ES2219101T3 - COATING OF A ALUMINUM ALLOY SUBSTRATE. - Google Patents

Abstract

A method for the pretreatment of an aluminum alloy sheet having a surface part in order to improve the adhesion of a polymer coating to said surface part, comprising: (a) in a first container, pretreatment of a sheet of aluminum alloy having a surface part comprising aluminum oxide or aluminum hydroxide with a pretreatment solution consisting essentially of water and an organophosphorus compound, thereby forming a layer comprising a reaction product of said compound and said oxide or hydroxide, and contaminating said solution with aluminum ions; (b) transfer of at least a portion of said solution to a second container containing a cation exchange resin comprising a polymer and aluminum ions are absorbed on said resin, thereby producing a treated solution containing said compound and which has a reduced concentration of aluminum ions; and (c) return of said treated solution to said first container.

Description

Coating of an alloy substrate aluminum.

The present invention relates to a procedure for coating an alloy substrate Aluminum with a polymer. More in particular, the invention is refers to a procedure for pretreatment of a substrate of aluminum alloy with a copolymer of vinylphosphonic acid - Acrylic acid before the polymer coats the substrate.

While aluminum itself protects itself against corrosion by forming an oxide coating Natural, protection is not complete. In the presence of moisture and electrolytes, aluminum alloys corrode much more Quickly than pure aluminum.

According to the above, there is a need of treating aluminum alloy substrates with pretreatments or other chemicals that provide resistance to Improved corrosion as well as good adhesion for polymers.

In the prior art, they have been formed chemical conversion coatings on alloys of aluminum by "converting" a metal surface in a strongly adherent coating, part of which consists in an oxidized form of aluminum. Conversion coatings Chemistry provide great resistance to corrosion and adhesion enhanced by polymer coatings. It is provided typically a conversion coating chromium phosphate contacting aluminum with a aqueous solution containing hexavalent chromium ions, ions phosphate and fluoride ions. In recent years studies have appeared concerning the contaminating effects of chromates and phosphates discharges into waterways from such procedures. Due to the high solubility and the strong oxidizing character of the ions of hexavalent chromium treatment procedures should be used expensive waste to reduce hexavalent chromium ions to Trivalent chromium ions for waste disposal.

Attempts have been made in the prior art to produce chromate-free conversion coatings Acceptable for aluminum. For example, some coatings Chromate-free conversion contain zirconium, titanium, hafnium and / or silicon, sometimes combined with fluorides, agents surfactants and polymers such as polyacrylic acid. In spite of the considerable efforts that have been made previously there are no still a coating by conversion or primer without chromate completely satisfactory to improve adhesion and resistance to Corrosion of coated aluminum alloy substrates with polymer. Polymer adhesion and resistance to corrosion are important features in the sheets of aluminum alloy used to make bodies and bottoms of food containers and beverage container funds.

Attempts have also been made in the art above to pretreat substrates with different compounds of organophosphorus before coating them with a polymer. As used in the present specification the term "compounds of organophosphorus "includes organophosphoric acids, acids organophosphines, organophosphonic acids as well as different salts, esters, partial salts and partial esters of such acids For example, Dutch patent application No. 263,668, filed on April 14, 1961, describes a procedure in the that steel sheets are treated with an acid copolymer vinylphosphonic / acrylic acid before coating with a alkyd resin enamel. While some pretreatments of organophosphorus can take place properly, these are expensive to implement. According to this, there is still a need to provide an efficient procedure and economical for the pretreatment of an alloy substrate aluminum with an organophosphorus compound before applying a polymer coating.

A main objective of the present invention is provide an efficient and economical procedure for the pretreatment of an aluminum alloy substrate with a organophosphorus compound before application of a polymer coating.

To achieve this main objective the This procedure provides the removal of aluminum and other cations of pretreatment solutions, thereby Avoid expensive disposal of such solutions.

From the following detailed description, will make other objectives and advantages of the present invention apparent for specialists in the art.

The only figure is a flow chart of the procedure of the present invention.

In accordance with the present invention, provides a procedure for coating a substrate of Aluminum alloy with an organic polymer. The substrate of Aluminum alloy can be provided in the form of a sheet, extrusion or molding and is preferably a sheet.

They are suitable for the practice of this invention different aluminum alloys available in the form of sheet, including alloys belonging to the AA2000 series, 3000, 5000, 6000 and 7000. Aluminum alloys are preferred - AA5000 series magnesium and particularly alloys AA5042 and AA5182. The sheet made from these alloys is useful for forming bodies or bottoms of containers for polymer coated foods, and container bottoms for drinks.

Aluminum alloys suitable for panels Bottom containers such as AA5182 are supplied as a ingot or billet or slag by molding techniques known in The technique. Before processing, the ingot or billet is subjected to homogenization with high temperature. The alloy piece is hot foil to provide an intermediate standard sheet. For example, the material can be hot rolled to a metal inlet temperature of approximately 371º - 524ºC (700º-975ºF) to provide an intermediate product that presents a thickness of approximately 0.254 cm to 0.381 cm (0.100 inches at 0,150 inches). This material is cold rolled to provide a sheet that varies in thickness from about 0.0152 to 0.0381 cm (0.006 to 0.015 inches). An alloy sheet of AA5182 H19 grade grade aluminum. Alloy sheet AA5042 aluminum for bottom panels is preferably grade temple H19.

Aluminum alloys such as AA5042 are They supply as an ingot that is homogenized. Then you hot rolled up to give an intermediate caliber of approximately 0.254 to 0.381 cm (0.100 inches to 0.175 inches). Typically the intermediate gauge product is tempered, continue with hot rolled and then cold rolled until a final gauge product that has a thickness of approximately 0.0152 to 0.0381 cm (0.006 to 0.015 inches). He cover the sheet with a polymer and then stretch and re-stretches in food container bodies. AA5042 quality aluminum alloy sheet of temper H2x.

The natural oxide coating on a Aluminum alloy sheet surface is usually sufficient for the practice of the present invention. He natural oxide coating ordinarily presents a thickness of about 3-5 nm (30-50 angstoms). For one better corrosion protection the oxide coating can created by treatments such as anodic oxidation or hydrothermal treatment in water, water vapor or solutions aqueous.

The aluminum alloy sheet of the invention It is usually cleaned with an alkaline surface cleaner to remove any residual lubricant that adheres to the surface and then rinse with water. Cleaning can be avoided If the residual lubricant content is negligible.

The surface of the cleaned sheet is pretreated then in a first container with a composition comprising a aqueous solution of an organophosphorus compound. The solution preferably contains about 1-20 g / l of a copolymer of vinylphosphoric acid - acrylic acid (copolymer of VPA-AA). Solutions containing approximately 4-10 g / l of the copolymer. The copolymer comprises normally about 5 to 50 mol% acid vinylphosphonic, preferably about 20 to 40% in moles The VPA-AA copolymer may have a molecular weight of about 20,000 to 100,000, preferably from about 50,000 to 80,000. A copolymer of Particularly preferred VPA-AA contains approximately 30 mol% of VPA and approximately 70 mol% From aa. The solution has a temperature of approximately 38º-93ºC (100º-200ºF), more preferably about 49º-82ºC (120º-180ºF). A particularly preferred solution. It has a temperature of approximately 77ºC (170ºF).

The surface of the sheet can be soaked in the composition or the composition can be coated with roller or spray on the surface of the sheet. It gets in operation of a continuous cleaning and pretreatment line preferred at approximately 152 - 457 meters per minute (500 - 1500 feet per minute). It is enough a contact time of approximately 8 seconds between the surface of the sheet and the composition when the line operates at 305 meters per minute. He VPA-AA copolymer reacts with the coating of oxide or hydroxide to form a layer on the surface of the sheet.

The aluminum alloy sheet that passes to through the pretreatment solution contaminates it with ions of different elements, including aluminum, magnesium, iron, chrome and manganese. The pretreatment solution loses effectiveness when the concentration of aluminum increases above approximately 150-200 ppm. According to this a procedure is provided for the removal of aluminum ions and other metals from the pretreatment solution

At least part of the solution of pretreatment is transferred to a second container containing a cation exchange resin. The resin can be provide as pills, beads, fibers or particles and preferably it is a hard spherical gel type pearl. Resin it has a minimum total capacity in the form of hydrogen, wet, 1.9 meq / ml. A preferred resin has a size of mean particle of approximately 650 µm (micrometers), a specific density of 1.22 - 1.23 and a volumetric density of approximately 0.7999 kg / l (49.9 lb / ft3).

The resin is preferably a gel comprising a styrene-divinylbenzene copolymer functionalized with acid groups, preferably sulfonate groups. So alternatively the copolymer can be functionalized with acid groups phosphonic or arsonic acid groups. An exchange resin Particularly preferred cationic is marketed by The Dow Chemical Company of Midland, Michigan, with the trade name of DOWER G-28 (H).

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

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

Optionally the pretreated sheet can be rinse with water to remove excess copolymer from VPA-AA The rinse water preferably has a temperature of approximately 77º - 82ºC (170º - 180ºF). He rinse water is concentrated by removing water in excess so that the VPA-AA copolymer can be Recycle. Some preferred concentration techniques include reverse osmosis and membrane filtration. Behind the concentration the rinse water can be transferred to the first container in order to recover the copolymer of VPA-AA

The primed sheet is coated with a polymer composition that preferably includes a polymer organic dispersed in an organic solvent. Three polymers of Preferred coatings are epoxies, poly (chloride of vinyl) and polyesters. Suitable epoxies include epoxies modified phenolics, epoxies modified with polyester, epoxy and epoxy modified polyvinyl chloride crosslinkable The polymer composition may be clear or may contain pigment particles. The pigment particles are preferably titanium dioxide, alumina or silica. They prefer titanium dioxide particles in a size range of mean particle of 0.5 to 10 µm (micrometers).

Alternatively, the primed sheet can be Coating by electrocoating, slot coating, extrusion coating, flow coating, coating by spraying or other coating procedures in continuous.

The polymer coated sheet is dried, dried coil and then finally conforms to container bodies or in container bottom panels.

As shown schematically in the Figure, an alloy sheet coil 10 of Aluminum - AA5182-H 19 series magnesium which has a thickness of approximately (8.8 mm) 224 µm (micrometers) The sheet 10 is cleaned with a surface cleaner alkaline in a tank 20 to remove any residual lubricant on the surface of the sheet. The cleaned sheet is then cleared in a 30 bath of deionized water.

The cleaned and rinsed sheet is pretreated in a first container 40 with a solution comprising approximately 10 g / l of a VPA-AA copolymer containing approximately VPA at 30 mole percent and approximately 70 mole percent AA units, dissolved in water. The solution has a temperature of approximately 77ºC (170ºF) and contains initially about 10 ppm of aluminum. The copolymer of VPA-AA reacts with an oxide coating or aluminum hydroxide on the surface of the sheet to form a layer comprising a reaction product of the copolymer and the oxide or hydroxide.

The pretreated sheet is then rinsed with water 50 to remove excess copolymer of VPA-AA. He rinse water 50 preferably has a temperature of approximately 77º - 82ºC (170º - 180ºF).

The lightened sheet is coated with a roller polymer composition 60 preferably including a polymer organic and pigment particles dispersed in a solvent organic. The organic polymer is preferably an epoxy resin. Some suitable epoxies include phenolic modified epoxies, epoxies modified with polyester, poly (vinyl chloride) cross-linked epoxy and epoxy modified.

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

In order to maintain a low concentration of metal ions in the pretreatment solution, are transferred periodically portions of the solution from the first container 40 to a second container 100 containing a resin of cation exchange A particularly preferred resin is markets Dow Chemical Company of Midland, Michigan under the trade name strong cation exchange resin DOWEX G-26 (H). The strong cation exchange resin It is marketed as hard spherical beads with a mesh size 650 µm dry (micrometers). Exchange resin strong cationic is a gel consisting of a copolymer of styrene - divinylbenzene functionalized with sulfonate groups. He resin treatment produces a treated solution that presents a concentration of aluminum that is optimally less than approximately 10 ppm The treated solution is returned by a conduit 110 from the second container 100 to the first container 40.

The cation exchange resin begins to saturate metal salts over time. The resin is regenerated by washing with a strong acid solution 120, such as HCl at 6-10% by volume or 6-12% sulfuric acid by volume in water. The metallic salts 120 washed from the second container 100 are withdraw from the process.

The rinse water used from the rinse with water 50 is also recycled to recover the copolymer of VPA-AA The rinse water used is sent first place to a concentrator 140 where water is removed, for example by reverse osmosis or membrane ultrafiltration. The water of concentrated rinse is then returned to the first container 40.

The cation exchange procedure of the The present invention maintains the concentrations of aluminum at Acceptable levels in the pretreatment solution. One is placed 200 ml aliquot of the pretreatment solution at 60 ° C (140 ° F) containing 10 g / l of VPA-AA copolymer, 350 ppm of aluminum and other metals in a 250 ml Erlenmeyer glass that Contains 40 ml in wet volume of DOWEX resin G-26 (H) in hydrogenated form. The flask in a water bath and kept at 60ºC (140ºF) for 16 - 20 hours. The resin is prepared by washing with 400-600 ml of 6% HCl by volume, followed by rinsing with 600-800 ml of water deionized

After 16 to 20 hours of contact time filter the pretreatment solution and rinse the resin with 25 ml of deionized water. The solution is analyzed and the results are presented below in the table. All the corrections are corrected. concentrations to reflect a volume of 200 ml in order to compare.

TABLE

Pretreatment solution analysis Element Concentration initial After G-26 (H) (ppm) (ppm) To the 350 5.3 Na 14 0.5 Yes eleven 12 Faith 22 18 AC 4.1 0.8 Mg 100 0.3 Mn 1.5 n.d. Neither 0.6 n.d. Zn 0.3 n.d. Cr eleven 10 K 1.8 0.5 P 820 777 n.d. = no detectable

Claims (10)

1. A procedure for pretreatment of a aluminum alloy sheet presenting a surface part in order to improve the adhesion of a polymer coating to said surface part, comprising:

(to)

in a first container, pretreatment of an aluminum alloy sheet that it has a surface part comprising aluminum oxide or aluminum hydroxide with a pretreatment solution constituted essentially by water and an organophosphorus compound, thereby a layer is formed comprising a reaction product of said compound and said oxide or hydroxide, and contaminating said solution with aluminum ions;

(b)

transfer of at least a part of said solution to a second container that it contains a cation exchange resin comprising a polymer and are absorbed in the same aluminum ions on said resin, thus producing a treated solution containing said compound and presenting a reduced concentration of ions of aluminum; Y

(c)

return of bliss treated solution to said first container.

2. The method of claim 1, in the that said sheet comprises an aluminum alloy of the series AA2000, 3000, 5000, 6000 or 7000, and which also includes:

(d)

Coating of said layer with a coating composition comprising a polymer selected from the group consisting of poly (chloride vinyl), epoxies and polyesters.

3. The method of claim 1, in the that said resin comprises a styrene-vinylbenzene copolymer functionalized with sulfonate groups. 4. The method of claim 1, in the that the treated solution contains less than about 75 ppm of aluminum ions 5. The method of claim 1, in the that the treated solution contains less than about 25 ppm of aluminum ions 6. The method of claim 1 which It also includes:

(and)

after the step (a), rinsing said substrate with water, whereby produces rinse water containing said compound of organophosphorus and aluminum ions,

(F)

concentration of said rinse water by eliminating the water thereof, Y

(g)

return to first container of at least part of the rinse water treated in the stage (f).

7. The method of claim 1, in the that said organophosphorus compound comprises a copolymer of vinylphosphonic acid - acrylic acid. 8. The method of claim 7, in the that said copolymer has a molecular weight of approximately 20,000 to 100,000. 9. The method of claim 7, in the that said pretreatment solution comprises approximately 1 - 20 g / l of said copolymer. 10. The method of claim 7, in which said pretreatment solution has a temperature of approximately 49-93 ° C in step (a).