Influence of various raw materials on soft foam
Influence of raw materials on soft foam
1、Polyether
As the main raw material, polyether reacts with isocyanate to generate urethane, which is the skeleton reaction of foam products. In the case of the same functionality, when the molecular weight increases, the tensile strength, elongation and resilience of the foam increases, and the reaction activity of the same kind of polyether decreases; in the case of the same equivalent value (molecular weight/functionality), when the functionality increases, the reaction is relatively accelerated, and the cross-linking degree of the generated urethane is increased, and the hardness of the foam is increased, the elongation rate decreases. The average off-energy of polyol should be above 2.5, if the average off-energy is too low, the foam body will have poor recovery after being pressurized.
If the dosage of polyether is high, it is equivalent to the reduction of other raw materials (TDI, water, catalyst, etc.), which is easy to cause the foam products to crack or collapse.
If the dosage of polyether is small, the foam product is hard, the elasticity is reduced, and the handfeel is bad.
2、Foaming agent
Generally in the manufacture of density greater than 21 polyurethane block foam, only the use of water (chemical blowing agent) as a blowing agent, in low-density formulations or ultra-soft formulations before the use of methylene chloride (MC) and other low-boiling compounds (physical blowing agent) as an auxiliary blowing agent.
The auxiliary blowing agent will reduce the density and hardness of the foam, and the curing will be slowed down due to the absorption of part of the reaction heat by its vaporization, which requires an increase in the amount of catalyst. Due to the absorption of heat, the danger of core burning is avoided.
Foaming ability can be used to foam index (100 parts of polyether water or water equivalent number) to reflect: m — foaming agent dosage
Foaming index IF = m (water) + m (F-11) / 10 + m (MC.) / 9 (100 parts of polyether)
Water as a blowing agent reacts with isocyanate to generate urea bond and release a large amount of CO2 and heat, which is a chain growth reaction.
The amount of water is more, the density of the foam decreases and the hardness increases, while the pillars of the bubble holes become smaller and weaker, which reduces the load-bearing capacity and is easy to collapse the bubble and crack the bubble. The amount of TDI consumed increases, more heat is released, and it is easy to burn the heart. If the amount of water exceeds 5.0 parts, a physical foaming agent must be added to absorb some of the heat to avoid the occurrence of core burning.
Less water, the amount of catalyst is reduced accordingly, but the density increases.
3、Toluene diisocyanate
General soft foam with TDI80/20, 2, 4 and 2, 6 isomers of the mixture. Available cooling method for the preparation of T100 that is, pure 2,4TDI.
TDI dosage = (8.68 + m water x 9.67) x TDI index. TDI index is generally 110-120.
The isocyanate index increases in a certain range, the foam hardness increases, but after reaching a certain point the hardness no longer increases significantly, while the tear strength, tensile strength and elongation decrease, the foam forms large holes, the closed cell rises, the resilience decreases, the surface is sticky for a long time, and the maturing time is long, causing the core burning.
Low isocyanate index will cause foam cracks, poor resilience, poor strength, compression permanent deformation is larger, the surface has a moist feeling.
