JPH06331966A - Liquid crystal optical element and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Objective] To manufacture a high-performance liquid crystal optical element using polymer-dispersed liquid crystal. [Structure] In a liquid crystal cell in which a pair of upper and lower substrates 2 and 3 having a transparent electrode 1 and a lower substrate 3 are bonded together via a spacer / sealant resin 4, a dissolved substance composed of a liquid crystal material, a polymerizable material and a polymerization initiator. 5 from the light source 7 provided with the filter layer 6 on the melt 5 and within the light absorption wavelength (λC to λC ′) region of the polymerization initiator, which is the light absorption wavelength (λA) of the liquid crystal material. .About..lamda.A ') and light 8 outside the light absorption wavelength region (.lamda.B to .lamda.B') of the polymer material to perform polymerization by polymerizing liquid crystal optical element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal optical element using a polymer dispersed liquid crystal in which a liquid crystal is dispersed and held in a polymer resin matrix, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, polymer-dispersed liquid crystal (hereinafter referred to as PDLD) in which a nematic liquid crystal is dispersed and held in a polymer having the same refractive index as liquid crystal molecules is used between a pair of upper and lower substrates having electrodes. A liquid crystal optical element which is sandwiched between the two and changes the refractive index of the liquid crystal depending on the presence or absence of an electric field to switch between the scattering state and the transmitting state has attracted much research and developer attention (Japanese Patent Publication No. 58-501631). JP-A-60-2
No. 52687, and Japanese Patent Publication No. 61-502128).

3 and 4 are schematic views showing the display principle of this liquid crystal optical element. When no voltage is applied (Fig. 3),
Since the molecular axis of the liquid crystal 9 is oriented in a random direction, the refractive index of the liquid crystal region is different from that of the surrounding polymer matrix 10, and the light incident on the liquid crystal optical element (incident light 11) becomes scattered light 12, resulting in , A scattering state is obtained. On the other hand, when an electric field is applied to the transparent electrode 1 (FIG. 4), the molecular axes of the liquid crystal 9 are aligned in the direction of the electric field, and for the light incident perpendicularly on the substrate, the refractive index of the liquid crystal region is the surrounding polymer. Matrix 10
The light (incident light 11) incident on the liquid crystal optical element becomes transmitted light 13, and as a result, a transmitted state is obtained.

Since the liquid crystal optical element using this PDLC utilizes the scattering of light, it is not necessary to use a polarizing plate.
As compared with a conventional twisted nematic (TN) type liquid crystal optical element, which requires a polarizing plate to obtain linearly polarized light, a brighter display with a wider viewing angle can be displayed. The PDLC manufacturing method includes a solvent casting method in which a polymer and a liquid crystal are dissolved in a common solvent and cast on a substrate (J. Membrance Sci., V.
ol. 11, p. 39-52, Jan. , 1982),
Impregnation method of impregnating liquid crystal into the pores of a polymer porous membrane (A
Applied Physics Letters, vo
l. 48, no. 1, p. 22-24, Jan. 198
2), an emulsification method in which a liquid crystal is emulsified and dispersed in a polymer aqueous solution and cast (SID Int. Symp. Dig. T).
ech. , Vol. 16. p. 68, 1985), a uniform solution of a liquid crystal and a polymerizable monomer is prepared, and this is subjected to phase separation by polymerization to form a phase separation structure (Appli.
ed physics Letters, vol. Four
8, no. 4, p. 269-271, Jan. 198
5) etc. Of these manufacturing methods, the impregnation method is rarely applied industrially. Although there are application examples of the emulsification method, the solvent casting method, and the polymerization method, when the PDLC is applied to a display such as a liquid crystal optical element, the PDLC is formed on a substrate having electrodes, and the positions of a pair of upper and lower substrates are precisely aligned. It is necessary to bond the substrates by an emulsification method or a solvent casting method which requires evaporation of water or a solvent as a dispersion solvent on the substrates. Therefore, when applied to a display, a polymerization method that does not require a solvent is suitable, and in particular,
A photopolymerization method, which has a short polymerization time and is extremely easy to manufacture, is often used, and its application to a projection type display has been studied (Japanese Patent Laid-Open No. 1-229232).

[0005]

[Problems to be Solved by the Invention] However, PDLC
When a liquid crystal optical element using is prepared by a photopolymerization method,
Depending on the wavelength region of light used for polymerization and irradiation conditions, the liquid crystal material or the polymerizable material, which is a constituent material of PDLC, is deteriorated, which often causes the performance of the liquid crystal optical element to be impaired. This is because when the wavelength region of light for polymerization overlaps the light absorption wavelength region of the constituent material of PDLC, the constituent material absorbs light and photodegradation starts,
As a result, the performance of the liquid crystal optical element deteriorates.

An object of the present invention is to solve the above-mentioned problems of a liquid crystal optical element using PDLC, to provide a method for manufacturing a liquid crystal optical element that does not cause deterioration of performance, and to provide a liquid crystal optical element having high performance characteristics. Is to provide.

[0007]

In order to achieve the above object, the first aspect of the present invention provides at least the light absorption wavelength region (λC to λC ') of the polymerization initiator which is one of the constituent materials of PDLC. Similarly, a part of the above-mentioned constituent material is used so that it does not overlap the light absorption wavelength area (λA to λA ′) of the liquid crystal material and the light absorption wavelength area (λB to λB ′) of the polymerizable material which are constituent materials of PDLC. A method for producing a liquid crystal optical element as a second invention is a liquid crystal optical element formed by using a composition containing
Light having a wavelength within the range of λC to λC ′,
In addition, it is a method for producing a liquid crystal optical element in which polymerization is completed by irradiating light having a wavelength outside the range of λA to λA ′ and λB to λB ′.

[0008]

In the first invention, the polymerization is performed by irradiating light having a wavelength within the light absorption wavelength range of the polymerization initiator and having a wavelength outside the light absorption wavelength range of the liquid crystal material and the polymerizable material. By doing so, light absorption of the liquid crystal material or the polymerizable material can be suppressed, and the liquid crystal optical element has high performance without deterioration of the constituent material of PDLC. Further, in the second invention, the liquid crystal optical element can be manufactured without causing deterioration of the constituent material of the PDLC as in the above.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The liquid crystal optical element of the present invention and the manufacturing method thereof will be described below with reference to the drawings. FIG. 1 is a diagram showing an outline of a method for manufacturing a liquid crystal optical element using the PDLC of the present invention. Transparent electrode 1 made of indium / tin oxide
A pair of upper and lower substrates 2 and 3 on which the above are formed are prepared, and they are bonded to each other through the spacer / sealing resin 4 to complete an empty cell. Then, a melted material 5 obtained by heating and stirring a composition containing liquid crystal, an uncured photopolymerizable material, and a polymerization initiator is injected from the opening of the empty cell. After the injection, the opening is sealed, and the melt 5 is irradiated with light 8 having a wavelength in a certain region from a light source 7 equipped with a filter layer 6 such as an ultraviolet cut filter so that a desired wavelength can be irradiated. A liquid crystal cell composed of PDLC was completed.

FIG. 2 is a sectional view showing the structure of a liquid crystal optical element completed by the above manufacturing method. By light irradiation,
Polymerization of the polymerizable material proceeds, phase separation occurs, and PDLC in which the liquid crystal 9 is dispersed and held in the polymer matrix 10 is formed. Hereinafter, specific examples will be described in more detail.

(Embodiment 1) Two pieces of glass on which a transparent electrode made of indium tin oxide is formed are prepared, and as shown in FIG. 5, one of the supporting plates (for example, the lower substrate 11) also serves as a spacer on the surface thereof. As the sealing resin 12, an acid anhydride-curable epoxy resin in which glass fibers having a diameter of 13 μm are dispersed is printed with a width of 0.2 mm on the other periphery leaving an opening 13 having a width of 5 mm at the center of only one side. Then, the upper substrate 14 and the lower substrate 11 were pressed against each other and heated at 140 ° C. for 4 hours to be cured and adhered to complete an empty cell.

Next, 8.200 g of liquid crystal (trade name: BL-035) manufactured by Merck Ltd. as a liquid crystal material, 0.954 g of an acrylic monomer as a polymerizable material, and an acrylic oligomer as an oligomer. 0.808
g, 0.038 g of 2,4-diethylthioxanthone (manufactured by Nippon Kayaku Co., Ltd.) as a photopolymerization initiator was prepared, and the composition composed of the components described above was sufficiently stirred at 55 ° C. Material A) was adjusted. 6 to 12 show the light absorption spectra of each component. As can be seen from these spectra, as the polymerization initiator, a material having a light absorption region which does not partially overlap with the light absorption regions of the liquid crystal, the monomer, and the oligomer used was selected.

Next, the melt A was injected from the opening 13 into the empty cell manufactured by the above-mentioned manufacturing method at 55 ° C. After the injection is completed, the opening 13 is sealed, and the high pressure mercury lamp is used as a light source at 55 ° C. to complete the polymerization of the polymerizable material, and the PDL
A liquid crystal optical element made of C was completed. At this time, the high-pressure mercury lamp had an ultraviolet cut filter (Toshiba Glass Co., Ltd.).
(Production: Y-43) was attached to the liquid crystal optical element so that the wavelength of the light was 400 nm or more (FIG. 10 shows the light transmission characteristics of Y-43). The intensity of the polymerized light is 24.5 mW / cm ² , and the irradiation time is 10 seconds. The characteristics of the completed liquid crystal optical element were evaluated by using the voltage holding characteristics when a rectangular wave having a frame period of 30 Hz, a voltage of ± 5 V and an ON time of 60 μsec was applied to the liquid crystal cell as an index. The voltage holding characteristic was quantified as a voltage holding ratio, and the voltage accumulated within the ON time in which the voltage did not change at all during the frame period was set to 100%. When the performance of the liquid crystal optical element is deteriorated due to the deterioration of the constituent materials, the voltage holding characteristic is deteriorated and the voltage holding ratio is lowered. The voltage holding ratio of the liquid crystal optical element produced this time was 79.8% at 40 ° C., which was a high value.

(Embodiment 2) Two pieces of glass on which a transparent electrode made of indium tin oxide is formed are prepared, and as shown in FIG. 3, one of the supporting plates (for example, the lower substrate 11) also serves as a spacer on the surface thereof. As the sealing resin 12, an acid anhydride-curable epoxy resin in which glass fibers having a diameter of 13 μm are dispersed is printed with a width of 0.2 mm on the other periphery leaving an opening 13 having a width of 5 mm at the center of only one side. Then, the upper substrate 14 and the lower substrate 11 were pressed against each other and heated at 140 ° C. for 4 hours to be cured and adhered to complete an empty cell.

Next, 8.200 g of a liquid crystal (trade name: ZLI-4792) manufactured by Merck Ltd. was used as a liquid crystal material, and the same acrylic monomer as described in Example 1 was used as a polymerizable material in an amount of 0.200 g. 954 g, and as an oligomer,
Prepare 0.808 g of the same acrylic oligomer as described in Example 1 and 0.038 g of benzyl dimethyl ketal (manufactured by Nippon Kayaku Co., Ltd.) as a photopolymerization initiator,
A composition comprising the above-mentioned components is thoroughly stirred at 55 ° C,
A lysate (hereinafter referred to as lysate B) was prepared. 9 and 1
3 shows the light absorption spectra of ZLI-4792 and benzyl dimethyl ketal. 9, FIG. 13 and FIG. 6, FIG.
As can be seen from the spectra of the monomer and oligomer shown in, the polymerization initiator is
And a material having a light absorption region that does not partially overlap with the light absorption region of the oligomer was selected.

Next, the melt B was injected from the opening 13 into the empty cell manufactured by the above-mentioned manufacturing method at 55 ° C. After the injection is completed, the opening 13 is sealed, and the high pressure mercury lamp is used as a light source at 55 ° C. to complete the polymerization of the polymerizable material, and the PDL
A liquid crystal optical element made of C was completed. At this time, the high-pressure mercury lamp had an ultraviolet cut filter (Toshiba Glass Co., Ltd.).
(Product name: L-39) was attached to the liquid crystal optical element so that the wavelength of the light was 360 nm or more (FIG. 11 shows the light transmission characteristics of L-39). The intensity of the polymerized light is 24.5 mW / cm ² , and the irradiation time is 10 seconds. The voltage holding ratio of the completed liquid crystal optical element is 40 ° C.
97.3%, which was an extremely high value.

COMPARATIVE EXAMPLE 1 BL035 as a liquid crystal material
(Manufactured by Merck Co., Ltd.), the same materials as those described in Example 1 were used as the monomer and oligomer materials, and benzyl dimethyl ketal was prepared as the polymerization initiator. The light absorption wavelength range of benzyl dimethyl ketal (Fig. 13) is BL
It is completely included in the light absorption wavelength region of 035 (FIG. 8). With the same weight ratio, each of the above materials was sandwiched between empty cells produced by the production method described in Example 1, and the wavelength region of light for polymerization was 360 nm or more (light absorption wavelength region of benzyl dimethyl ketal). Inner light), the same ultraviolet cut filter (Toshiba Glass Co., Ltd .: trade name L-39) as that described in Example 2 was attached to the high-pressure mercury lamp, and polymerization was carried out to produce a liquid crystal optical element. did. Irradiation intensity,
The irradiation time is the same as that described in Example 1. The voltage holding ratio of the completed liquid crystal optical element was 35.2% at 40 ° C., which was considerably lower than that of Example 1.

Comparative Example 2 Lysate B described in Example 2
Was sandwiched between the empty cells produced by the production method described in Example 1, and the ultraviolet light transmitting filter (manufactured by Toshiba Glass Co., Ltd.) : Product name UV-29) was attached, and the melt B was polymerized to produce a liquid crystal optical element (U in FIG. 14).
V-29 shows the light transmission characteristics). The irradiation intensity and irradiation time are the same as those described in Example 1. The voltage holding ratio of the completed liquid crystal optical element was 70.5% at 40 ° C.
It was lower than that of.

In the present embodiment, the proportion of liquid crystal in PDLC is 82% by weight, but it is not limited to this. The polymerizable material is not limited to the acrylic monomer used this time, and commercially available products other than the acrylic monomer can be applied. Further, the oligomer is not limited to the acrylic oligomer described above.

In the embodiment of the present invention, the wavelength of the light for polymerization is adjusted by attaching the filter layer to the light source, but other than that, the filter layer may be attached to the substrate side. The same effect can be achieved by using a monochromator instead of the filter.

[0021]

INDUSTRIAL APPLICABILITY In the present invention, polymerization is performed by irradiating light having a wavelength selected so that at least a part of the light absorption wavelength region of the polymerization initiator does not overlap with the light absorption wavelength region of the liquid crystal material and the polymerizable material. By performing the above, it is possible to realize a liquid crystal optical element having high performance characteristics without deterioration of the constituent material of PDLC.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a method for producing a liquid crystal optical element using a polymer dispersed liquid crystal of the present invention.

FIG. 2 is a schematic cross-sectional view of a liquid crystal optical element manufactured by the manufacturing method of the present invention.

FIG. 3 is an explanatory view showing a display principle of a liquid crystal optical element when a voltage is not applied.

FIG. 4 is an explanatory diagram when the same voltage is applied.

FIG. 5 is a schematic plan view of a liquid crystal optical element manufactured by the manufacturing method of the present invention.

FIG. 6 is an optical absorption spectrum diagram of the monomer material used in Example 1.

7 is a light absorption spectrum diagram of the oligomer material used in Example 1. FIG.

FIG. 8: Optical absorption spectrum of BL035

FIG. 9 is an optical absorption spectrum diagram of ZLI4792.

FIG. 10 is a light transmission characteristic diagram of the ultraviolet cut filter Y-43.

FIG. 11 is a light transmission characteristic diagram of the ultraviolet cut filter L-39.

FIG. 12 is an optical absorption spectrum diagram of 2,4-diethylthioxanthone.

FIG. 13: Optical absorption spectrum of benzyl dimethyl ketal

FIG. 14 is a light transmission characteristic diagram of an ultraviolet transmission filter UV-29.

[Explanation of symbols]

 1 Transparent Electrode 2 Upper Substrate 3 Lower Substrate 4 Spacer / Seal Resin 5 Dissolved Material 6 Filter Layer 7 Light Source 8 Light for Polymerization 9 Liquid Crystal 10 Polymer Matrix

Claims (2)

[Claims] 1. A liquid crystal optical element using a polymer-dispersed liquid crystal produced by irradiating a composition containing a liquid crystal material, a polymerizable material and a polymerization initiator with light, in a light absorption wavelength range of the polymerization initiator. A liquid crystal optical element characterized in that at least a part thereof does not overlap with the light absorption wavelength region of the liquid crystal material and the polymerizable material. 2. A composition comprising a liquid crystal material, a polymerizable material and a polymerization initiator is sandwiched between substrates having a pair of electrodes,
In the method for manufacturing a liquid crystal optical element that completes the polymerization of a polymerizable material by light irradiation, the light absorption wavelength range of the liquid crystal material is λA to λA ′, and the light absorption wavelength range of the polymerizable material is λB to λ.
B ′, where the light absorption wavelength region of the polymerization initiator is λC to λC ′, the composition is light in the region of λC to λC ′ and outside the regions of λA to λA ′ and λB to λB ′. A method for producing a liquid crystal optical element, which comprises irradiating light to perform polymerization.