JPH05254057A - Polypropylene resin coated steel pipe - Google Patents

Abstract

PURPOSE:To provide a polyproplene resin coated steel pipe generating no deterioration of a polypropylene resin coating layer and improved in durability. CONSTITUTION:A coating layer is formed from a polypropylene resin compsn. prepared by compounding 0.05-3 pts.wt. of 3,9-bis{20[3-(3-t-butyl-4-hydroxy-5- methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5 ,5]undecane and 0.05-3 pts.wt. of dialkyl-3,3'-thiodipropionate with 100 pts.wt. of a polypropylene resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene resin-coated steel pipe, and more particularly to a coated steel pipe in which deterioration of a polypropylene resin coating layer is prevented and durability is improved.

[0002]

2. Description of the Related Art It has been conventionally known to coat a surface of a steel pipe with a polypropylene resin layer, for example, through a modified polypropylene resin layer with an unsaturated carboxylic acid or an anhydride thereof for the purpose of preventing corrosion of a steel pipe. There is.

However, the conventional polypropylene resin-coated steel pipe has a problem that the polypropylene resin-coated layer is deteriorated at an early stage when it is used for underground burying or the like, especially when it is brought into contact with water in the ground. Then, conventionally, for example, tetrakis [methylene-3- (3 ′,
5'-di-t-butyl-4'-hydroxyphenyl) propionate] Methane or the like is added to prevent the polypropylene resin coating layer from being deteriorated due to contact with water. At present, the improvement has not yet reached the level that can withstand this.

[0004]

In view of the present situation, the present inventors have made diligent studies to prevent deterioration of the polypropylene resin coating layer during use of the polypropylene resin coated steel pipe, and as a result, the polypropylene resin as the coating layer was selected. It has been found that the deterioration of the resin can be prevented by using the combined antioxidant as the antioxidant to be blended, and the present invention has been accomplished. Therefore, the present invention provides a polypropylene resin coating layer. It is an object of the present invention to provide a polypropylene resin-coated steel pipe which is prevented from deterioration and has improved durability.

[0005]

The polypropylene resin-coated steel pipe of the present invention has a polypropylene resin coated on the surface thereof with an adhesive layer consisting of a modified polypropylene resin modified with an unsaturated carboxylic acid or an anhydride thereof, as described below. (A)
And the component (B) are added in an amount of 0.
It is characterized by being coated with a coating layer made of a polypropylene resin composition blended in an amount of 05 to 3 parts by weight. (A) 3,9-bis {2- [3- (3-t-butyl-4
-Hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl} -2,4,8,10-
Tetraoxaspiro [5.5] undecane and 1,
At least one compound selected from the group consisting of 3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (B) dialkyl-3,3 ′ -Thiodipropionate,
And at least one compound selected from the group consisting of pentaerythritol-tetra (β-alkyl-thiopropionate) (wherein the alkyl group has 12 to 18 carbon atoms).
Is. )

The polypropylene resin used in the polypropylene resin composition of the present invention includes a homopolymer of propylene, propylene, ethylene, butene-1,
Pentene-1, hexene-1,4-methyl-pentene-
1-α-olefins, unsaturated carboxylic acids such as acrylic acid, ethyl acrylate, maleic anhydride and their derivatives, vinyl esters such as vinyl acetate and vinyl butyrate, unsaturated aromatic compounds such as styrene and methylstyrene, etc. And a random, block, or graft copolymer with Of these, a propylene-ethylene block copolymer is preferable.

In the present invention, the component (A) blended with the polypropylene resin is 3,9-bis {2-
[3- (3-t-Butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl} -2,4,8,10-tetraoxaspiro [5.
5] Undecane and 1,3,5-trimethyl-2,
It is at least one compound selected from the group consisting of 4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, and compounds other than these compounds deteriorate the polypropylene resin as the coating layer. Preventive effect cannot be obtained.

The component (B) to be blended with the polypropylene resin in the present invention is a dialkyl-3,3'-thiodipropionate having an alkyl group of 12 to 18 carbon atoms and pentaerythritol. -Tetra (β-alkyl-thiopropionate), which is at least one compound selected from the group consisting of the following: No deterioration prevention effect can be obtained.

Specific examples of these components (B) include dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate and distearyl-.
3,3′-thiodipropionate, lauryl stearyl-3,3′-thiodipropionate, pentaerythritol-tetra (β-lauryl-thiopropionate), pentaerythritol-tetra (β-stearyl-thio) Propionate) and the like, among which, distearyl-
3,3'-thiodipropionate and pentaerythritol-tetra (β-lauryl-thiopropionate) are preferred.

In the present invention, the component (A), and
The blending amount of the component (B) is 100% of the polypropylene resin.
0.05 to 3 parts by weight with respect to 0 parts by weight, and 0.
It is preferably from 1 to 1 part by weight. If the amount of both components (A) and (B) is less than this range, the effect of preventing deterioration of the polypropylene resin will be insufficient. On the other hand, if the amount exceeds the range, bleed-out to the coating layer surface and coloring of the coating layer itself Problems such as occur.

The polypropylene resin composition constituting the coating layer of the polypropylene resin-coated steel pipe of the present invention essentially consists of the polypropylene resin mixed with the above-mentioned components (A) and (B). You may mix | blend a specific component. Examples of the additional component include an antioxidant other than the components (A) and (B), a light stabilizer, a neutralizer, a lubricant, an antistatic agent, a metal deactivator, a colorant, a dispersant, There are nucleating agents, fillers, resins other than the polypropylene resin, rubber and the like.

In particular, 2,6-di-t is used as an antioxidant.
-Butylphenol, 4,4'-thiobis (3-methyl-6-t-butylphenol), 4,4'-butylenebis (3-methyl-6-t-butylphenol), 2,
2'-methylenebis (4-methyl-6-t-butylphenol), 2,2'-ethylidenebis (4,6-di-t)
-Butylphenol), hindered phenolic compounds such as d, l-α-tocopherol, tris (mixed-mono and di-nonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, Bis (2,4-di-t-butylphenyl) pentaerythritol-diphosphite, tetrakis (2,4)
-Di-t-butylphenyl) 4-4'-biphenylene-
Aromatic phosphorus compounds such as diphosphonite are added in an amount of 0.001-1 based on 100 parts by weight of the polypropylene resin.
By blending it in an amount of part by weight, it is possible to improve the stability against deterioration when the polypropylene resin composition is molded into the coating layer in the present invention.

Further, by mixing 5 to 30 parts by weight of talc, mica, glass fiber or the like as a filler with respect to 100 parts by weight of the polypropylene resin, the scratch resistance of the coating layer is improved, and as a result, the coated steel pipe. The pushing depth of can be reduced. Examples of the additional component resin and rubber include low / medium / high density polyethylene, polybutene, ethylene-propylene copolymer rubber, ethylene-butene copolymer rubber and the like.

The modified polypropylene resin which constitutes the adhesive layer in the present invention is the same polypropylene resin as exemplified in the coating layer, which is obtained by using an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid or itaconic acid, or these. It is obtained by a known method such as melt-kneading in an extruder in the presence of a radical generator by adding the anhydride.

The polypropylene resin-coated steel pipe of the present invention is
The inner surface or the outer surface of the steel pipe is coated with a coating layer made of the polypropylene resin composition via an adhesive layer made of the modified polypropylene resin.

Steel tubes are subjected to various surface treatments such as chromate treatment, rust-preventive treatment such as zinc phosphate treatment, or sandblasting, grid blasting, shot blasting, acid cleaning, etc., before fusing an adhesive layer to the surface thereof. It is preferable to use those subjected to blasting or surface contamination removal treatment, etc., and it is preferable to apply a primer such as epoxy resin, urethane resin or unsaturated polyester resin to the surface of the steel pipe in advance.

As a method of coating the adhesive layer and the coating layer on the steel pipe, a known method can be applied, for example, an extrusion coating method, a powder coating method or the like. The thickness of the adhesive layer in the present invention is about 0.05 to 1.0 mm, and the thickness of the coating layer is about 0.5 to 6.0 mm.

[0018]

Example: Shot blasted steel pipe (SGP, 2
0A) is preheated to 180 ° C., and maleic anhydride modified polypropylene resin (melt flow rate 1.3
g / 10 minutes, manufactured by Mitsubishi Petrochemical Co., Ltd., trade name "MODIC P"
-300F ") was melt-extruded using an extrusion coating device equipped with a round die to form an adhesive layer having a thickness of 0.2 mm. Subsequently, on the adhesive layer, propylene-ethylene block copolymer resin (melt flow rate 0.5 g / 10 minutes), various antioxidants shown in Table 1 with respect to 100 parts by weight of the resin, etc. Each composition containing the compound shown in Table 1 in parts by weight was melt-extruded using an extrusion coating apparatus equipped with a round die to form a coating layer having a thickness of 2 mm, and a polypropylene resin-coated steel pipe was produced.

Each of the obtained coated steel pipes was cut into a length of 300 mm, and the inner and outer peripheral surfaces of each steel pipe were brought into contact with water by passing clean water (oxygen content 7 ppm) at 80 ° C. 500
After the passage of 0 hours, stop water flow and visually observe the occurrence of cracks on the outer surface of the steel pipe. Furthermore, for each steel pipe after water flow, the time until brittle fracture is reached in an air circulation oven at 150 ° C. It was measured. The results are shown in Table 1.

[0020]

[Table 1]

The symbols of antioxidants in Table 1 indicate the following compounds, respectively. A-1; 3,9-bis {2- [3- (3-t-butyl-
4-Hydroxy-5-methylphenyl) propionyloxy] -1,1'-dimethylethyl} -2,4,8,1
0-Tetraoxaspiro [5.5] undecane A-2; 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)
Benzene B-1; distearyl-3,3′-thiodipropionate B-2; pentaerythritol-tetra (β-lauryl-
Thiopropionate) C-1; tetrakis [methylene-3- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane C-2; tris (2,4-di-t). -Butylphenyl) phosphite C-3; 2,6-di-t-butyl-4-methylphenol

[0022]

EFFECTS OF THE INVENTION The polypropylene resin-coated steel pipe of the present invention comprises a resin composition in which a specific amount of polypropylene resin is used in combination with a specific antioxidant as a coating layer, so that the coating layer is deteriorated even when contacted with water. Is prevented and the durability is improved.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Inagaki 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Petrochemical Co., Ltd. Yokkaichi Research Institute

Claims (1)

[Claims] 1. A polypropylene resin containing 100 parts by weight of the following components (A) and (B) via an adhesive layer made of a modified polypropylene resin modified with an unsaturated carboxylic acid or an anhydride thereof on the surface of a steel pipe. 0.0 for each
A polypropylene resin-coated steel pipe, characterized by being coated with a coating layer comprising a polypropylene resin composition mixed in an amount of 5 to 3 parts by weight. (A) 3,9-bis {2- [3- (3-t-butyl-4
-Hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl} -2,4,8,10-
Tetraoxaspiro [5.5] undecane and 1,
At least one compound selected from the group consisting of 3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (B) dialkyl-3,3 ′ -Thiodipropionate,
And at least one compound selected from the group consisting of pentaerythritol-tetra (β-alkyl-thiopropionate) (wherein the alkyl group has 12 to 18 carbon atoms).
Is. )