AMORPHOUS CARBON COATING METHOD FOR RUBBER ROLLER

Abstract

The present invention relates to a carbon coating method for a rubber roller, in which a DLC (Diamond-Like Carbon) coating is applied to the surface of the rubber roller using an ion source. In order to prevent problems such as surface cracks caused by heat and ultraviolet radiation generated during the plasma-based coating process, the method controls the coating cycle by distributing the coating time and aging time (also referred to as cooling time) into a single unit coating cycle.

Claims

1. A method for forming a DLC (Diamond-Like Carbon) coating layer on the surface of a rubber roller, the method comprising: alternately repeating a deposition process for forming the DLC coating layer and a cooling process, wherein the DLC coating layer is formed within a time range that does not cause deformation of the rubber roller surface, followed by a cooling period.

2. The method of claim 1, wherein a ratio of the deposition time to the cooling time for forming the DLC (Diamond-Like Carbon) coating layer is in the range of 1:1/3 to 1.

3. The method of claim 1, wherein the method for forming the DLC (Diamond-Like Carbon) coating layer comprises one of PECVD (Plasma Enhanced Chemical Vapor Deposition), ion plating, laser ablation, and filtered vacuum arc plasma.

4. The method of claim 1, wherein the DLC (Diamond-Like Carbon) coating layer is formed in a vacuum chamber, and the method comprises: loading the rubber roller into the vacuum chamber and performing vacuumization; performing plasma cleaning prior to vacuum deposition for forming the DLC coating layer, wherein the plasma cleaning is conducted by supplying an inert gas into the vacuum chamber and generating plasma, selecting a cleaning time in the range of 20 to 40 minutes, and providing a cooling time in the range of 15 to 30 minutes after the plasma cleaning.

5. The method of claim 4, wherein, after the cooling time following the plasma cleaning, a buffer layer is formed prior to the formation of the DLC (Diamond-Like Carbon) coating layer, the buffer layer comprises one of CrN and CrC, TiN and TiC, or WN and WC, and is formed using a PVD source equipped with a sputter target of one of Cr, Ti, or W; the formation of the CrN, TiN, or WN layer is carried out by applying power to the PVD source equipped with the sputter target and supplying an inert gas and nitrogen (N.sub.2), wherein only the inert gas is supplied at the initial stage and the nitrogen supply is gradually increased to form a gradient layer; the CrC, TiC, or WC layer is formed by applying power to the PVD source equipped with the sputter target and supplying an inert gas and a hydrocarbon gas; a cooling time is provided after the buffer layer formation; and a ratio of the buffer layer formation time to the cooling time is in the range of 1:1/3 to 1.

6. The method of claim 5, wherein, after forming the buffer layer, a hydrocarbon gas is supplied to a linear ion source and a bias is applied to the rubber roller to form a DLC (Diamond-Like Carbon) coating layer, wherein the coating is performed in three cycles, each comprising a coating time of 18 to 33 minutes and a cooling time of 8 to 33 minutes, and an additional coating is performed for 18 to 33 minutes, completing a total of four coating cycles.

7. The method of claim 6, wherein, in the final cycle of forming the DLC (Diamond-Like Carbon) coating layer, an additional cooling time of 8 to 33 minutes is provided after the 18 to 33-minute coating process.

8. The method of claim 4, wherein the plasma cleaning is carried out by supplying an inert gas such as Ar to the linear ion source at a flow rate of 50 to 300 sccm, applying a current of 0.5 to 2.0 A and a voltage of 1000 to 2000 V to generate plasma, and applying a bias current of 0.5 to 0.9 A and a bias voltage of 50 to 300 V to the rubber roller.

9. The method of claim 5, wherein the buffer layer is formed using a first and a second sputter source, and the method comprises: (Step 1) supplying an inert gas into a vacuum chamber at a flow rate of 100 to 300 sccm, applying a current of 5 to 20 A and a voltage of 300 to 1000 V to the first and second sputter sources, and applying a bias current of 0.3 to 0.5 A and a bias voltage of 50 to 300 V to the rubber roller for 7.5 to 8.5 minutes; (Step 2) supplying an inert gas at 100 to 300 sccm and nitrogen gas at 6 to 8 sccm, applying a current of 5 to 20 A and a voltage of 300 to 1000 V to the first and second sputter sources, and applying a bias current of 0.25 to 0.35 A and a bias voltage of 50 to 300 V to the rubber roller for 3.5 to 4.5 minutes; (Step 3) supplying an inert gas at 100 to 300 sccm and nitrogen gas at 9 to 11 sccm, applying the same power conditions, and applying a bias current of 0.3 to 0.5 A and a bias voltage of 50 to 300 V to the rubber roller for 3.5 to 4.5 minutes; (Step 4) supplying an inert gas at 100 to 300 sccm and nitrogen gas at 12 to 14 sccm, applying a current of 5 to 20 A and a voltage of 300 to 1000 V to the sputter sources, and applying a bias current of 0.3 to 0.5 A and a bias voltage of 50 to 300 V to the rubber roller for 3.5 to 4.5 minutes; (Step 5) supplying an inert gas at 100 to 300 sccm and a hydrocarbon gas at 15 to 17 sccm, applying the same current and voltage to the sputter sources, and applying a bias current of 0.3 to 0.5 A and a bias voltage of 50 to 300 V to the rubber roller for 6.5 to 7.5 minutes; and providing a cooling time of 18 to 22 minutes after the steps above.

10. The method of claim 3, wherein the DLC (Diamond-Like Carbon) coating layer is formed using a linear ion source, and a current of 0.5 to 2.0 A and a voltage of 1000 to 2000 V are applied to the linear ion source, a hydrocarbon gas is supplied at a flow rate of 50 to 200 sccm, and a bias current of 0.5 to 0.7 A and a bias voltage of 50 to 300 V are applied to the rubber roller to form the DLC coating layer, wherein the coating is performed in three cycles, each consisting of a coating time of 18 to 33 minutes and a cooling time of 8 to 33 minutes, and an additional coating is performed for 18 to 33 minutes, completing a total of four coating cycles.

11. The method of claim 10, wherein, after the 18 to 33-minute coating process in the fourth and final cycle, an additional cooling time of 8 to 33 minutes is provided.

12. The method of claim 6, wherein a gas containing F or a gas containing Si is additionally supplied to the linear ion source to form a DLC (Diamond-Like Carbon) coating layer doped with F or Si.

13. A rubber roller manufactured by the method according to claim 12, wherein the DLC (Diamond-Like Carbon) coating layer formed on the rubber roller has a surface roughness (Ra) in the range of 0.61 to 0.68 m.

14. A DLC (Diamond-Like Carbon) coating material formed on the surface of a rubber roller, the coating material being manufactured by the method according to claim 12.

15. The DLC (Diamond-Like Carbon) coating material of claim 14, wherein the coating material has a surface roughness (Ra) in the range of 0.61 to 0.68 m on the surface of the rubber roller.

16. A coating system for forming a DLC (Diamond-Like Carbon) coating layer on the surface of a rubber roller, the system comprising: a vacuum chamber; a linear ion source and a sputter source installed in the vacuum chamber; an ion guiding device including a magnet or an electromagnet installed in the linear ion source to densify ions and plasma toward the rubber roller to be coated; a raw material supply unit for supplying material to the linear ion source; a jig for fixing and rotating the rubber roller; a power supply unit for supplying power to the linear ion source and the sputter source and for applying bias power to the rubber roller; and a process control unit for alternately performing coating and cooling processes; wherein the process control unit controls the power supply such that the deposition and cooling processes for forming the DLC coating layer are alternately repeated, thereby forming the DLC coating layer within a time range that does not deform the surface of the rubber roller, and subsequently providing a cooling period.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG. 1 is a photograph showing the surface hardening issue of a rubber roller and the occurrence of cracks and breakage in the coating layer formed by conventional techniques.

[0051] FIG. 2 is a schematic diagram illustrating the hybrid plasma coating system according to the present invention.

[0052] FIG. 3 is a photograph showing the surface of a rubber roller before and after carbon coating is applied according to the present invention.

[0053] FIG. 4 is a microscopic photograph showing that stains (scratches) originally present on the surface of the rubber roller are covered by the carbon coating according to the present invention.

[0054] FIG. 5 is a photograph showing the result of an adhesion test (indentation test) performed on the carbon-coated surface of a rubber roller according to the present invention.

[0055] FIG. 6 is a photograph showing the result of a tilting test performed on the carbon-coated surface of a rubber roller according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0056] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0057] The rubber roller having a DLC (Diamond-Like Carbon) coating layer formed according to the present invention is an industrial rubber roller applicable to various industries, including secondary battery electrode manufacturing.

[0058] The rubber material may include various types such as NBR, EPDM, silicone, and polyurethane (PU).

[0059] FIG. 1 is a photograph showing surface hardening of a rubber roller and the occurrence of cracks and breakage in the coating layer formed by conventional techniques. It illustrates that scratches occur on films produced using rubber rollers due to surface hardening, and that cracks appear in the DLC coating layer applied using an ion source, with breakage observed during tilting tests.

[0060] These issues occur even when the coating process is performed at room temperature, because the ions and plasma supplied into the chamber by the ion source generate heat and ultraviolet radiation, resulting in an actual process temperature of approximately 70 to 80 C. In other words, although the process starts at room temperature, the heat generated during coating deforms the rubber roller surface, and the ultraviolet radiation emitted by the plasma further contributes to such deformation.

[0061] Therefore, in order to form a DLC (Diamond-Like Carbon) coating layer on the rubber roller surface without cracks, the present invention adopts a method in which the coating and aging (cooling) processes are alternately performed as a single unit cycle to control heat generation during the coating process. Specifically, by maintaining the ratio of the coating time to the cooling time within the range of 1:1/3 to 1, deformation of the rubber roller is prevented during the coating process. This alternating method of coating and aging can be applied to various DLC coating processes, including PECVD (Plasma Enhanced Chemical Vapor Deposition), ion plating, laser ablation, and filtered vacuum arc plasma.

[0062] The present invention is based on PECVD (Plasma Enhanced Chemical Vapor Deposition) using a linear ion source and performs DLC (Diamond-Like Carbon) coating by employing a hybrid plasma coating system that includes an additional PVD (Physical Vapor Deposition) source (sputter source) for forming a buffer layer. The buffer layer may include combinations such as CrN/CrC, TiN/TiC, or WN/WC.

[0063] FIG. 2 is a schematic diagram illustrating the hybrid plasma coating system according to the present invention.

[0064] The hybrid plasma coating system combines a PVD source and a linear ion source. The linear ion source is further equipped with an ion guiding device based on a magnet or electromagnet, which densifies the generated plasma around the rubber roller to be coated. Two PVD sources and two linear ion sources may be arranged, and these sources can be radially positioned within the chamber.

[0065] The DLC (Diamond-Like Carbon) coating process for a rubber roller using the hybrid plasma coating system is as follows.

[0066] The rubber roller is loaded into the chamber and vacuumized to a pressure of 10.sup.4 to 10.sup.3 torr. At room temperature, an inert gas such as Ar is supplied to the linear ion source at a flow rate of 50 to 300 sccm, and a current of 0.5 to 2.0 A and a voltage of 1000 to 2000 V are applied to generate plasma for plasma cleaning. A bias current of approximately 0.5 to 0.9 A and a bias voltage of 50 to 300 V may be applied to the rubber roller. The shaft of the rubber roller, being metallic, may be used to apply the bias. The cleaning time is selected within the range of 20 to 40 minutes, and a cooling time of 15 to 30 minutes is provided after plasma cleaning. The cleaning time is determined within a range that does not cause deformation of the rubber roller surface, and the cooling step is applied thereafter to protect the surface. The cooling period may be achieved by pausing the process or by supplying an inert gas at room temperature at a flow rate of 80 to 100 sccm.

[0067] After the cleaning step, a buffer layer is formed using the PVD source of the plasma coating system.

[0068] The buffer layer is composed of a CrN layer and a CrC layer; specifically, the CrN layer is formed on the base material, followed by the CrC layer. Power is applied to the PVD source equipped with a Cr sputter target, and an inert gas such as Ar and nitrogen (N.sub.2) are supplied. The process is carried out while applying a bias to the rubber roller. After the buffer layer is formed, a cooling period is again provided.

[0069] During the formation of the CrN layer, only an inert gas (Ar) is initially supplied, and the nitrogen supply is gradually increased to form a gradient layer. In the final stage of the buffer layer formation, a hydrocarbon gas is supplied to improve adhesion.

Specifically:

[0070] (Step 1) An inert gas is supplied at 100 to 300 sccm. A current of 5 to 20 A and a voltage of 300 to 1000 V are applied to both the first and second sputter sources (the voltage for the second sputter source may be slightly higher). A bias current of 0.3 to 0.5 A and a bias voltage of 50 to 300 V are applied to the rubber roller, and the process is conducted for 7.5 to 8.5 minutes. [0071] (Step 2) An inert gas (100 to 300 sccm) and nitrogen gas (6 to 8 sccm) are supplied. A current of 5 to 20 A and a voltage of 300 to 1000 V are applied to the sputter sources (the voltage for the second sputter source may be slightly lower). A bias current of 0.25 to 0.35 A and a bias voltage of 50 to 300 V are applied to the rubber roller, and the process is carried out for 3.5 to 4.5 minutes. [0072] (Step 3) An inert gas (100 to 300 sccm) and nitrogen gas (9 to 11 sccm) are supplied. A current of 5 to 20 A and a voltage of 300 to 1000 V are applied to the sputter sources. A bias current of 0.3 to 0.5 A and a bias voltage of 50 to 300 V are applied to the rubber roller, and the process is performed for 3.5 to 4.5 minutes. [0073] (Step 4) An inert gas (100 to 300 sccm) and nitrogen gas (12 to 14 sccm) are supplied. A current of 5 to 20 A and a voltage of 300 to 1000 V are applied to the sputter sources (the voltage for the second sputter source may be slightly higher). A bias current of 0.3 to 0.5 A and a bias voltage of 50 to 300 V are applied to the rubber roller, and the process is conducted for 3.5 to 4.5 minutes. [0074] (Step 5) An inert gas (100 to 300 sccm) and a hydrocarbon gas (C.sub.2H.sub.2) at 15 to 17 sccm are supplied. A current of 5 to 20 A and a voltage of 300 to 1000 V are applied to the sputter sources. A bias current of 0.3 to 0.5 A and a bias voltage of 50 to 300 V are applied to the rubber roller, and the process is conducted for 6.5 to 7.5 minutes.

[0075] After these steps, a cooling time of 18 to 22 minutes is provided. During this period, either an inert gas at room temperature is supplied, or the system is placed in a resting state without gas supply.

[0076] In the above, when the buffer layer is composed of TiN/TiC, the same process is carried out using a Ti target in the sputter source. Likewise, when the buffer layer is composed of WN/WC, the process is performed using a W target in the sputter source.

[0077] Next, a DLC (Diamond-Like Carbon) coating is applied onto the buffer layer.

[0078] In this method, a current of 0.5 to 2.0 A and a voltage of 1000 to 2000 V are applied to each of the linear ion sources (two linear ion sources are used in this embodiment). A hydrocarbon gas such as C.sub.2H.sub.2 is supplied at a flow rate of 50 to 200 sccm. A bias current of 0.5 to 0.7 A and a bias voltage of 50 to 300 V are applied to the rubber roller to form the DLC (Diamond-Like Carbon) coating. The coating is performed over four cycles, each consisting of a coating time of 18 to 33 minutes followed by a cooling time of 8 to 33 minutes. In the final cycle, the cooling time following the 18 to 33-minute coating may be omitted.

[0079] In this manner, by alternately performing coating and aging steps, a high-quality DLC (Diamond-Like Carbon) coating can be formed on rubber materials that are highly susceptible to thermal deformation.

[0080] Meanwhile, one or more of a hydrocarbon gas, CF.sub.4 gas, and a silicon-containing gas such as TMS (tetramethylsilane), SiH.sub.4, Si.sub.2H.sub.6, or SiH.sub.2Cl.sub.2 may be supplied to the raw material supply unit of the linear ion source. In addition, hydrogen (H.sub.2) may be further supplied to create a reducing atmosphere. By repeating the coating and cooling steps under these conditions, a ternary nanocomposite coating layer can be formed on the surface of the rubber roller.

[0081] The above process is carried out using the following coating system.

[0082] The above process is carried out using a coating system comprising: [0083] a vacuum chamber; [0084] a linear ion source and a sputter source mounted in the vacuum chamber; [0085] an ion guiding device, including a magnet or an electromagnet, installed in the linear ion source to densify ions and plasma toward the rubber roller to be coated; [0086] a raw material supply unit for supplying material to the linear ion source; [0087] a jig for fixing and rotating the rubber roller; [0088] a power supply unit for supplying power to the linear ion source, the sputter source, or the ion guiding device, and for applying bias power to the rubber roller; and [0089] a process control unit for alternately performing coating and cooling processes; [0090] wherein the process control unit controls the power supply such that the deposition and cooling processes for forming the DLC (Diamond-Like Carbon) coating layer are alternately repeated, thereby forming the DLC coating layer within a time range that does not deform the surface of the rubber roller, and subsequently providing a cooling period.

[0091] The process control unit also controls the plasma cleaning and buffer layer formation processes, as described above, by alternately allocating process time and aging time (cooling time).

[0092] The surface roughness of the DLC (Diamond-Like Carbon) coating layer manufactured according to the present invention is Ra in the range of 0.61 to 0.68 m, Rz in the range of 3.74 to 3.84 m, and Ry in the range of 4.46 to 4.73 m.

[0093] The thickness of the DLC (Diamond-Like Carbon) layer may be in the range of 0.3 to 5.0 m, and the thickness of the buffer layer may be in the range of 0.2 to 1.0 m.

[0094] In addition, according to the present invention, the DLC (Diamond-Like Carbon) coating layer formed on the surface of the rubber roller has enhanced durability, with a hardness in the range of 13.5 to 28 GPa and 1300 to 2700 Hv, thereby ensuring long-term service life.

[0095] In the above, when forming the DLC (Diamond-Like Carbon) coating layer, a gas containing F and/or a gas containing Si may additionally be supplied to the linear ion source to form F-DLC, Si-DLC, or DLC doped with both F and Si.

[0096] FIG. 3 is a photograph showing the surface of a rubber roller before and after carbon coating is applied according to the present invention. It can be visually confirmed that the coated surface is uniform and of high quality.

[0097] FIG. 4 is a microscopic photograph showing that stains (scratches) originally present on the surface of the rubber roller are covered by the carbon coating according to the present invention.

[0098] FIG. 5 is a photograph showing the result of an adhesion test (indentation test) conducted on the carbon-coated surface of a rubber roller according to the present invention. The test results indicated HF1 and HF3 levels.

[0099] FIG. 6 is a photograph showing the result of a tilting test conducted on the carbon-coated surface of a rubber roller according to the present invention. No breakage of the coating is observed during tilting, even under optical microscope observation.

[0100] In this manner, a high-quality DLC (Diamond-Like Carbon) coating layer having high hardness, low friction, and excellent chemical resistance can be effectively implemented on the surface of a rubber roller, which is vulnerable to heat.

[0101] Unless otherwise defined, all technical and scientific terms used in the present specification have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries should be interpreted as having meanings consistent with their ordinary usage in the relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined otherwise. Throughout the specification, when a component is referred to as being included or comprising another component, it does not exclude the possibility of including additional components unless otherwise explicitly stated. Also, the singular forms shall include the plural forms unless the context clearly dictates otherwise.

[0102] In addition, in the present specification, expressions such as on, above, or upper and under or lower refer to positions relative to the target part, and do not necessarily mean positions located in the upward or downward direction with respect to gravity.

[0103] The scope of rights of the present invention is not limited to the embodiments described above but is defined by the claims. It will be apparent to those skilled in the art that various modifications and variations can be made within the scope of the claims.

INDUSTRIAL APPLICABILITY

[0104] The present invention is applicable to industrial rubber-coated rollers, including rubber-coated rollers used in secondary battery manufacturing processes, various rubber-coated rollers employed in film production industries, and wringer rollers used in acid cleaning lines for metal surface treatment.