TW202413553A - Transparent conductive film capable of being properly used in touch sensors due to bendability and high water resistance - Google Patents

Abstract

Provided is a transparent conductive film, which includes a substrate; a metal nanowire layer disposed on the substrate; and a water-blocking protective layer having water-absorbent particles and disposed on the metal nanowire layer. When subjected to FTIR detection, the transparent conductive film has a first absorption peak in a wave number region of 2750 cm-1 to 3000 cm-1, and a second absorption peak in a wave number region of 3000 cm-1 to 3750 cm-1. The maximum peak intensity ratio of the first absorption peak and the second absorption peak is 0.18 to 0.50, and the haze value of the transparent conductive film is 1.7% or less. The transparent conductive film of the present invention can improve bending resistance and visibility of the transparent conductive film of the prior art. Due to bendability and high water resistance, the transparent conductive film of the present invention can be properly used in touch sensors.

Description

Transparent conductive film

The present invention relates to a transparent conductive film, in particular to a bendable transparent conductive film containing silver nanowires and having high water-blocking properties.

Transparent conductive films containing silver nanowire layers have long been used in touch sensing electrodes for touch sensors.

For example, the patent TWI675895 discloses a transparent conductive sheet, which at least comprises: a conductive layer using a metal material as a conductive substance, and an adhesive layer in contact with the conductive layer. Furthermore, the adhesive layer comprises an acrylic copolymer containing a hydrophilic acrylic monomer as a copolymer component, and at least one migration inhibitor selected from the group consisting of a moisture absorbent and a metal ion scavenger.

Thus, the transparent conductive sheet of TWI675895 patent can suppress the occurrence of disconnection or short circuit due to the migration of the metal material constituting the conductive layer.

However, since the touch sensing electrode is located in the visible area of the touch panel, the concentration of the hydrophilic monomer in the adhesive layer is usually as high as 15% or more in the prior art such as the TWI675895 patent, which will affect the visibility of the electrode (including visible light transmittance and haze). In addition, the moisture absorber and metal ion capture agent contained in the adhesive layer will also affect the visibility of the electrode, thus adversely affecting the visibility of the entire touch panel.

In addition, the thickness of the adhesive layer is also related to the visibility of the overall touch electrode. Therefore, how to maintain the electrical properties of the conductive film and maintain good visibility while having the function of bending resistance has become an urgent problem to be solved.

To solve the above problems, the present invention includes a transparent conductive film in one embodiment, which includes: a substrate; a metal nanowire layer disposed on the substrate; a water-blocking protective layer having water-absorbing particles and disposed on the metal nanowire layer; wherein, the transparent conductive film has a first absorption peak in the wave number region of 2750 cm ^-1 -3000 cm ^-1 and a second absorption peak in the wave number region of 3000 cm ^-1 -3750 cm ^-1 using Fourier transform infrared spectroscopy (FTIR), the maximum peak intensity ratio of the first absorption peak to the second absorption peak (second absorption peak/first absorption peak) is 0.18-0.50, and the haze value of the transparent conductive film is less than 1.7%.

In one embodiment, a ratio of a spectral integration area of the first absorption peak to a spectral integration area of the second absorption peak is 0.618-1.410.

In one embodiment, the transparent conductive film includes a plurality of electrodes formed of metal nanowires.

In one embodiment, the line spacing between the plurality of electrodes is 30-200 μm.

In one embodiment, the transparent conductive film has a line resistance variation rate of less than 10% under the test conditions of direct current and voltage 5V, high temperature and high humidity environment 85°C/85%, when the line spacing is x μm and the power is on for y hr, wherein x and y satisfy the following relationship: y=0.53179x+364.47977.

In one embodiment, after the transparent conductive film is powered on for 400 hours under the test conditions of direct current and voltage 5V, high temperature and high humidity environment 85℃/85%, its line resistance change rate is less than 10%.

In one embodiment, the visible light transmittance of the transparent conductive film is 92-97%.

In one embodiment, the yellowness (b*) of the transparent conductive film is less than 0.5.

In one embodiment, the thickness of the water-blocking protective layer is 1-15 μm.

In one embodiment, the volume percentage of the water-absorbing particles in the water-blocking protective layer is 1-5%.

The transparent conductive film of the present invention can improve the problems of the prior art transparent conductive film such as the inability to withstand bending and poor visibility. Moreover, since the transparent conductive film of the present invention has the properties of being bendable and highly water-resistant, it can be appropriately applied to touch sensors.

The following is a description of the implementation of the present invention through specific embodiments. People skilled in the art can understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified and changed based on different viewpoints and applications without departing from the spirit of the present invention.

Unless otherwise specified in the context, the singular forms "a", "an" and "the" used in the specification and the attached patent claims include plural meanings.

Unless otherwise specified in the text, the term "or" used in the specification and the attached patent claims includes the meaning of "and/or".

Unless otherwise specified in the text, the term "A~B" used in the specification and the attached patent application scope includes the meaning of "above A and below B". For example, the term "30~150 μm" includes the meaning of "above 30 μm and below 150 μm".

<Transparent conductive film> First, please refer to FIG. 1 to explain a transparent conductive film 10 of an embodiment of the present invention. As shown in FIG. 1 , the transparent conductive film 10 includes: a substrate 1, a metal nanowire layer 2, and a water-blocking protective layer 3. The metal nanowire layer 2 is disposed on the substrate 1, and the water-blocking protective layer 3 is disposed on the metal nanowire layer 2.

As for the material of the substrate 1, any one of the group consisting of polyethylene terephthalate (PET), cycloolefin copolymer (COP), colorless polyimide (CPI), polyethylene naphthalate (PEN), polycarbonate (PC) and polyethersulfone (PES) can be selected. In addition, as for the thickness of the substrate 1, it can be 15-125 μm, preferably 25-100 μm, and more preferably 30-50 μm. Here, if the thickness of the substrate 1 is less than 15 μm, it is difficult to operate in the process, and the tension is not well controlled and it is easy to cause film breakage, which increases the difficulty of the process; on the other hand, if the thickness of the substrate 1 is greater than 125 μm, it will affect the overall optics and flexibility.

Next, as for the metal nanowire layer 2, it includes metal nanowires covered by the covering layer, and any metal nanowires can be used, including but not limited to: silver, gold, copper, nickel, and gold-plated silver. Among them, from the perspective of cost and conductivity, silver nanowires are preferred, and their manufacturing methods can refer to US Patents US8454721B2 and US9672950B2, and the entire texts of these patents are incorporated herein by reference. Among them, the covering layer can be a polymer material with an adhesive, such as an acrylate resin such as epoxy acrylic, urethane acrylic, polyester acrylic, and polyether acrylic resins, and its purpose is to fix the silver nanowires to form the metal nanowire layer 2. Furthermore, the thickness of the metal nanowire layer 2 is preferably 20-120 nm, more preferably 30-100 nm, and most preferably 40-90 nm, and the thickness of the metal nanowire layer 2 can be measured by slicing the metal nanowire sample and performing SEM cross-sectional analysis. A metal nanowire layer 2 within this thickness range can achieve a better conductive effect in combination with the water-blocking protective layer described later.

Furthermore, as for the material of the water-blocking protective layer 3, it is mainly composed of a polymer material with a specific water permeability range, such as acrylic rubber, silicone, polyolefin rubber, polyurethane rubber, rubber, epoxy rubber, etc. In addition, the water-blocking protective layer 3 includes water-absorbing particles 4, and the volume percentage of the water-absorbing particles 4 in the water-blocking protective layer 3 is preferably 1-5%. If both the water absorption effect and the visibility requirements can be achieved, there is no need to limit the relative volume of the water-absorbing particles. As for the water-absorbing particles 4, they can include polyolefin amide polymers, including but not limited to polyethylene modified by polyimide block copolymers, etc. The main colloidal structure of the polyethylene modified by the polyimide block copolymer mentioned above is composed of 95-99% polyolefin chain segments, and the water-absorbing functional groups come from amine groups that can combine with water. Surprisingly, the water-absorbing particles 4 used in the present invention only need 1-5 volume % of the water-blocking protective layer 3 to achieve the effect of having water absorption to avoid disconnection and short circuit caused by metal (such as silver) ion migration and having overall good visibility.

Compared with the prior art, an embodiment of the present invention can effectively avoid the problem of poor overall optical properties, especially excessive haze value, by controlling the proportion of water-absorbing particles to less than 5 volume % of the water-blocking protective layer. If the proportion of water-absorbing particles is greater than 5 volume % of the water-blocking protective layer, the adhesion between the protective layer and the metal nanowire layer may be reduced, causing the overall structure of the transparent conductive film to peel off when bent, thereby causing the generation of a short circuit. On the other hand, if the proportion of water-absorbing particles is less than 1 volume % of the water-blocking protective layer, the ideal water absorption effect cannot be obtained.

In addition, the thickness of the water barrier protective layer is also related to the overall properties of the transparent conductive film. If the thickness of the water barrier protective layer increases, the adhesion between the layers can be improved and peeling can be avoided; however, if the thickness of the water barrier protective layer is too thick, it may affect the overall optical properties of the transparent conductive film. Therefore, the thickness of the water barrier protective layer is preferably 1~15 μm, more preferably 5~15 μm, and particularly preferably 5~10 μm. Here, if the thickness of the water barrier protective layer is less than 1 μm, the metal of the metal nanowire layer will be oxidized, thereby affecting the conductivity; on the other hand, if the thickness of the water barrier protective layer is greater than 15 μm, the contact impedance will increase, hindering the transmission of electrical signals.

In addition, when considering the thickness of the water-blocking protective layer, it is still necessary to consider the filling rate of the water-absorbing particles together to avoid affecting the visibility of the transparent conductive film (such as haze). Specifically, when the thickness of the water-blocking protective layer is less than 1 μm, the water-blocking protective effect may not be fully exerted; on the other hand, when the thickness of the water-blocking protective layer is greater than 15 μm, it may affect the overall optical properties of the transparent conductive film.

[Examples] The present invention is described in detail below through examples and comparative examples.

<Reference Example> PET (Toray, Inc., U483) was used as the substrate material, and the thickness of the substrate was 50 μm. Then, a nanosilver wire layer was coated on the substrate, and the thickness of the nanosilver wire layer was 40 nm. In the reference example, the transparent conductive film of the reference example was formed without coating a water-blocking protective layer.

(Measurement of optical properties) The visible light transmittance (T%), haze (%) and yellowness (b*) of the transparent conductive film can be measured by known measurement methods. For example, a desktop transmission haze meter (BYK Gardner, Haze-guard plus) can be used to measure the light transmittance and haze of the transparent conductive film by the transmission method; and a UV/visible light spectrophotometer (PerkinElmer, Lambda 650) can be used with a 150mm integrating sphere to measure the transmission spectrum, and then the yellowness (b*) can be calculated by the equation of the CIE standard observer function. In the present invention, the haze of the transparent conductive film needs to be less than 1.7%, and the visible light transmittance (T%) is preferably 92~97%, and the yellowness (b*) is preferably less than 0.5.

Then, according to the content of water-absorbing particles and the thickness of the water-blocking protective layer in Table 1 below, a water-blocking protective layer was further coated on the nanosilver wire layer of the reference example to prepare transparent conductive films of Examples 1 to 7 and Comparative Examples 1 to 2; wherein the water-blocking protective layer of each Example and Comparative Example is an acrylic glue and contains a specific content of polyethylene modified by polyimide block copolymer as water-absorbing particles. Afterwards, the optical properties of the transparent conductive films of the reference example, Examples 1 to 7 and Comparative Examples 1 to 2 were measured, and the results are summarized in Table 1 below.

[Table 1] Reference example Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Embodiment 6 Embodiment 7 Comparison Example 1 Comparison Example 2 Water-blocking protective layer Water-absorbent particles - few few few middle middle middle many many many thickness - 5µm 10µm 15µm 5µm 10µm 15µm 5µm 10µm 15µm Optical properties Visible light transmittance (T%) 93.5 93.4 93.4 93.2 93.2 93.3 93.2 92.9 92.6 92.4 Fog(%) 0.46 0.48 1.03 1.55 0.56 1.09 0.56 1.28 2.94 2.98 Yellowness(b*) 0.21 0.23 0.28 0.36 0.25 0.32 0.25 0.20 0.38 0.51

First, it can be seen from Table 1 that the transparent conductive film of the reference example has the lowest haze (0.46%) without a water-blocking protective layer. However, because nanosilver itself has an inherent electrolytic ionization problem, especially under the conditions of electricity and water vapor, silver ion migration is prone to occur, which in turn reduces the reliability of nanosilver. Therefore, the transparent conductive film of the reference example has a short life (refer to the silver migration test described later), and it is necessary to further apply a water-blocking protective layer without affecting the optical properties as much as possible.

Secondly, as shown in Table 1, after applying the water-blocking protective layer, although the water-blocking protective layer has little effect on the visible light transmittance, it has a greater effect on the haze and yellowness. It can be seen from Examples 1 to 6 that when the content of water-absorbing particles is low (about 1±0.5 volume %) or medium (about 2.5±0.5 volume %), the thickness of the water-blocking protective layer can be 5 to 15 µm, and the phenomenon of silver ion migration can be suppressed under acceptable conditions (haze value is less than 1.7% and yellowness is less than 0.5).

Furthermore, it can be seen from Table 1 that when the content of water-absorbing particles is high (about 5±0.5 volume %), if the thickness of the water-blocking protective layer is 10 µm or 15 µm (refer to Comparative Examples 1-2), the haze value rises sharply (greater than 1.7%), and the yellowness is also observed to be greater than 0.5 in Comparative Example 2, so Comparative Examples 1-2 are not good. This phenomenon is because the polarity of -CH group and -NH group in water-absorbing particles is incompatible. In Comparative Examples 1-2, the content of water-absorbing particles is too high and the water-blocking protective layer is too thick, resulting in an increase in intermolecular hydrogen bonds, so the molecular arrangement is disordered, which further causes a rapid increase in haze and yellowness. It can be seen that when the content of the water-absorbing particles is 1±0.5~2.5±0.5 volume %, even if the thickness of the water-blocking protective layer is 15 µm, the desired haze value (below 1.7%) of the present invention can be met; however, when the content of the water-absorbing particles is 5±0.5 volume %, when the thickness of the water-blocking protective layer is 10 µm or 15 µm, the desired haze value of the present invention cannot be met.

Next, for further discussion of the above phenomenon, please refer to Figure 2 and Tables 2 and 3. Figure 2 is the FTIR spectrum of the transparent conductive film of the reference example and Examples 1, 4, and 7. In addition, by normalizing the absorption spectrum intensity, the peak intensity value of each can be calculated from Figure 2, and the integrated absorption spectrum method can be used to calculate the integrated area of each spectrum from Figure 2; the results are summarized in the following Tables 2 and 3.

[Table 2] Reference example Embodiment 1 Embodiment 4 Embodiment 7 Second absorption peak intensity without 0.180127 0.173252 0.378471 First absorption peak intensity without 0.999191 0.946306 0.921892 Strength ratio - 0.180 0.183 0.411

As shown in FIG2 , because the reference example does not apply a water-blocking protective layer, the characteristic peaks of -CH and -NH from the water-absorbing particles are not observed. Also, as shown in FIG2 , the characteristic peaks of -CH can be observed at about 2945 cm ^-1 in Examples 1, 4, and 7, and the characteristic peaks of -NH can be observed at about 3450 cm ^-1 . In addition, the maximum intensity of the characteristic peaks of -CH in Examples 1, 4, and 7 is 0.922-0.999, which is relatively similar among the Examples; in contrast, the maximum intensity of the characteristic peaks of -NH is 0.173-0.378, which is relatively different among the Examples.

In addition, the maximum peak intensity ratio (second absorption peak/first absorption peak) of the characteristic peak of the -CH group (the first absorption peak in the wave number region of 2750 cm ^- 1-3000 cm- ¹ ) and the characteristic peak of the -NH group (the second absorption peak in the wave number region of 3000 cm ^- 1-3750 cm ^-1 ) in Figure 2 represents the ability to absorb water. The larger the maximum peak intensity ratio (also referred to as the intensity ratio), the better the water absorption ability. In the present invention, the maximum peak intensity ratio of the first absorption peak to the second absorption peak is 0.18~0.50. If the intensity ratio is less than 0.18, the number of NH bonds is too low to achieve sufficient water absorption/water blocking effect. In contrast, if the intensity ratio is greater than 0.50, the optical properties may decrease, and even when the thickness of the water-blocking protective layer is low (for example, 5 μm), the haze may be greater than 2%, which is not conducive to the further application of the transparent conductive film.

Specifically, since the main component of the water-absorbing particles used in the present invention is composed of polyimide, which is an organic polymer material containing an imide ring (-CO-NH-CO-), and its molecular chain contains a large number of aromatic groups (such as benzene rings, imide bonds, etc.), the polyimide material not only has excellent thermal stability and mechanical, electrical and chemical properties, but also has high water absorption properties.

In addition, as shown in FIG. 2 and Table 3 below, when the ratio of the spectral integration area of the first absorption peak to the spectral integration area of the second absorption peak (spectral integration area of the second absorption peak/spectral integration area of the first absorption peak) is 0.618~1.410, a proper balance can be achieved between the water absorption characteristics and the optical properties.

[table 3] Reference example Embodiment 1 Embodiment 4 Embodiment 7 Second absorption peak integrated area without 71.553 74.688 165.863 First absorption peak integrated area without 115.769 114.503 117.659 Area ratio - 0.618 0.652 1.410

Then, the following sample preparation method was used to prove that the present invention can inhibit the occurrence of nanosilver migration mechanism.

(Sample manufacturing method) First, according to the process of Figure 4, samples for silver migration test are prepared based on the reference example and Example 1 respectively. Specifically, the sample preparation includes nanosilver and copper pad patterning process (S1~S6) and copper window opening process (S7~S10). S1: A metal copper layer 5 with a thickness of about 200 nm is sputter-plated on the metal nanolayer (nanosilver wire layer) 2 of the transparent conductive film of the reference example. In addition, a metal copper layer 5 with a thickness of about 200 nm is sputter-plated on the water-blocking protective layer (not shown) of the transparent conductive film of Example 1. S2: Continuing from S1, a layer of photoresist 6 is coated on each copper layer 5. S3: Following S2, the first photomask is used for exposure and development process to define the circuit and electrode pattern of the nanosilver wire layer and the copper pad (layer). S4: Following S3, copper etching is performed using copper etching liquid to complete the copper circuit and electrode production. S5: Following S4, nanosilver etching is performed using silver etching liquid to complete the nanosilver wire electrode production. S6: Following S5, the photoresist is stripped and removed using a stripping liquid to complete the patterning process of the nanosilver wire layer and the copper pad (layer). S7: Continuing from S6, a layer of photoresist 6' is coated on the transparent conductive film after the nanosilver and copper pad are patterned. S8: Continuing from S7, a second photomask is used to perform an exposure and development process to define the copper window pattern. S9: Continuing from S8, copper etching is performed using a copper etching solution. S10: Finally, a stripping solution is used to strip the photoresist 6' after S9, thus completing the copper window process and obtaining samples for silver migration test.

The samples for silver migration test were placed in a high temperature and high humidity environment (85℃/85%), and a direct current (DC) and a voltage of 5V were applied to track the change of the resistance of the nanosilver wire in the nanosilver wire layer over time under these test conditions; the width of the nanosilver wire electrode was 100 μm, and the spacing (line spacing) between the nanosilver wire electrodes was 50 μm. Please refer to Figures 3 and 5 for the results of the silver migration test. In addition, the line spacing between the nanosilver wire electrodes can be adjusted between 30~200μm.

FIG3 is a graph of silver migration test of the reference example and Example 1. As shown in FIG3, the line resistance change rate of the transparent conductive film of the reference example is greater than 10% after about 45 hours (hr) of power-on; in contrast, the line resistance change rate of the transparent conductive film of Example 1 is greater than 10% after about 450 hours of power-on. It can be seen that, compared with the transparent conductive film of the reference example, the transparent conductive film of Example 1 can extend its life (the time point when the line resistance change rate increases to greater than 10%) by nearly 10 times, from 45 hours to 450 hours under the strict silver migration test conditions (DC direct current and voltage 5V, high temperature and high humidity environment 85℃/85%). In addition, the line resistance change rate of the transparent conductive film of Example 1 is only about 8% after being powered on for 400 hours.

As shown in Figure 5, since the line width of the electrode generally does not affect the migration of silver ions, the test was conducted under the conditions of fixed line width of 100μm and line distance (Gap Distance) of 30μm, 50μm, 100μm and 200μm respectively. The resistance change rate at 380hr, 390hr, 420hr and 470hr was less than 10%. Therefore, it can be seen that the line distance and life (Life time) are linearly related, and the relationship can be expressed as y=0.53179x+364.47977 (x= gap distance, y= Life time).

From the above results, it can be seen that the reliability of the transparent conductive film of the present invention is greatly improved by covering the water-blocking protective layer, which can further improve the stability of the performance of the nanosilver wire layer in electronic products.

The transparent conductive film of the present invention can be applied to the touch sensing electrode of a touch sensor. In addition, it can also be applied to flat/flexible touch displays, organic photovoltaics (OPV), OLED lighting, smart windows and other products that may contain transparent conductive films.

In summary, the transparent conductive film of the present invention and its application have at least the following excellent technical effects: 1. The transparent conductive film of the present invention has a bendable effect, and can maintain interlayer adhesion without reducing the conductivity of the conductive layer. 2. The transparent conductive film of the present invention can inhibit the migration of silver ions in harsh environments, and can have excellent visibility without reducing the conductivity, especially the haze characteristics are very obvious.

The present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope indicated in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

1: Substrate 2: Metal nanowire layer 3: Water-blocking protective layer 10: Transparent conductive film 4: Water-absorbing particles 5: Copper layer 6: Photoresist S1~S10: Steps

FIG1 is a schematic diagram of a transparent conductive film of an embodiment of the present invention. FIG2 is an FTIR spectrum of the transparent conductive film of the reference example and embodiments 1, 4, and 7. FIG3 is a silver migration test diagram of the reference example and embodiment 1. FIG4 is a flow chart of the preparation of the silver migration test sample. FIG5 is a graph showing the relationship between the line spacing and the life of the silver migration test sample.

1: Substrate

2: Metal nanowire layer

3: Water-blocking protective layer

4: Water-absorbent particles

10: Transparent conductive film

Claims (10)

A transparent conductive film comprises: a substrate; a metal nanowire layer disposed on the substrate; a water-blocking protective layer having water-absorbing particles and disposed on the metal nanowire layer; wherein, the transparent conductive film, using FTIR detection, has a first absorption peak in the 2750 cm ^- 1-3000 cm ^-1 wave number region, a second absorption peak in the 3000 cm ^- 1-3750 cm ^-1 wave number region, the maximum peak intensity ratio of the first absorption peak to the second absorption peak (second absorption peak/first absorption peak) is 0.18-0.50, and the haze value of the transparent conductive film is less than 1.7%. The transparent conductive film as described in claim 1, wherein the ratio of the spectral integrated area of the first absorption peak to the spectral integrated area of the second absorption peak is 0.618-1.410. A transparent conductive film as described in claim 1, wherein the transparent conductive film comprises a plurality of electrodes formed by metal nanowires. A transparent conductive film as described in claim 3, wherein the line spacing between the plurality of electrodes is 30-200 μm. A transparent conductive film as described in claim 4, wherein the line resistance change rate of the transparent conductive film is less than 10% under the test conditions of direct current and voltage 5V, high temperature and high humidity environment 85°C/85%, when the line spacing is x μm and the power is applied for y hr, wherein x and y satisfy the following relationship: y=0.53179x+364.47977. The transparent conductive film as described in claim 1, wherein the line resistance change rate of the transparent conductive film is less than 10% after being powered for 400 hours under the test conditions of direct current and voltage 5V, high temperature and high humidity environment 85°C/85%. The transparent conductive film as described in claim 1, wherein the visible light transmittance of the transparent conductive film is 92-97%. The transparent conductive film as described in claim 1, wherein the yellowness of the transparent conductive film is less than 0.5. The transparent conductive film as described in claim 1, wherein the thickness of the water-blocking protective layer is 1-15 μm. The transparent conductive film as described in claim 1, wherein the volume percentage of the water-absorbing particles in the water-blocking protective layer is 1-5%.

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