Method for making liquid crystal display screen

A method for making a liquid crystal display screen includes the following steps. Firstly, providing a base including a surface. Secondly, forming carbon nanotube structure on the surface of the base to obtain a first electrode plate preform, the carbon nanotubes of each carbon nanotube structure being oriented along the extending direction thereof. Thirdly, forming a fixing layer to cover the carbon nanotube structure, thereby obtaining a first electrode plate. Fourthly, repeating the above-described steps, thereby obtaining a second electrode plate. Lastly, forming a liquid crystal layer between the fixing layers of the first electrode plate and the second electrode plate, the carbon nanotubes of the first electrode plate being perpendicular to that of the second electrode plate, thereby forming the liquid crystal display screen.

RELATED APPLICATIONS

BACKGROUND

1. Field of the Invention

The present invention relates to methods for making liquid crystal display screens.

2. Discussion of Related Art

Referring toFIG. 3, a conventional liquid crystal display screen100for liquid crystal display (LCD), according to the prior art, generally includes a first electrode plate104, a second electrode plate112, and a liquid crystal layer118. The first electrode plate104is located opposite to the second electrode plate112. The liquid crystal layer118is located between the first electrode plate104and the second electrode plate112. A first transparent electrode layer106and a first alignment layer108are formed in that order on an inner surface of the first electrode plate104, which faces toward the liquid crystal layer118. A first polarizer102is formed on an outer surface of the first electrode plate104, which faces away from the liquid crystal layer118. A second transparent electrode layer114and a second alignment layer116are formed in order on a surface of the second electrode plate112, which is near the liquid crystal layer118. A second polarizer110is formed on an outer surface of the second electrode plate112, which faces away from the liquid crystal layer118.

The quality and performance of the alignment layers108,116are key factors that determine the display quality of the liquid crystal display screen100. A high quality liquid crystal display screen demands steady and uniform arrangement of liquid crystal molecules1182of the liquid crystal layer118. This is achieved in part by a correct arrangement of the liquid crystal molecules1182at the alignment layers108,116. Materials to make the alignment layers108,116are typically selected from the group comprising of polystyrene, ramification of polystyrene, polyimide, polyvinyl alcohol, epoxy resin, polyamine resin, and polysiloxane. The selected materials are used to created a preform of each alignment layer108,116. The preform is then treated by one method selected from the group comprising of rubbing, incline evaporating oxide silicon, and atomic beam alignment micro-treatment. Therefore, grooves are formed on the treated surfaces of the preform, and the alignment layer108,116is obtained. The grooves affect the arrangement and orientations of the liquid crystal molecules118.

In the liquid crystal display screen100, the liquid crystal molecules1182are rod-like. A plurality of parallel first grooves1082are formed at an inner surface of the first alignment layer108. A plurality of parallel second grooves1162are formed on an inner surface of the second alignment layer116. The first grooves1082are perpendicular to the second grooves1162. The grooves1082,1162function so as to align the orientation of the liquid crystal molecules1182. Particularly, the liquid crystal molecules1182adjacent to the alignment layers108,116are aligned parallel to the grooves1082,1162respectively. When the grooves1082and1162are at right angles and the substrates104and112are spaced appropriately, the liquid crystal molecules1182can automatically twist progressively over 90 degrees from the top of the liquid crystal layer to the bottom of the liquid crystal layer118.

The alignment layers108and116can be made using a rubbing method. The rubbing method will be explained in reference to alignment layer116as an example of the known method. The manufacturing method for the alignment layers116generally includes the following steps: coating a layer of alignment material, such as polyimide, on the inner surface of the second transparent electrode layer114; and rubbing the surface of the alignment material using rubbing cloth to form the plurality of fine grooves1162.

However, some drawbacks arise from a mechanical contact of the rubbing cloth with the surface of the alignment material. This method is complicated because a baking process of the polyimide layer is very time-consuming, and the rubbing introduces large electrostatic charges as well as plenty of dust contamination, which in turn requires other facilities and cleansing processes to eliminate. Additionally, the rubbing cloth has a limited lifespan and needs to be replaced frequently.

What is needed, therefore, is to provide a method for making a liquid crystal display screen with a simple fabrication process.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the present method for making the liquid crystal display screen, in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

References will now be made to the drawings to describe, in detail, various embodiments of the present method for making the liquid crystal display screen.

Referring toFIGS. 1 and 2, a method for making a liquid crystal display screen300includes the following steps: (a) providing a first base322including a surface; (b) forming a first carbon nanotube structure324aon the surface of the first base322to form a first electrode plate preform320, the first carbon nanotube structure324aincluding a plurality of carbon nanotube films328arranged in parallel and located separately; (c) forming a first fixing layer324band covering the first carbon nanotube structure324a, thereby obtaining a first electrode plate330; (d) repeating the above-described steps, thereby obtaining a second electrode plate310; and (e) placing a liquid crystal layer338between the fixing layers of the first electrode plate330and the fixing layers of the second electrode plate310, the carbon nanotube in the first electrode plate330being perpendicular to the carbon nanotube in the second electrode plate310, thereby forming the liquid crystal display screen300.

In step (a), the material of the first base322is selected from the group comprising of glass, quartz, diamond, and plastics. The first base322can be made of flexible materials, such as cellulose triacetate (CTA). In the present embodiment, the first base322is made of CTA. A thickness of the first base322is 2 millimeters, a width of the first base322is 20 centimeters, and a length of the first base322is 30 centimeters.

Moreover, after step (a), a process of cleaning the first base322is also included. The process can be carried out by using organic solvents or de-ionized water. Finally, the first base322can be dried by protective gases.

Step (b) includes the following substeps: (b1) providing an array of carbon nanotubes, specifically, providing a super-aligned array of carbon nanotubes; (b2) cutting the array of carbon nanotubes to form a plurality of uniformly sub-arrays of carbon nanotubes; (b3) pulling out a plurality of parallel carbon nanotube films328from the sub-arrays of carbon nanotubes by using a pulling tool (e.g., adhesive tape, pliers, tweezers, or another tool allowing multiple carbon nanotubes to be gripped and pulled simultaneously); and (b4) placing a plurality of parallel carbon nanotube films328on the surface of the first base322to form the first electrode plate preform320.

In step (b1), the super-aligned array of carbon nanotubes can be formed by the following substeps: (b11) providing a substantially flat and smooth substrate; (b12) forming a catalyst layer on the substrate; (b13) annealing the substrate with the catalyst at 700 to 900° C. in atmosphere such as air for 30 to 90 minutes; (b14) heating the substrate with the catalyst up to a range of 500 to 740° C. in a furnace in protective gas; (b15) supplying a carbon source gas into the furnace for 5 to 30 minutes and growing a super-aligned array of the carbon nanotubes from the substrate.

In step (b11) the substrate can be a P-type silicon wafer, an N-type silicon wafer, or a silicon wafer with a film of silicon oxide thereon. In the present embodiment, a 4 inches P-type silicon wafer is used as the substrate.

In step (b12) the catalyst can be made of iron (Fe), cobalt (Co), nickel (Ni), or any combination alloy thereof.

In step (b14) the protective gas can be a nitrogen (N2) gas, ammonia (NH3) gas or a noble gas. In step (b15) the carbon source gas can be a hydrocarbon gas such as ethylene (C2H4), methane (CH4), acetylene (C2H2), ethane (C2H6) or any combination thereof.

The super-aligned array of carbon nanotubes means an array of carbon nanotubes including a plurality of carbon nanotubes being parallel to each other and substantially perpendicular to the surface of the substrate. In the present embodiment, the super-aligned array of carbon nanotubes can be approximately 200 to 900 micrometers in height. The super-aligned array of carbon formed under the above conditions is essentially free of impurities such as carbonaceous or residual catalyst particles. The carbon nanotubes in the super-aligned array are packed together closely by van der Waals attractive force. The super-aligned array proves to be an advantageous medium to produce carbon nanotube films.

In the present embodiment, the super-aligned array of carbon nanotubes is fabricated by chemical vapor deposition method. The super-aligned array of carbon nanotubes includes a plurality of carbon nanotubes parallel to each other and more or less perpendicular to the substrate. The carbon nanotubes in the array can be single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes. Diameters of the single-walled carbon nanotubes approximately range from 0.5 to 10 nanometers. Diameters of the double-walled carbon nanotubes approximately range from 1 to 50 nanometers. Diameters of the multi-walled carbon nanotubes approximately range from 1.5 to 50 nanometers.

The array of carbon nanotubes related in step (b1) is not limited to the above-described method. Alternatively, methods such as the graphite electrode constant current arc discharge deposition method and the laser evaporation deposition method can also be used to fabricate the array of carbon nanotubes.

In step (b2), a plurality of uniformly and separately located sub-arrays of carbon nanotubes are obtained after cutting the array of carbon nanotubes. The distance between adjacent sub-arrays of carbon nanotubes approximately ranges from 10 micrometers to 200 micrometers.

Methods of cutting the array of carbon nanotubes include laser beam scan cutting or electron beam scan cutting. The cutting process is undertaken in an atmosphere or an oxygenous environment. In the present embodiment, the laser beam scan cutting method is applied to cut the array of carbon nanotubes. The width of the laser beam approximately ranges from 10 micrometers to 200 micrometers, the power of the laser beam approximately ranges from 10 watts to 50 watts, and the velocity of the laser beam scan approximately ranges from 10 to 1000 millimeters per minute.

In step (b3), a method of pulling out a plurality of parallel carbon nanotube films328by using a tool includes the following substeps: (b31) selecting a plurality of carbon nanotube segments of a predetermined width from each sub-array of carbon nanotubes; and (b32) pulling the carbon nanotube segments at an even/uniform speed to achieve a plurality of parallel carbon nanotube films328.

The carbon nanotube segments having a predetermined width can be selected by using a pulling tool, such as adhesive tapes, pliers, tweezers, or other tools allowing multiple carbon nanotubes to be gripped and pulled simultaneously to come in contact with the super-aligned array. The pulling direction is substantially perpendicular to the growing direction of the super-aligned array of carbon nanotubes and parallel to the cutting direction.

More specifically, during the pulling process of each sub-array of carbon nanotubes, as the initial carbon nanotube segments are drawn out, other carbon nanotube segments are also drawn out end-to-end due to the van der Waals attractive force between ends of adjacent segments. This process of drawing ensures that a continuous, uniform a plurality of parallel carbon nanotube films328can be formed. The extending direction of the carbon nanotubes in each carbon nanotube films328is parallel to the pulling direction. The pulling/drawing method is simple, fast, and suitable for industrial applications.

After step (b3), a plurality of parallel carbon nanotube films can be placed separately or overlapped on the surface of the first base322along a same direction to form first carbon nanotube structure324a. The distance between adjacent first carbon nanotube structures324aapproximately ranges from 10 to 250 micrometers.

Due to a plurality of parallel carbon nanotube films328being sticky in the some embodiments, a plurality of parallel carbon nanotube films328can be directly adhered to the first base322. In other embodiments the attachment of a plurality of parallel carbon nanotube films328to the first base322, includes a step of forming an adhesive layer on the first base322is further included after the first base322has been dried. A plurality of parallel carbon nanotube films328can be fixed on the first base322via an adhesive agent or transparent conductive glue. In the present embodiment, a plurality of parallel carbon nanotube films328can be fixed on the first base322via alcohol.

Each carbon nanotube film328includes a plurality of carbon nanotube joined end-to-end and attracted by van der Walls attractive force therebetween. Thus, a number of uniformly distributed and parallel gaps are defined between carbon nanotubes. Therefore, the gaps are used as microgrooves that align the molecules of liquid crystal.

Furthermore, a step (b5) of treating the first carbon nanotube structure324awith an organic solvent is carried out after the step (b4). In step (b5), the first carbon nanotube structure324aon the surface of the first base322is soaked in an organic solvent. The organic solvent may be a volatilizable organic solvent, such as ethanol, methanol, acetone, dichloroethane, chloroform, and any combination thereof. The organic solvent is ethanol in the present embodiment. This process can be performed through applying some organic solvent onto the surface of the first carbon nanotube structure324aor dipping the first carbon nanotube structure324ainto the organic solvent. After being soaked by the organic solvent, microscopically, carbon nanotube strings will be formed by some adjacent carbon nanotubes bundling together, due to the surface tension of the organic solvent. In one aspect, due to the decrease of the specific surface area via bundling, the mechanical strength and toughness of the first carbon nanotube structure324aare increased and the coefficient of friction of the first carbon nanotube structure324ais reduced.

In step (c), the first fixing layer324bis formed on the first carbon nanotube structure324a, thus forming a first alignment layer324. When the materials of the first fixing layer324bare selected from the group comprising of diamonds, silicon nitrogen, hydride of random silicon, silicon carbon, silicon dioxide, aluminium oxide, tin oxide, cerium oxide, zinc titanate, and indium titanate, the first fixing layer324bis fabricated by means of evaporating, sputtering, and plasma enhanced chemical vapor deposition. When the materials of the first fixing layer324aare selected from polyethylene ethanol, polyamide, polymethyl methacrylate, and polycarbonate, the first fixing layer324bis sprayed on the first carbon nanotube structure324a. A thickness of the first fixing layer324bapproximately ranges from 10 nanometers to 2 micrometers.

In the present embodiment, the first fixing layer324bis made of organic materials. The method includes the following steps: (c1) dissolving powder of an organic material into a solvent to form a solution; (c2) dipping the solution on the first carbon nanotube structure324aand spinning the first carbon nanotube structure324ain a spinning machine; and (c3) heating the first carbon nanotube structure324ato form the first fixing layer324bon the first carbon nanotube structure324a.

In step (c1), the organic material is polyimide (PI). The solvent is a volatile organic solvent. The concentration of the solution ranges from 1% to 10%. In the present embodiment, the solvent is γ-butyrolactone. The concentration of the PI solution is 5%.

In step (c2), the amount of PI solution dipped on the first carbon nanotube structure324adetermines the thickness of the first fixing layer324b. Generally, the thickness of the first fixing layer324branges from 10 nanometers to 2 micrometers. The spinning rate ranges from 1000 to 8000 rotations per minute (r/min). In the present embodiment, the spinning rate is 5000 r/min and the spinning time is 60 seconds. As a result, the thickness of the first fixing layer324bis 80 nanometers.

In step (c3), the heating treatment is used to remove the residual solvent and to dry the first carbon nanotube structure324a. In the present embodiment, the heating temperature is 250° C. and the heating time is 60 seconds. The heating temperature and the heating time are selected according to user-specific needs.

Due to the carbon nanotube films328in the first carbon nanotube structure324ahaving gaps between adjacent carbon nanotubes, when the first fixing layer324bis covered on the first carbon nanotube structure324a, a plurality of parallel first grooves (not shown) are formed on the first fixing layer324bto align the molecules of liquid crystal. The first alignment layer324includes the first carbon nanotube structure324aand the first fixing layer324b. Because the first fixing layer324bcan prevent the first carbon nanotube structure324afrom being saturated, the first alignment layer324is not removed when the first alignment layer324comes in contact with the liquid crystal molecules or atmosphere for a long period of time. Thus, the present alignment layer has a good alignment quality if used in the liquid crystal screen.

In step (d), the second electrode plate310includes a second carbon nanotube structure304a, a second fixing layer304band a second base302. The second carbon nanotube structure304ais formed on a surface of the second base302to form a second electrode plate preform308. The second fixing layer304bis formed on the second carbon nanotube structure304a, thus forming a second alignment layer304. The structure of the second electrode plate310is similar to that of the first electrode plate330. From the description of the first fixing layer324b, a plurality of second grooves (not shown) are also formed on the second Fixing layer304bto align the liquid crystal molecules.

In step (e), the liquid crystal material is dipped into the first electrode plate330and the second electrode plate310via a tube, and as a result, a liquid crystal layer338is formed therebetween. The liquid crystal layer338includes a plurality of rod-like liquid crystal molecules. In the present embodiment, the first fixing layer304aand the second fixing layer324bare adjacent to the liquid crystal layer338disposed to form the liquid crystal screen300. Specifically, the first grooves are placed along the X-axis and the second grooves are placed along the Z-axis. Furthermore, the circumference between the first electrode plate330and the second electrode plate310is sealed by silicon sulfide rubber 706B seal glue. It takes one day for the seal glue to solidify after spreading the seal glue on the edge of the first electrode plate330and the second electrode plate310.

A step of connecting an electrode leading wire to each carbon nanotube structure is needed before sealing the first electrode plate330and the second electrode plate310. The electrode leading wire is used to apply a voltage to the liquid crystal display screen300.

In order to maintain enough spacing between the first electrode plate330and the second electrode plate310, a plurality of spacers (not shown) are placed between them. The size and the material of the spacer can be selected based on user-specific needs. In the present embodiment, a plurality of polyethylene (PE) balls are dispersed in the ethanol, and the solution containing the PE balls are put into the first electrode plate330and the second electrode plate310. After the ethanol has evaporated, the PE balls between the first electrode plate330and the second electrode plate310are used as spacers. The diameter of the PE balls ranges from 1 to 10 micrometers.

Because the carbon nanotubes in the carbon nanotube layer are arranged in parallel, the carbon nanotube layer has a polarization to light, and as a result, can be used to replace the conventional polarizer. In order to obtain a better effect of polarization, at least one polarizer is placed on the first electrode plate330and the second electrode plate310, and faces away from the liquid crystal layer338.

The extending direction of the first carbon nanotube structure324ais perpendicular to the extending direction of the second carbon nanotube structure304a. Therefore, the crossed area of the first carbon nanotube structure324aand the second carbon nanotube structure304ain the space defines a pixel. Due to the first alignment layer324and the second alignment layer304including a number of first carbon nanotube structure324aand second carbon nanotube structure304a, respectively, a plurality of pixels is formed in the liquid crystal display screen300.

The present method for making the liquid crystal display screen300has many advantages. Specifically, due to gaps existing within the carbon nanotube structure, the fixing layer covered on the carbon nanotube structure also directly forms a plurality of grooves. Therefore, an additional process for forming grooves is not needed, thereby reducing the fabricating cost and simplifying the production process. Furthermore, by overlapping a fixing layer on the carbon nanotube structure, this ensures that the carbon nanotube structure of the alignment layer does not fall off when it comes in contact with the liquid crystal layer.

It is also to be understood that above description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.