China Clay

     CERAMIC :- Historically speaking china clay was first used in ceramics and this is still possibly the best known application today despite the fact that it has long been overtaken by paper.  In this United Nation, a number of products fall under the general heading of ceramics and are usually divided into the following categories such as structural clay products, including bricks, drain tiles, sewez pips, glazed tiles, terracotta, refractories, white ware pottery or stoneware and porcelain.  In the first category of structural clays, the type of clay used must have particular property under such headings as plasticity, green strength (which eases handling firing, shrinkage, vitrification range and fired colour).  In fact, china clay is just one type of clay used in the fabrication of these products and usually the china clay used is not particularly pure or high grade.

     Raw material for the manufacture of refractories are again many.  However, nearly all refractory clays are composed predominantly of kaolinite.  This includes clay such as flint clay etc., which are dealt separately elsewhere.  Relatively pure china clay having PCE in the range of Orton Cone 33 and above are used for this purpose.

     White ware is usually composed of feldspar, flint or quartz and suitable clay.  The most commonly used clays are china clay and/or ball clays.  China clay is better crystallized than ball clay and is consequently slightly more refractory.  Both these clay confirm to the required properties as outlined for structural clays.

     In stoneware making various clays are suitable.  It is not the products to fire white and so china clay are used due to non-availability of low fusing clays.  The basic ingredients in porcelain are clay, feldspar and quartz.  The clay must have adequate plasticity associated with finer particle sizes.  A lot of porcelain goes into electrical ware as insulators, wherein factors such as conductivity, dielectric constant, power factor, power loss and other parameters are important.   High purity china clay and ball clays excel in this field.  Specification (IS: 2840-1985) for ceramic industry is Click Here

     RUBBER :- China clay is used as filler or an extender in both natural and synthetic rubber.  Using 100 percent pure rubber in rubber products is expensive and reinforcing agents are incorporated in the mix to improve certain physical properties as well as to lower the cost.  Additive to china clay tend to improve the tensile strength of rubber and its resistance to tear and abrasion.  The principle manufacturers using large quantities of china clay (hard varieties) make such products as footware, cable etc., Softer grades of china clay do not have the reinforcing effect of the hard grades and are used to lower electricity and improve abrasion resistance.   Products such as floor tiles and certain soft rubber goods make use of soft china clay grades in their compounding.

     There are number of competing materials used as filters and extenders in rubber.  Barytes for example, being heavy is incorporated in rubber products.  Where high density is an important criteria.  Calcium carbonate is a leading competitor and is comparable in cost.  Precipitated silica and silicates are used extensively in the compounding of rubber and to import the highest reinforcing characteristics of all the filter discussed above.  However, high cost prohibits their adoption in large quantities.  Specification (IS: 505-1978) for industry is Click Here

     PAPER :- In paper, china clay is used as a filter and for coating. As a filter, it is used to fill the interstices of the paper fibers.  This gives improved opacity and colour and imparts a smoother surface to the finished paper, thus, improving its affinity for printing ink.  Also, china clay is less expensive than paper pulp and therefore, effectively lowers paper production costs.  It is inert to other ingredients a coating material china clay has all the above properties plus other advantages such as high gloss, brightness and low viscosity at high solids content.  The later is important, since at today’s fast paper production rates the coatings must be applied at high solid contents to impart the correct thickness and opacity to the paper all in a very short space of time.  China clay flows well under these critical conditions and steel manages to give the paper a smooth and even film.  Its platy structure elands itself particularly to the production of high gloss papers. Aluminum hydroxide or hydride has replaced china clay in those fields owing to its extra whiteness and gloss.  Magazines such as Life in the US can contain up to 20% by weight of china clay.  In an untreated form, china clay is not particularly bright but by using chemical beneficiation means such bleaching, grades of coating clays with brightness exceeding 90% are now common.  Air floated grades are not certainly used for coating paper, and all coating grades of china clay are water washed.  Some heat-treated china clay may be used for filling paper where abrasion resistance is required.

     China clay mix with comparatively little competition in the paper industry because of its low cost and good performance.  Precipitated calcium carbonate is the main competitor and is used by paper manufacturers in conjunction with china clay for coating purpose.  It tends to have higher brightness then china clay used alone and also responds better to ink application.  Specification (IS: 505-1978) for paper coating & textiles is Click Here

     PLASTICS :- As with rubber, china clay is used as a filler and reinforcing agent in the manufacture of certain plastics.  For example, manufactures of polyvinyl chloride make use of it for this purpose, as it serves to augment and enhance some of the physical properties that make PVC harder wearing in wire insulation made of PVC, heat treated china clay imparts a high electrical resistivity which allows the use of this type of insulation in applications that had formerly required more expensive polymers.  In glass reinforced polyesters china clay products have helped to eliminate production problems in the manufacture of automobile body parts.  In this application china clay products give good flow characteristics to the glass fiber reinforcing media resulting in a stronger and more uniform part.

     This is a big area of growth for china clay.  As far as other applications in plastics are concerned, china clay has found only limited markets mainly because of poor dispersibility in systems it is used to a reasonable extent in vinyl floor coverings but competes with talc in this field.  Although china clay is cheaper than talc in certain products use of talc is preferred as it promotes translucency in the finished products.  Whereas, use of china clay leads to capacity. Specification (IS: 505-1978) for filler in paper is Click Here

     PAINT :- In the paint industry, china clay is used because of its whiteness and its pacifying effect attainable at a relatively low cost.  As a filter or extender, it cuts down the amount of expensive pigment required to formulate paint.  To quality as a filter, the china clay must be easily dispersed in the mix have a good colour, possess anti setting powers and have good rheological properties as well as fine particle size.  It is mostly used in interior, flat, wall paint and in metal industrial primers.  Washed grades of china clay wet easily in water and are therefore, particularly suited to latex paints.  Because of its plate like structure, china clay helps the pains to move easily over surface and contributed to hiding power.  Its use in exterior paints is limited, since it ends not to have the durable qualities of talc and calcium carbonate, which are its major competitors.  Calcined or heat treated grades of china clay because of their resistance to abrasion and their dry hiding power, are being increasingly used by paint manufacturers.  They are also much suited to latex systems, which facilitate the formulation of paint products.

     China clay is used as an extender or suspending agent in the manufacture of white paint.  The ISI has not standardized any Specification for this use.  However, the properties like anti setting and tinting affect, colloidal nature, softness, freedom from grit, white color and fine size are some of the qualities which make china clay suitable for use in paint and distemper manufacture.

     INSECTICIDES :- China clay is used in the manufacture of disinfectant like DDT.  The ISI (IS: 505-1978) has standardized the Specifications for use of china clay in insecticide industry as Click Here

     COSMETIC & PHARMACEUTICALS :-  Superfine china clay is utilized for the manufacture of products like powder; adhesive, surgical plaster lotion and ointment for external use, porcelain for dental preparation.   China clay for medical purpose must be free from lead, arsenic and other metal, which the human body will not tolerate.  It should have no frothing. Particle size, frothing and sedimentation value are the three important factors, considered in the selection of china clay for pharmaceutical purpose.

     OTHER USES :- These are the main application of china clay.  In its filling capacity china clay has a number of other important applications which need to be mentioned.  Although in terms of tonnage the markets are relatively small, china clay is used widely as a filter in the fabrication of certain adhesives and in textile coating and backings.  In the adhesive groups, air floated china clay is used in limited quantities in cheap adhesive cements made of reclaimed rubber, where it lowers cost and improve workability.  It is also used in low cost adhesive for floor tiles based on asphalt.  Some adhesive are filled with water washed china clay, particularly those made out of starch, dextrin, etc. which are used for bonding paper.  In textile coating, water washed china clay serves essentially the same function as in paper coating and in carpet backing china clay is used in formulations made from natural rubber latex. Another market similar to paint is printing inks, but this is a relatively small outlet.

     Among slightly more general-purpose applications but not less importance are uses of china clays in fertilizers where it is used as a caking agent or as a conditioner and in insecticides as a carrier.