JPH01304402A - Plastic optical phase plate - Google Patents

Abstract

PURPOSE:To produce the large-area optical phase plate at a low cost by orienting the polar groups in a solid soln. of the polyvinylidene fluoride and polymethyl methacrylate in which the prescribed ratio of the polyvinylidene fluoride is incorporated. CONSTITUTION:This optical phase plate consists of the solid soln. of the polyvinylidene fluoride and the polymethyl methacrylate in which <=75wt.% polyvinylidene fluoride is incorporated. The plastic optical phase plate in which the polar groups of this solid soln. and oriented to the specified direction is used. The difference in elongation between both is solved and the heat resistance is improved by adding the polyvinylidene fluoride to the polymethyl methacrylate to prepare the solid soln. in such a manner. Light transmittability is improved as well while optical anisotropy is maintained.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to provide an optical phase plate with a large area at a low cost with respect to an optical phase plate used in display devices and the like. A plastic optical phase plate is used, which is made of a solid solution of polyvinylidene fluoride and polymethyl methacrylate, and the polar groups in this solid solution are oriented in a certain direction.

[Industrial application field]

The present invention relates to plastic optical phase plates.

With the development of optical communications using lasers as light sources, various optical control elements such as optical switches and optical modulators used therein are also being improved.

Furthermore, light control elements are widely used not only in optical communications but also in display devices such as liquid crystal display elements and plasma displays.

[Conventional technology]

Optical elements such as phase plates are widely used in display devices.

For example, regarding a liquid crystal display device that uses a simple matrix method, the electro-optic characteristics are steep, so 5TN (Sup
er Twisted Nematic) Display is performed using liquid crystals, but because liquid crystals exhibit optical anisotropy, the display is colored, so there is a problem that black and white display is not possible until then. .

In other words, when circularly polarized light is converted into linearly polarized light by passing through a polarizing plate and enters a liquid crystal cell, the light becomes elliptically polarized light and exits the liquid crystal cell because the liquid crystal has optical anisotropy. The degree of this differs depending on the wavelength.

Therefore, this emitted light is made incident on the optical phase plate, which causes the liquid crystal cell to perform the opposite action on the incident light to return it to linearly polarized light, and this linearly polarized light is emitted through an analyzer.
An image is being displayed.

For this reason, until now optical phase plates have been made using acidic potassium dihydrogen phosphate (KH).
2PO4 abbreviation KDP) and lithium niobate (LiNbO
It is constructed using anisotropic optical crystals such as *).

However, it takes a great deal of time and effort to grow crystals of these materials and then cut and polish them to form elements, making them quite expensive.

For this reason, there is a demand for cost reduction not only for the above-mentioned optical phase plate but also for optical elements.

[Problem to be solved by the invention]

Conventional optical elements are manufactured by cutting out inorganic single crystals, so they are expensive, and optical elements with large areas are difficult to manufacture.

Therefore, since some polymer materials have optical anisotropy, it is a challenge to put optical phase plates into practical use using these materials.

[Means to solve the problem]

The above problem can be solved by using a plastic optical phase plate made of a solid solution of polyvinylidene fluoride and polymethyl methacrylate containing 75% by weight or less of polyvinylidene fluoride, in which the polar groups in the solid solution are oriented in a certain direction. It can be solved.

[Effect]

The present invention utilizes the property that polyvinidene fluoride (hereinafter abbreviated as PVDF) has an atomic group with a large dipole moment in its molecule, and can be oriented in one direction by applying an electric field or stretching it. It is.

That is, PVDF has a structural formula as shown in FIG. 4, and has a large dipole moment due to the C--F bond.

However, there are two types of PV leaves: α-type crystals and β-type crystals.
In the α type, the orientation directions of the polar groups constituting the unit cell are alternately opposite, so the unit cell cancels out and has no polarity.

However, the β type forms a polar crystal with a high dielectric constant because all of the polar groups constituting the unit cell are oriented in a certain direction.

It is known that in order to change the α-type to the β-type, a high electric field may be applied at a temperature higher than the glass transition temperature, or -axis or two-wheel stretching may be performed.

On the other hand, as an optical element, it is necessary to have excellent light transmittance, but PVDF has an extremely low light transmittance of about 12%, and cannot be used as an optical material.

The inventors have previously proposed the use of a solid solution of PVDF and polymethyl methacrylate (commonly known as PMH) as a material suitable for the cladding of a plastic optical fiber or a flat light guide. (Special application 1986-2556
No. 83) The gist of this proposal is that polycarbonate (abbreviated as PC), which has excellent heat resistance, has traditionally been used as the core of plastic optical fibers.
Also, as a cladding, P has a lower refractive index than PC.
MMA is used, but while the elongation of PC is about 90%, the elongation of PMMA is only about 5%, so it easily breaks due to external stress.

Therefore, in order to solve this problem, a solid solution of PMMA with Pv leaf added thereto is used, which solves the elongation problem and also improves heat resistance.

On the contrary, the present invention mainly uses PV fibers and improves light transmittance while maintaining optical anisotropy by adding PMMA thereto.

Figure 1 shows the light transmittance versus the fraction (weight% mixing ratio) of PMMA and PVDF, and Figure 2 shows the light transmittance of PMMA and PVDF.
The relationship between heat deformation temperature and elongation with respect to the fraction of F is shown.

That is, to construct a plastic optical phase plate, pv
It is necessary that the leaf fraction is as large as possible and that the light transmittance is high.

Here, as shown in Figure 1, the light transmittance of PVDF alone is only about 12%, as mentioned earlier, but as the amount of PMMA added increases, the transmittance increases rapidly, and PVDF
: PMM8-75%: If it exceeds 25%, the light transmittance is 80
% or more.

On the other hand, as shown in Fig. 2, in order to form a phase plate with optical anisotropy by a uniaxial or biaxial stretching method, PVDF:
It turns out that it is sufficient to use a mixture of PMMA = 70%:30%.

From the relationship between Figures 1 and 2, approximately PVDP: PM
It can be said that a mixture of MA=70%:30% is suitable for an optical phase plate.

〔Example〕

Example 1: A mixture of PVDP:PMMA = 70%:30% was placed in a glass crucible, and in order to prevent air bubbles from entering during sample melting, this composition was placed in a vacuum device and the air inside the device was evacuated. 2 than 150℃, which is the heat distortion temperature of the ratio.
It was heated to 170° C., which is 0° C. higher, to melt it, and this melt was used to form a thin plate with a thickness of 0.511.

Next, this plastic thin plate is sandwiched between parallel plate electrodes,
After applying a direct current electric field of 5 KV/cm at a temperature of 150° C., the direction of the electric field is set to two directions, and polarization is performed.
A 1/4 wavelength plate for a wavelength of 633 nm was obtained by naturally cooling to room temperature while an electric field was applied and removing the electrodes.

Example 2: Same as Example 1 PVDP: PMMA=70%:3
A mixture consisting of 0% was uniaxially stretched 4 times at the heat deformation temperature of 150°C, and a 1/4-fold film for a wavelength of 633 nm with a thickness of 0.5% was drawn.
A four-wavelength plate was obtained.

FIG. 3 shows the intensity of transmitted light when the rotation angle of the analyzer is changed for quarter-wave plates made by these two methods.

In other words, it can be seen that Figure (A) shows the case where linearly polarized light with a wavelength of 633 nm is incident, and that beautiful circularly polarized light is obtained. On the other hand, in the same figure (B), the polarizer is removed and circularly polarized light is incident, and it can be seen that the circularly polarized light has become linearly polarized light.

〔Effect of the invention〕

A plastic optical phase plate formed according to the present invention can exhibit performance equivalent to that formed using an inorganic optical crystal such as KDP or LiNb0t, and thus a large-area optical phase plate can be manufactured at low cost. It becomes possible to do so.

[Brief explanation of the drawings] Figure 1 is a relationship diagram between the fraction of PMMA and PVDF and light transmittance, Figure 2 is a relationship diagram between heat distortion temperature and elongation with respect to the fraction of PMMA and PVDF, and Figure 3 Figures (A) and (B) are diagrams showing the transmitted light elasticity with respect to the analyzer rotation angle, and Figure 4 shows the structural formula of PVDF. F'M Okisha PVDF's related accounts

Claims (1)

[Claims] A plastic optical phase plate comprising a solid solution of polyvinylidene fluoride and polymethyl methacrylate containing 75% by weight or less of polyvinylidene fluoride, wherein polar groups in the solid solution are oriented in a certain direction.