JP2015114503A - Two-band cholesteric liquid crystal film and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new two-band cholesteric liquid crystal film and an efficient method of manufacturing it.SOLUTION: The cholesteric liquid crystal film is a hardened material of a liquid crystal composition containing a polymerizable mesogen compound and a chiral agent as a cyclic compound whose twist force is changed by an intramolecular dimerization reaction. In transmission spectrum measurement, a transmission spectrum is shown which includes a first selection reflection wavelength band, a second selection reflection wavelength band having a wavelength longer than the first selection reflection wavelength band, and a transmission band disposed between the first selection reflection wavelength band and second selection reflection wavelength band.

Description

  The present invention relates to a two-band cholesteric liquid crystal film and a method for producing the same.

  A cholesteric liquid crystal film is a film in which a spiral structure is formed in liquid crystal molecules by adding a chiral agent to an untwisted nematic liquid crystal and reflects circularly polarized light corresponding to the helical period (helical pitch) (selective reflection). Have a wavelength band.

  The cholesteric liquid crystal film having a plurality of selective reflection wavelength bands is, for example, a cholesteric liquid crystal film obtained by applying a liquid crystal mixture containing a polymerizable mesogenic compound and a polymerizable chiral agent to an alignment substrate and irradiating with ultraviolet rays. A cholesteric liquid crystal film is known which has a single layer of liquid crystal film and has at least two independent selective reflection wavelength bands (Patent Document 1).

JP 2004-333671 A

  According to Patent Document 1, in order for the cholesteric liquid crystal film to have at least two independent selective reflection wavelength bands, the remaining polymerizable mesogenic compound is moved with the progress of polymerization, and the polymerizable mesogenic compound in the latter half of the polymerization : It is necessary to change the mixing ratio of the polymerizable chiral agent in the film thickness direction.

  However, the migration (diffusion) of the polymerizable mesogenic compound takes time, and the production efficiency of the cholesteric liquid crystal film described in Patent Document 1 has not been sufficient.

  Therefore, the present inventors examined a chiral agent. As a result, a chiral agent that is a cyclic compound whose torsional force is changed by an intramolecular dimerization reaction, the first selective reflection wavelength band in the transmission spectrum measurement, A second selective reflection wavelength band that is longer than the first selective reflection wavelength band, and a transmission band that is between the first selective reflection wavelength band and the second selective reflection wavelength band. It has been found that a cholesteric liquid crystal film exhibiting a transmission spectrum (in this specification, sometimes referred to as “two-band cholesteric liquid crystal film”) can be efficiently produced.

  An object of the present invention is to provide a novel two-band cholesteric liquid crystal film and an efficient manufacturing method thereof.

  The present invention is a cured product of a liquid crystal composition containing a polymerizable mesogen compound and a chiral agent that is a cyclic compound whose torsional force is changed by an intramolecular dimerization reaction. A selective reflection wavelength band, a second selective reflection wavelength band that is longer than the first selective reflection wavelength band, and between the first selective reflection wavelength band and the second selective reflection wavelength band. A cholesteric liquid crystal film exhibiting a transmission spectrum having a transmission band in

  Here, the term “twisting force” (Helical Twisting Power, HTP) in the present invention means a force that a chiral agent induces torsion in the molecular arrangement of liquid crystal molecules.

  When the spiral structure of the cholesteric liquid crystal film is right-twisted (when the twist direction is right), the cholesteric liquid crystal film reflects right circularly polarized light, and when the spiral structure of the cholesteric liquid crystal film is left-twisted (twist direction is left) ), The cholesteric liquid crystal film reflects left circularly polarized light. That is, for example, when natural light is incident on a right-twisted cholesteric liquid crystal film, right-handed circularly polarized light corresponding to the selective reflection wavelength band is reflected and left-handed circularly polarized light is transmitted. Circularly polarized light having a wavelength other than the selective reflection wavelength band is not reflected but is transmitted as it is. Further, when the right circularly polarized light is incident on the right twisted cholesteric liquid crystal film, the right circular polarized light corresponding to the selective reflection wavelength band is reflected. On the other hand, since there is no left circularly polarized light to be transmitted, the transmittance (%) is theoretically 0%. Right-handed circularly polarized light having a wavelength other than the selective reflection wavelength band is not reflected but is transmitted as it is.

In the present invention, “selective reflection wavelength band” refers to “a wavelength region (range) in which the transmittance is 30% or less for circularly polarized light corresponding to the twisted direction of the cholesteric liquid crystal film”, and “transmission band” For circularly polarized light corresponding to the twist direction of the cholesteric liquid crystal film, it means a wavelength region (range) in which the transmittance is greater than 30%, and “transmittance” is “the intensity of light that passes through the substance” And the ratio of the intensity of incident light as a percentage. " That is, the transmittance T (%) is
T = I / I ₀ × 100
(In the formula, I is the intensity of transmitted light, and I ₀ is the intensity of incident light.)
It is represented by Here, the transmittance in the first selective reflection wavelength band and the second selective reflection wavelength band is the transmittance of light incident from the front (normal) direction.

  The first selective reflection wavelength band can include a selective reflection wavelength band for light having a wavelength in the visible light range. Further, the second selective reflection wavelength band can include a selective reflection wavelength band for light having a wavelength in the visible light region or the infrared region.

  As one embodiment of the present invention, the first selective reflection wavelength band includes a selective reflection wavelength band for light having a wavelength in the visible light range, and the second selective reflection wavelength band has light in the visible light range or infrared range. The two-band cholesteric liquid crystal film of the present invention, which includes a selective reflection wavelength band with respect to, corresponds to a color (selective reflection color) corresponding to a short wavelength light to a long wavelength light when the viewing direction is changed obliquely from the front. Some colors seem to change (red shift).

  The present invention also includes a step of forming a coating film by applying a liquid crystal composition containing a polymerizable mesogenic compound and a chiral agent that is a cyclic compound whose torsional force is changed by an intramolecular dimerization reaction to a substrate ( A), and in a state where the surface of the coating film opposite to the substrate is in contact with a gas containing oxygen, the polymerizable mesogenic compound is polymerized in preference to intramolecular dimerization of the chiral agent, And a step (B) of obtaining a cholesteric liquid crystal film that is a cured product of the liquid crystal composition, wherein the cholesteric liquid crystal film has a first selective reflection wavelength band and the first selective reflection wavelength in transmission spectrum measurement. A transmission spectrum having a second selective reflection wavelength band on the longer wavelength side of the band, and a transmission band between the first selective reflection wavelength band and the second selective reflection wavelength band To provide a method for producing a cholesteric liquid crystal film.

  A two-band cholesteric liquid crystal film can be efficiently produced by the method for producing a two-band cholesteric liquid crystal film of the present invention.

  Moreover, the manufacturing method of the cholesteric liquid crystal film of this invention may be equipped with the process of forming the cholesteric orientation of the said polymerizable mesogenic compound between a process (A) and a process (B).

  The inventors speculate that the use of a chiral agent, which is a cyclic compound whose torsional force is changed by an intramolecular dimerization reaction, causes the cured product of the liquid crystal composition to be a two-band cholesteric liquid crystal film based on the following principle. ing.

  The liquid crystal composition is applied to the substrate to form a coating film, and the surface of the coating film opposite to the substrate (that is, the surface of the coating film) is in contact with a gas containing oxygen, and the chiral agent molecule When the polymerizable mesogen compound is polymerized in preference to the dimerization, the polymerization of the polymerizable mesogen compound has priority over the intramolecular dimerization of the chiral agent on the substrate side. On the other hand, on the opposite side (front side) of the substrate, polymerization of the polymerizable mesogen compound is inhibited and slowed by oxygen, but the intramolecular dimerization of the chiral agent proceeds on the front side in the same manner as on the substrate side. In comparison, the polymerizable mesogen compound is polymerized under the situation where the intramolecular dimerization reaction of the chiral agent has proceeded.

Here, when the helical pitch is P, the chiral agent concentration is c, and the twisting force is β, the relationship P = (c · β) ⁻¹ holds, and the center wavelength λ = n · P (n is the selective reflection) Therefore, when the torsional force (β) of the chiral agent changes due to intramolecular dimerization, the wavelength of selective reflection also changes.

  Therefore, the cured product of the liquid crystal composition becomes a two-band cholesteric liquid crystal film having different selective reflection wavelength bands on the substrate side and the surface side.

  According to the present invention, a novel two-band cholesteric liquid crystal film and an efficient manufacturing method thereof are provided.

4 is a diagram showing a transmission spectrum of light incident from the front direction in the two-band cholesteric liquid crystal film of Example 1. FIG. 6 is a diagram showing a transmission spectrum of light incident from the front direction in the two-band cholesteric liquid crystal film of Example 2. FIG. 6 is a diagram showing a transmission spectrum of light incident from the front direction in the two-band cholesteric liquid crystal film of Example 3. FIG. It is a figure which shows the transmission spectrum of the light which injected from the front direction in the two zone cholesteric liquid crystal film of Example 4. FIG. It is a figure in the two zone cholesteric liquid crystal film of Example 5 which shows the transmission spectrum of the light which injected from the direction of 20 degree | times (namely, 20 degree | times with respect to the normal direction) from the front direction and the front direction.

  Hereinafter, embodiments of the present invention will be described in detail.

[Two-band cholesteric liquid crystal film]
Since the two-band cholesteric liquid crystal film of the present invention is a cured product of a liquid crystal composition containing a polymerizable mesogenic compound and a chiral agent that is a cyclic compound whose torsional force is changed by an intramolecular dimerization reaction, The liquid crystal composition will be described.

  As the chiral agent, which is a cyclic compound whose twisting force is changed by an intramolecular dimerization reaction, contained in the liquid crystal composition, any appropriate chiral agent capable of aligning a polymerizable mesogenic compound into a desired cholesteric structure is adopted. The The chiral agent may be polymerizable or non-polymerizable, and may be liquid crystal or non-liquid crystal. By using such a chiral agent, the cured product of the liquid crystal composition can be a two-band cholesteric liquid crystal film. Only 1 type may be used for a chiral agent and it may use 2 or more types together.

  Examples of the intramolecular dimerization reaction include a photoreaction such as an ultraviolet reaction. Intramolecular dimerization reactions include irreversible reactions such as reversible reactions and cyclization reactions. An irreversible reaction such as a cyclization reaction is preferable from the viewpoint of obtaining a stable two-band cholesteric liquid crystal film by suppressing fading, color unevenness, fading and the like.

As described above, “twisting force” means a force that a chiral agent induces torsion in the molecular arrangement of liquid crystal molecules. The twisting force of the chiral agent before the intramolecular dimerization reaction is not particularly limited, but is preferably 10 μm ⁻¹ or more, more preferably 20 μm ⁻¹ or more. Not only can the amount of chiral agent added be reduced, but also a decrease in performance of the polymerizable nematic liquid crystal (liquid crystal phase temperature range, birefringence, etc.) and phase separation upon curing of the liquid crystal composition can be suppressed.

  The amount of change in the torsional force of the chiral agent due to the intramolecular dimerization reaction depends on the torsional force before the reaction and is not unambiguous, and is not particularly limited, but the two-band cholesteric liquid crystal film has a desired first selective reflection. In order to have the wavelength band and the second selective reflection wavelength band, it is preferable that the amount of change in torsional force is large. When the twisting force increases, the twisting force after the reaction is preferably 3/2 times or more, more preferably 2 times or more, further preferably 3 times or more, based on the twisting force before the reaction. . When the twisting force decreases, the twisting force after the reaction is preferably 2/3 times or less, more preferably 1/2 times or less, even more preferably 1 on the basis of the twisting force before the reaction. / 3 times or less.

  For example, when the selective reflection color corresponding to the first selective reflection wavelength band is blue and the selective reflection color corresponding to the second selective reflection wavelength band is red, the selective reflection color changes from at least blue to red. Only a torsional force change amount (approximately twice or 1/2 times) is required.

  The cyclic compound whose torsional force is changed by the intramolecular dimerization reaction preferably has a cinnamic acid site as a reaction site. By introducing the cinnamic acid moiety into the molecule of the cyclic compound, the cyclization reaction of the cyclic compound is likely to occur, and the cyclization reaction can proceed at a high reaction rate in a short time. In addition, a cyclic compound having two cinnamic acid sites undergoes an intramolecular dimerization reaction in which two cinnamic acid sites form a cyclobutane ring when irradiated with ultraviolet rays, and the twisting force is reduced.

  In addition, if the cyclic compound whose torsional force is changed by the intramolecular dimerization reaction has a structure (such as having a polymer group or a rotaxane structure) that does not diffuse in the liquid crystal composition when the liquid crystal composition is cured, White turbidity due to orientation defects and phase separation of the cured product of the composition hardly occurs. Further, when the cyclic compound has a structure that absorbs light (such as a benzene ring), the reaction rate is improved and the production time is shortened.

  When the cyclic compound whose torsional force is changed by the intramolecular dimerization reaction exhibits liquid crystallinity, it is excellent in compatibility with the polymerizable mesogenic compound, and the liquid crystallinity of the polymerizable mesogenic compound is hardly impaired during mixing. Moreover, since the addition amount of the chiral agent can be increased at the time of mixing, the preferable range of the twisting force of the cyclic compound is not limited to the above, and a lower twisting force may be used. Further, the cyclic compound suppresses the alignment defects of the cured product of the liquid crystal composition and white turbidity due to phase separation.

  Specific examples of the chiral agent that is a cyclic compound whose torsional force is changed by an intramolecular dimerization reaction include a cyclic compound represented by the following formula (1a), (2a), or (3a).

[In formulas (1a) to (3a), each R independently represents hydrogen or a monovalent substituent, X and Y each represent a divalent group, and either X or Y represents a chiral moiety (“chiral Also referred to as “part”. ]

  The cyclic compounds represented by the above formulas (1a) to (3a) are compounds that can form a cyclobutane ring by an intramolecular dimerization reaction according to the following reaction scheme (I), (II), or (III), respectively. .

[R, X and Y in Formulas (1b) to (3b) have the same definitions as R, X and Y in Formulas (1a) to (3b), respectively. ]

  The chiral site of the chiral agent is introduced into either X or Y in the formula via a spacer or directly. Although the structure of a chiral site | part is not specifically limited, The following are mentioned as a preferable example.

  Preferable examples of the cyclic compounds represented by the formulas (1a) to (3a) include the following.

In formulas (1c) to (3c), R ^{1 to} R ⁶ each independently represent hydrogen, fluorine, chlorine, iodine, bromine or an alkyl group. When R ^{1 to} R ⁶ are alkyl groups, the alkyl group is preferably a linear or branched alkyl group having 1 to 8 carbon atoms.

In formulas (1c) to (3c), X ¹ and X ² each independently represent a divalent group having any one of the following structures. In the following three structural formulas, n and m represent integers of 0 or more, but in the two structural formulas on the left and right sides, the sum of n and m is preferably 4 to 16. In the central structural formula, n is preferably 4 to 16. Furthermore, in the case of the structural formula on the right side (ie when chiral carbon is present), it is preferable to introduce a chiral moiety at a position close to the aromatic ring in formulas (1c) to (3c), and in that case, n or m It is preferable that either one is 0-1.

In formulas (1c) to (3c), Y ^{1 to} Y ⁴ each independently represent a divalent group having any one of the following structures.

(R ⁷ represents an alkylene group. The alkylene group is preferably a linear or branched alkylene group having 1 to 8 carbon atoms. R ⁸ represents fluorine, chlorine, iodine, bromine or an alkyl group. Is preferably a linear or branched alkyl group having 1 to 8 carbon atoms.)

  Preferable examples of the cyclic compounds represented by the formulas (1c) to (3c) include the following.

(Here, n and m in X ¹ and X ² are n ¹ and m ¹ and n ² and m ² respectively.)

  The content ratio of the chiral agent in the liquid crystal composition is preferably 1 to 20% by mass, more preferably 1.5 to 15% by mass, and further preferably 2 to 10% by mass based on the total amount of the liquid crystal composition. It is. When the content of the chiral agent is 1% by mass or more, cholesteric alignment and helical pitch can be formed more sufficiently and reliably, and when it is 20% by mass or less, the temperature range exhibiting a liquid crystal state is narrow. Can be reliably suppressed.

  In the case where the chiral agent is a liquid crystal, the content ratio is not limited to the above, and may be large because there is no risk of impairing the liquid crystallinity of the polymerizable mesogenic compound.

  The liquid crystal composition contains a polymerizable mesogen compound in addition to a chiral agent that is a cyclic compound whose torsional force is changed by an intramolecular dimerization reaction. Any appropriate polymerizable mesogenic compound can be adopted as the polymerizable mesogenic compound. For example, the polymerizable mesogenic compounds described in JP-T-2002-533742 (WO00 / 37585), EP358208 (US52111877), EP66137 (US4388453), WO93 / 22397, EP02661712, DE195504224, DE44081171, and GB2280445 can be used. As specific examples of such polymerizable mesogenic compounds, for example, commercially available products such as LC242 (manufactured by BASF), E7 (manufactured by Merck), and LC-Silicon-CC3767 (manufactured by Wacker-Chem) can also be used. .

  As the polymerizable mesogenic compound, for example, liquid crystal monomers described in JP-A No. 2003-287623 (paragraphs 0035 to 0047) can be preferably used. Only one type of polymerizable mesogenic compound may be used, or two or more types may be used in combination.

  Although there is no restriction | limiting in the temperature which shows the liquid crystal phase of the compound which shows a nematic phase or a cholesteric phase, Since a heating apparatus becomes unnecessary, it is preferable that it is room temperature.

  The content of the polymerizable mesogen compound in the liquid crystal composition is preferably 75 to 97.5% by mass, more preferably 80 to 97.5% by mass, and still more preferably 85 based on the total amount of the liquid crystal composition. ˜97.5% by mass. When the content of the polymerizable mesogenic compound is 75% by mass or more, the liquid crystal state exhibited by the liquid crystal composition becomes better, and cholesteric alignment can be more reliably formed. Further, when the content of the polymerizable mesogenic compound is 97.5% by mass or less, the content of the chiral agent can be relatively sufficiently ensured, and the helical pitch and the cholesteric alignment can be more reliably formed. Can do.

  In addition, when the chiral agent is a liquid crystal, the amount of the chiral mesogenic compound can be increased without impairing the liquid crystallinity of the polymerizable mesogenic compound. You can also.

  The liquid crystal composition may further contain a polymerization initiator, preferably a photopolymerization initiator. Any photopolymerization initiator may be employed as the photopolymerization initiator. Although not particularly limited, radical or cationic photopolymerization initiators that can be cleaved by visible light or ultraviolet light to initiate polymerization are preferable. For example, IRGACURE 651, IRGACURE 184, DAROCUR 1173, IRGACURE 2959, IRGACURE 127 , IRGACURE 907, IRGACURE 369, IRGACURE TPO (all manufactured by BASF) and the like can be used.

  The content ratio of the polymerization initiator in the liquid crystal composition is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass based on the total amount of the liquid crystal composition. When the content ratio of the polymerization initiator exceeds 10% by mass, the temperature range in which the liquid crystal composition exhibits a liquid crystal state becomes narrow and may become cloudy.

  Furthermore, a photosensitizer can be added to the liquid crystal composition as long as the effects of the present invention are not impaired. Examples of the photosensitizer include benzophenones such as anthraquinones and Michler's ketone.

  The content ratio of the photosensitizer in the liquid crystal composition is preferably 0.1 to 7% by mass, more preferably 1 to 4% by mass based on the total amount of the liquid crystal composition.

  Moreover, you may add a crosslinking agent to a liquid-crystal composition. When a crosslinking agent is added to the liquid crystal composition, the two-band cholesteric liquid crystal film that is a cured product thereof is three-dimensionally crosslinked, and is excellent in heat resistance reliability and physical strength.

  Although it does not specifically limit as a crosslinking agent, For example, the polyfunctional vinyl type compound which has two or more polymerizable functional groups, such as an acryl group and a methacryl group, an organometallic compound, an aldehyde type compound, etc. are mentioned, Especially, Functional vinyl compounds are preferred.

  Examples of the polyfunctional vinyl compound include trimethylolpropane tri (meth) acrylate and pentaerythritol tetra (meth) acrylate. Moreover, it is preferable that a polyfunctional vinyl type compound contains a liquid crystal formation site.

  Moreover, the usage-amount of a crosslinking agent becomes like this. Preferably it is 1-20 mass parts with respect to 100 mass parts of total amounts of 3 components of a polymerizable mesogen compound, a chiral agent, and a polymerization initiator, More preferably, it is 2-2. 10 parts by mass.

  In order to improve the film surface smoothness and appearance of the two-band cholesteric liquid crystal film, a surface conditioner can be added to the liquid crystal composition. As the surface conditioner, a silicon-based surface conditioner, a fluorine-based surface conditioner, an acrylic surface conditioner, or the like can be used. Among these, Fluorad. 171 (manufactured by 3M), ZonylFSN (manufactured by Dupont), and BYK361 (manufactured by Big Chem Japan) are preferable.

  The content ratio of the surface modifier in the liquid crystal composition is 0.01 to 1% by mass, preferably 0.02 to 0.5% by mass, more preferably 0.03 to 0.2% based on the total amount of the liquid crystal composition. % By mass.

  Examples of other additives include an anti-aging agent, a modifier, a surfactant, a dye, a pigment, a discoloration inhibitor, an ultraviolet absorber, and a polymerization inhibitor. These additives may be used alone or in combination of two or more. More specifically, examples of the anti-aging agent include phenol compounds, amine compounds, organic sulfur compounds, and phosphine compounds. Examples of the modifier include glycols, silicones, and alcohols. Can be mentioned. Examples of the surfactant include silicone-based, acrylic-based, and fluorine-based surfactants. In addition, an additive for adjusting the phase transition temperature and the birefringence can also be used.

  Next, a two-band cholesteric liquid crystal film that is a cured product of the liquid crystal composition described above will be described. The two-band cholesteric liquid crystal film has a first selective reflection wavelength band, a second selective reflection wavelength band that is longer than the first selective reflection wavelength band, and the first selection in transmission spectrum measurement. A cholesteric liquid crystal film showing a transmission spectrum having a transmission wavelength band between a reflection wavelength band and the second selective reflection wavelength band.

“Selective reflection wavelength band” refers to “a wavelength region (range) where the transmittance is 30% or less for circularly polarized light corresponding to the twist direction of the cholesteric liquid crystal film”, and “transmission band” refers to “the cholesteric liquid crystal film For circularly polarized light corresponding to the twist direction, it means a wavelength region (range) in which the transmittance is larger than 30%, and “transmittance” means “the intensity of light passing through the substance and the incident light. The ratio of the strengths of each other as a percentage. That is, the transmittance T (%) is
T = I / I ₀ × 100
(In the formula, I is the intensity of transmitted light, and I ₀ is the intensity of incident light.)
It is represented by Here, the transmittance in the first selective reflection wavelength band and the second selective reflection wavelength band is the transmittance of light incident from the front (normal) direction.

  Of course, the wavelength of light incident from the front (normal) direction may be in the ultraviolet region (200 to 380 nm), the visible light region (380 to 780 nm), and the infrared region (780 nm to 1 mm). It may be in any wavelength region without being limited to the region.

  The first selective reflection wavelength band and the second selective reflection wavelength band can include a selective reflection wavelength band for light having an arbitrary wavelength. For example, the first selective reflection wavelength band can include a selective reflection wavelength band for light having a wavelength in the visible light range. Further, the second selective reflection wavelength band can include a selective reflection wavelength band for light having a wavelength in the visible light region or the infrared region.

  Note that light having a certain wavelength is not limited to light having one wavelength. The first selective reflection wavelength band or the second selective reflection wavelength band may include a selective reflection wavelength band for two or more lights having different wavelengths.

  The first selective reflection wavelength band and the second selective reflection wavelength band may be in any wavelength region. It may be in the ultraviolet region, visible light region, or infrared region, or may be a wavelength region straddling these regions.

  The first selective reflection wavelength band is preferably in the wavelength region of 400 to 700 nm, and particularly preferably in the wavelength region of 400 to 650 nm.

  The second selective reflection wavelength band is preferably in the wavelength region of 550 to 900 nm, particularly preferably in the wavelength region of 550 to 800.

  In particular, as the two-band cholesteric liquid crystal film, the first selective reflection wavelength band is in the wavelength region of 500 to 650 nm, the second selective reflection wavelength band is in the range of 700 to 800 nm, or the first selective reflection. It is suitable that the wavelength band is in the wavelength region of 400 to 500 nm and the second selective reflection wavelength band is in the wavelength region of 550 to 650 nm.

  Specifically, as a two-band cholesteric liquid crystal film, the first selective reflection wavelength band is 550 to 610 nm, the second selective reflection wavelength band is 710 to 780 nm, and the first selective reflection wavelength band is 530. ˜580 nm, the second selective reflection wavelength band is 710-760 nm, the first selective reflection wavelength band is 530-580 nm, the second selective reflection wavelength band is 710-740 nm, One having a selective reflection wavelength band of 440 to 500 nm and a second selective reflection wavelength band of 560 to 640 nm may be mentioned.

  The two-band cholesteric liquid crystal film may have a selective reflection wavelength band other than the first selective reflection wavelength band and the second selective reflection wavelength band.

  The two-band cholesteric liquid crystal film has a first helical pitch corresponding to the first selective reflection wavelength band and a second helical pitch corresponding to the second selective reflection wavelength band. There may be a plurality of selective reflection wavelength bands corresponding to the first helical pitch and the second helical pitch, respectively, and the first selective reflection wavelength band and the second selective reflection wavelength band are from the front direction. It is only a selective reflection wavelength band of incident light.

Therefore, the two-band cholesteric liquid crystal film has a selective reflection wavelength band (third selective reflection wavelength band) of light incident from a direction other than the front (an oblique direction) corresponding to the first helical pitch and a second helical pitch. Can further have a selective reflection wavelength band (fourth selective reflection wavelength band) of light incident from an oblique direction corresponding to. Here, the third selective reflection wavelength band and the fourth selective reflection wavelength band may be in any wavelength region, but the third selective reflection wavelength band is shorter than the first selective reflection wavelength band. The fourth selective reflection wavelength band is a wavelength area shorter than the second selective reflection wavelength band. The center wavelength of selective reflection with respect to incident light from the front (normal) direction is λ (0), and the center wavelength of selective reflection of light incident at an angle θ with respect to the normal direction is λ (θ). sometimes,
λ (θ) = λ (0) · cos θ
This is because the center wavelength λ (θ) of selective reflection decreases as the incident angle of light increases, that is, shifts to the short wavelength side (blue shift).

  Therefore, depending on what wavelength range the first selective reflection wavelength band to the fourth selective reflection wavelength band of the two-band cholesteric liquid crystal film are, the selection that is visually recognized when viewed from the front and obliquely The reflected color (including colorless) may be different.

  For example, the first selective reflection wavelength band includes a selective reflection wavelength band for light having a wavelength in the visible light range, the second selective reflection wavelength band includes a selective reflection wavelength band for light having a wavelength in the infrared range, A third selective reflection wavelength band including a selective reflection wavelength band for light having a wavelength in the ultraviolet range, and a fourth selective reflection wavelength band including a selective reflection wavelength band for light having a wavelength in the visible light range; When the liquid crystal film is viewed from the front, the selective reflection color corresponding to the first selective reflection wavelength band is visually recognized, and when viewed from the oblique direction, the selective reflection color corresponding to the fourth selective reflection wavelength band is visually recognized. Actually, the third selective reflection wavelength band of the two-band cholesteric liquid crystal film is a wavelength region shorter than the first selective reflection wavelength band, and the fourth selective reflection wavelength band is more than the second selective reflection wavelength band. If the viewing direction is changed diagonally from the front even though the wavelength region is on the short wavelength side, the color of the two-band cholesteric liquid crystal film will change from the selective reflection color of short wavelength light to the selective reflection color of long wavelength light. It seems to change (red shift). That is, it is possible to cause a color change different from that of a normal cholesteric liquid crystal film having only one selective reflection wavelength band (which causes a blue shift).

  Specifically, as such a two-band cholesteric liquid crystal film, yellow-green is visible when viewed from the front, red is visible when viewed from the diagonal, green is viewed from the front, and when viewed from the diagonal Red is visible, blue-green is seen from the front, red is seen from the diagonal, blue is seen from the front, red is seen from the diagonal, from the front For example, blue is visually recognized, and gold is visually recognized when viewed from an oblique direction.

  The first selective reflection wavelength band and the second selective reflection wavelength band include a selective reflection wavelength band for light having a wavelength in the visible light range, and the third selective reflection wavelength band for light having a wavelength in the ultraviolet range. A two-band cholesteric liquid crystal film including a selective reflection wavelength band and a fourth selective reflection wavelength band including a selective reflection wavelength band for light having a wavelength in the visible light range is the first selective reflection wavelength band when viewed from the front. The selective reflection color corresponding to the second selective reflection wavelength band is visually recognized, and the selective reflection color corresponding to the fourth selective reflection wavelength band is visually recognized from an oblique direction.

  Specifically, as such a two-band cholesteric liquid crystal film, magenta is visually recognized when viewed from the front, blue is viewed when viewed from the diagonal, and orange (copper) is viewed from the diagonal, from the diagonal. The one where yellow-green is visually recognized is seen.

  Next, the use of the two-band cholesteric liquid crystal film will be described. The two-band cholesteric liquid crystal film can be suitably used for a color material, an IR filter, a band pass filter, a UV reflection film, a brightness enhancement film, a light control film, a retardation plate, a notch filter, and the like. In particular, it is useful as a reflective film that reflects light having a wavelength in the first selective reflection wavelength band and the second selective reflection wavelength band.

  A two-band cholesteric liquid crystal film, particularly one having a different selective reflection color when viewed from the front and when viewed from an oblique direction, can be used as a security medium. For example, if an article to which a two-band cholesteric liquid crystal film is applied is an authentic article and an article that is not an authentic article, whether or not the target article is an authentic article is determined based on whether or not the selective reflection color is visible. Easy to identify. In particular, a two-band cholesteric liquid crystal film that appears to cause a red shift can be characterized by exhibiting a color change different from that of a normal cholesteric liquid crystal film that causes a blue shift.

  In addition, since the intramolecular dimerization reaction of the cyclic compound represented by any one of the above formulas (1a) to (3a) that is a chiral agent is an irreversible reaction, the two-band cholesteric liquid crystal film includes an intramolecular dimerization reaction. Those in which a cyclobutane ring is formed by a quantification reaction (that is, cyclic compounds represented by formulas (1b) to (3b)) can be included. The two-band cholesteric liquid crystal film may contain an unreacted chiral agent.

[Manufacturing method of two-band cholesteric liquid crystal film]
Next, a method for producing a two-band cholesteric liquid crystal film will be described. In the production of a two-band cholesteric liquid crystal film, first, the liquid crystal composition described above is applied to a substrate to form a coating film (step (A)).

  The liquid crystal composition may be applied as it is on the substrate, or may be dissolved or dispersed in a solvent and applied onto the substrate. Examples of the solvent include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, methylene chloride, trichloroethylene, tetrachloroethylene, chlorobenzene, and orthodichlorobenzene, phenol, p-chlorophenol, o-chlorophenol, phenols such as m-cresol, o-cresol, p-cresol, aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, 1,2-dimethoxybenzene, acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, Ketone solvents such as cyclohexanone, cyclopentanone, 2-pyrrolidone, N-methyl-2-pyrrolidone, ester solvents such as ethyl acetate and butyl acetate, t-butyl alcohol, glyce Alcohol solvents such as ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol and 2-methyl-2,4-pentanediol, amide solvents such as dimethylformamide and dimethylacetamide Nitrile solvents such as acetonitrile and butyronitrile, ether solvents such as diethyl ether, dibutyl ether, tetrahydrofuran and dioxane, carbon disulfide, ethyl cellosolve, butyl cellosolve and the like. These solvents may be used alone or in combination of two or more.

  Examples of the coating method include spin coating, casting, roll coating, flow coating, die coating, printing, dip coating, cast film formation, bar coating, and gravure printing. .

  There are no particular restrictions on the material, shape, structure, thickness, etc. of the substrate, and it is the optimal substrate from the viewpoints of properties such as dimensional stability, thickness uniformity, strength, heat resistance, chemical resistance, water resistance, and cost. Is selected. The substrate may be appropriately selected from known ones.

  Examples of the resin that is a material for the substrate include a polymer obtained by polymerizing one or more polymerizable monomers or a mixture thereof. When the polymer is a copolymer obtained by polymerizing two or more polymerizable monomers, the copolymer includes a random copolymer, an alternating copolymer, a block copolymer, and a graft copolymer. Any copolymer may be used. The resin substrate may be a composite substrate such as a substrate in which two or more kinds of resins are laminated.

  In particular, as the substrate, various plastic films are preferably used from the viewpoint of cholesteric alignment of the liquid crystal. Examples of the plastic include cellulose resins such as triacetyl cellulose (TAC), polyolefins such as polyethylene, polypropylene, poly (4-methylpentene-1), cycloolefin polymer, polyimide, polyimide amide, polyether imide, polyamide, Polyether ether ketone, polyether ketone, polyketone sulfide, polyether sulfone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, polyvinyl alcohol, epoxy resin And phenol resin. The plastic film can be obtained, for example, by stretching a plastic.

  The material of the substrate may be glass, such as ordinary soda glass. A substrate made of a combination of resin and glass can be used.

  Moreover, what has arrange | positioned the above plastic films and sheet | seats on the surfaces, such as metal substrates, such as aluminum, copper, and iron, a ceramic substrate, and a glass substrate, can be used as a substrate.

On the surface of the substrate on which the liquid crystal composition is applied, a film such as a SiO ₂ oblique deposition film may be formed.

  The thickness of the substrate is preferably 5 to 500 μm, more preferably 10 to 200 μm, and still more preferably 15 to 150 μm. If it is such thickness, since it has sufficient intensity | strength as a board | substrate, generation | occurrence | production of problems, such as fracture at the time of manufacture, can be prevented, for example.

  The thickness of the coating film of the liquid crystal composition is not particularly limited, but is preferably 3 to 50 μm, more preferably 3 to 25 μm, and still more preferably 4 to 20 μm. If the thickness is greater than 3 μm, it is easy to form a sufficient helical pitch, and if the thickness is less than 50 μm, the alignment regulating force acts sufficiently, so that alignment failure is unlikely to occur. Moreover, it is preferable that it is 50 micrometers or less also from a cost surface.

  In the present embodiment, the formation of the cholesteric orientation of the polymerizable mesogenic compound is preferably performed after the step (A) and before the step (B) described later.

  Then, in a state where the surface of the formed coating film opposite to the substrate (that is, the coating film surface) is in contact with a gas containing oxygen, the polymerizable mesogenic compound is preferentially given over the intramolecular dimerization of the chiral agent. Polymerize (step (B)).

  Then, on the substrate side, the polymerization of the polymerizable mesogenic compound has priority over the intramolecular dimerization of the chiral agent. On the other hand, on the opposite side (front side) of the substrate, polymerization of the polymerizable mesogen compound is inhibited and slowed by oxygen, but the intramolecular dimerization of the chiral agent proceeds on the front side in the same manner as on the substrate side. In comparison, the polymerizable mesogen compound is polymerized under the situation where the intramolecular dimerization reaction of the chiral agent has proceeded.

  There is no limitation on the gas containing oxygen, and the oxygen concentration may be set as appropriate depending on the desired characteristics of the two-band cholesteric liquid crystal film, but is at least 0.5% by volume or more based on the total amount of gas, and 10 volumes. % Or more is preferable. The gas containing oxygen may be the atmosphere (oxygen concentration: about 21% by volume). The use of air that does not require special equipment is preferable from the viewpoint of cost.

  The gas containing oxygen may contain any appropriate inert gas. Examples of the inert gas include nitrogen, argon, helium, neon, xenon, krypton, and the like. Among these, nitrogen is preferred because it is the most versatile and low cost.

  The intramolecular dimerization of the chiral agent and the polymerization of the polymerizable mesogen compound can be performed by irradiating light such as visible light or ultraviolet light, and the intensity (exposure illuminance) of light such as visible light or ultraviolet light is increased. By doing so, the latter can be prioritized over the former.

For example, the intensity of light is preferably 15 to 100 mW / cm ² , more preferably 20 to 90 mW / cm ² , and still more preferably 20 to 80 mW / cm ² . However, the light intensity can be further reduced by increasing the content ratio of the photopolymerization initiator or the photosensitizer in the liquid crystal composition. For example, if the content of the photosensitizer in the liquid crystal composition is 2% by mass, the intensity of light 3 mW / cm ² or more, preferably to 4~60mW / cm ^2.

  The wavelength of light is preferably 160 to 500 nm, more preferably 220 to 450 nm, and still more preferably 280 to 420 nm.

The light irradiation time varies depending on the intensity of light to be irradiated. For example, when the light intensity is 50 mW / cm ² , it is preferably 1 to 600 seconds, more preferably 5 to 500 seconds, and still more preferably 10 ~ 400 seconds. However, the light irradiation time can be shortened by increasing the content ratio of the photopolymerization initiator or the photosensitizer in the liquid crystal composition. In this case, the irradiation time is preferably 1 to 60 seconds, more preferably 3 to 50 seconds.

  Although the temperature at which the liquid crystal composition is irradiated with light such as visible light or ultraviolet light depends on the polymerizable mesogenic compound used, it cannot be generally stated, but is preferably 10 to 150 ° C, more preferably 20 to 120 ° C. More preferably, it is 25-90 degreeC. Note that when the heating temperature is low, the viscosity of the liquid crystal composition increases, and alignment defects may occur in the cured product. In addition, when the heating temperature is high, the liquid crystal composition may undergo a phase transition to an isotropic phase, and the cured product may not be selectively reflected.

  In addition, the wavelength of light is set to a wavelength other than the intramolecular dimerization wavelength of the chiral agent, the polymerizable mesogen compound is polymerized, and then the wavelength of light is set to the intramolecular dimerization wavelength of the chiral agent, Polymerization of the polymerizable mesogen compound by polymerizing the polymerizable mesogenic compound by setting the light wavelength to the intramolecular dimerization wavelength of the chiral agent and then polymerizing the polymer rather than the intramolecular dimerization of the chiral agent. It is possible to prioritize the polymerization of the functional mesogenic compound. Here, the wavelength other than the intramolecular dimerization wavelength is preferably the cleavage wavelength of the photopolymerization initiator.

  For example, since the cleavage wavelength of the absorption edge on the long wavelength side of the photopolymerization initiator IRGACURE TPO is 420 nm and the intramolecular dimerization wavelength of the above-mentioned cyclic compound is 315 nm, it is one of the emission lines of a high-pressure mercury lamp first. By irradiating only light having a wavelength of 405 nm, and then irradiating light having a wavelength of 315 nm and then optionally 405 nm, the polymerization of the polymerizable mesogenic compound can be prioritized over the intramolecular dimerization of the chiral agent.

  In addition, after hardening of a liquid crystal composition is complete | finished, a board | substrate may peel and it does not need to peel.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited at all by the Example.

  Unless otherwise specified, “parts” and “%” in the examples are based on mass. Table 1 shows the structures and physical properties of all the compounds used in the examples.

<Evaluation method>
(Measurement of transmission spectrum)
A spectroscope USB4000 (manufactured by Ocean Optics) equipped with a polarizing microscope eclipse lv100 POL (manufactured by Nikon Corp.) having a two-band cholesteric liquid crystal film formed on an alignment substrate as a measurement sample and having an optical fiber BIS600-VIS-NIR. And measured. The light incident on the two-band cholesteric liquid crystal film is from the front (normal) direction. The transmittance when right-handed circularly polarized light was incident from the normal direction to the substrate not coated with the liquid crystal composition was used as a reference (transmittance of 100%). Also, when the right circularly polarized light is incident at an angle of 20 degrees from the normal direction and the transmittance is measured, the transmission when the right circularly polarized light is incident from the normal direction on the substrate not coated with the liquid crystal composition is also used. The rate was used as a reference (transmittance 100%). In addition, the setting of the analysis software Spectra Suite used at the time of the transmittance | permeability measurement was made into the box car width | variety once about the integration time of about 400 milliseconds.

  In the transmission spectrum measurement, a wavelength region (range) having a transmittance of 30% or less was defined as a selective reflection wavelength band.

(Adjustment of irradiation intensity)
Ultraviolet irradiation was performed using SPOT 9-250UB (manufactured by USHIO INC.), Which is a UV irradiation device with variable intensity.

(Measurement of thickness)
The thickness of the two-band cholesteric liquid crystal film (after ultraviolet irradiation) was measured using an alpha step IQ (manufactured by Yamato Kagaku Co., Ltd.) which is a step measuring device.

(Visibility)
The color of the two-band cholesteric liquid crystal film viewed from the front and the color of the two-band cholesteric liquid crystal film viewed from the direction of 45 degrees from the front were visually recognized.

[Synthesis Example 1: Synthesis of Compound 1]
Compound 1 shown in Table 1 was synthesized according to the following synthesis scheme.

(Step 1) Synthesis of 4- (4-pentenyloxyl) cinnamic acid (compound (a)) 1 equivalent of trans-4-hydroxycinnamic acid was placed in an eggplant type flask and dissolved in ethanol. To this solution was added a catalytic amount of potassium iodide (KI) dissolved in water, 3 equivalents of potassium hydroxide (KOH), and 1.2 equivalents of 5-bromo-1-pentene dissolved in ethanol. Stir for 24 hours. Then, after returning to room temperature, unnecessary ethanol was removed by an evaporator, water was added, and acidified by adding dilute hydrochloric acid to precipitate an ionized product. The resulting precipitate was filtered and washed with water to obtain the target compound (a).

(Step 2): Synthesis of Compound (b) Compound (a) 2.2 equivalents and (R)-(+)-2-methyl-1,4-butanediol 1 equivalent were dissolved in dehydrated dichloromethane in an eggplant-shaped flask. I let you. To this solution, 2.4 equivalents of DCC (dicyclohexylcarbodiimide) and a catalyst amount of DMAP (4-dimethylaminopyridine) were added and stirred at room temperature for 24 hours. Thereafter, the DCC urea solid produced by the reaction was filtered off from the reaction solution, and the filtrate was concentrated under reduced pressure. Purification by silica column chromatography using chloroform as a developing solvent gave the target compound (b).

(Step 3): Synthesis of Compound 1 In a 1 L three-necked flask, 500 mg of compound (b) and 1 L of dehydrated dichloromethane were placed, and the atmosphere was purged with nitrogen gas, followed by stirring at room temperature for 2 hours to uniformly dissolve the sample. Thereafter, 0.2 equivalent of Grubbs catalyst first generation dissolved in dehydrated dichloromethane was added in three portions at intervals of several hours, and the mixture was stirred at room temperature for 24 hours. The resulting reaction solution was concentrated under reduced pressure, purified by alumina column chromatography and silica column chromatography using dichloromethane as a developing solvent, and further recrystallized from ethyl acetate-hexane to obtain Compound 1. If necessary, it was further purified by recycled GPC.

[Example 1]
1 weight of a mixture comprising 90 parts by weight of a polymerizable mesogenic compound LC242 (manufactured by BASF), 8 parts by weight of compound 1 being a chiral agent, and 2 parts by weight of Irg907 (manufactured by BASF) being a photopolymerization initiator. 100 parts by weight of chloroform was added to the part to prepare a chloroform solution.

The solution is cast on an alignment substrate obtained by rubbing a glass substrate coated with polyimide, and irradiated with ultraviolet rays having an ultraviolet irradiation intensity of 23 mW / cm ² at 70 ° C. in the atmosphere (oxygen concentration 21% by volume) for 300 seconds. A band cholesteric liquid crystal film was obtained.

[Example 2]
A two-band cholesteric liquid crystal film was obtained in the same manner as in Example 1 except that the ultraviolet irradiation intensity was 48 mW / cm ² .

[Example 3]
A two-band cholesteric liquid crystal film was obtained in the same manner as in Example 1 except that the ultraviolet irradiation intensity was 73 mW / cm ² .

[Example 4]
Except for 86 parts by weight of a polymerizable mesogenic compound, 10 parts by weight of a chiral agent, 2 parts by weight of Michler's ketone as a photosensitizer, an ultraviolet irradiation intensity of 4.4 mW / cm ² , and an ultraviolet irradiation time of 30 seconds. In the same manner as in Example 1, a two-band cholesteric liquid crystal film was obtained.

[Example 5]
A two-band cholesteric liquid crystal film was obtained in the same manner as in Example 1, except that the polymerizable mesogenic compound was 89 parts by weight, the chiral agent was 9 parts by weight, the ultraviolet intensity was 73 mW / cm ² , and the ultraviolet irradiation time was 120 seconds. It was.

  Table 2 summarizes Examples 1-5. Moreover, the transmission spectrum of the light which injected from the front (normal) direction of the 2 zone | band cholesteric liquid crystal film of Examples 1-5 is shown in FIGS. 1-5, respectively. FIG. 5 also shows a transmission spectrum of light incident from a direction inclined 20 degrees from the front (normal) direction of the two-band cholesteric liquid crystal film of Example 5. In FIG. 5, the transmission spectrum on the long wavelength side is a transmission spectrum of light incident from the front (normal) direction, and the transmission spectrum on the short wavelength side is a direction inclined by 20 degrees from the front (normal) direction. It is the transmission spectrum of the light which injected from. In addition, the vertical axis | shaft of FIGS. 1-5 is a transmittance | permeability (%), and a horizontal axis is a wavelength (nm).

  The two-band cholesteric liquid crystal film of the present invention can be suitably used for color materials, IR filters, bandpass filters, UV reflection films, brightness enhancement films, light control films, retardation films, notch filters, and the like. In particular, it is useful as a reflective film that reflects light having a wavelength in the first selective reflection wavelength band and the second selective reflection wavelength band.

A two-band cholesteric liquid crystal film, particularly one having a different selective reflection color when viewed from the front and when viewed from an oblique direction, can be used as a security medium.

Claims (6)

A cured product of a liquid crystal composition containing a polymerizable mesogenic compound and a chiral agent that is a cyclic compound whose torsional force is changed by an intramolecular dimerization reaction,
In transmission spectrum measurement,
A first selective reflection wavelength band;
A second selective reflection wavelength band on the longer wavelength side than the first selective reflection wavelength band;
A transmission band between the first selective reflection wavelength band and the second selective reflection wavelength band;
A cholesteric liquid crystal film exhibiting a transmission spectrum having   The cholesteric liquid crystal film according to claim 1, wherein the first selective reflection wavelength band includes a selective reflection wavelength band for light having a wavelength in the visible light range.   The cholesteric liquid crystal film according to claim 1 or 2, wherein the second selective reflection wavelength band includes a selective reflection wavelength band for light having an infrared wavelength.   The cholesteric liquid crystal film according to claim 1, wherein the second selective reflection wavelength band includes a selective reflection wavelength band for light having a wavelength in the visible light range. A step (A) of forming a coating film by applying a liquid crystal composition containing a polymerizable mesogenic compound and a chiral agent which is a cyclic compound whose torsional force is changed by an intramolecular dimerization reaction to a substrate;
The polymerizable mesogenic compound is polymerized in preference to intramolecular dimerization of the chiral agent in a state where the surface of the coating film opposite to the substrate is in contact with a gas containing oxygen, and the liquid crystal composition And a step (B) of obtaining a cholesteric liquid crystal film which is a cured product of
The cholesteric liquid crystal film is used for transmission spectrum measurement.
A first selective reflection wavelength band;
A second selective reflection wavelength band on the longer wavelength side than the first selective reflection wavelength band;
A transmission band between the first selective reflection wavelength band and the second selective reflection wavelength band;
A method for producing a cholesteric liquid crystal film, which exhibits a transmission spectrum having The method for producing a cholesteric liquid crystal film according to claim 5, comprising a step of forming a cholesteric alignment of the polymerizable mesogenic compound between the step (A) and the step (B).