Bortnik, Lev (Harmonim Street 1/2 Nesher, 36810, IL)
|1.||An acidic, waterthinnable paint composition suitable for rust conversion and corrosion inhibition.|
|2.||A composition according to claim 1, which is water based.|
|3.||A composition according to claim 1 or 2, which is thermally stable up to at least 250°C.|
|4.||A composition according to any one of the previous claims, which is thermally stable up to 400°C.|
|5.||A composition according to any one of the previous claims having a pH of less than 5.|
|6.||A composition according to the previous claim having a pH between 2.5 and 3.5.|
|7.||A composition according to any one of the previous claims, suitable for treating rust layers of more than 20um thickness.|
|8.||A composition according to the previous claim, suitable for treating rust layers of more than 50pm thickness.|
|9.||A composition according to any one of the previous claims, comprising alkyd resins, an acid, iron oxide pigment, a stabilizer, and metallic zinc or zinccontaining compound.|
|10.||A composition according to claim 9, further comprising at least one compound selected from the group consisting of additives, fillers, surfactants, thickeners and additional pigments.|
|11.||A composition according to claim 10 wherein the additives are selected from the group consisting of chlorides, phosphates and sulfates of alkali and earth alkali metals.|
|12.||A composition according to claim 11 wherein said additives are selected from the group consisting of NaCI, MgCl2, MgSO4, and mixtures thereof.|
|13.||A composition according to claim 9 wherein the alkyd resins are water emulsions of acrylic resins, vinyl resin polymers, and mixtures thereof.|
|14.||A composition according to any one of claims 9 to 13 wherein the alkyd resins have solid content of 45% to 55%.|
|15.||A composition according to any one of claims 9 to 14 wherein the acid is phosphoric acid.|
|16.||A composition according to any one of claims 9 to 15 wherein the iron oxide forms at least 2% (w/w) thereof.|
|17.||A composition according to the previous claim, wherein the iron oxide forms 7% (w/w) thereof.|
|18.||A composition according to any one of claims 9 to 17 wherein the stabilizer is selected from the group consisting of propanol, propylene glycol, anhydride ions of phosphor and fluorine, and mixtures thereof.|
|19.||A composition according to the previous claim wherein the stabilizer is selected from the group consisting of WRACLA, BYK 154, and DISPEX.|
|20.||A composition according to the previous claim wherein the stabilizer is WRACLA.|
|21.||A composition according to any one of claims 9 to 20, wherein the fillers are selected from the group consisting of silicon oxide, barium sulfate, and mixtures thereof.|
|22.||A composition according to any one of claims 9 to 22 further comprising surfactant compositions.|
|23.||A composition according to the previous claim wherein the surfactants are selected from the group consisting of BYK 036, BYK190, and BYK360, and mixtures thereof.|
|24.||A composition according to any one of claims 9 to 23 wherein the thickener is hydroxyethylcellulose.|
|25.||A composition according to claim 1 comprising 20%60% alkyd resin, 2%5% phosphoric acid, 10%30% pigments, 3%20% fillers, 0.1%1% stabilizer, 0.1%0.5% thickener, 1%3.5% additives, all percentages w/w, and the balance water.|
|26.||An object that is painted with a paint composition according to any one of the preceding claims.|
|27.||An object according to claim 26, which is made of iron.|
|28.||A method for protecting an object from corrosion and converting rusty portions thereof into noncorrosive portions, the method comprising painting the object with the paint composition according to any one of claims 1 to 25.|
FIELD OF THE INVENTION This invention relates to rust converting and rust inhibiting coatings.
BACKGROUND OF THE INVENTION Many compositions for removal and inhibition of corrosion are known in the literature. Some examples to such compositions are listed below.
US 4,462,829 describes a rust converting and rust inhibiting primer, which comprises an aqueous suspension or aqueous emulsion of alkyd resin, pigments, a drying accelerator and a surfactant, and may be thinned by non-polar solvents such as petroleum spirits.
US 5,312,491 describes rust inhibiting compositions that contain oxime compounds as a rust converter and have improved elasticity.
US 5,476890 describes a water thinnable primer, effectively adherent to rusted metal substrates that has a neutral pH of around 7.
US 4,086,182 describes a rust transforming composition comprising an aqueous dispersion of a synthetic binding agent, a polymeric esterification product and acid anhydrides. On application to rusty iron the composition gives deep black lacquerlike corrosion-resistant film.
SUMMARY OF THE INVENTION The invention provides, according to one of its aspects, an acidic water thinnable paint for rust conversion and corrosion inhibition. The application of the
paint of the invention to a rusted surface results in rust conversion and generation of an elastic passivation film, which exhibits strong adhesion to the metal surface.
In this context acidic means having a pH of less than 5, preferably between 2.5 and 3.5. The acidity of the paint of the invention is advantageous since it allows a most efficient rust converting. Thus, the paint of the invention may be used for treating rust layers of more than 20pm thickness, and some paint compositions according to the invention are suitable for treating rust layers of more than 50, um.
As the treated rust layer is thicker a larger number of paint composition layers may be required.
The paint according to the invention typically shows very high thermal stability, and deformations are found to occur only around 250°C to 400°C, depending on the specific embodiment. The minimum film forming temperature (MFFT) of paint compositions according to the invention is typically 5°C and in some embodiments may be as low as 0°C.
The paint of the invention creates a coating, which is capable of simultaneously acting as bonding, inhibiting and protecting layer. The coating includes the products of the reaction between the painted object (whether rusted or not) and the paint composition. The coating thus formed is strong and self-curing, and under normal environmental conditions requires no additional protective lacquer/paint overcoat. Furthermore, the coating may be easily over-coated with a wide variety of paints in order to manipulate its final color, or in order to grant it additional protection. Such additional protection may be needed when the coating is used under severely corrosive environmental conditions, for example, when the coated objects are ducts for corrosive chemicals.
The paint of the invention comprises alkyd resins, an acid, iron oxide pigment, and a stabilizer. Typically, the paint according to the invention also comprises additives, fillers, surfactants, thickeners and additional pigments.
The alkyd resin is preferably a water emulsion of acrylic resins, vinyl resins, polymers and mixtures thereof. Its solid content is preferably from 45% to 55%.
The acid is preferably phosphoric acid.
The iron oxide, Fe203, is at least 2% (w/w) of the paint of the invention, preferably 7%.
Nonlimiting examples of stabilizers that may be useful in preparing a composition according to the invention are propanol, propylene glycol, anhydride ions of phosphor and fluorine, and mixtures thereof. Several commercially available stabilizers that were found to be suitable for use according to the present invention are DISPEXTM, manufactured by CIBA Speciality chemicals of Basel, Switzerland, BYK 154, produced by BYK Chemie Gmbh, Wesel, Germany; and WRACLATM, manufactured by the PCI GROUP, USA. As shown below, WRACLATM is most preferable.
Suitable fillers should be acidic (of pH 5 and below) and may include, but are not restricted to silicon oxide and barium sulfate.
As well known in the art, surfactant compositions may be added to the paint in order to prevent it from creating bubbles, to enhance its flexibility, and the like.
Non-limiting examples to these are the commercially available BYK-036, BYK-190, and BYK-360, all manufactured by BYK-Chemie GmbH of Wesel, Germany.
A non-limiting example of a thickener suitable for use in accordance with the present invention is hydroxyethylcellulose.
Additives that may improve the quality of the paint of the present invention are inorganic salts, typically chlorides, phosphates and sulfates of alkali and earth alkaline metals, preferably NaCl, MgCl2, and MgS04. Such additives improve the paint stability under severe humidity conditions. One way to provide such additives to the composition is to replace at least part of the water with seawater.
According to another aspect of the present invention there is provided an object that is painted with a paint composition according to the invention.
Preferably, such an object is made of iron.
According to another aspect of the present invention there is provided a method for protecting an object from corrosion and converting rusty portions
thereof into non-corrosive portions, the method comprising painting the object with the paint composition of the invention.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS In order to understand the invention and to see how it may be carried out in practice, some specific embodiments will now be described, by way of non-limiting examples only.
EXAMPLE 1 Paint was prepared as follows: to 26 part of phosphoric acid (40% in water) were added 2 parts of zinc molibdenum ortho phosphate hydrate, 1 part of sodium chloride. The rest of the ingredients were added to the solution thus obtained.
0.4 parts of hydroxyethyl cellulose and 0.9 parts of WRACLA were mixed with 44 parts of water. To this solution were added 15 parts of zinc aluminum phosphate, 6 parts of barium sulphate and 6 parts of Silicon oxide, and the mixture was thoroughly mixed to obtain a dispersion.
A ferrous oxide pigment is prepared by grinding 15 parts of micronized Fe203 to 6-7 Hegman Alkyd resin was prepared from 50 parts vinyl acrylic copolymer (53-55% solids) and 50 parts of acrylic copolymer (46-50% solids) together with BYK 036, BYK 190 and BYK 380.
All the solutions were mixed together and the pH was stabilized at around 3.5
EXAMPLES 2-4 The following table summarizes formulations of paints prepared according to the invention: Table 1 Parts Example 1 Example 2 Example 3 Example 4 2 Zinc ZnO Zn Zn (2.1 parts) molybdenum orthophosphate hydrate NaCI NaCI NaCI 1 MgC12 MgSO4 MgSO4 MgSO4 15 Zinc aluminum Zinc Zinc molybdenum Zinc molybdenum polyphosphate molybdenum orthophosphate orthophosphate hydrate orthophosphate hydrate hydrate hydrate All the other ingredients, quantities and method of preparation are like those given under EXAMPLE 1 above. (Example 1 in the table is a repetition of EXAMPLE 1).
Testing examples 1-4 The coatings with the above-described compositions were applied to rusted metallic substrate panels by a brush. The coatings were applied in the amount 80-100 g/m2 in a crosswise pattern. Two coats were applied with the drying time between each coat of 60 min. After that, the coatings were dried for 24 hours. After drying, the panels were placed into a salt spray cabinet with a concentration of 5% NaCI at a cabinet for 300,500,1000 and 1500 hours exposure and then tested. The properties tested included flexibility test in accordance with ASTM D522 and adhesion and general appearance test in accordance with Israeli Standard SI 785 Part 27. The panels coated by commercially available rust converting coatings were tested as well. The obtained results are summarized in tables 2 and 3 below.
Table 2 Coating after 100 hrs in salt cabinet after 300 hrs. in salt cabinet According to Bend Adhesion Appearance Bend test Adhesion appearance invention test Example 1 Pass 0 Change color Pass 2 No change Example 2 Pass 0 Change color Pass 4 Bubbles Example 3 pass 0 Change color Pass 5 No change Example 4 Pass 0 Change color Pass 0 No change Conventional Bubbles Granville Bubbles Hammerite T. Metal Bubbles Failed 5 Bubbles
Table 3 Coating after 500 hrs in salt cabinet after 1000 hrs. in salt cabinet after 1500 hours in salt cabinet According to Bend Adhes. Appear. Bend Adh. Appear. Bend Adh. Appear. invention test Test Test Example Pass 0 No change Fail 15mm 2 no change Fail 20mm 5 No change Example 2 Pass 1 No change Fail 25mm 4 no change Fail23 mm 5 No change Example 3 Pass 1 Nochange Fail20 mm 2 no change Good 5 No change Example 4 Pass 0 No change Fail 1 2mm 4 no change Fail 17mm I No change Conventional Granville Bubbles bubbles bubbles Cracks bubbles bubbles Hammerite Bubbles bubbles bubbles T. Metal
EXAMPLES 5-8 In table 4 bellow there are represented experimental results obtained with compositions of Example 2 above, where the stabilizer WRACLA was replaced by other stabilizers. The results are of tests preformed as explained above.
Table 4 No. Stabilizer Quantity 100 hr. check out 300 hr. check out 500 hr. check out 2 3 l 2 2 3 Pass 0 Cracking Pass 3 Cracking no. 8 no. 4 6 Parmetol 0.3 Pass 2 Blister Fail 3 Rusting, DF18-ing 20 blistering no. 6 mm no. 8-1 7 Dispex 0.4 Fail 3 Blister- A40 23mm ing no. 6 8 Propanol 0.3 Pass 2 No Pass 2 Blistering Pass 3 Bubbles bubbles no. 6 No. 4
1. bend test (ASTM D 522-Flexibility) 2. adhesion (ASTM D 3359) 3. appearance (ASTM D 714-87, D 610) EXAMPLES 9 and 10 The thermal stability of the following paint compositions was checked and it was found that only at 250°C thermal deformations are induced in the composition of example 9, and in the composition of example 10, thermal deformations were induced only at 400°C. Both compositions had BYK 036 as a surfactant. The pH of the composition of example 9 stabilized on 3.1, and that of example 10 on 2.8. It may be generally stated that reducing the amount of alkyd
resins in the composition allows for stability under higher temperatures, but may cause the painted layer to be more fragile. The formulations of the paint compositions of example 9 and 10 are given in table 5 below.
Table 5 Component Parts in example 9 Parts in example 10 Phosphoric acid (40%) 26 24 MgSO4 Zinc powder 2 2. 1 NaCl 1 Hydroxyethylcelluslose 0.4 0.4 Water 44 43 WRACLA# stabilizer 0.9 0.9 Zinc molibedenum 6 - orthophosphate hydrate Zinc aluminum-8 polyphosphate hydrate BaS04 6 6 SiO2 17 21 Fez03 15 15 Acryli copolymer 46 40 (46-50% solids) Vinyl acrylic copolymer 46 40 (53-55% solids)