JPH01123081A - Production of metal sheet precoated with chemical film having excellent scratch-resistance - Google Patents

Abstract

PURPOSE:To produce metal sheet precoated with chemical film having excellent scratch-resistance, by applying a liq. for chemical treatment contg. phosphoric acid compd. silica sol and partially reduced chromic acid to the surface of metal, by drying and thereafter by precoating. CONSTITUTION:The liq. for chemical treatment contg. the phosphoric acid compd., the silica sol and further, as occasion demands, org. compd. having hydroxyl or carboxyl group, or bivalent or higher metal ion as main component, is applied to the surface of metal by 10-100mg/m<2> as the totals amt. of adhered Cr. The chromic acid reduced to 3/7-8/1 Cr<3+>/Cr<6+> ratio, is used as the chromic acid above-mentioned. And, the phosphoric acid compd. is used in 0.1-1.0 H3 PO4/Cr<3+> ratio or H3PO4/bivalent or higher metal ion ratio, expressed in terms of H3PO4. The applied liq. for chemical treatment above-mentioned is dried by heating and thereafter, the metal sheet is precoated. Thereby, the metal sheet precoated with the chemical film having excellent scratch-resistance and corrosion resistance, is obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides pre-coated metal sheets with chemical conversion coatings having excellent scratch resistance, such as steel sheets, aluminum sheets, titanium sheets, galvanized steel sheets, and aluminum-plated steel sheets. , lead-plated steel plate,
The present invention also relates to methods of manufacturing various alloy-plated steel sheets.

(Prior art and its problems) There are chromate treatment, phosphate treatment, etc. as chemical conversion treatments for paint bases on metal surfaces, but phosphate treatment is often used. This is because there are concerns about the properties of the paint base seen in chromate treatment, specifically, concerns about adhesion, water resistance, and scratch resistance.

However, solutions to this problem have been studied, and for example, electrolytic chromate treatment is known and is currently used for pre-coating base treatment. However, although this method is effective for plating with a rough surface such as electrolytic galvanizing, it has not been able to provide satisfactory scratch resistance for all galvanized steel sheets.

In addition, in the case of coating type chromate, a method of adding water-soluble resin etc. (JP-A-59-123775,
9-14552) and chromate treatment containing silica sol have also been developed, but their reliability as a coating base is still poor. The biggest reason for this is that the cathode becomes alkaline due to moisture and dissolved oxygen in a corrosive atmosphere, which causes chromate to elute.Furthermore, the resulting chromate film is amorphous and smooth, which causes problems in scratch resistance. This is because it occurs. For example, the number 10 for rust prevention
A film obtained from a chromate solution using mμ silica sol has excellent film uniformity, but is smooth and has poor scratch resistance.

An improvement plan is a chromate treatment method using white carbon, which is disclosed in Japanese Patent Application Laid-Open No. 53-92339. This uses a chromate solution consisting of reduced chromic acid and secondary agglomerated large-diameter silica, or white carbon, and aims to make the reduced chromic acid less soluble in water and the white carbon to roughen the surface. shall be.

However, in this case, the bonding force of chromate is insufficient to bond large particle size silica, so adhesion and corrosion resistance are not necessarily sufficient, and silica precipitation and uneven appearance are likely to occur.

Furthermore, in the case of large particle size silica, the surface roughness is only a few hundred microns, so it is difficult to obtain scratch resistance comparable to that of a phosphate film. Furthermore, the insolubility in water depends only on reduced chromic acid, which is insufficient.

In addition to the above-mentioned Japanese Patent Application Laid-Open No. 59-123775 as a chromate treatment method containing a phosphoric acid compound, Japanese Patent Application Laid-Open No. 56-35
Publication No. 778 has been published. However, none of these techniques is aimed at improving scratch resistance. The former is a chromate treatment method consisting of polyacrylic acid, hexavalent chromic acid, and phosphoric acid, and the combination of these three components increases the affinity with the top coat, while the latter is a hexavalent chromate treatment method. This is an amorphous chromate film composed of chromic acid, silica sol, and birophosphoric acid, with an emphasis on corrosion resistance.

In this way, it is a satisfactory chromate for painting bases.
There is still a demand for precoated metal plates with chemical conversion coatings that have excellent scratch resistance, adhesion, and water resistance.

(Means for Solving the Problems) The present invention meets these demands, and can be solved by the method described below.

(1) Phosphoric acid compound, silica sol and CS on the metal surface
The main component is chromic acid reduced to a +/Cr6+ ratio of 377 to 9/l, and the phosphoric acid compound is equivalent to orthophosphoric acid (H3
PO4) Ratio of trivalent chromium in reduced chromic acid (lI
, po4. /cr3'') is 0.1 to 1.0, and the total amount of Cr deposited is 10 to 100 mg/
A method for producing a pre-coated metal plate with a chemical conversion film having excellent scratch resistance, which comprises coating the pre-coated metal plate with a chemical conversion coating and applying a pre-coated coating after drying with heat.

(2) Phosphoric acid compound, silica sol and Cr on the metal surface
3*/Cr6* ratio is 377 to 9/11. :
The main component is reduced chromic acid, an organic compound having a hydroxyl group or a carboxyl group, and the phosphoric acid compound is converted to orthophosphoric acid (83PO4), and the ratio of trivalent chromium in the reduced chromic acid (II3PO4/Cr") is 0.1
A pre-coated metal with a chemical conversion film with excellent scratch resistance characterized by applying a chemical conversion treatment solution of ~1.0 to the metal surface in a total amount of 10-100 mg/rn' of Cr deposited, heating and drying, and then applying a pre-coat coating. Method of manufacturing the board.

(3) Phosphoric acid compound, silica sol, metal ions with two or more values and Cr''/Cr'° ratio on the metal surface is 377 to 9/1
A chemical conversion treatment solution containing chromic acid reduced to as a main component and having a ratio of phosphoric acid compound equivalent to orthophosphoric acid (H3Po<) and divalent or higher metal ions from 0.1 to 1.0 is applied to the metal surface. A method for producing a pre-coated metal plate with a chemical conversion film having excellent scratch resistance, characterized in that the total amount of Cr deposited is 10 to 100 mg/rn'', heated and dried, and then pre-coated.

The chemical conversion treatment liquid used in the present invention is acidic and contains phosphate ions, so it reacts well with metal surfaces.

The chemical conversion film obtained by the powder method is a phosphate compound in which metal ions and Cr'' are bonded to phosphate ions due to the elution of the underlying metal, an inorganic compound in which phosphate ions are bonded to silica sol, and a chromium/chromate film. Because it is composed of a composite film of amorphous and crystalline materials, it has a high coefficient of friction and is as resistant to water as phosphate treatment, whereas conventional paint-on chromate films are amorphous and smooth. It has excellent water resistance and is the perfect base for painting.

The reduced chromic acid is prepared by adding an organic reducing agent (for example, starch, sucrose, glucose, phenolic compound, oxalic acid, etc.) to an aqueous chromic acid anhydride solution to which phosphoric acid is added if necessary, or an inorganic reducing agent (for example, hydrazine, phosphorous acid, etc.). , metal powder, etc., to reduce the Or''/Cr6'' ratio to 377 to 9/1.
The optimal range is 6 to 7/3. If the Cr''/Cr'+ ratio is too low, a chromium chromate film containing a large amount of soluble monophosphate and hexavalent chromium will be formed, resulting in an amorphous, smooth film that is easily soluble in water; If it is too high, the stability of the chromate solution deteriorates, and the crystalline chromate film itself has poor workability, resulting in insufficient corrosion resistance. The pl+ of the chromate solution is preferably 1 to 3 from the viewpoint of reaction with the metal surface and formation of a poorly soluble film.

The phosphoric acid compound which is one of the main components of the chromate solution used in the present invention includes orthophosphoric acid, 1.2.3 phosphate compounds, etc., but orthophosphoric acid 113PO4 is preferred.

The concentration is calculated by converting the total chromium compound as CrO2, converting the phosphoric acid compound into orthophosphoric acid, and calculating the 3% concentration in reduced chromic acid.
The valent chromium is Cr"", and the ratio 83PQ4/Cr" can be applied to be 0.1 to 1.0, but preferably 0.2 to 0.
．． It is 8. Also, H, PO4/SiO□ ratio 0.01 to 0
．． 5 is preferred. If 83PO4 exceeds these upper limits, water-soluble primary phosphates are likely to be formed, and the adhesion of the paint will deteriorate. Moreover, if it is less than these lower limits, the scratch resistance of the resulting film will be reduced, making it difficult to achieve the objective.

Silica (S+02) is preferably a fine silica sol with a particle size of about 1 to 100 millimicrons, and the concentration is the ratio to phosphoric acid (
+13P0415102) and preferably 0.01 to 0.5. If the silica concentration is too high, the workability of the chromate film itself will deteriorate, while if it is too low, the scratch resistance and paint adhesion will deteriorate, making it difficult to obtain the effects of the present invention.

Other organic compounds containing water-soluble hydroxyl or carboxyl groups that are one of the other components of the chemical conversion treatment solution used in this method include copolymers of maleic acid (PMM), polyacrylic acid (PAA), polyvinyl alcohol, phenol, These include gallic acid, tannic acid, pyrogallol, and progelsin. , the amount added is organic compound/Cr(1
3 weight ratio is 0.01 to 1.0, preferably 0.01 to 1.0
It is 0.271. When the ratio is 1 or more/1, the life of the liquid and the scratch resistance after coating deteriorate.

What is important here is that these organic compounds need to be added after reducing the chromic acid to a predetermined Cr''/Cr''' ratio. Otherwise, the organic compound will be destroyed by oxidation, making it difficult to obtain the desired quality.

Scratch resistance is improved by adding divalent or higher valence metal ions to the chemical conversion treatment solution. Examples of metal ions are M g
3 +, Ca2°, Ba2+, Sr3+C "32, Z
n3+Ai3+Fe"°, Ni3+Go3+Mn3+M
o3+Tj3+Zr3+Si4+. These metal ions combine with phosphoric acid and chromium and contribute to I-solubility, roughness, and insulation of the film. The feeding method is to add these as oxides, hydroxides, carbonates, phosphates, and dichromates.

The amount added is expressed as the added metal ion Men+, and the ratio of the sum of trivalent chromium (Cr''' + y e n + ) and phosphoric acid is 113PO4/[Cr 3 + + M e
n + ] may be 0.1 to 1.0, preferably 0.1 to 0.7. If it is less than 0.1, the scratch resistance effect will be weak, and if it exceeds 1.0, water-soluble primary phosphate will be likely to be formed and the adhesion of the paint will deteriorate.

The coating amount of the chemical conversion treatment liquid in the present invention is lrn' on the metal surface.
The amount of Cr deposited is 10 to 100 mg/m, preferably 10 to 30 mg/m". If the amount of Cr exceeds 100 mg/m", cohesive failure of the chemical conversion coating tends to occur, which is undesirable. If Crl is less than Omglrd, the desired effect of the present invention will be small.

The method of applying the chemical conversion treatment liquid as described above is by using a roll coater.
It can be carried out by well-known means such as a single squeeze roll, an air knife, and dipping, and the heating and drying method is not limited to hot air, gas burner, infrared rays, high frequency baking, etc.

After chemical conversion treatment, pre-coating is applied. The type of paint and film thickness are not limited in the present invention; conventional pre-coating can be used.

(Function) The function of the method of the present invention will be described in the case where galvanized steel sheets are targeted.

The reaction in this method may be expressed as follows.

Zn+2tl" + 2H2P04- + C
r2O, "--" knee Zn, (PO4)3* H20+
Cr" + CrO4'-・- (1) Cr" +
Cr, O," + H" + H2PO4-
-9” L knee (:rPO4+Cr(OH)+e Cr
O4+820 ”・-(2) Mene +L H,p
04- +n H+ 0ll-→Me (PO4
? , +n) I20 +++ ++ +
++ (3) [StO□ ・ H2O medium 2H”
+ 21□, 04-0H-5iO□・
p2oS+ H2O (4) That is, phosphoric acid dissolves zinc (formula (1)), and as a result, the pH at the interface increases, and formulas (1), (2), (3) ) , (4
) of sparingly soluble zinc phosphate (Zn= (PO4)
3) Chromium phosphate (CrPO4)% Silica phosphorus oxide (SiO□.P2O5) is precipitated.

Due to the reaction between phosphoric acid and zinc, a portion of dichromate ions, which are hexavalent chromium, are reduced to trivalent chromium ions, resulting in the formation of poorly soluble chromium phosphate and chromium chromate (Cr
(OH)3・crO4) film is formed.

By pre-containing Cr3+ in the chromate solution,
These films are formed by the reaction of a small amount of zinc with phosphoric acid. If there is too much hexavalent chromium, the interfacial pH will not rise sufficiently, and soluble chromium monophosphate ((:r (H2
It forms PO4)3) and becomes easily soluble in water. The added metal ions with a valence of two or more also form poorly soluble phosphates by the same action as trivalent chromium. When the interface p)I increases, silica undergoes particle growth due to dehydration bonding between silica particles and a polymerization reaction via phosphoric acid and CS+, resulting in polymerization.

The film-forming effect of the present invention can be considered as described above.

Since the resulting film is composed of water-insoluble phosphate, it forms a crystalline film compared to the conventional amorphous chromium chromate film, resulting in a pre-coated steel sheet with excellent scratch resistance and corrosion under the coating. can be obtained.

(Example 1) A hot-dip galvanized steel sheet with a zinc coating weight of 90 G.O.D.
After applying the chemical conversion treatment liquid shown in the table using a natural coater, drying with hot air at 300℃ for 3 seconds, then applying an epoxy base coat to a dry film thickness of 5μ, baking, and drying the epoxy top coat. A pre-coated steel plate was produced by coating with a coating thickness of 15μ using a reverse coater and baking at a final plate temperature of 200°C.

As comparative materials, chemical conversion coatings treated with chromate treatment using chromic acid and silica sol that do not contain phosphoric acid, and spray-type phosphate treatment were evaluated.

The evaluation method and criteria are as follows.

(a) Evaluation of scratch resistance (a) Measurement of dynamic friction coefficient of chemically treated surface A steel rod with a diameter of 1.3 mm at the tip is brought into vertical contact with the sample surface, a load is applied from above, and the steel rod is moved horizontally by 100 mm/mm.
The force at that time was measured using a load cell, and the coefficient of friction (μ) was calculated by dividing it by the applied load. Commercially available equipment was used.

(a) Coin test method A coin was tilted at 60 degrees to scratch the surface of a pre-coated metal plate so as to reach the base, and the width of the metallic shiny surface (exposed base) generated at that time was shown in mm.

(b) Paint Adhesion A bent plate was held at 180° with the painted surface facing up, held down with flat presses, the tape was peeled off from the bent part, and adhesion to the tape was evaluated. When the number of plates to be sandwiched is one, it is indicated as "11 bending", and when there are 3+2 plates, it is indicated as "2T bending".

(C) Cut out a corrosion-resistant sample to a size of 50 x 150, and use a cutter to make a cross cut from the coating surface to the substrate in the lower half.
The end and back sides were sealed. The sample was subjected to salt spray test (J
ISZ2371 continuous method) was performed for 1000 hours, and then the bulge from the crosscut was measured and expressed in mm.

Sample Nos. 1 to 4 have a phosphoric acid/trivalent chromium ratio of 0.2 to 1.
．． This is an example of the present invention in which the Cr 3 + /Cr 8 + ratio (R: 515) was changed to 0, and a chemical liquid was used in which the chromic acid ratio of silica sol was changed to 2. The friction coefficient increases in proportion to the amount of phosphoric acid, and the scratch resistance in the coin test is also improved, although it is not as good as phosphate treatment (No. 13).

Sample Nos. 5 to 8 have a Cr+/Cr6+ ratio of Bi2 to 0/1.
The comparison site where No. 8 was changed with no reduction is an example of the present invention.

No.5.6 shows good scratch resistance and adhesion, but N.
o7 showed a high reduction rate and poor corrosion resistance. No
8 is inferior in friction coefficient and coin test.

Nos. 9 to 11 are treatment solutions corresponding to No. 2, with different amounts of Cr attached. The coefficient of friction increases in proportion to the amount of adhesion, but peeling occurred after bending 11 at around 90 mg/rn' of Cr. No. 12 is a comparative example using a chemical liquid that does not contain phosphoric acid. The coefficient of friction is low, and it is also large during peeling by coin test.

(Example 2) According to the procedure of Example 10, a chemical conversion film was formed using the chemical conversion treatment liquid composition and application conditions shown in Table 2, and pre-coating was performed for evaluation. In Table 2, the adhesion was evaluated with 01 bending (without narrowing the plate).

No. 2 is an example of a chemical conversion film that does not contain organic compounds and is 01
While some peeling was observed upon bending, no peeling was observed in samples Nos. 14 to 21 containing organic compounds. N.

In No. 17, when T (ratio of organic compound and C'03) is 0.4, the friction coefficient decreases and the scratch resistance decreases.

(Example 3) Example! To the aqueous solution of No. 4 +l"", M g 2*
, Ca” were added at 5 g/l each (No. 22).
, No. 23, and No. 24) were prepared, processed into hot-dip galvanized steel sheets using the same method, and coated with pre-coat paint to create pre-painted steel sheets. H3PO4/ [Cr”+
Me"] ratio is 0.7. The friction coefficient of all samples is 0.45 to 0.46, and the coin test is 0.4 amm.
Only the metallic light and surface of the surface were exposed. Also, no bending wounds were observed in Paint Adhesion 11.

(Effects of the Invention) The chromate conversion treatment of the present invention is extremely simple compared to phosphate treatment, which is employed as a pretreatment for pre-painted steel sheets.

Chromating phosphates improves productivity, saves energy and labor, and reduces pollution problems such as drainage.

Another great advantage is that it does not depend on the type of metal, unlike phosphates.

In addition, in terms of quality, it has improved corrosion resistance compared to phosphates, so it has the potential for a wider range of uses.

Agent Patent Attorney Masaaki Aki Sawa 1 other person

Claims (3)

[Claims] (1) Phosphoric acid compound, silica sol and Cr on the surface of the metal
The main component is chromic acid reduced to a ^3^+/Cr^6^+ ratio of 3/7 to 9/1, and the phosphoric acid compound is converted to orthophosphoric acid (H_3PO_4) and is the trivalent chromic acid in the reduced chromic acid. Chromium ratio (H_3PO_4/Cr^3^+) is 0.1 to 1
．． 0 chemical conversion treatment solution to 1 as the total Cr adhesion amount on the metal surface.
A method for producing a pre-coated metal plate with a chemical conversion film having excellent scratch resistance, which comprises applying 0 to 100 mg/m^2, heating and drying, and then pre-coating. (2) Phosphoric acid compound, silica sol and Cr on the metal surface
The main component is chromic acid reduced to a ^3^+/Cr^6^+ ratio of 3/7 to 9/1, an organic compound having a hydroxyl group or a carboxyl group, and the phosphoric acid compound is converted to orthophosphoric acid ( H_3PO_4) and 3 in reduced chromic acid
The ratio of valent chromium (H_3PO_4/Cr^3^+) is 0.
A chemical conversion coating with excellent scratch resistance characterized by applying a chemical conversion treatment solution of 1 to 1.0 to the metal surface at a total Cr deposition amount of 10 to 100 mg/m^2, heating and drying, and then pre-coating. A method for manufacturing pre-coated metal sheets. (3) Phosphoric acid compound, silica sol, divalent or higher metal ions and Cr^3^+/Cr^6^+ ratio of 3/3 on the metal surface.
A chemical conversion treatment liquid whose main component is chromic acid reduced to 7 to 9/1, and whose ratio of phosphoric acid compound equivalent to orthophosphoric acid (H_3PO_4) to divalent or higher metal ions is 0.1 to 1.0. The total amount of Cr deposited on the metal surface is 10 to 100 mg/m.
^2 A method for producing a pre-coated metal plate with a chemical conversion film having excellent scratch resistance, which is characterized by applying a pre-coat coating after coating and heating and drying.