WO2008136732A1

WO2008136732A1 - An isocyanate terminated polymer and use of the same in a radiation curable polyurethane dispersion

Info

Publication number: WO2008136732A1
Application number: PCT/SE2008/000305
Authority: WO
Inventors: Kent SÖRENSEN; Henrik Bernquist
Original assignee: Perstorp Specialty Chemicals Ab
Priority date: 2007-05-04
Filing date: 2008-04-30
Publication date: 2008-11-13
Also published as: EP2147033A1; SE0701095L; EP2147033A4

Abstract

The present invention refers to an isocyanate terminated polymer obtainable by subjecting 10- 90% by weight of at least one diol optionally in combination with at least one polyol, said diol and said optional polyol, having a molecular weight of at most 5000 g/mol, 1-40% by weight of at least one hydrophilic compound, 20-60% by weight of at least one isocyanate and 0.1- 30% by weight of at least one polyol monoacrylate, monomethacrylate and/or monocrotonate to co-polymerisation optionally in the presence of a catalyst, a solvent and/or a polymerisation inhibitor. In a further aspect, a UV curing polyurethane dispersion comprising said polymer is disclosed.

Description

AN ISOCYANATE TERMINATED POLYMER AND USE OF THE SAME IN A RADIATION CURABLE POLYURETHANE DISPERSION

The present invention refers to an isocyanate (NCO) terminated polymer obtained by co- polymerisation of at least one diol optionally in combination with at least one polyol (alcohol having three or more hydroxyl groups), at least one hydrophilic compound, at least one isocyanate and at least one polyol monoacrylate, monomethacrylate and/or monocrotonate. In a further aspect, the present invention refers to the use of said polymer as pre-polymer in preparation of a radiation curable polyurethane dispersion.

A conventional, such as a non UV curable polyurethane dispersion (PUD) has in general good coating properties but deficient chemical and abrasion resistance due to the lack of crosslinking. A crosslinkable polymer can be obtained by incorporation of unsaturated groups. Systems that are 100% UV curable have a high degree of crosslinking that provides coatings with high hardness, high chemical resistance and high gloss. However, due to the high crosslinking density these systems have poorer flexibility, are tacky until they are cured and are not sprayable without using organic solvent and/or skin irritating low viscous monomers.

The two most common routs to obtain a UV curable PUD are either to make a physical blend of a conventional PUD and external acrylates or to end cap a NCO terminated pre-polymer with a monohydroxyfunctional acrylate, such as 2-hydroxyethyl acrylate or pentaerythritol triacrylate. There is, however, a further need for improving chemical resistance, hardness, abrasion and scratch resistance and other mechanical properties of coatings used in applications, such as wood, flooring, parquet, cabinets, furniture, plastic and metal coatings, especially hard flexible coatings, adhesives and printing inks.

The published International application WO 2006/089935 discloses radiation curable polyurethane dispersions comprising at least one compound having at least two free isocyanate groups, at least one allophanate group and at least one radically polymerisable C=C double bound attached through the allophanate group, at least one compound with at least one isocyanate reactive group and at least one radically polymerisable C=C double bound, at least one compound with at least one isocyanate reactive group and at least one acidic group and at least one basic compound. In disclosed dispersions, acrylic groups are distributed along the polyurethane chain, providing a higher acrylate concentration and a more homogeneous crosslinking network resulting in improved properties suitable for coatings. These polyurethane dispersions form, when cured, coating films having substantial hardness with maintained flexibility.

It has quite unexpectedly been found that an isocyanate (NCO) terminated polymer comprising units from at least one polyol monoacrylate, monomethacrylate and/or monocrotonate advantageously can be used in polyurethane dispersions providing similar excellent coating properties as for instance the polyurethane dispersions disclosed in WO 2006/089935, but with the benefit of a reduced number of process steps. Unlike for example the UV- and heat-curable polyurethane dispersion disclosed in the US patent 6747088, a polyurethane dispersion prepared using the isocyanate terminated pre-polymer of the present invention only needs UV radiation, no heat, to cure. Another advantage of the isocyanate terminated polymer of the present invention is that it is aqueous dispersible without the addition of any second binder component. Polyisocyanates like for example the one disclosed in the US patent 6162506 is not aqueous dispersible without the addition of latex.

The isocyanate terminated polymer of the present invention is obtainable by subjecting a) 10-90%, preferably 20-50% and most preferably 20-40%, by weight of at least one diol optionally in combination with at least one polyol, said diol and said optional polyol having a molecular weight of at most 5000 g/mol, b) 1-40%, preferably 3-15% and most preferably 4-10%, by weight of at least one hydrophilic compound, c) 20-60%, preferably 30-50% and most preferably 30-45%, by weight of at least one isocyanate, and d) 0.1-30%, preferably 1-20% and most preferably 5-15%, by weight of at least one polyol monoacrylate, monomethacrylate and/or monocrotonate, to co-polymerisation optionally in the presence of a catalyst, a solvent, a polymerisation inhibitor and/or other auxiliary components known in the art.

Said diol and said optional polyol are in preferred embodiments of the present invention selected from the group consisting of polyester diols and polyols, polyether diols and polyols and polycarbonate diols and polyols. These diols and polyols, containing at least two reactive groups which enable them to react with isocyanates, preferably have an average molecular weight within the range of 100 and 5000 g/mol, and can be exemplified by poly(hexanediol adipate).

Said hydrophilic compound is preferably a polyol having an incorporated or pendant hydrophilic functionality, ionic or non-ionic, which is incorporated in the pre-polymer to make it self-dispersible in water. The hydrophilic compound is most preferably a polyol, alkoxylated, such as ethoxylated, propoxylated and/or butoxylated, polyol and/or alkylated species there of and/or an amine comprising anionic salt groups, or acid which may be converted to such anionic salt groups, like carboxylate or sulphonate salt groups. The hydrophilic compound can in specific preferred embodiments be exemplified by dimethylolpropionic acid, dimethylolbutyric acid, α,α-bis(hydroxymethyl)valeric acid, α,α- bis(hydroxy)propionic acid and/or 3,5-dihydroxybenzoic acid.

The most preferred isocyanate is a diisocyanate or a triisocyanate. Suitable isocyanates are found hi the group consisting of for instance hexamethylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, tetramethylxylylene diisocyanate, 1,6-hexane diisocyanate, trimethylhexane diisocyanate, 1,12-dodecane diisocyanate, cyclohexane diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, bicyclohexylmethane diisocyanate, nonane triisocyanate, isophorone isocyanurate, 1,6-hexane diisocyanate isocyanurate, hydrogenated methylene diphenyl diisocyanate and methylene diphenyl diisocyanate. The most preferred isocyanate is isophorone diisocyanate.

Said polyol monoacrylate, monomethacrylate and/or monocrotonate is in the most preferred embodiments of the present invention a glycerol and/or a 2-alkyl-2-hydroxyalkyl-l,3- propanediol monoacrylate, monomethacrylate and/or monocrotonate in its cis or trans form. Said glycerol and/or said 2-alkyl-2-hydroxyalkyl- 1,3 -propanediols include alkoxylated, such as ethoxylated, propoxylated and/or butoxylated, species thereof. Preferred embodiments of said 2-alkyl-2-hydroxyalkyl-l,3-propanediols can be exemplified by trimethylolethane, trimethylolpropane and trimethylolbutane and/or said alkoxylated species thereof. Said polyol monoacrylate, monomethacrylate and/or monocrotonate is hi its most preferred embodiments trimethylolpropane monoacrylate, monomethacrylate and/or monocrotonate. Said monoacrylate, monomethacrylate and/or monocrotonate is suitably prepared by conventional and known in the art acrylation processes, such as transesterification and esterification in presence of a catalyst. Catalysts which can be used to accelerate the reaction of the isocyanates are in embodiments of the present invention amines or organometallic compounds such as tin(II) or tin(III) octoate, diazadicyclo[2.2]octane or most preferably dibutyltin dilaurate. The reaction is monitored by the consumption of isocyanate groups and is allowed to continue until a constant NCO value is obtained.

Suitable solvents are preferably found among glycol ethers, glycol ether esters, carboxylic acid esters, ketones, alkanols and aliphatic, cycloaliphatic, aromatic hydrocarbons, n-alkyl pyrrolidinones and/or alkylene carbonates. A suitable solvent is for instance dipropylene glycol dimethyl ether or n-methyl pyrrolidinone.

A polymerisation inhibitor is, to prevent the acrylates from polymerisation at the elevated temperatures during the synthesis, suitably used. Inhibitors can be exemplified by phenothiazine, 4-methoxyphenol or hydroquinone and derivatives thereof.

In a further aspect, the present invention relates to the use of at least one polymer, according to the present invention, as pre-polymer in preparation of a radiation curable polyurethane dispersion (PUD). Said dispersion comprises a) 5-80%, preferably 35-45%, by weight of said polymer, b) 0.1-10%, preferably 0.5-3%, by weight of at least one neutralisation agent, and c) 20-90%, preferably 40-65%, by weight of water, and optionally d) 0.1-5%, preferably 0.5-2%, by weight of a chain extender, such as a diamine and/or a triamine.

Photochemically and/or thermally activating initiators may optionally be added and if desired UV absorbers, light stabilisers, pigments, fillers and/or other auxiliary additives.

Said neutralisation agent is added for neutralisation of the carboxylic or sulphonic acid groups to provide a stable salt. Suitable neutralisation agents for converting acid groups into anionic salt groups before dispersion in water can be volatile organic bases and/or non-volatile bases. Suitable organic bases can be selected from a group consisting of ammonia, trimethyl amine, triethyl amine, triisopropyl amine, and tributyl amine. Suitable non-volatile inorganic bases are preferably bases comprising alkali metals such as lithium, sodium or potassium. These bases can be used in the form of inorganic or organic salts, preferably in the form of hydrides, hydroxides, carbonates or bicarbonates.

The water dispersible isocyanate terminated pre-polymer is then added to water, or water is added to the pre-polymer to form the dispersion.

Optionally a chosen part of the remaining isocyanates in the dispersed isocyanate terminated pre-polymer can be chain extended using a polyamine. The chain extender is preferably a water soluble aliphatic, cycloaliphatic or aromatic polyamine with an average functionality between 2 and 4, most preferably 2 or 3, such as ethylene diamine, hexamethylene diamine, 1 ,4-cyclohexylene diamine, piperazine, N-methyl-propylene diamine, isophorone diamine and/or diethylene triamine.

The obtained aqueous radiation curable polyurethane dispersion may further comprise coalescent agents and/or reactive diluents such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, trimethylolbutane, glycerol, pentaerythritol, di- trimethylolpropane, di-trimethylolbutane, di-pentaerythritol, 2-butyl-2-ethyl- 1,3 -propanediol, 2-ethyl-2-methyl-l,3-propanediol and/or acrylated, methacrylated or crotonated derivatives. Other suitable coalescent agents and reactive diluents are alkoxylated and allylated species of above said polyhydric alcohols.

Said aqueous radiation curable polyurethane dispersion obtained is suitably used in coating compositions with high demands on hardness, abrasion and scratch resistance, flexibility and chemical resistance. The dispersion may comprise additional components, such as photo initiators, pigments, dyes, defoamers, fillers and known in the art coating auxiliaries. Obtained coatings exhibit high hardness, scratch resistance, chemical resistance and a substantially reduced or even eliminated surface tack. Even after physical drying only, polyurethane dispersions comprising the polymer of the present invention, have good coating properties and good mechanical properties, especially good hardness. This is a major advantage compared to conventional UV curing polyurethane dispersions, which usually obtain satisfactorily properties only after UV curing. Coatings comprising the inventive polymer exhibit even greater hardness and still good flexibility and excellent chemical resistance after radiation curing. Polymers according to the present invention can suitably be used in coating of three dimensional objects wherein it is difficult to UV irradiate all surfaces, coatings applied in thick layers and in pigmented systems.

By incorporating the acrylate groups along the polyurethane chain instead of using monofunctional acrylates such as 2-hydroxyethyl acrylate to end cap the polyurethane, higher molecular weight polymers and higher concentration of unsaturation are obtained. The acrylate groups distributed along the polyurethane chain enables higher cross linking density. Compared to a UV polyurethane dispersion which consists of physical blend of polyurethane polymer and acrylate oligomers, the UV polyurethane dispersion containing the inventive polymer will have very good coating properties even when not UV cured.

The present invention is further explained with reference to enclosed embodiment Examples, which are to be construed as illustrative and not limiting in any way.

- Example 1 is a comparison example outside the scope of the invention wherein a conventional polyurethane dispersion is prepared.

- Example 2 illustrates the invention and refers to a process wherein a UV curable polyurethane dispersion is prepared at a molar ratio polyol to hydrophilic compound to polyol monoacrylate of 1 : 1 : 1.

- Example 3 illustrates the invention and refers to a process wherein a UV curable polyurethane dispersion is prepared at a molar ratio polyol to hydrophilic compound to polyol monoacrylate of 1 : 1 :2.

- Example 4 refers to coating evaluations of the polyuretane dispersions obtained in Examples 1-3.

Example 1 (Comparative)

Step 1 : Polymer Formulation

45.5% by weight of poly(hexanediol adipate) was charged into a glass reactor equipped with stirrer, condenser, nitrogen inlet and thermometer and dried at 80⁰C for 30 min under vacuum. The temperature was then decreased to 50 ⁰C followed by addition of 6.1% by weight of dimethylolpropionic acid, 18.1% by weight of dipropylene glycol dimethyl ether and 0.045% by weight of dibutyltin dilaurate under stirring and while purging the reactor with dry nitrogen. 30.3% by weight of isophorone diisocyanate was slowly added, where after the temperature was increased to 75°C. The reaction was run until a constant NCO value was obtained, determined by standard NCO back titration method.

Step 2: Neutralisation and Chain Extension of Polymer

39.8% by weight of the polymer obtained in Step 1 was charged into a reactor according to the first stage and the temperature was increased to 50⁰C followed by addition of 1.5% by weight of triethyl amine. After 5 min of mixing the agitation was increased from 120 to 300 rpm and 57.8% by weight of water was added without foaming. The heater was removed and after 5-10 min 1.0% by weight of ethylene diamine was added and the temperature of the dispersion was allowed to cool to room temperature with maintained stirring.

Example 2

Step 1 : Polymer Formulation

35.0% by weight of poly(hexanediol adipate) was charged into a glass reactor equipped with stirrer, condenser, nitrogen inlet and thermometer and dried at 80⁰C for 30 min under vacuum. The temperature was then decreased to 50 ⁰C followed by addition of 4.7% by weight of dimethylolpropionic acid, 18.8% by weight of dipropylene glycol dimethyl ether, 0.035% by weight of dibutyltin dilaurate, 0.0033% by weight of phenothiazine and 6.6% by weight of trimethylol propane mono acrylate under stirring and while purging the reactor with dry nitrogen. 34.9% by weight of isophorone diisocyanate was slowly added, where after the temperature was increased to 75°C. The reaction was run until a constant NCO value was obtained.

Step 2: Neutralisation and Chain Extension of Polymer The procedure of Step 2 in Example 1 was repeated.

Example 3

Step 1 : Polymer Formulation

28.6% by weight of poly(hexanediol adipate) was charged into a glass reactor equipped with stirrer, condenser, nitrogen inlet and thermometer and dried at 80⁰C for 30 min under vacuum. The temperature was then decreased to 5O⁰C followed by addition of 3.8% by weight of dimethylolpropionic acid, 18.8% by weight of dipropylene glycol dimethyl ether, 0.029% by weight of dibutyltin dilaurate, 0.0054% by weight of phenothazine and 10.7% by weight of trimethylol propane mono acrylate under stirring and while purging the reactor with dry nitrogen. 38.0% by weight of isophorone diisocyanate was slowly added, where after the temperature was increased to 75°C. The reaction was run until a constant NCO value was obtained.

Physical properties of the polyurethane dispersions obtained in Examples 1-3 are presented in Table 1 below.

Example 4

Application and curing of clear coatings

4% of the photo initiator, Irgacure 500 (CIBA, Be), was added to the polyurethane dispersions obtained in Examples 1-3, which was then applied, using a K-bar wire applicator, to various substrates in coat thickness of approximately 100 μm. The water and solvent was removed from the coated substrates at a temperature of 80 °C during 30 min and finally the coatings made from the dispersions of Examples 2 and 3 were cured with a UV dose of 1000 mJ/cm².

Hardness, flexibility and chemical resistance of the coatings were evaluated and the results are presented in Table 2.

Hardness was determined by the Kδnig pendulum hardness according to DIN EN ISO 1552.

High value represents great hardness.

Flexibility was measured by the Erichsen flexibility according to ISO 1520. High value represents good flexibility.

Chemical resistance was measured after 7 days at 23°C at 50% RH trough double rubs of methyl ethyl ketone on the coatings applied on glass.

Table 1

As seen from Table 2 the pendulum hardness is improved with increasing amounts of acrylates. The pendulum hardness is substantially increased when UV cured. Despite the high hardness the flexibility is maintained in all coatings. The chemical resistance is substantially improved compared to the conventional coating based on the dispersion of Example 1 with the UV cured coatings in example 2 and 3 which all show a great chemical resistance. Table 2 also shows that the non UV cured coatings of Example 2 and 3 obtain better results than the conventional polyurethane dispersion from Example 1.

Claims

1. An isocyanate terminated polymer, characterised in that said polymer is obtained by subjecting a) 10-90% by weight of at least one diol optionally in combination with at least one polyol, said diol and said optional polyol, having a molecular weight of at most 5000 g/mol, b) 1 -40% by weight of at least one hydrophilic compound, c) 20-60% by weight of at least one isocyanate, and d) 0.1-30% by weight of at least one polyol monoacrylate, monomethacrylate and/or monocrotonate, to co-polymerisation optionally in presence of an active amount of a catalyst, a solvent and/or a polymerisation inhibitor.

2. An isocyanate terminated polymer according to claim 1, characterised in that said diol and said optional polyol is present in an amount of 20-50% by weight.

3. An isocyanate terminated polymer according to claim 1, characterised in that said diol and said optional polyol is present in an amount of 20-40% by weight.

4. An isocyanate terminated polymer according to any of the claims 1-3, characterised in that said diol or said optional polyol is a polyester polyol, a polyether polyol and/or a polycarbonate polyol.

5. An isocyanate terminated polymer according to any of the claims 1-4, characterised in that said polymerisation inhibitor is a radical polymerisation inhibitor.

6. An isocyanate terminated polymer according to any of the claims 1-5, characterised in that said hydrophilic compound is present in an amount of 3-15% by weight.

7. An isocyanate terminated polymer according to any of the claims 1-5, characterised in that said hydrophilic compound is present in an amount of 4-10% by weight.

8. An isocyanate terminated polymer according to any of the claims 1-7, characterised in that said hydrophilic compound is dimethylolpropionic acid and/or dimethylolbutyric acid.

9. An isocyanate terminated polymer according to any of the claims 1-8, characterised in that said isocyanate is present in an amount of 30-50% by weight.

10. An isocyanate terminated polymer according to any of the claims 1-8, characterised in that said isocyanate is present in an amount of 30-45% by weight.

11. An isocyanate terminated polymer according to any of the claims 1-10, characterised in that said isocyanate is a diisocyanate or a triisocyanate.

12. An isocyanate terminated polymer according to claim 11, characterised in that said isocyanate is hexamethylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, tetramethylxylylene diisocyanate, 1,6-hexane diisocyanate, trimethylhexane diisocyanate, 1,12-dodecane diisocyanate, cyclohexane diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, bicyclohexylmethane diisocyanate, nonane triisocyanate, isophorone isocyanurate and/or 1,6-hexane diisocyanate isocyanurate.

13. An isocyanate terminated polymer according to any of the claims 1-12, characterised in that said polyol monoacrylate, monomethacrylate and/or monocrotonate is present hi an amount of 1-20% by weight.

14. An isocyanate terminated polymer according to any of the claims 1-12, characterised in that said polyol monoacrylate, monomethacrylate and/or monocrotonate is present hi an amount of 5-15% by weight.

15. An isocyanate terminated polymer according to any of the claims 1-14, characterised in that said polyol in component d) is glycerol or a 2-alkyl-2-hydroxyalkyl- 1,3 -propanediol and/or an alkoxylated species thereof.

16. An isocyanate terminated polymer according to claim 15, characterised in that said alkoxylated species is an ethoxylated, propoxylated and/or butoxylated species of said glycerol and/or said 2-alkyl-2-hydroxyalkyl- 1,3 -propanediol.

17. An isocyanate terminated polymer according to claim 15 or 16, characterised in that said 2-alkyl-2-hydroxyalkyl-l,3-propanediol is trimethylolethane, trimethylolpropane and/or trimethylolbutane.

18. An isocyanate terminated polymer according to any of the claims 1-15, characterised in that said polyol monoacrylate, monomethacylate and/or monocrotonate is trimethylolpropane monoacrylate, trimethylolpropane monomethacrylate and/or trimethylolpropane monocrotonate.

19. An isocyanate terminated polymer according to any of the claims 1-18, characterised in that said optional catalyst is dibutyltin dilaurate.

20. An isocyanate terminated polymer according to any of the claims 1-19, characterised in that said optional solvent is a glycol ether, a glycol ether ester, a carboxylic acid ester, a ketone, an alkanol and/or an aliphatic, cycloaliphatic and/or aromatic hydrocarbon.

21. An isocyanate terminated polymer according to claim 20, characterised in that said optional solvent is dipropylene glycol dimethyl ether.

22. An isocyanate terminated polymer according to any of the claims 1-21, characterised in that said optional polymerisation inhibitor is phenothiazine and/or 4-methoxyphenol.

23. Use of a polymer according to any of the claims 1-22, in preparation of a radiation curable polyurethane dispersion.

24. Use according to claim 23, wherein said polyurethane dispersion comprises a) 5-80% by weight of said polymer, b) 0.1-10% by weight of at least one neutralisation agent, and c) 20-90% by weight of water, and optionally d) 0.1 -5% by weight of a chain extender.

25. Use according to claim 24, wherein said polymer is present in an amount of 35-45% by weight.

26. Use according to claim 24 or 25, wherein said neutralisation agent is present in an amount of 0.5-3% by weight.

27. Use according to any of the claims 24-26, wherein said neutralisation agent is a volatile organic base.

28. Use according to claim 27, wherein said volatile organic base is ammonia, trimethyl amine, triethyl amine, triisopropyl amine and/or tributyl amine.

29. Use according to any of the claims 24-26, wherein said neutralisation agent is a nonvolatile inorganic base containing an alkali metal.

30. Use according to claim 29, wherein said alkali metal is lithium, sodium or potassium.

31. Use according to any of the claims 24-30, wherein water is present in an amount of 40- 65% by weight.

32. Use according to any of the claims 24-31, wherein said optional chain extender is present in an amount of 0.5-2% by weight.

33. Use according to any of the claims 24-32, wherein said optional chain extender is an aliphatic, cycloaliphatic or aromatic diamine and/or triamine.

34. Use according to claim 33, wherein said diamine is ethylene diamine, hexamethylene diamine, 1,4-cyclohexylene diamine, piperazine, N-methyl -propylene diamine and/or isophorone diamine.

35. Use of a polyurethane dispersion according to any of the claims 24-34, in wood, flooring, parquet, cabinets, furniture, plastic and metal coatings, adhesives and/or printing inks.