Stretchable conductor sheet and paste for forming stretchable conductor sheet

Abstract

A first object of the present invention is to provide a stretchable conductor sheet that exhibits isotropic conductivity when stretched in a predetermined direction or in a direction perpendicular to the predetermined direction, and a paste for forming a stretchable conductor sheet, which is used for the stretchable conductor sheet. A second object of the present invention is to provide a stretchable conductor sheet having a small change in specific resistance even when repeatedly twisted, and a paste for forming a stretchable conductor sheet, which is used for the stretchable conductor sheet. A third object of the present invention is to provide a stretchable conductor sheet having a small change in specific resistance even when repeatedly washed, and a paste for forming a stretchable conductor sheet, which is used for the stretchable conductor sheet. The first object of the present invention can accomplish a stretchable conductor sheet having a thickness of 3 to 800 μm, the stretchable conductor sheet comprising at least conductive particles, inorganic particles surface-treated with a hydroxide and / or an oxide of one or both of Al and Si, and a flexible resin having a tensile elastic modulus of 1 MPa or more and 1000 MPa or less, wherein in each of two orthogonal directions, a specific resistance change ratio of the sheet at a time of elongation by 40% with respect to an original length is less than ±10% in an elongation direction.

Description

TECHNICAL FIELD[0001]The present invention relates to a stretchable conductor sheet used for an electrical wiring or the like. In particular, the present invention relates to a stretchable conductor sheet which has improved durability against repeated elongation and which can be used for a wiring portion, an electrode portion or the like when incorporating electronics into a garment (an item of clothing) or the like, and a paste for forming a stretchable conductor sheet, which is used for the stretchable conductor sheet.BACKGROUND ART[0002]Recently a wearable electronic device intended to use an electronic device having input / output function, calculation function, and communication function in a state of being very close to or in close contact with a body has been developed. As such a wearable electronic device, devices with an accessory-type shape such as a wristwatch, eyeglasses, and earphones, and a textile-integrated device where electronic functions are incorporated into a garm...

AI Technical Summary

Benefits of technology

[0032]It is well known that a stretchable conductor composition including a conductive filler and a binder resin generally develops direction-dependent anisotropy in conductivity depending on an extrusion direction in sheet formation, or an application direction. Efforts have been made to minimize anisotropy in conductivity by an engineering technique to the extent that anisotropy in conductivity is normally negligible. However, it has been found that repeated cutoff of a conductive path by microcracks generated due to elongation deteriorated the conductivity of a sheet obtained from the stretchable conductor composition. The microcracks are easily generated in a direction perpendicular to an elongation direction when first elongation occurs. When elongation occurs in different directions after second and subsequent elongations, deformation in different directions is reduced by the deformation centering on the mic racks generated first. Thus, once a sheet and film of the stretchable conductor composition is elongated, anisotropy is resultantly developed in conductivity.

[0033]On the other hand, in the first embodiment of the present invention, the composition and sheet contains specific inorganic particles. Normally, since non-conductive inorganic particles hinder conductivity, use of non-conductive inorganic particles in a conductive composition containing a conductive filler and a binder resin is not preferred except that an extremely small amount of nano-sized silica particles are added for the purpose of improving printing property and the like. However, according to the first embodiment of the present invention, inorganic particles surface-treated with a hydroxide and / or an oxide of one or both of Al and Si improve dispersibility of the inorganic particles in a flexible resin, the inorganic particles function as a key factor in resin deformation when the resin portion is deformed by an external force, the resin shrinks with the key factor as a local center when shrinking after removal of the external force, and therefore the resin is more easily restored to a shape close to that before stretching as compared to a case where the key factor is not present. Therefore, generation of microcracks in first elongation deformation can be suppressed, and inorganic particles decentralize the orientation of microcracks, resulting in development of such an excellent effect that anisotropy in X and Y directions is considerably improved.

[0034]In addition, according to the first embodiment of the present invention, it is possible to efficiently produce a wiring such as a horseshoe-shaped wiring (corrugated wiring) from a stretchable conductor sheet having isotropic conductivity.

[0035]In addition, according to the second embodiment of the present invention, it is possible to reduce a change in specific resistance even when the wiring is repeatedly twisted (hereinafter, sometimes referred to as twist resistance). The effect (twist resistance) may be developed in accordance with the following action mechanism That is, when the resin portion is two-dimensionally deformed by twist, inorganic particles function as a key factor in resin deformation, and when the resin portion deformed by elongation in the plane direction is restored to an original state, the resin returns to an initial state with the key factor as a local center. Therefore, restoration anisotropy is reduced. When this mechanism is extended to three-dimensional deformation, the same effect is developed in the thickness direction by using inorganic particles having a smaller aspect ratio, the inorganic particles also function as a key factor in resin deformation for three-dimensional deformation such as twist, and the resin returns to an initial state with the key factor as a local center in removal of twist, so that the resin is more easily restored to a shape close to that before twist as compared to a case where the key factor is not present, and for example, the restoring force after twist in a predetermined direction (e.g. positive direction) is equal to the restoring force after twist in a direction (e.g. negative direction) opposite to the predetermined direction. Thus, even when twist is repeatedly applied due to washing or dressing, a change in specific resistance can be reduced.

[0036]On the other hand, when the stretchable conductor sheet of the present invention is used for a horseshoe-shaped wiring (corrugated wiring)(see FIG. 7), deformation is absorbed by twist resistance rather than stretch resistance, and thus the stretching ratio is substantially reduced, so that stretching durability is further improved.

[0037]Further, the present inventors have observed many cases where conductivity is reduced when a garment having an electrical wiring obtained from the stretchable conductor sheet is washed. The present inventors have found that such reduction of conductivity is caused by fine cracks generated in the stretchable conductor sheet and falling / loss of a part of the stretchable conductor sheet, and that partial falling of the stretchable conductor sheet is caused by buckling failure of the stretchable conductor sheet due to compression. Thus, the stretchable conductor sheet of the third embodiment of the present invention includes a predetermined range of voids therein. Normally, in a conductive composition containing a conductive filler and a matrix resin, such voids are not preferred because they inhibit conductivity. However, the present inventors have found that moderately controlled voids develop a dynamic cushioning effect of absorbing compressive deformation to prevent buckling failure due to compression. As a result, a change in specific resistance in repeated occurrence of compressive deformation can be reduced (i.e. compression resistance can be imparted), and washing resistance can be improved.

Problems solved by technology

However, it is clear that such a method is not suitable for mass production.

However, metal foil varies also in the thickness direction due to the twist deformation, and thus if the metal foil is used as a part of a garment, the garment has uncomfortable wearing feeling, which is not preferable.

In addition, when the metal foil undergoes excessive deformation due to washing or the like, permanent plastic deformation occurs in the metal foil, and the wiring may have the problem of the durability.

Images