GB2344449A

GB2344449A - Liquid crystal display panel

Info

Publication number: GB2344449A
Application number: GB0004296A
Authority: GB
Inventors: Si-Hyun Lee
Original assignee: Samsung Display Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1995-11-24
Filing date: 1996-11-12
Publication date: 2000-06-07
Anticipated expiration: 2016-11-12
Also published as: GB0004296D0; GB2344449B

Abstract

A plurality of grooves are formed in a transparent substrate 21 using etching paste 19. Red filter material 10 is added to some of the grooves and photoresist material 59 to the others using a doctor blade 31. The resulting filter is exposed and developed, and the procedure repeated for green and blue filters. The resulting filters are used in a liquid crystal display. Alternatively, in an unclaimed variation, the material for each colour may be placed in all the empty grooves, and then developed using a photomask in only the intended areas (figure 7). Also disclosed are photolithographic methods for creating such filters: creating the grooves for each colour and filling them before creating the next grooves, either using a new photoresist layer for each set of grooves (figure 4) or re-using the same layer each time (figure 5).

Description

LIQUID CRYSTAL DISPLAY PANEL AND PROCESS FOR MANUFACTURING THE SAME The present invention relates to a liquid crystal display panel and a process for manufacturing the same. It is particularly applicable to a liquid crystal display panel having a wide color reproduction range and good color characteristics as a result of employing a color filter with good planarity, and a process for manufacturing such a liquid crystal display panel.

A liquid crystal display provides a lighter weight and smaller size display than a display using a cathode ray tube, and thus it may be conveniently portable. Further, it has the advantage of not radiating electromagnetic waves considered harmful to health. Therefore, the liquid crystal display is widely used both for small displays (e. g., of an electronic calculator) and large displays (e. g., of a notebook computer).

A structure of the conventional liquid crystal display panel is shown in FIG. 1. Referring to FIG. 1, a process for manufacturing such a liquid crystal display panel will be described.

Black matrixes 15 are formed on a glass substrate 11, and a red filter 16, a green filter 17 and a blue filter 18 are respectively formed between the black matrixes 15. Here, the combination of the black matrixes 15, red filter 16, green filter 17 and blue filter 18 is commonly referred to as a color filter layer. To planarize the color filter layer and to enhance chemical resistance, a protective film 13 is formed thereon, and an indium-tin oxide (ITO) electrode layer 14 is then formed atop the protective layer.

When forming the red, green and blue filters, a red coloring resin composition is first coated on the whole surface of the substrate 11 having black matrixes formed therein. This is exposed through a photo mask and then developed to produce the red filter 16. The above procedure is repeated for green and blue compositions, respectively, to produce the green and blue filters 17 and 18.

A general photosensitive coloring resin composition includes a binding resin, pigments, a dispersing agent, a photo-polymerizable monomer, a photo-polymerization initiator, dilution solvents and additives. Such a photosensitive coloring resin composition can be obtained according to the following procedure.

First, binding resin and pigment are mixed with dispersing agent, such that the pigment is sufficiently dispersed into the resin. Then, the photo-polymerizable monomer and photo-polymerization initiator are added, to form a mixture. Finally, the mixture is diluted with solvent, to form a photosensitive coloring resin composition.

When a liquid crystal display panel is manufactured by the above procedure, since the coloring resin composition is coated on the whole surface of the substrate, the coloring resin composition is used for an undesired portion of the substrate, thus greatly lowering the utility of a material.

Also, in the photosensitive coloring resin composition for the color filter, since the ratio of photosensitizer and bonding resin amounts to more than 50%, the ratio of pigment is rather low.

On the other hand, the protective film is generally disposed between the color filter layer and ITO electrode layer. Before and after the protective film formation, a grinding process in which the whole surface of the substrate is planarized should be accomplished.

As above, the process for manufacturing the conventional liquid crystal display panel is complicated, and the thusobtained liquid crystal display panel has a narrow color reproduction range and poor color characteristics.

The object of the present invention is to provide a liquid crystal display panel having a wide color reproduction range and good color characteristics, by employing a color filter with good planarity, without a separate grinding process.

Another object of the present invention is to provide a suitable process for manufacturing the above liquid crystal display panel.

According to the present invention, there is provided a process for manufacturing a liquid crystal display panel comprising the steps of: (a) etching a transparent substrate with etching agent in paste state to form a plurality of grooves in the transparent substrate; (b) adding a red coloring resin composition to a proportion of said grooves and adding a photoresist to the grooves to which coloring resin composition was not added and exposing and then developing the resultant structure to form a red filter; (c) repeating step (b) for green and blue color resin compositions, to form a green filter and a blue filter, respectively; and (d) forming in sequence a protective film and an electrode layer on the surface of the resultant structure.

A specific embodiment of the invention is described in detail below, by way of example, with reference to the attached drawings, in which: FIG. 1 illustrates the structure of a liquid crystal display panel according to prior art; FIG. 2-3 illustrate the structure of a liquid crystal display panel according to embodiments of the present invention; FIGS. 6 is a series of step-by-step diagrams showing a process for manufacturing of the liquid crystal display panel according to an embodiment of the present invention; and FIGS. 4,5 and 7 are step-by step diagrams showing processes for manufacturing of liquid crystal display panels.

FIG. 2-3 illustrate the structure of a liquid crystal display panel according to the present invention.

Referring to FIG. 2, color filters of red, green and blue 26', 27'and 28'are formed in the grooves of the transparent substrate 21'. Here, the upper surface of the color filters is at the same level as the surface of the transparent substrate.

A protective film 23'and an electrode layer 24'are formed in sequence on the color filters of red, green and blue 26', 27'and 28'.

Black matrixes are formed on the other substrate having an opposite electrode layer (not shown).

In the liquid crystal display shown in FIG. 3, black matrixes 25 are formed between the respective color filters.

FIG. 4A-F show a process for manufacturing a liquid crystal display panel.

In this process, a plurality of grooves are formed in a glass substrate by photolithography, and a coloring resin composition is added to the grooves to form a color filter.

A photoresist layer 9 is formed on the glass substrate 21. Here, the thickness of the photoresist layer is preferably 1-1. 5ym. A predetermined portion of the photoresist layer 9 is exposed and developed, to form a photoresist pattern (FIG.

4A).

The glass substrate 21 is etched by using the photoresist pattern and a mixed solution of hydrofluoric acid and hydrochloric acid (FIG. 4B) to form a grooves. At this time, etching depth depends on the ratio of hydrofluoric acid and hydrochloric acid in the etching solution and etching time.

It is preferable that the etching depth is about 0. 5-0. 6pm.

The photoresist pattern on the surface of the glass substrate 21 is completely removed. Then, a red coloring resin composition 10 is added to the grooves by using a doctor blade 31, to form a red filter 26 (FIG. 4C-D).

The above process is repeated with a green coloring resin composition 32 and a blue coloring resin composition 33, to form a green filter 27 and a blue filter 28, respectively (FIG. 4D-F). Then, black matrixes are formed between the color filters in the same manner as the color filter formation, to form a color filter layer.

A protective film and an ITO electrode layer are formed on the surface of the resultant, in sequence, to thus produce the liquid crystal display panel shown in FIG. 2.

FIG. 5A-F show another process for manufacturing a liquid crystal display panel. In this process, the initially coated photoresist layer is used throughout, without the repetitious process of removing the photoresist layer and coating it again before and after a color filter formation step.

The photoresist layer 9 is first formed on the surface of the glass substrate 21. A predetermined portion of the photoresist layer 9 is exposed and developed, to form a photoresist pattern (FIG. 5A). The glass substrate 21 is etched by using the photoresist pattern and the mixed solution of hydrofluoric acid and hydrochloric acid, to form grooves (FIG. 5B).

A red coloring resin composition 10 is added to the grooves by using a doctor blade 31, to form a red filter 26 (FIG. 5C-D).

The predetermined portion of the photoresist layer in the resultant is exposed and developed to form grooves in the glass substrate, and then a green coloring resin composition 32 is added to the grooves, to form a green filter 27 (FIG.

5D-E).

The above process is repeated for a blue color resin composition, to form a blue filter 28 (FIG. 5E).

The photoresist pattern on the surface of the glass substrate 21 is completely removed (together with the color filter part at the same level), to form color filters 26,27 and 28 (FIG. 5F). Black matrixes are then formed between the color filters in the same manner as the color filter formation to form a color filter layer.

A protective film is formed on the color filter layer and an ITO electrode layer is formed atop the protective film, to thus produce the liquid crystal display panel.

FIG. 6A-F show a process according to the invention for manufacturing a liquid crystal display panel by a printing method.

A plurality of grooves are formed in the glass substrate 21 by a printing method such as screen printing or offset printing. That is, the glass substrate is etched with an etching agent in paste state 19. The glass substrate is etched and washed, to form a plurality of grooves in the substrate 21 (FIG. 6A-C).

A red coloring resin composition 10 is added to some of the grooves and a photoresist 59 is added to the rest of the grooves (FIG. 6D). The resultant is exposed and developed, thus forming a red filter 26. Here, in adding a coloring resin composition or photoresist to the grooves, the doctor blade 31 is used. A green coloring resin composition 32 is added to some of the remaining grooves and a photoresist 59 is added to the rest of the grooves (FIG. 6E). The resultant is exposed and then developed, to form a green filter 27 in the same manner as the red filter formation. A blue coloring resin composition is added to the rest of the grooves, to form a blue color filter 28 (FIG. 6F).

As can be seen from the above, this manufacturing process is very simple and thus mass production of the liquid crystal display panel is possible.

FIG. 7A-I show an alternative process for manufacturing a liquid crystal display panel by a printing method.

A plurality of grooves are formed by using etching paste 19 in the same manner as the above process (FIG. 7A-C).

A red coloring resin composition 10 is added to all grooves (FIG. 7D). The resultant is exposed through the photo mask and then developed to form a red filter 26 (FIG. 7E-F).

Similarly, a green coloring resin composition 32 is added to all remaining grooves (FIG. 7G). The resultant is exposed through the photo mask and developed, to form a green filter 27 (FIG. 7H). Then, the same process is repeated for blue color, to form a blue filter 28 (FIG. 7I).

Hereinbelow, examples of liquid crystal display panel structures will be referred to in connection with a comparative example.

(Example 1) A photoresist layer was formed on the surface of a glass substrate to a thickness of about 1.2ym. A predetermined portion of the photoresist layer was exposed and developed to form a pattern. Then, the glass substrate was etched with a mixed solution of hydrofluoric acid and hydrochloric acid, to form grooves having a depth of about 0.6hum.

The photoresist pattern on the surface of the glass substrate was removed. Then, a red coloring resin composition was added to the grooves, to form a red filter.

The red coloring resin composition included liotrogen red GD (Dongyang Ink Co. of Japan) as a red pigment, acrylate resin as a bonding resin, pentaerythritoltetraacrylate as a photo-polymerizable monomer and phthalocyanidine copper derivative as a dispersing agent.

The above process was repeated for green and blue color resin compositions, to form a green filter and a blue filter, respectively. Ionolgrin YS (Dongyang Ink Co. of Japan) was used as a green pigment, and ionolbul ES (Dongyang Ink Co. of Japan) was used as a blue pigment.

Black matrix elements were disposed between the color filters, to form a color filter layer. A protective film was formed on the color filter layer and then an ITO electrode layer was formed atop the protective film.

(Example 2) A glass substrate was etched by a screen printing method, to form grooves having a depth of about 0.6ym. Here, a paste mixture of hydrofluoric acid and hydrochloric acid was used as an etching agent.

A red coloring composition including liotrogen red GD (Dongyang Ink Co. of Japan) as a red pigment, acrylate resin as a bonding resin, pentaerythritoltetraacrylate as a photopolymerizable monomer and phthalocyanidine copper derivative as a dispersing agent was added to the grooves. The composition was exposed through a photo mask and developed to form a red filter.

The above process was repeated for green and blue colors, to form a green filter and a blue filter, in sequence. Here, ionolgrin YS (Dongyang Ink Co. of Japan) was used as the green pigment, and ionolbul ES (Dongyang Ink Co. of Japan) was used as the blue pigment.

Black matrix elements were formed between the color filters, to form a color filter layer. A protective film was formed on the color filter layer, and then an ITO electrode layer was formed atop the protective film.

(Comparative Example) A color filter layer having a black matrix and a color filter was formed on a glass substrate by a conventional method. With the exception that the coloring resin composition contained a lower ratio of acrylate resin, photopolymerizable monomer or dispersing agent to pigment, the same composition as Examples 1 and 2 was used as the coloring resin composition.

Planarity of the color filter layer and utility of a material wre measure for Example 1 and the comparative example. Here, a planarity of the color filter layer is defined as a thickness variation of the color filter layer.

As the result, while the planarity of the color filter layer of the comparative example was about O. 1pm and the utility of a material was about 10%, the planarity of the color filter layer of the Example 1 was about 0.01-0.02Um and the utility of a material was about 90%.

As can be seen from the above, there is a great difference in the utility of a material between Example 1 and comparative example. That is, in the comparative example, the coloring resin composition of the respective color was coated on the whole surface of the substrate in order to form a color filter layer, and on the contrary, in Example 1, the coloring resin composition of the respective color was added selectively to the grooves in the glass substrate to form the color filter layer. Thus, the utility of a material of color filter layer in the Example 1 was much greater than that of the comparative example.

Further, the ratio of a bonding resin or photosensitizer to a pigment in a coloring resin composition of Examples 1 and 2 was considerably lower than for the comparative example.

Accordingly, color reproduction and the color characteristics of the liquid crystal display panel in the Examples 1 and 2 are better than for the comparative example.

According to aspects of the present invention, since the green filter, blue filter and red filter are formed in the glass substrate so that the surface of the glass substrate is at the same level of the upper surface of the color filter layer, the utility of a material and the planarity of the color filter layer are improved. Also, in the coloring resin composition for the color filter, since the ratio of the photosensitizer or bonding resin to the pigment is remarkably small, the color reproduction and color characteristic of the liquid crystal display panel are enhanced.

Claims

CLAIMS:

1. A process of manufacturing a liquid crystal display panel comprising the steps of: (a) etching a transparent substrate with etching agent in paste state to form a plurality of grooves in the transparent substrate; (b) adding a red coloring resin composition to a proportion of said grooves and adding a photoresist to the grooves to which coloring resin composition was not added and exposing and then developing the resultant structure to form a red filter; (c) repeating step (b) for green and blue color resin compositions, to form a green filter and a blue filter, respectively; and (d) forming in sequence a protective film and an electrode layer on the surface of the resultant structure.

2. A process for manufacturing a liquid crystal display panel as claimed in claim 1, wherein said transparent substrate is etched with a mixed solution of hydrofluoric acid and hydrochloric acid in said step (a) of forming the grooves by etching the transparent substrate.

3. A process for manufacturing a liquid crystal display panel as claimed in claim 1 or 2, wherein a doctor blade coating method is used in said step (b) and (c) of adding the coloring resin composition to the grooves.

4. A process for manufacturing a liquid crystal display panel as claimed in claim 1, wherein the etching depth of said transparent substrate is not greater than one fifth of the depth of said transparent substrate.

5. A liquid crystal display panel manufactured by the process of any of claims 1 to 4.