JP2001329084A - Plastic sheet having smoothness and optical sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic sheet having excellent surface smoothness and excellent properties required as an optical sheet such as a substrate for a liquid crystal display device, and to provide a excellent optical sheet. SOLUTION: The plastic sheet is obtained by coating a solvent on a plastic sheet and subjecting the coated sheet to drying treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic sheet having excellent flatness and small retardation.
The present invention relates to an optical sheet manufactured using this.

[0002]

2. Description of the Related Art Conventionally, a glass substrate has been adopted as a transparent electrode substrate for a liquid crystal display element. However, in a liquid crystal display element using a glass substrate, the thickness of the liquid crystal display element itself is reduced because the glass substrate itself is thick. It is difficult and it is difficult to reduce the weight, and there is a problem in terms of impact resistance. As a method of improving the disadvantages of the glass substrate liquid crystal display device, reduction in weight and improvement in impact resistance by manufacturing a liquid crystal display device using an optical plastic sheet are being studied. For example, JP-A-53-68099 and JP-A-54-126559 disclose liquid crystal display elements using a long polyester film on which a conductive metal oxide material is deposited instead of a glass substrate. Although production is indicated, unlike a glass substrate which can obtain extremely good smoothness by polishing, it is hard to say that a plastic sheet has excellent surface smoothness. In particular, STN is required to obtain high-definition display.
In the case of a (Super Twisted Nematic) type liquid crystal display device, the surface smoothness of the plastic sheet is reduced because the display is performed by utilizing the birefringence of the liquid crystal between the substrates, the spacing of which is controlled in units of 0.1 μm. It has become extremely important.

As a method for solving the surface smoothness, there has been proposed a method in which a liquid ultraviolet curable resin composition or a thermosetting resin composition is poured onto a polished glass surface or the like and cured to obtain a sheet. . However, this method has a problem that the obtained sheet is brittle and breaks or chipes during handling, and the advantage of using a plastic sheet over a glass substrate is not sufficiently exhibited. further,
This method has low productivity and results in expensive substrates.

[0004]

An object of the present invention is to provide a plastic sheet and a good optical sheet having excellent surface smoothness and excellent characteristics for an optical sheet such as a substrate for a liquid crystal display device. To provide.

[0005]

That is, a first aspect of the present invention is to apply a solution for dissolving the plastic sheet on the plastic sheet and then to perform a drying treatment, wherein the plastic sheet has a smoothness. Further, the second invention is an optical sheet manufactured using the first plastic sheet.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of plastics used as a plastic sheet in the present invention include polyester, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, polyimide, polyamideimide, polycarbonate and epoxy. Resins, acrylic resins, norbornene resins and mixtures thereof can be mentioned. Among them, polyethersulfone having a good balance of transparency, heat resistance, workability, and impact resistance is particularly preferable in the production of liquid crystal display elements. The thickness of the plastic sheet material is preferably 10 to 500 μm or less, more preferably 50 to 400 μm or less. If the thickness of the plastic sheet is less than 10 μm, it is easy to cut and it is difficult to handle. In addition, if the thickness of the plastic sheet exceeds 500 μm, it becomes difficult to adhere to a roll.

[0007] The solvent used in the present invention is plastic Small used as a plastic sheet raw material.
Solubility parameter (δ
With respect to 2), the absolute value of the difference from the solubility parameter (δ1) of the solvent is 3 (cal / cm ³ ) ^1/2 or less (| δ1−δ2 | ≦
3 (cal / cm ³ ) ^1/2 ) is preferred, and more preferably 2 (cal / cm ³ ) ^1/2 or less. If the absolute value of the difference between the solubility parameter of the polymer used for the plastic sheet and the solvent exceeds 3 (cal / cm ³ ) ^1/2 , the solubility of the solvent in the plastic will be significantly reduced, and the unevenness on the plastic surface will be smooth. No. Examples of solvents used in polyethersulfone, which have a good balance of transparency, heat resistance, workability, and impact resistance in the production of liquid crystal display elements, are as follows: 1-
Examples thereof include, but are not limited to, methyl-2-pyrrolidone, dichloromethane, N, N-dimethylformamide, cyclohexanone, and γ-butyrolactone. In addition, these solvents are (| δ1−δ2 | ≦
As long as 3.0 (cal / cm ³ ) ^1/2 ) is satisfied, any solvent composition of two or more kinds may be used.

In the present invention, a leveling agent may be added to the solvent applied to the plastic sheet, if necessary. Examples of leveling agents include calcium perfluoroalkyl sulfonate, potassium perfluoroalkyl sulfonate, ammonium perfluoroalkyl sulfonate, perfluoroalkyl ethylenoxide, perfluoroalkyl trimethyl ammonium salt, and fluorinated alkyl esters. be able to.

The plastic sheet of the present invention is obtained by applying a solution for dissolving the plastic sheet onto a plastic sheet raw material and then performing a drying treatment.
A plastic sheet having a smooth surface can be manufactured. Methods for applying these solvents on the surface of the plastic sheet include roll coating, spray coating, die coating, and knife coating. The drying treatment is preferably performed at a temperature lower than the glass transition temperature of the plastic sheet in order to prevent deformation of the plastic sheet.

[0010]

The present invention will be described below in more detail with reference to examples and comparative examples. The optical properties of the sheet were measured by the following methods. (1) Sheet thickness Average value measured at intervals of 20 mm in the width direction of the plastic sheet using a contact dial gauge. (2) The maximum surface roughness of the plastic sheet (Rma
x) Contact type precision step meter (manufactured by TENCOR INSTRUMENTS, AlPHA-ST
2mm in the width direction of the plastic sheet by EP200)
The maximum value of the unevenness measured for the entire width at the scan width of.

Example 1 Polyethersulfone having a thickness of 200 μm and a maximum surface roughness (Rmax) of 0.3 μm (solubility parameter δ2 = 12.6 (cal / c)
Using m ³ ) ^1/2 ) as a plastic sheet, the following processing was performed using a manufacturing apparatus having an unwinder, a coater, a heating and drying zone, and a winder. First, 1
-Methyl-2-pyrrolidone (solubility parameter δ1
= 11.3 (cal / cm ³ ) ^1/2 | δ1-δ2 | = 1.3
(Cal / cm ³ ) ^1/2 ) was stirred at 30 ° C. and coated with a gravure roll coater at a coater part to a thickness of 10 μm before drying, and heated in a heating drying zone at 100 ° C. for 5 minutes to remove the solvent. After that, the plastic sheet was wound up. Rma of the solvent-coated surface of the obtained plastic sheet
When x was measured, it was 0.02 μm. Next, on this plastic sheet, by a DC magnetron method,
A mixed gas of oxygen / argon gas of 9% was introduced from the state of the initial vacuum degree of 3 × 10 ^-4 Pa, and sputtering was performed under the conditions of 3 × 10 ^-1 Pa to obtain SiO ₂ having a thickness of 500 °. Subsequently, as a transparent conductive film, also oxygen from the state of the initial vacuum degree 3 × 10 ^-4 Pa by a DC magnetron method /
1 × 10 ^-1 Pa by introducing a mixed gas of 4% of argon gas
Sputtering under the conditions of In / In + S
Indium tin oxide having an atomic ratio of n of 0.98 (IT
O) was obtained. As a result of the measurement, the film thickness was 1
600 ° and the non-resistance was 4 × 10 ⁻⁴ Ω-cm. IT
After forming O, a resist is applied and developed, and pattern etching is performed at 10 vol% HCL as an etchant at a liquid temperature of 40 ° C., a diagonal length of 3 inches, L / S = 150/50.
A display pattern of μm was formed. After pattern formation, ST
After applying an orientation film for N and performing a baking treatment at 150 ° C. for 2 hours, a rubbing treatment was performed so as to obtain a 240 ° twist orientation. After the rubbing treatment, the spacer is sprayed, a sealant is applied, and the seal is cured at 130 ° C. to form a cell,
The liquid crystal composition for STN was injected. A polarizing plate was attached to a position where the contrast was maximized to produce a liquid crystal display device. When a lighting test was performed on the liquid crystal display element at a driving voltage of 0 V to ± 5 V, good display was exhibited without any display unevenness due to an abnormal cell gap of the liquid crystal.

Example 2 A thickness of 200 μm and a surface roughness of 200 μm
Polyether sulfone with a maximum (Rmax) of 0.3 μm
(Solubility parameter δ2 = 12.6 (cal / c
m^Three)^1/2Example 1 was used as a plastic sheet
 The following processing was performed using the same manufacturing apparatus. First, melt
1-methyl-2-pyrrolidone / toluene = 5 /
5 mixed solution (solubility parameter δ = 10.1 (cal /
cm^Three)^1/2 | Δ1-δ2 | = 2.5 (cal / cm ^Three)^1/2)
Gravure roll in the coater part stirred at 30 ° C
Apply with a coater to a thickness of 10 μm before drying, and heat and dry
Remove the solvent by heating at 100 ° C for 5 minutes in
The plastic sheet was wound up. Got plus
When the Rmax of the solvent-coated surface of the tic sheet was measured.
It was 0.04 μm. Thereafter, the liquid crystal was made in the same manner as in Example 1.
A display element was created. This liquid crystal display element is driven at a driving voltage of 0 V.
When a lighting test was performed at ± 5 V from
No display unevenness due to top error
Was.

Comparative Example 1 Polyethersulfone having a thickness of 200 μm and a maximum surface roughness (Rmax) of 0.3 μm (solubility parameter δ2 = 12.6 (cal / c)
m ^{3) 1/2)} used as a plastic sheet raw, was next processed using the same manufacturing apparatus of Example 1. First, a 1-methyl-2-pyrrolidone / toluene = 2/8 mixed solution (solubility parameter δ = 9.38) was used as a solvent.
(Cal / cm ³ ) ^1/2 | δ1-δ2 | = 3.22 (cal / c
The mixture obtained by stirring m ³ ) ^1/2 ) at 30 ° C. was applied with a gravure roll coater in a coater part so as to have a thickness of 10 μm before drying.
After heating at 100 ° C. for 5 minutes in a heating drying zone to remove the solvent, the plastic sheet was wound up. When Rmax of the obtained plastic sheet on the solvent-coated surface was measured, it was 0.15 μm. Thereafter, a liquid crystal display device was prepared in the same manner as in Example 1. When a lighting test was performed on this liquid crystal display element at a driving voltage of 0 V to ± 5 V, display unevenness occurred due to an abnormal cell gap of the liquid crystal.

[0014]

The sheet obtained according to the present invention is transparent.
Also, when the liquid crystal display element is manufactured as a transparent electrode substrate for a liquid crystal display element, it is lighter and harder to break than a glass substrate, and has a good display without unevenness. Shown. The optical sheet manufactured as described above is extremely useful industrially, and is useful as a transparent substrate for a liquid crystal display element, a substrate for an optical mirror, or the like.

Claims (4)

[Claims] 1. A plastic sheet having smoothness, wherein a solution for dissolving the plastic sheet is applied to the plastic sheet and then dried. 2. The difference between the solubility parameter (δ1) of the solution for dissolving the plastic sheet and the solubility parameter (δ2) of the plastic sheet is 3 (cal / cm ³ ) ^1/2 or less.
2. The expression (| δ1-δ2 | ≦ 3 (cal / cm ³ ) ^1/2 ).
A plastic sheet having the described smoothness. 3. An optical sheet using the plastic sheet according to claim 1. 4. The optical sheet according to claim 3, wherein the plastic is polyether sulfone.