JPS602354A - Plastic coated steel pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plastic-coated steel pipe that has a modified polyolefin resin layer and a polyolefin resin layer and has excellent adhesion and high-temperature corrosion resistance.

As shown in Figure 1, conventional plastic-coated steel pipes are made by first removing scale by pickling or plasticizing the surface of the steel pipe, and then applying a chromate-based chemical conversion treatment liquid to the outer surface of the material steel pipe A.・There are products in which a baked layer B is formed, and then a reaction-curing epoxy primer C is applied and cured before or after heating this steel pipe, and then a modified polyolefin resin layer and a polyolefin resin layer are sequentially coated. .

However, such plastic-coated steel pipes are unfavorable due to the handling of the chromate-based chemical conversion slurry applied as a pre-treatment agent and the contamination of the working environment during the application and φ steps. Pollution prevention measures are also necessary.

■ It is necessary to heat the steel pipe to a high temperature in order to bake the chromate chemical treatment solution or improve its adhesion with the epoxy primer, but this places a heavy burden on the cooling process after plastic coating and hinders productivity. appears.

There are various problems that need to be solved, such as, to eliminate this problem, if a method is adopted that does not apply any chromate-based chemical conversion treatment, even if it is possible to maintain adhesion performance at high temperatures, A contradictory phenomenon appears in which the corrosion resistance performance deteriorates.

As a result of various studies to solve the above-mentioned disadvantages, the present invention has been developed by using a specific silane coupling agent as a pretreatment agent on the surface of the steel pipe, and then layering a reaction-curing epoxy primer on top of it. The inventors discovered that it is possible to make a plastic steel pipe that is very strong and has excellent corrosion resistance at high temperatures, which led to the present invention.

The present invention provides a plastic coating characterized in that a boxy-based silane coupling agent layer, a layer of reaction-curing epoxy primer, a modified polyolefin resin layer, and a polyolefin resin layer are laminated on the outer surface of a steel pipe in order from the inside. It concerns steel pipes.

The epoxy silane coupling agent used in the present invention is
It is used in the form of an aqueous solution or an aqueous dispersion, and the campling agent used is one formed by the following formula.

AR'5jB3 +3J-120-+AR'Si(0I
l) A functional group having an epoxy group such as '3 +3HB, B
-OR.

-0CORS R is a lower alkyl group, R' is -(CH,
)-~n is 0 to 6) When using the above epoxy-based silane coupling agent, the concentration of the aqueous solution should be 0.5 to 10% by weight from the viewpoint of expected performance, storage stability, and price.
Moreover, it is desirable to use it within about one week after preparing it to the working concentration.

Any reaction-curing epoxy primer can be used as long as it improves adhesion to the modified polyolefin resin layer covering the surface layer, but based on comprehensive judgment from various perspectives, epichlorohydrin-bisphenol A It has been found that the best results are likely to be obtained when using a two-component hot-melting epoxy resin consisting of:

As the modified polyolefin 4-layer resin, modified polyethylene,
The material may be selected from among modified polypropylene, ethylene-ethyl acrylate copolymer (4:EA), a mixture of the above-mentioned EEA and polyethylene, or modified or modified derivatives thereof.

Further, the polyolefin resin forming the outermost layer includes polyethylene and polypropylene.

The plastic-coated steel pipe according to the present invention can be used, for example, in a second
It can be obtained by the production line shown in the figure. That is, a steel pipe 6 that has previously been passed through an epoxy silane coupling agent coating device 1 and dried in a dryer 2 is passed through a reaction-curing epoxy primer coating device 4 to coat the surface with a primer, and then heated using a heating device 5. After curing, the modified polyolefin resin is extruded using an extrusion die 6, and the polyolefin resin is extruded using an extrusion die 7, which are sequentially coated onto a steel pipe 6, and passed through a cooling device 8 to form a product.

In the case of such a production line, it is sufficient that an epoxy-based silane coupling agent layer is formed on the surface of the steel pipe 3 and dried before it reaches the primer coating device 4. The drying method can be arbitrarily selected from conventionally known methods and may be either online or offline.

Specifically, for example, coating methods include a roll transfer method, a soaking and ironing method, a shower ironing method, and a dipping method. For example, there is also a coating method as shown in FIG. 6. In the figure, numeral 9 is a restorable straining member such as rubber. The drying method is to heat the steel pipe in advance to about 80-100℃, or apply it to the steel pipe at room temperature and then apply it to a temperature of 80-100℃.
It is also possible to use a method of heating the steel pipe to about 0° C. or higher, passing it through a hot air circulation furnace, an infrared heating furnace, etc., or a composite drying device using a combination of these.

In Fig. 2, the modified polyolefin resin extrusion die 4 and the polyolefin resin extrusion die 5 are separated, but a coextrusion die that can extrude two types of molten resin simultaneously, albeit separately, is used. It's not even a moat that's good.

Furthermore, the method for forming the modified polyolefin resin film is not limited to extrusion, and for example, a powder coating method may be employed.

A partial cross section of the plastic-coated steel pipe of the present invention obtained as described above is as shown in FIG.
indicates a steel pipe material from which scale has been removed by pickling or blast treatment, G indicates an epoxy silane camping agent layer, H indicates a single layer of reaction-curing epoxy primer, C indicates a modified polyolefin resin layer, and J indicates a polyolefin resin layer. .

In addition, H in the figure is 20 to 100 μm, SI is 0.05 to 0.5
-1J ii Satisfactory results can be obtained if the thickness is approximately 1.0 to 10 mm.

EXAMPLES The present invention will be specifically explained below with reference to Examples.

Example A plastic coated steel pipe was manufactured under the following conditions.
; 80A glint blasting 5.5m length pretreatment*1, 1. Epoxy silane camping agent,
6% aqueous solution 2, amino-based silane coupling agent, 3% aqueous solution 6, chromate-based chemical conversion treatment solution, (*2) 4, unused primer *3; 2-component warm-type epoxy resin coating amount: approx. 4
0 g/ff1' wl coating resin; acid anhydride kraft polyethylene, 0.2
Thick high-density polyethylene 2.0 thickness *1: Drying conditions 80℃ x 1 minute, 150℃ x 2/1 standard *2: m fabric weight Approximately 300 rng/m' in terms of chrome*
3: Drying conditions 150°C x 1 minute Adhesion and high test method of the obtained plastic coated steel pipe Adhesion test: 26°C, tensile speed 50”% 180 in winter
° Beer method cathode peeling trial: 6% saline, initial Holity 6.2 end φ
, -1.5V, 40℃ x 60 days, 60℃ x 60 days From the results in the table, it is recognized that the adhesion strength shows good values regardless of the type or presence of pretreatment agent. In terms of high-humidity cathodic stripping performance, it was confirmed that there was a significant difference depending on the presence or absence of pretreatment or the type of pretreatment agent, and that the use of the epoxy-based silane coupling agent of the present invention exhibited extremely excellent effects. Ta.

Particularly when the drying temperature of the pretreatment agent is 80° C., the present invention exhibits effects that are far superior to others.

Furthermore, in the case of using an amino-based coupling agent, which is not covered by the present invention, the unexpected result was that it was inferior to the case of No. 4 (not used).

As described above, the present invention is characterized in that, in plastic-coated steel pipes, an epoxy-based silane coupling agent is used in the pretreatment of the steel pipes, and an epoxy primer is used as a primer, but at this time, no epoxy primer is used at all. In some cases, the adhesion between the modified polyolefin resin layer is poor (6”/cm under the same conditions as the above test).
The results obtained are as follows:

[Brief explanation of drawings]

Figure 1 is a partial cross-sectional view of a coated steel pipe made by the conventional method, 3...
Steel pipe, 1... Primer coating device 5... Heating device, 7... Extrusion die, 8... Cooling device. Agent Patent Attorney Sanro Kimura

Claims (1)

[Claims] A plastic-coated steel pipe characterized in that an epoxy silane coupling agent layer, a reaction-curing epoxy primer layer, a modified polyolefin resin layer, and a polyolefin resin layer are laminated on the outer surface of the steel pipe in order from the inside.