How to Use Small Additives in Slow Rebound Sponge Formula?

The formula for slow rebound sponge is similar to regular sponge with minor differences. Apart from the major difference in the main ingredient polyether, some additives can be interchangeable. However, for the production of high-quality products, careful consideration and selection of additives are still necessary.

1. Choice of Amine

The most classic amine used for slow rebound sponge is Dabco33-LV from the American Air Products. The dosage is generally 0.3-0.8 parts of the total polyether. It is formulated with 33% triethylenediamine and 67% di(propylene glycol) (DPG). The reason for recommending this product is because it uses di(propylene glycol) as a solvent. Some may ask, is a solvent of this kind important? The answer is yes. Looking at the ability to dissolve triethylenediamine, there are many alcohol compounds that can be used as solvents: such as propylene glycol, diethylene glycol, ethylene glycol, 1,4-butanediol, etc. Among these small-molecule alcohols, di(propylene glycol) has the largest molecular weight and the lowest hydroxyl value. As we all know, low molecular weight alcohols can be used as chain extenders or crosslinking agents. This means that these small-molecule alcohols can consume TDI, resulting in: on one hand, it reduces the TDI index, and on the other hand, it easily causes closed-cell sponges.

2. Choice of Tin

Craftsmen who have experienced with regular sponges often like to use stannous octoate (T-9) to create slow rebound, but the author suggests using dibutyltin dilaurate (D22, T-12, also known as K-19 domestically). Stannous octoate is suitable for creating medium to low density sponges. Its characteristic is that it is quick to stick initially but lacks strength later on. It is not good for post-curing when used with high-density sponges. T-9 is prone to hydrolysis, and slow rebound itself has a slow start (generally controlled to start at around 160 seconds), so it is in contact with water for a long time, leading to some hydrolysis, affecting curing. Dibutyltin dilaurate does not hydrolyze, and its initiation, gelation, and curing are stable with good post-curing properties.

Some peers have mentioned that the sponge's tensile strength is not good. The author suggests using dibutyltin dilaurate, and the feedback received was that the tensile strength improved. If using T-9, the dosage is between 0.1-0.4 parts. If using dibutyltin dilaurate, the dosage can be controlled between 0.03-0.05. For slow rebound on assembly lines, the dosage can be reduced to 0.001-0.01 parts. For export orders that restrict the use of tin catalysts, the author suggests using bismuth carboxylate to replace tin.

3. Choice of Silicone Oil

A typical slow rebound silicone oil is B8002, with a dosage between 0.5-2 parts. It is used less for high-density sponges and more for low-density sponges. It is used more for manual foaming and less for machine foaming. In recent years, domestic silicone oil suppliers have developed many silicone oils for slow rebound, and their performance is also good. Some use L-580 for slow rebound, and in this case, the amount of silicone oil should be reduced, as L-580 is more active.

4. Use of Pigments

The use of pigments is basically the same as for regular sponge. Just be cautious when dealing with black sponges because the carbon black used to prepare black pigments is hydrophobic, which can affect the compatibility of various components in the formula and the efficiency of the catalysts. Many colleagues have encountered the phenomenon of easy cracking of black sponges, and the reason lies here. Therefore, when creating black sponges, proper adjustments should be made to the catalyst dosage. These are personal work experiences provided for reference only, and feedback and corrections from colleagues are welcome.