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Introduction of polyurethane catalyst
Edit:Nantong Yutai Chemical Products Co., Ltd.   UpDate:2019-05-23

Polyurethane catalyst

In the production of polyurethane foams, tertiary amines have long been used as catalysts. The main function of the tertiary amine is to balance and control the gelation and foaming reactions in order to adequately control the foaming process. The type and concentration of the amine catalyst can be selected to suit the process requirements, such as the foaming pattern, reaction time (e.g., creaming period, foaming and gelling time), and even the outer skin of the foam. The amount of amine catalyst can be adjusted to improve gas permeability and minimize density variations.

Since most of the amine catalysts sold on the market contain different amines, their activities are obviously different. Some prefer a catalytic foaming reaction and a poorer catalysis for the gelation reaction.

Silicone surfactant

In the production of polyurethane foams, silicone is mainly used as a surfactant. Its basic function is to reduce the surface tension of the mixture, thereby improving the mixing of various components, adjusting the size of the nucleus and bubbles, thereby controlling the cell structure, improving the stability of foaming, and preventing cell agglomeration. Otherwise it will cause bubbles.

In each of the formulations used to produce sheet-like flexible foams, the minimum required amount of silicone is added. Below the minimum amount, the bubbles or cells are coarsened.

A good open cell foam can be obtained by increasing the amount of silicone from a minimum to a suitable level. The slight increase in the amount exerted on the properties of the foam is very small. The only significant difference is the relaxation (settling or subsidence). When the amount of silicone is high, the obtained foam is relatively tight, and the corresponding amount of tin is narrowed. When the silicone concentration is further increased, the foam is more tight, which affects compression set and load bearing properties.

Organotin catalyst

The organic derivative of tin is a strong gelling reaction catalyst. When used in combination with an amine catalyst, it can well control and adjust the balance between foaming and gelling in the polyurethane foam formation process.

Stannous octoate is the most commonly used tin catalyst for the production of soft flaky foam.

When the amount of stannous octoate is below the minimum value, the resulting foam will crack due to insufficient gelation and excessive foaming. A slight open-cell foam with a slight relaxation (settling or depression) can be obtained by slightly increasing the concentration of stannous octoate. Further increasing the concentration of the tin catalyst prevents slack and the foam gradually becomes tight. Increasing the amount of tin can cause a weak to severe shrinkage because the gelation rate is too fast to form a strong bubble window that is difficult to burst.

In the cold cure/high resilience molding process, a very small amount of dibutyltin dilaurate is used to improve the original strength of the foam.

Other additives

1. Flame retardant

A variety of flame retardants are commercially available, but not every one is suitable, and a few are known to be carcinogenic.

Adding a small amount (not more than 2 parts per hundred parts of polyol) of flame retardant generally only slightly affects or affects the physical properties of the foam. Increasing the amount of flame retardant will have a significant adverse effect.

2. Crosslinking agent and chain extender

They are active substances that can enter the polymer structure by chemical reaction. In order to produce a foam having a higher load carrying capacity, crosslinking within the polymer is advantageous.

However, since the activity of these crosslinkers is generally very high, the choice of species, the determination of the concentration, and which polyol to use in combination are critical issues.


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