JPH081745A - Cladding tube manufacturing method - Google Patents

Abstract

(57) [Summary] [Structure] Resin 1 is applied to the outer peripheral surface of the metal tube 14 by the round die method.
It is a method of coating 2 with a coated tube. Forming die 11
Warm water is pressed against the molten resin that is pushed out in a more cylindrical shape and is about to come into contact with the outer peripheral surface of the metal tube 14 at a pressure of atmospheric pressure or higher. [Effect] The resin coating 12 ′ having a uniform thickness can be adhered to the outer periphery of the metal tube 14 with a high adhesive force without causing a flaw in the resin coating 12 ′, and a good adhesive strength can be obtained even with a high viscosity adhesive. Moreover, even if the preheating temperature of the metal tube 14 is lowered, the same adhesive strength as at high temperature can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated tube in which a metal tube has an outer peripheral surface coated with a thermoplastic resin such as polyethylene.
The present invention relates to a method of manufacturing with a round die method.

[0002]

2. Description of the Related Art Conventionally, as a method for manufacturing a coated tube in which a metal tube is coated with a thermoplastic resin such as polyethylene via an adhesive resin, a T die method shown in FIG. 2 and a round die method shown in FIG. is there. Among them, the T-die method is a method in which the resin 2 extruded in a sheet form from the molding die 3 after being press-fitted into the molding die 3 in a molten state by the extruder is skew-rotated to the outer peripheral surface of the metal tube 1 which is advanced. This is a method for producing a coated tube by coating in a spiral shape.

Further, in the round die system, the molten resin 2 is extruded into a cylindrical shape from the molding die 3 by press-fitting the molten resin 2 into the resin passage 3a formed inside the molding die 3 from the extruder. This is a method of producing a coated pipe by continuously coating the outer peripheral surface of the metal pipe 1 which has passed through the molding die 3 with a molten resin.

As a method of adhering the resin to the metal tube by these two types of methods, generally, the roll 4 is used in the T-die method, but the molten resin extruded in a cylindrical shape is used in the round die method. The contraction force in the circumferential direction when stretched in the direction is used. However, since the force of pressing the resin against the metal pipe is extremely weak only by the shrinkage force of the resin, the adhesive resin needs to have good fluidity. Further, in order to obtain fluidity, it is necessary to raise the preheating temperature of the metal tube.

That is, in the round die method, it is more difficult to apply an adhesive resin having a higher melting point than in the T die method, it is difficult to manufacture a product having a high shear adhesive strength at a high temperature, and the pipe preheating temperature during coating is increased. In order to raise the height, it is necessary to consider deterioration of the inner surface coating when coating a metal tube whose inner surface is coated. Alternatively, heat resistant inner coating is required,
There is a problem.

Therefore, in order to solve the above-mentioned problems in the round die system, a system in which an arcuate roll 5 as shown in FIG. 4 is pressure-bonded to a metal tube 1 coated with a molten resin, or a molding as shown in FIG. By depressurizing the inside of the die 3 below atmospheric pressure, the molten resin that naturally tries to come into contact with the outer peripheral surface of the metal tube 1 is forcibly brought into contact with the die 3 to reduce the adhesive force, or as shown in FIG. A pressurizing method (Japanese Patent Application Laid-Open No. 51-131570) or the like is proposed in which air is blown from the outer peripheral surface of the molten resin which is extruded from the molding die 3 and comes into contact with the outer peripheral surface of the metal tube 1. ing.

[0007]

However, the roll pressure bonding method shown in FIG. 4 has a problem that the resin coating 2'is broken because the peripheral speeds of the central portion and both ends of the roll 5 are different. Further, in the case of the pressure reducing system shown in FIG.
Since the metal pipe 1 of about m is continuously connected and covered through the connecting metal fitting 6, air is brought in when the connecting portion of the metal pipe 1 enters the molding die 3, and the connecting metal fitting 6 is used for the molding metal die 6. When inside the molding die 3, the air in the metal tube 1 flows out from the connecting portion when the inside of the molding die 3 exists, and the inside of the molding die 3 is brought to the atmospheric pressure state. As a result, the state of the resin coating 2 ′ becomes unstable, and there is a problem that a coated metal tube having a uniform film thickness cannot be obtained.

Further, in the case of the pressure system shown in FIG.
Since air is blown from the outer peripheral surface of the molten resin that is trying to contact the outer peripheral surface of the metal tube 1, the resin coating 2 ′ is vibrated, resulting in an unstable state of the resin coating 2 ′ and a uniform film thickness. However, there is a problem that the coated metal tube cannot be obtained. In addition, in the case of this method, since the resin coating 2'contacts the outer peripheral surface of the metal tube 1 in a vibrating state, air is brought in between these two and a portion where adhesion cannot be obtained occurs. There is also a problem.

The present invention has been made in view of the problems in the above-mentioned conventional round die system, and it is possible to obtain a resin coating film having a large adhesive force and a uniform thickness, and also to have a flaw in the resin coating film. It is an object to provide a method for producing a cladding tube that does not occur.

[0010]

In order to achieve the above-mentioned object, a method of manufacturing a coated pipe according to the present invention is such that, when a resin is coated on the outer peripheral surface of a metal pipe by a round die system, a cylindrical shape is produced from a molding die. The hot water is pressed against the molten resin that is pushed out to contact the outer peripheral surface of the metal pipe at a pressure of atmospheric pressure or more from the outer peripheral surface.

[0011]

In the method for producing a coated pipe of the present invention, hot water is pressed against the molten resin extruded in a cylindrical shape from the molding die to contact the outer peripheral surface of the metal tube at a pressure of atmospheric pressure or more. The resin coating having a uniform thickness can be brought into close contact with the outer periphery of the metal tube with a high adhesive force without giving a flaw to the resin coating.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a cladding tube according to the present invention will be described below with reference to an embodiment shown in FIG. FIG. 1 is a schematic cross-sectional view for explaining the method for manufacturing a cladding tube of the present invention.

In FIG. 1, reference numeral 11 denotes a molding die having the same structure as that of a conventional molding die, and a resin flow channel 11a formed therein has a resin 1 melted by an extruder (not shown).
When 2 is press-fitted, the molten resin 12 is extruded into a cylindrical shape from the outlet 11b formed on the downstream side surface of the molding die 11.

Numeral 13 is arranged on the downstream side of the forming die 11 and tends to come into contact with the outer peripheral surface of the metal pipe 14 which is extruded in a cylindrical shape from the outlet 11b of the forming die 11 and passed through the forming die 11. It is a pressure ring for causing hot water of, for example, 30 to 50 ° C. to act on the molten resin 12 from the outer peripheral surface thereof at a pressure of atmospheric pressure or higher. In the present embodiment, three rooms 13b to 13d are formed by partitioning the hot water supplied from the hot water inlet 13a opened on the outer periphery in the line transfer direction.
In this example, the resin 12 is pressed from the outer peripheral surface at a pressure equal to or higher than the atmospheric pressure when the metal tube 14 passes through the through hole 13e opened in the center.

In the case of this embodiment, first, the room 1 on the upstream side
The resin 12 is pressure-bonded to the outer peripheral surface of the metal tube 14 by the hot water guided to 3b, and the adhesive force of the resin 12 to the metal tube 14 is increased by the hot water guided to the remaining chambers 13c and 13d. .

When the coated pipe is manufactured by the above-described method of the present invention, the metal pipe 1 is formed without causing a flaw in the resin coating 12 ', has a uniform thickness, and has high adhesion.
The resin coating 12 ′ can be coated over the entire outer circumference of 4.
In addition, according to the method of the present invention, good adhesive strength can be obtained even with a high-viscosity adhesive, and even if the preheating temperature of the pipe is lowered, the same adhesive strength as at high temperature can be obtained.

A polyethylene having a nominal diameter of 100 A is used as a coating resin, and modified polyethylene is used as an adhesive [MFR (melt frothrate)] to change the amount of the adhesive MFR and the preheating temperature of the metal pipe. 3, a round die method (conventional method), a decompression method shown in FIG. 5, an air pressurization method shown in FIG. 6, and a method of the present invention shown in FIG. 1 [30 ° C. hot water at 30 mmH ₂
A coating tube having a resin film thickness of 1.5 mm was manufactured. The results of measuring the adhesive strength and the fluctuation range of the film thickness at that time are shown in Table 1 below.

[0018]

[Table 1]

As is clear from Table 1, according to the method of the present invention, the adhesive strength not obtained by the conventional method can be obtained, and the adhesive strength almost equal to that of the decompression method can be obtained. You can see that there are few.

[0020]

As described above, according to the method for manufacturing a cladding tube of the present invention, the molten resin extruded in a cylindrical shape from the molding die to contact the outer peripheral surface of the metal tube is heated with warm water. Since it is operated at a pressure higher than atmospheric pressure, it is possible to bring the resin coating of uniform thickness into close contact with the outer periphery of the metal tube with a high adhesive force without scratching the resin coating. In addition, according to the method of the present invention, good adhesive strength can be obtained even with a high-viscosity adhesive, and even if the preheating temperature of the pipe is lowered, the same adhesive strength as at high temperature can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining a method of manufacturing a cladding tube according to the present invention.

FIG. 2 is a schematic diagram for explaining a conventional T-die system.

FIG. 3 is a schematic cross-sectional view for explaining a conventional round die system.

FIG. 4 is a schematic diagram for explaining a conventional roll pressure bonding method.

FIG. 5 is a schematic cross-sectional view for explaining a conventional pressure reducing method.

FIG. 6 is a schematic cross-sectional view for explaining a conventional air pressure system.

[Explanation of symbols]

 11 Molding Die 12 Resin 12 'Resin Coating 13 Pressure Ring 14 Metal Tube

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area B29L 9:00 23:00

Claims (1)

[Claims] 1. When coating the outer peripheral surface of a metal tube with a resin by a round die method, the molten resin extruded in a cylindrical shape from a molding die and trying to contact the outer peripheral surface of the metal tube is larger than the outer peripheral surface. A method for producing a cladding tube, characterized in that hot water is pressed at a pressure of at least atmospheric pressure.