KR890003586B1 - Phosphating processes and compositions - Google Patents

Abstract

A chlorate- and chloride-free compsn. for forming a protective coating on a metal surface comprises 0.8-2.5 wt.% zinc, 10-25 wt.% phosphate, 1.5-10 wt.% nitrate, 0.1-1.2 wt.% nickel, 0.5-1.5 wt.% boro fluoride and/or silicofluoride, 0.25-2 wt.% nitrobenzene sulphonate and 0.05-0.7 wt.% manganese. The compsn. is useful for zinc-phosphating of automobile bodies prior to electro-dip lacquering, and can be easily formulated to be effective for a sprayor dip- application.

Description

Phosphate Composition and Method of Use

The present invention relates to phosphate compositions and methods of use thereof useful for forming protective coatings on metal surfaces.

On metal surfaces, it is common to coat phosphate coatings on metal surfaces before applying paint or lacquer to prevent corrosion and to ensure that the lockers adhere well. In general, zinc phosphate coating is used before applying lacquer, in particular by electroimmersion, usually using an aqueous solution of zinc phosphate containing an oxidizing agent.

Conventional zinc phosphate solutions require the formation of zinc: phosphate in a ratio of 1: 1 to 4 at elevated temperatures in the presence of oxidants such as nitrates and chlorates, such as 70 to 90 ° C., thus requiring a large amount of thermal energy. In addition, the properties of the obtained coatings were not very satisfactory, especially in the case where automobile parts or other automobile bodies were used for coating.

Therefore, the automotive industry currently uses a specially developed zinc phosphate method, which is divided into the following two types for the coating of automotive parts or automotive bodies.

The first method is to formulate zinc and phosphate in the usual proportions, but add a considerable amount of manganese to it at a very low temperature. This method has the advantage of very low energy consumption and a very satisfactory result at the highest level. This method was first proposed by British Patent No. 983,924, and thereafter, British Patent No. 2,072,225 proposes a method of using a mixture of chlorate and nitrobenzene sulfonate as an oxidant as an improvement of the above method. This method comprises, for example, 3.5 g / l zinc, 0.5 g / l manganese, 0.2 g / l nickel, phosphate 11.6 g / l, nitrate 4 g / l, sodium nitrobenzene sulfonate 1 g / l, sodium chlorate 3.5 g / l, A solution containing 1 g / l tartarate and 0.7 g / l borofluoride is used.

As a second method, another important method used to phosphate the surface of automobile parts or fuselage is the low zinc method, i.e. the amount of zinc is less than 1.6 g / l, mainly 1.2 g / l. There is a method using a very small amount of zinc compared to the conventional method. Such methods are described, for example, in German Patent Application Nos. 2,232,067 and British Patent Nos. 2,046,312, 2,074,611 and 2,093,075. In these methods, the use ratio of zinc: acetate is generally in the range of 1: 8 to 100.

In general, low zinc processes require strong oxidizing agents, so the use of chlorate in combination with nitrite and / or nitrate has become commonplace in industrial applications. Some of these methods use manganese selectively, but generally do not. In addition, nickel is generally used in the low zinc method, but in larger amounts than in other conventional methods, such as 1 g / l.

In particular, British Patent No. 2,074,611 describes a low zinc method using a large amount of an oxidation promoter. According to this method, the maximum amount of zinc used is generally higher than the maximum amount of zinc prescribed in the conventional low zinc method. Less, ie the amount of zinc here is less than 1.3 g / l.

Since these low zinc methods generally have to be carried out at a temperature of 40 to 70 ° C., they consume more thermal energy than in the low temperature method described above. However, the coatings obtained according to these methods are excellent in their properties, for example, when exposed for a long time under corrosive conditions, they have a slightly better anticorrosion effect than when the coatings are formed using the low temperature method described above.

Regarding the acceleration system for the low zinc method and the acceleration system for the conventional zinc phosphate method, for example, many patent technologies such as European Patent No. 60716 are known. These several patents occasionally list general references relating to the use of one or more oxidants, several of which are selected from a list, which frequently includes nitrobenzene sulfonates, chlorates and nitrates. From a practical point of view, when nitrobenzenesulfonates are used they must be used in combination with known chlorates, which are very potent oxidation promoters (see eg, British Patent Nos. 1542222 and 2072225), and therefore this accelerator system is very satisfactory for many purposes. Although it can be provided, it is not desirable to contain chlorate because in some cases there is a risk of contamination of the coating by chloride ions.

Accordingly, it is an object of the present invention to form a protective coating on the metal surface having excellent general properties such as corrosion resistance as in the conventional low zinc method, while coating can be performed under lower temperature conditions than in the low lobe method. The present invention provides a phosphate composition and a method of using the same.

In order to achieve this object of the present invention, it has been considered to be a method of increasing the power of the accelerator system, for example, by using a method of increasing the amount of chlorate and / or a method in which a significant amount of manganese is present.

However, the inventors have surprisingly maintained that the amount of manganese in the composition at a very low level does not contain chlorate, but can be produced at bath temperatures lower than the temperature range allowed by conventional low zinc methods. It has been found that phosphate compositions having superior properties in terms of production can also be prepared.

Such compositions of the present invention need to contain zinc in amounts or slightly more than those typically used in conventional low zinc processes, and use of nitrobenzene sulfonates, polyfluorides and nickel in the amounts as specified below. There is a need.

In addition, the conventional low zinc method is generally performed only by the spray method, and if it is to be applied by the dipping method, there is a difficulty in preparing the solution specially, while the phosphate composition prepared according to the present invention is sprayed. It has the advantage of being equally effective in both law and immersion.

Hereinafter, the present invention will be described in detail.

The present invention is a composition useful for forming a protective coating on the metal surface, the composition is 0.8 to 2.5 parts by weight salt, 10 to 25 parts by weight of phosphate, nitrate, 1.5 to 10 parts by weight, 0.1 to 1.2 parts by weight of nickel, silica 0.5 to 1.5 parts by weight of fluoride or borofluoride or mixtures thereof, 0.25 to 2 parts by weight of nitrobelsen sulfonate (measured by sodium salt) and 0.05 to 0.7 parts by weight of manganese, substantially containing chlorate and chloride It is characterized by the absence.

Hereinafter, the present invention will be described in more detail.

The phosphate composition according to the present invention is initially prepared in the form of a concentrate, but in use, the concentrate is prepared in the form of a working solution in which it is diluted to a sufficient amount of water so that it is 1,000 parts by weight. Silver zinc, for example, will contain 0.8 to 2.5 g / z of zinc.

The composition of the present invention may contain up to 1.5 parts by weight of hydroxy carboxylic acid such as tartarate, if the content exceeds 1.5 parts by weight, it becomes difficult to form a coating.

On the other hand, the phosphate composition preferably contains 0.8 to 2.5 parts by weight, preferably 1.4 to 2 parts by weight of zinc, if the amount of zinc is 0.8 parts by weight or less, the formation of the coating is very slow, whereas If the amount is 2.5 parts by weight or more, it is not preferable because the coating to be formed becomes very thick and the adhesion is poor.

And, the amount of phosphate is 10 to 25 parts by weight, preferably 12 to 18 parts by weight. If the amount of phosphate is less than 10 parts by weight, it is difficult to form a coating, and if it contains more than 25 parts by weight, there is a disadvantage that the process is uneconomical.

In the composition of the present invention, the content ratio of zinc: phosphate (Zn: PO ₄ ) is 1: 4 to 1:30, preferably 1: 6 to 1:13, and most preferably 1: 8 or less, to the maximum. Is less than or equal to 1:10. In addition, the total acid value of the use liquid is generally 10 to 40 points, particularly preferably 15 to 25 points, and the free acid content of the use liquid is preferably 0.5 to 5 points, particularly 0.5 to 3 points. The content ratio of free acid to total acid is generally 1:10 to 1:30, preferably about 1:15 to 1:25.

In addition, the amount of nitrate which is the composition according to the present invention is preferably 1.5 to 10 parts by weight, preferably 3 to 6 parts by weight, if the amount of nitrate is 1.5 parts by weight or less, the formation rate of the coating is very slow, whereas 10 If it is more than weight part, it is uneconomical and it is not preferable.

In the composition, it is preferable to add 0.5 to 1.5 parts by weight of silicofluoride or borofluoride or a mixture thereof, and when the amount is less than 0.5 parts by weight, the composition is very difficult to form a coating on the surface for some metals. The disadvantage is that some other metals must be coated at undesirable temperatures. On the other hand, if the amount exceeds 1.5 parts by weight, there is no additional benefit obtained thereby, only the process becomes uneconomical. In particular, although the use of borofluoride is recommended in British Patent No. 2,046,313, the inventors have found that the use of silicofluoride not only results in a faster coating rate but also a more uniform coating. It has been found to be applied to the present invention.

In addition, the amount of nickel in the composition is preferably 0.1 to 1.2 parts by weight, preferably 0.15 to 0.35 parts by weight. If the amount of nickel is 0.1 parts by weight or less, it is difficult to perform the corrosion process of the coating, while 1.2 parts by weight. If this is the case, the process becomes uneconomical with little benefit.

In the composition of the present invention, nitrobenzenesulfonate is generally to be used as the sodium salt, the amount of which is used is 0.25 to 2 parts by weight, preferably 0.5 to 1.5 parts by weight. If the amount is 0.25 parts by weight or less, the formation rate of the coating is very slow, and if it is 2 parts by weight or more, it is not preferable because the thickness of the coating is formed too thin.

In addition, although the composition of the present invention may not contain manganese, it is generally preferable to contain manganese at least 0.05 parts by weight or more and 0.7 parts by weight (ie, 0.7 g / l in the working liquid). It is particularly preferable to contain 0.1 to 0.25 parts by weight, since the higher the coating, the rougher the surface is obtained. If the amount of manganese is 0.05 parts by weight or less, the adhesion of the coating to the surface of the zinc is bad, and if it is more than 0.7 parts by weight it is not preferable because a very coarse coating is obtained.

In addition, the present invention provides a method of using the phosphate composition comprising the addition of a sufficient amount of water to the phosphate composition as described above to make the use solution so that the whole is 1,000 parts by weight, and then contacting the metal surface to form a protective coating. It is about.

That is, when the protective coating is to be formed on the surface of a metal such as iron, zinc or aluminum by using the use liquid according to the present invention, the surface of the metal is first cleaned and then the use liquid is sprayed, immersed or usually used. This can be done by contacting the metal surface according to another method. In the case of using the spray method, it is generally carried out for 45 seconds to 3 minutes, and in the case of using the immersion method, it is better to continuously immerse for 2 to 5 minutes. Moreover, the mixing method of the said methods, for example, spray-immersion-spray, can also be performed continuously.

As mentioned above, the temperature of the use liquid during the contact with the metal surface is generally 25 to 55 ° C, but preferably 40 ° C or less, and more preferably about 25 to 35 ° C. The metal surface may be washed with water after being brought into contact with the working solution, and may be chemically treated by a conventional method such as a dilute aqueous solution of a chromium compound. Then, the metal surface may be washed again with water and dried by a conventional method.

The coating thus formed exhibits excellent corrosion resistance even when prolonged exposure under corrosive conditions and can serve as a suitable base for painting.

On the other hand, when using the use liquid, it can be supplemented with a conventional method, generally an alkaline promoter supplement containing sodium hydroxide and nitrobenzene sulfonate and a separate acid supplement containing other components.

The present invention will be described in detail based on the exemplary embodiment as follows.

EXAMPLE

Zinc 1.5g / l, phosphate 13.9g / l, nitrate 5.12g / l, nickel 0.24g / l, manganese 0.17g / l, silicon fluoride 1g / l and sodium nitrobenzene sulfonate 1g / l, The used solution was prepared such that the total acid content was 21 points and the free acid content was 1 point.

The solution temperature was maintained at about 30 DEG C while continuously spraying the solution on a previously prepared steel surface. After spraying, the surface was washed with water, washed with chromium compound, then washed with water and dried again, and painting was carried out by cathodic electroimmersion.

When supplementation of the immersion bath was required, two supplements were used. The supplements used were 39.95 g / l sodium hydroxide and 39 g / l sodium nitrobenzene sulfonate, 108 g / l zinc oxide, A solution of 282 g / l phosphoric acid, 7 g / l magnesium carbonate and 24.7 g / l 35% H ₂ SiF ₆ , with a total acid content of 32.5 points and a free acid content of 7.9 points.

The coated steel surface showed excellent corrosion resistance and paint adhesion.

Claims (7)

In a composition useful for forming a protective coating on a metal surface, the composition is 0.8 to 2.5 parts by weight of zinc, 10 to 25 parts by weight of phosphate, 1.5 to 10 parts by weight of nitrate, 0.1 to 1.2 parts of nickel, silicofluoride or boro 0.5 to 1.5 parts by weight of fluoride or a mixture thereof, 0.25 to 2 parts by weight of nitrobenzene sulfonate (measured as sodium salt) and 0.05 to 0.7 parts by weight of manganese, and are substantially free of chlorate and chloride. Phosphating composition made into. The method of claim 1, wherein the composition is characterized in that it contains up to 1.5 parts by weight of stannate. The composition according to claim 1 or 2, wherein the composition is in the form of a use liquid prepared by adding sufficient water so that the total amount thereof is 1,000 parts by weight. 4. The composition of claim 3, wherein the composition has a total acid value of 10 to 40 points, a content of free acid of 0.5 to 5 points, and a ratio of free acid to total acid of 1:10 to 1:30. The phosphate composition according to claim 1, wherein the ratio of zinc to phosphate is 1: 4 to 1:30 by weight. A composition useful for forming a protective coating on a metal surface, the composition of which is 0.8 to 2.5 parts by weight of zinc, 10 to 25 parts by weight of phosphate, 1.5 to 10 parts by weight of nitrate, 0.1 to 1.2 parts of nickel, silicofluoride or borofluoride. 0.5 to 1.5 parts by weight of a lide or mixture thereof, 0.25 to 2 parts by weight of nitrobenzene sulfonate (measured as sodium salt) and 0.05 to 0.7 parts by weight of manganese, which is sufficient for a phosphate composition that is substantially free of chlorate and chloride. Method of using a phosphate composition, characterized in that to form a coating solution by adding water to make a total of 1,000 parts by weight, and then contacting the metal surface at a temperature of 25 to 55 ℃. 7. The method of claim 6, wherein the gold surface is a steel surface.