JP2596243B2 - Plastic fusion joint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermoplastic resin such as a polyethylene resin (hereinafter abbreviated as PE) or a polybutene resin (hereinafter abbreviated as PB), particularly a resin which is not suitable for bonding with an adhesive. Plastic fusion joints. More specifically, the present invention relates to a plastic fusion joint in which the formation of a sink mark at a fusion portion on the inner surface of the joint, which causes defective fusion during fusion bonding, is prevented.

[0002]

2. Description of the Related Art Plastic tubes made of polyolefin resin such as PB and PE are not sufficiently compatible with general-purpose adhesives due to insufficient compatibility between the resin and general-purpose adhesives. It is often joined by a plastic heat-sealing joint. For example, when connecting the pipes by a socket-type heat fusion joint, as shown in FIG. 5, the inner surface 2a of the socket 2 and the outer surface 1a of the connected pipe 1 are heated and melted, respectively. The pipe end is pushed into the socket for connection. When a branch portion is provided in the pipe, as shown in FIGS.
A branch saddle 6 having a branch portion 8 protruding therefrom is used as a fusion joint, and a saddle body inner surface 7a of the branch saddle 6 and a fusion bonding surface 1d of the pipe 1 to the saddle body portion 7 are heated, respectively. Then, the saddle 6 is pressed and fused to the tube 1 to form a branch portion, and finally a branch hole 1c is formed.
Thereafter, when another tube is thermally fused to the branch portion 8, the connection of the branch tube is completed.

[0003]

However, at the time of heat fusion, an uneven flow of the molten resin occurs on the heated inner surface 2a or 7a of the fusion joint (the socket 2 or the saddle 6). When taken in, as shown in FIG.
It has been often experienced that a molten sink portion H is formed at the tip of a, resulting in poor fusion. When an internal pressure or an axial force is applied to the pipe 1, stress concentration occurs in the molten sink portion H, and considering long-term use, there is a danger that a crack is generated from this portion due to a creep phenomenon peculiar to plastic. When the saddle 6 is fused to the tube 1,
As shown in FIGS. 7 to 9, a molten sink portion H is formed at both ends of the saddle main body 7 and at both sides of the branch hole, resulting in poor fusion, which causes the same problem as described above. In particular, around the branch hole, the saddle 6 is fused to the tube 1 and then the hole 1 is added to the tube 1.
Another problem is that cracks are likely to occur in the welded portion due to the perforation of c. An object of the present invention is to provide a plastic fusion joint in which the above-mentioned problems have been solved, that is, the formation of a molten sink portion during fusion has been prevented.

[0004]

The present inventors have paid attention to the fact that the above-mentioned formation of the sink mark in the heat-sealed joint is caused by the relaxation phenomenon of the orientation of the resin in the melted part. As a result of examining the relationship between the degree of orientation and the melting sink, it was found that if the degree of orientation of the molecules of the inner surface portion that is melted during the heat fusion of the fusion joint is suppressed to a certain level or less, no melting sink occurs, and the present invention Completed.

The present invention is a plastic fusion joint characterized in that the resin has a molecular orientation of 50% or less at a fusion bonding portion with a member to be connected.

The fusion joint of the fusion joint having a degree of molecular orientation of 50% or less removes the surface layer of this portion of the molded body obtained by an appropriate molding method such as injection molding with a thickness of 2 mm or more, or
The molded body can be obtained by annealing the resin in a temperature range of (melting point−50 ° C.) to (melting point) for 1 to 7 days.

The degree of molecular orientation of the resin at the fusion joint is determined by the method described below. When the case of polyethylene (PE) resin is described, as shown in FIG.
The X-ray counter fixes the (110) plane reflection of PE at 21.6 °, makes X-rays (CuKα rays) incident on a plate-shaped test piece having a thickness of 2 mm, and counts scattered X-rays with the counter. As shown in FIG. 10, the X-ray diffraction measurement is performed by rotating the test piece β around the sample surface normal by β = 0 to 360 ° at 20 ° / min. The obtained X-ray interference diagram is as shown in FIG. The half width (α °) of the peak of the X-ray interference diagram is obtained,
The degree of orientation of the PE molecule is calculated from Equation 1.

The degree of orientation = (180 ° −α °) / 180 ° × 100 (%) (1)

[0009]

As described above, as a result of examining the relationship between the degree of orientation of the molecules in the fusion joint and the molten sink, it has been found that the molten sink of the fused joint is generated by the following mechanism.
Even in the case of a plastic fusion joint, even in the case of a socket as shown in FIG. 5, since it is not a simple cylindrical shape, most are formed by an injection molding method instead of an extrusion method. In injection molding, molding is performed while cooling the mold to room temperature or a temperature slightly higher than that. Therefore, during molding, the molten resin starts to crystallize near the surface of the mold having a high cooling effect from the mold. Since the crystallization starts near this mold and the shear flow in the mold, the molten resin near the mold surface is frozen in a state where it is molecularly oriented in the flow direction, and stress is applied after filling the mold. No relaxation occurs. Therefore, the resin molecules in the surface layer of the molded body have a high degree of orientation and remain in a tensioned state. Therefore, at the time of heat fusion between the fusion joint and the connected pipe, when the heat fusion portion of the joint (the inner surface 2a in the case of the socket 2 and the inner surface 7a of the main body portion in the case of the saddle 6) is melted, the tension that has been completely extended. Since the molecules that have been fixed in shape are relaxed in stress (relaxation of orientation), uneven flow of the molten resin occurs, a molten sink portion H is formed, and poor fusion occurs.

In order to prevent the formation of sink marks caused by such a mechanism, it is important to prevent the relaxation of the orientation of the melted resin molecules in the surface layer of the joint at the time of fusion. As a result, when the degree of orientation of the resin molecules in the fusion joint portion of the fusion joint with the member to be joined is 50% or less, the relaxation of the tension during fusion does not occur so remarkably that the fusion sink does not occur. I found it.

When a fusion joint is manufactured by an injection molding method,
The resin molecules on the surface of the obtained molded body are inevitably highly oriented for the reasons described above, and the degree of molecular orientation is generally 50%.
And in many cases is about 50-60%. Therefore,
It is necessary to reduce the molecular orientation of the resin on the joint surface of the fusion joint to 50% or less by performing some processing.

The method of reducing the molecular orientation of the resin at the fusion joint of the fusion joint to 50% or less is not particularly limited, and any method can be adopted as long as this object is achieved. For example, a method of removing the resin in the surface layer portion of the molded body until a resin having a molecular orientation of 50% or less appears on the surface, or a method in which the orientation of the resin in the surface layer portion of the molded body is relaxed by heat treatment (annealing) in advance. A method is possible in which the degree of resin orientation on the surface is reduced to 50% or less. However, if the molding conditions of the injection molding, for example, the molding temperature and the mold temperature, are selected so that the resin molecules in the surface layer portion of the molded body are relaxed to some extent during molding, the resin on the surface of the fused portion can be formed only by injection molding. It is also possible to obtain a molded article having a degree of molecular orientation of 50% or less.

After the injection molding, by removing the surface layer resin at a portion to be a fusion bonding portion of the molded body, the molecular orientation degree can be reduced to 50%.
% Or less, the surface layer of this portion of the molded body is scraped off to a thickness of 2 mm or more, preferably 2 to 6 mm. Therefore, in the case of this method, when molding the joint by injection molding, in consideration of this shaving, a molded body in which the thickness of the fusion bonding portion (in the case of the socket 2, the inner surface 2 a) is increased by the removed amount. It is necessary to design the mold to obtain it.
The shaping of the fusion-bonded portion of the molded body can be carried out by any method. For example, the resin in the surface portion can be accurately removed to a desired shape by cutting.

If the thickness to be removed is less than 2 mm, a layer having a molecular orientation of more than 50% may remain on the surface of the joint, and it is possible to prevent the relaxation of the orientation of the resin at the time of heat fusion which leads to poor fusion. become unable. As the thickness to be removed increases, the degree of molecular orientation of the resin coming out on the surface decreases, which is effective in preventing the relaxation of the orientation. However, when the thickness exceeds 6 mm, the thickness of the molded body in consideration of the removed amount is considered. In consideration of heat shrinkage that occurs immediately after injection molding, it is difficult to design a mold, and the precision of the product is reduced. Therefore, the thickness to be removed is preferably 6 mm or less.

The molded body obtained by injection molding is annealed for 1 to 7 days in the temperature range of (melting point -50 ° C.) to (melting point) of the resin. The degree of molecular orientation can be reduced to 50% or less. In this case, the molecular orientation degree of the resin is reduced to 50% or less over the entire surface of the molded article, not only the fusion joint, unless a means for heating only the fusion joint is employed. There are no particular inconveniences. If the heat treatment temperature during this annealing is lower than the melting point of the resin (−50 ° C.),
Even after annealing for a long time, the relaxation of the molecular orientation is still insufficient, and it is generally difficult to reduce the degree of molecular orientation of the joint surface layer to 50% or less. Cannot be reliably prevented. On the other hand, if the heat treatment temperature during annealing is higher than the melting point of the resin,
Degradation of the joint resin and deformation of the joint due to heat are likely to occur.

If the annealing time of the resin in the temperature range of (melting point −50 ° C.) to (melting point) is less than one day (24 hours), the molecular orientation is not sufficiently relaxed, and the resin of the surface layer portion is not sufficiently relaxed. Since the molecular orientation remains large, the formation of molten sink due to relaxation of the resin orientation during thermal fusion cannot be reliably prevented. If the annealing time exceeds 7 days, the joint resin may be degraded or the joint may be deformed by heat.

The kind of the raw material resin constituting the fusion joint of the present invention is not particularly limited as long as it is a thermoplastic resin of heat fusion property. Examples of useful resins are polyolefin resins such as PE resin, PB resin. The method for producing the resin is not particularly limited. The molding of the joint is often performed by an injection molding method, but the molding method is not particularly limited to this.
The present invention is also applied to, for example, a fusion joint formed by a blow molding method or an injection blow molding method. Further, although the external insertion type joint has been described with reference to the drawings, the heat fusion joint of the present invention may be an internal insertion type inserted inside the connected member. In this case, since the fusion bonding portion with the member to be connected is, of course, the outer surface of the joint, the degree of molecular orientation of the resin on the outer surface serving as the fusion bonding portion may be 50% or less. .

[0018]

Next, the present invention will be described more specifically with reference to the following examples, which illustrate the functions and effects of the present invention.

Examples 1 and 2 and Comparative Example 1 As shown in FIG. 1 and FIG.
As an example, a case where the PE resin pipe 1 having an outer diameter of 60 mm is connected by using the PE resin socket 11 whose inner surface is cut and removed is set to 0. The socket 11 has a thickness of Amm on the inner surface 12a of the molded body obtained by injection molding.
(2.5 mm in Example 1, 5.0 mm in Example 2, Comparative Example 1
In this case, the inner surface is retreated to 11a by removing by 1.0 mm). Thereby, the inner diameter of the socket is set to 60 mm, which is equal to the outer diameter of the PE resin pipe as the connected member. The thermal fusion of the tube 1 to the socket 11 is performed in the same manner as in the prior art, that is, the joint between the inner surface of the socket and the outer surface of the tube is heated by, for example, a hot plate (electric heater) to a molten state. This is done by pushing the end into the socket and allowing it to cool.

[To examine the state of formation of molten sink by fusion splicing, the fused socket and pipe are cut in the axial direction of the tube, and the cross section is visually inspected for the presence of molten sink.
If the size of the molten sink is 1 mm or more,
"With melting sink", if less than 1 mm, "No melting sink"
Judged . On the other hand, the degree of orientation of PE molecules on the surface of the inner surface 11a of the socket 11 used as a joint was measured by the method described below. That is, a plate-shaped test piece having a thickness of 2 mm is cut out from the surface of the inner surface 11a of the joint obtained by cutting and removing the inner surface after injection molding, and the P-shaped specimen is subjected to X-ray diffraction as described above.
The degree of orientation of the E molecule was determined. The above results are summarized in Table 1. FIG. 2 is a longitudinal section showing a fusion splicing state in Examples 1 and 2. When the inner surface of the socket after the injection molding was cut and removed from the surface with a thickness of 2 mm or more, a portion of the inner surface of the socket 11 in which the orientation of the PE molecules was large was cut and removed. As a result, as shown in Table 1, the PE molecules on the inner surface were removed. Has a degree of orientation of 50% or less, no sink marks are formed, and good fusion is obtained in which the joints are completely adhered as shown in FIG. On the other hand, in Comparative Example 1 in which the thickness of the cut and removed portion of the inner surface of the socket after the injection molding was 1 mm, a portion where the orientation of the PE molecules was large remained on the inner surface of the socket 11 without being removed. Has a degree of orientation of more than 50%, and molten sink H is formed at the end of the socket as shown in FIG. 』

Examples 3 and 4 and Comparative Example 2 As shown in FIG. 3 and FIG.
As an example, a case where the inner surface of the saddle main body is cut and removed is used to fuse to the PE resin tube 1 having an outer diameter of 60 mm using a branch saddle 16 made of PE resin. As shown in FIGS. 3 (a) and 3 (b), the branch saddle 16 has a thickness Bmm (2.5 mm in Example 3) of the surface layer of the inner surface 19a of the main body of the branched saddle-shaped molded product obtained by injection molding. In Example 4,
The inner surface of the main body was retracted to 17a by removing by 5.0 mm (5.0 mm in Comparative Example 2 and 1.0 mm in Comparative Example 2). Thereby, the radius of curvature of the inner surface of the saddle main body portion is set to 30 mm so as to be fitted to a 60 mm outer diameter PE resin pipe as a connected member. Thermal fusion between the saddle 16 and the tube 1 is performed by the same conventional method as described above.

In order to examine the state of the formation of the molten sink due to the fusion splicing, the fused branch saddle and the pipe were cut in the axial direction of the pipe 1, and the presence or absence of the molten sink at the welded portion was visually inspected.
The inner surface 1 of the main body of the branch saddle 16 used as a joint
The degree of orientation of PE molecules on the surface of 7a was determined by X-ray diffraction using a 2 mm-thick plate-like specimen cut out from the surface of the inner surface 17a in the same manner as described above. Table 2 shows the above results.
Are shown together. FIG. 4 is a cross-sectional view showing a state of fusion splicing in Examples 3 and 4. When the inner surface of the branched saddle main body after injection molding was cut away from the surface with a thickness of 2 mm or more, a portion of the inner surface of the saddle 16 where the orientation of PE molecules was large was cut and removed. As a result, as shown in Table 2, The degree of orientation of the PE molecules on the surface is 50% or less, no sink marks are formed, and good fusion is obtained in which the joints are completely adhered as shown in FIG. On the other hand, in Comparative Example 2 in which the thickness of the inner surface of the saddle body after the injection molding was removed by cutting was 1 mm, a portion having a large orientation of PE molecules remained on the inner surface of the saddle 16 without being removed. Has a degree of orientation of more than 50%, and molten sink H is generated as shown in FIG.

Examples 5 and 6 and Comparative Example 3 In this example, a PE resin pipe having an outer diameter of 60 mm was used as in Examples 1 and 2 by using an annealed PE resin socket as a fusion joint member. An example of the case of connecting is shown.
This socket has a molded body obtained by injection molding for 10 minutes.
Annealed at 0 ° C. for C hours. The annealing was performed by allowing the compact to stand in a hot-air circulation type thermostat. Since the melting point of the used PE resin is 127 ° C., the annealing temperature is from (melting point−50 ° C.) to (melting point) of the resin.
Temperature range. The thermal fusion of the PE resin tube to the socket and the subsequent test are performed in the same manner as in Examples 1 and 2. The test results are summarized in Table 3. As can be seen from Table 3,
In Comparative Example 3 in which the annealing time was less than 24 hours (1 day), the relaxation of the orientation of the PE molecules on the inner surface of the socket was insufficient, and the degree of molecular orientation still exceeded 50%. As a result, at the time of thermal fusion, molten sink H is generated as shown in FIG. 6, resulting in poor fusion. On the other hand, when the annealing time is one day or more, the state of tension on the surface of the molded body due to injection molding,
That is, high molecular orientation is sufficiently relaxed by annealing,
The degree of orientation of the PE molecules is reduced to 50% or less, the formation of molten sink is prevented, and good fusion in which the joints are completely adhered as shown in FIG. 2 is obtained.

Examples 7 and 8 and Comparative Example 4 In this example, as in Examples 3 and 4, a PE resin having an outer diameter of 60 mm was used as a fusion joint member using a branch saddle made of annealed PE resin. An example of the case of fusing to a tube will be described. The used branch saddle was obtained by injection molding,
A molded body with a radius of curvature of 30 mm on the inner surface of the saddle body is 100
Annealed at C for D hours. Annealing was performed by placing the compact in a hot-air circulation type thermostat. The PE resin used for molding had a melting point of 127 ° C. as in Examples 5 and 6. The thermal fusion between the branch saddle and the PE resin tube and the subsequent test are performed in the same manner as in Examples 3 and 4. The test results are summarized in Table 4. As can be seen from Table 4, in Comparative Example 4 in which the annealing time was less than 24 hours (1 day), the relaxation of the orientation of the PE molecules on the inner surface of the socket was insufficient, and the degree of molecular orientation exceeded 50%. As a result, molten sinks are generated during thermal fusion, resulting in poor fusion. On the other hand, when the annealing time is one day or more, the tension state of the molded body surface, that is, the high molecular orientation, is sufficiently relaxed by the annealing by the injection molding, the degree of orientation of the PE molecules is reduced to 50% or less, and The formation of sink marks is prevented, and a good fusion is obtained in which the joints are completely adhered as shown in FIG.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

[0029]

According to the plastic fusion joint of the present invention, the degree of molecular orientation of the resin at the fusion joint portion with the member to be connected is reduced to 50 by performing an appropriate treatment such as cutting or annealing after injection molding. % Or less, the resin in this portion is sufficiently relaxed in orientation. Therefore, when a connected member such as a plastic pipe is heat-sealed using such a joint, it is possible to prevent the melted resin on the joint surface from causing an orientation relaxation phenomenon, thereby preventing the resin from flowing unevenly. The occurrence of sink marks in the welded joint caused by the excessive flow is prevented. As a result, stress concentration on the molten sink portion, which has conventionally been a problem, can be reduced, so that cracks and the like do not occur even when used for a long period of time, and the reliability of the fusion joint increases. Therefore, the present invention is useful as a highly reliable heat-fused joint that can be used for a long period of time without worry.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one example of a socket-type fusion joint of the present invention.

FIG. 2 is a longitudinal sectional view showing a state where the socket-type fusion joint of FIG. 1 is fused to a connected pipe.

FIGS. 3 (a) and 3 (b) are longitudinal sectional views showing an example of a branch saddle type fusion joint of the present invention in a pipe axis direction and a direction perpendicular to the pipe axis, respectively.

FIG. 4 is a longitudinal sectional view showing a state where the branch saddle type fusion joint of FIG. 3 is fused to a connected pipe.

FIG. 5 is a longitudinal sectional view showing an example of a conventional socket type fusion joint and a connected pipe in a state where a fusion portion is heated and fused.

FIG. 6 is a longitudinal sectional view showing a state where the socket type fusion joint and the connected pipe of FIG. 5 are fused.

FIG. 7 is a perspective view of a state in which a branch saddle type fusion joint is fused to a connected pipe.

FIG. 8 is a longitudinal sectional view in a pipe axis direction showing a state in which a conventional branch saddle type fusion joint is fused to a connected pipe.

FIG. 9 is a longitudinal cross-sectional view in a direction perpendicular to the pipe axis, showing a state in which a conventional branch saddle type fusion joint is fused to a connected pipe.

FIG. 10 is an explanatory diagram of an X-ray diffraction method for measuring the degree of molecular orientation of a resin.

FIG. 11 is an X-ray interference diagram 1 obtained by X-ray diffraction measurement.
It is an example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Connected pipe 1c Branch hole 10 Joint member H Melt sink 2,11 Socket 6,16 Branch saddle 11a Socket inner surface after cutting and removal 12a Socket inner surface after injection molding 17a Saddle main body inner surface after cutting and removing 19a Inner surface of the original saddle body after injection molding

Claims (3)

(57) [Claims] 1. A plastic fusion joint, wherein a degree of molecular orientation of a resin at a fusion bonding portion with a member to be connected is 50% or less. 2. A fusion bonding part having a molecular orientation degree of 50% or less,
The plastic fusion joint according to claim 1, which is obtained by removing a surface layer of the molded body with a thickness of 2 mm or more. 3. A fusion bonding part having a molecular orientation degree of 50% or less,
The plastic fusion joint according to claim 1, wherein the molded body is obtained by annealing the resin in a temperature range of (melting point -50 ° C) to (melting point) of the resin for 1 to 7 days. .