The Preparation And Study Of Polyurethane Coatings With PTC Effect

On the basis of plenty of relative references about conductive composites of polymer matrix/carbon black. A new idea has been put forward for conductive composites, that is, by adding organic crystals into amorphous PU matrix (coating) without PTC effect to prepare coatings with PTC effect.In this paper, carbon black (N550) is chosen as conductive functional medium by taking fully into account the price, dispersion etc. At first, the solidify of PU was studied. The structure of organic crystal A , crystal B, crystal C and crystal D are indicated with XRD and the results show that crystal A and crystal D are monoclinic crystal. The structure of PU after sliding is indicated with IR and the results show that the chemical reaction reduced between crystal A(crystal D) and PU.The effect of carbon black on the resitivity of PU/CB composites was studied in this paper. The structure is indicated with SEM and the results show that the room temperature resitivity of composites descend 9 grades and the percolation is about 19%. SEM shows carbon black modified by coupling agent can disperse in PU matrix equably.The effect of organic crystal on the conductive property of PU/CB composites was studied in this paper weightily. The structure and thermal property of composites are indicated with SEM, XRD and DSC. The results show that PU/CB composites adding crystal B and crystal C display no PTC effect, but the room temperature resitivity of composites increase with the increasing of the content of organic crystal; the composites adding crystal A and crystal D displays obvious PTC effect and the PTC strength is 1~3 grades. The results of IR shows the chemical reaction reduces between crystal A(crystal D) and PU;XRD shows that amorphous PU becomes semi-cry stallion. The results show that only the crystals that can react with PU display PTC effect, the adding easyly crystal show no PTC effect. The result of DSC shows that the switch temperature of PU/CB/organic crystal composites is accord with the melting point of organic crystal and can be controlled by controlling the melting point of organic crystals.