesive to the 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 coated films thereof; and / or ii) The method of embodiment 11, wherein the method further comprises applying the adhesive at a press speed of greater than 50 m / min, or greater than 100 m / min.

[0139] 13. A method of manufacturing a kit according to any of the preceding embodiments, comprising: a) reacting an aliphatic isocyanate with a polyester and / or polyether polyol to obtain an isocyanate-functionalized aliphatic polyurethane prepolymer comprising monomer units derived from an aliphatic isocyanate monomer; b) reducing the residual isocyanate monomer present in the prepolymer to less than 0.1% (w / w) of the prepolymer; c) introducing a polyol crosslinker into the kit The method includes the steps of:

[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, tetramethylxylene diisocyanate, pentamethylene diisocyanate, and combinations thereof; and / or ii) the aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of isophorone diisocyanate, 1,6-hexane diisocyanate, xylylene diisocyanate, and combinations thereof; and / or iii) the amount of isocyanate monomer is reduced by stripping the prepolymer using a series of one or more thin film evaporators and / or molecular evaporators; 14. The method of embodiment 13.

[0141] 15.i) the isocyanate-functionalized aliphatic polyurethane prepolymer is the isocyanate-functionalized aliphatic polyurethane prepolymer of any one of embodiments 3 to 6; and / or ii) step a) comprises reacting the aliphatic isocyanate with a polyester polyol, optionally the polyester polyol being the polyester polyol of embodiment 6 or 7; and / or iii) before step a), the method further comprises reacting a mixture of aromatic dicarboxylic acids and aliphatic dicarboxylic acids with at least one polyol to form a polyester polymer; and optionally wherein the at least one polyol is a mixture of linear and branched glycols, and optionally the linear and branched glycols are present in an amount of 500 gmol -1 Less than, for example, 200 gmol -1 15. The method of embodiment 13 or 14, wherein the hydroxybenzoate has a molecular weight of less than 1000 mg / kg.

[0142] 16. The method according to any one of embodiments 13 to 15, wherein the method does not comprise a solvent.

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

[0144] 18. Use of a kit according to any of the preceding embodiments to improve the adhesive strength under retort conditions of a multi-laminate structure formed from a flexible film and a laminating adhesive formed from components of the kit, optionally wherein the retort conditions include heating at 100°C or above for 20 minutes, e.g., heating at 120°C for 30 minutes or at 135°C for 20 minutes.

Claims

1. 1. A solventless laminating adhesive kit comprising: a) an isocyanate-functionalized aliphatic polyurethane prepolymer comprising monomeric units derived from an aliphatic isocyanate monomer, wherein the aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, methylene dicyclohexyl diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, pentamethylene diisocyanate, and combinations thereof; and b) a polyol crosslinker; wherein the amount of free isocyanate monomer present in said polyurethane prepolymer is 0.1% (w / w) or less of said prepolymer.

2. 2. The kit of 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, e.g., the aliphatic isocyanate monomer is xylylene diisocyanate.

3. 3. The kit of claim 1 or 2, 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.

4. 4. The kit of any one of claims 1 to 3, wherein the isocyanate-functionalized, aliphatic polyurethane prepolymer has a viscosity at 80°C of between 800 mPa and 20,000 mPas, e.g., between 1,000 mPas and 10,000 mPas, or between 2,000 mPas and 7,000 mPas, wherein the viscosity is measured according to the method described herein.

5. 5. The kit according to any one of claims 1 to 4, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer has an isocyanate group content (% NCO) between 3% and 16%, such as between 5% and 10%.

6. 6. The kit of any one of claims 1 to 5, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is derived from 95 mol % or more aliphatic isocyanate monomers, based on the total isocyanate monomers incorporated into the prepolymer.

7. The kit of any one of claims 1 to 6, wherein the isocyanate monomers incorporated into the isocyanate-functionalized aliphatic polyurethane prepolymer are exclusively aliphatic isocyanate monomers.

8. The kit according to any one of claims 1 to 7, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is derived from a polyol, such as a polyester polyol and / or a polyether polyol.

9. 9. The kit of claim 8, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is derived from a polyester polyol comprising monomer units derived from aromatic monomers.

10. 10. The kit of claim 8 or 9, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is derived from at least 50 wt% polyester polyol, based on the total amount of polyol incorporated into the prepolymer.

11. 11. The kit of any one of claims 8 to 10, wherein the polyester polyol from which the isocyanate-functionalized aliphatic polyurethane prepolymer is derived comprises monomer units derived from an aromatic dicarboxylic acid and monomer units derived from an aliphatic dicarboxylic acid.

12. 12. The kit of any one of claims 8 to 11, wherein the polyester polyol is derived from 10 to 55 wt% aromatic dicarboxylic acid, such as 15 to 45 wt%, or 15 to 35 wt% aromatic dicarboxylic acid.

13. 13. The kit of any one of claims 8 to 12, wherein the polyester polyol is derived from 10 wt% to 55 wt% aliphatic dicarboxylic acids, such as 15 wt% to 45 wt%, or 15 wt% to 35 wt% aliphatic dicarboxylic acids.

14. The polyester polyol from which the isocyanate-functionalized aliphatic polyurethane prepolymer is derived comprises monomer units derived from a mixture of linear and branched glycols, and optionally, the linear and branched glycols are at least 500 gmol －１ less than, for example, 200 gmol －１ 14. The kit of claim 8, wherein the kit has a molecular weight of less than 1000 ribonucleotides.

15. 15. The kit according to any one of claims 8 to 14, wherein the polyester polyol and / or the polyether polyol each have a number average molecular weight of 1000 g / mol or less.

16. The kit according to any one of claims 8 to 15, wherein the polyester polyol and / or the polyether polyol is linear.

17. 17. The kit of any one of claims 8 to 16, wherein the molar ratio of NCO groups of the aliphatic isocyanate monomer to HO groups of the polyol is from 5:1 to 2:1, for example from 4:1 to 2:1, or from 3:1 to 2:

1.

18. 18. The kit of any one of claims 1 to 17, wherein the polyol crosslinker is a linear or branched polyether polyol and / or a linear or branched polyester polyol, and optionally i) the polyol crosslinker is a linear or branched polyester polyol, or ii) the polyol crosslinker is a mixture of at least one linear or branched polyester polyol and at least one linear or branched polyether polyol.

19. The kit of any one of claims 1 to 18, wherein the polyol crosslinker is a polyester polyol formed from one or more glycols and one or more dicarboxylic acids.

20. 20. The kit of claim 19, wherein the 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 foregoing glycols, and / or combinations thereof.

21. 21. The kit of claim 19 or 20, wherein the dicarboxylic acid is selected from the group consisting of aliphatic dicarboxylic acids, i.e., 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, i.e., terephthalic acid, isophthalic acid, and combinations thereof.

22. 22. The kit of any of claims 19 to 21, wherein the polyester polyol of the polyol crosslinker is derived from a non-glycol polyol such as trimethylolpropane.

23. 23. The kit of any one of claims 1 to 22, wherein the polyol crosslinker is a polyester polyol containing tertiary amine groups in the backbone.

24. The kit of any one of claims 1 to 23, wherein the polyol crosslinker does not include a silane compound capable of reacting with an isocyanate, such as an aminosilane.

25. The kit of any one of claims 1 to 24, wherein the polyurethane prepolymer of part a) is incorporated into a composition comprising an additional polyisocyanate.

26. 26. The kit of claim 25, wherein the additional polyisocyanate is an aliphatic polyisocyanate selected from the group consisting of aliphatic polyisocyanate trimers, aliphatic polyisocyanate allophanates, aliphatic polyisocyanate biurets, aliphatic polyisocyanate oligomers, aliphatic polyisocyanate urediones, and combinations thereof.

27. 27. The kit of claim 25 or 26, wherein the additional aliphatic polyisocyanate has a viscosity at 23°C of 3,000 mPas or less, e.g., 2,000 mPas or less, 1,000 mPas or less, or 500 mPas or less.

28. 28. The kit of any one of claims 25 to 27, wherein the additional aliphatic polyisocyanate is selected from the group consisting of hexamethylene diisocyanate trimer, hexamethylene diisocyanate allophanate, hexamethylene diisocyanate biuret, and combinations thereof.

29. 29. The kit of any one of claims 25 to 28, wherein the wt% ratio of the polyurethane prepolymer to the additional polyisocyanate in the composition comprising the additional aliphatic polyisocyanate is from 8:1 to 1:1, such as from 5:1 to 2:1, or from 3:1 to 2:

1.

30. A lamination adhesive comprising the components of the solventless lamination adhesive kit of any one of claims 1 to 29 mixed into a single composition.

31. 31. A retort pouch comprising the lamination adhesive of claim 30.

32. 1. A method for providing a multi-laminate structure, comprising: a) forming a lamination adhesive from the components of a kit according to any one of claims 1 to 29 or providing a lamination adhesive according to claim 30; and b) applying said lamination adhesive to a flexible film; The method comprising:

33. 33. The method of claim 32, 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, and coated films thereof.

34. 34. The method of claim 32 or 33, comprising applying the adhesive at a press speed of more than 50 m / min, or more than 100 m / min.

35. 35. A laminated bonded structure obtainable from the method of any one or more of claims 32 to 34.

36. 36. The structure according to claim 35, which is suitable for preparing a retort pouch that does not suffer from peeling defects under retort conditions of 100°C or higher.

37. 37. The structure of claim 35 or 36, wherein the laminate has an interlayer T-peel adhesion strength of greater than 1.5 N / 15 mm, or greater than 2.0 N / 15 mm, or greater than 2.5 N / 15 mm, before and after retort.

38. A method for producing the kit according to any one of claims 1 to 37, comprising the steps of: a) reacting an aliphatic isocyanate monomer with a polyester and / or polyether polyol to obtain an isocyanate-functionalized aliphatic polyurethane prepolymer comprising monomer units derived from said aliphatic isocyanate monomer; b) reducing the residual isocyanate monomer present in the aliphatic polyurethane prepolymer to less than 0.1% (w / w) of the prepolymer; c) introducing a polyol crosslinker into the kit wherein the aliphatic isocyanate monomer is a diisocyanate selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, methylene dicyclohexyl diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, pentamethylene diisocyanate, and combinations thereof.

39. 39. The method of claim 38, 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.

40. 40. The method of any one of claims 38 or 39, wherein the amount of isocyanate monomer is reduced by stripping the prepolymer using a series of one or more wiped film evaporators and / or short path evaporators.

41. 41. The method of any one of claims 38 to 40, wherein the isocyanate-functionalized aliphatic polyurethane prepolymer is the isocyanate-functionalized aliphatic polyurethane prepolymer of any one of claims 3 to 10.

42. 42. The method of any one of claims 38 to 41, wherein step a) comprises reacting the aliphatic isocyanate with a polyester polyol.

43. 43. The method of claim 42, wherein the polyester polyol is the polyester polyol of any one of claims 11 to 16.

44. 44. The method of any one of claims 38 to 43, wherein prior to step a), the method further comprises reacting a mixture of aromatic and aliphatic dicarboxylic acids with at least one polyol to form the polyester polyol.

45. 45. The method of claim 44, wherein the at least one polyol is selected from the group consisting of neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, monoethylene glycol, and combinations thereof.

46. 46. ​​The method of any one of claims 38 to 45, wherein the kit does not include a solvent.

47. Use of a kit according to any one of claims 1 to 46 for forming a lamination adhesive.

48. 48. The use of claim 47, wherein the laminating adhesive forms part of a retort package, such as a pouch.

49. 49. Use of a kit according to any one of claims 1 to 48 for improving the adhesive strength under retort conditions of a multi-laminate structure formed from a flexible film and a laminating adhesive formed from the kit compared to a multi-laminate structure formed from the flexible film and a laminating adhesive not formed from a kit of the present invention, wherein the adhesive strength is the strength required to separate at least two layers of the multi-laminate structure bonded with the adhesive, measured at 100 mm / min at room temperature (25°C).

50. 50. The use of claim 49, wherein the retort conditions comprise heating at or above 100°C for 20 minutes, such as heating at 120°C and 1.5 bar for 30 minutes, or heating at 135°C and 2.6 bar for 20 minutes.

51. 51. The use according to claim 49 or 50, wherein the retort conditions comprise placing the multi-laminate structure in an autoclave at between 1.5 bar and 3 bar, for example at 1.5 bar or 2.6 bar.

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