JPS6124179B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to multilayer epoxy coated steel materials and steel products. More specifically, it relates to a coated steel material or steel product whose surface is coated with an anticorrosive epoxy powder coating and which is further coated with a modified epoxy powder coating to have improved scratch resistance, low-temperature flexibility, and low-temperature impact resistance. Epoxy-coated steel materials or steel products, such as epoxy-coated steel pipes, are widely used, but epoxy coatings have poor properties such as scratch resistance, low-temperature flexibility, and low-temperature impact resistance, so they cannot be assembled during cargo transportation or in extremely cold regions. The coating film may crack or peel off during pipeline installation such as processing work and burying work, which has the disadvantage of impairing corrosion protection. In order to overcome this drawback, various methods have been proposed for imparting flexibility to epoxy resins, but epoxy resins with flexibility do not have the inherent characteristics of epoxy resins, such as water resistance, moisture resistance, and corrosion resistance. Contributing properties are reduced and heat resistance is impaired. The present invention provides a coated steel pipe free from the above-mentioned defects by undercoating with an anticorrosion epoxy powder coating and then topcoating with a highly flexible modified epoxy powder coating.The gist thereof is as follows: The surface of steel materials or steel products is coated with a thick film of anti-corrosion epoxy powder coating containing anti-rust pigments and/or inorganic fillers.
A multi-layer epoxy-coated steel material or steel product, which is coated with an undercoat of 100 to 800 μm, and then coated with a topcoat of a modified epoxy powder coating with a thickness of 50 to 300 μm to protect the undercoat, and the modified A multilayer epoxy-coated steel material or steel product characterized in that the epoxy powder coating contains at least one compound selected from the following (a), (b), and (c) as a modifier. (a) Polyester having at least one functional group selected from hydroxyl group and carboxyl group at the end of the molecule and having an equivalent weight of 500 to 2,500 (b) A glass transition point of 70°C or less and a softening point of 200 ℃ or less and a number average molecular weight of 5000 or more (c) Diene rubber or derivative thereof having a hydroxyl group or carboxyl group at the molecular end To explain the present invention in detail, the anticorrosion epoxy powder used in the present invention The body paint contains an epoxy resin containing at least two epoxy groups in the molecule and an epoxy equivalent of 170 to 3,500, a curing agent for the epoxy resin, a rust preventive pigment and/or an inorganic filler as essential components. There are things that do. The epoxy resins used here include epoxy resins with an epoxy equivalent of 450 to 3,500 manufactured from bisphenol A and epichlorohydrin; phenol novolak resins, and epoxy resins with an epoxy equivalent of 170 to 500 manufactured from cresol novolak resin and epichlorohydrin. Epoxy resin: Epoxy resins having an epoxy equivalent of 200 to 800, which are produced from brominated bisphenol A, brominated phenol novolak resin, brominated cresol novolak resin and epichlorohydrin, are mainly used. Epoxy resin curing agents used in anti-corrosion epoxy powder coatings include phenol, catechol,
One or more types of novolac type phenolic resins derived from formaldehyde and phenolic compounds such as resorcinol, bisphenol A, and cresols, dicyandiamide, guanidine derivatives, carboxylic acid dihydrazides, imidazole compounds, and derivatives thereof are used. Also, known tertiary amine compounds, dimethylurea compounds, etc. may be used in combination as curing accelerators. The inorganic fillers used in anti-corrosion epoxy powder coatings are used to improve the water resistance of the coating, and include quartz,
Powders such as silica stone, glass, calcium silicate, gypsum, barium sulfate, mica, and titanium oxide are blended. In addition, anti-rust pigments for the purpose of preventing rust on steel include Cr-based, Pb-based, Zn-based, Mo-based, Fe-based, Al-based
Various anti-rust pigments such as zinc chromate,
Examples include strontium chromate, lead silicate, zinc phosphate, zinc molybdate, mica-like iron oxide, iron phosphate, aluminum phosphate, and aluminum dihydrogen tripolyphosphate. In addition to these ingredients, extender pigments, coloring pigments, flow regulators, anti-sagging agents, anti-mold agents, etc. are blended as necessary, and the mixture is melt-kneaded, cooled, crushed and classified, and the powder flow regulator is added to the post. Powder coatings are produced by blending. The total amount of the inorganic filler and anti-rust pigment (if only one is used, the amount) is 20 parts by weight or more, preferably 30 to 100 parts by weight, based on 100 parts by weight of the epoxy resin and curing agent for epoxy resin. be. Preferably, by using an inorganic filler and a rust preventive pigment in combination, good paintability and excellent corrosion resistance are achieved. The amount of the curing agent for epoxy resin to be used is such that the equivalent ratio of the active hydrogen group to the epoxy group of the epoxy resin is 0.5 to 2.0 in the case of an active hydrogen-containing curing agent. In the case of curing agents that harden through catalytic action, the optimum amount to be blended must be determined in relation to the physical properties, so the amount cannot be determined unconditionally, but approximately 0.5 parts by weight per 100 parts by weight of the resin. ~
It is 10 parts by weight. Next, the modified epoxy powder coating used in the present invention will be described. The epoxy resin used in modified epoxy powder coatings has an epoxy equivalent weight of 800 and is manufactured from bisphenol A and epichlorohydrin.
~3500 Ebis type epoxy resin is preferred.
Although it is possible to use epoxy equivalents having an epoxy equivalent of 800 or less and about 170, it is blended so that 80% by weight or more of epoxy equivalents have an epoxy equivalent of 800 or more. Epoxy resins other than those listed above include epoxy resins derived from mononuclear polyphenols such as hydroquinone and catechol and epichlorohydrin, bisphenol F, phenol novolac resin, cresol novolac resin, brominated bisphenol A, and other nuclear polyvalent phenols. and various epoxy resins derived from bisphenol A alkylene oxide addition diol and various polyols and epichlorohydrin, epoxy resins derived from aminophenols and polyamines, alicyclic epoxy resins,
Hydantoin type epoxy resins and the like can be mixed and used as necessary. In this case as well, the mixing ratio of the Ebibis type epoxy resin with those having an epoxy equivalent of 800 or more is 20% by weight or less. In the present invention, at least one selected from the following (a), (b) and (c) is used as a modifier for the epoxy powder coating. (a) Polyester having at least one functional group selected from hydroxyl group and carboxyl group at the molecular end and having an equivalent weight of 500 to 2,500 (b) A glass transition point of 70°C or lower and a softening point of 200°C. ℃ or less and a number average molecular weight of 5000 or more (c) Diene rubber or its derivatives having hydroxyl or carboxyl groups at the molecular ends The amount of modifier used is the main component of the modified epoxy powder coating. The amount is 5 parts by weight or more, preferably 10 to 50 parts by weight, based on 100 parts by weight of the total amount of the epoxy resin and epoxy resin curing agent. If it is less than 5 parts by weight, the flexibility modification effect will be poor, and if it exceeds 50 parts by weight, the heat resistance will be impaired. Polyesters having hydroxyl or carboxyl groups at the molecular ends are produced from dicarboxylic acids and glycols by esterification. At this time, in addition to the glycol component, a polyhydric alcohol such as triol or tetraol may be used in combination by replacing a part of the glycol component. When producing polyester, if the reaction composition contains an excess of carboxyl groups, a polyester with mainly carboxyl groups at the end of the molecule will be obtained, and if the amount of hydroxyl groups is added in excess, a polyester with hydroxyl groups at the end of the molecule will be obtained. Further, a polyester having a hydroxyl group at the end can be obtained by obtaining a polymer having equal amounts of carboxyl groups and hydroxyl groups, and then adding glycol to depolymerize it. Furthermore, a polyester mainly having a hydroxyl group at the molecular end can also be obtained by deglycolizing a diester obtained by reacting a dicarboxylic acid with a large excess of glycol. Furthermore, a polyester having a hydroxyl group at the molecular end can also be obtained by reacting a dicarboxylic acid with a low-molecular-weight alcohol to form a diester and then reacting it with a glycol to perform a transesterification reaction. Dicarboxylic acids used in the production of these polyesters include terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, and 3,6-endomethylene. Examples include tetrahydrophthalic acid, succinic acid, maleic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, and the like. Two or more of these dicarboxylic acids may be used in combination. Glycols include ethylene glycol, propylene glycol, butane-1,3-diol, butane-1,4-diol, neopentyl glycol, hexane-1,6-diol, cyclohexanediol, 1,4-bishydroxymethyl-benzene. , diethylene glycol, hydrogenated bisphenol A, etc. are used. Further, as glycols, polymeric glycols such as polyoxyethylene glycol, polyoxypropylene glycol, and polyoxytetramethylene glycol are used in combination for the purpose of imparting flexibility. A branched structure may also be introduced into the polyester by using a small amount of polyhydric alcohol such as glycerin, trimethylolpropane, or pentaerythritol. Other polyesters include lactone ester type polyesters, which are obtained by ring-opening polymerization of lactone compounds using glycol or polyhydric alcohol as an initiator, and have hydroxyl groups at the molecular ends. As the lactone compound, ε-caprolactone is commonly used. To derive a polyester having a terminal carboxyl group from a lactone ester type polyester, maleic anhydride, succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, etc.
This method is based on a method in which an anhydride of a 1,2-dicarboxylic acid compound is subjected to a ring-opening addition reaction. Specific examples of these polyesters include Nippon Ester Co., Ltd.'s ER6000 series as a hydroxyl group-terminated polyester, and the ER8000 series as a carboxyl group-terminated polyester. In addition, Toyobo Co., Ltd.'s Vylon is a polyester with hydroxyl or carboxyl groups.
There is the GV series. In addition, the company's Byron RV series and GX are high molecular weight polyester grades.
There is a series. As lactone type polyesters, Daicel Chemical Co., Ltd.'s Plaxel series and Plaxel H
series, and Union Carbide's
There is a POP series. However, these polyesters have functional group equivalents (i.e., hydroxyl group equivalents when they have hydroxyl groups, carboxyl group equivalents when they have carboxyl groups, and carboxyl group equivalents when they have both).
Village of hydroxyl group equivalent and carboxyl group equivalent)
is 500 to 2,500, preferably 700 to 2,000. Furthermore, polyester powder having a number average molecular weight of less than 5000, which is commercially available for paints, is usually used. On the other hand, the thermoplastic polyester has a glass transition point of 70°C or lower, preferably -60 to 50°C, and a softening point of
The temperature used is 200°C or lower, preferably 60 to 160°C, and a number average molecular weight of 5,000 or higher, preferably 7,000 to 50,000. Specifically, at least two or more dibasic acids such as terephthalic acid, isophthalic acid, and adipic acid,
There are polyesters derived from cocondensation polymerization with at least two or more glycols such as ethylene glycol, diethylene glycol, neopentyl glycol, and polytetramethylene glycol, and polyesters derived from ε-caprolactone. Diene rubbers or derivatives thereof having hydroxyl groups or carboxyl groups at the molecular ends used in modified epoxy powder coatings include butadiene or butadiene copolymers, and residual double bonds contained in these diene rubbers can be Derivatives obtained by hydrogenation are also included. Styrene and acrylonitrile are mainly used as copolymerization monomers for producing the butadiene copolymer. These diene rubbers having a hydroxyl group or a carboxyl group at the end are called telechelic diene rubbers. This telechelic diene rubber has a normal number average molecular weight.
More than 1000, thousands of products are manufactured, including liquid,
Or it is wax-like or rubber-like. Preferably, those having a number average molecular weight of 1000 to 5000 are used. These diene rubbers are polymerized by a living anionic polymerization method, and depending on the type of polymerization terminator, they become telechelic diene rubbers with hydroxyl or carboxyl group terminals. The butadiene and acrylonitrile copolymerization system is polymerized by radical polymerization, and a functional group is introduced using an initiator or a chain transfer agent. Specific examples of these telechelic diene rubbers and their derivatives include BF
GOODRICH Hycar CTB, CTBN, CTBNX
Series: PoLy-BD series by ARCO CHEM.; NISSO-PBG series and C series (all product names) by Nippon Soda Co., Ltd. Epoxy resin curing agents used in modified epoxy powder coatings include acid anhydrides, imidazole compounds and derivatives thereof, dicyandiamide, guanidine compounds, carboxylic acid dihydrazides, and the like. Examples of acid anhydrides include pyromellitic anhydride, trimellitic anhydride, benzophenonetetracarboxylic anhydride, nadic anhydride, chlorendic anhydride, tetrahydrophthalic anhydride, 5-(2,5-
diketotetrahydrofuryl)-3-methyl-3-
Cyclohexene-1,2-dicarboxylic anhydride Ethylene glycol bistrimelitate anhydride Examples include polyazelaic acid polyanhydride and polysebacic acid polyanhydride. Examples of imidazole compounds include imidazole bone nuclei such as 2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, and 2-phenyl-4-methylimidazole. There are compounds in which carbon atoms at the 2-, 4-, and 5-positions are substituted with hydrogen, an alkyl group, or an aryl group, and 2-phenylimidazole compounds in which the 4-, 5-, or both positions are substituted with a methylol group. Derivatives of these imidazole compounds include 1-benzylimidazoles, cyanoethylated imidazoles, organic acid salts derived from cyanoethylated imidazole and organic acids, imidazole derivatives modified with aminotriazine compounds, and metal salts. There are complex salts with imidazole. Examples of guanidine compounds include 1,3-diphenylguanidine, p-tolylguanide, xylenylguanide, 2,3-guanylurea, 2,4
- Guanylurea, 2,6-xylenyl biguanide, phenyl biguanide, etc. Examples of carboxylic acid dihydrazide include oxalic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, hexadecanedioic acid dihydrazide, isophthalic acid dihydrazide, phthalic acid dihydrazide, terephthalic acid dihydrazide, etc. . Two or more of these curing agents for epoxy resins can also be used in combination. Further, a known curing accelerator may be used to improve the reaction rate. The blending ratio of the curing agent to the epoxy resin is appropriately determined in consideration of the functional groups in the modifier and in relation to the functional groups of the curing agent. When using a compound having an acid anhydride group or active hydrogen as a curing agent, the functional group equivalent of the curing agent is 0.5 per equivalent of the epoxy group of the epoxy resin.
~2 preferably selected from the range of 0.7 to 1.2. In producing modified epoxy powder coatings, in addition to the epoxy resin, curing agent for epoxy resin, and modifier described above, curing accelerators, inorganic fillers, pigments, flow agents, antioxidants, antibacterial agents, etc. are used. It is mixed appropriately. These raw materials are crushed, weighed and mixed, then melt-kneaded using an extruder or rolls, cooled, coarsely crushed, finely crushed, and classified. After classification, a powder fluidity regulator is added afterwards and mixed uniformly to form a powder coating. Average particle size is usually 10μm for spray painting.
~70 μm. When formulating the above-mentioned modified epoxy powder coating, adding a large amount of inorganic filler will impair the flexibility and elongation of the coating film, so it should be less than 20% by weight, preferably 10% by weight of the total formulation.
It is better to keep it to . This article describes a multilayer coating method for the outer surface of steel pipes using the anticorrosive epoxy powder coating obtained as described above and the modified epoxy powder coating. Steel pipes undergo surface cleaning treatments such as degreasing and rust removal. Blasting improves paint adhesion. Blast steel pipe is 170~250℃ preferably 200℃
It is heated to ~240°C and first an anti-corrosion epoxy powder coating is electrostatically sprayed to form a molten coating.
At this time, the coating film should be 100μm to 800μm, preferably 100μm.
m to 600 μm, particularly preferably 200 to 450 μm. A modified epoxy powder coating is then electrostatically sprayed to form a second coating film. The modified epoxy coating film has a thickness of 50 μm to 300 μm, preferably about 100 μm. Heating of the steel pipe is continued until both coatings are completely cured, and then cooled to obtain a double coated steel pipe. In this method of applying a flexible epoxy powder coating after applying an anticorrosion epoxy powder coating, the anticorrosion epoxy coating may be in a partially cured state or a partially cured state by the time the latter is applied. It may be in a completely cured state. The effects of the present invention can also be achieved by reheating a steel pipe coated with anticorrosive epoxy powder paint and coating it with a flexible epoxy powder paint. but,
Continuous coating method is preferred for energy saving. On the other hand, prior to the anticorrosion powder epoxy coating, an epoxy or phenol primer may be applied to prepare the base and improve anticorrosion properties. Although steel pipes have been taken as an example above, steel plates, steel bars, steel tanks, towers and tanks, etc. can also be targeted as steel materials or steel products. Next, the present invention will be explained in more detail with reference to Examples. In the following examples, parts represent parts by weight. Epoxy equivalent, hydroxyl group equivalent, and carboxyl group equivalent were each measured as follows. The epoxy equivalent was measured by the perchloric acid method, the hydroxyl group equivalent by the phthalic anhydride-pyridine method, and the carboxyl group equivalent by the alkaline titration method, and the weight per gram equivalent of each functional group was expressed in grams. The number average molecular weight was determined by the terminal group determination method for polyesters, and by the gel permeation chromatography method for diene rubbers. The glass transition point was measured by differential thermal analysis, and the softening point was measured by the ring and ball method. [Production example of anti-corrosion epoxy powder coating A] 90 parts of an epoxy resin with an epoxy equivalent of 850 synthesized from bisphenol A and epichlorohydrin, 10 parts of an epoxy resin with an epoxy equivalent of 180 synthesized from a phenol novolak resin and epichlorohydrin as a curing agent. 2.3 parts of dicyandiamide, 0.2 parts of 2-phenylimidazole as a hardening accelerator, 40 parts of calcium silicate as a filler, 15 parts of fine mica
1 part Bengara as a pigment, 5 parts titanium dioxide, 0.1 part acrylic resin as a flow regulator, 1.0 part fine silica, and an epoxy silane coupling agent.
An anticorrosive epoxy powder coating consisting of 0.5 parts was produced by melt-kneading, cooling, crushing, and classifying using conventional methods. During production, the epoxy resin and dicyandiamide were melt-kneaded and then cooled and ground, and the coupling agent was used by adsorbing it on calcium silicate. [Production example of anti-corrosion epoxy powder coating B] 40 parts of an epoxy resin with an epoxy equivalent of 700 synthesized from bisphenol A and epichlorohydrin, 40 parts of an epoxy resin with an epoxy equivalent of 930, and an epoxy equivalent of 180 synthesized from a phenol novolak resin and epichlorohydrin. 20 parts of epoxy resin, 18 parts of phenol novolac resin as a hardening agent, 0.3 parts of 2-methylimidazole as a hardening accelerator, 20 parts of fine mica powder, and 20 parts of calcium silicate as a filler.
1 part, amorphous silica powder 2 parts, lead silicate 5 parts as a rust preventive pigment, carbon black 1 part as a pigment, and Modaflow 1 part as a flow control agent. Manufactured. [Production of modified epoxy powder coating] A modified epoxy powder coating according to the formulation shown in Table 1 was produced by a melt-kneading method using an extruder. Paint No. 7 using liquid rubber is prepared in advance.
After melting and mixing epoxy resin and liquid rubber at 170℃,
It was used after cooling and coarsely crushing. Explanation of the raw materials used in the table (all are trade names or trademarks): Epicote 1055 Epoxy resin synthesized from bisphenol A/epichlorohydrin, epoxy equivalent 800-900 Epicote 10077 Only epoxy equivalent
1750-2200 Epicote 1009 Epoxy resin synthesized from bisphenol A and epichlorohydrin, with an epoxy equivalent of 2400-3300 (or more oil-based shell epoxy products) DICY Dicyandiamide (Nippon Carbide Products) 2P4MHZ 2-Phenyl-4-methylhydroxymethyl (Shikoku) Chemical products) 2MZ 2-methylimidazole (Shikoku Kasei products) Aerosil #200 Fine powder silica (Nippon Aerosil products) Modaflow Flow regulator (Monsanto Chemical products) DIURON Dichlorophenyldimethylurea (DuPont products) MINUSIL Silica powder PENNSYLVANIA GLASS Corp. products) Hycar CTBN1300×13 Carboxyl group equivalent
1880 nitrile rubber (BF Goodrich product) Prototype A Hydrogenated diene rubber product with hydroxy equivalent of 1300 (manufacturing method: below) ER-8100 Polyester with carboxyl group equivalent of 840 (Nippon Ester product) ER-8200 Polyester with carboxyl group equivalent of 1560 (Nippon Ester product) ER-6610 Polyester with a hydroxyl group equivalent of 1810 (Nippon Ester product) RV-300 Polyester with a molecular weight of approximately 20,000 and a softening point of 123°C (Toyobo product) Plaxel 240 Lactone type polyester with a hydroxyl group equivalent of 2000 (Daicel Chemical) Product) Plaxel H4 Lactone type polyester with a molecular weight of approximately 40,000 and a softening point of 60°C (Daicel Chemical Products) [Hydrogenated diene rubber product. Manufacturing method of prototype A] Polyhydroxypolyptadiene (R-45HT. produced by Arcc Chem.) was placed in 10 autoclaves.
n3110, [-OH] = 0.82meq/g, cis-1.4:15
%, trans-1.4:58%, vinyl:27% polybutadiene liquid rubber) 3Kg, cyclohexane 3
After charging 300 g of carbon-supported ruthenium (5%) catalyst (manufactured by Nippon Engelhard Co., Ltd.) and replacing the inside of the system with purified argon, high-purity hydrogen gas was started to be supplied into the autoclave, and heating was started at the same time. It took about 30 minutes for the inside of the autoclave to reach steady conditions (internal temperature 100°C, internal pressure 150 Kg/cm ² ). The reaction was carried out under these conditions for 15 hours. As a result of analysis by infrared absorption spectrum, the obtained polymer was found to be a hydrocarbon polymer containing almost no doublets. [-OH] of this polymer was 0.81 meq/g. This polymer is abbreviated as prototype A.

【table】

[Table] Example 1 JIS G3141 SPCC-SD steel plate (1.0×60×120mm)
After degreasing with Triclean vapor, the surface was blasted with cast iron grit. The steel plate was then heated for 20 minutes in a hot air circulation heating furnace at 240°C, and then electrostatically sprayed with anticorrosive epoxy powder coating A to a film thickness of 300±50μ. Next, about 100 μm of No. 1 modified epoxy powder coating was spray-coated on this and cured in a 240° C. heating oven for 5 minutes to obtain a multi-layer coated steel plate. In order to investigate the adhesion of the multi-layer coating obtained, a tape peeling test was performed with six cross cuts reaching the steel plate at 2 mm width intervals, and no peeling was observed between the coating layers or between the steel plate and the coating. Ta. Next, the radius of the unpainted surface of the multi-layer coated steel plate is
The bending resistance of the multilayer coating was investigated by bending it in the longitudinal direction along a jig with curvatures of 28 m/m and 18 m/m. The test was conducted at -20℃ and -30℃ in an air-cooled thermostat.
It was carried out in As a result, no abnormality was observed in the multilayer coating film under any conditions. On the other hand, when a bending test was conducted under the same conditions using only the anticorrosive epoxy powder coating A, the coating film was found to break under all conditions.
Severe cracks occurred when a jig with a curvature of 18 m/m was used. Example 2 and Comparative Example 1 In the same manner as in Example 1, a coated plate obtained using anticorrosion epoxy powder coating A was coated with an approximately 100μ upper layer of modified epoxy powder coating Nos. 2 to 8. A steel plate was manufactured and a low temperature bending test was conducted. As a result, no breakage of the coating film was observed in any case. On the other hand, for modified epoxy powder coatings No. 3, 4, and 7, powder coatings were prepared with the formulations excluding the polyester and diene rubber as modifiers, multilayer coating was performed in the same way, and low temperature bending tests were performed. (Comparative Example 1), all the coating films were broken. Example 3 A steel plate treated in the same manner as in Example 1 using anti-corrosion epoxy powder coating B was preheated in a 200°C heating furnace to reduce the film thickness.
After electrostatic coating, approximately 100
Modified epoxy paint No. 1, No. 1 to have a film thickness of μ.
3. After coating the upper layer of No. 4, heat at 240℃ 5
A multi-layer coated steel plate was obtained by post-curing in a heating furnace for 30 minutes.
When this was subjected to a low-temperature bending test similar to Example 1, it was found that -20℃ and -
There was no breakage of the coating film at 30℃, but the radius of curvature
At 18 m/m, hair cracks occurred in the paint film. On the other hand, in the case of a single layer coating of only anticorrosive epoxy powder coating B, severe cracks occurred under all conditions. Example 4 A JIS SGP steel pipe with a diameter of 300/280 mm and a length of 1 m was surface blasted with cast iron grit and then heated to 240°C with an infrared heater. Anticorrosive epoxy powder coating A was electrostatically sprayed onto this preheated steel pipe to a film thickness of 300±50 μm. After 30 seconds, electrostatically spray No. 3 modified epoxy powder paint to approximately 100 μm.
After forming a coating film, heating was performed again at 240° C. for 5 minutes using an infrared heater to completely cure the coating film. The steel pipe was then water-cooled to obtain a double-layer coated steel pipe. In order to investigate the adhesion of the coating film on the obtained double-layer coated steel pipe, a tape peeling test was performed on six cross cuts reaching the steel pipe at intervals of 2 mm in width, and no peeling was observed between the coating film layers or between the steel plate and the coating film. Nakatsuta. Next, a test piece measuring 2 cm in the circumferential direction and 20 cm in the length direction was cut from the double-layer coated steel pipe, and a bending test was performed by aligning the length direction with jigs with radii of 280 mm and 180 mm, respectively. At this time, the surface in contact with the jig was a non-painted surface, and the test was conducted in a refrigerant at -20°C and -30°C. As a result, the multi-layered modified epoxy paint No. 3 did not cause any cracks in the paint film, but when a similar test was conducted using only the anticorrosive epoxy paint A, significant cracks occurred in the paint film. In addition, when the above double-layer coated steel pipe was subjected to an impact test using a Gardner type falling weight impact tester, the result was 40 ld・inch.
In contrast, in the case of anticorrosive epoxy paint A alone, it showed failure in a 30 ld.inch pass;
40ld・inch fracture was observed; the impact resistance of the multi-layer coated steel pipe was improved. Comparative Example 2 Anticorrosive epoxy powder coatings A and B each contain 40% carboxyl group-terminated polyester ER-8200.
Example 1
300°C at 240°C and 200°C, respectively.
An attempt was made to impart flexibility to the anticorrosive epoxy powder coating by coating with a film thickness of ±50μ and post-curing at 240°C for 5 minutes. The low-temperature bending test of this product shows a hair crack when the radius of curvature is 28mm, and the radius of curvature is 28 mm.
In the case of 18 mm, cracks occurred and the improvement effect was judged to be insufficient. As is clear from the above results, it is clear that the multi-layer coated steel material or steel product of the present invention is effective in improving low temperature flexibility, which is a drawback of anticorrosive epoxy paints, and also in improving impact resistance.

Claims (1)

[Scope of Claims] 1. The surface of a steel material or steel product is coated with an anticorrosive epoxy powder coating containing anticorrosive pigments and/or inorganic fillers with a film thickness of 100 to 800 μm, and a modified epoxy powder is applied on top of this. A coated epoxy-coated steel material or steel product that is coated with a top coat of body paint with a film thickness of 50 to 300 μm and a protective coat of the undercoat film,
The modified epoxy powder coating contains the following as a modifier:
Multi-layer epoxy coated steel materials and steel products characterized by containing at least one compound selected from (a), (b) and (c) (a) at least one functional group selected from hydroxyl groups and carboxyl groups; (b) Thermoplastic polyester having a glass transition point of 70°C or lower, a softening point of 200°C or lower, and a number average molecular weight of 5,000 or higher (c) Hydroxyl group or diene rubber having a carboxyl group at the molecular end or its derivative 2 Content (total amount) of rust-preventive pigment and/or inorganic filler in anti-corrosion epoxy powder coating
However, 20 parts by weight per 100 parts by weight of the epoxy resin and curing agent for epoxy resin contained in the paint.
The multilayer epoxy coated steel material and steel product according to claim 1, wherein the amount is at least part by weight. 3 The content of the modifier in the modified epoxy powder coating is 5 to 100 parts by weight based on 100 parts by weight of the total amount of the epoxy resin and curing agent for epoxy resin contained in the coating. The multilayer epoxy-coated steel material and steel product according to item 1 or 2. 4. Claims in which the epoxy resin that is the main component of the modified epoxy powder coating is an epoxy resin containing 80% by weight or more of an epoxy resin manufactured from bisphenol A and epichlorohydrin and having an epoxy equivalent of 800 to 3,500. The multilayer epoxy-coated steel material and steel product according to any one of Items 1 to 3. 5. Claims 1 to 4, wherein the epoxy resin that is the main component of the anticorrosion epoxy powder coating is an epoxy resin containing at least two epoxy groups in the molecule and having an epoxy equivalent of 170 to 3,500. Multi-layer epoxy-coated steel materials and steel products according to any of the above. 6. The multilayer epoxy coated steel material and steel product according to any one of claims 1 to 5, wherein the surface of the steel pipe is coated with multilayer epoxy. 7. The multilayer epoxy coated steel material and steel product according to claim 6, wherein the outer surface of the steel pipe is coated with multilayer epoxy.