ANTI-CORROSIVE PROTECTIVE COMPOSITION

Abstract: Anti-corrosive protective compositions for metal, which composition contains a curable binder with after curing low water and oxygen permeability and at least one filler composed of solid parts, characterised in that the filler contains expanded polymer parts with a size of 1 to 100 micrometers.

Description: ANTI-CORROSIVE PROTECTIVE COMPOSITION The present invention concerns an anti-corrosive protective composition for metal, which composition contains a curable binder with after curing, a low water- and oxygenpermeability and at least one filler composed of solid parts. Such compositions are used to avoid or to slow down the oxidation of easily oxidizable metals, especially iron and steel. These compositions are applied in a liquid or powder form and harden on the metal surface. Rustformation on iron and steel is mainly the result of the formation of innumerable anodes and cathodes on the surface of the metal when it is exposed to oxygen and moisture. We can find a characteristic example of the formation of rr.icro-battεries on metal surfaces which are only partly protected and are therefore unequally subjected to the influence of weather-circumstances. On the parts with a high oxygen concentration cathodes are formed while on the parts with a low oxygen concentration anodes are formed. The present electron theory shows that these micro-batteries are the cause of corrosion. An electrochemical tension appears between the electrodes, hydrogen is formed at the cathodes while iron dissolves at the anode. The most obvious protection against corrosion consists of the application of a water- and gasimper eable coating on the metal surface. This principle of metal protection is known as the "barrier effect" and all existing anti-corrosive compositions are in a certain way based on this "barrier effect". The fillers of known compositions of the preceding kind are inert or mostly active pigments. Active pigments, materials which form combinations with oxygen and moisture and slow down the noxious influence of oxygen and moisture on the metal, improve the protection. These active pigments are mostly composed of lead, chromium, barium, molybdenum, zinc, calcium, strontium or phosphates. The activity of these pigments is limited in time, amongst other things because of their reaction with water and oxygen. Moreover the most of these pigments are harmful for the environment, wherefore their use will be increasingly limited. Inert or inactive pigments are the classical pigments, although there is a preference for lamellar and inert materials such as aluminium silicate, magnesium silicate, magnesium aluminium silicate, iron-magnesium aluminium silicate, aluminium powder, zinc dust, barium sulphate, quartz, iron oxide, titanium dioxide, etc. Some of these minerals can already be treated with polymers such as epoxy or silanes in order to obtain better adhesion to the binder. These minerals have sufficient water- and gasimpermeability. But if the adhesion of the binder on their surface is not good, a space is formed in which water accumulates, the so-called water bags. To prevent the formation of such water bags and thus to prevent the permeability of the coating, some minerals are consequently treated. Besides these pigments the known compositions usually contain other fillers to reduce the cost price and possibly some solvents which facilitate the application of the coating on the metal surface. It is generally accepted that a good anti-corrosive protective coating should be as dense as possible, in other words any hollow space, no matter how small, should be avoided as these spaces drastically reduce the protective quality of the coating. In order to obtain these properties the known compositions are composed of a very strong ramificated polymer binder which adheres rε arquably, preferably to fillers treated with adhesion promotors. Thus the formation of hollow spaces in the cured coating is avoided at all costs. As well as to prevent porosity in the coating, pigments and fillers are added in a lower volume concentration than the binder, which means that the pigment volume concentration is lower than the critical pigment volume concentration of the composition. The good anti-corrosive protective compositions which are known are therefore relatively expensive. The object of the present invention is to remedy this disadvantage and to supply an anti-corrosive protective composition for metals which provides an excellent protection but nevertheless is relatively cheap. To this end the filler contains expanded pclymerparts with a size of 1 to 100 micrometer. The inventor has surprisingly found that not only the use of polymer microparts in an anti-corrosive protective coating is possible, but that, moreover, the use of these microparts improves the corrosion resistance of the coating considerably, reduces the blister formation, lowers the saltformation of some pigments, increases the adhesion and results in compositions with properties previously unknown. Such microparts are known as such. There are expanded vinylidene chloride-acrylonitrile copolymer microspheres available on the market under the name Expancel. Applications of these microspheres are described in "Polymers Paint Colour Journal" of 27th November 1985 and 23rd July 1986. These expanded organic microspheres are usually used in water-based compositions such as decorative water-thinable interior housεpaints. The intention is mainly to reduce the price and the density and to improve the applicability. The exteriorly use of these microspheres is not recommended because of the sensitivity to U.V.-rays. Consequently it does not seem advisable for a professional to rely on such microspheres as a filler in an anti-corrosive protective composition. Generally speaking, a professional using expanded polymer microparts will expect the same disadvantages as with microspheres or microparts of an other material, namely the formation of hollow spaces in the cured composition. Through these spaces gasses and vapors can move freely thus substantially decreasing the protective activity of the composition which relies just on the formation of a water- and gasimpermeable protective layer. Water-vapor, which can damage the composition by fast evaporation or freezing, may also accumulate in these spaces. These spaces also cause a strong decrease in the mechanical and chemical resistance of the composition. In a particular form of embodiment of the invention the expanded polymerparts are microspheres, particularly hollow microspheres. Especially for anti-corrosive protective coatings for metal, a prejudice exists against the use of polymer microspheres, as these compositions are usually susceptible to weather influences and it is generally accepted that, for instance, a coating with expanded polymerparts as a filler is not weather-resistant, has insufficient mechanical properties and does not fulfill its protective function satisfactorily because of its porosity. In this form of embodiment, thanks to the addition of the expanded polymer microspheres, it is possible to obtain compositions with such anti-corrosive properties as cannot be obtained without the use of these parts or by using conventional fillers. In a useful form of embodiment of the invention the composition contains 0.05 to 6 wt% expanded polymerparts, calculated on the total wt% of the composition before curing. In a particularly useful form of embodiment, of the invention the polymerparts are obtained from vinylidene chloride-acrylonitrile copoly e . Other particularities and advantages of the invention will appear from the following description of an anti-corrosive protective composition according to the invention. This description is only given as example and does not limit the invention. An anti-corrosive protective composition according to the invention consists of a curable binder and 0.05 to 6 wt%, calculated on the total weight of the composition before curing, hollow microspheres with a size of 1 to 100 micrometer of an expanded polymer, very useful are the microspheres with one diameter between 1 and 100 micrometer. A very suitable polymer is vinylidene chloride-acrylonitrile copolymer. Such a suitable copolymer in the form of microspheres with the desired size is on the market under the name ΞXPANCEL, more specially the type DE 12 of the Swedish company Expancel. The blowing agent used for expansion is still present in the hollow microspheres. 3esides the necessary chemical and mechanical properties the used binders will also have a low water- and oxygenpermeability. Silicate, epoxy and polyurethane are most suitable for these applications, nevertheless other binders such as alkyd, styrene, chlorinated rubber, vinyl and some dispersions can also be used successfully. Silicates are very useful for welding primers because of their anorganic nature amongst other things. Epoxy and polyurethane are very suitable as binder since they harden as a result of chemical polymerisation as a result of which a strong ramificated and extremely dense polymer net-work can be obtained. A strong ramificated polymer net-work is hard and closed and therefore extremely water- and gasirapermeable. Besides these expanded polymerparts the usual ingredients for anti-corrosive protective compositions such as plasticizεrs, pigments, other fillers, catalysts, products for improving the adhesion, anti-oxidants, hardeners, viscosity modifying products, etc, can be added to the binder. The anti-corrosive protective composition is especially useful as anti-corrosive coating for, for example, iron or steel. This composition can be applied in liquid or powder form whereafter it will harden to the desired hardness. For the application in liquid form, one or more solvents and possibly dispersing agents may be added to the binder. The present invention will be illustrated in more detail with the following examples of compositions and in comparison a few reference compositions not based on the invention will also be given. REFERENCE A A zincrich anti-corrosive primer based on a polyurethane binder and obtained by mixing in a dissolver of : 721 parts by weight MDI polyurethane prεpolymer containing 16 wt% free -NCO groups, 7356 parts by weight zinc dust with a particle size of 2.8 to 3.2 micrometer, 44 parts by weight bentonitε type trεatεd mont orillonit (BENTONE 34) , 1379 parts by weight solvεnt (SOLVESSO 100) EXAMPLE 1 Rεferencε A is repeated but 160 parts by volume zinc dust arε rεplacεd by 160 parts by volume hollow expanded microspheres of vinylidenε chloride-acrylonitrile copolymer with an average size of 12 micrometer (EXPANCEL 551 DE 12) EXAMPLE 2 Reference A is repeated but 330 parts by volume zinc dust are replaced by 330 parts by volume Expancel 551 DE 12 EXAMPLE 3 Reference A is repeated but 550 parts by volume zinc dust arε replaced by 550 parts by volume Expancel 551 DE 12 REFERENCE B An anti-corrosive micaceous iron oxide surfacεr and topcoat based on a polyurethane binder and obtained by mixing in a dissolver of : 2038 parts by weight MDI polyurethane prepoly εr containing 16 wt% free -NCO groups 2125 parts by weight magnesium silicate with an average particle size of 1.2 micrometer 1426 parts by weight lamellar micaceous iron oxide (Haematite) with a particle size that is 92-94% smaller than 63 micrometεr. 437 parts by weight aluminium paste, 65% aluminium non-leafing with a particle size of 45 micrometer in white spirit-solventnaphta 81 parts by weight bentonite type treated montmorillonit (BENTONE 34) 3893 parts by weight solvent {SOLVESSO 100) EXAMPLE 4 Reference B is repeated but all the fillers (magnesium silicate, micaceous iron oxide and aluminium paste) are replaced by an equal volume of hollow expanded microspheres of vinylidene chloride-acrylonitrile copolymer with a size of 12 micrometer. EXAMPLE 5 Refεrencε B is rεpεatεd and 60 parts by wεight Expancel 551 DE 12 are added, so that the total pigment volume concentration increases 15.90 % compared to reference B EXAMPLE 6 Example 4 is repeated and 60 parts by weight Expancel 551 DE 12 are added, so that the total pigment volume concentration increases 15.90 % compared to Example 4 REFERENCE C An anti-corrosive primer, surfacer and topcoat based on a olyurethane-tar combination and obtained by mixing in a dissolver of : 1994 parts by weight MDI polyurethane prepoly er containing 16 wt% free -NCO groups 1968 parts by weight waterfrεe tar (CTC 15P30 - CINDU) 2931 parts by weight magnesium silicate with an average particle size of 1.2 micrometer 147 parts by weight bentonite type treated montmorillonit (BENTONE 34) 2960 parts by weight solvent (XYLENE) EXAMPLE 7 Reference C is repeated and tar and magnesium silicate are replaced by 21 parts by weight of the above mentioned Expancel 551 DE 12. The total pigment volume concentration therεforε increases 7.5 % compared to Referεncε C. The compositions thus obtained : references A, B, C and the examplεs 1 to 7 are applied on untreated degreased metal plates in a dry layer of 100 micrometer. In the middle the Cross of Evans is engraved. Then the plates are placed obliquely in a corner of 15 degrees off perpεndicular in the saltspray apparatus and are exposed for 500 hours to a saltatmosphere of 5% sodium in watεr at a temperature of 45 degrees Centigrade. The testrεsults are represented in the following tables. TABLE Ruststains on the surface Rustspots on the metal Rust in the cross Blisters at the cross Blisters on the surface Formation of zincsalts REF . B EX. 4 EX . EX . Ruststains on thε surfacε 4 6 8 9 Rustspots on the metal 7 9 9 10 Rust in the cross 5 4 6 5 Blisters at the cross 7 6 9 7 Blisters on the surface 8 8 8 8 Formation of zincsalts REF. EX. 7 Ruststains on the surface Rustspots on the metal Rust in the cross Blisters at the cross Blisters on the surface Formation of zincsalts Values : 0 = bad 5 = average 10 = very good From the tables above thε extreme importance of the present invention is obvious. The blister and zincsalt formation on zincrich paints is strongly counteracted (REF. A, EX. 1, 2 and 3) , the quality of inert pigmentεd cured compositions is grεatly i provεd (REF. B, EX. 4, 5 and 6) and it is evεn possiblε to rεplacε thε high quality but black and environmentally unfriεndly tarcomposition with a tarfree variant (REF. C, EX. 7) Of course these good properties are not limited exclusively to moisture-curing polyurethane binders, they can also be obtained with other binders such as silicates, epoxy, styrene, two-component polyurethanes, alkyds, chlorinated rubber, vinyl, silicons and some dispersions. Moreover the scope of the present invention is not limited to the forms of embodiment described above and within the scope of the patent application many changes can be made to the describεd forms of embodiment.

Claims: CLAIMS 1. Anti-corrosive protective composition for metal, which composition contains a curable binder with after curing a low water- and oxygenpermeability and at least one filler composed of solid parts, characterised in that the filler contains expanded polymerparts with a size of 1 to 100 micrometer. 2. A protective composition according to the preceding claim, characterisεd in that the expanded polymerparts are microspheres. 3. Protective composition according to the preceding claim, characterised in that the microspheres are hollow microspherεs. 4. Protective composition according to any one of the precεding claims, characterised in that it contains 0.05 to about 6 wt% εxpandεd polymerparts, calculated on the total weight of the composition before hardening. 5. Protectivε composition according to any onε of the preceding claims, charactεrisεd in that the expanded polymerparts are made of a gasimper eable polymer. 6. Protective composition according to the preceding claim, characterised in that the polymerparts are made from vinylidene chloride-acrylonitrile copolymer. 7. Protective composition according to any one of the claims 5 and 6, characterised in that the expanded polymerparts still contain a blowing agent. 8. Protective composition according to any one of the preceding claims, characterised in that the binder comεs from at lεast one of the following groups : polyurεthanε, epoxy, silicatε, alkyd, styrene, acryl, chlorinated rubber and vinyl.

Inventors: GLORIEUX HUGO ALBERT MAURITS, GLORIEUX, HUGO, ALBERT, MAURITS
Applicants: GEHA NV, GEHA, NAAMLOZE VENNOOTSCHAP
Application year: 1991
Main classification: C09D5
IPC codes: C08L101, C09D5, C09D125, C09D133, C09D163, C09D167, C09D175