JPS63189804A - Phase difference plate - Google Patents

Abstract

PURPOSE:To obtain a phase difference plate having uniform quality by maintaining the measured value of retardation by a polarizing microscope within a 475-625nm range and disposing a film or sheet under crossed nicols in such a manner that the optical main axis thereof is 45 deg., thereby decreasing the color difference DELTAE* when measured to <=20. CONSTITUTION:The phase difference plate is obtd. by uniaxially stretching a polycarbonate polymer to form a film or sheet. The retardation of the polarizing microscope is maintained in the 475-625nm range and the film or sheet is disposed under the crossed nicols in such a manner that the optical main axis thereof is 45 deg. to decrease the color difference DELTAE* when measured to <=20 at the time of forming the above-mentioned phase difference plate. A cross uniaxial stretching method by a tentering method is used as a method for uniaxial stretching and the phase difference having the uniform quality is obtd. by using the film having <=10% neck-in rate in uniaxial stretching.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a novel retardation plate.

[Prior art]

A retardation plate is a film or sheet-like material that has birefringence.The light that passes through the retardation plate has a different refractive index in two orthogonal directions, so there is a phase difference between the orthogonal rays after passing through the retardation plate. occurs.

As a retardation plate, there is a so-called 2λ plate which has a function of producing a phase difference of 2λ with respect to the wavelength λ of an incident light beam, which is currently commercially available and in practical use. This Xλ plate is obtained by uniaxially stretching a cellulose acetate film.

The 2λ plate is a circularly polarizing plate attached at a 45 degree angle to the optical principal axis of a linear polarizing plate, and has an anti-glare function that cuts reflected light, so it is used in various anti-glare materials including VDT filters. ing.

In addition to the cellulose resins mentioned above, vinyl chloride resins (Japanese Patent Publication No. 45-3
4477, JP-A-56-125702, etc.)
, polycarbonate resin (Japanese Patent Publication No. 41-12190, Japanese Patent Application Laid-open No. 56-130703, etc.), acrylonitrile resin (Japanese Patent Application Publication No. 56-130702, etc.)
, styrene resin (JP-A-56-125703)
, polyolefin resins (JP-A-60-24502, etc.) have been proposed, but all of them are so-called λ plates with a measured retardation value (hereinafter referred to as R value) of around 135 nm. There is no description at all about the method of manufacturing the λ plate. Note that the R value is expressed as the product of the thickness of the film or sheet and the birefringence Δn of the film, that is, R=ΔnXt.

[Problem that the invention seeks to solve]

Although the application of a λ plate that produces a phase difference of λ to the wavelength λ of incident light in various optical applications is being considered, it has a satisfactory quality, that is, an R value of 475 to 625 nm, and is not optically suitable. At present, there is no retardation plate that is free from color unevenness.

[Means for solving problems]

The present invention was completed as a result of repeated research to manufacture a novel retardation plate, that is, a λ plate, as described above.

The present invention is a film or sheet formed by uniaxially stretching a polycarbonate polymer, which has a retardation value measured by a polarizing microscope of 475 to 625 nm.
, and the color difference ΔE9 is 20 or less when measured by arranging the film or sheet under crossed nicols with its optical principal axis at 45 degrees. be.

The polycarbonate polymer used in the present invention is 4.
Transparent grades are required for polycarbonates or copolymerized polycarbonates made from 4'-dihydroxydiarylalkane. In order to use the above polycarbonate polymer as a retardation plate, the polycarbonate polymer is formed into a film or sheet by a known film forming method, such as a solvent casting method, a calendar method, or an extrusion method, and then stretched appropriately in a uniaxial direction. This is achieved by As a method for stretching in the uniaxial direction, known uniaxial stretching methods such as a transverse uniaxial stretching method using a tenter method, an inter-roll compression stretching method, and a longitudinal-axial stretching method using rolls having different circumferential speeds can be employed.

In the present invention, the most effective stretching method for obtaining a retardation plate with optically small color unevenness and small fluctuation in retardation is a transverse uniaxial stretching method using a tenter that does not substantially cause neck-in.

However, using the inter-roll compression stretching method and the vertical
Even in the axial stretching method, the neck-in rate (100X (
The object of the present invention can be achieved by suppressing A-B)/A) to 10% or less, preferably 5% or less.

Optical color unevenness can be quantitatively expressed as ΔE'' defined below. That is, L* when placed under crossed Nicols so that its optical principal axis is 45 degrees.
, a*, b'J values are JIS=Z・8729 (L
It is measured using a spectrophotometric needle or a spectrometer according to the "a"b" color system and the L* u* v "method of displaying object color using the color system).

For the above sample of n different locations, 1, am, be
(ΔE”)IIJ is calculated from the following formula.

(ΔE′)i,j = (((ΔL”)i,j)”+((Δa*)>
, j) Z+((Δb*)1.j)t) I/!
However, ΔL”)i, j= (L”)i−(L”)j(
Δa") i+j= (a")i-(a'")j(Δb"
) i, j = (b" ) i - (b") ji = 1 ~ n j = 1 ~ n i qb j The maximum value among these (ΔE") i, j is ΔE1. Number of measurements n Although it is preferable to have a large number of
A sample at point 0 is taken and measured, and calculated using the above formula.

When ΔE1 is 20 or more, color unevenness and rainbow patterns are observed with the naked eye under crossed Nicol conditions, and the film cannot be used as an optical film.

The λ plate of the present invention has an average wavelength of natural light (S = 550 nm)
The retardation value measured using a polarizing microscope is adjusted to 475 to 625 nm, preferably 525 to 575 nm.

〔Effect of the invention〕

The retardation plate obtained in this way is 2λ
This is a retardation plate that produces a retardation of λ, unlike A4 film that produces a retardation of λ, and can be used for new applications such as various optical applications such as optical filters, and applications for liquid crystal displays.

〔Example〕

The present invention will be explained below with reference to Examples. Note that the R value in the Examples was measured using a Senarmont compensator attached to a polarizing microscope, and a halogen lamp was used as the light source. ΔE'' was measured and calculated using a spectrophotometer according to the method described in the above specification.

Example 1 A transparent polycarbonate film (extrusion product) with a thickness of 100 μm and a width of 200 mm was preheated at a temperature of 170°C, and then horizontally uniaxially stretched using a tenter method at a temperature of 160°C to obtain a film with a thickness of about 50 μm, A stretched film with a width of 400 mm was obtained. The stretched film has an R value of about 565.
nm, 8E9 has a uniform quality of 8.3 and can be used as a λ plate.

Example 2 A stretched film having a thickness of about 30 μm and a width of 600 mm was obtained in the same manner as in Example 1. The stretched film has an R value of about 590.
nm, ΔE1 is 5.0, it has homogeneous quality and can be used as a λ plate.

Example 3 A transparent polycarbonate film (extruded film product) with a thickness of 100 μm and a width of 50'Omm was passed between a pair of rolls at 150°C and compressed and stretched in the vertical axis, resulting in a thickness of approximately 55 μm and a width. A stretched film of 480 mm (neck-in rate: 4%) was obtained. The film has an R value of about 540 nm, Δ
E1 has a uniform quality of 12.7 and can be used as a λ plate.

Example 4 A transparent polycarbonate film (extrusion product) with a thickness of 100 μm and a width of 500 mm was preheated at a temperature of 160° C., and then stretched longitudinally and axially between rolls having different circumferential speeds to a thickness of about 60 μm. A stretched film with a width of 465 mm (neck-in rate of 7%) was obtained. The film is R
The value is about 500 nm, ΔE° is 1, and it has homogeneous quality and can be used as a λ plate.

[Comparative example]

Comparative Example 1 In Example 4, stretching was carried out by increasing the distance between the rolls of the longitudinal-axial stretching device to obtain a stretched film with a thickness of about 60 μm and a width of 400 mm (neck-in rate 20%). The film has an R value of approximately 500 nm and a ΔE0 of 30, and color unevenness and rainbow patterns are observed under crossed nicols, making it unusable as a λ plate.

Comparative Example 2 Preheating was performed at 180°C in Example 4, and the thickness was about 5
A stretched film with a diameter of 0 μm and a width of 300 mm (neck-in rate of 40%) was obtained. The film has an R (direction of about 80 nm, ΔE
" was 70, and color unevenness and rainbow patterns were observed under crossed nicols, making it unusable as a λ plate.

Claims (3)

[Claims] (1) A film or sheet formed by uniaxially stretching a polycarbonate polymer, with a retardation value measured by a polarizing microscope of 475 to 625 nm.
and has a color difference ΔE^■ of 20 or less when the film or sheet is placed under crossed Nicols so that its optical principal axis is 45 degrees. . (2) The retardation plate according to claim 1, wherein a transverse uniaxial stretching method using a tenter method is used as the method for stretching in the uniaxial direction. (3) As a film or sheet formed by stretching in a uniaxial direction, the neck-in rate in uniaxial stretching is 1.
The retardation plate according to claim 1, characterized in that a film having a content of 0% or less is used.