Nonionic hydrophilic crosslinking agent dispersion with thermally latently bonded urethane / urea groups

Abstract

This invention relates to a method for preparing at least one blocked polyisocyanate, comprising the steps of: (A) reacting at least one polyisocyanate with at least one thermally degradable blocking agent to obtain at least one partially blocked polyisocyanate; (B) reacting the at least one partially blocked polyisocyanate from step (A) with at least one nonionic hydrophilic agent to obtain an intermediate; and (C) reacting the intermediate obtained in step (B) with at least one thermally degradable blocking agent to obtain the at least one blocked polyisocyanate, relating to blocked polyisocyanates obtained in a corresponding manner for use in the production of coatings, adhesives, sealants or elastomers, the corresponding coatings, adhesives, sealants or elastomers, and substrates with coatings obtainable using the at least one blocked polyisocyanate of the present invention.

Description

[0001] This invention relates to a method for preparing at least one blocked polyisocyanate, comprising the following steps: (A) reacting at least one polyisocyanate with at least one heat-removable blocker to obtain at least one partially blocked polyisocyanate; (B) reacting the at least one partially blocked polyisocyanate from step (A) with at least one nonionic hydrophilic agent to obtain an intermediate; and (C) reacting the intermediate obtained in step (B) with at least one heat-removable blocker to obtain the at least one blocked polyisocyanate, wherein the blocked polyisocyanate is used in the production of coatings, adhesives, sealants or elastomers, and the corresponding coatings, adhesives, sealants or elastomers, and substrates with coatings obtainable using the at least one blocked polyisocyanate of the present invention.

[0002] In recent years, the importance of water-based paints and coatings has increased significantly due to increasingly stringent emission guidelines regarding solvents released during paint application. Although water-based paint systems are now available for many applications, they often do not reach the high quality levels of conventional solvent-based paints in terms of solvent and chemical stability, or elasticity and mechanical load-bearing capacity.

[0003] Waterborne paint systems based on waterborne polyurethane dispersions often still contain a significant amount of solvent. It is generally impossible to avoid these solvents in polyurethane dispersions because the production of the corresponding dispersions from prepolymers typically requires solvents, or so-called co-solvents (coalescing agents) must usually be added to the dispersion to achieve a lower minimum film-forming temperature. This ensures that a sufficiently hard layer is formed at or below room temperature during coating film formation. Polyurethane dispersions and paint formulations also often lack storage stability in the absence of solvents.

[0004] For example, the solvent NMP (N-methylpyrrolidone) is still sometimes used in the fields of aqueous dispersions and paints. One example is the carboxylic acid hydrophilic polyisocyanate crosslinking agent dispersion with dimethylpyrazole blocked isocyanate groups described in EP-A 0 942 023. These crosslinking agent dispersions and paints made from them contain NMP as a cosolvent.

[0005] Due to viscosity, it is not possible to produce the DMP-blocked polyisocyanate crosslinking agent described in EP-A 0 942 023 without a co-solvent by omitting the solvent.

[0006] The nonionic hydrophilic polyisocyanate crosslinking agent dispersion with pyrazole-blocked isocyanate groups described in WO 1997 / 012924 contains approximately 7% by weight butylethylene glycol as a co-solvent. Similar to NMP, it is characterized by a relatively high boiling point. Separating it for the purpose of producing a solvent-free aqueous dispersion is not feasible.

[0007] DE 19914885 describes polyurethane dispersions with dimethylpyrazole-blocked isocyanate groups for use in the production of glass fiber adhesives. These dispersions are made using an organic solvent, which is then removed from the dispersion by distillation after dispersion in water.

[0008] DE 3613492 describes an acetone process for producing solvent-free polyurethane-polyurea dispersions. In this process, the unblocked prepolymer is prepared as a 20 to 50% by weight solution in a volatile organic solvent, such as acetone, and the solvent is removed by distillation after dispersion in water.

[0009] For example, in DE 19914885, 50% or 62% by weight of acetone is used to replace NMP in the method according to EP-A 0 942 023 to obtain DMP-blocked polyisocyanate crosslinking agents, but these lack storage stability.

[0010] DE 10 2006 025313 A1 discloses a method for preparing solvent-free aqueous polyurethane crosslinking agent dispersions having pyrazole-blocked isocyanate groups. This method yields blocked polyisocyanates, wherein the polyisocyanate is reacted with a heat-removable blocking agent, followed by a reaction with a hydroxycarboxylic acid and a di- or polyfunctional chain extender. The aqueous dispersions thus obtained have good usability for producing solvent-resistant baking varnishes, but exhibit limited stability in some formulations.

[0011] Therefore, the object of the present invention is to provide a method for preparing blocked polyisocyanates and aqueous dispersions containing blocked polyisocyanates, which avoids the disadvantages of prior art methods and has the potential to obtain aqueous dispersions with particularly high storage stability and applicable to the widest possible range of formulations.

[0012] These objectives are achieved by the method of the present invention for preparing at least one blocked polyisocyanate, the method comprising the following steps:

[0013] (A) Reacting at least one polyisocyanate with at least one heat-removable blocking agent to obtain at least one partially blocked polyisocyanate.

[0014] (B) React the at least one partially blocked polyisocyanate from step (A) with at least one nonionic hydrophilizing agent to obtain an intermediate.

[0015] (C) React the intermediate obtained in step (B) with at least one heat-removable blocking agent to obtain the at least one blocked polyisocyanate.

[0016] These objectives are also achieved by the blocked polyisocyanates of the present invention obtainable by the method of the present invention.

[0017] These objectives are also achieved through the use of the blocked polyisocyanates of the present invention in the production of coatings, adhesives, sealants or elastomers.

[0018] These objectives are also achieved by coatings, adhesives, sealants, or elastomers of the present invention that contain at least one of the closed-type polyisocyanates of the present invention.

[0019] These objectives are also achieved by the substrate of the present invention having a coating available using at least one of the blocked polyisocyanates of the present invention.

[0020] This invention relates to a method for preparing at least one blocked polyisocyanate as described above. The various steps of the method of this invention are described in detail below. The method steps of this invention are preferably performed in the order of (A), followed by (B), followed by (C), and optionally followed by (D).

[0021] Step (A) of the method of the present invention includes reacting at least one polyisocyanate with at least one heat-removable blocking agent to obtain at least one partially blocked polyisocyanate.

[0022] According to the present invention, at least one polyisocyanate is used. According to the present invention, a substantially uniform polyisocyanate is preferred. According to the present invention, a mixture comprising two, three, or more different polyisocyanates may also be used.

[0023] The suitable polyisocyanates used according to the invention can be NCO functional compounds known to those skilled in the art, preferably having a functionality of 2 or greater. According to the invention, these preferences are aliphatic, alicyclic, aryliphatic, and / or aromatic di- or triisocyanates and their higher molecular weight reaction products, particularly having structures of iminooxadiazine dione, isocyanurate, urea dione, carbamate, urethane, biuret, urea, oxadiazine trione, oxazolidinone, acylurea, and / or carbodiimide, further preferably having two or more free NCO groups.

[0024] Preferred di- or triisocyanates according to the present invention are, for example, tetramethylene diisocyanate, cyclohexane 1,3- and 1,4-diisocyanate, hexamethylene diisocyanate (HDI), 1-isocyanate-3,3,5-trimethyl-5-isocyanate-methylcyclohexane (isophorone diisocyanate, IPDI), methylene bis(4-isocyanate-cyclohexane), tetramethylphenyl dimethylene diisocyanate (TMXDI), nonane triisocyanate, and toluene diisocyanate (TDI). Diphenylmethane 2,4'- and / or 4,4'-diisocyanate (MDI), triphenylmethane 4,4'-diisocyanate, naphthalene 1,5-diisocyanate, 4-isocyanate methyl-1,8-octane diisocyanate (nonane triisocyanate, triisocyanate nonane, TIN), pentamethylene diisocyanate (PDI) and / or undecane 1,6,11-triisocyanate, and any mixture thereof, optionally mixed with other di-, tri- and / or polyisocyanates.

[0025] The polyisocyanates preferred in this invention typically have an isocyanate content of 0.5% to 50% by weight, preferably 3% to 30% by weight, and more preferably 5% to 25% by weight.

[0026] According to a preferred embodiment of the invention, the method uses a compound of higher molecular weight, i.e., a compound derived from di- or triisocyanates in the case of a partial reaction of isocyanate groups, having isocyanurate, carbamate, urethane, biuret, iminooxadiazine trione, oxadiazine trione and / or urea dione groups and based on aliphatic and / or alicyclic isocyanates.

[0027] In the method of the present invention, compounds having higher molecular weights having biuret, iminooxadiazine dione, isocyanurate and / or urea dione groups and based on hexamethylene diisocyanate, isophorone diisocyanate and / or 4,4'-dicyclohexylmethane diisocyanate are particularly preferred.

[0028] In step (A) of the method of the present invention, the at least one polyisocyanate is reacted with at least one heat-removable sealing agent.

[0029] Crucially, in the first step, the at least one polyisocyanate is reacted with at least one first heat-removable blocking agent, wherein, according to the invention, it is preferable that not all present NCO groups are blocked in step (A). Typically, in step (A), the at least one heat-removable blocking agent is added in an amount sufficient to block the present isocyanate groups, ranging from 10 to 50 mol%, preferably 20 to 40 mol%.

[0030] According to a preferred embodiment of the present invention, in step (A) of the method of the present invention, 10 to 50 mol% of the present NCO groups, more preferably 20 to 40 mol%, are reacted with the at least one heat-removable sealing agent.

[0031] According to the present invention, the at least one heat-removable sealing agent used in step (A) can be any of the various reagents that are suitable to those skilled in the art.

[0032] Preferably, the at least one heat-removable sealing agent used in step (A) of the method of the present invention is selected from 1H-pyrazoles such as 3,5-dimethylpyrazole, lactams such as caprolactam, phenols, ketoximes such as butanone oxime, acetone oxime, methyl ethyl ketone oxime or cyclohexanone oxime, amines such as... N - tert-butylbenzylamine or diisopropylamine, triazole, esters containing deprotonable groups such as diethyl malonate, ethyl acetoacetate or mixtures thereof, and / or mixtures with other blocking agents.

[0033] Preferred examples of 1H-pyrazole according to the present invention are 3,5-dimethylpyrazole or mixtures containing 3,5-dimethylpyrazole.

[0034] Preferred examples of ketoximes according to the present invention are selected from butanone oxime, acetone oxime, methyl ethyl ketone oxime, and mixtures thereof.

[0035] Preferred examples of lactams according to the present invention are caprolactam or mixtures containing caprolactam.

[0036] More preferably, in step (A) of the method of the present invention, at least one heat-removable blocking agent selected from autolactam, 3,5-dimethylpyrazole, methyl ethyl ketone oxime and mixtures thereof is used, with 3,5-dimethylpyrazole being particularly preferred.

[0037] Preferably, the at least one thermally eliminable blocking agent used in step (A) according to the invention is selected to eliminate the blocked polyisocyanate, for example, at a temperature below 200°C, preferably 100 to 170°C, more preferably 110 to 140°C. An example of determining the elimination temperature is thermogravimetric analysis, in which a pre-dried sample is heated at a rate of 10 K / min under a nitrogen stream. Preferably, the mentioned temperature range applies to cases where there is no catalyst that lowers the elimination temperature and no reactive nucleophiles, such as primary or secondary amines.

[0038] Step (A) of the method of the present invention can generally be carried out under all reaction conditions that are deemed suitable by those skilled in the art.

[0039] Step (A) of the method of the present invention is preferably carried out at a temperature of 50 to 120°C, more preferably 60 to 100°C.

[0040] Step (A) of the method of the present invention can be carried out in any apparatus that a person skilled in the art would deem suitable, such as in a stirring apparatus.

[0041] Preferably, the at least one polyisocyanate is initially loaded in pure substance form. Step (A) of the method of the present invention can also be carried out in a solvent, such as acetone. The at least one heat-removable sealing agent is then added to the at least one polyisocyanate, preferably in pure substance form.

[0042] Typically, in step (A), the at least one heat-removable blocking agent is added in an amount of 5 to 80 mol%, preferably 20 to 50 mol%, sufficient to block the present isocyanate groups.

[0043] Step (A) of the method of the present invention is preferably carried out for such a long time that the added blocking agent has completely reacted. The theoretical isocyanate group content after step (A) of the method of the present invention is typically 10% to 30% by weight, preferably 12% to 20% by weight.

[0044] According to the present invention, the reaction product obtained in step (A) may be subjected to post-treatment or purification steps known to those skilled in the art. Preferably, according to the present invention, the reaction mixture obtained in step (A) is further processed directly according to step (B).

[0045] Step (B) of the method of the present invention includes reacting the at least one partially blocked polyisocyanate from step (A) with at least one nonionic hydrophilic agent to obtain an intermediate.

[0046] According to a preferred embodiment of the invention, the product obtained from step (A) is reacted in step (B). More preferably, step (B) is carried out in the same apparatus used to perform step (A).

[0047] At least one nonionic hydrophilic agent is used in step (B). According to the invention, in step (B) of the method of the invention, all nonionic hydrophilic agents deemed suitable by those skilled in the art can generally be used. According to the invention, "nonionic" means that the hydrophilic agent substantially has no ionic or ionizable groups. This preferably means that the nonionic hydrophilic agent used according to the invention has neither anionic nor cationic groups, i.e., its amount is < 1 equivalent charge / gram of hydrophilic agent. This similarly applies to ionizable groups, i.e., groups that can be readily converted into charged groups, such as carboxylic acid groups.

[0048] According to a preferred embodiment of the present invention, the at least one nonionic hydrophilic agent is selected from polyoxyethylene ethers containing at least one hydroxyl or amino group.

[0049] These can be obtained by alkoxylation of suitable initiator molecules in ways known per se. Suitable initiator molecules are, for example, saturated monools such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, isopentanol, hexanol, octanol and nonanol, n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol, cyclohexanol, isomethylcyclohexanol or hydroxymethylcyclohexane, 3-ethyl-3-hydroxymethyloxetane or tetrahydrofurfuryl alcohol, and diethylene glycol monoalkyl ethers, such as diethylene glycol monobutyl ether. Ethers, unsaturated alcohols such as allyl alcohol, 1,1-dimethylallyl alcohol, or oleyl alcohol, aromatic alcohols such as phenol, isocresol, or methoxyphenol, arylaliphatic alcohols such as benzyl alcohol, anisyl alcohol, or cinnamyl alcohol, secondary monoamines such as dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, bis(2-ethylhexyl)amine, N-methyl- and N-ethylcyclohexylamine, or dicyclohexylamine, and heterocyclic secondary amines such as morpholine, pyrrolidine, piperidine, or 1H-pyrazole. Preferred initiator molecules are saturated monools. Particularly preferred are diethylene glycol monobutyl ethers as initiator molecules.

[0050] Epoxides, especially ethylene oxide and propylene oxide, are suitable for alkoxylation reactions and can be used in any order or in mixtures for alkoxylation reactions.

[0051] Preferably, ethylene oxide and propylene oxide are added to the initiator in a block manner.

[0052] The polyepoxide polyether is a pure polyethylene oxide polyether or a mixed polyepoxide polyether, wherein the epoxy units are composed of ethylene oxide units at least 30 mol%, preferably at least 40 mol%, of the epoxy units. Preferred nonionic compounds are monofunctional mixed polyepoxide polyethers having at least 40 mol% ethylene oxide units and a maximum of 60 mol% propylene oxide units.

[0053] The preferred nonionic hydrophilizing agent has a number-average molar mass of 300 to 4000 g / mol, more preferably 400 to 2500 g / mol.

[0054] Methoxylated polyethylene glycol is particularly preferred as a nonionic hydrophilic agent, and methoxylated polyethylene glycol having a number-average molar mass of 350 to 750 g / mol is particularly preferred.

[0055] Step (B) of the method of the present invention is preferably carried out at a temperature of 50 to 120°C, more preferably 60 to 100°C.

[0056] Step (B) of the method of the present invention is preferably carried out for such a long time that the added hydrophilic agent has completely reacted. The theoretical isocyanate group content after step (B) of the method of the present invention is typically 3% to 20% by weight, preferably 5% to 15% by weight.

[0057] According to the present invention, the intermediate obtained in step (B) may be subjected to post-processing or purification steps known to those skilled in the art. Preferably, according to the present invention, the reaction mixture obtained in step (B) is further processed directly according to step (C).

[0058] In step (B) of the method of the present invention, it is preferred to obtain at least one polyisocyanate whose isocyanate groups have been blocked or occupied by a nonionic hydrophilic agent to a degree of 20 to 90 mol%, preferably 30 to 80 mol%.

[0059] To accelerate reaction steps, especially steps (A), (B), and / or (C), a catalyst may be added to the reaction mixture. Suitable catalysts are systems known in isocyanate chemistry, such as tertiary amines, tin compounds, zinc compounds, or bismuth compounds, or basic salts.

[0060] Step (C) of the method of the present invention includes reacting the intermediate obtained in step (B) with at least one heat-removable blocking agent to obtain the at least one blocked polyisocyanate.

[0061] In step (C) of the method of the present invention, the intermediate obtained in step (B) is reacted with at least one heat-removable sealing agent.

[0062] According to the invention, it is possible that the heat-removable sealant used in steps (A) and (C) is the same. It is also possible that the heat-removable sealant used in steps (A) and (C) is not the same, but different.

[0063] The present invention preferably relates to the method of the present invention, wherein the at least one heat-removable sealant used in step (A) is the same as the at least one heat-removable sealant used in step (C).

[0064] Preferably, the at least one heat-removable sealing agent used in step (C) of the method of the present invention is selected from 1H-pyrazoles such as 3,5-dimethylpyrazole, lactams such as caprolactam, phenols, ketoximes such as methyl ethyl ketone oxime, acetone oxime, methyl ethyl ketone oxime or cyclohexanone oxime, amines such as... N - tert-butylbenzylamine or diisopropylamine, triazole, esters containing deprotonable groups such as diethyl malonate, ethyl acetoacetate or mixtures thereof, and / or mixtures with other blocking agents.

[0065] Preferred examples of the compound classes mentioned have been mentioned above regarding step (A).

[0066] More preferably, in step (C) of the method of the present invention, at least one heat-removable blocking agent selected from autolactam, 3,5-dimethylpyrazole, methyl ethyl ketone oxime and mixtures thereof is used, with 3,5-dimethylpyrazole being particularly preferred.

[0067] Preferably, the at least one thermally eliminable blocking agent used in step (C) according to the invention is selected to eliminate the blocked polyisocyanate, for example, at a temperature below 200°C, preferably 100 to 170°C, more preferably 110 to 140°C. Preferably, the mentioned temperature range applies to cases where there is no catalyst that lowers the elimination temperature and no reactive nucleophiles, such as primary or secondary amines.

[0068] Step (C) of the method of the present invention can generally be carried out under all reaction conditions that are deemed suitable by those skilled in the art.

[0069] Step (C) of the method of the present invention is preferably carried out at a temperature of 50 to 120°C, more preferably 60 to 100°C.

[0070] Step (C) of the method of the present invention can be carried out in any apparatus that is deemed suitable by those skilled in the art; step (C) is preferably carried out in the same reactor in which steps (A) and (B) are also carried out.

[0071] According to a preferred embodiment of the present invention, the at least one heat-removable sealing agent is preferably added in pure substance form to the intermediate obtained from step (B).

[0072] Generally, in step (C), the at least one heat-removable blocking agent is added in an amount of 95 to 100 mol%, preferably 98 to 100 mol%, sufficient to block the isocyanate groups present before step (C).

[0073] In step (C) of the method of the present invention, it is preferred to obtain at least one polyisocyanate whose isocyanate groups have been blocked or occupied by a nonionic hydrophilic agent to a degree of 95 to 100 mol%, preferably 98 to 100 mol%.

[0074] Step (C) of the method of the present invention is preferably carried out for such a long time that the added blocking agent has completely reacted. The theoretical isocyanate group content after step (C) of the method of the present invention is therefore typically 0% to 1% by weight, preferably 0% to 0.3% by weight. The same preferred isocyanate group content after step (C) also applies to values ​​determined by titration analysis.

[0075] According to the present invention, the reaction product obtained in step (C) may be subjected to post-processing or purification steps known to those skilled in the art, such as filtration and / or heat treatment.

[0076] According to a preferred embodiment of the present invention, step (C) is followed by step (D):

[0077] (D) Disperse the at least one blocked polyisocyanate obtained in step (C) in water.

[0078] Optional step (D) of the method of the present invention can be performed by methods known to those skilled in the art. Preferably, water is added to the reaction mixture obtained in step (C). Alternatively, the reaction mixture obtained in step (C) is added to water.

[0079] Step (D) of the method of the present invention can be performed at all temperatures known to those skilled in the art. Water is preferably added at a temperature of 5 to 90°C, more preferably 15 to 50°C in the dispersion container. More preferably, the resulting dispersion is stirred at a temperature of 20 to 80°C, more preferably 30 to 50°C. Further stirring before filtration or filling into containers is preferably at least 30 minutes, more preferably at least 2 hours.

[0080] In step (D), it is preferable to add sufficient water so that an aqueous dispersion having a solid content of 20% to 60% by weight, more preferably 30% to 50% by weight, is obtained after step (D).

[0081] The aqueous dispersion obtained in step (D) preferably has a pH value of 5 to 9, more preferably 6 to 8.

[0082] The aqueous dispersion obtained in step (D) preferably has a viscosity of 10 to 5000 mPa∙s, more preferably 50 to 3000 mPa∙s, which is determined at 23°C in each case by means of rotational viscosity determination according to DIN 53019-2008.

[0083] The aqueous dispersion obtained in step (D) preferably has an average particle size of 10 to 400 nm, more preferably 20 to 200 nm, which is determined by laser correlation spectroscopy after diluting the sample with softened water in each case (instrument: Malvern Zetasizer 1000, Malvern Inst. Limited).

[0084] In addition to the reaction steps mentioned, the isocyanate group may optionally be further reacted, for example with NCO reactive amines and / or alcohols.

[0085] For example, organic diamines or polyamines may be used, such as ethylene-1,2-diamine, 1,2- and 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, isophorone diamine (IPDA), a mixture of isomers of 2,2,4- and 2,4,4-trimethylhexamethylenediamine, 2-methylpentamethylenediamine, diethylenetriamine, 4,4-diaminodicyclohexylmethane and / or dimethylethylenediamine, or a mixture of at least two of these.

[0086] As a further component, optional polyols with a molecular weight range of 62 to 399 g / mol having a maximum of 20 carbon atoms may be used, especially non-polymeric polyols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene-1,2-diol, propylene-1,3-diol, butane-1,4-diol, butane-1,3-diol, cyclohexanediol, cyclohexane-1,4-diethanol, hexane-1,6-diol, neopentyl glycol, hydroquinone dihydroxyethyl ether, bisphenol A (2,2-bis(4-hydroxyphenyl)propane), hydrogenated bisphenol A (2,2-bis(4-hydroxycyclohexyl)propane), trimethylolpropane, trimethylolethane, glycerol, pentaerythritol, and any mixtures thereof with each other.

[0087] Examples of polymeric polyols are polyether polyols, polyester polyols, polyacrylate polyols, polyurethane polyols, polycarbonate polyols, polyester polyacrylate polyols, polyurethane polyacrylate polyols, polyurethane polyester polyols, polyurethane polycarbonate polyols, and polyester polycarbonate polyols, which are known in polyurethane coating technology.

[0088] Suitable monofunctional compounds include, for example, ethanol, n-butanol, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, 2-ethylhexanol, 1-octanol, 1-dodecanool, and 1-hexadecanool.

[0089] Examples of further suitable compounds are primary / secondary amines, such as methylamine, ethylamine, propylamine, butylamine, octylamine, laurylamine, stearylamine, isononoxypropylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, N-methylaminopropylamine, diethyl(methyl)aminopropylamine, morpholine, piperidine, diethanolamine, 3-amino-1-methylaminopropane, 3-amino-1-ethylaminopropane, 3-amino-1-cyclohexylaminopropane, 3-amino-1-methylaminobutane, 6-aminohexanoic acid, alanine, aspartic acid, glutamic acid, glutamine, glycine, ethanolamine, 3-aminopropanol, neopentylamine, or mixtures of at least two of these.

[0090] For example, according to the invention, 0.1 to 10 mol% of the NCO group of the polyisocyanate can be reacted with a further amine or alcohol. In a preferred variant, the reaction is carried out with a difunctional or trifunctional low molecular weight alcohol. Preferably, according to the invention, in a further variant, none of the aforementioned further components are used.

[0091] In this application, the number-average molecular weight of the blocked polyisocyanate dispersion of the present invention was determined by gel permeation chromatography (GPC) at 23°C with DMAc (N,N-dimethylacetamide) as the eluent. The procedure was performed according to DIN 55672-1. The weight-average molecular weight of the blocked polyisocyanate of the present invention is preferably from 1000 to 100000 g / mol, more preferably from 2000 to 20000 g / mol.

[0092] The content of acidic ionic groups and / or ionizable groups, such as carboxylic acid groups, carboxylate groups, sulfonic acid groups, or sulfonate groups, in the blocked polyisocyanates of the present invention is preferably low. More preferably, it does not contain acidic ionic groups and / or ionizable groups.

[0093] This invention also relates to blocked polyisocyanates obtainable by the method of this invention. Compared to blocked polyisocyanates obtained from the prior art, the blocked polyisocyanates obtained by this method are characterized by their easier conversion into storage-stable aqueous dispersions. Specifically, the blocked polyisocyanates prepared according to this invention have an average particle size of 10 to 400 nm, more preferably 20 to 200 nm, in the aqueous dispersion, as determined by laser correlation spectroscopy (instrument: Malvern Zetasizer 1000, Malvern Inst. Limited) after dilution of the sample with softened water in each case. The blocked polyisocyanates prepared according to this invention typically have a zeta potential of 0 to -15 V, preferably -0.1 to -15 V.

[0094] The present invention also relates to a polyisocyanate at least partially blocked by at least one heat-removable blocking agent and hydrophilized by at least one nonionic hydrophilizing agent, wherein it has a zeta potential of 0 to -15 V, preferably -0.1 to -15 V. To determine the zeta potential, a small sample is significantly diluted with a 1 mmol potassium chloride solution and homogenized by stirring. To establish a pH of 8.0, a dilute hydrochloric acid or sodium hydroxide solution is used. The zeta potential is then determined at 23 °C in a ZetaSizer 3000HSA (Malvern Instruments, Herrenberg, Germany).

[0095] In a preferred embodiment of the invention, the blocked polyisocyanate of the invention has an acid value of less than 30 mg KOH / g polymer, preferably less than 10 mg KOH / g polymer, and very preferably less than 5 mg KOH / g polymer. The blocked polyisocyanate of the invention preferably has an acid value of at least 0 mg KOH / g polymer. Acid value here refers to the mass of potassium hydroxide (in milligrams) required to neutralize 1 gram of the tested sample (measured according to DIN EN ISO 2114 - June 2002). The neutralized acid, i.e., the corresponding salt, naturally has an acid value of zero or reduced. The acid value of the corresponding free acid is crucial here according to the invention.

[0096] The description of the method of the invention applies accordingly to the blocked polyisocyanates of the present invention, based on the general and preferred embodiments.

[0097] The closed-cell polyisocyanate dispersion of the present invention can be used, for example, to produce preferably bakeable coatings (paints) for coating substrates preferably made of metal, mineral materials, glass, wood, or plastic. A preferred embodiment includes coating glass fibers, basalt fibers, and carbon fibers, or the resulting products, with a formulation containing the closed-cell polyisocyanate dispersion of the present invention. A particularly preferred substrate is glass fiber. For this purpose, the coatings of the present invention can be applied by molding, scraping, dipping, spraying, such as compressed air spraying or airless spraying, and by electrostatic application, such as high-speed rotating clock spraying. The thickness of the dry film can be, for example, from 0.01 to 120 µm. The dried film is cured by baking in a temperature range of 90 to 190°C, preferably 110 to 180°C, more preferably 120 to 160°C. Crosslinking can also be substantially or partially achieved during the compounding process with the polymer matrix.

[0098] This invention also relates to the use of the blocked polyisocyanate of this invention in the production of coatings, adhesives, sealants or elastomers.

[0099] The present invention also relates to coatings, adhesives, sealants or elastomers comprising at least one of the blocked polyisocyanates of the present invention.

[0100] The present invention also relates to a substrate having a coating available using at least one of the closed-type polyisocyanates of the present invention.

[0101] For the production of coatings (baking paint), adhesives and elastomers, the polyisocyanate-crosslinker dispersion of the present invention having blocked isocyanate groups can be mixed with at least a bifunctional isocyanate reactive compound, such as any polyol component (preferably in the form of an aqueous dispersion).

[0102] Such polyol components can be polyhydroxy polyesters, polyhydroxy polyurethanes, polyhydroxy polyethers, polycarbonate diols, or polymers having hydroxyl groups, such as polyhydroxy polyacrylates, polyacrylate polyurethanes, and / or polyurethane polyacrylates known per se. They typically have a hydroxyl value of 20 to 200, preferably 50 to 130 mg KOH / g. The hydrophilic modification of these polyhydroxy compounds, which is typically required for the production of dispersions, is achieved by methods known per se, such as those disclosed in, for example, EP-A-0 157 291, EP-A-0 498 156, or EP-A-0427 028.

[0103] It can also be mixed with other alcohol-reactive compounds, such as amino crosslinking resins, such as melamine resins and / or urea resins, to perform additional crosslinking during baking.

[0104] Paints, inks, adhesives, and other formulations can be produced from the dispersions of the present invention using methods known per se. In addition to blocked polyisocyanates and optionally polyols or film-forming agents, conventional additives and other auxiliaries (e.g., pigments, fillers, leveling agents, defoamers, catalysts, release agents, antistatic agents) may be added to the formulations.

[0105] The invention is illustrated by examples. Example

[0106] Chemicals used:

[0107] Desmodur® Ultra N 3300 isocyanurate based on hexamethylene diisocyanate, Covestro Deutschland AG, Leverkusen, DE

[0108] Other chemicals were purchased from Sigma-Aldrich Chemie GmbH, Taufkirchen, DE.

[0109] Unless otherwise stated, all percentage data refer to weight percentage (weight %).

[0110] Unless otherwise stated, all analytical measurements were performed at 23°C.

[0111] The viscosity shown was determined at 23°C using a rotational viscometer from Anton Paar Germany GmbH of Ostfildern, Germany, according to the rotational viscosity determination method in DIN 53019-2008.

[0112] Unless otherwise expressly stated, NCO content shall be determined by volumetric means in accordance with DIN-EN ISO 11909-2007.

[0113] The particle size was determined by laser correlation spectroscopy (instrument: Malvern Zetasizer 1000, Malvern Inst. Limited) after diluting the sample with softened water.

[0114] The solid content was determined by heating the weighed sample to 120°C. The solid content was then calculated by reweighing the sample at constant weight.

[0115] Using infrared spectroscopy (at 2260 cm⁻¹) -1 The spectral bands were used to check for free NCO groups.

[0116] As a storage test, 250 mL of dispersion was dispensed in each case and stored at room temperature and 40°C. Visual inspection was performed to check for sedimentation. Samples exhibiting sedimentation were deemed unstable.

[0117] To determine the zeta potential, a small sample was significantly diluted with 1 mmol potassium chloride solution and homogenized by stirring. A dilute hydrochloric acid or sodium hydroxide solution was used to establish a pH of 8.0. The zeta potential was then measured at 23 °C using a ZetaSizer 3000HSA (Malvern Instruments, Herrenberg, Germany).

[0118] Acid value was determined according to DIN EN ISO 2114 - June 2002.

[0119] Comparative Example 1:

[0120] Initially, 234 g of Desmodur Ultra N 3300 was loaded into a standard stirring apparatus and heated to 40°C. Then, 110.5 g of 3,5-dimethylpyrazole (DMP) was added fractionally to the melt to keep the temperature below 75°C. The mixture was stirred at 80°C until the theoretical isocyanate content was below approximately 0.59% by weight. Subsequently, 49.5 g of methoxy polyethylene glycol with a number-average molar mass of 750 g / mol was added, and the mixture was stirred at 80°C until isocyanate groups were no longer detectable by infrared spectroscopy. Then, 591 g of deionized water was added under vigorous stirring, and the mixture was stirred at 40°C for an additional 180 minutes.

[0121] The resulting dispersion has the following properties:

[0122] Solid content: Approximately 39.5% by weight

[0123] pH value: Approximately 5.8

[0124] Viscosity approximately 10 mPa∙s

[0125] Average particle size (LKS): 369 nm

[0126] The dispersion formed two phases overnight, making it unsuitable for further testing.

[0127] Comparative Example 2:

[0128] Initially, 234 g of Desmodur Ultra N 3300 was loaded into a standard stirring apparatus and heated to 40 °C. Then, 49.5 g of methoxylated polyethylene glycol with a number-average molar mass of 750 g / mol was added, and the mixture was stirred at 80 °C until the theoretical isocyanate content was below approximately 16.8% by weight. Subsequently, 110.5 g of 3,5-dimethylpyrazole (DMP) was added fractionally to the melt to keep the temperature below 80 °C. The mixture was stirred at 80 °C until isocyanate groups were no longer detectable by infrared spectroscopy. Then, 591 g of deionized water was added under vigorous stirring, and the mixture was stirred at 40 °C for an additional 180 minutes.

[0129] The resulting dispersion has the following properties:

[0130] Solid content: Approximately 39.8% by weight

[0131] pH value: Approximately 5.6

[0132] Viscosity approximately 10 mPa∙s

[0133] Average particle size (LKS): 343 nm

[0134] The dispersion formed two phases overnight, making it unsuitable for further testing.

[0135] Example 3: DMP as a sealing agent

[0136] Initially, 234 g of Desmodur Ultra N 3300 was loaded into a standard stirring apparatus and heated to 40°C. Then, 58.2 g of 3,5-dimethylpyrazole (DMP) was added fractionally to the melt to keep the temperature below 80°C. Next, 49.5 g of methoxylated polyethylene glycol with a number-average molar mass of 750 g / mol was added, and the mixture was stirred at 80°C until the theoretical isocyanate content was below approximately 6.46% by weight. Subsequently, 52.2 g of 3,5-dimethylpyrazole (DMP) was added fractionally to the melt to keep the temperature below 80°C. The mixture was stirred at 80°C until isocyanate groups were no longer detectable by infrared spectroscopy. Then, 591 g of deionized water was added under vigorous stirring, and the mixture was stirred at 40°C for an additional 180 minutes.

[0137] The resulting dispersion has the following properties:

[0138] Solid content: Approximately 39.0% by weight

[0139] pH value: Approximately 5.9

[0140] Viscosity approximately 10 mPa∙s

[0141] Average particle size (LKS): 129 nm

[0142] Zeta potential: -11.9 V

[0143] Acid value: < 0.2 mg KOH / g

[0144] The dispersion is stable at room temperature and 40°C for at least 4 weeks. No phase separation occurred during this period.

[0145] Example 4: Methyl ethyl ketone oxime as a blocking agent

[0146] Initially, 234 g of Desmodur Ultra N 3300 was loaded into a standard stirring apparatus and heated to 40°C. Then, 51.3 g of methyl ethyl ketone oxime was slowly added to the melt to keep the temperature below 80°C. Next, 61.2 g of methoxy polyethylene glycol with a number-average molar mass of 750 g / mol was added, and the mixture was stirred at 80°C until the theoretical isocyanate content was below approximately 6.41% by weight. Subsequently, 47.3 g of methyl ethyl ketone oxime was slowly added to the melt to keep the temperature below 80°C. The mixture was stirred at 80°C until isocyanate groups were no longer detectable by infrared spectroscopy. Then, 520 g of deionized water was added under vigorous stirring, and the mixture was stirred at 40°C for another 180 minutes, during which approximately 100 g of additional water was used for dilution.

[0147] The resulting dispersion has the following properties:

[0148] Solid content: Approximately 34.4%

[0149] pH value: Approximately 5.7

[0150] Viscosity: Approximately 30 mPa∙s

[0151] Average particle size (LKS): 47 nm

[0152] The dispersion is stable at room temperature and 40°C for at least 4 weeks. No phase separation occurred during this period.

[0153] Example 5: Caprolactam as a blocking agent

[0154] 234 g of Desmodur Ultra N 3300 was initially loaded into a standard stirring apparatus and heated to 40 °C. Then, 68.3 g of caprolactam was added to the melt to keep the temperature below 80 °C. Next, 51.9 g of methoxy polyethylene glycol with a number-average molar mass of 750 g / mol was added, and the mixture was stirred at 80 °C until the theoretical isocyanate content was below approximately 6.26% by weight. Subsequently, 61.5 g of caprolactam was added to the melt to keep the temperature below 80 °C. The mixture was stirred at 80 °C until isocyanate groups were no longer detectable by infrared spectroscopy. Then, 624 g of deionized water was added under vigorous stirring, and the mixture was stirred at 40 °C for an additional 180 minutes.

[0155] The resulting dispersion has the following properties:

[0156] Solid content: Approximately 39% by weight

[0157] pH value: Approximately 5.8

[0158] Viscosity: Approximately 20 mPa∙s

[0159] Average particle size (LKS): 92 nm

[0160] The dispersion is stable at room temperature and 40°C for at least 4 weeks. No phase separation occurred during this period.

Claims

1. A method for preparing an aqueous dispersion, comprising the following steps: (A) Reacting at least one polyisocyanate with at least one heat-removable blocking agent to obtain at least one partially blocked polyisocyanate, wherein the at least one heat-removable blocking agent is selected from one or more of 1H-pyrazole, lactam, ketooxime, and amine, wherein the at least one polyisocyanate is added in pure substance form. (B) Reacting the at least one partially blocked polyisocyanate from step (A) with at least one nonionic hydrophilic agent to obtain an intermediate, wherein the at least one nonionic hydrophilic agent is selected from polyoxyethylene ethers containing one hydroxyl group, wherein the isocyanate groups of the intermediate are blocked or occupied by the nonionic hydrophilic agent to a degree of 20 to 90 mol%, wherein the nonionic hydrophilic agent has a number-average molar mass of 400 to 2500 g / mol. (C) React the intermediate obtained in step (B) with at least one heat-removable blocking agent to obtain at least one blocked polyisocyanate, wherein the at least one heat-removable blocking agent is selected from one or more of 1H-pyrazole, lactam, ketooxime, and amine, wherein the theoretical isocyanate group content after step (C) is 0% by weight, and (D) Disperse the at least one blocked polyisocyanate obtained in step (C) in water to form the aqueous dispersion.

2. The method of claim 1, wherein: (A) Reacting at least one polyisocyanate with at least one heat-removable blocking agent to obtain at least one partially blocked polyisocyanate, wherein the at least one heat-removable blocking agent is selected from one or more of lactams, ketoximes, and amines; and (C) The intermediate obtained in step (B) is reacted with at least one heat-removable blocking agent to obtain the at least one blocked polyisocyanate, wherein the at least one heat-removable blocking agent is selected from one or more of lactams, ketoximes, and amines, wherein the theoretical isocyanate group content after step (C) is 0 by weight.

3. The method of claim 1, wherein the at least one polyisocyanate is selected from compounds having isocyanurate, carbamate, urethane, biuret, iminooxadiazine trione, oxadiazine trione and / or urea dione groups and based on aliphatic and / or alicyclic diisocyanates.

4. The method of claim 1, wherein the at least one polyisocyanate is selected from compounds having biuret, iminooxadiazine dione, isocyanurate and / or urea dione groups and based on hexamethylene diisocyanate, isophorone diisocyanate and / or dicyclohexylmethane-4,4'-diisocyanate.

5. The method according to any one of claims 1 to 4, wherein the at least one heat-removable sealant used in step (A) is the same as the at least one heat-removable sealant used in step (C).

6. The method of any one of claims 1 to 4, wherein the aqueous dispersion has a volume average particle size of 10 to 400 nm, and is determined by laser correlation spectroscopy after diluting the sample with softened water.

7. An aqueous dispersion obtained by the method as described in any one of claims 1 to 6.

8. Use of the aqueous dispersion of claim 7 in the production of coatings, adhesives, sealants or elastomers.

9. A coating, adhesive, sealant, or elastomer comprising the aqueous dispersion as described in claim 7.

10. A substrate having a coating prepared by the aqueous dispersion as described in claim 7 coated thereon.