JP2003075799A - Blue light diffraction element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer liquid crystal having small wavelength dispersion of a refractive index and a small refractive index and absorption in a wavelength region of blue color and to provide a polymerizable liquid crystal composition to obtain the polymer liquid crystal and a blue light diffraction element using the polymer liquid crystal. SOLUTION: The blue light diffraction element having a diffraction grating formed of the polymer liquid crystal obtained by polymerizing the polymerizable liquid crystal composition containing at least a kind of polymerizable liquid crystal compound having a saturated carbon ring or a saturated heterocycle is provided.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a blue light diffraction element,
And a polymerizable liquid crystal composition for producing the same.

[0002]

2. Description of the Related Art A polymerizable liquid crystal compound having a polymerizable functional group in a liquid crystal molecule (hereinafter also referred to as a polymerizable liquid crystal monomer).
Has both a property as a polymerizable monomer and a property as a liquid crystal. Therefore, when the polymerizable liquid crystal monomer is polymerized in an oriented state, a polymer in which the orientation is fixed, that is, a polymer liquid crystal is obtained. The polymer liquid crystal thus obtained has optical anisotropy based on the refractive index anisotropy of the liquid crystal skeleton, and can impart special characteristics by controlling the liquid crystal alignment state. It is applied to devices.

Among such polymerizable liquid crystal monomers,
In particular, a photopolymerizable liquid crystal monomer having a photopolymerizable functional group is an excellent compound that can easily produce a polymer liquid crystal by irradiating light to polymerize it.

As described in Japanese Patent Application Laid-Open No. 11-211905, a polarization hologram using this polymer liquid crystal exhibits high light utilization efficiency due to its excellent polarization dependence. At this time, if the lattice gap of the polymer liquid crystal is filled with a filler and the refractive index of the filler is matched with the ordinary light refractive index of the polymer liquid crystal, the 0th-order transmittance becomes maximum. Further, assuming that the grating height d, the refractive index anisotropy Δn of the polymer liquid crystal, and the wavelength λ, the diffraction efficiency of the ± 1st order becomes maximum when Δn · d = λ / 2 is satisfied.

In recent years, the wavelength of light has been shortened in order to increase the capacity of optical disks. Currently, CDs and DVDs use semiconductor laser light with wavelengths of 780 nm and 650 nm, but next-generation DVDs that follow these have wavelengths of 300 nm.
Development of an optical disk for using a blue laser beam of up to 450 nm is in progress. Along with this, an optical element that diffracts the light used in the optical head (hereinafter, also referred to as a diffraction element).
As for the above, it is necessary to develop a polymer liquid crystal (hereinafter, also referred to as a material) for a blue light diffractive element, which is compatible with blue light.

The requirements for the material for the diffractive element are (1) the molar absorption coefficient of the material at the oscillation wavelength of the light source, which affects the transmission characteristics of the light used, is as small as possible (2) Japanese Patent Laid-Open No. 11-211905. When a polarization hologram, which is a kind of diffractive element, is formed by forming a grating of a birefringent medium as described and filling a transparent filler having a refractive index equal to the ordinary refractive index of the polymer liquid crystal, The optical properties (refractive index and wavelength dispersion of refractive index) of the material for use and the transparent filler are well matched.

In general, a polymer liquid crystal used for a conventional CD or DVD diffractive element has a drastic change in refractive index when the wavelength band of light used is 450 nm or less.
That is, it is a material having a large refractive index wavelength dispersion. Also,
The method of changing the refractive index greatly differs depending on the material.
Since light having a wavelength of 450 nm or less is used in the next-generation DVD, it is difficult to match the refractive index between the material and the transparent filler with the conventional diffractive element material. (B) When the oscillation wavelength of the light source set at the initial stage is deviated, the transmittance decreases when transmitting light, and the diffraction efficiency decreases due to the generation of higher-order diffracted light when diffracting light. There was a problem.

Among the conventional polymer liquid crystals used in the diffractive elements for CDs and DVDs, those having a high refractive index and a high refractive index anisotropy are used in order to achieve miniaturization and high efficiency of the element. It has been used a lot. In general, a material having a high refractive index has a large refractive index wavelength dispersion, and the refractive index tends to increase particularly at shorter wavelengths. Also generally,
A material having a large refractive index wavelength dispersion also absorbs light with an increase in the refractive index at a short wavelength. Therefore, the conventional diffractive element material also has a problem that the transmittance of short wavelength light such as blue light is low.

[0009]

DISCLOSURE OF THE INVENTION An object of the present invention is that the wavelength dispersion of the refractive index is small, and the wavelength band of blue light (300 to 4).
A blue light diffractive element using a polymer liquid crystal having a small refractive index at 50 nm) and a small light absorption, and a polymerizable liquid crystal composition for producing the same.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides a diffraction formed by a polymer liquid crystal obtained by polymerizing a polymerizable liquid crystal composition containing at least one polymerizable liquid crystal compound having a saturated carbon ring or a saturated heterocycle. A blue light diffractive element having a grating is provided.

The present invention is a polymerizable liquid crystal containing at least one polymerizable liquid crystal compound having a saturated carbocycle or a saturated heterocycle represented by the following formula 1 (hereinafter also referred to as compound 1 and the same in other cases). Provided is a blue light diffraction element having a diffraction grating formed of a polymer liquid crystal obtained by polymerizing a composition.

[0012] _{^{CH 2 = CR 1 -X 1 -}} (Y 1) m -Z 1 - (E 1) p -Z 2 -E 2 -Z 3 - E 3 -Z 4 - (E 4) q -Z 5 -R ² ... Formula 1 The symbols in the formula have the following meanings. R ¹ : a hydrogen atom or a methyl group. R ² : an alkyl group which may have a substituent, a hydrogen atom, a halogen atom or a cyano group. X ¹ : a single bond, -COO-, -OCO- or -O-. _{^{Y 1: -CH 2 -, -}} OCH 2 CH 2 - or -CH ₂
CH ₂ O-. m: an integer of 0 to 10. ^{Z 1, Z 2, Z 3} , Z 4, Z 5: each independently represent a single bond, -O -, - OCO -, - COO -, - CO -, - C
ONH-, -NHCO-, -NH-, -C≡C-, -C
_{H = CH -, - CH 2} CH 2 -, - N = CH -, - CH
= N- or -N = N-. E ¹ , E ² , E ³ , E ⁴ : each independently a divalent ring group, and at least one of the existing rings is a saturated carbocycle or a saturated heterocycle. One or more hydrogen atoms in the ring may be substituted with a fluorine atom, a chlorine atom or a methyl group. p and q: 0 or 1 independently of each other.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The polymerizable liquid crystal compound according to the present invention is a polymerizable liquid crystal compound having a polymerizable functional group and a mesogenic skeleton, and a saturated carbocycle or a saturated heterocycle (hereinafter collectively referred to as a mesogen skeleton). Also referred to as a saturated ring). Since the saturated ring has a smaller polarity than the unsaturated ring, the refractive index and refractive index anisotropy of the polymer liquid crystal obtained by polymerizing the polymerizable liquid crystal composition containing the polymerizable liquid crystal compound have a saturated ring. The value is lower than that of no polymer liquid crystal. Generally, wavelength dispersion of a polymer liquid crystal having a low refractive index is small. Particularly, in the case of light having a short wavelength such as blue light, the polymer liquid crystal of the present invention has a value smaller than the refractive index of the polymer liquid crystal having no saturated ring. In general, a material having a small refractive index wavelength dispersion has a small increase in absorption of light with an increase in the refractive index at a short wavelength.

The saturated carbocycle is a saturated cyclic compound composed of carbon atoms and hydrogen atoms, and the number of carbon atoms constituting the ring is preferably 3-10. The saturated heterocycle is a saturated cyclic compound composed of carbon atoms, hydrogen atoms and heteroatoms, and the number of atoms constituting the ring is preferably 3-10. Further, examples of the hetero atom include an oxygen atom, a sulfur atom and a nitrogen atom. Examples of the saturated ring include a cyclopentane ring, a cyclohexane ring, a bicyclo [2.2.2] octane ring and a dioxane ring, and a cyclohexane ring is preferable. 2 consisting of these rings
As the valent ring group, a trans-1,3-cyclopentylene group, a trans-1,4-cyclohexylene group, a 1,4-bicyclo [2.2.2] octylene group as described below,
There is a trans-1,3-dioxane-2,5-diyl group.

[0015]

[Chemical 1]

A liquid crystal compound having a cyclohexane ring and a polymerizable liquid crystal composition containing the compound are preferable because they have a low melting point and a stable liquid crystal phase is easily developed at room temperature.

The polymerizable liquid crystal compound having a saturated ring in the present invention is preferably Compound 1.

E ¹ , E ² , E ³ , and E ⁴ are each independently a divalent ring group, and at least one of the existing rings is
One is a saturated carbocycle or a saturated heterocycle. The existing ring means E ² and E ³ which include E ¹ when p is 1 and include E ⁴ when q is 1. One or more hydrogen atoms in the ring may be substituted with a fluorine atom, a chlorine atom or a methyl group.

A specific divalent ring group is trans-
1,3-cyclopentylene group, trans-1,4-cyclohexylene group, 1,4-bicyclo [2.2.2] octylene group, trans-1,3-dioxane-2,5-diyl group, 1 , 4-phenylene group, 2,6-naphthalenediyl group, 2,5-pyridinediyl group, 2,5-pyrimidinediyl group, 3,6-pyrandiyl group and the like. Preferred are a trans-1,4-cyclohexylene group and a 1,4-phenylene group.

Compound 1 is optionally substituted 1,4
In the case of having a phenylene group, the compound is preferable because it exhibits liquid crystallinity in a wide temperature range. Further, when the hydrogen atom of the divalent ring group of Compound 1 is replaced, the melting point is generally lowered, and particularly when it is replaced by a fluorine atom, the viscosity is lowered. Substituents can be selected according to the purpose.

The spacer (Y ¹ ) _m in compound 1 is
The shorter the length, the harder the polymer liquid crystal after polymerization and the smaller the temperature dependence of the refractive index anisotropy, which is preferable. m = 0, Y ¹
Is —CH ₂ — and m = 1 to 6, or Y ¹ is —CH ₂
It is preferable that CH ₂ O- and m = 1 to 2.

Z ¹ , Z ² , Z ³ , Z ⁴ and Z ⁵ are each independently a single bond, --O--, --OCO--, --COO--,
-CO-, -CONH-, -NHCO-, -NH-,-
C≡C -, - CH = CH - , - CH 2 CH 2 -, - N =
CH-, -CH = N- or -N = N-, but among them, a single bond, -O-, -OCO-, -COO-, -CO.
— Or —CH ₂ CH ₂ — is preferable because the refractive index anisotropy becomes small. Especially single bond, -O-, -OCO
— Or —CH ₂ CH ₂ — is preferable because the melting points of the compound 1 and the composition containing it are low. A low melting point is preferable because the composition exhibits liquid crystallinity in a wide temperature range.

X ¹ is a single bond, --COO--, --OCO--.
Or it is -O-, and -COO- is preferable.

R ¹ is a hydrogen atom or a methyl group,
A hydrogen atom is preferred.

R ² is an alkyl group which may have a substituent, a hydrogen atom, a halogen atom or a cyano group,
Of these, an alkyl group in which a hydrogen atom may be substituted with a fluorine atom or a chlorine atom is preferable because Compound 1 has a low melting point and exhibits liquid crystallinity in a wide temperature range. Further, the polymer liquid crystal obtained by polymerizing the composition containing the compound has a low refractive index anisotropy. Among the alkyl groups, those having 1 to 10 carbon atoms are more preferable.

The compound 1 is preferably a compound represented by the formula 2. _{^{CH 2 = CR 1 -X 1 -E}} 2 -Z 3 -E 3 -R 2 ··· formula ^{2 R 1, X 1, E} 2, Z 3, E 3, R 2 are each Formula 1
Is the same as in.

As the compound 1, for example, a compound represented by the following formula 3 is suitable. _{CH 2 = CH-COO-Ph} -OCO-Cy-R 3 ··· Equation 3 Ph is more one hydrogen atom in the group, a fluorine atom, or 1 to be substituted by a chlorine atom or a methyl group, A 4-phenylene group, Cy is a trans-1,4-cyclohexylene group in which a hydrogen atom in the group may be substituted, and R ³ is an alkyl group having 1 to 8 carbon atoms. Ph and C described below
y also represents the same group as above.

Specifically, 4- (trans-4'-n-propylcyclohexylcarbonyloxy) phenyl acrylate, 4- (trans-4'-n-butylcyclohexylcarbonyloxy) phenyl acrylate, 4-
(Trans-4′-n-pentylcyclohexylcarbonyloxy) phenyl acrylate, 4- (trans-
4'-n-hexylcyclohexylcarbonyloxy)
Phenyl acrylate is preferably exemplified.

The polymerizable liquid crystal composition in the present invention includes, in addition to Compound 1, a polymerizable liquid crystal compound other than Compound 1, a polymerizable non-liquid crystal compound, a non-polymerizable liquid crystal compound, and a non-polymerizable non-liquid crystal compound (hereinafter collectively referred to as "Compound 1"). Therefore, it is desirable to add other compounds as appropriate) to obtain a composition having desired properties. The ratio of the polymerizable liquid crystal compound having a saturated ring in the composition is preferably 10% (based on mass, the same applies hereinafter) or more. When it is 10% or more, the refractive index anisotropy of the composition becomes small and the wavelength dispersion of the refractive index becomes small, which is preferable. More preferably, it is 10 to 90%.

Other compounds are preferably contained in the composition in an amount of 10 to 90%, and one kind or a combination of two or more kinds can be used.

When the polymerizable non-liquid crystal compound and / or the non-polymerizable non-liquid crystal compound is contained, the ratio of the compound in the composition is not particularly limited as long as the composition has a liquid crystallinity. In the case of containing a non-polymerizable liquid crystal compound and / or a non-polymerizable non-liquid crystal compound, the ratio of the compound in the composition may be within a range in which the polymer liquid crystal polymerized with the composition becomes a solid. It is not particularly limited.

As the other compound, for example, a polymerizable liquid crystal compound represented by the formula 4 is preferable since it has a low melting point and a low refractive index anisotropy. _{CH 2 = CH-COO-Ph} -OCO-Ph-R 4 ··· formula 4 ^{R 4} represents an alkyl group having 1 to 8 carbon atoms.

Specifically, 4- (4'-n-propylphenylcarbonyloxy) phenyl acrylate, 4-
(4'-n-butylphenylcarbonyloxy) phenyl acrylate, 4- (4'-n-pentylphenylcarbonyloxy) phenyl acrylate, 4- (4'-
Preferable examples are n-hexylphenylcarbonyloxy) phenyl acrylate.

As the other compound, the polymerizable liquid crystal compound represented by the formula 5 is also preferable because it has a low melting point and exhibits liquid crystallinity in a wide temperature range. _{CH 2 = CHCOO-Ph-OCO} -Ph-OCOO-R 5 ··· formula 5 ^{R 5} is a straight alkyl group having 1 to 8 carbon atoms.

Concretely, 4- (4 '-(n-propoxycarbonyloxy) benzoyloxy) phenyl acrylate, 4- (4'-(n-butoxycarbonyloxy) benzoyloxy) phenyl acrylate, 4-
(4 '-(n-pentyloxycarbonyloxy) benzoyloxy) phenyl acrylate, 4- (4'-
(N-Hexyloxycarbonyloxy) benzoyloxy) phenyl acrylate is preferably exemplified.

The polymerizable liquid crystal composition in the present invention desirably exhibits a liquid crystal phase in a wider range, and is -30 to 15
It is preferably adjusted so as to develop a liquid crystal phase in a temperature range of 0 ° C., further -10 to 120 ° C.

The polymerizable liquid crystal composition in the present invention is
The composition is preferably adjusted so that the molar extinction coefficient is 5 or less at a wavelength of 340 nm, and further 0.1 or less at a wavelength of 405 nm.

The polymer liquid crystal in the present invention is obtained by polymerizing the polymerizable liquid crystal composition. Examples of the polymerization method include a photopolymerization method and a thermal polymerization method, and the photopolymerization method is preferable. In the photopolymerization method, it is preferable to polymerize the polymerizable liquid crystal composition in an oriented state. Further, in the case of photopolymerization, the use of a photopolymerization initiator enables efficient polymerization. The photopolymerization initiator is not particularly limited, but acetophenones, benzophenones, benzoins, benzyls, Michler's ketones, benzoin alkyl ethers, benzyl dimethyl ketals, thioxanthones and the like can be preferably used. The photopolymerization initiator may be used alone or in combination of two or more. The amount of the photopolymerization initiator used is preferably 0.1 to 10%, and particularly preferably 0.3 to 2% with respect to the composition.

Examples of the light used for photopolymerization include ultraviolet rays and visible rays. At this time, glass, plastic or the like can be used as the support of the polymerizable liquid crystal composition. The surface of the support is subjected to orientation treatment. The orientation treatment may be carried out by directly rubbing the surface of the support with natural fibers such as cotton and wool, synthetic fibers such as nylon and polyester, or after coating polyimide or polyamide on the coated surface with the above fibers or the like. You may. Next, spacers such as glass beads are arranged on the surface of the support, a plurality of the supports are controlled to face each other at desired intervals, and the polymerizable liquid crystal composition of the present invention is injected and filled between the supports. .

In order to polymerize the polymerizable liquid crystal composition in the oriented state, it is preferable to keep the composition in the liquid crystal state during the polymerization. In order to maintain the liquid crystal state, the ambient temperature may be set in the range from the melting point _Tm to the nematic phase-isotropic phase transition point _Tc . However, since the refractive index anisotropy is extremely small at a temperature close to _Tc , the upper limit of the ambient temperature is ( _Tc- 1).
0) C. or less is more preferable.

The polymer liquid crystal of the present invention has a wavelength of 400 to 45.
If the ordinary refractive index in 0 nm light is 1.6 or less,
When the wavelength of the light used is 450 nm or less, it is preferable because the refractive index is not rapidly changed and the material has a small molar absorption coefficient.

The polymer liquid crystal of the present invention may be used while being sandwiched between supports, or may be used by peeling it from the supports.

When the polymerizable liquid crystal composition is polymerized in a non-aligned state, the obtained polymer liquid crystal is aligned and a diffractive element is prepared from the aligned polymer liquid crystal. For example, a polymer liquid crystal solution can be applied to the surface of a support that has been subjected to an alignment treatment and dried to form a coating film made of an aligned polymer liquid crystal.

The polymer liquid crystal thus produced is suitable for the blue light diffraction element of the present invention, and an optical head can be produced using the blue light diffraction element. The blue light diffraction element of the present invention may be a polarization hologram element. By using this polarization hologram element in an optical head having a blue light source, an optical head for a blue light source with high light utilization efficiency can be manufactured.

[0045]

Examples [Example 1: Preparation of liquid crystal composition containing compound 1]
4- (4′-n-butylphenylcarbonyloxy) phenyl acrylate (Compound 6 below, also referred to as A1 below), 4- (4′-n-pentylphenylcarbonyloxy) phenyl acrylate (Compound 7 below, A below)
Also called 2. ), 4- (4′-n-hexylphenylcarbonyloxy) phenyl acrylate (Compound 8 below, hereinafter also referred to as A3), 4- (trans-4′-n).
-Propylcyclohexylcarbonyloxy) phenyl acrylate (compound 9 below, hereinafter also referred to as A4),
4- (trans-4′-n-pentylcyclohexylcarbonyloxy) phenyl acrylate (compound 1 below
0, hereinafter also referred to as A5. ) Was used to prepare a composition B1. The composition ratio of the composition B1 is a mass ratio of A1: A2: A.
3: A4: A5 = 0.2: 0.2: 0.2: 0.2:
It was set to 0.2. _{CH 2 = CHCOOPh-OCO-Ph} -C 4 H 9 ··· Formula _{6 CH 2 = CHCOOPh-OCO-} Ph-C 5 H 11 ··· Formula _{7 CH 2 = CHCOOPh-OCO-} Ph-C 6 H 13 · ... equation _{8 CH 2 = CHCOOPh-OCO-} Cy-C 3 H 7 ··· equation _{9 CH 2 = CHCOOPh-OCO-} Cy-C 5 H 11 ··· formula 10 the composition B1 in nematic liquid crystal at room temperature Yes, Tc was 71 ° C. Also, this composition has a temperature of 25 ° C. and 589 nm
The refractive index anisotropy Δn in was 0.127.

[Example 2: Preparation of polymer liquid crystal] 5 cm × 5 c
A polyimide solution as an orienting agent was applied to a m × 0.5 mm glass plate with a spin coater, dried, and then rubbed in a certain direction with nylon cloth to prepare a support.
Two supports were attached to each other with an adhesive so that the orientation-treated surfaces face each other to prepare a cell 1. that time,
Glass beads are mixed in the adhesive and the distance between the supports is 3μ
It was adjusted to be m.

A photopolymerization initiator "Irgacure 907 (manufactured by Ciba Geigy)" was added to the composition B1 of Example 1 by 0.2% with respect to the composition, and the mixture was injected into the cell 1 at 70 ° C. Then the accumulated light quantity of ultraviolet intensity of 80 mW / cm ² at 30 ° C. was irradiated so as to be 5300mJ / cm ^2, subjected to photopolymerization to fabricate a polymer liquid crystal D1. Polymer liquid crystal D1
Table 1 shows the refractive index at each wavelength.

[0048]

[Table 1]

[Example 3 (Comparative example): Preparation of polymer liquid crystal not containing compound 1] 4-acryloyloxy-4'-cyanobiphenyl (compound 11 below, also referred to as A6 below), 4- (3-acryloyl) Oxypropyl) oxy-4′-cyanobiphenyl (Compound 12 below, A below)
Also called 7. ), 4- (4′-n-butylphenylcarbonyloxy) phenyl acrylate (the following compound 1
3, hereinafter also referred to as A8. ), 4- (4′-n-pentylphenylcarbonyloxy) phenyl acrylate (Compound 14 below, also referred to as A9 below)
2 was produced. The composition ratio of the composition B2 is a mass ratio and is A6:
A7: A8: A9 = 0.25: 0.25: 0.25:
It was set to 0.25. CH ₂ = CHCOOPhPhCN ··· formula _{11 CH 2 = CHCOO (CH 2} ) 3 OPhPhCN ··· formula _{12 CH 2 = CHCOOPh-OCO-} Ph-C 4 H 9 ··· formula _{13 CH 2 = CHCOOPh-OCO-} Ph -C ₅ H ₁₁ · · · formula 14 the composition B2 are nematic liquid crystal at room temperature, _{T c} showed 71 ° C.. Also, this composition has a temperature of 25 ° C. and 589 nm.
The refractive index anisotropy Δn in was 0.20.

Polymer liquid crystal D2 was prepared in the same manner as in Example 2 except that the composition B2 was used. Polymer liquid crystal D
Table 2 shows the refractive index of each of the two wavelengths.

[0051]

[Table 2]

Example 2 using compound 1 having a saturated carbocycle
It was found that the polymer liquid crystal D1 of No. 1 had a low ordinary light refractive index at 405 nm of 1.6 or less, and the wavelength dispersion of the refractive index was small.

[Example 4: Application to optical element and optical head] 5
A glass substrate having a size of 5 cm x 5 cm x 0.5 mm was coated with polyimide as an aligning agent using a spin coater, dried, and then rubbed in a certain direction with nylon cloth to prepare a support. A cell 2 was produced by bonding two supports with an adhesive so that the orientation-treated surfaces face each other. At that time, glass beads were mixed into the adhesive to adjust the distance between the supports to 3 μm.

A photopolymerization initiator "Irgacure 907 (manufactured by Ciba-Geigy Co.)" was added to the composition B1 of Example 1 by 0.2% with respect to the composition, and the mixture was injected into the cell 2 at 70 ° C. Next, ultraviolet rays were irradiated at 25 ° C. to perform photopolymerization to prepare a polymer liquid crystal D1. Then, after peeling off one support from the polymer liquid crystal D1, the polymer liquid crystal D1 is etched.
A grid of 1 was formed. Then, the concave portion of the grating is
filled with a transparent filler (enthiol-based compound) whose refractive index matches the ordinary refractive index of the polymer liquid crystal D1 in nm,
A blue light diffraction element, that is, a polarization hologram for blue light was produced. The hologram has a 0-th order transmittance of 95% for light having a wavelength of 405 nm and a backward ± 1st-order diffraction efficiency of 40%.
%Met.

[Example 5 (Comparative Example)] A polarization hologram was prepared in the same manner as in Example 4 except that the composition B2 was used instead of the composition B1. Was 80%, and the diffraction efficiency in the return ± 1st order was 20%.

[0056]

The polymer liquid crystal used in the blue light diffraction element of the present invention has a small refractive index and refractive index wavelength dispersion, and therefore has a small ordinary light refractive index even for short wavelength light such as blue light. Therefore, the blue light diffraction element of the present invention is suitable as a component such as an optical head using a blue light source.

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Claims (10)

[Claims] 1. A blue light diffraction element having a diffraction grating formed of a polymer liquid crystal obtained by polymerizing a polymerizable liquid crystal composition containing at least one polymerizable liquid crystal compound having a saturated carbon ring or a saturated heterocycle. . 2. The blue light diffraction element according to claim 1, wherein the polymerizable liquid crystal compound having a saturated carbon ring or a saturated hetero ring is a polymerizable liquid crystal compound represented by the formula 1. _{^{CH 2 = CR 1 -X 1 -}} (Y 1) m -Z 1 - (E 1) p -Z 2 -E 2 -Z 3 - E 3 -Z 4 - (E 4) q -Z 5 -R 2 ... Formula 1 The symbols in the formula have the following meanings. R ¹ : a hydrogen atom or a methyl group. R ² : an alkyl group which may have a substituent, a hydrogen atom, a halogen atom or a cyano group. X ¹ : a single bond, -COO-, -OCO- or -O-. _{^{Y 1: -CH 2 -, -}} OCH 2 CH 2 - or -CH ₂
CH ₂ O-. m: an integer of 0 to 10. Z < ¹ >, Z < ² >, Z < ³ >, Z < ⁴ >, Z < ⁵ >: each independently a single bond, -O-, -OCO-, -COO-, -CO-,-.
CONH-, -NHCO-, -NH-, -C≡C-,-
_{CH = CH -, - CH 2} CH 2 -, - N = CH -, - C
H = N- or -N = N-. E ¹ , E ² , E ³ , E ⁴ : each independently a divalent ring group, and at least one of the existing rings is a saturated carbocycle or a saturated heterocycle. One or more hydrogen atoms in the ring may be substituted with a fluorine atom, a chlorine atom or a methyl group. p and q: 0 or 1 independently of each other. 3. One or more of the rings in which E ¹ , E ² , E ³ and E ⁴ are present may be trans in which one or more hydrogen atoms may be substituted with a fluorine atom, a chlorine atom or a methyl group. −
The blue light diffraction element according to claim 2, which is a 1,4-cyclohexylene group. 4. The blue light diffraction element according to claim 1, wherein the polymerizable liquid crystal compound having a saturated carbon ring or a saturated heterocycle is a compound represented by formula 2. _{^{CH 2 = CR 1 -X 1 -}} (Y 1) m -Z 1 -E 2 -Z 3 -E 3 -R 2 ··· formula ^{2 R 1, X 1, Y} 1, Z 1, Z 3, R ² is the formula 1
Is the same as in. E ² and E ³ are each independently a divalent ring group, and at least one of the rings is a saturated carbocycle or a saturated heterocycle. One or more hydrogen atoms in the ring may be substituted with a fluorine atom, a chlorine atom or a methyl group. m is an integer of 0-10. 5. The blue light diffraction element according to claim 1, wherein the polymerizable liquid crystal compound having a saturated carbon ring or a saturated hetero ring is a compound represented by formula 3. _{CH 2 = CH-COO-Ph} -OCO-Cy-R 3 ··· formula 3 ^{R 3} is an alkyl group having 1 to 8 carbon atoms. Ph is a 1,4-phenylene group in which one or more hydrogen atoms in the group may be substituted with a fluorine atom, a chlorine atom or a methyl group, and Cy is trans in which a hydrogen atom in the group may be substituted. It represents a -1,4-cyclohexylene group. 6. A polymerizable liquid crystal composition comprising a polymerizable liquid crystal compound having a saturated carbon ring or a saturated hetero ring in the composition.
The blue light diffraction element according to any one of claims 1 to 5, containing 0% (based on mass) or more. 7. The polymer liquid crystal according to claim 1, which is obtained by polymerizing the polymerizable liquid crystal composition by irradiating it with ultraviolet light or visible light in an aligned state. Blue light diffractive element. 8. The blue light diffractive element according to claim 1, wherein the polymer liquid crystal is a polymer liquid crystal having an ordinary light refractive index of 1.6 or less in light having a wavelength of 400 to 450 nm. 9. The polymerizable liquid crystal composition according to claim 1 for producing the blue light diffraction element according to claim 1. 10. An optical head comprising the blue light diffraction element according to claim 1.