High-solids coating composition

Abstract

The present invention pertains to a coating composition based on a specific epoxy-functional siloxane oligomer and an amine-functional polyorganosiloxane. The coating composition is suitable for use on substrates subjected to outdoor conditions, in particular conditions where a high durability, a high UV resistance, and good anti-corrosive properties are required.

Claims

1. A coating composition made from the admixture of (1) an amine-functional polyorganosiloxane having a number average degree of polymerization of 10 or more, and (2) an epoxy-functional organosiloxane oligomer, wherein the epoxy functional organosiloxane oligomer comprises units selected from the group consisting of:
(R.sup.1R.sup.2R.sup.3SiO.sub.1/2).sub.a  (i)
(R.sup.1R.sup.3SiO.sub.2/2).sub.b  (ii)
(R.sup.1R.sup.1SiO.sub.2/2).sub.c  (iii)
(R.sup.1SiO.sub.3/2).sub.d  (iv)
(R.sup.3SiO.sub.3/2).sub.e, and  (v)
(SiO.sub.4/2).sub.f  (vi) wherein each of a, b, c, d, e and f is independently 0 or an integer; the number average of the number of units a+b+c+d+e+f in the epoxy functional organosiloxane oligomer ranges from 2 to 9; the number average of a+b+e≧2; the R.sup.1 groups are the same or different and each represents a monovalent hydrocarbon radical having 1-9 carbon atoms or a C.sub.1-C.sub.6 alkoxy group, the R.sup.2 groups are the same or different and each represents represent an OH group or a C.sub.1-C.sub.6-alkoxy group; the R.sup.3 groups are the same or different and each represents a monovalent hydrocarbon radical having 1-11 carbon atoms, each R.sup.3 group substituted with at least one epoxy group; wherein an average of at least 70% of the units of the epoxy-functional organosiloxane oligomer comprise an R.sup.3 group, and wherein the amounts of the amine-functional polyorganosiloxane and the epoxy-functional organosiloxane oligomer are such that the ratio of active hydrogen equivalents to epoxy equivalents in the coating composition is between 0.3:1 to 1.1:1.

2. The coating composition according to claim 1 wherein the coating composition has at least one of a solids content of at least 70 weight % and/or or a volatile organic content (VOC) not exceeding 250 g/l, determined according to EPA Federal Method 24.

3. The coating composition according to claim 2 wherein the amine-functional polyorganosiloxane has an active hydrogen equivalent weight of from 100 to 1,500 g/eq.

4. The coating composition according to claim 2, wherein the epoxy equivalent weight of the epoxy-functional organosiloxane oligomer ranges from 109-430 g/eq.

5. The coating composition according to claim 2, wherein the coating composition has a viscosity of less than 15 Poise at 25° C., determined using a cone and plate viscometer in accordance with BS 3900 Part A7 2000 (and/or ISO 2884-1 1999) with a shear rate of 10,000 s.sup.−1.

6. The coating composition according to claim 1 wherein the amine-functional polyorganosiloxane has an active hydrogen equivalent weight of from 100 to 1,500 g/eq.

7. The coating composition according to claim 6, wherein the ratio of active hydrogen equivalents to epoxy equivalents in the coating composition is greater than 0.6:1 but less than 1:1.

8. The coating composition according to claim 6, wherein an average of less than 50% of the silicon atoms in the amine-functional polyorganosiloxane have bound thereon a hydrocarbon group substituted with an amine-functional group.

9. The coating composition according to claim 1, wherein the epoxy equivalent weight of the epoxy functional organosiloxane oligomer ranges from 109-430 g/eq.

10. The coating composition according to claim 1 wherein the coating composition hardens to form a coating in ambient conditions.

11. The coating composition according to claim 1, wherein the coating composition has a viscosity of less than 15 Poise at 25° C., determined using a cone and plate viscometer in accordance with BS 3900 Part A7 2000 (and/or ISO 2884-1 1999) with a shear rate of 10,000 s.sup.−1.

12. The coating composition according to claim 1, wherein the ratio of active hydrogen equivalents to epoxy equivalents in the coating composition is greater than 0.6:1 but less than 1:1.

13. The coating composition according to claim 1, wherein an average of less than 50% of the silicon atoms in the amine-functional polyorganosiloxane have bound thereon a hydrocarbon group substituted with an amine-functional group.

14. The coating composition according to claim 1 wherein the amine-functional polyorganosiloxane comprises units selected from the group consisting of
(R.sup.4.sub.3SiO.sub.1/2).sub.a  (i)
(R.sup.4.sub.2SiO.sub.2/2).sub.b  (ii)
(R.sup.4SiO.sub.3/2).sub.c, and  (iii)
(SiO.sub.4/2).sub.d  (iv) wherein R.sup.4 is independently an alkyl group or an aryl group, optionally substituted with an amine group; a has a value of less than 0.4; b has a value of greater than 0.15; c has a value of greater than zero to 0.7; d has a value of less than 0.2; the value of a+b+c+d=1; 3 to 50 mole percent of silicon atoms contain amine functional hydrocarbon groups in units (i), (ii) or (iii); the —NH— equivalent weight of the amine functional polyorganosiloxane is from 100 to 1500; greater than 20 weight percent of unit (ii) is present in the amine functional polyorganosiloxane poly siloxane; less than 10 weight percent of unit (ii) are Me.sub.2SiO.sub.2/2 units in the amine functional polyorganosiloxane; and greater than 50 weight percent of silicon-bonded R groups are silicon-bonded aryl groups.

15. The coating composition according to claim 1 further comprising one or more components selected from the group consisting of adhesion promoting agents, fillers, pigments, solvents, curing accelerators and additives.

16. The coating composition according to claim 1, further comprising aluminium flake.

17. A kit comprising, as separate parts, a first part comprising an amine-functional polyorganosiloxane and a second part comprising an epoxy-functional organosiloxane oligomer, wherein the amine-functional polyorganosiloxane and the epoxy-functional organosiloxane are according to claim 1.

18. A method of coating a substrate comprising mixing the first and second parts of the kit as defined in claim 17 to form a mixture, applying a layer of the mixture to the substrate, and allowing the layer to harden to form a coating.

19. The coating composition according to claim 1, wherein the coating composition is a primer, an intermediate, a finish or a primer/finish coating.

20. An object coated with the coating composition according to claim 1.

Description

EXAMPLE 1: INVESTIGATION INTO DRY TIMES

(1) A paint base was prepared using the materials presented in Table 1.1. A high-speed disperser, Dispermat Model AE01-M-EXS, was used with the TiO.sub.2 being ground into the resin at 4000 rpm until 50μ grind is achieved. Generally samples were prepared in either 750 mL or 250 mL tins using a 40 mm diameter mixer blade. The amine functional polyorganosiloxane had an Amine Hydrogen Equivalent Weight (AHEW) of 255 gmol.sup.−1. The paint base had an AHEW of 604 gmol.sup.−1.

(2) TABLE-US-00001 TABLE 1.1 Material Weight (g) Amine-functional 150.0 polyorganosiloxane Xylene 16.66 Titanium dioxide 188.69

(3) The paint base above was then used in the formulation of Table 1.2, with a calculated VOC of 90.4 gL.sup.−1. The VOC was calculated by the addition of the solvent present in paint mixture to the alcohol evolved upon the siloxane condensation reaction that occurs upon film formation.

(4) TABLE-US-00002 TABLE 1.2 Material Weight (g) Paint base (described in Table 1.1) 9.35 Alkoxy-functional polyorganosiloxane 1.59 Aminopropyltrimethoxysilane (APTMS) 0.493 Epoxy-functional siloxane oligomer 5.0

(5) Two different types of epoxy-functional organosiloxane oligomer were used, with different degrees of oligomerisation. Both oligomers were prepared from the same two monomers, monomer a and monomer b. For monomer a, R1 was a methyl group, R2 was a hydroxyl group and R3 was a propyl glycidyl ether group. For monomer b, R1 was a methyl group, R3 was a propyl glycidyl ether group and there was no R2.

(6) Type 1 had a degree of oligomerisation of less than 10, in accordance with the invention with a ratio of a:b of 2:3.15. Type 2 had a degree of oligomerisation above 10, so it is comparative. Both Epoxy functional siloxanes had an epoxy equivalent weight of 190 gmol.sup.−1.

(7) The alkoxy-functional polyorganosiloxane was liquid methoxy-functional polyorganosiloxane with a theoretical Si content of 87%. It had a specific gravity of 1.156 at 25° C., a viscosity of 120 cSt at 25° C. and a weight average molecular weight of 1400.

(8) The stoichiometry of the system (when including the amine contribution from the APTMS) was 0.798 equivalents of amine to 1 equivalent epoxy or 79.8%.

(9) Viscosities of the paint compositions were measured using a cone and plate viscometer in accordance with BS 3900 Part A7 2000 with a shear rate of 10,000 s.sup.−1. Dry times were assessed at 10° C./80% relative humidity using both a BK dry-track recorder. Results are presented in table 1.3.

(10) TABLE-US-00003 TABLE 1.3 Sample Mix Viscosity (Poise) Time to hard dry (hours) Type 1 (invention) 4 8 Type 2 (comparative) 5 14

(11) As can be seen from Table 1.3, the paint composition according to the invention, which comprised an epoxy-functional organosiloxane oligomer with a degree of oligomerisation of less than 10 has a time to hard dry which is substantially reduced as compared to the comparative composition, while the mix viscosity directly after manufacture was such as is suitable for standard paint application.

(12) This result is surprising since it has been established both practically and theoretically since the early-mid 20th century that in step-growth polymerisations (such as epoxy amine curing processes), reactivity of functional groups is independent of the size of molecule to which it is attached (Principles of Polymerization (4th Ed.), George Odian, Publisher: Wiley-Interscience, Chapter 2, Part 2-1: Reactivity of Functional Groups, p 40-44).

EXAMPLE 2: ANTICORROSIVE TESTING

(13) Using the same paint base as in Example 1 above the paint was prepared with a calculated VOC of 90.4 gL.sup.−1 and a composition as presented in Table 2.1.

(14) TABLE-US-00004 TABLE 2.1 Material Weight (g) Weight (%) Paint base (described in Table 1.1) 35.51 57 Alkoxy-functional polyorganosiloxane 6.06 10 Aminopropyltrimethoxysilane 1.87 3 Epoxy-functional organosiloxane 19.0 30 oligomer

(15) The epoxy-functional siloxane oligomer was the oligomer used in Example 1 with a degree of polymerisation of less than 10.

(16) Materials were mixed using a spatula for 1-2 minutes then applied to a series of 6″×4″ steel panels which had been grit blasted to Sa 2½ standard. The paint was applied using a 300 μm draw down bar and the samples left to cure for 7 days before a 3 mm circular defect was introduced to the coating after which the panels were placed into accelerated testing.

(17) Anticorrosive performance was assessed by visual inspection of panels exposed in salt spray chambers running a Prohesion® cycle according to ASTM G85 Annex A5 of: 1 hour condensation cycle with an aqueous solution of 0.35% (NH.sub.4).sub.2SO.sub.4+0.05% NaCl at ambient temperature. 1 hour dry cycle at 35° C.

(18) Panels were assessed regularly according to ISO 4628/2 and ASTM D714-02 and after 4000 hours were found to exhibit no blistering. The results are presented in Table 2.2.

(19) TABLE-US-00005 TABLE 2.2 ASTM ISO 4628/2 D714-02 Hours on test Density Size Density Size 0 0 — None — 400 0 — None — 650 0 — None — 850 0 — None — 1650 0 — None — 2300 0 — None — 2700 0 — None — 3500 0 — None — 4000 0 — None —

(20) From the results in Table 2.2 it can be seen that even after prolonged periods of time in an accelerated aging test no corrosion was observed.

EXAMPLE 3: DURABILITY TESTING

(21) Using the same paint base as above a paint was prepared with a calculated VOC of 90.4 gL.sup.−1. The composition is presented in Table 3.1 below.

(22) TABLE-US-00006 TABLE 3.1 Material Weight (g) Weight (%) HALS (hindered amine light stabilizers) 0.166 1 Paint base (table 1.1) 9.35 56 Alkoxy-functional polysiloxane 1.59 10 Aminopropyltrimethoxysilane 0.493 3 Epoxy-functional siloxane oligomer 5.0 30

(23) The epoxy-functional siloxane oligomer was the oligomer used in Example 1 with a degree of polymerisation of less than 10.

(24) Materials were then mixed using a spatula for 1-2 minutes then applied to a series of 6″×3″ aluminium Q panels which had been abraded with wet/dry paper and washed with acetone to remove any dirt. The paint was applied using a 300 μm draw down bar and the samples were left to cure for 7 days before placing into accelerated weathering.

(25) Accelerated weathering was undertaken using a QUVa cabinet from Q-Lab following ASTM G154. The panels were exposed to a cycle of 4 hours UV exposure @ 60° C. followed by 4 hours condensation @ 45° C. This cycle was repeated continuously.

(26) The results are presented in Table 3.2. All gloss measurements quoted are for 60° gloss and were measured using Sheen Tri-glossmaster. For delta E calculations, L, a and b values were measured using datacolor check II instrument.

(27) TABLE-US-00007 TABLE 3.2 Hours on % Gloss test retention Delta E 500 95.8 1.94 1000 91.3 1.73 1,600 91.2 1.61 3,000 89.9 1.67 6,500 86.8 1.49 11,000 84.25 1.45

(28) The data in Table 3.2 shows that the gloss retention is high and the Delta E of the coating composition according to the invention is low, even after prolonged testing.