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UNITED STATES MINERAL RESOURCES 



INDUSTRIAL FILLER USES AND 

 REQUIREMENTS 



Of the varied industries using mineral fillers, each 

 has specific requirements for the fillers it consumes. 

 Much of the following information on the use of 

 fillers was obtained from Cummins (1960). 



ASPHALT OR BITUMINOUS COMPOSITIONS 



Fillers are used in asphalt composition for road 

 paving, roofing, reservoir linings, tile, joint sealers, 

 battery boxes, and many other products to increase 

 the viscosity, melting point, resistance to mechanical 

 stress, hardness, or resistance to weathering. In 

 many products the filler is loaded to nearly 50 per- 

 cent, and in items such as asphalt tile, filler is the 

 major component. In asphalt products the filler par- 

 ticles form an interlocking skeletal lattice which 

 provides high viscosity and strength. Therefore, 

 fibrous or platy particle shape is a more important 

 property of the filler for asphalt products than are 

 color and smoothness. 



Paint 



Fillers used in paint are known as extenders be- 

 cause they hold more expensive pigments in suspen- 

 sion and upon drying form the paint film which 

 supports and spreads out the pigment. Here the de- 

 sirable mineral properties are platy or fibrous parti- 

 cle shape, smoothness and extreme fineness, high 

 reflectance, and low oil absorption. The latter is im- 

 portant because most paints use oil and resins as 

 vehicles, and therefore more pigment filler can be 

 used per volume of oil and drying time is reduced if 

 the oil is not absorbed by the filler particles. Desira- 

 ble qualities sought through the proper choice of ex- 

 tender are consistency of film formation, film tough- 

 ness, resistance to weathering, flatness, opacity, and 

 a reduction of costs through using less prime pig- 

 ment. Generally a mixture of extenders is used in 

 order to get the desired paint qualities. With the 

 increased use of water-based latex paints some con- 

 sideration is given to the alkalinity of the filler in 

 order to increase corrosion resistance. Most fillers 

 are inert, but some, such as wollastonite, produce 

 alkaline suspensions (Andrews, 1970), which are 

 desirable to decrease "rusting through" of nail heads 

 and rusting of paint cans and are compatible with 

 pigments that would react if used in low pH suspen- 

 sion. Uniform fineness of particles is extremely 

 important for paint extenders, because coarse par- 

 ticles show on thin paint films. For most uses, fillers 

 must pass a 325-mesh screen, but as paint extenders 

 they are ground to micron sizes, and techniques to 

 grind particles finer are actively sought. 



PLASTICS 



Plastic floor tile has long been a major consumer 

 of asbestos and other fillers. Inasmuch as the plas- 

 tics industry is rapidly expanding and developing 

 new products, many more types of mineral fillers 

 are being used. The consumption of talc, wollaston- 

 ite, and other fillers is rapidly expanding for this 

 use because of the strength, electrical and heat re- 

 sistance, and whiteness of these fillers. Carbon 

 black is used to increase resistance of polyethylene 

 to sunlight aging although it was used initially as 

 a pigment. Properties desired from fillers in plastics 

 are color, strength, electrical and heat resistance, 

 increased melting point, stiffness, decreased brittle- 

 ness, and low shrinkage. Many plastic products con- 

 tain nearly 50 percent filler, which is responsible 

 for most of the physical properties of the products. 



RUBBER 



The rubber industry is a major consumer of fillers 

 used as reinforcing agents to increase tear resist- 

 ance, abrasion resistance, stiffness, heat dissipation, 

 and electrical resistance and to intensify color. Much 

 research has been done by the rubber industry to 

 understand the actual physical function of filler 

 particles in rubber (Huber Corp., 1955; Cummins, 

 1960). Particle size required for rubber fillers de- 

 mands nearly 100 percent passing through a 325- 

 mesh screen. Grit particles tend to cause tearing 

 and excess wear of cutting and extruding equipment. 

 The percentage of loading fillers depends upon the 

 desired quality of the finished rubber product, and 

 a wide range up to more than 50 percent is common. 

 For white rubber products color is important, and 

 barite, zinc oxide, and titanium oxide are used with 

 kaolin. Barite is also used to increase specific grav- 

 ity, as in rubber mallets. Carbon black is the major 

 reinforcing pigment used by the rubber industry. 

 Kaolin also is an important rubber filler and is used 

 to increase hardness and abrasion resistance. Very 

 fine grained kaolin produces hard rubber, hence is 

 known as "hard clay." "Soft clay," a coarser clay, 

 allows rubber to remain soft. 



PAPER 



Another major consumer of fillers is the paper 

 industry. This industry uses mineral fillers in two 

 ways, one as a filler or loader, in which filler mixed 

 with bonding agents fills the voids between the felted 

 cellulose and textile fibers to be rolled out as the 

 paper sheet, and the other as a surfacing material 

 or coating where whiteness, opacity, and gloss are 

 desired. Pigments and mineral fillers, for example 

 flux-calcined diatomite with Ti02, are often used in 



