It belongs to chemical blowing agent.
01 polyisocyanates the most commonly used polyisocyanates in the industrial production of polyurethane foam are toluene diisocyanate (TDI), polymethylene polyphenyl isocyanate (Papi), diphenylmethane diisocyanate (MDI) and liquefied MDI (l-mdi).
03 Polyester polyol Ordinary low viscosity aliphatic polyester polyol, such as polyglycol adipate glycol with hydroxyl value of about 56mgKOH/g, or polyester polyol with a small amount of branched chain, can be used to manufacture polyester type polyurethane soft foam.
By adding appropriate auxiliary agents, the most important of which is a series of foaming auxiliary agents related to foaming, a large amount of foam is generated in the reaction products, thus obtaining polyurethane foam products.
Some liquefied modified MDI can be used as substitutes for TDI in the production of polyurethane soft foam, such as high-density polyurethane soft foam and semi hard foam or microporous polyurethane elastic materials.
A small amount of polyether glycol can be used as auxiliary raw material and mixed with polyether triol in the soft foam formula.
Due to the high thermal conductivity and permeability of carbon dioxide, physical foaming agent must be used for the rigid polyurethane foam formula requiring high thermal insulation performance.
TDI is mainly used to produce flexible polyurethane foam in the foam industry.
Papi can be mixed with TDI to produce cold cured and high resilience foams.
The main component of polyurethane foam (PU foam) is polyurethane, and the raw materials are mainly polyisocyanate and polyol.
In the field of foam plastics, Papi and modified Papi are mainly used to produce various hard polyurethane foams, and a small amount of them are used to produce high resilience soft foam, whole skin foam and semi-hard foam.
Semi hard foam formula generally uses some high molecular weight polyethers, especially high active polyether polyols and some hard foam polyethers with high functionality and low molecular weight.
In general, polyether polyols with high functionality and high hydroxyl value are used for hard foam formulation, so as to produce sufficient crosslinking degree and rigidity.
PAPI is also called crude MDI and polymerized MDI.
Polymer polyol can be used to produce high hardness soft block foam, high resilience foam, thermoformed soft foam, semi-rigid foam, self skinning foam, reaction injection molding (RIM) products, etc., which can reduce the thickness of products, reduce the density of foam and reduce the cost, increase the opening of foam, and give products certain flame retardancy.
The hydroxyl value of rigid foam polyether polyol is generally 350~650mgKOH/g, and the average functionality is above 3.
At present, there are few products on the market.
02 Polyether polyols Polyether polyols used to produce polyurethane soft foam are generally long chain and low functional polyethers.
Phthalic anhydride polyester alcohol with lower hydroxyl value can also be used in high resilience soft foams, whole skin foam and semi-rigid foam, as well as non foam polyurethane materials.
The average molecular weight of typical PAPI products ranges from 30 to 400, and the NCO mass fraction is 31% to 32%.
04 Polymer polyol Polymer polyol (grafted polyether polyol) contains rigid homopolymers, copolymers and graft polymers of styrene and acrylonitrile.
Among them, high activity polyether is mainly used for high resilience soft foam, and can also be used for semi-hard foam and other foam products.
These vinyl polymers act as organic “fillers” to improve the bearing capacity.
The ones with high hydroxyl value can be used to produce rigid polyurethane foam and rigid polyisocyanurate foam.
Generally, the hard foam formula is mixed with two polyethers, and the average hydroxyl value is about 4000mgKOH/g.
The average functionality of low viscosity PAPI is generally between 2.5 and 2.9.
In the production of polyurethane soft foam, in order to obtain soft foam with low density, and not to stiffen the foam due to excessive water, it is generally necessary to control the amount of water and add an appropriate amount of physical foaming agent as an auxiliary foaming agent.
Through carbon dioxide gas generated by reaction with isocyanate, viscoelastic foam materials are expanded, foamed and cured to obtain various polyurethane foams.
In the soft foam formula, the functionality of polyether polyol is generally 2~3, and the average molecular weight is between 2000~6500.
It is generally obtained by ring opening polymerization of 1,2-epoxypropane or copolymerization with a small amount of ethylene oxide with glycerol (glycerol) as the starting agent, and its molecular weight is generally 3000-7000.
Polyurea polyol (PHD dispersion) is also a special polymer modified polyol, which can be used for high resilience soft foam, semi hard foam and soft foam.
Polyether triol is most commonly used in soft foam.
Polyester polyols have high reactivity.
There are also some special polyols used in the production of polyurethane foam, such as vegetable oil polyols, rosin polyester polyols, and polymer polyester polyols.
Aromatic polyols are synthesized with binary acids (such as phthalic anhydride, terephthalic acid, etc.) and small molecular glycols (diethylene glycol, etc.) or polyols as raw materials.
The reaction activity of MDI is higher than that of TDI, and the volatilization toxicity is lower.
Because a large amount of heat is generated in tens of seconds at the initial stage of material mixing in the production of hard foam, it needs the blowing agent to absorb part of the heat, and at the same time, the gasification of the blowing agent makes the foam expand and foam.
CFC-11 (trichloromethane fluoride) was industrialized in the late 1920s.
05 blowing agent water is an important blowing agent in the production of polyurethane materials.
Polyether polyols with low unsaturation and high molecular weight can be used in the production of soft foam to reduce the amount of TDI.
At present, polyester Pu block foam is only used in a small number of fields such as clothing accessories.
CFC-11 is an ideal foaming agent in the production of polyurethane foam due to its non combustibility, suitable boiling point, easy gasification, low gas phase thermal conductivity, low toxicity, good compatibility with polyurethane raw materials, non corrosiveness, low price, simple foaming process and other characteristics..
