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(11) | EP 0 363 200 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Improvement of zinc phosphate treatment for cold working |
| (57) The present invention provides a zinc phosphating method for cold working which hardly
produces sludge and can be carried out in a short period of time. The method comprises
treating a steel material with a surface conditioning solution comprising 1 to 20
ppm of titanium ion and having a pH of 8 to 11, and then treating it with a chemical
solution comprising zinc ion in a concentration of 1 to 20 g/l, phosphate ion in a
concentration of at least 5 g/l, nitrate ion in a concentration sufficient to have
a concentration ratio of phosphate ion / nitrate ion of at least 1/3, pyrophosphate
or tripolyphosphate ion in a concentration of 0.2 to 2 g/l, Fe (II) ion in a concentration
of 0.1 to 20 g/l and a material decomposing nitrite ion and not oxidizing the Fe (II)
ion in a concentration of at least 0.05 g/l. |
FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
[0002] Hitherto, before conducting cold working on steel materials, the steel materials are generally subjected to surface treatment in order to reduce friction between the steel materials and a tool for cold working.
[0003] The surface treatment is generally carried out with a treatment solution containing zinc ion, iron ion, phosphate ion and nitrate ion. However, a treatment temperature is as high as 85 to 99 °C and a treatment period is as long as 10 to 40 minutes. Sludge which seems iron salts also accumulates in a treating bath and it is necessary to clean it so often.
[0004] In order to obviate the defects, it is proposed that a nitrite be added into the treatment solution as an oxidizing agent. The method lowers the treating temperature and reduces the treating period, but does not reach sufficient level. An amount of sludge is also improved, but cleaning of the treating bath should be still required quite often.
[0005] Japanese Kokai Publication 82478/1982 proposes that the steel materials be treated with a surface conditioning agent containing phosphate ion, a titanium compound and a chlorate and then subjected to zinc phosphating treatment using nitrite ion as a promoting agent.
[0006] Japanese Kokai Publication 25480/1983 also proposes theel the zinc phosphating treatment bath contain a perchlorate as an oxidizing agent in addition to nitric acid.
[0007] Japanese Kokai Publication 79782/1986 proposes that steel be treated with a surface conditioning agent containing titanium ion and then treated with a zinc phosphate treating solution containing ferric ion at a pH of 3.3 to 4.5 and at a temperature of 10 to 40 °C.
[0008] The methods proposed in the above publications do not reduce an amount of sludge sufficiently and some improvements are necessary.
SUMMARY OF THE INVENTION
[0009] The present invention provides a zinc phosphating method for cold working which hardly produces sludge and can be carried out in a short period of time. The method comprises treating a steel material with a surface conditioning solution comprising 1 to 20 ppm of titanium ion and having a pH of 8 to 11, and then treating it with a chemical solution comprising zinc ion in a concentration of 1 to 20 g/l, phosphate ion in a concentration of at least 5 g/l, nitrate ion in a concentration sufficient to have a concentration ratio of phosphate ion / nitrate ion of at least 1/3, pyrophosphate of tripolyphosphate ion in a concentration of 0.2 to 2 g/l, Fe (II) ion in a concentration of 0.1 to 20 g/l and a material decomposing nitrite ion and not oxidizing the Fe (II) ion in a concentration of at least 0.05 g/l.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The first step of the present invention is treating a steel material with a surface conditioning solution. The surface conditioning solution contains titanium ion in a concentration of 1 to 20 ppm. The titanium ion may be provided from titanium sulfate, titanyl sulfate, titanium oxide and the like. If the titanium ion is less than 1 ppm, its film forming ability is poor and causes lack of hiding, non-uniformity and corrosion. If it is more than 20 ppm, technical effects therefrom do not increase in proportion to increase of the amount of the titanium ion and it is uneconomical. The conditioning solution has a pH of 8 to 11, preferably about pH 9. If the solution has a pH of less than 8, the titanium ion is unstable and the surface conditioning ability is poor. If the solution has a pH of more than 11, the solution is so strong in alkalinity than it neutralized subsequent bath and makes the bath unstable. For adjusting pH, sodium carbonate, sodium tertiary phosphate, sodium hydroxide etc. can be added into the solution.
[0011] The surface conditioning solution contains phosphate ion as a main component. The phosphate ion can be provided from orthophosphoric acid, sodium orthophosphate, ammonium orthophosphate, pyrophosphoric acid, sodium pyrophosphate, ammonium pyrophosphate, tripolyphospharic acid, sodium tripolyphosphate, ammonium tripolyphsphate and the like. A concentration of phosphate ion is not limited, but generally within the range of 0.5 to 10 g/l, preferably within the range of 1 to 4 g/l. Amounts of less than 0.5 g/l make titanium ion unstable. Amounts of more than 10 g/l do not enhance their technical effects in proportion to the increase of the concentration.
[0012] The second step of the present invention is treating the surface conditioned steel material with a special chemical solution. The chemical solution contains zinc ion in a concentration of 1 to 20 g/l, preferably 2 to 10 g/l. Amounts of less than 1 g/l injure film forming ability. Amounts of more than 20 g/l are uneconomical. The zinc ion may be provided by dissolving a zinc compound in orthophosphoric acid or nitric acid. Examples of the zinc compounds are metal zinc per se, zinc oxide, zinc carbonate, zinc hydroxide, zinc nitrate and the like.
[0013] The chemical solution further contains phosphate ion in a concentration of at least 5 g/l, preferably at least 10 g/l. The phosphate ion can be introduced as generally described in the first step. Amounts of less than 5 g/l injure film forming ability.
[0014] In addition to zinc ion and phosphate ion, nitrate ion is added into the chemical solution to keep metal ion. The nitrate ion may be introduced from nitric acid or a nitrate. The nitrate ion can be added in a concentration sufficient to meet a concentration ratio of phosphate ion / nitrate ion of at least 1/3, preferably at least 1/1. Amounts of less than 1/3 injure film forming ability.
[0015] The chemical solution also contains pyrophosphate or tripolyphosphate ion in a concentration of 0.2 to 2.0 g/l, preferably 0.2 to 1.0 g/l. The ion inhibits the growth of coating crystal and the increase of a coating weight when iron ion accumulates. Weights of less than 0.2 g/l reduce the inhibiting effects. If a weight is more than 2.0 g/l, the inhibiting effects are too high.
[0016] The chemical solution further contains ferrous ion (Fe (II) ion) in a concentration of 0.1 to 20 g/l. The amount of 0.1 g/l can be immediately attained when the steel material is immersed in the solution. Amounts of more than 20 g/l inhibit etching iron and therefore extend the treating period.
[0017] The solution should contain a material decomposing nitrite ion and not oxidizing the Fe (II) ion in a concentration of at least 0.05 g/l. The nitrite ion is produced by the reduction of nitrate ion when iron ion is oxidized. The nitrite ion generally oxidizes ferrous ion and promote the production of sludge. Accordingly, in the present invention, the material which decomposes the nitrite ion is added to the chemical solution. Examples of the materials are urea, sulfamic acid, thiosulfuric acid, sulfurous acid and the like. Amounts of less than 0.05 g/l can not inhibit the production of nitrite ion.
[0018] The chemical solution of the present invention may contain nickel ion, copper ion, a fluorine compound and the like. The nickel ion may be introduced from nickel hydroxide, nickel carbonate, nickel oxide, nickel nitrate and the like. The copper ion may be from copper hydroxide, copper carbonate, copper oxide, copper nitrate and the like. Examples of the fluorine compounds are hydrofluoric acid, silicofluoric acid, borofluoric acid and the like. Nickel ion may be preferably present in an amount of 0.02 to 1 g/l. Copper ion may be preferably present in an amount of 0.01 to 0.2 g/l.
[0019] The treating temperature of the present invention is not specifically limited, but generally within the range of 30 to 60 °C, preferably within the range of 40 to 50 °C. The treating period can be varied by the treating temperature, but preferably within the range of 4 to 10 minutes.
[0021] According to the present invention, an amount of sludge reduces to 1/5 to 1/50 in comparison with a conventional method using a nitrite. Accordingly, frequency of cleaning sludge in a treating bath significantly reduces.
EXAMPLES
[0022] The present invention is illustrated by the following Examples, which however are not to be construed as limiting the present invention to their details.
Example 1
[0024] Zinc phosphating process was acid rinse → water rinse → surface conditioning → chemical treatment → water rinse → neutralization → drying.
[0025] Acid rinse was conducted at room temperature for 30 minutes in aqueous solution containing hydrochloric acid in an amount of 15 % by weight and iron ion in an amount of 1 to 10 % by weight.
[0026] Surface conditioning was conducted at room temperature for 10 seconds in an aqueous solution in which Fixisodine 5N-5 (available from Nippon Paint Co,. Ltd.) was dissolved in water in an amount of about 0.2 %. The composition of the surface conditioning agent is shown in Table 1.
[0027] Chemical treatment was conducted in a chemical solution. The chemical solution was prepared by adding an additive (sodium pyrophosphate, urea) to a chemical treating agent (10 % zinc oxide, 30 % phosphoric acid, 8 % nitric acid), and heating to 50 °C at which steel wool was immersed therein to dissolve ion ion. The ion composition excepting ferrous ion can be adjusted as shown in Table 1 using zinc nitrate, phosphoric acid, nitric acid and the like.
[0028] Neutralization was conducted in a 1 % solution of NP Sealer No. 6 (available from Nippon Paint Co., Ltd.) at 80 °C for three minutes.
[0029] The zinc phosphated hard steel wire was drawn using a lubricating agent (Coashin A available from Kyoei Oil and Fat Company). The apparatus for wire drawing was a non slip type wire drawing apparatus. Wire drawing was conducted using 8 dies at a wire drawing rate of 800 m/min to draw from 3 mm φ to 0.95 mm φ. It has an area reducing rate of 90 %.
[0030] Evaluation was made on appearance after zinc phosphating process, coating weight, sludge amount and wire drawing properties.
Examples 2 to 7
[0031] Wire drawing was conducted as generally described in Example 1 with the exception that the surface conditioning agent and the chemical solution have compositions shown in Table 1.
Comparative Examples 1 to 6
[0032] Wire drawing was conducted as generally described in Example 1 with the exception that the surface conditioning agent and the chemical solution have compositions shown in Table 1. In Comparative Example 5, the chemical treatment was not conducted because of sludge in a large amount. In Comparative Example 7, Granodraw 10 N and Torner 30 H were used as chemical solution (both available from Nippon Paint Co., Ltd.).
1. A process comprising treating a steel material with a surface conditioning solution
comprising 1 to 20 ppm of titanium ion and having a pH of 8 to 11, and then treating
it with a phosphating solution comprising zinc ion in a concentration in the range
of 1 to 20 g/l, phosphate ion in a concentration of at least 5 g/l, nitrate ion in
a concentration sufficient to have a concentration ratio of phosphate ion/nitrate
ion of at least 1/3, pyrophosphate or tripolyphosphate ion in a concentration of 0.2
to 2 g/l, Fe (II) ion in a concentration in the range of 0.1 to 20 g/l and an oxidant
material, which decomposes nitrite ion and does not oxidize the Fe (II), in a concentration
of at least 0.05 g/l.
2. The process according to claim 1 wherein said surface conditioning solution comprises
phosphate ion in a concentration in the range of 0.5 to 10 g/l.
3. The process according to claim 1 or claim 2 wherein zinc ion is present in the
phosphating solution at a concentration in the range of 2 to 10 g/l.
4. The process according to any preceding claim wherein phosphate ion is present in
the phosphating solution in a concentration of at least 10 g/l.
5. The process according to any preceding claim wherein nitrate ion is present in
the phosphating solution in a concentration sufficient to meet a concentration ratio
of phosphate ion/nitrate ion of at least 1/1.
6. The process according to any preceding claim wherein pyrophosphate or tripolyphosphate
ion is present in the phosphating solution in a concentration in the range of 0.2
to 1.0 g/l.
7. The process according to any preceding claim wherein the oxidant material is urea,
sulfamic acid, thiosulfuric acid or sulfurous acid.
8. The process according to any preceding claim wherein the phosphating solution further
contains nickel ion, copper ion and/or a fluorine compound.
9. The process according to any preceding claim, in which the treated steel is subsequently
subjected to cold working, preferably wire drawing.