Apparatus and method for coating polyimide layer

Abstract

An apparatus for coating a polyimide layer includes a printing table in which a substrate is provided, an inkjet head having an injection surface with nozzles for injecting a polyimide liquid onto the substrate, a polyimide liquid supply tank filled with the polyimide liquid, an ultrasonic cleaner in which a cleaning liquid for cleaning the inkjet head is stored for cleaning the inkjet head with vibrations in the cleaning liquid generated by applying an ultrasonic signal, and a wiper for wiping an injection surface of the inkjet head.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of embodiments of the invention. In the drawings:

FIG. 1 is a schematic view illustrating an accumulation problem in an apparatus for coating a polyimide layer according to the related art;

FIG. 2 is a view illustrating a configuration of an apparatus for coating a polyimide layer,

FIG. 3 illustrates the ultrasonic cleaning operation of one of the inkjet heads 110 shown in FIG. 2;

FIG. 4 is a flowchart of an implementation of a method of coating a polyimide layer; and

FIGS. 5 to 7 are views explaining each process step of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a view illustrating a configuration of an apparatus for coating a polyimide layer. Referring to FIG. 2, an apparatus for coating a polyimide layer comprises a printing table 100, an inkjet head 110, a polyimide liquid supply tank 102, an ultrasonic cleaner 130, and a wiper 140. A substrate 120 to which a coating of polyimide layer will be provided is positioned on the printing table 100. The substrate 120 can be a color filter substrate or a thin film transistor array substrate of a liquid crystal display.

A plurality of inkjet heads 110 are arranged in parallel with each other over the substrate 120, and each inkjet head 110 is connected to the polyimide liquid supply tank 102. The polyimide liquid supply tank 102 receives polyimide liquid from a pressure tank 101, and supplies the polyimide liquid to the inkjet head 110 at a predetermined constant pressure and flow rate. Polyimide liquid has the advantage of being heat resistant, chemically stable and high reliability.

A gas connection pipe provides nitrogen (N₂) to the pressure tank 101. A polyimide liquid recovery connection pipe provides polyimide liquid recovered from the inkjet head to the pressure tank 101. A polyimide supply connection pipe through which polyimide liquid is provided to the polyimide supply tank 102 through a filter is connected to the pressure tank 101. Further, each connection pipe is provided with a valve for controlling amount of the content passing through the connection pipes and the pressure in the connection pipes.

A jetting surface of each inkjet head 110, which faces the substrate 120, is provided with a plurality of nozzles 111 for jetting the polyimide liquid therethrough. The inkjet head 110 scans over the substrate 120 while jetting the polyimide liquid onto the substrate 120, thereby forming a polyimide layer on the substrate 120. After jetting the polyimide layer onto the substrate, the jetting surface of the inkjet head 110 is wet with the polyimide liquid. The polyimide liquid remaining on the jetting surface of the inkjet head 110 is then removed by a wiping with a wiper 140 and the inkjet head can be further cleaned by an ultrasonic cleaning operation with an ultrasonic cleaner 130. Then, the inkjet head 110 can be wiped again with wiper 140 to remove any residual cleaning liquid after the ultrasonic cleaning operation. In the alternative, the inkjet head can be first ultrasonically cleaned and then wiped without first wiping the inkjet head. In yet another alternative, the inkjet head can be first sprayed with a solvent, ultrasonically cleaned and then wiped without first wiping the inkjet head. Such cleaning methods, maintain the inkjet head and the jetting surface of the inkjet head in a state such that polyimide liquid can be jetted uniformly.

FIG. 3 illustrates the ultrasonic cleaning operation of one of the inkjet heads 110 shown in FIG. 2. The ultrasonic cleaner 130 includes a storage unit 131 that stores cleaning liquid, an ultrasonic oscillator 133 that is mounted within the storage unit 131 for applying an ultrasonic signal to the cleaning liquid 132 to vibrate the cleaning liquid 132, and a controller 134 that controls the ultrasonic oscillator 133, as shown in FIG. 3. The ultrasonic cleaner 130 cleans the inkjet head 110 by vibrating the cleaning liquid in and around the inkjet head 110.

The storage unit 131 of the ultrasonic cleaner 130 stores the cleaning liquid 132 into which the inkjet head is dipped during an ultrasonic cleaning process. The storage unit 131 can be configured to clean each inkjet head 110 individually, as shown in FIG. 3, or a groups of inkjet heads 110. Further, the ultrasonic cleaner 130 can be mounted so as to be movable up to an inkjet head 110 to dip the inkjet in cleaning solution and movable down from the inkjet head 110 away from the ultrasonic cleaner 130.

The ultrasonic oscillator 133 is arranged in a lower part or a side part of the storage unit 131 and receives an electrical ultrasonic signal from the controller 134. The ultrasonic oscillator 133 is in contact with the cleaning liquid 132. The ultrasonic oscillator 133 converts the electrical ultrasonic signal from the controller 134 to a mechanical signal and for vibrating the converted mechanical signal through a medium of the cleaning liquid 132. As shown in FIG. 3, the ultrasonic oscillator 133 is in position opposite to the injection surface of the inkjet head so that the ultrasonic oscillator 133 can clean an inner wall of a nozzle as well as the injection surface of the inkjet head 110. More specifically, cavitation is generated in the cleaning liquid 132 by generation of vibration such that polyimide particles remaining on inner wall and the outer surface of the inkjet head 110 are removed. The controller 134 applies an ultrasonic signal for operating the ultrasonic oscillator 133 with an ultrasonic signal having a frequency in a range of about 20 kHz to about 400 kHz. The cleaning liquid 132 can be isopropyl alcohol.

FIG. 4 is a flowchart of an implementation of a method of coating a polyimide layer. FIGS. 5 to 7 are views explaining each process step of FIG. 4.

As shown in, the substrate 120 is arranged on the printing table 100, as described in step S20 of FIG. 4. The substrate 120 can be a thin film transistor array substrate or a color filter substrate for use in a liquid crystal display.

Next, a polyimide liquid vessel filled with polyimide liquid is loaded into the polyimide liquid supply tank 102, as described in step S21 of FIG. 4. Subsequently, the polyimide liquid is supplied to the inkjet head 110 installed over the print table 100, and then jetted on the substrate 120 through the nozzles 111 provided on the jetting surface of the inkjet 110 to coat polyimide liquid onto the substrate 120, as described in step S22 of FIG. 4.

Next, as shown in FIG. 5, a first cleaning operation of removes polyimide particles A2 remaining on the inkjet head 110 by spraying a solvent onto the inkjet head 110 using a high pressure gas, as described in step S23 of FIG. 4. The high pressure gas can be a nitrogen (N₂) gas. The solvent can be water, polyimide liquid or N-methyl pyrrolidone imide-based polar solvent to remove both cured and uncured polyimide liquid. After the first cleaning operation, polyimide particles A2 still remain on an inner wall of the nozzle 111 of the ink my head 110.

Next, after dipping the inkjet head 110 into the cleaning liquid 132 by moving the storage unit 131 of the ultrasonic cleaner 130 into position, as shown in FIG. 6, a second cleaning operation to remove fine polyimide particles A2 remaining on an inner wall of the inkjet head 110 is performed by generating vibration in the cleaning liquid 132 through an ultrasonic oscillator 133 that receives an ultrasonic signal to, as described in step S24 of FIG. 4.

If vibration is generated in the cleaning liquid 132 toward the inkjet head 110, bubbles are formed by the change of a sound pressure. The bubbles emit a strong sound wave that collide with the fine polyimide particles A2 as the bubbles move past the inner wall of the inkjet head 110. As a result of this phenomenon, fine polyimide particles A2 remaining on the inner wall of the inkjet head 110 are peeled or agitated off of the inner wall of the inkjet head 110.

As shown in FIG. 7, a third cleaning operation in which the nozzles 111 of the inkjet head 110 are wiped by moving the wiper 140 while the wiper 140 comes in contact with the injection surface of the ink head 110, as described in step S25 of FIG. 4. After the first and second cleaning operations are completed, the third cleaning operation cleans cleaning liquid adhered after the second cleaning operation as well as polyimide particles A2 remaining on the injection surface of the inkjet head 110.

To clean the liquid inkjet head 110 of a polyimide layer coating apparatus for forming a polyimide layer with an inkjet method, a first cleaning uses a solvent, a second cleaning uses vibration generated by an ultrasonic signal, and a third cleaning of uses a wiper 140 so that fine polyimide particles A2 can be removed from the inkjet head 110 can be clearly removed. According to embodiments of the invention, by removing fine particles remaining on an inner wall of a nozzle of an inkjet head prior to a process of coating a polyimide layer by an inkjet method, a line stain due to a pinhole failure or the clogging of the nozzle can be prevented. Furthermore, the lifetime of the inkjet head can be extended.

It will be apparent to those skilled in the art that various modifications and variations can be made in the apparatus and method for coating a polyimide layer of embodiments of the invention without departing from the spirit or scope of the invention. Thus, it is intended that embodiments of the invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

1. An apparatus for coating a polyimide layer comprising: a printing table in which a substrate is provided;an inkjet head having an injection surface with nozzles for injecting a polyimide liquid onto the substrate;a polyimide liquid supply tank filled with the polyimide liquid;an ultrasonic cleaner in which a cleaning liquid for cleaning the inkjet head is stored for cleaning the inkjet head with vibrations in the cleaning liquid generated by applying an ultrasonic signal; anda wiper for wiping an injection surface of the inkjet head.

2. The apparatus of claim 1, wherein the ultrasonic cleaner includes: a storage unit that stores the cleaning liquid;a ultrasonic oscillator that is mounted in the storage unit for applying ultrasonic vibrations to the cleaning liquid; anda controller that controls an operation of the ultrasonic oscillator with electrical ultrasonic signals.

3. The apparatus of claim 2, wherein the storage unit is mounted so that the inkjet head can be dipped into the cleaning liquid.

4. The apparatus of claim 2, wherein the ultrasonic oscillator is in contact with the cleaning liquid and converts the electrical ultrasonic signal from the controller to a mechanical signal to vibrate the converted mechanical signal through the cleaning liquid.

5. The apparatus of claim 2, wherein the ultrasonic oscillator is in a position opposite to the injection surface of the inkjet head.

6. The apparatus of claim 1, wherein the cleaning liquid includes isopropyl alcohol.

7. The apparatus of claim 1, wherein the ultrasonic signal has a frequency in a range of about 20 kHz to about 400 kHz.

8. A method of coating a polyimide layer comprising: positioning one of a thin film transistor array substrate and a color filter substrate on a printing table;providing a polyimide liquid into a polyimide liquid supply tank;supplying the polyimide liquid to the inkjet head and injecting the polyimide liquid on the substrate;spraying a solvent onto the inkjet head to clean the inkjet head;dipping the inkjet head into a cleaning liquid and vibrating the cleaning liquid with an ultrasonic signal to clean inside of the inkjet head; andwiping an injection surface of the inkjet head by contacting a wiper to the injection surface and moving the wiper.

9. The method of claim 8, wherein the spraying a solvent includes pressurizes the cleaning liquid with a gas.

10. The method of claim 9, wherein the gas includes nitrogen gas.

11. The method of claim 8, wherein the solvent includes one of polyimide liquid and water.

12. The method of claim 8, wherein the ultrasonic signal has a frequency in a range of about 20 kHz to about 400 kHz.

13. The method of claim 8, wherein the inkjet head is dipped in a cleaning liquid within an ultrasonic cleaner.

14. The method of claim 13, wherein the ultrasonic cleaner includes: a storage unit that stores the cleaning liquid;a ultrasonic oscillator that is mounted in the storage unit for applying ultrasonic vibrations to the cleaning liquid; anda controller that controls an operation of the ultrasonic oscillator with electrical ultrasonic signals.

15. The method of claim 14, wherein the ultrasonic oscillator is in a position opposite to the injection surface of the inkjet head.

16. The method of claim 14, wherein the ultrasonic oscillator is in contact with the cleaning liquid and converts the electrical ultrasonic signal from the controller to a mechanical signal to vibrate the converted mechanical signal through the cleaning liquid.

17. The method of claim 8, wherein the cleaning liquid includes isopropyl alcohol.