KR101520471B1 - Dielectric barrier discharge reactor for surface treatment - Google Patents

Abstract

A dielectric barrier discharge reactor capable of increasing the surface treatment efficiency of a large area substrate to be processed. The dielectric barrier discharge reactor is provided with first and second drive electrodes which are arranged to face each other with a central slit provided therebetween and to be surrounded by respective dielectric bodies and to face each other with respect to the first and second drive electrodes And a ground electrode for supporting the substrate to be processed. The distance between the first and second driving electrodes and the ground electrode is smaller than the distance between the first driving electrode and the second driving electrode.

Description

TECHNICAL FIELD [0001] The present invention relates to a dielectric barrier discharge reactor for surface treatment,

The present invention relates to a plasma reactor for surface treatment, and more particularly to a dielectric barrier discharge (DBD) reactor operating at atmospheric pressure.

Polymers are widely used in a variety of industries due to their transparency, flexibility, low cost, and chemical inertness. However, since the polymer has a low surface energy, surface modification is required for various applications. In addition to polymers, materials such as metals and glass may require surface modification depending on the application.

Plasma is useful for surface treatment because it can change the surface properties without affecting the bulk properties of the material. The surface of the polymer exposed to the plasma is cleaned with the removal of residual impurities and functionalized as new functionalities are added. In particular, the use of oxygen and nitrogen radicals is known to be effective in increasing the surface energy of the polymer and improving surface properties such as wettability, adhesiveness, and printability.

Dielectric barrier discharge (DBD) reactors operating at atmospheric pressure are able to provide abundant active species without expensive vacuum systems and are effective for surface treatment of polymer substrates. Generally, a dielectric barrier discharge occurs between two metal electrodes, and at least one metal electrode is covered by a dielectric to limit the discharge current and prevent the plasma discharge from transitioning to a thermal arc.

However, the dielectric barrier discharge becomes a normal filament discharge mode at atmospheric pressure. This is because the oxygen contained in the air changes the plasma discharge into the filament mode very strongly. Therefore, there is a great difficulty in generating a large-area homogeneous plasma under atmospheric pressure conditions in which air is mixed.

Disclosed is a dielectric barrier discharge reactor capable of enhancing a surface treatment efficiency of a substrate to be processed with a large area by avoiding a filament discharge mode, realizing a uniform discharge mode over a large area, and providing oxygen and nitrogen radicals to a substrate to be processed. ≪ / RTI >

The dielectric barrier discharge reactor according to an embodiment of the present invention includes first and second driving electrodes which are disposed opposite to each other with a central slit through which a discharge gas is provided and are surrounded by respective dielectrics and to which the same voltage is applied, And a ground electrode disposed opposite to the first and second driving electrodes with respect to the substrate and supporting the substrate to be processed. The distance between the first and second driving electrodes and the ground electrode is smaller than the distance between the first driving electrode and the second driving electrode.

The thickness of the bottom wall facing the discharge space in the dielectric may be smaller than the thickness of the inner wall facing the central slit. The first and second driving electrodes may be disposed to face each other along the horizontal direction, and the substrate to be processed may be positioned below the first and second driving electrodes with the discharge space therebetween.

Each of the first and second driving electrodes may be composed of a vertical part and a horizontal part connected to a lower end of the vertical part. The two horizontal portions can be arranged in the direction away from each other at the end of the vertical portion.

On the other hand, each of the first and second driving electrodes may have a constant vertical width and a constant horizontal width. In this case, the thickness of the outer wall of the dielectric may be greater than the thickness of the bottom wall facing the discharge space and the thickness of the inner wall facing the central slit.

The first and second driving electrodes may receive the same AC voltage having a driving frequency of 1 kHz or more. Each of the first and second driving electrodes has a predetermined length and the substrate to be processed can be transported along the direction in which the first and second driving electrodes face each other in the surface treatment process.

According to the present embodiment, the plasma discharge can be started and maintained outside the reactor where the substrate to be processed is located, and the filament mode can be avoided and a uniform discharge can be realized. And the surface energy of the substrate to be treated is increased by the oxygen and nitrogen radicals flowing from the outer substrate, so that the surface of the substrate can be effectively treated.

1 is a perspective view of a DBD reactor according to a first embodiment of the present invention.
2 and 3 are cross-sectional views of the DBD reactor shown in FIG.
FIGS. 4 and 5 are photographs of a plasma discharge when the DBD reactor shown in FIG. 1 is driven.
6 is a cross-sectional view of a DBD reactor according to a second embodiment of the present invention.
FIG. 7 is a graph showing a discharge behavior according to a time change in the DBD reactor of the first embodiment shown in FIG.
FIG. 8 is a graph showing a discharge behavior according to a voltage magnitude in the DBD reactor of the first embodiment shown in FIG.
9 is a graph showing the emission spectrum of a DBD reactor measured using an emission spectrometer.
10 is an enlarged photograph showing the contact angle test results of the liquid on the substrate before and after the surface treatment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

FIG. 1 is a perspective view of a dielectric barrier discharge reactor according to a first embodiment of the present invention, and FIGS. 2 and 3 are sectional views of a dielectric barrier discharge reactor shown in FIG.

Referring to FIGS. 1 to 3, a dielectric barrier discharge (hereinafter DBD) reactor 100 of the first embodiment includes a first and a second And a ground electrode 50 disposed opposite to the first and second driving electrodes 10 and 20 with the driving electrode 10 and the discharge space 40 interposed therebetween. The ground electrode 50 supports the substrate 60 to be processed.

The first and second driving electrodes 10 and 20 are located at the same height and face each other along the horizontal direction (the transverse direction in FIG. 2) with the central slit 30 interposed therebetween. The first and second driving electrodes 10 and 20 are connected to a power supply unit to receive the same AC voltage. The frequency of the AC voltage is 1kHz or more. The ground electrode 50 is positioned below the first and second driving electrodes 10 and 20 and faces the first and second driving electrodes 10 and 20 along the vertical direction (vertical direction in FIG. 2).

The first and second driving electrodes 10 and 20 are completely surrounded by the respective dielectric bodies 70 so that there is no part exposed to the atmosphere. The dielectric 70 may be formed of a dielectric material such as alumina, and may have a rectangular parallelepiped shape having a predetermined width and height. The space between the two dielectric bodies 70 facing each other becomes the central slit 30. [ The ground electrode 50 is exposed to the atmosphere and supports the substrate 60 to be processed. The substrate 60 may be formed of any one of polymer, metal, and glass.

The first driving electrode 10 is composed of a vertical part 11 and a horizontal part 12 and the second driving electrode 20 is also composed of a vertical part 21 and a horizontal part 22. The horizontal portions 12 and 22 are connected to the lower ends of the vertical portions 11 and 21. The two vertical portions 11 and 21 face each other along the horizontal direction and the two horizontal portions 12 and 22 face the ground electrode 50 along the vertical direction.

The two horizontal portions 12, 22 are arranged in a direction away from each other at the ends of the vertical portions 11, 21. That is, when the first driving electrode 10 is arranged in a letter shape, the second driving electrode 20 is arranged in a U-shape, and the first and second driving electrodes 10, Facing each other symmetrically.

The corners where the vertical portions 11 and 21 and the horizontal portions 12 and 22 contact with each other are rounded with a predetermined curvature so that the electric field can be prevented from concentrating on the corners. In FIGS. 1 and 2, the vertical portions 11 and 21 and the horizontal portions 12 and 22 contact each other vertically for convenience.

The gas distributor 80 is located above the central slit 30 and injects the discharge gas into the central slit 30. The discharge gas includes an inert gas, such as helium or argon, which induces a homogeneous discharge. The discharge gas discharged from the gas distributor 80 flows into the discharge space 40 between the first and second driving electrodes 10 and 20 and the substrate 60 after passing through the center slit 30, Mixed.

The distance d1 between the first and second driving electrodes 10 and 20 and the ground electrode 50 is smaller than the distance d2 between the first driving electrode 10 and the second driving electrode 20. [ The thickness t1 of the bottom wall facing the horizontal portions 12 and 22 of the dielectric 70 toward the discharge space 40 is equal to the thickness t2 of the inner wall facing the vertical portions 11 and 21 and facing the central slit 30 ).

According to the above-described shape condition, the plasma discharge is generated in the discharge space 40 between the first and second driving electrodes 10 and 20 and the ground electrode 50, not inside the reactor corresponding to the center slit 30, And is maintained only in the discharge space 40 without diffusing toward the inside of the reactor. In this case, since the seed electrons and the surface charge also remain outside the reactor, a uniform discharge is induced in the discharge space 40.

Since the space between the inside of the reactor corresponding to the central slit 30 and the space between the two discharge spaces 40 connected to the central slit 30 is a portion where the ratio of the discharge gas is high but the electric field is applied unevenly, to be. Since the outer portion of the discharge space 40 is a portion having a high proportion of the outside air, the filament mode is also likely to occur.

The two discharge spaces 40 described above are not only a part where discharging is started first due to the shape characteristics described above but also discharge gas is directly supplied from the central slit 30 therebetween, Do. In addition, since the two discharge spaces 40 are portions where a strong and uniform electric field is applied, a uniform discharge can be realized.

The plasma generated in the discharge space 40 is mixed with the outside air flowing from the outside. At this time, the outside air does not contribute to a homogeneous discharge, but oxygen and nitrogen serving as a functionalization flow into the discharge space, Increases energy. That is, oxygen and nitrogen are introduced into the discharge space and the surface energy of the substrate 60 is increased by ion collision. Therefore, the surface of the substrate 60 can be effectively treated.

The vertical portions 11 and 21 and the horizontal portions 12 and 22 of the first and second driving electrodes 10 and 20 are formed in a rectangular shape having a predetermined area, 2 driving electrodes 10 and 20 along the longitudinal direction (the transverse direction in FIG. 3).

The substrate 60 to be processed can be transported along the direction in which the first and second driving electrodes 10 and 20 face each other (the transverse direction in FIG. 2). In this case, the uniformity of surface treatment of the substrate 60 depends only on the discharge uniformity along the longitudinal direction of the first and second driving electrodes 10, 20.

Since the discharge space 40 is formed along the longitudinal direction of the first and second driving electrodes 10 and 20, the discharge intensity can be uniformed along the longitudinal direction of the first and second driving electrodes 10 and 20, As a result, the large area substrate 60 can be uniformly surface-treated.

4 and 5 are photographs of a plasma discharge when the DBD reactor according to the first embodiment is driven. Figure 4 shows a side view of a DBD reactor, and Figure 5 shows a front view of a DBD reactor.

4, the plasma discharge is initiated in a discharge space between the first and second driving electrodes and the substrate to be processed at a low voltage (0.6 kV), and even at high voltages (1.0 kV and 1.5 kV) It can be confirmed that a plasma discharge occurs only between the driving electrode and the substrate to be processed.

5, no filament discharge was observed even at a high voltage of 1.5 kV, and the plasma discharge generated on the substrate to be processed exhibited excellent uniformity along the longitudinal direction of the first and second driving electrodes (the horizontal direction in FIG. 5) . Therefore, a defect-free surface treatment can be performed on a large-area substrate to be processed.

As described above, in the DBD reactor 100 of this embodiment, the plasma discharge is first started in the above-described discharge space 40 in which the electric field is uniformly applied while the ratio of the discharge gas is high, so that the uniform discharge can be maintained, The surface of the substrate 60 can be effectively treated by increasing the surface energy of the substrate 60 by the high-density oxygen and nitrogen radicals.

6 is a cross-sectional view of a DBD reactor according to a second embodiment of the present invention.

6, the DBD reactor 200 of the second embodiment is similar to the DBD reactor 200 of the first embodiment except that the first and second driving electrodes 101 and 201 have a constant horizontal width and a constant vertical width, And has a configuration similar to that of the first embodiment. The same reference numerals are used for the same members as in the first embodiment.

The distance d1 between the first and second driving electrodes 101 and 201 and the ground electrode 50 is the same as the distance d1 between the first driving electrode 101 and the second driving electrode 201, Is smaller than the distance d2. The thickness t1 of the bottom wall facing the ground electrode 50 of the dielectric 70 is smaller than the thickness t2 of the inner wall facing the central slit 30 and the thickness t3 of the outer wall is smaller than the thickness t2 And the thickness t1 of the bottom wall.

The plasma discharge is initiated in the discharge space 40 between the first and second driving electrodes 101 and 201 and the ground electrode 50 and does not spread toward the inside of the reactor and the discharge space 40 A uniform discharge can be maintained.

FIG. 7 is a graph showing a discharge behavior according to a time change in the DBD reactor of the first embodiment shown in FIG. 7 (A) shows a positive pulse section, and (B) shows a negative pulse section. The voltage of the first and second driving electrodes applied to the experiment was 1.0 kV, the frequency was 80 kHz, the flow rate of the discharge gas (helium) was 5 liter / min, and the interval between the dielectric and the substrate to be processed was 1 mm.

7, the discharge in the positive pulse section is initiated in the discharge space between the driving electrode and the ground electrode, and is not diffused to the inside of the reactor (center slit part) in the entire section, maintain. In addition, it can be confirmed that strong and local luminescence inducing the filament mode is not observed in the entire section.

FIG. 8 is a graph showing a discharge behavior according to a voltage magnitude in the DBD reactor of the first embodiment shown in FIG. The frequency of the drive voltage used in the experiment, the flow rate of the discharge gas (helium), and the distance between the dielectric and the substrate to be processed are the same as those in Fig.

Referring to FIG. 8, as the applied voltage increases, the plasma discharge expands toward the center of the reactor, and the plasma discharge is located closer to the center of the reactor in the positive pulse section than in the negative pulse section. However, no discharge inside the reactor corresponding to the central slit is observed in all the pulse sections.

In the above-described first and second embodiments, the alternating voltage applied to the first and second driving electrodes has a high frequency characteristic of 1 kHz or more. The drive frequency is related to the number of seed electrons left after the discharge is turned off. If the seed electrons completely disappear before the next dielectric breakdown, the breakdown voltage is increased, and in this case, discharge is easily initiated at the localized position, so that the filament discharge easily occurs. Since the number of seed electrons is proportional to the driving frequency, the DBD reactors 100 and 200 described above can cause a homogeneous discharge due to the high frequency driving of 1 kHz or more.

9 is a graph showing the emission spectrum of a DBD reactor measured using an emission spectrometer. Helium gas was used as the discharge gas, and the intensity unit of the vertical axis of the graph is arbitrary unit.

9, helium gas is used as a discharge gas, but the presence of nitrogen ions and oxygen radicals having a high density can be confirmed as the outside air flows into the discharge space.

Oxygen and nitrogen radicals form -COOH, -OH, and amine groups on the polymer surface to increase the surface energy of the polymer. In particular, oxygen radicals are known to be more effective in increasing the surface energy of polymers than nitrogen radicals. The high density of nitrogen and oxygen observed in FIG. 9 indicates that the DBD reactor of the present invention is effective for surface treatment of the substrate to be treated.

10 is an enlarged photograph showing the contact angle test results of the liquid on the substrate before and after the surface treatment. 10 (A) shows the surface before the surface treatment and (B) shows the surface treatment.

Referring to Fig. 10 (A), the contact angle of the liquid to the substrate to be processed before the plasma treatment is about 80 degrees. Referring to FIG. 10B, it can be seen that the contact angle of the liquid with respect to the substrate to be processed after the plasma treatment is approximately 10 degrees or less, and the contact angle with respect to the plasma before the plasma treatment is greatly reduced. The smaller contact angle of the liquid means that the surface energy of the substrate is increased.

Since the substrate to be processed formed of a polymer can not be sintered at a high temperature, the adhesion is greatly reduced as compared with glass. Thus, by increasing the surface energy of the polymer by surface treatment with a plasma, adhesion can be greatly improved when stacking other layers thereon. The substrate to be processed formed of a polymer can be used for a substrate of a bending display device or for other purposes.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Of course.

100, 200: Dielectric barrier discharge reactor
10, 101: first driving electrode 20, 201: second driving electrode
30: central slit 40: discharge space
50: ground electrode 60: substrate to be processed
70: Dielectric 80: Gas distributor

Claims (8)

First and second driving electrodes disposed opposite to each other with a center slit provided with a discharge gas therebetween and surrounded by respective dielectrics and to which the same voltage is applied; And
And a ground electrode disposed opposite to the first and second driving electrodes across the discharge space and supporting the substrate to be processed,
Wherein a distance between the first and second driving electrodes and the ground electrode is smaller than a distance between the first driving electrode and the second driving electrode,
Wherein a thickness of a bottom wall facing the discharge space in the dielectric is smaller than a thickness of an inner wall facing the central slit. delete The method according to claim 1,
Wherein the first and second driving electrodes are disposed to face each other along the horizontal direction,
Wherein the substrate to be processed is positioned below the first and second driving electrodes with the discharge space interposed therebetween. The method of claim 3,
Wherein each of the first and second driving electrodes comprises a vertical part and a horizontal part connected to a lower end of the vertical part,
Wherein the two horizontal portions are disposed in a direction away from each other at an end of the vertical portion. The method of claim 3,
Wherein each of the first and second driving electrodes has a constant vertical width and a constant horizontal width. 6. The method of claim 5,
Wherein the thickness of the outer wall of the dielectric is larger than the thickness of the bottom wall facing the discharge space and the thickness of the inner wall facing the central slit. 7. The method according to any one of claims 1 to 6,
Wherein the first and second driving electrodes receive the same alternating voltage having a driving frequency of 1 kHz or more. 7. The method according to any one of claims 1 to 6,
Each of the first and second driving electrodes has a predetermined length,
Wherein the substrate is transported along a direction in which the first and second driving electrodes face each other in a surface treatment process.

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