Dichroic polarizer and method for making the same

Details Dichroic polarizer and method for making the same Dichroic polarizer and method for making the same

2001-04-02

2003-05-13

Juba, Jr., John (Department: 2872)

Optical: systems and elements

Polarization without modulation

With color filter

C359S490020, C359S492010, C359S506000, C359S900000, C349S194000, C252S521600

Reexamination Certificate

active

06563640

ABSTRACT:

FIELD OF THE INVENTION
The invention belongs to the class of thermostable and lightfast dichroic polarizers manufactured using thin films of dichroic organic substances, in particular, the organic dyes in which molecules of a dichroic organic substance are ordered in a crystalline lattice and which are deposited onto either a rigid or a flexible substrate surface.
The proposed dichroic polarizers may be used under crude production and operation conditions: in the automobile industry for the triplex windscreen glass production, in illuminating equipment, in the architectural and construction glass manufacture. They may also be used in the liquid-crystal (LC) displays operating at high temperatures and illumination intensity levels.
BACKGROUND OF THE INVENTION
In GB 2162790A, issued Feb. 12, 1986, a dichroic polarizer is described which is an organic polymer-substance film containing a dichroic substance and having a crystalline lattice with the single-axis orientation coefficient no less than 70%. The dichroic-substance fraction in the polarizing film is 0.1-0.2% while the polarizer thickness is 40-170 microns. The large polarizer thickness, however, limits the field of its application. In particular, because of the large thickness, it can not be used as the internal polarizer in LC indicators. Moreover, the polarizer of this type, being effective in the visible spectrum range, can not provide high dichroism in the infrared spectrum region because the molecule planes of the dichroic substance are not oriented with respect to each other.
A dichroic-polarizer analogous to the one proposed is described in PCT WO 94/28073, published Dec. 8, 1994. This polarizer is a film containing no less than 70% of at least one dichroic organic substance with the planar-structure molecules (or molecule fragments). The molecules form orientation-ordered ensembles in which the molecule planes, as well as optical-transition dipole moments lying in these planes, are oriented perpendicularly, or almost perpendicularly, to the axis of the polarizing film macroscopic orientation.
The drawback of such a dichroic polarizer lies in the fact of presence of linear threadlike particles characterized by low correlation between the dipole moment orientation in the, molecules belonging to different linear particles. This does not allow improvement of the polarizer optical characteristics. Moreover, because of these particles, sufficient homogeneity can not be provided on the entire polarizer-film surface during manufacturing.
A method of dichroic polarizer manufacturing analogous to the proposed technique is also described in PCT WO 94/28073, published Dec. 8, 1994. In this method, the LC solution of an organic dye is deposited onto the substrate surface, is oriented, and then dried at 20-80° C.
The disadvantage of this method is that it does not provide sufficiently high extent of organic dye molecule orientation and, therefore, does not allow to essentially improve the polarizer optical characteristics.
SUMMARY OF THE INVENTION
The present invention improves the polarizer operation characteristics. The present invention the spectral range of the polarizer operation and simultaneously improves the polarizer's polarizing characteristics.
The present invention provides a dichroic polarizer containing a film which contains at least one dichroic organic substance, the molecules or molecule fragments of the said substance having planar structures, wherein at least part of the film has a crystalline structure, at least one of the said dichroic substances is a dichroic substance with at least one maximum in its spectral absorption curve in each of the spectral ranges, 400-700 nm and/or 200-400 nm, and 0.7-13 microns, and the order parameter S has a value no less than 0.8, the said parameter corresponding to at least one maximum on the spectral absorption curve in the 0.7-13 micron spectral range and being determined according to the formula
S
=(
D
⊥
−D
∥
)/(
D
⊥
+2
D
∥
),
where D
⊥
and D
∥
are optical densities in the polarized light for, respectively, perpendicular and parallel orientation of the polarization plane of the polarizer with respect to the polarization plane of incident electromagnetic radiation.
DESCRIPTION OF THE INVENTION
The dichroic polarizer includes a film containing at least one dichroic organic substance, the molecules or molecule fragments of the said substance having planar structures, wherein at least part of the film has a crystalline structure. At least one of the said dichroic substances is a dichroic substance with at least one maximum in its spectral absorption curve in each of the spectral ranges, 400-700 nm and/or 200-400 nm, and 0.7-13 microns. The order parameter S has a value no less than 0.8, the said parameter corresponding to at least one maximum on the spectral absorption curve in the 0.7-13 micron spectral range and being determined according to the formula
S
=(
D
⊥
−D
∥
)/(
D
⊥
+2
D
∥
),
where D
⊥
and D
∥
are optical densities in the polarized light for, respectively, perpendicular and parallel orientation of the polarization plane of the polarizer with respect to the polarization plane of the spectrometer electromagnetic radiation.
In some cases, the order parameter is no less than 0.85. In some other cases, the order parameter has the value no less than 0.88.
When the planes of all molecules are exactly parallel to each other, the polarizer's polarization axis is perpendicular to the molecule planes. However, since scatter is in fact almost always present in the angle parameters of the molecule plane orientation, the polarization axis direction can be determined as the direction corresponding to the maximum intensity of the electromagnetic radiation flux passed through the film. This maximum intensity practically coincides with the maximum transmission coefficient determined when rotating the polarization plane of the linearly polarized electromagnetic radiation falling onto the film perpendicularly to the film surface. When the polarization axis is determined in this manner, it is not necessary to allow for the scatter in the orientation angles of dipole moments of separate molecules. The <<polarization axis>> term is used below in this particular sense.
The polarizer may not absorb in the visible spectral range. In this case, the order parameter is no less than 0.6 for the wavelength of at least one maximum of the spectral absorption curve in the 200-400 nm spectral range. In some cases, the order parameter is no less than 0.75.
The order parameter is no less than 0.8 for the wavelength for at least one maximum of the spectral absorption curve in the 400-700 nm spectral range. In some cases, the order parameter is no less than 0.85.
The crystal structure of at least a part of the film is a three-dimensional crystalline lattice formed by the molecules of at least one dichroic organic substance. Under optimal manufacturing conditions, the crystal structure of the entire film surface can be obtained. If deposition is imperfect, at least a part of the film has crystalline structure. Perfection of the crystal structure can be experimentally estimated using the electron-diffraction patterns (B. K. Vainstein,
The x
-
ray diffraction on chain molecules
Moscow: USSR Academy of Sciences Press, 1963, p.310). For the proposed polarizers, the crystal structure of at least part of the said film is a three-dimensional crystalline lattice formed by molecules of at least one dichroic organic substance, the angular diffusion of the meridional reflection is no more than 18°, the said diffusion being determined from the diffraction pattern of the said film for the electron beam incidence being normal to the polarizer surface.
The crystalline lattice can have triclinic, monoclinic, or rhombic symmetry. The crystalline lattice parameter b determined from the diffraction pattern is 3.2 to 3.7 Å in the direction parallel to that of the polarization axis. In some cases, the

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