Method of producing hydrocarbon-expanded rigid polyurethane foam

Details Method of producing hydrocarbon-expanded rigid polyurethane foam Method of producing hydrocarbon-expanded rigid polyurethane foam

1998-09-11

2000-06-06

Cooney, Jr., John M.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

521170, 521172, 521173, 521174, C08J 904

Patent

active

060719788

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

It is known that polyurethane rigid foams can be blown with low-boiling alkanes. Cyclic alkanes are used to advantage here because they make an outstanding contribution to the thermal conductivity of the expanded material due to their low gaseous thermal conductivity. Cyclopentane is preferably used.
The beneficial properties when used as an insulator in domestic refrigerators have to be compared with a disadvantageous commercial situation. Thus, a specific quality of polystyrene inner container has to be used, as a result of the solvent properties of cyclopentane.
Furthermore, cyclopentane has the disadvantage, due to its relatively high boiling point of 49.degree. C., that it condenses at low temperatures such as are conventional during the use of polyurethane rigid foams as insulators in domestic refrigerators. Due to the undesired condensation of the blowing agent, a reduced pressure is produced in the cells which again has to be offset by an elevated foam strength or increased density.
Compared with the acyclic homologous pentane compounds, n-pentane and i-pentane, cyclopentane incurs higher manufacturing costs. n-pentane or i-pentane blown systems have been known for some time in the field of polyurethane rigid foams. However, the higher gaseous thermal conductivities, as compared with cyclopentane,which result in poorer thermal insulation capacity of the corresponding expanded systems is a disadvantage.
The object of the present invention was to develop a n-pentane or i-pentane blown rigid foam in which the disadvantages mentioned above are overcome and in particular in which low thermal conductivities are produced.
Surprisingly, it has now been found that polyol formulations based on specific polyethers and/or polyesters and polyisocyanates, which have a specific surface tension with respect to n-pentane or i-pentane as blowing agent, produce expanded materials with particularly low thermal conductivities.


SUMMARY OF THE INVENTION

The invention provides a process for preparing polyurethane rigid foams from polyols and polyisocyanates as well as blowing agents and optionally foam auxiliary agents, characterised in that the polyurethane rigid foam is obtained by reacting groups and a molecular weight of 250 to 1,500, which have a surface tension of 6 to 14 mN/m with respect to i-pentane and/or n-pentane as blowing agent, surface tension of 4.0 to 8 mN/m with respect to i-pentane or n-pentane as blowing agent.


DETAILED DESCRIPTION OF THE INVENTION

Polyol formulations according to the invention preferably contain polyethers with a molecular weight of 250 to 1,500, obtained by the polyaddition of 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. % of propylene oxide to starter compounds.
Preferred compounds are sorbitol started polyethers with a molecular weight of 500 to 1,400 based on 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. % of 1,2-propylene oxide; sucrose started polyethers with a molecular weight of 500 to 1,400 based on 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. % of 1,2-propylene oxide; trimethylolpropane started polyethers with a molecular weight of 250 to 850 based on 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. % of 1,2-propylene oxide; glycerine started polyethers with a molecular weight of 250 to 850 based on 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. % of 1,2-propylene oxide; o-toluylene-diamine started polyethers with a molecular weight of 250 to 850 based on 70 to 100 wt. % of ethylene oxide and 0 to 30 wt. % of 1,2-propylene oxide.
According to the invention the polyol formulations preferably contain polyesters with a molecular weight of 200 to 600 formed from aromatic and aliphatic dicarboxylic acids and polyols containing at least 2 hydroxyl groups. Examples of dicarboxylic acids are phthalic acid or phthalic anhydride, terephthalic acid, isophthalic aid, malonic acid and succinic acid. The following are preferably used as the alcohol component for esterification: ethylene glycol, di, tri or tetraethylene glycol or mixture

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