This application claims priority to and the benefit of Korean Patent Application No. 2012-0094649, filed Aug. 29, 2012, the disclosure of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a method of producing a polymer dispersed liquid crystal device with a cooling plate and a polymer dispersed liquid crystal device using the same.
2. Discussion of Related Art
Existing eyeglasses used by people with weak vision are of a fixed strength, and thus it is necessary to replace the eyeglasses as vision worsens. Especially, when farsightedness occurs as people age, people who were already myopic have difficulty seeing text both near and far. Out of existing eyeglasses, sunglasses are widely used by people with normal vision to block direct sunlight and UV rays, especially overseas. In recent years, in order to find solutions to the problems of the existing eyeglasses, research on smart electronic eyeglasses has been underway. The principle is using an optical shutter function for blocking or transmitting light which is a fundamental role of the liquid crystal. The optical shutter employing such liquid crystal is referred to as a crystal device, or simply a device, in order to differentiate it from the existing eyeglasses. The crystal device can be electronically operated based on the external light intensity. When the external light intensity is high, that is, light is strong, the liquid crystal shutter is largely open, whereas when light is weak, the liquid crystal shutter opens little so as to control the amount of light. By combining these features with an electronic circuit serving as a switch in addition to a sensor for measuring the external light intensity, it is possible to configure electronic eyeglasses employing a so-called autoshading function of a crystal device which performs more active functions than the sunglasses. In addition, a focal length of the crystal device can be adjusted by controlling the voltage applied to the electrodes which are divided into multiple levels such that electrodes are effectively arranged in the vicinity of high-refractive-index liquid crystal or the crystal device is formed in a three-dimensional manner. In this case, by combining a distance measurement sensor with an electronic circuit having an electrode driving control function, it is possible to manufacture electronic eyeglasses having a strength function which can cope with myopia or hypermetropia. Further, the smart electronic eyeglasses in which the above-described autoshading function and the degree function are combined and a variety of software is installed are under development.
Such a crystal device uses a nematic liquid crystal in the manufacturing of a TFT-LCD. Due to the limitation of the material itself, the reaction rate of the nematic liquid crystal is relatively slow, and a manufacturing process thereof is complex, requiring many manufacturing facilities. Further, additional films such as a polarizing plate are necessary. In particular, in terms of the basic principle of the nematic liquid crystal, polarizing plates are attached to the front and rear surfaces of the nematic liquid crystal device one by one, and thus the cost increases and light transmittance is reduced by 35% or more. Furthermore, a very complex process including an alignment process using polyimide and a liquid crystal injection process degrades a yield of the nematic liquid crystal and the productivity.
Recently, in order to overcome the shortcomings of such a nematic liquid crystal device, new liquid crystal materials and crystal devices have been proposed.
In terms of the basic principle of the nematic liquid crystal, with simple manufacturing processes and manufacturing facilities, the polymer dispersed liquid crystal does not require the polarizing plate and the polyimide alignment for an array of liquid crystal. As a result, light transmittance reaches 100% in theory and it is possible to overcome most problems of the nematic liquid crystal described above.
However, because a material made of a polymer is employed, the polymer dispersed liquid crystal device has a problem in that a driving voltage is higher than the nematic liquid crystal. When the driving voltage is high, an electrical efficiency for driving the polymer dispersed liquid crystal device decreases and the battery consumption increases. Further, it is very dangerous since the user wears the electrical eyeglasses in front of her or his eyes. When the driving voltage is 30 V or more, the manufacturing cost of a driving circuit increases greatly. Accordingly, it is necessary to improve the characteristics of the driving voltage, which is one of the biggest shortcomings of the polymer dispersed liquid crystal device.
The present invention has been made in view of the above-described problems and an object of the invention is to provide a method of producing a polymer dispersed liquid crystal device capable of lowering a driving voltage without a significant effect on other electro-optical characteristics of the polymer dispersed liquid crystal device.
The invention relates an effective method of removing heat generated by light in the ultraviolet (UV) light irradiation process in the production process of the polymer dispersed liquid crystal device using a cooling plate.
The method of producing the polymer dispersed liquid crystal device of the invention includes: (a) a step of forming a gap by bonding two to seven substrates with a spacer absorbed therebetween using a UV adhesive; (b) a step of injecting a liquid crystal mixture in which a pre-polymer and liquid crystal are mixed into the gap; and (c) a step of curing and cooling, in which curing with UV light and cooling with a cooling plate are preformed. In addition, the invention relates to the polymer dispersed liquid crystal device produced according to the above-described method.
According to the producing method of the invention using the cooling plate capable of effectively removing heat with a relatively simple method, it is possible to improve driving voltage characteristics and decrease the producing cost of the polymer dispersed liquid crystal device.
The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which:
a) and 2(b) illustrate an embodiment of a production process flow of a UV curable PDLC device.
a) and 3(b) are photographs showing microstructures of a PDLC device and a polymer network liquid crystal.
a) and 4(b) illustrate curves between an applied voltage and light transmittance of the polymer crystal device according to a liquid crystal concentration while the cooling is performed 4(a) or not performed 4(b).
a) and 6(b) illustrate curves between an applied voltage and light transmittance of the polymer liquid crystal device according to the UV curing intensity while the cooling is performed 6(a) or not performed 6(b).
a) and 8(b) illustrate gradient changes in the driving range of the PDLC device while the cooling is performed or not performed, where 8(a) is based on the liquid crystal concentration and 8(b) is based on the UV curing intensity.
a) and 9(b) illustrate response rate changes of the PDLC device according to the presence of the cooling plate in the UV irradiation process and the liquid crystal concentration, where 9(a) is rising response time and 9(b) is falling response time.
a) and 10(b) illustrate response rate changes of the PDLC lens according to the presence of the cooling plate in the UV irradiation process and the UV curing intensity, where 10(a) is rising response time and 10(b) is falling response time.
a) and 13(b) are microscopic photographs of the PDLC droplet size according to the presence of the cooling plate.
a) and 14(b) are scanning electron microscopic (SEM) photographs of the PDLC droplet size according to the presence of the cooling plate.
A method of producing a polymer dispersed liquid crystal (PDLC) device of the invention includes: (a) a step of forming a gap by bonding two to seven substrates with a spacer absorbed therebetween using a UV adhesive; (b) a step of injecting a liquid crystal mixture in which a pre-polymer and liquid crystal are mixed into the gap; and (c) a step of curing and cooling, in which curing with UV and cooling with a cooling plate are performed.
As illustrated in
In general, the PDLC is configured with elliptical liquid crystal droplets having a diameter of 2 to 5 μm which are uniformly dispersed on the polymer film having a thickness of 20 to 50 μm.
In step (a), the substrate is not limited thereto, but may be an indium-tin oxide deposited glass, polycarbonate, polyethylene terephthalate, polyethylenesulfone, polyimide, a polycyclic olefin, polyalylate, polyethylene naphthalate or polyether ether ketone.
Step (a) is a step of forming a gap by bonding two to seven substrates with a spacer absorbed therebetween using a UV adhesive and may be manufactured by a photolithography method using a spacer having a height of 5 to 50 μm with a negative PR on the substrate.
The material of the spacer may be poly(methyl methacrylate) (PMMA) but is not limited thereto.
Step (b) is a step of injecting a liquid crystal mixture in which a pre-polymer and liquid crystal are mixed into the gap. The PDLC device includes a pre-polymer for forming a polymer and liquid crystal, and the pre-polymer but may be an acrylate-based, thiolene-based, or epoxy-based pre-polymer, but is not limited thereto. The acrylate-based pre-polymer is a monomer having an acrylic acid structure consisting of a vinyl group and a carboxylic acid terminal group. The thiolene-based pre-polymer is a monomer an S—H bond is added to double or triple carbon bonds by free radicals or ionic reactions. The epoxy-based pre-polymer may be a monomer having an epoxy bond.
An embodiment of the invention uses NOA 65 (a monomer mixture of (tetrafunctional allylether (4-AE) and trifunctional thiol (3-SH)+benzo-phenone photoinitiator).
As the liquid crystal (LC), liquid crystal having a refractive index similar to the pre-polymer may be used, but it is not limited thereto, and may be an E7 liquid crystal. The E7 liquid crystal consists of n-pentylcyanobiphenyl (5CB) (51%), n-heptylcyanobiphenyl (7CB) (25%), n-octyloxycyanobiphenyl (80CB) (16%), and n-pentylcyanoterphenyl (8%). The E7 liquid crystal forms a nematic intermediate phase in the range of −30° C. to 61° C.
The mass ratio between the pre-polymer and the liquid crystal may be from 50:50 to 20:80.
Step (c) is a step of curing and cooling, in which curing with UV and cooling with a cooling plate are performed. The UV curing intensity may be 80 to 780 μW/cm2, and a temperature in the UV irradiation process is maintained in the range of 5 to 25° C. using the cooling plate.
According to the embodiment of the invention, the PDLC is produced by a polymerization induced phase separation (PIPS) process in which the pre-polymer and E7 liquid crystal are uniformly dispersed, and then the UV curing is performed so as to polymerize the pre-polymer and induce phase separation from the liquid crystal. The PDLC is configured with elliptical droplets having a diameter of 2 to 5 μm which are uniformly dispersed on the polymer film having a thickness of 20 to 50 μm.
The cooling plate prevents the temperature from rising in the UV curing process.
The cooling plate allows the water to continuously circulate inside copper metal having a fast heat transfer rate so as to quickly and effectively remove the heat energy generated by the UV light while curing the pre-polymer with the UV irradiation from the PDLC device and maintain a low temperature, thereby producing the PDLC device with a low temperature in the range of X to Y° C. Compared to a nematic liquid crystal device, the PDLC device has many advantages in terms of the electro-optical characteristics and the producing process characteristics. However, due to the characteristics of the PDLC device and the chemical composition thereof, the driving voltage is very high, which causes an increase in the cost of the driving circuit and the control circuit of the PDLC device, and it has disadvantages in mobile communication devices due to large battery consumption. Therefore, by simply using the cooling plate in the UV irradiation process, it is possible to reduce the power consumption, and the manufacturing cost of the driving circuit and the control circuit by at least 25%.
As illustrated in
The invention relates to the PDLC device produced by the above-described producing method. The PDLC device according to the invention decreases the driving voltage, improves the reaction rate, and increases the contrast ratio, and furthermore, reduces the producing cost of the PDLC device, decreases the manufacturing cost of the driving circuit, and reduces the power consumption, due to a decrease in the driving voltage.
The electro-optical characteristics of the PDLC device (lens) are determined based on a thickness of the PDLC portion and a size and a distribution of the liquid crystal droplets. However, when the thickness of the PDLC device is very small, it is difficult to acquire high haze and a high contrast ratio value. Therefore, when the thickness thereof is fixed about 30 μm, since the electro-optical characteristics of the PDLC device are changed only by the liquid crystal droplets, a ratio between the liquid crystal droplets and the polymer, the UV irradiation intensity, temperature, a type of additives, and concentration may have an affect thereon.
a) and 3(b) illustrate an embodiment of the PDLC device and show photographs of operating the PDLC device having a cell gap of 30 μm in which a ratio of NOA 65 to the liquid crystal (E7) is 40:60 and microstructures of the polymer network liquid crystal.
Hereinafter, in order to help with understanding of the invention, embodiments will be described in detail, but the exemplary embodiments should be considered in a descriptive sense only and the invention is not limited by following embodiments. These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.
A producing process of the PDLC device is given below (
Next, using a magnetic stirrer provided in the mixer, NOA 65 and E7 were stirred for 24 hours at room temperature to be mixed uniformly such that the ratio between NOA 65 and E7 was 20:80, 30:70, 40:60, and 50:50. The liquid crystal mixture was poured into the gap.
Curing through irradiation was performed with a UV curing intensity of 80 μW/cm2 to 780 μW/cm2, the center wavelength of the UV light was 365 nm, and the time for irradiation was 3 hours for sufficient UV irradiation. When the UV curing intensity was higher, the time for irradiation was 1.5 hours in consideration of reliability in heat generation and mercury.
The PDLC was produced using the cooling plate in the UV irradiation while the temperature was maintained at 20° C.
(1) A Change of Light Transmittance Based on a Ratio Between NOA 65 and E7, and a Liquid Crystal Concentration Dependency on the Applied Voltage
1) A Change of Light Transmittance
A change of light transmittance of the polymer liquid crystal according to the external voltage was investigated while the temperature was constantly maintained at 20° C. using the cooling plate, or the temperature was maintained high at 70 to 80° C. without the cooling plate during the UV irradiation, under the same curable conditions of the UV irradiation intensity of 580 μW/cm2 by varying the ratio between the liquid crystal (E7) and the polymer (NOA 65) from 50:50 to 80:20 (
2) A Liquid Crystal Concentration Dependency on the Applied Voltage at the Event of the Driving Voltage-Light Transmittance of 90%
A liquid crystal concentration dependency on the applied voltage when the driving voltage-light transmittance was 90% as measured by curves in
(2) A Change of Light Transmittance According to the UV Irradiation Intensity and a UV Curing Intensity Dependency on the Applied Voltage
1) A Change of Light Transmittance
When the ratio between the liquid crystal (E7) and the polymer (NOA 65) was fixed to 60:40, and the UV irradiation intensity varied from 80 μW/cm2 to 780 μW/cm2, a change of light transmittance of the polymer liquid crystal according to the external voltage was investigated while the temperature was constantly maintained at 20° C. using the cooling plate, or the temperature was maintained high at 70 to 80° C. without the cooling plate during the UV irradiation (
UV curing intensity (mW/cm2)=42.5×UV curator setting value (%)−86
The UV curator setting values used in the experiment and actual UV intensities correspond to Table 1. Table 1 shows the UV curator setting value and actual UV intensity.
Comparing
2) A UV Curing Intensity Dependency on the Applied Voltage at the Event of the Driving Voltage-Light Transmittance of 90%
A UV curing intensity dependency on the applied voltage when the driving voltage-light transmittance was 90% as measured by curves in
(3) Electro-Optical Characteristics
A gradient change in the driving range of the PDLC device while the cooling was and was not performed according to the liquid crystal concentration and the UV curing intensity was investigated (
(4) Response Rate of the PDLC Device
A response rate of the PDLC device with or without the cooling plate was investigated (
(5) Contrast Ratio
A contrast ratio of the cured PDLC device in which the ratio between MOA 65 and E7 was set to 40%:60% with the UV curing intensity of 16% (580 μW/cm2) was measured (
(6) Polymer Liquid Crystal Droplet
Optical microscopic photographs and scanning electron microscope (SEM) photographs of the PDLC device with or without the cooling plate were observed (
In the measurement results in
As illustrated in
In addition, when the cooling plate is used, it is possible to easily adjust the temperature of the PDLC device during the UV curing process by adjusting the temperature of the water.
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20140065917 A1 | Mar 2014 | US |