JPS59101326A - Method of joining water-crosslinkable polyolefin pipe - Google Patents

Abstract

PURPOSE:To butt and join the titled pipes firmly, by heating watercrosslinkable polyolefin pipes over specified lengths from their ends to the melting point or over, and pressing the end surfaces to be joined, which forms uniform beads with a specified size around the joined ends of the pipes. CONSTITUTION:When water-crosslinkable polyolefin pipes are to be butted and joined, and the end surfaces 2 of the pipes 1 and lengths of 1-20mm. of the pipes measured from the end surfaces 2 are heated at a temperature of (t+60)-(t+ 160) deg.C wherein (t) represents the melting point of the water crosslinkable polyolefin that constitutes the pipes and below 400 deg.C. Then the ends 2 are pressed and joined, which should form beads around the joined ends of the pipes with the following relationships satisfied: 4>=H/W>=0.5 and H=aT wherein T is the thickness of the pipes in mm., H is the height of the beads measured from the outer wall surface of the pipes in mm., W is the width of the beads in mm. and (a) is 0.12-0.6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for connecting water-crosslinkable polyolefin pipes.

Pipes made of general non-crosslinked polyolefin can be easily butt-connected by heating and melting the end faces, making piping construction easy. It cannot be used as a commercial pipe.

On the other hand, pipes made of cross-linked polyolefins that have been developed in recent years have excellent physical properties such as heat resistance and resistance to environmental stress cracking. Unlike non-crosslinked polyolefin pipes, it is difficult to firmly connect them by heat melting, and there is a problem that the pipe workability is poor. As a result of intensive research to solve the above problems, the present inventors have developed a pipe made of water-crosslinkable polyolefin.
While the pipes are still in a low cross-linked state, the end faces to be connected and their vicinity are heated to a predetermined temperature, and then the pipes are connected to each other so as to form so-called beads of predetermined dimensions on the outer circumferential wall of each connection end of the pipe. The present invention was achieved by discovering that a strong connection can be achieved by crimping.

That is, the present invention provides a method for butt-connecting water-crosslinkable polyolefin pipes, in which the end face of the pipe to be connected and a portion 1 to 20 m in length in the axial direction of the pipe from this end face are connected to the melting point of the water-crosslinkable polyolefin. When t'c, it is heated to a temperature of (t+60>'C or more, N+160)'C or less and 400°C or less, and then the end faces are crimped together to reduce the wall thickness of the pipe. T h+m
), when the height and width of the bead from the pipe outer wall surface are respectively H (ms) and W (1), 4≧H/W≧0.5 and H=aT (however, a=0.12 ~0.6) A bead is formed substantially uniformly around the connecting end of the pipe so as to satisfy the following relationship.

Various water-crosslinkable polyolefins are already known, and the water-crosslinkable polyolefin constituting the pipe in the present invention may be any of these conventionally known water-crosslinkable polyolefins. For example, as one of them, it has a hydrolyzable organic group and
Water-crosslinkable polyolefins containing siloxane compounds having ethylenically unsaturated groups can be mentioned. This water-crosslinkable polyolefin comprises a polyolefin such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, etc., the above-mentioned ethylenically unsaturated siloxane compound, a free radical generator, and optionally a free radical generator. , and a silanol condensation catalyst.

In the above, the ethylenically unsaturated siloxane compound typically includes vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, etc., and the radical generator includes dicumyl peroxide, lauroyl peroxide, Peroxides such as propionyl peroxide, benzoyl peroxide, di-t-butyl peroxide, t-butyl hydroperoxide,
Conventionally known conventional compounds such as azo compounds such as azobisisobutyronitrile and azoisobutylvaleronitrile are appropriately used. In addition, various silanol condensation catalysts are already known, such as dibutyltin dilaurate, dibutyltin diacetate I,
Dibutyltin dioctoate, stannous acetate, stannous caprylate, zinc naphthenate, zinc caprylate, cobalt naphthenate, etc. are used as appropriate.

Further, as another example of the water-crosslinkable polyolefin, a copolymer of ethylene and the ethylenically unsaturated siloxane compound described in JP-A No. 55-9611 and, if necessary, a copolymer as described above may be used. A water-crosslinkable polyolefin containing a silanol condensation catalyst can also be suitably used.

Among the above-mentioned methods, the method of the present invention uses a pipe made of water-crosslinkable polyethylene in which the polyolefin is polyethylene, in particular, the above-mentioned ethylenically unsaturated silane compound, a radical generator, and, if necessary, a silanol condensation catalyst. It can be suitably applied to water-crosslinkable polyethylene pipes made of polyethylene.

In particular, among such water-crosslinkable polyethylenes, the first particularly preferred one has a density of 0.930 to 0°955, M
When 1 is 0.2 to 3.0 g/10 min, it is high density polyethylene. This type of polyethylene has a high melting point,
This is because it has excellent heat resistance, excellent environmental stress cracking resistance before crosslinking, and a high degree of gel fraction attainment due to water crosslinking. This is because polyethylene with a higher density than the above does not have sufficient environmental stress cracking resistance, while polyethylene with a lower density than the above has a low melting point and does not have sufficient heat resistance. The second particularly preferred polyethylene in the present invention
is density 0.920-0.935, M I 0.2-3
．． It is called low and medium density linear polyethylene with 0g/10min. Such polyethylene also has the same advantages as the first polyethylene.

However, the water-crosslinkable polyolefin that can be used in the present invention is not limited to those exemplified above.

In the method of the present invention, prior to heating the end faces to be connected and their vicinity, these are preferably beveled. Generally, pipes made of water-crosslinkable polyolefins are already somewhat crosslinked from the beginning due to moisture in the atmosphere, and this tendency is particularly noticeable in the surface layer of the pipe.

In this way, when the gel fraction differs between the surface layer and the inner layer of the pipe, a good butt connection may be hindered, so as shown in FIG.
and its corners are removed. This processing is called groove processing.

Further, according to the present invention, as will be described later, after heating the end faces to be connected and the vicinity thereof, the pipe end faces are heated so as to form a bead of a predetermined size that is fused to each other around the outer wall of each connecting end. The beads formed on the inner wall surface of the pipe act as resistance to the passage of fluid within the pipe. Therefore, in the beveling process, it is desirable to make the bevels at the corners of the inner wall of the pipe larger in order to make the bead formed on the inner wall of the pipe as small as possible.

Next, for fusion splicing of water-crosslinkable polyolefin pipes,
It is preferable that the gel fraction of the polyolefin is as small as possible at least at the fusion spliced site. Normally, water-crosslinkable polyolefins already have a gel fraction of about 5% or more before the water-crosslinking step, as described above, but the gel fraction of this level before water-crosslinking can be reduced by the method of the present invention. There is no problem in implementing it. However, when the gel fraction is 60% or more, the pipes cannot be sufficiently fused and connected even by heating, and the pipes cannot be firmly connected even by additional cross-bridges after fusion. The gel fraction must be less than 60%, preferably 55%.
% or less. In addition, the pipe is
It is not necessary that the gel fraction be less than 60% over the entire region, but only in the heated region.

According to the method of the present invention, the end face to be connected and a portion of 1 to 20 lengths in the axial direction from this end face, where the melting point of the polyolefin is t'c, are (1160)'C or more,
(t4-160) Heat to a temperature of 400°C or less. Here, the above-mentioned melting point means the melting peak (°C) determined by differential thermal analysis.
It can be measured by the method described on pages 78 to 183 (published by Asakura Shoten in 1965). The heating temperature is (t
When the temperature is lower than +60)'C, the heating is insufficient and it is difficult to form a bead with the dimensions described below, and as a result, the joint does not have high strength. Also,
When the heating temperature exceeds (t+160)'C or 400°C, it is not preferable because the strength of the pipe may actually decrease. It should be noted that if the entire pipe near the connection part is heated, the rigidity will be lost and crimping of the end face will be hindered, so only the end face and the pipe portion extending 1 to 20 inches in length from the end face in the axial direction are heated. More specifically, the axial length from the end surface that requires heating depends on the pipe and its wall thickness, and when the wall thickness of the pipe is 1 to 3011 mm, it is generally 1 to 20 mm, but preferably 1 mm. ~1(In, particularly preferably 2~
It is 7fi.

The heating means is not particularly limited and may be a hot plate or a torch, and the heating time is not particularly limited as long as the above conditions are satisfied. However, usually a few seconds to a few minutes is sufficient.

Then, as described above, the end face and 1 to 20
After heating the n+ portion, this heated portion is kept at a temperature above the above-mentioned melting point and the end surfaces are crimped together. According to the present invention, as shown in FIG. It has been found that when the bead 3 is formed on the outer wall surface along the line 2, the size and shape of the bead is the main factor governing the strength of the connection. Here, the term "bead" refers to an annular bulge or protuberance that is continuous from the wall surface of the pipe and is fused to each other at the connecting end surface, and in the present invention, a bead formed on the outer wall surface of the pipe is By specifying the dimensions and shape, a strong butt connection was made possible.

According to the present invention, the heat formed on the outer wall surface of the pipe must satisfy the following conditions. That is, when the wall thickness of the pipe is T (mm), the height of the bead from the outer surface of the pipe is H (mwl), and the width is W (ms>), 4≧H/W≧0.5 and H= It is necessary to satisfy the following relationship: aT (however, a=0.12 to 0.6). Preferably, 3≧H
/W≧1.

When the bead height is smaller than the above lower limit, the crimp force is insufficient and a strong butt connection cannot be achieved;
When it is larger than the above upper limit, the connection strength is high, but the pressing force is too large, the H/W becomes excessively large, and a large fluid resistance is formed particularly on the inner wall surface of the pipe, which is not preferable.

After the connection work as described above, the pipe body and the connection portion are water-bridged to obtain a connection pipe having a strong connection portion. Since the connection obtained as described above already has relatively high strength, water supply and hot water supply can be carried out at 5 kg/cm.
When carrying out the process at a low pressure of approximately ♂ or below, the pipe can be water-bridged while being used for such water supply and hot water supply. Generally, water crosslinking is carried out by passing water at room temperature to 100°C, but preferably at 50°C.
Water at a temperature of ~100°C is preferred.

As described above, according to the present invention, after heating the connection end surfaces of the pipes to be connected from the rose 1 to a predetermined temperature, a bead having a predetermined size and shape is formed on the connection end surfaces, thereby making it possible to strengthen the pipes with a strong connection. can be obtained.

The present invention will be explained below with reference to Examples. In addition, in the following, parts represent parts by weight.

Example density 0.95 g/cl, Ml, 100 parts of polyethylene with a density of 5 g/10 min, 2 parts of vinyl trime I xysilane,
A water-crosslinkable polyethylene composition consisting of 0.15 parts of dicumyl peroxide and 0.05 parts of dibutyltin 4 dilaurate was formed into a pipe and cut into a length of 25 cm.

The melting point of the polyethylene in this pipe was 129°C.

Next, the end surfaces of the pipes to be connected were heated under conditions 2 of experiment numbers 1 to 11 shown in the table, the end surfaces were crimped together, and then immersed in hot water at 90°C for 60 hours. Water crosslinked.

The bead width, H/W ratio, height, gel fraction before connection, and strength of the connection part of the connection pipe thus obtained are shown in the table. In the above, the gel fraction was measured in accordance with JIS C3005, item 26, and the strength of the connection part was
The pressure of the water filled in the pipe was gradually increased at a rate of 20 kg/cA/min, and the water pressure was expressed as the water pressure at which the pipe burst or water leaked from the connection.

Comparative Example Regarding the same pipe as the example, experiment numbers 1 to 1 shown in the table
Beads were formed and connected under conditions outside the scope of the present invention in No. 7. The width of the bead of the connecting pipe obtained in this way, H
/W ratio, height, and strength of the connection part are shown in the table.

3

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a beveled pipe, and FIG. 2 is a sectional view showing a connected pipe. 1... Pipe, 2... Connection end surface, 3... Bead. 119- Figure 1

Claims (1)

[Claims] (1) In the method of connecting water-crosslinkable polyolefin pipes with a hat, the end face of the pipe to be connected and a portion of length 1 to 20 mm in the axial direction of the pipe from this end face are connected to the melting point of the water-crosslinkable polyolefin at t°C. When (t
+60)'C or more and (t+160)°C or less,
The pipe is heated to a temperature of 400'C or less, and then the end faces are pressed together, and the thickness of the pipe is T (Ill), and the height and width of the bead from the outer wall of the pipe are H (m).
m) and W(+u), each connection end of the pipe is adjusted so as to satisfy the following relationship: 4≧H/W≧0.5 and H=aT (however, a=0.12 to 0.6) A method for connecting water-crosslinkable polyolefin pipes, the method comprising forming a bead substantially uniformly around the periphery of the pipe.