Reasons for weight loss of polyurethane self-skinned foam plastic products--for reference only
Times: 2020-07-08 | Hit：1505
Polyurethane products themselves have many characteristics. Since the weight of the product changes during the post-curing process, the weight change of the self-skinned product is a complex change due to its own characteristics.
In the production process of self-skinning products, after the reaction is completed, the product is taken out of the mold cavity. The weight must be weighed first, and then the holes should be vented to prevent the product from shrinking. After a period of time, weigh the product and you will find that the weight has changed, that is, the product becomes lighter.
The first is the weight loss caused by the volatilization of the physical foaming agent (the molecular weight of the physical foaming agent is greater than that of air). During this weight loss process, only physical changes occur.
Secondly, the black material isocyanate in the production ratio of polyurethane products is excessive. The excess isocyanate will react with water to release carbon dioxide. When -NCO reacts with the hydroxyl group in the polyether, the influence of steric hindrance and other reasons is not all- NCO can react with the hydroxyl group, and there are still some free NCO groups, which will also react with water and emit carbon dioxide gas to volatilize.
In actual production, due to other side reactions, operating conditions, temperature, humidity, etc., the amount of weight loss varies. Different manufacturers, different products, and different isocyanate indexes have different effects on the weight loss of products. Different polyethers and isocyanates used by manufacturers have different steric effects, which will also affect the weight loss of products. According to calculations and our factory's production experience, the general weight loss is between 7~10%, but the loss of different products is different, and it needs to be explored from the production.
In the production process of self-skinning products, after the reaction is completed, the product is taken out of the mold cavity. The weight must be weighed first, and then the holes should be vented to prevent the product from shrinking. After a period of time, weigh the product and you will find that the weight has changed, that is, the product becomes lighter.
The first is the weight loss caused by the volatilization of the physical foaming agent (the molecular weight of the physical foaming agent is greater than that of air). During this weight loss process, only physical changes occur.
Secondly, the black material isocyanate in the production ratio of polyurethane products is excessive. The excess isocyanate will react with water to release carbon dioxide. When -NCO reacts with the hydroxyl group in the polyether, the influence of steric hindrance and other reasons is not all- NCO can react with the hydroxyl group, and there are still some free NCO groups, which will also react with water and emit carbon dioxide gas to volatilize.
In actual production, due to other side reactions, operating conditions, temperature, humidity, etc., the amount of weight loss varies. Different manufacturers, different products, and different isocyanate indexes have different effects on the weight loss of products. Different polyethers and isocyanates used by manufacturers have different steric effects, which will also affect the weight loss of products. According to calculations and our factory's production experience, the general weight loss is between 7~10%, but the loss of different products is different, and it needs to be explored from the production.
Liu Bin