Views: 1000 Author: Site Editor Publish Time: 2022-07-29 Origin: Site
Foaming agent is one of the essential raw materials in the process of polyurethane foam, which plays a key role in the foaming process.
The structure of the homogenizer determines its main properties and foaming performance. The structure-activity relationship of the homogenizer is as follows: hydrogen containing silicone oil with high hydrogen content deteriorates foaming performance; With the increase of molecular quantity, the foaming performance is improved in general. The end type of polyether in addition also affects the foaming performance. In order to obtain an excellent foaming agent, the products of different structures must be mixed and used.
Application
The homogenizer plays a central regulating role in the production of polyurethane foam by one step process. The process of one-step production of polyurethane foam plastic is made of a variety of raw materials (such as isocyanate, polyol, water or foaming agent) in a very short time (generally no more than 1 minute) chemical reaction, from liquid into colloid into polymer, which experience foaming, consolidation and other complex processes; There is isocyanate and polyol reaction to form polycarbamate, isocyanate and water to form an unstable carbamate, and then decompose into amine and carbon dioxide, carbamate group on the nitrogen atom of hydrogen and isocyanate reaction, The formation of urea-formate and the reaction of hydrogen on the nitrogen atom of the urea-group with isocyanate to form diureas are the reactions of chain growth, gas generation and cross-linking respectively. In order to make the foaming uniform, foam stability, uniform bubble hole made of elastic foam, must use the foaming agent, foaming agent is as follows:
(1) Each component of the nucleation and emulsification formula. Due to the miscibility of each component in the foam formula, if the emulsification effect is not good, it will produce local hydrophilic substances in the moment rich region, in these regions, there will be a high concentration of urea formation, which may lead to early hard urea precipitation, and then affect the opening and some physical properties of the foam. Therefore, the surfactant with strong emulsifying ability is needed to make it mixed evenly, so that the foaming reaction and crosslinking reaction can proceed smoothly.
(2) Reduce the surface tension of the system to facilitate the formation of bubble nuclei and the occurrence of bubbles, and stabilize the foam. Because of adding stabilizer, reduce the surface of the material ability, stir to make nuclear mixed with air to form bubbles, the bubbles nuclear have similar "nucleus" effect, reaction generated when our fleet into the generated bubble, and the bubble away L growing, uniform distribution and not make the bubble holes with large holes and hole and make the bubble boiling and hole collapse. In the whole reaction process, the number of bubbles does not increase, and the size of bubbles is consistent due to the presence of foaming agent.
(3) Make the foam open and "punch". The bubbles in the soft foam must be open to make the product soft and elastic. The rate OF reaction BETWEEN water and ISocyanate is higher than that between isocyanate and polyol, so a large amount of solid polyurea is generated at the beginning of foaming. It is an antifoaming agent, which can help to open and explode holes. Opening and exploding holes are the stages of soft foam foam must appear, otherwise there will be closed cell phenomenon, resulting in the decline of foam performance. But the opening and exploding holes must appear when the foaming reaction and gel reaction are basically completed and reach equilibrium. That is, when the foam has reached its peak and is strong enough to support its own weight, otherwise it will cause the foam to sag. The homogenizer can dissolve the polyurea generated in the initial foaming stage, and help the opening and exploding holes to realize the foaming connection in the later foaming stage.
It can be seen from the above points that the foam homogenizer not only plays the role of the foam, but also has an impact on the specific gravity, elasticity and tension of the foam. Different types of homogenizer are needed for different active raw materials, different use conditions and different foaming forms.