JP7625485B2 - Conductive Fabric - Google Patents

Description

The present invention relates to a conductive fabric. More specifically, the present invention relates to a conductive fabric that has excellent bending resistance.

As a flexible conductive member, a metal-containing coating formed on the surface of a polymer film is used. However, conductive members in which a metal-containing coating is formed on the surface of a polymer film have insufficient durability in terms of conductivity when bent at sharp angles or repeatedly bent.

For example, Patent Document 1 discloses a flexible circuit board for repeated bending applications, which has a tensile modulus of elasticity of 4 to 6 GPa at 25°C and a thickness of 14 to 17 μm on a polyimide insulating layer, a wiring circuit having a thickness of 7 to 13 μm, a ratio (tc/tp) of the thickness of the wiring circuit (tc) to the thickness of the polyimide insulating layer (tp) of 0.4 to 0.95, and a circuit protection layer having a thickness of 15 to 30 μm on the wiring circuit, with the aim of improving durability against bending.

International Publication No. 2012/020677

However, even with the flexible circuit boards described in Patent Document 1, the improvement in bending resistance is still not sufficient.

The inventors conducted various studies on conductive fabrics in which a conductive sheet member having a mesh-shaped substrate embedded inside a conductive film made of a conductive composition is laminated on the surface of a substrate fabric. As a result, they found that when the arithmetic mean roughness of the front and back surfaces of the conductive sheet member is different and the surface with the relatively smaller arithmetic mean roughness is laminated on the substrate fabric side, the conductive fabric exhibits extremely excellent bending resistance, which led to the completion of the present invention.

That is, the present invention provides a conductive fabric in which a conductive sheet member having a mesh-shaped substrate embedded inside a conductive film made of a conductive composition is laminated on the surface of a substrate fabric,
The mesh-like substrate has openings so that the opening ratio is 30% or more,
an arithmetic mean roughness Ra ₁ (unit: μm) of a first surface of the conductive sheet member and an arithmetic mean roughness Ra ₂ (unit: μm) of a second surface of the conductive sheet member satisfy a relationship of Ra ₁ >Ra ₂ ;
The conductive fabric is characterized in that the second surface of the conductive sheet member is laminated on the base fabric side.

It is preferable that the ratio of the arithmetic mean roughness Ra ₁ (unit: μm) of the first surface of the conductive sheet member to the arithmetic mean roughness Ra ₂ (unit: μm) of the second surface of the conductive sheet member, Ra ₂ /Ra _1, is within the range of 0.1 to 0.5.

The second surface of the conductive sheet member preferably has an arithmetic mean roughness _Ra2 in the range of 0.1 to 1.0 μm.

It is preferable that a portion of the mesh substrate is exposed on the second surface of the conductive sheet member.

The present invention provides a conductive fabric that suppresses the decrease in conductivity due to repeated bending deformation.

1 is a schematic cross-sectional view showing an example of a conductive fabric of the present invention.

The member constituting the conductive portion of the conductive fabric of the present invention is a conductive sheet member in which a mesh-shaped substrate is embedded inside a conductive film made of a conductive composition.

The conductive composition of the present invention preferably contains conductive particles and a polymer resin. Examples of conductive particles include carbon particles, carbon nanotubes, and metal particles. Among these, metal particles are preferable when a high degree of conductivity is required. Examples of metal particles are preferably one type selected from the group consisting of silver particles, nickel particles, and copper particles, or a mixture of two or more types.

The primary particle size of the conductive particles is preferably 0.01 to 10.00 μm. When the primary particle size of the conductive particles is within the range of 0.01 to 10.00 μm, the effect of reducing resistance by increasing the contact ratio between conductive particles and preventing disconnection by densely blending the conductive particles can be obtained. The particle shape of the conductive particles may be spherical, needle-shaped, scale-shaped, polyhedral, irregular, etc., and is not particularly limited.

The conductive particle content is preferably 50 to 95% by mass relative to the mass of the conductive composition. If the conductive particle content is within this range, a conductive film with excellent conductivity can be formed.

The polymer resin to be blended in the conductive composition of the present invention is not particularly limited, but examples include acrylic resin, phenoxy resin, polyvinyl formal resin, polystyrene resin, polyvinyl butyral resin, polyester resin, polyamide resin, polyimide resin, xylene resin, polyurethane resin, epoxy resin, etc. Other conductive polymer materials such as polypyrrole and PEDOT may also be used.

The blending ratio of the polymer resin is preferably 5 to 50% by mass relative to the mass of the conductive composition. If the blending ratio of the polymer resin is within this range, a smooth conductive film can be formed in which the particles are more uniformly dispersed.

The conductive composition may contain other components such as solvents, viscosity adjusters, leveling agents, wettability adjusters, preservatives, and stabilizers.

The mesh-like substrate in the present invention has a woven structure made of warp and weft threads. The warp and weft threads constituting the mesh-like substrate are preferably synthetic fibers such as nylon, polyester, acrylic, vinylon, polyethylene, and polypropylene. The warp or weft threads are preferably filament threads. They may be either monofilament or multifilament threads. The diameter of the warp or weft threads is preferably 20 to 70 μm. The diameters of the warp and weft threads may be the same or different, but in order to achieve bending resistance that is independent of the bending direction, it is preferable that the warp and weft threads are made of the same diameter.

The weave density of the warp and weft threads of the mesh substrate is adjusted so that the opening ratio is 30% or more. By setting the weave density appropriately while taking into consideration the fineness of the warp and weft threads, a mesh substrate with an opening ratio of 30% or more can be woven. It is more preferable that the opening ratio is 30 to 50%. The weave of the mesh substrate is not particularly limited to plain weave, twill weave, satin weave, etc. Plain weave is preferable in that bending resistance independent of the bending direction can be obtained when a conductive fabric is formed. The opening ratio can be measured by analyzing an image of one surface of the mesh substrate and calculating the area ratio of the part where no warp or weft threads are present per unit area.

The conductive sheet member of the present invention has a structure in which the mesh-shaped substrate is embedded inside a conductive film made of the conductive composition. The conductive composition is filled so as to penetrate the openings of the mesh-shaped substrate and cured to form a conductive film. At this time, the mesh-shaped substrate may be completely embedded inside the conductive film formed by curing the conductive composition, that is, in a covered state with no exposed parts. A part of the mesh-shaped substrate may be exposed from one or both surfaces of the conductive sheet member.

When the thickness of the mesh-like substrate is T _B μm and the thickness of the conductive film formed by curing the conductive composition is T _M μm, it is preferable that the value of T _M /T _B is in the range of 1.1 to 1.5. If the value of T _M /T _B is within this range, it is possible to achieve both flexibility and surface conductivity of the conductive sheet member. A more preferable range of T _M /T _B is 1.1 to 1.2.

The conductive sheet member has a first surface and a second surface which are in a front-back relationship. Here, it is essential that the arithmetic mean roughness Ra ₁ (unit: μm) of the first surface and the arithmetic mean roughness Ra ₂ (unit: μm) of the second surface are formed so as to satisfy the relationship Ra ₁ > Ra _2. It is preferable that the value of Ra 2 /Ra 1, which is the ratio of the arithmetic mean roughness Ra ₁ (unit: μm) of the first surface of the conductive sheet member to the arithmetic mean roughness _{Ra 2} (unit: μm) of the _second surface of the conductive sheet member, is within a range of 0.1 to 0.5.

Here, the arithmetic mean roughness Ra can be measured using a surface roughness measuring instrument SV-3000 (manufactured by Mitutoyo Corporation). The measurement conditions are in accordance with JIS B 0601:1994.

The second surface of the conductive sheet member preferably has an arithmetic mean roughness _Ra2 in the range of 0.1 to 1.0 μm. Furthermore, it is preferable that a part of the mesh-like substrate is exposed on the second surface of the conductive sheet member. This allows the obtained conductive fabric to have a low resistance increase rate (%) in a repeated bending test. In other words, a conductive fabric having excellent conductivity with excellent bending resistance can be obtained.

As a method for manufacturing the conductive sheet member of the present invention, a method can be adopted in which a releasable substrate having an arithmetic mean roughness smaller than that of the mesh substrate is first arranged, and the mesh substrate is placed on the releasable substrate, and the conductive composition having fluidity is applied from above the mesh substrate. Various printing methods including screen printing can be used as the application method. If a knife coating method is adopted as the application method, the arithmetic mean roughness of the conductive sheet member on the side where the knife contacts can be roughly equivalent to the arithmetic mean roughness of the mesh substrate. As a result, the arithmetic mean roughness of the side where the knife contacts can be formed larger than the arithmetic mean roughness of the side of the conductive sheet member on which the releasable substrate is arranged, that is, the side opposite to the side where the knife contacts. In other words, the side on which the releasable substrate is arranged becomes the second surface of the conductive sheet member, and the side on which the knife contacts becomes the first surface of the conductive sheet member. Here, by setting the value of T _M /T _B , which is the ratio of the thickness T _B of the mesh-like substrate to the thickness T _M of the conductive film formed by curing the conductive composition, in the range of 1.1 to 1.5, it is possible to obtain the effect of making it easier to control the arithmetic mean roughness of the first surface by the knife coating method.

As another method, a method can be adopted in which the conductive composition is applied to a first releasable substrate, and then the mesh-like substrate and the second releasable substrate are placed in this order before being cured to form a film, and the mesh-like substrate is embedded inside the conductive film made of the conductive composition by applying pressure from above. At this time, the arithmetic mean roughness of the first and second releasable substrates is copied to form the surface of the conductive film. Therefore, by appropriately selecting the arithmetic mean roughness of the first and second releasable substrates, the desired arithmetic mean roughness can be imparted to the first and second surfaces of the obtained conductive sheet member. That is, the arithmetic mean roughness of the second releasable substrate arranged on the side that becomes the second surface of the conductive sheet member is made smaller than the arithmetic mean roughness of the first releasable substrate arranged on the side that becomes the first surface of the conductive sheet member. In the conductive sheet member obtained by this method, the arithmetic mean roughness Ra ₂ of the second surface can be made smaller than the arithmetic mean roughness Ra ₁ of the first surface.

The conductive fabric of the present invention has a structure in which the conductive sheet member is laminated on at least one surface of the base fabric. The conductive sheet member may be laminated on the entire surface of the base fabric. Alternatively, the conductive sheet member may be cut to form circuits or electrodes of a desired shape, which are then laminated on a part of the base fabric. In this case, it is essential that the second surface of the conductive sheet member is laminated on the base fabric side. In other words, of the front and back surfaces of the conductive sheet member, the surface having the smaller arithmetic mean roughness is laminated on the base fabric side. This makes it possible for the obtained conductive fabric to maintain a high level of conductivity even when repeatedly bent.

When laminating the conductive sheet member onto the surface of the base fabric, it can be laminated and fixed using known means. Various adhesives may be used, or a method may be used in which a so-called hot melt type polymer resin is used in the conductive composition that constitutes the conductive sheet member. There are no particular limitations on the hot melt type polymer resin, but examples include polyurethane resin, acrylic resin, polyester resin, polyamide resin, olefin resin, EVA resin, etc.

The conductive sheet member can be laminated on the surface of the base fabric by heat pressing or the like. For example, a hot melt resin can be laminated between the second surface side of the conductive sheet member and the base fabric, and then the hot melt resin can be laminated by heat pressing. As the hot melt resin, a sheet-like hot melt resin may be used, or a liquid hot melt resin may be applied to the second surface of the conductive sheet member. For example, a transfer press (manufactured by Hashima Co., Ltd.: model number HP-4536A-12) can be used as the heat press machine. The conditions of the heat press treatment are preferably in the range of a press temperature of 100 to 160°C and a press pressure of 50 to 500 g/ ^cm2 .

A sheet-like hot melt resin may be laminated on one side of the mesh-like substrate in advance, and the conductive composition may be applied from the other side of the mesh-like substrate to form a conductive sheet member with an adhesive layer made of hot melt resin. In this case, it is required that the arithmetic mean roughness of the surface of the sheet-like hot melt resin on the side laminated on one side of the mesh-like substrate is smaller than the arithmetic surface roughness of the mesh-like substrate. This allows the arithmetic surface roughness of the second side of the conductive sheet member to be smaller than the arithmetic mean roughness of the first side of the conductive sheet member.

Examples of the substrate fabric on which the conductive sheet member is laminated include fiber substrate fabrics such as woven fabrics, knitted fabrics, and nonwoven fabrics. Examples of the fiber material include natural fibers such as cotton, hemp, wool, and silk, regenerated fibers such as rayon and cupra, semi-synthetic fibers such as acetate and triacetate, and synthetic fibers such as polyamide (nylon 6, nylon 66, etc.), polyester (polyethylene terephthalate, polytrimethylene terephthalate, etc.), polyurethane, and polyacrylic, and two or more of these may be combined. Among them, substrate fabrics made of synthetic fibers with excellent strength and chemical resistance are preferred, and substrate fabrics made of synthetic fibers such as polyester fibers and nylon fibers are more preferred. The thread may be a monofilament thread or a multifilament thread formed by bundling multiple fibers. The fineness of the thread is not particularly limited, but is preferably 10 to 170 dtex. The substrate fabric may be dyed, antistatically treated, flame-retardant, calendared, etc., as necessary. The thickness of the base fabric is not particularly limited, but is preferably 0.02 to 1.00 mm. If the thickness of the base fabric is within the range of 0.02 to 1.00 mm, it can maintain a suitable texture and flexibility even after laminating the conductive sheet.

Example 1
A polyester mesh fabric: T230-40 (manufactured by Yamani Co., Ltd.: arithmetic mean roughness 0.67 μm, thickness T _B = 60 μm) using monofilament (wire diameter 40 μm) for both warp and weft threads as a mesh-like substrate was prepared. The opening ratio of this polyester mesh fabric was 40%. A release substrate having an arithmetic mean roughness of the surface of 0.26 μm was attached to one side of this mesh-like substrate, and CI-1036 (manufactured by Engineered Materials Systems) containing silver particles (blending ratio 50 to 60 mass%) as a conductive composition ink was applied to the opposite side of the mesh-like substrate by screen printing. The screen printer used was SSA-PC560A (manufactured by Seria Engineering Co., Ltd.). The printing conditions are shown in Table 1.

After printing, the sheet was dried at 100°C for 10 minutes in a constant temperature dryer DRS620DA (manufactured by Toyo Seisakusho Co., Ltd.) to form a conductive film (thickness T _M = 66 μm) to obtain a conductive sheet member. The surface on which the release substrate was attached was the second surface, and the Ra ₂ /Ra ₁ value of the obtained conductive sheet member was 0.22. The mesh substrate was not exposed on the first surface of the obtained conductive sheet member, and the area ratio of the mesh substrate exposed on the second surface was 16.3%. A hot melt sheet UH203 (manufactured by Nihon Matai Co., Ltd.) was attached to the second surface of the conductive sheet member, and the sheet was cut out to a width of 1 mm and a length of 120 mm. In addition, a polyester plain weave fabric TE5880 (warp thread 30 dtex/36f; 192 threads/inch, weft thread 62 dtex/150f; 122 threads/inch), which is a substrate fabric, was cut out to a width of 10 mm and a length of 120 mm. The conductive sheet member cut out from the central portion in the width direction of the base fabric was laminated and adhered to the substrate fabric to obtain a conductive fabric.

Example 2
A conductive fabric was obtained in the same manner as in Example 1, except that T300-35 (manufactured by Yamani Co., Ltd.: arithmetic mean roughness 0.38 μm, thickness T _B = 54 μm) with an opening ratio of 35% and a wire diameter of 35 μm was used as the mesh-like substrate. The surface to which the releasable substrate was attached was designated as the second surface, and the Ra ₂ /Ra ₁ value of the obtained conductive sheet member was 0.35. The mesh-like substrate was not exposed on the first surface of the obtained conductive sheet member, and the area ratio of the mesh-like substrate exposed on the second surface was 18.2%.

(Comparative Example 1)
A conductive fabric was obtained in the same manner as in Example 1, except that the first surface side of the conductive sheet member was laminated onto the base fabric.

(Comparative Example 2)
A conductive fabric was obtained in the same manner as in Example 2, except that the first surface side of the conductive sheet member was laminated onto the base fabric.

A bending test was performed on the conductive fabrics obtained in the above examples and comparative examples using a DLD111L tabletop durability tester (manufactured by Yuasa System Co., Ltd.), and the resistance values before and after the bending test were measured using an RM3545-02 (manufactured by Hioki E.E. Corporation). The bending conditions consisted of bending the conductive fabric 180° so that the surface on which the conductive sheet member was laminated was on the inside, and bending was repeated 20,000 times with a bending radius of 2 mm. The rate of increase in resistance after the bending test relative to the resistance before the bending test was calculated as the resistance increase rate (%), and is shown in Table 2. It can be said that the lower the resistance increase rate (%), the higher the bending durability of the conductivity.

1: Conductive fabric
2: Conductive sheet member 3: Conductive film (cured conductive composition)
4: Mesh-like substrate 5: Adhesive 6: Substrate fabric S ₁ : First surface S ₂ : Second surface T _B : Thickness of mesh-like substrate T _M : Thickness of conductive film

Claims (4)

A conductive fabric is formed by laminating a conductive sheet member, which is formed by embedding a mesh-shaped substrate inside a conductive film made of a conductive composition, on a surface of a substrate fabric,
The mesh-like substrate has openings so that the opening ratio is 30% or more,
an arithmetic mean roughness Ra ₁ (unit: μm) of a first surface of the conductive sheet member and an arithmetic mean roughness Ra ₂ (unit: μm) of a second surface of the conductive sheet member satisfy a relationship of Ra ₁ >Ra ₂ ;
A conductive fabric characterized in that the second surface of the conductive sheet member is laminated on the base fabric side. The conductive fabric according to claim 1, characterized in that the ratio of the arithmetic mean roughness Ra ₁ (unit: μm) of the first surface of the conductive sheet member to the arithmetic mean roughness Ra ₂ (unit: μm) of the second surface of the conductive sheet member, Ra ₂ /Ra _1, is within the range of 0.1 to 0.5. The conductive fabric according to claim 1 or 2, wherein the second surface of the conductive sheet member has an arithmetic mean roughness _Ra2 in the range of 0.1 to 1.0 μm. The conductive fabric according to any one of claims 1 to 3, characterized in that a portion of the mesh-like substrate is exposed on the second surface of the conductive sheet member.

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