High temperature crosslinking dispersion

Abstract

The present invention relates to a process for the preparation of at least one blocked polyisocyanate comprising the following steps: (A) reacting at least one polyisocyanate with at least one thermally cleavable blocking agent selected from the group consisting of monofunctional primary alcohols and mixtures thereof to obtain at least one partially blocked polyisocyanate, (B) reacting the at least one partially blocked polyisocyanate from step (A) with at least one non-ionic hydrophilizing agent to obtain an intermediate, and (C) reacting the intermediate obtained in step (B) with at least one thermally cleavable blocking agent selected from the group consisting of monofunctional primary alcohols and mixtures thereof to obtain the at least one blocked polyisocyanate, to the blocked polyisocyanate obtained in a corresponding manner, to the use of the blocked polyisocyanate for the production of a coating composition, an adhesive, a sealant or an elastomer, to the corresponding coating composition, adhesive, sealant or elastomer, and to a substrate with a coating obtained 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 blocking agent selected from monofunctional primary alcohols and mixtures thereof 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 blocking agent selected from monofunctional primary alcohols and mixtures thereof to obtain the at least one blocked polyisocyanate, wherein the blocked polyisocyanate is used in the production of coating compositions, adhesives, sealants or elastomers, and substrates having coatings obtainable using the at least one blocked polyisocyanate of the present invention.

[0002] In recent years, the importance of waterborne paints and coating compositions has increased significantly due to increasingly stringent emission guidelines regarding solvents released during paint application. Although waterborne 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 resistance.

[0003] Waterborne paint systems based on waterborne polyurethane dispersions often still contain a considerable 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 during film formation of the coating composition, even at or below room temperature. PUR dispersions and paint formulations also often lack storage stability in the absence of solvents.

[0004] For example, the solvent N-methylpyrrolidone (NMP) is still sometimes used in the fields of aqueous dispersions and paints. One example is, for instance, the carboxylic acid hydrophilic polyisocyanate crosslinker dispersions having dimethylpyrazole blocked isocyanate groups described in EP-A 0 942 023. These crosslinker 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 cosolvent by omitting the cosolvent.

[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 organic solvents, which are then removed from the dispersions by distillation after dispersion in water.

[0008] DE 3613492 describes an acetone method for producing solvent-free polyurethane-polyurea dispersions. An 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 PUR 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-free 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 usability in a wide variety of formulations. Furthermore, the blocked polyisocyanates contained in the aqueous dispersions should only convert to unblocked polyisocyanates at high temperatures, for example, above 170°C.

[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 thermally eliminable blocking agent selected from monofunctional primary alcohols and mixtures thereof 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 thermally eliminable blocking agent selected from monofunctional primary alcohols and mixtures thereof 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 coating compositions, adhesives, sealants or elastomers.

[0018] These objectives are also achieved by coating compositions, adhesives, sealants, or elastomers of the present invention that contain at least one of the blocked 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.

[0021] Step (A) of the method of the present invention includes reacting at least one polyisocyanate with at least one thermally eliminable blocking agent selected from monofunctional primary alcohols and mixtures thereof 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 homogeneous polyisocyanate is preferably used. According to the present invention, a mixture comprising two, three, or more different polyisocyanates may also be used.

[0023] The suitable polyisocyanate used according to the invention can be an NCO functional compound known to those skilled in the art, preferably having a functionality of 2 or greater. According to the invention, this is preferably an aliphatic, alicyclic, aryliphatic, and / or aromatic di- or triisocyanate and its 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, and 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-isocyano-3,3,5-trimethyl-5-isocyanate methylcyclohexane (isophorone diisocyanate, IPDI), methylene bis(4-isocyanate cyclohexane), tetramethylphenyl dimethylene diisocyanate (TMXDI), nonane triisocyanate, and toluene diisocyanate (TD). I) 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, in this method, compounds having isocyanurate, carbamate, urethane, biuret, iminooxadiazine trione, oxadiazine trione and / or urea dione groups and based on aliphatic and / or alicyclic isocyanates, i.e., derived from di- or triisocyanates in the case of reaction of some isocyanate groups, are used.

[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 thermally eliminable blocking agent selected from monofunctional primary alcohols and mixtures thereof. The primary alcohols of the present invention are characterized in that two protons are attached to a carbon atom bonded to a hydroxyl group. Methanol is also included among the primary alcohols. Preferably, the at least one thermally eliminable blocking agent used in step (A) according to the present invention is selected to eliminate the blocked polyisocyanate, for example, at a temperature above 170°C, preferably 180 to 300°C, more preferably 190 to 250°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.

[0029] Crucially, in the first step, the at least one polyisocyanate is reacted with at least one first heat-removable blocking agent selected from monofunctional primary alcohols and mixtures thereof, wherein, according to the invention, preferably, all present NCO groups are not blocked in this 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, 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 blocking agent used in step (A) is selected from monofunctional primary alcohols and mixtures thereof.

[0032] Suitable monofunctional primary alcohols are preferably selected from methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, n-butoxyethanol, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, 2-ethylhexanol, 1-octanol, 1-dodecanol, 1-hexadecanol, 2-methyl-1-propanol, 2,2-dimethyl-1-propanol, 2-methyl-1-butanol, and mixtures thereof. The molar mass of a suitable monofunctional primary alcohol is preferably less than 250 g / mol, more preferably less than 150 g / mol.

[0033] 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.

[0034] Step (A) of the method of the present invention is preferably carried out at a temperature of 50 to 140°C, more preferably 60 to 110°C.

[0035] 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.

[0036] 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.

[0037] 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%.

[0038] Therefore, it is preferred that at least one polyisocyanate is obtained in step (A) of the method of the present invention, wherein the isocyanate groups are thermally reversibly blocked to a degree of 10 to 50 mol%, preferably 20 to 40 mol%.

[0039] 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. After step (A) of the method of the present invention, the theoretical isocyanate group content of the reaction mixture is typically 10% to 30% by weight, preferably 12% to 20% by weight.

[0040] 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).

[0041] 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.

[0042] 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).

[0043] 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. Preferably, it 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 also applies to ionizable groups, i.e., groups that can be readily converted into charged groups, such as carboxylic acid groups.

[0044] 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.

[0045] These can be obtained by alkoxylation of suitable initiator molecules in ways known per se. Suitable initiator molecules are, for example, saturated monools selected from 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. Unsaturated alcohols, such as allyl alcohol, 1,1-dimethylallyl alcohol, or oleyl alcohol; aromatic alcohols, such as phenol, isocresol, or methoxyphenol; aryl aliphatic 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 and mixtures thereof. Preferred initiator molecules are saturated monools. Diethylene glycol monobutyl ether is particularly preferred as an initiator molecule.

[0046] Epoxyalkanes suitable for alkoxylation reactions, especially ethylene oxide and propylene oxide, can be used in any order or in mixtures for alkoxylation reactions.

[0047] Preferably, ethylene oxide and propylene oxide are added to the initiator in a block manner.

[0048] The polyepoxide polyether is a pure polyethylene oxide polyether or a mixed polyepoxide polyether, wherein the epoxy units consist of ethylene oxide units at a level of at least 30 mol%, preferably at least 40 mol%. Preferred nonionic compounds are monofunctional mixed polyepoxide polyethers having at least 40 mol% ethylene oxide units and up to 60 mol% propylene oxide units. In a particularly preferred variant, only ethylene oxide units are contained, except for the initiator.

[0049] The preferred nonionic hydrophilizing agent has a number-average molar mass of 300 to 4000 g / mol, more preferably 400 to 2500 g / mol.

[0050] Methoxylated polyethylene glycol is very particularly preferred as a nonionic hydrophilic agent, and methoxylated polyethylene glycol having a number-average molar mass of 350 to 750 g / mol is especially preferred.

[0051] In a preferred variant of the invention, the hydrophilizing agent used can be eliminated under conditions comparable to those of a sealing agent, i.e., at a corresponding temperature. However, hydrophilizing agents typically do not volatilize under the typical baking conditions of the coating.

[0052] Step (B) of the method of the present invention is preferably carried out at a temperature of 50 to 140°C, more preferably 60 to 120°C.

[0053] 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.

[0054] 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).

[0055] 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%.

[0056] Step (C) of the method of the present invention comprises reacting the intermediate obtained in step (B) with at least one thermally eliminable blocking agent selected from monofunctional primary alcohols and mixtures thereof to obtain the at least one blocked polyisocyanate.

[0057] 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.

[0058] 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).

[0059] Preferably, the at least one heat-removable occlusive agent used in step (C) of the method of the present invention is selected from monofunctional primary alcohols and mixtures thereof.

[0060] Preferred examples of the compound classes mentioned have been mentioned above regarding step (A).

[0061] 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 above 170°C, preferably 180 to 300°C, more preferably 190 to 250°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.

[0062] 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.

[0063] Step (C) of the method of the present invention is preferably carried out at a temperature of 50 to 140°C, more preferably 60 to 120°C.

[0064] Step (C) of the method of the present invention can be performed in any apparatus that a person skilled in the art would deem suitable. Step (C) is preferably performed in the same reactor in which steps (A) and (B) are also performed.

[0065] 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).

[0066] Generally, in step (C), the at least one heat-removable blocking agent is added in an amount of 90 to 120 mol%, preferably 95 to 105 mol%, sufficient to block the isocyanate groups present before step (C).

[0067] 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%.

[0068] 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. After step (C) of the method of the present invention, the theoretical isocyanate group content of the reaction mixture is therefore typically 0% to 1% by weight, preferably 0% to 0.3% by weight.

[0069] 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.

[0070] 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.

[0071] According to a preferred embodiment of the present invention, step (C) is followed by step (D):

[0072] (D) Disperse the at least one blocked polyisocyanate obtained in step (C) in water.

[0073] 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).

[0074] Step (D) of the method of the present invention can be carried out at all temperatures known to those skilled in the art. Water is preferably added at a temperature of 5 to 120°C, more preferably 15 to 50°C in the dispersion vessel. More preferably, the resulting dispersion is stirred at a temperature of 20 to 80°C, more preferably 30 to 50°C.

[0075] In step (D), it is preferable to add such a large amount of water that an aqueous dispersion with a solid content of 20% to 60% by weight, more preferably 30% to 50% by weight, is obtained after step (D).

[0076] The aqueous dispersion obtained in step (D) preferably has a pH value of 4 to 10, more preferably 6 to 8.

[0077] 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.

[0078] The aqueous dispersion obtained in step (D) preferably has a volume 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).

[0079] In addition to the reaction steps mentioned above, the isocyanate groups may optionally be further reacted, for example with NCO reactive amines and / or alcohols.

[0080] 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-trimethylhexanediamine, 2-methylpentanediamine, diethylenetriamine, 4,4-diaminodicyclohexylmethane and / or dimethylethylenediamine, or a mixture of at least two of these.

[0081] 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, 1,3-butanediol, 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.

[0082] 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.

[0083] 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.

[0084] For example, according to the invention, 0.1 to 10 mol% of the NCO group of the present polyisocyanate can be reacted with a further amine or a further alcohol, preferably not conforming to the definition of the blocking agent in step (A) or (C). Preferably, according to the invention, none of the further components mentioned herein are used.

[0085] 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.

[0086] 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, acidic ionic groups and / or ionizable groups are absent.

[0087] In a preferred embodiment of the invention, the acid value of the blocked polyisocyanate of the invention is less than 30 mg KOH / g, preferably less than 10 mg KOH / g, and very preferably less than 5 mg KOH / g, in each case based on the blocked polyisocyanate, i.e. based on the reaction products from method steps A) to C) of the invention.

[0088] Acid value here refers to the mass of potassium hydroxide (in milligrams) required to neutralize 1 gram of the analyzed sample (measured according to DINEN ISO 2114 - June 2002). The neutralized acid, i.e., the corresponding salt, naturally has an acid value of zero or reduced. Of paramount importance according to the invention is the acid value of the corresponding free acid.

[0089] 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.

[0090] The present invention also relates to polyisocyanates at least partially blocked by at least one thermally eliminable blocking agent selected from monofunctional primary alcohols and mixtures thereof, and hydrophilized by at least one nonionic hydrophilizing agent, characterized in that they have 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 1 mmol potassium chloride solution and homogenized by stirring. To establish a pH of 8.0, dilute hydrochloric acid or sodium hydroxide solution is used. The zeta potential is then determined at 23 °C in a ZetaSizer3000HSA (Malvern Instruments, Herrenberg, Germany).

[0091] 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 (measured according to DIN EN ISO 2114 - June 2002) in milligrams required to neutralize 1 gram of the tested sample. 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 according to the invention. The descriptions of the method of the invention with respect to the blocked polyisocyanate of the invention apply accordingly to the general and preferred embodiments.

[0092] The closed-cell polyisocyanate dispersion of the present invention can be used, for example, to produce preferably bakeable coating compositions (baking varnishes) for coating substrates preferably made of metal, mineral materials, glass, wood, or plastic. Suitable substrates according to the invention are, for example, surfaces, fibers, particles, woven fabrics, knitted fabrics, nonwoven fabrics, and combinations thereof. For this purpose, the coatings of the present invention can be applied by smearing, scraping, dipping, spraying, such as compressed air spraying or airless spraying, and by electrostatic application, such as high-speed rotating clock application. The thickness of the dry film can be, for example, from 0.01 to 120 µm. The dried film is preferably cured by baking in a temperature range of 90 to 190°C, preferably 110 to 180°C, more preferably 120 to 160°C. In the case of coating fibers, crosslinking can be carried out during fiber drying or during subsequent heat treatment. Alternatively, crosslinking can also be substantially or partially achieved during the compounding process with the polymer matrix.

[0093] This invention also relates to the use of the blocked polyisocyanate of this invention in the production of coating compositions, adhesives, sealants or elastomers.

[0094] The present invention also relates to coating compositions, adhesives, sealants or elastomers comprising at least one of the blocked polyisocyanates of the present invention.

[0095] 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.

[0096] To produce coating compositions (baking paint), adhesives, and elastomers, the polyisocyanate-crosslinking agent 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).

[0097] 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. These typically have a hydroxyl value of 20 to 200 mg KOH / g, 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-0 427 028.

[0098] 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.

[0099] 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 any polyols or film-forming agents, conventional additives and other auxiliaries (e.g., pigments, fillers, leveling agents, defoamers, catalysts, release agents, antistatic agents) can be added to the formulations.

[0100] The invention is illustrated by examples. Example

[0101] Chemicals used:

[0102] Desmodur® Ultra N 3300 isocyanurate based on hexamethylene diisocyanate, Covestro Deutschland AG, Leverkusen, DE

[0103] Other chemicals were purchased from Sigma-Aldrich Chemie GmbH, Taufkirchen, DE.

[0104] Unless otherwise stated, all percentage data refer to weight percentage (weight %).

[0105] Unless otherwise stated, all analytical measurements were performed at 23°C.

[0106] 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.

[0107] Unless otherwise expressly stated, NCO content shall be determined by volumetric means in accordance with DIN-EN ISO 11909-2007.

[0108] The particle size was determined by laser correlation spectroscopy (instrument: Malvern Zetasizer 1000, Malvern Inst. Limited) after diluting the sample with softened water.

[0109] The solid content was determined by heating the weighed sample to 120°C. Under constant weight, the solid content was calculated by weighing the sample again.

[0110] Using infrared spectroscopy (at 2260 cm⁻¹) -1 The spectral bands were used to check for free NCO groups.

[0111] 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.

[0112] To determine the zeta potential, a small amount of 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).

[0113] Acid value was determined according to DIN EN ISO 2114 - June 2002.

[0114] Embodiments of the present invention: Butyl ethylene glycol (BG, butoxyethanol) as a blocking agent.

[0115] Initially, 234 g of Desmodur Ultra N 3300 was loaded into a standard stirring apparatus and heated to 40 °C. Then, 68.9 g of butoxyethanol was slowly added to the melt to keep the temperature below 80 °C. Next, 91.8 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 5.25% by weight. Subsequently, 53.9 g of butoxyethanol 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, 580 g of deionized water was added under vigorous stirring, and the mixture was stirred at 40 °C for another 180 minutes.

[0116] The resulting dispersion has the following properties:

[0117] Solid content: Approximately 39% by weight

[0118] pH value: Approximately 5.3

[0119] Viscosity approximately 70 mPa∙s

[0120] Average particle size (LCS): 66 nm

[0121] Zeta potential: -12.5 mV

[0122] Acid value: 0.20 mg KOH / g

[0123] The dispersion is stable at both 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 thermally eliminable blocking agent selected from monofunctional primary alcohols to obtain at least one partially blocked polyisocyanate, 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 thermally eliminable blocking agent selected from monofunctional primary alcohols to obtain at least one blocked polyisocyanate, wherein the theoretical isocyanate group content of the reaction mixture after step (C) is 0% by weight; and (D) Disperse the at least one blocked polyisocyanate obtained in step (C) in water to form an aqueous dispersion.

2. 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.

3. 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 4,4'-dicyclohexylmethane diisocyanate.

4. The method according to any one of claims 1 to 3, 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).

5. The method of any one of claims 1 to 3, 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.

6. An aqueous dispersion obtained by the method as described in any one of claims 1 to 5.

7. Use of the aqueous dispersion as described in claim 6 in the production of coating compositions, adhesives, sealants or elastomers.

8. A coating composition, adhesive, sealant, or elastomer comprising the aqueous dispersion as described in claim 6.

9. A substrate coated with a coating made using the aqueous dispersion as described in claim 6.