JP6223215B2 - Method for producing photoresponsive cross-linked liquid crystal polymer film and photoresponsive cross-linked liquid crystal polymer film obtained by the production method - Google Patents

Description

  The present invention relates to a method for producing a photoresponsive crosslinked liquid crystal polymer film and a photoresponsive crosslinked liquid crystal polymer film obtained by the production method.

  Photoresponsive liquid crystal polymer film is a highly functional material that has both anisotropy based on liquid crystallinity and polymer moldability, and has been extensively applied and put into practical use in a wide range of fields. Is expected.

  For example, Non-Patent Document 1 reports the molecular length effect of an azobenzene cross-linking agent on the light motion of a cross-linked liquid crystal polymer film.

  Patent Document 1 discloses a light-driven actuator including a crosslinked liquid crystal polymer molded body containing a photochromic molecule that can be reversibly isomerized by irradiation with ultraviolet rays or visible light. Patent Document 2 discloses a light-driven rotor in which the crosslinked liquid crystal polymer molded body is formed into an endless belt shape.

  Here, the production of the conventional liquid crystal polymer film requires the following complicated steps.

FIG. 2 is a process diagram showing an outline of a conventional method for producing a liquid crystal polymer film.
A conventional method for producing a liquid crystal polymer film includes a raw material preparation step, a cell preparation step, a photopolymerization step, and a collection step. In the raw material preparation step, each raw material including a liquid crystal material, a photopolymerization initiator and the like is blended (S101) and dried under reduced pressure (S102).

  The obtained raw material mixture is usually a powder and is used in the photopolymerization step described below. On the other hand, a cell (substrate) for polymerizing this raw material mixture is prepared. In the cell manufacturing process, the glass substrate which is a constituent material of the cell is washed (S103), polyimide is applied, and an alignment film is formed (S104). The obtained alignment film is annealed (S105) and rubbed (S106).

  Two glass substrates with alignment films prepared in this way are prepared, and these glass substrates are bonded together to produce a cell (substrate) (S107). Subsequently, in the photopolymerization step, the cell obtained in the cell production step is first heated (S108), the raw material mixture in the powder state obtained in the raw material preparation step is melted, and two glass substrates of the cell are obtained. In the meantime, a capillary phenomenon is used for injection (S109), the cell is cooled while strictly controlling the temperature drop (S110), and light irradiation is performed to photopolymerize the raw material. After the polymerization is completed, in the collecting step, the cell made of the glass substrate is broken (S112), and the liquid crystal polymer film is collected (S113).

Japanese Patent No. 5224261 Japanese Patent No. 5067964

Ryuta Sasaki, Junichi Mamiya, Motoki Kinoshita, Atsushi Shishido, Tomiki Ikeda, “Molecular length effect of azobenzene crosslinker on photodynamics of cross-linked liquid crystal polymer film”, 60th Polymer Symposium (2011)

The production of the conventional liquid crystal polymer film has the following problems. (1) Although a considerable amount of time and a long time (approximately 2 days) are required, only a small amount of film can be obtained; (2) continuous production is difficult; (3) the reason for using a glass substrate Therefore, it is difficult to increase the area; (4) Since the raw material mixture is injected between the two glass substrates of the cell using the capillary phenomenon, it is difficult to control the film thickness of the film.
In addition, when trying to increase the film thickness in order to develop good photoresponsiveness, there is also a problem that the orientation regulating force in the thickness direction is not reached, the molecular orientation is disturbed, and the film becomes cloudy. is there.

  Accordingly, the object of the present invention is to solve the above-mentioned problems of the prior art, eliminate the complexity of manufacturing, and increase the area while easily achieving good film thickness control in a short time. The present invention provides a method for producing a photoresponsive cross-linked liquid crystal polymer film that enables continuous production of a formed film, achieves a thick film while preventing white turbidity of the film, and has good photoresponsiveness. is there.

  As a result of intensive studies, the present inventors have found that the above problem can be solved by applying a photopolymerizable monomer solution on the alignment film by a wet coating method under a condition where the vapor pressure of the solvent is 100 mmHg or less, The present invention has been completed.

That is, the present invention is as follows.
1. Wet coating method using a photopolymerizable monomer solution containing at least a polyfunctional liquid crystal monomer, a monofunctional liquid crystal monomer, a polyfunctional photoresponsive monomer, a photopolymerization initiator and a solvent under a condition that the vapor pressure of the solvent is 100 mmHg or less By applying onto the alignment film by removing the solvent, forming a photopolymerizable film,
A method for producing a photoresponsive cross-linked liquid crystal polymer film, comprising: irradiating the photopolymerizable film with light in a non-oxygen atmosphere to polymerize the photopolymerizable monomer to form a film.
2. 2. The method for producing a photoresponsive cross-linked liquid crystal polymer film according to 1 above, wherein the polyfunctional photoresponsive monomer is a polyfunctional photoresponsive monomer having an azobenzene structure.
3. The solvent is tetrahydrofuran, toluene, methyl ethyl ketone, dichloromethane, isopropyl alcohol, isobutyl alcohol, methyl cellosolve, ethyl acetate, butyl acetate, xylene, cyclohexanone, cyclopentanone, methyl isobutyl ketone, benzene, normal hexane, ethylene glycol, methoxypropyl acetate. The method for producing a photoresponsive crosslinked liquid crystal polymer film according to 1 or 2 above, which is at least one selected from N-methyl-2-pyrrolidone, formyldimethylamine, cyclohexane, acetone, methanol and ethanol.
4). The method for producing a photoresponsive crosslinked liquid crystal polymer film according to any one of 1 to 3, wherein the step of forming the film is performed in a nitrogen gas atmosphere.
5. The method for producing a photoresponsive cross-linked liquid crystal polymer film according to any one of 1 to 4, wherein the step of forming the film is performed without covering the photopolymerizable film with a cover material.
6). It provided 25 cm ² or more of the alignment film on a support to form a film of 25 cm ² or more large area, method for manufacturing the photoresponsive crosslinked liquid crystal polymer film according to any one of the 1 to 5 .
7). A photoresponsive cross-linked liquid crystal polymer film having a thickness of 1 to 30 μm and a large area of 25 cm ² or more, comprising a polyfunctional liquid crystalline monomer, a monofunctional liquid crystalline monomer and a polyfunctional photoresponsive monomer as monomer units.

  In the production method of the present invention, since a photopolymerizable film formed by applying a photopolymerizable monomer solution onto an alignment film by wet coating is photopolymerized, it is necessary to use a glass substrate as in the prior art. In addition, the formation rate and control of the photopolymerizable film can be facilitated, and the area can be increased. Furthermore, in the production method of the present invention, a photopolymerizable film is formed by applying a photopolymerizable monomer solution on the alignment film by a wet coating method under the condition that the vapor pressure of the solvent is 100 mmHg or less. By keeping the vapor pressure of the solvent low, sufficient time is ensured for the alignment of the liquid crystalline monomer, and the film is thickened (for example, 1 μm or more) while providing good photoresponsiveness while preventing clouding of the film. be able to.

  Therefore, according to the present invention, it is possible to eliminate the complexity of manufacturing, enable continuous production of a large-area film while easily achieving a good film thickness control in a short time, It is possible to provide a method for producing a photoresponsive cross-linked liquid crystal polymer film that achieves a thick film while preventing white turbidity of the film and has good photoresponsiveness.

  In addition, according to the embodiment using a polyfunctional photoresponsive monomer having an azobenzene structure, an optical functional material capable of converting light energy into kinetic energy can be easily and quickly achieved while controlling the film thickness. In a large area, continuous production can be performed while providing good photoresponsiveness. In particular, a polyfunctional photoresponsive monomer having an azobenzene structure has a low degree of freedom of liquid crystal molecules in a solution state, and it is difficult to align the liquid crystal molecules in a desired direction. Although the raw material preparation step, cell preparation step, photopolymerization step and sampling step as shown in FIG. 2 were adopted, even when a polyfunctional photoresponsive monomer having an azobenzene structure was used according to the present invention, it was wet. A coating method can be employed, and the above-described remarkable effects can be achieved.

  The solvent is tetrahydrofuran, toluene, methyl ethyl ketone, dichloromethane, isopropyl alcohol, isobutyl alcohol, methyl cellosolve, ethyl acetate, butyl acetate, xylene, cyclohexanone, cyclopentanone, methyl isobutyl ketone, benzene, normal hexane, ethylene glycol, methoxypropyl. According to the form which is at least one selected from acetate, N-methyl-2-pyrrolidone, formyldimethylamine, cyclohexane, acetone, methanol and ethanol, further thickening is achieved while preventing clouding of the film, Further excellent photoresponsiveness can be imparted.

  Moreover, according to the form which performs the process of forming a film in nitrogen gas atmosphere, it becomes possible to prepare a non-oxygen atmosphere at low cost.

  Moreover, according to the form which performs the process of forming a film, without coat | covering a photopolymerizable film | membrane with a cover material, the effort and cost accompanying film formation can be reduced further. In the prior art, if there is no cover material (if both sides are not surrounded by an alignment film), there is a problem that sufficient alignment of the liquid crystal molecules cannot be ensured. Even if it is not used (even if the alignment film is used only on one side), sufficient alignment of liquid crystal molecules can be obtained. Conventionally, when a photopolymerizable film is coated with a cover material, oxygen remains due to irregularities of liquid crystal molecules, and even in a non-oxygen atmosphere state, the residual oxygen inhibits the photopolymerization reaction. In this form, such an adverse effect of residual oxygen can be prevented.

Further, in the embodiment providing a 25 cm ² or more alignment films on the support, it is possible to manufacture the photoresponsive crosslinked liquid crystal polymer film of 25 cm ² or more large area unprecedented. Moreover, the thickness can also be 1 micrometer-30 micrometers, and it has favorable photoresponsiveness.

FIG. 1 is a process diagram showing an outline of the production method of the present invention. FIG. 2 is a process diagram showing an outline of a conventional method for producing a liquid crystal polymer film. 3 (a) and 3 (b) are diagrams for explaining the structure of the film obtained by the present invention.

Hereinafter, the present invention will be described in more detail.
The method for producing a photoresponsive cross-linked liquid crystal polymer film of the present invention comprises a polyfunctional liquid crystal monomer, a monofunctional liquid crystal monomer, a polyfunctional photoresponsive monomer, a photopolymerization initiator and a photopolymerizable monomer containing at least a solvent. Applying the solution onto the alignment film by a wet coating method under a condition where the vapor pressure of the solvent is 100 mmHg or less, removing the solvent, and forming a photopolymerizable film (photopolymerizable film forming process); A process of forming a film (film forming process) by irradiating the photopolymerizable film with light in an oxygen atmosphere to polymerize the photopolymerizable monomer.

(Photopolymerizable film forming process)
The photopolymerizable monomer solution used in the present invention is obtained by dissolving a polyfunctional liquid crystalline monomer, a monofunctional liquid crystalline monomer, a polyfunctional photoresponsive monomer, and a photopolymerization initiator in a solvent.

Preferred examples of these monomers include those having a polymerizable group at the terminal and a mesogenic group composed of a cyclic unit or the like. Examples of the cyclic unit serving as a mesogenic group include biphenyl, phenylbenzoate, phenylcyclohexane, azoxybenzene, azomethine, azobenzene, phenylpyrimidine, diphenylacetylene, diphenylbenzoate, and bicyclohexane. Cyclohexyl benzene, terphenyl, and the like. In addition, the terminal of these cyclic units may have substituents, such as a cyano group, an alkyl group, an alkoxy group, a halogen atom, for example.
In addition, the monomers may be bonded via a spacer portion that imparts flexibility. Examples of the spacer portion include a polymethylene chain and a polyoxymethylene chain. The number of repeating structural units forming the spacer portion is appropriately determined depending on the chemical structure of the mesogenic portion, but the repeating unit of the polymethylene chain is 0 to 20, preferably 2 to 12, and the repeating unit of the polyoxymethylene chain is 0 to 0. 10, preferably 1-3.

  Examples of the functional group contained in these monomers include a polymerizable group such as a (meth) acryloyloxy group, a (meth) acrylamide group, a vinyloxy group, a vinyl group, or an epoxy group. A (meth) acryloyloxy group or a (meth) acrylamide group is preferred.

  From the viewpoint of the effects of the present invention, the polyfunctional liquid crystal monomer and the monofunctional liquid crystal monomer are preferably phenylbenzoate compounds.

  The polyfunctional liquid crystalline monomer can be represented by, for example, the following formula (1).

(In formula (1), n represents an integer of 3 to 9.)
N in the formula (1) is preferably an integer of 4 to 8, and more preferably an integer of 5 to 7.

1,4-bis [4- (6-acryloyloxyhexyloxy) benzoyloxy] -2-methylbenzene (a compound in which n is 6 in the compound represented by the formula (1)) as a polyfunctional liquid crystalline monomer. Hereinafter, “C6A”) can be synthesized as shown in the following scheme, for example.
That is, compound 1 is obtained by synthesizing Williamson ether to ethyl parahydroxybenzoate, and compound 1 is synthesized by deprotecting compound 1. Further, Compound 3 is obtained by subjecting Compound 2 to a Schotten-Baumann reaction, and finally C6A is synthesized by dehydrating condensation of Compound 3 and methylhydroquinone.

  Moreover, a monofunctional liquid crystalline monomer can be represented, for example by following formula (2).

(In formula (2), n represents an integer of 3 to 9)
N in Formula (2) is preferably an integer of 4 to 8, and more preferably an integer of 5 to 7.

As a monofunctional liquid crystalline monomer, 4-hexyloxyphenyl 4- (6-acryloyloxyhexyloxy) benzoate (a compound represented by the formula (2), wherein n is 6, hereinafter referred to as “A6BZ6”) Can be synthesized, for example, as shown in the following scheme.
That is, Compound 4 is obtained by synthesizing Williamson ether to hydroquinone, and A6BZ6 is synthesized by dehydrating and condensing Compound 4 with Compound 3 synthesized according to the synthesis scheme of C6A.

  The polyfunctional photoresponsive monomer is not particularly limited, and known monomers can be used. For example, azobenzene that undergoes trans-cis isomerization, stilbene structure, spiropyran that can undergo ring-opening-ring-closing photoisomerization, diaryl structure, etc. Can be mentioned. Among them, azobenzene represented by the following formula isomerizes from a rod-shaped trans isomer to a bent cis isomer when irradiated with ultraviolet light of about 300 to 400 nm, although it depends on a substituent bonded to the azobenzene skeleton. And when visible light of about 500 to 650 nm is irradiated, it returns to the original trans form, and the intermolecular distance greatly changes during isomerization, so that it can be mentioned as a particularly preferable example.

  Among these, from the viewpoint of the effect of the present invention, a polyfunctional photoresponsive monomer having an azobenzene structure represented by the following formula is preferable.

(In formula (3), n represents an integer of 1 to 6)
N in Formula (3) is preferably an integer of 2 to 5, and more preferably an integer of 3 to 4.

As a multifunctional photoresponsive monomer, 4,4′-bis [3- (acryloyloxy) propyloxy] azobenzene (a compound represented by the formula (3), wherein n is 3, hereinafter referred to as “DA3AB” For example, can be synthesized as shown in the following scheme.
That is, Compound 5 is obtained by synthesizing Williamson ether to paranitrophenol, and Compound 6 is obtained by reducing Compound 5. Compound 7 is synthesized by azo coupling of compound 6. Further, Compound 8 is obtained by performing Williamson ether synthesis again on Compound 7. Finally, DA3AB is synthesized by subjecting compound 8 to a Schotten-Baumann reaction.

  The solvent for dissolving the various monomers is required to have a vapor pressure of 100 mmHg or less when the photopolymerizable monomer solution is applied onto the alignment film by a wet coating method. Use of a solvent having a vapor pressure of 100 mmHg or less suppresses the volatilization rate of the solvent at the time of drying, so that even when a thick film is produced, the molecular orientation during the production of the photopolymerizable film is maintained. And a photoresponsive cross-linked liquid crystal polymer film having good photoresponsiveness can be obtained.

  Although the vapor pressure varies depending on the ambient temperature, since the working environment of a general coating process is 5 to 50 ° C., it is preferable to select a solvent having a vapor pressure of 100 mmHg or less in this temperature range. The more preferable vapor pressure is 10 to 90 mmHg, and the particularly preferable vapor pressure is 15 to 80 mmHg.

The vapor pressure at a certain temperature of the solvent is calculated using, for example, the Antoine formula shown by the following formula (4).
log ₁₀ P [mmHg] = AB / (t + C) (4)
In the formula (4), P is the vapor pressure, t is the temperature (° C.), and A, B, and C are Antoine constants specific to the substance.
From the above equation (4), the vapor pressure (mmHg) can be calculated by P = 10 ⁽ AB ^{/ (t + C))} .

  The solvent used in the present invention is preferably tetrahydrofuran, toluene, methyl ethyl ketone, dichloromethane, isopropyl alcohol, isobutyl alcohol, methyl cellosolve, ethyl acetate, butyl acetate, xylene, cyclohexanone, cyclopentanone, methyl isobutyl ketone, benzene, Examples thereof include at least one selected from normal hexane, ethylene glycol, methoxypropyl acetate, N-methyl-2-pyrrolidone, formyldimethylamine, cyclohexane, acetone, methanol and ethanol.

  In the present invention, even a solvent having a vapor pressure exceeding 100 mmHg can be used as a mixture of two or more. Even when two or more solvents are mixed, the vapor pressure of the whole solvent can be adjusted to 100 mmHg or less so that it can be suitably used in the method of the present invention. The vapor pressure of the mixed solvent is applicable to the following Raoul's law that the vapor pressure of each component of the mixed solution is represented by the product of the vapor pressure of each pure liquid and the molar fraction in the mixed solution.

  For example, when a mixed solvent of tetrahydrofuran (vapor pressure of 129.68 mmHg (17,289 Pa) at 20 ° C., solvent A) and toluene (vapor pressure of 21.86 mmHg (20,914 Pa) at 20 ° C., solvent B) is used as the solvent. When the molar fraction of tetrahydrofuran is 0.7, the partial pressure of solvent A in the mixed solvent is 91 mmHg, and the partial pressure of solvent B is 7 mmHg.

  Examples of the photopolymerization initiator include benzoin ether photopolymerization initiator, acetophenone photopolymerization initiator, α-ketol photopolymerization initiator, aromatic sulfonyl chloride photopolymerization initiator, and photoactive oxime photopolymerization initiator. Initiator, benzoin photopolymerization initiator, benzyl photopolymerization initiator, benzophenone photopolymerization initiator, ketal photopolymerization initiator, thioxanthone polymerization initiator, acylphosphine oxide photopolymerization initiator, titanocene photopolymerization An initiator or the like can be used. A photoinitiator can be used individually or in combination of 2 or more types.

  Specifically, examples of the benzoin ether photopolymerization initiator include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, and benzoin isobutyl ether. Examples of the acetophenone-based photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone [for example, trade name “Irgacure 184” (manufactured by Ciba Specialty Chemicals, etc.), 2,2-diethoxyacetophenone, 2,2-dimethoxy. -2-phenylacetophenone, 4-phenoxydichloroacetophenone, 4- (t-butyl) dichloroacetophenone and the like. Examples of the α-ketol photopolymerization initiator include 2-methyl-2-hydroxypropiophenone, 1- [4- (2-hydroxyethyl) phenyl] -2-methylpropan-1-one, and the like. . Examples of the aromatic sulfonyl chloride photopolymerization initiator include 2-naphthalene sulfonyl chloride. Examples of the photoactive oxime photopolymerization initiator include 1-phenyl-1,1-propanedione-2- (o-ethoxycarbonyl) -oxime. Examples of the benzoin photopolymerization initiator include benzoin. Examples of the benzyl photopolymerization initiator include benzyl. Examples of the benzophenone photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3,3′-dimethyl-4-methoxybenzophenone, polyvinyl benzophenone, α-hydroxycyclohexyl phenyl ketone, and the like. Examples of the ketal-based photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethane-1-one [for example, trade name “Irgacure 651” (manufactured by Ciba Specialty Chemical Co., Ltd.]) and the like. . Examples of the thioxanthone photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, dodecylthioxanthone, and the like. Examples of the acylphosphine oxide photopolymerization initiator include trade name “Lucirin TPO” (manufactured by BASF). Examples of the titanocene photopolymerization initiator include trade name “Irgacure 784” (manufactured by BASF).

  In the photopolymerizable monomer solution of the present invention, the blending ratio of the polyfunctional liquid crystalline monomer (a), the monofunctional liquid crystalline monomer (b), and the polyfunctional photoresponsive monomer (c) is a desired domain size (for example, 0. 5 μm or more) and the crosslink density may be determined. For example, the molar ratio is (a) 30 to 70 mol%, (b) 10 to 50 mol%, and (c) 10 to 40 mol%. More preferably, (a) 40-60 mol%, (b) 20-40 mol%, (c) 15-35 mol%. It is preferable for the blending ratio of each monomer to be in the above-mentioned range since the liquid crystal phase of the mixture is manifested.

  In the photopolymerizable monomer solution, the blending ratio of the photopolymerization initiator is, for example, 1 with respect to the total number of functional groups (polymerizable groups) of the monomers (a), (b), and (c). It is preferable to set it as -10 mol%, More preferably, it is 2-5 mol%. It is preferable for the blending ratio of the photopolymerization initiator to be in the above range because it is from the viewpoint of reaction efficiency and molecular weight control.

  In addition, a well-known various additive can also be mix | blended with a photopolymerizable monomer solution as needed. Examples of the additive include leveling agents, organic nanomaterials such as carbon nanotubes, fullerenes, and graphene, and inorganic nanomaterials such as gold, silver, copper, and silica.

  In the photopolymerizable monomer solution of the present invention, a polyfunctional liquid crystalline monomer, a monofunctional liquid crystalline monomer, a polyfunctional photoresponsive monomer, a photopolymerization initiator, and additives used as necessary are contained in a solvent. For example, it is preferable to melt | dissolve in the range of 0.01-0.20 mass%, and it is more preferable to melt | dissolve in the range of 0.02-0.10 mass%. It is preferable for the amount of all components to be dissolved in the solvent to be in the above-mentioned range since this is from the viewpoint of adjusting the solution viscosity during coating.

  As a method for preparing the photopolymerizable monomer solution, it can be prepared by a known method. For example, a polyfunctional liquid crystalline monomer, a monofunctional liquid crystalline monomer, a polyfunctional photoresponsive monomer and a photopolymerization initiator are added to a solvent, It can be prepared by heating if necessary and stirring and mixing.

The obtained photopolymerizable monomer solution is applied on the alignment film by a wet coating method to form a photopolymerizable film.
Any appropriate method can be adopted as the wet coating method. Examples thereof include a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (comma coating method and the like).

  Although there is no restriction | limiting in particular as an alignment film, What is excellent in the wettability of a photopolymerizable monomer solution and can orientate a polyfunctional liquid crystalline monomer and a monofunctional liquid crystalline monomer in a specific direction is preferable. As such an alignment film, specifically, for example, polyamide, polyimide, lecithin, silica, polyvinyl alcohol, ester-modified polyvinyl alcohol, a polymer in which the degree of saponification of polyvinyl acetate is adjusted, a silane coupling agent, or the like is applied. An alignment film formed as described above can be given. Further, the surface of the substrate may be rubbed as it is.

  Examples of the alignment treatment method include rubbing treatment, oblique vapor deposition treatment, microgroove method, stretched polymer film method and the like. From the viewpoint of the ease of the manufacturing process and the high degree of alignment uniformity, it is preferable to use a rubbing process as the alignment processing method.

  What is necessary is just to adjust suitably as thickness of application | coating according to the intended purpose of a film, for example, may apply | coat so that the thickness after solvent removal may be 1-30 micrometers.

It is desirable to remove the solvent from the formed coating film by drying. The drying temperature may be appropriately adjusted depending on the solvent to be used, but when polyvinyl alcohol is used, for example, 80 to 120 ° C. is preferable, and the drying time is preferably 60 to 240 seconds, for example. Moreover, when water is used for a solvent, 90-110 degreeC is preferable, for example, and as drying time, 100-200 seconds are preferable, for example. Residual solvent can be reduced by drying under the above-mentioned conditions.
Molecules on the film surface formed from the photopolymerizable monomer solution by this drying step are aligned along one direction.

(Film formation process)
In the step of forming the film, the photopolymerizable film is irradiated with light in a non-oxygen atmosphere to polymerize the photopolymerizable monomer.
Here, the non-oxygen atmosphere referred to in the present invention is substantially free of oxygen, for example, preferably having an oxygen concentration of 500 ppm or less, more preferably 200 ppm or less, and even more preferably 100 ppm or less. Especially, it is preferable to form a film in nitrogen gas atmosphere from a viewpoint that a non-oxygen atmosphere can be prepared at low cost.
The light irradiation only needs to activate the photopolymerization initiator and cause the reaction of the monomer component. As the energy beam irradiation device, a conventional device can be used. For example, when irradiating ultraviolet rays, a mercury lamp, a fluorescent lamp, a sodium lamp, a metal halide lamp, a xenon lamp, a neon tube, a neon lamp, a high-intensity discharge lamp, or the like can be used.

  In the present invention, the photopolymerizable monomer can be polymerized without covering the photopolymerizable film with a cover material. Thereby, the effort and cost accompanying film formation can be further reduced. In the prior art, there is a problem that the orientation of the liquid crystal molecules cannot be sufficiently secured unless both sides of the photopolymerizable film are surrounded by the orientation film using a cover material. However, in the present invention, even if the covering with the cover material is omitted (even if the alignment film is used only on one side), sufficient alignment of the liquid crystal molecules can be obtained. In the prior art, when the photopolymerizable film is coated with a cover material, oxygen remains due to the irregularities of the liquid crystal molecules, and even if a non-oxygen atmosphere is subsequently provided, the residual oxygen inhibits the photopolymerization reaction. However, in the present invention, such an adverse effect of residual oxygen can be prevented.

In the present invention, it is possible to provide a photoresponsive cross-linked liquid crystal polymer film having a large area of 25 cm ² or more, which is not conventional.
Such a photoresponsive cross-linked liquid crystal polymer film having a large area may be formed by providing an alignment film of 25 cm ² or more on a support, and performing the photopolymerizable film forming step and the film forming step.

Examples of the material for the support include known polymers such as triacetyl cellulose (TAC), polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, cycloolefin polymer, and other general-purpose polymers, elastomers, silicon rubber, metal thin films, paper, and the like. Can be used.
The shapes of the alignment film and the support are not particularly limited.
In addition, the thickness of the photoresponsive crosslinked liquid crystal polymer film having a large area of 25 cm ² or more of the present invention is, for example, 1 μm to 30 μm, preferably 2 to 20 μm, from the viewpoint of providing good photoresponsiveness. .

Hereinafter, the manufacturing method of the photoresponsive crosslinked liquid crystal polymer film of the present invention will be described with reference to FIG.
FIG. 1 is a process diagram showing an outline of the production method of the present invention described above.
In the photopolymerizable film forming step, a polyfunctional liquid crystalline monomer, a monofunctional liquid crystalline monomer, a polyfunctional photoresponsive monomer, and a photopolymerization initiator are dissolved in a solvent to prepare a raw material mixture (S10). Subsequently, an alignment film is prepared (S11), a rubbing process is performed (S12), the raw material mixture prepared above is applied onto the alignment film by a wet coating method, the solvent is removed, and a photopolymerizable film is formed. (S13).
In the film forming step, the photopolymerizable film is irradiated with light in a non-oxygen atmosphere to polymerize the photopolymerizable monomer (S14), and the formed film is collected (S15).

As described above, the manufacturing method of the present invention solves the problems in the manufacturing process of the conventional liquid crystal polymer film as shown in FIG. 2, and (2) continuous in a short time (for example, within 1 hour). Production is possible, (3) large area can be achieved, and (4) the wet coating method is adopted, so that the film thickness can be easily controlled.
Furthermore, in the production method of the present invention, a photopolymerizable film is formed by applying a photopolymerizable monomer solution onto the alignment film by a wet coating method using a solvent having a vapor pressure of 100 mmHg or less. Sufficient time for the alignment of the liquid crystalline monomer is ensured, the alignment regulating force in the thickness direction reaches, and good photoresponsiveness can be provided without causing the film to become cloudy.

The photoresponsive cross-linked liquid crystal polymer film of the present invention has a domain region which is an alignable region of mesogen, which is a hard core part directly involved in liquid crystal alignment, and the polymer skeleton has a three-dimensional network as shown in FIG. A structure 30 is formed. As a result, the oriented mesogen is gently restrained in the polymer matrix, and the movement of the polymer skeleton strongly correlates with the orientation of the mesogen. More preferably, the crosslinked structure has a structure in which orientational order is maintained over a long distance.
As described above, when the monomer 32 having an azobenzene structure is employed as the polyfunctional photoresponsive monomer, when irradiated with ultraviolet light, the rod-shaped trans body shown in FIG. 3 (a) is bent as shown in FIG. 3 (b). Isomerized to cis form. When the isomerized azobenzene is irradiated with visible light, it returns to the original trans form. By isomerization from the trans isomer to the cis isomer, the orientational order of the mesogen is lowered and an anisotropic contraction is induced as shown by an arrow A. In FIG. 3, 34 is a polyfunctional liquid crystalline monomer, and 36 is a monofunctional liquid crystalline monomer.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not restrict | limited to the following example.

[Example 1]
(Step of forming a photopolymerizable film)
The following monomers were used as the photopolymerizable monomer solution.
Multifunctional liquid crystalline monomer: C6A (prepared by the above scheme)
Monofunctional liquid crystalline monomer: A6BZ6 (prepared by the above scheme)
Multifunctional photoresponsive monomer: DA3AB (produced by the above scheme)
Photoinitiator: BASF titanocene photopolymerization initiator represented by the following formula (trade name “Irgacure 784”)

Solvent: Tetrahydrofuran (THF) (From the Antoine formula, the vapor pressure P at 20 ° C. is 129.68 mmHg, and the vapor pressure P at 10 ° C. is 80.58 mmHg.)
Additive: Leveling agent manufactured by BYK-Chemie (trade name “BYK361”)

  In the photopolymerizable monomer solution, polyfunctional liquid crystalline monomer: monofunctional liquid crystalline monomer: polyfunctional photoresponsive monomer was mixed at a ratio of 60:20:20 (mol%). The photopolymerization initiator was blended so as to be 2 mol% with respect to the total number of functional groups (polymerizable groups) of the monomers. The leveling agent was blended so as to be 0.05% by mass with respect to the entire photopolymerizable monomer solution. It dissolved in THF so that the whole density | concentration of each of these raw materials might be 15 mass%, and it stirred with the stirrer for 1 hour, and prepared the photopolymerizable monomer solution.

  The detail of each raw material mix | blended with the photopolymerizable monomer solution below is shown.

Subsequently, saponified TAC (Fuji Film Co., Ltd., triacetyl cellulose, 40 μm thickness) was used as a support.
Polyvinyl alcohol (PVA) aqueous solution (VC-10 manufactured by JVP, fully saponified type, 5 wt% aqueous solution) is applied to the TAC with a wire bar # 5, and the condition is 100 ° C. for 3 minutes. A PVA film was formed on the TAC by putting in a drying oven and drying. The formed PVA film surface was rubbed about 5 times in one direction with a rayon cloth and subjected to rubbing treatment to obtain an alignment film for aligning liquid crystal molecules. In addition, in order to suppress the repelling of the photopolymerizable monomer solution during the next wet coating, the TAC and PVA films were neutralized using an ionizer SJ-F305 manufactured by Keyence Corporation.
Subsequently, the photopolymerizable monomer solution was applied onto the PVA alignment film with a wire bar # 9 in an atmosphere of 10 ° C., and dried in a drying oven at 50 ° C. for 3 minutes to remove the solvent. A photopolymerizable film (TAC / PVC film / photopolymerizable film) was obtained. After removing the solvent, the cross section in the dry state (after film formation) was observed with a scanning electron microscope (SEM). As a result, the thickness of the photopolymerizable film was 1.1 μm.

(Film formation process)
Next, the TAC / PVC film / photopolymerizable film was put into a purge box purged with nitrogen (oxygen concentration ≦ 100 ppm), and a wavelength filter (Shibuya Optical Co., Ltd. Long Pass Filter, OG530, 3 mm thickness, manufactured by Shibuya Optical Co., Ltd.) Output through a heat-absorbing filter (KG5, 2 mm thickness) so that light having a wavelength of 500 to 600 nm is selectively transmitted and the irradiation surface has an irradiation energy density of ^{2 to 3} mW / cm ^2. The adjusted ultra-high pressure mercury lamp (UV-CURE850 manufactured by JATEC Co., Ltd.) was irradiated to the photopolymerizable film for about 30 minutes to polymerize the photopolymerizable monomer to form a 200 mm × 300 mm size film.

The following evaluation was performed about the obtained film.
(1) Optical properties (1-1) When measured with a haze meter, it was confirmed that the film had a transmittance of 88% and a haze of 1.1% and a high transparency and orientation at a wavelength of 590 nm.
(1-2) When the thickness of the film formation part of the sample film obtained by cross-sectioning with a freezing microtome was measured with a scanning electron microscope (SEM), it was confirmed that the sample film had a thickness of about 1.1 μm. It was.

(2) Photoresponsiveness <Measurement conditions>
Apparatus: Tensile mode of TA Instruments viscoelasticity measuring apparatus RSA III Sample: Acrylic adhesive (25 mm thickness) / PET (polyethylene terephthalate, 25 mm thickness) for the purpose of eliminating evaluation variations due to UV absorbers contained in TAC / The polymerized photoresponsive cross-linked liquid crystal polymer layer was transferred to a base material made of an acrylic pressure-sensitive adhesive (thickness 25 mm) to prepare a specimen to be evaluated.
Evaluating specimen setting conditions: Evaluating specimen width 5 mm, distance between chucks 10 mm, distortion 0.1% (constant)
UV irradiation conditions: The specimen to be evaluated is chucked, subjected to 0.1% distortion, waits for 10 minutes, and then UV (ultraviolet light) is applied to the entire chucking portion at a wavelength of 365 nm and an irradiation energy density of 80 mW / cm ^2. ). The stress at which the azobenzene in the photoresponsive cross-linked liquid crystal polymer layer isomerized by UV irradiation and the sample bends accordingly was evaluated.
Definition of generated stress: The difference between the stress before UV irradiation and the maximum stress value after irradiation was defined as the stress [MPa] generated by the optical response.

  As a result of evaluation under the above conditions, the sample to be evaluated showed a high generated stress of 12.2 MPa.

[Example 2]
In Example 1, a mixed solvent composed of the following two types of solvents A and B was used as a solvent in the photopolymerizable monomer solution. The atmospheric temperature at the time of application | coating of a photopolymerizable monomer solution was 20 degreeC, and it carried out similarly to Example 1, and produced the photoresponsive bridge | crosslinking type liquid crystal polymer film.
Solvent A: Tetrahydrofuran (boiling point 66 ° C., vapor pressure 129.68 mmHg at 20 ° C., molar fraction 0.7)
Solvent B: Toluene (boiling point 110 ° C., vapor pressure 21.86 mmHg at 20 ° C.)
Partial pressure of mixed solvent (calculated from Raoul's law): partial pressure of solvent A 91 mmHg, partial pressure of solvent B 7 mmHg

The optical characteristics measured with a haze meter were confirmed to be a film having a transmittance of 88% and a haze of 1.0% at a wavelength of 590 nm and a high degree of transparency and orientation. In the thickness measurement of the film-forming part using a scanning electron microscope (SEM), it was confirmed that it has a thickness of about 1 μm.
In the photoresponsiveness test, the sample to be evaluated of Example 2 showed a high generated stress of 13.0 MPa.

Example 3
In Example 1, a mixed solvent composed of the following two types of solvents A and B was used as a solvent in the photopolymerizable monomer solution. The atmospheric temperature at the time of application | coating of a photopolymerizable monomer solution was 20 degreeC, and it carried out similarly to Example 1, and produced the photoresponsive bridge | crosslinking type liquid crystal polymer film.
Solvent A: Tetrahydrofuran (boiling point 66 ° C., vapor pressure 129.68 mmHg at 20 ° C., molar fraction 0.75)
Solvent B: cyclohexanone (boiling point 155 ° C., vapor pressure 1.20 mmHg at 20 ° C.)
Partial pressure of mixed solvent (calculated from Raoul's law): Solvent A partial pressure of 97 mmHg, Solvent B partial pressure of 0.5 mmHg

The optical characteristics measured with a haze meter were confirmed to be a film having a transparency of 89% transmittance and a haze of 1.2% and a high orientation at a wavelength of 590 nm. In the thickness measurement of the film-forming part using a scanning electron microscope (SEM), it was confirmed that it has a thickness of about 1.1 μm.
In the photoresponsiveness test, the specimen to be evaluated of Example 3 showed a high generated stress of 12.8 MPa.

[Comparative Example 1]
Photoresponsive cross-linked liquid crystal polymer film in the same manner as in Example 1 except that the photopolymerizable monomer solution was applied to the PVA alignment film with a thickness of 1.2 μm with wire bar # 9 in an atmosphere of 20 ° C. Was made. The vapor pressure P of THF at 20 ° C. is 129.88 mmHg from the Antoine formula.

  The film was visually judged to be cloudy, and had a transmittance of 65.5% and a haze of 12% at a wavelength of 590 nm. Moreover, in the photoresponsiveness test, the sample to be evaluated of Comparative Example 1 exhibited a generated stress of 6 MPa.

[Comparative Example 2]
A film was produced according to the prior art described in FIG. As a result, a photoresponsive cross-linked liquid crystal polymer film having characteristics equivalent to those of Example 1 could be produced, but it took time to produce (it took 25 hours or more than Example 1), and the size was as small as 10 mm × 10 mm. It was poor in practicality. Moreover, the film thickness of the sample to be evaluated of Comparative Example 1 was 19 μm, and the generated stress was 5 MPa.

(Reference Example 1)
The coating environment temperature was set to 20 ° C. (vapor pressure of the solvent: 129.68 mmHg), the wire bar was changed to # 4, and coating / drying was repeated three times in the same manner as in Example 1 except that the film was laminated. The photoresponsive cross-linked liquid crystal polymer was produced by the method. When the obtained coating film was measured with a haze meter, it was confirmed that a film having a transmittance of 88.4% at a wavelength of 590 nm, a transparency of haze of 1.2% and a high orientation (thickness 1 μm) was made. Since the coating / drying process was repeated for the present invention, it took time to obtain a desired coating film.

  The production method of the present invention eliminates the complexity of production, can easily produce a film with a large area continuously while achieving good film thickness control in a short time, and A photoresponsive cross-linked liquid crystal polymer film that achieves good photoresponsiveness can be provided, and the obtained film is useful for, for example, an actuator, a plastic motor, a micro flow path (valve), a robot arm, and the like.

30 Three-dimensional network structure 32 Monomer having azobenzene structure 34 Multifunctional liquid crystalline monomer 36 Monofunctional liquid crystalline monomer

Claims (7)

Wet coating method using a photopolymerizable monomer solution containing at least a polyfunctional liquid crystal monomer, a monofunctional liquid crystal monomer, a polyfunctional photoresponsive monomer, a photopolymerization initiator and a solvent under a condition that the vapor pressure of the solvent is 100 mmHg or less By applying onto the alignment film by removing the solvent, forming a photopolymerizable film,
A method for producing a photoresponsive cross-linked liquid crystal polymer film, comprising: irradiating the photopolymerizable film with light in a non-oxygen atmosphere to polymerize the photopolymerizable monomer to form a film.   The method for producing a photoresponsive cross-linked liquid crystal polymer film according to claim 1, wherein the polyfunctional photoresponsive monomer is a polyfunctional photoresponsive monomer having an azobenzene structure.   The solvent is tetrahydrofuran, toluene, methyl ethyl ketone, dichloromethane, isopropyl alcohol, isobutyl alcohol, methyl cellosolve, ethyl acetate, butyl acetate, xylene, cyclohexanone, cyclopentanone, methyl isobutyl ketone, benzene, normal hexane, ethylene glycol, methoxypropyl acetate. The photoresponsive crosslinked liquid crystal polymer film according to claim 1 or 2, which is at least one selected from N, methyl-2-pyrrolidone, formyldimethylamine, cyclohexane, acetone, methanol, and ethanol. Production method.   The method for producing a photoresponsive cross-linked liquid crystal polymer film according to any one of claims 1 to 3, wherein the step of forming the film is performed in a nitrogen gas atmosphere.   The process of forming the said film is performed, without covering the said photopolymerizable film | membrane with a cover material, Manufacture of the photoresponsive bridge | crosslinking type liquid crystal polymer film as described in any one of Claims 1-4. Method. Provided 25 cm ² or more of the alignment film on a support to form a film of 25 cm ² or more large area, photoresponsive crosslinked liquid crystal polymer film of any one of claims 1 to 5 Manufacturing method. A photoresponsive cross-linked liquid crystal polymer film having a thickness of 1 to 30 μm and a large area of 25 cm ² or more, comprising a polyfunctional liquid crystalline monomer, a monofunctional liquid crystalline monomer and a polyfunctional photoresponsive monomer as monomer units.

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