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Specialty Minerals Talcs for Adhesives and Sealants

Talc is a hydrous magnesium silicate mineral with a platy crystal structure that can be seen in the scanning electron micrograph shown here. While it is often used as a cost-reducing filler in replacing more expensive polymers, some special properties of talc improve the performance of the adhesive or sealant in which it is used. The plates add reinforcement and stiffness to polymers, help reduce cracking of thick films or masses, and provide good sandability. Talc is also inert, oleophilic (oil loving), and hydrophobic, which can add chemical and water resistance to products. It also adds non-thixotropic viscosity build and increases thermal conductivity.

Talcs in Adhesives and Sealants
The improvement that talcs provide in water and chemical resistance can be advantageous in DIY (do-it-yourself) and OTC (over-the-counter) caulks that are based on less durable polymers such as water-based acrylics, vinyl acetates, and solvent-based butyls. Because high-performance sealants using urethanes, silicones, and other long-service-life polymers generally have enough inherent durability, talc is not needed but certainly can be added if more water or chemical resistance is desired. Applications for talcs in adhesives and sealants include:

  • Auto body putties – talc-filled unsaturated polyesters used in auto body repairs. Talc improves the sandability of the cured putty and provides a smooth surface as well as reducing cracking. It also adds non-thixotropic viscosity. Two different talc sizes are generally used, a smaller one of about 1.5 microns for viscosity with a larger one of about 7 to 8 microns for sandability and filling.
  • Tape Joint Compounds – talc is used as the second extender in the compounds to fill gaps between gypsum wall boards, along with ground calcium carbonate (GCC). Talc provides easy application, cracking resistance during drying, and good sandability, resulting in a smooth finish; 7 or 8 micron talcs are used. Click here to read more about tape joint compounds.
  • Butyl Caulks – talcs ease the processing and improve moisture resistance while reducing cost.
  • Water-based Acrylic and Vinyl Acetate Caulks – talcs improve weatherability and durability by adding barrier properties and water and chemicals. Smaller particles add viscosity, while larger particles have lower oil absorptions, allowing higher loadings. Click here to read more about water-based caulks using Specialty Minerals resistance mineral fillers.
  • Epoxy Adhesives – for strengthening, viscosity build and as a cost-reducing filler. 

 
Specialty Minerals Talcs for Adhesives and Sealants
SMI has been mining and processing talcs since the early 1950’s at our Barretts, Montana, plant. We manufacture a full range of products, from ultrafine, 0.8 micron, to 8 microns. Smaller-particled products yield greater increases in thickening and reinforcement while larger-particled products can be included at higher filler loadings for greatest economy. Some applications require high brightness and/or controlled color consistency; in others, color is not critical, so general-purpose talcs are acceptable.

The choice of product type depends on the degree of whiteness and brightness required and the degree to which the top size (the size of the largest particles) needs to be controlled to provide a good finish for exposed surfaces.

  • Talcron® talcs – are the brightest and have careful top size control.
  • Sericron® talcs – are lower than in brightness but the lot-to-lot color consistency is controlled. Their top sizes are larger for grades of the same median particle-sized Talcron® talcs.
  • Microtalc® talcs – are general-purpose talcs with lower color and larger top sizes.
  • Body Filler talc – is a 7 to 10 micron talc with low oil absorption for highest filler loading of auto body putties.


All SMI GCC, dolomite, and talc plants are ISO 9001 certified and use careful process controls and strict quality procedures to ensure that customers receive products with the required performance.

 

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