Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Reexamination Certificate
1999-03-31
2001-01-30
Kelly, C. H. (Department: 1721)
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
C252S299670, C252S582000, C430S001000, C430S002000
Reexamination Certificate
active
06180028
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal composition which comprises acrylic acid derivative compounds, and high molecular liquid crystal obtained by polymerizing it.
DESCRIPTION OF THE BACKGROUND
A photopolymerizable liquid crystal monomer having photopolymerizable functional groups imparted to a liquid crystal monomer, has both characteristics as a monomer and characteristics as liquid crystal. Therefore, when a photopolymerizable liquid crystal monomer is irradiated with light in the aligned state, it undergoes polymerization as aligned, and a polymer having a fixed alignment can be obtained. The high molecular liquid crystal thus obtained has an optical anisotropy based on the refractive index anisotropy of liquid crystal skeleton, and has special properties imparted by controlling liquid crystal alignment conditions. Accordingly, applications to e.g. a phase shift film or an optical head to be used for an optical head device are desired.
An optical head device is a device wherein light from a light source is converged on an optical disk to write information on the optical disk, or reflected light from the optical disk is received on a light-receiving element to read information on the optical disk. The optical head to be used for it functions as a beam splitter.
Heretofore, as an optical head, one having isotropic diffraction gratings formed on glass or plastic obtained by forming rectangular gratings (relief type) by dry etching or injection molding, or one obtained by forming anisotropic diffraction gratings on crystal surface showing refractive index anisotropy and combining a 1/4 wavelength plate therewith to obtain polarization selectivity, has been known.
However, with regard to the isotropic diffraction gratings, the incoming utilization efficiency is about 50% and the outgoing utilization efficiency is about 20%. Accordingly, it is limited to about 10% for incoming and outgoing, and the incoming and outgoing efficiency tends to be low, such being problematic.
On the other hand, with regard to a method wherein using a plate of crystal showing a refractive index anisotropy such as LiNbO
3
, anisotropic diffraction gratings are formed on the surface to obtain polarization selectivity, and high incoming and outgoing efficiency is utilized, the crystal showing the refractive index anisotropy is expensive itself, and its application to the field of home uses is difficult. Further, in the case of forming the gratings by a proton exchange method, in general, protons in the proton exchange liquid are likely to diffuse into the LiNbO
3
substrate, and thus there is a problem that it is difficult to form the gratings having a small pitch.
In the case of using a photopolymerizable liquid crystal monomer, by making it high molecular liquid crystal after controlling liquid crystal alignment conditions, high incoming and outgoing efficiency as crystal showing a refractive index anisotropy can be obtained. For example, there is a method to fill the high molecular liquid crystal into the gratings to obtain high efficiency. In the method, in a liquid crystal cell having the surface of one side of the substrate fine-processed to form rectangular gratings, a liquid crystal monomer is aligned so that the major axis direction of the liquid crystal monomer is parallel to the gratings, followed by polymerization to obtain high molecular liquid-crystal. By optimizing grating depth so that the normal light refractive index of the high molecular liquid crystal is equal to the refractive index of the grating substrate, high incoming and outgoing efficiency can be obtained.
Theoretically, the maximum incoming and outgoing efficiency can be obtained when the formula &lgr;/2=&Dgr;n·d is satisfied where d is the grating depth, &Dgr;n is the refractive index anisotropy of the high molecular liquid crystal and &lgr; is the wavelength, and high light utilization efficiency can be obtained with ± first order diffracted light efficiency of about 40%, and with a total of about 80%.
As another example, a method wherein high molecular liquid crystal is filled into a liquid crystal cell having transparent electrodes patterned into stripes, to obtain high efficiency, may be mentioned. The liquid crystal monomer is aligned in the substrate face so that the major axis direction is perpendicular to the stripe directions, voltage is applied thereto, and the liquid crystal monomer sandwiched between the top and bottom transparent electrodes is aligned on the substrate face so that it is perpendicular to the substrate face. The alignment conditions are controlled periodically at a part where the electrode exists and a part where it does not exist, and polymerization is conducted to obtain high molecular liquid crystal. In this case too, the maximum incoming and outgoing efficiency can be obtained when &lgr;
=&Dgr;n·d is satisfied.
As the material for high molecular liquid crystal is cheap, it can be applied to home uses, and it is expected as an excellent optical head. As the characteristics of the optical head, high durability and high incoming and outgoing efficiency at a fine pitch (10 &mgr;m or shorter) are required.
As the photopolymerizable liquid crystal monomer, for example, a compound represented by the formula 3, the formula 4 or the formula 5:
CH
2
═CHCOO—Ph—C≡C—Ph—(CH
2
)
5
H formula 3
CH
2
═CHCOO—Cy—Cy—(CH
2
)
4
H formula 4
CH
2
═CHCOO—Ph—Cy—(CH
2
)
3
H formula 5
wherein Ph is a 1,4-phenylene group and Cy is a trans-1,4-cyclohexylene group, has been known (Takatsu and Hasebe, text from the 106th photopolymer symposium, III-1).
However, there are problems that the compound represented by the formula 3 (hereinafter referred to as compound 3, and the same applies to the other) has a tolan group in the molecule, and thus it does not have durability.
Further, with regard to the compound 4 and the compound 5, the monomer has a small refractive index anisotropy of at most 0.1, and thus the refractive index anisotropy of the liquid crystal composition comprising it can not be made high, such being problematic. Further, as the refractive index anisotropy of high molecular liquid crystal decreases to about half after polymerization, in the case of using a compound having a low refractive index anisotropy as the main component of the liquid crystal composition, it is difficult to make fine pitch while keeping a high incoming and outgoing efficiency, such being problematic.
Namely, in the case of filling high molecular liquid crystal into the gratings, when the wavelength is 0.65 &mgr;m, the grating depth of at least 3 &mgr;m is required when the refractive index anisotropy is less than 0.1. However, the fine-process of the gratings having a large aspect ratio is very difficult. Further, in the case of conducting the alignment control by the electric field by using the patterned transparent electrodes, as the alignment of liquid crystal at the part where no electrode pattern exists is disturbed by influences of the leakage electric field, it tends to be difficult to control the alignment when the aspect ratio is large.
Accordingly, in order to make a fine pitch, it is required that the refractive index anisotropy of high molecular liquid crystal is at least 0.1.
DISCLOSURE OF THE INVENTION
The present invention provides a liquid crystal composition having an excellent durability and a high refractive index anisotropy, i.e. a liquid crystal composition which comprises a compound represented by the following formula 1 and a compound represented by the following formula 2, and high molecular liquid crystal obtained by polymerizing it:
CH
2
═CHCOO—X—O—Ph—Ph—CN formula 1
CH
2
═CHCOO—Ph—Ph—CN formula 2
wherein X is an alkylene group, and Ph is a 1,4-phenylene group. Ph is a 1,4-phenylene group also in the formulae 7 to 10.
REFERENCES:
patent: 5354498 (1994-10-01), Akashi et al.
patent: 5558813 (1996-09-01), Akashi et al.
patent: 5560864 (1996-10-01), Goulding
patent: 567
Gunjima Tomoki
Hotaka Hiroki
Kurosawa Mitsuru
Sato Hiromasa
Tanabe Yuzuru
Asahi Glass Company Ltd.
Kelly C. H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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