JPH0895049A - Rubbing method and manufacturing method using it for optical compensating sheet - Google Patents

Abstract

PURPOSE: To eliminate rubbing unevenness caused in rubbing so as to carry out stable rubbing continuously for a long time by making the numbers of revolutions for respective rolls different from each other when a long film, on which an oriented film is applied, is continuously rubbed by means of the plural rubbing rolls. CONSTITUTION: When a surface of a long film 5, in which an oriented film is formed on one side, is continuously rubbed by means of rubbing rolls 3, the plural rubbing rolls 3 are used in order, and in this continuous rubbing method for the long film 5, the number of revolutions of plural rubbing rolls 3 vary from each other. At least one in the plural rubbing rolls 3 has a diameter different from those of others. In this way, rubbing is carried out by means of the plural rubbing rolls 3 in order while regulation is carried out so that a cycle of liquid crystal orientation unevenness due to the vibration of one rubbing roll 3 varies from a cycle of liquid crystal orientation unevenness due to the vibration of other rubbing rolls 3, and consequently, rubbing without any unevenness can be accomplished.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubbing method for imparting an alignment regulating force to an alignment film for aligning liquid crystal molecules, and more specifically, a rubbing method for performing a uniform alignment regulating force with good reproducibility and stability. And a method for producing an optical compensation sheet produced thereby.

[0002]

2. Description of the Related Art CRTs, which are the mainstream display devices for office automation equipment such as Japanese word processors and desktop personal computers
Have been converted into liquid crystal display elements which have the great advantages of thinness, light weight, and low power consumption. Most of the liquid crystal display elements (hereinafter, referred to as LCDs) that are currently popular use twisted nematic liquid crystals. The display method using such a liquid crystal can be roughly classified into a birefringence mode and an optical rotation mode.

An LCD using the birefringence mode has a twisted angle of 90 ° or more in the alignment of liquid crystal molecules and has steep electro-optical characteristics, so that it has a simple matrix without active elements (thin film transistors or diodes). A large-capacity display can be obtained by the time-divisional behavior with the electrode structure in the shape of a circle. But,
It has the disadvantage that the response speed is slow (several hundred milliseconds) and that gradation display is difficult.
It does not exceed the display performance of LCD and MIM-LCD.

In the TFT-LCD and the MIM-LCD, an optical rotation mode display mode (TN type liquid crystal display element) in which the alignment state of liquid crystal molecules is twisted by 90 ° is used. This display method is the most influential method as compared with other types of LCDs, since it has a fast response speed (several tens of milliseconds), easily obtains a black-and-white display, and shows a high display contrast. However, since the twisted nematic liquid crystal is used, there is a problem in the viewing angle characteristics that the display color and the display contrast change depending on the viewing direction due to the principle of the display system.
It does not exceed the display performance of T.

Japanese Unexamined Patent Publication Nos. 4-229828 and 4-2.
As disclosed in Japanese Patent No. 58923, a method has been proposed in which an optical compensation sheet is arranged between a pair of polarizing plates and a TN type liquid crystal cell to increase the viewing angle. The optical compensation sheet proposed in the above patent publication has a phase difference of almost zero in the direction perpendicular to the liquid crystal cell, and does not exert any optical action from the front.
A phase difference appears when tilted, and the phase difference that appears in the liquid crystal cell is compensated. However, even with these methods, the viewing angle of LCD is still insufficient, and further improvement is desired. In particular, when considered as a vehicle-mounted type or as a substitute for a CRT, it is the current situation that the current viewing angle cannot support at all.

Further, in JP-A-4-366808 and JP-A-4-366809, a viewing angle is improved by using a liquid crystal cell containing a chiral nematic liquid crystal having an inclined optical axis as an optical compensation sheet. It is a layered liquid crystal system, which is expensive and very heavy. Further, JP-A-5-80323 proposes a method of using an optical compensation sheet having an optical axis inclined with respect to a liquid crystal cell. However, since uniaxial polycarbonate is sliced and used obliquely. However, there is a problem that it is difficult to obtain a large-area optical compensation sheet at low cost. Further, Japanese Patent Application No. 5582/1993 describes a method of using a photoisomerizable substance and using a retardation film having an inclined optical axis.
According to this method, a liquid crystal display device having a wide viewing angle characteristic, a light weight, and a low cost can be realized. However, the drawback of this method is that the retardation film is not sufficiently stable against heat and light. Further, Japanese Patent Application Laid-Open No. 5-215921 proposes a method for optically compensating an LCD by a birefringent plate in which a rod-shaped compound exhibiting liquid crystallinity is sandwiched between a pair of substrates subjected to alignment treatment. This plan is no different from the so-called double-cell type compensator that has been proposed in the past, and it causes a great increase in cost and is practically unsuitable for mass production. Further, as long as a rod-shaped compound is used, the birefringent plate cannot improve the omnidirectional viewing angle of the TN LCD for optical reasons described later. Further, in Japanese Patent Laid-Open Nos. 3-9326 and 3-291601, there is described a plan to apply a polymer liquid crystal to a film-shaped substrate on which an alignment film is provided to form an optical compensator for LCD. But
Since it is impossible to orient the molecules obliquely by this method, it is also impossible to improve the omnidirectional viewing angle of the TN type LCD.

Further, EP 0576304 A1 describes a method for improving the viewing angle characteristics by using a retardation plate whose refractive index characteristic shows negative uniaxiality and whose optical axis is inclined. Although this method certainly improves the viewing angle greatly compared to the conventional one, it still has a CRT
It was not possible to improve the viewing angle enough to consider alternatives.

Therefore, the inventor of the present invention has filed Japanese Patent Application No. 5-23653.
It was found from No. 9 specification that the optical compensation sheet in which the discotic molecules are oriented obliquely significantly improves the viewing angle of the TN LCD. Then, in producing such an optical compensation sheet in a roll shape, an alignment film is provided on a transparent film, and it is considered that the means for applying and aligning a discotic liquid crystal as a discotic molecule is the best, The suitability for mass production was examined. As a result, it was found that when an organic film which seems to have the highest versatility is used as an alignment film, a continuous film of discotic liquid crystal alone can be formed thereon. According to the study by the present inventors, the optical compensation sheet for improving the viewing angle of the TN type liquid crystal cell is a negative uniaxial optical anisotropic body having an optical axis inclined from the normal direction, and the inclination from the normal direction is TN. It must be optimized according to the characteristics of the liquid crystal cell. However, since the oblique alignment angle of the discotic liquid crystal is determined by the discotic liquid crystal molecular structure in the case of the organic alignment film, the oblique alignment angle can be adjusted by selecting the liquid crystal species. However, in producing such an optical compensation sheet in a roll,
It was found that the rubbing treatment is important in order to uniformly align the liquid crystal molecules on the transparent film after the alignment film is provided on the transparent film.

For the alignment of liquid crystal molecules, a method using an inorganic alignment film such as Si or an organic alignment film subjected to rubbing treatment is known. The rubbing method is a method for aligning liquid crystals on a long film. It is common. The rubbing is a method in which the surface of the alignment film is rubbed in one direction with a pile cloth or the like, and the liquid crystal is aligned in the rubbed direction.
The rubbing process is required to be performed uniformly over the entire surface of the substrate, and the sheet-shaped one is performed as shown in FIG. By the way, when a long film substrate is used as the substrate, continuous processing as shown in FIG. 5 is performed.

Usually, in the case of continuous processing, the orientation regulating force depends on the radius of the rubbing roll, the number of revolutions of the rubbing roll, the pushing depth of the raised pile of the rubbing cloth, the conveying speed of the substrate and the like. Particularly, it is necessary to strictly control the pushing depth of the raised pile of the rubbing roll.
The parallelism of the roller with respect to the substrate is ensured by the method disclosed in Japanese Unexamined Patent Publication No. 202112.
However, in the case of continuous treatment, one roll can perform rubbing only once, and therefore the rubbing roll must be rotated at a high speed in order to increase the rubbing efficiency. Therefore, the roundness of the rotation of the roll becomes important. If the accuracy of the roundness is poor, not only the fluctuation of the pushing depth but also the vibration of the rotation due to the eccentricity becomes large, which causes a slight vibration in the entire roll and further in the entire device. As a result, this vibration causes fluctuations in the alignment control force, which affects the liquid crystal alignment. This effect is
It may appear as uneven optical properties of the optical compensation sheet formed by applying liquid crystal.

[0011]

With the recent increase in the size of liquid crystal display plates, there has been a serious problem of reduced visibility due to uneven alignment of liquid crystals due to vibration of these rubbing rolls and devices. Furthermore, with the addition of a wider and faster rubbing process, there has been an urgent need to develop a method capable of reliably removing the unevenness caused by these vibrations. An object of the present invention is to reduce liquid crystal alignment unevenness caused by rubbing when a continuous film is subjected to continuous rubbing treatment. further,
Using that method to produce an optical compensation sheet with uniform optical properties.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and (1) when continuously rubbing the surface of a long film having an alignment film formed on one surface thereof with a rubbing roll. A continuous rubbing method for a long film which sequentially uses a plurality of rubbing rolls, wherein the number of revolutions of the plurality of rubbing rolls is different from each other, (2) at least one of the plurality of rubbing rolls The continuous rubbing method according to (1) above, which has a diameter different from other diameters, (3) after coating an alignment film material on a transparent support and performing a rubbing treatment, a layer containing at least one discotic compound is formed. A method of manufacturing an optical compensation sheet, wherein the rubbing treatment is the method of (1) or (2) above.

[0013]

Based on the above construction, the period of the unevenness of liquid crystal alignment caused by the vibration of one rubbing roll and the period of the unevenness of the liquid crystal alignment caused by the vibration of the other rolls are adjusted so as to be different from each other. By sequentially rubbing with, it is possible to rub the liquid crystal alignment evenly. The cycle of unevenness due to vibration can be adjusted by appropriately changing the rotation speed of the roll and the diameter of the roll.

As a typical liquid crystal alignment method used in the present invention, there is a method using a polyimide film. This is a nematic liquid crystal or discotic liquid crystal, which is obtained by applying polyamic acid (for example, SE-7210 manufactured by Nissan Kagaku Co., Ltd.) to a long film, baking the film at 100 ° C. to 300 ° C. to form an alignment film, and then rubbing the nematic liquid crystal or discotic liquid crystal. This is a method of orienting. Further, as another example, an alkyl chain-modified Poval (for example, MP203 manufactured by Kuraray Co., Ltd., R
(1130 etc.) is used as an alignment film, baking is not necessary and the alignment ability with respect to the nematic liquid crystal or the discotic liquid crystal can be imparted only by rubbing. In addition, if an organic polymer forming a hydrophobic surface such as polyvinyl butyral or polymethylmethacrylate is used as the alignment film, most of them can impart the liquid crystal alignment ability by rubbing the surface.

The discotic compound of the present invention means a discotic liquid crystal as listed below, and a reaction product of a discotic liquid crystal which no longer exhibits liquid crystallinity due to reaction with other low molecular weight compounds or polymers. And the like mean all compounds having a molecule itself having optically negative uniaxiality.

Typical discotic liquid crystals include, for example, C.I. Report of Destrade et al., Mo
l. Cryst. Liq. Cryst. Volume 71, 111
Page (1981), benzene derivatives,
Triphenylene derivatives, truxene derivatives, phthalocyanine derivatives, B.I. Report of Kohne et al., Ange
w. Chem. Vol. 96, p. 70 (1984) and cyclohexane derivatives described in J. Am. M. Lehn et al., J. Chem. Soc. Chem. Commu
n. , Pp. 1794 (1985), J. Research report by Zhang et al. Am. Chem. Soc. Volume 116, 2
Examples thereof include azacrown-based and phenylacetylene-based macrocycles described on page 655 (1994). Other than those listed below, if the molecule itself has negative uniaxial optical anisotropy and the optical axis is obliquely oriented with respect to the substrate surface by the oblique alignment film, It is not limited to the substance.

[0017]

[Chemical 1]

[0018]

[Chemical 2]

[0019]

[Chemical 3]

[0020]

[Chemical 4]

Negative uniaxiality in the present invention means a relationship of n1 <n2 = n3, where n1, n2, and n3 are the refractive indices in the triaxial direction of a sheet having optical anisotropy in the order of decreasing values. I have. Therefore, it has a characteristic that the refractive index in the optical axis direction is the smallest. However, it is not necessary that the values of n2 and n3 are exactly equal, and it is sufficient if they are almost equal.

The transparent film of the present invention preferably has good light transmittance. Specifically, the light transmittance is 80%
It is preferably at least 90%, more preferably at least 90%. Therefore, a support formed of a material having a small intrinsic birefringence value, which is sold under the trade name of Zeonex (Nippon Zeon), ARTON (Nippon Synthetic Rubber), Fujitac (Fuji Film), or the like is preferable. However, even for materials with a large intrinsic birefringence value such as polycarbonate, polyacrylate, polysulfone, and polyethersulfone, it is possible to form an optically isotropic support by controlling the molecular orientation during film formation. It is possible, and they are preferably used.
Specifically, when the plane orientation main refractive index of the support is Nx, Ny, the thickness direction main refractive index is Nz, and the thickness is d, the range of the plane orientation Re value represented by the following formula (2) is: The thickness is 20 nm to 300 nm, more preferably 30 nm to 150 nm. By satisfying the condition of this plane orientation, a remarkable effect is obtained in improving the viewing angle characteristics.

Formula (1) Re = ((Nx + Ny) / 2−Nz) × d

When the optical compensation sheet of the present invention is produced, a step for obtaining a uniform oblique orientation is required in the production process. Specifically, the step of uniformly rubbing a long film coated with an alignment film, the step of applying a discotic liquid crystal, and the step of raising the temperature to the discotic liquid crystal formation temperature include UV light irradiation in the case of a crosslinkable molecule. This is a step of performing a crosslinking treatment and cooling. As a result, the liquid crystal has a uniform oblique orientation and becomes a solid at room temperature without breaking the orientation. The temperature at which the discotic liquid crystal used in the present invention takes a discotic liquid crystal phase is preferably 90 ° C. or higher and 300 ° C. or lower, particularly preferably 90 ° C. or higher and 1
It is 50 ° C or lower.

As a method other than the above method for obliquely aligning the discotic liquid crystal coated on the substrate, there are magnetic field orientation and electric field orientation as methods other than the orientation film. In this method, after the discotic liquid crystal is applied to the substrate, a zone for applying a magnetic field or an electric field at a desired angle is required, but the zone itself needs to be adjusted to a temperature at which the discotic liquid crystal is formed. .

FIG. 1 is a diagram showing an outline of the present invention. This rubbing method is performed by using the accompanying long substrate conveying devices 1 and 2, a plurality of rubbing rolls 3 having an outer diameter of 60 mm to 150 mm, and a roll 4 for conveying a substrate having an outer diameter of 60 mm to 150 mm arranged on the opposite side of the substrate. Consist of the composition. In this alignment treatment apparatus, the long film substrate 5 is conveyed by the conveying device at a constant tension and at a conveying speed of 1 to 100 m / min, as indicated by arrow E.
It is designed to be transported in the direction of. Film substrate 5
An alignment film made of the above-mentioned polyimide, alkyl-modified poval, or the like is formed on the upper surface of the. The rubbing roll 3 is formed by winding a rubbing cloth such as velvet around the outer peripheral surface of the roll body. Rubbing roll 3
Is freely rotatable in the horizontal direction around the center in the axial direction for setting the rubbing angle as required, and is also vertically movable. In this method, first, the rubbing roll 3, which has been standing by above the film substrate 5, is lowered to a predetermined position, brought into contact with the alignment film surface of the film substrate, and further sunk to a certain depth. Next, the film substrate 5 is moved to the arrow E with a constant tension and a constant speed by the accompanying transfer devices 1 and 2.
Transport in the direction of. Here, the rubbing roll 3 is moved in the direction opposite to the transport direction of the film substrate 5, that is, in the direction of arrow E.
Rotate at a constant rotational peripheral speed of 00 to 800 m / min. Then, the surface of the alignment film on the film substrate 5 which is continuously conveyed is continuously and sequentially rubbed by the rubbing roll 3. At this time, even if one or more rubbing rolls are installed, when the number of rotations is the same, the rubbing roll 3 causes minute vibrations, and periodical unevenness of rubbing due to the vibrations is likely to occur. Uneven regulation is likely to occur.

In the present invention, a plurality of rubbing rolls 3 are sequentially arranged in series and the number of revolutions thereof is set to be different from each other, whereby the above-mentioned periodic unevenness can be completely eliminated. Further, at this time, by using a plurality of rolls having different diameters as shown in FIG. 2, it is possible to more effectively eliminate the periodic unevenness. Furthermore, as shown in FIG. 3, by wrapping the rubbing roll without directly contacting the backup roll, the vibration of the rubbing roll can be effectively absorbed, so that the periodic unevenness can be eliminated more effectively. I can. .

[0028]

EXAMPLES The present invention will be described in detail below based on examples. Example 1 A 100 μm thick film of triacetyl cellulose (Fujitac manufactured by Fuji Photo Film Co., Ltd.) was used as a substrate, and an alkyl-modified poval (Kuraray Co., Ltd.) was used as an alignment film on the substrate.
MP203) was applied to a thickness of 1 μm. This was subjected to rubbing treatment by the rubbing method shown in FIG. 1 of the present invention. As Example 1, the outer diameter of the rubbing roll is 80 m.
3 m, outer diameter of film substrate transfer roll 60 mm3
Book, film substrate transport speed 100 m / min, rubbing roll rotation speed 1000 rpm for first roll, 1300 for second roll
The third rpm was set to 1700 rpm. The rubbing treatment was carried out under the condition that the film substrate conveyance tension was 1 kgf / cm substrate width. Then, a coating solution having the following formulation is applied on the rubbing-treated film alignment film by a bar coater to a dry film thickness of 2 μm. CAB531 ・ ・ ・ ・ ・ ・ ・ ・ 12 parts TE-8 (m = 4) ・ ・ ・ 100 parts SR306 ・ ・ ・ ・ ・ ・ 10 parts Irgacure 907 ・ ・ ・ ・ ・ ・ 2 parts Methyl ethyl ketone ・ ・ ・・ 400 parts where CAB531 is cellulose acetate butyrate from Eastman Chemical Company, TE-8 is the discotic liquid crystal described above, SR306 is tripropyrene glycol diacrylate from Somar Co., Ltd., and IRGACURE 907 is Ciba-Geigy Co., Ltd. of Japan. Is a photopolymerization initiator. This coated film was passed through a heating zone at 140 ° C. for 2 minutes in a heated state, then irradiated with UV light and crosslinked to obtain an optical compensation sheet sample.

Example 2 The rotation speeds of the three rubbing rolls used in Example 1 were 600 rpm, 1700 rpm and 2300 rpm, respectively.
A film having a layer containing discotic liquid crystal was prepared under the same conditions as in Example 1 except that the above was set.

Example 3 The diameter of the three rubbing rolls used in Example 1 was 80 m.
A film having a layer containing a discotic liquid crystal was prepared under the same conditions as in Example 1 except that those having a thickness of m, 120 mm, and 150 mm were used.

Comparative Example All three rubbing rolls of Example 1 were rotated at 15 revolutions.
A film having a layer containing a discotic liquid crystal was prepared under the same conditions as in Example 1 except that the film was rubbed at 00 rpm.

The optical compensation films of Examples 1 to 3 and Comparative Example 1 were used as TN type liquid crystal cells (the product of the difference in the refractive index between the extraordinary ray and the ordinary ray of the liquid crystal and the gap size of the liquid crystal cell was 510 nm and the twist angle was 87). 6) was mounted as shown in FIG. 6, and the visibility was evaluated (color unevenness) by an actual image. Further, the alignment disorder of the liquid crystal on the surface of these optical compensation films was observed with a polarization microscope.

Table 1 shows the results of the visibility evaluation and the results of observation with a polarizing microscope.

[0034]

[Table 1]

According to the results shown in Table 1, the optically-compensatory film obtained by the constitution of the present invention has a uniform orientation of the applied liquid crystal, and even when it is mounted on the TN cell, the displayed image has a high display quality without disturbance. It was confirmed to show.

[0036]

As described above, according to the present invention, when a long film coated with an alignment film is continuously rubbed using a plurality of rubbing rolls, the rotation speed of each roll is adjusted. By setting it differently,
Alternatively, it was found that by making the diameters of the rolls different at the same time, uneven rubbing generated during rubbing can be eliminated, and stable rubbing treatment can be performed continuously for a long time.

[Brief description of drawings]

FIG. 1 shows a rubbing processing apparatus according to an embodiment of the present invention.

FIG. 2 shows a rubbing apparatus (when roll diameters are different) according to an embodiment of the present invention.

FIG. 3 shows a conventional rubbing apparatus for processing a sheet-shaped substrate.

FIG. 4 shows a conventional long film rubbing apparatus.

FIG. 5 shows a conventional long film rubbing apparatus.

FIG. 6 shows a structure of a TN type liquid crystal display panel.

[Explanation of symbols]

 1: Film substrate transport device (feeding unit) 2: Film substrate transport device (feeding unit) 3; Rubbing roll 4; Substrate support roll 5; Film substrate TNC: TN type liquid crystal cell A, B: Polarizing plate PA, PB: Polarized light Axis RF1, RF2: Optical compensation film BL: Backlight R1, R2: Rubbing direction of optical compensation film

Claims (3)

[Claims] 1. A continuous rubbing method for a long film, wherein a plurality of rubbing rolls are successively used when continuously rubbing the surface of a long film having an alignment film formed on one side thereof with a rubbing roll. The continuous rubbing method is characterized in that the rotation speed of each is different from each other. 2. The continuous rubbing method according to claim 1, wherein at least one of the plurality of rubbing rolls has a different diameter from the other diameters. 3. A method for producing an optical compensation sheet, which comprises coating an alignment film material on a transparent support, rubbing it, and then forming a layer containing at least one discotic compound.
The method for producing an optical compensation sheet, wherein the rubbing treatment is the method according to claim 1 or 2.