Organic Coatings Adaptable to Fue Storage ,J. E. COWLING, I. J. EGGERT',
AND .4.
L. ALEXANDER
Naval Research Laboratory, Washington 25, D . C .
T
HE large scale construction of prestressed, underground, concrete fuel storage tanks (10) lined with organic coatings assumed an important role in the Navy's fuel storage program throughout World War 11. This program was made possible and accelerated by the immediate availability of fuelinert linings for sealing the concrete against seepage and simultaneously preserving fuel quality. The prime characteristic of such linings was, of course, their complete inertness toward the solvent or softening action of a large variety of petroleum fuels. These included fuel ranging from high alkylate gasolines to products of 40% aromaticity. Although the program was conceived initially as a temporary, wartime expedient to conserve steel, subsequent experience has indicated that in a t least a few instances maintenance and repair have been more moderate than for similar steel facilities. In any event, these tanks are a continuing important factor in the fuel storage program and their maintenance in a highly efficient condition remains essential. Furthermore, rapidly increasing demands for jet fuel storage capacity have imposed additional requirements on the character of lining materials which must be given additional consideration in designs for possible new construction and in the rehabilitation of existing storage capacity. References (1, 5, 9, 10) to the necessity for lining concrete tanks intended for gasolines point to t'he permeability of fairly dense concrete to some of the components of low viscosity petroleum fuels, Data published ( 9 ) by the cement industry indicate the necessity for lining concrete structures designed for contact, with low viscosity oils and hydrocarbon's to prevent loss through penetration. In an early study of the penetration of concrete by aviation gasoline ( 2 ) it was reported that a mediumsize unlined tank of dense, crack-free, high quality concrete might be expected to lose about 1% of its capacity of fuel through seepage during the first few months of service. I n this process it was postulated ( 2 ) that gum formation would eventually effectively seal the concrete against further seepage. This gum would result from inhibitor removal as the gasoline permeated the alkaline concrete. However, because of the wide variation in the composition of gasolines, depending upon origin, there will be great variation in gum-forming tendencies. A gasoline high in aromat'ics might even dissolve gums left by previous batches of fuel and in no case could gums be relied upon to seal minor cracks. As a practical matter, cracks and voids almost inevitably appear in concrete with age, necessitating the use of some type of coating or sealer to prevent leakage of liquid contents. During the exigencies of war, this necessity was magnified many times during construction in remote areas where skilled labor and adequat,e supervision were not always provided. The worth of inert linings sufficiently extensible and adherent t o move with the surface and bridge these small ruptures is a t once apparent. From the point of view of engine designers it is even more important that linings be provided for concrete tanks in order to preserve fuel quality, since excessive gum formation constitutes a hazard to engine operation. Many of the inhibitors current during World War I1 were gradually extracted by contact with water of either excessively high or low pH. Experiments ( 2 ) to 1
Present address, United Chromium, Inc., Carteret, N. J.
elucidate this point resulted in the conclusion that an unIined tank of 50,000-gallon capacity could serve as live storage for immediate use only, but could not be tolerated for prolonged strategic storage. Recently available gum inhibitors are much less susceptible to removal by unfavorable environments, but storage facilities must' be capable of accepting all fuels permitted by specification. Therefore, both prudence and practical considerations dictate the use of linings. It was concluded that all linings for the entire World War TI construction program should be based upon either polysulfide rubbers or vinyl polymers (4), both classes of which are noted for their resistance to hydrocarbons. The urgency of the situation permitted no time for a comprehensive and systematic study of the problem and so several proprietary products from t,hese polymeric types were pressed into service. The rubber linings were of two types: a calendered Type A Thiokol (8) sheet that wa.s applied in wallpaper fashion using a special adhesive, and a Type MX Thiokol (8) latex applicable by either brush or spray. In the case of the latex a high quality Osnaburg fabric was embedded in the film for physical reinforcement. The vinyl systems consisted of a series of coats of vinyl paink of outstanding resistance to all fuels. An inspection in 1946 (5) of a wide cross section of these facilities after several years of service fully justified the initial choice of lining materials, but a t the same time revealed some shortcomings. For instance, although vinyl coating systems provided excellent inertness and sealing qualities, they lacked extensibility enough to bridge even relatively small cracks occuring in concrete with age and/or settling; and the polysulfide rubber linings were susceptible to mold and fungus attack (Figure 1) in tropical and subtropical climates. A more detailed inspection in 1949 (5) of approximately 50 tanks following varying periods of service in a variety of fuels brought to light a number of additional facts which largely governed the subsequent research program. As an example, it was found that the polysulfide rubber calendered sheet (Thioko! Type FA sheet) was less inert than the latex (Type MX). In addition, in the application and curing of the adhesive used with the sheeting the slightest inferiority in workmanship could result in subsequent adhesion failures. Live steam and very hot water were sometimes used in cleaning processes t o the detriment of any and all linings, but especially so in the case of FA sheet, resulting in extreme blistering as illustrated by Figure 2. Presumably the blisters resulted from vaporization of pockets of fuel which had managed to permeate the lining in small quant'ities, and t'he blisters deflated and sagged upon cooling. It was! of course, recommended that this unnecessarily severe cleaning procedure be eliminated. Prolonged contact with Diesel fuel tended to degrade both types of polysulfide rubber and in a single instance where mercaptan content of an early procurement of jet, fuel JP-3 had exceeded specifications, these linings were severely attacked (Figure 2). Normally the attack by jet fuel is a t a retarded rate ( 7 ) . The more detailed inspection of vinyl systems permitted by the specifications revealed t'heir uniform inertness toward attack by the various fuels as well as toward mold and fungus growth. In some instances considerable crazing and checking of the film
1977
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
1978
Vo!. 46, No. 9
and water. The panela were suspended eo that, sectors of about one third of the coat,ing were exposed to water, fuel, and vap Coated panels xere thus exposed for 3 days a t 130 F., then n removed and air-dried for 2 days a t roo~iitemperature, a which the entire process was repeated rvith a second fuel. In 28 days one cycle was completed and rocedure repeat>eduntil ure did not muse ewlicv film failure or for a t,otal of six cycles removal from test. Coatings remaining satisfactory at the conclusion of thi.5 test n w e considered worthy of further and more extensive investigation. While initially all accelerated evaluations of fuel incrtne~i: n-ere made on steel. it eventually became necessary to inclutlc small concrete blocks in the sanie procedure, in order to dixriniiiiate betn-ceii product's applied from n-:itei, dispersions. which B F R rule ~ v w inapplicable e to
Figure 1.
Polysulfide Rubber Lining Suffering from 3Iold and Fungus Attack 4pproknatcl3 S > Par5 after installation i n subtropical location
vc-ere evident, due in part perhap? to the leaching out of plasticizers, but vhere the concrete as of escellent quality no lealiagc resulted from these apparent film failures. The only objections to the use of vinj-1 linings n-ere their lack of extensibility and therefore their inability to bridge sinall c r ~ ~ cand k ~ ,the problem of coping with the large quantitics of hazardous solvent VRPOI'P evolved during their application (1). DEVELOPMENT O F \EW EINIKGS
The Saval Research Laboratoq- undrrtoolc research on this problem in 1949 nith a twofold objective: to devise methods and materials for t,he rehabilitation of tankage in need of r e p i r , much of which \vas in the process of changing over to storage of jet fuel: and to develop more permanent linings of greater incrtness to any foreseeable petroleum fuel and preferably applicable lvit,hout, the use of hazardous solvents. The linings of both concrete and steel t,anlrs were concurrent considerations, but the need of designing better linings for concrete was paramount, as Bureau of Ships Formula 113 ( 3 , 6) provided a fully satisfactor?- lining for steel, thoroughly lxovecl by use in cargo tankers. Its sole objectionable charactel rras t,he great volume of hazardous solvent vapor t o be removed during applicat,ion. Thus it, appeared that room for major improvement of linings for steel could best be achieved t,hrough removal of this hazard. ~IETHODS: Because all satisfactory linings must be incrt to solvent, attack by fuels, initial efforts were directed tonard the establishment, of this characteristic of all likely materials and those found lacking n-ere elinlinat,ed from further consideration. Three procedures, one presumed to be accelerated, were established for estimating the life of prospectire coatings against the deteriorating influences of several fuels and water. Each involved the cyclic exposure of experimental linings to four typical fuel blends reprePent,illg a woss section of all those likelj- t o be encountered in service and including those of pronounced deteriorative influence. 1'01. % 1.
Aromatic blend .$viation gasoline 115/146 (3Iil-l~-65i2)
Toliicne
Xylene
.)
?: -1.
Benzene Aviation gasoline l l 5 i 1 4 3 (AIil-F-5.572) Jet fuel J P - 3 (,71il-F-j624) Diesel fuel (hIi1-F-8961, class 3, 50 cetane)
60 20
Figure 2. 6 pper. I,oiLer.
Type
F 4 Polysulfide Rubber Sheeting
Seriouul, damaged by improper cleaning techniques Rad13 deteriorated b) j p t fuel rtorage
oncl phase of coating evaluation c o m p r i d a fuclinertiicss test in which the prospective linings w r e applied t o the interior of miniature concretr tanks buried in wet soil to a. depth of 6 inches (Figure 3). One quart of t,ap wat,er and a gallon of one of the test fuels were added to each small tank, ivhich ~ v a $then sealed against evaporation and allovied to stand for 30 days. At the end of this period the tanks were emptied and the coatings allowed to air-dry for 5 days, after which fuel and xater were again added to the tank and the step 'ivap repeated-a complete cycle requiring 140 days. This cycle was continued indefinitely or until evidence of pronounced failure occurred. Currently several mat,erials have performed successfully in excess of 3 years.
15
A
I n the accelerated test the mperimental coatings 'ivere applied t o steel panels, 3 X 5 inches, which then X ~ I suspended P in glass jars two thirds filled nlth a 50150 quantity oi one of the teqt fuelq
Because the details of application and material handling on the scale required for field structures are often very different from laboratory scale methods, the need for an intermediate or pilot scale evaluation was rerognized. Consequently, for the third and filial evaluation of the inertnws of experimental linings, E reduced scale tank fariii w a ~erectcvl, consisting of f i v ~
September 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
1979
the force required to st'rip off a 1-inch width of coating. The block was clamped in the upper set' of jaws of a Scott tensile tester and the free end of the I-inch strip attached to the lon-er jaws by folding back the fabric reinforcement. (In preparing the test specimen, approximately 10 inches of free fabric were allowed at one end of the block in order to facilitate this attachment,.) The machine is operated in normal fashion and records graphically the pounds of pull required to remove t8he1-inch width of lining from the length of the block (Figure 6). The stripping rate should be no less than 2 nor more than 10 inches per minute to ensure reproducible result's.
Figure 3. Small Concrete Test Tanks Partially Buried in Wet Soil concrete tanks of 1000-gallon capacity each, as illustrated in Figure 4.
A pumping and distribution system was arranged, such that fuel could be moved readily from any given tank t,o another. Four of the five tanks were lined with the coatings that had displayed outstanding performance in the tests already described. The remaining tank was lined, half and half, with a high quality vinyl paint and a polysulfide rubber (latex type), both of which qualified under Bureau of Yards and Docks Specifications L4a ( 3 ) and both of which saw extensive service during World War 11. Each of four tanks was then filled with one of the test fuels previously mentioned together with a layer of about 3 inches of water. T h e fuels were cycled through the five t,anks in steps of a different fuel each 30 days, thus providing a 30-day drying out period in the cycle and a complete rotation in 6 months. The fuels were replaced annually to avoid excessive contamination and dilution by one another. This test was continuous and as experimental linings failed they were removed and replaced by &her prospective materials-thus closely approaching the rehabilitation procedures encountered in actual service. Once the inertness of a film was established, additional data relating to its Adhesion, extensibility, and toughness were required before it could be recommended for navy-wide usage. To determine these related propert,ies a "strip-off adhesion test" was devised. The experimental coating systems with an embedded fabric for reinforcement were applied t,o cast concrete blocks (Figure 5 ) . The fabric normally was embedded in the second or third coat of material and is of special significance here because it is also used for reinforcement of the better linings in full scale applications. After thorough curing, a razor blade was used tlo cut two parallel slits 1 inch apart in order to make possible the measurement of
Figure 7 illustrates a typical recording of data from the test. By stripping the coating back a t an angle of 180°, films of poor flexibility are indicated immediately, and although the embedded fabric possesses sufficient strength in most instances to prevent rupture, a visual examination of the stripped film gives some indication of the material's physical integrity or toughness. Typical formulations based on a wide range of polymeric types possessing any possible attractive properties for this application wcre examined by these methods. These included nylon, vinyl acetat)e and vinyl chloride copolymers, furans, polyesters, epoxides, phenolics, polysulfide rubber, acrylonitrile rubber, neoprene, and acrylonitrile-vinylidine chloride copolymers. With the exception of the nitrile rubbere and neoprene, many products based upon the remaining materials displayed fair to good inertness toward the test fuels. Difficulties of application and lack of extensibility were considered sufficient to exclude nylon, furans, phenolics, epoxides, and polyesters from further consideration under present circumstances. Observations on the epoxides indicate excellent qualities except extensibility, and there is evidence that this quality may be improved sufficiently to warrant their further consideration a t a future time. EXPERIhIE3TS AND RESULTS
Data attesting to the resist'ance of a variety of coatings to the solvent' action of the test fuels a t elevated temperature (130" F.) are listed in Table I. Results are shown after 168 days (six cycles), during which exposure alternated between each of the four Fuels with a 2-day drying period between. Table I contains several formulations which were approved against Specifications L4a, along with a number of others which have been proposed as possessing equivalent characteristics. Slight blistering occurred in the case of vinyl systems, usually more pronounced a t the fuelwater interface, and minor rusting ~ r a noted s elsewhere. Thepolysulfide rubber-vinyl resin emulsiona x-ere either laboratory formulations or materials of known composition submitted under contract in support of t>hisresearch program. They are pigmented
Figure 4. Pilot Scale Tank Farm Each tank is capable of containing approximately 1000 gallons of fuel
1980
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
Vol. 46, No. 9
TABLE I. FUEI~WATER RESISTASCE OF REPRESESTATIVE COATISGS OX STEEL AT 130’ F. Coating Type Polysulfide rubber (Thiokol WD-6)“
Thickness, Mils 8.0
Vinyls, b
6.5
Polysulfide rubber-vinyl emulsion (WD-G/V>lCH) Polysulfide rubber-vinylidene emulsion (WD-6/ Saran F-120Ie
8,1 8.6
Vinyls, b 6.8 7.1 Vinyl b , C T’inylbr C 6.9 Vinylb 7.0 Fuel-resistant elastomer h , 125. O i Vinylidine chloride-aorylonitriled 7.0 8.0 Polysulfide rubber-vinyl emulsion (WD4,’VBGH) e Polysulfide rubber-vinyl emulsion (WD-G/VYHH) e 8.0
0
b c rl e
were carried out using the miniature concrete tanks instead of steel panels, as it was impossible t’o apply the latex satisfactoril3- to xt,eel. Many likely combinations were tried; and although all topcoats adhered well initially, only oneBureau of Ships Formula 113shov-ed promise over an extended period. All except this formula failed! usually by loss of adhesion xithin 6 months, but Bureau of Ships Formula 113 has functioned as a satisiactory topcoat for over 4 years. The rewlts of this experiment are illujtrat,ed hy Table I11 and Figures 10 and 11. On the basis of this laboratory scale performance, the lining system consisting of a pol>-sulfide ruhber base (four to five coats of Thiokol Latex ST’D-G), and topcoats of vinylidirie chlorideacrylonitrile copolymer (four t o six coats of Saran E’120, 1000 cps. grade, pigmented) vr-as judged to fulfill the first objective satisfactorily. It has been uaed in practice t o restore to service a large number of concrete bulk fuel tanks. Its obvious drawbacks are the large number of coats required and the use of a very volatile and hazardous solvent, (mi.th;-l ethyl ketone) with the saran. Kevertheless, iIs excellent inert,ness and physical and its ready adaptability ‘to a wide range of conditions,
Film Condition after 168 Days AdheOver-all sion Blistering Rust rating Poor Sone Minor Fair to Good Good Minutespots None Good Good 1,small None Very good Poor Excessive Severe Poor Good None None Excellent Good Noderate Moderate Fair Poor None Moderate Fair Fair 1, small None Very good Good Moderate Uoderate Fair Fair Severe Severe Poor (Complete failure, diecontinued after 60 days) Good Kumerous Gerere Poor Good None K’one Very good
Approved for use as tank lining against BuDocks Spec. L l a . Proprietarv products. Submitted-for use as tank lining against BuDooks Spec. L4a. BuShips Formula 113, approved lining for tankers. Reverse-phase emulsions pigmented ivith Micalith-G.
-
Figure 5. Coated Concrete Blocks Prepared for Strip-QE -4dhesion Test Kith Xcalith-G and are representative of early formulations of this t,ype. Their performance can be subst,antially improved by their application over one coat of “pretreat,ment primer” MilP-15328. Subsequent tables reveal other improvements in these formulas. Table I1 gives the results of a similar study of typical coatings applied to the minature concrete tanks (phase two in the 1a.boratory evaluat,ion of inertness). The results of there experiments confirmed service observations of the properties of the two general classes of linings-namely, t,hat vinyl-base materials possess the requisite inertness but lack extensibility, while roughly the opposite is true of polysulfide elastomers. These results are illust,rated by Figures 8 and 9. The laboratory test methods are relat,ively more Severe than any conditions which conceivably could be encountered in service, but this is desirable (and essential), since practical results must be obtained in a reasonable period of time. Obviously, a quick solut,ion to the first objective of this program would result if a coating system could be devised coupling the inertness of the vinyls n-ith the elasticity of polysulfide rubber. Two approaches to such a Eolution were made-(1) laminatedt,ype linings consisting of the rubber as an elastic base with various vinyl compositions as topcoats, and (2) emulsions of vinyl resins with polysulfide rubber latices. The lat,ter are known as “reverse-phase” emulsions from the technique used in their production. The first of these two approaches v a s explored bj. applying vinyl paints as topcoats to a polysulfide rubber base coat (Thio-
Figure 6. Scott Tensile Testing RIachine Used for Determination of‘ Strip-off Adhesion
September 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
1981
as well as inhibit corrosion. Red lead and litharge were most valuable in this respect. Film Condition Tables I V to VI shoiv the CheckOver-all Ing Other rating data substantiating these con. . . . Soft Poor clusions. It is noteworthy Severe , ,. ., Poor t’hat reverse-phase formulas Severe Cracking Poor Severe Cracking Poor using Vinylite VYHH are , .... Very good S&ie Poor much inferior t o similar Slight Hardening Fair forinulas using Vinylite VAGH .. .. ., .. Discolored Fair+ and Saran F-120 when unpigSome loss of Fair adhesion mented, or when pigmented ..., ..... Good with inactive pigments. Hom.... , .... Excellent ever, when red lead or litharge was used to pigment the VYHH vehicles, the inert ness, toughness. adhesion, and inhibition of corrosion were greatly improved Experimmts nom in progress indicate these lead pigments to be similarly effective with other vinyl resinThiokol emulsions, but in some case3 the degree of improvement is not b o easily observed because of the inherent superior quality of the resins themselves. The inclusion of a corrosion-inhibitive lead pigment is an obvious logical choice for applications to steel. These pigmentation studies also revealed that Micalith, zinc oxide, Bentones, and few other much cheaper pigments produced fully satisfactory reversc-phase formulas with Vinylite VSGH or Saran F-120, but were unsatisfactory with the VYHH formulations
TABLE 11. FUEL-WATER RESISTANCE OF REPRESENTATIVE COATINGS ON CONCRETE N o . of
Coating Type Polysulfide rubberavb Vinyla, b Vinylas b Vinylbrd Vinyl b, d Vinyl h d Fuel-resistant elastomer b , d Vinylidine-acrylonitrile Polysulfide rubber-vinyl emulsion (WD-G/ VAGH)i Polysulfide rubber-vinyl emulsion b r f Polysulfide rubber-vinylidene emulsion (WD6/Saran 17-120)b.f3b‘
Days in Test 735c 735C 700: 770 980 805C 840
Coats 6 6 8 6 5 6 One a t 125 mils 6 980 6 805 5
805
6
805
Auproved for use as tank lining against BuDocks Spec. L4a. b Proprietary products. c Days in test until judged unsatisfact,ory. d Submitted for use as tank lining against BuDocks Spec. L4a. e BuShips Formula 113 approved lining for tankers. i Reverse-phase emulsidns uigniented with Micalith-G. B Best formula a
Blidering Moderate Moderate
.. .. . .. .
M&rate Slight Slight Slight Slight
....
fully wairantcd its usc on an interim basis pending the development of a still better lining. Concurrently with the investigation of laminar linings of vinyl resins and polysulfide rubber, experiments were conducted with emulsions of these two materials (see Tablee I11 and IV) in further efforts to combine the desirable qualities of each. T o 100 parts of the rubber latex a t 50% solids are slorvly added with stirring 20 parts of a 20% solution of Vinylite VMCH in methyl isobutyl ketone (MIK). 4 s the VPIICH is added the batch gradually thickens until a point is reached a t which water is expelled from the heavy dough. At this point 35 parte, or 70% TABLE 111. FUEL-WATER INERTXESS OF EXPERIVEXTAL LININGSON COSCRETE of the water initially present, are reFilm Condition __.___ moved. Then 23 parts of methyl isoOver-all butyl ketone are added t o thin the heavy NO. Formula Coats Blistering Checking Other Rating doughlilte emulsion to 50% solids. None None Slight discolor Very good (1510 d a w ) Using this as a base stock, solutions of None Coatings UnsatisfacCory (210 days) Slight separated a wide variety of other vinyl and related col -WD-G’(prime) None Coatings Unsatisfactory Slight polymers can be added to provide many TAGH topcoat separated (105 days) Kejerse-phase emulsion Minor None Slight hardening, Pair (980 days) different types of vehicle formulations. Parts some loss in Thiokol WD-6 60 adhesion The choice of solvents is limited priVinylite VAGH 3 5 , 2 marily to the ketones, and a “balanced” Vinylite VMCH 4.8 Micalith G 20.0 solvent containing several of the ketones Reverse-phase emulsion None None Slight disrolor Very good -P50a-.r t”.s (980 days) is usually necessary for optimum results. Thiokol WD-6 These vehicles are actually true soluSaran F-120 46 (Less a dhcsion than forinula 1) Vinylite VMCH 4 tions of vinyl resin into which fine partiMioalith-G 20 Controls, Spec. L4a cles of polysulfide rubber latex have been 6 Polysiilfide rubherc Moderate Nonc Soft, Poor emulsified. (Other rubber latexes may (Judged unsatisfactory in 735 days) be similarly employed to provide a still 7 Vinylc Moderato Severe ....... Poor (Judged unsatisfactory in 735 days) greater range of vehicle characteristics. ) Best formula. b Used unpigmented initially. later used in pigmented forin as BuSliips Formula 113. The resultant coatings display chemical Proprietary linings submittkd against BuDocks Spec. L4a. inertness characteristic of the continuous phase-Le., the vinyl-coincident with a TABLE Iv. FU1CIrWATE.R I N E R T N E S S O F ~ N P I G R I E R ’ T E DREVERSE-PHASE COATINGS ON flexibility and extensibility in proportion STEELAT 130” F. to theincorporated rubber. I n the latter (Applied over one coat of pretreatment priiuer MIL-P-I 5328) respect they possess a marked advantage Formula, Solids, W t . 3 ’3 Over-all Vinyl resin Polysulfide Thickness, Rating over most conventional vinyl paints in composition rubber Mils Adhesion Blistering Rust (168 Days) that the “rubber plasticizer” is nonex50 F-120arb 30 WD-6C 6.8 Good None None Very good 20 V M C H d tractable. 50 VAGHd 30 WD-6 6 . 8 Fair Slight Slight Good Evaluation of inertness of these 20 VXlCH reverse-phase formulas pointed to their 50 VYHHd 30 WD-6 7 0 Fair Aloderate Moderate Fair applicability to both steel and concrete. 20 VMCII Especially significant were the pigmen70 VXZCH 30 WD-6 6.6 None Very good Very good None tation studies, which revealed that some a Best formula. b Saran F-120 1000 cps. grade. lead pigments would substantially inC Thiokol WD-6. Vinylitea. crease inertness of the coating and a t the same time enhance adhesion to steel
INDUSTRIAL AND ENGINEERING CHEMISTRY
1982
Formula, Solids, \TchPig men t Vehicle 95 Ti02 5 2 . VYHH ?IC 17 5 T-lIcrL 30 WD-C 45 Ti02 5 2 . 8 VYHIH 50 biicalith 17.5 VlIC H 5C 30 JVD-0
TlIickness, lIils
Adhesion
Blistering
Rust
Over-all Rating (168 Daya)
:%
95 ZnO 5C
5 2 , 5 1:YHH 17 5 T l I C H 30 T1-D-O 62.5 V Y H H 1 7 . 5 T-BICH 30 m D - 6
45 Ti02 50 ZnO 5 C
5 2 , 5 VYHH 1 7 . 5 V3ICH 30 TTn-6 52.5 VYHH 1 7 . 5 VhICH 30 WD-T,
100 Xed lead 50 Ti02 50 Red lead
10.2
Poor
Yev-crz
Severe
Poor
10.2
Fair
Xinor
AIinor
Fair
10.7
Good
Pjone
None
\
5.7
Poor
Serere
Severe
Poor
10 2
hcellent
None
Xone
Excellent
10.7
Excellent
Sone
None
Excellent
7.5
Very good
Sone
None
Very good
os Formula, Solids, W t . % Pigment Vehicle 3 7 . 5 VTHH 100 Blue lead sulfate 1 2 . 3 T &ICE1 50.0 \V D-6 100 T h i t e lead carbonate 3 7 . 5 T'YEIH 1 2 . 5 VhICH 50 0 N-D-G 100 Litharge& 3 7 . 5 VYHH 1 2 , 5 V3ICH 5 0 . 0 \TD-G 3 7 , j VYHH 100 White lead sulfate 1 2 . 5 VMCH 5 0 . 0 WD-G 100 Lead chromate 3 7 . 5 VYHH 1 2 . 5 VRICH 5 0 . 0 WD-6 100 Red leada 3 7 . 5 VYHH 1 2 . 5 VhICH 00.0 WD-6
7.0
rair
bIoderate
Moderate
Poor
7.2
Good
Sone
None
Very gaod
7.1
Excellent
None
Sone
Excellent
7.0
Poor
Nodernte
Berere
Poor
7.5
Good
Xonc
Kone
Very good
7.B
Very good
Sone
None
Very good
Best formulas.
Vol. 46, No. 9
been recommended lor lining stuz1 huik fuel s o r a g e fscilit,iea. All of thc satisfactory linings (Iypes now accept,able for these applications are limited to the more inert vinyl resins, polysulfide rubbers, and vinylidhe chlorideacrylonitrile copolymers. Vinyl coatings properly formulated and plasticized possess the required inertness to resist solvent attack, Their use alone is limit'etl by their lack of estensihility,
Figure 12. 50/50 Blend of Saran F-122-420 to Thiolcol
wn-6-
Liming applied entirely f r o m a q u e o u s e m u l i i o x ix full, xati5factory a f t e r 840 days i n test.
TABLE X. I V E R TOF~ REWRRF-PH~SE E~~ COATIXGS UVDER OF 650 DAYS
~ R I O U STESTCOWITIO\~ti- END
Coating Composition, Parts VAGR 35 YYHH 35 T-MCH 5 VhICII 5 W 11-li ti0 WD-e 60 hlic. G 20 illir. G 20 Failed (31 days) Failed ( I f ,days) Failed (200 days) Failed (50 days) El. soft Failed (204 days) Perfect Perfect Perfect Failed (277 days) ~~~~~
_ _ _ T e s. t Conditions _ ~ ~ ~ ~ ~ €120 ~~~~
Type uf
4.8"
VXCH 4
T~mij., Test WD-8 50 surface 1:. iiiiid Mi?. Q 20 SR-Gisea water5 Failed f850 days) Steel 130 Good (650 days) Steel Room SR-G/sea mater SR-F/sea water Perfect Concrete 130 Perfect 130 Jt'-4Cc Steel Perfect JP-4C Concrete 130 a Best formula. SR-6, 60% (by vol.), iso-octane, 20% toluene, 15% xylene, 575 benzene. C JP-?C-Mil-F-3lG1B.
~.
v i i c t r -io
-
wu-6 60 Mic. G 20 Failed (16 days) Failed (100 days) 81. soft Perfect Perfect,
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
