GB2141436A - Anti-pollution coating composition - Google Patents

Abstract

A pollution-proofing coating composition for surfaces of marine structures has, as a film-forming component, a mixture of a room temperature-curing silicone rubber intermediate condensate with a liquid paraffin-petrolatum mixture. A film obtained by applying this composition to a substrate exhibits low critical surface tension and low viscosity and prevents the surface from undergoing pollution by the adhesion of marine organisms thereto when exposed to seawater.

Description

SPECIFICATION Anti-pollution coating composition This invention relates to anti-pollution (pollutionproofing) coating compositions to be applied to underwatersurfacessuch asthe hulls of ships and the exterior of marine structures and seawater facilities in orderto protectthe surfaces exposed to seawater against adhesion of marine organisms.

The adhesion of marine organismstothehulls of ships and the exterior surfaces of marine structures and seawater facilities is a serious economic problem. To cope with this unwanted phenomenon, there has been adopted a method of coating the surface of such surfaces exposed to seawater with a pollutionproofing paint. The paint contains a toxic pollutionproofing component released gradually in minute amounts into seawaterto discourage the adhesion of marine organisms (hereinafter referred to simply as "pollution") giving rise to damage to the underwater surfaces. Such paints generally contain one of a variety of inorganiccopper or organictin compounds as the pollution-proofing component. However, for environmental reasons it is desirable in the future to change the technology concerned and employ nontoxic pollution-proofing paints.

Techniques for preventing pollution as aforesaid by coating the surfaces of marine structures with silicone rubber of a type curing at room temperature have been disclosed for example in U.S. Patent No.

3,702,778, Japanese Patent Gazette 53-35974, Japanese Patent Gazette 56-26272, and Japanese Gazette laid open application 56-92971.

Research has however shown that the pollutionproofing effect of the silicone rubber is maintained for only a short period (about three months) and that the silicone rubber exhibits poorfilm-forming properties, is very costly and fails to adhere fastto the surfaces of various conventional corrosion-proofing paints.

According to one aspect ofthe present invention, there is provided a pollution-proofing coating composition for surfaces of marine structures having as a film-forming component thereof a mixture of a room temperature-curing silicone rubber intermediate condensatewith a liquid paraffin-petrolatum mixture.

The composition of this invention will generally possess the same order of critical surface tension as the silicone rubber and have its components combined in a ratio falling within the miscibility range of the two components.

The silicone rubber intermediate condensate used in the composition of this invention will generally contain a terminal reactive group, for example an alkoxy group (-OR),an acyloxygroup

an oxime group (-ON=C), ora cyanate group (-NCO) and, informing the composition of this invention, generally will initially be dissolved in a solvent, for example, toluene, xylene, or mineral spirit in a concentration preferably falling within the range of 40 to 60% by weight. Asilicone rubber of this type will typically haveterminal moieties of one of the following general formulae::

(wherein R1, R2 and Reach denote independently an alkyl group, an allyl group, or a vinyl group).

Examples ofthe other possible reactive groups in terminal moieties of the intermediate condensate are

and--OO-TiOC (wherein Rand R' each denote an alkyl group or an ally group).

The liquid paraffin used in forming the liquid paraffin-petrolatum mixture preferably has a dyna micviscosityat400C in the range of SOto 110 centistokes. The petrolatum preferably has a semisolid wax consistency with a melting point in the range of 45" to 85"C and viscidity at 25"C in the range of 80to 210.The liquid paraffin and the petrolatum are preferably combined in a ratio such that the resultant mixture will acquire dynamic viscosity at 25"C in the range of 5,000 to 10,000 centistokes and preferably a critical surface tension of not more than 2.3 dynes/cm when a film thereof is dried. lithe viscosity is more than the upper limit or less than the lower limit ofthe range mentioned above and the critical surface tension is more than 2.3 dynes/cm, the coating composition will possess an inferior pollution-proofing property.

The mixing ratio by weight of the liquid paraffin and the petrolatum preferablyfalls within the range of 1 3:1, preferably 2 -- 3 : 1. If ratiodeviates from this range, the applied film of the coating composition will again possess a lower pollutionproofing property.

The liquid paraffin-petrolatum mixture is preferably incorporated in the room temperature-curing silicone rubber intermediate condensate in a proportion falling in the range of 35 to 95%, more preferably 50 to 75%, based on the intermediate condensate.

This percentage is expressed on a weight basis as are all percentages set out hereinafter. If the proportion is lessthan the lower limit ofthefirst aforementioned range,the composition produced possesses inferior pollution-proofing character. If it is more than the upper limit of this range, the liquid paraffin-petrolatum mixture may possess poor miscibility with the silicone rubberintermediatecondensateand,conse- quently, the composition produced will have a deficientfilm-forming property and adhesivity.

When applying the coating composition of this invention, the composition will be employed in a process forming the second aspect of this invention according to which a corrosion-proof paintfilm is provided on the surface and this is covered with a pollution-proofing coating to be exposed to seawater composition according to the first aspect ofthis invention. This corrosion-proofing film may be provided using one of many types of paint, for example, a chlorinated rubber, vinyl chloride polymer, epoxy resin, tar-epoxy resin, or urethane resin-based paint.

When the coating composition of this invention is directly applied to the surface of the corrosionproofing film, it shows relatively poor adhesion ta the film and, therefore, peels off, To ensure perfect adhesion of the composition to the film, the procedurewhich is preferably adopted isto applythe corrosion-proofing paintfirstly, apply to thisfilm of the corrosion-proofing paint one layer of a composition prepared by combining the same corrosionproofing paintwith3to 10%, based on this paint, of a 40 to 60% toluene (and/orxylene) solution of the aforementioned silicone rubber intermediate condensate, drythis applied solution layer, and then apply to the dried layer the coating composition of this invention.This procedure is effective in enhancing the adhesion between the film ofthe corrosionproofing paint applied to the surface of the marine structure and thefilm of the coating composition of this invention because it interposes between these two films a layer of a mixture of the aforementioned corrosion-proofing paint with the silicone rubber intermediate condensate. The silicone rubber intermediate condensate incorporated in the corrosionproofing paint intimately mixes with the corrosionproofing paint of the second layerand becomes intimately associated with the silicone rubber in termediate condensate ofthe coating composition of this invention, and finally cures.Thus, the intermediate condensate manifests a sort of anchoring effect and ensuresfirm adhesion betweenthetwofilms. By the use ofthe intermediate layer as described above, the use of the coating composition ofthis invention becomes a very practicable proposition.

The coating composition of this invention is formed by combining the room temperature-curing silicone rubber intermediate condensate with the mixture of the liquid paraffin and the petrolatum obtained bythe purification of a petroleum distillate, in the presence of an organic solvent. This composition can be applied to the surface of a given substrate with the aid of an ordinary coating tool such as a brush or spray.

The applied film of the coating composition is subject to the aetion of moisture (water) in the atmosphere which causes itto undergo a chemical reaction and cure. On curing, the applied film becomes converted into a film consisting of a combination of silicone rubber with liquid paraffin-petrolatum mixture. This film shows low critical surface tension of about 20 dyneslcm.

The pollution-proofing ability of the film is believed to be a result ofthe low critical surface tension ofthe combination of silicone rubberwith liquid paraffin- petrolatum mixture. It has been demonsatrated through experiments that the mixing ratio between the liquid paraffin and the petrolatum and the mixing ratio between the liquid paraffin-petrolatum mixture and silicone rubber have significant effects upon the pollution-proofing ability ofthe coating composition.

This is because the exposure of the cured film ofthe coating co composition to seawater has the effect of enlarging the molecularfreedom ofthewater- repelling group (chieflyCH = in the case of silicone rubber) oriented on the surface ofthe silicone rubber constitutingthe matrix of the film when suitable mixing ratios are employed.

Thefollowing Examples illustrate this invention: EXAMPLES 1 TO 8 A series of experiments was carried out using differentformulations ofthe coating composition of this invention bywayofillustration only. In the examples, the proportions of the components are expressed invariably in % by weight Table 1 shows mixing ratios between liquid paraffin and petrolatum employed and Table 2 shows typical formulations using the mixtures of Table 1, room temperature-curing typesilicon rubber intermediate condensate (expressed in solids content) and organic solvent Table 1 Component Formulation A B C D Liquid paraffin JIS K-2231 equivalent 1.5 2 2.5 3 Petrolatum JIS K-2235 equivalent * JIS = Japanese Industrial Standard Table 2 Example No.

Component 1 2 3 4 5 6 7 8 Room temperature temp curing V type silicone rubber intermediate con densate 36 34 32 36 38 36 34 36 Liquid paraffin petrolatum mixture Formulation A 20 30 25 Formulation B 25 20 20 Formulation C 15 Formulation D 20 Organic solvent Toluene 44 21 28 25 47 24 Xylene 20 10 19 44 Mineral spirit 41 20 Total 100 100 100 100 100 100 100 100 ( 73 (%) 55.6 73 93.755.69.555.673.555.6 To prepare a coating composition ofthis invention, liquid paraffin and petrolatum were weighed out in amounts corresponding to the appropriate ratio as shown in Table 1. These components were kneaded in a plastics or iron vessel to form a mixture.Then a prescribed amount of this mixture was placed in a solution prepared in advance bydissolving a room temperature-curing type silicone rubber intermediate condensate in an organic solvent and subsequently stirred until homogeneous with a stirrer, to produce the coating composition of this invention.

Examples 9 to 26 The coating compositions of the various preceding examples were applied to both sides of a steel plate (100x300x3 mm) ion a dryfilm thickness of 100 microns after the sides of the steel plate had been first coated with a corrosion-proofing paint of epoxy type or tar-epoxy type and then coated furtherwith a paint prepared by adding KE45TS (45% toluene solution) indicated in Table 2 in a solids concentration of 3 to 10% to the aforementioned corrosion-proofing paint.

The coated steel plates were immersed in seawater and, after 3 months, 12 months and 24 months, were tested for heir pollution-proofing character. For comparison, steel plates which were coated with compositions obtained by mixing silicone rubber intermediate condensate with 70%, based on the intermediate condensate, of either the liquid paraffin or petrolatum and steel plates which were coated by following the procedure ofthis invention, exceptthat the formation ofthe interposed layer of composition was omitted, were subjected to the same test. The results of the immersion test are shown in Table 3.

From the table it is noted that the coating composition ofthis invention exhibits outstanding pollutionproofing abilityfora long time.

In Table 3 the percentages represent mixing ratios of silicone rubber intermediate condensate solution to the same paint as the primer.

Table 3 Example Primer Inter- Coating composition 3 months' 12 months' 24 months' layer of Example immersion immersion immersion

9 10% 1 No pollution No pollution Slight adhesion of slime 10 2 Same as above Same as above Same as above 11 Fsn,y name as above name 55 above Same as above paint 12 4 Same as above Same as above Same as above 13 5 Same as above Same as above Slight adhesion of green laver an barnacles 14 3% 6 Same as above Same as above Same as above 15 7 name 55 above name as above Slight adhesion of slime 18 8 name as above name 55 above name as above 17 2 name 55 above name as above name 55 above 18 10% 4 name 55 above name 55 above name as above 19 5 name 55 above name 55 above Slight adhesion of graen laver Tar- and barnacles 20 epoxy 6 name as above name as above name as above 21 5% 7 Same as above Same as above Slight adhesion of slime 22 8 name as above name as above Same as above 23 2 name as above Separation of No aged coat inter 24 layer 4 name as above name as above 25 Comparison 1 (con- Heavy adhesion taining 70% of of green laver 5% Epoxy liquid paraffin) paint 26 Comparison 2 (con- Same as above taxing 70E af petrolatum)

Claims (14)

1. A pollution-proofing coating composition for surfaces of marine structures having as a filmforming componentthereof a mixture of a room temperature-curing silicone rubber intermediate con densate with a liquid paraffin-petrolatum mixture.

2. A pollution-proofing coating composition according to Claim 1, wherein the liquid paraffinpetrolatum mixture constitutes from 35to 95% by weight ofthe mixture thereof with silicone rubber intermediate condensate.

3. A pollution-proofing coating composition according to Claim 1 or2, wherein the mixing ratio by weight of the liquid paraffin and the petrolatum falls in the range of from 1: 1 to 3: 1.

4. A pollution-proofing composition according to any one ofthe preceding claims, wherein the petrolatum has a melting point offrom 45 to 85 and a viscidity in the range from 80 to 210 at 25 C.

5. A pollution-proofing composition according to any one ofthe preceding claims, wherein the liquid paraffin has a dynamic viscosity at 40 C of from 50 to 110 centistokes.

6. Apollution-proofing coating composition according to any one ofthe preceding claims, wherein the room temperature-curing silicone rub ber intermediate condensate comprises a reactive terminal group containing at least one group selected from alkoxy, acyloxy, oxime and cyanate groups.

7. Apollution-proofing coating composition according to any one of the preceding claims, wherein the liquid paraffin-petrolatum mixture has a viscosity at 25 C in the range of from 5,000 to 10,000 centistokes.

8. A pollution-proofing coating composition according to any one of the preceding claims, which has a composition such that afilm thereof applied to a substrate, has a critical surface tension of not more than 2.3 dynes/cm on drying.

9. A pollution-proofing coating composition substantially as described in any of the foregoing Examples 1 to 8.

10. Amethod of providing a pollution-proofing coating on a surface of a marine structure, which comprises providing a corrosion-proof paintfilm on the surface and covering this with a pollutionproofing coating composition according to any one ofthe preceding claims.

11. A method as claimed in Claim 10, wherein the paintfilm isformedfromachlorinated rubber,vinyl chloride polymer-, epoxy resin tar epoxy resin- or urethane resin-containing paint.

12. A method as claimed in Claim 10 or 11, wherein an intermediate layer is appliedto the surface and dried before applying said coating composition, which intermidiate layer is produced by mixing said paint with, based on the paint, 3 to 10% of a 40 to 60% toluene and/orsylene solution ofthe silicone rubber intermediate condensate.

13. Amethod of providing a pollution-proof coating on a surface of a marinestructure, substantially as described in any one of the foregoing Examples 9to 24.

14. A marine structure which has been provided with a pollution-proof coating as claimed in any one of Claims 1 to 9 of by the method of any one of Claims 10to13.