JP4319896B2 - Water-soluble resin-coated steel sheet containing inorganic phosphoric acid with excellent press workability and corrosion resistance - Google Patents

Description

  The present invention relates to an inorganic phosphoric acid-containing water-soluble resin coating excellent in press workability and corrosion resistance, and particularly relates to a coating effective when applied to a hot-rolled high-tensile steel plate.

  Generally, hot-rolled steel sheets that have been pickled have a risk of rusting during warehouse storage until they are shipped as products. Therefore, if plating or chemical conversion treatment is not performed, the primary rust prevention coating with rust prevention oil is applied. Processed and shipped to a secondary processor. In the secondary processing company, after appropriately performing secondary processing and assembling, the remaining rust preventive oil and the like are degreased, subjected to chemical conversion treatment, and coated thereon to obtain a product. Although such anti-rust oil application also served as a lubrication function during press processing, it was only a temporary measure, and even if the anti-rust property was insufficient and some lubricity could be expected, the processing conditions were severe. When processing pressed materials, die seizure and steel plate cracking are likely to occur, and new high-performance press oil must be applied for lubrication. Accordingly, instead of rust-preventing oil, a process having superior rust-preventing properties and lubricity is required, and a method of applying a resin coating to the surface of a steel sheet and shipping it to a secondary processor has recently attracted attention. In particular, as demand for high-strength steel sheets has increased in fields such as automobiles, improvements in press workability have been strongly demanded. In press forming of high-tensile steel plates, particularly high lubricity is required in order to facilitate the flow of the steel plates into the mold. The present invention relates to an inorganic phosphoric acid-containing water-soluble resin film that has high rust resistance even when directly processed on a high-strength steel sheet or the like and is excellent in lubricity during press working. In general, a high-tensile steel plate is inferior in chemical conversion treatment and electrodeposition coating properties as compared with a normal steel plate, but this problem is also solved.

Conventionally, various proposals have been made public regarding organic coatings excellent in lubricity, primary rust prevention, and electrodeposition coating properties. For example, a hydrophilic resin composition containing 100 parts by weight of a hydrophilic resin solid content having a glass transition temperature of 20 to 120 ° C., 5 to 50 parts by weight of a lubricant solid content, and 1 to 100 parts by weight of a rust preventive agent, A technique for applying 0.5 to 5.0 g / m ² (per one side) on the surface of a cold-rolled steel sheet has been proposed (see Patent Document 1). This patent relates to a non-delaminating organic coating that is excellent in primary rust prevention and lubricity, and it is not necessary to remove the organic coating by alkali cleaning after processing the steel sheet, and it is possible to perform chemical conversion treatment or electrodeposition coating as it is .
An invention for improving the formability of a hot-rolled high-tensile steel sheet by adjusting the surface roughness of the steel sheet is also disclosed. For example, by defining the surface texture (Ra) after pickling performed after hot rolling as 1.7 to 3.0 μm, a hot-rolled high-tensile steel sheet excellent in adhesion between press formability and viscoelastic material is obtained. There is an invention to be obtained (see Patent Document 2).
JP-A-8-257494 JP-A-5-222485

However, in Patent Document 1, even if it is said to be excellent in lubricity, it cannot be said that the lubricity is sufficient when it is applied to a high-strength, high-tensile steel plate and the mold is damaged. In addition, there is an increase in costs such as an increase in press power and the like, and since there is no blending of phosphate, electrodeposition coating properties and post-coating adhesion properties (post-coating adhesion properties) are insufficient. In addition, when the chromate disclosed as a rust inhibitor is used, environmental considerations are also required.
Although Patent Document 2 discloses press formability and surface roughness, it is intended to improve the affinity with a viscoelastic material used in a vibration-absorbing composite steel sheet having a multilayer sandwich structure. There is no disclosure or suggestion of means for simultaneously satisfying rusting properties, electrodeposition coating properties, and corrosion resistance.
This invention makes it a subject to solve the trouble of the above-mentioned prior art, and the coating amount and composition ratio of the coating agent for forming the inorganic phosphoric acid-containing water-soluble resin film on the steel sheet surface texture and the steel sheet surface It is intended to provide a steel sheet that can exhibit excellent press workability and corrosion resistance by combining rationally. Another object of the present invention is to provide an inorganic phosphoric acid-containing water-soluble resin-coated steel sheet that is useful when applied to a high-strength, high-strength steel sheet.

In order to solve the above-mentioned problems, the first invention of the present invention is a hot-rolled steel sheet having a surface roughness (Ra) after pickling of 1.2 μm to 3.0 μm, and is inorganic to 100 parts by weight of the organic resin. Press workability and corrosion resistance characterized by directly applying an inorganic phosphoric acid-containing resin containing 40 to 65 parts by weight of a phosphoric acid compound and 30 to 55 parts by weight of colloidal silica to 0.8 to 4.5 g / m ^2. It is an inorganic phosphoric acid-containing water-soluble resin-coated steel sheet that is excellent in water.
Also, before Symbol inorganic phosphoric acid-containing water-soluble resin preferably contains an acrylic resin and / or styrene resin. Furthermore, pre-inorganic phosphoric acid compound is more preferable to contain manganese phosphate and / or magnesium phosphate.
In addition, when the steel plate according to the present invention is a high-tensile steel plate, the effect of reducing the press forming load is remarkable.

According to the inorganic phosphoric acid-containing water-soluble resin-coated steel sheet according to the present invention described above, the following effects can be expected.
(1) Since the primary rust prevention property is good, rust does not occur even when waiting for shipment or storage for a long time without applying rust prevention oil.
(2) The lubricity of the surface coating is high, and it is not necessary to apply press oil at the time of pressing at the secondary processing manufacturer.
(3) Since chromate treatment is not performed, chromium does not elute, which is advantageous for environmental measures.
(4) Even if a secondary processing manufacturer passes the chemical conversion treatment line and performs chemical conversion treatment, there will be no obstacle.
(5) When the steel plate of the present invention is press-formed, the press-forming load can be reduced, so that it is particularly effective when applied to a high-tensile steel plate.
(6) Electrodeposition painting performance and corrosion resistance after painting can be greatly improved.

Hereinafter, the present invention will be described based on the best embodiment.
First, in this invention, it is necessary to maintain the steel plate surface roughness (Ra) after pickling in the range of 1.2 micrometers-3.0 micrometers. Usually, the surface roughness (Ra) after pickling of a hot-rolled steel sheet is at most about 1.5 μm, but in the present invention, this is defined in the above range. By maintaining the roughness within this range and applying a resin containing colloidal silk on the fine irregularities on the surface of the steel sheet, the press formability is improved and the press forming load is greatly reduced. This technique is different from the conventional technique of improving the formability by applying a lubricating resin onto a steel plate having a flat surface. When the surface roughness (Ra) is less than 1.2 μm, colloidal silica or water-soluble resin blended as a lubricant is easily peeled off by friction with the mold during press molding, and rather causes deterioration of press moldability. . When the roughness of the steel sheet surface is in the range of 1.2 to 3.0 μm, the press formability is kept good by the action of colloidal silica contained in the irregularities. Further, if the surface roughness (Ra) exceeds 3.0 μm, the steel sheet surface becomes rough and the amount of water-soluble resin filling the valley increases, which is not preferable in terms of cost, and the coating thickness of the inorganic phosphoric acid-containing resin is reduced. Increases the press forming load and deteriorates the appearance.
In addition, the surface roughness of a steel plate not only changes by the unevenness | corrugation of the roll surface at the time of hot-rolling a steel plate, but is influenced by the steel plate component. In particular, the roughness tends to increase as the Si content increases. This is because the influence of the surface scale remaining before hot rolling is large. Such a high Si material having a high surface roughness has obtained a high elongation by controlling the metal structure in order to prevent cracking in press molding, but by using the technology of the present invention in combination, a higher press Exhibits moldability.

Next, in the present invention, it is necessary to contain an inorganic phosphate compound and colloidal silica as a resin film formed on the steel sheet surface. The inorganic phosphate compound is an essential composition for improving the primary rust prevention property, electrodeposition coating property and corrosion resistance after coating, for example, phosphoric acid such as Mn, Cu, Co, Mg, Fe, Sn, Al, etc. What is necessary is just to mix | blend a compound individually or in combination. In particular, it has been confirmed by experiments of the present inventors that inclusion of manganese phosphate and / or magnesium phosphate is effective for exhibiting excellent electrodeposition coating properties and corrosion resistance after coating. It was. On the other hand, colloidal silica is blended in order to improve lubricity and rust prevention.
In the present invention, by specifying the surface roughness of the steel sheet, the resin coating amount, the blending of inorganic phosphoric acid and colloidal silica, and preferably the blending ratio thereof, a resin-coated steel sheet having the intended performance is obtained. Specifically, the surface roughness, coating amount and colloidal silica are added to improve the surface lubricity of the steel sheet, to reduce the press molding load, and to exhibit primary rust preventive properties with inorganic phosphoric acid, Further, the electrodeposition coating property is improved by blending inorganic phosphoric acid and colloidal silica (particularly, the blending ratio) to improve post-coating corrosion resistance.

The organic resin that is the basic composition of the resin film coated on the steel sheet surface of the present invention is a water-soluble or water-dispersed hydrophilic resin because it forms a desired resin film after being applied to the steel sheet surface and dried. Polyacrylic resin, polyurethane resin, styrene resin, etc. are suitable, but particularly in the case of the present invention, adhesion to the steel sheet and post-coating properties, and other additives to be blended In view of the above relationship, it is desirable to mainly use an acrylic resin and / or a styrene resin.
Any acrylic resin and / or styrene resin must be water-soluble in order to facilitate application to the steel sheet and drying. For this purpose, it has acrylic acid and hydroxy compounds such as hydroxyethyl acrylate and hydroxypropyl acrylate, and glycidyl groups such as glycidyl acrylate and β-methylglycidyl ether. A compound or a resin having a hydroxyl group-containing monomer based on an ethylenically unsaturated carboxylic acid or styrene unsaturated carboxylic acid is preferred.
In the present invention, it is essential in the present invention to mix the above-mentioned inorganic phosphate compound and colloidal silica with this organic resin, but in particular, by specifying the blending ratio, adhesion after coating, electrodeposition coating properties, lubricity Has been found to have a positive effect. For this reason, in this invention, 40-65 weight part of inorganic phosphate compounds and 30-55 weight part of colloidal silica shall be contained with respect to 100 weight part of organic resins.
When the blending ratio of the inorganic phosphate compound is less than 40 parts by weight, the electrodeposition coating property and the corrosion resistance after coating are lowered. Moreover, when the compounding ratio of the inorganic phosphate compound exceeds 65 parts by weight, the primary rust preventive property tends to deteriorate. For these reasons, the blending ratio of the inorganic phosphate compound is set in the range of 40 to 65 parts by weight with respect to 100 parts by weight of the organic resin.
Moreover, the blending ratio of colloidal silica is 30 to 55 parts by weight with respect to 100 parts by weight of the organic resin. When the lower limit is less than 30 parts by weight, the lubricity is significantly lowered, and particularly, it is applied to high-tensile steel sheets. This is because the effect of reducing the press-forming load in the case of reducing is small. Moreover, even if it mix | blends exceeding 55 weight part of an upper limit, while an effect is saturated, the contact area of resin and a steel plate will decrease by the amount of colloidal silica in resin increasing, and it will cause the fall of paint adhesiveness on the contrary. Due to inconvenience, the upper limit was kept at 55 parts by weight.

The inorganic phosphoric acid-containing resin having such a blending ratio is directly applied to the surface (both sides) of a hot rolled steel sheet having a surface roughness (Ra) after pickling of 1.2 μm to 3.0 μm. The coating method may be appropriately selected according to other conditions such as spray coating, roll coating coating, dip coating, brush coating, curtain flow coating, etc., which are usually used. In addition, although drying after painting is sufficient as natural drying, light baking drying may be performed in some cases.
The resin coating amount is in the range of 0.8 to 4.5 g / m ² per one side of the steel sheet. When the coating amount is less than 0.8 g / m ² , when the surface roughness of the steel sheet is approximately 3.0 μm, which is the upper limit, the resin is insufficient to fill the valley, and the resin coating targeted by the present invention is formed. There is a possibility that it cannot be formed. On the other hand, if the coating amount exceeds the upper limit of 4.5 g / m ² , the effect is saturated and the electrodeposition coating property is deteriorated. Accordingly, the resin coating amount is in the range of 0.8 to 4.5 g / m ² , but the particularly preferable range is 1.5 to 3.5 g / m ² .
In the steel sheet of the present invention in which the resin film of such an application amount is formed, sufficient lubricity is maintained, so that it can be formed without applying press oil at the time of pressing, and electrodeposition In addition to being excellent in paintability and corrosion resistance, it has many advantages that no obstacles occur even if chemical conversion treatment is performed by passing through a chemical conversion treatment line.

Table 1 shows the relationship between the steel sheet surface roughness (average roughness Ra) and the coating amount of the inorganic phosphoric acid-containing resin, the press molding load, and the appearance after pressing. Invention Example Nos. 1 to 10 and Comparative Examples Nos. 11 to 14 contain 55 parts by weight of inorganic phosphoric acid and 40 parts by weight of colloidal silica with respect to 100 parts by weight of the organic resin, Comparative Example. No. 15 is a resin coating film containing 55 parts by weight of inorganic phosphoric acid and 20 parts by weight of colloidal silica. No. 16 is 55 parts by weight of inorganic phosphoric acid and 20 parts by weight of colloidal silica with respect to 100 parts by weight of the organic resin.
The organic resin used here was hydroxybutyl acrylate, and the inorganic phosphoric acid was manganese phosphate.
In addition, the appearance after pressing is evaluated by the damage ratio of the resin coating film,
A: Smooth (no breakage),
○: Damaged part is 5% or less of the whole,
Δ: Damaged part is more than 5% and not more than 10%,
X: Damaged part occurs in more than 10%,
It was judged on the basis of that. Here, press forming was performed by deep drawing 80 mm of a material having a plate thickness of 2.6 mm and φ360 mm with a cylindrical punch of φ175 mm.
If the surface roughness and the resin coating amount are within the scope of the present invention from Table 1 (Invention Examples No. 1 to 10), the press molding load was reduced and the appearance after pressing was good. On the other hand, when it was out of the scope of the present invention (Comparative Examples No. 11 to 16), the press molding load was high, the appearance after pressing was also damaged, and the product was rejected. Further, in Comparative Example No. 15, the coating amount is within the range of the present invention, but the roughness of the steel sheet is low and the colloidal silica content is also low, so the lubricity is greatly reduced, the press forming load is high, and the press Later appearance was also poor. In Comparative Example No. 16, the resin coating amount was 0.7 g / m ^2, which was less than the lower limit of the present invention, and the press molding load and the appearance after pressing were poor.

Table 2 shows the relationship between the contents of inorganic phosphoric acid and colloidal silica and the primary rust prevention property, electrodeposition coating property, and post-coating corrosion resistance.
Resin coating by directly applying 3.0 g / m ^{2 of} an inorganic phosphoric acid-containing water-soluble resin having a blending ratio shown in Table 2 to a high-tensile steel plate having a surface roughness (Ra) of 2.0 μm and a tensile strength of 620 MPa. A steel plate was obtained. The organic resin used here was hydroxypropyl acrylate, and the inorganic phosphoric acid was manganese phosphate. The evaluation criteria of primary rust prevention property, electrodeposition coating property, and post-coating corrosion resistance in Table 2 are as follows.
(1) Primary rust prevention property It evaluated by the rusting area ratio after spraying 5% concentration salt water on the test piece for 24 hours. The evaluation criteria are as follows.
◎: No rusting ○: Rust area ratio 0.5% or less △: Rust area ratio 0.5% to 1.0% or less ×: Rust area ratio 1.0% or more (2) Electrodeposition coating Adhesiveness A steel plate coated with a resin was immersed in a coating liquid at 28 ° C., and a voltage of 300 V was applied with the steel plate side as a cathode to form an electrodeposition coating film having a thickness of 20 μm. Furthermore, in order to harden a coating film, the baking process of 170 degreeC x 20 min was performed. The evaluation of the coating film was performed by cutting a 5 mm square with cuts reaching the base metal in a 5 mm square (preparing 100 pieces), dipping it in water at 40 ° C. for 2 hours, and drying immediately, and then using cello tape (CAT405A made by Nichiban) 24) was applied and peeled off, and the adhesion of the coating film was evaluated based on whether or not the coating film adhered to the tape.
The evaluation criteria are as follows.
◎: Number of coatings adhered to tape: 0 ○: Number of coatings adhered to tape: 1 to 3 △: Number of coatings adhered to tape: 4 to 5 ×: Number of coatings adhered to tape : 6 or more (3) Corrosion resistance after painting The corrosion resistance after painting was obtained by immersing a steel plate sample into which the coating film was cut to a length of 50 mm with a cutter in 5% salt water at 55 ° C. for 240 hr. It was made to dry later, it peeled off after attaching a cellophane tape (CAT405A-24 made from Nichiban), and it evaluated by the peeling width from a notch part. The evaluation criteria are as follows.
◎: Peel width 3 mm or less ○: Peel width 3 mm or more and 5 mm or less Δ: Peel width 5 mm or more and 7 mm or less ×: Peel width 7 mm or more

From Table 2, when either the primary rust prevention property or electrodeposition coating property is inferior, the corrosion resistance after coating is also inferior, and when the inorganic phosphoric acid ratio is high, the primary rust prevention property tends to be high. However, when it exceeds 65 parts by weight, it is understood that the electrodeposition coating property is lowered, and further, when the colloidal silica is less than 30 parts by weight or more than 55 parts by weight, the electrodeposition coating property is lowered.
In Table 2, no. Although 28 and 30-35 satisfy Claim 1 of the present invention, they are outside the scope of Claim 2, and are therefore displayed as comparative examples for convenience. Of course, these Comparative Examples No. For 28 and 30 to 35, the press forming load was reduced and the appearance after pressing was satisfactory. Therefore, it can be said that these examples are steel plates that can be sufficiently put into practical use by being used in a mode in which each characteristic is utilized.

Claims (4)

In a hot rolled steel sheet having a surface roughness (Ra) after pickling of 1.2 μm to 3.0 μm, 40 to 65 parts by weight of an inorganic phosphate compound and 30 to 55 parts of colloidal silica with respect to 100 parts by weight of an organic resin. An inorganic phosphoric acid-containing water-soluble resin-coated steel sheet excellent in press workability and corrosion resistance, wherein 0.8 to 4.5 g / m ^{2 of} an inorganic phosphoric acid-containing resin containing parts by weight is directly applied. Inorganic phosphoric acid-containing water-soluble resin is an acrylic resin and / or claim 1 Symbol placement of inorganic phosphoric acid-containing water-soluble resin coated steel sheet characterized by containing the styrene resin. The inorganic phosphate-containing water-soluble resin-coated steel sheet according to claim 1 or 2 , wherein the inorganic phosphate compound contains manganese phosphate and / or magnesium phosphate. The inorganic phosphoric acid-containing water-soluble resin-coated steel sheet according to any one of claims 1 to 3 , wherein the steel sheet is a high-tensile steel sheet.