Application of cold pigments in coatings

With the development of society, the user's performance requirements for pigments are getting higher and higher, simple coloring properties can not meet the functional requirements of customers for pigments, therefore, in order to meet the basic requirements of coloring at the same time, pigments with other properties are constantly developed. Pigments used in building coatings need to have weather resistance, temperature resistance, environmental protection and energy-saving properties, with the continuous improvement of domestic energy-saving coating requirements, cold pigments in the field of building coatings more and more widely used. In this paper, combined with the principle of the role of cold pigments, the definition of cold pigments and related standards, as well as the application of
in
.1, the concept of cold pigments
With the continuous improvement of energy-saving requirements in the field of construction, the coating products are required to have insulation and cooling performance, the related insulation and reflect the sun's thermal energy coating system came into being. The thermal energy that the coating can reflect sunlight is mainly provided by pigments in the coating system, of which the more representative is the cold pigment. From the author's point of view, cold pigment is a pigment with cold effect, its cold effect is generally in contact with the sun to play a role. As a cold pigment, there must be three properties at the same time: high cover, excellent weather resistance and high near-infrared reflectivity. Composite Inorganic Pigments MMO (Mixed Metal Oxide Colored Pigments)/CICP (Complex Inorganic Colored Pigments) is energy efficient due to its excellent weather and temperature resistance and good covering power, while many composite inorganic pigments have better performance in reflecting solar thermal energy. In foreign countries, the application of cold pigments made of cold paint products have more than 30a practical experience, of which the use of cold pigments are mainly derived from composite inorord pigments cold pigments. In China, the demand for energy-saving coatings is increasing, the corresponding standards such as JG/T235-2014 "building reflection insulation coating" was officially introduced, the first time in China set up in addition to white other colors of the cold effect indicators, from the quantitative numerical point of view of color, the cold pigment put forward clear requirements, so that the application of cold pigments more standardized.2, the role of cold pigments
solar light by wavelength can be divided into γ-ray band, X-ray band, ultraviolet, visible and infrared (also divided into near-infrared and far-infrared) band, due to the protection of the atmosphere, the solar energy into the Earth's surface band only a small amount of ultraviolet light (5% of the energy reaching the Earth's surface), visible light (43%) and near-infrared band (52%). In the UV band, because it accounts for only 5% of the energy, and the UV penetration is very strong, so that the various colors of its reflectivity is low, so this paper focuses on visible light and near-infrared band color and pigment reflectivity. The reflection, absorption and conduction of light usually occurs when sunlight hits the surface of an object. Within the visible light band, the reflectivity curve for each color is unique. Because color is the principle of reflection imaging, within the visible light band, reflection imaging also reflects the performance of the color reflecting the energy of sunlight. Taking white pigments and black pigments commonly used in the coating industry as an example, titanium dioxide reflects more than 80% of visible light, although the reflectivity in the near-infrared band is reduced after 1500nm, but the overall solar reflectivity (full reflectivity) is still high, which is why white is perceived as a cold color in daily life. The reflectivity of carbon black to sunlight is very low overall. The principle of reflection imaging requires that black must be fully absorbed in the visible light band, but not all black pigments in the near-infrared band are like carbon black. Figure 1 shows the reflectivity curve of three different black pigments in the visible and near-infrared bands. Cold black pigments have a very high reflectivity in the near-infrared region, and after more than 1500nm bands, cold black pigments reflect even better than titanium dioxide. Therefore, the performance of high reflectivity in the near-infrared band is the key reason why the black pigment becomes cold black pigment. In practical application, the same 2 pure black aluminum plate, one with carbon black, the other with cold black pigment, under the same conditions, with infrared lamp to simulate near-infrared light on the surface, 2 aluminum plate temperature difference can reach 10 degrees C.
Figure 1 3 black sunlight reflectivity
3, cold pigment determination
for long-term outdoor use, and with efficient energy-saving effects, the use of cold pigments required excellent weather resistance and high near-infrared reflectivity. Another attribute is required for cold pigments: high masking force, which can be explained from the test results in Tables 1 and 2. As can be seen from Table 1, PY-97 yellow has a total solar reflectivity (TSR) of 71.4% and 55.0% on different white and black substrates at a brightness L∗ value of 85.10, both reaching 16.4% of the sun's total The difference in reflectivity results in a very transparent organic pigment due to PY-97, whose reflectivity is actually derived from the high reflectivity of the white substrate, and when the substrate is black, the reflectivity is reduced accordingly due to the transparent properties of the PY-97 pigment (because the reflectivity of the black substrate is low). Titanium dioxide is a pigment with high cover and high reflectivity, and as the L∗ value increases (i.e. the addition of titanium dioxide), the sun's full reflectivity of different substrates in white and black increases to 93.42, respectively, at the time of the increase in the brightness L∗ 4%, the difference between the two 4.9%, compared to L∗ value at 85.10, when the L∗ value rose to 93.42, the difference significantly reduced, which also shows from another angle because of the increase in the addition of titanium dioxide, improve the cover and reflectivity characteristics. Therefore, if the pigment cover force is low, high transparency, it does not have a good reflective ability to sunlight, must be added through the substrate or at the same time like titanium dioxide, high cover force and high reflectivity of other materials to achieve the function of high reflectivity, such pigment reflection performance is not their own, but with the help of other materials to achieve, so can not be called cold pigment, can only be called cold effect pigment.Table
1 reflectivity of different colors on black and white surfaces
As can be seen from Table 2, both blue-phase cold black and STD standard cold-black masking performance and near-infrared reflectivity performance are very good, while weather resistance is also very good, is a more comprehensive performance of cold black pigments.
2 The reflectivity of carbon black and cold black pigments on the black-and-white surface4, the application of cold pigments
4.1 related standards
In 2008, China introduced the first standard on cold paint JG/T235-2008 "building reflection insulation paint", the solar reflectivity requirements: solar reflection ratio (white) ≥80, the standard only for white requirements, it is well known that white pigments, especially titanium dioxide, from a certain point of view is actually natural cold paint. In 2014, the JG/T235-2008 standard was revised to the JG/T235-2014 Building Reflection Insulation Coatings. Taking into account the practical application of other colors and the requirements of cold, the brightness L∗ value is divided into ≤40, 40 to 80, ≥803 intervals, for different intervals put forward the corresponding full reflectivity and near-infrared reflectivity requirements≤∗≥ ≥ 40;L∗ in the 40-80 range, the sun's full reflection ratio is ≥40, the near-infrared reflection ratio is ≥ (L∗ value/100), L∗≥ value is ≥80, the sun's full reflection ratio is ≥65, and the near-infrared reflection ratio is ≥80. The test found that the color coating of cold pigment was used, and the reflection curve could be used mostly through the requirements of JG/T235-2014, and Figures 2 and 3 were the actual test results in the full reflectivity TSR and near-infrared reflectivity NISR bands of color cold pigments.
Figure 2 TSR full reflectivity scattering map of color cold pigments
Figure 3 NISR near-infrared reflectivity scattering map of color cold pigments
Application of 4.2 white and black cold pigments

4.2.1 white at high brightness and the amount added
Table 3 is the white addition and phase condition after the L∗ value exceeds 80.
3 White additions and ∗ after the L∗ value exceeds 80
As can be seen from Table 3, when the brightness L∗ value exceeds 80, the requirements of the JG/T235-2014 standard are required. Near-infrared reflectivity ≥80, for white, if the use of ordinary titanium dioxide is generally not up to the requirements of near-infrared reflectivity, but after the use of a special cold titanium white products, although the standard requirements, but the amount of addition and color have changed significantly (Figure 4). As can be seen from Figure 4, when using cold titanium white as a white pigment, when the L∗ value exceeds 80, in order to meet the requirements of the JG/T235-2014 standard, in addition to the need to increase the amount of addition, the color b∗ value is significantly yellow. The purer the white (blue phase), the better, and if the most basic attribute of the color is changed in order to meet the requirements of the standard, the standard requirements in the range of the brightness L∗ value may need to be further revised.
Figure 4 the color of the white pigment with ordinary titanium dioxide and cold titanium white as the white pigment after the L∗
value exceed∗s 80
With the increase of L∗ value, cold titanium white needs to be added to the cold black pigment to improve the corresponding reflectivity and full reflectivity, Figure 5 shows the change of the a∗∗ and b∗ values of the cold black pigment SPP-3025 when using ordinary titanium dioxide and 2 cold titanium white dilution. Figure 6 shows the difference between the ∗ and cold titanium dioxide when the value of cold black pigments is different in L.
5 Cold black pigment SPP-3025 in the use of ordinary titanium dioxide and 2 cold titanium white dilution corresponding to the L∗ value, a∗ value and b∗ value change
∗ And infrared reflected titanium dioxide color difference
From Figure 6, it can be seen that the use of cold titanium white on cold black pigment dilution, and the use of ordinary titanium white powder dilution contrast, in the same L∗ value, cold titanium white dilution of the color color will be red, yellow, visual feeling is not as pure as blue. This is the same as in the high-brightness L∗ value greater than 80 when the white chroma deviation problem, as black, in order to meet the requirements of the JG/T235-2014 standard, if the use of cold titanium white dilution, as the most basic attribute color of black color will change, so it is recommended that in some bright L∗ value range of the standard requirements of the necessary revision of reflectivity limits.
4.2.3 Application of white natural sand in real stone paint sand
The main additions to real stone paint products are white natural color sand and artificial white color sand (see Table 4), there is currently no standard for cold products related to real stone paint and color sand, if JG/T235-1 The 2014 standard requires the cold effect of real stone paint, in practical application found that after the L∗ value of more than 70 natural white sand or artificial white sand (natural white sand and ordinary titanium white powder covered with artificial white sand) as much as less than the requirements of the JG/T235-2014 standard. In order to make the real stone paint also meet the JG/T235-2014 standard, when the L∗ value is greater than 70, white sand must be covered with cold titanium pigment, but this results in a phenomenon such as 4.2.1 white in the high-brightness phase and addition amount———
4 Natural white sand and conventional titanium white powder covered white sand at a brightness L∗ value greater than 70 reflectivity5, conclusion
(1) cold pigments and cold effect pigments are different, in practical applications, the current more attention to the solar reflectivity performance requirements. But for cold pigments, the required triple attributes are indispensable: high masking color, excellent weather resistance, and high near-infrared reflectivity. Combined with some challenges in the implementation of the JG/T235-2014 standard, it is recommended that when using cold pigments, not only have certain requirements for reflectivity, but also emphasize the requirements of high masking force and excellent weather resistance, so that cold pigments can be used reasonably in practice.
(2) Composite inorgeable pigment MMO/CICP has excellent weather and temperature resistance, some pigments also have a very good performance of reflecting solar thermal energy, so derived from the composite inorgeable pigment cold pigment system, more in line with the requirements of cold pigments.
(3) combined with the existing problems in practical applications, it is recommended to make the following amendments to the JG/T235-2014 standard: only emphasize that high near∗-infrared reflectivity will be more in line with practical applications>
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