PROCESS TO PREPARE AQUEOUS POLYURETHANE DISPERSIONS THAT ARE SUBSTANTIALLY FREE OF VOLATILE ORGANIC COMPOUNDS AND THAT HAVE A HIGH SOLIDS CONTENT

Abstract

A process for the preparation of a polyurethane dispersion with at least one extension agent B that has x hydroxyl groups and y amine groups, where x+y≥2 with x and y equal or larger than 0, and that has an additional functional group that is capable of forming a salt, such that the dispersion of the polyurethane has a solids content of at least 50 weight percent and does not contain acetone or other solvents or amines that have a boiling point of below 250° C.

Claims

1. A process for the preparation of a polyurethane dispersion substantially free from volatile organic compounds comprising the steps of: i) synthesizing, in the absence of acetone, a polyurethane prepolymer from isocyanates, polyols, which may include polyols with hydrophilic groups, and a component A, said component A having x hydroxyl groups and y amine groups, wherein both x and y independently can be 0 or more than 0 and wherein x+y≥2, and having an additional functional group that is capable of forming a salt; and ii) dispersing the obtained prepolymer into a water phase optionally comprising other additives, (iii) adding one or more neutralizing agents such as alkaline metal hydroxide prior to, simultaneously with or after dispersing the prepolymer in water and, (iv) forming simultaneously with or subsequent to the dispersing polyurethane by reacting with one or more extension agents comprising a component B, said component B having x hydroxyl groups and y amine groups, wherein both x and y independently can be 0 or more than 0 and wherein x+y≥2 and having an additional functional group that is capable of forming a salt, such that the dispersion of the polyurethane has a solids content of at least 50 weight percent.

2. The process according to claim 1, wherein the additional functional group present in component A and/or component B is selected from a carboxylate group, a sulfonate group and a phosphate group.

3. The process according to claim 1, wherein component B contains one or multiple amino groups and one or multiple sulfonate groups such as sodium 2-[(2-aminoethyl)amino]ethane-sulfonate.

4. The process according to claim 1, wherein component A is a carboxyl containing diol.

5. The process according to claim 1, wherein the isocyanates are aliphatic di-isocyanates, aromatic di-isocyanates, or a mixture of aromatic and aliphatic di-isocyanates, such as toluene-2,4-diisocyanate, toluene-2,6-diisocyanate and mixtures thereof, diphenylmethane-4,4-diisocyanate, 1,4-phenylenediisocyanate, dicyclohexyl-methane-4,4′-diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclo-hexylisocyanate, 1,6-hexyldi-isocyanate, 1,5-pentyldiisocyanate, 1,3-bis(isocyanatomethyl)cyclo-hexane, 2,2,4-trimethyl-1,6-diisocyanatohexane (2,2,4-isomer, 2,4,4-isomer, or mixture thereof), 1,4-cyclohexyldiisocyanate, norbonyldiisocyanate, p-xylylene diisocyanate, 2,4′-diphenylmethane diisocyanate, and/or 1,5-naphthylene diisocyanate.

6. The process according to claim 1, wherein the polyols are selected from polyester polyols, polyesteramide polyols, polyether polyols, polythioether polyols, polycarbonate polyols, polyacetal polyols, polyolefin polyols or polysiloxane polyols or mixtures thereof, and wherein the diols or triols have a molecular weight below about 500.

7. The process according to claim 1 wherein the solids content of the aqueous polyurethane dispersion is at least about 55 weight percent.

8. The process according to claim 1 wherein the solids content of the aqueous polyurethane dispersion is at least about 60 weight percent.

9. The process according to claim 1, wherein the amount of component B is such that between about 0.05 to about 0.50 of molar equivalent of isocyanate reactive groups from component B is added with respect to the isocyanate functions that are present in the amount of prepolymer and the remaining isocyanate functions are extended by other extension agents, such as hydrazine, ethylene diamine, propylene diamine, 5-amino-1,3,3-trimethyl-cyclohexanemethyl-amine, or amine terminated polyethers, wherein the total amount of extension agent employed is such that the ratio of isocyanate reactive groups in the total amount of extension agent to the isocyanate groups in the prepolymer is in the range from about 0.7:1 to about 2.0:1.

10. The process according to claim 1, wherein the amount of component A is being about 0.1 and about 5 weight percent calculated on the total weight of the prepolymer.

11. The process according to claim 1, wherein the aqueous polyurethane dispersion has a total VOC content of less than about 1000 ppm.

12. The process according to claim 1, wherein the aqueous polyurethane dispersion has a total VOC content of less than about 500 ppm.

13. The process according to claim 1, wherein the aqueous polyurethane dispersion has a total VOC content of less than about 100 ppm.

14. A dispersion obtainable by the process of claim 1.

15. A coating or film obtained from a dispersion as defined in claim 14.

Description

[0035] According to an embodiment of the present invention component A and component B may the same or different compounds, the latter being preferred.

[0036] In the context of an embodiment of the present invention, the extension agent, or at least one of the extension agents in case a mixture of extension agents is used, is a component B. Component B could be used as the sole extension agent but preferably it is used in combination with other types of extension agent. Preferably the amount of component B is such that between about 0.02 to about 0.70, preferably between about 0.05 and about 0.50 and most preferably between about 0.05 and about 0.30, of equivalent of isocyanate reactive groups is added with respect to the isocyanate functions that are present in the prepolymer and the remaining isocyanate functions are extended by other extension agents. Preferred amongst the other extension agents are hydrazine, ethylene diamine, propylene diamine, 5-amino-1,3,3-trimethyl-cyclohexanemethyl-amine, and amine terminated polyethers such as, for example, Jeffamine D-230 from Huntsman Chemical Company.

[0037] The total amount of extension agent employed should be approximately equivalent to the free NCO groups in the prepolymer; the ratio of active hydrogens in the total extension agent to NCO groups in the prepolymer preferably being in the range from about 0.7:1 to about 2.0:1. Of course when water is employed as an extension agent, these ratios will not be applicable since the water, functioning both as extension agent and dispersing medium, will be present in a gross excess relative to the free NCO groups.

[0038] While polyurethane prepolymers may retain some isocyanate reactivity for some period of time after dispersion, for purposes of an embodiment of the present invention, a polyurethane prepolymer dispersion is considered to be a fully reacted polyurethane polymer dispersion. Also, for purposes of an embodiment of the present invention, a polyurethane prepolymer or polyurethane polymer can include other types of structures such as, for example, urea groups.

[0039] The aqueous polyurethane dispersion comprises at least about 50 wt %, preferably at least about 55 wt %, more preferably at least about 60 wt % of polyurethane polymer particles based on total mass of the dispersion. As conventionally done by the skilled person, the weight percentage is calculated beforehand, taking into account which components evaporate and which components do not evaporate. The solids percentage is at a later stage measured to confirm: thereto, a small amount is weighted, then put in an oven at about 105° C. during one hour and the remaining amount is measured. In this control step, a higher or longer temperature/time regime can be chosen as well, if there are slowly evaporating components present.

[0040] If desired, amounts of emulsifiers, defoamers, flame retardants, thickeners, stabilizers, anti-oxidants and/or anti-settling agents may be included in the prepolymer or the water phase, or may be added to the aqueous polyurethane dispersion.

[0041] The prepolymer thus prepared and a water phase are being mixed to obtain a polyurethane dispersion, wherein the extension agent, if the extension agent is different from water, can be added to the water phase prior to the dispersing step, or can be added during the dispersing step, or can be added to the dispersion after the dispersing step. Optionally, neutralization agents, undiluted or with water diluted additives, like emulsifiers, defoamers, flame retardants, thickeners, stabilizers, anti-oxidants and/or anti-settling agents can be added to the water phase or to the dispersion.

[0042] The viscosity of the aqueous polyurethane dispersion of the invention is generally lower than about 1000 mPa.Math.s, preferably lower than about 750, more preferably lower than about 500, and most preferably lower than about 250 mPa.Math.s, as measured at about 25° C. using a Brookfield LVF Viscometer.

[0043] The above-described specific embodiments are all embodiments in accordance with the present invention. The various embodiments may be mutually combined. A feature described for one particular embodiment may be taken up, incorporated in or otherwise combined with other particular embodiments unless the laws of physics would forbid such combinations.

[0044] One or more embodiment of the present invention will be further elaborated by the following non-limiting working examples. Parts and percentages of components referred to in these working examples are drawn to the weight of the total composition wherein these components are present, like in the other parts of the description and claims, unless otherwise indicated.

EXAMPLES

Example 1: Preparation of Polyurethane Dispersion

[0045] Under a nitrogen atmosphere a mixture of 415 g of a poly(tetramethylene ether) glycol with a molecular weight of 2000, 57 g of a polycarbonate diol, derived from hexanediol, with a molecular weight of 1000 and 4 g of dimethylolpropanoic acid were heated to 50° C. while stirring. 70 g of 3-isocyanatomethyl-3,5,5-trimethylcyclo-hexylisocyanate and 25 g of hexamethylene diisocyanate were added and the mixture was heated to 85° C. and stirred for 1.5 hours to form a polyurethane prepolymer. The reaction was cooled down and the amount of remaining NCO was measured. The prepolymer was dispersed into a water phase consisting of 390 g of water, 15 g of Synperonic PE/L62 (an emulsifier from Croda), 1.2 g of potassium hydroxide and 13 g of Vestamin A95 (a solution of sodium 2-[(2-aminoethyl)amino]ethane-sulfonate from Evonik). Subsequently, 8 g of hydrazine hydrate was added and the dispersion was stirred for 15 minutes. The solids content of the dispersion was 60%. The viscosity of the dispersion was 200 mPa.Math.s, as measured at 25° C. using a Brookfield LVF Viscometer.

Example 2: Preparation of Polyurethane Dispersion

[0046] Under a nitrogen atmosphere a mixture of 205 g of a polycarbonate diol, derived from pentane diol and hexane diol, with a molecular weight of 2000, 205 g of a polycarbonate diol, derived from hexanediol, with a molecular weight of 1000, 4 g of dimethylolpropanoic acid and 14 g of Ymer-120 (a linear difunctional polyethylene glycol monomethyl ether from Perstorp) were heated to 50° C. while stirring. 115 g of 3-isocyanatomethyl-3,5,5-trimethylcyclo-hexylisocyanate and 30 g of hexamethylene diisocyanate were added and the mixture was heated to 85° C. and stirred for 1.5 hours to form a polyurethane prepolymer. The reaction was cooled down and the amount of remaining NCO was measured. The prepolymer was dispersed into a water phase consisting of 390 g of water, 15 g of Synperonic PE/L62 (an emulsifier from Croda), 1.8 g of potassium hydroxide, 6 g of Vestamin A95 (a solution of sodium 2-[(2-aminoethyl)-amino]ethanesulfonate. from Evonik) and 3 g of hydrazine hydrate. Subsequently, 13 g of hydrazine hydrate was added and the dispersion was stirred for 15 minutes. The solids content of the dispersion was 60%. The viscosity of the dispersion was 200 mPa.Math.s, as measured at 25° C. using a Brookfield LVF Viscometer.

Example 3: Preparation of Polyurethane Dispersion

[0047] Under a nitrogen atmosphere a mixture of 200 g of a polycarbonate diol, derived from pentane diol and hexane diol, with a molecular weight of 2000, 200 g of a polycarbonate diol, derived from hexanediol, with a molecular weight of 1000, 4 g of dimethylolpropanoic acid and 14 g of Ymer-120 (a linear difunctional polyethylene glycol monomethyl ether from Perstorp) were heated to 50° C. while stirring. 100 g of 3-isocyanatomethyl-3,5,5-trimethylcyclo-hexylisocyanate and 50 g of 2,2,4-trimethylhexamethylene diisocyanate were added and the mixture was heated to 85° C. and stirred for 1.5 hours to form a polyurethane prepolymer. The reaction was cooled down and the amount of remaining NCO was measured. The prepolymer was dispersed into a water phase consisting of 390 g of water, 15 g of Synperonic PE/L62 (an emulsifier from Croda), 3.7 g of potassium hydroxide, 6 g of Vestamin A95 (a solution of sodium 2-[(2-aminoethyl)amino]ethanesulfonate. from Evonik) and 3 g of hydrazine hydrate. Subsequently, 13 g of hydrazine hydrate was added and the dispersion was stirred for 15 minutes. The solids content of the dispersion was 60%. The viscosity of the dispersion was 200 mPa.Math.s, as measured at 25° C. using a Brookfield LVF Viscometer.

Example 4: Solvent Resistance Testing of Polyurethane Dispersions

[0048] Each of the dispersions of Examples 1 to 3 was applied on a glass sheet at a thickness of 600 μm. The glass sheet with the applied film on it was dried for 1 day at room temperature and subsequently for 8 hours at 80° C. in an oven. Samples of the dried film were subjected to a solvent uptake test with water, ethanol or MEK (methylethylketone or 2-butanone) as solvent. In this test, pieces of dried and weighted film are immersed into water, ethanol or MEK for 1 hour and then the increase of the weight of the film is determined. A lower weight increase is better.

TABLE-US-00001 TABLE 1 Weight increase Weight increase Weight increase Example water.sup.a ethanol.sup.b MEK.sup.c Example 1 8.2 215 262 Example 2 14.8 535 46 Example 3 14.6 562 46 .sup.aWeight increase is the % weight increase of the film as result of immersing into water. .sup.bWeight increase is the % weight increase of the film as result of immersing into ethanol. .sup.cWeight increase is the % weight increase of the film as result of immersing into MEK (methylethylketone, or 2-butanone).

[0049] The results of the solvent resistance tests presented in Table 1 demonstrate that dried films made from the aqueous polyurethanes dispersions of the invention (Examples 1 to 3) have good resistance against water, as the weight increase upon immersing in water was low.

Example 5: Testing of Dispersions on VOC

[0050] The polyurethane dispersions of the Examples 1 to 3 were tested on presence of volatile components. The results are reported in Table 2.

[0051] The amount of total volatile organic compounds (TVOC) was measured according to the VDA 277 method with Headspace analysis. The apparatus used was an Interscience Trace 1300 Gas Chromatograph Interscience ISQ (Single Quadrupole MS). The column was Restek Stabil Wax®-MS, 30 meter, 0.25 mmID, 0.25 μm df. The GC oven temperature program was: 3 minutes isothermal at 50° C., then heating to 200° C. at a rate of 12° C./minute, followed by 4 min isothermal at 200° C. The sample preparation was: 100 mg of the liquid sample was transferred into the Headspace vial. The samples were put in the Headspace oven for 5 hours at 120° C., and 1 ml of the vapor was injected into the GCMS. The samples were measured in duplicate. The mean TVOC value and main emission compounds (>1 μgC/g) are reported. The TVOC values were calculated as acetone equivalent.

TABLE-US-00002 TABLE 2 TVOC VDA 277 (μgC/g) Example ‘Acetone’ 1 0 2 21 3 13

[0052] The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

[0053] Note that in the specification and claims, “about” or “approximately” means within twenty percent (20%) of the numerical amount cited.

[0054] Although the invention has been described in detail with particular reference to these embodiments, other embodiments can achieve the same results. Variations and modifications of embodiments of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference.