Transparent conductive film substrate and transparent conductive film

Abstract

The present invention provides a transparent conductive film substrate and a transparent conductive film. The transparent conductive film substrate is capable of achieving a transparent conductive film that suppresses curling, whitening, and cracking and exhibits a small in-plane retardation. The transparent conductive film substrate comprises a predetermined polycarbonate resin and exhibits a low dimensional shrinkage in both a first direction and a second direction perpendicular to the first direction.

Description

Technical Field

[0001] The present invention relates to a substrate for a transparent conductive film and a transparent conductive film. Background Art

[0002] Conventionally, various resin films have been used as substrates for transparent conductive films used in touch panels and other applications. Examples of materials used to construct such resin films include polyethylene terephthalate (PET) and cycloolefin resin (COP). However, conventional transparent conductive films can sometimes curl, whiten, and / or crack.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-190406 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a substrate for a transparent conductive film that can realize a transparent conductive film with suppressed curling, whitening, and cracking and a small in-plane retardation.

[0008] Solutions for solving problems

[0009] The substrate for the transparent conductive film in an embodiment of the present invention comprises a polycarbonate resin, has a dimensional shrinkage at 145°C of less than 0.2% in each of a first direction and a second direction orthogonal to the first direction, suppresses whitening and cracking in a sebum resistance test, and has an in-plane phase difference Re(550) of less than 5 nm.

[0010] In one embodiment, the substrate has a thickness of 10 μm to 80 μm.

[0011] In one embodiment, the polycarbonate resin is substantially composed of a structural unit represented by the following general formula (I) and a structural unit represented by the following general formula (II), and satisfies the following conditions (a) to (d), wherein the structural unit represented by the general formula (I) is derived from an aliphatic diol compound having an aliphatic hydrocarbon group bonded to a terminal hydroxyl group.

[0012]

[0013] (In general formula (I), Q represents a hydrocarbon group having 3 or more carbon atoms which may contain atoms of different kinds. R1 to R4 each independently represent a group selected from the group consisting of a hydrogen atom, an aliphatic hydrocarbon group having 1 to 30 carbon atoms, and an aromatic hydrocarbon group having 6 to 20 carbon atoms. n and m each independently represent an integer from 0 to 10. However, when Q does not contain an aliphatic hydrocarbon group bonded to a terminal hydroxyl group, n and m each independently represent an integer from 1 to 10. In addition, at least one of R1 and R2, and at least one of R3 and R4 are each selected from the group consisting of a hydrogen atom and an aliphatic hydrocarbon group.)

[0014]

[0015] (In the general formula (II), R1 and R2 each independently represent a halogen atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 6 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a cycloalkoxy group having 6 to 20 carbon atoms, or an aryloxy group having 6 to 20 carbon atoms. p and q represent integers of 0 to 4. X represents a single bond or a group selected from the group of divalent organic groups represented by the following general formula (II').)

[0016]

[0017] (In the general formula (II'), R3 and R4 each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and R3 and R4 may be bonded to form an aliphatic ring.)

[0018] (a) has a structure represented by the following general formula (III).

[0019]

[0020] (In general formula (III), k represents an integer of 4 or greater, i represents an integer of 1 or greater, l represents an integer of 1 or greater, and k' represents an integer of 0 or 1. R represents a linear or branched hydrocarbon group, a phenyl group optionally containing fluorine, or a hydrogen atom. Of the total amount of the above resin, i = 1 in an amount of not less than 70% by weight.)

[0021] (b) The ratio of the structural unit represented by the general formula (I) to the structural unit represented by the general formula (II) is 1 to 30:99 to 70 (molar ratio)%.

[0022] (c) The weight average molecular weight (Mw) is 30,000 to 100,000.

[0023] (d) The content of the structural units represented by the following general formulas (1) and (2) is each 2000 ppm or less in terms of bisphenol acid relative to the total amount of the structural units constituting the polycarbonate resin.

[0024] General formula (1):

[0025]

[0026] General formula (2):

[0027]

[0028] (X in the above general formulae (1) and (2) is the same as that in general formula (II).)

[0029] In one embodiment, the transparent conductive film substrate has a glass transition temperature (Tg) of 145° C. or higher.

[0030] Effects of the Invention

[0031] According to an embodiment of the present invention, by using a film containing a specified polycarbonate resin and having a small dimensional shrinkage rate in both a first direction and a second direction orthogonal to the first direction, a substrate for a transparent conductive film can be obtained, which can achieve a transparent conductive film with suppressed curling, whitening and cracking and a small in-plane phase difference. DETAILED DESCRIPTION

[0032] Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0033] A. Overall structure of the transparent conductive film substrate

[0034] The transparent conductive film substrate according to an embodiment of the present invention is composed of a film containing a polycarbonate resin. The polycarbonate resin used in the present invention is typically substantially composed of the structural unit represented by the above-mentioned general formula (I) and the structural unit represented by the general formula (II).

[0035] In embodiments of the present invention, the transparent conductive film substrate exhibits a dimensional shrinkage at 145°C of 0.2% or less, preferably 0.15% or less, in each of a first direction and a second direction perpendicular to the first direction. The first direction corresponds, for example, to the MD direction in the manufacturing method described below, and the second direction corresponds, for example, to the TD direction. When the dimensional shrinkage at 145°C falls within this range, a transparent conductive film substrate can be obtained in which whitening and / or cracking and curling are suppressed.

[0036] In an embodiment of the present invention, the in-plane phase difference Re(550) of the transparent conductive film is less than 5 nm, preferably less than 4.5 nm. The smaller the in-plane phase difference Re(550), the better, and its lower limit is ideally 0 nm, for example, it can be 1 nm. When the in-plane phase difference is within such a range, a substrate for a transparent conductive film in which the generation of whitening and / or cracks and the occurrence of curling can be suppressed can be obtained. It should be noted that in this specification, "Re(λ)" is the in-plane phase difference measured at 23°C with light of a wavelength of λ nm. For Re(λ), when the thickness of the layer (film) is set to d(nm), it is calculated by the formula: Re=(nx-ny)×d. Therefore, "Re(550)" is the in-plane phase difference measured at 23°C with light of a wavelength of 550 nm. Here, "nx" is the refractive index in the direction where the in-plane refractive index becomes the largest (i.e., the slow axis direction), and "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction).

[0037] The substrate for the transparent conductive film can exhibit an inverse wavelength dispersion characteristic in which the in-plane phase difference increases with the wavelength of the measuring light, a positive wavelength dispersion characteristic in which the in-plane phase difference decreases with the wavelength of the measuring light, or a flat wavelength dispersion characteristic in which the in-plane phase difference hardly changes with the wavelength of the measuring light.

[0038] In embodiments of the present invention, whitening and / or cracking of the transparent conductive film substrate is suppressed in a sebum resistance test. By suppressing whitening and / or cracking of the transparent conductive film substrate, a transparent conductive film that is advantageous for image display can be obtained.

[0039] The thickness of the transparent conductive film substrate is preferably 10 μm to 80 μm, more preferably 10 μm to 60 μm, and even more preferably 10 μm to 40 μm. When the thickness of the transparent conductive film substrate is within this range, a transparent conductive film substrate can be obtained in which whitening and / or cracking and curling are suppressed.

[0040] The glass transition temperature of the transparent conductive film substrate is preferably 145°C or higher, more preferably 150°C or higher. When the glass transition temperature is within this range, the transparent conductive film substrate can be used at high temperatures and residual strain can be reduced during molding, thereby reducing the birefringence (and consequently, the in-plane retardation) of the resulting transparent conductive film substrate.

[0041] 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 this range, a transparent conductive film with excellent transportability and handleability can be obtained. According to embodiments of the present invention, it is possible to achieve both excellent elastic modulus (strength) and excellent flexibility or flexural resistance (softness) as described above. It should be noted that the elastic modulus is measured in accordance with JIS K 7127:1999.

[0042] The transparent conductive film substrate preferably has a tensile elongation of 70% to 200%. A tensile elongation within this range is advantageous in that it is less likely to break during transportation. The tensile elongation is measured in accordance with JIS K 6781.

[0043] B. Polycarbonate resin

[0044] (1) Structural unit represented by general formula (I)

[0045] The structural unit represented by general formula (I) is derived from an aliphatic diol compound. The aliphatic diol compound in the present invention is a compound having an aliphatic hydrocarbon group bonded to a terminal hydroxyl group. The terminal hydroxyl group is a hydroxyl group that contributes to the formation of a carbonate bond with the aromatic polycarbonate prepolymer through an ester exchange reaction.

[0046] Examples of the aliphatic hydrocarbon group include an alkylene group and a cycloalkylene group, and a part of these may be substituted with an aromatic group, a heterocyclic ring-containing group, or the like.

[0047]

[0048] In the general formula (I), Q represents a hydrocarbon group having 3 or more carbon atoms, which may contain atoms of different species. The lower limit of the carbon number of the hydrocarbon group is preferably 3, more preferably 6, and even more preferably 10, and the upper limit is preferably 40, more preferably 30, and even more preferably 25.

[0049] Examples of the heteroatom include oxygen atom (O), sulfur atom (S), nitrogen atom (N), fluorine atom (F) and silicon atom (Si). Among these, oxygen atom (O) and sulfur atom (S) are particularly preferred. The hydrocarbon group may be linear, branched or cyclic. In addition, Q may include cyclic structures such as aromatic rings and heterocycles.

[0050] In the above general formula (I), R1, R2, R3 and R4 each independently represent a group selected from the group consisting of a hydrogen atom, an aliphatic hydrocarbon group preferably having 1 to 30 carbon atoms, more preferably 1 to 10 carbon atoms, and an aromatic hydrocarbon group preferably having 6 to 20 carbon atoms, more preferably 6 to 10 carbon atoms.

[0051] Specific examples of the aliphatic hydrocarbon group include linear or branched alkyl groups and cycloalkyl groups. Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, n-hexyl, and isohexyl. Examples of the cycloalkyl group include cyclohexyl. Examples of the aromatic hydrocarbon group include phenyl and naphthyl.

[0052] At least one of R1 and R2, and at least one of R3 and R4 are each selected from the group consisting of a hydrogen atom and an aliphatic hydrocarbon group. It is particularly preferred that R1 to R4 each independently represent a group selected from the group consisting of a hydrogen atom and an aliphatic hydrocarbon group preferably having 1 to 30 carbon atoms, more preferably 1 to 10 carbon atoms. Particularly preferred aliphatic hydrocarbon groups include linear or branched alkyl groups. Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, and isopentyl.

[0053] It should be noted that it is most preferred that all of R1 to R4 are hydrogen atoms. That is, the aliphatic diol compound from which the above-mentioned general formula (I) can be derived is preferably a primary diol compound, and more preferably a primary diol compound other than a linear aliphatic diol.

[0054] n and m each independently represent an integer of preferably 0 to 10, more preferably 0 to 4. However, when Q does not contain an aliphatic hydrocarbon group bonded to a terminal hydroxyl group, n and m each independently represent an integer of preferably 1 to 10, more preferably 1 to 4.

[0055] The aliphatic diol compound from which the structural unit (I) is derived is a compound having a divalent alcoholic hydroxyl group represented by the following general formula (A): In general formula (A), Q, R1 to R4, n, and m are the same as those in the general formula (I).

[0056] HO-(CR1R2) n -Q-(CR3R4) n -OH…(A)

[0057] Specific examples of the terminal structures "HO-(CR1R2)n-" and "-(CR3R4)m-OH" include the following structures.

[0058]

[0059]

[0060] Ra, Rb = hydrogen, linear or branched alkyl, phenyl, naphthyl, m = integer greater than 1

[0061]

[0062] Ra, Rb = hydrogen, linear or branched alkyl, phenyl, naphthyl, m = integer greater than 1

[0063] (2) Structural unit represented by general formula (II)

[0064] The aromatic polycarbonate-forming unit of the polycarbonate resin of the present invention is a structural unit represented by the general formula (II).

[0065]

[0066] In the general formula (II), R1 and R2 each independently represent a halogen atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 6 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a cycloalkoxy group having 6 to 20 carbon atoms, or an aryloxy group having 6 to 20 carbon atoms. p and q represent integers of 0 to 4. X represents a single bond or a group selected from the group consisting of divalent organic groups represented by the following general formula (II').

[0067]

[0068] In the general formula (II'), R3 and R4 each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and R3 and R4 may be bonded to form an aliphatic ring.

[0069] Examples of the aromatic dihydroxy compound from which the structural unit represented by the general formula (II) is derived include compounds represented by the following general formula (II”).

[0070]

[0071] In the above general formula (II"), R1 to R2, p, q and X are the same as those in the above general formula (II).

[0072] Specific examples of such aromatic dihydroxy compounds include bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)octane, bis(4-hydroxyphenyl)phenylmethane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, bis(4-hydroxyphenyl)diphenylmethane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 1,1-bis(4-hydroxy-3-tert-butylphenyl)propane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 2,2-bis(4-hydroxy-3-phenylphenyl)propane, 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane. alkane, 2,2-bis(4-hydroxy-3-bromophenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclopentane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(4-hydroxy-3-methoxyphenyl)propane, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxy-3,3'-dimethylphenyl ether, 4,4'-dihydroxyphenyl sulfide, 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfide, 4,4'-dihydroxydiphenyl sulfoxide, 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfoxide, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfone, etc.

[0073] Among them, 2,2-bis(4-hydroxyphenyl)propane is cited as a more preferred example because of its stability as a monomer and the ease of obtaining a product containing a small amount of impurities.

[0074] As the aromatic polycarbonate-forming unit in the present invention, structural units derived from multiple types of the above-mentioned various monomers (aromatic dihydroxy compounds) can be combined as needed for the purpose of controlling the glass transition temperature, improving the fluidity, improving the refractive index, and controlling optical properties such as reducing birefringence.

[0075] (3) Requirement (a)

[0076] The polycarbonate resin of the present invention is characterized by having a structure represented by the following general formula (III): In general formula (III), (I) represents a structural unit represented by general formula (I), and (II) represents a structural unit represented by general formula (II).

[0077]

[0078] In the general formula (III), R represents a linear or branched hydrocarbon group, a phenyl group optionally containing fluorine, or a hydrogen atom. Specifically, R includes methyl, propyl, isopropyl, ethyl, butyl, isobutyl, pentyl, isopentyl, hexyl, tetrafluoropropyl, tert-butylphenyl, pentafluorophenyl, and the like.

[0079] In the above general formula (III), k represents the average chain length of the chain (aromatic polycarbonate chain) formed by the aromatic polycarbonate forming units. The aromatic polycarbonate forming units are the structural units that constitute the main body of the polycarbonate resin of the present invention, and the aromatic polycarbonate chain formed therefrom constitutes the main polymer structure of the polycarbonate resin. k is preferably 4 or greater, more preferably 4 to 100, and even more preferably 5 to 70. If the chain length is not longer than the specified length, the number of structural sites represented by "-(I)i-" increases relatively, resulting in an increase in the random copolymerizability of the polycarbonate resin of the present invention and a tendency to lose heat resistance and other characteristics that are inherent to the polycarbonate resin.

[0080] The structural unit "-(II)k-" (aromatic polycarbonate chain) is a structural unit derived from an aromatic polycarbonate prepolymer, and its weight average molecular weight (Mw) is preferably 5,000 to 60,000, more preferably 10,000 to 50,000, further preferably 10,000 to 40,000, and particularly preferably 15,000 to 35,000.

[0081] If the molecular weight of the aromatic polycarbonate chain is too low, the polycarbonate resin of the present invention may be more affected by the physical properties of the copolymer components. Although this can improve the physical properties, it may not be sufficient to maintain the useful physical properties of the aromatic polycarbonate.

[0082] If the molecular weight of the aromatic polycarbonate chain is too high, the polycarbonate resin of the present invention may not have high fluidity while maintaining the useful physical properties of the aromatic polycarbonate.

[0083] i represents the average chain length of the moiety "-(I)i-" formed from the structural unit derived from the aliphatic diol compound. i is preferably 1 or greater, more preferably 1 to 5, even more preferably 1 to 3, particularly preferably 1 to 2, and most preferably 1. The closer the average chain length is to 1, the more preferred. If the average chain length of the aliphatic diol moiety "-(I)i-" is too long, heat resistance and mechanical strength will decrease, and the effects of the present invention will not be achieved.

[0084] l represents the average chain length of the structural unit "-[-(II)k-(I)i-]l-" formed by the aromatic polycarbonate chain and the aliphatic diol moiety. l is 1 or greater, preferably 1 to 30, more preferably 1 to 20, and particularly preferably 1 to 10. k' is preferably an integer of 0 or 1. That is, the aliphatic diol moiety "-(I)i-" may have aromatic polycarbonate chains on both sides or only on one side, and in most cases, has aromatic polycarbonate chains on both sides.

[0085] In the polycarbonate resin, the ratio (molar ratio) of the aromatic polycarbonate chain "-(II)k-" to the aliphatic diol moiety "-(I)i-" is not particularly limited. However, based on the average value of the entire polycarbonate resin, "-(II)k-" / "-(I)i-" is preferably 0.1 to 3, more preferably 0.6 to 2.5, and particularly preferably 2. Furthermore, k / l is not particularly limited, but is preferably 2 to 200, and even more preferably 4 to 100.

[0086] In the polycarbonate resin of the present invention, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more of the total polymer molecules constituting the resin have i = 1. That is, resins are generally aggregates of polymer compounds (polymer molecules) having various structures and molecular weights, but the polycarbonate resin of the present invention is characterized by being an aggregate of polymer compounds comprising 70% by weight or more of a structure in which a long-chain aromatic polycarbonate chain (-(II)k-) is bonded to a single structural unit (-(I)-) derived from an aliphatic diol compound. If the proportion of polymer compounds with i = 1 is less than 70% by weight, the proportion of copolymer components is high, and thus the resin is easily affected by the physical properties of the copolymer components, failing to maintain the inherent physical properties of the aromatic polycarbonate. The proportion of polymer compounds with i = 1 in the polycarbonate resin of the present invention can be analyzed by 1H-NMR analysis of the polycarbonate resin.

[0087] (4) Requirement (b)

[0088] In the polycarbonate resin of the present invention, the ratio of the structural unit represented by the general formula (I) to the structural unit represented by the general formula (II) is preferably 1-30:99-70 (molar ratio), more preferably 1-25:99-75 (molar ratio), and even more preferably 1-20:99-80 (molar ratio).

[0089] If the proportion of the structural unit represented by general formula (I) is too low, the high molecular weight and high fluidity characteristic of polycarbonate resins are not satisfied. If it is too high, the excellent physical properties inherent in aromatic polycarbonate resins, such as mechanical strength and heat resistance, are impaired.

[0090] The polycarbonate resin of the present invention may contain structures derived from other copolymer components within the scope of the present invention. Ideally, the polycarbonate resin of the present invention contains the structural unit represented by general formula (I) in an amount of preferably 1 to 30 mol%, more preferably 1 to 25 mol%, and even more preferably 1 to 20 mol%, relative to the total amount of the structural units.

[0091] (5) Requirement (c)

[0092] The polycarbonate resin of the present invention has a weight average molecular weight (Mw) of preferably 30,000 to 100,000, more preferably 30,000 to 80,000, and even more preferably 35,000 to 75,000, and has both a high molecular weight and high fluidity.

[0093] If the weight-average molecular weight of a polycarbonate resin is too low, the melt tension becomes low when used in blow molding, extrusion molding, and other applications, resulting in drawdown and unsatisfactory molded products. Furthermore, when used in injection molding, unsatisfactory molded products may be produced due to stringing and other issues. Consequently, the resulting molded products may have reduced mechanical properties, heat resistance, and other physical properties. Furthermore, the oligomer domain may increase, and properties such as organic solvent resistance may also decrease.

[0094] If the weight-average molecular weight of a polycarbonate resin is too high, injection molding of precision parts and thin materials becomes difficult, and molding cycle times become long, negatively impacting production costs. Therefore, measures such as increasing the molding temperature are necessary. However, high temperatures can lead to gelation, the formation of heterogeneous structures, and an increase in the N value.

[0095] (6) Requirement (d)

[0096] The polycarbonate resin of the present invention contains at least one of the structural units represented by the following general formulae (1) and (2) (hereinafter referred to as "structural unit (1)" and "structural unit (2)") as a different structure. X in the following general formulae (1) and (2) is the same as X in the above-mentioned general formula (II).

[0097] Structural unit (1):

[0098]

[0099] Structural unit (2):

[0100]

[0101] It should be noted that the two structural formulas (i) and (ii) in the above structural formula (2) are isomers and cannot be distinguished analytically. Therefore, they are treated as the same structure in the present invention. Therefore, when referring to structural formula (2) in the present invention, it refers to either or both of the above structural formulas (i) and (ii). In addition, the content of structural unit (2) in the present invention refers to the total amount of the above two structural formulas (i) and (ii).

[0102] In the present invention, the content of at least one of the structural units (1) and (2) is preferably 2000 ppm or less, more preferably 1500 ppm or less, further preferably 1000 ppm or less, particularly preferably 500 ppm or less, and most preferably 300 ppm or less, in terms of bisphenol acid, relative to the total amount of the structural units constituting the aromatic polycarbonate resin. If the content of both structural units (1) and (2) exceeds 2000 ppm, the degree of branching tends to increase, and thermal stability tends to decrease. In addition, since these structural units are naturally occurring branched chains, there are disadvantages such as difficulty in easily controlling the degree of branching by adjusting the amount of branching agent added, resulting in decreased fluidity and poor moldability.

[0103] As described above, in the present invention, the content of at least one of the structural units (1) and (2) needs to be 2000 ppm or less in terms of bisphenol acid. This means that either structural unit (1) or (2) may be 2000 ppm or less. In a preferred embodiment, the content of at least structural unit (1) is 2000 ppm or less, more preferably 1500 ppm or less, further preferably 1000 ppm or less, particularly preferably 500 ppm or less, and most preferably 300 ppm or less. In particular, structural unit (1) has a significant effect on retention stability and color tone. A low content of structural unit (1) significantly improves thermal stability and color tone.

[0104] Next, the content of both structural units (1) and (2) is preferably 2000 ppm or less, more preferably 1000 ppm or less, further preferably 1000 ppm or less, particularly preferably 500 ppm or less, and most preferably 300 ppm or less, in terms of bisphenol acid.

[0105] Furthermore, the total proportion of the structural units represented by the structural units (1) and (2) is preferably 5000 ppm or less, more preferably 3000 ppm or less, further preferably 2000 ppm or less, particularly preferably 1000 ppm or less, and most preferably 600 ppm or less, in terms of bisphenol acid.

[0106] The details of the structural units represented by general formulae (I) and (II) used in the present invention are described in, for example, JP-A-2014-101417, the contents of which are incorporated herein by reference.

[0107] A commercially available polycarbonate resin may be used. An example of the commercially available polycarbonate resin is "Iupizeta (registered trademark)" manufactured by Mitsubishi Gas Chemical Co., Ltd.

[0108] C. Method for manufacturing a transparent conductive film substrate

[0109] The method for producing a transparent conductive film substrate according to an embodiment of the present invention comprises forming a film-forming material (resin composition) containing the polycarbonate resin described in the above section A into a film shape and stretching the formed film.

[0110] In addition to the polycarbonate resin, the film-forming material may further include other resins as described above, additives, and solvents. Any appropriate additive may be used depending on the intended purpose. Specific examples of additives include reactive diluents, plasticizers, surfactants, fillers, antioxidants, anti-aging agents, UV absorbers, leveling agents, thixotropic agents, antistatic agents, conductive materials, and flame retardants. The amount, type, combination, and addition of the additives may be appropriately determined depending on the intended purpose.

[0111] As a method for forming a film from a film-forming material, any appropriate molding method can be used. As a specific example, compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, cast coating (for example, tape casting), calendaring, hot pressing, etc. can be listed. Extrusion molding or cast coating are preferred. This is because the smoothness of the film obtained can be improved and good optical uniformity can be obtained. Molding conditions can be suitably set according to the composition, type, and desired properties of the transparent conductive film substrate of the resin used.

[0112] Film stretching is typically performed by biaxial stretching, more specifically, sequential biaxial stretching or simultaneous biaxial stretching. This is because it allows for a transparent conductive film substrate with a small in-plane retardation Re(550). Sequential biaxial stretching or simultaneous biaxial stretching is typically performed using a tenter. Therefore, the film is typically stretched in the longitudinal and width directions of the film.

[0113] The stretching temperature can vary depending on the desired in-plane retardation and thickness of the transparent conductive film substrate, the type of resin used, the thickness of the film used, the stretch ratio, and other factors. Specifically, the stretching temperature is preferably between Tg+5°C and Tg+50°C, and more preferably between Tg+10°C and Tg+40°C, relative to the film's glass transition temperature (Tg). By stretching at such a temperature, embodiments of the present invention can produce a transparent conductive film substrate having suitable properties.

[0114] The stretching ratio can vary depending on the desired in-plane phase difference and thickness of the transparent conductive film substrate, the type of resin used, the thickness of the film used, the stretching temperature, etc. When biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching) is adopted, the stretching ratio in the first direction (for example, the longitudinal direction) and the stretching ratio in the second direction (for example, the width direction) are preferably as small as possible, and more preferably substantially equal. In such a configuration, a transparent conductive film substrate with a small in-plane phase difference Re (550) can be obtained. When biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching) is adopted, the stretching ratio in the first direction (for example, the longitudinal direction) and the second direction (for example, the width direction) can each be, for example, 1.1 to 3.0 times.

[0115] In an embodiment of the present invention, the stretching speed is preferably 10% / second or less, more preferably 7% / second or less, further preferably 5% / second or less, and particularly preferably 2.5% / second or less. By stretching a film comprising a specific polycarbonate resin as described above at such a small stretching speed, a substrate for a transparent conductive film having a small in-plane phase difference Re(550) can be obtained. The lower limit of the stretching speed may be, for example, 1.2% / second. If the stretching speed is too small, the productivity sometimes becomes impractical. It should be noted that when biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching) is adopted, the difference between the stretching speed in the first direction (for example, the longitudinal direction) and the stretching speed in the second direction (for example, the width direction) is preferably as small as possible, and more preferably substantially equal. With such a configuration, the in-plane phase difference Re(550) of the transparent conductive film substrate can be reduced.

[0116] D. Transparent conductive film

[0117] The transparent conductive film substrates described in Items A and B above are suitable for use in transparent conductive films. Therefore, embodiments of the present invention also include transparent conductive films. The transparent conductive film of an embodiment of the present invention includes: the transparent conductive film substrates described in Items A and B above, and a conductive layer. The conductive layer is typically formed on the visible side surface of the transparent conductive film substrate. The transparent conductive film may have an index matching (IM) layer, a hard coating (HC) layer, and / or an anti-blocking hard coating (ABHC) layer as needed.

[0118] (Conductive layer)

[0119] The conductive layer is typically a transparent conductive layer, and the total light transmittance of the conductive layer is preferably 80% or higher, more preferably 85% or higher, and even more preferably 90% or higher.

[0120] The density of the conductive layer is preferably 1.0 g / cm 3 ~10.5g / cm 3 , more preferably 1.3 g / cm 3 ~8.0g / cm 3 .

[0121] The surface resistance value of the conductive layer is preferably 0.1 Ω / □ to 1000 Ω / □, more preferably 0.5 Ω / □ to 500 Ω / □, and even more preferably 1 Ω / □ to 250 Ω / □.

[0122] Representative examples of the conductive layer include conductive layers comprising metal oxides. Examples of the metal oxide include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Among them, indium-tin composite oxide (ITO) is preferred.

[0123] 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 this range, a conductive layer having excellent conductivity and light transmittance can be obtained.

[0124] The conductive layer can typically be formed on the surface of the film substrate by sputtering.

[0125] (Refractive Index Matching (IM) Layer)

[0126] The IM layer can be formed on one side of the conductive layer. The IM layer can adopt a structure well known in the industry, so detailed description is omitted.

[0127] (Hard Coat (HC) Layer)

[0128] The HC layer can be formed between the IM layer and the transparent conductive film substrate. The HC layer can adopt a structure well known in the industry, and therefore detailed description thereof will be omitted.

[0129] (Anti-blocking hard coating (ABHC) layer)

[0130] The ABHC layer can be formed on the surface of the transparent conductive film substrate opposite to the HC layer. Details of the ABHC layer are described, for example, in Japanese Patent Application Laid-Open No. 2016-107503. The contents of this publication are incorporated herein by reference.

[0131] [Example]

[0132] The present invention will be described in detail below by way of examples, but the present invention is not limited to these examples. The measuring methods for the various properties in the examples are as follows. It should be noted that, unless otherwise specified, "parts" and "%" in the examples are by weight.

[0133] (1) In-plane phase difference Re(550)

[0134] The transparent conductive film substrates obtained in the Examples and Comparative Examples were cut into pieces 4 cm long and 4 cm wide to serve as measurement samples. The in-plane retardation and thickness-direction retardation of these samples were measured using an Axoscan (manufactured by Axometrics) at a wavelength of 550 nm and a temperature of 23°C.

[0135] (2) Dimensional shrinkage

[0136] The dimensional shrinkage of the transparent conductive film substrate in the MD direction and TD direction is measured as follows. Specifically, the transparent conductive film substrate is cut into a test piece with a width of 100 mm and a length of 100 mm, and a cross scratch is given to the four corners. The length (mm) of the MD direction and the TD direction before heating at the four points in the center of the cross scratch is measured using a CNC three-dimensional measuring machine (LEGEX774 manufactured by Mitutoyo Corporation). Then, it is put into an oven and heat treated (145°C, 60 minutes). After cooling at room temperature for 1 hour, the length (mm) of the MD direction and the TD direction after heating at the four points in the four corners is measured again using a CNC three-dimensional measuring machine. The measured values ​​are substituted into the following formula to calculate the thermal shrinkage of each of the MD direction and the TD direction.

[0137] Dimensional shrinkage (%) = [[length before heating (mm) - length after heating (mm)] / length before heating (mm)] × 100

[0138] (3) Sebum resistance test

[0139] The transparent conductive films obtained in the Examples and Comparative Examples were cut into 5 cm x 5 cm pieces. Using a hand roller, adhesive was applied to the ITO film-formed surface and the other surface. The adhesive surface was then attached to one surface of an alkali glass plate to produce a test piece. The resulting test piece was immersed in an oleic acid solution at 65°C and 90% RH for 72 hours. Test pieces that were transparent upon removal were marked as 0, while those that showed whitening or cracking were marked as x.

[0140] (4) Curl

[0141] The transparent conductive film obtained in the embodiment and the comparative example was cut into a size of 20 cm × 20 cm. After heating at 145 ° C for 60 minutes with the ITO surface facing up, it was cooled at room temperature (23 ° C) for 1 hour. Then, the sample was placed on a horizontal surface with the ITO layer facing up, and the height of the central part from the horizontal surface was measured (curl value A). In addition, the heights of the four corners from the horizontal surface were measured respectively, and the average value (curl value B) was calculated. The value (AB) obtained by subtracting the curl value B from the curl value A was calculated as the curl amount. When the curl value is in the range of 0 mm to 50 mm, it is recorded as 0, and otherwise it is recorded as ×.

[0142] <Example 1>

[0143] 1-1. Preparation of polycarbonate resin film

[0144] A polycarbonate resin, "Iupizeta (registered trademark)" (Tg: 174°C), manufactured by Mitsubishi Gas Chemical Co., Ltd., was vacuum dried at 120°C for 5 hours, and then a polycarbonate resin film having a thickness of 100 μm was produced using a film forming apparatus equipped with a single-screw extruder (manufactured by Isuzu Kakoki, screw diameter 25 mm, barrel set temperature: 295°C), a T-die (width 200 mm, set temperature: 295°C), a cooling roller (set temperature: 140-150°C), and a winder.

[0145] 1-2. Preparation of Transparent Conductive Film Substrate

[0146] The polycarbonate resin film obtained above was simultaneously biaxially stretched to a ratio of 2 in both the longitudinal and transverse directions. The stretching temperature was [Tg + 25°C]. This yielded a transparent conductive film substrate (thickness 25 μm). The resulting transparent conductive film substrate had an in-plane retardation Re (550) of 2.8 nm and a dimensional change ratio (MD / TD) of 0.06 / 0.04.

[0147] 1-3. Fabrication of Transparent Conductive Film

[0148] An anti-blocking hard coat (ABHC) layer was formed on one surface of the transparent conductive film substrate obtained above, and a hard coat (HC) layer was formed on the surface opposite to the ABHC layer. A refractive index matching (IM) layer was formed on the surface of the HC layer opposite to the transparent conductive film substrate. ITO was sputtered onto the surface of the IM layer opposite to the HC layer to form a conductive layer, thereby obtaining 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.

[0149] <Example 2>

[0150] A transparent conductive film substrate was obtained in the same manner as in Example 1 except that the thickness was changed to 15 μm. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 2.1 nm, and the dimensional change ratio (MD / TD) was 0.04 / 0.04. Furthermore, a transparent conductive film was obtained using the obtained transparent conductive film substrate in the same manner as in Example 1. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

[0151] <Example 3>

[0152] A transparent conductive film substrate was obtained in the same manner as in Example 1 except that the thickness was changed to 40 μm. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 2.8 nm, and the dimensional change ratio (MD / TD) was 0.08 / 0.09. Furthermore, a transparent conductive film was obtained using the obtained transparent conductive film substrate in the same manner as in Example 1. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

[0153] <Example 4>

[0154] A transparent conductive film substrate was obtained in the same manner as in Example 1, except that the stretching temperature was set to [Tg + 20°C]. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 3.4 nm, and the dimensional change rate (MD / TD) was 0.09 / 0.1. Furthermore, a transparent conductive film was obtained using the obtained transparent conductive film substrate in the same manner as in Example 1. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

[0155] <Comparative Example 1>

[0156] A transparent conductive film substrate was obtained in the same manner as in Example 1 except that the thickness was changed to 90 μm. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 4.7 nm, and the dimensional change ratio (MD / TD) was 0.22 / 0.22. Furthermore, a transparent conductive film was obtained using the obtained transparent conductive film substrate in the same manner as in Example 1. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

[0157] <Comparative Example 2>

[0158] A transparent conductive film substrate was obtained in the same manner as in Example 1 except that an ultra-high retardation polyethylene terephthalate film (manufactured by Mitsubishi Chemical Corporation, trade name "Diafoil") was used instead of the polycarbonate resin film. 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. Furthermore, a transparent conductive film was obtained using the obtained transparent conductive film substrate in the same manner as in Example 1. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

[0159] <Comparative Example 3>

[0160] A transparent conductive film substrate was obtained in the same manner as in Example 1 except that a polycycloolefin film (manufactured by Zeon Corporation, trade name "ZEONOR", Tg: 160°C) was used instead of the polycarbonate resin film. The in-plane retardation Re(550) of the obtained transparent conductive film substrate was 1.2 nm, and the dimensional change ratio (MD / TD) was 0.07 / 0.08. Furthermore, a transparent conductive film was obtained using the obtained transparent conductive film substrate in the same manner as in Example 1. The obtained transparent conductive film was subjected to the evaluations of (3) and (4) above. The results are shown in Table 1.

[0161] [Table 1]

[0162]

[0163] <Evaluation>

[0164] Table 1 clearly shows that the transparent conductive film substrates of the examples of the present invention exhibited suppressed whitening and / or cracking in the sebum resistance test, as well as reduced curling. This is presumably achieved by stretching the film comprising the specific polycarbonate resin. Furthermore, a comparison of the examples with the comparative examples clearly demonstrates that the use of a polycarbonate resin and a transparent conductive film substrate within a specified thickness range yields excellent properties (small in-plane retardation and small dimensional shrinkage).

[0165] Industrial applicability

[0166] The transparent conductive film substrate of the present invention is suitable for use in a transparent conductive film. By using the transparent conductive film substrate of the present invention, a transparent conductive film that is advantageous for image display can be obtained.

Claims

1. A transparent conductive film comprising a transparent conductive film substrate and a conductive layer formed on a surface of the substrate. The substrate comprises a polycarbonate resin, The dimensional shrinkage of the substrate at 145° C. is 0.2% or less in each of a first direction and a second direction perpendicular to the first direction. In the sebum resistance test, whitening and cracking of the substrate were suppressed. The in-plane phase difference Re(550) of the substrate is 5 nm or less, The thickness of the substrate is 10 μm to 15 μm.

2. The transparent conductive film according to claim 1, wherein The polycarbonate resin is substantially composed of a structural unit represented by the following general formula (I) and a structural unit represented by the following general formula (II), and satisfies the following conditions (a) to (d), wherein the structural unit represented by the general formula (I) is derived from an aliphatic diol compound having an aliphatic hydrocarbon group bonded to a terminal hydroxyl group, In the general formula (I), Q represents a hydrocarbon group having 3 or more carbon atoms which may contain atoms of different kinds, R1 to R4 each independently represent a group selected from the group consisting of a hydrogen atom, an aliphatic hydrocarbon group having 1 to 30 carbon atoms, and an aromatic hydrocarbon group having 6 to 20 carbon atoms, n and m each independently represent an integer of 0 to 10, wherein when Q does not contain an aliphatic hydrocarbon group bonded to a terminal hydroxyl group, n and m each independently represent an integer of 1 to 10, and at least one of R1 and R2, and at least one of R3 and R4 are each selected from the group consisting of a hydrogen atom and an aliphatic hydrocarbon group, In the general formula (II), R1 and R2 each independently represent a halogen atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a cycloalkyl group having 6 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a cycloalkoxy group having 6 to 20 carbon atoms, or an aryloxy group having 6 to 20 carbon atoms, p and q represent integers of 0 to 4, and X represents a single bond or a group selected from the group of divalent organic groups represented by the following general formula (II'). In the general formula (II'), R3 and R4 each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms, and R3 and R4 are optionally bonded to form an aliphatic ring. (a) having a structure represented by the following general formula (III), In the general formula (III), k represents an integer of 4 or greater, i represents an integer of 1 or greater, l represents an integer of 1 or greater, k' represents an integer of 0 or 1, and R represents a linear or branched hydrocarbon group, a phenyl group optionally containing fluorine, or a hydrogen atom, wherein i=1 in 70% by weight or more of the total amount of the resin. (b) The ratio of the structural unit represented by the general formula (I) to the structural unit represented by the general formula (II) is 1 to 30:99 to 70 (molar ratio), (c) a weight average molecular weight (Mw) of 30,000 to 100,000, (d) the content of the structural units represented by the following general formulas (1) and (2) is 2000 ppm or less, respectively, in terms of bisphenol acid, relative to the total amount of the structural units constituting the polycarbonate resin; General formula (1): General formula (2): X in the above-mentioned general formulae (1) and (2) is the same as X in the general formula (II).

3. The transparent conductive film according to claim 1 or 2, wherein The glass transition temperature (Tg) of the substrate is 145° C. or higher.

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