Application of Hollow Glass Sphere in epoxy zinc-rich primer

Epoxy zinc-rich primer is one of the most important and widely used heavy-duty anti-corrosion coatings for large-scale steel structures, especially in the field of anti-corrosion of ships and marine engineering. In order to ensure the long-term anti-corrosion of steel, the protection period is extended by increasing the content of zinc powder and increasing the thickness of the coating film, which will increase the invalid load of steel structures and may bring environmental impact.
The anti-corrosion effect of epoxy zinc-rich primer mainly relies on zinc powder to play a cathodic protection role. The content of zinc powder in the dry film of zinc-rich primer is sometimes as high as 60 ~ 85%, of which nearly 40% of zinc powder does not play a cathodic protection role, and zinc is expensive, resulting in a great cost waste.
Cost advantage
1. The cost advantage of the application of Hollow Glass Sphere in epoxy zinc-rich primer
Due to the large amount of zinc powder in epoxy zinc-rich primer and the high price, the current epoxy zinc-rich primer, in addition to zinc powder as a functional filler, but also the use of relatively low-priced phosphorus iron powder and titanium iron powder and other auxiliary anti-rust pigments, used to reduce coating costs.
Hollow Glass Sphere is a hollow thin-walled spherical powder filler, the composition of borosilicate glass, inert glass material and other components of chemical reaction. Hollow Glass Sphere are normal spheres and have the smallest oil absorption under the same volume condition, which is helpful to improve the volume solid content and critical pigment and filler volume content (CPVC) of the coating.
From a cost point of view, the price per kilogram of zinc powder (density of 7.14g/cm3) is about 30 CNY/kg, the price per kilogram of phosphorus iron powder (density of 6.8g/cm3) is about 4.5 CNY/kg, and the price per kilogram of Hollow Glass Sphere (density of 0.38g/cm3) is about 35 CNY/kg. The ratio of cost per unit volume, zinc powder: phosphorus iron powder: Hollow Glass Sphere =(30 x 7.14): (4.5 x 6.8): (35 x 0.38)= 214: 31: 13. It can be seen that in several materials, the unit volume cost of Hollow Glass Sphere is the lowest, which is only one tenth of that of zinc powder.
Comparison of volume solid content of Hollow Glass Sphere in zinc-rich primer:





 

Note: HL20 and HL38 are HOLLOWLITE Hollow Glass Sphere with densities of 0.20g/cm3 and 0.38g/cm3 respectively.
Dispersion aid/anti-settling
2. Hollow Glass Sphere in epoxy zinc-rich primer to help dispersion and anti-settling effect
The volume effect of Hollow Glass Sphere helps to improve the dispersion of zinc powder, and at the same time, because its spherical structure is similar to a ball bearing, it can improve the fluidity of the coating. For epoxy zinc rich primer this kind of high density coating, supplemented by thixotropic anti settling agent, in epoxy zinc rich primer can prevent zinc powder and other conductive filler settlement, improve the efficiency of zinc powder.
Anti-penetration
3. Hollow Glass Sphere in epoxy zinc-rich paint in the anti-penetration effect
Hollow Glass Sphere have a wider particle size distribution and are more tightly packed than flaky cloud iron powder. When used in epoxy zinc-rich paint intermediate paint, it can reduce the porosity in the coating, slow down the penetration rate of water vapor and oxygen, effectively block the galvanic effect, fail to produce electrolyte, slow down the corrosion rate of steel, and obtain good and stable long-term protection. The schematic diagram of anti-penetration is shown in Figure 1.
Hollow Glass Sphere micron size, high compressive strength, can prevent the collapse of the coating, improve the coating dry film thickness. The data show that a coating thickness of 400 μm can provide protection to the steel beyond the average penetration resistance level of other fillers.

　






 

Fig.1 Schematic diagram of anti-penetration of Hollow Glass Sphere

crack resistance
4. The role of Hollow Glass Sphere in preventing crack propagation in epoxy zinc-rich primers
The isotropy of the Hollow Glass Sphere can prevent the warping and shrinkage of the paint film due to inconsistent stress, improve the anti-cracking ability of the paint film and prevent the expansion of the micro cracks of the paint film (as shown in Figure 2), so as to improve the water permeability of the paint film.
The Hollow Glass Sphere will absorb energy when impacted, improve the impact resistance of the coating film, and reduce the cracking and shrinkage of the coating film. The inside of the hollow glass microspheres is a thin gas with low thermal conductivity, which can block heat transfer to the steel structure, reduce the damage to the coating film caused by the thermal expansion and contraction of the steel structure, and also protect the steel substrate from rapid heating and quenching. Fatigue caused by shock and prolong service life.
 
 

Fig.2 Cracking resistance and microcrack propagation of paint film under microscope

(Citing Journal Materials Performance, Vol. 54, Issue 11, 2015, pp. 16-18)
Self-healing
5. The role of Hollow Glass Sphere in the self-healing of epoxy zinc-rich primer
Hollow Glass Sphere also play an important role in the shielding function of the paint film. It can be observed from Figure 2 that insoluble corrosion products (chloride, oxide) will be deposited on the surface of the Hollow Glass Sphere to fill the cracks in the paint film and play the role of self-healing of the cracks, thus preventing the corrosion products from contacting the steel substrate.

　　

 

Fig.3 Elemental analysis of sphere surface

(Citing Journal Materials Performance, Vol. 54, Issue 11, 2015, pp. 16-18)
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