US3755018A

US3755018A - Composition and process for inhibiting corrosion of non-ferrous metal surfaced articles and providing receptive surface for synthetic resin coating compositions

Info

Publication number: US3755018A
Application number: US00137682A
Authority: US
Inventors: R Miller
Original assignee: Eltzroth & Ass J M
Current assignee: Eltzroth & Ass J M; Eltzroth J & Ass Inc us
Priority date: 1971-04-26
Filing date: 1971-04-26
Publication date: 1973-08-28
Anticipated expiration: 1990-08-28
Also published as: GB1372297A; DE2218899A1; FR2134521B1; CA983355A; FR2134521A1; DE2218899C2; JPS556113B1

Abstract

Compositions and a process are provided for inhibiting corrosion of non-ferrous metal surfaces and for producing a surface to which synthetic resin coating compositions will adhere so that the resultant coatings have satisfactory impact and bending resistance, together with resistance to creeping corrosion between the metal and the dried resin coating.

Description

United States Patent Miller Aug. 28, 1973 [5 COMPOSITION AND PROCESS FOR 3,404,046 111/1968 Russell et al 148/62 X INHIBITING CORROSION 0 3,380,858 4/1968 Champaneriea et al 148/61 NON FERROUS METAL SURFACE!) 3,098,775 7/1963 Thirsk 143/62 3,501,352 3/1970 Shah 148/62 ARTICLES AND PROVIDING RECEPT IVE SURFACE FOR SYNTHETIC RESIN COATING COMPOSITIONS Russell C. Miller, Chicago, 111.

J. M. Elt zroth & Associates, Inc., Schaumburg, 111.

Filed: Apr. 26, 1971 Appl. No.: 137,682

Inventor:

Assignee:

Field of Search 148/62, 6.21

References Cited UNITED STATES PATENTS 7/1968 Russell et a1 148/62 Primary Examiner-Ralph S. Kendall Attorney-Johnston, Root, OKeeffe, Keil, Thompson & Shurtlefi ABSTRACT 4 Claims, No Drawings COMPOSITION AND PROCESS FOR INI-IIBITING CORROSION OF NON-FERROUS METAL SURFACED ARTICLES AND PROVIDING RECEPTIVE SURFACE FOR SYNTHETIC RESIN COATING COMPOSITIONS BACKGROUND Non-ferrous metal surfaced articles, for example, aluminized and galvanized iron and steel, aluminum, aluminum-zinc alloys, magnesium, and magnesiumaluminum alloys may suffer surface deterioration by corrosion through contact with the atmosphere or moisture, or both. Chemical passivation treatments are widely used to inhibit or suppress such surface corrosion.

One of the passivating treatments employed for this purpose consists in treating the non-ferrous metal surface with an aqueous solution of chromic acid, or a mixture of chromic acid and dichromate, preferably with a part of the hexavalent chromium reduced to the trivalent state.

While chromic acid based passivating solutions have been widelyadopted, they have been by no means effective in preventing corrosion under all conditions, particularly in high speed operations and especially where the treated surface is further coated with a synthetic resin coating composition which dries to form a synthetic resinous film. The manner in which the nonferrous metal surface is pretreated may make the difference between satisfactory adherence of the resinous film to the substrate and non-adherence as well as satisfactory resistance of the coating or film to impact, bending, and creeping corrosion between the surface of the metal and the resinous film.

It would be desirable, therefore, to provide a process in which corrosion of the non-ferrous metal surface is inhibited and wherein the non-ferrous metal surface is receptive to a synthetic resinous coating composition so that the resultant coated products containing a dried film of the resin have satisfactory impact and bending qualities as well as resistance to creeping corrosion beneath the coating of synthetic resin. It would also be desirable to provide a process in which non-ferrous metal surfaced articles such as aluminized; and galvanized sheets, coils, wires, tubes and rods, can be treated at higher linear speeds of, say, 100 to 500 feet per minute or even higher so as to produce a treated article which is corrosion resistant and has a surface which will adhere to synthetic resin coating compositions, thereby producing coated articles having the physical and chemical characteristics previously mentioned.

OBJECTS One of the objects of the present invention is to provide a new and improved process for making said nonferrous metal surfaced articles, for example, galvanized iron and steel, with surfaces inhibited against corrosion and adapted to adhere to synthetic resin coating compositions, thereby producing articles coated with a synthetic resinous film having satisfactory impact and bending resistance and resistance to creeping corrosion between the metal and the resinous coating.

Another object of the invention is to provide a process of the type described in which a non-ferrous metal surfaced article is brought into contact at a high rate of speed, for example, at a linear speed of at least 100 feet per minute, with an aqueous solution of a composition which will inhibit corrosion of the surface of said article and at the same time enhance the receptivity of said surface for synthetic resin coating compositions.

A further object of the invention is to produce new and useful compositions for treating non-ferrous metal surfaces which are effective for the purposes previously indicated. Other objects will appear hereinafter.

BRIEF SUMMARY OF THE INVENTION In accordance with the invention a non-ferrous surfaced article is treated with an aqueous chromate depositing solution containing hexavalent chromium and trivalent chromium, together with fluoboric acid and- /or fluosilicic acid in sufficient amount to enhance adherency of the resultant surface to organic film forming polymers which dry to a water resistant coating, with the further proviso that said solution is free from phosphoric acid and phosphates and free from nitric acid in any appreciable amount other than that occurring by generation within the chromate depositing solution.

DETAILED DESCRIPTION OF THE INVENTION The composition of the chromate depositing solution should be such that it will be effective when a nonferrous metal surfaced article is brought into contact with it at a linear speed of at least feet per minute and preferably 100 to 500 feet per minute at a pH of 1.5 to 2.5, to deposit a minimum amount of chromate expressed as chromium of at least 0.2 mg/sq.ft. Thereafter, the resultant surface can be coated or painted with a composition comprising an organic film forming polymer which dries to a water resistant coating. If the coating composition containing the polymer is nonaqueous, the chromium coated non-ferrous metal surface should be rinsed with water and dried to an acceptable degree (depending on the particular organic resin) before the coating composition is applied. Preferably, the final rinse water should be on the acid pH side using a very small amount of the chemical treatment bath itself. The amount used should be minimized, using just enough to produce a pH value of 4.5 to 6.0 (electrometric) in said final rinse.

It is essential for the baked or primer-baked systems (polyvinyl chloride, acrylic, epoxy, melamine, polyester, etc.) to be laid-down" on a neutral or slightly acidic substrate surface, but free of chrome or water spots or stains, or any powdery or loose surface contamination.

Apparently, fluoboric acid removes oxide films from the surface of the metal without replacing them with water soluble substances which cause inferior adherence of the synthetic resin coating compositions. Fluosilicic acid has a similar action. On the other hand, strong mineral acids such as nitric acid and sulfuric acid in any appreciable amount in the chromate depositing solution tend to produce water soluble substances on the surface of the metal which leads to inferior adhesion of synthetic resin coating compositions. This does not occur so readily, however, where radicals such as the sulfate or fluoride radicals are present in the form of a metallic salt dispersible in the solution. Boric acid can also be a component of the solution. In addition the solution can contain reducing agents such as, for example, sodium sulfite and/or sodium nitrite, which are added for the purpose of partially reducing hexavalent chromium to trivalent chromium. Phosphoric acid and phosphates are not used because they are reactive with non-ferrous metal surfaces to form phosphates which might interfere with chromium deposition on the surface.

. In carrying out the process of the invention the temperature of the chromate depositing solution for use on a non-ferrous metal surfaced article is normally within the range of 80 to 210 F. and usually 100 to 1 F.

The time of contact between the chromate depositing solution and the non-ferrous metal surfaced article will normally be within the range of one second to sixty seconds. However, in operations where high speed coating is not required the time of contact may be much longer. In the latter case the pH of the solution can also be somewhat higher, but would be within the range of 0.8 to 5.0.

The chromate depositing solution can have a solids content within the range from 0.2 gram per liter to 75.0 grams per liter, the remainder being water, and the chemical composition should be essentially the follow- Ingredients Grams per Liter Hexavalent chromium (expressed as CR) 0.05-50.0 Trivalent chromium (expressed as Cr) 0.033.0 Fluoride or bifluoride (expressed as F) 0.03-30 Borate (expressed as B, 0,) 0.0l3.0 Fluoborate (expressed as BF 0.03-10.0 Sulfate (expressed as S0.) 0.0I3.0 Magnesium (expressed as Mg) 0.01-3.0 Aluminum (expressed as Al) 0.0l3.0 Iron (expressed as Fe) 0.01-0.05 Nickel (expressed as Ni) 0.0l-0.05 Optional:

Acetate (if increased wetting rate is desired) 0.0l0.l Acid stable surfactant (for increased wetting) 001-01 In addition where the chromate depositing solution does not initially contain trivalent chromium, sodium nitrite, sodium sulfite, or other reducing agents can be added. The quantity of sodium nitrite and the quantity of sodium sulfite would usually be within the range of 0.05 to 0.2 grams per liter.

.The invention will be further illustrated but is not limited by the following examples in which the quantities are stated in parts by weight unless otherwise indicated.

EXAMPLE I A chromate depositing solution was prepared having the following composition:

Ingredients Grams per Liter Na cr, O 2 H, O 6.75 CrO, 1.36 NaF 1.36 H, B0, 1.16 NaHSO, 0.89 Na, SO, 0.2 NaNO, 0.2 MgSO. 0.67 HBF. 50%) 2.73 M80; trace FeSO trace This composition makes up to a gram per liter chromium depositing solution.

Clean strips of hot-dip galvanized steel were immersed in the above composition at a temperature of 125 F. and agitated manually for a period of 3 to 5 seconds after the pH had been adjusted to a value of 2.0 by adding NaOH.

The resultant strips were then rinsed with cold water, rinsed with hot water, dried, and aged for 72 hours at room temperature after which they were painted with an acrylic resin paint. The resultant product showed excellent paint adherence with resistance to creeping corrosion beneath the paint film.

EXAMPLE II A chromate depositing solution was prepared having the following composition:

Ingredients Grams per Liter K2 CT: 1 5.55 CrO, 2.22 NaF 1.15 H, B0, 2.00 NaHSO 0.90 Na, so, 0.2 NaNO, 0.2 4) a 0.70 HBF. (50%) 2.50 M50, trace FeSO trace This composition makes up to approximately a 15 gram per liter chromium depositing solution.

The pH was adjusted to 3.0 by adding NaOH and the temperature was raised to F.

Clean strips of hot dip galvanized steel were immersed in the resultant solution and agitated manually for a period of 3 to 5 seconds.

The resultant strips were then rinsed with cold water, rinsed with hot water, dried, and aged for 72 hours at room temperature after which they were painted with an acrylic resin paint. The product showed excellent paint adherence with resistance to creeping corrosion between the paint film.

EXAMPLE III A chromate depositing solution was prepared having the following composition:

Ingredients Grams per Liter Na, Cr, 0 2 H, O 2.88 CrO, 2.88 NH F'HF 1.00 H, B0, 0.80 NaHSO 0.66 Na, SO, 0.1 NaNO, 0.1 MgSO, 0.50 HBF (50%) 1.66 M80. trace FeSO. trace This composition makes up to approximately a 10 gram per liter chromate depositing solution.

The pH value of the solution was raised to 3.5 by adding NaOH and the temperature was raised to F.

Hot dip galvanized steel was immersed in this solution for 3 to 5 seconds and the resultant product thereafter rinsed, dried, agedand painted as described in Example I with very satisfactory results.

EXAMPLE IV A chromate-depositing solution was prepared having the following composition:

Ingredients Grams per Liter Na, Cr, 0, 2 H, O 1.66 CrO, 0.33 NaF 0.33 H, B0; 0.33 NaI-ISO, 0.10 Na, SO, 0.05 NaNO, 0.05 MgSO 0.10 HBF. (50%) 0.66 N' O trace FeSO trace .This composition makes up to approximately a 3.5 gram per liter solution.

The pH value of the solution was adjusted to 2.0 by adding NaOl-l. The temperature of the bath was raised to 175 F. and clean aluminum strips were immersed therein for 5 to seconds. The resultant aluminum strips were all cold rinsed and warm rinsed with water. Thereafter they were dried, painted with an acrylic resin paint, baked and aged.

EXAMPLE V The procedure was the same as in Example 1 except that the pH of the solution was adjusted to 1.5 by adding HBF, and the temperature was raised to 150 F. Clean strips of mill-run aluminum were immersed in the solution with agitation for a period of 5-l0 seconds. The resultant aluminum strips were then rinsed with cold water, followed by a warm water rinse and dried. They were thereafter painted with an acrylic resin paint, baked and aged.

EXAMPLE VI EXAMPLE VII The procedure was the same as in Example lII except that the pH of the solution was adjusted to 2.0, and clean aluminum strips were immersed in the solution at a temperature of 165 F. for a period of 5-10 seconds with agitation. The resultant strips were subsequently recovered, rinsed, dried and painted as described in Example VI.

EXAMPLE VIII The chromate depositing solution was made up as described in Example IV. The pH value was adjusted to 1.5 by adding HBF The temperature of the bath was adjusted to 150 F. and clean strips of hot dip galvanized steel were immersed therein and agitated manually for a period of 3 to 5 seconds. Thereafter the resultant strips were rinsed, dried, aged and painted as described in Example I.

The procedures described in Examples IV to VII were also carried out using clean strips of aluminum alloy 3003 and 2024.

The sheet panels produced as described in the examples were coated with primer coats and also with primer coats and finish coats. Various primer coats were used, for example, Lily Varnish Primer 465 and 11 PL Primer 12870. Various finish coats were used, for example, Acrylic JT 411-3, Duracron Super 610 and Duracron Super 810. The resultant products were subjected to corrosion resistance tests (ASTM-B-l 17- 64). They were also subjected to pull-away tests with pressure sensitive adhesive tape (3-M transparent No. 600). They were subjected to various bending tests including pull-away tests at the bend. In addition they were subjected to hardness tests and impact tests. The impact tests were made on a Gardner impact tester at pressures of 130-160 pounds per square inch'. The products satisfactorily passed these tests.

While acrylic resin coating compositions are especially useful, other organic film forming polymers can be employed, for example, polyvinyl chloride, epoxy resins, mixed epoxy-acrylic resins, polyester resins and polyurethane resins.

In the practice of the invention as will be seen from the foregoing examples, the chromate depositing solution is normally made up first as a solution containing hexavalent chromium compounds, namely, dichromates and chromic acid, together with other additives. In general, the chemical composition of the initial solutions is essentially as follows:

Ingredients Grams per Liter Dichromates (e.g., Na, Cr, 0, 2

or K, Cr, 0,) 1.66-6.75 Chromic acid 0.33-2.88 Sodium or ammonium fluoride or bifluoride 0.33-1.36 Boric acid 0.33-2.00 Sodium acid sulfate 0.10-0.90 Aluminum sulfate 0-0.70 Magnesium sulfate 0-0.70 Fluoboric acid (50%) 0.66-2.75 Nickel sulfate (NiSO trace Iron Sulfate (FeSO trace To this solution the reducing agents'are added to generate trivalent chromium in situ. As indicated by the examples, it is preferable to use sodium nitrite and sodium sulfite as reducing agents and the amount used is approximately one percent of each, based on the total weight of all of the materials contained in the concen trated aqueous solution. Other reducing agents can be employed such as, for example, zinc dust, cadmium dust, potassium sulfite, sodium bisulfite, sodium hydrosulfite, and sodium thiosulfate.

Nitrates can also be used in the foregoing compositions and their presence in low concentrations give better coatings and product excellent undercoated sur faces for application of organic coatings.

It will be understood that while the operating pH for high speed production is usually within the range of 1.5 to 2.5, the pH can vary within the broader range of 0.8 to 5.0 under other operating conditions depending upon time of contact of liquid and substrate, temperature, concentration, preliminary preparation, and method of application. It is important that the nonferrous metal substrate be clean and that all oxide be removed therefrom before treatment with the chromium depositing solution. The time of treatment can vary from one second to five minutes and the solids concentration of the treating chromium depositing solution from 0.5 ounce per gallon to 12 ounces per gallon. The non-ferrous metal surface can be immersed in the chromium depositing solution with or without agitation or the chromium deposition solution can be applied by spraying or by a combination of spraying and immersion.

The presence of trivalent chromium is particularly important where the non-ferrous metal surface is composed of aluminum or aluminum alloy materials. In hot dip galvanized lines hexavalent chromium is produced by the action of the acid on zinc and at least a minimum amount of reducing agent should always be present to insure the development of trivalent chromium.

While the invention has been described particularly with respect to zinc and aluminum surfaces, especially aluminum, aluminum alloys and aluminized and galvanized iron and steel, it is also applicable to other nonferrous metal surfaces including magnesium, magnesium-aluminum alloys, copper and copper alloys, and copper-clad phenolic sheets.

The invention makes it possible to provide nonferrous metal surfaced articles which are inhibited against corrosion and adapted to adhere to synthetic resin coating compositions thereby producing articles coated with a synthetic resinous film having satisfactory impact and bending resistance and resistance to creeping corrosion between the metal and the resinous coating.

The invention is hereby claimed as follows:

1. A chromate deposition composition having a solids content within the range from 0.2 gram per liter to 75.0 grams per liter, the remainder being water, and consisting essentially of the following:

Ingredients Grams per Liter Hexavalent chromium (expressed as Cr) 0.05-50.0 Trivalent chromium (expressed as Cr) 0.03-3.0 Fluoride or bifluoride (expressed as F) 0.03-3.0 Borate (expressed as B 0,) 001-30 Fluoborate (expressed as BF 0.03-l0.0 Sulfate (expressed as S 0.0l3.0 Magnesium (expressed as Mg) 0.0l-3.0 Aluminum (expressed as Al) 0101- lron (expressed as Fe) 0.01-0.05

Nickel (expressed as Ni) Acetate (as acetate radical) 2. A chromate depositing composition consisting essentially of an aqueous solution of the following:

3. A composition as claimed in claim 2 containing a sufficient amount of a reducing agent to convert a part of the hexavalent chromium to trivalent chromium.

4. A composition as claimed in claim 3 in which the reducing agent consists essentially of sodium sulfite and sodium nitrite each in proportions of 0.05 to 0.2 gram per liter.

Claims

2. A chromate depositing composition consisting essentially of an aqueous solution of the following: Ingredients Grams per Liter Dichromates 1.66-6.75 Chromic acid 0.33-2.88 Sodium or ammonium fluoride or bifluoride 0.33-1.36 Boric acid 0.33-2.00 Sodium acid sulfate 0.10-0.90 Aluminum sulfate 0-0.70 Magnesium sulfate 0-0.70 Fluoboric acid (50%) 0.66-2.75 Nickel sulfate (NiSO4) trace Iron sulfate (FeSO4) trace
3. A composition as claimed in claim 2 containing a sufficient amount of a reducing agent to convert a part of the hexavalent chromium to trivalent chromium.
4. A composition as claimed in claim 3 in which the reducing agent consists essentially of sodium sulfite and sodium nitrite each in proportions of 0.05 to 0.2 gram per liter.