Solar reflective coating composition

Abstract

A solar reflective coating composition includes: a film-forming resin; a plurality of near-IR transparent pigments dispersed in the film-forming resin, the plurality of near-IR transparent pigments including a first perylene pigment and a second perylene pigment different from the first perylene pigment; and a near-IR reflective pigment dispersed in the film-forming resin, the near-IR reflective pigment different from the first perylene pigment and the second perylene pigment. When formed into a cured coating over a substrate, the cured coating exhibits an off-white or grey color. The solar reflective coating composition is substantially free of carbon black. The present invention is also directed to a substrate having a surface at least partially coated with a solar reflective coating composition and a method of preparing a low weight aerospace component.

Claims

1. A solar reflective coating composition comprising: a film-forming resin; a plurality of near-IR transparent pigments dispersed in the film-forming resin, the plurality of near-IR transparent pigments comprising a first perylene pigment and a second perylene pigment different from the first perylene pigment; and a near-IR reflective pigment dispersed in the film-forming resin, the near-IR reflective pigment different from the first perylene pigment and the second perylene pigment, wherein, when formed into a cured coating over a substrate, the cured coating exhibits an off-white or grey color, and wherein the solar reflective coating composition is substantially free of carbon black, wherein the cured coating exhibits the off-white or grey color as defined by the following CIELAB values as measured using an integrating sphere with D65 Illumination, 10 observer with specular component included: a L* value ranging from 40 to 95; an a* value ranging from 2 to 2; and a b* value ranging from 6 to 6.

2. The coating composition of claim 1, wherein the first perylene pigment comprises a green-shade perylene pigment and the second perylene pigment comprises a purple-shade perylene pigment.

3. The coating composition of claim 1, wherein the near-IR reflective pigment comprises titanium dioxide.

4. The coating composition of claim 3, wherein the titanium dioxide is dispersed in the film-forming resin in powder form.

5. The coating composition of claim 1, wherein the cured coating exhibits a total solar reflectance of at least 45% as measured in accordance with ASTM E903-12.

6. The coating composition of claim 1, wherein the cured coating fully hides the substrate at a dry film thickness of less than or equal to 2.5 mils, according to ASTM D6762.

7. A substrate comprising a surface at least partially coated with the solar reflective coating composition of claim 1.

8. The substrate of claim 7, wherein the substrate is an aerospace component.

9. The substrate of claim 8, wherein the aerospace component comprises a carbon fiber reinforced polymer composite.

10. The substrate of claim 7, wherein the solar reflective coating composition, when cured, is the sole coating layer on the substrate.

11. The substrate of claim 7, wherein the solar reflective coating composition, when cured, has a dry film thickness of less than or equal to 2.5 mils.

12. The substrate of claim 7, further comprising a basecoat layer underlying at least a portion of the solar reflective coating composition.

13. The substrate of claim 7, wherein the near-IR reflective pigment comprises titanium dioxide.

14. The substrate of claim 13, wherein the titanium dioxide is dispersed in the film-forming resin in powder form.

15. The substrate of claim 7, wherein the first perylene pigment comprises a green-shade perylene pigment and the second perylene pigment comprises a purple-shade perylene pigment.

16. The substrate of claim 7, wherein the solar reflective coating composition, when cured, exhibits a total solar reflectance of at least 45% as measured in accordance with ASTM E903-12.

17. A method of preparing a low weight aerospace component comprising: coating at least a portion of surface of an aerospace component with the coating composition of claim 1; and curing the solar reflective coating composition to form a solar reflective layer.

18. The method of claim 17, wherein the solar reflective layer has a dry film thickness of less than or equal to 2.5 mils.

19. A vehicle comprising a surface at least partially coated with the solar reflective coating composition of claim 1.

20. The vehicle of claim 19, wherein the vehicle is an aircraft.

21. The coating composition of claim 1, wherein the cured coating exhibits a L* value ranging from 55 to 95.

Description

EXAMPLES

(1) The following examples are presented to demonstrate the general principles of the invention. The invention should not be considered as limited to the specific examples presented.

Example 1

(2) Coating compositions were prepared including the components listed in Table 1. For each coating composition, the component or components listed as 1a-1k were premixed to form the pigmented base coating component. Components 2 and 3, the activator and thinner, were then added and the coating composition mixed to uniformity just prior to application.

(3) TABLE-US-00001 TABLE 1 Comp. Comp. Pure Pure Comp. Comp. Comp. Component Grey 1 Grey 2 Grey 3 Grey 4 Grey 5 White 1 White 2 Grey 1 Purple 1 Green 1 1a Untinted White 58.62 58.34 49.81 48.59 48.4 Base.sup.1 1b IR Transparent 0.5 0.78 9.38 Black Base.sup.2 1c Yellow Tint 0.04 0.04 Base.sup.3 1d Red Tint Base.sup.4 0.01 0.01 1e Tinted Grey 59.17 Base.sup.5 1f Tinted Grey 59.19 Base.sup.6 1g Tinted White 59.17 Base.sup.7 1h Tinted White 59.19 Base (With Carbon Black).sup.8 1i Tinted Grey Base 59.19 (With Carbon Black).sup.9 1j IR Transparent 9.15 Black Tint (Purple).sup.10 1k IR Transparent 9.11 Black Tint (Green).sup.11 2 Activator.sup.12 22.98 22.98 22.98 22.97 22.97 22.98 22.97 22.97 23.79 23.92 3 Thinner.sup.13 17.85 17.85 17.85 17.84 17.84 17.85 17.84 17.84 18.47 18.57 .sup.1Pigmented polyol base component commercially available from PPG Aerospace PRC-DeSoto as DESOTHANE HS CA8000/BAC7067 (Sylmar, CA). .sup.2Pigmented polyol base component commercially available from PPG Aerospace PRC-DeSoto as DESOTHANE HS CA8000/SR8000 (Sylmar, CA). Includes a mixture of Components 1j and 1k. .sup.3Pigmented polyol base component at approximately 76% solids in solvent and a P:B = 1.39 with binder consisting of a blend of approximately 68% polyester polyol (100% active, hydroxyl humber = 230) and 32% polycaprolactone (100% active, hydroxyl value = 218), pigments consisting of approximately 44% yellow iron oxide (PY42) and 56% barium sulfate and a mixture of additives such as dispersants, UV protection package, anti-settling modifiers and other common additives known to those familiar with the art (Sylmar, CA). .sup.4Pigmented tint base component at approximately 73% solids in solvent and a P:B = 1.03 with binder consisting of a blend of approximately 68% polyester polyol (100% active, hydroxyl humber = 230) and 32% polycaprolactone (100% active, hydroxyl value = 218), pigments consisting of approximately 24% quinacridone red (PV19) and 76% barium sulfate and a mixture of additives such as dispersants, UV protection package, anti-settling modifiers and other common additives known to those familiar with the art (Sylmar, CA). .sup.5Pigmented polyol base component commercially available from PPG Aerospace PRC-DeSoto as DESOTHANE HS CA8000/SR1343 (Sylmar, CA). Component 1e included a mixture of Components 1a and 1b, and was substantially free of carbon black. .sup.6Pigmented polyol base component commercially available from PPG Aerospace PRC-DeSoto as DESOTHANE HS CA8000/BAC2001 (Sylmar, CA). Component 1f included a mixture of Components 1a and 1b, and was substantially free of carbon black. .sup.7Pigmented polyol base component commercially available from PPG Aerospace PRC-DeSoto as DESOTHANE HS CA8000/SR1408 (Sylmar, CA). Component 1h was substantially free of carbon black. .sup.8Pigmented polyol base component commercially available from PPG Aerospace PRC-DeSoto as DESOTHANE HS CA8000/BAC70846 (Sylmar, CA). Component 1h included carbon black. .sup.9Pigmented polyol base component commercially available from PPG Aerospace PRC-DeSoto as DESOTHANE HS CA8000/BAC707 (Sylmar, CA). Component 1i included carbon black. .sup.10Pigmented dispersion component prepared in a manner consistent with U.S. Pat. No. 9,057,835 B2 Example 2. Component 1j included titanium dioxide, but was substantially free of carbon black. .sup.11Pigmented dispersion component prepared in a manner consistent with U.S. Pat. No. 9,057,835 B2 Example 6. Component 1j included titanium dioxide, but was substantially free of carbon black. .sup.12Isocyanate oligomer based hardener component commercially available from PPG Aerospace PRC-DeSoto as DESOTHANE HS CA8000B Activator (Sylmar, CA). .sup.13Solvent based thinner component commercially available from PPG Aerospace PRC-DeSoto as CA8000C (Sylmar, CA).

Example 2

(4) Coating compositions prepared in Example 1 (the grey primer made using a combination of infrared transparent black pigments (Grey 3) and the grey primer made using carbon black (Comp. Grey 1)) were tested.

(5) The samples from Table 2 were prepared as follows: 1 mil of a carbon black paint (commercially available from PPG Aerospace PRC-DeSoto as DESOTHANE HS CA8000/BAC701 (Sylmar, Calif.)) was applied to 36 panels of 2024 T3 aluminum to mimic the near-IR absorption of a carbon fiber composite substrate. On top of this was applied 0.8 mils of a chrome free primer (commercially available as DESOPRIME CF/CA7502A from PPG Aerospace PRC-De-Soto (Sylmar, Calif.)). The coating compositions Grey 3 and Comp. Grey 1 were spray applied thereover by hand using a Binks Mach 3 HVLP type spray gun and a 95AS spray cap to a dry film thickness that provided full hiding. Percent Total Solar Reflectance (% TSR) was measured using a LAMBDA 950 S ultraviolet/visible/near-IR spectrophotometer (PerkinElmer) following ASTM E903-12.

(6) The maximum temperature reached under a heat lamp was also measured. This was carried out using a testing apparatus defined in ASTM B4803-10 consisting of an insulated wooden box, IR lamp and a digital thermometer using a Type J thermocouple. The two panels were placed side-by-side, but not in contact, 15.5 inches directly under the IR lamp and monitored for temperature until both panels reached a maximum temperature, which did not increase any further.

(7) The results are provided in Table 2. The sample coated with Comp. Grey 1 reflected 43% of the total solar radiation, whereas the sample coated with Grey 3 reflected 72%, for a relative increase in performance of 44%. The samples coated with Grey 3 had a maximum temperature that was 19.1 F. (10.6 C.) less than the sample coated with Comp. Grey 1.

(8) TABLE-US-00002 TABLE 2 Grey 3 Comp. Grey 1 % Total Solar Reflectance 72 43 Difference in % TSR 29 % Improvement in % TSR 40 Maximum Temperature Measured 153.9 (67.7) 173.0 (78.3) Under Heat Lamp F. ( C.) Difference in Temperature F. ( C.) 19.1 (10.6) % Improvement in Maximum 11 Temperature

Example 3

(9) Several of the coating compositions prepared in Example 1 were applied to full hiding over a byko-chart Brushout 5DX Card (Byk-Gardner catalog No. 2856). The samples were then characterized for CIELAB color using an integrated sphere with D65 Illumination and 10 observer with specular included on a Datacolor 600 spectrophotometer to measure L*, a*, b*, C*, h, and E* color values. Table 3 shows the CIELAB characterizations for the prepared samples.

(10) TABLE-US-00003 TABLE 3 Comp. Comp. Grey 5 Purple 1 Green 1 Absolute L* 78.11 67.72 80.97 Absolute a* 0.82 9.32 3.97 Absolute b* 3.73 16.91 0.32 Absolute C* 3.82 19.31 3.98 Absolute h 258 299 185 L* 10.39 2.86 C* 15.49 0.16 h 41 73 E* 19.61 5.45 (CIE76)

(11) The grey color in Grey 5 (from Example 1) was achieved by blending two infrared transparent pigments (perylene pigments) as demonstrated by the measurements included in Table 3. Grey 5 blended a green-shade perylene pigment and a purple-shade perylene pigment.

(12) Each of the individual perylene pigments in Comp. Purple 1 and Comp. Green 1 utilized alone at a high enough concentration and applied at a suitable dry film thickness yields a coating that appears black to the human eye. However, when the perylene pigment is utilized in combination with titanium dioxide (as in Comp. Purple 1 and Comp. Green 1 of Example 1) in a single coating, one IR transparent black pigment results in a purple shade, and the other results in a green shade. This is illustrated by comparing Grey 5 with Comp. Purple 1 and Comp. Green 1. Grey 5 is a neutral grey using a blend of the two IR transparent black pigments. For Comp. Purple 1 and Comp. Green 1, that blend was replaced with an equivalent amount by weight of just the individual pigment tints.

(13) Table 3 shows that there is a difference in color between Grey 5 and Comp. Purple 1, with a E of 19.61 and a difference in color between Grey 5 and Comp. Green 1, with a E of 5.45. The L*, a*, and b* values indicate that Grey 5 exhibits an off-white or grey shade, while the L* and h indicate that Comp. Purple 1 exhibits a purple shade and Comp. Green 1 exhibits a green shade.

Example 4

(14) Several coating compositions from Example 1 were applied over a substrate and coating stack as follows. An untinted white basecoat (commercially available from PPG Aerospace PRC-DeSoto as Desothane HS CA8000/BAC7067 (Sylmar, Calif.)) was sprayed over an aluminized paper (commercially available as part 20PAP10X15SV from Alufoil Products Co., Inc. (Hauppauge, N.Y.)). The coating compositions were spray applied thereover by hand using a Binks Mach 3 HVLP type spray gun and a 95AS spray cap to a dry film thickness that provided full hiding. Hiding was determined using ASTM D6762 on Leneta black and white hide strips. The cured film coating density for the samples in Table 4 was 1.57 g/cc. The CIELAB color characterizations for these samples, % TSR, and the thickness required for full hiding are shown in Table 4.

(15) TABLE-US-00004 TABLE 4 Comp. Pure Comp. White 2 Grey 1 Grey 1 Grey 2 Grey 3 Grey 4 Absolute L* Value 95.59 78.07 93.03 91.71 90.34 77.80 Absolute a* Value 0.72 1.88 0.88 0.87 0.84 1.88 Absolute b* Value 1.10 0.69 0.17 0.40 0.82 0.69 Absolute C* 1.31 2.00 0.90 0.96 1.17 2.00 Absolute h 123 160 169 205 224 160 % Total Solar Reflectance 84 44 82 80 79 69 Dry Film Thickness of 2.65 1.45 2.45 2.05 1.53 1.45 Coating Required to Provide Full Hiding (mils) Weight of Cured Coating 38 21 35 29 22 21 at Full Hiding Thickness to Cover Wing (kg)

(16) Given an aircraft wing with a surface area of 360.5 m.sup.2, typical for a Boeing 787 type aircraft using carbon fiber composite materials, application of the coating composition would result in a range of 21 kg to 38 kg of paint on the aircraft wing for full hiding, as shown in Table 4. In order to maximize the % TSR, it would be necessary to apply a thicker layer and incur a significant weight penalty. Thus, Comp. Pure White 2, while having the best % TSR, would add weight to the component. Meanwhile, Comp. Grey 1 would have the lowest weight, but has a comparatively low % TSR.

Example 5

(17) The samples shown in Table 5 (using coating compositions from Example 1) were prepared as described in Example 2, with a black coating followed by a primer coating and then finally Grey 3 or Comp. Pure White 1. An additional sample was prepared by spraying Comp. Pure White 1 as the highly solar reflective underlayer while Grey 3 was sprayed thereover as a pigmented topcoat, resulting in a two layer coating system. Hiding was determined using ASTM D6762 on Leneta black and white hide strips. Results from these samples are shown in Table 5.

(18) TABLE-US-00005 TABLE 5 Comp. Grey 3 over Pure Comp. Pure Grey 3 White 1 White 1 Single Layer Two Layers % TSR 72 80 75 Dry Film Thickness of 1.8 2.8 4.0 Coating Required to Provide Full Hiding (mils) Cured Film Coating Density (g/cc) 1.57 1.57 1.57 Approximate Surface Area 360.5 360.5 360.5 of Boeing 787 Wing (m2) Weight of Cured Coating at Full Hiding 25.9 40.3 57.5 Thickness to Cover Wing (kg) Weight Savings vs. Two Layers (kg) 31.6 % Weight Savings 55

(19) The % TSR of the two layer system was greater than a single layer of Grey 3. However with the two layer system, the total thickness of the two layers was 4.0 mils compared to 1.8 mils for Grey 3. Therefore, Grey 3 demonstrated a weight savings of 55% over the Gray 3 over Comp. Pure White 1 without a significant loss of % TSR.

(20) The present invention further includes the subject matter of the following clauses.

(21) Clause 1: A solar reflective coating composition comprising: a film-forming resin; a plurality of near-IR transparent pigments dispersed in the film-forming resin, the plurality of near-IR transparent pigments comprising a first perylene pigment and a second perylene pigment different from the first perylene pigment; and a near-IR reflective pigment dispersed in the film-forming resin, the near-IR reflective pigment different from the first perylene pigment and the second perylene pigment, wherein, when formed into a cured coating over a substrate, the cured coating exhibits an off-white or grey color, and wherein the solar reflective coating composition is substantially free of carbon black.

(22) Clause 2: The coating composition of clause 1, wherein the first perylene pigment comprises a green-shade perylene pigment and the second perylene pigment comprises a purple-shade perylene pigment.

(23) Clause 3: The coating composition of clause 1 or 2, wherein the cured coating exhibits the off-white or grey color as defined by the following CIELAB values as measured using an integrating sphere with D65 Illumination, 10 observer with specular component included: a L* value ranging from 40 to 95; an a* value ranging from 2 to 2; and a b* value ranging from 6 to 6.

(24) Clause 4: The coating composition of any of the preceding clauses, wherein the near-IR reflective pigment comprises titanium dioxide.

(25) Clause 5: The coating composition of clause 4, wherein the titanium dioxide is dispersed in the film-forming resin in powder form.

(26) Clause 6: The coating composition of any of the preceding clauses, wherein the cured coating exhibits a total solar reflectance of at least 45% as measured in accordance with ASTM E903-12.

(27) Clause 7: The coating composition of any of the preceding clauses, wherein the cured coating fully hides the substrate at a dry film thickness of less than or equal to 2.5 mils, according to ASTM D6762.

(28) Clause 8: A substrate comprising a surface at least partially coated with the solar reflective coating composition of any of clauses 1-7.

(29) Clause 9: The substrate of clause 8, wherein the substrate is an aerospace component.

(30) Clause 10: The substrate of clause 9, wherein the aerospace component comprises a carbon fiber reinforced polymer composite.

(31) Clause 11: The substrate of any of clauses 8-10, wherein the solar reflective coating composition, when cured, is the sole coating composition on the substrate.

(32) Clause 12: The substrate of any of clauses 8-11, wherein the solar reflective coating composition, when cured, has a dry film thickness of less than or equal to 2.5 mils.

(33) Clause 13: The substrate of any of clauses 8-12, further comprising a basecoat layer underlying at least a portion of the solar reflective coating composition.

(34) Clause 14: The substrate of any of clauses 8-13, wherein the near-IR reflective pigment comprises titanium dioxide.

(35) Clause 15: The substrate of any of clause 14, wherein the titanium dioxide is dispersed in the film-forming resin in powder form.

(36) Clause 16: The substrate of any of clauses 8-15, wherein the first perylene pigment comprises a green-shade perylene pigment and the second perylene pigment comprises a purple-shade perylene pigment.

(37) Clause 17: The substrate of any of clauses 8-16, wherein the solar reflective coating composition, when cured, exhibits the off-white or grey color as defined by the following CIELAB values as measured using an integrating sphere with D65 Illumination, 10 observer with specular component included: a L* value ranging from 40 to 95; an a* value ranging from 2 to 2; and a b* value ranging from 6 to 6.

(38) Clause 18: The substrate of any of clauses 8-17, wherein the solar reflective coating composition, when cured, exhibits a total solar reflectance of at least 45% as measured in accordance with ASTM E903-12.

(39) Clause 19: A method of preparing a low weight aerospace component comprising: coating at least a portion of surface of an aerospace component with the coating composition of clause 1; and curing the solar reflective coating composition to form a solar reflective layer.

(40) Clause 20: The method of clause 19, wherein the solar reflective layer has a dry film thickness of less than or equal to 2.5 mils.

(41) Clause 21: A vehicle comprising a surface at least partially coated with the solar reflective coating composition of nay of clauses 1-7.

(42) Clause 22: The vehicle of clause 21, wherein the vehicle is an aircraft.

(43) Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.