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First, distinguish three completely different cooling mechanisms. Many formulas combine reflective fillers, barrier fillers, and radiation emitting fillers together, commonly known as the “reflection+barrier+radiation three in one insulation” infrared technology

The solar heat is mainly concentrated at 0.3-2.5 μ m (ultraviolet+visible+near-infrared); 8-13 μ m is the atmospheric infrared window and the radiation heat dissipation channel

1. High refractive index reflective filler: Reflecting sunlight directly. Principle: The greater the difference between the refractive index of the filler and the refractive index of the resin, the stronger the Mie scattering and the higher the near-infrared reflection; The particle size matches the near-infrared wavelength, resulting in optimal scattering  

2. Rutile titanium dioxide: n ≈ 2.7, silicon aluminum coated infrared reflective titanium dioxide, specifically designed for the near-infrared range of 700-2500 nm; The particle size of 0.2-0.4 μ m is optimal for infrared reflection, not the finer the better; Light/white thermal insulation topcoat main, with an addition amount of 15-30%

3. Barium sulfate: n ≈ 1.64, moderate refractive index, weather resistance, low oil absorption, auxiliary reflection, does not absorb infrared, often compounded with titanium dioxide to improve sedimentation and enhance paint film density. Outdoor acid rain resistance is superior to heavy calcium

4. Flake mica: stacked in sheets to form multiple reflective interfaces, while shielding water vapor, improving weather resistance and corrosion resistance, assisting reflection, and adding 2-5%

5. Nano alumina: with a refractive index of 1.76, it does not reflect the main sunlight. Its strength lies in high emission in the mid to long infrared range of 8-13 μ m. It is a radiation cooling filler used in radiation cooling systems to radiate the accumulated heat out into outer space

Misconception: Ordinary calcium carbonate has high infrared absorption and is only suitable for indoor use. Outdoor insulation should be minimized as much as possible; Carbon black and ordinary iron oxide will absorb a large amount of near-infrared radiation, causing a sharp drop in solar reflectivity

Hollow barrier filler: locks in air, reduces the thermal conductivity of the coating. It does not reflect sunlight and is the heat absorbed by the coating, making it difficult to conduct to the substrate. It belongs to the category of “insulation and heat resistance”

Hollow ceramic microspheres: thermal conductivity of 0.04~0.08 W/(m · K), high temperature resistance, non absorbent, preferred for industrial storage tanks and high-temperature steel structures; Be sure to stir at low speed. After crushing, the insulation should be discarded directly. Add 10-20%

Hollow glass microspheres HGM: lower thermal conductivity, lower cost, and weaker temperature resistance than ceramic beads; Pay attention to hydrophobic modification, otherwise the water-based system will lose water absorption, thermal insulation, and water resistance

Aerogel powder: the lowest thermal conductivity (0.02 – 0.03), expensive, generally 5 – 10% compounded, can not be added in large quantities alone, viscosity explosion, and brittle paint film

Key point: Hollow microspheres and titanium dioxide are classic partners: titanium dioxide is responsible for “less heat absorption”, while hollow beads are responsible for “the heat absorbed cannot be transferred in”

High infrared emission filler: It radiates the heat stored in the coating outward, targeting the 8-13 μ m atmospheric window. Even during the day, it can radiate heat outside the atmosphere, achieving passive cooling; Most commonly used: nano alumina, nano SiO ₂, special zirconates, strontium titanate; The dark cold pigment system heavily relies on these types of fillers

Differentiation: Ordinary white titanium dioxide has strong solar reflection, but low mid to far infrared emissivity; Aluminum oxide just makes up for this shortcoming

Difficulty in dark insulation

Ordinary organic colorants will consume near-infrared light, causing a sharp drop in reflectivity; Solution: Infrared cold pigments, such as titanium chromium brown, cobalt blue, and iron chromium black; Visible light absorption color development, near-infrared high reflection, black can also achieve solar reflectivity>70%, but the cost is much higher than that of white system

1. Prioritize system objectives:

Ordinary color steel tiles/storage tank white cooling: rutile infrared titanium dioxide+barium sulfate+hollow ceramic microspheres+a small amount of mica

High end radiation cooling model (continuous cooling day and night): On top of it, 3-6% nano gamma alumina is added to increase the emission rate by 8-13 μ m

Dark insulation: titanium dioxide reduction, replaced with CICP cold pigment, combined with barium sulfate and nano alumina

2. Principle of particle size matching: Near infrared wavelength of 700-2500 nm, optimal particle size of filler ≈ 1/2 wavelength: mainly 0.3-1 μ m; Graded particle size achieves wide band scattering, while single particle size reflects narrow bands

3. Color to base ratio control: The color to base ratio of reflective insulation paint is generally high, ranging from 1.2 to 2.0; High paint film looseness, water and salt spray resistance, collapse process red line:

Hollow microspheres should be added and stirred at low speed, and sanding is strictly prohibited; Once the shell is broken, the hollow structure disappears and the insulation directly fails

Pre grinding and dispersion of titanium dioxide, aluminum oxide, and barium sulfate can cause optical scattering defects due to agglomeration, resulting in poor reflectivity and easy water whitening

Surface modification of fillers: treated with silane coupling agent to reduce hydrophilicity, while also considering water resistance, water whitening resistance, and thermal insulation

High frequency stepping pit

1. Blindly adding hollow microspheres: limited insulation improvement, sudden increase in paint film pores, soaring water absorption, water resistance to whitening, foaming, salt spray paint peeling

2. Use ordinary titanium dioxide: strong UV absorption, poor near-infrared reflection, and fast outdoor aging

3. Agglomeration of fillers: Poor dispersion of nano alumina and nano silica not only does not improve reflection, but also introduces a large number of interface defects, which aggravates water whitening

4. Confuse “reflection” and “insulation”: prioritize high reflection fillers for surface cooling; Hollow microspheres are the main choice for substrate insulation and heat resistance; Many people have rebelled