JPH0687162A - Production of synthetic resin-lined pipe - Google Patents

Abstract

PURPOSE:To obtain a method for producing a synthetic resin-lined pipe having a superior adhesion of a synthetic resin lining layer to a metal pipe and superior heat resistance and durability with high efficiency at a low cost. CONSTITUTION:Polytannic acid obtained by polymerizing tannic acid or a solution containing -10wt.% solid component and 1-30 pts.wt. pyrocatechol based on 100 pts.wt. of polytannic acid is applied to the inner and/or outer surface of a metal pipe and baked. In the metal pipe, a synthetic resin layer is bonded to the surface treated with the polytannic acid or the polytannic acid solution using an adhesive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a synthetic resin lining pipe, in which a synthetic resin layer made of a vinyl chloride resin or the like is adhered to an inner surface and / or an outer surface of a metal pipe with an adhesive, and particularly The present invention relates to a method for obtaining a synthetic resin lining tube having excellent adhesiveness and thermal shock resistance.

[0002]

2. Description of the Related Art Conventionally, in order to improve touch resistance, a synthetic resin layer made of vinyl chloride resin or the like is lined on the inner surface of a metal pipe such as a steel pipe using a hot melt type adhesive mainly composed of synthetic rubber. There is known a synthetic resin lining pipe formed of the above (for example, Japanese Patent Publication No. 2-37378).

However, in the known synthetic resin lining pipe as described above, the adhesiveness of the synthetic resin lining layer to the metal pipe and the heat resistance of the adhered portion are not always sufficient. Therefore, when a thermal shock is applied, such as when repeatedly passing a low temperature fluid and a high temperature fluid alternately,
There has been a problem that the adhesive strength is lowered with time and the synthetic resin lining layer is peeled off. In addition, rust may be generated on the inner surface of the metal pipe in the portion where the synthetic resin lining layer is peeled off, and this rust may contaminate the fluid. Therefore, the above-mentioned synthetic resin lining pipe has been unsuitable for use in applications where deterioration of water quality is a serious problem, such as for drinking water.

As a method for improving the rust prevention and adhesion of a steel pipe, a method using a coupling agent such as a silane type or titanium type is known. However, even if the silane coupling agent is used to improve rust prevention and adhesiveness, the durability is not sufficient, and therefore both the waterproofness and the adhesiveness gradually decrease over time, and the cost is also very high. There was a problem of getting stuck. Further, when a titanium-based coupling agent is used, it is necessary to bake at a high temperature of about 400 ° C. during processing, and the cost becomes very high.

Further, an epoxy resin composition to which a polyphosphate salt is added has also been proposed as an adhesive capable of enhancing the rust preventive property (Japanese Patent Laid-Open No. 62-158714, etc.). This polyphosphate shows excellent anti-corrosion properties. However, when the polyphosphate-containing epoxy resin composition is used as an adhesive in the method for producing a synthetic resin-lined steel pipe, the cured adhesive product is relatively hard, and therefore the thermal shock resistance of the bonded portion is not sufficient. . That is, as described above, when the low-temperature fluid and the high-temperature fluid are repeatedly passed, the synthetic resin lining layer is liable to peel due to thermal shock, and the water quality is deteriorated due to the outflow of amine.

As another rust preventive material, there is a resin containing a conventionally known lead-based or chromium-based synthetic pigment mixed therein, but since such a synthetic pigment is extremely toxic, drinking water, etc. It is not suitable for use in piping.

[0007]

DISCLOSURE OF THE INVENTION The object of the present invention is to improve the adhesion of a synthetic resin lining layer to a metal pipe, and to improve the thermal shock resistance and durability of the bonded portion, and therefore to prevent rust. It is an object of the present invention to provide a method capable of efficiently manufacturing a synthetic resin lining pipe having satisfactory properties at low cost.

[0008]

According to the first aspect of the present invention, polytannic acid obtained by polymerizing tannic acid is applied to at least one of the inner surface and the outer surface of a metal tube and then baked to obtain the metal. A method for producing a synthetic resin-lined steel pipe, characterized in that a synthetic resin layer is bonded to the surface of the pipe treated with polytannic acid with an adhesive.

Further, the invention according to claim 2 has a solid content concentration of 1 to 30 parts by weight of pyrocatechol dissolved in 100 parts by weight of polytannic acid obtained by polymerizing tannic acid. 10% by weight polytannic acid solution,
A synthetic resin lining tube, characterized in that after coating on at least one of the inner surface and the outer surface of the metal tube, it is baked and a synthetic resin layer is adhered to the surface of the metal tube treated with the polytannic acid solution with an adhesive. Is a manufacturing method.

Further, the adhesive preferably has a carboxyl group equivalent of 3 as described in claim 3.
00 to 4000 and an average molecular weight of 1000 to 6
Epoxy resin is contained in an amount of 5 to 200 parts by weight with respect to 100 parts by weight of a saturated polyester resin of 000, and 1
An adhesive composition is used in which at least one epoxy group-containing compound having 3 or 4 epoxy groups in the molecule accounts for 10 mol% or more based on the total of the saturated polyester resin and the epoxy resin.

The details of the structure of the present invention will be described below. Treatment with polytannic acid according to claim 1 As described above, the invention according to claim 1 uses a metal tube in which at least one of the inner surface and the outer surface is treated with the specific polytannic acid. As the polytannic acid, for example, a polytannic acid obtained by polymerizing tannic acid represented by the following formula (I) is used, and preferably, a polytannic acid solution containing the polytannic acid in the range of 5 to 50% by weight is used. Is used.

[0012]

[Chemical 1]

If the concentration is less than 5% by weight, it is difficult to uniformly apply the required amount of polytannic acid to the inner surface and / or the outer surface of the metal tube, that is, to form a uniform polytannic acid film. It is impossible to obtain sufficient rust prevention and adhesiveness. On the other hand, if the above concentration exceeds 50% by weight, the fluidity of the polytannic acid solution becomes low, and thus it takes a long time for coating. Not only that, an unnecessarily thick polytannic acid film is formed, so that it becomes difficult to apply the adhesive evenly thereon, and the adhesiveness is deteriorated.

As a method of applying the polytannic acid solution to the metal tube, the method of immersing the metal tube in the polytannic acid solution is relatively simple, and thus is preferable. However,
If you want to avoid applying to the inner surface of the metal tube, especially when the metal tube is long, seal the lower end of the metal tube with a rubber stopper etc. with the metal tube standing, and put the polytannic acid solution in the metal tube. Is preferred, and then the rubber stopper is removed and the polytannic acid solution is withdrawn from the lower end. The extracted polytannic acid solution can be used repeatedly several times.

Prior to the application of the polytannic acid solution, it is preferable to remove rust on the surface of the metal tube in advance by acid treatment or the like. The baking after application of the polytannic acid solution is preferably maintained at a temperature of 100 to 200 ° C. for about 5 to 30 minutes. The baking treatment at a temperature lower than 100 ° C. and for less than 5 minutes results in insufficient formation of the polytannic acid film, and when the baking treatment is performed at a temperature exceeding 200 ° C. and a time exceeding 30 minutes, the productivity is remarkably reduced. As a heating method at the time of baking, a method of charging in a hot air oven or an appropriate method such as induction heating can be adopted, but if induction heating is used, productivity can be dramatically improved.

A polytanni containing pyrocatechol according to claim 2.
Treatment with an acid solution In the invention according to claim 2, pyrocatechol is dissolved at a ratio of 1 to 30 parts by weight of pyrocatechol to 100 parts by weight of polytannic acid obtained by polymerizing tannic acid as described above. A polytannic acid solution containing pyrocatechol having a solid content concentration of 1 to 10% by weight is used. Here, as the polytannic acid, the polytannic acid obtained by polymerizing the tannic acid represented by the above formula (I) is used as in the case of the invention described in claim 1.

In the invention according to claim 2, the polytannic acid solution having a solid content concentration of 1 to 10% by weight is used so that the solid content required for the inner surface of the steel pipe is uniform when the solid content concentration is less than 1% by weight. This is because it becomes difficult to apply it to the resin, a uniform film cannot be formed, and sufficient rust prevention and adhesiveness cannot be obtained. On the other hand, the solid content concentration is 10
If it exceeds 5% by weight, the fluidity of the polycatenic acid solution containing pyrocatechol becomes low, so that it takes a long time to apply it.
In addition, a thicker film than necessary is formed, and it becomes difficult to apply the adhesive uniformly, and the adhesiveness deteriorates.

Pyrocatechol is dissolved in the above-mentioned ratio, because when the compounding ratio of pyrocatechol is less than 1 part by weight, the adhesion to steel pipe and the rust preventive property are insufficient.
When it exceeds the weight part, the film is not formed uniformly, and as a result,
This is because the adhesion durability is not sufficient.

The step of applying the pyrocatechol-containing polytannic acid solution of the invention described in claim 2 to a metal tube and baking it is carried out by the same method as the treatment in the invention described in claim 1.

Adhesive According to the invention described in claims 1 and 2, a synthetic resin is adhered to the surface treated with the polytannic acid or the pyrocatechol-containing polytannic acid solution with an adhesive to obtain a synthetic resin lining pipe. However, as the adhesive that can be used, it is preferable to use the above specific adhesive composition as described in claim 3.

The saturated polyester resin used for the adhesive in the invention of claim 3 is a saturated polyester resin whose main chain has an ester bond essentially consisting of-(C--COO--C)-. As described above, those having a carboxyl group equivalent in the range of 300 to 4000 and an average molecular weight of 1000 to 6000 are used. When the carboxyl group equivalent and the average molecular weight are out of the above ranges, the curing rate becomes slow, the heating requires a high temperature and a long time, the thermal deterioration of the lining resin occurs, and the productivity decreases. Is generated.

The epoxy resin used in the adhesive of the invention of claim 3 is one or more appropriate epoxy resins such as bisphenol type, novolac type, aliphatic type or alicyclic type. Can be used. However, as described above, at least one compound containing 3 or 4 epoxy groups in the molecule has a total of 10 or more relative to the total of the saturated polyester resin and the epoxy resin (based on the average molecular weight). The reason why it is necessary to occupy more than mol% is that if it is less than 10 mol%, the degree of crosslinking becomes too low and sufficient heat resistance cannot be obtained. Further, when a compound containing 5 or more epoxy groups in the molecule is used, the crosslink density becomes too high, the elastic modulus of the cured product becomes high, and the heat resistance of the finally obtained synthetic resin lining pipe is increased. It is not preferable because the impact resistance is lowered.

Examples of the epoxy resin having 3 or 4 epoxy groups in the molecule include trimethylolpropane triglycidyl ether, tetrakis (glycidyloxyphenyl) ethane, triglycidyl (trishydroxyethyl) isocyanurate, and glycerol. Triglycidyl ether, sorbitol triglycidyl ether, sorbitol tetraglycidyl ether, pentaerythritol triglycidyl ether, pentaerythritol tetraglycidyl ether, diglycerol triglycidyl ether, tris (glycidyloxyphenyl) methane, phenol novolac type epoxy with a degree of polymerization of 3 and 4. Examples thereof include resins and cresol novolac type epoxy resins having a polymerization degree of 3 or 4.

The epoxy resin is blended in a proportion of 5 to 200 parts by weight with respect to 100 parts by weight of the unsaturated polyester resin. If it is less than 5 parts by weight, the cured product becomes hard,
This is because peeling easily occurs due to the thermal stress generated when the lining pipe is used, and if the amount exceeds 200 parts by weight, the curing speed becomes slow, and therefore the curing requires a high temperature and a long time, which causes thermal deterioration of the lining resin. This is because it occurs.

In the adhesive according to the third aspect, a curing accelerator may be blended to increase the curing rate. Examples of the curing accelerator include chromium (III) hexanoate, chromium (III) pentanoate, chromium (III) butyrate, and chromium 2-ethylhexanoate (II).
I), chromium (III) decanoate, chromium (III) oleate, chromium (III) stearate, chromium (III) toluate, chromium (III) cresolate,
Chromium (III) tricarboxylate compounds such as chromium (III) benzoate, chromium (III) alkyl benzoate, chromium (III) alkoxy benzoate, chromium (III) naphthenate, and chromium (III) alkoxide, di-isopropoxy Bis (acetylacetonate)
Titanium, isopropoxy (2-ethylhexanediolato) titanium, di-n-butoxy-bis (triethanolaminato) titanium, hydroxybis (lactate) titanium, titanium chelate compound, triphenylphosphine, aluminum (III) acetyl Examples include, but are not limited to, acetonates and the like.

Manufacturing process of synthetic resin lining pipe In the invention described in claim 1, after treating the inner surface and / or the outer surface of the metal tube with polytannic acid as described above, for example, the adhesive agent according to claim 3 is applied. A synthetic resin lining pipe is obtained by bonding the synthetic resin layer using the pipe. Similarly, in the invention described in claim 2, after treating the inner surface and / or the outer surface of the metal tube with the specific pyrocatechol-containing polytannic acid solution, for example, the synthetic resin using the adhesive agent according to claim 3 is used. By adhering the layers, a synthetic resin lining tube is obtained. In these cases, as the synthetic resin layer, it is convenient to use a synthetic resin tube that has been formed into a tubular shape in advance, but a synthetic resin sheet or the like may be attached to the inner surface and / or the outer surface of the steel tube via the adhesive. Good.

When the synthetic resin pipe is attached to the inner surface of the metal pipe with an adhesive, a conventionally known method called a swelling method or a diameter reducing method can be used.
Further, examples of the synthetic resin used for forming the synthetic resin lining layer include vinyl chloride resins such as vinyl chloride resin and chlorinated vinyl chloride resin.

[0028]

In the invention described in claim 1, since at least one of the inner surface and the outer surface of the metal tube is treated with the specific polytannic acid, the durability and thermal shock resistance of the bonded portion are enhanced. The details of the reason why the durability and the thermal shock resistance are improved are not clear, but polytannic acid forms a coordinate bond with the surface of the metal tube, and at the same time, the phenol residue in the uncoordinated polytannic acid remains. It is considered that the durable adhesive strength is enhanced by the reaction of the group with the adhesive or the formation of hydrogen bond.

Further, in the invention described in claim 2, since at least one of the inner surface and the interface of the metal tube is treated with the specific pyrocatechol-containing polytannic acid solution,
The durability and thermal shock resistance of the bonded portion are improved. The details of the reason why the durability and the thermal shock resistance are improved are not clear, but polytannic acid and pyrocatechol form a coordination bond with the surface of the steel pipe, and at the same time, phenol in tannic acid which is not coordinating is formed. It is considered that the residue reacts with the epoxy resin or forms a hydrogen bond to enhance the durable adhesion.

Further, in the invention described in claim 3, since the specific adhesive composition is used as an adhesive, the phenol residue in the polytannic acid reacts with the epoxy resin or forms a hydrogen bond. It is considered that the durability and adhesion are enhanced. Further, since the above-mentioned adhesive is mainly composed of polyester and forms a layer having high flexibility, the stress generated by the difference in linear expansion coefficient between the metal tube and the synthetic resin lining layer is relieved by elastic deformation, and therefore the synthetic resin is used. It is considered that the durability and thermal shock resistance of the lining pipe are enhanced.

[0031]

The present invention will be clarified by describing non-limiting examples of the present invention.

[Examples of the Invention According to Claim 1] Blending of Adhesives As shown in Table 1 below, each adhesive component is weighed (the blending ratio unit in Table 1 is part by weight) and kneaded. By doing so, the adhesives of Formulation Examples 1 to 6 were prepared.

[0033]

[Table 1]

Details of the adhesive components shown in Table 1 are as follows. Saturated polyester resin ... Product name by Huls, Inc .: Dy
nacol 8330 (molecular weight 4000, carboxyl group equivalent 2000-3000).

Tactics 742 ... Product made by Dow Chemical Japan, semi-solid trifunctional epoxy resin compound having epoxy equivalent of 160 Epicoat 1001 ... Product made by Yuka Shell Epoxy Co., Ltd.
Bisphenol A type solid epoxy resin having an epoxy equivalent of 450 Epicoat 828 ... A product manufactured by Yuka Shell Epoxy Co., Ltd., a bisphenol A type liquid epoxy resin having an epoxy equivalent of 190.

Next, using the adhesives of the above formulation examples 1 to 6,
Experiments were conducted according to the following Experimental Examples 1 and 2 to evaluate the durability and thermal shock resistance of the bonded portion. Experimental Example 1 5 g of each of the adhesives of the above Formulation Examples 1 to 6 was sandwiched between release-treated polyethylene terephthalate films, and 150
A pressure of 3 kg / cm ² was applied at a temperature of ° C and hot pressing was performed for 1 minute to form a film having a thickness of 50 µm.

The adhesive film obtained as described above was applied to a glass transition point of 120 ° C., 120 mm × 25 mm × thickness of 3 m.
m chlorinated vinyl chloride resin plate, 125 mm x 25 mm
× It is sandwiched between an iron plate with a thickness of 0.3 mm, and it is 40 at 180 ° C.
Heat-cured for a minute, and adhesive test piece (overlap area is 25 x
100 mm) was produced.

Regarding the above-mentioned iron plate, as shown in the lower part of Table 1, a polytannic acid solution (a product manufactured by Teika Co., Ltd.) was used in the experiments of the films obtained by using the adhesives of the formulation examples 1 to 4 and 6. Name: K-Polymer L) applied, 140
An iron plate which had been kept in a dryer at 0 ° C. for 10 minutes and applied with a polytannic acid solution and baked was used. Also,
For the experiment of the film obtained by using the adhesive of formulation example 5, an iron plate not treated with the polytannic acid was used.

Using the adhesive test piece obtained as described above, 90 ° peel strength was measured at 25 ° C. and a pulling speed of 50 mm / min. Also, the same adhesion test piece was dipped in hot water of 85 ° C for 3 days and then dried to obtain 25 ° C and a pulling speed of 50 m.
The 90 ° peel strength was measured in m / min. The results are shown in Table 2 below.
Shown in.

[0040]

[Table 2]

As is clear from Table 2, the adhesive test piece for the film of Formulation Example 5 which was not treated with polytannic acid showed spontaneous peeling after being immersed in hot water at 85 ° C. for 3 days. On the other hand, spontaneous peeling was not observed in the formulation examples 1 to 4 and the formulation example 6 in which the polytannic acid treatment was performed. In addition, as compared with Formulation Example 6, in Formulation Examples 1 to 4, initial adhesive strength was high, and sufficient peel strength was exhibited even after being immersed in hot water at 85 ° C for 3 days. It is considered that this is because the adhesives of Formulation Examples 1 to 4 are the adhesive compositions belonging to the invention described in claim 2 and the formulation example 6 does not satisfy the composition described in claim 2.

Experimental Example 2 Each of the adhesives of Formulation Examples 1 to 6 was applied to the outer peripheral surface of a chlorinated vinyl chloride resin pipe having an outer diameter of 49 mm and an inner diameter of 40 mm with a thickness of about 100 to 150 μm, and inserted into a steel pipe having an inner diameter of 50 mm. The air pressure inside the chlorinated vinyl chloride resin pipe is 3 kg / cm
² Put it in the oven at 190 ℃ with the added state,
After 90 minutes, it was taken out and allowed to cool at room temperature to obtain a synthetic resin lining steel pipe.

Table 1 shows the used steel pipes.
As shown in the lower part of the above, for the formulation examples 1 to 4 and 6, those treated with polytannic acid in the same manner as in the case of Experimental example 1 were used. Further, when a synthetic resin-lined steel pipe was obtained using the adhesive of formulation example 5, a steel pipe not subjected to the polytannic acid treatment was used.

The synthetic resin-lined steel pipe obtained as described above is immersed in water at 25 ° C. for 5 minutes and then immediately immersed in hot water at 85 ° C. for 5 minutes as one cycle.
The cooling and heating cycle is repeated, and after a predetermined cycle, a portion having a length of 2 cm from the end of the synthetic resin lining steel pipe is cut,
Dried. Thereafter, the dried cut portion is divided into 12 equal parts in the circumferential direction to obtain divided test pieces 1 to 12, and the shear strength (kg / c) is applied to each divided test piece at a load speed of 20 kg / sec.
m ² ) was measured. The results are shown in Table 3.

[0045]

[Table 3]

As is apparent from Table 3, in the case of formulation example 5 using a steel pipe not treated with polytannic acid,
After 300 cycles, the shear strength was significantly reduced,
After 0 cycle, it was remarkably reduced, and a peeled portion (a portion having a shear strength value of 0) was also recognized.

On the other hand, in the formulation examples 1 to 4, the steel pipe treated with the polytannic acid and the adhesive composition according to the invention as claimed in claim 3 were used. Even if it shows strength and repeats the heat cycle of 300 cycles and 500 cycles,
It can be seen that no peeling was observed and sufficient peeling strength was maintained.

Example of the Invention According to Claim 2 Preparation of Adhesive and Pyrocatechol-containing Polytannic Acid Solution
Manufacture As shown in Table 4 below, each adhesive component was weighed and kneaded to prepare an adhesive used in Formulation Examples 11 to 17. Also, the treatment solutions used in the formulation examples 11 to 17 were prepared by weighing and blending the respective components in the treatment solution section of Table 4 below.

All the units of the blending ratio in Table 4 are parts by weight.

[0050]

[Table 4]

Details of each component in Table 4 are as follows. Saturated polyester resin ... Product made by Huls: Dyna
coll 8330 (molecular weight 4000, carboxyl group equivalent 2000-3000).

Tactix 742 ... Product made by Dow Chemical Japan: Semi-solid trifunctional epoxy resin compound having epoxy equivalent of 160. AMC-2 ... Product name: Chromium (III) tricarboxylate manufactured by Aerojet General Corporation.

K polymer L ... Trade name manufactured by Teika: polytannic acid aqueous solution having a solid content of 42% by weight. Next, using the adhesives and treatment solutions prepared in the above formulation examples 11 to 17, experiments were conducted according to the following Experimental Examples 3 and 4, and the durability and thermal shock resistance of the bonded portions were evaluated.

Experimental Example 3 First, each of the treatment solutions prepared in Formulation Examples 11 to 17 was applied to the outer surface of an iron plate of 125 mm × 25 mm × thickness of 0.3 mm and kept in a drier at 140 ° C. for 10 minutes. It was held, and the treatment solution was applied and baked. In addition, about the formulation example 17, such treatment with the polytannic acid solution was not performed.

0.5 g of each of the adhesives of Formulation Examples 11 to 17 was applied to each of the iron plates prepared as described above, and canvas (No. 9) was overlaid on the surface coated with the adhesive. Then, it was heat-cured at a temperature of 120 ° C. for 40 minutes to prepare an adhesive test piece (overlap area: 25 mm × 100 mm).

Using this adhesive test piece, 90 ° peel strength was measured at 25 ° C. at a pulling speed of 50 mm / min.
Also, the same adhesion test piece was immersed in water at 85 ° C. for 3 days and then dried, and at 9 ° C. at 25 ° C. and a pulling speed of 50 mm / min.
The 0 ° peel strength was measured. The results are shown in Table 5 below.

[0057]

[Table 5]

As is clear from Table 5, in the formulation example 17 in which the polytannic acid treatment was not carried out, the initial peel strength was 1
It was as small as 7 kg / 25 mm, and spontaneous peeling occurred after immersion in hot water. In addition, in the formulation example 15 treated with only the K polymer L having a solid content concentration of 42% by weight, similarly, the initial peel strength was as small as 12 kg / 25 mm, and spontaneous peeling occurred after immersion in hot water. This is because K polymer L having a solid content concentration of 42% by weight is blended with 10 parts by weight of pyrocatechol, so that the solid content concentration becomes too high, and it becomes difficult to uniformly apply the adhesive. Is considered to have decreased.

On the other hand, in the formulation examples 11 to 14 which enter the invention of claim 2, sufficient strength is exhibited in both the initial peel strength and the peel strength after immersion in hot water, and after immersion in hot water. In peeling strength, almost no decrease was observed. Further, even when compared with Formulation Example 16 corresponding to the embodiment of the invention described in claim 1, since there is almost no decrease in peel strength after immersion in hot water, it has excellent thermal shock resistance and durable adhesiveness. I understand.

Experimental Example 4 An external diameter of 54.4 mm was applied to each of the adhesives of the above-mentioned formulation examples 11 to 17.
× Inner diameter 42 mm × Wall thickness 3 mm Chlorinated vinyl resin tube is applied to the outer peripheral surface, inserted into a steel tube with an inner diameter of 56.5 mm and wall thickness of 7 mm, the steel tube is reduced in diameter by a roll, and the oven is kept at 80 ° C for 60 minutes. After leaving it for a while, it was taken out and allowed to cool at room temperature to obtain a synthetic resin lining steel pipe.

Table 4 shows the used steel pipes.
As shown in the lower part of the table, the ones treated with each treatment solution in the same manner as in Experimental Example 3 were used. In addition, about the mix example 17, the said steel pipe is not processed.

The synthetic resin-lined steel pipe obtained as described above is dipped in water at 25 ° C. for 5 minutes and then immediately dipped in hot water at 85 ° C. for 5 minutes as one cycle.
The cooling and heating cycle is repeated, and after a predetermined cycle, a portion having a length of 2 cm from the end of the synthetic resin lining steel pipe is cut,
Dried. After that, the dried cut portion is divided into 12 equal parts in the circumferential direction, and the divided test piece No. 1 to 12 were obtained. For each divided test piece, shear strength (kg
/ Cm ² ) was measured. The results are shown in Table 6 below.

[0063]

[Table 6]

As is clear from Table 6, in the compounding example 17 using the steel pipe not subjected to the polytannic acid treatment, the variation in the shear strength was observed in the circumferential direction even before the cooling / heating cycle and after the cooling / heating cycle 2000 cycles. ,
It was observed that the shear strength was significantly reduced.

Similarly, in Formulation Example 15 using a polycatenic acid solution containing pyrocatechol having an excessively high solid content concentration, the shear strength varies in the circumferential direction before the cooling / heating cycle, and after 2000 cycles of the cooling / heating cycle. It was confirmed that the shear strength was significantly reduced.

On the other hand, in Formulation Examples 11 to 14, the steel pipe was treated with the above-mentioned specific pyrocatechol-containing polytannic acid solution. Probably because the shear strength did not fluctuate even in the initial state, and the cold and heat cycle was 2000 cycles. It can be seen that sufficient peeling strength is maintained even after.
In Formulation Example 16, although sufficient adhesiveness was shown before the cold heat cycle, it was observed that the shear strength was partially reduced after the cold heat cycle of 2000, whereas in the above Blend Examples 11 to 14, the cold heat resistance was decreased. Even after 2000 cycles, such a decrease in peel strength was not observed.

[0067]

As described above, according to the first and second aspects of the present invention, the metal tube is pretreated with the specific polytannic acid and pyrocatechol-containing polytannic acid solution, and then the adhesive is applied. Since the synthetic resin layer is used to obtain a synthetic resin lining tube, the synthetic resin lining layer has a high adhesiveness to the metal tube, and a synthetic material that exhibits excellent durability even when repeatedly subjected to thermal shock. It becomes possible to provide a resin lining pipe. Moreover, since the step of treating the metal pipe with the above-mentioned specific polytannic acid or polycatenic acid solution containing pyrocatechol can be performed relatively easily, there is no fear of increasing the cost of the synthetic resin lining pipe.

When the adhesive of the invention described in claim 3 is used, the saturated polyester resin has sufficient flexibility, so that a synthetic resin lining tube further excellent in thermal shock resistance and durable adhesion is obtained. Can be provided.

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Claims (3)

[Claims] 1. A polytannic acid obtained by polymerizing tannic acid is applied to at least one of an inner surface and an outer surface of a metal tube and then baked, and the surface of the metal tube treated with polytannic acid is bonded with an adhesive. A method for manufacturing a synthetic resin lining pipe, which comprises bonding a synthetic resin layer. 2. A polytannic acid solution having a solid content concentration of 1 to 10% by weight, which is obtained by dissolving 1 to 30 parts by weight of pyrocatechol in 100 parts by weight of polytannic acid obtained by polymerizing tannic acid. Characterized in that, after being applied to at least one of the inner surface and the outer surface of the metal tube, it is baked, and a synthetic resin layer is adhered to the surface of the metal tube treated with the polytannic acid solution by an adhesive.
Manufacturing method of synthetic resin lining pipe. 3. The adhesive has a carboxyl group equivalent of 300 to 4000 and an average molecular weight of 1000.
To 100 parts by weight of the saturated polyester resin of 6000 to 5 parts by weight of the epoxy resin, and at least one or more epoxy group-containing compounds having 3 or 4 epoxy groups in one molecule. The method for producing a synthetic resin lining pipe according to claim 1 or 2, wherein the adhesive composition accounts for 10 mol% or more with respect to the total of the saturated polyester resin and the epoxy resin.