Flame retarded polyurethane foams having reduced discoloration

The discoloration of low density polyurethane foams produced with certain flame retardants is reduced by incorporating phenothiazine into the foam. The phenothiazine can be employed by admixing with the flame retardant from about 0.25 to about 5.0 percent phenothiazine by weight of the flame retardant.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to flame retarded polyurethane 
foams, and particularly concerns flame retarded, low density polyurethane 
foams having improved color characteristics. 
2. The Prior Art 
When low density polyurethane foams are treated with flame retardants to 
reduce their flammability, certain physical properties of the foams are 
detrimentally affected. One of the frequent problems is scorching of the 
center of the foam buns which results in unacceptable color of the foam. 
This discoloration is reduced to an acceptable level pursuant to the 
present invention by incorporating phenothiazine into the foam. 
It is known in the prior art to utilize phenothiazine to prevent 
propagation of free radical reactions that can cause scorch in 
polyurethane foams. Such reactions generally involve the ether moieties of 
the polyether employed in the foam formulation. Various compositions that 
are normally present in polyurethane foam formulations can catalyze these 
free radical reactions that cause the scorching. Among such compositions 
are tertiary amines which can be present in the formulation as catalysts 
for the reaction of isocyanate with water or with polyol, or as 
amine-started polyols or both, and various metallic compounds that can be 
present as impurities. These problems are described in U.S. Pat. No. 
3,214,397. 
The present invention is distinguished from the prior art in that the foams 
utilized according to the present invention do not become unacceptably 
scorched in the absence of the flame retardant. When the flame retardant 
is added to the foam formulation, however, unacceptable scorch results. It 
is a theory of the present invention that this scorching is the result of 
acidity produced by the flame retardant. The phenothiazine acts as an acid 
acceptor, thereby preventing the unacceptable scorching of the foam. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the color of low density urethane 
foams treated with flame retardants is improved by the addition of 
phenothiazine to the foam. 
Many flame retardants cause color problems in low density urethane foams. 
The discoloration occurs when the foam becomes scorched during cure. This 
scorching is believed to be caused by acidity that is produced by the 
flame retardant. An acid scorching mechanism is especially likely in the 
cases where the foam does not scorch on curing in the absence of a flame 
retardant. By providing a phenothiazine acid acceptor in accordance with 
the present invention these scorch problems are overcome. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention is particularly concerned with low density 
polyurethane foams that do not become unacceptably scorched when cured in 
the absence of a flame retardant. 
The present invention is also particularly concerned with poly 
(haloethyl-ethyleneoxy) phosphoric acid esters used as flame retardants in 
low density polyurethane foams. Such flame retardants are described, for 
example, in U.S. Pat. No. 3,896,187. 
Flame retardant compositions comprised of mixtures of poly 
(haloethyl-ethyleneoxy) phosphoric acid esters and other flame retardants 
are also included in the scope of the present invention. Said other flame 
retardants include tris(haloalkyl) phosphates such as tris(dibromopropyl) 
phosphate, tris(.beta.-chloroethyl) phosphate and tris 
(.beta.-chloropropyl) phosphate among others. 
The flame retardants are employed in a flame retardant effective amount, 
generally from about 3 percent to about 20 percent by weight of the polyol 
in the foam formulation. 
The phenothiazine utilized in accordance with the present invention can be 
admixed with the foam formulation by conventional techniques. For example, 
it can be added alone or in combination with other ingredients of the foam 
formulation. It can also be admixed with the flame retardant composition 
prior to admixture of the flame retardant with the foam formulation. 
Phenothiazine employed in the foams of the present invention is generally 
provided in amounts from about 0.25 percent to about 5.0 percent by weight 
of the flame retardant composition. Accordingly, a flame retardant 
composition incorporating the phenothiazine therein can be conveniently 
prepared prior to incorporation into the foam formulation. 
Numerous conventional foam formulations for low density polyurethane foams 
can be utilized in accordance with the present invention. The selection of 
ingredients and process conditions can easily be determined by those 
skilled in the art. 
The color of the foams of the present invention can be evaluated by 
numerous recognized methods as set forth, for example, in Principles of 
Color Technology, Fred W. Billinger, Jr. and Max Saltzman (Wiley 
Interscience, 1966) 
In the experimental work on the present invention, a Hunter colorimeter was 
utilized to measure color differences pursuant to the color-difference 
formula: 
EQU .DELTA. E (Hunter) = (.DELTA.L.sup.2 +.DELTA.a.sup.2 
+.DELTA.b.sup.2).sup.1/2 
Where: 
EQU .DELTA. E (Hunter) = color difference 
EQU .DELTA. L = lightness compared to standard 
EQU .DELTA. a = redness, if positive, or greenness, if negative, compared to a 
standard 
EQU .DELTA. b = yellowness, if positive, or blueness, if negative, compared to 
a standard 
All of the values for .DELTA. L, .DELTA. a and .DELTA. b are calculated 
within the Hunter instrument by electrical means and read directly from 
its dials. The most commonly used standard of color comparison is a pure 
white sample. A white tile was used in the experimental work on the 
present invention. 
The present invention will be more fully illustrated in the Examples which 
follow.

EXAMPLES 
Six foam formulations were prepared. The basic foam formulation components 
for each one were as follows: 
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3500 Molecular weight polyether polyol 
100 grams 
80/20 Toluene diisocyanate (110 Index) 
61.1 grams 
Water 5.0 grams 
Non-hydrolyzable silicone surfactant 
1.1 gram 
Diazabicyclo octane catalyst (33% active) 
0.3 gram 
N-Ethylmorpholine catalyst 
0.05 gram 
50% Stannous octoate 0.4 gram 
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The six foam formulations were designated Foam A, Foam B, Foam C, Foam D, 
Foam E and Foam F. The Foam B formulations was admixed with a flame 
retardant and the foam formulations for foams C through F were admixed 
with the same flame retardant and various amounts of phenothiazine. 
After mixing all of the foam ingredients, the materials for each foam were 
poured into a 12 .times. 12 .times. 5 inch cake box. When the foam buns 
completed their rises, thermocouples were inserted into the centers of the 
buns. When the thermocouples recorded 150.degree. C., they were removed 
from the buns. The buns were then placed into a preheated microwave oven 
that had been calibrated so that 350 grams of water would increase in 
temperature by 50.degree. C. when heated for 4 minutes. The buns were 
cured in the oven for four minutes, and then removed and allowed to cure 
at room temperature for an additional 30 minutes. 
Following the cure of the buns, a one inch thick slice was cut 
perpendicular to the rise from the center of each bun. A 2 inch square 
sample was then removed from the center of each slice. A Hunter colormeter 
was then used to measure the values for calculating color difference. 
The following table is a summary of this experimental work. 
TABLE 
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Foam A B C D E F 
______________________________________ 
FR* (grams) 
-- 8.0 8.0 8.0 8.0 8.0 
phenothiazine 
-- -- 0.4 0.08 0.04 0.02 
(grams) 
.DELTA.E (Hunter)** 
8.81 49.21 13.29 10.30 10.49 11.82 
______________________________________ 
*2:1 blend of poly(chloroethyl-ethyleneoxy) phosphoric acid ester: tris 
(dichloropropyl) phosphate 
**The standard was a piece of white tile having an E(Hunter) value of 
zero. 
The color differences value in the foregoing table illustrate the 
substantial color improvement brought about by addition of phenothiazine 
to the flame retarded foam formulations. 
Having set forth the general nature and some examples of the present 
invention, the scope is now particularly set forth in the appended claims.