JP2004047915A - Conductive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve conductivity and to prevent the performance decline of an adhesive material layer by selecting the conductive filler of an optimum average particle diameter and mixing it in the base material of the conductive sheet in the conductive sheet. <P>SOLUTION: In the conductive sheet, the conductive filler having the average particle diameter equal to or more than the thickness of a supporting body is selected and mixed in. Also, the conductive filler having the average particle diameter equal to or more than the thickness for which the supporting body and the adhesive material layer are put together in the state of applying weight and compressing them is selected and mixed in. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
[Industrial applications]
The present invention relates to a conductive sheet or a conductive tape that is attached to a housing or a cover of an electronic device, a cable, or the like and shields generated electromagnetic waves.
[0002]
[Prior art]
2. Description of the Related Art In recent years, various types of electronic devices, such as personal computers and mobile phones, have become widespread, and electromagnetic waves are generated from these devices, which has an adverse effect on human bodies and precision equipment. Therefore, in order to prevent electromagnetic waves from leaking from electronic devices, a conductive material is attached to a housing, a cover, a cable, or the like of these devices to shield the electromagnetic waves.
[0003]
As one of the conductive materials, there is a conductive sheet or a conductive tape (hereinafter, these are collectively referred to as a conductive sheet). The conductive sheet is convenient for a place where the bulk is to be reduced, such as an electronic device housing and a lid, a harness, and other gaps, and is used in close contact with them.
[0004]
FIG. 3 shows an example of the conductive sheet. The foil film layer 5 made of a very thin metal foil or a component of a conductive paint is attached to the surface of the support 6 because it has no strength of itself, and is used integrally with the support 6. Examples of the support 6 include synthetic resin films such as PET (polyethylene terephthalate) and urethane foam. However, since the support 6 has no electrical conductivity, the conductive filler (support side) 8 is mixed. Examples of the conductive filler 8 include particles of metal, carbon, graphite, and the like.
[0005]
In most cases, the adhesive 7 having double-sided adhesiveness is attached to the back surface of the support for use by attaching to a member such as a housing of an electronic device. However, since the adhesive 7 also has no electrical conductivity, it is necessary to separately mix a conductive filler (on the adhesive layer side) 9 with the adhesive 7. Since the particle diameters of the conductive fillers 8 and 9 are not actually constant, they are shown in different sizes in the figure.
[0006]
[Problems to be solved by the invention]
The conductive sheet found in the prior art described above, for each of the support and the adhesive, each mixed with a different conductive filler, the conductive filler on the support side and the conductive filler on the adhesive layer side. Does not always contact. For this reason, the conductivity varies depending on the portion of the conductive sheet, which often causes poor conduction, and the electromagnetic wave shielding effect may be significantly impaired.
[0007]
Further, since the conductive filler lowers the adhesive strength of the pressure-sensitive adhesive, it is not possible to mix a large amount of the conductive filler in order to improve the conductivity. Conversely, if the adhesive strength is to be maintained, the thickness of the adhesive layer must be increased, and the flexibility, which is an advantage of a thin sheet, is impaired, and the cost is increased.
[0008]
The present invention has been made in view of these problems, and it is an object of the present invention to provide a conductive sheet capable of reliably realizing electromagnetic wave shielding without impairing the inherent characteristics of the conductive sheet in actual use.
[0009]
[Means for Solving the Problems]
The present invention provides a conductive sheet in which a conductive foil film layer is formed on the surface of a support provided with a conductive filler, and a pressure-sensitive adhesive layer is formed on a back surface of the support, with respect to the thickness of the support. It is characterized in that the average particle size of the conductive filler is selected from those shown in the following formula.
t _F ≧ t _S
Here, t _F : average particle diameter t _S of the conductive filler: thickness of the support.
Further, the conductive filler is selected from those having an average particle size represented by the following formula with respect to the thickness of the laminated support and pressure-sensitive adhesive layer when the weight is applied.
When the weighting _{W, t F} ≧ _t W
Here, t _F : average particle size of the conductive filler t _W : thickness of the support and the pressure-sensitive adhesive layer when the weight W is applied.
BEST MODE FOR CARRYING OUT THE INVENTION
The configuration of the present invention will be described in more detail with reference to FIG.
[0012]
First, the conductive filler 4 is mixed into the support 2 serving as the base material of the conductive sheet. As the support 2, a synthetic resin such as PET, acrylic, urethane or the like, or a rubber-based material can be used. Usually, these materials are dissolved in a solvent such as toluene and the like. Is evaporated and hardened. Examples of the conductive filler include metal materials such as copper, silver, nickel, iron, and aluminum, and carbon-based materials such as carbon black and graphite. However, in consideration of conductivity, a metal material is preferable. Can be Since the particle size of the conductive filler 4 is not actually constant, the size is changed in the drawing.
[0013]
Then, a conductive foil film layer 1 is formed on the surface of the support 2. As the foil film layer 1, a metal material such as copper, nickel, or aluminum can be used, and a thin layer is formed on the support 2 by plating, coating, or the like.
[0014]
On the other hand, an adhesive layer 3 is formed on the back surface of the support 2. The pressure-sensitive adhesive layer 3 is a double-sided adhesive tape made of a natural rubber-based, latex-based, acrylic-based, or silicon-based material, and adheres to the support 2.
[0015]
The average particle size of the conductive filler 4 is generally about 1 to 50 μm, but is preferably selected based on the thickness of the support in the present invention. That is, the average particle diameter (t _F ) of the conductive filler 4 is selected from those at least larger than the thickness (t _S ) of the support. In actual use of the conductive sheet, a load is applied, so that usually sufficient conduction can be obtained.
t _F ≧ t _S
[0016]
However, in actual use, the mixing of the conductive filler 4 having an excessively large particle diameter into the pressure-sensitive adhesive layer lowers the adhesive strength. Find the diameter (t _F ). That is, when the load applied to the conductive sheet is small, the particle size of the conductive filler 4 must be increased, but when the load is large, the particle size of the conductive filler 4 can be reduced. As the method, the average particle size (t _F ) of the conductive filler 4 can be obtained by the following equation. At this time, since the approximate weight (W) is known from the configuration of the electronic device to be incorporated, the total thickness of the support 2 and the pressure-sensitive adhesive layer 3 after being compressed by the weight is experimentally known, and the conductive filler The average particle size can be easily obtained.
When the weighting _{W, t F} ≧ _t W
[0017]
FIG. 2 shows the relationship between the weight and the conductive filler 4 at that time.
(A) is a state where no weight is applied to the conductive sheet (W = 0), and at this time, the support 2 and the pressure-sensitive adhesive layer 3 have a natural thickness (t _W0 ) which is not compressed; The conductive filler 4 also needs to have the same height (t _F0 ). The illustrated shape of the conductive filler 4 is schematically shown to explain the height, and actually has a different shape and arrangement.
[0018]
(B) is a state in which a weight W1 is applied to the conductive sheet. At this time, the thickness of the superposed support 2 and the adhesive layer 3 is (t _W1 ), and the height of the conductive filler 4 is also approximately A height equal to this would be sufficient. Therefore, the illustrated height (t _F1 −t _W1 minutes) becomes excessive.
[0019]
(C) shows a state in which a weight W2 is further applied to the conductive sheet. At this time, the thickness of the support 2 and the pressure-sensitive adhesive layer 3 superposed on each other becomes _tW2 , and the height of the conductive filler 4 is almost the same. A height equal to Therefore, the height shown _(t F2 _{-t W2} minutes) is further excess.
[0020]
As described above, under the condition that the weight is applied to the conductive sheet, the average particle size of the conductive filler 4 can be reduced. For example, when a weight is applied to the conductive sheet and the thickness of the support 2 and the pressure-sensitive adhesive layer 3 overlapped with each other becomes と な っ, the average particle diameter of the conductive filler 4 theoretically also becomes 1 /. Since it is 2, the volume is reduced to 1/8, so that the ratio of the particle component added to the base material can be greatly reduced. In addition, the influence on the pressure-sensitive adhesive layer 3 can be reduced, and a decrease in the adhesive strength can be prevented to some extent.
[0021]
With the above-described configuration, the conductive sheet of the present invention can be used to electrically connect the single conductive filler 4 to the pressure-sensitive adhesive layer 3 from the foil film layer 1 via the support 2 without relaying a plurality of conductive fillers. In addition, the conductive layer 4 can be reliably and electrically conducted, and a decrease in the adhesive performance of the adhesive layer 3 due to the incorporation of the conductive filler 4 can be reduced, so that the electronic device can be stably used.
[0022]
【Example】
Hereinafter, the present invention will be described based on examples.
[0023]
Embodiment 1
After 50 parts by weight of a solvent-based urethane resin was mixed with 10 parts by weight of a conductive filler containing copper as an ingredient and having an average particle diameter of 50 μm, volatiles were evaporated to form a sheet-like support having a thickness of 40 μm. Then, a conductive paint containing copper was applied to the surface of the support to form a film layer having a thickness of 50 μm. On the other hand, a pressure-sensitive adhesive having double-sided adhesiveness was attached to the back surface of the support to form a conductive sheet.
[0024]
As a comparative example, 50 parts by weight of a solvent-based urethane resin was mixed with 10 parts by weight of an electrically conductive filler having an average particle diameter of 50 μm, and then volatiles were evaporated to form a sheet-like support having a thickness of 40 μm. Then, a conductive coating containing a copper-based component was applied to the surface of the support to form a film layer having a thickness of 5 μm. Separately, a pressure-sensitive adhesive having double-sided adhesion was prepared by dispersing a filler having an average particle diameter of 50 μm having conductivity in the same manner as described above. Then, the surface of the pressure-sensitive adhesive layer in which the filler was distributed was attached to the back surface of the support to form a conductive sheet.
[0025]
The electrical resistance values of the conductive sheets prepared in Example 1 and Comparative Example were compared. As a result, the electric resistance of the conductive sheet of Example 1 was always 0.05 Ω or less irrespective of the measurement position of the sheet surface, whereas the electric resistance of the conductive sheet of the comparative example depended on the measurement position of the sheet surface. The values ranged from 0.05 Ω or less to 0.2 Ω, and it was found that there was considerable variation in electric resistance depending on the measurement position.
[0026]
Embodiment 2
A conductive sheet was produced in the same manner as in Example 1. At this time, the average particle size of the conductive filler was set to be equal to the thickness of the compressed state of the support and the pressure-sensitive adhesive layer, and was selected to be 20 μm to 30 μm. The measurement of the electric resistance was performed in a state of being compressed.
[0027]
As a result, the electrically conductive sheet produced in Example 2 had an electrical resistance value of 0.05 Ω or less for all of the sheets subjected to the expected load, and was effective for actual use without impairing the electrical conductivity. found.
[0028]
【The invention's effect】
With the above-described configuration, the conductive sheet of the present invention can be used to electrically connect the single conductive filler 4 to the pressure-sensitive adhesive layer 3 from the foil film layer 1 via the support 2 without relaying a plurality of conductive fillers. In addition, the conductive layer 4 can be reliably and electrically conducted, and a decrease in the adhesive performance of the adhesive layer 3 due to the incorporation of the conductive filler 4 can be reduced, so that the electronic device can be stably used.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a conductive sheet according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a conductive sheet showing a behavior when a weight is applied in an embodiment of the present invention. Sectional view of sheet [Explanation of reference numerals]
REFERENCE SIGNS LIST 1 foil film layer 2 support 3 adhesive layer 4 conductive filler 5 conductive paint 6 support 7 adhesive 8 conductive filler (support side)
9 Conductive filler (adhesive layer side)

Claims (2)

A conductive foil film layer is formed on the surface of a support on which a conductive filler is disposed, and in a conductive sheet having an adhesive layer formed on the back surface of the support, the thickness of the support is represented by the following formula. A conductive sheet, wherein a conductive filler having an average particle size is selected from those.
t _F ≧ t _S
Here, t _F : average particle diameter t _S of the conductive filler: thickness of the support The conductive sheet according to claim 1, wherein the conductive filler has an average particle size relative to a thickness of the support and the pressure-sensitive adhesive layer when the weight is applied.
When the weighting _{W, t F} ≧ _t W
Here, t _F : average particle diameter of the conductive filler t _W : thickness of the support and the pressure-sensitive adhesive layer when the weight W is applied.

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