JP3419568B2 - Method for improving light reflectivity of polymer liquid crystal layer and polymer liquid crystal layer structure - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the light reflectance of polymer liquid crystals and a polymer liquid crystal layer structure.

[0002]

2. Description of the Related Art A uniform and stable liquid crystal molecular alignment is essential and essential for liquid crystal displays. This is because when a liquid crystal is used for a display element, it is based on the fact that the molecular alignment state is changed according to an external field and the change in the optical characteristics of the liquid crystal cell is converted into a visual change. Generally, in order to efficiently generate an alignment suitable for the optical characteristics of the liquid crystal, a layer adjacent to the liquid crystal layer is subjected to an alignment treatment. The types of liquid crystal molecular alignment include homeotropic alignment, homogeneous alignment, tilt alignment, hybrid alignment, twist alignment, planar alignment, and focal conic alignment. These molecular arrays can be formed by aligning the substrate surface. The substrate surface alignment treatment includes vertical alignment treatment, parallel alignment treatment, and tilt alignment treatment. Substrate surface orientation treatment methods include methods of forming molecules that physically or chemically adsorb on the substrate surface, methods of dissolving an aligning agent in liquid crystal, and methods of physically deforming the substrate surface and aligning liquid crystal molecules along it. To be

By carrying out such an orientation treatment, the molecular arrangement becomes uniform and stable, which leads to the improvement of optical characteristics.

[0004]

Generally, when the liquid crystal layer is formed without performing the alignment treatment, the optical characteristics are lower than when the alignment treatment is performed. For example, when a cholesteric liquid crystal is simply formed on a substrate, light of a wavelength corresponding to the spiral pitch of the cholesteric liquid crystal is reflected, but the substrate is rubbed in one direction before forming the cholesteric liquid crystal. Then, the amount of reflected light increases. Further, when the liquid crystal layer is formed after forming the layer for improving the orientation under the liquid crystal layer, the amount of reflected light increases.
However, the rate of increase is low in each of the methods, and the method of rubbing described above has a reflectance of 3 as described later in the embodiment section.
It is about 0% or less.

It is an object of the present invention to provide a method for improving the light reflectance of a polymer liquid crystal layer and a polymer liquid crystal layer structure capable of significantly improving the reflectance of light of a specific wavelength. .

[0006]

The above objects are achieved by the present invention described in (1) to (6) below. (1) A method for improving the light reflectance of a polymer liquid crystal layer using a polymer cholesteric liquid crystal or a polymer chiral nematic liquid crystal, which comprises a fluorine-based nonionic surfactant adjacent to the polymer liquid crystal layer. A polymer liquid crystal characterized by providing a surfactant-containing layer or adding a fluorine-based nonionic surfactant to the polymer liquid crystal layer itself to improve the reflectance for light of a specific wavelength. Method for improving light reflectance of a layer. (2) A polymer liquid crystal layer structure comprising a polymer liquid crystal layer whose light reflectance is improved by the method (1) above, and a support for supporting the polymer liquid crystal layer, wherein A polymer liquid crystal layer structure having a reflectance of 35% or more. (3) The polymer according to (2) above, wherein the surfactant-containing layer is provided between the support and the polymer liquid crystal layer, and contains 0.1 to 100 wt% of a fluorine-based nonionic surfactant. Liquid crystal layer structure. (4) The polymer liquid crystal layer structure according to (2) or (3), wherein the surfactant-containing layer has a thickness of 20 Å or more. (5) When the fluorine-based nonionic surfactant is added to the polymer liquid crystal layer itself, the polymer liquid crystal layer contains 0.1 to 30 wt.
% Of the fluorine-based nonionic surfactant, the polymer liquid crystal layer structure according to (2) above. (6) The polymer liquid crystal layer structure according to any one of (2) to (5), wherein the polymer liquid crystal layer has a thickness of 0.5 to 20 μm.

[0007]

In the polymer liquid crystal layer and the polymer liquid crystal layer structure whose light reflectance is improved by the method of the present invention,
With the structure as described above, the reflectance of light having a specific wavelength is 35% or more. As a result, when the polymer liquid crystal layer of the present invention is used for surface coating of an article, the color tone becomes vivid and the lightness also improves. Further, when the polymer liquid crystal layer or structure of the present invention is used for a display medium, the reflectance is improved, so that the contrast between the liquid crystal portion and the non-liquid crystal portion is improved and the visibility of the display object is improved. Furthermore, when the polymer liquid crystal layer or structure of the present invention is used as a temperature indicating material, it has excellent visibility because of its high color lightness and saturation. Each has an economic effect that the amount of the polymer liquid crystal for obtaining a certain constant reflectance may be small.

[0008]

Specific Structure The specific structure of the present invention will be described in detail below.

In the method for improving the light reflectance of a polymer liquid crystal layer of the present invention, a surfactant-containing layer containing a fluorine-based nonionic surfactant is provided adjacent to the polymer liquid crystal layer,
Alternatively, a fluorine-based nonionic surfactant is added to the polymer liquid crystal layer itself to improve the reflectance of the polymer liquid crystal layer for light of a specific wavelength.

The polymer liquid crystal layer structure of the present invention comprises a substrate, a polymer liquid crystal layer, and if necessary, a surfactant-containing layer provided adjacent to the polymer liquid crystal layer. According to the method of the present invention, a fluorine-based nonionic surfactant is added to the surfactant-containing layer or the polymer liquid crystal layer.
A fluorine-based nonionic surfactant may be added to the polymer liquid crystal layer itself while providing the surfactant-containing layer. Further, the polymer liquid crystal layer structure of the present invention has a reflectance of 35% or more for light of a specific wavelength. The upper limit of this reflectance is about 50%.

<Fluorine-based nonionic surfactant and surfactant-containing layer> Examples of the fluorine-based nonionic surfactant include hydrogen atoms of oxyethylene group, oxypropylene group and alkyl group in the surfactant molecule. A part of or all of is replaced with a fluorine atom, a type of fluorine-based surfactant,
Preferably, a perfluoroalkyl group having 4 to 20 carbon atoms and a polyalkylene oxide having a polymerization degree of 4 to 50 are added, for example, perfluoroalkyl polyethylene oxide adduct, perfluoroalkyl polypropylene oxide adduct, and preferably the same perfluoroalkyl polypropylene oxide adduct. It is desirable to use an acrylate oligomer containing a fluoroalkyl group, a hydrophilic group and a lipophilic group (perfluoroalkyl group-containing acrylate oligomer).

When the surfactant-containing layer is provided, it is preferable that the surfactant-containing layer is a resin layer containing a fluorine-based nonionic surfactant. At this time, it is preferable that the fluorine-containing nonionic surfactant is contained in the surfactant-containing layer in an amount of 0.1 wt% or more, particularly 0.5 wt% or more. When the amount of the fluorine-based nonionic surfactant is less than the above, sufficient orientation cannot be obtained and the reflectance becomes low. Further, the surfactant-containing layer may constitute the surfactant-containing layer only with a fluorine-based nonionic surfactant. At that time, Langmuir-Blodgett (LB)
Since the film also functions, the LB film may be formed on the substrate by the Langmuir-Blodgett method, and the polymer liquid crystal layer may be formed thereon. However, the surfactant-containing layer is usually
A resin layer containing a fluorine-based nonionic surfactant,
Fluorine-based nonionic surfactant content of 0.1-50
It is preferably set to wt%.

As the resin which can be used in the surfactant-containing layer, acrylic, urethane, polyester, vinyl chloride, vinyl acetate, epoxy, phenoxy, polyamide resin and their copolymers are preferable. In addition, various kinds of inorganic, organic and organic fillers and various additives may be appropriately added to the surfactant-containing layer.

As shown in FIG. 1, the surfactant-containing layer 2 is preferably arranged between the support 1 and the polymer liquid crystal layer 3, but may be on the polymer liquid crystal layer. . The thickness of the surfactant-containing layer 2 is 20Å both when the surfactant-containing layer is arranged between the support 1 and the polymer liquid crystal layer 3 and when it is arranged on the polymer liquid crystal layer. The above is preferable. However, when the surfactant-containing layer 2 is a resin layer containing a fluorine-based nonionic surfactant, it is preferably 0.1 μm or more. The upper limit of the thickness of the surfactant-containing layer 2 is not particularly limited, but considering the light transmittance, it is preferably 500 μm or less.

When the above-mentioned fluorine-based nonionic surfactant is contained in the polymer liquid crystal layer, the polymer liquid crystal layer structure has a structure as shown in FIG. The content in the polymer liquid crystal layer is 0.
It is preferably 1 to 30% by weight, particularly preferably 0.3 to 20% by weight. When the content of the fluorine-based nonionic surfactant is less than the above range, sufficient orientation cannot be obtained and the reflectance is low, and when it exceeds the above range, the plasticization of the coating film becomes remarkable.

<Substrate> The substrate may be a flexible sheet or a rigid plate. Further, it may be the whole or a part of the article. However, in order to visually confirm the coloring due to the selective reflection wavelength from the polymer liquid crystal layer, it is preferable to make it visible light absorbing,
Paper or a plastic film provided with a light absorption layer, or a black plastic film such as polyethylene terephthalate (PET) may be used. The light absorbing layer may be a layer containing carbon black or the like, and the black plastic film may be one in which carbon black is kneaded. Further, this substrate itself may contain a fluorine-based nonionic surfactant. In this case, the surfactant-containing layer may be omitted. When the substrate itself contains a fluorine-based nonionic surfactant, the substrate is preferably formed of a resin, and as the resin, polyethylene terephthalate, polyvinyl chloride, polyamide, polyimide or the like can be used. preferable.

When the polymer liquid crystal layer structure of the present invention is used as a display medium or the like, the thickness of the support is 50 to 500 μm.
m, preferably 100 to 300 μm.

<Polymer Liquid Crystal Layer> The polymer liquid crystal in the polymer liquid crystal layer is preferably a polymer cholesteric liquid crystal or a polymer chiral nematic liquid crystal having a function of selective reflection in the visible light region. The above wavelength range is usually 4
It is preferably from 00 to 700 nm, but depending on the case, it may be from 400 to 750 nm, and may include the infrared region.

The thickness of the polymer liquid crystal layer is 0.5 to 2
It is preferably about 0 μm. The reason is that if the thickness is too thin, the amount of reflected light is small and a sufficient reflectance cannot be obtained, and if the thickness is too large, the reflectance similarly decreases.

Here, as the polymer liquid crystal, a polymer cholesteric liquid crystal will be representatively described in detail.

The polymer cholesteric liquid crystal preferably has a structure represented by the following chemical formula 1, but is not limited thereto.

[0022]

[Chemical 1]

The above-mentioned polymer cholesteric liquid crystal exhibits a cholesteric liquid crystal phase at a temperature not lower than the glass transition temperature (Tg) and lower than the isotropic phase transition temperature (Tc), and therefore selective reflected light can be obtained. And isotropic phase transition temperature (Tc)
At the above temperature, it shows an isotropic phase and becomes transparent.

The polymer cholesteric liquid crystal of Chemical formula 1 has a glass transition temperature (Tg) of 40 ° C. or higher, preferably 50 to 1
It is about 00 ° C. The isotropic phase transition temperature (Tc) is 1
It is preferably 00 ° C or higher, preferably 150 ° C to 250 ° C.

The polymer liquid crystal layer is preferably composed only of liquid crystal such as the polymer cholesteric liquid crystal of Chemical formula 1, but in some cases, polyvinyl chloride, polyvinyl acetate,
A resin such as an epoxy resin, a phenoxy resin, an acrylic resin, a polyurethane or a polyester may be contained in an amount of 80 wt% or less of the entire polymer liquid crystal layer layer.

The chemical formula 1 will be described in detail. R ₁ represents the above cholesterol group, R ₂ represents a biphenyl group, a cyanophenyl group, a methoxyphenyl group, a cyanobiphenyl group,
It represents an alkylbiphenyl group, a chlorophenyl group and the like.
The substitution position of the phenyl group in the biphenyl group represented by R ₂ is not particularly limited, but preferably 4-biphenyl group and the like can be mentioned. Further, biphenyl groups having different phenyl group substitution positions may be mixed. Also,
Even when R ₂ is a cyanophenyl group, the substitution position of the cyano group is not particularly limited, but preferably 4-cyanophenyl group and the like can be mentioned, and cyanophenyl groups having different substitution positions of the cyano group are mixed. You may have. further,
Even when R ₂ is a methoxyphenyl group, the substitution position of the methoxy group is not particularly limited, but preferably 4-methoxyphenyl group and the like can be mentioned, and methoxyphenyl groups having different substitution positions of the methoxy group are mixed. You may have.

In the chemical formula 1, a and d are 2 respectively.
It represents an integer of 4 and particularly preferably 3. a
It is usually preferred that d and d are the same, but they may be different in some cases. Further, it is preferable that b and e each represent 0 or 1, and c and f each represent 1. x is preferably 0.1 to 0.7. n represents an average degree of polymerization and is preferably 2.5 to 10, and more preferably 3 to 7.

Specific examples of the polymer cholesteric liquid crystal of Chemical formula 1 are shown below.

In a specific example, R ₁ in Chemical formula ₁
The combinations of R ₂ , a, d, b, e, c, f, x and n are shown in Table 1.

[0030]

[Table 1]

The polymer cholesteric liquid crystal of Chemical formula 1 is a known compound, and its synthesis method is FHKreuzer, et al., Mo.
l. Electron., 3, 1 , 9 (1987), FHKreuzer, et al., M
ol.Cryst.Liq.Cryst., 199 , 345 (1991).

The reflected light band can be defined by appropriately setting x among the above factors. Specifically, a = 3, b = 1, c = 1, d = 4, e = 0, f
= 1, when x = 0.15, the center reflection wavelength is about 720 nm, and when x = 0.25, the center reflection wavelength is about 560 nm, and x =
When it is set to 0.50, the central reflection wavelength is about 410 nm, and red, green, and blue are exhibited, respectively.

The polymer liquid crystal layer structure of the present invention selectively reflects light as described above, and its reflectance is preferably 35% or more, and the reflection wavelength is in the visible light range, It is preferable that the peak is sharp.

A protective layer containing a resin such as acrylic, urethane, polyester, vinyl chloride, vinyl acetate, epoxy, phenoxy, polyamide resin or a copolymer thereof as a main component may be provided on the uppermost layer. Good.

In the polymer liquid crystal layer structure of the present invention, a coating liquid of polymer cholesteric liquid crystal or polymer chiral nematic liquid crystal is applied on a support and dried to form a liquid crystal layer. The coating liquid is prepared by containing a polymer cholesteric liquid crystal or a polymer chiral nematic liquid crystal in an organic solvent. Examples of the organic solvent include toluene,
It is desirable to use cyclohexanone, tetrahydrofuran, or a mixed solvent thereof. When a fluorine-based nonionic surfactant is added to the liquid crystal layer, it is added to the above coating liquid. The coating method is not particularly limited,
A bar coating method, a gravure coating method, a roll coating method, an air knife coating method or the like may be used. Most of the liquid crystal layers exhibit a cholesteric color or a chiral nematic color after coating and drying, but some liquid crystals require aging at a temperature of Tg or higher and lower than Tc.

When the above-mentioned surfactant-containing layer is provided, a predetermined resin and a fluorine-based nonionic surfactant are contained in an organic solvent to prepare a coating solution, which is then applied onto the support or It is formed by coating on the polymer liquid crystal layer and drying. The organic solvent used and the coating method may be the same as those used in the case of the polymer liquid crystal layer.

When a protective layer is provided, if necessary, it may be provided by coating or the like, using a coating liquid containing a predetermined resin in accordance with the polymer liquid crystal layer.

[0038]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

Example 1 On a black polyethylene terephthalate substrate having a thickness of 188 μm, various surfactants (No. 1, 7, shown in Table 2) with respect to solid content of water-based polyester urethane emulsion resin (HW350 manufactured by Dainippon Ink and Chemicals, Inc.) were used. 8) was added by 1 wt% and a surfactant-containing layer having a thickness of 1.5 μm was formed with a bar coater. The surfactant No. 1 is a fluorine-based nonionic surfactant, and the surfactants Nos. 7 and 8 are a hydrocarbon-based nonionic surfactant and a hydrocarbon-based anionic surfactant, respectively. . Further, a THF solution of a polymer liquid crystal shown in the following chemical formula 2 was applied on this surfactant-containing layer with a bar coater to form a 3 μm liquid crystal layer, and a sample No. of polymer liquid crystal layer structure having the structure shown in FIG. 1 was formed. .1, 7, and 8 were produced. For comparison, without the surfactant-containing layer,
A sample No. 9 in which a liquid crystal layer was directly formed on the substrate and a sample No. 10 in which the surface of the substrate was rubbed were also prepared. The reflection spectrum of the sample of the polymer liquid crystal layer structure obtained here is shown in FIG. 3, and the maximum reflectance is shown in Table 3.

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Chemical 2]

As is clear from the results, the maximum reflectance of the polymer liquid crystal layer structure of sample No. 1 containing the fluorine-based nonionic surfactant was 37.5%, but other samples Is 2 without a surfactant-containing layer
Sample Nos. 7 and 8 having a surfactant-containing layer containing a hydrocarbon-based surfactant at 4.0% had a reflectance of 2 on the contrary.
It fell to 0.0% and 15.0%. The polymer liquid crystal layer structure of Sample No. 1 exhibited a red color, and the half value width showing the sharpness of the reflection peak was 90 nm.

Example 2 A THF solution prepared by adding 1 wt% of each of the various surfactants (Nos. 1 to 8) shown in Table 2 above to the polymer cholesteric liquid crystal shown in Chemical formula 2 on a black 188 μm thick polyethylene terephthalate substrate. Was applied using a percoater and dried to form a polymer liquid crystal layer having a thickness of 3 .mu.m, thereby forming sample Nos. 11 to 18 of the polymer liquid crystal layer structure having the structure shown in FIG. In addition, a sample was prepared in which no surfactant was added to the liquid crystal layer, and this was designated as sample No. 19.

The reflection spectrum of each sample is shown in FIG. 4, and the maximum reflectance is shown in Table 4. As is clear from these, Sample No. 1 containing a fluorine-based nonionic surfactant was added.
1 to 13 are compared with sample Nos. 14 to 16 containing a fluorine-based ionic surfactant, sample Nos. 17 and 18 containing a hydrocarbon-based surfactant, and sample No. 19 containing no surfactant. It can be seen that the reflectance is significantly improved. From these, it is considered that the fluorine-based nonionic surfactant contributes to the improvement of the orientation of the cholesteric liquid crystal. In addition, this polymer liquid crystal layer structure exhibited a red color, and the half value width showing the sharpness of the reflection peak was 80 nm.

[0046]

[Table 4]

[0047]

EFFECTS OF THE INVENTION In order to improve the alignment of liquid crystal molecules, it is not necessary to align the substrate surface as in the conventional case, and a fluorine-based nonionic surfactant is added to the lower layer of the polymer liquid crystal layer, or a fluorine-based nonionic surfactant is added. The reflectance of visible light of the liquid crystal is improved simply by adding the surface active agent to the liquid crystal.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a layer structure of a polymer liquid crystal layer structure of the present invention.

FIG. 2 is a cross-sectional view showing another example of the layer structure of the polymer liquid crystal layer structure of the present invention.

FIG. 3 is a diagram showing reflection spectra of polymer liquid crystal layer structures of Example 1 of the present invention and Comparative Example.

FIG. 4 is a diagram showing reflection spectra of polymer liquid crystal layer structures of a second example of the present invention and a comparative example.

[Explanation of symbols]

1 support 2 Surfactant-containing layer 3 Polymer liquid crystal layer structure

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-61-118703 (JP, A) JP-A-5-341289 (JP, A) JP-A-52-148153 (JP, A) JP-A-5-148153 333313 (JP, A) JP-A-6-230371 (JP, A) JP-A-1-285920 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/137 G02F 1 / 1337

Claims (6)

(57) [Claims] 1. A method for improving the light reflectance of a polymer liquid crystal layer using a polymer cholesteric liquid crystal or a polymer chiral nematic liquid crystal, comprising a fluorine-based nonionic surfactant adjacent to the polymer liquid crystal layer. It is characterized by providing a surfactant-containing layer containing it or adding a fluorine-based nonionic surfactant to the polymer liquid crystal layer itself to improve the reflectance for light of a specific wavelength. Method for improving light reflectance of molecular liquid crystal layer. 2. A polymer liquid crystal layer structure comprising a polymer liquid crystal layer having an improved light reflectance by the method according to claim 1, and a support for supporting the polymer liquid crystal layer, the polymer liquid crystal layer structure having a specific wavelength. A polymer liquid crystal layer structure having a light reflectance of 35% or more. 3. The high-performance surfactant according to claim 2, wherein the surfactant-containing layer is provided between the support and the polymer liquid crystal layer, and contains 0.1 to 100 wt% of a fluorine-based nonionic surfactant. Molecular liquid crystal layer structure. 4. The thickness of the surfactant-containing layer is 20Å
The polymer liquid crystal layer structure according to claim 2 or 3, which is the above. 5. When the fluorine-based nonionic surfactant is added to the polymer liquid crystal layer itself, the polymer liquid crystal layer is adjusted to 0.1%.
The polymer liquid crystal layer structure according to claim 2, which contains ˜30 wt% of a fluorine-based nonionic surfactant. 6. The polymer liquid crystal layer has a thickness of 0.5 to 2
The polymer liquid crystal layer structure according to any one of claims 2 to 5, which has a thickness of 0 µm.