Multilayer-structured aluminum nitride and aluminum oxide film coated product and production method thereof

Abstract

The present invention is a metallic material coated with multilayer-structured aluminum nitride and aluminum oxide films. The coating is applied using physical vapor deposition techniques onto the metallic material to prevent discoloration and tarnishing when exposed to air. Additionally, the coated layers enhance the strength of the coated metal.

Description

[0001] Description

[0002] Title of Invention

[0003] MULTILAYER-STRUCTURED ALUMINUM NITRIDE AND ALUMINUM OXIDE FILM COATED PRODUCT AND PRODUCTION METHOD THEREOF

[0004] Technical Field

[0005] Material science, specifically related to multilayer-structured aluminum nitride and aluminum oxide film coated product.

[0006] Background Art

[0007] Silverware is a top-ranking export product in the jewelry and gem sector of the country. Besides being designed as jewelry, silver is also used to create souvenirs for significant events that reflect Thai identity, such as souvenirs for the Asia-Pacific Economic Cooperation (APEC) 2022 meetings. However, a common problem faced by silverware manufacturers and producers is tarnishing and discoloration, which affects the brightness, gloss, and color of silver jewelry, leading to dark stains. Tarnishing occurs when pure silver or silver alloy comes into contact with an atmosphere containing sulfur components, such as hydrogen sulfide (EES), resulting in the formation of silver sulfide (Ag?S), which coats the surface of the silver with a black layer, causing it to lose its luster.

[0008] Currently, silver manufacturers employ three methods to slow down or prevent tarnishing:

[0009] L Alloying with Precious Metals or Semi-Metals: Alloying with metals such as palladium or semi-metals such as germanium can help delay tarnishing.

[0010] 2. Electroplating with Corrosion-Resistant Metals: Electroplating with metals that have a similar appearance to silver and resist corrosion, such as rhodium or palladium, can prevent silver from coming into contact with the atmosphere. However, this can alter the color of the silver according to the metal used for plating.

[0011] 3. Coating or Spraying with Transparent Polymers: Coating with transparent polymers such as hexadecanethiol self-assembled monolayers (SAM) or lacquers can effectively prevent tarnishing, although there may be slight changes in brightness and color. Additionally, polymers can peel off and degrade when exposed to heat or ultraviolet light from the environment. Further to prior inventions, the U.S. patent application number US20090004386A1 discusses preventing silver tarnish by depositing a thin metal oxide film using atomic layer deposition (ALD) techniques. Trimethylaluminum ((CFhjsAl) is used as a precursor with water to form an aluminum oxide (AI2O3) film with a thickness of 0.1 nanometers per cycle on silver, at temperatures between 80 to 400°C, with the optimal temperature being 200°C and an appropriate film thickness of 2 to 20 nanometers. Other possible metal oxides for deposition include titanium dioxide (TiO?), chromium oxide (CUCh), zirconium oxide (ZrO?), indium oxide (ImCh), or niobium oxide (btuOs).

[0012] U.S. patent application number US20110217564A1 describes a method for coating metal surfaces to prevent tarnish using a three-layer film. The first layer involves removing tarnish caused by sulfur gas by immersing in a solvent containing nanoparticles such as silver, diamond, platinum, silica, and corundum, using ultrasonic techniques for uniform dispersion and rapid drying with air. The second layer involves coating with aluminum oxide and titanium oxide films to prevent tarnishing using various techniques including ALD, plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), or Sol-gel techniques. The third layer involves polymer coating under vacuum conditions mixed with silver nanoparticles or porous silica containing silver or erbium nanoparticles using ALD.

[0013] U.S. patent application number US20210348270A1 describes a coating process for preventing tarnish on precious and non-precious metals, including metals plated with precious metals. The coating process consists of three layers: the first layer is a silver-copper alloy containing 0.1 to 10% copper by weight with a thickness of 1-3 micrometers. The second layer is aluminum oxide (AI2O3) with a thickness of 0.5 to 100 nanometers. The third layer is titanium dioxide (TiCL) with a thickness of 0.5 to 100 nanometers, using ALD or PVD techniques.

[0014] Thai patent application number 1801003771A describes a process to reduce tarnish on silver jewelry using ion implantation in a vacuum system that generates nitrogen ions and directly bathes the silver jewelry, resulting in a chemical reaction with the silver surface to form silver nitride (AgNs), improving the mechanical properties of the silver surface, making it scratch-resistant and tarnish-free in use.

[0015] Thai patent application number 2301004700 discusses coating silver surfaces with aluminum nitrides using PVD techniques, producing an aluminum nitride film with a thickness of 70-200 nanometers. When silver coated with aluminum nitride film was tested for tarnish resistance in an environment with 75 ml / m3hydrogen sulfide gas for 6 hours, the silver coated with aluminum nitride film showed no significant color change to the average observer. Additionally, when left in the atmosphere for 2 months, the coated silver showed no significant color change to the average observer.

[0016] From the aforementioned, various methods for preventing tarnish and discoloration on metals are noted. Chemical methods require the use of chemicals in the coating process, posing dangers to both manufacturers and consumers. Moreover, the adhesion of the film to the material is lower compared to physical vapor deposition methods, leading to film peeling. In the case of PVD techniques to prevent tarnishing and discoloration of metals, there are no reports of climate testing results according to DIN-Norm 9022-2 standards. This test involves placing samples in a controlled environment at 55°C and 92% relative humidity for 120 hours. Samples passing this climate test indicate the ability to prevent tarnish and discoloration in actual use.

[0017] The inventors have developed a multilayer-structured aluminum nitride and aluminum oxide film coating process to prevent discoloration of silver, silver-coated metals, and other metals. This process not only prevents tarnish on silver, silver-coated metals, and other metals but also increases hardness, scratch resistance, and prevents color change when tested by the climate test method according to DIN-Norm 9022-2 standards.

[0018] Summary of Invention

[0019] The product is characterized as a metallic material coated with a multilayer-structured film of aluminum nitride and aluminum oxides using physical vapor deposition (PVD) techniques on a metallic substrate.

[0020] The objective of this invention is to prevent the discoloration of metallic materials made from silver and other metals by coating them with a multilayer-structured film of aluminum nitride and aluminum oxides using PVD techniques. This coating method ensures strong adhesion to the surface of the material, preventing easy peeling. It helps protect against discoloration, ultraviolet (UV) light, and chemical reactions with the air, which are the main causes of surface discoloration of the metallic material.

[0021] Detailed Description of the Invention The multilayer-structured aluminum nitride and aluminum oxide film coating process comprises the following steps: a. Coating the metallic surface from an aluminum target using physical vapor deposition techniques: The metallic material, after undergoing surface cleaning, is placed in the vacuum chamber of the physical vapor deposition machine. b. Coating the metallic surface with the first film layer using physical vapor deposition techniques: Argon and nitrogen gases are released at a flow rate ratio of 45-55:45-55, respectively. The metallic material is heated to a temperature of 55-65°C, and an electric current of 3-6 amperes is applied to the aluminum target, resulting in an aluminum nitride film on the metallic surface with a thickness of 1-65 nanometers, preferably 35-50 nanometers. c. Coating the metallic surface with the second film layer using physical vapor deposition techniques: Argon and oxygen gases are released at a flow rate ratio of 45- 55:45-55, respectively. The metallic material is heated to a temperature of 55-65°C, and an electric current of 3-6 amperes is applied to the aluminum target, resulting in an aluminum oxide film with a thickness of 1-100 nanometers, preferably 40-70 nanometers. d. Coating the metallic surface with the third film layer using physical vapor deposition techniques: Argon and nitrogen gases are released at a flow rate ratio of 45-55:45-55, respectively. The metallic material is heated to a temperature of 55-65°C, and an electric current of 3-6 amperes is applied to the aluminum target, resulting in an aluminum nitride film on the metallic surface with a thickness of 1-65 nanometers, preferably 35-50 nanometers. e. Coating the metallic surface with the fourth film layer using physical vapor deposition techniques: Argon and oxygen gases are released at a flow rate ratio of 45-55:45-55, respectively. The metallic material is heated to a temperature of 55-65°C, and an electric current of 3-6 amperes is applied to the aluminum target, resulting in an aluminum oxide film with a thickness of 1-100 nanometers, preferably 40-70 nanometers.

[0022] The metal that has undergone the coating process exhibits the following characteristics: The metal is coated with a multilayer-structured film of aluminum nitride and aluminum oxides, with a total film thickness ranging from 4 to 330 nanometers, preferably 150 to 240 nanometers.

[0023] The first coating layer is an aluminum nitride film with a thickness ranging from 1 to 65 nanometers, preferably 35 to 50 nanometers.

[0024] The second coating layer is an aluminum oxide film with a thickness ranging from 1 to 100 nanometers, preferably 40 to 70 nanometers.

[0025] The third coating layer is an aluminum nitride film with a thickness ranging from 1 to 65 nanometers, preferably 35 to 50 nanometers.

[0026] The fourth coating layer is an aluminum oxide film with a thickness ranging from 1 to 100 nanometers, preferably 40 to 70 nanometers.

[0027] Experimental Results

[0028] The coating of the metallic material was performed using DC magnetron sputtering with multilayer-structured aluminum nitride and aluminum oxide films. The color measurements were conducted using the CIE Lab* color system, where the three variables are defined as follows: L* indicates lightness, with values ranging from 0 to 100 (0 is black and 100 is white); a* describes the color axis from green (negative a*) to red (positive a*); b* describes the color axis from blue (negative b*) to yellow (positive b*). The color difference (AE) was calculated by comparing the samples with a reference silver metal, as shown in Table 1.

[0029] When the color difference (AE) was calculated compared to the reference silver metal (Sample 1), it was found that Sample 2, Sample 3, Sample 4, and Sample 5 had AE values of 0.30, 0.52, 0.80, and 1.11 , respectively. The AE value must be less than 2.50, indicating no significant color change for the average observer.

[0030] When Sample 5 was further coated with a fifth layer of aluminum nitride film with a thickness of 45 nanometers and a sixth layer of aluminum oxide film with a thickness of 60 nanometers, the color difference (AE) compared to the reference silver metal (Sample 1 ) was 2.05 . The AE value must be less than 2.50 , indicating no significant color change for the average observer. However, the six-layer film coating process took more than 3 hours, which is impractical for industrial applications. Therefore, this invention selects a coating process with four layers of multilayer-structured aluminum nitride and aluminum oxide films. Table 1 : Color Difference (AE) of Silver Coated with Multilayer-structured

[0031] Aluminum Nitride and Aluminum Oxide Films

[0032] Coating of the metallic material using DC magnetron sputtering with multilayer- structured aluminum nitride and aluminum oxide films results in the hardness of the material, as shown in Table 2. It was found that the hardness of silver increases when coated with multilayer-structured aluminum nitride and aluminum oxide films.

[0033] Table 2: Hardness of Reference Silver and Silver Coated with Multilayer-structured

[0034] Aluminum Nitride and Aluminum Oxide Films

[0035] When Sample (6), which is uncoated silver, and Sample (5), which is silver coated with multilayer-structured aluminum nitride and aluminum oxide films (as described in Table 2 ) , were subjected to a climate test to evaluate their ability to prevent color shade changes, the test conditions were set according to DIN-Norm 9 0 2 2 -2 standards. The test conditions included a temperature of 55 ° C, a relative humidity of 92% , and a duration of 120 hours.

[0036] After the climate test, the color measurements of Samples (5) and (6) were compared to the reference silver (Sample 1) and the color difference (AE) was calculated, as shown in Table 3.

[0037] It was found that Sample (6) had a color difference (AE) of 7.31, whereas Sample (5) had a color difference (AE) of 1 .61 . A AE value less than 2.50 indicates no significant color change for the average observer.

[0038] Table 3 : Color Difference (AE) of Samples (5 ) and (6 ) Tested for Color Shade Change Prevention Using the Climate Test According to DIN-Norm 9022-2

[0039] Best Mode for Carrying Out the invention

[0040] As described in the Detailed Description of the Invention.

Claims

AMENDED CLAIMS received by the International Bureau on 23 September 2025 (23.09.2025)Claims1. A multilayer-structured aluminum nitride and aluminum oxide film coated product, comprising a metallic material, which is selected from a silver or silver alloy, coated with four layers of aluminum nitride and aluminum oxide films. The first layer is the one in contact with the surface of the metallic material, wherein each of the layer is as follows: the first layer is an aluminum nitride film; the second layer is an aluminum oxide film; the third layer is an aluminum nitride film; the fourth layer is an aluminum oxide film, wherein the total thickness of the four layers is preferably in the range of 150 to 240 nanometers. wherein the thickness of the aluminum nitride film layer is preferably in the range of 35 to 50 nanometers, and the thickness of the aluminum oxide film layer is preferably in the range of 40 to 70 nanometers.

2. The multilayer-structured aluminum nitride and aluminum oxide film coated product according to claim 1, wherein the metallic material is selected from such products as jewelry or metallic appliances.

3. The multilayer-structured aluminum nitride and aluminum oxide film coated product according to claim 2, wherein the jewelry or metallic appliances are selected from rings, earrings, or necklaces.

4. A production method of a multilayer-structured aluminum nitride and aluminum oxide films coated product according to any one of claims 1 to 3, comprising the following steps: a. Coating the surface of the metallic material from an aluminum target using physical vapor deposition techniques, wherein the metallic material, after surface cleaning, is placed in the vacuum chamber of the physical vapor deposition machine; b. Coating the surface of the metallic material with the first film layer using physical vapor deposition techniques by releasing argon and nitrogen gases,heating the metallic material, and applying an electric current to the aluminum target to form an aluminum nitride film on the metallic material; c. Coating the surface of the metallic material with the second film layer using physical vapor deposition techniques by releasing argon and oxygen gases, heating the metallic material, and applying an electric current to the aluminum target to form an aluminum oxide film; d. Coating the surface of the metallic material with the third film layer using physical vapor deposition techniques by releasing argon and nitrogen gases, heating the metallic material, and applying an electric current to the aluminum target to form an aluminum nitride film on the metallic material; e. Coating the surface of the metallic material with the fourth film layer using physical vapor deposition techniques by releasing argon and oxygen gases, heating the metallic material, and applying an electric current to the aluminum target to form an aluminum oxide film.

5. The production method of a multilayer-structured aluminum nitride and aluminum oxide films coated product according to claim 4, wherein the physical vapor deposition techniques for coating the metallic material from an aluminum target is sputtering being the preferred technique.

6. The production method of a multilayer-structured aluminum nitride film coated product according to claims 4 or 5, wherein the flow rate ratio of argon and nitrogen gases is in the range of 45 to 55 : 45 to 55, respectively.

7. The production method of a multilayer-structured aluminum nitride and aluminum oxide films coated product according to any one of claims 4 to 6, wherein the heating temperature of the metallic material during coating is in the range of 55 to 65°C.

8. The production method of a multilayer-structured aluminum nitride and aluminum oxide films coated product according to any one of claims 4 to 7, wherein the electric current applied to the aluminum target is in the range of 3 to 6 amperes.

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