JP7113962B2 - Manufacturing method of cholesteric liquid crystal film - Google Patents

Description

The present disclosure relates to methods for manufacturing cholesteric liquid crystal films.

An optical film using a liquid crystal film with large optical anisotropy is known.
In such an optical film, the liquid crystal film is manufactured by, for example, applying a coating liquid containing a liquid crystal compound onto a member to be coated, drying the liquid crystal compound, and optionally subjecting the liquid crystal compound to orientation treatment, polymerization of the liquid crystal compound, and the like. be.

Japanese Patent Application Laid-Open No. 2016-150286 discloses that in a method for producing an optical film, a coating film of a liquid crystal material coated on a film-forming surface of a base material is transported into a drying oven together with the base material, and the solvent is removed. , a liquid crystal layer is formed. In addition, it is described that other than drying, alignment treatment of liquid crystal molecules, polymerization of liquid crystal monomers, and the like may be performed. It is disclosed that it can also be oriented.

In addition, JP 2010-536782 discloses the application of mechanical shear to the liquid crystal layer by applying a knife blade to the liquid crystal layer as one of the treatments of the liquid crystal layer to generate the desired liquid crystal phase. It is

By the way, as a cholesteric liquid crystal film, the helical axis of the cholesteric liquid crystal is parallel to the film surface direction and arranged in a specific direction when viewed from the top, so that it can be applied to an optical film such as an aerial imaging device. is expected to apply.
In particular, there is an increasing demand for a cholesteric liquid crystal film in which the alignment of the helical axes as described above has little variation within the film surface.

Although the above-mentioned JP-A-2016-150286 discloses that a shearing force is applied to the lyotropic liquid crystal, there is no description of a cholesteric liquid crystal film in which the helical axes are aligned parallel to the film surface direction. not
In addition, although the above-mentioned Japanese National Publication of International Patent Application No. 2010-536782 discloses a treatment to be performed on the liquid crystal layer to generate a desired liquid crystal phase, mechanical shearing may affect the dry state of the liquid crystal layer. There is no description as to whether it is applied in the case of degree. Furthermore, JP-T-2010-536782 only describes that the axis of the molecular helix extends laterally with respect to the layer, and the axis is parallel to the film surface direction and the layer is on the top surface. There is no clear description of lining up in a particular direction when viewed. Therefore, in the liquid crystal layer described in JP-T-2010-536782, it is difficult to imagine that the in-plane variations in the alignment of the axes of the molecular helices are small.

Therefore, the problem to be solved by one embodiment of the present invention is that the helical axes of the cholesteric liquid crystal are parallel to the film surface direction and are aligned along a specific direction when viewed from above, and the alignment is uniform within the film surface. To provide a method for manufacturing a cholesteric liquid crystal film with a small amount.
Hereinafter, the fact that there is little variation in the arrangement of the helical axes within the film surface is also referred to as "excellent alignment accuracy".

Specific means for solving the problems include the following aspects.

<1> Step A of applying a coating liquid containing a solvent, a rod-shaped thermotropic liquid crystal compound, and a chiral agent to a substrate to form a coating film;
A step B of drying the formed coating film to a residual solvent rate of 50% by mass or less;
A step C of applying a shearing force to the surface of the dried coating film;
A method for producing a cholesteric liquid crystal film in which the helical axes are parallel to the film surface direction and perpendicular to the shear direction.

<2> The method for producing a cholesteric liquid crystal film according to <1>, wherein step C is a step of applying a shearing force having a shear rate of 1000 sec ^-1 or more.
<3> The method for producing a cholesteric liquid crystal film according to <1> or <2>, wherein the temperature of the coating film surface in step C is 50°C to 120°C.

<4> The method for producing a cholesteric liquid crystal film according to any one of <1> to <3>, wherein the application of shear force in step C is performed with a blade.
<5> The method for producing a cholesteric liquid crystal film according to any one of <1> to <3>, wherein the application of the shearing force in step C is performed using an air knife.

<6> The method for producing a cholesteric liquid crystal film according to any one of <1> to <5>, further comprising a step of curing the coating film after step C.
<7> The method for producing a cholesteric liquid crystal film according to any one of <1> to <6>, wherein the coating film has a thickness of 30 μm or less when the shear force is applied in step C.
<8> The method for producing a cholesteric liquid crystal film according to any one of <1> to <7>, wherein the coating film has a thickness of 10 μm or less after applying the shearing force in step C.

According to one embodiment of the present invention, the helical axis of the cholesteric liquid crystal is parallel to the film surface direction and aligned along a specific direction when viewed from the top, and the alignment has little variation within the film surface (i.e. , excellent alignment accuracy) is provided.

FIG. 1 is a schematic diagram for explaining an example of a method for manufacturing a cholesteric liquid crystal film of the present disclosure.

Hereinafter, the method for manufacturing the cholesteric liquid crystal film of the present disclosure will be described in detail.
In the present disclosure, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

In the present disclosure, a numerical range indicated using "to" indicates a range including the numerical values before and after "to" as the minimum and maximum values, respectively.
In the numerical ranges described step by step in the present disclosure, upper or lower limits described in a certain numerical range may be replaced with upper or lower limits of other numerical ranges described step by step. In addition, in the numerical ranges described in the present disclosure, upper or lower limits described in a certain numerical range may be replaced with values shown in Examples.
In addition, when the code|symbol described in several drawing is the same, it points out the same object.

The present inventors have found a novel liquid crystal alignment method using a process of applying a shear force to the coating film, the helical axis of the cholesteric liquid crystal is parallel to the film surface direction and aligned perpendicular to the shear direction, In addition, a cholesteric liquid crystal film with little variation in the alignment within the film surface (that is, excellent alignment accuracy) was obtained.
Specifically, a method of applying a shearing force to the surface of a coating film obtained by coating and drying a coating liquid containing a solvent, a rod-shaped thermotropic liquid crystal compound (hereinafter also referred to as a specific liquid crystal compound), and a chiral agent. is. In particular, by applying a shearing force to the coating film dried to a residual solvent rate of 50% by mass or less, the helical axis of the cholesteric liquid crystal is aligned parallel to the film surface direction and perpendicular to the shearing direction, and further , a cholesteric liquid crystal film having little variation in the alignment within the film plane (that is, having excellent alignment accuracy) can be obtained.
In addition, in this new liquid crystal alignment method, since the liquid crystal is aligned by shearing force, an alignment film (also referred to as an alignment layer), which is usually provided adjacent to the cholesteric liquid crystal film, is unnecessary. .

Here, in the present disclosure, arranging the helical axes of the cholesteric liquid crystal parallel to the film surface direction is also referred to as “horizontal alignment”, and the helical axis of the cholesteric liquid crystal is parallel to the film surface direction of the cholesteric liquid crystal film (in other words, , perpendicular to the film thickness direction of the cholesteric liquid crystal film). However, it is not required that the helical axis of the cholesteric liquid crystal is strictly horizontal to the film plane direction of the cholesteric liquid crystal film, and the angle formed by the cholesteric liquid crystal helical axis and the film plane direction of the cholesteric liquid crystal film is 45°. Anything less than that shall be included in the "horizontal orientation" in this disclosure. The angle between the helical axis of the cholesteric liquid crystal and the film surface direction of the cholesteric liquid crystal film is preferably in the range of 0° to 40°.

Further, the helical axes of the cholesteric liquid crystal are arranged perpendicular to the shearing direction means that the helical axes of the cholesteric liquid crystal are arranged perpendicular to the direction in which the shearing force is applied during the production of the cholesteric liquid crystal film. In other words, when a long cholesteric liquid crystal film is manufactured, if shear force is applied in the long direction, the helical axis of the cholesteric liquid crystal is perpendicular to the long direction of the cholesteric liquid crystal film when viewed from above (in other words, For example, it means that they are arranged parallel to the short direction of the cholesteric liquid crystal film. However, it is not required that the helical axis of the cholesteric liquid crystal is strictly perpendicular to the shear direction. shall be encompassed by "perpendicular to the shear direction". The angle between the helical axis of the cholesteric liquid crystal and the shear direction is preferably in the range of 60° to 120°.

The following method is used to confirm the alignment of the helical axes of the cholesteric liquid crystal in the cholesteric liquid crystal film.
First, it is possible to confirm that the helical axes of the cholesteric liquid crystal are parallel to the film surface direction and perpendicular to the shear direction by using a cross-Nicol polarized transmission photograph and a cross-sectional SEM photograph by a polarizing microscope.
A cholesteric liquid crystal has a layered structure in which layers composed of molecular groups of specific liquid crystal compounds are stacked. Within each layer, the molecules of each specific liquid crystal compound are aligned in a fixed direction, and the alignment direction of the molecules in each layer deviates so as to turn spirally as it progresses in the stacking direction.
Therefore, in the crossed nicol polarized transmission photograph, the region corresponding to the layer in which the molecules of the specific liquid crystal compound are aligned perpendicularly or nearly perpendicularly to the photographing direction appears light, and the region other than the layer appears dark.
Therefore, in the cross-Nicol polarized light transmission photograph of the upper surface of the cholesteric liquid crystal film, a regular striped pattern due to the above density is confirmed. It can be confirmed that they are aligned perpendicular to the direction.
Among the regular striped patterns, one line (uninterrupted line) consisting of a light part in the center of the photograph is selected, and if the angle between this line and the shearing direction is less than 45°, the The angle formed by the helical axis and the shear direction shall be less than 90°±45°.
In addition, the fact that the helical axes of the cholesteric liquid crystal are aligned parallel to the film surface direction can be confirmed by photographing a cross section in the thickness direction of the cholesteric liquid crystal film at a magnification of 5000 using a scanning electron microscope (SEM). It can be confirmed by a cross-sectional SEM photograph). Here, the cross section in the thickness direction of the cholesteric liquid crystal film is a cross section cut along a direction perpendicular to the shearing direction (for example, the conveying direction of the coating film).
In the cross-sectional SEM photograph, one continuous cholesteric liquid crystal is selected, and if the angle between the spiral axis of the cholesteric liquid crystal and the film surface direction of the cholesteric liquid crystal film is less than 45°, the spiral axis of the cholesteric liquid crystal is aligned with the film. It can be said that they are arranged parallel to the surface direction.

The following method is used to confirm that the alignment accuracy of the cholesteric liquid crystal film is excellent.
A 2 cm square test piece is cut out from the object to be checked. Place the test piece on a black background, take a photograph of the same size under a white light, and binarize the obtained photograph with image processing software (for example, Jtrim). Then, the number of white pixels is obtained from the binarized image, and this is defined as the area of the "white area".
If there is a minute variation in the alignment of the helical axis of the cholesteric liquid crystal, scattering occurs in that area and appears as the above-mentioned "white area."
The smaller the ratio of the white region (that is, the area ratio of the white region) to the total area of the test piece in the photograph (that is, the total number of white and black pixels in the binarized image), the more the alignment of the helical axes of the cholesteric liquid crystal. It can be judged that the alignment accuracy is excellent.
For example, one indicator is that the ratio of the white area to the total area of the test piece in the photograph is 10% or less.

Based on the above knowledge, the manufacturing method of the cholesteric liquid crystal film of the present disclosure is as follows.
That is, the method for producing a cholesteric liquid crystal film of the present disclosure includes a step A of applying a coating liquid containing a solvent, a rod-shaped thermotropic liquid crystal compound, and a chiral agent on a substrate to form a coating film; It has a step B of drying the film until the residual solvent rate in the film is 50% by mass or less, and a step C of applying a shearing force to the surface of the dried coating film.
By having these steps A, B, and C, it is arranged parallel to the film surface direction (that is, horizontally oriented) and perpendicular to the shear direction, and further, the variation in the film surface of the arrangement A cholesteric liquid crystal film with less is obtained.

Hereinafter, each step of the method for manufacturing a cholesteric liquid crystal film of the present disclosure will be described in detail with reference to the drawings.
An example of the method for manufacturing the cholesteric liquid crystal film of the present disclosure, shown in FIG. .
The method for producing a cholesteric liquid crystal film according to the present disclosure is not limited to a continuous roll-to-roll process, and each step may be performed sequentially on a sheet of substrate.

[Step A]
In step A, a coating solution containing a solvent, a rod-shaped thermotropic liquid crystal compound, and a chiral agent (hereinafter also referred to as a coating solution for forming a liquid crystal layer) is applied onto a substrate to form a coating film.
Note that the application of the liquid crystal layer forming coating liquid in the step A is performed on the base material wound on the backup roll from the viewpoint that the application can be performed while the base material is stretched and the coating accuracy is improved. is preferred.

An example of process A will be described with reference to FIG.
As shown in FIG. 1, the long base material F wound in a roll shape is sent out at its leading end and conveyed via the conveying roll 50. First, when the base material F is conveyed through the conveying roll 50, the liquid crystal layer forming liquid crystal layer is first coated by the coating means 10. Application of the application liquid is performed.
As shown in FIG. 1, it is preferable that the application of the liquid crystal layer forming liquid by the application means 10 is performed in the area where the base material F is wound on the backup roll 12 .

(Base material)
The substrate is not particularly limited, and may be a member that functions as a part of the optical film together with the cholesteric liquid crystal film, or an object to be coated with the coating liquid that is peeled off from the cholesteric liquid crystal film. It may be a member to be used.
In particular, a polymer film is preferably used as the substrate in consideration of applicability to roll-to-roll systems and easiness of winding on a backup roll.

For optical film applications, the substrate preferably has a total light transmittance of 80% or more.
For optical film applications, when a polymer film is used as the substrate, it is preferable to use an optically isotropic polymer film.
Examples of the substrate include polyester-based substrates (films or sheets of polyethylene terephthalate, polyethylene naphthalate, etc.), cellulose-based substrates (films or sheets of diacetylcellulose, triacetylcellulose (TAC), etc.), and polycarbonate-based substrates. , Poly (meth) acrylic base material (film or sheet such as polymethyl methacrylate), polystyrene base material (polystyrene, acrylonitrile styrene copolymer film or sheet), olefin base material (polyethylene, polypropylene, cyclic or Polyolefin having a norbornene structure, ethylene propylene copolymer film or sheet), polyamide base material (polyvinyl chloride, nylon, aromatic polyamide film or sheet), polyimide base material, polysulfone base material, poly Ethersulfone base material, polyether ether ketone base material, polyphenylene sulfide base material, vinyl alcohol base material, polyvinylidene chloride base material, polyvinyl butyral base material, poly(meth)acrylate base material, polyoxy Transparent base materials such as methylene-based base materials and epoxy resin-based base materials, and base materials made of blend polymers obtained by blending the above polymer materials, and the like can be used.

The thickness of the substrate is preferably, for example, 30 μm to 150 μm, more preferably 40 μm to 100 μm, in consideration of production aptitude, production cost, optical film application, and the like.

The base material may be one in which a layer is formed in advance on the above polymer film.
Examples of the layer to be formed in advance include an alignment layer having an alignment regulating force with respect to a liquid crystal compound, such as a rubbing alignment layer and a photo-alignment layer, and an adhesion layer.

(Coating liquid for liquid crystal layer formation)
The liquid crystal layer-forming coating liquid used in step A contains a solvent, a rod-shaped thermotropic liquid crystal compound, and a chiral agent. In addition, the liquid crystal layer-forming coating liquid may contain other components as necessary.

-solvent-
An organic solvent is preferably used as the solvent.
Specific examples of organic solvents include amide solvents (e.g., N,N-dimethylformamide), sulfoxide solvents (e.g., dimethylsulfoxide), heterocyclic compounds (e.g., pyridine), hydrocarbon solvents (e.g., benzene, hexane, etc.). , alkyl halide solvents (e.g., chloroform, dichloromethane), ester solvents (e.g., methyl acetate, butyl acetate, etc.), ketone solvents (e.g., acetone, methyl ethyl ketone, cyclohexanone, etc.), ether solvents (e.g., tetrahydrofuran, 1,2- dimethoxyethane, etc.). Among them, halogenated alkyl solvents and ketone solvents are preferable as the organic solvent.
An organic solvent may be used individually by 1 type, and 2 or more types may be used.

-Rod-shaped thermotropic liquid crystal compound (specified liquid crystal compound)-
A rod-like thermotropic liquid crystal compound (that is, a specific liquid crystal compound) refers to a liquid crystal compound having thermotropic properties and a rod-like molecular structure.
In particular, the specific liquid crystal compound is preferably a compound having a polymerizable group. The polymerizable group possessed by the specific liquid crystal compound is preferably an unsaturated polymerizable group, an epoxy group, or an aziridinyl group, more preferably an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group. It is particularly preferred to have
Specific examples of specific liquid crystal compounds include Makromol. Chem. , 190, 2255 (1989), Advanced Materials 5, 107 (1993), U.S. Pat. No., No. 95/24455, No. 97/00600, No. 98/23580, No. 98/52905, JP-A-1-272551, JP-A-6-16616, JP-A-7-110469 JP-A-11-80081, JP-A-2001-328973, and the like.
Furthermore, as the specific liquid crystal compound, for example, those described in JP-A-11-513019, JP-A-2007-279688, etc. can also be preferably used, but the compounds are not limited to these.

As the specific liquid crystal compound, for example, a compound represented by the following general formula (1) is preferably used as a liquid crystal compound having normal wavelength dispersion characteristics.

In general formula (1), Q ¹ and Q ² are each independently a polymerizable group, and L ¹ , L ² , L ³ and L ⁴ are each independently a single bond or a divalent linking group , A ¹ and A ² each independently represent a divalent hydrocarbon group having 2 to 20 carbon atoms, and M represents a mesogenic group.

Examples of the polymerizable groups represented by Q ¹ and Q ² include the polymerizable groups possessed by the specific liquid crystal compound described above, and preferable examples are the same.
Linking groups represented by L ¹ , L ² , L ³ and L ⁴ include -O-, -S-, -CO-, -NR-, -CO-O-, -O-CO-O- , -CO-NR-, -NR-CO-, -O-CO-, -O-CO-NR-, -NR-CO-O-, and a divalent selected from the group consisting of NR-CO-NR- is preferably a linking group of Here, R is an alkyl group having 1 to 7 carbon atoms or a hydrogen atom.
At least one of L ³ and L ⁴ is preferably -O-CO-O-.
In general formula (1), Q ¹ -L ¹ - and Q ² -L ² - are CH ₂ ═CH—CO—O—, CH ₂ ═C(CH ₃ )—CO—O—, and CH ₂ ═ C(Cl)--CO--O-- is preferred, and CH ₂ ═CH--CO--O-- is most preferred.

The divalent hydrocarbon group having 2 to 20 carbon atoms represented by A ¹ and A ² is preferably an alkylene group, an alkenylene group, or an alkynylene group having 2 to 12 carbon atoms, and particularly preferably has 2 to 12 carbon atoms. 2 to 12 alkylene groups are preferred. The divalent hydrocarbon group is preferably chain-shaped and may contain non-adjacent oxygen or sulfur atoms. Moreover, the divalent hydrocarbon group may have a substituent, and examples of the substituent include halogen atoms (fluorine, chlorine, bromine), cyano groups, methyl groups, ethyl groups, and the like.

The mesogenic group represented by M is a group showing the main skeleton of liquid crystal molecules that contributes to liquid crystal formation.
The mesogenic group represented by M is not particularly limited. Handbook Editing Committee, Liquid Crystal Handbook (Maruzen, 2000), particularly Chapter 3, can be referred to.
More specifically, the mesogenic group represented by M includes structures described in paragraph 0086 of JP-A-2007-279688.
The mesogenic group is preferably, for example, a group containing at least one cyclic structure selected from the group consisting of aromatic hydrocarbon groups, heterocyclic groups and alicyclic groups. Among them, the mesogenic group is preferably a group containing an aromatic hydrocarbon group, more preferably a group containing 2 to 5 aromatic hydrocarbon groups, and 3 to 5 aromatic hydrocarbon groups. A group containing a hydrogen group is more preferred.
More preferably, the mesogenic group is a group containing 3 to 5 phenylene groups, wherein the phenylene groups are linked by --CO--O--.
The cyclic structure contained in the mesogenic group may further have an alkyl group having 1 to 10 carbon atoms such as a methyl group as a substituent.

Specific examples of the compound represented by formula (1) are shown below, but the present invention is not limited thereto. "Me" represents a methyl group.

As the specific liquid crystal compound, a rod-like liquid crystal compound having reverse wavelength dispersion may be used.
As the reverse wavelength dispersion rod-shaped liquid crystal compound, the liquid crystal compound represented by the general formula 1 of JP-A-2016-81035, and the general formula (I) or (II) of JP-A-2007-279688. compounds that are More specifically, the specific liquid crystal compound with reverse wavelength dispersion includes the compounds shown below, but the present disclosure is not limited thereto.

The specific liquid crystal compound may be used singly or in combination of two or more.
The content of the specific liquid crystal compound in the liquid crystal layer-forming coating liquid is preferably 70% by mass or more and less than 100% by mass, more preferably 90% by mass to 99% by mass, based on the mass of the total solid content.
In addition, solid content refers to the component except a solvent.

-Chiral agent-
Chiral agents include various known chiral agents (for example, Liquid Crystal Device Handbook, Chapter 3, Section 4-3, Chiral Agents for TN and STN, p. 199, Japan Society for the Promotion of Science 142nd Committee, ed., 1989). You can choose from
Chiral agents generally contain an asymmetric carbon atom, but axially chiral compounds or planar chiral compounds that do not contain an asymmetric carbon atom can also be used as chiral agents.
Examples of axially or planarly chiral compounds include binaphthyl, helicene, paracyclophane, and derivatives thereof.

The chiral agent may have a polymerizable group.
When the chiral agent has a polymerizable group and the specific liquid crystal compound used in combination also has a polymerizable group, the polymerization reaction between the chiral agent having a polymerizable group and the specific liquid crystal compound having a polymerizable group causes the specific liquid crystal compound to A polymer having repeat units derived from the derivatized repeat units and repeat units derived from the chiral agent is obtained.
The polymerizable group possessed by the chiral agent having a polymerizable group is preferably the same kind of group as the polymerizable group possessed by the specific liquid crystal compound. The polymerizable group possessed by the chiral agent is preferably an unsaturated polymerizable group, an epoxy group, or an aziridinyl group, more preferably an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group. Especially preferred.

Also, the chiral agent may be a liquid crystal compound.
Examples of chiral agents exhibiting strong twisting force include JP-A-2010-181852, JP-A-2003-287623, JP-A-2002-80851, JP-A-2002-80478, and JP-A-2002-302487. Examples include chiral agents described in publications and the like, and these can also be preferably used in the liquid crystal layer-forming coating liquid of the present disclosure.
Furthermore, for the isosorbide compounds described in each of the above publications, isomannide compounds having a corresponding structure can be used as a chiral agent. can also be used as a chiral agent.

The content of the chiral agent in the liquid crystal layer-forming coating liquid is preferably 0.5% by mass to 10.0% by mass, more preferably 1.0% by mass to 3.0% by mass, based on the mass of the total solid content. preferable.

-Other ingredients-
The liquid crystal layer-forming coating liquid may contain other components such as an alignment control agent, a polymerization initiator, a leveling agent, and an alignment aid, if necessary.

• Alignment Control Agent As the alignment control agent, those capable of reducing the tilt angles of the molecules of the specific liquid crystal compound at the air interface or making them substantially horizontal are preferable.
Examples of such an alignment control agent include compounds described in paragraph numbers [0012] to [0030] of JP-A-2012-211306, and paragraph numbers [0037] to [0044] of JP-A-2012-101999. Compounds described in JP-A-2007-272185 paragraph numbers [0018] to [0043] fluorine-containing (meth) acrylate polymer described in JP-A-2005-099258 compound described in detail along with the synthesis method etc.
A polymer containing polymerized units of a fluoroaliphatic group-containing monomer in an amount of more than 50% by mass based on the total polymerized units described in JP-A-2004-331812 may also be used as the alignment control agent.

Examples of other alignment control agents include vertical alignment agents. By adding a vertical alignment agent, the vertical alignment of the liquid crystal compound can be controlled. Examples of vertical alignment agents that can be preferably used include boronic acid compounds and/or onium salts described in JP-A-2015-38598, and onium salts described in JP-A-2008-26730.

The content of the alignment control agent in the coating solution for forming the liquid crystal layer is preferably 0% by mass to 5.0% by mass, more preferably 0.3% by mass to 2.0% by mass, based on the mass of the total solid content. .

・Polymerization initiator As a polymerization initiator, both a photopolymerization initiator and a thermal polymerization initiator are used. Polymerization initiators are preferred.
Examples of photopolymerization initiators include α-carbonyl compounds (e.g., compounds described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (compounds described in US Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (e.g., compounds described in US Pat. No. 2,722,512), polynuclear quinone compounds (e.g., compounds described in US Pat. Nos. 3,046,127 and 2,951,758), triaryls Combinations of imidazole dimers and p-aminophenyl ketones (e.g., compounds described in US Pat. No. 3,549,367), acridine and phenazine compounds (e.g., JP-A-60-105667, US Pat. No. 4,239,850) compounds), oxadiazole compounds (e.g., compounds described in US Pat. No. 4,212,970), acylphosphine oxide compounds (e.g., JP-B-63-40799, JP-B-5-29234, JP-A-10 -95788, compounds described in JP-A-10-29997) and the like.

The content of the polymerization initiator in the liquid crystal layer-forming coating liquid is preferably 0.5% by mass to 5.0% by mass, and 1.0% by mass to 4.0% by mass, based on the mass of the total solid content. more preferred.

The solid content of the coating solution for forming the liquid crystal layer is, for example, preferably in the range of 25% to 40% by mass, more preferably 25% to 35% by mass, based on the total mass of the coating solution for forming the liquid crystal layer. A range is more preferred.

(coating)
As the applying means (corresponding to the applying means 10 in FIG. 1) for applying the liquid crystal layer forming coating liquid, a known applying means is applied.
Specific examples of coating means include extrusion die coater method, curtain coating method, dip coating method, spin coating method, print coating method, spray coating method, slot coating method, roll coating method, slide coating method, blade coating method, and gravure. Means using a coating method, a wire bar method, or the like can be mentioned.

(backup roll)
A backup roll (corresponding to the backup roll 12 in FIG. 1) preferably used in step A is a member on which the base material can be wound and continuously conveyed, and is rotationally driven at the same speed as the base material conveyance speed.
The backup roll used in step A is not particularly limited, and a known roll can be used.
As the backup roll, for example, one whose surface is plated with hard chrome can be preferably used.
The thickness of the plating is preferably 40 μm to 60 μm from the viewpoint of ensuring conductivity and strength.
Further, the surface roughness of the backup roll is preferably 0.1 μm or less in terms of surface roughness Ra, from the viewpoint of reducing variations in the frictional force between the base material and the backup roll.

The backup roll used in step A is a heat treatment from the viewpoint of accelerating the drying of the coating film and suppressing brushing of the coating film due to a decrease in the film surface temperature (that is, whitening of the coating film due to fine condensation). May be warmed.
The surface temperature of the backup roll may be determined according to the composition of the coating film, the curing performance of the coating film, the heat resistance of the substrate, and the like. preferable.

It is preferable that the surface temperature of the backup roll used in step A is detected and the surface temperature of the backup roll is maintained by temperature control means based on the detected temperature.
The backup roll temperature control means includes heating means and cooling means. Induction heating, water heating, oil heating, or the like is used as the heating means, and cooling with cooling water is used as the cooling means.

The diameter of the backup roll used in step A is preferably 100 mm to 1000 mm, more preferably 100 mm to 800 mm, from the viewpoints of easy winding of the base material, easy application by a coating means, and the production cost of the backup roll. Preferably, 200 mm to 700 mm is more preferable.

The conveying speed of the base material on the backup roll in the step A is preferably 10 m/min or more and 100 m/min or less from the viewpoint of securing productivity and the viewpoint of coatability.

The wrap angle of the substrate with respect to the backup roll is preferably 60° or more, more preferably 90° or more, from the viewpoints of stabilizing the transportation of the substrate during coating and suppressing the occurrence of thickness unevenness in the coating film. Also, the upper limit of the wrap angle can be set to 180°, for example.
Note that the wrap angle is an angle formed by the direction in which the substrate is conveyed when the substrate contacts the backup roll and the direction in which the substrate is conveyed when the substrate separates from the backup roll.

[Step B]
In step B, the coating film formed is dried to a residual solvent content of 50% by mass or less.
The residual solvent rate in the coating film in step B is preferably 40% by mass or less, more preferably 30% by mass or less. The lower limit of the residual solvent rate in the coating film in step B is preferably 10% by mass from the viewpoint of easily suppressing deterioration of the coating surface condition.
The residual solvent rate in the coating film may be 50% by mass or less immediately before the step C, for example, after drying by the drying means described later and during transportation before being subjected to the step C Secondly, the residual solvent rate in the coating film should be 50% by mass or less.
In step B, the density of the specific liquid crystal compound in the coating film increases during the process in which the residual solvent rate becomes 50% by mass or less, resulting in cholesteric liquid crystals. The cholesteric liquid crystal in step B often has a helical axis parallel to the surface direction of the coating film. However, in the coating film in which the residual solvent rate is 50% by mass or less in step B, the direction of the helical axis of the cholesteric liquid crystal varies within the plane when viewed from above.

An example of step B will be described with reference to FIG.
In step B, the coating liquid for forming the liquid crystal layer is applied by the coating means 10 , and then the coating film is dried by the drying area of the drying means 20 .
The dried coating film is transported to process C via transport rolls 52 . In step B, the residual solvent rate in the coating film may be 50% by mass or less before the shearing force is applied to the coating film surface in step C.

(dry)
A known drying means is applied as the drying means (corresponding to the drying means 20 in FIG. 1) used for drying the coating film.
Specific examples of drying means include means using a method using an oven, a hot air machine, an infrared (IR) heater, or the like.
In drying with a hot air machine, hot air may be applied from the side opposite to the coating film forming surface of the base material, and a diffusion plate may be installed so that the coating film surface does not flow with hot air. .
Drying may also be performed by suction. Drying by suction is a method of reducing the percentage of residual solvent in the coating film by using a decompression chamber or the like having an exhaust mechanism to suck gas on the coating film.
The drying conditions may be conditions that allow the residual solvent content in the coating film to be 50% by mass or less, and may be determined according to the composition, coating amount, transport speed, and the like of the coating film for forming the liquid crystal layer.

Here, the residual solvent rate of the coating film is measured by the absolute dry method.
Specifically, a part of the coating film is scraped off, dried at, for example, 60° C. (below the temperature at which the material constituting the coating film volatilizes) for 24 hours, and the residual solvent ratio is determined from the change in mass before and after drying. This is repeated 3 times, and the average value of the 3 times is taken as the residual solvent ratio.

[Step C]
In step C, a shearing force is applied to the surface of the dried coating film.
As described above, the coating film after drying in step B is in a state in which the directions of the helical axes of the cholesteric liquid crystals vary within the plane when viewed from above.
Therefore, in the manufacturing method of the cholesteric liquid crystal film of the present disclosure, the step C is performed after the step B to reduce the variation in the direction of the helical axis of the cholesteric liquid crystal when the coating film is viewed from above. Specifically, in step C, a shearing force is applied to the surface of the coating film after step B.
When a shearing force is applied to the surface of the coating film, the shearing force causes the helical axes of the cholesteric liquid crystals to be regularly aligned perpendicular to the shearing direction. As a result, through step C, the helical axes of the cholesteric liquid crystal are aligned parallel to the film surface direction and perpendicular to the shear direction, and the alignment is less varied within the film surface (that is, the alignment accuracy A cholesteric liquid crystal film is obtained.
A cholesteric liquid crystal film with excellent alignment accuracy can be confirmed by the fact that when the cholesteric liquid crystal film is viewed from above, the scattering region (the white region described above) is small.
From the viewpoint of improving the uniformity of the shearing force, it is preferable that the application of the shearing force to the coating film surface in the step C is performed on the base material wound on the backup roll.

An example of process C will be described with reference to FIG.
In step C, the drying means 20 scrapes off the upper surface of the coating film after drying, in which the residual solvent content in the coating film is 50% by mass or less, with a blade 30 to apply a shearing force.
Thereby, a shearing force is applied along the conveying direction of the coating film (that is, the conveying direction of the substrate).
As shown in FIG. 1 , it is preferable that the blade 30 apply shearing force to a region where the base material F is wound on the backup roll 32 .

In FIG. 1, the blade 30 is used to apply a shearing force to the coating surface, but the present disclosure is not limited to this, and the helical axes of the cholesteric liquid crystals can be aligned perpendicularly to the shearing direction. Any possible method may be used. Means for applying a shearing force other than blades include air knives, bars, applicators, and the like.

(shear rate)
In step C, when a shear force is applied to the surface of the dried coating film, the higher the shear rate, the easier it is to obtain a cholesteric liquid crystal film with excellent alignment accuracy. Specifically, the shear rate is preferably 1000 sec ^-1 (1/sec) or more, more preferably 10000 sec ^-1 (1/sec) or more, and 30000 sec ^-1 (1/sec ) or more is more preferable.
Note that the upper limit of the shear rate is, for example, 1.0×10 ⁶ seconds ⁻¹ (1/sec) or less.
For example, as shown in FIG. 1, when a shear force is applied to the coating film surface with the blade 30, the shear rate is determined by setting the shortest distance between the blade 30 and the substrate to "d", and the thickness of the coating film in contact with the blade. It is obtained by "V/d", where "V" is the conveying speed (that is, the relative speed between the coating film and the blade).
In addition, when applying a shear force to the coating film surface with an air knife, the shear rate was set to "h", which is the thickness of the coating film after shearing, and "V", the relative speed between the coating film surface and the substrate surface. is obtained from "V/2h".

(Applying shear force by blade)
As shown in FIG. 1, in the case of the method of applying a shearing force to the coating film surface with a blade 30, it is preferable to scrape off the upper surface of the coating film.
In other words, in the application of the shearing force by the blade, the thickness of the coating film is regulated by the blade.
The film thickness of the coating film after the shearing force is applied by the blade may be 1/2 or less or 1/3 or less of the thickness before the shearing force is applied. However, as the lower limit of the film thickness regulation, for example, it is preferable that the thickness of the coating film after the shearing force is applied by the blade is 1/4 or more of the thickness before the shearing force is applied.

There are no particular restrictions on the shape, material, etc. of the blade used to apply the shearing force.
The blade may be a plate-shaped member made of metal such as stainless steel, or a plate-shaped member made of resin such as Teflon (registered trademark) or PEEK (polyetheretherketone).
From the viewpoint of easily imparting a constant shearing force to the coating film, it is preferable to use a metal plate-shaped member, and the thickness of the tip that contacts the coating film (that is, the thickness along the transport direction of the coating film) is preferably a metal plate-shaped member having a thickness of 0.1 mm or more (preferably 1 mm or more). The upper limit of the thickness of the metal plate member is, for example, about 10 mm.

(Applying shear force by air knife)
In the method of applying a shearing force to the surface of the coating film using an air knife, the shearing force is applied by blowing compressed air onto the upper surface of the coating film using an air knife.
The shear rate imparted to the coating film can be adjusted by the speed at which the compressed air is blown (that is, the flow rate).
The direction of the compressed air blown by the air knife may be the same as or opposite to the conveying direction of the coating film. It is preferable that the direction is the same as the conveying direction of the coating film from the viewpoint of preventing adhesion.

(Temperature of coating film surface)
In step C, the temperature of the coating film surface to which the shear force is applied depends on the phase transition temperature of the specific liquid crystal compound used, but is generally preferably from 50 ° C. to 120 ° C., and at 60 ° C. to 100 ° C. It is more preferable to have
By setting the temperature of the coating film surface within the above range, it becomes easier to align the helical axes of the cholesteric liquid crystals perpendicularly to the shearing direction by applying a shearing force, and a cholesteric liquid crystal film with high alignment accuracy can be obtained.
Here, the temperature of the coating film surface is a value measured using a radiation thermometer whose emissivity is calibrated with a temperature value measured by a non-contact thermometer. Measurements are taken with no reflectors within 10 cm of the surface on the side opposite to the surface to be measured (back side).

(backup roll)
A backup roll (corresponding to the backup roll 32 in FIG. 1) preferably used in the step C is a member capable of continuously conveying the base material wound thereon, and is rotationally driven at the same speed as the base material conveying speed.
The backup roll used in step C is the same as the backup roll used in step A, and preferred embodiments are also the same.
In addition, the process A and the process C may be performed on one backup roll.

The backup roll used in step C may be heated from the viewpoint of controlling the temperature of the surface of the coating film within the above range.
The surface temperature of the backup roll is, for example, preferably 50°C to 120°C, more preferably 60°C to 100°C.

It is preferable that the surface temperature of the backup roll used in step C is detected and the surface temperature of the backup roll is maintained by temperature control means based on the detected temperature.
The temperature control means for the backup roll is the same as the backup roll used in step A.

The diameter of the backup roll used in step C is preferably 100 mm to 1000 mm, more preferably 100 mm to 800 mm, from the viewpoints of easy winding of the base material, easy application of shear force, and the production cost of the backup roll. Preferably, 200 mm to 700 mm is more preferable.

The conveying speed of the base material on the backup roll in step C is preferably 10 m/min or more and 100 m/min or less from the viewpoint of ensuring productivity and improving the uniformity of the shear force.

The wrap angle of the substrate with respect to the backup roll in step C is preferably 60° or more, more preferably 90° or more, from the viewpoints of stabilizing the transportation of the substrate during coating and increasing the uniformity of the shearing force. Also, the upper limit of the wrap angle can be set to 180°, for example.

The thickness of the coating film when the shearing force is applied in step C (that is, the thickness of the coating film dried in step B) is 70 μm from the viewpoint of increasing the alignment accuracy of the helical axis of the cholesteric liquid crystal due to the shearing force. It is preferably 50 μm or less, more preferably 15 μm to 50 μm.

The thickness of the coating film after applying the shearing force in step C is preferably 10 μm or less from the viewpoint of increasing the alignment accuracy of the helical axis of the cholesteric liquid crystal due to the shearing force.
Moreover, the thickness of the coating film obtained through the step C (that is, the coating film after being subjected to the shearing force in the step C) may be determined according to the application.
The thickness of the coating film obtained through step C is preferably, for example, 5 μm or more.

[Step D]
In the method for producing a cholesteric liquid crystal film of the present disclosure, when the coating film contains a polymerizable compound (specifically, a specific liquid crystal compound having a polymerizable group, a chiral agent having a polymerizable group, etc.), after step C, It is preferable to include a step D of curing the coating film.
In step D, it is preferable to apply heat or irradiate active energy rays to the coating film to which the shearing force has been applied to cure the coating film.
In consideration of production aptitude and the like, it is preferable to use curing with active energy rays emitted from the active energy ray irradiation means 40 as shown in FIG.

There are no particular restrictions on the means for irradiating the active energy ray as long as it is a means for imparting energy capable of generating active species in the coating film to be irradiated.
Specific examples of active energy rays include α-rays, γ-rays, X-rays, ultraviolet rays, infrared rays, visible rays, electron beams, and the like. Among these, ultraviolet rays are preferably used as active energy rays from the viewpoint of curing sensitivity and availability of equipment.

Examples of ultraviolet light sources include lamps such as tungsten lamps, halogen lamps, xenon lamps, xenon flash lamps, mercury lamps, mercury xenon lamps, carbon arc lamps, and various lasers (e.g., semiconductor lasers, helium neon lasers, argon ion lasers, etc.). lasers, helium-cadmium lasers, YAG (Yttrium Aluminum Garnet) lasers), light-emitting diodes, cathode ray tubes, and the like.
The peak wavelength of ultraviolet rays emitted from the ultraviolet light source is preferably 200 nm to 400 nm.
Moreover, the exposure energy amount of ultraviolet rays is preferably 100 mJ/cm ² to 500 mJ/cm ² , for example.

As described above, a cholesteric liquid crystal film is produced on the substrate.
A laminate of a substrate and a cholesteric liquid crystal film may be used as an optical film.

[Other processes]
The manufacturing method of the cholesteric liquid crystal film of the present disclosure may have other steps in addition to the steps A to D described above.
Other steps include a step of forming an alignment layer on the substrate used in step A.
That is, the substrate used in step A may be a substrate provided with an alignment layer.

(Orientation layer)
The alignment layer is not particularly limited as long as it is a layer capable of imparting an alignment regulating force to the liquid crystal compound.
The alignment layer can be provided by, for example, rubbing treatment of an organic compound (preferably polymer), oblique vapor deposition of an inorganic compound, or formation of a layer having microgrooves.
Moreover, the alignment layer may be an alignment layer in which an alignment function is produced by application of an electric field, application of a magnetic field, or light irradiation.
When the substrate is made of a resin, depending on the type of resin (eg, PET (polyethylene terephthalate), etc.), the substrate may be directly oriented (eg, rubbed) without providing an orientation layer. The surface of the material can also function as an alignment layer.

In the method for producing a cholesteric liquid crystal film of the present disclosure, an alignment layer is not essential, and the helical axes of the cholesteric liquid crystals can be aligned by applying a shearing force to the coating film in step C without using an alignment layer.

[Optical film]
In the method for producing a cholesteric liquid crystal film of the present disclosure, when an optically isotropic polymer film is used as a substrate and a cholesteric liquid crystal film is formed on this polymer film, the resulting laminate can be used as an optical film. can.
Also, the cholesteric liquid crystal film itself may be used as an optical film.
The cholesteric liquid crystal film obtained by the method for producing a cholesteric liquid crystal film of the present disclosure can exhibit a function as a light reflecting layer. Therefore, it is also suitable as an optical film used in an aerial imaging device.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[Example 1]
(Preparation of base material)
A long triacetyl cellulose (TAC) film (manufactured by Fuji Film Co., Ltd., refractive index 1.48) having a thickness of 80 μm and a width of 300 mm was prepared as a base material.

(Preparation of Liquid Crystal Layer Forming Coating Liquid 1)
After mixing each component described below, the mixture was filtered through a polypropylene filter having a pore size of 0.2 μm to prepare a coating liquid 1 for forming a liquid crystal layer.

- Liquid crystal layer forming coating solution 1 -
・Rod-shaped thermotropic liquid crystal compound (compound (A) below): 100 parts by mass ・Chiral agent (compound (B) below): 2.5 parts by mass ・Photopolymerization initiator: 3 parts by mass (IRGACURE (registered trademark) 907, BASF)
Alignment regulator (compound (C) below): 0.2 parts by mass Vertical alignment agent (compound (D) below): 0.5 parts by mass Solvent (methyl ethyl ketone): 215 parts by mass

(Step A and Step B)
The coating liquid 1 for forming a liquid crystal layer was applied onto the continuously conveyed base material using a die coating method, and then passed through an oven at 70° C. for 60 seconds to dry the coating film.
Regarding step A, specifically, the substrate is conveyed onto a backup roll having a surface temperature of 25° C. and an outer diameter of 300 mm, and as shown in FIG. was used to apply the coating liquid 1 for liquid crystal layer formation.
The conveying speed of the substrate in steps A and B was 10 m/min.
Moreover , the thickness of the coating film after drying was 50 μm, and the coating width was 250 mm.

(Process C)
A shearing force was applied to the dried coating film with a stainless steel blade (thickness at tip: 1 mm).
Specifically, for step C, first, a blade was placed on a backup roll having a surface temperature of 70° C. and an outer diameter of 500 mm so that the tip thereof was positioned 20 μm apart from the substrate surface. Also, the blade was kept at 70°C. Then, the substrate having the coating film that had undergone the step B was transported onto a backup roll, and the coating film surface was pressed against a blade to scrape off the upper surface of the coating film.
The shear rate imparted by the blade was 10000 sec ^-1 .
The thickness of the coating film after the step C was 10 μm.
In addition, the conveying speed of the base material in the process C was 12 m/min.

(Process D)
Using a high-pressure mercury lamp, the coating film after step C was irradiated with ultraviolet rays at an exposure energy of 500 mJ/cm ² to cure the coating film.
As described above, a cholesteric liquid crystal film was produced on the substrate.

[Examples 2 to 3, Comparative Example 2]
A cholesteric liquid crystal film was produced on a substrate in the same manner as in Example 1, except that the drying conditions (specifically, the drying time) in step B were changed to change the solvent residual ratio in the coating film.

[Example 4]
A cholesteric liquid crystal film was produced on a substrate in the same manner as in Example 1, except that the transport speed of the coating film in step C was changed to 36 m/min.

[Example 5]
A cholesteric liquid crystal film was produced on a substrate in the same manner as in Example 1, except that the following orientation layer forming step was performed before step A.

(Orientation layer forming step)
-Preparation of alignment layer composition A-
A mixture of 96 parts by mass of pure water and PVA-205 (polyvinyl alcohol manufactured by Kuraray Co., Ltd.) was stirred and dissolved in a container kept at 80° C. to prepare an alignment layer composition.
The alignment layer composition was applied using a #6 bar onto the triacetyl cellulose (TAC) film, which was continuously conveyed, and then dried in an oven at 100°C for 10 minutes. Rubbing treatment was performed in the direction perpendicular to the

[Example 6]
(Step A and Step B)
The liquid crystal layer forming coating liquid 1 described above was applied onto the continuously conveyed base material using a die coating method, and then passed through an oven at 70° C. for 60 seconds to dry the coating film.
Regarding step A, specifically, the substrate is conveyed onto a backup roll having a surface temperature of 25° C. and an outer diameter of 300 mm, and as shown in FIG. was used to apply the coating liquid 1 for liquid crystal layer formation.
The conveying speed of the substrate in steps A and B was 10 m/min.
Moreover , the thickness of the coating film after drying was 50 μm, and the coating width was 250 mm.

(Process C)
A shearing force was applied to the dried coating film with an air knife.
Specifically for step C, the substrate having the coating film that has undergone step B is conveyed to a backup roll having a surface temperature of 70° C. and an outer diameter of 500 mm, and compressed air is applied to the coating film surface on the backup roll with an air knife. guessed The blowing direction of the compressed air was the same as the conveying direction of the coating film.
The shear rate imparted by the air knife was 10000 sec ^-1 .
The thickness of the coating film after the step C was 10 μm.
In addition, the conveying speed of the base material in the process C was 12 m/min.

(Process D)
Using a high-pressure mercury lamp, the coating film after step C was irradiated with ultraviolet rays at an exposure energy of 500 mJ/cm ² to cure the coating film.
As described above, a cholesteric liquid crystal film was produced on the substrate.

[Examples 7-8]
A cholesteric liquid crystal film was produced on a substrate in the same manner as in Example 6, except that the drying conditions (specifically, the drying time) in step B were changed to change the solvent residual ratio in the coating film.

[Example 9]
A cholesteric liquid crystal film was produced on a substrate in the same manner as in Example 1, except that the transport speed of the coating film in step C was changed to 36 m/min.

[Example 10]
A cholesteric liquid crystal film was produced on a substrate in the same manner as in Example 6, except that the orientation layer forming step was performed in the same manner as in Example 5 before the step A.

[Comparative Example 1]
A cholesteric liquid crystal film was produced on a substrate in the same manner as in Example 3, except that Step C was not performed.

〔evaluation〕
(Observation with a polarizing microscope)
Using a polarizing microscope NV100LPOL manufactured by Nikon Corporation, a cross-Nicol polarized transmission photograph of the upper surface of the cholesteric liquid crystal film was taken, and the stripe pattern (that is, the pattern generated at the helical pitch) and the state of the orientation defect were observed from the photograph image. .

The helical axis of the cholesteric liquid crystal was confirmed by the above-described method based on the striped pattern appearing in the crossed Nicol polarized transmission photograph, and evaluated according to the following criteria.
By confirming that the striped patterns are aligned parallel to the transport direction of the coating film, it can be confirmed that the spiral axis of the cholesteric liquid crystal is aligned perpendicular to the transport direction (that is, the shear direction) of the coating film.
-Evaluation criteria-
A: The striped pattern is clearly visible in parallel with the conveying direction of the coating film, and there is no orientation defect in which a part of the striped pattern is interrupted.
B: The striped pattern is clearly visible in parallel with the conveying direction of the coating film, but an alignment defect in which a part of the striped pattern is interrupted is slightly visible.
C: The striped pattern appears to be aligned parallel to the conveying direction of the coating film, but there are many alignment defects in which a part of the striped pattern is interrupted.
D: Striped pattern is not visible.

(Observation by SEM)
A cross section of the cholesteric liquid crystal film was observed using an SEM (SU3500 manufactured by Hitachi High-Technologies Corporation), and it was confirmed by the above-described method whether or not the helical axis of the cholesteric liquid crystal was parallel to the film surface direction.
-Evaluation criteria-
A: The helical axis of the cholesteric liquid crystal is parallel to the film surface direction.
B: The helical axis of the cholesteric liquid crystal is not parallel to the film surface direction.

(Evaluation of Orientation Accuracy)
Alignment accuracy in the cholesteric liquid crystal film was evaluated by confirming the scattering region (ie, the white region in the photograph) due to fine variations in the alignment of the spiral axis of the cholesteric liquid crystal by the method described above.

The measured scattering of the optical film was evaluated according to the following criteria. It was judged that the smaller the scattering area (that is, the white area in the photograph), the better the alignment accuracy, that is, the less the film surface variation.
-Evaluation criteria-
A: The ratio of the white area to the total area of the test piece (that is, the area ratio) is 0% (in other words, no white area is seen in the photograph).
B: The ratio of the white region to the total area of the test piece (that is, the area ratio) is 10% or less.
C: The ratio of the white region to the total area of the test piece (that is, the area ratio) is more than 10%.

As shown in Table 1, in all the cholesteric liquid crystal films obtained in Examples, the helical axis of the cholesteric liquid crystal is parallel to the film surface direction (the helical axis of the cholesteric liquid crystal and the film surface direction of the cholesteric liquid crystal film angle = 50° to 90°) and are arranged along a specific direction when viewed from above, and there is little variation in the arrangement within the film surface (that is, the alignment accuracy is excellent).

The disclosure of Japanese Patent Application No. 2019-064853 filed on March 28, 2019 is incorporated herein by reference in its entirety.
All publications, patent applications and technical standards mentioned herein are to the same extent as if each individual publication, patent application and technical standard were specifically and individually noted to be incorporated by reference. incorporated herein by reference.

Claims (8)

A step A of applying a coating liquid containing a solvent, a rod-shaped thermotropic liquid crystal compound, and a chiral agent to a substrate to form a coating film;
A step B of drying the formed coating film to a residual solvent rate of 50% by mass or less;
A step C of applying a shearing force to the surface of the dried coating film;
A method for producing a cholesteric liquid crystal film in which the helical axes are parallel to the film surface direction and perpendicular to the shear direction. 2. The method for producing a cholesteric liquid crystal film according to claim 1, wherein step C is a step of applying a shearing force with a shear rate of 1000 sec ^-1 or more. 3. The method for producing a cholesteric liquid crystal film according to claim 1, wherein the temperature of the coating film surface in step C is 50.degree. C. to 120.degree. 4. The method for producing a cholesteric liquid crystal film according to any one of claims 1 to 3, wherein the application of the shearing force in step C is performed with a blade. 4. The method for producing a cholesteric liquid crystal film according to any one of claims 1 to 3, wherein the application of shearing force in step C is performed with an air knife. 6. The method for producing a cholesteric liquid crystal film according to any one of claims 1 to 5, further comprising a step of curing the coating film after step C. 7. The method for producing a cholesteric liquid crystal film according to any one of claims 1 to 6, wherein the coating film has a thickness of 30 μm or less when a shearing force is applied in step C. 8. The method for producing a cholesteric liquid crystal film according to any one of claims 1 to 7, wherein the coating film has a thickness of 10 μm or less after being subjected to the shearing force in step C.

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