JPH0820029B2 - Pipe based on polyolefin resin for forming pipe line, joint for connecting the pipe, and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin pipe for forming a long-distance pipe, a joint for connecting the same, and a method for manufacturing the same.

BACKGROUND OF THE INVENTION The use of polyolefin resin pipes in pipelines that distribute fluids such as city gas within and between cities is known. Generally, in the laying of this pipeline, the ends of two pipes whose ends are abutted against each other are covered with tubular joint sleeves made of a polyolefin resin made of the same material as the pipes, and heat welded to both ends of the pipes. The heat required for this welding is provided by a resistance heater embedded in the sleeve body during sleeve manufacture.

This pipe connection technique is time-consuming and requires skill and know-how. In this pipe connection method, a polyolefin resin, especially a thermoplastic material mainly composed of polyethylene or a copolymer of ethylene is used. Known polyolefin resins make effective use of their ability to soften by heating and self-weld, but at the same time, they have some drawbacks.

In particular, when pressure or high temperature is applied for a long time, it tends to creep, may crack under mechanical stress, has poor chemical resistance, and is sensitive to abrasion when laying in a groove. To be

In addition, thick pipes must be used because the pipelines must withstand the pressure of the transport fluid and the mechanical and chemical effects from the outside or inside for decades of service. As a result, the pipe used is effective. This is not just a matter of the amount of material needed, but a problem of slower production rates, which are limited by the extruder output used to make the pipe.

Moreover, the heavy and bulky size of the pipe is of course inconvenient for transporting and laying the pipe.

FIGS. 8 to 11 of JP-A-56-11248 describe a pipe, a connecting pipe, and a T-shaped pipe in which a silane-grafted polyethylene layer 1 and a silanol condensation catalyst mixture layer 2 are laminated. A silanol condensation catalyst is indispensable for crosslinking silane-grafted polyethylene, but when a masterbatch having a high concentration of silanol condensation catalyst is used, there is a drawback that the silanol condensation reaction occurs in the extruder and solidifies. The purpose of this patent (see page 1, lower right column to page 2, upper right column) is to eliminate this drawback. In this patent, the silanol condensation catalyst blending layer 2 and the silane graft polyethylene layer 1 are separated. The silanol condensation catalyst is transferred from the silanol condensation catalyst blending layer 2 to the silane-grafted polyethylene layer 1 by stacking them to carry out the silanol condensation reaction (see page 3, lower right column, lines 3 to 11). ). Therefore, the catalyst concentration in the silanol condensation catalyst blending layer 2 is high, and 5.0 parts (the ratio to the total weight is 4.7% by weight) of dibutyltin dilaurate is used in the example described in Example 1. On the other hand, the silane-grafted polyethylene layer 1 has a dibutyltin dilaurate concentration of 0. Therefore, the initial concentration gradient between the two layers is 4.7 / 0. The thickness of each layer before pressing is 1 mm or less,
The thickness of the laminate is 2 mm. Due to the high concentration gradient of dibutyltin dilaurate in the method described in this patent, the welding characteristics of both layers 1, 2 are very different, thus weakening the adhesion of the welded parts and causing leakage.

DISCLOSURE OF THE INVENTION The object of the present invention is to solve the above-mentioned drawbacks of known pipes, and moreover, the pipes based on polyolefin resin for forming long-distance pipelines, which can use the conventional pipe connection techniques as they are. To provide.

Means for Solving the Problems The first object of the present invention is to provide a first grafted vinyltrimethoxysilane, which is then hydrolyzed and crosslinked.
A tubular wall composed of two coaxial layers obtained by co-extruding an inner layer forming a core made of the above polyolefin resin and an outer layer forming a surface layer made of a weldable thermoplastic second polyolefin resin. An extruded pipe for laying a long pipeline by connecting end portions with each other, which comprises dibutyltin dilaurate, which is a hydrolysis catalyst of trimethoxysilane group, on the wall of the pipe, 1) The polyolefin resin of No. 1 is cross-linked with 30% by weight or more of a cross-linking agent, and the initial crosslinkable composition before co-extrusion contains trimethoxysilane groups and dibutyltin dilaurate, the amount of dibutyltin dilaurate being the initial composition. Is about 0.05% by weight of the total weight of 2), the outer diameter of the pipe is 32.1 to 150 mm, and 3) the thickness of the pipe wall is 3.1 m when the outer diameter of the pipe is 32.1 mm.
Mechanical properties in which two coaxial layers are intimately integrated with each other, characterized by being from m to 15 mm when the outer diameter of the pipe is 150 mm, and 4) the thickness of the outer layer is 0.1 to 2 mm. Excellent in heat resistance and easy to heat weld.

A second subject of the invention is a first trivinylsilane grafted, then hydrolyzed and crosslinked.
Is a hydrolysis catalyst of a trimethoxysilane group on a tube wall, which has an outer layer forming a core made of a polyolefin resin and an inner layer forming a surface layer made of a thermoplastic second polyolefin resin that can be welded. Made of thermoplastic material containing dibutyltin dilaurate,
In the tubular joint sleeve for connecting the above pipes, 1) the first polyolefin resin is cross-linked with 30% by weight or more of a cross-linking agent, and the cross-linkable initial composition thereof before co-extrusion has a trimethoxysilane group. Dibutyltin dilaurate, wherein the amount of dibutyltin dilaurate is approximately 0.05% by weight of the total weight of the initial composition, 2) the outer layer and the inner layer having a thickness of 1 to 4 mm. Are intimately integrated with each other and the inner layer is a joint sleeve which is welded to the outer layer of the pipe by welding means.

A third subject of the invention is approximately 0,0 of the total initial weight of the composition.
Prepare a composition for the inner layer that constitutes the core consisting of a thermoplastic polyolefin resin containing 05 wt% dibutyltin dilaurate and vinyltrimethoxylane, and a composition for the outer layer consisting of a weldable thermoplastic polyolefin resin Then, the two compositions are coextruded to form a tubular element having two coaxial layers of tube wall of the two compositions, and the tubular element is placed in a humid atmosphere to form a core. The method for producing a pipe is characterized in that:

The greatest advantage of the present invention is that the wall thickness of the pipe is thin, and therefore the weight is light, the manufacturing cost is low, the manufacturing can be performed in a small facility, and the pipe based on polyolefin is used. The point is that the mechanical strength and durability can be improved.

In fact, creep resistance experiments under pressure have demonstrated that the pipe of the present invention can maintain the stress resistance at the same value as when it was first used, for a significantly longer time than the conventional pipe. Therefore, the pipe according to the invention is particularly suitable for the production of pipelines.

Further, since other properties such as abrasion resistance and chemical resistance are similarly improved, even if the surface layer used for welding the tip at the time of pipe joining is relatively weak, there is almost no problem.

In the pipe or joint sleeve of the present invention, the surface layer and the core are tightly integrated by molding each composition by extrusion molding or injection molding before the crosslinking of the composition forming the core occurs.

The grafting of the alkoxysilane and the crosslinking to make the core into a crosslinked resin can be carried out in two steps or in one step. Alkoxysilane grafted by opening a saturated bond is added. In this case, it is possible to add a usual additive that causes crosslinking after extrusion. In the case of carrying out in one step, a grafting initiator is added to the composition and the grafting reaction is carried out during extrusion at the extrusion temperature.

It is also possible to provide an intermediate layer between the core and the surface layer or a series of intermediate layers with a graded composition from one layer to another. In a preferred embodiment of the invention using the same polyolefin resin as the basic constituents of the core and the surface layer, the proportion of alkoxysilane from one layer to another,
Therefore, the cross-linking ratio of the polyolefin can be gradually changed. In this case, the degree of cross-linking on the surface of the pipe is kept low to the extent that welding is possible, and the degree of cross-linking in the layer forming the core is such that the overall mechanical resistance and long-term durability are at desired values. To a relatively high crosslinking rate.

From this viewpoint, the degree of crosslinking in the core material is 30% or more, preferably between 50% and 70%. In the case of the surface layer, the degree of cross-linking may be 0, but if it is, for example, 2% to 5%,
There is an advantage that the shear resistance can be improved without adversely affecting the weldability.

The polyolefin polymer and copolymer compositions crosslinked by unsaturated alkoxysilanes are known per se, and the constituents of the pipe and joint sleeve compositions according to the invention are also known per se. Similarly, its selection and blending ratio are known. In the present invention, it is preferable to use polyethylene or polypropylene as the base thermoplastic polymer, and further copolymers with these monomers and monomers compatible therewith, such as propylene (for ethylene), ethylene chloride or vinyl acetate. Is preferably used.

The grafting agent and the cross-linking agent used in the composition constituting the core are vinyltrimethoxysilane having an ethylenic double bond for grafting and causing a condensation reaction by hydrolysis. The composition further contains a radical polymerization initiator and a hydrolysis catalyst of vinyltrimethoxysilane.

The coupling sleeve may be straight or curved so as to form all branches or distribution channels of the pipeline, and may also have multiple branches, for example T-shaped or Y-shaped. Good.

In a modification of the present invention, it is also possible to directly connect the tip portions of two continuous pipes fitted to each other.
In this case, the fitting technique usually used to lay a pipeline of thermoplastic pipe in a house, that is, the end of one pipe is expanded in a tulip shape, and the tip of the connected pipe is fitted into it. A joint technique that heats the entire periphery of the tulip-shaped portion to ensure welding can be applied. That is, at the tulip, welding occurs between the outside of one pipe and the inside of the other pipe. In order for this joining technique to be applicable, a tubular surface core of crosslinked polyolefin resin is provided with one thermoplastic surface layer on the inner surface and one thermoplastic surface layer on the outer surface.

Since the core of the pipe is a cross-linked polyolefin resin,
There is also the additional advantage of thermal cross-linking during pipe joining and the application of pressure for effective welding.

 Hereinafter, description will be given with reference to the accompanying drawings.

In FIG. 1, two pipes are indicated by 1, 2 and a joint sleeve 3, respectively. Each of the pipes 1 and 2 is made of a cylindrical tubular tube wall, which has two coaxial layers made of thermoplastic resin, namely an inner core 4 and an outer surface layer 5.
It is composed of layers.

The joint sleeve 3 has a size that covers the ends of the two pipes without a gap, and the pipe wall is also composed of two cylindrical coaxial layers. In this case the core 6 is on the outside and the surface layer 7 is on the inside. The joint sleeve 3 has welding means represented by a resistance heater 8. The resistance heater 8 is embedded at approximately the interface between the two layers of the joint sleeve. It will be readily appreciated that welding can also be accomplished by heating the outside of the fitting sleeve.

The pipe can be extruded. The coupling sleeve can be extruded or injection molded. In any case, the tubular element or pipe or fitting sleeve is formed from each composition as two coherent layers of the desired size, followed by crosslinking of the crosslinkable composition for the core. By doing so, the pipe and the coupling sleeve can be finally integrated.

EFFECTS OF THE INVENTION The pipe of the present invention has greater durability than conventional polyethylene pipes, does not creep under pressure for a long time, significantly improves mechanical properties at high temperature, has no risk of cracking, and is resistant to cracking. Improves chemical resistance and wear resistance. These improvements make it possible, without risk, to reduce the thickness to 50% compared to pipes currently made mainly of thermoplastic materials. This is an important technological and economic advance, a significant reduction in raw material costs, and an improvement in production rate. Further, the cross section of the hole in the center of the pipe is increased, which means that the transportation capacity of the piping network is significantly increased.

Next, examples of the present invention will be described, but the present invention is not limited to the following examples.

Example Two different compositions based on polyethylene are prepared and fed to the inlet of an extruder with two coaxial dies at a temperature of 150 ° C to 250 ° C.

The first composition fed to the die was polyethylene with a density of 0.956 and a melt index of 0.1 at 190 ° C and 2.16 bar, the second composition was a crosslinkable polyethylene composition capable of grafting and crosslinking. In addition to polyethylene, the composition comprises 1-2 wt% vinyltrimethoxysilane, 0.05-0.2 wt% dicumyl peroxide, and 0.05 wt% dibutyltin dilaurate, based on the total weight of the composition. There is. The graftable and crosslinkable crosslinkable polyethylene has a density of 0.948 and a melt index of 0.2 at 190 ° C and 2.16 bar.

When heated in the mixing zone of the extruder, the organic peroxide dicumyl peroxide opens the ethylene double bond and grafts the vinyl silane onto the polyethylene chain.

The coaxial two-layer tubular element extruded from the extruder is cut into a desired pipe length and then exposed to moisture in the atmosphere and stored for several days. This leads to crosslinking of the composition constituting the inner layer of the pipe by hydrolysis of the grafted trimethoxysilane groups and silanol condensation. This reaction is catalyzed by dibutyltin dilaurate in the composition.

In the final product pipe, only the inner layer, which constitutes a basic part of the wall thickness of the tube, is crosslinked, while the outer surface layer remains thermoplastic.

The dimensions in the cross section are as follows: Outer diameter of pipe: 32.1 mm Overall wall thickness: 3.1-3.2 mm Outer layer thickness: 0.4 mm Also, extruded from extruder to check resistance. The obtained tubular element was cut perpendicularly to the axis line into a short pipe having a length of about 20 cm, which was hydrolyzed in hot water at 80 ° C. for 8 hours to ensure crosslinking. After drying, two short pipes were joined end to end using a conventional heat-sealable fitting sleeve marketed under the name "Innogaz".

The sample thus obtained was placed in a bath at 80 ° C. under hydrostatic pressure such that the stress σ calculated by the following formula was 4 MPa to: σ = P (D−e) / 2e (where D Is the outer diameter of the pipe, e is the thickness of the entire pipe wall, P
Represents the pressure in the pipe.) The pressure P was 0.85 MPa or 8.5 bar.

The stress σ was applied to four similar samples for 8,800 hours, but there was almost no change.

Furthermore, after being left at a temperature of 20 ° C. for 24 hours, the sample was placed under a pressure of 20 bar for 168 hours, but no rupture occurred.

In a variation of the above example, one of two different stages of grafting and cross-linking of vinylmethoxysilane can be done before extrusion and the other after extrusion. In this case, a mixture containing polyethylene, vinyltrimethoxysilane, and an organic peroxide that is a reaction initiator is heated, extruded, granulated to obtain polyethylene grafted in advance, and this is supplied to an extruder. In doing so, a masterbatch containing a catalyst that causes a condensation reaction by hydrolysis is added. The melt index at 190 ° C. and 5 bar of the above composition is 0.5.

The proportion of hydrolysable unsaturated silanes can be varied within wide limits, for example 0.5 to 5% by weight of the total weight of the composition.

The total thickness of the pipe wall is between 10 and 15 mm for a pipe with an outer diameter of 150 mm. The heat-sealable surface layer can vary for example between 0.1 and 2 mm, more usually between 0.05 and 5 mm.

The pipes can be easily joined by conventional techniques, ie by heat welding the outer surface layer. For this,
Although it is possible to use the above-mentioned commercially available joint sleeve, it is preferable to use the joint sleeve shown in FIG. 1 which is also manufactured by the method of the present invention.

Since this joint sleeve has a cross-linked polyethylene layer 6 on its outer surface, it exhibits mechanical resistance, heat resistance and chemical resistance similar to those of pipes, and this joint sleeve shrinks when heated. Therefore, apply pressure to the pipe. This is preferable for welding.
The inner heat-sealable layer 7 is for example between 1 and 4 mm thick. The resistance heater 8 embedded in the joint sleeve has a temperature of 150-200 ° C. required for welding on the outer layer 5 of the pipe.
Can be heated up. The polyethylene of the joint sleeve, at least the polyethylene of the heat-sealable layer 7, is preferably, for example, 30% by weight thereof is copolymerized with vinyl acetate in order to improve the adhesion ability by heat welding.

The inner layer 7 of the joint sleeve of FIG. 1 extends as an inner crown 9 at the center of the joint sleeve. The inner crown 9 comes between the ends of the pipe wall when the ends of the two pipes are joined together.

The example shown in FIG. 2 shows a case where the pipes 11 and 12 of the present invention are connected to each other without using a special joint sleeve. In this case, the pipe is coextruded into three coaxial layers using the same composition as above. The central layer constituting the core 14 is a cross-linked polyolefin-based material,
The outer layer 15 and the inner layer 17, which are surface layers, are made of a thermoplastic or heat-weldable polyolefin resin.

In the industrial manufacturing process, the pipe extruded from the extruder is cut, placed in a tunnel furnace and left in an atmosphere of saturated steam at 100 ° C. for about 2 hours to ensure cross-linking. This crosslinking takes place only in the core of the pipe, ie in the layer of polyolefin grafted with silane.

When connecting two pipes 11 and 12, first
The tip of 11 is heated to the softening point temperature, a mandrel having the same diameter as the outer diameter of the pipe 12 is inserted to form a tulip shape shown by 13, and the tulip-shaped portion is cooled to room temperature and solidified around the mandrel. Then let the pipe pull out. Then, the corresponding tip of the pipe 12 is inserted into the tulip-shaped portion 13 and the tulip is heated from the outside to ensure that the inner surface layer of the pipe 11 is heat-welded onto the outer surface layer 15 of the pipe 12.

When the tulip-shaped portion is cooled, the tulip-shaped portion shrinks due to the property of the crosslinked polyolefin resin forming the core, and the adhesive effect of the two thermoplastic layers welded to each other is improved.

The present invention is not limited to the details of the above-described embodiments, can be variously modified without departing from the scope of the present invention, and includes means equivalent to the above means and a combination thereof.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of the end portions of two pipes whose ends are abutted to each other and the corresponding joint sleeves. FIG. 2 is a cross-sectional view of the tip portions of two pipes connected to each other. [Main reference numbers] 1, 2 ... Pipe, 3 ... Joint sleeve 4 ... Core, 5 ... Surface layer 8 ... Electrical resistor

Claims (8)

[Claims] 1. An inner layer (4) constituting a core of a first polyolefin resin grafted with vinyltrimethoxysilane and then hydrolyzed and crosslinked, and a second thermoplastic polyolefin which can be welded. Dibutyltin dilaurate, which is a hydrolysis catalyst of trimethoxysilane group, is formed on the tube wall, which has a tube wall composed of two coaxial layers obtained by coextrusion with an outer layer (5) constituting a surface layer made of a resin. In an extruded pipe for laying a long pipeline by connecting end portions to each other, including: 1) The first polyolefin resin is crosslinked with 30% by weight or more of a crosslinking agent and before coextrusion The crosslinkable initial composition comprises trimethoxysilane groups and dibutyltin dilaurate, the amount of dibutyltin dilaurate being approximately 0.05% by weight of the total weight of the initial composition. , 2) the outer diameter of the pipe is 32.1～150Mm, 3) the thickness of the tube wall, 3.1m outer diameter of the pipe when the 32.1mm
m to 15 mm when the outer diameter of the pipe is 150 mm, 4) the outer layer (5) has a thickness of 0.1 to 2 mm, and the two coaxial layers are closely integrated with each other. A pipe with excellent mechanical properties and easy to heat weld. 2. The pipe according to claim 1, wherein the polyolefin resins of the inner layer (4) and the outer layer (5) are the same type of resin. 3. The pipe according to claim 2, wherein the polyolefin resin is polyethylene or an ethylene copolymer. 4. An outer layer (6) constituting a core consisting of a first polyolefin resin grafted with vinyltrimethoxysilane and then hydrolyzed and crosslinked, and a second thermoplastic polyolefin which can be welded. A thermoplastic material comprising dibutyltin dilaurate, which is a hydrolysis catalyst for trimethoxysilane groups, on the tube wall, having an inner layer (7) constituting a surface layer of resin. In a tubular joint sleeve for connecting pipes according to paragraph 1, 1) the first polyolefin resin is cross-linked with 30% by weight or more of a cross-linking agent, and the initial cross-linkable composition before tri-extrusion is trimethoxy. Containing silane groups and dibutyltin dilaurate, the amount of dibutyltin dilaurate being approximately 0.05% by weight of the total weight of the initial composition, 2) the inner layer ( The thickness of 7) is 1 to 4 mm, the outer layer (6) and the inner layer (7) are closely adhered to each other, and the inner layer (7) is welded by the welding means (8). Coupling sleeve welded to the outer layer (5) of the. 5. Joint sleeve according to claim 4, characterized in that the welding means (8) is a resistance heater embedded in the joint sleeve. 6. An inner layer (7) in the middle section of the joint sleeve, in which the end to be joined by the joint sleeve is sandwiched between the tips of two consecutive pipes arranged opposite each other. 6. A coupling sleeve according to claim 4 or 5 having an annular crown (9) which projects radially inward from 7. A composition capable of being welded to a composition for an inner layer (4), which constitutes a core made of a thermoplastic polyolefin resin containing dibutyltin dilaurate and vinyltrimethoxylane in an amount of approximately 0.05% by weight of the total initial weight of the composition. A composition for the outer layer (5) made of a different thermoplastic polyolefin resin is prepared, and these two compositions are co-extruded so that the tube wall is
5. Forming a tubular element having two coaxial layers of one composition and placing the tubular element in a moist atmosphere to crosslink the composition comprising the core.
The method for manufacturing the pipe according to any one of claims. 8. The method of claim 7, wherein the weldable thermoplastic polyolefin resin is an ethylene / vinyl acetate copolymer.