JP2020122125A - Base material for transparent conductive film and transparent conductive film - Google Patents

Abstract

To provide a base material for transparent conductive film that can achieve a transparent conductive film with curling, whitening and cracking suppressed and in-plane phase difference being small.SOLUTION: Such a film is used that contains a predetermined thermoplastic plastic and has small dimensional shrinkage in both a first direction and a second direction orthogonal to the first direction.SELECTED DRAWING: None

Description

The present invention relates to a transparent conductive film substrate and a transparent conductive film.

Conventionally, various resin films have been used as a base material of a transparent conductive film used for a touch panel or the like. Examples of materials forming such a resin film include polyethylene terephthalate (PET) and cycloolefin-based resin (COP). However, in the conventional transparent conductive film, curling, whitening and/or cracks may occur.

JP, 2017-190406, A

The present invention has been made to solve the above-mentioned conventional problems, and the purpose thereof is to curl, whitening and cracks are suppressed, and an in-plane retardation can be realized a small transparent conductive film. It is to provide a substrate for a transparent conductive film.

The substrate for transparent conductive film in the embodiment of the present invention contains a thermoplastic resin, and has a dimensional shrinkage ratio at 145° C. of 0. 1 in each of the first direction and the second direction orthogonal to the first direction. It is 2% or less, whitening and cracks are suppressed in the sebum resistance test, and the in-plane retardation Re(550) is 5 nm or less.
In one embodiment, the substrate has a thickness of 10 μm to 80 μm.
In one embodiment, the thermoplastic comprises 1 wt% to 15 wt% glutarimide units, 1 wt% to 6 wt% methacrylic acid units, and 0.5 wt% to 10 wt% methacrylic anhydride units. % And a copolymer containing methyl methacrylate units as the remaining content.
In one embodiment, the thermoplastic is a polymer mixture containing 10% by weight to 90% by weight of component (A) and 90% by weight to 10% by weight of component (B). Is a copolymer containing 80% by weight to 99% by weight of methyl methacrylate units and 1% by weight to 15% by weight of glutarimide units, and the component (B) contains polymethylmethacrylate.
In one embodiment, the substrate for transparent conductive film has a glass transition temperature (Tg) of 145°C or higher.

According to an embodiment of the present invention, by using a film containing a predetermined thermoplastic and having a small dimensional shrinkage ratio in both the first direction and the second direction orthogonal to the first direction, the curl is reduced. It is possible to obtain a base material for a transparent conductive film, which can realize a transparent conductive film with suppressed whitening and cracks and a small in-plane retardation.

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Substrate for Transparent Conductive Film The substrate for a transparent conductive film according to the embodiment of the present invention comprises a film containing a thermoplastic and preferably further containing an elastomer.

In the embodiment of the present invention, the dimensional shrinkage at 145° C. of the transparent conductive film substrate is 0.2% or less in the first direction and the second direction orthogonal to the first direction. , Preferably 0.15% or less. The first direction corresponds to, for example, the MD direction in the manufacturing method described later, and the second direction corresponds to, for example, the TD direction. When the dimensional shrinkage ratio at 145° C. is in such a range, a transparent conductive film substrate in which whitening and/or cracking and curling are suppressed can be obtained.

In the embodiment of the present invention, the in-plane retardation Re(550) of the transparent conductive film is 5 nm or less, preferably 4.5 nm or less. The in-plane retardation Re(550) is preferably as small as possible, and the lower limit thereof is ideally 0 nm and may be, for example, 1 nm. When the in-plane retardation is in such a range, it is possible to obtain a substrate for a transparent conductive film in which the occurrence of whitening and/or cracks and the occurrence of curl are suppressed. In the present specification, “Re(λ)” is an in-plane retardation measured with light having a wavelength of λ nm at 23°C. Re(λ) is calculated by the formula: Re=(nx−ny)×d when the thickness of the layer (film) is d (nm). Therefore, “Re(550)” is an in-plane retardation measured with light having a wavelength of 550 nm at 23° C. Here, “nx” is the refractive index in the direction in which the in-plane refractive index becomes maximum (that is, the slow axis direction), and “ny” is in the direction in the plane orthogonal to the slow axis (that is, the fast phase). Refractive index in the axial direction).

The transparent conductive film substrate may have an inverse dispersion wavelength characteristic in which the in-plane retardation increases with the wavelength of the measurement light, and the in-plane retardation has a positive wavelength with which the retardation decreases with the wavelength of the measurement light. It may exhibit dispersion characteristics, or may exhibit flat wavelength dispersion characteristics in which the in-plane retardation hardly changes depending on the wavelength of the measurement light.

In the embodiment of the present invention, in the sebum resistance test, whitening and/or cracking of the transparent conductive film substrate is suppressed. By suppressing whitening and/or cracking of the transparent conductive film substrate, a transparent conductive film advantageous for image display can be obtained.

The thickness of the transparent conductive film substrate is preferably 10 μm to 80 μm, more preferably 10 μm to 60 μm, and further preferably 10 μm to 40 μm. When the thickness of the transparent conductive film base material is within such a range, a transparent conductive film base material in which the occurrence of whitening and/or cracks and the occurrence of curl are suppressed can be obtained.

The glass transition temperature of the transparent conductive film substrate is preferably 145° C. or higher, more preferably 150° C. or higher. On the other hand, the glass transition temperature is preferably 170° C. or lower, more preferably 160° C. or lower. If the glass transition temperature is within such a range, the transparent conductive film substrate can be used at a high temperature, and the residual strain during molding can be reduced. The birefringence of the base material (as a result, the in-plane retardation) can be reduced.

The elastic modulus of the transparent conductive film substrate is preferably 50 MPa to 350 MPa at a tensile speed of 100 mm/min. When the elastic modulus is within such a range, a transparent conductive film having excellent transportability and operability can be obtained. According to the embodiment of the present invention, it is possible to achieve both excellent elastic modulus (strength) and excellent flexibility or bending resistance (softness) as described above. The elastic modulus is measured according to JIS K 7127:1999.

The tensile elongation of the transparent conductive film substrate is preferably 70% to 200%. When the tensile elongation is in such a range, it has an advantage that it is unlikely to break during transportation. The tensile elongation is measured according to JIS K 6781.

B. Thermoplastics are typically 1 wt% to 15 wt% glutarimide units, 1 wt% to 6 wt% methacrylic acid units, and 0.5 wt% to 10 wt% methacrylic anhydride units. % And the rest of the content mainly comprises copolymers containing methylmethacrylate units. The copolymer typically contains 69% by weight to 97.5% by weight of methyl methacrylate units. The copolymer may contain monomer units other than the above.

Thermoplastics are characterized by a haze below 2% (haze value, 23° C.).

The thermoplastic is typically a polymer mixture containing 10% to 90% by weight of component (A) and 90% to 10% by weight of component (B). The component (A) is a copolymer containing 80 wt% to 99 wt% of methyl methacrylate units and 1 wt% to 15 wt% of glutarimide units, and the component (B) contains polymethyl methacrylate.

As component B, impact-resistant modified polymethylmethacrylate may be included.

Thermoplastics are characterized by a haze below 2% (haze value, 23° C.).

Examples of thermoplastics include polymethylmethacrylate (PMMA) and polymethylmethacrylimide (PMMI).

Details of thermoplastics are described in, for example, JP-A-2006-57104. The description of the publication is incorporated herein by reference.

A commercially available product may be used as the thermoplastic. Examples of commercially available products include PLEXIMID TT50 (manufactured by Daicel-Evonik).

C. Elastomer Any appropriate elastomer can be used as the elastomer. Representative examples of elastomers include acrylic elastomers, rubbery polymers, polyamide elastomers, polyethylene elastomers, styrene elastomers and butadiene elastomers. The elastomers may be used alone or in combination.

A commercially available product may be used as the acrylic elastomer. Examples of the commercially available product include "High heat resistant grade XB series" manufactured by Aron Kasei Co., Ltd.

Examples of the styrene-based elastomer include elastomers containing polystyrene, which is a hard segment, and polybutadiene, polyisoprene, and a copolymer of polybutadiene and polyisoprene, which are soft segments, and hydrogenated products thereof.

The blending ratio of the above thermoplastics and the above elastomers is preferably 70:30 to 99:1, more preferably 85:15 to 95:5.

D. Method for Producing Base Material for Transparent Conductive Film A method for producing a base material for transparent conductive film according to an embodiment of the present invention is a method for producing a film-forming material (resin composition) containing the thermoplastic plastic and the elastomer according to the above item A. Forming into a film and stretching the formed film.

The film-forming material may contain, in addition to the above thermoplastics and elastomers, other resins as described above, may contain additives, and may contain solvents. Any appropriate additive can be adopted as the additive depending on the purpose. Specific examples of the additives include reactive diluents, plasticizers, surfactants, fillers, antioxidants, antioxidants, ultraviolet absorbers, leveling agents, thixotropic agents, antistatic agents, conductive materials, flame retardants. Is mentioned. The number, type, combination, addition amount, etc. of the additives can be appropriately set according to the purpose.

As a method for forming a film from the film-forming material, any suitable molding method can be adopted. Specific examples include compression molding method, transfer molding method, injection molding method, extrusion molding method, blow molding method, powder molding method, FRP molding method, cast coating method (for example, casting method), calender molding method, heat press. Law etc. are mentioned. An extrusion molding method or a cast coating method is preferable. This is because the smoothness of the obtained film can be improved and good optical uniformity can be obtained. The molding conditions can be appropriately set according to the composition and type of the resin used, the characteristics desired for the transparent conductive film substrate, and the like.

The stretching method of the film is typically biaxial stretching, and more specifically, sequential biaxial stretching or simultaneous biaxial stretching. This is because a substrate for a transparent conductive film having a small in-plane retardation Re(550) can be obtained. Sequential biaxial stretching or simultaneous biaxial stretching is typically performed using a tenter stretching machine. Therefore, the stretching direction of the film is typically the length direction and the width direction of the film.

The stretching temperature may vary depending on the in-plane retardation and thickness desired for the transparent conductive film substrate, the type of resin used, the thickness of the film used, the stretching ratio, and the like. Specifically, the stretching temperature is preferably Tg+5° C. to Tg+50° C., and more preferably Tg+10° C. to Tg+40° C. with respect to the glass transition temperature (Tg) of the film. By stretching at such a temperature, a transparent conductive film substrate having suitable properties in the embodiment of the present invention can be obtained.

The draw ratio may vary depending on the in-plane retardation and thickness desired for the transparent conductive film substrate, the type of resin used, the thickness of the film used, the stretching temperature, and the like. When biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching) is adopted, the stretching ratio in the first direction (for example, the length direction) and the stretching in the second direction (for example, the width direction). The magnification is preferably as small as possible, more preferably substantially equal. With such a structure, a substrate for a transparent conductive film having a small in-plane retardation Re(550) can be obtained. When biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching) is adopted, the stretching ratio is in the first direction (for example, the length direction) and the second direction (for example, the width direction). For each, it can be, for example, 1.1 times to 3.0 times.

In the embodiment of the present invention, the stretching rate is preferably 10%/sec or less, more preferably 7%/sec or less, further preferably 5%/sec or less, and particularly preferably 2.5. %/Second or less. By stretching the film containing the specific thermoplastic as described above at such a low stretching speed, a substrate for a transparent conductive film having a small in-plane retardation Re(550) can be obtained. The lower limit of the stretching speed can be, for example, 1.2%/sec. If the stretching speed is too low, the productivity may not be practical. When biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching) is adopted, the stretching speed in the first direction (for example, the length direction) and the second direction (for example, the width direction) The stretching speed is preferably as small as possible, more preferably substantially equal. With such a configuration, the in-plane retardation Re(550) of the transparent conductive film substrate can be made small.

E. Transparent Conductive Film The substrate for transparent conductive film described in the above items A and B is suitably used for a transparent conductive film. Therefore, embodiments of the present invention also include transparent conductive films. The transparent conductive film according to the embodiment of the present invention includes the transparent conductive film substrate described in the above A and B, and a conductive layer. The conductive layer is typically formed on the viewing side surface of the transparent conductive film substrate. The transparent conductive film may have an index matching (IM) layer, a hard coat (HC) layer and/or an anti-blocking hard coat (ABHC) layer, if necessary.

(Conductive layer)
The conductive layer is typically a transparent conductive layer. The total light transmittance of the conductive layer is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more.

The density of the conductive layer is preferably ^{1.0g / cm 3 ~10.5g / cm 3} , more preferably from ^{1.3g / cm 3 ~8.0g / cm 3} .

The surface resistance value of the conductive layer is preferably 0.1Ω/□ to 1000Ω/□, more preferably 0.5Ω/□ to 500Ω/□, and further preferably 1Ω/□ to 250Ω/□.

A typical example of the conductive layer is a conductive layer containing a metal oxide. Examples of the metal oxide include indium oxide, tin oxide, zinc oxide, indium-tin complex oxide, tin-antimony complex oxide, zinc-aluminum complex oxide, and indium-zinc complex oxide. Of these, indium-tin composite oxide (ITO) is preferable.

The thickness of the conductive layer is preferably 0.01 μm to 0.06 μm, more preferably 0.01 μm to 0.045 μm. Within such a range, a conductive layer having excellent conductivity and light transmittance can be obtained.

The conductive layer can be typically formed on the surface of the film substrate by sputtering.

(Index matching (IM) layer)
The IM layer may be formed on the surface on one side of the conductive layer. A configuration well known in the industry can be adopted for the IM layer, and thus detailed description thereof will be omitted.

(Hard coat (HC) layer)
The HC layer may be formed between the IM layer and the transparent conductive film substrate. A well-known configuration in the industry can be adopted for the HC layer, so a detailed description thereof will be omitted.

(Anti-blocking hard coat (ABHC) layer)
The ABHC layer may be formed on the surface of the transparent conductive film substrate opposite to the HC layer. Details of the ABHC layer are described in, for example, JP-A-2016-107503. The description of the publication is incorporated herein by reference.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples. The method of measuring each characteristic in the examples is as follows. In the examples, “parts” and “%” are based on weight unless otherwise specified.

(1) Front phase difference Re (550)
The transparent conductive film substrate obtained in each of the examples and comparative examples was cut into a length of 4 cm and a width of 4 cm to obtain a measurement sample. The in-plane retardation and the thickness direction retardation of the measurement sample were measured using a product name "Axoscan" manufactured by Axometrics. The measurement wavelength was 550 nm and the measurement temperature was 23°C.
(2) Dimensional Shrinkage The dimensional shrinkage in the MD and TD directions of the transparent conductive film substrate was measured as follows. Specifically, the transparent conductive film substrate was cut into a width of 100 mm and a length of 100 mm (test piece), and four corners were scratched with a cloth, and four points in the MD and TD directions at the four central portions of the cloth scratch were cut. The length (mm) before heating was measured by a CNC coordinate measuring machine (LEGEX774 manufactured by Mitutoyo Corporation). Then, it put into the oven and heat-processed (145 degreeC, 60 minutes). After cooling for 1 hour at room temperature, the lengths (mm) after heating in the MD and TD directions at the four points of the four corners are measured again by a CNC coordinate measuring machine, and the measured values are substituted into the following formula. The heat shrinkage rates in the MD direction and the TD direction were obtained.
Dimensional shrinkage rate (%)=[[length before heating (mm)-length after heating (mm)]/length before heating (mm)]×100
(3) Sebum resistance test The transparent conductive films obtained in Examples and Comparative Examples were cut into a size of 5 cm x 5 cm, and an adhesive was attached to the surface on which the ITO film was formed and the other surface with a hand roller, A test piece was obtained by sticking the adhesive surface on one side of an alkali glass. The obtained test piece was immersed in an oleic acid solution for 72 hours under the conditions of 65° C. and 90% RH, and after taking it out, the transparent one was marked with ◯, and the one with whitening or cracks was marked with x.
(4) Curl The transparent conductive films obtained in Examples and Comparative Examples were cut into a size of 20 cm×20 cm. After heating at 145° C. for 60 minutes with the ITO surface facing upward, the mixture was allowed to cool at room temperature (23° C.) for 1 hour. Then, the sample was placed on a horizontal surface with the ITO layer facing upward, and the height from the horizontal plane of the central portion (curl value A) was measured. Further, the heights of the four corners from the horizontal plane were measured, and the average value (curl value B) was calculated. A value obtained by subtracting the curl value B from the curl value A (AB) was calculated as the curl amount. If the curl value was in the range of 0 to 50 mm, it was evaluated as ◯, and the others were evaluated as x.

<Example 1>
1-1. Preparation of thermoplastic/elastomer mixed resin film 90 parts of product name "PLEXIMID TT50" (Tg: 151°C) manufactured by Daicel-Evonik, which is a polymethylmethacrylimide (PMMI) resin as a thermoplastic, and an acrylic elastomer (Aron Kasei, high heat resistant grade XB series) 10 parts were mixed and vacuum dried at 100° C. for 5 hours, and then a single screw extruder (Isuzu Kako Co., Ltd., screw diameter 25 mm, cylinder set temperature: 275° C.) ), a T-die (width 200 mm, setting temperature: 275° C.), a chill roll (setting temperature: 120 to 130° C.), and a film forming apparatus equipped with a winder to form a PMMI/elastomer mixed resin film having a thickness of 100 μm. It was made.

1-2. Preparation of Substrate for Transparent Conductive Film The PMMI/elastomer mixed resin film obtained above was simultaneously biaxially stretched twice in the length direction and the width direction. The stretching temperature was [Tg+25°C]. In this way, a transparent conductive film substrate (thickness 25 μm) was obtained. The in-plane retardation Re(550) of the obtained substrate for transparent conductive film was 3.8 nm, and the dimensional change rate (MD/TD) was 0.15/0.16.

1-3. Preparation of transparent conductive film An anti-blocking hard coat (ABHC) layer is formed on one surface of the substrate for transparent conductive film obtained above, and a hard coat is formed on the surface opposite to the ABHC layer. An (HC) layer was formed. An index matching (IM) layer was formed on the surface of the HC layer opposite to the transparent conductive film substrate. On the surface of the IM layer opposite to the HC layer, ITO was sputtered to form a conductive layer to obtain a transparent conductive film. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

<Example 2>
A substrate for a transparent conductive film was obtained in the same manner as in Example 1 except that the thickness was 15 μm and the amount of the elastomer added was 20 parts. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 3.9 nm, and the dimensional change rate (MD/TD) was 0.14/0.14. Further, in the same manner as in Example 1, a transparent conductive film was obtained using the obtained substrate for transparent conductive film. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

<Example 3>
A transparent conductive film substrate was obtained in the same manner as in Example 1 except that the thickness was 40 μm. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 3.1 nm, and the dimensional change rate (MD/TD) was 0.19/0.18. Further, in the same manner as in Example 1, a transparent conductive film was obtained using the obtained substrate for transparent conductive film. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

<Example 4>
A transparent conductive film substrate was obtained in the same manner as in Example 1 except that the thickness was 25 μm, the amount of the elastomer added was 5 parts, and the stretching temperature was [Tg+20° C.]. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 4.9 nm, and the dimensional change rate (MD/TD) was 0.16/0.19. Further, in the same manner as in Example 1, a transparent conductive film was obtained using the obtained substrate for transparent conductive film. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

<Comparative Example 1>
A transparent conductive film substrate was obtained in the same manner as in Example 1 except that the thickness was 90 μm. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 3.1 nm, and the dimensional change rate (MD/TD) was 0.22/0.22. Further, in the same manner as in Example 1, a transparent conductive film was obtained using the obtained substrate for transparent conductive film. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

<Comparative example 2>
The same procedure as in Example 1 was performed except that an ultrahigh retardation polyethylene terephthalate film (product name "Diafoyl" manufactured by Mitsubishi Chemical Co., Ltd.) was used in place of the polymethylmethacrylimide (PMMI) resin, and no elastomer was added. Thus, a transparent conductive film substrate was obtained. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 1500 nm, and the dimensional change rate (MD/TD) was 0.6/0.6. Further, in the same manner as in Example 1, a transparent conductive film was obtained using the obtained substrate for transparent conductive film. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

<Comparative example 3>
Example 1 except that a polycycloolefin film (product name “Zeonoa” manufactured by Nippon Zeon Co., Tg: 160° C.) was used in place of the polymethylmethacrylimide (PMMI) resin, and no elastomer was added. Similarly, a transparent conductive film substrate was obtained. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 1.2 nm, and the dimensional change rate (MD/TD) was 0.07/0.08. Further, in the same manner as in Example 1, a transparent conductive film was obtained using the obtained substrate for transparent conductive film. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

<Evaluation>
As is clear from Table 1, the transparent conductive film substrate of the example of the present invention has suppressed whitening and/or cracks and curl in the sebum resistance test. It is speculated that this can be achieved by stretching a film containing a particular thermoplastic. Furthermore, as is clear when comparing the example and the comparative example, by using a transparent conductive film substrate containing a thermoplastic and having a thickness in a predetermined range, excellent properties (small in-plane retardation and It can be seen that a small dimensional shrinkage ratio) is obtained.

The base material for transparent conductive films of the present invention is suitably used for transparent conductive films. By using the transparent conductive film substrate of the present invention, a transparent conductive film advantageous for image display can be obtained.

Claims (6)

Including thermoplastics,
The dimensional shrinkage ratio at 145° C. is 0.2% or less in the first direction and the second direction orthogonal to the first direction,
Whitening and cracks are suppressed in the sebum resistance test,
The in-plane retardation Re(550) is 5 nm or less,
Substrate for transparent conductive film. The substrate for a transparent conductive film according to claim 1, wherein the substrate has a thickness of 10 μm to 80 μm. The thermoplastic contains 1 wt% to 15 wt% of glutarimide units, 1 wt% to 6 wt% of methacrylic acid units, 0.5 wt% to 10 wt% of methacrylic anhydride units, and the remaining contents. The substrate for a transparent conductive film according to claim 1, which contains a copolymer containing a methyl methacrylate unit. The thermoplastic is
A polymer mixture containing 10% by weight to 90% by weight of the component (A) and 90% by weight to 10% by weight of the component (B),
The component (A) is a copolymer containing 80% by weight to 99% by weight of methyl methacrylate units and 1% by weight to 15% by weight of glutarimide units,
The component (B) contains polymethylmethacrylate,
The substrate for a transparent conductive film according to claim 1. The substrate for a transparent conductive film according to claim 1, which has a glass transition temperature (Tg) of 145° C. or higher. A transparent conductive film, comprising the transparent conductive film substrate according to claim 1 and a conductive layer.