During the synthesis process of the adduct type organic silicone pressure-sensitive adhesive, we encountered some recurring problems. Therefore, I would like to seek your advice.
Process Routeㄩ The raw materials used are 110% raw rubber and methyl MQ silicone resin (silicone oil type), with toluene as the solvent. The main agent is first heated at 105∼C to mix evenly, then cooled to 40∼C. Subsequently, the diluent, inhibitor, crosslinking agent, and catalyst are added successively. Finally, it is cured at 150∼C for 1 to 5 minutes.
Test Conditions: The range of ratios that have been tested is - 110 parts of raw rubber : 2 parts of MQ resin = 1:0.5 to 2 (by mass ratio), and the molar ratio of SiH/Vi⁺ in the crosslinking agent = 0.5 to 8 (the vinyl content of the main rubber is calculated as 1:1.3). However, the peel strength of the resulting rubber layer under all conditions is extremely low, estimated to be only a few grams per inch, with almost no practical adhesion.
Key Questions:
1. Is this result a normal occurrence?
2. If it is abnormal, where might the problem lie?
Additional Background**: Previously, a batch of samples was successfully prepared, with good wetting properties and a peel strength of approximately 600 g/inch. However, after prolonged contact with the steel plate, residual glue would occur. But since then, even using the same process, this result could not be replicated. During this period, the MQ resin was replaced (it was still from the same supplier, as the initial purchase quantity was exhausted). It is unknown if this is related to this issue.
I sincerely request that experienced seniors offer guidance and clarification. Thank you!
(Note: Here,⁺ refers to the total amount of vinyl groups in the main adhesive, and the amount of crosslinking agent is calculated based on this standard.)
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