Kaolin, Performance Attributes of Flash vs. Commodity Calcination

Methodsin Coatings Systems

What is calcined Kaolin?

Commercial grades of Kaolin are generally either available as one of four forms: Air floated Water Washed Calcined Surface Modified

Calcination: in the simplest sense, water washed grades, chosen to achieve a desired finished product requirement, are ground, heat treated at temperatures near or above 650C, and ground again to reduce fused particles formed during the calcination. Calcining methods can be either flash with pneumatically conveyed feed material experiencing a residence time measured in seconds, but at elevated temperatures, or by soak methods which take as much as twenty or thirty minutes to complete. Soak calciners can be of either vertical or rotary design, as opposed to flash calcinations' pneumatic conveyance, are consistent in terms of being gravity fed.

Calcination ProcessConventional Calcination

Flash Calcination

Calcined Kaolin Process

Feed stock for calcination comes from water washing process.

Conventional calciners are large multi-hearth furnaces or kilns, fired typically between 1400F (760C) and 2000F (1100C).

Kaolin is introduced into the furnace and the crystalline bound water of hydration (14% by weight) is driven off. Impurities not able to be removed in the water washing process are oxidized.

A vertical calciner.

Clay is gravity fed.

Residence time 20-30 minutes.

Calcined Kaolin Process

The calcination procedure is tightly monitored through advanced technology and process controls, optimizing consistency.

After calcination, Kaolin is cooled, and milled to reduce aggregates formed during the calcination process.

Characteristics such as oil demand, brightness, and opacity are dramatically increased through calcination.

Calciner discharge, >650 C

Conventionally calcined Kaolin clay (ICEBERG)

Flash Calcination Process Flash calcination is a process that introduces

water washed Kaolin to a hot gas stream for a few seconds.

Crystalline bound water of hydration is removed rapidly, expanding the kaolin platelet and creating an amorphous particle containing nanometer sized internal air voids.

The result of flash calcination is a unique particle structure and different physical form from conventional calcined Kaolins.

Opacity is derived from the internal voids which cannot be wet out in a resin system.

Hiding power and tint strength is dramatically improved over conventional calcined Kaolins.

Flash calcination (OPTIWHITE)

Conventional versus Flash Calcined

Brightness 86-95 Oil absorption 50-100+ Good abrasion and scrub

resistance in paints Good dry hiding above CPVC Moderate wet hiding Much improved electrical

properties vs. hydrous feedstock

Very low solubility/reactivity Very inert (essential in

pharmaceutical rubber) Low LOI (loss on ignition)

Brightness range 83-91 Oil absorption 55-80 Very good abrasion and scrub

resistance Very good dry and wet hiding

power (opacity) Improved flattening and touch

up properties Particle size distribution to

achieve excellent tint strength Very reactive in cement mixes Excellent electrical attributes in

PVC (Polyvinyl Chloride compounds)

Excellent TiO2 Extender

Conventional Flash

Wet and Dry Opacity Demonstration

Conventional versus Flash Calcined Two paints were made up with no TiO2 or

other extenders.

One paint contained only conventionally calcined clay, the other flash calcined clay.

The drawdowns display the contribution to opacity when comparing only the calcined clays.

Iceberg Optiwhite Lot 901-069 Lot 601-1311 E B

Lbs/100 GAL (Grams/Liter) (%) Lbs/100 GAL (Gram/Liter) (%)

Water 522.0 625.0 57.0% 515.0 616.6 56.62% Nuosept 95 0.5 0.6 0.05% 0.5 0.6 0.05% 250 HBR 8.0 9.6 0.87% 8.0 9.6 0.88% AMP-95 3.0 3.6 0.33% 3.0 3.6 0.33% Tamol 731 8.0 9.6 0.87% 8.0 9.6 0.88% KTPP 2.0 2.4 0.22% 2.0 2.4 0.22% CO-630 2.0 2.4 0.22% 2.0 2.4 0.22% Ethylene Glycol 15.0 18.0 1.64% 15.0 18.0 1.65% Texanol 12.0 14.4 1.31% 12.0 14.4 1.32% Colloid 643 4.0 4.8 0.44% 4.0 4.8 0.44% Flash Calcined ----- ----- ----- 100.0 119.7 11.0% Conventional calcined 100.0 119.7 10.91% ----- ----- ----- UCAR 379 240.0 287.4 26.19% 240.0 287.4 26.39%

EVALUATION RESULTS Hiding, 3 Mil Bird Blade on 2C Opacity Chart Reflectance 0.863 0.857 Contrast Ratio 0.105 0.208 Angular Sheen 85 Degree 3.2 1.7 60 Degree 3.1 3.1 Tint Strength Reflectance 0.559 0.559 Application Properties: Brushout/Touchup on Sealed/Unsealed Wallboard Viscosity 98 95 Lab Color L 94.95 94.46 a -0.98 -0.95 b 5.39 5.23

The contrast ratio showed a significant improvement with the flash calcined Kaolin.

Conventional versus Flash Calcined

An extenders contribution to wet opacity can be measured by wetting it out in mineral oil.

After being allowed to dry, drops of mineral oil were placed on the film. The oil was then spread across.

The flash calcined clay exhibited much better wet hiding than the conventional calcined clay.