JP2003083477A - Multiple tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multiple tube having excellent corrosion resistance, hot water resistance and durability b making it free from problems in forming property and failures such as exposure of a metallic tube by contraction of a polyolefine resin layer at a tube end part and detachment of inner surface of the metallic tube and an adhesive layer. SOLUTION: This multiple tube comprises a middle layer for adhering a metallic outer layer and a polyolefine resin composition inner layer between the outer layer and the inner layer. The middle layer is made of adhesive polyolefine resin composition including laminar silicate, and the inner layer is made of polyolefine resin composition not including laminar silicate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite pipe in which the inner surface of a metal pipe is coated with a polyolefin resin composition and which has excellent corrosion resistance and is suitable for applications such as water supply, hot water supply, chemical transportation, and drainage.

[0002]

2. Description of the Related Art Polyolefin resins are inexpensive, chemically stable and excellent in corrosion resistance. Therefore, such a composite pipe in which the inner surface of a metal pipe such as an iron pipe to be the outer layer is coated with the polyolefin resin to be the inner layer directly or through an intermediate layer is widely used as a pipe for transferring hot water, chemical liquids, etc. ing.

However, in the case of such a composite pipe, the linear expansion coefficient of the polyolefin resin forming the inner layer is significantly larger than the linear expansion coefficient of the metal forming the outer layer. Therefore,
When a high temperature fluid flows intermittently in the composite pipe,
The metal outer layer and the polyolefin resin inner layer repeatedly expand and contract in the tube axis direction (length direction) and in the diametrical direction according to their respective linear expansion coefficients, and peeling occurs between the layers. As a result, fluid enters between the outer layer and the inner layer or the middle layer,
Alternatively, the molding strain remaining in the polyolefin resin forming the inner layer is released and the inner layer shrinks, drawing in significantly from the end of the metal tube and the fluid directly touches the metal tube, resulting in rust and corrosion on the metal tube. It could cause an accident.

In order to solve this problem, in Japanese Patent Laid-Open No. 55-161639, 20 parts by weight of a granular inorganic filler such as calcium carbonate or calcium silicate through an intermediate layer in a metal tube serving as an outer layer. By providing a synthetic resin tube including the above as the inner layer, a composite tube has been proposed in which the linear expansion coefficient of the inner layer is reduced to reduce the difference in expansion and contraction between the inner layer and the outer layer due to temperature change, and in JP-A-5-118473. A composite pipe in which a metal pipe as an outer layer and a synthetic resin pipe as an inner layer are melt-bonded through an intermediate layer made of an adhesive synthetic resin containing a fibrous inorganic filler, which is arranged between the metal pipe and the synthetic resin pipe. Is proposed.

[0005]

However, JP-A-55-55
In the composite pipe described in Japanese Patent No. 161639, since the synthetic resin pipe forming the inner layer contains a large amount of an inorganic filler in the synthetic resin, the shape is difficult to be collected during molding, and the screw of the molding machine is easily worn. In addition to the above problems, the material of the synthetic resin tube becomes brittle, the surface has poor smoothness, and the water absorption is high.

Also in the composite pipe of Japanese Patent Laid-Open No. 5-118473, it is necessary to add a large amount of fibrous inorganic filler to the adhesive synthetic resin in order to achieve low expansion and contraction of the intermediate layer. , The shape is difficult to collect during molding,
There is a problem that the screw of the molding machine is easily worn, and there is also a problem that the effect of reducing expansion and contraction of the intermediate layer is not sufficient.

The present invention has been made in view of the problems of the prior art as described above, has no problem in moldability, and the inner surface of the metal layer of the metal layer due to shrinkage of the polyolefin resin layer at the end of the tube. It is an object of the present invention to provide a composite pipe which is free from defects such as exposure to water and peeling between the inner surface of the metal layer and the intermediate layer and which is excellent in corrosion resistance, hot water resistance and durability.

[0008]

In order to achieve such an object, the composite pipe according to claim 1 of the present invention (hereinafter referred to as
The "composite pipe of claim 1" is a composite pipe provided with an intermediate layer for joining the outer layer and the inner layer between an outer layer made of a metal and an inner layer made of a polyolefin resin composition. It is characterized in that it is formed of an adhesive polyolefin resin composition containing layered silicate and the inner layer is formed of a layered silicate-free polyolefin resin composition.

The composite pipe according to claim 2 of the present invention (hereinafter,
The "composite pipe of claim 2" is the composite pipe of claim 1, wherein the intermediate layer is mixed with 100 parts by weight of the adhesive polyolefin resin in a proportion of 1 part by weight or more and 15 parts by weight or less. The adhesive polyolefin resin composition was used.

A composite pipe according to claim 3 of the present invention (hereinafter,
The "composite pipe of claim 3") is a composite pipe of claim 1 or 2, wherein the adhesive polyolefin resin is selected from the group consisting of a carboxylic acid group (carboxyl group), a carboxylic acid anhydride group and a hydroxyl group. The adhesive polyolefin resin having at least one kind of functional group in the molecule is used.

A composite pipe according to claim 4 of the present invention (hereinafter,
The "composite pipe of claim 4" is defined in claims 1 to 3.
In any of the composite tubes, at least one selected from the group consisting of swelling smectite clay minerals and swelling mica was used as the layered silicate.

In the present invention, the metal layer is generally formed by using a metal pipe such as a steel pipe, a plated steel pipe, a stainless steel pipe, an aluminum pipe and a copper pipe. These metal tubes are subjected to degreasing treatment with an alkali or the like, oxide film removal treatment such as rust with hydrochloric acid, sulfuric acid, nitric acid or the like, and then rust prevention treatment with zinc phosphate, iron phosphate, oxalic acid, etc.
Further, in order to improve the adhesiveness, it is preferable to perform coupling treatment, primer treatment, chromate treatment and the like.

In the present invention, the adhesive polyolefin resin constituting the adhesive polyolefin resin composition is a carboxylic acid-modified polyolefin resin obtained by modifying a polyolefin resin with an unsaturated carboxylic acid or an anhydride thereof, as in claim 3. Ethylene-methacrylic acid copolymer, ethylene-acrylic acid copolymer, ethylene-maleic anhydride copolymer, saponified ethylene-vinyl acetate copolymer, ethylene-maleic anhydride-acrylic acid ester copolymer, ethylene A polymer having at least one functional group selected from the group consisting of a carboxylic acid group such as an acrylic acid ester copolymer, a carboxylic acid anhydride group and a hydroxyl group in the molecule is preferable.

The polyolefin resin used as a raw material for the modified polyolefin resin is low-density polyethylene,
Co-weight of medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, polybutene, ethylene and α-olefin such as propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene Coalescence or the like is used. In particular, linear low-density polyethylene is preferable because of its good modification (grafting) efficiency. Further, the carboxylic acid-modified polyolefin resin, specifically,
An unsaturated carboxylic acid or its anhydride is added to a polyolefin resin, which is melt-kneaded by an extruder or roll in the presence of a radical generator such as di-t-butylperoxide, etc. It can be obtained by grafting an unsaturated carboxylic acid or its anhydride. Incidentally, these carboxylic acid-modified polyolefin resins are commercially available.

As the unsaturated carboxylic acid or its anhydride, maleic acid, acrylic acid, methacrylic acid, maleic anhydride, citraconic acid anhydride, itaconic acid anhydride or the like is used.

In the present invention, the layered silicate is added to the resin in order to reduce the linear expansion coefficient. The layered silicate means a silicate mineral having an exchangeable cation between layers, and is usually It is formed by aggregating fine flaky crystals having a thickness of about 1 nm and an average aspect ratio of about 20 to 200 by ionic bonds. The type of layered silicate is
For example, but not limited to, smectite clay minerals such as montmorillonite, saponite, hectorite, beidellite, stevensite, nontronite; natural minerals such as vermiculite, halloysite, sepiolite; swelling mica (swelling mica), etc. Examples thereof include synthetic mica. These layered silicates may be natural or synthetic, and montmorillonite and synthetic mica are preferably used.

The exchangeable cations existing between the layers of the layered silicate may be ion-exchanged with a cationic surfactant or the like in advance. In particular, when a non-polar adhesive polyolefin resin is used, it is better to make the layers hydrophobic beforehand by, for example, cation exchange using a cationic surfactant having a hydrophobic group. It is preferable because a high affinity can be obtained between the salt and the adhesive polyolefin resin. In addition, as described above, a material in which the layers of the layered silicate are ion-exchanged with a cationic surfactant having a hydrophobic group is referred to as "organized layered silicate". Since it is more easily dispersed in a resin than non-organized layered silicate, it is preferably used.

The above-mentioned cationic surfactant having a hydrophobic group is not particularly limited, but examples thereof include cationic surfactants such as quaternary ammonium salt and quaternary phosphonium salt, preferably having a carbon number. A quaternary ammonium salt having 8 or more alkyl chains is used. That is, when the alkyl chain having 8 or more carbon atoms is not contained, the hydrophilicity of the alkylammonium ion may be strong and it may be difficult to sufficiently depolarize the layers of the layered silicate. Examples of the quaternary ammonium salt having an alkyl chain having 8 or more carbon atoms include lauryltrimethylammonium salt, stearyltrimethylammonium salt, trioctylammonium salt, distearyldimethylammonium salt (hereinafter referred to as “DSDM”), diester. Hardened tallow dimethylammonium salt, distearyldibenzylammonium salt and the like can be mentioned.

The cation exchange capacity of the layered silicate is not particularly limited, but is preferably 50 meq / 100 g or more and 200 meq / 100 g or less. If it is less than 50 meq / 100 g, the amount of the cationic surfactant intercalated between the crystal layers by ion exchange may be small, and the layers may not be sufficiently depolarized. If the amount is more than the equivalent amount / 100 g, the bond strength between the layers of the layered silicate becomes strong, and it may be difficult to delaminate the crystal flakes. In addition,
The cation exchange capacity is the amount of cations that can be exchanged with 100 g of the layered silicate.

The amount of the layered silicate compounded in the adhesive polyolefin resin composition is not particularly limited, but as described in claim 2, 1 part by weight or more of the layered silicate is added to 100 parts by weight of the adhesive polyolefin resin. The proportion is preferably 15 parts by weight or less, more preferably 2 parts by weight or more and 13 parts by weight or less. That is, if it is less than 1 part by weight, the effect of reducing the linear expansion coefficient of the resin is small, and if it exceeds 15 parts by weight, the formability, tensile strength, ductility and the like of the adhesive polyolefin resin containing the layered silicate are lowered and the cost is high. There is a risk that

In addition to the layered silicate, the adhesive polyolefin resin composition may further contain an antioxidant, a flame retardant, a pigment, a filler, an antistatic agent, if necessary, as long as the performance of the present invention is not impaired. Additives such as agents, lubricants, tackifiers, and other resins can be mixed. As the other resin mixed in the adhesive polyolefin resin composition, a polyolefin resin having a good compatibility with the adhesive polyolefin resin is preferable.

The method of mixing the adhesive polyolefin resin and the layered silicate is not particularly limited. For example, the adhesive polyolefin resin and the layered silicate, and if necessary, other additives may be added in a twin-screw extruder, Laboplast mill. And the like, and then melt-kneading while heating.

In order to provide the above-mentioned adhesive polyolefin resin composition layer on the inner surface of the metal tube, (1) a tubular body made of the adhesive polyolefin resin composition is extruded and this tubular body is inserted inside the metal tube. After that, a method of expanding the tubular body along the inner surface of the metal tube by heating (2) inserting the tubular body inside the metal tube, and then reducing the diameter of the metal tube with a roll or the like to form the metal tube. A method of laying it along the outer wall surface of the tubular body, (3) a method of spraying the powder of the adhesive polyolefin resin composition on the inner surface of the metal tube, and then heating and melting the powder, (4) using a metal strip, A method is used in which the above-mentioned adhesive polyolefin resin tube is extrusion-coated on the inner surface immediately after forming the tube into a tube and welding the joint edges.

Further, an inner layer made of a polyolefin resin is provided on the inner surface of the intermediate layer made of the adhesive polyolefin resin composition containing a layered silicate. The polyolefin resin forming the inner layer is not particularly limited, but includes low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, polybutene, ethylene and propylene, 1-butene,
Random, block or graft copolymers with α-olefins such as 1-hexene, 4-methyl-1-pentene and 1-octene, propylene and butene-1, pentene-
Α-such as 1, hexene-1,4-methyl-pentene-1
An ordinary unmodified polyolefin resin such as a random, block, or graft copolymer with an olefin is used. Further, an adhesive polyolefin resin such as a silane-modified polyolefin resin or a carboxylic acid-modified polyolefin resin is also used.

Also in the case of the polyolefin resin composition constituting the inner layer, antioxidants, flame retardants, pigments, fillers, antistatic agents, lubricants, adhesives, etc. may be used as necessary within the range of not impairing the performance of the present invention. Additives such as a imparting agent, and other resins can be added. On the inner surface of the intermediate layer made of the adhesive polyolefin resin composition containing the layered silicate,
In order to provide an inner layer made of a layered silicate-free polyolefin resin composition, in addition to the same methods as the above (1) to (4), (5) an adhesive polyolefin resin composition and a polyolefin resin composition are used. A method of coextrusion molding on the inner surface of the metal tube is adopted.

The thicknesses of the intermediate layer and the inner layer and the ratio of the thicknesses of the two are appropriately set in consideration of the types and properties of the resin / layered silicate, the types and properties of the fluid, moldability, cost, etc. Generally, it is preferable to set both layers in the range of 0.2 mm to 3 mm. The layered silicate-containing adhesive polyolefin resin layer and the layered silicate-free polyolefin resin layer may be clearly separated, and are not clearly separated and are layered from the outer layer side in contact with the metal pipe to the inner layer side. The silicate content may be gradually reduced. Further, the layered silicate-containing adhesive polyolefin resin layer and the layered silicate-free polyolefin resin layer,
A plurality of each may be provided.

[0027]

[Function] The layered silicate is highly dispersed in the adhesive polyolefin resin without using an organic dispersion liquid or a low molecular weight substance such as an olefin oligomer having a hydrogen-bonding functional group. Since the intermediate layer does not elute into a chemical solution and the linear expansion coefficient of the intermediate layer becomes small, it exhibits an effect of suppressing the thermal expansion and contraction.

By adding the layered silicate to the adhesive polyolefin resin, the gas barrier property is enhanced, and the absorption and permeation of water, hot water, water vapor, etc. from the intermediate layer is hindered.
Peeling between the metal layer and the intermediate layer, or rust or corrosion of the metal layer is prevented. Moreover, since the inner layer made of the polyolefin resin composition not containing the layered silicate is provided along the inner surface of the intermediate layer made of the adhesive polyolefin resin composition containing the layered silicate, the layered silicate is hot water or a chemical solution. Therefore, the layered silicate is not likely to be eluted, and the intermediate layer and the inner layer have the same compatibility with each other, so that the intermediate layer and the inner layer are firmly bonded.

Further, the layered silicate can be added in a smaller amount as compared with the case where a conventional polyolefin resin composition containing an inorganic filler is used, so that the formability and surface performance are adversely affected. There is no. The inclusion of the layered silicate in the polyolefin resin composition used for the inner layer means that a low molecular weight substance such as an organic dispersion liquid or an olefin oligomer containing a hydrogen-bonding functional group necessary for dispersion is hot water or This is not preferable because it may be eluted into a chemical solution or the like, and at the same time, water may penetrate into the eluted marks to cause separation between the metal layer and the intermediate layer or the inner layer, or rust or corrosion of the metal layer.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below by comparing specific examples thereof with comparative examples thereof.

(Example 1) One side of a steel strip was subjected to degreasing treatment with an alkaline solution, oxide film removal treatment with nitric acid, anticorrosion treatment with zinc phosphate, and epoxy primer treatment. Welded, outer diameter 114.3m
A steel pipe having a thickness of 2.0 mm and a wall thickness of 2.0 mm was produced, and 100 parts by weight of a maleic anhydride-modified polyethylene resin (Admer NE065 manufactured by Mitsui Chemicals, Inc.) was mixed with DSDM-modified montmorillonite (distearyl dimethyl ammonium) in the steel pipe. Organized montmorillonite (Southern Clay Prod) obtained by ion exchange of sodium ions between montmorillonite layers with chloride by 120 milliequivalent / 100g
ucts Inc. DSDM-modified montmorillonite manufactured by K.K., Cloisite 20A)) 10 parts by weight of a layered silicate-containing adhesive polyolefin resin as an intermediate layer, and
Medium density polyethylene containing no layered silicate (density 0.935 g / cm ³ , MFR 1.2 g / 10 min)
Two layers were simultaneously extruded to obtain a composite pipe having a three-layer structure in which an intermediate layer having a thickness of 0.5 mm and an inner layer having a thickness of 2.5 mm were formed on the inner surface thereof.

Example 2 A maleic anhydride-modified polypropylene resin (Admer QE06 manufactured by Mitsui Chemicals, Inc.) was used as an intermediate layer.
0) 100 parts by weight of swelling mica with DSDM (organic swelling mica obtained by ion exchange of sodium ions between mica layers with distearyldimethylammonium chloride in 100 milliequivalents / 100 g (manufactured by Corp Chemical)
SDM modified swelling mica, trade name MAE-100)) 3
And an inner layer made of polypropylene (MF).
(R 0.5 g / 10 min) except that the composite tube was formed in the same manner as in Example 1 to obtain a composite tube having a three-layer structure.

Example 3 An ethylene-acrylic acid copolymer (Primacor 3340 manufactured by Dow Chemical Co.) was used as an intermediate layer.
100 parts by weight of DSDM-modified montmorillonite (distearyldimethylammonium chloride was used to produce 120 milliequivalents / 1 of sodium ions between montmorillonite layers).
00g ion-exchanged organized montmorillonite (Southe
rn Clay Products Inc. A composite tube having a three-layer structure was obtained in the same manner as in Example 1 except that the layered silicate-containing adhesive polyolefin resin was 20 parts by weight of DSDM-modified montmorillonite (trade name: Cloisite 20A)).

Example 4 The intermediate layer was saponified with an ethylene-vinyl acetate copolymer having a weight ratio of 6: 4 (Mersen H6051 manufactured by Tosoh Corporation) and medium density polyethylene (density 0.93).
5 g / cm ³ , MFR 1.2 g / 10 min) mixture 10
0 parts by weight of DSDM-modified swelling mica (organic swelling mica obtained by ion exchange of sodium ion between mica layers with distearyldimethylammonium chloride at 100 milliequivalent / 100 g) (DSDM-modified swelling mica manufactured by Corp Chemical Co., Ltd. A composite tube having a three-layer structure was obtained in the same manner as in Example 1 except that the layered silicate-containing adhesive polyolefin resin was composed of 5 parts by weight of MAE-100)).

Comparative Example 1 A maleic anhydride-modified polyethylene resin (Admer NE065 manufactured by Mitsui Chemicals, Inc.) was used as the intermediate layer.
In the same manner as in Example 1 except that the inorganic filler-containing adhesive polyolefin resin was composed of 100 parts by weight and 20 parts by weight of glass short fibers (average diameter 13 μm, average fiber length 500 μm) as the inorganic filler. A composite tube with a three-layer structure was obtained.

Comparative Example 2 A maleic anhydride-modified polyethylene resin (Admer NE065 manufactured by Mitsui Chemicals, Inc.) was used as the intermediate layer.
In the same manner as in Example 1 except that the inorganic filler-containing adhesive polyolefin resin was composed of 100 parts by weight and 5 parts by weight of glass short fibers (average diameter 13 μm, average fiber length 500 μm) as the inorganic filler. A composite tube with a three-layer structure was obtained.

The operation of passing hot water at 90 ° C. for 3 minutes and then tap water at 20 ° C. for 3 minutes through the 5 m composite pipes prepared in Examples 1 to 4 and Comparative Examples 1 and 2 was performed 500 times.
Repeated 00 cycles, repeated heating-cooling durability evaluation was performed. Table 1 shows the results of the repeated heating-cooling durability evaluation, and the situation at the time of manufacturing the composite pipe of each of the examples and comparative examples.
It was shown to.

[0038]

[Table 1]

As shown in Table 1, in Examples 1 to 3, repeated heating and cooling with hot and cold water also
A composite pipe was obtained in which peeling between the metal pipe and the resin layer and shrinkage of the resin layer at the pipe end did not occur, and in Example 4, peeling between the metal pipe and the resin layer was caused by repeated heating and cooling. A composite tube that did not occur was obtained. In addition, Example 1,
In Nos. 2 and 4, no abnormality such as difficulty in coordinating the shape of the intermediate layer during the two-layer melt extrusion of the intermediate layer and the inner layer was observed.

On the other hand, in Comparative Example 1, a composite pipe was obtained in which neither peeling of the metal pipe from the resin layer nor shrinkage of the resin layer at the end of the pipe occurred even after repeated heating and cooling. However, during the two-layer melt extrusion of the intermediate layer and the inner layer, it was found that the shape of the intermediate layer was difficult to be collected. In Comparative Example 2, no abnormalities such as difficulty in forming the shape of the intermediate layer were observed during the two-layer melt extrusion of the inorganic filler-containing adhesive polyolefin resin (intermediate layer) and the polyolefin resin (inner layer). However, it was confirmed that, due to repeated heating and cooling, a gap of about 1 mm was generated between the intermediate layer and the steel pipe at both pipe ends, and the intermediate layer and the inner layer were contracted by 5 mm from the steel pipe.

[0041]

As is apparent from the above description, the composite pipe of the present invention can be separated from the metal layer and the intermediate layer and the inner layer and the inner layer at the pipe end by repeated heating and cooling with hot water and cold water. No shrinkage occurs, and it has excellent hot water resistance, corrosion resistance, and durability. Further, since a high effect can be obtained with a small amount of the layered silicate content, there is no problem that the shape is not easily collected during molding, the screw of the molding machine is easily worn, and the moldability is excellent.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3H111 AA01 BA01 BA15 BA31 BA34                       CA52 CB04 CB09 DA08 DA11                       DA26 DB03 DB05 DB10                 4F100 AA03C AA03H AB01A AC03C                       AC03H AC10C AC10H AK03B                       AK03C AK04 AK62B AK62C                       AK66B AK66C AL05C AL07                       AL07C BA03 BA07 BA10A                       BA10B DA11 EH17 EH20                       GB31 GB90 JB02 JJ03 JK06                       JL00 JL11 JL11C YY00C

Claims (4)

[Claims] 1. A composite pipe comprising an outer layer made of metal and an inner layer made of a polyolefin resin composition, and an intermediate layer for joining the outer layer and the inner layer, wherein the intermediate layer is an adhesive polyolefin containing a layered silicate. A composite pipe, which is formed of a resin composition and whose inner layer is formed of a layered silicate-free polyolefin resin composition. 2. The intermediate layer comprises an adhesive polyolefin resin 10
The composite pipe according to claim 1, wherein the composite pipe is formed of an adhesive polyolefin resin composition containing 0 part by weight of a layered silicate in a proportion of 1 part by weight or more and 15 parts by weight or less. 3. The adhesive polyolefin resin has in its molecule at least one functional group selected from the group consisting of a carboxylic acid group, a carboxylic acid anhydride group and a hydroxyl group.
Alternatively, the composite pipe according to claim 2. 4. The layered silicate is at least one selected from the group consisting of swelling smectite clay minerals and swelling mica, according to any one of claims 1 to 3. Composite pipe.