阅读说明：本技术 胆甾醇型液晶膜的制造方法 (Method for producing cholesteric liquid crystal film ) 是由 国安谕司 斋川保 市桥光芳 中山元 远山浩史 于 2020-03-25 设计创作，主要内容包括：本发明的一实施方式提供一种胆甾醇型液晶膜的制造方法,所述胆甾醇型液晶膜的螺旋轴与膜面方向平行且沿着与剪切方向垂直的方向排列,所述胆甾醇型液晶膜的制造方法包括：工序A,在基材上涂布含有溶剂、棒状热致液晶化合物及手性试剂的涂布液来形成涂膜；工序B,使所形成的涂膜中的残留溶剂率干燥至50质量％以下；及工序C,对干燥后的涂膜表面赋予剪切力。(One embodiment of the present invention provides a method for producing a cholesteric liquid crystal film having a helical axis parallel to a film plane direction and aligned in a direction perpendicular to a shear direction, the method comprising: a step (A) of applying a coating liquid containing a solvent, a rod-like thermotropic liquid crystal compound, and a chiral agent onto a substrate to form a coating film; a step (B) for drying the residual solvent content in the formed coating film to 50 mass% or less; and a step C of applying a shear force to the surface of the dried coating film.)

1. A method for producing a cholesteric liquid crystal film having a helical axis parallel to a film plane direction and aligned in a direction perpendicular to a shear direction, the method comprising:

a step (A) of applying a coating liquid containing a solvent, a rod-like thermotropic liquid crystal compound, and a chiral agent onto a substrate to form a coating film;

a step (B) for drying the residual solvent content in the formed coating film to 50 mass% or less; and

and a step C of applying a shear force to the surface of the dried coating film.

2. The method of manufacturing a cholesteric liquid crystal film according to claim 1,

step C of imparting a shear rate of 1000 second^-1The step of shearing force described above.

3. The method for producing a cholesteric liquid crystal film according to claim 1 or 2, wherein,

the temperature of the coating film surface in the step C is 50 to 120 ℃.

4. The method of manufacturing a cholesteric liquid crystal film according to any one of claims 1 to 3, wherein,

the shear force in step C is applied by a doctor blade.

5. The method of manufacturing a cholesteric liquid crystal film according to any one of claims 1 to 3, wherein,

the shearing force in step C is applied by 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 the step C.

7. The method of manufacturing a cholesteric liquid crystal film according to any one of claims 1 to 6, wherein,

the thickness of the coating film when a shear force is applied in step C is 30 μm or less.

8. The method of manufacturing a cholesteric liquid crystal film according to any one of claims 1 to 7, wherein,

the thickness of the coating film after the shear force is applied in step C is 10 μm or less.

Technical Field

The present invention relates to a method for producing a cholesteric liquid crystal film.

Background

An optical film using a liquid crystal film having a large optical anisotropy is known.

In such an optical film, the liquid crystal film is manufactured, for example, as follows: a coating liquid containing a liquid crystal compound is applied to a member to be coated and dried, and alignment treatment of the liquid crystal compound, polymerization of the liquid crystal compound, and the like are performed as necessary.

Japanese laid-open patent publication No. 2016-150286 discloses the following: in the method for producing an optical film, a coating film of a liquid crystal material applied to a film-forming surface of a substrate is conveyed together with the substrate into a drying furnace, and a liquid crystal layer is formed by removing a solvent. Further, it is described that the liquid crystal molecules can be aligned in addition to drying, and polymerization of liquid crystal monomers can be performed, and in particular, it is disclosed that the liquid crystal molecules can be aligned in a predetermined alignment by applying a shear force to the lyotropic liquid crystal.

Further, the following is disclosed in japanese unexamined patent publication No. 2010-536782: as one of the processes for producing a liquid crystal layer of a desired liquid crystal phase, a knife edge is applied to the liquid crystal layer and mechanical shear is applied to the liquid crystal layer.

Disclosure of Invention

Technical problem to be solved by the invention

As a cholesteric liquid crystal film, it is expected to be applied to an optical film for use in an aerial image forming apparatus or the like by aligning a helical axis of cholesteric liquid crystal in parallel with a film surface direction and in a specific direction in a plan view.

In particular, there is an increasing demand for cholesteric liquid crystal films with less variation in the alignment of the helical axis within the film surface.

Although the above-mentioned Japanese patent laid-open No. 2016-150286 discloses the application of shear force to a lyotropic liquid crystal, it does not describe any cholesteric liquid crystal film in which the helical axis is aligned in a direction parallel to the film surface direction.

In addition, although japanese unexamined patent application publication No. 2010-536782 discloses a treatment of a liquid crystal layer for producing a desired liquid crystal phase, it does not describe the application of mechanical shearing to the extent of the drying state of the liquid crystal layer. Furthermore, in japanese patent application publication No. 2010-536782, only the axis of the molecular helix is described as extending in the lateral direction with respect to the layer, and the content that the axis is aligned in parallel with the film surface direction and in a specific direction in a plan view of the layer is not explicitly described. Therefore, in the liquid crystal layer described in japanese laid-open patent publication No. 2010-536782, the deviation of the alignment of the axes of the molecular helices in the plane is less likely to be small.

Accordingly, an object to be solved by one embodiment of the present invention is to provide a method for producing a cholesteric liquid crystal film in which a helical axis of cholesteric liquid crystal is aligned in parallel with a film surface direction and along a specific direction in a plan view, and the alignment has little variation in film surface.

Hereinafter, the case where the deviation of the arrangement of the helical axes in the film plane is small is also referred to as "excellent alignment accuracy".

Means for solving the technical problem

Specific means for solving the problems include the following means.

< 1 > A method for producing a cholesteric liquid crystal film having a helical axis parallel to a film plane direction and aligned in a direction perpendicular to a shear direction, comprising:

a step (A) of applying a coating liquid containing a solvent, a rod-like thermotropic liquid crystal compound, and a chiral agent onto a substrate to form a coating film;

a step (B) for drying the residual solvent content in the formed coating film to 50 mass% or less; and

and a step C of applying a shear force to the surface of the dried coating film.

< 2 > the method for producing a cholesteric liquid crystal film according to < 1 >, wherein the step C is a step of applying a shear rate for 1000 seconds^-1The step of shearing force described above.

< 3 > the method for producing a cholesteric liquid crystal film, according to < 1 > or < 2 >, wherein the temperature of the surface of the coating film in the step C is 50 ℃ to 120 ℃.

< 4 > 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 the step C is performed by a doctor 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 the step C is performed by 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 the step C.

< 7 > the method for producing a cholesteric liquid crystal film, according to any one of < 1 > to < 6 >, wherein the thickness of the coating film when the shear force is applied in the step C is 30 μm or less.

< 8 > the method for producing a cholesteric liquid crystal film, according to any one of < 1 > to < 7 >, wherein the thickness of the coating film after the application of the shearing force in the step C is 10 μm or less.

Effects of the invention

According to one embodiment of the present invention, there is provided a method for producing a cholesteric liquid crystal film, in which a helical axis of cholesteric liquid crystal is aligned in parallel to a film surface direction and along a specific direction in a plan view, and the alignment has little variation in a film surface (that is, excellent alignment accuracy).

Drawings

Fig. 1 is a schematic diagram for explaining an example of a method for producing a cholesteric liquid crystal film according to the present invention.

Detailed Description

The method for producing a cholesteric liquid crystal film according to the present invention will be described in detail below.

In the present invention, the term "step" includes not only an independent step but also a step that can achieve the intended purpose of the step even when the step is not clearly distinguished from other steps.

In the present invention, the numerical range represented by "to" represents a range including numerical values before and after "to" as the minimum value and the maximum value, respectively.

In the numerical ranges recited in the present invention, the upper limit or the lower limit recited in a certain numerical range may be replaced with the upper limit or the lower limit recited in another numerical range recited in a stepwise manner. In addition, in the numerical ranges described in the present invention, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the values shown in the examples.

In addition, when the reference numerals in the drawings are the same, the same objects are referred to.

The present inventors have found a novel liquid crystal alignment method using a step of applying a shear force to a coating film, thereby obtaining a cholesteric liquid crystal film in which the helical axis of cholesteric liquid crystal is aligned parallel to the film surface direction and in a direction perpendicular to the shear direction, and the alignment has little variation in the film surface (i.e., excellent alignment accuracy).

Specifically, the following method is used: a shear force is applied to the surface of a coating film obtained by applying and drying a coating liquid containing a solvent, a rod-like thermotropic liquid crystal compound (hereinafter, also referred to as a specific liquid crystal compound) and a chiral agent. In particular, it has been found that a cholesteric liquid crystal film in which the helical axis of cholesteric liquid crystal is aligned parallel to the film surface direction and in the direction perpendicular to the shear direction and further the alignment thereof is less deviated within the film surface (i.e., excellent alignment accuracy) can be obtained by applying a shear force to a coating film dried to have a residual solvent content of 50 mass% or less.

In addition, in the new liquid crystal alignment method, since the alignment of the liquid crystal is performed by the shear force, the following effects are also exhibited: an alignment film (also referred to as an alignment layer) disposed adjacent to the cholesteric liquid crystal film is generally not required.

In the present invention, the case where the helical axis of the cholesteric liquid crystal is aligned in parallel with the film surface direction is also referred to as "horizontal alignment", which means that the helical axis of the cholesteric liquid crystal is aligned horizontally with respect to the film surface direction of the cholesteric liquid crystal film (in other words, perpendicularly to the film thickness direction of the cholesteric liquid crystal film). However, the helical axis of the cholesteric liquid crystal does not need to be strictly horizontal to the film surface direction of the cholesteric liquid crystal film, and when the angle formed by the helical axis of the cholesteric liquid crystal and the film surface direction of the cholesteric liquid crystal film is less than 45 °, it is considered to be included in the "horizontal alignment" in the present invention. The angle formed by 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 °.

The helical axis of the cholesteric liquid crystal is aligned in a direction perpendicular to the shear direction, which means that the helical axis of the cholesteric liquid crystal is aligned perpendicular to the direction in which the shear force is applied when the cholesteric liquid crystal film is produced. That is, when a shear force is applied in the longitudinal direction in the production of a long cholesteric liquid crystal film, the helical axis of cholesteric liquid crystal is aligned perpendicular to the longitudinal direction of the cholesteric liquid crystal film (in other words, parallel to the short-side direction of the cholesteric liquid crystal film) in a plan view. However, the helical axis of the cholesteric liquid crystal does not need to be strictly perpendicular to the shear direction, and when the angle formed by the helical axis of the cholesteric liquid crystal and the shear direction is less than 90 ° ± 45 °, it is considered to be included in "perpendicular to the shear direction" in the present invention. The angle formed by the helical axis of the cholesteric liquid crystal and the shear direction is preferably in the range of 60 ° to 120 °.

The following method was used to confirm the alignment of the helical axis of the cholesteric liquid crystal in the cholesteric liquid crystal film.

First, the alignment of the helical axis of the cholesteric liquid crystal parallel to the film surface direction and in the direction perpendicular to the shear direction was confirmed by using a cross-nicol polarized light transmission photograph and a cross-sectional SEM photograph taken by a polarized light microscope.

Cholesteric liquid crystals have a laminated structure in which layers composed of a group of molecules of a specific liquid crystal compound are laminated. In each layer, molecules of each specific liquid crystal compound are aligned in a predetermined direction, and the alignment direction of the molecules in each layer is deviated so as to turn into a spiral shape as it advances in the lamination direction.

Therefore, in the cross nicol polarized light transmission photograph, a region of the layer aligned in a state perpendicular or nearly perpendicular to the photographing direction corresponding to the alignment direction of the molecules of the specific liquid crystal compound appears lighter, and a region other than the layer appears darker.

Therefore, in the cross nicol polarized light transmission photograph of the upper surface of the cholesteric liquid crystal film, it was confirmed that the helical axis of the cholesteric liquid crystal was aligned in the direction perpendicular to the shear direction by aligning the regular fringe pattern in parallel with the shear direction based on the above-described shade.

In the regular stripe pattern, a line (non-broken) composed of a light portion is selected in the central portion of the photograph, and if the angle formed by the line and the shear direction is less than 45 °, the angle formed by the helical axis of the cholesteric liquid crystal and the shear direction is less than 90 ° ± 45 °.

When the helical axis of the cholesteric liquid crystal is aligned in a direction parallel to the film surface direction, the cross section of the cholesteric liquid crystal film in the thickness direction can be confirmed by a photograph (also referred to as a cross-sectional SEM photograph) taken with a Scanning Electron Microscope (SEM) at a magnification of 5000. Here, the cross section in the thickness direction of the cholesteric liquid crystal film is a cross section cut along a direction orthogonal to the shear direction (for example, the transport direction of the coating film).

In the cross-sectional SEM photograph, one cholesteric liquid crystal is selected without interruption, and if the angle formed by the helical axis of the cholesteric liquid crystal and the film surface direction of the cholesteric liquid crystal film is less than 45 °, it can be said that the helical axis of the cholesteric liquid crystal is aligned in the direction parallel to the film surface direction.

The following method was used to confirm whether or not the alignment accuracy in the cholesteric liquid crystal film was excellent.

A2 cm square test piece was cut out from the specimen. The test piece is placed on a black background, an equi-magnification photograph is taken under white light, and the resulting photograph is subjected to binarization processing using image processing software (e.g., Jtrim, etc.). Then, the number of white pixels is obtained from the binarized image, and this is set as the area of the "white region".

When the alignment of the helical axes of the cholesteric liquid crystals varies slightly, scattering occurs in this region, and the region appears as the "white region".

The smaller the proportion of the white region in the total area of the test piece in the photograph (i.e., the total number of white and black pixels in the binarized image) (i.e., the area ratio of the white region), the smaller the deviation of the alignment of the helical axis of the cholesteric liquid crystal in the film surface, and it can be judged that the alignment accuracy is excellent.

For example, it is an index that the proportion of the white region in the total area of the test piece in the photograph is 10% or less.

Based on the above findings, the method for producing a cholesteric liquid crystal film of the invention is as follows.

That is, the method for producing a cholesteric liquid crystal film of the invention includes: a step (A) of applying a coating liquid containing a solvent, a rod-like thermotropic liquid crystal compound, and a chiral agent onto a substrate to form a coating film; a step (B) for drying the residual solvent content in the formed coating film to 50 mass% or less; and a step C of applying a shear force to the surface of the dried coating film.

By including the steps a, B and C, a cholesteric liquid crystal film which is aligned in a direction parallel to the film surface direction (i.e., horizontal alignment) and perpendicular to the shear direction and which has little variation in alignment within the film surface can be obtained.

Hereinafter, each step of the method for producing a cholesteric liquid crystal film according to the present invention will be described in detail with reference to the drawings.

An example of the method for producing a cholesteric liquid crystal film of the invention shown in fig. 1 is a method using a continuous flow in a Roll-to-Roll (Roll) system using a long substrate that is continuously conveyed.

The method for producing a cholesteric liquid crystal film of the invention is not limited to a continuous flow in a roll-to-roll system, and the steps may be sequentially performed on a single substrate.

[ Process A ]

In step a, a coating liquid containing a solvent, a rod-like thermotropic liquid crystal compound, and a chiral agent (hereinafter, also referred to as a liquid crystal layer forming coating liquid) is applied to a substrate to form a coating film.

The coating liquid for forming a liquid crystal layer in step a may be applied in a state where the substrate is laid, and is preferably applied to the substrate wound around a backing roll from the viewpoint of improving the coating accuracy.

An example of the step a will be described with reference to fig. 1.

As shown in fig. 1, when the long-sized base material F wound in a roll shape is fed at its leading end and conveyed by the conveying roller 50, first, the coating unit 10 applies the coating liquid for forming the liquid crystal layer.

As shown in fig. 1, the coating of the coating liquid for liquid crystal layer formation by the coating unit 10 is preferably performed in a region where the base material F is wound on the backing roll 12.

(substrate)

The substrate is not particularly limited, and may be a member that functions as part of the optical film together with the cholesteric liquid crystal film, or may be a coated object that is a target of coating the coating liquid, and may be a member that is peeled off from the cholesteric liquid crystal film.

In particular, a polymer film is preferably used as the base material in view of applicability to a roll-to-roll system and ease of winding on a back roll.

When used in an optical film, the total light transmittance of the substrate is preferably 80% or more.

When the polymer film is used as a substrate in an optical film, an optically isotropic polymer film is preferably used.

Examples of the substrate include polyester substrates (films or sheets of polyethylene terephthalate, polyethylene naphthalate, and the like), cellulose substrates (films or sheets of diacetylcellulose, Triacetylcellulose (TAC), and the like), polycarbonate substrates, poly (meth) acrylic substrates (films or sheets of polymethyl methacrylate, and the like), polystyrene substrates (films or sheets of polystyrene, acrylonitrile-styrene copolymer, and the like), olefin substrates (films or sheets of polyethylene, polypropylene, polyolefin having a cyclic or norbornene structure, ethylene-propylene copolymer, and the like), polyamide substrates (films or sheets of polyvinyl chloride, nylon, aromatic polyamide, and the like), polyimide substrates, polysulfone substrates, polyethersulfone substrates, polyetheretherketone substrates, polyphenylene sulfide substrates, polyether sulfone substrates, and the like, A transparent substrate such as a vinyl alcohol-based substrate, a polyvinylidene chloride-based substrate, a polyvinyl butyral-based substrate, a poly (meth) acrylate-based substrate, a polyoxymethylene-based substrate, or an epoxy resin-based substrate, or a substrate made of a mixed polymer obtained by mixing the above polymer materials.

The thickness of the substrate is, for example, preferably 30 to 150 μm, more preferably 40 to 100 μm, in view of manufacturing applicability, manufacturing cost, application to an optical film, and the like.

The substrate may be a substrate having a layer formed on the polymer film in advance.

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 adhesive layer.

(coating liquid for liquid Crystal layer formation)

The coating liquid for forming a liquid crystal layer used in the step a contains a solvent, a rod-like thermotropic liquid crystal compound, and a chiral agent. The coating liquid for forming a liquid crystal layer may contain other components as necessary.

-solvent-

As the solvent, an organic solvent is preferably used.

Specific examples of the organic solvent include an amide solvent (e.g., N-dimethylformamide), a sulfoxide solvent (e.g., dimethylsulfoxide), a heterocyclic compound (e.g., pyridine), a hydrocarbon solvent (e.g., benzene, hexane, etc.), an alkyl halide solvent (e.g., chloroform, dichloromethane), an ester solvent (e.g., methyl acetate, butyl acetate, etc.), a ketone solvent (e.g., acetone, methyl ethyl ketone, cyclohexanone, etc.), and an ether solvent (e.g., tetrahydrofuran, 1, 2-dimethoxyethane, etc.). Among these, as the organic solvent, an alkyl halide solvent and a ketone solvent are preferable.

One kind of the organic solvent may be used alone, or two or more kinds thereof may be used.

Rod-like thermotropic liquid crystalline compound (specific liquid crystalline compound) -

The rod-like thermotropic liquid crystal compound (i.e., the specific liquid crystal compound) refers to a liquid crystal compound having thermotropic properties and having a rod-like molecular structure.

In particular, the specific liquid crystal compound is preferably a compound having a polymerizable group. The polymerizable group of the specific liquid crystal compound is preferably an unsaturated polymerizable group, an epoxy group or an aziridine group, more preferably an unsaturated polymerizable group, and particularly preferably an ethylenically unsaturated polymerizable group.

Specific examples of the specific liquid crystal compounds include compounds described in Makromol. chem., 190, 2255 (1989), Advanced Materials 5, 107 (1993), U.S. Pat. No. 4683327, U.S. Pat. No. 5622648, U.S. Pat. No. 5770107, International publication No. 95/22586, International publication No. 95/24455, International publication No. 97/00600, International publication No. 98/23580, International publication No. 98/52905, Japanese patent laid-open No. 1-272551, Japanese patent laid-open No. 6-16616, Japanese patent laid-open No. 7-110469, Japanese patent laid-open No. 11-80081, and Japanese patent laid-open No. 2001-328973.

Further, as the specific liquid crystal compound, for example, compounds described in Japanese patent application laid-open No. 11-513019 and Japanese patent application laid-open No. 2007-279688 can be preferably used, but the specific liquid crystal compound is not limited thereto.

As the specific liquid crystal compound, for example, a compound represented by the following general formula (1) can be preferably used as the liquid crystal compound having a positive wavelength dispersion characteristic.

[ chemical formula 1]

(1)Q¹-L¹-A¹-L³-M-L⁴-A²-L²-Q²

In the general formula (1), Q¹And Q²Each independently is a polymerizable group, L¹、L²、L³And L⁴Each independently represents a single bond or a 2-valent linking group, A¹And A²Each independently represents a 2-valent hydrocarbon group having 2 to 20 carbon atoms, and M represents a mesogenic group.

As by Q¹And Q²The polymerizable group represented by (a) includes polymerizable groups possessed by the above-mentioned specific liquid crystal compound, and preferable examples are the same.

As a result of L¹、L²、L³And L⁴The linking group represented is preferably a divalent linking group selected from the group consisting of-O-, -S-, -CO-, -NR-, -CO-O-, -O-CO-O-, -CO-NR-, -NR-CO-, -O-CO-NR-, -NR-CO-O-and NR-CO-NR-. Wherein R is an alkyl group having 1 to 7 carbon atoms or a hydrogen atom.

And, L³And L⁴At least one of them is preferably-O-CO-O-.

In the general formula (1), Q¹-L¹-and Q²-L²-is preferably CH₂＝CH-CO-O-、CH₂＝C(CH₃) -CO-O-and CH₂Most preferably, it is CH (cl) -CO-O —₂＝CH-CO-O-。

As represented by A¹And A²The 2-valent hydrocarbon group having 2 to 20 carbon atoms is preferably an alkylene group, alkenylene group or alkynylene group having 2 to 12 carbon atoms, and particularly preferably an alkylene group having 2 to 12 carbon atoms. The 2-valent hydrocarbon group is preferably a chain, and may contain an oxygen atom or a sulfur atom which is not adjacent to each other. The 2-valent hydrocarbon group may have a substituent, and examples of the substituent include a halogen atom (fluorine, chlorine, bromine), a cyano group, a methyl group, an ethyl group, and the like.

The mesogenic group represented by M is a group representing a main skeleton of a liquid crystal molecule contributing to the formation of a liquid crystal.

The mesogenic group represented by M is not particularly limited, and for example, reference may be made to "FlusseKristalle in Tabellen II" (published in 1984, Leipzig), particularly pages 7 to 16, and the documentation of the Committee for the compilation of liquid crystal presentations, liquid crystal presentations (Bolus, published in 2000), particularly Chapter 3.

More specifically, examples of the mesogenic group represented by M include the structures described in paragraph 0086 of Japanese patent application laid-open No. 2007-279688.

The mesogenic group is preferably a group containing at least one cyclic structure selected from the group consisting of an aromatic hydrocarbon group, a heterocyclic group, and an alicyclic group. 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 further preferably a group containing 3 to 5 aromatic hydrocarbon groups.

Further preferably, the mesogenic group is a group containing 3 to 5 phenylene groups and having the phenylene group bonded thereto through-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 the general formula (1) are shown below, but the compound is not limited thereto. "Me" represents a methyl group.

[ chemical formula 2]

Further, as the specific liquid crystal compound, a rod-like liquid crystal compound having a reverse wavelength dispersion property can be used.

Examples of the rod-like liquid crystal compound having reverse wavelength dispersibility include a liquid crystal compound represented by the general formula 1 of Japanese patent laid-open publication No. 2016-81035 and a compound represented by the general formula (I) or (II) of Japanese patent laid-open publication No. 2007-279688. More specifically, the specific liquid crystal compound having the reverse wavelength dispersion property includes the following compounds, but the present invention is not limited thereto.

[ chemical formula 3]

One kind of the specific liquid crystal compound may be used alone, or two or more kinds may be used simultaneously.

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, and more preferably 90% by mass to 99% by mass, based on the mass of the total solid content.

The solid component means a component other than the solvent.

Chiral reagents-

The chiral reagent can be selected from various known chiral reagents (for example, a liquid crystal device manual, chapter 3, items 4-3, chiral reagents for TN and STN, page 199, published by the 142 th committee of Japan society of academic interest, 1989).

Chiral agents generally contain asymmetric carbon atoms, but axially asymmetric compounds or surface asymmetric compounds that do not contain asymmetric carbon atoms can also be used as chiral agents.

Examples of the axially asymmetric compound or the surface asymmetric compound include binaphthyl, spiroalkene, p-cycloaralkyl and derivatives thereof.

The chiral agent may have a polymerizable group.

In the case where the chiral agent has a polymerizable group and the specific liquid crystal compound used at the same time also has a polymerizable group, a polymer having a repeating unit derived from the specific liquid crystal compound and a repeating unit derived from the chiral agent can be obtained by a polymerization reaction between the chiral agent having a polymerizable group and the specific liquid crystal compound having a polymerizable group.

The polymerizable group of the chiral agent having a polymerizable group is preferably the same kind of group as the polymerizable group of the specific liquid crystal compound. The polymerizable group of the chiral agent is preferably an unsaturated polymerizable group, an epoxy group or an aziridine group, more preferably an unsaturated polymerizable group, and particularly preferably an ethylenically unsaturated polymerizable group.

Also, the chiral agent may be a liquid crystal compound.

Examples of the chiral reagent exhibiting a strong twisting power include the chiral reagents described in, for example, Japanese patent application laid-open Nos. 2010-181852, 2003-287623, 2002-80851, 2002-80478, and 2002-302487, and they can also be preferably used in the coating liquid for forming a liquid crystal layer in the present invention.

Furthermore, with respect to the isosorbide compounds described in the above-mentioned respective patent publications, isomannide compounds having a corresponding structure may be used as the chiral reagent, and with respect to the isomannide compounds described in the above-mentioned respective patent publications, isosorbide compounds having a corresponding structure may be used as the chiral reagent.

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

Other ingredients-

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

Alignment control agent

As the alignment control agent, an alignment control agent capable of reducing or substantially leveling the tilt angle of the molecules of the specific liquid crystal compound at the air interface is preferable.

Examples of such an orientation controlling agent include compounds described in paragraphs [0012] to [0030] of Japanese patent laid-open No. 2012-211306, compounds described in paragraphs [0037] to [0044] of Japanese patent laid-open No. 2012-101999, fluorine-containing (meth) acrylate polymers described in paragraphs [0018] to [0043] of Japanese patent laid-open No. 2007-272185, and compounds described in detail in Japanese patent laid-open No. 2005-099258 together with a synthesis method.

Further, a polymer containing polymerized units of a fluoroaliphatic group-containing monomer in an amount of more than 50% by mass based on all the polymerized units, as described in Japanese patent application laid-open No. 2004-331812, can also be used as an orientation controlling agent.

As an example of another orientation controlling agent, a vertical orientation agent is mentioned. By blending the vertical alignment agent, the vertical alignment of the liquid crystal compound can be controlled. As examples of the vertical alignment agent, a boric acid compound and/or an onium salt described in Japanese patent laid-open No. 2015-38598, an onium salt described in Japanese patent laid-open No. 2008-26730, and the like can be preferably used.

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

Polymerization initiator

As the polymerization initiator, any of a photopolymerization initiator and a thermal polymerization initiator can be used, but the photopolymerization initiator is preferable from the viewpoint of suppressing deformation of the substrate due to heat, deterioration of the liquid crystal layer-forming composition, and the like.

Examples of the photopolymerization initiator include an α -carbonyl compound (e.g., compounds described in the specifications of U.S. Pat. Nos. 2367661 and 2367670), an acyloin ether (e.g., compounds described in the specifications of U.S. Pat. No. 2448828), an α -hydrocarbon-substituted aromatic acyloin compound (e.g., compounds described in the specification of U.S. Pat. No. 2722512), a polyquinone compound (e.g., compounds described in the specifications of U.S. Pat. Nos. 3046127 and 2951758), a combination of a triarylimidazole dimer and a p-aminophenyl ketone (e.g., compounds described in the specification of U.S. Pat. No. 3549367), an acridine and phenazine compound (e.g., compounds described in Japanese patent laid-open publication No. Sho 60-105667 and U.S. Pat. No. 4239850), an oxadiazole compound (e.g., compounds described in the specification of U.S. Pat. 4212970), Acylphosphine oxide compounds (e.g., those described in Japanese patent publication No. 63-40799, Japanese patent publication No. 5-29234, Japanese patent laid-open No. 10-95788, and Japanese patent laid-open No. 10-29997).

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

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

(coating)

As a coating unit (corresponding to the coating unit 10 in fig. 1) that coats the coating liquid for forming the liquid crystal layer, a known coating unit can be applied.

Specific examples of the coating unit include units utilizing extrusion die coating, curtain coating, dip coating, spin coating, printing coating, spray coating, slit coating, roll coating, slide coating, doctor blade coating, gravure coating, wire bar coating, and the like.

(Back roll)

The backing roll (corresponding to the backing roll 12 in fig. 1) preferably used in the step a is a member capable of winding the substrate and continuously conveying the substrate, and is rotationally driven at the same speed as the conveying speed of the substrate.

The backing roll used in step a is not particularly limited, and a known backing roll can be used.

As the back roller, for example, a back roller having a hard chrome plated surface can be preferably used.

The thickness of the plating layer is preferably 40 μm to 60 μm from the viewpoint of securing conductivity and strength.

Further, the surface roughness Ra of the back roll is preferably 0.1 μm or less from the viewpoint of reducing the variation in the frictional force between the base material and the back roll.

The backing roll used in step a may be heated from the viewpoint of enhancing the drying promotion of the coating film, and from the viewpoint of suppressing the fogging of the coating film due to a decrease in the film surface temperature (that is, whitening of the coating film due to the occurrence of fine condensation).

The surface temperature of the backing roll may be determined depending on the composition of the coating film, the curing property of the coating film, the heat resistance of the substrate, and the like, and is, for example, preferably 40 to 120 c, more preferably 40 to 100 c.

The back roll used in the step a preferably detects the surface temperature, and the surface temperature of the back roll is maintained by a temperature control means based on the detected surface temperature.

The temperature control unit of the back roller is a heating unit and a cooling unit. As the heating means, induction heating, water heating, oil heating, or the like can be used, and as the cooling means, cooling using cooling water can be used.

The diameter of the backing roll used in step a is preferably 100mm to 1000mm, more preferably 100mm to 800mm, and still more preferably 200mm to 700mm, from the viewpoint of ease of winding the substrate, ease of coating by the coating means, and cost of manufacturing the backing roll.

The conveying speed of the base material in the back roll in step a is preferably 10m/min to 100m/min from the viewpoint of ensuring productivity and coatability.

From the viewpoint of stabilizing the conveyance of the base material during coating and suppressing the occurrence of thickness unevenness of the coating film, the lap angle of the base material with respect to the backing roll is preferably 60 ° or more, and more preferably 90 ° or more. The upper limit of the overlap angle may be set to 180 °, for example.

The lap angle is an angle formed by the conveyance direction of the base material when the base material is in contact with the back roll and the conveyance direction of the base material when the base material is separated from the back roll.

[ Process B ]

In the step B, the residual solvent content in the formed coating film is dried to 50 mass% or less.

The residual solvent ratio in the coating film in step B is preferably 40% by mass or less, and more preferably 30% by mass or less. The lower limit of the residual solvent content in the coating film in the step B is preferably 10 mass% from the viewpoint of easily suppressing the deterioration of the coated surface state.

The residual solvent ratio in the coating film may be 50% by mass or less immediately before the step C, and for example, may be 50% by mass or less during the transport period after the drying by a drying means described later until the step C is performed.

In the step B, the density of the specific liquid crystal compound in the coating film increases to form cholesteric liquid crystal in the process in which the residual solvent ratio is 50 mass% or less. The helical axis of the cholesteric liquid crystal in step B is generally parallel to the film surface direction of the coating film. However, in the step B, the coating film having a residual solvent ratio of 50 mass% or less is in a state where the orientation of the helical axis of the cholesteric liquid crystal varies in a plane view.

An example of the step B will be described with reference to fig. 1.

In step B, after the liquid crystal layer forming coating liquid is applied by the coating unit 10, the coating film is dried in the drying region of the drying unit 20.

The dried coating film is conveyed to step C via a conveyance roller 52. In the step B, the residual solvent ratio in the coating film may be 50 mass% or less before the shear force is applied to the surface of the coating film in the step C.

(drying)

As a drying unit (corresponding to the drying unit 20 in fig. 1) for drying the coating film, a known drying unit is applied.

Specific examples of the drying unit include units using a method using an oven, a fan heater, an Infrared (IR) heater, or the like.

In the drying by the fan heater, the hot air may be blown from the surface of the base material opposite to the surface on which the coating film is formed, or a diffusion plate may be provided so that the surface of the coating film does not flow by the hot air.

Further, the drying may be performed by air suction. The drying by suction is a method of reducing the residual solvent ratio in the coating film by absorbing the gas on the coating film using a decompression chamber or the like having an exhaust mechanism.

The drying conditions may be conditions such that the residual solvent ratio in the coating film is 50 mass% or less, and may be determined according to the composition, coating amount, transport speed, and the like of the coating film for forming a liquid crystal layer.

Here, the residual solvent ratio of the coating film was measured by an absolute drying method.

Specifically, a part of the coating film is scraped off, dried at 60 ℃ (temperature not higher than temperature at which the material constituting the coating film does not volatilize) for 24 hours, and the residual solvent ratio is determined from the change in mass before and after drying. This step was carried out 3 times, and the average of the 3 times was taken as the residual solvent ratio.

[ Process C ]

In step C, a shear force is applied to the surface of the dried coating film.

As described above, the coating film after being dried in the step B is in a state where the orientation of the helical axis of the cholesteric liquid crystal is deviated in a plane view.

Therefore, in the method for producing a cholesteric liquid crystal film of the invention, the step C is performed after the step B, and the variation in the orientation of the helical axis of the cholesteric liquid crystal in a plan view of the coating film is reduced. Specifically, in step C, a shear force is applied to the surface of the coating film after step B.

By applying a shear force to the surface of the coating film, the shear force causes the helical axis of the cholesteric liquid crystal to be regularly aligned perpendicular to the shear direction. As a result, by performing the step C, a cholesteric liquid crystal film in which the helical axis of the cholesteric liquid crystal is aligned in parallel to the film surface direction and in the direction perpendicular to the shear direction, and further the alignment has little variation in the film surface (that is, excellent alignment accuracy) can be obtained.

A cholesteric liquid crystal film having excellent alignment accuracy can be confirmed by a case where a scattering region (white region described above) is small when the cholesteric liquid crystal film is viewed in a plan view.

In addition, in the step C, when a shear force is applied to the surface of the coating film, it is preferable to apply the shear force to the base material wound around the backing roll, from the viewpoint of improving the uniformity of the shear force.

An example of the step C will be described with reference to fig. 1.

In step C, the upper surface of the dried coating film, in which the residual solvent content in the coating film is 50 mass% or less by the drying unit 20, is scraped off by a scraper 30, and a shear force is applied.

Thereby, a shear force is imparted along the conveyance direction of the coating film (i.e., the conveyance direction of the substrate).

As shown in fig. 1, the application of the shear force by the doctor blade 30 is preferably performed in a region where the base material F is wound on the backing roll 32.

In fig. 1, the doctor blade 30 is used when applying a shear force to the surface of the coating film, but the present invention is not limited thereto, and any method may be used as long as the helical axis of the cholesteric liquid crystal can be aligned perpendicular to the shear direction. Examples of the means for applying a shearing force other than the doctor blade include an air knife, a bar, and an applicator.

(shear rate)

In the step C, when a shear force is applied to the surface of the dried coating film, the higher the shear rate is, the more easily a cholesteric liquid crystal film having excellent alignment accuracy can be obtained. Specifically, the shear rate is preferably 1000 seconds^-1(1/sec) or more, more preferably 10000 seconds or more^-1(1/sec) or more, and more preferably 30000 seconds^-1(1/sec) or more.

The upper limit of the shear rate is, for example, 1.0X 10⁶Second of^-1(1/sec) or less.

For example, as shown in fig. 1, when a shear force is applied to the surface of the coating film by the doctor blade 30, the shear rate is determined from "V/d" when the shortest distance between the doctor blade 30 and the substrate is "d" and the conveyance speed of the coating film in contact with the doctor blade (i.e., the relative speed of the coating film and the doctor blade) is "V".

When a shear force is applied to the surface of the coating film by the air knife, the shear rate is determined from "V/2 h" when the thickness of the coating film after the application of the shear force is "h" and the relative velocity between the surface of the coating film and the surface of the substrate is "V".

(shear force application by doctor blade)

As shown in fig. 1, when a method of applying a shearing force to the surface of the coating film by the doctor blade 30 is used, it is preferable to scrape the upper surface of the coating film.

That is, when a shear force is applied by a doctor blade, the thickness of the coating film is regulated by the doctor blade.

The film thickness of the coating film after the shear force is applied by the doctor blade may be 1/2 or less, or 1/3 or less, as compared to before the shear force is applied. However, as the lower limit of the film thickness limitation, for example, the film thickness of the coating film after the shear force is applied by the doctor blade is preferably 1/4 or more than before the shear force is applied.

The shape, material, and the like of the blade used for applying the shear force are not particularly limited.

The scraper may be a plate-like member made of metal such as stainless steel, or may be a plate-like member made of resin such as teflon (registered trademark) or PEEK (polyether ether ketone).

From the viewpoint of easily imparting a predetermined shear force to the coating film, it is preferable to use a metal plate-like member, and a metal plate-like member in which the thickness of the tip portion in contact with the coating film (i.e., the thickness along the direction of conveyance of the coating film) is 0.1mm or more (preferably 1mm or more) is preferable. The upper limit of the thickness of the metal plate-like member is, for example, about 10 mm.

(shear force application Using air knife)

In the case of a method of applying a shear force to the surface of a coating film by an air knife, the shear force is applied by blowing compressed air to the upper surface of the coating film by the air knife.

The shear rate imparted to the coating film can be adjusted by the velocity (i.e., flow velocity) of the blown compressed air.

The direction in which the compressed air is blown by the air knife may be the same direction as the direction in which the coating film is conveyed, or may be opposite to the direction, but is preferably the same direction as the direction in which the coating film is conveyed, from the viewpoint that the coating film fragments scraped by the blown compressed air are less likely to adhere to the coating film again.

(temperature of coating film surface)

In the step C, the temperature of the surface of the coating film to which the shear force is applied depends on the phase transition temperature of the specific liquid crystal compound used, but is usually preferably 50 to 120 ℃, more preferably 60 to 100 ℃.

When the temperature of the surface of the coating film is in the above range, the helical axis of the cholesteric liquid crystal can be easily aligned perpendicular to the shear direction by applying a shear force, and a cholesteric liquid crystal film having 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 noncontact thermometer. The measurement was performed in a state where no reflection object was present within 10cm from the surface on the side opposite to the measurement surface (back surface side).

(Back roll)

The backing roll (corresponding to the backing roll 32 in fig. 1) preferably used in the step C is a member capable of winding the substrate and continuously conveying the substrate, and is rotationally driven at the same speed as the conveying speed of the substrate.

The back roll used in step C is the same as the back roll used in step a, and the preferred embodiment is the same.

Alternatively, the step a and the step C may be performed on one back roll.

The backing roll used in the 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 backing roll is, for example, preferably 50 to 120 ℃ and more preferably 60 to 100 ℃.

The back roll used in the step C preferably detects the surface temperature, and the surface temperature of the back roll is maintained by a temperature control means based on the detected surface temperature.

The temperature control means of the back roll is the same as the temperature control means of the back roll used in step a.

The diameter of the back roll used in step C is preferably 100mm to 1000mm, more preferably 100mm to 800mm, and even more preferably 200mm to 700mm, from the viewpoint of ease of winding the substrate, ease of applying a shear force, and cost of manufacturing the back roll.

The conveying speed of the base material in the back roll in the step C is preferably 10m/min to 100m/min from the viewpoint of ensuring productivity and improving uniformity of the shearing force.

From the viewpoint of stabilizing the conveyance of the base material at the time of coating and improving the uniformity of the shearing force, the lap angle of the base material with respect to the back roll in the step C is preferably 60 ° or more, and more preferably 90 ° or more. The upper limit of the overlap angle may be set to 180 °, for example.

From the viewpoint of further improving the alignment accuracy of the helical axis of the cholesteric liquid crystal due to the shear force, the thickness of the coating film when the shear force is applied in step C (i.e., the thickness of the coating film dried in step B) is preferably 70 μm or less, more preferably 50 μm or less, and still more preferably 15 to 50 μm.

From the viewpoint of further improving the alignment accuracy of the helical axis of the cholesteric liquid crystal due to the shear force, the thickness of the coating film after the shear force is applied in the step C is preferably 10 μm or less.

The thickness of the coating film obtained through step C (i.e., the coating film after the shear force is applied in step C) can be determined according to the application.

The thickness of the coating film obtained through the step C is preferably 5 μm or more, for example.

[ Process D ]

In the method for producing a cholesteric liquid crystal film of the invention, when a polymerizable compound (specifically, a specific liquid crystal compound having a polymerizable group, a chiral agent having a polymerizable group, or the like) is contained in the coating film, it is preferable to further include a step D of curing the coating film after the step C.

In the step D, for example, the coating film after the shear force is applied is preferably cured by heating or irradiation with active energy rays.

In view of manufacturing applicability and the like, curing by an active energy ray irradiated from an active energy ray irradiation unit 40 shown in fig. 1 is preferably used as the step D.

The irradiation means of the active energy ray is not particularly limited as long as it is means for applying energy capable of generating active species in the irradiated coating film.

Specific examples of the active energy ray include an α ray, a γ ray, an X ray, an ultraviolet ray, an infrared ray, a visible ray, and an electron beam. Among them, from the viewpoint of curing sensitivity and easy availability of the apparatus, ultraviolet rays are preferably used as the active energy rays.

Examples of the light source of ultraviolet rays include lamps such as a tungsten lamp, a halogen lamp, a xenon flash lamp, a mercury xenon lamp, and a carbon arc lamp, various lasers (for example, a semiconductor laser, a helium neon laser, an argon ion laser, a helium cadmium laser, a YAG (Yttrium Aluminum Garnet)) laser), a light emitting diode, and a cathode ray tube.

The peak wavelength of the ultraviolet light emitted from the ultraviolet light source is preferably 200nm to 400 nm.

Further, the exposure energy of ultraviolet rays is preferably 100mJ/cm, for example²～500mJ/cm²。

Thereby, a cholesteric liquid crystal film was produced on the substrate.

A laminate of a substrate and a cholesteric liquid crystal film may be used as the optical film.

[ other Processes ]

The method for producing a cholesteric liquid crystal film of the invention may further include other steps in addition to the above steps a to D.

As another step, a step of forming an alignment layer on the substrate used in step a may be mentioned.

That is, the substrate used in step a may be a substrate provided with an alignment layer.

(alignment 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 a method such as rubbing treatment of an organic compound (preferably a polymer), oblique evaporation of an inorganic compound, or formation of a layer having microgrooves.

The alignment layer may be an alignment layer that generates an alignment function by applying an electric field, a magnetic field, or light irradiation.

In the case where the base material is made of a resin, depending on the kind of the resin (for example, PET (polyethylene terephthalate)), the surface of the base material may be made to function as an alignment layer by directly subjecting the support to an alignment treatment (for example, a rubbing treatment) without providing an alignment layer.

In the method for producing a cholesteric liquid crystal film of the invention, the alignment layer is not essential, and by applying a shear force to the coating film in the step C, the helical axis of the cholesteric liquid crystal can be aligned without using the alignment layer.

[ optical film ]

In the method for producing a cholesteric liquid crystal film of the invention, when an optically isotropic polymer film is used as a base material and a cholesteric liquid crystal film is formed on the polymer film, the resulting laminate can be used as an optical film.

Further, the cholesteric liquid crystal film itself may be used as the optical film.

The cholesteric liquid crystal film obtained by the method for producing a cholesteric liquid crystal film of the invention can function as a light reflecting layer. Therefore, it is also preferable as an optical film used in an aerial image forming apparatus.

Examples

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

[ example 1]

(preparation of substrate)

As a substrate, a triacetyl cellulose (TAC) film (FUJIFILM Corporation, refractive index 1.48) having a thickness of 80 μm and a width of 300mm was prepared in a long form.

(preparation of coating liquid for liquid Crystal layer formation 1)

After mixing the components 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.

Coating liquid for liquid crystal layer formation 1-

A rod-like thermotropic liquid crystal compound (the following compound (a)): 100 parts by mass

Chiral reagents (the following compound (B)): 2.5 parts by mass

Photopolymerization initiator: 3 parts by mass

(IRGACURE (registered trademark) 907, BASF corporation)

An orientation limiting agent (the following compound (C)): 0.2 part by mass

A vertical alignment agent (the following compound (D)): 0.5 part by mass

Solvent (methyl ethyl ketone): 215 parts by mass

[ chemical formula 4]

Compound (A)

Compound (B)

Compound (C)

Compound (D)

(Process A and Process B)

Coating liquid 1 for liquid crystal layer formation was applied on a continuously conveyed substrate by a die coating method, and then passed through an oven at 70 ℃ for 60 seconds to dry the coating film.

In step A, specifically, the substrate was conveyed on a backing roll having a surface temperature of 25 ℃ and an outer diameter of 300mm, and the coating liquid 1 for forming a liquid crystal layer was applied to the substrate wound on the backing roll by a die coating method as shown in FIG. 1.

The substrate transfer speed in the steps A and B was 10 m/min.

The residual solvent ratio of the coating film after drying before the step C was measured by the above-described method and found to be 1.1% by mass.

The thickness of the dried coating film was 50 μm, and the coating width was 250 mm.

(Process C)

The dried coating film was subjected to a shear force by a stainless steel doctor blade (thickness of the tip portion was 1 mm).

Specifically, in step C, the doctor blade was set so that the tip end portion thereof was 20 μm away from the surface of the substrate on the backing roll having a surface temperature of 70 ℃ and an outer diameter of 500 mm. And, the temperature of the blade was maintained at 70 ℃. Here, the substrate having the coating film subjected to the step B was transferred to a backing roll, and the surface of the coating film was closely attached to a doctor blade to scrape the upper surface of the coating film.

The shear rate imparted by the above doctor blade was 10000 seconds^-1。

The thickness of the coating film subjected to the step C was 10 μm.

In addition, the conveying speed of the base material in the step C was 12 m/min.

(Process D)

Using a high-pressure mercury lamp at an exposure energy of 500mJ/cm²The coating film after the step C is irradiated with ultraviolet rays 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 formed 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 and the solvent residual ratio in the coating film was changed.

[ example 4]

A cholesteric liquid crystal film was formed on the substrate in the same manner as in example 1, except that the conveying speed of the coating film in the 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 alignment layer forming step was performed before step a.

(alignment layer Forming Process)

Preparation of the alignment layer composition A

A mixture of 96 parts by mass of pure water and PVA-205(KURARAY co., LTD, polyvinyl alcohol) was stirred and dissolved in a vessel kept at 80 ℃ to prepare an alignment layer composition.

The alignment layer composition was coated on the continuously conveyed triacetyl cellulose (TAC) film using a #6 bar, followed by drying in an oven at 100 ℃ for 10 minutes, and then rubbing treatment was performed in a direction orthogonal to the conveyance direction of the base material.

[ example 6 ]

(Process A and Process B)

The coating liquid 1 for forming a liquid crystal layer described above was applied to a continuously conveyed substrate by a die coating method, and then passed through an oven at 70 ℃ for 60 seconds to dry the coating film.

In step A, specifically, the substrate was conveyed on a backing roll having a surface temperature of 25 ℃ and an outer diameter of 300mm, and the coating liquid 1 for forming a liquid crystal layer was applied to the substrate wound on the backing roll by a die coating method as shown in FIG. 1.

The substrate transfer speed in the steps A and B was 10 m/min.

The residual solvent ratio of the coating film after drying before the step C was measured by the above-described method and found to be 1.1% by mass.

The thickness of the dried coating film was 50 μm, and the coating width was 250 mm.

(Process C)

The dried coating film is subjected to a shearing force by an air knife.

Specifically, in the step C, the substrate having the coating film obtained in the step B was transferred to a back roll having a surface temperature of 70 ℃ and an outer diameter of 500mm, and compressed air was blown onto the surface of the coating film on the back roll by an air knife. The blowing direction of the compressed air is the same direction as the conveying direction of the coating film.

The shear velocity imparted by the above air knife was 10000 seconds^-1。

The thickness of the coating film subjected to the step C was 10 μm.

In addition, the conveying speed of the base material in the step C was 12 m/min.

(Process D)

Using a high-pressure mercury lamp at an exposure energy of 500mJ/cm²The coating film after the step C is irradiated with ultraviolet rays to cure the coating film.

As described above, a cholesteric liquid crystal film was produced on the substrate.

[ examples 7 to 8]

A cholesteric liquid crystal film was formed on the substrate in the same manner as in example 6, except that the drying conditions (specifically, the drying time) in step B were changed and the solvent residual ratio in the coating film was changed.

[ example 9 ]

A cholesteric liquid crystal film was formed on the substrate in the same manner as in example 1, except that the conveying speed of the coating film in the step C was changed to 36 m/min.

[ example 10 ]

A cholesteric liquid crystal film was formed on a substrate in the same manner as in example 6, except that the alignment 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 formed on the substrate in the same manner as in example 3, except that the step C was not performed.

[ evaluation ]

(Observation with a polarized light microscope)

An orthogonal nicols polarized light transmission photograph of the upper surface of the cholesteric liquid crystal film was taken using a polarized light microscope NV100LPOL manufactured by Nikon Corporation, and a fringe pattern (i.e., a pattern generated with a spiral pitch) and a state of an alignment 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 fringe pattern appearing in the crossed nicols transmission photograph, and evaluated based on the following criteria.

By making it possible to confirm that the stripe pattern is aligned parallel to the conveyance direction of the coating film, it is possible to confirm that the helical axis of the cholesteric liquid crystal is aligned perpendicular to the conveyance direction (i.e., the shear direction) of the coating film.

Evaluation criteria-

A: the stripe pattern was clearly seen to be arranged parallel to the conveying direction of the coating film and there was no orientation defect in which a part of the stripe pattern was discontinuous.

B: the stripe pattern was clearly seen to be aligned parallel to the conveyance direction of the coating film, but a part of the discontinuous alignment defect of the stripe pattern was slightly seen.

C: the stripe pattern was seen to be aligned parallel to the direction of conveyance of the coating film, but the stripe pattern had many orientation defects partially intermittently.

D: no stripe pattern is visible.

(Observation by SEM)

The cross section of the cholesteric liquid crystal film was observed by SEM (SU 3500 manufactured by Hitachi High-Tech Corporation), and it was confirmed by the above-mentioned method whether the helical axis of the cholesteric liquid crystal was parallel to the film surface direction.

Evaluation criteria-

A: the spiral 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 plane direction.

(evaluation of orientation accuracy)

The alignment accuracy in the cholesteric liquid crystal film was evaluated by confirming scattering domains (i.e., white domains in the photograph) due to fine variations in the alignment of the helical axis of the cholesteric liquid crystal by the above-described method.

The measured scattering of the optical film was evaluated in the following criteria. It was judged that the less the scattering region (i.e., white region in the photograph), the more excellent the alignment accuracy (i.e., the less the film surface deviation).

Evaluation criteria-

A: the proportion of the white region in the total area of the test piece (i.e., the area ratio) was 0% (in other words, the white region was not visible in the photograph).

B: the proportion of the white region in the total area of the test piece (i.e., the area ratio) is 10% or less.

C: the proportion of the white region in the total area of the test piece (i.e., the area ratio) was more than 10%.

[ Table 1]

As shown in table 1, it was found that the cholesteric liquid crystal films obtained in the examples were all aligned along a specific direction in a plan view such that the helical axes of the cholesteric liquid crystals were parallel to the film surface direction (the angle formed by the helical axis of the cholesteric liquid crystal and the film surface direction of the cholesteric liquid crystal film was 50 ° to 90 °), and had little variation in the alignment in the film surface (i.e., had excellent alignment accuracy).

The invention of japanese patent application 2019-064853, filed on 28.3.2019, is incorporated by reference in its entirety into this specification.

All documents, patent applications, and technical standards cited in the present specification are incorporated by reference into the present specification to the same extent as if each document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.