WO1992007974A1

WO1992007974A1 - Phosphate conversion coating composition and process

Info

Publication number: WO1992007974A1
Application number: PCT/US1991/007668
Authority: WO
Inventors: Hitoshi Ishii; Toshi Miyawaki; Shigeo Tanaka
Original assignee: Henkel Corp
Current assignee: Henkel Corp
Priority date: 1990-10-24
Filing date: 1991-10-16
Publication date: 1992-05-14
Anticipated expiration: 1993-04-24
Also published as: KR920008214A; JP2794013B2; KR100234498B1; AU8959891A; JPH04160165A

Abstract

A phosphate conversion coating composition that gives superior results, particularly in phosphating surfaces including aluminum, has a composition containing water and: (A) 0.4 - 2.5 g/L of zinc(II) ions, (B) 0.5 to 3.5 g/L of nickel(II) ions, (C) 0.4 to 2.0 g/L manganese(II) ions, (D) at least 8 g/L of phosphate ions, (E) 2.0 to 20 g/L of nitrate ions, (F) 10 to 250 ppm of nitrite ions, (G) not more than 1,000 ppm of aluminum ions, and (H) 10 to 3,500 ppm total fluorine in anions, and the composition has a nickel ion to aluminum ion molar ratio that is at least 1.6, a total fluorine to aluminum ion molar ratio that is at least 5.0, and a nickel ion to total fluorine molar ratio that is at least 0.3.

Description

PHOSPHATE CONVERSION COATING COMPOSITION AND PROCESS

TECHNICAL FIELD

The present invention relates to a phosphate conver¬ sion treatment aqueous liquid composition (also called a "bath" below) which will form strongly paint-adherent phos- phate films with excellent post-painting corrosion resist¬ ance on the surfaces of iron, zinc, and aluminum metal structures, particularly sheet metal structures such as automobile bodies, household electrical appliances, and the like. A phosphate conversion treatment composition ac- cording to this invention is very well suited to be a pretreatment for cationic electrodeposition painting operations.

The compositions and processes according to this in¬ vention are particularly well suited for treating a sheet metal structure which is made up of at least one type of ferrous metal containing material, such as steel sheet, galvanized steel sheet, zinc alloy plated steel sheet, galvannealed steel sheet, or the like, and an aluminum material selected from aluminum sheet and aluminum alloy sheet. (Both pure aluminum and aluminum alloys that are predominantly aluminum are to be understood herein below as included within the term "aluminum", and both pure zinc and alloys that are predominantly zinc are to be understood herein below as included within the term "zinc", unless the context requires otherwise.) BACKGROUND ART

The aluminum ion present in a phosphate conversion treatment composition typically acts as an interfering ion for the conversion reactions. As a consequence, when alum- inum is subjected to a phosphate conversion treatment, the aluminum ion concentration in the treatment composition must be suppressed below a particular prescribed concen¬ tration. The prior art offers the following examples which illustrate this principle: (1) removal of the aluminum ion as a precipitate through the addition of particular types of additives to the phosphate treatment composition (Japanese Patent Ap- plication Laid Open [Kokai or Unexamined] Number 57-70287 [70,287/82]); (2) the use of specific proportions for the free acidity and free fluorine (Japanese Patent Application Laid Open Number 63-157879 [157,879/88]).

With regard to these related art examples, the afore¬ said invention (1) comprises a method for the precipita- tive removal of the aluminum ion which, however, requires removal of the sludge component precipitated as the fluor- ide. A substantial filtration plant is required for the elimination of this sludge, and this method suffers from, problems with both equipment and production technology, i.e., an unavoidable expansion of the installation and treatment of the discharged sludge industrial waste. The aforesaid invention (2) comprises a method in which the proportions for both the free acidity and free fluorine are restricted. Nevertheless, if aluminum ion is introduced during the treatment process into the treatment composition in excess of a certain quantity, the presence of the alum- inum ion will still inhibit formation of the phosphate con¬ version film and prevent the execution of an acceptable conversion process. DESCRIPTION OF THE INVENTION Problem to Be Solved by the Invention The present invention aims to provide a satisfactory phosphate conversion coating treatment for surfaces in¬ cluding aluminum, without requiring as large a sludge re¬ moval volume and/or suffering the low limitations on ac¬ ceptable levels of aluminum ions in the composition as were observed in the prior art. Summary of the Invention

The present invention introduces a phosphate conver¬ sion treatment composition, particularly for iron-aluminum sheet metal structures, that characteristically comprises, preferably consists essentially of, or most preferably con¬ sists of: (A) a source of zinc ions to provide from 0.4 to 2.5 grams per liter (hereinafter "g/L") of zinc(II) ions,

(B) a source of nickel ions to provide from 0.5 to 3.5 g/L of nickel(II) ions,

(C) a source of manganese ions to provide from 0.4 to 2.0 g/L manganese(II) ions,

(D) a source of phosphate ions to provide at least 8 g/L of phosphate ions,

(E) a source of nitrate ions to provide from 2.0 to 20 g/L of nitrate ions, (F) a source of nitrite ions to provide from 10 to 250 parts per million by weight ("ppm") of nitrite ions, (G) not more than 1,000 ppm of aluminum ions, and (H) a source of fluoride and/or complex fluoride ions to provide from 10 to 3,500 ppm total fluorine, said composition being further characterized by a nickel ion/aluminum ion molar ratio that is at least 1.6, a total fluorine/aluminum ion molar ratio that is at least 5.0, and a nickel ion/total fluorine molar ratio that is at least 0.3. Preferably the free acidity of the composition is in the range from to 0.1 to 1.5 points.

This invention makes possible a substantial increase in the permissible aluminum ion content of phosphating con¬ version treatment composition over previous values. This in turn makes possible the execution of a satisfactory phosphate conversion treatment on any material, such as aluminum material, cold rolled steel sheet, and zinc and/or zinc alloy plated steel sheet, without resorting to pre- cipitative removal of the aluminum ion. Furthermore, a completely satisfactory post-painting corrosion resistance and paint film adherence are also achieved, in particular when the invention is applied as a pretreatment for cat¬ ionic electrodeposition painting.

In the description of the invention, the stoichiomet- ric equivalent as phosphate ions of any phosphoric acid

(H₃P0₄) and any anions formed by its ionization that are present in the composition is to be understood as part of phosphate content of the composition as specified.

Details of Preferred Embodiments of the Invention

The zinc ion and phosphate ion are film source mater¬ ials for formation of the phosphate film. The presence of zinc ion in excess of 2.5 g/L precludes the formation of a good, strongly corrosion-resistant film. On the other hand, a uniform, fine, and dense film cannot be obtained at less than 0.4 g/L zinc ion. The phosphate ion should be present within the range of 8 to 30 g/L. Good films cannot be obtained below this lower limit, while exceeding the upper limit is uneconomical since no further improve¬ ment in performance is obtained thereby.

The fluorine component is preferably added in the form^' of one or more selections from among the fluoride ion and complex fluoride ions, and a total fluorine of 10 to 3,500 ppm as F is required. A satisfactory conversion process will not normally be achieved on the treatment substrate when either the upper or lower limit value is violated.

Aluminum ion concentrations in excess of 1,000 ppm prevent a satisfactory conversion process on the treatment substrate. From a practical standpoint, the concentration level cannot usually be reduced to below 1 ppm during actual operation when there is aluminum in the workpieces to be treated. Moreover, the total fluorine/aluminum ion molar ratio must be at least 5; lower values preclude a satisfactory film formation just as does an impermissible total fluorine concentration.

The nickel and manganese ions function to provide minute, fine film crystals. The post-painting corrosion resistance and the paint film adherence are also improved as a result of the improvement in the film crystals deriv¬ ing from the uptake of these metal components into the film. The manganese ions must be added at 0.4 to 2.0 g/L. The aforementioned benefits do not manifest to a satisfac- tory degree when this lower limit is not met, while exceed¬ ing this upper limit in fact adversely affects the post painting corrosion resistance. The nickel ion is a par- ticularly crucial metal additive component from the stand¬ point of the painting performance, and it should be added at 0.5 to 3.5 g/L. As for the manganese ion, the afore¬ mentioned activities do not manifest to a satisfactory de- gree when the lower limit is not met, while exceeding the given upper limit degrades the conversion process.

In addition, a specific balance must be maintained between the nickel ion and total fluorine and between the nickel ion and aluminum ion in order to provide a satis- factory post-painting corrosion resistance for the treat¬ ment workpiece. In concrete terms, the nickel ion/aluminum ion molar ratio must be at least 1.6, and the nickel ion/ total fluorine molar ratio must be at least 0.3. The painting performance of the treatment workpiece will de- teriorate when either of the prescribed molar ratios (con¬ centration balances) is violated.

With regard to the nitrate ion, it may be added as a nitrate salt at the same time as addition of the metal ion, but the nitrate ion concentration should be 2.0 - 20 g/L. The treatment composition will not be stable when this low¬ er limit is not met, while the corrosion resistance deter¬ iorates when the given upper limit is exceeded.

The addition of nitrite ion to provide at least 10 ppm as a film formation accelerator is necessary in order to increase the initial conversion reaction rate in treatment by the present invention's treatment composition and bring about the rapid formation of a uniform film. A uniform film will not be formed when this quantity of addition falls below the lower limit. Exceeding 250 ppm of nitrite is economically disadvantageous since no further incremen¬ tal effect is obtained for aluminum materials and zinc plated steel sheet. With regard to cold-rolled steel sheet, a satisfactory film weight is not obtained when the given upper limit is exceeded, and the painting performance is therefore degraded.

The free acidity of the treatment composition prefer¬ ably should also be controlled. At less than 0.1 points, not only can a stable treatment composition not usually be obtained, but an inferior conversion tends to occur, in particular in the case of cold-rolled steel sheet. A uni¬ form, dense, and fine film will not usually be obtained on the sheet metal structure under consideration when 1.5 points is exceeded. The total acidity is governed by the phosphoric acid concentration and metal ion concentration in the treatment composition, and, given that these concen¬ trations fall within the specified ranges, is not specif- ically limited.

The treatment composition according to the present invention is preferably applied within the temperature range of 25 to 55 ° C. While the preferred treatment meth¬ od is immersion, the benefits associated with the present invention are not compromised even by spray treatment, or by any other method of contacting the composition with the workpieces for an adequate time to produce a conversion coating thereon.

Further appreciation of the invention may be obtained by consideration of the following examples and comparison examples.

Examples

Examples 1 to 7 (according to the invention) and Co - parison Examples 1 to 4 are described below. In these examples, the following tests were performed and their results are reported after the description of the tests.

Metal sheet samples

(1) Aluminum sheet (according to Japanese Industrial Standard {"JIS"} 5052, abbreviated below as Al sheet)

(2) Cold-rolled steel sheet (SPCC, abbreviated below as

SPC)

2

(3) Duplex eleσtrogalvanized steel sheet (20 g/m each surface, abbreviated below as EG) Each of these three types of sheet, each with a thickness of 0.8 millimeter ("mm") was cut to dimensions of 70 x 150 mm, and a circular hole with 5 mm radius was punched in each sheet, with the center of the hole at a point half way between the two longer sides and about 20 mm from one of the shorter sides. One sheet of each type was then hung on an iron jig with three hooks spaced so as to provide a distance of 15 mm between the nearer long edges of adjacent sheet, with the SPC sheet in the middle of the array of sheets. The array of sheets and their supporting jig are then treated in this form through the treatment steps out- lined below.

Treatment method

(1) spray degreasing with FINECLEANER L4460 from Nihon Parkerizing at 42° C for 120 seconds;

(2) 30 second spray wash with tap water at room tempera- ture;

(3) 20 second surface conditioning spray with PREPALENE™ ZN from Nihon Parkerizing at room temperature;

(4) immersion phosphate conversion treatment with compo¬ sitions as shown in the tables below at 42° C for 120 seconds;

(5) 30 second spray tap water wash at room temperature;

(6) 20 second spray wash at room temperature with deion- ized water (conductivity = 0.2 microSiemens/cm) ;

(7) water drain and dry at 110° C for 180 seconds.

Measurement of free acidity

A 10 milliliter ("mL") sample of the treatment compo¬ sition was titrated to neutrality with 0.1 N aqueous NaOH solution using bromophenol blue as the indicator. The "point" (pt) value is the number of milliliters of 0.1 N aqueous NaOH solution required for the color change from yellow to blue.

Electrodeposition painting

(1) Painting with type HB2000L cationic electrodeposition paint from Kansai Paint at a composition temperature of 28° C using a voltage of 250 volts for 180 seconds to produce a paint film thickness of 20 micrometers;

(2) 20 second spray wash with tap water;

(3) 20 second spray wash with de-ionized water having a conductivity of 0.2 microSiemens/cm; (4) Bake at 175° C for 30 minutes.

Intermediate coating and top coating

• • • • T

(1) Intermediate coating with Amilac N-2 Sealer, a ela- mine alkyd resin paint from Kansai Paint, applied to a dry-film thickness of 30 microns using an air spray- er, allowed to sit for 10 to 20 minutes, then baked at 140° C for 30 minutes; then

(2) Top coating with Amilac White M3, a melamme alkyd resin paint from Kansai Paint, applied to a dry-film thickness of 40 micrometers using an air sprayer, al- lowed to sit for 10 to 20 minutes, then baked at 140° C for 30 minutes.

Post-painting performance evaluation

(1) Secondary water-resistance adherence testing

The tricoated sheet was immersed in deionized water at 40° C for 240 hours. A checkerboard-like pattern of one hundred (100) squares 2.0 mm on each side was then scribed, deeply enough to reach the substrate, on the sample using a sharp cutter. This was followed by peeling with cello¬ phane tape pressed against the scribed area, and the number of peeled squares was counted and reported in the tables. The best score is zero and the worst is 100 for this test.

(2) Composite cycle test

A cross was scribed into the tricoated sheet using a sharp cutter so as to reach the substrate, and the sheet was then subjected to 5 cycles, wherein each cycle con¬ sisted of salt spray testing according to JIS-Z 2371 for 24 hours followed by exposure to air at 50° C with 70 % relative humidity for 144 hours. After five cycles, the maximum single-side blister width from the cross cut was measured and reported according to the criteria shown in Table 1.

Table 1 EVALUATION DEFINITIONS FOR COMPOSITE CYCLE TESTING

Score Maximum Sin le-Side Blister Width in mm for:

Table 2 reports the quantitative characteristics of the treatment compositions used in each example and com¬ parison example and also reports the results for the paint¬ ing performance testing. The results in Table 2 make it clear that an excellent paint performance was obtained in each of Examples 1 through 7 according to the invention while a satisfactory paint performance was not obtained in the case of Comparison Examples 1 through 4.

Table 2. Treatment bath compositions and painting performances for the examples and comparison examples

(Table 2 is continued on the next page) Table 2. Treatment bath compositions and painting performances for the examples and comparison examples

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fTable 2 is continued on the next page) Table 2. Treatment bath compositions and painting performances for the examples and comparison examples

(continued from previous page)

Claims

1. An aqueous liquid composition of matter comprising water and:

(A) a source of zinc ions to provide from 0.4 to 2.5 g/L of zinc(II) ions,

(B) a source of nickel ions to provide from 0.5 to 3.5 g/L of nickel(II) ions,

(C) a source of manganese ions to provide from 0.4 to 2.0 g/L manganese(II) ions, (D) a source of phosphate ions to provide at least 8 g/L of phosphate ions,

(E) a source of nitrate ions to provide from 2.0 to 20 g/L of nitrate ions,

(F) a source of nitrite ions to provide from 10 to 250 ppm of nitrite ions,

(G) not more than 1,000 ppm of aluminum ions, and

(H) a source of fluoride and/or complex fluoride ions to provide from 10 to 3,500 ppm total fluorine, said aqueous liquid composition having a nickel ion to aluminum ion molar ratio that is at least 1.6, a total fluorine to aluminum ion molar ratio that is at least 5.0, and a nickel ion to total fluorine molar ratio that is at least 0.3.

2. A composition according to claim 1, wherein the con- centration of phosphate ions is not more than 20 g/L and the concentration of aluminum ions is at least 1 ppm.

3. A composition according to claim 2, having a free acid concentration in the range from 0.1 to 1.5 points.

4. A composition according to claim 1, having a free acid concentration in the range from 0.1 to 1.5 points.

5. A process for applying a protective coating including a phosphate conversion coating layer to a metal surface selected from the group consisting of aluminum, zinc, and iron, said process comprising a step of contacting said metal surface with an aqueous liquid composition of matter comprising water and: (A) a source of zinc ions to provide from 0.4 to 2.5 g/L of zinc(II) ions,

(B) a source of nickel ions to provide from 0.5 to 3.5 g/L of nickel(II) ions, (C) a source of manganese ions to provide from 0.4 to 2.0 g/L manganese(II) ions,

(D) a source of phosphate ions to provide at least 8 g/L of phosphate ions,

(E) a source of nitrate ions to provide from 2.0 to 20 g/L of nitrate ions,

(F) a source of nitrite ions to provide from 10 to 250 ppm of nitrite ions,

(G) not more than 1,000 ppm of aluminum ions, and

6. A process according to claim 5, wherein, in said aque¬ ous liquid composition, the concentration of phosphate ions is not more than 20 g/L and the concentration of aluminum ions is at least 1 ppm.

7. A process according to claim 6, wherein said aqueous liquid composition has a free acid concentration in the range from 0.1 to 1.5 points.

8. A process according to claim 5, wherein said aqueous liquid composition has a free acid concentration in the range from 0.1 to 1.5 points.

9. A process according to claim 8, wherein said metal surface is contacted with said composition at a temperature in the range from 25 - 55 ° C.

10. A process according to claim 7, wherein said metal surface is contacted with said composition at a temperature in the range from 25 - 55 ° C.

11. A process according to claim 6, wherein said metal surface is contacted with said composition at a temperature in the range from 25 - 55 ° C.

12. A process according to claim 5, wherein said metal surface is contacted with said composition at a temperature in the range from 25 - 55 ° C.

13. A process according to claim 12, wherein said metal surface has a first portion consisting of aluminum and a second portion consisting of iron, zinc, or both iron and zinc.

14. A process according to claim 11, wherein said metal surface has a first portion consisting of aluminum and a second portion consisting of iron, zinc, or both iron and zinc.

15. A process accordi.ng to clai.m 10, wherei.n sai.d metal surface has a first portion consisting of aluminum and a second portion consisting of iron, zinc, or both iron and zinc.

16. A process according to claim 9, wherein said metal surface has a first portion consisting of aluminum and a second portion consisting of iron, zinc, or both iron and zinc.

17. A process according to any one of claims 5 - 16, comprising a step of covering the phosphate conversion coating formed with an electrodeposited paint.