Hybrid solvent-based polyurethane adhesives

Abstract

An adhesive composition comprises a polyurethane polymer, a solvent, and a co-solvent, wherein the polyurethane polymer is a thermoplastic polyurethane having an internally and / or externally hydrophilicated molecular weight Mw of ≥50,000 g / mol as determined by gel permeation chromatography using N,N-dimethylacetamide as an eluent against a polystyrene standard, the solvent is a polar aprotic solvent such as MEK, and the co-solvent is water. The polyurethane polymer, solvent, and co-solvent are present in amounts such that they form a dispersion. The polyurethane polymer content is ≥10% by weight based on the total weight of the composition, and the weight ratio of solvent to co-solvent is ≥1:1 ​​to ≤4:1.

Description

[0001] This invention relates to an adhesive composition comprising a polyurethane polymer, a solvent, and water. The invention further relates to a method for preparing an adhesive composition, a method for bonding two surfaces, and the use of a mixture of solvent and co-solvent for dissolving a thermoplastic polyurethane polymer.

[0002] High molecular weight contact-activated and / or heat-activated solvent-based polyurethane adhesives and coatings remain widely used in DIY, footwear, wood, textiles, construction, and automotive applications. Their main advantage is their good compatibility with a wide range of substrates. Polyurethane solvent-based adhesives are typically applied uniformly to the two substrates to be bonded. A key characteristic of these adhesives is their ability to provide high initial bond strength immediately after the substrates are brought into contact under pressure. They are also known for their good mechanical properties, such as high tensile strength and elongation, as well as their elastic and tough bond lines.

[0003] The polyurethane polymers that form the basis of high molecular weight solvent-based polyurethane adhesives are primarily produced using solution polymerization. The most common solvent used in this method remains toluene, which is difficult to extract completely from polyurethane polymers that are typically supplied as dry granules. Therefore, solvent formulations of these high molecular weight polymers often still use toluene as a co-solvent. Because such materials have rather low solubility in common solvents at ambient temperatures, such as 20°C, only 10-15% by weight of the polymer solids content can typically be achieved.

[0004] Similarly, polyurethane polymers used in high molecular weight solvent-based coatings are typically produced in solvents. Common applications for these coatings are wood and textile coatings.

[0005] Other solvent systems used for polyurethanes may be based on ketones, such as acetone or methyl ethyl ketone (MEK). Mixed solvent systems may include MEK and alcohols. Adhesive formulations that are highly viscous or solid at room temperature in combination with thickeners are described in the prior art.

[0006] GB 1527596 A discloses a method for preparing a solution of a thickening film-forming polymer material in a solvent with a dielectric constant of 5.0 to 50.0, comprising reacting the solution with C at a temperature above room temperature. 8-36The alkali metal salts of fatty acids are mixed and the mixture is cooled without substantial stirring. One example discloses a composition having the following components: 20 wt% linear polyurethane, 10 wt% alkylphenol resin Alresen PA104, 40 wt% methyl ethyl ketone, 29.7 wt% ethanol, and 0.3 wt% sodium stearate. The procedure is described in the following quotation: "Methyl ethyl ketone is filled into a container equipped with a reflux condenser; the linear polyurethane is added with stirring. After about 2.5 hours, when the solution appears homogeneous, the alkylphenyl resin is added and stirring continues for 1 / 2 hour. Then, a hot solution of sodium stearate in ethanol (20°C) is slowly added with stirring and the entire mixture is heated to about 60°C. After a completely homogeneous mixture is reached, the resulting mixture is cooled."

[0007] EP 0024864 A1 relates to a synthetic rubber-based solvent adhesive for use in glue rods, wherein the adhesive comprises a solution of: (a) a linear branched-chain polyurethane rubber, (b) a carboxylated butadiene-acrylonitrile rubber containing at least 50% by weight of butadiene, and (c) a reaction product of sorbitol and benzaldehyde in a non-aqueous solvent system. The solvent system may contain at least one polar solvent selected from isobutanol, diacetone alcohol, and 2-methoxyethanol, and a second solvent selected from methyl ethyl ketone, ethyl acetone, and toluene.

[0008] US 2009 / 269589 A1 discloses an anti-blocking, radiation-curable coating system based on a high molecular weight aqueous polyurethane dispersion, a method for preparing the coating system, the use of the coating system as a paint and / or adhesive, and articles and substrates having such paints and / or adhesives.

[0009] The purpose of this invention is to provide a polyurethane solvent-based adhesive composition that, compared with conventional solvent-based adhesive compositions, exhibits good wetting behavior, good adhesive strength, and lower VOC content on polymer substrates.

[0010] This objective is achieved by the adhesive composition according to the invention. The invention also relates to methods for preparing adhesive compositions, methods for bonding two surfaces, and the use of mixtures of solvents and co-solvents for suspending thermoplastic polyurethane polymers, and advantageous embodiments thereof. These can be freely combined unless the context clearly indicates otherwise.

[0011] Therefore, an adhesive composition is provided comprising a polyurethane polymer, a solvent, and a co-solvent, wherein the polyurethane polymer is a thermoplastic polyurethane having an internally and / or externally hydrophilicated molecular weight Mw of ≥50,000 g / mol as determined by gel permeation chromatography using N,N-dimethylacetamide as an eluent and a reference polystyrene standard, the solvent is a polar aprotic solvent, the co-solvent is water, the polyurethane polymer, the solvent, and the co-solvent are present in amounts such that they form a dispersion, and the polyurethane polymer content is ≥10% by weight based on the total weight of the composition.

[0012] The polyurethane polymer preferably comprises structural units derived from aliphatic diisocyanates and / or structural units derived from polyester diols. Linear polyester polyurethanes can be prepared by reacting a) a polyester diol with a molecular weight greater than 600 g / mol and optionally b) a diol with a molecular weight of 62 to 600 g / mol as a chain extender with c) an aliphatic diisocyanate, while adhering to an equivalent ratio of hydroxyl groups of components a) and b) to isocyanate groups of component c) of 1:0.9 to 1:0.999, wherein component a) comprises, to a degree of at least 80% by weight, a polyester diol with a molecular weight of 1500 to 3000 based on (i) adipic acid and (ii) 1,4-dihydroxybutane and / or neopentyl glycol.

[0013] Further preferably, component c) comprises isophorone diisocyanate and hexamethylene diisocyanate. Also preferably, the alkanediol b) is selected from: 1,2-dihydroxyethane, 1,3-dihydroxypropane, 1,4-dihydroxybutane, 1,5-dihydroxypentane, 1,6-dihydroxyhexane, or a combination of at least two thereof, in an amount of up to 200 hydroxy equivalents based on component a).

[0014] The polyurethane may also contain urea groups and is therefore considered a polyurethane / polyurea compound.

[0015] The polyurethane can be crystalline, meaning it crystallizes at least partially after the dispersion is dried. The crystallization temperature of the polyurethane material, determined by DSC at a cooling rate of 20 K / min, can be 20 °C or higher, preferably 40 °C or higher.

[0016] Examples of suitable polar aprotic solvents include ketones such as methyl ethyl ketone or acetone, ethers such as tetrahydrofuran, carbonates such as dimethyl carbonate, and esters such as ethyl acetate. If mixtures of polar aprotic solvents are used, these mixtures are also referred to as “solvents” in the context of this invention.

[0017] Internally hydrophilic thermoplastic polyurethanes are understood to be those thermoplastic polyurethanes that contain ionic and / or nonionic hydrophilic groups via chemical bonds.

[0018] The ionic group can be cationic or anionic in nature. Compounds that act as cationic, anionic, or nonionic hydrophilic agents include those containing, for example, sulfonium, ammonium, phosphonium, carboxyl, sulfonate, or phosphonate groups, or groups that can be converted into the above groups through salt formation (potential ionic groups), or polyether groups, and those that can be incorporated into polyurethane, for example, via existing isocyanate reactive groups.

[0019] The neutralizing agent required for salt formation can be added to the salt-forming group in stoichiometric proportions or in excess. To generate anionic groups, an organic base such as a tertiary amine or an inorganic base such as an alkali metal hydroxide or ammonia is added. In this case, a tertiary amine, such as triethylamine, triethanolamine, or dimethylethanolamine, is preferred. Preferred suitable isocyanate reactive groups are hydroxyl and amine groups.

[0020] Preferred nonionic hydrophilic agents are polyoxyethylene ethers containing at least one hydroxyl or amino group. These polyethers may contain 30% to 100% by weight of units derived from ethylene oxide.

[0021] Externally hydrophilic thermoplastic polyurethanes are understood to be thermoplastic polyurethanes already combined with emulsifiers. Ionic emulsifiers, such as alkali metal salts and ammonium salts of fatty acids or aryl (alkyl)sulfonic acids, and nonionic emulsifiers, such as ethoxylated alkylbenzenes with an average molecular weight of 500 g / mol to 10000 g / mol, are suitable. Other examples of suitable emulsifiers are AB and ABA block copolymers of poly(ethylene oxide) and poly(butyl acrylate) or polyethers starting from lauryl alcohol.

[0022] The migration of emulsifiers from thermoplastic polyurethane materials into solvents and / or cosolvents is also within the scope of this invention.

[0023] A combination of internally hydrophilic thermoplastic polyurethane and external emulsifier is also feasible.

[0024] In the compositions according to the invention, the polyurethane polymer, solvent, and co-solvent are provided in amounts such that they form a dispersion. The discontinuous phase of the dispersion may comprise the polymer, and may also comprise the solvent and / or co-solvent, depending on the solvent and co-solvent system used. The continuous phase of the dispersion may comprise the solvent and / or co-solvent. For example, literature data indicates that MEK and water are a homogeneous mixture at 20°C when MEK contains 11% (mass / mass) water. Increasing the proportion of water leads to increased phase separation, such that the aqueous phase is dispersed in the solvent.

[0025] The presence of a dispersion can be assessed by visual inspection. If the composition is milky or cloudy, a dispersion is present. Conversely, if the composition is clear, no dispersion is present. Unless otherwise specified, the assessment of the presence of a dispersion should be performed at 20°C.

[0026] The weight ratio of solvent to co-solvent is ≥1∶1 to ≤4∶1. Preferably, it is ≥2∶1 to ≤3∶1.

[0027] In the compositions according to the invention, the hydroxyl content may be ≥15% by weight based on the total weight of the composition. This can be determined by titration according to DIN 53420-1. The total OH content, expressed as a weight percentage, can also be calculated from the formulation as follows:

[0028]

[0029] Where: f = number of OH groups per molecule, M OH =Molar mass of OH (17 g / mol), M 质子助溶剂 = Molar mass of proton-co-solvent (g / mol).

[0030] The total OH content [%] of the total formulation is calculated as follows:

[0031]

[0032] In the composition according to the invention, the polyurethane polymer content is ≥10% by weight based on the total weight of the composition. Preferably, it is ≥15% by weight to ≤50% by weight, and more preferably ≥20% by weight to ≤40% by weight.

[0033] The compositions according to the invention can be formulated into two-component (2K) adhesives by adding a crosslinking agent. The crosslinking agent itself can be internally or externally hydrophilic, or even used without hydrophilication. Preferably, in one embodiment, the composition further comprises an aliphatic isocyanate crosslinking agent. Examples of suitable aliphatic isocyanate crosslinking agents include pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and H... 12 -MDI isocyanate-functionalized isocyanurates, urea diketones, urea carbamates, iminooxadiazine diketones, ethyl carbamates and ureas, as well as the above-mentioned diisocyanates themselves, preferably have an isocyanate (NCO) content of ≥3% by weight, preferably ≥5% by weight, and more preferably ≥10% by weight of crosslinking agent.

[0034] The isocyanate content of the complete formulation including isocyanate is preferably ≥0.1%, more preferably ≥0.15%, and most preferably ≥0.2%.

[0035] In another embodiment, the composition has a viscosity of ≤10000 mPa s as determined by rotational viscosity at 23°C and 30 rpm according to DIN EN ISO 3219. Preferably, the viscosity is ≥10 mPa s to ≤10000 mPa s, more preferably ≥50 mPa s to ≤5000 mPa s, and most preferably ≥300 mPa s to ≤3000 mPa s.

[0036] The viscosity of this formulation is conducive to good application properties by means of, for example, brushing, spraying or roller coating.

[0037] In another embodiment, the polyurethane polymer has a storage modulus G' of ≥4 kPa, measured according to ISO 6721-10 using a plate / plate viscometer at 100°C and an angular frequency of 1 / s. Preferably, the storage modulus is ≥4 kPa to ≤1000 kPa, more preferably ≥50 kPa to ≤800 kPa, and most preferably ≥75 kPa to ≤600 kPa.

[0038] The storage modulus of polyurethane polymers contributes to adhesive properties such as tackiness and initial bond strength after solvent drying. Too low a modulus means too low an initial bond strength, while too high a modulus means insufficient wetting of the substrate and requires higher pressure during bonding, which may damage the substrate.

[0039] In another embodiment, the polyurethane polymer comprises urea groups. While not wishing to be bound by theory, it is conjectured that the solvent / co-solvent combination of the present invention can effectively disrupt the interactions between urea groups of adjacent polymer chains, thereby dissolving the polyurethane. Urea groups can be incorporated into the polyurethane via the reaction of free NCO groups with water, followed by decarboxylation. This can occur during the production of aqueous polyurethane dispersions. Other means of forming urea groups in the polyurethane include reacting free NCO groups with diamine chain extenders, monoamine chain terminators, and / or amino-functionalized internal hydrophilic agents such as sodium 2-[(2-aminoethyl)amino]ethanesulfonate (AAS salt).

[0040] The presence of urea groups in polyurethane polymers can be detected by infrared (IR) spectroscopy. Particular interest is found in the following absorption range: 1680-1620 cm⁻¹. -1 and 1584-1545cm -1 .

[0041] Preferably, the polyurethane has a thickness of 3040-2770 cm⁻¹. -1 (Asymmetric CH2 and CH3 stretching vibrations) range 1680-1620 cm⁻¹ -1 The infrared absorption ratio is ≥1.5 to ≤4 within the range. Additionally or alternatively, this polyurethane has an infrared absorption ratio of 3040-2770 cm⁻¹. -1With 1584-1545cm -1 The infrared absorption ratio is ≥5 to ≤10 within the range. Additionally or alternatively, this polyurethane has an infrared absorption ratio of 3040-2770 cm⁻¹. -1 Infrared absorption in the range of 1680-1620 cm⁻¹ -1 and 1584-1545cm -1 The ratio of the sum of infrared absorptions within the range is ≥1 to ≤3.

[0042] In another embodiment, the polyurethane polymer has been separated from the aqueous polyurethane dispersion. This has the advantage of automatically providing hydrophilic and urea groups in the polymer. Polymer separation can be achieved by freezing the dispersion, which causes the polyurethane to agglomerate into macroscopic particles. These particles can then be filtered and dried to obtain the separated polyurethane polymer.

[0043] In another embodiment, the solvent includes methyl ethyl ketone (MEK), ethyl acetate, a mixture of MEK and acetone, or a mixture of ethyl acetate and acetone. The weight ratio of MEK to water is ≥1:1 ​​to ≤4:1, preferably ≥2:1 to ≤3:1. In the mixture of MEK or ethyl acetate and acetone, their weight ratio is preferably ≥1:1 ​​to ≤3:1. The weight ratio of MEK / acetone or ethyl acetate / acetone mixture to water is ≥1:1 ​​to ≤4:1, preferably ≥1.1:1 to ≤3:1.

[0044] Preferably, the composition according to the invention has a pH range of 4.5 to 9.5, more preferably 5 to 9, and most preferably 6 to 8.5. If necessary, a suitable acid, such as hydrochloric acid, a base, such as an amine, or a buffer solution, such as phosphate buffer, can be used to adjust the pH according to the desired range.

[0045] In another embodiment, the solvent is present in an amount of ≤70% by weight based on the total weight of the composition. Preferably, the solvent is present in an amount of ≤60% by weight, and more preferably ≤50% by weight, thus contributing to the increasing industrial efforts to reduce the content of volatile organic compounds (VOCs) in their production.

[0046] A further aspect of the invention is a method for preparing an adhesive composition comprising providing a polyurethane polymer in a solvent and a cosolvent, wherein the polyurethane polymer is an internally and / or externally hydrophilic thermoplastic polyurethane having a weight-average molecular weight Mw of ≥50,000 g / mol (preferably ≥50,000 g / mol to ≤350,000 g / mol) as determined by gel permeation chromatography using N,N-dimethylacetamide as an eluent against a polystyrene standard, wherein the solvent is a polar aprotic solvent, the cosolvent is water, the polyurethane polymer, the solvent, and the cosolvent are present in amounts such that they form a dispersion, and the polyurethane polymer content is ≥10% by weight based on the total weight of the composition. The weight ratio of solvent to cosolvent is ≥1:1 ​​to ≤4:1, preferably ≥2:1 to ≤3:1.

[0047] For details, refer to the description of the compositions according to the invention. These details also apply here and will not be repeated for the sake of brevity.

[0048] In one embodiment, the method further includes adding an aliphatic isocyanate crosslinking agent. For details, refer to the description of the compositions according to the invention. These details also apply here and will not be repeated for the sake of brevity.

[0049] In another embodiment, the polyurethane polymer comprises urea groups. For details, refer to the description of the compositions according to the invention. These details also apply here and will not be repeated for the sake of brevity.

[0050] In another embodiment, the polyurethane polymer comprises structural units derived from aliphatic diisocyanates and / or structural units derived from polyester diols. For details, refer to the description of the compositions according to the invention. These details also apply here and will not be repeated for the sake of brevity.

[0051] In another embodiment, the polyurethane polymer has been separated from the aqueous polyurethane dispersion prior to its delivery. For details, refer to the description of the compositions according to the invention. These details also apply here and will not be repeated for the sake of brevity.

[0052] In another embodiment, the solvent comprises methyl ethyl ketone (MEK), ethyl acetate, a mixture of MEK and acetone, or a mixture of ethyl acetate and acetone. The weight ratio of MEK to water is ≥1:1 ​​to ≤4:1, preferably ≥2:1 to ≤3:1. In the mixture of MEK or ethyl acetate and acetone, their weight ratio is preferably ≥1:1 ​​to ≤2:1. The weight ratio of MEK / acetone or ethyl acetate / acetone mixture to water is ≥1:1 ​​to ≤4:1, preferably ≥1.1:1 to ≤3:1.

[0053] A further aspect of the invention is a method of bonding two surfaces, comprising contacting at least one surface with an adhesive composition according to the invention and bonding the two surfaces.

[0054] A further aspect of the invention is the use of a mixture of solvent and cosolvent for dispersing a thermoplastic polyurethane polymer, wherein the polyurethane polymer is an internally and / or externally hydrophilic thermoplastic polyurethane having a mass-average molecular weight Mw of ≥50,000 g / mol (preferably ≥50,000 g / mol to ≤350,000 g / mol) as determined by gel permeation chromatography using N,N-dimethylacetamide as an eluent against a polystyrene standard, wherein the solvent is a polar aprotic solvent, the cosolvent is water, and the polyurethane polymer, solvent, and cosolvent are present in amounts such that they form a dispersion. The weight ratio of solvent to cosolvent is ≥1:1 ​​to ≤4:1. Preferably ≥2:1 to ≤3:1. For details, refer to the description of the compositions according to the invention. These details also apply here and will not be repeated for brevity. It is emphasized that the polyurethane polymer content in the dispersion may be ≥10% by weight based on the total weight of the dispersion. Preferably ≥15% by weight to ≤50% by weight, and more preferably ≥20% by weight to ≤40% by weight.

[0055] In one embodiment, the solvent comprises methyl ethyl ketone or a mixture of methyl ethyl ketone and acetone. For details, refer to the description of the compositions according to the invention. These details also apply here and will not be repeated for the sake of brevity. Example

[0056] The invention will be further described with reference to the following embodiments, but it is not intended to be limited thereto.

[0057] method

[0058] The room temperature (RT) is 23°C. Unless otherwise stated, all percentages are based on weight percentages of total weight.

[0059] Viscosity is measured as rotational viscosity at 30 rpm on a Brookfield viscometer using LV 1 to 4 rotors (depending on the expected viscosity) according to DIN EN ISO 3219. For samples forming a gel, a nominal viscosity >50000 mPas is assumed.

[0060] Storage modulus (G') was measured using a plate / plate oscillating viscometer at 100°C and an angular frequency of 1 / s, according to ISO 6721-10.

[0061] The mass-average molecular weight (Mw) was determined by size exclusion gel permeation chromatography (GPC) using N,N-dimethylacetamide (DMAc) as the eluent at 60 °C. Analysis was performed at a flow rate of 1.0 mL / min on a SECucity GPC-System from PSS Polymer Service, with a PSS GRAM column equipped with a RID detector. Polystyrene samples with known molecular weights were used for calibration.

[0062] The mass loss was determined in grams per minute by recording the weight difference between a 2.0 g sample (t = 0 min) stored in a 36 mm diameter open PP container and the residual weight after storage in a fume hood at 23 °C and 30% RH for 2 minutes. The mass loss of deionized water (2.00 g) served as a reference. The measurements were repeated 5 times, and the average mass loss was found to be 0.005 g / min.

[0063] Mass loss factor (MLF) = (mass loss of sample [g / min]) / (mass loss of water [g / min])

[0064] The pH value of the formulation was assessed using universal pH test strips from Fisher Scientific.

[0065] Stability tests were performed by freezing the prepared mixture (25 mL in a 100 mL Schott glass container) at -18 °C for 60 minutes, followed by thawing and shaking (by hand for 1 minute). If no condensation was observed, the thawed sample was classified as stable.

[0066] After the samples were applied to PVC strips (containing 30% plasticizer) and PP substrates (50 μm wet) using a scraper, the wetting behavior was determined by visual inspection. Wetting behavior was classified as excellent (1): 100% to 90% coverage of the coated substrate area and no island formation observed after 10 seconds; acceptable (2): 80% to 90% coverage of the coated substrate area and no island formation observed; and poor (3): less than 80% coverage of the coated substrate area and / or island formation observed.

[0067] Material

[0068] Polyester polyurethane polymer:

[0069] Polymer A is an aliphatic, crystalline polyester polyurethane / urea supplied as a solid powder for adhesive applications. The polymer has a glass transition temperature (DSC, 20 K / min) of -50 °C, a melting temperature (DSC, 20 K / min) of 49 °C, a storage modulus of 207 kPa at 100 °C, and a molecular weight (Mw) of 144,620 g / mol. Polymer A is hydrophilic both internally and externally. Dispersion A is a commercially available aqueous dispersion of Polymer A for adhesive applications, with a solid content of approximately 50% by weight.

[0070] Polymer A was prepared from dispersion A via a three-step process: 1) 1 liter of dispersion A was frozen in a 1-liter plastic container at -18°C for 48 hours and then thawed at room temperature for 24 hours. 2) The resulting suspension of white polymer agglomerates in water was filtered to obtain a solid material with a water content of <20%. 3) The wet agglomerates were dried in a vacuum at a temperature of <40°C to a water content of <0.5%.

[0071] Polymer B is an aliphatic, crystalline polyester polyurethane / urea solid powder for adhesive applications, wherein the polymer has a glass transition temperature (DSC, 20 K / min) of -51 °C, a melting temperature (DSC, 20 K / min) of 49 °C, a storage modulus of 77.4 kPa at 100 °C, and a Mw of 91895 g / mol. Polymer B is hydrophilic both internally and externally. Dispersion B is a commercially available aqueous dispersion of Polymer B for adhesive applications, having a solid content of approximately 50% by weight. Polymer B is prepared from Dispersion B in the same manner described with respect to Polymer A / Dispersion A.

[0072] Polymer D is an aliphatic, crystalline polyester polyurethane / urea solid powder for adhesive applications, wherein the polymer has a glass transition temperature (DSC, 20 K / min) of -51 °C, a melting temperature (DSC, 20 K / min) of 49 °C, a storage modulus of 503 kPa at 100 °C, and a Mw of approximately 341210 g / mol. Polymer D is hydrophilic both internally and externally. Dispersion D is a commercially available aqueous dispersion of Polymer D for adhesive applications, having a solid content of approximately 50% by weight. Polymer D is prepared from Dispersion D in the same manner described with respect to Polymer A / Dispersion A.

[0073] Prepare hybrid solvent compositions according to the table below. Examples of the invention are marked with an asterisk (*).

[0074] Prepare hybrid solvent-based 1K adhesive formulations according to procedure a), b), or c):

[0075] a) Provide a polyurethane dispersion in a 500 mL glass screw-cap vial, then add the desired solvent mixture under magnetic stirring until a mixture is obtained.

[0076] b) In a 500 mL glass screw cap bottle, add the solid polymer to the desired solvent mixture and shake on a shaker at a rate of 160 rpm.

[0077] c) Provide the polyurethane dispersion in a 500 mL glass screw-cap vial, then add the desired solvent mixture and the desired amount of solid polymer under magnetic stirring until a mixture is obtained.

[0078] The experimental results are summarized in the table below. Embodiments of the present invention are marked with (*).

[0079]

[0080]

[0081] The experimental results show that, compared with pure aqueous systems, the hybrid adhesive composition according to the present invention exhibits better wetting behavior on low-energy surfaces such as PVC and PP.

[0082] If the adhesive composition is prepared starting from dried polyurethane material, this has the added advantage of longer material storage stability. Liquid compositions can be prepared only in the required amount and immediately before application as an adhesive.

[0083] Due to the reduced water content, a wider range of substrates can be considered for use with the compositions according to the invention. This includes substrates that would be negatively affected by purely water-based adhesives. Similarly, the composition evaporates at a higher rate than purely water-based systems.

[0084] Compared to pure solvent-based systems, the compositions according to the present invention have lower VOC (volatile organic compound) content. Compared to pure solvent-based systems, solid content and open time can be increased. Higher solid content can also translate into a greater dry film thickness of the applied adhesive.

[0085] Adhesion tests were conducted on 12*2cm PVC test strips at a plasticizer loading of 30%, using samples according to Comparative Examples 1, 2, 15, 16, 17 and all samples of the present invention.

[0086] The adhesive sample was brushed onto an 8 cm section of each substrate, which equates to approximately 0.1 mm of solid adhesive layer after drying. The strips were dried in a hot air oven at 65°C after application until the solvent and water were completely evaporated. Two still-warm strips (each treated with the same adhesive composition) were pressed together at 4 bar for 60 seconds. The bonded strips were stored at 23°C and 50% humidity for 7 days, and then subjected to a 180° peel test at 20 mm / s.

[0087] All specimens achieved a bond strength exceeding 8 N / mm, thus meeting the requirements for typical footwear applications.

Claims

1. An adhesive composition comprising a polyurethane polymer, a solvent, and a co-solvent, Its features The polyurethane polymer is a thermoplastic polyurethane with an internally and / or externally hydrophilicated molecular weight Mw of ≥ 50,000 g / mol, as determined by gel permeation chromatography using N,N-dimethylacetamide as an eluent and a reference polystyrene standard. The solvent is a polar aprotic solvent. The co-solvent is water. The polyurethane polymer, solvent, and co-solvent are present in amounts such that they form a dispersion. The polyurethane polymer content is ≥ 10% by weight based on the total weight of the composition. The solvent is present in an amount of ≤ 70% by weight based on the total weight of the composition, and The weight ratio of solvent to co-solvent is ≥ 1:1 to ≤ 4:

1. The polyurethane polymer thereon has been separated from the aqueous polyurethane dispersion.

2. The composition according to claim 1, further comprising an aliphatic isocyanate crosslinking agent.

3. The composition according to claim 1 or 2, having a viscosity of ≤ 10000 mPa·s as determined by rotational viscosity at 23°C and 30 rpm according to DIN EN ISO 3219.

4. The composition according to claim 1 or 2, wherein the polyurethane polymer has a storage modulus G' of ≥ 4 kPa as measured using a plate / plate viscometer according to ISO 6721-10 at 100°C and an angular frequency of 1 / s.

5. The composition according to claim 1 or 2, wherein the polyurethane polymer comprises a urea group.

6. The composition according to claim 1 or 2, wherein the solvent comprises methyl ethyl ketone, ethyl acetate, a mixture of methyl ethyl ketone and acetone, or a mixture of ethyl acetate and acetone.

7. A method for preparing an adhesive composition, comprising providing a polyurethane polymer in a solvent and a co-solvent, Its features The polyurethane polymer is a thermoplastic polyurethane with an internally and / or externally hydrophilicated molecular weight Mw of ≥ 50,000 g / mol, as determined by gel permeation chromatography using N,N-dimethylacetamide as an eluent and a reference polystyrene standard. The solvent is a polar aprotic solvent. The co-solvent is water. The polyurethane polymer, solvent, and co-solvent are present in amounts such that they form a dispersion. The polyurethane polymer content is ≥ 10% by weight based on the total weight of the composition. The solvent is present in an amount of ≤ 70% by weight based on the total weight of the composition, and The weight ratio of solvent to co-solvent is ≥ 1:1 to ≤ 4:

1. The polyurethane polymer thereon has been separated from the aqueous polyurethane dispersion.

8. The method of claim 7, further comprising adding an aliphatic isocyanate crosslinking agent.

9. The method according to claim 7 or 8, wherein the polyurethane polymer comprises a urea group.

10. The method according to claim 7 or 8, wherein the solvent comprises methyl ethyl ketone, ethyl acetate, a mixture of methyl ethyl ketone and acetone, or a mixture of ethyl acetate and acetone.

11. A method for bonding two surfaces, comprising: - To bring at least one surface into contact with the adhesive composition according to any one of claims 1 to 6 and - Join two surfaces.

12. Use of mixtures of solvents and co-solvents for dispersing thermoplastic polyurethane polymers. Its features The polyurethane polymer is a thermoplastic polyurethane with an internally and / or externally hydrophilicated molecular weight Mw of ≥ 50,000 g / mol, as determined by gel permeation chromatography using N,N-dimethylacetamide as an eluent and a reference polystyrene standard. The solvent is a polar aprotic solvent. The co-solvent is water. The polyurethane polymer, solvent, and co-solvent are present in amounts such that they form a dispersion. The solvent is present in an amount of ≤ 70% by weight based on the total weight of the composition comprising the polyurethane polymer, the solvent, and the cosolvent, and The weight ratio of solvent to co-solvent is ≥ 1:1 to ≤ 4:

1. The polyurethane polymer thereon has been separated from the aqueous polyurethane dispersion.

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