As a major application areas,hereunder are the main performance requirements of calcined kaolin for coatings.
Firstly, as the primary indicator of calcined kaolin , whiteness stability is very important, if too large fluctuations affect the optical properties of the coating , resulting in different batches of the same product formulations chromatic aberration. We usually refers whiteness i.e. blue light ( wavelength of 457nm) reflectance of the material surface.
As the other indicators of calcined kaolin has a direct relationship with the particle , if the particle size is not detailed enough , or failure, will be reflected by other indicators . Method for the determination of particle size calcined kaolin clay , typically a centrifugal sedimentation method , gravity sedimentation method, a laser analysis method.
A hiding power is when the object is coated with a coating , the pigment in the coating can cover the surface to be coated of the background , so that the coloring ability of the coating and then exposed through not . Hiding method for determining calcined kaolin is used in black and white paper , half of the paper is white , the other half is pure blackboard . The calcined kaolin at a fixed formulation , a formulation similar to the production of coatings formulated coating , coating with a uniform thickness on the black and white paper to measure the whiteness degree of the white section of the board and the board in the section of the drying oven , the ratio between the two is calcined kaolin hiding .
Although the calcined kaolin through ultrafine grinding,but in the paint,in the high viscosity of the mother liquor inside ,between the particles are not separate but mutually group together. Calcined kaolin can be dispersed in the coating system of this capacity to the called dispersion.Dispersibility usually test by hagemeyer granularity level table,tablet and strip scraper.
325 mesh residue on sirve refers to the percentage of the total weight requirements , these indicators paint a certain quality of an object weight after washing left on the screen is as small as possible .
Oil absorption value is the lowest quality 100g calcined kaolin in the oil needs to be completely wetted , usually the unit is g / 100g. Coatings require calcined kaolin suction is 50g / 100g ~ 60g / 100g of moderate oil absorption is too high, the viscosity of the coating formulation is made with the same large , in order to reduce the viscosity of the base must increase the amount of paint , increasing the cost ; suction value is too low , the coating is made of easy settlement,bad open cans performance.
Calcined kaolin sedimentation volume reflects the settling performance in coatings , directly affects the performance of the paint cans . This indicator should be as high as possible , the more difficult the higher the sedimentation of the pigment , will remain in good coating uniformity .
pH value reflects the pH of calcined kaolin . Coatings require the pH value should be between 6 and 8 , is substantially close to neutral .
Pigments made from paint and after painting , paint by sun and rain , will yellowing , loss of light powder. Pigments can resist these changes occur capability called weathering . Calcined kaolin, chemically active light is not strong , so there is good weather resistance.
Other indicators of calcined kaolin for coatings are acid , alkaline, mixing performance , wet performance , density, etc.Calcined kaolin at room temperature does not react with any acid , it will not react chemically with any other substances. Therefore, the calcined kaolin having good acid and alkali resistance, good mixing properties with other substances . Calcined kaolin has the advantage of low density ( 2.62 ) , making the paint factory purchase of raw materials denominated in weight , but by volume pricing to sell , not only economically advantageous terms, with a high pigment volume concentration (PVC) is still under the same formula , Therefore widely welcomed by the coating factory.