JP2008218060A - Transparent conductive film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent conductive film capable of sufficiently suppressing the occurrence of Newton ring when used for a touch panel while maintaining the favorable durability. <P>SOLUTION: The transparent conductive film comprises a substrate 10, a transparent conductive layer 20 disposed on one surface of the substrate 10, and an intermediate layer interposed between the transparent conductive layer 20 and the substrate 10 and including binder resin 31 and a plurality of resin particles 32 dispersed in the binder resin 31. The plurality of resin particles 32 are unified to one another as one body. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transparent conductive film.

  A resistance touch panel (hereinafter referred to as “touch panel”) generally has a configuration including a pair of transparent electrodes facing each other. When one transparent electrode of the touch panel is pressed, the pressed portion comes into contact with the other transparent electrode, and electricity is generated. A pressed portion is detected based on this energization. The transparent electrode conductive film is often used as a transparent conductive film on the pressed side (upper electrode), and generally has a configuration in which a transparent conductive layer is provided on a substrate such as a transparent film.

  In the touch panel, Newton rings generated when the transparent conductive film is pressed may be a problem. In the vicinity of the pressing part, the Newton ring is reflected on the surface of the transparent conductive layer of the transparent conductive film distorted by pressing, and on the surface of the transparent conductive layer of the transparent conductive film on the opposite side through the transparent conductive film. This is thought to be caused by interference with the reflected light. When Newton rings are generated, the visibility of the display device provided with the touch panel is lowered. Therefore, it is desired to suppress the generation as much as possible.

As a method for suppressing the occurrence of Newton rings, methods for forming a transparent conductive film on a surface roughened by embossing or etching have been proposed (Patent Documents 1 and 2). In addition, a transparent conductive film in which a transparent conductive layer is provided on a hard coat layer having an uneven surface formed of particles has also been proposed (Patent Document 3).
JP 7-169367 A JP-A-8-281856 JP 11-291383 A

  However, according to the study by the present inventors, in the case of the conventional method by roughening or uneven shape, although the generation of Newton rings is suppressed to some extent, there is a problem that the durability of the transparent conductive film is lowered. It became clear that there was. If the durability of the transparent conductive film is insufficient, stress is concentrated in a narrow area when repeatedly pressed, the transparent conductive film is damaged, and the electrical resistance value of the transparent conductive layer may fluctuate greatly.

  Then, an object of this invention is to provide the transparent conductive film which can fully suppress generation | occurrence | production of a Newton ring when used for a touch panel, maintaining favorable durability.

  The transparent conductive film according to the present invention includes a base material, a transparent conductive layer provided on one side of the base material, and the transparent conductive layer and the base material, and a binder resin and a plurality of resin particles And an intermediate layer in which at least some of the plurality of resin particles are combined and integrated with each other.

  When the transparent conductive film according to the present invention is used for the transparent electrode on the pressed side of the touch panel, the resin particles and the binder resin when light transmitted through the transparent conductive film on the pressed side passes through the intermediate layer. It is scattered by the difference in refractive index and the like. As a result, interference between reflected lights due to the optical path difference is less likely to occur, and the occurrence of Newton rings is suppressed. Further, according to the study by the present inventors, a plurality of resin particles are combined and integrated with each other, and the resin particles and the binder resin are compatible with each other in the vicinity of the interface. It is believed that the durability of the film is maintained at a good level.

  The resin particles may be unevenly distributed on the transparent conductive layer side or the substrate side in the thickness direction of the intermediate layer.

  When the resin particles are unevenly distributed on the transparent conductive layer side, light scattering can be more efficiently generated and durability can be improved.

  When the resin particles are unevenly distributed on the substrate side, for example, heating the resin particles arranged on the substrate and fusing the resin particles together to combine and integrate the resin particles; It can be easily manufactured by a method including a step of forming a transparent conductive layer separately from this step. According to this method, the transparent conductive layer can be prevented from being deteriorated by heating for fusing the resin particles.

  According to the transparent conductive film of the present invention, it is possible to sufficiently suppress the occurrence of Newton rings when used in a touch panel while maintaining good durability.

  Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

  FIG. 1 is a cross-sectional view schematically showing one embodiment of a transparent conductive film. A transparent conductive film 1 shown in FIG. 1 includes a base material 10, a transparent conductive layer 20 provided on one surface side of the base material 10, and an intermediate layer 30 interposed between the transparent conductive layer 20 and the base material 10. Consists of When using the transparent conductive film 1 as a transparent electrode of a touch panel, for example, a pair of transparent conductive films 1 are used in a state in which the transparent conductive layer 20 is bonded through a spacer so that the transparent conductive layer 20 faces inward.

  The intermediate layer 30 is a layer including a binder resin 31 and a plurality of spherical resin particles 32 dispersed in the binder resin 31. The resin particles 32 are dispersed in the binder resin 31 in the form of a combined body composed of a plurality of spherical resin particles 32 that are bonded together and integrated.

  The bonded body of resin particles can be formed, for example, by a method in which the resin particles are heated and fused together. This heating may be performed with the resin particles dispersed in an uncured binder resin. When the resin particles are combined and integrated with each other by heating in a state of being dispersed in an uncured binder resin, the resin particles and the binder resin are compatible with each other at the interface and the reinforcing effect by the resin particles is strengthened. Further, the effect of improving the durability can be obtained more remarkably. The heating conditions are appropriately adjusted so that the resin particles are fused together in consideration of the melting point of the resin particles. Specifically, the combined body is appropriately formed usually by heating at 80 to 120 ° C. for about 30 minutes to 1 hour. FIG. 2 is a photomicrograph of an example of the resin particles 32 in which a plurality of combined bodies are formed by such a method.

  The resin particles 32 have a refractive index different from that of the binder resin 31. From the viewpoint of enhancing the Newton ring prevention effect, the difference in refractive index between the resin particles 32 and the binder resin 31 is preferably 0.02 to 0.1.

  Moreover, it is preferable that the resin particle 32 has a glass transition temperature of 20 degrees C or less. Thereby, the softness | flexibility of a transparent conductive film improves and durability improves more notably.

  The resin particles 32 are substantially spherical particles made of resin. Preferable specific examples of the resin constituting the resin particle 32 include acrylic resin, polystyrene, polyester, polyolefin, polyamide, polycarbonate, polyurethane, silicone resin, and fluororesin. These may be copolymers obtained by copolymerizing two or more types of monomers. Among these, the resin particles 32 are preferably particles composed of a resin different from the binder resin. For example, when the binder resin is an acrylic resin, the resin particles 32 are preferably polyurethane particles composed of polyurethane.

  It is preferable that a reactive substituent that is bonded to the binder resin 31 is introduced on the surface of the resin particle 32. Examples of reactive substituents include groups having an ethylenic double bond such as an acryloyl group, a methacryloyl group, and a styrene group, and epoxy groups, hydroxyl groups, carboxyl groups that react in the presence of water, acid, alkali, catalyst, or heat. , A group having an alkoxyl group, an acyl group, or an amino group.

  The ratio of the resin particles 32 in the intermediate layer 30 is preferably 20 to 60% by volume. By making the ratio of the resin particles 32 within this range, the effect of Newton ring suppression is particularly remarkable.

  As in the embodiment of FIG. 1, it is not always necessary that all of the resin particles 32 in the intermediate layer 30 form a combined body, and the resin particles are dispersed individually without departing from the gist of the present invention. 32 may be present. Specifically, it is preferable that 30% or more of the total number of the resin particles 32 forms a bonded body.

  The binder resin 31 is not particularly limited as long as it is a transparent resin that can fix the resin particles 32. The binder resin 31 is typically formed of a light or thermosetting resin composition. As the resin composition used for forming the binder resin 31, for example, an acrylic resin composition containing an acrylic monomer having a (meth) acryl group is used. This acrylic resin composition preferably contains a polymer having a (meth) acryl group, an acrylic monomer having a (meth) acryl group, and a photopolymerization initiator.

  The transparent conductive layer 20 is a layer containing, for example, a binder resin and a plurality of transparent conductive particles aggregated in the binder resin. The binder resin constituting the transparent conductive layer 20 is typically formed of a light or thermosetting resin composition, like the binder resin 31. The binder resin of the transparent conductive layer 20 and the binder resin 31 of the intermediate layer 30 may be made of the same type of resin, or may be made of different resins. The interface between the two is not necessarily clear, and they may be integrated to form a single phase.

  The transparent conductive particles are composed of a transparent conductive oxide. Specific examples of the transparent conductive oxide include indium oxide, indium oxide doped with at least one element selected from the group consisting of tin, zinc, tellurium, silver, gallium, zirconium, hafnium, and magnesium. Tin, tin oxide doped with at least one element selected from the group consisting of antimony, zinc and fluorine, zinc oxide, and zinc oxide from the group consisting of aluminum, gallium, indium, boron, fluorine and manganese One doped with at least one selected element can be mentioned. Among these, most typically, particles of indium tin composite oxide (ITO) in which tin is doped into indium oxide are used as transparent conductive particles.

  The ratio of the transparent conductive particles to the transparent conductive layer 20 is preferably 30 to 80% by volume. When this ratio is less than 30% by volume, the resistance value of the transparent conductive layer 20 tends to increase, and when it exceeds 80% by volume, the mechanical strength of the transparent conductive film 1 tends to decrease.

  Although the base material 10 will not be restrict | limited especially if it is a film-form thing which can support the intermediate | middle layer 30 and the transparent conductive layer 20, A transparent film is used suitably. Specifically, a film of polyester such as polyethylene terephthalate (PET), polyolefin such as polyethylene and polypropylene, polycarbonate, acrylic resin, polynorbornene resin, or polysiloxane resin is used as the substrate 10. Alternatively, a glass substrate may be used as the base material 10.

  The transparent conductive film 1 includes, for example, a step of forming a resin particle layer including a binder resin 31 and a resin particle 32 made of an uncured photocurable resin composition on the base material 10, and a resin by heating the resin particle layer. A step of fusing the particles 32 together to form a combined body in which a plurality of resin particles 32 are bonded together, a step of curing the binder resin 32 by light irradiation to form the intermediate layer 30; And a step of forming the transparent conductive layer 20 on the layer 30. When bonding the resin particles, the resin particle layer is preferably heated at a temperature equal to or higher than the glass transition temperature of the resin particles.

  The transparent conductive layer 20 includes, for example, a step of preparing a dispersion liquid containing transparent conductive particles, a binder resin, and a solvent in which transparent conductive particles are dispersed, a step of applying the dispersion liquid on the intermediate layer 30, and a coating step. It is formed by a method including a step of removing the solvent from the dispersed liquid and a step of curing the binder resin by light irradiation or heating. In this case, instead of performing light irradiation before forming the transparent conductive layer as described above, a step of applying a dispersion on a resin particle layer containing an uncured binder resin, and a binder in the resin particle layer A transparent conductive film may be obtained through a step of curing the resin and the binder resin in the dispersion by light irradiation to form an intermediate layer and a transparent conductive layer. Thus, manufacturing efficiency can be improved by hardening the binder resin which comprises an intermediate | middle layer and a transparent conductive layer simultaneously.

  Alternatively, the transparent conductive layer is formed on the dummy substrate by a method including a step of applying the dispersion on the dummy substrate, a step of removing the solvent from the applied dispersion, and a step of curing the binder resin by light irradiation or heating. A transparent conductive film may be obtained through a process of forming the transparent conductive layer on the intermediate layer from the dummy substrate. According to this method, a transparent conductive film in which the resin particles are unevenly distributed on the substrate side in the intermediate layer can be easily obtained.

  Although it does not specifically limit as a solvent used for the dispersion liquid which disperse | distributes transparent conductive particles, Organic solvents, such as toluene, xylene, methyl isobutyl ketone, and methyl ethyl ketone, are used suitably. The dispersion is obtained, for example, by dispersing transparent conductive particles in a solvent by a bead mill and mixing this with a binder liquid containing an uncured binder resin.

  It goes without saying that the present invention is not limited to the embodiment as described above. For example, the resin particles may be unevenly distributed on the transparent conductive layer side in the thickness direction of the intermediate layer. In this case, continuous reflection between the opposing transparent conductive layer surfaces can be further efficiently reduced. In addition, the ratio of the binder resin in the vicinity of the interface with the base material is increased, so that the adhesion of the intermediate layer to the base material is improved, and the stress applied to the transparent conductive layer is reduced when the transparent conductive film is pressed. Is prompted. This makes it possible to obtain a particularly remarkable durability improvement effect. Alternatively, the resin particles may be unevenly distributed on the substrate side in the thickness direction of the intermediate layer. Such a transparent conductive film in which resin particles are unevenly distributed can be obtained, for example, by forming the intermediate layer in two stages of a layer containing resin particles and a layer not containing resin particles. Further, another layer may be provided between the base material and the intermediate layer. Examples of the other layers include layers having functions such as a buffer layer, a conductive auxiliary layer, a diffusion preventing layer, an ultraviolet shielding layer, a colored layer, and a polarizing layer.

  The transparent conductive film according to the present invention is suitably used as a transparent electrode of a touch panel. The touch panel is, for example, a pair of transparent conductive films having a base material and a transparent conductive layer provided on one surface side of the base material, and the pair of transparent conductive layers disposed facing each other with the transparent conductive layers facing inward. A conductive film and a spacer interposed between the pair of transparent conductive films are provided.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

Example 1 Production of Transparent Conductive Film
A polyethylene terephthalate (PET) film (manufactured by Teijin Ltd., 100 μm thickness) was prepared as a substrate. Contains acrylic polymer (average molecular weight of about 200,000, containing 20 acryloyl groups on average per molecule) and polyurethane particles (average particle size 15 μm, glass transition temperature −45 ° C.), and the proportion of polyurethane particles is 20% by volume of the total 2 parts by weight of a mixture, 4 parts by weight of polyethylene glycol dimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: 23G), and dipentaerythritol hexaacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: A- 1 part by weight of DPH), 3 parts by weight of ethoxylated bisphenol A diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: A-BPE-10), and a photopolymerization initiator (manufactured by Ciba Specialty Chemicals Co., Ltd.) Product name: IRGACURE 369) 0.1 parts by mass and methyl ethyl ketone (MEK) 500 parts by mass , To prepare a coating solution by mixing. The polyurethane particles used had acryloyl groups introduced on the surface.

This coating solution was applied onto a PET film by a bar coating method, and MEK was volatilized and polyurethane particles were fused by a heat treatment at 120 ° C. for 1 hour to form a bonded body. Thereafter, the resin was cured by UV irradiation with an integrated illuminance of 1000 mJ / cm ^{2 using} a high pressure mercury lamp as a light source.

60% by volume of ITO powder (average particle size 30 nm), 20 parts by mass of acrylic polymer (average molecular weight of about 150,000, average 30 acryloyl groups and 25 trimethoxysilyl groups per molecule), and ethoxylated bisphenol 15 parts by mass of A diacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: ABE-300), 10 parts by mass of dipentaerythritol hexaacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: A-DPH), 5 parts by weight of trimethylolpropane trimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: TMPT), 1 part by weight of a photopolymerization initiator (manufactured by Ciba Specialty Chemicals Co., Ltd., trade name: IRGACURE 819), and methyl ethyl ketone ( A paste was prepared by mixing 100 parts by mass of MEK). This paste was applied to the upper surface of the intermediate layer by a bar coating method, and MEK was volatilized to form a transparent conductive layer having a thickness of 5 μm. The transparent conductive layer was irradiated with UV having an integrated illuminance of 3000 mJ / cm ^{2 using} a high pressure mercury lamp as a light source in a nitrogen atmosphere to cure the acrylic resin composition. By the above procedure, a transparent conductive film in which an intermediate layer and a conductive particle layer were formed in this order on a PET film was obtained.

Example 2
A transparent conductive film was obtained in the same manner as in Example 1 except that acrylic resin (acrylic copolymer) particles (average particle size: 10 μm) were used instead of the polyurethane particles.

Example 3
A transparent conductive film was obtained in the same manner as in Example 1 except that polystyrene copolymer particles (average particle size: 5 μm) containing styrene were used instead of the polyurethane particles.

Comparative Example 1
A transparent conductive film was obtained in the same manner as in Example 1 except that the polyurethane particles were not used.

Comparative Example 2
For comparison, a commercially available ITO sputter film in which a silica layer is formed by sputtering on an embossed PET film and an ITO layer is formed on the silica layer by sputtering is used as a transparent conductive film. Using.

Durability Evaluation of Transparent Conductive Film A 50 mm square test piece was cut out from each of the transparent conductive films of the above Examples and Comparative Examples. Using a four-terminal four-probe surface resistance measuring instrument (MCP-T600 manufactured by Mitsubishi Chemical Corporation), the electrical resistance value is measured as the initial resistance value at a measurement point near the predetermined center of the transparent conductive layer surface of the test piece. did.

  Next, the test piece was wound around a metal cylinder having a diameter of 5 mm so that the transparent conductive layer was on the outside. Thereafter, the resistance value of the surface of the transparent conductive layer of the test piece peeled off from the cylinder was measured in the same manner as described above. The obtained measured value was taken as the resistance value after the test. Then, the ratio of the resistance value after the test to the initial resistance value was calculated, and this was used as the resistance change rate. The obtained results are shown in Table 1.

Newton ring A test piece of 50 mm square was cut out from each transparent conductive film obtained above. Next, a double-sided adhesive tape having a size of 5 mm × 45 mm and a thickness of 100 μm was attached to the surface of the transparent conductive layer so that a square frame of 50 mm × 50 mm was formed. A 50 mm × 50 mm glass plate was bonded to the double-sided pressure-sensitive adhesive tape while being aligned with the frame of the attached double-sided pressure-sensitive adhesive tape. This obtained the test touch panel by which the transparent conductive film and the glass plate were arrange | positioned facing. Near the center of the transparent conductor of the obtained touch panel, a polyacetal pen having a pointed portion of R = 0.8 was brought into contact, and a load of 200 g was applied in that state. The presence or absence of Newton rings at that time was confirmed visually. The results are shown in Table 1.

  As shown in Table 1, in the case of the example in which the intermediate layer containing the binding particles was formed, the generation of Newton rings in the touch panel was not recognized. The resistance change rate was small, and the durability was further improved as compared with Comparative Example 1 in which no binding particles were used. On the other hand, in the case of Comparative Example 2 in which an uneven shape was formed on the surface of the transparent conductive layer by using an embossed PET film, the generation of Newton rings was not recognized, but the resistance value changed greatly. As a result, a significant decrease in durability was observed.

  From the above results, according to the present invention, it is possible to provide a transparent conductive film capable of sufficiently suppressing the occurrence of Newton rings when used in a touch panel while maintaining good durability. confirmed.

It is sectional drawing which shows one Embodiment of a transparent conductive film. It is a microscope picture which shows an example of the state with which the some resin particle couple | bonded together and was integrated.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Transparent conductive film, 10 ... Base material, 20 ... Transparent conductive layer, 30 ... Intermediate | middle layer, 31 ... Binder resin, 32 ... Resin particle | grains.

Claims (4)

A substrate;
A transparent conductive layer provided on one side of the substrate;
An intermediate layer that is interposed between the transparent conductive layer and the substrate, and includes a binder resin and a plurality of resin particles, and at least some of the plurality of resin particles are combined and integrated with each other;
A transparent conductive film comprising:   The transparent conductive film according to claim 1, wherein the resin particles are unevenly distributed on the transparent conductive layer side or the base material side in the thickness direction of the intermediate layer.   The transparent conductive film according to claim 1, wherein the resin particles are unevenly distributed on the transparent conductive layer side in the thickness direction of the intermediate layer. The transparent conductive film according to claim 1, wherein the resin particles are unevenly distributed on the substrate side in the thickness direction of the intermediate layer.