Method of forming polymer-dispersed liquid crystal film including dichroic dye

In a method of forming a polymer-dispersed liquid crystal (PDLC) film, the presence of dichroic dye in a polymer may be prevented or reduced by diffusing dichroic dye into a PDLC layer, and a PDLC display device having improved visibility may be formed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2010-0098342, filed on Oct. 8, 2010, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

BACKGROUND

Example embodiments relate to methods of forming a polymer-dispersed liquid crystal film, and more particularly, to methods of forming a polymer-dispersed liquid crystal film including dichroic dye.

2. Description of the Related Art

Polymer-dispersed liquid crystal (PDLC) display devices are devices in which light is scattered or transmitted by applying an electric field to the PDLC. The electric field allows for a change in the refractive indexes of a polymer and a liquid crystal uniformly mixed in a PDLC. In PDLC display devices, light is allowed to pass or is blocked by using only an electric field and not an orientation film or a polarizing plate. Also, a contrast of a display device may be improved by mixing a PDLC and dichroic dye. Generally, when dichroic dye is mixed with a liquid crystal, dichroic dye is inclined to be aligned in the same orientation as the liquid crystal. Thus, when dichroic dye is mixed with a PDLC, dichroic dye may be aligned or randomly distributed according to an orientation of liquid crystal included in the PDLC, thereby causing an optical change.

Conventionally, a PDLC film including dichroic dye is formed by injecting a mixed solution including a liquid crystal, a photo-polymerizable material, and dichroic dye between two substrates and exposing the mixed solution to ultraviolet (UV) rays, thereby curing the mixed solution. In this regard, the photo-polymerizable material refers to a material that is polymerized by photo-polymerization, and may be a monomer or an oligomer. Through the UV curing process, the liquid crystal is uniformly dispersed in the polymer, and dichroic dye may be uniformly present in the polymer and the liquid crystal. However, in a display device including a PDLC film formed by the method described above, dichroic dye present in the polymer may adversely affect optical characteristics of the display device. That is, dichroic dye present in the polymer may be immobilized by the UV curing process and the immobilized dichroic dye does not have an optical anisotropy. Thus, the dichroic dye adversely affects visibility of the display device. In addition, during the UV curing process, dichroic dye present in the polymer may continuously absorb UV rays to degrade UV curing characteristics.

SUMMARY

Example embodiments provide methods of forming a polymer-dispersed liquid crystal film including dichroic dye. Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of example embodiments.

According to example embodiments, a method of forming a polymer-dispersed liquid crystal (PDLC) film includes forming a PDLC layer on a first substrate, the PDLC layer including a liquid crystal and a polymer, coating a mixed solution on an upper surface of the PDLC layer, the mixed solution including a liquid crystal and dichroic dye, diffusing the liquid crystal and dichroic dye of the mixed solution into the PDLC layer such that the PDLC layer includes the dichroic dye and attaching a second substrate to the upper surface of the PDLC layer including the dichroic dye.

The forming the PDLC layer on the first substrate may include injecting a solution between the first substrate and a third substrate spaced apart from the first substrate, the solution including the liquid crystal and a photo-polymerizable material, irradiating ultraviolet (UV) rays to the solution and separating the third substrate from an upper surface of the PDLC layer. The third substrate may include a releasing material that enables the third substrate to be separated from the PDLC layer.

The forming the PDLC layer on the first substrate may include placing a solution on the first substrate, the solution including the liquid crystal and a photo-polymerizable material and irradiating UV rays to the solution under an inert gas atmosphere to form the PDLC layer. The coating the mixed solution on the upper surface of the PDLC layer may include a process selected from the group consisting of spraying, dipping and roll coating processes. The diffusing the liquid crystal and dichroic dye of the mixed solution into the PDLC layer may include increasing the temperature of the first substrate. Each of the first and second substrates may include at least one of a TFT and a color filter.

According to example embodiments, a method of forming a polymer-dispersed liquid crystal (PDLC) film may include forming a PDLC layer on a first substrate, the PDLC layer including a liquid crystal and a polymer, coating a mixed solution on an upper surface of the PDLC layer, the mixed solution including a liquid crystal, a photo-polymerizable material, and dichroic dye, diffusing the liquid crystal, the photo-polymerizable material, and dichroic dye of the mixed solution into the PDLC layer such that the PDLC layer includes the dichroic dye and attaching a second substrate to an upper surface of the PDLC layer including the dichroic dye and irradiating ultraviolet (UV) rays thereto.

According to example embodiments, a method of forming a polymer-dispersed liquid crystal (PDLC) film by using a roll-to-roll process includes coating a solution on a first substrate using a first roller, the solution including a liquid crystal and a photo-polymerizable material, placing a third substrate on an upper surface of the solution using a second roller, irradiating UV rays to the solution to form a PDLC layer, the PDLC layer including the liquid crystal and a polymer, separating the third substrate from an upper surface of the PDLC layer using a third roller, coating a mixed solution on the upper surface of the PDLC layer, the mixed solution including a liquid crystal and dichroic dye, diffusing the liquid crystal and the dichroic dye of the mixed solution into the PDLC layer such that the PDLC layer includes the dichroic dye and attaching a second substrate to the upper surface of the PDLC layer including the dichroic dye.

According to example embodiments, a method of forming a polymer-dispersed liquid crystal (PDLC) film by using a roll-to-roll process includes coating a solution on a first substrate using a roller, the solution including a liquid crystal and a photo-polymerizable material, forming a PDLC layer by irradiating ultraviolet (UV) rays to the solution under an inert gas atmosphere, the PDLC layer including liquid crystal and a polymer, placing a mixed solution on an upper surface of the PDLC layer, the mixed solution including a liquid crystal and dichroic dye, diffusing the liquid crystal and the dichroic dye of the mixed solution into the PDLC layer such that the PDLC layer includes the dichroic dye, and attaching a second substrate to the upper surface of the PDLC layer including the dichroic dye.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout and the size or thickness of each element may be enlarged for clarity. In this regard, example embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, example embodiments are merely described below, by referring to the figures, to explain the present description.

FIGS. 1 through 9are views for explaining a method of forming a polymer-dispersed liquid crystal (PDLC) film including dichroic dye, according to example embodiments. Referring toFIG. 1, a PDLC layer120′ is formed on a first substrate110. In this regard, a polymer121is formed in a network form in the PDLC layer120′, and a liquid crystal122is dispersed in the polymer. The first substrate110may be a transparent substrate, such as a glass substrate, or a flexible substrate, for example. Also, although not illustrated inFIG. 1, the first substrate110may further include at least one first component111selected from a thin film transistor (TFT) and a color filter.

A method of forming the PDLC layer120′ on the first substrate110will now be described in detail.FIGS. 5 through 7are views for explaining an example of the method of forming the PDLC layer120′ on the first substrate110. Referring toFIG. 5, a third substrate150is disposed spaced apart from the first substrate110. In this regard, the third substrate150may be a transparent substrate. Subsequently, a solution125including a liquid crystal and a photo-polymerizable material is injected between the first substrate110and the third substrate150. In this regard, the photo-polymerizable material refers to a material that is cured and polymerized by photo-polymerization. The photo-polymerizable material may include at least one of a monomer and an oligomer.

Referring toFIG. 6, ultraviolet (UV) rays are irradiated to the solution125through the third substrate150. Through the UV irradiation process, the photo-polymerizable material in the solution125is cured to form the polymer121, thereby forming the PDLC layer120′ including the liquid crystal122and the polymer121between the first substrate110and the third substrate150. In the PDLC layer120′, the polymer121is formed in a network form, and the liquid crystal122is uniformly dispersed in the polymer121. Referring toFIG. 7, the third substrate150is separated from an upper surface of the PDLC layer120′. The third substrate150may be formed of a releasing material that enables the third substrate150to be easily separated from the PDLC layer120′.

FIGS. 8 and 9are views for explaining another example of the method of forming the PDLC layer120′ on the first substrate110. Referring toFIG. 8, a solution125including a liquid crystal and a photo-polymerizable material is coated on the first substrate110. Referring toFIG. 9, UV rays are irradiated to the solution125, including the liquid crystal and the photo-polymerizable material, coated on the first substrate110. In this regard, the UV irradiation process may be performed under an inert gas atmosphere. The inert gas may be, for example, a nitrogen gas or a helium gas, but is not limited thereto. Through the UV irradiation process, the photo-polymerizable material in the solution125is cured to form the polymer121, thereby forming the PDLC layer120′, including the liquid crystal122and the polymer121, on the first substrate110. In the PDLC layer120′, the polymer121is formed in a network form, and the liquid crystal122is uniformly dispersed in the polymer121.

Subsequently, referring toFIG. 2, a mixed solution130, including a liquid crystal and dichroic dye is coated on the upper surface of the PDLC layer120′ formed on the first substrate110. When mixed with a liquid crystal, dichroic dye has the same orientation as the liquid crystal. The dichroic dye may be, for example, black, red, green, blue, yellow, magenta, or cyan, and may also be of other colors. The coating of the mixed solution130may be performed by, for example, spraying using an inkjet ejecting device, dipping, or roll coating. However, the coating method is not limited thereto and various other coating methods may also be used to coat the mixed solution130on the upper surface of the PDLC layer120′. A given time after the mixed solution130including the liquid crystal and dichroic dye is coated on the upper surface of the PDLC layer120′, the liquid crystal and dichroic dye of the mixed solution130diffuse into the PDLC layer120′. InFIG. 2, the diffusion directions of the liquid crystal and dichroic dye of the mixed solution130into the PDLC layer120′ are indicated by dash arrows. In addition, if the first substrate110is heated in this process, the liquid crystal and dichroic dye may diffuse more rapidly.

When the diffusion process is finished, as illustrated inFIG. 3, a PDLC layer120including a dichroic dye123is formed on the first substrate110. In the PDLC layer120, the liquid crystal122, the dichroic dye123, and the polymer121are uniformly dispersed. Due to the diffusion, the dichroic dye123is present only in the liquid crystal122in the PDLC layer120. In other words, the dichroic dye123is not present in the network-shaped polymer121.

Referring toFIG. 4, a second substrate140is placed on an upper surface of the PDLC layer120including the dichroic dye123. In this regard, like the first substrate110, the second substrate140may be a transparent substrate, such as a glass substrate, or a flexible substrate, for example. Also, the second substrate140may further include a second component141selected from a TFT and a color filter. A substrate including at least one of a TFT and a color filter has a lower aperture ratio, and thus, may degrade UV curing characteristics. Thus, a substrate including at least one of a TFT and a color filter may not be used as a substrate through which UV rays are transmitted during the UV curing process. In example embodiments, when a display device including the PDLC layer120including the dichroic dye123is manufactured, a substrate including a TFT may be used as the first substrate110and a substrate including a color filter may be used as the second substrate140. Alternatively, a substrate including a TFT may be used as the second substrate140and a substrate including a color filter may be used as the first substrate110.

As described above, by diffusing the dichroic dye123into the PDLC layer120′ including the liquid crystal122and the polymer121, the PDLC layer120in which the dichroic dye123is present only in the liquid crystal122is formed. By doing so, visibility and UV curing characteristics of a display device including the PDLC layer120may be improved.

FIGS. 10 through 12are views for explaining a method of forming a PDLC film including a dichroic dye223, according to example embodiments. Hereinafter, a difference between the method according to the example embodiment illustrated inFIGS. 10 through 12and the method according to the example embodiment illustrated inFIGS. 8 and 9will be described in detail.

Referring toFIG. 10, a PDLC layer220′ is formed on a first substrate210. The first substrate210may be a glass substrate or a flexible substrate, and may further include a first component211selected from a TFT and a color filter. In this regard, in the PDLC layer220′, a first polymer221is present in a network form and a liquid crystal222is uniformly dispersed in the first polymer221. The PDLC layer220′ may be formed on the first substrate210by using the method described with reference toFIGS. 5 through 7or the method described with reference toFIGS. 8 and 9. The methods will not be described herein.

Referring toFIG. 11, a mixed solution230including a liquid crystal, dichroic dye, and a photo-polymerizable material is coated on an upper surface of the PDLC layer220′. In this regard, the photo-polymerizable material refers to a material that is cured and polymerized by photo-polymerization. The photo-polymerizable material may include at least one material of a monomer and an oligomer. The coating of the mixed solution230may be performed by, for example, spraying using an inkjet ejecting device, dipping, or roll coating. However, the coating method is not limited thereto and various other coating methods may also be used to coat the mixed solution230on the upper surface of the PDLC layer220′.

A given time after the mixed solution230, including the liquid crystal, dichroic dye, and the photo-polymerizable material, is coated on the upper surface of the PDLC layer220′, the liquid crystal, dichroic dye, and the photo-polymerizable material of the mixed solution230diffuse into the PDLC layer220′. InFIG. 11, the diffusion directions of the liquid crystal, dichroic dye, and the photo-polymerizable material of the mixed solution230into the PDLC layer220′ are indicated by dash arrows. Due to the diffusion process, the dichroic dye223is present in the liquid crystal222. Also, if the first substrate210is heated in this process, the liquid crystal, dichroic dye, and the photo-polymerizable material may diffuse more rapidly.

Referring toFIG. 12, when the diffusion of the liquid crystal, dichroic dye, and the photo-polymerizable material is finished, a PDLC layer220including the dichroic dye223is formed. In this regard; due to the diffusion, the dichroic dye223is present only in the liquid crystal222, and is not present in the first polymer221. Subsequently, a second substrate240is placed on an upper surface of the PDLC layer220including the dichroic dye223, and UV rays are irradiated thereto. In this regard, like the first substrate210, the second substrate240may be a transparent substrate, such as a glass substrate, or a flexible substrate, for example. Also, the second substrate240may further include a second component241selected from a TFT and a color filter. Since the photo-polymerizable material present in the PDLC layer220contacting the second substrate240is cured in the UV irradiation process, the second substrate240may be more strongly attached to the upper surface of the PDLC layer220. In addition, since the photo-polymerizable material present in the PDLC layer220including the dichroic dye223is cured in the UV irradiation process, a second polymer221amay be additionally formed in a network form.

Hereinafter, a method of forming a PDLC film including dichroic dye by using a roll-to-roll process, according to example embodiments, will be described in detail.FIG. 13is a view for explaining a method of forming a polymer-dispersed liquid crystal film including dichroic dye, according to example embodiments, in which the method includes a roll-to-roll process.

Referring toFIG. 13, a solution325, including a liquid crystal and a photo-polymerizable material, is coated on a first substrate310that is moving, by using a first roller361(operation a). The first substrate310may be a transparent substrate, such as a glass substrate, or a flexible substrate, for example. Also, the first substrate310may further include a first component311selected from a TFT and a color filter. The first substrate310moves due to rotation of a fourth roller364. The coating of the solution325may be performed by transferring the solution325coated on an outer surface of the first roller361onto an upper surface of the first substrate310due to rotation of the first roller361. A third substrate350is attached to an upper surface of a layer of the solution325coated on the first substrate310by using a second roller362(operation b). The third substrate350wound on the outer surface of the second roller362is attached to the upper surface of the layer of the solution325due to rotation of the second roller362. In this regard, the third substrate350may be a transparent, flexible substrate formed of a releasing material that enables the third substrate350to be easily separable.

UV rays are irradiated to the solution325, including the liquid crystal and the photo-polymerizable material, through the third substrate350(operation c). Through the UV irradiation process, the photo-polymerizable material in the solution325is cured to form a polymer, thereby forming a PDLC layer320′, including the liquid crystal and the polymer, between the first substrate310and the third substrate350. The third substrate350is separated from an upper surface of the PDLC layer320′ by using a third roller363(operation d). The third substrate350is separated from the upper surface of the PDLC layer320′ due to rotation of the third roller363, thereby winding on an outer surface of the third roller363.

A mixed solution330, including a liquid crystal and dichroic dye, is coated on the upper surface of the PDLC layer320′ (operation e). The coating of the mixed solution330may be performed by, for example, spraying the mixed solution330on the upper surface of the PDLC layer320′ by using an inkjet ejecting device370. However, the coating method is not limited thereto. For example, the coating of the mixed solution330may be performed by using various other coating methods, such as dipping or roll coating, for example.

A given time after the mixed solution330, including the liquid crystal and dichroic dye, is coated on the upper surface of the PDLC layer320′, the liquid crystal and dichroic dye of the mixed solution330diffuse into the PDLC layer320′, thereby forming a PDLC layer320including dichroic dye (operation f). In the PDLC layer320, the liquid crystal, dichroic dye, and the polymer are uniformly dispersed and due to the diffusion, the dichroic dye is present only in the liquid crystal. Also, if the first substrate310is heated in the diffusion process, the liquid crystal and dichroic dye may diffuse more rapidly.

Finally, a second substrate340is attached to an upper surface of the PDLC layer320including the dichroic dye, thereby completing the formation of a PDLC film (operation g). In this regard, the attachment of the second substrate340may be performed by, for example, lamination. Like the first substrate310, the second substrate340may be a transparent substrate and may further include a second component341selected from a TFT and a color filter. As described above, according to example embodiments, a PDLC film, including dichroic dye, is more easily formed at a greater scale by using a roll-to-roll process.

FIG. 14is a view for explaining a method of forming a polymer-dispersed liquid crystal film including dichroic dye, according to example embodiments, in which the method includes a roll-to-roll process.

Referring toFIG. 14, a solution425, including a liquid crystal and a photo-polymerizable material, is coated on a first substrate410that is moving by using a first roller461(operation a). The first substrate410may be a transparent substrate, such as a glass substrate, or a flexible substrate, for example. In addition, the first substrate410may further include a first component411selected from a TFT and a color filter. The first substrate410moves due to rotation of a second roller462. The coating of the solution425may be performed by transferring the solution425coated on an outer surface of the first roller461onto an upper surface of the first substrate410due to rotation of the first roller461. In a chamber480under an inert gas atmosphere, UV rays are irradiated to the solution425including the liquid crystal and the photo-polymerizable material (operation b). In this regard, the inert gas may be, for example, a nitrogen gas or a helium gas, but is not limited thereto. Through the UV irradiation process, the photo-polymerizable material in the solution425is cured to form a polymer, thereby forming a PDLC layer420′, including the liquid crystal and the polymer, on the upper surface of the first substrate410.

A mixed solution430, including a liquid crystal and dichroic dye, is coated on the upper surface of the PDLC layer420′ (operation c). The coating of the mixed solution430may be performed by, for example, spraying the mixed solution430on the upper surface of the PDLC layer420′ by using an inkjet ejecting device470. However, the coating method is not limited thereto. For example, the coating of the mixed solution430may be performed by using various other coating methods, such as dipping or roll coating, for example. A given time after the mixed solution430, including the liquid crystal and dichroic dye, is coated on the upper surface of the PDLC layer420′, the liquid crystal and dichroic dye of the mixed solution430diffuse into the PDLC layer420′, thereby forming a PDLC layer420including dichroic dye (operation d). In the PDLC layer420, the liquid crystal, dichroic dye, and the polymer are uniformly dispersed and due to the diffusion, the dichroic dye is present only in the liquid crystal. Also, if the first substrate410is heated in the diffusion process, the liquid crystal and dichroic dye may diffuse more rapidly.

Finally, a second substrate440is attached to an upper surface of the PDLC layer420including the dichroic dye, thereby completing the formation of a PDLC film (operation e). In this regard, like the first substrate410, the second substrate440may be a transparent substrate and may include a second component441selected from a TFT and a color filter. In example embodiments, attachment and separation of a third substrate (see350ofFIG. 13) is not performed. Thus, a PDLC film including dichroic dye may be more easily formed.

As described above, according to example embodiments, the presence of dichroic dye in a polymer may be prevented or reduced by diffusing dichroic dye into a PDLC layer. By using the method, a PDLC display device with higher visibility may be embodied. In addition, a PDLC film including dichroic dye is formed by using a roll-to-roll process.