JP2003057439A - Optical film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film having no in-plane orientation of molecules, excellent liquid crystal display properties and further having moisture resistance. SOLUTION: The optical film is composed of a thermoplastic polymer film A layer having a thermoplastic polymer film B layer having a mean refractive index Nb different from the mean refractive index Na of the thermoplastic polymer film A layer laminated on at least one surface thereof and is characterized by having >=0.1 nm and <=10 nm retardation Rd in the surface direction of the optical film and >=20 nm and <=60 nm retardation Rth in the thickness direction of the film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical film having no liquid crystal orientation in the plane and excellent in liquid crystal display property and having moisture resistance. The present invention relates to an optical film having excellent optical characteristics and protective function as a protective cover layer.

[0002]

2. Description of the Related Art A polarizing film is used for liquid crystal displays and the like, and its structure is composed of three layers in which protective layers are laminated on both sides of a polarizer. As the polarizer, a uniaxially oriented film in which iodine or a dye is adsorbed and dispersed in polyvinyl alcohol (hereinafter referred to as PVA) is usually used. This PVA-based polarizer has low mechanical properties, and has the drawback that it contracts due to heat or moisture and the polarizing function deteriorates. Therefore, it is used as a laminated body in which protective layers are adhered to both surfaces thereof. . Here, the protective layer, there is no retardation in the plane direction, high light transmittance, excellent moisture resistance and heat resistance, excellent mechanical properties, the surface is smooth, Good adhesion to the polarizer is required. Therefore, conventionally, cellulose triacetate has been used as the protective layer of the polarizer.

However, long-term moisture resistance of cellulose triacetate is insufficient, and therefore, under high temperature and high humidity,
For example, in an environment of 80 ° C. and 90 RH%, the polarizer deteriorates in about 100 hours, which causes a problem in durability of liquid crystal display. In addition, since methylene chloride must be used for the production of cellulose triacetate, there has been concern about its effect on the environment. In order to solve these problems, JP-A-4-339821 and JP-A-5-212
In 828, JP-A-10-130402, JP-A-10-101907, retardation is unlikely to occur in place of cellulose triacetate,
Moreover, it has been shown to use a water-resistant thermoplastic norbornene-based resin.

[0004]

However, when the thermoplastic norbornene resin is used as the protective layer of the polarizer, not only the retardation Rd in the plane direction but also the retardation Rth in the thickness direction becomes extremely small. for,
There was a deviation of polarization from the polarizer, and the optical design had to be redone. In addition, since the strong adhesiveness with PVA cannot be obtained, there is a drawback that the deterioration of the polarizer is accelerated. In addition, since the water vapor transmission rate is low, evaporation of water from the water-containing polarizer may cause evaporation of water at the interface between the polarizer and the protective layer, which may cause a so-called blistering phenomenon, which is a problem for optical applications. It was a lot of things.

Therefore, the present invention has an object to provide an optical film in which the above-mentioned drawbacks are improved. That is, it is an object of the present invention to provide an optical film which has no in-plane molecular orientation and is excellent in liquid crystal display and has moisture resistance.

[0006]

The objects of the present invention are achieved by the following items (1) to (8). (1) An optical film in which a thermoplastic polymer film B layer having an average refractive index Nb different from the average refractive index Na of the thermoplastic polymer film A layer is laminated on at least one surface of the thermoplastic polymer film A layer. And the retardation Rd in the plane direction of the optical film is 0.1 nm or more 1
Retardation R of 0 nm or less and in the thickness direction
An optical film having a th of 20 nm or more and 60 nm or less. (2) Absolute value of average refractive index difference between A layer and B layer | Na-N
b | is 0.03 or more, The optical film as described in (1). (3) The optical film as described in (1) or (2), wherein the average refractive index Nb of the B layer is smaller than the average refractive index Na of the A layer. (4) Water vapor transmission rate of the optical film is 40 g / (m ²
· 24 hrs · d / 50 μm) or less, The optical film as described in any one of (1) to (3). (5) The thermoplastic polymer constituting the layer A is one or more thermoplastic high polymers selected from polyester, cyclic polyolefin, hydrogenated polystyrene, polycarbonate, polyarylate, polysulfone, polyethersulfone, and modified products thereof. It is a molecule | numerator, The optical film in any one of (1)-(4) characterized by the above-mentioned. (6) The thermoplastic polymer that constitutes the layer B is one or more thermoplastic polymers selected from polyvinyl alcohol, hydrophilic acrylic resin, and hydrophilic polyarylate (1) to (5) ) The optical film according to any one of 1. (7) The optical film according to any one of (1) to (6), wherein the optical film is used as a polarizer protective layer. (8) A peelable thermoplastic polymer C layer is provided on at least one surface of the thermoplastic polymer film A layer, and the thermoplastic polymer C layer after peeling the thermoplastic polymer C layer has high thermoplasticity. The method for producing an optical film according to (1) to (7), characterized in that a molecular film B layer is provided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below.

The thermoplastic polymer constituting the layer A of the thermoplastic polymer film used in the present invention is not particularly limited as long as it can form a transparent film. For example, an amorphous thermoplastic resin or the like is used. can do. Specifically, polyester, cyclic polyolefin, hydrogenated polystyrene, polycarbonate, polyarylate, polysulfone, polyethersulfone, acrylic resin,
And one or more thermoplastic polymers selected from modified products thereof. In the case of the present invention, cyclic copolymerized polyolefin, hydrogenated polystyrene resin and the like are preferable from the viewpoint of low water absorption rate, low water vapor transmission rate, high light transmission rate and high glass transition temperature, and cyclic copolymerized polyolefin is particularly preferably used. Here, cyclic copolymerized polyolefin having a polar group is also preferably used. When a crystalline thermoplastic resin is used, transparency may be deteriorated by heating and optical anisotropy may occur. Therefore, it is preferable to use an amorphous thermoplastic resin.

As the cyclic copolymerized polyolefin, for example, a high Tg polyolefin having a norbornene skeleton and a glass transition temperature (Tg) of 120 ° C. or higher, a tetracyclododecene derivative or the tetracyclododecene can be copolymerized. And a polymer obtained by hydrogenating a polymer obtained by metathesis polymerization of such an unsaturated cyclic compound. JP-A-60-168708,
JP-A-62-252406, JP-A-62-252
407, JP-A-63-145324, JP-A-63-264626, and JP-A-2-133413.
Japanese Patent Laid-Open Publication No. 1-240517, Japanese Patent Publication No. 57-
Examples thereof include the polymers exemplified in Japanese Patent No. 8815. Especially on the side chain of cyclic copolymerized polyolefin,
(CH ₂ ) nCOOR (wherein n is 0 to 5 and R is hydrogen or a hydrocarbon group having 1 to 12 carbon atoms), and the like, and a polar group such as norbornene group 2
Those having about 1 to 5 polar groups are preferably used. Here, since the amount of the polar group affects the water vapor permeability, the water absorption rate, and the coefficient of humidity expansion, it is preferable to select an amount that does not impair their functions.

The thermoplastic polymer which constitutes the thermoplastic polymer film B layer used in the present invention can form a transparent film and has an average refraction with the thermoplastic polymer which constitutes the thermoplastic polymer film A layer. There is no particular limitation as long as the ratio is different, but a hydrophilic polymer is preferable, and specifically, one or more thermoplastic polymers selected from PVA, hydrophilic acrylic resin and hydrophilic polyarylate are used. It is preferably used. Of course, a mixture of these thermoplastic polymers may be used. In the present invention, PVA is particularly preferably used because of its adhesion to the polarizer.

In the present invention, the absolute value | Na-Nb | of the average refractive index difference between the A layer and the B layer is preferably 0.03 or more. If the absolute value of the average refractive index difference is smaller than 0.03, the polarization may be disturbed and the display quality of the liquid crystal display may deteriorate.

An optical film in which the average refractive index Nb of the B layer is smaller than the average refractive index Na of the A layer is preferable. B
When the average refractive index Nb of the layer is larger than the average refractive index Na of the A layer, reflection at the interface becomes large, and the quality of liquid crystal display may deteriorate.

Here, the average refractive index is obtained by the following equation. Average refractive index N = (Nx + Ny + Nz) / 3 (where Nx is the refractive index of the in-plane slow layer axis of the film,
Ny is the refractive index of the in-plane advanced layer axis of the film, and Nz is the refractive index in the thickness direction of the film).

The thickness of the thermoplastic polymer film B layer used in the present invention must be smaller than the thickness of the thermoplastic polymer film A layer. When the thickness of the B layer is equal to or larger than the thickness of the A layer, the optical film of the present invention has no stiffness, which is not preferable.

The thickness of the layer A of the thermoplastic polymer film is not particularly limited, but is preferably 1 to 1000 μm, more preferably 10 to 500 μm, and particularly preferably 20 to 20.
It is 0 μm.

The thickness of the layer B of the thermoplastic polymer film is not particularly limited, but is preferably 0.01 to 100 μm.
m, more preferably 0.1 to 50 μm, and particularly preferably 1 to 20 μm.

The optical film of the present invention has an average refractive index Nb different from the average refractive index Na of the thermoplastic polymer film A layer on at least one surface of the thermoplastic polymer film A layer.
It is necessary that the thermoplastic polymer film B layer is laminated.

The retardation Rd in the plane direction of the optical film of the present invention is 0.1 nm or more and 10 nm or less,
Retardation Rth in the thickness direction is 20 nm or more and 60 n
It must be m or less. Rd is preferably 0.1 nm or more and 5 nm or less. If Rd exceeds 10 nm, polarization is disturbed and liquid crystal display becomes difficult, which is not preferable. Rth is preferably 30 nm or more and 50
nm or less. Rth is less than 20nm or 60n
When it exceeds m, polarization is disturbed and liquid crystal display becomes difficult, which is not preferable.

Here, Rd and Rth are obtained from the following equations. Rd = (Nx−Ny) × d Rth = {(Nx + Ny) / 2−Nz} × d (wherein, Nx is the refractive index of the in-plane slow layer axis of the laminated film, and Ny is the in-plane advance of the laminated film. Is the refractive index of the layer axis,
Nz is the refractive index in the thickness direction of the laminated film. Also,
d is the thickness of the laminated film).

The optical film of the present invention has a water vapor transmission rate of 40 g / (m ² · 24 hrs · d / 50 μm).
m) The following is preferable. Water vapor transmission rate is 40
A film exceeding g / (m ² · 24 hrs · d / 50 μm) may have reduced long-term moisture resistance. Where d
Is the thickness of the film used for the measurement.

The method for producing the optical film of the present invention is not particularly limited, but the following method is preferably used. That is, a peelable thermoplastic polymer C layer is provided on at least one surface of the thermoplastic polymer film A layer, and the thermoplastic polymer C layer is peeled off to form a thermoplastic polymer on the A layer. This is a method for producing an optical film of the present invention by providing a film B layer. By using the C layer,
The retardation of the A layer and thus the optical film of the present invention can be easily controlled within the range of the present invention.

Here, the thermoplastic polymer used in the thermoplastic polymer C layer can be used without limitation as long as it is a film-forming thermoplastic polymer. Polyester is preferred, and polyethylene terephthalate is particularly preferred.

The preferred embodiments of the production method of the present invention are shown below, but the present invention is not limited thereto.

A laminate CAC obtained by laminating a thermoplastic polymer A used for the thermoplastic polymer film A layer and a thermoplastic polymer C used for the thermoplastic polymer C layer which can be separated from the A layer. It is manufactured by the following method. That is, the thermoplastic polymers A and C are melted by a known uniaxial, biaxial, tandem extruder or the like, and the respective melted resin streams are laminated by a confluent unit in front of the cap called a feed block, or are respectively formed in the cap in a manifold. By laminating the resin flow widened in step (1) at the die land part to form a laminated film composed of three-layer laminated C / A / C, the melt laminated film is closely cooled and solidified on a moving cooling medium such as a drum. A cast film composed of three-layer laminated C / A / C is obtained. At this time, in order to reduce oxygen during melting as much as possible, it is preferable to dry the material in advance by vacuum to completely deaerate it, to perform vacuum extrusion, or to perform at least one of nitrogen displacement extrusion and the like. . It is also preferable to add an antioxidant to the raw material. If such measures are not taken, the thermoplastic polymer may undergo an oxidative reaction during melting, resulting in gelation or fixed streak called a streak streak. The material of the surface of the extruder cylinder that comes in contact with the thermoplastic polymer is not usually chromium plating or nitriding steel, but is preferably a ceramic material having excellent releasability such as TiN or SUS material. .

As a method of laminating the A layer and the C layer, a die laminating method capable of adjusting the thickness of each layer is excellent and is preferably used.

A C / A / C three-layer laminated molten film is brought into close contact with a cooling drum to be cooled and solidified. A casting method in which the central portion and the end portion of the film are landed substantially simultaneously is preferably used. . For this purpose, it is important to select the C layer resin and control the temperature of the cooling drum.

When the three-layer laminate C / A / C is brought into close contact with a cooling drum for cooling, the film is subjected to air knife, air chamber, press roll method, liquid paraffin coating method, electrostatic loading method, etc. It is preferable to cast by an adhesion improving means such as a selected method. Particularly, the electrostatic printing method is preferably used.

It is preferable that the laminated cast film composed of the three-layer laminated CAC is cooled and then immediately subjected to surface activation treatment such as plasma treatment after peeling off the C layers on both sides. If the layer C is left for a long time after peeling, an oxide layer may be formed on the surface of the layer A.

Subsequently, an aqueous solution of the thermoplastic polymer B used for the layer B of the thermoplastic polymer film is subjected to, for example, reverse (roll) coating, gravure coating, knife coating, air knife coating, roll coating, blade cord, beat coating. A method of forming the layer B by drying after coating with a coating layer or the like is preferably used.

Here, the thickness of each layer can be measured by a known method, for example, β-ray, IR absorption method, optical interference or absorption of infrared rays and the like.

The use of the film of the present invention is not particularly limited as long as it is an optical use, but it is preferably used as a polarizer protective layer. As an example thereof, the B layer surface of the optical film of the present invention is heat treated with a water-soluble adhesive D layer such as PVA on both surfaces of a polarizer P having a thickness of about 20 mm which is uniaxially oriented with polyvinyl alcohol and iodine as main constituent components. An example of the protective layer is a polarizer used when a polarizing plate having a structure of A / B / D / P / D / B / A is laminated and laminated.

[0032]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited thereto.

(Measurement Method of Physical Property Values) The measurement method of physical property values used in the present invention will be described below.

1. Glass transition point: Tg Using a DSC-II type measuring device manufactured by Perkin Elmer Co., Ltd., a sample weight of 10 mg and a temperature rising rate of 20 ° C./under a nitrogen stream.
The temperature is raised in minutes, and the temperature at which the baseline starts to erect is Tg.
And

2. Light transmittance, reflectance The total light transmittance of visible light in the wavelength range of 300 to 700 nm was measured using a spectrophotometer U-3410 (Hitachi Ltd.), and the light transmittance at 550 nm was defined as the light transmittance. . Further, the reflectance was similarly measured using this device.

3. Retardation Sodium D line (589 nm) was used as a light source and placed on a polarizing microscope equipped with a crossed Nicol so that the sample film surface was perpendicular to the optical axis, and the retardation caused by the birefringence n of the sample film was calculated from the compensation value of the compensator. I asked.

4. Water vapor transmission rate 40 ° C, 90% RH according to JIS-K7129 B direction
And was converted to a thickness of 50 μm. The unit is g / (m
² · 24 hrs · d / 50 μm). Where d
Is the thickness of the film used for the measurement.

5. Liquid crystal display liquid crystal display device using vertical alignment type liquid crystal cell (VL-1
A pair of polarizing plates and a pair of optical compensation films provided in 530S, manufactured by Fujitsu Ltd. were peeled off, and the films produced instead were attached and visually observed. The evaluation criteria are as follows, and ⊚ and ○ were judged to be acceptable. ◎: Black is displayed in black and white so that the brightness of the room is not noticeable. ◯: There is no problem in the front direction, but the tightness of black is slightly worse in the diagonal direction. Δ: Black tightness deteriorates slightly in the front direction x: Black tightness is poor.

6. Long-term humidity resistance The sample prepared by the above method 5 is used at 80 ° C and 90% RH.
After maintaining for 200 hours in the above atmosphere, visual evaluation was performed.
The evaluation criteria are as follows, and ⊚, ○, and △ were judged to be acceptable. ◎: Black is displayed in black and white so that the brightness of the room is not noticeable. ◯: There is no problem in the front direction, but the tightness of black is slightly worse in the diagonal direction. Δ: Black tightness deteriorates slightly in the front direction x: Black tightness is poor.

Example 1 Using a cyclic olefin copolymer (“Zeonor” manufactured by Nippon Zeon Co., Ltd., Tg: 165 ° C.), which is a norbornene-based resin, as the layer A of the thermoplastic polymer film, ZEONOR was vacuum dried according to a conventional method. After degassing the water content and the dissolved oxygen, the material from the raw material hopper to the extruder was supplied to a 150 mm vacuum extruder in which nitrogen was replaced, and melted at 285 ° C. On the other hand, polyethylene terephthalate (intrinsic viscosity: 0.65, Tg: 70 ° C.) was vacuum-dried in accordance with a conventional method as a resin C for laminating and peeling from the resin A, and then fed to a 65 mm melt extruder to be
After melting at 80 ° C and passing each through a filter that removes foreign matter of 15 μm or more, after laminating in a die so as to have three layers of C / A / C, a 1200 mm wide crow die-shaped T It was extruded from the die die (set so that the resin flow direction was horizontal) onto the top of the casting drum at a distance of 50 mm between LDs. At this time, the narrow angle formed by the resin flow direction and the molten resin film in the die land portion is 0.
It was degree. In order to improve the adhesion between the drum and the resin film, a specular chrome plating drum (drum diameter: 180
0 mm, maximum surface roughness Rt: 0.1 μm) and 30 m /
It was adhered and cooled and solidified at a speed of min. The thus-obtained three-layer cast film had a total thickness of 60 μm composed of 5/50/5 μm, and the thickness unevenness of the whole layer and A layer was as small as 3% or less in both the longitudinal direction and the width direction, and The A layer had no thickness unevenness due to landing vibration of 3 to 10 Hz even when frequency analysis of thickness unevenness was performed, and was excellent in thickness uniformity. Furthermore, it is an amorphous 50 μm film that is completely isotropic with a frontal retardation of 3 nm and has no surface defects such as craters and die stripes. Also, there is no width variation at the edges and the light transmittance is 400 to 700 nm. In the range of 90% or more, the sheet was transparent and completely amorphous, and was an optically excellent sheet. The C layer on one side was peeled from the three-layer film, and the peeled A resin film surface was immediately subjected to plasma discharge treatment, and subsequently, modified polyvinyl alcohol (saponification degree: 87.7).
%) A layer B of the thermoplastic polymer film is formed by using an aqueous solution.
Coated in layers. The dried layer B had a thickness of 5 μm. The characteristics of the A / B layer thus obtained have Tg = 1.
60 ° C., retardation in front direction is 2 nm, retardation in thickness direction is 25 nm, center line average surface roughness Ra
Is 2 nm, Young's modulus is 200 kg / mm ² , and light transmittance is 92.
%Met. The A / B layer thus obtained and the PVA-based polarizer film of 80 μm were adhered using water in which gum arabic was dissolved. The adhesive strength between these layers was 1.2 kg / cm, indicating that they were firmly bonded. For this reason, the polarization characteristics and appearance of the polarizer did not change even when left in high humidity for a long time.
The results are summarized in Table 1.

Example 2 A sample was prepared and evaluated in the same manner as in Example 1 except that the resin for the layer B used in Example 1 was changed from modified PVA to polyether sulfone. Since the B layer had a high refractive index, the liquid crystal display property was slightly lowered, but there was no problem and a suitable optical film was obtained.

Example 3 A sample was prepared and evaluated in the same manner as in Example 1 except that the resin for the layer A used in Example 1 was changed from ZEONOR to a polyethylene terephthalate copolymer. Since the water vapor transmission rate was rather large, the long-term moisture resistance was slightly lowered, but there was no problem and a suitable optical film was obtained.

Comparative Example 1 A thickness of 50 μm was obtained in exactly the same manner as in Example 1 except that the thermoplastic polymer film B layer was not formed and only the resin A was formed as a single layer.
A single-layer film consisting of layer A was prepared. The evaluation results of this film are shown in Table 1. The front direction retardation of the obtained film was 4 nm, and the thickness direction retardation was 7 nm. When viewed with a liquid crystal display device,
The display quality was low. Moreover, the long-term moisture resistance was also inferior.

[0044]

[Table 1]

[0045]

According to the present invention, it is possible to provide a polarizing plate which has no in-plane molecular orientation and is excellent in liquid crystal display and has moisture resistance.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H049 BA02 BB23 BB27 BB28 BB29                       BB43 BB54 BC10                 2H091 FA08X FA08Z FB02 GA16                       LA16 LA30                 4F100 AK01A AK01B AK01C AK02A                       AK03A AK12A AK21B AK21C                       AK25B AK25C AK42 AK43A                       AK45A AK54A AK55A AL06A                       BA02 BA03 BA06 BA10B                       BA10C BA15 GB41 JA20B                       JA20C JB05B JB05C JB16A                       JB16B JB16C JD04 JL14C                       JN10 JN18A JN18B JN18C                       YY00B YY00C

Claims (8)

[Claims] 1. An average refractive index N of the thermoplastic polymer film A layer on at least one surface of the thermoplastic polymer film A layer.
The thermoplastic polymer film B layer having an average refractive index Nb different from a is an optical film laminated thinner than the A layer, and has a retardation Rd in the plane direction of the optical film.
Is 0.1 nm or more and 10 nm or less, and the retardation Rth in the thickness direction is 20 nm or more and 60 nm or less. 2. Absolute value | N of average refractive index difference between layer A and layer B
The optical film according to claim 1, wherein a-Nb | is 0.03 or more. 3. The average refractive index Nb of the B layer is smaller than the average refractive index Na of the A layer.
The optical film according to. 4. The water vapor transmission rate of the optical film is 40 g /
(M ² · 24 hrs · d / 50 μm) It is below, The optical film in any one of Claims 1-3 characterized by the above-mentioned. 5. The thermoplastic polymer constituting the layer A is polyester, cyclic polyolefin, hydrogenated polystyrene,
Polycarbonate, polyarylate, polysulfone,
The optical film according to any one of claims 1 to 4, which is one or more thermoplastic polymers selected from polyether sulfone and modified products thereof. 6. The thermoplastic polymer constituting the layer B is one or more thermoplastic polymer selected from polyvinyl alcohol, hydrophilic acrylic resin and hydrophilic polyarylate. The optical film as described in any one of 5 above. 7. The optical film according to claim 1, which is used as a polarizer protective layer. 8. A peelable thermoplastic polymer C layer is provided on at least one surface of a thermoplastic polymer film A layer, and the thermoplastic polymer C layer is heat-treated on the peeled thermoplastic polymer film A layer. The method for producing an optical film according to claim 1, wherein a layer B of the plastic polymer film is provided.