Two-component polyurethane adhesive with durable adhesion to inorganic substrates

Abstract

A two-part polyurethane adhesive with limited or no silane adhesion promoters in the polyol component that has improved adhesion to uncoated inorganic substrates.

Description

[Background technology]

[0001] Polyurethane (PU) is a well-known type of adhesive known as a two-component or 2K adhesive. Such adhesives can be used in a variety of applications, such as in passenger vehicle assembly, particularly when welding two dissimilar materials together during manufacturing is difficult or impractical. Typically, a 2K PU adhesive formulation has a first resin component containing one or more isocyanates and a second curing agent component containing one or more polyols. When the two components are mixed, the isocyanates and polyols react to form the adhesive. Polyurethane adhesives can be formulated to cure at room temperature or upon exposure to specific conditions.

[0002] As the adhesive cures, it can form strong adhesive bonds to many types of substrates. However, in certain applications, such as the assembly of passenger cars, the bonded assemblies are often heavy and large (e.g., spanning several meters). As a result, the flexibility of the cured adhesive is important, as are other properties such as the adhesive's contribution to the overall stiffness of the part. The cured adhesive must also have stable physical properties, such as Young's modulus, shear strength, and elongation at break, throughout the temperature window (e.g., -30°C to 80°C) in which a vehicle is typically operated. Obtaining sufficient adhesive strength while maintaining desirable adhesive properties is particularly challenging between two dissimilar substrates, such as inorganic substrates and plastics, and often requires the application of expensive coatings on the inorganic substrate to enable proper adhesion. There is a need in the art for improvements that could eliminate the need for costly pre-treatment of substrates prior to assembly, particularly in passenger cars. Summary of the Invention [Means for solving the problem]

[0003] Disclosed is an uncured adhesive formulation comprising: (a) a first component comprising an isocyanate and 0.4% to 5% by weight of the first component of a silane adhesion promoter; and (b) a second component comprising: i) 10% to 80% by weight of the second component of a polyol, the polyol having a molecular weight of at least 400 g / mol; and ii) 1% to 15% by weight of the second component of a diol, the diol having a molecular weight of 200 g / mol or less. The second component may comprise less than 3% by weight of the silane adhesion promoter. The inventors surprisingly discovered that limiting or eliminating the silane adhesion promoter from the second component allows for the production of a stable assembly of two dissimilar substrates without requiring surface pretreatment for coating one or more of the dissimilar substrates.

[0004] The uncured adhesive formulation is in the form of a kit in which the first and second components are not mixed prior to use. The components of the kit may be packaged together, packaged separately, or sold together or separately.

[0005] Also described are cured adhesives produced by mixing the first and second components of the adhesive formulation and curing the mixture. Similarly, methods of curing adhesive formulations are described that include mixing the first and second components of the adhesive formulation and curing the mixture. Cured adhesives prepared by the described methods are also disclosed.

[0006] Further disclosed is a method of applying the uncured or partially cured mixture to an inorganic substrate before fully curing the mixture. Suitable exemplary substrates include uncoated, corrosion-resistant aluminum or steel. Additionally, a method of forming an assembly (and product thereof) is described in which an inorganic substrate coated with the adhesive formulation mixture can be applied to a second, non-inorganic substrate and the adhesive mixture fully cured to form a bonded assembly with the cured adhesive therebetween. DETAILED DESCRIPTION OF THE INVENTION

[0007] I. First (Isocyanate) Component The first component of the adhesive formulation kit is the isocyanate component, abbreviated as "IsoC" in the following examples. Typically, the isocyanate component includes an isocyanate, such as a monomeric or polymeric isocyanate (or a prepolymer thereof, as described below), and an adhesion promoter, which is described in more detail below.

[0008] A. Monomeric isocyanate The isocyanate component can include any monomeric isocyanate commonly used in polyurethane technology. Non-limiting examples include m-phenylene diisocyanate, methylene diphenyl diisocyanate (MDI), 4,4'-methylene diphenyl diisocyanate, 2,2'-methylene diphenyl diisocyanate, 2,4-methylene diphenyl diisocyanate, toluene diisocyanate (TDI), toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, naphthyl-ene-1,5-diisocyanate, methoxyphenyl-2,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, 4,4'-biphenylene diisocyanate, 3,3 Examples of suitable monomeric isocyanates include 4,4'-dimethoxy-biphenyl diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, 3,3'-dimethyl-diphenylmethane-4,4'-diisocyanate, 4,4',4"-triphenylmethane triisocyanate, toluene-2,4,6-triisocyanate, 4,4'-dimethyl-diphenylmethane-2,2,5,5'-tetraisocyanate, and mixtures thereof. The monomeric isocyanate may be present in the first component in an amount of 0 to 30% by weight, for example, 1 to 25% by weight, 2 to 20% by weight, 5 to 20% by weight, 10 to 20% by weight, or 10 to 15% by weight of the first component.

[0009] B. Polymeric isocyanate Any polymer of a monomeric isocyanate may also be used, including in combination with a monomeric isocyanate. Examples include any derivative or polymer of the isocyanates mentioned above. Other examples include polyisocyanates containing urethane, urea, biuret, carbodiimide, uretonimine, allophonate, or other groups formed by the reaction of isocyanate groups. The isocyanate component may also include polymeric MDI (a mixture of MDI and poly-MDI, commonly referred to as "polymeric MDF"). Other examples include "liquid MDI" products, which are mixtures of MDI and poly-MDI derivatives with biuret, carbodiimide, uretonimine, or allophonate linkages. The polymeric isocyanate may be present in the first component in an amount ranging from 0 to 30% by weight of the first component, for example, 1 to 25%, 2 to 20%, 5 to 20%, 10 to 20%, or 10 to 15% by weight.

[0010] C. Isocyanate-terminated prepolymer The isocyanate component can include isocyanates prepared by reacting a monomeric or polymeric isocyanate with a polyol or a low molecular weight diol or triol. For example, any of the polyols described below with respect to the polyol component or any of the polyols described in, for example, WO2016205252A1, which is incorporated by reference, can be used.

[0011] The polyol used to prepare the isocyanate-terminated prepolymer can have a molecular weight (MW, g / mol) of 200 to 10,000, a MW of 800 to 8,000, a MW of 800 to 6,000, e.g., 200 to 3,000, 500 to 3,000, or 1,000 to 3,000 g / mol. In addition, the polyol can have a nominal functionality of 2 to 3. The polyol can also have an OH number in the range of 20 to 80 mg KOH / g, e.g., 25 to 75, 30 to 70, 30 to 60, or 40 to 60 mg KOH / g.

[0012] The reaction of an isocyanate with a polyol can produce an isocyanate-containing prepolymer having a polyether segment capped with an isocyanate, resulting in a polymer with terminal isocyanate groups. Each prepolymer molecule contains a polyether segment corresponding to the structure of the polyol used in the prepolymer-forming reaction after removal of the hydroxyl groups. If a mixture of polyols is used, a mixture of prepolymer molecules can be formed. For example, in addition to prepolymers that can be end-capped with polyols, in other embodiments, a variety of other prepolymers can be produced by multimolecular weight buildup. For example, a prepolymer can have a diisocyanate in the center of the prepolymer's chemical structure, with two hydroxyl groups attached to the ends of the structure, which can be end-capped with isocyanates.

[0013] In one embodiment, for example, the prepolymer may comprise an MDI end-capped prepolymer formed from an EO (ethylene oxide) and / or PO (propylene oxide)-based polyol, such as a polymeric diol, triol, or mixture thereof. The resulting prepolymer may have an equivalent weight (EW) of up to 5,000, 1,000-4,000, and 2,000-3,500. Molecular weight values ​​reported here and elsewhere refer to number average molecular weights measured by gel permeation chromatography (GPC) equipped with a triple detector for absolute molecular weight calibration, unless otherwise specified.

[0014] In another embodiment, the prepolymer can be prepared by combining (1) a polyol or mixture of polyols with (2) a low equivalent weight (e.g., less than 350 equivalents) isocyanate or polyisocyanate or mixtures thereof. Low equivalent weight isocyanates typically have an isocyanate equivalent weight of up to 350, 80-350, 80-250, 80-200, or 80-180. The amount of such low equivalent weight isocyanate that can be used can be significantly greater than the amount needed simply to cap the polyol with isocyanate sites.

[0015] After reaction, the above combination can produce a mixture of prepolymer and unreacted starting low equivalent weight isocyanate. If desired, additional amounts of isocyanate can then be blended into this prepolymer / unreacted low equivalent weight mixture. For example, the mixture can be combined with one or more aliphatic isocyanates, such as aliphatic isocyanates based on hexamethylene diisocyanate or polymers thereof. A more detailed discussion of prepolymer technology can be found in U.S. Patent Application Publication No. 2020 / 0407611 A1, which is incorporated by reference for its teachings on prepolymer technology.

[0016] D. Adhesion promoters The isocyanate component can include an adhesion promoter, such as a silane, an epoxy silane, an amino silane, or a combination thereof. The adhesion promoter can, for example, constitute 0.4 to 5% of the total weight of the isocyanate component. In some embodiments, the adhesion promoter can be present in the isocyanate component in an amount ranging from 0.5 to 5% by weight of the isocyanate component, e.g., 0.6 to 4% by weight, 0.8 to 3% by weight, 1 to 3% by weight, or 2 to 3% by weight.

[0017] Adhesion promoters include compounds having at least one functional group that has an attractive force toward the desired substrate surface, the cured adhesive applied to the substrate, or both. Examples of adhesion promoters include titanates, carboxylated branched or linear PEI, and silane compounds. Non-limiting examples include silane adhesion promoters with reactive functional groups, such as epoxy silanes (e.g., γ-glycidoxypropyltrimethoxysilane, such as Silquest A187) or mercaptosilanes (e.g., γ-mercaptopropyltrimethoxysilane, such as Silquest A189). In one embodiment, the adhesion promoter is not an aminosilane. In a further embodiment, the isocyanate component does not include an aminosilane. In a further embodiment, none of the components of the kit include an aminosilane.

[0018] II. Second (Polyol) Component The second component is a polyol component, abbreviated as "Poly C" in the following examples. The second component typically comprises: i) 10% to 80% by weight of the second component of a polyol having a molecular weight of at least 400 g / mol; and ii) 1% to 15% by weight of the second component of a diol having a molecular weight of 200 g / mol or less. In some embodiments, the polyol and diol can both have two hydroxyl groups per molecule, but are distinguished from each other in that the diol has a lower molecular weight than the polyol.

[0019] A. Polyol In some embodiments, the second component comprises 15% to 75% polyol by weight of the second component. In other embodiments, the second component comprises 20% to 70% polyol by weight of the second component. In other embodiments, the second component comprises 25% to 65% polyol by weight of the second component. In other embodiments, the second component comprises 30% to 60% polyol by weight of the second component. In other embodiments, the second component comprises 35% to 55% polyol by weight of the second component. In other embodiments, the second component comprises 40% to 50% polyol by weight of the second component. In other embodiments, the second component comprises 45% to 50% polyol by weight of the second component.

[0020] The molecular weight of the polyol can vary. In some embodiments, the polyol has a molecular weight of 400 g / mol to 3,000 g / mol. In another embodiment, the polyol has a molecular weight of 500 g / mol to 2,500 g / mol. In another embodiment, the polyol has a molecular weight of 600 g / mol to 2,000 g / mol. In another embodiment, the polyol has a molecular weight in the range of 700 g / mol to 1,900 g / mol. In another embodiment, the polyol has a molecular weight in the range of 800 g / mol to 1,800 g / mol. In another embodiment, the polyol has a molecular weight in the range of 900 g / mol to 1,700 g / mol. In another embodiment, the polyol has a molecular weight in the range of 1,000 g / mol to 1,700 g / mol. In another embodiment, the polyol has a molecular weight in the range of 1,100 g / mol to 1,700 g / mol. In another embodiment, the polyol has a molecular weight in the range of 1,200 g / mol to 1,700 g / mol. In another embodiment, the polyol has a molecular weight in the range of 1,300 g / mol to 1,700 g / mol. In another embodiment, the polyol has a molecular weight in the range of 1,400 g / mol to 1,700 g / mol. In another embodiment, the polyol has a molecular weight in the range of 1,500 g / mol to 1,700 g / mol.

[0021] Generally, the polyol can be any polyol used in polyurethane technology. For example, the polyol can be a glycerin-initiated propoxylated or ethoxylated polyol or any propoxylated or ethoxylated polyol prepared from other trifunctional and difunctional initiators. In some embodiments, the polyol can be a polyether polyol or a mixture of polyether polyols. In another embodiment, the polyol can be a propylene oxide homopolymer or copolymer or a propylene oxide copolymer containing 70% to 99% by weight of propylene oxide and 1% to 30% by weight of ethylene oxide. Such copolymers of propylene oxide and ethylene oxide may be preferred when a single polyether polyol is present. When two or more polyether polyols are present, it may be preferred that at least one of the polyols is such a copolymer of propylene oxide and ethylene oxide. In the case of a copolymer, propylene oxide and ethylene oxide can be randomly copolymerized, block copolymerized, or both. In some embodiments, about 50% or more of the hydroxyl groups in the polyether polyol or mixture of polyether polyols are primary hydroxyl groups, with the remainder of the hydroxyl groups being secondary hydroxyl groups. In other embodiments, about 70% or more of the hydroxyl groups in the polyether polyol or mixture thereof can be primary hydroxyl groups.

[0022] In additional embodiments, the polyol can be a polyether polyol or a polyester polyol. Other suitable polyols useful in the polyol component can include polypropylene-based diols such as VORANOL 1010L having a molecular weight of 500 g / mol, VORANOL 2000L having a molecular weight of 1,000 g / mol, VORANOL CP4610, a glycerin-initiated ethylene oxide-based propoxylated triol having an average molecular weight of 1,600 g / mol, and mixtures thereof.

[0023] In certain embodiments, the polyol is a glycerin-initiated ethylene oxide-based propoxylated triol having a molecular weight of 1,500 g / mol to 1,700 g / mol, which may be present at 15% to 75%, 20% to 70%, 25% to 65%, 30% to 60%, 35% to 55%, 40% to 50%, or 45% to 50% by weight of the second component.

[0024] B. Low Molecular Weight Diols Diols having a molecular weight of 200 g / mol or less function as chain extenders. The second component may comprise 1% to 15% diol by weight of the second component. In some embodiments, the second component may comprise 2% to 14% diol by weight of the second component. In some embodiments, the second component may comprise 3% to 12% diol by weight of the second component. In some embodiments, the second component may comprise 4% to 10% diol by weight of the second component. In some embodiments, the second component may comprise 5% to 8% diol by weight of the second component. In some embodiments, the second component may comprise 6% to 8% diol by weight of the second component.

[0025] Typically, the diol can have at least two carbon atoms, can be branched, linear, or functionalized, and can have at least two hydroxyl groups per molecule. In some embodiments, the diol can be a linear or branched aliphatic diol having 2 to 20 carbons, e.g., 2 to 18 carbons, 2 to 16 carbons, 2 to 14 carbons, 2 to 12 carbons, 2 to 10 carbons, 2 to 8 carbons, or 2 to 6 carbons. In various embodiments, the diol has a molecular weight of 20 to 200 g / mol, e.g., 20 to 150 g / mol, 40 to 150 g / mol, 50 to 130 g / mol, or 60 to 120 g / mol.

[0026] In some embodiments, the diol has the formula C x H y O zwhere x is an integer ranging from 2 to 20, y is an integer equal to x+m, where m is an integer ranging from 4 to 12, and z is an integer equal to xn, where n is an integer ranging from 0 to 6. Non-limiting examples include monoethylene glycol (MEG), diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 2,3-dimethyl-1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,4-butanediol, or 1,6-hexanediol. In one embodiment, the diol can be monoethylene glycol, 1,4-butanediol, or a mixture thereof.

[0027] C. Adhesion promoter The present inventors have surprisingly discovered that the presence of an adhesion promoter in the polyol component of an adhesive formulation prior to curing of the two components adversely affects adhesive performance after curing, for example, as determined by a 3,000-hour salt spray test. Specifically, in some embodiments, the presence of a silane adhesion promoter adversely affects adhesive performance. Silanes, such as epoxy silanes, are typically bifunctional organosilanes with reactive epoxy groups and hydrolyzable alkoxy groups. Epoxy silanes can typically promote adhesion between organic polymers and inorganic materials, such as metals, dyes, fillers, and glass.

[0028] In some embodiments, the polyol component of the adhesive formulation contains limited or no adhesion promoters, such as silane adhesion promoters. For example, in some embodiments, the polyol component of the adhesive formulation contains no more than 3% by weight of the polyol component of an adhesion promoter, such as a silane. In another embodiment, the polyol component of the adhesive formulation contains no more than 2.5% by weight of the polyol component of an adhesion promoter, such as a silane. In another embodiment, the polyol component of the adhesive formulation contains no more than 2% by weight of the polyol component of an adhesion promoter, such as a silane. In another embodiment, the polyol component of the adhesive formulation contains no more than 1.5% by weight of the polyol component of an adhesion promoter, such as a silane. In another embodiment, the polyol component of the adhesive formulation contains no more than 1% by weight of the polyol component of an adhesion promoter, such as a silane. In another embodiment, the polyol component of the adhesive formulation contains no more than 0.5% by weight of the polyol component of an adhesion promoter, such as a silane. In another embodiment, the polyol component of the adhesive formulation contains no more than 0.4% by weight of the polyol component of an adhesion promoter, such as a silane. In another embodiment, the polyol component of the adhesive formulation comprises no more than 0.3% by weight of the polyol component of an adhesion promoter such as a silane. In another embodiment, the polyol component of the adhesive formulation comprises no more than 0.2% by weight of the polyol component of an adhesion promoter such as a silane. In another embodiment, the polyol component of the adhesive formulation comprises no more than 0.1% by weight of the polyol component of an adhesion promoter such as a silane. In another embodiment, the polyol component of the adhesive formulation comprises no more than 0.05% by weight of the polyol component of an adhesion promoter such as a silane. Finally, in some embodiments, the polyol component of the adhesive formulation does not comprise an adhesion promoter such as a silane.

[0029] III. Other compounding additives Any component of the adhesive kit may optionally contain several other additives to achieve or enhance particular performance characteristics, cure behavior, morphology properties, etc. Typically, these additional additives may be present in the first component (the isocyanate component), the second component (the polyol component), or both. Non-limiting examples of suitable additives are described below.

[0030] A. Scavengers and Compatibilizers In one embodiment, optional additives useful in the formulation may include gas and water scavengers to avoid additional water absorption in the adhesive and to avoid NCO-water reactions. Such undesirable reactions can lead to bubble formation in the adhesive due to CO2 release caused by the reaction of NCO with water. In another embodiment, compatibilizers may be used in the formulation to further improve wetting performance and improve mixing between the polyol and isocyanate components. These optional additives and components, when used in the adhesive formulation, may typically be present in amounts ranging from 0% to 15%, 0.1% to 10%, or 1% to 5% by weight, by weight of the formulation as a whole or of any of its components.

[0031] B. Chemical Rheology Modifiers Chemical rheology modifiers can be used in the formulation. Typically, different grades of polyamine compounds, for example, with different molecular weights and functionalities, can be used. In one embodiment, the polyamine compound includes, for example, any one or more of the following compounds: trimer Jeffamine T 403 having a molecular weight of 403 g / mol, dimer Jeffamine D-400 having a molecular weight of 400 g / mol, dimer Jeffamine D200 having a molecular weight of 200 g / mol, and mixtures thereof. Chemical rheology modifiers can be used to speed up the initial gelation of the formulation, thereby benefiting from superior sagging resistance. Furthermore, the rapid increase in viscosity upon cure of the formulation reduces the risk of CO2 formation in thermally accelerated curing processes. When used in adhesive formulations, rheology modifiers can be present in amounts typically ranging from 0% to 15%, 0.1% to 10%, and 1% to 5% by weight, based on the weight of the entire formulation or any of its components.

[0032] C.Catalyst The adhesive formulation may include a catalyst capable of catalyzing the reaction between hydroxyl groups and isocyanate groups. The catalyst may be present in the isocyanate component, the polyol component, or both. In some examples, the catalyst is present in the polyol component. In other examples, the catalyst is present in the polyol component but not in the isocyanate component.

[0033] The catalyst may include, for example, one or more latent room-temperature (about 25°C) organometallic catalysts. The latent room-temperature organometallic catalyst may include tin, zinc, bismuth, or a combination thereof. For example, the latent room-temperature organometallic catalyst may include one or more catalysts such as zinc alkanoate, bismuth alkanoate, dialkyltin alkanoate, dialkyltin mercaptide, dialkyltin bis(alkylmercaptoacetate), dialkyltin thioglycolate, or mixtures thereof. Specific examples include dioctyltin mercaptide, dibutyl mercaptide, dibutyl mercaptide, dibutyl mercaptide, bis(dodecylthio)dimethylstannane, dimethyltin bis(2-ethylhexylmercaptoacetate), dioctyl carboxylate, dioctyltin neodecanoate, and mixtures thereof.

[0034] Other catalysts useful in adhesive formulations are any catalysts that can be further heat activated (referred to as "heat-sensitive catalysts") or otherwise catalyze a reaction. In one embodiment, such catalysts can include, for example, cyclic amidine catalyst compounds such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene, 2,4,6-tris-(dimethylaminomethyl)-phenol, and mixtures thereof.

[0035] In a further embodiment, the adhesive formulation may include a combination of a latent tin-containing catalyst and a heat-sensitive amine-based catalyst. Both the tin-containing organic catalyst and the amine-based catalyst may be readily incorporated into the isocyanate component, the polyol component, or both the isocyanate and polyol components.

[0036] In a further embodiment, any non-tin based metallo-organic catalyst that exhibits a similar cure rate or catalytic profile to the above tin based catalysts can be used as the catalyst ingredient in the adhesive formulation. For example, a useful bismuth based catalyst includes bismuth(III)-neodecanote, and a useful zinc based catalyst includes zinc-neodecanote.

[0037] In yet another embodiment, non-tin or non-amine catalysts useful in adhesive formulations include carboxylic acid-blocked catalysts such as DBU carboxylic acid-blocked catalysts. For example, the DBU carboxylic acid-blocked catalyst can be TOYOCAT DB41 catalyst (a carboxylic acid DBU salt available from Tosoh Corporation), POLYCAT SA-102 / 10 (a carboxylic acid DBU salt available from Air Products), and mixtures thereof. Other useful catalysts include tertiary amine and organic acid-based catalysts such as TOYOCAT DB40, TOYOCAT DB60, and TOYOCAT DB70 available from Tosoh Corporation, 1H-1,2,4-triazole-based amine catalysts such as TOYOCAT DB30 available from Tosoh Corporation, and acid-blocked amines including mixtures thereof. Any other known heat-sensitive amine catalysts can also be used, such as TOYOCAT F22 available from Tosoh Corporation, triethylenediamine (TEDA), and mixtures thereof. In one embodiment, useful catalysts may be selected from tin catalysts such as di-n-octyltin bis[isooctylmercaptoacetate], amine catalysts such as POLYCAT SA1 / 10 and TOYOCAT DB60, and mixtures thereof.

[0038] Typically, the amount of catalyst in an adhesive formulation can range from 0.005% to 2.0%, 0.01% to 1.0%, and 0.015% to 0.07% by weight, based on i) the total weight of the formulation, or ii) the total weight of the first or second component (i.e., the polyol component or the isocyanate component) of the formulation. In an exemplary embodiment, when a tin catalyst such as di-n-octyltin bis[isooctylmercaptoacetate] is used in the adhesive formulation, the concentration of such catalyst in the formulation or any of its components can be from 0.005% to 1.0%, 0.02% to 0.08%, and 0.03% to 0.05% by weight, based on the total weight of the entire formulation or any of its components.

[0039] In another exemplary embodiment, when a heat sensitive amine catalyst such as POLYCAT SA1 / 10 is used in the adhesive formulation, the concentration of such catalyst in the formulation can be 0.01% to 2.0%, 0.01% to 1.0%, and 0.015% to 0.025% by weight based on the weight of the entire formulation or any of its components.

[0040] In yet another exemplary embodiment, when a catalyst such as TOYOCAT DB60 is used in the adhesive formulation, the concentration of such catalyst in the formulation can be 0.01 wt. % to 2.0 wt. %, 0.01 wt. % to 1.0 wt. %, and 0.045 wt. % to 0.065 wt. % based on the weight of the entire formulation or any of its components.

[0041] If the catalyst concentration is less than 0.005 wt. % of the total formulation, the catalyst used may not be effectively activated in the formulation, resulting in a "poor" storage stability of the resulting formulation, i.e., residual water present in the formulation may deactivate a small amount of catalyst. If the catalyst concentration exceeds about 2.0 wt. %, the components present in the formulation may react too quickly, resulting in a short open time, i.e., an open time of less than 3 minutes, for example. In addition, a high catalyst level in the formulation (e.g., greater than about 2.0 wt. %) may result in increased handling and formulation costs for the resulting formulation.

[0042] D. Filler The adhesive formulation may optionally include a filler. The filler may be a particulate filler. The particulate filler is a solid material at room temperature and does not dissolve in the polyol component or other ingredients of the isocyanate component. The filler may be a material that does not melt, volatilize, or decompose under the conditions of the curing reaction between the polyol component and the polyisocyanate component. The filler may be, for example, inorganic fillers such as glass, silica (e.g., fumed silica), boron oxide, boron nitride, titanium oxide, titanium nitride, fly ash, calcium carbonate, and various alumina-silicates (including clays such as wollastonite and kaolin), metal particles such as iron, titanium, aluminum, copper, brass, bronze, and the like, cured particles of polyurethane, epoxy, phenol-formaldehyde, or cresol-formaldehyde resins, thermosetting polymer particles such as crosslinked polystyrene, thermoplastic resins such as polystyrene, styrene-acrylonitrile copolymer, polyimide, polyamide-imide, polyetherketone, polyether-etherketone, polyethyleneimine, poly(p-phenylene sulfide), polyoxymethylene, polycarbonate, and various types of carbon such as activated carbon, graphite, molecular sieves, carbon black, and mixtures thereof.

[0043] The particulate filler, in one embodiment, can be in the form of particles having a size of 50 nanometers (nm) to 100 micrometers (μm). In another embodiment, the filler can have a particle size (d50) of 250 nm or more in one embodiment, 500 nm or more in another embodiment, and 1 μm or more in yet another embodiment. In other embodiments, the filler can have a particle size (d50) of 50 μm or less, 25 μm or less, or 10 μm or less. Particle size is conveniently measured using dynamic light scattering or laser diffraction for particles having a size less than 100 nm.

[0044] In some embodiments, the particulate filler particles may have an aspect ratio of at most 5, an aspect ratio of at most 2, or an aspect ratio of at most 1.5. In another embodiment, some or all of the filler particles may be grafted onto one or more polyether polyols of the polyol component.

[0045] Typically, when fillers are present in the adhesive formulation, they comprise 80 wt% or less of the total weight of the adhesive formulation. In alternative embodiments, the amount of filler present in the adhesive formulation may typically range from 0.1 wt% to 80 wt%, 0.1 wt% to 70 wt%, 0.1 wt% to 60 wt%, 0.1 wt% to 50 wt%, 0.1 wt% to 40 wt%, 0.1 wt% to 30 wt%, 0.1 wt% to 25 wt%, or 0.1 wt% to 20 wt%, based on the total weight of the components in the formulation.

[0046] The optional filler may be present in the isocyanate component, the polyol component, or both. For example, in one exemplary embodiment, the filler may be carbon black, and a concentration of carbon black may be present in the isocyanate component. When carbon black is present in the isocyanate component and no other fillers are present, the carbon black filler may comprise, for example, 1% to 50%, 2% to 40%, 5% to 30%, or 10% to 25% by weight of the isocyanate component, based on the weight of the isocyanate component.

[0047] In another exemplary embodiment, a concentration of filler can be present in the polyol component. When a filler is present in the polyol component, the filler can comprise, for example, 1% to 80%, 5% to 70%, 10% to 60%, or 20% to 60% by weight of the polyol component, based on the weight of the polyol component.

[0048] The filler present in the polyol component can be the same as the filler present in the isocyanate component, or the filler present in the polyol component can be different from the filler present in the isocyanate component. For example, in one embodiment, carbon black filler can be used in the isocyanate component at a concentration of, for example, 15% to 20% by weight, and calcined clay, calcium carbonate, or talc can be used in the polyol component at a concentration of, for example, 30% to 60% by weight. Fillers can be easily incorporated into the isocyanate component, the polyol component, or both the isocyanate component and the polyol component.

[0049] IV. Methods for Producing Adhesive Components, Curing Adhesives, and Applying Adhesives to Substrates In one embodiment, a method for preparing a 2K PU adhesive formulation of the present invention includes providing an isocyanate component and a polyol component. When provided as a kit, the adhesive components can be packaged together or separately. Once the adhesive is ready to be used to bond substrates together, the components can be mixed, compounded, or blended together, which results in a reaction product when the combination of components cures. If desired, one or more additional optional components can be added to the formulation. For example, at least one catalyst or at least one filler can be added to either component of the adhesive formulation before or after mixing the components together.

[0050] The amounts of isocyanate and polyol components useful in producing the reaction product that makes up the adhesive formulation can vary, but once the isocyanate and polyol components are combined (separately and independently) and ready to be mixed together to form the reaction product adhesive, the isocyanate and polyol components can be mixed in a ratio ranging from 2:1 to 1:2, for example 1:1.

[0051] When the components are prepared separately and independently, the ingredients can be mixed together at the desired concentrations described above at 5°C to 80°C, for example 15°C to 50°C, or for example at room temperature. In one embodiment, mixing of the ingredients can be done under vacuum. The order of mixing is not important; two or more compounds can be mixed together, followed by the addition of the remaining ingredients. The adhesive formulation ingredients that make up the components can be mixed together by any known mixing process and equipment.

[0052] In another embodiment, a method of joining two substrates can include forming a layer of adhesive at the bondline between the two substrates and curing the layer at the bondline to form a cured adhesive bonded to each of the substrates. For example, the method can include mixing an isocyanate component with a polyol component, forming a layer of adhesive at the bondline between the two substrates to form an assembly, partially curing the adhesive layer at the bondline at room temperature or by irradiating a portion of the assembly with heat or infrared radiation, and then completing the curing of the adhesive layer in a separate curing step.

[0053] Application of the adhesive to the substrates to be bonded together can be carried out by any known device, such as a metering / mixing / dispensing device, capable of combining and applying (as an adhesive) predetermined amounts of the isocyanate and polyol components to selected portions of the substrate. For example, in an automobile manufacturing process, the two components can be supplied in two separate containers. The first component can be drawn from one tank while the second component is drawn from another tank, and both streams can be mixed together using a known static or dynamic mixer as the combined adhesive components are applied to the substrate. A partial curing step can be carried out by heating only one or more predetermined localized portions of the assembly to cure only one or more predetermined localized portions of the adhesive layer at the bondline, producing an adhesive layer having at least partially cured and uncured portions, which can then be cured in a subsequent and separate curing step.

[0054] In one embodiment, a method for bonding at least a first substrate to at least a second substrate can include the following steps: (1) contacting a polyol component and an isocyanate component and mixing the components at a temperature of, for example, 10 to 40°C or 20 to 30°C to form a homogeneous adhesive mixture; (2) applying the adhesive mixture to at least a portion of the first substrate; (3) contacting a second substrate with the first substrate such that the mixture is disposed between the first and second substrates and forms a bond line; and (4) exposing at least a portion of the mixture to heat under conditions such that the mixture is sufficiently partially cured to bond the first and second substrates sufficiently, i.e., with sufficient strength, so that the substrates can be moved. The method can further include step (5) of fully curing the mixture by heating the two partially cured substrates at a temperature for a period of time such that the two substrates are fully bonded together. Heat can be applied in step (4) by any known heating means, such as infrared heating. The time between steps (4) and (5) can be about 1 hour or more in one embodiment, about 24 hours or more in another embodiment, and can be any time between the above two times.

[0055] Curing the adhesive composition forms a structure comprising two or more substrates bonded together with a cured adhesive based on the curable adhesive formulation, the cured adhesive being disposed between respective portions of the substrates. In one embodiment, the substrates may comprise heterogeneous substrates, i.e., substrates of different materials, such as metals, e.g., aluminum, uncoated or uncoated laser-pretreated aluminum, glass, plastic, thermosetting resins, fiber-reinforced plastics, or mixtures thereof. In a preferred embodiment, one or both of the substrates may be fiber-reinforced plastics.

[0056] V. Specific Exemplary Embodiments The following non-limiting embodiments show specific examples of combinations of materials that can be used in combination in the first and second components of the adhesive kit. It will be understood that cured products from the following components are contemplated, such as substrates bonded to a cured adhesive, including combinations of one inorganic substrate such as a metal (e.g., steel or aluminum, such as steel or aluminum that is not coated with an adhesive but has been pretreated for corrosion protection, for example, using electrocoating, laser pretreatment, passivation, or TiZr surface pretreatment) and another non-metallic substrate, which are bonded together by the cured adhesive sandwiched therebetween.

[0057] [Table 1]

[0058] [Table 2]

[0059] [Table 3]

[0060] [Table 4]

[0061] [Table 5] [Example]

[0062] The following examples further illustrate the present disclosure. The scope of the present disclosure and claims is not limited by the scope of the following examples.

[0063] I. Material Isonate 143 (available from DOW Chemical Company) is a modified pure MDI with a functionality of 2.2, a molecular weight of 319 g / mol, and a viscosity of 40 mPa·s.

[0064] Voranate 220 (available from DOW Chemical Company) is a polymeric MDI with a functionality of 2.7, a molecular weight of 367 g / mol, and a viscosity of 220 mPa·s.

[0065] Isonate M342 (available from DOW Chemical Company) is a modified pure MDI with a functionality of 2.0, a molecular weight of 360 g / mol, and a viscosity of 640 mPa·s.

[0066] Desmodur N3400 (available from Bayer Materials Sciences) is an aliphatic polyisocyanate based on hexamethylene bisisocyanate.

[0067] TIB 720 is a bismuth-carboxylate catalyst available from TIB Chemicals.

[0068] Formrez UL29 is a tin-based dioctyltin mercaptide catalyst (CAS 26401-97-8) available from Momentive.

[0069] 1,8-Diazabicyclo[5.4.0]undec-7-ene ("DBU", CAS 229-713-7), a carboxylic acid blocked catalyst, is available from Tosoh Corporation as TOYOCAT DB41 (carboxylic acid DBU salt) or from Air Products as POLYCAT SA-102 / 10 (carboxylic acid DBU salt).

[0070] TOYOCAT F22 is a heat-sensitive amine catalyst available from Tosoh Corporation.

[0071] Voranol 400 is a polypropylene homopolymer having an average molecular weight of 212 g / mol and an OH number of about 55 mg KOH / g, available from DOW Chemical Company.

[0072] Voranol 2000L is a polypropylene homopolymer with an average equivalent molecular weight of 1000 g / mol and an OH number of about 55 mg KOH / g, available from DOW Chemical Company.

[0073] Voranol CP4610 is a glycerin initiated propoxylated and ethoxylated based triol with an average equivalent molecular weight of 1603 g / mol and an OH number of about 35 mg KOH / g, available from DOW Chemical Company.

[0074] Poly bd® R20LM is a liquid hydroxyl-terminated polymer of butadiene having a molecular weight of 1300 g / mol and a polydispersity of 2, available from Cray Valley.

[0075] Vorapel™ D3201 is a hydrophobically modified (polybutylene oxide) diol with an average molecular weight of 1921-2125 g / mol and an OH number of about 56 mg KOH / g, available from The Dow Chemical Company.

[0076] PolyTHF is a poly(tetramethylene oxide) diol with a molecular weight of 1950-2050 g / mol and a hydroxyl number of 54.7-57.5.

[0077] 1,4-Butanediol was purchased from Arco Chemica and distributed by Schweizerhall Chemie. MEG is monoethylene glycol available from DOW Chemical Company.

[0078] KaMin100C (IMERYS) has an average particle size of approximately 2 μm (90% > 10 m) and a particle size of approximately 8.5 m 2 The calcined kaolin is pre-dried (55% SiO2, 45% Al2O3) with a BET surface area of ​​0.01g / g and a pH of 6.0-6.5.

[0079] Aerosil® R202 is a hydrophobically modified polydimethylsiloxane coated fumed silica available from Evonik Industries.

[0080] Silquest A 187 = gamma-glycidoxypropyltrimethoxysilane available from Momentive Performance Materials.

[0081] Silquest A 189 is gamma-mercaptopropyltrimethoxysilane available from Momentive Performance Materials.

[0082] Dynasylan GLYEO is gamma-glycidoxypropyltriethoxysilane available from Evonik.

[0083] II. Method Rheology: Rotational viscosity / yield stress: Bohlin CS-50 rheometer, C / P20, rise / fall 0.1-20s -1 , evaluated by the Casson model.

[0084] Thermal analysis: Dynamic mechanical analysis (DMA): The glass transition temperature Tg was determined by DMA measurement and defined as the maximum value of tan δ. Test method: Temperature range: -40°C to +150°C, Frequency: 1 Hz, Heating rate: 3°C / min.

[0085] Lap shear strength according to DIN EN 1465:2009: performed on laser-pretreated aluminum 5182 substrates with a thickness of 1 mm (laser substrate pretreatment was performed by cleanLASER (Herzogenrath, Germany) using a CL 600 laser system) or on heptane-cleaned electrocoated steel CR4, bond area 10 x 25 m, adhesive layer thickness 1 mm. The failure modes after the lap shear test are analyzed and classified as cohesive failure (CF), adhesive failure (AF) and corrosion failure (COR). Values ​​are rounded to the nearest multiple of 10%.

[0086] The lap shear strength tests after 3000 hours of salt spray were performed in the same way as the first specimens, except that they were exposed to the salt spray environment for the specified time before testing. After curing at room temperature for 7 days, the specimens were stored in a salt spray chamber (5% NaCl in deionized water) for 3000 hours.

[0087] Tensile test (DIN ISO EN-527-1:2012-06): A 2 mm thick plate of the cured adhesive is prepared and cured at room temperature for 7 days. Dogbone-shaped test specimens are cut from the plate. The dimensions comply with DIN ISO EN-527-1. The test is carried out on a ZwickRoell tensile testing machine.

[0088] III. Discussion This disclosure focuses on the isocyanate component of two-part polyurethane adhesives. The polyol component formulation is listed in Table 1. Table 2 summarizes the differences between the comparative isocyanate component recipes and the inventive recipes. Physical data, specifically lap shear strength, Young's modulus, shear strength, and elongation on laser-pretreated steel, initially and after 3000 hours of salt spray corrosion, are summarized in Table 3. The data are for premixed two-part (2K) polyurethane adhesives based on a 1:1 mixture of the specified polyol and isocyanate components. The polyol components are differentiated by the presence of epoxy silane in the formulation. PolyC1 formulation contains 3% epoxy silane, while PolyC2 does not contain epoxy silane.

[0089] [Table 6]

[0090] The isocyanate formulations are distinguished by the presence of silane in the formulations of the present invention, whereas the reference formulations do not contain silane.

[0091] Reference formulations Ref.IsoC1 and Ref.IsoC2 are distinguished by the polyol used in the synthesis of the prepolymer. Ref.IsoC2 contains Vorapel D3201 in the prepolymer, a hydrophobic polyol compared to the less hydrophobic Voranol 1010L. All inventive examples, except Inv.IsoC9, use a hydrophobic polyol.

[0092] Inv.IsoC8 of the present invention is based on formulation Ref.IsoC2 with the addition of 3% epoxy silane.

[0093] Inv.IsoC3 is also based on formulation Ref.IsoC2 with the addition of 3% epoxy silane and an additional amount of isocyanate, which increases with the content of M220, the amount being chosen so that all the methoxy groups present in the 3% silane can react with the additional isocyanate groups and the NCO / OH index compared to the reference without silane remains the same.

[0094] Ref.IsoC6 corresponds to Inv.IsoC3 without the addition of silane.

[0095] Inv.IsoC4 corresponds to Inv.IsoC3 with mercaptosilane instead of epoxysilane.

[0096] Inv. IsoC5 corresponds to Inv. IsoC3 with γ-glycidoxypropyltriethoxysilane instead of γ-glycidoxypropyltrimethoxysilane.

[0097] Ref.IsoC7 is based on Ref.IsoC6 but contains the same amount of methanol as present in the 3% silane of Inv.IsoC3 to demonstrate that the positive effect is due to the silane and not the addition of a monofunctional alcohol.

[0098] Inv.IsoC9 contains the more hydrophilic polyol Voranol 1010L instead of Vorapel D3201 in Inv.IsoC3 to demonstrate that the positive effect on adhesion to laser-pretreated aluminum is not due to the effect of a hydrophobic prepolymer.

[0099] [Table 7]

[0100] [Table 8]

[0101] *For the silane component in the NCO component, the equivalent weight was calculated based on the assumption that the methoxy groups of the silane react directly and completely with the isocyanate.

[0102] [Table 9]

[0103] [Table 10]

[0104] *AF = adhesive failure, CF = cohesive failure

[0105] Table 3 shows the results of all tests of various inventive and reference isocyanate components tested with two polyol components. The advantage addressed by this invention is the combination of a cohesive failure mode of the adhesive after 3000 hours of salt spray corrosion on laser pretreated aluminum, and a lap shear strength of greater than about 10 MPa, more preferably even 12 MPa.

[0106] Reference Examples 1 and 2, which contain silane in the polyol component, show 100% adhesive failure in all three cases after 3000 hours of salt spray. Furthermore, the lap shear strength is less than 10 MPa, which is insufficient for certain applications. The presence of silane in the polyol component of the adhesive formulation does not have a positive effect on adhesion to laser-pretreated aluminum, and a comparison of Examples 5 and 6 of the present invention shows a slight negative effect when silane is present in PolyC.

[0107] Example 3 of the present invention, which contained epoxy silane in the isocyanate component, showed a complete cohesive failure mode even after 3000 hours of salt spray, and the lap shear strength was 13.8 MPa, showing no decrease.

[0108] Inventive Examples 5, 7, and 8, which contain increasing amounts of NCO and various types of silanes in the formulation, all exhibit not only a complete cohesive failure mode after 3000 hours of salt spray, but also a complete retention of lap shear strength, suggesting a positive effect from the presence of silanes in the isocyanate component.

[0109] Inventive Example 6, which contains silane in both components, exhibits a complete cohesive failure mode, but exhibits a lower lap shear strength of only 11 MPa than the other inventive examples.

[0110] Reference Example 4, which had increased NCO content in the isocyanate component and no silane in either component, showed complete adhesion failure after 3000 hours of salt spray corrosion cycling and the formulation failed, suggesting that the positive effect on adhesion was not due to increased NCO content in the formulation.

[0111] Reference Example 9, which contained methanol added to the isocyanate component but no silane in either component, showed complete adhesion failure after 3000 hours of salt spray corrosion cycling and the formulation was rejected, suggesting that the positive effect of adhesion to laser-pretreated aluminum was due to the presence of silane in the isocyanate component, rather than due to end-capping of the polymer with methanol.

[0112] Inventive Example 9, which contains a more hydrophilic polyol in the isocyanate component prepolymer, not only exhibits a perfect cohesive failure mode after 3000 hours of salt spray, but also retains full lap shear strength, suggesting that the positive effect on adhesion is due to the presence of silane in the isocyanate component and is seen across different prepolymers with different chemistries.

[0113] The features and advantages of the present disclosure are apparent from the detailed description, and the claims encompass all such features and advantages. Many variations will occur to those skilled in the art, and all variations equivalent to those described in this disclosure are included within the scope of the present disclosure. Those skilled in the art will understand that the concepts underlying the present disclosure can be used as a basis for designing other compositions and methods to achieve the multiple objectives of the present disclosure. Therefore, the claims should not be construed as being limited by the description or examples.

Claims

1. a) a first component comprising an isocyanate and 0.4% to 5% by weight of said first component of a silane adhesion promoter; b) a second component comprising: i) 10% to 80% by weight of said second component of a polyol having a molecular weight of at least 400 g / mol; and ii) 1% to 15% by weight of said second component of a diol having a molecular weight of 200 g / mol or less; and less than 3% by weight of said second component of a silane adhesion promoter; wherein the first and second components are in the form of an unmixed kit.

2. 10. The adhesive formulation of claim 1, wherein said second component comprises less than 2.5%, less than 2%, less than 1%, less than 0.5%, or less than 0.25% by weight of said second component of said silane adhesion promoter, or said second component does not comprise any silane adhesion promoter.

3. 3. The adhesive formulation of claim 1 or 2, wherein the second component does not include any aminosilanes.

4. The adhesive formulation of any one of claims 1 to 3, which does not contain any aminosilanes.

5. The adhesive formulation of any one of claims 1 to 4, further comprising a catalyst capable of catalyzing the reaction of hydroxyl groups with isocyanate groups.

6. The adhesive formulation of any one of claims 1 to 5, wherein the isocyanate is a monomeric isocyanate, a polymeric isocyanate, an isocyanate-terminated prepolymer, or a combination thereof.

7. 7. The adhesive formulation of any one of claims 1 to 6, wherein the polyol is a diol or glycerin-initiated triol having residues of ethylene oxide, propylene oxide, or a combination thereof, and the polyol has a molecular weight in the range of 400 g / mol to 3,000 g / mol.

8. The diol has the formula C x H y O z 8. The adhesive formulation of any one of claims 1 to 7, having the formula: wherein x is an integer ranging from 2 to 20, y is an integer equal to x+m, where m is an integer ranging from 4 to 12, and z is an integer equal to x-n, where n is an integer ranging from 0 to 6.

9. 9. The adhesive formulation of any one of claims 1 to 8, further comprising from 0.1% to 80% by weight of the adhesive formulation of a filler.

10. A cured adhesive produced by mixing the first and second components of the adhesive formulation of any one of claims 1 to 9 and curing the mixture.

11. 10. A method for curing an adhesive formulation according to any one of claims 1 to 9, comprising mixing the first and second components of the adhesive formulation and curing the mixture.

12. The method of claim 11, wherein the first and second components of the adhesive formulation are mixed in a ratio ranging from 2:1 to 1:

2.

13. 13. The method of claim 11 or 12, wherein the first and second components of the adhesive formulation are mixed in a 1:1 ratio.

14. A method according to any one of claims 11 to 13, wherein the first and second components of the adhesive formulation are mixed at a temperature in the range of 10°C to 40°C.

15. 15. The method of claim 14, wherein the first and second components of the adhesive formulation are mixed at a temperature ranging from 20°C to 30°C.

16. A cured adhesive prepared by the method according to any one of claims 11 to 15.

17. 16. The cured adhesive of claim 15, exhibiting a lap shear strength of greater than 5 MPa, greater than 7 MPa, greater than 10 MPa, or greater than 12 MPa.

18. The method of any one of claims 11 to 15, further comprising applying the mixture to an inorganic substrate before fully curing the mixture.

19. 20. The method of claim 18, wherein the substrate is an uncoated, corrosion-resistant aluminum or steel substrate.

20. 20. The method of claim 18 or 19, further comprising bonding the inorganic substrate with the mixture applied thereto to a second substrate that is not inorganic to form a bonded assembly before fully curing the mixture.

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