DEVELOPING A COMPLETE COOL COLOR SOLUTION FOR THE COATINGS INDUSTRY

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1 DEVELOPING A COMPLETE COOL COLOR SOLUTION FOR THE COATINGS INDUSTRY Jordi Fernández Urbán, Juan Manuel Somoza, Fabiana Requeijo, Patrícia Pérez Masnou Nubiola (a FERRO company) 1. ABSTRACT It is well known that black or dark surfaces heat up under the sun, while white surfaces remain cool. This heat build-up is related to the level of absorption of Near Infrared (NIR) wavelengths from the sun and one way to measure it is by Total Solar Reflectance (TSR), expressed as a percentage of the light reflected by the studied surface. Those pigments allowing high reflection of NIR from the substrate and thus a high TSR are referred to as cool pigments and are usually associated to Complex Inorganic Color Pigments. Ferro Corporation has long been supplying the market with this kind of high performance pigments and their cool properties are well known in the market. However, other pigment chemistries not so widely used for cool coatings are also suitable for this application, such as high performance Ultramarines and Zinc Ferrites manufactured by Nubiola, recently acquired by Ferro Corporation. One of the immediate synergies to offer to the Coatings industry by the united Ferro-Nubiola forces is the development of a complete color solution for cool applications in a wider spectrum of systems with different performance requirements. In this paper the cool performance of Ultramarines and Zinc Ferrites is proved and the color and performance synergies with Complex Inorganic Color Pigments in the Blue, Beige and Black color space are explored. 2. INTRODUCTION TO THE COOL CONCEPT 2.1 What is the cool concept about? The solar radiation that reaches the Earth s surface ranges over a broad spectrum of wavelengths (of about 280 to 2500 nm) and it can be divided in three different regions: Ultraviolet (UV): <400nm. UV light can cause damage to our skin and it is responsible for polymer degradation. Visible: from 400 to 700nm. The visible region is the portion of the spectrum that is visible to the human eye, and contains all the colors that we can distinguish. Near Infrared (NIR): from 700 to 2500 nm. IR light causes chemical bonds to vibrate, which translates into a temperature increase. The intensity of the solar radiation is not the same in the entire spectrum, and each region has a different contribution to the total solar energy we receive. The NIR contain 52% of the solar energy, and it is mainly in the shorter wavelengths (see Figure 1). This first region of the NIR (from 700 to 1000 nm, NIR1) is responsible for 50% of the solar energy of the NIR, while the second NIR region (from 1000 to 1450, NIR2) contributes with 30%, and the third NIR region (>1450nm, NIR3) only with 20%. 1

2 Fig 1. Solar energy distribution When sunlight reaches a material, part of the radiation is absorbed, heating the surface and the surrounding air by convection. Heat is also transported by conduction into the material, increasing the temperature on the other side by convection. For example, dark roofs absorb more radiation than white roofs or cool roofs, which can reflect up to 80% of sunlight. The higher reflection of cool roof coatings contributes to lower surface temperatures, and less heat build-up inside the building. (1) 2.2 Why is the cool concept important? The use of cool materials, which reduce the heating effect of sunlight, can provide benefits in different areas such as: Global warming migration: reducing atmospheric temperatures in urban settlements and counter some of the anticipated temperature increases due to Global Warming (2) Energy savings: for example, reducing electricity demand to cool heat island effects (3) (4), or reducing cabin temperature, fuel consumption and CO 2 emissions in cars (5) Health & safety Coatings and coated materials performance during use, such as the cases of: o Metal roofs, where thermal stress leads to coatings damage. In this case, the use of cool roofs means reduced material and labor costs as the life of the coating is extended. o EIFS (Exterior Insulation Finishing System): Insulation board is typically made out of PS, and its maximum service temperature is about 75ºC; so, at higher temperatures it begins to deform. Cool coatings are used to reduce thermal stress on insulation board by preventing high temperatures. 2.2 How can we measure the cool effect? There are different ways to measure the interaction of solar radiation with a material, and therefore to evaluate its cool effect. One of the most common is to measure the energy absorbed by Total Solar Reflectance (TSR), but there are others ways. Total Solar Reflectance (TSR) TSR is the percentage of the incident solar energy which is reflected by a material surface. Its calculation requires taking the raw reflectance data and applying solar weighting factors for each wavelength collected. These factors 2

3 and calculations are contained within the respective norms (e.g. ASTM G173). (6). It gives a scale, where the higher the TSR, the cooler the surface. As a reference: o A cool white surface can show a TSR>65% (that means that less than 35% of solar energy is absorbed). o And a conventional dark surface usually shows a TSR between 5-15% (85-95% of solar energy is absorbed) For example, Figure 2 shows the reflectance curves of two coatings, black and white, pigmented with Titanium Dioxide and Carbon black pigments, with TSR values of %TSR=84 and %TSR=5 respectively. Fig 2. Reflectance curves of a cool white coating and a dark black coating. Solar Reflectance Index (SRI) SRI is a value that incorporates both solar reflectance and thermal emittance in a single value to represent the temperature of a material exposed to sunlight. This index compares how hot a surface would get compared to a standard black and a standard white surface (4). It is calculated as the relative temperature of a surface (Ts) with respect to the standard white (Twhite with SRI=100) and the standard black (Tblack with SRI=O) under standard solar and environmental conditions: = h 100 It also gives an SRI scale from 0 to 100, where the higher, the cooler. As a reference in this case: o Standard black (reflectance=0.05; emitance=0.90) = 0, temperature rise o =50ºC in full sun Standard white (reflectance=0.80; emitance=0.90)=100, temperature rise=8.1ºc in full sun Due to the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100. Test method is described in ASTM E1980. (7) Surface temperature The cool effect can also be measured simply by measuring the surface temperature in different ways: o o Using thermographic cameras, in outdoor exposures for example. Temperature measurement (with a thermocouple) of surfaces exposed to natural sun light (outdoor exposure) or to artificial lights such as IR lamps or accelerated weathering cabinets (Xe-Arc light). Energy savings The energy savings derived from the use of cool coatings is a realistic way to measure the benefits of the cool effect. For example, it was demonstrated by a Titanium Dioxide manufacturer that the use of a highly reflective white coating instead of a conventional red roof coating (of lower TSR), can produce 3

4 a 45% energy savings in the air conditioning needed to keep a house cool at a certain temperature. (8) 3. A WIDER RANGE OF COOL PIGMENTS Pigments with low absorbance in the NIR are usually referred to as cool pigments. They allow formulating white and also non-white coatings that can reflect the NIR portion of sunlight, which results in a cooler surface when exposed to the sun than coatings using pigments with strong NIR absorbance ( hot pigments). Ferro Corporation has a wide range of cool pigments based on Complex Inorganic Color Pigments CICP (such as Nickel Titanate, Chrome Titanate, Cobalt Blue, Chromium Iron Oxide and others). They are high performance pigments in terms of heat and weather fastness, and they are suitable for the most demanding environments such as roofing applications where long life warranties are issued. With the acquisition of Nubiola, now Ferro Corporation can include ultramarine blues and zinc ferrites to their cool pigment range. It enlarges Ferro s Blue and Beige color spaces for cool solutions, by adding new alternatives for the formulation of the most suitable cost effective cool color for each specific application. This paper reviews the interaction of Ultramarine Blue and Zinc Ferrites with NIR radiation that identifies them as cool pigments. For this characterization, the reflectance curves in a coating containing these pigments alone in full shade were studied. This paper also reveals the benefits of their use in applications such as cool blue shades in decorative paints, cool blacks in an automotive paint system and cool beige shades in powder coating. Two NUBIOLA high performance pigments were selected for this purpose: Nubicoat HRD (PB29): the most Reddish Ultramarine Blue, specifically designed and quality controlled for coatings. Nubifer Y-905K (PY119): yellowish tan Zinc Ferrite, high heat fastness pigment ideal for powder, coil and stoving coatings. Reflectance curves and TSR values were mainly measured using a spectrophotometer UV-Vis/NIR Agilent Cary 5000, which covers a wavelength range from 280 to 2680nm. It reports reflectance curves, and also total TSR and the TSR values in each region. 4. EXPERIMENTAL WORK AND TESTS RESULTS 4.1. Ultramarine Blue Ultramarine Blue is an inorganic pigment whose color has been classified as Pigment Blue 29/C.I by the Color Index System. Chemically it is a sodium aluminum sulphosilicate. This pigment is the synthetic form of a mineral called Lazurite. Ultramarine Blue has a clean and bright reddish blue shade. This makes Ultramarine Blue different to any other blue pigment in the market and due to this fact very attractive. 4

5 Nubicoat HRD is the most reddish Ultramarine Blue for coatings. It is easy to disperse, and it provides a very clean, reddish blue color unmatchable by any combination of pigments Characterization of Ultramarine Blue cool properties a) Experimental work Two solvent based short oil alkyd paints were prepared: one containing Nubicoat HRD at PVC=15% (full shade) and a control paint without pigment. Paints were applied on a black and white Leneta opacity chart, at 100 microns wet film thickness, and the reflectance curve of each application was measured on white and on black background. b) Results and discussion Figure 3 shows the reflectance spectrum of the two coatings applied on white background. Fig 3. Reflectance curves on white background of SB alkyd paints (PVC=15%, WFT=100µ). In these reflectance curves, it can be seen that Nubicoat HRD strongly absorbs in the visible region (responsible for its blue shade). In the NIR region, Nubicoat HRD weakly absorbs part of the NIR radiation in the first zone (from 700 to 1100); but it has very low absorption in the NIR2 and NIR3 (almost same curve profile as the control). Figure 4 shows the spectrum of the same coatings on black background. Here, it can be seen that the Nubicoat HRD doesn t increase the reflectance (same curve profile as control), so it doesn t show strong IR-scattering. Fig 4. Reflectance curves on black background of SB alkyd paints (PVC=15%, WFT=100µ). c) Conclusions According to these observations, Ultramarine Blue can be recognized as a cool pigment due to its low absorption in the NIR; and thus it is suitable for cool paints, preferably applied on white or NIR reflective surfaces, or in combination with NIRscattering pigments. Similar results can be found in the bibliography (9) (10). 5

6 4.1.2 Cool blue shades Ultramarine Blue is usually combined with Titanium Dioxide to produce coatings with characteristic blue color shades. One typical application is decorative water based acrylic paints (wall painting for example) where Ultramarine Blue is commonly used in reduced shades. In this type of applications, the cool properties are becoming more and more important every day, and in consequence its TSR measurements are of interest. a) Experimental work Four different blue reduced shades were formulated in water based acrylic coatings using different Titanium Dioxide and Nubicoat HRD ratios, and paints were applied on a black and white Leneta opacity chart, at 200 microns wet film thickness. The CIElab coordinates of the coatings were measured, and each color was identified by its lightness (L* value: from the darker blue shade with L=24.6, up to the lighter blue shade with L=65.9). b) Test results Figure 6 shows the reflectance curves and TSR values (on white background) of the four water based acrylic coatings with different reduced blue shades. It can be seen, that the higher the dosage of Titanium Dioxide, the higher the reflectance, as well as the TSR values, due to the high IR reflectance effect of the Titanium Dioxide. So, the lighter, the cooler. The addition of Ultramarine Blue has not a significant impact on the NIR reflectance, and in the lighter shades it keeps high IR reflectance and high TSR values. Fig 5. Reflectance curve and TSR values of WB acrylic paints with different TiO2/Nubicoat HRD ratio (WFT=200µ, on white Leneta opacity chart). c) Conclusions The low NIR absorbance of Nubicoat HRD allows formulating cool coatings of light reduced blue shades with high IR reflectance and high TSR values Cool Blacks Pigment Brown 29 is a widely used IR reflectance pigment for the formulation of cool black coatings, but it doesn t have a deep black shade due to its yellowish undertone. The addition of Nubicoat HRD enhances bluish undertone of these cool black pigments. The effect of this Ultramarine Blue addition on the TSR of this black pigment was tested, to assure that Nubicoat HRD allows keeping its cool properties. 6

7 a) Experimental work The experimental work was done in a typical automotive solvent based paint system. It consists of a two coat system (wet & wet) of a pigmented acrylic melamine basecoat and a polyurethane clearcoat on top. Two different basecoats were prepared, one pigmented just with 15% Pigment Brown 29 (Ferro V-785), and another by adding 3.75% Nubicoat HRD and reducing the dosage of Pigment Brown 29 down to 11.25%. b) Results and discussion Color enhancement. The colorimetrical data of the whole system (CIELab data in Table 1) show that the coating containing Nubicoat HRD has less yellowish undertone than the coating without it (b value is considerably reduced). So, the addition of this Ultramarine Blue enhances the bluish undertone of this black coating. Cool Black coating 15% PBr29 Cool Black coating + HRD 3.75% HRD + 11,25% PBr29 Differences (delta) L a b Table 1. CIELab data of SB automotive paint system (acrylic-melamine base coat + polyurethane clear coat) applied on an aluminum panel. Effect on cool properties Figure 6 shows the reflectance curves and TSR values of these coatings (on aluminum background). They were also compared with another pigmented with a hot black pigment (carbon black). It is clearly seen that carbon black strongly absorbs the radiation of the entire spectrum, thus the coating has a very low TSR value (5%). On its side, Pigment Brown 29 appears black in the visible portion, but reflects in the NIR radiation, which means less heat build-up and an increase in the TSR of the coating up to 20%. The addition of Nubicoat HRD doesn t modify the reflectance curve of Pigment Brown 29, and its TSR value remains very similar. So, it keeps intact the cool properties of the black coating. Fig 6. Reflectance curve and TSR values of SB automotive paint system (acrylic-melamine base coat + polyurethane clear coat) applied on an aluminum panel. c) Conclusions Nubicoat HRD enhances the bluish undertone of cool black coatings made with Pigment Brown 29 whilst maintaining their cool performance intact. 7

8 4.2 Zinc Ferrite Zinc Ferrite is an inorganic pigment whose tan color has been classified as Pigment Yellow 119/C.I (Zinc Ferrite) by the Color Index System. Its basic chemical composition is a spinel Fe 2O 3.ZnO. Being slightly redder than Yellow Iron Oxides, the main differential benefit vs such pigments is their enhanced heat fastness. Nubifer Y-905K is easy to disperse, and it has high weather and heat fastness (up to 260ºC for 5 min, measured in polypropylene) Characterization of Zinc Ferrite cool properties a) Experimental work Two solvent base short oil alkyd paints were prepared: one containing Nubifer Y-905K at PVC=10% (full shade) and a control paint without pigment. Paints were applied on a black and white Leneta opacity chart, at 100 microns wet film thickness, and the reflectance curve of each application was measured on white and on black background. b) Results and discussion Figure 7 shows the reflectance spectrum of the two coatings applied on white background. Fig 7. Reflectance curves on white background of SB alkyd paints (PVC=10%, WFT=100µ). In these reflectance curves, it can be seen that Nubifer Y-905K weakly absorbs part of the NIR radiation in the first area of the NIR (from 700 to 1500nm); but it has very low absorption in the NIR3 (almost same curve profile as control). Figure 8 shows the spectrum of the same coatings on black background. Here, it can be seen that the Nubifer Y-905K increases the reflectance in the entire NIR region, so it shows IR-scattering. Fig 8. Reflectance curves on black background of SB alkyd paints (PVC=10%, WFT=100µ). 8

9 c) Conclusions According to these observations, Zinc Ferrite could be useful as a cool pigment for some specific applications, due to its moderate absorption in the NIR, and its NIRreflectance. 4.6 Cool beige shades The high heat fastness of Zinc Ferrite makes it the ideal pigment for use in applications where Yellow Iron Oxides fail due to their limited temperature resistance, such as powder coatings and stoving coatings. Nubifer Y-905K is used in these paint systems for the formulation of cost-efficient beige, brown, red and green color shades and therefore, it is interesting to explore the cool performance of these coatings. a) Experimental work Two different beige reduced shades were formulated in polyester-haa powder coating using different Nubifer Y-905K and Titanium Dioxide ratios to achieve depths of shade of 1/9 and 1/25 (with 15% total color pigmentation). Paints were applied on aluminum panels and cured at 200ºC. The CIElab coordinates of the coatings were measured, and each color was identified by its lightness (L* value: darker beige shade with L=75.2, and lighter beige shade with L=87.6). b) Results and discussion Figure 9 shows the reflectance curves and TSR values of the two polyester-haa powder coatings of different reduced beige shade. It can be seen that the higher the dosage of Titanium Dioxide, the higher the reflectance, as well as the TSR values, due to the high IR reflectance effect of the Titanium Dioxide. So, the lighter, the cooler. The addition of Nubifer Y-905K does not have a significant impact on the NIR reflectance and in the lighter shades it keeps high IR reflectance and high TSR values. Fig 9. Reflectance curve and TSR values of polyester-haa powder coating with different TiO2/Nubifer Y- 905K ratio (DFT=70µ, on aluminum panels). c) Conclusions According to these observations, Nubifer Y-905K can be used in cool medium-to-light beige formulations with high IR reflectance and high TSR values. 5. FINAL CONCLUSIONS Regarding the cool properties of Ultramarine Blues, we can conclude that: 9

10 Nubicoat HRD can be recognized as a cool pigment due to its low absorption in the NIR. And, it can be suitable for cool paints, preferably applied on white or NIR reflective surfaces, or in combination with NIR-scattering pigments. Nubicoat HRD allows formulating cool coatings of light reduced blue shades with high IR reflectance and high TSR values. Nubicoat HRD enhances the bluish undertone of cool black coatings made with Pigment Brown 29 whilst maintaining their cool performance intact. Regarding the cool properties of Zinc Ferrites, we can conclude that: Nubifer Y-905K could be useful as a cool pigment for some specific applications, due to its moderate absorption in the NIR, and its NIR-reflectance. Nubifer Y-905K allows formulating cool medium-to-light beige coatings with high IR reflectance and high TSR values. ACKNOWLEDGEMENTS FMM.Verdú (Grupo Visión y Color - Universitat d Alacant), Ricard March (Nubiola BCN R&D), Dani Lladó (Nubiola BCN Application & Marketing), Joan Monllonch (Nubiola BCN Application), Alex Capuz (Nubiola BCN Marketing), and the Nubiola BCN R&D and Application technicians for all the lab work done. BIBLIOGRAPHIC REFERENCES (1) Cool colors, Cool Roofs, part 2 Lawrence Berkeley National Laboratory (2) European Climate Change policy beyond 2012, World energy council, 2009 (3) The long-term effect of increasing the albedo of urban areas, Akbari, Matthews, Seto, 2012 (4) Reduction of Urban Heat Islands: compendium of strategies - Cool Roofs, Climate Protection Partnership Division in the U.S. Environmental Protection Agency s Office of Atmospheric Programs (EPA) (5) Cool-colored cars to reduce air-conditioning energy use and reduce CO2 emissions, Lawrence Berkeley National Laboratory for California Energy Commission (6) ASTM G173-03(2012), Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37 Tilted Surface, ASTM International, West Conshohocken, PA, 2012 (7) ASTM E , Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Sloped Opaque Surfaces, ASTM International, West Conshohocken, PA, 2001 (8) Method for measuring energy savings on highly reflective coatings, D.Bustos, DuPont Titanium Technologies Mexico (9) Solar spectral optical properties of pigments Part II: survey of common colorants, Ronnen Levinson, Paul Berdahl, Hashem Akbari. Lawrence Berkeley National Laboratory (10) Characterizing the radiative properties of pigments for cool roofs, R.Levinson. Heat Island Group / Lawrence Berkeley National Laboratory 10

11 NUBIOLA is a specialized worldwide producer of Inorganic Pigments with more than 100 years of experience in the marketplace. We are committed to sustainable growth based on the technical and production capabilities that permits to market innovative and efficient products. That commitment explains its position of world s largest Ultramarines producer as well as reliable partner in a wide range of pigments such as Iron Oxides, Zinc Ferrites, Chrome Oxide Greens, Chrome Yellows and Molybdate Oranges, Bismuth Vanadates as well as Corrosion Inhibitors. Our company employs about 750 people, has 5 production plants all over the world and a joint venture in China and sells to more than 85 countries. Customers are mainly in the Plastics, Coatings, Construction, Printing Ink, Artist s Colors, Cosmetics, Soap, Detergents, Rubber, Ceramic and other industries. Since July 7th, 2015, we are part of Ferro Corporation. Ferro (NYSE: FOE) is a US-based, leading global supplier of technology-based performance materials, including glass-based coatings, pigments and colors, and polishing materials. 11