JPH08270870A - Connection method for bodies to be connected by electro-fusion connection member - Google Patents

Abstract

PURPOSE: To prevent abrupt rise in temperature of a heating body after the start of fusion and maintain a temperature range so as to realize a proper connected for a sufficient time by controlling, at a constant, a current to feed the heating body comprising thermoplastic resin containing conductive particles. CONSTITUTION: A heating body 2 of an electric-fusion connection member 1 comprises a thermoplastic resin which contains conductive particles at a specified density. Also the electric-fusion connection member 1 comprises the heating body 2, a base body 3 which covers the heating body 2 and gives a mechanical strength to the heating body 2, and insulates thermally and electrically from the outside, and a power supply electrode 4 which is fitted tightly and fixedly onto the outer periphery of the heating body 2. Then bodies to be connected 5 are inserted from opening ports located at both ends of the electric-fusion connection member 1. In addition, a fixed current power supply 6 is connected to the terminal 4 of the connection member, and a set current is passed. Thus, after current transmission is started from the fixed current power supply 6, the heating body 2 can reach a fusion start temperature in a relatively short time, and efficient heating and fusion can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joining method for joining objects to be joined, such as thermoplastic resin pipes, by utilizing heat generated when a heating element made of a thermoplastic resin containing conductive particles is energized. .

[0002]

2. Description of the Related Art Various electrofusion-bonding members are known as joints or sealing materials for joining objects to be joined such as pipes made of thermoplastic resin such as polyethylene. The electric fusion bonding member has a built-in heating element that generates heat when energized, and thereby melts a part of the bonding member and a part of the object to be bonded, thereby melting and bonding the object to be bonded.

As a heating element, a heating wire embedded in a fusion layer in a joining member is typically used. However, in this type of heating element, there is a large temperature difference between the heating wire and its surroundings, so that the fusion layer is formed. However, it is difficult to know the temperature and the melting state thereof accurately, and the used heating wire remains as a foreign substance in the joined portion of the joined pipe or the like.

Another type of heating element is one in which conductive particles such as carbon black are kneaded and contained in the same thermoplastic resin as the pipe to be joined, that is, a heating element containing conductive particles. is there. In this type of heating element, the heating element itself also serves as the fusion layer, and since the conductive particles are fine particles, they are completely integrated with the fusion layer, and they become foreign matter in the pipe after joining. It has the feature that it does not.

In the conductive particle-containing heating element, it is necessary to attach a power feeding electrode capable of ensuring a sufficient contact area to the end portion of the heating element to uniformly feed power. If the contact area of the power supply electrode is locally biased, or if the contact area itself is insufficient, there is a risk that the electrode mounting portion will be deformed due to local overheating.

The applicant of the present application has proposed several electrodes for electric fusion bonding members which are effective in solving such a problem (for example, Japanese Patent Application No. 4-26226 and Japanese Patent Application No. 5-26226). -53055, etc.).

As described above, even if the condition of using the power-supplying electrode having an appropriate structure is satisfied, the dependence of the electrical characteristics on the temperature and the molten state, which is peculiar to the conductive particle-containing heating element, is still maintained. There are the following problems derived from sex.

FIG. 1 is a diagram for qualitatively explaining the temperature-resistance value relationship of a conductive particle-blended heating element. As can be seen, the resistance value increases with temperature and decreases rapidly after the onset of melting. FIG. 2 shows temporal changes in current, temperature, and resistance value, which are generally observed when a constant voltage is applied to a conductive particle-containing heating element having temperature-resistance value characteristics as shown in FIG. FIG.

Initially, when a large current flows and the temperature of the heating element rises, the resistance value increases and it becomes difficult for the current to flow. However, after reaching the melting start temperature, the resistance value rapidly decreases, so that a large current flows again and the temperature also rapidly increases. Therefore, it rapidly passes through a temperature range in which a suitable molten state is realized, and it is difficult to obtain a suitable fused state by catching such a temperature range and cutting the current. In order to suppress the rapid temperature rise after reaching the melting start temperature, the voltage may be lowered, but in that case, it took a too long time to reach the melting start temperature, resulting in poor work efficiency.

To solve this problem, in principle,
The internal temperature of the heating element may be detected by some method and the current may be cut off when the temperature reaches a predetermined temperature. For example, the temperature detecting end may be embedded in the heating element, and the current control device may be operated by the detected temperature signal. Further, the thermal fuse may be blown to cut the current depending on the temperature of the heating element. However, it has been experienced that these methods have the following drawbacks.

It is not preferable to provide a temperature detecting hole in the joining member to reach the heating element in order to embed the temperature detecting end, because a stress concentration portion is created in the joining member and the strength of the joining member is reduced.

Since the allowable range of the set temperature of the current control device for ensuring an appropriate joining state is narrow and the temperature characteristics of the joining members cannot be avoided to some extent, they can be commonly applied to many joining members. It is difficult to set a proper set temperature.

In the method using the thermal fuse, it is difficult to determine the fusing temperature with high accuracy, and the mounting position of the thermal fuse has a great influence, so that it is difficult to select the position. In addition, in order to achieve an appropriate joining state,
It is necessary to maintain a predetermined temperature for a certain period of time, and therefore it is desirable that the current can be controlled to be turned on and off, but it is impossible to perform such control once the thermal fuse is blown.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for joining a thermoplastic resin-made article to be joined by an electric fusion-bonding member having a conductive particle-blended type heating element. Prevents a rapid temperature rise after the start and keeps the temperature range where a proper bonding state is achieved for a sufficient time, which enables highly accurate temperature control, which is safer and more reliable. It is to provide a joining method with good work efficiency.

[0015]

The above problems can be solved by controlling the current supplied to the heating element to a constant value.

[0016]

As described above, the resistance value of the conductive particle-containing heating element increases with temperature. However, unlike the case where power is supplied from a constant voltage power supply, the power supply when powering from a constant current power supply increases in proportion to the resistance value of the heating element, so if the level of power supply is sufficiently higher than the heat dissipation loss. The temperature rise of the heating element will be gradually accelerated. Therefore, the temperature of the heating element rapidly approaches the melting start temperature, and for example, heating can be performed efficiently in a shorter time as compared with the case of using a constant voltage power supply whose power supply is almost the same immediately after the start of energization. be able to.

When the temperature of the heating element reaches the melting start temperature, the resistance value suddenly starts to decrease. Therefore, when power is supplied from the constant current power supply, the supplied power decreases as the resistance value decreases, so that the temperature change of the heating element becomes slower.
However, since the power supply to the extent of compensating for the heat radiation loss is continued, it is possible to stably maintain the temperature range in which an appropriate bonding state is realized for a certain time.

The magnitude of the electric current supplied to the heating element is
Set as appropriate according to the construction environment in which the joining members are used, such as wind speed and sunshine. At that time, the supply current is set so that the temperature range in which an appropriate bonding state is realized can be maintained for a certain period of time after the melting start temperature of the heating element is reached.

(Constant Current Power Supply) The constant current power supply used in the present invention is not particularly limited as long as it can set an output current and has a capacity capable of supplying a predetermined electric power. For example, a schematic block diagram may be shown in FIG. This is to change the duty ratio of the output pulse of the control circuit according to the output signal from the current detection circuit, thereby controlling the output voltage of the voltage variable circuit including the switching element.

(Heating element) The heating element of the electric fusion bonding member used in the present invention is made of a thermoplastic resin containing conductive particles at a predetermined concentration.

As the thermoplastic resin used for the heating element, for example, high density polyethylene, medium density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, ethylene-butene-1 copolymer, polypropylene, polybutene-1, poly- 4-methylpentene-1, ethylene-
Olefin polymers such as propylene rubber, ethylene-propylene-diene terpolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, ethylene-vinyl chloride copolymer; aromatic vinyl such as polystyrene -Based polymer; S-I type, S-S type, S-I
-S type, S-B-S type, S-I-S-I-S type, and other aromatic vinyl compounds represented by styrene (S) and conjugated dienes such as isoprene (I) and butadiene (B) Hydrocarbon-based thermoplastic elastomers such as composed block copolymers and hydrogenated products thereof; polybutadiene,
Examples include polyisoprene, styrene-butadiene copolymer, unvulcanized rubber such as chloroprene rubber and butyl rubber, and these may be used as a mixture.

Among these polymers, an olefin polymer is preferable from the viewpoints of adhesion to a substrate, integral molding property, fusion property to a member to be joined, and the like. In particular, a polymer obtained by polymerizing only an olefin monomer or Copolymers are preferred.

Examples of the conductive particles include conductive carbon black, graphite powder, metal particles (powder of copper, iron, nickel, etc.) and mixtures thereof.

The content of the conductive particles in the heating element is usually 5% by weight or more, preferably 10% by weight or more, particularly preferably 20% by weight or more, and usually 35% by weight or less, preferably 30% by weight or less. Is. If the content is too low, the electrical resistance (volume resistivity) becomes too large, and the amount of heat generation becomes small, so that the work efficiency of bonding is reduced, or the voltage required for power supply must be increased. If the content is too large, the electrical resistance becomes too low and a large current flows temporarily, so the capacity of the power supply device must be increased.

The method of mixing the thermoplastic resin and the electrically conductive particles is not particularly limited, and the thermoplastic resin and the conductive particles are molded into a shape that is easy to process, such as a Banbury mixer, plastomill, mixing roll, pressure kneader or extrusion mixer. The molding method is also not particularly limited, and a desired shape such as a tubular shape or a plate shape is formed by extrusion molding, injection molding, blow molding, rotational molding, compression molding, or the like.

(Electrode) In order to energize the heating element, an electrode having a sufficient contact area with the heating element is provided so as to sandwich the heating portion of the heating element. The electrodes are formed by a method such as sticking a thin metal plate to the heating element, fitting a copper ring, and thermocompression-bonding the braided wire. The electrodes are provided with terminals for connecting a power supply when energized. In addition, it is preferable to cover parts other than the terminals with a base body described later to reduce the risk of electric shock or electric leakage.

(Substrate) In the electrofusion-bonding member used in the present invention, the purpose is to maintain the shape of the heating element layer during melting.
Usually, it has a substrate that does not deform to a predetermined shape or melt at the bonding temperature. In addition, the use of a base body cuts off the heating element from the outside, so there is little danger of electric shock, etc. The heat generated by the heating element is difficult to escape due to the heat insulation effect, so the energization time can be shortened, the joint area is reinforced, and the heating element is protected. There is also the effect of.

Some resins constituting the substrate are not used depending on the bonding temperature, but crosslinked or non-crosslinked high density polyethylene, medium density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, ethylene-propylene copolymer Polyolefin resin such as polymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, polypropylene; polynorbornene resin,
Thermosetting resins such as polyurethane resins, epoxy resins, and polyester resins; mixtures of the above-mentioned hydrocarbon-based thermoplastic elastomer and unvulcanized rubber; and the like. The cross-linking method in the case of cross-linking is not limited, and a chemical cross-linking method using an organic peroxide, a water cross-linking method using a silane-modified polyolefin, an irradiation cross-linking method of irradiating with ionizing radiation, and the like can be used.

Among these, for example, a thermosetting resin produced by a reaction injection molding method such as a polynorbornene-based resin molded product or a polyurethane resin can be easily molded into a substrate, and the molded substrate has a shape memory property. Therefore, it is preferable that the electrofusion-bonding member can be used after being deformed in advance into a shape that is easy to work. The polynorbornene-based resin is particularly preferable because it has a good fluidity of the reaction liquid used for the production, and a large-sized and complicated shape can be produced by the reaction injection molding method.

(Shape of electrofusion-bonding member) The shape of the electrofusion-bonding member in the present invention is not particularly limited, and may be pipe-shaped, flat-plate-shaped or the like depending on the purpose of use such as pipe joints, sealing members, reinforcing members and the like. Shape. When a substrate is used, the substrate and the heating element are usually integrated by a method such as providing an adhesive layer between the two, if necessary.

In any shape, a fusion layer may be provided between the heating element and the article to be joined. The fusing layer is made of a thermoplastic resin that easily fuses with both the thermoplastic resin that constitutes the heating element and the article to be joined, and enables good joining even when both are difficult to fuse directly with each other. To do. From various thermoplastic resins that can be used to form the heating element, a resin that is easily fused with both the heating element and the article to be joined is selected and used.

In the case of a pipe-shaped pipe joint, the pipe is molded so that its inner diameter is the same as or slightly smaller than the outer diameter of the pipe to be joined. If the inner diameter of the pipe joint is larger than the outer diameter of the objects to be joined, fusion cannot be performed. In the case of having a substrate, the heating element, which is a pipe-shaped inner layer, is covered by the substrate, which is also a pipe-shaped outer layer.

(Manufacturing Method of Joining Member) The manufacturing method is not particularly limited. For example, in the case of an electrofusion-bonding member having a base made of polynorbornene-based resin, a heating element molded in a predetermined shape is fixed in a mold, and the inner surface of the mold and the base contact surface of the heating element are separated from each other. It can be manufactured by a reaction injection molding method in which a reaction solution is filled in the space to cause a reaction. In this case, the contact surfaces of the base body and the heating element are fused by reaction heat to form an integral molded article.

In the case of a pipe-shaped pipe joint, the body to be joined is inserted into the hollow portion of the pipe joint to energize and fuse it. As described above, the inner diameter of the pipe joint is the outer diameter of the pipe to be joined. Since it is formed to be the same as or slightly smaller than the above, it may be difficult to insert the article to be joined in practice. In such a case, for example, if the base is made of a resin having a shape memory property such as the above-mentioned polynorbornene-based resin, and the pipe joint is expanded by applying an external force at room temperature or under heating, the insertion work can be performed. It will be easier. When the base body is heated to a temperature higher than the thermal deformation temperature during energization, the shape of the base body returns to the inner diameter before the diameter expansion, and a good joining state is obtained.

(Object to be bonded) The object to be bonded in the present invention is made of a thermoplastic resin. The thermoplastic resin is not particularly limited as long as it can be fused to the heating element of the joining member or the fusion layer, and may be a crosslinked resin. Specific examples include polyolefins such as polyethylene, polypropylene and polybutylene.
A specific example of a preferable member to be joined is a crosslinked polyethylene pipe having a non-crosslinked polyolefin layer as the outermost layer. Usually, the resin of the outermost layer determines the conditions under which an appropriate bonding state is realized. For example, when the resin of the outermost layer is non-crosslinked polyethylene, if it can be maintained in the range of 200 to 220 ° C. for 1 minute or more, a proper bonding state with the heating element can be obtained.

[0036]

EXAMPLES The present invention will be described in detail below with reference to the accompanying drawings by citing examples and comparative examples.

FIG. 3 is a perspective view showing the construction of the electro-fusion-bonding member 1 used in this example and the comparative example. The electrofusion-bonding member 1 includes a heating element 2 made of a thermoplastic resin containing conductive particles, and a base 3 which covers the heating element 2 to give mechanical strength to the heating element 2 and which is thermally and electrically insulated from the outside. And a power supply electrode 4 that is wound around and fixed to the outer periphery of the heating element 2. The article 5 to be joined is inserted through the openings at both ends of the electrofusion-bonding member 1. Each of these components will be described in detail below.

(Molding of heating element) 70% by weight of linear low-density polyethylene and 30% by weight of conductive carbon black (Ketjenblack EC) were mixed in a Banbury mixer, and extrusion molding was performed to obtain an inner diameter of 125 mm and a thickness of 3 mm. A pipe-shaped heating element was obtained and cut into a length of 120 mm. Two scare-sized braided wires were melt-pressed using a hot plate roll so as to make one round around the outer circumference of the pipe-shaped heating element at positions of 10 mm inward from both ends. Furthermore, terminals were attached to each braided wire by soldering. The two terminals were mounted perpendicular to the axis of the pipe.

Thus, a heating element having a current-carrying cross-sectional area of 15.4 square cm, an effective length of the pipe-shaped heating portion of 10 cm, and a resistance value of about 1.5 ohm (20 ° C.) was obtained.

(Formation of Substrate) Dicyclopentadiene 75
And 25 parts by weight of the asymmetric cyclopentadiene trimer, 5 parts by weight of a styrene-isoprene-styrene block copolymer (Quinton 1170, Shell) and a phenolic antioxidant (IRGANOX 101) were used.
(0, manufactured by Ciba Geigy) was dissolved in 2 parts and divided into two parts. One part was 40 mmol, 44 mmol and 20 mmol of diethylaluminum chloride, n-propanol and silicon tetrachloride, respectively, as a part of the catalyst component. To obtain a reaction stock solution, and on the other hand, tri (tridecyl) ammonium molybdate as a part of the catalyst component was prepared to a concentration of 10 mmol to prepare another reaction stock solution.

A pipe-shaped heating element equipped with terminals was fixed in a mold, and a mixture of the above-mentioned two types of reaction stock solutions which had been impinged and mixed between the outer peripheral surface and the inner surface of the mold was injected immediately after mixing to carry out polymerization. After the reaction was completed (3 minutes or more after the injection), it was taken out to obtain an electrofusion-bonding member on which a 5 mm-thick substrate made of dicyclopentadiene-based resin was formed by reaction injection molding. In addition, in this electric fusion bonding member, the above-mentioned terminal projects from the base body.

(Expansion of Diameter, Insertion of Objects to be Joined) The inner diameters of both ends of the electro-fusion-bonded member thus prepared were expanded by about 2% using metal rods, and a non-crosslinked polyethylene pipe (outer diameter 125
mm) were respectively inserted from both ends of the joining member and fixed so that the ends of both pipes were in contact with each other at the center. In addition,
A thermocouple was embedded in the tip of one polyethylene pipe so that the temperature of the contact surface between the polyethylene pipe and the heating element could be measured.

(Electrification) A constant current power source 6 having a schematic structure shown in FIG. 4 is connected to a terminal 4 of a joining member as shown in FIG.
The set current was set to 20 A and the maximum voltage was set to 90 V for energization.

The power supply is about 0.8 kW immediately after the start of energization.
The maximum power is about 1.8 after about 40 seconds after the increase.
After showing kW, it gradually decreases, and after about 45 seconds is about 1.5.
After about 60 seconds, it became about 0.8 kW. The energization was completed about 3 minutes after the energization was started.

The temperature measured by the thermocouple rises almost linearly for about 45 seconds after the start of energization and reaches about 120 ° C., after which the rate of temperature rise gradually decreases to about 10 ° C.
The temperature was maintained at 200 to 220 ° C from 0 seconds to 3 minutes.

FIG. 6 is a diagram qualitatively explaining the above-mentioned energization state. The horizontal axis of the figure represents the elapsed time after the start of energization, and the vertical axis represents the temperature, voltage, current, and resistance on a relative scale. Further, the position of the dotted line marked "melting start" in the figure corresponds to the time point 45 seconds after the start of energization, at which the maximum value of the electric power was seen above. It should be noted that, since the scale of elapsed time is drawn in agreement with that of FIG. 2 described above, the difference in behavior between the two becomes clear by comparison.

(Inspection) After the completion of energization, the sample was left for one day and inspected for a fused state. No particular problem was found.

(Comparative Example) The same conditions as those in the above-described example were used except that a constant voltage power source of 40 V was used instead of the constant current power source.

The power consumption is about 0.8 kW immediately after the start of energization.
, Then decreased, and after about 80 seconds, decreased to 0.3 kW and then increased rapidly.

The temperature rises almost linearly and reaches about 120 ° C. after about 80 seconds, and thereafter the temperature rise gradually accelerates to about 12 ° C.
After 0 seconds, the temperature reached 300 ° C., and I felt a danger and stopped energizing.

Incidentally, the progress of the energization state in this comparative example was almost the same as that shown in FIG.

When the fusion state was inspected by leaving it for one day after the completion of energization, voids that were considered to be caused by decomposition were observed in the heating element layer, and there was a problem in terms of fusion strength.

[0053]

EFFECTS OF THE INVENTION According to the joining method by the electric fusion joining member having the heating element made of the thermoplastic resin containing the conductive particles according to the present invention, it takes a relatively short time after the start of energization from the constant current power source. The heating element can reach the melting start temperature, and efficient heating and melting can be performed.

Further, according to the present invention, after the temperature of the heating element reaches the melting start temperature, the power supply does not naturally decrease and the temperature rises excessively, and the heating element is fused to the object to be joined. Provided is a safe and reliable joining method that can reach suitable temperature.

[0055]

[Brief description of drawings]

FIG. 1 is a diagram qualitatively illustrating a temperature-resistance value relationship of an electric fusion bonding member.

FIG. 2 is a diagram qualitatively explaining temporal changes in temperature, current, and resistance value when power is supplied to the electric fusion bonding member at a constant power supply voltage.

FIG. 3 is a perspective view of an electric fusion bonding member used in Examples and Comparative Examples.

FIG. 4 is a block diagram of a constant current power supply used in an embodiment.

FIG. 5 is a diagram of electric circuits used in Examples and Comparative Examples.

FIG. 6 is a diagram qualitatively illustrating temporal changes in temperature, voltage, and resistance value when power is supplied with a constant supply current in the example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electric fusion bonding member 2 ... Heating element 3 ... Base material 4 ... Electrode 5 ... To-be-bonded body 6 ... Power supply device

Claims (1)

[Claims] 1. A joining method for joining an article to be joined made of a thermoplastic resin by an electric fusion-bonding member having a heating element made of a thermoplastic resin containing conductive particles, and supplying the article to the heating element during the joining process. A joining method characterized in that the current is controlled to be constant.