US3852125A

US3852125A - Surface conversion treated magnesium

Info

Publication number: US3852125A
Application number: US00385114A
Authority: US
Inventors: J Brown
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1971-10-26
Filing date: 1973-08-02
Publication date: 1974-12-03
Anticipated expiration: 1991-12-03

Abstract

A magnesium article treated with an aqueous surface conversion treating composition prior to application of a painted or photoresist coating. The composition comprises a water solution of about 9.4 to about 19.5 grams per liter NH4 ; about 50 to about 103 grams per liter PO4 ; about 1.0 to about 2.8 grams per liter Ca ; and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl , NO3 , SO4 , and is characterized by having a pH of about 3.0 to about 4.5. Magnesium sheet with at least a portion of the surface treated with an aqueous composition of about 60 to about 125 grams per liter of final composition of monobasic ammonium phosphate; sufficient calcium salt of a strong mineral acid to produce a Ca concentration of about 1.0 to about 2.8 grams per liter, and sufficient pH modifier selected as required from the group consisting of phosphoric acid and ammonium hydroxide to produce a pH of about 3.0 to about 4.5, has a phosphate layer promoting adherence of a photoresist material and/or paint to the magnesium surface. The treated magnesium sheet is preferably formed by contacting the surface with the liquid composition at a temperature of up to about 120*F. and rinsing the reacted surface in liquid water maintained at a temperature of up to about 130*F.

Description

United States atent 1 1 1 3,852,125

Brown Dec. 3, 1974 i 1 SURFACE CONVERSION TREATED [57] ABSTRACT MAGNESIUM A magnesium article treated with an aqueous surface [75] Inventor: James A. Brown, Midland, Mich. conversion treating composition prior to application of a painted or photoresist coating. The composition [73] Asslgnee' 33 2:: 323 Company comprises a water solution of about 9.4 to about 19.5

grams per liter Nl-lf; about to about 103 grams per [22] Filed: Aug. 2, 1973 liter POf; about 1.0 to about 2.8 grams per liter 4 Ca; and a total of about 1.9 to about 4.8 grams per [21] Appl 3851l4 liter of ions selected from the group consisting of Cl,

Related US. Application Data N0 S0 and is characterized by having a pH of [63] Continuation-impart of Ser. No. 192,558, 0m. 26, about -0 to about 4.5-

19713 B; 3,784,417 which is 3 Magnesium sheet with at least a portion of the surface commuanomn'part of treated with an aqueous composition of about to 1970 abandonedfl about grams per liter of final composition of monobasic ammonium phosphate; sufficient calcium [:2] 08.81. 148/615 Salt of a Strong mineral acid to produce a Ca++ d 5 Z 6 concentration of about 1.0 to about 2.8 grams per 1 0 5 36 liter, and sufficient pH modifier selected as required from the group consisting of phosphoric acid and ammonium hydroxide to produce a pH of about 3.0 to

[56] References cued about 4.5, has a phosphate layer promoting adherence UNITED STATES PATENTS of a photoresist material and/or paint to the 1,709,894 4/1929 Burdick l48/6.l5 R magnesium surface.

3,015,593 1/1962 Jayne 148/6.l5 R Y a 3,090,709 5/1963 1161111616 l48/6.l5 The treated magnesum Sheet Preferably formed by 3 104 177 9 1963 06103111101 148/6.l5 z contacting the'surface with the liquid composition at a 3:178:320 4/1965 Henricks..... l48/6.15 2 temperature of b and "nsmg the 3,218,200 11/1965 Henricks 148/6.15 z reacted Surface in liquid Water maintained at a 3,288,655 11/1966 Harwell et al 148/6.15 2 emperature of up to about F.

3,409,525 1l/l968 Taylor, Jr. et al.. l48/6.l5 Z

3,784,417 1 1974 Brown 148/6.l5 R

Primary ExaminerRalph S. Kendall Attorney, Agent, 0 r F1'rr1 1:wil lia rn Y ates Robe t 22 Claims N0 Drawmgs W. Selby SURFACE CONVERSION TREATED MAGNESIUM The present application is a continuation-in-part of copending application, Ser. No. 192,558, filed Oct. 26, 1971 by James A. Brown, now Pat. No. 3,784,417 which is a continuation-in-part of abandoned application, Ser. No. 89,130, filed Nov. 12, 1970.

BACKGROUND OF THE INVENTION hering paint or photoresist materials to the magnesium surfaces.

Other objects and advantages will become apparent during the course of the following description of the invention.

SUMMARY OF THE INVENTION The above objects and advantages have been 'achieved in an aqueous composition comprising a water solution of about 9.4 to about 19.5 grams per liter NI-l and about 50 to about 103 grams per liter POf. The composition further includes about 1.0 to about 2.8 grams per liter Ca and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl, N0 and S0,. The composition is characterized by a pH of about 3.0 to about 4.5. Throughout the specification and appended claims are available for preparing a metal for application of an overcoating, a new surface conversion treatment was i needed for magnesium photoengraving sheet, which would promote effective adhesion between the magnesium and the photoresist material.

Photoresist materials are those which are suitable for coating on metal and have a minimum shelflife, i.e., storage time, of approximately six months. Polyvinyl cinnamate type photoresists are an example of such overcoatings. Photoresist materials, especially those utilized in powderless etching baths, inherently have poor adhesion and etch resistance, when applied to bare magnesium surfaces.

To be satisfactorily employed as a pretreatment prior to application of a photoresist, a surface conversion composition should possess certain characteristics. Foremost among these are that the conversion solution should be such that it can be readily and rapidly applied to a clean magnesium surface to produce a light colored coating, which promotes adhesion between the magnesium surface and the overcoating of photoresist. The conversion layer should possess the characteristic of providing sufficient adherence of the photoresist to permit a detergent scrubbing and re-etching with dilute nitric acid without failure of the resist film after removal of the plate from a powderless etching bath. Moreover, the conversion layer formed on the magnesium surface must be compatible with the photoresist so that no detrimental reaction will occur between said layer and the photoresist to substantially effect the shelf-life of a coated product.

The treatment should also enhance the adhesion characteristics between the magnesium surface and paint applied thereto.

It is, therefore, an object of this invention to provide a composition capable of conditioning a magnesium surface for application of an overcoating of paint or photoresist materials.

It is another object of this invention to provide a method of preparing a surface conversion composition capable of improving the adherence between magnesium metals and photoresist and paint coatings.

It is yet another object of this invention to provide a process of using an improved composition to coat magnesium or magnesium alloy surfaces precedent to adall proportions are specified relative to a liter of finished or completed composition, unless otherwise indicated.

The aforementioned acidic aqueous composition is applied as a liquid to the clean surface of magnesium alloys at a temperature of up to about 120F. As used herein the term clean meanssubstantially free of oxide and oily materials. Uponcontacting a clean magnesium surface with the composition, a reaction occurs uniformly over the magnesium surface. The reacting is evidenced by a visually continuous lighter colored metallic or white surface coating on the magnesium. To realize the benefits of this treatment, the magnesium alloy surface should be rinsed in liquid water at a temperature of up to about l3( )F. The rinse watercan eitherbe ordinary tap water or distilled water without materially altering the effectiveness of this invention.

In a preferred embodiment, the aqueous composition comprises about 60 to about 125 grams per liter of monobasic ammonium phosphate; sufficient calcium salt of a strong acid to produce a Ca concentration of about 1.0 to about 2.8 "grams per liter; and sufficient pH modifier selected as required from the group consisting of phosphoric acid and ammonium hydroxide to produce a pH of about 3.0 to about 4.5. Various calcium salts of strong mineral acids are included in this composition. Among the suitable calcium salts are calciumchloride, calcium nitrate, and calcium sulfate. The hydrated derivatives of the aforementioned compounds are also suitable, for example, approximately 4 to about 10 grams per liter of CaCl .2H O supplies sufficient Ca and Cl to produce a satisfactory treating composition. Moreover, anhydrous calcium chloride and other hydrated forms thereof, such as they monohydrate, dihydrate, or hexahydrate are also acceptable when they are employed in amounts sufficient to provide the required amount of Ca ion.

Sufficient calcium ion can be attained in said composition by addition of a single calcium salt of a strong mineral acid such as, for example, calcium chloride, calcium nitrate and calcium sulfate. Moreover, any combination of these calcium bearing compounds in an amount sufficient to provide Ca ion within the stipulated range can be used.

It has been ascertained that a further improvement in performance will be realized when the previously described aqueous composition comprises about to about grams per liter of monobasic ammonium phosphate and an amount of Ca ion as furnished by about 6 to about 8 grams per liter of dihydrated calass-21 225 cium chloride or equivalent quantities of anhydrous or absorb dye from the photoresist causing poor contrast and an undesirably rough photoresist coating.

Aluminum, magnesium, zinc, and various chromates may be present, along with other impurities normally associated with commercial sources of ingredients used in the composition without hindering the effective utilization of said solution.

The composition of this embodiment can be further characterized as being ionically neutral. That is, the specific combination of compounds forming this solution results in the occurrence of equivalent ionic charges in the final conversion composition.

Various methods of forming said composition can be visualized, but it is preferred that the composition be produced by a process comprising mixing together water with about 60 to about 125 grams per liter of final composition of monobasic ammonium phosphate; sufficient calcium salts of a strong mineral acid to produce a Ca concentration of about 1.0 to about 2.8 grams per liters of final composition; and sufficient pH modifier to adjust. the pH of the final composition to about 3.0 to about 4.5 wherein said pHmodifier is selected as required from the group consisting of phosphoric acid and ammoniumhydroxide. The mode of mixing the composition is unimportant and can be accomplished by a number of methods. Mixing by stirring, passing of air through the solution, vibrating thecontainer for said composition or agitation with an impeller are among the satisfactory means of mixing the composition.

Varying amounts of precipitate will usually form during the aforementioned mixing. To reduce the concentration of precipitate, which is believed to be primarily composed of calcium phosphate, a step of removing the precipitate from the final composition can be incorporated after the mixing or agitation has been concluded. While the precipitate can be easily removed by means of a centrifuge it is preferred the precipitate be removed by filtering the composition through a medium having pores no greater than about 50 microns in diameter. Use of the filtered composition for treating metallic surfaces prior to painting or coating with a photoresist will result in a smooth surface free of calcium phosphate precipitate.

Though the above mixing process is completely operable, it is oftentimes desirable to have a composition containing a minimum of precipitate prior to filtering. This can be of economic benefit when substantial quantities of the conversion liquid are being formed. The precipitation of calcium phosphate can be minimized by sequentially mixing the aforementioned constituents in the recited order together in water. A further reducvolume and concentration of the solution may be accomplished at any step by a further addition of water.

In the practice of treating magnesium surfaces according to the invention, a clean magnesium surface is contacted with a described aqueous composition at a liquid temperature of up to about 120F. for a sufficient time to permit a lighter colored metallic or white coating to form on the surface. After removing the magnesium from the aqueous bath, the reacted surface is rinsed with liquid water at a temperature of up to about 130F. Temperatures exceeding those stated above I should be avoided, since the phosphate coating begins to significantly redissolve in water at higher temperatures. Any means of cleaning the metal surface prior to reacting with said composition is satisfactory. Exemplarily of such cleaning methods are contacting the surface with rotating abrasive brushes, alkaline solutions, a pumice slurry, and the like. Rinsing of the sheet after cleaning can be adequately accomplished in water.

The precise method of treating the magnesium with the composition is not critical so long as the composition uniformly contacts the metal surface. Methods such as spraying, dipping, brushing, or swabbing are tion in precipitate can be effected by dissolving the calcium compound in water prior to mixing with the remaining constituents in the composition. Adjusting the among those completely satisfactory methods foreseeable to those skilled in the art.

Prior to applying a photoresist material to the treated metal surface to form photoengraving plate, or applying paint to the treated'metallic surface, it is preferable that drying of the rinsed surface can be adequately dried by exposure to air or a heating means such as electrical coils or a plurality of heat lamps.

A uniform phosphate coating can be applied to a magnesium surface, such as sheet or plate, within about i minute at reaction temperatures up to about 120F. when contacting is carried out by immersion or spraying the-solution onto the magnesium surface. Reacting times as short as about 15 seconds up toabout 45 seconds have proven to be adequate and are preferred; in general, it is desired that reacting be accomplished at a low temperature and it is, therefore, desirable that temperatures of about F. to about F. be maintained during the reacting period.

EXAMPLE 1 A surface conversion composition was prepared in a 55 gallon polyethylene lined drum using the following sequence of steps: I

a. filling the 55 gallon drum three-fourths full with water, b. adding 50 milliliters of phosphoric acid (H PO c. dissolving 26 pounds of monobasic ammonium phosphate (Ni-1 11 1 0,) in the solution of step b while mixing with a turbine type agitator,

d. adding 935 grams of dihydrated calcium chloride (CaCl .2l-l O) while continuing the agitation,

e. adding sufficient water to the drum to obtain a total solution volume of 45 gallons,

f. holding the solution of step e overnight to permit any precipitate that may have formed to settle,

g. filtering the solution into a clean drum through a 25 micron filter.

The pH of the final composition was tested and determined to be 3.89.

Treatment of a magnesium alloy sheet with this composition produced a visually uniform surface coating.

EXAMPLE 2 A second surface conversion composition was prepared in a 157 gallon tank by sequentially carrying out the following steps:

a. adding 125 gallons of water to the tank and starting a circulating pump for agitation,

b. adding 250 milliliters of phosphoric acid to the tank containing water,

c. dissolving 115 pounds of monobasic ammonium phosphate in the solution of step (b),

(1. adding 1 ounces of dihydrated calcium chloride, which had been previously dissolved in 4 gallons of water, to the solution of step (c),

e. adding sufficient water to form 157 gallons of solutlon,

f. while agitation was continued, the solution was filtered through a 25 micron filter bed for 1 hour and recycled into the tank.

The final composition was determined to have a pH of 3.75.

EXAMPLE 3 A surface conversion composition with a pH of 3.56 I

was prepared in 225 gallon capacity tank as follows:

a. adding about 150 gallons of water and then 800 milliliters of phosphoric acid to the tank,

b. dissolving, with agiation, 200 pounds of monobasic ammonium phosphate in the solution of step a,

c. dissolving 16.5 pounds of technical grade dihydrated calcium chloride in 12 gallons of water and then adding the calcium chloride solution to the step b solution while strongly agitating the solution,

d. mixing sufficient water with the step c solution to form 225 gallons of solution and then filtering this solution through a micron media.

A satisfactory surface coating was obtained on the hereinafter described PE alloy magnesium sheet treated with a conversion solution prepared as above.

EXAMPLE 4 A surface conversion solution with a pH of about 3.0 is prepared as described in Example 3 except that approximately l,500 milliliters of phosphoric acid is added to the solution to increase the acidity. PE alloy magnesium sheet treated with this solution will have a surface with a useable coating.

EXAMPLE 5 An 18 inch by 24 inch by 0.064 inch magnesium alloy sheet was treated with the composition of Example 2. The magnesium base alloy sheet had an alloy designation of PE and had a nominal chemical composition of tated by pumping through a recirculatory type system. The return composition was directed toward the immersed magnesium sheet through ports in two pipes beneath the bath surface.

Upon removal ofthe magnesium sheet from the composition, the sheet was rinsed by spraying with water which was maintained at a temperature of 65F. to F. and then dried by heating to a temperature of 250F. in an infrared drying oven. After drying the surface, a polyvinyl cinnamate type photoresist was applied to the surface to form photoengraving sheet.

Upon further processing, it was ascertained that the phosphate coating promoted sufficient adhesion between the magnesium sheet and photoresist material to permit the photoresist overcoating to resist acid attack in the image areas of the photoengraving sheet. Furthermore, the adhesion characteristics were sufficient to allow scrubbing with a detergent and re-etching with dilute nitric acid after the processed photoengraving sheet was removed from a powderless etching bath without failure or a loss of the resist film from image areas. The photoengraving sheet so produced had a shelflife of a minimum of six months.

EXAMPLE 6 Magnesium alloy PE sheet was processed in a manner similar to that of Example 5 and painted with one coat of Dulux Black Enamel 83-005 after the magnesium surface had dried. The painted surface was tested for adherence of the paint to the sheet, corrosion protection in a 5% salt spray, and blistering at F. in an atmosphere having a relative humidity of 95%. The tests indicated the phosphate conversion coating provided an adequate base for painting the metal surface.

What is claimed is:

l. A magnesium body having a surface layer formed by treating at least a portion of the magnesium surface with an aqueous composition comprising a water solution of about 9.4 to about 19.5 grams per liter NHJ; about 50 to about 103 grams per liter POJ"; about 1.0 to about 2.8 grams per liter Ca; and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl, N0 and S0 the composition being characterized by a pH of about 3.0 to about 4.5.

2. The magnesium body of claim 1 wherein the aqueous composition used to form the surface layer had a pH of about 3.4 to about 3.7.

3. The magnesium body of claim 1 wherein the surface layer was formed by treating with the aqueous composition at a temperature of up tov about F.; and then rinsing treated surface in liquid water at a temperature of up to about F. I

4. The magnesium body of claim 1 wherein the calcium ion was at least partially supplied by calcium chloride.

5. The magnesium body of claim 1 wherein the'calcium ion was at least partially supplied by calcium nitrate.

6. The magnesium body ofclaim 1 wherein the calcium ion was at least partially supplied by calcium sulfate.

7. The magnesium body of claim 1 wherein the surface layer is at least partially coated with a photoresist material.

8. The magnesium body of claim 1 wherein contacting is carried out with the aqueous composition after filtering the composition through a medium with pores no greater than about 50 microns in diameter.

9. A magnesium body having a surface layer formed by contacting at least a portion of the magnesium surface at a temperature of up to about 120F. with a liquid aqueous composition consisting essentially of a water-solution of about 9.4 to about 19.5 grams per liter NHJ; about 50 to about 103 grams per liter POf; about 1.0 to about 2.8 grams per liter Ca; and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl, N and 80 the composition being characterized by a pH of about 3.0 to about 4.5.

10. The magnesium body of claim 9 wherein the calcium ion was at least partially supplied by calcium chloride.

11. The magnesium of claim 9 wherein the magnesium surface was contacted with the aqueous composition for a time of up to about one minute.

12. The magnesium of claim 9 wherein the aqueous composition treated surface is a phosphate containing layer promoting effective adhesion of a photoresist to the magnesium surface.

13. The magnesium of claim 9 wherein the treated magnesium surface is at least partially coated with a photoresist.

14. The magnesium of claim 9 wherein the magnesium is a sheet with the treated surface at least partially coated with a layer of photoresist to form a photoengraving sheet with a shelf-life of at least. about 6 months.

15. The magnesium of claim 9 wherein the treated surface is at least partially coated with an adherent layer of a polyvinylcinnamate photoresist.

16. The magnesium of claim wherein the magnesium surface is an alloy having a designation of PE.

17. The magnesium of claim 16 wherein the calcium ion was at least partially supplied by calcium chloride.

18. Magnesium photoengraving sheet characterized by a shelf-life of at least about 6 months with at least a portion of one surface treated with an aqueous composition consisting' essentially of about 60 to about 125 grams per liter of monobasic ammonium phosphate;

. sufficient calcium salt of a strong mineral acid to produce a Ca" concentration of about 1.0 to about 2.8 grams per liter; and sufficient pH modifier selected as required from the group consisting of phosphoric acid and ammonium hydroxide to produce a pH of about 3.0 to about 4.5; the treated surface having thereon a photoresist layer.

19. The photoengraving sheet of claim 18 wherein the calcium salt is calcium chloride.

20. The photoengraving sheet of claim 19 wherein the treated surface is a phosphate containing layer promoting effective adhesion of a photoresist to the magnesium surface and the photoresist is a polyvinylcinnamate type.

21. The photoengraving sheet of claim 18 wherein the aqueous composition consists essentially of about to about grams per liter monobasic ammonium phosphate; and sufficient calcium salt to produce a Ca concentration of about 1.8 to about 2.4 grams per liter.

22. The photoengraving sheet of claim 21 wherein the aqueous composition includes sufficient pH moditier to produce a pH of about 3.4 to about 3.7.

Claims

1. A MAGNESIUM BODY HAVING A SURFACE LAYER FORMED BY TREATING AT LEAST A PORTION OF THE MAGNESIUM SURFACE WITH AN AQUEOUS COMPOSITION COMPRISING A WATER SOLUTION OF ABOUT 9.4 TO ABOUT 19.5 GRAMS PER LITER NH4+; ABOUT 50 TO ABOUT 103 GRAMS PER LITER PO4--; ABOUT 1.0 TO ABOUT 2.8 GRAMS PER LITER CA++; AND A TOTAL OF ABOUT 1.9 TO ABOUT 4.8 GRAMS PER LITER OF IONS SELECTED FROM THE GROUP CONSISTING OF C1-, NO3-, AND SO4--; THE COMPOSITION BEING CHARACTERIZED BY A PH OF ABOUT 3.0 TO ABOUT 4.5.

3. The magnesium body of claim 1 wherein the surface layer was formed by treating with the aqueous composition at a temperature of up to about 120*F.; and then rinsing treated surface in liquid water at a temperature of up to about 130*F.

5. The magnesium body of claim 1 wherein the calcium ion was at least partially supplied by calcium nitrate.

6. The magnesium body of claim 1 wherein the calcium ion was at least partially supplied by calcium sulfate.

9. A magnesium body having a surface layer formed by contacting at least a portion of the magnesium surface at a temperature of up to about 120*F. with a liquid aqueous composition consisting essentially of a water-solution of about 9.4 to about 19.5 grams per liter NH4 ; about 50 to about 103 grams per liter PO4 ; about 1.0 to about 2.8 grams per liter Ca ; and a total of about 1.9 to about 4.8 grams per liter of ions selected from the group consisting of Cl , NO3 , and SO4 , the composition being characterized by a pH of about 3.0 to about 4.5.

14. The magnesium of claim 9 wherein the magnesium is a sheet with the treated surface at least partially coated with a layer of photoresist to form a photOengraving sheet with a shelf-life of at least about 6 months.

16. The magnesium of claim 15 wherein the magnesium surface is an alloy having a designation of PE.

18. Magnesium photoengraving sheet characterized by a shelf-life of at least about 6 months with at least a portion of one surface treated with an aqueous composition consisting essentially of about 60 to about 125 grams per liter of monobasic ammonium phosphate; sufficient calcium salt of a strong mineral acid to produce a Ca concentration of about 1.0 to about 2.8 grams per liter; and sufficient pH modifier selected as required from the group consisting of phosphoric acid and ammonium hydroxide to produce a pH of about 3.0 to about 4.5; the treated surface having thereon a photoresist layer.

21. The photoengraving sheet of claim 18 wherein the aqueous composition consists essentially of about 80 to about 105 grams per liter monobasic ammonium phosphate; and sufficient calcium salt to produce a Ca concentration of about 1.8 to about 2.4 grams per liter.

22. The photoengraving sheet of claim 21 wherein the aqueous composition includes sufficient pH modifier to produce a pH of about 3.4 to about 3.7.