Polymer dispersed liquid crystal display with improved afterimage

Abstract

The invention relates to a polymer dispersed liquid crystal display with improved afterimage. Specifically, one embodiment of the present application provides a polymer dispersed liquid crystal display including a first electrode; a second electrode on the first electrode; the PDLC layer is arranged between the first electrode and the second electrode; wherein the PDLC layer comprises liquid crystal droplets and a polymer surrounding the liquid crystal droplets, the size of the liquid crystal droplets is in the range of 0.8 to 1.5 [mu] m, the thickness of the PDLC layer is in the range of 15 to 25 [mu] m, and wherein the polymer dispersed liquid crystal display has a plurality of individually driven domains.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0104611, filed on August 10, 2023, which is incorporated herein by reference as if fully set forth herein. Technical Field

[0003] The present application relates to a smart window called a polymer dispersed liquid crystal display (PDLCD), and more particularly, to a polymer dispersed liquid crystal display (PDLCD) with improved afterimage caused by haze difference. Background Art

[0004] The present application relates to a smart window called a polymer dispersed liquid crystal display (PDLCD), and more particularly, to a polymer dispersed liquid crystal display (PDLCD) with improved afterimage caused by haze difference.

[0005] Polymer dispersed liquid crystal (PDLC) displays have the advantages of simple manufacturing and low power consumption. PDLC displays are one of the most widely used smart windows.

[0006] Generally, liquid crystals are dispersed in the polymer system of a polymer dispersed liquid crystal display (PDLCD), and in the absence of an initial potential difference, the scattering state of incident light can be controlled, and by applying a potential difference to the film and aligning the liquid crystal molecules in the same direction as the light direction, the transparent state of incident light passing through without scattering can be controlled.

[0007] Meanwhile, polymer dispersed liquid crystal displays (PDLCDs) can drive multiple domains individually. However, when one of the individually driven domains changes to a scattering mode, the liquid crystal arrangement state differs from that of other adjacent domains, resulting in a problem of residual images due to the difference in haze between domains, and then, if there is no difference in haze between domains, the residual images disappear.

[0008] Therefore, research is ongoing to improve the afterimage between domains in polymer dispersed liquid crystal displays (PDLCDs). Summary of the invention

[0009] One embodiment of the present invention is to provide a polymer dispersed liquid crystal display with improved afterimage.

[0010] One embodiment of the present invention is to provide a smart window manufactured using a polymer dispersed liquid crystal display.

[0011] In addition to the above-mentioned objects of the present disclosure, other objects and features of the present disclosure will be clearly understood by those skilled in the art from the following description of the present disclosure.

[0012] One embodiment of the present invention for achieving the above technical problem provides a polymer dispersed liquid crystal display, which includes a first electrode, a second electrode on the first electrode, and a PDLC layer disposed between the first electrode and the second electrode, wherein the PDLC layer includes liquid crystal droplets and a polymer surrounding the liquid crystal droplets, and the size of the liquid crystal droplets is in the range of 0.8 to 1.5 μm, and the thickness of the PDLC layer is in the range of 15 to 25 μm, and has a plurality of separately driven domains.

[0013] The polymer may be formed from a polymer precursor containing the first compound represented by Chemical Formula 1.

[0014] The first compound may be 5 to 50 wt % based on the total content of the polymer precursor.

[0015] The liquid crystal droplet may include the second compound represented by Chemical Formula 2.

[0016] The second compound may be 3 to 20 wt % based on the total content of the liquid crystal droplets.

[0017] The liquid crystal droplet may include the third compound represented by Chemical Formula 3.

[0018] The concentration of the third compound may be in the range of 50 to 1000 ppm.

[0019] The first electrode and the second electrode may include a transparent conductive material.

[0020] The transparent conductive material may include at least one of indium tin oxide (ITO) and indium zinc oxide (IZO).

[0021] Another embodiment of the present invention provides a smart window manufactured using the polymer dispersed liquid crystal display. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description in conjunction with the accompanying drawings, in which:

[0023] Figure 1 is a cross-sectional view of a polymer dispersed liquid crystal display according to an embodiment of the present invention.

[0024] Figure 2 is a diagram showing an afterimage in a polymer dispersed liquid crystal display according to an embodiment of the present invention.

[0025] Figure 3 is a diagram showing the movement of liquid crystal in a liquid crystal droplet according to an electric field.

[0026] Figures 4A to 4Cis a diagram showing a manufacturing process of a polymer dispersed liquid crystal display.

[0027] Figure 5 is a schematic diagram illustrating a haze measurement method. DETAILED DESCRIPTION

[0028] The advantages and features of the present disclosure and their implementation methods will be explained by the following embodiments described with reference to the accompanying drawings. However, the present disclosure can be implemented in different forms and should not be interpreted as being limited to the embodiments described herein. On the contrary, these embodiments are provided to make the present disclosure comprehensive and complete, and to fully convey the scope of the present disclosure to those skilled in the art. In addition, the present disclosure is limited only by the scope of the claims.

[0029] The shapes, sizes, ratios, angles, and quantities disclosed in the drawings used to describe the embodiments of the present disclosure are merely examples, and therefore, the present disclosure is not limited to the details shown. Throughout the specification, the same reference numerals represent the same elements. In the following description, when the detailed description of the relevant known function or configuration is determined to be unnecessarily obscure the main points of the present disclosure, the detailed description will be omitted.

[0030] In case of using “including,” “having,” and “comprising” described in the present disclosure, another part may be added unless “only to” is used. Terms in the singular form may include plural forms unless otherwise specified.

[0031] When explaining an element, the element is interpreted as including an error range although not explicitly described.

[0032] In describing a positional relationship, for example, when the positional relationship is described as “on”, “above”, “below”, and “immediately adjacent to”, more than one part may be disposed between two other parts unless “just” or “directly” is used.

[0033] As shown in the figures, spatially relative terms such as "below," "beneath," "lower," "above," and "upper" may be used herein to easily describe the relationship of one or more elements to another one or more elements. It should be understood that these terms are intended to cover different orientations of the device as well as the orientations shown in the accompanying drawings. For example, if the device shown in the figure is reversed, a device described as being arranged "below" or "below" another device may be arranged "above" the other device. Thus, the exemplary term "below or below" may include both "below or below" and "above" orientations. Similarly, the exemplary term "above" or "upper" may include both "above" and "below or below" orientations.

[0034] When describing a time relationship, for example, when a time sequence is described as "after," "afterwards," "next," and "before," discontinuous cases may be included unless "directly" or "directly" is used.

[0035] It should be understood that although the terms "first", "second", etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element without departing from the scope of the present disclosure.

[0036] It should be understood that the term "at least one" includes all combinations associated with any one item. For example, "at least one of a first element, a second element, and a third element" may include all combinations of two or more elements selected from the first, second, and third elements and each element of the first, second, and third elements.

[0037] As can be fully understood by those skilled in the art, the features of the various embodiments of the present disclosure can be partially or completely combined or combined with each other, and can interoperate and drive technology differently from each other. The embodiments of the present disclosure can be performed independently of each other, or can be performed together in a mutually dependent relationship.

[0038] When adding reference numerals to components of each of the drawings describing embodiments of the present disclosure, the same components may have the same symbols as may be displayed on other drawings.

[0039] Figure 1 is a cross-sectional view of a polymer dispersed liquid crystal display 100 according to an embodiment of the present invention.

[0040] refer to Figure 1 , the polymer dispersed liquid crystal display 100 may include a first electrode 121 and a second electrode 122 .

[0041] The first electrode 121 and the second electrode 122 may each include a transparent conductive material. For example, the first electrode 121 and the second electrode 122 may each include at least one of indium tin oxide (ITO) and indium zinc oxide (IZO). Preferably, the first electrode 121 and the second electrode 122 may be indium tin oxide (ITO).

[0042] refer to Figure 1 The polymer dispersed liquid crystal display 100 may include a PDLC layer 110. Specifically, the PDLC layer 110 may be disposed between the first electrode 121 and the second electrode 122.

[0043] Although not shown in the figure, the polymer dispersed liquid crystal display 100 may include a first substrate and a second substrate. Specifically, the first substrate and the second substrate may each include a transparent material. For example, the first substrate and the second substrate may include at least one of a single glass layer and a transparent plastic film.

[0044] According to an embodiment of the present invention, the PDLC layer 110 may include liquid crystal droplets 111 and polymers 112. Specifically, a plurality of liquid crystal droplets 111 may be distributed in the PDLC layer 110. Specifically, the PDLC layer 110 includes liquid crystal droplets 111 and polymers 112, and the polymers 112 surround the liquid crystal droplets 111.

[0045] The liquid crystal droplets 111 are phase-separated from the polymer 112. Specifically, when the polymer liquid crystal mixture 113 is cured, the PDLC layer 110 may be formed, and the dispersion of the liquid crystal droplets 111 and the polymer 112 in the PDLC layer 110 may be increased. In this process, the polymer 112 may be distinguished from the liquid crystal droplets 111 in a phase-separated manner.

[0046] According to an embodiment of the present invention, the thickness of the PDLC layer 110 may be in the range of 15 to 25 μm. Specifically, in order to scatter the liquid crystal droplets 111 and stabilize the manufacturing process of the polymer dispersed liquid crystal display 100, the thickness of the PDLC layer 110 is preferably in the range of 15 to 25 μm.

[0047] Figure 2 is a diagram showing an afterimage in a polymer dispersed liquid crystal display according to an embodiment of the present invention.

[0048] refer to Figure 2 When the second domain D2 of the polymer dispersed liquid crystal display 100 changes from the transmission mode to the scattering mode, an afterimage may occur due to the difference in haze with another adjacent first domain D1. Specifically, the difference is caused by the different liquid crystal arrangements of the first domain D1 and the second domain D2.

[0049] refer to Figure 2 (a), the polymer dispersed liquid crystal display 100 has a plurality of individually driven domains, wherein the first domain D1 is in a scattering state and the second domain D2 is in a transmissive state.

[0050] Next, refer to Figure 2 (b), when the second domain (D2) changes from the transmission mode to the scattering mode after a certain period of time (T1), a haze difference occurs between the first domain (D1) and the second domain (D2), resulting in an afterimage.

[0051] Next, refer to Figure 2(c), after a predetermined time T2, the second domain D2 completely changes to the scattering mode, so that there is no haze difference between the first domain D1 and the second domain D2, and therefore no afterimage occurs. Therefore, in order to prevent afterimages due to haze differences, the time T2 should be shortened. Specifically, when a specific domain changes to the scattering mode, the time T2 for the complete scattering mode needs to be shortened.

[0052] The numerical definition of afterimage is Figure 2 The haze difference Δhaze between D1 and D2 after 5 seconds when D2 is turned from on to off in the state (a). If Δhaze is 0.3%, afterimage is usually not felt, but if it exceeds 0.3%, afterimage is felt.

[0053] Figure 3 is a diagram showing the movement of liquid crystal in a liquid crystal droplet according to an electric field.

[0054] Specifically, refer to Figure 3 , changing from state (1) to state (3) shows the step of changing from a scattering state to a transmissive state, and changing from state (3) to state (1) means changing from a transmissive state to a scattering state. In essence, Figure 3 The process from state (3) to state (1) corresponds to Figure 2 The second domain D2 changes from a transmission state to a scattering state. Figure 3 The time from state (4) to state (1) corresponds to Figure 2 T2 time.

[0055] according to Figure 2 and 3 , in order to shorten the time T2 for changing from state (4) to state (1), the force or surface energy for attracting the liquid crystal from the surface of the liquid crystal droplet 111 must be large. Specifically, the liquid crystal droplet 111 and the polymer 112 interact as the same organic material. Figure 3 , when the electric field is removed during the process of progressing from state (3) to state (1), it is advantageous from the viewpoint of free energy to align the liquid crystal parallel to the surface of the liquid crystal droplet 111. If the size of the liquid crystal droplet 111 is small, the ratio of surface area to volume is large, and the liquid crystal is more likely to align parallel to the surface of the liquid crystal droplet 111, thereby changing the state from Figure 3 The state (4) quickly progresses to Figure 3 status (1).

[0056] As described above, according to an embodiment of the present invention, the size of the liquid crystal droplet 111 may be in the range of 0.8 μm to 1.5 μm. If the size of the liquid crystal droplet 111 is in the range of 0.8 μm to 1.5 μm, when the liquid crystal droplet 111 changes from a transmission state to a scattering state, it quickly progresses from the transmission state to the scattering state, so that no haze difference occurs, thereby preventing the occurrence of an afterimage. Here, no afterimage occurs means that the haze difference between domains is within 0.3%. When the haze difference is less than or equal to 0.3%, a person cannot visually feel the haze difference.

[0057] On the other hand, when the size of the liquid crystal droplet 111 is less than 0.8 μm, the red wavelength is not scattered in the polymer dispersed liquid crystal display 100. As a result, the polymer dispersed liquid crystal display 100 generally appears red. In addition, there are problems of reduced scattering efficiency and reduced haze in a scattered state.

[0058] Moreover, when the size of the liquid crystal droplet 111 is greater than 1.5 μm, the residual image is not removed in a short time. According to the embodiment and the comparative example, when it exceeds 1.5 μm, the difference in haze within 5 seconds after the PDLC is changed from the on state to the off state is greater than 0.3%. Therefore, in order to prevent the residual image, the liquid crystal droplet 111 is adjusted within the range of 0.8 to 1.5 μm. More preferably, the liquid crystal droplet can be adjusted within the range of 0.8 to 1.3 μm.

[0059] According to an embodiment of the present invention, the liquid crystal droplets 111 in the PDLC layer 110 are controlled by the curing conditions in the process. Specifically, the curing conditions are that the intensity of the ultraviolet light is 2 to 6 mW / cm 2 , the temperature during curing is 25 to 45° C. As a result, the size of the liquid crystal droplet 111 can be adjusted within the range of 0.8 to 1.5 μm.

[0060] According to an embodiment of the present invention, in order to prevent the afterimage of the polymer dispersed liquid crystal display 100, it is necessary to increase the interfacial energy of the polymer 112. Specifically, when the interaction between the liquid crystal and the polymer 112 is increased at the interface between the polymer 112 and the liquid crystal droplet 111 to increase the energy of the interface, the afterimage can be prevented.

[0061] The liquid crystal is substituted with cyano (-CN) or fluorine (-F) and the like. Such a substituent is composed of atoms having high electronegativity to utilize the characteristics of induced dipoles. If a hydroxyl group (-OH) is present at the interface, hydrogen at the interface and fluorine or nitrogen of the liquid crystal can form a hydrogen bond. Therefore, if a hydroxyl group (-OH) is present at the interface, the energy of the interface increases, and the interaction between the polymer 112 and the liquid crystal increases, thereby preventing residual images.

[0062] According to an embodiment of the present invention, the polymer 112 may be formed of a polymer precursor including a first compound represented by Chemical Formula 1.

[0063] In this case, the polymer precursor may be said to be before the curing of the polymer 112. Specifically, the polymer precursor may include a first compound represented by Chemical Formula 1, and the polymer 112 may be formed by curing.

[0064] [Chemical formula 1]

[0065]

[0066] M represents a methyl group or hydrogen, n and m are 0-9, and the sum of n and m is 1-10.

[0067] According to an embodiment of the present invention, Chemical Formula 1 may be any one group selected from Chemical Formulas 1-1 to 1-13.

[0068] [Chemical formula 1-1]

[0069]

[0070] [Chemical formula 1-2]

[0071]

[0072] [Chemical formula 1-3]

[0073]

[0074] [Chemical formula 1-4]

[0075]

[0076] [Chemical formula 1-5]

[0077]

[0078] [Chemical formula 1-6]

[0079]

[0080] [Chemical formula 1-7]

[0081]

[0082] [Chemical formula 1-8]

[0083]

[0084] [Chemical formula 1-9]

[0085]

[0086] [Chemical formula 1-10]

[0087]

[0088] [Chemical formula 1-11]

[0089]

[0090] [Chemical formula 1-12]

[0091]

[0092] [Chemical formula 1-13]

[0093]

[0094] According to an embodiment of the present invention, the first compound represented by Chemical Formula 1 may be 5 to 50 wt % based on the total content of the polymer precursor. In order to prevent afterimages by increasing the energy of the interface, the first compound needs to be 5 to 50 wt % based on the total content of the polymer precursor.

[0095] On the other hand, when the content of the first compound relative to the total content of the polymer precursor is less than 5% by weight, the afterimage reducing effect caused by the first compound does not appear.

[0096] In addition, when the first compound exceeds 50 wt % of the total content of the polymer precursor, it may be difficult to control other physical properties of the polymer.

[0097] According to an embodiment of the present invention, the liquid crystal droplet 111 may include the second compound represented by Chemical Formula 2.

[0098] [Chemical formula 2]

[0099]

[0100] In Chemical Formula 2, R11 refers to at least one of a C2-C10 alkyl group, a vinyl group, and an alkoxy group, Ring A refers to a phenyl group or a cyclohexyl group, (F) refers to fluorine or hydrogen, and R22 refers to a C2-C10 alkyl group, fluorine, or a cyano group.

[0101] According to an embodiment of the present invention, Chemical Formula 2 may be any one group selected from Chemical Formulas 2-1 to 2-11.

[0102] [Chemical formula 2-1]

[0103]

[0104] [Chemical formula 2-2]

[0105]

[0106] [Chemical formula 2-3]

[0107]

[0108] [Chemical formula 2-4]

[0109]

[0110] [Chemical formula 2-5]

[0111]

[0112] [Chemical formula 2-6]

[0113]

[0114] [Chemical formula 2-7]

[0115]

[0116] [Chemical formula 2-8]

[0117]

[0118] [Chemical formula 2-9]

[0119]

[0120] [Chemical formula 2-10]

[0121]

[0122] [Chemical formula 2-11]

[0123]

[0124] The second compound is a material necessary to maintain the clearing point of the liquid crystal droplet 111 at 100° C. or higher.

[0125] According to an embodiment of the present invention, the second compound represented by Chemical Formula 2 may be 3 to 20 wt %. Specifically, wt % refers to 3 to 20 wt % based on the total content of the liquid crystal droplet 111. In order to keep the liquid crystal droplet 111 at a transparent point above 100°C, the second compound needs to be maintained at 3 to 20 wt %.

[0126] On the other hand, when the second compound is less than 3 wt %, it may be difficult to maintain the clearing point of the liquid crystal droplet 111 at 90° C. or more.

[0127] In addition, when the second compound exceeds 20% by weight, the possibility of crystallization at low temperature increases, resulting in a problem of crystal precipitation.

[0128] According to an embodiment of the present invention, the liquid crystal droplet 111 may further include a third compound represented by Chemical Formula 3.

[0129] [Chemical formula 3]

[0130]

[0131] The third compound represented by Chemical Formula 3 serves to prevent a chain reaction during a radical reaction caused by heat in the PDLC layer 110 .

[0132] According to an embodiment of the present invention, the concentration of the third compound may be in the range of 50 to 1000 ppm. In order to ensure the thermal stability of the PDLC layer 110, the concentration of the third compound needs to be maintained in the range of 50 to 1000 ppm.

[0133] On the other hand, when the concentration of the third compound is less than 50 ppm, there is a problem that the effect of preventing a radical reaction due to heat in the PDLC layer 110 is reduced, and as a result, thermal stability in the PDLC layer 110 is reduced.

[0134] In addition, when the concentration of the third compound exceeds 1000 ppm, the transparent point of the liquid crystal droplet 111 decreases, resulting in a problem that the electro-optical characteristics of the polymer dispersed liquid crystal display 100 are deteriorated.

[0135] According to an embodiment of the present invention, the polymer dispersed liquid crystal display 100 may be provided with a power source 130 capable of applying a driving voltage to the first electrode 121 and the second electrode 122 .

[0136] refer to Figure 4C , in a state where no driving voltage is applied to the first electrode 121 and the second electrode 122, i.e., in an open circuit state, an electric field may not be generated between the first electrode 121 and the second electrode 122. In this case, the liquid crystal droplet 111 is arranged not to have a certain directionality, and the incident light is scattered, resulting in an opaque scattering state.

[0137] Moreover, reference Figure 4C , the first electrode 121, the second electrode 122, and the power source 130 may be electrically connected to each other, so that an electric field may be generated between the first electrode 121 and the second electrode 122 in a closed circuit state. The direction of the electric field may be perpendicular to the first electrode 121 and the second electrode 122. The liquid crystal droplet 111 may be aligned in a direction parallel to the electric field. That is, the long axis of the liquid crystal droplet 111 is arranged parallel to the direction of the electric field, and the incident light passes through without scattering, becoming a transparent transmission state.

[0138] Figures 4A to 4C is a diagram showing a manufacturing process of the polymer dispersed liquid crystal display 100 .

[0139] Specifically, refer to Figure 4A In the manufacturing process of the polymer dispersed liquid crystal display 100 , the polymer liquid crystal mixture 113 is applied to one surface of the first electrode 121 , and then the second electrode 122 is bonded thereon using a roller, thereby manufacturing the polymer dispersed liquid crystal unit 101 .

[0140] Then, refer to Figure 4B , the first electrode 121 including the polymer liquid crystal mixture 113 is irradiated with ultraviolet rays (UV) to cure the polymer liquid crystal mixture 113, thereby manufacturing the polymer dispersed liquid crystal display 100.

[0141] Next, refer to Figure 4C A power source 130 connecting the first electrode 121 and the second electrode 122 may be provided.

[0142] In this case, in a state where no driving voltage is applied to the first and second electrodes 121 and 122, ie, in an open state, an electric field may not be generated between the first and second electrodes 121 and 122. In this case, the liquid crystal droplet 111 may be arranged not to have certain directionality.

[0143] Moreover, the first electrode 121, the second electrode 122, and the power source 130 may be electrically connected to each other so that an electric field may be generated between the first electrode 121 and the second electrode 122 in a closed circuit state. The direction of the electric field may be perpendicular to the first electrode 121 and the second electrode 122. The liquid crystal droplet 111 may be aligned in a direction parallel to the electric field. That is, the long axis of the liquid crystal droplet 111 may be parallel to the direction of the electric field.

[0144] Figure 5 is a schematic diagram illustrating a haze measurement method.

[0145] Specifically, Figure 5 2 is a schematic diagram illustrating a method for measuring the haze of a polymer dispersed liquid crystal (PDLC). Here, the polymer dispersed liquid crystal (PDLC) may correspond to the PDLC layer 110 of the present invention.

[0146] refer to Figure 5 , the light incident on the polymer dispersed liquid crystal (PDLC) is defined as I0, the light transmitted head-on within an error range of ±2.5° of the incident light (I0) is defined as Ir, and when Is is the light in the transmitted light excluding the light transmitted head-on (Ir), the haze is defined as Is / (Ir+Is).

[0147] Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the following Examples are only for helping to understand the present invention, and the scope of the present invention is not limited to these Examples.

[0148] Examples 1-4 and Comparative Examples 1-3

[0149] In order to improve the present invention, polymer dispersed liquid crystal displays were prepared using various polymer / liquid crystal mixtures. The contents of the polymer / liquid crystal mixtures are shown in Table 1 below.

[0150] [Example 1]

[0151] The polymer precursor was prepared in the content shown in Table 1, and the ratio of the first compound was 10%. HKH-015 (Bayi Co.) was used as the liquid crystal, and 3 wt% of (Chemical Formula 2-4) and 4 wt% of (Chemical Formula 2-5) were present as the second compound, and 0.03 wt% of an antioxidant (4-sec-butyl-2,6-di-tert-butylphenol; TIC Co.) was added as the third compound. The polymer precursor and the liquid crystal were mixed in a ratio of 50:50, and the initiator was mixed in an amount of 1 wt% to prepare a "polymer / liquid crystal mixture".

[0152] The first electrode and the second electrode were used by sputtering ITO onto an A4165 PET film manufactured by Toyobos Corporation, and an electrode in which the ITO electrode layer was removed to a width of 60 μm using a laser trimmer was used as the pixel electrode ITO-PET. After the pixel electrode ITO-PET was coated with a slot die, the polymer / liquid crystal mixture was laminated with the common electrode (commonelectrode) ITO-PET, and a 3 mW / cm2 laser with a wavelength of 365 nm was used. 2 UV lamp, the accumulated light amount was 1 J. After preparation, a 17 μm PDLC layer was prepared, and the size of the liquid crystal droplets is shown in Table 1 below.

[0153] [Examples 2-4, Comparative Examples 1-3]

[0154] The polymer precursor was prepared according to the contents of Table 1. HGKH-015 liquid crystal was used except for Comparative Example 1, and the second compound contained 7%. Regarding the third compound, as shown in Table 1, Examples 2 to 4 added 0.03 wt %, and Comparative Examples 1 to 3 did not add 0.03 wt %. The liquid crystal of Comparative Example 1 was E7 (Merck Co., Ltd.) and did not contain the second compound and the third compound.

[0155] In addition, the preparation process of the PDLC film is the same as that of Example 1. The results are summarized in Table 1.

[0156] [Table 1]

[0157]

[0158] NOA65:Norland Optical Adhesive 65(Edmond Optics Korea)

[0159] 2-EHA: 2-ethylhexyl acrylate (Aldrich)

[0160] 2-EHMA: 2-ethylhexyl methacrylate (Aldrich)

[0161] HDDA: 1,6-Hexanediol diacrylate (Aldrich)

[0162] HEM: 2-Hydroxyethyl methacrylate (Aldrich)

[0163] 4-HBA: 4-Hydroxybutyl acrylate (Aldrich)

[0164] TPO: 2,4,6-Trimethylbenzoyl-diphenyl-phosphine oxide (Ciba Special Chemicals)

[0165] For the polymer dispersed liquid crystal displays of Examples 1 to 4 and Comparative Examples 1 to 3 thus prepared, i) haze (afterimage), ii) haze (reliability), and iii) 90° C. OFF scattering haze were confirmed.

[0166] i) Haze (afterimage) measurement

[0167] refer to Figure 2 , after applying 48V voltage in the second domain D2 for 10 seconds, the voltage is turned into the off state, and the haze 2 is measured after 5 seconds, and then the haze 1 is measured in the off state of the first domain D1, and then the haze 1 minus the haze 2 is expressed as the afterimage.

[0168] Haze (reliability)

[0169] refer to Figure 2 , a voltage of 48 V was applied to the second domain D2, and the haze A was measured, the polymer dispersed liquid crystal display in the closed state was placed in a high temperature chamber of 85° C. and heated for 168 hours, and then the polymer dispersed liquid crystal display was cooled to room temperature, a voltage of 48 V was applied to the second domain D2, and the haze B was measured. In this case, the value obtained by subtracting the haze B from the haze A is expressed as haze (reliability).

[0170] iii) 90℃OFF scattering haze

[0171] The 90° C. OFF scattering haze refers to the haze measured when the polymer dispersed liquid crystal display is heated to 90° C. without applying electricity.

[0172] iv) Measuring haze

[0173] The light incident on the polymer dispersed liquid crystal (PDLC) is defined as I0, the light transmitted head-on within an error range of ±2.5° of the incident light (I0) is defined as Ir, and when Is is the light in the transmitted light excluding the light transmitted head-on (Ir), the haze is defined as Is / (Ir+Is).

[0174] As a haze measuring instrument, NDH 7000II from Nippon Denshoku was used, and as a measurement standard, ASTM D1003 was used.

[0175] Referring to Table 1, the following results can be confirmed.

[0176] According to Examples 1 to 4, the size of the liquid crystal droplets is 1.5 μm or less, the Δ haze (afterimage) is 0.3% or less, and the afterimage level is very good. In addition, in the polymer, the Δ haze (afterimage) of Examples 2 to 4 in which the proportion of the first compound is 30% by weight is 0.2% or less, but in Example 1 in which the proportion of the first compound is 10% by weight, the Δ haze (afterimage) is 0.25%, which is higher than the Δ haze of other examples. As a result, the smaller the size of the liquid crystal droplets, the greater the proportion of the first compound, and the lower the afterimage. In contrast, in Comparative Examples 1 to 3 in which the size of the liquid crystal droplets is 1.5 μm or more and the first compound is not included, the Δ haze (afterimage) is very high, being 0.9% or more.

[0177] In addition, the Δ haze (reliability) of the examples containing the second compound in the liquid crystal was within 0.5%, but the Δ haze (reliability) of the comparative examples not containing the second compound was above 2.0%. As described above, the second compound is used to prevent the degradation of the PDLC layer due to heat.

[0178] In Comparative Example 1 not containing the third compound, the 90°C OFF scattering haze (%) was 20%, and the shielding ability was almost lost, but other Examples and Comparative Examples showed very good values ​​of 85% or more.

[0179] According to the present disclosure, the following advantageous effects can be obtained.

[0180] The polymer dispersed liquid crystal display according to an embodiment of the present invention can improve afterimages caused by a haze difference between domains.

[0181] In addition to the above-mentioned effects, other features and advantages of the present invention may be described below or may be clearly understood from these techniques and descriptions by those having ordinary skill in the art to which the present invention pertains.

[0182] In addition to the above-mentioned effects, other features and advantages of the present invention may be described below or may be clearly understood from these techniques and descriptions by those having ordinary skill in the art to which the present invention pertains.

[0183] In addition to the above-mentioned effects, other features and advantages of the present invention will be described below or will be clearly understood from these techniques and descriptions by those having ordinary skill in the art to which the present invention pertains.

[0184] It will be apparent to those skilled in the art that the above disclosure is not limited by the above embodiments and drawings, and that various substitutions, modifications and variations may be made to the disclosure without departing from the spirit or scope of the disclosure. Therefore, the scope of the disclosure is defined by the appended claims, and all variations or modifications derived from the meaning, scope and equivalent concepts of the claims are intended to fall within the scope of the disclosure.

Claims

1. A polymer dispersed liquid crystal display, comprising: a first electrode; a second electrode on the first electrode; as well as a PDLC layer disposed between the first electrode and the second electrode; wherein the PDLC layer comprises liquid crystal droplets and a polymer surrounding the liquid crystal droplets, The size of the liquid crystal droplets is in the range of 0.8 μm to 1.5 μm, The thickness of the PDLC layer is in the range of 15 μm to 25 μm, and The polymer dispersed liquid crystal display has a plurality of independently driven domains.

2. The polymer dispersed liquid crystal display according to claim 1, wherein the polymer is formed by a polymer precursor containing a first compound represented by Chemical Formula 1: [Chemical formula 1] M means methyl or hydrogen, n and m are 0-9, and the sum of n and m is 1-10. 3 . The polymer dispersed liquid crystal display according to claim 2 , wherein the first compound is 5 wt % to 50 wt % based on the total content of the polymer precursor.

4. The polymer dispersed liquid crystal display according to claim 1, wherein the liquid crystal droplet comprises a second compound represented by Chemical Formula 2: [Chemical formula 2] R 11 It refers to at least one of C2-C10 alkyl, vinyl and alkoxy, (F) means fluorine or hydrogen, Ring A is phenyl or cyclohexyl, and R 22 It refers to C2-C10 alkyl, fluorine or cyano. 5 . The polymer dispersed liquid crystal display according to claim 4 , wherein the second compound is 3 wt % to 20 wt % based on the total content of the liquid crystal droplets.

6. The polymer dispersed liquid crystal display according to claim 1, wherein the liquid crystal droplet comprises a third compound represented by Chemical Formula 3: [Chemical formula 3] 7 . The polymer dispersed liquid crystal display according to claim 6 , wherein a concentration of the third compound is in the range of 50 ppm to 1000 ppm. 8 . The polymer dispersed liquid crystal display of claim 1 , wherein the first electrode and the second electrode comprise a transparent conductive material. 9 . The polymer dispersed liquid crystal display of claim 8 , wherein the transparent conductive material comprises at least one of indium tin oxide (ITO) and indium zinc oxide (IZO).

10. A smart window comprising the polymer dispersed liquid crystal display according to any one of claims 1 to 9.

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