JPH0322817B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyolefin-coated steel pipe coated with polyolefin via a primer layer and an adhesive layer. Polyolefin-coated steel pipes are often used as line pipes for transporting crude oil, natural gas, etc., but the facility environments are often subject to harsh environmental conditions.
The coating layer requires high adhesion and corrosion resistance. Polyolefin resin is a non-polar crystalline resin.
Although it has excellent chemical stability and mechanical properties, it has poor adhesion to steel pipes. For this reason, a modified polyolefin having excellent mechanical properties (for example, a copolymer of ethylene and acrylic acid, a copolymer of ethylene and maleic anhydride, etc.) is used as an adhesive layer under the polyolefin layer. This modified polyolefin adhesive layer has excellent primary adhesion to the steel pipe surface, but when exposed to a severe corrosive environment, the adhesion decreases.As a countermeasure, an epoxy resin-based primer is usually applied to the steel pipe surface as an adhesive base. It is used. Therefore, polyolefin coated steel pipes are manufactured by the following procedure. After removing the distribution film on the surface of the steel pipe by sandblasting, shotblasting, etc., a primer composition consisting of an epoxy resin and an amine hardener is applied, and the temperature of the steel pipe is lowered using an induction heater or hot air oven. Raise the temperature to 130-200℃,
It is thermally cured by its latent heat or hot air. The primer film may be damaged by the conveyor roll,
After being sufficiently cured to prevent peeling, it is passed through the next conveyor roll, and further coated with a polyolefin resin via a modified polyolefin resin adhesive layer using a melt extrusion method or the like. Currently used epoxy primers cure at temperatures of 130℃ or higher for 3 to 4 hours.
It is necessary to heat the steel pipe for several minutes, and there are major restrictions when coating the steel pipe while moving it in the axial direction of the steel pipe with conveyor rolls. That is, in order to transport the steel pipe smoothly, the distance between the transport rollers must be less than half the length of the steel pipe. Assuming that the distance between the conveying rollers is 3 m and the time required for curing the primer is 3 minutes, the steel pipe conveying speed must be 3 m/3 minutes = 1 m/minute or less. In addition to this low productivity, a large amount of thermal energy is required to heat the steel pipe, and there is a strong desire to shorten the curing time of the primer. In order to solve this problem, the present inventors focused their research on an ultraviolet curable composition that cures in a short time and does not require thermal energy during curing, and finally completed the present invention. The present invention provides a polyolefin-coated steel pipe in which the surface of the steel pipe is coated with a polyolefin layer via a primer layer and an adhesive layer, wherein the primer layer comprises (a) an epoxy compound and a monocarboxylic compound having an ethylenically unsaturated bond; An unsaturated epoxy ester which is a reaction product of (b) a monomer having an ethylenically unsaturated group capable of addition polymerization with the unsaturated epoxy ester (c) an ultraviolet curable composition containing a photosensitizer. The present invention relates to a polyolefin-coated steel pipe characterized by the following. By using this ultraviolet curable composition according to the present invention as a primer, the time required for curing the primer is significantly shortened, so the productivity of polyolefin-coated steel pipes is significantly improved. The advantage is that the thermal energy required for curing is saved. The ultraviolet curable composition used as the primer layer in the present invention (hereinafter referred to as the composition of the present invention) will be explained below. (a) Unsaturated epoxy ester (a) Epoxy compound: An epoxy compound synthesized by the reaction of bisphenol A and epichlorohydrin or methylepichlorohydrin (hereinafter abbreviated as (methyl)epichlorohydrin) (manufactured by Ciel Chemical, Epicote #827, # 828, #834,
#1001, #1004, #1007, manufactured by Dainippon Ink,
Epicron #800, #1000, etc.); Epoxy compounds obtained by reacting novolaks or resols obtained by reacting phenols and formaldehyde under acidic or alkaline catalysts with (methyl)epichlorohydrin (manufactured by Dow Chemical Company, DEN
#431, #438, #448, etc.); Epoxy compounds obtained by reacting polyols with (methyl)epichlorohydrin (Dow Chemical Company, DER #732, #736)
Epoxy compounds obtained by reacting polybasic acids with (methyl)epichlorohydrin (Nippon Kayaku, AK#737, #838, Dainippon Ink, Epiclon #200, #300, #400, etc.); Poly Examples include epoxy compounds obtained by reacting alkylene glycol and (methyl)epichlorohydrin. In addition, the above epoxy compound and a monobasic acid (e.g. acetic acid, propionic acid, benzoic acid, etc.) and/or a dibasic acid (e.g. succinic acid, adipic acid, dimer acid, phthalic acid, etc.) are mixed so that the epoxy group remains in the molecule. An epoxy ester compound obtained by reacting with a suitable equivalent ratio can also be used. (b) Monocarboxylic compounds having ethylenically unsaturated bonds: acrylic acid, methacrylic acid, crotonic acid,
Cinnamate, itaconic acid monoalkyl esters (e.g. methyl ester, ethyl ester, etc.)
can be exemplified. Two or more of these may be used in combination. The unsaturated epoxy ester is obtained by reacting the epoxy compound and the unsaturated monocarboxyl compound in approximately equivalent amounts. The reaction proceeds by heating to 100 to 130°C, but a tertiary amine such as N,N-dimethylaniline, pyridine, triethylamine, hexamethylenediamine, N,N-dimethylaminoethyl methacrylate, etc. may be used as a catalyst. The process progresses smoothly. The reaction is usually completed in 5 to 10 hours and the desired unsaturated epoxy ester is obtained. (b) Monomers capable of addition polymerization with unsaturated epoxy compounds: Monomers having ethylenically unsaturated groups capable of addition polymerization with the unsaturated epoxy esters used in the present invention include those conventionally used in the field. For example, methyl (meth)acrylate (indicates both methyl acrylate and methyl methacrylate; the same applies hereinafter),
Ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate,
2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxy Ethyl (meth)acrylate, carbitol (meth)
Acrylate, dipropylene glycol monomethyl ether mono(meth)acrylate, triethylene glycol monomethyl ether mono(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, ethylene glycol di(meth)acrylate, Diethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, 1,6
- hexanediol di(meth)acrylate,
Examples include neopentyl glycol di(meth)acrylate, trimethylolpropane triacrylate, and the like. These may be used alone or in combination of two or more. Among these compounds, (meth)acrylate is used for the purpose of adjusting the viscosity when coating the composition of the present invention, and is mixed in an amount of up to 100 parts by weight per 100 parts by weight of the above unsaturated epoxy ester. This is desirable. Mixing an excessive amount will result in a decrease in the curability of the composition of the present invention. In addition, di(meth)acrylate and compounds having three or more (meth)acryloyl groups are used to adjust hardenability, but if used in large quantities, they impede adhesion to steel pipes, so their use It is necessary to pay attention to the amount. In addition, in order to improve curability, unsaturated polyesters (for example, those obtained by co-condensing phthalic acid, diethylene glycol, and acrylic acid),
It is also possible to use unsaturated polyurethane (e.g., 1 mol of trimethylolpropane: 3 mol of tolylene diisocyanate adduct with 3 mol of 2-hydroxyethyl (meth)acrylate) mixed into the above composition. However, these tend to reduce the adhesion with steel pipes and with modified polyolefins, so it is necessary to pay attention to the amount used. (c) Photosensitizers: Photosensitizers used in the present invention include benzoin, benzoin ether, benzoin isopropyl ether, and other benzoin alkyl ethers, anthraquinones, 2-ethylanthraquinone, and other anthraquinones, benzophenone,
Acetophenones such as acetophenone and 2,2-diethoxy-2-phenylacetophenone;
Thioxanthone such as 2-chlorothioxanthone and 2-methylthioxanthone, benzyl dimethyl ketal, 2-hydroxy-2-methyl-
Examples include 1-phenylpropan-1-one. These can be used alone or in combination of two or more. This photosensitizer may be present in the coating composition from 0.5 to
Blend in a range of 10% by weight. If the amount is less than the specified amount, the curing of the composition of the present invention will be slow during ultraviolet curing, while if it is in excess, the curability will not improve and it will be economically disadvantageous. In addition to the above-mentioned components (a) to (c), the composition of the present invention may contain, if necessary, antifoaming agents, anti-sagging agents, surface conditioners, rust preventives, fillers, colorants, solvents, and other conventional coating materials. The materials used in the composition may be blended within a range that does not adversely affect curability or corrosion resistance. Next, in order to coat a steel pipe with the composition of the present invention, conventionally known techniques may be employed, such as airless spraying, roller coating, brush coating, ironing, and the like. The composition applied to the steel pipe may then be cured by irradiating it with ultraviolet light for 1 to 10 seconds according to a conventional method. As a source of ultraviolet rays, ordinary high-pressure mercury lamps, metal halide lamps, etc. can be used.For example, if multiple 6KW high-pressure mercury lamps (lamp voltage 6KW, emission length 50cm) are placed around the steel pipe so that the surface of the steel pipe is uniformly irradiated. good. Next, a modified polyolefin is applied by a conventional extrusion coating method to form an adhesive film, and then a polyolefin is coated by an extrusion coating method to produce a polyolefin-coated steel pipe. Furthermore, the composition of the present invention can be used to perform phosphate-based and chromic acid-based inorganic chemical conversion treatments (dipping method or composite treatment solution coating method with silica sol) that are applied to ordinary coating bases before coating steel pipes. Even when combined with the surface treatment primer according to the present invention, polyolefin-coated steel pipes with even better adhesion and water resistance can be produced. In this way, the present invention provides sufficient adhesive strength,
It is possible to economically and practically produce a polyolefin-coated steel pipe having corrosion resistance, and it can be said to have great industrial significance. Hereinafter, the present invention will be explained in more detail based on resin synthesis examples and examples. In addition, "parts" and "%" in the examples are "parts by weight" and "% by weight" respectively.
means. For convenience of the experiment, a steel plate test piece was used in place of the steel pipe in the example. Synthesis Example 1 In a flask equipped with a stirrer, reflux condenser, thermometer, and dropping funnel, 950 g (approximately 2 epoxy equivalents) of epichlorohydrin-bisphenol A type epoxy resin (manufactured by Ciel Chemical, trade name Epicote #1001),
Add 729 g of tetrahydrofurfuryl acrylate, 1.8 g of hydroquinone, and 9.1 g of N,N-dimethylaminoethyl acrylate, and heat to 100°C.
While stirring, 144 g (2 mol) of acrylic acid was added dropwise over 1 hour. Thereafter, the mixture was reacted at the same temperature for 5 hours. The acid value of the resulting resin composition was 3. Synthesis Example 2 Into a flask equipped with a stirrer, reflux condenser, thermometer, and dropping funnel, 1900 g (approximately 2 epoxy equivalents) of epichlorohydrin-bisphenol A type epoxy resin (manufactured by Ciel Chemical, trade name Epicote #1004),
1363 g of tetrahydrofurfuryl acrylate, 3.4 g of hydroquinone, and 17 g of N,N-dimethylaminoethyl acrylate were added and heated to 100°C, and 144 g (2 moles) of acrylic acid was added dropwise over 1 hour with stirring. Thereafter, the mixture was allowed to react at the same temperature for 7 hours. The acid value of the obtained resin composition was 3.5. Synthesis Example 3 Into a flask equipped with a stirrer, reflux condenser, thermometer, and dropping funnel, 380 g (approximately 2 epoxy equivalents) of epichlorohydrin-bisphenol A type epoxy resin (manufactured by Ciel Chemical, trade name Epicote #828),
349 g of tetrahydrofurfuryl acrylate, 0.9 g of hydroquinone, and 4.4 g of N,N-dimethylaminoethyl acrylate were added and heated to 100°C, and 144 g (2 moles) of acrylic acid was added dropwise over 1 hour with stirring. Thereafter, the mixture was reacted at the same temperature for 4 hours. The acid value of the resulting resin composition was 5. Synthesis Example 4 Into a flask equipped with a stirrer, reflux condenser, thermometer, and dropping funnel, 760 g (approximately 4 epoxy equivalents) of epichlorohydrin-bisphenol A type epoxy resin (manufactured by Ciel Chemical, trade name Epicote #828),
Tetrahydrofurfuryl acrylate 264g, adipic acid 146g (1 mol), hydroquinone 1.3g,
N,N-dimethylaminoethyl acrylate 6.4
After heating at 120° C. for 1 hour with stirring, 144 g (2 mol) of acrylic acid was added dropwise over 1 hour at the same temperature with stirring. Thereafter, the mixture was reacted at the same temperature for 4 hours. The acid value of the resulting resin composition was 3.5. Examples 1 to 7 and Comparative Example 1 Steel plates (dimensions 3.2 x 70 x 150 mm) and applied onto a 2KW high-pressure mercury lamp (manufactured by Nippon Battery, product name HI-20N, emission length 25
cm, a condensing type lamp was used), and was cured by passing it through a position 8 cm from the bottom end of the lamp in a direction perpendicular to the length direction of the lamp at a speed of 3 m/min. On the film of the ultraviolet curable composition obtained as above, a sheet of modified polyethylene (manufactured by Mitsui Petrochemicals, trade name Admer NE050) is heat-fused at 170°C to form a film with a thickness of 300 to 400μ. A preheated polyethylene film (a low density polyethylene film with an MI value of 1.5 and a density of 0.925, film thickness 3 to 4 mm) was then pressed onto the polyethylene film at a temperature of 170°C and a pressure of 0.1 Kg/cm ² for 2 minutes. A laminate of steel plates was obtained. In Comparative Example 1, the surface of the steel plate was sandblasted without applying a UV-curable composition film, and after preheating to 170°C, the modified polyethylene and polyethylene film were coated. Furthermore, in Examples 6 and 7 (Table 2), the first
Before applying the formulations of Examples 1 and 2 in the table onto a steel plate (3.2t x 70 x 150mm) whose surface was sandblasted, the steel plate was preheated to 50-60℃, and the steel plate was coated with a chromic acid-based chemical compound. In Example 6, a treatment solution (a coating-drying treatment in which ethylene glycol is mixed with an aqueous CrO ₃ solution to reduce 40% of CrO ₃ and colloidal silica (particle size 14 μm) is mixed therein) was used (Example 6), and in Example 7, Similarly, phosphoric acid was applied to a steel plate preheated to 50-60℃.
Ca-based chemical conversion treatment solution (H ₂ PO ₄ 100 to 1 water
g, 200 g of CaPO ₄ and colloidal silica (particle size
A coating-drying treatment in which 30 g of 14 m
^m2 ). The adhesive strength and corrosion resistance of the thus obtained laminate were tested by the following method. The results are shown in Table 2. [Adhesion strength] After making a 10mm-wide scratch on the laminate that reaches the steel surface, part of it is peeled off and the 180° peel strength (adhesion strength) between the steel surface and the polyethylene film is measured using Tensilon.
Measurement was performed at 20°C and a tensile speed of 10 mm/min. In addition, in order to test the change in adhesive strength of the laminate over time, the adhesive strength was measured at 20°C using the above method after 300 hours of accelerated weathering exposure using a Sunshine Weather-Ometer. [Corrosion resistance] Drill a 5 mm wide hole in the laminate until the steel base is exposed, immerse it in 3% saline solution at room temperature, and apply a voltage to the laminate to increase the potential relative to the Cu/CuSO ₄ standard electrode. was set at -1.5V, and the degree of attack was measured by the penetration distance of the knife blade. As is clear from the results in Table 1, the laminates having the ultraviolet curable composition of the present invention as a primer (Examples 1 to 5) were compared to the laminates having no primer layer (Comparative Example 1). It has strong adhesive strength and excellent corrosion resistance. Further, when a chemical conversion treatment is applied to the base of this ultraviolet curable primer (Examples 6 to 7), even better corrosion resistance is obtained.

[Table] *2 Benzoin isobutyl ether

【table】

Claims (1)

[Scope of Claims] 1. A polyolefin-coated steel pipe in which the surface of the steel pipe is coated with a polyolefin layer via a primer layer and an adhesive layer, wherein the primer layer comprises (a) an epoxy compound and a monomer having an ethylenically unsaturated bond; An unsaturated epoxy ester which is a reaction product with a carboxyl compound (b) A monomer having an ethylenically unsaturated group capable of addition polymerization with the unsaturated epoxy ester (c) An ultraviolet curable composition containing a photosensitizer A polyolefin-coated steel pipe characterized by being made of polyolefin.