Effect of Diluent on Composite Quality

For dry compounding with two-component adhesives, dilution with a solvent is required for uniform coating and for infiltration.

The main solvents are ethyl acetate, toluene, methyl ethyl ketone and so on. Many factors must be taken into consideration when selecting the solvent. Since toluene is toxic, it is difficult to dry, and it tends to produce residual components. Methyl ethyl ketone smells heavy and the price is high, so ethyl acetate is generally used, and its purity requirements are met. 99%, water ≤ 0.2%, because the curing agent -N = C = O system accumulate double bonds, very lively, and water react to produce amines and emit CO2.

The reaction consumes the curing agent, which reduces the amount of curing agent involved in the reaction with the glue, and at the same time releases CO2, so that the glue layer contains bubbles, which is extremely unfavorable to dry compounding, and often results in surface quality problems affecting the adhesive strength. Similarly, the active hydrogen of isocyanate groups and alcohols, polyols, and other hydroxyl-containing compounds that react to form carbamates and react with organic acids (hydroxyl groups) to form acylate wrists will affect the normal use of the glue. Therefore, dilution must be performed during compounding. Agent for testing.

There must be a clarification here. Some composite manufacturers believe that adding more diluent can reduce the cost, and this view is wrong. Diluent in the compounding process only plays a role in uniform coating and facilitates infiltration. The real adhesive effect is glue and curing agent. , And the diluent has evaporated, as long as a certain amount of dry glue is applied, less diluent is more economical.