JP2001088215A - Method for producing polymeric sheet and optical polymeric sheet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for continuously producing a polymeric sheet excellent in surface smoothness and reduced in retardation and an optical polymeric sheet using the same. SOLUTION: An uncompleted polymeric sheet of which the temp. (T1) is 20 deg.C<=T1<TD with respect to the glass transition point (Tg) and thermal decomposition temp. (TD) of a polymer is brought into close contact with a smooth surface of which the max. surface roughness (Rmax) is Rmax<=0.1 μm in a close contact process and passed through a heating process wherein temp. (T2) is Tg<=T2<TD in the close contact state with the smooth surface to produce a polymeric sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently producing a polymer sheet having excellent planar smoothness and small retardation, and an optical sheet produced using the same. It is about.

[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 a polymer sheet have been 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 was shown, it was hard to say that it was excellent in optical properties. In order to solve this problem, we conducted research to apply polymer sheets with excellent optical isotropy to these applications, and found that sheet retardation due to molecular orientation of the polymer was a serious drawback. Do you get it. For example, in a TN (Twisted Nematic) type liquid crystal display device, incident light linearly polarized by a polarizing plate becomes elliptically polarized light which is partially different from the birefringence of the sheet and the deviation in the sheet plane, thereby lowering the contrast. This causes display unevenness. Furthermore, in order to obtain a higher definition display than a TN type liquid crystal display device, STN (Super Twisted Nematic)
In the case of a liquid crystal display device of the type, the problem due to the retardation caused by the molecular orientation of the polymer is becoming more and more serious because the optical retardation developed from the birefringence is used.

Further, as a liquid crystal cell using a polymer sheet is put to practical use, a display area is increased, and it is required that a substrate is hardly deformed in order to maintain a uniform gap between electrodes, that is, to maintain a so-called gap. ing. In some cases, the thickness of the base material exceeds 100 μm to 300 μm. Since the retardation of the sheet is obtained by multiplying the difference between the refractive index of ordinary light and that of extraordinary light by the thickness of the sheet, an urgent improvement of the above problem is desired in this regard. Further, it is required that the retardation is small not only in the front direction but also in the oblique direction so that the screen is easy to see even when the display is viewed from an oblique direction. As a method for improving the retardation of an optical material, a method using a special polycarbonate having a special dihydric phenol as a structural unit (JP-A-63-10802)
No. 3), a method of blending a material having a positive intrinsic birefringence and a negative material (T. Inoue et al., Journal of Polymer Scien
ce, Part B, 25, 1629 (1987)), a method of graft copolymerizing a polycarbonate having a positive intrinsic birefringence and a negative polystyrene (Nikkei New Materials, September 26, 1988, pp. 60-62). ), A method using a norbornene-based resin having a polar group (functional materials, January 1993,
Articles on pages 40 to 52) have been proposed, but none of them have been put to practical use.

[0004] This is because, during a short time from the time when the sheet extruded by the extrusion method is cooled and solidified by the cooling roll and wound up, the shear stress generated in the die and the resin discharged from the die slip are stretched. This is because the temperature distributions generated in the flow direction and the thickness direction due to the above-mentioned problems make it impossible to avoid the molecular orientation in the plane and the thickness direction generated in the sheet, and the production method is complicated and impractical. Regarding the surface smoothness, in the melt extrusion method using a generally known T die or coat hanger die, the shear stress or stagnation in the flow path through which the molten polymer passes, and further, the surface of the die and Streaks called die lines, which are said to occur due to the accuracy of the lip, are generated on the sheet surface, reducing the surface smoothness. As a means to improve the surface smoothness, a thermoplastic polymer is dissolved in a solvent,
Although a solvent casting method of coating and drying a film or a metal belt or the like is performed, productivity and a residual solvent in the sheet when the sheet thickness is increased become a problem. On the other hand, an injection molding method in which a thermoplastic polymer is sealed in a mold whose surface is finished with high precision can be used to control the retardation as is known for optical discs, but the injection molding method has a thickness of several mm. Seat is the limit,
It cannot cope with a thickness of several hundred μm.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polymer sheet having excellent surface smoothness and a small retardation, and having no problem as a polymer sheet for optics such as a substrate for a liquid crystal display device. An object of the present invention is to provide a production method capable of efficiently and continuously producing usable polymer sheets, and to provide an optical polymer sheet having good characteristics by using a resin suitable for this method.

[0006]

The present invention relates to an unfinished polymer having a sheet temperature (T1) of 20 ° C. ≦ T1 <TD with respect to the glass transition point (Tg) and the thermal decomposition temperature (TD) of the polymer. The maximum (Rmax) of the surface roughness is R
This is a method for producing a polymer sheet, wherein the polymer sheet is adhered to a smooth surface of max ≦ 0.1 μm and passed through a heating step with a temperature (T2) of Tg ≦ T2 <TD in a state of being adhered to the smooth surface. As a preferred embodiment, there is provided a method for producing the polymer sheet, wherein the smooth surface is a roll or an endless belt. As a further preferred embodiment, there is provided the method for producing a polymer sheet, wherein the close contact step is performed by a nip roll, an endless belt, or a charging and fixing method. Further, the present invention is a polymer sheet for optics produced by the method for producing a polymer sheet, preferably a polymer sheet for optics wherein the polymer is polyethersulfone.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The thickness of the polymer sheet of the present invention is as follows.
It is preferably from 50 μm to 1000 μm, more preferably from 150 μm to 500 μm. If the thickness of the polymer sheet is less than 50 μm, it is difficult to handle, and it is difficult to maintain the cell gap of the liquid crystal display element. In particular, it is not possible to maintain the cell gap in a large-area liquid crystal display element. When the thickness exceeds 1000 μm, the liquid crystal display causes a display defect called a double image, and the thickness of the liquid crystal display element is increased, which is not preferable in function.

The planar retardation of the polymer sheet of the present invention is preferably 20 nm or less, more preferably 10 nm or less.
nm or less. Plane retardation is defined as Re =
It is expressed by (Nx−Ny) × d, where Nx is the maximum refractive index on the inner surface of the polymer sheet, and Ny is the minimum refractive index on the inner surface of the polymer sheet. d is the thickness of the sheet. If the retardation exceeds 20 nm, the contrast of the liquid crystal display decreases, and the display becomes invisible.

The maximum surface roughness (Rmax) of the polymer sheet of the present invention is preferably 0.1 μm or less,
More preferably, it is 0.05 μm or less. If the maximum surface roughness exceeds 0.1 μm, an abnormal cell gap of the liquid crystal occurs, resulting in display failure.

The present invention will be described in the order of the production process. The unfinished polymer sheet to be used has a glass transition point (T
g) and thermal decomposition temperature (TD), the sheet temperature (T
Any sheet can be used if 1) is in the range of 20 ° C. ≦ T1 <TD. Examples thereof include, but are not limited to, polyester, polyethersulfone, polycarbonate, epoxy resin, acrylic resin, norbornene-based polymer, and resin blended therewith. In particular, heat resistance,
Polyether sulfone having a good balance between processability and impact resistance is particularly preferred. If the temperature of the sheet is lower than 20 ° C., it takes too much energy to reduce the irregularities on the surface of the polymer sheet, which is not economically practical. On the other hand, if the temperature exceeds TD, a sheet cannot be produced because the polymer is thermally decomposed.
As the unfinished polymer sheet used in the present invention, a sheet produced in a separate step may be used, or a sheet extruded with a T die or a coat hanger die may be used.

The smooth surface of the present invention employs a roll, an endless belt, a flat pressing plate, or the like. Instead of pressing the sheet with a flat pressing plate to improve the surface smoothness,
Rolls or endless belts are preferred from the viewpoint of continuous productivity. The maximum surface roughness (Rmax) of the smooth surface to which the unfinished polymer sheet is adhered needs to be Rmax ≦ 0.1 μm, preferably 0.05 μm or less. If it exceeds 0.1 μm, it is transferred to the surface of the polymer sheet, so that one surface of the polymer sheet is also 0.1 μm or more, which is a problem as an optical sheet.

As the adhesion step for bringing the unfinished polymer sheet into close contact with the smooth surface, any method capable of perfect adhesion such as various nip rolls, endless belts, charging and fixing, and pressing can be used.
An endless belt or a fixed charging system is preferred.
If the adhesion is incomplete, the transfer of the surface roughness of the smooth surface to the unfinished polymer sheet becomes incomplete, and the surface irregularities of the sheet are enlarged, so that the target polymer sheet cannot be obtained.

Next, the unfinished polymer sheet moves to a heating step in which the temperature (T2) is Tg ≦ T2 <TD, while being in close contact with the smooth surface. Here, since the polymer can move, the surface roughness of the smooth surface is transferred to the surface in close contact with the smooth surface of the unfinished polymer sheet, and the opposite surface is the weight of the sheet and the surface of the polymer. The surface is flattened by the tension, and the unevenness of the surface of the unfinished polymer sheet is extremely small, so that good smoothness can be obtained. At the same time, the internal strain at the time of the unfinished sheet is greatly relaxed, and a polymer sheet in which the molecular orientation between the surface and the inside of the sheet is nearly uniform, that is, the retardation value and the angle dependence thereof are greatly reduced is obtained. . Here, the heating method in the heating step includes far infrared heater heating, infrared heater heating, heating medium oil, water vapor, laser heating,
And the like. Among them, a method capable of heating to Tg ≦ T2 <TD in accordance with the polymer sheet can be used. The passage time of the heating step varies depending on the kind of the polymer and the thickness of the sheet, but is 2 to 60 seconds, preferably 3
10 to 10 seconds. The polymer sheet obtained by such a production method has a small warpage, and when a liquid crystal display element is prepared using the polymer sheet, good display without display unevenness can be obtained. That is, a good optical polymer sheet is obtained.

[0014]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to the examples. The optical properties of the sheet were measured by the following methods. (1) Sheet thickness 20 m in the width direction of the polymer sheet with a contact type dial gauge
Average value measured at m intervals. (2) Maximum surface roughness of polymer sheet (Rmax) Contact type precision step meter (manufactured by TENCOR INSTRUMENTS, AlPHA-ST)
EP200) is the maximum value of the concavities and convexities measured over the entire width of the polymer sheet at a scan width of 2 mm in the width direction. (3) Retardation of Polymer Sheet The retardation at 0 ° and 40 ° from the normal direction was measured using a three-dimensional refractive index measuring device manufactured by Oji Scientific Instruments. (4) Maximum surface roughness of the smooth surface (Rmax) The unevenness when the entire width is measured at a cutoff length of 0.8 mm in the width direction of the metal belt using a contact type surface roughness meter manufactured by Mitutoyo Corporation. Maximum value.

Example 1 Polyether sulfone (Tg)
= 226 ° C., TD 400 ° C. or more) were charged into an extruder, and at an extrusion temperature of 350 ° C., the maximum surface roughness (Rma) was obtained.
Extrusion was performed using a die having x) of 0.4 μm and a lip gap of 3 mm. The unfinished polymer sheet at 230 ° C. extruded from the die was used as a smooth surface to obtain the maximum surface roughness (Rm
ax) was extruded onto a roll having a diameter of 0.05 μm and a diameter of 1.5 m, and was brought into close contact with a smooth surface roll with a nip roll at 210 ° C. Then, the unfinished sheet was moved to a heating step heated to 300 ° C. by an infrared heater in a state where the unfinished sheet was kept in close contact with the roll, and passed through for 5 seconds to obtain a thickness of 200
A polymer sheet of μm was prepared. As a result, the retardation at 0 degree is 2 nm, and the retardation at 40 degree is 3 nm.
nm, and the Rmax of the surface of the polymer sheet in contact with the roll surface is 0.04 μm, and the Rmax of the surface in contact with the nip roll is 0.07 μm stably and continuously. I was able to. 200 obtained
μm thick sheet, molecular weight 1540, melting point 70 ° C
Epoxy acrylate prepolymer (manufactured by Showa Polymer,
VR-60) 100 parts by weight, butyl acetate 400 parts by weight,
A solution obtained by stirring and dissolving 100 parts by weight of cellosolve acetate and 2 parts by weight of benzoin ethyl ether at 50 ° C. was applied using a gravure roll coater,
The mixture was heated at 10 ° C. for 10 minutes to remove the solvent, and irradiated with a high-pressure mercury lamp of 80 w / cm at a distance of 15 cm for 30 seconds to cure the resin, thereby forming an organic layer having a thickness of 0.5 μm on both sides.
Next, an initial vacuum degree of 3 × 10 ⁻⁴ Pa was applied to this sheet by a DC magnetron method, and oxygen / argon gas was 9%.
Was introduced, and an inorganic layer was formed under a condition of 3 × 10 ^-1 Pa to obtain 500-mm thick SiO ₂ . Next, as a transparent conductive film, the initial vacuum degree was similarly set to 3 × 10 ⁻⁴ Pa by a DC magnetron method, and a mixed gas of oxygen / argon gas 4% was introduced to produce a transparent conductive film under the conditions of 1 × 10 ⁻¹ Pa. In which the atomic ratio of In / In + Sn is 0.98,
_A transparent conductive film made of ₂ O ₃ was obtained. As a result of the measurement, the film thickness was 1
600 ° and the non-resistance was 4 × 10 ⁻⁴ Ω-cm. After film formation, a resist is applied and developed, and an etchant of 10
The pattern was etched in a vol% HCL solution at a liquid temperature of 40 ° C. to form a display pattern having a diagonal length of 3 inches and L / S = 150/50 μm. After pattern formation, an alignment film for STN is applied, and a baking treatment is performed at 150 ° C. for 2 hours.
A rubbing treatment was performed so as to have a 40 ° twist orientation. After the rubbing treatment, a spacer is sprayed, a sealant is applied, and the seal is cured at 130 ° C. to form a cell, and STN is applied.
Liquid crystal composition 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 of this liquid crystal display element was performed, no display unevenness due to sheet retardation or liquid crystal cell gap abnormality was observed, and a favorable display with a contrast ratio of 45 was shown.

<< Example 2 >> A thickness of 450 μm at 23 ° C.
m, Rmax = 0.2 μm alicyclic epoxy resin (Tg
(232 ° C.) as a smooth surface, and was completely fixed by charging and fixed on an endless belt having a maximum surface roughness (Rmax) of 0.05 μm and a length of 5 m. Then, it is moved to a heating step heated to 280 ° C. by an infrared heater,
It was passed for 20 seconds to produce a polymer sheet having a thickness of 450 μm. As a result, the retardation at 0 degrees is 3n.
m, the retardation at 40 degrees is 4 nm, and
Rm of surface of polymer sheet in contact with endless belt surface
ax is 0.05 μm, and Rmax of the opposite surface is 0.5 μm.
A polymer sheet having a thickness of 1 μm was obtained stably and continuously. Hereinafter, a liquid crystal display was manufactured in the same manner as in Example 1. When a lighting test of this liquid crystal display element was performed,
No display unevenness due to sheet retardation or liquid crystal cell gap abnormality was observed, and good display with a contrast ratio of 40 was shown.

Comparative Example 1 A polymer sheet was prepared in the same manner as in Example 1 except that the heating step was performed at a temperature of 210 ° C. Among the conditions for preparing the polymer sheet, the 0 ° retardation of the polymer sheet was 25 nm. Yes, and the retardation at 40 degrees was 29 nm. Further, the die line shape remained on the sheet surface, and Rmax was 0.5 μm. Using this polymer sheet, a liquid crystal display device was manufactured in the same manner as in Example 1. As a result, display defects due to cell gap abnormality due to die lines were observed. The contrast ratio is 30
And lower than Example 1.

<< Comparative Example 2 >> A procedure was performed in the same manner as in Example 1 except that a polymer sheet was produced without using a heating step.
The Rmax of the sheet was 0.5 μm. Using this polymer sheet, a liquid crystal display device was manufactured in the same manner as in Example 1. As a result, display defects due to cell gap abnormality due to die lines were observed. The contrast ratio is 3
0, which was lower than Example 1.

[0019]

According to the method of the present invention, a polymer sheet having a small retardation and good surface smoothness can be stably obtained.
Continuous production can be performed efficiently. Further, the sheet obtained by the present invention is optimal as an optical polymer sheet,
When a liquid crystal display device was manufactured as a transparent electrode substrate for a liquid crystal display device, not only was the glass substrate lighter and less likely to break, but also a good display without display unevenness was exhibited.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) B29L 11:00 B29L 11:00 31:34 31:34 F term (Reference) 4F100 AK01A AK55A BA01 GB41 GB90 JK15 4F207 AA34 AG01 AH73 AK04 KA01 KK51 4F209 AA34 AG01 AH73 AK04 PA03 PA05 PB02 PC16 PG12 PH02 PH03 PJ09 PN03

Claims (7)

[Claims] 1. The sheet temperature (T1) is 20 ° C. ≦ with respect to the glass transition point (Tg) and the thermal decomposition temperature (TD) of a polymer.
An unfinished polymer sheet satisfying T1 <TD is adhered to a smooth surface having a maximum surface roughness (Rmax) of Rmax ≦ 0.1 μm in the adhering step, and a temperature (T
2) passing through a heating step of Tg ≦ T2 <TD. 2. The method according to claim 1, wherein the smooth surface is a roll or an endless belt. 3. The method for producing a polymer sheet according to claim 2, wherein said contacting step is performed by a nip roll. 4. The method for producing a polymer sheet according to claim 2, wherein the contacting step is performed by an endless belt. 5. The method for producing a polymer sheet according to claim 2, wherein the adhesion step is performed by charging and fixing. 6. An optical polymer sheet produced by the method for producing a polymer sheet according to claim 1. 7. The optical polymer sheet according to claim 6, wherein the polymer is polyether sulfone.