US2287218A - Antifouling composition - Google Patents

Description

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June 25, 1942.

ANTIFOULING COMPOSITION George H. Young and Peter Gray, Pittsburgh, Pa., assignors to Stoner-Mudge, Inc., Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application January 9, 1941,

Serial No. 373,830

3 Claims.

This invention relates to antifouling compositions capable of application to the surfaces of structures which are subjected to submersion in sea water for the purpose of preventing fouling by cirripede Crustacea (barnacles), algae (sea weeds) and other marine organisms known to contribute to fouling of submerged surfaces. It relates specifically to antifouling compositions consisting of mixtures of certain phenolic compounds, certain high boiling coal tar bases, and aromatic unsaturated aldehydes, dispersed in suitable film-forming vehicles and volatile solvents. Our compositions find particular application in the protection from fouling of metal structures such as ship hulls, pier supports, and flying boat hulls, where use of prior art copperand mercury-containing antifouling paints results in deleterious galvanic corrosion due to the electrochemical action of dissimilar metals in contact; they are also applicable to nommetallic surfaces.

The following organisms are known to contribute to fouling:

Hydroid coelenterates Porifera (sponges) Cirripede Crustacea (barnacles) Ascidea (sea-squirts) Algae (sea weeds) Of these, only the algae and cirripedes present any problem. Coelenterates, Porifera and Ascidea are not only very slow growing but have also a loose, non-calcareous attachment cement and may be removed with a scrubbing brush without damage to the underlying surface. If the structure be required for service in the eastern South Atlantic, or in the Indian Ocean, sponges immediately present a. problem for these waters abound in calcareous and silicious forms; calcareous Bryozoa may also be anticipated in these places.

The majority of algae have a non-calcareous attachment and need be considered here only insofar as they might give rise to a blanket covering over the protective coat. Algae are sensitive to about M x copper solutions and we have found that the incorporation of 1% by weight of copper drier in the protective coat will prevent algal adhesion. It may be pointed out that algae have a very high magnesium content and are therefore likely to flourish on aluminum alloys containing a considerable quantity of this element. Itis known that the free-swimming infective stages of some forms which have been studied are attracted to regions of low pH. These factors must be taken into consideration in designing a protective coating free from the usual metallic poisons. As the concentration of copper required to kill larval cirripedes is more than a hundred times that required to kill developmental stages of algae, the latter are usually ignored in formulating the ordinary copperloaded antifouling. coatings.

Cirripedespresent the major problem for two reasons. First, their larvae may reach a concentration of 1x10 per gallon of sea water in localised swarms; second, they begin to lay down calcareous adhesive plates within six hours of their first attachment. It is obvious that, if a swarm of this density should be drifted against a surface not rapidly lethal to them, the whole area will become immediately covered and the value of the antifouling coat lost.

The larva of the barnacle hatches from a floating egg as a nauplius"; this is a conical animal, from 0.05 mm. to 0.5 mm. in length, furnished with three pairs of anteriorswimming legs. The nauplius undergoes a number of moults, at each of which it acquires more pairs of swimming legs and finally the original anterior swimming legs become modified into feelers and jaws. The free swimming attachment stage, the appearance of which indicates the termination of moulting, is known as the cypris larva. The swimming feet project from the open valves and the most anterior pair of the original appendages, serving as tactile sense organs in other forms, are modified into stalkecl suction cups. Should these cups touch any surface, they immediately adhere, partly by suction and partly, in some forms, with the aid of a sticky secretion filling the lower half of the cup. The animal immediately commences to turn until the back rests against the surface to which the cups were originally attached. Further sticky secretion is produced so that the animal now lies firmly embedded in a rapidl hardening drop of cement, with itslegs waving free'for the collection of food. From the time of original adhesion to the stage just described is only two hours. calcareous depositions now appear in the cement base, and calcareous plates are laid down in the original valves. If the barnacle is of the sessile type, no further change takes place except an increase in size; stalked barnacles elaborate a further secretion which, coupled with a growth in the body wall, pushes the animal away Irom the original attachment till it lies at the end of a stalk.

It is thus evident that the ideal protective coat must prevent the original adhesion of the suction discs; and that any coat is worthless which does not kill the animal before the back has secreted its adherent cement base. This is seldom the case with the usual antifouling paints. These latter compositions depend for their efiicacy upon the lethal action of dissolved copper and mercury ions. Since the concentration to be effective is quite high and must be continuously maintained in the immediate neighborhood of the submerged surface being protected, it is necessary to incorporate as a pigment large quantities of copper and copper-mercury. salts into the paint vehicle in order to provide a reservoir of soluble metal ions. In ordinary applications, this means that there will be particles of metal and of metal oxides or salts in direct contact with the surface being protected. And in the presence of sea water such metallic contact between dissimilar metals leads to accelerated corrosion and pitting. In the case of steel boat hulls or pier supports the pitting action is serious but not particularly dangerous; in the case of light gage aluminum alloy sheet, such as is used for the skin" of dying boat hulls, pontoons, and the like, the pitting action resulting from use of metaland metal oxide-containing antifouling compositions is extremely damaging.

A typical copper-containing antifouling composition is described in U. S. Patent 2,176,597. Other prior art compositions employ copper and mercury salts as the toxic agents. Exemplary is the composition listed by the Bureau of Construction and Repair of the U. S. Navy (general specification-appendix 6 (April, 1939), page 6'7).

Formula RC' Pounds re- Materials It is an object of our invention to provide an antifouling composition which prevents adhesion of the suction discs of the larval, cirripede Crustacea, or which kills before secretion of its adherent cement base. It is a further object of our invention to provide an eflective antifouling composition for metal structures, which contains no heavy metal or metal oxide toxic agents. Another oblect of our invention is to provide an effective antifouling composition which may be applied as a clear varnish i1 desired, or which may be pigmented with inert pigment and dyes to yield any desired finish color.

These objects may be attained by incorporating into a suitable under-water varnish vehicle,

one or more compounds selected from a group consisting oi! (a) the lower alkyl, aryl, and alicyclic substituted phenols and their chlorinated derivatives, (of which o-cyclohexyl phenol and 2 chloro-o-phenyl phenol ar typical), (b) the pyridine and benzopyridine cyclic nitrogen coal tar bases and their lower alkyl-substituted homologs, (of which pyridine, quinoline, qulnaldine, and trimethyl pyridine are typical), and (c) aromatic unsaturated mono-aldehydes containing one olefinic linkage in the side chain carrying the aldehyde group, (of which cinnamaldehyde and its lower alkyl nuclear-substituted homologs are typical).

It is a common characteristic of all of these toxic agents that they are condensed-ring compounds whose saturated aqueous solutions contain at least 1X 10- moles of compound per liter, that they possess low vapor pressures at ordinary temperatures and pressures (usually but not necessarily boiling above 230 C. at atmospheric pressure), that they are soluble in the familiar coal tar solvents used in varnish formulation (typically toluol, xylol and solvent naphtha), and that they are all mild antioxidants. They are strongly anaesthetic to the tissues of the suction discs of marine arthropods, and are rapidly lethal to marine arthropods in concentrations of the order of magnitude of 1 10- molar.

We have specified lower alkyl, aryl and allcyclic substituted pheno in group a. By this we means that the substituting radicals may be methyl, ethyl, propyl, butyl and higher alkyl radicals containing up to 6 carbon atoms; and we means to include the cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl radicals; and we mean to include the phenyl radical. By specifying their chlorinated derivatives it will be understood that we' mean to include derivatives containing chlorine either in the parent phenol nucleus, in the substituting radical, or in both.

We hav specified lower alkyl-substituted homologs of pyridine and benzopyridine in group b. By this we mean the substituting radicals may be methyl, ethyl, propyl, butyl and higher homologous alkyl radicals containing up to 6 carbon atoms. 7

Similarly, we have specified lower alkyl nuclear substituted homologs of aromatic unsaturated mono-aldehydes in group c. By this we mean the substituting radicals may be methyl, ethyl, propyl, butyl and higher homologous alkyl radicals containing up to 6 carbon atoms.

Throughout the specification and claims it will be understood that the term lower is meant to designate alkyl and/or aryl groups containing no more than 6 carbon atoms.

While we have found that the incorporation of any one compound selected from the above broad group into a suitable varnish vehicle results in an efiective antifouling coating composition, our experiments show that a combination of two compound types, one from each of the subclasses a, b or c, is pronouncedly more efiective; and when we incorporate all three compound types there results an antifouling composition which is extremely toxic to marine arthropods, and which has an extremely rapid reaction upon arthropod larvae contacting surfaces coated with it. This experimentally demonstrable complementary action of the three types of compounds is not understood; it is not a simple additive eflect. It seems likely that the compounds of sub-class c ar the most strongly anaesthetic in action, and that the so anaesthetized arthropods are thus rendered more susceptible to the lethal action of the compounds of sub-classes a and b. Generally we find the ortho-substituted members of sub-class a to be more rapid in action than the para-substituted.

Typical compounds of the three classes above described are tabulated below:

Class a p-Cyclohexyl phenol Chlorinated cresols p-Tert. butyl phenol (mixed) p-Tert. amyl phenol o-Cresol o-Cyclohexyl phenol Thymol o-Tert. amyl phenol 2 chloro o phenyl o-Tert; butyl phenol phenol o-p-Cresols (crude cut) 2,4-dichlor phenol 1,3-xylenol Trichlor phenol Chlorinated x ylenols p-Chlor phenol (mixed) o-Chlor phenol p-Phenyl phenol Class I;

Pyridine Mixed pyridine bases Quinoline (B.Pt. 230-270 C.) Isoquinoline Mixed pyridine bases Quinaldine (B.Pt. 260-263 C.) Trimethyl pyridine aadipyridyl Tripyridyl 2-ethyl quinoline Class Cinnamaldehyde 2 phenyl -crotonaldeo Methyl cinnamaldehyde hyde 3 phenyl crotonaldep Methyl cinnamaldehyde hyde 3 phenyl buten 2, Trimethyl cinnamalde- 3-al-1 hyde 4 phenyl buten 2.

' p-Tert. butyl cinnamal- 3-al-1 dehyde 3-orthotolyl crotonaldehyde In formulating our antifouling compositions we prefer to use crude mixtures and rather broad fractionated cuts rather than to incorporate the pure compounds. Thus, we find that the product resulting from chlorination of a crude xylenol cut is somewhat superior to that resulting from chlorination of any single isolated xylenol. Similarly, we find that broad cuts or the coal tar bases of sub-class b are superior for our purpose to the pure compounds. The pyridine base cut boiling in the range 230"-270 C. is particularly effective. Further, we may employ with outstanding advantage any of the commercially able to employ resinous vehicles having substantially lower water permeability than dare he the case with prior art compositions; consequently, our antii'ouling coatings have a substantially longer service life, and are themselves protective against corrosive influences which are destructive of the underlying surface. The prior art antii'oullng paints, on the other hand, function by chalking of! succeeding layers of watersoitened, degraded, non-illm-forming decomposition products.

available basic coal tar pitches (not to be confused with ordinary coal tar) resulting from the prior separation of pyridine and other lower boiling coal tar bases. In general we find that any coal tar pitch containing at least one cyclic nitrogen base boiling above 230 C. at atmospheric pressure is particularly suited to our purpose. The compounds of sub-class 0 will ordinarily be added. in the form of rather narrow fractionated cuts. We find the technical grade of cinnamaldehyde itself to be particularly. suited for our purpose.

In the choice of the resinous components of our antifouling compositions we are not restricted to the oils and oleoresinous type of materials usually employed in metal-containing antifouling paints. Since our toxic agents are soluble in our varnish solvents we obtain a film in which the toxic compounds are molecularly dispersed, unlike the prior art compositions in which the pigment-like toxic salts are actually aggregates exceeding several microns in diameter. As a result of this molecular dispersion of our toxic agents we were We have found that practically any resinous composition soluble in, or capable of dilution with, coal tar hydrocarbons which yields films permeable to water at a rate of not less than 25 milligram oi water per mil 0! film thickness per square inch per 24 hours when tested by the free film diffusion-cell method (Wray and Van Horst, Ind. Eng. Chem. 28, 1268-9 (1936)) will function satisfactorily as the film-forming carrier for our organic toxic agents. In the table below we list the approximate permeability characteristics of a number of resinous coating materials.

Permeability in While there is no fixed upper limit to the permeability of our resinous vehicle, there is manifestly no advantage in employing a vehicle which is so rapidly permeable as to permit the toxic agent to be leached out in a short time and thus rapidly deplete the protective film of its antifouling agents. We have found that resinous vehicles having permeabilities not greater than 300 milligrams of water per mil of thickness per square inch per 24 hours are generally adequate for our purpose, though we prefer vehicles of permeability in the range of 30 to 130.

We have experimented widely and we find that the so-called spar-varnishes" made from phenolaidehyde resins having oil lengths of 25-50 gallons, the 011 being typically a mixture of equal parts of chinawood and linseed oils, are excellent carriers for our toxic agents. In employing such drying-oil modified varnishes it is necessary to double the normally contained quantity oi added cobalt, lead and manganese driers to overcome the antioxidant effect of the toxic agents For certain special applications, as to fiyint boat hulls and pontoons, it may be advisable to: other reasons to employ a varnish based on i thermoplastic synthetic resin of the polyviny chloride, polyvinyl chloride-acetate (known commercially as vinylite VYHF), chlorinated rubber or polymethacrylate ester ty W by evaporation of solvent alone, and our toxi agents may be incorporated directly into the resin solution without any addition of driers. Thl resulting antifouling films posssess all the sur face hardnes of the unmodified resins, are tack free, flexible, and tightly adherent. If desirec they may be pigmented in the usual manna with inert pigments and dyes.

Other resins which may be used as vehicles ii our antil'ouling compositions are those derived by heating drying oils with polybasic acidpolyhydric alcohol condensation products (typically drying-oil modified phthalic anhydrideglycerol resinoids). ester gum varnishes, ureaformaldehyde condensation products, cellulose mixed esters (typically cellulose aceto-butyrate and cellulose aceto-propionate) and cellulose ethers (typically ethyl cellulose).

In any case, we add up to l per cent by weight oi a soluble copper organic compound, such as copper llnoleate, copper resinate, copper naphthenate, or copper oleate, to inhibit algae growth as distinguished from barnacle encrustation.

For the sake of simplicity, we shall hereafter refer to our resinous vehicles as "permeable resinous organic film forming vehicles," and it will be understood that by this term we mean to include any resinous coating material having a permeability rate of 25 to 300 milligrams of water per mil of film thickness per square inch per 24 hours when tested by the previously described diffusion-cell method. Our experiments indicate that any resinous coating material responsive to this definition will serve as a satisfactory carrier for the toxic agents of our antifouling compositions.

While there is no fixed limitation upon the amount of toxic compounds which may be incorporated with the resinous vehicle, there is a practical upper limit in that too great an addition may yield films which are soft, non-adherent. and easily damaged. We are able to add as much as 50 per cent by weight of toxic compound. based on the total non-volatile content, without too material a degradation of the desirable properties of hardness, adhesion, and inertness to degradation by moisture and other influences. Conversely, there is a practical lower limit to the amount of toxic agent which may be added. Our experiments indicate that films containing as little as 2 per cent by weight of toxic compound are effective antifouling coatings. Our preferred compositions contain 20-30 per cent by weight of toxic compounds, based on the total non-volatile content. It will, of course, be understood that for our purposes the toxic agents are considered as non-volatile constituents, in contradistinction to the volatile solvents and diluents in which the resins and toxic agents are dispersed.

The following examples will serve to illustrate our invention, it being understood that we are not limited to the specific materials there described, nor to the specific compositions given.

Example 1 Toxic agents: Per cent Thymol 12.0 Copper linoleate 0.5 Vehicle:

Phenolic varnish 37.5

Base resin Bakelite BR- 254, (a pphenyl phenol HCHO resinoid) Oil length 25 gal. Oil composition 50% tung oil 50% linseed oil Solvents:

Stodsol 38.2 Xylol Dipentene 5.9

Add 25 ml. cobalt ciisolate drier and 70.5 ml. lead ciisolate drier per gallon of the above varnish; allow to stand 48 hours before application.

Example 2 Toxic agents: Per cent Coal tar base fraction B. Pt. 230- 270 C 10.0 Technical cinnamaldehyde 2.5 Copper oleate 1.0 Vehicle:

Oicoresinous varnish 36.5

Base resin Ester gum Oil length 33 gal.

Oil composition 60% tung oil 40% linseed oil Solvents:

Stodsol 28.2 Hifiash naphtha 10.0 Xylol 5.9 Dipentene 5.9

Add 16.7 ml. manganese ciisolate drier, 25 ml. cobalt oilsolate drier. and 71 ml. lead oilsolate drier per gallon of the above varnish; allow to stand 48 hours before application.

The solvent composition of Example 1. 50.0

Add 25 ml. of cobalt ciisolate drier and 85 ml. of lead oilsoiate drier per gallon of the above varnish; allow to stand 48 hours before application.

Example 4 Toxic agents: Per cent Z-chJoro-o-phenyl phenol 5.0 Coal tar base fraction B. Pt. 260- 263 C 5.0 Coal tar pitch 5.0 Pentachlor phenol 5.0 2,4-dimethyl cinnamaldehyde 4.0 Copper linoleate 1.0

Vehicle:

Oleoresinous varnish 251 Base resin ..Rosin grade WW Oil length ..25 gal. Oil composition ..'l0% linseed oil 30% tung oil Solvents:

The solvent composition of Example 2- 50.

Add 20 ml. manganese oilsolate drier, 25 m cobalt oilsolate drier and 85 ml. lead oilsolat drier per gallon of the above varnish: allow t 100,0 stand 48 hours before application.

Example 5 Toxic agents: Per cent 1,3-xyienol 0.5 Cinnamaldehyde 0.5 Coal tar base fraction B; Pt. 260- 270 C 0.5 Copper linoleate 0.2

Vehicle:

Copolymer of 85% vinyl chloride and 15% vinyl acetate 18.3

Solvents:

Isophorone 20.0 Cyclohexanone 10.0 Hexone 10.0 Hiflash naphtha 25.0 Xylol 15.0

' 100.0 Example 6 Toxic agents: Per cent o-Cyclohexyl phenol 5.0 o-Tert. amyl phenol 3.0 2,4-dichlorphenol 1.0 Tripyridyl 2.0 Quinoline 1.5 Copper resinate 0.5

Vehicle:

Oil-modified polybasic acid polyhydric alcohol resin 3'7 .0 Base resin .Phthalic giyceride of acid number 10-20 Oil length .50%

Oil composition '.60% linseed oil 40% soyabean oil Solvents:

Stodsol 25.0 Xylol 12.0 Dipentene 5.0 V. M. & P. naphtha 8.0

Add ml. cobalt oilsolate drier, 15 ml. manganese oilsolate drier, and 75 ml. lead oilsolate drier per gallon of the above varnish; allow to stand 48 hours before application.

Example 7 Toxic agents: Per cent 'Ihymol 1.0 Cinnamaldehyde 0.5 Coal tar p h 1.0 Copper linoleate 1.0

Vehicle:

Copolymer of methyl methacrylate (80%) and methyl acrylate (20%)-- 26.5 Solvents:

alcohol resin modified with 70% linseed oil 20% Solvents: Per cent Butyl acetate 25.0 Cellosolve acetate 5.0 Hifiash naphtha 10.0 Xylol 15.0 Dipentene; 5.0

Example 9 Toxic agents:

The composition of Example 7 5 Vehicle:

Chlorinated rubber--. 20

Solvents:

The composition of Example 7 It will be observed that all of the above examples yield clear varnishes. They may be pigmented to any desired color in the usual manner by grinding with the usual pigments and dyes in aballmill,orby grinding a e I :na n roll mill in a semi-paste consisting of the toxic agents and resins in sufiicient of the solvent mixture to yield a semi-paste. After grinding, the pigmented paste may be thinned to brush or spray consistency with a thinner having the composition of the specified solvent mixture.

Having described our invention and having shown the advantages attendant on its use, we claim as our invention:

1. An antifouling composition comprising (1) at least one toxic agent selected from the group consisting of the lower alkyl, aryl, and alicyclic substituted phenols in which the substituting group contains no more than 6 carbon atoms, together with their chlorinated derivatives; (2) at least one toxic agent selected from the group consisting of the pyridine and benzopyridine cyclic nitrogen coal tar bases and their lower alkyl-substituted homologs in which the substituting group contains no more than 6 carbon atoms; (3) at least one toxic agent selected from the group consisting of the aromatic unsaturated mono-aldehydes containing one double bond in the sidechain carrying the aldehyde group together with their lower alkyl nuclear-substituted homologs in which the substituting group contains no more than 6 carbon atoms; (4) a permeable resinous organic iilm-forming vehicle; and

(5) a volatile organic solvent for the whole composition.

2. The composition of claim 1 in which the percentage by weight of toxic component lies between 2 and 50, based on the total solids, and that of the permeable resinous organic filmiorming material correspondingly lies between 98 and 50; the whole being dispersed in a mixture of volatile organic solvents.

3. An antifouling composition comprising from 2 to 50% by weight of a mixture of 2-chloro-ophenyl phenol, quinaldine, and cinnamic aldehyde, dispersed in a drying-oil modified phenolformaldehyde varnish of oil length 25-50 gallons, the oil consisting of 30-70 parts of linseed oil and 70-30 parts of tung oil.

GEORGE H. YOUNG. PETER GRAY.