APPLICATION METHOD OF WATER-BORNE PAINT ON A NON-FERROUS METAL PRODUCT

Abstract

 Method of application of water-soluble lacquer comprising 75 to 80 weight% of acrylic dispersion, 4,75 to 5,75 weight% of additive for wettability, dispersion and anti-foamability, 0,1 to 0,1 weight% of corrosion inhibitor, 2 to 10 weight% of water soluble organic corrosion inhibitor based on a mixture of potassium octadecanoate, tripotassium phosphate and 2,2,2"-nitroethanol, 5 to 10 weight% of anticorrosion pigment based on oxy-amino phosphate complex of calcium and manganese, and water, on non-ferrous metal product, characterised in that the lacquer diluted with 8 to 18 weight% of water is applied by pneumatic spraying under the pressure of 0,15 to 0,45 MPa at room temperature ranging from 18 to 23 °C and with relative air humidity max. 80% on the non-ferrous metal product surface with room temperature ranging from 18 to 23 °C in an interval of min. 3 °C above the dew point, wherein drying at room temperature ranging from 18 to 23 °C occurs for lacquer application.

Description

State of the Art

[0001] The present invention relates to the field of non-ferrous metal products protection, especially non-ferrous aluminum-based metals, against corrosive attack.

Background of the Invention

[0002] Nowadays, a technology of surface protection of metallurgical steel products using water-soluble transparent lacquer as described in Czech patent no. 304190. The disclosed technological process comprises, at first, preheating of a metallurgical product to a temperature between 38 and 45 °C, subsequently spraying of the lacquer diluted with 10 to 15 weight% of water under air pressure of 0,2 to 0,4 MPa, followed by air drying for 10 minutes at ambient temperature, followed by drying at the temperature from 68 to 78 °C for 30 minutes and then cooling down in air at ambient temperature.

[0003] It is generally known fact about protection of steel and other non-ferrous metals surfaces and their alloys, that they are usually not coated, because they create their own protective oxide layer. Specifically, it is difficult to achieve desired adhesion of the coating system of the aluminum, and therefore only those paints and technologies may be used, which are specially designated for aluminum. A significant drawback is production of transparent lacquer. In all cases it is necessary to clean the surface thoroughly before applying a coating and the majority of current coating compositions do not have desired adhesion to the non-ferrous metals and their alloys.

[0004] Among technologies of protection of steel alloy products belongs a process of anodization of aluminum. It is formation of chemically resistant aluminum oxide layer on the steel alloy surface by electrotechnical method using anodic oxidation. A product made of steel alloy serving as anode is electrolyzed in the acid aqueous solution, wherein hydrogen is released on the cathode and aluminum oxide is released on the anode. The acid present in the electrolyte slowly dissolves the resulting aluminum oxide and therefore creates nanopores in the surface layer. These openings allow the electrolyte solution and the current to reach aluminum substrate and continue increasing the layer width in comparison to the process of passivation. A drawback with using acidic solutions is their difficult disposal as well as the difficulty to provide the perfect cleanliness of the product surface before application.

[0005] Further, there is a possibility of application of pigmented powder paint by the means of electrostatic spraying with subsequent heat setting, wherein for securing of good lacquer adhesion, it is recommended to apply a thin phosphate layer on aluminum alloy in advance. This layer is obtained from anodic oxidation of aluminum alloy in aqueous electrolyte of phosphoric acid. A drawback of this process is securing the cleanliness of the surface before the application of phosphate layer, the application of a phosphate layer and heat treatment of the coated powder, what results in increased energetic demands of the whole process.

[0006] Another part of the state of the art are applications of solvent based pigment coatings specially designed for aluminum alloys. A drawback is high VOC (volatile organic compounds) content in the coatings and a necessity of application of thicker layers. Moreover, decrease in adhesion of coating on aluminum surface may occur.

Summary of the Invention

[0007] The summary of the present invention is the innovation of non-ferrous, especially aluminum, alloy surfaces using transparent water-soluble nanolacquer applied on their surface without any significant demands on surface cleanliness.

[0008] The object of the present innovative invention is a method of application of water-soluble lacquer comprising 75 to 80 weight% of acrylic dispersion, 4,75 to 5,75 weight% of additive for wettability, dispersion and anti-foamability, 0,1 to 0,2 weight% of corrosion inhibitor, 2 to 10 weight% of water soluble organic corrosion inhibitor based on a mixture of potassium octadecanoate, tripotassium phosphate and 2,2,2"-nitroethanol, 5 to 10 weight% of anticorrosion pigment based on oxy-amino phosphate complex of calcium and manganese, and water, on non-ferrous metal product, characterised in that the lacquer diluted with 8 to 18 weight% of water is applied by pneumatic spraying under the pressure of 0,15 to 0,45 MPa at room temperature ranging from 18 to 23 °C and with relative air humidity max. 80% on the non-ferrous metal product surface with room temperature ranging from 18 to 23 °C in an interval of min. 3 °C above the dew point, wherein drying at room temperature ranging from 18 to 23 °C occurs for lacquer application.

[0009] The proposed dilution including the application pressure was experimentally tested and customized according to the recommendations of lacquer manufacturer, so as to achieve the lacquer adhesion to the substrate, represented by a non-ferrous, especially metal based on aluminum, metal product. When not sticking to the maximum relative humidity and dew point, poor adhesion to the substrate may occur. In case the interval is lower than 3 °C, the surface gets bedewed and therefore the adhesion of water solution having different chemical composition than water used for lacquer dilution occurs, and this may cause poor adhesion and overall lacquer quality. Lacquer application and coating requires dry surface, not bedewed surface, before application.

[0010] Using the above discussed method, wet film thickness from 150 to 200 µm is achieved, and after the final drying (setting), dry film thickness from 40 to 60 µm is achieved.

[0011] It had been proven in practice that the permissible level of dusting of non-ferrous metal product surface before lacquer application is according to 2/2

SN ISO 8502-3, i.e. an amount of dust grade 2, dust particles size class 2.

[0012] Products, of which the surface is supposed to be protected by the method of the present invention, are made of non-ferrous metals, especially metals based on aluminum. For achieving optimal anti-corrosion properties it is necessary to stick to the prescribed technological process of coating system for non-ferrous metal production.

[0013] Subject to the above innovative method of transparent protective water-soluble lacquer application, a compact non-stick lacquer layer is formed, with dry thickness of 40 to 60 µm with protective nano layer thickness of 25 to 50 nm, on the phase interface non-ferrous metal (aluminum, its alloys, etc.)/film (lacquer), with corrosion resistance longer than 200 hours determined by corrosion test with salt spray according to

SN EN ISO 9227 (corrosion tests in artificial atmosphere - salt spray test). After this corrosion test with salt spray, the coating system exhibits damage parameters according to

SN EN ISO 4628: blistering of film - grade 0 (without blisters), cracking of film - grade 0 (without cracking), flaking of film - grade 0 (without flaking). Adhesion of the coating system to the substrate material is determined by cross-cut testing and X-cut testing according to

SN EN ISO 16276-2 exhibits classification grade 0.

[0014] The composition of used water-soluble lacquer and its additional preferred embodiments are disclosed in RU 2441044 C1. Resulting properties of such modified alloy comprises better adhesion, surface transparency, and corrosion resistance - against environment from moderate to high levels of corrosion aggressiveness (grade C3 to C5) including coastal areas. An advantage of protective lacquer composition is also very low VOC (volatile organic compounds) content.

[0015] Insoluble passivation nanolayer of the surface of the non-ferrous metal, e.g. aluminum alloy, product is formed even without thorough cleaning of the surface. Dusting of the surface of the input material before protective lacquer application is determined according to

SN ISO 8502-3. The results of laboratory tests show that the size of dust particles on the surface of non-ferrous metal product for effective lacquer coating is max. 2 and dusting grade is max. 2. In case of high surface contamination of non-ferrous metal product, preferably a simple chemical degreasing pre-treatment of the non-ferrous metal surface is carried out before lacquer application, after the degreasing the product is rinsed with water, and after the rinsing the product surface is dried.

[0016] For degreasing, preferably an alcalic degreasing formulation with pH ranging from 8,5 to 10,5 is used. Degreasing occurs at room temperature, i.e. about 18 to 23 °C, for 2 to 8 min. according to degreasing technology. The purpose of degreasing is to remove undesirable impurities in the form of grease, dust, etc. from the surface.

[0017] The rinsing water temperature during rinsing may be from 18 to 23 °C, preferably heated water may be used for increasing the rinsing efficiency. The purpose of rinsing is to remove residues of impurities, dust and degreasing formulation from the product surface.

[0018] Drying of the non-ferrous metal product surface is preferably made using compressed air or elevated temperature, preferably 60 to 80 °C for about 5 min. The purpose is to remove rinsing water from the product surface.

[0019] After carrying out the above discussed chemical pre-treatment of the surface, an application of transparent protective water-soluble nanolacquer follows. The application occurs according to the above stated technological conditions.

[0020] A layer of transparent protective water-soluble nanolacquer may be applied up to dry film thickness of 60 µm, wherein maximum protection efficiency is provided by passivation nanolayer with thickness of 50 µm, which inhibits the penetration of water and oxygen to the non-ferrous metal product surface.

Description of Preferred Embodiments

[0021] The present invention will be further clarified by the means of following preferred embodiments. The water-soluble transparent protective lacquer, of which the composition is disclosed in patent specification RU 2441044 C1, was applied on aluminum alloy used in automobile industry and for laboratory use of lacquer manufacturers, so called Standards.

[0022] Lacquer contained 75 to 80 weight% of acrylic dispersion, 4,75 to 5,75 weight% of additive for wettability, dispersion and anti-foamability, 0,1 to 0,2 weight% of corrosion inhibitor, 2 to 10 weight% of water soluble organic corrosion inhibitor based on a mixture of potassium octadecanoate, tripotassium phosphate and 2,2,2"-nitroethanol, 5 to 10 weight% of anticorrosion pigment based on oxy-amino phosphate complex of calcium and manganese, and water.

[0023] The surface of treated product exhibited a high degree of contamination, therefore the chemical pre-treatment of the surface was made before the application of film. Alkaline degreasing formulation was used for surface degreasing. For various samples of non-ferrous material on aluminum base, dilution was experimentally tested, and based on the results, pH ranges from 8,5 to 10,5. Particularly, type, amount and holding force of adhesion of impurities on the surface have influence on pH value, which may vary in the given range. In this case, degreasing technology was chosen by dipping, the degreasing time 2 to 8 min. depending on the amount of impurities, type of contamination and their adhesion to the substrate. Degreasing occurred at normal room temperature, i.e. about 18 to 22 °C. Degreasing was followed by rinsing with water, the temperature of water ranged from 18 to 22 °C, wherein heated water may be used for increasing rinsing efficiency. Rinsing removed residues of impurities, dust and degreasing formulation from the product surface. Rinsing was followed by drying of the product surface using elevated temperature of 60 to 80 °C for about 5 min., what resulted in the shortening of technological time.

[0024] After the chemical pre-treatment of the surface, an application of transparent protective water-soluble nanolacquer followed. The application was carried out under following technological conditions: method of application - pneumatic spraying, operating pressure - 0,15 to 0,45 MPa, dilution with 8 to 18 weight% of water, ambient temperature ranging from 18 to 23 °C, the temperature of coated material ranging from 18 to 23 °C with interval min 3 °C above the dew point, relative air humidity max. 80%, the wet film thickness from 150 to 200 µm, dry film thickness from 40 to 60 µm. The application of lacquer was followed by setting at standard room temperature - ranging from 18 to 23 °C. After the setting following the said application method, a compact non-stick layer with dry film thickness from 40 to 60 µm is formed, with the protective nanolayer thickness from 25 to 50 nm, on the phase interface non-ferrous metal (aluminum and its alloys, etc.).

[0025] Technological parameters of coating system application are shown in the Table 1.

Table 1: Parameters of coating system application

Coating system	Transparent water-soluble lacquer
Application method	Pneumatic spraying
Dilution	8 - 18% (water from the water supply system)
Room temperature (ambient)	about 18 to 23°C
Temperature of the substrate	18 to 23°C with the interval of min. 3°C above the dew point
Ambient temperature during setting of film	about 18 to 23°C
Relative air humidity	max. 80%
Dry film thickness (DFT)	40 to 60 µm
Wet film thickness (WFT)	150 to 200 µm

Determination of lacquer dry film thickness:

[0026] Dry film thickness (DFT) is determined according to

SN EN ISO 2808. A non-destructive method using digital thickness gauges is used. A zero value of thickness gauge is calibrated on a smooth test board, micron value is calibrated using calibrated etalon. This value is higher than the measured value. An individual dry film thickness lower than 80 % of nominal dry film thickness is not accepted. The number of measurements and evaluation of the measured values was in compliance with

SN EN ISO 12944 and

SN EN ISO 2808.

[0027] The results of an examination of lacquer dry film thickness are shown in the Table 2. An average dry film thickness was determined 45,3 µm.

Table 2: Measured values of lacquer dry film thickness

Measurement number	Dry film thickness DFT [µm]
1	47,9
2	45,8
3	43,1
4	47,0
5	43,2
6	49,1
7	46,2
8	42,3
9	41,4
10	46,7
Average value [µm]	45,3

[0028] The film exhibited corrosion resistance longer than 200 hours determined by the corrosion test with salt spray according to CSN EN ISO 9227 (Corrosion tests in artificial atmosphere - salt spray test). After the corrosion test with salt spray, the coating system exhibited following damage parameters according to

SN EN ISO 4628: blistering of film - grade 0 (without blisters), cracking of film - grade 0 (without cracking), flaking of film - grade 0 (without flaking).

Coating system adhesion test:

[0029] Coating system adhesion test was carried out according to

SN EN ISO 16276-2 and the results together with photographic documentation are shown in the Table 3. When evaluating of coating system resistance, a cut in the shape of rectangular grid (cross-cut) or in the X-shape (X-cut) is made, so as to penetrate up to the substrate material. The test itself is carried out using special self-adhesive tape with pre-defined adhesion, when the tape is stuck on the cross-cut or X-cut and the damage (adhesion) of the coating system to the substrate material is evaluated after the subsequent tearing off. Adhesion of the coating system to the substrate material determined by the cross-cut or X-cut test according to

SN EN ISO 16276-2 exhibited classification grade 0.

Industrial Applicability

[0030] The present invention will be suitable for protection of products from non-ferrous metals, e.g. parts of automobiles, with a coated layer of protective lacquer with thickness of 60 µm, further in the production of rolled aluminum sheets for transport protection as well as for protection of non-ferrous, e.g. aluminum, profiles during transportation and storage. Other applications of this technology are suitable in the field of non-ferrous metal alloys protection, e.g. galvanized sheets.

Claims

1. Method of application of water-soluble lacquer comprising 75 to 80 weight% of acrylic dispersion, 4,75 to 5,75 weight% of additive for wettability, dispersion and anti-foamability, 0,1 to 0,2 weight% of corrosion inhibitor, 2 to 10 weight% of water soluble organic corrosion inhibitor based on a mixture of potassium octadecanoate, tripotassium phosphate and 2,2,2"-nitroethanol, 5 to 10 weight% of anticorrosion pigment based on oxy-amino phosphate complex of calcium and manganese, and water, on non-ferrous metal product, characterised in that the lacquer diluted with 8 to 18 weight% of water is applied by pneumatic spraying under the pressure of 0,15 to 0,45 MPa at room temperature ranging from 18 to 23 °C and with relative air humidity max. 80% on the non-ferrous metal product surface with room temperature ranging from 18 to 23 °C in an interval of min. 3 °C above the dew point, wherein drying at room temperature ranging from 18 to 23 °C occurs for lacquer application.

2. Method of application of water-soluble lacquer according to the claim 1, characterized in that before the lacquer application, a pre-treatment of degreasing, followed by rinsing and subsequent drying of the product surface, is carried out.

3. Method of application of water-soluble lacquer according to the claim 2, characterized in that alkaline degreasing formulation with pH ranging from 8,5 to 10,5 is used.

4. Method of application of water-soluble lacquer according to the claim 2 or 3, characterized in that the drying of the product surface is carried out by the means of compressed air or elevated temperature.

5. Method of application of water-soluble lacquer according to any of the previous claims, characterized in that the wet film thickness is between 150 and 200 µm.