The Necessary Process of Drying the Impregnated Wet Paper
The first is the evaporation process of low molecular weight volatiles (including solvents) in solvents and resins; two, the resin molecules continue to undergo a certain degree of condensation. The former is a process of physical change while the latter is a process of chemical change. After the completion of the drying process,
only a few volatile components in the adhesive paper (cloth) and a certain degree of soluble resin flow with the laminating process should be achieved.
The process of drying is the process of heat transfer of the heat carrier and the transformation of the mass transfer of the humid body. It is also the process of transforming the adhesive paper (cloth) resin structure from the A stage to the B stage. With the deepening of heating and drying, the resin of glued paper (cloth)
has a certain degree of condensation reaction, and the crosslinking density and molecular weight are increasing. At the end of drying, the composition of the resin that can be dissolved in A and B phases of some organic solvents is usually reduced to 75%~95%. Strictly controlling the degree of curing conversion of resin is
a very important process control in glue processing. During the drying process, impregnated resins also changed in the molecular weight distribution structure.
According to the gel permeation chromatography (GPC) technology, the Japanese experts used the gel permeation chromatography (GPC) to determine and statistics the epoxy – dioxygen resin system of the FR-4 semi – solidified film before and after the drying of the epoxy – dioxygen resin system (Figure 2-5, table 2-11). The results showed that the percentage of the resin mass decreased in the low molecular weight (as the monomer) part and the middle molecular weight part. Among them, the decrease of the low molecular weight area is larger than that of the middle molecular weight area, while the percentage of the resin in the high molecular weight part increases. The increase is in 6%~7%. The dispersion coefficient (Mw/Mn) of the whole resin changed little.