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PVC Plastisol Sealants with Specialty Minerals Precipitated Calcium Carbonates

PVC (polyvinyl chloride) plastisol sealants are among the highest volume sealants used in the manufacture of automobiles, trucks, and buses. An individual vehicle incorporates PVC plastisols in many places, but the uses generally fall into three categories: sealing the body against entry of wind, rain, dust and noise; improving the quality of the car and ride by deadening sound as well as reducing hood flutter; and protecting against corrosion with underbody coatings. For body sealing, plastisols fill joints and seams between body panels, on the floor pan, where the drip rail meets the roof, at center pillar seams, at welded joints, joints at door corners, and in the trunk. They are also used to seal joints in various subassemblies such as the wheelhouse.

The other significant use for PVC plastisol sealants outside automotive is airport runway and highway joint filling and crack sealing.

PVC plastisols are dispersions of a polyvinyl chloride polymer in a plasticizer. The PVC is generally a 95 percent PVC/5 percent vinyl acetate copolymer. The vinyl acetate is included as an internal plasticizer for the resin. Phthalates such as DIDP (diisodecyl phthalate) and DINP (diisononyl phthalate) are typically the plasticizers used. Antiflutter compounds are generally modified with styrene-butadiene rubbers (SBR) while those used on airfields and highways are modified with coal tar to make them jet fuel-resistant (JFR) grades.

Plastisols are single-component sealants that are heat cured to form a continuous solid mass or film. In automobile manufacturing, they are applied during body assembly and cured during the paint bake cycle. Application can be by extrusion, spray, brushing, or thumbing. Each of these methods requires a formulation with a different rheological profile—differing degrees of yield value, package viscosity, shear thinning, high shear viscosity, and slump and sag control.


PVC Plastisol Sealants with SMI Ultrafine and Nano Precipitated Calcium Carbonates
Coated ultrafine or nano precipitated calcium carbonates (PCCs) rank among the most commonly used rheological additives in automotive PVC plastisol sealants. PCCs build an internal structure in the plastisol that is shear thinning and thixotropic. PCCs add viscosity, yield value, control of slump and sag, and control of extrusion rate or spraying viscosity. Though most often used as the sole thixotrope in the plastisol, they can also be used to extend or partially replace other, more expensive thickeners. PCCs can reduce the costs of a formulation. Often, the total cost of a PCC plus ground calcium carbonate (GCC) filler package is less than the total cost of the conventional rheological additive plus GCC filler package. The package cost should be considered because PCCs are used at higher levels—20 to 50 percent, replacing part of the normal filler—and act as both thixotrope and functional filler. Changing the ratio of PCC to GCC permits the adjustment of the high shear viscosity of the sealant and changes the extrusion time or rate. More PCC increases the extrusion time; less PCC decreases it.

PCCs also reinforce the cured sealant and, in plastisols, help neutralize any hydrochloric acid (HCl) that may be liberated from degraded PVC, which might otherwise cause corrosion.

Specialty Minerals Inc. (SMI) produces a range of coated ultrafine and nano PCCs for PVC plastisol sealants. With sizes of 60 or 70 nanometers (0.06 or 0.07 micron), SMI nano PCCs are true nano particles—by definition, 0.1 micron or less. They are coated—some with stearic acid, some with proprietary coatings.

The SMI PCC products recommended for use in PVC plastisols are:

  • Calofort® SV PCC – highest efficiency, under normal plant mixing conditions. This PCC provides high viscosity at low shear rates while maintaining extrusion rate. It is a stearic acid coated 0.07 micron nano PCC manufactured in SMI’s plant in Birmingham, U.K.
  • Ultra-Pflex® PCC – high efficiency, outstanding uniformity. This PCC is a 0.07 micron stearic acid coated nano PCC manufactured in SMI’s plant in Adams, Massachusetts.
  • Calofort® SM PCC – this PCC is for products that should have lower viscosity and faster extrusion rate while maintaining slump and sag control, or where high loadings of PCC are desired. It is a 0.07 micron coated PCC manufactured in Birmingham.
  • Thixo-Carb® HP PCC – in plants that have very high shear dispersion equipment such as three roll mills, this PCC will produce the highest viscosity and enable the reduction or elimination of fumed silica. This PCC is a 0.06 micron stearic acid coated nano PCC manufactured in Adams.

Click on a product’s name to download the technical data sheet for that product.

A range of SMI PCCs manufactured in the U.S. were tested in SMI’s Sealant Laboratory in a model automotive PVC plastisol formulation. Click here to read about this formulation and the results.

Click here for more information on PCC function in sealants and on the range of SMI PCCs offered for sealants. Information on how particle size, hydrophobicity, and surface moisture affect the choice of a PCC grade for a given application can be viewed by clicking here. A PCC application/polymer selector chart can be viewed by clicking here.


Other SMI Minerals in PVC Plastisol Sealants
PVC plastisol sealants contain a high level of filler to reduce cost and to add mildly thixotropic viscosity. A small to medium-size GCC is typical with finer grades building more viscosity and coarser grades allowing higher loadings. SMI manufactures several families of high-brightness GCCs (ground calcium carbonates) and ground dolomites (calcium magnesium carbonates) in the U.S. for use in plastisols. These include the Vicron® and Marblewhite® GCCs made in Adams, Massachusetts, and Lucerne Valley, California, the Rivercal™ GCCs, and the Dolocron® ground dolomites made in Canaan, Connecticut. Click here to read more about these fillers.

Because barites are known to absorb sound, we recommend SMI’s Baricron™ white barites for sound-deadening sealants and coatings. These products are a family of products – 1.5 to 8 microns in size. Click here to read more about them.

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