KR850001441B1 - Composition for treatment of steel zinc aluminium and alloy thereof surfaces - Google Patents

Abstract

The composition, according to this invention, is 57.3 wt.% phosphoric acid; 5.4 wt% urea; an inhibitor that is selected from tiourea, total 0.5 wt.% of chromium, nickel, cobalt, copper, zinc; and more than one species of transition metal salt, which is selected from manganese.

Description

Pretreatment composition for coating metal surfaces of steel, zinc, aluminum or alloys based on them

The present invention relates to a composition for pretreatment for coating metal surfaces of steel, zinc, aluminum or alloys based on these. Until now, there have been significant problems in coating paints or materials containing certain metals on metal surfaces. For example, it is difficult to coat hard metals on other types of metal surfaces, ie steel surfaces, and even though they can be coated, they need to go through several stages of electroplating, which require time and expertise to implement. There was.

As another example, it is known to be very difficult to attach resin-based paints to newly made zinc coated steel surfaces.

Whether the paint is based on acrylic resins or other resinous materials, the paints may or may not require physical connection, so these paints typically have been covered by the coating layer over months or years. It has been recognized that it is not possible to paint surfaces such as newly made zinc-clad steel until it is completely changed by. As another example, it is usually known to be the most difficult to coat other types of metals or protective coatings on aluminum surfaces.

This is known to date due to the properties of well-known oxides formed on the surface of aluminum metal.

These three examples point out the difficulties encountered so far and practical problems in the art related to coating metal surfaces.

The present invention relates to the treatment of metal surfaces consisting of ferrous, non-ferrous metals and alloys, to facilitate bonding of surface coatings after treatment and to assist in the surface pretreatment of metals that do not easily damage the surface by subsequent oxidation. It is about composition.

The present invention is to coat a metal surface with a solution that is formulated to exhibit an effective coating effect on the metal surface, which can provide a base which can be more effectively protected than in the conventional case, and in some cases is effective or economical For reasons of phosphorus, it is possible to coat what has not been possible to coat the surface of the metal until now.

The composition solutions invented by the inventors suitable for use on corroded metal surfaces have been described.

Typically, the treatment of the metal surface has been based on the concept that it removes the oxidized surface which is almost inevitably present on the metal surface, whether the metal is wiped clean, shiny or severely corroded.

Therefore, the metal surface is mainly treated in two ways. The first is based on the removal of corrosion sites, and the coating of metal surfaces with materials that can be dissolved and removed by substantially eroding the metal oxides as well as the metals underneath the oxides. Metal oxides are physically removed in anticipation of their removal, and the surfaces are covered with an impermeable membrane to seal the surface from water or other corrosive substances.

However, these two methods did not show any remarkable improvement, and in most cases treated with these methods, the damage of the metal surface worsened after a long period of time.

If pickling is typically done by immersing steel in hydrochloric acid, in addition to the fact that the surface is irregularly corroded by hydrochloric acid, incidentally, the hydrochloric acid itself must be neutralized or removed by quenching. This is because it leaves behind a factor that can cause an increase.

On the other hand, acids such as phosphoric acid may be used for pickling, but they are rarely used for removing the oxide film because they are expensive and appear late.

However, sometimes the steel sheet is first removed with an sulfuric acid oxide solution and then washed with water and then immersed in 2% phosphoric acid containing a very small amount of iron at high temperature, ie at 80-90 ° C.

This is a useful iron phosphate coating for subsequent coating.

In fact, the failure to simply cover a metal surface with a material that forms an impermeable film is due to drying of the cured film, or sometimes to provide condensation water, that is to say more generally in one or more places where the surface is broken and looser than the metal surface. Due to the continuous feeding between the attached membranes, not only water penetrates into the critical plane, but the membrane retains this water, so the membrane and the metal provided by the trapped air actually provide condensed water that promotes corrosion. This is because it is almost impossible not to get wet between the surfaces.

The first finding of the present invention is of significant value for painting metal surfaces in which oxides are inevitably formed on surfaces exposed to air. The coating material used is less or less reactive to the metal oxide than to erode the metal oxide, so the reaction product, ie, gas or other material, diffuses through the oxide without blocking or substantially affecting the pores of the oxide. It is formulated to react with matter.

Thus, the material of the present invention reacts with a metal on the surface on which the oxide is formed when it reaches the base of the oxide, that is to say a material that is substantially more reactive to the base metal than the oxide. By coating the surface of the material, the material was selected or formulated to diffuse through the pores of the oxide and then to erode the underlying metal to remove or burn the oxide without significant reaction.

The second finding of the present invention relates to the problem of limiting corrosion and providing a better basis to be effectively coated.

By incorporating substances with large molecular weights into the composition at significant concentrations, they can limit acid erosion or base erosion, thereby limiting the rate of release of the gas by first limiting the rate of reaction, while at the same time By being in the vicinity, metal ions, especially metal ions with high ionization sequences, are contained in the solution, causing acid erosion or base erosion, so that the reaction product is in solution with displacement potential of other metals, which forms a base. It has been found that there is a high possibility to form a strong adhesion bond with a sensitive metal bond or to form a complex compound by binding to or around a reaction site as long as a complex molecule is present in the solution.

Therefore, this solution has the property of actually protecting the metal exposed by acid erosion or base erosion from oxidation.

Thus, by treating the surface thus pretreated with metal build up or coating with an organic or inorganic coating, and with the solution present in the coating method, or with other methods of neutralizing it, Metals can be coated with materials or methods that could not be bonded or could not be bonded economically.

The present invention is a form of the metal surface treatment method comprising the steps of pretreating the surface and forming a protective coating layer on the pretreated metal surface. Pretreatment of the surface in this method involves painting a solution which is formulated so as not to react substantially with any oxides on the metal surface, which is an oxide unless the pores present in the oxide on the metal surface are blocked by the reaction product. Between the highly ionized metal ions in the surface metal and the metal ions in the solution composition by coating the oxidized surface metal and the surface metal by reacting with the oxidized surface metal that diffuses through and provides the metal surface. It causes ion exchange, which substantially inhibits the access of metals or gases, thereby significantly inhibiting the oxidation of metals forming surfaces.

Forming the protective coating layer on the pretreated metal surface consists of coating an appropriate coating material by electrodeposition or other methods on the pretreated metal surface as described above.

Pretreatment of the surface with the solution according to the present invention resulted in the formation of a surface which has not been obtained in the past, and the continuous coating can be achieved by applying a method for electrodeposition or application or other methods. This is because they found the possibility of coating metals by electrodeposition, which could not be coated with conventionally effective fixing by showing good fixation, and similarly, in the case of the coating solution, it may be combined with the solution remaining on the surface to some extent. If so, the bond adhesion can be increased significantly.

Therefore, the method according to the present invention is not only dependent on the method of physically removing rust or erosion with a very strong acid and subsequent treatment, but also can be applied once, and the need for removal is no longer present. In addition, many materials can be treated in that state, and they can be directly coated in a short time without being disturbed by the presence of a lot of rust or other oxides at the bottom.

The concept of the present invention is completely contrary to the conventional concept, and the solution is formed and the surface is treated so as not to erode the oxide of the metal, and the reaction with the concept oxide does not prevent the access to the base metal. Experimental results show that the metal oxides formed on the surface can be decisively preferentially eroded, and the experimental results show that all of the metal oxides formed on the surface show porosity in the form of corrosion and the composition is suitable for any metal or oxide selected. The composition should also be one capable of wetting the oxide and if not generally it is necessary to diffuse the composition through the oxide by adding an additive such as a suitable surfactant to assist the wetting.

These actions can be more easily understood by referring to the compositions of the present invention which are useful for many metals having oxides on the surface. It will also be understood that the compositions surprisingly contain substances that each provide a single function or a complex function, but this function is provided by the joint action of two or more materials.

And reference to a preferred composition does not necessarily limit the applicability of the method of the present invention to such a composition, although the components of the composition provide significant advantages, and the same functions and important advantages if one recognizes the basic concepts of the present invention. Many other compositions that provide the same can also be envisioned.

Preferred solutions contain acid, with preference being given to phosphoric acid made from 82% H ₃ PO ₄ , which is a commercially available acid known as syrup phosphoric acid. Orthophosphoric acid is tribasic acid, forming three salts corresponding to three-step ionization. Primary phosphate is more soluble in water than tertiary phosphate. The solution also contains a significant amount of urea. Typically, a mixture of 82% orthophosphoric acid mixed with an aqueous solution of urea in a ratio of 1 part by weight of urea to 1 part by weight of a phosphoric acid solution produces a strong acid and water-soluble crystalline adduct. In a particularly preferred solution, phosphoric acid is present in excess of the required amount to produce this adduct.

Preferred solutions also contain significant amounts of sulfates of copper, nickel, chromium, manganese, cobalt and zinc. They have a number of functions, one of which acts as an activator to help erode the oxidized surface metals that provide the metal surface, as well as continuously depositing the metal on the metal surface to stabilize the surface.

The precipitate also contains the phosphate produced when the preferred solution acts to grow on the phosphate first layer.

And typically, when this solution is applied to a metal surface, such as iron, copper, the cathode of the metal in the solution, for example, dissolved iron, precipitates out on iron and forms a local cell with iron, thereby forming a rate of iron dissolution. To increase. Thus, phosphate coatings form rapidly, creating a center for most crystal growth.

In an example, the copper film formed on the steel surface is uniformly attached when the present solution is applied by soldering or when the surface temperature of the steel sheet is raised to about 80 degrees Celsius. In order to form a thick film, the steel sheet is drained and then immersed in nickel sulfate or chromium sulfate for a few minutes to precipitate nickel phosphate or chromium phosphate underneath iron phosphate and finally a layer of pure nickel phosphate or chromium phosphate is formed.

The term "phosphate" is simply predicated, but in particular the crystalline salt of urea and orthophosphoric acid in the presence of urea mixed with the product. Therefore, the absorption barrier is formed in the rusted region of the sample by the urea phosphate complex, and the reaction rate is also slower than that of the solution absorbed by rust.

For metal oxides, autophoretic or electrophoretic separation of excess phosphoric acid after the reaction is completed promotes erosion of oxidized surface iron rather than the non-oxidation zone that provides a reservoir of acid.

The urea therefore acts like an inhibitor and also has additional properties which are a major advantage of the method in the present invention.

The first characteristic of the element is that it helps to wet the oxidized metal surface and exhibits creep due to its ability to crystallize and recrystallize at the cross section.

Another advantageous property is the combination of urea and phosphoric acid, and another feature is that it provides a particularly high concentration of highly viscous layer on the metal surface, which first significantly reduces the action of reducing the size of the bubble formation so that the action is carried out throughout the surface. More uniformly, the effect is a micro-etch or a viscosity-like effect rather than a macro-etch and is substantially insoluble but provides a good binder for subsequent coatings. It was shown to provide a complex in response. Urea is also useful because it is suitable for use as a complex molecule in electroplating technology.

Although the examples cited above have been specifically applied to steel surfaces, it can be clearly understood that they can be applied to other metal surfaces.

As an example, aluminum alloys are well suited for the treatment process of the present invention and, as in the case of steel, alloys of aluminum must also be suitably degreased as a suitable solvent to remove fatty compounds typically present on the metal surface.

After heating the aluminum portion to about 90 degrees Celsius and immersing it in the solution for about 5 minutes, a significant amount of corrosion products are removed from the aluminum portion and a slight etching is observed.

When treated with this solution, copper precipitates in the form of brittleness can be seen on the surface of aluminum. The copper precipitate can be easily removed by washing or rubbing to a clean aluminum surface, but in the present invention, it is preferable to leave copper in the plating bath by electroplating directly in the copper, nickel or chromium plating bath.

Copper can be substituted in the action but provides a good basis for the action to proceed.

The choice of the various compounds or substances that make up the solution will depend on many factors, including the effectiveness of the materials to be used, the cost, the safety of use and the long-term effects.

There are many suitable combinations of solutions, and at least in view of the broad concept of the present invention, it can be seen that there must be a discovery of the technology to effectively formulate the compound and provide a useful basis for subsequent successive coatings upon application. .

This solution has the important advantage of being relatively safe and cost-effective from the point of view of toxicity, and is relatively simple, economical and can be used extensively on the majority of metal surfaces.

However, it should be emphasized that this solution is to be recognized as typical and does not at least limit the concept of the invention to the broad concept of the invention.

Typically, acids or bases with relatively low dissociation constants can be used in the composition with or instead of phosphoric acid. The dissociation constants of phosphoric acid are typically 7.5 × 10 ⁻³ and acetic acid having a dissociation constant of 1.8 × 10 ^-5 All formic acids of 1.8 × 10 ⁻⁴ are suitable.

Typically other acids that can be used to satisfy the other side of the composition include oxalic acid, carbonic acid, hydrogen selenide, hydrofluoric acid, and the like.

As the base, ammonia, dimethylamine, methylamine, trimethylamine and the like can be used.

Substances useful as inhibitors, as well as weakly dissociated acids or bases, are required in significant concentrations.

The application emphasizes not only the action as an inhibitor, but also the name used in this case to indicate the form of the suitable substance.

Materials of high molecular weight, such as polysaccharides, urea or substituted urea, amides, thioureas and substituted thioureas, are suitable as inhibitors.

This, of course, does not limit the scope of the invention but is merely illustrative of the form of molecules. Significant concentrations of inhibitors first inhibit the action of acids on the oxides of the metals, facilitate diffusion through the oxides into the oxidized surface metals, and limit the access of the reacting base and the material that forms the oxides from the outside, resulting in In combination with other parts of the compound, it forms a complex compound with the oxidized surface metal or is compatible with it.

Finally, metal ions need to be provided to contribute to back surface stabilization, and typically the metal ions are sulfate transition elements. Sulfates are generally water soluble and are exemplified in the present context mainly dealing with aqueous solutions and these salts are more economical than other water soluble salts.

The general terminology of the present invention has been described so far, and then, an embodiment providing a method for carrying out the present invention will be described, and the present invention will be better understood by referring to the present embodiment.

The composition and preparation method of the first coating solution on the metal surface are as follows.

400 g of dry urea (46% N0.4 burette) was dissolved in 1600mι of hot water (85 ° C) and 200mι of sulfate solution was added. The sulfate solution was prepared by dissolving copper sulfate, cobalt sulfate, chromium sulfate, nickel sulfate, manganese sulfate, and zinc sulfate in 1140 mι of water each. To the mixture was added 3200 mM of industrial 82% phosphoric acid.

In this way, a solution of about 5ι is obtained.

The weight ratio of the solution is as follows.

Urea 5.4% Chromium Sulfate 0.08%

Phosphoric Acid 57.3% Nickel Sulfate 0.08%

Water 36.7% manganese sulfate 0.08%

Copper Sulfate 0.08% Zinc Sulfate 0.08%

Cobalt Sulfate 0.08%

In the following examples this solution will be referred to as a solution of a preferred embodiment of the invention.

Example 1

First, the metal products to be plated were cleaned by conventional methods such as solvent cleaning, emulsion cleaning, and alkali cleaning to remove grease, oil, and non-solid solids. In the case of mill scale or rust, it is of course suitable to use weathering, wire crushing, pickling, grit blasting or flame cleaning. In the present invention, the new steel could be cleaned with a solvent such as 80% by weight perchlorethylene and 20% by weight butanol, or a solvent such as methyl ethyl ketone when the initial temperature of the test piece was 20-100 degrees Celsius. The test piece was suitably washed by immersing it in the solution of the preferred embodiment of the present invention at 40 ° C-100 ° C. The immersion time depends on the temperature, but is generally between 10 seconds and 1 minute at 100 ℃. If the specimen is first heated to 100-140 ° C. and then immersed in the solution of the preferred embodiment of the present invention, a fine bubble group is generated from the specimen, indicating that micro-etching has occurred and the surface is ready for the next treatment. It represents.

The metal products were then placed in electroplating baths, for example copper plating baths containing the following materials:

Sodium cyanide NaCN 37g / ι Roselle salt KNaC ₄ H ₄ O ₆ 4H ₂ O 50g / ι

Copper Cyanide CuCN 30g / ι Sodium Carbonate Na ₂ CO ₃ 38g / ι

Operation condition:

50-70 ° C, 2-6A / dm ² , 2-6V, pH 12.2-12.8, current efficiency 50-60%, rolled and annealed copper anode, steel vat, glass cyanide 3-6g / ι

Metal products can also be treated in electroplating baths, ie chromium plating baths, which contain:

Chromate CrO ₃ 450g / ι

Sulfuric acid H ₂ SO ₄ 4.5g / ι

This solution was boiled with 12.5 g / ι citric acid, 18 g / tar tartaric acid or 25 g / O oxalic acid to slightly reduce the solution.

Operation condition:

40-50 ° C, 12-20A / dm ² , current efficiency 12-15%, 4-5V, 7% antimony lead anode, bat made of steel.

Example 2

When the metal product to be heated is zinc or zinc alloy such as used for die casting, the solution of the preferred embodiment of the present invention can be painted by carrying out a brushing, spraying or dipping method. Since the dissolution rate of zinc is much greater than that of steel, it is appropriate to reduce the immersion temperature and time to prevent the surface from being severely corroded, for example, 5-10 seconds at 40 degrees Celsius. The copper plating bath shown in Example 1 is used for a die cast alloy based on zinc and zinc, wherein the pH value is too low and must be adjusted by adding sodium hydroxide and too high tartaric acid. The chromium plating solution for direct plating on zinc and zinc based diecast alloys is as follows.

Chromic Acid CrO ₃ 331g / ι Sodium Hydroxide NaOH 48g / ι

Sulfuric acid H ₂ SO ₄ 0.6g / ι

Operation condition:

15-21 ℃, current density 100A / dm ² , 6-12V.

Example 3

When the metal product to be plated is sheet or cast aluminum or aluminum alloy, it is best to coat the solution of the preferred embodiment of the present invention on the metal product at a temperature of about 20 ° to 40 ° C. It can measure as a brittle copper thin film is formed.

The test piece was then transferred to a copper plating solution such as an alkaline copper composition.

Copper Sulfate CuSO ₄ 5H ₂ O 15g / ι Triethanolamine N (CH ₂ CH ₂ OH) ₃ 22g / ι

Sodium oxalate Na ₂ C ₂ O ₄ 10g / ι

Operation condition:

20 ° C., 0.3-0.6 A / dm ² , copper anode, bat: Bats lined with earthenware or polymer.

Alternatively, it may be transferred directly to the chromium plating solution as in Example 1.

Or A.E. It may be transferred to a self-catalyzed copper plating bath, a non-current plating bath proposed in Cahill, US Patent No. 2,874,072 (1959).

For example, the solution is formulated as follows.

Copper Nitrate Cu (NO ₃ ) ₂ 3H ₂ O 15g / ι Sodium Tartrate Potassium NaKC ₄ H ₄ O ₆ 4H ₂ O 30g / ι

Sodium hydroxide NaOH 20g / ι Remaining amount to 1 liter of water

Fill formaldehyde HCHO 36% solution 100mι with water

Sodium bicarbonate NaHCO ₃ 10g / ι

Or transfer to a zincate solution containing 525 g of sodium hydroxide and 100 g of zinc oxide per liter, immerse for 1-3 minutes at 20 degrees Celsius, wash with water and copper-plated in the copper plating bath already mentioned, and then from the same solution as in Example 1. Plate with hard chrome.

Example 4

The metal product is treated with a solution of a preferred embodiment of the present invention and then immersed in a concentrated solution of metal sulphate or phosphate at 40-100 degrees Celsius for 5 seconds-1 minutes, whereby metal phosphate such as chromium phosphate is added to the metal product. A sheath is produced. Suitable solutions are as follows.

Chromium Sulfate 280g Orthophosphoric Acid 600mι

Water 600mι

Another example of a solution is as follows.

Chromium Phosphate 200g Orthophosphate (82%) 20mι

Water 600mι

Example 5

As in Example 4, but using sulfates or phosphates of metals such as cobalt, nickel, manganese, silver, gold, platinum and zinc.

Example 6

This practice relates to the direct plating on a metal phase in a single solution of copper in a one step method.

Suitable solutions are as follows.

Orthophosphoric acid (82%) 58% Copper sulfate 10%

Urea or Thiourea 6%

Copper sulfate may be substituted with sulfates of nickel, cobalt, manganese, zinc, silver or gold, or may be replaced with chromic acid to plate these metals directly on the metal surface.

Example 7

After pretreating the surface of the aluminum alloy casting using the solution of the preferred embodiment of the present invention, a conventional plating solution consisting of 250 g / ι of chromic acid and 25 g / ι of sulfuric acid was operated at 300 A / ft ² , 4-8 V. Hard chromium was plated on the surface.

These examples are only examples and do not limit the scope of the present invention.

Claims (1)

Steel, zinc aluminum composed of an inhibitor selected from 57.3 wt% phosphoric acid, 5.4 wt% urea and thiourea and a total amount of 0.5 wt% salt of at least one transition metal selected from chromium, nickel, cobalt, copper, zinc and manganese Or a composition for pretreatment for coating a metal surface of an alloy based on these.