DE3927131A1 - METHOD FOR THE PRODUCTION OF MANGANIZED ZINC PHOSPHATE LAYERS ON GALVANIZED STEEL - Google Patents

Abstract

In a process for phosphatizing electrolytically and/or hot-dip galvanized steel strip, the steel strip is briefly treated with acidic phosphatizing solutions which contain, in addition to zinc and phosphate ions, manganese and nickel cations and anions of oxygen-containing acids with an accelerator effect. The weight ratio of nickel cations to nitrate anions is ajusted to between 1:10 and 1:60 and the weight ratio of manganese cations nitrate anions is adjusted to between 1:1 and 1:40.

Description

The present invention relates to a process for phosphating of electrolytically and / or hot dip galvanized steel strip below Formation of manganese and nickel-containing zinc phosphate layers. These manganese and nickel-containing zinc phosphate layers are Spraying, spray diving and / or dipping with aqueous solutions applied.

Process for phosphating surfaces of iron, steel, zinc and their alloys and aluminum have long been state of the art Technique (Ullmann's Encyklopadie der technischen Chemie, 4th Edition, Volume 15, pages 686 and 687). The phosphating of said Surfaces serve to increase the adhesion of paint layers and to improve the corrosion protection.

From W.A. Roland and K.-H. Gottwald, "metal surface" 42nd year, 1988/6 are manganese-modified zinc phosphate coatings as a liability known for modern finishes. Here is executed that the use of manganese ions in addition to zinc and nickel ions in Low-zinc phosphating demonstrated the corrosion protection improved, especially when using surface-refined Thin sheets. The incorporation of manganese into the zinc phosphate coatings results to smaller and more compact crystals with increased alkali stability. At the same time the working width of Phosphatierbädern elevated; Also aluminum can be combined with steel and electrolytic or hot-dip galvanized steel are layered phosphating, ensuring the generally achieved quality standard is.  

DE 32 45 411 A1 discloses a process for phosphating electrolytically galvanized metal products, in particular electrolytically galvanized steel strips, by short-term treatment with acidic phosphating solutions, which in addition to zinc and phosphate ions may contain further metal cations and / or anions of oxygen-containing acids with accelerating action. In these processes, zinc phosphate layers of weight per unit area are formed below 2 g / m². It works with acidic phosphating solutions whose content of Zn ²⁺ cations is about 1 to 2.5 g / l, while the free acid content in the range of 0.8 to 3 points and the acidity total acid / free acid in the range of 5 to 10 are kept. The duration of treatment should not be significantly higher than 5 s.

Preferably, working with nitrate-containing phosphating, wherein the weight ratio of Zn ²⁺ / NO₃ ^- in the range of 1: 1 to 1: 8 and the weight ratio of PO₄ ^3- / NO₃ ^- in the range of 1: 0.1 to 1: 2, 5 is held.

From EP 01 06 459 A1 a phosphating process is known, formed in the manganese and nickel-containing zinc phosphate coatings become. The presence of fluoride ions is also known as Essentially regarded as the concentration upper limit of 10 g / l Nitrate anions.

From EP 01 12 826 B1 is a high nickel phosphating process known. This is a molar ratio of nickel to zinc in the range of 5.2: 1 to 16: 1 provided.

In addition, from EP 01 75 606 a phosphating process in particular, to the use of ferrous Phosphatierungsbädern is turned off. Furthermore, as  Accelerator used a series of organic substances while the presence of manganese is not required. Furthermore is the setting of certain ratios of zinc to nickel and Zinc to iron demanded.

The phosphating process used today in practice of electrolytically and / or hot-dip galvanized steel strip Restrictions on their disposal are desirable is. This is how it is to ensure adequate corrosion protection deemed necessary, areal masses of Form phosphate deposits of less than 2 g / m². The consequence of a comparatively high basis weight is often one unsatisfactory to poor adhesion of subsequent coatings, especially when phosphated and coated material is deformed. The duration of the phosphating lies in the in the Practice usually used above 2 s, in particular at belt speeds of about 60 to 120 m / min.

It is known that by the application of nickel cations in the Phosphating solutions improved adhesion and corrosion protection values can be achieved. However, this is within the scope of It has been found that an increase in the Nickel concentration, which helps to improve the corrosion protection value leads, at the same time a darkening of the manganese and nickel-containing zinc phosphate layer causes.

The object of the present invention is now, at treatment times from 2 to 30 s while preserving the corrosion protection values a darkening of the zinc phosphate layers to electrolytic and / or hot dip galvanized steel strip. at the same time should the nickel content of known literature on Substitution by manganese can be greatly lowered to one  Corrosion protection and a paint adhesion as in the automotive industry used in the continuous process Band phosphating to achieve. It was self-evident provided that dense, closed layers of phosphate coating be formed at the mentioned treatment times and also the deformation properties are satisfactory. Deliberately while the invention wants to thin support materials of the phosphate layers but without the uniform coverage the galvanized steel strip with a fine crystalline, solid Adhere to an adherent, self-contained zinc phosphate layer have to.

The above objects are achieved by a method for phosphating electrolytically and / or hot dip galvanized Steel strip with formation of manganese and nickel-containing Zinc phosphate coatings by short-term treatment with acidic Phosphating solutions is applied, taking the duration of the treatment 2 to 30 s, the phosphating in the temperature range from 40 to 70 ° C and the phosphating solutions according to the following conditions:

Content of Zn ²⁺ cations: From 0.02 to 0.75 g / l, Content of Mn ²⁺ cations: 0.2 to 2.0 g / l, Content of Ni ²⁺ cations: 0.1 to 2.0 g / l, Content of PO₄ ^3- anions: 10 to 20 g / l, Content of NO₂ ^- anions: 0.5 to 30 g / l, Content of "free acid": in the range of 1.6 to 3.0 points, Content of "total acid": in the range of 12 to 40 points.

Here, the weight ratio of Ni ²⁺ cations to NO₃ ^- - anions in the range of 1:10 to 1: 60 and the weight ratio of Mn ²⁺ cations to NO₃ ^- anions in the range of 1: 1 to 1: 40 set become.

In Chr. Ries, "Monitoring of Phosphating Baths", Electroplating, 59 (1968) No. 1, pages 37-39 (Eugen G. Leuze-Verlag, Saulgau) are both the terms of the parameters mentioned here as also described their destination in detail. The score of the Free acid is accordingly defined as the number ml of 0.1N NaOH used to titrate 10 ml of bath solution against dimethyl yellow, Methyl orange or bromophenol blue is required. The total acid score results as the number ml of 0.1 N NaOH, which in the Titrate 10 ml of bath solution using phenolphthalein is required as an indicator until the first pink coloration.

Accordingly, the combination is for the process according to the invention all mentioned parameters are essential:

The concentration of Zn ²⁺ cations is kept in a very low limited range. Small amounts of zinc ions are added to the treatment bath at the beginning to accelerate the cation balance adjustment. Zinc is known to be quickly dissolved out of the galvanized tape by the acid phosphating solutions. If the zinc content is more than 0.75 g / l, the adhesion of a subsequently applied paint is markedly deteriorated.

If the manganese cation content is less than 0.2 g / l the manganese content in the zinc phosphate layer is so low that the Adhesion between the substrate and the coating after cataphoresis is insufficient. On the other hand, if the manganese content more than 2.0 g / l, no further improved effects for  the subsequent coating can be achieved. However, divorce at elevated manganese concentration from the phosphating solution Precipitation, so that the provision of a stable solution is impossible.

The simultaneous presence of nickel cations and manganese cations causes an exceptionally good paint adhesion as well as extraordinary good corrosion protection values of the zinc phosphate coating after the Lacquer coating.

If the content of phosphate anions of the solution is less than 10 g / l is, a defective zinc phosphate layer is formed. On the other hand, if the phosphate content is more than 20 g / l, then no additional beneficial effects are achieved. The Use of larger amounts of phosphate is thus economical Reasons with disadvantages.

An essential component of the present invention is the weight ratio of nickel cations to nitrate anions and the weight ratio from manganese cations to nitrate anions. As is known, performs the simultaneous use of nickel and manganese cations to improved corrosion protection values, but in the literature method for a dark color of the zinc phosphate layer. Although the coloring of this zinc phosphate layer plays in the automotive industry is not a paramount role, however for example, in the manufacture of household appliances due the following often applied very thin paint layers of Color of zinc phosphate layer of extraordinary importance.

Another essential criterion of the present invention is the treatment time of the phosphating. While in the automotive industry for phosphating usually times above  120 s is used in the phosphating of galvanized Steel band definitely aimed for a time below 1 min. in the The meaning of the present invention is therefore the duration of the treatment between 2 to 30 s. Particularly preferred is a Duration of treatment from 3 to 20 s.

The essential advantage of the present invention is that zinc phosphate coatings on galvanized steel strip according to the invention can be produced which have a bright surface appearance, although they contain nickel. At the same time, however, the salary nickel over the prior art by substitution significantly reduced with manganese without sacrificing the corrosion protection value become. This has both ecological and economic importance, since here for the first time a manganese-containing trication method for the Belt sector is described.

In a preferred embodiment of the present invention the process for phosphating electrolytically and / or hot dipped galvanized steel strip, characterized in that the Phosphating solutions meet the following conditions:

Content of Zn ²⁺ cations: 0.4 to 0.6 g / l, Content of Mn ²⁺ cations: 0.9 to 1.1 g / l, Content of Ni ²⁺ cations: 0.6 to 0.9 g / l, Content of PO₄ ^3- anions: 12 to 16 g / l, Content of NO₃ ^- anions: 10 to 30 g / l.

Another preferred embodiment of the present invention is that the weight ratio of nickel cations to Nitrate anions in the range of 1:20 to 1:60. in the Within the scope of the present invention, it has been found that one too  large amount of nitrate negative for the phosphating process such as too low a nickel content. This will be the Corrosion protection values negatively affected. In a further preferred Embodiment of the present invention is the weight ratio from manganese cations to nitrate anions in the range of 1: 6 to 1: 20 set. As a result, in particular the Wet paint adhesion are positively influenced.

Of particular importance to the present process is the Usability for both the phosphatization of electrolytic than also from hot dip galvanized steel strip. For electrolytically galvanized Steel strip is the presence of fluoride anions in the Practice not required, but also disturbs the presence of Fluoride the phosphating process is not. When using However, hot-dip galvanized steel strip may require the use of Fluoride anions may be required, especially if it is aluminum cations to complex. Accordingly, another preferred Embodiment of the present invention characterized in that the phosphating solutions have a content of fluoride anions of 0.1 to 1.0 g / l, preferably 0.4 to 0.6 g / l.

The phosphating itself occurs at moderately elevated temperatures in the range of about 40 to 70 ° C. Especially suitable is the temperature range be from 55 to 65 ° C. Any technically usable Possibility of applying the treatment solution is suitable. In particular, it is thus possible to use the new method both by means of Spray technique as well as in the dipping process.

Before applying the phosphating solution must be electrolytically and / or hot dip galvanized surface completely be water wettable. This is in continuously operating conveyor systems usually given. If the surface of the galvanized  Tape should be oiled for storage and corrosion protection, so is this oil before phosphating with already known suitable To remove funds and procedures. The water-wettable galvanized metal surface is then before applying the Phosphatierungslösung appropriate a known, activating Subjected to pretreatment. Suitable pretreatment procedures are described in particular in DE-OS 20 38 105 and DE-OS 20 43 085. Accordingly, the subsequently to be phosphated Metal surfaces treated with solutions that act as activating agents essentially titanium salts and sodium phosphate together with organic components such as alkyl phosphonates or Containing polycarboxylic acids. As the titanium component may be preferred soluble compounds of titanium such as potassium titanium fluoride and in particular Titanyl sulfate can be used. As sodium phosphate comes in general disodium orthophosphate used. titanium-containing Compounds and sodium phosphate are in such proportions used that the titanium content is at least 0.005 wt .-%, based on the weight of the titanium-containing compound and the Sodium phosphate.

As in the prior art - for example in DE-OS 32 45 411 - described, it can also for the inventive method or the zinc phosphate layers produced there after are advantageous, in a subsequent process step the phosphate layers produced to passivate. Such passivation can, for example, with diluted chromic acid or mixtures of chromic and phosphoric acid respectively. The concentration of chromic acid is generally between 0.01 and 1.0 g / l. Between the phosphating and the post-treatment step is rinsed with water.

By the method according to the invention are zinc phosphate coatings with a basis weight of zinc phosphate layers of  produced less than 2 g / m², which is a closed fine crystalline Having structure and the electrolytically and / or hot-dip galvanized Steel strip a desirable, even, light gray Give appearance. Such a phosphated steel strip can also be processed without subsequent painting. The after the according to the invention produced thin phosphate layers behave in many deformation processes cheaper than the with the hitherto conventional methods produced phosphate layers of a higher basis weight. But also applied later organic coatings show over the prior art significantly improved adhesion, both during and after the Forming processes.

In a preferred embodiment of the present invention when using electrolytically galvanized steel strip area-related masses of the zinc phosphate layer in the range of 0.7 up to 1.6 g / m². When using hot dip galvanized Steel strip is the production of a basis weight of the Zinc phosphate layer in the range of 0.8 to 1.6 g / m² as a special advantageous to emphasize.

The method according to the invention allows the application of the nickel and manganese-containing zinc phosphate layer by itself in the state of Technique known techniques such as spraying, diving and / or spray diving, in particular their combined method.

The surface layers produced with the aid of the method according to the invention are in all areas where phosphate coatings be applied, well usable. A particularly advantageous application lies in the preparation of the metal surfaces for the paint, in particular the electrocoating.

Examples

Within the usual process sequence with the steps:

• 1. Cleaning and degreasing:
  Use of surfactant-containing alkaline cleaning agents (such as RIDOLINE® C 72) in spraying at 50 to 60 ° C and treatment times of 5 to 20 s.
• 2. Rinse
• 3. Activate:
  Use of titanium salt-containing agents (such as FIXODINE® 950) in spraying at 20 to 40 ° C and treatment times of 2 to 4 s.
• 4. phosphating:
  Composition see Table 1.
• 5. Rinse
• 6. Post passivation:
  Use of chromium-containing or chromium-free post-passivation agents (such as DEOXYLYTE® 41B or DEOXYLYTE® 80) in spraying or immersion at 20 to 50 ° C and treatment times of 2 to 6 s.
• 7. Squeezing off:
  Supernatant fluid is removed without compacting the layer using squeegee rollers.
• 8. Dry
  The tape dries after squeezing by self-heat.

the surface treatment of electrolytically galvanized was carried out Steel (both sides 7.5 μm Zn) and hot-dip galvanized Steel (support on both sides 10 μm Zn).

It became a surface-related with electrolytically galvanized steel (ZE) Mass of 0.6 to 1.6 g / m² and hot-dip galvanized Steel (Z) has an areal mass of the phosphate layer of 0.8 up to 1.6 g / m².  

Table 1

Composition of phosphating baths

As substrate to be phosphated in the examples were electrolytic Galvanized steel on both sides (7.5 / 7.5 μm zinc) for testing by means of VW-P 1210 Wechselklimatest and hot dip galvanized Steel (10/10 μm zinc) selected for the salt spray test.

Typical layer analysis (determination quantitatively by atomic absorption spectroscopy, AAS) of the process on electrolytically galvanized Stole:

With the aid of Examples 1, 3 and 4 and the comparative example obtained sheets were corrosion tests with alternating climate according to VW standard P 1210 over 15 and 30 days test time and corrosion tests in the salt spray test according to DIN 50 021 SS, 1008 h.

As a paint coating for the test VW P1210 was the standard KET primer FT 85 7042, manufacturer BASF Lacke and colors AG, related, while for the salt spray test the polyester primer BASF Universal No. 21110, 4 μm, and Unitecta Polyester Topcoat No. 509 203 5002, 16 μm.  

1. VW Wechselklimatest P 1210

15 days

30 days

2nd salt spray test

In the determination of the bubble level of paints according to DIN 53 209 is a blistering that occurs during painting by specifying the Bubble level defined. The bubble level according to this standard is a measure for blistering on a paint by frequency the bubbles per unit area and size of the bubbles. The bubble level is indicated by a code letter and a code for the Frequency of bubbles per unit area and a code letter and a measure of the size of the bubbles.

The code letter and the code m0 means no bubbles while M5 according to the bubble level images according to DIN 53 209 defines a certain frequency of bubbles per unit area.

The size of the bubbles is indicated by the letter g and the code ranging from 0 to 5. Identifier letter and code g0 has the importance of freedom from blisters, while with g5 the size of the  Bubbles according to the bubble level images of DIN 53 209 reproduced is.

By comparing the paint after the test with the bubble wheel images the bubble level is determined whose image matches the appearance of the bubble Painting is most similar.

According to DIN 53 167, the salt spray test is in accordance with this standard to the behavior of paints, coatings and similar coatings on exposure to sprayed sodium chloride solution determine. If the coating has weak spots, pores or injuries on, then from there prefers an infiltration the coating takes place. This leads to a reduction of liability or loss of adhesion and corrosion of the metallic substrate.

The salt spray test is used to detect such errors and the infiltration can be determined.

Infiltration within the meaning of this standard is defined by one attached injury site (Ritz) or existing Weak points (eg pores, edges) outgoing penetration of sodium chloride solution in the interface between coating and Underground or in the interface between individual coatings. The width of the zone with reduced or lost adhesion serves as a measure of the resistance of the coating on the respective substrate against the action of sprayed sodium chloride solution.

The VW standard P 1210 defines a changeover test, which consists of a combination different, standardized test procedures. So is in the  Course of - in the present case - 15 and 30 days one test cycle complied with, which consists of

4 h salt spray test according to DIN 50 021,
4 h rest time at room temperature and
16 h rest time at room temperature and
16 h condensation water contact climate according to DIN 50 017.

At the beginning of the test, the test sheet with a defined amount Steel shot decided certain grain size distribution. After expiration The test time is assigned a code for the degree of corrosion. According to the key figures from 1 to 10, the key figure denotes 1 an invisible corrosion, while with a code 10 practically the entire surface is corroded.

In the T-Bend test, the sample is different for 1 to 2 s Bend radii parallel to the rolling direction bent by 180 °, where the coating is on the outside. The smallest Bending radius, which allows a tore-free bending of the sample determined Adhesion at a 180 ° bend. In the test T0 The sheet without liner is evenly within 1 to 2 s bent by 180 °. The sheet is immediately after bending with a magnifying glass magnified tenfold. A tightening of the Test method is to stick an adhesive film on the edge squeeze and tear down quickly. Then the amount assessed the demolished paint.

Claims (12)

1. A process for the phosphating of electrolytically and / or hot-dip galvanized steel strip to form manganese and nickel-containing zinc phosphate layers by brief treatment with acid phosphating, wherein
the duration of the treatment is 2 to 30 s, the phosphating is carried out in the temperature range of 40 to 70 ° C and
the phosphating solutions meet the following conditions: Content of Zn ²⁺ cations: From 0.02 to 0.75 g / l, Content of Mn ²⁺ cations: 0.2 to 2.0 g / l, Content of Ni ²⁺ cations: 0.1 to 2.0 g / l, Content of PO₄ ^3- anions: 10 to 20 g / l, Content of NO₃ ^- anions: 0.5 to 30 g / l, Content of "free acid": in the range of 1.6 to 3.0 points, Content of "total acid": in the range of 12 to 40 points, and where
the weight ratio of Ni ²⁺ cations to NO 3 ^- anions in the range of 1:10 to 1:60 and
the weight ratio of Mn ²⁺ cations to NO 3 ^- anions is adjusted in the range of 1: 1 to 1:40. 2. The method according to claim 1, characterized in that the phosphating correspond to the following conditions: Content of Zn ²⁺ cations: 0.4 to 0.6 g / l, Content of Mn ²⁺ cations: 0.9 to 1.1 g / l, Content of Ni ²⁺ cations: 0.6 to 0.9 g / l, Content of PO₄ ^3- anions: 12 to 16 g / l, Content of NO₃ ^- anions: 10 to 30 g / l, 3. The method according to at least one of claims 1 and 2, characterized characterized in that the treatment duration is 3 to 20 s. 4. The method according to at least one of claims 1 to 3, characterized in that the weight ratio of Ni ²⁺ cations to No₃ ^- anions in the range of 1:20 to 1: 60 is set. 5. The method according to at least one of claims 1 to 4, characterized in that the weight ratio of Mn ²⁺ cations to NO₃ ^- anions in the range of 1: 6 to 1: 20 is set. 6. The method according to at least one of claims 1 to 5, characterized in that the phosphating solutions have a content of F ^- anions of 0.1 to 1.0 g / l. 7. The method according to at least one of claims 1 to 5, characterized in that the phosphating solutions have a content of F ^- anions of 0.4 to 0.6 g / l. 8. The method according to at least one of claims 1 to 7, characterized characterized in that the phosphating in the temperature range of 55 to 65 ° C is performed.   9. The method according to at least one of claims 1 to 8, characterized characterized in that the basis weight of the zinc phosphate layers less than 2 g / m². 10. The method according to at least one of claims 1 to 8, characterized characterized in that the basis weight of the zinc phosphate layers when using electrolytically galvanized steel strip 0.7 to 1.6 g / m². 11. The method according to at least one of claims 1 to 8, characterized characterized in that the basis weight of the zinc phosphate layers when using hot dip galvanized steel strip 0.8 to 1.6 g / m². 12. The method according to at least one of claims 1 to 11, characterized characterized in that electrolytically and / or hot dip galvanized Steel strip is used, the previously known per se Activation pretreatment, especially with titanium-containing Activation solutions, has been subjected.