FREE RADICAL-CURABLE COATING AND SEALANT COMPOSITIONS WITH IMPROVED SURFACE CURE PROPERTIES

Abstract

Inhibition by oxygen of the peroxide-initiated cure of a composition based on (meth)acrylates or other compounds containing free radical-polymerizable functional groups is mitigated by inclusion of one or more polythiols in the composition. Such compositions may be formulated as multi-part systems, which are useful for the preparation of coatings and sealants.

Claims

1. A multi-part system either a) or b) comprising, as separately packaged components, either: a) a Part A comprising at least one compound having two or more free radical-polymerizable functional groups and at least one polythiol compound comprising two or more thiol groups and a Part B comprising at least one free radical initiator; or b) a Part A comprising at least one compound having two or more free radical-polymerizable functional groups, a Part B comprising at least one polythiol comprising two or more thiol groups and a Part C comprising at least one free radical initiator.

2. The multi-part system of claim 1, wherein the free radical-polymerizable functional groups are ethylenically unsaturated functional groups.

3. The multi-part system of claim 1, wherein the free radical-polymerizable functional groups are selected from the group consisting of allyl groups, (meth)acrylate groups and combinations thereof.

4. The multi-part system of claim 1, wherein Part A comprises at least one hydroxyl-functionalized (meth)acrylate.

5. The multi-part system of claim 1, wherein Part A comprises at least one hydroxyl-functional epoxy (meth)acrylate.

6. The multi-part system of claim 1, wherein Part A comprises at least one urethane (meth)acrylate.

7. The multi-part system of claim 1, wherein the at least one compound having two or more free radical-polymerizable functional groups comprises at least one crosslinking monomer which is a dual functional monomer comprising at least three free radical-polymerizable functional groups selected from the group consisting of allyl groups, (meth)acrylate groups and combinations thereof, including at least one allyl group and at least one (meth)acrylate group.

8. The multi-part system of claim 1, wherein Part A comprises at least one epoxy (meth)acrylate and at least one crosslinking monomer which is a dual functional monomer comprising at least three free radical-polymerizable functional groups selected from the group consisting of allyl groups, (meth)acrylate groups and combinations thereof, including at least one allyl aroup and at least one (meth)acrylate group.

9. The multi-part system of claim 1, wherein Part A additionally comprises at least one compound having a single free radical polymerizable group.

10. The multi-part system of claim 1, wherein Part A comprises at least one compound having at least one (meth)acrylate functional group, at least one hydroxyl functional group and at least one epoxy group per molecule.

11. The multi-part system of claim 1, wherein the at least one polythiol compound includes at least one polythiol compound having a molecular weight of from 350 Daltons to 2000 Daltons.

12. The multi-part system of claim 1, wherein the at least one polythiol compound includes at least one polythiol compound having a molecular weight of from 400 Daltons to 1000 Daltons,

13. The multi-part system of claim 1, wherein the at least one polythiol compound includes at least one polythiol compound comprising three or more thiol groups.

14. The multi-part system of claim 1, wherein the at least one polythiol compound includes at least one polythiol compound comprising three to six thiol groups,

15. The multi-part system of claim 1, wherein the at least one polythiol compound includes at least one polythiol compound comprising two or more thiol-functionalized carboxylate groups having a structure OC(O)(CH.sub.2).sub.nSH, where n is 1 or 2.

16. The multi-part system of claim 1, wherein the at least one polythiol compound includes at least one polythiol compound obtained by esterifying a polyalcohol with a thiol-functionalized carboxylic acid.

17. The multi-part system of claim 1, wherein the at least one polythiol compound includes at least one polythiol compound selected from the group consisting of pentaerythritol tetra(3-mercaptopropionate), trimethyloipropane tri(3-mercaptopropionate), pentaerythritol tetra(2-mercaptoacetate) and trimethylolpropane tri(2-mercaptoacetate).

18. The multi-part system of claim 1, wherein the at least one polythiol compound includes at least one polythiol compound having a thiol equivalent weight of from 80 Daltons to 450 Daltons.

19. The multi-part system of claim 1, comprising from 0.01 to 15 percent by weight of polythiol compound based on the total weight of said multi-part system, either a) with respect to Part A+Part B or b) with respect to Part A+Part B+Part C.

20. The multi-part system of claim 1, comprising from 0.1 to 5 percent by weight of polythiol compound based on the total weight of said multi-part system, either a) with respect to Part A+Part B or b) with respect to Part A+Part B+Part C.

21. The multi-part system of claim 1, wherein Part A further comprises at least one promoter.

22. The multi-part system of claim 21, wherein the at least one promoter comprises one or more transition metals.

23. The multi-part system of claim 1, wherein the at least one free radical initiator includes at least one peroxide.

24. The multi-part system of claim 1, wherein Part A additionally comprises at least one free radical stabilizer.

25. The multi-part system of claim 1, wherein Part A additionally comprises at least one wax.

26. The multi-part system of claim 1, comprising not more than 5 weight % in total, based on the total weight of said multi-part system, either a) with respect to Part A+Part B or b) with respect to Part A+Part B+Part C of compounds having a boiling point of less than 250 C. at 760 mm Hg.

27. A method of forming a coating or sealant on a surface of a substrate, comprising combining either Part A and Part B according to multi-part system a) as defined in claim 1 or combining Part A, Part B and Part C according to multi-part system b), to form a coating or sealant composition, applying the coating or sealant composition to the surface of the substrate and curing the coating or sealant composition.

28. The method of claim 27, wherein the curing of the coating or sealant composition is carried out in the presence of oxygen and the cured coating or sealant composition has a thickness as low as 0.003 inches (76),

29. A cured coating or sealant obtained by combining either Part A and Part B of multi-part system a) as defined in claim 1 to 26 or by combining Part A, Part B and Part C of the multi-part system b), to form a coating or sealant composition, applying the coating or sealant composition to a surface of a substrate and curing the coating or sealant composition.

30. A coating or sealant composition comprising at least one compound having two or more free radical-polymerizable functional groups, at least one polythiol compound comprising two or more thiol groups and at least one free radical initiator,

31. A method of forming a coating or sealant on a substrate comprising combining Part A and Part B of a) of claim 1 or combining Part A, Part B, and Part C of b) to form a mixture and applying the mixture to the substrate.

32. The method according to claim 31, wherein the coating or sealant is used for concrete or concrete repair or for metals or in gels coats for fiber composites.

33. The method according to claim 31, wherein the coating or sealant is used in construction, especially in building construction and civil engineering and in industry.

Description

EXAMPLES

[0109] The following examples demonstrate the utility and advantages of two-component peroxide cure coating compositions in accordance with the present invention. Three-part systems may be formulated in a similar way, but in such three-part systems the polythiol is kept separate from the (meth)acrylate oligomers/monomers and from the peroxide. Viscosities were measured using a Brookfield DV-III RVT Viscometer. Gel Times were measured on 25 g samples using a Sunshine Gel Meter. Specified amounts of a formulation were poured into aluminum weighing pans to measure Shore D Hardness using ASTM D2240 as the test method. Coating test panels were prepared using a wire-wound drawdown bar designed to apply the specified coating thickness. Tack-free Cure Time for these samples was measured using a Byk-Gardner Dry Time Recorder. Physical properties were tested using the ASTM D638 Tensile Test Method.

Comparative Examples 1-3

[0110] The two part coating compositions of Comparative Examples 1-3 were each based on the combination of (meth)acrylate oligomers/monomers listed in Table 1 (the amounts listed are in parts by weight). The (meth)acrylate oligomers/monomers are identified by trade name and are commercially available from Sartomer USA, LLC (Exton, Pa.):

[0111] CN1963an aliphatic polyester-based urethane dimethacrylate oligomer

[0112] CN132a low viscosity aliphatic diacrylate oligomer

[0113] SR350a trimethacrylate monomer (trimethylolpropane trimethacrylate)

[0114] SR217a low viscosity aliphatic monoacrylate monomer

[0115] SR523an allyl functional methacrylate monomer

[0116] The Cur-Rx metal accelerator is a vanadium octoate-based drier available from Borchers.

[0117] Part A of the coating composition was prepared by warming the oligomers to 60 C. and then mixing them into the monomers using a mechanical mixer equipped with a cowls blade at low shear until homogeneous. The cure accelerators described in Table 1 were then mixed into the oligomer/monomer mixture at low shear to make up Part A. The peroxide initiators were added as Part C at the levels listed in Table 1 and were stirred into Part A by hand until homogeneous.

[0118] The resulting coating compositions were applied by drawdown bars onto aluminum test panels at 15-20 mil thickness and then placed in a 55 C. oven. All three coating compositions exhibited acceptable application viscosity and gel time. The coating composition initiated with benzoyl peroxide (Comparative Example 1) required 48 hours to cure tack-free. The coating compositions initiated with cumene hydroperoxide (Comparative Examples 2 and 3) cured tack-free in less than 24 hours (3 hours in the case of the composition containing PRO13379 activator). However, the attainment of even shorter tack-free curing times would be highly desirable, provided that application viscosity and gel time remain acceptable.

TABLE-US-00001 TABLE 1 Comparative Examples 1-3 Formulation and Coating Properties Comparative Comparative Comparative Example 1 Example 2 Example 3 Part A CN1963 40 40 45 CN132 20 20 20 SR350 20 20 10 SR217 20 20 15 SR523 20 20 10 Dimethyl-p-Toluidine 0.10 6% Cobalt Octoate 0.50 Accelerator Cur-Rx Metal 0.20 Accelerator Dimethyl Aniline 0.10 Vanadium/Copper-based 4.0 Activator Part B Benzoyl Peroxide 1.0 (40% active) Luperox CU80 Cumene 2.0 2.0 Hydroperoxide Properties Part A Coating Resin 680 680 680 Viscosity @25 C. (cP) Gel Time @ 25 C., 24 5 3 25 g sample (min) Cure Time @ 55 C., >24 >6, <22 3.0 0.015 coating thickness (hr) Appearance Slight Brown Clear Clear

Comparative Example 4, Inventive Examples 5 and 6

[0119] The two-part coating compositions of Comparative Examples 4 and 5 and Inventive Example 6 were each based on the combination of (meth)acrylate oligomers/monomers listed in Table 2 (the amounts listed are in parts by weight). The (meth)acrylate oligomers/monomers are identified by trade name and are commercially available from Sartomer USA, LLC (Exton, Pa.):

[0120] CN1963an aliphatic polyester-based urethane dimethacrylate oligomer

[0121] CN132a low viscosity aliphatic diacrylate oligomer

[0122] SR350a trimethacrylate monomer (trimethylolpropane trimethacrylate)

[0123] SR420monofunctional acrylate monomer

[0124] SR644a polypropylene glycol (400) dimethacrylate

[0125] SR523an allyl functional methacrylate monomer

[0126] Thiocure PETMP is pentaerythritol-tris(3-mercaptopropionate), available from Bruno Bock.

[0127] A thiocarbamate free radical stabilizer was added to all three compositions to extend the gel time. Additionally, a 10% paraffin wax solution (Byk S781) was added to all three compositions to improve the ambient cure time at a less than 0.015 coating thickness. Part A of each composition was prepared by warming the oligomers to 60 C. and then mixing them into the monomers using a mechanical mixer equipped with a cowls blade at low shear until homogeneous. The activator (promoter) mixtures (except for the vanadium/copper-based activator) were then mixed into the oligomer-monomer mixture at low shear. The thiocarbamate stabilizer, vanadium/copper-based activator and the paraffin wax solution were then mixed into the oligomer-monomer mixture at low shear until homogeneous in the order they are listed in Table 2 to make up Part A. A polythiol (Thiocure PETMP) was also included in the formulations of Inventive Examples 5 and 6 and found to improve the surface cure characteristics.

[0128] The combination of the vanadium/copper-based activator and paraffin wax significantly improved the cure time at ambient temperature, but resulted in a mottled surface having reduced gloss. The addition of the polythiol in Inventive Examples 5 and 6 significantly enhanced cure time and resulted in coatings having a smooth surface with improved gloss. The addition of the thiocarbamate was also found to result in extended gel times.

TABLE-US-00002 TABLE 2 Comparative Example 4 and Inventive Examples 5 and 6 Formulation and Coating Properties Comparative Inventive Inventive Example 4 Example 5 Example 6 Part A CN1963 45 45 45 CN132 20 20 20 SR350 10 10 10 SR420 15 15 15 SR644 10 10 SR523 10 Thiocarbamate Stabilizer 0.8 0.8 0.6 Vanadium/Copper-based 12.0 12.0 12.0 Accelerator Byk S781 Paraffin Wax 1.0 1.0 1.0 Thiocure PETMP Polythiol 2.0 0.2 Part B Luperox CU80 Cumene 2.0 2.0 2.0 Hydroperoxide Properties Gel Time @ 25 C., 18 6 23 25 g sample (min) Cure Time @ 23 C., 2.0 0.5 2.0 0.003 coating thickness (hr) Appearance Mottled, Mottled, Smooth, Low Low Moderate Gloss Gloss Gloss