JP2006007537A - Conductive sheet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive sheet capable of well ensuring a continuity with a housing or the like though a pressure-sensitive adhesive layer is formed on one side, and its manufacturing method. <P>SOLUTION: When sheet materials, each of which is formed from a composition prepared by filling silicone with a conductive filler, are stacked and bonded under pressure, the particles of the filled conductive filler collide with each other and a part of the conductive filler is extruded from the surfaces of the sheet materials as shown by Figs. (A) and (B). If the pressure-sensitive adhesive layer is formed on the surface of the conductive sheet, a part of the conductive filler is protruded to the pressure-sensitive adhesive layer from the surfaces of the sheet materials and, even if the pressure-sensitive adhesive layer has insulating properties, the continuity of the conductive sheet can be ensured in a state that the pressure-sensitive adhesive layer is held. Accordingly, even when the conductive sheet is used so as to be held in the gap of the housing in a small-sized device such as a portable telephone or the like, it can be easily fixed to the housing through the pressure-sensitive adhesive layer and the continuity with the housing is well ensured to well shield electromagnetic waves. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a conductive sheet obtained by filling a base material with a conductive filler, and more particularly to a conductive sheet having an adhesive layer formed on one side thereof, and a method for manufacturing the same.

Conventionally, a conductive sheet obtained by filling a base material such as silicone rubber with a conductive filler such as graphite coated with nickel has been considered (see, for example, Patent Document 1). When such a conductive sheet is sandwiched as a gasket in a gap between metal casings, for example, electromagnetic waves can be prevented from passing through the gap and used for noise countermeasures of various devices. Therefore, the demand for this type of conductive sheet is increasing in various fields such as a mobile phone, a liquid crystal display, a car navigation device, and a notebook personal computer.
JP 2003-59341 A

  This type of conductive sheet is used by being fixed to a housing or the like. Some base materials such as silicone rubber have self-adhesiveness (so-called tackiness), but tackiness is lost when a large amount of conductive filler is filled in order to improve conductivity. For this reason, this type of conductive sheet is generally fixed to a housing or the like by using an adhesive layer made of an adhesive or the like and a double-sided adhesive tape.

  However, since the adhesive and the double-sided pressure-sensitive adhesive tape are insulative, there is a possibility that the continuity between the casing and the conductive sheet cannot be obtained and a sufficient electromagnetic shielding effect cannot be obtained. The device has been devised to cut the tape, etc. as much as possible to ensure the contact portion between the conductive sheet and the housing. However, as the equipment is downsized, the conductive sheet itself may be cut into smaller pieces. In such a case, it cannot respond sufficiently.

  Therefore, the present invention has been made for the purpose of providing a conductive sheet that can ensure good conduction with a housing and the like, and a method for manufacturing the same, even though an adhesive layer is formed on one side. .

  The invention according to claim 1, which has been made to achieve the above object, is a conductive sheet formed by filling a base material with a conductive filler, and is configured by filling the base material with the conductive filler and curing. A plurality of sheet materials laminated and pressure-bonded to each other before and an adhesive layer formed on the outermost sheet material surface after the lamination, wherein at least a part of the conductive filler is the surface of the sheet material It protrudes to the above-mentioned adhesion layer.

  In the present invention configured as described above, a plurality of sheet materials configured by filling a base material with a conductive filler are laminated and pressure-bonded to each other before being cured. If it carries out like this, the conductive filler with which the sheet material laminated | stacked mutually will collide, and a part of at least one conductive filler will be extruded from the surface of a sheet material. In the present invention, an adhesive layer is formed on the surface of the laminate formed by laminating a plurality of sheet materials as described above, that is, on the surface where at least a part of the conductive filler protrudes from the surface of the sheet material as described above. is doing.

The invention described in claim 2 is characterized in that, in addition to the structure described in claim 1, the plurality of sheet materials are laminated and pressure-bonded with a support layer interposed therebetween.
In addition to the structure of Claim 1 or 2, the invention described in Claim 3 has an average particle size of 10 to 100 μm of the conductive filler, and 75 to 325 parts by weight of the conductive filler in each of the sheet materials ( It is characterized by being filled (with respect to 100 parts by weight of the substrate).

In addition to the structure in any one of Claims 1-3, invention of Claim 4 is characterized by the said conductive filler being the graphite which provided electroconductivity.
Invention of Claim 5 is a manufacturing method of the electroconductive sheet which manufactures the electroconductive sheet with which the base material was filled with the electroconductive filler, Comprising: The 1st process of filling the base material with the electroconductive filler, A second step of forming the base material filled with the conductive filler in the first step into a sheet shape, and a plurality of the base materials formed into a sheet shape in the second step are laminated and pressure-bonded before curing. It is characterized by comprising a third step and a fourth step of forming an adhesive layer on at least one surface of the base material laminated and pressure-bonded in the third step.

  In the present invention, a plurality of substrates filled with a conductive filler in the first step and formed into a sheet shape in the second step are laminated and pressure-bonded in the third step before curing. By this step, the conductive fillers filled in the sheet-like base materials stacked on each other collide, and a part of at least one of the conductive fillers is extruded from the surface of the sheet-like base material. In the fourth step, an adhesive layer is formed on the surface of the base material from which at least a part of the conductive filler protrudes from the surface.

  As described above, in the invention according to the first aspect, at least a part of the conductive filler protrudes from the surface of the sheet material to the adhesive layer. For this reason, although the pressure-sensitive adhesive layer is formed on one side, it is possible to satisfactorily ensure electrical continuity with the housing or the like via the pressure-sensitive adhesive layer. Therefore, the conductive sheet of the present invention can be easily fixed to the housing even when used in a small device such as a mobile phone, a liquid crystal display, a car navigation device, a notebook computer, etc. In addition, it is possible to shield the electromagnetic wave satisfactorily by ensuring good conduction with the casing.

  In the invention described in claim 2, the plurality of sheet materials are laminated and pressure-bonded with the support layer interposed therebetween. Also in this case, as described above, at least a part of the conductive filler is pushed out from the surface of the sheet material, and conduction can be ensured. In the present invention, the mechanical strength of the conductive sheet can be improved by the support layer. Furthermore, since the elongation of the conductive sheet itself is suppressed by providing the support layer, the volume resistivity of the conductive sheet itself is stabilized.

  Therefore, in the present invention, in addition to the effect of the invention described in claim 1, by improving the mechanical strength, it is possible to satisfactorily prevent tearing at the time of work such as reattachment even when it is cut into thin pieces. In addition, there is an effect that stable conductivity can be obtained by suppressing the elongation of the conductive sheet itself.

  In the invention of claim 3, the average particle diameter of the conductive filler is set to 10 to 100 μm, and 75 to 325 parts by weight of the conductive filler is filled in each sheet material (with respect to 100 parts by weight of the base material). Therefore, as described above, a phenomenon in which a part of the conductive filler is pushed out from the surface of the sheet material is more likely to occur. For this reason, in addition to the effect of the invention according to claim 1 or 2, in the present invention, the conductive filler protrudes better from the surface of the sheet material to the adhesive layer, and is electrically connected to the housing or the like via the adhesive layer. As a result, it is possible to ensure better.

  In the invention described in claim 4, graphite imparted with conductivity is used as the conductive filler. Since the surface of graphite is rough and rough, the phenomenon that a part of the conductive filler is pushed out from the surface of the sheet material is more likely to occur as described above. For this reason, in this invention, in addition to the effect of the invention according to any one of claims 1 to 3, the conductive filler protrudes more satisfactorily from the sheet material surface to the adhesive layer, and the casing via the adhesive layer As a result, it is possible to ensure better electrical continuity. As a method of imparting conductivity to graphite, a method of coating the graphite surface with nickel by a carbonyl method or a pure fluidized bed chemical vapor deposition method (CVD method) can be considered. In order to ensure conductivity, a method of covering the surface with silver, gold, stainless steel or the like is also conceivable.

  In the invention described in claim 5, since the adhesive layer is formed on the surface of the base material from which at least a part of the conductive filler protrudes, the obtained conductive sheet has the adhesive layer formed on one side. In addition, it is possible to satisfactorily ensure electrical connection with the housing or the like through the adhesive layer. Therefore, the conductive sheet manufactured by the method of the present invention can be applied to the casing even when used in a small device such as a mobile phone, a liquid crystal display, a car navigation device, and a notebook personal computer. Fixing is easy, and it is possible to shield the electromagnetic wave satisfactorily by ensuring good conduction with the casing.

  In addition, the method of causing a part of the conductive filler to protrude from the surface of the base material only has to be laminated before curing the base material formed into a sheet shape. Such a conductive sheet can be easily manufactured. The step of curing the base material may be performed between the third step and the fourth step, may be omitted depending on the type of the base material, and may be performed after the fourth step depending on the type of the adhesive layer. You may implement.

  Next, embodiments of the present invention will be described with reference to the drawings. The applicant of the present application created a conductive sheet as follows. First, a conductive filler and a vulcanizing agent were kneaded with silicone rubber as a base material according to the formulation shown in Table 1 below (first step). As a kneading method, in addition to a method using a kneader, a two-roll, a mixer and the like can be used.

Nickel-coated graphite 40% is a coating of 40% by weight of nickel on 60% by weight of graphite, with an average particle size of 74 μm and an apparent density of 1.8 kg / cm ³ .

  The kneaded product was further swollen with an organic solvent (toluene or xylene) and stirred to form a liquid, and coated on the substrate 2 (PET, PI, woven fabric, etc.) to a predetermined thickness. After coating, only the organic solvent was dried to obtain an unvulcanized sheet 1 as a sheet material as shown in FIG. 1 (second step). By repeating the above process twice, as shown in FIG. 1A, two drums 5 and 6 formed by winding the unvulcanized sheet 1 together with the base material 2 were obtained. In addition, as shown to FIG. 1 (A), the drums 5 and 6 were wound so that the base material 2 might become the outer side, respectively.

  The base material 2 and the unvulcanized sheet 1 are fed out from the drums 5 and 6 and stacked so that the unvulcanized sheets 1 face each other as shown in FIG. (Third step). Thus, by laminating and pressing the two unvulcanized sheets 1, the conductive fillers filled in the unvulcanized sheet 1 collide with each other, and a part of the conductive fillers from the surface of the unvulcanized sheet 1. Is pushed out.

  FIGS. 2A and 2B are SEM images showing the surface state of the unvulcanized sheet 1 in a state where the base material 2 is peeled off when the above-mentioned lamination and pressure bonding is performed using the mat type base material 2. (200 times), (A) is a plan view, and (B) is a cross-sectional view. 2A and 2B, it can be seen that a part of the conductive filler protrudes from the surface of the unvulcanized sheet 1 by about 70 μm. When the embossed type base material 2 is used, as shown in FIGS. 2C and 2D, the degree of protrusion is slightly reduced, but at least a part of the conductive filler is similarly formed of the unvulcanized sheet 1. It protrudes from the surface by about 5 μm. That is, in the manufacturing method described above, a part of the conductive filler protrudes from the surface of the unvulcanized sheet 1 by 5 to 70 μm.

  Next, the unvulcanized sheet 1 thus laminated and pressure bonded was inserted into an atmosphere at 170 ° C. and vulcanized for 2 hours. Subsequently, an adhesive layer 12 was formed on one side of the uncured sheet 1 of about 0.5 mm obtained in this way as shown in FIG. Process). As the adhesive layer 12, a silicone-based adhesive layer (trade name “SD4570”: manufactured by Toray Dow Corning Silicone) was used.

  Further, instead of directly laminating and pressing the two unvulcanized sheets 1, as shown in FIG. 3B, the unvulcanized sheet 1 is sandwiched with a support layer 13 such as a glass cloth, an aluminum foil, or a conductive cloth. You may use what laminated | stacked and crimped | bonded. In this case, by improving the mechanical strength of the conductive sheet 10, it is possible to satisfactorily prevent tearing during work such as re-sticking even when it is cut into thin pieces. Further, in this case, since the elongation of the conductive sheet 10 itself can be suppressed by the support layer 13, the conductivity of the conductive sheet 10 itself can be stabilized.

  FIGS. 3A and 3B are cross-sectional views (cross-sectional schematic views) schematically illustrated for the purpose of explanation. Therefore, the protruding state of the conductive filler, the distribution state of the protruding conductive filler, and the protruding amount vary depending on the average particle diameter and the filling amount of the conductive filler. In addition, the conductive fillers protruding from the unvulcanized sheet 1 are not actually arranged neatly as shown in FIGS. 3 (A) and 3 (B). Further, when the conductive sheet 10 of each of the above embodiments is manufactured in a state of being cut finely, a release paper is attached to the surface of the adhesive layer 12, but the conductive sheet 10 is made into a roll shape with a long length. The release paper can be omitted when the product is rolled up.

  Next, the physical properties of the conductive sheet 10 of the type shown in FIG. 3A obtained as described above were examined. The results of the compression resistance test are shown in FIGS. 4 (A) and 4 (B). As shown in FIG. 4 (A), the conductive sheet 10 exhibited extremely excellent conductivity, both 66 mm × 2 mm and 45 mm × 4 mm. This is presumably because the conductive filler protrudes from the surface of the unvulcanized sheet 1 to the adhesive layer 12, and even if the adhesive layer 12 is insulative, conduction can be ensured across the adhesive layer 12. Further, when the conductive filler protrudes from the surface of the unvulcanized sheet 1, the oxide film formed on the surface of the unvulcanized sheet 1 is broken.

  Accordingly, the conductive sheet 10 is easily fixed to the casing via the adhesive layer 12 when used in a small device such as a mobile phone, a liquid crystal display, a car navigation device, a notebook personal computer or the like. In addition, even if the adhesive layer 12 is insulative, it is possible to ensure good electrical continuity with the housing and shield the electromagnetic waves well.

Further, the compressive force applied to the conductive sheet 10 changed substantially linearly as shown in FIG. From this experimental result, it can be seen that the conductive sheet 10 has good elasticity. Furthermore, the thermal conductivity of the conductive sheet 10 measured by the rapid thermometer QTM-500 (Kyoto Electronics Industry Co., Ltd.) is 2.0 W / mK, and the low resistance of the four-probe measurement method (based on JIS K7194) The volume resistivity measured with a rate meter Loresta-GP MCP-T600 (Mitsubishi Chemical Corporation) was 1.4 × 10 ⁻¹ Ω · cm, and the result of the ball tack test was 80 mm. The thermal conductivity, volume resistivity, and rolling ball tack (conforming to ASTM D3121) were measured using a 130 mm × 75 mm sample.

  Next, the change in volume resistivity was measured by changing the filling amount of the conductive filler. The results are shown in Table 2 and FIG.

  As is apparent from Table 2 and FIG. 5, the volume resistivity of the conductive sheet 10 decreases as the filling amount of the conductive filler (nickel coated graphite) increases, but the filling amount is 100 parts by weight. Saturates when exceeding. This is considered to be because when the filling amount is reached, a so-called percolation phenomenon occurs in which the conductive fillers are connected in the base material of the conductive sheet 10 to form a network. Further, in the filling amount where the percolation phenomenon occurs, the conductive filler collides in a ball shape when the two unvulcanized sheets 1 are laminated and pressed, and a part of the conductive filler is on the surface of the unvulcanized sheet 1. It is presumed that the phenomenon of being pushed out from is more likely to occur. Therefore, in this case, electrical conduction across the adhesive layer 12 can be further ensured.

  As a result, in order to make the conductive filler protrude better from the surface of the unvulcanized sheet 1 to the adhesive layer 12, the filling amount of the conductive filler is 75 to 325 parts by weight (more preferably 100 parts by weight or more). I found it desirable to do. If the average particle size of the conductive filler is in the range of 10 to 100 μm, the desirable volume% is considered to be the same.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and can be implemented in various forms without departing from the gist of the present invention. For example, as a molding method of the unvulcanized sheet 1, various methods such as press molding and calendar molding can be applied in addition to coating. In addition to the above, various conductive fillers and substrates can be used. However, since the surface of graphite is rough and rough, the phenomenon that a part of the conductive filler is pushed out from the surface of the unvulcanized sheet 1 as described above is more likely to occur. Therefore, as the conductive filler, it is desirable to use graphite having conductivity.

  Various methods of laminating and pressure-bonding two unvulcanized sheets 1 are also conceivable. For example, as shown in FIG. 6, the unvulcanized sheet 1 and the substrate 2 fed out from the drums 5 and 6 are guided by the guide roller 24 so that the unvulcanized sheets 1 face each other, and then laminated by the laminating roll 25. -It may be crimped. Moreover, as shown in FIG. 7, you may wind up the unvulcanized sheet 1 and the base material 2 which were let out from the drums 5 and 6 with one winding roll 26 so that the unvulcanized sheets 1 may face each other. .

  Also in these cases, the two unvulcanized sheets 1 are laminated and pressure-bonded, and then heated to vulcanize to obtain the same conductive sheet 10 as described above. Moreover, when using the winding roll 26 as shown in FIG. 7, since the unvulcanized sheet 1 which has already been laminated and pressure-bonded and wound is further pressed, the unvulcanized sheets 1 are further strengthened. Can be crimped.

  Furthermore, also in these cases, if the support layer 13 is fed out from another drum (not shown) and sandwiched between the two unvulcanized sheets 1, the conductivity as illustrated in FIG. Sheet 10 can be obtained.

  Furthermore, in the above-described embodiment, two unvulcanized sheets 1 configured in the same manner are laminated and pressure-bonded, but unvulcanized sheets 1 having different configurations may be laminated and pressure-bonded. For example, when the thicknesses of the unvulcanized sheets 1 laminated and pressure-bonded with each other are different, the thinner unvulcanized sheet 1 is more likely to protrude the conductive filler from the surface. Moreover, when one base material is made softer than the other base material by changing the composition of the base materials of the unvulcanized sheet 1 that are laminated and pressure-bonded to each other, the softer unvulcanized sheet 1 is removed from the surface. It becomes easy for the conductive filler to protrude. In these cases, by forming the adhesive layer 12 on the side where the conductive filler is likely to protrude, the influence of the adhesive layer 12 and the oxide film can be more effectively eliminated by the protrusion of the conductive filler, and conduction with the housing or the like can be achieved. Can be secured even better. The conductive sheet of the present invention may be manufactured by laminating and pressure-bonding three or more sheet materials (unvulcanized sheet 1).

It is explanatory drawing showing the manufacturing process of the electroconductive sheet to which this invention was applied. It is a SEM image showing the surface state of the unvulcanized sheet which comprises the electroconductive sheet. It is a cross-sectional schematic diagram showing the structure of the electroconductive sheet. It is explanatory drawing showing the physical property of the electroconductive sheet. It is a graph showing the change according to the mixing | blending of the conductive filler of the volume resistivity of the electroconductive sheet. It is explanatory drawing showing the modification of the manufacturing process of the said electroconductive sheet. It is explanatory drawing showing the other modification of the manufacturing process of the said electroconductive sheet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Unvulcanized sheet 2 ... Base material 5, 6 ... Drum 10 ... Conductive sheet 12 ... Adhesive layer 13 ... Support layer

Claims (5)

A conductive sheet formed by filling a base material with a conductive filler,
A plurality of sheet materials that are configured by filling the base material with the conductive filler and laminated and pressure-bonded to each other before curing,
An adhesive layer formed on the outermost sheet material surface after the lamination,
And at least a part of the conductive filler protrudes from the surface of the sheet material to the adhesive layer. The conductive sheet according to claim 1, wherein the plurality of sheet materials are laminated and pressure-bonded with a support layer interposed therebetween. The average particle size of the conductive filler is 10 to 100 µm, and each of the sheet materials is filled with 75 to 325 parts by weight of the conductive filler (with respect to 100 parts by weight of the base material). The conductive sheet according to 1 or 2. The conductive sheet according to claim 1, wherein the conductive filler is graphite imparted with conductivity. A method for producing a conductive sheet for producing a conductive sheet in which a base material is filled with a conductive filler,
A first step of filling the substrate with a conductive filler;
A second step of forming the base material filled with the conductive filler in the first step into a sheet;
A third step of laminating and press-bonding the base material formed into a sheet shape by the second step, and then pressing the base material;
A fourth step of forming an adhesive layer on at least one surface of the base material laminated and pressure-bonded in the third step;
The manufacturing method of the electroconductive sheet characterized by the above-mentioned.