JP2000273204A - Thermoplastic polymer sheet and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a thermoplastic polymer sheet excellent in precision in thickness, not having die lines and sparingly causing a warp of the sheet. SOLUTION: This thermoplastic polymer sheet is produced by the melt extrusion of a thermoplastic polymer through a T-die or a coathanger die so as to form a sheet-like product, by transferring it while retaining the surface temperature difference between the front surface and the back one of a molten sheet within 15 deg.C and by subjecting the molten sheet to a cooling process to solidify it. The sheet is made of a thermoplastic polymer having >=150 deg.C glass transition temperature and has a sheet thickness of 150-1,000 μm, an in-plane thickness tolerance (R max) of <=20 μm, the sheet surface roughness of <=0.1 μm and a sheet plane retardation of <=20 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermoplastic polymer sheet and a method for producing the same. The thermoplastic polymer sheet of the present invention is excellent in thickness accuracy and has little sheet warpage. The thermoplastic polymer sheet of the present invention is suitable for applications such as spacers that require high thickness accuracy, optical sheets where a display function is required, for example, a polishing spacer, a high-precision motor unit. It is suitable as a sliding spacer, a transparent sheet for a display device, or the like.

[0002]

2. Description of the Related Art In general, a thermoplastic polymer sheet produced by a melt extrusion method does not have sufficient thickness accuracy.
In addition, curling occurs and the reliability of the spacer used for maintaining the gap with high precision is poor.

For this reason, a metal plate such as aluminum or copper is used as a spacer for maintaining a high-precision gap. As in the case of a Si wafer polishing spacer for a semiconductor, a metal spacer is polished as in the case of a Si wafer, and the metal powder becomes a trace impurity when a pattern circuit is formed in a later step, causing a short circuit between circuits.

A glass substrate is conventionally used for an optical sheet such as a transparent electrode substrate for a liquid crystal display device. In such a liquid crystal display device, it is difficult to reduce the thickness and weight of the liquid crystal display device because the glass substrate itself is thick. In addition, sufficient properties have not been obtained in terms of flexibility and impact resistance.

In order to solve the drawbacks of the conventional glass substrate liquid crystal display device, it has been proposed to manufacture a liquid crystal panel using a plastic film. For example, JP-A-53-68099 and JP-A-54-126559
Japanese Patent Application Laid-Open No. H11-163,878 discloses a technique for continuously manufacturing a liquid crystal display element panel in which a conductive metal oxide material is deposited on a long polyester film instead of a glass substrate, but sufficient optical characteristics can be obtained. Not. In addition, such a sheet has poor thickness accuracy as an optical sheet, and a die line is generated on a film.

In order to obtain a thermoplastic resin sheet having excellent properties that can be used for optical applications, there is a problem of an increase in the retardation of the sheet due to the molecular orientation generated in the melt extrusion film forming process. For example, TN (Twist
(ed Nematic) type liquid crystal display element, the incident light linearly polarized by the polarizer becomes elliptically polarized light that is partially different from the birefringence of the transparent electrode sheet and the deviation in the sheet plane, resulting in a decrease in contrast and display unevenness. Is generated.

Conventionally, when melt extrusion is performed using a T-die or a coat hanger die, in order to improve the thickness accuracy, it is necessary to reduce the variation in pressure at the die outlet due to shear stress or stagnation in the flow path of the thermoplastic polymer. Or
A method of improving the accuracy of the surface of the die and the lip, which is a cause of uneven stripes called a die line, and a method of providing a guide roll have been adopted, but they have not been solved yet.

As a method for producing a polymer sheet having good thickness accuracy, a solvent casting method in which a thermoplastic polymer is dissolved in a solvent, coated on a film or a metal belt, and dried, is also known. And the solvent remains in the sheet.

Further, as another method, there is an injection molding method in which a thermoplastic polymer is sealed in a mold whose dimensions have been finished with high precision and molded. Although such a method is used for molding a CD disk and has sufficient productivity, the injection molding method is limited to a sheet having a thickness of several mm, and it is not possible to obtain a more precise thickness accuracy of several hundred μm. Can not.

A method of performing post-processing to improve the curl resistance of a sheet is also known. For example, a method of pressing a sheet at a certain interval using a plate whose surface is finished with high precision, but such a method has low productivity and is not suitable for mass production. Further, in the method of removing the warpage of the sheet using the cooling roll, it is necessary to make the cooling roll along the sheet extremely large, which is not economical.

Further, even when the polymer sheet is cooled and solidified on a flat surface (having no curvature), the sheet is likely to be warped. Thus, it is very difficult to produce a thermoplastic polymer sheet having excellent thickness accuracy and small sheet warpage.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermoplastic polymer sheet which is excellent in thickness accuracy, has no die line, and has less warpage of the sheet, and a method for producing the same.

[0013]

The present inventors have conducted various studies on such a conventional method for producing a thermoplastic polymer sheet, and found that the temperature of the molten resin from the die to the cooling step was strictly controlled. As a result, the present inventors have found that a product having extremely excellent dimensional accuracy and having no curl can be obtained, thereby completing the present invention.

The first invention of the present application has a glass transition point of 150.
Consisting of a thermoplastic polymer having a temperature of at least 150 ° C.
1000 μm, sheet thickness tolerance (Rmax) 20 μm
The present invention provides a thermoplastic polymer sheet having a sheet surface roughness of 0.1 μm or less, and a planar retardation of the sheet of 20 nm or less.

According to a second aspect of the present invention, a thermoplastic polymer is melt-extruded into a sheet from a known die such as a T-die or a coat hanger die, and the surface temperature difference between the front side and the back side of the molten sheet is within 15 ° C. And then moving the molten sheet to a cooling step so as to be solidified, thereby providing a method for producing the thermoplastic polymer sheet.

A third aspect of the present invention provides a transparent electrode sheet using the above-mentioned thermoplastic polymer sheet as a substrate.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, an unexpectedly uniform sheet was obtained by maintaining the temperature distribution on the sheet surface from the tip of the die slip to the cooling roll as small as possible. The die lip tip zone in the usual melt extrusion method is heated by radiant heat, and a measure is taken to prevent a non-uniform temperature distribution from occurring in the molten sheet. However, due to heat dissipation using air as a medium, the temperature of the polymer sheet decreases, and the front and back sides of the sheet surface,
An uneven temperature distribution occurs at left and right positions in the sheet width direction. Further, the molecular orientation is completely solidified by contact with the cooling portion.

In the method of the present invention, the section from the tip of the lip to the cooling roll is sufficiently insulated along the flow of the sheet and strict temperature control is performed. For example, a method of controlling the temperature by shutting off the film extruded from the die until the film touches the cooling roll from the outside air with a metal plate or a heat insulating material, or installing a heater etc. to forcibly control the temperature A method of controlling and managing is included. In addition, there is a method of installing a baffle plate for eliminating a temperature change due to an air flow occurring near a cooling roll or a die, and furthermore, controlling an ambient temperature in a room so as not to generate an air flow. Any of various methods may be used as long as strict temperature control can be performed along the sheet flow in the section up to the cooling roll.

In the process in which the melt-extruded thermoplastic polymer sheet is transferred to the cooling part, the surface temperature difference between the front side and the back side of the belt-shaped thermoplastic polymer sheet is set within 15 ° C., preferably within 10 ° C. I do. If the surface temperature difference between the front side and the back side of the polymer sheet is larger than this, birefringence in the thickness direction of the polymer sheet will increase, and irregularities on the sheet surface called die lines will increase, and surface accuracy will deteriorate.

In the process in which the melt-extruded thermoplastic polymer sheet is transferred to the cooling part, the surface temperature difference in the width direction of the strip-shaped molten sheet is set within 15 ° C., preferably within 10 ° C. If the surface temperature difference in the width direction of the sheet is larger than this, the thickness accuracy is reduced. This is considered to be caused by uneven stretching caused by a difference in elasticity due to temperature distribution when the polymer sheet is stretched from the die slip and cooled by the cooling roll. In addition, the adhesiveness to the cooling roll also becomes uneven, and the birefringence in the plane and in the thickness direction deteriorates due to uneven cooling efficiency. Further, the die line increases as described above, and the surface accuracy of the sheet deteriorates.

In the present invention, assuming that the glass transition point of the melt-extruded thermoplastic polymer sheet is Tg,
Temperature of dies such as dies and coat hanger dies (D1)
Is Tg + 80 <D1 <Tg + 150 [° C.]. The temperature (D1) of T die or coat hanger die is Tg +
If the temperature is lower than 80 [° C.], the resin has a high viscosity and a back pressure is applied to the die, so that the die cannot be extruded. D1 is Tg + 1
When the temperature is higher than 50 ° C., the resin is thermally decomposed, which leads to discoloration or generation of foreign matter.

The surface temperature (S1) of the polymer sheet when coming into contact with the cooling portion is Tg + 30 <S1 <Tg + 100
[° C.]. The surface temperature (S1) of the polymer sheet is Tg
When the temperature is lower than +30 [° C.], the polymer sheet is stretched from the die slip and cooled by the cooling roll, but the birefringence in the plane of the polymer sheet increases during stretching. If the surface temperature (S1) of the polymer sheet is equal to or higher than Tg + 100 [° C.], the temperature difference from the cooling roll is too large, and the stress when the sheet is formed becomes large, so that the birefringence increases and the cooling capacity becomes insufficient. The polymer sheet is easily fused to the cooling roll, resulting in poor appearance.

The cooling roll temperature (R1) is Tg-3.
0 <R1 <Tg + 30 [° C.]. If the cooling roll temperature (R1) is lower than Tg-30 [° C.], cooling wrinkles occur and the appearance becomes poor. Cooling roll temperature (R1) is Tg +
If the temperature is higher than 30 ° C., the polymer sheet is fused to the cooling roll, resulting in poor appearance.

The thickness of the thermoplastic polymer sheet is from 150 to
1000 μm is preferable, and 200 to 50 is more preferable.
0 μm. If the thickness of the polymer sheet is thinner than this, it is difficult to handle when using a general-purpose liquid crystal panel manufacturing line, and it is difficult to maintain the cell gap of the liquid crystal, especially for large-area liquid crystal display devices. Can not do it. On the other hand, if the thickness exceeds this range, the liquid crystal display causes a display defect called double image, and the thickness of the liquid crystal display element is further increased, which is not preferable in function.

The retardation of the plane is preferably 2
It is 0 nm or less, more preferably 10 nm or less. The flat retardation is represented by Re = (Nx−Ny) × d, where Nx is the maximum refractive index in the polymer sheet plane, and Ny is the minimum refractive index in the polymer sheet plane. is there. d is the thickness of the sheet. 20n retardation
m, the contrast of the liquid crystal display decreases,
The display becomes invisible.

The in-plane thickness tolerance of the polymer sheet is 20 μm.
Or less, more preferably 10 μm or less.
If the in-plane thickness tolerance exceeds 20 μm, the cell may not be divided even if it is half-cut at the time of assembling the liquid crystal cell. In addition, it is difficult to use it for a high-precision spacer.

Maximum surface roughness (Rmax) of the polymer sheet
Is preferably 0.1 μm or less, more preferably 0.0 μm or less.
5 μm or less. If the maximum of the surface roughness is larger than 0.1 μm, an abnormal cell gap of the liquid crystal occurs and a display failure occurs.

The glass transition point (Tg) of the thermoplastic polymer used in the present invention is preferably 150 ° C. or higher, more preferably 180 ° C. or higher. If the Tg of the thermoplastic polymer is lower than 150 ° C., the sheet is softened at the heat treatment in the liquid crystal assembling step, for example, at the temperature of firing the alignment film and curing the seal, resulting in a product failure. Examples of such a thermoplastic resin include polysulfone, polyethersulfone, polyetherimide, norbornene-based resin, polyarylate and a resin obtained by blending them. This is preferable in that there is little change. The resin used in the present invention may contain a small amount of a stabilizer, a lubricant, a dye or the like as an additive depending on the purpose.

The optical properties of the sheet of the present invention were measured by the following methods. Measurement method of sheet temperature: A thermocouple was brought into contact with the surface of the thermoplastic polymer sheet melt-extruded from a die, and the temperature was measured. Sheet thickness: It is an average value measured in the plane of the polymer sheet with a contact type dial gauge. In-plane thickness tolerance: The difference between the maximum and minimum values measured in the plane of the polymer sheet with a contact dial gauge.

The maximum surface roughness (Rma) of the polymer sheet
x) Contact type precision step meter (AIPHA-STE manufactured by TENCOR INSTRUMENTS)
P200) is the maximum value of the concavities and convexities measured over the entire width at a scan width of 2 mm in the width direction of the polymer sheet. Retardation of Polymer Sheet The retardation at a wavelength of 550 nm was measured using a polarizing microscope BH2 manufactured by Olympus Optical Co., Ltd. and a Berek compensator.

[0031]

Next, the present invention will be described more specifically with reference to examples and comparative examples. [Example 1] Polyether sulfone resin (Sumitomo Chemical Industries, Ltd.)
Victrex PES4100G, Tg = 22
(6 ° C.) was melt-extruded from a coat hanger die, and the molten thermoplastic polymer sheet was subjected to a cooling step to produce a thermoplastic polymer sheet. In addition, stainless steel covers were placed at both sides where the distance from the surface of the polymer sheet to the width of the cooling roll was 50 mm between the lip tip and the cooling roll to surround the sheet. Die temperature 350
° C and the cooling roll temperature were set to 220 ° C. The temperature difference between the front and back surfaces of the polymer sheet was 5 ° C., the temperature difference between the surfaces in the width direction was 8 ° C., and the temperature of the polymer sheet when the cooling roll contacted the polymer sheet was 300 ° C. The thickness of the obtained sheet was 400 μm.

As a result, the in-plane thickness tolerance of the polymer sheet
(Rmax) is 15 μm, the retardation in the plane is 15 nm, and the maximum surface roughness of the polymer sheet is
A sheet having a high dimensional accuracy (Rmax) of 0.06 μm was obtained.

The sheet obtained in Example 1 (400 μm thick)
An organic layer was formed on m) as follows. That is,
Epoxy acrylate prepolymer (Showa Polymer Co., Ltd.)
VR-60, molecular weight 1540, melting point 70 ° C) 100
Parts by weight, 400 parts by weight of butyl acetate, 100 parts by weight of cellosolve acetate and 2 parts by weight of benzoin ethyl ether were stirred and dissolved at 50 ° C. to prepare a uniform solution, which was then coated on the sheet using a gravure roll coater. Applied. Then, heating at 80 ° C. for 10 minutes to remove the solvent,
80 w / cm high pressure mercury lamp at a distance of 15 cm
The resin was cured by irradiation for 2 seconds to form an organic layer having a thickness of 0.5 μm. Organic layers were formed on both sides. Next, a mixed gas of oxygen / argon gas of 9% was introduced at an initial degree of vacuum of 3 × 10 ⁻⁴ Pa, and an inorganic layer of SiO ₂ was formed on the sheet by a DC magnetron method under a condition of 3 × 10 ⁻¹ Pa. Was formed (500 mm thick). When the oxygen barrier property of this inorganic film was measured by the Mocon method, it was 1 cc / 24 hr · m.
² , and the surface resistivity was measured to be 8.1 × 10
¹² Ω.

Next, a transparent conductive film was formed by the DC magnetron method. That is, the initial degree of vacuum is 3 × 10 ^−4.
A mixed gas of oxygen / argon gas 4% is introduced at Pa,
A film is formed under the condition of 1 × 10 ⁻¹ Pa, and In / In
In ² O ³ , SnO ² having an atomic ratio of + Sn of 0.98
Was obtained. As a result of the measurement, the film thickness was 160
0 °, and the specific resistance was 4 × 10 ⁻⁴ Ω-cm. After film formation, a resist is applied and developed, and an etchant of 10
vol% HCl, pattern etching in liquid temperature 40 ° C,
An active matrix pattern having a diagonal length of 3 inches and L / S = 150/50 μm was formed. After pattern formation, an orientation film was applied, baked at 150 ° C. for 2 hours, and then rubbed. After the rubbing treatment, a spacer was sprayed, a sealant was applied, the seal was cured at 150 ° C. to form a cell, and a liquid crystal was injected. After liquid crystal injection,
The substrate was divided by half-cutting, but could be divided without any problem. In addition, when a polarizing plate was attached to the position where the contrast was maximized and a lighting test was performed, no break was seen at all, and a display with good contrast was observed without any display defects due to sheet retardation or liquid crystal cell gap abnormality. Indicated.

Example 2 Amorphous norbornene resin manufactured by Zeon Corporation: ZEONOR1600 (Tg16)
5 ° C.), the die temperature was set to 250 ° C., and the cooling roll temperature was set to 180 ° C. to produce a sheet. The temperature difference between the front and back surfaces of the polymer sheet is 5 ° C., the temperature difference between the surfaces in the width direction is 8 ° C., and the temperature of the polymer sheet when the cooling roll contacts the polymer sheet is 220 ° C. , Surround the area from the lip tip to the cooling roll with a stainless steel enclosure,
A sheet having a thickness of 600 μm was formed. As a result, a polymer sheet having an in-plane thickness tolerance (Rmax) of 18 μm, a retardation in a plane of 15 nm, and a maximum surface roughness (Rmax) of 0.06 μm of the polymer sheet is obtained. I got

Comparative Example 1 A sheet was produced in the same manner as in Example 1 except that the stainless steel enclosure was removed.
The temperature difference between the front and back of the sheet was 17 ° C, and the width direction was 20 ° C. The thickness tolerance of the obtained sheet was 30 μm, the retardation was 40 nm, and the surface roughness was 0.2 μm. Similarly, when assembled as a liquid crystal cell, disconnection occurred at the time of cell division of the liquid crystal cell, and the yield was reduced due to inability to divide the cell. Furthermore, the contrast of the liquid crystal device was poor, and display defects due to cell gap unevenness occurred.

Comparative Example 2 A sheet was prepared in the same manner as in Example 1 except that a heater was provided and the temperature at which the polymer sheet was brought into contact with the cooling roll was set at 340 ° C. . The thickness tolerance of the obtained sheet is 25μ.
m, the retardation is 70 nm, and the sheet surface roughness is 0.1.
It was 05 μm. When a liquid crystal cell was assembled using this sheet in the same manner as in Example 1, the contrast was poor and the display was difficult to see.

[0038]

The thermoplastic polymer sheet of the present invention has a small flat retardation, is excellent in surface smoothness, has little substrate warpage, and has no die line. This sheet is optimal as a spacer sheet and an optical sheet. For example, when it is mounted on a liquid crystal display panel as a transparent electrode sheet for a flexible liquid crystal display element, it shows a high definition display without display unevenness.

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Claims (7)

[Claims] 1. A sheet made of a thermoplastic polymer having a glass transition point of 150 ° C. or higher, a sheet thickness of 150 to 1000 μm, a sheet thickness tolerance (Rmax) of 20 μm or less, a sheet surface roughness of 0.1 μm or less, and A thermoplastic polymer sheet having a sheet retardation of 20 nm or less. 2. The polymer sheet according to claim 1, wherein the thermoplastic polymer is polyether sulfone. 3. A method in which a thermoplastic polymer is melt-extruded from a T-die or a coat hanger die into a sheet and is moved while maintaining the surface temperature difference between the front and back sides of the molten sheet within 15 ° C. The method for producing a thermoplastic polymer sheet according to claim 1, wherein the sheet is subjected to a cooling step to be solidified. 4. A difference in surface temperature in the width direction of the molten sheet is 15
The method for producing a thermoplastic polymer sheet according to claim 3, wherein the temperature is within ° C. 5. The method for producing a thermoplastic polymer sheet according to claim 3, wherein heat is provided between the die and the cooling step. 6. The glass transition point of the thermoplastic polymer is Tg,
Assuming that the temperature of the T die or the coat hanger die is D1,
Tg + 80 ° C. <D1 <Tg + 150 ° C. If the surface temperature of the thermoplastic polymer when subjected to the cooling step is S1, Tg + 30 ° C. <S1 <Tg + 100 ° C. If the cooling roll temperature is R1, Tg− 30 ° C <R1 <T
The method for producing a thermoplastic polymer sheet according to claim 3, wherein the temperature is g + 30 ° C. 7. A transparent electrode sheet using the thermoplastic polymer sheet according to claim 1 as a substrate.