JPH0362145B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a polyolefin-coated metal pipe,
More specifically, the present invention relates to a polyolefin-coated metal tube with excellent high-temperature cathode peelability. (Prior Art) Polyolefin-coated metal pipes have been increasingly used in pipelines for transporting oil, natural gas, etc. because of their excellent anticorrosion performance.
Usually, such pipelines are used for a long period of time once they are laid, so they are coated with polyolefin and the like, and are also coated with cathodic protection.
However, when this cathodic protection is performed, if there is a pinhole or other penetrating flaw in the outer coating, the area around the penetrating flaw becomes a cathode, and the adhering moisture is electrolyzed by the anticorrosion current, producing hydrogen and alkali. This has the disadvantage that a phenomenon called cathodic peeling occurs in which the coating film peels off, resulting in a decrease in corrosion protection. The cathodic peeling resistance of polyolefin-coated steel pipes decreases as the operating environment temperature rises, so improving the high-temperature cathodic peeling resistance is an important issue, especially when used in high-temperature environments. In order to improve the cathodic peeling resistance of polyolefin-coated metal tubes, several methods have been proposed in which the surface of the metal tube is pre-treated with a base treatment. For example, as shown in FIG. 3, in order from the inside of the metal tube 1, a chromate treatment agent layer 2, a thermosetting epoxy resin layer 6, a modified polyolefin resin layer 4
There is also a polyolefin-coated metal tube on which a polyolefin resin layer 5 is laminated, and as this thermosetting epoxy resin, for example, as seen in JP-A-59-222275, diglycidyl ether of bisphenol A is the main component. A mixture of an epoxy resin and an inorganic pigment mixed with an amino curing agent and cured by reaction, or a diglycidyl ether of bisphenol A and bisphenol as seen in JP-A-59-62373. A mixture of diglycidyl ethers of F cured with an amine curing agent can be used. (Problems to be Solved by the Invention) However, when diglycidyl ether of bisphenol A is used in thermosetting epoxy resin as a surface treatment agent for such polyolefin-coated metal pipes, Since the reaction of the diglycidyl ether of phenol A is small, the diglycidyl ether of bisphenol A is not sufficiently crosslinked by the curing reaction, and the heat resistance of the resulting coating film is reduced, resulting in poor high-temperature cathodic peelability.
In addition, when diglycidyl ether of bisphenol F is used in a thermosetting epoxy resin as a surface treatment agent for metal pipes, the reactivity of the diglycidyl ether of bisphenol F is too high. The ether is excessively crosslinked by the curing reaction, and the curing strain that occurs at the interface between the resulting coating film and the chromate treatment agent layer increases, causing peeling at the interface in the cathodic peel test at high temperatures, resulting in a high temperature cathode resistance. There is a problem that peelability deteriorates, and it has been difficult to obtain a polyolefin-coated metal tube with excellent cathodic peelability at high temperatures using conventional techniques. An object of the present invention is to provide a polyolefin coated tube with excellent cathode peeling resistance at high temperatures. (Means for Solving the Problems) As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have developed a layer of chromate treatment agent containing a silica-based dispersant, a bisphenol treatment agent layer, and a bisphenol treatment agent layer on the outer surface of a steel pipe from the inside. A polyolefin-coated metal tube laminated with a thermosetting epoxy resin layer made of a mixture of AD diglycidyl ether, a polyfunctional epoxy resin, an inorganic pigment, and an amine curing agent, a modified polyolefin resin layer, and a polyolefin resin layer, As a chromate treatment agent containing a silica-based dispersant, use a mixture of 2 to 45 g of a silica-based dispersant to 100 g of chromic anhydride in the treatment agent, and as a polyfunctional epoxy resin for thermosetting epoxy resin. Tetraglycidyl metaxylene diamine, tetraglycidyl-1,3-bisaminomethylcyclohexane, tetraglycidyl amino diphenylmethane, triglycidyl-p-aminophenol, trimethylolpropane triglycidyl ether, tri(glycidoxyphenyl)butane, tetra (glycidoxyphenyl)ethane, and 3,9-bis(3-aminopropyl)-2, as an amine curing agent for thermosetting epoxy resin.
Phenyl glycidyl ether modified product of 4,8,10-tetraoxaspiro[5,5′]undecane, i.e. or a modified polyamine consisting of a condensate of m-xylene diamine and epichlorohydrin, i.e. A polyolefin-coated metal tube with excellent high-temperature cathode peelability, characterized by using. The present inventors have discovered that the following can be obtained, leading to the present invention. That is, as shown in FIG. 1, the present invention includes a chromate treatment agent layer 2 containing a silica-based dispersant, a diglycidyl ether of bisphenol AD, a polyfunctional epoxy resin, and an inorganic pigment on the outer surface of a metal tube 1 in order from the inside. and a polyolefin-coated metal tube with excellent cathodic peeling resistance at high temperatures, characterized by laminating a reaction-curing epoxy resin layer 3 made of a mixture of amine-based curing agent, a modified polyolefin resin layer 4, and a polyolefin resin layer 5. It is something. Hereinafter, the present invention will be explained in detail. The metal pipe used in the present invention is a cast iron pipe or a steel pipe. Also, plated steel pipes with improved corrosion resistance on the inner surface of the pipes.
Also includes metal double pipes, etc. Examples include plated steel pipes in which the inner surface of the steel pipe is coated with zinc, aluminum, chromium, nickel, zinc-nickel, zinc-nickel-cobalt-chromium, etc., and metal double pipes in which the following metals are bonded to the inner surface. The outer layer of the metal double pipe is steel pipe or cast iron pipe, and the inner layer is copper, aluminum, brass,
Titanium, austenitic stainless steel, ferritic stainless steel, austenitic-ferritic stainless steel, aluminum-magnesium alloy, nickel-chromium-iron alloy, nickel-molybdenum alloy, nickel-molybdenum-chromium-tungsten alloy, titanium There is no problem as long as the outer layer is made of a metal or alloy such as a palladium alloy, a titanium-molybdenum-zirconium alloy, or a titanium-aluminum-vanadium alloy, and the outer layer is a cast iron pipe or a steel pipe. The chromate treatment agent used in the present invention is obtained by partially reducing a chromic acid aqueous solution prepared by dissolving chromic acid anhydride (CrO ₃ ) in distilled water with an organic reducing agent.
It is a mixture of valent chromium ions and trivalent chromium ions and a silica-based dispersant, but if necessary, some of the chromic acid can be replaced with water-soluble chromate or water-soluble dichromate. It can be replaced with a water-soluble metal salt. Organic reducing agents used for partial reduction of chromium from hexavalence to trivalence include monohydric alcohols such as methyl alcohol and ethyl alcohol, polyhydric alcohols such as polyvinyl alcohol, glycerin, and sorbitol, diethanolamine, and triethanolamine. Alkylolamines, formic acid, etc.
Saturated carboxylic acids such as acetic acid and oxalic acid, aromatic polyhydric alcohols such as pyrogallol, unsaturated carboxylic acids such as succinic acid and adipic acid, etc. are used. These reducing agents are used in amounts necessary to maintain the desired ratio of hexavalent chromium to total chromium. The desired ratio is a weight ratio of hexavalent chromium to total chromium in the range of 0.25 to 0.85. Regarding this ratio, the weight ratio of hexavalent chromium to total chromium is
If the weight ratio is less than 0.25, the corrosion resistance of the chromate treatment agent layer will be significantly reduced, and if this weight ratio is 0.85 or more, the adhesiveness between the metal tube surface and the chromate treatment agent will be significantly reduced. Water-soluble chromates and dichromates that partially replace chromic acid are chromates and dichromates of alkali metals, alkaline earth metals, iron group metals, and the like. Furthermore, if a hardly soluble precipitate is formed in the chromate treatment solution, an acid such as sulfuric acid, nitric acid, or phosphoric acid may be added to dissolve the precipitate. The silica-based dispersant to be mixed with the chromate treatment agent may be an inorganic silica-based dispersant such as colloidal silica, silica fine powder, silicomolybdate fine powder, silicotungstic acid fine powder, or a silica-based dispersant that is decomposed in the chromate treatment agent. These are tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane that can serve as a silica source, and one type or a mixture of two or more of these is used. The above-mentioned silica-based dispersant has the effect of stabilizing the dispersion of each component in the chromate treatment liquid and making the film obtained by applying the chromate treatment liquid on the surface of the metal tube insoluble in water. The amount of silica-based dispersant mixed is 100g of chromic anhydride.
Mix at a ratio of 2 to 45 g. If the amount of silica-based dispersant mixed is less than 2g, the above effect will hardly be achieved, and if the amount mixed is more than 45g, the fluidity of the chromate treatment agent will deteriorate significantly, inhibiting the smoothness of the coating obtained by applying it to the surface of the metal pipe. It is not desirable because it Before applying the chromate treatment agent to the surface of the metal tube, scale and the like on the surface of the tube are removed by pickling, sandblasting, grit blasting, shot blasting, or the like. When a chromate treatment agent is applied to the surface of a metal pipe from which scale has been removed, hexavalent chromium is reduced due to the oxidation effect on the pipe surface and heating of the pipe after application, promoting insolubilization, and inorganic substances that are poorly soluble in water. It becomes a film. The appropriate baking temperature for the chromate treatment agent is 120 to 250°C (metal tube surface temperature). If the surface temperature of the metal tube is below 120℃, it will take a very long time for the chromate treatment agent layer to become insolubilized, making it unsuitable for practical use.If it exceeds 250℃, the excessive reduction of the chromate treatment agent will proceed rapidly, and the Deteriorates corrosion resistance. Further, the amount of the chromate treatment agent deposited is preferably 350 to 1200 mg/m ² in terms of total chromium weight. If the amount of this adhesion is less than 350 mg/m ² , the anticorrosion properties of the chromate treatment agent cannot be exhibited, and if it is more than 1200 mg/m ² , a strong film will not be formed and the adhesive strength will deteriorate. Next, a thermosetting epoxy resin made of a mixture of diglycidyl ether of bisphenol AD, a polyfunctional epoxy resin, an inorganic pigment, and an amine curing agent used in the present invention will be described. The above thermosetting epoxy resin consists of 100 parts by weight of diglycidyl ether of bisphenol AD, 1 to 50 parts by weight of a polyfunctional epoxy resin, and 1 to 30 parts by weight of an inorganic pigment.
It is desirable to mix parts by weight and then mix an equivalent amount of the amine curing agent into the mixture. The diglycidyl ether of bisphenol AD mentioned above has a molecular structure of and n is an epoxy resin in the range of 0 to 4. The molecular structure of the diglycidyl ether of bisphenol AD above is the molecular structure of the diglycidyl ether of bisphenol A, i.e. (n is in the range of 0 to 4), the number of methyl groups is small and the reactivity is high, so the bisphenol
The crosslinking reaction between the diglycidyl ether of AD and the polyfunctional epoxy resin progresses sufficiently, and the heat resistance of the resulting coating film improves, so it has a remarkable effect on improving high-temperature cathodic peelability. When the diglycidyl ether of bisphenol A is used instead of the diglycidyl ether of bisphenol AD mentioned above, the bisphenol A
Because the reactivity of the diglycidyl ether of bisphenol A is low, the crosslinking reaction between the diglycidyl ether of bisphenol A and the polyfunctional epoxy resin becomes insufficient, and the heat resistance of the resulting coating film decreases.
High temperature cathode peelability does not improve. Furthermore, when the diglycidyl ether of bisphenol F is used instead of the diglycidyl ether of bisphenol AD, the reactivity of the diglycidyl ether of bisphenol F is too high. Excessive crosslinking reaction occurs between the diglycidyl ether and the polyfunctional epoxy resin, and curing strain increases at the interface between the resulting coating film and the chromate treatment agent layer, resulting in peeling at the interface. As a result, the high temperature cathode peelability is significantly reduced. The above-mentioned polyfunctional epoxy resin is an epoxy resin containing three or more epoxy groups in the molecule. The above polyfunctional epoxy resin has a large number of epoxy groups, which are functional groups for crosslinking reactions, in its molecules, so by adding it to the diglycidyl ether of bisphenol AD and curing it, the resulting coating film becomes three-dimensional. Since it is highly crosslinked and its heat resistance is significantly improved, its high-temperature cathode peelability is greatly improved. The above polyfunctional epoxy resin and bisphenol
For mixing AD with diglycidyl ether, bisphenol AD diglycidyl ether
It is desirable to mix the polyfunctional epoxy resin in an amount of 1 to 50 parts by weight per 100 parts by weight. Regarding the above mixing ratio, bisphenol AD
If the amount of polyfunctional epoxy resin mixed with 100 parts by weight of diglycidyl ether is less than 1 part by weight, the above effect will hardly be obtained, and if it is more than 50 parts by weight, excessive crosslinking reaction will occur, and the curing strain will increase, resulting in a high temperature resistant cathode. This is not preferable because the releasability deteriorates. As the above polyfunctional epoxy resin, tetraglycidyl metaxylene diamine Tetraglycidyl-1,3-bisaminomethylcyclohexane , tetraglycidylaminodiphenylmethane , triglycidyl-p-aminophenol , trimethylolpropane triglycidyl ether , tetra(glycidoxyphenyl)propane , tetra(glycidoxyphenyl)ethane The above polyfunctional epoxy resin and bisphenol
By adding an inorganic pigment to the mixture of AD and diglycidyl ether, the water resistance of the resulting film at high temperatures is improved, which has the effect of significantly improving cathodic peeling resistance. Regarding mixing the above mixture of the diglycidyl ether of bisphenol AD and the polyfunctional epoxy resin with the above inorganic pigment, It is desirable to mix the inorganic pigment in an amount of 1 to 30 parts by weight. Regarding the above mixing ratio, bisphenol AD
If the amount of inorganic pigment added to 100 parts by weight of diglycidyl ether is less than 1 part by weight, there will be little effect on high temperature and water resistance, and if it is more than 30 parts by weight, the viscosity of the primer will increase significantly and the smoothness of the resulting film will be affected. It is not desirable because it causes damage. The inorganic pigments added to the mixture of the diglycidyl ether of bisphenol AD and the polyfunctional epoxy resin include silica, silicomolybutenic acid, silicotungstic acid, titanium dioxide, iron oxide, mica, zinc oxide, molybdenum trioxide, Fine powder or flakes of tungsten trioxide, nickel oxide, etc. can be used. By adding an equivalent amount of an amine curing agent to the mixture of the above bisphenol AD diglycidyl ether, polyfunctional epoxy resin, and inorganic pigment and heating it, it cures with extremely excellent heat resistance, water resistance, and salt water resistance. Since a coating film is obtained, high-temperature cathodic peeling resistance is significantly improved. The above amine curing agent is a modified polyamine of m-xylene diamine (hereinafter referred to as "curing agent A") having the following molecular structure, that is, and 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro[5,5]undecane having the following molecular structure, i.e. is a phenyl glycidyl ether with the following molecular structure, i.e. (hereinafter referred to as "curing agent B"). Since the above-mentioned curing agent A and curing agent B have a thermostable benzene nucleus in their molecules, they can be mixed with the above-mentioned diglycidyl ether of bisphenol AD, polyfunctional epoxy resin, and inorganic pigment and heated. As a result, the heat resistance, water resistance at high temperatures, and salt water resistance of the resulting cured coating film are significantly improved. When m-xylylenediamine is used alone instead of the curing agent A, the reactivity of the m-xylylenediamine is too high, resulting in a large curing strain of the resulting coating. Peeling occurs at the interface between the film and the chromate treatment agent layer, reducing high-temperature cathode peelability. Moreover, instead of the curing agent B, 3,9-bis(3-aminopropyl)-
2,4,8,10-tetraoxaspiro [5,5]
When undecane is used alone, the curing agent does not contain a benzene nucleus with good thermal stability in its molecules, so the heat resistance of the resulting coating film decreases and high-temperature cathodic peelability does not improve. Amine-based curing agents other than the above-mentioned curing agent A and curing agent B, such as m-phenylenediamine, P,
When using P′-diaminodiphenylmethane, etc., the reactivity of the curing agent is extremely high, so the curing strain of the resulting coating film becomes extremely large, and the interface between the coating film and the chromate treatment agent layer increases. Peeling occurs and the high temperature cathode peelability is significantly reduced. Also,
When an acid anhydride curing agent such as methylnadic acid, methylhexahydrophthalic anhydride, etc. is used in place of the curing agent A and curing agent B described above, a high temperature is required to sufficiently cure the coating film. If it is cured at a high temperature, it generates intense heat, generates an irritating odor, and causes thermal deterioration of the coating film, resulting in a significant decrease in high-temperature cathode peelability. In order to adjust the curing time of the mixture of the curing agent A or curing agent B, diglycidyl ether of bisphenol AD, a polyfunctional epoxy resin, and an inorganic pigment (hereinafter referred to as "epoxy resin AD"), the epoxy There is no problem even if a small amount of a curing accelerator such as 2-ethyl-4-methylimidazole or 2,4,6-tris(dimethylaminomethyl)phenol is added to the resin AD. Furthermore, the modified polyolefin resin and polyolefin resin used in the present invention will be explained. The polyolefin used in the present invention refers to low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, ethylene-propylene block or random copolymer, ethylene-butene-1 block or random copolymer. Alternatively, it is one type or a mixture of two or more types of thermoplastic resins such as ethylene-propylene-diene terpolymer. The modified polyolefin resin used in the present invention includes polyolefins such as maleic acid, acrylic acid,
Modified with unsaturated carboxylic acid or its anhydride such as methacrylic acid, itaconic acid, and hymic acid;
Alternatively, modified products thereof are appropriately diluted with polyolefin, silicon-grafted polyolefins obtained by grafting unsaturated silane compounds such as vinyltrimethoxysilane to polyolefins, or silicone-grafted polyolefins diluted with polyolefins, etc. However, other modified polyolefin resins may also be used. Furthermore, if the modified polyolefin resin layer requires heat resistance or high strength,
General commercially available silica powder, titanium oxide powder, glass powder, slag powder, mica powder, wollastonite powder, Mapico powder, molybten trioxide powder, silicomolybutenic acid powder, tungsten trioxide powder, silicotungsten powder is added to the above modified polyolefin resin. It is also possible to use one or more kneaded reinforcing materials such as inorganic fillers such as acid powder or fibrous fillers such as glass fibers, slag fibers, carbon fibers, and ceramic fibers. In addition, if weather resistance is required for the polyolefin resin layer, weather-resistant materials such as carbon black, inorganic pigments, or organic pigments can be kneaded with the polyolefin resin described above. When heat resistance and high strength are required, commercially available silica powder, titanium oxide powder, glass powder, slag powder, mica powder, wollastonite powder, molybten trioxide powder, silicomolybutenic acid powder, tungsten trioxide powder, Inorganic fillers such as silicotungstic acid powder, glass fiber, carbon fiber,
One or more reinforcing materials such as fibrous fillers such as slag fibers, ceramic fibers, stainless steel fibers, copper fibers, and aluminum fibers may be kneaded and used. The polyolefin-coated metal tube according to the present invention is
For example, it can be obtained by the manufacturing method shown in FIG.
That is, the chromate treatment agent is applied to the surface of the metal tube 1 from which scale and the like have been removed by the chromate treatment agent application device 7, and baked by the heating device 8. Next, the epoxy resin AD is applied to the surface using the coating device 9, and heated and cured using the post-heating device 10. Next, a modified polyolefin resin is applied to the surface using a modified polyolefin resin coating device 11, a polyolefin resin 5 is extruded and coated using a T-die 12, and the tube is cooled using a cooling device 13 to produce a polyolefin-coated metal tube. do. In the case of the manufacturing method described above, after the chromate treatment agent is applied to the surface of the metal tube 1 and baked by the heating device 10, and before the metal tube reaches the modified polyolefin resin coating device 13, the metal It is good if a thermosetting epoxy resin layer is formed on the surface of the pipe and is sufficiently cured.The above epoxy resin AD can be applied by spraying with a spray paint machine, roll coating, ironing, brushing, flow coating, etc. Any of the conventionally known methods can be appropriately selected and used. The method of heating the metal tube using the post-heating device 12 is as follows:
The method can be appropriately selected from conventionally known methods such as high-frequency induction heating, far-infrared heating, laser irradiation heating, and gas heating. Regarding the above-mentioned post-heating device 12, when the above-mentioned metal tube 1 has a large wall thickness, the heating device 10 has a large heating capacity, and the above-mentioned thermosetting epoxy resin layer is sufficiently cured, the post-heating device 12 There is no problem even if the heating is omitted. In addition, in FIG. 2, a method of electrostatically coating modified polyolefin resin powder is used in the modified polyolefin resin coating device 13, but a method of extrusion coating the modified polyolefin resin using a T-die or a round die, Conventionally known methods can be employed, such as a method in which a modified polyolefin resin and a polyolefin resin are stacked as two layers and extruded from a single T-die or round die. A partial cross section of the polyolefin-coated metal tube according to the present invention obtained as described above is as shown in FIG. Chromate treatment agent layer containing a silica-based dispersant; 3 is a thermosetting epoxy resin layer consisting of a mixture of bisphenol AD diglycidyl ether, a polyfunctional epoxy resin, an inorganic pigment, and an amine curing agent; 4 is a modified polyolefin resin Layer 5 indicates a polyolefin resin layer. In addition, 2 in the figure is 350 to 1200 as the total chromium weight.
With a coating weight of mg/ ^m2 , 3 has a thickness of 5 to 350μ, 4
Good results can be obtained when the thickness of 5 is 0.05 to 0.5 mm, and the thickness of 5 is 0.1 to 10 mm. Hereinafter, the present invention will be specifically explained with reference to Examples. (Example) Example 1 A steel pipe (200A x 5500m length x 5.8mm thickness) was grit blasted, and a chromate treatment agent containing a silica-based dispersant was applied to the surface of the pipe to reduce the total amount of chromium deposited to 620.
mg/ ^m2 , heated to 190℃ and baked for 3 minutes, then applied epoxy resin AD to a film thickness of 50μ using a spray paint machine, and then applied modified polyethylene resin to a film thickness of 150μ. The polyethylene resin was coated electrostatically to give a film thickness of 3.2 mm, and the polyethylene resin was extruded and coated using a T-die to a film thickness of 3.2 mm, and then cooled to produce a polyethylene-coated steel pipe (A) according to the present invention. At that time, the chromate treatment agent containing the above-mentioned silica-based dispersant and the epoxy resin AD were prepared in the following manner. Chromate treatment agent containing silica-based dispersion: In an aqueous solution containing 8% by weight of chromic anhydride,
Polyvinyl alcohol was added for reduction, and the weight ratio of hexavalent chromium to total chromium was adjusted to 0.72. Next, 5 g of silica fine powder was mixed and dispersed as a dispersant into this aqueous solution 1, and then pyrogallol was added and further reduced to adjust the weight ratio of hexavalent chromium to total chromium to 0.62. . Epoxy resin AD: A mixture of the following components and composition was used. Diglycidyl ether of bisphenol AD
100 parts by weight Tetraglycidyl metaxylene diamine 11 parts by weight Silica fine powder 3 parts by weight Modified polyamine of m-xylylene diamine (having the following molecular structure) 37 parts by weight In addition, as a comparison material, a heat treatment material corresponding to JP-A No. 59-222275, which is made of a mixture of the following ingredients and composition in place of the epoxy resin AD in the same manner as the polyethylene-coated steel pipe (A) above, was also used. Polyethylene-coated steel pipe coated with curable epoxy resin (B), diglycidyl ether of bisphenol A
100 parts by weight Silica fine powder 3 parts by weight Modified polyamine of m-xylylene diamine
35 parts by weight, and a polyethylene-coated steel pipe coated with a thermosetting epoxy resin corresponding to JP-A No. 59-62373, which is made of a mixture of the following components and composition, instead of the diglycidyl ether of bisphenol A mentioned above. (C) was produced. diglycidyl ether of bisphenol A
50 parts by weight diglycidyl ether of bisphenol F
50 parts by weight Silica fine powder 3 parts by weight Modified polyamine of m-xylylene diamine
33 parts by weight Regarding the above polyethylene coated steel pipes A to C, adhesion test (measurement temperature 25°C, peel angle 90°, peeling speed 50 mm/min), high temperature cathodic peel test (test temperature 90°C, electrolyte solution 3% NaCl) , voltage −1.5V [Cu/
[CuSO ₄ standard electrode], initial Holliday diameter 5 mmφ, test days 90 days, and after the test, the Holliday diameter χ mm was measured, and the converted peeling radius R was calculated using the following formula; The results are shown in Table 1.

[Table] From the results in Table 1, there is a remarkable difference in the performance of both adhesion and high-temperature cathode peeling resistance, especially between the chromate treatment agent containing a silica-based dispersant as a surface treatment agent and the epoxy resin AD. The polyethylene coated steel pipe (A) according to the present invention using a polyethylene coated steel pipe (A) is a polyethylene coated steel pipe corresponding to JP-A-59-222275, which is made of a mixture of a chromate treatment agent, diglycidyl ether of bisphenol A, an inorganic pigment, and an amine hardening agent. JP-A-59-1999-, which consists of a coated steel pipe (B), a chromate treatment agent, a diglycidyl ether of bisphenol F, a diglycidyl ether of bisphenol A, a mixture of an inorganic pigment and an amine curing agent.
It was confirmed that significantly superior results were obtained compared to the polyethylene-coated steel pipe (C) coated with a thermosetting epoxy resin corresponding to Publication No. 62373. Example 2 The above polyethylene-coated steel pipe (A) was produced in the same manner as in Example 1, except that the type of dispersant mixed in the chromate treatment agent was changed as follows. Dispersant: 1 Fine powder silica 2 Colloidal silica 3 Tetraethoxysilane 4 No additive The above polyethylene coated steel pipe was subjected to the above adhesive force test and high temperature cathodic peel test, and the comparative results are shown in Table 2.

[Table] From the results in Table 2, the performance of both adhesive strength and high-temperature cathode peeling resistance decreases slightly when no dispersant is added, but when a dispersant is added, the performance decreases slightly. Good results were obtained regardless of the type of chromate treatment agent, confirming that it is necessary to mix a dispersant into the chromate treatment agent of the present invention. Example 3 The above-mentioned polyethylene-coated steel pipe (A) was produced in the same manner as in Example 1, except that the type of polyfunctional epoxy resin used in preparing the epoxy resin AD was changed as follows. Polyfunctional epoxy resin; 1 Tetraglycidyl metaxylene diamine 2 Tetraglycidyl-1,3-bisaminomethylcyclohexane 3 Tetraglycidyl amino diphenylmethane 4 Triglycidyl-P-aminophenol 5 Trimethylolpropane triglycidyl ether 6 Tri(glycidyl oxyphenyl) (enyl)butane 7 Tetra(glycidoxyphenyl)ethane 8 No additive The above polyethylene coated steel pipe was subjected to the above adhesive force test and high temperature cathodic peel test, and the comparison results are shown in Table 3.

【table】

[Table] From the results in Table 3, the performance of both adhesive strength and high-temperature cathode peeling resistance decreases slightly when a multifunctional epoxy resin is not added, but when a multifunctional epoxy resin is added. showed good results regardless of the type of polyfunctional epoxy resin, confirming that it is necessary to add a polyfunctional epoxy resin to the epoxy resin AD according to the present invention. Example 4 The above-mentioned polyethylene-coated steel pipe (A) was produced in the same manner as in Example 1, except that the type of inorganic pigment used in preparing the epoxy resin AD was changed as follows. Inorganic pigments: 1 Silica fine powder 2 Titanium oxide fine powder 3 Zirconium oxide fine powder 4 Zinc oxide fine powder 5 Iron oxide fine powder 6 Molybdenum trioxide fine powder 7 Tungsten trioxide fine powder 8 Mica flakes 9 Additive-free The above polyethylene coating The steel pipes were subjected to the above-mentioned adhesive force test and high temperature cathode peel test, and the comparative results are shown in Table 4.

【table】

[Table] From the results in Table 4, the performance of both adhesion and high-temperature cathode peeling resistance decreases slightly when inorganic pigments are not added, but when inorganic pigments are added, Good results were obtained regardless of the type of inorganic pigment, and it was confirmed that it is necessary to add an inorganic pigment to the thermosetting epoxy resin according to the present invention. Example 5 The above-mentioned polyethylene-coated steel pipe (A) was prepared in the same manner as in Example 1, except that the type of curing agent used in preparing the epoxy resin AD was changed as follows. Amine curing agent; 1 modified polyamine of m-xylylene diamine 2 3,9-bis(3-aminopropyl)-2,
Modified product of 4,8,10-tetraoxaspiro[5,5]undecane modified with phenyl glycidyl ether 3 m-xylylenediamine 4 3,9-bis(3-aminopropyl)-2,
4,8,10-tetraoxaspiro[5,5]undecane 5 m-phenylenediamine 6 p,p'-diaminodiphenylmethanoic anhydride curing agent; 7 Methylnadic anhydride 8 Hexahydrophthalic anhydride The above polyethylene The coated steel pipes were subjected to the above-mentioned adhesive force test and high temperature cathode peel test, and the comparative results are shown in Table 5.

[Table] From the results in Table 5, it can be seen that the modified polyamine of m-xylene diamine or 3,9-bis(3-aminopropyl)- 2, 4,
It was confirmed that good results could be obtained when a modified product obtained by modifying 8,10-tetraoxaspiro[5,5]undecane with phenyl glycidyl ether was used. (Effects of the Invention) As is clear from the examples, the polyolefin-coated steel pipe according to the present invention is significantly superior in adhesion between the steel pipe and the modified polyolefin resin layer and in high-temperature cathode peeling resistance, compared to conventional polyolefin-coated steel pipes. As a result, we have been able to provide polyolefin-coated steel pipes with unprecedented durability.

[Brief explanation of drawings]

FIG. 1 is a partial cross-section of a polyolefin-coated metal tube according to the present invention, FIG. 2 is a schematic explanatory diagram showing an embodiment of the present invention, and FIG. 3 is a partial cross-section of a polyolefin-coated metal tube according to a conventional method. . 1...Metal tube, 2...Chromate treatment agent layer containing a silica-based dispersant, 3...Thermosetting consisting of a mixture of diglycidyl ether of bisphenol AD, a polyfunctional epoxy resin, an inorganic pigment, and an amine curing agent type epoxy resin layer, 4... modified polyolefin resin layer, 5... polyolefin resin layer, 6...
...Thermosetting epoxy resin layer consisting of a mixture of diglycidyl ether of bisphenol A, an inorganic pigment and an amine curing agent, or a diglycidyl ether of bisphenol A, a diglycidyl ether of bisphenol F, an inorganic pigment and an amine curing agent Thermosetting epoxy resin layer consisting of a mixture of curing agents, 7...Chromate treatment agent coating device, 8...Heating device, 9...Thermosetting epoxy resin coating device,
10... Post-heating device, 11... Modified polyolefin resin coating device, 12... Die, 13... Cooling device.

Claims (1)

[Claims] 1. A chromate treatment agent layer containing a silica-based dispersant, a bisphenol AD layer on the outer surface of a steel pipe from the inside,
diglycidyl ether, polyfunctional epoxy resin,
A polyolefin-coated metal tube laminated with a thermosetting epoxy resin layer consisting of a mixture of an inorganic pigment and an amine curing agent, a modified polyolefin resin layer, and a polyolefin resin layer, which is treated as a chromate treatment agent containing a silica-based dispersant. A mixture of 2 to 45 g of silica-based dispersant to 100 g of chromic anhydride in the agent is used, and tetraglycidyl meta-xylene diamine, tetraglycidyl-1, tetraglycidyl-1, Any of 3-bisaminomethylcyclohexane, tetraglycidylaminodiphenylmethane, triglycidyl-p-aminophenol, trimethylolpropane triglycidyl ether, tri(glycidoxyphenyl)butane, tetra(glycidoxyphenyl)ethane and 3,9-bis(3-aminopropyl)-2, as an amine curing agent for thermosetting epoxy resin.
Phenyl glycidyl ether modified product of 4,8,10-tetraoxaspiro[5,5′]undecane, i.e. or a modified polyamine consisting of a condensate of m-xylylenediamine and epichlorohydrin, i.e. A polyolefin-coated metal tube with excellent high-temperature cathode peelability, characterized by using.