Volume 7 Issue 1

Volume 7 Issue 1

What’s Happening at Missouri S&T:
(formerly UMR)

Short Course Dates

We will be offering ?Basic Composition of Coatings" March 28-April 1, 2011 (Spring 11). The Basic Composition course is intended for new personnel in the coatings profession. It targets the components of coatings (resin, pigments, extenders, solvents and additives), testing and specifications, general formulation and manufacturing methods. Basic Composition is primarily a lecture course with several laboratory demonstrations.

We will be offering ?Introduction to Paint Formulation"  May 9-13, 2011 (Spring 11). This course is intended to give the person a fundamental knowledge of how to approach a starting formulation and troubleshoot it. This course involves both lecture and laboratory work.

We will be offering "Introduction to Coatings Composition and Specifications" July 18-20, 2011 (Summer 11), course designed for the new coatings person in areas such as sales, marketing or production. The course was initiated by a number of raw material companies and distributors requesting a course with this format. This course is not as heavily technical as is our “Basic Composition of Coatings" and “Introduction to Paint Formulation" courses. The ?Introduction to Coatings Composition and Specifications" course is a two and a half day course which will discuss the types of coatings, the basic composition of coatings and the tests and specifications used by the industry. This course will allow the participant to gain the fundamentals needed to work in this industry and to communicate more clearly.

For more information see our web site at http://coatings.mst.edu/index.html and to register contact Catherine Hancock at cemv26@mst.edu or coatings@mst.edu or call 573-341-4419. **These courses are held on the Rolla campus**

Technical Insights on Coatings Science

Application of hollow microspheres in coatings

Sagar Gade, Graduate Research Student, Missouri S&T

Hollow glass, polymeric or ceramic microspheres materials are used in coatings or composites exhibit unusual mechanical and heat-insulation properties [1]. In many countries, heat insulation by means of coatings is achieved by adding hollow or solid microspheres in acrylic based coatings [2]. Many coatings are developed with high absorbtivity in visible regime and very low emissivity in IR regime for architectural as well as industrial coatings [3].

Issues like stringent environmental regulations, customer requirements and competitive markets can be tackled with innovative raw material usage and developing new processes. There are many raw materials available which can be called ‘answers awaiting questions’; a good example being microspheres. 

These specialty materials are used for many purposes in many diverse industries. It’s an innovative raw material in the coating industry and diverse because both solid and hollow are readily available.  Solid spheres are most commonly use in reflective traffic paints, where the micro spheres are used as reflectors of light.   

Hollow micro spheres are small, spherical particles ranging in sizes of 12-300 microns in diameter, and wall thickness up to 0.1 micron. As these microspheres are hollow, the true density is very low ranging from 0.60 g/cc to as low as 0.025 g/cc. Organic hollow microspheres are mostly composed of polystyrene, polyacrylonitrile or phenolic materials while inorganic are glass, ceramic or fly ash from thermal power plant [4].

Glass Micro spheres

Glass Microspheres give high heat and chemical resistance with density ranges of 0.125 - 0.60 g/cc. The collapse strength depends directly on the wall thickness and thus to density, thus the higher the density, the strength increases.

Solid or hollow glass micro spheres are used in various applications in the coatings industry. They are commonly used to improve the performance of epoxy primers, powder coatings, floor applications, aircraft paints and industrial coatings. Hollow spheres are used in thermal insulating coatings for construction and transportation applications, and also for acoustic insulation coatings [4]. Hollow glass micro spheres with density 0.6 g/cc with a fine particle size distribution can be used in flat wall paint.

Plastic Micro spheres

Thermoplastic micro spheres are compressible hollow particles with thin shell wall having densities as low as 0.025 g/cc. As resilient plastic materials,  these microspheres can deform under stress (during high shear mixing or pumping), and  there is very low to no breakage. The compressible nature of plastic can absorb impact, reducing damage caused by stone chips, foot traffic or freeze-thaw cycles [4].

Use in Paint and Coatings

Uniform spherical shaped microspheres have lower surface area then irregular fillers and extender pigments, which means a lower resin demand.  Another benefit to the spherical shape is the ability to roll past one another, hence there is minimal impact on viscosity when they are added to a liquid. As coatings are manufactured on weight basis and sold on volume basis, micro spheres are used to increase the solid content of a coating, maintaining application and flow properties. Higher volume solids reduce VOC, shrinkage and drying time.

As hollow spheres lower the density of materials they are added to, e.g. coatings, composite, filler in plastics etc. If added in coatings, it will atomize better while spraying and it will give less spatter while rolling also sag less once applied. [4]

One of the most important applications microspheres have been developed for is the Space Shuttle program.  When the space shuttle re-enters the earth's atmosphere, incredible heat is generated due to increasing air friction. In order to prevent the space shuttle from burning up during re-entry, NASA scientists developed a superior insulating material using Ceramic technology. This technology can now be applied to roofs and sidewalls of buildings, piping, ducts, tanks, various storage devices, refrigerated containers, cold rooms, etc. in order to insulate them from the radiant heat of the sun and the atmosphere by using hollow ceramic spheres.

Stagnant air is a bad conductor of heat because heat is transferred by convection currents. Stagnant air inside hollow spheres acts as an insulator for heat and hence can be used as heat insulating material in coatings. This characteristic of hollow microspheres allows improved thermal and acoustic insulation properties of coatings or composites. Currently, markets taking advantage of this property include fire retardant materials, sensitive acoustic equipment, and roof coatings.

Applications of Hollow Microspheres  

• All Types of Roofs - Flat or Slopping, made of Concrete, Metal or Asbestos Cement,
• Side Walls of Residential and Commercial Buildings, Hotels and Hospitals, Construction Office,
• Roofs and Sidewalls at Process Control Rooms, Surveillance Towers, Manufacturing Plants and similar constructions and structures
• Piping in Air Conditioning Systems, Steam Pipes, Thermo Fluid Pipes, Boilers
• Exterior of Storage Tanks for Crude Oil, Chemicals, Solvents, Natural and Petroleum Gas, Storage Devices at Petroleum and Petrochemical Industries,
• Grain Silos, Fishing Trawlers, Cold Storage, Refrigerated Trucks and Containers
• Exterior Roofs of Public Transport Vehicles, Railway Passenger Coaches

Limitations

Large particle sizes of microspheres can result in surface texture, meaning gloss reduction. Today, however, fine size hollow glass microspheres are available for coatings requiring higher gloss and thin layer deposition [4]. Microspheres have low density, which means the particles have the tendency to become airborne while being added to the batch.  Also for the same reasons, floating or phase separation can occur in the finished mix.

Conclusion

Hollow micro spheres (especially glass microspheres) offer improved scrub and burnish properties, gloss, stain resistance, viscosity control, thermal insulation and sound-dampening characteristics.  No other conventional additive can match the multiple performance benefits of hollow micro spheres. Their hollow structure, low density and small particle size make them ideal for use as extenders for paint formulations.  With particle sizes considerably finer than previously available, hollow micro spheres can be used in thin-film coatings to improve integrity. In the case of glass microspheres, they do not absorb resin, allowing more resin to be available in film forming; the result being a tighter and more uniform film with improved durability [5]. Micro spheres may also be added to improve hiding properties or to replace some of the titanium dioxide (TiO₂), depending on the formulation, equivalent tint strength can be achieved with 5-10% replacement of TiO₂.

Reference

1.       L.A.Dombrovsky , Infrared radiative properties of polymer  coatings containing  hollow microspheres, Int J Heat Mass Tran. 50 (2007), pp. 1516-1527

2.       M.L.German and P.S.Grinchuk, Mathematical model for calculating the  heat-protection properties of the composite  coating “ceramic  microspheres – binder”, J. Eng. Phys. Thermophys. 75 (2002) (6), pp. 1301–1313

3.       L.A. Dombrovsky, Modeling of thermal radiation of a polymer  coating containing  hollow microspheres, High Temp. 43 (2005) (2), pp. 247–258.

4.       Chris Rosenbusch, The benefits of Microspheres, Paints and Coating Industry, August 2003, 76-78

5.       Bill Shaker, ‘Sphericel®’ Paints and Coating Industry, October 2005