Agents for the surface treatment of zinc or zinc alloy products

Description

Field of the Invention

[0001] The invention concerns agents for the surface treatment of zinc or zinc alloy products and a method for the surface treatment of zinc or zinc alloy products in which these agents are used.

Background to the Invention

[0002] In the past zinc die-cast products, or zinc plated products where zinc has been plated on steel or the like, have been used in various fields. Chromate treatments have been widely used as surface treatments for imparting corrosion resistance to these products, but replacement methods have been investigated from various points of view since hexavalent chromium is toxic. However, there are great expectations of a method of surface treatment which is equivalent to chromate treatment in terms of low cost and corrosion resistance.

[0003] Hence the inventors have carried out various investigations with a view to obtaining an agent for the surface treatment of zinc or zinc alloy products which provides excellent corrosion resistance at low cost and the present invention has been realized. JP-A-2001 279 462, JP-A- 63161176 and GB-A-1 042 108 all disclose antimony-containing conversion coating solutions.

Summary of the Invention

[0004] The present invention is defined by the claims forming part of this specification which also discloses the following:

(1) An agent for the surface treatment of zinc or zinc alloy products which is characterized in that it includes at least one water-soluble compound which contains antimony, bismuth, tellurium or tin.

(2) An agent for the surface treatment of zinc or zinc alloy products which is characterized in that it includes at least one water-soluble compound which contains antimony, bismuth, tellurium or tin, and a nickel salt and/or a manganese salt.

(3) An agent for the surface treatment of zinc or zinc alloy products which is characterized in that it includes at least one water-soluble compound which contains antimony, bismuth, tellurium or tin, a nickel salt and/or a manganese salt, and tannins and/or thioureas.

(4) An agent for the surface treatment of zinc or zinc alloy products according to (2) or (3) above in which the nickel and manganese salts are selected from among the sulphates, chlorides, nitrates and phosphates.

(5) An agent for the surface treatment of zinc or zinc alloy products according to any of (1) to (4) above which also includes inorganic additives selected from among the inorganic acids and iodine compounds.

(6) An agent for the surface treatment of zinc or zinc alloy products according to any of (1) to (5) above which also includes organic additives selected from among the amino acids, starch, cellulose, gelatin, rosin and poly(vinyl alcohol).

(7) A method for the surface treatment of zinc or zinc alloy products which is characterized in that a zinc or zinc alloy product is immersed in an aqueous solution which contains an agent for the surface treatment of zinc or zinc alloy products as disclosed in any of (1) to (6) above.

(8) A method for the surface treatment of zinc or zinc alloy products according to (7) above which is characterized in that the zinc or zinc alloy product is also immersed in an aqueous solution which contains a sealing treatment agent.

(9) A method for the surface treatment of zinc or zinc alloy products according to (8) above in which the sealing treatment agent is selected according to the colour of the zinc or zinc alloy product.

[0005] Zinc or zinc alloy products can be provided with excellent corrosion resistance at low cost by means of this invention.

[0006] An agent for the surface treatment of zinc or zinc alloy products as described includes at least one water-soluble compound which contains antimony, bismuth, tellurium or tin. Ideally it also includes nickel salts and/or manganese salts, and most desirably it also includes tannins and/or thioureas.

[0007] Die-cast zinc products and zinc plated products where zinc has been plated on steel or the like are included among the zinc or zinc alloy products, and at least the surface of the product should comprise zinc or zinc alloy.

[0008] The water-soluble compounds which contain antimony, bismuth, tellurium or tin are soluble in water under acidic or alkaline conditions, and they include, for example, antimony pentachloride, antimony pentoxide, antimony sulphate, antimony tribromide, antimony trichloride, antimony trioxide, antimony trisulphide, antimony benzoate, antimony tartrate, bismuth chloride, bismuth citrate, bismuth fluoride, bismuth hydroxide, bismuth tri-iodide, bismuth sulphate, bismuth oxychloride, bismuth acetate, bismuth benzoate, bismuth tartrate, bismuth carbonate, bismuth nitrate, bismuth salicylate, bismuth trisulphide, potassium tellurate, potassium tellutite, potassium stannate and tin sulphate. The amounts compounded differ according to the type of water-soluble compound, but generally the amounts compounded are of the order of from 0.5 to 50 g/L, and preferably of the order of from 1 to 20 g/L.

[0009] The agents for the surface treatment of zinc or zinc alloy products as described include at least one of these water-soluble compounds which contain antimony, bismuth, tellurium or tin, but antimony or bismuth are especially desirable since they are reactive again on being wetted with water after a film has been formed on the surface of a zinc or zinc alloy product and a new film is formed so that the corrosion resistance life expectancy is prolonged. Furthermore, by using two, three or all four of antimony, bismuth, tellurium and tin conjointly the adhesion, hardness and smoothness of the film are improved and it is also possible to control the colour effectively. From these points of view the most ideal combinations in the case of conjoint use are those combinations of two or more including antimony and/or bismuth. In connection with the colour there is a tendency towards increased blackness, greyness, whiteness and whiteness as more antimony, bismuth, tellurium or tin, respectively, is compounded.

[0010] The inclusion in the agents for the surface treatment of zinc or zinc alloy products as described in addition to at least one of these water-soluble compounds which contains antimony, bismuth, tellurium or tin of a nickel salt and/or a manganese salt is ideal for reinforcing the corrosion resistance. The amount compounded is generally of the order of from 1 to 20 g/L, and preferably of the order of from 5 to 10 g/L.

[0011] Salts selected from among the sulphates, chlorides, nitrates and phosphates are preferred for the nickel salts and manganese salts. These nickel salts and manganese salts can reinforce the corrosion resistance and, for example, manganese sulphate is most desirable for improving the corrosion resistance by improving adhesion, and in the case of the nickel salts, and especially nickel sulphate, the conjoint use of the hypophosphite is especially desirable for improving the hardness in addition to the corrosion resistance. The amount of hypophosphite compounded is generally of the order of from 1 to 20 g/L and preferably of the order of from 5 to 10 g/L.

[0012] Furthermore, by including tannins such as tannic acid and the like and/or thioureas such as thiourea or salts thereof the dispersion properties are improved and the corrosion resistance is improved even more, and the gloss is increased and a beautiful colour can be obtained. The amounts in which these materials are compounded are generally of the order of from 5 to 50 g/L and preferably of the order of from 10 to 30 g/L.

[0013] Moreover, various other additives can be added to the agents for the surface treatment of zinc or zinc alloy products as described in accordance with the intended purpose. Examples include inorganic additives selected from among the inorganic acids, except for sulphuric acid and hydrochloric acid, and iodine compounds such as iodine and potassium iodide, and organic additives selected from among the amino acids, starch, cellulose, gelatin, rosin and poly(vinyl alcohol). The amounts compounded are generally of the order of from 0.5 to 10 g/L, and preferably of the order of from 1 to 5 g/L. By including these additives the film is made more dense, the hardness is improved and it is possible to prolong the life expectancy of the corrosion resistance.

[0014] The agents for the surface treatment of zinc or zinc alloy products of this invention may be used as acidic or alkaline baths. The reaction rate is greater on the acidic side and tends to be low on the alkaline side and so they are preferably used at a pH of from 4 to 5 to obtain the optimum reactivity, but they are not limited to this pH range.

[0015] Moreover, various additives other than those indicated above, such as dispersing agents, dispersion promoters and compounding ingredients for imparting an intended colour can be added appropriately to the agents for the surface treatment of zinc or zinc alloy products as described in accordance with the intended purpose.

[0016] When carrying out the surface treatment of a zinc or zinc alloy product using an agent for the surface treatment of zinc or zinc alloy products of this invention the zinc or zinc alloy product is immersed in an aqueous solution which contains this surface treatment agent and a corrosion resistant film is formed on the surface of the zinc or zinc alloy product. The thickness of this film can be determined appropriately according to the intended purposes but it is generally from 0.5 to 2 µm. At the time of the immersion treatment of the zinc or zinc alloy product the oxide which is attached to the surface has preferably been removed beforehand by the usual means such as de-greasing, acid washing, neutralization, etching and the like. The immersion treatment of the zinc or zinc alloy product is generally carried out at a temperature of from 15 to 40°C, and preferably of from 20 to 30°C, and for a period of about 5 minutes. For example, if a temperature exceeding 40°C is used then the rate of formation of the film is increased and so more rigorous quality control is desirable. The immersion treated zinc or zinc alloy product is then washed and dried in the usual way. The colour of the film which is formed on the surface of the zinc or zinc alloy product in this way differs according to the components of the agent for surface treatment purposes.

[0017] In this invention the zinc or zinc alloy products which have been immersion treated in the way outlined above are preferably also immersed in an aqueous solution which contains a sealing treatment agent to seal the pinholes. The sealing treatment agent is preferably selected in accordance with the colour of the zinc or zinc alloy product, and examples include (yellow) boric acid, ammonium oxalate; (yellow-brown) chromic acid, citric acid, tartaric acid, phthalic acid, malic acid; (whitish-yellow) succinic acid and (greyish-yellow) maleic acid. The sealing treatment is preferably carried out by immersion in an aqueous solution which contains some 5 to 10 g/L of a sealing treatment agent as indicated above generally at a temperature of from 20 to 40°C for a period of the order of from 1 to 5 minutes. Then the product is preferably washed in pure water at a temperature of from 50 to 60°C and dried.

[0018] The invention is described in more detail below by means of illustrative examples, in which examples 4, 5, 7 and 10 arc agents in accordance with the invention, whereas examples 1-3 use other agents.

Example 1

[0019] A zinc-plated steel bolt (length about 70 mm) was immersed and treated for 2 minutes at 35°C in an aqueous solution (pH 3 to 5) which contained 2 g/L of tin sulphate, 5 g/L of manganese sulphate, 2 g/L of iodine, 5 g/L of potassium iodide and 10 g/L of tannic acid and a green coloured film was obtained.

Example 2

[0020] A zinc-plated steel bolt (length about 70 mm) was immersed and treated for 2 minutes at 35°C in an aqueous solution (pH 5 to 6) which contained 2 g/L of tin sulphate, 5 g/L of manganese sulphate, 1 g/L of selenous acid, 8 g/L of sulphuric acid and 10 g/L of tannic acid and a gold coloured film was obtained.

Example 3

[0021] A zinc-plated steel bolt (length about 70 mm) was immersed and treated for 2 minutes at 20°C in an aqueous solution (pH about 5) which contained 2 g/L of tin sulphate, 25 g/L of nickel sulphate, 20 g/L of sodium hypophosphite, 30 g/L of ammonium sulphate, 15 g/L of boric acid and 15 g/L of glycerine and a bronze coloured film was obtained.

Example 4

[0022] A zinc-plated steel bolt (length about 70 mm) was immersed and treated for 2 minutes at 20°C in an aqueous solution (pH 4 to 5) which contained 15 g/L of antimony tartrate, 25 g/L of manganese sulphate, 10 g/L of ammonium oxalate and 5 g/L of thiourea and a black coloured film was obtained.

Example 5

[0023] A zinc-plated steel bolt (length about 70 mm) was immersed and treated for 2 minutes at 20°C in an aqueous solution (pH about 10) which contained 15 g/L of antimony tartrate, 25 g/L of manganese sulphate, 2 g/L of pyrophosphoric acid, 25 g/L of caustic soda, 5 g/L of thiourea and 5 g/L of potassium permanganate and a yellow coloured film was obtained.

Example 6

[0024] A zinc-plated steel bolt (length about 70 mm) was immersed and treated for 2 minutes at 25°C in an aqueous solution (pH about 10) which contained 3 g/L of bismuth chloride, 25 g/L of manganese sulphate, 25 g/L of caustic soda, 5 g/L of thiourea and 2 g/L of potassium permanganate and a brown coloured film was obtained.

Example 7

[0025] A zinc-plated steel bolt (length about 70 mm) was immersed and treated for 3 minutes at 25°C in an aqueous solution (pH about 11) which contained 6 g/L of antimony dioxide, 25 g/L of manganese sulphate, 30 g/L of caustic soda, 5 g/L of thiourea and 5 g/L of potassium perchlorate and a coffee coloured film was obtained.

Example 8

[0026] A zinc-plated steel bolt (length about 70 mm) was immersed and treated for 2 minutes at 40°C in an aqueous solution (pH about 11) which contained 5 g/L of bismuth nitrate, 25 g/L of manganese sulphate, 30 g/L of caustic soda, 40 g/L of zinc nitrate and 50 g/L of diethylene glycol and a grey coloured film was obtained.

Example 9

[0027] A zinc-plated steel bolt (length about 70 mm) was immersed and treated for 2 minutes at 20°C in an aqueous solution (pH 4 to 5) which contained 15 g/L of potassium tellurate, 25 g/L of manganese sulphate, 10 g/L of ammonium oxalate and 5 g/L of thiourea and a black coloured film was obtained.

Example 10

[0028] A zinc-plated steel bolt (length about 70 mm) was immersed and treated for 2 minutes at 20°C in an aqueous solution (pH 4 to 5) which contained 15 g/L of antimony tartrate, 5 g/L of bismuth chloride, 25 g/L of manganese sulphate, 10 g/L of ammonium oxalate and 5 g/L of thiourea and a black coloured film was obtained.

[0029] Good corrosion resistance was observed on spraying salt water for 72 hours onto the immersion treated bolts obtained in Examples 1 to 10 described above and testing the corrosion resistance in respect of salt water.

[0030] The immersion treated bolts obtained in Examples 1 to 10 described above were immersed generally at about 30°C for from 2 to 3 minutes in an aqueous solution which contained from 5 to 10 g/L of a sealing treatment agent as indicated below according to the colour, and then they were washed in pure water at from 50 to 60°C and dried and a further improvement in corrosion resistance was observed.

[0031] (Green) Iodine; (Gold) Selenous acid; (Bronze) Boric acid; (Black) Ammonium oxalate; (Yellow) Picric acid; (Brown) Potassium permanganate; (Coffee coloured) Potassium perchlorate; (Grey) Maleic acid.

[0032] By means of the present invention it is possible to provide an agent for surface treatment which can impart excellent corrosion resistance to zinc or zinc alloy products at low cost.

Claims

1. An agent for the surface treatment of zinc or zinc alloy products, comprising an aqueous solution of at least one water-soluble compound which contains antimony, characterised in that the solution contains:

(a) 15 g/L of antimony tartrate, 25 g/L of manganese sulphate, 10 g/L of ammonium oxalate and 5 g/L of thiourea, and has a pH of 4 to 5; or

(b) 15 g/L of antimony tartrate, 25 g/L of manganese sulphate, 2 g/L of pyrophosphoric acid, 25 g/L of caustic soda and 5 g/L of potassium permanganate, 5 g/L of thiourea, and has a pH of about 10; or

(c) 6 g/l of antimony dioxide, 25 g/L of manganese sulphate, 30 g/L of caustic soda, 5 g/L of thiourea and 5 g/L potassium perchlorate, and has a pH of about 11,

2. An agent according to claim 1, characterised in that the solution that contains 15 g/L antimony tartrate, 25 g/L of manganese sulphate, 10 g/L ammonium oxalate and 5 g/L of thiourea also contains 5 g/L of bismuth chloride.

3. A method for the surface treatment of a zinc or zinc alloy products, by immersing the zinc or zinc alloy product in an agent for the surface treatment of zinc or zinc alloy products characterised in that the agent is an agent in accordance with any preceding claim.

4. A method according to claim 3, characterized in that the zinc or zinc alloy product is also immersed in an aqueous solution which contains a sealing treatment agent.

5. A method according to claim 3 or 4 when dependent from claim 1(c) or 4, characterised in that the zinc or zinc alloy product is immersed in the agent for the surface treatment of zinc or zinc alloy products for 3 minutes at a temperature of 25°C.

6. A method according to claim 3 or 4 characterised in that the zinc or zinc alloy product is immersed in the agent for the surface treatment of zinc or zinc alloy products for 2 minutes at a temperature of 20°C.

Ansprüche

1. Mittel zur Oberflächenbehandlung von Zink- oder zinklegierungsprodukten, umfassend eine wässrige Lösung mindestens einer wasserlöslichen Verbindung, die Antimon enthält, dadurch gekennzeichnet, dass die Lösung

(a) 15 g/L Antimontartrat, 25 g/L Mangansulfat, 10 g/L Ammoniumoxalat und 5 g/L Thioharnstoff enthält und einen pH-Wert von 4 bis 5 aufweist oder

(b) 15 g/L Antimontartrat, 25 g/L Mangansulfat, 2 g/L Pyrophosphorsäure, 25 g/L Ätznatron, 5 g/L Kaliumpermanganat und 5 g/L Thioharnstoff enthält und einen pH-Wert von etwa 10 aufweist oder

(c) 6 g/L Antimondioxid, 25 g/L Mangansulfat, 30 g/L Ätznatron, 5 g/L Thioharnstoff und 5 g/L Kaliumperchlorat enthält und einen pH-Wert von etwa 11 aufweist.

2. Mittel nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung, die 15 g/L Antimontartrat, 25 g/L Mangansulfat, 10 g/L Ammoniumoxalat und 5 g/L Thioharnstoff enthält, außerdem 5 g/L Bismutchlorid enthält.

3. Verfahren zur Oberflächenbehandlung von Zink- oder Zinklegierungsprodukten durch Eintauchen des Zink- oder Zinklegierungsprodukts in ein Mittel zur Oberflächenbehandlung von Zink- oder Zinklegierungsprodukten, dadurch gekennzeichnet, dass es sich bei dem Mittel um ein Mittel nach einem der vorhergehenden Ansprüche handelt.

4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, dass man das Zink- oder Zinklegierungsprodukt außerdem in eine wässrige Lösung, die ein Versiegelungsbehandlungsmittel enthält, eintaucht.

5. Verfahren nach Anspruch 3 oder 4, wenn von Anspruch 1(c) oder 4 abhängig, dadurch gekennzeichnet, dass man das Zink- oder Zinklegierungsprodukt über einen Zeitraum von 3 Minuten bei einer Temperatur von 25°C in das Mittel zur Oberflächenbehandlung von Zink- oder Zinklegierungsprodukten eintaucht.

6. Verfahren nach Anspruch 3 oder 4, dadurch gekennzeichnet, dass man das Zink- oder Zinklegierungsprodukt über einen Zeitraum von 2 Minuten bei einer Temperatur von 20°C in das Mittel zur Oberflächenbehandlung von Zink- oder Zinklegierungsprodukten eintaucht.

Revendications

1. Agent pour le traitement de surface de produits en zinc ou alliage de zinc, comprenant une solution aqueuse d'au moins un composé hydrosoluble qui contient de l'antimoine, caractérisé en ce que la solution contient :

(a) 15 g/l de tartrate d'antimoine, 25 g/l de sulfate de manganèse, 10 g/l d'oxalate d'ammonium et 5 g/l de thio-urée, et a un pH de 4 à 5 ; ou

(b) 15 g/l de tartrate d'antimoine, 25 g/l de sulfate de manganèse, 2 g/l d'acide pyrophosphorique, 25 g/l de soude caustique, 5 g/l de permanganate de potassium et 5 g/l de thio-urée, et a un pH d'environ 10 ; ou

(c) 6 g/l de dioxyde d'antimoine, 25 g/l de sulfate de manganèse, 30 g/l de soude caustique, 5 g/l de thio-urée et 5 g/l de perchlorate de potassium, et a un pH d'environ 11.

2. Agent selon la revendication 1, caractérisé en ce que la solution qui contient 15 g/l de tartrate d'antimoine, 25 g/l de sulfate de manganèse, 10 g/l d'oxalate d'ammonium et 5 g/l de thio-urée contient également 5 g/l de chlorure de bismuth.

3. Procédé pour le traitement de surface de produits en zinc ou alliage de zinc, par immersion du produit en zinc ou alliage de zinc dans un agent pour le traitement de surface de produits en zinc ou alliage de zinc, caractérisé en ce que l'agent est un agent selon l'une quelconque des revendications précédentes.

4. Procédé selon la revendication 3, caractérisé en ce que le produit en zinc ou alliage de zinc est également plongé dans une solution aqueuse qui contient un agent de traitement de scellement.

5. Procédé selon la revendication 3 ou 4 lorsque dépendante de la revendication 1(c), ou 4, caractérisé en ce que le produit en zinc ou alliage de zinc est plongé dans l'agent pour le traitement de surface de produits en zinc ou alliage de zinc pendant 3 minutes à une température de 25 °C.

6. Procédé selon la revendication 3 ou 4, caractérisé en ce que le produit en zinc ou alliage de zinc est plongé dans l'agent pour le traitement de surface de produits en zinc ou alliage de zinc pendant 2 minutes à une température de 20 °C.