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Background :
Various grades of kaolin are produced to enable end-users to produce a specific level of performance in their products. Typically the major features a papermaker is seeking in order to keep his clients coming back and a pigment supplier can influence is:
To obtain these often-contradictory properties it is necessary to blend kaolins with other pigments like calcium carbonate, talc, titanium dioxide, satin white, etc.
Therefore performance in the sheet is the important criteria for kaolin although it can be difficult to introduce a product, which may have unusual pigment properties particularly if those properties are regarded as impacting on processing efficiencies. The growth in alkaline sizing and use of GCC & PCC including in-house and satellite plants may affect kaolin volumes in the years ahead.
Various grades of kaolin are produced to enable end-users to produce a specific level of performance in their products. Typically the major features a papermaker is seeking in order to keep his clients coming back and a pigment supplier can influence is:
- Sheet of paper looks good (colour, brightness, smoothness, opacity)
- Sheet of paper prints well (ink absorption and ink pigment holdout, low linting tendency, roughness)
To obtain these often-contradictory properties it is necessary to blend kaolins with other pigments like calcium carbonate, talc, titanium dioxide, satin white, etc.
Therefore performance in the sheet is the important criteria for kaolin although it can be difficult to introduce a product, which may have unusual pigment properties particularly if those properties are regarded as impacting on processing efficiencies. The growth in alkaline sizing and use of GCC & PCC including in-house and satellite plants may affect kaolin volumes in the years ahead.
Kaolin Types
Kaolin is produced from ore-bodies with inherent and largely unalterable properties. The process plant seeks to manufacture grades of kaolin, which consumer expectations (table 1). Generally an ore-body will limit the range of products that can be economically produced. As a consequence, European consumers have a history of using coarse English clays whilst Asian consumers and US have been helped by a wide range of high brightness Georgian kaolin that can range from ultrafine particle size to coarser delaminated kaolins. The Asian market uses a simple classification system based on brightness and, to a lesser extent, particle size. The system was based originally on conventional water-washed grades of kaolin.Calcined kaolins and delaminated kaolins are viewed as specialty kaolins and filler kaolins are a separate segment altogether.
Kaolin is produced from ore-bodies with inherent and largely unalterable properties. The process plant seeks to manufacture grades of kaolin, which consumer expectations (table 1). Generally an ore-body will limit the range of products that can be economically produced. As a consequence, European consumers have a history of using coarse English clays whilst Asian consumers and US have been helped by a wide range of high brightness Georgian kaolin that can range from ultrafine particle size to coarser delaminated kaolins. The Asian market uses a simple classification system based on brightness and, to a lesser extent, particle size. The system was based originally on conventional water-washed grades of kaolin.Calcined kaolins and delaminated kaolins are viewed as specialty kaolins and filler kaolins are a separate segment altogether.
Typical paper kaolin grades.
Filler grades
Key Characteristics : Brightness & Particle size distribution
This is a low cost grade competing with carbonate and talc. The market is dominated by variable quality product from Indonesia. A high brightness, low cost kaolin with good brightness could appeal to Japanese papermills.
Filler grades
Key Characteristics : Brightness & Particle size distribution
This is a low cost grade competing with carbonate and talc. The market is dominated by variable quality product from Indonesia. A high brightness, low cost kaolin with good brightness could appeal to Japanese papermills.
Delaminated
Key Characteristics : Brightness ,Aspect ratio, surface area and to a lesser extent particle size distribution
Delaminated kaolins not widely used in Asia currently, however, good growth prospects as this product is used in the fastest growing segment, lightly coated paper. Trend is to use No 2 grade kaolin. Brazilian producers have developed high brightness, low viscosity products in this sector and are making inroads.
Key Characteristics : Brightness ,Aspect ratio, surface area and to a lesser extent particle size distribution
Delaminated kaolins not widely used in Asia currently, however, good growth prospects as this product is used in the fastest growing segment, lightly coated paper. Trend is to use No 2 grade kaolin. Brazilian producers have developed high brightness, low viscosity products in this sector and are making inroads.
Calcined
Key Characteristics: Brightness,Opacifying power
Highest value clay due to high energy (calciner) required in production, low bulk and consequently high shipping costs. The market for calcined continues to grow as whiteness standards are driven ever higher by competitive pressures including use in newsprint grades.
Key Characteristics: Brightness,Opacifying power
Highest value clay due to high energy (calciner) required in production, low bulk and consequently high shipping costs. The market for calcined continues to grow as whiteness standards are driven ever higher by competitive pressures including use in newsprint grades.
No 1 Coating
Key Characteristics :Brightness ,Particle size distribution,Viscosity
High brightness is the key feature and is typically >90 %GE with recent developments raising limits to 91% GE. Particle size distribution can be quite fine (98%<2µm) to coarse (85%<2µm) although the mid range and fine grades are dominant.
Key Characteristics :Brightness ,Particle size distribution,Viscosity
High brightness is the key feature and is typically >90 %GE with recent developments raising limits to 91% GE. Particle size distribution can be quite fine (98%<2µm) to coarse (85%<2µm) although the mid range and fine grades are dominant.
No 2 Coating
Key Characteristics: Medium brightness,Particle size distribution,Viscosity
The brightness range is 2-3 points below No 1 grades. The dominant grades are at the coarse end and the fine end. Some overlap with delaminated grades has occurred with the coarser grades.
Key Characteristics: Medium brightness,Particle size distribution,Viscosity
The brightness range is 2-3 points below No 1 grades. The dominant grades are at the coarse end and the fine end. Some overlap with delaminated grades has occurred with the coarser grades.
Kaolin - Processing and Manufacturing
The processing of kaolin varies greatly from company to company; each kaolin producer uses different equipment and methods and companies that use identical methods may use them at different points during processing. An example of the extensive processing of kaolin is found in those products intended for the paper industry. The greatest demand for kaolin-based pigments comes from the paper industry, which uses them to coat and fill papers and boards. There are many ways to produce these pigments. One of the methods used is the water washed process. Generally, in the processing of water washed clays, water is used as a transport and process medium involving the following steps: Blunging, de-gritting, centrifuging, brightness enhancement, filtering and drying, additional processing such as calcining, packing mainly in bulker bags or 25 kg bags and shipping. In addition some kaolin may be surface coated with silane chemical to assist in the bonding between kaolin and rubber compounds or polymers. This is an example of added value product where the value can be about twice that of an uncoated grade. Some consumers of kaolin prefer to add the silane during in-house processing. Kaolins, which have been highly processed, are called functional fillers/pigments to indicate the intrinsic value they now command. With the Environment in mind industrial white minerals are becoming increasingly popular as natural, safer and often less expensive alternatives to chemicals.
The processing of kaolin varies greatly from company to company; each kaolin producer uses different equipment and methods and companies that use identical methods may use them at different points during processing. An example of the extensive processing of kaolin is found in those products intended for the paper industry. The greatest demand for kaolin-based pigments comes from the paper industry, which uses them to coat and fill papers and boards. There are many ways to produce these pigments. One of the methods used is the water washed process. Generally, in the processing of water washed clays, water is used as a transport and process medium involving the following steps: Blunging, de-gritting, centrifuging, brightness enhancement, filtering and drying, additional processing such as calcining, packing mainly in bulker bags or 25 kg bags and shipping. In addition some kaolin may be surface coated with silane chemical to assist in the bonding between kaolin and rubber compounds or polymers. This is an example of added value product where the value can be about twice that of an uncoated grade. Some consumers of kaolin prefer to add the silane during in-house processing. Kaolins, which have been highly processed, are called functional fillers/pigments to indicate the intrinsic value they now command. With the Environment in mind industrial white minerals are becoming increasingly popular as natural, safer and often less expensive alternatives to chemicals.
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