JP2010007031A - Polymerizable liquid crystalline composition, optically anisotropic material, optical element, and optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymerizable liquid crystalline composition and an optically anisotropic material which are excellent in light resistance, to provide an optical element which is excellent in light resistance, and to provide an optical head device using the optical element. <P>SOLUTION: The polymerizable liquid crystalline composition includes a compound represented by CH<SB>2</SB>=CX<SP>1</SP>-COO-L<SP>1</SP>-B<SP>1</SP>-A<SP>1</SP>-B<SP>2</SP>-Cy-Cy-B<SP>3</SP>-A<SP>2</SP>-B<SP>4</SP>-L<SP>2</SP>-OCO-CX<SP>2</SP>=CH<SB>2</SB>of 15-60 mass%, a compound represented by CH<SB>2</SB>=CX<SP>3</SP>-COO-L<SP>3</SP>-B<SP>5</SP>-A<SP>3</SP>-B<SP>6</SP>-Cy-B<SP>7</SP>-A<SP>4</SP>-B<SP>8</SP>-R<SP>1</SP>of 15-30 mass%, and a compound represented by CH<SB>2</SB>=CX<SP>4</SP>-COO-L<SP>4</SP>-B<SP>9</SP>-Cy-B<SP>10</SP>-Cy-B<SP>11</SP>-R<SP>2</SP>of 25-55 mass%. As a diffraction grating 2 fabricated by using the composition is excellent in lightfastness, it can form an optical head device suitable for increase in capacity by using a blue laser beam as a light source 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polymerizable liquid crystal composition, an optically anisotropic material, an optical element, and an optical head device.

  Concavities and convexities called pits are provided on the surface of an optical disc such as a CD (Compact Disk) and a DVD (Digital Versatile Disk). The optical head device is a device that can read information recorded in pits by irradiating an optical disc with laser light and detecting the reflected light.

  For example, linearly polarized light emitted from the light source reaches the information recording surface of the optical disc via a beam splitter, a collimator lens, a phase difference plate, and an objective lens. Here, the forward linearly polarized light passes through the beam splitter as it is, and is converted into circularly polarized light by the phase difference plate. This circularly polarized light is reflected by the information recording surface of the optical disk to become reversely circularly polarized light, and then follows the return path in the order of the objective lens, the phase difference plate, and the collimator lens, contrary to the forward path. Then, the light is converted into linearly polarized light orthogonal to that before incidence by the return phase retardation plate. As a result, the direction of the linearly polarized light is shifted by 90 degrees from that of the forward path light, and the traveling direction is bent by 90 degrees to reach the photodetector when passing through the beam splitter.

  In the optical head device, if the optical disc is shaken when reading or writing information, the focus position of the beam spot shifts from the recording surface. This is detected and corrected to make the beam spot an uneven pit on the recording surface. Servo mechanism to follow the is required. Such a mechanism is configured to detect the track position by focusing the beam spot irradiated by the laser light source on the recording surface and to follow the target track. Further, in the optical head device, it is necessary to prevent the laser light reflected without hitting the pit on the recording surface from returning to the light source as it is.

  For this reason, the optical head device requires an optical element that modulates the laser light from the light source (polarization, diffraction, phase adjustment, etc.). For example, the retardation plate described above has an effect of giving different refractive indexes to incident light according to the angle formed by the optical axis of the retardation plate and the phase plane of the incident light, and further shifting the phase of the two component light generated by birefringence have. The two lights whose phases are shifted are combined when they are emitted from the phase difference plate. Since the magnitude of the phase shift is determined by the thickness of the phase difference plate, by adjusting the thickness, a quarter wavelength plate for shifting the phase by π / 2, a half wavelength plate for shifting π, and the like are produced. For example, linearly polarized light that has passed through a quarter wavelength plate becomes circularly polarized light, but linearly polarized light that has passed through a half wavelength plate becomes linearly polarized light whose polarization plane is inclined by 90 degrees. The servo mechanism described above is configured by combining a plurality of optical elements using such properties. The optical element is also used to prevent the laser light reflected without hitting the pit on the recording surface from returning to the light source.

The above optical element can be manufactured using a liquid crystal material. For example, a liquid crystal molecule having a polymerizable functional group has both properties as a polymerizable monomer and properties as a liquid crystal. Accordingly, when polymerization is performed after aligning liquid crystal molecules having a polymerizable functional group, an optically anisotropic material in which the alignment of liquid crystal molecules is fixed is obtained. Since the optically anisotropic material has optical anisotropy such as refractive index anisotropy derived from a mesogen skeleton, a diffractive element, a retardation plate, and the like are produced using this property. As an optically anisotropic material, for example, in Patent Document 1, a liquid crystalline composition containing a compound represented by CH ₂ = CH—COO—Ph—OCO—Cy—Z (Z: alkyl group) is polymerized. An optically anisotropic material is disclosed. Patent Document 2 also discloses a compound represented by CH ₂ = CHCOO-Ph-OCO-XY (X: 1,4-phenylene group or 1,4-trans-cyclohexylene group, Y: alkyl group). An optically anisotropic material obtained by polymerizing a liquid crystalline composition containing benzene is disclosed.

Incidentally, the optical element described above generally requires the following characteristics.
1) It has an appropriate retardation value (Rd value) according to the wavelength used and application.
2) In-plane optical characteristics (Rd value, transmittance, etc.) are uniform.
3) There is almost no scattering or absorption at the wavelength used.
4) It is easy to match optical characteristics with other materials constituting the element.
5) The wavelength dispersion of refractive index and refractive index anisotropy is small at the wavelength used.

  In particular, it is important to have a proper Rd value of 1). Here, the Rd value is a value determined by the relationship of Rd = Δn × d using the refractive index anisotropy (Δn) and the thickness (d) in the light propagation direction. In order to obtain a desired Rd value, if the Δn of the liquid crystal material forming the optical element is small, it is necessary to increase the thickness d. However, when the thickness d increases, it becomes difficult to align the liquid crystal, and it becomes difficult to obtain desired optical characteristics. On the other hand, when Δn is large, it is necessary to reduce the thickness d, but in this case, precise thickness control becomes difficult. Therefore, it is very important for the liquid crystal material to have an appropriate Δn value.

  In recent years, in order to increase the capacity of an optical disk, it has been promoted to reduce the wavelength of laser light used for writing and reading information to reduce the size of concave and convex pits on the optical disk. For example, a laser beam having a wavelength of 780 nm, a DVD having a wavelength of 650 nm, and a BD (Blue-ray Disk) or HDDVD (High-Definition Digital Versatile Disk) having a wavelength of 405 μm are used. It is conceivable that the wavelength will be further shortened in the next-generation optical recording media, and the use of laser light with a wavelength of 300 to 450 nm (hereinafter also referred to as blue laser light) tends to increase in the future. However, the optically anisotropic materials described in Patent Document 1 and Patent Document 2 are not sufficiently resistant to blue laser light.

  For example, if a phase difference plate made of liquid crystal is arranged in an optical head device using blue laser light as a light source, aberrations occur with the passage of time, the transmittance decreases, or the Rd value is reduced. And may fluctuate. This is presumably because the constituent material of the phase difference plate was damaged by the exposure to the blue laser beam. When aberration occurs, the light (light beam) emitted from the light source and passing through the collimator lens and the phase difference plate cannot reach a single point when it passes through the objective lens and reaches the surface of the recording medium. Then, the light use efficiency is lowered, and the efficiency of reading and writing information is lowered. Further, when the transmittance is lowered, the intensity of light reaching the surface of the recording medium and the photodetector is weakened, and the efficiency of reading and writing information is reduced as described above. Further, when the Rd value fluctuates, for example, a desired ellipticity or extinction ratio of linearly polarized light cannot be maintained in the wave plate. As a result, the optical head device may not function.

JP 2004-263037 A Japanese Patent Laid-Open No. 10-195138

  The present invention has been made in view of the above points. That is, an optical element that modulates laser light having a wavelength of 300 nm to 450 nm is required to have an optically anisotropic material that is less deteriorated even when exposed to light in this wavelength band and has excellent durability and liquid crystallinity. It has been. For such anisotropic materials, the structure of the liquid crystal compound is extremely important. Therefore, an object of the present invention is to provide a polymerizable liquid crystal composition having good light resistance against blue laser light and capable of obtaining desired liquid crystallinity after polymerization.

  Another object of the present invention is to provide an optically anisotropic material with good light resistance to blue laser light.

  Another object of the present invention is to provide an optical element having good light resistance to blue laser light and an optical head device using the optical element.

  Other objects and advantages of the present invention will become apparent from the following description.

  In the first aspect of the present invention, the compound represented by the following formula (1) is represented by 15 to 60% by mass, the compound represented by the following formula (2) is represented by 15 to 30% by mass, and the following formula (3). 25 to 55% by mass of a compound to be produced.

_{^{CH 2 = CX 1 -COO-L}} 1 -B 1 -A 1 -B 2 -Cy-Cy-B 3 -A 2 -B 4 -L 2 -OCO-CX 2 = CH 2 (1)

_{^{CH 2 = CX 3 -COO-L}} 3 -B 5 -A 3 -B 6 -Cy-B 7 -A 4 -B 8 -R 1 (2)

_{^{CH 2 = CX 4 -COO-L}} 4 -B 9 -Cy-B 10 -Cy-B 11 -R 2 (3)

In the above formula, X ^{1 to} X ⁴ are each independently a hydrogen atom or a methyl group, and B ^{1 to} B ¹¹ are each independently a single bond, —COO— or —OCO—.

L ¹ , L ³ and L ⁴ are each independently — (CH ₂ ) _n —O—, — (CH ₂ ) _n — or a single bond when B ¹ , B ⁵ and B ⁹ are single bonds. , B ¹ , B ⁵ and B ⁹ are —COO— or —OCO—, it is — (CH ₂ ) _n —, in which case n is an integer of 1-12. Moreover, it may have an etheric oxygen atom between the carbon-carbon bonds of the alkylene group, and part or all of the hydrogen atoms may be substituted with fluorine atoms.

L ^2, when ^{B 4} is a single _{bond, -O- (CH 2) m -} , - (CH 2) m - or a single bond, when ^{B 4} is -COO- or -OCO- of, - ( CH _{2) m} - is. However, in any case, m is an integer of 1-12. Moreover, it may have an etheric oxygen atom between the carbon-carbon bonds of the alkylene group, and part or all of the hydrogen atoms may be substituted with fluorine atoms.

A ^{1 to} A ⁴ are each independently a 1,4-phenylene group or a trans-1,4-cyclohexylene group, and some or all of the hydrogen atoms may be substituted with fluorine atoms.

R ¹ and R ² are each independently an alkyl group having 1 to 12 carbon atoms, and some or all of the hydrogen atoms may be substituted with fluorine atoms.

  Cy is a trans-1,4-cyclohexylene group, and part or all of the hydrogen atoms may be substituted with fluorine atoms.

In the first aspect of the present invention, the compound represented by the formula (1) preferably exhibits liquid crystallinity. In this case, A ¹ and A ² in the formula (1) are preferably 1,4-phenylene groups in which some or all of the hydrogen atoms may be substituted with fluorine atoms.

In the first embodiment of the present invention, A ³ and A ⁴ in formula (2) are trans-1,4-cyclohexylene groups in which some or all of the hydrogen atoms may be substituted with fluorine atoms. It is preferable.

  According to a second aspect of the present invention, there is provided an optically anisotropic material comprising a polymer of the polymerizable liquid crystalline composition according to the first aspect of the present invention.

  According to a third aspect of the present invention, there is provided an optical element comprising the optically anisotropic material according to the second aspect of the present invention.

  According to a fourth aspect of the present invention, there is provided an optical head device comprising the optical element according to the third aspect of the present invention.

  According to the 1st aspect of this invention, it can be set as the polymeric liquid crystalline composition which has favorable light resistance with respect to a blue laser beam, and can obtain desired liquid crystallinity after superposition | polymerization.

  According to the 2nd aspect of this invention, it can be set as the optically anisotropic material with favorable light resistance with respect to a blue laser beam.

  According to the 3rd aspect of this invention, it can be set as the optical element with favorable light resistance with respect to a blue laser beam.

  According to the fourth aspect of the present invention, an optical head device suitable for increasing the capacity can be obtained.

The mechanism of fluctuation of the Rd value due to exposure to blue laser light is not always clear. However, the Rd value is expressed by the following formula: Rd = Δn (value of refractive index anisotropy) × d (thickness in the light propagation direction)
It can be inferred that the orientation of the mesogenic group of the side chain that determines the Δn value is disturbed more specifically, because the Δn value fluctuates when irradiated with blue laser light.

  This inventor discovered that the fluctuation | variation of Rd value was suppressed by making a specific polymerizable liquid crystalline composition contain a specific crosslinking material. The cross-linking material may be either liquid crystalline or non-liquid crystalline, but is preferably liquid crystalline in the present invention. When the cross-linking material is a non-liquid crystalline compound, the compatibility with other compounds is remarkably lowered, or the liquid crystallinity of the composition is liable to be lowered even if compatible. For this reason, the density | concentration which can mix a crosslinking material will be suppressed by the comparatively low level, and the effect by bridge | crosslinking, ie, the suppression effect of Rd value fluctuation | variation, will not fully be exhibited. On the other hand, a cross-linking material that exhibits liquid crystallinity can be mixed at a high concentration without causing a decrease in compatibility with other compounds and a decrease in liquid crystallinity of the composition after mixing. Even if the anisotropic material obtained by polymerizing this composition is exposed to blue laser light, fluctuations in the Rd value are suppressed.

  As said crosslinking material, the compound represented by following formula (1) can be used.

_{^{CH 2 = CX 1 -COO-L}} 1 -B 1 -A 1 -B 2 -Cy-Cy-B 3 -A 2 -B 4 -L 2 -OCO-CX 2 = CH 2 (1)

  Furthermore, as a result of intensive studies, the inventor mixed the compound represented by the formula (1) with the compounds represented by the following formulas (2) and (3), thereby improving the light resistance to blue laser light. It was found that a polymerizable liquid crystal composition can be obtained. According to the polymerizable liquid crystalline composition of the present invention, for example, an optically anisotropic material capable of keeping the fluctuation of the Rd value within a narrow range can be obtained.

_{^{CH 2 = CX 3 -COO-L}} 3 -B 5 -A 3 -B 6 -Cy-B 7 -A 4 -B 8 -R 1 (2)

_{^{CH 2 = CX 4 -COO-L}} 4 -B 9 -Cy-B 10 -Cy-B 11 -R 2 (3)

  In the polymerizable liquid crystal composition of the present invention, the concentration of the compound represented by the formula (1) is preferably 15% by mass or more, particularly 20% by mass or more from the viewpoint of the effect of suppressing the fluctuation of the Rd value. If it exists, the effect becomes large and is preferable. On the other hand, the concentration of the compound represented by the formula (1) is preferably 60% by mass or less from the viewpoint that the light resistance can be increased by reducing the absorption in the wavelength band of blue laser light. Moreover, it is preferable that the density | concentration of the compound represented by Formula (2) shall be 15 mass% or more from the point of the suppression effect of Rd value fluctuation | variation. On the other hand, from the viewpoint of compatibility, the concentration of the compound represented by the formula (2) is preferably 30% by mass or less, and particularly preferably 25% by mass or less. Furthermore, the compound represented by the formula (3) is a compound added to improve the compatibility as the liquid crystal of the polymerizable liquid crystal composition, but if it is too much, the effect of suppressing Rd fluctuation tends to be reduced. The concentration is preferably 25% by mass to 55% by mass, and more preferably 25% by mass to 45% by mass.

  The compounds of the formulas (1) to (3) may be contained in one or more kinds in the above amounts. For example, the polymerizable liquid crystal composition includes one type of compound represented by the formula (1), two types of compounds represented by the formula (2), and two types of compounds represented by the formula (3). Can be included. In this case, content of the compound represented by Formula (2) should just be in the range of 15 mass%-30 mass% as a whole. Moreover, content of the compound represented by Formula (3) should just be in the range of 25 mass%-55 mass% as a whole.

  In the polymerizable liquid crystal composition, the proportion of the compound represented by the formula (1) is preferably increased as much as possible within a range not causing a decrease in compatibility with other compounds or a decrease in liquid crystallinity. The ratio of the compound represented by the formula (2) and the compound represented by the formula (3) is preferably about 25:75 (molar ratio). If the proportion of the compound of formula (2) is too large, the liquid crystallinity is lowered. On the other hand, if the proportion of the compound of formula (2) is too small, the fluctuation of the Rd value when exposed to blue laser light becomes large.

In Formula (1) to Formula (3), X ^{1 to} X ⁴ are each independently a hydrogen atom or a methyl group, and B ^{1 to} B ¹¹ are each independently a single bond, —COO— or —OCO. -.

L ¹ , L ³ and L ⁴ are each independently — (CH ₂ ) _n —O—, — (CH ₂ ) _n — or a single bond when B ¹ , B ⁵ and B ⁹ are single bonds. , B ¹ , B ⁵ and B ⁹ are —COO— or —OCO—, — (CH ₂ ) _n —. However, in any case, n is an integer of 1-12. Moreover, it may have an etheric oxygen atom between the carbon-carbon bonds of the alkylene group, and part or all of the hydrogen atoms may be substituted with fluorine atoms.

L ^2, when ^{B 4} is a single _{bond, -O- (CH 2) m -} , - (CH 2) m - or a single bond, when ^{B 4} is -COO- or -OCO- of, - ( CH _{2) m} - is. However, in any case, m is an integer of 1-12. Moreover, it may have an etheric oxygen atom between the carbon-carbon bonds of the alkylene group, and part or all of the hydrogen atoms may be substituted with fluorine atoms.

A ^{1 to} A ⁴ are each independently a 1,4-phenylene group or a trans-1,4-cyclohexylene group, and some or all of the hydrogen atoms may be substituted with fluorine atoms. Here, from the viewpoint of developing liquid crystallinity, it is preferable to introduce a phenylene group in a polycyclic compound having three or more rings. However, excessive introduction of a phenylene group may increase the absorption in the oscillation wavelength band of the blue laser by widening the conjugated system to increase the wavelength of the absorption edge. In particular, when adjacent phenylene groups are directly bonded or when bonded via a linking group having conjugation properties such as a —COO— group, the conjugate length further increases, and in the wavelength band of the blue laser. It will show stronger absorption. For this reason, introduction of a phenylene group needs to be kept to the minimum necessary. Specifically, the number of molecules that can be introduced into one molecule is preferably 1 for bicyclic compounds and up to 2 for compounds with 3 or more rings. Furthermore, when introducing two, it is preferable to set it as the structure where phenyl groups do not couple | bond together directly, or the structure which does not couple | bond together through the coupling group which shows conjugation property.

R ¹ and R ² are each independently an alkyl group having 1 to 12 carbon atoms, and some or all of the hydrogen atoms may be substituted with fluorine atoms.

  Cy is a trans-1,4-cyclohexylene group, and part or all of the hydrogen atoms may be substituted with fluorine atoms.

The compounds represented by formula (2) and formula (3) may or may not exhibit liquid crystallinity alone, but A ³ and A ⁴ in formula (2) are hydrogen atoms. A trans-1,4-cyclohexylene group which may be partially or wholly substituted with fluorine atoms is preferred. On the other hand, as described above, the compound represented by the formula (1) preferably exhibits liquid crystallinity alone. In this case, A ¹ and A ² in the formula (1) are preferably 1,4-phenylene groups in which some or all of the hydrogen atoms may be substituted with fluorine atoms.

  Specific examples of the compound represented by the formula (1) include Non-Patent Document 1 (R. Cassano, R. Dabrowski, J. Dziaduszek, N. Picci, G. Chidichimo, G. de Filpo, F. Puoci, Tetrahedron. Letters, 48 (8), 1447-1450, 2007).

  The polymerizable liquid crystalline composition of the present invention is a compound other than the compounds represented by the formulas (1) to (3), for example, a polymerizable liquid crystal other than these compounds, as long as the effects of the present invention are not impaired. A polymerizable compound, a polymerizable non-liquid crystal compound, a non-polymerizable liquid crystal compound, a non-polymerizable non-liquid crystal compound, or the like can be included. For example, the amount of an additive such as a polymerization initiator, a polymerization inhibitor, a chiral agent, an antioxidant, an ultraviolet absorber, a light stabilizer or a dye may be 5% by mass or less based on the polymerizable liquid crystalline composition. Preferably, it is more preferably 2% by mass or less. In addition, when other compounds are added, they are used within the range not impairing the effects of the present invention. Usually, the total amount of the compounds represented by the formulas (1) to (3) is the polymerizable liquid crystal composition. The content is preferably 90% by mass or more, and more preferably 95% by mass or more.

  Next, the optically anisotropic material of the present invention will be described.

  The optically anisotropic material of the present invention comprises a polymer obtained by polymerizing the above-described polymerizable liquid crystalline composition in a state where the composition exhibits a liquid crystal phase and the liquid crystal is aligned.

In order to keep the polymerizable liquid crystalline composition in a state of exhibiting a liquid crystal phase, the atmospheric temperature may be set to be equal to or lower than the nematic phase-isotropic phase transition temperature (T _c ). However, since Δn of the liquid crystal composition becomes extremely small at a temperature close to T _c , the upper limit of the ambient temperature is preferably set to (T _c −10) or less.

  Polymerization includes photopolymerization and thermal polymerization. Photopolymerization is preferred because it is easy to cure while maintaining liquid crystallinity. The light used for photopolymerization is preferably ultraviolet light or visible light. When carrying out photopolymerization, it is preferable to use a photopolymerization initiator, among which acetophenones, benzophenones, benzoins, benzyls, Michler's ketones, benzoin alkyl ethers, benzyldimethylketals and thioxanthones are selected as appropriate. The photopolymerization initiator used is preferably used. A photoinitiator can be used 1 type or in combination of 2 or more types. The amount of the photopolymerization initiator is preferably 0.005% by mass to 5% by mass and more preferably 0.01% by mass to 1% by mass with respect to the total amount of the liquid crystal composition.

  As described above, the optically anisotropic material is obtained by polymerizing a polymerizable liquid crystalline composition in a state where the composition exhibits a liquid crystal phase and the liquid crystal is aligned. For example, it can be obtained by polymerizing a polymerizable liquid crystal composition in a state of being sandwiched between a pair of substrates whose surfaces are subjected to an alignment treatment. Specific examples will be described below.

  First, a transparent substrate is prepared.

  As the transparent substrate, for example, a substrate made of a material having a high visible light transmittance can be used. Specifically, in addition to inorganic glass such as alkali glass, alkali-free glass and quartz glass, polyester, polycarbonate, polyether, polysulfone, polyethersulfone, polyvinyl alcohol, and fluorine-containing polymers such as polyvinyl fluoride, etc. A substrate made of a transparent resin is exemplified. In view of high rigidity, it is preferable to use a substrate made of inorganic glass. Although the thickness of a transparent substrate does not have limitation in particular, Usually, it can be 0.2 mm-1.5 mm, Preferably it is 0.3 mm-1.1 mm. If necessary, the transparent substrate may be provided with a surface treatment layer made of an inorganic material or an organic material for the purpose of preventing alkali elution, improving adhesion, preventing reflection or hard coating.

  Next, an orientation process is performed on the surface of the transparent substrate.

For example, an alignment film is formed on a transparent substrate, and an alignment process is performed on the alignment film. The alignment film only needs to have a function of aligning liquid crystals. For example, an organic material such as polyimide, polyamide, polyvinyl alcohol, polyvinyl cinnamate, and polystyrene, or an inorganic material such as SiO ₂ and Al ₂ O ₃ is used. Can be used. Specifically, the alignment treatment can be performed using a rubbing method or the like. For example, the surface of the alignment film is rubbed in one direction with a rubbing cloth such as cotton, wool, nylon, rayon and polyester so that the liquid crystal molecules are aligned in that direction. Note that the transparent substrate may be subjected to alignment treatment by directly rubbing the surface of the transparent substrate with a rubbing cloth without providing the alignment film. Besides the rubbing method, the alignment of the liquid crystal molecules can be made uniform by oblique SiO deposition, ion beam method, photo-alignment film, or the like.

  Next, an optically anisotropic material is formed on the alignment film.

  Separately from the above transparent substrate (hereinafter referred to as the first substrate), a second substrate having an alignment film formed on the surface is newly prepared. This alignment film may be formed in the same manner as the first substrate. Next, a mold release process is performed on the surface of the second substrate on the side where the alignment film is formed. As the release agent, for example, a fluorosilane-based or fluorine-containing polymer having a fluorine-containing aliphatic ring structure can be used. Next, the first substrate is overlapped with the second substrate with a gap and temporarily bonded. At this time, the surface of the second substrate that has been subjected to the mold release process and the surface of the first substrate on which the alignment film is formed face each other. Moreover, the opening part which can be filled with polymeric liquid crystalline composition from the outside is provided. Next, the polymerizable liquid crystal composition of the present invention is injected between the substrates through this opening. For the injection, a vacuum injection method may be used, or a method utilizing capillary action in the atmosphere may be used. After injecting the polymerizable liquid crystalline composition, the polymerizable liquid crystalline composition is polymerized by irradiating light of a predetermined wavelength. If necessary, heat treatment may be further performed after the light irradiation. Thereafter, by removing the temporarily bonded second substrate, a structure in which an alignment film and an optically anisotropic material are formed on the first substrate can be obtained. In the present embodiment, the polymerizable liquid crystal composition is oriented in a direction substantially parallel to the surface of the first substrate, and the optically anisotropic material is obtained in a state where this orientation is fixed.

  Moreover, formation of an optically anisotropic material can also be performed as follows, for example.

  First, a first substrate having an alignment film formed thereon and a second substrate having an alignment film formed thereon and a release agent applied thereto are prepared. Next, the polymerizable liquid crystalline composition of the present invention is dropped onto the alignment film formed on the first substrate. Thereafter, the second substrate is overlapped with the first substrate such that the application surface of the release agent is on the polymerizable liquid crystalline composition side. Next, the polymerizable liquid crystal composition is polymerized by irradiating light of a predetermined wavelength. Thereafter, when the second substrate is removed, a structure in which an alignment film and an optically anisotropic material are formed on the first substrate can be obtained in the same manner as described above.

  In the above two examples, the second substrate is removed. However, the optically anisotropic material can be used for the optical element while being sandwiched between the first substrate and the second substrate. In this case, when the first substrate and the second substrate are overlapped and bonded, the substrate interval is controlled by using a sealing material mixed with a spacer. In addition, spacers for controlling the substrate gap may be sprayed on the in-plane portion where the sealing material is not provided. Polymerization of the polymerizable liquid crystalline composition is performed after the composition is injected between the substrates through an opening provided in a part of the sealing material, and then the opening is sealed with an adhesive. For the injection, a vacuum injection method may be used, or a method utilizing capillary action in the atmosphere may be used. Further, without providing an opening in the sealing material, a through hole is formed in one of the substrates, and after pouring the polymerizable liquid crystal composition from the through hole, the through hole may be sealed with an adhesive. it can. Furthermore, after a sealing material is applied to the periphery of the first substrate, the liquid crystalline composition may be dropped on the inside thereof, and the second substrate may be overlaid from above. According to this method, liquid crystal can be injected and sealed at the same time.

  The optically anisotropic material of the present invention can be used as a material for an optical element. This optically anisotropic material has good light resistance to blue laser light. Therefore, even if the optical element using this is exposed to blue laser light, it is possible to suppress occurrence of aberration, decrease in transmittance, and fluctuation in Rd value over time. The

  Examples of the optical element of the present invention include an optical element used for a purpose of modulating the phase state and / or wavefront state of blue laser light. Specifically, a diffraction element such as a polarization hologram or a phase plate mounted on the optical head device can be used. An example of a polarization hologram is an example in which light emitted from a laser light source is reflected by an information recording surface of an optical disc, and signal light generated thereby is separated and guided to a light receiving element. Examples of phase plates that are used as half-wave plates to control the phase difference of the light emitted from the laser light source, or examples that are installed in the optical path as quarter-wave plates to stabilize the output of the laser light source. Etc. Further, as other examples, a phase plate for a projector, a polarizer, and the like can be given.

  The method for manufacturing an optical element includes the above-described method for forming an optically anisotropic material. However, in the above example, only the alignment film was touched for the sake of simplicity of explanation. However, by providing an electrode for the purpose of controlling optical characteristics or providing a reflective film for the purpose of use as a reflective element, It can be set as an element. Further, depending on the purpose, it is possible to provide a Fresnel lens configuration, a diffraction grating, a colored layer for color tone adjustment, a low reflection layer for suppressing stray light, or the like on the surface of the substrate.

  The optical element of the present invention may be a combination of two optical elements. Further, the optical element may be used in combination with another optical element such as a lens, a wavefront correction surface, a phase difference plate, a diaphragm or a diffraction grating. When two optical elements are combined, the optical elements using two substrates may be formed and then stacked, or two liquid crystal layers may be formed in the three substrates. Good.

  The diffraction grating which is an example of the optical element of the present invention will be described below.

  In the diffraction grating, first members made of the first material containing the optically anisotropic material of the present invention and second members made of the second material having an isotropic refractive index are alternately arranged. And has a lattice-like structure. By alternately arranging the first member and the second member, the light transmitted through these members interfere with each other and diffract. Moreover, since the 1st material which comprises a 1st member differs from the 2nd material which comprises a 2nd member, a phase difference arises between the light which permeate | transmits these. Here, it is preferable that the first member and the second member are alternately arranged at a substantially constant pitch. Thereby, the interference between the light diffracted through the first member and the light diffracted through the second member becomes good, and the diffraction efficiency can be improved. The first member and the second member are preferably in contact with each other. As a result, light incident on portions other than these can be reduced or eliminated, so that light incident on the diffraction grating can be used effectively. The diffraction grating may include a member other than the first member and the second member.

  In the above example, when the first material is processed into a lattice shape to form the first member, a processing method by plasma etching is generally employed. Here, since the polymerizable liquid crystalline composition of the present invention can increase the crosslinking density while maintaining liquid crystallinity, the obtained optically anisotropic material is a material excellent in light resistance. Therefore, the damage that the optically anisotropic material receives when the first material is plasma-etched is smaller than that of the material that does not use the polymerizable liquid crystalline composition of the present invention.

  The optical element of the present invention is suitable for use in an optical information processing reproducing apparatus that records information on an optical recording medium and / or reproduces information recorded on the optical recording medium. For example, the optical element according to the present invention is preferably arranged in the optical path of the laser beam of the optical head device. Particularly, it is suitable for an optical head for an optical head device using blue laser light such as BD (Blue-ray Disk) and HDDVD (High-Definition Digital Versatile Disk).

  For example, in an optical head device provided with the above diffraction grating, light reflected from the optical recording medium is diffracted by the diffraction grating. In addition to the diffraction grating, this optical head device includes a light source that generates light incident on the diffraction grating, an objective lens that condenses the light emitted from the light source onto the optical recording medium, and the light reflected by the optical recording medium. It is possible to have a detector for detecting.

  FIG. 1 shows an example of an optical head device according to the present invention.

  In FIG. 1, the light emitted from the light source 1 passes through the diffraction grating 2 and is condensed on the optical disk 4 by the objective lens 3. Next, the light reflected by the optical disk 4 passes through the objective lens 3 again, and is diffracted by the diffraction grating 2 to reach the photodetector 5. As the light source 1, a normal laser light source used in a normal optical head device is used. Specifically, a semiconductor laser is suitable, but other lasers may be used. Since the diffraction grating of the present invention has good light resistance to blue laser light, the capacity of the optical head device can be increased by using blue laser light as a light source. In FIG. 1, the diffraction grating 2 functions as a hologram beam splitter. Then, by inserting the quarter wavelength plate 6 between the diffraction grating 2 and the optical disc 4, the polarization direction of the linearly polarized light emitted from the light source 1 can be rotated 90 degrees between the forward path and the return path. . As a result, the transmittance can be increased for the light in the forward polarization direction, and the diffraction efficiency can be increased for the light in the backward polarization direction. Further improvement can be achieved.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

  Examples of the present invention and comparative examples will be described below.

Example 1.
<Adjustment of polymerizable liquid crystalline composition>
As the compound represented by the above formula (1), the following compound (1-1) and compound (1-2) were used. Moreover, the following compound (2-1) and compound (2-2) were used as a compound represented by Formula (2). Furthermore, the following compound (3-1) and compound (3-2) were used as a compound represented by Formula (3).

  These were mixed in the ratios shown in Table 1 to prepare polymerizable liquid crystal compositions S1 to S3. In addition, 0.5 mass% of “Irgacure 754” (trade name) manufactured by Ciba Specialty Chemicals was added to each composition as a photopolymerization initiator.

  As shown in Table 1, good liquid crystallinity was confirmed in all of the compositions S1, S2 and S3.

Example 2
<Production of optical elements K1 to K3>
First, two glass substrates having a length of 5 cm, a width of 5 cm, and a thickness of 0.5 mm were prepared, and a polyimide solution was applied to each glass substrate with a spin coater and dried. Then, each of the obtained polyimide films was rubbed with nylon cloth in a certain direction to obtain an alignment film. Next, after applying a release agent on the alignment film of one glass substrate, this substrate was bonded to the other glass substrate through an epoxy-based sealing material to obtain a cell. At this time, the surfaces on which the alignment films were formed were made to face each other, and the directions of the alignment treatment performed on the respective glass substrates were made the same. Further, glass beads having a diameter of 3 μm were added to the sealing material so that the distance between the glass substrates was 3 μm.

The polymerizable liquid crystal composition S1 of Example 1 was injected into the obtained cell. Next, the polymerizable liquid crystalline composition S1 is subjected to photopolymerization by irradiating UV light having an intensity of 50 mW / cm ^{2 so} that the integrated light amount becomes 9,000 mJ / cm ² at a temperature at which the composition exhibits a liquid crystal phase. It was. Thereby, an optical element K1 was obtained. In addition, after injecting the polymerizable liquid crystalline composition S2 of Example 1 into another cell produced in the same manner as described above, photopolymerization was performed in the same manner as the polymerizable liquid crystalline composition S1 to obtain an optical element K2. Obtained. Furthermore, also about polymerizable liquid crystalline composition S3, after inject | pouring into the cell produced by the same method, photopolymerization similar to the above was performed and the optical element K3 was obtained.

  When the optical elements K1, K2, and K3 were observed, it was found that the liquid crystal was horizontally aligned in the rubbing direction of the substrate. Each optical element was transparent in the visible light region, and no scattering was observed. Table 2 shows the polymerization conditions of each composition and the results of measuring the Δn value of each optical element with respect to laser light having a wavelength of 405 nm.

Example 3 FIG.
<Evaluation of optical elements K1 to K3>
The optical elements K1, K2, and K3 obtained in Example 2 were irradiated with a Kr laser (multimode with wavelengths of 407 nm and 413 nm), and the light resistance of each optical element to blue laser light was evaluated. The irradiation conditions were set to a temperature of 80 ° C. and an integrated exposure energy of 40 W · hour / mm ² .

  The change in transmittance (wavelength: 405 nm) at the blue laser light irradiated portion after the test was less than −0.5% in all of the optical elements K1, K2, and K3. In addition, the variation in aberration was less than 5 mλ in all of the optical elements K1, K2, and K3 (λ = 405 nm). Furthermore, in any of the optical elements K1, K2, and K3, the fluctuation of the Rd value was less than 1%, and no deterioration was observed.

Comparative Example 1
<Adjustment of polymerizable compositions S4 and S5>
Polymerizable composition S4 which does not contain the compound represented by the formula (1) described above, and the polymerizable composition which does not contain any of the compound represented by the formula (1) and the compound represented by the formula (2) S5 was adjusted.

  The compound (2-1), the compound (2-2), the compound (3-1) and the compound (3-2) of Example 1, the compound (4-1) and the compound (4- 2) were mixed at a ratio shown in Table 3 to prepare polymerizable liquid crystal compositions S4 and S5. In addition, 0.5 mass% of “Irgacure 754” (trade name) manufactured by Ciba Specialty Chemicals was added to each composition as a photopolymerization initiator.

  As shown in Table 3, although the compound of Formula (1) was not included, good liquid crystallinity was confirmed in the polymerizable composition S4 including the compounds of Formula (2) and Formula (3). On the other hand, the polymerizable composition S5 containing the compound of the formula (3) but not containing the compounds of the formulas (1) and (2) did not exhibit liquid crystallinity.

Comparative Example 2
<Production of optical element K4>
Into a cell produced in the same manner as in Example 2, the polymerizable composition S4 of Comparative Example 1 was injected at a temperature of 90 ° C. Next, the polymerizable composition S4 was subjected to photopolymerization by irradiating ultraviolet rays having an intensity of 50 mW / cm ² at a temperature of 70 ° C. so that the integrated light amount was 9,000 mJ / cm ² . Thereby, an optical element K4 was obtained.

  When the optical element K4 was observed, it was found that the liquid crystal was horizontally aligned in the rubbing direction of the substrate. Further, the optical element K4 was transparent in the visible light region, and no scattering was observed. Furthermore, when the Δn value of each optical element with respect to laser light having a wavelength of 405 nm was measured, it was 0.03.

Comparative Example 3
<Evaluation of optical element K4>
The optical element K4 obtained in Comparative Example 2 was irradiated with a Kr laser (multimode with wavelengths of 407 nm and 413 nm) to evaluate the light resistance against blue laser light. The irradiation conditions were a temperature of 80 ° C. and an integrated exposure energy of 40 W · hour / mm ² .

  The change in transmittance (wavelength: 405 nm) at the blue laser light irradiation site after the test was less than −0.5%, and the variation in aberration was less than 5 mλ (λ = 405 nm), but the Rd value was 10%. The deterioration was observed, and deterioration at the irradiated site was confirmed.

  Since the polymerizable liquid crystalline composition of the present invention has high light resistance to blue light and desired liquid crystal properties are easily obtained, various optical elements, in particular, optical disks and optical elements that use strong blue light are used. It can be suitably used for applications where a refractive index material is required. Furthermore, this optical element can be used for a diffraction grating, a hologram element, a lens element, an aberration correction element, a retardation plate, and the like, and is particularly suitable for an optical head device using blue laser light.

It is an example of the block diagram of the optical head apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Diffraction grating 3 Objective lens 4 Optical disk 5 Optical detector 6 1/4 wavelength plate

Claims (7)

The compound represented by the following formula (1) is 15 to 60% by mass, the compound represented by the following formula (2) is 15 to 30% by mass, and the compound represented by the following formula (3) is 25 to 55% by mass. Including
_{^{CH 2 = CX 1 -COO-L}} 1 -B 1 -A 1 -B 2 -Cy-Cy-B 3 -A 2 -B 4 -L 2 -OCO-CX 2 = CH 2 (1)
_{^{CH 2 = CX 3 -COO-L}} 3 -B 5 -A 3 -B 6 -Cy-B 7 -A 4 -B 8 -R 1 (2)
_{^{CH 2 = CX 4 -COO-L}} 4 -B 9 -Cy-B 10 -Cy-B 11 -R 2 (3)
X ^{1 to} X ⁴ are each independently a hydrogen atom or a methyl group,
B ^{1 to} B ¹¹ are each independently a single bond, —COO— or —OCO—,
L ¹ , L ³ and L ⁴ are each independently — (CH ₂ ) _n —O—, — (CH ₂ ) _n — or a single bond when B ¹ , B ⁵ and B ⁹ are a single bond, When B ¹ , B ⁵ and B ⁹ are —COO— or —OCO—, it is — (CH ₂ ) _n — (in this case, n is an integer of 1 to 12), and the carbon-carbon of the alkylene group It may have an etheric oxygen atom between the bonds, and part or all of the hydrogen atoms may be substituted with fluorine atoms,
L ^2, when ^{B 4} is a single bond _{-O- (CH 2) m -,} - (CH 2) m - or a single bond, when ^{B 4} is -COO- or -OCO- of - (CH ₂ ) _M- (where m is an integer of 1 to 12 in any case), and may have an etheric oxygen atom between the carbon-carbon bonds of the alkylene group. Part or all may be substituted with a fluorine atom,
A ^{1 to} A ⁴ are each independently a 1,4-phenylene group or a trans-1,4-cyclohexylene group, and some or all of the hydrogen atoms may be substituted with fluorine atoms,
R ¹ and R ² are each independently an alkyl group having 1 to 12 carbon atoms, and some or all of the hydrogen atoms may be substituted with fluorine atoms,
Cy is a trans-1,4-cyclohexylene group, and a part or all of a hydrogen atom may be substituted by a fluorine atom, The polymerizable liquid crystalline composition characterized by the above-mentioned.   The polymerizable liquid crystalline composition according to claim 1, wherein the compound represented by the formula (1) exhibits liquid crystallinity. The polymerizable property according to claim 2, wherein A ¹ and A ^{2 in} the formula (1) are 1,4-phenylene groups in which some or all of hydrogen atoms may be substituted with fluorine atoms. Liquid crystalline composition. A ³ and A ^{4 in} the formula (2) are trans-1,4-cyclohexylene groups in which some or all of hydrogen atoms may be substituted with fluorine atoms. 4. The polymerizable liquid crystal composition according to any one of 3 above.   An optically anisotropic material comprising a polymer of the polymerizable liquid crystalline composition according to any one of claims 1 to 4.   An optical element comprising the optically anisotropic material according to claim 5. An optical head device comprising the optical element according to claim 6.