WO2005096084A1

WO2005096084A1 - Optical phase modulation film and method of manufacturing the same

Info

Publication number: WO2005096084A1
Application number: PCT/KR2004/001284
Authority: WO
Inventors: Taemin Kim
Original assignee: Advue Co.,Ltd.
Priority date: 2004-04-02
Filing date: 2004-05-29
Publication date: 2005-10-13
Also published as: KR100484417B1

Abstract

Provided is an optical phase modulation film which is attached to a final front surface of an LCD using liquid crystal to act as an optical compensation film. The optical phase modulation film includes a liquid crystal alignment film which homogeneously orients the liquid crystal by a surface alignment process using photo irradiation or rubbing or by ion beam irradiation, and simultaneously, homeotropically orients the liquid crystal which is not surface alignment processed, a liquid crystal layer oriented on the liquid crystal alignment film, having a predetermined optical axis, and having a first pattern formed of a liquid crystal layer in a homogeneous alignment and a second pattern formed of a liquid crystal layer in a homeotropic alignment, and a substrate supporting the liquid crystal alignment film and the liquid crystal layer. A layer formed of the liquid crystal alignment film and the liquid crystal layer is stacked more than one layer.

Description

Description OPTICAL PHASE MODULATION FILM AND METHOD OF MANUFACTURING THE SAME Technical Field

[1] The present invention relates to an optical phase modulation film attached to a front surface of an LCD and acting as an optical compensation film, and more particularly, to an optical phase modulation film having a structure designed to perform an optical phase modulation of an image by the performing an optical phase modulation function according to each pattern thereof and simultaneously giving a process that minimizes the number of manufacturing steps by varying a liquid crystal alignment structure, and a method of manufacturing the same. Background Art

[2] In general, conventional technologies relating to a patterned optical phase modulation film are largely classified into two types according to the structure and manufacturing method thereof.

[3] Referring to FIG. 1, U.S. Patent No. 5,327, 285 discloses a method of fabricating a micropolarizer 100. In the micropolarizer 100, polarization of a polarizing film disposed at a final surface of an LCD is differentiated in units of pixels or pixel groups to make the polarization directions of first and second polarization patterns 110 and 120 perpendicular to each other. Thus, when a 3-D stereo image is represented, an image of each pattern is recognized differently by the left or right eyes.

[4] In this case, the polarization of the micropolarizer 100 is formed using poly vinyl alcohol(PVA) as a medium and the polarization pattern is formed by photo etching.

[5] Referring to FIG. 2, European Patent No. 0,829,744 A2 discloses a method in which a patterned retarder 200 is patterned such that first and second retarder patterns 210 and 220 attached on a polarization film disposed at a final surface of an LCD can make polarizations thereof perpendicularly to each other. The first retarder pattern 210 diffracts an exit light of the polarization film by 90 ° such that the aligned film of liquid crystal has a characteristic of a half wavelength retardation. The second retarder pattern 220 is formed by aligning the liquid crystal so as not to diffract an exit light of the polarization film. In result, the first and second retarder patterns 210 and 220 are formed as two different retardation patterns respectively. In this case, the alignment of liquid crystal of the patterned retarder 200 is formed by rubbing and the polarization pattern is formed by photo etching. [6] Nevertheless, the above U.S. and Europe patents have the following drawbacks.

[7] Firstly, since the pattern of the optical phase modulation films (100 and 200) are formed by photo etching, a series of processes such as coating, developing, etching, coating, and developing are complicated and expensive.

[8] Secondly, the polarity of the micropolarizer 100 is lower than a conventional polarization film formed by elongation.

[9] Thirdly, if the alignment is processed by a rubbing method when the patterned retarder 200 is formed, a possibility of impurities involved is highly increased and the rubbed surface may be scratched. Since the uniformity of alignment is not good, the final products have a bad optical quality and also manufacturing process yield gets lower.

[10] Thus, an optical phase modulation film using the micropolarizer 100 and the patterned retarder 200 is difficult to be manufactured economically. Disclosure of Invention Technical Solution

[11] To solve the above and/or other problems, the present invention provides an optical phase modulation film having a structure designed to perform an optical phase modulation of an image by the performing an optical phase modulation function according to each pattern thereof and simultaneously giving a process that minimizes the number of manufacturing steps by varying a liquid crystal alignment structure, and a method of manufacturing the same.

[12] According to an aspect of the present invention, there provided a n optical phase modulation film which is attached to a final front surface of an LCD using liquid crystal to act as an optical compensation film, the optical phase modulation film comprising, a liquid crystal alignment film which is homogeneously aligned by a surface alignment process using light irradiation or rubbing method or by ion beam irradiation and simultaneously the liquid crystal film which is not surface oriented is homeotropically aligned, a liquid crystal layer oriented on the liquid crystal alignment film and having two patterns formed a liquid crystal layer each, that is, the first pattern made of a liquid crystal layer in a homogeneous alignment with a predetermined optical axis, and the second pattern made of a liquid crystal layer in a homeotropic alignment, and a substrate supporting the liquid crystal alignment film and the liquid crystal layer, wherein a layer formed of the liquid crystal alignment film and the liquid crystal layer is stacked by more than one layer at least .

[13] According to another aspect of the present invention, a method of manufacturing an optical phase modulation film comprising coating a liquid crystal alignment film on a substrate, separately forming the first pattern which is surface-processed by placing a photomask designed in a particular format on the liquid crystal alignment film and radiating a polarized light or ion beam, and the second pattern which is not surface- processed, and simultaneously aligning a homogeneous alignment part (the second pattern) and a homeotropic alignment part (the first pattern) by coating photoreactive liquid crystal on the liquid crystal alignment film, and cross-linking the aligned liquid crystal layer by photo-irradiating. Advantageous Effects

[14] According to the present invention, the optical phase modulation film and the method of manufacturing the same have the following advantages.

[15] Firstly, since only one alignment process is needed to form two patterns of the patterned optical phase modulation film in the present invention, the number of major manufacturing processes can be reduced by half.

[16] Secondly, since the optical phase modulation film is manufactured by using only one type of alignment film, a complicated etching process is not needed at all.

[17] Thirdly, since no difference exists in brightness between the first and second patterned areas of liquid crystal, a depth of 3-D realism is enhanced.

[18] Fourthly, since the homeotropic oriented part which is not polarization-diffracted provides only a viewing angle compensation effect, not diffracts a polarized exit beam of an LCD. Thus, the optical phase modulation film has the additional function as an optical compensation film and can compensate the quality of the conventional image.

[19] Fifthly, the optical phase modulation film is formed into a multilayer so that the first pattern of each layer has a quarter wave plate (QWP) retardation characteristic. In addition, since the optical axis is appropriately arranged to efficiently perform polarization-diffraction, an image having a superior 3-D realism can be accomplished when a 3-D stereo image is represented.

[20] Sixthly, since the manufacturing process and the composition of materials are simple, a raw cost for mass production is low.

[21] Seventhly, since the optical phase modulation film can be simply attached on a final LCD product, attachment and use thereof is easy.

[22] Bghthly and the lastly, since the optical phase modulation film is attached to the LCD, an existing image quality is compensated. Also, an LCD capable of representing both 2-D and 3-D images is available. Description of Drawings [23] FIG. 1 is a view illustrating a conventional optical phase modulation film;

[24] FIG. 2 is a view illustrating another conventional optical phase modulation film;

[25] FIG. 3 is a view illustrating the manufacturing steps of an optical phase modulation film according to an embodiment of the present invention;

[26] FIG. 4 is a graph showing a characteristic of a liquid crystal alignment film according to the present invention;

[27] FIG. 5 is a view illustrating a multilayered optical phase modulation film according to the present invention; and

[28] FIG. 6 is a view illustrating a state in which a black matrix is applied to the optical phase modulation film according to the present invention. Best Mode

[29] FIG. 3 through FIG. 6 shows respectively a manufacturing process of an optical phase modulation film according to an embodiment of the present invention, and characteristics of a liquid crystal alignment film, a state of the optical phase modulation film being applied, and a state of a black matrix being applied. Referring to FIG. 3 through FIG. 6, a liquid crystal alignment film 10 which is homogeneously aligned by a surface alignment process using light irradiation or rubbing method or by ion beam irradiation and simultaneously the liquid crystal film which is not surface oriented is homeotropically aligned, a liquid crystal layer 20 oriented on the liquid crystal alignment film 10 and having two patterns formed a liquid crystal layer each, that is, the first pattern 21 made of a liquid crystal layer 20 in a homogeneous alignment with a predetermined optical axis, and the second pattern 22 made of a liquid crystal layer in a homeotropic alignment, and a substrate 30 supporting the liquid crystal alignment film 10 and the liquid crystal layer 20, wherein a layer formed of the liquid crystal alignment film 10 and the liquid crystal layer 20 is stacked by more than one layer at least .

[30] Firstly, the optical phase modulation film 1 is formed by combining a liquid crystal alignment film 10, the liquid crystal layer 20, and the substrate 30. In particular, since the first and second patterns 21 and 22 of the liquid crystal layer 20 have different polarizations or diffract light so as to have different polarizations, the first pattern 21 diffracts a polarized exit light of an LCD 50 by 90 ° while the second pattern 22 maintains the polarized exit light as it is.

[31] When the optical phase modulation film 1 is attached on the final polarization film of the LCD 50, since both the first and second patterns 21 and 22 need to align the liquid crystal to be suitable for each optical characteristic, the first pattern 21 diffracts light such that a main optical axis of an aligned liquid crystal to have a predetermined angle with respect to the direction of the polarizing exit light, while the alignment of the second pattern 22 maintains a existing polarization direction of exit light by making the main optical axis of an aligned liquid crystal matching the polarizing direction of the exit light.

[32] That is, in the first and second patterns 21 and 22 of the liquid crystal layer 20 in the present invention, in order to maintain the existing polarization direction, the liquid crystal of the second pattern 22 is homeotropically aligned.

[33] Also, the polarization-diffraction of the first pattern 21 is available by making a phase modulation characteristic of the aligned liquid crystal into a half wavelength, and more effectively, by making the phase modulation characteristic into a 1/4 wavelength and appropriately aligning the optical axis to form a stacked structure.

[34] The above method requires liquid crystal alignment for both patterns and thus a corresponding liquid crystal alignment process is needed.

[35] Thus, as a new optical phase modulation film structure, in the present invention, the first pattern 21 is made of homogeneously aligned liquid crystal so as to have a predetermined angle with respect to a polarized exit light, while the second pattern 22 is made of homeotropically aligned liquid crystal. It is a characteristic that a liquid crystal alignment process is not needed for formation of the second pattern 22.

[36] An optical phase modulation film 1 is characteristically manufactured by coating a liquid crystal alignment film 10 on a substrate 30, separately forming the first pattern 21 which is surface-processed by placing a photomask 40 designed in a particular format on the liquid crystal alignment film 10 and radiating a polarized light or ion beam, and the second pattern 22 which is not surface-processed, and simultaneously aligning a homogeneous alignment part (the second pattern) and a homeotropic alignment part (the first pattern) by coating photoreactive liquid crystal on the liquid crystal alignment film 10, and cross-linking the aligned liquid crystal layer 20 by photo-irradiating.

[37] There are various types for the liquid crystal alignment film 10 and there is an alignment film having characteristics of both homogeneous alignment and homeotropic alignment. For example, an alignment film can be used which has a characteristic of homeotropically orientated liquid crystal when a surface alignment process (hydrophobicity between liquid crystal and an alignment film) such as optical alignment, rubbing, or ion beam is not performed after a film is coated on the substrate 30 and homogeneously orientating liquid crystal after the surface alignment process is performed so as to sufficiently reduce surface energy. In particular, in the present invention a liquid crystal alignment film is preferably used which is capable of non- contact alignment (rubbing is a contact type alignment) such as optical alignment or ion beam alignment.

[38] The liquid crystal alignment film 10 is surface-processed by a polarized light or ion beam with a photomask interposed therebetween to distinguish the first and second patterns 21 and 22. The first pattern part passing through the photomask is surface- processed by a polarized light (ion beam) so that a surface energy decreases and thus liquid crystal is homogeneously aligned. The second pattern part which is not surface- processed by being blocked by the photomask maintains the original surface energy of the alignment film so that liquid crystal is homeotropically aligned.

[39] The homeotropically aligned part does not change a direction of a polarization of the exit light of the LCD. The homogeneously aligned part has a predetermined angle with respect to a polarized exit light so that, by diffracting a polarization direction, the first and second patterns 21 and 22 can be formed with one surface process method only.

[40] Also, when the patterns are formed in the above method, since a boundary surface between the first and second patterns is a crossing part where the homeotropic alignment and the homogeneous alignment of the liquid crystal each other. Accordingly, such alignment has a semi-homeotropic alignment in which an inclination with respect to a flat surface of the liquid crystal is not constant. The photomask is designed such that such area is included in the area of a black matrix 70 which distinguishes pixels of the LCD, thus improving an image quality.

[41] The semi-homeotropic alignment can be partially formed by a flatness of a surface of the alignment film. Since diffraction or brightness of light is hardly decreased unless liquid crystal is not close to the homogeneous alignment with respect to a horizon (surface) the second pattern 22 which is not surface-processed does not affect the image quality by the homeotropic alignment or semi-homeotropic alignment of the liquid crystal, rather provides an optical compensation effect in some cases to improve the image quality of an LCD.

[42] The alignment film generally has a characteristic shown in FIG. 4, that is, a characteristic of a reverse 'S' shape in which a surface energy is lowered by receiving light energy (or ion beam). The alignment film having the above characteristic can be well applied to the present invention.

[43] Since the processes of coating the liquid crystal alignment film 10, a surface alignment process, and coating of liquid crystal are very simple, to improve an effect of the optical phase modulation film according to the present invention, a multilayered optical phase modulation film may be formed by repeating the above processes. In this case, the thickness of a liquid crystal layer of the first pattern 21 is adjusted to have a light diffracting characteristic of a quarter wave plate (QWP) so that the polarized exit light of the LCD can be efficiently diffracted as light diffraction of red, green, and blue colors are sufficiently made.

[44] The second pattern part which is homeotropically oriented and not polarization- diffracted does not diffract an polarized exit light of the LCD but provides a viewing angle compensation effect only, so that a function as an optical compensation film is added.

[45] When liquid crystal of the second pattern part is not either homeotropically aligned or homogenously aligned so that the optical axis thereof is isotropic, brightness is lowered due to dispersion of light in the part. In this case, the optical phase modulation film has an irregular optical scattering so that use thereof is difficult.

[46] The liquid crystal used in the present invention has the characteristics similar to that of nematic liquid crystal used for a general LCD having optical anisotropy and dielectric anisotropy. However, the present liquid crystal is reactive mesogen of which the optical anisotropy is very large so that a thin film can exhibit an optical phase modulation characteristic and which is designed to be a solid phase by being cross- linked by light (photo). A commercialized material is preferably used therefor.

[47] The optical phase modulation film according to an embodiment of the present invention is manufactured as follows.

[48] First, as shown in FIG. 3, an optical alignment material is coated by a thickness of 0.7 mm on a glass substrate 30, and a heat treatment is performed at 100+5 ° C for 20-40 minutes. The optical alignment material is a derivative of poly vinyl cinnamate made by introducing a cinnamate side chain to polyvinyl and an alkyl material is used as the end of the side chain.

[49] The film formed after the heat treatment is hydrophobic so as to homeotropically orientate liquid crystal and is changed to be hydrophilic by a predetermined surface treatment (photo, rubbing, or ion beam) so as to homogeneously orientate liquid crystal. Any alignment material having a similar characteristic can be applied for the present invention.

[50] The present material is solved in a solvent (cyclo-pentanone) by a predetermined amount so as to be filtered in a pore size of 0.2 um (nominal) to remove impurities, and then spin-coated at about 1500 rpm. Here, the spin coating can be substituted with all coating methods used to form a thin film, such as dispensing coating or roll coating, If the coating method is suitable for the preceding and following steps and can be optimized for the corresponding process. The thickness of 20-100 nm is generally sufficient for the film.

[51] Next, the first and second patterns 21 and 22 are formed by photo-irradiating the photomask 40 processed to a particular pattern on the glass substrate 30 in a coated state. Although the photomask 40 may have a desired pattern, it is general in a manufacturing process of an optical phase modulation film for a 3-D stereo image to form the pattern in units of pixel lines.

[52] Photo is irradiated by polarized UN ray of about 230-400 nm to provide a liquid crystal alignment capability to the part exposed on the light. Here, the amount of irradiation may be within the range of about 0.5-10 joule/cm. Also, an ion beam can be irradiated as a non-contact type surface process to provide a liquid crystal alignment capability.

[53] Then, liquid crystal is coated on the glass substrate 30 (in a surface-processed state). Any coating method used to form a thin film, such as dispensing coating or roll coating, can be used as a coating method. The coating method suitable for the preceding and following steps is selected by considering optimization of a corresponding process.

[54] However, since the thickness of the coated liquid crystal dominates a phase modulation characteristic, a fine adjustment of the thickness is needed. In the present embodiment, a film having an about 1 m m thickness is formed. The part (the first pattern) which is surface-processed after coating is aligned based on the polarization direction of the photo-irradiating so as to form a predetermined optical axis (to have a predetermined first angle with respect to a polarized exit light of the LCD). The part (the second pattern) which is not surface -processed is basically homeotropically oriented.

[55] A boundary area between the first and second patterns 21 and 22 is a transition area of liquid crystal alignment in a semi-homeotropically aligned state. The photomask can be designed such that the boundary area is hidden in an area of the black matrix 70 disposed between pixels of an LCD.

[56] In this case, the liquid crystal is reactive mesogen and used by being diluted in a solvent (PGMEA). The solvent is volatilized at about 50 ° C after coating and the liquid crystal is cross-linked by irradiating a UN ray at about 365 nm. The atmosphere of the above process is maintained by nitrogen to restrict a side reaction of liquid crystal cross-linking. The amount of irradiation may be within a range of about 0.5-10 joule/cm.

[57] The optical phases of multiple layers can be formed by repeating the above processes. The optical axis of the first pattern of the second layer formed on the first pattern of the first layer in the optical phase modulation film 1 forms a second angle with respect to the direction of the polarized exit light of the LCD, and the liquid crystal of the second pattern of the second layer formed on the second pattern of the first layer is homeotropically aligned. Thus, a multilayered optical phase modulation film is formed and the above sequence enables a single or double layer structure according to the phase modulation characteristic of liquid crystal.

[58] In particular, as shown in FIG. 5, when the optical phase modulation film 1 is formed in a double layer, the first pattern of the layers (10 and 20) of the optical phase modulation film firstly contacting a final polarization film of the LCD 50 has a photo diffracting characteristic of a quarter wave plate (QWP). An angle between the optical axis thereof and the direction of the polarized exit light of the LCD makes 22.5 degrees in a direction to diffract the polarized light. The first pattern of the optical phase modulation film layers 10 ' and 20 ' has a photo diffracting characteristic of a quarter wave plate (QWP) as well. An angle between the optical axis thereof and the direction of the polarized exit light of the LCD makes 67.5 degrees in a direction to diffract the polarized exit light.

[59] In the present embodiment, the optical phase modulation film 1 is attached to the LCD 50 having the first and second layers (10 and 20; 10 ' and 20 ' ) sequentially formed on the substrate 30 interposed therebewteen. Accordingly, the second layer (10 and 20) firstly contacts the final polarization film of the LCD and the first layer (10 ' and 20 ' ) contacts the final polarization film next.

[60] Also, since a case of forming the optical phase modulation film 1 in a single layer is simpler, polarization may be 45 ° in a direction for diffraction using the optical phase modulation of the first pattern as a half wavelength.

[61] As shown in FIG. 6, in a step of applying the optical phase modulation film 1 to the LCD 50 through a color filter part 60, the black matrix 70 which distinguishes pixels of the LCD 50 is applied to the semi-homeotropic alignment part which is the crossing part of the homeotropic and the homogeneous alignment in the optical phase modulation film 1 so that the image quality is improved. Industrial Applicability [62] As described above, the present invention can be used in various fields such as a field where the optical phase modulation film is attached to a final front surface of an LCD to act as a 3-D film for stereoscopic image processing and also an optical compensation film.

Claims

[1] An optical phase modulation film which is attached to a final front surface of an LCD using liquid crystal to act as an optical compensation film, the optical phase modulation film comprising: a liquid crystal alignment film which homogeneously orients the liquid crystal by a surface alignment process using light irradiation or rubbing or by ion beam irradiation and simultaneously homeotropically orients the liquid crystal which is not surface-alignment-processed; a liquid crystal layer oriented on the liquid crystal alignment film, having a predetermined optical axis, and having a first pattern formed of a liquid crystal layer in a homogeneous alignment and a second pattern formed of a liquid crystal layer in a homeotropic alignment; and a substrate supporting the liquid crystal alignment film and the liquid crystal layer, wherein a layer formed of the liquid crystal alignment film and the liquid crystal layer is stacked more than one layer.

[2] The optical phase modulation film of claim 1, wherein the first pattern polarization-diffracts the phase modulation characteristic in the aligned liquid crystal layer to a half wavelength or 1/4 wavelength.

[3] The optical phase modulation film of claim 1, wherein the second pattern is a semi-homeotropic alignment in which alignment of the liquid crystal layer is homeotropic or a orientation thereof is not constant.

[4] A manufacturing method of an optical phase modulation film comprising: coating a liquid crystal alignment film on a substrate; separately forming a first pattern which is surface-processed and a second pattern which is not surface-processed, by placing a photomask designed in a particular format on the liquid crystal alignment film and a polarized photo irradiation or ion beam; simultaneously aligning a homogeneous alignment part (the second pattern) and a homeotropic alignment part (the first pattern) by coating photoreactive liquid crystal on the liquid crystal alignment film; and cross-linking by photo irradiating onto the aligned liquid crystal on the liquid crystal film.