JP2009220328A - Polyolefin-coated steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyolefin-coated steel material having superior resistance to the cold/heat cycle, strength of the coating layer at high temperatures, resistance to cathode detachment, low-temperature impact resistance and corrosion resistance. <P>SOLUTION: The polyolefin-coated steel material consists of an epoxy primer layer formed with a composition which comprises a mixed epoxy resin ingredient comprising a bisphenol-A type epoxy resin, bisphenol-F type epoxy resin and o-cresol novolak type epoxy resin, a phenolic hardening agent, a hardening accelerator and an inorganic filler, a polyolefin adhesive layer and a polyolefin layer, laminated in this order on the surface of a surface-treated steel material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polyolefin-coated steel material. More particularly, the present invention relates to a polyolefin-coated steel material obtained by sequentially laminating an epoxy primer layer, a polyolefin adhesive layer, and a polyolefin layer on the outer surface of a steel material.

  In general, steel materials corrode when exposed to the atmosphere, the ground, and seawater without taking measures against the surrounding environment. Therefore, in various construction pipes such as oil, gas, water and sewage, electric cables and the like, and construction materials for civil engineering such as steel pipe piles and steel sheet piles, a polyolefin-coated steel material whose outer surface is covered with polyethylene or polypropylene is used. Such polyolefin-coated steel materials are being used in various environments such as a high-temperature wetted environment and a cryogenic environment. Therefore, realization of better anticorrosion performance is strongly demanded.

  However, polyolefins used for coating steel materials have poor adhesion to steel materials due to their chemical stability. Therefore, in general, polyolefin-coated steel materials prevent the polyolefin from peeling from the steel materials by interposing a polyolefin adhesive layer made of a modified polyolefin between the steel material and the polyolefin coating layer. However, polyolefin-coated steel materials with only an adhesive layer interposed may cause a decrease in adhesive strength when used in wet, wet environments such as in the ground, in the sea, and at the bottom of the sea, and the coating layer may peel off from the steel material. is there. Further, in an environment where the anticorrosion is used in combination, there is a problem that the coating layer is easily peeled off from a coating defect due to overcorrosion prevention current (this phenomenon is called cathode peeling). For this reason, polyolefin-coated steel used in wet / water-contact environments or in environments where electrical protection is used is first coated with an epoxy-based primer, and then a modified polyolefin layer and a polyolefin layer are sequentially laminated on the steel. By doing so, excellent adhesion strength over a long period of time is given.

  As such an epoxy primer, liquid epoxy, solid epoxy diluted with an organic solvent, powder epoxy, etc. are generally used. In recent years, the transition to powder epoxy has progressed from the viewpoint of environmental countermeasures. As the coating treatment for applying an epoxy primer layer / polyolefin adhesive layer / polyolefin coating layer to the outer surface of a steel material, German Patent (DE-A) 1965802 (Patent Document 1), 2257135 (Patent Document) 2), 2944809 (patent document 3) and 3230955 (patent document 4), British patent (GB) 1554233 (patent document 5), European patent (EP-A) No. 57823 (Patent Document 6). In addition, as an epoxy primer used for such coating treatment, it is known to use an epoxy primer in which dicyandiamide is used as a curing agent for an epoxy resin and crystals or amorphous silicic acid is blended in the filler.

  In recent years, with the development of resources such as oil and natural gas on the seabed or polar regions due to increasing energy demand, polyolefin coatings coated on steel structures and line pipes in hot or cold environments Long-term durability is becoming a problem. However, the coated steel material using the epoxy primer has a drawback that the adhesive strength after immersion in hot water is lowered. Due to this defect, the polyolefin layer easily peels off after being immersed in hot water, and there is a problem that the corrosion resistance is impaired. In addition, it was difficult to prevent peeling over a long period of time at a high temperature of 60 ° C. or higher in terms of cathode peel resistance. Furthermore, when pipeline laying work or the like is performed in a cryogenic environment such as −30 to −45 ° C., the coating is cracked due to impact such as contact between the coated steel material and heavy machinery or collision between the coated steel materials, and the polyolefin layer becomes The corrosion resistance may be impaired by peeling from the steel material.

In Japanese Patent Application Laid-Open No. 2000-190422 (Patent Document 7), which is an application by the applicants of the present application, a powder epoxy primer layer, a polyolefin adhesive layer, and a polyolefin layer are provided on the surface of a steel material that has undergone a base treatment. Sequentially laminated polyolefin-coated steel material, wherein the powder epoxy primer layer is a mixture of a bisphenol A type epoxy resin and an o-cresol novolac type epoxy resin, the ratio of which is 97/3 to 50/50 by weight. A polyolefin-coated steel material characterized by being a powder epoxy primer layer comprising a mixed epoxy resin component, a phenolic curing agent, an imidazole-based curing accelerator and / or an imidazoline-based curing accelerator, and an inorganic filler. Are listed. It is described that this polyolefin-coated steel material is excellent in hot water adhesion, high temperature cathode peel resistance, and low temperature impact resistance. However, even if the primer layer is cured at a temperature lower than the conventional curing temperature due to the recent increase in interest in the environment and the demand for CO ₂ emission reduction, and also due to the effects of high crude oil in recent years, There has been a demand for means for providing a polyolefin-coated steel material having performances such as anti-corrosion properties equal to or higher than those of conventional ones.

  JP-A-2000-109728 (Patent Document 8) discloses an epoxy resin (A) having a skeleton of bisphenol A and / or bisphenol F having an epoxy equivalent of 500 to 2500 g / eq, and a phenolic curing agent (B ) Is an essential component. However, in this patent document 8, examples using bisphenol A type epoxy resin (a), bisphenol F type epoxy resin (b) and o-cresol novolac type epoxy resin (c) as in the present application are not performed. However, it has not yet been possible to form a coating film having the property of maintaining impact resistance as desired by the present application.

German Patent (DE-A) No. 1965802 German Patent No. 2257135 German Patent No. 2944809 German Patent No. 3230955 British Patent (GB) 1542333 European Patent (EP-A) No. 57823 JP 2000-190422 A JP 2000-109728 A

  The present invention solves the above-mentioned conventional problems, the object of which is obtained by sequentially laminating an epoxy primer layer, a polyolefin adhesive layer, and a polyolefin layer on the outer surface of the steel material, An object of the present invention is to provide a polyolefin-coated steel material that is excellent in coating layer strength at high temperatures, resistance to cathodic peeling, and resistance to low-temperature impact, and that can maintain corrosion resistance for a long period of time.

The present invention
An epoxy primer layer formed from a composition containing the following components (a), (b), (c) and (d); a polyolefin adhesive layer; and a polyolefin layer; Sequentially laminated, polyolefin coated steel:
(A) Bisphenol A type epoxy resin (a), bisphenol F type epoxy resin (b) having a softening point of 75 to 128 ° C. and an epoxy equivalent of 600 to 2200 g / eq, and o-cresol novolac type epoxy resin (c) A mixture of
The weight ratio of [(a) + (b)] / (c) is 95/5 to 50/50,
The weight ratio of (a) / (b) is 5/95 to 95/5.
Mixed epoxy resin component,
(B) A phenolic curing agent having an average phenol hydroxyl group equivalent of 200 to 800 g / eq, and the amount of the phenol hydroxyl group of this phenolic curing agent is 0 with respect to 1 equivalent of the epoxy group of the mixed epoxy resin component (A). A curing agent component that is .4 to 0.9 equivalents;
(C) An imidazole-based curing accelerator and / or an imidazoline-based curing accelerator, and the amount of the curing accelerator is 0.1 to 15.0 parts by weight with respect to 100 parts by weight of the curing agent component (b). A curing accelerator component,
(D) It is an inorganic filler, and the amount of the inorganic filler is 100 parts by weight with respect to the total amount of the mixed epoxy resin component (a), the curing agent component (b) and the curing accelerator component (c). 10 to 100 parts by weight of an inorganic filler component:
This achieves the above object.

  The ground treatment of the steel material is preferably a chromate treatment.

The present invention further relates to an epoxy powder primer composition for use in the production of a polyolefin-coated steel material, comprising the following components (A), (B), (C) and (D):
(A) Bisphenol A type epoxy resin (a), bisphenol F type epoxy resin (b) having a softening point of 75 to 128 ° C. and an epoxy equivalent of 600 to 2200 g / eq, and o-cresol novolac type epoxy resin (c) A mixture of
The weight ratio of [(a) + (b)] / (c) is 95/5 to 50/50,
The weight ratio of (a) / (b) is 5/95 to 95/5.
Mixed epoxy resin component,
(B) A phenolic curing agent having an average phenol hydroxyl group equivalent of 200 to 800 g / eq, and the amount of the phenol hydroxyl group of this phenolic curing agent is 0 with respect to 1 equivalent of the epoxy group of the mixed epoxy resin component (A). A curing agent component that is .4 to 0.9 equivalents;
(C) An imidazole-based curing accelerator and / or an imidazoline-based curing accelerator, and the amount of the curing accelerator is 0.1 to 15.0 parts by weight with respect to 100 parts by weight of the curing agent component (b). A curing accelerator component,
(D) It is an inorganic filler, and the amount of the inorganic filler is 100 parts by weight with respect to the total amount of the mixed epoxy resin component (a), the curing agent component (b) and the curing accelerator component (c). 10 to 100 parts by weight of an inorganic filler component:
Also provide.

The polyolefin-coated steel material of the present invention has excellent cold-heat cycle resistance, maintenance of coating layer strength at high temperatures, and excellent properties even when the epoxy primer layer is cured at a temperature lower than the conventional curing temperature. It has the characteristic of having impact resistance. The polyolefin-coated steel material according to the present invention has excellent hot water adhesion, cathode peel resistance, low temperature impact resistance, cold heat cycle resistance, etc., so that it is severe under high temperature wetted environments and extremely low temperature environments. There is an advantage that it can be used for a long time even under conditions. The polyolefin-coated steel material of the present invention further ensures the above-described excellent performance even when the curing temperature at the time of forming the coating layer is set lower, so that in addition to the above-described advantages, the energy cost and CO ₂ emission are further increased. There is an advantage that the amount can be reduced.

The steel material (1) used in the present invention such as the steel material (1) is a cold rolled steel plate, a hot rolled steel plate, a steel plate such as a thick steel plate, a shape steel such as an H-shaped steel, an I-shaped steel, an L-shaped steel, or a steel sheet pile. Steel bars, steel wires, cast iron pipes, steel pipes, steel pipe sheet piles, and the like. A clad steel material obtained by laminating a metal such as stainless steel, titanium, aluminum, nickel, copper, or an alloy thereof can be used on the surface of these steel materials. Moreover, the plating steel materials etc. which performed the plating process on the surface of steel materials can also be used. The steel material is used after first being subjected to rust removal treatment such as blast treatment, degreasing and pickling treatment.

When the steel material (1) is used by forming the chromate film (2) as a base treatment before forming the epoxy primer layer (3), the steel material (1) is desirable because it provides better corrosion resistance. For example, the chromate treatment agent is prepared by adding fine particles of silica to a reducing aqueous solution in which an organic reducing agent or the like is added to an aqueous solution of chromic anhydride and heated to partially reduce hexavalent chromium in the aqueous solution to trivalent chromium. A dispersed mixture or the like is applied to a steel material, and the steel material is heated and baked. When the chromate film (2) has a thickness of ²⁰ to 1000 mg / m ^{2 in} terms of the total chromium adhesion after heating and baking, good results are obtained. If it is less than 20 mg / m ² , a sufficient anticorrosion effect cannot be obtained, and if it exceeds 1000 mg / m ² , the cohesive strength of the chromate film is lowered, and the adhesion to the steel material may be lowered.

Epoxy primer layer (3)
The epoxy primer layer (3) contains the mixed epoxy resin component (a), phenolic curing agent component (b), curing accelerator component (c), and inorganic filler component (d), which will be described in detail below, as essential components. It is formed from an epoxy powder primer composition.

Mixed epoxy resin component (I)
In the present invention, bisphenol A type epoxy resin (a), bisphenol F type epoxy resin (b) and o-cresol novolac type epoxy resin (c) are used as the mixed epoxy resin component (A) of the epoxy powder primer composition. included. By using an epoxy powder primer composition containing such a mixed epoxy resin component (I), it has excellent heat stability and good adhesion to steel even when cured at a lower temperature. A coated steel material will be obtained.

  As the bisphenol A type epoxy resin (a), one having a softening point of 75 to 128 ° C. and an epoxy equivalent of 600 to 2200 g / eq is desirable. If the softening point is less than 75 ° C., fusion between the powder particles may easily occur during storage of the epoxy powder primer composition. On the other hand, when the softening point exceeds 128 ° C., the melt viscosity becomes high, the wettability with the steel material base material is deteriorated, and the adhesion is likely to deteriorate (cathode releasability and cold heat cycle resistance are reduced). The softening point is preferably 90 to 110 ° C. If the epoxy equivalent is less than 600 g / eq, the molecular weight is generally small and the softening temperature may be lowered. As a result, the storage stability of the powder coating may be deteriorated. On the other hand, when it exceeds 2200 g / eq, the molecular weight is generally increased and the softening temperature may be too high. As a result, the smoothness of the resulting coating film may be impaired. The epoxy equivalent is preferably 650 to 1100 g / eq.

  What is marketed can be used as a bisphenol A type epoxy resin (a). Specifically, for example, Epototo YD-014 (epoxy equivalent 900-1000 g / eq, softening point 91-102 ° C., manufactured by Tohto Kasei), Epototo YD-017 (epoxy equivalent 1750-2100 g / eq, softening point 117-127) ° C, manufactured by Toto Kasei Co., Ltd.), Epototo YD-904 (epoxy equivalent 900-1000 g / eq, softening point 96-107 ° C, manufactured by Toto Kasei Co., Ltd.), Epototo YD-907 (epoxy equivalent 1300-1700 g / eq, softening point 117) ˜127 ° C., manufactured by Tohto Kasei Co., Ltd.), Epicoat 1003F (epoxy equivalent 700-800 g / eq, softening point approximately 96 ° C., manufactured by Japan Epoxy Resin Co.), Epicoat 1004F (epoxy equivalent 875-975 g / eq, softening point approximately 103 ° C. , Japan Epoxy Resin Co., Ltd.), Epicoat 1005F (Epoxy 950 to 1050 g / eq, softening point of about 107 ° C., manufactured by Japan Epoxy Resin Co., Ltd., Araldide XAC5007 (epoxy equivalent of 600 to 700 g / eq, softening point of about 90 ° C., manufactured by Ciba Geigy Corporation of Japan), Araldide GT7004 (epoxy equivalent of 730 to 30%) 830 g / eq, softening point of about 100 ° C., manufactured by Ciba-Geigy Corporation), Araldide GT7097 (epoxy equivalent 1650-2000 g / eq, softening point of about 120 ° C., manufactured by Ciba-Geigy Corporation), and the like. These may be used alone or in combination of two or more.

  In the present invention, by using the bisphenol F type epoxy resin (b) in combination with the bisphenol A type epoxy resin (a) and the o-cresol novolak type epoxy resin (c), the low temperature curability and the thermal cycle resistance are improved. Will be. The weight average molecular weight can be measured by a gel permeation chromatography (GPC) method using polystyrene as a standard.

  The softening point of the bisphenol F type epoxy resin (b) is preferably 80 to 120 ° C. When the softening point is less than 80 ° C., fusion may easily occur between the powder particles during storage of the epoxy powder primer composition. On the other hand, when the softening point exceeds 120 ° C., the melt viscosity becomes high, the wettability with the steel base material is deteriorated, and the adhesion may be lowered (cathode releasability and cold cycle resistance are lowered). The softening point is more preferably 80 to 100 ° C. The epoxy equivalent of the bisphenol F type epoxy resin (b) is preferably in the range of 800 to 2500 g / eq. When the epoxy equivalent is less than 800 g / eq, the molecular weight is generally small and the softening temperature may be lowered. On the other hand, if it exceeds 2500 g / eq, the molecular weight generally increases and the softening temperature may be too high. The epoxy equivalent is more preferably 900 to 1600 g / eq.

  As the bisphenol F type epoxy resin (b), a commercially available product can be used. Specifically, for example, Epototo 2004 (epoxy equivalent 900 to 1000 g / eq, softening point 80 to 90 ° C., manufactured by Tohto Kasei Co., Ltd.), Epototo 2005RL (epoxy equivalent 1100 to 1300 g / eq, softening point 91 to 96 ° C., Tohto Kasei Co., Ltd. Company name), jER4005P (epoxy equivalent of 1050 to 1250 g / eq, manufactured by Japan Epoxy Resin), jER4007P (epoxy equivalent of 2100 to 2450 g / eq, manufactured by Japan Epoxy Resin), and the like. These may be used alone or in combination of two or more.

  Incidentally, paragraphs 0006 and 0007 of JP-A-8-323288 describe bisphenol A type epoxy resins and bisphenol F type epoxy resins as crystalline epoxy resins. However, the use of bisphenol F-type epoxy resin as a powder coating composition has a problem of poor blocking properties. When blocking occurs in the powder coating composition, the resulting coating film may be rough or glossy, and may cause poor adhesion. Also in the painting work, there is a possibility of causing problems such as occurrence of clogging in the painting machine. In contrast, in the present invention, a bisphenol A type epoxy resin (a), a bisphenol F type epoxy resin (b) having a softening point of 75 to 128 ° C. and an epoxy equivalent of 600 to 2200 g / eq, and o-cresol novolak. Mold epoxy resin (c) with a weight ratio of [(a) + (b)] / (c) of 95/5 to 50/50 and a weight ratio of (a) / (b) of 5/95 to 95 By using in the range of / 5, the effect of improving low-temperature curability without such problems as blocking properties, and excellent cold resistance even when cured at such a low temperature Cycleability, maintenance of coating layer strength at high temperatures, and excellent impact resistance were ensured.

  The softening point of the o-cresol novolac type epoxy resin (c) is preferably 60 to 100 ° C. When the softening point is less than 60 ° C., fusion may easily occur between the powder particles during storage of the epoxy powder primer composition. On the other hand, when the softening point exceeds 100 ° C., the melt viscosity becomes high, the wettability with the steel material base material is deteriorated, and the adhesion may be lowered (cathode releasability and cold cycle resistance are lowered). The softening point is more preferably 70 to 90 ° C.

  The o-cresol novolac type epoxy resin (c) is not particularly limited, and examples of commercially available products include the following. For example, Epototo YDCN-702 (epoxy equivalent 195 to 220 g / eq, softening point about 75 ° C., manufactured by Tohto Kasei Co., Ltd.), Epototo YDCN-704 (epoxy equivalent 195 to 220 g / eq, softening point about 90 ° C., manufactured by Tohto Kasei Co., Ltd.) ) Etc. These may be used alone or in combination of two or more.

In the present invention, the weight ratio of the bisphenol A type epoxy resin (a), the bisphenol F type epoxy resin (b) and the o-cresol novolac type epoxy resin (c) satisfies the following conditions:
The weight ratio of [(a) + (b)] / (c) is 95/5 to 50/50,
The weight ratio of (a) / (b) is 5/95 to 95/5.
When the mixing ratio of the o-cresol novolac epoxy resin (c) is less than 5 with respect to the bisphenol A type epoxy resin (a) and the bisphenol F type epoxy resin (b), sufficient heat resistance stability is obtained. Cannot be achieved, and the thermal cycle resistance is inferior. On the other hand, when the mixing ratio of the o-cresol novolac type epoxy resin (c) exceeds 50, the resulting cured product has an excessively high elastic modulus, resulting in low-temperature impact resistance and cold-heat cycle resistance.
Moreover, when the mixing ratio of the bisphenol F type epoxy resin (b) is less than 5 with respect to the bisphenol A type epoxy resin (a), the low-temperature curability and the thermal cycle resistance are inferior. When the mixing ratio of the bisphenol F type epoxy resin (b) exceeds 95, the high temperature heat resistance and the like are inferior.

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

  In formula, m represents the integer of 1-4. When m is less than 1, as described in detail below, when bisphenol A is used as a raw material, it cannot be present, and when m exceeds 4, the reaction proceeds too much during synthesis, Since the synthesis becomes difficult, it is limited to the above range. It does not specifically limit as a compound represented by the said general formula (A), For example, what is obtained by reaction of a bisphenol A type epoxy resin (a) and bisphenol A etc. can be mentioned. The curing agent has a phenolic hydroxyl group equivalent of 200 to 800 g / eq. If it is less than 200 g / eq, the softening point of the epoxy powder primer composition is lowered, and fusion between powder particles is likely to occur during storage of the epoxy powder primer composition, and the storage stability is lowered. When it exceeds 800 g / eq, the reactivity is lowered and the cathode peelability is lowered.

  What is marketed can be used as said hardening | curing agent. Specifically, for example, TH-4100 (phenolic hydroxyl group equivalent of about 725 g / eq, softening point of about 110 ° C., manufactured by Tohto Kasei Co., Ltd.), EpiCure 171N (phenolic hydroxyl group equivalent of 200 to 286 g / eq, softening point of about 80 ° C. And Epoxy 170 (phenolic hydroxyl group equivalent of 286 to 400 g / eq, softening point of about 90 ° C., manufactured by Japan Epoxy Resin Co., Ltd.). These may be used alone or in combination of two or more.

  The compounding quantity of a hardening | curing agent component makes the phenolic hydroxyl group of a phenolic hardening | curing agent 0.4-0.9 equivalent with respect to 1 equivalent of epoxy groups of a mixed epoxy resin component. If the phenolic hydroxyl group equivalent is less than 0.4, the curing agent is too small and the epoxy resin becomes insufficiently polymerized, and the performance as an epoxy powder primer composition cannot be exhibited. Moreover, when it exceeds 0.9, the epoxy group of the mixed epoxy resin almost reacts, and the reactive site in the epoxy powder primer composition decreases, so that the thermoplastic adhesive and the epoxy primer layer laminated on the primer The adhesive strength between the two decreases, and the peel strength decreases.

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

In the formula, R ¹ represents a hydrogen atom, an alkyl group having 1 to 17 carbon atoms, or a phenyl group. R ² represents a hydrogen atom or a methyl group. It does not specifically limit as said C1-C17 alkyl group, For example, a methyl group, an ethyl group, n-propyl group, i-propyl group etc. can be mentioned. It does not specifically limit as said imidazole type hardening accelerator, You may use what is marketed. Specifically, for example, 2MZ (2-methylimidazole, manufactured by Shikoku Chemical Industries), 2PZ (2-phenylimidazole, manufactured by Shikoku Chemicals), C11Z (2-undecylimidazole, manufactured by Shikoku Chemicals), C17Z (2-heptadecylimidazole, manufactured by Shikoku Kasei Kogyo Co., Ltd.) and the like can be mentioned. These may be used alone or in combination of two or more.

  It does not specifically limit as said imidazoline series hardening accelerator, You may use what is marketed. Specifically, 2MZL (2-methylimidazoline, manufactured by Shikoku Kasei Kogyo Co., Ltd.), 2E · 4MZL (2-ethyl-4-methylimidazoline, manufactured by Shikoku Kasei Kogyo Co., Ltd.) and the like can be mentioned. These may be used alone or in combination of two or more.

  The compounding quantity of a hardening accelerator is mix | blended 0.1 to 15.0 weight% with respect to the quantity of a hardening | curing agent component (b). If it is less than 0.1% by weight, the curing is not promoted, and if it exceeds 15.0% by weight, the reactivity of the epoxy powder primer composition becomes too high, blocking is likely to occur even at room temperature, and storage stability is improved. It becomes defective.

Inorganic filler component (d)
As the inorganic filler component (d), the inorganic filler is contained in an amount of 10 to 100% by weight based on the total amount of the mixed epoxy resin component (b), the phenolic curing agent component (b) and the curing accelerator component (c). Let The inorganic filler contributes to stress relaxation of the formed epoxy primer layer, improves the adhesion to the steel substrate, and also contributes to the blocking of the corrosion factor, thereby improving the cathode peeling resistance. If the amount of the inorganic filler is less than 10%, a sufficient effect cannot be obtained, and if it exceeds 100% by weight, the melt viscosity of the epoxy powder primer composition becomes high and the wettability with the steel substrate becomes poor, and the adhesion is poor. (Cathode peeling resistance and cold heat cycle resistance are reduced). Examples of the inorganic filler include extender pigments such as alumina, silica, barium sulfate, calcium carbonate, clay, talc, and mica; colored inorganic pigments such as titanium dioxide, bengara, carbon black, and iron oxide; zinc phosphate, phosphorus Examples thereof include rust preventive pigments such as aluminum oxide; metal powders such as zinc powder and aluminum powder.

Formation of epoxy primer layer Preparation of epoxy powder primer composition containing the above mixed epoxy resin component (a), curing agent component (b), curing accelerator component (c) and inorganic filler component (d) Each of the above components is preliminarily mixed using a super mixer, Henschel mixer, etc., then introduced into a kneader such as a kneader or extruder, melt kneaded, then cooled and coarsely pulverized, and further finely pulverized. It can prepare by grind | pulverizing and grind | pulverizing and classifying to a desired particle size. The conditions for melt kneading can be appropriately selected depending on the raw material components used. Moreover, it is preferable that the particle size is 5-50 micrometers in a volume average particle diameter. These adjustments can be performed by classification for adjusting the particle size distribution by removing large particles and fine particles. Furthermore, the epoxy powder primer composition used in the present invention may contain additives and auxiliaries such as a leveling agent, a fluidization aid, and a degassing agent depending on the application.

  Examples of the method for applying the epoxy powder primer composition to the steel include coating methods generally used in the powder field, such as electrostatic coating and fluid dipping. After the epoxy powder primer composition is thus adhered to the steel surface, the steel material is heated with an induction heating device or the like to melt and cure the epoxy powder primer composition, thereby forming the epoxy primer layer (3). be able to. Moreover, the epoxy primer layer (3) is formed by preheating the steel material, and attaching the epoxy powder primer composition to the heated steel surface by electrostatic coating or the like, and then melting and curing it. You can also

  The epoxy primer layer (3) thus formed preferably has a thickness of 10 to 500 μm. If the film thickness is less than 10 μm, the corrosion resistance may be insufficient, and if it exceeds 500 μm, the low-temperature impact resistance may decrease.

Polyolefin adhesive layer (4) and polyolefin layer (5)
The polyolefin adhesive layer (4) may be anything as long as it has excellent adhesion with the epoxy primer layer (3) and fusion with the polyolefin layer (5), but maleic anhydride is grafted onto the polyolefin. Use of maleic anhydride-modified polyolefin is preferable because of excellent adhesiveness with the primer layer. Good results are obtained when the polyolefin adhesive layer (4) has a thickness of 0.02 to 1.0 mm. If it is 0.02 mm or less, the adhesive strength with the primer layer is insufficient. Moreover, when it exceeds 1.0 mm, it is not preferable from a viewpoint of economical efficiency. As a method for forming the polyolefin adhesive layer, a melt extrusion method in which a molten modified polyolefin is coated by being extruded from an extruder is suitable. In this case, the two-layer T die can be used to extrude the two layers so that the polyolefin adhesive is the lower layer and the polyolefin is the upper layer, thereby forming the polyolefin adhesive layer (4) and the polyolefin layer (5) simultaneously. .

  For the polyolefin layer (5) used in the present invention, general commercially available polyethylene or polypropylene can be used. In addition, carbon black, color pigments, antioxidants, ultraviolet absorbers, lubricants, flame retardants, antistatic agents, and the like can be mixed and used depending on the application. The polyolefin layer (5) preferably has a thickness of 0.3 mm or more because sufficient corrosion resistance can be obtained. The molding method of the polyolefin layer (5) is preferably a melt extrusion method.

  The polyolefin-coated steel material of the present invention has excellent cold-heat cycle resistance, maintenance of coating layer strength at high temperatures, and excellent properties even when the epoxy primer layer is cured at a temperature lower than the conventional curing temperature. It has the characteristic of having impact resistance. The polyolefin-coated steel material of the present invention has an advantage of exhibiting excellent anticorrosion properties even in a high temperature wetted environment or a severely cold environment. Specifically, in the present invention, by using the epoxy powder primer composition containing the above components (a), (b), (c) and (d), an epoxy primer layer of a polyolefin-coated steel material is formed. The cryogenic thermal cycle resistance for land use was significantly improved.

In addition, in the polyolefin-coated steel material of the present invention, the reason why the cryogenic thermal cycle resistance is remarkably improved is that in the components (a), (b), (c) and (d) contained in the epoxy powder primer composition Using a mixture of bisphenol A type epoxy resin (a), bisphenol F type epoxy resin (b) and o-cresol novolac type epoxy resin (c) as mixed epoxy resin component (a), and specifying these amounts Thus, it is considered that the fluidity at the time of curing of the epoxy powder primer composition and the compatibility with the curing agent component (b) are improved, thereby improving the corrosion resistance. Further, in the present invention, even when the curing temperature at the time of forming the coating layer is set lower, a polyolefin-coated steel material having excellent anticorrosion properties can be obtained in this way. And there is an advantage that CO ₂ emission can be reduced.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on weight unless otherwise specified.

Example 1
a) Preparation of Epoxy Powder Primer Composition No. 1 in Table 1 1, 70 parts by weight of a bisphenol A type epoxy resin (a) (Etototo YD-014 manufactured by Tohto Kasei Co., Ltd., epoxy equivalent 900 to 1000 g / eq, softening point 91 to 102 ° C.), bisphenol F type epoxy resin (b ) (Etototo 2004, manufactured by Tohto Kasei Co., Ltd., epoxy equivalent 900-1000 g / eq, softening point 80-90 ° C.) , 10 parts by weight of a softening point (about 75 ° C.), 21 parts by weight of phenolic curing agent (Epicure 171N manufactured by Japan Epoxy Resin, phenolic hydroxyl group equivalent 200 to 286 g / eq, softening point about 80 ° C.) Hydroxyl group equivalent 0.6), 2-methylimidazole (2 Z) 0.6 parts by weight (3% by weight with respect to the curing agent) and 12 parts by weight of barium sulfate (10 parts by weight with respect to 100 parts by weight of the total amount of epoxy resin, curing agent and curing accelerator) (Nippon Spindle Co., Ltd.) was premixed for about 3 minutes. Subsequently, melt-kneading extrusion was performed on the conditions of about 100 degreeC with the Kneader (made by Busus). The extruded product was cooled to room temperature and coarsely pulverized, and then finely pulverized by an atomizer (manufactured by Fuji Powder Co., Ltd.) to obtain an epoxy powder primer composition having an average particle size of 35 μm.

b) Production of polyethylene-coated steel pipe The outer surface of the steel pipe (SGP250A × 5500 mm length × 6.6 mm thickness) was rusted by grid blasting, and the chromate treatment agent (the weight ratio of trivalent chromium to the total chromium in the aqueous solution was 0. 4. A silica weight ratio of 2.0 and a phosphoric acid weight ratio of 1.0) were applied with a brush and dried. The total chromium adhesion amount of the chromate film was 500 mg / m ² . The chromated steel pipe was placed on a skew turning type conveying device and conveyed in the tube axis direction while rotating. This steel pipe is heated with a high frequency induction heating device so that the surface temperature becomes 160 ° C., and the epoxy powder primer composition prepared in (a) is used as an electrostatic powder coating machine (GX3300, manufactured by Onoda) and electrostatic powder. Electrostatic coating was performed using a body gun (GX107, manufactured by Onoda) to form an epoxy primer layer. The thickness of the formed epoxy primer layer was 0.10 mm after curing.
Modified polyethylene (modified polyethylene obtained by modifying a homopolymer of ethylene with maleic anhydride, the amount of maleic anhydride added to 1 g of modified polyethylene is 1 × 10 ⁻⁵ mol) and low density polyethylene (density 0.92, carbon black (2.5 wt% blending) was extruded from a T-die as a single layer, and the steel pipe surface on which the epoxy primer layer was formed was spirally coated. The thickness of the modified polyethylene layer was 0.15 mm, and the thickness of the polyethylene layer was 2.5 mm. Immediately after coating, a roll made of silicone rubber was pressed to crimp the coating layer, and the polyethylene coating layer was firmly fused, and then water-cooled from the outer surface to obtain a polyethylene-coated steel pipe.

Examples 2-17
Epoxy powder primer compositions having the compositions shown in Examples 2 to 17 in Table 1 were prepared in the same manner as in Example 1 (a). In addition, the compounding quantity of the epoxy resin of Table 1 is a weight ratio, the compounding ratio of a hardening | curing agent is the phenolic hydroxyl group equivalent in a hardening | curing agent with respect to 1 equivalent of epoxy groups in an epoxy resin component, and the mixing | blending of a hardening accelerator. The ratio is part by weight (% by weight) with respect to 100 parts by weight of the curing agent, and the blending amount of the inorganic filler is part by weight (% by weight) with respect to 100 parts by weight of the total amount of epoxy resin, curing agent and curing accelerator.
And the polyethylene coated steel pipe using the epoxy powder primer composition described in Examples 2-17 of Table 1 was manufactured in the same manner as Example 1 (b). In Tables 1 and 2, “C11Z” indicates 2-undecylimidazole (manufactured by Shikoku Chemicals).

Comparative Examples 1-15
Epoxy powder primer compositions having compositions shown in Comparative Examples 1 to 15 in Table 2 were prepared in the same manner as in Example 1 (a). In addition, the compounding quantity of the dicyandiamide of Comparative Examples 13-15 is the weight% with respect to 100 weight part of mixed epoxy resin components. And the polyethylene coated steel pipe using the epoxy powder primer composition described in the comparative examples 1-15 of Table 2 was manufactured in the same way as Example 1 (b).

  The polyethylene-coated steel pipes obtained by the above examples and comparative examples were subjected to evaluation tests according to the following. The test results are summarized in Table 3.

Evaluation of hot water adhesion Adhesion scratches reaching the steel pipe substrate with a cutter knife were made in the polyethylene-coated steel pipes obtained in Examples and Comparative Examples with a width of 10 mm along the circumferential direction. A part of the coating layer was peeled off, and this was used as a jig holding part. This part was grasped with a jig of a tensile tester, the coating layer was peeled off from the steel pipe at an environmental temperature of 23 ° C., a peeling angle of 90 °, and a peeling speed of 10 mm / min, and an initial 90 ° peel strength was measured. The other polyethylene-coated steel pipe obtained in the example was immersed in hot water at 80 ° C. for 100 days. After the immersion, the polyethylene-coated steel pipe was taken out, the same operation as described above was performed, and the 90 ° peel strength was measured after the immersion.

Evaluation of Cathodic Peeling Resistance Drilling holes with a diameter of 9 mm reaching the steel tube base material were drilled in the polyethylene-coated steel tube coatings obtained in the examples and comparative examples, and immersed in 3% saline solution, at a constant temperature of 60 ° C., −1.5 V. A cathode peeling test was performed by applying a voltage of (saturated calomel electrode) for 30 days. After the test was completed, the coating was removed, and the distance from the initial hole end to the peeling tip (peeling distance) was measured.

Evaluation of low temperature impact resistance The polyethylene-coated steel pipes obtained in the examples and comparative examples were subjected to a falling weight impact test using a punch having a tip diameter of 15.875 mm in accordance with the provisions of ASTM G14. The test was conducted at -45 ° C. After completion of the test, the presence or absence of cracks in the coating was visually determined.

Evaluation of cold-heat cycle resistance The polyethylene-coated steel pipes obtained in the examples and comparative examples were subjected to one cycle of “−60 ° C. atmosphere × 8 hours → 25 ° C. warm water immersion × 15 hours → 23 ° C. (room temperature) atmosphere × 1 hour”. Fifteen cycles of cooling and heating were performed. Subsequently, the presence or absence of peeling of the coating on the end surface portion of the polyethylene-coated steel pipe after the cycle was visually evaluated.

Tables 1-2 below show the compositions of Examples 1-17 and Comparative Examples 1-15. The descriptions in Tables 1 and 2 are as follows:
Epototo YD-014: bisphenol A type epoxy resin (a), manufactured by Tohto Kasei Co., Ltd., epoxy equivalent 900-1000 g / eq, softening point 91-102 ° C.
Epototo 2004: Bisphenol F type epoxy resin (b), manufactured by Tohto Kasei Co., Ltd., epoxy equivalent 900-1000 g / eq, softening point 80-90 ° C.
Epototo YDCN702: o-cresol novolak type epoxy resin (c), manufactured by Tohto Kasei Co., Ltd., epoxy equivalent of 195 to 220 g / eq, softening point of about 75 ° C.
Epicure 171N: curing agent (b), manufactured by Japan Epoxy Resin Co., phenolic hydroxyl group equivalent of 200 to 286 g / eq, softening point of about 80 ° C.
2MZ: 2-methylimidazole, manufactured by Shikoku Kasei Kogyo Co., Ltd.
C11Z: 2-undecylimidazole, manufactured by Shikoku Kasei Kogyo Co., Ltd.
Means.

^＊：比較例１３〜１５における硬化剤（ロ）の量は、混合エポキシ樹脂成分（イ）１００重量部に対する重量％を示す。

^* : The amount of the curing agent (b) in Comparative Examples 13 to 15 indicates wt% with respect to 100 parts by weight of the mixed epoxy resin component (a).

As is clear from Table 3, the examples satisfying all the conditions defined in the present invention are superior in heat-resistant water adhesion, cathode peel resistance, low-temperature impact resistance, and thermal cycle resistance compared to the comparative examples. Is shown.
On the other hand, Comparative Examples 1 and 2 in which the weight ratio of (a) / (b) is outside the range of 5/95 to 95/5 in the mixed epoxy resin component (I) is inferior in the thermal cycle resistance. Further, Comparative Examples 3 to 4 were inferior in hot water adhesion and cathode peel resistance.
Comparative Example 5 in which the weight of (c) is large in the weight ratio of [(a) + (b)] / (c) is inferior in cathode peel resistance, low temperature impact resistance, and cold heat cycle resistance. The comparative example 6 with a small weight of c) was inferior in the thermal cycle resistance.
In Comparative Examples 7 to 15, the blending ratio of any of the mixed epoxy resin component (A), the curing agent component (B), the curing accelerator component (C), and the inorganic filler component (D) is within the scope of the present invention. In the case of deviating from the above, it was confirmed that the effect of the present invention was not obtained.

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

Since the polyolefin-coated steel material of the present invention has excellent hot water adhesion, cathodic peel resistance, low temperature impact resistance, cold heat resistance, etc., it is a severe environment such as a high temperature wetted environment or a cryogenic environment. There is an advantage that it can be used for a long time even under conditions. The polyolefin-coated steel material of the present invention further ensures the above-described excellent performance even when the curing temperature at the time of forming the coating layer is set lower, so that in addition to the above-described advantages, the energy cost and CO ₂ emission are further increased. There is an advantage that the amount can be reduced.

It is a schematic sectional drawing of the polyolefin covering steel material of this invention.

Explanation of symbols

  1: Steel material, 2: Chromate film, 3: Epoxy primer layer, 4: Polyolefin adhesive layer, 5: Polyolefin layer.

Claims (3)

An epoxy primer layer formed from a composition containing the following components (a), (b), (c) and (d); a polyolefin adhesive layer; and a polyolefin layer; Sequentially laminated, polyolefin coated steel:
(A) Bisphenol A type epoxy resin (a), bisphenol F type epoxy resin (b) having a softening point of 75 to 128 ° C. and an epoxy equivalent of 600 to 2200 g / eq, and o-cresol novolac type epoxy resin (c) A mixture of
The weight ratio of [(a) + (b)] / (c) is 95/5 to 50/50,
The weight ratio of (a) / (b) is 5/95 to 95/5.
Mixed epoxy resin component,
(B) A phenolic curing agent having an average phenol hydroxyl group equivalent of 200 to 800 g / eq, and the amount of the phenol hydroxyl group of the phenolic curing agent is 0 with respect to 1 equivalent of the epoxy group of the mixed epoxy resin component (A). A curing agent component that is .4 to 0.9 equivalents;
(C) Imidazole-based curing accelerator and / or imidazoline-based curing accelerator, and the amount of the curing accelerator is 0.1 to 15.0 parts by weight with respect to 100 parts by weight of the curing agent component (b). A curing accelerator component,
(D) An inorganic filler, and the amount of the inorganic filler is based on 100 parts by weight of the total amount of the mixed epoxy resin component (a), the curing agent component (b) and the curing accelerator component (c). An inorganic filler component that is 10 to 100 parts by weight.   The polyolefin-coated steel material according to claim 1, wherein the ground treatment of the steel material is a chromate treatment. An epoxy powder primer composition used for producing a polyolefin-coated steel material, comprising the following components (A), (B), (C) and (D):
(A) Bisphenol A type epoxy resin (a), bisphenol F type epoxy resin (b) having a softening point of 75 to 128 ° C. and an epoxy equivalent of 600 to 2200 g / eq, and o-cresol novolac type epoxy resin (c) A mixture of
The weight ratio of [(a) + (b)] / (c) is 95/5 to 50/50,
The weight ratio of (a) / (b) is 5/95 to 95/5.
Mixed epoxy resin component,
(B) A phenolic curing agent having an average phenol hydroxyl group equivalent of 200 to 800 g / eq, and the amount of the phenol hydroxyl group of the phenolic curing agent is 0 with respect to 1 equivalent of the epoxy group of the mixed epoxy resin component (A). A curing agent component that is .4 to 0.9 equivalents;
(C) an imidazole-based curing accelerator and / or an imidazoline-based curing accelerator, wherein the amount of the curing accelerator is 0.1 to 15.0 parts by weight with respect to 100 parts by weight of the curing agent component (b). A curing accelerator component,
(D) An inorganic filler, and the amount of the inorganic filler is based on 100 parts by weight of the total amount of the mixed epoxy resin component (a), the curing agent component (b) and the curing accelerator component (c). An inorganic filler component that is 10 to 100 parts by weight.

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