JPH107850A - Polypropylene composition for coating steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition resistant to the deterioration of a coating layer even in contact with wet soil at a high temperature in the case of using the composition for the coating of a steel pipe and exhibiting excellent durability by compounding a polypropylene resin with a specific amount of a specific antioxidant. SOLUTION: This composition is produced by compounding (A) 100 pts.wt. of a polypropylene resin with (B) 0.05-3 pts.wt. of a compound of the formula (X)2 CH-CH2 -CH(X)-CH3 [X is a group of the formula (R1 and R4 are each a 1-8C alkyl; R2 , R3 , R5 and R6 are each H or a 1-8C alkyl; R6 is preferably a 1-8C alkyl)] e.g. 1,1,3-tris[2-methyl-4-(3,5-di-t-butyl-4-hydroxypenylpropionlyoxy)-5- t-butylphenyl]butane} and, as necessary, (C) an antioxidant other than the component B, e.g. a sulfur-based antioxidant or a hindered amine stabilizer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene composition for coating steel pipes, and more particularly, to a polypropylene composition for coating steel pipes which prevents degradation of a polypropylene resin when the coated steel pipe is buried in high-temperature water and has excellent durability. Things.

[0002]

2. Description of the Related Art Conventionally, an adhesive resin layer made of, for example, a modified polypropylene resin modified with an unsaturated carboxylic acid or its anhydride is provided on the outer surface of a steel pipe for the purpose of preventing corrosion of a steel pipe used for a pipeline or the like. Through
It has been practiced to coat a polypropylene resin layer.
Recently, the operating temperature of the pipeline has been increased due to the improvement of transportation efficiency by high-temperature transportation of heavy oil and the centralized heating system in the district. However, in the conventional steel pipe coating with a polypropylene resin, there is a problem that the polypropylene resin coating layer is deteriorated at an early stage due to contact with high-temperature water such as a hot spring under high-temperature operation or underground burying. .

[0003] Among them, with regard to prevention of deterioration of steel pipes in contact with dry soil, steel pipes are made of polyolefin resins obtained by adding the following antioxidants (a) and (b) to polyolefin resins such as polyethylene resin and polypropylene resin. Has been proposed to reduce the adsorption and escape of the antioxidant by soil and suppress the deterioration of the coating layer (see Japanese Patent Publication No. 6-15221). (A) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)
Benzene and / or 4,4'-thio-bis- (3-methyl-6-t-butylphenol) (b) Poly [{6- (1,1,3,3-tetramethylbutyl) imino-1,3 , 5-Triazine-2,4-diyl {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene} (2,2,6,6-tetramethyl-4-piperidyl) imino {] And / or poly-2,2,4-trimethyl-1,2-dihydroquinoline

Further, polyolefin resins such as polyethylene resin and polypropylene resin have the following (I) and (I)
It has been proposed that the steel pipe is coated with a polyolefin resin to which the antioxidant of I) is added, so that the adsorption and escape of the antioxidant by soil is further reduced and the deterioration of the coating layer is remarkably suppressed. Japanese Patent Publication No. Hei 6-143493). (I) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)
Benzene alone or 4,4'-thio-bis-
Mixture of (3-methyl-6-t-butylphenol) (II) N, N'-bis (3-aminopropyl) ethylenediamine-2,4-bis [N-butyl-N- (1,
2,2,6,6-pentamethyl-4piperidyl) amino] -6-chloro-1,3,5-triazine condensate alone or in combination with poly-2,2,4-trimethyl-1,
Mixture of 2-dihydroquinoline Also, regarding prevention of deterioration of steel pipe due to contact with water, tetrakis- [methylene-3- (3 ′, 5′-di-tert-butyl-4′-hydroxyphenyl) propionate] methane Has been proposed, but at present it has not yet been improved to such an extent that it can be put to practical use.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polypropylene composition for coating a steel pipe in which deterioration of a polypropylene resin coating layer is prevented and durability of the steel pipe at the time of contact with high-temperature water is improved. Things.

[0006]

In view of this situation, the present inventors have made intensive studies to prevent the deterioration of the polypropylene resin coating layer when using a polypropylene resin steel pipe coating, particularly in high-temperature water. By blending a specific antioxidant with the polypropylene resin as the coating layer, it has been found that the deterioration of the resin layer can be prevented,
The present invention has been completed. The polypropylene composition for coating steel pipes of the present invention comprises a polypropylene resin 10
The composition is characterized in that 0.05 to 3 parts by weight of a phenol compound represented by the following general formula [1] is added to 0 parts by weight. General formula [1] [Wherein X is the following general formula [2]

[0007]

Embedded image

(Wherein R ₁ and R ₄ may be the same or different and each represents an alkyl group having 1 to 8 carbon atoms;
R ₂ , R ₃ , R ₅ , and R ₆ may be the same or different and each represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. ) Is shown. ]

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION

[I] Steel Pipe The steel pipe used as the steel pipe coating in the present invention is a steel pipe made of alloy steel such as carbon steel and stainless steel.
It is also possible to use a clad steel pipe with improved corrosion resistance of the steel pipe or a steel pipe subjected to dispersion plating.

[II] Polypropylene Resin Composition (Polypropylene Resin Coating Layer) (1) Constituents (a) Polypropylene Resin The polypropylene resin used in the polypropylene resin composition of the present invention includes propylene homopolymer,
Alternatively, propylene, an α-olefin such as ethylene, butene-1, pentene-1, hexane-1, and 4-methyl-pentene-1, an unsaturated carboxylic acid such as acrylic acid, ethyl acrylate, and maleic anhydride; Derivatives, vinyl esters such as vinyl acetate, styrene, unsaturated aromatic compounds such as methyl styrene and the like, random, block,
Alternatively, a graft copolymer or the like can be used. Among these, a propylene / ethylene block copolymer is preferred.

(B) Phenol compound In the polypropylene resin composition of the present invention, the phenol compound blended in the polypropylene resin is a phenol compound represented by the following general formula [I]. General formula [1] [Wherein, X represents a group represented by the following general formula [2]. General formula [2]

[0012]

Embedded image

(Wherein R ₁ and R ₄ may be the same or different and each represents an alkyl group having 1 to 8 carbon atoms;
R ₂ , R ₃ , R ₅ , and R ₆ may be the same or different and each represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. )] Specific examples of each symbol represented by the phenol compound represented by the general formula [I] are as follows. As R ₁ and R ₄ , an alkyl group having 1 to 8, preferably 1 to 5 carbon atoms, each of which is linear,
It may be either branched or cyclic. Specifically, methyl, ethyl, n-propyl, isopropyl, n
-Butyl group, isobutyl group, sec-butyl group, ter
t-butyl group, pentyl group, isopentyl group, sec-
Pentyl group, tert-pentyl group, 2-methylbutyl group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, cyclohexyl group, heptyl group, n-octyl group, isooctyl group, sec-octyl group, Examples include a tert-octyl group and a 2-ethylhexyl group. R ₂ , R ₃ , R ₅ and R ₆ each represent a hydrogen atom, a methyl group,
Ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, sec-pentyl group, tert-pentyl group, 2-methylbutyl Group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, cyclohexyl group, heptyl group, n-octyl group, isooctyl group, sec-octyl group, tert-octyl group, 2-ethylhexyl group, etc. An alkyl group having 1 to 8, preferably 1 to 5 carbon atoms, which may be linear, branched or cyclic.

X in the compound of the general formula [1]
Is not necessarily the same for all three,
Usually, it is preferable that they are the same. The general formula [1]
Is usually 1,1,3-tris (2-methyl-
4-hydroxy-5-tert-butylphenyl) butane or 1,1,3-tris (3-methyl-4-hydroxy-5-tert-butylphenyl) butane and the like;
5-di-tert-butyl-4-hydroxyphenylpropionic acid or 3-methyl-5-tert-butyl-4
It is obtained by a chemical reaction with -hydroxyphenylpropionic acid or the like or the corresponding propionyl chloride, etc., and is a crude product of the reaction (a compound produced as a by-product in the reaction may be mixed at an arbitrary ratio). It may be.

Specific examples of the phenol compound represented by the general formula [1] include 1,1,3-tris [2-methyl-4- (3,5-di-tert-butyl-4-hydroxyphenyl). Propionyloxy) -5-tert-butylphenyl] butane, 1,1,3-tris [3-methyl-4- (3,5-di-tert-butyl-4-hydroxyphenylpropionyloxy) -5-butylphenyl ] Butane, 1,1,3-tris [2-methyl-4-
(3-methyl-5-tert-butyl-4-hydroxyphenylpropionyloxy) -5-tert-butylphenyl] butane, 1,1,3-tris [3-methyl-
4- (3-methyl-5-tert-butyl-4-hydroxyphenylpropionyloxy) -5-tert-butylphenyl] butane.

The feature of the phenol compound represented by the general formula [1] is that it is a hindered phenol compound having a hindered phenyl ester structure. That is, in an environment where water is present, hindered phenol exhibits an antioxidant effect at the beginning of use, and when the hindered phenyl ester is altered by the action of water during use,
Since hindered phenol is newly generated and continuously exhibits the ability to prevent oxidative deterioration, a longer-term effect of preventing oxidative deterioration can be exhibited as compared with conventional antioxidants. By blending the general formula [1] component with the polypropylene resin, the effect of preventing the degradation of the resin is exhibited.

(2) Amount ratio In the polypropylene resin composition of the present invention, the compounding amount of the phenol compound represented by the general formula [1] is 0.05 to 3 parts by weight, preferably 100 parts by weight of the polypropylene resin. 0.1 to 2 parts by weight. If the amount of the phenol compound is less than the above range, the effect of preventing deterioration is insufficient. On the other hand, if it exceeds the above range, deterioration, bleeding and discoloration during processing when coating the surface of the steel pipe with the polypropylene resin composition occur. That is, in the extrusion coating, the composition undergoes deterioration or discoloration when subjected to shearing or heating by an extruder at the time of extrusion molding of a molten sheet or a molding machine such as a T-die or a round die. In the case of powder coating or fluid immersion, it is not possible to improve the stability of the composition against deterioration, discoloration, and the like, when the powder particles are melted by heating to form a film.

(3) Additional component (optional component) The polypropylene resin composition constituting the coating layer comprising the polypropylene composition for coating steel pipes of the present invention is obtained by mixing the above-mentioned general formula [1] component with polypropylene resin. Although it is essential, additional components other than these can be blended. Specific examples of such additional components include antioxidants, light stabilizers, ultraviolet absorbers, neutralizing agents, lubricants, nucleating agents, antistatic agents other than the above-mentioned general formula [1] component,
Examples include a colorant, a dispersant, a metal deactivator, a filler, a resin other than the polypropylene resin, and a rubber. In particular, the effect of the present invention is further exhibited by using a sulfur-based antioxidant or a hindered amine-based stabilizer in combination.

The sulfur antioxidant Examples of sulfur-based antioxidants, dill ulch people dipropionate, distearyl thiodipropionate, dimyristyl thiodipropionate, dialkyl thiodipropionate such disilazide waist thiodipropionate Dialkyl disulfides such as pionates and distearyl disulfide; alkylthiopropionic acids such as tetrakis [methylene (laurelthiopropionate)] methane and tetrakis [methylene (stearylthiopropionate)] methane; and polyhydric alcohols And the like,
It is not limited to these. The compounding amount of the sulfur-based antioxidant is preferably 0.5 to 10 times the phenol compound represented by the general formula [1]. Particularly preferably, the amount is 1 to 7 times.

[0020] Specific examples of the hindered amine stabilizer hindered amine stabilizers, N, N '
-Bis (3-aminopropyl) ethylenediamine-2,
4-bis [N-butyl-N- (1,2,2,6,6-pentamethyl-4piperidyl) amino] -6-chloro-
1,3,5-triazine condensate, poly [｛6- (1,
1,3,3-tetramethylbutyl) amino-1,3,5
-Triazine-2,4-diyl} (2,2,6,6-
Tetramethyl-4-piperidyl) imino {hexamethylene} (2,2,6,6-tetramethyl-4-piperidyl) imino}], dimethyl-1- (2-hydroxyethyl) -4-hydroxy-2 succinate , 2,6,6-tetramethylpiperidine polycondensate, poly- {2-N, N'-
Di (2,2,6,6-tetramethyl-4-piperidyl)
Hexanediamine-4- (N-monophyllino) symtriazine} and the like. The amount of the hindered amine-based stabilizer is preferably 0.2 to 5 times the amount of the phenol compound represented by the general formula [1]. Particularly preferably, the amount is 0.3 to 4 times.

Other antioxidants As other antioxidants , 2,6-di-t-butyl-4-methylphenol, 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,
Hindered phenol compounds such as 6-di-t-butylphenol), d, l-α-tocopherol, tris (mixed-mono and di-nonylphenyl) phosphite, tris (2,4-di-t-butyl) Phenyl) phosphite, bis (2,4-di-t-butylphenyl) pentaerythritol-diphosphite, tetrakis (2,4-di-t-butylphenyl) 4-4′-biphenylene-diphosphonite and the like 0.01 to 3 parts by weight of the aromatic phosphorus compound or the like can be suitably blended with respect to 100 parts by weight of the polypropylene resin.

Filler Also, as a filler, preferably 0.1 to 50 parts by weight of talc, mica, glass fiber or the like is blended with respect to 100 parts by weight of the polypropylene resin, so that the indentation depth of the coating layer is reduced. Can be smaller.

Resin / Rubber Examples of the resin or rubber as an additional component include low / medium / high density polyethylene, polybutene, ethylene / propylene copolymer rubber, and ethylene / butene copolymer rubber. The compounding amount is preferably 1 to 40 parts by weight based on 100 parts by weight of the polypropylene resin.

[III] Other layers (1) Adhesive resin layer (modified polypropylene resin) An adhesive resin layer made of a modified polypropylene resin is used between the steel pipe and the polypropylene resin coating layer to adhere them. Is common. As the modified polypropylene resin constituting the adhesive resin layer, the same polypropylene resin as that exemplified in the coating layer is used, and acrylic acid, methacrylic acid, maleic acid, unsaturated carboxylic acids such as itaconic acid or anhydrides thereof are used. And kneading in an extruder in the presence of a radical generator in a known manner. The modified polypropylene resin may also contain a phenolic compound represented by the general formula [1], and together with the addition to the polypropylene resin layer, a more excellent corrosion resistance effect of the steel pipe is exhibited. You. In this case, the amount of each component is preferably 0.05 to 3 parts by weight, particularly preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the modified polypropylene resin.

(2) In addition to the above adhesive resin layer, if necessary, for example, a chemical conversion coating such as a chromate coating or a phosphate coating, or a primer coating such as an epoxy resin, a urethane resin or an unsaturated polyester resin primer coating. Can be formed.

[IV] Layer Thickness The thickness of the adhesive resin layer is generally 0.05 to 2 mm, preferably 0.1 to 1 mm, and the thickness of the coating layer is generally 0.5 to 5 mm, preferably 1 to 4 mm. , Good results can be obtained. Good results are obtained when the thickness of the primer coating layer is generally 5 to 100 μm, preferably 10 to 50 μm.

[V] Coating Method (1) Method As a method for coating a steel pipe with the above-mentioned adhesive resin layer made of the modified polypropylene resin and the coating layer made of the polypropylene resin composition, a conventionally known method is applied. For example, for coating on the outer surface of a steel pipe, an extrusion coating method using a T-die or a round die, an electrostatic powder coating method, a fluid immersion method, etc. can be applied. A law or the like can be applied.

(2) Structure The structure of the resin-coated steel pipe obtained in this way is, for example, as shown in FIG. 1, a modified polypropylene resin adhered to the outside of the steel pipe whose scale has been removed by blasting or pickling. A chromate coating or a phosphate coating is formed on the outside of a resin-coated steel pipe having a three-layer structure in which a layer and a polypropylene resin coating layer are formed, or a steel pipe whose scale has been removed by blasting or pickling as shown in FIG. After forming a treated film, the outer surface of a four-layer resin-coated steel pipe having a modified polypropylene resin adhesive layer and a polypropylene resin coating layer formed thereon, or a steel pipe whose scale has been removed by blasting or pickling as shown in FIG. Then, after forming a chemical conversion coating such as a chromate coating or a phosphate coating, an epoxy resin, a urethane resin or an unsaturated polyester resin-based primer coating was formed. ,
A five-layer resin-coated steel pipe having a modified polypropylene resin adhesive layer and a polypropylene resin coating layer formed thereon, and a modified polypropylene resin adhesive layer and a steel pipe having scale removed by blasting or pickling as shown in FIG. A chemical conversion coating such as a chromate coating or a phosphate coating is formed on the inside of a three-layer resin-coated steel pipe having a polypropylene resin coating layer or a steel pipe whose scale has been removed by blasting or pickling as shown in FIG. After forming, a resin-coated steel pipe having a four-layer structure in which a modified polypropylene resin adhesive layer and a polypropylene resin coating layer are formed, or inside the steel pipe whose scale has been removed by blasting or pickling as shown in FIG. After forming a chemical conversion coating such as a chromate coating or a phosphate coating, a primer of epoxy resin, urethane resin or unsaturated polyester resin is used. After forming the coat, mention may be made of resin-coated steel pipe and the like of the modified polypropylene resin adhesive layer and the polypropylene resin garments layer formed was five-layer structure.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. Examples 1 to 6 and Comparative Examples 1 to 6 Manufacture of coated steel pipe (outer diameter 216 mmφ × length 5500 mm × thickness 9 m)
m) Grit blasting the outer surface to remove rust, and apply a chromate treatment agent to the surface to achieve a total chromium adhesion of 500 mg.
/ M ² , and heated to 190 ° C. for drying. Further, an epoxy primer was spray-coated on the surface so as to have a film thickness of 50 μm, cured, and subjected to a base treatment. Then, with the surface temperature at 180 ° C., a maleic anhydride-modified polypropylene resin (melt flow rate: 1.3 g / 10 minutes, manufactured by Mitsubishi Chemical Corporation, trade name “Modec P-300F”) was added to a round die. Was melt-extruded using an extrusion coating device provided with an adhesive resin layer having a thickness of 200 μm on the outer surface of the steel pipe.
Next, a propylene / ethylene block copolymer resin (melt flow rate 1.2 g / l) was placed on the adhesive resin layer.
0 minutes), with respect to 100 parts by weight of the resin, the compounds such as various antioxidants shown in Table 1 were added in parts by weight shown in Table 1, and
0.1 parts by weight of tris (2,4-di-t-butylphenyl) phosphite as a processing stabilizer and 0.05 parts by weight of hydrotalcite as a neutralizing agent are mixed at 230 ° C. Was melt-kneaded with an extruder. Each of the compositions (each composition was mixed with 1 part by weight of titanium white based on 100 parts by weight of the resin and colored white) was melt-extruded and coated using an extrusion coating apparatus equipped with a round die to obtain a thickness of 2 .
A 5 mm coating layer was formed to produce a polypropylene resin coated steel pipe.

Evaluation : The obtained polypropylene resin coating layer of the steel pipe was peeled off, a rectangular test piece of 15 mm × 60 mm was cut out, and a lid filled with a mixture of silica sand and water (1: 1 by weight) was provided. It was put into a cylindrical pressure-resistant container made of stainless steel (inner diameter 27 mm × inner height 110 mm). The container was placed in an oven at 150 ° C., and the inside of the container was opened at regular intervals, and the presence or absence of deterioration of the test piece was visually observed and determined. In the judgment, the time until the test piece was embrittled was defined as the life. Table 1 shows the results of these determinations.

[0031]

[Table 1] The symbols such as antioxidants in Table 1 indicate the following compounds, respectively. A1; a phenolic compound represented by the following general formula [3]: general formula [3]

[0032]

Embedded image

B1: pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (Ciba Geigy: Irganox 1010) B2: 1,3,5 trimethyl-2, 4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)
Benzene (Ciba Geigy: Irganox 1330) C1; N, N'-bis (3-aminopropyl) ethylenediamine-2,4-bis [N-butyl-N- (1,2,
2,6,6-pentamethyl-4piperidyl) amino]-
6-chloro-1,3,5-triazine condensate (Ciba Geigy: Chimasorp 119FL) C2; poly [{6- (1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine- 2,4-diyl {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) imino}] (Ciba-Geigy) : Chimasorp 944LD) D1; Pentaerythrit-tetra (β-lauryl-thiopropionate) (Cipro Chemical Co., Ltd .: Seanox 41)
2S) D2; distearyl thiodipropionate (Yoshitomi Pharmaceutical: DSTP Yoshitomi)

From the results shown in Table 1, only the film of the polypropylene resin composition of the example containing the antioxidant of the present invention was subjected to a severe acceleration test (test in a pressure test container filled with wet silica sand at 150 ° C.). However, it can be understood that the embrittlement time is long and excellent durability is exhibited.

[0035]

The steel pipe coated with the polypropylene resin composition of the present invention is obtained by coating a resin composition in which a specific amount of an antioxidant having a specific structure is blended with a polypropylene resin, and is wet at a high temperature. Even in contact with soil, deterioration of the coating is prevented, and excellent durability can be exhibited.

[Brief description of the drawings]

FIG. 1 is a partial cross section of a steel pipe having a three-layer structure in which the outer surface of a steel pipe is coated with a polypropylene resin composition of the present invention.

FIG. 2 is a partial cross section of a steel pipe having a four-layer structure in which the outer surface of the steel pipe is coated with the polypropylene resin composition of the present invention.

FIG. 3 is a partial cross section of a steel pipe having a five-layer structure in which the outer surface of the steel pipe is coated with the polypropylene resin composition of the present invention.

FIG. 4 is a partial cross section of a steel pipe having a three-layer structure in which the inner surface of the steel pipe is coated with the polypropylene resin composition of the present invention.

FIG. 5 is a partial cross section of a steel pipe having a four-layer structure in which the inner surface of the steel pipe is coated with the polypropylene resin composition of the present invention.

FIG. 6 is a partial cross-sectional view of a steel pipe having a five-layer structure in which the inner surface of a steel pipe is coated with the polypropylene resin composition of the present invention.

[Explanation of symbols]

1 Steel pipe from which scale has been removed by blasting or pickling 2 Modified polypropylene resin adhesive layer 3 Polypropylene resin coating layer 4 Chemical conversion coating layer such as chromate coating or phosphate coating 5 Epoxy resin, urethane resin or unsaturated polyester resin Primer coating layer

Continued on the front page (72) Inventor Kimiho Kosegaki 1 Tohocho, Yokkaichi-shi, Mie Mitsubishi Chemical Corporation Yokkaichi Research Institute (72) Inventor Sadao Nagase 1 Tohocho, Yokkaichi-shi, Mie Mitsubishi Chemical Corporation (72) Inventor Yoshiaki Mizutani Yoshikazu Mizutani 1st Tohocho, Yokkaichi-shi, Mie Mitsubishi Chemical Corporation (72) Inventor Ryo Bankyu 1 Tohocho, Yokkaichi-shi, Mie Mitsubishi Chemical Inside Yokkaichi Research Institute, Inc.

Claims (6)

[Claims] 1. A polypropylene composition for coating steel pipes, comprising a phenolic compound represented by the following general formula [1] in an amount of 0.05 to 3 parts by weight per 100 parts by weight of a polypropylene resin 100. Stuff. General formula [1] [Wherein, X represents a group represented by the following general formula [2]. General formula [2] (Here, R ₁ and R ₄ may be the same or different, each represents an alkyl group having 1 to 8 carbon atoms, and R ₂ , R ₃ ,
R ₅ and R ₆ may be the same or different and each represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. )] 2. The polypropylene composition for coating steel pipes according to claim 1, wherein X in the general formula [1] is the same substituent. (3) R ₆ in the general formula (2) is
The polypropylene composition for coating steel pipes according to claim 1, which is an alkyl group of 8 above. 4. The polypropylene composition for coating steel pipes according to claim 1, wherein the phenolic compound represented by the general formula [1] is used in combination with another antioxidant. 5. The polypropylene composition for coating steel pipes according to claim 4, wherein the other antioxidant is a sulfur-based antioxidant. 6. The polypropylene composition according to claim 4, wherein the other antioxidant is a hindered amine stabilizer.