Adding a thermal curing agent can lead to increased heat resistance and glass transition temperature. As shown in FIGS. 3, A1 and A2 represent the curves before and after adding the thermal curing agent, respectively; and the curves D1 and D2 represent the values after differential computation on curves A1 and A2, respectively, representing the extent of the change of curves A1 and A2. As can be seen from the analysis results from TMA (thermomechanical analysis) shown in FIG. 3, the addition of the thermal curing agent leads to a trend that the thermal deformation slows down. Accordingly, adding a thermal curing agent can lead to increase of the heat resistance.