JP3000896B2 - Manufacturing method of organic composite coated steel sheet with excellent scratch resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method of forming a chromate film and an organic composite resin film containing silica in a resin on a zinc or zinc alloy-plated steel sheet (hereinafter collectively referred to as a zinc-based plated steel sheet). The present invention relates to a method for producing an organic composite coated steel sheet having a three-layer structure of a zinc-based plating film / chromate film / organic composite resin film.

More specifically, the present invention is to improve the adhesion between a chromate film and an organic composite resin film, so that the organic composite coated steel sheet has a flaw caused by a tension pad at the time of slitting and a flaw caused by a die at the time of press working. The present invention relates to a method for producing an organic composite coated steel sheet having excellent scratch resistance, in which the steel sheet is less likely to be scratched due to rubbing between the steel sheets during transportation or the like, and is less likely to lose its appearance when used without painting.

[0003]

2. Description of the Related Art An organic composite coated steel sheet having a zinc-plated steel sheet as a base material and a chromate film and an organic composite resin film containing silica sequentially formed on the surface of the base material has been known for its excellent corrosion resistance and uniform appearance. It is widely used without painting, mainly for building material manufacturers.

[0004] Organic composite coated steel sheets are generally subjected to chromate treatment and coating with a resin solution containing silica after plating on a steel strip-shaped zinc-coated steel sheet, and after baking the coating film, are stored in a coil form. You. Then, at the time of shipping, the coil is rewound, slit (cut) to the specified dimensions, and then stacked and transported. The user generally presses without painting and assembles it into the final product.

[0005] The organic composite coated steel sheet is often scratched during the above-mentioned handling. For example, at the time of slitting, the organic composite-coated steel plate is pressed by a pad called a tension pad in order to take up a winding tension. At this time, a pad flaw may be generated by the tension pad. Also, when stacking and transporting slit organic composite coated steel sheets, flaws called ablation caused by rubbing of the steel sheet surfaces, and contact flaws occur when they come into contact with the mold during press working Sometimes.

[0006] Such scattering of scratches causes deterioration of corrosion resistance and discoloration of black, so that the product is rejected as poor appearance especially in the case of an organic composite coated steel sheet premised on no painting. In some cases, there has been a strong demand for improvement of scratch resistance for the purpose of preventing scratches at the time of slitting, stacking conveyance, press working, and the like.

Further, since the organic composite coated steel sheet has a resin film on the uppermost layer, if a rust-preventive oil is used during storage by a user or a processing oil (lubricating oil) is used before press working, the resin is coated. The appearance may be deteriorated due to the penetration of oil into the film. In order to eliminate this point and the degreasing process after processing (in general, an organic solvent harmful to the environment is used), organic composite coated steel sheets are generally used without oiling, and are more resistant to scratches. There is a demand for improved sex.

As a conventional technique for improving the scratch resistance of an organic composite coated steel sheet, for example, a special hardener is added to a resin (Japanese Patent Application Laid-Open No. 3-136840) or the resin baking temperature is increased to a higher temperature. According to Japanese Unexamined Patent Publication No. 3-197131, the hardness of the uppermost resin film is increased so that the resin film is hardly damaged. Further, a special hollow resin particle is added to the organic composite resin film (Japanese Patent Application Laid-Open No. Hei 4-27537) or a lubricant is added (Japanese Patent Application Laid-Open Nos. 5-169587 and 5-51763). It is also known to improve the lubricity of the coating and thereby improve the scratch resistance.

[0009]

The above prior arts all improve the scratch resistance of the organic composite coated steel sheet by modifying the uppermost organic composite resin film. No attempt has been made to improve the scratch resistance of the organic composite coated steel sheet by modifying the chromate film.

In order to improve the scratch resistance of an organic composite coated steel sheet caused by rubbing with a tension pad, rubbing between steel sheets, contact with a mold or the like, the present inventors have proposed an organic composite coated steel sheet of the uppermost layer. Modification of the resin film alone is not enough, and it is important to improve the chromate film, especially to improve the adhesion of the chromate film to the organic composite resin film and to make it difficult for the organic composite resin film to peel off. Was.

[0011] Japanese Patent Application Laid-Open No. 4-285179 discloses that an aqueous composition containing a silane coupling agent is applied to a chromate-treated steel sheet to improve the adhesion of the coating film and improve the scratch resistance. However, this method also improves the adhesion between the organic composite resin layer and the chromate film layer by the composition of the resin film, and does not aim at improving the chromate film itself.

An object of the present invention is to improve the scratch resistance, including tension pad resistance, by improving the adhesion between a chromate film and an organic composite resin film thereover by modifying the chromate film. An object of the present invention is to provide a method for producing an organic composite coated steel sheet capable of obtaining a composite coated steel sheet.

[0013]

Means for Solving the Problems As a result of repeated studies to achieve the above object, the present inventors have found that the chromate film and the upper organic composite resin film inhibit the adhesion. By knowing that the Zn ions eluted into the processing solution from the base metal plating layer during processing and the fluctuations in pH during processing, by regulating these conditions to a certain range,
The present inventors have found that the adhesion between the chromate film and the upper organic composite resin film is significantly improved, and have reached the present invention.

Here, the present invention is directed to a method of forming a metal Cr on a surface of a galvanized steel sheet by a reactive or coating type chromate treatment.
Equivalent coating weight to form a chromate film of 5~200 mg / m ^2, of organic composite coated steel sheet which comprises forming an organic composite resin coating adhesion amount 0.2 to 3.5 g / m ² containing silica thereon In the production, the chromate treatment is performed while controlling the Zn content of the treatment liquid to 30 g / l or less, or while controlling the pH of the treatment liquid to 1.0 to 5.0. This is a method for producing an organic composite coated steel sheet having excellent properties.

In a preferred embodiment, the organic composite resin film contains 2 to 20 parts by weight of lubricant particles having an average particle size of 10 μm or less based on 100 parts by weight of the total amount of silica and resin on a solid content basis. Contains in proportions. Hereinafter, the present invention will be described in detail.

Base Metal Plated Steel Sheet The base material of the organic composite coated steel sheet of the present invention is a zinc-based coated steel sheet,
That is, a galvanized steel sheet and a zinc alloy-coated steel sheet (including a galvannealed steel sheet). Examples of the zinc alloy plating type are any alloy plating containing Zn as a main component, such as Zn—Ni, Zn—Fe, Zn—Co, and Zn—Al. Further, the zinc-based plated steel sheet may be a zinc-based composite (eutectoid) -coated steel sheet in which an additive for imparting functionality is eutectoid in the plating film. However, pure zinc plating has the most remarkable effects of the present invention because the hardness of the plating film is low and the plating film is easily scratched. Therefore, a preferred base material is a galvanized steel sheet.

The method of plating a zinc-based plated steel sheet is not particularly limited, and is a hot-dip plating method of dipping in a molten metal, an electroplating method of electrically depositing, and a vapor-phase plating method of depositing from steam (e.g., vapor deposition, sputtering, etc.). ). In addition, the adhesion amount of the plating film of the galvanized steel sheet
(Hereinafter, the amount of adhesion per one side) is generally 0.5 to
It is in the range of 80 g / m ² , preferably 10 to 40 g / m ² .

[0018] By immersing the chromate treatment base material plated steel sheet to a chromate treatment liquid deposition amount of metallic Cr terms is formed on the plated surface a chromate film of 5~200 mg / m ^2.

The formation of a film of a zinc-based plated steel sheet by chromate treatment is represented by, for example, 2Cr ⁶⁺ + 3Zn → 2Cr ³⁺ + 3Zn ²⁺ ‥‥. That is, dissolution of zinc by chromate treatment solution
(Ionization of Zn) reduces Cr ⁶⁺ (CrO ₃ or dichromate) to Cr ³⁺ , and the formed Cr ³⁺ and acid anions (e.g., sulfate or phosphate ions) in the solution are converted. This results in the formation of a film made of a hardly soluble chromium salt. The above reaction in which zinc is eluted can be said to be an etching reaction of Zn. Some of the dissolved Zn ions are Cr ⁶⁺ or Cr
Reacts with ³⁺ and is incorporated into the film.

The above reaction is an example of the reaction found in the reactive chromate treatment. In the coating type chromate treatment, a reducing agent is used instead of Zn, and in the electrolytic type chromate treatment, film formation occurs by reducing Cr ⁶⁺ to Cr ³⁺ , respectively, electrically. However, even in the case of the coating type chromate treatment, the above reaction occurs due to the contact between the plated steel sheet and the chromate treatment solution, and the zinc elutes from the plating film of the base material to a different degree. As a result, in the reaction type and coating type chromate treatments, when the chromate treatment liquid is used continuously, the Zn content in the treatment liquid increases with the use time. Further, the pH of the chromate treatment liquid varies with the use time. In the electrolytic chromate treatment, since a negative potential is applied to the plated steel sheet of the base material, the elution reaction of zinc is prevented.

In the present invention, when a chromate film is formed by a reaction type or coating type chromate treatment, the Zn content of a chromate treatment solution that gradually increases if left untreated.
The content and pH are below 30 g / l for Zn content,
The pH is controlled in the range of 1.0 to 5.0. Accordingly, when an organic composite resin film containing silica is formed on the chromate film, the adhesion of the chromate film to the resin film is significantly increased.

When the Zn content of the chromate treatment liquid is more than 30 g / l, it becomes difficult to secure the adhesion of the chromate film to the organic composite resin film. Preferably, this Zn
Control the content to 20 g / l or less. Chromate treatment solution
Although the reason why the Zn content inhibits the adhesion with the organic composite resin film is not completely elucidated, the brittle and very fine Zn-Cr oxide crystals are formed on the surface of the base steel sheet during chromate treatment. Grows, the resin film and this fine Zn-Cr
It is presumed that peeling of the chromate layer and the organic composite resin film occurs between the oxide crystals and the formation of an amorphous chromate film required for ensuring adhesion to the resin film. As a result, friction with the tension pad,
It is considered that the resin film is easily peeled off due to rubbing between the steel sheets, contact with the mold, or the like, and the scratch resistance is deteriorated.

If the pH of the chromate treatment liquid is as low as less than 1.0, the Zn etching reaction with the plated steel sheet (eg, the above reaction) becomes excessive, and the amount of zinc eluted (accordingly,
In addition, it is difficult to control (Zn content), and Zn on the surface of the plating film is locally etched, so that the plating surface becomes brittle and the adhesion between the resin film and the chromate film is reduced. On the other hand, the pH of the chromate treatment solution is 5.
If the value is higher than 0, Zn ions eluted from the base metal plating layer into the processing solution will precipitate as hydroxides, which causes a problem in the processing step. In addition, even if a slight amount of Zn dissolved on the plating surface reacts with chromic acid to form an amorphous chromate film with good adhesion to the resin film, the adhesion between the plating layer and this amorphous chromate film deteriorates. Therefore, the adhesion of the resin film cannot be sufficiently secured. Therefore, in any case, the resin film is easily peeled off by rubbing or the like, and the scratch resistance is reduced. The preferred pH range of the chromate treatment solution is 1.5 to 4.0, more preferably 2 to 3.

The Zn content of the chromate treatment solution can be estimated from the treatment amount or the like, but can be easily measured by analyzing the treatment solution by an appropriate analytical method such as an atomic absorption method. The pH can be easily measured by conductivity measurement or a pH meter.

The Zn content is not more than 30 g / l, preferably 20 g / l
In order to perform the following management, a part or the whole of the chromate treatment liquid may be withdrawn at an appropriate time and replaced with a new liquid. If necessary, remove the extracted chromate treatment solution with Zn
Can be removed using a precipitation reaction or the like, and components such as Cr ⁶⁺ compounds (chromic acid, dichromate, etc.) and acids can be supplied to regenerate and reuse. To control the pH, an appropriate acid may be replenished as needed. In addition, by adopting an auto drain (automatic liquid exchange process) that periodically or continuously extracts and replenishes part of the chromate treatment solution, the Zn content and / or pH of the chromate treatment solution are automatically adjusted. Can also be managed.

As described above, in the present invention, a chromate film is formed by a reactive or coating type chromate treatment in which the Zn content and the pH of the treatment liquid increase or fluctuate with time. The chromate treatment can be performed in the same manner as in the related art, except for the management of the Zn content and / or the pH described above.

The reaction type chromate treatment is generally carried out by immersing a zinc-based plated steel sheet as a base material in an aqueous solution in which a Cr ⁶⁺ compound and, if necessary, an acid and other additives are dissolved.
In order to promote film formation, a reducing agent may be added to the reaction type chromate treatment liquid. The immersion time is relatively long, at least 5 seconds, usually 10 to tens of seconds. Accordingly, the amount of Zn eluted during the treatment increases, and the method of the present invention is the most effective chromate treatment method. The steel sheet removed from the chromate treatment liquid is then washed with water to remove soluble Cr ⁶⁺ and then dried.

The coating type chromate treatment solution usually contains a reducing agent in addition to the Cr ⁶⁺ compound. Further, the coating type chromate treatment liquid may contain a dispersion type additive such as silica and an aqueous resin in addition to a water-soluble additive such as an acid. In the coating type chromate treatment, a zinc-coated steel sheet as a base material is treated for a short time (usually 10 seconds or less, for example, 1 to 5 seconds).
After dipping, the excess liquid can be squeezed with a roll, or the treatment liquid can be applied to the base steel sheet by a roll or spray. The method of the present invention is particularly effective when treating by dipping or spraying. The treated steel sheet dries immediately. This drying is usually performed by heating, and during the drying, Cr ⁶⁺ in the film is reduced to Cr ³⁺ by the action of a reducing agent to form a film.

As described above, the adhesion amount of the chromate film is 5 to ²⁰⁰ mg / m ² . When the amount is less than 5 mg / m ² , corrosion resistance, which is an important performance of the organic composite coated steel sheet, cannot be secured, and it becomes difficult to form a uniform chromate film layer on the steel sheet surface. The adhesion between the composite resin film and the chromate film cannot be secured. On the other hand, when the Cr adhesion amount is larger than 200 mg / m ² , cohesive failure occurs in the chromate film layer, and it is also impossible to secure a sufficient adhesion between the organic composite resin film and the chromate film. Also, an increase in the amount of deposited Cr leads to an increase in the chromate treatment time, so that the amount of Zn etched on the plating surface increases, and the Zn in the chromate treatment solution increases.
An excessively large amount of Cr attached is not preferable in that the control of the Zn content becomes difficult because the content increases. Further, an excessive increase in the amount of deposited Cr is disadvantageous in terms of cost. Preferred Cr
Coating weight is in the range of 10~150 mg / m ^2.

Formation of Organic Composite Resin Film A resin solution containing silica is then applied to the chromate-treated zinc-coated steel sheet, and the film is usually dried or cured by baking to obtain an organic composite resin film (silica / resin coating). (Composite film) is formed with an adhesion amount of 0.2 to 3.5 g / m ² .

The type of resin used is preferably a resin having a large environmental barrier effect from the viewpoint of corrosion resistance and having excellent degreasing resistance to solvent degreasing and alkali degreasing performed by a user. Examples of suitable resins include acrylic resins, epoxy resins, urethane resins, and the like. A resin liquid used for coating is prepared by mixing silica with a base resin obtained by mixing one or more of these resins. The resin liquid is a solvent-type resin liquid using an organic solvent and an aqueous resin (eg, an emulsion resin, a water-soluble resin)
Although any of the resin liquids consisting of is preferably used, an aqueous resin is preferable.

Silica promotes film formation and has an action of trapping corrosion products. When silica is contained in a resin, corrosion resistance is further improved. The silica may be either colloidal silica (silica sol, aqueous silica) or gas phase silica (fumed silica, dry silica). In the case of an aqueous resin, it is preferable to use colloidal silica or hydrophilic gas phase silica. The average particle size (average primary particle size) of silica is preferably in the range of 3 to 20 nm, and the compounding amount thereof is such that the content in the resin film (that is, the ratio to the total amount of silica and resin on a solid basis) is SiO _2. Is preferably in the range of 5 to 40% by weight.

In addition to the resin and silica, the resin solution may be provided with a crosslinking agent, a reaction accelerator, a catalyst,
Various additives such as a silane coupling agent, a colorant, and a rust preventive pigment may be added as necessary. Further, as described later, it is preferable to add a solid lubricant powder to the resin liquid so that the obtained organic composite resin film contains lubricant particles having a specific particle size.

The organic composite resin film has a dry weight of 0.2 to 3.
It is formed so as to have an adhesion amount of 5 g / m ² . When the adhesion amount of the resin film is less than 0.2 g / m ² , sufficient corrosion resistance cannot be secured as the organic composite coated steel sheet. On the other hand, when the amount of resin
If it is larger than g / m ² , the resin layer itself is likely to undergo cohesive failure in the resin layer, so that the scratch resistance is rather reduced. A preferable resin coating weight is in the range of 0.5 to 1.8 g / m ² .

As described above, it is preferable to add a solid lubricant powder to the organic composite resin film. In addition to improving the adhesion between the chromate film and the resin film by controlling the Zn content and / or the pH in the liquid during the chromate treatment, the lubricating particles are contained in the resin film to improve the slipperiness. In addition, the scratch resistance is further improved, and scratches due to rubbing with the tension pad, rubbing between steel plates, contact with a mold or the like are less likely to occur.

The solid lubricant used in the present invention may be any of those generally used in the production of lubricated steel sheets, such as synthetic polyolefin waxes such as polyethylene and fluororesins such as polytetrafluoroethylene. .

The average particle size of the lubricant particles is 10 μm or less. If the average particle size is larger than 10 μm, since the lubricant particles are present on the surface of the resin film in such a way as to stick out the head,
When the lubricant is shaved by a tension pad, a mold, or the like, the coating becomes flawed. The preferred average particle size of the lubricant is in the range of 0.2-5.0 μm. Average particle size 0.2
When it is smaller than μm, the effect of adding the above-mentioned lubricant decreases.

The lubricant is contained in the resin film at a ratio of 2 to 20 parts by weight, preferably 5 to 10 parts by weight, based on 100 parts by weight of the total of silica (SiO ₂ ) and the resin on a solid basis. .
If the ratio of the lubricant is less than 2 parts by weight, the effect of adding the above lubricant cannot be sufficiently obtained. On the other hand, if a large amount of lubricant is present in the resin film in an amount of more than 20 parts by weight, the lubricant particles may stick out on the surface of the resin film, or the lubricant may bleed to the surface during baking of the resin film, and the lubricant may be removed. Since it appears on the surface and the lubricant on the surface is easily peeled off by rubbing with the tension pad, the mold, the steel plates, etc., the scratch resistance is rather lowered.

The above-described chromate film and organic composite resin film can be formed on both sides or one side of a base material plated steel sheet, depending on the application. Alternatively, the chromate film may be formed on both surfaces, and the organic composite resin film may be formed on only one surface. The organic composite coated steel sheet of the present invention,
Although it has sufficient corrosion resistance and scratch resistance that can be used without painting, it is of course possible to apply further painting if desired.

[0040]

EXAMPLES The method for producing an organic composite coated steel sheet of the present invention will be specifically described with reference to the following examples. In the following examples,% is% by weight unless otherwise specified.

(Example 1) As a base material of a zinc-coated steel sheet, electric Zn having an adhesion amount (per one side) of 20 g / m ² was used.
A plated steel sheet and an electric Zn-13% Ni alloy plated steel sheet were used. Each of these was a double-sided plated steel sheet and was manufactured by a continuous plating line. The thickness of the steel sheet is 0.
8 mm.

The treating solution used for the chromate treatment was prepared by ^adding ethylene oxide as a reducing agent to a chromic acid aqueous solution having a concentration of 40 g / l of total Cr so that the ratio of Cr ⁶⁺ / Cr ³⁺ becomes 1/1. The aqueous solution was prepared by adding 15 g / l of sulfuric acid and 3 g / l of silicic acid to the aqueous solution to which glycol was added. In order to investigate the effects of the Zn content and pH in the chromate treatment solution, zinc sulfate was added to the treatment solution to adjust the Zn content, and the pH of the treatment solution was adjusted.
Was adjusted by adding sulfuric acid or sodium hydroxide.

Using this chromate treatment solution, a coating type or reaction type chromate treatment was performed on any one of the zinc-based plated steel sheets at a constant temperature of 40 ° C. In the coating type chromate treatment, after immersing the steel sheet in the treatment liquid for 2 seconds, the excess treatment liquid is squeezed out with a roll and immediately
Performed by drying in an oven at 10 ° C for 10 seconds. The reactive chromate treatment was carried out by immersing the steel sheet in the same treatment liquid for 10 to 30 seconds, washing sufficiently with water to wash away soluble Cr ^6+, and then drying with hot air. The adhesion amount of the chromate film was changed by the squeezing amount at the time of roll squeezing in the coating type chromate treatment and by the immersion time in the reaction type chromate treatment.

After the chromate films are formed on both sides of the zinc-coated steel sheet as the base material, the acrylic emulsion is added to the zinc-based steel sheet in an amount of 20% based on the total amount of resin and silica on a solid basis.
Amount of silica (colloidal silica with an average particle size of 10 nm)
And optionally 25 parts by weight or less of a lubricant (polyethylene wax of various particle sizes) based on 100 parts by weight of the total solid content of the resin and silica, and uniformly mixed resin solution,
Apply with a bar coater on one side of the chromate film,
The coating film was baked by heating at a sheet temperature of 100 ° C. for 12 seconds to produce an organic composite coated steel sheet.

The organic composite coated steel sheet was evaluated for corrosion resistance and scratch resistance, which are important basic properties when no painting was performed, as follows. [Corrosion resistance] JIS Z 23 for specimens of organic composite coated steel sheet
A salt spray test specified in 71 was carried out, and a white rust generation time until 5% or more of white rust was generated with respect to the entire evaluation area was examined. Based on the results of conventional organic composite coated steel sheets, the base material is electric Zn
The corrosion resistance was judged to be acceptable if the white rust generation time was 200 hours or more for the plated steel sheet and if the white rust generation time was 600 hours or more for the electric Zn-Ni plated steel sheet.

[Scratch Resistance] With respect to the scratch resistance, two types of abrasion resistance against scratches due to rubbing between the organic composite coated steel sheets and tension pad resistance due to rubbing with the tension pad were examined.

[0047] As shown in resistant ablatable Figure 1, the two strip-type specimens of the same organic composite coated steel sheet, crossed by a surface to form an organic composite resin coating (resin surface) to the inner cross section 200 g /
After applying a torsion force in the direction of the arrow to the test piece while applying pressure by placing a weight of mm ² and rubbing the test pieces together,
A corrosion test was conducted for 480 hours with a humidity tester at a relative humidity of 95% or more and a temperature of 50 ° C. After the corrosion test, the state of scratches on the resin surface and the state of corrosion (rust generation) were visually observed. Ablation resistance was determined according to the following criteria. When the resin film did not contain a lubricant, a score of 4 or higher was passed, and when a lubricant was added to the resin film for the purpose of improving scratch resistance, a score of 5 was passed.

5: No scratches, no rusting 4: Slight scratches, no rusting 3: Half scratching, slight rusting 2: Scratching severity, light rusting 1: Resin peeling, severe rusting over the entire surface.

[0049] The test was performed as indicated in resistance to tension pad resistance Figure 2. That is, a 10 m diameter was placed at the center of the test piece fixed on a movable table with the resin side up.
Place the load rod having a diameter of 5mm through felting pad slider of m, while applying a load so that the average surface pressure on the loading bar is 100 g / mm ^2, as indicated by the arrow movable The test piece was reciprocated a predetermined number of times (moving width: 12 mm, moving speed: 4 mm / sec) to slide the pad slider against the resin surface. The temperature of the test piece was set to 50 ° C. in consideration of the influence of frictional heat with the pad. The resin surface after the sliding was visually observed, and the tension pad resistance was determined based on the following criteria. If this rating is 4 or more, the tension pad resistance is acceptable.

5: no pad flaw, no metallic luster 4: slight pad flaw, no metallic luster 3: half pad flaw, metallic luster 2: full pad flaw, metallic luster light 1: full pad flaw, metallic luster Full-scale test results show the plating type of the base steel sheet of the organic composite coated steel sheet,
Table 1 shows the Zn content and pH of the chromate treatment solution, the chromate treatment method, the adhesion amount of the chromate film (in terms of Cr), the adhesion amount of the organic composite resin film, the lubricant content, and the particle size.

[0051]

[Table 1]

As can be seen from Table 1, from Nos. 1 to 8, the amount of Cr adhering to satisfy corrosion resistance and scratch resistance is 5 to 200 mg / m 2.
² , In particular, the amount of Cr adhesion that gives the best tension pad resistance is
It can be seen that is 10~150 mg / m ^2.

From Nos. 9 to 12, it can be seen that as the Zn content of the chromate treatment liquid increases, the scratch resistance deteriorates. N
o. From 13 to 19, it can be seen that the adhesion amount of the organic composite resin film satisfying the corrosion resistance and the scratch resistance is 0.2 to 3.5 g / m ² . In particular, 0.5 to 1.8 g / m ² provides good tension pad resistance.

According to Nos. 20 to 24, when a lubricant is added for the purpose of further improving the scratch resistance, the particle size of the lubricant is effective at 10 μm or less. It can be seen that the particle size of the lubricant is optimally 0.2 to 5.0 μm. From Nos. 25 to 30, it is understood that the addition amount of the lubricant is preferably 2 to 20 parts by weight, and particularly when paying attention to the tension pad resistance, 5 to 10 parts by weight is the best.

(Example 2) An organic composite coated steel sheet was prepared in the same manner as in Example 1 using a chromate treatment solution having a constant pH of 3.0, and the effect of the Zn content in the chromate treatment solution was investigated in detail. did.

An electro-pure Zn-plated steel sheet was used as the base steel sheet. After forming a chromate film with a Cr adhesion of 80 mg / m ² by reactive chromate treatment using a treatment solution having a different Zn content, lubrication was performed. 0.8 μm of organic composite resin film without agent
(Equivalent to 0.9 g / m ² ). The scratch resistance (ablation resistance and tension pad resistance) of the obtained organic composite coated steel sheet was evaluated in the manner described above.

FIG. 3 shows the result. In FIG. 3, the upper score shows the ablation resistance, and the lower score shows the tension pad resistance. From FIG. 3, it can be seen that the chromate treatment solution Zn
If the content is 30 g / l or less, good scratch resistance can be obtained.
It is understood that the content is 20 g / l or less.

Example 3 The Zn content of the chromate treatment solution was
An organic composite coated steel sheet was produced in the same manner as in Example 1 while keeping the rate constant at 10 g / l, and the effect of the pH of the chromate treatment solution was investigated in detail.

An electro-pure Zn-plated steel sheet was used as the base steel sheet. After forming a chromate film having a Cr adhesion of 40 mg / m ² by a coating type chromate treatment using a treatment solution having a different pH, a lubricant was added. 1.0 μm (1.
(Equivalent to 2 g / m ² ). The scratch resistance (ablation resistance and tension pad resistance) of the obtained organic composite coated steel sheet was evaluated in the manner described above.

FIG. 4 shows the results. FIG. 4 also shows the ablation resistance in the upper part and the tension pad resistance in the lower part.
From FIG. 4, it can be seen that when the pH of the chromate treatment solution is 1.0 to 5.0, the scratch resistance is good, and particularly when focusing on the tension pad resistance, the optimum pH range is in the range of 1.5 to 4.0.

[0061]

As described above in detail, in the method for producing an organic composite coated steel sheet of the present invention, the Zn content and / or the pH
By controlling the chromate treatment while maintaining the temperature within the appropriate range, improving the flaw resistance of the organic composite coated steel sheet, especially the tension pad resistance, which was impossible with the modification of the resin film as proposed so far. Becomes possible.

Furthermore, by forming an organic composite resin film containing an appropriate lubricant after performing such a chromate treatment, it is possible to further improve the scratch resistance.

Therefore, according to the method of the present invention, scratches due to rubbing between the tension plates at the time of slitting, scratches due to rubbing between the steel plates during transportation, and scratches due to contact with the mold during press working, etc. The product appearance and product yield are improved because uncoated organic composite coated steel sheet products with reduced cracking can be easily manufactured, and the corrosion resistance is further improved because the flaws cause deterioration of the corrosion resistance. . Thus, the economic effect of the present invention is expected to be very large.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a method for evaluating abrasion resistance against rubbing between steel plates.

FIG. 2 is an explanatory view showing a method for evaluating tension pad resistance.

FIG. 3 shows that the Zn content in the chromate treatment liquid is scratch resistant
7 is a graph showing the effect on (upper = abrasion resistance, lower = tension pad resistance).

Fig. 4 The pH in the chromate treatment solution is scratch resistant (upper = ablation resistance, lower = tension pad resistance)
4 is a graph showing the effect on the stiffness.

Claims (3)

(57) [Claims] Claims 1. A chromate film having a coating weight of 5 to ²⁰⁰ mg / m ^{2 in} terms of metal Cr is formed on a surface of a zinc or zinc alloy-plated steel sheet by a reaction type or coating type chromate treatment,
In the production of the organic composite coated steel sheet comprises forming an organic composite resin coating adhesion amount 0.2 to 3.5 g / m ² containing silica thereon, the Zn content of the treated liquid the chromate treatment 30 g / l It is characterized by performing while managing as follows,
A method for producing an organic composite coated steel sheet having excellent scratch resistance. ^2. A chromate film having a coating weight of 5 to ²⁰⁰ mg / m ^{2 in} terms of metal Cr is formed on a surface of a zinc or zinc alloy-plated steel sheet by a reactive or coating type chromate treatment.
In the production of the organic composite coated steel sheet comprises forming an organic composite resin coating adhesion amount 0.2 to 3.5 g / m ² containing silica thereon, the pH of the processing liquid the chromate treatment
A method for producing an organic composite coated steel sheet having excellent scratch resistance, wherein the method is carried out while controlling the temperature to 1.0 to 5.0. 3. The organic composite resin film has an average particle size of 10 μm.
3. The method according to claim 1, wherein the lubricant particles are contained in an amount of 2 to 20 parts by weight based on 100 parts by weight of the total amount of silica and resin on a solid content basis.