September 1954
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
but they display good adhesion and extensibility-two essential qualities for a fully satisfactory lining. Some polysulfide rubbers can be emulsified with vinyl resin solutions to offer a satisfactory coating material combining the best qualities of both components. The resultant vehicles can be improved further by pigmentation with stabilizing corrosion-inhibitive pigments-notably red lead and litharge. A copolymer of vinylidene chloride-acrylonitrile (Saran F-120) is among the more fuel-inert materials adaptable as a lining for fuel tanks. It is applicable alone to steel (Bureau of Ships Formula 113), but in lining concrete it is best utilized as an overcoating for a much more extensible material such as polysulfide rubber. I t is adaptable in this role to a very wide range of conditions encountered in repair and maintenance and has been particularly valuable as a method of extending the life of linings in old tanks, especially during conversion to storage of the more deleterious fuels-Diesel and jet. Probably the most significant achievement has been the development of a fully satisfactory lining applicable entirely from material in aqueous dispersion, thus eliminating solvent hazards. Because the coating can be applied at high solids content, fewer coats are needed. The lining is a combination of a vinylidene chloride-acrylonitrile copolymer with a polysulfide rubber. The stability of the mixed latex is limited through entirely adequate ( I to 2 months), and for this reason it is normally recommended that the materials be blended on the job.
1985
ACKNOWLEDGMENT
The authors wish to express their appreciation to Earl Corliss, Bureau of Yards and Docks, for his interest and suggestions throughout this research. LITERATURE CITED
(1) Allen, F. €I., and Fore, Dan, J r . , IND.ENG.CHEM.,45, 374 (1953). (2) Bureau of Reclamation, Lab. Rept. CH-40 (May 1943). (3) Bureau of Ships, “White and Orange Vinylidene Resin (Saran)
Solutions,” Paint Formula 113. (4) Bureau of Yards and Docks. Specifications L4a (May 1947). (5) Cowling, J. E., Eggert, I. J., and Alexander, A. L., “Organic Coatings Adaptable to Fuel Storage,” N R L Rept. 3685. (ti) Cranmer, W. W., Corrosion, 8 , 195-204 (June 1952). (7) Eggert, I. J., and Cowling, J. E., “Development of Organic Coatings for Use as Linings of Bulk Fuel Storage Tanks,” NRL Memo. Rept. 2 (April 1962). (8) Fettes, E. M., and Jorczak, J. S., IXD. EXG.CIXEX.,42,12217 (1950). (9) Portland Cement Association, Structures Bureau, “Concrete Information No. ST4,” June 1942. (IO) Spamer, bl. A,, ,J, Am. Concrete Inst., 40, 417-28 (1944). RECEIVED for review March 20, 1954. ACCEPTED April 8, 1954. Presented before the Division of Paint, Plastics, and Printing Ink Chemistry CHEMICAL SOCIETY, Chicago, Ill. The a t the 124ch Meeting of the AMERICAV views and opinions expressed herein are those of the authors and do not necessarily represent those of the Navy Dcpartrnent or other Departmerib of Defense activities.
Synthetic Latex Scrub esistant Intumescent Coatings I. J. CUMRIINGS Plastics Department, Coatings Technical Service, The Dow Chemical Co., Midland, Mich.
HE subject of fire-retardant coatings embraces a wide field of materials and methods. Depending upon the nature of the problem a t hand, the formulator may proceed along one of several lines. Grubb and Cranmer (6) reviewed the problems involved in selecting fire-retardant paints for steel surfaces of ships, and pointed out that flaming can be satisfactorily prevented through the use of paints of high pigment volume, utilizing an alkyd resin binder. In an efficient fire-retardant coating for acoustical tile board, described by Weil, Mod, and Chapman (11), the intumescent water- or oil-base coatings gave positive protection to the combustible basic fiber. The various types of fire-retardant coatings formulated for surface treatment were well classified into two groups, including intumescent and nonintumescent types of both aqueous and nonaqueous systems. The type of product represented by acoustical tile and decorative wallboard plank requires an efficient fire-retardant coating in order to meet fire-resistance specifications. This product consists of vegetable or viood fiber fabricated into low density sheets which are inherently combustible. The intumescent type of fire-retardant coating does an effective job in protecting the base fiber, when exposed to a fire of moderate intensity and duration, by virtue of the insulating char formation. A well-known intumescent composition consists essentially of a blend of ammonium phosphate salts, starch, pigment, and an amine-formaldehyde resin. Such a composition is described in a patent assigned to the Albi Manufacturing Co. (7‘). It has been demonstrated that this type of intumescent coating can be modified to enhance water resistance and flexibility of the dried coating film. Stilbert and Cummings ( I O ) discussed the addition
of a vinyl chloride copolymer latex binder to the *41bi-R type of intumescent coating system. The work described herein is a continuation of the development of the use of a synthetic latex product in fire-retardant, intumescent coatings. In the previously reported work ( I O ) a number of serious limitations were inherent, in the formulations discussed. In general, there can be listed some characteristics thought desirable for an improved intumescent coating composition. Ample \vet coating life to allow a wide latitude in handling. Wide range of p H in which to formulate. 4 composition free of reactive material such as formaldehyde based resins. Good resistance of the dried coating to checking and discoloration upon aging. A minimum amount of objectionable odor. In addition to these desirable properties the coating system should meet federal specifications for fire resistance equal to or better than the slow burning classification ( 4 ) and wet scrub-resistance ( 5 ) . There is considerable incentive for manufacturers of low density fiber wallboard and acoustical tile to adopt a fire-retardant coating for their product which will be decorative and durable as well aa efficient. Such coatings would normally be applied continuously to the board as one additional process step toward a completed sales product. For such continuous application it is important that the coating system be simple to make up in large scale equipment. The wet coating should have good stability and a readily
1986
INDUSTRIAL AND ENGINEERING CHEMISTRY
PERCENT LATEX BINDER (SOLIDS)-20 1600 'PRE DRYING TREATMENT (I) 0 PRE HEAT - 5 MINUTES AT 175°F:
4 , 1
OVEN DWELL TIME (MINUTES AT 3 0 0 ' E I
Figure 1. Effect of Drying Conditions on Coating Properties
cont,rolled consistency for i 2 hours or longer. Simplicit,)- of make-up and application in the manufacturing plant makes for less supervisory cont,rol and helps to eliminate costly waste.
Vol. 46, No. 9
2. Pass the slurry t,wice through a high speed stone mill with the stories barely in contact. 3. Add latex t o dispersion from (2) and stir approxini:iic,ly 15 minutes with medium agit,at,ion. Some further agitation is desirable just before application. The aqueous dispersion without the latex can be prepared as above up to a total solids content of 75%. Depending upon the latex binder level used, the resultant solids of the complete coating would be 65 to 70%. Tile cxo:iting doev not require an aging period prior t,o application. It is perniissible to &ore the prepared coating for 10 to 14 days vvit'hout deleterious results. .Ilthough shelf lire on the latex-based intumescent coating has not been studied in detail, \vet samples m r e examined after a 4-month storage. Tests on coat,ings prepared from t,hese aged samples indicated that wet scrub-resistance had decreased approximately 507,. Intuniescent quality \va>unaffwted. For d l t tion a S o . 92, T)-pc CT'-45406, l a b equipped wit,h a stainless s k e l Huiti oratory De w:w used. The wet coatings were upplicd to tip arid flui fiherbosld p n n i ~ l 12 i inrhei square and 0.375 inch thick. 310-t of thc teat dat:x w r e obtained on uncoated (natural) bawd of :L type liaving a smooth, uniform surface. A. coating weight of 40 pound8 ol dry coating per 1000 q u a r t . feet, applied in a single spray application, was used for all the 3 in previous work (10) that test data obtained. It ~ a reported a 40-pound coating weight lcvel was suffii&nt to eliniiriat,e the variable effects on coating properties of board surface fibc?r-;. Depending upon the nature of the surface of prime-coated boards, sat,isfactory intumescence ran be obtained a t coating weights a3 low as 20 pounds of dry coating per 1000 square feet. However, adhesion difficulties arise wheii an attempt is made t,o apply the latex-based intumescent, coating o w r a glo
SAMPLE PREPARATION
Laboratory methods and techniques are difficult to trailslate int,o manufacturing plant' practice. The methods used to prepare coated samples of t,he lates-based intumescent coating, however, were developed ait,h an understanding of the plant facilities which are in existence. There is some choice, for example, in t,he method for the initial dispersion of ingredients in Ivater. A mixer utilizing high fluid velocities and high rates of shear can be used to obtain a satisfactory dispersion when the ingredients are obtained in a finely ground dry state. If the dry ingredients are fairly coarse, 3 to 4 hours in a pebble mill will result in a fine aqueous dispersion. A high speed stone mill, vhich will handle systems having a wide range of solids content, was chosen for thc laborat,ory preparation of samples. This method of preparing a a finely ground aqueous dispersion is rapid and efficient. Perhaps the most difficult to correlate between laboratory and production plant practice is the information on drying and fusing the coating. Because satisfactory fusion of the latex polymer particles is dependent upon at'tainment of a temperature near the fusion point-Le., approximately 330" F.-the drying schedule beconies somewhat critical. For plant appli~at~ion short drying t,imes are important. Most plants manufacturing acoustic tile and wallboard are equipped with st,eam-heated or gas-fired ovens designed to evaporate large amounts of water in a relatively short period . These ovens will blow air across the surface of the board a t temperatures ranging from 200" to 600' F. The test d a h indicate t'hat a satisfactory degree of fusion can be obtained in 4 t,o 5 minutes of total drying time a t 300" F. in a 4-cubic foot laboratory oven. An efficient gas-fired, forced air production plant drying oven can attain fusion of t,he iritumesrent coating film in 1.5 to 2 minutes. PREPARATION OF CoATIXG AND TESTPANEL.The strps in making up the coating are listed as fol1on.s:
1. Using a paddle-type mixcr, prepare a slurry of all ingredients of the intumexent formulation except the latex.
Figire 2,
4pparatus for Inclined Panel Test
DKBIAG AS!) C'DSDITIOSTSG O F Coamu Pmm. The cquipment used for drying the coated test panels consisted of a Despatch electric laboratory oven. A blower unit and temperature controls maintained a uniform temperature throughout the 4cubic foot oven chamber. A drying and fu3ion temperature of 300" F. was used for all test panels prepared. I n order to maintain sufficient control to allon- a st,udy of coating system variables, a 10-minute air-dry treatment was adopted prior t o fusion of t8he
INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1954
1987
Figure 3. Coated Panel after 20-Minute Flame Test a t 15% Latex Binder Level
Figure 4. Coated Panel after 20-Minute Flame Test a t 20% Latex Binder Level
coating film a t 300' F. The heating period was varied from 1 to 7 minut,es in order to ascertain t'he optimum. A conditioning period of 24 to 48 hours was used to enable thc dried, coated panels t80reach equilibrium conditions with the testing laboratory. A 24hour aging period at laboratory conditions was used for coated panels which were tested directly following coating application. The panels which were subjected to accelerated aging conditions of high temperature and high relative humidity were allowed to condition in the laboratory for 48 hours prior to testing. Because of the high temperature fusion requirements of the unplasticized latex binder, the drying schedule for the wet intumescent coating is somewhat critical. There is a close relationship between evaporation of the m t e r in the coating film and the coalescence of the latex polymer particles. If removal of water from the wet coating is carried too far a t a temperature considerably lower than the fusion temperature, the final properties of the coating will be less than optimum. It, was determined that drying efficiency could be greatly increased by minimizing hydrophylic material content and raising the total solids of the coating Listed below is the forinulation used in the study of drying variables of Figure 1.
TEST PROCEDURE
Parts by Weight
Ingredients
56 10
22
12
33 50 Total solids, % Latex binder solids,
X
1:s 5
20
Figure 1 illustrates the effect of wet scrub-resistance of the dried coating a t three different conditions of predrying. Curves 2 and 3 indicate that the predrying treatments used were not optimum. The most rea1ist.k conditions are illustrated by curve 4. Although the length of time needed at 300" F. is greater than for any of the other three systems, it is apparent that the total drying schedule to obtain a satisfactory degree of coating film fusion is relatively short. The multiple-stage drying units utilized in the low density fibrous wallboard industry would closely approximate optimum drying and fusion conditions for this coating system. This is due to the high efficiency of drying and utilization of two or more temperature zones throughout the oven chamber.
WETSCRUB-RESISTANCE. R e t scrub tests were made on the coated fibrous insulating board using the Gardner straight-line scrub tester from the Henry A. Gardner Laboratory, Inc., Bethesda 14, Md. This instrument !vas used in the procedure of t>he Federal Specification 5 , Section E-9, paragraph F-31. .4 I-pound weighted brush was drawn horizontally across the specimen a t approximately 40 oscillations per minute. The 0.5% soap solution required by the specification was used to maintain the board in a wet condition. In general, the coated board was scrubbed to 10% of the board surface showing as an end point. FIRETESTS. Two test methods were utilized for the study of fire-resistant properties of the latex-based intumescent coating. The data relating to the effect of formulation variables on quality of intumescence were based on the use of the inclined panel test ( 2 ) which is a modification of a British t'est ( 1 ) . The apparatus is pictured in Figure 2. The t,est requires a test specimen 12 inches square to be supported on it plane making an angle of 45" with the horizontal. One cubic centimeter of absolute ethyl alcohol is pipetted into the brass cup located on the cork under the test specimen. Quality of int)umeseence is evaluated by visual observation. The test of greatest general interest to insulation board manufacturers and use as the basis for B specification covering the classification of fire-resist,ant fibrous wallboard has been described (4). In this test a material must withstand 20-minute exposure to gas flame to qualify for the "sloxy-lxuning classification." Figures 3 and 4 picture the test panels coated a t two different latex binder levels following the 20-minute flanie exposure. These panels consisted of prime-coated low density fibrous board panels 12 inches square and 0.5 inch thick. These panels were drilled prior to the application of 40 pounds of dry coating per 1000 square feet of the latex-based intumescent coating. It was noted during these tests that, the initial bubbling of the coating occurred at 600" to 800" F. 811 surface flaming from the board ceased after 13 minutes of test. 911 flaming ceased within 20 seconds after the test flame was removed. At no time during the test did the flames reach the angle iron supports. KO parts of the panels dropped out either during or following the testing. The panels pictured in Figures 3 and 4 were rated as slow-burning
(4).
INDUSTRIAL AND ENGINEERING CHEMISTRY
'1988
Vol. 46 No. 9
GENERAL FORBlULA DEVELOPMENT
~IATERIALS FOR IKTCMESCESCE. The first step in the evaluation of materials necessarg- for an intumescent composition n-as to set up a generalized formula in \vhic.li various ingredients could be tested. Parts b:- Kciglit
Item 1
2 8
4 5
CO?,lPOSITIOS
Group I
Inorganic fire-retaydant salt Organic nitrogen coinpound NonreEinous carbonareoils comporinkl PiornPnt
~ ^ _ _ " _ _ "
Latex binder solids
56 10
2i.5 1
7 5
Group I1
Nonoammonium phosphate Diammonium phosphate Dibasic calcium phosphate Ammonium sulfate-phosphoric acid (3 t o 2 i Ammonium sulfamate-sulfamic acid ( I to I ) Dicyandianiido Urea Guanyl urea phosphate Glycine
It was desired to screcn from a large group of available materials 1,3-DimethyIiirea the most useful compounds which noulti fidl into t h o c:rtcagoi.L- o!' C:roup 111 Starch items 1,2, and 3. In Mannitol d-Galactose this phase of the inGlucose vestigation a single Pentaerythritol p r o p e r t y of t h e dried coating was studied-quality of intumescence. profile whirh were subjected to this test. The height of cli:tr Table I lists three show1 in the center and right-hand panels represents sa groupings of matetory intumescence. rials Tvhich Tvere Quality of intumescence is a difficult property to describcx acic-. selected partly on quately. Sufficient data m r e not obtained to illustrate conithe basis of the pletely the manifestation3 of intumescent quality. These initems l i s t e d i n clude, homver, good foam volunie at low coating w:ig t h e generalized foam volume when diluted by nonintumoxing ingrndi formula, and w r e ability of foam structure to i;t;lntl lip uncter flaming for extenrlctl e v a l u a t e d in t'he time pcriods. s a n i c weight relaIt is indicated by t,he data in Table I1 that we tionships a s i n d i is enhance(! by avoiding the U P cat8ed in t,he genThe intumescent quality of a eralized f o r m u 1a,. was good. On the basis of so By utilizing phate, and diammonium phosphate were eliminated from fuit,lit:i, selected combinainvestigation. tions containing one The function of the pigment item in the generalized fonnuh material from each was not studied. Titanium dioxide was selected solely on tbc group, t h e most basis of superior hiding power. Considerable information has useful combinations been reported on the use of pigments and fillers (8)in fire-retaitlwere selected. The ant coatings. It !vas not intended to overlook the value of cercriterion for select,ain specific pigments in intumescent coatings. It, is assumed t,ion was satisfacthat the benefits resulting from a proper choice of these inorganic. tory i n t u m e s c e n t filler materials would be supplemental to the system de quality of the dried herein. coating and a reTYPEOF LATEXBIXDER.I n order t o select' the most efficient Figure 5 . \isual Comparison of sultant pH of the Tntuniescent Quali t? nt composition, the coati~ig type of latex binder lor the inturn aqueous mixture of lormula below was used. 4.0 or higher. Parts by Weight Ingredient? I n Table 11 the most useful blends of the three groups of ma56 Monoammonium plionpliate 10 terials examined are list,ed in complete coating formulas, which Dicyandiamide 21 2 Pentaerythritol were evaluated for T e t scrub-reei&nce and intumescent quality. 0.3 Sodium alginate 12 Titanium dioxide The forniulations listed in Tahle I1 were prepared by grinding all 75 Kater 23 ingredienk except the lates for 3 hours in a pekible mill. For Latex binder solids evaluat,ion purposes 40 pounds of dry coating per 1000 square feet were sprayed onto natural, amo o t h - s u r f a c e insulation Parts by Weight board panels. All coatirigs i z 3 i ~ e 7 8 9 1 0 1 t Ingredients were dried a t 300" F. for 5 56 56 56 56 86 66 56 Z6 5G .. .. 1Ionoammonium phosphate .. ,. .. , , ,, ., , . ., .. 56 jfj Dianimoniurn phosphatr minutes and aged 24 hour, 1 . , . ,, 10 .. .. .. .. .. .. Gtianyl urea ptiosi>hate prior t o testing. Thewet scruhID .. . IO . . . .. .. Glycine 10 I0 . .. Urea resistance '*Yas determined by 10 10 10 )!I 10 Dicyandiainidr 21.2 2 1 ' 2 2 1 . 2 21.2 , 21 2 Starch ineasuriiig the number of cycleh 21.2 21.2 21.2 21'.2 . . .. . , -. 2i:a Mannitol 21.2 on a Gardner scrub tester necesPentaerythritol 6:s 0 ' 3 0 . 3 6 . 3 0 : 3 013 o : ~ 0.3 o 3 O : R 0:3 Sodium alginate sary to expose 10% of the board 12 12 12 12 A2 12 Titanium dioxide l a 12 1% !% 12 nO 30 50 ,a0 50 50 50 50 60 00 50 b'ater surface. The inclined panel 38.4 3 5 . 4 35.4 3 5 . 1 35.4 35.4 3 5 . 4 33.4 35.4 Uoiv Latex 714.0 ( X C 6 solids) 3 5 . 4 3 6 . 4 method ( 2 ) y a s used as the __ ________-__- Wet Scrub-Resistance, Cy&_ fire test for determining quality BO 40 100 100 10 15 20 50 180 5 15 of intumescence. Figure 5 il I u s t r a t e s three panels in
INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1954
1989
TABLE 111. EVALUATION OF SYNTHETIC LATEXTYPES IZ INTUMESCEXT COMPOSITIOX
Chemical Composition of Polymer Vinyl chloride-vinylidene chloride Vinylidene chloride-vinyl chloride Vinylidene chloride-acrylonitrile Vinyl chloride copolymer Vinyl chloride Vinyl acetate Chloroprene Acrylic Butadiene-acrylonitrile Styrene-butadiene Ssyrene-butadiene (acid-stable) Styrene
Figure 6.
Electron Micrograph of Dow Latex 744-B
Table 111lists the different types of synthetic latices evaluated in this formula. For those latices which were compatible with the system, coated panels were prepared for further testing. The wet coatings were dried for 5 minutes a t 300’ F. and aged for 24 hours prior to testing. Scrub resietance was determined with a Gardner scrub tester and intumescent quality by the inclined panel fire test method.
Compatibility
OK OK OK OK OK Coagulated Coagulated Coagulated Coagulated Thickened OK OK
Coating Film Pioperties Scrub resistIntuance, cycles t o mesoent 10% board quality exposure Good 600 Good 1300 Fair 2000 Good 10 Good 10
... ... ...
...
G’o’o’d Poor Poor
70 60 150
... ,..
...
Although several latex types were compatible to a certain degree the most useful were the copolymers of vinyl chloride and vinylidene chloride. Because good light stability is a required property for a decorative coating binder material, Dov; Latex 7WB, a copolymer of vinyl chloride and vinylidene chloride, o as selwted for further work. Dow Latex 744-B, hereafter referred to as “the latex,” has been described by Stilbert and Clack (9). Like all latexes, it is a colloidal dispersion of microscopic particles of polymer in water. Figure 6 is an electron micrograph of this latex. The long, sharp shadow indicates that the unmodified particles are not deformed during drying at room temperature. Table IV lists typical properties of the latex and latex solids. The latex has a relatively lo^ surface tension. When dried at room temperature, a nonflammable, high melting, white powder ie deposited. I n order to form a film a t low drying temperatures the latex must be modified with film-forming latices, plasticizer emulsions, or certain liquid plasticizers. When drying temperatures a t or near the fusion point of the polymer are used, however, a large amount of polymer particle coalescence is ob-
MONOAMMONIUM PHOSPHATE
MONOAMMONIUM PHOSPHATE
A
OR
OR
MANNITOL
DlCYANDlAMlDE
Figure 7. Effect of Composition Variation on Intumescent Quality System monoammonium phosphate-urea mannitol Coating Composition 3-component system Sodium alginate Titanium dioxide Water Latex solids
or dicyandiamidestarch or
Parts b y Weight 87.2 0.3 12.0 50.0 17.7
Figure 8.
Effect of Composition Variation on Coating Properties
System monoammonium phosphate-dicyandiamidepentaerythritol Coating Composition 3-component system Sodium alginate Titanium dioxide Water Latex solids
Parts by Weight 87.2 0.3 12.0 50.0 17.7
Numbers on diagram indicate initial scrub resistance of compositions, cycles t o 10% board exposure.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1990 10,000
I
HUMIDITY CYCLE
Vol. 46 No. S
24 HRS AT 90'E
AND
,000
-__/--_L_ ___
I
_-__
I___
7-=
COATING WEIGHT --(LBs DRY COAT"G/iOOO
100
SQ F T )-40
-
DRYING CONDITIONS IO MINUTES : AIR DRY 5 MINUTES AT 300'F (FORCED AIR L A B OVEN) 0 SCRUB RESISTANCE 0 CHAR AREA (SP I N . - C S 4 2 - 4 9 )
+
m o
3-
ix
22
+I?-
4
v)
W
BOO
Y ---+.-
- -
__
Figure 9.
+-
i
0
0
,---+--
4 00
0
IO 20 30 40 50 60 PERCENT LATEX BINDER (SOLIDS)
70
Effect of Latex Binder Content on Coating Properties
TABLE
IV. TYPICAL PROPERTIES L.4TEX
11 13
Surface tension, dynes Iier c i n Evaporated solids, 70 Specific p a r i t y at 2 5 . C. Weight per gallon, pounds Viscosity, cp. Pounds of solids per gallpn Paiticle size, aveiage, iiiicion
LLTEXSOLID^ Specific gravityoat 2Zo C.
Llelting point, C. Heat stability Light stability Burning rate Refractive index
8.0 i 0 5 34 0-35 0 5 0 0 ~ 0 5 1 l Q 5 = 0 001. 10 520
J
henonresinous carbonaceous materials test,ed, starch end pentaerythritol appeared to be the most efficient from t,he stmilpoint of intumescence. Pentaerythritol, however, was sei( as the most useful because of it's good moisture resistance itii0' contribution t o excellent intumescent quality.
Figure 11. Effect of Nine Cycles at 90" F. and 90% Relative Humidity on Scrub Resistance and Intumescence Left. Intial, 1200 scrub oyclcs Right. After exposure, 500 cycles
EFFECT O F COATING AUD CONDITIOY V4RI4BLES OY COATING PROPERTIES
EFFECT OF LATEX BIXDERCONTEXT.Figure 9 indicates that latex binder level may be varied \Tithin a wide range without de-
INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1954
MONOAMMONIUM
PHOSPHATE
A
SATISFACTORY
1991
which to work, as measured by initial properties of intumescence and wet scrub resistance. As might be expected, the scrubresistance figures increase in the direction of the least soluble ingredient-pentaerythritol. The latex binder content of 15% used for the coating> represented in Figures 8 and 12 is about the minimum level consistent with any degree of desired film properties. This low latex binder level was chosen deliberately in order to highlight the effects due to variations in the three-component system. The trend would perhaps be similar a t higher binder levels, but not so marked. Figure 12, in comparison with Figure 8, illustrates the effect on wet scrub resistance and intumescent quality of six cycles of exposure a t high humidity. .4s might be expected, the scrubresistance values of the compositions represented on the trilinear diagram were greatly reduced as a result of the cyclic exposure. Significant is the indicated area in which the intumescent quality is the most persistent. The intumescent coating formula utilized for the test work reported here would fall just inside the area. of satisfactory intumescence of Figure 12 on the 64% monoammonium phosphate line. StiXMARY
Figure 12. Effect of Composition Variation and High Humidity Exposure on Coating Properties System monoammonium phosphate-dicyandiamide-pentaerythritol Coating Composition 3-component system Sodium alginate Titanium dioxide Water Latex solids
Parts by Weight 87.2 0.3 12.0 50.0 17.7
Numbers on diagram indicate scrub resihtance of compositions, cycles t o 10% board exposure, following 6 cycles of high humidity exposure. Humidity cycle: 24 hours a t 90° F. and 90% re!ative humidity plus 48 hours a t laboratory conditions.
tracting from the fire-resistance quality of the intumebcent coating, and that a latex binder content greater than 50% could be successfully formulated and used. Fire-resistance, in this study, was measured by the inclined panel method. The formation of foam char above 40y0 latex binder was fragile and contained large hollow cavities. This type of foam, while showing up well under the inclined panel test, would probably not be adequate for a longer and more severe fire test. For application on low density fibrous wallboard and acoustical tile a latex binder content of 20 to 25% would probably be sufficient. Where extreme flexibillty and toughness of the coating film are of paramount importance, a latex binder content of 40 to 50% mould be the most satisfactory. EFFECTOF EXPOSURE AT HIGHHUYIDITY.An accelerated aging test which enables the technician to study the durability of protective coating systems consists of cycling at controlled conditions of high tempwature and high humidity. The conditions of the cycle were 90' F. and 90% relative humidity. The intumescent coating must retain its coating film properties as ell as fire-resistant quality in order to function as a protective coating. I t is apparent from Figure 10 that the latex-based intumescent coating possesses a satisfactory degree (100 scrub cycles or better) of wet scrub-resistance after nine cycles at 90" F. and 90% relative humidity. Figure 11 shows the slight difference in intumescent quality of the test panels before and after nine humidity cyvles of exposure. The panels chosen for the photograph were coated with the intumescent coating at a latex binder level of 25%.
EFFECTOF COMPOSITION VARIATIONA N D EXPOSURE AT HIGH HUMIDITY.Figure 8 indicates the useful area on a trilinear plot of the system monoammonium phosphate-dicyandiamide-pentaerythritol. There is considerable latitude for the formulator in
An intumescent, fire-retardant composition was selected from a study of three-component systems investigated on a trilinear diagram. The most useful system contained monoammonium phosphate, dicyandiamide, and pentaerythritol. 9 synthetic latex binder of the vinyl chloride-vinylidene chloride type was selected for the intumescent coating system from a group of twelve different types. The data indicate that good wet scrub resistance and fire resistance are obtainable over a wide range of latex binder content. The synthetic latex binder is utilized without a plasticizer and requires a drying schedule sufficient to coalesce the latex polymer particles. As scrub resistance of the intumescent coating film is dependent upon fusion of the latex binder, considerable care must be taken to dry the wet coating properly. Short drying schedules are recommended, utilizing temperatures near the fusion temperature of the latex-i.e.. 330" F. Atmospheric conditions of high temperature and high humidity were simulated by accelerated testing of the latex-based intumescent coating a t 90' F. and 90% relative humidity. The data indicate that a 20 to 25% synthetic latex binder level imparts good resistance to accelerated tests designed to cause failure of the intumescent coating film. The formulating procedure for preparation of the latex-based intumescent coating is simple and direct. A high speed stone n d l is used to prepare the aqueous dispersion in a quick and efficient make-up procedure. il short mixing period is required to blend the synthetic latex with the aqueous dispersion. Aging characteristics of the finished wet coating mix are not critical for fartory manufacture. Storage and handling up to 2 weeks can be accommodated satisfactorily. LITERATURE CITED
(1) British Standard Specification 476, 1932. (2) Commercial Standard CS 42-49, Government Printing Office,
Washington, D. C., 1949. R.E., Matheson, L. il., and Bradford, E. B., J . CoZZoid Sci., 6, 108 (1951). (4) Federal Specification SS-A-I Ma, Government Printing Office, Washington, D. C., 1948. (5) Ibid., TT-P-88a. (6) Grubb, Robert, and Cranmer, W.IT.,Presented at 123rd Meeting, ACS, Los Angeles, March 1953. ( 7 ) Jones, Grinnell, Juda. Walter, and 53011, Samuel (to Albi Manufacturing Co.). U. S.Patent 2,523,626 (Sept. 26, 1950). (8) Murray, T. NI., Liherti, Felix, and Allen, A. O., Presented at 123rd Meeting, ACS, Los Angeles, March 1953. (9) Stilbert, E. K., and Clack, H. L., Tappz, 34, No. 8, 337-46 (1951). (IO) Stilbert, E. K., and Cummings, I. J., IND. ENG. CHEM.,45, 748-54 (1953). (11) Weil, A. C., Mod, G. W.,and Chapman, W. A,, Presented at 123rd Meeting, ACS, Los Angeles, March 1953. (3) Dillon,
RECEIVED for review Piovember 9, 1958. ACCEPTED April 30, 1954 Presented before the Division of Paint, Plastics, and Printing I n k Chemistry a t the 124th Meeting of the h E R I C b N CHEnrrCAL SOCIETY, Chicago, Ill
