Method for producing aqueous polyurethane dispersion

Abstract

The present invention relates to an aqueous polyurethane dispersion, a process for preparing same, a composition comprising same, a coating comprising same, and a coated article obtained by coating an article with the coating.

Description

Technical Field

[0001] The present invention relates to an aqueous polyurethane dispersion, a process for preparing the same, a composition comprising the same, a coating comprising the same, and a coated article obtained by coating an article with the coating. Background Art

[0002] Aqueous polyurethane dispersions are widely used in coatings, adhesives, sealants and printing inks. Formulations of aqueous polyurethane dispersions comprise many components, namely polyols, isocyanates, chain extenders, and ionic centers that enable the polyurethane to be dispersed in water. Aqueous polyurethane dispersions are very common commercial products. Several processes that can be used to prepare aqueous polyurethane dispersions are known in the art. Known processes include, for example, the acetone process, the prepolymer mixing process, the emulsifier / shear force process, the melt emulsification process, the ketimine process and the spontaneous dispersion process of solids. The processes are summarized in Methoden der organischen Chemie (Houben-Weyl. 4. Auflage, Volume E20, H Bartl, J. Falbe, Stuttgart, New York, Thieme 1987, pp. 1671-1682 and H. Pandya, P. Mahanwar; Advanced Industrial and Engineering Polymer Research 3 (2020) pp. 102-110.

[0003] The acetone method, similar to the teachings in US3,479,310 and DE1,495,847, is of particular importance. In this method, the NCO-terminated polyurethane prepolymer is first prepared, then dissolved in an inert solvent, and finally chain-extended in solution to form a relatively high molecular weight polyurethane. The incorporation of hydrophilic groups necessary for dispersion is achieved by incorporating diols containing ionic, possibly ionic or nonionic hydrophilic groups, into the prepolymer, or by using a corresponding amine as a chain extender. Dispersion is carried out discontinuously in a container equipped with a stirrer and optionally baffles. The solvent used is generally distilled off from the container immediately after dispersion in water.

[0004] In the prepolymer mixing method, the polyurethane prepolymer is first prepared by reacting a polyisocyanate, a polyol, and an anionic internal surfactant, sometimes in the presence of a solvent and / or a reactive diluent. The anionic internal surfactant is either contained in the polymer backbone chain or is a pendant from the polymer backbone. This anionic internal surfactant is typically dimethylolpropionic acid (DMPA), a molecule containing two hydroxyl groups, and a carboxylic acid group. The hydroxyl groups react with the isocyanate group to produce an NCO-terminated prepolymer having a pendant carboxyl group. This prepolymer is dispersed under shear force in water with or without a surfactant or emulsifier, using a suitable volatile neutralizing agent such as trimethylamine (TEA). The neutralizing agent reacts with the carboxyl groups of DMPA to form a water-soluble salt. Subsequently, a diamine or triamine chain extender is added to produce the finished polyurethane dispersed in water free of free NCO groups.

[0005] US5692937 discloses aqueous dispersions of polyurethane ionomer reaction products of dimethylolpropionic acid neutralized with a base selected from polyester polyols (e.g., poly(diethylene glycol adipate)), aliphatic diisocyanates (e.g., IPDI), tertiary amines (e.g., triethaylamines), and alkali metal hydroxides.

[0006] US5965195 discloses a cosolvent-free aqueous, anionic dispersion of polyurethane urea of ​​an NCO prepolymer prepared from aliphatic diisocyanates, macrodiols, 2,2-bis-(hydroxymethyl)alkane monocarboxylic acids and diols having Mw of 62 to 400, a monofunctional chain arrester, water, and a neutralizing agent. Ammonia and dimethylethanolamine (2-(dimethylamino)ethanol (DMAE) or N,N,-dimethylethanolamine (DMEA)) are used as neutralizing agents.

[0007] WO2003 / 035710A1 discloses hydroxyl-functional polyurethane dispersions prepared from polycarbonate polyols, IPDI, DMPA, butanediol, trimethylolpropane (TMP), diethanolamine (DEA), and TEA.

[0008] US2006 / 0205869 discloses a solvent-free, electrosterically stabilized polyurethane dispersion based on isophorone diisocyanate (IPDI), polypropylene glycol (PPG), 1,4-butanediol, dimethylpropionic acid (2,2-bis(hydroxymethyl)propionic acid; DMPA), and sodium hydroxide as a neutralizing agent.

[0009] US2011 / 0306724 discloses solvent-free aqueous polyurethane dispersions comprising a polyurethane polymer containing a reaction product of an isocyanate-terminated prepolymer, which includes a polyisocyanate, a polyol, an isocyanate-reactive compound having one or more ionic groups or potentially ionic groups per molecule, at least one isocyanate chain arrester (e.g., a monofunctional alcohol or amine), and a neutralizing agent that reacts with the isocyanate-reactive compound and the chain extender. When used as a neutralizing agent, it is taught that more volatile tertiary amines, e.g., those with a boiling point below 100°C, are advantageous because the salts formed from these amines have the ability to decompose.

[0010] WO2017 / 042178A1 discloses a method for preparing aqueous polyurethane dispersions. The method involves an NCO-terminated polyurethane prepolymer formed from a reaction mixture containing a polyether polyol, an anionic internal surfactant such as DMPA, and an aliphatic polyisocyanate such as IPDI, in the absence of a tin-containing catalyst. N,N-dimethylethanolamine (DMEA) was added dropwise to neutralize the carboxyl groups of DMPA.

[0011] WO2017 / 137237A1 discloses a method for preparing an aqueous, organic solvent-free polyurethane dispersion. The method comprises an NCO-terminated polyurethane prepolymer formed from a reaction mixture containing a polyol, a polyisocyanate, an anionic stabilizer such as DMPA, and at least one nonionic stabilizer containing at least two hydroxyl groups, such as a diol. The DMPA in the polyurethane prepolymer is neutralized by the dropwise addition of dimethylaminoethanol (DMAE).

[0012] CN111171272A discloses aqueous polyurethane dispersions based on IPDI, PPG, sulfamate hydrophilic chain extension agents, and cationic end-sealing reagents such as dimethylethanolamine (DMEA) or diethylethanolamine (DEEA).

[0013] Conventional aqueous polyurethane dispersions prepared according to a multi-step process using TEA as a neutralizing agent are stable at pH 6.5–9. However, when the pH drops below 6.5, the aqueous polyurethane dispersion becomes unstable because polyurethane without the amines necessary for stability in acidic environments remains. As a result, the polyurethane polymer precipitates from the dispersion and becomes unusable.

[0014] Another drawback is that when the aqueous polyurethane dispersion dries, volatile neutralizing agents such as TEA evaporate into the atmosphere. Therefore, TEA becomes an air pollutant.

[0015] Glass fiber producers have a long-standing need for glass fiber sizing based on aqueous polyurethane dispersions containing fine particle sizes that can be used under both acidic and basic conditions that are not harmful to the environment. Therefore, the objective was to provide an aqueous polyurethane dispersion that overcomes the obstacles and shortcomings of prior art aqueous polyurethane dispersions.

[0016] Surprisingly, it has now been found that avoiding volatile neutralizing agents such as TEA in the manufacturing process, and adding dialkylethanolamines such as dimethylethanolamine or diethylethanolamine to the polyurethane prepolymer formation process, leads to the avoidance of VOCs and thus air pollution. By adding dimethylethanolamine or diethylethanolamine to the polyurethane prepolymer formation process, the dimethylethanolamine or diethylethanolamine reacts with the polyurethane prepolymer chain to form DMEA-terminated polyurethane prepolymers, at least partially, which act as non-volatile polymeric tertiary amines. This enables the production of aqueous polyurethane dispersions with the fine particle size required for glass fiber sizing. Furthermore, this aqueous polyurethane dispersion can maintain dispersion stability at pH 4.1 to 9+. Moreover, the aqueous polyurethane dispersion is VOC-free and therefore can be used without causing air pollution. [Prior art documents] [Patent Documents]

[0017] Patent Document 1 US3,479,310 Patent Document 2 DE1,495,847 Patent Document 3 US5692937 Patent Document 4 US5965195 Patent Document 5 WO2003 / 035710A1 Patent Document 6 US2006 / 0205869 Patent Document 7 US2011 / 0306724 Patent Document 8 WO2017 / 042178A1 Patent Document 9 WO2017 / 137237A1 Patent Document 10 CN111171272A Non-Patent Literature

[0018] Non-Patent Literature 1 Methoden der organischen Chemie (Houben-Weyl. 4th Edition, Volume E20, H Bartl, J. Falbe, Stuttgart, New York, Thieme 1987, pp. 1671-1682 Non-Patent Literature 2 H. Pandya, P. Mahanwar; Advanced Industrial and Engineering Polymer Research 3 (2020), pp. 102-110 Summary of the Invention Problems to be Solved by the Invention

[0019] The present invention aims to provide an aqueous polyurethane dispersion, a method for preparing the same, a coating containing the same, and a coated article obtained by coating an article with the coating. Means for Solving the Problems

[0020] According to one aspect of the present invention, there is provided a method for preparing an aqueous polyurethane dispersion obtainable by the present invention, wherein i) a) at least one polyol, b) at least one anionic internal surfactant comprising at least two NCO-reactive groups and at least one negatively charged functional group, preferably a carboxyl group, c) dimethylethanolamine or diethylethanolamine, and d) at least one polyisocyanate, preferably at least one aliphatic, cycloaliphatic or aromatic di- or triisocyanate forming an NCO-terminated polyurethane prepolymer from a reaction mixture consisting of, wherein at least one polyisocyanate is used in excess relative to the molar ratio of isocyanate groups to NCO-reactive groups and hydroxyl groups of other components of the reaction mixture; ii) dispersing the polyurethane prepolymer into a continuous aqueous phase under application of shearing force, preferably by mechanical stirring, to obtain a prepolymer dispersion; iii) reacting the prepolymer dispersion with at least one chain extender to obtain the aqueous polyurethane dispersion comprising a method is provided, wherein steps i), ii) and iii) are carried out in the absence of an organic solvent.

[0021] According to another aspect of the present invention, there is provided an aqueous polyurethane dispersion obtained by the method according to the present invention.

[0022] According to another aspect of the present invention, there is provided a composition comprising the aqueous polyurethane dispersion according to the present invention.

[0023] According to yet another aspect of the present invention, a coating comprising an aqueous polyurethane dispersion obtained by the present invention is provided.

[0024] According to yet another aspect of the present invention, a coated article containing glass fibers coated with a coating according to the present invention is provided.

[0025] In yet another aspect of the present invention, the use of the aqueous polyurethane dispersion according to the present invention in the manufacture of coated articles is provided. [Modes for carrying out the invention]

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art. In the event of any conflict between a definition of a term herein and a meaning generally understood by those skilled in the art relating to the present invention, the definition herein shall prevail.

[0027] As used herein, "and / or" refers to one or all of the elements referred to.

[0028] As used herein, the articles “a,” “an,” and “the” mean one or more (including plurals), unless the context specifically indicates otherwise.

[0029] As used herein, “one or more” means, with respect to at least one, one, two, three, four, five, six, seven, eight, nine or more of the referenced species. Similarly, “at least one” means one or more, i.e., including one, two, three, four, five, six, seven, eight, nine or more. As used herein with respect to any component, “at least one” refers to the number of chemically distinct molecules, i.e., the number of different types of the referenced species, but not the total number of molecules.

[0030] As used herein, “including” and “comprising / containing” are intended to cover situations where only the elements mentioned are present, and situations where not only the elements mentioned but also other unmentioned elements are present.

[0031] All described scopes are comprehensive and combinable.

[0032] Unless otherwise specified, all percentages in this invention are by mass.

[0033] The term "room temperature" refers to a temperature of 23°C ± 2°C.

[0034] The term "polyurethane" or "polyurethane polymer" refers to a polymer having one or more urethane (-N(H)-C(O)-O-) and / or urea (-N(H)-C-(O)-N-) bonds.

[0035] Since the structure of polyurethane can be complex, the polyurethanes described in this invention are discussed in relation to the various monomers used to form the polyurethane.

[0036] As used herein, "NCO" refers to the isocyanate group -N=C=O. As used herein, "NCO terminus" refers to a polyurethane prepolymer containing at least one free NCO group at one of its termini.

[0037] The carboxylate group of the present invention is -COO - It means...

[0038] In this invention, the carboxyl group refers to the -COOH group.

[0039] Method for preparing an aqueous polyurethane dispersion The present invention further relates to a method for preparing an aqueous polyurethane dispersion, i) a) at least one polyol, b) At least one anionic internal surfactant comprising at least two NCO reactive groups and at least one negatively charged functional group, preferably a carboxyl group, c) Dimethylethanolamine, and d) At least one polyisocyanate, preferably at least one aliphatic, alicyclic, or aromatic di- or triisocyanate The process involves forming an NCO-terminated polyurethane prepolymer from a reaction mixture composed of the following: at least one polyisocyanate is used in excess of the isocyanate group relative to the molar ratio of the NCO-reactive groups and hydroxyl groups of the other components of the reaction mixture; ii) A step of obtaining a prepolymer dispersion by dispersing a polyurethane prepolymer in a continuous aqueous phase, preferably by mechanical stirring under the application of shear force, iii) A step of reacting a prepolymer dispersion with at least one chain extender to obtain an aqueous polyurethane dispersion. Includes, This invention relates to a method in which steps i), ii), and iii) are carried out in the absence of organic solvents.

[0040] Step i) Formation of polyurethane prepolymer In step i), the NCO-terminated polyurethane prepolymer is a) at least one polyol, b) At least one anionic internal surfactant comprising at least two NCO reactive groups and at least one negatively charged functional group, preferably a carboxyl group, c) Dimethylethanolamine or diethylethanolamine, and d) At least one polyisocyanate, preferably at least one aliphatic, alicyclic, or aromatic di- or triisocyanate The reaction mixture is formed from the following, and at least one polyisocyanate is used in excess of the isocyanate group relative to the NCO-reactive groups and hydroxyl groups of the other components of the reaction mixture.

[0041] The polyurethane prepolymer formation reaction is usually carried out at a high temperature, preferably in the range of 55°C to 105°C, more preferably in the range of 60°C to 100°C, and even more preferably in the range of 70°C to 95°C, over a period of 1 to 24 hours, preferably 2 to 10 hours.

[0042] In a preferred embodiment, step i) is performed under oscillation, more preferably at 100 rpm to 1,200 rpm, for example, 200 rpm.

[0043] The polyurethane prepolymer formation reaction is typically continued until the free isocyanate content (NCO%) reaches or comes very close to the calculated value determined by titration with butylamine using standard bromophenol blue. A preferred value for the free isocyanate content in the polyurethane prepolymer is in the range of 1% to 10% by mass, preferably 2.5% to 7% by mass, relative to the total mass of the polyurethane prepolymer.

[0044] The resulting polyurethane prepolymer is typically in a solid or liquid state, preferably a liquid state.

[0045] The ionic groups present in the polyurethane prepolymer are converted to ionic form by partial or complete reaction with the tertiary amine of the polymeric tertiary amine simultaneously formed in situ during step i).

[0046] Once the free isocyanate content reaches the predetermined value defined above, the temperature is typically lowered to, for example, 75°C to 90°C. Below 60°C, the viscosity of the polyurethane prepolymer is too high to disperse properly, resulting in an insufficient particle size.

[0047] In a preferred embodiment, the reaction mixture in step i) further comprises an organic antioxidant.

[0048] In another preferred embodiment, the reaction mixture in step i) further comprises a nonionic internal surfactant, preferably a linear monohydroxyl-functional polyethylene glycol monomethyl ether (methyl PEG; M-PEG). When a shear force is applied, M-PEG stabilizes the aqueous polyurethane dispersion in the dispersion step ii).

[0049] In another embodiment, the polyurethane prepolymer formation reaction is carried out in the presence of an added catalyst, such as a metal catalyst, a tin catalyst, or an organic catalyst. In a preferred embodiment of the present invention, the reaction mixture contains only a small amount of organic catalyst, or more preferably no catalyst at all as defined above.

[0050] Step ii) Dispersion in water In step ii), the polyurethane prepolymer obtained in step i) is dispersed in a continuous aqueous phase under the application of shear force to obtain a prepolymer dispersion.

[0051] The continuous aqueous phase is preferably water, or a mixture of water and an external nonionic surfactant (e.g., Emulsogen® LCN 118), more preferably a mixture of water and an external nonionic surfactant that does not contain an organic solvent. The presence of the external nonionic surfactant supports the formation of small particle sizes and therefore shear stability.

[0052] Step ii) is usually carried out at a high temperature, preferably in the range of 30°C to 80°C, more preferably in the range of 50°C to 70°C, for example, 60°C.

[0053] A continuous aqueous phase is preferably added on top of the polyurethane prepolymer.

[0054] In a preferred embodiment, shear force is induced by mechanical stirring, for example using a mechanical stirrer, at a maximum of 2,000 rpm, preferably 200 rpm to 1,500 rpm, more preferably 800 rpm to 1,200 rpm, for example 1,000 rpm, typically for a period of 10 seconds to 10 minutes, preferably 1 to 5 minutes, for example 3 minutes, to form a water-in-oil dispersion.

[0055] In a preferred embodiment, the water-in-oil dispersion is mixed with water to form an oil-in-water dispersion.

[0056] Step iii) - Chain extension In step iii), at least one chain extender is reacted with the isocyanate end groups of the polyurethane prepolymer to obtain an aqueous polyurethane dispersion.

[0057] The chain extender contains at least two terminal NCO-reactive groups. Suitable chain extenders for the present invention are hydrazine, alkylenediamine or cycloalkylenediamine, or diamines such as silane-containing diamines, preferably ethylenediamine (EDA), isophoronediamine, piperazine, or polyetheramine. Diols such as alkyldiols, including but not limited to 1,4-butanediol and 2-butyl-2-ethyl-1,3-propanediol, or water can also be used. The aforementioned chain extender also contains but not limited to (3-aminopropyl)triethoxysilane (APTES) and may be combined with end-sealing reagents such as silane-containing amines. Silane-containing amines can further promote substrate adhesion.

[0058] The chain extension reaction typically proceeds to the point of essentially the entire conversion of the isocyanate group, i.e., the chain extender is continuously added until the free isocyanate group is no longer detectable. It is generally preferable that the chain extension reaction proceeds to the entire conversion of the isocyanate group. In one embodiment, up to 80% of the chain extender's stoichiometric amount is added to the prepolymer dispersion. The remaining free NCO groups react with water. The conversion can be monitored by techniques well established in the art, for example, by IR spectroscopy.

[0059] Step iii) is usually carried out at room temperature.

[0060] In a preferred embodiment, step iii) is performed under oscillation, more preferably at 100 rpm to 1,000 rpm, for example, 500 rpm.

[0061] The equivalent ratio of the two terminal NCO-reactive groups of the chain extender in step iii) to the free isocyanate groups (NCO%) of the polyurethane prepolymer is typically 40 mol% to 80 mol%, preferably 60 mol% to 80 mol%.

[0062] Steps i), ii), and iii) are preferably carried out in the absence of organic solvents.

[0063] In another embodiment, step iii) is carried out in the presence of a catalyst and / or high temperature. Optionally, the aqueous polyurethane dispersion is preferably degassed overnight.

[0064] Water-based polyurethane dispersion (PUD) Aqueous polyurethane dispersions are obtained by the methods according to the present invention as described herein.

[0065] In preferred embodiments, the aqueous polyurethane dispersion contains water.

[0066] In one embodiment, the aqueous polyurethane dispersion is an anionic nonionic polyurethane dispersion derived from an anionic compound, preferably DMEA and DMPA, and a nonionic compound, preferably M-PEG.

[0067] The number-average molecular weight (Mn) of the polyurethane in the aqueous polyurethane dispersion is preferably 1,000 g / mol to 10,000 g / mol.

[0068] In preferred embodiments, the aqueous polyurethane dispersion of the present invention does not contain sulfur-containing compounds such as amino-functional sulfonic acids (e.g., Vestamin® A 95; commercially available from Evonik).

[0069] In preferred embodiments, the aqueous polyurethane dispersion of the present invention does not contain a volatile organic compound (VOC) selected from the group consisting of triethylamine, dimethylcyclohexylamine, ethyldiisopropylamine, diethanolamine, triethanolamine, dimethylethanolamine, diethylethanolamine, methyldiethanolamine, and aminomethylpropanol.

[0070] In another preferred embodiment, the aqueous polyurethane dispersion of the present invention does not contain a neutralizing agent selected from the group consisting of ammonia, sodium hydroxide, potassium hydroxide, lithium hydroxide, and calcium hydroxide.

[0071] In another preferred embodiment, the aqueous polyurethane dispersion of the present invention does not contain an organic solvent selected from the group consisting of acetone, toluene, dipropylene glycol dimethyl ether (DPGDME), and N-methyl-pyrrolidone (NMP).

[0072] In a more preferred embodiment, the aqueous polyurethane dispersion of the present invention is free of volatile organic compounds (VOCs) and organic solvents.

[0073] In its most preferred embodiment, the aqueous polyurethane dispersion of the present invention is free of volatile organic compounds (VOCs), neutralizing agents, and organic solvents.

[0074] The solid content of the aqueous polyurethane dispersion is determined by weighing the residue of the sample after heating and moisture removal, and is preferably 20% to 70% by mass, more preferably 30% to 65% by mass, and most preferably 35% to 60% by mass, relative to the total mass of the aqueous polyurethane dispersion.

[0075] The viscosity is determined by a Brookfield viscometer, spindle 4, 20 rpm, and is preferably in the range of 50 mPas to 10,000 mPas, preferably 100 mPas to 1,000 mPas, more preferably 200 mPas to 600 mPas, and most preferably 250 mPas to 450 mPas. The viscosity is usually adjusted by adding a thickener to suit the desired coating form. Suitable viscosity modifiers and thickeners are well known in the art.

[0076] The particle size is typically determined by dynamic light scattering (DLS) to be in the range of 50 nm to 1,000 nm, preferably 100 nm to 900 nm, more preferably 20 nm to 800 nm, even more preferably between 300 nm and 750 nm, and most preferably between 500 nm and 700 nm.

[0077] polyol At least one polyol in the reaction mixture of step i) of the method of the present invention is a non-functionalized polyol, that is, it does not contain any functional groups other than hydroxyl groups. The polyol may include at least one polyether polyol and / or at least one polyester polyol. Preferably, the polyol includes at least one polyether polyol and optionally at least one polyester polyol, at least one polycarbonate polyol, or any mixture of two or more of the aforementioned polyols. A polyether polyol, or a mixture of at least one polyether polyol with one or more polyester polyols, is particularly preferred.

[0078] Polyether polyols suitable for the present invention as described herein include polyalkylene glycol homo- or copolymers, preferably polypropylene glycol homo- or copolymers, polyethylene glycol homo- or copolymers, polytetramethylene ether glycol (poly(THF) or PTMEG) homo- or copolymers, or polypropylene glycol / polyethylene glycol block copolymers, or mixtures thereof. In various embodiments, the polyether polyol has a number-average molecular weight Mn of 400 g / mol to 10,000 g / mol, preferably 500 g / mol to 3,000 g / mol.

[0079] Polyester polyols suitable for the present invention as described herein include those obtainable by reacting a dicarboxylic acid with a polyol in a polycondensation reaction. The dicarboxylic acid may be aliphatic, alicyclic, aromatic, and / or derivatives thereof, such as anhydrides, esters, or acid chlorides. Specific examples of these include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid or sebacic acid, phthalic acid, isophthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimeric fatty acids, and dimethyl terephthalate. Suitable examples of polyols include monoethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 3-methylpentane-1,5-diol, neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,6-hexanediol, 1,8-octane glycol, cyclohexanedimethanol, 2-methylpropane-1,3-diol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol, and polybutylene glycol. Alternatively, they can be obtained by ring-opening polymerization of cyclic esters, preferably ε-caprolactone.

[0080] Polycarbonates suitable for the present invention as described herein can be obtained by reaction with diols of carbonic acid derivatives, such as diphenyl carbonate, dimethyl carbonate, or phosgene. Suitable examples of such diols include ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 1,4-bishydroxymethylcyclohexane, 2-methyl-1,3-propanediol, 2,2,4-trimethylpentanediol-1,3-dipropylene glycol, polypropylene glycol, dibutylene glycol, polybutylene glycol, bisphenol A, tetrabromobisphenol A, and lactone-modified diols. The diol component preferably contains 40% to 100% by mass of hexanediol, preferably 1,6-hexanediol and / or hexanediol derivatives. More preferably, the diol component includes examples that exhibit an ether or ester group in addition to the terminal OH group.

[0081] Hydroxyl polycarbonates must be substantially linear. However, they can be selectively branched by incorporating polyfunctional components, particularly low molecular weight polyols. Suitable examples include glycerin, trimethylolpropane, hexanetriol-1,2,6, butanetriol-1,2,4, trimethylolpropane, pentaerythritol, quinitol, mannitol, and sorbitol, methyl glycosides, and 1,3,4,6-dianehydrohexite.

[0082] Suitable polycarbonate polyols, though not limited to these, may be obtained under the trademark names Desmophen® C3200 (Covestro) and Kuraray C2050 (poly-(3-methyl-1,5-pentanediol, 1,6-hexanediol) carbonate; Kuraray).

[0083] The reaction mixture may further contain a monomer diol, such as 1,4-butanediol.

[0084] At least one of the polyols is preferably a polyether polyol.

[0085] In a more preferred embodiment, the polyol is polypropylene glycol (PPG), or a mixture comprising one or more PPGs having varying number-average molecular weights.

[0086] In various embodiments, the number-average molecular weight of the polyol is determined by gel permeation chromatography at 40°C using tetrahydrofuran as the mobile phase and polystyrene as the control standard, preferably 400 g / mol to 5,000 g / mol, more preferably 500 g / mol to 3,000 g / mol, more preferably 800 g / mol to 2,500 g / mol, and most preferably 1,000 g / mol to 2,000 g / mol. In even more preferred embodiments, the polyol is a mixture of polypropylene glycols having molecular weights of 400 g / mol to 500 g / mol, for example 425 g / mol, and 900 g / mol to 100 g / mol, for example 1,025 g / mol.

[0087] The amount of polyol is preferably 10% to 90% by mass, more preferably 10% to 80% by mass, and most preferably 40% to 70% by mass, relative to the total mass of the reaction mixture.

[0088] The hydroxyl functional value of the polyol is preferably 1 to 3, more preferably 1.8 to 2.4, and most preferably 2.0.

[0089] Anionic internal surfactant The reaction mixture in step i) of the method according to the present invention further comprises at least one anionic internal surfactant comprising at least two NCO reactive groups and at least one negatively charged functional group, preferably a sulfonic acid group or a carboxylic acid group, more preferably a carboxylic acid group.

[0090] The NCO-reactive group is preferably selected from the group consisting of a hydroxyl group, a mercapto group, and an amino group, and more preferably the NCO-reactive group is a hydroxyl group.

[0091] Sulfonic acid groups or carboxylic acid groups can be used directly in the form of their salts, such as sulfonates or carboxylate salts.

[0092] In a more preferred embodiment, the anionic internal surfactant is a carboxyl group-containing anionic internal surfactant. At least one anionic internal surfactant of the present invention is preferably selected from the group consisting of 2,2-bis(hydroxyalkyl)alkane monocarboxylic acids, particularly 2,2-bis(hydroxymethyl)alkane monocarboxylic acids having a total of 5 to 8 carbon atoms, and amino acids. The amino acid is preferably one or more selected from the group consisting of lysine, 6-aminocaproic acid, and proline.

[0093] A particularly preferred carboxylic acid group-containing anionic internal surfactant according to the present invention is selected from the group consisting of 2,2-bis(hydroxymethyl)propionic acid (dimethylolpropionic acid; 2,2-dihydroxymethylpropionic acid; DMPA) or 2,2-dihydroxymethylbutyric acid.

[0094] In the most preferred embodiment of the present invention, the anionic internal surfactant is DMPA. DMPA is commercially available from Perstorp.

[0095] The anionic groups in the aqueous polyurethane dispersion of the present invention are mainly derived from an anionic internal surfactant. The amount of the anionic internal surfactant is preferably 0.1% to 3% by mass relative to the total mass of the reaction mixture.

[0096] Dimethylethanolamine (DMEA; DMAE) or diethylethanolamine (DEEA) The reaction mixture in step i) of the method according to the present invention further comprises dimethylethanolamine or diethylethanolamine. DMEA or DEEA acts as a chain arrester that limits the molecular weight of the polyurethane prepolymer formed.

[0097] The amount of DMEA or DEEA is more than 100% of the stoichiometric amount required to neutralize the anionic internal surfactant, preferably 110% to 130%, for example, 120%. Any excess DMEA or DEEA is corrected to the required amount if the pH of the system decreases. DMEA or DEEA stabilizes the polyurethane by forming additional polymeric tertiary amines.

[0098] DMEA or DEEA is usually added in one or more divided portions.

[0099] In a preferred embodiment, dimethylethanolamine is used.

[0100] Dimethylethanolamine is marketed by Eastman under the trade name Amietol® M21 or NeoRez® R-2005 as a DSM.

[0101] Polyisocyanate The reaction mixture in step i) of the method according to the present invention further comprises at least one polyisocyanate. The polyisocyanate according to the present invention is a compound represented by the general formula R(NCO)n [wherein R represents an organic compound containing any number of carbon atoms, provided that n≧2].

[0102] Any known compound can be used as a polyisocyanate, typical examples of which include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- or 1,4-diisocyanate (CHDI), 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (isophorone diisocyanate; IPDI), and dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI; The HMDI comprises 2- or 4-isocyanatocyclohexyl-2'-isocyanatocyclohexylmethane, 1,3- or 1,4-bis-(isocyanatomethyl)-cyclohexane, bis-(4-isocyanato-3-methylcyclohexyl)methane, 1,3- or 1,4-a,a,a'a'-tetramethylxylylenediisocyanate, 2,4- or 2,6-toluenediisocyanate (TDI), 2,2'-, 2,4'- or 4,4'-methylenediphenyldiisocyanate (MDI), 1,5-naphthalenediisocyanate (NDI), p-phenylenediisocyanate (PPDI), or m-phenylenediisocyanate and xylylenediisocyanate (XDI).

[0103] In a preferred embodiment, at least one polyisocyanate in the reaction mixture in step i) is at least one aliphatic, alicyclic, or aromatic di- or triisocyanate.

[0104] In a more preferred embodiment, at least one polyisocyanate is dicyclohexylmethane-4,4'-diisocyanate (H12MDI), isophorone diisocyanate (IPDI), 2,4- or 2,6-toluene diisocyanate (TDI), or hexamethylene diisocyanate (HDI), or a mixture thereof.

[0105] In a more preferred embodiment, at least one polyisocyanate is isophorone diisocyanate (IPDI) or hexamethylene diisocyanate (HDI), or a mixture thereof.

[0106] In the most preferred embodiment, at least one polyisocyanate is IPDI. IPDI is commercially available from Covestro.

[0107] In step i), at least one polyisocyanate of the reaction mixture is used in excess of the isocyanate group relative to the molar ratio of the NCO-reactive group and hydroxyl group (OH) of the other components of the reaction mixture, i.e., at a concentration exceeding the stoichiometric concentration required for complete reaction with the hydroxyl group.

[0108] The OH / NCO equivalent ratio is preferably 1:1.1 to 1:4, more preferably 1:1.5 to 1:2.5. Preferably, the amount of polyisocyanate is 20% to 150% in excess of the stoichiometric concentration required for complete reaction with the hydroxyl group.

[0109] The amount of polyisocyanate is preferably 5% to 70% by mass, more preferably 5% to 40% by mass, even more preferably 5% to 35% by mass, and most preferably 10% to 30% by mass, relative to the total mass of the reaction mixture.

[0110] Chain extender The chain extender of the present invention contains at least two NCO-reactive groups.

[0111] The chain extender is preferably selected from the group consisting of water, diols, mono-, di-, and trifunctional amines, and mono-, di-, and trifunctional hydroxylamines.

[0112] The chain extender is more preferably hydrazine, alkylenediamine, cycloalkylenediamine, silane-containing diamine, alkyldiol, or polyetherdiamine.

[0113] The chain extender is most preferably selected from the group consisting of ethylenediamine (EDA), hydrazine, water, isophoronediamine, dihydrazide adipate, diethylenetriamine, diethanolamine, ethanolamine, and N-(2-hydroxyethyl)-ethylenediamine.

[0114] In preferred embodiments, the chain extender is a diamine, more preferably an ethylenediamine. EDA is commercially available from BASF.

[0115] additives The aqueous polyurethane dispersion of the present invention may further contain additives. Useful additives include antioxidants, stabilizers, surfactants, biocides, and reaction diluents.

[0116] Antioxidant The aqueous polyurethane dispersion of the present invention may contain an antioxidant. Suitable antioxidants for the present invention are preferably one or more selected from the group consisting of metal carbamic acid compounds, phenolic antioxidants, amine-type antioxidants, and heterocyclic antioxidants, most preferably phenolic antioxidants.

[0117] The amount of organic antioxidant is preferably 0.06% to 2.0% by mass, with the amount of polyurethane being 100% by mass.

[0118] The phenolic antioxidant is preferably one or more alkylhindered phenols, polycyclic hindered phenols, and alkylthiohindered phenols.

[0119] In a preferred embodiment, the antioxidant is butylhydroxytoluene (BHT). BHT is commercially available from Sasol.

[0120] surfactants In one embodiment of the present invention, the aqueous polyurethane dispersion contains an external surfactant. In a preferred embodiment, the surfactant is an APE-free surfactant (an alkylphenol ethoxylate-free surfactant). In another embodiment, the surfactant is a nonionic surfactant. Commonly known surfactants include, for example, Emulsogen® LCN-118, EPN 118, LCN 088, LCN 158, LCN 217, TS 200 (Clariant), Rhodasurf® BC 840, B1, BC-610 (Solvay), and Genapol® LA 160, LA 070, T250 (Clariant). In a more preferred embodiment, the nonionic surfactant is selected from the group consisting of Emulsogen® LCN 118 (Clariant), Rhodasurf® BC 840 (Solvay), and Genapol® LA 160 (Clariant).

[0121] composition The present invention further relates to compositions comprising an aqueous polyurethane dispersion according to the present invention as described herein.

[0122] The compositions of the present invention described herein are characterized in that the composition is a coating, adhesive, sealant, or printing ink.

[0123] coating The present invention further relates to a coating comprising an aqueous polyurethane dispersion according to the present invention as described herein.

[0124] Coatings containing the aqueous polyurethane dispersion of the present invention as described herein exhibit excellent chemical resistance, good flexibility, excellent abrasion resistance and cohesive strength, and excellent low-temperature chip resistance, while being VOC-free and therefore environmentally friendly. Coatings according to the present invention adhere to a wide range of substrates and can be formulated with additives to enhance their properties.

[0125] Coated articles The present invention further relates to articles coated with coatings according to the present invention as described herein. In preferred embodiments, the articles are made of glass fiber.

[0126] use The present invention further relates to the use of the aqueous polyurethane dispersions described herein in the manufacture of coated articles.

[0127] The aqueous polyurethane dispersion of the present invention is useful as a coating for glass fibers.

[0128] Furthermore, the use of the aqueous polyurethane dispersion of the present invention includes coatings such as UV coatings, floor coatings, sanitary coatings, leather coatings, plastic coatings, textile coatings, nonwoven fabric coatings, wood coatings, adhesives, concrete coatings, automotive coatings, transparent coatings, and corrosion-resistant coatings.

[0129] It is understood that all embodiments of the methods disclosed herein are similarly applicable to the disclosed dispersions, compositions and uses, and vice versa.

[0130] The following examples are given to illustrate the present invention. These examples are given for illustrative purposes only and should not be considered as limiting the present invention. [Examples]

[0131] material Chemical suppliers Arcol® PPG 1025 Polyol; Polypropylene glycol (PPG); Mn = 1025 g / mol; (Commercially available from Covestro) Arcol® PPG 425 Polyol; Polypropylene glycol (PPG); Mn = 425 g / mol; CAS # 25322-69-4; (Commercially available from Covestro) Fomrez (registered trademark) YA8-1 polyester polyol; (commercially available from LANXESS) Polyglykol M2000S Linear monohydroxyl-functional polyethylene glycol monomethyl ether (methyl PEG; M-PEG); (Commercially available from Clariant) DMPA 2,2-dihydroxymethylpropionic acid; CAS# 4767-03-7; (Commercially available from Perstorp) DMEA (Dimethylethanolamine; N,N-dimethylethanolamine); CAS# 108-01-0; Amietol® M21; (Commercially available from Eastman) BHT antioxidant; butylhydroxytoluene; (commercially available from Sasol) Irganox® 1010 Pentaerythritol Tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate); (Commercially available from BASF) IPDI diisocyanate; isophorone diisocyanate; CAS# 4098-71-9; (commercially available from Covestro) Desmodur® W Diisocyanate; H12MDI; (Commercially available from Covestro) EDA chain extender; ethylenediamine; (commercially available from BASF) Emulsogen® LCN-118: Nonionic surfactant, C11 oxo alcohol; HLB value = 14; (Commercially available from Clariant) Genapol® LA 160 nonionic surfactant; (commercially available from Clariant) TEA neutralizing agent; triethylamine; CAS# 121-44-8; boiling point 87°C; (commercially available from Eastman) Biocide MIT / BIT compound; (marketed under the trade name Preventol® by LANXESS) Deionized water

[0132] method: The measurements according to this invention shall be performed at 23+2°C unless otherwise specified.

[0133] The solids content (SC%) of an aqueous polyurethane dispersion is measured by heating a known amount of the sample at a high temperature until a constant weight is obtained. The heating residue is used to calculate the % solids content.

[0134] The free isocyanate group (NCO) content in the polyurethane prepolymer is determined by dissolving the sample in toluene and reacting the unreacted NCO groups with excess butylamine. The remaining amine is then titrated with hydrochloric acid solution to the bromophenol blue endpoint.

[0135] The pH of the aqueous polyurethane dispersion is measured at 23°C using a standard pH meter.

[0136] The viscosity of the aqueous polyurethane dispersion is measured using a Brookfield viscometer, spindle 4, at 20 rpm.

[0137] The particle size of the aqueous polyurethane dispersion is measured by dynamic light scattering (DLS) using a Malvern 3000 particle size analyzer.

[0138] Gel permeation chromatography is used to measure the number-average and mass-average molecular weight of polyurethane. An aqueous polyurethane dispersion is coated onto a polytetrafluoroethylene plate, and the coated plate is air-dried at room temperature to obtain a dry film. An appropriate amount of the dry film is weighed and dissolved in tetrahydrofuran at a concentration of 8 mg / mL. The test is performed using an Agilent 1260 (column temperature = 36°C, injection volume = 60 EL, flow rate = 0.7 mL / min). The test results are obtained based on a polystyrene standard as a control, and fractions with a molecular weight of 100 or more are selected for calculation.

[0139] Aqueous polyurethane dispersions are synthesized according to the following method.

[0140] [Table 1]

[0141] Method for producing aqueous polyurethane dispersion (the present invention) Deionized water was divided into a first water charge (15% by mass) and a second water charge (85% by mass). The first water charge (15% by mass) was mixed with the nonionic surfactant Emulsogen® LCN-118 at 400 rpm and maintained in a 60°C oven for 5 hours. PPG 1025, PPG 425, Polyglykol M2000S, DMPA, DMEA, BHT, and IPDI were loaded into a flask in the following order to form a reaction mixture, which was then agitated at 200 rpm for 5 hours at 75°C to prepare a polyurethane prepolymer. The NCO% value of the polyurethane prepolymer was measured to verify the target NCO%. Based on the final NCO% of the polyurethane prepolymer, the amount of EDA to be added was determined.

[0142] Next, a dispersion process was carried out. The polyurethane prepolymer was oscillated at a 1,000 rpm oscillator speed, and a mixture of the first water charge and Emulsogen® LCN-118 was added to the polyurethane prepolymer. The mixture was oscillated at 1,000 rpm for 3 minutes, and a second water charge was added to form a prepolymer dispersion. The prepolymer dispersion was cooled in an ice / water bath until the reaction mixture reached 30°C.

[0143] EDA, pre-diluted with five times the volume of water, was added, and the mixture of the prepolymer dispersion and chain extender was cooled to 25°C at 500 rpm. Then, it was agitated at 200 rpm for 24 hours. Finally, the aqueous polyurethane dispersion was removed from the agitator, and its solid content (SC%), pH, viscosity, and particle size were measured (shown in Table 4).

[0144] [Table 2]

[0145] Method for producing aqueous polyurethane dispersion (comparative example) Deionized water was divided into a first water charge (15% by mass) and a second water charge (85% by mass). The first water charge (15% by mass) was mixed with the nonionic surfactant Emulsogen® LCN-118 and maintained in a 60°C oven for 5 hours. PPG 1025, PPG 425, Polyglykol M2000S, DMPA, BHT, and IPDI were loaded into a flask in the following order to form a reaction mixture, which was shaken at 200 rpm for 5 hours at 75°C. The NCO% value of the polyurethane prepolymer was measured to verify the target NCO%. Based on the final NCO% of the polyurethane prepolymer, the amount of EDA to be added was determined.

[0146] The next step was the neutralization of DMPA by adding TEA as a neutralizing amine to the polyurethane prepolymer, which was oscillated at 200 rpm for 30 minutes at 75°C.

[0147] Next, a dispersion process was carried out. The polyurethane prepolymer was oscillated at a 1,000 rpm oscillator speed, and a mixture of the first water charge and Emulsogen® LCN-118 was added to the polyurethane prepolymer. The mixture was oscillated at 1,000 rpm for 3 minutes, and a second water charge was added to form a prepolymer dispersion. The prepolymer dispersion was cooled in an ice / water bath until the reaction mixture reached 30°C.

[0148] EDA, pre-diluted with five times the volume of water, was added, and the mixture of the prepolymer dispersion and chain extender was cooled to 25°C at 500 rpm. Then, it was agitated at 200 rpm for 24 hours. Finally, the aqueous polyurethane dispersion was removed from the agitator, and its solid content (SC%), pH, viscosity, and particle size were measured (shown in Table 4).

[0149] [Table 3]

[0150] Method for producing aqueous polyurethane dispersions (comparative): The following components were loaded into a flask in the order listed below to form a reaction mixture, which was then shaken at 200 rpm for 3 hours at 85°C. The NCO% value of the polyurethane prepolymer was measured to verify the target NCO%. Based on the final NCO% of the polyurethane prepolymer, the amount of EDA to be added was determined.

[0151] The next step was the neutralization of DMPA by adding DMEA. Deionized water and DMEA were loaded into a container and stirred at 800 rpm. A polyurethane prepolymer was added to the mixture containing water and DMEA and stirred for a further 10-20 minutes to form a prepolymer dispersion.

[0152] EDA, pre-diluted with five times the volume of water, was added, and the mixture of the prepolymer dispersion and chain extender was stirred for 2 hours. A biocide dissolved in water was added, and the mixture was stirred for a further 1 hour.

[0153] [Table 4]

[0154] Table 4 shows that when subjected to a lower pH environment (pH adjusted to 6.1, 5.1, and 4.12 using 25% acetic acid), Example 1 of the present invention remains stable and maintains comparable particle size at pH 7.18, while Comparative Examples 2 and 3 precipitate at pH < 6.5.

[0155] Example 1 of the present invention contains a non-volatile polymeric tertiary amine. The aqueous polyurethane dispersion of the present invention is VOC-free (for example, does not contain amines such as TEA or DMEA, or solvents such as acetone or toluene). The VOC-free aqueous polyurethane dispersion has comparable SC% (solids content), pH, viscosity, and particle size to Comparative Examples 2 and 3.

[0156] By reacting dimethylethanolamine with the polyurethane prepolymer chain, a non-volatile polymeric tertiary amine is simultaneously synthesized during the polyurethane prepolymer formation process. Under acidic conditions such as pH 4, the polymeric amine remains as part of the polymer chain. Furthermore, the aqueous polyurethane dispersion remains stable at such low pH levels. Therefore, the aqueous polyurethane dispersion is stable at pH 4.1 to 9+, which is preferred for glass fiber sizing applications. Glass fiber producers do not need to flush the system when switching from alkaline sizing to acidic sizing.

[0157] The addition of DMEA, and therefore the formation of polymeric tertiary amines in the prepolymer mixture during prepolymer formation step i), allows for the avoidance of another neutralization step compared to the comparative method shown in Example 2, thus providing an additional process improvement.

Claims

1. A method for producing an aqueous polyurethane dispersion, i) a) At least one polyol, b) At least one anionic internal surfactant comprising at least two NCO reactive groups and at least one negatively charged functional group, c) 110% to 130% of dimethylethanolamine or diethylethanolamine in a stoichiometric amount required to neutralize the anionic internal surfactant, and d) At least one type of polyisocyanate, The process involves forming an NCO-terminated polyurethane prepolymer from a reaction mixture composed of the following: at least one polyisocyanate is used in excess of the isocyanate group relative to the molar ratio of the NCO-reactive groups and hydroxyl groups of the other components of the reaction mixture; ii) A step of obtaining a prepolymer dispersion by dispersing a polyurethane prepolymer in a continuous aqueous phase under the application of a shear force after step i), iii) A step of reacting the prepolymer dispersion with at least one chain extender after step ii) to obtain an aqueous polyurethane dispersion. Includes, Steps i), ii), and iii) are carried out in the absence of an organic solvent. The process does not include a neutralization step of adding a neutralizing agent to the NCO-terminated polyurethane prepolymer formed by step i), Step i) comprising a polymeric tertiary amine formed from the dimethylethanolamine or the diethylethanolamine, A method for producing an aqueous polyurethane dispersion.

2. A method for producing an aqueous polyurethane dispersion according to claim 1, wherein at least one polyol is a polyether polyol.

3. A method for producing an aqueous polyurethane dispersion according to claim 1, wherein at least one anionic internal surfactant comprises 2,2-bis(hydroxymethyl)propionic acid (DMPA) or 2,2-dihydroxymethylbutyrate.

4. A method for producing an aqueous polyurethane dispersion according to claim 1, wherein at least one polyisocyanate is selected from the group consisting of dicyclohexylmethane-4,4'-diisocyanate (H12MDI), isophorone diisocyanate (IPDI), 2,4- or 2,6-toluene diisocyanate (TDI), or hexamethylene diisocyanate (HDI), or a mixture thereof.

5. A method for producing an aqueous polyurethane dispersion according to claim 1, wherein step ii) includes a step of dispersing a polyurethane prepolymer in a continuous aqueous phase.

6. A method for producing an aqueous polyurethane dispersion according to claim 1, wherein the chain extender in step iii) contains at least two NCO-reactive groups.

7. A method for producing an aqueous polyurethane dispersion according to claim 1, wherein the reaction mixture in step i) further comprises a nonionic internal surfactant.

8. The method for producing an aqueous polyurethane dispersion according to claim 1, wherein the dispersion of the polyurethane prepolymer in the continuous aqueous phase is carried out by mechanical stirring.

9. The method for producing an aqueous polyurethane dispersion according to claim 2, wherein the polyether polyol is selected from a polyalkylene glycol homopolymer or copolymer or a mixture thereof.

10. The method for producing an aqueous polyurethane dispersion according to claim 2, wherein the polyether polyol is selected from polypropylene glycol homo- or copolymer, polyethylene glycol homo- or copolymer, polytetramethylene ether glycol homo- or copolymer, polypropylene glycol / polyethylene glycol block copolymer, or a mixture thereof.

11. The method for producing an aqueous polyurethane dispersion according to claim 4, wherein the polyisocyanate is isophorone diisocyanate.

12. The method for producing an aqueous polyurethane dispersion according to claim 6, wherein the chain extender in step iii) is selected from the group consisting of ethylenediamine (EDA), hydrazine, water, isophoronediamine, dihydrazide adipate, diethylenetriamine, diethanolamine, ethanolamine, and N-(2-hydroxyethyl)-ethylenediamine.

13. The method for producing an aqueous polyurethane dispersion according to claim 7, wherein the nonionic internal surfactant is a linear monohydroxyl-functional polyethylene glycol monomethyl ether (M-PEG).

14. The method for producing an aqueous polyurethane dispersion according to claim 1, wherein the product of step iii) does not contain volatile organic substances (VOCs).

15. The method for producing an aqueous polyurethane dispersion according to claim 1, wherein the product of step iii) does not contain a sulfur-containing compound.

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