JPH07287120A - Optical compensating sheet - Google Patents

Abstract

PURPOSE:To optimize optical characteristics of the base film used and to increase the visual angle range of a TN-type LCD by forming a layer containing a discotic liquid crystal on an intraplane oriented transparent film. CONSTITUTION:A layer containing a discotic liquid crystal is formed on an intraplane oriented transparent film. The intraplane orientation is such a state that the triaxial refractive indexes of the base film satisfy nx=ny>nz, wherein nx, ny are refractive indices in the directions of optical axes perpendicular to each other in the film plane and nz is the refractive index in the thickness direction of the film. Further, it is preferable that the intraplane orientation degree calculated as DELTAn.d of the transparent film ranges 20 to 300nm, wherein d is the thickness of the base film and DELTAn=(nx+ny)/2-nz. Thus, characteristics of angle of field can be largely improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensation sheet, and more particularly to an optical compensation sheet useful for improving the viewing angle characteristics of display contrast and display color.

[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) which 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 a birefringence mode has a twisted angle of 90 ° or more in the alignment of liquid crystal molecules and has steep electro-optical characteristics. Therefore, a simple matrix is provided without active elements (thin film transistors or diodes). A large-capacity display can be obtained by time-divisional driving with the electrode structure. But,
An LCD using this birefringence mode has a drawback that the response speed is slow (several hundreds of milliseconds) and gradation display is difficult. Therefore, a liquid crystal display element (TFT-LCD, MIM-LCD, etc.) using an active element is used. The display performance of) is exceeded.

For the TFT-LCD and MIM-LCD, a display system (TN type liquid crystal display element) of optical rotation mode in which the alignment state of liquid crystal molecules is twisted by 90 ° is used. This display method is the most effective method for high image quality compared with other LCDs because it has a fast response speed (tens of milliseconds), white display is easily obtained, and high display contrast is exhibited. is there. However, since the twisted nematic liquid crystal is used, there is a problem in view angle characteristics that the display color and the display contrast are changed depending on the viewing direction due to the principle of the display system, and the display performance of the CRT cannot be exceeded.

Japanese Unexamined Patent Publication No. 4-229828 and Japanese Unexamined Patent Publication No. 4-2
As disclosed in Japanese Patent No. 58923, a method has been proposed in which a viewing angle is increased by disposing a retardation film between a pair of polarizing plates and a TN type liquid crystal cell. The retardation film proposed in the above-mentioned patent publication has a retardation 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, the current viewing angle cannot cope with the situation.

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 a retardation film. It is a two-layer liquid crystal system, which is expensive and very heavy. Further, in JP-A-4-113301 and JP-A-5-80323,
For liquid crystal cells, a method of using a retardation film whose optical axis is inclined has been proposed, but since a uniaxial polycarbonate is used by obliquely slicing, a large area retardation film is provided at low cost. There was a problem that it was difficult to obtain. Further, JP-A-5-157913 and EP057630.
4A1 proposes a method of using a retardation film having an optical axis inclined by specially stretching a polycarbonate, but it is still difficult to obtain a large area retardation film at low cost. . Furthermore, Japanese Patent Application No. 5
No. 5823 describes a method of using a retardation film in which an optical axis is inclined by using a photoisomerizable substance. 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, in Japanese Patent Laid-Open No. 215921/1993, there is proposed a plan for optically compensating an LCD with a birefringent plate in which a rod-shaped compound exhibiting liquid crystal properties at the time of curing is sandwiched between a pair of aligned substrates. However, 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 is TN for the optical reason described later.
It is impossible to improve the omnidirectional viewing angle of the type LCD. 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. However, since it is impossible to orient molecules obliquely with this method, TN-type LCDs are also used.
It is impossible to improve the omnidirectional viewing angle.

Therefore, the inventor of the present invention has filed Japanese Patent Application No. 5-23653.
No. 9 invented an optical compensation sheet in which a discotic liquid crystal is aligned by an alignment film. The optical properties of the base film used to make this sheet were initially isotropic, but if a base film with some anisotropy is used, it will be isotropic depending on the degree of anisotropy. It has been found that the viewing angle of the TN type LCD with the optical compensation sheet is wider or narrower than when the base film is used.

[0009]

Therefore, an object of the present invention is to significantly improve the viewing angle of a TN type LCD by optimizing the optical characteristics of a base film used in an optical compensation sheet having a layer containing discotic liquid crystal. It is to provide an optical compensation sheet that can be expanded.

[0010]

Means for Solving the Problems The above-mentioned problems are (1) an optically compensatory sheet comprising a layer containing a discotic liquid crystal formed on a plane-oriented transparent film, and (2) a plane-oriented transparent film. After rubbing the top, or after forming the alignment film on the plane-oriented transparent film, or after forming the alignment film on the plane-oriented transparent film and further rubbing treatment, a layer containing a discotic liquid crystal on it. The optical compensatory sheet characterized by being formed, (3) the degree of plane orientation of the plane-oriented transparent film is 20 to 20 in terms of Δn · d.
It is achieved by the optical compensation sheet according to the above (1) or (2), which has a thickness of 300 nm.

The usefulness of the present invention will be described below. First,
The optical utility will be described with reference to the drawings using a TN LCD as an example. 1 and 2 show polarization states of light propagating in a liquid crystal cell when a sufficient voltage equal to or higher than a threshold voltage is applied to the liquid crystal cell. Since the transmittance characteristic of light particularly when a voltage is applied greatly contributes to the viewing angle characteristic of the contrast, a case where a voltage is applied will be described as an example. FIG. 1 is a diagram showing a polarization state of light when light is vertically incident on a liquid crystal cell. When the natural light L0 is vertically incident on the polarizing plate A having the polarization axis PA, the light transmitted through the polarizing plate PA becomes the linearly polarized light L1.

When a sufficient voltage is applied to the TN type liquid crystal cell, the alignment state of the liquid crystal molecules is schematically shown as a model with one liquid crystal molecule, which is represented by LC in the schematic diagram. Modeling the liquid crystal molecules in a liquid crystal cell, when the LC major axis in the schematic diagram is parallel to the light path, a difference in refractive index occurs on the incident surface (in the plane perpendicular to the light path). Since it does not exist, linearly polarized light propagates even when it passes through the liquid crystal cell. Polarization axis P of polarizing plate B
When B is set to be perpendicular to the polarization axis PA of the polarizing plate A, the linearly polarized light L2 that has passed through the liquid crystal cell cannot pass through the polarizing plate B and is in a dark state.

FIG. 2 is a diagram showing a polarization state of light when the light obliquely enters the liquid crystal cell. Natural light of incident light L
When 0 is obliquely incident, the polarized light L1 transmitted through the polarizing plate A becomes almost linearly polarized light. (In the actual case, it becomes elliptically polarized due to the characteristics of the polarizing plate). In this case, the refractive index anisotropy of the liquid crystal causes a difference in the refractive index on the incident surface of the liquid crystal cell, and the light L2 transmitted through the liquid crystal cell is elliptically polarized light and is not completely blocked by the polarizing plate B. As described above, in the case of oblique incidence, blocking of light in a dark state becomes insufficient, which causes a large reduction in contrast, which is not preferable.

An object of the present invention is to provide an optical compensator capable of preventing a reduction in contrast due to such oblique incidence and improving viewing angle characteristics. FIG. 3 shows an example of using the optical compensation sheet manufactured by the present invention. An optical anisotropic element RF1 having an optical axis inclined from the normal line direction of the liquid crystal cell is arranged between the polarizing plate A and the liquid crystal cell TNC.
The optically anisotropic element RF1 is a birefringent body in which the phase difference increases as the angle of light incident on the optical axis increases.
An optical anisotropic element RF2 having an optical axis inclined from the normal line direction of the liquid crystal cell is arranged between the polarizing plate B and the liquid crystal cell TNC. The optically anisotropic element RF2 is a birefringent body having the same optical characteristics as RF1. When the natural light L0 is obliquely incident on the liquid crystal display device having such a structure as in the case of FIG. 2, the optical modulation described below occurs. First, it is converted into linearly polarized light L1 by the polarizing plate A, and is modulated into elliptically polarized light L3 by the phase delay action when passing through the optically anisotropic element RF1. Next, when passing through the liquid crystal cell TNC, the elliptically polarized light L of the opposite phase
When it is modulated to 4 and further transmitted through the optical anisotropic element RF2, it is returned to the original linearly polarized light L5 by the phase delay action. With such an effect, the natural light L0 can obtain the same transmittance even under various oblique incidences, and it is possible to obtain a liquid crystal display element capable of high-quality display without viewing angle dependence.

It is presumed as follows that the viewing angle of the liquid crystal display device can be greatly improved by the optical compensation sheet manufactured according to the present invention. Most TN-LCDs adopt a normally white mode.
In this mode, the transmittance of light from the black display portion is significantly increased as the viewing angle is increased, resulting in a sharp drop in contrast. The black display is the state when a voltage is applied. At this time, the liquid crystal molecules in the TN liquid crystal cell are aligned as in the model of FIG. When the arrangement of the liquid crystal molecules is approximated by a plurality of refractive index ellipsoids having substantially the same triaxial refractive index, it becomes as shown in FIG. 4B, and the optical axis of the TN liquid crystal cell is slightly tilted from the direction normal to the cell surface. It can be regarded as a laminated body of four positive uniaxial optical anisotropic bodies and two positive uniaxial optical anisotropic bodies whose optical axes are in the same direction as the normal direction.

If the liquid crystal cell can be regarded as a laminate of four positive uniaxial optical anisotropic bodies, in order to compensate for it, negative uniaxial optics composed of the same combination of optical axis tilt angles as the laminate is used. It is preferable to use four anisotropic plates. In the case of the present invention,
The discotic liquid crystal layer acts as a negative uniaxial optical anisotropic body with the optic axis slightly tilted from the normal direction to the cell surface, and the optic axis is oriented in the same direction as the normal direction to the cell surface. That is, the plane-oriented base film acts as the uniaxial optically anisotropic body. For these reasons, it is presumed that the negative uniaxial optically anisotropic laminate of the present invention has significantly improved the viewing angle characteristics.

In a particular discotic liquid crystal, when the discotic liquid crystal phase is solidified in the aligned state, the structure is kept stable below the discotic liquid crystal phase / solid phase transition temperature. It is also thermally stable.

The discotic liquid crystals in the present invention are those listed below, but the molecules themselves have negative uniaxiality and the optical axis is oriented obliquely to the substrate surface by the oblique orientation film. If it is, it is not particularly limited to the following substances.

[0019]

[Chemical 1]

[0020]

[Chemical 2]

[0021]

[Chemical 3]

Negative uniaxiality of the discotic liquid crystal layer in the present invention means that n ₁ <n when the refractive indices of the liquid crystal layer in the triaxial directions are n ₁ , n ₂ , and n _{3 in the} order of increasing values. ₂ = n ₃
Have a relationship of. Therefore, it has a characteristic that the refractive index in the optical axis direction is the smallest. However,
The values of n ₂ and n ₃ do not have to be exactly equal, they need to be approximately equal. Specifically, if | n ₂ −n ₃ | / | n ₂ −n ₁ | ≦ 0.2, there is no practical problem. Further, as a condition for greatly improving the viewing angle characteristics of the TFT or TN type liquid crystal cell, it is preferable that the optical axis of the liquid crystal layer has an inclination β of 5 ° to 50 ° from the normal direction of the sheet surface, It is more preferably 10 degrees to 40 degrees. Further, when the thickness of the liquid crystal layer is a, it is preferable that the condition of 50 ≦ Δn ′ · a ≦ 300 (nm) is satisfied. However, Δn ′ = (n
₂ + n ₃₎ is / 2-n _1.

There are various methods for the alignment treatment of the discotic liquid crystal that can be used in the present invention. There is a combination of discotic liquid crystal and substrate in which effective alignment can be obtained simply by rubbing the surface of the substrate and coating it on it, but the most versatile method is to use an alignment film. As the alignment film, an inorganic oblique vapor deposition film or an alignment film obtained by rubbing a specific organic polymer film corresponds to this.
Also, a thin film such as an LB film made of an azobenzene derivative, which undergoes isomerization by light and in which molecules are oriented and uniformly arranged, is also applicable.

A polyimide film is a typical organic alignment film. This is obtained by applying a polyamic acid (for example, SE-7210 manufactured by Nissan Kagaku Co., Ltd.) to the substrate surface.
The discotic liquid crystal can be aligned by rubbing after firing at 0 ° C to 300 ° C. Also,
Alkyl chain modified poval (eg M manufactured by Kuraray Co., Ltd.
P203, R1130, etc.) does not need to be baked, and the orientation ability can be imparted only by rubbing. In addition, most of the organic polymer films forming a hydrophobic surface such as polyvinyl butyral and polymethylmethacrylate can impart the discotic liquid crystal alignment ability by rubbing the surface. A typical example of the inorganic oblique vapor deposition film is a SiO oblique vapor deposition film. In this method, SiO vaporized particles are obliquely applied to the surface of the base film in a vacuum chamber to form an obliquely vapor-deposited film having a thickness of about 20 to 200 nm to form an alignment film. When the discotic liquid crystal is oriented by this vapor deposition film, the optical axis of the liquid crystal layer is directed to a specific direction on a plane perpendicular to the surface of the base film including the trajectory of the SiO vapor deposition particles.

The alignment film has a function of determining the alignment direction of the discotic liquid crystal molecules coated thereon.
However, since the orientation of the discotic liquid crystal depends on the orientation film, it is necessary to optimize the combination. next,
The discotic liquid crystal molecules that have once been oriented are oriented at an angle θ with respect to the substrate surface, but in the one-component system, the angle of oblique orientation does not change much depending on the type of alignment film, and may take a value specific to the discotic liquid crystal molecules. Many. When two or more discotic liquid crystal molecules are mixed, the tilt angle can be adjusted within a certain range by the mixing ratio. Therefore, for controlling the tilt angle of the oblique alignment, it is effective to select a discotic liquid crystal type and further mix two or more types of discotic liquid crystal molecules.

The base film material used in the optical compensation sheet of the present invention is required to have a good light transmittance and, in addition, be plane-oriented. The plane orientation referred to in the present invention is a state in which the relationship of the triaxial refractive index of the base film satisfies nx = ny> nz. However, nx and ny are refractive indices in the optical axis directions orthogonal to each other in the film plane, and nz is a refractive index in the thickness direction of the film. Further, the values of nx and ny do not have to be exactly the same, and it is sufficient if they are almost equal. Specifically, if | nx-ny | / | nx-nz | ≦ 0.2, there is no practical problem. Further, when the thickness of the base film is d, it is preferable that the condition of 20 ≦ Δn · d ≦ 300 (nm) is satisfied. However, Δn = (nx
+ Ny) / 2-nz. Specifically, a film 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 Photo Film Co., Ltd.) is preferable. However, polycarbonate, polyarylate,
Even with materials having a large intrinsic birefringence value such as polysulfone and polyethersulfone, it is possible to form a plane-oriented film with Δn · d = 20 to 300 nm by controlling the molecular orientation during film formation. Can also be suitably used.

Magnetic field orientation and electric field orientation are available as methods other than the above in which the discotic liquid crystal coated on the substrate is oriented obliquely. 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 it is necessary to adjust the zone itself to a temperature at which a discotic nematic phase is formed. is there.

[0028]

EXAMPLES The present invention will be described in detail below based on examples. Example 1 80 μm thick film of triacetyl cellulose (Fujitack manufactured by Fuji Photo Film Co., Ltd., size 250 mm × 25)
(0 mm) as a substrate, and an alkyl chain-modified Poval (MP203 manufactured by Kuraray Co., Ltd.) as an alignment film is applied thereon to a thickness of 1 μm. The Poval film is rubbed by a rubbing machine to give orientation ability. Then, a discotic liquid crystal material prepared by mixing the above-mentioned discotic liquid crystal TE-8 and TE-8 at a blending ratio of 4: 1 was dissolved in a methyl ethyl ketone liquid to make 10 wt% and applied at 3000 rpm by a spin coater. Thus, a film-like material having a 1 μm thick discotic liquid crystal non-alignment layer was prepared. This film-like material was placed in a constant temperature bath set at 145 ° C. for 5 minutes, then brought into contact with a metal surface set at 10-20 ° C. and rapidly cooled to orient the discotic liquid crystal layer to obtain an optical compensation sheet sample. Got

Example 2 A polycarbonate film of 100 μm thickness (Iupilon manufactured by Mitsubishi Gas Chemical Co., Inc.) was placed at 165 ° C., and the length of the polycarbonate film was 4 respectively.
% Was drawn to obtain a substrate. Alkyl-modified Poval (MP203 manufactured by Kuraray Co., Ltd.) as an alignment film on this substrate
Is applied to a thickness of 1 μm. The Poval film is rubbed by a rubbing machine to give orientation ability. Then, a discotic liquid crystal material prepared by mixing the above-mentioned discotic liquid crystal TE-8 and TE-8 at a blending ratio of 4: 1 was dissolved in a methyl ethyl ketone solution to make 10 wt% and a solution was applied at 3000 rpm by a spin coater. Thus, a film-like material having a 1 μm thick discotic liquid crystal non-alignment layer was prepared. This film-like material was placed in a constant temperature bath set at 145 ° C. for 5 minutes, then brought into contact with a metal surface set at 10-20 ° C. and rapidly cooled to orient the discotic liquid crystal layer, thereby obtaining an optical compensation sheet sample. Got

Comparative Example 1 A glass plate having a thickness of 1 mm was used as a substrate, and an alkyl-modified poval (MP203 manufactured by Kuraray Co., Ltd.) as an alignment film was applied thereon to a thickness of 1 μm. The Poval film is rubbed by a rubbing machine to give orientation ability. On top of that, the above-mentioned discotic liquid crystals TE-8 and TE-8:
A discotic liquid crystal material mixed in a blending ratio of 1 was dissolved in a methyl ethyl ketone solution to make 10 wt% and was applied at 3000 rpm by a spin coater, and 1
A plate-shaped product having a μ-thickness discotic liquid crystal non-alignment layer was prepared. This plate-like material was placed in a constant temperature bath set at 145 ° C. for 5 minutes, then brought into contact with a metal surface set at 10-20 ° C. and rapidly cooled to orient the discotic liquid crystal layer to obtain an optical compensation plate sample. Got

COMPARATIVE EXAMPLE 2 A 100 μm thick polycarbonate film (Iupilon manufactured by Mitsubishi Gas Chemical Co., Inc.) was used at 165 ° C. for each length and width.
3% stretching was performed to obtain a substrate. An alkyl-modified Poval (MP20 manufactured by Kuraray Co., Ltd.) was used as an alignment film on this substrate.
3) is applied to a thickness of 1 μm. The Poval film is rubbed by a rubbing machine to give orientation ability. in addition,
The above-mentioned discotic liquid crystal TE-8 and TE-8
Liquid crystal material mixed with 4: 1 blend ratio was dissolved in methyl ethyl ketone solution to 10 wt% and applied at 3000 rpm with a spin coater to form a film with a 1μ thick discotic liquid crystal non-alignment layer. I created a thing. This film-like material was placed in a constant temperature bath set at 145 ° C. for 5 minutes, then brought into contact with a metal surface set at 10-20 ° C. and rapidly cooled to orient the discotic liquid crystal layer to obtain an optical compensation sheet sample. Got

The Δ values of the substrates used in the examples and comparative examples
Shimadzu ellipsometer (AEP-10)
The angle dependence of retardation was determined by setting 0) in the transmission mode, and the optimum triaxial direction refractive index was calculated from the obtained angle dependence.

The product of the difference in refractive index between the extraordinary ray and the ordinary ray of the liquid crystal and the gap size of the liquid crystal cell is 480 nm, and the twist angle is 90.
The optical compensation sheets obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were mounted on a TN type liquid crystal cell at 0 ° as shown in FIG. 5, and the transmittance (T) at a 40 Hz rectangular wave of 0 V to 5 V was measured with respect to the liquid crystal cell. The angle dependence of) was measured by LCD-5000 manufactured by Otsuka Electronics. The angle from the direction normal to the surface of the liquid crystal cell to the position where the contrast ratio (T _1V / T _5V ) shows 10 was defined as the viewing angle, and the viewing angle in the vertical and horizontal directions was obtained. Here, the measurement of only the TN type liquid crystal cell without any optical compensation sheet was set as Comparative Example 3. The results are shown in Table 1. Incidentally, FIG.
In, the arrow indicates the rubbing direction on the optical compensation sheet,
Also, the rubbing direction in the liquid crystal cell is shown. Figure 5
In the optical compensation sheet, the discotic liquid crystal layer is 2
Both are on the liquid crystal cell side.

[0034]

[Table 1]

[0035]

As is clear from Table 1, the optical compensation sheet of the present invention can greatly widen the viewing angle of a TN type liquid crystal cell. On the other hand, when the substrate is a completely isotropic body as in Comparative Example 1, the viewing angle improving effect is recognized as compared with Comparative Example 3 in which nothing is mounted, but the viewing angle improving in the upper part is 3
It does not reach 0 °, which is insufficient. In addition, when the surface orientation of the base film exceeds the range of the present invention as in Comparative Example 2, the viewing angle improving effect is also reduced. Therefore, by using the optical compensation sheet of the present invention, the viewing angle of the TN type liquid crystal cell can be extremely widened.

[Brief description of drawings]

FIG. 1 is a diagram showing a polarization state of light when light is vertically incident on a liquid crystal cell.

FIG. 2 is a diagram showing a polarization state of light when light obliquely enters a liquid crystal cell.

FIG. 3 is a diagram showing an example of use of an optical compensation sheet.

FIG. 4 is a liquid crystal molecule alignment model diagram when a voltage is applied to a TN liquid crystal cell, and a diagram in which optical characteristics thereof are approximated.

FIG. 5 is a diagram showing a relationship among a polarization axis of a polarizing plate, a rubbing direction of a liquid crystal cell, and a rubbing direction of an optical compensation sheet alignment film when measuring viewing angle characteristics in Examples and Comparative Examples.

[Explanation of symbols]

TNC: TN type liquid crystal cell A, B: polarizing plate PA, PB: polarization axis L0: natural light L1, L5: linearly polarized light L2: modulated light after passing through the liquid crystal cell L3, L4: elliptically polarized light LC: TN type liquid crystal cell State of liquid crystal molecules when a sufficient voltage is applied to the electrodes RF1, RF2: Optical compensation sheet BL: Backlight R1, R2: Rubbing direction of the optical compensation sheet

Claims (3)

[Claims] 1. An optical compensatory sheet comprising a plane-oriented transparent film and a layer containing discotic liquid crystal formed on the transparent film. 2. After rubbing the surface-oriented transparent film, or after forming the orientation film on the surface-oriented transparent film, or after forming the orientation film on the surface-oriented transparent film and further rubbing the same. An optical compensation sheet having a layer containing discotic liquid crystal formed thereon. 3. The plane orientation degree of the plane orientation transparent film is Δ
The optical compensation sheet according to claim 1 or 2, wherein the value of n · d is 20 to 300 nm.