JP3295238B2 - Film substrate for liquid crystal display panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film substrate for a liquid crystal display panel which realizes a film liquid crystal display panel having excellent optical characteristics and excellent display quality. It can be used as a substrate material for display applications such as body photoelectrodes, surface heating elements, and organic EL electrodes.

[0002]

2. Description of the Related Art In recent years, there has been a high demand for liquid crystal display elements such as thinner, lighter, larger, arbitrary shapes, and curved surface display. In particular, as the use of wearable and portable devices such as pagers, mobile phones, electronic organizers, and pen input devices has expanded, liquid crystal display panels using plastic instead of conventional glass substrates have been studied, and some have become practical. It has begun to be transformed. Such a plastic substrate satisfies the demand for weight reduction and thinning as compared with a glass substrate.

[0003]

A conventional plastic substrate is inferior to a glass substrate in optical characteristics. That is, glass has the property of being optically isotropic in nature. On the other hand, in the case of plastic, when it is formed into a film shape, it has birefringence due to molecular orientation, based on the correlation between the film forming conditions of the plastic film, the optical elastic coefficient specific to the resin, and the characteristics such as birefringence.

[0004] If the plastic film used as the substrate has birefringence, the display quality of the display, such as coloring of the display and lowering of the contrast, is remarkably reduced. This is because, in order for the liquid crystal display to exhibit a display function, it follows the principle of visualization of display by optical switching of polarized light.

In order to solve these problems, there have been proposed improvements to reduce the birefringence (retardation) of the resin, and a method of cast polymerization molding with a single sheet. However, in the conventionally proposed method, productivity is extremely low because a very special resin material is used, special production conditions are set, and molding is performed over a single sheet over time. For this reason, there was no cost competitiveness with respect to conventionally used glass substrates.

[0006] The present invention has been made to solve the above-mentioned problems in the prior art,
That is, an object of the present invention is to reduce the birefringence of a polymer film used for a liquid crystal display panel substrate and obtain a liquid crystal display panel film substrate having excellent display quality with high productivity.

[0007]

The film substrate for a liquid crystal display panel of the present invention is a polymer film formed by continuous film formation, and the resin constituting the film has a positive value of the refractive index anisotropy. NMD> nMD, where nMD is the refractive index of the film along the flow direction of the film when formed, nTD is the refractive index of the film along the width direction perpendicular to the flow direction, and d is the thickness of the film. , And (nTD-
nMD) .times.d.ltoreq.40 nm, and a polymer film having a variation in molecular orientation axis of the film within an angle of. +-. 30 degrees with respect to the width direction of the film is used as the substrate.

First, as a polymer film used as a substrate in the present invention, a resin having a positive refractive index anisotropy of a constituent resin is used. Positive refractive index anisotropy means that when a polymer film is formed, the refractive index in the direction of the molecular orientation axis is maximized.

When a polymer film is formed by continuous film formation by a conventional method, the molecular orientation is oriented in the direction of film flow. That is, the flow direction of the film at the time of film formation is defined as MD.
Direction, and the refractive index of the film along that direction is nM
D, and the width direction of the film perpendicular to the flow direction (MD direction) is referred to as the TD direction, and if the refractive index of the film along that direction is expressed as nTD, then nMD> nTD.

By the way, in order to construct a liquid crystal display panel using a polymer film as a substrate, various processes are continuously performed. At this time, in the drying process of wet coating such as oxygen / nitrogen air barrier layer processing, moisture barrier processing, hard coat processing, etc., and the vacuum process such as transparent conductive film processing, the influence of tension and heating affects the film. Will happen. For this reason, the molecular orientation in the flow direction of the film is disturbed, and the difference between the processed nMD and nTD is larger than the difference between the initial nMD and nTD.
This is because when the polymer film is heated and tension is applied in the MD direction, the orientation is further strengthened when the polymer film is molecularly oriented in the MD direction.

As a result, even if a polymer film having a low birefringence is formed in order to reduce the birefringence, the birefringence varies in a later step, and the display quality of the liquid crystal panel is significantly reduced depending on the film portion. Would.

In order to improve the productivity of the wet coating process or the vacuum process, a method of increasing the heating temperature and increasing the running speed of the film is used. In order to improve the running speed, it is necessary to set a high tension in the running direction of the film. Under the influence of such heating temperature and tension, improving the productivity and reducing the birefringence of the liquid crystal substrate have been contradictory events.

Therefore, in order to achieve both the productivity of the film substrate for a liquid crystal display panel made of a polymer film and the reduction of the birefringence, it is necessary to re-orient the molecular orientation in the MD direction even when the film is heated under tension. The molecular orientation axis of the polymer film (in the case where the optical anisotropy is positive, the direction in which the in-plane refractive index is the maximum, that is, the slow axis) is set in the TD direction perpendicular to the MD direction so that alignment is unlikely to occur. It is necessary to tilt it. This makes it difficult to be affected by the tension even in a state where the tension in the heating atmosphere is applied in various processes, and further, it is possible to make it hard to receive a change such as an increase in the birefringence.

In the polymer film of the present invention, the molecular orientation axis of the film is at least 45 degrees from the MD direction.
If it is tilted in the D direction, the influence of the tension is reduced. In order to further ignore the influence, it is necessary in the present invention that the molecular orientation axis is inclined at least 60 degrees from the MD direction in the TD direction (that is, within ± 30 degrees with respect to the TD direction as an axis). Become.

That is, if the molecular orientation axis is within the range of ± 30 degrees with respect to the TD direction, even when tension is applied in a heated atmosphere, the molecular orientation axis is unlikely to be caused, and the heat in the width direction of the film is not increased. Shrinkage causes shrinkage in the width direction, and as a result, the birefringence decreases. As a means for controlling the molecular orientation axis of the polymer film in the TD direction to within ± 30 degrees, the balance of the forces applied in the MD direction and the TD direction during film formation is adjusted, and shrinkage of the film generated in the TD direction is performed. It can be developed by applying sufficient stress to the film.

When the tension applied to the film cannot be adjusted, or when a process requiring a relatively large tension is required, the molecular orientation axis is in a range of ± 20 degrees with respect to the TD direction. Is more preferable.

The film has a characteristic (nTD-nM
If D) × d ≦ 50 nm, a liquid crystal display having good visibility without coloring of the liquid crystal when used for a liquid crystal substrate can be obtained. In the present invention, in order to further reduce the degree of coloring, it is necessary that (nTD−nMD) × d ≦ 40 nm. In particular, when it is used for a substrate of an STN liquid crystal display element, (nTD−nMD) × d ≦ 20n
m is more preferable.

A film having such characteristics is formed by forming a polymer film by a melt extrusion method or a solution film forming method, and then changing the glass transition temperature of the film to the glass transition temperature-1.
The film can be continuously heat-treated in a temperature range of 0 ° C. to be thermally shrunk in the width direction and adjusted to (nTD−nMD) × d ≦ 40 nm, thereby achieving high productivity.

Further, in order to ensure long-term reliability of the liquid crystal display device, the polymer film used as the substrate should have a barrier process for preventing intrusion of oxygen and moisture on the film, and a solvent-resistant process having a crosslinked structure by a hard coat process. And transparent electrode processing is preferably performed.

When the barrier layer is formed by, for example, a wet coating method, the barrier material may be polyvinyl alcohol, a polyvinyl alcohol-based polymer such as polyvinyl alcohol-ethylene copolymer, polyacrylonitrile, or polyacrylonitrile. A known coating material such as a polyacrylonitrile-based polymer of acrylonitrile-styrene copolymer or polyvinylidene chloride can be used. The film can be formed on the film by a known wet coating method, for example, a reverse roll coating method, a gravure coating method, or a die coating method.

When the barrier layer is formed by a dry process such as sputtering or vacuum evaporation, known barrier materials such as Si, Al, Ti, Mg and Z are used.
A thin film of an oxide, nitride or oxynitride of at least one metal selected from r or a mixture of two or more metals can be formed by a known method.

The thickness of such a barrier layer may be set to a thickness that allows the desired barrier performance to be exhibited. It is also possible to laminate two or more types of parier layers in an appropriate combination.

The hard coat layer for imparting solvent resistance may be made of a known material such as a resin structure having a silicone resin-based crosslinked structure, a crosslinked structure of an acrylic resin, or a crosslinked structure of an epoxy resin. It can be formed by using a coating and curing method.

In the case where the barrier layer and the hard coat layer and the substrate and the laminated structure are mutually formed, a primer layer can be appropriately provided in order to improve the adhesion between the respective layers. As the primer layer, a silicon-based material containing a silane coupling agent, an isocyanate crosslinked product of an acrylic resin, a tetrabutyl titanate-based material, or the like can be appropriately provided by a wet coating method.

When such a film is used as a film substrate for a liquid crystal display panel, it is necessary to form a transparent conductive film. As the transparent conductive film, indium-tin oxide which is also used for a glass substrate is preferably used. The indium-tin oxide transparent conductive film can be formed as a thin film having desired light transmittance and conductivity by a known method such as sputtering, vapor deposition, or ion plating. In order to improve the adhesion between the indium-tin oxide and the underlying layer serving as the substrate, it is also possible to select the primer layer described above and to undercoat.

Incidentally, a barrier layer, a hard coat layer,
In a process of laminating a transparent conductive film layer and the like, by continuously performing a process with a roll, an electrode for a liquid crystal display panel having excellent characteristics and excellent productivity can be obtained. When performing such a continuous treatment, a heat treatment is required to improve the tension for running the film and the characteristics of the coating layer or the sputtered layer. However, by using the polymer film of the present invention as a substrate, a birefringence that adversely affects display is minimized, and a liquid crystal display panel having excellent optical characteristics can be realized.

The polymer film used as the substrate is preferably a thermoplastic polymer film having an amorphous structure. However, from the viewpoint of heat resistance, the resin constituting the polymer film has a glass transition temperature of 120 ° C. or higher, and is preferably a polycarbonate film or a polymer film. More preferably, it is any of an arylate film, a polysulfone film, a polyethersulfone film, and an amorphous polyolefin film.

As the polymer film used as the substrate, those having excellent dimensional stability are preferably used, and the dimensional stability in the flow direction and the width direction of the film after the heat treatment at 120 ° C. for 1 hour is preferable. More preferably, it is 0.1% or less.

Further, the film thickness of the polymer film should be determined by the display quality of the liquid crystal display panel and the ease of handling in the process as an electrode substrate for liquid crystal display. Assuming that the enclosing process is performed by a continuous roll process, a film having a thickness of 50 to 500 μm is preferably used. Further, from the viewpoint of the balance between the display quality of the liquid crystal display panel and the handling in the process, a film having a thickness of 70 to 300 μm is preferably used.

Here, a method of measuring parameters according to the present invention will be described. First, (nTD−nMD) × d
Represents the magnitude of the phase difference resulting from the difference in the speed of light due to the difference in the refractive index in the film plane when the light incident on the film travels in the direction orthogonal to the plane of the film. To measure this value, a birefringence measuring device or a retardation measuring device is required. Many of the polymer films preferably used in the present invention have a wavelength dependence of a retardation value, and it is necessary to define a measurement wavelength. The inventors set the measurement wavelength at 590 nm using a transmission type chromatic dispersion retardation measuring apparatus M-150 manufactured by JASCO Corporation.

The direction of the molecular orientation axis of the film is defined as the maximum refractive index axis in the film plane of the polymer film of the present invention (the refractive index principal axis of the nTD of the film, that is, the slow axis).
And the angle formed by the TD. The direction of the molecular orientation axis can also be easily measured by the M-150 measuring device.

[0032]

Example 1 A polycarbonate film was formed from a polycarbonate resin whose bisphenol component consisted of only bisphenol A. At that time, the film was formed by a melt extrusion method and by adjusting the molecular orientation while adjusting the balance of the tension applied in the MD / TD directions.

The resulting film had a film width of 1080 mm, a thickness of d = 125 μm, and an nTD of 1.5.
837, nMD = 1.5834, that is, (nTD−n
MD) × d = 37.5 nm, and the variation in the direction of the molecular orientation axis of the film was ± 28 degrees with respect to TD.

Further, this film was set in a suspension type heat treatment machine, and the heating temperature was 130.degree.
A continuous heat treatment was applied at 5 m / min. After this heat treatment, nTD = 1.5836, nMD = 1.5834, that is, (nTD−nMD) × d = 25 nm, and the variation in the direction of the molecular orientation axis of the film is ± 25 degrees with respect to TD. Was.

Then, a primer layer and a barrier coat layer were formed on the film. At that time, as the primer layer, a coating liquid obtained by diluting a product name “PC7A” manufactured by Shin-Etsu Chemical with a mixed solvent of methyl isobutyl ketone and n-butyl acetate in 1/1 was used. As the barrier coat layer, a polyvinyl alcohol resin (trade name “PVA-
117 ”) was sufficiently washed with hot water to remove sodium acetate as an impurity to a ppm level, and then a coating solution dissolved in purified water was used. The primer layer was continuously coated and dried (each at a drying temperature of 130 ° C.) using a Meyer bar coater and the barrier coat layer using a reverse roll coater. As a result, a primer layer having a thickness of 0.5 μm and a barrier coat layer having a thickness of 3 μm were laminated on the polycarbonate film.

Further, a hard coat layer was formed on the barrier coat layer. At that time, a coating solution obtained by diluting Nippon Seika's trade name “NS-2451” with isopropyl alcohol was used as a hard coating agent. This coating liquid was applied and dried (drying temperature: 135 ° C.) with a reverse roll coater to form a hard coat layer having a thickness of 8 μm.

A primer layer was formed on the opposite side of the film on which such a laminate was formed. That is, Nippon Soda's trade name “Atron NSi” was diluted with isopropyl alcohol, and coated and dried using a micrograb coater to form a primer layer having a thickness of 50 nm.
Further, an indium-tin oxide thin film layer as a transparent conductive thin film was formed on the primer layer by sputtering. Therefore, an indium-tin oxide target (molar ratio: indium /
(Tin = 90/10, packing density is 90%). Then, the film was set in the continuous sputtering device, and 1.3 mP
After evacuating to the pressure of a, Ar / O ₂ = 98.5 / 1.
A mixed gas having a mixing ratio of 5 was introduced to reduce the atmospheric pressure to 0.27.
Pa. Then, the substrate temperature was set to 60 ° C., and DC sputtering was performed at an input power density of 1 W / cm ² to form a transparent conductive thin film. This transparent conductive film has a thickness of 30.
nm, and the surface resistance was 240 Ω / □. The light transmittance of the film substrate at 550 nm was 84%.

Then, the optical properties of the film subjected to such treatment were re-evaluated. The result is nTD = 1.5
835, nMD = 1.5834, that is, (nTD−n
MD) × d = 12.5 nm, and the variation in the direction of the molecular orientation axis of the film was ± 23 degrees with respect to TD.

As described above, in the substrate using the polymer film of Example 1, the refractive index anisotropy of the resin constituting the film has a positive value before and after the process of forming the laminate, and nTD> nMD and (nTD−nMD) × d ≦
It has an optical property that the dispersion of the molecular orientation axis of the film is in a range of ± 30 degrees with respect to the width direction of the film.

Further, the film substrate for a liquid crystal display panel obtained as described above is sandwiched between two polarizing plates, and each of the film and the polarizing plate is rotated under transmitted light to confirm whether or not to color. went. As a result, no coloring was observed, and a film substrate for a liquid crystal display panel which could be combined with a polarizing plate in a very wide range (in other words, without specifying the optical axis of the substrate) could be obtained.

[0041]

Example 2 The methylene chloride solution film formation gave optical properties of nTD = 1.5836 and nMD = 1.583.
5, ie, (nTD−nMD) × d = 12.5 nm, except that a polycarbonate film in which the direction of the molecular orientation axis of the film and the nTD direction was within ± 30 degrees was used as the substrate. Using the same material and process as in Example 1, the same laminated structure as in Example 1 was produced.

First, after the heat treatment,
nTD = 1.5837 and nMD = 1.5835, that is, (nTD−nMD) × d = 25 nm, and the angle between the direction of the molecular orientation axis of the film and the TD direction was ± 25 degrees.

Subsequently, at a stage after forming the laminate, n
TD = 1.5837, nMD = 1.5836, that is, (nTD−nMD) × d = 12.5 nm, and the angle between the direction of the molecular orientation axis of the film and the TD direction was ± 25 degrees.

As described above, in the substrate using the polymer film of Example 2, the refractive index anisotropy of the resin constituting the film has a positive value before and after the process of forming the laminate, and nTD> nMD and (nTD−nMD) × d ≦
It has an optical property that the dispersion of the molecular orientation axis of the film is in a range of ± 30 degrees with respect to the width direction of the film.

Further, the film substrate for a liquid crystal display panel obtained as a result is sandwiched between two polarizing plates, and each of the film and the polarizing plate is rotated under transmitted light to confirm whether or not coloring is performed. went. As a result, no coloring was observed, and a film substrate for a liquid crystal display panel which could be combined with a polarizing plate in a very wide range (in other words, without specifying the optical axis of the substrate) could be obtained.

[0046]

[Comparative Example] Optical properties are nTD = 1.5834, nMD
= 1.5838, that is, (nMD−nTD) × d = 5
0 nm, and the angle between the direction of the molecular orientation axis of the film and the MD direction is within ± 30 degrees (that is, the angle between TD and
The same laminated structure as in Example 1 was made using the same material and process as in Example 1 except that a polycarbonate film (0 ° or more) was used as the substrate.

First, after the heat treatment,
nTD = 1.5833, nMD = 1.5837, that is, (nMD−nTD) × d = 50 nm, and the angle between the direction of the molecular orientation axis of the film and the MD direction was ± 25 degrees.

Subsequently, at a stage after forming the laminate, n
TD = 1.5833, nMD = 1.5838, that is, (nMD−nTD) × d = 62.5 nm, and the angle between the direction of the molecular orientation axis of the film and the MD direction was ± 25 degrees.

Further, the film substrate for a liquid crystal display panel obtained as a result is sandwiched between two polarizing plates, and each of the film and the polarizing plate is rotated under transmitted light to confirm whether or not to be colored. went. Then, there was a position where coloring occurred, which was not suitable for use as a liquid crystal display panel in combination with a polarizing plate.

[0050]

As described in detail above, the present invention reduces the birefringence of a polymer film used for a liquid crystal display panel substrate, and provides a liquid crystal display panel film substrate having excellent display quality with good productivity. Obtainable.

Continuation of the front page (56) References JP-A-1-169425 (JP, A) JP-A-5-57858 (JP, A) JP-A-5-93907 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) G02F 1/1333 500

Claims (5)

(57) [Claims] 1. A polymer film formed by continuous film formation, wherein the resin constituting the film has a positive value of the refractive index anisotropy, and the film along the film flow direction when the film is formed. When the refractive index is nMD, the refractive index of the film along the width direction perpendicular to the flow direction is nTD, and the thickness of the film is d, nTD> nMD, and (nTD−nM
D) × d ≦ 40 nm, and further using a polymer film having a variation in molecular orientation axis of the film within an angle of ± 30 degrees with respect to the width direction of the film as a substrate, for a liquid crystal display panel. Film substrate. 2. A polymer film used as a substrate,
After being formed by a melt extrusion method or a solution casting method, the film has a glass transition temperature to a glass transition temperature of -10.
The film is continuously heated in the temperature range of ℃
2. The film substrate for a liquid crystal display panel according to claim 1, wherein (nTD-nMD) .times.d.ltoreq.40 nm. 3. A polymer film used as a substrate,
The film according to any one of claims 1 to 2, wherein a barrier process for preventing intrusion of oxygen and moisture on the film, a solvent-resistant process having a crosslinked structure by a hard coat process, and a transparent electrode process are performed. A film substrate for a liquid crystal display panel according to the above. 4. A polymer film used as a substrate,
The glass transition temperature of the resin constituting the polymer film is 1
The liquid crystal display according to any one of claims 1 to 3, wherein the temperature is 20 ° C or higher, and the film is one of a polycarbonate film, a polyarylate film, a polysulfone film, a polyethersulfone film, and an amorphous polyolefin film. Film substrate for panels. 5. The polymer film used as a substrate,
The liquid crystal display according to any one of claims 1 to 4, wherein the dimensional stability in each of the flow direction and the width direction of the film is 0.1% or less after heat treatment at 120 ° C for 1 hour. Film substrate for panels.