JP2910637B2 - Lubricated steel sheet with excellent conductivity - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lubricated steel sheet having high corrosion resistance and excellent conductivity, having a corrosion-resistant chromate film having both conductivity and lubricity on a plated steel sheet.

[0002]

2. Description of the Related Art In the fields of home appliances, electric and electronic devices, etc., there are products that require shielding of electromagnetic waves, and in such products, the conductive performance of a steel sheet is regarded as important. Some products require grounding properties, and the conductive performance of the steel sheet is an important required performance depending on the type of the product.

On the other hand, in recent years, regulations on organic solvents used for degreasing press oils for environmental protection have been made. Therefore, a lubricated steel sheet has been developed that gives lubricity to the steel sheet itself and can be press-formed without applying press oil.
It is actually being used.

[0004] As a conventional lubricated steel sheet, for example, Japanese Patent Application Laid-Open No. 4-320837 discloses an organic-inorganic composite having a chromate layer on a plated steel sheet and further containing a hydrophilic resin, a fluororesin and silica. A surface-treated steel sheet on which a lubricating film is formed is disclosed. Although this surface-treated steel sheet has a high level of lubrication performance, the non-conductive organic
Since the surface is densely covered with the inorganic composite coating, the conductive performance is low. Furthermore, since two layers, a chromate film and a lubricating film, are formed on the plated steel sheet in separate steps, the number of steps is increased and the cost is increased.

JP-A-63-114635 and JP-A-1-114635
No. 130762 discloses that after a chromate treatment of a plated steel sheet, a water-soluble or water-dispersible organic resin emulsion is electrostatically atomized and dispersed on a chromate film to form a thin resin layer. A surface-treated steel sheet is disclosed. In this method, the organic resin is used for imparting corrosion resistance and anti-fingerprint property, and the lubricating performance is not improved because the chromate film does not contain a lubricant. In addition, Japanese Unexamined Patent Application Publication No.
As in JP-A-320837, two steps of chromate treatment and electrostatic coating of resin are required for a plated steel sheet, and the number of steps is large and the cost is high.

JP-A-3-219086 discloses an acrylic emulsion resin having a specific composition emulsified with a nonionic emulsifier, a lubricant dispersion dispersed with a nonionic emulsifier, and optionally a phosphate ion, silica, , Ni, Mn and
One of heavy metal ions and fluorine ions selected from Zn
It describes that a chromate treatment solution having a pH of 5 or less containing one or more species is applied to a galvanized steel sheet and lubricated. It is described that a sparingly soluble salt is formed with the phosphate ion Cr ^3+, and a heavy metal ion forms a sparingly soluble chromate, both of which contribute to the improvement of corrosion resistance. However, in Examples, since phosphoric acid and heavy metal ions are always added together, it has not been clarified that sole addition of phosphate or heavy metal ions improves corrosion resistance. In addition, when heavy metal ions are added to a chromate treatment solution containing an acrylic emulsion resin, a crosslinking reaction of the resin is caused to cause gelation of the solution at an early stage. It significantly deteriorates the uniformity and appearance of the chromate film and significantly shortens the service life of the liquid. Furthermore, when heavy metal ions are present in the presence of Cr ³⁺ which has become a poorly soluble salt due to simultaneous addition of phosphoric acid, gelation of the liquid appears more remarkably.

Japanese Patent Application Laid-Open No. 6-192849 discloses that a hot-dip-coated steel sheet is subjected to a reactive ion-containing chromate treatment, and then to a water-dispersible organic resin, a nonionic emulsifier, a silicone-modified polyether-based defoamer, and a melting point. A lubricated surface-treated steel sheet consisting of treatment with a coating type chromate treatment solution containing a polymer resin powder at a temperature of 100 ° C or higher is described. However, since the chromate treatment is performed twice, the cost increases, Performance is also insufficient.

JP-A-6-192850 discloses a chromate treatment solution containing a water-dispersible urethane resin, a nonionic emulsifier, a silicone-modified polyether antifoam, a polymer resin powder having a melting point of 100 ° C. or higher, and a pigment. Is described. Since this chromate treatment liquid contains a pigment, defects are easily generated in the film, the corrosion resistance is reduced, and the cost is high.

[0009]

As described above, it is conventionally known that when a chromate film containing a resin and a lubricant is formed on a plated steel sheet, the lubrication performance of the plated steel sheet is improved. However, since this type of film generally has poor conductivity, the conventional lubricated steel sheet could not satisfy the high conductivity required for products requiring electromagnetic shielding and grounding.

[0010] Therefore, there is still a demand for a low-cost surface-treated steel sheet having both a lubricating property and a conductive property in the fields of home appliances and electric / electronic devices. In response to this demand, the present invention uses a plated steel sheet as a base material,
By forming a layer-type film, the purpose is to provide a lubricated steel sheet having excellent conductivity, which imparts the same or better lubrication performance as an oiled steel sheet without deteriorating the conductivity performance. I do.

According to the present invention, there is provided a lubricated steel sheet having a lubricant-containing chromate film having an adhesion amount of 5 to 120 mg / m ^{2 in} terms of metal Cr on a plated surface of a plated steel sheet, wherein the chromate film is formed of H ₃ Phosphoric acid in an amount of PO ₄ / Cr weight ratio of 0.3 to 2 and at least one selected from acrylic, urethane, polyolefin and polyester in an amount of resin solids / Cr weight ratio of 0.5 to 20 Contains at least one kind of water-dispersible organic resin and at least one kind of lubricant having an average particle diameter of 0.1 to 20 μm selected from natural wax and synthetic wax in such an amount that the lubricant solid content / Cr weight ratio is 0.01 to 5. And Koba
Metal ions of sodium, nickel, manganese, and zinc,
Also provided is a lubricated steel sheet having excellent conductivity, characterized in that it is a chromate film containing no silica.

In a preferred embodiment, the chromate film further contains fluoride in such an amount that the F / Cr weight ratio becomes 0.01 to 0.5.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The lubricated steel sheet of the present invention comprises a plated steel sheet as a base material, and a chromate film containing phosphoric acid, an organic resin, a wax-based lubricant and optionally a fluoride on a plated surface thereof. It consists of the formed surface-treated steel sheet.

The type of the base steel sheet is not particularly limited, and examples thereof include Zn, Ni, Al, Mn, Pb, Cr, Co, Fe and Mg.
A plated steel sheet having a plating film made of one or more metals may be used. A multi-layer plated steel sheet having two or more plating layers can also be used as a base material. Preferred plated steel sheets are Zn-based (pure Zn or Zn alloy) or Al-based (pure Al or Al alloy) plated steel sheets.

[0015] Plating methods include electroplating, hot-dip plating,
Any method such as vapor deposition plating may be used. Although the amount of plating is not particularly limited, it is generally 1 to 15 per side.
0 g / m ² . The base material may be either a single-side plated steel sheet or a double-side plated steel sheet.

A first feature of the present invention is that the amount of a chromate film formed on a plating surface of a base material plated steel sheet is
That is, it was 5 to 120 mg / m ^{2 in} terms of Cr. If the Cr-equivalent weight is less than 5 mg / m ² , the primary rust-preventing ability is generally lowered, and the base plating may be corroded before the steel sheet is used by a customer after the steel sheet is manufactured. In addition, the Cr equivalent adhesion amount is 12
If it exceeds 0 mg / m ^2, conductivity will be degraded due to an increase in film thickness. The preferred Cr equivalent amount is in the range of 20 to 80 mg / m ² .

The second feature of the present invention is that the chromate film is
It contains 0.3 to 2 phosphoric acid in H ₃ PO ₄ / Cr weight ratio. The purpose of adding phosphoric acid is to improve corrosion resistance by strengthening the chromate film, to reduce yellowness due to H ₃ PO ₄ —Cr complex formation, and to improve fingerprint resistance by lowering yellowness. When considering use for home appliances, intense yellow color is not preferable in appearance. Also, in consideration of the handling property in using the material, the adhesion of the fingerprint becomes a serious problem. These problems are solved by the addition of phosphoric acid.

If the H ₃ PO ₄ / Cr weight ratio is less than 0.3, the yellowness increases, the corrosion resistance deteriorates, and the fingerprint resistance deteriorates remarkably. On the other hand, when the weight ratio of H ₃ PO ₄ / Cr exceeds 2, Cr ^{6+ in} the film is remarkably reduced, and at the same time, the film is hardened, and the corrosion resistance is greatly deteriorated. In view of these points, the preferred H ₃ PO ₄ / Cr weight ratio is in the range of 0.4 to 1.5. Examples of the phosphoric acid, in addition to orthophosphoric acid, metaphosphoric acid, can be used condensed phosphoric acid such as polyphosphoric acid, in which case the amount to use in terms of H ₃ PO ₄ or if the above range.

The third feature of the present invention is that the chromate film contains one or more organic resins selected from acrylic, polyolefin, urethane and polyester. The resin is water-dispersible because it is used by dispersing it in an aqueous chromate treatment solution.
(That is, an emulsion resin), and may be either thermoplastic or thermosetting. Acrylic, polyolefin, urethane and polyester emulsion resins are all commercially available.

By the addition of these organic resins, the formation of a chromate film is reinforced and the corrosion resistance is improved. Moreover,
These organic resins have a high affinity for the lubricant powder present together in the chromate film and are therefore effective in firmly retaining the powder in the film. In addition, since the above-mentioned organic resins used in the present invention have high flexibility, the flexibility of the formed chromate film can be increased, and the coverage of the processed portion in the case of press molding can be improved. As a result, Also, high corrosion resistance can be maintained in the processed part. For example, with an epoxy resin, such an effect cannot be obtained because the flexibility of the film is relatively poor.

The organic resin has a resin solids / Cr weight ratio of 0.5
It is present in the chromate film in an amount of up to 20. If this weight ratio is less than 0.5, not only the corrosion resistance of the processed part but also the corrosion resistance of the flat part is significantly deteriorated. Further, the fixing of the lubricant becomes insufficient, and the lubricating effect of the lubricant is reduced. On the other hand, when the weight ratio exceeds 20, the organic film having no conductivity is thick and covers the steel sheet surface, so that the conductivity is deteriorated and the performance particularly important in the present invention is not exhibited. The resin solids / Cr weight ratio is preferably in the range of 0.75 to 15.

A fourth feature of the present invention is that the chromate film contains a wax-based lubricant having an average particle size of 0.1 to 20 μm. Lubricants include natural wax and synthetic wax
(Eg, polyethylene wax, oxidized polyethylene wax, etc.). Other solid lubricants, such as fluororesin and graphite, are unsuitable because of their large deformation resistance as described below.

The lubricating effect of the wax-based lubricant is caused by low resistance to deformation of the lubricant (hereinafter referred to as shear deformation) occurring during processing. For this reason, a lubricant having a larger particle diameter has a larger amount of shear deformation and is more effective as a lubricant. If the particle size is less than 0.1 μm, the amount of shear deformation is too small, and the shear deformation required for lubrication sufficient to withstand the processing of the steel sheet cannot be given. On the other hand, if the particle diameter is larger than 20 μm, the fixing of the lubricant by the organic resin becomes incomplete, and a sufficient lubricating effect cannot be obtained.
The preferred average particle size is in the range of 0.3 to 10 μm.

This lubricant has a lubricant solids / Cr weight ratio.
It is added to the chromate film in an amount of 0.01 to 5. If the weight ratio is less than 0.01, a sufficient lubricating effect cannot be obtained, and if it exceeds 5, the lubricant will densely cover the surface of the chromate film, resulting in insufficient conductivity. The preferred lubricant solids / Cr weight ratio is from 0.03 to 3.

A fifth feature of the present invention is that the chromate film does not contain silica. Generally, silica is often added to a chromate film for the purpose of improving corrosion resistance. However, it has been found that silica is a substance having no conductivity, and if it is present in a film, the level of conductivity required for an electromagnetic wave shield or ground cannot be maintained. Therefore, in the present invention, no silica is contained in the chromate film.

In a preferred embodiment of the present invention, the chromate film further contains a fluoride. When a fluoride is added, the plating surface is etched during application of the chromate treatment solution by the fluorine ions liberated from the fluoride, whereby the adhesion between the chromate film and the base plating film is strengthened, and the workability and corrosion resistance are further improved.

As the fluoride, any one which releases fluorine ions can be used. Examples include hydrofluoric acid, zircon hydrofluoric acid, hydrofluoric acid, titanium hydrofluoric acid, borofluoric acid, and ammonium salts or alkali metal salts of these acids. Acid (H ₂ SiF ₆ ). When the fluoride is added, the amount of F / Cr is 0.01 to
0.5. Excessive addition of fluoride having a weight ratio of more than 0.5 lowers the stability of the processing solution and causes significant deterioration of the corrosion resistance of the film. When the weight is less than 0.01, the etching effect by the fluoride is hardly obtained. The preferred F / Cr weight ratio is in the range of 0.02 to 0.45.

The chromate treatment solution used for forming the chromate film of the present invention is a hexavalent chromium compound (eg, chromic acid,
Chromate, bichromate, etc.) or an aqueous solution containing a hexavalent chromium compound and a trivalent chromium compound, adding the phosphoric acid, organic resin, lubricant and optionally fluoride in a predetermined amount, It can be prepared by dissolving or dispersing. In addition, a small amount of a surfactant, a dispersant, and the like can be added to the chromate treatment liquid, if desired.

Various coating means such as dipping, roll coating, spraying and curtain flow coating can be used for coating the chromate treatment liquid. Thereafter, the coating is generally dried by heating to form a chromate coating. This drying is preferably performed at a temperature not exceeding the melting point or softening point of the resin and the wax-based lubricant contained in the chromate film,
Usually, about 50 to 150 ° C is normal. Thus, as schematically shown in FIG. 1, a chromate film in which the wax-based lubricant is uniformly dispersed in the chromate film composited with the organic resin is formed on the surface of the plated steel sheet. Lubricant particles appear on the surface of this chromate film as shown in the figure, but since the lubricant does not completely cover the surface, high lubrication performance that enables press molding without oil coating, electromagnetic wave shielding and grounding And the high conductive performance required for the same can be secured at the same time.

If necessary, it can be coated after molding to form a coating film which is in good contact with the chromate coating. When it is desired to secure conductivity for the purpose of shielding electromagnetic waves or grounding, a conductive paint may be applied.

[0031]

EXAMPLES The present invention will be specifically described with reference to examples. In Examples,% is% by weight unless otherwise specified. The following a
As the test materials, four types of double-sided plated steel sheets of (a) to (d) were used.
The treatment was performed with a chromating solution containing phosphoric acid (orthophosphoric acid), a lubricant, and optionally fluoride (hydrofluorosilicic acid). This chromate treatment liquid was prepared by adding an organic resin of the type shown in Table 1 and a lubricant together with phosphoric acid and optionally hydrofluoric acid at a ratio shown in Table 1 to a commercially available partially reduced chromate treatment liquid.

Test plated steel sheet (test material) a: Electric Zn-coated steel sheet (20 g / m ² ) b: Hot-dip Zn coated steel sheet (90 g / m ² ) c: Hot-dip Zn-55% Al alloy coated steel sheet (75 g / m ² ) m ² ) d: Electric Zn-12% Ni alloy plated steel sheet (20 g / m ² ) The details of the water-dispersible organic emulsion resin and lubricant used are as follows. Acrylic resin: (Hoechst Synthetic Movinyl 700, solid content 47%) Polyolefin resin: (Chuo Rika Kogyo ET-8, solid content
35%) Urethane resin: (Dai Nippon Ink Hydran AP-20,
(Solid content 30%) Polyester resin: (Toyobo Vironal MD1200,
Synthetic wax: polyethylene wax (solid content 10-50)
%) Natural wax: oxidized polyethylene wax (solid content 10 ~
50%).

The chromate treatment was performed by immersing the test plated steel sheet in a chromate treatment solution, removing excess treatment solution by centrifugation, and then drying at 100 ° C. for 1 minute. The adhesion amount of the formed chromate film was as shown in Table 1.

The conductivity, lubricity,
And the corrosion resistance was investigated. Table 2 summarizes the test results. Regarding corrosion resistance, especially when used in home appliances, etc., in consideration of not only red rust from the steel sheet but also the corrosion appearance of the plating itself is considered to be poor, in this example, the base material is a Zn-containing plated steel sheet. Therefore, white rust due to Zn corrosion was regarded as the occurrence of corrosion.

Conductivity test apparatus: Surface resistance measuring instrument (SQ meter) Pressing load: 130 g Contact measuring area: 0.9 mm diameter Operating speed: 2 cm / min

Lubricity test device: Bowden sliding device Load: 500 g

Plate corrosion resistance tester : Salt spray tester Condition: JIS-Z2371 Test material: Seal the end and back surfaces with adhesive tape Evaluation criteria: Time up to 5% area of white rust 240 hours or more ‥‥ 1 120 to 240 hours ‥‥ 2 72 to 120 hours ‥‥ 3 24 to 72 hours ‥‥ 4 Less than 24 hours ‥‥ 5 Score 1 to 4 passed.

Processed part corrosion resistance tester : Salt water spray tester Condition: JIS-Z2371 Test material: After 90 ° bending, seal the end face and back face with adhesive tape Evaluation criteria: Up to 5% white rust generation area ratio Time 120 hours or more ‥‥ 1 72-120 hours ‥‥ 2 48-72 hours ‥‥ 3 12-48 hours ‥‥ 4 Less than 12 hours ‥‥ 5 Score 1-4 passed.

[0039]

[Table 1-1]

[0040]

[Table 1-2]

[0041]

[Table 2-1]

[0042]

[Table 2-2]

[0043]

[Table 2-3]

[0044]

[Table 2-4]

[0045]

[Table 2-5]

As can be seen from Table 2, the lubricated steel sheet of the present invention in which a chromate film containing an organic resin, a wax-based lubricant, phosphoric acid and optionally fluoride is formed on a plated steel sheet, And the lubricity rating has passed, and it combines high levels of conductivity and lubricity.
The corrosion resistance of the processed part as well as the flat part was good.

[0047]

The lubricated steel sheet of the present invention has both high lubricity that can be press-formed without oil coating and high conductivity required for electromagnetic wave shielding and grounding. Is also particularly useful as a steel sheet for home appliances and electronic / electric devices because it exhibits excellent corrosion resistance. Further, the lubricated steel sheet can be efficiently and inexpensively manufactured only by subjecting the plated steel sheet to a chromate treatment.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a lubricated steel sheet according to the present invention.

Continuing from the front page (72) Inventor Yukihiro Yoshikawa 4-5-33 Kitahama, Chuo-ku, Osaka City Inside Sumitomo Metal Industries Co., Ltd. (72) Inventor Ken Toyasu 4-5-33 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries Co., Ltd. In-company (56) References JP-A-3-219086 (JP, A) JP-A-6-192850 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 22/00- 22/86 B32B 15/08

Claims (2)

(57) [Claims] 1. A lubricated steel sheet having a lubricant-containing chromate film with an adhesion amount of 5 to 120 mg / m ^{2 in} terms of metal Cr on a plated surface of a plated steel sheet, wherein the chromate film is
Phosphoric acid in an amount of H ₃ PO ₄ / Cr weight ratio of 0.3 to 2 and acrylic, urethane, polyolefin and polyester in an amount of resin solids / Cr weight ratio of 0.5 to 20 At least one kind of water-dispersible organic resin and at least one kind of lubricant having an average particle diameter of 0.1 to 20 μm selected from natural wax and synthetic wax in such an amount that the lubricant solid content / Cr weight ratio is 0.01 to 5; Contains cobalt, nickel
A lubricated steel sheet having excellent conductivity, characterized in that it is a chromate film containing no metal ions of manganese, zinc, and zinc . 2. The lubricated steel sheet according to claim 1, wherein the chromate film further contains an amount of fluoride such that the F / Cr weight ratio becomes 0.01 to 0.5.