AU653251B2 - Improved coating solution - Google Patents

Description

P/00/0011 Regulation 3.2

AUSTRALIA

D tn tn A nt in0n COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: GIBSON CHEMICALS LIMITED w o o o oo o o *o r Actual Inventor(s): Robert Maurice ELLIS and Lindsay

WILLIAMS

Frank Goulding Address for service in Australia: CARTEP SMITH BEADLE Qantas h.use 2 Railway Parade Camberwell Victoria 3124 Australia Attorney Code CD Invention Title: IMPROVED COATING SOLUTION The following statement is a full description of this invention, including the best method of performing it known to us: Our Ref: #854 BMH:WB 09-27gib -1- -2- This invention relates to the application to metal surfaces of coatings which are corrosion resistant and to which paints, inks, lacquers and other overlying coatings adhere.

This invention particularly relates to aqueous coating solutions which are generally acidic and free of chromates and ferricyanide and which form the aforementioned ty,'es of coatings on aluminium and other metallic surfaces.

Corrosion resistant coatings such as those of the present invention find particular application in the manufacture of aluminium beverage cans and it will be with such application in mind that the following invention will be described. It will, however, be appreciated that the invention has broad application in the metal processing industry in general.

It is desirable, particularly in the manufacture of aluminium cans, that corrosion resistant coatings applied to aluminium surfaces do not alter the bright shiny appearance of the aluminium even though the final product may completely or partially be covered with overlying siccative coatings. The corrosion resistant coatings should preferably also have properties such that these overlying coatings adhere tightly thereto.

The corrosion resistant coatings should preferably also have the ability to withstand discolourati, of the aluminium surface when subjected to hot water of about 65°C to about 0 C, referred tu in the can industry as "Pasteurisation". This treatment can cause uncoated S 20 or inadequately coated aluminium surfaces to blacken or otherwise discolour. In addition to this property it is desirable that aluminium surfaces treated with these conversion coatings be able to undergo a simple testing procedure to confirm the presence of the coating. One such test employed in the can industry is known as the "muffle test". A sample of cleaned and treated aluminium surface is placed in a muffle furnace at about 550 C for about 5 minutes. The presence of the coating is indicated by a colour change of the aluminium surface.

Corrosion resistant coatings of the present invention can also find application in the treatment of steel surfaces and zinc and aluminium coated materials such as galvanised zinc coated or aluminium-zinc coated steels. The corrosion resistant coatings should preferably exhibit the ability to prevent the formation of white rust on zinc coated surfaces exposed to the atmosphere. Such coatings should preferably also have properties such that any overlying siccative coatings, such as for example, paints or lacquers, adhere tightly

SM-OMBSON.SP~

7 Septmber 199 -3thereto.

In order to prevent the formation of white rust on galvanised or zinc coated steel it is generally accepted that the treatment of a surface with a chromate imparts excellent anti corrosive properties at low cost. However the use of chromate is under constant scrutiny with respect to pollution regulations, toxicity to exposed workers and disposal problems. Chromate treatments have a distinct disadvantage in that they provide for inferior adhesion of paint.

In another process, treatment of the zinc coated steel with a phosphate provides for improved paint adhesion thereto however corrosion resistance is inferior to the chromate treated substates.

Phosphate coatings, such as these, also find application in the treatment of steel, where they provide for excellent adhesion of siccative coatings. Coatings of this type however do not impart substantial anticorrosive properties to the treated metal surfaces and subsequent processing, such as for example, the absorption of protective oils onto the phosphate coating or the use of a chromating dip may have to be employed in order to provide for adequate corrosion protection.

Phosphating processes for metals are well known and numerous patents have been established over the last 70 years. In essence, phosphating processes are relatively simple, comprising of mildly acidic phosphate solutions, with pH in the range of 3 to 5.5, and often S 20 containing metal salts such as for example zinc salts, molybdenum salts, nickel salts or manganese salts.

Most phosphating solutions are proprietary mixtures and the processes are often known by their trade names. In general the processes provide coatings of complex metal phosphates on steel or zinc based alloys by treatment in or with a solution of acid 25 phosphates. The coatings provide for, in these proprietary formulations, good adhesion of siccative coatings. However they often do not provide for adequate corrosion protection without the need for subsequent anticorrosive processes such as for example the use of chromates.

Aqueous coating solutions which provide useful alternatives to chromate and ferricyanide containing systems are known. However, such systems have limited appeal only since they require exploitation within a narrow range of operating parameters such as pH, temperature and contact times.

SM-OIMSON.SPC

7 Stmlbntf 19M -4- Accordingly it is an object of the present invention to provide an aqueous coating solution which is chromate and ferricyanide free and which can be applied within a less restrictive range of parameters such as pH, temperature and contact times.

It is a further object of the present invention to provide a process for treating metal surfaces with a chromate and ferricyanide free solution to produce a corrosion free coating.

In accordance with one aspect of the present invention there, is provided a chromate and ferricyanide free aqueous coating solution containing between 0.01 and 100 g/1 phosphate, between 0.001 and 10 g/1 fluoride, between 0.01 and 10 g/1 molybdate and one or more compounds of titanium, zirconium, hafnium or cerium in a total amount of between 0.005 to 10 g/l, calculated as the weight of the respective metal(s).

Preferably, the solution has a pH in the range of from 0 to 8.

The solution of the present invention can be used to treat bright shiny aluminium surface in manner such that the bright shiny appearance of the surface is not altered, while forming on the surface a uniformly colourless and clear coating which provides for 15 corrosion resistance and to which overlay, for example, siccative coatings adhere. An aluminium surface treated in this manner is capable of undergoing the so-called "muffle test" to confirm the presence of the clean and colourless coating.

0"V. In accordance with another aspect of the present invention there is provided a process for producing a corrosion 'esistant coating, which comprises treating a metal 20 surface with a chromate and ferricyanide free aqueous solution containing between 0.01 and 100 g/l phosphate, between 0.001 and 10 g/l fluoride, between 0.01 and 10 g/1 molybdate, and one or more components of titanium, zirconium, hafnium or cerium in a total amount of from 0.005 to 10 g/l, calculated as the weight of the respective metal(s) at a pH of from 0 to 8. The treated metal surface is then rinsed with water or other convenient rinsing agent and tried by any convenient conventional means.

Prior to treating the metal surface with the coating solution it may be appropriate to pre-treat the metal surface with, for example, degreasers, alkali cleaners or acidic cleaning solutions.

1 Spccmb 1991 In accordance with yet another aspect of the present invention there is provided a process for producing a .orrosion resistant coating, which comprises treating a metal surface with a chromate and ferricyanide free aqueous solution containing between 0.01 and 100 g/l phosphate, between 0.001 and 10 g/1 fluoride, between 0.01 and 10 g/1 molybdate, between 0.01 and 10 g/1 nickel, and one or more components of titanium, zirconium, hafnium or cerium in a total amount of from 0.005 to 10 g/1 at a pH of from 0 to 8.

The incorporation of nickel into the aqueous coating solution provides for improved coating times in situations where the surface to be coated contains a high percentage of zinc, as for example, die-cast metals or galvanised parts. The inclusion of nickel salts in the coating solution will typically reduce contact times by as much as 50% in certain circumstances.

The corrosion resistant properties of coatings formed from coating solutions within the. scope of the present invention include the ability to withstand blackening or discolouration of an aluminium surface when subjected to a "pasteurisation test" of hot water having a temperature of 65'C to about 75"C, at a pH of 8.8 to 9.1 for a period of time at least 20 minutes up to as long as 30 minutes and the ability to prevent the occurance of white-rust formation of on zinc or aluminium/zinc alloy coated steel surface when exposed to the atmosphere for a period of time of at least 30 days up to as long as days or more.

The coating solutions of the present invention are capable of effectively forming the aforementioned types of coatings in the absence of hexavalent chromium and materials such as ferricyanide and ferrocyanide. In addition the coating process has been found to be tolerant of a variety of surface cleaning procedures used prior to the coating stage and is capable of providing a primary cleaning action.

The coating solutions of the present invention can be prepared from a variety of source compounds which contain the aforementioned essential ingredients (ie a titanium, zirconium, hafnium and/or cerium compound, a fluoride compound, a molybdenum compound and a phosphate compound) and which are soluble in the solution.

The source of the titanium, zirconium, hafnium or cerium can be, for example, the ammonium and alkali metal salts of fluotitanates, fluozirconates and fluohafnates and also the metallic fluorides. In addition the coating solutions can be prepared from a mixture of soluble compounds of which one contains titanium, zirconium, hafnium or cerium, such as for example, water soluble sulphate or nitrate salts and the other of which contains fluoride.

SM-CISUONSPC

Sc(cmber 1991 -6- As to the source of molybdenum there can be used soluble molybdate compounds such as for example molybdic acid and sodium molybdate.

Satisfactory coatings can be produced from coating solutions containing as little as about 4 x10 4 molar of either titanium, zirconium, hafnium or cerium (about 0.02 g/1 Ti, about 0.05 g/l Zr, about 0.09 g/1 of Hf and about 0.07g/l of Cc) and about 5 x 10~ molar molybdenum (about 0.05 g/1 Mo). In coating solutions which utilise a mixture of Ti, Zr, Hf or Ce, the total amounts of these metals should be at least about 4 x 10- 4 molar. The amounts of these ingredients, however, may be required to be increased in order to produce satisfactory coatings depending on other parameters of the coating process as will be discussed below.

Titanium, zirconium, hafnium or cerium can be used in amounts up to their solubility in the acidic aqueous coating solution. The solubility limits of the ingredients will depend on other parameters of the coating solution, including particularly, the amount of fluoride in the coating solution. These parameters should be controlled sch that the 15 formation of titanium, zirconium, hafnium or cerium precipitates are avoided. The formation and accumulation of any type of precipitate in the coating solution is undesirable :and will tend to interfere with the application of the coating, cause deposition on the coated metal surface, which can adversely affect coating properties, and cause the clogging of spray nozzles in spray applications.

20 The coating solution of the present invention can be formulated in such a way, as for example, by the incorporation of dissolved nickelous salts or manipulation of the various parameters of the coating process, such that a mixture of metal types may process C through the same coating solution and effectively forming the aforementioned types of coatings in the absence of hexavalent chromium and materials such as ferricyanide and ferrocyanide.

The incorporation of soluble nickelous salts into the coating solution of the present invention at between 0.01 and 10 g/1 nickel will, in certain circumstances, afford improved coating times where particular metals or metal alloys such as for example zinc or iron, are to be contacted.

SM-GIBSON.SPC

7 ScWpmber 1992 -7- As to the source of the nickel there can be used, for example, soluble nickelous compounds such as water soluble chlorides, carbonates, nitrates and sulphates.

As to the fluoride concentration, the minimum concentration should be that which is sufficient to combine with all the titanium, zirconium, hafnium or cerium present to form a water soluble complex therewith, for example, a fluotitanate, fluozirconate, fluohafnate or fluocerate. The formation of these soluble complexes deter or prevent the formation of titanium. zirconium or hafnium precipitates.

Several other cousiderations should be taken into account with respect of fluoride concentration in the coating solutions. The coating solution of the present invention will dissolve the substrate metal, for example, aluminium or zinc and a gradual build-up of dissolved aluminium or zinc will occur. To prevent or deter any adverse affects of the build-up of these metals in solution on the coating process, the coating solution should contain sufficient fluoride to complex the dissolved metals. The amount of fluoride required will depend on the degree to which dissolved metal builds-up in the coating i 15 solution and will be dependent on various factors such as, for example, the method by which the solution is contacted with the metal substrate or alloy and the shape of the surface being treated.

As to the source of flouride any material which can provide flouride and which is soluble in the coating solution may be used provided it does not contain a constituent which may adversely affect the coating process. Materials such as hydrofluoric acid and its salts, alkali metal bifluorides, HzSiF 6 or HBF 4 may be used as well as complex fluorides of titanium, zirconium, hafnium or cerium. However if the latter fluoride complexes arc used there should be added to the coating solution additional material which is a source of fluoride for complexing the aluminium or zinc that builds up during continuous use.

The :pH of the coating solution can vary over a wide range, for example, from about 1 to about 8. At higher pH's phosphate precipitation can be a problem. Preferably, a pH within the range of about 1.0 to about 5.0 is used. The pH of the solution may be adjusted by using appropriate amounts of phosphoric acid, nitric acid, sulphuric acid or any acid which will not adversely affect the coating process.

SM-GIBSONSPC

7 SeFtmbc 1992 -8- The temperature of the coating solution should be such that the reactive ingredients of the solution bond to the metal surface. The coatings can be applied to the metal surface over a wide temperature range of from 0°C up to about 95 0 C. Preferably from room temperature up to about 90 0 C. A temperature range of about 40 0 C to about 80 0 C is particularly preferred. The temperature of application is dependent on various parameters of the coating operation including, for example, the contact time of the solution with the metal surface, the type of metal to be coated and the reactivity of the solution which in turn depends on the pH and concentration of ingredients in the coating solution.

The coating solution should be applied to a clean metal surface. Available cleaning compositions such as alkaline or acidic cleaning solutions can be used to clean the metal surface according to conventional techniques prior to the coating application.

The coating solution can be formulated in such a way, as for example, by the addition of surface active agents, such that a primary cleaning action can be provided. The surface active agents employed to provide the cleaning action of the coating solution should S 15 be present in sufficient concentration such that surface soils, for example, drawing lubricants and protective oils, can be readily removed. The choice of surface active agents should be such that the coating process is not adversely affected and the cleaning action is adequately provided. Surface active agents, such as for example, nonyl phenol alkoxylates, octylphenyl, alkoxylates, oxyethylene glycol rosin esters and propoxylated S 20 alcohol ethoxylates can readily be employed. When employed, the surface active agents will be in the range of from 0.01 to 100 g/1.

Other additives used as sequesterants may be added to the coating solution formulation. Such agents assist in manitaining dissolved metal ions in soluction. When added, such sequestering agetns may be employed in the range of from 0.05 to 50 g/l.

Preferred sequestering agents include polyhydroxy compounds having up to 7 carbon atoms such as sodium gluconate or heptogluconate.

The thickness of the coating formed on the metal surface is dependent on a number of parameters including solution contact time, temperature, type of metal being processed, concentration and pH. In the case of aluminium, for example coating weights of about 120 SM-oCISONSPC7 7 ScpAmbet 1992 -9g/m 2 are typically desired. In the case of steel, for example, coating weights of from 300 iM,'m 2 to 1000 mg/m 2 are typically required for applications where siccative coatings such as for example, paints or lacquers, are to be applied. Coating weights of up to 1500 mg/rm 2 or more may be desired in certain specific circumstances. Determination of contact times necessary to produce coating thicknesses within these aforementioned ranges will have to be made on a case by case basis. In general, contact times of from about 2 seconds to about 60 seconds will be required with coating times of up to about 120 seconds or more being used in some circumstances.

Once the conversion coating has been applied to the metal surface, it is rinsed with water and dried by conventional means, such as by passage through an oven. An overcoat of paint, ink, lacquer, plastic resin, either water or solvent borne or organic coatings provided for by powder coating methods may then be applied by conventional techniques.

The coating solution of the present invention can be prepared conveniently by dilution of an aqueous concentrate of the ingredients with an appropriate amount of water.

15 In a continuous coating operation, it is important to properly replenish the solution in order to maintain the effectiveness of the coating process. Various ingredients comprising the solution are depleted as a result of reactions which take place during the formation of the coating. These ingredients must be replenished by either monitoring the amounts of each individual ingredient in the coating solution and adding it as it is depleted S 20 or it can be accomplished by adding an aqueous concentrate of the ingredients in such a ratio as to maintain the effectiveness of the coating solution.

Examples The examples below are illustrative of the practice of the present invention and are not intended to be limiting or exhaustive thereof.

The alummium surfaces treated with the solutions identified in the examples, unless otherwise stated, were drawn aluminium cans which were first degreased, as necessary, in an acidic aqueous cleaning solution consisting of sulphuric acid, fluoride and detergents and then rinsed in free flowing tap water. The coating solutions were then applied by immersion techniques as set out below. After treatment with the identified solutions the SM-OM3tO.SPC 7S 9mmbc 1I 10 aluminium surfaces were rinsed in free flowing tap water and dried in an oven at 110 0

C

for about 2 minutes.

The following tests were employed to evaluate the relative degree of coating present and the corrosion resistance of the treated aluminium surface.

Muffle Test A clean and treated can is placed in a muffle furnace at 550°C for about 5 minutes.

The presence of the coating is indicated by a light yellow, through golden brown, to a dark purple-brown discolouration, depending on the amount of coating present.

This type of test is conveniently used as a simple and efficient on-line procedure to estimate the coating weights present on production items. The colour intensity of the coated aluminium surface being in proportion to the coating thickness.

Pasteurisation Test A clean and treated can is immersed in a water bath containing 0.3 g/l sodium borate and 0.1 g/1 potassium fluoride at a pH range of 8.8 to 9.1 for a period of about minutes at 65-70C. After immersion the cans are rinsed with free flowing tap water and allowed to dry before examination for presence of staining effects.

A cleaned only can, when subjected to this form of test, rapidly turns a black or brown colour. It will be seen from the following examples below that treatment of the e aluminium surfaces with the coating solutions of the present invention resulted in surfaces 20 which were not blackened or otherwise discoloured or which resisted blackening or other discolouration when subjected to the pasteuisation test. The results of the tests were rated out of 10 as follows: 10, perfect, no blackening; 7, acceptable and 0, total failure, severe blackening.

Table 1 below demonstrates the interdependence of molybdenum and titanium levels on coating formation and water stain resistance (pasteurisation test) of aluminium surfaces.

Phosphate was present in the solution at 9 g/1 (as PO), fluoride present at 1.3 g/l. Bath temperature was held at 60°C with a contact time of 10 seconds at a pH of 2.

SMG BSO.SPC 7 Sptember 1991 11- Table 1 Sample anuber Ho cone. Ti conc. Muffle Test Pasteurisation Colour test 1 0.28 0.07 light 4 0.28 0.15 0.28 0.10 0.10 0.17 golden brown light golden brown

I

e r sc r r Table 2 demonstrates the dependence of the coating formation and muffle test colouration of aluminium surfaces on levels of phosphate present in solution. The cans were immersed for 10 seconds at a temperature of 60"C and the solution made up to contain SO 4 2 at 4.8 g/l, F at 0.9 g/l, Mo at 0.18 g/l, Ti at 0.07 g/1. The solution was maintained at a pH of 2.

Table 2 Sample number Phosphate cone. Muffle test colour 5 0 none 6 0.2 very light tan 7 0.4 golden brown 8 1.0 golden brown Table 3 demonstrates the broad pH range under which coatings can be applied to aluminium surfaces. The coatings were applied by immersion at 60 0 C. The solution was made-up to contain P0 4 3 at 3 g/1, F at 0.45 g/l, Mo at 0.09 g/ and Ti at 0.05 g/1. The coated aluminium was subjected to the muffle test as an indication of coating weight.

SM-amsoONSPC I7 stUptmb 12- Table 3 Sample number pH Contact time Muffle test (seconds) colour 1.8 2 3 4 golden brown golden brown golden brown golden brown golden brown golden brown golden brown *a *a Table 4 demonstrates the broad temperature ranges under which the coating may be applied to the aluminium surface. The coating solution was made-up to contain P043- at 15 4.8 g/l, F" at 0.9 g/l, Mo at 0.18 and Ti at 0.07 g/1. The pH of the solution was maintained at 2.

Table 4 e Sample number 20 16 17 18 19 20 21 22 23 24 26 27 28 29 Temperature (oC) Contact time (seconds) pale yellow light tango light tan light tan light tan golden brown golden brown golden brown golden brown dark brown dark brown very dark brown purple brown purple brown Muffle Test colour SM-GlBSONSPC 7 September 1992 13 a* ft 9 Table 5 demonstrates the effect of contact times on the aluminium coating at 50 and 0 C. The solution was made up to contain 3 g/1 P0 4 0.45 g/1 F, 0.09 g/1 Mo and 0.05 g/l Ti. The pH of solution was maintained at 2.

Table Sample number Temperature Contact Time Muffle Test (seconds) colour 60 2 golden brown 31 60 5 golden brown 32 60 10 golden brown 33 60 15 dark brown 34 60 20 purple brown 50 2 light tan 36 50 5 golden brown 37 50 10 golden brown 38 50 15 golden brown 39 50 20 dark brown Table 6 demonstrates the concentration dependence on coating formation on aluminium surfaces and corrosion resistance. A concentrate of coating solution was madeup to contain 160 g/1 P0 4 3 2.3 g/1 F, 2g/l Ti and 5 g/1 Mo at a pH of 1.8 and applied to the aluminium surface at varying concentrations by immersion, at 60 0 C for 10 seconds.

SM-GIBSON.SPC

7 Sepmber 1992 14 Table 6 Dilution of' concentrate Sampile number Muf fle Pasteurisation volume) test test dark golden brown golden brown light brown 9

S*

*9 Table 7 demonstrates that the coating formation on the aluminium surface will form in the presence of surface active agents such as gluconates and surfactants. The solution was made up to contain 3 g/l P0 4 0.45 g/l F, 0.09 gil Mo and 0.05 gil Ti. The pH of the solution was maintained at 2, with a temperature of Table 7 Sample Gluconate Surfactarnt 1* Surfactant 2* Muffle Contact Number (gil) (gil) test time (sec) 9e 9* 99*9 .9 44 9 999* 1 46 0.1 47 0.1 48 0.2 49 0.2 0.3 51 0.3 52 0.4 53 0.4 *Surfactant 1 is Teric GN5 (ICI Aust) *Surfactant 2 is Teric 160 qJCI Aust) golden brown golden brown grey brown grey brown tan tans brown brown brown brown SM-GMSON.SPC SM-OU3ONSPV7 SeOAmjbrrt 199 15 Table 8 demonstrates that the coating solution can also be used to clean and form coatings on aluminium surfaces in a single phase process. A concentrate of the cleaning/coating solution was made-up to contain 160 g/1 P04 3 2.3 g/1 2 g/l Ti, 5 g/1 Mo, 20 g/1 Teric 164 (registered trademark of ICI Australia) and 25 g/1 Teric RA 1315 (registered trademark of ICI Aust). A pH of 2 was maintained in the diluted solutions at a temperature of Table 8 9 9* 9 9 9 r 9.

4. 9 4 0 @9 *8 4* *4 *0 9.

9S** 4

S

*9

S

Sample number Dilution of concentrate Contact time Muffle Test volume) (seconds) colour 54 2 10 brown 55 2 20 brown 56 4 10 purple brown 15 57 4 15 purple brown 58 4 20 purple brown It can also be demonstrated that the coating solution can also be used to form coatings on steel surfaces.

Coating weights of steel specimens coated with the coating of the present invention 20 may be determined using conventional procedures. The coated specimen to be analysed is carefully weighed on an analytical balance and immersed for 5 minutes in a 50 g/litre chromic acid solution at 74°C. The specimen is then rinsed thoroughly in hot water and quickly dried. The specimen should then be re-weighed immediately. The weight difference divided by the surface area of the specimen is the calculated coating weight.

Table 9 demonstrates the temperature ranges under which the coating may be applied to steel surfaces. The coating solution was made-up to contain PO4- at 8 g/1, F~ at 2.5 g/l, Mo at 0.25 g/1 and Ti at 0.1 g/l. The pH of solution was maintained at 2.

SM-OIBONSPC 7 &Snbt 92 -16- Table 9 Sample Temperature Contact Coating Number (seconds) weigh (mg/m') 300 120 120 120 120 120 530 400 800 1250 2050 2050

S

*5

S

S.

Table 10 demonstrates the effect of contact time on the steel coating at 55 and 65 0

C.

The solution was made up to contain 8 g/1 PO 4 2.5 g/1 F- 0.25 g/1 Mo and 0.1 g/1 Ti.

The pH of solution was maintained at 2.

Table Sample Temperature Contact time Coating weigh Number (minutes) (mg/m 2 5* 5

S

*5 560 800 1550 670 1250 2510 3490 Table 11 demonstrates the concentration dependence on coating formation on steel surfaces. A concentrate of coating solution was made up to contain 160 g/l P0 4 3 2.3 g/1 F, 2 g/1 Ti and 5 g/1 Mo at a pH of 1.8 and applied to the metal surface by immersion at varying concentrations at the stated temperatures for 5 minutes.

SM-GISSONrSF" SSptemr 1992 17 Table 11 Sample Dilution Temperature Coating weight Number of concentrate (mg/1) volume) 480 530 750 610 750 1150 530 830 1550 2510 3250 3440 S

S

S* S 0 S.r

S

S

S. S S S

S

S S. S S I

S

The conversion coatings applied to aluminium surfaces, using the coating solutions 20 of the present invention, were analysed by scanning electron microscopy techniques and found to contain, as integral components of the surface thus formed, molybdenum, titanium and phosphorus in the approximate atomic ratio of 2 3 5 respectively. The ratio of these essential elements of the coating appeared constant within the broad range of solution operation parameters such as pH, temperature and contact times.

Figures 1 and 2, below, illustrate the Auger depth profile of aluminium and zinc alloy coated steel surfaces immersed in a coating solution of the present invention as set out below.

Sample 84, as analysed by Auger techniques, is an aluminium surface immersed for seconds at a temperature of 60°C in a coating solution made-up to contain 4.8 g/l P43", 0.9 g/l F, 0.18 g/l Mo and 0.07 g/l Ti at a pH of 2. As can be seen from the plot P, Ti

SM-GUBSON.SPC

7 Sct~mtt 1992 18 and Mo are present as essential components of the coating thus formed on the aluminium surface.

Sample 85, as analysed by Auger techniques, is a zinc/aluminium alloy coated steel surface immersed for 5 seconds at a temperature of 60°C in a coating solution made up to contain 6.5 g/1 P0 4 3 2 g/1 0.2:5 g/l Mo, 0.09 g/1 Ti and 0.2 g/l Ni. As can be seen from the plot P, Ti and Mo are present as essential components of the coating so formed on the metal surface. The presence of nickel in the coating solution, which provides for improve coating times, is not directly incorporated into the coating.

Coating weights of the coatings of the present invention on zinc alloy coated steel can be determined by immersing a clean, accurately weighed sample in a solution of g/1 ammonium dichromate and 280 g/1 ammonium hydroxide for 4 minutes at 21 0 C. The sample should then be rinsed in hot water and immediately dried, The sample is then reweighed and the difference in weight divided by the sample surface area calculated to give the coating weight.

Table 12 demonstrates the improvement of coating formation by the coating solution on zinc or zinc allol coated steel when nickel is incorporated into the formulation. Zinc or zinc alloy coated steel samples immersed in a coating solution made up to contain 6.4 g/1 PO 4 3 1.2 g/F, 0.25 g/1 Mo and 0.09 g/1 Ti for 5 seconds at 60°C were analysed for coating weights at varying Ni concentrations as indicated below.

20 Table 12 0 0000 00 0 0000 Sample Alloy coating Ni concentration Coating weight Number on steel (mg/m') 86 Zinc Aluminium 0 240 87 Zinc Aluminium 0.25 360 88 Galvanised 0 150 89 Galvanised 0.25 280 SM-O(BSONSPC 7 Septembr 199 19 From the above examples it can be demonstrated that the present invention provides a coating solution which permits the formation of a conversion coating on the surface of aluminium in a manner such that the bright shiny surface of the aluminium is unaltered.

The coated surface has the ability to withstand discolouration when subjected to pasteurisation and to which overlying siccative coatings adhere. The coating solution exhibits the capacity to be tolerant of incomplete precleaning processes and has the ability to clean and coat metal surfaces in a single step operation.

It can also be demonstrated from the foregoing examples that the present invention provides a coating solution which permits the formation of a conversion coating on the surface of steel and galvanised or zinc and zinc alloy coated steel. The coated surface has the ability to withstand corrosion and improve the adhesion of overlying siccative coatings.

S.:a.

S*

SM-GOmIJON.SPC 7 Sptembe 1991

Claims (23)

1. A chromium and ferricyanide-free aqueous treating and coating solution which includes 0.01 to 100 g/1 phosphate, 0.001 to 10 g/l fluoride, 0.01 to 10 g/l molybdate and at least one titanium, zironium, hafnium or cerium compound, said at least one titanium, zirconium, hafnium or cerium compound being present in an amount of from 0.005 to 10 g/l, calculated as the weight of the respective metal(s).

2. The solution according to claim 1 wherein the solution has a pH in the range of 0 to 8.

3. A treating and coating solution according to claim 2 which includes 0.01 to 100 g/l phosphate, 0.001 to 10 g/1 fluoride, 0.01 to 10 g/l molybdate and 0.005 to g/l of a titanium compound, calculated as the weight of titanium.

4. A treating and coating solution according to any one of the preceding claims which further includes a nickel compound wherein nickel is present in the solution in the range of from 0.01 to 10 g/1. :i 15

5. A treating and coating solution according to any one of the preceding claims which further includes a sequesterant in an amount of 0.05 to 50 g/l.

6. A treating and coating solution according to claim 5 wherein the sequesterant is sodium gluconate or heptogluconate.

7. A treating and coating solution according to any one of the preceding claims S** 20 which further includes a surface active agent in the range of from 0.01 to 100 g/1.

8. A treating and coating solution according to claim 7 wherein the surface active agent is selected from one or more of the group consisting of nonyl phenol alkoxylates, oxycthylene glycol rosin esters, propoxylated alcohol ethoxylates, and octylphenyl alkoxylates.

9. A process for providing a corrosion resistant coating to a metal surface which process comprises the sequential steps of: treating the metal surface with a chromate and ferricyanide free solution consisting essentially of at least one titanium, zirconium, hafnium or cerium compound, a fluoride compound, a molybdenum compound and a phosphate compound wherein the coating solution contains from 0.01 to 100 g/l phosphate, 0.001 to 10 g/1 fluoride, from 0.01 to 10 g/l molybdate, and one or more titanium, s& hafnium, zirconium or cerium compound in a total amount of from 0.005 to 10 g/l, 7 Se 1 tae 1992 21 calculated as the weight of the respective metal, at a temperature within the range of from 0°C to about 95 C for a contact time sufficient to provide a corrosion resistant coating to said metal surface, the pH of said coating solution being maintained in the range of from 0 to 8, rinsing said coated metal surface with water or other convenient rinsing agent, and drying the coated metal surface.

A process according to claim 9 which comprises, in addition to the phosphate, fluoride and niolybdate, a titanium compound in the range of from 0.005 to 10 g/l, calculated as the weight of titanium.

11. A process according to claim 10 wherein the titanium compound is replaced either in full or in part by either one or more qf hafnium, zirconium or cerium.

12. A process according to any one of claims 9 to 11 wherein the coating solution further comprises a nickel compound in the range of from 0.01 to 10 gi1. 15

13. A process according to any one of claims 9 to 12 wherein the coating 9o solution further includes a sequesterant in the range of from 0.05 to 50 g/1.

14. A process according to claim 13 wherein the sequesterent is a polyhydroxy compound having up to 7 carbon atoms.

A process according to any one of claims 9 to 14 wherein the coating 20 solution further includes a surface active agent in the range of from 0.01 to 100 g/l.

16. A process according to claim 15 wherein the surface active agent is selected from one or more of the group consisting of nonyl phenol alkoxylates, propoxylated alcohol ethoxylates, octyl phcnyl alkoxylates and oxyethylene glycol rosin .oo esters. o* 25

17. A process according to any one of claims 9 to 16 wherein the metal surface treated is aluminium, aluminium alloy, zinc, zinc alloy or steel.

18. A process according to claim 17 wherein the metal surface treated is aluminium cans or can stock.

19. A process according to any one of claims 9 to 18 wherein the metal surface is pretreated with an alkaline or acidic cleaning agent.

A process according to any one of claims 9 to 19 wherein the treating and coating solution is applied to the metal surface by spraying, immersion or rolling. 26 July 1994 22

21. A process according to any one of claims 9 to 20 which includes the further step of applying to said coating an overlying siccative coating by a water borne solution which may contain a polyester.

22. A metal surface having a corrosion resistant coating whenever applied by a process according to any one of claims 9 to 21.

23. A chromate and fcrricyanide free aqueous treating and coating solution and process for providing a corrosion resistant coating to a metal surface, substantially as hereinbefore described with reference to any one or more of the examples. DATED: 19 July 1994 CARTER SMITH BEADLE Patent Attorneys for the Applicant: GIBSON CHEMICALS LIMITED •c rI oJ ooo It Vaml~t1992 ABSTRACT This invention relates to metal surface coatings which are corrosion resistant yet allow the adhesion thereto of paints, inks, lacquers and other overlaying coatings. The invention particularly relates to the provision of a chromate and ferricyanide free coating solution which contains, as essential ingredients at least one titanium, zirconium, hafnium or cerium compound, a fluoride compound, a molybdenum compound and a phosphate compound. ea.e **e se* e 4 9 O S* a aa *a I .Q SM-01BSON.spa 7 StLmbet 19M