Water-based transparent iron oxide pastes are recognized by the market for their environmental friendliness, functionality (UV protection, weathering) and aesthetic value. With the tightening of global green regulations (e.g. EU REACH) and the growing demand for high-end manufacturing, a new product, Tech-6752, has emerged to provide a new option for the preparation of transparent iron oxide pastes.

I.About Transparent Iron Oxide

01 .Why is it transparent?​

Transparent iron oxide (Transparent Iron Oxide) is a class of nanoscale inorganic powders, used for pigment coloring direction of common α-Fe₂O₃ (Iron Red) and α-Fe₂O₃-H₂O (Iron Yellow), the size of the particles is usually in the range of 10-100 nm, far less than the visible wavelength of 380-760 nm. 760 nm, so there is no scattering effect on light, showing high transparency. Common examples are: Transparent Iron Yellow P.Y.42, Transparent Iron Red P.R.101 and so on.

02 .Synthesis process and morphology​

Taking transparent iron oxide red (α-Fe₂O₃) as an example, in order to achieve high transparency, the particle size needs to be controlled in the nanometer scale, at which time the bypass effect of light is enhanced. Existing production processes:

*Electron microscopy: P.R. 101 Sicotrans Red L 2817 needle morphology

• Wet synthesis (e.g., neutralization and precipitation, hydrothermal)

Tend to produce needle-like or spindle-shaped particles. The advantage of the needle-like structure is that the high aspect ratio enhances the orderly arrangement in the coating and enhances light transmission, making it suitable for high-end scenarios such as metallic flash paints.

• Dry process (e.g. calcination)

Produce spherical particles, commonly used in ordinary transparent iron oxide red, want to achieve transparency, need to be smaller particle size (<50nm) to compensate for the high technical difficulties, the actual production of spherical transparent iron oxide red accounted for a low percentage.

 

Why is it difficult to prepare?

Transparent iron oxides (including iron red, iron yellow, etc.) have become ideal coloring materials for high-end waterborne wood paints, automotive metal paints, and industrial coatings due to their nanometer-sized particle sizes (~100nm), high transparency, and excellent weathering resistance. However, its high specific surface area and surface energy also bring huge technical pain points:

 

01 .Poor dispersion stability

​ Nanoparticles spontaneously agglomerate and flocculate due to their high surface energy. Transparent iron oxide pigments have a high specific surface area (80-100 m²/g), which makes it difficult to completely and stably encapsulate the pigment. Thermodynamically, agglomeration is an inevitable tendency to reduce the surface energy, and kinetic stability is forced by hyperdispersants.

Transparent Iron Oxide Red Pigment

 

02 .Viscosity control is difficult

​​When the pigment content is >20%, the viscosity of the dispersed system increases exponentially. This is because the nanoparticle spacing is narrowed, forming a “gel-like network structure”, free dispersant molecules are entangled and thickened, and the heat of milling shear intensifies the Brownian motion of the particles, which promotes agglomeration.

Transparent iron oxide red pulp dispersion (left normal, right appears gelatinous)

 

03 .Balance of coloring power and transparency

Taking transparent iron oxide red pigment paste as an example, its transparency depends on the transparent iron oxide pigment particle size D50<½ visible wavelength (i.e. about <200 nm), once the pigment cluster size >200 nm, the light scattering will be enhanced and the coating haze will rise.

Lower particle sizes are not always better. Pigment particles <50 nm in size bring high transparency but also low coloring power. This is due to the surge in specific surface area, resulting in a high percentage of surface atoms, which in turn reduces the efficiency of visible light absorption. It has been found that the recommended particle size for transparent iron oxide red pastes is between 90-220nm, which satisfies both high transparency and high coloring power, but this places high demands on the molecular weight distribution (PDI) of the hyperdispersant.

 

Particle size above visible wavelength, transparency positively correlates with coloring power

04. Compounding Silver Paste Problems

In the preparation of champagne gold paste, in which the flake silver powder has a reflectivity of >95% for full-band visible light, forming a strong specular reflection and masking the absorption-reflection spectrum of iron pigments. It is also possible that the silver particles float up and the iron oxide pigment sinks after standing, or the dispersants compete with each other for adsorption, which challenges the dynamic balance of the dispersant in the drying process with a high degree of complexity.

 

Tech-6752 new options

Tech-6752 is a polymer type hyperdispersant containing several pro-pigment groups, which has very good viscosity reduction effect on inorganic pigments, as well as brightening effect. It has high gloss and low foam, strong coloring power, and is suitable for dispersing all kinds of inorganic pigments in aqueous system. It is especially suitable for water-based resin-free transparent iron oxide pigment color paste.

01. basic recipe

We choose the specific surface (Specific surface) in 80-85 m² / g of waterborne transparent iron oxide pigment (needle), the amount of dispersant added to the amount of 15% of the pigment (effective portion), 20-30% of the high pigment concentrates with the process of testing, the basic formula is as follows:

02 .performance comparison

We choose the same type of dispersant performance comparison, test conditions: selection of zirconium beads grinding media, vibration machine grinding 6h, color paste filtration, with paint water-based hydroxypropyl varnish: color paste = 10:1 scraper (RDS18 # wire rod about 41.1um wet film), compared with the dispersion of iron oxide red / iron yellow performance differences.

Transmittance: the degree of light transmission contrast reduction in brightlight 

Light Transmission: Tech-6752 ≈ International Competitors > Similar Products

 

Haze: the degree of scattering under strong light and natural light, Tech-6752 are good

 

 

Clarity: degree of translucency and text clarity

Use the DATACOLOR color reader ColorReaderPRO to determine the L* value of the black card portion. Generally speaking, the lower the L* value, the better the transparency of the coated film and the higher the clarity.

4) Color rendering: even plate/strong light reflection of the display effect

The same kind of product shows obvious color deviation. Due to the different degree of deflocculation under the same grinding process, the grinding efficiency of Tech-6752 is superior.

Transparent iron oxide red (α-Fe₂O₃) has a correlation between particle size and its color performance, generally speaking, the smaller the particle size, the more the color tends to be blue-green phase, transparent iron oxide yellow is the same. This phenomenon stems from the interaction of optical principles and material properties, the balance of light scattering and absorption:

Particle size is larger than the visible wavelength, dominated by scattering, reflecting red/yellow light is dominant, showing violet or deep red.

Particle size is smaller than visible wavelengths, dominated by absorption. The absorption of short wavelength light (blue-green light) is enhanced by small particle size, and the green component of reflected light is relatively increased.

03 .Compound Silver Paste​​

Mixed with water-based silver paste after the paste state, Tech-6752 is not easy to blister, long time storage without delamination, strong sense of metal, high gloss.

Front Side Lighting

Positive View – Positive Light: Tech-6752 has a good metallic feel

 

Summary​

The extraordinary experience of Tech-6752 Super Transparent Iron Oxide Paste brings better transparency, clarity and gloss, as well as extraordinary metallic feeling. In the future, Tiger Auxiliary will focus on breaking through the dispersion and stabilization of more nano oxides to empower high-end environmental protection pastes.