Vacuum Coating Process for Tableware Sets: Cups, Plates, Bowls, and Dishes – Procedures, Target Materials, and Gases for Different Colors

Vacuum coating has become a pivotal technology in the tableware manufacturing industry, offering enhanced aesthetics, durability, and functionality to everyday items like cups, plates, bowls, and dishes. This advanced process involves depositing thin films of various materials onto the surface of tableware under high-vacuum conditions, ensuring uniform coverage, adhesion, and resistance to wear, corrosion, and temperature changes. Below is a detailed breakdown of the vacuum coating process specifically tailored for tableware sets, along with the target materials (targets) and gases required to achieve different colors, ensuring both technical accuracy and practical applicability.

1. Pre-Coating Preparation

The success of vacuum coating largely depends on thorough pre-treatment, as contaminants on the tableware surface can compromise film adhesion and quality. This stage consists of three key steps: cleaning, drying, and loading. First, the tableware (cups, plates, bowls, dishes) undergoes ultrasonic cleaning using a mild alkaline detergent solution. This process effectively removes oil, dust, fingerprints, and residual manufacturing debris—common contaminants that can cause pinholes or peeling in the coating. The ultrasonic waves generate microscopic bubbles that implode, dislodging particles without scratching the tableware’s surface, which is crucial for preserving the base material (typically glass, ceramic, or food-grade plastic). After cleaning, the tableware is rinsed with deionized water to eliminate detergent residues, then dried in a vacuum oven at 80–120°C for 30–60 minutes. This step ensures complete moisture removal, as even trace water vapor can react with coating materials during the vacuum process, leading to defects. Finally, the dried tableware is carefully loaded onto rotating fixtures inside the vacuum chamber. The fixtures are designed to rotate 360 degrees, ensuring that all surfaces—including the inner walls of cups and the undersides of plates—receive uniform coating.

2. Vacuum Chamber Evacuation

Once the tableware is loaded, the vacuum chamber is sealed and evacuated to remove air and moisture. This step is critical because air molecules can interfere with the deposition of the coating film, leading to uneven thickness and poor adhesion. The evacuation process is performed in two stages: roughing and high vacuum. First, a rotary vane pump reduces the pressure inside the chamber to approximately 10⁻³ mbar (millibars), removing most of the air. Next, a diffusion pump or turbomolecular pump further lowers the pressure to 10⁻⁶ to 10⁻⁸ mbar, creating a high-vacuum environment. This ultra-low pressure minimizes collisions between coating particles and air molecules, allowing the particles to travel in straight lines from the target to the tableware surface. During evacuation, the temperature inside the chamber is gradually raised to 60–100°C to drive off any remaining moisture adsorbed on the tableware surface, ensuring optimal coating conditions.

3. Plasma Cleaning (Optional but Recommended)

For tableware made of materials with low surface energy (such as plastic or glass), plasma cleaning is an optional but highly recommended step to improve film adhesion. In this process, a small amount of inert gas (typically argon) is introduced into the vacuum chamber, and an electric field is applied to ionize the gas, creating a plasma. The plasma ions bombard the tableware surface, removing any remaining organic contaminants and activating the surface by increasing its roughness and surface energy. This activation process enhances the chemical bonding between the tableware and the coating film, reducing the risk of peeling or chipping during use. Plasma cleaning typically lasts 5–10 minutes, depending on the material of the tableware and the desired adhesion level.

4. Coating Deposition: Target Materials and Gases for Different Colors

The coating deposition process involves vaporizing or sputtering a target material and depositing it onto the tableware surface. The choice of target material and gas determines the color, finish, and properties of the coating. Below are the most common colors used for tableware, along with the corresponding target materials and gases:

4.1 Silver (Metallic Finish)

Silver is a popular choice for tableware due to its elegant metallic appearance and corrosion resistance. The target material used for silver coating is high-purity silver (Ag, 99.99% purity). The deposition method is typically magnetron sputtering, where a high-voltage electric field is applied to the silver target, causing silver atoms to be ejected (sputtered) into the vacuum chamber. Argon (Ar) is used as the sputtering gas, as it is inert and does not react with the silver target or the tableware surface. The argon ions bombard the silver target, dislodging silver atoms that then deposit onto the rotating tableware, forming a thin, uniform silver film (thickness: 50–100 nm). This coating is durable, scratch-resistant, and provides a bright, reflective finish suitable for formal and everyday use.

4.2 Gold (Metallic Finish)

Gold coating adds a luxurious touch to tableware, making it ideal for special occasions. The target material is high-purity gold (Au, 99.99% purity), and the deposition method is magnetron sputtering. Similar to silver coating, argon (Ar) is used as the sputtering gas to avoid chemical reactions. For a warmer gold tone, a small amount of copper (Cu) can be added to the gold target (Au-Cu alloy, 90% Au + 10% Cu). The coating thickness ranges from 50–150 nm, depending on the desired depth of color. Gold coatings are highly corrosion-resistant and maintain their luster even after repeated use and cleaning.

4.3 Rose Gold (Metallic Finish)

Rose gold is a trendy color for modern tableware, characterized by its warm, pinkish-gold hue. The target material is an alloy of gold, copper, and silver (Au-Cu-Ag, typically 75% Au + 20% Cu + 5% Ag). Magnetron sputtering is used, with argon (Ar) as the sputtering gas. The copper content in the alloy gives the coating its pinkish tone, while the silver enhances its brightness and durability. The coating thickness is usually 60–120 nm, ensuring a uniform, scratch-resistant finish that complements both contemporary and classic tableware designs.

4.4 Black (Matte or Glossy Finish)

Black coating is versatile, suitable for minimalist and modern tableware. Two common target materials are used: titanium nitride (TiN) and chromium nitride (CrN) for glossy black, or titanium carbonitride (TiCN) for matte black. For glossy black, magnetron sputtering is performed using a titanium (Ti) or chromium (Cr) target, with nitrogen (N₂) as the reactive gas. The titanium or chromium atoms react with nitrogen in the vacuum chamber to form TiN or CrN, which deposits onto the tableware as a glossy black film (thickness: 80–150 nm). For matte black, a titanium-carbon (Ti-C) target is used, with a mixture of nitrogen (N₂) and methane (CH₄) as reactive gases. The carbon content from methane creates a matte finish, while nitrogen enhances durability. Argon (Ar) is added as a sputtering gas to improve film uniformity.

4.5 Blue (Metallic or Iridescent Finish)

Blue coatings range from deep metallic blue to iridescent light blue, depending on the target material and coating thickness. For metallic blue, a cobalt (Co) target is used with oxygen (O₂) as the reactive gas, forming cobalt oxide (CoO) which deposits as a deep blue film (thickness: 70–120 nm). For iridescent blue, a titanium dioxide (TiO₂) target is used, with argon (Ar) as the sputtering gas. The thickness of the TiO₂ film is carefully controlled (100–200 nm) to create interference effects, resulting in a shimmering, iridescent blue finish. Alternatively, a silicon (Si) target with oxygen (O₂) can be used to form silicon dioxide (SiO₂), which, when deposited in thin layers, produces iridescent blue hues.

4.6 Red (Metallic Finish)

Red coatings for tableware are achieved using a copper oxide (CuO) target or a iron oxide (Fe₂O₃) target. For metallic red, a copper (Cu) target is used with oxygen (O₂) as the reactive gas, forming CuO which deposits as a bright red film (thickness: 90–150 nm). For a deeper red, an iron (Fe) target is used with oxygen (O₂), forming Fe₂O₃ (hematite) which has a rich, deep red color. Argon (Ar) is added as a sputtering gas to ensure uniform deposition. Red coatings are popular for festive tableware and add a vibrant touch to dining settings.

5. Post-Coating Treatment

After the coating is deposited, the vacuum chamber is gradually vented to atmospheric pressure to avoid damaging the coating due to sudden pressure changes. The tableware is then removed from the chamber and undergoes post-coating treatment to enhance durability and performance. This includes annealing in a low-temperature oven (100–150°C) for 30–60 minutes, which improves the adhesion of the coating film and reduces internal stresses. For tableware intended for food contact, a clear protective topcoat (typically SiO₂ or Al₂O₃) is applied using the same vacuum coating process. This topcoat is food-safe, scratch-resistant, and prevents the coating from reacting with food or cleaning agents. Finally, the tableware is inspected for coating uniformity, color consistency, and adhesion using specialized equipment such as a profilometer (for thickness measurement) and a cross-cut tester (for adhesion testing).

6. Quality Control and Packaging

Quality control is a critical final step to ensure that the coated tableware meets industry standards. Each piece is visually inspected for defects such as pinholes, scratches, uneven color, or peeling. Thickness measurements are taken at multiple points to ensure the coating meets the specified range (50–200 nm, depending on the color and material). Adhesion testing involves making a cross-hatch pattern on the coating with a sharp blade and applying adhesive tape—if the coating does not peel off, it passes the test. The tableware is also tested for food safety, ensuring that no harmful substances leach into food when in contact with the coating. Once approved, the coated tableware is carefully packaged in protective materials to prevent scratching during transportation and storage.