JPS6211077B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention removes and suppresses the oxidation scale that forms on the surface of the steel material when it is furnace-cooled and rapidly cooled steel material that has been subjected to high heat treatment in a non-oxidizing atmosphere, such as during furnace brazing. The present invention relates to a painting pretreatment agent and a painting pretreatment method that make it possible to apply cationic electrodeposition coating. Normally, when painting the surface of a steel material, a chemical conversion film such as zinc phosphate is formed on the surface of the steel material as a base, and a coating film is formed on this film. However, parts made of steel materials are joined by furnace brazing etc. In order to obtain desired parts, in order to improve the mechanical properties of steel materials, as known from Japanese Patent Publication No. 56-25903,
Steel material after brazing heat treatment at 1100℃~1150℃
The furnace is cooled to near the transformation point of 570°C to 720°C, and then rapidly cooled. However, in this case, iron oxide and an oxide film (oxide scale) are generated on the surface of the steel material, and if chemical conversion coating treatment is applied without removing this oxide scale, the adhesion between the chemical conversion coating and the steel material, the adhesion of paint to the surface of the chemical conversion coating, etc. The corrosion resistance of the paint film is poor. For this reason, oxidized scale is removed using physical means such as shot blasting, and chemical means using inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as oxalic acid, but physical means do not completely remove it. Moreover, chemical means can cause deterioration of the steel surface due to hydrogen brittleness and deterioration of the chemical conversion film due to the generation of yellow rust if water washing is not completed. In this case, pickling, water washing, neutralization and Various treatments such as rust prevention must be carried out. In addition, even if a chemical conversion film is formed by removing oxide scale as described above, there is a limit to its corrosion resistance.Recently, in order to improve the durability of the base film, electrodeposition coating is applied, or alternatively, a chemical conversion film is used. There is a growing demand for applying electrodeposition coating directly to steel materials. However, when the above-mentioned treatment agent that removes oxidized scale is used, the treatment agent reacts with the electrocoating paint to cause aggregation and deterioration, and also causes contamination of the electrocoat bath liquid with miscellaneous ions. In order to avoid changes in adhesion properties and deterioration of quality due to surface adhesion of agglomerates, when electrodeposition coating is applied, sufficient cleaning treatment using immersion water washing, spray washing, or a combination of these must be carried out during the process. This not only increases the number of steps and man-hours, but also requires equipment costs and a large amount of space, resulting in high costs. To explain this in more detail, electrodeposition paints are roughly divided into anionic electrodeposition paints and cationic electrodeposition paints, depending on their basic electrodeposition mechanism, and the resin used in cationic electrodeposition paints is epoxy. A polyamino resin with a backbone of resin, acrylic resin, etc., which is usually neutralized with an acid such as an organic acid and made water-soluble (water-dispersed).
Since it is positively charged, if a basic substance is mixed in, the water-soluble paint will become insolubilized again. Not only that, but it also reacts with negative ions such as Cl ^- , PO ₄ ^3- , and SO ₄ ^2- , resulting in aggregation. In addition, the resin used in anionic electrodeposition paints is a polycarboxylic acid resin with a backbone of polyester, epoxy ester, polyacrylic acid ester, etc., and is usually neutralized with a base such as organic amino or caustic potash.
Since the paint is water-solubilized (water-dispersed) and negatively charged, if an acidic substance is mixed in, the water-soluble paint becomes insolubilized again. The above cleaning treatment is required in any case of anionic electrodeposition coating using . Therefore, in view of the above points, an object of the present invention is to provide a coating pretreatment agent that suppresses and removes the generation of oxidized scale during the rapid cooling treatment of steel materials, and which does not cause insolubilization or aggregation of cationic electrodeposition paints. It consists of an aqueous solution containing 1.0 to 13.0% by weight of hydroxycarboxylic acid and glycol ethers, respectively. The second invention of the present invention aims to provide a painting pretreatment method using the treatment agent of the first invention, in which a steel material that has been subjected to high heat treatment in a non-oxidizing atmosphere is cooled in a furnace, and then the steel material is cooled in a furnace. is characterized in that after it is rapidly cooled with the treatment agent of the first invention, cationic electrodeposition coating is applied without a water washing step. The hydroxycarboxylic acid contained in the treatment agent of the present invention has the effect of chelating and dissolving iron oxide and functions as an oxidation scale remover, and the glycol ethers function as a cooling agent and evaporation accelerator. In this case, biloxycarboxylic acid reacts directly with anionic electrodeposition paints and causes paint agglomeration, but cationic electrodeposition paints do not have any adverse effects because they are of the same type as the neutralizing agent, and glycol ethers do not cause evaporation. Because it is easy to oxidize, it is almost never brought into the electrodeposition paint bath, and even if it is brought in, it has no effect on electrodeposition because it is non-conductive. Malic acid, tartaric acid, citric acid, etc. are used as hydroxycarboxylic acids, but their content
If it is less than 1.0% by weight, the function as a scale remover will be reduced and oxidized scale will remain, resulting in decreased durability even after electrodeposition coating, and if it exceeds 13.0% by weight, scale removal will be poor. However, the content is limited to 1.0 or more, as the amount of paint brought into the electrodeposition paint bath decreases and the pH of the bath decreases, making liquid management difficult.
13.0% by weight. In addition, diethylene glycol monobutyl ether, carbitol, triethylene glycol monomethyl ether, etc. are used as glycol ethers, but if the content thereof is less than 1.0% by weight, the function as a coolant and evaporation accelerator will decrease. If the content exceeds 13.0% by weight, evaporation of the processing agent itself becomes active and consumption of the processing agent increases, so the content should be 1.0 to 13.0% by weight. shall be. Next, an example of the pre-painting treatment method of the second invention using this treatment agent will be explained based on the illustrated treatment apparatus. In the drawings, reference numeral 1 denotes a conveyor device that sequentially moves the trays 2 in the direction of the arrow intermittently in one takt by a pusher.The front end of the conveyor device 1 is equipped with a lifting device 1-a that raises the trays 2 toward the supply side. The section is equipped with a lifting device 1-b for lowering the tray 2 to the original position where it is pushed by a pusher, and a heating furnace 3 extending along the length is provided on the upper surface of the lifting device 1-b.
are provided, the front part of which is configured as a preheating chamber 5, each of which is equipped with an electric resistance heater. The heating furnace 3 is connected to a gas conduit 4 into which any non-oxidizing gas such as decomposed ammonia, nitrogen gas, reducing gas, etc. is introduced, and the material to be processed is prepared in a non-oxidizing atmosphere. Heating and brazing heating were performed. A water jacket-type furnace cold chamber 6 is connected to the rear of the heating furnace 3, and a shutter device is provided at the rear end of the furnace cold chamber 6 and the front end of the heating furnace 3 to open and close in conjunction with tact feeding. It has 7,7. Reference numerals 8 and 8 indicate gas outlet pipes. In this way, the furnace cooling of the treated material was also carried out in a non-oxidizing atmosphere. A cooling chamber 9 is provided at the rear of the furnace cooling chamber 6 and connected thereto, and a cooling tank 10 containing the treatment agent of the present invention is provided on the lower surface of the chamber 9, and a gas for introducing non-oxidizing gas into the interior thereof is provided. The introduction pipe 11 and the gas discharge pipe 8 for discharging the gas are connected, and a shutter device 12 is provided at the lower end of the pipe to open and close in conjunction with tact feeding.
will be established. In this way, the material to be treated was cooled in an atmosphere of non-oxidizing gas. 13 receives the tray 2 thereon and raises and lowers it to immerse the material to be treated in the tray 2 in the coolant liquid for a predetermined time;
A lifting device is shown to provide rapid cooling to this material.
Reference numeral 14 denotes a supply tank equipped with a pump 15 connected to the cooling tank 10, which partially replaces the liquid in the tank 10 with new liquid as necessary, and constantly maintains the liquid temperature preferably from 5°C to 45°C.
It was maintained at ℃. In the apparatus configured as described above, the steel material with brazing filler metal set at each joint is placed on the tray 2, sent to the preheating chamber 5, preheated there, and then transported to the heating furnace 3. For example in
Brazing is performed by heating to 1100℃ to 1150℃. Next, the steel material is placed in the furnace cooling chamber 6, where it is kept at a temperature below the transformation point where deformation due to heat is small even if it is later rapidly cooled, i.e.
Cool to about 570℃~720℃. After the furnace cooling, the steel material is led to the next cooling chamber 9, and immersed in the treatment agent of the present invention in a cooling tank 10 disposed below this cooling chamber 9 to be rapidly cooled. Thereafter, the steel material is pulled up from the cooling tank 10, taken out from the cooling chamber 9, and subjected to cationic electrodeposition coating without going through a water washing process, and then subjected to a top coat after baking to produce a product. In addition, if the material to be treated has a hollow or bag-shaped part such as a pipe, use a spray method to apply a chemical conversion coating to the parts of the surface with good throwing power, and apply the chemical conversion coating to areas where the coating has poor throwing power, such as the inner surface. Electrodeposition coating may also be applied, and in this case, even if the treatment agent remains on the inner surface, it does not affect the electrodeposition, so that a product of good quality can be obtained. Furthermore, since the material to be treated is subjected to high heat treatment in a non-oxidizing atmosphere, oil such as anti-corrosion oil is completely removed, and the quality of the stabilized coating film can be improved without being mixed into the electrodeposition coating. Next, examples and comparative experimental examples of the above pretreatment method will be described. Examples will be described below. (Example 1) Malic acid as hydroxycarboxylic acid (HA)
A pretreatment agent consisting of water and 4.5% by weight of diethylene glycol monobutyl ether remaining as 1.5% by weight glycol ethers was prepared in advance in a cooling tank. Two pieces of SPCC steel are lined up, copper brazing material is set at the joint, and preheated to around 200℃ in a preheating chamber with a non-oxidizing atmosphere made of decomposed propane gas, then gradually transferred to a heating furnace and heated to 1150℃. The brazing filler metal was melted and flowed into the joint and held for 3 minutes. After cooling in a furnace to 700°C, it was quenched by immersion in a treatment agent kept at 25°C. When taken out after 1 minute, no scale was observed on the surface and a shiny test piece was obtained. After a further 1 minute, cationic electrodeposition coating (Power Top U manufactured by Nippon Paint Co., Ltd.) was applied at 300 V for 1.5 minutes. Furthermore, when baked at 180°C for 15 minutes, the surface appearance was good, and the corrosion resistance test after topcoating (solvent acrylic type) showed excellent results. (Example 2) Using the same treatment agent and the same method as Example 1, it was brazed in a furnace, then rapidly cooled, and after 1 minute, it was taken out, and then cationic electrodeposition was applied (Shinto Paint Co., Ltd.'s S-bia).
CED), baked at 200℃ for 15 minutes, the surface appearance was good, and the corrosion resistance test after topcoating also showed good results. (Example 3) Tartaric acid 2% by weight Carbitol 5% by weight in the cooling tank
The remaining water was prepared in advance as a treatment agent, and brazed in a furnace in the same manner as in Example 1.
After being incinerated to 680°C, it was rapidly cooled by immersion in the above treatment agent, and a glossy test piece was obtained with no oxidized scale. After another minute Example 1
Cationic electrodeposition coating was performed using the same method as above, and after baking, a top coat was applied, and the corrosion resistance test was also good. (Example 4) Using a treatment agent consisting of 2% by weight of tartaric acid and 5% by weight of carbitol and remaining water, the surface was rapidly cooled in the same manner as in Example 2, and further baked after cationic electrodeposition, and the surface appearance was good. The results of the corrosion resistance test were also good. (Example 5) Same as Example 1, citric acid 3% by weight, triethylene glycol monomethyl ether 5% by weight remaining,
Similar results were obtained when a treatment agent consisting of water was used, and after quenching, cationic electrodeposition was applied as a top coat. (Comparative Experiment Example 1) When an aqueous solution consisting of 6% by weight of condensed sodium phosphate and water remaining was brazed in a furnace in the same manner as in Example 1, and then cooled in a furnace and rapidly cooled at 700°C, some scale was observed. Ta. When the test piece was removed after 1 minute and subjected to cationic electrodeposition at 300V for 1.5 minutes, not only paint aggregates adhered to the surface of the test piece, but also destruction of the paint film was observed. (Comparative Experiment Example 2) In the same manner as in Example 1, quenching was performed using a treatment solution consisting of 1.5% by weight of malic acid and 4.5% by weight of diethylene glycol monobutyl ether, remaining water, followed by anionic electrodeposition coating (Power Coat manufactured by Nippon Paint Co., Ltd.).
9000), some paint film destruction and agglomerates adhering to the surface of the test piece were observed, and good results could not be obtained. The table below summarizes the results of the above examples and comparative experiments.

【table】

[Table] As described above, according to the present invention, an aqueous solution containing 1.0 to 13.0% by weight of hydroxycarboxylic acid and glycol ethers is used as a pre-painting treatment agent, and hydroxycarboxylic acid is used as an oxidation scale remover. In addition, glycol ethers function as coolants and evaporation accelerators, suppressing the generation of oxidized scale during the rapid cooling treatment of steel materials, and even when the treatment agent is brought into the cationic electrodeposition paint bath, it does not cause agglomeration of the paint. Even if cationic electrodeposition coating is applied without rinsing after quenching,
It is possible to form an electrodeposited coating film with good corrosion resistance without paint agglomeration or coating repellency, and has the effect of reducing the number of steps, reducing equipment costs and improving productivity.

[Brief explanation of the drawing]

The drawing is a side view of an example of an apparatus used to carry out the method of the present invention.

Claims (1)

[Scope of Claims] 1. A pre-painting agent for steel comprising an aqueous solution containing 1.0 to 13.0% by weight of each of a hydroxycarboxylic acid and a glycol ether. 2. Steel materials subjected to high heat treatment in a non-oxidizing atmosphere are cooled in a furnace, and then quenched with a treatment agent consisting of an aqueous solution containing 1.0 to 13.0% by weight of hydroxycarboxylic acid and glycol ethers, followed by a water washing step. A method for pre-painting steel materials, characterized in that a cationic electrodeposition coating is applied without any pretreatment.