Fire-retardant paint, when activated by the heat of fire, reacts to form a thick, low-density, polymeric coating or char layer. Water vapor and sulphur dioxide are released during the intumescent reaction

Fish, R. H.

Fohlen, G. M.

Parker, J. A.

Sawko, P. M.

English

NASA Technical Reports Server

September 1970
	
Brief 70-10450 
NASA TECH BRIEF
	 [N I ^ 4,z]oj 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
application. Tech Briefs are available on a subscription basis from the Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Intumescent Coatings as Fire Retardants 
The development of fire-retardant coatings to pro-
tect surfaces which may be exposed to fire or extreme 
heat is a subject of intense interest to many industries. 
A fire-retardant paint has been developed which rep-
resents a new chemical approach for preparing in-
tumescent coatings, and potentially, is very important 
to fire-prevention authorities. 
The requirements for a superior coating include 
ease of application, suitability to a wide variety of 
surfaces and finishes, and stability over an extended 
period of time within a broad range of ambient tem-
perature and humidity conditions. 
These innovative coatings, when activated by the 
heat of a fire, react to form a thick, low-density, poly-
meric coating or char layer. Water vapor and sulphur 
dioxide are released during the intumescent reaction. 
Two fire-protection mechanisms thus become avail-
able: (1) the char layer retards the flow of heat, due to 
the extremely low thermal conductivity; and (2) water 
vapor and sulfur dioxide are released, providing fire-
quenching properties. Still another mechanism func-
tions in cases where the char, by virtue of its high 
oxidation resistance and low thermal conductivity, 
reaches a sufficiently high temperature to re-radiate 
much of the incident heat load. 
The coatings consist of dispersions of selective salts 
of a nitro-amino-aromatic compound. Specifically, 
para-nitroaniline bisulfate and the ammonium salt of 
para-nitroaniline-ortho suphuric acid (2-amino-5-
nitrobenzenesulphuric acid) are used. Suitable ve-
hicles are cellulose nitrate of lacquer grade, a 
nitrile-phenolic modified rubber, or epoxy-polysulfide 
copolymer. Three separate formulations have been 
developed. A solvent is usually employed, such as 
methylethyl ketone, butyl acetate, or toluene, which 
renders the coatings suitably thin and which evap-
orates after the coatings are applied. Generally, the
intumescent material is treated as insoluble in the 
vehicle, and is ground and dispersed in the vehicle and 
solvent like an ordinary coating pigment. 
The char found on intumescence is better in terms 
of yield and physical properties than chars obtained 
from many previously known intumescent materials. 
Prior to intumescence, the coating has a density of 
85 pounds per cubic foot. After intumescence, the 
density is approximately 0.3 pound per cubic foot. 
The linear expansion of the coatings ranges from 70 to 
200 times the applied coating thickness. 
Notes: 
I. Despite the fact that the char yield has better 
physical properties than those of previously known 
intumescent materials, a problem of char retention 
in some environments still exists. High-velocity 
air flow and high acceleration can cause the very 
light char to fall off. One approach under study 
to resolve the problem is to include fibrous ma-
terial in the coating mix. 
2. One of the intumescent coatings has been shown 
to retain both mechanical and thermal properties 
when exposed to a high humidity/temperature 
environment. In addition, the other coatings retain 
some utility at limited humidity/temperature rang-
es. 
A specific paint developed at Ames Research Center 
extended the time for the backface of a steel disk 
to reach a temperature of 400°F to more than 4 
minutes. An unprotected disk reached 400°F in 21 
seconds. 
An interesting application of one of the coatings 
is in small compartments, where, in the event of 
a fire, the coating swells, filling the compartment 
or void completely. Experiments have shown that 
this technique will extinguish the fire.
(Continued onerleat) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19700000434 2020-03-17T00:49:24+00:00Z
Requests for further information may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B70-10450
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA. Code 
GP, Washington, D.C. 20546. 
Source: J. A. Parker, G. M. Fohlen,

P. M. Sawko and R. H. Fish

Ames Research Center

(A RC- 10099) 
Brief 70-10450	 Category 04


Intumescent Coatings as Fire Retardants

The development of fire-retardant coatings to protect surfaces which may be exposed to fire or extreme heat is a subject of intense interest to many industries. A fire-retardant paint has been developed which represents a new chemical approach for preparing intumescent coatings, and potentially, is very important to fire-prevention authorities. The requirements for a superior coating include ease of application, suitability to a wide variety of surfaces and finishes, and stability over an extended period of time within a broad range of ambient temperature and humidity conditions. These innovative coatings, when activated by the heat of a fire, react to form a thick, low-density, polymeric coating or char layer. Water vapor and sulphur dioxide are released during the intumescent reaction. Two fire-protection mechanisms thus become available: (1) the char layer retards the flow of heat, due to the extremely low thermal conductivity; and (2) water vapor and sulfur dioxide are released, providing fire quenching properties. Still another mechanism functions in cases where the char, by virtue of its high oxidation resistance and low thermal conductivity, reaches a sufficiently high temperature to re-radiate much of the incident heat load. The coatings consist of dispersions of selective salts of a nitro-amino-arornatic compound. Specifically, para-nitroaniline bisulfate and the ammonium salt of para-nitroaniline-ortho sulphuric acid (2-amino-5-nitrobenzenesulphuric acid) are used. Suitable vehicles are cellulose nitrate of lacquer grade, a nitrite-phenolic modified rubber, or epoxy-polysulfide copolymer. Three separate formulations have been developed. A solvent is usually employed, such as methylethyl ketone, butyl acetate, or toluene, which renders the coatings suitably thin and which evaporates after the coatings are applied. Generally, the intumescent material is treated as insoluble in the vehicle, and is ground and dispersed in the vehicle and solvent like an ordinary coating pigment. The char found on intumescence is better in terms of yield and physical properties than chars obtained from many previously known intumescent materials. Prior to intumescence, the coating has a density of 85 pounds per cubic foot. After intumescence, the density is approximately 0.3 pounds per cubic loot. The linear expansion of the coatings ranges from 70 to 200 times the applied coating thickness

Intumescent Coatings as Fire Retardants

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