Two-component polyurethane hot melt adhesive with high initial and final strength

Description

[0001] The present invention relates to a process for producing bonds based on two-component polyurethane adhesives for semi-structural and structural bonds, which are applied as a melt and have a high handling strength.

[0002] Structural two-component polyurethane adhesives made from polyols and polyisocyanates have long been state-of-the-art. They cure rapidly after mixing and can therefore absorb and transfer forces within a short time. Structural adhesives, also known as construction adhesives or assembly adhesives, are used in the manufacturing industry to bond components together in such a way that the adhesive bond forms part of a permanently resilient structure. Such adhesives are typically viscoelastic and must meet high standards in terms of processability, strength, and adhesion forces.

[0003] Polyurethane adhesives made from polyols and polyisocyanates are known from the prior art. Both the polyol and polyisocyanate components are liquid at room temperature, meaning their glass transition temperatures and, where appropriate, melting points are below 23 °C. For example, applications DE 102007062529 and EP 2655466 describe liquid polyurethane adhesives composed of at least one higher-functional polyol component. This is intended to achieve high final strengths combined with high elongation. These properties are necessary, for example, for bonding wind turbine blade shells.

[0004] WO 02 / 083807 A1 describes an adhesive formulation containing a polyisocyanate in the form of an NCO-functionalized polyurethane prepolymer, as well as an OH-functional resin and a polyester polyol.

[0005] EP 0590398 A1 describes a two-component adhesive composition containing a polyester, another polyol with a functionality greater than 2, and NCO-functional polyurethane prepolymer.

[0006] WO 91 / 15530 A1 discloses two-component adhesive compositions for reactive hot melt adhesives. In addition to an NCO-functional prepolymer, the composition comprises a polyester polyol that is solid at room temperature.

[0007] WO 94 / 12552 A1 discloses a one-component reactive hot melt adhesive which is obtained by initially introducing a mixture of a polyether glycol and a polyester polyol which is solid at room temperature and then adding MDI and reacting it.

[0008] Liquid two-component polyurethane adhesives are also described in applications WO2009 / 015149, EP 2706075, and EP 2700666. These structural adhesives are said to exhibit good metal and plastic adhesion, a uniform modulus of elasticity over a wide temperature range, and are suitable for bonding in the automotive sector.

[0009] The disadvantage of the systems described above is a comparatively low handling strength immediately after joining the substrates. However, high initial or handling strength is necessary to enable high cycle times in production. For sufficient handling strength, a tensile shear strength of at least 0.3 MPa is required before the fixations can be released (A. Lutz, S. Schmatloch, "Structural Bonding of Fiber Composites in Vehicle Construction," lightweight design, March 2014).

[0010] In state-of-the-art liquid two-component polyurethane systems, the cohesion of the adhesive bond is achieved solely through chemical crosslinking of the polyol component with the polyisocyanate component and is therefore dependent on the reaction progress. Therefore, the adhesive bonds are not yet mechanically resilient immediately after application, and the substrates may shift relative to each other. Typical curing times until handling strength is reached are between 40 minutes and 6 hours (see A. Lutz, S. Schmatloch, "Structural Bonding of Fiber Composites in Vehicle Construction," lightweight design, March 2014).

[0011] Curing can be accelerated by adding catalysts. In addition to the well-known tin-containing systems, EP 2706075, for example, describes a metal chelate complex that enables rapid and bubble-free curing. However, crosslinking and thus handling strength are highly dependent on the choice of catalyst and the correct dosage.

[0012] To enable rapid further processing, the bonds are pre-cured using two-component adhesives that are liquid at room temperature, either over a large area or in specific areas, using thermal processes such as infrared heating or induction at temperatures between approximately 60 and 120 °C. The disadvantage of this process is an additional processing step.

[0013] The object of the present invention is therefore to provide an improved two-component (semi-)structural adhesive.

[0014] Surprisingly, it can be demonstrated within the scope of the present invention that formulations according to the present invention fulfill this complex task. In contrast to the prior art, the formulation used according to the invention contains not only liquid components, but also constituents that are solid at room temperature in one or both components. This means that at least one component has a melting point and / or a glass transition point above 23°C.

[0015] The adhesives of the present invention possess not only high final strength and elongation, but also good handling strength after bonding. In the context of the present invention, handling strength refers to the necessary bond strength to allow bonded substrates to be subjected to further processing without additional mechanical fixation. Furthermore, the use of catalysts or thermal pre-reactions after application can be omitted. This allows for short cycle times during the joining process, and the susceptibility to errors during dispensing can be minimized.

[0016] A first subject of the present invention is a process for producing bonds based on two-component polyurethane adhesives comprising a first component A containing at least one polyester A1 which is solid at room temperature and at least one polyol A2 having a hydroxyl group functionality greater than 2.0 and optionally additives and a second component B containing polyurethane prepolymers containing isocyanate groups and optionally additives, comprising the separate melting of the A and B components depending on the melt viscosity to temperatures above the melting and / or glass transition points of all constituents in both components, mixing the two liquid components A and B and subsequent application to the substrates to be bonded.

[0017] The A component of the polyurethane adhesives consists of a mixture of a polyester A1, which is solid at room temperature, and at least one polyol A2 with a hydroxyl group functionality greater than 2.0.

[0018] The polyesters A1 used in the invention are solid at room temperature, i.e., the glass transition temperature and / or melting point of A1 are above room temperature of 23 °C. The polyesters A1 can be either amorphous or crystalline. The glass transition point and melting point are determined using the DSC method according to DIN 53765.

[0019] Polyesters A1 can be produced by polycondensation of di- or polyols and di- or polycarboxylic acids or their derivatives. In principle, there are no restrictions on the monomers used in the synthesis of the polyesters. Polyester A1 is preferably based on di- or polycarboxylic acids selected from succinic acid, adipic acid, sebacic acid, dodecanedioic acid, terephthalic acid, isophthalic acid, phthalic acid, and hexahydrophthalic acid, and on di- or polyols selected from ethylene glycol, neopentyl glycol, neopentyl glycol hydroxypivalate, 1,4-butanediol, butylethylbutanediol, cyclohexanedimethanol, and 1,6-hexanediol.

[0020] In the context of the present invention, di- or polycarboxylic acids or their derivatives are understood to mean in particular the acids and their anhydrides.

[0021] Polyesters with a glass transition point above 23 °C are preferably obtained from aromatic di- or polycarboxylic acids such as terephthalic acid and isophthalic acid; there are no preferred monomers with respect to the diol. Polyesters with a melting point above 23 °C are preferably obtained from linear aliphatic di- or polycarboxylic acids, such as succinic acid, adipic acid, sebacic acid, and dodecanedioic acid, or terephthalic acid and linear aliphatic diols, such as 1,4-butanediol and 1,6-hexanediol.

[0022] Polycarboxylic acids and polyols with higher functionalities can also be used. Mixtures of different polyesters A1 can be used within the scope of the present invention.

[0023] The polyesters A1 preferably have a functionality of at least one hydroxyl end group. Polyesters A1 preferably have a functionality between 1.0 and 3.0, with hydroxyl functionalities of 2.0 being particularly preferred. The hydroxyl functionality of the polyester is controlled by the functionalities of the diols or polyols and dicarboxylic or polycarboxylic acids used.

[0024] The number-average molecular weight of polyester A1 is 100–10,000 g / mol, preferably 1,000–5,000 g / mol. It is determined according to DIN 55672-1 using gel permeation chromatography in tetrahydrofuran as eluent and polystyrene for calibration.

[0025] Depending on the functionality and molecular weight of the polyols, the concentration of hydroxyl end groups is between 10 and 500 mg KOH / g, preferably between 20 and 50 mg KOH / g, determined titrimetrically according to DIN 53240-2. The concentration of acid end groups, determined according to DIN EN ISO 2114, is below 2 mg KOH / g, preferably below 1 mg KOH / g.

[0026] Polyol A2 can be amorphous or crystalline and solid or liquid at room temperature. Polyol A2 can also be a mixture of different polyols; it is essential that at least one polyol in the mixture A2 has a hydroxyl group functionality greater than 2.0.

[0027] The polyol A2 or polyol mixture A2 used according to the invention has a functionality of more than two hydroxyl end groups. Functionalities between 2.1 and 5 are preferred; the hydroxyl group functionality of polyol A2 is particularly preferably 3.0.

[0028] The polyol or polyol mixture A2 used according to the invention can be any known polyol, for example polyethers, polyacrylates, polycarbonates or hydroxy-terminated polyolefins or polyesters.

[0029] In the case of polyethers, these are preferably polyethylene glycols, polypropylene glycols, polytetrahydrofuran or copolymers thereof.

[0030] In the case of polyacrylates, these are preferably polyacrylates which have at least one hydroxy functionality and are accessible by free radical polymerization of acrylates or methacrylates, such as methyl methacrylate, butyl methacrylate, hydroxyethyl acrylate or hydroxyethyl methacrylate

[0031] In the case of polycarbonates, these are preferably reaction products of dialkyl or diaryl carbonates, such as dimethyl carbonate or diphenyl carbonate, and linear aliphatic diols, such as 1,5-pentanediol or 1,6-hexanediol.

[0032] In the case of hydroxy-terminated polyolefins, these are preferably polybutadienes, which are prepared via radical polymerization of butadiene with hydrogen peroxide as initiator.

[0033] Polyol A2 is preferably a polyester or a mixture of polyesters produced by polycondensation of di- or polyols and di- or polycarboxylic acids or their derivatives. Particularly preferred monomers are the dicarboxylic acids adipic acid, isophthalic acid, and terephthalic acid, and trimellitic anhydride is the trifunctional carboxylic acid. Ethylene glycol, neopentyl glycol, 1,6-hexanediol, and trimethylolpropane are particularly suitable polyols. However, the monomers can also be any other known di- or polycarboxylic acids and di- or polyols.

[0034] The hydroxyl group functionality of the polyester is determined by the functionalities of the monomers used. To achieve a hydroxyl group functionality of the polyester greater than 2.0, the average functionality of the di- or polyols must exceed the average functionality of the di- or polycarboxylic acids. This is achieved, for example, when only dicarboxylic acids but a mixture of bi- and trifunctional polyols are used as monomers.

[0035] The number-average molecular weight of polyol A2 or the components of the polyol mixture is 100 - 10 000 g / mol, preferably 500 - 3000 g / mol, determined according to DIN 55672-1 by gel permeation chromatography in tetrahydrofuran as eluent and polystyrene for calibration.

[0036] Depending on the functionality and molecular weight of the polyols, the concentration of hydroxyl end groups is between 10 and 500 mg KOH / g, preferably between 50 and 150 mg KOH / g, determined titrimetrically according to DIN 53240-2.

[0037] The concentration of acid end groups, determined according to DIN EN ISO 2114, is below 5 mg KOH / g, preferably below 2 mg KOH / g and particularly preferably below 1 mg KOH / g.

[0038] There are no restrictions regarding the glass transition temperature and melting point for Polyol A2 or the polyols used in the mixtures, i.e. Polyol A2 or the polyols can be solid or liquid.

[0039] The weight ratio between polyester A1 and polyol A2 is between 1:9 and 9:1, preferably between 1:5 and 5:1 and most preferably between 1:2 and 2:1.

[0040] The second component B of the two-component polyurethane adhesive consists of polyurethane prepolymers containing isocyanate groups. The latter consist primarily of the reaction product of at least one polyol with an excess of polyisocyanates. A mixture of different polyols is preferably used.

[0041] The polyol or polyol mixture of component B can be any known polyol, for example polyethers, polyacrylates, polycarbonates, hydroxy-terminated polyolefins or polyesters.

[0042] Polyesters or mixtures of polyesters are preferably used as polyols for the preparation of component B. The polyesters used are produced by polycondensation of di- or polyols and di- or polycarboxylic acids or their derivatives. Particularly preferred monomers are the dicarboxylic acids adipic acid, isophthalic acid, and terephthalic acid, and the trifunctional carboxylic acid trimellitic anhydride. Ethylene glycol, neopentyl glycol, hydroxypivalic acid neopentyl glycol, 1,6-hexanediol, and trimethylolpropane are particularly suitable polyols. However, the monomers can also be any other known di- or polycarboxylic acids and di- or polyols.

[0043] The polyol used in component B or the components of the polyol mixture used have a functionality of at least one hydroxyl end group. Functionalities between 1 and 5 are preferred, particularly between 2 and 3.

[0044] The number-average molecular weight of the polyols used in component B is 100–20,000 g / mol, preferably 500–5,000 g / mol. Depending on the functionality and molecular weight of the polyols, the concentration of hydroxyl end groups is between 10 and 500 mg KOH / g, preferably between 20 and 150 mg KOH / g, determined titrimetrically according to DIN 53240-2. The concentration of acid end groups, determined according to DIN EN ISO 2114, is below 5, preferably below 2 mg KOH / g, and particularly preferably below 1 mg KOH / g. There are no restrictions regarding the glass transition temperature and melting point of the polyols used in component B.

[0045] The aforementioned polyols or polyblends must be reacted with polyurethane prepolymers containing isocyanate groups for use as component B. For this purpose, the polyol or polyol blend is reacted with an excess of polyisocyanates at temperatures up to 170 °C, preferably between 80 and 130 °C, depending on the viscosity of the respective formulation. The polyisocyanates used have an isocyanate functionality of at least 2.0.

[0046] Di- or multifunctional, aromatic, aliphatic, or cycloaliphatic isocyanates, as well as carbodiimide-modified isocyanates or isocyanate-terminated prepolymers, can be used as polyisocyanates. Examples of suitable polyisocyanates are 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, toluene diisocyanate isomers, isophorone diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and mixtures thereof. Aromatic polyisocyanates are particularly preferred, with particular preference being given to 4,4'-diphenylmethane diisocyanate and mixtures of 4,4'-diphenylmethane diisocyanate and 2,4'-diphenylmethane diisocyanate.

[0047] The OH:NCO ratio of the polyols, based on all polyols in both component A and component B of the adhesive formulation, to the polyisocyanate used to produce component B is 1:0.8 to 1:3, preferably 1:1.0 to 1:1.5, and particularly preferably 1:1.1. To avoid side reactions with residual moisture, the polyol or polyol mixture is degassed at reduced pressure before reacting with the isocyanate. Component B must be stored under inert conditions for the same reasons.

[0048] Furthermore, additional additives can also be used in component B. Suitable additives for component A and / or B include fillers, rheology modifiers, pigments or dyes, non-functionalized polymers, flame retardants, tackifiers, waxes, plasticizers, drying agents, adhesion promoters, fibers, latent hardeners, hydrolysis stabilizers, anti-aging agents, and auxiliaries. Catalysts may also be included, but these are not mandatory.

[0049] These can include rheology modifiers such as Aerosil®; non-functionalized polymers, e.g., thermoplastic polyurethanes (TPU) and / or polyacrylates and / or ethylene-vinyl acetate copolymers (EVA); pigments or fillers, e.g., talc, silicon dioxide, titanium dioxide, barium sulfate, calcium carbonate, carbon black, or colored pigments; external flame retardants; tackifiers such as rosin resins, hydrocarbon resins, phenolic resins, waxes, plasticizers, drying agents, adhesion promoters, fibers, latent hardeners, hydrolysis stabilizers, as well as anti-aging agents and auxiliaries. Rheology modifiers, especially lampblack, talc, and chalk, are preferred.

[0050] The total proportion of additives in each component is 0 to 50 wt.%, preferably 5 to 30 wt.%.

[0051] Components A and B are stored separately until the two-component polyurethane adhesive is used according to the invention. Both components can generally be stored for several weeks at room temperature and in the absence of moisture.

[0052] Another object of the present invention is the use of the two-component polyurethane adhesives for producing bonds.

[0053] The two-component polyurethane adhesive is applied as a melt at temperatures above room temperature and is characterized by high initial strength and good final strength combined with high elongation. The adhesive thus meets the requirements for bonded joints with short cycle times, enabling rapid further processing while withstanding high mechanical loads.

[0054] The process according to the invention for producing bonds based on two-component polyurethane adhesives comprises the separate melting of the A and B components, depending on the melt viscosity, to temperatures above the melting and / or glass transition points of all constituents in both components, preferably at least 70 °C; mixing the two liquid components A and B, and subsequent application to the substrates to be bonded.

[0055] After melting components A and B, they are mixed as a melt and the resulting adhesive formulation is applied directly to the substrates to be bonded without further storage.

[0056] The two liquid components A and B are mixed together in a mixing ratio of between 1:3 and 3:1, preferably between 1:2 and 2:1, and particularly preferably 1:1 by volume. The ingredients, in particular the additives in components A and B, are selected so that both components have similar viscosities and can be mixed well. Mixing can be carried out dynamically or statically. The two components are preferably processed from heatable cartridges using a manual or pneumatic gun and a static mixer. The two components can also be filled into larger containers such as drums or hobbocks and, before processing, melted and dosed and mixed using pumping systems in suitable melting systems, for example heatable drum melting systems.The hot melt adhesive is applied to the substrate as a melt shortly after mixing the components and is bonded to a second substrate by briefly pressing it on within the open time.

[0057] There are basically no restrictions on the application of the two-component hot melt adhesive. It is particularly suitable for bonding applications where sufficient handling strength must be achieved quickly, for example, to enable short cycle times.

[0058] The adhesion can be adjusted for a wide range of substrates using the polyols used. Examples of possible substrates include metals such as steel or aluminum; plastics such as polyamide, polycarbonate, polyethylene terephthalate, or ABS; especially fiber-reinforced plastics (FRPs) such as carbon fiber- or glass fiber-reinforced polyesters or epoxies (CFRP and GFRP); and sheet molding compounds (SMC); as well as wood, glass, glass ceramics, concrete, mortar, bricks, and stones.

[0059] The advantage of the described application process using the two-component polyurethane adhesive is improved handling strength compared to the prior art due to a faster build-up of cohesion. Immediately after application, the cooling of the melt initially leads to physical setting through crystallization and / or solidification of the polymers below their melting point and / or glass transition point. Significantly earlier than chemical crosslinking, thermoplastic physical setting enables the adhesive to achieve high handling strength after a short time and thus rapid further processing of the bonded substrates. The addition of catalysts is therefore not necessary, as the setting behavior is controlled by the physical properties of the polyols and polyisocyanates. Chemical, irreversible curing takes place in a parallel, but significantly slower, step.This creates a stable polyurethane network that ensures high final strength.

[0060] The application process for a two-component polyurethane hot melt adhesive on which the present invention is based is described in WO89 / 01503. However, the chemical composition of the components used there is not further specified; in the examples, an epoxy resin with secondary hydroxyl groups is mentioned as the polyol component. In particular, the functionality of the components used, which is important for the invention, is not discussed in detail in the prior art. However, this is crucial for developing sufficient final strength that meets the requirements of a semi-structural or structural adhesive. Within the scope of the present invention, it is shown that the properties of the adhesive can be specifically adjusted by mixing bifunctional and higher-functional polyols in component A, resulting in sufficient final strength with simultaneous high elongation.This requires a suitable combination of the individual polyols in the mixture: At least one component A1 of component A must have a glass transition temperature and / or a melting point above room temperature of 23 °C to achieve sufficient handling strength. Furthermore, at least one other component A2 of component A must have a hydroxyl group functionality greater than two to achieve a sufficiently high crosslinking density and thus cohesion.

[0061] In particular, the process according to the invention is suitable for producing bonds based on two-component polyurethane adhesives for the (semi-)structural bonding of temperature-sensitive carbon fiber reinforced composite materials.

[0062] The type and scope of bonding are not limited. Bonding is particularly common in the automotive and transportation sectors, the construction industry, and the woodworking industry.

[0063] The cured hot melt adhesive has a tensile strength of more than 5 MPa, preferably more than 10 MPa, and an elongation at break of more than 100%, preferably more than 150%, at 23 °C.

[0064] The determination of tensile strength and elongation at break is carried out according to DIN 53504 / DIN EN ISO 527 at a speed of 100 mm / min on a 2 mm thick sample that was conditioned for 7 days at 20 °C and 65% relative humidity.

[0065] The cured hot melt adhesive has a tensile shear strength at 23 °C of more than 5 MPa, preferably more than 10 MPa at an adhesive thickness of 2 mm. The tensile shear strength is determined according to DIN EN 1465 at a speed of 12 mm / min.

[0066] The handling strength of 0.3 MPa is reached after 60 minutes at the latest, preferably after 30 minutes at the latest, and most preferably after 15 minutes at the latest. Handling strength refers to the bond strength required to allow bonded substrates to be subjected to further processing without additional mechanical fixation. Handling strength is determined using the tensile shear strength according to DIN EN 1465.

[0067] Even without further elaboration, it is assumed that a person skilled in the art can utilize the above description to the fullest extent possible. The preferred embodiments and examples are therefore to be construed merely as descriptive and not as limiting disclosures in any way. The present invention is explained in more detail below using examples. Alternative embodiments of the present invention are obtainable in an analogous manner. Examples:

[0068] In the examples, the following polyesters are used as polyols: P1 is a room temperature solid, non-crystalline polyester made of C2, C5 and C10 diols and adipic acid, terephthalic acid and isophthalic acid with an OH number of 50 mg KOH / g.

[0069] P2 is a crystalline polyester made from adipic acid and hexanediol, solid at room temperature, with an OH number of 50 mg KOH / g.

[0070] P3 is a room temperature liquid polyester made of C2 and C5 diols and adipic acid, terephthalic acid and isophthalic acid with an OH number of 100 mg KOH / g.

[0071] P4 is a room-temperature solid, non-crystalline polyester made from C2 and C5 diols, terephthalic acid, and isophthalic acid with an OH number of 70 mg KOH / g. P5 is a room-temperature solid, crystalline polyester made from adipic acid and hexanediol with an OH number of 30 mg KOH / g.

[0072] General manufacturing instructions for component A: The quantities of polyesters P1, P2 and P3 specified in Table 1 are melted in a flat-ground flask, homogenized for 30 minutes at 130 °C and filled without bubbles.

[0073] The fillers are incorporated in a Speedmixer (Speedmixer™< DAC 150 from Flack Tek Inc.) under exclusion of atmospheric moisture. The polyol mixture is melted, the weights of lamp black, Aerosil, and talc specified in Table 1 are added, and the mixture is homogenized for 5 minutes at 90 °C and 3000 rpm. The mixture is then filled into a cartridge. Alternatively, the fillers can be incorporated in a Dispermat. The mixture is then briefly degassed to prevent bubbles.

[0074] General preparation instructions for component B: In a flat-ground flask, melt the amounts of dried polyesters P1, P2, and P3 specified in Table 1 to 130 °C. Then, add the amount of 4,4'-diphenylmethane diisocyanate (MDI) specified in Table 1 and rapidly homogenize. Stir for 30 minutes at 130 °C under a protective gas atmosphere to ensure complete reaction of the reactants.

[0075] The isocyanate-containing prepolymer is then filled into moisture-proof cartridges without bubbles.

[0076] The fillers are incorporated in a Speedmixer (Speedmixer™< DAAC 150 from Flack Tek Inc.) under atmospheric humidity. The prepolymer is melted, the weights of talc and chalk specified in the table are added, and the mixture is homogenized for 5 minutes at 90 °C and 3000 rpm. The mixture is then filled into a moisture-proof cartridge.

[0077] Alternatively, the fillers can be incorporated in a dispersant. The mixture is then briefly degassed to prevent bubbles. Table 1: Production of the individual components in the Speedmixer (Example 1) and in the Dispermat (Example 2) A component OH functionality Tg [°C] T m [°C] OH number [mg KOH / g] Sample weight [g] A1 P1 2 24 - 50 12,5 A1 P2 2 -65 54 50 7,5 A2 P3 3 -29 - 100 40 Flame soot 101 1)< 0,6 Aerosil ®< R 202 2)< 1,2 Finntalc M 15 3)< 6,0 B component OH functionality Tg [°C] T m [°C] OH number [mg KOH / g] Sample weight [g] B1 P1 2 25 - 50 12,5 B1 P2 2 -65 54 50 17,5 B2 P3 3 -30 - 100 10 4.4' - MDI 4)< 18,4 Finntalc M 15 3)< 5,8 Chalk Omyabond 520-OM 6)< 23,6 1) Carbon black from Orion Engineered Carbons 2) Silica-based thixotropic agent from Evonik Industries AG 3) Magnesium silicate from Mondo Minerals 4) 4,4'-diphenylmethane diisocyanate, e.g. Lupranat ME from BASF 5) Calcium carbonate from Qmya AG Table 2: Preparation of the individual components in the Speedmixer (Example 3) and in the Dispermat (Example 4) A component OH functionality Tg [°C] T m [°C] OH number [mg KOH / g] Sample weight [g] A1 P4 2 20 - 70 10 A1 P5 2 -60 55 30 9 A2 P3 3 -29 - 100 40 Flame soot 101 0,6 Aerosil R 202 1,2 Finntalc M 15 5,9 B component OH functionality Tg [°C] T m [°C] OH number [mg KOH / g] Sample weight [g] B1 P4 2 20 - 70 10 B1 P5 2 -60 55 30 21 B2 P3 3 -30 100 10 4.4'- MDI 17,9 Finntalc M 15 5,9 Chalk Omyabond 520-OM 23,4 Application of two-component polyurethane adhesives using a static mixer

[0078] Components A and B are stored separately and melted at 90 °C prior to use. Both cartridges are the same size to ensure a 1:1 mixing ratio. The cartridges, heated to 90 °C, are plugged together. A static mixer (Sulzer MCH 13-24), also heated to 90 °C, is screwed on and inserted into a cartridge gun. The pressure applied to the cartridge gun forces the individual components through the static mixer and mixes them by pulling the gun trigger. To ensure thorough mixing of the two components, the first strand discharged from the length of the static mixer is discarded.

[0079] The mixed adhesive is applied to the substrates to be bonded within the open time and characterized. The adhesive line of the uncured adhesive is 2 mm. The resulting adhesive properties are summarized in Table 3. Table 3: Adhesive properties Example 1 Example 2 Example 3 Example 4 Open time [s] 510 590 200 210 Setting time [s] 480 450 180 180 Handling strength [min] 30 30 10 10 Tensile strength [N / mm 2 ] 15 12 19 16 Elongation at break [%] 240 200 190 170 Lap shear strength PC [MPa] 10 10 10 9 Tensile shear strength CFRP [MPa] 11 9 12 10

[0080] To determine the open time, paper strips are pressed onto the adhesive bead at 30-second intervals. Once the surface of the adhesive bead is tack-free, the paper strips are removed. The open time corresponds to the time interval at which the paper strip can be removed without fiber tearing.

[0081] Setting time is the time required for two 100 mm long, 20 mm wide, and 5 mm thick wooden substrates bonded together in a T-shape to reach a strength at which they can no longer be separated by a 2 kg load. The bonded area is 400 mm².

[0082] To create the bond, the adhesive is applied to the surface of the first substrate to be bonded in a layer thickness of 2 mm and bonded to the counter substrate in the shape of a "T." The long leg is then loaded with a 2 kg weight at intervals of 30 seconds.

[0083] The setting time is the time at which the weight is suspended, the load of which the bond has withstood.

[0084] To determine the tensile strength and elongation at break, a 2 mm thick film is produced from the adhesive mass. After a storage period of 7 days at 20 °C and 65 % relative humidity, dumbbell-shaped specimens with a length of 80 mm, a web length of 30 mm, and a web width of 4 mm are punched out according to DIN EN 53504 and pulled to break using a tensile testing machine at 23 + / - 2 °C at a speed of 100 mm / minute. The tensile strength is determined from the ratio of the measured maximum force to the initial cross-section of the specimen. The elongation at break is the quotient of the

[0085] Change in length compared to the original length in percent.

[0086] Tensile shear strengths are determined on single-cut overlapped bonds in accordance with DIN EN 1465 using a tensile testing machine at a speed of 12 mm / minute at a temperature of 23 + / - 2 °C until the bond breaks. The polycarbonate (PC) substrates to be bonded are cleaned with isopropanol. The peel ply of the carbon fiber-reinforced plastic (CFRP) substrates based on an epoxy resin matrix is ​​removed. No further pretreatment is performed.

[0087] The adhesive thickness is 2 mm. The bonded area is 300 mm².

[0088] The bonds were stored for 7 days at 20 °C and 65% relative humidity prior to testing. The fracture pattern was cohesive in each case.

[0089] When determining the handling strength, the point in time after joining the CFRP substrates at which the tensile shear strength is 0.3 MPa is determined.

Claims

1. Method for producing adhesive bonds based on two-pack polyurethane adhesives comprising a first pack A containing at least one polyester A1 which is solid at room temperature and at least one polyol A2 having a hydroxyl group functionality greater than 2.0 and optionally additives, and a second pack B containing polyurethane prepolymers having isocyanate groups and optionally additives, comprising the separate melting of the A and B packs, depending on the melt viscosity, at temperatures above the melting points and / or glass transition points of all the constituents in the two packs, mixing of the two liquid packs A and B and subsequent application to the substrates to be bonded.

2. Method according to Claim 1, characterized in that the polyesters A1 have a functionality of at least one hydroxyl end group.

3. Method according to Claim 1 or 2, characterized in that the glass transition temperature and / or the melting point of A1, determined by the DSC method according to DIN 53765, is above 23°C.

4. Method according to one or more of Claims 1 to 3, characterized in that the polyol A2 comprises polyethers, polyacrylates, polycarbonates or hydroxyl-terminated polyolefins or polyesters.

5. Method according to one or more of Claims 1 to 4, characterized in that the polyol A2 comprises polyesters.

6. Method according to one or more of Claims 1 to 5, characterized in that the polyurethane prepolymers having isocyanate groups consist of the reaction product of at least one polyol with an excess of polyisocyanates.

7. Method according to Claim 6, characterized in that the polyisocyanates used are di- or multifunctional, aromatic, aliphatic or cycloaliphatic isocyanates, and carbodiimide-modified isocyanates or isocyanate-terminated prepolymers.

8. Method according to one or more of Claims 1 to 7, characterized in that the additives for pack A and / or B are selected from the group comprising fillers, rheology modifiers, pigments or dyes, nonfunctionalized polymers, flame retardants, tackifiers, waxes, plasticizers, desiccants, adhesion promoters, fibres, latent hardeners, hydrolysis stabilizers, and ageing stabilizers and auxiliaries.

9. Method according to any of Claims 1 to 8, characterized in that the adhesive bonds are in the automotive and transport sector, in the construction industry and in the wood processing industry.

10. Method according to any of Claims 1 to 9, characterized in that the two liquid packs A and B are mixed with one another in a mixing ratio between 1:9 and 9:1 per cent by volume.