KR20010056719A - Compensation Method of color and luminance along viewing angle for reflective polarizer - Google Patents

Abstract

PURPOSE: A method of compensating phase shift and brightness according to viewing angle of reflective polarizer improves the phase shift and the brightness according to the viewing angle of a reflective cholesteric liquid crystal polarizer using a liquid crystal film homeotropically aligned by using an alignment layer. CONSTITUTION: An optical alignment layer has a carbon-carbon triple bond and a carbon-carbon double bond as a photoreaction-functional group. A homeotropically-aligned film is manufactured by fixing the alignment state through the light irradiation after a thermosetting nematic liquid crystal is homeotropically aligned by using the alignment layer. Exactly, an optical alignment material is dissolved in an organic solvent of MEK, THF and toluene then this solution is thinly coated on a plastic of PET, PC and TAC by using a roll coating method. The coated film passes through a dryer to remove the solvent, then it is irradiated by using a UV irradiator or is rewound without irradiating with UV ray. A hypergolic nematic liquid crystal is irradiated with the UV ray after it is coated on the film and dried, Therefore, the homeotropically-aligned film is formed by fixing the homeotropically aligned state after the curing process.

Description

Compensation method of color and luminance along viewing angle for reflective polarizer}

The present invention relates to a color difference and luminance compensation method according to a viewing angle of a reflective polarizer using a vertically aligned liquid crystal film.

In general, homeotropic films produced by vertically aligning nematic liquid crystals exhibit positive birefringence characteristics, so the cholesteric liquid crystal (CLC) film and the film having negative birefringence characteristics are used at an angle. By compensating for color shift and brightness, the film can be used as a compensation film or an optical component for improving the viewing angle characteristic of a liquid crystal display (hereinafter referred to as LCD).

Until now, in order to vertically align nematic liquid crystals, a method of injecting a liquid crystal into a glass cell coated with indium tin oxide (ITO) and applying an electric or magnetic field has been used. Have the following disadvantages:

First, it is difficult to manufacture a large-area film, and secondly, the process is complicated, such as coating the ITO on a glass plate and dispersing a spacer for thickness control, integrating a lens, and then injecting a liquid crystal. When the viscosity of the liquid crystal material is high, injection is difficult and difficult to use.

Therefore, it is impossible to manufacture a large area film with a thickness uniformity by such a method.

At present, LCDs are becoming larger in size, and large LCDs require a compensation film to improve viewing angle characteristics according to an operation mode, and a homeotropic film exhibiting positive birefringence characteristics is required. Can be used.

The existing method is described in J. Appl. Phys, 81, 1962 (1997), Appl. Phys. Lett, 73, 470 (1998), Appl. Phys. Lett, 68, 2819 (1996), Appl. Phys. Lett., 22, 386 (1973) describes a method for producing a homeotropic film.

According to the prior art, the nematic liquid crystal material is inserted between the glass coated with ITO, and an electric field is applied to the vertical alignment, or lecithin, DMOAP (dimethyl-octadecyl-3-aminopropyl trimethoxysilyl). A thin film was applied to the alignment material such as chloride) on the glass plate by spin coating, and then a nematic liquid crystal material was applied on the glass plate to realize vertical alignment.

However, the method using the glass plate coated with ITO is difficult to manufacture a large-area film, and the process is complicated, such as coating the ITO on the glass plate and dispersing the spacers for thickness control, bonding the glass plate, and then injecting the liquid crystal. When the viscosity of the liquid crystal material to be used is high, the injection is difficult to use has a disadvantage.

On the other hand, the alignment material such as lecithin or DMOAP is known to vertically align the nematic liquid crystals applied thereon by having a polar terminal functional group on the surface of the glass plate and an alkyl functional group of the length perpendicular to the surface of the glass plate. have.

Therefore, the substrate (substrate) is not a glass (plastic), such as PET (plastic) is not applicable, there is a disadvantage that can not be produced a large area film by a continuous process.

Conventional photo-alignment method is a next-generation alignment method that can freely adjust the alignment direction and the pretilt angle of the liquid crystal, and applies alignment force to the alignment layer by irradiating linearly polarized ultraviolet rays on the substrate coated with the photo-alignment material. Way. At this time, the orientation direction is changed by the incident direction of irradiated ultraviolet rays, and the pretilt angle is changed by the irradiation energy.

In order to solve the above disadvantages, the present invention has produced a liquid crystal film vertically aligned using an alignment film, and an object thereof is to provide a method for improving color difference and luminance according to the viewing angle of the cholesteric liquid crystal polarizing plate.

In order to achieve the above object, the present invention is a vertical alignment of the curable nematic liquid crystal using a new alignment film, and then fixing the alignment state by light irradiation to manufacture a vertically aligned film, the prepared vertical alignment film It is characterized in that it comprises a second process for improving the color difference and the luminance according to the viewing angle of the reflective cholesteric liquid crystal polarizing plate using.

The photoalignment film used in the present invention has a carbon-carbon triple bond or a carbon-carbon double bond as a polymer material as a photoreactive functional group.

At this time, the polymer main chain is polyacrylate, polysiloxane, polymethacrylate, polysaccharide, polysaccharide, polyvinyl alcohol, and the like. The moieties are connected by ester or ether linkages.

The photoreaction portion contains a carbon-carbon triple bond, and has one or two benzene rings, in which the H, F, Cl, CN, CF ₃ , OCF ₃ , C _n H _{2n + 1} , OC _n H _It contains a substituent of _{2n + 1} .

As an example of the photo-alignment film used for this invention, the following structural formula is mentioned.

[constitutional formula]

Wherein P ₁ is polysaccharide or polyvinyl alcohol, P ₂ is polyacrylate or polymethacrylate, and P ₃ is polysiloxane. Wherein X, Y, Z are H, F, Cl, CN, CF ₃ , OCF ₃ , C _n H _{2n + 1} (n = 1-7), OC _n H _{2n + 1} (n = 1-7), k = 0-1 and m = 0-7.

The photo-alignment material is dissolved in an organic solvent such as MEK, THF, Toluene, etc. to prepare a solution, and then the solution is thin-film roll-coated on a plastic film such as PET, PC, or TAC. After application, the applied film is passed through a dryer to remove the solvent, and then rewinded after only drying with UV irradiation or without light irradiation.

Thus, a thin film of a solution in which a curable nematic liquid crystal was dissolved in an organic solvent such as MEK, THF, and toluene was applied by a roll coating method on a film coated with an optical alignment layer, and the solvent was removed when the applied film passed through the dryer. At the same time, the nematic liquid crystal is vertically aligned.

The film from the dryer was irradiated with light using a UV irradiator to perform a curing reaction to fix a vertically aligned state, thereby preparing a vertically aligned liquid crystal film.

Vertical alignment of the prepared liquid crystal film can be confirmed by placing the film between vertically aligned polarizers and measuring extinction rate and measuring the refractive index. By adjusting the concentration, coating speed and the like can be adjusted to 1-20㎛.

The vertical alignment liquid crystal film compensation plate prepared as described above was inserted and bonded between the cholesteric liquid crystal film and the lambda / 4 phase difference film, and the linear polarizing plate was bonded to the lambda / 4 phase difference film to prepare a reflective polarizing plate.

The cholesteric liquid crystal film used at this time serves to pass a part of the incident light (50%) by polarizing it to the left or right circle and reflect the remaining part (50%) to the light of polarization opposite to the transmitted light. Liquid crystal layers having different wavelength regions of different layers were laminated to cover the entire visible light region (400 nm-800 nm), with the long wavelength side facing the light source and the short wavelength side facing the compensation film.

Compensation film was produced by the above-described method, because the color and polarization of the cholesteric liquid crystal layer is transmitted according to the angle is changed to use a film having a thickness of 4-6㎛ for proper compensation of this phenomenon.

The λ / 4 retardation film is used to make circularly polarized light into linearly polarized light, and a retardation film having a center wavelength of 460 nm is used.

And since the linear polarization degree of the light which passed the (lambda) / 4 phase (s) difference film was not uniformly high for all wavelengths, the linear polarizing plate was used in order to acquire a high linear polarization degree.

1A and 1B are diagrams illustrating a structure of change in luminance and curves of color coordinates according to angles when a compensation plate to which the present invention is applied is inserted (solid line) and not inserted (dotted line).

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1A and 1B are structural diagrams of luminance change curves and color coordinates according to angles when a compensation plate to which the present invention is applied is inserted (solid line) and not inserted (dotted line). First, a photo-alignment material was synthesized.

First, the structure is shown in the above structural formula, using polysaccharide as P ₁ , having a carbon-carbon double bond as a photoreaction portion, m and k is O, X is OC ₅ H ₁₁ , Y is H Having functional group was used.

This alignment material was prepared to have a concentration of 2wt% in MEK, and this solution was applied on a PET film by a roll coating method, and the solvent was dried in a dryer, followed by UV light irradiation.

At this time, the drying conditions were 75 ℃, UV light irradiation used a 300W (center wavelength 360nm) lamp (lamp).

The nematic liquid crystal material was applied onto the film on which the photo-alignment film was applied. At this time, a curable nematic liquid crystal material (BASF) was used as the nematic liquid crystal material.

First, a curable nematic liquid crystal material and a photoinitiator (IG 184, Ciba-Geigy) were dissolved in MEK to prepare a solution with a solution concentration of 40 wt% and a photo initiator content of 5 wt%.

After applying the thin film on the PET film to which the photo-alignment film is applied by the roll coating method, the solution thus prepared is vertically oriented by nematic liquid crystal material by drying and removing the solvent in a drier, and then proceeding polymerization by UV light irradiation. The film was prepared while fixing the orientation state.

At this time, the drying conditions were 80 ℃, UV light irradiation used a 300W (center wavelength 360nm) lamp.

The produced homeotropic nematic liquid crystal film had a thickness of 4 μm, and the refractive index measurement resulted in N _x = N _y = 1.535 and N _z = 1.668, from which a vertically aligned liquid crystal film was prepared. Confirmed.

As shown in the above structural formula, polysiloxane is used as P ₃ , carbon-carbon triple bond is used as the photoreaction portion, m is 1, k is 0, X is OC ₅ H ₁₁ , and Y is a functional group having a structure of H. It was.

The alignment material was prepared to have a concentration of 2wt% in MEK, and the solution was applied onto the PET film by a roll coating method, and then the solvent was removed from the dryer.

At this time, the drying conditions were 80 ℃, UV light irradiation used a 300W (center wavelength 360nm) lamp.

The thickness of the prepared homeotropic nematic liquid crystal film was 3.7 μm, and the results of Nx = Ny = 1.538 and Nz = 1.652 were obtained by measuring the refractive index, and it was confirmed that the vertically aligned liquid crystal film was prepared. .

Referring to the operation and description thereof according to the structure of the optical alignment material according to the above structure.

As described above, a cholesteric liquid crystal film having a preferential spiral structure having different selective reflection wavelength regions was stacked to prepare a circularly polarized light separation layer in which the selective reflection wavelength region includes all visible light regions.

The 4.7 micrometer-thick vertically oriented liquid crystal film produced as mentioned above was bonded to the short wavelength side of a cholesteric liquid crystal layer.

Then, the λ / 4 retardation film made of polycarbonate having a center wavelength of 460 nm was bonded onto the vertically aligned liquid crystal film, and the linear polarizing plate was again bonded to the upper side to prepare a reflective polarizing plate.

The fabricated reflective polarizer was installed on the LCD backlight, and the luminance variation and color coordinates according to the viewing angle were examined for the vertically aligned liquid crystal film compensation plate and the non-inserted liquid crystal film compensation plate.

As shown in FIG. 1A, it can be seen that the change in luminance according to the angle when the compensation plate is inserted is smaller than the change in luminance according to the angle when the compensation plate is not inserted.

In addition, as shown in FIG. 1B, the change in color coordinates is also smaller depending on the angle than when the compensation plate is not inserted. In particular, the change in color coordinates shows a significant difference at 50 ° and 60 °.

As described above, the present invention compensates for improving the viewing angle characteristic of a liquid crystal display (LCD) by improving the color difference and luminance according to the viewing angle of the reflective cholesteric liquid crystal polarizing plate using the liquid crystal film vertically aligned using the alignment film. It has the effect which can be used as a film or an optical element.

Claims (7)

A first process of preparing a vertical alignment film by vertically aligning the curable nematic liquid crystal using an alignment film having a carbon-carbon triple bond and a carbon-carbon double bond photoreactive functional group, and then fixing the alignment state through light irradiation; ; Comprising a second process for improving the color difference and the luminance according to the viewing angle of the reflective cholesteric liquid crystal polarizing plate using the prepared vertical alignment film, color difference and luminance compensation method according to the viewing angle of the reflective polarizing plate. The method of claim 1, wherein the first process is A first step of preparing a solution by dissolving the photo-alignment material in an organic solvent of MEK, THF, and toluene; A second step of coating the prepared solution on a plastic film of PET, PC, TAC using a roll coating method; A third step of removing the solvent by passing the applied film through a dryer and irradiating with a UV irradiator or rewinding only after drying without light irradiation; The fourth step of manufacturing a vertically oriented liquid crystal film by applying a ignitable nematic liquid crystal on the film from the dryer and drying and irradiating light using a UV irradiator and then proceeding the curing reaction to fix the vertically oriented state Color difference and luminance compensation method according to the viewing angle of the reflective polarizer. The method of claim 2, wherein the fourth step Color difference and luminance compensation method according to the viewing angle of the reflective polarizing plate, characterized in that for producing and using a vertical alignment liquid crystal film that is a compensation film having a positive birefringence characteristics. According to claim 3, wherein the vertical alignment liquid crystal film A method of compensating color difference and luminance according to a viewing angle of a reflective polarizing plate, comprising a polymer main chain of a photosensitive polymer alignment layer of polysaccharide, polyvinyl alcohol, polyacrylate, polymethacrylate, and polysiloxane. According to claim 3, wherein the vertical alignment liquid crystal film Color difference and luminance compensation method according to the viewing angle of the reflective polarizing plate, characterized in that the photoreaction portion of the photosensitive polymer alignment layer and the polymer backbone is composed of ether (ether) or ester (ester) bond. According to claim 3, wherein the vertical alignment liquid crystal film Color difference and luminance compensation method according to the viewing angle of the reflective polarizing plate, characterized in that the manufacturing using a plastic sheet (film) or a film as a substrate (substrate). The method of claim 1, wherein the second process Part of the light incident on the cholesteric liquid crystal film is polarized to the left circle or the right circle, and the other part is reflected to the polarized light opposite to the transmitted light. A first step of stacking and manufacturing a liquid crystal layer; A second step of directing the long wavelength side of the film toward the light source and contacting the short wavelength side with the compensation film; Inserting and bonding the produced vertically aligned liquid crystal film between the cholesteric liquid crystal film and the predetermined retardation film; A fourth step of manufacturing a reflective polarizing plate by bonding a linear polarizing plate on the predetermined retardation film; And Viewing angle of the reflective polarizer according to the fifth step of compensating the compensation film using a film having a predetermined thickness to compensate for the change in color and polarization degree transmitted by the cholesteric liquid crystal layer according to the angle Color difference and luminance compensation method according to.