JP6987633B2 - Transparent film base material for touch sensor panel and touch sensor panel using it - Google Patents

Description

The present invention relates to a transparent film base material for a touch sensor panel and a touch sensor panel using the same.

Conventionally, glass has been used as a base material for a touch panel. However, glass has drawbacks such as being fragile and heavy, and does not have a sufficient material for making the touch panel thinner, lighter, and more flexible in recent years. Therefore, the use of a resin film such as a polyimide film as a base material for a touch panel instead of glass is being studied.

The polyimide used for the polyimide film is known as a resin having excellent heat resistance and dimensional stability. In particular, the aromatic polyimide obtained by the polycondensation reaction between the aromatic tetracarboxylic acid dianhydride and the aromatic diamines can be used even under high temperature conditions of 400 ° C. or higher and has excellent dimensional stability. There is. However, since aromatic polyimide is generally colored from light yellow to yellow, it is used as a material for electronic devices and the like that require transparency (for example, a substrate film for a transparent electrode such as a touch sensor panel). It was not suitable for application to (materials, etc.). Therefore, studies on aliphatic polyimides with excellent transparency are underway so that they can be applied to applications that require transparency, and conductive laminates using a substrate film made of aliphatic polyimides have been developed. ing. For example, Patent Document 1 discloses a transparent conductive film having excellent transparency, heat resistance, etc., in which a transparent conductive thin film is laminated on a substrate made of an aliphatic polyimide.

Japanese Unexamined Patent Publication No. 2004-111152

However, the conventional polyimide film as described above has a problem in visibility at the time of bending, and does not have sufficient characteristics for use as a base material for a flexible touch panel. Further, the base material of the touch panel is also required to have excellent process characteristics at the time of manufacturing the touch panel such as heat resistance and solvent resistance.

The present invention has been made in view of such circumstances, and provides a transparent film base material for a touch sensor panel having excellent visibility at the time of bending and process characteristics at the time of touch panel manufacturing, and a touch sensor panel using the same. The purpose is.

In order to achieve the above object, the present invention contains a polyimide polymer and an inorganic component, has a yellowness of 5 or less, a thickness direction phase difference _Rth of 200 nm or less, and an absolute photoelastic coefficient. Provided is a transparent film substrate for a touch sensor panel having a value of 30 × 10 ^-12 Pa ^-1 or less and a linear expansion coefficient of 50 ppm / ° C. or less.

According to the transparent film base material for a touch sensor panel, a polyimide polymer and an inorganic component are contained, and the yellowness, the phase difference _Rth in the thickness direction, the absolute value of the photoelastic coefficient, and the linear expansion coefficient are determined. Within the above range, the visibility at the time of bending and the process characteristics at the time of manufacturing the touch panel such as heat resistance and solvent resistance are excellent. In particular, it is difficult to obtain excellent visibility at the time of bending only by having high transparency of the film substrate, for example. On the other hand, in the transparent film base material for the touch sensor panel, the polyimide polymer and the inorganic component are used in combination, _{and the absolute values of the yellowness, the phase difference Rth} in the thickness direction, and the photoelastic coefficient are within a predetermined range. By doing so, it is possible to sufficiently suppress the contrast change and the hue change at the time of bending, and as a result, excellent visibility can be realized. Further, by using the polyimide-based polymer and the inorganic component in combination and setting the coefficient of linear expansion within a predetermined range, excellent process characteristics can be obtained.

The transparent film base material for the touch sensor panel can have an absolute value of the photoelastic coefficient of 23 × 10 ^-12 Pa ^-1 or less. When the absolute value of the photoelastic coefficient is 23 × 10 ^-12 Pa ^-1 or less, the phase difference change of the film due to stress is smaller and the light transmission characteristic is less likely to change. Therefore, the transparent film substrate is bent. Better visibility of time can be obtained.

In the transparent film base material for a touch sensor panel, the inorganic component can be a silicon material containing a silicon atom. Further, the silicon material can contain silica particles. By using a silicon material containing a silicon atom as an inorganic component and by containing silica particles, visibility and process characteristics at the time of bending can be further improved.

In the transparent film base material for a touch sensor panel, the content of the inorganic component can be 30 to 60% by mass based on the total solid content of the transparent film base material. When the content of the inorganic component is in the above range, the transparent film base material for the touch sensor panel becomes more excellent in transparency, flexibility, visibility at the time of bending, and process characteristics.

The transparent film substrate for the touch sensor panel can have a thickness of 20 to 50 μm. When the thickness of the transparent film base material is within the above range, the transparency, the flexibility, the visibility at the time of bending, and the process characteristics at the time of manufacturing the touch panel become more excellent.

In the transparent film substrate for the touch sensor panel, the in-plane phase difference R ₀ can be 20 nm or less. When the in-plane phase difference R ₀ is in the above range, the visibility at the time of bending can be improved.

The present invention also provides a touch sensor panel comprising the transparent film base material for a touch sensor panel of the present invention and an element layer having a detection element formed on the transparent film base material for a touch sensor panel. .. When the touch sensor panel is bent, the contrast change and the hue change of the bent portion are sufficiently suppressed, and the visibility is excellent.

According to the present invention, it is possible to provide a transparent film base material for a touch sensor panel, which is excellent in visibility at the time of bending and process characteristics, and a touch sensor panel using the transparent film base material.

It is schematic cross-sectional view which shows one Embodiment of the display device provided with the touch sensor panel.

Hereinafter, the present invention will be described in detail according to the preferred embodiment thereof.

[Transparent film base material for touch sensor panel]
The transparent film base material for a touch sensor panel according to the present embodiment (hereinafter, also simply referred to as “transparent film base material”) contains a polyimide-based polymer and an inorganic component, has a yellowness of 5 or less, and has a thickness. The directional retardation _Rth is 200 nm or less, the absolute value of the photoelastic coefficient is 30 × 10 ^-12 Pa ^-1 or less, and the linear expansion coefficient is 50 ppm / ° C. or less. Further, the in-plane retardation _R0 of the transparent film substrate is preferably 20 nm or less.

The yellowness (YI value) of the transparent film base material can be determined in accordance with JIS K 7373: 2006. The yellowness of the transparent film substrate according to the present embodiment is 5 or less, preferably 3 or less. When the yellowness is 5 or less, the transparent film base material can obtain excellent visibility at the time of bending.

The thickness direction retardation R _th for the transparent film substrate 1 direction refractive index N _x in the film _plane, N _x the the refractive index in the direction orthogonal to the N _y, the refractive index in the thickness direction of the film N _{It is calculated by the formula (A), where z} and the thickness of the film are d (nm). Here, N _x is the refractive index in the slow _{phase axis direction, N y} is the refractive index in the phase advance axis direction, and N _x > N _y is satisfied.
R _th = {(N _x + N _y ) /2-N _z } × d (nm)… (A)

The in-plane retardation R _{0 of the transparent film substrate is defined as N x for} the refractive index in one direction in the film surface, _{N y for} the refractive index in the direction orthogonal to N _x, and d (nm) for the thickness of the film. , (B) is calculated. Here, N _x is the refractive index in the slow _{phase axis direction, N y} is the refractive index in the phase advance axis direction, and N _x > N _y is satisfied.
R ₀ = (N _{x −} N _y ) × d (nm)… (B)

R _th of the transparent film substrate, a phase difference measuring apparatus manufactured by Oji Scientific Instruments Co., Ltd. (trade name: KOBRA) can be measured by. The thickness direction retardation _{R th} of this embodiment the transparent film substrate according is at 200nm or less, is preferably not more than 190 nm, more preferably 150nm or less, further preferably 120nm or less, It is particularly preferably 50 nm or less, and extremely preferably 40 nm or less. When the phase difference _{Rth in the} thickness direction is 200 nm or less, excellent visibility at the time of bending can be obtained. The Rth of the transparent film substrate may be 30 nm or more, may be larger than 50 nm, or may be 100 nm or more from the viewpoint of the film _{forming process.}

The absolute value of the photoelastic coefficient of the transparent film substrate is obtained from the relationship between the stress applied to the transparent film substrate and birefringence. Here, photoelasticity refers to a phenomenon in which when an external force is applied to an isotropic substance to cause internal stress, it exhibits optical anisotropy and exhibits birefringence. When the stress acting on a substance (force per unit area) is σ and the birefringence is Δn, the stress σ and the birefringence Δn are theoretically proportional and can be expressed as Δn = Cσ. This C is the photoelastic coefficient. In other words, if the stress σ acting on the substance is taken on the horizontal axis and the birefringence Δn of the substance when the stress is applied is taken on the vertical axis, the relationship between the two is theoretically a straight line, and the gradient of this straight line is The photoelastic coefficient C. The photoelastic coefficient of the transparent film substrate can be measured by a phase difference measuring device (trade name: KOBRA) manufactured by Oji Measuring Instruments Co., Ltd. The absolute value of the photoelastic coefficient of the transparent film substrate according to the present embodiment is 30 × 10 ^-12 Pa ^-1 or less, preferably 29 × 10 ^-12 Pa ^-1 or less, and more preferably 25 × 10 ^{It is -12} Pa ^-1 or less, more preferably 23 × 10 ^-12 Pa ^-1 or less, and particularly preferably 20 × 10 ^-12 Pa ^-1 or less. When the absolute value of the photoelastic coefficient is 30 × 10 ^-12 Pa ^-1 or less, the phase difference change of the film due to stress is small and the light transmission characteristic is difficult to change. Therefore, the transparent film base material is used at the time of bending. Excellent visibility can be obtained. The absolute value of photoelastic coefficient of the transparent film substrate according to the present embodiment can be ^{0 Pa -1} or more, preferably 0.1 × ¹⁰ -12 ^{Pa -1} or higher, more preferably 1 × 10 ^-12 Pa ^-1 or more, more preferably 10 × 10 ^-12 Pa ^-1 or more, particularly preferably 14 × 10 ^-12 Pa -1 or more, and extremely preferably 15 × 10 ^-12 Pa ^{-1. It is -1} or more. A transparent film substrate having an absolute value of the photoelastic coefficient of 0.1 × 10 ^-12 Pa ^-1 or more is easy to industrially produce and easily obtains better flexibility.

The method for adjusting the absolute value of the photoelastic coefficient of the transparent film substrate to 30 × 10 ^-12 Pa ^-1 or less is not particularly limited, but for example, a solvent-soluble polyimide polymer may be used, or the elasticity of the transparent film substrate may be used. By increasing the ratio or increasing the content of the inorganic particles, the absolute value of the photoelastic coefficient of the transparent film substrate can be lowered.

The coefficient of linear expansion of the transparent film substrate is a value measured as an average coefficient of linear expansion (also referred to as an average coefficient of linear expansion) in an arbitrary temperature range in accordance with JIS K7197. The coefficient of linear expansion of this embodiment is a value in the temperature range of 90 to 150 ° C. The coefficient of linear expansion of the transparent film substrate according to the present embodiment is 50 ppm / ° C. or less, preferably 40 ppm / ° C. or less. When the coefficient of linear expansion is 50 ppm / ° C. or less, the transparent film base material can obtain excellent process characteristics at the time of manufacturing a touch panel.

(Polyimide-based polymer)
The transparent film substrate contains a polyimide-based polymer. In the transparent film base material, the content of the polyimide-based polymer can be 40% by mass or more, preferably 40 to 70% by mass, preferably 45 to 65% by mass, based on the total amount of the transparent film base material. Is more preferable, and 50 to 60% by mass is further preferable. As a result, the transparent film base material becomes more excellent in transparency, flexibility, visibility at the time of bending, and process characteristics.

As used herein, the polyimide polymer means a polymer containing at least one repeating structural unit represented by the formula (PI), the formula (a), the formula (a') or the formula (b). Among them, it is preferable that the repeating structural unit represented by the formula (PI) is the main structural unit of the polyimide-based polymer from the viewpoint of the strength and transparency of the transparent film substrate. The repeating structural unit represented by the formula (PI) is preferably 40 mol% or more, more preferably 50 mol% or more, still more preferably 70 mol, based on all the repeating structural units of the polyimide-based polymer. % Or more, particularly preferably 90 mol% or more, and even more preferably 98 mol% or more.

G in the formula (PI) represents a tetravalent organic group, and A represents a divalent organic group. ^{G 2} in the formula (a) represents a trivalent organic group, and A ² represents a divalent organic group. In the formula (a'), G ³ represents a tetravalent organic group, and A ³ represents a divalent organic group. ^{G 4} and ^{A 4} in the formula (b) represents each a divalent organic group.

In the formula (PI), the organic group of the tetravalent organic group represented by G (hereinafter, may be referred to as the organic group of G) is an acyclic aliphatic group, a cyclic aliphatic group, and an aromatic group. Examples include groups selected from the group consisting of groups. From the viewpoint of transparency and flexibility of the transparent film substrate, G is preferably a tetravalent cyclic aliphatic group and a tetravalent aromatic group. Examples of the aromatic group include a monocyclic aromatic group, a condensed polycyclic aromatic group, and a non-condensed polycyclic aromatic group in which the aromatic groups are directly or interconnected by a bonding group. From the viewpoint of transparency and suppression of coloring of the transparent film substrate, the organic group of G is a cyclic aliphatic group, a cyclic aliphatic group having a fluorine-based substituent, and a monocyclic aromatic group having a fluorine-based substituent. It may be a fused polycyclic aromatic group having a group, a fluorine-based substituent, or a non-condensed polycyclic aromatic group having a fluorine-based substituent. As used herein, the fluorine-based substituent means a group containing a fluorine atom. The fluorine-based substituent is preferably a fluoro group (fluorine atom, −F) and a perfluoroalkyl group, and more preferably a fluoro group and a trifluoromethyl group.

More specifically, the organic group of G is, for example, a saturated or unsaturated cycloalkyl group, a saturated or unsaturated heterocycloalkyl group, an aryl group, a heteroaryl group, an arylalkyl group, an alkylaryl group, a heteroalkylaryl. It is selected from groups that have a group and any two of these (which may be the same) and are linked to each other directly or by a linking group. Examples of the bonding group include -O-, an alkylene group having 1 to 10 carbon atoms, -SO _2- , -CO- or -CO-NR- (R is a methyl group, an ethyl group, a propyl group and the like having 1 to 1 carbon atoms. (Representing an alkyl group of 3 or a hydrogen atom).

The tetravalent organic group represented by G usually has 2 to 32 carbon atoms, preferably 4 to 15 carbon atoms, more preferably 5 to 10 carbon atoms, and further preferably 6 to 8 carbon atoms. When the organic group of G is a cyclic aliphatic group and an aromatic group, at least one of the carbon atoms constituting these groups may be replaced with a heteroatom. Examples of the heteroatom include O, N or S.

Specific examples of G include a group represented by the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), and the formula (26). * In the formula indicates a bond. Z in the formula (26) is a single bond, -O-, -CH _2- , -C (CH ₃ ) _2- , -Ar-O-Ar-, -Ar _{-CH 2-Ar-, -Ar-} Represents C (CH ₃ ) _2- Ar- or -Ar-SO _2- Ar-. Ar represents an aryl group having 6 to 20 carbon atoms, and examples thereof include a phenylene group. At least one of the hydrogen atoms of these groups may be substituted with a fluorine-based substituent.

In the formula (PI), the organic group of the divalent organic group represented by A (hereinafter, may be referred to as the organic group of A) is derived from an acyclic aliphatic group, a cyclic aliphatic group and an aromatic group. Divalent organic groups selected from the group of The divalent organic group represented by A is preferably a divalent cyclic aliphatic group and a divalent aromatic group. The aromatic group includes a monocyclic aromatic group, a fused polycyclic aromatic group, and a non-condensed polycyclic aromatic group having two or more aromatic rings, which are directly or linked to each other by a bonding group. The group is mentioned. From the viewpoint of transparency and suppression of coloring of the transparent film substrate, it is preferable that a fluorine-based substituent is introduced into the organic group of A.

More specifically, the organic group of A is, for example, a saturated or unsaturated cycloalkyl group, a saturated or unsaturated heterocycloalkyl group, an aryl group, a heteroaryl group, an arylalkyl group, an alkylaryl group, a heteroalkylaryl. It is selected from groups that have a group and any two of them (which may be the same) and are linked to each other directly or by a linking group. Examples of the heteroatom include O, N or S, and examples of the bonding group are -O-, an alkylene group having 1 to 10 carbon atoms, -SO _2- , -CO- or -CO-NR- (R is methyl). An alkyl group having 1 to 3 carbon atoms such as a group, an ethyl group and a propyl group, or a hydrogen atom) can be mentioned.

The number of carbon atoms of the divalent organic group represented by A is usually 2 to 40, preferably 5 to 32, more preferably 12 to 28, and further preferably 24 to 27.

Specific examples of A include a group represented by the formula (30), the formula (31), the formula (32), the formula (33) and the formula (34). * In the formula indicates a bond. Z ^{1 to} Z ³ are independently single-bonded, -O-, -CH _2- , -C (CH ₃ ) _2- , -SO _2- , -CO- or -CO-NR- (R is Represents an alkyl group having 1 to 3 carbon atoms such as a methyl group, an ethyl group, and a propyl group, or a hydrogen atom). In the following groups, Z ¹ and Z ² and Z ² and Z ³ are preferably in the meta or para position with respect to each ring, respectively. Further, ^{it is preferable that the single bond between Z 1} and the terminal, the single bond between Z ² and the terminal, and ^{the single bond between Z 3} and the terminal are in the meta-position or the para-position, respectively. One example of A is that Z ¹ and Z ³ are -O- and Z ² is -CH _2- , -C (CH ₃ ) _2- or -SO _2- . One or more of the hydrogen atoms of these groups may be substituted with a fluorine-based substituent.

At least one of A and G is at least selected from the group in which at least one hydrogen atom among the hydrogen atoms constituting these is composed of a fluorine-based substituent, a hydroxyl group, a sulfone group, an alkyl group having 1 to 10 carbon atoms, or the like. It may be substituted with one kind of functional group. Further, when the organic group of A and the organic group of G are cyclic aliphatic groups or aromatic groups, respectively, it is preferable that at least one of A and G has a fluorine-based substituent, and both A and G have a fluorine-based substituent. It is more preferable to have a fluorine-based substituent.

^{G 2} in the formula (a) is a trivalent organic group. This organic group can be selected from the same groups as the organic group of G in the formula (PI) except that it is trivalent. Examples of G ² include the formulas (20), formulas (21), formulas (22), formulas (23), formulas (24), formulas (25) and formulas (26) given as specific examples of G. A group in which any one of the four bonds of the represented group is replaced with a hydrogen atom can be mentioned. ^{A 2} in formula (a) can be selected from the same groups as A in formula (PI).

^{G 3} in formula (a') can be selected from the same groups as G in formula (PI). A ³ in the formula (a ') may be selected from the same groups as A in the formula (PI).

^{G 4} in formula (b) is a divalent organic group. This organic group can be selected from the same groups as the organic group of G in the formula (PI) except that it is a divalent group. Examples of G ⁴ include equations (20), (21), equations (22), (23), equations (24), equations (25), and equations (26) given as specific examples of G. A group in which any two of the four bonds of the represented group are replaced with a hydrogen atom can be mentioned. A ⁴ in the formula (b) may be selected from the same groups as A in the formula (PI).

The polyimide-based polymer contained in the transparent film substrate includes diamines and a tetracarboxylic acid compound (including an acid chloride compound and a tetracarboxylic acid compound analog such as a tetracarboxylic acid dianhydride) or a tricarboxylic acid compound (acid chloride). It may be a condensed polymer obtained by polycondensing with at least one of a compound and a tricarboxylic acid compound analog such as tricarboxylic acid anhydride). Further, a dicarboxylic acid compound (including an analog such as an acid chloride compound) may be polycondensed. The repeating structural unit represented by the formula (PI) or the formula (a') is usually derived from diamines and tetracarboxylic acid compounds. The repeating structural unit represented by the formula (a) is usually derived from diamines and tricarboxylic acid compounds. The repeating structural unit represented by the formula (b) is usually derived from diamines and dicarboxylic acid compounds.

Examples of the tetracarboxylic acid compound include an aromatic tetracarboxylic acid compound, an alicyclic tetracarboxylic acid compound and an acyclic aliphatic tetracarboxylic acid compound. Two or more kinds of tetracarboxylic acid compounds may be used in combination. The tetracarboxylic acid compound is preferably a tetracarboxylic dianhydride. Examples of the tetracarboxylic dianhydride include aromatic tetracarboxylic dianhydride, alicyclic tetracarboxylic dianhydride and acyclic aliphatic tetracarboxylic dianhydride.

The tetracarboxylic acid compound is an alicyclic tetracarboxylic acid compound and an aromatic tetracarboxylic acid compound from the viewpoints of solubility of the polyimide-based polymer in a solvent, transparency when a transparent film base material is formed, and flexibility. Is preferable. From the viewpoint of transparency and suppression of coloring of the transparent film substrate, the tetracarboxylic acid compound is an alicyclic tetracarboxylic acid compound having a fluorine-based substituent and an aromatic tetracarboxylic acid compound having a fluorine-based substituent. Is preferable, and it is more preferable that it is an alicyclic tetracarboxylic acid compound.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, alicyclic tricarboxylic acids, acyclic aliphatic tricarboxylic acids and their related acid chloride compounds, acid anhydrides and the like. The tricarboxylic acid compound is preferably an aromatic tricarboxylic acid, an alicyclic tricarboxylic acid, an acyclic aliphatic tricarboxylic acid and an acid chloride compound related thereto. Two or more kinds of tricarboxylic acid compounds may be used in combination.

The tricarboxylic acid compound is preferably an alicyclic tricarboxylic acid compound or an aromatic tricarboxylic acid compound from the viewpoints of solubility of the polyimide-based polymer in a solvent, transparency when a transparent film substrate is formed, and flexibility. .. From the viewpoint of transparency and suppression of coloring of the transparent film substrate, the tricarboxylic acid compound is preferably an alicyclic tricarboxylic acid compound having a fluorine-based substituent and an aromatic tricarboxylic acid compound having a fluorine-based substituent.

Examples of the dicarboxylic acid compound include aromatic dicarboxylic acid, alicyclic dicarboxylic acid, acyclic aliphatic dicarboxylic acid and acid chloride compounds related thereto, acid anhydride and the like. The dicarboxylic acid compound is preferably an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid, an acyclic aliphatic dicarboxylic acid and an acid chloride compound related thereto. Two or more kinds of dicarboxylic acid compounds may be used in combination.

The dicarboxylic acid compound is preferably an alicyclic dicarboxylic acid compound or an aromatic dicarboxylic acid compound from the viewpoint of solubility of the polyimide polymer in a solvent, transparency when a transparent film substrate is formed, and flexibility. .. From the viewpoint of transparency and suppression of coloring of the transparent film substrate, the dicarboxylic acid compound is preferably an alicyclic dicarboxylic acid compound having a fluorine-based substituent and an aromatic dicarboxylic acid compound having a fluorine-based substituent.

Examples of diamines include aromatic diamines, alicyclic diamines and aliphatic diamines. Two or more kinds of diamines may be used in combination. From the viewpoint of solubility of the polyimide polymer in a solvent, transparency and flexibility when a transparent film substrate is formed, the diamines may be an alicyclic diamine and an aromatic diamine having a fluorine-based substituent. preferable.

When such a polyimide polymer is used, it has particularly excellent flexibility, high light transmittance (for example, 85% or more, preferably 88% or more with respect to light of 550 nm), and low yellowness. It is easy to obtain a transparent film substrate having a YI value (for example, 5 or less, preferably 3 or less) and a low haze (for example, 1.5% or less, preferably 1.0% or less).

The polyimide-based polymer may be a copolymer containing a plurality of the above-mentioned repeating units of different types. The weight average molecular weight of the polyimide polymer is usually 10,000 to 500,000. The weight average molecular weight of the polyimide polymer is preferably 50,000 to 500,000, more preferably 70,000 to 400,000. The weight average molecular weight is a standard polystyrene-equivalent molecular weight measured by GPC. The larger the weight average molecular weight of the polyimide polymer, the easier it is to obtain high flexibility. However, if the weight average molecular weight of the polyimide polymer is too large, the viscosity of the varnish becomes high and the processability tends to decrease. There is.

The polyimide-based polymer may contain a halogen atom such as a fluorine atom that can be introduced by the above-mentioned fluorine-based substituent or the like. Since the polyimide polymer contains a halogen atom, the elastic modulus of the transparent film substrate can be improved and the yellowness can be reduced. As a result, it is possible to suppress the occurrence of scratches and wrinkles on the transparent film base material and improve the transparency of the transparent film base material. The halogen atom is preferably a fluorine atom. The content of the halogen atom in the polyimide-based polymer is preferably 1 to 40% by mass, more preferably 1 to 30% by mass, based on the total mass of the polyimide-based polymer.

In the polyimide-based polymer, when a film (layer) having a thickness of 50 μm made of the polyimide-based polymer is formed, the total light transmittance of the polyimide-based polymer film is 85% or more, and the polyimide-based polymer has a high height. A transparent polyimide-based polymer having a molecular film yellowness (YI value) of 10 or less is preferable. The total light transmittance is preferably 90% or more. The yellowness is preferably 5 or less. By using such a transparent polyimide-based polymer, a highly transparent transparent film base material can be obtained. Further, the total light transmittance of the polyimide polymer film is more preferably 91% or more, further preferably 92% or more. The yellowness is more preferably 3 or less, and particularly preferably 2.5 or less. Here, the polyimide-based polymer film can be formed by applying and drying a polyimide-based polymer dissolved in a solvent. The total light transmittance of the polyimide-based polymer film can be determined in accordance with JIS K7105: 1981. The yellowness YI of the polyimide-based polymer film can be determined in accordance with JIS K 7373: 2006.

(Inorganic component)
The transparent film substrate further contains an inorganic component. By containing the inorganic component, the strength of the transparent film base material can be increased, and the process characteristics at the time of manufacturing the touch panel such as heat resistance and solvent resistance can be enhanced.

The inorganic component is preferably a silicon material containing a silicon atom. Further, the inorganic component preferably contains inorganic particles. An example of an inorganic particle is a particle containing a silicon atom. An example of a particle containing a silicon atom is a silica particle. Other examples of inorganic particles are titania particles, alumina particles, zirconia particles.

The average primary particle diameter of the inorganic particles can be 200 nm or less, preferably 10 to 100 nm, and more preferably 20 to 50 nm. The reason why the average primary particle diameter of the inorganic particles is preferably within the above range is that the transparency of the film is improved when the average primary particle diameter is 200 nm or less, and the film is when the average primary particle diameter is 10 nm or more. This is because the strength of the particles is improved. The measurement of the primary particle size can be a directional diameter by a transmission electron microscope (TEM). The average primary particle diameter can be obtained by measuring the primary particle diameter at 10 points by TEM observation and as an average value thereof.

When the transparent film substrate contains inorganic particles, the content ratio of the polyimide-based polymer to the inorganic particles can be 1: 9 to 9: 1 in terms of mass ratio, and can be 3: 7 to 8: 2. Is preferable. When the compounding ratio of the polyimide polymer and the inorganic particles is within the above range, the transparency and the mechanical strength tend to be improved.

Inorganic particles may be bonded to each other by a molecule having a siloxane bond (−SiOSi−).

The inorganic component may contain an organic silicon compound such as a quaternary alkoxysilane such as tetraethyl orthosilicate, or an inorganic component derived from a metal alkoxide such as a metal alkoxide having an amino group. Such an inorganic component can be, for example, _{a molecule having a SiO 2} or a siloxane bond (−SiOSi−). When the inorganic particles and the organosilicon compound are mixed in the varnish for forming the transparent film base material, a structure in which the inorganic particles are bonded to each other by molecules having a siloxane bond is formed in the obtained transparent film base material. To. By having such a structure, the transparent film base material becomes more excellent in transparency, flexibility, visibility at the time of bending, and process characteristics.

In the transparent film base material, the content of the inorganic component can be 30 to 60% by mass, preferably 35 to 55% by mass, preferably 40 to 50% based on the total solid content of the transparent film base material. More preferably, it is by mass%. As a result, the transparent film base material becomes more excellent in transparency, flexibility, visibility at the time of bending, and process characteristics.

The transparent film base material may further contain other components as long as the transparency and flexibility are not impaired. Examples of other components include antioxidants, mold release agents, stabilizers, bluing agents, flame retardants, lubricants, leveling agents and the like.

The thickness of the transparent film base material is appropriately adjusted depending on the intended use, but can be, for example, 20 to 50 μm, preferably 22 to 45 μm, and more preferably 25 to 40 μm. When the thickness of the transparent film base material is within the above range, the transparency, the flexibility, the visibility at the time of bending, and the process characteristics at the time of manufacturing the touch panel become more excellent.

This transparent film substrate can have a total light transmittance of 85% or more, preferably 90% or more, in accordance with JIS K7631-1: 1997. Further, this transparent film base material can have a haze of 1.5% or less, preferably 1.0% or less, in accordance with JIS K 7136: 2000.

(Production method)
Next, an example of the method for manufacturing the transparent film base material of the present embodiment will be described.

A polyimide-based varnish is prepared by dissolving a solvent-soluble polyimide-based polymer polymerized using a known polyimide-based polymer synthesis method in a solvent. The solvent may be any solvent that dissolves the polyimide-based polymer, and for example, DMAc, DMF, DMSO, γ-butyrolactone, or a combination thereof can be used. The polyimide-based polymer may be any solvent-soluble polyimide-based polymer, and includes alicyclic tetracarboxylic acid dianhydride, aromatic diamines, alicyclic diamines, and acyclic aliphatic diamines. It is preferable to have a structure of a single substance or a combination of two or more kinds.

The polyimide-based varnish may contain water in addition to the above solvent. Since the varnish contains water, it _{is easy to obtain a transparent film substrate in which the yellowness, the phase difference Rth} in the thickness direction, the absolute value of the photoelastic coefficient, and the linear expansion coefficient satisfy the above-mentioned conditions.

The polyimide-based varnish can further contain the above-mentioned inorganic particles. Further, the polyimide-based varnish can also contain an organosilicon compound such as the above-mentioned tetraethyl orthosilicate or the like quaternary alkoxysilane.

When the polyimide-based varnish contains inorganic particles, the varnish can further contain a linker for bonding the inorganic particles to each other by a siloxane bond. An example of a linker is a metal alkoxide such as alkoxysilane. Examples of metal alkoxides are metal alkoxides having an amino group, examples of which are 3-aminopropyltriethoxysilane and 3- (2-aminoethylamino) propyltrimethoxysilane. The amino group of the linker can catalyze the reaction of the inorganic particles with the linker.

The amount of the linker added can be 0.1 to 100 parts by mass with respect to 100 parts by mass of the solid content (polyimide-based polymer and inorganic particles) of the polyimide-based varnish, and is 0.5 to 50 parts by mass. Is preferable.

Further, an additive may be added to the polyimide varnish, and as an additive, for example, an antioxidant, a mold release agent, a stabilizer, a bluing agent, a flame retardant, a lubricant, a leveling agent and the like are added. You may.

Next, the above-mentioned polyimide-based varnish is applied onto a PET substrate, a SUS belt, or a glass substrate to form a coating film by a known roll-to-roll or batch method, and the coating film is dried. , A film is obtained by peeling from the substrate.

The coating film is dried at a temperature of 50 to 350 ° C. by evaporating the solvent under conditions of an inert atmosphere or reduced pressure as appropriate. The coating film may be dried in multiple steps by changing the temperature conditions. In that case, the temperature can be raised toward the latter stage.

Further, the coating film may be further dried after being peeled from the substrate. That is, the coating film can be dried on the base material as the first drying, then peeled off from the base material, and further dried as the second drying. The second drying can be performed by attaching a gold frame to the coating film peeled off from the base material. The second drying can be performed at a higher temperature than the first drying, for example, the first drying can be performed at 50 to 150 ° C. and the second drying can be performed at 180 to 350 ° C. Further, each of the first drying and the second drying may be performed in multiple stages by changing the temperature conditions.

[Touch sensor panel and display device]
FIG. 1 is a schematic cross-sectional view showing an embodiment of a display device provided with a touch sensor panel. The display device 100 shown in FIG. 1 has an organic EL device 50, a touch sensor panel 70, and a front plate 90, and is housed in a housing (not shown). The space between the organic EL device 50 and the touch sensor panel 70, and the space between the touch sensor panel 70 and the front plate 90 are adhered, for example, with an optical adhesive (Optical Clear Adaptive, OCA) (not shown).

The organic EL device 50 includes an organic EL element 51, a first substrate 55, a second substrate 56, and a sealing material 59.

The organic EL element 51 has a pair of electrodes (first electrode 52 and second electrode 53) and a light emitting layer 54. The light emitting layer 54 is arranged between the first electrode 52 and the second electrode 53.

The first electrode 52 uses a conductive material having light transmission as a forming material. The second electrode 53 may have light transmission. Known materials can be used as the first electrode 52 and the second electrode 53.

The light emitting layer 54 can be made of a known light emitting material constituting the organic EL element, and may be either a low molecular weight compound or a high molecular weight compound.

In the organic EL device 50, when electric power is supplied between the first electrode 52 and the second electrode 53, carriers (electrons and holes) are supplied to the light emitting layer 54, and light is generated in the light emitting layer 54. The light generated in the light emitting layer 54 is emitted to the outside of the organic EL device 50 via the first electrode 52 and the first substrate 55.

The first substrate 55 uses a material having light transmission as a forming material. The second substrate 56 may have light transmission. The first substrate 55 and the second substrate 56 are bonded to each other by a sealing material 59 arranged so as to surround the periphery of the organic EL element to form a sealing structure for internally sealing the organic EL element. ing.

As a material for forming either one or both of the first substrate 55 and the second substrate 56, a known transparent resin such as an acrylic resin can be used.

The touch sensor panel 70 has a substrate 71 and an element layer 72 having a detection element formed on the substrate 71.

The transparent film base material for the touch sensor panel of the present embodiment is used for the substrate 71.

A known detection element composed of a semiconductor element, wiring, a resistor, or the like is formed on the element layer 72. As the configuration of the detection element, a configuration that realizes a known detection method such as a matrix switch, a resistance film method, and a capacitance type can be adopted.

The touch sensor panel 70 using the transparent film base material for the touch sensor panel of the present embodiment on the substrate 71 is excellent in visibility because the contrast change and the hue change of the bent portion are sufficiently suppressed when bent. ..

The front plate 90 is made of a light-transmitting material and functions as a protective member for protecting the display device. As the front plate 90, a known transparent resin such as an acrylic resin can be used.

Further, the display device 100 adds various functional layers such as an ultraviolet absorbing layer, a hard coat layer, an adhesive layer, a hue adjusting layer, and a refractive index adjusting layer as a part of each of the above-mentioned members or as another member. It can also be provided with a layer of light.

Since the display device 100 includes the touch sensor panel 70 using the transparent film base material for the touch sensor panel of the present embodiment, the contrast change and the hue change of the bent portion are sufficiently suppressed when the display device 100 is bent, and the organic EL device 50 is provided. The visibility of the display is excellent.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example 1]
(Preparation of polyimide varnish)
20% by mass γ-butyrolactone solution of polyimide having a glass transition temperature of 390 ° C (“Neoprim” manufactured by Mitsubishi Gas Chemicals, Inc., a polyimide polymer containing a repeating structural unit of formula (PI)), solid in γ-butyrolactone A polyimide-based varnish was prepared by mixing a dispersion liquid in which silica particles having a minute concentration of 30% by mass (average primary particle diameter 30 nm) and a dimethylacetamide solution of alkoxysilane having an amino group were mixed and stirred for 30 minutes.

Here, the blending amount of each of the above components is such that the content of the silica particles is 50% by mass based on the total amount of the silica particles and the polyimide-based polymer (solid content of the polyimide-based varnish) (100% by mass). It was adjusted. Further, in the polyimide-based varnish, the amount of the alkoxysilane having an amino group added was 1.5 parts by mass with respect to 100 parts by mass of the total amount of the silica particles and the polyimide-based polymer (solid content of the polyimide-based varnish).

(Manufacturing of transparent film base material for touch sensor panel)
A polyimide-based varnish is applied to a glass substrate, heated at 50 ° C. for 30 minutes, then at 140 ° C. for 10 minutes, then heated at 210 ° C. for 1 hour, and peeled off from the glass substrate to form a polyimide-based polyimide having a thickness of 25 μm. I got a film. This polyimide film was used as a transparent film base material for a touch sensor panel.

[Example 2]
The same as in Example 1 except that the blending amount of each component was adjusted so that the content of the silica particles was 55% by mass based on the total amount of the silica particles and the polyimide-based polymer at the time of preparing the polyimide-based varnish. Then, a polyimide-based varnish was prepared and a transparent film base material for a touch sensor panel was manufactured using the polyimide-based varnish.

[Example 3]
The same as in Example 1 except that the blending amount of each component was adjusted so that the content of the silica particles was 30% by mass based on the total amount of the silica particles and the polyimide-based polymer at the time of preparing the polyimide-based varnish. Then, a polyimide-based varnish was prepared and a transparent film base material for a touch sensor panel was manufactured using the polyimide-based varnish.

[Example 4]
18% by mass γ-butyrolactone solution of polyimide "KPI-MX300F (100)" manufactured by Kawamura Sangyo Co., Ltd., dispersion liquid in which silica particles (average primary particle diameter 30 nm) having a solid content concentration of 30% by mass are dispersed in γ-butyrolactone. , A dimethylacetamide solution of alkoxysilane having an amino group was mixed, and the mixture was stirred for 30 minutes to prepare a polyimide-based varnish.

Here, the blending amount of each of the above components was adjusted so that the content of the silica particles was 50% by mass based on the total amount of the silica particles and the polyimide-based polymer. Further, in the polyimide-based varnish, the amount of the alkoxysilane having an amino group added was 1.5 parts by mass with respect to 100 parts by mass of the total amount of the silica particles and the polyimide-based polymer.

(Manufacturing of transparent film base material for touch sensor panel)
A polyimide-based varnish is applied to a glass substrate, heated at 50 ° C. for 30 minutes, then at 140 ° C. for 10 minutes, then heated at 210 ° C. for 1 hour, and peeled off from the glass substrate to form a polyimide-based polyimide having a thickness of 25 μm. I got a film. This polyimide film was used as a transparent film base material for a touch sensor panel.

[Comparative Example 1]
Preparation of polyimide varnish and transparent film base material for touch sensor panel using the same as in Example 1 except that silica and alkoxysilane having an amino group were not added at the time of preparation of polyimide varnish. Fabrication was performed.

[Comparative Example 2]
A polyimide-based varnish was prepared and a transparent film base material for a touch sensor panel was produced using the polyimide varnish in the same manner as in Example 3 except that the thickness of the transparent film base material for the touch sensor panel was 50 μm.

[Comparative Example 3]
Preparation of polyimide varnish and transparent film base material for touch sensor panel using the same as in Example 4 except that silica and alkoxysilane having an amino group were not added at the time of preparation of polyimide varnish. Fabrication was performed.

[Comparative Example 4]
The same as in Example 4 except that the blending amount of each component was adjusted so that the content of the silica particles was 40% by mass based on the total amount of the silica particles and the polyimide-based polymer at the time of preparing the polyimide-based varnish. Then, a polyimide-based varnish was prepared and a transparent film base material for a touch sensor panel was manufactured using the polyimide-based varnish.

[Measurement of phase difference _{Rth in the thickness direction]
The phase difference Rth} in the thickness direction of the transparent film substrate of Examples and Comparative Examples was measured using a phase difference measuring device (manufactured by Oji Measuring Instruments Co., Ltd., trade name: KOBRA). The results are shown in Table 1.

[Measurement of photoelasticity coefficient]
The transparent film substrate of Examples and Comparative Examples was cut into a width of 20 mm and a length of 150 mm to obtain a test piece. _{The in-plane phase difference R0} was measured with tensile stresses of 0 MPa, 3 MPa, 6 MPa, 9 MPa, and 12 MPa applied in the long side direction of the test piece. The quotient obtained by dividing each in-plane phase difference R ₀ by the thickness of the test piece is the birefringence Δn. The horizontal axis plots the tensile stress σ, and the vertical axis plots the birefringence Δn when the stress acts on the test piece, and the slope when the relationship between the two is approximated by the least squares method so that Δn = Cσ. The absolute value of C was obtained and used as the photoelastic coefficient. The results are shown in Table 1.

[Measurement of optical characteristics]
(Yellowness)
The yellowness (Yellow Index: YI) of the transparent film substrate of Examples and Comparative Examples was measured by an ultraviolet-visible near-infrared spectrophotometer V-670 manufactured by JASCO Corporation. After performing background measurement in the absence of a sample, a transparent film substrate was set in a sample holder, transmittance was measured for light of 300 to 800 nm, and tristimulus values (X, Y, Z) were determined. .. From these three stimulus values, YI was calculated based on the following formula. The results are shown in Table 1.
YI = 100 × (1.2769X-1.0592Z) / Y

(Total light transmittance)
For the total light transmittance of the transparent film substrate of Examples and Comparative Examples, the transmittance for light of 300 to 800 nm was measured using an ultraviolet visible near infrared spectrophotometer V-670 manufactured by JASCO Corporation. The total light transmittance (Tt) of the transparent film substrates of Examples and Comparative Examples was more than 90%.

[Measurement of coefficient of linear expansion]
The transparent film substrates of Examples and Comparative Examples were cut into 5 mm wide and 20 mm long to obtain test pieces. In accordance with JIS K7197, the temperature rises from 25 ° C to 180 ° C at a rate of 10 ° C / min using a thermomechanical analyzer (TMA) "EXSTAR-6000" manufactured by SII Nanotechnology Co., Ltd. Then, the amount of deformation of the test piece at each temperature was measured. The linear expansion coefficient (average linear expansion coefficient) of the test piece was obtained from the amount of deformation in the temperature range of 90 to 150 ° C. The case where the film size increases (expands) as the temperature rises is regarded as positive (plus), and the case where the film size decreases (shrinks) as the temperature rises is regarded as negative (minus). The results are shown in Table 1.

[Measurement of glass transition temperature]
The glass transition temperature (Tg) of the transparent film substrate of Examples and Comparative Examples was measured using DSC Q200 manufactured by TA Instruments, the measurement sample amount: 5 mg, the temperature range: room temperature to 400 ° C., and the temperature rise rate: 10 ° C./min. It was measured under the condition of. The results are shown in Table 1. It can be said that the higher the glass transition temperature, the higher the heat resistance of the transparent film substrate and the better the process characteristics.

[Measurement of elastic modulus]
As an elastic modulus measuring device, Autograph AG-IS manufactured by Shimadzu Corporation was used. A strip-shaped transparent film substrate having a width of 10 mm and a length of 100 mm was prepared as a test piece. A tensile test was performed under the conditions of a chuck distance of 50 mm and a tensile speed of 20 mm / min, and the tensile elastic modulus of the transparent film substrate was measured. The results are shown in Table 1.

[Evaluation of solvent resistance]
The transparent film substrate of Examples and Comparative Examples was cut into a width of 50 mm and a length of 50 mm to obtain a test piece. Each of these test pieces was immersed in a large excess amount of methyl ethyl ketone (MEK), left at 25 ° C. for 1 hour, and then changes in the test pieces were observed. Those in which no change was observed in the test pieces were evaluated as "A", and those in which the test pieces were dissolved or whitened were evaluated as "B". The results are shown in Table 1. If the evaluation result is A, it can be said that the transparent film base material has high solvent resistance and excellent process characteristics.

[Evaluation of visibility when bending]
The transparent film substrates of Examples and Comparative Examples were cut into a width of 10 mm and a length of 100 mm to obtain test pieces. This test piece was bent 180 ° at the central portion in the longitudinal direction, and the presence or absence of contrast change and hue change at the bent portion was visually observed. Those having a small contrast change and hue change in the bent portion and having good visibility were evaluated as "A", and those having a large contrast change or hue change in the bent portion and having poor visibility were evaluated as "B". The results are shown in Table 1.

50 ... organic EL device, 70 ... touch sensor panel, 71 ... substrate, 72 ... element layer, 90 ... front plate, 100 ... display device.

Claims (4)

Contains polyimide polymer and inorganic components,
The inorganic component contains silica particles, and the content of the inorganic component is 30 to 60% by mass based on the total solid content of the transparent film base material.
The yellowness is 5 or less, the phase difference _Rth in the thickness direction is 200 nm or less, the absolute value of the photoelastic coefficient is 30 × 10 ^-12 Pa ^-1 or less, and the linear expansion coefficient is 50 ppm / ° C. or less. , Transparent film substrate for touch sensor panel. The transparent film base material for a touch sensor panel according to claim 1, wherein the absolute value of the photoelastic coefficient is 23 × 10 ^-12 Pa ^{-1 or less.} The transparent film substrate for a touch sensor panel according to claim 1 or 2 , which has a thickness of 20 to 50 μm. A touch sensor comprising the transparent film base material for a touch sensor panel according to any one of claims 1 to 3 and an element layer having a detection element formed on the transparent film base material for a touch sensor panel. panel.

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