JPH05203809A - Phase difference plate - Google Patents

Abstract

PURPOSE:To improve optical characteristics, such as visual field angle, transmit tance and retardation value, by forming a protective layer consisting of a metal oxide on both surfaces or one surface of a uniaxially stretched film or sheet consisting of a polyvinyl alcohol(PVA) system. CONSTITUTION:The protective layer consisting of the metal oxide is formed on both surfaces or one surface of the uniaxially stretched film or sheet consisting of the PVA system. The metal oxide in such a case is preferably the metal oxide having excellent optical transparency, heat resistance and thermal stability and includes, for example, metal compds., such as silicon oxide, indium oxide, tin oxide, titanium oxide, aluminum oxide, zirconium oxide, magnesium fluoride and zinc sulfide. The metal oxide is used as a raw material for vapor deposition and any of a vacuum vapor deposition, sputtering method or ion plating method is used at the time of forming the protective layer. Then, the optical characteristics, such as dependency in visual angles, transmittance, retardation value and change in the size of the phase difference plate, are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation plate having excellent optical characteristics such as viewing angle, transmittance and retardation value.

[0002]

2. Description of the Related Art A retardation film is a film or sheet having birefringence. The light passing through the phase difference plate has different refractive indexes in two directions orthogonal to each other, so that a phase difference occurs between the light rays that are orthogonal to each other after passing. A so-called quarter-wave plate having a function of producing a quarter-wave retardation with respect to a wavelength λ of an incident light beam is commercially available as a retardation plate and is put to practical use. It is used as a beam splitter for a laser beam as an element for mutually exchanging linearly polarized light and circularly polarized light, or is used in combination with a linear polarizer to form a circularly polarizing plate.

In addition, STN type liquid crystal display (STN
-LCD) elliptically polarizing plates and retardation plates are used to prevent color shift. A film or sheet made of PVA or a derivative thereof has been studied and used as a retardation plate, but because of its poor moisture resistance, the properties (retardation value (R value),
There is a problem that the PVA-based film or sheet cannot be used alone, because the weight or size of the film or sheet varies greatly.

Therefore, a cellulose-based film such as cellulose triacetate or cellulose diacetate, a polycarbonate-based film, or the like is formed on one or both sides of a PVA-based film or sheet.
A retardation plate formed by using a polymer film such as a polymethylmethacrylate film, a polystyrene film, a polyester film such as polyethylene terephthalate or a polysulfone film as a protective layer is generally used.

[0005]

However, in the retardation plate having such a polymer film as a protective layer, it is often the case that the physical properties required for high optical properties, which are rapidly advancing year by year, cannot be met. . In other words, since its thickness requires a considerable thickness from the viewpoint of workability and physical properties, the viewing angle becomes narrow when it is used as a liquid crystal display panel, and the display cannot be clearly confirmed when viewing the display panel from an angle. However, it is not sufficiently satisfactory when used in a considerably harsh atmosphere from the viewpoint of moisture resistance, and development of a retardation plate having higher optical characteristics is strongly desired.

[0006]

However, the inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, formed a protective layer of a metal oxide on both sides or one side of a PVA-based uniaxially stretched film or sheet. The inventors have found that the retardation plate formed as described above meets such an object, and completed the present invention. In the present invention, by using the metal oxide as the protective layer as described above, it becomes possible to make the protective film thinner, and the optical characteristics of the retardation plate, in particular, the widening of the viewing angle and the high transmittance are improved. Despite the thinning, it was found that such a protective layer also exhibits an excellent effect on moisture resistance, and dimensional changes of the retardation plate and fluctuations of the retardation value, etc. are further reduced compared to conventional ones. did. Hereinafter, the present invention will be described in detail.

In the present invention, a PVA type uniaxially stretched film or sheet is used. Examples of the PVA-based material constituting the film or sheet include PVA, PVA obtained by reacting PVA with aldehydes in the presence of an acid, for example, polyvinyl butyral resin, polyvinyl formal resin, and other so-called polyvinyl acetal resin and other copolymerized PVA. Derivatives are included, but are not limited to. Of these, PVA having a high degree of saponification and a high degree of polymerization is preferable because it has good heat resistance. That is, the saponification degree is preferably 95% or more, and further 9
9% or more, particularly 99.5% or more, and a degree of polymerization of 10
It is preferably 00 or more, and more preferably 1000 to 3000.

The PVA-based uniaxially stretched film or sheet is a raw film or sheet prepared by forming a PVA-based resin by a usual method such as a casting method, an extrusion method or a calendering method, and the amount is about 1.1 to 4 times. Uniaxially stretched, 150-25
At 0 ° C. for about 10 to 30 seconds, preferably 200 to 230
30 ~ thickness obtained by heat treatment for 10 ~ 25 seconds at
It is about 60 μm, preferably about 40 to 50 μm, and has a physical retardation value of 30 to 800 n.
It is a base material having a moisture resistance of about m.

In order to obtain a retardation plate having a constant optical principal axis and a small number of optical color spots, the original film or sheet should have good thickness accuracy and be as optically uniform as possible. preferable. It is not preferable that a die line or the like is generated during film formation on the film or sheet. In order to obtain a retardation plate having an optically small color spot in the present invention, a neck-in rate (100 × (A−B) / defined by a film width A before stretching and a film width B after stretching.
It is preferable to suppress A) to 20% or less.

As the uniaxial stretching method, for example, the film is preheated by passing the film through a large number of rolls, and then stretched to a predetermined ratio by two pairs of stretching rolls, and a plurality of rolls are stretched. A method in which preheating and stepwise stretching are performed concurrently while passing through the film, and a method in which a predetermined draw ratio is obtained, a method such as a lateral uniaxial stretching method in which the film is stretched in the width direction by a tenter method can be adopted.

Stretching is appropriately performed depending on the intended use of the retardation plate. That is, the retardation value means the main stretching direction (MD direction) and the direction perpendicular thereto (TD direction).
Is defined as the product of the refractive index difference (II _MD- II _TD ) and the thickness (d) of the retardation film or sheet at, and the phase difference of the transmitted light when the linearly polarized light in the orthogonal relationship is incident in the same phase When the stretching treatment is performed so that the retardation value (R value) means a value of, for example, 1/4 of the wavelength (λ) of the used light beam, a 1/4 wavelength plate is obtained, When the stretching treatment is performed so that the value becomes, the half-wave plate can be obtained.

When the light used is visible light, the retardation value as a quarter wave plate is in the range of 95 to 170 nm. Therefore, by combining the ¼ wavelength plate and the linear polarizer in this range, accurate circularly polarized light in a certain visible light can be obtained. Various additives such as an ultraviolet absorber and a stabilizer may be added to the PVA type retarder according to the present invention. Further, the molecular blending is made permanent by the heat treatment performed after the stretching.

In the present invention, a protective layer of a metal oxide is formed on both sides or one side of the PVA type uniaxially stretched film or sheet produced as described above. The metal oxide in the present invention is preferably one having excellent optical transparency, heat resistance or thermal stability, and examples thereof include silicon oxide, indium oxide, tin oxide, titanium oxide, aluminum oxide, zirconium oxide, magnesium fluoride, and sulfide. Metal compounds such as zinc may be mentioned. In forming the protective layer, such a metal oxide may be used as a vapor deposition material, and any one of a vacuum vapor deposition method, a sputtering method and an ion plating method may be used.

For example, in the case of the vacuum vapor deposition method, 1
It is heated and evaporated by an electron beam and high frequency induction heating resistance heating system under a vacuum of 0 ^-2 to 10 ^-5 Torr. When the sputtering method or the ion plating method is adopted, a transparent thin film layer having higher adhesiveness can be formed as compared with the vacuum vapor deposition method.
The thickness of such protective layer is from 10 to 500 nm, preferably 5
A suitable thickness is from 0 to 300 nm, and if the thickness is less than 10 nm, the moisture resistance is insufficient, and if the thickness exceeds 500 nm, the film is likely to curl and the surface becomes optically nonuniform, which is not preferable.

The PVA-based retardation plate can sufficiently exhibit the effects of the present invention as it is in practical use. However, if necessary, it may be further improved in a cellulose-based film, a polystyrene-based film, a polyester-based film, a polysulfone-based film, or the like. It does not matter if the molecular films are laminated.
The retardation plate thus obtained is very excellent in optical characteristics such as viewing angle, transmittance, retardation value, etc., and can sufficiently meet recent highly required physical properties.

[0016]

[Working] The retardation plate of the present invention comprises a PVA-based uniaxially stretched film or sheet having a protective layer of a metal oxide formed on both sides or one side thereof, whereby the viewing angle dependence, the transmittance, the retardation value, the retardation plate are obtained. The optical characteristics such as dimensional change are further improved as compared with the conventional products.

[0017]

The present invention will be described in more detail below with reference to examples. Example 1 Uniaxially stretched polyvinyl alcohol film having an average degree of polymerization of 2000 and an average degree of saponification of 99.7 mol% and a thickness of 50 μm (stretching ratio 1.2 times, heat treated at 200 ° C. for 15 seconds after stretching) 5 × on both surfaces Under vacuum of 10 ^-5 Torr, silicon monoxide (SiO) with a purity of 99.9% is heated and evaporated by an electron beam heating method to form a transparent thin film layer of silicon oxide having a thickness of 100 nm on both surfaces of the polyvinyl alcohol film. And a protective layer was obtained. The viewing angle of such a retardation plate, the transmittance,
The weight change rate, the dimensional change rate, and the R value were measured using the following methods. The weight change rate, the dimensional change rate, and the R value change were measured using a retardation plate that was left standing at 40 ° C. and 95% RH for 500 hours. The results are summarized in Table 1.

(Viewing angle) A polarization microscope (Nikon POH-I type) equipped with a Babinet type compensator was attached with a universal rotary table, and the sample was tilted at 50 ° for measurement. R ₅₀ °: value when the sample is tilted by 50 ° R ₀ °: value when the sample is perpendicular to the incident light

(Transmittance) The transmittance was measured using a color difference meter (Sz-Σ80, manufactured by Nippon Denshoku Industries Co., Ltd.). A C / 2 (halogen lamp) was used as a light source. (Rate of change in weight) The weight of the retardation film dried in a desiccator and the weight of the film after the moisture resistance test are measured and calculated by the following formula. 100 x [(weight after moisture resistance test)-(weight in absolute dry)] / (weight in absolute dry)

(Dimensional change rate) The length of the retardation film when absolutely dried in a desiccator and the length of the film after the moisture resistance test are measured and determined by the following formula. 100 × [(length after moisture resistance test)-(length in absolute dry)] / (length in absolute dry) (measurement of R value) Polarizing microscope with Babinet type compensator (Nikon POH-I Type) and the compensation method.
The light source is white light.

Example 2 In Example 1, the purity was 99.9% instead of silicon monoxide.
A 150 nm-thick transparent thin film layer was formed using the aluminum oxide of Example 1 to prepare a retardation film. The properties of the obtained retardation film were measured according to Example 1. The results are summarized in Table 1. Example 3 Instead of silicon monoxide in Example 1, the purity is 99.9%.
A 100 nm-thick transparent thin film layer was formed using the silicon dioxide of Example 1 to prepare a retardation film. The properties of the obtained retardation film were measured according to Example 1. The results are summarized in Table 1.

Example 4 In Example 1, polyvinyl alcohol was used to obtain a polymerization degree of 170.
A retardation film was prepared and evaluated in the same manner as in Example 1, except that the saponification degree was changed to 0, the saponification degree was 99.8 mol%, and the stretching ratio was 1.15. The results are summarized in Table 1. Comparative Example 1 A retardation film was prepared by adhering a 50 μm thick triacetyl cellulose film on both sides of a uniaxially stretched polyvinyl alcohol film similar to that of Example 1. The properties of the obtained retardation film were measured according to Example 1. The results are summarized in Table 1.

[0023]

[Table 1]

[0024]

[Effect] In the present invention, by forming a protective layer of a metal oxide on both sides or one side of a PVA-based uniaxially stretched film or sheet, optical properties such as viewing angle, transmittance, retardation value, dimensional change of retardation plate, etc. can be obtained. A retardation plate having excellent characteristics can be obtained.

Claims (1)

[Claims] 1. A retardation plate comprising a polyvinyl alcohol-based uniaxially stretched film or sheet on which a protective layer of a metal oxide is formed on both sides or one side.