JPH0125830B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rust prevention method for spot welded overlapping surfaces,
More specifically, the present invention relates to a method for preventing rust on spot welded overlapping surfaces using a hot melt type rust preventive agent that can be spot welded. Conventionally, spot welding has been widely used in most metal processing industries because it is a very simple and efficient method of joining metal plates. For the most part, this is done unprocessed and naked. As a result, spot welded overlapping surfaces are prone to rust, and complete rust prevention treatment is impossible after welding. The development of methods has been a major challenge for many years. Currently, some parts of the industry use zinc-rich paint to prevent rust by applying it to the overlapping surfaces of spot welds, but since it is a solvent-based paint, there is a risk of fire due to organic solvents, and there are health concerns for the human body. In addition to these problems, zinc-rich paint contains a high concentration of zinc dust, which is an amphoteric metal, so it has poor chemical resistance such as acid resistance and alkali resistance, and it takes time for the paint film to harden and dry. However, it has not yet become widespread. In addition, the 2-cord zinc chrome metal formulation is made by baking an epoxy resin zinc-rich paint onto a steel plate that has been coated with a chemical solution containing chromic acid and zinc powder, etc., and has a thin film with excellent rust prevention and good spot welding properties. Therefore, it is used as a rust prevention treatment method that can be spot welded, but the painting process is two steps and the baking temperature is very high, resulting in poor workability. In addition to problems with chemical resistance, there are also problems with the toxicity of chromic acid, so it is rarely used as a rust prevention method for spot welded overlapping surfaces. In view of the above-mentioned current situation, the present inventors have discovered that the present invention has excellent rust prevention and spot welding properties, as well as good paint film adhesion, water resistance, moisture resistance, and chemical resistance, and that it reduces the risk of fire and hygiene for the human body. As a result of intensive research to develop a rust prevention method for spot welding overlapping surfaces that is free of problems and has excellent workability, we have developed a method for spot welding overlapping surfaces by interposing a hot melt type rust preventive agent and then performing spot welding. The present inventors have found that all of the above-mentioned objectives are satisfied, and have finally completed the present invention. That is, the present invention relates to a method for preventing rust of spot welded overlapping surfaces, which is characterized in that spot welding is performed with a hot melt rust preventive agent interposed between the spot welded overlapping surfaces. The spot weldable hot melt rust preventive used in the present invention is one that has excellent rust prevention and spot weldability, and has good coating film adhesion, physical strength, water resistance, humidity resistance, and chemical resistance. If available, it can be used in a wide range of applications, especially those with a softening point of 40 to 180℃ and a penetration degree of 2.
~60, and those having a volume resistivity of 10 ¹⁴ Ω·cm or less can be preferably used. Specific examples of the hot melt type rust preventive agent used in the present invention include those described in Examples below. Further, the form of the hot melt type rust preventive agent when interposed between the spot welded overlapping surfaces is not particularly limited, but the following three types are preferable. (i) A method in which the hot melt type rust preventive agent is applied by heating and melting, (ii) a method in which the hot melt type rust preventive agent is applied in the form of a film or sheet, and (iii) a method in which the hot melt type rust preventive agent is applied in the form of a powder. This is an aspect in which the The method for forming the form (i) is generally to use a hot melt applicator that is suitable for the application conditions and the shape and size of the object to be coated, to apply it to one side of the spot welded overlapping surface, and then quickly overlap it. At the same time, do spot welding. Hot-melt applicators are those that use hot-melt rust inhibitors molded into specific shapes such as strings, rods, and cylinders, those that use pellets, lumps, and other shapes. In addition to applicators that can be used without worrying too much, there are automatic types, manual types, fixed types, portable types, etc., and it is possible to use the one that is more suitable for the shape, size, quantity, etc. of the object to be coated. can. Further, as an applicator, either a nozzle type or a wheel type (or roller type) can be used. As for method (ii), in which the hot melt rust preventive agent is interposed in the form of a sheet or film, the thickness is usually 50 to 50 mm.
A sheet or film of about 1000 μm, width 3 to 50
A piece cut to about mm is selected according to the size, shape, etc. of the spot welding overlapping surface, placed on the spot welding overlapping surface, spot welding is performed, and then heated and melted. It is convenient for use to cut the sheet or film to a certain width, apply an adhesive as it is or apply adhesive to both sides, and then roll it into a coil with a release paper sandwiched between the sheets or films. The means for interposing the sheet or film between the spot-welded overlapping surfaces is not limited in any way, and can be carried out by hand or by machine. The method (iii) of applying the hot melt rust preventive powder is to apply the hot melt rust preventive powder to the surface to be coated using an engraved roll or the like, and then perform spot welding.
After that, it is heated and melted. The particle size of the powder depends on the size of the object to be coated, the desired film thickness,
It varies depending on the type of coating machine, but generally 5 to 300 μm
Can be used to a certain extent. The rust prevention method for spot welded overlapping surfaces of the present invention is as follows:
It has excellent rust prevention and spot welding properties, and also has good paint film adhesion, water resistance, moisture resistance, and chemical resistance, and has no fire danger or hygiene problems for the human body, and is excellent in workability. Therefore, vehicles, electrical equipment,
It can be used in most metal processing industries such as various machines, office equipment, steel furniture, building materials, etc., and has excellent rust prevention effects on spot welded overlapping surfaces. Examples will be shown below, but the present invention is not limited to the following examples. Preparation of hot melt rust preventive agent Each component shown in Table 1 (component amounts indicate parts by weight)
After stirring and mixing with a dissolver under heating at 200℃ to make them uniform, rust preventives Nos. 1 to 9 and 13 to 16 were made into pellets with a diameter of 4 mm, a width of 18 mm, and a thickness of 100 μm.
and 300μm films respectively, and No.10
~12 was ground into powder with a particle size of 10-50 μm using a pulverizer. Table 2 shows the properties of the above hot melt rust preventive agent. However, the characteristics are measured by the method described below.
evaluated. (1) Softening point was tested according to JIS-K-2207-5.4 (petroleum asphalt, softening point test method). (2) Penetration was tested in accordance with JIS-K2207-5.1 (petroleum asphalt, penetration test method). (3) Volume resistivity was measured using an ultra-high resistance measurement sample box (manufactured by Takeda Riken Co., Ltd.) - 4329A - High Resistance Meter (manufactured by Yokogawa Heuretsu Packard Co., Ltd.). (4) In the hot water spray test, a sample heated and melted at 200°C was coated on one side of a steel plate (70 x 150 x 2 mm) with a film thickness of 200 μm.
Using a test piece coated with a spatula (one coat),
The test was conducted for 1000 hours according to the hot water spray test method of JIS-Z-2371, and the degree of rust development was observed. The results were divided into three grades: no abnormality (◯), slight rust (△), and considerable rust (x). (5) For hot water resistance, test pieces prepared in the same manner as (4) were tested.
After being immersed in a 3% sodium chloride aqueous solution at 20℃ for 3 months, the condition of the coating film was observed and the results were: No abnormality (○), Slight rust (△), and Considerable rust (×).
The evaluation was divided into three stages. (6) For water resistance, test pieces prepared in the same manner as (4) were tested at 20
After being immersed in tap water at ℃ for 3 months, the condition of the coating film was observed and evaluated in 3 grades: no abnormality (◯), slight softening and swelling (△), and considerable softening and swelling (x). (7) For moisture resistance, test pieces prepared in the same manner as in (4) were tested at 50°C.
℃, 98% R・H・ After testing for 3 months in a humidity tester, the state of the coating film was observed, and there was no abnormality (○).
Slight softening and swelling (△), considerable softening and swelling (×) 3
The evaluation was divided into stages. (8) Adhesion was tested according to the test method of JIS A 6909-5.5 (synthetic resin emulsion sand wall spray material, adhesion strength), and the adhesion strength was measured as a unit of adhesion.
Expressed in kg/ ^cm2, evaluation was divided into 7 or more (○), 4 or more and less than 7 (△), and less than 4 (x).

【table】

【table】

【table】

[Table] Example 1 Pellet Nos. 1 to 9 of Table 1 above were applied using a wheel-type hot melt applicator (melting temperature
220℃) onto a steel plate (70 x 150 x 0.8 mm).
Width 20mm from the end parallel to the long side, thickness 100μm and
It was coated to a thickness of 300 μm, and a steel plate of the same size was immediately placed on top of it, parallel to the long side, with a width of 20 mm from the edge. The coating workability was good with little odor and relatively low viscosity. After this product was allowed to cool to room temperature, the overlapping portions were spot welded. Example 2 Width 18 mm, thickness 100 μm and
A 300μm film is placed on two steel plates (70×150×0.8
mm) are stacked parallel to the long side with a width of 18 mm,
Spot welding was performed on the overlapped parts. The workability was very simple and good, just by sandwiching the film between steel plates. Example 3 The powders of Nos. 10 to 12 in Table 1 were placed on a steel plate (70×150×
0.8mm) parallel to the long side to a width of 20mm from the edge and film thickness (molten film thickness) of 100μm and 300μm, and on top of that, apply a steel plate of the same size to a width of 20mm from the edge parallel to the long side.
We overlapped them by 1/4 inch and spot welded the overlapped parts. As for the application workability, there is little scattering of powder and there is no odor.
It was easy and good. Comparative Example 1 Using the pellets Nos. 13 to 16 in Table 1 prepared by the above method, coating and spot welding were carried out in the same manner as in Example 1. Paint workability was No. 13, although there was little odor in all cases.
and No. 16 had extremely high viscosity and poor workability. Comparative Example 2 Using the films Nos. 13 to 16 in Table 1 prepared in the manner described above, they were sandwiched between the overlapped surfaces for spot welding in the same manner as in Example 2, and spot welding was performed. The coating workability was as good as in Example 2. Comparative Example 3 An epoxy resin solvent type (coating material content 25% by weight) zinc-rich paint with a PWC (unweighted zinc in the dry coating film) of 90 was applied to (1) a long steel plate (70 x 150 x 0.8 mm). From the edge parallel to the side, the width is 20mm and the film thickness (dry) is 25μm and 100μm.
After applying the material to the surface and allowing it to air dry for 24 hours, a steel plate of the same size was overlapped on top of it, parallel to the long side, with a width of 20 mm from the end, and the overlapping portion was spot welded. (2) Film thickness (dry) of 25 μm on two steel plates of the same size as (1), parallel to the long side and 20 mm wide from the end.
After applying to 60μm and drying naturally for 24 hours,
Two sheets of the same film thickness were stacked so that the coated surfaces overlapped, and spot welding was performed at the overlapped portion. Since the paint work is solvent-based, there is a strong organic solvent odor when painting, and the work area requires complete ventilation for hygiene and fire protection reasons.In addition, it takes 24 hours to cure and dry before spot welding. It took 72 hours. The spot weldability of the spot welds performed in Examples and Comparative Examples and the characteristics of the obtained spot welds were tested and evaluated by the methods described below. (1) For spot weldability, if spot welding is possible under condition a (○), if it is not possible under condition a but possible under condition b (△), if it is not possible even under condition b (×)
The evaluation was divided into three stages.

[Table] (2) Welding strength is measured by measuring the tensile shear strength of the spot welded part, and if the tensile breaking load (Kg) is 200 or more (○),
150 or more and less than 200 (△), less than 150 (×) 3
Evaluated in stages. (3) In the salt spray test, after sealing the bare steel plate part with a two-component epoxy resin clear paint,
Tested for 1000 hours according to the salt spray method of Z2371, observed the condition inside the overlapping surfaces, and divided into three levels: no abnormality (○), slight rust (△), and considerable rust (x). evaluated. (4) Salt water resistance is determined by sealing the bare steel plate in the same manner as in (3), and then soaking it in a 3% sodium chloride aqueous solution at 20°C.
After being immersed for a month, the condition of the overlapping surfaces was observed and evaluated in three grades: no abnormality (◯), slight rust (△), and considerable rust (x). (5) Degreasing agent resistance is based on alkaline degreasing agent (Chemicoat No. 146K, non-silicate type, manufactured by Chemicoat Co., Ltd.)
After immersing in a 5% solution of for 10 minutes at 60℃, the condition of the overlapping surfaces was observed. No abnormality (○),
The evaluation was divided into three levels: slight deterioration (△) and considerable deterioration (×). (6) Chemical conversion coating treatment agent resistance is determined by adding 0.3% neutralizer (Chemicoat No. 31) and accelerator (Chemicoat (8) 26 , both manufactured by Chemicoat Co., Ltd.) 0.1%
After dipping at 55° C. for 5 minutes, the condition of the overlapping surfaces was observed and evaluated in three grades: no abnormality (◯), slight deterioration (△), and considerable deterioration (×). The results of these tests are shown in Table 4.

【table】

[Table] As shown in the test results listed in Tables 2 and 4 and in Examples, the results shown in Examples 1 to 3,
The rust prevention method for spot welded overlapping surfaces of the present invention achieves good results in all items, has excellent rust prevention ability and spot welding properties, and has excellent paint film adhesion, water resistance, moisture resistance, and chemical resistance. It has been demonstrated that the material has good properties, poses no fire risk or hygienic problems to the human body, and has excellent workability. On the other hand, Comparative Example 1 using hot melt rust preventive agent No. 13, which does not contain petrolatum oxide, its calcium salt, calcium petroleum sulfonate, or wax, had high viscosity during application and poor workability.
Hot melt rust preventive agent No. 14 has poor rust prevention properties such as salt spray test and salt water resistance, and does not use conductive materials such as carbon black, graphite powder, iron phosphide powder, and zinc powder, and No. 15 has a small additive amount. had a high volume resistivity, and in Comparative Example 1 using these, spot welding could not be performed. Resin-only hot melt rust preventive agent No.16
In addition to having a high volume resistivity, the coating film had poor antirust ability, and in Comparative Example 1 using this, spot welding could not be performed. Comparative Example 3, which used zinc-rich paint, had a strong organic solvent odor during painting, which caused hygiene and fire service law problems, and the paint film hardened and dried slowly, so it was applied only to one side of the overlapping spot welding surface. (1) of Comparative Example 3
When the film thickness was 25 μm, the spot weldability and welding strength were good, but the rust prevention ability on the non-coated surface was poor, and the coating film deteriorated in the degreasing agent resistance and chemical conversion coating treatment agent tests. was seen. Spot welding was not possible with a film thickness of 100 μm. Comparative Example 3 (2), which was applied to both sides of the overlapping spot welding surfaces, had good spot weldability, welding strength, and rust prevention ability when the film thickness was 25 μm, but the degreasing agent resistance and chemical conversion coating were poor. Deterioration of the coating film was observed in terms of treatment agent properties. Spot welding was not possible when the film thickness was 60 μm.

Claims (1)

[Scope of Claims] 1. A rust prevention method for point welded overlapping surfaces, which comprises performing spot welding with a hot melt rust preventive agent interposed between the point welded overlapping surfaces; 2. After performing point welding. Claim 1, characterized in that the hot melt rust preventive agent is heated and melted.
3. The rust prevention method according to claim 1 or 2, wherein the hot melt rust preventive agent is applied in a heated and melted state; 4. The hot melt rust preventive agent is applied in the form of a sheet or film. 5. The rust prevention method according to claim 1 or 2, in which the hot melt rust preventive agent is present in the form of a powder; 6. The hot melt rust preventive agent is softened. The rust prevention method according to any one of claims 1 to 5, wherein the temperature is 40 to 180°C, the penetration is 2 to 60, and the volume resistivity is 10 ¹⁴ Ω·cm or less.