Fohlen, G. M.

Parker, J. A.

English

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ATTN OF: GP 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
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us~ /Sc i en t i f i c  & Technical Inf ornation D i v i ~ i o n  
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U. S. Patent No. 
Government or 
Corporate Employee 
Applied Space products, Inc. 
Pa10 Alto, California 
8 
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Source (if applicable) t 
NASA Patent Case No. .I ARC-10099-1 
NOTE - If th i s  patent covers an invention made by a corporate 
employee of a NASA Contractor, the following is applic&ler 
yes @ NO O 
pursuant t o  Section 305(a) of the National Aeronautics and 
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Copy of Patent crited above 
https://ntrs.nasa.gov/search.jsp?R=19710005994 2020-03-17T02:38:59+00:00Z
United States Patent 06, pate,kd act, 3,535,138 20, 1970
1 2 
vention, this active material is para-nitroaniline sulfate 3,535,130 
INTUMESCENT PAWTS having the general formula 
James E. Webb, Administrator of the National Aeronau- 
tics and Space Admiowation, wilh r e s m  to an in- 
vention of John A. Parker, Los Altos, and George M. 5 
Fohlen, Millbrae, Calif. 
N o  Drawing. FSled Feb. 9, 1968, Ser. No. 704,224 
Int. CI. C09d 5/18 
U.S. CI. 1 0 6 1 5  'laims wherein a and 6 are molar proportions and are pref- 
10 erably both unity o r  near unity. Instead of sulfuric acid 
ABSTRACT OF THE DLSGUlSURE salts, sulfonic acid salts may be employed, e.g., the salts 
of benzene and toluene sulfonic acids. 0-nitroaniline sul- 
This invention relates to intumescent paints useful for fate or sulfonate may also be used, as may the sulfates 
fire protection. The intumescent material is an aromatic and sulfonates of other nitro amino aromatic communds 
nitroamino compound in the form of its sulfate, either 15 as explained hereinafter. 
dissolved or dispersed in a vehicle, or prepolymerized, Hereinafter, for convenience, para-nitroanaline will be 
or both. Upon heating, such a paint intumesces, chars referred to  as PNA. 
and provides a flame resistant coating. The acid sulfate of PNA may be prepared in various 
ways. We have found it convenient merely to mix PNA 
20 in 98% sulphuric acid in the calculated amount with o r  
~h~ invention described herein was made in the per- without the use of a solvent. The preferred acid salt is 
forn~ance of work under a NASA contract and is subject the equimolar *It* 
to the provisions of Section 305 of the National Aero- 
nautics and Space Act of 1958, Public Law 85-568 (72 25 
Stat. 435; 42 USC 2457). 
This invention relates to intumescent paints which are 
intended for fire protection. 
At present, paints are available which, when applied to 
a surface and then subjected to heat, will intumesce and 30 This salt is a pow hich is mentioned in Beil- 
expand. The expanded material, being of a porous heat stein in vol. XII, page 715. 
insulating character, provides a degree of protection As a powdery solid, PNA sulfate requires a vehicle be- 
against heat transfer, flame, etc. However, previously fore it can be applied as a paint. Proper selection of a 
available intumescent paints are unsatisfactory for sev- vehicle is important. We have found that cellulose ni- 
era1 reasons, such as the following: 35 trates of the grade commonly used for lacquers are good 
Conventional intumescent paints have very limited ef- vehicles, such being dissolved in suitable solvents such as 
ficiency in applications of interest such as the protection alcohols and ketones. The selected vehicle should be one 
of substrates under a l/lo" steel plate or sheet. In a typical which undergoes chemical decomposition without explo- 
fuel fire, producing what is equivalent to radiative heat- sion at temperatures of about 150-200" C., or which is 
ing rates of 30,000 B.t.u. hr. ft.2, the back face tempera- 40 thermoplastic at such temperatures. In either case, the 
ture rise of unprotected 7/50" steel plate may be from 65" vehicle does not interfere with intumescence, as would 
to 400" F. in as little as 20-30 seconds. The coatings re- a vehicle which remains rigid at such temperatures and 
sulting from application of the subject paints of this in- therefore restrains intumescense. 
vention to this substrate in thickness of 50-60 mils re- A suitable example of a vehicle is a product available 
quire as much as 5 minutes to reach 400" F. 45 commercially as Parlodion (trademark of Mallinckrodt 
Conventional intumescent paints are usually sensitive Chemical Works for a purified form of pyroxylin strips) 
to attack by water and other solvents. The subject paints and a suitable solvent for this vehicle is methyl ethyl 
of [hi\ invention are resistant to water immersion and to ketone. Other similar cellulose nitrates and other similar 
the action of jet fuel and similar flammable hydrocarbons. solvents will be apparent to one skilled in the art of 
Conventional intumescent coatings are not as resistant 50 paints and lacquers. 
to scuffing and abrasion as are those of the present in- In a typical formulation, 35 to 55 parts of PNA sulfate 
vention. are dispersed in 5-10 parts of cel lulw nitrate and the 
Chars resulting from thermal action on conventional balance (q.s. bo make 1 0  parts) of wlvenl. 
intumescent coatings are usually sensitive to thermal ero- Paints prepared in this manner are adherent (o many 
sion by flames. Chars formed by -paints of the present 55 types of surfaces, for example woad, gawr, asbe8%orrj 
invention are much more stable. aluminum, steel even when primed with zinc chromate. 
ft is an object of the present invention to provide in- When a surface coated wilk sctch a p i n t  is h e a a ,  @ 
tumescent paint9 which are more eRe:ecfive than tho% by fire, the paint intumesces Lo a very hi& degre. 
heretofore available and which have one or more of the example, a layer of such paint 0.055 inch thick will 
advantage\ indicated above. 60 i r f lumc~e Bcr a thickness of I to 1% inclle. In so doing, 
The above and other objects of the invention wjll be it f o r m  a black polymer consisting of closed cells, having 
apparent from the ensuing description and the appznded cb high degrse of heat resislanca. a d  hermat stability and 
claims. having a low thern~al conductivity. The volatile product 
In accordance with the invention, a certain class of po- of intumescenoe is for the most part water and sulfur 
lymerizable, intumescent material is employed, either in 65 dioxide, which act as good savengew to swwp away on- 
monomeric form or in partially polymerized form, such corning hot gae8 and to suppress flames. 
nla1eri;ll being di\per\ed in a suitable vehicle if necessary. We believe that the reactions which occur during in- 
In the preferred form of this embodiment of the in- tumescencd of the sulfate of PNA are inter-molecular 
3,535,130 
3 4 
condensation reactions involving the amino and nitro Thus we have ddiscovered &at it is mssibte to ptymerize 
groups lo link and condense rings and form new rings. PNA sulfate to a solid material witlaout causing intu- 
The sulfuric acid is reduced lo SO2 during intumescence mescence and that the resulting solid of moderakly low 
and becomes part of the volatile gazs. The empirical molecular weigkt (is. ,  a low degree of ptgmerizahion) 
formula of the black polymer formed at  240-250' C. intumesces when heated above a b u t  100-200" C. This 
is approximately CeH3N20S~.3 ,  indicating that C ,  N, N ' solid, moreover, is soluble or disprsible in volatile sol- 
and 0 enter into ring and polymer formation. Excess vents. Such solutions, disprsiobs and emulsions may be 
PNA, if any, is lost in large part by violatilization. applied as paints. 
The yield of char depends upon the time of heating, The following examples will further illustrate the prac- 
degree of flame exposure, etc. Yields of 25 to 55% are ,,, tice and advantages of the invention. 
common. These chars are not very adherent to surfaces 
unless the surface has been primed, e.g., by means of an EXAMPLE I 
epoxy or polyurethane primer. The char has a closed A mixture of PNA sulfate prepared by reacting 239 
cell structure, is thermally and oxidationally stable and grams of PNA witk 171 grams of concentrated sulfuric has a density typically about 0.1 to 0.3 pound per cubic 18 ,,id is dispersed in a solution obtained by dissolving 60 As a result, the char has very low thermal cOn- grams of parlodion in 285 grams of ethyl ketone ductivity. Intumescence begins about 220-240" C., the and 114 grams of ethyl alcohol. ~-i~ mixture is ground 
char continues to react and give off low molecular weight in a pebble mill until a dispersion of 4-5 on the H~~~~~~ (SO2, water, COa, etc.1 UP to 500" C. The char scale is atta&d. A stable paint is then obtained, which is stable up to 1000' C. 20 may be sprayed, rolled o r  brush applied as a typical Emphasis has been placed 'POn the "Ifate PNA; lacquer giving a wet film density of 1.10. After air dry- it is the preferred material. However, the sulfate (or ing, a film density in the range of to is obtained, 
sulfonate) o r  ortho nitroaniline and even meta-nitro- with abrasion resistance. The unpigmented coat- 
aniline may be used although the meta compound does ing is opaque and re~-brown in color, T~ improve the 
not intumesce as much as desired. 25 coating's resistance to attack by H20, a top coating of In general, sulfates and sulfonates of nitro amino aro- the vehicle of the class wed for the intumescent coating, 
matic generally may be used where witions e.g., cellulose nitrate, can be used. With the top coating, in ortho relation to the amino and nitro groups are open. the paint is completely unaffected by water and fuel Examples of such nitro amino aromatic compounds in immersion. 
addition to those mentioned above are the following: 30 When exposed to a temperature of abut 2500 c., this 
coating expands about 100 times volumetrically, and un- 
H 2 N ( , 0 o a  
degrees a change in density from 85 Ib./cubic foot to 0.3 
Ib./cubic foot. A coating of about 50 mils when appiied 
to xe steel plate and exposed to a jet fuel fire gave a back 
33 faca kmperature rise of 350" F. in about 4 minutes. 
Nlrp 
I I-nitro41iaph~hyl. 11 4- amino-4'-nitro blplianyl EXAMPLE I1 
anilue 
To prepare a polymeric derivative of PNA acid sulfate, 
NO: NII: 40 a mixture of 239 grams of p-nitroaniline and 171 grams 
of sulfuric acid is heated carefully to about 150" C. for 
2 hours to give a dark viscous mass which can be ad- 
mixed with solvents and short inorganic fibers such as 
NHS NO$ glass or carbon or fillers. It can then be applied to give 
I11 1,6diaminw4,8di- IV 2amino-7-nitro-fluorene a suitable coating after air drying. 
nitro naphthalene 4.3 It  will therefore be apparent that a new and useful 
intumescent paint has been provided. 
We claim: 
1. A composition of matter comprising: 
(a)  35-55 parts by weight of a material which under- 
NO¶ 50 goes intumescence upon heating, 
N (b) 5-10 parts by weight of a cellulose nitrate ve- 
H hicle, and 
V 3-amino-Biiitro furan VI bnltmimtoic anhydride (c) from 35-60 parts by weight of a lower alcohol or 
ketone solvent for components (a)  and (b); NHCOCHo 65 said intumescent material being an acid salt of an aro- 
matic nitro amino compound of the group consisting 
of the sulfuric acid salt, benzene sulfonic acid salt, 
o r  loluene sulfonic acid salt of para-nitromiline, 
N O S  orlho - nitroarmiline, 1 - nitro-4-naphthylamine, 4- 
VII 4-nltro-acetaulllde CiO aminl - 4'-nitro - biphenyl, 1,5-diamino4,8-dinitro 
nahhalena.  2 - amino-7-nitro-auorene, 3-amino-5- 
It will be seen that the class of ovrabtble m m ~ u n d s  
includes carbocyclic and heterocyclic rings; that an ortho 
position may be occupied as in 5-nitro-isatoic anhydride, 
provided the opttjlcr substibent is readily re-emowd on 
heating (in this case, by expulsion of C 0 2 )  and that the 
nitro and amino groups need not be in convendonal p- 
or o- relation but may be separakd by several carbon 
atoms. Thus in the compound 4-amino-4' nitrodiphenyl, 
the amino and nitro arouas are seaarated bv coniuaated 
system and effectively-in &ra relatibn lo each oth&.- 
We have also discovered that the n e d  for a vehicle 
such as cellulose nitrate may be dispensed with by carry- 
ing out a controlled prepolynlerization of PNA sulfate 
(or a substitute) so that i t  is a viscous or solid male~ial. 
ni&o haan; 5-nitro-isatoic anhydride, or 4-nitro- 
ase tadge  asld mixtures of said salts, 
2. The cscmpositioa of claim 1 wherein the acid sale 
us i s  the sulfuric acid salt of para-nitroaailine, 
3. The ilornposition of claim I wherein ehe acid salt 
is Ihe k e r z a e  sullonic acid sale of para-nilroaniline. 
4.TFhe composition of claim 1 vdherein the acid salt 
is the toluene suIfonic acid salt of para-nit-roaniline. 
70 5. The cornpsition of claim 1 wherein the solvent is 
meUlyi ethyl kebne. , 
6, A mehad of protecting a solid surirace against fire 
and heat which comprise? applying to the surface an ad- 
herent continuous coating compriuing: 
75 (a)  35-55 parts by weight of an intumescent rr~ateriirl 
5,635, $30 
5 
which i s  an acid salt of an aromatic nitro auimo 
8 
References Cit& 
compound of the group consisting of the sulfuric acid 
salt, benzene sulfonic acid salt, or toluene sulfonic UNITED STATES PthgEMTS 
acid salt of para-nitroaniline, ortho-nitmaniline, f -  958,335 4/1904 Schmidt ------------ I S 1 9 5  
nitro-4-naph(hylamine, 4 - amino-4'-nitro - biphenyl, 1,3157216 911919 Doerflinger --------- f06--i95 
1,s - &amino - 4,s - &itro naphtha]ene, 2 - amino- 2208,640 711940 McGill -------- 106---195 XR 
7 - nitrofluorene, 3 - amino - 5 - nitro furan, 5-nitro- 3313 1,071 411964 Hunter et al. -------- 1 0 6 1 5  
isatoic anhydride, or 4-nitro-acetanilide, and mix- FOREIGN PATENTS 
tures of said salts, 
(b) 5-10 parts by weight of cellulose nitrate, and lo  963,674 4/1957 Germany. (c) from 35-60 parts by weight of ethyl alcohol- JULIUS FROME, primary  in^^ 
methyl ethyl ketone solvent. 
7. The method of claim 6 wherein the acid salt is the L. B. HAYES, Assistant Examiner 
sulfuric acid salt of para-nitroaniline. 
8. The method of claim 6 wherein the acid salt is ~e 16 U.S. C1. X.R. 
benzene sulfonic acid salt of para-nitroaniline. 106186 ,  195; 117-136; 2 5 L 8 . 1  * 


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