Hot melt adhesive composition with adjustable cure behavior

Abstract

The present invention relates to a hot-melt adhesive composition: a) a blocked polyurethane prepolymer PU, b) at least one isocyanate-reactive compound P, c) at least one thiol compound T, and d) at least one metal catalyst C, which can catalyze the reaction between isocyanate groups and isocyanate-reactive groups and which can form a thiol complex, wherein the blocked polyurethane prepolymer PU is a polyurethane prepolymer of the formula (I) wherein R 1 is a p-valent group of a linear or branched isocyanate-terminated polyurethane prepolymer after removal of the isocyanate groups; p has a value of 2 to 8; and R 2 is a blocking group which is eliminated at temperatures of 100 °C or more, preferably at temperatures of 130 °C or more.

Description

Technical Field

[0001] This invention relates to reactive hot melt adhesives and to their use as assembly adhesives, lamination adhesives, or adhesives for constructing sandwich components (particularly in the automotive industry). Background Technology

[0002] Hot melt adhesives are solvent-free adhesives that are solid at room temperature and are applied as a melt to the substrate to be bonded. The adhesive solidifies upon cooling and forms a physical bond with the substrate. Conventional hot melt adhesives are non-reactive adhesives that soften again upon heating and are therefore unsuitable for use at elevated temperatures. Reactive hot melt adhesives contain polymers with reactive groups (which enable chemical curing of the adhesive, for example, through crosslinking of polymer chains). Due to the cured polymer matrix, reactive hot melt adhesives do not soften upon heating, making them suitable for use at elevated temperatures. Chemical curing of the polymer can be initiated, for example, by exposing the adhesive composition to water. Moisture-curing hot melt adhesives typically contain polymers functionalized with isocyanate or silane groups (which enable crosslinking of polymer chains upon contact with water, particularly moisture in the air).

[0003] Typical reactive hot melt adhesives used as assembly adhesives in the automotive industry include moisture-curing polyurethane and polyolefin-based hot melt adhesives. Moisture-curing polyurethane hot melt (PU-RHM) adhesives consist primarily of isocyanate-terminated polyurethane prepolymers, obtained by reacting a suitable polyol (typically a diol) with a stoichiometric excess of a polyisocyanate (typically a diisocyanate). Upon contact with water, the residual isocyanate groups of the polyurethane prepolymer form carbamic acid, which is unstable and decomposes into amines and carbon dioxide. The amines react rapidly with other isocyanate groups to form urea linkages. Moisture-curing polyolefin hot melt (PO-RHM) adhesives typically consist primarily of amorphous polyalphaolefins (APAOs) functionalized with silane groups. Upon contact with water, the silane groups of the polyolefin polymer (e.g., methoxysilane groups) react with water to form silanols, which, as part of a condensation reaction, subsequently react with other silanol groups to form covalent bonds between the individual polymer molecules.

[0004] Both reactive and non-reactive hot melt adhesives are widely used in industry to produce composite components via film lamination technology. In a typical film lamination method, a molten hot melt adhesive is first applied to the surface of a first substrate to form an adhesive film, which is then brought into contact with the surface of a second substrate to create an adhesive bond between the two substrates. Conventional hot melt adhesives exhibit relatively short open times, and when applied as a film to the surface of a substrate, the adhesive solidifies rapidly and loses its ability to wet the surface of the second substrate.

[0005] A significant disadvantage of conventional moisture-curing hot melt adhesives is that the rate of the curing reaction is limited by the availability of water. Therefore, in moisture-curing adhesive systems, the curing time (i.e., the time required for the adhesive to reach full curing) is relatively long. This is a significant disadvantage, particularly in automotive assembly processes, where laminated parts are used immediately in another part of the process without storage. Furthermore, with thicker adhesive layers, the curing reaction is severely limited by the diffusion of moisture within the adhesive layer, leading to the formation of curing gradients and increased curing time.

[0006] Therefore, it is desirable to provide new types of reactive hot melt adhesives that are well-suited for use in industrial assembly methods, particularly in applications using lamination techniques. Preferably, the adhesive should have adjustable curing behavior, wherein the curing time and the onset of the curing reaction can be adjusted independently of current environmental conditions, particularly independent of ambient temperature and relative humidity. Summary of the Invention

[0007] The object of the present invention is to provide a reactive hot melt adhesive composition that overcomes or at least mitigates the disadvantages of prior art reactive hot melt adhesives discussed above.

[0008] In particular, the object of the present invention is to provide a reactive hot melt adhesive composition having adjustable curing behavior in terms of activation temperature and curing time. This adhesive composition should preferably exhibit improved storage stability and should be obtained using a more reliable / stable and safer production method.

[0009] It has been surprisingly discovered that this objective can be achieved using the features of claim 1.

[0010] Specifically, according to the present invention, a hot melt adhesive composition is provided, the composition comprising:

[0011] a) Closed-cell polyurethane prepolymer (PU),

[0012] b) At least one isocyanate reactive compound P,

[0013] c) At least one thiol compound T, and

[0014] d) At least one metal catalyst C, which catalyzes the reaction between isocyanate groups and isocyanate reactive groups and can build a thiol complex.

[0015] The closed polyurethane prepolymer PU is a polyurethane prepolymer of formula (I).

[0016]

[0017] Where R 1 It is a p-valence group of a linear or branched isocyanate-terminated polyurethane polymer after the isocyanate groups have been removed.

[0018] p has values ​​from 2 to 8; and

[0019] R 2 These are blocking groups that are eliminated at 100°C or higher.

[0020] It has been proven that the combination of a closed polyurethane prepolymer, an isocyanate reactive compound, and a special catalyst system comprising a metal catalyst and a complexing agent having at least one thiol group enables the provision of reactive hot melt adhesives with tunable curing behavior. In particular, such hot melt adhesives have a wide application window because the activation temperature can be tailored to the application requirements. Furthermore, due to the use of polyurethane prepolymers with closed isocyanate groups, this adhesive can be prepared using a more reliable / stable and safer production method. The hot melt adhesive composition has also demonstrated excellent storage stability, even at higher temperatures.

[0021] Additional aspects of the invention are set forth in the separate independent claims. Preferred embodiments of the invention are summarized throughout the specification and dependent claims. Detailed Implementation

[0022] The subject of this invention is a hot melt adhesive composition comprising:

[0023] a) Closed-cell polyurethane prepolymer (PU),

[0024] b) At least one isocyanate reactive compound P,

[0025] c) At least one thiol compound T, and

[0026] d) At least one metal catalyst C, which catalyzes the reaction between isocyanate groups and isocyanate reactive groups and can form a thiol complex.

[0027] The closed polyurethane prepolymer PU is the closed polyurethane prepolymer of formula (I).

[0028]

[0029] Where R 1 It is a p-valence group of a linear or branched isocyanate-terminated polyurethane polymer after the isocyanate groups have been removed.

[0030] p has values ​​from 2 to 8; and

[0031] R 2 The blocking group is eliminated at a temperature of 100°C or higher, preferably at a temperature of 110°C or higher.

[0032] The prefix "poly" in the name of a substance, such as "polyol" or "polyisocyanate," indicates that the substance contains two or more functional groups per molecule that appear in its name. For example, a polyol is a compound having two or more hydroxyl groups, and a polyisocyanate is a compound having two or more isocyanate groups.

[0033] The term "polymer" refers to a collection of chemically homogeneous macromolecules produced by a polymerization reaction (polymerization, addition polymerization, condensation polymerization), wherein the macromolecules are different in terms of their degree of polymerization, molecular weight, and chain length. The term also includes derivatives of said collection of macromolecules produced by polymerization reactions, i.e., compounds obtained by reactions involving the addition or substitution of functional groups in, for example, predetermined macromolecules, and which may be chemically homogeneous or chemically heterogeneous.

[0034] When the isocyanate group of an isocyanate is directly bonded to an aliphatic, alicyclic, or aryl-aliphatic structural moiety, the isocyanate is called "aliphatic." The corresponding functional group is therefore called an aliphatic isocyanate group. Similarly, when the isocyanate group of an isocyanate is directly bonded to an aromatic structural moiety, the isocyanate is called "aromatic." The corresponding functional group is therefore called an aromatic isocyanate group.

[0035] The term "primary amine group" refers to an NH2 group attached to one organic group, while the term "secondary amine group" refers to an NH group attached to two organic groups (which may also be part of a ring). Therefore, an amine with one primary amine group is called a "primary amine", an amine with one secondary amine group is correspondingly called a "secondary amine", and an amine with one tertiary amine group is called a "tertiary amine".

[0036] The term "molecular weight" refers to the molar mass (g / mol) of a molecule or a portion of a molecule (also called a "structural moiety"). The term "average molecular weight" refers to the number-average molecular weight (Maverage) of an oligomer or polymeric mixture of molecules or structural moieties. nThe molecular weight can be determined by conventional methods, preferably by gel permeation chromatography (GPC) under the following conditions: using polystyrene as a standard, using a styrene-divinylbenzene gel with porosities of 100 Å, 1000 Å and 10000 Å as a column, and depending on the molecule, using tetrahydrofuran as a solvent at 35 °C or 1,2,4-trichlorobenzene as a solvent at 160 °C.

[0037] The term "softening point" or "softening temperature" refers to the temperature at which a compound softens in a rubbery state, or the temperature at which the crystalline portion of the compound melts. The softening point can be measured using the ring and ball method according to DIN EN 1238:2011.

[0038] The term "glass transition temperature" (T) g The glass transition temperature (T0) represents the temperature above which the polymer component becomes soft and flexible, and below which the polymer component becomes hard and glassy. g It is preferred to determine the loss modulus (G'') curve by means of dynamic mechanical analysis (DMA), using an applied frequency of 1 Hz and a strain level of 0.1% as the peak value.

[0039] The term "melting temperature" refers to the temperature at which a material undergoes a transition from a solid to a liquid state. Melting temperature (T) m The measurement is preferably performed using differential scanning calorimetry (DSC) at a heating rate of 2 °C / min, according to ISO 11357-3:2018. The measurement can be performed using a Mettler Toledo DSC 3+ device, and T... m The value can be determined from the measured DSC curve with the help of DSC software. If the measured DSC curve shows several peak temperatures, the first peak temperature from the lower temperature side in the thermogram is taken as the melting temperature (T). m ).

[0040] The term "open time" refers to the length of time during which an adhesive applied to a substrate surface remains able to form an adhesive bond after it has come into contact with another substrate.

[0041] The term "amount or content of at least one component X" in a composition, such as "amount of the at least one thermoplastic polymer TP," refers to the sum of the individual amounts of all thermoplastic polymer TP contained in the composition. For example, if the composition contains 20% by weight of at least one thermoplastic polymer TP, the sum of the amounts of all thermoplastic polymer TP contained in the composition is equal to 20% by weight.

[0042] The term "room temperature" refers to a temperature of approximately 23°C.

[0043] In this document, the use of the terms “independently” in combination with substituents, radicals, or groups should be interpreted as allowing substituents, radicals, or groups with the same name in the same molecule to appear simultaneously with different meanings.

[0044] Preferably, R 2 Substituents selected independently from the group consisting of:

[0045]

[0046] Where R 5 R 6 R 7 and R 8 Each is independently an alkyl, cycloalkyl, aralkyl, or arylalkyl group, or R 5 With R 6 Together, or R 7 With R 8 Together, they form part of a ring with optional substitution of 4 to 7 elements.

[0047] In addition, R 9 R 9' and R 10 Each is independently a hydrogen atom, alkyl or aralkyl or arylalkyl group or alkoxy or aryloxy or arylalkoxy group, and R 11 It is an alkyl group.

[0048] R 12 R 13 and R 14 Each is independently an alkylene group having 2 to 5 carbon atoms and optionally having a double bond or a substituted alkylene group, or a phenylene group or a hydrogenated phenylene group.

[0049] Finally, R 15 R 16 and R 17 Each is independently a hydrogen atom or an alkyl group or an aryl group or an aralkyl group, and R 18 It is an aralkyl group or a monocyclic or polycyclic, substituted or unsubstituted aromatic group optionally having an aromatic hydroxyl group.

[0050] More preferably, R 2 Substituents selected independently from the group consisting of:

[0051]

[0052] Its preferred choice is the group consisting of the following:

[0053]

[0054] Mode The preferred substituents are phenol after removing the phenolic hydrogen atom and hydroxybenzyl alcohol and benzyl alcohol after removing the hydroxyl group.

[0055] In one or more embodiments, the substituent R in formula (I) 2 It is either phenol after removing the phenolic hydrogen atom or ε-caprolactam after removing the hydrogen atom bonded to nitrogen.

[0056] Mode Particularly preferred substituents are monophenols after the removal of a phenolic hydrogen atom. Particularly preferred examples of these substituents are those selected from the group consisting of: , , , and ,in particular .

[0057] The Y group is preferably a saturated, aromatic, or olefinically unsaturated hydrocarbon group having 1 to 20 carbon atoms, particularly 1 to 15 carbon atoms. Preferred Y groups are particularly allyl, methyl, nonyl, dodecyl, phenyl, alkyl ethers (especially methyl ethers), carboxylic acid esters, or unsaturated C groups having 1 to 3 double bonds. 15 Alkyl group. Most preferably, Y is selected from alkyl ethers (especially methyl ethers) and unsaturated C having 1 to 3 double bonds. 15 A group composed of alkyl groups.

[0058] In one or more embodiments, the substituent R in formula (I) 2 It is a monophenol (preferably selected from phenol (monohydroxybenzene), cresol, 4-methoxyphenol (HQMME), resorcinol, catechol, cashew nut shell oil, and nonylphenol) after removing the hydrogen atom of phenol, or ε-caprolactam after removing the hydrogen atom bonded to nitrogen.

[0059] In one or more embodiments, the hot melt adhesive composition comprises 50-95% by weight, more preferably 60-90% by weight, or even more preferably 65-85% by weight of a closed polyurethane prepolymer (PU).

[0060] Specifically, the closed polyurethane prepolymer PU is made by reacting a polyurethane prepolymer PUP having terminal isocyanate groups with at least one of the formula R 2 H is obtained by reacting isocyanate reactive blocking agent B.

[0061] In this document, the term "polyurethane polymer" refers to polymers prepared by the so-called diisocyanate addition polymerization method. This also includes polymers that contain little or no urethane groups. Examples of polyurethane polymers are polyether-polyurethane, polyester-polyurethane, polyether-polyurea, polyurea, polyester-polyurea, polyisocyanurates, and polycarbodiimides.

[0062] Furthermore, the term "polyurethane prepolymer" refers to an isocyanate-functionalized polyurethane polymer containing unreacted isocyanate groups. Polyurethane prepolymers can be obtained by reacting an excess of polyisocyanate (especially diisocyanate) with a polyol. They are isocyanate-terminated, meaning they contain unreacted isocyanate groups at the chain ends. The terms "isocyanate-functionalized polyurethane polymer" and "polyurethane prepolymer" are used interchangeably.

[0063] In one or more embodiments, the polyurethane prepolymer PUP is obtained by reacting at least one polyol PO with at least one diisocyanate I at a molar ratio of at least 3 (preferably at least 3.5) of isocyanate groups to hydroxyl groups, and optionally subjecting the resulting reaction mixture to treatment (preferably by distillation) to reduce the amount of residual monomeric diisocyanate.

[0064] The reaction between polyol PO and diisocyanate I can be carried out, for example, in a temperature range of 60-160°C, preferably 80-140°C, optionally in the presence of a catalyst. As will be understood, the reaction time depends on the temperature used, but can be, for example, in the range of 30 minutes to 6 hours, preferably in the range of 30 minutes to 3 hours, more preferably in the range of 30 minutes to 1.5 hours. Suitable catalysts include, for example, metal catalysts, such as Coscat® 83 (from Vertellus Performance Materials Inc.), and tin catalysts.

[0065] In one or more embodiments, the polyurethane prepolymer PUP has an average isocyanate functionality in the range of 1.2-3.0, preferably in the range of 1.5-2.5, as determined according to ISO 14896-2009 standard method A, and / or an isocyanate content in the range of 0.5-25% by weight, preferably in the range of 1.0-20% by weight, as determined by the method defined in ISO 11909:2007 standard.

[0066] Particularly suitable diisocyanates include monomeric aliphatic, alicyclic, and aromatic diisocyanates.

[0067] In this document, the term "monomer diisocyanate" refers to an organic compound having two isocyanate groups separated by divalent hydrocarbon groups, preferably having an average molecular weight of not more than 1000 g / mol. In particular, monomer diisocyanates do not contain urethane groups, and oligomers or polymeric products of diisocyanate monomers (e.g., adducts of monomer diisocyanates) are not considered "monomer diisocyanates" in the context of this invention.

[0068] Preferably, diisocyanate I is a monomeric diisocyanate, more preferably having a number-average molecular weight (M) of not more than 750 g / mol, more preferably not more than 500 g / mol, and more preferably not more than 350 g / mol. n () monomeric diisocyanate.

[0069] Examples of suitable monomeric diisocyanates include aliphatic and aromatic monomeric diisocyanates, such as 1,6-hexamethylene diisocyanate (HDI), 2-methylpentamethylene-1,5-diisocyanate, 2,2,4- and 2,4,4-trimethyl-1,6-hexamethylene diisocyanate (TMDI) and mixtures of these isomers, 1,10-dedecimethylene diisocyanate, 1,12-dodecimethylene diisocyanate, lysine diisocyanate, lysine ester diisocyanate, and cyclohexane. 1,3-Diisocyanate and cyclohexane 1,4-diisocyanate and mixtures of these isomers, 1-methyl-2,4- and -2,6-diisocyanocyclohexane and mixtures of these isomers (HTDI or H6TDI), 1-isocyano-3,3,5-trimethyl-5-isocyanomethylcyclohexane (=isophorone diisocyanate or IPDI), perhydro-2,4'- and -4,4'-diphenylmethane diisocyanate (HMDI or H12MDI) and mixtures of these isomers Compounds, 1,4-diisocyanate-2,2,6-trimethylcyclohexane (TMCDI), 1,3- and 1,4-bis(isocyanate-methyl)cyclohexane, m- and p-phenylenedimethyl diisocyanates (m- and p-XDI) and mixtures of these isomers, m- and p-tetramethyl-1,3- and 1,4-phenylenedimethyl diisocyanates (m- and p-TMXDI) and mixtures of these isomers, bis(1-isocyanate-1-methylethyl)naphthalene, 2,4- and 2,6-toluene Mixtures of diisocyanates and their isomers (TDI), 4,4'-diphenylmethane diisocyanate (which optionally contains a proportion of 2,4'- and / or 2,2'-diphenylmethane diisocyanate) (MDI), 1,3- and 1,4-phenylene diisocyanate (PDI) and mixtures of their isomers, naphthalene 1,5-diisocyanate (NDI), 3,3'-dimethyl-4,4'-diisocyanate-biphenyl (TODI), and bianisidine diisocyanate (DADI).

[0070] Suitable aliphatic and aromatic monomeric diisocyanates are commercially available, for example under the trade names Lupronat® (from BASF), Desmodur® (from Covestro), and Duranat® (from Asahi Kasei).

[0071] In one or more embodiments, the at least one diisocyanate I is selected from 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 2,2'-diphenylmethane diisocyanate (2,2'-MDI), or mixtures of these isomers, toluene diisocyanate (TDI) (particularly 2,4-toluene diisocyanate (2,4 TDI), 2,6-toluene diisocyanate (2,6 TDI), or mixtures of these isomers), 1,6-hexamethylene diisocyanate (HDI), and 1-isocyano-3,3,5-trimethyl-5-isocyanomethylcyclohexane (IPDI). Furthermore, those skilled in the art will recognize that industrial-grade monomeric diisocyanates can be present in the form of isomer mixtures and may contain oligomers as impurities.

[0072] Suitable polyols (PO) specifically include polyester polyols, polyether polyols, polycarbonate polyols, and poly(tetramethylene ether) glycols.

[0073] Preferred polyester polyols include liquid, amorphous, partially crystalline, and crystalline polyester polyols. These can be produced by reacting dihydroxy and trihydroxy (preferably dihydroxy) alcohols (e.g., 1,2-ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, dimer fatty alcohols, neopentanediol, glycerol, 1,1,1-trimethylolpropane, or mixtures thereof) with an organic dicarboxylic acid or trihydroxy alcohol. Carboxylic acids (preferably dicarboxylic acids), or their anhydrides or esters (e.g., succinic acid, glutaric acid, 3,3-dimethylglutaric acid, adipic acid, octanoic acid, sebacic acid, undecanoic acid, dodecanoic acid, azelaic acid, maleic acid, fumaric acid, phthalic acid, dimer fatty acids, isophthalic acid, terephthalic acid and hexahydrophthalic acid or mixtures thereof) can be obtained by reaction, and can also be obtained from polyester polyols prepared from lactones, such as from ε-caprolactone, also known as polycaprolactone.

[0074] Preferred polyester polyols include those obtained by reacting adipic acid, sebacic acid, or dodecanedicarboxylic acid (as dicarboxylic acids) with hexanediol or neopentyl glycol (as dihydroxyols). Further examples of suitable polyester polyols include those derived from oleochemical sources. This type of polyester polyol can be prepared, for example, by the complete ring-opening of an epoxidized triglyceride of a fatty mixture (containing at least a portion of olefinically unsaturated fatty acids) with one or more alcohols having 1-12 carbon atoms, followed by a subsequent partial transesterification of the triglyceride derivative to give an alkyl ester polyol having 1-12 carbon atoms in the alkyl group. Particularly suitable crystalline or semi-crystalline polyester polyols include adipic acid / hexanediol polyesters and dodecanedicarboxylic acid / hexanediol polyesters.

[0075] Particularly suitable polyether polyols include polyoxyethylene polyols.

[0076] These are polymers of ethylene oxide, 1,2-epoxypropane, 1,2- or 2,3-epoxybutane, oxetane, tetrahydrofuran, or mixtures thereof, optionally polymerized using starting molecules having two or more active hydrogen atoms (e.g., water, ammonia, or compounds having several OH- or NH- groups, such as 1,2-ethylene glycol, 1,2- and 1,3-propanediol, neopentyl glycol, diethylene glycol, triethylene glycol, isomeric dipropylene glycol and tripropylene glycol, isomeric butanediol, pentylene glycol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, undecanediol, 1,3- and 1,4-cyclohexanediethanol, bisphenol A, hydrogenated bisphenol A, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, glycerol, aniline, and mixtures thereof).

[0077] Polyoxyolefin polyols with low unsaturation (measured according to ASTM D-2849-69 and expressed as milliequivalents of unsaturation per gram of polyol (meq / g)) (which can be obtained, for example, using a so-called bimetallic cyanide complex catalyst (DMC catalyst)) and polyoxyolefin polyols with high unsaturation (which can be obtained, for example, using anionic catalysts such as NaOH, KOH, CsOH, or alkali metal alkoxides) are both preferred. Particularly preferred polyoxyolefin polyols are polymerization products of ethylene oxide and / or propylene oxide.

[0078] Particularly suitable polyether polyols include polyoxyethylene glycol and polyoxyethylene triol, especially polyoxyethylene glycol and triol and polyoxypropylene glycol and triol, which preferably have a number average molecular weight (Mn) in the range of 400-15000 g / mol, especially in the range of 500-10000 g / mol. n ).

[0079] Equally suitable polyether polyols are polyoxypropylene polyols called ethylene oxide-terminated ("EO-terminated") polyoxypropylene polyols. The latter are specific polyoxypropylene polyoxyethylene polyols, which are obtained, for example, by further alkoxylating pure polyoxypropylene polyols (especially polyoxypropylene glycol and triol) with ethylene oxide at the end of the polypropoxylation reaction, thus acquiring primary hydroxyl groups. In this case, polyoxypropylene polyoxyethylene glycol and polyoxypropylene polyoxyethylene triol are preferred.

[0080] Suitable polyether polyols are commercially available, for example under the trade names Acclaim®, Desmophen®, and Arcol® (all from Covestro); Voranol® (from Dow); and Dianol® (from Arkema).

[0081] Another particularly preferred polyol is a polycarbonate polyol, especially a dialkyl carbonate, a diaryl carbonate, or a polycondensation product of phosgene with a diol or triol (e.g., ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-hexanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, 1,12-octadecanediol, 1,4-cyclohexanediol, a dimerized fatty acid diol (dimeryl diol), a hydroxypivalic neopentyl glycol ester, glycerol, and 1,1,1-trimethylolpropane).

[0082] Small amounts of low molecular weight diols or polyols, such as 1,2-ethylene glycol, 1,2-propanediol, neopentyl glycol, diethylene glycol, triethylene glycol, isomeric dipropylene glycol and tripropylene glycol, isomeric butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, undecanediol, 1,3- and 1,4-cyclohexanediol, hydrogenated bisphenol A, dimer fatty alcohols, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, glycerol, pentaerythritol, sugar alcohols (e.g., xylitol, sorbitol, or mannitol), sugars (e.g., sucrose), other polyhydroxy alcohols, low molecular weight alkoxylated products of the above diols or polyols, and mixtures of the above alcohols, may be used in conjunction with them.

[0083] In one or more embodiments, based on the total weight of the polyurethane prepolymer PUP, the polyurethane prepolymer PUP has a monomer diisocyanate content of not more than 1.0% by weight, preferably not more than 0.5% by weight, and more preferably not more than 0.25% by weight.

[0084] Such polyurethane prepolymers (PUPs) can be obtained, for example, by treating (particularly by distillation) the reaction product of at least one polyol (PO) and at least one diisocyanate (I) to reduce the amount of residual monomeric diisocyanate. Suitable distillation methods include, for example, thin-film distillation and molecular distillation.

[0085] In one or more embodiments, based on the total weight of the hot melt adhesive composition, the hot melt adhesive composition has a monomeric diisocyanate content of less than 1.0% by weight, preferably less than 0.65% by weight, more preferably less than 0.5% by weight, even more preferably less than 0.35% by weight, and most preferably less than 0.1% by weight. Adhesive compositions with a monomeric diisocyanate content of less than 0.1% by weight can be used safely even without special protective measures and can therefore be sold in many countries without being labeled as hazardous (Xn).

[0086] The hot melt adhesive composition contains at least one isocyanate-reactive compound P as a second mandatory compound. The term "isocyanate-reactive" here refers to a compound having one or more functional groups that can react with isocyanate groups.

[0087] Particularly suitable isocyanate-reactive compounds include those having at least two isocyanate-reactive groups per molecule (preferably selected from amino, hydroxyl, and thiol groups), such as polyester polyols, polyether polyols, polycarbonate polyols, and polyether amines, preferably having a number-average molecular weight (Mn) of not more than 30,000 g / mol, more preferably not more than 20,000 g / mol. n ).

[0088] In one or more embodiments, the isocyanate reactive compound P is selected from polyether polyols and polyether amines, preferably having a number-average molecular weight (Mn) of 250-15000 g / mol, more preferably 350-10000 g / mol. n ) and / or have an average of 2-6, preferably 3-6, isocyanate reactive groups per molecule.

[0089] In one or more embodiments, the hot melt adhesive composition comprises 0.5-45% by weight, more preferably 1.5-35% by weight, even more preferably 5-30% by weight, and still more preferably 5-25% by weight of isocyanate reactive compound P.

[0090] In addition to the closed polyurethane polymer PU and the isocyanate reactive compound P, the hot melt adhesive composition further includes a catalyst system comprising at least one thiol compound T and at least one metal catalyst C, which catalyzes the reaction between isocyanate groups and isocyanate reactive groups and can form a thiol complex.

[0091] The presence of such a catalyst system in hot melt adhesive compositions, combined with a closed polyurethane prepolymer, has been found to enable the provision of hot melt adhesive compositions with tunable curing behavior, wherein the curing time and the onset of the curing reaction can be adjusted according to application requirements and independently of current environmental conditions. Furthermore, the use of this catalyst system has been found to result in improved storage stability of the adhesive compositions.

[0092] Preferably, the at least one thiol compound T contains an average of 1-5, more preferably 2-4 thiol groups per molecule.

[0093] In one or more embodiments, the at least one thiol compound T is selected from ethylene glycol di(3-mercaptopropionate), ethylene glycol di(2-mercaptoacetate), trimethylolpropane tri(3-mercaptopropionate), trimethylolpropane tri(2-mercaptoacetate), pentaerythritol tetra(3-mercaptopropionate), pentaerythritol tetra(2-mercaptoacetate), dipentaerythritol hexa(3-mercaptopropionate), dipentaerythritol hexa(2-mercaptoacetate), 2,3-dimercapto-1,3,4-thiadiazole, and 3,6-dioxa-1,8-octanedithiol.

[0094] Examples of suitable metal catalysts C include bismuth, zinc, tin, and zirconium compounds, which consist of complexes and salts of these metals.

[0095] In one or more embodiments, the metal catalyst C is selected from bismuth compounds, tin compounds, and zirconium compounds.

[0096] Particularly suitable bismuth compounds include bismuth(III) compounds, such as bismuth carboxylate (e.g., bismuth acetate, bismuth oleate, bismuth octanoate, or bismuth neodecanoate), bismuth nitrate, bismuth halides (e.g., bromides, chlorides, or iodides), bismuth sulfides, basic bismuth carboxylate (e.g., bismuth oxyneodecanate, basic bismuth gallate, or basic bismuth salicylate), and mixtures thereof. Particularly preferred bismuth compounds are bismuth carboxylate, especially bismuth neodecanoate.

[0097] Particularly preferred tin compounds include organotin compounds, especially organotin (IV) compounds, which are preferably selected from dibutyltin diacetate, dibutyltin dilaurate, dibutyltin dichloride, dibutyltin diacetylacetone, dimethyltin dilaurate, dioctyltin diacetate, dioctyltin dilaurate, dioctyltin diacetylacetone, bis[(2-ethyl-1-oxohexyl)oxy]dioctyltin, bis(neodecanoyloxy)dioctyltin, bis(dodecylthio)dioctyltin, and bis(dodecylthio)dimethyltin.

[0098] In one or more embodiments, the metal catalyst C is a bismuth(III) complex containing at least one 8-hydroxyquinoline-based ligand or a bismuth(III) complex containing at least one 1,3-ketoamide-based ligand.

[0099] Examples of bismuth(III) complexes containing at least one 8-hydroxyquinoline-based ligand are described in EP 1551895A1. Such compounds are preferably bismuth(III) carboxylate containing a molar equivalent of an 8-hydroxyquinoline ligand.

[0100] Examples of bismuth(III) complexes containing at least one 1,3-ketoamide-based ligand are described in EP 2791153. Such compounds are preferably bismuth(III) carboxylate containing 1 to 3 molar equivalents of a 1,3-ketoamide ligand.

[0101] Preferably, the molar ratio of all thiol groups in the at least one thiol compound T to all metal atoms in the at least one metal catalyst C is 1:1 to 20:1, more preferably 4:1 to 16:1.

[0102] The molar ratio between the thiol group of the thiol compound T and the metal atom of the catalyst C, which falls within the range described above, allows the curing time of the hot melt adhesive composition to be controlled (specifically within the curing limits of a particular composition), for example, by adjusting the content of the catalyst, the reactivity of the polyisocyanates and isocyanate reactive compounds present in the adhesive composition, and their amounts.

[0103] Hot melt adhesive compositions may additionally include auxiliary substances and additives, such as those selected from the group consisting of fillers, flame retardants, plasticizers, adhesion promoters, UV absorbers, UV and heat stabilizers, optical brighteners, pigments, dyes, and drying agents. Examples of suitable UV stabilizers that can be added to the adhesive composition include, for example, sterically hindered phenols.

[0104] Fillers suitable for use in hot melt adhesive compositions include, for example, inorganic and organic fillers, particularly natural, ground or precipitated calcium carbonate (which is optionally coated with fatty acids or fatty acid esters, particularly with stearic acid), baryte (heavy spar), talc, quartz powder, quartz sand, dolomite, wollastonite, kaolin, calcined kaolin, mica (potassium aluminum silicate), molecular sieves, alumina, aluminum hydroxide, magnesium hydroxide, silica (including finely divided silica from pyrolysis methods), industrially produced carbon black, graphite, metal powders such as aluminum, copper, iron, silver or steel, PVC powder or hollow spheres.

[0105] The hot melt adhesive composition described above can be prepared by melt-blending closed polyurethane prepolymer PU, isocyanate reactive compound P, thiol compound T and metal catalyst C at elevated temperatures to obtain a homogeneous mixture.

[0106] The term “melt blending” in this disclosure refers to a processing operation in which a polymer is heated to above its melting / softening point to mix or blend other materials (e.g., other polymers) into the polymer.

[0107] The melt mixing of the components can be performed using any conventional mixing equipment, such as a dispersion mixer, a planetary mixer (e.g., a planetary roller mixer), an extruder (e.g., a twin-screw extruder), a kneader (e.g., a Buss, Banbury, or roller kneader), or a twin-roll mill.

[0108] The term "homogeneously mixed mixture" in this disclosure refers to a composition in which the individual components are substantially uniformly distributed. Furthermore, a homogeneously mixed mixture can be a multiphase mixture. It will be apparent to those skilled in the art that regions with a slightly higher concentration of one of the components than other regions can be formed within a homogeneously mixed composition, and 100% uniform distribution of all components is generally not achievable. However, such mixed compositions with an "imperfect" distribution of components are also intended to be included in the term "homogeneously mixed mixture" according to the invention.

[0109] Hot melt adhesive compositions can be prepared using a method including the following steps:

[0110] - Melt the polyurethane prepolymer (PUP) in the reactor.

[0111] - The first part of adding sealing agent B and metal catalyst C to the reactor.

[0112] - A reaction is carried out between prepolymer PUP and blocking agent B to obtain a reaction mixture containing blocked polyurethane prepolymer PU.

[0113] - The isocyanate reactive compound P is added to the reaction mixture, and

[0114] - The second part of the thiol compound T and the metal catalyst C is added to the mixture thus obtained.

[0115] Alternatively, the hot melt adhesive composition can be prepared using a similar method, wherein the closed polyurethane prepolymer PU is prepared in a separate reactor and optionally stored before being mixed with the isocyanate reactive compound P, the thiol compound T and the metal catalyst C.

[0116] Another aspect of the invention is the use of the hot melt adhesive composition as described above as an assembly adhesive, a lamination adhesive, or as an adhesive for constructing sandwich elements.

[0117] Another aspect of the present invention is a method for bonding a first substrate to a second substrate, the method comprising the following steps:

[0118] I) Heating the hot melt adhesive composition as described above to provide a molten adhesive composition.

[0119] II) Apply the molten adhesive composition to the surface of the first substrate to form an adhesive film.

[0120] III) Heat the adhesive film to the reactivation temperature, and

[0121] IV) Mating the first substrate obtained in step II) or III) with the second substrate, such that the surface of the second substrate comes into contact with the adhesive film.

[0122] V) Optionally apply pressure to the first and / or second substrate.

[0123] The molten adhesive composition can be applied to the surface of the first substrate using any conventional technique, such as slot die coating, roll coating, extrusion coating, calendering coating, or spraying. Typical application temperatures for hot melt adhesive compositions are in the range of 80-135°C, preferably in the range of 80-125°C, and particularly in the range of 80-110°C.

[0124] The temperature to which the adhesive film is heated in step III (i.e., the reactivation temperature) depends on the implementation of the adhesive composition, particularly on the blocking group R. 2 Elimination temperature.

[0125] In one or more embodiments, in step III), the adhesive composition is heated to a temperature of 150°C or higher, preferably 160°C or higher, particularly 150-220°C, preferably 150-200°C.

[0126] Heating of the adhesive film can be performed using any conventional technique, such as heating in an oven, heating by airflow, or heating with infrared (IR) radiation.

[0127] After the adhesive film has come into contact with the surface of the second substrate, the adhesive composition develops an initial adhesive strength through physical curing upon cooling. Chemical curing of the adhesive begins after the blocking groups of the closed polyurethane prepolymer PU are eliminated. However, the curing reaction remains very slow as long as the metal catalyst C forms a thiol complex with the thiol compound T.

[0128] One advantage of this invention is that, when the adhesive is heated to the activation temperature (i.e., above the blocking temperature of the blocked polyurethane prepolymer PU), the blocking groups R... 2 The adhesive will not begin to cure before the elimination temperature.

[0129] Therefore, the pre-coated adhesive element, consisting of a first substrate and an adhesive film, can be stored for any period of time under normal room temperature conditions before being used in the production process. In the case of a normal moisture-curing adhesive composition, the adhesive film must come into contact with another substrate almost immediately after the adhesive is applied (at least within the adhesive's open time), because once the adhesive film comes into contact with moisture in the air, a moisture-induced curing reaction is triggered.

[0130] The hot melt adhesive compositions described above are therefore particularly suitable for use in industrial lamination methods, where the substrate is preferably pre-coated with the adhesive and temporarily stored for days or even months before being used to construct composite elements.

[0131] The first and second substrates can be composed of any conventional materials, including polymeric materials, metals, painted metals, glass, wood, wood-derived materials (e.g., natural fiber polypropylene (NFPP)), and fiber-based materials. Suitable polymeric materials include, for example, non-foamed and foamed polyethylene (PE) (especially high-density polyethylene (HDPE)), polypropylene (PP), propylene copolymers, glass fiber reinforced polypropylene (GFPP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polystyrene (PS), polycarbonate (PC), polymethyl methacrylate (PMMA), acrylonitrile butadiene styrene (ABS), polyamide (PA), thermoplastic olefin elastomers (TPO), and combinations thereof. Suitable fiber-based materials include, for example, woven and nonwoven fabrics, particularly comprising synthetic organic fibers.

[0132] Furthermore, the first and second substrates may consist of a single layer or multiple layers of different types of materials. The layers(s) composed of polymeric materials may additionally contain additives such as fillers, plasticizers, flame retardants, heat stabilizers, antioxidants, pigments, dyes, and antimicrobial agents.

[0133] Another aspect of the invention is a composite element that can be obtained by using the method described above for bonding a first substrate to a second substrate.

[0134] The composite elements of the present invention can be used, for example, to provide interior lining components for motor vehicles. Examples of such interior lining components include door panels, switch panels, rear cargo panels, roof liners, sliding roofs, center consoles, glove boxes, sun visors, pillars, door handles, armrests, floors, cargo floors and trunk area floors, as well as sleeper compartments and rear panels for trucks.

[0135] Example

[0136] In this embodiment, the commercially available products shown in Table 1 below are used.

[0137] Table 1

[0138]

[0139] The adhesive compositions presented in Table 2 are prepared according to the procedures described below.

[0140] Preparation of polyurethane prepolymers PUP1 and PUP2

[0141] Polyol PO1 or PO2 was charged into a stainless steel reactor and stirred under vacuum at 140°C for 120 minutes to dehydrate the components. The mixture was then cooled to 120°C, and diisocyanate I was added under a nitrogen atmosphere at a molar ratio of 4 isocyanate groups to hydroxyl groups. The resulting starting mixture was then stirred under vacuum at 120°C for 45 minutes to obtain a reaction mixture containing the reaction product of diisocyanate and polyol, as well as some unreacted diisocyanate I.

[0142] The resulting reaction mixture was distilled using a short-path evaporator (jacket temperature 170 to 180 °C, pressure 0.05 to 0.002 mbar, condensation temperature 47 °C) to reduce the content of volatile compounds, particularly unreacted (residual) diisocyanate. The resulting polyurethane prepolymers PUP1 and PUP2 had NCO contents of 7.6% and 2.9% by weight, respectively, as determined by the method defined in ISO 11909:2007, and residual diisocyanate monomer contents of 0.15–0.2% by weight. The prepolymer was stored at room temperature under moisture-free conditions prior to its use in preparing the closed polyurethane prepolymer.

[0143] Preparation of closed polyurethane prepolymers PU1 and PU2

[0144] Prepolymers PUP1 or PUP2 were first melted in an oven at 90°C. The molten prepolymer was then transferred to a stainless steel reactor and stirred at 110°C for 30 minutes. A portion of the amounts of blocking agent B and metal catalyst C (shown in Table 2) were then added, and the reaction was carried out at 110°C with continued stirring for one hour. FT-IR spectroscopy determined that the obtained blocked polyurethane prepolymers PU1 and PU2 were free of isocyanate groups.

[0145] Preparation of hot melt adhesive compositions

[0146] The closed prepolymer PU1 or PU2 is first loaded into a stainless steel reactor and melted at 100°C. Then, the isocyanate reactive compound P1 or P2, the thiol compound T, and the remaining amount of the metal catalyst C shown in Table 2 are added to the reactor, and the resulting mixture is stirred at 110°C for one hour.

[0147] Measurement methods

[0148] The adhesive composition was characterized using the following measurement methods.

[0149] Unsealing temperature

[0150] The unsealing temperature is measured by temperature scanning measurements (oscillation experiment: temperature range: 80-230℃; frequency: 1Hz; deformation: 10%). Therefore, the unsealing temperature is defined as the temperature at which the loss factor tanδ (in a graph of tanδ as a function of temperature) begins to decrease due to the initiation / start of the curing reaction.

[0151] Thermal stability - increase in viscosity

[0152] The thermal stability of the adhesive composition was analyzed by measuring the following:

[0153] 1) Viscosity increases during storage at 100°C for 16 hours.

[0154] 2) Time to reach maximum viscosity during storage at 120°C for 16 hours

[0155] The viscosity of the tested adhesive composition was measured at the appropriate temperature (isothermal) during an oscillation test (frequency: 10 Hz; deformation: 10%). Viscosity values ​​were measured at the start of the test and every 4 minutes thereafter until the end of the storage period.

[0156] Initial (peel) strength (Green (peel) strength) for TPO and acrylonitrile butadiene styrene (ABS)

[0157] The adhesive composition provided in the sealed tube was preheated to 110°C in an oven for 30 minutes. After heating, a sample of the molten adhesive was applied to the surface of a first polymer sample (TPO) having dimensions of 220 mm × 50 mm × 1 mm. The adhesive was applied as a film having dimensions of 150 mm × 50 mm and a thickness of 100 µm.

[0158] Subsequently, the adhesive layer on the TPO sample was heated at 180°C for 1 minute under an IR field. A second polymer sample (ABS) with the same dimensions as the first polymer sample was placed on the first polymer sample along the edge of the adhesive film to form a composite element, and pressed with a hydraulic press at a force of 0.75 kg / cm² for 30 seconds. The composite sample was stored under standard climatic conditions (23°C, 50% relative humidity) for a period of 60 minutes before measuring the initial strength of the adhesive composition.

[0159] The initial strength of the adhesive composition was determined as the 90° peel strength of the bond. The 90° peel strength was measured using a material testing apparatus (Zwick Z 2.5) meeting the requirements of DIN 53289 and at a traversing speed of 10 mm / min. First, the average force (between 15% and 90% of the sample length) was determined, and then the average peel strength was calculated by dividing the average peel force by the width of the composite sample.

[0160] The initial strength values ​​for each adhesive composition shown in Table 2 are obtained as the average of two measurements taken using the same composite element prepared with the same adhesive composition.

[0161] Table 2

[0162]

[0163] sf = substrate failure, cf = cohesive failure.

Claims

1. A hot melt adhesive composition comprising: a) Closed-cell polyurethane prepolymer (PU), b) At least one isocyanate reactive compound P, c) At least one thiol compound T, and d) At least one metal catalyst C, which catalyzes the reaction between isocyanate groups and isocyanate reactive groups and forms a thiol complex. The closed polyurethane prepolymer PU is a polyurethane prepolymer of formula (I). Where R 1 It is a linear or branched isocyanate-terminated polyurethane prepolymer with p-valent groups after the isocyanate groups have been removed. p has values ​​from 2 to 8; and R 2 The blocking group is eliminated at a temperature of 100°C or higher, preferably at a temperature of 130°C or higher.

2. The hot melt adhesive composition according to claim 1, wherein the substituent R 2 It is either phenol after removing the phenolic hydrogen atom or ε-caprolactam after removing the hydrogen atom bonded to nitrogen.

3. The hot melt adhesive composition according to claim 2, wherein the phenol is a monophenol, preferably selected from phenol (monohydroxybenzene), cresol, 4-methoxyphenol (HQMME), resorcinol, catechol, cashew nut shell oil, and nonylphenol.

4. The hot melt adhesive composition according to any one of the preceding claims, wherein the closed polyurethane prepolymer PU is formed by reacting a polyurethane prepolymer PUP having terminal isocyanate groups with at least one of the formula R 2 H is obtained by reacting isocyanate reactive blocking agent B.

5. The hot melt adhesive composition according to claim 4, wherein the polyurethane prepolymer PUP has an average isocyanate functionality in the range of 1.2-3.0, preferably in the range of 1.5-2.5, as determined according to ISO 14896-2009 standard method A, and / or an isocyanate content in the range of 0.5-25% by weight, preferably in the range of 1.0-20% by weight, as determined by the method defined in ISO 11909:2007 standard.

6. The hot melt adhesive composition according to claim 4 or 5, wherein the polyurethane prepolymer PUP is obtained by reacting at least one polyol PO with at least one diisocyanate I at a molar ratio of at least 3, preferably at least 4, and preferably by treating the resulting reaction mixture (preferably by distillation) to reduce the amount of residual monomeric diisocyanate.

7. The hot melt adhesive composition according to claim 6, wherein the at least one polyol PO is selected from polyester polyols, polyether polyols, polycarbonate polyols, and poly(tetramethylene ether) glycol.

8. The hot melt adhesive composition according to claim 6 or 7, wherein the at least one diisocyanate I is a monomeric diisocyanate, preferably having a number-average molecular weight (Mn) of not more than 500 g / mol, more preferably not more than 300 g / mol. n ).

9. The hot melt adhesive composition according to any one of claims 4-8, wherein the polyurethane prepolymer PUP has a monomeric diisocyanate content of not more than 1.0% by weight, preferably not more than 0.5% by weight.

10. The hot melt adhesive composition according to any one of the preceding claims, wherein the at least one isocyanate reactive compound P is selected from polyether polyols and polyether amines, preferably having a number average molecular weight (Mn) of 250-15000 g / mol, more preferably 350-10000 g / mol. n ), and / or on average, each molecule has 2-6, preferably 3-6, isocyanate reactive groups.

11. The hot melt adhesive composition according to any one of the preceding claims, wherein the at least one thiol compound T contains an average of 1-5, preferably 2-4, thiol groups per molecule.

12. The hot melt adhesive composition according to any one of the preceding claims, wherein the at least one thiol compound T is selected from ethylene glycol di(3-mercaptopropionate), ethylene glycol di(2-mercaptoacetate), trimethylolpropane tri(3-mercaptopropionate), trimethylolpropane tri(2-mercaptoacetate), pentaerythritol tetra(3-mercaptopropionate), pentaerythritol tetra(2-mercaptoacetate), dipentaerythritol hexa(3-mercaptopropionate), dipentaerythritol hexa(2-mercaptoacetate), 2,3-dimercapto-1,3,4-thiadiazole and 3,6-dioxa-1,8-octanedithiol.

13. The hot melt adhesive composition according to any one of the preceding claims, wherein the molar ratio of all thiol groups in the at least one thiol compound T to all metal atoms in the at least one metal catalyst C is 1:1 to 20:1, preferably 4:1 to 16:

1.

14. Use of the hot melt adhesive composition according to any one of the preceding claims as an assembly adhesive, a lamination adhesive, or as an adhesive for constructing sandwich elements.

15. A method for bonding a first substrate to a second substrate, the method comprising the following steps: I) Heating the hot melt adhesive composition according to any one of claims 1-13 to provide a molten adhesive composition. II) Apply the molten adhesive composition to the surface of the first substrate to form an adhesive film. III) Heat the adhesive film to the reactivation temperature, and IV) The first substrate obtained in step II) or III) is mated with the second substrate such that the surface of the second substrate is in direct contact with the adhesive film.

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