JPS642670B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a highly corrosion-resistant surface-treated steel sheet. Excellent corrosion resistance is required for steel plates used for objects whose inner surfaces are coated only by electrocoating, such as automobile bodies, and in recent years, surface-treated steel plates with high corrosion resistance have been used instead of the conventionally used cold-rolled steel plates. The trend is becoming stronger. The first example of such surface-treated steel sheets is galvanized steel sheets, but with this type of steel sheet, it is necessary to increase the amount of zinc deposited in order to improve corrosion resistance, and along with this, workability and weldability There is a problem of deterioration. In order to improve these problems, zinc alloy plated steel sheets and multi-layer plated steel sheets are being researched and developed to which one or more elements such as Ni, Fe, Mn, Mo, Co, Al, Cr, etc. are added. Compared to the above-mentioned galvanized steel sheet, the steel sheet can have improved corrosion resistance without deteriorating weldability and workability. However, when steel plates are applied to the bag structure and bent parts (hemming parts) of automobile body panels, the surface requires a high degree of corrosion resistance, so zinc alloy plated steel plates and multilayered steel plates such as those mentioned above are required. The problem with plated steel sheets is that their corrosion resistance is not quite sufficient. As a steel plate with a high degree of corrosion resistance, the
Research and development has been carried out on anti-corrosion steel sheets with zinc-rich coatings, such as the one seen in No. 6882, and the representative one is known as Zinchrome Metal. However, even with this anti-corrosion coated steel sheet, peeling of the coating may occur in the processed parts such as press forming, and it is still not fully satisfactory as a highly corrosion-resistant and anti-rust coated steel sheet that meets the requirements for automobile body materials. It's hard to say. On the other hand, regarding the exterior surfaces of automobile bodies, which are coated with cationic electrodeposition, intermediate coating, and top coating, conventionally, emphasis has been placed on paint finish (appearance) and paint adhesion over paint corrosion resistance, and for this reason, cold-rolled steel sheets are generally used. However, in recent years, as seen in Canada, the United States, and other countries, there has been a strong demand for improving the corrosion resistance of paint on the exterior of vehicle bodies.
Zinc or zinc alloy plated steel sheets are excellent for improving paint corrosion resistance, but this type of steel sheet has better paint finish (cratering resistance: pinhole-like appearance in cationic electrodeposition coating) than cold-rolled steel sheets. The occurrence of paint film defects is called the cratering phenomenon.The reason for this occurrence is not clear, but it does not occur on cold-rolled steel sheets, but occurs on coated or zinc alloy plated steel sheets.This cratering phenomenon Coating - It is observed even after the top coat is applied, and it greatly affects the paint finish.), paint adhesion (water resistant adhesion: paint adhesion test in a wet oil environment. Samples that have been coated with the top coat are washed with pure water (deionized water). water) for a predetermined period of time (5
10 days to 10 days) After soaking, remove and carve 100 goblets at intervals of 1 mm to 2 mm that reach the base (steel plate surface) on the coating surface, and evaluate the number of goblets that are removed by applying and peeling off the adhesive tape. . Cold-rolled steel sheets are excellent in this water-resistant adhesion, whereas zinc or zinc alloy plated steel sheets are inferior. ), it can be said that practical application is difficult. Conventionally, single-sided galvanized steel plates or single-sided anti-corrosion coated steel plates (each with one side left as a cold-rolled steel plate) have been used as rust-proof steel plates for automobiles. and exterior surfaces (inner surface: corrosion resistance, workability, spot weldability, etc.; exterior surface: paint finish, paint adhesion, paint corrosion resistance, workability, spot weldability, etc.). It is desired to develop a highly corrosion-resistant and rust-proof steel sheet that satisfies the requirements. The present invention has been researched and developed in view of the above circumstances, and aims to provide a highly corrosion-resistant and rust-proof steel sheet that can satisfactorily satisfy the basic characteristics of the inner and outer surfaces of automobile bodies and the like. For this reason, when the present invention is applied to an automobile body, etc., a zinc alloy plating film with an adhesion amount of 1 g/m ² or more and a chromate film with an adhesion amount of 1000 mg/m ² or less are applied from the bottom layer to one side constituting the inner surface of the car body. and amount of adhesion
It has a composite film formed by forming an organic composite silicate film of 0.5 to 4.0 g/ ^m2 , and the other surface that makes up the outer surface of the car body (painted surface) has a zinc coating on the lower layer side with a coating amount of 1 to 60 g/ ^m2 . It is defined as having a composite plating film in which an iron plating film or an iron-zinc alloy plating film with an iron content of 50 wt% or more is formed on the top layer with a coating amount of 0.5 to 10 g/ ^m2 . Basic characteristics. The present invention applies, from the lower layer side, (1) a zinc alloy plating film with a coating weight of 1 g/m ² or more, and (2) a chromate film with a coating weight of 1000 g/m ² or less on one side of a steel plate that constitutes the inner surface of a car body, etc. , (3) has an organic composite silicate film with an adhesion amount of 0.5 to 4.0 g/m ² , and on other surfaces that make up the outer surface of the car body, (1) has an adhesion amount of 1 to 60 g/m ² on the lower layer side.
(2) The top layer has an iron plating film or an iron-zinc alloy plating film with an iron content of 50 wt% or more. As a result, one side (inner surface) has high corrosion resistance that is superior to rust-proof steel plates such as the zinc chrome metal, while the other side (outer surface) has the same paint finish and paint adhesion as cold-rolled steel sheets. This makes it possible to create a double-sided treated steel sheet that has much better painted corrosion resistance (red rust resistance) than cold-rolled steel sheet. First, a single-sided surface treatment film corresponding to the inner surface of an automobile body will be described. On this one side, first, an alloy plating film using zinc as a base metal is formed as a base metal. This zinc alloy plating is less likely to corrode than ordinary zinc plating, and can exhibit high corrosion resistance due to the synergistic effect with the chromate film and organic composite silicate film formed thereon. This zinc alloy plating includes zinc-iron alloy plating, zinc-nickel alloy plating, zinc-manganese alloy plating, zinc-aluminum alloy plating, zinc-cobalt-chromium alloy plating, and any of these plating components.
It is possible to use one or more elements added such as Ni, Fe, Mn, Mo, Co, Al, Cr, etc.
Furthermore, it may be a composite plating made of two or more layers of the same or different types of plating as described above. As for the plating method for these zinc-based alloy platings, any practicable method such as electrolytic method, melting method, vapor phase method, etc. can be adopted, but in general, electroplating is advantageous due to the ease of single-sided plating. . In addition, the plating components in various alloy platings are as follows:
In Ni-Zn alloy plating, Ni content is 5 to 20wt%, Fe-
Zn alloy plating has an Fe content of 5 to 35 wt%, Mn-Zn alloy plating has a Mn content of 30 to 85 wt%, Zn-Al alloy plating has an Al content of 2 to 60%, and Zn-Co-Cr alloy plating has a Co content of 0.01 to 15. %, and the amount of Cr is about 0.01 to 1%. In addition, even in the case of plating two or more layers, the plating components of each layer are selected within the ranges described above. The plating adhesion amount for each plating is 1g/m ² per side.
If it is less than this, the corrosion resistance will deteriorate. Furthermore, even if the amount of plating exceeds 300 g/m ² , no significant improvement in corrosion resistance can be expected, and on the contrary, the cost will increase. The amount of plating deposited is usually 1 to 60g/
m ² , preferably in the range of 5 to 40 g/m ² . Next, the chromate film needs to have a chromium deposition amount (dry) of 1000mg/ ^m2 or less,
If it exceeds 1000mg/ ^m2 , the chromate film itself will peel off, resulting in film peeling during pressing, etc.
Workability deteriorates, and weldability also deteriorates.
However, if the amount of chromium deposited is less than 1 mg/m ² , the film will be non-uniform, which is not preferable. The preferred amount of chromate film is 10 to 200 mg/m ² (more than that in terms of metallic chromium)
It is. Such a chromate film is formed by coating-type or electrolytic-type chromate treatment. The coating-type chromate treatment liquid has a partially reduced chromic acid solution as its main component, and if necessary, it may also contain water-dispersible or water-soluble organic resin such as acrylic resin and/or silica with a thickness of several tens to several thousand angstroms. It contains particles (silica sol, fumed silica). in this case
The ratio of Cr ³⁺ /Cr ⁶⁺ is 1/1 to 1/3, and the PH is 1.5 to 1/3.
4.0 (more preferably 2-3) is preferable. Cr3 ⁺ /Cr6 ⁺
The ratio is adjusted to a predetermined ratio using a general organic reducing agent (for example, sugars, alcohols, etc.) or an inorganic reducing agent. In addition, as a coating type chromate treatment,
Any method such as a roll coater method, a dipping method, a spray method, etc. may be used, but the roll coater method is advantageous since it is necessary to perform the chromate treatment on only one side. In coating type chromate treatment, a film is obtained by drying without washing with water after the chromate treatment. Drying without rinsing in this way is
Normal water washing removes Cr ⁶⁺ , so
The ratio of Cr ³⁺ /Cr ⁶⁺ is maintained stably as it is,
This is for sealing by treatment with an organic composite silicate solution in the next step. On the other hand, in electrolytic chromate treatment, cathodic electrolysis treatment is performed in a bath containing chromic anhydride and one or more of anions such as sulfuric acid, phosphoric acid, fluoride, or halogen oxygen acid, and then washed with water and dried to form a film. to form. Comparing the chromate films produced by the above two treatment methods, the coated chromate film contains more hexavalent chromium in the film than the electrolytic chromate film, so it has superior corrosion resistance. When heat treated, the film becomes dense and strong, resulting in better corrosion resistance than electrolytic chromate. On the other hand, electrolytic chromate has the advantage of forming a film with a high degree of completeness regardless of the presence or absence of heat treatment. can also be said to be advantageous. In addition, the electrolytic type has the advantage that the amount of film deposited can be easily controlled. In any of the above methods, it is important to perform the chromate treatment on only one side and to prevent chromium from adhering to the other side. If even a small amount of chromium adheres to this other surface, the reactivity of the chemical conversion treatment will be poor and the quality of the coating will deteriorate. The organic composite silicate has water-dispersible silica as an essential component, and a water-soluble or water-dispersible organic polymer resin is mixed with this in the presence of a silane compound, and the mixture is heated at a temperature of 10°C or above and below the boiling point, preferably 50 to 90°C. It can be obtained by reacting in the temperature range of °C. Water-dispersed silica is so-called silica sol or colloidal silica, and has a particle size of several tens of angstroms to several thousand angstroms. Examples of water-soluble or water-dispersible organic polymer resins include polyvinyl alcohol, hydroxyethyl cellulose, polyester, alkyd, epoxy, and acrylic copolymers, but any resin may be used as long as it reacts with silica. However, when attaching importance to the adhesion of a cationic electrodeposition paint (based on epoxy resin), which is an undercoat for automobiles, epoxy resin is preferable, and it is preferable to contain at least 30 parts per 100 parts of organic resin. Further, the silane compound is used as a reaction accelerator when silica and organic resin are combined. As this silane compound, commercially available silane coupling agents may be used, such as vinyltriethoxysilane, vinyltris (β-
methoxyethoxy)silane, vinyltris(β-
methoxyethoxy)silane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N=β(aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, etc. Examples include alkoxysilane compounds. The mixing ratio of water-dispersible silica and water-soluble or water-dispersible organic resin in the organic composite silicate is 5:95 to 95:5 in weight percentage of solid content. The addition ratio of the silane compound is 0.5 to 15 wt% based on the total solid weight of silica and organic resin. The organic composite silicates obtained as described above may be used alone or in combination of two or more. Furthermore, molybdenum, tungsten, or vanadium oxygen acids or salts thereof, or titanium or zirconium alkoxide chelate compounds may be added. Corrosion resistance can be improved by adding one or more of these additives to 14 wt% or less, preferably 0.2 to 8 wt%, based on the total solid content of the silica sol and organic resin. Further, if a curing agent such as melamine is added to the organic composite silicate solution, a greater effect can be obtained. Film adhesion amount (dry) of the above organic composite silicate
must be selected in the range of 0.5g/m ² to 4.0g/m ² , more preferably in the range of 1.0g/m ² to 3.0g/m ² . If the adhesion amount is less than 0.5 g/m ² , sufficient corrosion resistance cannot be obtained, and if it is more than 4.0 g/m ² , spot weldability deteriorates, which is not preferable. In addition, in order to further improve corrosion resistance, after forming the chromate film and organic composite silicate film as described above, the surface plate temperature is 50 to 300°C, preferably
Preferably, the heat treatment is performed in a temperature range of 100 to 250°C. If the heating temperature exceeds 250℃, the corrosion resistance may deteriorate due to clutching of the chromate film or a decrease in soluble Cr ⁶⁺ , which has a passivating effect. The upper limit of heating temperature is ℃. The heating method may be any method such as hot air drying, infrared heating, induction heater, etc. as long as a predetermined temperature is obtained. Further, the heating holding time is about several seconds to several minutes, and holding for a long time is not only economically disadvantageous but also undesirable because there is a possibility that the film performance will deteriorate. The purpose of this heat treatment is first to thermally cure the film by the combination of silica sol/silica sol, silica sol/organic polymer, and organic polymer/organic polymer in the organic composite silicate component. For example, silica sol has the property of forming a dry film as water evaporates even at room temperature, and is basically an air-dry type, but when heated above 100°C, a condensation reaction occurs between the silanol groups (-Si-OH) of silica sol. It is estimated that during the formation of siloxane bonds (-Si-O-Si-), a condensation reaction between the silanol groups and the hydroxyl groups of the organic resin component results in a more dense film. The second purpose of the heat treatment is for Cr ⁶⁺ on the surface layer of the chromate film to react with polar groups such as hydroxyl groups and carboxyl groups in the organic composite silicate film to strengthen the bond between the two layers. Furthermore, the third purpose of the heat treatment is to improve the corrosion resistance by densifying the underlying chromate film. This effect is particularly significant in coated chromate films. That is, a dense chromic chromate film is formed by reduction of Cr ⁶⁺ and dehydration reaction by heating. Furthermore, when the chromate film contains silica, an organic resin, or both, a crosslinking reaction occurs between the chromium and these components during the heat treatment, making the chromate film even more dense and increasing its corrosion resistance. In contrast to the above-mentioned surface treatment film on one side, the other side, which corresponds to the outer surface of automobile bodies, etc., will be explained. On this one side, a composite plating film is formed by appropriately combining plating films according to each property. This makes it possible to simultaneously satisfy the cratering resistance, water resistance adhesion, and paint corrosion resistance required for the outer surface of automobile bodies and the like. First, the zinc-based plating film on the lower layer side is intended to improve paint corrosion resistance (red rust resistance and blistering resistance) as described above, and has a single-layer or multilayer structure of zinc plating or zinc alloy plating with zinc as the base metal. Consisting of In particular, zinc alloy plating has excellent paint corrosion resistance, and among these, Fe-Zn alloy plating (Fe content 40%
below, preferably 5 to 35%), Ni-Zn alloy plating (Ni content 5 to 20%), Mn-Zn alloy plating (Mn
content of 30 to 85%) is particularly good. In addition, the content of iron, nickel, and manganese (in the cutlet) in the above zinc alloy plating is determined from the viewpoint of corrosion resistance, and it is not desirable to have too much or too little outside this range because the corrosion resistance will deteriorate. . and one or two of the above zinc or zinc alloy plating films.
More than one species is formed into a single layer or multiple layers. In contrast to such a plating film on the lower layer side, in the present invention, in particular, the uppermost plating film is an iron plating film or an iron-zinc alloy plating film with an Fe content of 50 wt% or more, and the surface to be painted (outer surface ) to improve its cratering resistance and water-resistant adhesion. Although the mechanism of cratering occurrence and water-resistant adhesion deterioration in zinc or zinc alloy plated steel sheets is not clear, it is clear that these properties are good in the case of cold-rolled steel sheets, and that cratering occurs during cationic electrodeposition. When examining samples with degraded water-resistant adhesion, it was found that the peeling interface was due to interfacial failure between the phosphate film and the cationic electrodeposition coating, or cohesive failure within the phosphate film. The present inventors focused on the following points and selected the plating film for the top layer. That is, the present inventors first determined that the difference between a cold-rolled steel sheet and a zinc or zinc alloy plated steel sheet in terms of water-resistant adhesion and cratering resistance is due to the surface layer of the material and the phosphate film formed by reaction. It is assumed that this is due to the ingredients, crystal structure, etc. Here, the difference between the two in the material surface layer is that the Zn content in the zinc-plated steel sheet is 100 to 80 wt%, and the Fe content is naturally 100 wt% in the cold-rolled steel sheet. Similarly, the two types differ in terms of the phosphate film formed. For example, in zinc-plated steel sheets with a zinc content of 80 to 100 wt%, the phosphate film component is Hopite [Zn ₃ (PO ₄ ) ₂ .
4H ₂ O] and has a needle-like crystal structure, whereas in cold-rolled steel sheets, the phosphate film consists of Hopite and Phosphophyllite [Zn ₂ Fe (PO ₄ ) ₂ .
4H ₂ O], especially in the case of the immersion type phosphate treatment that has been widely used recently.
It is composed of phosphophyllite and has a columnar crystal structure. Based on these facts, we investigated a film that could provide the same anti-cratering properties and water-resistant adhesion properties as cold-rolled steel sheets, and obtained the following results regarding iron-zinc alloy plating. It is something. That is, from the viewpoint of plating surface characteristics, when the Fe content exceeds the range of 20 to 40 wt%, Phosphophyllite is formed in the phosphate film component, and as the Fe content in the plating layer increases, the ratio of Phosphophyllite increases. increases. In addition, the Fe content in the plating layer is
When the Fe content exceeds 50 wt%, an α phase (according to X-ray diffraction) is observed, and as the Fe content increases, the α phase also increases. In addition, the cratering resistance is
When the Fe content in the Zn alloy plating layer is 50wt% or more, it becomes almost equivalent to cold rolled steel sheet. Water resistant adhesion is almost the same as cold rolled steel sheet when the Fe content in the Fe-Zn alloy plating layer is 40wt% or more. Based on the above results, in the present invention, an iron plating film or an iron-zinc alloy plating film with an Fe content of 50 wt% or more is selected as the uppermost plating film. Next, to explain the adhesion amount of each of the above plating films, the top layer iron plating film or Fe content is
The plating amount of the iron-zinc alloy plating film of 50 wt% or more is 0.5 to 10 g/m ² , preferably 1 to 5 g/m ²
Selected within the range of If the adhesion amount is less than 0.5 g/m ² , the properties of the plating film on the lower layer side will appear, and the cratering resistance and water resistant adhesion will deteriorate. On the other hand, 10
If it exceeds g/m ² , the corrosion resistance and processability of the coating deteriorate, which is not preferable. The amount of zinc or zinc alloy plating on the lower layer side is 1 g/m ² to 60 g/m ² , preferably 10 g/m 2 to 60 g/m 2 .
It is selected in the range of ~40g/ ^m2 . Adhesion amount is 1g/
If less than 60g/ ^m2 , the corrosion resistance of the coating will deteriorate ^;
Exceeding this is not preferable because the workability of the plating film deteriorates and costs increase. The plating methods described above are not particularly limited. For example, electric, gas phase, and melt plating methods can be applied to zinc or iron-zinc alloy plating, and electric and gas phase plating methods can be applied to nickel-zinc alloy plating and manganese-zinc alloy plating. . As is clear from the above explanation, the steel sheet of the present invention has some kind of plating film formed on both sides, and it is possible to form different types of plating films on both sides or to perform plating treatment using different types of plating methods. However, compared to the plating film at the bottom layer on both sides, both can be formed by zinc alloy plating. Therefore, in order to industrially manufacture the steel sheet of the present invention, it is necessary to first coat both sides with the same zinc alloy plating. Alloy plating (Fe-Zn alloy plating, Ni-Zn alloy plating,
One type of Mn-Zn alloy plating) is applied, and then one side is coated with iron plating or
It is preferable to apply iron-zinc alloy plating with an Fe content of 50 wt% or more, and to form a first layer chromate film and a second layer organic composite silicate film on the other side for the inner surface. As mentioned above, any suitable plating method can be used to obtain the steel sheet of the present invention, but when forming different types of plating on both sides or forming the top layer plating for the outer surface, electroplating is used. The method is industrially advantageous. As described above, in the present invention, excellent painted appearance, paint adhesion, and paint corrosion resistance can be obtained on one side of the steel plate,
In addition, by creating a surface film structure that provides excellent unpainted corrosion resistance (and paintability) on the other side, it is possible to provide a steel sheet that meets the required characteristics of the inside and outside of the sheet in applications such as automobile bodies. . That is, on one side of the steel sheet of the present invention, corrosion of the material itself is prevented as much as possible by zinc alloy plating as a base, and corrosion resistance is improved by forming a chromate film thereon as a base.
Furthermore, by sealing with an organic composite silicate film as a top layer, it is possible to minimize the elution of Cr ⁶⁺ , which has a passivation effect in corrosive environments, and exhibit excellent corrosion resistance. In addition, the organic composite silicate film itself provides high corrosion resistance due to its excellent barrier effect and paint adhesion effect due to its organic components, and as a whole, it provides excellent unpainted corrosion resistance and appropriate paint adhesion. On the other side, the zinc plating on the lower layer provides excellent corrosion resistance and the iron or iron layer on the top layer.
Excellent paint finish and paint adhesion can be obtained by zinc alloy plating. Next, embodiments of the present invention will be described. [Example 1] (Example for application to the inner surface of a car body) Corrosion resistance tests were conducted on film structures on one side suitable for the inner surface of an automobile body, with different plating components and film adhesion amounts as shown in Table 1. Similar tests were also conducted on each steel plate shown in Table 2 as comparative materials. The plating components of each steel plate are as follows.
For each steel plate shown in the table and each steel plate having a chromate film and an organic composite silicate film in Table 2, the plated steel plate is degreased with alkaline, washed with water, dried, and then a coated chromate treatment liquid is applied with a roll coater. Alternatively, an electrolytic chromate film was formed by immersing it in an electrolytic chromate treatment bath, and after drying, an organic composite silicate treatment liquid was applied as a second layer using a roll coater. Further, after drying, heat treatment was performed as necessary, and a corrosion resistance test was conducted after being left for 10 days. Ni-Zn alloy electroplating ...Ni content 12% Fe-Zn alloy electroplating ...Fe content 25% Mn-Zn alloy electroplating ...Mn content 60% Paint-type chromate treatment liquid, electrolytic chromate conditions The details of the organic composite silicate treatment liquid and corrosion resistance test conditions are as follows. Γ Application type chromate treatment conditions Cr ³⁺ /Cr ⁶⁺ = 2/3, PH = 2.5 (pH adjusted with KOH), chromate treatment solution with solid content of 20 g/was applied with a roll coater at room temperature and then dried. Γ Electrolytic chromate treatment conditions CrO ₃ : 50g/, H ₂ SO ₄ : 0.5g/, bath temperature 50
℃ bath, current density 4.9A/dm ² , electrolysis time 2.0
It was cathodic electrolyzed in seconds, washed with water, and dried. Γ Organic composite silicate treatment liquid Acrylic composite silicate and epoxy composite silicate (organic resin: silica sol = 60:40, respectively) synthesized as follows were mixed at a ratio of 70:30 to prepare an organic composite silicate treatment liquid. (PH: 9.5, solid content
20%) (A) Synthesis of acrylic composite silicate Add isopropyl alcohol to a four-necked flask equipped with a thermometer, stirrer, condenser, and dropping funnel.
Add 180 parts of ethyl acrylate, 68 parts of methyl methacrylate, 15 parts of styrene, N-n.
A monomer mixture consisting of 15 parts of butoxymethylacrylamide, 38 parts of 2-hydroxyethyl acrylate, and 24 parts of acrylic acid was mixed with 2,2-'azobis(2,
The mixture is added dropwise over a period of about 2 hours together with a catalyst consisting of 6 parts of 4-dimethylcleronitrile. After the dropwise addition, the reaction was continued for another 5 hours at the same temperature, and the solid content was 63%.
A colorless and transparent resin solution with an acid value of 67 was obtained. By mixing 45 parts of 38% ammonia water with 500 parts of this acrylic copolymer resin solution, adding water and stirring thoroughly, an acrylic copolymer with a solid content of 20% and a pH of 9.5 is dispersed in water. I got the liquid. Pour 300 parts of this aqueous dispersion into a flask, add a predetermined amount of colloidal silica (manufactured by Nissan Chemical Industries, Ltd., trade name "Stotex N") while thoroughly stirring at room temperature, and then add γ-methacryloxypropyl. One part of trimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KBM503") was added dropwise and mixed under stirring, then heated to 85°C and kept at the same temperature for 2 hours to react. A dispersible acrylic composite silicate was obtained. (B) Synthesis of epoxy composite silicate 310 parts of bisphenol A type epoxy resin with an epoxy equivalent of 950 (manufactured by Ciel Chemical Co., Ltd., trade name "Epicote 1004"), 95 parts of linseed oil fatty acid, 95 parts of tung oil fatty acid, xylene Put 15 parts into a flask,
Gradually heat the mixture while passing nitrogen through it, raise it to 240℃, cool it, and when the temperature drops to 70℃, add 200 parts of ethylene glycol monoethyl ether to obtain an oil-modified epoxy resin solution with a solid content of 70% and an oxidation rate of 54. Ta. An epoxy composite silicate was obtained from this oil-modified epoxy resin solution in the same manner as in the case of A above. Γ Corrosion resistance test

[Table] M)

Claims (1)

[Claims] 1 Formed on one side from the bottom layer: a zinc alloy plating film with an adhesion amount of 1 g/m ² or more, a chromate film with an adhesion amount of 1000 mg/m ² or less, and an organic composite silicate film with an adhesion amount of 0.5 to 4.0 g/m ² In addition to having a composite film, the other side has a coating weight of 1 to 60 g/m on the lower layer side.
It has a composite plating film in which a zinc-based plating film is formed on the top layer, and an iron plating film ^or an iron-zinc alloy plating film with an iron content of 50 wt% or more is formed on the top layer with a coating amount of 0.5 to 10 g/m ² . Highly corrosion resistant surface treated steel sheet.