Three Major Problems Of PVC Coloring
The thermal stability and light resistance of PVC are poor. The decomposition of hydrogen chloride at 140 degrees centigrade, so the choice of coloring agent can not have a adverse reaction. In addition, the influence of pigment on PVC is reflected in whether pigment is reacted with PVC and other components of PVC products, and pigment itself is resistant to migration and heat resistance. Therefore, as far as PVC coloring is concerned, the characteristics of the resin and related auxiliaries are considered, and the characteristics of the pigments are combined. The following problems should be paid attention to when choosing a colorant.
Some of the ingredients in the coloring agent may cause the degradation of the resin. For example, iron ions and zinc ions are the catalysts for the degradation of PVC resin. Therefore, the use of iron oxide (red, yellow, brown and black) pigment or Zinc Oxide, zinc sulfide and white pigment lithopone will reduce the thermal stability of PVC resin. Some of the coloring agents may be associated with the degradation products of PVC resin. Such as ultramarine pigment acid resistance is poor, so in the PVC coloring process, with the PVC decomposition of hydrogen chloride produced by the interaction of losing their color.
Mobility occurs only in plasticized PVC products, and in the use of dyes or organic pigments. The transfer is part of the existing in the surrounding solvent soluble dye or pigment, the plasticizer penetrated into the surface of PVC products, the dissolved dye (pigment) particles were also brought to the products on the surface, thus lead to contact bleeding, bleeding or a solvent. Another problem is "Scaling". When colorants are dyed, they are freed from the system due to their poor compatibility or incompatibility. They are deposited on the surface of the processing equipment, such as the inner wall of the extruder and the inner wall of the die hole.
Refers to the ability of pigments to withstand a variety of climate. These include visible and ultraviolet light, moisture, temperature, atmospheric chlorination, and chemicals encountered during the use of products. The most important weatherability, including the persistence of color fading, powdering resistance and physical properties. Organic pigments are poor because of their different structures. In addition, the weatherability of the pigment is seriously affected in the formula containing white pigment.
The color fading, darkening, or color change of the pigment, usually caused by the reaction gene of the pigment. These reactive genes can interact with water or chemical agents in the atmosphere, acids and bases. For example, cadmium yellow will fade under the action of water and sunlight. Rissol red has good light resistance, suitable for most indoor applications, and it will fade badly when it is used outdoor with acid and alkali components. The determination method of dehydrochlorination was 180 degrees centigrade by JIS-K-6723. The time of dechloroethylene with uncoloured PVC compound is based on the time of dechloroethylene. The prolongation or retarding time is 5%, 10% interval meter, and the negative value means accelerated decomposition.