Polyester resins for polyurethane foams prepared by reacting two diacids, diethylene glycol, a poly(oxyethylene) glycol and a cross-linking polyol

The machine processing character as well as the stress-strain properties of polyester polyurethane foam are improved by the use of a cross-linking polyol, a viscosity increasing dicarboxylic acid or anhydride such as phthalic anhydride, and by the use of specific minor amounts of poly(oxyethylene) glycol, in the esterification formula of foam grade polyester resins. A nonhydrophillic flexible polyester based polyurethane foam is produced.

FIELD OF THE INVENTION 
This invention relates to improvements in flexible polyester bases 
polyurethane foams. Specifically, this invention relates to improvements 
in a number of physical properties in polyester based polyurethane foams 
and in the polyester resin formulation for making the foam. 
BACKGROUND AND DISCUSSION OF PRIOR ART 
Polyester based flexible polyurethane foams, are well known articles of 
commerce and are conventionally prepared by reacting polyesters with 
organic polyisocyanates in the presence of controlled amounts of water. 
Typical of such foams are those prepared from (a) polyesters derived, for 
instance, from the interaction of a glycol, such as diethylene glycol, and 
adipic acid or other dicarboxylic acid, sometimes in the presence of a low 
molecular weight cross-linking polyol containing at least 3 hydroxy 
groups, such as glycerol or trimethylol propane, (b) a polyisocyanate, 
usually a diisocyanate, such as tolylene diisocyanate, and (c) a small 
amount of water, the reaction being carried out in the presence of 
coupling agents or emulsifiers and catalysts. 
In U.S. Pat. No. 3,079,350, granted Feb. 26, 1963, to C. Bernstein, there 
is disclosed improvements in flexible polyurethane foams wherein polyester 
resins derived from mixed glycols provide highly hydrophilic foams. Such 
flexible urethane foams genrally require a high degree of cross-linking to 
increase the polyester viscosity to the range necessary for providing the 
desired foam quality but at the expense of reducing the stress-strain 
properties. This patent is incorporated herein by reference. 
In U.S. Pat. No. 3,298,974, granted Jan. 17, 1967, and U.S. Pat. No. 
3,399,154, granted Aug. 27, 1968, to C. Bernstein, et al, there is 
disclosed the manufacture of rigid (i.e., not flexible) polyurethanes 
wherein 0 to 100% of the total dicarboxylic acid in the polyester can be 
replaced with phthalic anhydride. 
In U.S. Pat. No. 3,769,245, granted Oct. 30, 1973, to Stewart, et al, there 
is disclosed the formulation of thermoplastic linear polyurethanes wherein 
linear hydroxyl terminated polymers, such as polyalkylene oxides, are 
added as part of the prepolymer. 
While such prior art polyurethanes were generally useful for their specific 
purposes, it was desired to provide flexible polyester polyurethane foams 
which would be readily processable and yet exhibit improved cell structure 
and physical properties over the prior art polyurethanes. 
It is therefore an object of the present invention to provide improved 
flexible polyester polyurethane foams and improved polyester resins for 
making same. 
It is a further object of the present invention to provide non-hydrophilic 
polyester polyurethane foams. 
It is another object of the present invention to provide polyester 
polyurethane foams over a wide range of densities. 
It is still a further object of the present invention to provide a flexible 
polyurethane foam having improved stress-strain properties, good machine 
processing character, cellular control, structure and integrity. 
BRIEF SUMMARY OF THE INVENTION 
The present invention provides an improved polyester resin wherein specific 
small quantities of cross-linking polyol are employed with small amounts 
of viscosity increasing diacid such as phthalic acid (anhydride), and 
small amounts of a poly(oxyethylene) glycol, to impart improved processing 
character to the resin and improved physical properties in the 
polyurethane foam produced therefrom. Specifically, the present polyester 
polyurethane foams show improved stress-strain properties and 
machinability, as well as being non-hydrophilic. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention comprises a polyester polyurethane composition for 
producing flexible polyester polyurethane foams, which comprises a 
predominantly diethylene glycol polyester formulation, including, in 100 
parts by weight of formulation, about 0.2-5.5 parts of a cross-linking 
polyol, about 1-12 parts by weight of a viscosity increasing diacid which 
replaces the diacid of the known polyester formulation, and about 1-15 
parts of poly(oxyethylene) glycol, whereby the formulation remains liquid 
at 70.degree. F. and has a viscosity between 18,000 to 30,000 cps, and 
preferably 22,000 to 25,000 cps. The present viscosity increasing diacid 
(anhydride) such as phthalic, terephthalic, isophthalic acid, fumaric 
acid, maleic acid and cycloaliphatic dicarboxylic acids such as 
cylohexanedicarboxylic acid are well known in the art and require no 
further discussion herein. Phthalic acid is the preferred acid in the 
present resin. 
A general formulation in parts by weight according to present invention is 
as follows: 
______________________________________ 
General 
Preferred 
Range Range 
______________________________________ 
Diethylene Glycol 30-50 35-45 
Aliphatic Dicarboxylic Acid 
40-60 42-50 
Viscosity Increasing Diacid 
1-12 6-9 
Poly(oxyethylene) Glycol 
1-15 2-8 
Cross-Linking Polyol 
0.2-5.5 1-4.5 
______________________________________ 
In another aspect, the present invention is a flexible polyester 
polyurethane foam produced from the aforesaid polyester resin formulation, 
wherein the foamed product exhibits improved tensile strength, elongation 
and tear strength (i.e. stress-strain properties) because of the lesser 
quantities of crosslinking polyol used in the resin. 
In the production of the polyester compositions of the present invention to 
produce novel flexible polyurethane foams, the diethylene glycol, the 
poly(oxyethylene) glycols and cross linking polyols are reacted with the 
mixture of the original dicarboxylic acid and the viscosity increasing 
dicarboxylic acid, (conveniently added as the anhydride) to form 
corresponding mixed esters as known in the art. 
It is believed that the increased viscosity by the limited concentration of 
the phthalic acid, for instance, which replaces part of the original 
dicarboxylic acid such as adipic acid, combined with the reduced branching 
by the limited addition of the low molecular weight cross-linking polyols, 
provides a formulation which surprisingly achieves a foamed product of 
improved physical properties. The machine processing and general foam 
quality are substantially improved because of the presence of 
poly(oxyethylene) glycol. 
The diethylene glycol may be mixed with small quantities of other low 
molecular weight between (62-150) glycols in the present composition such 
as propylene glycol-1,2; propylene glycol-1,3; butylene glycol-1,4; 
butylene glycol-1,3; butylene glycol-2,3; dipropylene glycol, and the 
like, for instance. However, diethylene glycol must be present in 
predominant amounts in the glycol mixture to arrive at the present resin 
product. 
Among the dicarboxylic acids, which are partially replaced with a viscosity 
increasing diacid, utilized in making foamed polyesters of the prior art, 
are primary adipic acid or glutaric acid, and azelaic acid, sebacic acid, 
and malonic acid, succinic acid, pimelic acid, suberic acid, and the like. 
Adipic acid is widely used. Although the art teaches mixtures of these 
acids, there is no suggestion of the present specific mixture as claimed. 
The poly(oxyethylene) glycols useful in the present invention are 
essentially linear hydroxy terminated compounds having ether linkages. 
These poly(oxyethylene) glycols generally have an average molecular weight 
between about 200 to 1,000. Of particular utility are those 
poly(oxyethylene) glycols having an average molecular weight of 300 to 800 
and especially about 400. Typical illustrations of such poly(oxyethylene) 
glycols are those sold under the trade name Carbowax, of Union Carbide 
Co., New York, N.Y. Mixtures of two or more of said poly(oxyetheylene) 
glycols can be used with good results, as well as mixtures with small 
amounts of higher poly(oxyalkylene) glycols such as polyoxypropylene 
glycol and partial copolymers wherein the poly(oxyethylene) glycol is in 
the predominant amount. Although the poly(oxyethylene) glycol may be 
present in an amount of about 2 to 8 percent, by weight, in the present 
resin, suprisingly, as little as 1% by weight is often effective to 
improve machine processing and produce the high quality flexible foam of 
the present invention, and 2 or 3 weight percent is often sufficient. The 
quantity of the other glycols in the mixture is determined by the Artisan, 
to yield a composition which is liquid at 70.degree. F. 
The cross-linking polyol is also added to the formulation in small 
quantities with further improvement in the physical properties of the foam 
product. Such cross-linking polyols include glycerol, trimethylol propane, 
sorbitol, pentaerythratol and the like, as known in the art. 
The organic diisocyantes, the tertiary amine catalysts, the emulsifying 
agents, the proportions thereof, the proportions of water, and the 
procedural techniques involved in the production of the polyester 
polyurethane foams from the novel polyester compositions are also well 
known in the art. 
As to the organic diisocyanates, tolylene diisocyanate (in commercial form 
it is usually a mixture containing about 80% of the 2,4 isomer and 20% of 
the 2,6 isomer), is preferred, but others, as known in the art, may be 
employed. 
The finished polyurethane foams of the invention are conveniently shaped in 
the form of conventional flexible bodies having a broad range of densities 
from about 2 to 6 lbs., for instance.