JP2921040B2 - Light control film and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light control film that exhibits a transparent state when no electric field is applied and a cloudy state when an electric field is applied, and a method for manufacturing the same.

[Prior Art] An example of using a liquid crystal to obtain a light-shielding effect has been known for a long time. A nematic liquid crystal is sandwiched between transparent substrates, and liquid crystal molecules are aligned along the electric field by applying an electric field to change the transparent state. There is known a so-called twisted nematic element which obtains a light-shielding effect when no electric field is applied. It has been pointed out that the light-shielding plate manufactured by this manufacturing method requires polarizing plates on both sides, and the amount of liquid crystal used is inexpensive, and it is not self-supporting.

On the other hand, there is a method of dispersing a liquid crystal in a polymer medium in order to increase the area by providing self-supporting properties. It is mainly a liquid crystal in which liquid crystal is dispersed in a polymer medium as a droplet having a diameter of about the wavelength of visible light (hereinafter, referred to as a polymer dispersed liquid crystal film). There are several methods for depositing and dispersing liquid crystal droplets.

(1) A liquid crystal is dissolved in a monomer or oligomer polymerizable by irradiation with ultraviolet light or electron beam or heat or a mixture thereof (hereinafter, referred to as a prepolymer), and the prepolymer is polymerized by irradiation with ultraviolet light or electron beam or heat. (2) a method in which the liquid crystal component is precipitated and dispersed as droplets, (2) a method in which the liquid crystal dissolved in the polymer medium is cooled by heating to lower the compatibility to precipitate the liquid crystal component as droplets, and (4) a method of dissolving a polymer medium in a common solvent and evaporating the solvent to precipitate liquid crystal components as droplets; (4) mixing a liquid crystal and a polymer in a general-purpose solvent to form an emulsified state; A method of evaporating and depositing liquid crystal components as droplets is known (JWDOAN
E et al., Mol. Cryst. Liq. Cryst., 1988, Vol. 165, pp. 533-57.
1). These can be formed into a thin film of several microns to several tens of microns by printing and casting, and can be laminated with a film with a transparent electrode.

The structure and function of the polymer-dispersed liquid crystal film manufactured by the above method will be described with reference to FIGS. 2 (a) and 2 (b). The dispersed liquid crystal molecules are precipitated and dispersed in the polymer medium as droplets. FIG. 2A shows the case where no electric field is applied, and the orientation of the liquid crystal molecules (18) in the droplet (16) is random.

 When incident light (24) enters this film, liquid crystal molecules (1
8) Refractive index n_LC(= (2n_⊥+ N ) / 3) and polymer media
(14) refractive index n_PIs large because of the large difference between
The incident light (24) is scattered (where n Is the liquid crystal molecule
Longitudinal refractive index, n_⊥Is the vertical index of refraction
). FIG. 2 (b) shows the case where an electric field is applied.
The liquid crystal molecules (18) in the droplet (16)
Orients along the direction. At this time, the refraction of liquid crystal molecules (18)
Rate (n_LC= N_⊥) And the refractive index n of the polymer medium (14)_PDifference with
Becomes less and becomes transparent.

Based on such a principle, it is applied to a wide range of fields such as a light shielding film and a shutter.

The polymer-dispersed liquid crystal film produced by the above method develops a transparent state when an electric field is applied. This means that when using it for in-vehicle use or private use,
When the application of the electric field is stopped for some accidental reason, for example, a power failure, disconnection, or battery exhaustion, the transparent state does not appear. When such a polymer-dispersed liquid crystal film is used as a fogged glass or a display for an automobile windshield, the windshield becomes opaque or erroneously displayed when an abnormality such as a power failure occurs. Occurs. Conversely, if it is almost transparent when there is no electric field and becomes cloudy when an electric field is applied, it is transparent and safe even if there is no electric field.

[Problems to be Solved by the Invention] An object of the present invention is to provide a light control film capable of obtaining a light-shielding effect by expressing a transparent state when no electric field is applied and a cloudy state when an electric field is applied, and a method for manufacturing the same. It was done.

The present inventors have conducted intensive studies so as to produce a light control film having a quick response, showing a cloudy state when an electric field is applied and a transparent state when no electric field is applied, unlike conventionally known light control films. As a result, the present invention has been accomplished.

[Means for Solving the Problems] That is, the present invention basically provides a liquid crystal composition in which dielectric anisotropy changes from positive to negative or from negative to positive depending on the frequency of an applied AC electric field in an organic polymer medium. Things are dispersed,
A light control film characterized by exhibiting a transparent state when no electric field is applied and exhibiting a cloudy state when an electric field is applied.

The main component of the liquid crystal composition used in the present invention is generally and preferably a nematic liquid crystal. Further, the polymer medium may be one produced by irradiation of ultraviolet rays or electron beams of a polymerizable monomer or oligomer or a mixture thereof, or a polymerization reaction by heat,
It can be said that this is a preferred embodiment.

As a method for producing a light control film of the present invention, a method for producing a light control film in which a liquid crystal composition is dispersed in an organic polymer medium, exhibits a transparent state when no electric field is applied, and develops a cloudy state when an electric field is applied. A liquid crystal composition whose dielectric anisotropy changes from positive to negative or from negative to positive depending on the frequency of an applied AC electric field is dispersed in a polymerizable monomer or oligomer or a mixture thereof, and the liquid crystal composition is transparent. As an example, it can be proposed that the above-mentioned polymerizable monomer or oligomer or a mixture thereof is subjected to a polymerization reaction in an applied state of an alternating electric field.

 Here, assuming that the dielectric anisotropy is Δε, Δε = ε −ε_⊥ And a liquid crystal compound and
It is uniquely determined by the components and composition of the liquid crystal composition.

 A cloudy state is achieved by applying an electric field, and a transparent state is achieved by applying no electric field.
To achieve this, the refractive index n of the liquid crystal molecules_LCAnd polymer medium
Refractive index n_PIs large when an electric field is applied and small when no electric field is applied.
Is necessary. Most polymer media have a refractive index
n_PIs about 1.4 to 1.55, and the refractive index of the liquid crystal molecule is n_⊥But
1.5, n Is about 1.7, the electric field
When the refractive index of the liquid crystal molecule and the refractive index of the polymer medium are n_⊥
n_PThat the liquid crystal molecules are aligned in one direction.
is necessary.

In order to align the liquid crystal molecules in one direction, an alternating electric field or a magnetic field may be applied. FIG. 2 (b) shows a state in which the initial alignment of the liquid crystal molecules is oriented to one side by the application of an AC electric field.

In the method based on the application of an AC electric field, if the liquid crystal has a positive dielectric anisotropy, it can be oriented along the electric field. In addition, when the method is based on the application of a magnetic field, the liquid crystal can be oriented along the direction of the magnetic field regardless of the positive or negative of the dielectric anisotropy. When a method of curing a prepolymer by photopolymerization described in (1) above when producing a polymer-dispersed liquid crystal film using this method, it is necessary to combine a light irradiation device and an external field application device. It is realistic to apply an AC electric field as an external field due to the restrictions described above. In the case of the above-mentioned (2) polymerization reaction by heat or the means of precipitation of (3) and (4), an AC magnetic field can be applied.

When using a liquid crystal whose dielectric anisotropy does not depend on the frequency of the applied electric field when producing a polymer-dispersed liquid crystal film in the above-mentioned electric field applied state, the formed film remains in a transparent state and forms a cloudy state. Can not be used as a shutter. In order to solve this, the present inventors have used liquid crystals whose dielectric anisotropy depends on the applied frequency. In particular, (Equation 1) and A mixture of formula (2), or (Equation 3) and And mixtures of the formula (4). When a magnetic field is applied, a transparent film can be produced by performing thermal polymerization while applying a magnetic field of about 15 K Oersted vertically to a cell containing liquid crystal with negative dielectric anisotropy, and it becomes cloudy when an AC electric field is applied A state can be formed.

As a prepolymer that can be polymerized by ultraviolet rays, electron beams or heat constituting a polymer medium, specifically, pentaerythritol triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, trimethylpropane triacrylate, hexane Examples thereof include diol-1,6-dimethacrylate, triethylene glycol diacrylate, and mixtures thereof. The content of the prepolymer of the material used in the production method of the present invention can be in the range of 1: 2 to 4: 1 by weight of the liquid crystal substance: unsaturated bond compound, preferably 1: 1 to 3: 1. : 1 range.

A known polymerization initiator may be used in the light control film material of the present invention, if desired.

FIG. 1 (a) is an explanatory diagram showing that the light control film of the present invention develops and maintains a transparent state when no electric field is applied. According to the figure, a polymer medium (14) sandwiched between transparent films (10) with two transparent electrodes (12) contains droplets (16) of liquid crystal molecules (18). As described above, the liquid crystal molecules (18) are polymerized in the state shown in FIG. 2 (b), that is, in a state where the long axes of the liquid crystal molecules are aligned parallel to the optical axis of the incident light (24). Since the medium (14) is cured, the liquid crystal molecules (18) maintain the vertical alignment state even when the electric field or magnetic field for alignment is removed. Thus, the light management film is light transmissive.

FIG. 1 (b) is an explanatory view showing that an electric field is applied to the light control film of the present invention so that the liquid crystal molecules (18) are arranged perpendicular to the direction of the electric field, and a white turbid state is developed.

[Effect of the Invention] The light control film of the present invention expresses a light-shielding effect when no electric field is applied and a transparent state when no electric field is applied, unlike the conventional type that exhibits a light-shielding effect when no electric field is applied and a transparent state when an electric field is applied. By doing so, it can be used safely even in a field where the electric field is suddenly unable to be supplied, such as on-vehicle use or private use, where the danger is imposed. Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to this.

[Embodiment] The present invention realizes a dimming film that exhibits a transparent state when no electric field is applied and a cloudy state when an electric field is applied. This effect will be described below with reference to examples.

<Example 1> Thick the mixture of the above components on a film with a transparent electrode
It is bar-coated to 20 μm and laminated with another film with a transparent electrode. This liquid crystal has low frequency (number 10
In an AC electric field of about 0 Hz, the dielectric anisotropy is positive, and at high frequencies (several thousands to tens of thousands Hz), the dielectric anisotropy is negative.

A polymerization reaction is caused by ultraviolet irradiation (640 mJ) in a state where an AC electric field (100 Vp-p, 100 Hz) is applied to the electrode, and the electrode is cured. After leaving the electric field applied for about 1 hour, a transparent film was obtained.

The haze ratio of this film was 10% when no electric field was applied, and 48% when an AC electric field (50 Vp-p, 10,000 Hz) was applied.

<Example 2> Instead of the compounds of (Formula 1) and (Formula 2) in Example 1, Was applied to a thickness of 20 μm by the same operation and laminated with a film with a transparent electrode. An AC electric field (10
(0 Vp-p, 80 Hz), and a transparent film was obtained by the same operation.

The haze ratio of this film was 8% when no electric field was applied, and 50% when an AC electric field (50 Vp-p, 10,000 Hz) was applied.

[Brief description of the drawings]

FIG. 1A is an explanatory view showing that the light control film produced by the production method of the present invention develops and maintains a transparent state when no electric field is applied, and FIG. It is explanatory drawing which shows that an electric field is applied to the light control film of this invention, and a liquid crystal molecule arrange | positions perpendicularly to an electric field direction and expresses a cloudy state. 2 (a) and 2 (b) are explanatory views showing a conventional light control film. 10 transparent film 12 transparent electrode 14 polymer medium 16 droplet 18 liquid crystal molecule 20 power supply 22 switch 24 incident light 26 scattered light 28 transmitted light

Continuation of the front page (56) References JP-A-1-145636 (JP, A) JP-A-3-209425 (JP, A) JP-A-1-135425 (JP, U) , A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1333

Claims (4)

(57) [Claims] A liquid crystal composition in which dielectric anisotropy changes from positive to negative or from negative to positive depending on the frequency of an applied AC electric field is dispersed in an organic polymer medium, and exhibits a transparent state when no electric field is applied. A light control film that develops a cloudy state when applied. 2. The light control film according to claim 1, wherein a main component of the liquid crystal composition is a nematic liquid crystal. 3. The method according to claim 1, wherein the polymer medium is produced by irradiating a polymerizable monomer or oligomer or a mixture thereof with ultraviolet rays or an electron beam, or by a heat polymerization reaction. 2) The light control film according to the above. 4. A method for producing a light control film in which a liquid crystal composition is dispersed in an organic polymer medium, exhibits a transparent state when no electric field is applied, and exhibits a cloudy state when an electric field is applied, comprising a polymerizable monomer. Alternatively, a liquid crystal composition whose dielectric anisotropy changes from positive to negative or from negative to positive depending on the frequency of an applied AC electric field is dispersed in an oligomer or a mixture thereof, and an AC electric field is applied so that the liquid crystal composition exhibits a transparent state. A method for producing a light control film, which comprises polymerizing the polymerizable monomer or oligomer or a mixture thereof in a state.