JPH04127103A - Phase difference plate and elliptical polarizing plate - Google Patents

Abstract

PURPOSE:To obtain the phase difference plate which lessens the change in phase difference by a change in visual point and incident angle by making the calculated value determined from the refractive indices in the phase lag axis direction, the phase advance axis direction and the thickness direction of the single layered film or laminate of double refractive films and the thickness thereof in such a manner as to satisfy specific conditions. CONSTITUTION:The phase difference plate is constituted of single layered film of the double refractive film 1 or the laminate of the double refractive films 2, 4. The laminate has an adhesive layer 3. This phase difference plate is so formed that the calculated value determined by equation: {(nx+ny)/2-nz}.d attains <=+ or - 30nm where the refractive indices in the phase lag axis direction, the phase advance axis direction and the thickness direction of the double refractive films 2, 4 are respectively designated as nx, ny, nz and the thickness thereof as d. The change in phase difference by the change in visual point and incident angle with the phase difference plate is prevented or suppressed in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a retardation plate whose retardation changes little due to changes in viewpoint or angle of incidence, and an elliptically polarizing plate using the retardation plate.

BACKGROUND ART Conventionally, birefringent crystal plates and stretched polymer films have been known as retardation plates used for forming quarter-wave plates, elliptically polarizing plates, and the like.

However, the phase difference changes greatly with changes in the viewpoint or the angle of incidence, and the range that exhibits the necessary phase difference characteristics is very narrow, requiring strict control of the angle at which the retardation plate is set relative to the reference direction, and the usage environment There was also a major problem with restrictions on For example, in the case of an elliptically polarizing plate, this problem appears as a problem in which color changes occur due to changes in viewpoint or angle of incidence during color observation using crossed nicols.

An object of the present invention is to overcome the above-mentioned problems and to develop a retardation plate whose retardation does not easily change with changes in viewpoint or angle of incidence, and an elliptically polarizing plate which does not easily change color.

Means for Solving the Problems In the present invention, the refractive indices in the slow axis direction, fast axis direction, and thickness direction are respectively l'lX, nV, and fi2, and the thickness is d.
In this case, the formula: l (nx+ny)/2-nz
A retardation plate characterized by being made of a birefringent film with a calculated value of ±30 nm or less as determined by l ・d, and a laminate of birefringent films, the slow axis direction of the birefringent film being When the refractive index in the fast axis direction and the thickness direction are nX% nV and nZ, respectively, and the thickness is d, the formula: I (nx+ny) /2-nz}
- A retardation plate characterized in that the sum of the calculated values for each birefringent film determined by d is ±30 nm or less, and a laminate of the above-mentioned retardation plate and linear polarizing plate. The present invention provides an elliptically polarizing plate having the following characteristics.

Effect The above formula: l (nx+ny)/2-nzl ・
By setting the calculated value by d to ±30 nm or less, it is possible to prevent or suppress changes in the phase difference due to changes in the viewpoint with respect to the retardation plate or the angle of incident light, and the closer the calculated value is to zero, the smaller the phase difference. The change in is also small. As is clear from the above equation, achieving such a value is achieved by reducing the difference between the average refractive index in the in-plane direction and the refractive index in the thickness direction of the birefringent film or its laminate. This can be done by reducing the thickness.

Note that the calculation value can be achieved by the method of laminating birefringent films because the phase difference due to each birefringent film can be superimposed or adjusted and controlled by lamination.

EXAMPLE The retardation plate of the present invention consists of a single layer of birefringent film 1 as illustrated in FIG. 1, or a laminate of birefringent films 2.4 as illustrated in FIG. Note that 3 is an adhesive layer. The retardation plate or the birefringent film constituting it may have a protective layer made of resin or the like.

Such a retardation plate has a refractive index of nxs nV in the slow axis direction, fast axis direction, and thickness direction of the birefringent film, respectively.
When z is nZ and the thickness is d, the formula: ((n
x+ny)/2nzl·d is formed so that the calculated value is ±30 nm or less. A retardation plate made of a single layer of birefringent film is formed using a birefringent film that satisfies such calculated values. On the other hand, in a retardation plate made of a laminate of birefringent films, the sum of the calculated values for each birefringent film is ±30n.
It is formed by laminating birefringent films in a combination that satisfies the following conditions. In that case, the number of laminated birefringent films is arbitrary. In terms of suppressing reduction in transmittance due to absorption loss, reflection loss at the laminated interface, etc., it is more advantageous to have a smaller number of laminated layers, and a laminate of 2.degree. 3 layers is preferable. In addition, from the viewpoint of ease of production, it is recommended to use a laminate consisting of a combination of a birefringent film whose slow axis of birefringence is in the direction of the stretching axis and a birefringent film whose fast axis is in the direction of the stretching axis. preferable.

The birefringent film can be formed, for example, by uniaxially or biaxially stretching a polymer film. In the present invention, there are no particular limitations on the type of polymer, and those with excellent transparency are preferred. The refractive index in the thickness direction of a birefringent film can also be controlled, for example, by applying voltage during production or stretching of the polymer film.

Note that an adhesive or a pressure-sensitive adhesive is usually used for laminating the birefringent films. In that case, an adhesive such as, but not limited to, an acrylic adhesive or a pressure-sensitive adhesive (one with good transparency is preferably used.Also, from the viewpoint of preventing changes in the optical properties of the birefringent film, curing and drying In addition, when laminating different types of birefringent films, an adhesive or an adhesive having a refractive index between those of the films is preferably used in terms of transmittance. Adhesives are preferably used.

The retardation plate of the present invention can be used in various optical devices as an optical element such as a quarter-wave plate, or as an elliptically polarizing plate.

As illustrated in FIG. 3, the elliptically polarizing plate of the present invention includes a retardation plate 5 made of a single layer or a laminate of the above-described birefringent film, and a linear polarizing plate 6, which are connected via an adhesive layer 3 or the like. , are stacked so that their optical axes are parallel or have a predetermined intersecting angle.

Example 1 A 50-thick polycarbonate film produced by applying a voltage of 15 KV in the thickness direction during melting was axially stretched by 15% at 160°C to obtain nx: 1.592, nV + 1
．． A retardation plate made of a birefringent film of 581s nz:1.586 was obtained.

Example 2 A birefringent film (nx: 1
．． 5912, ny + 1.5813, nz = 1.5
807) and a birefringent film (nx: 1.5889, ny: 1.589, n
z: 1.5903) Two sheets were laminated via an acrylic adhesive to obtain a retardation plate.

Example 3 A birefringent film (nx: 1
．． 589, ny: 1.583, nz: 1.58
28) and a birefringent film (nx: 1.5906, ny: 1.5881,
n z : 1.5909) were laminated via an acrylic adhesive so that their advance axes coincided to obtain a retardation plate.

Example 4 A retardation plate was obtained according to Example 3, except that the layers were stacked so that the advance axes intersected at an angle of 10 degrees.

Comparative Example 1 A birefringent film made of the same uniaxially stretched polycarbonate film as in Example 2 was used as a retardation plate.

Comparative Example 2 A birefringent film (Ilx: i
, 5sss, ny = 1.583, nz: 1.5827
) Two sheets were laminated via an acrylic adhesive to obtain a retardation plate.

Evaluation Test The retardation plates obtained in Examples 1 to 4 and Comparative Examples 1 and 2 described above were prepared so that the retardation was around 55 on-. The phase difference when the light was incident perpendicularly: RO, and the phase difference when the light was incident parallel to the slow axis direction at an incident angle of 30 degrees: R30 were investigated.

The results are shown in the table. The table also shows the formula = ((nx+ny)
/2-nzf·d Calculated value: Q value (in the case of a laminate, the sum of each birefringent film) is also written.

From the table, it can be seen that in the retardation plate of the example, the change in phase difference due to the change in the incident angle is small.

Example 5 The retardation plate and linear polarizing plate obtained in Example 2 were stacked with the fast axis of the retardation plate and the absorption axis of the linear polarizing plate intersecting at an angle of 45 degrees to obtain an elliptically polarizing plate. .

On the retardation plate side of the elliptically polarizing plate, a separate M and linear polarizing plate is arranged in a crossed nicol configuration to capture the vertically incident light, the incident light in the slow axis direction of the retardation plate at an incident angle of 30 degrees, and the advancing light. When the color change in the incident light in the phase axis direction was investigated, it was purple and showed almost no color change in any of the cases of vertically incident light, incident light in the slow axis direction, and incident light in the fast axis direction.

Comparative Example 3 Using the retardation plate obtained in Comparative Example 2, an elliptically polarizing plate was obtained according to Example 5.

When the color change was investigated according to Example 5 using the elliptically polarizing plate described above, the purple color of vertically incident light changed to yellow with incident light in the slow axis direction, and changed to green with incident light in the fast axis direction. did.

Effects of the Invention In the retardation plate of the present invention, changes in retardation due to changes in viewpoint or angle of incidence are small. As a result, it is possible to easily obtain an optical element or optical device that exhibits the necessary retardation characteristics over a wide range, such as an elliptically polarizing plate that exhibits almost no color change due to changes in viewpoint or angle of incidence.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views illustrating other retardation plates, respectively,
FIG. 3 is a cross-sectional view illustrating an elliptically polarizing plate. 1.2, 4: Birefringent film 3: Adhesive layer 5; Retardation plate 6: Linear polarizing plate Patent applicant Nitto Denko Corporation

Claims (1)

[Claims] 1. When the refractive indices in the slow axis direction, fast axis direction, and thickness direction are respectively nx, ny, and nz, and the thickness is d, the formula: {(nx+yv)/ A retardation plate comprising a birefringent film having a calculated value of ±30 nm or less as determined by 2-nz}·d. 2. Consisting of a laminate of birefringent films, where the refractive indices in the slow axis direction, fast axis direction, and thickness direction of the birefringent film are respectively nx, ny, and nz, and the thickness is d. , the sum of the calculated values for each birefringent film obtained by the formula: {(nx+ny)/2-nz}・d is ±30n
A retardation plate characterized in that the particle size is less than or equal to m. 3. An elliptically polarizing plate comprising a laminate of the retardation plate according to claim 1 or 2 and a linearly polarizing plate.