Reactive polyurethane hot melt adhesive with improved adhesion to metals

Abstract

Disclosed is a one-component hot melt polyurethane adhesive composition comprising the isocyanate-functionalized reaction product of a polyisocyanate mixed with a silicone oligomer of Structure 1 with a polyether polyol and / or a polyester polyol: Structure 1, the adhesive composition having an enhanced bond strength to metals such as aluminum compared to presently available adhesives. The composition is particularly useful in panel lamination applications.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to one-component reactive polyurethane hot melt adhesive compositions, and more particularly to such compositions having enhanced adhesion to metal components, particularly aluminum components. The present disclosure also relates to a method for improving the bond strength of one-component reactive polyurethane hot melt adhesive compositions to metal substrates, particularly aluminum substrates, more particularly uncleaned mill grade aluminum substrates, and a method of bonding a composite structure comprising metal components, particularly aluminum components, using a one-component reactive polyurethane hot melt adhesive composition. BACKGROUND

[0002] This section provides background information, which is not necessarily prior art.

[0003] Composite structures are widely used in the manufacture of vehicles in the transportation field. Examples of such composite structures include commercial trailers, train cars, aircraft parts, recreational vehicles, boats, and automobiles. One conventional composite structure includes a welded aluminum frame having a polymeric skin bonded to one surface, a wood skin bonded to the opposite surface, and a foam between the polymeric skin and the wood skin. Curable or reactive polyurethane adhesives are commonly used to bond the polymeric skin to the aluminum frame and to bond the wood skin to the aluminum frame.

[0004] Hot melt adhesives are single-component adhesives that are solid at room temperature, but upon heating, they melt into a liquid or fluid state, in which molten form they are applied to substrates. Upon cooling, the adhesive reverts to its solid form. One class of hot melt adhesives is thermoplastic hot melt adhesives. Thermoplastic hot melt adhesives do not crosslink or cure, and can be repeatedly heated to a fluid state and cooled to a solid state. Since thermoplastic hot melt adhesives do not crosslink or cure; the hard phase that forms upon cooling the thermoplastic hot melt adhesive imparts all of the cohesive strength, toughness, creep, and heat resistance of the final adhesive. Naturally, the thermoplastic nature limits the upper temperature at which such adhesives can be used.

[0005] Another class of hot melt adhesives is curable or reactive hot melt adhesives. Reactive hot melt adhesives start as thermoplastic materials that can be repeatedly heated to a molten state and cooled to a solid state. However, when exposed to the proper conditions, the components of a reactive hot melt adhesive crosslink and cure into an irreversible solid form. One class of reactive hot melt adhesives is polyurethane hot melt adhesives. Polyurethane hot melt adhesives contain isocyanate-terminated polyurethane prepolymers that react to chain extend, forming a new polymer. Polyurethane prepolymers are typically obtained by the reaction of a polyol with an isocyanate. The polyurethane prepolymers cure by moisture from the environment or moisture on the substrate diffusing into the adhesive and the subsequent reaction of the moisture with the isocyanate moieties in the prepolymer. The final adhesive product is an irreversibly crosslinked material.

[0006] Reactive hot melt adhesives must be maintained at a molten temperature during use. However, even when maintained under generally water-free conditions, reactive hot melt adhesives will slowly increase in viscosity when maintained in the molten state. Eventually, the equipment must be shut down and cleaned to remove the high viscosity hot melt adhesive. In a very undesirable scenario, the reactive hot melt adhesive can gel or phase separate in the equipment during use. Either scenario requires unplanned equipment downtime, disassembly, cleaning, and possibly replacement of parts that cannot be cleaned of the gelled hot melt adhesive. Reactive hot melt adhesives ideally have thermal stability, the ability to resist changes in viscosity over time when maintained in the molten state. Naturally, any gelling or phase separation of a reactive hot melt adhesive is considered a failure of thermal stability.

[0007] Additives are typically included in reactive hot melt adhesive formulations. However, large amounts of additives such as fillers adversely affect most reactive polyurethane hot melt adhesives and can significantly reduce thermal stability to undesirable levels. It is desirable to provide a reactive polyurethane hot melt adhesive that includes high levels of non-fossil fuel based, sustainable, renewable additives while maintaining thermal stability.

[0008] Good adhesion of the polyurethane adhesive to each composite part is desirable to add strength to the composite structure. Ideally, the internal strength of the adhesive and the bond strength to the substrate will be greater than some or all of the substrate materials to which the adhesive is bonded in order to ensure that the bonded substrate materials should fail under stress before the adhesive or the adhesive bond. Additionally, water can penetrate into the bonded composite structure. The adhesive should maintain as much of the initial bond strength during and after exposure to water as possible.

[0009] To enhance the adhesive bond strength, manufacturers use a multi-step cleaning process of the part prior to applying the adhesive and assembly as a composite structure. In the first step, the metal frame is cleaned to remove oil, grease, and dirt. Next, the frame is exposed to a conversion coating chemical in a bath or spray application, rinsed with water, and dried. The conversion coated frame is now ready for the adhesive and assembly to be applied as a composite structure. This process requires multiple large tanks of chemicals, lifting and drying equipment, and a large amount of space. In a different multi-step process, the metal frame is cleaned to remove oil, grease, and dirt. Next, the frame is manually wiped using a towel soaked with a conversion chemical such as Alodine wipes from Henkel Corporation, and dried. The conversion coated frame is now ready for the adhesive and assembly to be applied as a composite structure. This method does not require a conversion coating tank and associated equipment. However, manually wiping the entire frame requires a significant amount of effort and time, and has the risk that the worker can miss some areas of the frame.

[0010] It is desirable to provide a one-component hot melt polyurethane adhesive composition that has increased bond strength to one or more composite components. It is desirable to provide a one-component hot melt polyurethane adhesive composition that has increased bond strength without the need for a conversion coating on the metal part. It is desirable to provide a one-component hot melt polyurethane adhesive composition that substantially maintains the increased strength during and after exposure to water. SUMMARY

[0011] This section provides a general summary of the disclosure and not a comprehensive disclosure of its full scope or all of its features, aspects or objectives.

[0012] In one embodiment, the present disclosure provides a one-component reactive polyurethane hot melt adhesive made from a mixture comprising at least one organic polyisocyanate, at least one polyol, a silicone oligomer, and optionally other components and / or additives.

[0013] In one embodiment, the present disclosure is a method of bonding a skin or panel to a metal frame to form a reinforced composite structure comprising providing a one-component reactive polyurethane hot melt adhesive composition as described in any embodiment; heating the one-component reactive polyurethane hot melt adhesive composition to a molten state, disposing the one-component reactive polyurethane hot melt adhesive composition on a surface of at least one of the panel or the metal frame; disposing the surface of the panel in contact with the disposed adhesive and adjacent to a surface of the metal frame; and exposing the disposed adhesive to conditions that will initiate curing. In a preferred embodiment, the metal frame is aluminum and is not treated with a conversion coating. In a preferred embodiment, the metal frame is factory grade aluminum.

[0014] In one embodiment, this disclosure includes articles comprising the disclosed one-component reactive polyurethane hot melt adhesive composition in cured or uncured form.

[0015] In one embodiment, the compositions herein do not contain silane-modified polymers (SMPs).

[0016] In one embodiment, this disclosure includes the cured reaction product of the disclosed one-component reactive polyurethane hot melt adhesive composition.

[0017] These and other features and advantages of this disclosure will become more apparent to those skilled in the art from the detailed description of preferred embodiments. Generally, unless explicitly stated otherwise, the disclosed materials and methods may alternatively be formulated to include, constitute, or substantially consist of any suitable components, portions, or steps disclosed herein. The disclosed materials and methods may additionally or alternatively 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 unnecessary for achieving the function and / or purpose of this disclosure. Detailed Implementation Plan

[0018] Unless the context clearly indicates otherwise, the singular forms “a,” “one,” and “the” include plural indicators.

[0019] Unless otherwise defined, “about” or “approximately” used in conjunction with a numerical value means ±10%, preferably ±5%, more preferably ±1% or less.

[0020] Unless otherwise defined, "%" refers to weight percentage.

[0021] The term “substantially free” is intended herein to mean less than 10 wt.% of the applicable groups, compounds, mixtures or components based on the weight of the defined composition; typically less than 1 wt.%, preferably less than 0.5 wt.%, more preferably less than 0.1 wt.%, and ideally no more than trace amounts.

[0022] 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, this 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, i.e., one type of polymer or a mixture of several different polymers may be used.

[0023] Unless otherwise defined, the terms “comprising, comprises, comprised of” as used herein are synonymous with “including, includes” or “containing, contains” and are inclusive or open-ended, and do not exclude additional, unlisted members, elements or method steps.

[0024] When quantities, concentrations, sizes, and other parameters are expressed as ranges, preferred ranges, upper limits, lower limits, or preferred upper and lower limits, it should be understood that any range that can be obtained by combining any upper or preferred value with any lower or preferred value is also specifically disclosed, regardless of whether the obtained range is clearly mentioned in the context.

[0025] The open time of an adhesive refers to the time during which the adhesive can bond to a material.

[0026] As used herein, preferred and preferred to refer to embodiments of the present 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, and is not intended to exclude those other embodiments from the scope of the present disclosure.

[0027] 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 those determined by gel permeation chromatography.

[0028] Polyurethane hot melt adhesives are widely used in panel lamination processes. They offer good adhesion and structural bonding to a wide variety of materials. Their lack of reliance on solvents, rapid green strength, and good resistance to heat, cold, and various chemicals makes them ideal for the construction industry. In one embodiment, the disclosed hot melt adhesive is used for the lamination of entertainment vehicle panels and doors. Because forming these structures can involve complex lamination processes, it is important in these embodiments to have long open times of 6 minutes or more and high green strength to allow for the positioning of the components to be bonded. Furthermore, it is necessary to maintain the final cured strength of the bonded components even when they are exposed to extreme temperatures. It is desirable to provide a one-component reactive polyurethane hot melt adhesive that maintains cured strength at higher temperatures than existing formulations to allow for additional applications.

[0029] The disclosed hot melt adhesive includes isocyanate-functionalized prepolymers, which are reaction products comprising a mixture of at least one polyol, an excess of at least one organic polyisocyanate, and optionally one or more other components and / or additives. The isocyanate functionality allows the reaction product to crosslink and cure upon exposure to moisture. The hot melt adhesive may contain one or more of the following: isocyanate-functionalized prepolymers, silicone oligomers, and optionally, MA-SCA, inorganic fillers, thermoplastic polymers, tackifiers, catalysts, and additives. Preferably, the hot melt adhesive is free of organic solvents, water, and photoinitiators. In some preferred embodiments, the prepolymer reaction product is free of silicon atoms.

[0030] Organic polyisocyanates that can be used include alkylene diisocyanates, cycloalkylene diisocyanates, aromatic diisocyanates, and aliphatic-aromatic diisocyanates. Examples of isocyanates used in this disclosure include, but are not limited to: methylene diphenyl diisocyanate (MDI), isophorone diisocyanate (IPDI), hydrogenated methylene diphenyl diisocyanate (HMDI), toluene diisocyanate (TDI), ethylene diisocyanate, 1,1-ethylene diisocyanate, propylene diisocyanate, butylene diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, cyclopentyl-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, cyclohexyl-1,2-diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,2-diphenylpropane-4,4'-diisocyanate, etc. 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, dichlorohexamethylene diisocyanate, furanylpropylene diisocyanate, 1-chlorobenzene-2,4-diisocyanate, 4,4',4"-triisocyanate-triphenylmethane, 1,3,5-triisocyanate-benzene, 2,4,6-triisocyanate-toluene, 4,4'-dimethyldiphenyl-methane-2,2',5,5-tetraisocyanate, etc.

[0031] Organic polyisocyanates with a functionality of at least 3 can also be used. These are trimers and oligomers of the polyisocyanates mentioned above, for example, the formation of isocyanurate rings obtained through appropriate reactions of polyisocyanates, preferably diisocyanates. In the case of using oligomers, those with an average degree of oligomerization of about 3 to about 5 are particularly suitable. Isocyanates suitable for preparing trimers are the aforementioned diisocyanates, particularly preferably trimers of isocyanates HDI, MDI, or IPDI. Polymeric isocyanates are also suitable, for example, those obtained as bottom residues from the distillation of diisocyanates. In this context, polymeric MDI, which can be obtained as a distillation residue from the distillation of MDI, is particularly suitable.

[0032] The organic polyisocyanates that can be used may include one or more isocyanate-functionalized polyurethane prepolymers. A polyurethane prepolymer is a compound, for example, resulting from the reaction of a polyol component (or other actively hydrogen-functionalized compound) with an excess of at least one polyisocyanate having at least two functions. The term polyurethane prepolymer includes not only compounds with relatively low molecular weights, such as those formed by the reaction of a polyol with an excess of polyisocyanate, but also oligomers or polymers. The term polyurethane prepolymer also includes, for example, compounds formed by the reaction of 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 compounds such as methylene diphenyl diisocyanate (MDI), isophorone diisocyanate (IPDI), hydrogenated MDI (HMDI), and toluene diisocyanate (TDI).

[0033] The polyols that can be used include those used in the production of polyurethane, including but not limited to polyether polyols, polyester polyols, polycarbonate polyols, polyacetal polyols, polyamide polyols, polyesteramide polyols, polyalkylene polyether polyols, polysulfide polyols, and mixtures thereof, with polyether polyols, polyester polyols, polycarbonate polyols, and mixtures thereof being preferred.

[0034] Useful polyester polyols include those that can be obtained by reacting dicarboxylic acids with polyols in a polycondensation reaction. The dicarboxylic acids can be aliphatic, alicyclic, or aromatic and / or derivatives thereof, such as acid anhydrides, esters, or acyl chlorides. Specific examples of these are succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, dodecanoic acid, phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimer fatty acids, dodecanoic acid, and dimethyl terephthalate. Examples of suitable polyols are monoethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 3-methylpentane-1,5-diol, neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,6-hexanediol, 1,8-octanediol cyclohexanediol, 2-methylpropane-1,3-diol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, dibutylene glycol, tributylene glycol, tetrabutylene glycol, and polybutanediol. Alternatively, they can be obtained by ring-opening polymerization of cyclic esters, preferably caprolactone. Polyester polyols are commercially available, for example, Piotane polyols from Panolam Industries International and Dynacoll polyols from Evonik. Other suppliers include Stepan, COIM, and Lanxess. In some implementations, polyhexane adipate polyol is preferred.

[0035] Useful polyether polyols include linear and branched polyethers having hydroxyl groups. Examples of polyether polyols may include polyoxyethylene polyols, such as polyethylene glycol, polypropylene glycol, polybutanediol, etc. Furthermore, homopolymers and copolymers of polyoxyethylene polyols may also be used. Particularly preferred copolymers of polyoxyethylene polyols may include at least one adduct selected from the following compounds: ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, 2-ethylhexanediol-1,3-glycerol, 1,2,6-hexanetriol, trimethylolpropane, trimethylolethane, tri(hydroxyphenyl)propane, triethanolamine, triisopropanolamine, ethylenediamine, and ethanolamine. Most preferred polyether polyols include polypropylene glycol. Preferred polyether polyols have a number average molecular weight of 1,500-6,000 Daltons, more preferably 2,000-4,000 Daltons. Polyether polyols may comprise mixtures of polyether polyols.

[0036] Useful polycarbonate polyols can be obtained by reacting carbonate derivatives such as diphenyl carbonate, dimethyl carbonate, or phosgene with diols. Suitable examples of such diols include ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 1,4-dihydroxymethylcyclohexane, 2-methyl-1,3-propanediol, 2,2,4-trimethylpentanediol-1,3,dipropanediol, polypropylene glycol, dibutylene glycol, polybutanediol, bisphenol A, bisphenol F, tetrabromobisphenol A, and lactone-modified diols. In some embodiments, the diol component preferably contains 40-100 wt.% hexanediol, preferably 1,6-hexanediol and / or hexanediol derivatives. More preferably, the diol component includes examples exhibiting ether or ester groups in addition to the terminal OH groups. The polycarbonate polyol should be substantially linear. However, they can optionally be slightly branched by introducing multifunctional components, particularly low molecular weight polyols. Suitable examples include glycerol, trimethylolpropane, hexanetriol-1,2,6, glycerol-1,2,4, trimethylolpropane, pentaerythritol, p-cyclohexanediol, mannitol and sorbitol, methyl glycosides, and 1,3,4,6-dianhydrohexites.

[0037] Useful polyols also include polyols that are hydroxyl-functionalized polymers, such as hydroxyl-functionalized siloxanes, and polyols that contain additional functional groups such as vinyl or amino groups.

[0038] The adhesive comprises the organosilicon oligomer of structure 1: Structure 1 Each R' may be the same or different and is independently selected from hydrogen atoms and hydrocarbon residues having 1 to 12 carbon atoms, preferably methyl or ethyl, more preferably methyl. Ar is selected from aryl, which may be linked or fused polycyclic aryl. Ar is preferably phenyl, and n is an integer selected from 0-12, preferably 1-12. CAS No. 17938-09-9 (diphenyltetramethoxydisiloxane, n=1) is an example of an organosilicon oligomer of structure 1. CAS No. 2996-92-1 (phenyltrimethoxysiloxane, n=0) is an example of an organosilicon oligomer of structure 1. Organosilicon oligomers are commercially available or synthesized using the procedure provided in U.S. Patent No. 10800881 to Despotopoulou et al., the contents of which are incorporated herein by reference.

[0039] The adhesive may optionally include MA-SCA acids. MA-SCA acids are a subset of polybasic acids having an acidic group ultimately bonded to a single central atom. Examples of MA-SCA acids include sulfuric acid, phosphonic acid, phosphoric acid, and diphosphonic acid (pyrophosphate). MA-SCA acids surprisingly extend the time that the hot melt adhesive can maintain at operating temperature before the viscosity rises to the target level. In other words, adding MA-SCA acids to the hot melt adhesive surprisingly reduces the rate of viscosity increase of the hot melt adhesive when maintained at operating temperature.

[0040] Polyurethane adhesives and sealants used at room temperature can incorporate large amounts of filler without problems. However, adding large amounts of filler (e.g., 10 wt.% or more, or 20 wt.% or more) to hot melt adhesives will reduce the thermal stability of the hot melt adhesive, in some cases to levels that make highly filled hot melt adhesives commercially undesirable. Adding MA-SCA acid to highly filled hot melt adhesives unexpectedly improved the thermal stability of the highly filled hot melt adhesive. Although MA-SCA acid might be expected to interact undesirably with the filler, no such interaction was observed.

[0041] The binder may optionally include fillers. Fillers that can be used include inorganic materials such as calcium carbonate, kaolin, and dolomite. Calcium carbonate has been described as a sustainable, renewable, non-fossil fuel-based material. Other examples of suitable fillers can be found in George Wypych's Fillers Handbook (3rd edition, 2009) and Harry Katz and John Milewski's Handbook of Fillers and Reinforcements for Plastics (1978). Inorganic fillers are preferably present in an amount from about 10% to about 50% by weight, more preferably from 20% to 30% by weight, based on the total binder weight. Previous attempts to use large quantities of such fillers have resulted in hot-melt binders with short open times and undesirable increases in hot-melt binders, such as melting during use.

[0042] Adhesives may optionally include tackifiers, but are preferred. Tackifier selection includes natural and petroleum-derived materials and combinations thereof, as described below: CW Paul, “Hot Melt Ahesive,” Adhesion Science and Engineering -2, Surfaces, Chemistry and Applications, M. Chaudhury and AVPocius eds., Elsevier, New York, 2002, p. 718. Useful tackifiers include rosin esters, aromatic hydrocarbon resins, aliphatic modified aromatic hydrocarbon resins, phenolic modified terpene resins, phenolic modified aromatic resins, and pure monomer resins.

[0043] The adhesive preferably does not contain organosilanes, as these compounds tend to destabilize the adhesive when maintained at the operating temperature. Organosilanes may be useful in some embodiments if the stability of the adhesive at the operating temperature is less critical. The organosilanes that can be used are structurally different from the organosilicon oligomers of Structure 1 and include aminosilanes, such as secondary aminosilanes. A useful silane comprises at least two silyl groups, wherein three methoxy groups are bonded to each hindered secondary amino group or any combination thereof. An example of such a commercially available aminosilane is bis-(trimethoxysilylpropyl)-amine, such as Silquest A-1170. Other examples of available organosilanes include silanes having a hydroxyl functional group, a thiol functional group, or both, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxy-ethoxyethoxysilane, 3-aminopropyl-1-methyl-1-diethoxysilane, N-methyl-3-aminopropyltrimethoxysilane, N-butyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyl-1-methyl-dimethoxysilane. Organosilanes include (N-cyclohexylaminomethyl)methyldiethoxysilane, (N-cyclohexylaminomethyl)triethoxysilane, (N-phenylaminomethyl)methyldimethoxysilane, (N-phenylaminomethyl)trimethoxysilane, N-ethyl-aminoisobutyltrimethoxysilane, 4-amino-3,3-dimethylbutyltrimethoxysilane, N-(n-butyl)-3-aminopropyltriethoxysilane, N-(n-butyl)-3-aminopropylalkoxydiethoxysilane, bis(3-triethoxysilylpropyl)amine, and any combination thereof. Organosilanes are commercially available from many sources, such as Momentive Performance Materials (Silquest) and Evonik (Dynasylan).Some useful examples include Silquest Alink 15 (N-ethyl-3-trimethoxysilyl-2-methylpropylamine), Silquest Alink 35 (γ-isocyanopropyltrimethoxysilane), Silquest A174NT (γ-methacryloyloxypropyltrimethoxysilane), Silquest A 187 (γ-glycidoxypropyltrimethoxysilane), Silquest A 189 (γ-mercaptopropyltrimethoxysilane), Silquest A 597 (tris(3-(trimethoxysilyl)propyl)isocyanurate), Silquest A1110 (γ-aminopropyltrimethoxysilane), Silquest A1170 (bis(trimethoxysilylpropyl)amine), Dynasylan 1189 (N-butyl-3-aminopropyltrimethoxysilane), Silquest A1289 (bis-(triethoxysilylpropyltetrasulfide), and Silquest Y9669. (N-Phenyl-γ-aminopropyltrimethoxysilane).

[0044] The adhesive may optionally, but preferably, include thermoplastic polymers or copolymers, such as acrylics or EVA. The thermoplastic polymer may be functional, having portions that can react with other components in the adhesive, such as active hydrogen atoms, hydroxyl groups, amino groups, or (meth)acrylates, or may be non-functional. Acrylic polymers that may be used include acrylic polymers formed from acrylates, methacrylates, and mixtures thereof, as known in the art, and acrylic copolymers comprising at least one of methyl methacrylate monomers and n-butyl methacrylate monomers. Examples of such acrylic copolymers include Elvacite® 2013, a copolymer of methyl methacrylate and n-butyl methacrylate with a weight average molecular weight of 34,000; Elvacite® 2016, a copolymer of methyl methacrylate and n-butyl methacrylate with a weight average molecular weight of 60,000; and Elvacite® 4014, a copolymer of methyl methacrylate, n-butyl methacrylate, and hydroxyethyl methacrylate, with a weight average molecular weight of 60,000. Elvacite® polymers are available from Lucite International. Other examples of suitable acrylic polymers can be found in U.S. Patents 6,465,104 and 5,021,507, which are incorporated herein by reference. Preferably, the acrylic polymer has a weight-average molecular weight of 8,000-150,000, more preferably 25,000-100,000. It is preferably present in an amount of about 5% to 40% by weight, more preferably 10% to 30% by weight, based on the total weight of the adhesive. The acrylic polymer preferably has an OH value of less than 8, more preferably less than 5. The acrylic polymer preferably has a glass transition temperature (Tg) of about 35 to about 85°C, more preferably 45 to 75°C.

[0045] EVA copolymers are copolymers of ethylene and vinyl acetate. The two monomers can be copolymerized in any ratio. The resulting copolymer is characterized by the statistical distribution of monomer units in the polymer chain, and the properties of the EVA copolymer can vary over a wide range depending on the molar ratio of ethylene to vinyl acetate. For example, products with an ethylene content of less than 30% by weight are partially crystalline and thermoplastic, while products with a vinyl acetate content of about 40% to about 70% by weight are substantially amorphous. EVA copolymers are typically prepared by bulk polymerization, emulsion polymerization, or solution polymerization. The molecular weight of the EVA copolymer used according to the invention is in the range of about 10,000 to about 1,500,000. The vinyl acetate content in the EVA copolymer used according to the invention is in the range of 9% to 70% by weight, and preferably in the range of 20% to 55% by weight. Examples of suitable ethylene / vinyl acetate copolymers include commercially available ELVAX products from Dow, which have a vinyl acetate content of about 27% to 42% by weight. In addition, other monomers can also be combined with EVA copolymers to obtain the desired properties, including isocyanate reactive functional groups.

[0046] The binder may optionally include a catalyst commonly used in reactions with polyurethanes. Some useful catalysts include, for example, 2,2'-dimorpholine diethyl ether, triethylenediamine, dibutyltin dilaurate, and stannous octoate. A preferred catalyst is 2,2'-dimorpholine diethyl ether (DMDEE).

[0047] The composition may optionally include at least one filler selected from inorganic fillers such as calcium carbonate, powdered limestone, precipitated and / or pyrolytic silica, zeolite, bentonite, magnesium carbonate, diatomaceous earth, alumina, clay, tallow, titanium dioxide, iron oxide, zinc oxide, sand, quartz, flint, mica, powdered glass, and ground minerals; organic fillers such as carbon black, graphite, wood fiber, wood flour, sawdust, cellulose, cotton, pulp, wood chips, chopped straw, rice husks, and ground walnut shells; chopped fibers such as glass fiber, glass filament, polyacrylonitrile fiber, carbon fiber, Kevlar fiber, and polyethylene fiber; and hollow spheres having a mineral shell or a plastic shell, such as Glass Bubbles® and plastic hollow spheres commercially available from Expancel® or Dualite®. These hollow sphere fillers are composed of inorganic or organic materials and each has a diameter of 1 mm or less, preferably 500 μm or less. In one implementation, calcium carbonate can be used as a filler because it can be considered a sustainable, renewable, non-fossil fuel filler.

[0048] The adhesive may optionally include one or more of a variety of known hot melt adhesive additives, such as plasticizers, colorants, rheology modifiers, flame retardants, UV pigments, nanofibers, defoamers, antioxidants, stabilizers, thixotropic agents such as fumed silica, etc. Conventional additives compatible with the composition according to the invention can be determined simply by combining potential additives with the composition and determining their compatibility. If the additive is homogeneous within the product at room temperature and operating temperature, the additive is compatible.

[0049] In one embodiment, the hot melt adhesive comprises a mixture of reaction products, the mixture comprising: Typically, the adhesive composition may contain 30-99.9% of polyurethane prepolymer reaction product, more preferably 50-99.9% of polyurethane prepolymer reaction product.

[0050] The disclosed hot-melt adhesive can be prepared using the following procedure. Note that moisture must be removed from the polyurethane reaction. The polyol, any thermoplastic polymer, and any filler are added to a reactor and placed under heat and vacuum to remove moisture. Once dried, excess polyisocyanate is added to the reactor, which is maintained under heat and an inert gas barrier to remove moisture. After a suitable reaction time, the silicone oligomer and optionally a catalyst can be added to the reaction product and mixed in. The final product contains an isocyanate-functionalized prepolymer mixed with the remaining components and transferred to a moisture-proof container and sealed immediately. Optional components and additives (if used) can be added with the polyol or after the reaction. It may be necessary to dry the optional components to prevent reaction with the isocyanate portion of the adhesive composition.

[0051] The hot melt adhesive according to this disclosure can be applied in various ways, including by spraying, rolling, extrusion, and as beads. The disclosed hot melt adhesive is stable during storage, provided that moisture is removed. It can be applied to a range of substrates, including metals, wood, plastics, glass, and textiles.

[0052] When maintained at the temperatures and times used in commercial application equipment, the hot melt adhesive according to this disclosure will not gel or separate into multiple phases; for example, the hot melt adhesive can be maintained at 121°C for 24 hours. In some embodiments, when maintained at the temperatures and times used in commercial application equipment, the viscosity of the disclosed hot melt adhesive increases to 500% or less, preferably 200% or less, more preferably 100% or less. Holding samples in a sealed container at 121°C for 24 hours (e.g., excluding air and moisture) is used to approximate commercial conditions.

[0053] The present invention also provides a method for bonding articles together, comprising: providing a reactive hot melt adhesive in a cooled, generally solid form; heating the reactive hot melt adhesive to a molten form; applying a molten reactive hot melt adhesive composition in the molten form to a first article; contacting a second article with the composition applied to the first article; cooling and hardening the adhesive; and subjecting the applied composition to conditions that will allow the composition to fully cure into a composition having an irreversible solid form, said conditions including moisture. Hot melt adhesives are typically distributed and stored in their solid form and are prevented from curing during storage in the absence of moisture. The composition is heated to a molten form and applied in a molten form prior to application. Typical application temperatures are from about 80°C to about 145°C, typically about 120°C. Therefore, this disclosure includes reactive polyurethane hot melt adhesive compositions in an uncured solid form as they are normally stored and distributed, in a molten form immediately after melting before application, and in their irreversible solid form after curing.

[0054] After application, in order to adhere the articles together, the reactive hot melt adhesive composition is subjected to conditions that will allow it to harden and solidify into a composition having an irreversible solid form. Hardening or setting occurs as the liquid melt begins to cool from its application temperature to room temperature. Solidification (i.e., chain extension) into a composition having an irreversible solid form occurs in the presence of ambient moisture.

[0055] The disclosed reactive polyurethane hot melt adhesive compositions are particularly suitable as adhesives in reinforced composite structures. One example is a large reinforced composite panel used in the manufacture of recreational vehicles. Such a reinforced composite panel typically comprises one or two panels, or “skins,” laminated to opposite sides of a reinforced metal frame. The skin can include, for example, wood or wood products, plastics, fiber-reinforced plastics (FRP), metal or metal foil, high-pressure laminate (HPL) skins, or other materials. Typically, the outer skin is plastic or a plastic composite to resist weathering. If an inner skin is required, it is typically wood or laminated wood, such as Lauan plywood. The frame typically comprises multiple tubular metal sections welded together to form a structural frame. Typically, the tubular metal sections have a quadrilateral cross-sectional shape, with the bonding surfaces defined on opposite sides of the shape. Structural aluminum components are almost exclusively used in recreational vehicles to reduce the weight of the frame and the vehicle. Materials such as expanded polystyrene (EPS) foam sheets can be disposed between the skins in unoccupied spaces between the frames. A panel lamination method includes: applying a molten, one-component hot-melt polyurethane adhesive to some surfaces to be laminated; optionally atomizing with water to accelerate curing; placing the one or more skins into contact with the adhesive disposed on the frame surface; moving the assembled components through a pressing press to apply pressure to the assembled components and stacking the assembled components; and transferring or storing the components after initial setting and / or curing of the adhesive. The disclosed one-component reactive polyurethane hot-melt adhesive composition provides enhanced adhesive strength to aluminum frames, particularly untreated aluminum frames, compared to conventional adhesives.

[0056] For reinforced composite panels used in vehicles, an adhesion percentage of at least about 30%, preferably at least about 50%, more preferably at least about 70%, and most preferably at least about 90% is desirable. A 100% adhesion percentage would be ideal, as it indicates that the substrate fails before the adhesive bonds. While some of these adhesion strengths can be achieved with conventional reactive polyurethane hot melt adhesives bonded to anodized or conversion-coated aluminum frame members, it is impossible to consistently achieve even 30% adhesion strength using conventional reactive polyurethane hot melt adhesives with factory-grade aluminum frame members (e.g., untreated aluminum frame members received from the factory without cleaning and conversion coating or anodizing). Experimental data

[0057] The viscosity of the product (in centipoise (cP) was measured on a Brookfield DV-I+ viscometer with a heated sample cup and after equilibration at 121°C for 30 minutes using a #27 rotor.

[0058] Thermal stability was measured using the following aging test. Uncured polyurethane hot melt adhesive was filled into an aluminum tube, and the tube was sealed to exclude air and moisture. The tube and sample were thermally aged in an oven at 121°C for 24 hours. After aging, the viscosity of the sample was measured before and after thermal aging using a Brookfield viscometer (#27 rotor), and the percentage increase in viscosity was recorded. Exclusion of air and moisture helps prevent the aged sample from reacting with moisture. The aging test is an approximation of how the hot melt adhesive will react over time when held at the melting temperatures that are likely to occur during use. Viscosity change is defined as: (Final viscosity - Initial viscosity) / Final viscosity If the sample gels or separates after thermal aging, the viscosity after aging is not measured, and the thermal stability is considered unacceptable and ineffective.

[0059] NCO was monitored using a Brinkman Metrohm automatic titrator.

[0060] The percentage of bond was tested by applying the test composition at an effective coating weight of 10 to 12 g / sq ft (gsf) to untreated factory-grade hollow rectangular aluminum tubing. Factory-grade aluminum was used as is, without cleaning, anodizing, or conversion coating prior to testing. A sheet of Lauan plywood (approximately 3 mm thick) was placed on the applied adhesive and vacuum-pressed onto the adhesive and tubing for 1 hour. The laminate was allowed to cure for two days at room temperature and ambient humidity. The bond strength of the Lauan plywood to the aluminum was tested by attempting to pry the plywood off the tubing with a scraper. The percentage of Lauan plywood failure was visually assessed based on the amount of wood remaining bonded to the aluminum; for example, 90% bond meant 90% of the wood remained bonded (a good result), while 10% bond meant 10% of the wood remained bonded (a failed result). Results were recorded. The uncertainty range for the percentage of bond is approximately + or -5%. Organosilicon oligomers

[0061] Organosilicon oligomers are commercially available. Alternatively, organosilicon oligomers can be synthesized. Synthesis of diphenyltetramethoxydisiloxane (n=1 in Formula 1)

[0062] 195.2 g of phenyltrimethoxysilane can be placed in a 0.5 L three-necked round-bottom flask equipped with a magnetic stir bar, thermometer, and dropping funnel. Over a 7-hour period, 8.8 g of 1 N hydrochloric acid (water:methoxy molar ratio 6:1) can be added dropwise to the silane, ensuring the temperature of the mixture does not exceed 40 °C. The mixture can be stirred for 10 hours, after which the reaction is stopped, and the mixture is stored at 25 °C for at least one day before distillation. The reaction mixture is purified by vacuum distillation. Two fractions are separated under a vacuum of 1 mbar. The first fraction, at 130 °C, contains unreacted phenyltrimethoxysilane. The second fraction, separated at 230 °C, contains the desired product, 1,2-diphenyltetramethoxydisiloxane (36% yield). The following materials are used in the embodiments.

[0063] The preparation examples are shown below. Amounts are based on the total weight of the composition and are expressed in parts by weight.

[0064] The preparation examples are described below. In each case, the material is wet reactive, therefore the reaction, packaging, and storage are carried out under conditions that exclude moisture. Example 1 - Comparative Example

[0065] 185 parts of PPG2000 and 185 parts of PPG4000 were introduced into a heated stirred tank reactor with a vacuum connection, and 165 parts of Elvacite 2016, 115 parts of Elvax 210, 115 parts of Kristalex 3100, and 140 parts of polyester polyol were blended and melted therein. Moisture was then removed under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 88.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The contents of the reactor were stirred under nitrogen at 121°C for 15 minutes, and then stirred under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE) were added and stirred under nitrogen for 15 minutes. The product was then transferred to a moisture-proof container and immediately sealed for subsequent testing. Example 2 - The Invention

[0066] 185 parts of PPG2000 and 185 parts of PPG4000 were introduced into a heated stirred tank reactor with a vacuum connection, and 165 parts of Elvacite 2016, 115 parts of Elvax 210, 115 parts of Kristalex 3100, and 140 parts of polyester polyol were blended and melted therein. Moisture was then removed under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 88.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The contents of the reactor were stirred at 121°C under nitrogen for 15 minutes, and then stirred under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE), 0.3 parts of 85% phosphoric acid, and 5 parts of 1,3-diphenyltetramethoxydisiloxane were added, and stirred under nitrogen for 15 minutes. The product was then transferred to a moisture-proof container and immediately sealed for subsequent testing. Example 3 - The Invention

[0067] 185 parts of PPG2000 and 185 parts of PPG4000 were introduced into a heated stirred tank reactor with a vacuum connection, and 165 parts of Elvacite 2016, 115 parts of Elvax 210, 115 parts of Kristalex 3100, and 140 parts of polyester polyol were blended and melted therein. Moisture was then removed under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 88.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The contents of the reactor were stirred at 121°C under nitrogen for 15 minutes, followed by stirring at 121°C under vacuum for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE) and 5 parts of 1,3-diphenyltetramethoxydisiloxane were added, and the mixture was stirred under nitrogen for 15 minutes. The product was then transferred to a moisture-proof container and immediately sealed for subsequent testing. Example 4 - The Invention

[0068] 185 parts of PPG2000 and 185 parts of PPG4000 were introduced into a heated stirred tank reactor with a vacuum connection, and 165 parts of Elvacite 2016, 115 parts of Elvax 210, 115 parts of Kristalex 3100, and 140 parts of polyester polyol were blended and melted therein. Moisture was then removed under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 88.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The contents of the reactor were stirred at 121°C under nitrogen for 15 minutes, and then stirred under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE), 0.3 parts of 85% phosphoric acid, and 5 parts of phenyltrimethoxysilane were added and stirred under nitrogen for 15 minutes. The product was then transferred to a moisture-proof container and immediately sealed for subsequent testing. Example 5 - Comparative Example

[0069] 185 parts of PPG2000 and 185 parts of PPG4000 were introduced into a heated stirred tank reactor with a vacuum connection, and 165 parts of Elvacite 2016, 115 parts of Elvax 210, 115 parts of Kristalex 3100, and 140 parts of polyester polyol were blended and melted therein. Moisture was then removed under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 88.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The reactor contents were stirred under nitrogen at 121°C for 15 minutes, followed by stirring under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE), 0.3 parts of 85% phosphoric acid, and 5 parts of A-1110 were added, followed by stirring under nitrogen for 15 minutes. The product was then transferred to a moisture-proof container and immediately sealed for subsequent testing. Example 6 - Comparative Example

[0070] 185 parts of PPG2000 and 185 parts of PPG4000 were introduced into a heated stirred tank reactor with a vacuum connection, and 165 parts of Elvacite 2016, 115 parts of Elvax 210, 115 parts of Kristalex 3100, and 140 parts of polyester polyol were blended and melted therein. Moisture was then removed under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 88.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The contents of the reactor were stirred under nitrogen at 121°C for 15 minutes, and then stirred under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE) and 5 parts of A-1110 were added, and the mixture was stirred under nitrogen for 15 minutes. The product was then transferred to a moisture-proof container and immediately sealed for subsequent testing. Example 7 - The Invention

[0071] 185 parts of PPG2000 and 185 parts of PPG4000 were introduced into a heated stirred tank reactor with a vacuum connection, where 185 parts of polyester polyol were blended and melted. Moisture was then removed under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 50 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The reactor contents were stirred at 121°C under nitrogen for 15 minutes, followed by stirring under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE) and 5 parts of 1,3-diphenyltetramethoxydisiloxane were added, and the mixture was stirred under nitrogen for 15 minutes. The product was then transferred to a moisture-proof container and immediately sealed for subsequent testing. Example 8 - The Invention

[0072] 185 parts of PPG 2000 and 185 parts of PPG 4000 were introduced into a heated stirred tank reactor with a vacuum connection, and 165 parts of Elvacite 2016, 115 parts of Elvax 210, 115 parts of Foralyn 5020 F, and 140 parts of polyester polyol were blended and melted therein. Moisture was then removed under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 88.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The reactor contents were stirred at 121°C under nitrogen for 15 minutes, followed by stirring under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE) and 5 parts of 1,3-diphenyltetramethoxydisiloxane were added. The mixture was stirred under nitrogen for 15 minutes. The product was then transferred to a moisture-proof container and immediately sealed for subsequent testing. Example 9 - The Invention

[0073] 185 parts of PPG 2000 and 185 parts of PPG 4000 were introduced into a heated stirred tank reactor with a vacuum connection, and 165 parts of Elvacite 2016, 115 parts of Elvax 210, 115 parts of Sylvares SA 100, and 140 parts of polyester polyol were blended and melted therein. The mixture was then dehydrated under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 88.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The contents of the reactor were stirred at 121°C under nitrogen for 15 minutes, followed by stirring under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE) and 5 parts of 1,3-diphenyltetramethoxydisiloxane were added. The mixture was stirred under nitrogen for 15 minutes. The product was then transferred to a moisture-proof container and immediately sealed for subsequent testing. Example 10 - The Invention

[0074] 255 parts of PPG 2000 and 255 parts of PPG 4000 were introduced into a heated stirred tank reactor with a vacuum connection, and 165 parts of Elvacite 2016, 115 parts of Elvax 210, and 115 parts of Kristalex 3100 were blended and melted therein. Moisture was then removed under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 80.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The reactor contents were stirred at 121°C under nitrogen for 15 minutes, followed by stirring under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE) and 5 parts of 1,3-diphenyltetramethoxydisiloxane were added. The mixture was stirred under nitrogen for 15 minutes. The reaction product was then transferred to a moisture-proof container and immediately sealed for subsequent testing. Example 11 - The Invention

[0075] 106 parts of polyester-2 and 264 parts of polyester-3 were introduced into a heated stirred tank reactor with a vacuum connection, and 165 parts of Elvacite 2016, 115 parts of Elvax 210, 115 parts of Kristalex 3100, and 140 parts of polyester polyol were blended and melted therein. The mixture was then dehydrated under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 84.2 parts of 4,4'-diphenylmethane diisocyanate (MDI) were added. The contents of the reactor were stirred at 121°C under nitrogen for 15 minutes, followed by stirring under vacuum at 121°C for 2 hours. The reactor was then purged with nitrogen, and 1.5 parts of 2,2'-dimorpholine diethyl ether (DMDEE) and 5 parts of 1,3-diphenyltetramethoxydisiloxane were added. The mixture was stirred under nitrogen for 15 minutes. The reaction product was then transferred to a moisture-proof container and immediately sealed for subsequent testing.

[0076] As shown in the table above: Example 1 shows that conventional polyurethane reactive hot melt adhesives have good stability under heat, but exhibit very poor adhesion to untreated aluminum substrates. Example 7 demonstrates that a polyurethane reactive hot melt containing the disclosed silicone oligomer (1,3-diphenyltetramethoxydisiloxane, n=1 in Formula 1) can simultaneously exhibit good adhesion to untreated aluminum substrates and good thermal stability. Note that Example 7 does not contain Elvax 210, Kristalex 3100, or Elvacite 2016. Examples 5 and 6 demonstrate that a polyurethane reactive hot melt adhesive containing the correct silane can provide improved adhesion to untreated aluminum frames (the wood substrate failed before the adhesive bonded to the aluminum substrate). However, its thermal stability was not as good as expected, and it may even gel unacceptably during use. Example 4 shows that a polyurethane reactive hot melt adhesive containing the disclosed silicone oligomer (phenyltrimethoxysilane, n=0 in Formula 1) can simultaneously exhibit good adhesion to untreated aluminum substrates and good thermal stability. Example 3 shows that a polyurethane reactive hot melt adhesive containing the disclosed silicone oligomer (1,3-diphenyltetramethoxydisiloxane, n=1 in Formula 1) can simultaneously exhibit excellent adhesion to untreated aluminum substrates and good thermal stability. Example 2 illustrates a polyurethane reactive hot melt adhesive comprising both the disclosed silicone oligomer (1,3-diphenyltetramethoxydisiloxane, n=1 in Formula 1) and MA-SCA, which, compared to Example 3 without MA-SCA, simultaneously exhibits excellent adhesion to untreated aluminum substrates and even better thermal stability. Most embodiments of the present invention use a combination of polyether polyols and polyester polyols that have excellent results. Examples 10 and 11 show that polyurethane reactive hot melt adhesives containing only polyether polyols or only polyester polyols can also provide excellent results.

[0077] The tests described above focused on the improved adhesion of the disclosed polyurethane reactive hot melt adhesive to aluminum substrates. Another set of tests was conducted on uncleaned stainless steel substrates using the adhesive from Example 2. These tests used the same test procedures as the previously tested aluminum substrates. Six tests were performed, yielding an average failure rate of 45% for the wood substrates. These tests demonstrate that the disclosed polyurethane reactive hot melt adhesive can improve bond strength to stainless steel substrates.

[0078] The results show that introducing specific groups of organosilicon oligomers and optionally present MA-SCA acids into specific polyurethane reactive hot melt adhesives can provide reactive polyurethane hot melt adhesives that exhibit excellent adhesion to untreated metals while maintaining good stability under heat.

[0079] The terminology used herein is for the purpose of describing particular example implementations only and is not intended to be restrictive. The method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically stated otherwise. It should also be understood that additional or alternative steps may be employed.

Claims

1. A one-component reactive polyurethane hot melt adhesive comprising: a reaction product of an isocyanate-functional prepolymer including a mixture of at least one polyisocyanate and at least one polyol; a silicone oligomer of structure 1: Structure 1 wherein each R' is the same or different and is independently selected from a hydrogen atom or a hydrocarbon residue having 1 to 12 carbon atoms, R' is preferably a methyl or ethyl group, R' is more preferably a methyl group; Ar is selected from an aryl group, Ar is preferably a phenyl group; and n is an integer selected from 0-12, preferably 1-12.

2. The one-component reactive polyurethane hot melt adhesive of claim 1, wherein the polyol in the mixture comprises a polyether polyol, a polyester polyol, or a combination of a polyether polyol and a polyester polyol.

3. The one-component reactive polyurethane hot melt adhesive of claim 1 or 2, wherein the polyol in the mixture comprises a first polyether polyol having a molecular weight, a second polyether polyol having a different molecular weight than the first polyether polyol, and a polyester polyol.

4. The one-component reactive polyurethane hot melt adhesive of any one of claims 1 to 3, wherein the isocyanate-functional prepolymer is free of Si atoms.

5. The one-component reactive polyurethane hot melt adhesive of any one of claims 1 to 4, further comprising at least one of 10-50 wt% of an inorganic filler or 0-1 wt% of a MA-SCA acid.

6. The one-component reactive polyurethane hot melt adhesive of any one of claims 1 to 5, further comprising one or more of a thermoplastic resin, a tackifier, or a catalyst.

7. The one-component reactive polyurethane hot melt adhesive of any one of claims 1 to 6, further comprising a thermoplastic resin selected from an acrylic resin, an EVA resin, and a tackifier.

8. The one-component reactive polyurethane hot melt adhesive of any one of claims 1 to 7, further comprising 0-1 wt% of a MA-SCA acid selected from nitric acid, sulfuric acid, phosphonic acid, phosphoric acid, diphosphonic acid (pyrophosphoric acid), and combinations thereof.

9. The one-component reactive polyurethane hot melt adhesive of any one of claims 1 to 8, wherein the cured reaction product of the adhesive has a percent bond of at least 50.

10. A method of manufacturing a bonded reinforced composite structure comprising: providing an aluminum frame having a first bonding surface; providing a first panel having a bonding surface; providing a one-component reactive polyurethane hot melt adhesive, wherein the adhesive composition comprises: a reaction product of an isocyanate-functional prepolymer including a mixture of at least one polyisocyanate and at least one polyol; a silicone oligomer of structure 1: Structure 1 wherein each R' is the same or different and is independently selected from a hydrogen atom or a hydrocarbon residue having 1 to 12 carbon atoms, R' is preferably a methyl or ethyl group, R' is more preferably a methyl group; Ar is selected from an aryl group, Ar is preferably a phenyl group; and n is an integer selected from 0-12, preferably 1-12; heating the adhesive to a molten state; applying the molten adhesive on at least one bonding surface; positioning the first panel bonding surface in contact with the disposed adhesive and the frame bonding surface to form a composite structure; and curing the adhesive to bond the first panel to the metal frame.

11. The method of claim 10, wherein: the aluminum frame has a quadrilateral cross-section and a second bonding surface opposite the first bonding surface; and includes: providing a second panel having a bonding surface; applying the adhesive on at least one of the frame second bonding surface or the second panel bonding surface; positioning the second panel bonding surface in contact with the disposed adhesive and the frame second bonding surface; and curing the adhesive to bond the second panel to the metal frame.

12. The method of any one of claims 10-11, wherein at least one aluminum bonding surface is factory grade without cleaning.

13. The method of any one of claims 10-12, wherein at least one aluminum bonding surface does not have a surface conversion coating and / or an anodization treatment.

14. The method of any one of claims 10-13, wherein at least one aluminum bonding surface is conversion coated.

15. The method of any one of claims 10-14, wherein the first panel comprises a cured polymer and / or plywood.

16. The method of any one of claims 10-15, wherein the composite structure is free of mechanical fasteners to retain the first panel to the frame.

17. The method of any one of claims 10-16, further comprising positioning an insulator in a void region defined by the frame and first panel bonding surfaces.

18. Use of the one-component reactive polyurethane hot melt adhesive of any one of claims 1-9 to bond a material to aluminum.

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