COMPOSITIONS CONTAINING URETDIONE GROUPS CROSSLINKING AT LOW TEMPERATURES

Abstract

The invention relates to compositions containing A) at least one component having at least one uretdione group, B) at least one component having at least one hydroxyl group, C1) of at least one catalyst, containing a structural element of the general formula (I) and/or (II), wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 independently of each other represent the same or different radicals meaning saturated or unsaturated, linear or branched, aliphatic, cycloaliphatic, araliphatic or aromatic organic radicals with 1 to 18 carbon atoms that are substituted or unsubstituted and/or have heteroatoms in the chain, the radicals being capable of forming, even when combined with each other and optionally together with an additional heteroatom, rings with 3 to 8 carbon atoms that can optionally be further substituted, wherein R.sup.3, R.sup.4, R.sup.5 and R.sup.6 independently of each other can also represent hydrogen, and R.sup.7 represents hydrogen or a carboxylate anion (COO−), and C2) at least one catalyst containing at least one N,N,N′-trisubstituted amidine structure and having an amidine group content (calculated as CN2; molecular weight=40) of 12.0 to 47.0 wt.-%.

Claims

1. A composition comprising: A) at least one component comprising at least one uretdione group, B) at least one component comprising at least one hydroxyl group, C1) at least one catalyst comprising a structural element of general formulae (I) and/or (II) ##STR00004## in which R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 independently of one another stand for identical or different radicals which represent saturated or unsaturated, linear or branched, aliphatic, cycloaliphatic, araliphatic or aromatic organic radicals having 1 to 18 carbon atoms which are substituted or unsubstituted and/or have heteroatoms in the chain, wherein the radicals may also in combination with one another and optionally with a further heteroatom form rings having 3 to 8 carbon atoms which may optionally be further substituted, wherein R.sup.3, R.sup.4, R.sup.5 and R.sup.6 may independently of one another also represent hydrogen and R.sup.7 represents hydrogen or a carboxylate anion (COO), and C2) at least one catalyst comprising at least one N,N,N′-trisubstituted amidine structure and having an amidine group content (calculated as CN.sub.2; molecular weight=40) of 12.0% to 47.0% by weight.

2. The composition of claim 1, wherein component A) is selected from isocyanate-functional uretdione-containing compounds A1) or polyaddition compounds A2) obtainable by reaction of isocyanate-functional uretdione-containing compounds A1) with alcohols or amines.

3. The composition of claim 2, wherein component A1) is selected from uretdione-containing compounds based on PDI, HDI, IPDI, XDI, NBDI or H.sub.12-MDI.

4. The composition of claim 2, wherein polyaddition compounds A2) are selected from compounds which are produced by reaction of isocyanate-functional, uretdione-containing compounds A1) with at least difunctional polyols in the molecular weight range 62 to 22 000 and optionally monoalcohols while maintaining an equivalent ratio of isocyanate groups to isocyanurate-reactive groups of 2:1 to 0.5:1 and in solvent-free form have a content of free isocyanate groups of less than 5% by weight.

5. The composition of claim 1, wherein component B) is selected from at least difunctional polyols in the molecular weight range 62 to 22 000.

6. The composition of claim 1, wherein components A) and B) are present in amounts such that for each uretdione group of the component A) there are 0.5 to 2.0 hydroxyl groups of the component B).

7. The composition of claim 1, wherein component C1) is selected from catalysts containing a structural element of general formulae (I) or (II), in which R.sup.1 and R.sup.2 independently of one another stand for identical or different radicals which represent saturated or unsaturated, linear or branched, aliphatic, cycloaliphatic, araliphatic or aromatic organic radicals which have 1 to 12 carbon atoms, are substituted or unsubstituted and/or have heteroatoms in the chain, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 represent hydrogen and wherein R.sup.7 represents hydrogen or a carboxylate anion (COO.sup.−).

8. The composition of claim 1, wherein catalyst C1) is selected from imidazolium salts of the recited type with carboxylate anions.

9. The composition of claim 1, wherein catalyst C2) is selected from bicyclic catalysts containing N,N,N′-trisubstituted amidine structures of general formula (III) ##STR00005## in which m is an integer from 1 to 9 and n is an integer from 1 to 3.

10. The composition of claim 1, wherein catalyst C2) is 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).

11. The composition of claim 1, wherein catalysts C1) and C2) are each present in an amount of 0.0005% to 5% by weight, based on the total weight of the components A) and B), excluding any solvents, auxiliaries or additives present in these components.

12. (canceled)

13. A coating formulation comprising the composition of claim 1.

14. A substrate coated with a heat-cured coating formulation of claim 13.

15. A polyurethane plastic produced from the composition of claim 1.

16. The composition of claim 2, wherein component A1) is selected from uretdione-containing compounds based on PDI, HDI, IPDI, XDI, NBDI or H.sub.12-MDI which have an average NCO functionality of at least 1.6.

17. The composition of claim 2, wherein component A1) is selected from uretdione-containing compounds based on PDI, HDI, IPDI, XDI, NBDI or H.sub.12-MDI which have a content of uretdione structures (calculated as C.sub.2N.sub.2O.sub.2, molecular weight=84) of 10% to 25% by weight.

18. The composition of claim 1, wherein catalyst C1) is selected from the group consisting of 1,3-dimethylimidazolium 2-carboxylate, 1-ethyl-3-methylimidazolium 2-carboxylate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium 2-carboxylate, 1-ethyl-3-methylimidazolium pivalate and 1-butyl-3-methylimidazolium acetate.

19. The composition of claim 1, wherein catalysts C1) and C2) are each present in an amount of 0.0025% to 4% by weight, based on the total weight of the components A) and B), excluding any solvents, auxiliaries or additives present in these components.

20. The composition of claim 1, wherein catalysts C1) and C2) are each present in an amount of 0.005% to 2.5% by weight, based on the total weight of the components A) and B), excluding any solvents, auxiliaries or additives present in these components.

21. The composition of claim 1, wherein catalysts C1) and C2) are each present in an amount of 0.05% to 0.5%, based on the total weight of the components A) and B), excluding any solvents, auxiliaries or additives present in these components.

Description

EXAMPLES

[0109] All percentages are based on weight unless otherwise stated.

[0110] NCO contents were determined titrimetrically according to DIN EN ISO 11909:2007-05.

[0111] All viscosity measurements were recorded with a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) according to DIN EN ISO 3219:1994-10 at a shear rate 5 of 250 s-1.

[0112] Residual monomer contents were measured in accordance with DIN EN ISO 10283:2007-11 by gas chromatography with internal standard.

[0113] The compositions of the HDI-uretdione polyisocyanate were determined by gel permeation chromatography on the basis of DIN 55672-1:2016-03 (gel permeation chromatography (GPC)—part 1: tetrahydrofuran (THF) as eluent) with the modification that a flow rate of 0.6 ml/min rather than 1.0 ml/min was used. The proportions of the different oligomers from the chromatograms in area % which were determined by software assistance were in each case approximately equated with proportions in % by weight.

[0114] König pendulum damping was determined in accordance with DIN EN ISO 1522:2007-04 on glass plates.

[0115] The microhardness (surface hardness/Martens hardness at a test force of 0.6 mN) and the elastic deformation component of the coatings films were measured using a Fischerscope HM 2000 instrument according to DIN EN ISO 14577-1:2015-11.

[0116] Appearance measurements were carried out using a “Wave Scan” instrument from BYK-Gardner GmbH, Geretsried, DE. Values for dullness (the smaller the value, the less matt) and distinctness of image DOI (the larger the value, the higher the brilliance) are in each case reported as average values from five individual measurements.

[0117] Solvent resistance was determined using xylene as a typical coatings solvent. To this end a small amount of the solvent was added to a test tube and provided with a cotton pad at the opening so that an atmosphere saturated with xylene was formed inside the test tube. The test tube was subsequently placed with the cotton pad on the coating surface and remained there for 5 minutes. Once the solvent had been wiped off, the film was examined for destruction/softening/loss of adhesion. (0=no change, 5=film destroyed)

Starting Compounds

Production of an HDI Polyuretdione Crosslinker

[0118] According to the process described in example 1 of EP-A 0 789 017 1,3-bis(6-isocyanatohexyl)-1,3-diazetidin-2,4-dione (ideal bis(6-isocyanatohexyl)uretdione) was produced by tributylphosphine-catalyzed oligomerization of 1,6-diisocyanatohexane (HDI) and subsequent distillative workup. [0119] NCO content: 25.0% [0120] Monomeric HDI: <0.03% [0121] Viscosity (23° C.): 28 mPas

[0122] Analysis by gel permeation chromatography (GPC) reveals the following composition:

TABLE-US-00001 HDI uretdione (n = 2): 99.2% (according to GPC) HDI isocyanurat (n = 3): 0.4% (according to GPC) higher oligomers: 0.4% (according to GPC)

[0123] 1000 g (5.95 eq) of this ideal bis(6-isocyanatohexyl) uretdione (NCO content: 25.0%) were dissolved in 800 g of butyl acetate, 4.6 g (0.2% by weight) of a 10% solution of dibutyltin dilaurate (DBTL) in butyl acetate were added and the mixture was heated to 80° C. under dry nitrogen and with stirring. A mixture of 347.5 g (4.76 eq) of 2,2,4-trimethylpentane-1,3-diol and 154.7 g (1.19 eq) of 2-ethyl-1-hexanol was added dropwise to this solution over 2 hours. After a stirring time of 16 hours at 80° C. the NCO content was <0.2%. A practically colorless solution of an HDI polyurethane crosslinker (HDI-UD2) was obtained. [0124] NCO content: 0.16% [0125] Uretdione group content: 10.8% (calculated as C.sub.2N.sub.2O.sub.2, molecular weight 84) [0126] Uretdione functionality: 5 (calculated) [0127] Solids content: about 65% [0128] Viscosity (23° C.): 1400 mPas

Catalysts C1)

[0129] 1-Ethyl-3-methylimidazolium acetate (97%), Sigma-Aldrich Chemie GmbH, Munich, DE 1-Ethyl-3-methylimidazolium pivalate produced according to the process described in RSC Advances, 2019, Vol. 9, 4048-4053 by D. Hirose, S. B. Wardhana Kusuma, S. Nomura, M. Yamaguchi, Y. Yasaka, R. Kakuchi and K. Takahashi.

Catalyst C2)

[0130] 1,8-Diazabicyclo[5.4.0]undec-7-ene, DBU (98%), Sigma-Aldrich Chemie GmbH, Munich, DE

Examples 1 to 5 (Inventive and Comparative)

[0131] In each case 2.5 g (0.014 eq) of a commercially available, aromatics-free branched polyester polyol having a solids content of 75% in butyl acetate and an OH content of 9.5% based on solid resin, obtainable under the name Desmophen® 775 (Covestro Deutschland AG, Leverkusen, DE), were mixed with 10.4 g (0.014 eq) of the above-described HDI polyuretdione crosslinker corresponding to an equivalent ratio of hydroxyl groups to uretdione groups of 1:1 to afford a coating formulation and after addition of a catalyst component was applied to a degreased glass sheet using a film applicator in an applied film thickness of 180 μm.

[0132] After flashing off at room temperature for 5 minutes the coatings were cured at 100° C. over 30 min. In all cases completely transparent coatings were obtained.

[0133] The table below shows the type and amount of the catalysts added in each case and the coatings performance properties of the coatings obtained.

TABLE-US-00002 2 3 5 Compar- Compar- Compar- 1 ative ative 4 ative EMIM 50/0.23 50/0.23 — — — pivalate [mg]/[mmol] EMIM — — — 50/0.29 50/0.29 acetate [mg]/[mmol] DBU 44/0.28 — 44/0.28 44/0.28 — [mg][mmol] Flow visual good Structure good very good good assessment Color colorless colorless yellow colorless colorless Dullness 43.9 n.m. 38.2 n.d. n.d. DOI 66.8 n.m. 72.1 n.d. n.d. Pendulum 188 90 79 186  103  damping [s] Martens 154.15 216.28 35.29 n.d. n.d. hardness [N/mm2] (0.6 mN) Elastic 30.73 39.65 0.62 n.d. n.d. deformation component nIT [%] Xylene 0 0 5 0 2 resistance n.m.: not measurable n.d.: not determined

[0134] The comparison shows that the coating of inventive example 1 cures to give a fully crosslinked, hard coating having good optical properties. Although the coatings film from comparative example 3 has slightly better flow properties, it exhibits severe yellow discoloration. The low values for pendulum damping and microhardness and the very poor xylene resistance indicate that the system from comparative example 3 catalyzed exclusively with DBU does not crosslink under the selected curing conditions. The high hardness and good solvent resistance of the coatings film obtained according to comparative example 2 show that this too is fully crosslinked. However, the film surface is so severely structured that values for optical appearance were not able to be measured. The coatings film from comparative example 5, catalyzed exclusively with an imidazolium salt, has a markedly lower pendulum hardness and a lower xylene resistance than coatings 1 and 4 produced according to the invention.