A Novel Halogen-Free Flame Retarded Copper Clad Laminate Preparation And The Research Of The Flame Retardance Mechanism

A novel halogen-free flame retarded copper clad laminate is synthesized possessing both good physical properties and good flame retardancy. We also researched the flame retardance of the resinous composition which was the reaction product of benzoxazine and phosphorus-containing epoxy resin for copper clad laminate.The structural characteristics of the reaction product of benzoxazine and phosphorus-containing epoxy is analyzed by FTIR, 'H-NMR. The properties of the resin are also researched with methods of DSC, TGA and the small angle laser scanning.The result shows that benzoxazine have a good compatibility with phosphorus-containing epoxy in the whole curing process, which is an ex-thermal reaction. The resinous compound has a good heat-resistance, and thermal-degradation begins at temperature higher than 300℃.Glass cloth was impregnated with the resinous composition to obtain pregregs, and which are laminated with copper foils to make the copper clad laminates. Good performance of the halogen-free flame retarded copper clad laminate was revealed as follows. The glass transition temperature is 160℃, and flame retardancy reached US standard of UL94V-0. After cooking in water vapor of 2atm for 2 hours, the heat resistance of copper clad laminate is 385 seconds at 288℃. The flexural strength is 630.8MPa.The effects of additive flame retardant on the comprehensive properties are also researched. The results showed that flame retardancy improved with the addition of flame retardant, but the glass transition temperature is decreased at the same time. When the flame retardant reached some amount in this system, it will lead todecreasing of peel strength.Further more, the flame retardancy of the resin is also researched by the model resins. It revealed that the flame retardance of the resin acted both in the vapor phase and in the condensed phase. The phosphorus-nitrogen synergistic effect is presented in this system on the basis of results obtained on vertical burning tests. Especially there are 2.75wt% of phosphorus and 3.95wt% of nitrogen in the resin chains.The relationship of flame retardancy and thermal stability including char yield of the resin are also studied by TGA. It is proved that heat-resistance and char yield is not the primary considerable factor, although it indeed had some effects on flame retardancy of the resin.The structures of thermal degradation products are characterized by FTIR. The results showed that the charred layer of cured resinous composition was formed at 600℃, in which contained different aromatic species. P-O-P group linked with carbon by P-O-C bond and formed a complex phosphorus-carbon structure.Morphologic structures of the charred crusts of the resin are observed by scanning electron microscopy. The SEM photographs shows that the reason of the high char yield of the model resin D lies in the high aromatic contents in its structure. The higher strength also appears in the interior char layer of the model D.The flame retardancy of aluminum hydroxide(ATH) is also researched by TGA, DSC, SEM and XPS. In the process of heating, before thermal degradation of the resin, aluminum hydroxide loss its crystal water and that was an endothermic reaction. So the flame of the system is retarded or proponed. SEM photographs showed that, after burning of the resinous composition with ATH, the interior pole in the charred layer is just vessel-like, and there are great amounts of tiny articles in the surface of the interior charred layer. That is why the big specific surface area appears in the charred layer, which will also absorb smoke and flammability objects.