JP3163908B2 - Polyolefin resin coated steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel pipe or a steel pipe pile for pipeline piping, which is excellent in high-temperature water resistance and high-temperature cathodic separation resistance.
The present invention relates to a polyolefin resin-coated steel material used for steel sheet piles, reinforcing bars, and the like.

[0002]

2. Description of the Related Art A polyolefin resin-coated steel pipe used for a pipeline or the like will be described as an example. A steel pipe exposed to a severe environment where corrosion resistance is required at a high temperature is generally covered with a jacket such as a polyolefin resin having high corrosion resistance as a corrosion protection layer. In this polyolefin-coated steel pipe, a modified polyolefin-based adhesive resin having excellent adhesiveness and mechanical properties is used as an adhesive layer between the jacket and the steel pipe.

The adhesion between the adhesive layer and the metal has a high primary adhesive force, but when exposed to a corrosive environment, the adhesive force is reduced and the polyolefin resin is peeled off. Further, since the pipeline is used for several decades or more, as a countermeasure against the corrosion, an electrolytic protection is performed in combination with a polyolefin resin coating. However, when a flaw reaching the steel surface is attached to the polyolefin resin during pipeline construction or the like, the steel surface of the flaw portion serves as a cathode, and alkali is generated by anticorrosion current. For this reason, the steel material is corroded by the anticorrosion current, but on the other hand, so-called cathodic exfoliation, in which the polyolefin-coated anticorrosion layer is exfoliated by the generated alkali, may be a serious problem.

As a countermeasure, it has been practiced to apply a primer such as a chromate treatment or an epoxy resin to the surface of a steel pipe as an adhesive base treatment.

[0005] In recent years, however, with the increase in the temperature of the in-stream conveyed product of the line pipe, high-temperature water resistance and cathode peeling resistance at high temperatures have become important issues.

As a countermeasure, JP-A-60-23039
In Japanese Patent Application Laid-Open No. H11-264, a method for producing a laminate in which an amino-based silane coupling agent is applied after a chromic acid-based chemical conversion pretreatment is proposed. Further, JP-A-63-243279 discloses that
An undercoating method and undercoating solution have been proposed in which silica and a water-soluble organic substance are added to chromic acid having a Cr ³⁺ / Cr ⁶⁺ of 1 or less during the chromate treatment.

[0007]

However, the undercoat treatments disclosed in JP-A-60-23039 and JP-A-63-243279 have an effect on water resistance and cathode peeling resistance near normal temperature. However, it is difficult to maintain the adhesive performance over a long period of time in a high temperature environment of 80 ° C, and the water resistance at high temperatures and the cathodic peeling resistance have not yet achieved sufficient performance. It has been desired to develop a polyolefin resin-coated steel material that is more excellent in high-temperature water resistance and high-temperature cathodic peeling resistance than coated steel material.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have repeatedly studied baking conditions after application of a chromate treatment agent and chromate treatment agents to which various organic reducing agents have been added. As a result, the cathodic peeling resistance and water resistance at high temperatures have a high correlation with Cr ³⁺ / total Cr in the chromate-treated film, and the more Cr ³⁺ in the chromate-treated film, the more the cathodic peeling resistance is improved. However, of all Cr in the chromate treatment film, Cr ³⁺
As the ^content increases, the amount of Cr ⁶⁺ decreases. When the ^content of Cr ⁶⁺ decreases too much, the water resistance decreases. Therefore, specific Cr ³⁺ /
By using all Cr, both the cathode peeling resistance and the water resistance at high temperatures are significantly improved.

In order to improve not only the cathodic peeling resistance and water resistance at a high temperature but also the primary adhesion and the stability of the chromate film in the presence of an alkali by making the chromate film further contain a specific amount of silica. Can be.

The present invention has been completed and the present invention has been completed.

The present invention relates to a resin-coated steel material in which a chromate-treated layer, a primer layer, a modified polyolefin adhesive resin layer, and a polyolefin resin-coated layer are sequentially laminated on the surface of a steel material. ^{3 +} /
The total Cr is 0.51 to 0.95, and if necessary, silica is added in the chromate film in a weight ratio of 0.5 to the total chromium.
It is a polyolefin resin-coated steel material containing -2.5.

[0012]

Next, the present invention will be described in detail.

The steel material used in the present invention may be carbon steel, low alloy steel, alloy steel such as stainless steel, or the like. Further, as the steel material, in addition to a steel pipe used for a line pipe or a pipe, a steel pipe having various shapes such as a steel pipe pile, a steel sheet pile, and a reinforcing bar can be applied.

The outer surface of the steel material to be coated is cleaned in advance by appropriately combining known physical means such as shot blasting, grid blasting and sand blasting, and chemical means such as pickling and alkali degreasing. Preferably.

Next, the limitation of the chromate layer of the present invention will be described. In the chromate film of the present invention, Cr3 ⁺ / total Cr in the chromate film is 0.51 to 0.95. Here, Cr ³⁺ means the weight converted to Cr ₂ O ₃ , and total Cr means the sum of the weights converted from Cr ³⁺ and Cr ⁶⁺ to Cr ₂ O ₃ and CrO ₃ .

Cr ³⁺ in the chromate coating / total Cr is 0.
If it is less than 51, the cathode peeling resistance at a high temperature is significantly reduced. On the other hand, if the ratio of Cr ³⁺ / total Cr exceeds 0.95, the water resistance decreases. Therefore, Cr ³⁺ in the chromate film
/ All Cr was set to 0.51 to 0.95. More preferably, it is 0.51 to 0.80.

The Cr ³⁺ in the chromate film / total Cr is 0.
The reason why the cathode peeling resistance and water resistance at a high temperature in the range of 51 to 0.95 are excellent is not clear, but is presumed as follows.

In the cathode peeling, an alkali is generated from a flaw portion of the polyolefin resin due to an anticorrosion current, and peeling is performed by the generated alkali. Since Cr ³⁺ is hardly soluble in alkali, the Cr ³⁺ in the chromate film is a dominant factor in the cathode peeling, and the more Cr ³⁺ is, that is, the ratio of Cr ³⁺ / total C
When r is 0.51 or more, excellent cathode peeling resistance is exhibited. on the other hand,
If Cr ³⁺ / total Cr exceeds 0.95, since the Cr ⁶⁺ in the chromate coating are excellent in shade pole peeling property becomes low, the water resistance self-repairing effect is reduced with the Cr ⁶⁺ is It is thought to decrease.

In order to make Cr ³⁺ / total Cr 0.51 to 0.95, the following means can be used.

In the chromate film, the reduction reaction from Cr ⁶⁺ to Cr ³⁺ proceeds rapidly at a temperature of about 110 ° C. or more. Therefore, by baking at 110 to 350 ° C. after the application of the chromate treatment agent, the amount of Cr ³⁺ in the film can be increased. Alternatively, it can also be carried out by reducing Cr ⁶⁺ to Cr ³⁺ by adding a reducing agent at the time of preparing a chromate treatment agent in advance.

Here, baking means that the chromate film may be heated in a step of heating the steel material before the chromate treatment, a step of heating the steel material after the chromate treatment, or a step of heating the steel material after the chromate treatment step. Heating may be performed in a curing step and / or a preheating step of coating the polyolefin resin. If the baking temperature is low, the rate of the reduction reaction from Cr ⁶⁺ to Cr ³⁺ also decreases, so when curing the primer or coating the polyolefin resin at a low temperature, add a reducing agent to the chromate treatment agent in advance. Therefore, it is preferable to increase the amount of Cr ³⁺ .

Examples of the reducing agent include methanol, ethanol, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol, dipropylene glycol, butanediol, hexanediol, and starch. Can be used. Preliminarily increasing Cr ³⁺ / total Cr by adding a reducing agent is suitable for coating a polyolefin resin without baking at a high temperature.

Further, in order to increase the primary adhesion and stabilize the chromate film in an alkali, silica is added to the chromate film of the present invention in a weight ratio of 0.5 to 2.5 to the total chromium in the chromate film. It can be contained. If the content of silica is less than 0.5 in terms of the weight ratio to the total chromium, the alkali resistance of the chromate film is reduced, and the high-temperature cathodic peeling resistance is reduced. On the other hand, if the content of silica exceeds 2.5 in terms of the weight ratio to the total chromium, the proportion of silica in the chromate film becomes too large, and the flexibility of the chromate film is reduced. Decrease.

Here, silica refers to, for example, Aerosil 200, Aerosil 300, Aerosil OX050, Aerosil 380 manufactured by Nippon Aerosil Co., Ltd., Nip Seal E200, Nip Seal E200A manufactured by Nippon Silica Co., Ltd.
Fine particle silica such as nip seal 300A and nip seal L300, which is colloidal when dispersed in water. One or more of these fine particle silicas can be used.

The chromate-treated layer has a chromium adhesion amount (total chromium amount) of 50 mg / m ² to 10 from the viewpoint of high-temperature water resistance, high-temperature cathodic peel resistance, and prevention of a decrease in primary adhesion.
It is preferably set to 00 mg / m ² .

The primer layer includes a thermosetting primer containing a known epoxy resin and a curing agent as main components and optionally containing an inorganic pigment. Typical epoxy resins include bisphenol-type glycidyl ether, phenol novolak-type glycidyl ether, and the like, and examples of the curing agent include amine-based curing agents, disimine diamide-based curing agents, and imidazole-based curing agents. As the inorganic pigment, silica, alumina, talc, mica, chromium oxide and the like can be used, and if necessary, other additives, for example, a coloring pigment may be added. The form of the primer may be a two-part curing type primer or a one-part type primer in which a curing agent is microencapsulated. In addition to the epoxy resin, a primer containing urethane as a main component can be used, but an epoxy resin is preferable from the viewpoint of corrosion resistance.

[0027] A polyolefin resin coating layer is provided on the steel material subjected to the above-mentioned base treatment via a modified polyolefin adhesive resin layer. Since the polyolefin resin has relatively low adhesiveness, a modified polyolefin is interposed as an adhesive layer at the interface between the primer and the resin layer, and the resin layer is coated on the steel material via the adhesive. Maleic anhydride-modified polyolefin resin is a preferred adhesive because it exhibits particularly high adhesiveness.
In addition, adhesives based on ethylene copolymers (eg, ethylene / vinyl acetate copolymer), acrylic acid or carboxylic acid-modified polyolefin adhesives and the like can also be used. The thickness of the adhesive is not particularly limited and varies depending on the type of the adhesive, but is generally about 0.1 to 0.5 mm.

As the polyolefin resin constituting the resin coating layer, any of the polyolefin resins generally used for coating steel materials can be used. For example, any of low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, etc. may be used, and a small amount of another olefin or vinyl monomer (eg, propylene, vinyl acetate, acrylic acid, acrylate ester) is copolymerized. May be. In particular, when coating with polypropylene, a polypropylene containing 10 to 50% of an ethylene component is preferable, and particularly a product obtained by block copolymerizing a polyethylene component is more preferable. Polypropylene is
Easily embrittled at low temperatures, due to the effect of the polyethylene part,
This is because low-temperature embrittlement is significantly improved.

The polyolefin resin may contain conventional additives such as antioxidants, ultraviolet absorbers, pigments and fillers. In particular, the inclusion of an antioxidant is preferred.

The method of coating the polyolefin resin layer via the adhesive layer can be performed by a conventional method using a melt-round die co-extrusion coating, a melt T-die extrusion coating, or the like.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Carbon steel pipes for piping with a diameter of 216 mm (JIS
G 3452) was adjusted to a rust removal degree Sa3 by grid blasting, and while moving on a transport roll at a pipe moving speed of 3 m / min, the outer surface temperature of the steel pipe was heated to 40 ° C. using an induction heater. Chromium adhesion amount 250mg /
Chromate treatment was performed so as to obtain m ² . The chromate used was Cosmer 100 (manufactured by Kansai Paint Co., Ltd .: C
r ³⁺ / total Cr = 0.4) diluted with water (A in Table 1), and further added to Cr ³⁺ / total C in the chromate treatment solution.
In order to increase r, glycerin was added to Cosmer 100 to make Cr ³⁺ / total Cr 0.5 (see Table 1,
B) and three types of chromate treatment agents having Cr ³⁺ / total Cr of 0.7 (C in Table 1) were used.

Further, for a part of the chromating agent of (A), fine-particle silica (Nippon Aerosil Co., Ltd .: Aerosil 200) was added.

After the above-mentioned chromate treatment agent was applied, a chromate treatment layer was formed by heating and baking to a temperature shown in Table 1 using an induction heater.

Thereafter, in order to apply the primer, the mixture is allowed to cool or heat to the primer application temperature, then a two-pack type amine-cured epoxy primer (a) as a thermosetting primer, a microencapsulated imidazole-based curing agent and a dicyandiamide curing agent. Was applied so as to have a film thickness of 20 μm, respectively, using a one-component primer (b) containing Further, using an induction heater, the steel pipe was heated to the preheating temperature shown in Table 1 and hardened to form a primer layer. Immediately thereafter, a maleic anhydride-modified polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., Admer NE060) was used. 0.3
A 2.2 mm-thick polyethylene resin (manufactured by Showa Denko KK, S4002EX) was coated via an mm-thick adhesive layer to obtain an outer polyethylene resin-coated steel pipe.

Using a test piece cut from the resin-coated steel pipe, the chromate-treated film was subjected to ESCA analysis to measure Cr ³⁺ / total Cr in the chromate film. Table 1 shows the results.

The above chromating agents (A), (B),
(C) and a sample cut into 150 mm × 70 mm from a resin-coated steel pipe manufactured using the primers (a) and (b), using a hot salt water immersion test (immersion temperature of 90
C., 3% NaCl, 100 days), and after the test, the width of water penetration from the end face of the sample was measured to evaluate the secondary adhesion. In addition, the coating layer of the sample has a diameter of 5 mm reaching the steel surface.
The artificial flaw was placed in contact with a 3% NaCl salt solution kept at 80 ° C., and a voltage of −1.5 V was applied to the saturated calomel electrode.
Was maintained for 15 days, and the peeling distance from the artificial flaw after 15 days was measured to evaluate the cathode peeling resistance. Table 1 shows the results.

[0037]

[Table 1]

As shown in Table 1, in Examples 1 to 18 of the present invention, 90
No peeling was observed after 100 days of immersion in 3% NaCl and hot salt water at 0 ° C, and the cathode peeling resistance after 15 days at 80 ° C also showed extremely excellent performance. Therefore, the resin-coated steel pipe of the present invention has excellent high-temperature water resistance and cathodic peeling resistance.

On the other hand, in Comparative Examples 22 to 27, when Cr ³⁺ / total Cr in the chromate film is less than 0.51, the cathode peeling resistance is lowered, and when it exceeds 0.95, the water resistance is poor. Is declining.

Furthermore, Examples 19 to 21 of the present invention containing fine-particle silica also have excellent high-temperature water resistance and cathodic peeling resistance.

[0041]

The polyolefin resin-coated steel material according to the present invention is a polyolefin having an unprecedented high-temperature water resistance and high-temperature cathodic peeling resistance by setting the Cr ³⁺ / total Cr in the chromate-treated film to a specific range. A resin-coated steel material can be obtained.

Further, by containing silica, a polyolefin resin-coated steel material having excellent primary adhesion can be obtained.

[0043]

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 15/08 C23C 22/30

Claims (2)

(57) [Claims] 1. A resin-coated steel material in which a chromate treatment layer, a primer layer, a modified polyolefin adhesive resin layer, and a polyolefin resin coating layer are sequentially laminated on the surface of a steel material, wherein Cr ³⁺ / total Cr in the chromate coating is zero. .51 to 0.95
A polyolefin resin-coated steel material characterized by the following. 2. A steel material coated with a polyolefin resin, wherein the chromate film according to claim 1 further contains silica in a weight ratio of 0.5 to 2.5 with respect to the total chromium.