JPH0682947B2 - Method for producing conductive composite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention comprises a base material made of a polymer material, and conductive fibers dispersed on a base material, which are fused together to form an electromagnetic wave shielding property, antistatic property, etc. The present invention relates to a method for producing a conductive composite, which is capable of producing a conductive composite having excellent properties.

[Conventional technology]

In recent years, in various electronic devices such as computers and communication devices, their casings have been made electrically conductive in order to prevent disturbances due to electromagnetic waves from the outside, to prevent dissipation of electromagnetic waves generated inside, and to prevent disturbances due to static electricity. Will be required. In addition, most of the casings are made of polymeric materials such as synthetic resins for ease of molding and improvement of appearance. Therefore, by mixing conductive materials into these polymeric materials, Conductivity is being imparted.

Such conductive materials include carbon black, carbon fiber, and the like. In particular, metal fibers made of stainless steel, copper, aluminum, etc., have recently been recognized as having excellent conductivity.

Even when such a metal fiber having a small diameter and a large aspect ratio is used, by dispersing them uniformly and in contact with each other, the amount of the metal fiber used is reduced and excellent conductivity is exhibited. It has been proved that it is important to disperse such metal fibers in a polymer material uniformly and in contact with each other.

On the other hand, as a method of mixing conductive fibers into such a polymer material, for example, a pellet having a length of about 3 to 5 mm formed by mixing conductive fibers as disclosed in JP-A-58-150203 is formed. In addition, as disclosed in JP-A-59-109537 or the like, which mixes and kneads with the base material at a predetermined ratio upon molding, conductive fibers are directly mixed into the polymer material without molding into pellets. , A method of kneading has been proposed. In any method, mixing,
The kneaded molten material is injected into an injection molding machine, an extrusion molding machine,
Molded using a calendar roll, etc., in addition to the above-mentioned housing,
It is formed into a sheet. The sheet-shaped material may be used as it is, or may be appropriately heat-deformed to be molded into a predetermined shape.

[Problems to be solved by the invention]

However, in the case of using the pellets described above or in the conventional method of directly mixing and kneading, (a) not only the one in which pellets are preliminarily molded but also the one in which direct kneading is used because of difficulty in mixing and kneading work Since the length of the conductive fiber to be used is about 5 mm or less, a long conductive material cannot be used, and the conductivity of the molded product is poor.

(B) Moreover, in the mixing and kneading work, by applying a strong force to the fibers, most of the conductive fibers are likely to be cut into short fibers close to powder, and this tendency tends to occur especially when the above-mentioned small-diameter metal fibers are used. It will be noticeable.

(C) In the case where the pellet is preformed, the pellet is formed by cutting it from a long body. Bonding and entanglement are likely to occur, and therefore, high technology is required to uniformly disperse the fibers and obtain the desired conductivity.

(D) In the product molded by the subsequent molding step, the conductive fibers tend to be unevenly distributed inside the product, and the conductive fibers are easily arranged in one direction during molding such as injection and extrusion. Therefore, there is a problem that good conductivity cannot be obtained.

Further, it is difficult to form a thin film-like film having a thickness of, for example, several tens of micrometers or less by the above-mentioned various molding methods, and it is difficult to obtain desired conductivity. Therefore, in order to obtain the desired conductivity, it is necessary to mix a large amount of a conductive material, which deteriorates the strength and color, and sometimes impairs the required transparency.

INDUSTRIAL APPLICABILITY The present invention can uniformly disperse conductive fibers in the form of paper, and can reduce the breakage even when using small-diameter and relatively long conductive fibers, and reduce the mixing ratio of the conductive fibers to improve the conductivity. It is an object of the present invention to provide a conductive composite and a method for producing the same that can improve the above-mentioned problems and can solve the above problems.

Another object of the present invention is to provide a method for producing a conductive composite using a metal fiber having a small diameter and a large aspect ratio as the conductive fiber.

[Means for solving problems]

The present invention is directed to a continuously transferred polymeric material substrate,
A laminate forming step of forming a long laminate in which the conductive fibers are dispersed and dropped while being curved and bent irregularly and uniformly, and the conductive fibers are heated. And a method for producing a conductive composite, which comprises a step of bonding the base material and the conductive fibers by pressurization, for example, the conductive composite illustrated in FIGS. 1 and 2. Can be manufactured.

The electroconductive composite 1 shown in FIG. 1 forms an integrated two-layer structure, for example, a thin combined body 4 in which the electroconductive fibers 3 scattered on the upper layer surface are fused on the base material 2. The conductive composite 1 of FIG. 2 has a three-layer structure in which the conductive fiber 3 is sandwiched between the base materials 2 and 7 by further adding another base material 7 to the conductive fiber 3. Make up 4.

The base material 2 is made of thermoplastic synthetic resin such as ABS, polyethylene, nylon, vinyl chloride, polystyrene, polypropylene, and various rubber materials such as synthetic rubber, and is a polymer that can be softened by heating and fused to each other. It is formed using a material.

The conductive fiber 3 exhibits conductivity by adhering a metal film to polymer fibers such as carbon fibers, glass fibers, and fibers made of polymer material by plating, vapor deposition, etc. in addition to metal fibers. It is possible to use a material or a fiber mixed with powder such as carbon black or metal powder.
The base material 2 is obtained by subjecting a polymer material to a conductive treatment.
A material that can maintain conductivity even by fusion with is selected.

The metal fibers can be formed by using metals such as iron, nickel, aluminum, copper and titanium, or various alloys such as stainless steel and brass.

The conductive fiber 3 has a fiber diameter of about 2 to 100 μm, a fiber length of about 2 to 200 mm, and a length that can be efficiently dispersed in a papermaking state,
Select the one with the thickness. The aspect ratio (L / D) and the mixing ratio are determined in consideration of the use and purpose of the molded product, but as a preferable example, the aspect ratio is usually 200 or more, and the mixing ratio is relative to the combined body 4. Volume ratio of about 0.1 to 50%, more preferably about 0.3 to 15%. 50%
The above may be included. Further, when using a metal fiber or the like having good conductivity, it is possible to reduce the mixing ratio, and it is preferable to use a material having a small diameter, for example, about 2 to 30 μm and an aspect ratio of 200 or more to reduce the mixing ratio and to improve conductivity. Can be improved.

Further, for forming the metal fiber, for example, as disclosed in Japanese Patent Laid-Open No. 55-157443, a metal rod is cut by a tool while causing chatter vibration, a so-called chatter cutting method, or a single wire is formed by drawing or extrusion. Single wire drawing method to obtain continuous metal wires, and further, the diameter of the composite, which was proposed by Japanese Patent Publication No. 50-39069, into which a large number of single wires with external coating was inserted, was drawn out, and then coated. In addition to the so-called focused wire drawing method of removing the material and the outer tube, various methods can be used. Further, continuous fibers are, for example, Japanese Patent Publication No.
-4314 etc. disclose continuous cutting method of cutting fibers by using rollers with different peripheral speeds, or by cutting directly with a cutter, so-called sliver, chopped strands or other short metal fibers are cut. . In addition, in order to improve the entanglement, the metal fiber preferably has no sagging at the end.

Further, each conductive fiber 3 is dispersed uniformly in a papermaking state over substantially the entire surface by fusion of the base material 2 so that the conductive fibers 3 are successively and sequentially contacted, and each conductive fiber 3 is preferably at least The other conductive fiber 3 is contacted at that one position.

As shown in FIG. 3, the conductive fiber 3 has, in the conductive composite body 1, the bending portions 6 ... Which are curved and bent irregularly, and the pressing portion 6 is formed between the conductive fibers 3 and 3. The number of contact points is increased, and the conductivity of the conductive composite 1 is improved. In addition, the conductive fibers 3 form the integrated body 4 by heat-sealing the base material 2. In addition, the conductive fibers 3 are uniformly dispersed in a paper-making state because the generation of powder portions due to their breakage is suppressed. The term "paper-making" means a dispersed state that can be obtained by a general paper-making method.

Further, the conductive fibers 3 can be dispersed by the thickness method as well as the plane direction.

In the three-layer structure shown in FIG. 2, the conductive fiber 3 is sandwiched between the base materials 2 and 7 by attaching the base material 7 to the conductive fiber 3. 3 is loaded in the polymer material without exposing the surface, so that it prevents fluffing due to the conductive fibers on the surface and can be suitably used as an electromagnetic wave shield. The base material 7 is made of the same or different polymer material as the base material 2.

In the structure shown in FIG. 1, the conductive fibers 3 are partially exposed on the surface, and this conductive composite 1 is preferably used for antistatic purposes. In the case of FIG. 1 as well, the conductive fiber 3 can be prevented from being exposed.

The combined body 4 shown in FIGS. 1 and 2 is formed as a film-shaped long tape body having a thickness of 1 mm or less.

The conductive composite 1 can be formed into a film, a sheet, or a thick wall, and when the base material 2 is melted, it can be formed into various shapes such as a box-shaped body. .

An embodiment of the method for producing a conductive composite of the present invention capable of producing such a conductive composite will be described with reference to FIGS.

In this embodiment, short metal fibers made of, for example, stainless steel are used as the conductive fibers 3, and the base material 2 is a web-shaped material made of polymer fibers 5 obtained by fiberizing a polymer material.

The conductive fibers 3 are entangled between the fibers due to the fine irregularities on the surface, and remove the bond due to sagging at the time of cutting.
Dispersion is performed using the dispersion device 10 shown in the figure.

This dispersion device 10, for example, a carry-in conveyor 11 and a forming roll
The dispersing device 10 includes a supply device 15 for supplying the wound base material 2, and a pressurizing / heating device 16 in a row, which is provided with 12, a delivery roll 13, and an air blowing nozzle 14. Apparatus for continuously molding the conductive composite 1 by
Make up 20.

The carry-in conveyor 11, the forming roll 12, the delivery roll 13
On each surface of the
A, 12A and 13A are planted, and the carry-in conveyor 11 and the forming roll 12 rotate in the same direction, and the delivery roll 13 rotates in the opposite direction and at a relatively high speed.

The conductive fiber 3 is placed on the carry-in conveyor 11 and transferred to the forming roll 12 as it moves.

At that time, in the contact portion, the conductive fiber 3 is subjected to a tensile force by the two needle bodies 11A and 12A which are opposite to each other, and the bent portion 6 which is bent in an irregular three-dimensional manner is provided, and at the same time, the fibers are separated from each other. Mariya and bond are removed.

The rotation speeds of the carry-in conveyor 11 and the forming roll 12 are appropriately adjusted according to the length of the conductive fibers 3 and the entanglement condition. For example, for fibers with strong entanglement, the fibers are fed at the lowest speed possible. It is preferable to prevent cutting and breakage.

Since such a dispersion process involves breakage of the conductive fibers 3, the number of treatments is limited to the minimum number for sufficient dispersion.

The conductive fiber 3 adhered on the forming roll 12 is similarly transferred onto the delivery roll 13 which rotates at a high speed in the reverse direction, and then is scattered in the air by the air flow from the air blowing nozzle 14 therebelow. Further, the scattered conductive fibers 3 are uniformly dispersed in a papermaking state on the base material 2 fed from the feeding device 15 and fall to form the laminated body 8.

The base material 2 is made of the polymer fiber 5 as described above, and is formed into a long web 2A in advance by a device similar to the dispersion device 10 and has a coiled shape.
15 can continuously supply the base material 2 by rewinding the web body 2A to form the continuous long-sized laminated body 8.

In this way, the dispersion device 10 can perform a laminated body forming step of obtaining the laminated body 8 in which the conductive fibers 3 are uniformly dispersed and laminated on the base material 2 together with the supply device 15. Furthermore, as described above, the dispersion device 10 does not store the curved and bent conductive fibers 3 and deforms at the same time as the curved and bent base material 2
It is possible to disperse on top, and therefore, it is possible to suppress entanglement due to storage and to help in uniform dispersion. The polymer fiber 5 may be formed by a normal fiber forming method such as extrusion, or may be obtained by cutting a sheet body made of a polymer material, and a plurality of polymer materials made of different polymer materials may be used. The fibers 5 can be mixed and used.

Further, the polymer fiber 5 has a length of 10 to 20 obtained by cutting a continuous fiber.
Short fibers of about 0 mm can be preferably used, and shorter fibers can also be used. Further, the polymer fiber 5 is 5 to 500 μmm
A fiber having a fiber diameter of about a certain degree and a fiber having a smaller diameter or a larger diameter can be appropriately used. The cross-sectional shape may be circular, elliptical, or non-circular such as polygonal. The length, diameter, cross-sectional shape, material and the like of the polymer fiber 5 can be arbitrarily determined according to the characteristics of the target conductive composite 1 and in consideration of productivity.

The pressurizing and heating device 16 performs the bonding step, and includes, for example, heat rolls 17 and 17 arranged vertically, and the heat rolls 17 and 17 press the laminate 8 while heating it. Can be transported.

Further, the heat roll 17 heats beyond the softening temperature of the polymer material forming the base material 2. For example, when the polymer material is polyethylene, it is usually heated to about 120 to 200 degrees. In the heated state, the heat roll 17 presses the laminated body 8 so that the polymer fibers 5 are fused and bonded to each other in a sheet shape with reduced thickness. In addition, the conductive fiber 3 can maintain a dispersed state, and as a result, the conductive fiber 3 has a planar curved shape in which a three-dimensional curve is compressed in the thickness direction and mixes into one side of the base material 2. The electrically conductive composite body 1 in which the fibers 3 are uniformly dispersed on one surface thereof without directivity to form a paper-like distribution can be formed.

The conductive fibers 3 may be infiltrated into the base material 2 without being completely exposed, or may be mixed so that a part thereof is exposed by selecting heating and pressurizing conditions.

Further, by increasing the pressure in the semi-molten state of the base material 2, the conductive fibers 3 can also move with the flow of the base material 2. Therefore, the basis weight and the mixing rate of the conductive fibers 3 can be adjusted by adjusting the thickness. It can also be adjusted. Further, when adjusting the thickness, the conductive fibers 3 can be firmly brought into contact with each other to enhance the conductivity. When the temperature is relatively low or when the contact time with the heat roll 17 is short, the breathable conductive composite body 1 leaving the fibrous portion is formed.

FIG. 6 schematically shows another molding apparatus 20 for manufacturing the conductive composite body 1 shown in FIG.

In the present embodiment, the base material 2 and the base material 7 are formed by preliminarily forming a polymer material into the sheets 2B and 7B, and the conductive fiber 3 is uniformly applied to the sheet 2B rewound from the roll by using the dispersing device 10. Spread it like a paper. Moreover, after another sheet 7B is attached to the conductive fiber 3 so as to be superposed thereon, the base material 2 is pressed by using a pressure and heating device 16.
By fusion-bonding 7 to each other, a three-layer structure in which the conductive fiber 3 is sandwiched between the conductive fibers 3 is formed.

The pressurizing / heating device 16 may be variously modified, such as a so-called hot press, or a pressurizing device using a roll while being heated by a hot air flow.

〔Example〕

Conductive fiber obtained by cutting stainless steel fiber (SUS 316L) with a fiber diameter of 8 μm formed by the focused wire drawing method to a length of 15 mm is applied to a web made of polymer fibers with a polyethylene resin fiber diameter of 20 μm and fiber length of 20 mm. Fiber mixing ratio is 2VO1%,
Disperse so as to be 10 VO1%, and slowly heat at a heating temperature of 180 ° C. to prepare example products 1 and 2 made of a 0.1 mm thick joint as shown in FIG. The electrical characteristics and the like were measured. The result is the second For conductivity, the internal electrical resistance was measured at an applied voltage of 100 mV (DC) with a resistance meter.

The non-breakage ratio indicates a ratio obtained by dividing the average fiber length by the original fiber length.

Shown in the table. Compared to Comparative Example Product 1 and Comparative Example Product 2, Example Product 1 and Example Product 2 have better dispersibility of conductive fiber 2 and less breakage, and are excellent in conductive property and antistatic property. ing. In addition, each measurement was performed after preparing 5 test pieces of 10 cm square. In Comparative Examples 1 and 2, 10,000 conductive fibers formed by the focused wire drawing method of stainless steel SUS (316L) having a fiber diameter of 8 μm were sized with a resin to form pellets having a diameter of 3 mm and a length of 5 mm. . Also, the conductive fibers 3 were mixed in a pellet made of the same resin so that the mixing ratio of the conductive fibers 3 was 2% by volume. Heating again
A kneading process is performed, and in the state of being sufficiently dispersed and mixed, a calender roll is used to form a plate-shaped composite body having a thickness of 1 mm.

〔The invention's effect〕

As described above, the method for producing a conductive composite of the present invention is to integrate conductive fibers in a papermaking state on a base material made of a polymer material by fusing the polymer material together. Therefore, the kneading step can be omitted, the conductive fibers can be uniformly dispersed without directional damage, and various properties such as conductivity and electrostatic properties of the obtained conductive composite can be improved. Further, even when a metal fiber is used as the conductive fiber, a fiber having a small diameter and a large length can be adopted to reduce the breakage thereof. It also helps reduce the production rate by reducing the mixing ratio.

In addition, the conductive fiber and the base material can be freely combined, and in addition to the case-shaped thick product, it can be formed into a thin product such as a film or a sheet, and a transparent material is used as the base material. Sometimes
Coupled with the fact that the mixing ratio of conductive fibers can be reduced, the conductive composite exhibits excellent transparency.For example, it can be used as a screen for electromagnetic wave shielding such as a cathode ray tube, and as a wrapping paper for antistatic. Available as a wide range. Further, the base material is continuously supplied, and the conductive fibers are curved and bent and scattered at the same time, so that the product can be simplified and the productivity is increased, the product cost is reduced, and the uniform dispersion is achieved. It will be possible to improve conductivity and improve product quality. Further, it is useful for compounding various materials such that a conductive composite can be produced even if a rubber material which has been difficult to compound as a polymer material is used, and is excellent in industrial property.

[Brief description of drawings]

1 is a perspective view illustrating a conductive composite produced by the manufacturing method of the present invention, FIG. 2 is a cross-sectional view illustrating another example, FIG. 3 is a plan view illustrating a conductive fiber, and FIG. FIG. 5 is a perspective view schematically showing a dispersing device, FIG. 5 is a diagram illustrating a molding device,
FIG. 6 is a perspective view showing another example of the molding apparatus. 2 ... Substrate, 3 ... Conductive fiber, 4 ... Combined body, 5 ...
Polymer fiber, 6 ... Bending part, 7 ... Substrate, 10 ... Dispersing device, 16 ... Pressure, heating device, 20 ... Molding device.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication H01B 13/00 HCA P 7244-5G 501 P 7244-5G

Claims (3)

[Claims] 1. A conductive paper is uniformly dispersed in a paper-like form by being scattered and dropped while being curved and bent irregularly on a base material of a polymer material that is continuously transferred. A laminated body forming step of forming a long laminated body,
A method for producing a conductive composite, which comprises a bonding step of bonding the base material and the conductive fibers by heating and pressing the laminated body. 2. The conductive fiber is a metal fiber made of a metal such as iron, nickel, aluminum, copper, or titanium, or an alloy metal such as stainless steel or brass. A method for producing a conductive composite as described in the item. 3. The step of forming a laminate includes a step of superposing another base material of a polymer material of the same kind or different kind as the base material on the conductive fiber dispersed on the base material. The method for producing a conductive composite according to claim 1, wherein