JPH11141053A - Covered steel wire excellent in corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve corrosion resistance by forming a phosphatic compound layer on the surface of a steel wire, and then covering the element wire or stranded wire of the steel wire with organic resin comprising thermosetting resin or thermosetting resin powder paint. SOLUTION: Patenting, wire washing and wire drawing are applied in this order to steel wire material, and the steel wire material is submerged in a 10% sulfuric acid solution for five minutes at ordinary temperature to form a steel wire rid of a surface oxide layer. After a phosphatic compound treated layer of 0.5-10 g/m<2> in adhesion quantity to the surface area of the steel wire is formed on the surface of the steel wire, the element wire or stranded wire of the steel wire is covered with organic resin of 10 μm to 1 mm in thickness. Covering resin is to be phenol setting powder epoxy resin or low density polyethylene, amine setting agent added liquid epoxy resin. The steel wire is preheated to 120 deg.C to make the resin adhere to it by an electrostatic coater, and then heat-insulated in an induction heating type postheating furnace for membrane backing. Paint film adhesion and corrosion resistance can be improved with the introduction of the phosphatic compound layer under a paint film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel wire which is used, for example, as a tendon for prestressed concrete (hereinafter abbreviated as PC) and requires a high level of corrosion resistance for a long time after construction.

[0002]

2. Description of the Related Art PCs used as materials for structures such as bridges and buildings are subject to tensile stress when steel, which is a tendon inside, is corroded by neutralization of concrete or chloride ions derived from snow-melting salt. The strength of the steel material increases, and the volume of the steel material increases due to corrosion products, thereby causing cracks and the like. In the worst case, the structure is destroyed, which has a serious economic and social impact. Therefore, for the purpose of preventing corrosion of the steel wire, rust prevention by plating on the steel wire, primary rust prevention by treatment with a rust preventive agent, rust prevention by organic resin coating, and the like have been invented. In particular, with respect to organic resin coating, unbonded and after-bonded organic resin-coated steel wires have been invented for the purpose of application to an after-tension system.

[0003]

However, the plating is expensive in manufacturing cost and changes the physical properties of the steel wire itself due to heating during the hot-dip plating process, so that the use of the steel wire is limited. In the treatment with the rust preventive, the rust preventive effect is lost when the rust preventive is diffused and lost in the concrete environment. Since the coating of the organic resin has an effect of shielding the steel material from the external environment, a semi-permanent rust prevention performance can be expected by applying an appropriate coating material and an appropriate thickness of the coating layer. However, when the scratches on the resin layer reach the steel material due to handling during transportation or construction or fixing of the end portions, it is difficult to suppress the development of rust from the scratched portions only with the organic coating film.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a steel wire having a high corrosion resistance, which is used as a tendon for a PC. 0.5 to 10 g based on the surface area of steel wire
/ M has a phosphate compound layer ^2, a coated steel wire having excellent corrosion resistance, characterized by having the following organic resin layer thickness of 10μm or more 10mm in wire or stranded wire of the steel wire, (2 A) a coated steel wire having excellent corrosion resistance, wherein the organic resin layer in the above (1) is a thermosetting resin;
Further, (3) the coated steel wire having excellent corrosion resistance, wherein the organic resin layer in the above (1) is a thermosetting resin powder coating.

[0005] It is desirable to remove an oxide layer (black scale) on the surface of a raw steel wire in order to improve the adhesion of the phosphoric acid compound layer. As a method for removing the surface oxide layer, any of known methods such as pickling and shot may be used. After pickling, it may be neutralized by immersion in 2% soda ash solution for 30 seconds or the like and rinsed with neutral water. And Percolen Z
It is also preferred to carry out the treatment.

[0006] If the surface forming the crystal layer is contaminated with oxides, oils, smuts, etc., crystal growth unevenness is caused,
As a result, it is well known that so-called scalping occurs, and it is preferable to carry out the above-mentioned surface preparation also for the prevention thereof. The formation of the phosphoric acid compound-treated layer may be performed by any of known methods such as solution immersion and spray coating.

[0007] As a component of the treatment solution, a soluble phosphate of a metal from an alkali metal to iron is essential in an electrochemical voltage series, and an acid for etching a steel material surface and a promotion for promoting a crystal formation reaction are used. An agent may be added. As the soluble phosphate, typically, an aqueous solution in which zinc phosphate, manganese phosphate, calcium phosphate, iron phosphate, or the like is used alone or in combination of two or more kinds is typically used.

As an acid for etching steel material, phosphoric acid,
Inorganic and organic acids such as nitric acid, oxalic acid, boric acid and the like can be used. However, caution is required because sulfuric acid, hydrochloric acid, and the like have an adverse effect on the film formation depending on the added amount. Examples of the accelerator include metal ions such as Cu, Ni, and Co, and oxidizers such as nitrate, chlorate, bromate, and nitrite, and accelerators for phosphoric acid compound treatment such as hydroxylamin and sulfite. Can be used by selecting from those known as.

In general, the organic coating layer has a great effect on rust prevention of steel by preventing corrosion factors such as oxygen, water, chloride ions and the like from reaching the steel surface. However, when the coating film is scratched and reaches the steel material, the organic coating film does not have rust-preventive effect on the iron base exposed at the scratched portion.
Furthermore, when corrosion factors enter the interface between the organic coating film and the steel material from the flawed portion, the adhesion of the coating film to the steel material deteriorates, the coating film peels off the steel material, and the corrosion spreads along the peeling interface. A phenomenon also occurs.

In the present invention, by forming a compound layer which is chemically stable and has good adhesion to a steel material and an organic coating film under the organic resin layer, the compound layer at the coating film / steel material interface is formed. Suppresses corrosion from scratched parts by suppressing the corrosion reaction of steel and forming a highly water-resistant bond to both the steel and the coating to improve the adhesion between the coating and the steel. I do. The present invention provides a steel wire having a coating amount of 0.5 to 10 g / m
After forming the phosphate compound treatment layer ^2, it is characterized in coating the 10mm following organic resin or the thickness 10μm on the wire or stranded wire.

The reasons for limiting the adhesion amount of the phosphoric acid compound layer, the thickness of the organic resin and the like in the present invention will be described below. The adhesion amount is desirably in the range of 0.5 to 10 g / m ² . If the cleanliness of the steel material surface is low, or if the adhesion amount is less than 0.5 g / m ² due to contamination of the processing solution, the crystal growth is insufficient and the effect of improving the adhesion of the coating film is weak. On the other hand, 10 g / m
Even if the amount exceeds ² , the effect of improving the adhesion to the extent that the amount of adhesion is increased is not shown, which is uneconomical. In addition, since the crystal is hard and brittle, if the coating layer is too thick, it tends to undergo cohesive failure, which may result in poor adhesion.

The thickness of the organic resin coating film is 10 μm or more. If the film thickness is less than 10 μm, it is difficult to prevent defects (such as pinholes) in the coating film,
It is easy for corrosion factors such as water, oxygen, and various ions to penetrate the coating film and reach the steel material, and when the coating film has an external flaw, the flaw easily reaches the steel material surface. Therefore, the lower limit film thickness is set to 10 μm. Preferably, the coating thickness is 50 μm
If so, pinholes are unlikely to occur even when applying powder paint. As the film thickness increases, the effect of preventing pinholes, the penetration of corrosion factors, and the prevention of outer surface flaws from reaching the steel material improves. However, even if the film thickness is excessively large, the effect is flattened and uneconomical. Further, since an excessively thick film impairs performance such as bending workability of a steel wire and workability of fixing an end portion, the upper limit of the film thickness is set to 10 mm. When emphasis is placed on bending workability and workability for fixing the end portions, the thickness of the coating film is desirably 1 mm or less when a thermosetting resin paint is used.

The performance required for the coating film is the ability to inhibit the transmission of various corrosion factors including oxygen, water and chloride ions, and the adhesion to steel and concrete to be grouted. In order to ensure the above function over a long period of time, it is necessary that defects such as pinholes are not easily generated in the coating film, and cracks, scratches, peeling, and the like are not easily generated in handling after production.

In view of the above requirements, the type of resin is preferably a powdered epoxy resin. This is because, in a single coating operation, a coating film having a thickness of several tens to several hundreds of micrometers can be obtained in a single coating operation, the occurrence of pinholes is small, the adhesion to steel and concrete is excellent, the chemical resistance and the flexibility are high. It has excellent properties such as high resistance and impact resistance. As the main component of the powdered epoxy resin, various types such as bisphenol A type, F type, phenol type, etc. may be used based on their properties. Dicyandiamide, phenol type,
A catalyst such as an imidazole compound or a sulfonic acid compound may be used in combination with a curing agent such as an amine or an acid anhydride. Further, in addition to these, various pigments such as silica and titania may be added. As powder resin,
Further, any one of thermosetting resin systems such as polyester-based and acrylic-based resins, or any combination among several types including the epoxy resin may be used. As a coating method, any of known techniques such as powder spray, electrostatic powder spray, and fluidized bed immersion may be used.

It is also possible to use a solvent-based, solvent-less or water-based paint, which is suitable for uniformly forming a thin coating film having a thickness of about 10 to 100 μm with few pinholes. The type of resin is epoxy, urethane,
Any one of known coating resins such as polyester, acrylic, and fluorine, or a mixture of two or more of them may be used. As a coating method, any of known methods such as dipping, spraying, brushing, and electrostatic coating may be used. Regardless of the type of resin used, if heating of the steel material is required due to the method of coating, preheating may be applied after application of the base treatment.

[0016]

Embodiments of the present invention will be described below. As a material, a steel wire obtained by sequentially applying patenting, washing and drawing to a steel wire was used. The diameter of the steel wire was 5 mm.
The steel wire was immersed in a 10% sulfuric acid solution at room temperature for 5 minutes to remove the surface oxide layer, and covered the next layer within 1 hour.

The phosphoric acid compound-treated layer was formed according to the following procedure. Rinse: Rinse with distilled water for 1 minute Surface adjustment: Immerse in a 1% aqueous solution of Percolen Z (normal temperature) for 30 seconds Film formation: Immerse in a solution having the composition shown in Table 1 (liquid temperature 60 ° C.). The immersion time depends on the target adhesion amount. Rinse: Rinse twice with distilled water (60 ° C) for 60 seconds twice

[0018]

[Table 1]

As the coating resin, any one of phenol-cured powder epoxy resin, low-density polyethylene, and amine-curing agent-added liquid epoxy resin was used. The steel wire is preheated to 120 ° C. in advance, and after the resin is applied by an electrostatic coating machine, the temperature is 180 ° C. for 5 minutes in an induction heating type post-heating furnace.
And the film was baked. When low-density polyethylene was used, a steel wire preheated to 120 ° C. was coated with a round die by extrusion coating (resin extrusion temperature: 150 ° C.). The test material levels of the examples and comparative examples are as shown in Table 2.

[0020]

[Table 2]

The performance evaluation was performed by the following method. Salt spray test: Diameter 2 reaching the steel material on the surface of the coated steel wire
A drill flaw of mmφ was made, and the test was performed for 3000 hours based on ASTM B117-94. The results were evaluated by visual observation of the degree of rust generation and the blistering width of the coating film near the flaws.

The scores are as follows. 0: No peeling of the coating film near the flaws and no corrosion under the coating film 1: Peeling of the coating film near the flaws and progress of corrosion under the coating film A rating of 0 is practically preferable.

Liquid immersion test: A drill flaw having a diameter of 2 mmφ reaching the steel material was formed on the surface of the coated steel wire, and immersed in a solution at 25 ° C. for 45 days based on the ASTM G20 method. The solution is
NaOH 3 mol / l aqueous solution, CaCl ₂ 3 mol /
1 aqueous solution, Ca (OH) ₂ saturated aqueous solution, NaCl 3%
An aqueous solution was used. The results were evaluated by the average distance from the flaw of the peeled coating film together with the pressure-sensitive adhesive tape after the adhesive tape was stuck to the coating near the flaw.

The scores are as follows. 0: The peeling width of the coating film due to the adhesive tape is less than 1 mm. 1: The coating film having a width of 1 mm or more is seen, but does not extend over the entire circumference of the steel wire. The lower the rating, the more practically preferable, and 0 is the best. Table 3 shows the evaluation results.

[0025]

[Table 3]

In the salt spray test, No.
Nos. 1 to 12, Nos. 16, 17, Nos. 21 to 24, No. 27
The swelling of the coating film due to the generation of rust from the flaws is small. This can be said to be a significant improvement in corrosion resistance as compared with untreated steel wires (Comparative Examples Nos. 13 and 14). In Comparative Materials Nos. 13 and 14 having no phosphoric acid compound layer, coating film swelling occurred over the entire circumference of the wire having a diameter of 5 mm, and the steel material was corroded under the coating film swelling. It was confirmed that the progress of rust under the film was suppressed. In Comparative Examples Nos. 18 and 20 having no coating film, rust was generated on the entire surface, and the effect of suppressing corrosion due to the presence of the coating film was also confirmed.

In Comparative Example No. 25 in which low-density polyethylene was used as the coating resin, the coating was largely peeled off, and the steel material surface was widely corroded. In Comparative Example No. 26, many pinholes were generated because the coating film thickness was thin, and red rust spread over the entire surface of the steel material starting therefrom. In the solution immersion test, the immersion solution was Na
A difference was made with Cl and NaOH.

In NaCl immersion, Comparative Examples Nos. 13 and 14 having no phosphate compound treatment and Comparative Example No. 15 having a small amount of adhesion exhibited a large peeling width accompanying the peeling of the adhesive tape. There was evidence that the solution had penetrated the interface. Rust was also observed at the peeled portion. This tendency is also the same in Comparative Example No. 25, because the low-density polyethylene coating film has low chemical affinity for the phosphate compound-treated layer.

On the other hand, in the invention examples, the peel width is small. It can be seen that the undercoat treatment has good coating adhesion. However, Inventive Examples Nos. 1, 4 and 21 having a small amount of the undercoating treatment of 0.5 g / m ² or less have a slightly larger peeling width than the other inventive examples. In NaOH immersion, Comparative Example N
In o13, 14, and 25, the peeling of the adhesive tape caused the peeling of the coating film over the entire circumference of the steel wire, which indicates that the coating film adhesion was lower than that of the invention examples. CaCl ₂ , Ca (OH) ₂
In the immersion, except for Comparative Example No. 25, even when the coating film was forcibly peeled off, there was no evidence that the solution had entered.

[0030]

From the results of the evaluation of the above examples, the effect of improving the adhesion of the coating film and the corrosion resistance was observed by introducing the phosphoric acid compound layer under the coating film.

Claims (3)

[Claims] 1. A steel wire having a phosphoric acid compound layer having an adhesion amount of 0.5 to 10 g / m ² with respect to the surface area of the steel wire, and having a thickness of 10 μm or more on the strand or stranded wire of the steel wire. A coated steel wire having an excellent corrosion resistance, having an organic resin layer of 10 mm or less. 2. The coated steel wire having excellent corrosion resistance according to claim 1, wherein the organic resin layer is a thermosetting resin. 3. The coated steel wire according to claim 1, wherein the organic resin layer is a thermosetting resin powder coating.