JP5463999B2 - Manufacturing method of inner surface coated steel pipe for water piping - Google Patents

Description

  The present invention relates to a method for producing an inner surface-coated steel pipe for water piping that has high adhesion between a resin layer and a steel pipe and is excellent in corrosion resistance.

  2. Description of the Related Art Conventionally, pipes used for drainage or the like have been used internal hard vinyl chloride coated steel pipes in which a vinyl chloride resin is attached to the steel pipe inner surface in order to impart corrosion resistance to the steel pipe inner surface. However, since vinyl chloride resin has low impact resistance at low temperatures, the inner surface of the internal hard vinyl chloride coated steel pipe is not suitable for use in water pipes, etc. The covering layer may be damaged. Furthermore, in recent years, the generation of harmful substances when disposing of vinyl chloride resin, the load of separating steel pipes and vinyl chloride resin for placing vinyl chloride resin on the treatment route, etc. are large, and as a material with a large environmental load Recognition is also leaning.

  Other than the above coated steel pipe, an inner polyethylene coated steel pipe in which an inner coating layer is formed by powder coating in a heated state on the inner surface of a steel pipe that has been subjected to surface treatment such as chemical conversion treatment or primer treatment of polyethylene resin powder, etc. (For example, Japan Water Works Association Standard JWWA K132). However, this inner surface polyethylene-coated steel pipe may peel off from the end due to water contact at the end of the pipe depending on the environment.

  Further, a method is known in which a cross-linked polyethylene pipe is imparted with a shape restoring property and is heated and restored in a steel pipe to expand the diameter and coat the inner surface (see, for example, Patent Document 1). However, the method described in Patent Document 1 has a problem that sanitary properties of tap water cannot be ensured because there is an elution component from the crosslinking agent.

  In addition, a method of covering the inner surface of a steel pipe by imparting a shape restoring property to the polyethylene pipe is also disclosed (for example, see Patent Document 2). However, in the method described in Patent Document 2, it is necessary to once produce a resin tube made of polyethylene or the like and add a shape restoration property or the like to the resin tube. Furthermore, uniform inner surface coating becomes difficult at industrial speeds.

JP 2001-9912 A JP 2002-257265 A

As described above, pipes used for water pipes such as drainage are usually piped using pipe end anti-corrosion joints or the like in order to prevent corrosion at the pipe end where the interface between the steel pipe and the inner surface coating layer is exposed. . However, pipe ends may be exposed to a wetted environment due to defects during construction or long-term use, and the inner surface coating layer is required to have peel resistance in a wide temperature range from low temperature to high temperature. And if the peel resistance of the inner surface coating layer is low, when the pipe end is exposed to a wetted environment, the inner surface coating layer is peeled off and the peeled portion of the steel pipe is rusted. Become.
In view of such circumstances, the present invention advantageously solves the above-described problems, and is an inner surface-coated steel pipe that does not use a vinyl chloride resin, and has an inner surface coating for water pipes that has high peel resistance even in a wetted environment in a wide temperature range. It aims at providing the method of manufacturing a steel pipe.

  In order to achieve the above-mentioned object, the present inventors paid attention to the corrosion factors mixed in the manufacturing process of the inner surface coated steel pipe for water piping, and examined their influences. As a result, it was discovered that the mixing of chloride ions and moisture had a significant effect on the peeling resistance of the inner surface coating after production, and the water piping with greatly improved peeling resistance by controlling the amount of these mixing It was found that the inner surface coated steel pipe can be manufactured stably.

The summary of the method for producing an inner surface-coated steel pipe for water piping according to the present invention is as follows.
[1] It has a chemical conversion treatment film layer formed by performing a phosphate chemical conversion treatment on the inside of a steel pipe, and has a primer layer having an average thickness of 10 to 40 μm on the upper layer of the chemical conversion treatment film layer, A method for producing an internally coated steel pipe for water piping having a modified polyethylene resin layer on the primer layer, wherein the chloride ion concentration on the inner surface of the steel pipe before forming the primer layer is attached to sodium chloride. A method for producing an inner surface-coated steel pipe for water piping, wherein the amount is 3 mg / m ² or less in terms of amount.
[2] The method for producing an inner surface-coated steel pipe for water piping according to [1], wherein, when the primer layer is formed, the water content in the primer solution to be applied is 0.5% by mass or less.
[3] In the above [1] or [2], when forming the modified polyethylene resin layer, the water content in the polyethylene powder to be coated is 0.05% by mass or less. Of manufacturing inner surface-coated steel pipes.

  ADVANTAGE OF THE INVENTION According to this invention, the inner surface coated steel pipe for water piping with high peeling resistance is obtained. The inner surface-coated steel pipe for water piping according to the present invention has higher adhesion between the inner surface coating layer and the steel pipe than the conventional inner surface polyethylene-coated steel pipe, and the end of the pipe has been exposed to a wetted environment due to poor construction or long-term use. Sometimes more durable.

It is a figure which shows typically a part of inner surface coated steel pipe for water piping of this invention.

The present invention is described in detail below.
A part of the internally coated steel pipe for water piping according to the present invention is schematically shown in FIG. As shown in FIG. 1, the inner surface coated steel pipe for water piping according to the present invention has an average thickness of a chemical conversion coating layer 2 formed by subjecting the inside of a steel pipe 1 to a phosphate chemical conversion treatment and an upper layer of the chemical conversion coating layer 2. A primer layer 3 having a thickness of 10 to 40 μm,
It is an inner surface-coated steel pipe for water pipes having a modified polyethylene resin layer 4 as an upper layer of the primer layer.
The reason why the coating layer has the above configuration and order is as follows. Since the modified polyethylene resin as the uppermost layer is nonpolar, it does not directly adhere to the steel pipe surface. Therefore, in the present invention, adhesion is ensured by providing a chemical conversion film layer and a primer layer between the steel pipe and the modified polyethylene resin layer.
1) Steel pipe Although it does not specifically limit as a steel pipe which has the said coating layer, The outer diameter is about 10-170 mm, length is about 4-6 m normally, and thickness uses about 1.0-6.0 mm. Is preferred. The steel pipe used in the present invention may be subjected to blasting, pickling, chemical conversion, plating, primer treatment, or resin coating on the outer surface of the steel pipe. Further, the inner surface of the steel pipe is usually subjected to a blasting process, a pickling process, etc. so that a subsequent chemical conversion process or the like can be easily performed.

2) First, formation of a chemical conversion treatment film layer formed by performing a phosphate chemical conversion treatment will be described.
The chemical conversion treatment film layer of the present invention is obtained by subjecting a steel pipe to a phosphate chemical conversion treatment such as zinc phosphate and zinc calcium phosphate alone or in combination. The chemical conversion treatment can be performed by spraying or pouring the chemical conversion treatment liquid on the inner surface of the steel pipe, or by immersing the steel pipe in a bath of the chemical conversion treatment liquid, and an accelerator or the like may be used as appropriate. Moreover, it can also carry out in the state heated at 60 degreeC or more.

  The phosphate-based chemical conversion treatment and the pickling treatment performed as a pretreatment for the chemical conversion treatment are water-based treatments, and these treatments are manufacturing steps that can cause adhesion of chloride ions to the inner surface of the steel pipe. When chloride ions adhere to the inner surface of the steel pipe, the chloride ions are concentrated between the steel pipe and the primer layer, so that moisture is absorbed and rust grows. As a result, peeling of the inner surface coating layer occurs and the peeled portion of the steel pipe rusts, resulting in red water and the like.

Therefore, in this invention, the chloride ion density | concentration in the inner surface of the steel pipe before forming a primer layer shall be 3 mg / m < ² > or less converted into sodium chloride adhesion amount. Preferably it is 1 mg / m ² or less. After the chemical conversion treatment, before forming the primer layer, if the chloride ion concentration on the inner surface of the steel pipe exceeds 3 mg / m ² in terms of the amount of sodium chloride, rust growth under the inner surface coating layer is promoted. The peel resistance will deteriorate.

For example, by reducing the chloride ion concentration in the aqueous solution used as the final cleaning solution to 30 ppm or less, the chloride ion concentration on the inner surface of the steel pipe before forming the primer layer is converted to 3 mg / m ² in terms of sodium chloride adhesion. It can be as follows.

  Further, the chloride ion concentration on the inner surface of the steel pipe can be measured by the attached salt wiping method. In this method, the area defined by masking is wiped off with gauze soaked in distilled water, and the salt attached thereto is eluted in a certain amount of distilled water and its concentration is measured.

3) Next, formation of a primer layer having an average thickness of 10 to 40 μm laminated on the upper layer of the chemical conversion coating layer will be described.
The primer layer is formed by coating a primer solution obtained by diluting an epoxy resin and a curing agent on a chemical conversion treatment layer.
The epoxy resin used in the primer solution is preferably a bisphenol type epoxy resin. Inorganic pigments such as titanium oxide, silica, talc, muscovite, chromium oxide, and zinc phosphate may be added to the epoxy resin. Further, in order to improve the adhesiveness with the epoxy resin, the inorganic pigment may be subjected to chemical treatment such as silane coupling treatment.
The curing agent used for curing the epoxy resin is preferably dicyandiamide or a derivative thereof, or an acid anhydride compound and a derivative thereof. The blending ratio of the epoxy resin and the curing agent is appropriately set according to the purpose. In consideration of the glass transition temperature of the cured product, it is preferable to set the compounding ratio within a range in which the glass transition temperature of the cured product does not decrease.
Further, it is preferable to use a primer solution prepared by diluting an epoxy resin and a curing agent to 20 to 35% by mass with a solvent. And it is preferable to apply | coat a primer liquid to the steel pipe inner surface by methods, such as pouring into a steel pipe inner surface and spray-coating. It is preferable to heat the steel pipe before painting, or after painting, the steel pipe is heated by a method such as hot air or high-frequency induction heating, whereby the coated thermosetting resin composition is cured, and the primer layer is Can be formed. In addition, as a solvent used for solvent dilution of an epoxy resin and a hardening | curing agent, all the solvents normally used, such as an alcohol solvent, an ether solvent, and an ester solvent, are suitable.

  Moreover, the average thickness of the primer layer which consists of the above shall be 10-40 micrometers. If the thickness is less than 10 μm, sufficient adhesion may not be obtained. On the other hand, if the thickness exceeds 40 μm, dripping occurs during application and the film thickness tends to be non-uniform. This is because the adhesion is also saturated.

  In the step of forming the primer layer, when moisture is contained in the primer solution, it affects rust generation under the paint on the inner surface of the steel pipe. If the water content in the primer solution exceeds 0.5% by mass, rust growth is remarkably promoted, so the water content is preferably 0.5% by mass or less.

  The water content in the primer solution is managed by controlling the humidity at the location where the primer solution tank is installed and balancing it.

The water content in the primer solution can be measured by the Karl Fischer titration method defined in JIS K 0068 “Method for measuring water content of chemical products”.
4) Next, formation of the uppermost modified polyethylene resin layer will be described.
As the modified polyethylene resin, linear low-density polyethylene, high-pressure method low-density polyethylene, or high-density polyethylene graft-modified with an acid anhydride such as maleic anhydride can be used. The amount of modification is usually preferably 6% by mass or less, and can be modified by a conventional method. Usually, the melt index is preferably 2 or more and 8 or less.
In addition, the modified polyethylene resin may be mixed with other resins containing the above resin composition as a main component within a range not impairing the performance of the present invention, and an antioxidant or a pigment can be added as necessary. .
The modified polyethylene-based resin layer can be formed by coating the modified polyethylene powder with the steel pipe heated to 210 ° C. or higher and, if necessary, keeping the heat at 140 ° C. or higher.
The thickness of the modified polyethylene layer is preferably from 0.3 mm to 1.0 mm, more preferably from 0.5 mm to 0.9 mm. If it is thinner than 0.3 mm, the modified polyethylene layer is likely to be perforated due to wrinkles at the time of construction, and the highly water-permeable epoxy resin layer is exposed, which may impair corrosion resistance. If it is thicker than 1.0 mm, the efficiency in powder coating is lowered.
In addition, as a modified polyethylene resin layer, a known linear low density polyethylene, or a high pressure method low density polyethylene, or a polyethylene powder such as high density polyethylene is similarly coated on the modified polyethylene resin layer, A layer in which the total thickness of the modified polyethylene layer and the polyethylene layer is 0.5 mm to 1.0 mm may be formed. At this time, a copolymer resin of ethylene and a monomer having an unsaturated bond such as an ethylene-vinyl acetate copolymer resin or an ethylene-acrylic ester copolymer resin cannot be used because its softening temperature becomes too low. .

  In the step of forming the modified polyethylene-based resin layer, if the polyethylene powder contains moisture, it affects rust generation after coating the inner surface of the steel pipe. If the water content in the polyethylene powder exceeds 0.05%, the growth of rust is remarkably promoted, so the water content is preferably 0.05% or less.

  The water content in the polyethylene powder is managed by controlling and equilibrating the humidity at the location where the polyethylene powder tank is installed.

  The water content in the polyethylene powder can be measured by the Karl Fischer titration method defined in JIS K 0068 “Method for measuring water content of chemical products”.

Next, examples of the present invention will be described.
A modified polyethylene resin inner surface coated steel pipe (inner surface coated steel pipe for water piping) was manufactured, and a test piece was collected from the obtained inner surface coated steel pipe for water piping to investigate the anticorrosion performance. Test pieces 1 to 8 correspond to examples of the present invention, and test pieces 9 to 12 correspond to comparative examples. Details are shown below.

A steel pipe (inner diameter 27.6 mmφ, outer diameter 34 mmφ × 4 m) subjected to pickling treatment was immersed in a zinc calcium phosphate treatment solution at 80 ° C. and subjected to chemical conversion treatment. Next, a primer solution was applied to the inside of the steel pipe so as to have an average thickness of 25 μm, and was heated and cured at 130 ° C. to form a primer layer. The primer solution used was a bisphenol-type epoxy resin as the main agent and dicyandiamide as the curing agent, diluted with thinner to 20% by mass. The steel pipe was then heated to 230 ° C. After heating, the inner surface of the steel pipe was powder-coated with a powdered modified polyethylene resin obtained by modifying a linear low density polyethylene having a density of 0.923 and a melt index of 4.9 with maleic anhydride, and having a thickness of 0.6 to 0 A modified polyethylene resin layer having a thickness of 8 mm was formed. After coating, heat was retained in a furnace at 150 ° C. or higher, and then naturally cooled to obtain an inner surface coated steel pipe.
The amount of salt adhering to the inner surface of the steel pipe was changed by changing the amount of sodium chloride in the wash water after the chemical conversion treatment. The actual adhesion amount was confirmed by wiping analysis on the inner surface of the steel pipe.
The water content of the primer solution and the polyethylene powder was prepared by equilibrating each in a humidity chamber, and was confirmed by analyzing what was used in the production.
The anticorrosion performance was evaluated for hot water resistance.
After the production, the inner surface-coated steel pipe that had passed for one month was cut to a length of 50 cm and immersed in 3% by mass saline solution at 60 ° C. After 28 days, the state of peeling of the coating layer at the end of the steel pipe was observed, and “◎” indicates that there was no peeling from the end, “◯” indicates that it was less than 5 mm, and “x” indicates that it was 5 mm or more.

  The evaluation results obtained as described above are shown in Table 1 together with the experimental conditions.

  It can be seen that the example of the present invention is excellent in hot water resistance. On the other hand, in the comparative example, the hot water resistance is poor.

  The inner surface-coated steel pipe for water piping according to the present invention has excellent anticorrosion performance, so that it is optimal as an inner surface-coated steel tube used for, for example, when used in cold districts for water piping or when left outdoors during construction. .

1 Steel pipe 2 Chemical conversion coating layer 3 Primer layer 4 Modified polyethylene resin layer

Claims (3)

The steel pipe has a chemical conversion coating layer formed by subjecting it to a phosphate chemical conversion treatment. An upper layer of the chemical conversion coating layer has a primer layer having an average thickness of 10 to 40 μm. The upper layer is a method for producing an internally coated steel pipe for water pipes having a modified polyethylene resin layer, and the chloride ion concentration on the inner surface of the steel pipe before forming the primer layer is converted to the amount of sodium chloride attached 3 mg / m < ² > or less, The manufacturing method of the inner surface coated steel pipe for water piping characterized by the above-mentioned.   The method for producing an inner surface-coated steel pipe for water piping according to claim 1, wherein when forming the primer layer, the water content in the primer solution to be applied is 0.5 mass% or less.   The inner surface-coated steel pipe for water piping according to claim 1 or 2, wherein the moisture content in the polyethylene powder to be coated is 0.05% by mass or less when forming the modified polyethylene resin layer. Production method.

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