PROCESS TO PREPARE HALOGEN-FREE, FLAME-RETARDANT AQUEOUS POLYURETHANE DISPERSIONS

Abstract

A process for the preparation of an aqueous polyurethane dispersion having flame retardant properties and being halogen-free, obtainable by incorporating a phosphine oxide polyol into the polyurethane and which are useful as part of the coating of a flexible sheet-like substrate.

Claims

1. A process for the preparation of an aqueous polyurethane dispersion comprising the steps of: i) synthesizing a polyurethane prepolymer from isocyanates, polyols, which may include polyols with hydrophilic groups or polyols that have an additional functional group that is capable of forming a salt, and a phosphine oxide polyol; and ii) dispersing the obtained prepolymer into a water phase, (iii) adding one or more neutralizing agents prior to, simultaneously with or after dispersing the prepolymer in water, (iv) forming polyurethane by reacting with one or more extension agents simultaneously with or subsequent to the dispersing, after which optionally other additives may be added.

2. The process according to claim 1, wherein the phosphine oxide polyol is a phosphine-oxide containing at least two hydroxyalkyl groups and having the formula (HO—R′—).sub.2P(═O)R, wherein the R′ group is an alkyl chain of from about 2 to 5 carbon atoms which may be linear or branched or further substituted, and R is an alkyl, cycloalkyl or aryl radical of from about 2 to 8 carbon atoms which may also contain additional functional groups like hydroxyl or another phosphine oxide.

3. The process according to claim 1, wherein the phosphine oxide polyol is a phosphine-oxide containing at least two hydroxyalkyl groups and having the formula (HO—R′—).sub.2P(═O)R, wherein the R′ group is an alkyl chain of from 3 carbon atoms, which may be linear or branched or further substituted, and R is an alkyl, cycloalkyl or aryl radical of from about 2 to 8 carbon atoms which may also contain additional functional groups like hydroxyl or another phosphine oxide.

4. The process according to claim 1, wherein the phosphine oxide polyol is a phosphine oxide diol or a phosphine oxide triol.

5. The process according to claim 1, wherein the phosphine oxide polyol is iso-butyl-(bis-n-hydroxypropyl)phosphine oxide.

6. The process according to claim 1, wherein between about 1 weight % and about 20 weight % of the phosphine oxide polyol, compared to total weight of the polyol and isocyanate components in the prepolymer, is used.

7. The process according to claim 1, wherein between about 2 weight % and about 15 weight %, of the phosphine oxide polyol compared to total weight of the polyol and isocyanate components in the prepolymer, is used.

8. The process according to claim 1 wherein between about 3 weight % and about 12 weight % of the phosphine oxide polyol compared to total weight of the polyol and isocyanate components in the prepolymer, is used.

9. The process according to claim 1, wherein the phosphine oxide polyol is reacted simultaneously with all the other reactive components in the prepolymer or is reacted last with the isocyanate components, subsequent to the reaction of isocyanate components with other isocyanate-reactive components.

10. 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-cyclohexyldiiso-cyanate, norbonyldiisocyanate, p-xylylene diisocyanate, 2,4′-diphenylmethane diisocyanate, and/or 1,5-naphthylene diisocyanate.

11. 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 optionally diols or triols with molecular weight below about 500.

12. The process according to claim 1, wherein polyols with hydrophilic groups or polyols that have an additional functional group that is capable of forming a salt, are polyethoxy diol, a poly(ethoxy/-propoxy) diol, a diol containing a pendant ethoxy or (ethoxy/propoxy) chain, a diol containing a carboxylic acid, a diol containing a sulfonic group, a diol containing a phosphate group, a polyethoxy mono-ol, a poly(ethoxy/-propoxy) mono-ol, a mono-ol containing a pendant ethoxy or (ethoxy/propoxy) chain, a mono-ol containing a carboxylic acid or a sulphonic acid or salt, or mixtures thereof.

13. The process according to claim 1, wherein the extension agent is selected from a polyol, water, an amino alcohol, ammonia, a primary or secondary aliphatic, alicyclic, aromatic, araliphatic or heterocyclic amine especially a diamine, hydrazine or a substituted hydrazine, or a mixture thereof.

14. The process according to claim 1, wherein the neutralising agent is selected from a tertiary amines such as tripropylamine, dimethyl butyl amine, dimethyl ethanol amine, diethyl ethanol amine, triethylamine, 2-amino-2-methyl-1-propanol and N-ethylmorpholine, or an alkaline metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide or non-volatile tertiary amines such as N-butyldiethanolamine or N,N-bis[3-(dimethylamino)propyl]-N′,N′-dimethylpropane-1,3-diamine or mixtures thereof.

15. The process according to claim 1, wherein the prepolymer may contain between about 0% and about 35 weight % of co-solvents.

16. The process according to claim 1, wherein the prepolymer may contain less than about 20 weight % of co-solvents.

17. The process according to claim 1, wherein a solids content of the aqueous polyurethane dispersion is at least about 30 weight %.

18. The process according to claim 1, wherein a solids content of the aqueous polyurethane dispersion is preferably at least 35 weight %.

19. A dispersion obtainable by the process as defined in claim 1.

20. A coating or film obtained, from a dispersion as defined in claim 19

Description

DETAILED DESCRIPTION OF THE INVENTION

Examples

Example 1: Preparation of Polyurethane Dispersion

[0044] Under a nitrogen atmosphere a mixture of 425 g of a polycarbonate diol, derived from hexanediol, with a molecular weight of 2000, 250 g of dipropylene glycol dimethyl ether, 5 g of trimethylolpropane and 40 g of dimethylolpropanoic acid were heated to 50° C. while stirring. 240 g of 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate, together with 0.05 g of K-Kat 348 (from King Industries) as catalyst, were added and the mixture was heated to 85° C. and stirred for 1 hour. Subsequently, 35 g of iso-butyl-(bis-n-hydroxypropyl)phosphine oxide was added to the mixture which was kept at 85° C. and stirred for another hour to form a polyurethane prepolymer. The reaction was cooled down and the amount of remaining NCO was measured. A mixture was made of 450 g of the prepolymer and 8 g of triethylamine, and this mixture was dispersed into a water phase consisting of 520 g of water, 7 g of Aerosol OT-75 (a 75% solution of sodium dioctyl sulfosuccinate from Cytec Industries) and 9 g of hydrazine hydrate. The dispersion was stirred for an additional 15 minutes. The solids content of the dispersion was 35%. The viscosity of the dispersion was 140 mPa.Math.s, as measured at 25° C. using a Brookfield LVF Viscometer.

Example 2: Preparation of Polyurethane Dispersion

[0045] Under a nitrogen atmosphere a mixture of 435 g of a polycarbonate diol, derived from hexanediol, with a molecular weight of 2000, 250 g of dipropylene glycol dimethyl ether, 65 g of iso-butyl-(bis-n-hydroxypropyl)phosphine oxide and 25 g of dimethylolpropanoic acid were heated to 50° C. while stirring. 225 g of 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate together with 0.05 g of K-Kat 348 (from King Industries) as catalyst were added and the mixture was heated to 90° C. and stirred for 2 hours to form a polyurethane prepolymer. The reaction was cooled down and the amount of remaining NCO was measured. A mixture was made of 450 g of the prepolymer and 8 g of triethylamine, and this mixture was dispersed into a water phase consisting of 520 g of water, 10 g of Provichem 2588P (a 50% solution of sodium dioctyl sulfosuccinate in dipropylene glycol dimethyl ether, from Proviron Functional Chemicals NV) and 7 g of hydrazine hydrate. The dispersion was stirred for an additional 15 minutes. The solids content of the dispersion was 35%. The viscosity of the dispersion was 900 mPa.Math.s, as measured at 25° C. using a Brookfield LVF Viscometer.

Example 3: Evaluative Tests

[0046] Flame retardancy tests were performed after applying a mixture of the aqueous polyurethane dispersions and a crosslinker on hook and loop tapes, which were then dried during 2 minutes at 90° C. followed by curing for 3 minutes at 150° C. The amount applied on the hook and loop tape was between 50 and 60 g of dried mixture, per square meter of hook and loop tape. The hook and loop tapes were made from 6,6-polyamide, also known as nylon. The tape weight was 265 g per square meter for the hook black tape and 275 g per square meter of the hook red tape. Flame retardancy was evaluated by applying a flame (from an alcohol Bunsen burner) during 10 seconds to a small sample (approx. 8×10 cm) and measuring the total time that the flame remains burning until the flame was totally extinguished. Also evaluated was whether drops from the sample drop while burning or while extinguished.

TABLE-US-00001 Aqueous Polyurethane Burn time. Burn time. Dispersion Crosslinker Hook red tape Hook black tape Example 1   5% XR-5577.sup.a  8 seconds 15 seconds Example 1 2.4% Cymel 373.sup.b  7 seconds 12 seconds Example 2 2.4% Cymel 373  7 seconds 11 seconds RU-13-027.sup.c 2.4% Cymel 373 10 seconds 25 seconds, burning drops .sup.aXR-5577 is an aqueous polycarbodiimide crosslinker from Stahl Europe BV. .sup.bCymel 373 is an aqueous solution of a modified melamine from Allnex SA. .sup.cRU-13-027 is an aqueous polyurethane dispersion containing halogen flame retardant component, from Stahl Europe BV.

[0047] The burn times obtained with the mixtures of Example 1 and Example 2 were shorter than the burn time obtained with reference sample made from aqueous polyurethane dispersion RU-13-027, which contains an halogen component. This was the case for both types of hook and loop tape, the hook red PA 6,6 tape and the hook black PA 6,6 tape. For Example 1, Example 2 and reference RU-13-027 a modified melamine was used as crosslinker, and for Example 1 also an aqueous polycarbodiimide crosslinker was used as crosslinker. The burn times obtained with the mixtures of Example 1 were slightly longer with the aqueous polycarbodiimide crosslinker than with the modified melamine, but still shorter than the mixture of reference halogen-containing RU-13-027 with the modified melamine as the crosslinker. The results demonstrate that shorter or similar burn times can be obtained with the mixtures from halogen-free Examples 1 and 2 as with mixture from halogen-containing reference RU-13-027.

[0048] Note that in the specification and claims, “about” or “approximately” means within twenty percent (20%) of the numerical amount cited. The term “a”, “an”, and “the” means one or more unless otherwise specified.

[0049] Although embodiments of the present invention has been described in detail with particular reference to these embodiments, other embodiments can achieve the same results. Variations and modifications of an embodiment 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.