JP2000190422A - Polyolefin-coated steel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the anti-hot water adhesiveness, anti-high temperature cathode peeling properties and low temperature impact resistance by laminating an epoxy primer layer containing a specific essential component, a polyolefin adhesive layer and a polyolefin layer in that order on the surface of a steel material. SOLUTION: A powder epoxy primer layer 3, a modified polyolefin adhesive layer 4 and a polyolefin layer 5 are laminated sequentially on the surface of a steel material 1 treated with a primer coat. Powder epoxy primer contains the underdescribed four essential components (A), (B), (C), (D).(A) is a mixture of a bisphenol A-type epoxy resin with 75-128 deg.C softening point and an o-cresol nonvolac-type epoxy resin, (B) is a phenolic curing agent represented by the formula (m is 1-4), (C) is an imidazole curing promoter and (or) an imidazoline curing promoter and (D) is an inorganic filler. Besides, in order to impart a further outstanding corrosionproofness, a chromate coat 2 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a polyolefin-coated steel material. More specifically, an epoxy powder primer is applied to the outer surface of the steel material that has been subjected to the base treatment, and a polyolefin adhesive is coated on the outer surface. The present invention relates to a polyolefin-coated steel material which is excellent and can maintain corrosion resistance for a long time.

[0002]

2. Description of the Related Art Steel materials often corrode when exposed to the air, the ground, or seawater without taking measures to protect the surrounding environment. Therefore, in various piping such as oil, gas, water and sewage, electric cable, civil engineering building materials such as steel pipe piles and steel sheet piles, polyolefin-coated steel materials in which the outer surfaces of steel materials are coated with polyethylene, polypropylene or the like are frequently used.

[0003] Generally, polyolefin has poor adhesion to steel due to its chemical stability. Therefore, the polyolefin-coated steel material prevents separation of the polyolefin from the steel material by interposing a polyolefin adhesive layer made of a modified polyolefin between the steel material and the polyolefin coating layer. However, a polyolefin-coated steel material with only an adhesive layer interposed between it and the ground may be used in wet or wet environments, such as under the sea, under the sea, etc. is there. Further, in an environment in which cathodic protection is also used, there is a problem that the coating is easily peeled off from a coating defect as a starting point due to excessive corrosion protection current (this phenomenon is referred to as cathode peeling). Therefore,
Polyolefin-coated steel used in environments such as water-contact environments and in which cathodic protection is also used, by first applying an epoxy-based primer to steel and then sequentially laminating a modified polyolefin layer and a polyolefin layer on it, Excellent long-term adhesive strength is provided. As the epoxy primer, liquid epoxy, solid epoxy diluted with an organic solvent, powder epoxy, and the like are used. In recent years, the transition to powder epoxy has been progressing from the viewpoint of measures against environmental problems. German Patent (DE-A) discloses a coating system for applying an epoxy powder primer layer / polyolefin adhesive layer / polyolefin coating layer on the outer surface of a steel material.
Nos. 1965802, 2257135 and 29
Nos. 44809 and 3230955, British Patent (GB) 1542333, and European Patent (EP-A) 57823. As an epoxy powder primer in such coating systems,
Using dicyandiamide as a curing agent for the epoxy resin,
It is known to apply a powder primer in which a filler is mixed with crystals or amorphous silica.

[0004] In recent years, as the demand for energy has increased and the development of resources such as oil and natural gas on the seabed and polar regions has been activated, the long-term durability of polyolefin coatings on steel structures and line pipes in a high-temperature water-contact environment. Sex is a problem. However, a disadvantage of the coating system using the epoxy powder primer is that the adhesive strength after the hot water immersion is reduced, and thus the polyolefin layer is easily peeled off after the hot water immersion, and the corrosion resistance is impaired. . Also, with respect to cathode peeling resistance, it was difficult to prevent peeling at a high temperature of 60 ° C. or more for a long period of time. Furthermore, -30 to -45 ° C
When a pipeline is laid in an extremely low temperature environment, cracks occur in the coating due to impacts such as contact between the coated steel and heavy machinery and collision of the coated steel, etc., and the polyolefin layer peels off from the steel to prevent corrosion. It was sometimes damaged.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and uses a powder epoxy primer having excellent heat-resistant water adhesion, high-temperature cathode peeling resistance and low-temperature impact resistance. An object of the present invention is to provide a polyolefin-coated steel material.

[0006]

Means for Solving the Problems The inventors of the present invention have eagerly solved problems relating to heat-resistant water adhesion, high-temperature cathode peeling resistance, and low-temperature impact resistance of a polyolefin-coated steel material when a powder epoxy primer is used. investigated. Then, as shown in FIG. 1, a polyolefin-coated steel material in which a powdered epoxy primer layer (3), a modified polyolefin layer (4), and a polyolefin layer (5) are sequentially laminated on the surface of the steel material (1) subjected to the base treatment In (1), (2), (3) and (4) below, as powder epoxy primers
It has been found that a polyolefin-coated steel material excellent in heat-resistant water adhesion, high-temperature cathodic peeling resistance and low-temperature impact resistance can be obtained by using an epoxy primer layer containing a component as an essential component. In addition, (2) in FIG. 1 is a chromate film provided for imparting more excellent anticorrosion properties. (A) The softening point is 75 to 128 ° C and the epoxy equivalent is 600.
A mixed epoxy resin component comprising a mixture of bisphenol A-type epoxy resin of 2200 g / eq and o-cresol novolac-type epoxy resin, the ratio of which is 97 / 3-50 / 50 by weight, (b) Formula (A)
(Where m is 1 to 4), a phenolic curing agent having an average phenolic hydroxyl equivalent of 200 to 800 g / eq, and the amount of the phenolic hydroxyl is 1 equivalent of the epoxy group of the mixed epoxy resin component (a). A curing agent component which is 0.4 to 0.9 equivalents, (c) an imidazole-based curing accelerator and / or an imidazoline-based curing accelerator, wherein the compounding amount is the compounding amount of the curing agent component (b) 0.1 to 1
5.0% by weight of a curing accelerator component, (d) an inorganic filler, and the compounding amount is a total of the mixed epoxy resin component (a), the curing agent component (b), and the curing accelerator component (c). An inorganic filler component which is 10 to 100% by weight based on the amount.

[0007]

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[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Steel materials (1) used in the present invention include cold-rolled steel sheets, hot-rolled steel sheets, steel sheets such as thick steel sheets, H-section steels, and the like.
Shaped steel such as I-shaped steel and L-shaped steel, steel sheet pile, steel bar, steel wire, cast iron pipe, steel pipe, steel pipe sheet pile and the like. On the surface of these steel materials,
A metal such as stainless steel, titanium, aluminum, nickel, copper or the like, or a clad steel material obtained by laminating an alloy thereof can also be used. Also, a plated steel material obtained by plating a surface of a steel material can be used. The steel material is used after first being subjected to rust removal treatment such as blast treatment, degreasing and pickling treatment.

It is desirable to use the steel material (1) by forming a chromate film (2) as a base treatment before forming the powdered epoxy primer layer (3), since more excellent corrosion resistance can be obtained. The chromate treating agent is, for example, an organic reducing agent or the like added to an aqueous solution of chromic anhydride and heated to partially reduce the hexavalent chromium in the aqueous solution to trivalent chromium. The dispersed mixture or the like is applied to a steel material, and the steel material is heated and baked for use. Good results can be obtained when the chromate film (2) has a thickness of ²⁰ to 1000 mg / m ^{2 in} terms of the total amount of chromium deposited after heating and baking. If it is less than 20 mg / m ² , a sufficient anticorrosive effect cannot be obtained, and if it exceeds 1000 mg / m ² , the cohesive force of the chromate film decreases and the adhesion to the steel material decreases.

The powdered epoxy primer layer (3) comprises a mixed epoxy resin component (a), a phenolic curing agent component (b), a curing accelerator component (c), and an inorganic filler component (d) described in detail below. Are the essential components.

The mixed epoxy resin component (a) of the powder epoxy primer is a mixture of a bisphenol A type epoxy resin and an o-cresol novolak type epoxy resin. As a result, it is possible to have both excellent adhesion of the bisphenol A type epoxy resin to the steel base material and excellent heat resistance stability by adding the o-cresol novolak type epoxy resin. The mixing ratio of the bisphenol A type epoxy resin and the o-cresol novolak type epoxy resin is preferably 97/3 to 50/50 by weight.
If the mixing ratio of the o-cresol novolak epoxy resin is less than 3% by weight, sufficient heat stability cannot be obtained. On the other hand, if the content is more than 50% by weight, the elasticity of the obtained cured product becomes too high, and the impact resistance is reduced.

The bisphenol A type epoxy resin desirably has a softening point of 75 to 128 ° C. and an epoxy equivalent in the range of 600 to 2200 g / eq. If the softening point is less than 75 ° C, fusion between the powder particles is likely to occur during storage of the primer composition. If the softening point exceeds 128 ° C, the melt viscosity increases, the wettability with the steel base material becomes poor, and the adhesiveness becomes poor. Properties (cathode peelability decreases). The softening point is preferably between 90 and 110C. On the other hand, when the epoxy equivalent is less than 600 g / eq, the molecular weight generally becomes small and the softening temperature becomes too low, and 2200 g / eq.
If it exceeds eq, the molecular weight is generally increased and the softening temperature is too high, so that it is limited to the above range. The epoxy equivalent is preferably between 650 and 1100 g / eq.

As the bisphenol A type epoxy resin, commercially available ones can be used. Specifically, for example, Epototh YD-014 (epoxy equivalent: 900 to 1000 g / eq, softening point: 91 to 102)
° C, manufactured by Toto Kasei Co., Ltd.), Epototo YD-017 (epoxy equivalent: 1750-2100 g / eq, softening point 117-1)
27 ° C., manufactured by Toto Kasei Co., Ltd., Epototo YD-904 (epoxy equivalent: 900 to 1000 g / eq, softening point: 96 to 1)
07 ° C., manufactured by Toto Kasei Co., Ltd., Epototo YD-907 (epoxy equivalent: 1300 to 1700 g / eq, softening point 117)
~ 127 ° C, manufactured by Toto Kasei Co., Ltd.), Epicoat 1003F
(Epoxy equivalent 700-800 g / eq, softening point about 96
C, Yuka Shell Epoxy Co., Ltd.), Epicoat 1004F
(Epoxy equivalent 875-975 g / eq, softening point about 10
3 ° C, Yuka Shell Epoxy Co., Ltd.), Epicoat 1005
F (epoxy equivalent: 950-1050 g / eq, softening point: about 107 ° C., manufactured by Yuka Shell Epoxy), Araldide X
AC5007 (epoxy equivalent 600-700 g / eq,
Softening point about 90 ° C, manufactured by Ciba Geigy Japan, Araldide GT7004 (epoxy equivalent 730-830 g / e)
q, softening point of about 100 ° C, manufactured by Nippon Ciba Geigy), Araldide GT7097 (epoxy equivalent 1650-200)
0 g / eq, softening point of about 120 ° C., manufactured by Ciba-Geigy Japan). These may be used alone or in combination of two or more.

The o-cresol novolak type epoxy resin is not particularly limited, and the following are commercially available. For example, Epicoat 180S6
5 (epoxy equivalent: 205 to 220 g / eq, softening point: about 6
7 ° C, Yuka Shell Epoxy Co., Ltd.), Epotote YDCN
-704P (epoxy equivalent: 195 to 225 g / eq, softening point: about 90 ° C, manufactured by Toto Kasei Co., Ltd.) and the like. These may be used alone or in combination of two or more.

As the curing agent component (b), a phenolic compound represented by the general formula (A) (where m is 1 to 4) having excellent flexibility in order to improve the low-temperature impact resistance of the primer coating film. Use a curing agent.

[0016]

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In the formula, m represents an integer of 1 to 4. The above m
Is less than 1, when bisphenol A is used as a raw material, it cannot exist, as described in detail below. When m exceeds 4, the reaction proceeds too much during the synthesis, and the synthesis proceeds. Since it becomes difficult, it is limited to the above range. The compound represented by the general formula (A) is not particularly limited, and examples thereof include those obtained by reacting a bisphenol A type epoxy resin with bisphenol A. The above curing agent has a phenolic hydroxyl equivalent of 20.
0 to 800 g / eq. If it is less than 200 g / eq, the softening point of the primer composition is lowered, and fusion between powder particles is likely to occur during storage of the primer composition, and storage stability is lowered. If it exceeds 800 g / eq, the reactivity will decrease, and the cathode peeling property will decrease.

Commercially available curing agents can be used as the curing agent. Specifically, for example, TH-
4100 (phenolic hydroxyl group equivalent of about 725 g / eq,
Softening point about 110 ° C, manufactured by Toto Kasei Co., Ltd.), EpiCure 171
(Phenolic hydroxyl equivalent 200 to 286 g / eq, softening point about 80 ° C., manufactured by Yuka Shell Epoxy Co.), EXPURE 170 (phenolic hydroxyl equivalent 286 to 400 g / e)
q, a softening point of about 90 ° C., manufactured by Yuka Shell Epoxy Co., Ltd.). These may be used alone,
More than one type may be used in combination.

The amount of the curing agent component is such that the phenolic hydroxyl group of the phenolic curing agent is 0.4 to 0.9 equivalent per 1 equivalent of the epoxy group of the mixed epoxy resin component. When the phenolic hydroxyl group equivalent is less than 0.4, the amount of the curing agent is too small, so that the epoxy resin is insufficiently polymerized and the performance as the primer composition cannot be exhibited. Also,
When the ratio exceeds 0.9, the epoxy group of the mixed epoxy resin almost reacts, and the reactive active points in the primer composition decrease, so that the adhesiveness between the thermoplastic adhesive laminated on the primer and the primer composition is reduced. And the peel strength decreases.

As the curing accelerator component (c), an imidazole curing accelerator and / or an imidazoline curing accelerator represented by the following general formulas (B) and (C) are used.

[0021]

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[0022]

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In the formula, R ¹ is a hydrogen atom, having 1 to 17 carbon atoms.
Represents an alkyl group or a phenyl group. R ² represents a hydrogen atom or a methyl group. 1 to 17 carbon atoms
Is not particularly limited, and examples thereof include a methyl group, an ethyl group, an n-propyl group, and an i-propyl group. The imidazole-based curing accelerator is not particularly limited, and a commercially available one may be used. Specifically, for example, 2MZ (2-methylimidazole, manufactured by Shikoku Chemicals), 2PZ (2-phenylimidazole, manufactured by Shikoku Chemicals), C ₁₁ Z (2-undecylimidazole, manufactured by Shikoku Chemicals) ), C ₁₇ Z (2-
Heptadecyl imidazole, manufactured by Shikoku Chemicals). These may be used alone,
More than one type may be used in combination.

The imidazoline curing accelerator is not particularly limited, and commercially available ones may be used.
Specifically, for example, 2MZL (2-methylimidazoline, manufactured by Shikoku Kasei Kogyo), 2E · 4MZL (2-ethyl-4-methylimidazoline, manufactured by Shikoku Kasei Kogyo) and the like can be mentioned. These may be used alone,
More than one type may be used in combination.

The amount of the curing accelerator is determined by the amount of the curing agent component (b)
0.1 to 15.0% by weight based on the amount of 0.1
If it is less than 1% by weight, curing is not promoted, and if it exceeds 15.0% by weight, the reactivity of the primer composition becomes too high, blocking easily occurs even at room temperature, and storage stability becomes poor.

As the inorganic filler component (d), an inorganic filler is used in an amount of 10 to 100 with respect to the total amount of the mixed epoxy resin component (a), phenolic curing agent component (b) and curing accelerator component (c). % By weight. The inorganic filler contributes to the relaxation of the stress of the primer coating, improves the adhesion to the steel base material, and also improves the resistance to cathodic peeling by contributing to the blocking of corrosion factors. In particular, when zinc borate is used as the inorganic filler, good cathodic peeling resistance is exhibited due to the pH buffering action of borate ions. If the amount of the inorganic filler is less than 10%, a sufficient effect cannot be obtained and 100% by weight
Exceeding the melting point of the primer composition increases the wettability of the primer composition with the steel base material, and lowers the adhesion (the cathode peeling resistance decreases). As the inorganic filler,
In addition to zinc borate, extenders such as alumina, silica, precipitated barium sulfate, calcium carbonate, clay, talc, and mica; coloring inorganic pigments such as titanium dioxide, red iron oxide, carbon black, and iron oxide; zinc phosphate And rust preventive pigments such as aluminum phosphate; metal powders such as zinc powder and aluminum powder.

Further, the epoxy powder primer composition used in the present invention may contain a leveling agent, a fluidization aid,
It may contain additives and auxiliaries such as degassing agents.

The powdered epoxy composition having the above composition is kneaded by a melt blending method, then pulverized and classified, and used as a powder primer.

As a method of applying the powder primer to the steel material, the powder primer is attached to the steel material surface by an electrostatic coating method or a fluid immersion method, and then the steel material is heated by an induction heating device or the like. Is formed by melting and curing. Also,
The steel material may be heated in advance, and the powder primer may be adhered to the surface of the steel material, and may be melted and hardened. Good results are obtained when the epoxy primer layer (3) has a thickness of 10 to 500 μm. If it is less than 10 μm, the corrosion resistance is insufficient, and if it exceeds 500 μm, the low-temperature impact resistance is reduced.

As the polyolefin adhesive layer (4),
Any material may be used as long as it has excellent adhesiveness with the epoxy primer layer (3) and fusion property with the polyolefin layer (4). However, when a maleic anhydride-modified polyolefin obtained by graft-polymerizing maleic anhydride to a polyolefin is used, the primer layer may be used. It is excellent in adhesiveness with, and is suitable. Good results can be obtained when the thickness of the polyolefin adhesive layer (4) is 0.02 to 1.0 mm. If it is less than 0.02 mm, the adhesive strength with the primer layer is insufficient. Also, 1.0mm
Is not preferable from the viewpoint of economy. As a method for forming the polyolefin adhesive layer, a melt extrusion method in which a molten modified polyolefin is extruded from an extruder and coated is preferred. In this case, a two-layer T-die is used to extrude the two layers integrally so that the polyolefin adhesive is the lower layer and the polyolefin is the upper layer, and the polyolefin adhesive layer (4)
And the polyolefin layer (5) can be simultaneously formed.

Polyolefin layer (5) used in the present invention
Can be a commercially available polyethylene or polypropylene. In addition, carbon black, a coloring pigment, an antioxidant, an ultraviolet absorber, a lubricant, a flame retardant, an antistatic agent and the like can be mixed and used depending on the use. When the polyolefin layer (5) has a thickness of 0.3 mm or more, sufficient corrosion resistance can be obtained. As the molding method of the polyolefin layer (5), a melt extrusion method is preferable.

Examples and comparative examples in which low-density polyethylene is used as the polyolefin and a steel pipe is used as the steel material will be described below.

[0033]

EXAMPLES (Example 1) a) Preparation of epoxy powder primer composition As shown in FIG. 1, bisphenol A type epoxy resin (Epototo YD-014 manufactured by Toto Kasei) 90
Parts by weight, 10 parts by weight of o-cresol novolak type epoxy resin (Epicoat 180S65 manufactured by Yuka Shell Epoxy), 29 parts by weight of phenolic curing agent (Epicure 170 manufactured by Yuka Shell Epoxy) (phenolic hydroxyl group per equivalent of epoxy group) 0.6 equivalent), 0.9 parts by weight of 2-methylimidazole (3% by weight based on the curing agent), 39 parts by weight of zinc borate (30 parts by weight based on the total amount of the epoxy resin, the curing agent, and the curing accelerator) ) Was preliminarily mixed with a super mixer (manufactured by Nippon Spindle Co., Ltd.) for about 3 minutes. Next, melt kneading and extrusion were carried out at about 100 ° C. using a co-kneader (manufactured by Bus Corporation). The extruded compound was cooled to room temperature and coarsely pulverized, and then finely pulverized with an atomizer (manufactured by Fuji Paudal) to obtain an epoxy powder primer having an average particle diameter of 35 μm.

B) Production of polyethylene coated steel pipe Steel pipe (SGP250A × 5500 mm length × 6.6 mm)
Rust is removed by grid blasting on the outer surface of the layer, and the chromate treating agent (the weight ratio of trivalent chromium to all chromium in the aqueous solution is 0.4, the weight ratio of silica is 2.0, and the weight ratio of phosphoric acid is 1) .0) was applied with a brush and dried. The total amount of chromium deposited on the chromate film was 500 mg / m ² .
The chromate-treated steel pipe was placed on a skew-turning type transport device, and transported in the pipe axis direction while rotating. The steel pipe is heated by a high-frequency induction heating device so that the surface temperature becomes 180 ° C., and the epoxy powder primer composition prepared in (a) is coated with an electrostatic powder coating machine (GX3300, manufactured by Onoda).
Then, electrostatic coating was performed using an electrostatic powder gun (GX107, manufactured by Onoda). The thickness of the epoxy primer layer was 0.10 mm after curing. Modified polyethylene (a modified polyethylene obtained by modifying a homopolymer of ethylene with maleic anhydride, the amount of maleic anhydride added to 1 g of the modified polyethylene is 1 × 10 ⁻⁵ mol) and low-density polyethylene (density 0.92, carbon black (2.5% by weight) was extruded from the T-die as a two-layer structure, and spirally coated the surface of the steel pipe coated with the epoxy primer. The thickness of the modified polyethylene layer was 0.15 mm, and the thickness of the polyethylene layer was 2.5 mm. Immediately after the coating, a silicone rubber roll was pressed against the coating layer to press it tightly, and the polyethylene coating layers were firmly fused, and then water-cooled from the outer surface to obtain a polyethylene-coated steel pipe.

C) Evaluation of hot water adhesion In order to evaluate the hot water adhesion of the coating, the polyethylene coated steel pipe obtained in (b) was immersed in hot water at 80 ° C. for 100 days, and the peel strength was measured. A hot water immersion test was performed. After immersion, a cut wound reaching the steel pipe base was made in a width of 10 mm along the circumferential direction with a cutter knife, and the peel strength was measured at a peel angle of 90 ° and a peel speed of 10 mm / min, and compared with the peel strength before immersion. Peel strength before immersion is 240N / 10
mm, and the peel strength after immersion was 210 N / 10 mm.

D) Evaluation of Cathodic Peeling Resistance In order to evaluate the cathodic peeling resistance of the coating, a 9 mm diameter drill hole was made in the polyethylene-coated steel pipe coating obtained in (b) to reach the steel pipe base, and 3% sodium chloride was used. Immerse in water, 60 ℃
Under a constant temperature, a voltage of -1.5 V (to a saturated calomel electrode)
A cathode peel test was performed by applying voltage for 0 days. After the test, the coating was removed, and the distance (peeling distance) from the initial hole end to the peeling tip was measured. The peel distance was 8 mm.

E) Evaluation of low-temperature impact resistance In order to evaluate the impact resistance of the coating, the polyethylene-coated steel pipe obtained in (b) was subjected to a tip diameter of 15.875 mm in accordance with ASTM G14. A drop weight impact test using a punch was conducted. The test was performed at -45 ° C. After completion of the test, the presence or absence of cracks in the coating was visually determined. There were no cracks in the coating.

(Examples 2 to 23) 2-N
o. An epoxy powder primer composition having the composition shown in No. 23 was prepared in the same manner as in Example 1 (a). In addition, the compounding amount of the epoxy resin described in Table 1 is a weight ratio, and the compounding amount of the curing agent is the phenolic hydroxyl group equivalent in the curing agent per 1 equivalent of the epoxy group in the epoxy resin component, and the compounding amount of the curing accelerator is The weight% based on the amount of the curing agent and the blending amount of the inorganic filler are the weight% based on the total amount of the epoxy resin, the curing agent, and the curing accelerator. Then, in the same manner as in Example 1 (b),
Table 1 No. 2-No. A polyethylene-coated steel pipe using the epoxy powder primer composition described in No. 23 was produced.

These polyethylene-coated steel pipes were tested for heat-resistant water adhesion in the same manner as in Example 1 (c), for cathodic peeling resistance in the same manner as in Example 1 (d), and for low-temperature impact resistance in Example 1.
Evaluation was performed in the same manner as in (e). The test results are summarized in Table 3.

(Comparative Example) 24-No. 40
Example 1 was performed using an epoxy powder primer composition having the composition shown in Example 1.
Prepared in the same manner as (a). In addition, the comparative example No. 29
-No. The amount of dicyandiamide of No. 31 is a percentage by weight based on the epoxy resin. Then, in the same manner as in Example 1 (b), No. 24-No. A polyethylene-coated steel pipe using the epoxy powder primer composition described in No. 40 was produced.

These polyethylene-coated steel pipes were tested for heat-resistant water adhesion in the same manner as in Example 1 (c), for cathodic peeling resistance in the same manner as in Example 1 (d), and for low-temperature impact resistance in Example 1.
Evaluation was performed in the same manner as in (e). The test results are summarized in Table 3.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

As is clear from Table 3, Example No. 3 satisfying all the conditions specified in the present invention. Nos. 1 to 23 show excellent properties in all of the hot water adhesion, the cathode peeling resistance, and the low-temperature impact resistance as compared with the comparative examples. Also, in the present invention,
It can be seen that a polyethylene-coated steel pipe to which zinc borate was applied as an inorganic filler component in the epoxy powder primer layer provided particularly good results with respect to cathodic peeling resistance.

Although the case where high-density polyethylene or polypropylene is used for the polyolefin layer is not shown, it was confirmed that good results were obtained as in the case of low-density polyethylene.

[0047]

As is clear from the examples, the polyolefin-coated steel of the present invention is more resistant to hot water adhesion, cathodic peeling resistance and low-temperature impact resistance than polyolefin-coated steel using a conventional epoxy powder primer. , It is possible to maintain the anticorrosion property for a long time.

[Brief description of the drawings]

FIG. 1 is a view showing a coating configuration of a polyolefin-coated steel pipe of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel material 2 Chromate film 3 Powder epoxy primer layer 4 Modified polyolefin adhesive layer 5 Polyolefin layer

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hiroyuki Mimura 1 Kimitsu, Kimitsu City Inside the Nippon Steel Corporation Kimitsu Works (72) Inventor Hiroaki Yasuda 1 Kimitsu, Kimitsu City Nippon Steel Corporation Kimitsu F-term in steelworks (reference) 4F100 AA00B AA00H AA22A AA33B AB04A AB07 AH02 AH03B AH03H AK03C AK03D AK04 AK06 AK33B AK33H AK33K AK53B AK53K AL05 AR00C BA04 BA10ABA10B07 J03 CA03 J07 CA23

Claims (3)

[Claims] 1. An epoxy primer layer, a polyolefin adhesive layer containing the following four components (A), (B), (C) and (D) as essential components on a surface of a steel material subjected to a base treatment. A polyolefin-coated steel material characterized by sequentially laminating a polyolefin layer. (A) The softening point is 75 to 128 ° C and the epoxy equivalent is 600.
A mixed epoxy resin component comprising a mixture of bisphenol A-type epoxy resin of 2200 g / eq and o-cresol novolac-type epoxy resin, the ratio of which is 97 / 3-50 / 50 by weight, (b) Formula (A)
(Where m is 1 to 4), a phenolic curing agent having an average phenolic hydroxyl equivalent of 200 to 800 g / eq, and the amount of the phenolic hydroxyl is 1 equivalent of the epoxy group of the mixed epoxy resin component (a). A curing agent component which is 0.4 to 0.9 equivalents, (c) an imidazole-based curing accelerator and / or an imidazoline-based curing accelerator, wherein the compounding amount is the compounding amount of the curing agent component (b) 0.1 to 1
5.0% by weight of a curing accelerator component, (d) an inorganic filler, and the compounding amount is a total of the mixed epoxy resin component (a), the curing agent component (b), and the curing accelerator component (c). An inorganic filler component which is 10 to 100% by weight based on the amount. Embedded image 2. The polyolefin-coated steel material according to claim 1, wherein the inorganic filler component (d) is zinc borate. 3. The polyolefin-coated steel material according to claim 1, wherein a chromate treatment is performed as a base treatment.