Kaolin, water-washed clay

Airfloat clay, the type most used in rubber compounds, is dry-ground hydrous kaolin that has been air-separated to reduce impurities and control particle-size distribution. However, some water-washed clay (slurried in water and centrifuged or hydrocycloned to remove impurities) is used, because it contains a lower level of impurities and gives compounds that are more colorable. The water-washed clay also causes less die wear during extrusion. 

Standard water-washed kaolins come in a variety of particle size distributions, ranging from 0.2 to 9.5 pm in median particle size. These wet-processed clays tend to have more uniform physical properties and are preferred for uniformity and specific properties such as increased loadings and improved molding characteristics. Water-washed clays can be used as rheological modifiers in conjunction with other extenders to optimize flow characteristics and reduce cost... 

Water-washed day - Water-washed kaolin has been slurried in water and centrifuged or hydrocycloned to remove impmities and produce specific particle size fractions. The refined slurry is either dewatered (to reduce soluble impurities) and dried, or concentrated to 70% solids and sold in slurry form. Water-washed clays are often treated to improve brightness. This includes chemical bleaching and/or high-intensity magnetic separation to remove iron and titanium impurities. 

Adhesives and sealants - Kaolin is used to control flow, penetration, and specific adhesion on application, and adhesive strength, tear strength, tensile strength, and elongation after cure. For aqueous systems the choice of airfloated vs. water-washed clay is dictated by cost, color, abrasion, and rheological properties pre-cure and reinforcing properties post-cure. Stearate-coated clays are used for improved compatibility in nonaqueous systems. 

Fig. 2. (a) Brightness improvement obtained by the use of kaolin as a filler in paper and (b), opacity improvement obtained as pulp fibers are replaced with various kaolins. In both cases, A represents fine-particle calcined clay B, high brightness No. 1 kaolin C, coarse-particle water-washed kaolin and D,... 

Chem. Descrip. Hyd. kaolin clay CAS 1332-58-7 EINECS/ELINCS 296-473-8 Uses Filler for adhesives, paints, plastics, inks Features Water-washed functional filler intermediate brightness and particle size, moderate oil and water demand pulverized for easy dispersion... 

Chem. Descrip. Hyd. kaolin clay CAS 1332-58-7 EINECS/ELINCS 296-473-8 Uses Filler for adhesives, paints, plastics, inks Features Water-washed functional filler intermediate brightness and particle size, moderate oil and water demand Properties Spray-dried beads 0.7 m particle diam. 0.01% max. on 325 mesh fineness (Hegman) 5+ sp.gr. 2.60 bulking value 21.7 Ib/gal surf, area 12-16 nf/g oil absorp. 40-45 brightness 86-87.5 pH 6-7 (100 g clay/250 ml water) moisture (1% max.)... 

Imerys leads the European market for polymer end use. The aforementioned four companies supply the majority of the world s water-washed kaolin and are major exporters of the mineral. Other key producers are Thiele with 1.25 mtpa and Quarzwerke owned by Amberger Kaolinwerke (AKW) with 0.9 mtpa. Other US producers of air-floated grades are KT Clay (owned by Imerys) with >500 000tpa and Unimin with >500 000 tpa. It should be noted that European kaolin comes mostly from primary deposits and does not lend itself to the air-flotation process [10]. 

Clays A sample of kaolinite (Fisher Colloidal Kaolin) was washed several times with hydrochloric acid at pH 2, and then with distilled water and dried. Another sample was stirred for 24-48 hours with 10 FeCl, also at pH 2, washed with distilled water and dried, to give a dry product with a pronounced yellowish tinge. 

Delaminated kaolins differ from the standard water-washed grades in that they are thin platelets of varying widths, and they are devoid of stacks and ultrafines. Delaminated clays can be supplied in a variety of particle sizes and shapes. At... 

The United States is the leading supplier of kaolin cl, with about 40% of world production. Second largest is the United Kingdom with about 12%. US annual production capacity of 10 million metric tons is comprised of 40% water-washed, 15% airfloated, 13% calcined, and 10% delaminated clay. The major worldwide use for kaolin is in paper. In the US 40% of kaolin consumption is for coating and filling paper. Much lower but still substantial... 

Paper fillers - High-brightness, low-abrasion airfloated, water-washed and delaminated kaolins are used as pulp extenders in acid-sized paper, where they improve opacity, smoothness and ink receptivity. Partially calcined clay is used as a Ti02 extender. 

Rubber - About 80% of the kaolin for rubber is airfloated hard clay. Water-washed and delaminated clays are used for further improved color, physical propeties, and abrasion resistance. Calcined and smface-treated clays are used for improved electrical properties and ease of extrusion. 

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