JPS6357520B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to degreasing and activation of metal surfaces, in which a metal material and an insoluble electrode as a counter electrode are immersed in a degreasing solution, and positive and By performing current reversal electrolysis by alternately applying negative voltages and changing the ratio of positive voltage application to negative voltage application,
This is a method for efficiently degreasing and activating metal surfaces. (Prior Art) Generally, when plating or painting a metal surface, dirt such as oil or rust adhering to the surface must be removed by pre-treatment because it degrades the quality of the product. Pretreatment has a significant impact on quality and cost, and it is said that the majority of defects in plating factories are due to incomplete pretreatment. Dirt adhering to metal surfaces can be roughly divided into organic, inorganic, and mixtures of both. Oil and lipid stains are usually removed through solvent degreasing, alkaline degreasing, and electrolytic degreasing. Final electrolytic degreasing is used as a final degreasing method to completely remove oil and lipid stains that cannot be removed by solvent degreasing or alkaline degreasing. Electrolytic degreasing is performed by electrolyzing in an alkaline solution, which has a great effect of physically removing the hydrogen gas or oxygen gas generated from the metal surface during electrolysis.It can be degreased in a short time and also removes oils and lipids that are difficult to remove. It can be easily removed. Electrolytic degreasing methods commonly used at present include the following. (1) Cathode electrolytic degreasing: This method uses the metal to be treated as a cathode to degrease using the generated hydrogen gas.Compared to anodic electrolysis, the degreasing effect is greater because the amount of gas generated is larger, but the current distribution becomes uneven, making it difficult to obtain a uniform degreasing effect. There are drawbacks such as iron, copper, zinc, etc. dissolved in the degreasing solution being electrodeposited, causing poor adhesion, and embrittlement due to absorption of generated hydrogen. (2) Anodic electrolytic degreasing: This method uses the metal to be treated as an anode to degrease using the generated oxygen gas, and there is no electrodeposition of dirt, but since it is treated with an anode, depending on the type of metal, The surface may become rough due to dissolution, or a passivation film may be formed due to anodic oxidation, resulting in poor plating adhesion. (3) PR electrolytic degreasing: This method involves applying anode for 10 to 30 seconds;
There are two methods: a PR method with very little polarity change in which the cathode is used for 10 to 30 seconds and one cycle is 20 seconds or more, and a method in which degreasing is carried out at the cathode for 2 minutes or more and then anodic degreasing is carried out for 10 to 30 seconds. This method can compensate to some extent for the drawbacks of electrolytic degreasing of only the anode and cathode, but because the number of positive and negative conversions is small, the degreasing and activation effects are small as described later, and both cathodic degreasing and anodic degreasing are There are problems such as the need to install additional equipment. In the present invention, in the degreasing and activation of metal surfaces, in addition to conventional cathodic or anodic direct current electrolysis,
It has become clear that high-speed current reversal electrolysis with a cycle of 0.1 Hz or more and by changing the reversal ratio can enhance the degreasing effect and complete degreasing in a short time. Furthermore, this method makes it possible to obtain an active surface while maintaining the luster of the metal material.
We have discovered that it is possible to improve the adhesion of plating. (Object of the invention) The object of the present invention is to
By performing degreasing using high-speed current reversal electrolysis at 0.1 Hz or higher, the degreasing effect is enhanced, degreasing is carried out efficiently in a short time, and the luster of the metal material is not lost, resulting in an active and highly adhesive metal surface. The present invention provides a degreasing method for (Structure of the Invention) In the present invention, a metal material to be surface-treated such as steel, copper alloy, zinc alloy, etc. is immersed in a liquid such as an alkaline degreasing solution as a counter electrode of an insoluble electrode, and a 0.1. This method performs high-speed current reversal electrolysis by applying negative and positive voltages alternately at a frequency of Hz or more, increasing the degreasing effect and preventing metal dissolution and passivation to obtain a clean and active metal surface. be. Furthermore, a clean and active metal surface can also be obtained by changing the ratio of the application of a positive inversion voltage to the application of a negative voltage, that is, the inversion ratio. FIG. 1 shows a voltage application method using a conventional cathodic direct current electrolysis method, FIG. 2 shows a voltage application method using a conventional anodic direct current electrolysis method, and FIG. 3 shows a voltage application method according to the present invention. time in diagram
During time T ₁ , a negative voltage is applied to the metal to be treated to generate hydrogen gas, and during time T ₂ , a positive voltage is applied to the metal to be treated to generate oxygen gas while performing electrolytic degreasing. It is. Furthermore, in high-speed current reversal electrolysis, the effect differs depending on the ratio of the negative applied voltage time T ₁ to the positive applied voltage time for reversal, that is, the reversal ratio, so changing the reversal ratio can also improve cleanliness. This results in an active metal surface. Next, the present invention will be explained in more detail using examples. (Example 1) Electrolyte Sodium carbonate 30g / Sodium phosphate 20 Sodium hydroxide 5 Surfactant 1 Bath temperature 50℃ Current density 10A/dm ² Reversal ratio 10% Treatment time 5 minutes Rust prevention under the above conditions A carbon plate is used as the opposite electrode to the treated steel plate, and the reversal ratio is calculated as the time for positive current to flow (T ₁ )/time for one cycle (T ₁ + T ₂
) x 100 = reversal ratio (%) This reversal ratio was set as 10%, and the degreasing ratio was as shown in Table 1 when the frequency was changed.

[Table] For comparison, Table 1 also shows the degreasing rate of PR electrolysis with a reversal ratio of 50%. Frequency 0 of PR electrolysis is the degreasing rate of cathodic electrolysis without polarity change, and from this result it is clear that PR electrolytic degreasing with a low frequency can obtain almost the same degreasing effect as cathodic electrolysis, and there is no reversal effect due to polarity change. It is. On the other hand, the degreasing rate by high-speed current reversal electrolysis is significantly higher than that by conventional cathode electrolysis and PR electrolysis, and the degreasing effect tends to decrease slightly when the frequency exceeds 100Hz, but from the results in Table 1, it is found that the degreasing efficiency is 0.1Hz. It is clear that the above-described high-speed current reversal electrolysis can efficiently degrease in a short time. (Example 2) Table 2 shows the degreasing ratio when the reversal ratio was changed under the same conditions as in Example 1.

[Table] From this result, when the reversal ratio is 0, that is, the reversal ratio is 50%, which is a one-to-one reversal of cathode electrolysis and cathode time and anode time, the degreasing rate is low and is 10 to 30%.
The degreasing rate is large when the inversion ratio is . As described above, as well as the frequency of current reversal electrolysis, the reversal ratio at which a positive current is passed is also greatly involved in the degreasing effect. In this example, the best degreasing rate was achieved with a reversal ratio of 10%, but the reversal ratio naturally varies depending on the type of metal to be treated and the type of degreasing liquid. For example, when a brass surface coated with an oil-based abrasive that is difficult to degrease is degreased in a degreasing solution containing 10 g of sodium hydroxide and 10 g of an anionic surfactant, the degreasing effect is achieved at a reversal ratio of around 30%. A large and good metal surface is obtained.

[Table] Table 3 shows the incidence of smuts when changing the inversion ratio and frequency. frequency 13.3
At Hz, smut does not occur at all regardless of the reversal ratio, but at 0.1 Hz and 1 Hz, smut occurs when the reversal ratio is in the range of 10 to 30%, and does not occur when the reversal ratio is 50% or higher. By selecting the frequency and inversion ratio in this manner, an active metal surface free of smuts is obtained. (Example 3) Electrolyte No. 1 Sodium hydroxide 5g/, Sodium carbonate 30g/, Sodium phosphate 20g/, Surfactant 1g/ No. 2 Sodium hydroxide 40g/, Sodium orthosilicate 50g/, Surface active Agent 2g/ No. 3 Sodium hydroxide 5g/, Sodium orthosilicate 50g/, Surfactant 2g/ No. 4 Sodium carbonate 30g/, Sodium phosphate 20g/, Surfactant 1g/ Boiled degreasing liquid Sodium hydroxide 40g /, Sodium carbonate 30g/, Sodium phosphate 5g/
, surfactant 2g / Bath temperature 50℃ Current density 10A/dm ² Frequency 13.3Hz Reversal ratio 5% Processing time 5min Material Steel plate buffed with red and white oil-based abrasives

[Table] Table 4 shows the degreasing efficiency when steel plates buffed with an oil-based abrasive were degreased in various degreasing solutions using a carbon plate as a counter electrode under the above conditions. These results show that although the degreasing effect of electrolytic degreasing differs depending on the bath composition, current reversal electrolytic degreasing is more effective than cathodic electrolytic degreasing in all degreasing solutions, and that current reversing electrolytic degreasing is effective in degreasing. is clear. The degreasing efficiency can be further increased by using a combination of boiling immersion degreasing and current reversal electrolytic degreasing, and even current reversing electrolytic degreasing alone can have a great degreasing effect on abrasive stains like red bars. Because of the great effect of current reversal electrolysis, it is possible to degrease even with a weakly alkaline degreasing solution such as No. 4, and it can also be used to degrease copper alloys, zinc alloys, aluminum alloys, etc. that are easily corroded by degreasing solutions. Can be used effectively. (Example 4) Electrolyte Sodium hydroxide 40g / Sodium orthosilicate 20g / Surfactant 1g / Bath temperature 50℃ Current density 10A/dm ² Frequency 13.3Hz Reversal ratio 5% Processing time 5min Materials 15% sulfuric acid, 1% A steel plate that was immersed in a nitric acid mixture to form smuts.The steel plate that had formed smuts was de-smutted under the above conditions using a carbon plate as the counter electrode.
It was as shown in the table.

[Table] In other words, in cathodic electrolysis, smut remains as it is, impairing the appearance and adhesion after plating, but in treatment with electric current, smut is removed at the same time as degreasing, resulting in a clean and active metal surface. Smuts were easily removed by current reversal electrolysis in a 5% hydrochloric acid solution at room temperature for 2 to 3 minutes at a current density of 5 A/dm ² or less. Since smut is easily removed and activated using alkaline degreasing solution, hydrochloric acid solution, etc., there is no need to add special additives such as cyanide compounds or chelating agents to facilitate smut removal, which is a major advantage. There is also. Furthermore, the results of electroplating, bending, heating, and impact tests on the metal that had been degreased and activated by current reversal electrolysis showed extremely strong adhesion, indicating that high-speed current reversal electrolysis is sufficiently effective for degreasing and activation. One thing was recognized. (Effects of the Invention) As described above, according to the present invention, (1) In order to perform current reversal electrolysis by converting polarity at high speed and alternately generating hydrogen gas and oxygen gas at high speed, Dirt can also be easily removed. (2) By dissolving the metal to be treated, it is possible to prevent the electrodeposition of metal ions that exist as impurities in the bath, and since the influence of impurities is small, the degreasing liquid can be used for a long period of time, making it economical and preventing pollution. The effect from the surface is also great. (3) Since the formation of a passivation film produced by anodic electrolysis is eliminated, the activation treatment step with acid as a post-treatment can be omitted. (4) Since the degreasing effect is large, it is also possible to degrease metals other than steel that are easily corroded by alkaline solutions using a weak alkaline solution that does not corrode. (5) Since it is possible to reduce the dissolution of the metal material, it is possible to maintain the processing gloss of the material, and there is also less occurrence of smut, and if it occurs, it can be electrolyzed in an alkaline solution or an acid solution using this method. The smut can be removed and an active metal surface obtained. The present invention is not only useful for degreasing metal materials, but also has the effect of removing buff scum, smut, scale, and rust.

[Brief explanation of the drawing]

FIG. 1 shows the voltage waveforms of the conventional cathodic electrolysis method, FIG. 2 shows the voltage waveforms of the conventional anodic electrolysis method, and FIG. 3 shows the voltage waveforms of the high-speed current reversal electrolysis method according to the present invention.

Claims (1)

[Scope of Claims] 1. A metal to be treated and an insoluble counter electrode are each immersed in a degreasing solution, and negative and positive voltages are alternately applied between the metal to be treated and the counter electrode at high speed with a cycle of 0.1 Hz or more. In addition, the ratio of the time for applying a positive voltage to the time for applying a negative voltage to the metal to be processed, that is, the time for positive current to flow T ₁ /time for one cycle (T ₁ + T ₂ )×
When 100 is the reversal ratio, the reversal ratio is approximately 5% to 30
% degreasing and activation method by high-speed current reversal electrolysis.