JPH09277468A - Resin-coated aluminum pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin-coated aluminum pipe which has high adhesive strength between the surface of the aluminum pipe and a coating resin, which are hardly separated even in a secondary processing such as bending, and demonstrates good corrosion resistance even brought into contact with a corro sive substance. SOLUTION: In a resin-coated aluminum pipe, the resin is a mixture of 5-50wt.% of epoxy-modified polypropylene which is obtained by reacting polypropylene with a mixture of a vinyl monomer containing an epoxy group and an aromatic vinyl monomer and has an epoxy equivalent of 2,000 50,000g/eq and 95-5wt.% of polyamide.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a resin-coated aluminum tube. More specifically, it is a resin-coated aluminum tube that is used in a region that has excellent adhesive strength at the interface between the coating resin and the surface of the aluminum tube and that requires corrosion resistance (or corrosion resistance). The present invention relates to a resin-coated aluminum pipe used for automotive piping such as equipment piping, brake piping, power steering piping, oil piping, and other structural members.

[0002]

2. Description of the Related Art Conventionally, pipes made of pure aluminum or aluminum alloy (hereinafter
Sometimes referred to simply as aluminum tube) is widely used. This is because the aluminum pipe is lighter in weight and has better corrosion resistance than steel pipes and copper pipes. In particular, the aluminization of piping in the heat exchanger system is actively promoted, and the aluminum alloy used is also JI
S A3003 alloy, JIS A6063 alloy and the like, which are relatively excellent in strength and corrosion resistance, are often used.

[0003]

However, when aluminum pipes are used for pipes used for automobiles and other structural members, they are exposed to an environment where they come into contact with corrosive substances such as seawater and snow melting salts on the road. It was not appropriate to use a normal aluminum tube for the purpose, and it was unavoidable to limit the use to a part where the environment of use was not so strict, such as in an engine room.

As a means for improving the corrosion resistance of an aluminum tube, a method of applying powder coating such as nylon 12 or extrusion coating on the surface of the aluminum tube has been proposed and partially put into practical use. However, when nylon 12 is powder coated, the corrosion resistance is increased, but the strength of the coating is not sufficient for external damage due to flying stones, etc. There is a problem that the crevice corrosion of the interface will progress.

For the purpose of improving such drawbacks, it is possible to coat the surface of the aluminum pipe by extrusion coating of nylon 12, and in this case, a coating having good adhesive strength can be obtained, so that various automobile pipes can be obtained. It is suitable for various types (see JP-A-7-233480). However,
Nylon 12 is the most expensive polyamide resin,
From the viewpoint of cost reduction, coating with a cheaper resin material such as nylon 6 is desired. However, while Nylon 6 has excellent mechanical strength and excellent heat distortion resistance,
When extrusion coating is applied to the surface of an aluminum pipe, it has the disadvantage of poor adhesiveness at the interface and low adhesive strength, and is not suitable for members that undergo severe processing such as automobile piping and require corrosion resistance. There was a difficulty.

The objects of the present invention are as follows. (1) To provide a resin-coated aluminum tube which has excellent adhesive strength at the interface between the surface of the aluminum tube and the coating resin and which is difficult to peel off even when subjected to secondary processing such as bending. (2) To provide a resin-coated aluminum tube that exhibits excellent corrosion resistance even when exposed to an environment that comes into contact with a corrosive substance. (3) To provide an economically advantageous resin-coated aluminum pipe which has the characteristics of (1) and (2) above.

[0007]

In order to solve the above problems, the present invention provides a resin-coated aluminum tube in which the surface of an aluminum or aluminum alloy tube is coated with a resin, in which the resin coating is epoxy on polypropylene. The epoxy equivalent obtained by reacting the mixture of the group-containing vinyl monomer and the aromatic vinyl monomer is 2000 to 50.
000g / eq epoxy modified polypropylene 5-50
A resin-coated aluminum tube having excellent adhesion between the resin and the aluminum tube, which is a mixture of 95% by weight of polyamide resin and 95 to 50% by weight of polyamide resin.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below.
As the material of the aluminum pipe to be covered in the present invention, pure aluminum JIS A1100 alloy, Al
-Mn-based A3003 alloy, A3004 alloy, Al-M
g-based A5052 alloy, Al-Mg-Si-based A606
3 alloys and the like, but are not limited to these exemplified alloys. Also, regarding the manufacturing method of the aluminum tube, a seamless aluminum tube by the indirect extrusion method or the like is recommended from the viewpoint of corrosion resistance, but the invention is not limited to this, and hot extrusion processing or drawing that is usually adopted is used. It can be manufactured by processing. Further, the heat treatment during or after the manufacturing process is not particularly limited, and may be performed by a heat treatment method such as an annealing treatment, a solution treatment, or an aging treatment that is adopted when manufacturing an ordinary aluminum alloy base pipe. You can

If the aluminum tube is subjected to a chromate surface treatment to form a chromate film before being coated with a resin or a surface treatment with a silane coupling agent, the adhesion with the coating resin can be further improved. It is possible and preferable. When the chromate surface treatment is applied to the surface of the aluminum tube, it is usually immersed in an acid solution such as nitric acid or hydrochloric acid as a pretreatment, then immersed in an alkaline solution such as caustic soda or caustic potash, and further immersed in an acid solution. Washing·
A method of drying is adopted, but according to this method,
It is desirable to perform the pretreatment using a commercially available treatment liquid or the like.

The chromate treatment must be performed uniformly and evenly on the outer peripheral surface of the aluminum tube. The chromate treatment method itself may be a method usually performed on the outer peripheral surface of an aluminum tube, such as a phosphoric acid chromate treatment, a chromate chromate treatment, or a coating chromate treatment. The amount of chromium deposited after the chromate treatment was 10
It is preferably about 100 mg / m ² .

When the surface treatment is performed with a silane coupling agent, the silane compound is preferably a compound having at least one functional group selected from an epoxy group, a methacryloxy group, an amino group, a chloro group or a mercapto group and a hydrolyzable group. Specifically, epoxy-based compounds such as 3-glycidoxypropyltrimethoxysilane and 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-
Methacryloxy-based compounds such as methacryloxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, N-
(2-aminoethyl) 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) 3-aminopropylmethyldimethoxysilane and other amino-based compounds, 3-chloropropyltrimethoxysilane and other chloro-based compounds, and 3
Examples thereof include mercapto-based silane compounds such as mercaptopropyltrimethoxysilane.

The method of applying the silane compound to the aluminum tube is as follows.
A solution diluted with a solvent such as toluene and applied (or dipped) with a brush or a coating roll on the outer surface of an aluminum tube that has been pretreated in the same manner as in the case of chromate treatment, and then dried it can. As a surface treatment method other than the chromate treatment and the application of the silane compound, a method of forming an organic titanium salt coating used on the outer peripheral surface of the aluminum tube may be used.

The resin for coating the surface of the aluminum tube (hereinafter also referred to as coating resin) is an epoxy-modified polypropylene 5 obtained by reacting a mixture of polypropylene, an epoxy group-containing vinyl monomer and an aromatic vinyl monomer. ~ 5
It is a mixture of 0% by weight and 95 to 50% by weight of polyamide resin, and the epoxy equivalent of the epoxy-modified polypropylene must be in the range of 2000 to 50000 g / eq. If the epoxy equivalent of the epoxy-modified polypropylene exceeds 50,000 g / eq, the adhesive strength at the interface between the aluminum tube surface and the coating resin does not improve,
Not preferred. Further, if it is less than 2000 g / eq, not only the rate of increase in adhesive strength reaches a peak, but also the preparation becomes difficult, which is not preferable. A particularly preferable epoxy equivalent range of the epoxy-modified polypropylene is 3,000 to 2
It is 10,000 g / eq.

In the present invention, the epoxy equivalent of epoxy-modified polypropylene means JIS K7236.
In the measurement method based on, change the solvent to xylene,
The melting temperature and the titration temperature are respectively changed to 160 to 180 ° C., and the values obtained by measurement according to K7236 are referred to.

The propylene-based polymer is a propylene homopolymer or a copolymer mainly composed of propylene and another olefin monomer or an ethylenic vinyl monomer (each of which contains propylene in an amount of 75% by weight or more). Polymer). Specific examples include isotactic polypropylene, propylene-ethylene copolymer, propylene-butene copolymer and the like. These propylene-based polymers may be used alone or as a mixture of two or more kinds. Further, the propylene-based polymer may be mixed with another polymer in a type and amount that does not impair the properties.

Examples of the epoxy group-containing vinyl monomer include glycidyl methacrylate, glycidyl acrylate, allyl glycidyl ether, methacryl glycidyl ether and the like. These may be used alone or as a mixture of two or more. Glycidyl methacrylate is particularly preferable as the epoxy group-containing vinyl monomer. In order to keep the epoxy equivalent of the epoxy-modified polypropylene in the above range, the amount of the epoxy group-containing vinyl monomer added is preferably 10% by weight or less of the propylene polymer. If it exceeds 10% by weight, not only the product may have a low molecular weight, but also the composition may have adverse effects such as water absorption and mechanical properties. A particularly preferred amount of addition of the epoxy group-containing vinyl monomer is 0.1
It is in the range of 5% by weight.

When the propylene-based polymer is modified with the epoxy group-containing vinyl monomer, an aromatic vinyl monomer is added for the purpose of improving the grafting efficiency and the compatibility with the polyamide resin. To do. Examples of the aromatic vinyl monomer include styrene, methylstyrene, vinyltoluene, vinylxylene, ethylvinylbenzene, isopropylstyrene, chlorostyrene, dichlorostyrene, bromostyrene and the like, and these may be used alone or in a mixture. Good.

The amount of the aromatic vinyl monomer added is preferably 50% by weight or less of the propylene polymer. If it exceeds 50% by weight, the performance of polypropylene is impaired, which is not preferable. The preferred addition amount of the aromatic vinyl monomer is 1 to 35.
% By weight. The aromatic vinyl monomer is used to prevent the modified propylene-based polymer from having a low molecular weight, and to improve the compatibility with the polyamide-based resin described later, at least the same amount as the addition amount of the epoxy group-containing vinyl monomer. Above, it is preferable to add 1 to 5 times.

To modify the above propylene-based polymer,
A propylene-based polymer, an epoxy group-containing vinyl monomer and an aromatic vinyl monomer, in the presence of a radical initiator,
Melt kneading polymerization reaction. The melt-kneading polymerization reaction can be carried out using a closed container such as a Banbury mixer or a continuous kneader such as an extruder. From the viewpoint of industrial production such as granulation, a method using an extruder is preferable. When using an extruder, a twin-screw extruder is better than a single-screw extruder.
It is preferable because supply of reactants, kneading, control of polymerization time and the like are easy.

To modify the propylene-based polymer, the propylene-based polymer in the form of powder or pellets is fed to an extruder and heated while being heated to a temperature of 130 to 250 ° C. to melt the propylene-based polymer. A mixture of an epoxy group-containing vinyl monomer and an aromatic vinyl monomer is kneaded to cause a polymerization reaction, and then the strand discharged from the die is cooled and pelletized using a pelletizer. The monomer (mixture) may be mixed with the propylene-based polymer in advance and then supplied to the extruder, or a propylene-based polymer in a molten state may be fed from the middle of the extruder cylinder using a liquid feeder. May be supplied to. When the ropylene-based polymer is mixed in advance, it is preferably impregnated with a monomer (mixture).

The radical initiator that can be used in the polymerization reaction is easily dissolved in the monomer (mixture), and
Since this modification reaction is carried out at the melt-kneading temperature of the propylene-based polymer, the decomposition temperature for obtaining a half-life of 1 minute is preferably in the range of 130 to 250 ° C. Specifically, t-butylperoctate, bis (t-butylperoxy) trimethylcyclohexane, cyclohexanoneperoxide, benzoylperoxide, dicumylperoxide, t-butylperbenzoate,
Examples thereof include dimethyl-di (t-butylperoxy) hexane and dimethyl-di (t-butylperoxy) hexyne.

The amount of these radical initiators used is usually from 0.1 to 10 per 100 parts by weight of the monomer (mixture).
It is selected in the range of parts by weight, and the range of 1 to 5 parts by weight is particularly preferable. The radical initiator may be dissolved in the monomer (mixture) in advance and added, or may be added to the mixture of the propylene polymer and the monomer (mixture) using a liquid feeder.

Since the propylene-based polymer is a radical-disintegrating polymer unlike the ethylene-based polymer, if the polymer is simply melt-heated, the main chain is apt to be cut, so that the molecular weight is apt to decrease. Therefore, in the presence of organic peroxide, the monomer (mixture)
A modified propylene-based polymer having a low molecular weight can be obtained even by performing a melt-kneading reaction with. However, according to the method of performing the melt kneading reaction, preferably by reacting in the presence of a stabilizer, the monomer (mixture) efficiently undergoes a modification reaction,
A modified propylene-based polymer having no decrease in molecular weight can be obtained.

As the stabilizer that can be used for stabilizing the polypropylene-based polymer, one that does not interfere with the polymerization of the mixture of the epoxy group-containing vinyl monomer and the aromatic vinyl monomer is preferable. Specific examples thereof include hindered phenol stabilizers, phosphorus stabilizers, metal soaps, magnesium oxide, and antacid adsorbents such as hydrotalcite.

These stabilizers may be used alone or as a mixture of two or more kinds. The amount of the stabilizer added is usually selected in the range of 0.01 to 1 part by weight, preferably 0.05 to 0. 0, based on 100 parts by weight of the propylene polymer.
The range is 5 parts by weight. These stabilizers are preferably mixed in advance with the propylene polymer using a Henschel mixer or the like.

In order to adjust the epoxy equivalent of the epoxy-modified polypropylene within the above range, the type of propylene polymer, the type and amount of epoxy group-containing vinyl monomer, the type and amount of coexisting aromatic vinyl monomer, Type and amount of radical initiator, type and amount of stabilizer, temperature of melt-kneading polymerization reaction,
This is possible by appropriately combining the addition timing of the monomer, the addition method, and the like.

In the present invention, the polyamide resin is a polymer compound having an acid amide (-CONH-) as a repeating unit, which is obtained by ring-opening polymerization of lactam depending on the polymerization mode.
Examples thereof include those obtained by polycondensation of diamine and dibasic acid and those obtained by polycondensation of aminocarboxylic acid. These have a general name of nylon, and examples thereof include nylon 6, nylon 66, nylon 610, and nylon 12. Of these, nylon 6 and nylon 66 are particularly preferable. The molecular weight of these polyamide resins is not particularly limited, but usually the relative viscosity (ηrel)
Is 0.5 or more, preferably 2.0 or more.

As described above, nylon 6 among polyamide resins has excellent mechanical strength and heat resistance, and nylon 1
Since it is cheaper than the two-system material, it is essentially suitable as a resin for coating an aluminum tube, but has a fatal drawback that the adhesive strength when bonded to an aluminum tube becomes extremely low. The coating resin essential in the present invention is
Adhesion to an aluminum pipe is significantly improved by forming a mixture in which epoxy modified polypropylene having an epoxy equivalent within a specific range is blended, mixed and dispersed in nylon 6.

In the present invention, the mixing ratio of the epoxy modified polypropylene and the polyamide resin should be selected in the range of 5 to 50% by weight of the epoxy modified polypropylene and 95 to 5% by weight of the polyamide resin. If the epoxy-modified polypropylene is less than 5% by weight, the adhesiveness when the mixture is adhered to the aluminum pipe is insufficient, and if it is 50% by weight, the elongation at high temperature and the strength are lowered,
Extrusion coating on the surface of the aluminum tube becomes difficult, and neither is preferable.

A mixture of a polyamide resin and an epoxy-modified polypropylene is not extrusion-coated in a dry blended state, but a mixture of both components is melt-kneaded in advance by a twin-screw extruder or the like to sufficiently mix and disperse. It is preferred that the composition is made compatible with each other to form a compound for extrusion coating, and extrusion coating is performed with this compound.

In order to coat the surface of the aluminum tube with the above-mentioned coating resin, an extrusion coating method using a circular die which is usually used in the production of coated electric wires is recommended.
The thickness of the coating resin layer can be arbitrarily selected according to the size of the aluminum tube and the intended use of the product. Further, the coating resin layer can be formed by a powder coating method depending on the purpose of use of the product. Using the above coating resin, when the coating resin layer is formed by the powder coating method,
A coating resin layer having excellent adhesiveness and coating strength is formed as compared to the nylon 12 powder coated product.

When forming a coating resin layer on the surface of the aluminum tube by extrusion coating, in order to enhance the adhesiveness between the surface of the aluminum tube and the coating resin, the aluminum tube is preheated immediately before the extrusion coating operation. Need to do.
The temperature for preheating varies depending on the type of epoxy-modified polypropylene and the mixing ratio of the epoxy-modified polypropylene and the polyamide resin, but is usually 100.
To 350 ° C., more preferably 20
It is in the range of 0 to 300 ° C. Examples of the preheating method include a gas heating method and an induction heating method. Usually, the induction heating method is preferable because of uniform and quick heating.

The resin-coated aluminum pipe according to the present invention is
The surface of the aluminum tube is covered with a mixed resin of epoxy-modified polypropylene and polyamide resin, and the surface of the aluminum tube and the coating resin are firmly bonded, so the surface of the aluminum tube is protected from the corrosive environment and electrically insulated from the outside. Therefore, it exhibits extremely excellent corrosion resistance.
Therefore, in addition to the use of automotive pipes, it should be widely applied to various types of pipes for land transportation vehicles, railways, ships, construction, home appliances, etc., which require high corrosion resistance, or structural members. You can

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the examples described below as long as the gist thereof is not exceeded. In the examples described below, the epoxy equivalent analysis method and various evaluation tests were based on the methods described below.

(A) Epoxy equivalent In JIS K7236, the solvent chloroform is changed to xylene, and the dissolution temperature and titration temperature are set to 160-18.
The measurement was performed according to K7236 except that the temperature was changed to 0 ° C. Epoxy-modified polypropylene was dissolved in xylene heated to 160-180 ° C., tetraethylammonium bromide acetic acid solution was added with stirring while keeping the temperature to avoid precipitation, and 0.1 N excess was added using crystal violet as an indicator. According to the method of titrating with a chloric acid acetic acid solution.

(B) Tensile Strength The coating resin compounds obtained in Examples and Comparative Examples were measured according to ASTM D638. (C) Flexural Modulus The coating resin compounds obtained in Examples and Comparative Examples were measured according to ASTM D790.

(D) Vicat Softening Point The coating resin compounds obtained in Examples and Comparative Examples were measured according to JIS K7206. (E) Appearance evaluation after coating After coating the surface of the aluminum tube with the coating resin,
The appearance was visually observed. The evaluation results are as follows: the coating resin is uniform and the appearance is excellent, and the coating resin is not uniform and the aluminum pipe is partially exposed.
Displayed.

(F) Adhesive Strength Two scratches having a width of 3 mm are made along the length direction of the aluminum tube in the coating resin layer covering the aluminum tube, the coating resin layer is peeled off, and the end portion having a width of 3 mm is removed. The coating resin was peeled off in a 180 ° direction at a constant speed, and the adhesive strength was calculated from the load required for peeling according to the following equation. Adhesive strength (N / cm) = (load N required for peeling) x {10
/ (Peeling width mm)}

(G) CASS test The resin-coated pipes obtained in Examples and Comparative Examples were cut into a length of 15 cm, and one cut was made in the entire length in the longitudinal direction of the pipe.
A CASS continuous test according to H8681 for one month was performed. After the test, the presence / absence of crevice corrosion generated from the cut portion or the pipe end was examined.

[Example 1] Glycidyl methacrylate 2
A stabilizer was added to a mixture of 5% by weight, 5% by weight of styrene, and 93% by weight of polypropylene, and the mixture was melt-kneaded by an extruder and graft-modified to obtain epoxy-modified polypropylene pellets. The epoxy equivalent of the obtained epoxy modified polypropylene was 7900 g / eq. After mixing the obtained pellets and nylon 6 in a ratio of 3: 7, this mixture was kneaded using a twin-screw extruder to prepare a coating compound. Table 1 shows the results of evaluation of various physical properties of the obtained coating compound (coating resin).

Next, JIS with an outer diameter of 10 mm and a wall thickness of 1.0 mm
For A3003-O aluminum alloy tube, temperature 6
It was dipped in a 20% caustic soda aqueous solution at 0 ° C. for 30 seconds to be degreased, washed with water, immersed in a 10% aqueous nitric acid solution at room temperature for 30 seconds to be desmutted, and then washed with water. With respect to the tube subjected to such a pretreatment, 20 mg / m ^{2 of} chromium was adhered to the outer surface of the aluminum tube by a coating type chromate treatment. Thereafter, while preheating the aluminum tube to 250 ° C., the coating compound (coating resin) was coated by the round die extrusion coating method to produce a resin-coated aluminum tube having a film thickness of 100 μm. The results of evaluation of the resin-coated aluminum tube are shown in Table-2.

[Example 2] In the example described in Example 1, except that the compounding ratio of the epoxy-modified polypropylene pellets and nylon 6 was changed to 2: 8 to obtain a coating compound (coating resin), A resin-coated aluminum tube was produced by the same procedure as described in Example 1. The evaluation results are shown in Table-1 and Table-2.

Example 3 In the example described in Example 1, except that the compounding ratio of the pellets of epoxy-modified polypropylene and nylon 6 was changed to 4: 6 to obtain a coating compound (coating resin), A resin-coated aluminum tube was produced by the same procedure as described in Example 1. The evaluation results are shown in Table-1 and Table-2.

[Embodiment 4] A resin-coated aluminum pipe was prepared in the same manner as in Embodiment 1 except that the surface treatment (etching treatment and chromate treatment) of the aluminum pipe was omitted in the example described in Embodiment 1. Was manufactured.
The evaluation results are shown in Table-2.

Comparative Example 1 In the example described in Example 1, maleic anhydride was 4% instead of the epoxy modified polypropylene. Resin-coated aluminum was prepared by the same procedure as described in Example 2 except that carboxylic acid-modified polypropylene pellets obtained by melt-kneading a mixture containing 6% of styrene and the balance of polypropylene by an extruder and graft-reacting were used. The tube was manufactured. The evaluation results are shown in Table-2.

[Comparative Example 2] In the example described in Example 1, the coating compound was a commercially available mixture of nylon 6 and polypropylene (NA, manufactured by Ube Industries, Ltd.).
P1300), but a resin-coated aluminum tube was manufactured by the same procedure as described in Example 2. The evaluation results are shown in Table-2.

[Comparative Example 3] A resin-coated aluminum tube was produced by the same procedure as that described in Example 2, except that the commercially available nylon 12 was used as the coating compound in the example described in Example 1. did. The evaluation results are shown in Table-1 and Table-2.

[Comparative Example 4] In the example described in Example 1, except that the compounding ratio of the epoxy-modified polypropylene pellets and nylon 6 was changed to 6: 4 to obtain a coating compound (coating resin), A resin-coated aluminum tube was produced by the same procedure as described in Example 1. The evaluation results are shown in Table-1 and Table-2.

[0049]

[Table 1]

The following is clear from Table-1. (1) Compared with nylon 12 used as a coating resin in Comparative Example 3, the coating resin used in Examples 1 to 4 has elongation,
Bending elastic modulus shows a value equal to or more than equal, and since the elongation is particularly high, the resin coating is less likely to be damaged during bending of the resin-coated aluminum pipe after coating,
Excellent workability. (2) Further, also in terms of Vicat softening point, the coating resin used in Examples 1 to 4 exhibits a temperature equal to or higher than that of Nylon 12 of Comparative Example 3, and therefore, in terms of heat resistance of the coating resin, It can be seen that it is equal to or higher than nylon 12.

[0051]

[Table 2]

From Table-2, the following is clear. (1) From Table-2, all of the resin-coated aluminum pipes of Examples 1 to 5 did not cause film breakage during the coating operation with the resin, and good extrusion coating was possible. Further, when the aluminum tube is subjected to chromate treatment, the adhesive strength at the interface shows a good value of 28 to 65 N / cm. In particular, in Example 2, the adhesive strength was too high to measure the adhesive strength. Even in the case of Example 4 in which the aluminum tube was not subjected to chromate treatment, the adhesive strength was equal to or higher than that of the commercially available nylon 12 alone (Comparative Example 3). Also in the CASS test, no crevice corrosion was observed at the boundary between the coating resin and the aluminum pipe.

(2) On the other hand, in the resin-coated pipes of Comparative Examples 1 and 4, the resin film was broken during the extrusion coating operation, and a good sample could not be obtained, and the adhesion strength was measured. Could not be done. Further, the resin-coated pipe of Comparative Example 2 was
Although the extrusion coating operation was satisfactorily performed, the adhesion strength was significantly inferior to that of the example. In the CASS test, in Comparative Example 1, Comparative Example 2 and Comparative Example 4, crevice corrosion that seems to have occurred from the cut portion spread over the entire interface between the resin and the aluminum tube. Comparative Example 3 The resin-coated pipe was excellent in extrusion coating operability, and no crevice corrosion was observed after the CASS test, but the absolute value of the adhesive strength does not reach the adhesive strength of Examples 1 to 4 of the present invention.

[0054]

The present invention has the following particularly advantageous effects, and its industrial value is extremely large. 1. The resin-coated aluminum tube according to the present invention has excellent adhesive strength at the interface between the surface of the aluminum tube and the coating resin, and the coating resin is unlikely to peel off even when secondary processing such as bending is performed. 2. The resin-coated aluminum pipe according to the present invention exhibits excellent corrosion resistance even when exposed to an environment in which it contacts a corrosive substance. 3. The resin-coated aluminum pipe according to the present invention has the above-mentioned characteristics 1 and 2, and has a bonding strength equal to or higher than that of the conventional product even if it is not subjected to chromate treatment. Economically advantageous compared to.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C08G 59/32 NHW C08G 59/32 NHW C08L 23/26 LCV C08L 23/26 LCV 63/00 NJZ 63/00 NJZ 77/02 LQS 77/02 LQS // B29C 47/02 B29C 47/02 B29K 705: 02 B29L 9:00 23:00

Claims (2)

[Claims] 1. A resin-coated aluminum tube obtained by coating the surface of an aluminum or aluminum alloy tube with a resin, wherein the resin coating reacts polypropylene with a mixture of an epoxy group-containing vinyl monomer and an aromatic vinyl monomer. The obtained epoxy equivalent is 2000-50000 g /
5 to 50% by weight of epoxy modified polypropylene of eq,
A resin-coated aluminum tube having excellent adhesion between the resin and the aluminum tube, which is a mixture of 95 to 50% by weight of a polyamide resin. 2. The resin-coated aluminum tube according to claim 1, wherein the polyamide resin is nylon 6.