Low Gloss Polyurethane Coating Compositions

Abstract

The present disclosure describes a low gloss polyurethane one component powder coating composition comprising 90 to 100 wt % of a resin system comprising a thermosetting resin, an isocyanate curing agent for reacting with the thermosetting resin, and a polycarbonate diol, wherein: the thermosetting resin comprises a first hydroxyl functional polyester resin (i) having a hydroxyl value of between 200 and 250 mgKOH/g and a second hydroxyl functional polyester resin (ii) having a hydroxyl value of between 20 and 40 mgKOH/g, the weight ratio of (i):(ii) ranges from 15:85 to 35:65, the isocyanate curing agent comprises at least one unblocked uretdione curing agent, the ratio of isocyanate groups of the curing agent to hydroxyl group of the thermosetting ranges between 0.8 to 1.2, and the total weight % of the polycarbonate diol in the coating composition ranges from 1 to 10 wt % based on the total weight of the coating composition.

Claims

1. A one component powder coating composition comprising 90 to 100 wt % of a resin system comprising a thermosetting resin, an isocyanate curing agent for reacting with the thermosetting resin, and a polycarbonate diol wherein (a) the thermosetting resin comprises a first hydroxyl functional polyester resin (i) having a hydroxyl value of between 200 and 250 mgKOH/g, and a second hydroxyl functional polyester resin (ii) having a hydroxyl value of between 20 and 40 mgKOH/g, and the weight ratio of (i):(ii) ranges from 15:85 to 35:65, (b) the isocyanate curing agent comprises at least one unblocked uretdione curing agent, (c) the ratio of isocyanate groups of the curing agent to hydroxyl group of the thermosetting ranges between 0.8 to 1.2, and (d) the total weight % of the polycarbonate diol in the powder coating composition ranges from 1 to 10 wt % based on the total weight of the powder coating composition.

2. The one component powder coating composition of claim 1 comprising a maximum of 10 wt % of one or more other additives.

3. The one component powder coating composition according to claim 1 comprising 0 wt % of pigments.

4. The one component powder coating composition according to claim 1, wherein the isocyanate curing agent has an isocyanate equivalent weight ranging between 200 to 400 g/eq.

5. The one component powder coating composition according to claim 1, wherein the polycarbonate diol has a hydroxyl value of between 20 and 50 mgKOH/g.

6. The one component powder coating composition according to claim 1, wherein the polycarbonate diol has a number average molecular weight of between 1500 and 4000 g/mol.

7. The one component powder coating composition according to claim 1, wherein the isocyanate curing agent additionally comprises a blocked uretdione curing agent.

8. The one component powder coating composition according to claim 1, wherein at least 20 wt % of the isocyanate curing agent comprises an unblocked uretdione curing agent.

9. The one component powder coating according to claim 1, wherein the coating composition additionally comprises a non-isocyanate curing agent capable of reacting with carboxyl functional groups of the thermosetting resin.

10. The one component powder coating composition of claim 9 wherein the non-isocyanate curing agent comprises one β-hydroxyalkylamide curing agent.

11. The one component powder coating composition according to claim 9 comprising (a) 40 to 70 wt % of the thermosetting resin, (b) 15 to 40 wt % of the isocyanate curing agent, and (c) 0.5 to 7 wt % of the non-isocyanate curing agent wherein the wt % is based on the total weight of the powder coating composition.

12. A coated substrate comprising a substrate coated with a one component powder coating composition according to claim 1.

13. The coated substrate of claim 12, wherein the substrate is a metallic substrate.

Description

EXAMPLES

[0070] The following examples are provided by way of explanation and illustration and are not intended to limit the scope of the disclosure.

[0071] Test Methods [0072] A. Appearance/Smoothness—This parameter was rated by comparing the coating film with standard panels available from USA Powder Coating Institute (PCI). The PCI is a non-profit organisation based in Kentucky USA, who provide Powder Coating Visual Smoothness Standards. The Powder Coating Visual Smoothness Standards are a set of glossy black ten panels, showing the normal degrees of smoothness achievable with powder coatings. The best smoothness is a surface rated with 10 and the poor smoothness is a surface rated with 1. The evaluation is done visually. [0073] B. Film thickness of a cured film was measured using a Positector Model 6000 FN1, a coating thickness gauge from DeFlesko Corporation. Film thickness is reported as the highest of two readings measured in the top half and bottom half of the panel, in mils. [0074] C. Gloss was measured using BYK micro-TRI-gloss meter with calibration tile tray Cat #4522/4527 or equivalents. The gloss of the cured film on Al panel (AL-Q) was measured per ASTM D-523. The 60-degree gloss was reported in all cases. The gloss was reported in gloss units. The lower the gloss unit, the lower the gloss (more matte). [0075] D. Initial cross hatch adhesion test of lab samples to aluminium substrate was tested in accordance with ASTM D3359 cross cut tape test method B. This method provides for cutting through the film in a crosshatch pattern of specified spacing, and taping the cut area with Permacell #99 tape, and then rapidly removing the tape. The area with cuts is inspected to determine if paint has been loosened or removed and the area is given a rating. A test result was reported according to the test method from 0B-5B. 5B is a perfect rating and it means that none of the paint was removed. Panels tested are Al pre-treated. [0076] E. Delta b value was determined on Leneta panels at 3.0 mils. Delta b was measured with Datacolor 600 spectrophotometer under CIE lab, Daylight D65/10°, using Leneta 4×12 inches panels (half black and half white) sprayed with powder samples at 3.0 mils and cured for 20 min at 375° F. The b value of the white side of Leneta panels is the standard value. Delta b is the measure in the change on the yellow-blue axis of the CIELAB color scale from the standard value. Positive delta b indicates that the color is yellower, negative delta b indicates that the color is bluer. A better result (indicating less change in color) is when the delta b value is closer to zero. [0077] F. Methyl Ethyl Ketone (MEK) Rub resistance. A cotton tip applicator is saturated with MEK and rubbed a total of 50 double rubs back and forth across the surface of a test coating using approximately 2.6 cm strokes. Coatings exhibiting MEK resistance ratings of 4-5 have acceptable cure, physical properties and solvent resistance. The panels were rated as follow: [0078] Rating=5=Excellent chemical resistance—no rub-off of coating or pigmentation—no softening or dulling of coating surface. [0079] Rating=4=Very good chemical resistance—slight rub-off of coating or pigmentation. [0080] Rating=3=Fair to good chemical resistance—moderate slight rub-off of coating and pigmentation. [0081] Rating=2=Poor to fair chemical resistance—Heavy rub-off of coating pigmentation. [0082] Rating=1=Extremely poor or no chemical resistance—extreme rub-off of coating or pigmentation or complete rub to substrate. [0083] G. Evaluation of transparency of samples was based on measurement of the Haze value. The test is based on light transmission through the film of samples sprayed at a thickness of 3.0 mils over glass panels. Measurements were taken with OnColor spectrophotometer set up for haze measurement, calibrated beforehand using black and white calibration tiles in accordance with Standard method ASTM D1003. More transparent coatings have a lower haze value (%). [0084] H. Copper Accelerated Acetic Acid Salt spray (CASS) as per ASTM B368-09. This test method is used to determine corrosion resistance of the powder samples to the corrosive environment that could be created by CASS solution. Three test panels (Al treated) sprayed with powder samples at standard film thickness (3 mils) and cured at standard cure are vertical scribed as agreed between parties with an approved cutting device and then panels are placed in vertical position into a test chamber where a test solution consisting of 5% sodium chloride solution in DI water is treated with copper chloride for every liter of salt solution. The pH of the solution should be 3.0-3.1. The solution is then treated with glacial acetic acid to adjust the pH to 3.1-3.3 and then mixed with air and sprayed out into the test chamber using an atomized spray nozzle. The test duration is 168 hours. The test panels are then washed, dried off with compressed air and inspected for corrosion along the scribe, blisters, and corrosion at the edges. Three panels for each sample were tested. Internal laboratory tested panels were evaluated according with OEM specification FCA MS PA 6-7 which specifies as acceptable performance criteria 3.0 mm max creep from line scribe lines. [0085] I. A detailed analysis of the topography of the surfaces exposed and non-exposed to xenon light for samples sprayed over primer and liquid basecoat, was conducted in analytical lab using a scanning electronic microscope SEM and Laser Scanning Confocal Microscopy (LSCM). Imaging was performed with a Hitachi S-3400N SEM with a 15 kV acceleration voltage and a 50 Pa atmosphere. The sample was mounted at a 45° angle for imaging. A Keyence VK-8700 laser scanning confocal microscope was used to image the surface profiles of the samples. A 20×/0.46 objective was utilized with both red laser and white light sources. VK analyzer software was used for image post processing including first-order tilt correction and roughness analysis. The normal height cut-off filter in the analyzer software was applied on all images. The average surface roughness over an area (Sa) is the roughness analysis parameter used to quantify the surface topography of the samples. The Sa value expresses the absolute difference in height of each point compared to the arithmetical mean plane through the surface. The Sa values rank the roughness of the samples, from highest to lowest, in the order of B>A>C, which corresponds well to the visual observations. Sample A=non-exposed 3 coat panel, sample B=3 coat panel exposed for 2250 hours, and sample C=3 coat panel exposed for 3750 hours.

[0086] Application of Example Coating Compositions

[0087] Unless otherwise specified, coating compositions were sprayed using a Nordson Versa electrostatic spray gun (Nordson Corporation, Amherst, Ohio, USA) onto aluminum panels (AL-Q panels) size 3 in.×6 in. or 4 in.×12 in. from Q-panel Corporation USA. Some of the test panels were pre-treated and others were not pre-treated, depending on the test to be run. The coatings were cured for 20 min. to a metal substrate surface temperature of 375° F. (191° C.). Dry film thickness is 3 mils.

[0088] Coating Composition Samples 1 and 2—Comparison with Leading Commercial Powder Product

[0089] Coating composition Samples 1 and 2 according to the present disclosure were compared with a leading matte non-pigmented polyester-acrylic hybrid powder coating product on the market provided by AkzoNobel (Composition A*). Composition A* is a one component polyester/acrylic hybrid matte non-pigmented powder coating composition employing a carboxyl polyester resin and a glycidyl functional acrylic polymer as curing agent, as well as hydroxyl alkyl amide and other additives.

[0090] Coating composition Samples 1 and 2 were prepared by blending all the ingredients in Table 1 except the dry flow additive with a Prism mixer for 30 seconds at 2000 rpm, extruding with a long barrel extruder WP-30 twin screws extruder (Werner Pfleiderer, Ramsey, N.J., USA) at extrusion speed of 400 rpm, torque at 15-30% and extrusion temperature at max. 93° F. The molten extruded material was fed through cooled chilled rolls to form a solid sheet that was broken into small different sized chips. Dry flow additive was manually added and mixed with the chips by bag shaking for 30 seconds. The chips were ground into fine powder using a Brinkman grinder with 0.5 mm screen size and then screened through a USA 200 mesh (75 microns) from Vorti Sieve, Salem, Ohio, USA.

[0091] The coating properties of Samples 1 and 2 and the standard commercial product were tested in accordance with test methods A to H above. The test results are provided in Table 2. The test results show that the coatings of the present disclosure have superior appearance (smoothness, transparency, haze, yellowness) compared with the leading commercial polyester-acrylic hybrid powder coating, and similar durability properties.

TABLE-US-00001 TABLE 1 Sam- Sam- Component (wt %) ple 1 ple 2 Hydroxyl functional polyester, OHV 30.sup.1 48.902 0.000 90% Hydroxyl functional polyester OHV 30 + 10% 0.000 50.200 polycarbonate diol.sup.2 Hydroxyl polyester OHV 220.sup.3 16.168 16.767 Amide modified polyether.sup.4 1.497 1.497 Amide modified phenolated urea.sup.5 0.499 0.499 Cycloaliphatic uretdione without blocking agent.sup.6 27.745 12.924 Poly uretdione adduct internally blocked.sup.7 0.000 12.924 Tin stannous octoate.sup.8 0.998 0.998 Oligomeric hindered amine.sup.9 0.499 0.499 2 hydroxyl phenyl s thiazine.sup.10 0.998 0.998 Sterically hindered phenolic phosphite.sup.11 0.499 0.499 Hydrolytically organo phosphite.sup.12 0.499 0.499 Hydroxyl alkyl amide.sup.13 1.497 1.497 Aluminum oxide dry flow additive.sup.14 0.199 0.199 .sup.1CRYLCOAT E 04375 (OHV 30 mg KOH/g), Allnex Inc. USA (polymeric resin) .sup.210 wt % ETERNACOLL PH 300 UBE Spain and 90 wt % CRYLCOAT E04375 Allnex USA (polymeric resin) .sup.3CRYLCOAT E 04362 (OHV 220 mg KOH/g), Allnex USA (polymeric resin) .sup.4POWDERMATE 486CFL, Troy Chemical Corporation (flow additive) .sup.5POWDERMATE 542DG, Troy Chemical Corporation (degassing wax) .sup.6CRELAN EF 403 (LS 2147), Bayer AG USA (crosslinker) .sup.7VESTAGON B1540, Evonik (crosslinker) .sup.8OCTAFLOW ST-70, Estron Chemicals USA (catalyst) .sup.9HALS STABILIZER TINUVIN 622 LD, Basf USA (UV absorber) .sup.10ADDITIVE TINUVIN 405, Basf USA (UV absorber) .sup.11ANTIOXIDANT IRGAFOS 1076, Basf USA (antioxidant) .sup.12ANTIOXIDANT IRGAFOS 168, Basf USA (antioxidant) .sup.13Primid QM1260, EMS Chemie NA (crosslinker) .sup.14Evonik Corporation (flow additive)

TABLE-US-00002 TABLE 2 Composition Test Sample 1 Sample 2 A* A PCI rating (appearance) 9 9 7/8 B Film thickness, mils 3.0 3.0 3.0 C Gloss @ 60°, units (AL-Q panel 24.3 19.1 31 sprayed at 3.0 mils) D Initial cross hatch adhesion (panel 5B 5B 5B sprayed at 3.0 mils) E Delta b on Leneta white panels at 3.0 mils 2.1 2.1 4.1 F MEK rub resistance 4/5 4/5 4/5 G Transparency (Haze value %) at a film 60 55 >80 measured at 3 mils (on glass panel) H Corrosion resistance: Undercut <1 mm <1 mm <1 mm corrosion rating (pass) (pass) (pass) H Corrosion resistance Blister rating 10 10 10 (pass) (pass) (pass) *Comparative commercial product

[0092] Coating Composition Samples 2 to 10—how the Ratio of the First Hydroxyl Functional Polyester Resin to the Second Hydroxyl Functional Polyester Resin Affects Gloss of Coating

[0093] Coating composition Samples 2 to 10 were prepared by blending all the ingredients in Table 3 except the dry flow additive with a Prism mixer for 30 seconds at 2000 rpm, extruding with a long barrel extruder WP-30 twin screws extruder (Werner Pfleiderer, Ramsey, N.J., USA) at extrusion speed of 400 rpm, torque at 15-30% and extrusion temperature at max. 200° F. The molten extruded material was fed through cooled chilled rolls to form a solid sheet that was broken into small different sized chips. Dry flow additive was manually added and mixed with the chips by bag shaking for 30 seconds. The chips were ground into fine powder using the Brinkman grinder with 0.5 mm screen size and then screened through a USA 200 mesh (75 microns) from Vorti Sieve, Salem, Ohio, USA.

[0094] The formulations of Samples 2-10 are the same except the ratio of the first hydroxyl functional polyester resin (CRYLCOAT E 04362) to the second hydroxyl functional polyester resin (CRYLCOAT E04375) was varied between 0:100 to 100:0.

[0095] The coating compositions were applied to a AL-Q panel coated with black base coat (at 3.0 mil thickness). The gloss of all the coatings was measured in Gloss Units using a BYK micro-TRI-gloss meter according to the gloss test method noted above. Results are shown in Table 4 and FIG. 1.

TABLE-US-00003 TABLE 3 Component Sample # (wt %) 3* 4* 5* 6* 7 2 8 9* 10* 90% Hydroxyl 0 16.767 33.4835 40.220 46.906 50.200 53.593 60.279 66.967 functional polyester OHV 30.sup.1 + 10% polycarbonate diol.sup.2 Hydroxyl polyester 66.967 50.200 33.4835 26.747 20.061 16.767 13.374 6.688 0.000 OHV 220.sup.3 Amide modified 1.497 1.497 1.497 1.497 1.497 1.497 1.497 1.497 1.497 polyether.sup.4 Amide modified 0.499 0.499 0.499 0.499 0.499 0.499 0.499 0.499 0.499 phenolated urea.sup.5 Cycloaliphatic 12.924 12.924 12.924 12.924 12.924 12.924 12.924 12.924 12.924 uretdione without blocking agent.sup.6 Poly uretdione 12.924 12.924 12.924 12.924 12.924 12.294 12.924 12.924 12.924 adduct internally blocked.sup.7 Tin stannous 0.998 0.998 0.998 0.998 0.998 0.998 0.998 0.998 0.998 octoate.sup.8 Oligomeric 0.499 0.499 0.499 0.499 0.499 0.499 0.499 0.499 0.998 hindered amine.sup.9 2 hydroxyl phenyl s 0.998 0.998 0.998 0.998 0.998 0.998 0.998 0.998 0.998 thiazine.sup.10 Sterically hindered 0.499 0.499 0.499 0.499 0.499 0.499 0.499 0.499 0.499 phenolic phosphite.sup.11 Hydrolytically 0.499 0.499 0.499 0.499 0.499 0.499 0.499 0.499 0.499 organo phosphite.sup.12 Hydroxyl alkyl amide.sup.13 1.497 1.497 1.497 1.497 1.497 1.497 1.497 1.497 1.497 Aluminum oxide 0.199 0.199 0.199 0.199 0.199 0.199 0.199 0.199 0.199 dry flow additive.sup.14 Components 1 to 14 are the same as used in Samples 1 and 2 *Comparative Sample

TABLE-US-00004 TABLE 4 Sample # 3* 4* 5* 6* 7 2 8 9* 10* Percentage of 1.sup.st OH functional 100 77 53 43 32 27 22 11 0 polyester to total polyester in coating composition Percentage of 2.sup.nd OH 0 23 47 57 68 73 78 89 10 functional polyester to total polyester in coating composition AL-Q substrate top coated with 97.6 97.8 97.2 59.4 14.2 7.3 6.1 71.5 81.6 black basecoat (Gloss Unit) *Comparative Sample

[0096] The results show that when the resin comprises a first hydroxyl functional polyester resin (i) having a hydroxyl value of between 200 and 250 mgKOH/g and a second hydroxyl functional polyester resin (ii) having a hydroxyl value of between 20 and 40 mgKOH/g, and the weight ratio of (i):(ii) ranges from 15:85 to 35:65, the gloss of the coating is significantly lower.

[0097] Coating Composition Samples 11 to 17—how the Ratio Unblocked Uretdione to Blocked Uretdione Affects Gloss of the Coating

[0098] Coating composition Samples 11 to 17 were prepared by blending all the ingredients in Table 5 except the dry flow additive with a Prism mixer for 30 seconds at 2000 rpm, extruding with a long barrel extruder WP-30 twin screws extruder (Werner Pfleiderer, Ramsey, N.J., USA) at extrusion speed of 400 rpm, torque at 15-30% and extrusion temperature at max. 200° F. The molten extruded material was fed through cooled chilled rolls to form a solid sheet that was broken into small different sized chips. Dry flow additive was manually added and mixed with the chips by bag shaking for 30 seconds. The chips were ground into fine powder using the Brinkman grinder with 0.5 mm screen size and then screened through a USA 200 mesh (75 microns) from Vorti Sieve, Salem, Ohio, USA.

[0099] The formulations of Samples 11 to 17 are the same except the ratio of unblocked uretdione to blocked uretdione was varied between 0:100 to 100:0. The total weight of isocyanate curing agent is the same in all examples. The weight ratio of first hydroxyl functional polyester to second hydroxyl functional polyester was the same (27:73) in all cases.

[0100] The coating compositions were applied to an AL-Q panel coated with black base coat (at 3.0 mil thickness). The gloss of all the coatings was measured in Gloss Units using a BYK micro-TRI-gloss meter according to the gloss test method noted above. Results are shown in Table 6 and FIG. 2.

TABLE-US-00005 TABLE 5 Sample # Component (wt %) 11 12 13 14 15 16 17* 90% Hydroxyl functional 48.603 48.603 48.603 48.603 48.603 48.603 48.603 polyester OHV 30.sup.1 + 10% polycarbonate diol.sup.2 Hydroxyl polyester OHV 16.168 16.168 16.168 16.168 16.168 16.168 16.168 220.sup.3 Amide modified 1.497 1.497 1.497 1.497 1.497 1.497 1.497 polyether.sup.4 Amide modified 0.499 0.499 0.499 0.499 0.499 0.499 0.499 phenolated urea.sup.5 Cycloaliphatic uretdione 28.044 23.852 21.058 9.781 6.986 5.29 0.000 without blocking agent.sup.6 Poly uretdione adduct 0.000 4.192 6.986 18.263 21.058 22.754 28.044 internally blocked.sup.7 Tin stannous octoate.sup.8 0.998 0.998 0.998 0.998 0.998 0.998 0.998 Oligomeric hindered 0.499 0.499 0.499 0.499 0.499 0.499 0.499 amine.sup.9 2 hydroxyl phenyl s 0.998 0.998 0.998 0.998 0.998 0.998 0.998 thiazine.sup.10 Sterically hindered 0.499 0.499 0.499 0.499 0.499 0.499 0.499 phenolic phosphite.sup.11 Hydrolytically organo 0.499 0.499 0.499 0.499 0.499 0.499 0.499 phosphite.sup.12 Hydroxyl alkyl amide.sup.13 1.497 1.497 1.497 1.497 1.497 1.497 1.497 Aluminum oxide dry flow 0.199 0.199 0.199 0.199 0.199 0.199 0.199 additive.sup.14 Components 1 to 14 are the same as used in composition Samples 1 and 2 *Comparative Sample

TABLE-US-00006 TABLE 6 Sample # 11 12 13 14 15 16 17* Ratio of blocked/ 0/100 15/85 25/75 65/35 75/25 81/19 100/0 unblocked isocyanate AL-Q top coated 7.9 12.6 12.8 14.5 20.4 46.6 78.3 with black basecoat (Gloss Unit) *Comparative Example

[0101] The results show a reduction in gloss when greater than 20 wt % of the isocyanate curing agent comprises unblocked uretdione isocyanate curing agent. Formulating with unblocked uretdione isocyanate curing agent makes matte and flat matte transparent finishes possible.

[0102] Coating Composition Sample 18—how Polycarbonate Diol Affects the Aesthetics of the Coating

[0103] Coating composition Sample 18 was prepared by blending all the ingredients in Table 7 except the dry flow additive with a Prism mixer for 30 seconds at 2000 rpm, extruding with a long barrel extruder WP-30 twin screws extruder (Werner Pfleiderer, Ramsey, N.J., USA) at extrusion speed of 400 rpm, torque at 15-30% and extrusion temperature at max. 93° F. The molten extruded material was fed through cooled chilled rolls to form a solid sheet that was broken into small different sized chips. Dry flow additive was manually added and mixed with the chips by bag shaking for 30 seconds. The chips were ground into fine powder using a Brinkman grinder with 0.5 mm screen size and then screened through a USA 200 mesh (75 microns) from Vorti Sieve, Salem, Ohio, USA.

[0104] The formulations of Samples 1 and 18 are practically the same except that the resin system of Sample 18 includes polycarbonate diol.

TABLE-US-00007 TABLE 7 Sam- Sam- Component (wt %) ple 1 ple 18 Hydroxyl functional polyester, OHV 30.sup.1 48.902 0.000 90% Hydroxyl functional polyester OHV 30 + 10% 0.000 48.700 polycarbonate diol.sup.2 Hydroxyl polyester OHV 220.sup.3 16.168 16.200 Amide modified polyether.sup.4 1.497 1.500 Amide modified phenolated urea.sup.5 0.499 0.500 Cycloaliphatic uretdione without blocking agent.sup.6 27.745 28.100 Poly uretdione adduct internally blocked.sup.7 0.000 0.000 Tin stannous octoate.sup.8 0.998 1.000 Oligomeric hindered amine.sup.9 0.499 0.500 2 hydroxyl phenyl s thiazine.sup.10 0.998 1.000 Sterically hindered phenolic phosphite.sup.11 0.499 0.500 Hydrolytically organo phosphite.sup.12 0.499 0.500 Hydroxyl alkyl amide.sup.13 1.497 1.500 Aluminum oxide dry flow additive.sup.14 0.199 0.200 Components 1 to 14 are the same as listed for Table 1 above.

[0105] Significant surface topography differences were observed between Sample 1 and Sample 18 at the different exposure levels. The visual differences in topography correspond to the calculated average roughness parameter (Sa). The lower the Sa, the silkier and smoother the surface.

[0106] As shown in Table 8 below, the same trends in Sa are found within each sample set. The Sa of the 2250 hour exposure samples are greatest, followed by the 0 hour exposure samples, and the samples are smoothest after 3750 hours of Xe exposure. The coating made with Sample 1 is always rougher than the coating made with Sample 18 (containing polycarbonate diol) when comparing equivalent exposure time.

TABLE-US-00008 TABLE 8 Sa Value Xe Exposure Sample 1 Sample 18   0 hrs 1.35 1.14 2250 hrs 1.92 1.36 3750 hrs 1.25 0.83