Intumescent sheet material

Flexible intumescent sheet materials having greatly decreased negative expansion characteristics in the range of 200.degree. to 400.degree. C. and which are thermally resistant and resilient after expansion are disclosed. The flexible intumescent sheets are particularly useful for mounting automotive catalytic converter monoliths.

This invention relates to flexible intumescent sheet material having 
greatly decreased negative expansion characteristics in the range of 
200.degree. C. to 400.degree. C. and which is thermally resistant and is 
resilient after expansion. The invention further relates to flexible 
intumescent sheet material useful as a packing for mounting and 
positioning automotive catalytic converter monoliths. Due to the 
relatively high temperatures encountered in the catalytic process, ceramic 
has been the natural choice for catalyst supports. 
Ceramic bodies tend to be frangible and to have coefficients of thermal 
expansion differing markedly from those of metal containers. Thus, the 
mounting of the ceramic body in the container must provide resistance to 
mechanical shock due to impact and vibration and to thermal shock due to 
thermal cycling. Both thermal and mechanical shock may cause deterioration 
of the ceramic support which, once started, quickly accelerates and 
ultimately renders the device useless. 
Flexible intumescent sheet materials particularly suited for use in the 
mounting of automobile exhaust catalytic converters have been developed. 
However, it has been discovered that such intumescent sheet materials, 
disclosed for example, in U.S. Pat. No. 3,916,057 and British Pat. No. 
1,513,808, have a region of negative expansion beginning at about 
100.degree. C. and ranging up to 400.degree. C. Because of the negative 
expansion characteristics of these sheet materials, it has been found that 
the mounted catalyst support may become loose in the temperature range of 
100.degree.-400.degree. C. and until such time as the intumescent sheet 
material has passed through the negative expansion region and expanded 
sufficiently to recover to its original thickness. 
Vermiculite is well known in the art for its ability to exfoliate 
thermally, by treatment with hydrogen peroxide or under the influence of 
microwaves, with an expansion in volume of as great as 20 fold (see e.g., 
U.S. Pat. Nos. 3,753,923, 3,758,415 and 3,830,892). 
Sheet materials have heretofore been known including exfoliated or "popped" 
mica of either the synthetic type described in U.S. Pat. No. 3,001,571 or 
of vermiculite as described in U.S. Pat. Nos. 2,204,581 and 3,434,917. 
Insulating and accoustical sheet materials are described in U.S. Pat. No. 
2,481,391 which contain expanded vermiculite, and a light-weight firebrick 
containing expanded vermiculite is disclosed in U.S. Pat. No. 2,509,315. 
Intumescent compositions have been described employing unexpanded 
vermiculite in combination with various materials. Thus, U.S. Pat. Nos. 
2,526,066 and 3,744,022 disclose plaster wall board compositions 
containing unexpanded vermiculite. The incorporation of the unexpanded 
vermiculite into the wall board provides additional fire resistance but 
dehydration of the gypsum and expansion of the vermiculite together result 
in rapid impairment of the integrity of the board. 
Unexpanded vermiculite is utilized in a fire-retardant mastic coating in 
U.S. Pat. No. 3,090,764 and exfoliation serves as insulation when the 
coating is exposed to fire. Both expanded and unexpanded vermiculite are 
used in fire-protecting coatings of asphaltic compositions described in 
U.S. Pat. No. 3,556,819 and roofing materials containing layers of 
unexpanded vermiculite or other intumescent materials are disclosed in 
U.S. Pat. Nos. 2,782,129 and 3,365,322. 
It is known that the microwave expansion of vermiculite is more effective 
in the presence of polar molecules, such as water, urea, thiourea or 
cations such as Cu(NH.sub.3).sub.4 ++, Na+, Li+, Co+ or NH.sub.4 +. 
It has now been found that when vermiculite is ion exchanged with NH.sub.4 
+ cations and then combined with ceramic fibers in a papermaking 
operation, an intumescent sheet is formed which, when exposed to heat as 
from an engine exhaust, will intumesce (expand) at a temperature about 
100.degree. C. lower than a sheet containing untreated vermiculite, and 
that unexpectedly, the percent negative expansion is significantly 
reduced. 
It has been found that a sheet material may be produced from thus treated 
unexpanded vermiculite, inorganic fibrous materials and binders to provide 
a desirable degree of wet strength. The sheet material can be produced to 
desirable thickness from about 0.5 to about 5 mm. by paper making 
techniques as will be described more fully hereinbelow. 
Suitable binders can include various polymers and elastomers in latex form, 
as for example, natural rubber latices, styrene-butadiene latices, 
butadiene-acrylonitrile latices, latices of acrylate and methacrylate 
polymers and copolymers and the like. Suitable inorganic binders may 
include tetrasilicic fluorine mica in either the water-swelling 
unexchanged form or after flocculation as the exchanged salt with a di- or 
polyvalent cation as well as bentonite or fibrous materials such as 
asbestos. Organic and inorganic binders may be used in combination to 
produce sheet materials according to the present invention. 
The flexible intumescent sheet material is utilized in automobile exhaust 
catalytic converters as a mounting material by expansion in situ. The 
expanded sheet then holds the ceramic core or catalyst support in place in 
the container or canister. The thermal stability and resilience of the 
sheet after exfoliation compensate for the difference in thermal expansion 
of the metal canister and the ceramic substrate, for vibration transmitted 
to the fragile device and for irregularities in the metallic or ceramic 
surfaces. 
The sheet material may be formed by standard paper-making techniques, 
either hand laid or machine laid, taking suitable precautions to attain 
substantially uniform distribution of particles throughout the web. The 
sheet material may be provided with or temporarily laminated to a backing 
sheet of kraft paper, plastic film, non-woven synthetic fiber web or the 
like as desired. From 40 to 65% by weight of intumescent material, 
unexpanded treated flakes of vermiculite ore in particle sizes of from 
about 0.1 up to about 6 mm. and preferably up to about 2 mm. are combined 
in a large volume of water with solids in the proportions 25 to 50% 
inorganic fibrous materials, such as chrysotile or amphibole asbestos, 
soft glass fibers such as available under the tradename chopped E. glass, 
refractory filaments including zirconia-silica fibers, crystalline alumina 
whiskers and alumino-silicate fibers (available commercially under the 
tradenames Fiberfrax, Cerafiber and Kaowool) and 5 to 15% of binder as 
described above. Small amounts of surfactants, foaming agents and 
flocculating agents may also be added before forming the sheet. 
Flocculation is conveniently achieved using electrolytes such as alum, 
alkali or acid. Small amounts of organic fibrous materials may be added to 
impart additional green strength to the green sheet material. The 
intumescent material, inorganic fibrous material and organic latex binder 
are blended together in a large volume of water, of the order of 5 to 100 
times as much by weight and the flocculating agent or agents are added. A 
small amount of surfactant or foaming agent may also be employed in order 
to improve the dispersion of the intumescent material without going beyond 
the scope of the invention. In order to avoid the use of asbestos in 
making the sheet, because of possible health hazards associated with this 
material, substitution of glass fiber materials or refractory (glass or 
crystalline) filaments or whiskers is possible without impairing the 
quality of the sheet. In general, asbestos fibers are less expensive than 
other fibers. 
The sheet is conveniently formed by standard paper-making techniques either 
in a hand-sheet former or Fourdrinier screen. The resulting green sheet is 
compressed to give a dry weight density of about 0.35 g./ml. or more, 
dried at about 90.degree. C. to form a handleable, readily flexible, 
resilient, intumescent sheet material. A strip of the material about 2.5 
mm. thick can be curved to a radius of 5 cm. without cracking. 
Measurement of the usefulness of the intumescent sheet material of the 
invention involves its ability to expand and to generate and maintain 
sufficient force against casing and substrate so as to hold catalyzed 
ceramic substrates in metal containers and also its ability to absorb 
mechanical shock and to accommodate the differential dimensional changes 
resulting from thermal gradients. A method to test this thermal expansion 
behavior is summarized by the following procedure: 
A 9.53 mm diameter sample of intumescent sheet material is placed in a 
Theta Dilatronic II (Model MFE-715) Thermal Mechanical Analyzer, available 
from Theta Industries, Inc., Port Washington, NY. A 1350 gram weight is 
applied on a sample area of 38.5 mm.sup.2 giving an effective load of 
0.345 N/mm.sup.2. The sample thickness versus temperature is continuously 
recorded using an X-Y plotter. The most significant values are the maximum 
percent negative expansion, the temperature at which the intumescent sheet 
begins to expand and the maximum percent thermal expansion.

The following examples will more fully illustrate the best mode 
contemplated of practicing the invention. 
EXAMPLE 1 
A 5 gallon drum is filled with 3.6 gallons (30 lbs.) of water. 5 lbs. of 
ammonium dihydrogen phosphate (NH.sub.4 H.sub.2 PO.sub.4) (available from 
Stauffer Chem. Co.) is added and agitated until the ammonium phosphate is 
dissolved, about 15 minutes. To this mixture 50 lbs. of unexpanded 
vermiculite ore (#4 grade Zonolite, available from W. R. Grace & Co.) is 
added and allowed to stand for fifteen hours after which the liquid is 
poured off and the vermiculite dried at 100.degree. C. Twelve grams of the 
dried sample of treated vermiculite was placed in eight #10 crucibles. 
Each crucible was heat treated at a different temperature--225.degree., 
250.degree., 275.degree., 300.degree., 325.degree., 350.degree., 
375.degree., and 400.degree. C. The contents of each crucible were 
transferred to a 50 ml graduated cylinder and the volume was determined to 
the nearest 0.5 cc. Volume expansions were calculated and are shown in 
comparison to untreated vermiculite in Table I. 
TABLE I 
______________________________________ 
Volume Expansion of Vermiculite Ore 
Expansion Treated Untreated 
Temp. .degree.C. 
% Expansion % Expansion 
______________________________________ 
225 0 -- 
250 3.2 -- 
275 40 -- 
300 96.8 -7.4 
325 112.9 -10.7 
350 173.3 -7.4 
375 193.5 3.7 
400 206.6 67.9 
______________________________________ 
Next, 48 lbs. of alumina-silica ceramic fibers (washed Fiberfrax available 
from the Carborundum Co.) were mixed with water at a 1.5% solids, then 
pumped to a holding tank. To this mixture, 9.6 lbs. of a Hycar 1562X103 
butadiene-acrylonitrile latex (available from B. F. Goodrich Chemical Co.) 
was added and precipitated with a 10% alum solution (sufficient to reduce 
the pH to a range of 4.5-5), then 50 lbs. of the NH.sub.4 H.sub.2 PO.sub.4 
treated vermiculite was added. 
The resulting slurry was pumped out onto a moving vacuum wire belt and the 
water drawn off. The resulting sheet was dried and wound into rolls. It 
had a thickness of 1.3 mm and density of 0.53 g/cm.sup.3. 
Three thicknesses were stacked together and tested for expansion behavior 
over the range 0-750.degree. C. This behavior is shown in Table II. At 
240.degree. C., the intumescent sheet has shown only a 3.6% decrease in 
thickness. At 240.degree. C. expansion now begins and at 255.degree. C. 
the thickness is equal to the starting thickness. 
EXAMPLE 2 
Water (1200 ml) is poured into a mixing chamber of a large Waring Blender 
and to it is added 15.4 grams of alumina-silica ceramic fiber (washed 
Fiberfrax available from Carborundum Co.) followed by vigorous agitation 
for about 20 seconds. Then there is added 3.3 gm of a 
butadiene-acrylonitrile latex binder as 8 gm of 40% solution (available as 
Hycar 1562X103 from B. F. Goodrich Chemical Co.) followed by agitation for 
10 seconds, then the addition of 28 grams unexpanded vermiculite (No. 4 
grade Zonolite from W. R. Grace & Co.) which had been chemically treated 
with ammonium phosphate (40 gms NH.sub.4 H.sub.2 PO.sub.4 in 250 ml water 
to which 250 gms of #4 unexpanded vermiculite was added, then soaked for 
18 hours, filtered, and dried at 100.degree. C.). The fiber, latex and 
vermiculite slurry was further agitated for approximately 15 seconds. The 
latex is flocculated and at least partially deposited on the fibers by 
adding a small amount of 10% alum solution (sufficient to reduce the pH to 
a range of 4.5 to 5.0) to the slurry and mixed for about 10 seconds. The 
suspension is cast onto a hand former to give a hand sheet of about 
19.times.20 cm, total area about 380 cm.sup.2, which is dried. The sheet 
density averages 0.395 gm/cm.sup.3 with a thickness of 2.8 mm. The sheet 
is flexible and can be rolled around a radius of 5 cm. 
Expansion behavior of this sheet was tested and presented in Table II. 
EXAMPLE 3 
A solution of 80 grams of ammonium carbonate [(NH.sub.4).sub.2 CO.sub.3 
--Mallinckrodt AR grade] in 250 ml water was prepared and 250 grams of 
unexpanded vermiculite ore (#4 Zonolite, W. R. Grace) was added. The 
vermiculite was soaked for 18 hours, then filtered and dried at 
100.degree. C. in a forced air oven. A hand sheet was prepared using the 
same procedures and forming techniques as in Example 2 except that the 
ammonium carbonate treated vermiculite was used. The resulting intumescent 
sheet had an average density of 0.414 gm/cm.sup.3 and thickness of 2.87 
mm. One thickness of the sample sheet was tested for expansion behavior. 
Results are shown in Table II. 
EXAMPLE 4 
An ammonium acetate solution was prepared for cation exchange of 
vermiculite. A total of 60 grams of NH.sub.4 C.sub.2 H.sub.3 O.sub.2 
(ammonium acetate available from Mallinckrodt, Inc.) was added to 250 ml 
of water and agitated. To the resultant solution, 250 grams of unexpanded 
#4 vermiculite ore was added and allowed to soak for 18 hours. The 
vermiculite slurry was filtered then dried at 100.degree. C. A hand sheet 
was prepared using this ammonium acetate treated vermiculite as described 
in Example 2. The resulting intumescent sheet was flexible and had a 
density of 0.418 g/cm.sup.3 and thickness of 2.84 mm. One thickness of the 
hand sheet was tested for expansion behavior and reported in Table II. 
EXAMPLE 5 
An ammonium hydroxide solution was prepared using 250 ml NH.sub.4 OH (30% 
NH.sub.3) available from Mallinckrodt, Inc., and 250 ml water to which 250 
grams of #4 unexpanded vermiculite was added. The resultant slurry was 
soaked for 18 hours, then filtered and dried at 100.degree. C. A hand 
sheet was prepared using the ammonium hydroxide treated unexpanded 
vermiculite ore as described in Example 2. The resulting flexible 
intumescent sheet had a density of 0.415 gms/cm.sup.3 and thickness of 
2.84 mm. Expansion behavior was determined and the data is presented in 
Table II. 
EXAMPLE 6 
A urea solution was prepared using 50 gms of NH.sub.2 CONH.sub.2 (available 
as urea from Baker Chemicals) in 250 ml water to which 250 grams of #4 
unexpanded vermiculite had been added. The resultant vermiculite slurry 
was soaked for 18 hours, then filtered and dried at 100.degree. C. A 
handsheet was prepared using the urea treated unexpanded vermiculite as 
described in Example 2. The resulting intumescent sheet had a density of 
0.466 gms/cm.sup.3 and a thickness of 2.31 mm. Expansion behavior was 
determined and the data presented in Table II. 
EXAMPLE 7 
A urea solution was prepared using 150 gms of NH.sub.2 CONH.sub.2 
(available as urea from Baker Chemicals) in 250 ml of water to which 250 
grams of #4 unexpanded vermiculite was added. The resultant vermiculite 
slurry was soaked for 18 hours, then filtered and dried at 100.degree. C. 
A handsheet was prepared using the urea treated unexpanded vermiculite as 
described in Example 2. The resulting intumescent sheet had a density of 
0.437 gms/cm.sup.3 and a thickness of 2.39 mm. Expansion behavior was 
determined and the data presented in Table II. 
TABLE II 
__________________________________________________________________________ 
INTUMESCENT SHEET EXPANSION BEHAVIOR 
PERCENT VOLUME EXPANSION Max % Temp at 
@ .degree.C. Negative 
Expansion 
which 
25 100 
200 300 350 400 500 
600 
700 
800 
Exp. Temp Exp 
__________________________________________________________________________ 
= 0% 
Sheet of U.S. 
Pat. 
No. 3,916,057 
0 -3.4 
-9.4 -11.1 
-11.1 
- 9.8 
3.0 
11.0 
11.0 
10.3 
-11.1 
380 475 
Sheet of British 
Patent 1,513,808 
0 -4.9 
-12.6 
-15.0 
-15.3 
-11.3 
26.2 
45.6 
50.5 
47.6 
-15.3 
385 425 
Example 1 
NH.sub.4 H.sub.2 PO.sub.4 
0 -0.9 
-3.6 20.9 31.8 45.5 61.8 
67.3 
69.1 
66.4 
-3.6 245 255 
Example 2 
NH.sub.4 H.sub.2 PO.sub.4 
0 0 -3.2 -4.7 27.1 32.8 55.6 
68.9 
71.7 
64.1 
-4.7 310 320 
Example 3 
(NH.sub.4).sub.2 CO.sub.3 
0 -1.0 
-4.8 -6.7 0 10.5 52.4 
63.8 
63.8 
52.3 
-6.7 310 350 
Example 4 
NH.sub.4 C.sub.2 H.sub.3 O.sub.2 
0 -1.0 
-7.7 -9.6 7.7 23.1 61.5 
71.2 
71.2 
65.4 
-9.6 300 325 
Example 5 
NH.sub.4 OH 
0 0 -6.6 -9.4 45.3 50.9 61.3 
66.0 
66.0 
57.7 
-9.5 300 315 
Example 6 
NH.sub.2 CONH.sub.2 
0 -9.5 
-13.7 
-12.6 
-3.2 19.0 52.6 
61.1 
65.3 -13.7 
290 355 
Example 7 
NH.sub.2 CONH.sub.2 
0 -7.6 
-12.0 
50.0 70.0 93.0 92.0 
92.0 
62.0 
49.0 
-12.0 
200 225 
__________________________________________________________________________ 
Examination of Table II will clearly show that the sheets of the present 
invention begin expanding at a much lower temperature than a 
representative prior art sheet, have significantly lower maximum percent 
negative expansion and return to their original starting thickness at 
significantly lower temperatures. 
The sheet of British Pat. No. 1,513,808 is seen to have a maximum percent 
negative expansion (decrease in thickness) of 15.3% at 350.degree. C. 
Expansion of the sheet began at 385.degree. C. and at 425.degree. C., its 
thickness equalled its starting thickness. It will be appreciated that the 
high percent negative expansion can cause a severe problem with a loose 
catalytic converter while and immediately after the automobile has been 
driven off the assembly line. Since the automobile is run for such a short 
time, the catalytic converter and the intumescent mounting sheet may not 
have had enough time to reach normal operating temperatures in the range 
of 500.degree.-800.degree. C. Temperatures in the range of 
100.degree.-400.degree. C., however, are reached, which are sufficient to 
cause the intumescent mounting sheet to contract and pull away from the 
ceramic monolith due to the negative expansion characteristics of the 
sheet. The catalytic converter is now less tightly retained than at the 
time of assembly and extremely susceptible to damage from mechanical shock 
due to impact and vibration in the transportation and early driving 
phases. To overcome this severe problem, some automotive manufacturers 
have preheated the catalytic converter assemblies after fabrication but 
before mounting onto an automobile to insure that the intumescent mounting 
sheets had been properly expanded. This procedure has been unsatisfactory 
due to the high treating costs and the sacrifice to the appearance of the 
unmounted converter assemblies. 
The intumescent sheets of the present invention have all but eliminated the 
need for such pretreatment of converter assemblies.