KR20140036434A - Method of manufacturing vehicles using precoated steel sheet - Google Patents

Abstract

The present invention relates to a vehicle manufacturing method using a pre-coated steel sheet which prevents corrosion of a cut surface, created when a pre-coated steel sheet (a pre-primed steel sheet and a pre-finished steel sheet) is processed, or corrosion of a hem flange to enable the pre-coated steel sheet to be used for manufacturing a vehicle demanding an excellent appearance and physical property of a coating film. The vehicle manufacturing method according to the present invention comprises the steps of: manufacturing parts by mechanically processing the pre-coated steel sheet; assembling the parts into a vehicle body; and electro-deposition coating the assembled vehicle body. Thereby, resistance of the cut surface and of the hem flange to corrosion is enhanced.

Description

Manufacturing method of automobile using leading sheet steel {METHOD OF MANUFACTURING VEHICLES USING PRECOATED STEEL SHEET}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for enabling leaded steel sheet to be used in the manufacture of automobiles. More specifically, a cutting surface or a ham flange (hem) generated during processing of leaded steel sheet (pre-primed steel sheet and pre-finished steel sheet) The present invention relates to a method for preventing corrosion at the flange, so that the lead steel sheet can be used even in automobiles requiring excellent appearance and coating properties.

Currently, the coating process used in automobile manufacturing is mostly applied to a wet process, which is an uneconomical process. In order to improve the efficiency of the wet process recently, the development of some short-axis integrated processes such as 3C1B (3 coat 1 bake) and B1B2 (base coat 1 base coat 2), in which the middle and top coat processes are combined, is mainly developed. The trend is taking place.

However, in the integrated process, since the coating is performed in a wet-on-wet manner, the high temperature curing process of several steps can be shortened briefly, thereby greatly improving productivity, while the lower coating film is not dried. Since the upper coating film is formed, there is a problem in that mixing phenomena occur between the coating films, or the appearance properties and physical properties are greatly reduced as compared with the coating film formed by the existing coating process.

A precoated steel sheet is a steel sheet in which a predetermined coating film is formed after cleaning the steel sheet, and the pre-treatment process, electrodeposition process, Since some or all of the wet coating processes, such as the intermediate process and the top coat process, can be omitted, the steel sheet is expected to be markedly improved in terms of environmental friendliness and productivity in the automobile industry.

However, in manufacturing automobiles using lead sheet steel, machining processes such as machining and welding of the lead sheet steel are essential. In particular, corrosion may easily occur at a cut surface or a hem flange after machining. It is not yet applied to the automobile industry which requires a beautiful appearance and durability.

Therefore, in order to apply the lead steel sheet to automobiles, corrosion problems occurring after processing have to be solved, but related technologies have not been developed until now.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method that can prevent corrosion of a cut surface and a ham flange while using a lead length steel sheet, so that the lead length steel sheet can be applied to automobile manufacturing.

In addition, another object of the present invention is to provide a method that can prevent the corrosion of the cut surface and the ham flange, while also being able to implement a coating film having excellent appearance and coating properties, which can also be used for exterior panels of automobiles.

The first aspect of the present invention for solving the above problems, the step of machining the lead sheet steel sheet to make a part; Assembling the component to a vehicle body; And electroplating the assembled vehicle body; to provide a method for manufacturing an automobile, comprising improving the corrosion resistance of the cut surface of the lead steel plate and the ham flange.

In the first aspect of the present invention, the phosphate chemical conversion coating process may be performed before the electrodeposition coating.

In the first aspect of the present invention, the electrodeposition coating composition is at least one binder resin selected from the group consisting of polyesters, alkyds, acrylic resins and modified resins thereof, and at least one isocyanate group and melamine group The hardening | curing agent containing the above can be included.

In a first aspect of the present invention, the hydroxyl value of the binder resin may be 5 to 100 mgKOH / g.

In the first aspect of the present invention, the number average molecular weight of the binder resin may be 1,000 to 25,000.

In the first aspect of the present invention, the isocyanate group may be a block product of one or more kinds or derivatives thereof selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate and xylene diisocyanate. have.

In the first aspect of the present invention, the isocyanate group may be 0.9 to 1.2 of the resin hydroxyl group in stoichiometric ratio.

In the first aspect of the present invention, the melamine group may be one or more selected from the group consisting of alkylated, imino and carboxylated.

In the first aspect of the present invention, the melamine group may be 10 to 30% of the total resin content of the paint composition by weight ratio.

2nd aspect of this invention for solving the said another subject is 1 or more types of binder resin chosen from the group which consists of polyester, an alkyd, an acrylic resin, and the resin which modified it to the steel plate, and 1 or more types chosen from an isocyanate group And applying a coating composition comprising a curing agent including at least one selected from a melamine group to form a coating film; A primary curing step of heating the coating film; Machining the steel plate on which the first cured coating film is formed to make a part; A secondary curing step of heating the component to cure the coating film; Assembling the component to a vehicle body; And electroplating the assembled vehicle body; to provide a method for manufacturing an automobile, comprising improving the corrosion resistance of the cut surface of the lead steel plate and the ham flange.

In a second aspect of the present invention, the hydroxyl value of the binder resin may be 5 to 100 mgKOH / g.

In a second aspect of the present invention, the number average molecular weight of the binder resin may be 1,000 to 25,000.

In the second aspect of the present invention, the isocyanate group may be a block product of one or more kinds or derivatives thereof selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate and xylene diisocyanate. have.

In the second aspect of the present invention, the isocyanate group may be 0.6 to 1.0 of the resin hydroxyl group in stoichiometric ratio.

In the second aspect of the present invention, the melamine group may be one or more selected from the group consisting of alkylated, imino and carboxylated.

In the second aspect of the present invention, the melamine group may be 10 to 30% of the total resin content of the paint composition by weight ratio.

In a second aspect of the invention, the coating gloss after secondary curing may be at least 70% of the primary cured coating gloss.

In the second aspect of the present invention, in the first curing step, the coating film may be heated to 180 to 300 ℃.

In the second aspect of the present invention, the secondary curing step, the component may be heated to 140 to 200 ℃.

3rd aspect of this invention for solving the said another subject is 1 or more types of binder resin chosen from the group which consists of polyester, an alkyd, an acrylic resin, and the resin which modified it to the steel plate, and at least 1 type selected from the isocyanate group. And applying a coating composition comprising a curing agent including at least one selected from a melamine group to form a coating film; A primary curing step of heating the coating film; Machining the steel plate on which the first cured coating film is formed to make a part; Assembling the component to a vehicle body; Electroplating the assembled vehicle body; And curing the electrodeposited coating film, wherein, in the curing process of the electrodeposited coating film, the primary cured coating film is secondary cured.

In the second or third aspect of the present invention, the primary curing step may be performed for 10 seconds to 1 minute, and the secondary curing step may be performed for 15 to 40 minutes.

According to the coating method according to the present invention, it is possible to prevent the corrosion of the cut surface and the ham flange, which were a problem when using the lead steel sheet, while removing the middle, top and clear coat processes in the conventional automotive coating process. The steel sheet can be applied to automobile manufacturing processes.

In addition, according to the coating method according to an embodiment of the present invention, since the scratch resistance, color realization and glossiness of the coating film can be increased through the secondary curing after processing, it is excellent in exterior and exterior materials for automobiles and other beautiful appearance It can be applied to various fields where coating properties are required.

Figure 1 shows the results of the salt spray test for the electrodeposited coating specimen and the electrodeposited coating specimen after machining according to Example 1 of the present invention.
Figure 2 shows the results of the salt spray test for the electrodeposited coating specimen and the electrodeposited coating specimen after machining in accordance with Example 2 of the present invention.

The present inventors have studied to solve the problem of cut surface and ham flange corrosion and property degradation of the coating film in order to apply the lead-length steel sheet (pre-primed steel sheet and pre-finished steel sheet) to the automobile manufacturing process, Electrodeposition after assembling the machined lead steel sheet into the automobile body improves the corrosion resistance of the car body, the cut surface, and the ham flange, while reducing the color characteristics of the lead steel sheet substantially. In the case of using the lead coating material of the present invention, the physical properties of the coating film generated in the molding step can be partially recovered through the curing process after the electrodeposition coating, and thus it is found that the lead sheet steel can be applied to the exterior plate of the automobile. Came to.

In general, a preprimed steel sheet is a form of weldable thin plate, which is a method of performing an intermediate and top coat coating process immediately after cutting and processing without an electrodeposition process.

However, in the present invention, a 'preprimed steel sheet' is a non-welded steel sheet formed with a coating film required for automobiles, and after being cut and processed, is fastened to the vehicle body and then subjected to corrosion resistance of a portion such as a cut surface and a ham flange. After the electrodeposition coating process to impart, means a steel plate is performed in the middle or top coating process.

In addition, in this invention, a "prefinished steel sheet" means the steel plate by which all the coating films of the intermediate | middle and top coat were coated by the roll coating process.

In general, electrodeposition coating is performed after the formation process of the phosphate chemical film, and the chemical composition and hardness of rust preventive, corrosion resistance, high temperature, and oxidative property are formed by chemically treating the metal surface to form a film on the surface of the steel sheet. And increase the wear resistance.

Electrodeposition coating refers to a process in which electrolysis, electrophoresis, electroprecipitation, and electropenetration occur simultaneously when a current flows between a steel plate deposited with an anode or a cathode in an electrodeposition paint solution and its counter electrode.

The pre-primed steel sheet according to the present invention comprises a curing agent comprising at least one binder resin selected from the group consisting of polyesters, alkyds, acrylic resins and resins modified therefrom, and at least one kind selected from isocyanate groups or melamine groups. It is characterized by including the coating film formed by the coating composition containing.

The binder resin of the coating composition for pre-primed steel sheet contains a hydroxyl group, and the hydroxyl value is preferably 5 to 100 mgKOH / g, which is insufficient when the hydroxyl value is less than 5 mgKOH / g. It is because chemical-resistance and solvent resistance fall and, on the contrary, when hydroxyl value exceeds 100 mgKOH / g, workability according to high hardening density falls. The range of the more preferable hydroxyl value with respect to the binder resin of the said coating composition for preprimed steel sheets is 5-50 mgKOH / g.

The binder resin of the coating composition for pre-primed steel sheet is not particularly limited as long as it is within the range of the hydroxyl group value. For example, a polyester resin, an alkyd resin, or an acrylic resin may be used. It may be a resin modified these. Such resins may be used alone or in parallel.

In addition, the paint composition for pre-finish steel sheet according to the present invention is at least one binder resin selected from the group consisting of polyesters, alkyds, acrylic resins and modified resins thereof, at least one selected from the isocyanate group, and from the melamine group It includes a hardening agent including at least one selected, and can be applied to the steel sheet and subjected to the primary curing to perform mechanical processing, and then to recover the mechanical or chemical properties of the coating film damaged during the mechanical processing through the secondary curing It features.

The paint composition for the prefinished steel sheet according to the present invention can be adjusted to the processing step of the leaded steel sheet according to the present invention when it is applied to the leaded steel sheet by adjusting the mixing ratio between the binder resin and the curing agent as described above. There is a characteristic to one.

In general, the strength and flexibility of the coating film are opposite properties. High-strength coatings have excellent scratch resistance, but are brittle and have low chipping resistance and are very sensitive to heat. In contrast, highly flexible coatings are excellent in chipping resistance and less sensitive to heat, but are less scratch resistant. Such strength and flexibility are highly dependent on the crosslinking density of the binder resin and the curing agent constituting the coating film. The higher the crosslinking density of the thermosetting polymer, the smaller the difference between the glass transition temperature and the brittle transition temperature.

In view of the correlation between the crosslinking density and the coating film properties, the present inventors first give the desired physical properties necessary for the coating film processing in a short baking process, and then, after the processing is completed, the electrodeposition process improves the corrosion resistance of the cut surface and the ham flange. In addition, by performing the secondary curing of the pre-finish coating film at the same time as the curing process of the electrodeposition coating film, it was possible to improve the strength and scratch resistance of the coating film as well as the recovery of the appearance characteristics degraded by the processing process.

The binder resin of the prefinished steel sheet paint contains a hydroxyl group, and the hydroxyl value is preferably 5 to 100 mgKOH / g, and when the hydroxyl value is less than 5 mgKOH / g, the curability of the coating film is insufficient. This is because the chemical resistance and the solvent resistance decrease and, on the contrary, when the hydroxyl value exceeds 100 mgKOH / g, the recovery rate of the appearance by secondary curing is low. The more preferable hydroxyl value value for secondary curing is 5 to 50 mgKOH / g.

The binder resin of the paint for prefinished steel sheet is not particularly limited as long as it is within the range of the hydroxyl group value, and examples thereof include polyester resins, alkyd resins, or acrylic resins. It may be a resin modified these. Such resins may be used alone or in parallel.

The number average molecular weight of the binder resin of the lead field (preprimed and prefinished) steel sheet coating material is preferably in the range of 1,000 to 25,000, which is deteriorated in workability when the number average molecular weight is less than 1,000, and is high in excess of 25,000. This is because the viscosity lowers the solids content and is undesirable.

Isocyanate compounds may be used alone or in combination with other compounds as the curing agent for the coating material for the lead (pre-primed and pre-finished) steel sheet, melamine or melamine resin may be used as other curing agents, most preferably Preferably, the isocyanate compound and the melamine compound are used in combination.

In addition, the isocyanate compound may be a block product of one or more kinds or derivatives thereof selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate and xylene diisocyanate. For example, some or all of the isocyanate groups of isocyanate derivatives such as the isocyanate monomer or its biuret and isocyanurate may be prepared by blocking with a blocking agent. In addition, the blocking agent is ε-caprolactam, methyl ethyl ketone oxime, 1,2-pyrazole, diisopropylamine or 3,5-dimethylpyrazole (dimethylpyrazole) and the like can be used.

In the present invention, if the steel sheet that can be used in the lead steel sheet, for example, can be used regardless of the type, such as zinc alloy plated steel sheet, electro zinc plated steel sheet, hot dip galvanized steel sheet, zinc alloy plated steel sheet is a preferred example.

In addition, the lead coating composition according to the present invention is a thermosetting paint composition curable through heat treatment, specifically, it may be a one-component thermosetting coating composition.

In addition, another feature of the present invention is the first curing step of the coating film for forming after applying the above-described paint composition, the forming step, and the secondary curing of the coating film for improving the mechanical properties of the coating film and the appearance after molding A method for processing a lead sheet comprising a step.

The primary hardening step is to satisfy the processability and mechanical properties of the lead steel sheet. In addition, the secondary curing process means a recuring process of the first hardened coating film, and may be performed simultaneously with the curing process of the coating film formed by the electrodeposition process, and improves strength and scratch resistance and restores appearance properties. For the purpose of

In the first curing step, the heating temperature (the highest reaching temperature of the steel sheet) is preferably 180 ° C to 300 ° C, which is less than 180 ° C, and exhibits a slight adhesive property in an uncured state, and when it exceeds 300 ° C. This is because there is a problem that the appearance of the coating film is lowered due to too fast curing. More preferably, the heating temperature of the first curing step is in the range of 180 ° C to 250 ° C.

In addition, the first curing step is preferably carried out in 10 seconds to 5 minutes, which is less than 10 seconds hardening of the coating film is difficult to carry out the subsequent molding process, even within 5 minutes physical properties required in the molding process Not only can be provided, but if it exceeds 5 minutes, excessive curing may not be sufficient to recover physical properties in the secondary curing step. The heat treatment time (baking time) of the first curing step is more preferably 10 seconds to 2 minutes, and most preferably 10 seconds to less than 1 minute.

In addition, in the secondary curing step, the heating temperature (the highest temperature of the steel sheet) is preferably 140 ℃ to 200 ℃, which is a problem that the secondary curing does not proceed if less than 140 ℃, if the sulfur exceeds 200 ℃ This is because there is a problem that degeneration of the coating film due to the change can occur. More preferably, the heating temperature of the secondary curing step is in the range of 150 ° C to 180 ° C.

In addition, the secondary curing step is preferably carried out for 5 to 50 minutes, which is less than 5 minutes, the coating film is denatured when more than 50 minutes without increasing the crosslinking density required for secondary curing of the coating film is achieved This is because yellowing may occur. The heat treatment time (baking time) of the secondary curing step is more preferably 20 minutes to 35 minutes.

Hereinafter, the present invention will be described in more detail through embodiments of the present invention, but the scope of the present invention is not limited thereto.

Example 1

Table 1 to Table 4 show the composition of the paint for preprimed steel sheet developed by the present inventors. Resin VDA-0185-65 and ES-955 were supplied by PPG Korea and SK Chemicals.

Weight ratio of hardener to resin 20% 30% ingredient Product Name wt [%] wt [%] mill sol. Resin VDA-0185-65 23.30 22.74 Solvent Dibasic ester 13.11 12.79 Pigment Carbon black 0.73 0.71 Titanium oxide 9.47 9.24 Cr-free pigment 5.82 5.68 Leveling agent Modaflow 2100 0.36 0.35 Component adjustment Solvent Kocosol # 150 21.41 20.89 Hardener Cymel 303 LF 4.77 6.98 catalyst p-toluene sulfonic acid 0.55 0.60 Resin ES-955 20.49 20.00 Sum 100 100

Weight ratio of hardener to resin 20% 30% ingredient Product Name wt [%] wt [%] mill sol. Resin VDA-0185-65 23.30 22.74 Solvent Dibasic ester 13.11 12.79 Pigment Carbon black 0.73 0.71 Titanium oxide 9.47 9.24 Cr-free pigment 5.82 5.68 Leveling agent Modaflow 2100 0.36 0.35 Component adjustment Solvent Kocosol # 150 21.41 20.89 Hardener Cymel 1116 4.77 6.98 catalyst p-toluene sulfonic acid 0.55 0.60 Resin ES-955 20.49 20.00 Sum 100 100

Equivalent Ratio of Curing Agent to Resin 1.1 1.2 ingredient Product Name wt [%] wt [%] mill sol. Resin VDA-0185-65 22.95 22.81 Solvent Dibasic ester 12.91 12.83 Pigment Carbon black 0.72 0.71 Titanium oxide 9.32 9.27 Cr-free pigment 5.74 5.70 Leveling agent Modaflow 2100 0.36 0.36 Component adjustment Solvent Kocosol # 150 21.08 20.96 Hardener BL 3175 SN 5.42 5.87 catalyst Dibutyltindilaurate 1.08 1.20 Resin ES-955 20.42 20.30 Sum 100 100

Equivalent Ratio of Curing Agent to Resin 1.1 1.2 ingredient Product Name wt [%] wt [%] mill sol. Resin VDA-0185-65 22.12 21.92 Solvent Dibasic ester 12.45 12.33 Pigment Carbon black 0.69 0.68 Titanium oxide 8.99 8.90 Cr-free pigment 5.53 5.48 Leveling agent Modaflow 2100 0.35 0.34 Component adjustment Solvent Kocosol # 150 20.32 20.14 Hardener BL 4265 SN 8.25 8.92 catalyst Dibutyltindilaurate 1.63 1.78 Resin ES-955 19.69 19.50 Sum 100 100

In the case of melamine-based curing agent was calculated as a weight ratio to the resin based on the solid content (Table 1 and Table 2), the isocyanate-based curing agent was calculated based on the chemical equivalent ratio of the OH group and the NCO group.

[Example 2]

The resin and hardener ratios of the clear paints for the prefinish paints are shown in Table 5 below, where the resins were provided by SK Chemicals as ES-960. The crosslinking agent was Baxenden's BI7982, Bayer's Desmodur BL 3175SN (BL3175) and Cymel 325 (C325), and dibutyltin dilaurate (DBTL) was used as a catalyst.

Specimen No. BI7982 DBTL C303 p-TSA One 0.34 0.09 0.41 0.09 2 0.34 0.10 0.61 0.10 3 0.40 0.09 0.41 0.09 4 0.40 0.10 0.61 0.10 5 0.46 0.09 0.41 0.09 6 0.46 0.10 0.61 0.10 BL3175 DBTL C303 p-TSA 7 0.31 0.09 0.41 0.09 8 0.31 0.10 0.61 0.10 9 0.36 0.09 0.41 0.09 10 0.36 0.10 0.61 0.10 11 0.41 0.09 0.41 0.09 12 0.41 0.10 0.61 0.10

The characteristic of the clear coat paint was to improve the workability during the primary curing and the strength of the coating film during the secondary curing by controlling the curing reaction rate by using isocyanate and melamine simultaneously. The isocyanate-based curing agent was prepared in the range of equivalent ratio of 0.6 to 0.8 based on the OH group of the resin, and melamine was prepared by blending the mixing ratio of the resin and the curing agent to 10 to 15 wt% based on the solids content.

Using the paints according to Examples 1 and 2 shown in the above table was coated on galvanized steel (GI) having a thickness of 0.8mm, the physical properties of the coating film for each specimen was performed. At this time, the average thickness of the dry film formed on the specimen was 20㎛. Curing was carried out using an auto-discharge oven, and the peak metal temperature (PMT) was 232 ° C. for preprimed paint and 224 ° C. for prefinish paint.

The physical properties of the coating film thus formed were evaluated by thickness, gloss, pencil hardness, and MEK Rub test.

As a result, the pencil hardness of all the pre-primed steel sheet was more than HB, when using a melamine-based curing agent showed a higher hardness level as F. In the MEK rub test, all specimens showed a high value of 100 or more times, indicating a high level of cure density. Table 6 below shows the gloss, pencil hardness, and MEK-rub test results for the steel sheet on which the coated film was formed with the pre-finished paint.

sample Polish Pencil hardness MEK-rub 20 ° 60 ° 85 ° One 96.2 134 91.7 2H More than 100 times 2 93.4 137 93.6 F More than 100 times 3 87.9 134 92.7 F More than 100 times 4 87.1 132 93.4 F More than 100 times 5 75.1 119 92 H More than 100 times 6 78.5 129 89.7 F More than 100 times 7 80.9 128 87.2 F More than 100 times 8 72.3 125 91.9 2H More than 100 times 9 93.1 135 95 3H More than 100 times 10 84.5 134 88.9 F More than 100 times 11 86.6 135 93.6 H More than 100 times 12 86.2 130 94 F More than 100 times

The specimens were selected by referring to the test results of the lead sheet (pre-primed and pre-finished) steel sheets coated with the paint (pre-primed: specimens containing 20 wt% of Cymel 303LF relative to the resin, pre-finished: No. 12 Electrodeposition coating was performed, and electrodeposition coating was provided by PPG Korea.

First, prepare a test piece subjected to T-bending (1T, 2T) on a lead sheet (pre-primed and pre-finished) steel plate, and a test piece subjected to tensile elongation (10%, 20%). The electrodeposition process was performed.

The electrodeposition process was performed as follows.

First, the steel plate is immersed in degreasing solution (Chemkleen 177, PPG Korea) for 2 minutes, washed with water and washed. After immersing in a surface correction solution (Rinse Conditioner, PPG Korea) for 1 minute, and then immersed in phosphate solution for 2 minutes, washed with water to form a phosphate film. The prepared phosphate treated specimens were subjected to a cationic electrodeposition coating process. Electrode was connected by grounding the + pole to the specimen and the-pole to the paint.

At this time, the current varies depending on the electrodeposition paint thickness. In the present invention, the voltage is about 200 to 240V, the temperature is 28 to 34 ° C, and the electrodeposition time is about 2 to 4 minutes. After electrodeposition was washed with water and cured for 30 minutes in an oven at 180 ℃ to complete the electrodeposition coating process. At this time, the electrodeposition coating process to prevent corrosion due to damage of the cut surface and the coating film after mechanical processing to form a coating and coating film thickness does not affect the appearance properties of the lead steel sheet.

Tables 7 and 8 below show the results of the drawn color difference diagrams for lead steel sheets. Table 7 is a color difference diagram before the electrodeposition process of the lead sheet steel, and Table 8 is a color difference result after the electrodeposition process.

Table 9 shows the gloss results before the electrodeposition process of the lead steel sheet, and Table 10 shows the gloss results after the electrodeposition process.

In the results before and after the electrodeposition coating process, when the 10% stretched and 20% stretched to 0%, it is judged that the color difference due to the stretching and electrodeposition can be neglected in the case of pre-primed steel sheet. In this case, the color difference was more than 1% before electrodeposition, but after the electrodeposition process, the difference was greatly reduced and reached a negligible level.

This result is judged to be a physical property recovery by the two-step hardening which is a characteristic of the pre-finish steel sheet. Similar results were found in the case of gloss.

Steel plate Stretching L a b △ L Δa Δb ΔE free
Primed 0% (STD) 42.26 -1.93 -0.34 10% 42.29 -1.95 -0.51 0.03 0.02 0.17 0.17378 20% 41.85 -1.95 -0.43 0.41 0.02 0.09 0.42024 free
Finished 0% (STD) 33.29 1.61 2.19 10% 34.55 1.48 1.89 1.26 0.13 0.3 1.30173 20% 35.23 1.44 1.74 1.94 0.17 0.45 1.99875

Steel plate Stretching L a b △ L Δa Δb ΔE free
Primed 0% (STD) 42.63 -1.78 -0.71 10% 42.8 -1.77 -0.84 0.17 0.01 0.13 0.21424 20% 43.14 -1.74 -1.16 0.51 0.04 0.45 0.68132 free
Finished 0% (STD) 33.35 1.6 2.31 10% 33.4 1.61 2.78 0.05 0.01 0.47 0.47276 20% 33.71 1.55 2.5 0.36 0.05 0.19 0.41012

Stretching 20 ° 60 ° 85 ° free
Primed 10% 5.6 35.1 59.7 20% 3.2 24.4 49.4 free
Finished 10% 48.5 83.6 90.7 20% 14.3 52.4 81.1

Gloss Stretching 20 ° 60 ° 85 ° free
Primed 10% 5.6 34.4 59.6 20% 3.2 23.3 49.6 free
Finished 10% 76.7 99.2 95.1 20% 50.5 94.6 91.5

The specimens were also subjected to a salt spray test (SST) for 1000 hours. The results are presented in FIGS. 1 (preprimed steel) and 2 (prefined steel), and the left specimen is the specimen after electrodeposition and the right specimen is the specimen before electrodeposition.

As can be seen from Figs. 1 and 2, the corrosiveness in the cut surfaces of those with and without electrodeposition coating shows a remarkable difference. Therefore, when the electrodeposition coating is performed after machining using the lead steel sheet, the lead steel sheet can also be used in automotive processes requiring excellent appearance and corrosion resistance.

Claims (21)

Machining the lead sheet to make parts;
Assembling the component to a vehicle body; And
Electrodeposition of the assembled vehicle body; including the step of improving the corrosion resistance of the cut surface and the ham flange of the lead wire steel sheet. The method of claim 1,
A method for manufacturing a vehicle, characterized in that to perform a phosphate chemical conversion treatment process before the electrodeposition coating. 3. The method according to claim 1 or 2,
The coating composition coated on the lead steel sheet, at least one binder resin selected from the group consisting of polyesters, alkyds, acrylic resins and modified resins thereof, and a curing agent containing at least one member selected from the isocyanate group and the melamine group Method of manufacturing a vehicle comprising a. The method of claim 3, wherein
The hydroxyl value of the binder resin is 5 to 100 mgKOH / g of a method for manufacturing a vehicle, characterized in that. The method of claim 3, wherein
The number average molecular weight of the binder resin is a manufacturing method of the vehicle, characterized in that 1,000 to 25,000. The method of claim 3, wherein
The said isocyanate group is blockade of 1 or more types or its derivative (s) chosen from the group which consists of hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and xylene diisocyanate. The method of claim 3, wherein
The said isocyanate group is 0.9-1.2 of the resin hydroxyl group by stoichiometric ratio, The manufacturing method of the motor vehicle characterized by the above-mentioned. The method of claim 3, wherein
The melamine group is a method for producing a vehicle, characterized in that at least one member selected from the group consisting of alkylated, imino and carboxylated. The method of claim 3, wherein
The melamine group is a manufacturing method of a vehicle, characterized in that 10 to 30% of the total resin content of the paint composition by weight ratio. The steel sheet contains at least one binder resin selected from the group consisting of polyesters, alkyds, acrylic resins and resins modified therefrom, at least one selected from isocyanate groups, and at least one curing agent selected from melamine groups. Applying a coating composition to form a coating film;
A primary curing step of heating the coating film;
Machining the steel plate on which the first cured coating film is formed to make a part;
A secondary curing step of heating the component to cure the coating film;
Assembling the component to a vehicle body; And
Electrodeposition of the assembled vehicle body; including the step of improving the corrosion resistance of the cut surface and the ham flange of the lead wire steel sheet. 11. The method of claim 10,
The hydroxyl value of the binder resin is 5 to 100 mgKOH / g of a method for manufacturing a vehicle, characterized in that. 11. The method of claim 10,
The number average molecular weight of the binder resin is a manufacturing method of the vehicle, characterized in that 1,000 to 25,000. 11. The method of claim 10,
The said isocyanate group is blockade of 1 or more types or its derivative (s) chosen from the group which consists of hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and xylene diisocyanate. 11. The method of claim 10,
The said isocyanate group is 0.6-1.0 of the resin hydroxyl group by stoichiometric ratio, The manufacturing method of the motor vehicle characterized by the above-mentioned. 11. The method of claim 10,
The melamine group is a method for producing a vehicle, characterized in that at least one member selected from the group consisting of alkylated, imino and carboxylated. 11. The method of claim 10,
The melamine group is a manufacturing method of a vehicle, characterized in that 10 to 30% of the total resin content of the paint composition by weight ratio. 11. The method of claim 10,
A method of manufacturing an automobile, wherein after the second curing, the coating gloss is 70% or more of the primary cured coating gloss. 11. The method of claim 10,
The primary curing step, the manufacturing method of the vehicle, characterized in that for heating the coating to 180 to 300 ℃. 11. The method of claim 10,
The secondary curing step, the vehicle manufacturing method, characterized in that for heating the parts to 140 to 200 ℃. The steel sheet includes at least one binder resin selected from the group consisting of polyesters, alkyds, acrylic resins and resins modified therefrom, at least one selected from the isocyanate groups, and at least one curing agent selected from the melamine group. Applying a coating composition to form a coating film;
A primary curing step of heating the coating film;
Machining the steel plate on which the first cured coating film is formed to make a part;
Assembling the component to a vehicle body;
Electroplating the assembled vehicle body; And
Hardening the electrodeposited coating;
In the hardening process of the electrodeposition-coated coating film, the primary cured coating film is characterized in that the secondary curing. The method of claim 10 or 20,
The first curing step is performed for 10 seconds to 1 minute, the secondary curing step is a method of manufacturing a vehicle, characterized in that performed for 15 to 40 minutes.

Images