CZ20021422A3 - Method for coating aluminium alloy substrate - Google Patents

Abstract

An alluminum alloy substrate is pretreated with an aqueous solution containing an organophosphorus compound, preferably a vinylphosphonic acid-acrylic acid copolymer, before coating the substrate with a polymer. Passing the substrate through the solution contaminates it with aluminum and other elements. The pretreatment solution is rejuvenated by removing aluminum with a cation exchange resin that preferably contains a styrene-divinyl benzene copolymer functionalized with sulfonate groups. Rinsing the substrate contaminates the rinse water with the copolymer. The rinse water is concentrated by reverse osmosis or membrane ultrafiltration and retured to the pretreatment solution.

Description

METHOD OF COATING THE ALUMINUM ALLOY SUBSTRATE

Technical field

The present invention relates to a method of coating an aluminum alloy substrate with a polymer. In particular, the invention relates to a process for pretreating an aluminum alloy substrate with a vinylphosphonic acid-acrylic acid copolymer prior to coating the substrate with a polymer.

BACKGROUND OF THE INVENTION

Although aluminum protects itself against corrosion by forming a natural oxidation coating, protection is not complete. When moisture and electrolytes occur, aluminum alloys corrode much faster than pure aluminum.

Therefore, aluminum alloy substrates need to be treated with pretreatment or other chemicals that provide improved corrosion resistance as well as beneficial adhesion to polymers

To date, chemical conversion coatings have been formed on aluminum alloys by converting a metal surface into a sticky coating, some of which consisted of an oxidized form of aluminum. Chemical conversion coatings provide high corrosion resistance and improved adhesion of polymer coatings. The conversion coating of chromium and phosphate is usually provided by contacting aluminum with an aqueous solution containing hexavalent ions, phosphate ions and fluoride ions. In recent years, concerns about environmental pollution have been increasing with the effects of chromates and phosphates. 2.

• three titi • titi • titi • titi • titi • titi • ti * discharged into watercourses in such processes. Due to the high solubility and strong oxidation properties of hexavalent chromium ions, expensive waste disposal procedures must be used to reduce hexavalent chromium ions to trivalent chromium ions.

Attempts have been made in the art to produce acceptable conversion coatings for chromate-free aluminum. For example, some chromate-free conversion coatings contain zirconium, titanium, hafnium and / or silicon, sometimes combined with fluorides, surfactants and polymers such as polyacrylic acid. Despite the extensive efforts that have been made to date, chromate-free conversion coatings or the basis for improving the corrosion and adhesion resistance of aluminum alloy substrates are not entirely satisfactory. Polymer adhesion and corrosion resistance are important properties of the aluminum alloy sheet coating used to produce bodies and terminate food containers and beverage container ends.

Attempts have also been made in the art to pre-treat substrates with various organophosphorus compounds prior to coating them with a polymer. The term "organophosphoric compounds" as used herein includes organophosphoric acids, organophosphinic acids, organophosphonic acids, as well as various salts, esters, partial salts, and partial esters of such acids. For example, Dutch Patent No. 263,668, issued April 14, 1961, describes a process in which steel sheets are treated with a vinylphosphonic acid-acrylic acid copolymer prior to coating with alkyd resin enamel. Although some organophosphoric pretreatments may work similarly, it is costly to implement them. Thus, there remains a need to provide an efficient and cost-effective method of pretreatment

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an aluminum alloy substrate with an organophosphorus compound prior to application of the polymer coating.

SUMMARY OF THE INVENTION

It is an essential object of the present invention to provide an efficient and economical process for pretreating an aluminum compound substrate with an organophosphorus compound prior to applying the polymer coating.

To meet this basic object, our method provides for the removal of aluminum and other cations from the pretreatment solutions, thereby avoiding the costly disposal of such solutions.

Other objects and advantages of our invention will be apparent to those skilled in the art from the following detailed description.

Overview of the figure in the drawing

A single figure shows a flow diagram of a method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the invention, there is provided a method for coating an aluminum alloy substrate with an organic polymer. The aluminum alloy substrate may be in the form of a sheet, molded or cast, and is preferably sheet-shaped.

A variety of sheet-like aluminum alloys are suitable for practicing the present invention, including alloys.

belonging to the AA2000, 3000, 5000, 6000 and 7000 series. Aluminum and magnesium alloys of the AA5000 series, and in particular the AA5042 and AA5182 alloys are preferred. The sheet made of these alloys is useful for shaping into bodies and terminating the food container and the ends of the beverage containers.

Aluminum alloys suitable for container end sheets, for example AA5182, are provided as an ingot or billet or plate by known casting techniques. Prior to processing, the ingot or billet is subjected to homogenization at elevated temperature. The alloy billet is then hot rolled to obtain a calibrated sheet as an intermediate. For example, the material can be hot rolled at a metal inlet temperature of about 371 to 524 ° C to obtain an intermediate having a thickness of about 2.54 to 3.81 mm. This material is cold rolled to obtain a sheet having a thickness in the range of about 1.52 to 3.81 mm. We prefer AA5182 aluminum alloy sheet with H19 temper. The front end aluminum alloy sheet 5042 is preferably of a hardness grade H9.

Aluminum alloys, such as AA5042, are provided as an ingot that is homogenized. This is followed by hot rolling to an intermediate gauge of about 2.54 to 3.81 mm. Typically, the intermediate calibrated product is annealed, followed by hot rolling and then cold rolling to obtain a final calibrated product having a thickness of about 1.52 to 3.81 mm. The sheet is coated with polymer and then pulled and drawn again into the food container body. We prefer AA5042 aluminum alloy sheets with H2x hardness.

The natural oxide coating of the aluminum alloy sheet surface is generally sufficient to carry out our invention. The natural oxide coating typically has a thickness of about 3 to 5 nm. For better corrosion protection can. 5.

• oxide coating • oxide coating • oxide coating • oxide coating • oxide coating increase by treatment such as anodic oxidation or hydrothermal treatment in water, water vapor or aqueous solutions.

The aluminum alloy sheet of the present invention is typically cleaned with an alkaline surface cleaner to remove any residual lubricants that adhere to the surface and then rinsed with water. Cleaning can be avoided if the residual lubricant content is negligible.

The cleaned leaf surface is then pretreated in a first tank with a composition comprising an aqueous solution of an organophosphorus compound. The solution preferably contains about 1 to 20 g / l of a vinylphosphonic acid-acrylic acid copolymer (VPAA-AA copolymer). Solutions containing about 4 to 10 g / l of copolymer are preferred. The copolymer usually contains about 5 to 50 mole% vinylphosphonic acid, preferably about 20 to 40 mole%. The VPA-AA copolymer may have a molecular weight of about 20,000 to 100,000, preferably about 50,000 to 80,000. A particularly preferred VPA-AA copolymer comprises about 30 mole% VPA and about 70 mole% AA. The solution has a temperature of about 38 to 93 ° C, more preferably about 49 to 82 ° C. A particularly preferred solution has a temperature of about 77 ° C.

The sheet surface may be immersed in the composition or the composition may be rolled or sprayed onto the sheet surface. A preferred continuous cleaning and pretreatment line is operated at about 158 to 474 m per minute. A contact time of about 6 seconds between the sheet surface and the composition is sufficient when the line is operated at 316m per minute. The VPA-AA copolymer reacts with an oxide or hydroxide coating to form a layer on the sheet surface.

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The aluminum alloy sheet passing through the pretreatment solution contaminates the solution with ions of various elements, including aluminum, magnesium, iron, chromium and manganese. The pretreatment solution loses effectiveness when the aluminum concentration rises above about 150-200 ppm. Therefore, we provide a method for removing aluminum and other metal ions from a pretreatment solution.

At least a portion of the pretreatment solution is transferred to a second tank containing the cation exchange resin. The resin may be in the form of pellets, spheres, fibers or particles, and is preferably of the round spherical gel type. The resin has a minimum total hydrogen capacity of 1.9 meq / ml moisture. A preferred resin has an average particle size of about 650 µm, a specific gravity of about 1.22 to 1.23, and a bulk density of about 2.994 g / cm ³ .

The resin is preferably a gel comprising a copolymer of styrene and divinylbenzene with acidic functional groups, preferably sulfonic acid groups. Alternatively, the copolymer may comprise phosphonic acid and arsonic acid functional groups. A particularly preferred cation exchange resin is sold by the Dow Chemical Company of Midland, Michigan under the trademark DOWEX G-26 (H).

Less preferably, the cation exchange resin may comprise ethylene copolymerized with an unsaturated carboxylic acid such as acrylic acid.

After the pretreatment solution passes through a second container containing a reduced aluminum concentration. The concentration of aluminum in the treatment solution is less than about 75 ppm, more preferably less than 25 ppm and optimally about 10 ppm or less. The treatment solution containing the organophosphorus compound and the reduced aluminum concentration is returned to the first container.

The pretreated sheet may optionally be rinsed with water to remove excess VPA-AA copolymer. The rinse water preferably has a temperature of about 77-82 ° C. The rinse water is concentrated by removing excess water so that the VPA-AA copolymer can be recycled. Some preferred concentration techniques include reverse osmosis and membrane filtration. After concentration, the rinsing water may be transferred to the first container to restore the VPAAA value of the copolymer.

The prepared sheet is coated with a polymer composition, which preferably comprises an organic polymer dispersed in an organic solvent. Three preferred coating polymers are epoxides, polyvinyl chloride and polyesters. Suitable epoxides include phenol-modified epoxides, polyester-modified epoxides, epoxy-modified polyvinyl chloride, and epoxides with crosslinked bonds. The polymer compositions may be pure or may contain pigment particles. The pigment particles are preferably titanium dioxide, alumina or silica. Titanium dioxide particles having a mean particle size range of 0.5 to 10 microns are preferred.

Alternatively, the prepared sheet may be coated electrolytically, by slot coating, extrusion coating, spray coating, spray coating, or other permanent coating methods.

The polymer-coated sheet is dried, coiled and finally formed into container bodies or container front plates.

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DETAILED DESCRIPTION OF THE INVENTION

As schematically shown in the figure, there is provided a roll of AA5182-H19 sheet of aluminum and magnesium alloy having a thickness of about 224 microns. The sheet 10 is cleaned with an alkaline surfactant cleaner in a vat 20 to remove any residual lubricants from the sheet surface. The cleaned sheet is then rinsed in a deionized water bath 30.

The cleaned and rinsed sheet is pretreated in the first tank 40 with a solution containing about 10 g / l VPA-AA copolymer consisting of about 30 mole% VPA groups and about 70 mole% AA groups dissolved in water. The solution has a temperature of about 77 ° C and initially contains about 10 ppm aluminum. The VPA-AA copolymer reacts with a coating on the surface of an aluminum oxide or aluminum hydroxide sheet to form a layer containing the reaction product of the copolymer and an oxide or hydroxide.

The pretreated sheet is then rinsed with water 50 to remove excess VPA-AA copolymer. The rinsed water 50 preferably has a temperature of about 77-82 ° C.

The rinsed sheet is rolled with a polymer composition 60, which preferably comprises an organic polymer and pigment particles dispersed in an organic solvent. The organic polymer is preferably an epoxy resin. Some suitable epoxides include phenol-modified epoxides, polyester-modified epoxides, epoxy-modified polyvinyl chloride, and epoxides with crosslinked bonds.

The polymer coated sheet is dried in a hot air dryer 70 and then rolled up as a coated sheet product 80.

In order to maintain a low concentration of metal ions in the pretreatment solution, portions of the solution are: · · · · · · · · · · · · · · · · · · · · · 9.

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9 are periodically transferred from the first tank 40 to the second tank 100, which contains a cation exchange resin. In particular, a preferred resin is a solid cation exchange resin sold by Dow Chemical Company of Midland, Michigan, under the trademark DOWEX G-26 (H). This solid cation exchange resin is sold as hard round spheres of 650 microns (dry mesh). The solid cation exchange resin is a gel comprising a styrene-divinylbenzene copolymer with sulfonate functional groups. The resin treatment produces a treated solution having an aluminum concentration that is optimally less than about 10 ppm. The treated solution is returned via line 110 from the second reservoir 100 to the first reservoir 40.

The cation exchange resin eventually becomes saturated with metal salts. The resin is regenerated by washing with a strong acid solution 120 such as 6 to 10% HCl or 6 to 12% by volume. sulfuric acid in water. The metal salts 130 washed out of the second container 100 are discarded.

The rinsing water used from the aqueous rinsing 50 is also recycled to restore VPA-AA copolymer values. The flushing water used is first introduced into a concentration device 140 where water is removed, for example by reverse osmosis and membrane ultrafiltration. The concentrated rinse water is then returned to the first tank 40.

The cation exchange process of our invention maintains the aluminum concentration at acceptable levels in the pretreatment solution. A 200 ml aliquot of the 60 ° C pre-treatment solution containing 10 g / l VPA-AA copolymer, 350 ppm aluminum and other metals is placed in a 250 ml Ehrlenmeyer flask containing 40 ml wet volume of DOWEX G-26 (H) resin in ve · · · ···. 10 to the hydrogen cycle. The flask was placed in a water bath and kept at 60 ° C for 16-20 hours. The resin is prepared by washing with 400-600 mL 6% HCl by volume, followed by rinsing with 600-800 mL deionized water.

After 16 to 20 hours of contact time, the solution is preliminary filter treatment and the resin is rinsed with 25 ml deionized water. The solution is analyzed and the results are shown in the table below. All concentrations are corrected for comparison with respect to a volume of 200 ml. Table - analysis of the pretreatment solution Substance Initial concentration (ppm) After G-26 (H) (ppm) Al 350 5.3 On 14 0.5 Si 11 12 Fe 22nd 18 Ca 4.1 0.8 Mg 100 ALIGN! 0.3 Mn 1.5 n.d Ni 0, 6 n. d Zn 0.3 n. d Cr 11 10 TO 1,8 0.5 P 820 777

n.d = not detectable

One skilled in the art will appreciate that, with reference to some of the presently preferred embodiments, the described invention has the understanding that our invention may be embodied in another manner without the occurrence. 11 • to · • ··

To depart from the spirit and scope of the appended claims.

Claims (10)

PATENT CLAIMS (modified version) A method for pretreating an aluminum alloy sheet having a portion of a surface to improve the adhesion of a polymer coating to that portion of a surface, comprising: (a) in a first tank, an aluminum alloy sheet pretreatment having a portion of the surface comprising alumina or aluminum hydroxide with a solution consisting essentially of water and an organophosphorus compound, thereby forming a layer containing the reaction product of said compound and oxide or hydroxide and said solution contaminated with ions (b) transferring at least a portion of the solution to a second tank containing a polymer-containing cation exchange resin thereby adsorbing aluminum ions to the resin, thereby producing a treated solution containing the compound having a reduced concentration of aluminum ions; and (c) returning the treated solution to first tank. The method of claim 1, wherein the sheet comprises an aluminum alloy of the AA2000, 3000, 5000, 6000 or 7000 series and further comprises: (d) coating said layer with a coating composition comprising a polymer selected from the group consisting of polyvinyl chloride, epoxides and polyesters. * · · ······ · · · · · · · · · · 00 000 · «· 0 0 0 · ··· ·· ·· · ····· The process according to claim 1, wherein the resin comprises a copolymer of styrene and divinylbenzene with sulfonate functional groups. The method of claim 1, wherein the treated solution contains less than about 75 ppm aluminum ions. The method of claim 11, wherein the treated solution comprises less than about 25 ppm aluminum ions. The method of claim 1, further comprising: characterized in that (e) after step (a) rinsing the substrate with water, thereby producing rinse water comprising the organophosphorus compound and aluminum ions, and (g) concentrating said rinse water by removing water therefrom and (h) returning at least a portion of the rinse water treated in step (f) into the first container. The method of claim 1, wherein the organophosphorus compound comprises a vinylphosphonic acid / acrylic acid copolymer. The process of claim 7, wherein the copolymer has a molecular weight of about 20,000 to 100,000. • 9 • 9 • 9 • 9 • 9 • 9 • 9 · · · 9 9 ······ The method of claim 7, wherein the pretreatment solution comprises about 1 to 20 g / L copolymer. The process of claim 7, wherein the pretreatment solution has a temperature of about 49 to 93 ° C in step (a).