CA1042587A

CA1042587A - Intumescent sheet material

Info

Publication number: CA1042587A
Application number: CA237,979A
Authority: CA
Inventors: James A. Woolley; Robert M. Wydeven
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1974-11-04
Filing date: 1975-10-20
Publication date: 1978-11-14
Also published as: DE2549223A1; JPS5169507A; DE2549223C2; GB1513808A; JPS6238397B2; JPS6296581A

Abstract

Abstract of the Disclosure A flexible intumescent sheet material is provided containing vermiculite or other expandable mica employing inorganic fibers and elastomeric binder, which is useful in protecting catalytic pollution control devices from thermal or mechanical shock.

Description

~ ~~ 911,883 1~)42S87 INTUMESCENT SHEET MATERIAL
This invention relates to flexible intumescent sheet material which is thermally resistant and is resilient after expansion. ~he invention further relates to the use of the flexible intumescent sheet material as a packing in positioning catalyst supports within containers.
It has become recognized that catalytic devices are needed for (1) oxidation of carbon monoxide and hydrocarbons ~-and (2) reduction of the oxides of nitrogen in automobile exhaust in order to control pollution. Due to the relatively high temperatures encountered in these catalyzed processes, , ceramic has been the natural choice for catalyst supports.
Particularly useful supports are provided by ceramic honeycomb structures as described, for example, in U.S.
RE 27,747. ~ -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 cera-mic 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 j shock may cause deterioration of the ceramic support which, once started, quickly accelerates and ultimately renders the device useless. One material which has been foùnd useful as a packing material for these purposes is the composition of 30-85% intumescent material, 0-60% inorganic fibrous material, 10 to 70% inorganic binder and optionally small amounts of organic binders, etc. described in the copending Canadian application of R. A. Hatch and J. R. Johnson, Serial No. 205,533 filed July 24, 1974 having a common ~ , .

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1~4ZS87 assignee with the present application. We find that this material offers some disadvantages in application in that it tends to be rather stiff. This makes it difficult to roll the sheet material into supply rolls of small diameter.
It is an object of this invention to produce a flexible intumescent sheet material and particularly an intumescent sheet material which can be rolled around an arc with radius of 5 cm. or less without cracking when at least about 2.5 mm. thick. Other objects will be apparent 10 hereinelsewhere. -In accordance with these and other objects of the invention, it has been found that a sheet material may be pro-duced from unexpanded vermiculite, inorganic fibrous materials and organic binders. 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. -Organic 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.
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 ~)4Z587 :
and ror irregularities in the metallic or ceramic ~urface~.
The sheet material may be rormed by standard paper maklng techniques, elther hand lald or machlne lald, taking suitable precautions to attain substantially uniform distribution of particles throughout the web. The sheet material may be provided with or temporarily lamlnated to a backing sheet Or kraft paper, plastlc fllm~ non-woven synthetic rlber web or the like as desired. From 30 to 75 by weight of lntumescent material, unexpanded beneficiated flakes of vermiculite ore ln particle sizes of from about 0.1 up to about 6 mm. and prererably up to about 2 mm. are combined in a large volume of water with solids in the ~ ~;
proportions 20 to 65% lnorganic flbrous materials, such as chrysotlle or amphlbole asbestos, soft glass rlbers such as avallable under the tradename chopped E. glass, re~ractory --~ril~ments lncludlng zirconla-sillca fibers, crystalline alumina whlskers and alumino-slllcate ~ibers (available commerclally under the ~ ~ berfrax, Ceraflber and Kaowool) and 5 to 20% Or elastomer as descrlbed above. Small amounts Or sur~actants, foaming agents and floculatlng agents may also be added before ~ormlng the sheet.
Flocculation is convenlently ach~eved uslng electrolytes such as alum, alkall or acld. Small amounts Or organl¢ ~lbrous materials may be added to lmpart addl-tlonal green strength to the green sheet materlal. Theintumescent material, lnorganlc flbrous materlal and organlc latex blnder are blended together ln a large volume o~
water, o~ the order o~ 5 to 100 times as much by welght and the ~locculating agent or agents are added. A small amount Or surfactant or foamlng agent may also be employed in order ; ~3~

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1~14;~587 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 cry~talline) 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 Four-drinier screen. The resulting green sheet is compressed to ~ -give a dry weight density of about 0.5 g./ml., or more, dried at about 90 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. Intumescent sheet materials of the invention are expanded at temperatures up to 500 to 800 C.
Measurement of the usefulness of the intumescent sheet material of the invention involves estimate of 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 yet absorb mechanical shock and to accomodate the differential dimen-sional changes resulting from thermal gradients. Themethod employed is summarized by the following procedure:
A preweighed 7.5 cm. diameter sample of intumescent sheet material is placed between fused silica platens, as-sembled within a furnace mounted on the frame of a suitable testing machine, such as an Instron. The cross-head of the . . . . .. . . . .

1~4Z587 testing machine is then ad~usted so that the spacing between the fused silica platens is 3.56 + .03 mm. The corresponding force in (Newtons) is noted and designated -; - ;
as "preload force". The furnace is then heated to 625 C.
at a rate of about 300 C./hr. and the force generated is monitored on a strip chart recorder. The maximum force generated at 625 C. is noted. After allowing 20 minutes for furnace temperature and force stabilization, usually with a gradual decline from maximum force, the spacing -between the platens is varied between 3.56 + .03 mm. and -~
3.05 + .03 mm. for 120 times over about 10 min. These represent approximately maximum difference in dimensions due to temperature differences normally encountered between a substrate of 11.8 cm diameter in a casing of 12.4 cm.
inside diameter. The residual forces at the two spacings are noted initially and on the final cy`cle and are designated . .... . .
as "hot residual forces." The furnace is then cooled to 100 C. or lower and the spacing between platens is again varied 120 times between 3.56 and 3.05 mm. over about 10 min., the residual forces are again noted and are designated as "cold residual forces." The tested sample is then removed and reweighed to determine the weight of the thermally stable inorganic constituents. This weight is used to calculate the inorganic bulk density for the 3.05 mm. spacing. These densities usually ~re in the range of 0.4 to 1.1. The above-noted forces in Newtons are divided by the area of the sample, 45.58 cm.2, and converted to pressures in Newtons/cm.2.
The most significant values are the maximum pressure at 625 C., the hot residual pressure at 625 C. and 3.56 mm.
spacing and the cold residual pressure at 3.05 mm. spacing.

1~4'~587 Preload pressures of up to about 17 Newtons/cm.2 are typical depending upon the composition and density of the sample employed. Maximum pressures are rarely in excess of 100 Newtons/cm~ .
Hot and cold residual pressures range from 3.5 to 35 and 0.7 to 14 Newtons/cm.2, respectively, again depending on the composition and mass. In general, the greater the concentration of the intumescent material and the greater the sample density, the greater the pressures generated.
In employing an intumescent packing material with ceramic structures and particularly the present intumescent sheet materials, it is important to note that the force ~- -exerted against an unyieldable container during exfoliation ~ :
of the intumescent sheet may be great enough to crush the 15 ceramic substrate. Therefore, the thickness, density,~- -mass and resilience of the mat, its expandability and the gap between the cerami~c substrate and the container must be considered in designing and applying the intumescent -sheet material.
The mounting material o~ the invention is also tested using a "hot-shake" test which is an extremely severe accelerated test. This test is performed on a catalyst canister assembly using an exhaust gas simulator, which ~ simulates thermal conditions of exhaust gases from an j 25 engine and with the assembly coupled to a vibrator which simulates the extreme vibration of automotive conditions.
Failure of a mountlng system is determined by measuring the time required to displace a core from the canister , by about 3 mm. The displacement occurs as a result of mounting material failures produced by thermal shock, .' ,; ~
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: , 1C)~2587 mechanical s~ock, or a combination of l)oth. No data are available correlatin~ the total hours on the "hot-shake"
test equipment to mlles Or normal or test drlving.
A test catalytic canlster assembly is simultaneously tested ror mechanical and thermal shock resistance by attaching the catalytic converter assembly to a l~laremont Exhaust Gas Simulator, i~odel E~,S-3, and a L.A.B. Vibrator, -l~odel RV-16-50, available ~rom L.~.B. Corp., .Scaneateles, New York. The exhaust gas simulator ls set to produce 10 about Z8 + 2.8 g./sec. of propane exhaust gas at 732 +
: . . - --28 C. measured at the catalytic converter inlet. The -Vlbrator produces a converter movement Or about 5 mm. at ~ ~-75 Hz. This provldes acceleration of about 60 times that of gravity. Failure Or the mounting is derlned as time requlred to dl~place the core about 3 mm. An assembly made u~ing the mounting material o~ the invention assembled as described above will usually not fall withln 15 hours, i.e., 900 minutes. Survival for~that time i~ usually ~ -considered adequate as most such assemblies will then also sur~lve for much lon~er times, up to 100 hours.
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Having described the invention in general terms, -lt i8 now more specifically illustrated by examples.
The following examples will more fully illustrate -the best mode contemplated Or practicing the lnvention.
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Example 1 Water (1200 ml.) is poured into the mixing chamber Or a large Warlng 31endor and to lt ls added 13.34 g. Or glass fiber (washed Flberrrax available from the Carborundum Company) ~ollowed by vigorous a~itation for about 20 seconds. -30 Then there ls added 6. 6r g~ o~ styrene-butadiene as 16.68 g.

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~4'~587 of 40% latex (available as Hycar* 1562 x 103 from B. F.
Goodrich Chemical Co.) followed by agitation for 10 seconds, the addition of 46.7 g. unexpanded vermiculite ore (No. 3 grade Zonolite*,~ about 0.4 to 1.7 mm. diameter 5 from W. R. Grace and Co.) and further agitation for about 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) to the slurry and mixing for about 10 10 seconds. The suspension is cast onto a hand former to give a hand sheet of about 19 x 20 cm., total area about 380 cm.2, which is dried. The dry sheet is too low in density and an important step is to densif~ it. ~he sheet is compressed between platens to about 2.2 mm. thickness to give a density 15 f about o.8 g./ml. `It is flexible and can be rolled around a radius of 5 cm.
Strips of this prepared sheet are placed in the space between an about 11.8 cm. diameter cylindrical catalyst-impregnated ceramic substrate and an about 12.4 diameter 20 cylindrical container. The assembly is heated to 625 C. from room temperature at a rate of 300 C./hr. to exfoliate the -green sheet~ resulting in a securely mounted ceramic core .. . .
within the container.

Example 2 An intumescent sheet of the invention is prepared as described above in Example 1 using 2400 ml. of water, 22.14 g. glass fiber, 5.80 g. of styrene-butadiene (14.50 g. of 40~ latex), and 77.47 g. of vermiculite ore. It is cast as a sheet and compressed to about 3.5 mm. thickness. It can be rolled around a curve of radius 5 cm. without cracking *trade mark .

1~)4'~S87 portion of the sheet of about 45.58 cm.2 (weighing 12.76 grams) is placed between fused silica plating and tested as described above. It is first heated to 625 C. at 300 C./hr., and found to generate a maximum pressure of about 75 Newtons/cm.2 and thereafter to give hot and cold residual pressures in Newtons/cm.2 as indicated in Table 1.

Table 1 Spacing Residual Pressure at Residual Pressure at 625 C 25 C.
Initial after i20 Initial after 120 cvcIes c.Ycles v 3.56 mm. 74.6 49.7 14.8 10.8 3.05 mm. 16.1 3.3 Strips of the sheet material are placed in the spaces between an about 11.8 cm. diameter catalyst impregnated ceramic substrate and a mild steel cylindrical container of about 12.4 cm. inside diameter as described in Example 1 and heated to 625 C. from room temperature at a rate of about 300 C./HR. to exfoliate the intumescent sheet. The ceramic substrate is found to be securely mounted within the metal container. Such ring flanges and end cones are subsequently weIded to the metal container to produce a complete catalytic -converter assembly.

Example 3 Using the same procedures and forming techniques as in Example 1, intumescent sheets of varying thicknesses compressed to different densities are made using 7.5% Hycar*

1562glO3 binder, 30~ ~iberfrax* glass fiber and 62.5~ No. 4 unexpanded vermiculite ore. These resulting intumescent ~- 30 sheet materials are used to mount catalyst impregnated ceramic ' ~ .

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~4Z5~37 substrates in complcte catalytic converter as~emblies as descrlbed ln L`xample 1. The amounts of mountinr material provide inor~anic residues at ~. ns mm. thickness, hereln referred to as "end llSe densities", ran~lng from .32 g./ml.
to 1.12 g.~ml. The converters are t~len sub~ected to "hot shake" testing. The converter ln which there was an end use density of 0.32 K./ml. railed in 15 min., the others Or 0.48, 0.64, 0.80, o.gG and 1.12 g./ml. survived for 900 mlnutes when the tests were terminated.
Portions Or sheet materials of end use density Or 0.48, o.64 and o.80 are also characterized as to pressure genera-tion as described above. These showed maximum pressures of 10.5, 22.4 and ~3 Newtons/cm.2, respectively. These are tabulated in Newtons/cm.2 in Table 2.
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Table 2 1 ~ -Sample end use density Spacin~ Residual Pressure Residual Pressure g./ml. at ~6?5ff C. at 25 C. --Initialafter 120 Initialafter 120 __ cycles c~cles .48 3-56 4.3 1.7 0 0 0.4~ 3.0524.1 20.6 0.3 0.1 `

o.6ll 3.56]4.5 10.4 0 o -: -250.64 3 0552.6 47.6 1.8 1.3 0.80~ 3-5635.7 26.7 0.2 0.1 o.80 3.0598.1 9.0 13.8 9 6 Example 4 Uslng the 8ame batching and rorming techniques, as in ~xample 1, an intumescent sheet Or 2 1 mm. thickness and bulk density of .80 g./cc. is made usin~ the prccedures Or -10~

~4ZS~37 : -Example 1 to contain 12% styrene-butadiene binder, 35%
glass fiber, and 53% No. 4 vermiculite ore (size range .1 mm. to .6 mm. in diameter). This material is then used to fabricate a complete catalytic converter assembly as also described in Example 1. It is sub~ected to the "hot shake" test as described above and readily survives for 900 minutes. Similarly prepared catalytic converters in which the mounting material is an Inconel* ~-750 wire mesh, vermiculite ore, expanded vermiculite or a sheet -~
10 of glass fiber and latex without vermiculite fail to survive -for 900 minutes. The'-converter employing wire mesh survives for 415 minutes, the others all less than 45 minutes. In each case, except for the wire mesh, the same end-use bulk density of mounting material of o.48 g./ml. is attained.

ExampIe 5 The intumescent sheet materials of Examples 1 to 4 are provided with backing sheets of nonwoven webs of synthetic fiber or kraft paper and wound into rolls. It is - :
found that the rolls are readily unwound without tendency -for sticking between consecutive convulutions.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A flexible intumescent sheet material consisting essentially of from 30% to 75% by weight of expandable mica in particle sizes ranging from 0.1 to 6 mm, from 20% to 65% by weight of inorganic fibrous material and from about 5% to 20% of organic elastomeric binder, said sheet material having a density when dry of at least about 0.5 g./ml.

2. An intumescent sheet material according to claim 1 in which the expandable mica is vermiculite.

3. An intumescent sheet material according to claim 1 in which the inorganic fibrous material is asbestos, soft glass fiber or refractory alumino-silicate fiber.

4. An intumescent sheet material according to claim 1 additionally having a backing sheet of kraft paper, plastic film or nonwoven synthetic fiber web.

5. A process for the mounting of a ceramic structure in a metallic container comprising the steps of providing at least one thickness of a flexible intumescent sheet material between said ceramic structure and said container, said intumescent sheet material having a density when dry of at least about 0.5 g/ml. and being about 0.5 to 5 mm. thick and consisting of from 30% to 75% by weight of expandable mica in particle sizes ranging from 0.1 to 6mm., 5% to 20% of organic binder and 20% to 65% of inorganic fibrous material.