JP2002254493A - Resin pipe manufacturing method and inner surface resin lining steel pipe using the resin pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a resin pipe excellent in shape restoring properties with good productivity by using an inexpensive resin, and an inner surface resin lining steel pipe using the resin pipe. SOLUTION: In the method for manufacturing the resin pipe by forming a single-layered or multilayered structure from a thermoplastic resin comprising either one of a polyolefin, polyethylene, polypropylene and an ionomer resin and extruding the same from an extrusion mold, the shape of the molten thermoplastic resin is fixed on the downnstream side of the extrusion mold so that a diameter contraction ratio (%) represented by the formula: diameter contraction ratio (%): 100×(D-d)/D (wherein, D is the outer inner diameter of the extrusion mold and d is the outer diameter of the resin pipe) is not less than 3%.

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 resin tube made of a thermoplastic resin, and more particularly to a method for producing a resin tube having excellent shape restoring property due to residual stress applied in a molding step.

[0002]

2. Description of the Related Art In recent years, in order to improve corrosion resistance and the like, pipes used for water supply and drainage are often made of an inner resin lining steel pipe having an inner surface as a resin layer. Powder coating methods for body coating and forming a lining layer have been used.

However, the powder coating method has low productivity,
Since the equipment is expensive and it is difficult to uniformly adsorb the resin powder to the inner surface of the steel pipe, pinholes and the like are likely to occur, and when used for a long time as a water pipe, there is a problem that the corrosion resistance is deteriorated. Was.

As a technique for solving such a problem, Japanese Patent Application Laid-Open No. 2-57323 discloses a resin pipe made of a shape memory resin such as polynorbornene, styrene-butadiene copolymer, and trans-polyisoprene. A method is disclosed in which the diameter is reduced to a small value, inserted into a steel pipe, heat-restored, and then attached to the inner surface of the steel pipe to form an inner lining.

[0005] However, resins having shape memory properties are expensive per se and have problems in moldability, chemical resistance, hygiene and the like.

Japanese Patent Publication No. Hei 7-154410 discloses a method in which a polyethylene pipe is molded into a tubular shape, and a resin pipe having a shape restoring property obtained by reducing the diameter at a melting point or less is attached to the inner face of the steel pipe to perform inner lining. are doing.

However, a resin tube based on polyethylene or the like has a low glass transition temperature of room temperature or lower and is in a rubber elasticity region at room temperature. In addition, dimensional control was difficult because the shape was gradually restored at room temperature.

As a result, the outer diameter of the resin pipe increases, and it becomes impossible to insert the resin pipe inside the steel pipe to be lined with the inner surface.

Further, in order to impart shape resilience, it is necessary to re-heat and stretch the produced resin pipe, and then perform cooling and then re-cooling, so that the re-heating lowers the productivity and lengthens the equipment space. Was needed.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for stably and inexpensively manufacturing a resin pipe having excellent shape resilience used for an inner resin lining steel pipe.

[0011]

Means for Solving the Problems The present inventors have intensively studied a method for stably imparting excellent shape memory to a resin pipe made of a general-purpose thermoplastic resin.

As a result, when the diameter of the thermoplastic resin is reduced during the cooling and solidification from the molten state by using the difference between the extrusion speed at the time of extruding the thermoplastic resin from the extrusion die (die) and the take-up speed of the take-up machine, it is excellent. It is possible to manufacture resin pipes with excellent shape resilience (heat-expandability) and dimensional stability at room temperature, and insert the shape-recoverable resin pipe manufactured by such a method into a steel pipe and heat the inner surface. It has been found that a resin-lined steel pipe can be manufactured.

The present invention has been made based on the above findings and further studied. That is, the present invention provides: A method for manufacturing a resin tube for extruding a thermoplastic resin from an extrusion die, wherein the molten thermoplastic resin is fixed in shape at a diameter reduction ratio of 3% or more downstream of the extrusion die. Manufacturing method.

However, diameter reduction ratio (%): 100 × (D−d) / D where D: outer inner diameter of extrusion die d: resin pipe outer diameter Thermoplastic resin is polyolefin, polyethylene,
2. The method for producing a resin tube according to 1, wherein the resin tube is any one of a crosslinked polyethylene, a polypropylene, and an ionomer resin.

3. The molten thermoplastic resin downstream of the extrusion mold is composed of multiple layers, the inner layer is any one of polyethylene, cross-linked polyethylene, or polypropylene, and the outer layer is a resin having a lower crystallinity than the inner layer. 2. The method for producing a resin tube according to item 1, wherein

4. An inner resin-lined steel pipe, wherein a resin pipe manufactured by the method according to any one of 1 to 3 is disposed inside the steel pipe, and then the resin pipe is heated to form an inner lining layer.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for extruding a molten thermoplastic resin from an extrusion die (die) and solidifying it by cooling to form a resin tube. It is characterized in that a residual stress is applied in the process up to solidification.

FIG. 1 schematically shows a production line to which the present invention is applied. A thermoplastic resin 6 is extruded in a molten state from an extrusion die 2 by an extruder 1, and is vacuum-cooled by a pre-cooling device 3. In the course of passing through the tank 4, it is taken off by the take-off machine 5 while being solidified during molding, and becomes a resin tube.

In the present invention, the diameter of the molten resin on the downstream side from the extrusion mold 2 is reduced while being cooled and solidified from the molten state to fix the shape, thereby giving residual stress to the thermoplastic resin. For the diameter reduction, the diameter reduction ratio is determined by the following equation (1), and the diameter reduction ratio is 3% or more.

Reduction ratio (%) = (D−d) / D × 100 (1) where D: outer diameter of die, d: outer diameter of resin pipe. While cooling with water
Extrusion speed V1 from extrusion die 2 and take-up speed V2 of take-off machine
This is done by providing a speed difference to

When the diameter is reduced during the pre-water cooling, the surface cooling is promoted in a state in which the molten resin is cylindrical, which is effective for preventing the resin tube from flattening. More pressure can also be applied.

It is possible to install a sizing die at the entrance of the cooling water tank, but it is not particularly specified in the present invention.
When the sizing die is installed, the diameter of the sizing die is reduced before the sizing die is slightly contacted with the sizing die.

In the present invention, the kind of the thermoplastic resin is not particularly specified, and it is possible to use a resin having excellent shape restoring property to a resin having almost no heat restoring property by a usual molding method.

For example, as a resin having excellent shape restoring properties,
Styrene butadiene copolymer, polyurethane, polynorbornene, etc. can be used.Polyolefin resins such as polyethylene, polypropylene, polymethylpentene, polybutene, ionomer, polystyrene, polyethylene terephthalanolate, polycarbonate, etc. Engineering plastics can also be used.

A blended resin in which different kinds of resins are mixed may be used. For example, in the case of polyethylene, low density, medium density, high density, linear low density polyethylene and the like can be used.

In the case of polypropylene, a homopolymer, a random or block copolymer can be used, and in the case of crosslinked polyethylene, the base resin has a low density, a medium density, a high density,
Linear low density polyethylene or the like can be used.

In the present invention, it is not necessary to define properties such as MFR and molecular weight. If necessary, plasticizers, colorants, pigments, fillers, flame retardants, antioxidants, ultraviolet absorbers And additives such as a charging material, a lubricant and a tackifier.

Further, in the present invention, the molten resin extruded from the extrusion die can be composed of two or more layers.

Surface irregularities due to slight pre-cooling unevenness (unevenness due to non-uniformity of cooling water spray in pre-cooling before entering the cooling water tank) generated in the case of resin such as polyethylene, cross-linked polyethylene, polypropylene, etc. In the case of a steel pipe, bubbles are generated between the resin lining layer and the steel pipe, and the surface properties are impaired. It is.

When an adhesive resin is used for the outer surface, an inner resin-lined steel pipe having further excellent adhesion between the resin pipe and the steel pipe can be obtained.

The shape-restoring resin tube according to the present invention has better dimensional stability at room temperature than that described in the prior art, because of its high diameter reduction temperature and the portion where the resin is partially melted. This is considered to be because the residual stress is small and the elastic modulus of the resin is reduced, so that no excessive residual stress is caused.

[0032]

EXAMPLES Using various thermoplastic resins, resin pipes were produced on the lines schematically shown in FIG. The extruder was equipped with a double ring die (extrusion die), and a resin tube having an outer diameter of 155 φ and a thickness of 2.5 mm was manufactured.

With respect to the obtained resin tube, shape resilience, dimensional stability and surface characteristics of the resin tube were examined. Shape recovery is achieved by heating the molded resin tube to the same temperature as the die temperature.
The outer diameter after holding for 1 minute and 30 seconds was compared with the outer diameter of the resin tube before heating, and judged by the restoration rate A.

If the restoration rate A is 0.5 or more, it is judged as acceptable.
Not less than 〜 to less than 0.7, Δ, not less than 0.7 to less than 0.9,
0.9 or more was rated as □, and less than 0.5 was rated as failed.

Restoration ratio A = (DA−d) / (D−d) (2) where DA: heated to die temperature, outer diameter of resin tube after 1 minute and 30 seconds, D: outer inner diameter of die, d: Outer diameter of resin tube before heating.

For reference, the expansion coefficient B of the resin pipe was determined by the equation (3). The expansion coefficient B = 100 × (DA-d) (3) Was allowed to stand at room temperature for one month, and the change in outer diameter was measured with a caliper. If the change in outer diameter is less than 0.5%, it is considered as acceptable (O) and 0.5%
The above cases were rejected (x).

Regarding the surface properties, the surface irregularities were visually observed, and remarkable ones were rejected (x), slight ones were (△),
Those that were not observed at all were rated as acceptable (O).

Further, workability in lining the inner surface of the resin pipe was confirmed. The resin pipe before shape restoration is inserted into a blasted steel pipe (inner diameter 156 mmφ, length 4 m),
Thereafter, the surface of the steel pipe was heated to the die temperature at the time of manufacturing the resin pipe by a high frequency heating device, and the shape of the resin pipe was restored.
The resin portion protruding from the end of the steel pipe was cut and removed.

After the inner lining, the central part of the steel pipe is cut,
The lining condition was observed. The gap between the inner circumference of the steel pipe and the outer circumference of the resin lining layer was determined on the entire circumference, and was judged to be acceptable if the gap was less than 0.7 mm, (□) when there was no gap, (○) to 0.5 mm, 0.5 to 0 0.7 mm or less (△), and the case where even one location was 0.7 mm or more was rejected (×).

Tables 1 and 2 show the properties of the manufactured resin tube, such as the resin, the manufacturing conditions, and the shape resilience described above. In the examples of the present invention in which the diameter reduction ratio is 3% or more, excellent characteristics are obtained. Particularly good properties were obtained when polyolefin, polyethylene, cross-linked polyethylene, polypropylene, and ionomer were used as the resin.

Further, it has been confirmed that the expansion rate increases depending on the diameter reduction rate, but when the diameter reduction rate is small, the shape restorability is good but the dimensional stability is inferior.

In Table 1, irregularities were observed on the surface of the resin tube in Examples 10 to 15 and 18, but were not observed in Examples 29 to 42.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

[0046]

[Table 4]

[0047]

According to the present invention, a resin tube having excellent shape resilience can be manufactured with high productivity using inexpensive resin, and is extremely useful in industry.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a resin pipe production line to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Extruder, 2 ... Extrusion die (die), 3 ... Preliminary water cooling device, 4 ... Vacuum cooling device, 5 ... Take-off machine, 6 ... Thermoplastic resin.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B32B 1/08 B32B 1/08 A 15/08 15/08 K 27/32 27/32 E F16L 9/12 F16L 9/12 // B29K 23:00 B29K 23:00 105: 02 105: 02 B29L 9:00 B29L 9:00 23:00 23:00 (72) Inventor Yasuhiro Harada 1-1-1 Marunouchi, Chiyoda-ku, Tokyo No. 2 Inside Nippon Kokan Co., Ltd. (72) Inventor Akihiko Furuta 1-2-2 Marunouchi, Chiyoda-ku, Tokyo F-term (in reference) 3H111 AA01 BA02 BA15 BA34 CA52 CA53 CB02 CB03 CB08 DA08 DA26 DB03 DB05 EA04 4F100 AB01C AK03A AK04A AK07A AK70A AK70B BA02 BA03 BA07 BA10B BA10C DA11 EJ05A EJ462 JA11B JB20A JL02 JL15 4F207 AA03 AA04 AA11 AA22 AD03 AD12 AE01 AG03 A04 A08 A04 A08 A04 A04 A08 AA11 A04 A08 AA81 A04 A08 AA81 A02 A08 AA11 A04 A08 AA81 A02 D03 AD12 AE01 AG03 AG08 AH81 AK01 RA03 RC03 RC04 RG01 RG05 RG07 RG09 RG24 RG43 RG62 4F211 AA03 AA04 AA11 AA22 AD03 AD12 AE01 AG03 AG08 AH81 AK01 SA13 SC03 SD04 SD11 SD16 SG01 SH06 SP20 SP28

Claims (4)

[Claims] 1. A method for manufacturing a resin tube for extruding a thermoplastic resin from an extrusion die, comprising: fixing a molten thermoplastic resin at a diameter reduction ratio of 3% or more downstream of the extrusion die. A method for manufacturing a resin tube. However, diameter reduction ratio (%): 100 × (D−d) / D where D: outer inner diameter of extrusion die d: outer diameter of resin tube 2. The method according to claim 1, wherein the thermoplastic resin is any one of polyolefin, polyethylene, cross-linked polyethylene, polypropylene, and ionomer resin.
The method for producing a resin tube according to the above. 3. A resin in which a thermoplastic resin in a molten state downstream of an extrusion mold comprises a multilayer, an inner layer of which is any one of polyethylene, cross-linked polyethylene or polypropylene, and an outer layer having a lower crystallinity than the inner layer. The method for manufacturing a resin tube according to claim 1, wherein: 4. An inner surface, wherein a resin tube manufactured by the method according to claim 1 is disposed inside a steel tube, and thereafter, the resin tube is heated to form an inner surface lining layer. Resin-lined steel pipe.