Calcium carbonate coating

For electrical insulation china clay is commonly employed whilst various calcium carbonates (whiting, ground limestone, precipitated calcium carbonate, and coated calcium carbonate) are used for general purpose work. Also occasionally employed are talc, light magnesium carbonate, barytes (barium sulphate) and the silicas and silicates. For flooring applications asbestos has been an important filler. The effect of fillers on some properties of plasticised PVC are shown in Figure 12.21 (a-d). 

The adsorption of gas onto a solid surface can also be used to estimate surface energy. Both inverse gas chromatography (IGC) and isotherm measurement using the BET method [19] have been used. Further discussion and detailed references are given by Lucic et al. [20] who compare the application of IGC, BET and contact angle methods for characterising the surface energies of stearate-coated calcium carbonate fillers. 

Nevertheless, with regard to filler treatment and limestone impregnation, it is still considered difficult to coat calcium carbonate with silicone. As shown in Table 1, the commercial monomeric silanes that are used for coating the surfaces of fillers nowadays are not effective for coating calcite [19, 20, 21]. The idea that the production of a silicone-coated surface is difficult may result from the misconception that attachment of high silicone polymers to calcium carbonate is equally problematic. The issue of attachment of silicone to the mineral surfaces has still not been finally resolved [62]. 

WfamofiL pClResins] Precipitated stearate-coat calcium carbonate filler, impact modifier, processing aid for theinKq>lastics and pauns. 

WinnofiL [ICI Resins] Precipitated stearate-coated calcium carbonate filler, inquict modifier, processing aid for tham(q>lastics and patnis. 

More recently, Kotek at al. studied the effects of untreated (denoted as Cl) and stearate-treated calcium carbonate particles (denoted as C2) of 1.3 p.m on the tensile properties of P-PP. Moreover, stearate-coated calcium carbonate particles of 0.075 p,m (denoted as C3) are also used (44). The p-nucleating agent employed is based on an amide of dicarboxylic acid. The critical concentration of p-nucleator needed to achieve 61% P-PP is 0.03 wt% on the basis of the XRD analysis. With further increase in the p-nucleator content to 0.1 wt% (supercritical), the p-PP content increases, but very slightly, to 65%. Furthermore, the K value also depends... 

Stearic acid coated calcium carbonate (Multiflex SC) 17.5... 

Chert). Descrip. Stearate-coated calcium carbonate Uses Filler for water-based coatings and inks, paper, paper coatings, thermosets (glass-reinforced polyester), thermoplastics (PP, ABS), PVC pipe, siding, profiles, extrusion, film, sheeting, color cones., paint (gloss, semigloss, flat latex)... 

Chem. Descrip. Hollow composite microspheres (shell acrylonitrile copolymer coating calcium carbonate)... 

Chem. Descrip. Coated calcium carbonate CAS 471-34-1 EINECS/ELINCS 207-439-9 Uses Filler in plastics (PVCplastisols, automotive underseals, polyolefin moldings and film), paints (matte paints, primers, anticorrosion paints) Features Very low absorp. inc. load ability in masterbatches Properties Wh. microctyst. rhombohedral powd. fineness 24% < 2 p dens. 2.7 g/cm bulk dens. 1.4 g/cm (packed) oil absorp. 13/100 g powd. brightness 96% ref. index 1.59 pH 9 hardness (Mohs) 3 Micro-Cel T-38 [Celite]... 

Diatomaceous earth Magnesium oxide Pyrophyllite Quartz Silica, hydrated Sodium silicate Sodium silicoaluminate Terpene resin Wollastonite Xanthan gum extender, paints/coatings Calcium carbonate Kaolin extender, paper Calcium sulfate dihydrate extender, paper coatings Wollastonite extender, paper sizing Kaolin Xanthan gum extender, paperboard Wood flour... 

Figure 2.5 Shear viscosity of uncoated and stearate-coated calcium carbonate-filled polystyrene melt versus shear rate. (Reproduced with permission from Ref [10], Chapters.)...

McAmish, L. and Skelhom, D.Spunlaid fibers comprising coated calcium carbonate, processes for their production. 

The choice of antiblocking additive depends on the polymer, the desired film quality, and whether there is a pigment. Several inorganic substances are used, including synthetic amorphous precipitated silica, diatomaceous earths, nepheline syenite, calcined clay, coated calcium carbonate, magnesium carbonate, magnesium sulphate, mica, talc and various zeolites. Calcium carbonate particles are approximately spherical, but silica ones are irregular mica forms sheets and talc is plate-like. 

Imerys has introduced a range of Polcarb stearate-coated calcium carbonates for high gloss and good mechanical properties in such applications as window profiles, pipes and cable insulation. 

Some studies with filled and unfilled rigid PVC were made in our laboratory to describe the effect of chalk as additional stabilizer. A suspension PVC (K-value 70) with an organotin stabilizer (2 phr) and lubricants (1.8 phr) was used as the experimental material. A part of this compound was filled with a stearic acid coated calcium carbonate (10 phr) as an additional component. The PVC powder and the additives were mixed at a high speed in an intensive mixer. The received dry blends were pelletized by extrusion to get a better dispersion of the additives in the polymer material. Finally, the granulates were processed by injection molding to test specimens for measurements of mechanical properties. 

Papirer and co-workers have also used IGC to study stearic acid coated calcium carbonates [17]. In their work, a high surface area precipitated filler was used, and coating was from toluene solution. They also prepared fractional coating levels based on solution adsorption isotherms. Stearic acid treatment was again found to decrease both the dispersive and polar contributions of surface energy to values typical of a hydrocarbon. Both acidic and basic probes were used in this work and interestingly, the uncoated filler was found to contain sites capable of interaction with both. 

Manufacturers literature offers recommendations on estimating optimum coating levels, and in practice it is usually best to test several coating levels so that the required properties can be optimized. Even the concept of optimum properties is not straightforward, as illustrated in Figure 4 for a compound containing stearic acid coated calcium carbonate in polyethylene. While yield strength is at a maximum... 

Figure 4 Mechanical properties of compounds containing stearic acid coated calcium carbonate in polyethylene (a) tensile yield stress (b) impact energy using instrumented falling weight impact tester.

Blends of 40 wt% stearate coated calcium carbonate filler with polypropylene (PP) pellets were prepared in a 24 litre high speed mixer run at half speed of 1200 rpm under vacuum to prevent fluidisation and also remove any moisture present. Butyl stearate (0.1 wt%) was included to minimise filler separation during extruder feeding. Mixer discharge temperature was 110 °C. Figure 13.1 shows PP granules coated with filler. 

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