Hollow glass microspheres are used to achieve high levels of Total Solar Reflectance (TSR) in coatings

Blog Archive | 5 minutes  | Author: Adam Morgan , Ph.D.

White roof coatings have existed in hot countries for a long time. These coatings help to reflect solar energy back into the atmosphere, rather than heating up the building. To achieve this white finish, pigments and fillers like titanium dioxide and calcium carbonate are used.

This article demonstrates that, with the use of 3M hollow glass microspheres in a coating, one can achieve a high level of total solar reflection with the dry film. This helps to reduce the need for energy-intensive cooling systems. Lawrence Industries have a wealth of information and support from 3M around this topic so, if it is of interest, contact our technical sales team today.

It is worth noting that there are many coating applications possible with this technology and that it is not just restricted to improving the energy efficiency of buildings. Other examples that would benefit from the use of solar heat reflective coatings include caravans, mobile homes, cold storage distribution centres, refrigerated vehicles, oil and gas storage tanks, cryogenic tanks and tankers, and deck coatings.

Total solar emission is shown in the spectrum below (Figure 1). It comprises UV, visible and IR radiation – the latter responsible for heating. In this article, we will show that 3M hollow glass bubbles offer an excellent level of reflection in both the visible and IR regions of the spectrum.

Figure 1. Solar irradiance spectrum showing the contributions from UV, visible and IR radiation.

 

Testing 3M hollow glass microspheres for Total Solar Reflectance when incorporated into a coating

A waterborne coating was formulated for the subsequent TSR testing. Glass bubbles are compared with calcium carbonate on a volume replacement basis. For this study, 22.5% by volume of glass bubbles or calcium carbonate were used. Generic details of this formulation are given in Figure 2. Lawrence Industries can also supply you with the following components of the formulation: dispersing agents, acrylic binders, HEUR thickeners and the polysiloxane defoamer.

Figure 2. Waterborne coating starting point formulation, used in the subsequent solar reflectance and heat transfer tests.

A Perkin-Elmer spectrophotometer was used to analyse the Total Solar Reflectance of the subsequent coating at 400 microns. All 3M hollow glass microspheres outperformed the reference filler (calcium carbonate). However, it was the newer, smaller, high strength grades that gave the highest reflectance (Figure 3). Coatings formulated without bubbles show a 9% absorption of solar energy. This can be reduced to less than 6% with the use of new generation hollow glass microspheres - a reduction of over 33%. This correlates to impressive temperature reduction, as you will see in the next section. These coatings can also be applied with an airless sprayer, without breakage of the hollow glass microspheres.

Figure 3. Total Solar Reflectance of the coatings formulated from the starting point formulation given in Figure 2.

 

How does Total Solar Reflectance correlate with the reflection of heat?

Total Solar Reflectance improvements are good to see but what effect does this actually have on the thermal diffusivity through the coating? An experimental setup was constructed to investigate this question (Figure 4).

Figure 4. Each coating was painted onto an aluminium panel and exposed to an IR lamp. A thermocouple on the other side of a supporting polystyrene box was monitored over time, to investigate the thermal barrier presented by the coating.

A good correlation is found between Total Solar Reflectance and the level to which heat transfer is reduced through the coating. S28HS and S32HS both perform very well in this experiment - with a reduction of 10°C when compared to the coating containing only calcium carbonate (no hollow glass microspheres, Figure 5).

Figure 5. Temperature readings from the setup in Figure 4, when using different grades of hollow glass microsphere (or calcium carbonate) in the coating outlined in Figure 2.

 

What other benefits can 3M hollow glass bubbles impart to your coating?

Additionally, 3M hollow glass bubbles reduce microcracks forming in the coating, due to the reduction of shrinkage and warpage under temperature fluctuations. These cracks can form thermal bridges through the coating and areas for water infusion, leading to subsequent algae and fungal growth. Glass bubbles reduce crack formation when using nails or screws.

 

In summary

In this article, we have seen that:

  • 3M hollow glass bubbles offer a large reduction in solar energy absorption when compared with conventional fillers like calcium carbonate.
  • This reduction in solar absorption translates into a real cooling effect on the inside of the coated structure.
  • There are many applications for coatings in this field including buildings, cryogenic storage, refrigerated units etc. More are outlined at the beginning of this article.
  • High strength 3M glass bubbles can be used in airless spray application as well as brush and roller.
  • Microcracks are reduced with the usage of hollow glass microspheres

 

Interested? We have more information to share…

We have more data and starting point formulations available for this application. Please get in touch with our technical sales team on 01827 314151 or via the contact page, to discuss your project. They will be able to offer the best recommendation and practical tips for using these materials as well.

3M have an application support laboratory that can be utilised in support of projects as well. You can also submit a sample request through our 3M hollow glass bubbles product page.

Author: Adam Morgan , Ph.D.

Adam studied chemistry at the University of Warwick for 8 years, where he obtained a Ph.D. in the field of polymer and inorganic colloid science. He has been with Lawrence Industries since 2014 as a technical sales manager covering all industry areas. He is now responsible for marketing within the company as well.