JPS6151986B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyolefin coating having antifouling properties.

Polyolefin coatings, particularly polyethylene coatings, are applied to the outer surfaces of buried steel pipes or the inner surfaces of seawater intake pipes, and have demonstrated excellent anticorrosion performance for many years. Recently, it has also begun to be used for corrosion protection of steel pipe piles. Polyolefin not only has excellent anticorrosion properties and durability, but also has the advantage of less adhesion of shellfish and algae when used in contact with seawater as mentioned above.
However, the property of polyolefin that substances are difficult to adhere to it actually acts as a weakness. For example, even if paint is applied to polyolefin, its adhesion is weak and long-term durability cannot be expected.

Taking a seawater intake pipe as an example, coating the inner surface with polyolefin provides a sufficient anticorrosive effect, and usually hardly any shellfish adhere to the pipe. However, water retention areas within pipes are areas where shellfish are likely to adhere, and even with polyolefin, the adhesion of shellfish cannot be ignored. With general paint-type anti-corrosion coatings, special areas like this can be treated by overcoating with antifouling paint, but with polyolefin coatings, as mentioned above, problems remain when dealing with paint. . Some attempts have been made to incorporate an antifouling agent into polyolefin, but it is difficult to dissolve or disperse the antifouling agent into polyolefin, so it is not possible to incorporate the large amount of antifouling agent required for long-term antifouling. ,
It has not yet been completed.

The present inventors have conducted various studies on antifouling treatments for the above-mentioned polyolefin surfaces, and as a result, have achieved the present invention. The gist of the present invention is that a thin layer of ethylene-vinyl acetate copolymer containing an antifouling agent is provided on the surface of the anticorrosive polyolefin coating, and a thin layer of polyolefin is further provided on this. It has a polyolefin coating that has antifouling properties. Incidentally, examples of the polyolefin for coating according to the present invention include polyethylene, polypropylene, polybutene-1, and the like. These may be used alone or in combination, and may be modified to the extent that the anticorrosion performance is not impaired. Of course, carbon black, antioxidants, etc. may be added. The present invention will be explained in detail below.

First of all, FIG. 1 is a cross-sectional view schematically showing an embodiment of the coating of the present invention, in which a polyolefin layer 2 is provided on a base steel material 1, and then an ethylene-vinyl acetate copolymer layer containing an antifouling agent is provided. An embodiment is shown in which a thin layer 3 of composite (hereinafter abbreviated as EVA) is provided, which is further covered with a thin layer 2' of polyolefin.

Examples of antifouling agents include organic tin compounds such as triphenyltin hydroxide and tributyltin oxide, copper compounds such as cuprous oxide, and bactericidal and antifungal agents such as thiabendazole.

Next, EVA was selected as a base material that can dissolve or disperse a large amount of an antifouling agent and that can be easily heat-fused to polyolefin. In other words, a large amount of antifouling agent is required for long-term antifouling.
Since this antifouling agent is contained in EVA and is gradually released through the outermost layer of polyolefin, the antifouling effect can be maintained for a long period of time.

In this case, the type of EVA is not particularly limited, but one with 10 to 30% vinyl acetate groups and a melt index of 3 to 30 is suitable. Alternatively, EVA modified by partial saponification, carboxylic acid addition, etc. may be used. The higher the concentration of antifouling agent in EVA, the longer the antifouling effect will last, but approximately 10 to 60% is practical. Although the thickness of the antifouling agent-containing EVA can be selected as desired, a range of 100 to 1000 μm is suitable for practical use. Also, the thickness of the polyolefin covering this is 50
A range of ~500μ is practical.

Contains antifouling agent on anticorrosive polyolefin coating
In order to form a thin EVA layer and further a thin layer of polyolefin thereon, appropriate methods such as two-step thermal spraying, fluidized dipping, or heat fusion of a laminated sheet of antifouling agent-containing EVA and polyolefin may be employed. I can do it.

The polyolefin coating of the present invention has the following advantages.

Anticorrosive polyolefin, EVA containing antifouling agent,
The thin layers of polyolefin and polyolefin are firmly fused to each other, and there is no risk of peeling over a long period of time.

Since the antifouling agent-containing EVA thin layer comes into contact with the outside world through the polyolefin, the release of the antifouling agent is moderately suppressed, and the antifouling effect lasts for a long time.

When the antifouling function deteriorates, it is easy to update the function by reprocessing the surface layer.

It is advantageous in terms of safety and health because no organic solvent is used in the antifouling treatment.

Next, the effects of the present invention will be specifically explained using examples.

Example Two steel pipes with a nominal diameter of 125 mm and a length of 4 m were coated with polyethylene having a density of 0.935 and a melt index of 0.4 to a thickness of 2 mm by extrusion on the outer surface (designated as A and B).

A is a 0.2 mm polyethylene tape of the same quality as above, which was coated on one side with 19% vinyl acetate EVA containing 30% tributyltin oxide to a thickness of 0.3 mm while still retaining the residual heat from the above coating construction. (100mm
The coating of the present invention was completed by overlapping the layers (width) and spirally winding them without removing any layers. After cooling, the adhesion of the tape to the substrate was extremely strong.

B was used as a comparison material with the polyethylene coating still on.

As a result of immersing both test specimens A and B in the sea for two years, the coating of the present invention in A had no adhesion of shellfish or algae, whereas the comparative material B had some green algae and
Adhesion of celluloid and several dozen barnacles was observed.

In addition, A was estimated to have an antifouling life of 2 years or more based on the amount of residual antifouling agent, but the EVA coated on the surface
- The polyethylene coating was peeled off by heating, and then a thin layer of EVA and polyethylene with the same composition as the new material was applied by thermal spraying, making it possible to renew the inventive coating similar to the new material.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing the structure of the coating of the present invention. 1...Base steel material, 2,2'...Polyolefin, 3
...EVA containing antifouling agent.

Claims (1)

[Claims] 1. A polyolefin coating with antifouling properties, characterized in that a thin layer of ethylene-vinyl acetate copolymer containing an antifouling agent is provided on the surface of the anticorrosive polyolefin coating, and a thin layer of polyolefin is further provided on top of this. .