US20040112471A1

US20040112471A1 - Aqueous surface conditioner and surface conditioning method for phospating treatment

Info

Publication number: US20040112471A1
Application number: US10/250,527
Authority: US
Inventors: Yoshio Moriya; Arata Suda; Yasushi Takagi
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2001-01-09
Filing date: 2002-01-08
Publication date: 2004-06-17

Abstract

An aqueous surface conditioner for use in a phosphating treatment is provided which contains crystals having an average diameter of 5 μm or less in an amount of at least 0.1 g/L. The crystals are selected to have a two-dimensional epitaxy that matches within 3% of misfit with the crystal lattice of one phosphate coating selected from among (1) hopeite/Zn₃(PO₄)₂.4H₂O) and/or phosphophyllite (Zn₂Fe(PO₄)₂.4H₂O), (2) scholzite (CaZn₂(PO₄)₂.2H₂O) and (3) hureaulite (Mn₅(PO₄)₂[PO₃(OH]₂.4H₂O).

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an aqueous surface conditioner for use in a phosphate coating treatment performed on the surface of a metal material such as a sheet of iron, steel, zinc-plated steel, or aluminum in order to promote the chemical conversion reaction and shorten the duration thereof and to achieve greater fineness of the crystals that make up the phosphate coating. The invention also relates to a method for the surface conditioning of a metal material.

2. Discussion of the Related Art

The formation of fine and closely-spaced phosphate coating crystals on a metal surface has become necessary today in order to improve corrosion resistance after painting in the phosphating treatments performed on automobiles and to extend the life of pressing molds or reduce friction during pressing in phosphating treatments used for plastic working. In view of this, a surface conditioning step is carried out prior to a phosphate coating chemical conversion step for the purpose of activating the metal surface so that fine and closely-spaced phosphate coating crystals will be obtained and creating nuclei for the deposition of phosphate coating crystals. The following is a typical example of a phosphate coating chemical conversion process performed in order to obtain fine and closely-spaced phosphate coating crystals.

(1) degreasing

(2) multi-stage water rinsing

(3) surface conditioning

(4) phosphate coating chemical conversion treatment

(5) multi-stage water rinsing

(6) pure water rinsing

Surface conditioning is performed in order to make phosphate coating crystals finer and more closely-spaced. Compositions with this aim have been discussed in U.S. Pat. Nos. 2,874,081, 2,322,349, and 2,310,239, for example, and examples of the main constituent components of the surface conditioner include titanium, pyrophosphoric acid ions, orthophosphoric acid ions, and sodium ions. The above-mentioned surface conditioning compositions are called “Jernstedt salts,” and titanium ions and titanium colloids are included in aqueous solutions thereof. A metal that has been degreased and rinsed with water is immersed in an aqueous solution of one of the above-mentioned surface conditioning compositions, or a phosphating treatment surface conditioner is sprayed onto the metal, causing the titanium colloid to be adsorbed to the metal surface. The adsorbed titanium colloid forms the nuclei for phosphate coating crystal precipitation in the subsequent phosphate coating chemical conversion step, which promotes the chemical conversion reaction and makes the phosphate coating crystals finer and more closely-spaced. All of the surface conditioning compositions in industrial use today make use of Jernstedt salts. Various problems have been encountered, however, when a titanium colloid obtained from a Jernstedt salt is used in a surface conditioning process.

The first of these problems is that the phosphating treatment surface conditioner deteriorates over time. When a conventional surface conditioning composition is used, this composition is extremely effective in terms of making the phosphate coating crystals finer more closely-spaced immediately after an aqueous solution is produced. However, the titanium colloid agglomerates a few days after the aqueous solution is prepared. The phosphating treatment surface conditioner loses its effect within this time regardless of whether it has been used or not, and the phosphate coating crystals that are obtained end up being coarse.

Japanese Laid-Open Patent Application S63-76883 proposes a method for measuring the average particle diameter of the titanium colloid in a phosphating treatment surface conditioner, continuously discarding the phosphating treatment surface conditioner so that the average particle diameter will be less than a specified value, and supplying fresh surface conditioning composition in an amount corresponding to the discarded amount, thereby maintaining the surface conditioning effect at a constant level. However, while this method does allow the effect of the phosphating treatment surface conditioner to be maintained quantitatively, the phosphating treatment surface conditioner has to be discarded for the effect to be maintained. Also, a large quantity of phosphating treatment surface conditioner must be discarded with this method in order to keep the effect of the phosphating treatment surface conditioner at the same level as when the aqueous solution was first produced. Therefore, in actual practice, the wastewater treatment capacity of the plant where this method is used also comes into question, so the effect is maintained through a combination of continuous discarding and complete replacement of the phosphating treatment surface conditioner.

The second problem is that the effect and service life of a phosphating treatment surface conditioner are greatly affected by the hardness of the water used during replenishment. Industrial water is usually used for replenishing a phosphating treatment surface conditioner. As is commonly known, though, industrial water contains calcium, magnesium, and other such cationic components that are the source of the total hardness, although the amounts contained can vary greatly depending on the source of the industrial water. It is known that the titanium colloid that is the main component of a conventional phosphating treatment surface conditioner takes on an anionic charge in an aqueous solution, and the electrical repulsion thereof disperses the colloid and keeps it from settling. Therefore, if cationic components such as calcium or magnesium are present in large quantity in industrial water, the titanium colloid will be electrically neutralized by the cationic components, the repulsive force will be lost, agglomeration and settling will occur, and the effect of the colloid will be lost.

In view of this, a method has been proposed in which a condensed phosphate such as a pyrophosphate is added to a phosphating treatment surface conditioner for the purpose of sequestering the cationic components and maintaining the stability of the titanium colloid. Unfortunately, when a large quantity of condensed phosphate is added to a phosphating treatment surface conditioner, the condensed phosphoric acid reacts with the surface of a steel sheet and forms an inert film, which results in poor chemical conversion in the subsequent phosphate coating chemical conversion process. Also, in locales where the calcium or magnesium content is extremely high, purified water must be used for supplying and replenishing the phosphating treatment surface conditioner, which is a major drawback in terms of cost.

The third problem is that the temperature and pH are limited in their range. Specifically, if the temperature is over 35° C. and the pH is outside a range of 8.0 to 9.5, the titanium colloid will agglomerate and lose its surface conditioning effect. Therefore, the predetermined temperature and pH range must be used with a conventional surface conditioning composition, and the surface conditioning composition cannot be added to a degreasing agent or the like so that the effect of cleaning and activating a metal surface will be obtained with a single liquid over an extended period of time.

The fourth problem is that there is a limit to how fine phosphate coating crystals can be made through the effect of a phosphating treatment surface conditioner. The surface conditioning effect is obtained by causing the titanium colloid to adsorb to a metal surface and form the nuclei during phosphate coating crystal precipitation. Therefore, the more titanium colloid particles are adsorbed to the metal surface in the surface conditioning step, the finer and more closely-spaced the resulting phosphate coating crystals will be. The most obvious way to achieve this would be increase the number of titanium colloid particles in the phosphating treatment surface conditioner, that is, raise the titanium colloid concentration. When the concentration is increased, however, there is an increase in the frequency of collision between the titanium colloid particles in the phosphating treatment surface conditioner, and these collisions cause the titanium colloid to agglomerate and settle. The upper limit to the concentration of titanium colloids currently being used is 100 ppm or less (as titanium in the phosphating treatment surface conditioner), and it has been impossible to make phosphate coating crystals finer by increasing the titanium colloid concentration over this level.

In view of this, Japanese Laid-Open Patent Applications S56-156778 and S57-23066 disclose a surface conditioning method in which a suspension containing an insoluble phosphate of a divalent or trivalent metal is sprayed under pressure onto the surface of a steel strip as a surface conditioner other than a Jernstedt salt. With this surface conditioning method, however, the effect is only realized when the suspension is sprayed under pressure onto the target material, so this method cannot be used for surface conditioning in a phosphate coating chemical conversion treatment performed by ordinary dipping or spraying.

Japanese Patent Publication S40-1095 discloses a surface conditioning method in which a zinc plated steel sheet is dipped in a high-concentration suspension of an insoluble phosphate of a divalent or trivalent metal. The examples given for this method, however, are limited to a zinc plated steel sheet, and obtaining a surface conditioning effect requires the use of a high-concentration insoluble phosphate suspension of no less than 30 g/L.

Therefore, even though various problems associated with Jernstedt salts have been indicated, so far no one has proposed a new technique to replace them.

Also, because the mechanism by which these salts act is not clear, it is uncertain on which substances these salts will have a surface conditioning effect, and searching for these substances entailed a tremendous amount of labor.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the above-mentioned problems and provide a novel phosphating treatment surface conditioner that has excellent stability over time and is used to promote the chemical conversion reaction and shorten the duration thereof in a phosphate coating chemical conversion treatment, and to reduce the size of the resulting phosphate coating crystals.

The inventors examined means for solving the above problems, and closely studied the mechanism by which surface conditioners function. This led to the discovery that in the course of producing a phosphate coating, the coating components reach a state of supersaturation as the metal dissolves. The most important effect of a surface conditioner is that the crystals it produces function as nuclei for phosphate coating crystals. The performance of a surface conditioner is determined by how effectively it can act as crystal nuclei. In other words, the inventors found that crystals with a lattice constant close to that of phosphate coating crystals function as pseudo-crystal nuclei, resulting in a surface conditioning effect. Further research in this area led to the perfection of the present invention.

Specifically, the present invention relates to an aqueous surface conditioner for use in a phosphating treatment, which contains crystals having an average diameter of 5 μm or less in an amount of at least 0.1 g/L, said crystals having a two-dimensional epitaxy that matches within 3% of misfit with the crystal lattice of one phosphate coating selected from among (1) hopeite (Zn ₃(PO₄)₂.4H₂O) and/or phosphophyllite (Zn₂Fe(PO₄)₂.4H₂O), (2) scholzite (CaZn₂(PO₄)₂.2H₂O), and (3) hureaulite (Mn₅(PO₄)₂[PO₃(OH)]₂.4H₂O).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a concept diagram in which a LaMer diagram is applied to a surface conditioner (crystal growth steps); [0025]
FIG. 2 shows the unit crystal lattices for hopeite (zinc phosphate) and magnesium hydrogenphosphate; and [0026]
FIG. 3 is a diagram in which unit crystal lattices of hopeite have been arranged, with the grid-shaped solid line portion being a view of these crystal lattices viewed perpendicular to the (020) plane, and the dashed line portion being the unit crystal lattices of magnesium hydrogenphosphate arranged over these.[0027]

DETAILED DESCRIPTION OF THE INVENTION

In terms of how they are produced, phosphate coating crystals can be described by a LaMer diagram that shows the process in which crystals precipitate from a solution as a result of increased concentration. In general, as the solute concentration rises, crystal precipitation will not occur as soon as the saturation concentration is exceeded, and crystal production occurs only when the crystal nucleus production concentration C*[0028] _minis reached, after which the crystals grow, so the solute concentration decreases. Phosphate coating crystals are believed to precipitate through the same process, and this corresponds to when no surface conditioner is used (corresponds to the solid line portion in FIG. 1). In this case, crystal nuclei are produced only in the shaded area in FIG. 1. Because there are few crystal nuclei, the crystal coating is often coarse, and it takes a long time for the coating production reaction to conclude.
In contrast, when a surface conditioner is used, because the titanium colloid particles or the like that constitute this component function as pseudo-nuclei for the phosphate coating crystals, crystal growth already begins at a concentration C*x that is lower than the crystal nucleus production concentration C*[0029] _min. In this case, the number of crystal nuclei is determined by the number of titanium colloid particles or the like contained in the surface conditioner, so closely-spaced coating crystals can be produced by increasing the number of these particles. As shown in FIG. 1, the coating crystals are produced in a short time, so the phosphate chemical conversion treatment does not take as long. Here, the closer the concentration C*_xat which crystal growth commences on the pseudo-crystal nuclei is to the saturation concentration C_S, the less time it will take to produce the coating, so efficiency is higher.
Because of all this, substances capable of become pseudo-crystal nuclei in a surface conditioner were closely examined. [0030]
As a result, it was confirmed that when the phosphate coating is comprised mainly of hopeite and/or phosphophyllite, a surface conditioning effect will be observed with crystals of magnesium hydrogen phosphate (MgHPO[0031] ₄.3H₂O), zirconium oxide (ZrO₂), zinc oxalate (Zn(COO)₂), cobalt oxalate (Co(COO)₂), iron orthosilicate (Fe₂SiO₄), iron metasilicate (FeSiO₃), and magnesium borate (Mg₃(BO₃)₂); when the phosphate coating is comprised mainly of scholzite, this effect will be observed with crystals of anhydrous cobalt phosphate (CO₃(PO₄)₂), anhydrous zinc phosphate (γ-Zn₃(PO₄)₂), anhydrous zinc magnesium phosphate (Zn₂Mg(PO₄)₂), anhydrous zinc cobalt phosphate (γ-Zn₂Co(PO₄)₂), and anhydrous zinc iron phosphate (γ-Zn₂Fe(PO₄)₂); and when the phosphate coating is comprised mainly of hureaulite, this effect will be observed with crystals of calcium orthosilicate (Ca₂SiO₄.H₂O), calcium metaphosphate (Ca₃(PO₃)₆.10H₂O), and manganese(II) metaphosphate (Mn₃(PO₃)₆.10H₂O). The term “mainly” as used above means that the hopeite and/or phosphophyllite; scholzite; or hureaulite accounts for at least 50 mass %, and preferably at least 70 mass %, of the phosphate coating. These surface conditioning substances can be used singly or in combinations of two or more types according to the corresponding phosphate coating.
The inventors turned their attention to the lattice constant of the crystals of these surface conditioning substances, and found it to be close to the lattice constant of the phosphate coating crystals. If the crystal structures are similar, this means that these substances will be effective as pseudo-crystal nuclei; this is known as epitaxy. [0032]
Manmade rain is often given as an example of epitaxy. When a micropowder of silver bromide is scattered in water vapor that is supersaturated and supercooled, the silver bromide becomes the nuclei for the growth of ice crystals, resulting in rain. This phenomenon occurs because the lattice constant of the silver bromide crystals is extremely close to the lattice constant of ice, and the growth on one type of crystal of a different type of crystal with a similar lattice constant is known in the semiconductor field as epitaxial growth. [0033]
The inventors noted a surface conditioning effect in many different substances, and as a result learned that, as mentioned above, a substance that has a surface conditioning effect on a phosphate coating is a substance whose epitaxy closely matches that of the phosphate coating crystals. [0034]
The matching of epitaxy will now be discussed in detail. [0035]
FIG. 2 shows the unit lattice of hopeite (Zn[0036] ₃(PO₄)₂.4H₂O). The grid-shaped solid line portion in FIG. 3 is a view of these crystal lattices arranged and viewed perpendicular to the (020) plane. The dashed line portion in FIG. 3 illustrates the unit lattices of magnesium hydrogenphosphate (MgHPO₄.3H₂O) arranged over these, and the lattices match up well. Actually, zinc phosphate is deposited over magnesium hydrogenphosphate, and as long as there is a good match between the lattices as above, the crystals will seat well and grow readily. There is a certain amount of lattice misalignment in this example as well, and this is called misfit. In this example, the a axis of the zinc phosphate versus the b axis of the magnesium hydrogenphosphate is 10.6845/10.6067Å=1.0073, so the misfit is 0.7%. Similarly, the c axis of the magnesium hydrogenphosphate versus double the c axis of the zinc phosphate is 10.0129/(5.0284×2)=0.9956, so the misfit is −0.4%.
Naturally, the smaller the misfit, the better the match between the crystal lattices. What should be noted here is that the integer multiples of one lattice constant may also match another, and all plane combinations must be taken into account. [0037]
If we thus calculate the misfit in a two-dimensional plane for all plane combinations, we find that substances with a surface conditioning effect all have a two-dimensional misfit within 3%. [0038]
Table 1 is an example of calculating the misfit for the above-mentioned surface conditioning substances used when a zinc phosphate coating is hopeite and/or phosphophyllite (Zn[0039] ₂Fe(PO₄)₂.4H₂O). The two-dimensional misfit was within 3% in every case, and a surface conditioning effect was observed.
Furthermore, no surface conditioning effect was observed with substances in which the misfit was over 3%. [0040]
It is known that a zinc phosphate coating contains not only hopeite but also a large amount of phosphophyllite. Phosphophyllite has a crystal structure that is extremely similar to that of hopeite, and the crystal lattices are also very close, so the two precipitate as mixed crystals. [0041]
The above description of epitaxy was for when a zinc phosphate coating is produced, but the same applies to when the coating produced is scholzite or hureaulite. The misfit should be calculated by taking into account all possible arrangement combinations of the crystal lattice of scholzite or hureaulite instead of the crystal lattice of the zinc phosphate shown in FIG. 2. [0042]
Table 2 is an example of calculating the misfit for the above-mentioned surface conditioning substances used when a zinc phosphate coating is scholzite. The two-dimensional misfit was within 3% in every case, and a surface conditioning effect was observed when a scholzite coating was produced. [0043]
Table 3 is an example of calculating the misfit for the above-mentioned surface conditioning substances used when a zinc phosphate coating is hureaulite. The two-dimensional misfit was within 3% in every case, and a surface conditioning effect was observed when hureaulite was produced. [0044]
It is preferable for the two-dimensional misfit to be within 2.5%, whether with (1) hopeite and/or phosphophyllite, (2) scholzite, or (3) hureaulite. [0045]
The average diameter of the crystals of these surface conditioning substances must be no more than 5 μm, and 1 μm or less is preferable. The surface conditioning effect will be weak if the average diameter is over 5 μm. [0046]
There are no particular restrictions on the concentration of these crystals in the surface conditioner of the present invention, but the crystals must be contained in an amount of at least 0.1 g/L, with 0.1 to 50 g/L being preferable, and 1 to 5 g/L being even better. The surface conditioning effect will be inadequate if the amount is less than 0.1 g/L, but no further effect will be obtained by exceeding 50 g/L, so this would merely be a waste of money. [0047]
Another essential component of the surface conditioner of the present invention is water. This water may be purified water, tap water, or industrial water. The above-mentioned surface conditioning substances are usually suspended in water. If needed, a dispersant may be used to suspend the substances. [0048]
A monosaccharide, oligosaccharide, polysaccharide, etherified monosaccharide, etherified oligosaccharide, etherified polysaccharide, water-soluble macromolecular compound, or the like can be used as a dispersant. Examples of monosaccharides include glucose, fructose, mannose, galactose, and ribose; examples of oligosaccharides include sucrose, maltose, lactose, trehalose, and maltotriose; examples of polysaccharides include starch, dextrin, dextran, and glycogen; examples of etherified monosaccharides, oligosaccharides, and polysaccharides include compounds obtained by etherifying the hydroxyl groups of the constituent monosaccharides with substituents such as —NO[0049] ₂, —CH₃, —C₂H₄OH, —CH₂CH(OH)CH₃, and —CH₂COOH; and examples of water-soluble macromolecular compounds include polyvinyl acetate, partially hydrolyzed polyvinyl acetate, polyvinyl alcohol, polyvinyl alcohol derivatives (such as cyanoethylated acrylonitrile, acetalated formaldehyde, urethanated urea, and derivatives in which carboxyl groups, sulfone groups, amide groups, or the like have been introduced), and copolymers of vinyl acetate with copolymerizable monomers (such as acrylic acid, crotonic acid, and maleic anhydride).
There are no particular restrictions on the concentration of the dispersant as long as the amount is sufficient to disperse the crystals used in the present invention, but the concentration is usually 1 to 2000 ppm. [0050]
The material to be conditioned with the surface conditioner of the present invention is any metal material that will undergo a phosphate chemical conversion treatment, examples of which include steel, zinc and zinc plated materials, materials plated with zinc alloys, aluminum and aluminum plated materials, and magnesium. [0051]
The surface conditioner of the present invention is usually applied after the metal material has been degreased and rinsed with water, but this is not necessarily the case. The surface conditioning performed with the surface conditioner of the present invention is performed by bringing this conditioner into contact with the surface of a metal material for at least 1 second. More specifically and preferably, the metal material is either immersed in the conditioner for about 10 seconds to 2 minutes, or the conditioner is sprayed onto the metal material for about 10 seconds to 2 minutes. This treatment is ordinarily carried out with the surface conditioner at normal ambient temperature (i.e., about 15° C. to about 30° C.), but can be carried out at anywhere between normal temperature and about 80° C. Any of a great number of substances can be selected with the present invention as dictated by the intended application, so it is also possible to disperse these crystals in a degreasing agent, and perform the degreasing and surface conditioning at the same time. In this case the treatment is usually performed by immersion or spraying for about 1 to 3 minutes at 50 to 80° C. [0052]

EXAMPLES

Next, examples and comparative examples will be used to describe in detail the effect of applying the phosphating treatment surface conditioner of the present invention. A zinc phosphate-based treatment for automobiles is given as an example of a phosphating treatment, but the applications of the aqueous surface conditioner for use in a phosphating treatment pertaining to the present invention are not limited to this example. All instances of “%” below indicate mass %. [0053]
Test Sheets [0054]
The abbreviations for an descriptions of the test sheets used in the examples and comparative examples are given below. [0055]
SPC: cold rolled steel sheet, JIS G 3141 [0056]
EG: double-sided electrogalvanized steel sheet, plating basis weight: 20 g/m[0057] ²
Al: aluminum sheet, JIS 5052 [0058]
Alkali Decreasing Solution [0059]
FAINCLEANA L4460 (registered trademark of Nihon Parkerizing Co., Ltd.) was diluted to 2% with tap water and used in both the examples and the comparative examples. [0060]
Zinc Phosphate Treatment Solution [0061]
PALBOND L3020 (registered trademark of Nihon Parkerizing Co., Ltd.) was diluted with tap water, adjusted to a component concentration of 4.8%, 23 point total acidity, 0.9 point free acidity, and 3 point accelerator, and used in both the examples and the comparative examples (these concentrations are commonly used today in automotive zinc phosphate treatments). [0062]
The overall treatment process will now be discussed. [0063]
Treatment Steps [0064]
(1) alkali degreasing, 42° C., spraying for 120 seconds [0065]
(2) water rinsing, room temperature, spraying for 30 seconds [0066]
(3) surface conditioning, room temperature, immersion for 20 seconds [0067]
(4) zinc phosphate treatment, 42° C., immersion for 120 seconds [0068]
(5) water rinsing, room temperature, spraying for 30 seconds [0069]
(6) deionized water rinsing, room temperature, spraying for 30 seconds [0070]
Surface Conditioner [0071]
The method for preparing the phosphating treatment surface conditioner used in the examples will now be discussed. [0072]

Example 1

A magnesium hydrogenphosphate (MgHPO[0073] ₄.3H₂O) reagent was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder whose epitaxy matched within 3%. This powder was suspended in purified water and then filtered through a 5 μm paper filter. The magnesium hydrogenphosphate concentration was adjusted to 5 g/L, and this product was used as a surface conditioner.

Example 2

A zinc oxalate dihydrate (Zn(COO)[0074] ₂.2H₂O) reagent was baked for 1 hour at 200° C. and then analyzed with an X-ray analyzer, which confirmed it to be zinc oxalate (Zn(COO)₂). This was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder whose epitaxy matched within 3%. This powder was suspended in purified water and then filtered through a 5 μm paper filter. The zinc oxalate concentration was adjusted to 5 g/L, and this product was used as a surface conditioner.

Example 3

A cobalt oxalate dihydrate (Co(COO)[0075] ₂.2H₂O) reagent was baked for 1 hour at 200° C. and then analyzed with an X-ray analyzer, which confirmed it to be cobalt oxalate (Co(COO)₂). This was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder whose epitaxy matched within 3%. This powder was suspended in purified water and then filtered through a 5 μm paper filter. The cobalt oxalate concentration was adjusted to 5 g/L, and this product was used as a surface conditioner.

Example 4

12.3 g of a boric acid (H[0076] ₃BO₃) reagent and 12.1 g of a magnesium oxide (MgO) reagent were ground together in a mortar and then baked for 1 hour at 1000° C. This product was analyzed with an X-ray analyzer, which confirmed it to be magnesium borate (Mg₃(BO₃)₂). Unreacted boron oxide (B₂O₃) and magnesium oxide (MgO) were detected as impurities in this product. This was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder whose epitaxy matched within 3%. This powder was suspended in purified water and then filtered through a 5 μm paper filter. The magnesium borate concentration was adjusted to 5 g/L, and this product was used as a surface conditioner.

Example 5

10 g of zirconia sol NZS-30B made by Nissan Chemical Industries, Ltd. (a suspension containing 30% zirconium oxide fines with a diameter of 70 nm) was diluted to [0077]
1 L and used as a crystal material whose epitaxy matched within 3%. The product adjusted in this manner was used as a surface conditioner. [0078]

Comparative Example 1

A silicon dioxide (SiO[0079] ₂) reagent was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder. This powder was suspended in purified water and then filtered through a 5 μm paper filter. The silicon dioxide concentration was adjusted to 5 g/L, and this product was used as a surface conditioner.

Comparative Example 2

A magnesium oxide (MgO) reagent was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder. This powder was suspended in purified water and then filtered through a 5 μm paper filter. The magnesium oxide concentration was adjusted to 5 g/L, and this product was used as a surface conditioner. [0080]

Comparative Example 3

This is an example of not using a surface conditioner. Specifically, the surface conditioning (3) was omitted from the above-mentioned treatment steps. [0081]
Painting And Evaluation Steps [0082]
In the examples and the comparative examples, each test sheet that had undergone the above-mentioned zinc phosphate treatment steps (1) to (6) was painted with a cationic electrodeposition paint (ELECRON 2000, made by Kansai Paint) in a film thickness of 20 μm. This was baked for 25 minutes at 180° C., after which an intermediate coat (automotive-use intermediate coat made by Kansai Paint) was applied such that the intermediate coat thickness would be 40 μm, and this was baked for 30 minutes at 140° C. Each test sheet that had been given an intermediate coat was then given a top coat (automotive-use top coat made by Kansai Paint) in a top coat thickness of 40 μm, which was then baked for 30 minutes at 140° C. The triple-coated sheet with a total film thickness of 100 μm thus obtained was subjected to a saltwater spray test. [0083]
Method For Evaluating Zinc Phosphate Coating [0084]
(1) Appearance [0085]
Each sheet was examined visually and checked for unevenness or thin paint in the zinc phosphate coating. The evaluation was given as follows. [0086]
⊚ uniformly good appearance [0087]
◯ some unevenness [0088]
Δ unevenness and thin paint present [0089]
X severe thin paint [0090]
(2) Coating Weight (CW) [0091]
The mass of the treated sheet after the chemical conversion was measured (referred to as W1 (g)), then the chemical conversion treated sheet was subjected to a coating removal treatment with the stripper and stripping conditions given below, the mass of this product was measured (referred to as W2 (g)), and the coating weight was calculated using Formula I. [0092]
With a cold rolled steel sheet [0093]
stripper: 5% chromic acid aqueous solution [0094]
stripping conditions: 75° C., 15 min., immersion stripping [0095]
With a galvanized sheet [0096]
stripper: ammonium dichromate (2 mass %)+28% aqueous ammonia (49 mass %)+pure water (49 mass %) [0097]
Coating mass (g/m[0098] ²)=(W1-W2)/0.021 Formula (I)
Method For Evaluating Paint Film [0099]
The paint film was evaluated by the method given below in both the examples and the comparative examples. [0100]
(1) Saltwater Spray Test (JIS Z 2371) [0101]
An electropainted sheet in which cross-cuts had been made was sprayed for 960 hours with 5% saltwater. Upon completion of the spraying, the maximum width that peeled from the cross-cuts on one side was measured, and an evaluation was made. [0102]
Table 4 shows the characteristics of a chemical conversion coating obtained in a zinc phosphate treatment using the various phosphating treatment-use aqueous surface conditioners of the examples and comparative examples, and shows the results of a performance evaluation conducted after painting. A dash (-) in Table 4 means that the coating mass was not measured because the coating was not deposited properly. [0103]
It was confirmed from the results in Table 4 that the phosphating treatment aqueous surface conditioners whose epitaxy was within 3%, which were the products of the present invention, had a surface conditioning effect. [0104]
On the other hand, calculation of the epitaxy for SiO[0105] ₂and hopeite (Comparative Example 1) revealed the misfit to be SiO₂(a)/hopeite (c)=4.9732/5.0284=0.989, and SiO₂(c)/hopeite (a)=6.9236/10.6067=0.653, so the misfit was −1.1% and −34.7%.
Similarly, in Comparative Example 2, MgO (a)/hopeite (c)=4.213/5.0284=0.838, and MgO (a)×2/hopeite (a)=8.426/10.6067=0.794, so the misfit was −16.2% and −20.6%. (MgO is a cubic crystal, so only the a axis was used.) [0106]

Thus, it was confirmed that there was no surface conditioning effect with the comparative examples, in which the misfit was large and the epitaxy was different.

TABLE 1


Example of calculating misfit for hopeite

MgHPO₄.3H₂O	Zn₃(PO₄)₂.4H₂O	Misfit	ZrO₂	Zn₃(PO₄)₂.4H₂O	Misfit
b = 10.6845	a = 10.6067	+0.7%	a × 2 = 10.6258	a = 10.6067	+0.2%
c = 10.0129	c × 2 = 10.0568	−0.4%	c × sinβ = 5.0806	C = 5.0284	+1.0%
Fe₂SiO₄	Zn₃(PO₄)₂.4H₂O	Misfit	FeSiO₃	Zn₃(PO₄)₂.4H₂O	Misfit
b = 10.4805	a = 10.6067	−1.2%	c × 2 = 10.486	a = 10.6067	−1.1%
a × 3 = 18.2706	b = 18.3004	−0.2%	a = 18.418	b = 18.3004	+0.6%
Zn(COO)₂	Zn₃(PO₄)₂.4H₂O	Misfit	Co(COO)₂	Zn₃(PO₄)₂.4H₂O	Misfit
c × 2 = 10.662	a = 10.6067	+0.5%	c × 2 = 10.796	a = 10.6067	+1.8%
b = 5.123	c = 5.0284	+1.9%	b = 5.03	c = 5.0284	+1.9%
Mg₃(BO₃)₂	Zn₃(PO₄)₂.4H₂O	Misfit
a × 2 = 10.8028	a = 10.6067	+1.8%
c × 4 = 18.0284	b = 18.3004	−1.5%

TABLE 2


Example of calculating misfit for schoizite

Co₃(PO₄)₂	CaZn₂(PO₄)₂.2H₂O	Misfit	γ-Zn₃(PO₄)₂	CaZn₂(PO₄)₂.2H₂O	Misfit
b × 2 = 16.73	a = 17.12	−2.3%	b × 2 = 16.998	a = 17.12	−0.7%
a × 3 = 22.671	b = 22.20	+2.1%	a × 3 = 22.647	b = 22.20	+2.0%
γ-Zn₂(PO₄)₂	CaZn₂(PO₄)₂.2H₂O	Misfit	Zn₂Mg(PO₄)₂	CaZn₂(PO₄)₂.2H₂O	Misfit
b × 2 = 16.826	a = 17.12	−1.7%	b × 2 = 16.71	a = 17.12	−2.4%
a × 3 = 22.608	b = 22.20	+1.8%	a × 3 = 22.707	b = 22.20	+2.3%
γ-Zn₂Fe(PO₄)₂	CaZn₂(PO₄)₂.2H₂O	Misfit
b × 2 = 17.08	a = 17.12	−0.2%
a × 3 = 22.689	b = 22.20	+2.2%

TABLE 3


Example of calculating misfit for hureaulite

Ca₂SiO₄.H₂O	Mn₅(PO₄)₂(HPO₄)₂.4H₂O	Misfit	Ca₃(PO₃)₆.10H₂O	Mn₅(PO₄)₂(HPO₄)₂.4H₂O	Misfit
b = 9.198	b = 9.1172	+0.9%	a = 9.332	c = 9.482	−1.6%
a = 9.476	c = 9.482	−0.1%	b = 18.13	b × 2 = 18.2344	−0.6%
Mn₃(PO₃)₆.10H₂O	Mn₅(PO₄)₂(HPO₄)₂.4H₂O	Misfit
a = 9.219	b = 9.1172	+1.1%
b = 17.733	a = 17.618	+0.7%

TABLE 4


Type of
material	Example 1	Example 2	Example 3	Example 4	Example 5	Comp. Ex 1	Comp. Ex 2	Comp. Ex 3

Coating	SPC	⊚	◯	◯	⊚	Δ	X	X	X
appearance	EG	⊚	◯	◯	⊚	◯	X	X	X
	A1	⊚	◯	◯	⊚	Δ	X	X	X
Coating weight	SPC	2.1	2.3	2.2	2.0	2.5	—	—	—
(g/m²)	EG	2.4	2.2	2.3	2.3	2.6	—	—	—
	A1	1.7	1.6	1.6	1.5	1.8	—	—	—
Saltwater spray	SPC	1.0	2.0	2.5	1.0	4.0	5.0 or more	5.0 or more	5.0 or more
test of painted	EG	2.0	3.5	3.0	2.5	4.0	5.0 or more	5.0 or more	5.0 or more
sheet (max. peel	A1	0.5 or less	1.0	1.0	0.5 or less	1.0	2.5	2.0	2.5
width in mm)

Claims

What is claimed is:

1. An aqueous surface conditioner for use in a phosphating treatment comprising crystals having an average diameter of 5 μm or less in an amount of at least 0.1 g/L, said crystals having a two-dimensional epitaxy that matches within 3% of misfit with the crystal lattice of a phosphate coating comprising one or more species selected from the group consisting of hopeite (Zn₃(PO₄)₂.4H₂O), phosphophyllite (Zn₂Fe(PO₄)₂.4H₂O), scholzite (CaZn₂(PO₄)₂.2H₂O), and hureaulite (Mn₅(PO₄)₂[PO₃(OH)]₂.4H₂O).

2. The aqueous surface conditioner for use in a phosphating treatment according to claim 1, wherein the phosphate coating is comprised mainly of hopeite, phosphophyllite or a mixture of hopeite and phosphophyllite and the crystals are selected from the group consisting of magnesium hydrogenphosphate (MgHPO₄.3H₂O), zirconium oxide (ZrO₂), zinc oxalate (Zn(COO)₂), cobalt oxalate (Co(COO)₂), iron orthosilicate (Fe₂SiO₄), iron metasilicate (FeSiO₃), and magnesium borate (Mg₃(BO₃)₂) and mixtures thereof.

3. The aqueous surface conditioner for use in a phosphating treatment according to claim 1, wherein the phosphate coating is comprised mainly of scholzite and the crystals are selected from the group consisting of anhydrous cobalt phosphate (CO₃(PO₄)₂), anhydrous zinc phosphate (γ-Zn₃(PO₄)₂), anhydrous zinc magnesium phosphate (Zn₂Mg(PO₄)₂), anhydrous zinc cobalt phosphate (γ-Zn₂Co(PO₄)₂), anhydrous zinc iron phosphate (γ-Zn₂Fe(PO₄)₂) and mixtures thereof.

4. The aqueous surface conditioner for use in a phosphating treatment according to claim 1, wherein the phosphate coating is comprised mainly of hureaulite, and the crystals are one or more types selected from the group consisting of calcium orthosilicate (Ca₂SiO₄.H₂O), calcium metaphosphate (Ca₃(PO₃)₆. 10H₂O), manganese(II) metaphosphate (Mn₃(PO₃)₆.10H₂O) and mixtures thereof.

5. A method for conditioning a surface of a metal material, comprising contacting the surface of the metal material with the aqueous surface conditioner according to any of claims 1 to 4 prior to subjecting the surface of the metal material to phosphating treatment.