PVC Professional Knowledge - Titanium Dioxide
time2018/08/29
The high content of titanium dioxide will cause the increase of powder, but the damage to plastic products is reduced. The high content of titanium dioxide will cause the increase of powder speed and the decrease of impact strength. Generally, the best content of titanium dioxide in special-shaped materials is 5~12PHR.
Of up to 80 ℃ in the mixer, then adding titanium dioxide mixer, then the color brightness loss or damage due to friction is avoided or reduced greatly. The prerequisite, of course, is that the pigment can be completely wet and easily dispersed.
Color masterbatch coloring, it is best choice L/D is greater than 15 or efficient mixing effect of plastic machinery, and the best use of 100 ~ 120 - mesh, charging temperature around 10 ℃ can be improved, so that the color masterbatch melts in advance, promote its dispersion in the resin.
In the process of PVC processing, when the mixing shear force reaches its maximum, the abrasion effect of titanium dioxide is most serious on the contact surface between the mixer and the mixed material before it is wrapped by the polymer. In molding, the attrition of titanium pigment in plastics is negligible compared with the allowable amount, because there is no more direct contact between titanium dioxide and the inner wall of the machine.
Titanium dioxide, like other powder materials, also absorbs moisture from the surrounding environment. Moisture absorption depends on the relative humidity of the atmosphere around the pigment. The excessive moisture content of the pigment makes it easy to agglomerate the pigment and reduces its wettability.
When using titanium white without effective surface treatment, under the action of sunlight and water, PVC profile is easy to produce gray change phenomenon, seriously affecting the product appearance and color. Therefore, under the condition of lead stabilizer, the weathering resistance of titanium dioxide with good surface coating must be selected. (titanium pigment surface adsorption of water and oxygen, reaction produces primary free radicals, such as hydroxyl radicals OH HOO ˙ and peroxide hydroxyl radicals ˙. Free radicals from the pigment surface transfer to the substrate, hydroxyl radicals OH ˙ can react with organic molecules to generate the intermediate degradation products, and superoxide free radical HOO ˙ can restore lead salt to low state.)
Therefore, the general titanium dioxide applied in plastics needs surface treatment. Different varieties of inorganic oxides coated on the surface of titanium dioxide have different effects on the properties of titanium dioxide. Aluminum trioxide mainly improves the chemical stability of titanium dioxide, while silicon dioxide and zinc oxide mainly improve the weatherability of titanium dioxide.
After inorganic surface treatment, the pigment will contain chemical bonding water, but it can only be released when it is higher than the boiling point. This water generally does not have an impact on PVC processing, because it usually does not reach its boiling point at the PVC processing temperature.
In addition to the inorganic oxide coating on the surface of titanium dioxide particles, the treatment with organics can make the titanium dioxide powder easy to disperse in the pvc-u system, and at the same time reduce the moisture absorption of titanium dioxide particles.
The denser the surface inorganic coating, the lower the solubility of titanium dioxide in sulfuric acid, and the better the weatherability of titanium dioxide. Therefore, the acid solubility can be used as the basis to characterize the weatherability of titanium dioxide.