Highly transparent moisture-curing hot melt adhesive

Abstract

The present invention relates to an adhesive composition comprising a) at least one polyurethane prepolymer PU, b) at least one poly(meth)acrylate AC, and c) at least one catalyst CAT that optionally catalyzes the reaction of an isocyanate group with water, wherein the polyurethane prepolymer PU is obtained by a method comprising A) reacting at least one first polyol PO1 with at least one aliphatic diisocyanate ADI in a molar ratio of at least 3, preferably at least 3.5, isocyanate groups to hydroxyl groups, and B) optionally treating the reaction mixture obtained from step A) preferably by distillation to reduce the amount of residual monomeric diisocyanate.

Description

Technology Field

[0001] The present invention relates to a moisture-curing hot-melt adhesive with high transparency and improved heat resistance and UV resistance, and particularly to its use as an assembly adhesive, a laminating adhesive, or an adhesive for constructing sandwich elements in the automotive industry. Background Technology

[0002] Hot melt adhesives are solvent-free adhesives that are solid at room temperature and are applied to the substrate to be bonded in a molten form. Upon cooling, the adhesive solidifies and forms an adhesive bond with the substrate through physically occurring bonding. Conventional hot melt adhesives are non-reactive adhesives and are not suitable for use at high temperatures because they soften again upon heating. Reactive hot melt adhesives contain polymers with reactive groups that enable chemical curing of the adhesive, for example, through the crosslinking of polymer chains. Due to the chemically cured polymer matrix, reactive hot melt adhesives do not soften upon heating, making them suitable for use at high temperatures. Chemical curing of the polymer can be initiated, for example, by heating or by exposing the adhesive composition to water, such as atmospheric moisture. Moisture-curing hot melt adhesives typically contain polymers functionalized with isocyanate or silane groups, which enable crosslinking of polymer chains upon contact with atmospheric moisture.

[0003] Moisture-curing polyurethane hot melt (PUR-RHM) adhesives consist primarily of isocyanate-functional polyurethane polymers, which are obtained by reacting a suitable polyol, typically a polyester and / or polyether polyol, with a polyisocyanate, wherein the reaction is carried out in an excess molar ratio of isocyanate (NCO) groups to hydroxyl (OH) groups. The adhesive composition is cured by the reaction of residual isocyanate groups with water, which results in various chain extension and / or crosslinking reactions of the polymer. Fully cured polyurethane hot melt adhesives contain urea and / or urethane bonds, and, depending on the starting material used to provide the isocyanate-functional polymer, ester and / or ether bonds. Crosslinked hot melt adhesives do not remelt when heated. However, compared to adhesives with high crosslinking density, such as epoxy or silicone adhesives, PUR-RHM adhesives typically have lower heat resistance. This is a significant disadvantage that limits the use of PUR-RHM adhesives in many applications, particularly in the bonding of automotive exterior parts.

[0004] In the bonding of lighting components, particularly when using translucent foils, high transparency after curing of the adhesive is required. However, all standard PUR-RHMs are not very transparent after curing, making them unsuitable for use in bonding lighting components. Furthermore, it has been found that polyurethane adhesives commonly used in automotive applications turn yellow under UV exposure, even when stabilized against UV degradation.

[0005] Therefore, there is a need for a new type of moisture-curable polyurethane hot-melt adhesive with high transparency and improved thermal and UV stability. Such adhesives are particularly suitable for bonding lighting components, for example in automotive applications, especially when using transparent foils.

[0006] The object of the present invention is to provide an adhesive composition that overcomes or at least mitigates the disadvantages of the moisture-curable polyurethane hot-melt adhesive of the prior art as discussed above.

[0007] In particular, the objective of the present invention is to provide a moisture-curable polyurethane hot-melt adhesive composition that exhibits high transparency, thermal stability, and UV stability after curing.

[0008] Surprisingly, it was found that the objective could be achieved by the features of claim 1.

[0009] In particular, it has been found that the use of polyurethane prepolymers based on aliphatic diisocyanates can provide a reactive hot-melt adhesive composition that remains transparent after curing.

[0010] Specifically, according to the present invention, an adhesive composition comprising the following is proposed:

[0011] a) at least one polyurethane prepolymer PU ,

[0012] b) at least one poly(meth)acrylate AC , and

[0013] c) At least one catalyst that optionally catalyzes the reaction between the isocyanate group and water CAT ,

[0014] Here, polyurethane prepolymer PU was obtained by a method including the following steps:

[0015] A) At least one first polyol PO1 at least one aliphatic diisocyanate ADI and, a step of reacting with a molar ratio of isocyanate groups to hydroxyl groups of at least 3, preferably at least 3.5, and

[0016] B) Optionally, a step of treating the reaction mixture obtained from step A) preferably by distillation to reduce the amount of residual monomeric diisocyanate.

[0017] As revealed, since the layer of the adhesive composition maintains transparency after curing, the proposed adhesive composition is particularly suitable for use in bonding lighting components, especially when using translucent foils. Furthermore, the cured adhesive layer exhibits excellent thermal and UV stability, which is a highly valuable property in automotive applications. Finally, the adhesive composition also contains a small amount of diisocyanate monomer, which essentially reduces toxic emissions during adhesive application.

[0018] Further aspects of the invention are defined in additional independent claims. Particularly preferred embodiments are outlined throughout the description and in dependent claims. Specific details for implementing the invention

[0019] The subject of the present invention is an adhesive composition comprising the following:

[0020] a) at least one polyurethane prepolymer PU ,

[0021] b) at least one poly(meth)acrylate AC , and

[0022] c) At least one catalyst that optionally catalyzes the reaction between the isocyanate group and water CAT ,

[0023] Here, polyurethane prepolymer PU was obtained by a method including the following steps:

[0024] A) At least one first polyol PO1 at least one aliphatic diisocyanate ADI and, a step of reacting with a molar ratio of isocyanate groups to hydroxyl groups of at least 3, preferably at least 3.5, and

[0025] B) Optionally, a step of treating the reaction mixture obtained from step A) preferably by distillation to reduce the amount of residual monomeric diisocyanate.

[0026] In the names of substances such as "polyols" or "polyisocyanates," the prefix "poly" formally refers to substances containing two or more of the functional groups appearing in the name per molecule. 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.

[0027] The term “polymer” designates an assembly of chemically homogeneous macromolecules produced by multiple reactions (polymerization, polyaddition, polycondensation) in which the macromolecules differ in degree of polymerization, molecular weight, and chain length. The term also includes derivatives of said macromolecule assembly produced from multiple reactions, namely compounds obtained by reactions such as the addition or substitution of functional groups in predetermined macromolecules, for example, and which may be chemically homogeneous or chemically heterogeneous.

[0028] The term "polyurethane polymer" designates polymers produced by the so-called diisocyanate addition process. These also include polymers that are virtually or completely devoid of urethane groups. Examples of polyurethane polymers are polyether-polyurethane, polyester-polyurethane, polyether-polyurea, polyurea, polyester-polyurea, polyisocyanurate, and polycarbodiimide.

[0029] The term "polyurethane prepolymer" designates a polyurethane polymer containing one or more unreacted isocyanate groups. A polyurethane prepolymer can be obtained by reacting an excess of polyisocyanate with a polyol and is itself a polyisocyanate. The terms "isocyanate-functional polyurethane polymer" and "isocyanate-functional polyurethane polymer" are used interchangeably.

[0030] The term "molecular weight" refers to the molar mass (g / mol) of a molecule, or a portion of a molecule also referred to as a "moiety." The term "average molecular weight" refers to the number average molecular weight (M) of an oligomeric or polymeric mixture of molecules or moiety. n ) or weight-average molecular weight (M w It refers to ). The molecular weight can be determined by gel permeation chromatography (GPC) using polystyrene as a standard material, styrene-divinylbenzene gel with porosity of 100 Angstroms, 1000 Angstroms, and 10000 Angstroms as a column, and depending on the molecule, tetrahydrofuran as a solvent at 35°C or 1,2,4-trichlorobenzene as a solvent at 160°C.

[0031] The term "average OH-function" specifies the average number of hydroxyl (OH) groups per molecule. The average OH-function of a compound is the number average molecular weight (M) of the compound. n It can be calculated based on ) and hydroxyl value.

[0032] The term "open time" specifies the length of time during which an adhesive applied to the surface of a substrate can still form an adhesive bond after coming into contact with another substrate.

[0033] In the composition, "amount of at least one component X," e.g., "amount of at least one polyol," refers to the sum of the individual amounts of all polyols contained in the composition in this document. For example, if at least one polyol is a polyester polyol and the composition contains 20 weight% of at least one polyol, the sum of the amounts of all polyester polyols contained in the composition is equal to 20 weight%.

[0034] The term "room temperature" refers to a temperature of about 23°C.

[0035] The adhesive composition is a polyurethane prepolymer as a first essential component. PU Includes

[0036] According to the present invention, a polyurethane prepolymer PUis obtained using a method that includes the following steps:

[0037] A) At least one first polyol PO1 at least one aliphatic diisocyanate ADI and, a step of reacting with a molar ratio of isocyanate groups to hydroxyl groups of at least 3, preferably at least 3.5, and

[0038] B) Optionally, a step of treating the reaction mixture obtained from step A) preferably by distillation to reduce the amount of residual monomeric diisocyanate.

[0039] In step A) of the method, at least one first polyol PO1 and at least one aliphatic diisocyanate ADI A starting mixture comprising is provided, and the reaction is performed on a first polyol PO1 and aliphatic diisocyanates ADI and is performed to obtain a reaction mixture containing a first reaction product of some unconverted diisocyanate.

[0040] Polyurethane prepolymer obtained using a method comprising step A) and optionally step B) PU It is considered to contain all reaction products generated in step A) in the reaction between a hydroxyl group-containing compound and an isocyanate group-containing compound, which mainly include isocyanate-functional polyurethane polymers as well as any unconverted (residual) diisocyanates.

[0041] For example, if the starting mixture provided in step A) includes additional compounds that do not contain isocyanate or hydroxyl groups, such as non-functionalized polyolefin resins, these are polyurethane polymers obtained using the method. PU It is not considered to form part of.

[0042] The expression "reacting with a molar ratio of at least 3 isocyanate groups to hydroxyl groups" is understood to mean that in the starting mixture, that is, before any reaction between the isocyanate and hydroxyl groups occurs, the molar ratio of isocyanate groups to hydroxyl groups is at least 3. The reaction performed in step A) is the first polyol PO1 substantially all hydroxyl groups of, in particular at least 95%, preferably at least 99% of at least one second polyol PO1 It will convert the hydroxyl group.

[0043] The reaction in step A) can be carried out according to conventional methods used for the production of isocyanate-functional polyurethane polymers. For example, the reaction can be carried out at a temperature in the range of 50 to 180°C, preferably 60 to 160°C, optionally in the presence of a catalyst. The reaction time varies depending on the temperature used, but may be, for example, in the range of 30 minutes to 6 hours, particularly 30 minutes to 3 hours, preferably 30 minutes to 1.5 hours. Suitable catalysts used for the reaction in step A) include, for example, metal catalysts, such as Coscat®83 (manufactured by Vertellus Performance Materials Inc.) and tin catalysts.

[0044] In one preferred embodiment, a polyurethane prepolymer PU A method for obtaining [the product] comprises an additional step B) in which the reaction mixture obtained from step A) is preferably treated by distillation to reduce the amount of residual monomeric diisocyanate. Distillation processes suitable for use in step B) include, for example, thin-film distillation and molecular distillation.

[0045] In one exemplary embodiment, the polyurethane prepolymer obtained from step B) PU is a polyurethane prepolymer PUIt has a content of monomeric diisocyanate of 1.0 weight% or less, preferably 0.5 weight% or less, based on the total weight of the.

[0046] First polyol PO1 It is preferably selected from polyether polyols and polyester polyols.

[0047] Suitable polyether polyols, also known as polyoxyalkylene polyols, are ethylene ethylene optionally polymerized by a starting molecule having two or more active hydrogen atoms, such as, for example, water, ammonia, or compounds having two or more OH- or NH- groups, such as 1,2-ethanediol, 1,2- and 1,3-propanediol, neopentyl glycol, diethylene glycol, triethylene glycol, isomer dipropylene glycol and tripropylene glycol, isomer butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, undecanediol, 1,3- and 1,4-cyclohexanedimethanol, bisphenol A, hydrogenated bisphenol A, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, glycerol, aniline, and mixtures of the aforementioned compounds. It includes polymer products of oxide, 1,2-propylene oxide, 1,2- or 2,3-butylene oxide, tetrahydrofuran, or mixtures thereof.

[0048] For example, polyoxyalkylene polyols with low degree of unsaturation (measured according to ASTM D-2849-69 and expressed as milliequivalents of unsaturation per gram of polyol (meq / g)) produced by a bimetallic cyanide complex catalyst (DMC catalyst), and polyoxyalkylene polyols with relatively high degree of unsaturation produced by anionic catalysts such as, for example, NaOH, KOH, or alkali metal alkoxides, can both be used.

[0049] Particularly suitable polyether polyols include polyoxyalkylene diols or poly-oxyalkylene triols, in particular polyoxyethylene diols or polyoxyethylene triols. Polyoxyalkylene diols or polyoxyalkylene triols, more particularly those with a number average molecular weight (M n Polyoxypropylene diols and triols with a molecular weight in the range of 1,000 to 30,000 g / mol, and polyoxypropylene diols and triols with a number average molecular weight (Mn) of 400 to 8,000 g / mol are particularly suitable. Suitable polyether polyols are commercially available under trade names, for example, Acclaim®, Desmophene®, and Arcol® (all Covestro products).

[0050] Suitable polyester polyols are divalent and trivalent, preferably divalent, alcohols, e.g., 1,2-ethanediol, 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, dimeric fatty alcohols, neopentyl glycol, glycerol, 1,1,1-trimethylolpropane, or mixtures of the aforementioned alcohols, organic dicarboxylic acids or tricarboxylic acids, preferably dicarboxylic acids, or their anhydrides or esters, e.g., succinic acid, glutaric acid, 3,3-dimethylglutaric acid, adipic acid, suberic acid, sebacic acid, undecandioic acid. It can be obtained by reacting with dodecanedicarboxylic acid, azelaic acid, maleic acid, fumaric acid, phthalic acid, dimeric fatty acids, isophthalic acid, terephthalic acid, and hexahydrophthalic acid, or a mixture of the aforementioned acids. Polyester polyols prepared from lactones, such as ε-caprolactone, also known as polycaprolactone, are also suitable.

[0051] Preferred polyester polyols include those obtained by reacting adipic acid, sebacic acid, or dodecanedicarboxylic acid as a dicarboxylic acid with hexanediol or neopentyl glycol as a dihydric alcohol. Further examples of suitable polyester polyols include polyester polyols of oleochemical origin. Polyester polyols of this type can be prepared, for example, by fully ring-opening an epoxidized triglyceride of a fat mixture containing at least partially olefinically unsaturated fatty acids with one or more alcohols having 1 to 12 carbon atoms, and then partially ester-exchanging the triglyceride derivative to produce an alkyl ester polyol having 1 to 12 carbon atoms to an alkyl radical. Particularly suitable crystalline and partially crystalline polyester polyols include adipic acid / hexanediol polyesters and dodecanedicarboxylic acid / hexanediol polyesters.

[0052] In one embodiment, the first polyol PO1 has the following:

[0053] - Number average molecular weight (M) of 1,000 g / mol or less, preferably 750 g / mol or less, more preferably 500 g / mol or less, determined by gel permeation chromatography (GPC) using polystyrene as a standard substance. n ), and / or

[0054] - Hydroxyl value of 100 - 500 mg KOH / g, preferably 150 - 350 mg KOH / g, more preferably 200 - 300 mg KOH / g, determined according to ISO 4629-2:2016 standard.

[0055] In one preferred embodiment, the first polyol PO1It is a polyether polyol, preferably a polyether diol, and has a molecular weight of 1000 g / mol or less, preferably 750 g / mol or less, more preferably 500 g / mol or less, as determined by gel permeation chromatography (GPC) using polystyrene as a standard material.

[0056] In one preferred embodiment, an aliphatic diisocyanate ADI is an aliphatic monomeric diisocyanate, preferably having a number average molecular weight (M) of 1000 g / mol or less, preferably 500 g / mol or less, more preferably 400 g / mol or less, as determined by gel permeation chromatography (GPC) using polystyrene as a standard. n has ).

[0057] Isocyanates are called "aliphatic" when the isocyanate group is directly bonded to an aliphatic, alicyclic, or aryl-aliphatic moiety. Therefore, the corresponding functional group is called an aliphatic isocyanate group. Isocyanates are called "aromatic" when the isocyanate group is directly bonded to an aromatic moiety. Therefore, the corresponding functional group is called an aromatic isocyanate group.

[0058] The term "monomer" designates a molecule having at least one polymerizable group. Monomeric di- or polyisocyanates do not particularly contain urethane groups. In the context of the present invention, oligomers or polymer products of diisocyanate monomers, such as adducts of monomeric diisocyanates, are not monomeric diisocyanates.

[0059] Examples of suitable aliphatic monomeric diisocyanates include, for example, 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-decamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, lysine diisocyanates, lysine ester diisocyanates, cyclohexane 1,3-diisocyanate and cyclohexane 1,4-diisocyanate and mixtures of these isomers, 1-methyl-2,4- and -2,6-diisocyanatocyclohexane and mixtures of these isomers (HTDI or H6TDI). Includes 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (= isophorone diisocyanate or IPDI), 1,5-pentamethylene diisocyanate (PDI), perhydro-2,4'- and -4,4'-diphenylmethane diisocyanate (HMDI or H12MDI) and mixtures of these isomers, 1,4-diisocyanato-2,2,6-trimethylcyclohexane (TMCDI), and 1,3- and 1,4-bis(isocyanato-methyl)cyclohexane.

[0060] In one embodiment, an aliphatic monomeric diisocyanate ADI It is selected from the group consisting of 1,6-hexamethylene diisocyanate (HDI), 1,5-pentamethylene diisocyanate (PDI), and isophorone diisocyanate (IPDI).

[0061] Furthermore, those skilled in the art are aware that technical-grade products of diisocyanates may frequently contain mixtures of isomers or other isomers as impurities. Suitable aliphatic monomeric diisocyanates are commercially available, for example, under the trade name Desmodur (a product of Covestro).

[0062] In one exemplary embodiment, the adhesive composition comprises 15 to 75 weight%, preferably 25 to 70 weight%, and more preferably 35 to 65 weight% of a polyurethane prepolymer. PU Includes

[0063] The adhesive composition of the present invention comprises at least one poly(meth)acrylate as a second essential component. AC Includes additionally.

[0064] The term “(meth)acrylate” designates methacrylate or acrylate in this disclosure. The term “poly(meth)acrylate” refers to a (meth)acrylate monomer and a homopolymer, copolymer, and higher copolymer of one or more additional (meth)acrylate monomers and / or one or more additional monomers.

[0065] Suitable (meth)acrylate monomers include, for example, alkyl (meth)acrylates, such as methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate, lauryl acrylate, stearyl acrylate, behenyl acrylate, and branched isomers thereof, for example, isobutyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isooctyl acrylate, isooctyl methacrylate, and also cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate or 3,5-dimethyladamantyl acrylate.

[0066] Poly(meth)acrylate ACAdditional comonomers suitable for the synthesis of include vinyl compounds, such as ethylenedimethyl hydrocarbons having functional groups, vinyl esters, vinyl halides, vinylidene halides, nitriles of ethylenedimethyl hydrocarbons, phosphate esters, and zinc salts of (meth)acrylic acid. Examples of additional suitable comonomers include, for example, maleic anhydride, styrene, styrene compounds, acrylonitrile, vinyl acetate, vinyl propionate, vinyl chloride, (meth)acrylic acid, beta-acryloyloxypropionic acid, vinylacetic acid, fumaric acid, crotonic acid, aconitic acid, trichloroacrylic acid, itaconic acid, and maleic acid, and their amides.

[0067] Particularly suitable poly(meth)acrylates include, for example, homopolymers and copolymers obtained by free radical polymerization of one or more (meth)acrylate monomers in combination with at least one additional comonomer.

[0068] In one exemplary embodiment, poly(meth)acrylate AC has the following:

[0069] - Acid value of 15 mg KOH / g or less, preferably 10 mg KOH / g or less, determined according to EN ISO 2114:2002-06 and / or

[0070] - A glass transition temperature of 25°C or higher, preferably 50°C or higher, determined according to ISO 11357-1 standard, and / or

[0071] - Weight average molecular weight (M) of 15,000 to 100,000 g / mol, preferably 25,000 to 65,000 g / mol, determined by gel permeation chromatography (GPC) using polystyrene as a standard substance. w ).

[0072] In one exemplary embodiment, the adhesive composition comprises 15 to 65 weight%, preferably 35 to 55 weight%, of poly(meth)acrylate. AC Includes

[0073] In one additional embodiment, the adhesive composition further comprises the following:

[0074] d) at least one aliphatic polyisocyanate oligomer APO .

[0075] Surprisingly, aliphatic polyisocyanate oligomers APO An adhesive composition containing [it] was found to exhibit improved thermal stability.

[0076] The term “oligomer” in this disclosure designates a compound formed by the linkage of a small number of monomers, e.g., dimers, trimers, tetramers, and other polymeric materials. The term “polyisocyanate oligomer” may designate individual oligomers of diisocyanates or mixtures of oligomers, wherein these oligomers may be composed of similar or different diisocyanates.

[0077] In one preferred embodiment, an aliphatic polyisocyanate oligomer APO It has an average isocyanate activity of at least 2, preferably at least 2.5.

[0078] In one exemplary embodiment, an aliphatic polyisocyanate oligomer APOis an oligomer of an aliphatic diisocyanate, preferably hexamethylene 1,6-diisocyanate (HDI), 2-methylpentamethylene 1,5-diisocyanate, 2,2,4- and 2,4,4-trimethylhexamethylene 1,6-diisocyanate (TMDI), dodecamethylene 1,12-diisocyanate, cyclohexane 1,3- and 1,4-diisocyanate and any preferred mixture of these isomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), perhydrodiphenylmethane 2,4'- and 4,4'-diisocyanate (HMDI), 1,4-diisocyanato-2,2,6-trimethylcyclohexane (TMCDI), and 1,3 and It is selected from 1,4-bis(isocyanatomethyl)cyclohexane.

[0079] The technical form of a trimer of an aliphatic diisocyanate is typically a mixture of materials having different degrees of polymerization and chemical structures. Suitable commercially available trimers of an aliphatic diisocyanate comprise a technical oligomer mixture having an average isocyanate activity of 2.4 to 4.0 and, in particular, containing isocyanurate, iminooxadiazinedione, or biuret groups. Furthermore, allofanate, carbodiimide, uretonimine, or oxadiazinetrione groups may also be present. A preferred technical form of a trimer of an aliphatic diisocyanate is an oligomer mixture comprising a major portion of the aliphatic diisocyanate trimer in a mixture with dimers and higher oligomers. An oligomer mixture containing a small amount of monomeric diisocyanate, particularly having a content of monomeric diisocyanate of 1.0 wt% or less, preferably 0.5 wt% or less, much more preferably 0.25 wt% or less, and even more preferably 0.15 wt% or less, is particularly preferred.

[0080] Suitable commercially available technical oligomer mixtures of aliphatic diisocyanates include HDI biuret, e.g., Desmodur® N 100 and N 3200 (Coverstro products), Tolonate® HDB and HDB-LV (Vencorex products), and Duranate® 24A-100 (Asahi Kasei products); HDI isocyanurates, e.g., Desmodur® N 3300, N 3600, and N 3790 BA (all Coverstro products), Tolonate® HDT, HDT-LV, and HDT-LV2 (all Vencorex products), Duranate® TPA-100 and THA-100 (Asahi Kasei products), and Coronate® HX (Nippon Polyurethanes products); HDI iminooxadiazinedione, e.g., Desmodur® XP 2410 (Coverstro product); HDI allophanate, e.g., Desmodur® VP LS 2102 (Covestro product); and IPDI isocyanurate, e.g., in solution or solid form such as Desmodur® Z 4470 (Covestro product).

[0081] In one preferred embodiment, an aliphatic polyisocyanate oligomer APO is selected from hexamethylene diisocyanate (isocyanurate) trimer, hexamethylene diisocyanate biuret trimer, and isophorone diisocyanate (isocyanurate) trimer, preferably hexamethylene diisocyanate (isocyanurate) trimer and hexamethylene diisocyanate biuret trimer.

[0082] In one exemplary embodiment, the adhesive composition comprises 0.1 to 15 weight%, preferably 1 to 10 weight%, of an aliphatic polyisocyanate oligomer APO Includes

[0083] In one additional embodiment, a polyurethane prepolymer PU The method of obtaining includes the following additional steps:

[0084] C) the reaction mixture obtained from step A) or the distilled reaction mixture obtained from step B) at least one second polyol PO2 A step of mixing and carrying out the reaction with a molar ratio of isocyanate groups to hydroxyl groups of 1.7 - 4.0, preferably 1.9 - 3.5.

[0085] In step C) of the method, the reaction mixture from step A) or the distilled reaction mixture from step B) and the second polyol PO2 A starting mixture comprising is provided and a reaction is carried out to produce a first reaction product and a second polyol PO2 A reaction mixture containing the second reaction product is obtained.

[0086] The reaction in step C) can be carried out according to conventional methods used for the production of isocyanate-functional polyurethane polymers. For example, the reaction can be carried out at a temperature in the range of 50 to 180°C, preferably 60 to 160°C.

[0087] Polyurethane prepolymer obtained using a method comprising steps A) and C) or A), B), and C) PU It is considered to contain all reaction products generated in steps A) and C) in the reaction between a hydroxyl group-containing compound and an isocyanate group-containing compound, including mainly isocyanate-functional polyurethane polymers, as well as any unconverted (residual) diisocyanate.

[0088] For example, if the starting mixture provided in step C) includes additional compounds that do not contain isocyanate or hydroxyl groups, such as a non-functionalized polyolefin resin, these are polyurethane polymers obtained using the present method. PU It is not considered to form part of.

[0089] Second polyol PO2 A compound suitable for use as a first polyol PO1 In the context of, as discussed above, it includes polyether polyols and polyester polyols.

[0090] In one embodiment, the second polyol PO2 has the following:

[0091] - Number average molecular weight (M) determined by gel permeation chromatography (GPC) using polystyrene as a standard substance, of 10,000 g / mol or less, preferably 7,500 g / mol or less, particularly 350 to 5,000 g / mol, particularly 1,000 to 3,500 g / mol. n ), and / or

[0092] - Hydroxyl value of 150 mg KOH / g or less, preferably 100 mg KOH / g or less, particularly 10 to 100 mg KOH / g, particularly 25 to 75 mg KOH / g, determined according to ISO 4629-2:2016 standard.

[0093] In one preferred embodiment, the second polyol PO2 is a polyether polyol, preferably a polyether diol, and preferably has a hydroxyl value of 150 mg KOH / g or less, preferably 100 KOH / g or less, as determined according to the ISO 4629-2:2016 standard.

[0094] In one exemplary embodiment, a polyurethane prepolymer PU The reaction in step C) of the method for obtaining poly(meth)acrylate AC It is performed in the presence of.

[0095] A method having steps A) and C) or steps A) to C) as discussed above, a polyurethane prepolymer PU When used to obtain the reaction mixture obtained from step A) or the distilled reaction mixture obtained from step B), the second polyol PO2Poly(meth)acrylate before mixing with AC At least a portion of the total amount of the second polyol PO2 It may be desirable to dissolve at least a portion of it.

[0096] In one additional embodiment, poly(meth)acrylate AC At least a portion of the second polyol in step C) PO2 After dissolving in, the mixture obtained in this way is mixed with the reaction mixture obtained from step A) or the distilled reaction mixture obtained from step B).

[0097] It may be further preferable that the adhesive composition has a monomeric diisocyanate content of 1.5 weight% or less, preferably 1.0 weight% or less.

[0098] In one embodiment, the adhesive composition comprises at least one catalyst that catalyzes the reaction between an isocyanate group and water. CAT Includes additionally.

[0099] Examples of suitable catalysts include metal-based catalysts such as dialkyl tin complexes, particularly dibutyltin (IV) or dioctyltin (IV) carboxylates or acetoacetonates, such as dibutyltin dilaurate (DBTDL), dibutyltin diacetylacetonate, and dioctyltin dilaurate (DOTDL), additionally bismuth (III) complexes such as bismuth octoate or bismuth neodecanoate, zinc (II) complexes such as zinc octoate or zinc neodecanoate, and zirconium (IV) complexes such as zirconium octoate or zirconium neodecanoate.

[0100] Further examples of suitable catalysts include compounds containing amine groups, such as dimorpholinodialkyl ethers and / or dimorpholino-substituted polyalkylene glycols, such as 2,2'-dimorpholinodiethyl ether and 1,4-diazabicyclo[2.2.2]-octane. A combination of two or more catalysts may also be used, and a combination comprising one or more metal catalysts and one or more morpholino amine compounds is preferred.

[0101] The adhesive composition of the present invention may further include auxiliary materials and additives selected from the group consisting of, for example, plasticizers, adhesion promoters, ultraviolet absorbers, ultraviolet and heat stabilizers, fluorescent emitting agents, pigments, dyes, and drying agents.

[0102] Examples of suitable UV stabilizers that can be added to the adhesive composition include, for example, sterically hindered phenols, and suitable UV absorbers include, for example, hydroxybenzophenone, hydroxybenzotriazole, triazine, anilide, benzoate, cyanoacrylate, phenylformamidine, and mixtures thereof.

[0103] The total amount of these auxiliary materials and additives is preferably 10% by weight or less, more preferably 5% by weight or less, based on the total weight of the adhesive composition.

[0104] The adhesive composition of the present invention has excellent workability under typical application conditions of a hot melt adhesive, particularly at temperatures in the range of 85 to 200°C, which means that the adhesive has sufficiently low viscosity at the application temperature so that it can be applied to a substrate in a molten state. The adhesive composition also generates high initial strength immediately after application to the substrate upon cooling, even before initiating a crosslinking reaction with water, particularly atmospheric moisture.

[0105] The adhesive composition is preferably a one-component adhesive composition, more preferably a one-component hot-melt adhesive composition. In the context of the present invention, the term "one-component composition" refers to a composition in which all components of the composition are stored as a mixture within the same container or compartment.

[0106] A further aspect of the present invention is preferably the use of the adhesive composition of the present invention as an adhesive for automotive assembly for joining lighting components.

[0107] A further aspect of the present invention is a method for producing an adhesive composition of the present invention, the method comprising the following steps:

[0108] i) Polyurethane prepolymer PU The step of providing, and

[0109] ii) Polyurethane prepolymer PU The step of mixing with other components of the adhesive composition,

[0110] Here, step i) includes the following steps:

[0111] A) At least one first polyol PO1 at least one aliphatic diisocyanate ADI and, a step of reacting with a molar ratio of isocyanate groups to hydroxyl groups of at least 3, preferably at least 3.5, and

[0112] B) Optionally, a step of treating the reaction mixture obtained from step A) preferably by distillation to reduce the amount of residual monomeric diisocyanate.

[0113] The reaction in step A) can be carried out according to conventional methods used for the production of isocyanate-functional polyurethane polymers. For example, the reaction may be carried out at a temperature in the range of 50 to 180°C, preferably 60 to 160°C, optionally in the presence of a catalyst. The reaction time may vary depending on the temperature used, but may be, for example, in the range of 30 minutes to 6 hours, particularly 30 minutes to 3 hours, preferably 30 minutes to 1.5 hours. Suitable catalysts used for the reaction in step A) include, for example, metal catalysts, such as Coscat®83 (manufactured by Vertellus Performance Materials Inc.) and tin catalysts.

[0114] In one preferred embodiment, step i) comprises step B), which involves treating the reaction mixture obtained from step A) preferably by distillation to reduce the amount of residual monomeric diisocyanate. Distillation processes suitable for use in step B) include, for example, thin-film distillation and molecular distillation.

[0115] In one exemplary embodiment, step ii) is a polyurethane polymer PU poly(meth)acrylate AC , and aliphatic polyisocyanate oligomers APO At least one of the following, and a catalyst that catalyzes the reaction between an isocyanate group and water. CAT Includes mixing.

[0116] In one additional embodiment, step i) includes the following additional step:

[0117] C) the reaction mixture obtained from step A) or the distilled reaction mixture obtained from step B) at least one second polyol PO2 A step of mixing and carrying out the reaction with a molar ratio of isocyanate groups to hydroxyl groups of 1.7 - 4.0, preferably 1.9 - 3.5.

[0118] Step i) of the method, where this includes steps A) and C) or steps A) to C), the reaction mixture obtained from step A) or the distilled reaction mixture obtained from step B) is a second polyol PO2 Poly(meth)acrylate before mixing with AC At least a portion of the total amount of the second polyol PO2 It may be desirable to dissolve at least a portion of it.

[0119] In one additional embodiment, poly(meth)acrylate AC At least a portion of the second polyol in step C) PO2 After dissolving in, the mixture obtained in this way is mixed with the reaction mixture obtained from step A) or the distilled reaction mixture obtained from step B).

[0120] A further aspect of the present invention is a method for adhesively bonding a first substrate to a second substrate, the method comprising the following steps:

[0121] I) a step of heating the adhesive composition according to the present invention to provide a molten adhesive composition,

[0122] II) A step of applying a molten adhesive composition to the surface of a first substrate,

[0123] III) a step of bringing the applied adhesive into contact with the surface of the second substrate, and

[0124] IV) A step of chemically curing the applied adhesive with water, preferably atmospheric moisture.

[0125] The first and second substrates may be sheet-type articles or three-dimensional molded articles having first and second principal surfaces defined by peripheral edges and a thickness between them.

[0126] In a method of adhesively bonding a first substrate to a second substrate, the adhesive composition is heated to a temperature exceeding the softening point of the adhesive composition and applied to the surface of the first substrate in a molten state using any conventional technique, for example, by a roller, a brush, or pouring, and further distributed by, for example, a roller, a scraper, or a notched trowel.

[0127] After the applied adhesive comes into contact with the surface of the second substrate, the adhesive composition develops a specific initial adhesive strength through physical curing, that is, upon cooling. Depending on the application temperature and embodiment of the adhesive composition, particularly the reactivity of the adhesive, the chemical curing reaction may already begin while the adhesive composition is applied to the surface of the first substrate. However, typically, most of the chemical curing occurs after the application of the adhesive, specifically after the applied adhesive comes into contact with the surface of the second substrate.

[0128] The first and second substrates may be composed of any conventional materials, including polymeric materials, metals, painted metals, glass, wood, wood-derived materials such as natural fiber polypropylene (NFPP), and fiber materials. Suitable polymeric materials include, for example, polyethylene (PE), particularly high-density polyethylene (HDPE), polypropylene (PP), glass-fiber reinforced polypropylene (GFPP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polystyrene (PS), polycarbonate (PC), polymethyl methacrylate (PMMA), acrylonitrile butadiene styrene (ABS), polyamide (PA), and combinations thereof. The first and second substrates may be composed of a single layer or multiple layers of different types of materials. The layer(s) composed of polymeric materials may further contain additives such as fillers, plasticizers, flame retardants, heat stabilizers, antioxidants, pigments, dyes, and biocides.

[0129] In one exemplary embodiment, the first and / or second substrate has a transmittance in the visible light range of at least 85%, preferably at least 95%.

[0130] Examples

[0131] The following compounds and products presented in Table 1 were used in the examples.

[0132] Table 1

[0133]

[0134] Preparation of polyurethane prepolymer PU1

[0135] The first polyol (PO1) was charged into a stainless steel reactor and dehydrated by maintaining it under vacuum while stirring at 140°C for 120 minutes. The temperature of the mixture was lowered to 120°C, and an aliphatic diisocyanate (ADI) was added under a nitrogen blanket. Subsequently, the starting mixture thus obtained, having a molar ratio of isocyanate groups to hydroxyl groups of 4.0, was reacted by stirring under vacuum at 120°C for 45 minutes to obtain a reaction mixture containing the reaction product of the aliphatic diisocyanate (ADI) and the first polyol (PO1), as well as some unreacted aliphatic diisocyanate (ADI).

[0136] The reaction mixture obtained in this way was distilled to reduce the concentration of residual (unreacted) diisocyanate monomers. The distilled reaction mixture contained less than 0.3 wt% of residual diisocyanate monomers. The obtained polyurethane prepolymer (PU1) was stored at room temperature in a moisture-free environment.

[0137] Preparation of adhesive composition

[0138] The adhesive composition of the present invention was prepared in two different ways.

[0139] In the first method, the polyurethane prepolymer (PU1) and poly(meth)acrylate (AC) prepared as described above were charged into a stainless steel reactor. The mixture was maintained under vacuum while stirring at 140°C for 120 minutes to dehydrate the components and obtain a homogeneously mixed mixture. Subsequently, an aliphatic polyisocyanate oligomer (APO), a catalyst (CAT), and additives were added to the mixture under a nitrogen blanket. After mixing under vacuum for 45 minutes, the obtained adhesive composition was stored at room temperature in a moisture-free environment.

[0140] In the second method, the second polyol (PO2) and polymethacrylate (AC) were first charged into a stainless steel reactor. The mixture was maintained under vacuum while stirring at 140°C for 120 minutes to dehydrate the components and obtain a homogeneously mixed mixture. The temperature of the mixture was lowered to 120°C, and a polyurethane prepolymer (PU1 or PU2) was added to the mixture under a nitrogen blanket. The starting mixture thus obtained was reacted under vacuum at 120°C for 45 minutes while stirring to obtain a reaction mixture containing the reaction products of the polyurethane prepolymer (PU1 or PU2) and the second polyol (PO2). Subsequently, an aliphatic polyisocyanate oligomer (APO), a catalyst (CAT), and additives were added to the reaction mixture under a nitrogen blanket. After mixing under vacuum for 45 minutes, the obtained adhesive composition was stored at room temperature in a moisture-free environment.

[0141] Invention Example Ex-1 was prepared using the first method, and Reference Example Ref-1 and Examples Ex-2 to Ex-4 were prepared using the second method.

[0142] The proportions of the compounds presented in Table 2 were calculated based on the total weight of the manufactured adhesive composition.

[0143] measurement method

[0144] The adhesive composition was characterized using the following measurement method.

[0145] Viscosity at 130℃

[0146] The sample adhesive composition provided in a sealed tube was preheated in an oven at a temperature of 130°C for a period of 30 minutes. After heating, 12.3 g of the adhesive composition sample was weighed, placed in a disposable sleeve, and placed in a viscometer. Viscosity was measured at 110°C at a rotation speed of 5 revolutions per minute using a Brookfield DV-2 viscometer with spindle number 27 equipped with a Thermosel system. The value obtained after tempering for 20 minutes at the measurement temperature and measuring for 5 minutes was recorded as the representative viscosity.

[0147] Tensile superposition shear strength (LSS)

[0148] To provide the adhesive in a molten state, the adhesive was held in a 130°C oven for more than 30 minutes. After heating, a sample of the molten adhesive was applied to the surface of a wooden substrate with dimensions of 9 cm x 2 cm x 5 mm. The adhesive was applied as a coating film with dimensions of 2.5 cm x 1 cm and a thickness of 1 mm.

[0149] Immediately after applying the adhesive, a second wooden substrate having the same dimensions as the first wooden substrate was placed on the first wooden substrate along the edge of the adhesive film to form a test composite element. The second wooden substrate was pressed firmly against the first wooden substrate to remove air from the adhesive bond. A 150 g weight was placed on the top surface of the second wooden substrate. Any adhesive squeezed out from the joint was cut off with a knife. The overlap shear strength (LSS) of the test composite element was measured according to the EN 1465 standard using a material testing device (Zwick Z 020) and a test speed of 10 mm / min.

[0150] Overlapping shear strength was measured using a test composite element, and the first wood substrate and the second substrate were bonded and stored for 30 minutes to investigate the initial (green) adhesive bond strength obtained with the tested adhesive composition.

[0151] The overlap shear strength values ​​for each adhesive composition presented in Table 2 were obtained as the average of three measurements performed on the same test composite element prepared using the same adhesive composition.

[0152] Curing time

[0153] The sample adhesive composition provided in a sealed tube was preheated in an oven at a temperature of 140°C for 20 minutes. After heating, 20 g of the molten adhesive sample was applied to the surface of a silicone paper strip (B700 White, Laufenberg & Sohn KG) placed on a heating plate using a doctor blade. The dimensions of the silicone paper were 30 cm x 10 cm, and the adhesive was applied as a film with a thickness of 500 μm and dimensions of 30 cm x 6 cm. Before applying the adhesive film, the silicone paper strip and the doctor blade were heated to a temperature of 150°C using a heating plate.

[0154] Immediately after applying the adhesive, the silicone paper strip was removed from the heating plate and stored under standard climatic conditions (23°C, 55% relative humidity). The point at which the adhesive film solidified was recorded as the starting point of measurement. At a defined sampling time, a sample strip with dimensions of 10 cm x 1 cm was cut from the silicone paper strip and placed on a heating plate at a temperature of 150°C. The procedure was continued until the adhesive film on the sample strip no longer melted on the heating plate. The length of the time interval between the starting point of measurement and the last sampling point was recorded as the curing time of the adhesive composition (in hours).

[0155] The curing time values ​​presented in Table 2 were obtained as the average of three measurements performed with the same adhesive composition.

[0156] Opening hours

[0157] The sample adhesive composition provided in a sealed tube was first preheated in an oven at 110°C for 30 minutes. After heating, 20 g of the molten adhesive sample was applied to the surface of a silicone paper strip (B700 White, Laufenberg & Sohn KG) placed on a heating plate using a doctor blade. The silicone paper strip had dimensions of 30 cm x 10 cm, and the adhesive was applied as a film with a thickness of 500 μm and dimensions of 30 cm x 6 cm. Before applying the adhesive film, the silicone paper strip and the doctor blade were heated to a temperature of 110°C using a heating plate.

[0158] Immediately after applying the adhesive, the silicone paper strip was removed from the heating plate and placed on a plywood sheet at room temperature (23°C) with the adhesive film facing upward, and the time was recorded as the starting point of measurement. Every 10 seconds, a short strip of silicone-coated paper in the form of a roll measuring 10 cm x 1 cm was placed on the adhesive film (with the non-silicified surface facing outward) and slowly removed to separate the strip from the adhesive film. The procedure was repeated until the paper strip could no longer be removed from the adhesive film without damaging the paper strip or the adhesive film. The time interval between the starting point of measurement and the last sampling point was recorded as the opening time of the adhesive composition (in seconds).

[0159] The opening time values ​​presented in Table 2 were obtained as the average of three measurements performed with the same adhesive composition.

[0160] Residual monomeric diisocyanate content

[0161] The amount of unconverted monomeric diisocyanate in the adhesive composition was determined by HPLC (detection via photodiode array), and the measured value is expressed as weight% based on the total weight of the adhesive composition.

[0162] Shear Adhesion Breakdown Temperature (SAFT)

[0163] The adhesive composition provided in a sealed tube was preheated in an oven at a temperature of 140°C for 20 minutes. After heating, the molten adhesive sample was applied to the surface of a wood specimen (pine) with dimensions of 9 cm x 2 cm x 5 mm and a 1 mm copper wire as a spacer on the surface. The adhesive was applied as a film with dimensions of 2 cm x 2 cm and a thickness of 1 mm.

[0164] Immediately after applying the adhesive, a second wood specimen (pine) having the same dimensions as the first wood specimen was placed on top of the first wood specimen along the edge of the adhesive film. The second wood specimen was pressed firmly against the first wood specimen to remove air from the adhesive bond. A weight of 150 was placed on the top surface of the second wood specimen. Any adhesive squeezed out from the joint was cut off with a knife. Subsequently, the test specimens consisting of the bonded wood specimens were stored for 14 days under controlled standard ambient conditions (23°C, 40-60% relative humidity).

[0165] The test specimens were placed in an oven by suspending them vertically from a metal hook at one end of the first wooden specimen. A metal weight corresponding to a static load of 1 kg was attached to the bottom of the second wooden specimen of each test specimen. Three test specimens were placed in the oven at a time to measure thermal stability.

[0166] In the thermal stability measurement, the oven was first heated to a temperature 40°C lower than the expected bond failure temperature. The test specimen was maintained at this starting temperature for 60 minutes. If no bond failure occurred, the oven temperature was increased by 10°C and the measurement was continued for an additional 60 minutes. The oven temperature was increased in 10°C increments according to the procedure described above until bond failure occurred. The last temperature measured before bond failure occurred was recorded as the thermal stability temperature (SAFT).

[0167] The SAFT values ​​presented in Table 2 were obtained as the average of measurements performed on three identical test specimens prepared from samples of the same adhesive composition.

[0168] transparency

[0169] The transparency of the cured adhesive layer was measured using a Gretag D 200 measuring instrument (Gretag's transmittance meter).

[0170] UV and thermal stability

[0171] UV and thermal stability of adhesive compositions tested by applying cured adhesive layers of Ref-1 (840_104), Ex-1 (840_114), and Ex-4 (840_108) with a thickness of 500 μm to the following test.

[0172] UV stability was tested by applying a cured adhesive layer to three cycles of the Volkswagen exposure test PV1303, and thermal stability was tested by treating a cured adhesive layer with a thickness of 500 μm at 100°C or 120°C for 500 hours.

[0173] The results of the UV and thermal stability tests are presented in Figures 1-3.

[0174] The adhesive of the present invention tested remained transparent and did not undergo any color change during UV and heat treatment. However, the cured adhesive layer of Ref-1, comprising a polyurethane prepolymer based on aromatic diisocyanate monomers, changed color from transparent to yellow after three cycles of PV1303 treatment or heat treatment at 120°C.

[0175] Table 2

[0176]

Claims

Claim 1 As an adhesive composition, a) at least one polyurethane prepolymer PU ,b) at least one poly(meth)acrylate AC , and c) at least one catalyst that optionally catalyzes the reaction between the isocyanate group and water. CAT Includes, and the polyurethane prepolymer PU A) at least one first polyol PO1 at least one aliphatic diisocyanate ADI An adhesive composition obtained by a method comprising: a step of reacting with an isocyanate group to hydroxyl group molar ratio of at least 3, preferably at least 3.5; and a step of optionally treating the reaction mixture obtained in step A) preferably by distillation to reduce the amount of residual monomeric diisocyanate. Claim 2 In claim 1, the first polyol PO1 A number average molecular weight (M) of 1000 g / mol or less, preferably 750 g / mol or less, determined by gel permeation chromatography (GPC) using polystyrene as this standard material. n An adhesive composition having ). Claim 3 In claim 1 or 2, the first polyol PO1 An adhesive composition, which is a polyether polyol, preferably a polyether diol. Claim 4 In any one of claims 1 to 3, the aliphatic diisocyanate ADI A number average molecular weight (M) of 1000 g / mol or less, preferably 500 g / mol or less, determined by gel permeation chromatography (GPC) using polystyrene as a standard material, preferably M n An adhesive composition having an aliphatic monomeric diisocyanate. Claim 5 In any one of claims 1 to 4, the aliphatic diisocyanate ADI An adhesive composition selected from hexamethylene diisocyanate (HDI), 1,5-pentamethylene diisocyanate (PDI), and isophorone diisocyanate (IPDI). Claim 6 In any one of claims 1 to 5, 15 to 65 weight%, preferably 35 to 55 weight% of poly(meth)acrylate AC An adhesive composition comprising Claim 7 In any one of claims 1 to 6, d) at least one aliphatic polyisocyanate oligomer APO An adhesive composition further comprising Claim 8 In claim 7, the aliphatic polyisocyanate oligomer APO An adhesive composition selected from a hexamethylene diisocyanate (isocyanurate) trimer, a hexamethylene diisocyanate biuret trimer, and an isophorone diisocyanate (isocyanurate) trimer, preferably a hexamethylene diisocyanate (isocyanurate) trimer and a hexamethylene diisocyanate biuret trimer. Claim 9 In claim 7 or 8, 0.1 to 15 weight%, preferably 1 to 10 weight% of an aliphatic polyisocyanate oligomer APO An adhesive composition comprising Claim 10 In any one of claims 1 to 9, the polyurethane prepolymer PU An adhesive composition comprising the following additional steps for obtaining: C) the reaction mixture obtained in step A) or the distilled reaction mixture obtained in step B) at least one second polyol PO2 A step of mixing and carrying out the reaction with a molar ratio of isocyanate groups to hydroxyl groups of 1.7 - 4.0, preferably 1.9 - 3.

5. Claim 11 In item 10, the above-mentioned second polyol PO2 An adhesive composition in which is a polyether polyol, preferably a polyether diol. Claim 12 In either claim 10 or 11, the reaction in step C) is poly(meth)acrylate AC An adhesive composition performed in the presence of Claim 13 An adhesive composition according to any one of claims 1 to 12, having a content of monomeric diisocyanate of 1.5 weight% or less, preferably 1.0 weight% or less, based on the total weight of the adhesive composition. Claim 14 Preferably, the use of an adhesive composition according to any one of claims 1 to 13 as an adhesive for automobile assembly for joining lighting components. Claim 15 A method for adhesively bonding a first substrate to a second substrate, comprising: I) heating an adhesive composition according to any one of claims 1 to 13 to provide a molten adhesive composition; II) applying the molten adhesive composition to the surface of the first substrate; III) bringing the applied adhesive into contact with the surface of the second substrate; and IV) chemically curing the applied adhesive with water, preferably atmospheric moisture. Claim 16 A method according to claim 15, wherein the first and / or second substrates have a transmittance in the visible light range of at least 85%, preferably at least 95%.

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