JPH0245984B2 - KOKANHIFUKUYOJUSHISEKISOTAI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resin laminate, and more particularly to a resin laminate for coating a steel pipe that protects the surface of a steel pipe installed in soil or water such as seawater from corrosion. Conventionally, the surface of steel pipes installed underground or in water such as seawater is extremely susceptible to corrosion, and its protection is an extremely important issue. Therefore, it is being considered to coat the surface of the steel pipe with a corrosion-resistant resin such as polyolefin. However, since polyolefin is non-polar, it is not possible to apply a coating that can withstand practical use. In order to solve this drawback, a method of introducing polar groups into polyolefins has been proposed.
According to this method, it is possible to firmly adhere the polyolefin to the surface of the steel pipe. However, when the polyolefin comes into direct contact with salt water, such as during welding of steel pipes in seawater or due to scratches on the polyolefin coating, the contact surface with the steel pipe gradually peels off, making it impossible to protect the steel pipe. Therefore, the surface of the steel pipe is coated with polyolefin or the like after being coated with a primer such as epoxy resin. However, this method reduces the productivity of resin-coated steel pipes due to the addition of a primer treatment step. An object of the present invention is to provide a resin laminate for coating steel pipes that has sufficient salt water resistance and adhesiveness without the need for primer treatment on the surface of the steel pipes, and effectively prevents corrosion of the steel pipes. The present invention is a resin laminate for coating steel pipes, which is formed by sequentially laminating (A) a hydroxyl group-containing polymer layer, (B) a polyolefin resin layer modified with an unsaturated carboxylic acid or its derivative, and (C) a polyolefin resin layer. . Here, the (A) hydroxyl group-containing polymer layer (hereinafter referred to as (A) layer) can be any polymer having a hydroxyl group at the end of the molecule, and can be used without particular restriction. Examples include saponified copolymers, polyvinyl alcohol, polyvinylphenol, ethylene-vinyl alcohol copolymers, etc.
Saponified ethylene-vinyl acetate copolymer is preferred. Furthermore, among saponified ethylene-vinyl acetate copolymers, those containing 25 to 50 mol % of ethylene and a degree of saponification of 95% or more have good adhesion to steel pipes and oil resistance. Next, (B) a polyolefin resin layer modified with an unsaturated carboxylic acid or its derivative (hereinafter referred to as (B) layer) is a polyolefin resin modified with an unsaturated carboxylic acid or its derivative or this modified polyolefin resin layer. It means a mixture of a resin and at least one substance selected from unmodified polyolefin resin, ethylene-vinyl acetate copolymer, and ethylene-propylene rubber. Polyolefin resins to be modified include polyethylene, polypropylene, and copolymers of ethylene and propylene with other monomers. Examples of unsaturated carboxylic acids used for modifying polyolefin resins include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, citraconic acid, sorbic acid, mesaconic acid, and angelic acid. Further, its derivatives include acid anhydrides, esters, amides, imides, metal salts, etc., such as maleic anhydride, itaconic anhydride, citraconic anhydride,
Examples include methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, maleic acid monoethyl ester, acrylamide, maleic acid monoamide, maleimide, N-butylmaleimide, sodium acrylate, sodium methacrylate, etc. . The method for modifying the polyolefin resin with these unsaturated carboxylic acids or derivatives thereof is not particularly limited, and various known methods can be used. For example, the process proceeds by adding a radical initiator to a polyolefin resin and maleic anhydride in the presence or absence of a solvent and heating the mixture. During the reaction, other vinyl monomers such as styrene or rubbers such as liquid rubber and thermoplastic rubber may also be present. The content of unsaturated carboxylic acid or its derivative in the modified polyolefin resin thus obtained is usually 0.001 to 15% by weight, preferably 0.005 to 15% by weight.
It is in the range of 10% by weight. The unmodified polyolefin used in combination with the modified polyolefin resin is the same as the polyolefin to be modified. Further, the ethylene-vinyl acetate copolymer is not particularly limited, but one having a vinyl acetate content of 10 to 40% by weight is preferably used. Examples of the ethylene-propylene rubber include ethylene-propylene copolymer and ethylene-propylene-diene terpolymer. Preferred modified polyolefin resins in layer (B) include at least one of polyolefins modified with unsaturated carboxylic acids or derivatives thereof, unmodified polyolefins, ethylene-vinyl acetate copolymers, and ethylene-propylene rubber. It is a mixture with substances. The blending ratio of this mixture is 100,000 parts by weight or less, preferably 500 to 10,000 parts by weight of unmodified polyolefin, and 300 parts by weight or less, preferably 2 to 50 parts by weight of ethylene-vinyl acetate copolymer to 100 parts by weight of modified polyolefin. Parts by weight and 300 parts by weight or less of ethylene-propylene rubber, preferably 2 to 50 parts by weight, are suitable. If the unmodified polyolefin exceeds 100,000 parts by weight, the adhesion with layer (A) will decrease, and if the ethylene-vinyl acetate copolymer exceeds 300 parts by weight, the material strength of layer (B) will decrease. Moreover, if the laminate is damaged, the steel pipe may be corroded, which is not preferable. In addition, ethylene-propylene rubber
If it exceeds 300 parts by weight, it is not preferable because hot water resistance deteriorates and the steel pipe may be corroded if the laminate is damaged. Examples of the (C) polyolefin resin layer (hereinafter referred to as (C) layer) include olefin homopolymers, olefin copolymers, and mixtures thereof. Examples of olefin homopolymers include high-density polyethylene, low-density polyethylene, and linear Examples include low density polyethylene, polypropylene, polybutene-1, and poly-4-methylpentene-1. Examples of olefin copolymers include copolymers of ethylene and small amounts of propylene, butene, hexene, and the like. Particularly preferred polyolefin resins are high density polyethylene and polypropylene. In addition, in the resin laminate of the present invention, when polyethylene is used for the (C) layer, a modified or unmodified polyolefin based on polyethylene is used for the (B) layer, and when polypropylene is used for the (C) layer, ,
It is preferable to use a layer (B) based on modified or unmodified polyolefin based on polypropylene, which increases the adhesive strength between the layers.
Favorable results are obtained. The resin laminate of the present invention is made by laminating the above layers (A), (B), and (C) in sequence, and when coating the surface of a steel pipe with this resin laminate, layer (A) comes into contact with the steel pipe. use it as if That is, the (A) layer acts as an adhesive between the steel pipe and the (B) layer, and the (B) layer acts as an adhesive between the (A) layer and the (C) layer. The resin laminate of the present invention can be produced by various methods, but a multilayer coextrusion method is preferred, and for example, a round die method, a T-die method, etc. can be used. Further, it can also be manufactured by a multi-stage extrusion lamination method, a thermocompression bonding method, or the like.
The thickness of each layer may be determined appropriately considering the purpose of use, etc., but generally (A) layer 0.01 to 0.5 mm,
Preferably 0.03-0.3 mm, (B) layer 0.1-1.0 mm, preferably 0.2-0.5 mm, (C) layer 1-5 mm, preferably 2-
It should be 3 mm. The method of coating a steel pipe with the resin laminate of the present invention is not particularly limited and may be any commonly used method, but for example, a steel pipe heated to a surface temperature of 100 to 200°C may be rotated about its axis. There is a method of wrapping a resin laminate sheet with a surface temperature of 200 to 260°C while moving the resin. The resin laminate for coating steel pipes according to the present invention has good adhesion to steel pipes by using a hydroxyl group-containing polymer layer for the layer (A), and has excellent water resistance, especially resistance to warm salt water. are doing. Furthermore, it becomes the outer layer (C)
By using the polyolefin resin layer as the layer, corrosion on the surface of the steel pipe can be effectively prevented. In addition, according to the present invention, there is no need to perform primer treatment or the like on the surface of the steel pipe, resulting in excellent workability and productivity. Therefore, the resin laminate of the present invention can be widely used as a steel pipe coating material. Next, the present invention will be explained in detail with reference to examples. Examples 1 to 5 Maleic anhydride-modified polyolefin, unmodified polyolefin, ethylene-vinyl acetate copolymer, and ethylene-propylene rubber were dry-blended as modified polyolefin resins in the proportions shown in Table 1, and then kneaded at 200°C. A resin was obtained by extrusion. Next, (A) saponified ethylene-vinyl acetate copolymer, (B) the above modified polyolefin resin, and (C)
A sheet was manufactured by laminating three layers of polyolefin resin (A)-(B)-(C) and coextruding them. The thickness of each layer is (A)
The thickness of the layer was 0.02 mm, the layer (B) was 0.5 mm, and the layer (C) was 2.0 mm. Sandblasted steel plate (thickness 3mm, JIS G3141,
SPCC-SD) was placed on a hot plate, and the above sheets were stacked and heated and melted and pressed at 240° C. and 10 kg/cm ² for 10 minutes to obtain a resin-coated steel plate. Table 1 shows the results of the hot salt water peel test and 90° peel strength test of this resin-coated steel plate. The evaluation of the test was conducted as follows. Hot salt water peeling: Resin-coated steel pipes are soaked in 3% salt water at 80°C.
After being immersed in water for 6 days, the area of peeling between the steel pipe and the resin layer is expressed as a percentage. 90° peel strength: indicates the peel strength between (A) and (B). However, Comparative Example 1 shows the strength of peeling between the steel pipe surface and the (B) layer. Comparative Example 1 The same operations as in Examples 1 to 5 were performed except that layer (A) was not used. The results are shown in Table 1. Comparative Examples 2 and 3 (A) A thermosetting epoxy adhesive was applied onto the surface of the steel plate instead of the resin, and after a curing reaction was carried out at 160° C. for 10 minutes, the same operations as in Examples were carried out. The results are shown in Table 1. 【table】

Claims (1)

[Scope of Claims] 1. A steel pipe coating resin formed by sequentially laminating (A) a hydroxyl group-containing polymer layer, (B) a polyolefin resin layer modified with an unsaturated carboxylic acid or its derivative, and (C) a polyolefin resin layer. laminate. 2. The resin laminate according to claim 1, wherein the hydroxyl group-containing polymer is a saponified ethylene-vinyl acetate copolymer. 3 Polyolefin resin modified with unsaturated carboxylic acid or its derivative is (a) Polyolefin 100 modified with unsaturated carboxylic acid or its derivative
parts by weight, (b) 100,000 parts by weight or less of unmodified polyolefin, (c) 300 parts by weight or less of ethylene-vinyl acetate copolymer, and (d) 300 parts by weight or less of ethylene-propylene rubber. The resin laminate according to scope 1. 4. The resin laminate according to claim 1, wherein the polyolefin resin is high-density polyethylene or polypropylene.