US2743204A

US2743204A - Phosphate metal coatings

Info

Publication number: US2743204A
Application number: US306961A
Authority: US
Inventors: William S Russell
Original assignee: Parker Rust Proof Co
Current assignee: Parker Rust Proof Co
Priority date: 1952-08-28
Filing date: 1952-08-28
Publication date: 1956-04-24
Anticipated expiration: 1973-04-24
Also published as: BE522392A; GB733235A; FR1086955A; NL91161C; CH312218A; DE1072055B

Description

Un ed States. Patent PHOSPHATE..METAL. COATINGS;

William S; Russell; Royal Oak, Micl1., assignor to Parker Rush Proof' Company; Detroit; Mieln,v acorporatlom of Michi an .No Drawing. Application August 28', 1952),

Serial o. sop-p61: 12 Claims, (Cl. 148-615) The present invention relates to improvedphosphate coating compositionsv and. methods for forming. protective,

phosphate coatings on metallic surfaces including iron steel,.zinc and aluminum. In. particular thisinvention is concerned with animproved solution of'the coating-phosphate type, c. g., zinc, iron or manganese phosphate,

It is now well known "that the rate of formation of phosphate coatings on metallic surfaces from solutions of the coating-phosphate type, that is solutions containing a metallic ion which becomes a part of the integral coating formed on the surface, is greatly increased by the use of ox-itl-izingor accelerating agents. Typical oxidizing;

agents which have been suggested include nitrates, chlorates, bromates; sulfites, nitrites, perchlorates, periodates, permanganates, etc. Solutions of the CQafi J Phosphafe type operating under conventional commercialconditions of continuous production form coatings on, ferrous surfaces usually ranging in coating weight between-about 50 and 600 mg./sq ft. For corrosion resistantappliczi tions heavier coatings averaging about 160019 mg./sq. ft. are obtained by immersion for relatively long,

periods of time or by special surface preparation prior cemn eaest rnchelates w th I ethy e e am neetr ce ic. ac r iabi nei; (1th to coating or both. Heretofore it has not been possible" to produce coatings sufliciently heavy to serve as corrosion-resistant coatings in periods of timeas low as about. 10 minutes. A

e p incip l i c hep 'esent nvent on s. o Pr vide an improved phosphate coating solution which" is capable of producing unusuallg l eavy phosphate coatings on metallic. surfaces in short periods of time. I I

Another object is to provide an improved coating solution which produces heavy phosphate coatings on metallic.

surfaces when applied theretoeither by dipping orspray-f ing techniques. p

A further object of the present, invention is to provide a method for treating the surfaces of iron, steel and zinc to form a heavy phosphate coating thereon.

Still anotherobjective is to I provide an auxiliary accelerator which in combination with conventional oxidiiing -agents in a coating-phosphate solution greatly in creases the coating weights obtainable on me'tallic sur faces.

Other objects and advantageous features of the invention will become apparent upon considering the present disclosure in its entirety.

In accordance with this. invention, iLhas beenf oundham r d cati nate ca-s t e were phosphate type and having a pH in the range of 1.9 to 3.5

I face of the metal being coated. Coating-phosphate solu- V enter:t onal xi z ng g nt Q-h pre nt in: 0

saa s an -1 m:

I 2,743,204 Bate ted Apr. 24, 1956 are unexpectedly accelerated by the addition thereto of small quantities ofcertain organic chel'ating aggn flertain amino acids, and'parti'cul'arly" alpha "amino acids; such; asglycine, alanine and-,sarcosinei'form coins pleases. with certain metal ions such as iron, copper; zine; nick l). m. in 8. ion and this; complexingetfectively remotes-- such: ion tom. the olution, or: pr en h i' r m ar y ng. out theta ncrmalrreacticns. Polycarbox-L yliq alph aminosacids, such. as; ethylenediamine tetnm acetioaci have; even greater tendencies torfornistable metallic ions in comparable: fl ltiqnfin han. 9 h simpler minqiacidsi. Aqueous: solu ians. at pclycarhcxy ealnha amino acidsne ia kaliaeiuna u eand are known-to.- lose their chelatingaonompl xin b ty ecreasingpH on in otherwo-rds n. easin aodi y= hus, heeatra heavy-coat n we h s. wh wereqbt ine i nd. u ed; by: he. addition? b -ED111013; ties of such c; r,ga nicv chelatingiagentsi to relatinely: a inapho phate o utions were; not e pected. or he re en sincr a e in. oatineweight s.no -.-co p e elynde st od; Coating wei htaresnlting. from the presence in the coating solution ofiasrnali qnana itles ofi 'pol-y a boxy c amino ac have een. increase bit: as, anch n imes. verhat. whi s btained: undeniden ic tp cc ssing. o itions; except}; ton pres e.

t h mino. a i I ncphosphe es lu icns h r tage- PH, between an 5. hearty coa ing w ights. chem steris ic: of thisin nt on net ob ined n he ab ence of a. conveat nm ox d z g: a ent: Manganese an hi q Phosphat so ut s, o he o he andt'do. notreqn re a. to. ob ain he x ra hea y e t ns jaa hett Benedi t t m Or anic; h lati g a e which ha -been te n e par cular ys it-able f e pume esz t a" mye ti rta he pe y a-rb xy a pha am o ac ds ac t ci t oa Pr duct-Qt m ienisl ndt ie etraac t c. acre-d ri ab c r methrles d' The hem-t ns. ent maybeadd drtq: e c atiaa ieth Q5? thisiave tionint e f m. at he am n ac s. bus r. al bflityre on t Pref red. at th amiuoacids eemp oy dte I inner salt; as e sodium t h da t. an e ra maybe mployed- Sol t o s ha a e usetul t r e. p rpose at th s n ent eaand; th he general c ass fi ation 1.: coating-phosphate solutions which operate in continuous; PRQQH t K Z s balan d se utions hay n a. PH? b twe 31%? 19 3 5+ nslu e hep n tes titineman; S t ens :havms an ro en Queen: centration greater than phi-oi n? have. a tendanceeact as a pickle and to form undesirable pits on the surtions have 1 a. tendency. to; form large; quantitiesof inso1uble phosphates commonly called sludge, ancl as.the pHB approaches. 3.5 this tendency is greatly accentuated and renders. the. continuous. operation of the. S0lllti0n;6X-z tremely. diflicult. Maintenance. ofthe. pH-of 'the solution between the. limits. of. 1.9,, and. .3..5 is important andanecesz ary: to. thecc s ul ormat o at the. desi ed heartw 3 TABLE I oxidizing agent: Percent Chlorate .03-5.0 Bromate .03- .5 Nitrite .01-.15 Sulfite .02 .15

Other specific oxidizing agents which may be used are potassium iodate, sodium meta-nitrobenzene sulfonate, picric acid, hydroxylamine, etc. Typical concentrations which may be used are 0.02% to 0.5% potassium iodate, 0.03% to .5 sodium meta-nitrobenzene sulfonate, 0.01% to 0.3% picric acid and .01 to .3% hydroxylamine. The proportion given for each oxidizing agent is that proportion which causes a substantially equivalent amount of oxidizing or acceleration of the coating formation as 'is caused by any other oxidizing agent when present in the quantity shown. Nitrates may be used in manganese phosphate solutions at a concentration between 0.1% and 5% and may likewise be used in zinc phosphate solutions, although in certain cases they are not the most beneficial oxidizing agents with the latter solutions. When using nitrites it is preferable to maintain the temperature of the solution below about 140 F. inasmuch as the nitrite appears to react with the chelating agent and to decrease its effectiveness.

Increases in coating weight and improved resistance to corrosion have been observed to result from the addition of extremely small quantities of chelating agent to the coating solutions above described. Quantities as low as about .01% of ethylene diamine tetra-acetic acid or equivalent proportions of the tetra, tri or di sodium salts thereof, or of triglycine or the tetra-acetic acid derivative of trimethylenediamine are beneficial and produce increases in coating weight, and proportions up to about 3% of ethylene diamine tetra-acetic acid or its equivalent as the salt, may be used. The upper limit is not critical inasmuch as quantities in excess of 3% may be tolerated. The upper limit is usually determined on the basis of economy and ease of operation and proportions above about 1% have not been found to be necessary in the majority of applications. A few simple tests under operating conditions will easily establish the most desirable concentration. For example, in zinc phosphate solutions using chlorate as oxidizing agent, the preferred concentration of ethylene diamine tetra-acetic acid, based on the tetra sodium salt, is in the range of about .1% to about .3%. Proportions below about .01% ethylene diamine tetra-acetic acid have some beneficial effect, but the effect is not as pronounced as with concentrations exceeding 0.01%.

The following examples are given to illustrate in detail the improved compositions of this invention and the specific method which may be used in applying these compositions to metallic surfaces.

Example 1 An aqueous solution was made up with the following composition:

The solution operated at a pH of 23-335. Four inch by six inch cold rolled steel panels were cleaned of oil and other foreign material by conventional cleaning methods such as dry wiping followed by wiping in mineral spirits or a short pickle in sulfuric acid. The panels were then immersed in a solution of the above composition heated to 160 F.-200 F. for periods of 1, 3, 5, 10 and minutes. Coating weights received were 108 mg./sq. ft. after one minute, 110 mg./sq. ft. after three minutes and only 118 ing/sq. ft. after 15 minutes. The solution was then altered by adding .5 grams/liter of tetra sodium ethylene diamine tetra-acetate. A series of identi- 4 cally cleaned panels were then immersed in the new solution for l, 3, 5, 10 and 15 minutes. Coating weights obtained increased as follows:

The concentration of tetra sodium ethylene diamine tetraacetate was increased to .1%, .3%, .5%, 1%, 2% and 3% and a series of panels immersed in each solution for comparable time intervals. Coating weights obtained after three minutes in each of the solutions are as follows:

Coating wt., M n sq. it.

Tetra sodium ethylene diamine tetra-acetate Example 2 Grams/liter Zinc dihydrogen phosphate 18 Sodium bromate 5.5

The solution operated at a pH of 2.7-2.9.

Prelimi-narily cleaned cold rolled steel panels were immersed in the solution heated to about F. for three minutes. Coating weights averaging 55 rug/sq. it. were obtained. To the solution was then added 2.5 grams/ liter of the tetra sodium salt of ethylene diamine tetraacetic acid, and coating weights were observed to increase to an average of 313 rug/sq. ft. after otherwise identical treatment.

A series of compositions similar to those of Example 1 and 2 were made up in which the sodium chlorate and sodium bromate was replaced with other oxidizing agents including sodium nitrate, sodium nitrite, sodium sulfite, nitrobenzene sulfonate, hydroxylamine, etc. A few of these variations are given in the following examples.

Example 3 Grams/liter Manganese dihydrogen phosphate 20 Sodium nitrate 10 Triglycine .5 to 30 Example 4 Grams/liter Zinc 3 Phosphoric acid 12 Sodium m-nitrobenzene sulfonate 3 Ethylene diamine tetra-acetic acid .4 to 27 Example 5 Grams/liter Manganese dihydrogen phosphate 15 Sodium m-nitrobenzene sulfonate 6 Tetra sodium ethylene diamine tetra-acetate .5-30

am zes Tetmgs di m; ethvhndimie lte r r s tat 3+ -5-. 0

Corrosion resistance of the Coatings appeared to be somewhat better when thecoatingsfresulted from longer immersion periods, that -is,-; between-- and minutes and the temperature approaehed-"the upper" operating Bumper-bar stock, preliminarily-cleaned, was sprayedfor 6.0 seconds incthe above solution at 138 F. Coating. weights obtained varied: from 48. to .135 nag/sq ft.- The. SQ JliQ wast-altered byadding l. 'gram/litenof tetra sodium ethylene diamine tetra acetate. The. solution then had a pH of 2.7 and coating weight after sixty-second p y ried between 33.65am, 416 met/sq. ft.

' Examples v 1 Grams/liter Manganese dihydmgenphosphate Tetra sodiumethylene.-diamine tetra a cetate l to 6 Clean .c'old rolled'steel' panels processed inthis. solution.at.205 F. to 210 F. for 10,-minutes showed over 50% increase in coating weight as the result of adding 1 gram/liter of the chelatingagent-over that obtained without=the; .chelating agent. The heavie'stooatingwas' o tained at 3 gramszliter of the chelatiug agent.

Portions of this solution were modified by incorporating proportions of various oxidizing agents. within the above given ranges. Optimum concentrations of tetra sodium ethylene diamine tetra acetate are as follows:

ox iz n gen per ent. Chelat sagen er 1 ni rate g .1. damn- 025-06 .1 nitrite p .03-.,l0 .6 chlorate 0.3-1.0 .6 sodium m-nitro benzene sulfonate 0.1-1.6

A composition particularly useful for treating aluminum or aluminum alloy surfaces is given in Example 10.

Example 10 Pounds Phosphoric acid (75%) 37 Nitric acid, 42 B 71.5 Zinc oxide 42.5 Boric acid l8- Hydrofiuoric acid (60%) 16.5 Sodium bifiuoride 17 Water to make 500 gallons.

. Y xc ud a Zinnia- 04 Y Grams/liter; 1's NaClOs d 4' Operating'pH- 2.5-3.0

a coating having. a, weight of 367- rags. per Square ft. ,Various portions of the, basic solution were altered by incorporating minor quantities oftetra-sodium ethylene diamine tetra-acetate to produce coneentrati'ons;of'03%, 06%, 11%; 3% and-61%. Increases in coating weight were observed at each concentrationwith a coating weight of about 1",'550 -m gs. per square footioccurri'ng at 6% tetra sodium ethylenefdia-rnine tetrafacetate; Panels; of 24S Tstock werealso treatedin the alternating'portions of the basic solution andcomparableincreases: in coatingwei-ght were observed at each concentration up to amaximum of about 1,840 mgs. persquare footat' 6% concentration of, tetra sodium ethylene diaminetetraacetate. Then ost desirable concentration or; tetra sodium'ethylene diamine tetr a acetate in this solution appears to bebetween .3% and.6%

A solution particularly adapted for-coating zinc, galvanized iron or the like is givenin Example V a The. aqueous. solution .having theabove, analysisis: prefi stably f m d b a m rtqltq i ns oi sa lfi fh oluti n-@ 503 t fiv mi u e t menve a e coating weight of .445Qmgs pen. square, foot .was,. obtained,

quantities. ot, tetra. ettutlone diamine tetra-acetate.

;6%.-f. Theqoating weightswe gernoted to'increas fr nythg o e t ant t s pward a fat. bout 2.65. mgs. per square foot at a concentration of .6% of the tetra s di m. e h e e d smis te ra-amul t ,T e sw m ererating, concentration of tetra. sodi ethylenecliamiue @ua amtat mh twssw-3t%=and-6%- Whatisclaimedis; I I a 1. ,A. solution for producingv phosphate; coatings on eta l urf e ou stinses s tial fa Phgsphate met c edfi m he rou wast an z n a d. manganese. and an acetic acid, said solution having. ajpH'intherange-of-abont.1.9aud 3.5.. v

2. A composition for producing heavy phosphatevcoathuge on, metallic-surfaces inshort periods'of time which consistsessentiallyof an aqueous acidic. solution of a phosphatwt et lf t the ewe s ns fiasqf itqu zinc and manganese, an oxidizing agent and an acetic amino acid, said solution having pH in the range of 1.9 to 3.5.

3. A solution for producing heavy phosphate coatings on metallic surfaces in short periods of time consisting essentially of an aqueous acidic solution of a phosphate selected from the group consisting of zinc phosphate, iron phosphate and manganese phosphate, an oxidizing agent selected from the group consisting of nitrates, nitrites, chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, and hydroxylamine, and an acetic amino acid, said solution having a pH between 1.9 and 3.5.

4. A solution for producing heavy phosphate coatings on metallic surfaces in short periods of time consisting essentially of an aqueous acidic solution of a phosphate selected from the group consisting of zinc phosphate, iron phosphate and manganese phosphate, an oxidizing agent selected from the group consisting of nitrates, nitrites, chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, and hydroxylamine, and at least about .01% of on metallic surfaces in short periods of time consisting essentially of an aqueous acidic solution of a phosphate selected from the group consisting of zinc phosphate, iron phosphate and manganese phosphate, an oxidizing agent selected from the group consisting of nitrates, nitrites, chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, and hydroxylamine, and a chelating agent selected from the group consisting of ethylene diamine tetra-acetic acid, triglycine, the tetra-acetic acid derivative of trimethylene diamine and the alkali metal salts thereof in an amount equivalent to .01% to 3% of ethylene diamine tetra-acetic acid, said solution having a pH between 1.9 and 3.5. v

6. A solution for producing heavy phosphate coatings on metallic surfaces in short periods of time consisting essentially of an aqueous acidic solution of a phosphate selected from the group consisting of zinc phosphate, iron phosphate and manganese phosphate, an oxidizing agent selected from the group consisting of nitrates, nitrites, chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, and hydroxylamine, and about .01% to about 3% of ethylene diamine tetra-acetic acid, said solution having a-pH between,1. 9 and 3.5.

7. A method which comprises obtaining a corrosion resistantheavy coating on iron, steel and zinc by subjecting the surface of said metal to the action of an aqueous acidic solution of a phosphate of a metal from the group consisting of iron, zinc and manganese; and an acetic amino acid, the pH of the said solution being between 1.9 and 3.5

8. A method which comprises obtaining a heavy, corrosion resistant coating on a metal selected from the group consisting of iron, steel and zinc by subjecting the surface of said metal to the action of an aqueous acidic solution of a phosphate selected from the group consisting of zinc phosphate, iron phosphate and manganese phosphate, an

oxidizing agent selected from the group consisting of ni-,

trates, nitrites, chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, and hydroxylamine, and an acetic amino acid, said solutionhaving a pH between 1.9 and 3.5.

9. A method which comprises obtaining a heavy, corrosion resistant coating on a metal selected from the group consisting of iron, steel and zinc by'subjecting the surface of said metal to the action of an aqueous acidic solution of a phosphate and manganese phosphate, an oxidizing agent selected from the group consisting of nitrates, nitrites, chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, and hydroxylamine, and at least about .0l% of ethylene diamine tetra-acetic acid, said solution having a pH between 1.9 and 3.5.

10. A method which comprises obtaining a heavy, corrosion resistant coating on a metal selected from the group consisting of iron, steel and zinc by subjecting the surface of said metal to the action of an aqueous acidic solution of a phosphate selected from the group consisting of zinc phosphate, iron phosphate and manganese phosphate, an oxidizing agent selected from the group consisting of nitrates, nitrites, chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, and hydroxylamine, and a chelating agent selected from the group consisting of ethylene diamine tetra-acetic acid, triglycine, the tetra-acetic acid derivative of trimethylene diamine and the alkali metal salts thereof in an amount equivalent to .01% to 3% of ethylene diamine tetraacetic acid, said solution having a pH between 1.9 and 3.5.

11. A method which comprises obtaining a heavy, corrosion resistant coating on a metal selected from the group consisting of iron, steel and zinc by subjecting the surface of said metal to the action of an aqueous acidic solution of a phosphate selected from the group consisting of zinc phosphate, iron phosphate and manganese phosphate, an oxidizing agent selected from the group consisting of nitrates, nitrites, chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, and hydroxylamine, and about .01% to about 3% of ethylene diamine tetra-acetic acid, said solution having a pH between 1.9 and 3.5.

12. A composition for producing heavy phosphate coatings on metallic surfaces in short periods of time which consists essentially of an aqueous acidic solution of a phosphate of a metal from the group consisting of iron, zinc and manganese, an oxidizing agent, a fluoride and an acetic amino acid, said solution having a pH in the range of 1.9 to 3.5.

References Cited in the file of this patent UNITED STATES PATENTS 1,911,726 Tanner et al. May 30, 1933 2,132,883 Romig Oct. 11, 1938 2,298,280 Clifford et a1. Oct. 13, 1942 2,316,811 Romig Apr. 20, 1943 2,461,519 Bersworth Feb. 15, 1949 2,479,423 Snyder Aug. 16, 1949 FOREIGN PATENTS 663,650 Great Britain Dec. 19, 1949 OTHER REFERENCES .The Properties and Uses of Ethylenediamine Tetra Acetic Acid and Its Salts, published 1949 by the Bersworth Chemical Co., Framingham, Mass. Page 7 is particularly pertinent.

The Modern Chelating Agent, published 1949 by the Bersworth Chemical Co., Framingham, Mass. Pages 1, 8-11 and 13 are pertinent.

Claims

1. A SOLUTION FOR PRODUCING PHOSPHATE COATINGS ON METALLIC SURFACES CONSISTING ESSENTIALLY OF A PHOSPHATE OF A METAL SELECTED FROM THE GROUP CONSISTING OR IRON, ZINC AND MANGANESE, AND AN ACETIC AMINO ACID, SAID SOLUTION HAVING A PH IN THE RANGE OF ABOUT 1.9 AND 3.5.