JPS599036A - Method of coating cylindrical metallic shape with thermoplastic synthetic resin - 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 invention relates to a method for coating metal moldings, in particular steel tubes, with a thermoplastic synthetic resin, in particular polyethylene, according to the concept of claim 1.

The following is known from West German Patent Application Publication No. 1261431: That is, first epoxy resin/
The curing agent-mixture is applied and cured, and a small amount of polyethylene is sprayed onto it with a flame jet gun, and more polyethylene is sprayed after the epoxy film is cured.

In this case, the temperature of the metal surface must not exceed 100°C. According to an embodiment of the invention, curing of the epoxy resin film is carried out at a temperature of up to 60C for about 24 hours. Due to the large throughput of coating steel in large companies, this method is uneconomical due to the long curing time of the epoxy resin.

It is known from DE 1965802 to coat steel pipes with polyethylene. First, the steel tube is heated to a working temperature, preferably above 100C, and at this temperature an undercoat film of eboxy resin which becomes a network structure is formed. This is followed by extrusion wrapping a layer of ethylene copolymer around the cured epoxy resin membrane.
A layer of polyethylene is then extruded and wrapped around it. In this case, the first layer acts as an adhesive for the polyethylene layer. Again, throughput is limited by the downtime required to volatilize the reactants formed from the networked epoxy resin. This method is mainly applied to pipes with a diameter of about 600 m+ or less.

Furthermore, an undercoat film made of a curable eboxy resin mixture is formed on the surface of the steel tube at a temperature of 70-90C and has a heat-sensitive inner film, and on top of that, a layer of ethylene copolymer and a layer of polyethylene are coated with a double hose. It is known that extrusion molding is performed in the shape of (West German Patent No. 2222911).

After completion of the coating, the tube is allowed to remain for 3 minutes before being cooled to room temperature. At this time, the epoxy resin film has not yet completed curing. Completion of curing is achieved by standing at room temperature for approximately 24 hours at 65% humidity. Therefore, large amounts of processing often become a hindrance. Deviations from the above-described performance parameters of the process significantly slow or otherwise impede curing.

Furthermore, the following is known from DE 2257135: In other words, the surface of the steel pipe to be coated is
C. and the epoxy resin/curing agent mixture containing the solvent is applied electrostatically to a thickness of approximately 100 μm. Next, a thermoplastic synthetic resin coating consisting of an inner ethylene copolymer layer and an outer polyethylene layer is formed on this undercoat film.

The coated tube is then cooled with water to an average tube temperature of 40C. Next, the core of the tube was heated to an average temperature of 100C by electrical induction.
Heat to. At that time, the surface temperature of the tube reaches about 240C. At this temperature, the epoxy resin undercoat film will harden in a few seconds. Next, cool the coated tube at room temperature.
The formation of a 12 m long tube was determined by the speed of the tube before forming the hose-like layer mentioned in the embodiment of this invention (
20 m/miy+), film thickness and tube temperature documentation are often not sufficient to volatilize the solvent from the epoxy resin/curing agent mixture. However, the strip-shaped double layer
This method is very suitable for wrapping and coating tubes with a diameter of 0 ms or more.

The problem of the present invention is to improve the known method of coating tubes with hose-like double layers and to increase the coating speed of tubes, especially tubes with nominal diameters from 50 to 500 mm, in order to achieve high throughput. We are pursuing the possibility of speeding up the process.

The problem of the invention is solved by the features of patent claim 1. Advantageous additions are described in the implementation section.

By strictly adhering to the parameters of the process of the invention, in particular those of the layer volume relationship between the evoxy resin-basecoat and the thermoplastic synthetic resin coating, the amount of heat required for the curing of the specific eboxy resin can be reduced to a substantial fraction of the synthetic resin coating. It is estimated from the thickness and the heating temperature of at least 165CK. Additional heat treatment of the coated tube is no longer required.

Curing is independent of environmental temperature and relative humidity.

The invention will be explained in more detail by the following examples.

A steel tube with a length of 6 m and a diameter of 150 fins, without a heat-sensitive inner membrane, is heated electrically inductively to 17 (I?). For this purpose, the steel tube is moved through a forging coil at a speed of 20 m/min. The tube is then transported at a speed of 20 m/h through the irradiating infrared light, and the surface of the tube is further exposed to about 200 m/h.
heated to C. Subsequently, using a powdered precondensed epoxy resin/curing agent mixture, 30~
A film is formed by electrostatic coating in an amount that gives a film thickness of 50 μm.

At this time, the Eboogishi resin/curing agent-powder mixture is melted onto the tube surface. Heat-sensitive inner film force (approximately 110 rKL force on the tube surface) If it is not possible to heat the tube surface, the melting of the epoxy resin/hard heat-powder mixture will first occur, and a non-adhesive film will form. Ru. As the electrostatic coating forms a delicate epoxy resin/hardener film, the tube passes through a second ring of infrared radiation.
It is carried at a speed of 0m/mix and is heated by infrared light at about 20o.
CK is heated. This results in the formation of a cohesive undercoat film even when a heat-sensitive inner film is present.

1 from the epoxy resin-priming film by infrared irradiation.
The free reaction product 752 volatilizes within 0 seconds, and no curing of the undercoat film occurs until then. Instead of infrared irradiation, it is also possible to heat the epoxy resin-priming film by, for example, short-wave radiation. After exiting the second infrared radiation device, a thermoplastic double hose of ethylene copolymer and polyethylene is extruded onto the tube surface, with 1
4 from the epoxy base coat at a temperature of 65C to 190C.
This is done with 0 times more layer capacity. The thermoplastic article is then cooled to 50-60C on its outer surface within one hour in an open water bath and then left in the air. At that time, the temperature of the steel tube will be about 70-90C. This cooling completes the curing of the undercoat film.

The improvements obtained by the method of the invention are evident from the following table.

The invention can be used with particular advantage in tubes having an inner coating of heat-sensitive corrosion inhibitors such as eboxy resin lacquers, bitumen, cement mortars or the like.

Such tubes should be rated at 100% to avoid damage to the inner membrane.
It must be preheated to an average tube temperature of less than C.

This is advantageously done in two steps as described in the example. That is, first the tube is guided through an induction coil and
It is heated to 0C, and then only the surface area is heated to about 110GK by infrared irradiation just before undercoating. The purpose of the two-stage heating is to exceed the permissible average tube temperature and to minimize the amount of heat carried away during tube cooling.

Claims (1)

Claims: 1. For basecoating, a powdered precondensed epoxy resin/curing agent mixture, which cures within 50 to 70 minutes at a temperature of 145 to 155 C, is applied to a coating of 30 μm to 5 μm.
applied on a bar-shaped metal molding heated to at least 80 C in an amount resulting in a film thickness of 0 μm, followed by external action to melt the primer film and/or to volatilize free reaction products. The molded article passes through a heat source of about 20
0C and then apply a hose-like double layer onto the heated basecoat, the ethylene copolymerized part of which has been previously dried, at a temperature of 165C to 190C and at least 36C above the basecoat. In order to extrude with double the layer volume and cure the basecoat, the thermoplastic coating is heated at a temperature of 50C to 6C on its outer surface.
A heated rod-shaped metal molding, characterized in that it is limited to heating up to 0 C for about 1 hour and then cooled to room temperature, is first coated with the eboxy resin/curing agent mixture as a primer and then immediately coated with the eboxy resin/curing agent mixture. K, a thermoplastic resin coated with a thermoplastic synthetic resin by simultaneously extruding a layer made of an ethylene copolymer that acts as an adhesive and a thermoplastic synthetic resin layer provided thereon in the form of a double hose; A method of coating rod-shaped metal moldings, especially steel tubes, with polyethylene. 2. Claim characterized in that the molding to be coated with a heat-sensitive inner layer of artificial material, bitumen, cement-mortar or similar is heated to below 100C before being primed. The method described in paragraph 1. 3. The molded article to be coated is first heated to about 80C, and immediately before being primed, the surface area is further heated to about 20-30C using infrared irradiation. The method described in Section 2. 4. Process according to claim 1, characterized in that the moldings to be coated without a heat-sensitive inner layer are heated to at least 150C before being primed. 5. The molded article to be coated is first heated to about 170 tl', and just before priming the surface area is further heated to about 20-30 cm above that with infrared radiation. The method described in Section 4. 6. Process according to any one of claims 1 to 5, characterized in that the primed eboxy resin/curing agent mixture is heated externally with infrared radiation. 7. The method of claim 1, wherein the ethylene copolymer is dried at about 70°C for about 1.5 hours before being coated on the molding.