JP5898441B2 - Painted steel pipe for scaffold and manufacturing method thereof - Google Patents

Description

  The present invention relates to a coated steel pipe for scaffolding excellent in slip resistance, coating film adhesion and coating film strength, and a method for producing the same.

  A steel pipe formed by forming a steel plate into a cylindrical shape is used in a wide range of applications as a construction material such as a handrail or a scaffold pipe. Steel pipes used in these applications are required to have slip resistance from the viewpoint of ensuring the safety of a handrail user or a worker using a scaffold pipe. Therefore, in order to improve the slip resistance of the steel pipe, it has been proposed to subject the surface of the steel pipe to a roughening treatment (see, for example, Patent Document 1).

JP-A-10-030334

  As a means for improving the slip resistance of the steel pipe without roughening the surface of the steel pipe, it is conceivable to form an elastomer coating on the surface of the steel pipe. However, according to the conventional technology, the elastomer cannot be sufficiently adhered to the surface of the steel pipe, and a coated steel pipe having both slip resistance and coating film adhesion cannot be produced.

  On the other hand, when applying painted steel pipes to scaffold pipes, in addition to slip resistance and paint film adhesion, paint film strength is also required from the viewpoint of preventing the destruction of paint films by fastening each scaffold pipe with a clamp. The

  This invention is made | formed in view of this point, and it aims at providing the coated steel pipe for scaffolds which is excellent in slip resistance, coating-film adhesiveness, and coating-film intensity | strength.

  The present inventor forms the above-mentioned problem by forming a coating film made of a cured product of a resin composition containing a polyester having a predetermined molecular weight distribution as a main resin and a polyisocyanate compound as a curing agent. The present invention has been completed by finding out that the problem can be solved and further studying it.

That is, this invention relates to the following coated steel pipes for scaffolds.
[1] A coated steel pipe for scaffolding having a base steel pipe and a thermosetting resin coating film having a film thickness of 3 to 30 μm formed on the surface of the base steel pipe. The thermosetting resin coating film is a cured product of a resin composition containing a resin and an extender pigment; the thermosetting resin coating film is 20 ° C. The indentation depth when a load of 49 mN is applied with a cylindrical indenter with a diameter of 1 mm is 2 μm or more; the thermosetting resin coating film is immersed in boiling water for 1 hour and then in the atmosphere After being allowed to stand for 24 hours, a coated steel pipe for scaffolding in which the classification of the test result of the adhesion test conducted in accordance with JIS K 5600-5-6 is 0.
[2] The coated steel pipe for scaffolding according to [1], wherein the thermosetting resin coating film has a coating film softening temperature of 15 ° C. or less measured by the following method.
[Measurement method of softening temperature of coating film]
A load of 98 mN was applied to the thermosetting resin coating film cooled with liquid nitrogen with a cylindrical indenter having a diameter of 1 mm; the thermosetting resin coating film was heated at 5 ° C./min, and an indentation depth curve In the indentation depth curve, the intersection of the tangent line A at a temperature lower than the temperature at which the indenter begins to be pushed in and the tangent line B at the temperature at which the indentation speed becomes maximum is defined as the softening temperature of the coating film. To do.
[3] The thermosetting resin coating film has a number average molecular weight in the range of 20,000 to 40,000 and a weight average molecular weight of 100,000 or more, and 20 to 60 mass with respect to 100 mass parts of the polyester. [1] or [2], which is a cured product of a resin composition containing a part of the polyisocyanate compound and 5 to 40 parts by mass of the extender pigment based on 100 parts by mass of the polyester and the polyisocyanate. Painted steel pipe for scaffolding as described.

Moreover, this invention relates to the manufacturing method of the following coated steel pipes for scaffolds.
[4] preparing a base steel pipe formed from molten Al, Mg-containing Zn-plated steel sheet;
Polyisocyanate having a number average molecular weight in the range of 20,000 to 40,000 and a weight average molecular weight of 100,000 or more on the surface of the base steel tube, and 20 to 60 parts by mass with respect to 100 parts by mass of the polyester Applying a paint containing a compound and 5 to 40 parts by mass of extender pigment based on a total of 100 parts by mass of the polyester and the polyisocyanate; and baking the paint applied to the surface of the base steel pipe A method for producing a coated steel pipe for scaffolding, comprising:

  ADVANTAGE OF THE INVENTION According to this invention, the coating steel pipe for scaffolds which is excellent in slip resistance, coating-film adhesiveness, and coating-film intensity | strength can be provided.

The graph which shows the indentation depth curve obtained when measuring the softening temperature of the coating film formed from the coating material of No. 4

  The coated steel pipe for scaffold of the present invention has a base steel pipe and a thermosetting resin coating film formed on the surface of the base steel pipe. Hereinafter, each component will be described.

[Base steel pipe]
The base steel pipe is manufactured by deforming (pipemaking) a steel plate (steel strip). For example, the base steel pipe is a welded steel pipe. The steel plate to be the original plate is preferably a molten Al, Mg-containing Zn plated steel plate from the viewpoint of corrosion resistance.

  The kind of base steel plate of the molten Al, Mg-containing Zn-plated steel plate is not particularly limited. For example, as the base steel plate, a steel plate made of low carbon steel, medium carbon steel, high carbon steel, alloy steel, or the like can be used. When good press formability is required, a steel sheet for deep drawing made of low carbon Ti-added steel, low carbon Nb-added steel, or the like is preferable as the base steel sheet. For example, as a base steel plate, C: 0.05-0.25 mass%, Si: 0.01-1.5 mass%, Mn: 0.05-3.0 mass%, Al: 0.010-0 100% by mass, Ti: 0.010 to 0.150% by mass, B: 0.0001 to 0.0100% by mass, and if necessary, one or more of Nb, Cr, Mo, and P may be added in total 1 It is preferably contained within the range of 0.000% by mass or less and composed of the remaining Fe and inevitable impurities.

The molten Al, Mg-containing Zn plating layer includes a ternary eutectic structure of Al / Zn / Zn ₂ Mg. Each phase (Al phase, Zn phase, and Zn ₂ Mg phase) forming the ternary eutectic structure of Al / Zn / Zn ₂ Mg has an irregular size and shape, and is intricate with each other. Yes. The Al phase in the ternary eutectic structure is derived from the Al "phase at high temperature in the Al-Zn-Mg ternary equilibrium diagram (Al solid solution that dissolves Zn and contains a small amount of Mg). The Al "phase at high temperature usually appears separated into a fine Al phase and a fine Zn phase at room temperature. The Zn phase in the ternary eutectic structure is a Zn solid solution in which a small amount of Al is dissolved, and in some cases, Mg is further dissolved. The Zn ₂ Mg phase in the ternary eutectic structure is an intermetallic compound phase in the vicinity of a point where Zn is about 84% by mass in the Zn—Mg binary equilibrium diagram.

  The Al content of the plating layer is preferably in the range of 1.0 to 22.0 mass%, and the Mg content is preferably in the range of 1.5 to 10.0 mass%. When the Al content and the Mg content are out of the above ranges, the corrosion resistance may not be sufficiently provided. For example, the plating layer is made of Al: 1.0 to 22.0 mass%, Mg: 1.5 to 10.0 mass%, Si: 0.005 to 2.0 mass%, Ti: 0.001 to 0.00. 1% by mass, B: 0.001 to 0.045% by mass, balance: Zn and inevitable impurities.

  Although the thickness of a plating layer is not specifically limited, The inside of the range of 0.8-100.0 micrometers is preferable. When the thickness of the plating layer is less than 0.8 μm, scratches that reach the base steel sheet during handling are likely to enter, which may reduce the corrosion resistance. On the other hand, when the thickness of the plating layer is more than 100.0 μm, the plating layer and the base steel plate have different ductility, so that the plating layer and the base steel plate may be peeled off during pipe making.

  The thickness (wall thickness) and outer diameter of the base steel pipe are not particularly limited, and may be set as appropriate according to the application. For example, the thickness of the base steel pipe is about 0.5 to 6.0 mm, and the outer diameter of the base steel pipe is about 10 to 200 mm. Moreover, the shape of the base steel pipe of the present invention is not particularly limited, and may be appropriately selected depending on the application. For example, the shape of the base steel pipe is a round pipe or a square pipe.

  The pipe making method is not particularly limited, and may be appropriately selected from known methods according to the shape and size of the coated steel pipe. For example, a plated steel plate is formed into an open pipe shape by roll forming or rollless forming, and then the end in the width direction of the steel plate is welded (for example, high frequency welding). Next, after cutting the beat protruding portion protruding from the steel pipe, a thermal spray repair layer may be formed in the beat cut welded portion and the vicinity thereof. The thermal spraying method is not particularly limited, and may be one continuous spraying or two or more thermal spraying. Moreover, the kind of spraying material is not specifically limited, For example, what is necessary is just to select suitably from metals, such as Al and Zn.

The base steel pipe may be formed with a chemical conversion coating from the viewpoint of further improving the corrosion resistance and the coating film adhesion. In this case, the type of chemical conversion treatment is not particularly limited. Examples of the chemical conversion treatment include chromate treatment, chromium-free treatment, phosphate treatment and the like. Among these, a fluoroacid-based film mainly composed of titanium and a water-soluble resin is preferable because it exhibits a good coating film adhesion improving effect. The film thickness of the chemical conversion coating is not particularly limited as long as it is within a range effective for suppressing corrosion of the base steel pipe and improving coating film adhesion. For example, in the case of a chromate film, the film thickness may be adjusted so that the total Cr equivalent adhesion amount is 5 to 100 mg / m ² . Further, in the case of a chromium-free coating, the Ti-Mo composite coating has a range of 10 to 500 mg / m ² , and the fluoroacid-based coating has a fluorine equivalent or total metal element equivalent deposit of 3 to 100 mg / m ^2. The film thickness may be adjusted. In the case of a phosphate film, the film thickness may be adjusted so that the adhesion amount is 5 to 500 mg / m ² .

  The chemical conversion film can be formed by a known method. For example, the chemical conversion treatment liquid may be applied to the surface of a steel plate before pipe making or a steel pipe after pipe making by a method such as a roll coating method, a spin coating method, or a spray method, and dried without washing. The drying temperature and drying time are not particularly limited as long as moisture can be evaporated. From the viewpoint of productivity, the drying temperature is preferably in the range of 60 to 150 ° C. as the ultimate plate temperature, and the drying time is preferably in the range of 2 to 10 seconds.

[Thermosetting resin coating film]
The thermosetting resin coating film is a cured product of a resin composition containing a resin and an extender pigment. The thermosetting resin coating film is a coating film having an indentation depth of 2 μm or more and does not cause peeling of the coating film in the adhesion test. In this specification, “the indentation depth of the coating film” means the indentation depth of the coating film when a load of 49 mN is applied to the coating film with a cylindrical indenter having a diameter of 1 mm in an environment of 20 ° C. (See Examples). Further, “the coating film does not peel off in the adhesion test” means that the coated steel pipe is immersed in boiling water for 1 hour to apply a load to the coating film, and then allowed to stand in the atmosphere for 24 hours, and then JIS K 5600. -5-6: It means that the classification of the test result when the adhesion test (cross-cut method) is performed according to 1999 is 0 (see Examples). However, in JIS K 5600-5-6: 1999, it is described that a flat and non-distorted one is used as a test plate. However, in the evaluation of the coated steel pipe of the present invention, the steel pipe having a curved surface is used. The adhesion test shall be performed in the same procedure. Specifically, cross cutting is performed until the surface of the coated steel pipe (curved surface) reaches a base material, thereby forming a lattice pattern. And after affixing a tape on the surface (curved surface) of a coated steel pipe, it peels off a tape and observes whether the coating film has peeled. Other processes and evaluation methods are the same as in JIS K 5600-5-6 (see Examples).

  The film thickness of the thermosetting resin coating film is preferably in the range of 3 to 30 μm, and more preferably in the range of 5 to 30 μm. When the film thickness is less than 3 μm, it becomes difficult to make the indentation depth of the coating film 2 μm or more, and the slip resistance cannot be sufficiently exhibited. On the other hand, when the film thickness is more than 30 μm, it becomes easy to generate cracks during baking, which may impair the appearance of the coating film.

The indentation depth of the thermosetting resin coating film depends on the softening temperature of the thermosetting resin coating film. Therefore, in order to set the indentation depth of the thermosetting resin coating to 2 μm or more, the softening temperature of the thermosetting resin coating is preferably 15 ° C. or less. In the present specification, the “softening temperature of the coating film” means a temperature measured by the following procedures 1) to 3).
1) A load of 98 mN is applied to a thermosetting resin coating film cooled with liquid nitrogen with a cylindrical indenter having a diameter of 1 mm.
2) While applying a load of 98 mN with an indenter, the thermosetting resin coating film is heated at a heating rate of 5 ° C./min to obtain an indentation depth curve.
3) In the obtained indentation depth curve, the intersection of the tangent line A at a temperature lower than the temperature at which the indenter begins to be pushed in and the tangent line B at the temperature at which the indentation speed becomes maximum is the softening temperature of the coating film. (See FIG. 1).

  Thus, when the indentation depth of the thermosetting resin coating is 2 μm or more (the softening temperature of the coating is 15 ° C. or less), when an object comes into contact with the thermosetting resin coating, The contact area between the curable resin coating film and the object can be increased, and as a result, the slip resistance can be improved.

  In order to make the indentation depth of the thermosetting resin coating film containing a predetermined amount (explained later) of the extender pigment 2 μm or more and to withstand the adhesion test the coating film adhesion to the base steel pipe, For example, 1) A resin composition (paint) containing a polyester having a number average molecular weight in the range of 20,000 to 40,000 and a weight average molecular weight of 100,000 or more as a main resin, and 2) a polyisocyanate compound as a curing agent. It may be cured to form a thermosetting resin coating film.

  A resin composition (coating material) for forming a thermosetting resin coating film contains a polyester having a number average molecular weight within a range of 20,000 to 40,000 and a weight average molecular weight of 100,000 or more as a main resin. By containing a certain amount of polyester having a small molecular weight so that the number average molecular weight is 40,000 or less, the number of urethane bonds in the cured product can be increased. Since this urethane bond is a polar group, it improves the adhesion of the coating film to the base steel pipe surface. Moreover, the softening temperature of hardened | cured material can be lowered | hung by containing fixed amount polyester with a large molecular weight so that a number average molecular weight may be 20,000 or more and a weight average molecular weight may be 100,000 or more. Due to the lowering of the softening temperature, the indentation depth of the coating film can be 2 μm or more. In the present specification, “number average molecular weight” and “weight average molecular weight” are both average molecular weights in terms of polystyrene measured by gel permeation chromatography.

  The dispersity (weight average molecular weight Mw / number average molecular weight Mn) of the polyester resin is preferably in the range of 2 to 10. When the degree of dispersion is less than 2, the proportion of the high molecular weight component becomes excessive, the resin viscosity becomes too high, and it becomes difficult to form a paint. Moreover, the coating-film adhesiveness to the base-material steel pipe surface will also fall. On the other hand, when the degree of dispersion exceeds 10, the proportion of the low molecular weight component becomes excessive, and the indentation depth of the coating film becomes less than 2 μm.

  The kind of monomer component (dicarboxylic acid component, diol component, oxyacid component) constituting the polyester is not particularly limited.

  As the dicarboxylic acid component, aliphatic dicarboxylic acid or aromatic dicarboxylic acid can be used. Examples of the aliphatic dicarboxylic acid compound include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, dimer acid, fumaric acid and the like. Examples of the aromatic dicarboxylic acid include phthalic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and the like. These dicarboxylic acids may be used alone or in combination of two or more.

  As the diol component, aliphatic diol, aromatic diol and the like can be used. Examples of the aliphatic diol include ethylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6- Hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,4-cyclohexane Dimethanol, propylene glycol, neopentyl glycol, 3,3-diethyl-1,3-propanediol, 3,3-dibutyl-1,3-propanediol, 1,2-pentanediol, 1,3-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 2-methyl-2,4-pentanediol, -Methyl-1,5-pentanediol, 1,4-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, n-butoxyethylene glycol, Examples include cyclohexanedimethanol, hydrogenated bisphenol A, dimer diol, diethylene glycol, dipropylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and hexylylene glycol. Examples of aromatic diols include bisphenol A ethylene oxide adducts, propylene oxide adducts, and the like. These diols may be used alone or in combination of two or more.

  The oxyacid component is not particularly limited as long as it is a compound having one hydroxyl group and a carboxyl group in the molecule. Examples of oxyacids include lactic acid, glycolic acid, hydroxy-n-butyric acid, hydroxycaproic acid, hydroxydimethylbutyric acid, hydroxymethylbutyric acid, hydroxyisocaproic acid, hydroxybenzoic acid and the like. Of these, 6-hydroxycaproic acid is preferred. These oxyacids may be used alone or in combination of two or more.

  The method for preparing the polyester is not particularly limited. For example, what is necessary is just to esterify said dicarboxylic acid and diol by a well-known esterification reaction using an esterification catalyst as needed.

  The polyester is crosslinked with a curing agent. The curing agent is preferably a polyisocyanate compound that does not cause surface layer concentration and self-condensation. If the curing agent is concentrated on the surface layer or self-condensed, the hardness of the coating film increases and the indentation depth of the coating film may be less than 2 μm.

  The kind of polyisocyanate compound is not particularly limited. As the polyisocyanate compound, aliphatic polyisocyanate, alicyclic polyisocyanate, and the like can be used. Examples of aliphatic polyisocyanates include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, dodecane methylene diisocyanate, 1,6,11-undecane triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate (2, 6-diisocyanatomethyl caproate), bis (2-isocyanatoethyl) fumarate, bis (2-isocyanatoethyl) carbonate, 2-isocyanatoethyl-2,6-diisocyanatohexanoate, etc. . Examples of alicyclic polyisocyanates include isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, bis (2-isocyanatoethyl) -4-cyclohexene-1,2-di Examples include carboxylate, 2,5- and / or 2,6-norbornane diisocyanate.

  The polyisocyanate compound may be blocked with a blocking agent. Examples of the blocking agent include oximes, phenols, alcohols, lactams, diketones, mercaptans, ureas, imidazoles, carbamic acids and the like.

  Examples of commercially available polyisocyanate compounds that can be used include Takenate (Mitsui Chemicals Co., Ltd.), Sumidur (Sumika Bayer Urethane Co., Ltd.), Death Module (Suika Bayer Urethane Co., Ltd.), and Coronate (Nippon Polyurethane Industry Co., Ltd.). Is mentioned.

  The compounding ratio of the polyester and the polyisocyanate compound is such that the ratio (NCO / OH) of the isocyanate group (—NCO) of the polyisocyanate to the hydroxyl group (—OH) of the polyester is in the range of 0.8 to 1.2. Adjustment may be made so that it is preferably in the range of 0.9 to 1.1. When converted to parts by mass, the polyisocyanate compound is preferably in the range of 20 to 60 parts by mass with respect to 100 parts by mass of the polyester. When the compounding amount of the polyisocyanate compound is less than 20 parts by mass, the thermosetting resin coating film cannot be sufficiently formed. On the other hand, when the compounding amount of the polyisocyanate compound is more than 60 parts by mass, side reactions may occur excessively and the coating film hardness may be increased.

  As described above, the thermosetting resin coating film contains extender pigments. By blending the extender pigment, the coating strength of the thermosetting resin coating can be increased. Examples of extender pigments include barium sulfate, titanium oxide, silica, calcium carbonate and the like. The extender pigment preferably contains 5 to 40 parts by mass with respect to 100 parts by mass in total of the polyester and polyisocyanate described above. When the extender is less than 5 parts by mass, the coating film strength may not be sufficiently increased. Moreover, when the extender pigment is more than 40 parts by mass, the cohesive force of the coating film is excessively increased, and the slip resistance may be lowered.

  Moreover, the thermosetting resin coating film may contain arbitrary pigments, such as a color pigment, a metallic pigment, and a rust preventive pigment, besides the extender pigment. However, since these pigments may increase the cohesive strength of the coating film and reduce the slip resistance, the blending amount of various pigments is preferably within a range that does not affect the softening behavior of the coating film. The blending amount combined with the extender pigment should not exceed 40 parts by mass. Examples of the color pigment include titanium oxide, carbon black, chromium oxide, iron oxide, bengara, titanium yellow, cobalt blue, cobalt green, aniline black, phthalocyanine blue and the like. Examples of metallic pigments include pearl pigments and metal powders such as aluminum, stainless steel and nickel. Examples of rust preventive pigments include zinc phosphate, zinc phosphite, magnesium magnesium phosphate, magnesium phosphate, magnesium phosphite, silica, calcium ion exchanged silica, zirconium phosphate, aluminum trihydrogen phosphate, zinc oxide , Zinc phosphomolybdate, barium metaborate and the like.

  The thermosetting resin coating film can be formed by a known method. For example, a thermosetting resin paint containing polyester, polyisocyanate compound and extender pigment having a predetermined molecular weight distribution may be applied to the surface of the base steel pipe and baked. The method for applying the thermosetting resin paint is not particularly limited, and may be appropriately selected according to the shape of the base steel pipe. Examples of the coating method include a roll coating method, a flow coating method, a curtain flow method, a spray method, a dipping method, a dropping method, and the like. The film thickness of the paint can be adjusted by a felt diaphragm or an air wiper. The baking conditions may be, for example, baking at an ultimate plate temperature of 200 to 250 ° C. for 30 to 90 seconds.

  The coated steel pipe for scaffolding of the present invention is excellent in slip resistance because it contains a certain amount of polyester (soft segment) having a large molecular weight between crosslinks in the thermosetting resin coating film. In addition, the coated steel pipe for scaffold of the present invention contains a certain amount of polyester having a low molecular weight between crosslinks in the thermosetting resin coating film and has a certain amount of polar group (urethane bond), so that the coating film adhesion is excellent. ing. Furthermore, the coated steel pipe for scaffolding of the present invention includes an extender pigment in the thermosetting resin coating film, and thus has excellent coating film strength. That is, the coated steel pipe for scaffold of the present invention is excellent in all of slip resistance, coating film adhesion and coating film strength.

  The coated steel pipe of the present invention is excellent in slip resistance, coating film adhesion, coating film strength, and corrosion resistance, and is useful as a steel pipe for scaffolding pipes that are installed indoors and outdoors and used for building buildings, for example. It is.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not limited by these Examples.

1. After forming fabricated thickness 2.4mm of substrate steel, the molten Zn-6% Al-3% Mg alloy plated steel sheet of single side coating weight 90 g / ^{m 2} an open pipe-shaped, high-frequency welding both end portions in the width direction Thus, a base steel pipe (welded plated steel pipe) having an outer diameter of 48.6 mm was produced. Next, after the welded portion was beat-cut, a thermal spray repair layer having a width of 10 mm was formed by triple spraying of Al, Zn, and Al.

2. Preparation of paint Polyesters were prepared from dicarboxylic acids, diols and oxyacids having the compositions shown in Tables 1 and 2. The number average molecular weight in terms of polystyrene of the obtained polyester was in the range of 15000 to 42000, and the weight average molecular weight in terms of polystyrene was in the range of 45000 to 18000 (see Tables 1 and 2). The number average molecular weight and weight average molecular weight in terms of polystyrene were measured using a high-speed GPC system (HLC-8220; Tosoh Corporation). As the column, KF-800D and KF-805L (both Showa Denko KK) were used. Tetrahydrofuran (THF) was used as the eluent, and a differential refractometer was used as the detector. From the obtained polyester, polyisocyanate compound (Desmodur; Sumitomo Bayer Urethane Co., Ltd.) and extender pigments, paints (Nos. 1 to 12) having the compositions shown in Tables 1 and 2 were prepared.

  About each coating material (No. 1-12), the indentation depth of the coating film (film thickness of 15 μm) formed from the coating material and the softening temperature of the coating film were measured using a thermomechanical analyzer (TMA8140C; Rigaku Corporation). It was measured. The indentation depth of the coating film was measured by applying a load of 49 mN to the coating film using a cylindrical indenter having a diameter of 1 mm in an environment of 20 ° C. The softening temperature of the coating film was measured by the following procedure. First, a load of 98 mN was applied to the coating film cooled with liquid nitrogen with a cylindrical indenter having a diameter of 1 mm. Next, while applying a load to the coating film, the coating film was heated at a heating rate of 5 ° C./min to obtain an indentation depth curve. In the obtained indentation depth curve, the intersection of the tangent A at a temperature lower than the temperature at which the indenter begins to be indented and the tangent B at the temperature at which the indentation speed becomes maximum is defined as the softening temperature of the coating film (see FIG. 1).

  FIG. 1 is a graph showing an indentation depth curve obtained when measuring the softening temperature of a coating film formed from No. 4 paint. In the graph, “TMA” indicates an indentation depth curve, and “DTMA” indicates a differential curve of the indentation depth curve (TMA). As shown in FIG. 1, the softening temperature of the coating film for No. 4 paint obtained from the intersection of tangent line A and tangent line B was −25 ° C.

  Tables 1 and 2 show the measurement results of the indentation depth of the coating film and the softening temperature of the coating film for each of the paints (Nos. 1 to 12).

3. Preparation of painted steel pipe for scaffold The surface of the prepared base steel pipe was alkali degreased and washed with water. Spray a coating pretreatment liquid (hexafluorotitanic acid: 50 g / L, aminomethyl-substituted polyvinylphenol: 75 g / L, solvent: water) on the outer surface of each steel pipe so that the attached amount in terms of titanium is 10 mg / m ^2. And dried at 100 ° C. to form a pretreatment coating film.

  The above-mentioned paint (No. 1-12) was apply | coated to the surface of each base-material steel pipe which pre-painted, and it baked at 230 degreeC for 60 second, and formed the coating film with a film thickness of 5 micrometers.

4). Evaluation of Scaffolding Painted Steel Pipe (1) Slip Resistance Test The slip resistance test was performed using a steel plate (painted steel plate) before pipe forming in which a coating film was formed under the same conditions as the above-mentioned scaffold coated steel pipe. Specifically, each coated steel sheet (Examples 1 to 3) in which the above-described pre-coating film and paint film (paint Nos. 1 to 12) were formed on the surface of a molten Zn-6% Al-3% Mg alloy-plated steel sheet. Comparative Examples 1 to 9) and a base steel pipe (Comparative Example 10) on which only the pretreatment coating film was formed were subjected to a slip resistance test. The slip resistance test was performed by measuring the static friction coefficient under the conditions of an objective load of 200 g and a test speed of 8 mm / sec using a static friction coefficient measuring machine (TRIBOGEAR TYPE: 10; Shinto Kagaku Co., Ltd.) (reference standard). : JIS P 8147). Those with a static friction coefficient of 0.35 or more are marked with “◎”, those with 0.30 or more and less than 0.35 are marked with “◯”, those with a coefficient of static friction of 0.35 or more and less than 0.30 are marked with “△”, Those less than were evaluated as “x”.

(2) Adhesion test Adhesion tests were carried out on the respective coated steel pipes for scaffolds (Examples 1 to 3, Comparative Examples 1 to 9) to which the above-mentioned paints (No. 1 to 12) were applied. Specifically, first, each coated steel pipe for scaffolding was immersed in boiling water for 1 hour and then allowed to stand in the atmosphere for 24 hours. After 24 hours, referring to JIS K 5600-5-6, the surface (curved surface) of the coated steel pipe for scaffold was cross-cut, and a tape was attached to the part. The interval between the cuts and the position of the tape conformed to JIS K 5600-5-6. After the tape peeling, it was observed whether the coating film was peeled off. The evaluation method was performed according to JIS K 5600-5-6. That is, when the coating film was not peeled off at all (classification of the test result was 0), “◎” was evaluated, and when the coating film was peeled even a little (classification of the test result was 1 to 5), it was evaluated as “x”.

(3) Coating film strength test The coating film strength test was implemented about the coating steel pipe for scaffolds (Examples 1-3, Comparative Examples 1-9) which apply | coated the above-mentioned coating material (No. 1-12). Specifically, fastening and releasing of the coated steel pipe for scaffolding were repeated 10 times with a commercially available single pipe scaffolding clamp. Thereafter, the appearance of the fastening portion was visually evaluated. When the coating film was not broken, it was evaluated as “◯”. When the coating film was broken even a little, it was evaluated as “x”.

(4) Results Table 3 shows the results of the slip resistance test, adhesion test and coating strength test.

  From Table 3, it turns out that the coating steel pipe for scaffolds of Examples 1-3 is excellent in slip resistance, coating-film adhesiveness (adhesion), and coating-film intensity | strength.

  Since the coated steel pipe of the present invention is excellent in slip resistance, coating film adhesion, coating film strength and corrosion resistance, it is useful, for example, as a steel pipe for scaffolding pipes installed indoors and outdoors.

Claims (3)

A coated steel pipe for scaffolding having a base steel pipe and a thermosetting resin coating film having a film thickness of 3 to 30 μm formed on the surface of the base steel pipe,
The base steel pipe is a steel pipe made from molten Al, Mg-containing Zn-plated steel sheet,
The thermosetting resin coating film is a polyester having a number average molecular weight in the range of 20,000 to 40,000 and a weight average molecular weight of 100,000 or more, and 20 to 60 parts by mass of the polyester with respect to 100 parts by mass of the polyester. It is a cured product of a resin composition containing an isocyanate compound and 5 to 40 parts by mass of an extender pigment with respect to 100 parts by mass in total of the polyester and the polyisocyanate ,
The thermosetting resin coating film has a thickness of 15 μm, and has an indentation depth of 2 μm or more when a load of 49 mN is applied with a cylindrical indenter having a diameter of 1 mm in an environment of 20 ° C. And
The thermosetting resin coating film is immersed in boiling water for 1 hour, and then allowed to stand in the air for 24 hours, and then classified as a result of an adhesion test performed in accordance with JIS K 5600-5-6. Is 0,
Painted steel pipe for scaffolding. The coated steel pipe for a scaffold according to claim 1, wherein the thermosetting resin coating film has a coating film softening temperature of 15 ° C or less measured by the following method when the film thickness is 15 µm .
[Measurement method of softening temperature of coating film]
A load of 98 mN is applied to the thermosetting resin coating film cooled with liquid nitrogen with a cylindrical indenter having a diameter of 1 mm;
Heating the thermosetting resin coating film at a heating rate of 5 ° C./min to obtain an indentation depth curve;
In the indentation depth curve, the intersection of the tangent A at a temperature lower than the temperature at which the indenter begins to be indented and the tangent B at the temperature at which the indentation speed becomes maximum is defined as the softening temperature of the coating film. Preparing a base steel pipe made of molten Al, Mg-containing Zn-plated steel sheet;
Polyisocyanate having a number average molecular weight in the range of 20,000 to 40,000 and a weight average molecular weight of 100,000 or more on the surface of the base steel tube, and 20 to 60 parts by mass with respect to 100 parts by mass of the polyester Applying a paint containing a compound and 5 to 40 parts by mass of an extender pigment based on 100 parts by mass of the polyester and the polyisocyanate;
Baking the paint applied to the surface of the base steel pipe;
A method for producing a coated steel pipe for scaffolding, comprising:

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