JPH03234527A - Polyolefin coated steel material - Google Patents

Abstract

PURPOSE:To obtain a polyolefin coated steel material which is superior in adhesion after immersion into hot water in addition to high-temperature cathode peeling resistance, by a method wherein chromate treatment which is superior in both hot water resistance and adhesion is performed to the ground. CONSTITUTION:A chromate treatment agent 4 comprised of a mixture, which is obtained by adding silica particulates and a silane coupling agent by reducing partly a mixed solution of phosphoric acid and chromic acid anhydride with a high-molecular reducing agent, is applied to the surface of a steel material 5 and baked. Then coating 1 of a primer 3, a modified polyolefin adhesive agent 2 and polyolefin are laminated in order. With this construction, a polyolefin coated steel material superior both in cathode peeling resistance and adhesion after immersion into hot water under a high temperature is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a polyolefin-coated steel material, and particularly when used in a high-temperature environment, there is a decrease in water-resistant adhesion between the coating and the steel material and cathodic peeling resistance. This invention relates to polyolefin-coated steel materials that significantly suppress the

(Prior Art) Polyolefin-coated steel materials have excellent corrosion resistance, and are therefore used for corrosion protection of steel pipes, steel sheet piles, and the like. Polyolefin-coated steel pipes have also become popular in vibrating lines for oil, natural gas, etc. due to their anti-corrosion properties. Also,
In recent years, in order to improve the transport of heavy oil, the material being transported in pipes has become hotter due to measures such as heating heavy oil to lower its viscosity before transporting it, making it important to improve performance in operating environments exceeding 60°C. This has become an issue. The performance of the chromate treatment agent required for polyolefin-coated steel materials used in high-temperature environments includes improvement in cathodic peeling resistance and prevention of deterioration in adhesion.

As shown in Japanese Unexamined Patent Publication No. 1-280545, the present inventors have discovered that the surface of a steel pipe can be treated with a chromate treatment agent containing phosphoric acid and fine silica particles.
We have provided a method for improving cathode peeling resistance under usage environments exceeding ℃. Regarding the prevention of adhesion reduction, Japanese Patent Laid-Open No. 62-48543 describes the use of a composite laminated steel plate using a chromate treatment agent containing phosphoric acid and a silane coupling agent to strengthen the adhesive force between the steel plate and the resin. There is a proposal for a manufacturing method.

(Problem to be Solved by the Invention) The chromate-treated polyolefin-coated steel material disclosed in JP-A-1-280545 has good high-temperature cathode peelability up to 80°C, but when immersed in hot water, the resin The adhesion between steel materials decreases. Also, JP-A-62-48
The chromate treatment agent to which phosphoric acid and a silane coupling agent were added, as proposed in No. 543, has high cathode releasability at high temperatures. The present invention improves the chromate treatment agent proposed in JP-A No. 1-280545 to provide a polyolefin-coated steel material that has excellent high-temperature cathodic peeling resistance and excellent adhesion between the coating and the steel material after immersion in hot water. It is something to do.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention is directed to Japanese Patent Laid-Open No. 1-280
The coating structure shown in No. 545 was the result of extensive research into improving the chromate treatment agent. In other words, a chromate treatment agent consisting of a mixture of a mixed aqueous solution of phosphoric acid and chromic anhydride partially reduced with a polymer reducing agent, and silica-based fine particles and a silane coupling agent added to the surface of the steel material is applied and baked. Later, it was discovered that by sequentially laminating a brimer, a modified polyolefin adhesive, and a polyolefin coating, a polyolefin-coated steel material with excellent cathodic peeling resistance at high temperatures and adhesion after immersion in hot water could be obtained. , led to the present invention. This polyolefin-coated steel material is shown in FIG. In FIG. 1, on the surface of a steel material 5, a chromate treatment agent layer 4 containing phosphoric acid, silica-based fine particles, and a silane coupling agent, a primer layer 3 made of a thermosetting epoxy resin, a modified polyolefin adhesive layer 2, and a polyolefin The present invention relates to a polyolefin-coated steel material characterized by sequentially laminating coatings or cross-linked polyolefin coatings 1, which has excellent cathodic peeling resistance at high temperatures and adhesion between the coating and the steel material after immersion in hot water.

The present invention will be explained in detail below.

The steel material used in the present invention is carbon steel or alloy steel such as stainless steel or titanium alloy steel. In addition, on the surface of carbonate steel, stainless steel, copper, aluminum, titanium, aluminum-magnesium alloy, nickel-chromium-iron alloy, nickel-molybdenum alloy, nickel-molybdenum-chromium/tungsten alloy, titanium-palladium alloy, etc. It may also be a steel material laminated with a metal such as an alloy or a titanium-aluminum-panazicum alloy. Furthermore, plating of zinc, aluminum, nickel, copper, etc. on the surface of carbonated steel, alloy plating of zinc-iron, zinc-aluminum, zinc-nickel, zinc-nickel-cobalt, etc., or these platings/alloy platings. It may also be a steel material subjected to dispersion plating in which fine particles of an inorganic material such as silica or titanium oxide are dispersed.

Next, the chromate treatment agent used in the present invention will be explained.

The chromate treatment agent used in the present invention is water obtained by dissolving phosphoric acid and chromic anhydride (CrO2) in distilled water WI71!
i is partially reduced with an organic reducing agent, phosphoric acid, hexavalent chromium ions and trivalent chromium ions are mixed, and silica-based fine particles and a water-soluble silane coupling agent are mixed. If necessary, replace part of the phosphoric acid with pyrophosphoric acid,
It can be replaced with condensed phosphoric acid such as tripolyphosphoric acid.

Examples of organic reducing agents used for partial reduction of chromium from hexavalent to trivalent chromium include alcohols such as methyl alcohol and ethyl alcohol, alkylolamines such as jetanolamine and triethanolamine, formic acid, acetic acid, and oxalic acid. Monomolecular reducing agents such as saturated carboxylic acids, aromatic polyhydric alcohols such as pyrogallol, unsaturated carboxylic acids such as succinic acid and adipic acid, or polymer reductions such as starches such as wheat starch and corn starch, and polyvinyl alcohol. Agents can be used. To improve the adhesion of the coating after immersion in hot water and the high-temperature cathodic peelability, it is necessary to use a polymer reducing agent, especially starch containing a large amount of amylopectin, such as corn starch, with a hydrolytic enzyme such as amyloglucosidase. Dextrin obtained by partial hydrolysis (average molecular weight 50,000-250,000) or partially saponified polyvinyl acetate having a molecular weight of 60,000-140,000 is preferable.

The dextrin and partially saponified vinyl acetate are used in amounts necessary to maintain the desired ratio of hexavalent chromium to total chromium. The desired ratio is preferably a weight ratio of hexavalent chromium to total chromium in the range of 0.25 to 0.65. Regarding this ratio, if the weight ratio of hexavalent chromium to total chromium is less than 0.25 or 0.65 g, the adhesion after immersion in hot water tends to decrease.

In addition, the weight ratio of hexavalent chromium to the total chromium mentioned above is 0.
The amount of dextrin required to achieve a range of 0.25-0.65 is the weight ratio to the total chromium in the chromate treatment solution.
．． The amount of partially saponified vinyl acetate is in the range of 0.10-0.58 in weight ratio to the total chromium in the chromate treatment solution.

Phosphoric acid added to the chromate treatment agent has the following effects. In order to lower the pH of the chromate treatment solution,
This increases the reactivity between the steel material and the chromate treatment agent, and increases the reducibility of hexavalent chromium to trivalent chromium by heating and baking, producing a highly insoluble chromate film. In addition, phosphoric acid can be used to remove hydroxyl groups on the surface of silica-based fine particles,
By bonding to free or coordinated chromium ions, the chromate film is integrated, making it insoluble in hot water, and the film also peels off against alkali generation during cathodic peeling tests. It is thought that it will be difficult to do so.

The amount of phosphoric acid added is preferably such that the weight ratio of phosphate ions to total chromium is in the range of 0.2-3.0.

If the amount of phosphoric acid added is less than 0.2 or more than 3.0, the adhesion after immersion in hot water tends to decrease.

Next, as the silica-based fine particles to be added to the chromate treatment agent, for example, Aerosil 2 manufactured by Nippon Aerosil Co., Ltd.
00, Aerosil 300, Aerosil 380, Aerosil 0X50, Nip Seal L300 from a certain company, Nippon Silikani.
, Nip Seal 300A, Nip Seal E200, Nip Seal E200^, etc., Aerosil C0K84, Aerosil/I/MOX8 manufactured by Nippon Aerosil Co., Ltd.
0, silica-alumina fine particles such as Tx Rosil MOx170, Snowtex 0, Snowtex OL manufactured by Yasan Kagaku Kogyo Co., Ltd.

Snowtex O5, Snowtex OML, Catalyst Chemical Industry Co., Ltd.'s Cataloid SN, Catal
colloidal silica such as oid SA, Cataloid 520L, alumina sol 100 manufactured by Yasan Kagaku Kogyo Co., Ltd.
One type or a mixture of two or more types of silica-alumina sol such as Alumina Sol 200 is used.

When the above-mentioned silica-based fine particles are used in combination with the silane coupling agent described below, they have a remarkable effect on making the chromate coating insoluble in hot water or aqueous alkaline solution. It is desirable to add the silica-based fine particles in an amount such that the weight ratio of the silica-based fine particles to the total chromium in the chromate treatment solution is in the range of 0.5 to 3.5. 3. The amount of silica-based fine particles added is less than 0.5.
5, the adhesion after immersion in hot water tends to decrease.

Next, as the silane coupling agent added to the chromate treatment agent, γ-anilinopropyltrimethoxysilane, n-butylaminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, A water-soluble silane coupling agent such as γ-glycitoxypropyltrimethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane is used.

In the above silane coupling agent, the highly reactive methoxy group (St-OCL) is hydrolyzed in an aqueous solution to generate a silanol group (Si-OH). The generated silanol groups react with chromium ions, phosphate ions, polymer reducing agents, or hydroxyl groups on the surface of silica-based fine particles, thereby significantly improving the insolubility of the chromate coating in hot water. Furthermore, since methyl alcohol produced by hydrolysis of methoxy groups is a reducing agent, heating baking sometimes promotes the reduction of water-soluble hexavalent chromium to insoluble trivalent chromium, making the chromate film more insoluble. Furthermore, regarding the adhesion between the chromate film and the primer layer, since the silane coupling agent has an amino group or an epoxy group, these organic functional groups are attached to the primer's amino group,
It easily bonds with epoxy groups and has a remarkable effect on improving the adhesion between the chromate film and the primer layer. The amount of the water-soluble silane coupling agent added is preferably in the range of 0.15-3.0 in terms of weight ratio to the total chromium in the chromate treatment solution. The amount of water-soluble silane coupling agent added is 0.
．． Less than 15 and 3. Of! In this case, the adhesion after immersion in hot water tends to decrease.

Before applying the chromate treatment agent, if there is scale, oil, etc. on the surface of the steel material, it is necessary to perform alkali degreasing, pickling, sandblasting, grid blasting, shot blasting, etc. to remove the surface deposits. There is. The baking temperature of the chromate treatment agent after application is 5.
0-300°C is suitable. When the steel surface temperature is less than 50°C, dehydration and chromium reduction within the chromate treatment agent layer tend to be insufficient.At 300°C, the chromate treatment agent decomposes. Further, the amount of the chromate treatment agent deposited is preferably 20-900 mg/+2 in terms of total chromium weight.

If it is less than 20111 g/l112, the effect of chromate treatment will not be exhibited, and if it is less than 91) Omg/m2, a strong film will not be formed and the adhesion will deteriorate.

Next, the brimer used in the present invention will be explained.

The brimer used in the present invention mainly contains an epoxy resin, a curing agent, and an inorganic pigment. As an epoxy resin,
Bisphenol A, AD.

Diglycidyl ether of F or phenol novolac type glycidyl ether can be used alone or in combination. As the curing agent, alicyclic modified amine, aliphatic amine, dicyandiamide curing agent, imidazole curing agent, etc. are used. Further, as the inorganic pigment, silica, titanium oxide, thorastonite, mica, chromium oxide, etc. are used as appropriate. Further, in order to improve the wettability with resin, the surface of the above pigment may be subjected to chemical treatment such as aluminum-silica treatment, silane coupling treatment, phosphate treatment, etc.

Next, the modified polyolefin adhesive used in the present invention will be explained.

The modified polyolefin adhesive used in the present invention refers to known polyolefins such as polyethylene, polypropylene, and nylon, and known polyolefin copolymer resins, and unsaturated carboxylic acids such as maleic acid, acrylic acid, and methacrylic acid, or These are conventionally known modified polyolefins, such as those modified with an acid anhydride, or those obtained by appropriately diluting the modified product with a polyolefin resin.

Next, the polyolefin coating or crosslinked polyolefin coating used in the present invention will be explained.

The polyolefin coating used in the present invention is mainly composed of conventionally known polyolefins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, straight-line low-density polyethylene, polypropylene, nylon, and ethylene-propylene block or random combinations. polymer,
The resin includes a known polyolefin copolymer such as a polyamide-propylene block or random copolymer.

The crosslinked polyolefin coating is mainly composed of a crosslinked polyolefin obtained by crosslinking the above polyolefin by subjecting it to electron beam irradiation or the like. As other components, pigments, filling reinforcement agents, etc. can be added. Pigments include silica, silica/alumina, rutile titanium oxide, glass, mica, iron oxide red, zirconium silicate, magnesium silicate, talc, barium sulfate, alumina, zinc chromate, strontium chromate, lead cinnamide, and lead zinc oxide. , aluminum phosphate, calcium phosphate, silicomolybdic acid, silicotungstic acid, zinc phosphomolybdate, and other commercially available pigments, and when aesthetic appearance is required, cadmium yellow polyazo yellow, quinophthalone yellow, isoindolinone yellow, quinacridone yellow, Coloring pigments such as red red, polyazo brown, azo lake yellow, perylene red, phthalocyanine blue, phthalocyanine green, red red, cobalt aluminate, aniline black, carbon black, ultramarine blue, and fine aluminum powder can also be added. . Filling reinforcements include glass, slag,
These include inorganic fiber fillers such as silicon carbide, carbon, boron, boron nitride, and alumina, and organic fillers such as nylon, polyester, vinylon, aramid, and Kevlar.

(Example) Example 1 and Comparative Example In order to specifically explain the present invention, chromate treatment agent A according to the present invention using various silane coupling agents will be described below.
-E and, for comparison, JP-A-1-280
A comparative example using the chromate treatment agent F-1 corresponding to No. 545 and JP-A No. 62-48543 will be given.

<Preparation example of chromate treatment solutions A-H of Examples> Chromate treatment solutions A-E of Examples contained 38.48 g of chromic anhydride as a chromate stock solution.

Chromic acid was reduced by adding 2.56 g of dextrin to a solution of 30.95 g of phosphoric acid dissolved in 428.03 g of distilled water and stirring with heating. After cooling, 400 g of an aqueous solution containing 10% by weight of silica-based fine particles was added to this liquid and stirred. As the silica-based fine particles, Aerosil 200 manufactured by Nippon Aerosil Co., Ltd. was used. Separately from this solution, an aqueous solution containing 20% by weight of water-soluble silane coupling agents A-E was prepared and used by mixing with the above-mentioned chromate stock solution at a weight ratio of 9:1. At this time, the weight ratio of hexavalent chromium to total chromium in the solution is 0.60, the weight ratio of phosphoric acid to total chromium is 1.5, the weight ratio of silica-based fine particles to total chromium is 2.0, and the weight ratio to total chromium is 1.5. The weight ratio of the silane coupling agent was 1.0.

Preparation example of chromate treatment liquid F as a comparative example> JP-A-1-2
The chromate treatment solution F of the comparative example corresponding to No. 80545 includes chromic anhydride 38.4881 phosphoric acid 30.9
5 g of chromic acid was dissolved in 528.03 g of distilled water, 2.56 g of dextrin was added, and the mixture was heated and stirred to reduce chromic acid. After cooling, 1400 g of an aqueous solution containing 10% by weight of Aerosil 200 was added to this solution and stirred to prepare a treatment solution. At this time, the ratio of hexavalent chromium to total chromium after reduction was 0.60, the weight ratio of phosphoric acid to total chromium was 1.5, and the weight ratio of silica-based fine particles to total chromium was 2.0.

Preparation example of chromate treatment liquid G as a comparative example〉JP-A-1-2
Comparative example chromate treatment liquid G corresponding to No. 805115
As, chromic anhydride 38.46g, phosphoric acid 30.9g
5 g dissolved in 477.72 g of distilled water, 5% by weight partially saponified polyvinyl acetate aqueous solution (Saponification degree 287)
%) was added and heated and stirred to perform partial reduction. After cooling, add 10% by weight of Aerosil 20 to this liquid.
400 g of an aqueous solution containing 0 was added and stirred to prepare a treatment solution. At this time, the ratio of hexavalent chromium to total chromium after reduction is 0.60, and the weight ratio of phosphoric acid to total chromium is 1.
5. The weight ratio of silica-based fine particles to total chromium is 2.0.
Met.

Preparation example of chromate treatment liquid H as a comparative example> JP-A-62-
Chromate treatment of comparative example corresponding to Publication No. 48543?
As lH, chromic acid was reduced by adding 2.56 g of dextrin to a solution of 38.45 g of chromic anhydride and 10.32 g of phosphoric acid dissolved in 848.66 g of distilled water and stirring with heating. To this was added 100 g of a 20% by weight aqueous γ-aminopropyltriethoxysilane solution. At this time, the ratio of hexavalent chromium to total chromium after reduction is 0.60, and the weight ratio of phosphoric acid to total chromium is 0.60.
5. The weight ratio of the silane coupling agent to the total chromium was 1.0.

Preparation example of chromate treatment liquid I as a comparative example> JP-A-62-
As a comparative example chromate treatment solution T corresponding to Publication No. 48543, 38.48 g of chromic anhydride was mixed with 62 g of distilled water.
1.60 g of dextrin was added to 0.24 g of the solution and heated and stirred to reduce chromic acid. To this was added 330.0 g of a 0.1% by weight 2-acryloyloxyacid phosphonyi aqueous solution and 6.7 g of a 10% by weight γ-glycidoxypropyltrimethoxysilane aqueous solution.
Added. At this time, the ratio of hexavalent chromium to total chromium after reduction was 0.75. The composition of the liquid is shown below.

Crys:
38.46g/kg2-Acryloyloxyacid phosphinide 20. 33g/kg γ-glycitoxypropyltrimethoxysilane o, 67
g/kg Cr”/Cr”= 0.33 As a manufacturing method for polyolefin-covered NfA material, steel plate (9
x 150 x 300 mm> was subjected to grid blasting, and a prepared chromate treatment agent was applied to the surface at a chromium adhesion amount of 410 to 440 mg/m20 mm, and after drying, baking was performed at 200°C. After cooling the steel plate to room temperature, coat the steel plate with a spray coater to a film thickness of 50 μm, heat it to a surface temperature of 220°C to harden it, and apply modified polyethylene adhesive to a film thickness of 200 μm for 1 hour. was applied. Thereafter, a polyolefin coating having a thickness of 3.0 mm, which had been extruded using a T-die, was applied under pressure and then cooled to produce a polyolefin-coated steel material. Regarding the above coated steel materials,
Hot water immersion test (test temperature = 100°C, immersion time: 60
Measurement of adhesion after 00 hours (measurement temperature: 2 room temperature, peel angle:
90 degrees, peeling rate: 50 + n + n/min, measuring beer strength when peeling off the coating) and high temperature cathodic peeling test (test temperature: 80°C, electrolyte = 3%-NaCfi)
, voltage: 1.5 V [Cu/CuSO4, standard electrode, initial holiday diameter: 3.2 mmφ, number of test days = 12
Estimated peeling radius of paint film after completion of test for 0 days: ((X/
2)"-(3,2/2] 2)"'ma+, X is the coating film peeling diameter). The results are shown in Table 1. 's1
From the results in the table, it can be seen that the example of the present invention in which the chromate treatment solution contains phosphoric acid, silica-based fine particles, and a water-soluble silane coupling agent is different from that in JP-A No. 1-280545, which does not contain a water-soluble silane coupling agent. It can be seen that significantly superior results are obtained compared to the corresponding Comparative Examples F and G, and the Comparative Examples H and I corresponding to JP-A No. 62-48543, which do not contain silica-based fine particles.

Example 2 and Comparative Example Next, examples will be given in which the amounts of the silane coupling agent, silica particles, and phosphoric acid added are changed in the present invention.

Preparation Example-2 of Chromate Treatment Solution A chromate treatment solution was prepared in the same manner as in Example 1 of the chromate treatment solution, and the amount of the silane coupling agent added in the chromate treatment solution was changed to form the polyolefin coating described above. Manufactured steel products. The polyolefin-coated steel material was subjected to the above-mentioned adhesion measurement after immersion in hot water and a high-temperature cathode peeling test. The results are shown in Figure 2.

From the results shown in FIG. 2, particularly good results can be obtained when the amount of silane coupling agent added to the chromate treatment solution is at a weight ratio of 0.15 to 3.0 to the total chromium. Note that even when the amount added was 4.0, the results were better than when the amount added was 0.

Preparation Example-3 of Chromate Treatment Solution A chromate treatment solution was prepared in the same manner as in Example 1 of the chromate treatment solution, and the amount of silica-based fine particles added in the chromate treatment solution was changed to prepare the polyolefin-coated steel material described above. was produced. The polyolefin-coated steel material was subjected to the above-mentioned adhesion measurement after immersion in hot water and a high-temperature cathode peeling test. The results are shown in Figure 3.

From the results shown in Figure 3, the amount of silica-based fine particles added to the chromate treatment solution is 0.5 in terms of weight ratio to the total chromium.
Good results are obtained within the range of −3.5.

<Preparation example of chromate treatment liquid-4> A chromate treatment liquid was prepared by the same method as in Example 1 of the chromate treatment liquid, and the amount of phosphoric acid added in the chromate treatment liquid was changed, and the above-mentioned polyolefin-coated steel material was prepared. Manufactured. For this, the adhesion force measurement after immersion in hot water and the high temperature cathode peeling test were conducted. The results are shown in Figure 4.

From the results shown in Figure S4, the amount of phosphoric acid added to the chromate treatment solution is 0.2-3.
Good results are obtained in the range of 0.

(Effects of the invention) As is clear from the examples, by applying chromate treatment to the base, which has excellent hot water resistance and adhesion,
In addition to the high-temperature cathode peelability proposed in No. 280545, it is now possible to provide a polyolefin-coated steel material that has unprecedented adhesion after heat immersion.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the polyolefin-coated steel material according to the present invention, and Figure 2 is the weight ratio of the silane coupling agent to the total chromium in the chromate treatment solution, the adhesion strength after hot water immersion (6000 hours), and the high-temperature cathode peeling. Figure 3 shows the relationship between the converted peeling radius after the test and the weight ratio of perilla-based fine particles to the total chromium in the chromate treatment solution, the adhesion force after hot water immersion (6000 hours), and high-temperature cathode peeling. A graph showing the relationship between the converted peel radius after the test, and Figure 4 shows the weight ratio of phosphoric acid to total chromium in the chromate treatment solution, the adhesion strength after hot water immersion (6000 hours), and the relationship after the high temperature cathode peel test. It is a graph showing the relationship with the converted peeling radius. 1... Polyolefin coating 2... Modified polyolefin adhesive layer 3... Brimer layer 4... Chromate treatment agent layer 5... Steel materials and other 4 people Figure 2 Silane coupling agent 1/Suri ROM (weight Ratio) l: Polyolefin coating 2: Modified polyolefin adhesive layer 3 Nib rimer layer 4: Chromate treatment agent layer 5: Steel f Isilica/↑Chromium (weight ratio)

Claims (1)

[Scope of Claims] 1. A heavy anti-corrosion coated steel material in which a coating layer consisting of a chromate treatment layer, a primer layer, a modified polyolefin adhesive layer, and a polyolefin resin layer is sequentially laminated on the entire surface or a part of the surface of the steel material, , a polyolefin characterized in that, as the chromate treatment agent, a mixture of phosphoric acid and chromic anhydride is partially reduced with an organic reducing agent, and silica-based fine particles and a silane coupling agent are added. Coated steel. 2 As a silane coupling agent, γ-anilinopropyltrimethoxysilane, n-butylaminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β
The polyolefin-coated steel material according to claim 1, characterized in that a water-soluble silane coupling agent such as -(3,4-epoxycyclohexyl)ethyltrimethoxysilane is used. 3. The polyolefin-coated steel material according to claim 1, wherein the amount of the silane coupling agent added is 0.15-3.0 in weight ratio to total chromium. 4. The polyolefin-coated steel material according to claim 1, wherein the amount of silica fine particles added is 0.5 to 3.5 in weight ratio to total chromium. 5 The amount of phosphoric acid added is 0.0 in weight ratio to total chromium.
2. The polyolefin-coated steel material according to claim 1, wherein the polyolefin-coated steel material has a molecular weight of 2-3.0.