Laminating adhesive for compostable flexible packaging

Abstract

A one-component, moisture curable lamination adhesive that provides a surprisingly high bond strength and a desired failure mode when bonding a paper film to a polymer film, even at a low adhesive coat weight of 1 to 2 pounds per order. Paper films and polymer films bonded with 1 to 2 lbs per order of the disclosed adhesives have properties suitable for use as flexible packaging materials for food or pharmaceuticals, and the flexible packaging materials are compostable at ASTM 6400.

Description

Technical Field

[0001] This disclosure generally relates to a one-component, moisture-curable polyurethane laminating adhesive for manufacturing flexible packaging. More specifically, this disclosure generally relates to a solvent-free, one-component, moisture-curable polyurethane laminating adhesive that can bond paper films to polymer films to provide compostable flexible packaging. Background of the Invention

[0002] This section provides background information, which is not necessarily prior art to the inventive concepts associated with this disclosure.

[0003] Product packaging has evolved from sealed metal cans and glass bottles to sealed flexible packaging, such as bags. As an example, tuna is now available in both traditional metal cans and flexible bags. Flexible packaging, when filled with food or other products and closed or sealed, can be easily manipulated by the user. Flexible packaging typically consists of two layers of flexible packaging material that cover and seal most of its perimeter to form an internal cavity. Typically, the two layers of flexible packaging material are heat-sealed by applying heat and pressure to fuse the polymer layers together around most of the packaging perimeter. Food or other products are placed in the cavity through the opening, and the opening is closed by heat-sealing the open layers together. Sealed packaging and sealed products can be heated for preservation purposes. In some demanding applications, sealed packaging and sealed products can be boiled, i.e., heated to 100°C or higher.

[0004] Flexible packaging materials are prepared by laminating two or more layers of film. Each film is selected for specific properties. For example, a flexible packaging material can be a laminate of paper film and plastic film. In some embodiments, the plastic film is in contact with the food, and the paper film is the outer surface.

[0005] In another embodiment, the flexible packaging material can be a three-layer laminate. The inner layer will contact the packaged product. Polypropylene, having the desired product contact properties and heat-sealing properties, can be used as the inner layer. An optional intermediate layer can be used to provide a barrier against moisture, oxygen, and / or light. A metal film or foil has the desired barrier properties, and a metal film such as aluminum foil can be used as the intermediate layer. The outer layer will provide protection for the packaging and also provides a surface for printing information such as contents, packaging date, warnings, etc. Polyester film is tough, can receive printing ink, and can be used as the outer layer. The thickness of the flexible packaging material can range from about 13 to about 75 micrometers (0.0005 inches to 0.003 inches).

[0006] Each layer of flexible packaging material is bonded to the adjacent layers with an adhesive. The adhesive can be applied to the layers from a solution of a suitable solvent using gravure printing or a smooth roller coating roller, or from a solvent-free state using special application machinery, and then the layers are laminated onto the adjacent layers. If necessary, the laminated packaging material is dried and rolled into a roll.

[0007] Despite the existence of many possible types of adhesives, polyurethane-based adhesives are preferred for use in flexible packaging materials because they possess many desirable properties, including good adhesion to materials in each layer, high peel strength, heat resistance such as that from heat sealing or retorting, and resistance to food. Typically, two-component polyurethane adhesives are used. The first component is the isocyanate portion of a (isocyanate-functionalized) polyurethane prepolymer, obtained by reacting an excess of diisocyanate with a polyether and / or polyester containing two or more active hydrogen groups per molecule. The second component is typically a polyol. These two components are combined just before use to initiate a curing reaction between the components and are applied to the surface of the film to be laminated.

[0008] In some embodiments, solvents are used as diluents for certain polyurethane laminating adhesives because those mixed adhesives are too viscous to be reliably applied in liquid form during roll-to-roll lamination. Solvent-based or water-based laminating adhesives are limited by application speeds at which the solvent or water can be effectively removed in an oven. Due to drying limitations, typical linear speeds for solvent-based and water-based laminating adhesives are 300 to 600 feet per minute. In other embodiments, the laminating adhesive is solvent-free (an adhesive that can be applied in 100% solids and contains no organic solvents or water). Solvent-free laminating adhesives have significant advantages because they can be applied and run at very high linear speeds because there is no solvent or water that must be removed from the adhesive during the drying step. Typical linear speeds for solvent-free adhesives are 900 to even 2000 feet per minute, linear speeds that are impossible to achieve with solvent-based and water-based laminating adhesives. Therefore, solvent-free laminating adhesives are superior to solvent-based or water-based adhesives. However, at such high linear speeds, some solvent-free adhesives will form filaments between the rolls, and in more severe cases, the filaments may break into fine particles, creating fog in the atmosphere. Neither of these situations is desirable for laminating adhesives.

[0009] Cured adhesives must provide adequate peel strength to prevent delamination and food containment at room temperature and the high temperatures encountered during food packaging, processing, and supply. The properties of the cured adhesive must also be unaffected by contact with food.

[0010] There are numerous regulations governing the use of flexible packaging materials in food packaging applications. These regulations, of course, require that food packaging be safe when in contact with food. The migration of adhesive components (such as unreacted isocyanate monomers) into food is a concern. Excess isocyanate in laminating adhesives can react with moisture in the packaged product to form aromatic primary amines. The US FDA requires that the concentration of aromatic primary amines in flexible packaging materials used for food contact be below the detection limit (2 parts per billion (ppb) when tested by the migration test (also known as the BfR test method)). One solution is to keep the flexible packaging material in storage until the adhesive components have fully reacted. After the adhesive components have fully reacted, the flexible packaging material forms pouches. Unfortunately, this can take a long time, up to several weeks, when using lower molecular weight prepolymers and polyol laminating adhesives, and involves storing large quantities of expensive flexible laminates before use.

[0011] In response to the growing environmental challenges posed by plastic waste, there is a need to increase recycling and reuse. Composting is a natural recycling method in which organic materials are decomposed by microorganisms in the soil, and the nutrients they contain become part of the soil, such as humus, known as compost. By definition, compostable products are biodegradable. However, compostable products must also decompose safely and promptly in appropriate composting facilities or home compost heaps to become part of available soil-enhanced compost. To ensure the quality of compost and increase the volume of compostable waste, more food packaging materials need to be made compatible with various composting requirements.

[0012] Many attempts have been made to use biodegradable polymers to produce compostable or biodegradable pressure-sensitive adhesives (PSAs). Such efforts have used polylactic acid (PLA) and sulfonated copolyesters to produce hot-melt adhesives for beverage cups (US20200079981). A limitation of this approach is the poor thermal stability and high moisture sensitivity of PLA. It is unsuitable for many food packaging applications exposed to varying temperature and humidity conditions. Others have used bio-based materials such as epoxidized soybean oil (EP3089868) to prepare compostable water-based adhesives; however, performance has been undesirably limited.

[0013] Biodegradable polyurethanes (PURs) have been used to develop compostable or biodegradable pressure-sensitive adhesives (PSAs), such as aliphatic polyester polyol polyurethanes (US6307003) used as solvent-based PSAs, or PUR reactive hot melt adhesives based on polyester polyol polyurethanes (EP3155034). These approaches offer a wide range of properties, but their application is limited due to volatile organic compound (VOC) concerns and specific application requirements.

[0014] The aim is to provide a lamination adhesive that makes flexible packaging more compostable. Summary of the Invention

[0015] This section provides a general overview of this disclosure, rather than a full disclosure of its entire scope or all its features, aspects or objectives.

[0016] In one embodiment, this disclosure includes a one-component laminating adhesive. The compostable one-component laminating adhesive comprises a polyisocyanate, a highly functional polyol, and a linear diol.

[0017] In one embodiment, this disclosure includes a one-component laminating adhesive. The compostable one-component laminating adhesive comprises an aromatic polyisocyanate, a highly functional polyol, and a linear polyester diol.

[0018] In one embodiment, this disclosure includes a compostable laminate for flexible packaging; comprising: a paper film; a polymer film; and a one-component laminating adhesive. The one-component laminating adhesive comprises an aromatic polyisocyanate, a highly functional polyol, and a linear polyester diol.

[0019] In one embodiment, this disclosure includes a compostable laminate for flexible packaging; comprising: a paper film; a polymer film; and a one-component laminating adhesive. The one-component laminating adhesive comprises an aromatic polyisocyanate, a highly functionalized polyol, and a linear polyester diol. The laminate is compostable according to ASTM D6400.

[0020] Generally, unless otherwise expressly stated, the disclosed materials and methods may alternatively be formulated to include, consist of, or substantially consist of any suitable components, portions, or steps disclosed herein. The disclosed materials and methods may also be formulated to be free of, or substantially free of, any components, materials, ingredients, adjuvants, portions, substances, and steps used in prior art compositions or otherwise unnecessary for achieving the function and / or purpose of this disclosure.

[0021] These and other features and advantages of this disclosure will become more apparent to those skilled in the art from the detailed description of the preferred embodiments. Detailed Implementation

[0022] Unless the context clearly indicates otherwise, the singular forms “a,” “a,” and “the” include plural indicators.

[0023] Unless otherwise defined, "%" refers to the weight percentage of the composition.

[0024] As used in relation to numerical values ​​in this document, "about" or "approximately" refers to a value of ±10%, preferably ±5%, and more preferably ±1% or less.

[0025] The term “substantially free” is intended herein to mean that the applicable groups, compounds, mixtures or components comprise less than 10% by weight; typically less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.1% by weight, and ideally not more than trace amounts, based on the weight of the defined composition.

[0026] Unless otherwise defined, "at least one" means one or more, i.e., 1, 2, 3, 4, 5, 6, 7, 8, 9 or more. Regarding components, the indication refers to the type of component, not the absolute number of molecules. Therefore, "at least one polymer" means, for example, at least one type of polymer; that is, one type of polymer or a mixture of several different polymers may be used.

[0027] Unless otherwise defined, “liquid” means liquid or flowable under standard indoor conditions. Typically, liquid materials will have a viscosity of 50,000 cP or less, more usually 20,000 cP or less, or preferably 10,000 cP or less at room temperature. As used herein, room temperature is 23°C ± about 2°C.

[0028] The term "paper" includes films or substrates made primarily or solely of discontinuous cellulose fibers, which are typically wet-laid into nonwoven fiber webs.

[0029] Adhesive weight is provided in pounds per ream. This is the number of pounds of adhesive applied to one ream (3,000 square feet or 278.7 square meters) of bonding surface of a substrate to be bonded.

[0030] As used herein, the term “comprising” is synonymous with “including” or “containing”, and is inclusive or open-ended, and does not exclude additional, unlisted components, elements or method steps.

[0031] When quantities, concentrations, sizes, and other parameters are expressed in the form of ranges, preferred ranges, upper limits, lower limits, or preferred upper and lower limits, it should be understood that any range obtained by combining any upper or preferred value with any lower or preferred value or any value between the upper and lower limits is also specifically disclosed, regardless of whether the obtained range is clearly mentioned in the context.

[0032] The terms "preferred" and "preferred" are frequently used herein to refer to embodiments of this disclosure that may provide particular benefits in certain circumstances. However, the description of one or more preferred or preferred embodiments does not imply that other embodiments are useless, nor is it intended to exclude those other embodiments from the scope of this disclosure.

[0033] Unless otherwise specified, throughout this specification and claims, when referring to a polymer, the term molecular weight refers to the number-average molecular weight (Mn) of the polymer. Number-average molecular weight M n Molecular weights can be calculated based on end-group analysis (OH value according to DIN EN ISO 4629, free NCO content according to EN ISO 11909), or determined by gel permeation chromatography according to DIN 55672 using THF as the eluent. Unless otherwise specified, all given molecular weights are determined by gel permeation chromatography.

[0034] There are numerous definitions and standards for different aspects of biodegradability and compostability. Some standards include the Biodegradable Products Institute (BPI) according to ASTM D6400 and ASTM D6868, BPI certification scheme, compostable products, resins and intermediates; European Standard EN 14046, Assessment of the final aerobic biodegradability and disintegration of packaging materials under controlled composting conditions by analyzing the release of carbon dioxide; ASTM D5338, Standard Test Method for Determining the Aerobic Biodegradability of Plastic Materials under Controlled Composting Conditions, incorporating thermophilic temperatures; ASTM D6400-12, Standard Specification for Marking Plastics Designed for Biodegradable Composting in Municipal or Industrial Facilities; Australian Standard AS 5810:2010, Biodegradable Plastics for Home Composting – Biodegradable Plastics; and OECD 301 B and 301 C, Modified MITI Test – Degradability Ready Test, Chemicals for Activated Sludge JIS K 6950 – Aerobic Biodegradability Test.

[0035] Most relevant to this document is ASTM D6400, which defines the properties a material must possess to be claimed as "compostable" and thus recyclable through the composting of organic solid waste in an industrial environment. According to Section 6.3.2 of ASTM 6400, for a material composed of one or more polymers to be considered compostable, 90% of the organic carbon in the laminate must be converted to CO2 at the end of the test period, compared to a positive control. This allows 10% of the structure to remain in its original or partially compostable state.

[0036] Typically, solvent-free laminating adhesive is applied at a rate of 3 to 5 pounds per ream of substrate to provide the necessary bond strength for laminated structures containing paper and polymer films. Below this application weight, typical solvent-free adhesives do not provide sufficient strength to bond the structure, and the laminate may undesirably delaminate during use. Since laminating adhesives are non-compostable, a rate of 3 to 5 pounds per ream of laminating adhesive in paper / polymer film flexible packaging materials significantly contributes to the 10% non-compostable material permitted under ASTM 6400.

[0037] It has been unexpectedly discovered that the disclosed laminating adhesive can be used at a significantly reduced coating rate while maintaining acceptable strength of the bonded flexible packaging. The disclosed adhesive provides acceptable bond strength at very low coating weights. For example, the disclosed laminating adhesive provides acceptable fiber tear bond strength at a coating weight of 1.5 lbs / ream, and as low as 1.0 lbs / ream for some substrates. At 1.5 lbs / ream, the adhesive accounts for only 3% of the laminate structure, well below the permissible 10%. This contributes to the compostability of packaging made using the disclosed laminating adhesive. Furthermore, the laminating adhesive composition is advantageous in that it is free of volatile organic compounds (VOCs).

[0038] The disclosed laminating adhesive compositions comprise isocyanate (NCO) functional polyurethane prepolymer reaction products formed by the reaction of a mixture of one or more polyols and one or more polyisocyanates. The isocyanate equivalent in the mixture is in molar excess relative to the OH equivalent, such that the prepolymer reaction product is isocyanate (NCO) functional. The adhesive compositions may optionally contain a catalyst to control the curing rate of these adhesive compositions, and may optionally contain other additives to control rheological properties and other processability. The disclosed laminating adhesive compositions cure in the presence of moisture, which originates from the atmosphere, is present on the substrate, or is added by the operator during use. The cured reaction products form a thermosetting polyurethane crosslinked network, wherein CO2 is expelled as a byproduct of the curing process. The thermosetting reaction products form laminated adhesive layers (bonds) with good heat resistance, good chemical resistance, and good adhesion, are solvent-free, and can generally be applied at about 80°C.

[0039] The disclosed polyurethane adhesive compositions may comprise one-component compositions. Two-component polyurethane adhesive compositions (in which the components are stored separately and the mixing of the two components initiates the curing reaction) are formulated differently from one-component polyurethane adhesives. Two-component polyurethane adhesives require special handling and equipment; provide chemically different products; and are not interchangeable with one-component polyurethane adhesives for each application.

[0040] In one embodiment, the isocyanate-functionalized prepolymer is a reaction product comprising a mixture of a polyisocyanate component, a highly functional polyol component, and a polyol component.

[0041] The polyisocyanate component can be selected from compounds having two or more reactive isocyanate (NCO) moieties. Organic polyisocyanates that can be used include alkylene diisocyanates, cycloalkylene diisocyanates, aromatic diisocyanates, and aliphatic-aromatic diisocyanates. By way of example and not limitation, examples of isocyanates used in this disclosure include: methylene diphenyl diisocyanate (MDI), isophorone diisocyanate (IPDI), hydrogenated methylene diphenyl diisocyanate (HMDI), toluene diisocyanate (TDI), ethylidene diisocyanate, ethylidene diisocyanate, propylene diisocyanate, butylidene diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, cyclopentyl-1,3-diisocyanate, cyclohexyl-1,4-diisocyanate, cyclohexyl-1,2-diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,2-diphenylpropane-4,4'-diisocyanate, and diphenylene diisocyanate. Toluene diisocyanate, 1,4-naphthylene diisocyanate, 1,5-naphthylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, diphenyl-4,4′-diisocyanate, azobenzene-4,4′-diisocyanate, diphenyl sulfone-4,4′-diisocyanate, 2,4-toluene diisocyanate, dichlorohexamethylmethylene diisocyanate, furanyl diisocyanate, 1-chlorobenzene-2,4-diisocyanate, 4,4′,4”-triisocyanate-triphenylmethane, 1,3,5-triisocyanate-phenylene, 2,4,6-triisocyanate-toluene, 4,4′-dimethyldiphenylmethane-2, 2′,5,5-tetratetraisocyanate, etc.

[0042] Organic polyisocyanates with a functionality of at least 3 can also be used. These are trimers and oligomers of the polyisocyanates mentioned above, which can be obtained, for example, by the appropriate reaction of polyisocyanates, preferably diisocyanates, to form isocyanurate rings. When oligomers are used, those particularly suitable oligomers have an average degree of oligomerization of about 3 to about 5. Isocyanates suitable for preparing trimers are the diisocyanates mentioned above, and trimers of isocyanates HDI, MDI, or IPDI are particularly preferred. Polymeric isocyanates are also suitable, for example, polymeric isocyanates obtained as residues from the bottom products of distillation distillation of diisocyanates. Polymeric MDI, which can be obtained as a distillation residue from MDI distillation, is particularly suitable herein.

[0043] The organic polyisocyanates that can be used may include one or more isocyanate-functionalized polyurethane prepolymers. A polyurethane prepolymer is a compound, for example, produced by reacting a polyol component (or other active hydrogen-functionalized compound) with an excess of at least one polyisocyanate having a functionality of at least 2. The term polyurethane prepolymer includes not only compounds with relatively low molecular weights, such as those formed by reacting a polyol with an excess of polyisocyanate, but also oligomers or polymers. The term polyurethane prepolymer also includes, for example, compounds formed by reacting a trivalent or tetravalent polyol with a polyisocyanate in molar excess relative to the polyol. While such compounds are commercially available, methods for synthesizing such compounds are well known in the art. Preferred isocyanate-containing compounds are isomers of methylene diphenyl diisocyanate (MDI), isophorone diisocyanate (IPDI), hydrogenated MDI (HMDI), and toluene diisocyanate (TDI). The polyisocyanate component may comprise a single polyisocyanate or a combination of different polyisocyanates. In a preferred embodiment, the polyisocyanate component is an aromatic polyisocyanate, more preferably methylene diphenyl diisocyanate (MDI). Diphenylmethane diisocyanate (MDI) can be obtained from three isomers: 4,4'-diphenylmethane diisocyanate (4,4′-MDI), 2,4-diphenylmethane diisocyanate (2,4′-MDI), and 2,2′-diphenylmethane diisocyanate (2,2′-MDI). Mixtures of two or more of these isomers can be used for some or all of the polyisocyanate component. Alternatively, one or more of these isomers can be excluded. Modified forms of diphenylmethane diisocyanate can be used for some or all of the polyisocyanates. Useful examples of modified MDI include, for example, carbodiimide-modified diphenylmethane diisocyanate (carbodiimide-modified MDI), urea-formaldehyde-modified diphenylmethane diisocyanate (urea-formaldehyde-modified MDI), biuret-modified diphenylmethane diisocyanate (biuret-modified MDI), polymeric MDI, and combinations thereof.

[0044] The high-functionality polyol component comprises a polyol, preferably a polyester polyol, having an average of two or more primary hydroxyl groups and preferably also having an average of two or more secondary hydroxyl groups. The presence of both primary and secondary hydroxyl groups on the same polyol molecule is advantageous because it allows for reaction with the polyisocyanate component at different rates. High-functionality polyols are described in Simons' U.S. Patent Publication No. 2006 / 0105188, the contents of which are incorporated herein by reference. The high-functionality polyol is obtained by a two-step process comprising reacting a first polyol, predominantly containing secondary hydroxyl groups, with a stoichiometric excess of a reactant selected from polybasic acids, polybasic anhydrides, polybasic acid esters, and polyisocyanates to form an intermediate containing at least about two terminal functional groups selected from isocyanates, carboxylic acids, and carboxylic esters per molecule. The intermediate reacts with a stoichiometric excess of a second polyol predominantly containing primary hydroxyl groups to form the high-functionality polyol. Reacting these components in a single step would not provide an acceptable high-functionality polyol for use in laminating adhesives.

[0045] The polyol component differs from high-functionality polyol products. The polyol component affects compostability, the properties of the uncured adhesive composition, and the properties of the cured reaction products. Therefore, not every polyol can be used in compostable laminating adhesives. In this regard, polyester polyols are preferred, and polyether polyols should generally be avoided. In one embodiment, the polyol component is an aliphatic polyester polyol. Preferably, the polyol component is a linear aliphatic polyester polyol. It has been found that branched polyols result in uncured laminating adhesives with undesirably high viscosity, making them difficult or impossible to use. A useful type of linear polyester polyol is polycaprolactone polyol. Polycaprolactone can be prepared by ring-opening polymerization (ROP) under mild conditions using an "initiator" diol or triol and caprolactone monomer. This provides polycaprolactone polyols having 2, 3, or 4 hydroxyl functionalities in the molecule and a molecular weight of 200 to 5000 g / mol. Polycaprolactone polyols are thermoplastic and generally have a linear structure. Polycaprolactone polyols are available from many suppliers, including CAPA polycaprolactone polyols from Ingevity.

[0046] The mixture may optionally contain one or more auxiliary polyols that are different from the high-functionality polyol component and the polyol component. Some auxiliary polyols are, for example, polyester polyols, polybutadiene polyols, polycarbonate polyols, polyacetal polyols, polyamide polyols, polyesteramide polyols, polyalkylene polyether polyols, polysulfide polyols, and mixtures thereof.

[0047] Isocyanate-functionalized prepolymers can be present in the laminating adhesive composition in any suitable amount. It is useful when the isocyanate-functionalized prepolymer is present in the laminating adhesive composition in an amount of about 60% by weight to about 100% by weight.

[0048] The composition may optionally include a catalyst. The catalyst can be any moisture-curing catalyst used for polyurethanes, such as 2,2′-dimorpholinodiethyl ether, triethylenediamine, dibutyltin dilaurate, and stannous octoate. While metal-based catalysts can work, they are preferably not used. If present, an organic catalyst, such as the tertiary amine catalyst 2,2′-dimorpholinodiethyl ether (DMDEE), is preferred.

[0049] The composition may include organic solvents. Preferably, the composition does not contain organic solvents. Because the composition is isocyanate-functionalized water, moisture must be removed during the isocyanate-functionalized prepolymer and storage reaction to prevent undesirable curing.

[0050] The composition may optionally include one or more additives. Common adhesive additives include, for example, adhesion promoters, colorants, UV pigments, fillers, oils, plasticizers, rheology modifiers, and combinations thereof. Alternatively, the composition may be substantially free of any or all of these additives.

[0051] The adhesive compositions according to this disclosure may include solvents. Preferably, the adhesive compositions according to this disclosure may be substantially free of any solvents or water at any stage of formulation.

[0052] In one embodiment, the reaction product of a liquid moisture-curing polyurethane adhesive composition mixture comprises:

[0053] In one embodiment, the liquid moisture-curing polyurethane adhesive composition has the following properties: Using the disclosed laminating adhesive below the application temperature may cause the adhesive to atomize from the application device and string on the application device (forming adhesive strings or lines).

[0054] No specific method is required to prepare the laminating adhesive composition, and standard operating procedures can be used. In one embodiment, the laminating adhesive composition can be prepared by adding a polyisocyanate component to a reaction vessel. The reaction vessel is heated and placed under a vacuum or inert gas atmosphere to remove trace amounts of moisture. A catalyst may optionally be added before or during heating. Once the reaction vessel is substantially free of moisture, the polyol component is added under mixing and allowed to react with the polyisocyanate. If used, additives may be added before the polyisocyanate, if they do not interfere with the polyisocyanate-polyol reaction, or they may be added after the reaction is complete. The final laminating adhesive composition is transferred to a moisture-proof container and sealed to remove moisture.

[0055] Laminating adhesives are typically soft solids at room temperature. As the temperature rises, they become more pliable, turning into liquids in the range of 70-90°C. At 80°C, laminating adhesives are typically liquids with a viscosity of approximately 1600 cp.

[0056] The laminating adhesive is heated to approximately 80°C in the reservoir of a conventional laminator (Nordmeccanica Labo combi 400). The liquid laminating adhesive is picked up by rollers rotating in the reservoir and applied to the surface of a first paper film, plastic film, or metal foil. The laminating adhesive is gently applied as a coating, which provides the desired bond strength for the desired film. A second paper film, plastic film, or metal foil is guided onto the coated surface, and the two layers are laminated by rollers. The bonded laminate accumulates in the large rollers. Once the laminating adhesive has cured, the composite laminate can be formed in flexible packaging, for example, for containing food or pharmaceuticals.

[0057] Once applied, the laminating adhesive will cool back to a solid form and provide sufficient green strength to allow for the processing of composite laminates. In both liquid and solid forms, the applied laminating adhesive will react with moisture in the substrate and air to crosslink and cure into a permanent thermosetting form. The laminating adhesive will fully cure within 24 hours to 2 weeks, typically 1 week, depending on the moisture available in the substrate and environment.

[0058] The laminating adhesive can be applied to the film at rates of 1 to 3 lbs / ream; more typically 1 to 2 lbs / ream and as low as 1 to 1.5 lbs / ream. Even at these low application rates, the cured laminating adhesive will surprisingly provide enough bond strength to tear the fibers out of the paper film after only 3 days to 1 week of curing.

[0059] When applied at a very low rate of 1 to 3 lbs / ream to a paper and polyethylene terephthalate film laminate, the cured laminating adhesive will provide a bond strength of at least 100 g / sq inch after a 3-day curing time.

[0060] The disclosed one-component moisture-curing polyurethane laminating adhesive composition is particularly suitable for bonding long sheets of paper film to paper film, plastic film, or metal foil to form large rolls of composite laminate. Once the laminating adhesive has cured, the composite laminate can be formed in flexible packaging, such as for containing food or pharmaceuticals. The paper material is substantially compostable, and the cured laminating adhesive can be used at very low application rates, thus the entire composite laminate remains at least 90% compostable.

[0061] The laminated material prepared according to this disclosure can be used for packaging purposes in the same manner as conventional or known flexible packaging films. The laminated material is particularly suitable for forming flexible bag-shaped containers capable of being filled with and sealed with materials such as food or medicine. For example, two rectangular or square sheets of the laminated material can be stacked in a desired configuration or arrangement; preferably, the two polymer layers of the two sheets are adjacent to each other and can be heat-sealed. The three peripheral portions of the stacked assembly are then heat-sealed to form a bag with an open side to allow filling. Alternatively, a sheet of laminated material can be bent such that the polymer surfaces are adjacent, and two of the three open edges can be heat-sealed. Heat sealing can be readily achieved using a heating rod, heating knife, heating wire, pulse sealer, ultrasonic sealer, or induction heating sealer. The material is then packaged in the bag thus formed through the open edges and subsequently heat-sealed.

[0062] Bond strength test Prepare a laminate comprising a 4- to 5-inch wide paper substrate, which is bonded to a second 4- to 5-inch wide substrate of the desired test material using a desired amount and type of laminating adhesive. Apply the adhesive to provide 1 inch of adhesion along one edge of the substrate. Allow samples of the laminate to cure for 3 days, 1 week, and 2 weeks. Cured laminate strips, 1 inch wide and 4-5 inches long, are fabricated with a 1 inch x 1 inch bonded area. The unbonded edge of each test strip is placed in a tensile testing machine (Instron) to provide 180-degree pull. Samples are tested at 12 inches per minute, and the average force of three tests is recorded. Results are expressed in grams per force (gF).

[0063] High temperature bond strength test Prepare the sample as described in the adhesion test. Place the cured sample in a tensile testing machine. Once fixed to the tensile testing machine, place the sample in a 70°C environment for one minute. After starting the one-minute tensile test as described in the adhesion test, record the average force of three tests.

[0064] Hand-pulled bonding test Prepare the sample as described in the adhesion test. Hold the cured sample in each hand with an unbonded tail. Pull the unbonded tail at 180 degrees until the membrane separates. Visually evaluate the failure modes and fiber tears of the separated membrane.

[0065] Fiber tear assessment After testing the bond strength of the cured samples, the paper fibers of the polymer film are visually inspected for pull-out from the paper film and retention bonded to the polymer film. The score is based on the area of ​​bonded fibers per square inch of bonded area. Fiber tearing is a visual inspection for paper fibers on the relative film. After a 24-hour curing time, a minimum fiber tear of 10% is acceptable, but 50% or more is preferred. With longer curing times, the minimum fiber tear will increase to 50% or more.

[0066] Viscosity test Viscosity was tested at 100 rpm and the desired temperature using a Brookfield viscometer with an LVT#31 rotor. Before starting the test, the adhesive sample, rotor, and heater were preheated to the desired temperature. The sample was run for approximately ten minutes, and then the readings were taken.

[0067] Preparation of laminating adhesive The laminating adhesive sample was prepared as follows: The polyisocyanate component was added to a sealed container. The polyisocyanate component was heated in an inert atmosphere to remove moisture. Dry high-functionality polyol and linear polyester diol components were added to the dry polyisocyanate component with stirring. The polyisocyanate component was in equivalence excess compared to the total polyol component. The polyisocyanate component was allowed to react with the high-functionality polyol and linear polyester diol components. After the high-functionality polyol and linear polyester diol components had reacted, the isocyanate-functionalized laminating adhesive composition was transferred to a moisture-proof container and sealed to remove moisture.

[0068] The following substrates are used in the laminated samples. Each substrate is in a roller approximately 6 inches wide. PE (Polyethylene), 200 gauge (2.0 mils, 0.051 mm, 0.002 inches) thickness. PLA (polylactic acid) film metPET metallized one-sided polyester terephthalate, 48 gauge (0.48 mil, 0.12 mm, 0.00048 inch) thickness. PET (Polyethylene terephthalate), 48 gauge (0.48 mils, 0.12 mm, 0.00048 inches) thickness PET (ink) Polyester terephthalate - Printing side, 48 gauge (0.48 mils, 0.12 mm, 0.00048 inches) thickness OPP (Oriented Polypropylene) PET / ALU polyester terephthalate (48 gauge, 0.48 mils, 0.12 mm, 0.00048 inch thickness) bonded to aluminum foil. C1S coated paper on one side C1S Flipped paper with one side coated (the adhesive of the present invention is applied to the non-calendered side). Kraft paper cellophane film 70 lbs bright white printing paper Packaging paper printed on one side of DL media paper (adhesive applied to the non-printing side). Transparent paper Technoplex bandage paper is used as the base for bandages. Example Example 1

[0069] The following components are used to prepare the laminating adhesive. 1 MDI, purchased from Wanhua 2. A polyester polyol having an average of about two primary hydroxyl groups and about two secondary hydroxyl groups prepared according to U.S. Patent Publication No. 2006 / 0105188. 3 CAPA 2102 AJ, purchased from Ingenity. Example 1 is a solid at room temperature and has a viscosity of 1632 cp at 80°C, and is suitable for use as a laminating adhesive for films and foils. Example 2

[0070] The following components are used to prepare the laminating adhesive. 1 MDI, purchased from Wanhua 2. A polyester polyol having an average of about two primary hydroxyl groups and about two secondary hydroxyl groups prepared according to U.S. Patent Publication No. 2006 / 0105188. 3 CAPA 2102 AJ, purchased from Ingevity. Example 2 is a solid at room temperature and has a viscosity of 10,000 cp at 80°C. The melt viscosity of Example 2 is too high to be used as a laminating adhesive. Example 3

[0071] A laminating adhesive was prepared using the composition of Example 1. The adhesive was laminated onto various substrates and cured for 24 hours at room temperature and humidity (45% RH). The failure modes of the cured laminate were tested by pulling the unbonded side of the laminate by hand at 180 degrees orientation for 1 inch. The adhesive was applied to the calendered side of the paper via a roll coater at 80°C, with a second substrate applied and the lamination roll temperature at 80°C. 1 pound per ream of adhesive weight 2 ST is the tear in the identified substrate material. Example 4

[0072] A laminating adhesive was prepared using the composition of Example 1. The adhesive was laminated onto various substrates, and the laminates were cured for 3 days, 1 week, or 2 weeks, with room temperature bond strength and failure modes tested. The adhesive was applied to the calendered side of the paper via a roll coater at 80°C, followed by the application of a second substrate, with the lamination roll temperature at 80°C. 1 pound per ream of adhesive weight 2 Average bond strength 3FT stands for fiber tearing of the paper substrate, and ST stands for tearing of the identified substrate material. The laminating adhesives in each combination possessed sufficient strength and failure modes for use as flexible packaging materials. All fiber tear results were >50% and approached 100% until the paper film began to tear. Example 5

[0073] A laminating adhesive was prepared using the composition of Example 1. The adhesive was laminated onto various substrates, and the laminates were cured for 3 days, 1 week, or 2 weeks. High-temperature (70°C) bond strength and failure modes were then tested. For most samples, the adhesive was applied to the calendered side of the paper via a roll coater at 80°C, followed by the application of a second substrate, with the lamination roll gap temperature at 80°C. Use the following substrate: 1 pound per ream of adhesive weight 2. Average bond strength at high temperature

[0074] Even at high temperatures (80°C), the laminating adhesives in each combination possess sufficient strength and failure modes for use as flexible packaging materials. Fiber tearing results are all greater than 50%, and many approach 100%, until the paper substrate breaks. Example 6

[0075] A laminating adhesive was prepared using the composition of Example 1. The adhesive was laminated onto various substrates, and the laminate was cured for 1 day at room temperature and 40% humidity. Failure modes were tested by pulling the unbonded side of the laminate by hand for 1 inch at a 180-degree orientation. The adhesive was applied to the calendered side of the paper via a roll coater at 80°C, with a second substrate applied, and the lamination roll temperature was 80°C. 1 pound per ream of adhesive weight

[0076] After curing for only 24 hours at room temperature and 40% humidity, the laminating adhesives surprisingly exhibited enough fiber tear failure modes in each combination to be used as flexible packaging materials.

[0077] Example 7A: Preparation of a laminating adhesive using the composition of Example 1. The adhesive was laminated onto various substrates, and the laminates were cured for 3 days, 1 week, or 2 weeks, with room temperature bond strength and failure modes tested. The adhesive was applied to the calendered side of the paper via a roll coater at 80°C, followed by the application of a second substrate, with the lamination roll temperature at 80°C. 1 pound per ream of adhesive weight 2 Average bond strength 3FT stands for fiber tearing of the paper substrate, and ST stands for tearing of the identified substrate material. Example 8

[0078] A laminating adhesive was prepared using the composition of Example 1. The adhesive was laminated onto various substrates, and the laminate was cured for 3 days, 1 week, or 2 weeks. High-temperature (70°C) bond strength and failure modes were tested. The adhesive was applied to the calendered side of the paper via a roll coater at 80°C, with a second substrate applied, and the lamination roll temperature was 80°C. 1 pound per ream of adhesive weight 2 Average bond strength 3FT stands for fiber tearing of the paper substrate, and ST stands for tearing of the identified substrate material. Example 9

[0079] A laminating adhesive was prepared using the composition of Example 1. The adhesive was laminated onto various substrates, and the laminate was cured at room temperature and humidity for 1 day (24 hours). Failure modes were tested by pulling the unbonded side of the laminate by hand for 1 inch at a 180-degree orientation. The adhesive was applied to the auxiliary substrate (PET) via a roll coater at 80°C, with the main substrate applied and the lamination roll gap temperature at 80°C. 1. Weight of adhesive in pounds per ream

[0080] After a curing time of only 24 hours at room temperature and 40% humidity, the lighter coating weight of the laminate exhibits a failure mode of peeling from the substrate, which is acceptable but not preferred for use as a flexible packaging material. The laminate is expected to exhibit increased bond strength and increased fiber tearing at curing times of 3 days and 1 week. Example 10

[0081] A laminating adhesive was prepared using the composition of Example 1. The adhesive was laminated onto various substrates, and the laminates were cured for 3 days, 1 week, or 2 weeks. High-temperature bond strength and failure modes were tested. The primary substrate in each test was PET. The adhesive was applied to the PET primary substrate at 80°C using a roller coater, with the secondary substrate applied at the same temperature. 1 pound per ream of adhesive weight 2 Average bond strength 3FT stands for fiber tearing of the paper substrate, and ST stands for tearing of the identified substrate material.

[0082] All fiber tear results were or approximately 100%. Even with the lightest lamination adhesive coating weight, the 3-day curing time resulted in surprisingly high strength and expected failure modes, making it suitable for use as a flexible packaging material. Example 11

[0083] A laminating adhesive was prepared using the composition of Example 1. The adhesive was laminated onto various substrates, and the laminates were cured for 3 days, 1 week, or 2 weeks. High-temperature (70°C) bond strength and failure modes were tested. The primary substrate in each test was PET. The adhesive was applied to the PET primary substrate at 80°C using a roller coater, with the secondary substrate applied at the same temperature. 1 pound per ream of adhesive weight 2 Average bond strength 3FT stands for fiber tearing of the paper substrate, and ST stands for tearing of the identified substrate material.

[0084] All fiber tear results were or approximately 100%. Even at high temperatures (80°C), the laminating adhesive exhibited surprisingly high strength and expected failure modes on 41 lb C1S paper with very light coating weights (1 to 1.8 lbs / ream) for use as a flexible packaging material. For some other substrate combinations, such as Sample 11.5 using kraft paper, a longer curing time would be useful. Example 12 The laminating adhesive was prepared using the composition of Example 1. The adhesive was applied to a PET master substrate and a PE substrate using a roller coater at 80°C, with the lamination roll gap temperature at 80°C. The laminate was cured for 3 days, 1 week, or 2 weeks. After curing, two samples were stacked so that the PE surfaces were in contact and fused together to form a heat seal. The heat seal was formed by folding a single cured lamination strip to set the PE surfaces adjacent to each other. The heat seal was produced using SencorpWhite Model 12-ASL / 1 laminate set to 40 psi, 300°F, and a 1-second seal time. The room temperature strength and failure modes of the heat seal were tested. 1. Weight of adhesive in pounds per ream 2. Average bond strength 3 ST is the identification of membrane tear or substrate tear.

Claims

1. A one-component, isocyanate-functional, moisture-curable laminating adhesive comprising the reaction product of a mixture of the following: a polyisocyanate component, a highly functional polyester polyol component, and a linear polyester polyol component.

2. The one-component, isocyanate-functional, moisture-curable laminating adhesive of claim 1, wherein the high-functionality polyester polyol component has a functionality of about 4 and comprises about 2 primary hydroxyl groups and 2 secondary hydroxyl groups per molecule.

3. The one-component, isocyanate-functional, moisture-curable laminating adhesive of claim 1 or 2, wherein the linear polyester polyol component comprises polycaprolactone polyol.

4. A one-component, isocyanate-functional, moisture-curable laminating adhesive according to any one of claims 1 to 3, wherein when applied between a C1S paper film and a PET film at 1.5 lbs / ream, the curing reaction product of said adhesive provides >50% fiber tear and >100 g strength.

5. The single-component, isocyanate-functional, moisture-curable laminating adhesive of any one of claims 1 to 4, further comprising an additional polyol, which is different from the high-functionality polyester polyol component and the linear polyester polyol component.

6. A one-component, isocyanate-functional, moisture-curable laminating adhesive according to any one of claims 1 to 5, wherein the mixture comprises about 40 to 44% by weight of the polyisocyanate component; about 27 to 31% by weight of the high-functionality polyester polyol component and about 27 to 31% by weight of the linear polyester polyol component.

7. A flexible packaging laminate comprising a paper substrate bonded to a second substrate by a curing reaction product of a one-component, isocyanate-functional, moisture-curable laminating adhesive, wherein the one-component, isocyanate-functional, moisture-curable laminating adhesive comprises a reaction product of a mixture of: a polyisocyanate component, a high-functionality polyester polyol component, and a linear polyester polyol component.

8. The flexible packaging laminate of claim 7, comprising about 1 to 4 pounds, preferably about 1 to 3 pounds, more preferably about 1 to 1.5 pounds of adhesive per ream of substrate.

9. The flexible packaging laminate of claim 7 or 8, having an adhesive strength of greater than 100 g / m² and a fiber tear resistance of greater than 50%.

10. The flexible packaging laminate of any one of claims 7 to 9, wherein the flexible packaging material is compostable when tested under ASTM 6400.

11. The flexible packaging laminate of any one of claims 7 to 9, wherein the first substrate and the second substrate are each independently selected from paper film, polymer film, metallized polymer film or metal foil.

12. A flexible packaging body, comprising: The first part of the flexible laminate material has a periphery and includes a polymer film bonded to a paper film by a curing reaction product of a one-component laminating adhesive, the one-component laminating adhesive comprising an aromatic polyisocyanate, a highly functional polyol and a linear polyester diol. and The second part of the flexible laminate material has a periphery and includes a polymer film bonded to the paper film by a curing reaction product of a one-component laminating adhesive, the one-component laminating adhesive comprising an aromatic polyisocyanate, a highly functional polyol and a linear polyester diol. The first portion is disposed adjacent to the second portion, and the first portion is sealed to the second portion around at least some of the periphery to form a bag having an inner cavity for receiving material; The flexible packaging described therein is compostable when tested under ASTM 6400.

13. The flexible packaging of claim 12, wherein the polymer film of the first portion of the flexible laminate is disposed adjacent to the polymer film of the second portion of the flexible laminate, and the polymer film of the first portion of the flexible laminate is heat-sealed to the polymer film of the second portion of the flexible laminate around at least some of the periphery to form a bag having an inner cavity for receiving the material.

14. The flexible packaging of claim 12, wherein the first portion of the flexible laminate and the second portion of the laminate are opposite ends of a single sheet of flexible laminate folded together.

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