JPH04292936A - Composite formed body and manufacture and usage thereof - Google Patents

Abstract

PURPOSE:To make the fusion of the composite formed body concerned possible by passing electrical current through said body for a short period of time when the body is used as a joining member by a structure wherein heat generating body made of electrically conductive particle-containing thermoplastic polymer and base made of polyolefin-based resin, the form retention of which is held at the melting point of the thermoplastic polymer, are formed into an integral body. CONSTITUTION:The composite formed body (or two layer pipe) is obtained by integrally forming heat generating body 2, which is made of thermoplastic polymer loaded with electrically conductive particles such as carbon black or the like and the volume resistivity at 25 deg.C of which is 5X10<2>OMEGAcm or less, and a base 1, which is made of crosslinked or non- crosslinked polyolefin-based resin and the form retention of which is held at the melting point of the heat generating body 2. A socket-like coupling is constituted by fitting up electrodes 3 to the head generating body 2, which is produced by cutting the two layer pipe in specific length and, after that, the crosslinkable polyethylene is crosslinked in a steam saturation box. An electrode 3 in then fixed to the body 2 to constitute a coupling. Thus, by passing electrical current through the heat generating body 2 for raising temperature under the condition that low density polyethylene pipe 4 and 4' are inserted into the coupling, the surface of the pipes 4 and 4' are melted, resulting in fusing the head generating body 2 and the pipes together into an integral body.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a composite molded body having a heating element, and more particularly to a composite molded body suitable for joining, sealing, reinforcing, etc. a thermoplastic polymer molded body, a method for producing the same, and Regarding usage.

0002

[Prior Art] As pipe fittings and sealing materials made of olefin polymers such as polyethylene,
It is a well-known technique to use a material that can be fused to an olefinic polymer, such as the same or similar polymer, and to bond or seal the olefinic polymer by heat fusion. Conventionally, electrofusion joints are known, which are made of a polymer molded product in which a spirally wound heating wire is embedded, and the joint and the joint of the pipe are fused together by applying electricity to the heating wire. (Unexamined Japanese Patent Publication No. 1-206026).

[0003] However, this electrofusion joint is expensive due to the complicated manufacturing process, and a large amount of buried heating wires (often made of metal such as nichrome wire) are not required during heat fusion. However, from a long-term perspective, if it is used as it is buried, it will cause various problems because it is a corrosive substance, it is a material that does not easily adhere to polyolefin, and it is different from polymer and has high rigidity. This is undesirable from the viewpoint of the long-term stability of the joint (for example, it may cause fluid to leak from inside) that is suitable for various usage conditions.

[0004] Crosslinked polyolefin resin layer and carbon black-containing crosslinked polyolefin resin layer (conductive inner layer)
A heat-resilient tube for coating the inner surface of a tube, which is a tube that is folded in the axial direction into a fin shape and cooled and solidified with a cross-sectional shape smaller than the diameter of the circular cross-section of the original tube, is a known tube. (Unexamined Japanese Patent Publication No. 1986-2
No. 7134). When this heat-recoverable tube is inserted into the tube and electricity is applied to the conductive layer, the tube is thermally restored to its original diameter and the crosslinked polyolefin layer is brought into close contact with the inner surface of the tube. In this case, the conductive layer is
Since it is made of crosslinked polyolefin resin, it only functions as a heating element and does not function as a fusion layer.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a composite molded article that is easy to manufacture and is highly safe and suitable for use as a joining member, a sealing member, a reinforcing member, etc. Another object of the present invention is to provide a composite molded body that can be fused with electricity for a short period of time and has high efficiency in construction work when used as a joining member or the like. A further object of the present invention is to provide a composite molded article in which the adhesive layer can be selected depending on the material of the member to be joined, such as a thermoplastic polymer pipe. As a result of intensive research to overcome the problems of the prior art, the present inventors discovered that a heating element made of a thermoplastic polymer containing conductive particles and a crosslinked or non-crosslinked polyolefin resin. It has been found that a composite molded body formed integrally with a base body can achieve the above object.

[0006] This composite molded article can be produced by co-extruding the heating element layer and the base layer, or by irradiating one side of the heating element layer with ionizing radiation such as an electron beam to form a crosslinked layer (base layer). etc. can be easily obtained. Further, when the substrate is crosslinked, the crosslinking can be carried out by conventional methods such as silane crosslinking, chemical crosslinking, and ionizing radiation crosslinking. Furthermore, by forming a welding layer made of a thermoplastic polymer on the surface of the heating element, and by matching the material of the welding layer to the material of the parts to be joined made of the same thermoplastic polymer. fusion bonding is possible. Furthermore, fusing with the members to be joined can be easily performed by simply covering the joining portion of the members to be joined with the heating element or the fusion layer of the composite molded body and energizing the heating element. The composite molded article of the present invention can take various shapes and can be used in a wide range of fields such as sealing members and reinforcing members in addition to joining members. The present invention has been completed based on these findings.

[0007]

[Means for Solving the Problems] Thus, according to the present invention, a heating element (A) is made of a thermoplastic polymer containing conductive particles and has a volume resistivity of 5 x 102 Ωcm or less at 25°C. and a substrate (B) made of a crosslinked or non-crosslinked polyolefin resin that has shape retention properties at the melting point of the thermoplastic polymer, are integrally formed. Ru. Heating element (
A fusion layer (C) made of a thermoplastic polymer may be further formed integrally with or in close contact with the surface of A) opposite to the lamination interface with the substrate (B). Further, according to the present invention, using the composite molded body, a predetermined portion (D) of the molded body formed of a thermoplastic polymer is covered with a heating element (A) or a fusion layer (C), and then the heating element A method of using the composite molded article is provided, in which the heating element (A) or the fusion layer (C) and the predetermined portion (D) are fused together by applying electricity to (A).

The present invention will be explained in detail below. (Heating Element) Thermoplastic Polymer The thermoplastic polymer used as the matrix polymer of the heating element in the present invention may be any thermoplastic polymer as long as it can be molded into a predetermined shape when mixed with conductive particles. When the heating element and the base are integrated by coextrusion, the thermoplastic polymer needs to be capable of being integrally molded with the polyolefin resin of the base. Examples of such thermoplastic polymers include high-density polyethylene (PE), medium-density PE, low-density PE, ultra-high molecular weight PE, ethylene-propylene copolymer, ethylene-butene-1 copolymer, and polypropylene (PP). ), polybutene-1, polypentene-1
, poly4-methylpentene-1, ethylene-propylene rubber (EPR), ethylene-propylene-diene terpolymer (EPDM), ethylene-vinyl acetate copolymer,
Examples thereof include olefinic polymers mainly composed of olefinic monomers such as ethylene-acrylic acid ester copolymers and ethylene-vinyl chloride copolymers; aromatic vinylic polymers such as polystyrene; and mixtures thereof.

In addition, various block copolymers composed of aromatic vinyl compounds represented by styrene and conjugated dienes such as isoprene and butadiene, specifically, S-
I type, S-B type, S-I-S type, S-B-S type, S-I
-Hydrocarbon thermoplastic elastomers such as block copolymers such as S-I-S type, hydrides thereof, and mixtures thereof; polybutadiene, polyisoprene, styrene-
Examples include unvulcanized rubber such as butadiene copolymer, chloroprene rubber, and butyl rubber. These hydrocarbon-based thermoplastic elastomers and unvulcanized rubbers can be used by mixing with the above-mentioned olefin-based polymers and the like in any proportion. Among these polymers, olefin-based polymers are preferred from the viewpoint of adhesion to the substrate, integral moldability, fusion-adhesiveness to members to be joined, etc., and polyolefins composed only of olefin-based monomers are particularly preferred. Also,
These thermoplastic polymers contain fillers such as titanium oxide, calcium carbonate, aluminum hydroxide, and talc, colorants such as various pigments and dyes, antioxidants, ultraviolet absorbers,
By adding modifiers such as antifogging agents, antistatic agents, and adhesion improvers such as petroleum resins, it is possible to add color and improve weather resistance.

Conductive Particles Examples of the conductive particles contained in the thermoplastic polymer include carbon black, graphite powder, metal particles (powders of copper, iron, nickel, etc.), and mixtures thereof. The thermoplastic polymer containing conductive particles can be suitably used as a heating element by setting the volume resistivity at 25° C. to 5×10 2 Ω·cm or less, preferably 1×10 2 Ω·cm or less. The lower the volume resistivity, the better, but the lower limit possible with carbon black blending is about 1 Ω·cm. Therefore, the blending ratio of the conductive particles can be determined using the volume resistivity as an index. For example, KetjenBla, which has excellent conductivity among carbon blacks,
In the case of ck), it is usually 5 to 50% for the thermoplastic resin.
The content is 35% by weight, preferably 10 to 30% by weight.

[0011] Heating element A heating element is first made by combining a thermoplastic polymer and conductive particles.
It is melt-kneaded using a Banbury mixer, plastomill, mixing roll, pressure kneader, etc. to form a sheet, ribbon or pellet, and then extrusion molding, injection molding,
It is molded into a desired shape such as a tube or plate by blow molding, rotational molding, compression molding, etc. When integrally molded with the base, it is coextruded with the polyolefin resin constituting the base. As mentioned above, the heating element used in the present invention is 2
It is necessary that the volume resistivity at 5° C. be 5×10 2 Ω·cm or less. If the volume resistivity value is larger than this, non-uniform heat generation will occur due to energization, leading to defective fusion.

(Substrate) In the present invention, a crosslinked or non-crosslinked polyolefin resin having shape retention properties at the melting point of the thermoplastic polymer constituting the heating element is used as the substrate. As the base polyolefin resin,
For example, high-density PE, medium-density PE, low-density PE, ultra-high molecular weight PE, ethylene-propylene copolymer, ethylene-
1 of polyolefin resins such as vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, polypropylene, etc.
Mention may be made of species or mixtures of two or more species. Further, a mixture with the above-mentioned hydrocarbon thermoplastic elastomer or unvulcanized rubber can also be used.

[0013] When using a crosslinked polyolefin resin as a base, various crosslinking methods can be employed. Specifically, (1) a method of heat crosslinking using a polyolefin resin blended with various organic oxides (chemical crosslinking);
2) A method of crosslinking with water or steam using a silane-modified polyolefin grafted with a silane compound such as vinyltrimethoxysilane (silane crosslinking); (3) A method of crosslinking by irradiating with ionizing radiation such as electron beams or γ-rays. Examples include a method in which two or more of these methods are combined.

The following method is exemplified for integrally forming the heating element and the base. (1) A thermoplastic polymer containing conductive particles and a polyolefin resin blended with an organic oxide or a silane-modified polyolefin resin are coextruded, and then the polyolefin resin layer is crosslinked by heating or water Alternatively, there is a method of crosslinking using water vapor. According to this method, the entire polyolefin resin layer is crosslinked. (2) There is a method in which a thermoplastic polymer containing conductive particles and a polyolefin resin are coextruded, and then the surface of the polyolefin resin layer is crosslinked by irradiating ionizing radiation. According to this method, only the surface of the polyolefin resin layer of the substrate is crosslinked, and therefore the substrate is composed of a crosslinked layer and a non-crosslinked layer, but this case is also within the scope of the present invention.

(3) A method of coextruding a thermoplastic polymer containing conductive particles and a polyolefin resin. In this method, the polyolefin resin layer is not crosslinked. However, as the base polyolefin resin, use a polymer with a higher melting point than the thermoplastic polymer that makes up the heating element, or make it thicker than the heating element so that it can maintain its shape during fusion. It is necessary. (4) When the heating element uses a polyolefin resin as a matrix polymer, a method of molding the heating element into a predetermined shape and then crosslinking one side of the heating element with ionizing radiation to form a base consisting of a crosslinked layer. There is. In this case, the substrate contains conductive particles. In addition, if necessary,
An adhesive layer may be provided between the heating element and the base. Further, when the base body is a foamed body, a pyrolyzable foaming agent may be blended and crosslinked and foamed.

(Fusing Layer) The heating element may be formed integrally with or in close contact with a fusing layer made of a thermoplastic polymer. The polymer constituting the fusion layer must be capable of being fused to the heating element, and is generally appropriately selected from thermoplastic polymers constituting the heating element. Since the heating element and the fusion layer are fused together by heat generated during use, they do not necessarily need to be integrated in advance. When the heating element and the fusion layer are integrated, for example, a conventional lamination method such as heat fusion or coextrusion can be employed. In the case of bonding, sealing, etc., the material of the fusion layer is selected to be the same as or similar to the thermoplastic polymer molded body to be fused, so that strong fusion can be achieved.

Furthermore, when transferring high-purity water or high-purity chemicals, if the heating element comes into direct contact with the liquid, it may contaminate the liquid or, depending on the material, the heating element may swell. There are things I can't do. For example, ultra-high molecular weight polyethylene is used exclusively in gasoline containers and pipes because ordinary polyethylene tends to swell. Therefore, in order to prevent swelling of the parts that come into contact with gasoline, it is effective to use high-purity polyethylene or ultra-high molecular weight polyethylene as the adhesive layer. In this way, by providing a fusion layer made of a polymer that does not contain impurities or a polymer that is resistant to the liquid it comes into contact with, it is possible to compensate for the difference in material between the material of the member to be joined, such as a pipe, and the material of the heating element. Can be done.

(Composite molded product) The shape of the composite molded product of the present invention is not particularly limited, and can be determined as appropriate depending on the purpose of use, for example, as a pipe joint, a board joining member, a sealing member, a reinforcing member, etc. can. In the composite molded article of the present invention, a predetermined portion of a molded article made of a thermoplastic polymer is covered with a heating element or a fusion layer, and electricity is applied to the heating element to fuse the heating element or fusion layer and the predetermined portion. Depending on the method of attachment, it can be used as a joint member, sealing member, reinforcing member, etc. For example, the joint parts of two pipes made of olefinic polymer are inserted into the hollow part of a tubular composite molded body with a heating element or a fusion layer provided on the inner peripheral surface, and then the heating element is energized. By heating and fusing the heating element or the fusing layer, a joined pipe can be obtained. In this case, if the polymer of the heating element or the adhesive layer is made of the same olefin polymer,
When the heating element was energized, part of the outer circumferential surface of the pipe also melted.
Moreover, since they are made of the same material, they are firmly fused together. Even if the heating element and the fusion layer are not integrated, they will become integrated when electricity is applied.

[0019] As a means for energizing, a current-carrying electrode may be provided on the heating element so that it can be connected to a power source. The electrode material is preferably a heat-resistant material having an electrical resistance lower than that of the heating element, such as a conductive paint, a conductive paste, or a conductive metal such as copper. If the contact resistance between the electrode and the heating element is high, local heat generation will occur, so in order to reduce this, it is preferable to widen the contact area by using a method such as using a large number of thin copper wires. The current-carrying electrode may be placed at an appropriate location on the heating element so that the current flows uniformly to the location where the temperature of the heating element is to be increased. The shape of the electrode can be determined as appropriate, such as a linear shape or a ring shape. The base polyolefin resin needs to be able to maintain its shape without melting when the heating element and the adhesive layer are melted.

[0020]

[Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples. In addition, in the following examples, parts and percentages are based on weight unless otherwise specified.

[Example 1] (Water crosslinked) low density polyethylene (melt index 0.3, density 0.92, melting point 1
10° C.), 25% of conductive carbon black (Ketjenblack EC) was mixed in a Banbury mixer, formed into a sheet with a receiving roll, and then pelletized. On the other hand, silane-modified polyethylene (registered trade name Moldex S)
-161 (manufactured by Sumitomo Bakelite Co., Ltd.) and a crosslinking promoting catalyst were uniformly mixed in a tumbler at a ratio of 95:5 to prepare a compound for crosslinked polyethylene. Using an extrusion molding machine, the pellets for the heating element are made into an outer diameter of 36 mm and an inner diameter of 33 m.
A cross-linked polyethylene compound with a thickness of 3 mm was extruded on top of the pipe to create a two-layer pipe (pipe) in which the inner layer was the heating element and the outer layer was the cross-linked polyethylene. Since the degree of crosslinking of crosslinked polyethylene is low at the time of extrusion,
The heating element and crosslinked polyethylene were fused and integrated. The volume resistivity of this heat generating layer was 53 Ω·cm.

[0022] This pipe was cut to a length of 60 mm, and
The outer layer of crosslinked polyethylene was crosslinked by placing it in a steam saturated box at ℃ for 4 hours, and then drying. Next, as shown in FIG. 1, a socket-shaped joint was created by attaching a copper electrode 3 to the heating element layer 2 on the inner layer of the cut surface of this pipe. One week later, a low-density polyethylene pipe (outer diameter 32.5 mm, wall thickness 4
mm, length 80mm) insert two pieces 4 and 4' respectively,
When an AC voltage of 40 V is applied for 2 minutes from the electrode 3 of the joint, the temperature of the heating element 2 rises, the surface of the polyethylene pipes 4, 4' melts, a part of which flows out as a bead from the edge of the joint, and the heating element 2 rises in temperature. 2 and polyethylene pipes 4 and 4' were fused together. At this time, although the temperature of the crosslinked polyethylene 1 as the outer layer of the joint had increased, the surface did not become sticky and maintained its shape. After cooling, clamps were attached to both ends of the connected pipe, and a tensile test was performed at a speed of 10 mm/min using a tensile tester. As a result, the pipe failed due to stretching, and the joint and adhesive part were strongly connected. was.

[Example 2] Polybutene (manufactured by Mitsui Petrochemical Co., Ltd., Polybutene-1P-14) was used instead of low density polyethylene.
04C (melt index: 0.4, melting point: 125°C) was used to obtain a compound for a heating element, and a socket-shaped joint was produced in the same manner as in Example 1, except that this compound was used. The volume resistivity of this heat generating layer was 55 Ω·cm. Next, when this joint was used to join two polybutene pipes in the same manner as in Example 1, the joint and the joint were firmly connected.

[Example 3] The heating element pellets made in Example 1 were rolled into a sheet with a thickness of 2 mm at 150°C, and then cut into tanzak shapes with a width of 20 mm and a length of 100 mm. The surface was crosslinked by irradiation with an electron beam of 40 Mrad generated at an accelerating voltage of 200 kV. When this heating element was heated to 200° C., the non-irradiated surface melted and became sticky, but the irradiated surface was crosslinked, so although it became a little softer, it did not melt and become sticky. In this way, a plate-shaped composite molded article having the crosslinked layer on one side as a base was obtained. As shown in FIG. 3, copper electrodes 33 were attached to this plate-shaped composite molded body, and the terminals were taken out. This is placed on the seam of the two soft polyethylene plates 34, 34' so that the surfaces of the heating element 32 are in contact with each other, and when an AC voltage of 15V is applied, the heating element and both polyethylene plates are connected in about 90 seconds. was fused. At this time, the crosslinked layer 31 did not undergo melt-flow deformation.

[Example 4] The heating element pellets used in Example 1 and the same type of polyethylene (not containing carbon black) used in the pellets were coextruded to form a heating element layer of 2 mm and a polyethylene layer. (Fusing layer) A 1 mm plate-shaped composite molded body was obtained. The outer surface of the heating element layer of this composite molded article was irradiated with 40 Mrad of electron beams in the same manner as in Example 3 to crosslink the surface to form a base (crosslinked layer). Using the obtained plate-shaped composite molded body (substrate/heating element/fusion layer), two polyethylene plates were joined in the same manner as in Example 3, and the adhesive layer and both polyethylene plates were bonded together. were fused together.

[0026]

According to the present invention, it is possible to provide a composite molded article suitable as a highly safe joining member, sealing member, reinforcing member, etc. Moreover, the composite molded article of the present invention is
The manufacturing method is easy, and when used as a joining member, etc., it can be fused with electricity for a short time, and the construction work is efficient.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a specific example of a tubular composite molded article of the present invention, with the left figure being a longitudinal sectional view and the right figure being a lateral sectional view.

FIG. 2 is a cross-sectional view of the tubular composite molded article of the present invention used as a joining member for thermoplastic resin pipes.

FIG. 3: The left figure is a sectional view when the plate-shaped composite molded article of the present invention is used as a joining member for polyethylene plates, and the right figure is a front view.

[Explanation of sign]

1 Base made of crosslinked polyolefin resin 2 Heat generating layer 3 Electrodes 4, 4' Low density polyethylene pipe 5 Power supply 31 Base 32 made of crosslinked layer Heat generating layer 33 Electrodes 34, 34' Polyethylene plate 35 Power supply

Claims (3)

[Claims] Claim 1: Comprised of a thermoplastic polymer containing conductive particles, with a volume resistivity of 5 x 102Ω at 25°C.
・The heating element (A) with a size of 1 cm or less and the base (B) made of a crosslinked or non-crosslinked polyolefin resin that has shape retention properties at the melting point of the thermoplastic polymer are integrally formed. Composite molded body with characteristics. [Claim 2] A heating element (
A composite molding in which a fusion layer (C) made of a thermoplastic polymer is formed integrally with or in close contact with the heating element (A) on the opposite side of the laminated interface between A) and the base (B). body. 3. A predetermined portion (D) of the molded body made of a thermoplastic polymer is heated by heating the heating element (A) of the composite molded body according to claim 1 or the fusion layer ( C
), and the heating element (A) is energized to fuse the heating element (A) or the fusion layer (C) with the predetermined portion (D). How to use composite moldings.