JPH0419307B2 - - Google Patents

Description

Claim 1: An alkali-resistant phosphoric acid which deposits a phosphate conversion coating on a corrosive metal substrate by exposing the substrate to an acidic aqueous solution containing first and second divalent metal cations and phosphate ions. In the method of manufacturing a salt conversion coating, (a) the first divalent metal is selected from magnesium, nickel, cobalt and manganese cations, (b) the second divalent metal cation is a zinc cation, and (c) the concentration of the first and second divalent metal cations in the aqueous solution is such that the concentration of the first divalent metal cation in the solution is equal to the total divalent metal cation in the solution at the time of coating. A method for producing an alkali dissolution-resistant phosphate conversion coating, characterized in that the alkali dissolution-resistant phosphate conversion coating is maintained in a range of 84 to 94 mol%. 2. The method of item 1 above, wherein the concentration of the first divalent metal cation in the solution is at least 1.0 g/g/. 3. The method of claim 1, wherein the concentration of the second divalent metal cation in the solution is at least 0.2 g/. 4. The method according to item 3 above, wherein the concentration of the second divalent metal cation in the solution is 0.2 to 0.6 g/. 5. The method of claim 1, wherein the concentration of phosphate ions in the solution is at least sufficient to form dihydrogen phosphate with the metal cation. 6 The molar ratio of the first divalent metal cation to the second divalent metal cation is from 5.2:1 to 16:1.
The method according to item 1 above, which is within the range of. 7. Contacting a corrosive metal substrate with an acidic aqueous solution containing a first divalent metal cation, a second divalent metal cation, and a phosphate ion to remove the first divalent metal cation and the second divalent metal cation. forming a phosphate conversion coating consisting of a chemical bond of a valent metal cation and a phosphate ion;
divalent metal cations are removed from the solution in a greater proportion than the first divalent metal cations during the course of contacting the substrate with the solution, so that the first divalent metal cations in the solution are removed from the solution in a greater proportion than the first divalent metal cations. (a) the first metal cation is selected from magnesium, nickel, cobalt and manganese cations; b) selecting a zinc cation as the second divalent metal cation; and (c) adjusting the concentration of the first and second divalent metal cations in the aqueous solution to the concentration of the first divalent metal cation in the solution. said first divalent metal cation and said second divalent metal from said solution such that the concentration of metal cations is maintained in the range of 84 to 94 mole percent of the total divalent metal cations in the solution at the time of coating. The rate of cation removal is adjusted by replenishment of a replenishment concentrate comprising the first divalent metal cation and the second divalent metal cation in the same proportion. A method for producing an alkali-dissolved phosphate conversion coating, characterized by: 8. The method of claim 7, wherein the molar ratio of first divalent metal cations to second divalent metal cations in said replenishment concentrate is 18:82. 9. An alkali-resistant phosphate conversion coating in which a phosphate conversion coating is deposited on a corrosive metal substrate by exposing the substrate to an acidic aqueous solution containing first and second divalent metal cations and phosphate ions. (a) the first divalent metal cation is selected from magnesium, nickel, cobalt and manganese cations; (b) the second divalent metal cation is a zinc cation; (c) ) The concentration of the first and second divalent metal cations in the aqueous solution is such that the concentration of the first divalent metal cation in the solution is 84 to 94 of the total divalent metal cations in the solution at the time of coating. (d) maintaining the total acid content of said acidic aqueous solution in the range of 10 to 40% points; (e) controlling the free acid content of said acidic aqueous solution to be maintained in the range of 0.5 to 2.0% points; and (f) maintain a total acid/free acid ratio of the acidic aqueous solution between 10 and 50.
A method for producing an alkali dissolution resistant phosphate conversion coating characterized by maintaining the alkali dissolution resistance within the range of . 10. A method of producing an alkali-resistant phosphate conversion coating by exposing a corrosive metal substrate to an acidic aqueous solution containing first and second divalent metal cations and phosphate ions, comprising: (a) (b) selecting a zinc cation as the second divalent metal cation; (c) selecting the first divalent metal cation from magnesium, nickel, cobalt, and manganese cations; 1 and a second divalent metal cation in the solution at the time of coating.
and 84 to 94 of the total amount of second divalent metal cations.
(d) maintain the solution in the range of 100-150㎓ (38-65°C), and (e) maintain the substrate in the range of 30-120 seconds. A method for producing an alkali-resistant phosphate conversion coating, comprising contacting the coating with the solution. 11. The method of item 10 above, wherein the substrate is selected from iron, carbon steel, low alloy steel, aluminum or zinc. 12. The method of claim 10, wherein the first divalent metal cation is a nickel cation and the coating comprises a mixed metal phosphate in _a continuous nodular structure in the form of _Zn2Ni ( _PO4 ) _2.H2O . Method. 13. A method of producing an alkali-resistant phosphate conversion coating by exposing a corrosive metal substrate to an acidic aqueous solution containing first and second divalent metal cations and phosphate ions, comprising: (a) (b) selecting a zinc cation as the second divalent metal cation; (c) selecting the first divalent metal cation from magnesium, nickel, cobalt, and manganese cations; 1 and a second divalent metal cation in the solution at the time of coating.
and 84 to 94 of the total amount of second divalent metal cations.
(d) maintaining the solution at a temperature ranging from 100 to 150°C (38 to 65°C); A method for producing an alkali dissolution-resistant phosphate conversion coating, characterized in that the coating is brought into contact with a solution, and (g) the solution further contains fluoride ions. 14. The method according to item 13 above, wherein the fluoride ion is introduced as a fluoride, fluoroborate, fluorosilicate, or other complex fluoride, and is present in the solution in an amount ranging from 0.1 to 1.0 g/l. . 15 having a metal substrate and a phosphate converting coating deposited thereon, the coating comprising a mixed metal phosphate comprising at least one first divalent metal element and a second divalent metal element; , whose cations are combined in a compound with phosphate ions, wherein (a) the first divalent metal element in the coating is selected from magnesium, nickel, cobalt and manganese; ) the second divalent metal element is zinc, and (c) the first divalent metal content of the phosphate coating is at least 13.7% by weight, and the second divalent metal content of the coating is At least 25% by weight. A corrosion-resistant coated metal article characterized by: 16. Corrosion resistance according to item 15 above, wherein the first divalent metal is nickel, and the nickel content is at least 15 mol% of the content of the first divalent metal and the second divalent metal of the coating. Coated metal articles. 17. No. 15 above, wherein said coating comprises a mixed metal phosphate in a continuous nodular structure in the form of Zn ₂ Ni(PO ₄ ) _{2.4H 2 O.}
Corrosion-resistant coated metal article as described in . 18. The corrosion-resistant coated metal article of item 15 above, wherein the coating has a uniform weight of 1.3 g/m ² or less. BACKGROUND OF THE INVENTION AND PRIOR ART Zinc phosphate conversion coatings are applied to metal surfaces to prepare the substrate for paint and to prevent paint undercutting in corrosive environments. Initially, adhesion was the primary consideration when selecting a conversion coating. Smaller improvements in corrosion resistance have resulted from tighter, more adhesive coating systems (U.S. Pat.
3144360 and 3520737). In U.S. Pat. No. 3,810,792 to Ries et al., high nickel content was used to obtain a tight, dense phosphate layer within a short spray or bath immersion contact time for deep drawing purposes. A phosphate coating was used. Examples described in the Reese patent specification include a 100% nickel phosphate bath and a
Limited to those using a 69 mol% nickel phosphate bath. The Reese patent makes no mention of discontinuities in the properties of the phosphate as the film content varies. Unrestricted lease disclosure will not result in improvements in alkali resistance. The reasons for this are: (a) Reese uses nickel indiscriminately over a wide range of areas, resulting in him wandering blindly through compositions with no hope of improving alkali resistance; (b)
If Reese had discovered this, he would have certainly mentioned it, but Reese's examples do not show that there is a quantum jump in alkali dissolution and corrosion resistance after painting. It is from. Use of Layering Metals in Phosphate Conversion Coatings The methods by which these initial coatings were applied include using a solution containing layering metal cations, phosphate ions, and an oxidizing agent and spraying the solution onto the product to be coated; This included immersion in the bath. Typically, zinc, and in some cases calcium, iron or manganese, alone or in combination, were used as layer-forming ions. Phosphate ions were typically introduced by using phosphoric acid. Oxidizing agents are usually inorganic compounds, often consisting of salts of the metals mentioned above or salts of sodium or ammonium. Much of this technology remains unchanged as it is currently used. Nickel began to be introduced into the phosphate solution. Nickel has a constant reputation as a useful element as a layering metal for phosphate coatings of particularly homogeneous and continuous structure on steel, zinc, and sometimes aluminum. From the perspective of the prior art, it is clear that nickel was not originally added for the purpose of increasing corrosion resistance. With the exception of the Reese patent, relatively small amounts of nickel were added to the phosphate solution, always less than 6% of the weight of the solution. When nickel coexisted with zinc ions, an amount of nickel was added such that the nickel to zinc ratio was 1:1 or less (U.S. Pat. Nos. 4,053,328 and 3,723,334).
No. 4110128, No. 4153479 and No. 4231812). The study of the corrosion-preventing effect of phosphates was motivated by the increase in the amount of road salt used.However, there has been an increasing demand for phosphate coatings that consistently maintain high quality and are highly corrosion resistant. The problem of corrosion in automobiles has come to the fore as a result of the increased use of road de-icing salt. The amount of road salt used in the snowy regions of the United States and Canada has increased rapidly from about 1 million tons per year in the late 1950s to over 10 million tons today. For many years, it has been unclear why scratches in the paint and phosphate coatings on the exterior of a vehicle cause corrosion to occur over an area much wider than the width of the scratch itself. The Journal of Paint Technology (1968)
``Paint Adhesion Deterioration Mechanism on Steel Under Corrosive Environment'' by RR Wiggle, AG Smith and JV Petrocelli was published by RR Wiggle, AG Smith and JV Petrocelli.
Failure Mechanisms on Steel in Corrosive
An older study entitled ``Environments'' explains that alkaline dissolution of phosphate films is the cause of paint film undercuts. An alkaline environment is created by cathodic reduction of oxygen to hydroxyl ions (forming alkali-sodium hydride). An appropriate response is the Society of Automotive Engineers Transactions.
“Paint Deterioration, Steel Paint Failure, Steel Surface Quality and Accelerated Corrosion Test
Surface Quality and Accelerated Corrosion
This is explained in detail in Figures 1 and 2 of the paper titled ``Testing''. Simply put, damaged paint begins to rust in areas where the paint is gone inside the scratch. Iron oxide is produced from the basic metal by an anodic reaction in an electrolyte of water and sodium chloride. When iron dissolves to form ferrous ions (Fe <sup>2+</sup> ), electrons are simultaneously generated. Oxygen and water that permeate through the paint in the region adjacent to the anode region (representing the cathode) react there to form hydroxyl ions. The accumulation of hydroxyl ions creates a strongly basic liquid with a pH of 12.5 or higher. Conventional zinc phosphate dissolves in this highly basic liquid. Separation therefore occurs between the paint film and the substrate (sheet steel) on the vehicle body. If the paint is removed, for example by peeling off the tape applied to the scratched area, the paint adjacent to the scratch will be removed, but the underlying steel surface will remain shiny. This is due to the fact that high PH liquids are inhibitors of red mold formation. In actual use, of course, no tape is used, so the paint will peel off at the cut locations due to alkali dissolution of the phosphate film. This steel surface then begins to rust by the same mechanism common to the rusting of bare steel. Corrosion protection ability depends on the degree of surface carbon contamination The surface cleanliness of steel, especially the contamination of automobile steel sheets by carbonaceous deposits, plays an important role in the susceptibility to corrosion. Like the one made in a steel mill,
Even the presence of a very thin carbon layer deposited on the surface of the steel, in the presence of an electrolyte that favors the cathodic reduction of oxygen to hydroxyl ions, results in the formation of a phosphate coating suitable for optimal paint adhesion. This results in significant interference. The reason for this is that "pore areas" (either exposed spots or very thin areas in the zinc phosphate conversion coating caused by the presence of carbon) act as reactive sites for oxidation and reduction reactions. This is because it works. Satisfactory experimental results regarding this mechanism were published by the Society of Automotive Engines and Transactions.
R. published in Section 1, Volume 87 (1978).
“Quantitative test on the quality of zinc phosphate coatings” by W. Turilla and V. Hospadaruk.
It is described in a paper entitled "Test for Zinc Phosphate Coating Quality". This study represents a breakthrough in our understanding of the parameters that control the quality of zinc phosphate coatings as paint substrates. This paper established that zinc phosphate coatings are porous and that substrates with high surface carbon contamination always exhibit a porosity of at least 1.0-1.5%. Because it is difficult to improve rolling mill operations to eliminate this surface carbon contamination phenomenon, measures must be taken to address the detrimental porosity in the phosphate coating. Porosity in such phosphate coatings is detrimental because it promotes electrochemical corrosion activity of the substrate. The phosphate film is then subjected to the dissolving action of alkali (NaOH) present around the scratches in the paint, that is, around the areas where corrosion has started. Attempts to Reduce Corrosion Susceptibility The main prior art attempts to reduce the corrosion susceptibility of phosphated metals have involved (a) introducing inhibitors into the paint applied over the phosphate coating to protect it from corrosion; (b) the use of inhibitor rinses such as chromic acid (although this method was only partially effective in reducing corrosion susceptibility); and (c) the use of phosphate coatings during use. It involved a tighter coating system to prevent bumps. These attempts have not been very effective in reducing the alkali sensitivity of phosphate coatings. SUMMARY OF THE INVENTION The present invention relates to a method of increasing the alkali solubility resistance of phosphate conversion coatings on corrosive metal substrates, thereby reducing their corrosion susceptibility. The method employs a very critical narrow range of suitable layer-forming metal cations that form a unique mixed metal phase phosphate that provides strong resistance to alkaline dissolution. The coating is deposited by a chemical reaction between the substrate and an acidic aqueous solution containing first and second divalent layer-forming metal cations and phosphate ions. The method includes (a) selecting a first divalent metal cation to be magnesium, nickel, cobalt and manganese; (b) selecting a second divalent metal to be zinc; and (c) selecting a coating to be deposited. The amount of the first divalent metal cation included is at least
15.0 mol% and the content of second divalent metal cations is at least 25% by weight of the coating.
It is characterized by critical control of the amounts of first and second divalent metal cations present during the chemical reaction within a narrow range. The first divalent metal cation is selected from the group consisting of magnesium, nickel, cobalt and manganese cations (advantageously, the cation is nickel only) and It is controlled to be 84 to 94 mol%. Zinc is preferably present in an amount of at least 0.2 g/solution as Zn <sup>+2</sup> [advantageously from 0.2 to 0.6 g/as Zn <sup>+2</sup> or from 0.79 to Zn(H <sub>2</sub> PO <sub>4</sub> ) <sub>2 ]</sub> .
2.38g/] is included in the solute. If the first divalent metal cation is nickel, the deposited coating consists essentially of a mixed-metal phosphate in the form of connected nodules, likely including Zn <sub>2</sub> Ni(PO <sub>4</sub> ) <sub>2.4H 2</sub> O. However, the amount of nickel varies slightly within a narrow range. Advantageously <sup>, the coating is deposited in a substantially uniform amount of less than 120 mg/ft 2 .</sup> For a sufficient time at sufficient temperature and PH to achieve chemical reaction and precipitation of the phosphate coating on the substrate (i.e., 30-120 seconds, 100-150〓, PH 2.5-
3.5) Preferably, the substrate is exposed to a phosphating solution. Thereafter, excess solution not deposited as a coating is removed from the coated substrate. The molar ratio of the first and second metal cations is in the range of 5.2:1 to 16:1, and the first metal cation is included in the solution in an amount of at least 1.0 g per solution. Also included within the scope of the present invention is a method in which a phosphate coating solution is applied to the surface of a metal product that has been alkaline cleaned to coat the surface with a phosphate coating. The feature is that the average application amount is
1.3g/ <sup>m2</sup> (less than 120mg/ <sup>ft2</sup> ), i.e. 6.5
~1.3 g/ <sup>m2</sup> (60-120 mg/ <sup>ft2</sup> ) and a phosphate film containing at least 15 mole percent (13.7 wt.%) nickel is deposited. Such a phosphate coating has an oxidizing agent content and pH that are effective for chemical reaction with the target article, and (a) 84% of the metal cation.
a divalent layer-forming metal cation consisting of ~94 mole percent nickel and 16 to 6 mole percent zinc; and (b) an amount at least sufficient to form a dihydrogen phosphate between said metal cation. is obtained using an acidic aqueous coating solution having a solute content consisting essentially of phosphate ions. The article is comprised of a metal selected from the group consisting of iron, carbon steel, low alloy steel, aluminum and zinc. This method uses 0.4mg/
It is particularly advantageous when used in metal articles having a total surface carbon content greater than ft <sup>2</sup> . The phosphating solution preferably has a total acid content of 10 to 40 points, a free acid content of 0.5 to 2.0 points, and a total acid/free acid ratio of 10 to 50. When the method is applied to zinc metal products or substrates, a fluoride selected from the group consisting of fluorides, fluoroborates, fluorosilicates or other complex fluorides is preferably included in the solution. . Phosphate solution pH 2.5
It is desirable to maintain the temperature at ~3.5 and include a sufficient amount of nitrite and other oxidizing agents. The temperature during the phosphating process is kept at 100-150°C (38-65°C). Preferably, the metal product is exposed to such a solution for 30-120 seconds. The amount of nitrite used as an accelerator is 0.5-2.5 points or <sub>0.03-2</sub> as NaNO2
The desired amount is 0.14g/solution. Advantageously, the phosphate bath is regenerated with concentrated phosphate through a series of product coating operations. Since there is more zinc than nickel in the phosphate coating, the bath will be richer in nickel than zinc. Preferably, the replenishment solution or concentrate is formulated to consist essentially of about 18 mole percent nickel cations and 82 mole percent zinc cations (16.5 nickel - 83.5 percent zinc by weight). Alternatively, a portion of the nickel in the main coating solution can be replaced by a divalent layer-forming metal cation selected from the group consisting of cobalt, magnesium or manganese. The product obtained by carrying out the above process is characterized by a phosphate film, the main structure of which is composed of a mixed metal phase phosphate, one of the metals being
The species is zinc and the other metal is magnesium, nickel, cobalt or manganese. Preferably the coating has a nickel content of at least 15 mol% and the mixed metal phosphate is
Nickel/zinc phosphate. SUMMARY OF THE DRAWINGS Figures 1-3 show (1) the alkali sensitivity of coatings made using high nickel and conventional nickel content zinc phosphate baths, (2) the nickel in the coating as a function of the nickel in the bath; and (3) salt spray life as a function of nickel in the phosphate coating, respectively. Figure 4 is a set of photographs (4a to 4h) showing the results of spraying dark gray paint onto a steel plate, making scratches on each plate, and then subjecting them to a salt spray corrosion test. The original panels had different surface cleanliness and were phosphate treated with varying nickel content in the bath ranging from 33 to 77 mol% and zinc content before applying the paint. It's what I put there. Figures 5-8 are scanning electron micrographs (1500x magnification) of the crystal structure of the coatings corresponding to panel photographs 4a, 4c, 4e and 9c, respectively. Figure 9 is also a set of photos (9a to 9h),
Shows a steel plate sprayed with dark gray paint. Each panel was incrementally varied in nickel content (81
~85 mole %) in a phosphate bath before painting and scratching before subjecting to salt spray corrosion testing. Figures 10 to 13 are panel photographs 9g, 14a,
Scanning electron micrograph (1500x magnification) of the crystal structure of the coatings corresponding to 14c and 14e. FIG. 14 is a set of photographs similar to FIGS. 4 and 9 showing a corrosion test panel corresponding to a phosphate treatment bath having a nickel content of 90.5 to 92.3 mole percent. Figure 15 is a scanning electron micrograph (1500x magnification) of a coating made in a phosphate treatment bath containing greater than 95 mole percent nickel. Figure 16 is a photograph (Figures 16a-16d) of a hot-dip galvanized steel sheet coated with dark gray paint that has been subjected to a salt spray test. FIG. 17 is a graph showing the infrared spectra of coatings made using phosphate treatment baths of various nickel contents. The table summarizes the explanations for each panel used in Figures 4, 9, and 14, and (a)
Amount in mole % of zinc and nickel relative to the combination of Ni and Zn, weight % of nickel or zinc as % relative to the combination of nickel and zinc, 1
Composition of the bath used, including the weight in grams of each solute component per gram and the weight percent of each solute component relative to the total bath solution; (b) mole percent of nickel and zinc relative to total Ni and Zn, total nickel and zinc; The composition of the coating is shown, including the weight percentages of nickel and zinc, as well as the weight percentages of the major components in the coating. The table shows the physical property values of the coating for the panels shown in the table. DETAILED DESCRIPTION OF THE INVENTION It is common practice in the automotive industry to apply acidified zinc phosphate to metal vehicle bodies and structural components to form a zinc phosphate conversion coating on the metal surface. . This is usually accomplished by spraying or dip-coating metal vehicle bodies and parts. The phosphate coating serves to enhance the adhesion of paint systems applied thereon, thereby improving resistance to corrosion. The dramatic increase in alkali solubility resistance of the present invention is demonstrated by the dramatic increase in the life of the coating system when subjected to accelerated salt spray corrosion tests. Corrosion Reactions Corrosion in aqueous electrolytes is an electrochemical process that involves oxidation and reduction reactions. Oxidation reactions are anodic dissolution of steel or other metal substrates in which ions leave the metal to form corrosion products. Excess electrons left in the metal by the oxidation reaction are consumed in the cathodic reduction reaction. The main cathodic reaction is the reduction of dissolved oxygen to form hydroxyl ions. Another cathodic reaction that may occur in some cases is reduction by hydrogen ions. Two reduction reactions result in an increase in electrolyte PH at the cathode site. Anodic and cathodic reactions can occur at essentially the same atomic site. however,
Once a differential concentration gradient of oxygen or electrolyte is established,
The reaction sites become far apart. After a certain amount of rust has formed at the anodic site, most of the cathodic reduction of oxygen will occur around the rust deposit or flaw, ie, at the zinc phosphate coating/steel interface. Anodic oxidation of iron is limited to areas covered by rust. Due to the limited movement of oxygen through the rust scale and the relatively easy access of adjacent unrusted steel surfaces to atmospheric oxygen, a differential oxygen concentration cell is established. . An important consequence of differential oxygen concentration cells is the creation of a highly alkaline electrolyte at the phosphate/steel interface. The pH of the electrolyte increases to over 12 in a sodium chloride environment, and such conditions tend to cause undercutting of the primer paint. Undercutting by alkali sodium hydroxide is primarily due to dissolution of some zinc phosphate coatings (and to a lesser extent, saponification reactions of some reactive ester groups present in the primer resin). Once the undercut paint is destroyed, the pH of the electrolyte drops to a neutral value and corrosion of the newly exposed metal begins. Cathodically induced paint adhesion degradation is therefore an important precursor to uncontrolled corrosion of metals. The degree of primer paint undercutting in corrosive environments is determined by imperfections in the paint film (e.g., scratches), the chemistry of the primer and inhibitor used, and contamination present on the surface of the substrate prior to coating. It depends on the amount of material and the effectiveness of the phosphate coating as a barrier against lateral spread of corrosion. The present invention has succeeded in significantly increasing the effectiveness of phosphate coatings, regardless of the first three factors. Surface Carbon Of the three factors listed above, surface contamination has been the most significant obstacle to obtaining reliable improvements in phosphate coatings and must therefore be addressed. Carbonaceous residues on the steel or other metal substrate to be coated have a detrimental effect on the corrosion protection provided by paint and phosphate coatings. It has now been established by the prior art that there is a correlation between surface carbon contamination level and salt spray performance. Carbon contamination, by itself, can cause initial paint adhesion degradation and later corrosion problems. Carbonaceous deposits impede the phosphating reaction and subsequent precipitation of phosphate crystals, thus increasing the apparent porosity of the phosphate coating. The increased porosity increases the generation rate of hydroxyl ions by cathodic reduction of oxygen at the sites of the electrochemically active pores. Even levels of apparent porosity of only a few percentage points dramatically reduce the effectiveness of the phosphate coating. With conventional phosphate systems, porosity levels of about 0.5% or less, which are found at low levels of surface carbon contamination, are required to prevent cathodic undercutting of the primer. What is needed is that the phosphate coating be relatively insensitive to alkaline undercuts, regardless of the degree of carbon contamination. That is the purpose of this invention. The research underlying the present invention shows that zinc phosphate coatings containing at least 15 mole percent nickel based on Ni and Zn content and a threshold level of at least 25 weight percent zinc for the phosphate film or coating are alkaline. It has been shown that significant improvements in dissolution can be achieved. PREFERRED METHODS To deposit a phosphate film on the surface of an alkali-cleaned metal article or substrate, use a temperature and temperature sufficient to effect the chemical reaction and deposition of this type of film.
This is done by exposing the article or substrate to an acidic aqueous phosphate solution for a sufficient period of time under PH. The solution contains divalent metal cations and phosphate ions for forming the first and second layers, the first divalent metal cations being nickel, cobalt, magnesium and manganese (all of which contain zinc the second divalent metal cation is zinc, while the second divalent metal cation is zinc. The amounts of the first and second divalent metal cations are adjusted such that the first divalent metal cation content in the resulting film is at least 15 mole percent of the total cations. The prior art, particularly the Reese patent, imparts paint systems through the use of phosphating baths that include a lowest zinc threshold and have nickel concentrations within a very narrow range, as disclosed herein. It is clear that the quantum jump in corrosion protection was not noticed. This does not mention that the deficiencies in corrosion resistance exhibited by the paint system are due to deficiencies in the phosphate coating (see column 1, lines 65-72) and that the improvement of corrosion resistance is not specifically addressed as an object of the invention. It is self-evident since it is not mentioned (see column 2, lines 28-30). Reese discloses four examples, the first using a "100% nickel" bath, and the remaining three using 68.1, 68.1, and 68.9 mole percent (65.8, 68.9 mole percent), respectively.
65.7 and 66.6% by weight) nickel bath. Reese gave these examples to establish upper and lower limits for adhesion, and that the use of nickel phosphate coatings within strictly limited ranges when used as a paint base in corrosive systems. It is clear that he did not recognize the peculiar features. Lease disclosures are in Example 1, Column 550
-54, in which it is stated that the nickel phosphate coating is "... highly suitable as an adhesion base for subsequently applied lacquer and synthetic resin layers". Clearly, the emphasis is on phosphate deposition on metal substrates. Regarding Example 2, Reese stated that ``in corrosion tests, these were largely superior to, or at least equivalent to, known zinc phosphate layers, as shown by condensed moisture tests and salt spray tests.'' ing. As will be demonstrated below, salt spray corrosion resistance is not substantially improved when the nickel content is between 58 and 83 and between 95 and 100 mole percent of divalent layer-forming cations. Therefore, Reese's thesis is baseless even when interpreted in good faith, and is not based on technical data. The method disclosed herein further preferably includes:
Contains at least 6% nickel by weight of the total coating, with an average coating weight of 1.3 g/m ² (120 mg/m 2
ft ² ) is characterized by the precipitation of a phosphate film. The phosphate coating is obtained using an acidic aqueous coating solution having an oxidizing agent and solution pH effective to chemically react with the article or substrate.
The solute contained in the solution is (a) a divalent compound consisting of nickel in an amount of 84 to 94 mol% based on the total metal cations and zinc in an amount of 0.2 to 0.6 g per 1 of the solution as Zn ⁺² . Desirably, the layer consists essentially of a layer-forming metal cation, and (b) phosphate ions in an amount sufficient to form a dihydrogen phosphate with the metal cation. Alternatively, a portion of the nickel content may be replaced by a divalent layer-forming metal cation selected from the group consisting of cobalt, magnesium and manganese. More specifically, metal products are cleaned using an alkaline cleaner having a concentration of 2 to 10 points and maintained at a temperature of 100 to 140 degrees. The article is treated with an alkaline cleaner for about 30-120 seconds and then washed with water at a temperature of 100-140° for 30-120 seconds. A phosphating bath solution having a composition adjusted as specified above and maintained at a temperature of about 100-140°C is then sprayed onto the alkali-cleaned metal substrate, or the substrate is placed in the solution. Soak. The total acid content of the solution is 10-40 points, the free acid content is 0.5-2.0 points, and the total acid/free acid ratio is 10-50. The pH of the bath is adjusted to 2.5-3.5 and nitrite is present in the bath, preferably in an amount of 0.5-2.5 points. Exposure to the phosphate treatment bath was kept for approximately 30-120 seconds, and the application amount was 1.3 g/ ^m2 (120
mg/ft ² ). After exposure to the phosphating solution in this manner, rinse with water for 30 to 120 seconds at ambient temperature or 100°C.
Inhibitor cleaning, including chromate or other dissolved corrosion inhibitors, for 30 to 60 seconds at 120°C, and at ambient temperature.
Excess solution is removed from the article or substrate by a continuous cleaning process consisting of 15-30 second deionized water rinses. Phosphating Solutions Phosphating solutions contain nickel cations (or water, which has a lower solubility in alkaline solutions than zinc hydroxide) comprising at least 84 mole percent (82.5 weight percent) of the combined metal cations in the solution. oxides of magnesium, cobalt or manganese). However, the zinc cations in the phosphating solution are at least 0.2 g/Zn ⁺² .
, or 0.79g/Zn(H ₂ PO ₄ ) ₂ is important. The Ni/Zn molar ratio is 5.2:
It is within the range of 1 to 16:1. Thus, for example, if zinc has a nickel/zinc cation content of 16
If it is mol%, at least 0.2 g/[preferably 0.2 to 0.6 g/] of Zn ⁺² in the solution, or Zn
(H ₂ PO ₄ ) ₂ must contain 0.79 to 2.38 g/]. Therefore, the nickel content must be at least 1.0 g per bath solution (84 mol % of the total nickel/subsalt). This correlation between the lowest zinc content and the highest first divalent metal cation content is due to the fact that Zn ₂ M (PO ₄ ) ₂ 4H ₂ O (where M is magnesium, nickel, cobalt or manganese) and whose hydroxide is less soluble in alkaline solutions than the hydroxide of zinc This is a necessary condition. Such mixed metal phosphates contain high contents of magnesium, nickel, cobalt or manganese, preferably nickel, thereby resulting in significantly improved corrosion performance despite a significant degree of surface carbon contamination. . As shown in Figure 17, infrared spectra demonstrated that coatings made from baths containing less than 84 mole % nickel were structurally different from phosphate coatings formed from high nickel baths. . Furthermore, scanning electron micrographs show that phosphates produced from baths with nickel contents greater than 84 mol % exhibit rapid morphological changes. If the nickel content of the phosphate solution exceeds 94 mol%, coatings made from such phosphate solutions will be very thin and non-uniform (see Figure 15), and will have improved Corrosion performance benefits also decrease accordingly. If it exceeds 94 mol%,
It becomes extremely difficult to obtain the desired Ni/Zn ratio in the bath. If the nickel content in the phosphate solution is lower than 84 mole percent, the phosphate coating will not be able to produce the amount of favorable mixed-phase nodular phosphate structure necessary to dramatically increase salt spray corrosion resistance. . Those coatings do not have the desired alkali resistance.
If the zinc concentration is less than 0.2g/Zn ⁺² ,
The rate of formation of iron oxides and iron phosphates increases. The initial phosphate solution is conveniently prepared by making up a nickel and zinc phosphate solution concentrate, preferably from an oxide or carbonate and concentrated phosphoric acid. The concentration of metal ions in each of these separate solutions is approximately 120-140 g/g/. To make up a fresh phosphate bath using these metal phosphate concentrated stock solutions, appropriate amounts of each of these stock solutions and water are used to achieve the desired bath concentration as described above. During the deposition of the phosphate film, more zinc is deposited than nickel, so that during the phosphate treatment the bath is enriched with nickel. It is preferable to prepare a separate concentrated stock solution formulated as a replenisher, which contains 18 mol% nickel and 82 mol% nickel based on dissolved nickel and zinc cations.
of zinc. Substrate Preferably, the substrate is selected from the group consisting of iron, carbon steel, low alloy steel, aluminum and zinc.
If the substrate is zinc or aluminum, 0.1-1.0 g/ml of sodium fluoride is additionally added to the phosphate solution to promote the formation of a zinc phosphate film. Coating Product The coating product obtained has very good alkali solubility resistance (see Figure 1, which compares several test panels of the prior art and of the invention exposed to NaOH solution at pH 12.5). ) and excellent chemical bonding to the substrate. Zinc/nickel phosphate conversion coatings are the result of a chemical reaction with the substrate. The structure of the coating of the invention has the form of a nodule (see Figures 10-13).
The product of the invention has a nickel content in the coating of 15
Significantly improved salt spray performance with little or no undercutting of the paint even after 500 test hours, a phenomenon that occurs suddenly when the mole % (approximately 13.7% by weight) is exceeded. It is therefore particularly characterized (see Figure 3).
Adjusting the amount of nickel in the coating to 13.7% by weight or higher is easy by adjusting the amount of nickel in the bath to exceed 84 mol% (82.8% by weight) of Ni/Zn in the bath. (See Figure 2). This coating has high corrosion resistance even with a high degree of surface carbon contamination. Example Cutting sheet metal into panels with dimensions of 4 x 12″,
A series of test panels for Examples 1-13 were manufactured. These test panels were exposed to a phosphating solution (see table) of known chemical composition, washed and dried. A portion of selected panels were used to measure the coating weight, composition, morphology and structure of the phosphate coating. A dark gray base paint (epoxy ester-melamine resin primer) was applied to the remaining portions of these panels. After these samples were baked, an "X" shaped scratch was made to expose the metal and then subjected to an accelerated salt spray test after which the degree of undercutting of the paint was observed and/or measured. The salt spray test essentially involves exposing the panel to a mist of 5% sodium chloride solution in a chamber maintained at 35° C. according to the ASTM B117 standard test method. Example 1 A solution for a phosphating bath is prepared with the following composition: 2.22g/ Z(H ₂ PO ₄ ) ₂ 1.08g/ Ni(H ₂ PO ₄ ) ₂ 5.85g/ H ₃ PO ₄ 0.13g/ NaNO ₂ did. The total acid concentration of this bath at the time of formulation was 11.3
It was a point. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.8 points.
A total acid to free acid ratio of 14 was achieved. In a bath with this composition, dissolved nickel accounted for 33.3 mole percent of the dissolved divalent cations, and is representative of the composition currently used commercially in spray phosphating systems. Two types of steel panels were selected for phosphate treatment with the phosphate treatment compositions described above. The first type, designated as Q steel, has very low surface carbon contamination, typically 1 mg/m ² (0.093 mg/ft ² ).
The degree of contamination was lower than that of commercially available steel test panels. The second type of panel is cut from commercial auto body sheeting;
Identified as F4. This steel plate has a surface carbon value of
It was 1.8 to 6.2 mg/m ² (0.17 to 0.58 mg/ft ² ), and it was known that conventional primers sprayed on top of zinc phosphate quickly deteriorated in salt spray tests. 4.7 for Q steel and F4 steel panels
Spray cleaning for 2 minutes with a conventional alkaline cleaner with point strength and a temperature of 60℃ (140〓), spray rinsing with tap water at 60℃ for 30 seconds, and then heat the above solution to 60℃. A 2 minute spray phosphate treatment with a phosphate bath was applied. 20℃
The panels were spray rinsed with deionized water (68°) for 1 minute and then dried in an oven at 82°C (180°) for 5 minutes. None of these phosphate treated panels were post-treated with an inhibitor rinse. Steel panels coated with phosphate in this manner had a uniform, gray appearance and a coating weight of 1.62 g/m ² (150 mg/ft ² ). Chemical analysis showed that the nickel content of the phosphate coatings for both Q and F4 steels was 3.2% by weight based on the total nickel and zinc content in the coatings. This is equivalent to 3.5 mol% Ni. A 1500x scanning electron micrograph of the phosphate coating on Q steel is shown in FIG. This structure is representative of spray-applied commercial zinc phosphate coatings. Phosphate coated Q steel and F4 steel were spray coated with an epoxy ester-melamine resin based primer. The thickness of the paint after baking was approximately 23 μm. Salt spray test on painted and scribed panels
Performed according to ASTM B117 standard. The specification for the epoxy ester-melamine resin-based primers used in these tests is that the undercut of the paint should be 3 mm away from the scribe line when measured by tape stripping the entire surface of the panel. If this occurs, it will be a disqualification. The salt spray test on Test Panel Q was discontinued after 480 hours, and there was essentially no undercut from the scribe line (see Figure 4a). In contrast, test panel F4 failed after 96 hours of salt spray testing (see Figure 4b). Example 2 A solution for a phosphating bath is prepared with the following composition: 4.44g/ Zn(H ₂ PO ₄ ) ₂ 5.94g/ Ni(H ₂ PO ₄ ) ₂ 3.36g/ H ₃ PO ₄ 0.12g/ NaNO ₂ did. The total acid concentration of this bath at the time of formulation was 14.7 points. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.9 and a total acid to free acid ratio of 16. In a bath of this composition, dissolved nickel accounts for 57.9 mole percent of the dissolved divalent cations. Two types of steel panels Q and F4 described in Example 1
were spray cleaned and spray rinsed as described in Example 1. After the rinsing step, the panels were spray phosphated using the phosphate bath described above heated to 60°C. The panels were then spray rinsed with deionized water at 20°C and dried in an oven at 82°C for 5 minutes. As in Example 1, none of the panels were post-treated with an inhibitor rinse. Steel panels coated with phosphate using this method are
It has a uniform gray appearance and the coating amount is 1.71g/m ²
(159 mg/ft ² ). Chemical analysis revealed that the nickel content in the phosphate coating for both Q steel and F4 steel was 5.6% by weight of the total nickel and zinc content of the coating.
I learned that it is equal to This is equivalent to 6.2 mol% Ni. A scanning electron micrograph of this coating taken at 1500x is shown in Figure 6. The structure is still similar to the morphology of commercial spray-applied zinc phosphate coatings. Phosphate coated steel panels Q and F4 were spray coated with an epoxy ester-melamine resin based primer. As in Example 1, the thickness of the paint film after baking was 23 μm. The salt spray test was carried out again exactly as described in Example 1 and any undercut in the paint 3 mm from the scribe line was considered a failure. The salt spray test on Test Panel Q was discontinued after 480 hours and there was essentially no undercut from the scribe line (see Figure 4c). In contrast, test panel F4 failed before the 96 hour salt spray test was completed (see Figure 4d). Example ₃ A _phosphate bath solution was prepared having the following composition: 3.33g/Zn( _H2PO4 ) ₂ 6.80g/Ni( _H2PO4 ) _{22.71g / H3PO40.11g} / _NaNO2 . At the time of formulation, this bath had a total acid concentration of 14.1 points. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.9 points.
Therefore, the ratio of total acid to free acid was 16. In a bath of this composition, dissolved nickel accounts for 67.7 mole percent of the dissolved divalent metal cations. Two types of steel panels Q and F4 described in Example 1
A spray wash and a spray rinse were performed as detailed in Example 1. After rinsing process, 60℃
These panels were spray phosphated using the phosphate treatment bath described above heated to . The panels were then washed with deionized water at 20°C and dried in an oven at 82°C for 5 minutes. As in Example 1, none of the phosphate treated panels were post treated with an inhibitor rinse. Steel panels coated with phosphate by this method have a uniform gray appearance and the amount of coating is
It was 1.38g/m ² (125mg/ft ² ). Chemical analysis showed that for both Q and F4 steels, the nickel content of the phosphate coating was equal to 7.3% by weight of the total amount of nickel and zinc contained in the coating. this is
Equal to 8.1 mol% Ni. A scanning electron micrograph of this phosphate coating taken at 1500x is shown in Figure 7.
Again, this structure is still similar to spray applied commercial zinc phosphate coatings. Phosphate coated steel panels Q and F4 were spray coated with an epoxy ester-melamine resin based primer. As in Example 1, the thickness of the paint film after baking was approximately 23 μm. The salt spray test was again carried out exactly as detailed in Example 1, again with a
Any undercutting of the paint in mm was considered a disqualification. The salt spray test on Test Panel Q was discontinued after 480 hours and there was essentially no undercut from the scribe line (see Figure 4e). In contrast, test panel F4 failed before the end of the 72 hour salt spray test (see Figure 4f). Example 4 A phosphating bath solution was prepared having the following composition: 3.01g/Zn( _{H2PO4 ) 2} 10.07g/Ni( _{H2PO4 ) 20.89g /} H3PO40.14g _{/ NaNO2} . The total acid concentration of this bath at the time of formulation was 14.2 points. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.9 points, thus a total acid to free acid ratio of 16. In a bath of this composition, dissolved nickel accounts for 77.4 mole percent of the dissolved divalent cations. Two types of steel panels Q and F4 described in Example 1
A spray wash and a spray rinse were performed as detailed in Example 1. After rinsing process, 60℃
The panels were spray phosphated for 2 minutes using the phosphate bath described above heated to . The panels were then spray rinsed with deionized water at 20°C and dried in an oven at 82°C for 5 minutes. Example 1
As in the case of , no post treatment with inhibitor was performed on the phosphate treated panels. Steel panels coated with phosphate using this method are
It had a uniform, gray appearance and a coverage of 1.14 g/m ² (106 mg/ft ² ). Chemical analysis revealed that Q steel and
For both F4 steels, the phosphate and nickel content of the coating is 11.0% by weight of the total nickel and zinc content of the coating.
I learned that it is equal to This corresponds to 12.1 mol% Ni. Phosphate coated steel panels Q and F4 were spray coated with an epoxy ester-melamine resin based primer. As in Example 1, the thickness of the coating after baking was approximately 23 μm. The salt spray test was carried out exactly as in Example 1, with undercutting of the paint 3 mm from the scribe line still considered a failure. The salt spray test on Test Panel Q was discontinued after 480 hours and there was essentially no undercut from the scribe line (see Figure 4g). In contrast, test panel F4 failed within 72 hours of the salt spray test (see Figure 4h). Example ₅ A _phosphating bath solution was prepared having _the following composition: 2.14g/Zn( _H2PO4 ) ₂ 9.21g/Ni( _H2PO4 ) _{21.42g /} H3PO40.11g/ _NaNO2 . The total acid concentration of this bath at the time of formulation was 14.2 points. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.8 points and thus a total acid to free acid ratio of 18. In a bath of this composition, dissolved nickel is 81.5 mol% of dissolved divalent metal cations.
occupies The two steel panels Q and F4 described in Example 1 were spray cleaned as detailed in Example 1. After the rinsing step, the panels were spray phosphated for 2 minutes using the phosphate bath described above heated to 60°C. The panels were then spray rinsed with deionization at 20°C and dried in an oven at 82°C for 5 minutes. As in Example 1, the phosphate treated panels were not post-treated with an inhibitor rinse. Steel panels coated with phosphate using this method are
It had a uniform, gray appearance and a coverage of 1.17 g/m ² (109 mg/ft ² ). Chemical analysis revealed that Q steel and
For both F4 steels, the nickel content of the phosphate coating was found to be equal to 11.8% by weight of the total nickel and zinc content of the coating. This corresponds to 13.0 mol% Ni. Phosphate coated steel panels Q and F4 were spray coated with an epoxy ester-melamine resin based primer. As in Example 1, the thickness of the paint after baking was approximately 23 μm.
The salt spray test was again carried out exactly as described in Example 1, with undercutting of the paint 3 mm from the scribe line still considered a failure. The salt spray test on Test Panel Q was discontinued after 480 hours and there was essentially no undercut from the scribe line (see Figure 9a). In contrast, test panel F4 failed within 120 hours of the salt spray test. (See Figure 9b). Example ₆ A _phosphating bath solution was prepared having the following composition: 2.06g/Zn( _H2PO4 ) ₂ 9.56g/Ni( _H2PO4 ) _{21.18g /} H3PO40.12g _{/ NaNO2} . At the time of formulation, this bath had a total acid concentration of 14.3 points. The acidity of the bath was then adjusted by adding NaOH, increasing the concentration of free acid by 0.7 points,
Therefore, the total acid to free acid ratio was set at 20. In a bath of this composition, dissolved nickel accounts for 82.6 mole percent of the dissolved divalent cations. Two types of steel panels Q and F4 described in Example 1
A spray wash and a spray rinse were performed as detailed in Example 1. After rinsing process, 60℃
The panels were spray phosphated for 2 minutes using the phosphate bath described above heated to .
The panels were then spray rinsed with deionized water at 20°C and dried in an oven at 82°C for 5 minutes. As in Example 1, the phosphate treated panels were not post-treated with an inhibitor rinse. Steel panels coated with phosphate using this method are
It had a uniform, gray appearance and a coverage of 1.09 g/m ² (101 mg/ft ² ). It was found by chemical analysis that the nickel content of the phosphate coating for both the Q and F4 steels was equal to 12.3% by weight of the total nickel and zinc content of the coating. This corresponds to 13.6 mol% Ni. A scanning micrograph of the phosphate coating taken at 1500x is shown in Figure 8. This morphology is similar to that of commercial zinc phosphate, except that the crystal structure size is much finer. Phosphate coated steel panels Q and F4 were spray coated with an epoxy ester-melamine resin based primer. As in example 1,
The thickness of the coating film after baking was approximately 23 μm. Again a salt spray test was carried out exactly as in Example 1,
Undercutting the paint by 3mm from the scribe line was also considered a disqualification. The salt spray test on Test Panel Q was discontinued after 480 hours and there was essentially no undercut from the scribe line (see Figure 9c). In contrast, test panel F4 failed within 144 hours of the salt spray test. (See Figure 9d). Example ₇ A _phosphating bath solution was prepared having the following composition: 2.18g/Zn( _H2PO4 ) ₂ 10.07g/Ni( _H2PO4 ) _{22.08g /} H3PO40.12g _{/ NaNO2} . The total acid concentration of this bath at the time of formulation was 15.6 points. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.6 points and thus a total acid to free acid ratio of 26. In a bath of this composition, dissolved nickel accounts for 82.6 mole percent of the dissolved divalent cations. The two steel panels Q and F4 described in Example 1 were spray cleaned and spray rinsed as detailed in Example 1. After the rinsing step, the panels were spray phosphated for 2 minutes using the phosphate bath described above heated to 60°C. The panels were then spray rinsed with deionized water at 20°C and dried in an oven at 82°C for 5 minutes. Example 1
As in the previous case, no post-treatment with an inhibitor rinse was performed on the phosphate-treated panels. Steel panels coated with phosphate using this method are
It had a uniform, gray appearance and a coverage of 1.45 g/m ² (135 mg/ft ² ). Chemical analysis showed that for both the Q and F4 steels, the nickel content of the phosphate coating was equal to 13.1% by weight of the total nickel and zinc content of the coating. This corresponds to 14.4 mol% Ni. Phosphate coated steel panels Q and F4 were spray coated with an epoxy ester-melamine resin based primer. As in Example 1, the thickness of the coating after baking was approximately 23 μm.
The salt spray test was again carried out exactly as detailed in Example 1, with undercutting of the paint 3 mm from the scribe line still being considered a failure. The salt spray test on Test Panel Q was discontinued after 480 hours and there was essentially no undercut from the scribe line (see Figure 9e). In contrast, test panel F4 failed within 456 hours of the salt spray test. (See Figure 9f). The improvement in salt spray performance observed in Example 7 compared to Example 6 demonstrates the importance of the nickel content in the phosphate coating. Examples 6 and 7
Note that the nickel content in both baths is 82.6 mol%. However, compared to example 6, example 7
The high total to free acid ratio of the phosphate coating led to a high nickel content in the phosphate coating, which led to improved corrosion resistance. Example ₈ A phosphating bath solution was prepared having the following composition: 1.63g/Zn( _H2PO4 ) ₂ 9.00g/Ni( _H2PO4 ) _{22.95g / H3PO40.13g / NaNO2} . The total acid concentration of this bath at the time of formulation was 14.1 points. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.8 points and thus a total acid to free acid ratio of 18. In a bath with this composition, dissolved nickel accounts for 85.0 mole percent of the dissolved divalent cations. The two steel panels Q and F4 described in Example 1 were spray cleaned and spray rinsed as detailed in Example 1. After the rinsing step, the panels were spray phosphated for 2 minutes using the phosphate bath described above heated to 60°C. next
The panels were spray rinsed using deionized water at 20°C and then dried in an oven at 82°C for 5 minutes.
As in Example 1, the phosphate treated panels were not post-treated with an inhibitor rinse. Steel panels coated with phosphate using this method are
Uniform bluish-gray appearance and 0.90g/m ² (84mg/ft ² )
It had a coating amount of Chemical analysis showed that the nickel content of the phosphate coating for both the Q and F4 steels was equal to 14.6% by weight of the total nickel and zinc content of the coating. This corresponds to 16.0 mol% Ni. A scanning electron micrograph of this coating taken at 1500x is shown in Figure 10. This photograph shows a drastic change in morphology compared to those shown in the examples described so far, and it is clear that the entire structure has changed. Phosphate coated steel panels Q and F4 were spray coated with an epoxy ester-melamine resin based primer. As in example 1,
The thickness of the coating film after baking was approximately 23 μm. The salt spray test was again carried out exactly as detailed in Example 1, with undercutting of the paint 3 mm from the scribe line still being considered a failure. The salt spray test on Test Panel Q was discontinued after 480 hours and there was essentially no undercut from the scribe line (see Figure 9g). The salt spray test on test panel F4 was also stopped after 480 hours, but there was essentially no undercut from the scribe line (see Figure 9h). Example ₉ A phosphating bath solution was prepared having the following composition: 1.07g/Zn( _H2PO4 ) ₂ 9.90g/Ni( _H2PO4 ) _{20.96g / H3PO40.12g / NaNO2} . The total acid concentration of this bath at the time of formulation was 13.5 points. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.9 points and thus a total acid to free acid ratio of 15. In a bath with this composition, dissolved nickel accounts for 90.5 mole percent of the dissolved divalent cations. The two steel panels Q and F4 described in Example 1 were spray cleaned and spray rinsed as detailed in Example 1. After the rinsing step, the panels were spray phosphated for 2 minutes using the phosphate bath described above heated to 60°C. next
The panels were spray rinsed with deionized water at 20°C and dried in an oven at 82°C for 5 minutes. Steel panels coated with phosphate using this method are
Uniform bluish-gray appearance and 0.86g/m ² (80mg/ft ₂ )
It had a coating amount of Chemical analysis showed that for both Q and F4 steels, the nickel content of the phosphate coating was equal to 15.5% by weight of the total nickel and zinc content of the coating. This corresponds to 17.0 mol% Ni.
A scanning electron micrograph of this coating taken at 1500x is shown in Figure 11. This structure confirms the rapid change in morphology shown in FIG. 10, and suggests changes throughout the structure. Phosphate coated steel panels Q and F4 were spray coated with an epoxy ester-melamine resin based primer. As in Example 1, the thickness of the coating after baking was approximately 23 μm. The salt spray test was again carried out exactly as detailed in Example 1, with undercutting of the paint 3 mm from the scribe line still being considered a failure. Similar to Example 9 above, both test panels (Q and
The salt spray test for F4) was discontinued after 480 hours and there was essentially no undercut from the scribe line (see Figures 14a and 14b). Example ₁₀ A phosphating bath solution was prepared having the following composition: 1.71g/Zn _{( H2PO4} ) ₂ 17.69g/Ni( _H2PO4 ) _{22.75g / H3PO40.11g} / _NaNO2 . The total acid concentration of this bath at the time of formulation was 24.0 points. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.8 points and thus a total acid to free acid ratio of 30. In a bath with this composition, dissolved nickel accounts for 91.4 mole percent of the dissolved divalent cations. Two types of steel panels Q and F4 described in Example 1
A spray wash and a spray rinse were carried out as detailed in Example 1. After the rinsing step, the panels were spray phosphated for 2 minutes using the phosphate bath described above heated to 60°C. Then 20℃
Spray rinse the panel with deionized water, then
It was dried in an oven at 82°C for 5 minutes. As in Example 1, the phosphate treated panels were not post treated with an inhibitor rinse. Steel panels coated with phosphate using this method are
Uniform bluish-gray appearance and 0.62g/m ² (58mg/ft ₂ )
It had a coating amount of Chemical analysis showed that for both the Q and F4 steels, the nickel content of the phosphate coating was equal to 21.0% by weight of the total nickel and zinc content of the coating. This corresponds to 22.8 mol% Ni. A scanning electron micrograph of this coating taken at 1500x is shown in Figure 12. This structure is similar to that shown in FIGS. 10 and 11. Phosphate coated steel panels Q and F4 were spray painted with an epoxy ester-melamine resin based primer. As in Example 1, the thickness of the coating after baking was approximately 23 μm. The salt spray test was again carried out exactly as detailed in Example 1, with undercutting of the paint 3 mm from the scribe line still being considered a failure. As in Examples 8 and 9, the salt spray test on both test panels (Q and F4) was discontinued after 480 hours, and there was essentially no undercut from the scribe line. (Figures 14c and 14d
(see figure). Example ₁₁ A phosphating bath solution was prepared having the following composition: 1.55g/Zn _{( H2PO4} ) ₂ 18.04g/Ni( _H2PO4 ) _{22.89g / H3PO40.12g} / _NaNO2 . The total acid concentration of this bath at the time of formulation was 24.4 points. The acidity of the bath was then adjusted by adding NaOH to give a concentration of free acid of 0.5 points and thus a total acid to free acid ratio of 49. In a bath with this composition, dissolved nickel accounts for 92.3 mole percent of the dissolved divalent cations. The two steel panels Q and F4 described in Example 1 were spray cleaned and spray rinsed as detailed in Example 1. After the rinsing step, the panels were spray phosphated for 2 minutes using the phosphate bath described above heated to 60°C. The panels were then spray rinsed with deionized water at 20°C and dried in an oven at 82°C for 5 minutes. Example 1
As in, no post treatment with an inhibitor rinse was performed on the phosphate treated panels. Steel panels coated with phosphate using this method are
Uniform bluish-gray appearance and 0.52g/m ² (48mg/ft ² )
It had a coating amount of It was found by chemical analysis that the nickel content of the phosphate coating for both the Q and F4 steels was equal to 24.8% by weight of the total nickel and zinc content of the coating. This corresponds to 26.9 mol% Ni. A scanning electron micrograph of this coating taken at 1500x is shown in Figure 13. This organization is the 10th,
The structure is similar to that shown in Figures 11 and 12. Phosphate coated steel panels Q and F4 were spray painted with an epoxy ester-melamine resin based primer. As in Example 1, the thickness of the coating after baking was approximately 23 μm. The salt spray test was again carried out as detailed in Example 1, and undercutting of the paint 3 mm from the scribe line was again considered a failure. As in Examples 8, 9 and 10, the salt spray test on both test panels (Q and F4) was discontinued after 480 hours, and there was essentially no undercut from the scribe line. (Figures 14e and 14f
(see figure). Example ₁₂ A phosphating bath solution was prepared having the following composition: 0.63g/Zn _{( H2PO4} ) ₂ 12.22g/Ni( _H2PO4 ) _{21.10g /} H3PO40.11g _{/ NaNO2} . The total acid concentration of this bath at the time of formulation was 14.8 points. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.8 points, thus a total acid to free acid ratio of 18. In a bath with this composition, dissolved nickel accounts for 95.2 mole percent of the dissolved divalent cations. The two steel panels Q and F4 described in Example 1 were spray cleaned and spray rinsed as detailed in Example 1. After the rinsing step, the panels were spray phosphated for 2 minutes using the phosphate bath described above heated to 60°C. then 20
The panels were spray rinsed using deionized water at 0.degree. C. and dried in an oven at 82.degree. C. for 5 minutes. As in Example 1, the phosphate treated panels were not post treated with an inhibitor rinse. Steel panels coated with phosphate using this method are
It has a very uneven, streaked or spotted appearance;
The color ranged from light gray to black. Application amount is 0.28
It varied between ~0.70 g/m ² (26 and 65 mg/ft ² ). Chemical analysis of steel panel Q revealed that the content of the phosphate coating was equal to 41.3% by weight of the total nickel and zinc content of the coating. This corresponds to 43.9 mol% Ni. The coating also had a high iron content, which is undesirable. A scanning electron micrograph of this phosphate coating taken at 1500x is shown in Figure 15. This texture is similar to that observed for coatings with nickel contents in the range of 13-25% by weight, but with a visible non-uniform appearance, non-uniform coverage, and porosity. Due to the high corrosion resistance, it was deemed insufficient for commercial use and therefore no painted test panels were prepared for corrosion testing. Looking through Examples 1 to 12, ensuring excellent salt spray corrosion resistance for commercial sheet steel that may be contaminated with carbon, such as automotive sheet steel, which is subsequently applied with paint. It is clear that there is a very narrow, sharply differentiated range of nickel content to be applied to the nickel/zinc phosphate conversion coating. As shown through Examples 1-12, this nickel content range, characterized by a phosphate coating with a microstructure distinctly different from that of common commercial zinc phosphates, ranges from 14 mol % to 26 mol %. % of nickel, which is approximately 83.5% of the nickel dissolved in the phosphate bath.
It corresponds to 93.0 mol%. It is possible to vary these limits slightly depending on the ratio of total acid to free acid. For simplicity purposes, examples from Example 1
Up to 12, two types of steel were used, one with low surface carbon contamination and one with moderate surface carbon contamination, with a phosphate coating and one type of paint, namely epoxy ester. - Only the case where a primer based on melamine resin was applied by spray painting was described. In addition to many of the phosphates described in Examples 1 to 12, other compositions not included in these examples were used on various other substrates, such as various steels with different degrees of surface carbon contamination, hot-dip galvanized It should be understood that the same applies to steel and aluminum. Furthermore, in addition to the spray primer coatings described in Examples 1-12, salt spray corrosion on phosphate-treated test panels of these substrates was also observed after similar commercial cathodic electrodeposition primer coatings. I also took an exam. In these cases, again, excellent salt spray performance was reliably observed only when the nickel content in the phosphate bath was within the range of about 84-94 mole percent of dissolved divalent cations. The following additional examples are intended to illustrate the advantages obtained on substrates other than steel, specifically on the zinc surface of hot-dip galvanized steel; by the formation of a phosphate conversion coating with a nickel content within narrow limits established for Example 13 For a phosphating bath with the following composition: 1.42g/ Zn(H ₂ PO ₄ ) ₂ 13.02g/ Ni(H ₂ PO ₄ ) ₂ 2.05g/ H ₃ PO ₄ 0.47g/ NaF 0.08g/ NaNO ₂ A solution was prepared. The total acid concentration of this bath at the time of formulation was 18.1 points. The acidity of the bath was then adjusted by adding NaOH to give a free acid concentration of 0.7 points and thus a total acid to free acid ratio of 26. In a bath with this composition, dissolved nickel accounts for 90.7 mole percent of the dissolved divalent cations. Two types of steel panels Q and F4 described in Example 1,
The hot dip galvanized steel panels were then spray cleaned and spray rinsed as detailed in Example 1. After the rinsing step, the panels were spray phosphated for 2 minutes using the phosphate bath described above heated to 60°C. The panels were then spray rinsed with deionized water at 20°C and dried in an oven at 82°C for 5 minutes. As in Example 1, the phosphate treated panels were not post-treated with an inhibitor rinse. Steel panels coated with phosphate using this method are
Uniform bluish-gray appearance and 0.92g/m ² (85mg/ft ² )
It had a coating amount of . A gray-black coating was produced on the hot-dip galvanized steel panel with a coverage of 1.67 g/m ² (155 mg/ft ² ). Chemical analysis of the phosphate coatings on both steel plates showed that the nickel content was equal to 16.2% by weight of the total nickel and zinc content of the coatings. This corresponds to 17.7 mol% Ni. Phosphate coated steel panels Q and F4 and phosphate coated hot dip galvanized steel panels were spray coated with an epoxy ester-melamine resin based primer. As in Example 1, the thickness of the coating after baking was approximately 23 μm. The salt spray test was again carried out as detailed in Example 1, and undercutting of the paint 3 mm from the scribe line was again considered a failure. As in Examples 8, 9, 10 and 11, the salt spray test on both test steel panels (Q and F4) was discontinued after 480 hours, but undercut from the scribe line was essentially zero. Ta. After the exam starts
Although undercutting was observed in the hot-dip galvanized steel panels at 360 hours, the performance compared to that expected to be representative of commercial zinc phosphate.
Considerable improvement was observed. Figure 16 shows the 360 hour and 480 hour salt spray performance (Figures 16a and 16b) of hot-dip galvanized steel containing 17.7 mole % nickel in the phosphate coating, including 3.5 mole % nickel. Commercial zinc phosphate (Figures 16c and 1)
This shows that this is an improvement compared to Figure 6d). High nickel phosphates exhibit significant advantages in the degree of salt spray undercutting of the coating as well as in the development of undercutting over time. 5th, 6th, 7th, 8th, 10th, 11th, 12th and 13th
In another experiment to confirm the observed textural changes in the phosphate coating shown in the figure, attenuated total reflectance
Phosphate coatings representative of various levels of nickel in the phosphate treatment bath were examined by infrared analysis using a phosphate treatment bath technique. The experimental results summarized as a series of absorbance spectra are shown in Figures 17a-17f. FIG. 17a is a typical spectrum for commercial zinc phosphate corresponding to Example 1. In this spectrum, there is only a gradual change as the nickel concentration of the phosphate bath increases from 33.3 mole % corresponding to Example 1 to 82.6 mole % corresponding to Example 6.
However, as shown in Figure 17d, Example 8
At the same time as reaching a level of 85.0 mol% corresponding to
Gradual changes occur, supporting the tissue changes shown in the scanning electron micrograph of FIG. As shown in Figures 17e and 17f, corresponding to Examples 9 and 11, respectively, as the % nickel in the phosphate bath increases, the spectral changes become more pronounced. [Table] [Table] [Table] Examples 14 to 44 Examples using other metals as the first divalent metal are shown in the following tables. [Table] [Table] [Table] [Table] [Table]