JPH0563307B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a polyolefin-coated steel material, and more particularly to a polyolefin-coated steel material that has excellent long-term hot salt water resistance. (Prior Art) In order to prevent corrosion of steel materials such as steel and steel pipes, the surface of steel materials is increasingly coated with polyolefin resins such as polyethylene and polypropylene, which have excellent chemical stability. However, the environment in which these polyolefin-coated steel materials are used is such that, for example, in buried pipes used for heating an entire region, the pipe surface temperature is high, and especially in buried areas where the groundwater level is high, the entire pipe is below the groundwater level containing seawater. The situation is becoming extremely harsh, with polyolefin-coated steel materials being immersed in hot salt water. Generally, polyolefin resins are non-polar due to their chemical structure, so they cannot be directly bonded to highly polar surfaces such as steel. Therefore, a method has been adopted in which a polyolefin resin is coated with a modified polyolefin resin modified with an unsaturated carboxylic acid or its acid anhydride. However, the adhesive strength between the polyolefin and the steel material decreases as the temperature of the use environment, the amount of moisture in the use environment, or the salt concentration increases. When the above-mentioned coated steel material is used in an extremely harsh environment such as a hot salt water environment, it is particularly important to maintain the adhesive strength in hot salt water, that is, to improve the heat salt water resistance. In order to solve these problems, the present inventors developed a coating structure that uses a combination of chromate treatment and epoxy primer treatment for steel materials, and in particular, for the composition of the epoxy primer, a specific epoxy resin and m-xylene diamine are used. A method using a modified aliphatic polyamine obtained by reacting and adding an alkyl glycidyl ether to a condensate of epichlorohydrin and an inorganic pigment as main components (JP-A-1-150540);
No. 56-143223, JP-A-59-222275, JP-A-60-
As in No. 245544, we have proposed a method using an epoxy primer made by mixing a specific epoxy resin with an inorganic pigment and an amine curing agent and curing the mixture through a reaction. (Problems to be Solved by the Invention) These surface treatment methods are effective in improving heat brine resistance (immersion time within 8,000 hours) in hot brine at temperatures exceeding 90°C, or in improving high-temperature cathode removability. There is. However, JP-A-1-150540, JP-A-56-143223, JP-A-59-222275, JP-A-Sho
Even when chromate treatment and epoxy primer treatment as shown in No. 60-245544 are used together, the temperature at 90℃
It is difficult to maintain the adhesive strength between the coating and the steel material when the steel is immersed in hot salt water for more than 8,000 hours. Therefore, it is desired to develop a superior polyolefin-coated steel material that can maintain adhesive strength even when immersed in hot salt water at temperatures exceeding 90°C for over 8,000 hours. (Means for Solving the Problems) In order to solve the above-mentioned problems, the present inventors have attempted to solve the above-mentioned problems by
59-222275 and JP-A No. 60-245544, which uses a combination of chromate treatment and epoxy primer treatment.
As a result of improving the composition of the epoxy primer disclosed in Publication No. 150540, we found that phenol novolac-type glycidyl ether alone, or the phenol novolac-type glycidyl ether plus bisphenol A, AD, or F diglycidyl ether alone or It has been discovered that the above-mentioned problems can be solved by using an epoxy primer composed of an epoxy resin that is a mixture of two or more types, a modified polyamine that is a condensation of m-xylene diamine and epichlorohydrin, and an inorganic pigment, and the present invention It came to this. That is, the gist of the present invention is to provide a chromate treatment agent layer on the surface of steel, an epoxy primer layer containing the following three components (a), (b), and (c) as essential components, a modified polyolefin resin layer, and a polyolefin resin layer. This is a polyolefin-coated steel material that has excellent hot brine resistance over a long period of 8,000 hours or more, and is characterized by successive lamination of resin layers. (a) A phenol novolak type glycidyl ether alone, or the phenol novolak type glycidyl ether combined with bisphenol A,
An epoxy resin consisting of AD or F diglycidyl ether alone or in combination of two or more. (b) A modified polyamine obtained by condensing m-xylene diamine and epichlorohydrin. (c) Inorganic pigments. That is, as shown in FIG. 1, the present invention includes a chromate treatment agent layer 2 on the surface of a steel material 1, the above (a)
This invention relates to a polyolefin-coated steel material with excellent hot brine resistance, characterized by sequentially laminating an epoxy primer layer 3, a modified polyolefin resin layer 4, and a polyolefin resin layer 5, each of which includes components (b) and (c) as essential components. be. Hereinafter, the present invention will be explained in detail. First, the steel materials used in the present invention include steel pipes, shaped steel, steel plates made of alloy steel such as carbon steel and stainless steel.
Steel bars, steel molded products and structures, etc. outdoors,
It is a general term for things that are widely used underground, on the ground, and under the sea. Next, the coating structure in the present invention will be explained based on FIG. 1. The main point of the present invention is to have a structure in which a chromate treatment agent layer and an epoxy primer layer are interposed between the steel material 1 and the modified polyolefin resin layer 4, and the steel material 1 and the chromate treatment agent layer 2 shown in FIG. In between, a plating layer of zinc, aluminum, chromium, nickel, etc., an alloy plating layer of zinc-iron, zinc-nickel, zinc-nickel-cobalt, etc., a plating layer or an alloy plating layer containing silica alumina, silica-alumina, Even if there is a dispersed plating layer in which inorganic fine particles such as titanium oxide, silicon carbide, boron nitride, etc. are dispersed, the gist of the present invention will not be impaired in the slightest. Alternatively, the polyolefin resin layer may have a two-layer structure, with the upper layer being a polyolefin resin containing fiber reinforcing material, fine powder, or scale-like reinforcing material, and the lower layer being a polyolefin resin layer. Next, the epoxy primer used for forming the epoxy primer layer of the present invention is a mixture (d) in which an epoxy resin as a component (a) and an inorganic pigment as a component (c) are mixed in advance. Component (), a modified aromatic polyamine obtained by condensing m-xylene diamine and epichlorohydrin, was mixed such that the ratio of the epoxy equivalent of (d) to the active hydrogen equivalent of (b) was in the range of 0.6 equivalent to 2.0 equivalent. It is a mixture. The epoxy resin which is component (a) above refers to phenol novolac type glycidyl ether alone, or bisphenol A, AD, or F to the phenol novolac type glycidyl ether.
This is an epoxy resin consisting of diglycidyl ethers used alone or in combination of two or more. What is phenol novolax type glycidyl ether? The phenol novolak type glycidyl ether has a molecular structure of 312 to 6792 (0≦n≦40) from the viewpoint of heat-resistant brine resistance.
Moreover, the epoxy equivalent is in the range of 155 to 230. Applicable commercial products include Epicote 152 and Epicote 154 manufactured by Yuka Ciel Epoxy Co., Ltd., Epotote YDPN-638 and YDPN-601 manufactured by Toto Kasei Co., Ltd.
YDPN−602, DEN431 manufactured by Dow Chemical Japan Co., Ltd.
Examples include DEN438, DEN439, DEN485, and Ciba Geigy's EPN1136, EPN1139, and VPY307 grades. What is diglycidyl ether of bisphenol A? From the viewpoint of heat salt water resistance, it is desirable to have an epoxy equivalent in the range of 170 to 280. Applicable commercial products include the grades of Epicote 827 and Epicote 834 manufactured by Yuka Ciel Epoxy Co., Ltd., and Mitsui Oil. Epomitsuku R139, Epomitsuku R140, Epomitsuku R140P, Epomitsuku R140C manufactured by Kagaku Kogyo Co., Ltd.
Each grade of Epomitsuku R144, each grade of Adeka Resin EP4100, Adeka Resin EP4100E, Adeka Resin EP4200, and Adeka Resin EP4300 made by Asahi Denka, each grade of Epototo YD115, Epototo YD121, Epototo YD122, Epototo YD128, Epototo YD134 made by Toto Kasei Co., Ltd. DER317, DER330 manufactured by Chemical Nihon Sha,
Examples include DER331, DER333, DER383, and DER387 grades. In addition, the diglycidyl ether of bisphenol AD is It has a molecular structure of Can be mentioned. Furthermore, bisphenol F type diglycidyl ether is It has a molecular structure of 1, and preferably has an epoxy equivalent in the range of 170 to 185 from the viewpoint of heat salt water resistance, and a suitable commercial product includes Epicoat 807 manufactured by Yuka Ciel Epoxy Co., Ltd. By using an epoxy primer prepared by adding an inorganic pigment to the above-mentioned phenol novolak type glycidyl ether or a mixture of the phenol novolak type glycidyl ether and the above-mentioned epoxy resin, the long-term hot brine properties are significantly improved. Here, if the phenol novolac-type glycidyl ether has a high viscosity or is in a solid state at room temperature, for example, when using Epicote 154, it is diluted with a solvent or with diglycidyl ether of bisphenol F. Alternatively, a method in which the viscosity is lowered by diluting with other conventionally known reactive diluents etc. does not impede the gist of the present invention in the slightest. If a polyfunctional epoxy resin such as tetraglycidyl metaxylene diamine is used instead of the above-mentioned phenol novolac type glycidyl ether, the long-term heat resistance to salt water will rather deteriorate, which is not desirable. Furthermore, regarding the blending of the phenol novolac type glycidyl ether and the above-mentioned epoxy resin, the mixing amount of the phenol novolac type glycidyl ether with respect to 100 parts by weight of the above-mentioned epoxy resin is in the range of 1 to 100 parts by weight. Mixing is desirable. Regarding the mixing ratio,
If the amount of phenol novolac type glycidyl ether mixed with the epoxy resin is 1 part by weight or less, the above effects will hardly be obtained. Furthermore, if the molecular weight of the phenol novolak type glycidyl ether is 6792 or more, this is not desirable because it causes significant difficulties in handling. The modified polyamine that is a condensation of component (b) m-xylene diamine and epichlorohydrin is: It has a molecular structure of 328 or more (degree of polymerization n≧1) from the viewpoint of hot brine properties. Applicable commercial products include Gascamine G328 and G328S manufactured by Mitsubishi Gas Chemical Co., Ltd. (G328 with components having a degree of polymerization n=0 removed). However, from the viewpoint of work handling, the viscosity also increases as the molecular weight of the modified polyamine increases, so dilution with a solvent, other conventionally known low viscosity curing agents, or diluent is used. This does not pose any hindrance to the present invention. Regarding the mixing of the above mixture of epoxy resin and inorganic pigment with the above modified polyamine obtained by condensing m-xylene diamine and epichlorohydrin, the mixing ratio of the epoxy equivalent to the active hydrogen equivalent of the amine curing agent is 0.6 to 2.0. Range is preferred. If the mixing ratio is less than 0.6,
Long-term heat salt water resistance is significantly reduced. In addition, if the mixing ratio is greater than 2.0, the amount of unreacted amine curing agent remaining in the formed coating film will be significantly large, resulting in a high water absorption rate of the coating film, which may result in long-term immersion in heat-resistant salt water. The coating film swells and its hot brine properties are significantly reduced. Inorganic pigments, which are component (c), include titanium oxide (for example, KR380, KR460 manufactured by Titan Kogyo Co., Ltd.), silica (for example, Aerosil manufactured by Nihon Aerosil Co., Ltd.), and silica (for example, Aerosil manufactured by Nippon Aerosil Co., Ltd.).
200, Aerosil 300, Micron SR70,
SRC18, etc.), silica/alumina (COK84, MOX80, etc. manufactured by Nippon Aerosil Co., Ltd.), talc (Talcan Bauder PK-P, Micron White #5000, etc. manufactured by Hayashi Kasei Co., Ltd.), mica-like iron oxide (manufactured by Kikuchi Shiki Kogyo Co., Ltd.)
MI0−KS, etc.), muscovite (Librite RD100, Librite RD200, Librite manufactured by Seto Ceramic Materials Co., Ltd.)
RD300, etc.), Susolite mica (Kuraray 150)
-K1, 200-K1, 325-K1, etc.), aluminum tripolyphosphate (K-White #82 manufactured by Teikoku Kako Co., Ltd.),
K-White 105, etc.), chromium oxide (Cr ₂ O ₃ ), chromic phosphate (CrPO ₄ ), zinc phosphate (Zn ₃
(PO ₄ ) ₂・4H ₂ O), magnesium phosphate (MgHPO ₄・3H ₂ O), aluminum phosphate (AlPO ₄ ), synthetic iron oxide yellow (Titan Kogyo Mapico Yellow, etc.), synthetic iron oxide red (Titanium Mapikoretsu (manufactured by Kogyo Co., Ltd.), barium sulfate (BaSO ₄ ), zirconium phosphate (manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.)
ZSP100, ZSP110, Cera White, etc.), Carbon Black (Mitsubishi Chemical #3050, #3150,
#3250, #3750, #3970), zirconium silicate (Micropax, zirconyl, manufactured by Hakusui Chemical Industry Co., Ltd.)
MZ1000B manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.), zirconium oxide (BR-90G manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.),
Kaolin clay (SATINTONE- manufactured by Hayashi Kasei Co., Ltd.)
W) or a mixture of two or more thereof. Furthermore, in order to improve wettability with the epoxy resin, the surface of the pigment may be subjected to chemical treatments such as aluminum-silica treatment, silane coupling treatment, phosphoric acid treatment, etc. The amount of the inorganic pigment added is preferably 1 to 45 parts by weight per 100 parts by weight of the epoxy resin, which is the component (a), from the viewpoint of heat salt water resistance. In addition, in order to adjust the curing time of the epoxy primer according to the present invention, as a curing accelerator, for example, Kyuazol 2MZ, Kyuazol 2E4MZ, Kyuazol C11Z, Kyuazol C17Z, Kyuazol 2PZ, Kyuazol manufactured by Shikoku Kasei Co., Ltd.
There is no problem even if a small amount of imidazole curing accelerator such as 2P4MZ is added. Next, the chromate treatment agent used for forming the chromate treatment agent layer of the present invention will be explained. The chromate treatment agent used in the present invention is chromic acid (CrO ₂ ) partially reduced with an organic reducing agent such as corn starch so that the weight ratio of hexavalent chromium to total chromium is in the range of 0.35 to 0.65.
A silica-based chromate treatment agent containing fine silica powder added to an aqueous solution, a partially saponified polyvinyl acetate, and a high-molecular organic reducing agent such as dextrin, which is obtained by partially hydrolyzing starch with a hydrolase such as amyloglucosidase, are used to reduce the total chromium by hexavalent chromium. The weight ratio of
Add silica and silica to a mixed aqueous solution of partially reduced phosphoric acid and chromic acid so that the
Phosphoric acid added with fine silica powder such as alumina
A silica-based chromate treatment agent can be used. From the standpoint of high-temperature cathode stripping, the phosphoric acid-silica-based chromate treatment agent is desirable. Next, the polyolefin resin and modified polyolefin resin used for forming the polyolefin resin layer and modified polyolefin resin layer of the present invention will be explained. The polyolefin resins used in the present invention include conventionally known polyolefins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, and nylon, as well as ethylene-propylene block or random copolymers, and polyamides. - Conventionally known polyolefin copolymers such as propylene block or random copolymers. In addition, modified polyolefin resin is one obtained by modifying the above-mentioned polyolefin resin with an unsaturated carboxylic acid such as maleic acid, acrylic acid, or methacrylic acid or its acid anhydride, or one obtained by appropriately diluting the modified product with polyolefin resin. These are conventionally known modified polyolefins. Next, a method for manufacturing a polyolefin-coated steel material according to the present invention will be described using a polyolefin-coated steel pipe as an example. A polyolefin-coated steel pipe can be obtained, for example, by the manufacturing method shown in FIG. That is, the chromate treatment agent is applied to the surface of the steel pipe 1 from which scale and the like have been removed by the chromate treatment agent application device 6, and baked by the heating device 7. Next, an epoxy primer 3 is applied to the surface using an epoxy primer application device 8, and heated and cured using a post-heating device 9. Next, a modified polyolefin resin 4 is applied to the surface using a modified polyolefin resin coating device 10, and a polyolefin resin 5 is extruded and coated using a T-die 11, and then cooled using a cooling device 12 to coat the polyolefin resin. Obtain a coated steel pipe. In the case of the above manufacturing method, a chromate treatment agent is applied to the surface of the steel pipe 1,
After the steel pipe is baked by the heating device 9, before the steel pipe reaches the modified polyolefin resin coating device 10, and before the epoxy primer layer is formed on the surface of the steel pipe, the surface of the steel pipe is heated. It is sufficient that the epoxy primer layer is formed and sufficiently cured, and the above-mentioned epoxy primer application method is appropriately selected from conventionally known methods such as spray application using a spray paint machine, roll application, ironing application, brush application, and flow application. It can be used as The method for heating the steel pipe by the post-heating device 9 can be appropriately selected from conventionally known methods such as high-frequency induction heating, far-infrared heating, and gas heating. Furthermore, if the steel pipe is thick, the heating device 7 has a large heating capacity, and the epoxy primer layer is sufficiently cured, heating by the post-heating device 9 may be omitted. Furthermore, in FIG. 2, a method of electrostatically coating the polyolefin resin powder with the modified polyolefin resin coating device 10 is used, but a method of extrusion coating the modified polyolefin resin using a T-die or a round die, Conventionally known methods can be employed, such as a method of extruding and coating the resin and polyolefin resin as two layers from a T-die or a round die. (Function) A partial cross section of the polyolefin-coated steel material according to the present invention obtained as described above is as shown in FIG. Steel material from which 2
3 is a chromate treatment agent layer, 3 is an epoxy primer that requires the following three components, (a) phenol novolak type glycidyl ether alone, or bisphenol A, bisphenol A,
An epoxy resin consisting of AD or F diglycidyl ether alone or in combination of two or more. (b) A modified polyamine obtained by condensing m-xylene diamine and epichlorohydrin. (c) Inorganic pigments. 4 indicates a modified polyolefin resin layer, and 5 indicates a polyolefin resin layer. In addition, 2 in the figure is 250 to 250 as the total chromium weight.
Good results are obtained with a coating weight of 1200 mg/m ² and a thickness of 3 of 5 to 350 μm and a thickness of 5 of 1.0 to 10 mm. Hereinafter, the present invention will be specifically explained with reference to Examples. (Examples) First, in order to specifically explain the present invention, Examples 1 to 41 of primer formulations according to the present invention, and Comparative Examples 1 to 41 of primer formulations corresponding to JP-A-56-143223 as comparative examples. 4. Comparative Examples 5 to 31 of primer formulations corresponding to JP-A-59-222275 and JP-A-60-245544, Comparative Examples 32-40 of primer formulations other than the above, and JP-A-1-150540 Comparative Examples 41-47 of the corresponding primer formulations are shown in Table 1. In addition, the epoxy resins listed in Table 1 are listed in Table 2.
The curing agents are shown in Table 3, and the inorganic pigments are shown in Table 4. In addition, the amounts of the curing agent and inorganic pigment listed in Table 1 are the amounts (parts by weight) per 100 parts by weight of the epoxy resin, and the amounts of the solvent added are the amounts (parts by weight) per 100 parts by weight of the primer. be. In addition, the following and were used as chromate treatment agents for the surface treatment of steel materials. Cosmer #100 manufactured by Kansai Paint Co., Ltd., which is a silica-based chromate treatment agent Phosphoric acid-silica-based chromate treatment agent prepared by the following method First, the following solutions and were prepared. Mixed aqueous solution of phosphoric acid and chromic anhydride 49.2 g of phosphoric acid and 76.8 g of chromic anhydride were dissolved in 247.6 g of distilled water. 5% by weight aqueous solution of partially saponified polyvinyl acetate Partially saponified polyvinyl acetate having a molecular weight of 88,000 and a saponification degree of 87% was added to distilled water and left to swell for 2 hours. Next, this aqueous solution was heated to 98℃
The mixture was heated to completely dissolve it, and an aqueous solution containing 5% by weight of partially saponified polyvinyl acetate was prepared. 10% by weight Aerosil 200 aqueous solution Aerosil 200 manufactured by Nippon Aerosil Co., Ltd. was used as the silica-based fine particles. Add Aerosil 200 to distilled water and mix with high speed mixer (rotation speed 3000 rpm)
The mixture was stirred and dispersed to prepare an aqueous solution containing 10% by weight of Aerosil 200. Next, 106 g of a 5% by weight partially saponified polyvinyl acetate aqueous solution was added to 373.6 g of the above mixed aqueous solution of phosphoric acid and chromic anhydride, and heated to 90°C to release hexavalent chromium ions. One part was reduced to trivalent chromium ions. The weight ratio of hexavalent chromium to total chromium in the reduced aqueous solution was 0.60, and the weight ratio of PO ₄ ^3- to total chromium was 1.16. Then,
A chromate treatment agent according to the present invention was prepared by adding 515.6 g of the above 10% by weight Aerosil 200 aqueous solution to the above reduced aqueous solution. The weight ratio of SiO ₂ (Aerosil 200) to total chromium in the chromate treatment agent was 1.29. Next, an example of manufacturing a polyethylene-coated steel pipe according to the present invention using the primer and chromate treatment agent will be described. A steel pipe (200A x 5500mm length x 5.8mm thickness) was grid blasted, the chromate treatment agent or the above-mentioned chromate treatment agent was applied to the surface so that the total amount of chromium deposited was 550mg/ ^m2 , and the pipe was heated to 190℃. After baking for 3 minutes, apply a thick layer of epoxy primer.
It was applied to a thickness of 50 μm using a spray paint machine and cured. Next, a modified polyethylene resin was electrostatically applied to a film thickness of 200 μm, and a polyethylene resin was extruded to a thickness of 3.2 mm using a T-die, and then cooled to form a polyethylene-coated steel pipe A according to the present invention. Manufactured. Adhesion test (measurement temperature: 100°C, peel angle: 90 degrees, peeling speed: 50 mm/min), hot salt water immersion test (immersion temperature: 100°C, immersion time 16,000 hours, post-immersion adhesion test) for the above coated steel pipes ), cathode peel test [(initial Holliday diameter 5 mmφ, electrolyte 3% NaCl, voltage -
1.5V (Cu/CuSO ₄ , standard electrode), the peeling distance of the film after the test <(x-5)/2 mm, x is the diameter of the peeling of the film after the test>> The results are shown in Table 5. . As is clear from the results in Table 5, chromate treatment is applied as a base treatment for steel pipes, and phenol novolac type diglycidyl ether alone or bisphenol A diglycidyl ether is added to the phenol novolac type glycidyl ether. Ether, diglycidyl ether of bisphenol AD or diglycidyl ether of bisphenol F alone or as a mixture of two or more of them, an epoxy resin, a modified polyamine that is a condensation of m-xylene diamine and epichlorohydrin, and an inorganic By applying a pigmented epoxy primer, unprecedentedly good results can be obtained in high-temperature adhesion tests, hot salt water immersion tests, and high-temperature cathodic peel tests.

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[Table] *2: Manufactured by Mitsui Petrochemical Industries, Ltd.

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[Table] (Effects of the Invention) As is clear from the examples, the polyolefin-coated steel material of the present invention has an epoxy primer layer on the base that has excellent heat and salt water resistance compared to conventional polyolefin-coated steel materials, so it has excellent high-temperature adhesion. It has a remarkable effect of providing an unprecedented polyolefin-coated steel material, which has excellent properties such as hardness, hot salt water resistance, and high-temperature cathode peeling resistance.

[Brief explanation of the drawing]

FIG. 1 is a partial cross section of a polyolefin-coated steel material according to the present invention, and FIG. 2 is a schematic diagram showing an example of manufacturing a polyolefin-coated steel pipe as an example of the polyolefin-coated steel material according to the present invention. 1: steel material, 2: chromate treatment agent, 3: phenol novolax type glycidyl ether alone,
Alternatively, an epoxy resin prepared by mixing the phenol novolac type glycidyl ether with diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol AD, or diglycidyl ether of bisphenol F, either alone or in a mixture of two or more. and a modified polyamine obtained by condensing m-xylene diamine and epichlorohydrin,
and an epoxy primer layer composed of an inorganic pigment, 4: modified polyolefin resin layer, 5: polyolefin resin layer, 6: chromate treatment agent coating device, 7: heating device, 8: epoxy primer coating device, 9: post-heating device, 10: Modified polyolefin resin coating device, 11: T die, 12: Cooling device.

Claims (1)

[Scope of Claims] 1. In order from the inside of the steel surface, a chromate treatment agent layer, an epoxy primer layer containing the following three components (a), (b), and (c) as essential components, a modified polyolefin resin layer, A polyolefin-coated steel material having excellent heat and salt water resistance characterized by laminating a polyolefin resin layer and a polyolefin resin layer (a) Phenol novolak type glycidyl ether alone, or bisphenol A, bisphenol A,
Epoxy resin consisting of AD or F diglycidyl ether alone or in combination of two or more types. (b) Modified polyamine obtained by condensing m-xylene diamine and epichlorohydrin. (c) Inorganic pigment.