As a fundamental material for building decoration, ceramic tiles have surface quality that directly affects both the aesthetic appeal and the lifespan of a space. Traditional tile surface decoration mostly relies on glazes, screen printing, and three-dimensional firing techniques. While these can create certain colors and patterns, they have limitations when it comes to showcasing a metallic look, improving surface hardness, and resisting corrosion. With consumers upgrading their expectations, the market demand for tiles that combine metallic shine with excellent durability continues to grow.
The introduction of vacuum coating technology has opened up new possibilities for surface treatment of ceramic tiles. By borrowing the coating principles used for optical glass surfaces and modifying the related equipment—like adding ion bombardment cleaning systems and depositing transition layers—ceramic and other non-metal materials can be tightly bonded with metals like titanium and zirconium, forming corrosion-resistant or wear-resistant coatings. This technique is widely used in the deep processing of ceramic tile surfaces, producing dazzling effects in gold-like, platinum, and multicolor finishes, completely replacing products made from pure gold or platinum.
1.The technical principles and equipment setup of ceramic tile coating
1.1.Technical Principle
Vacuum coating for ceramic tiles mainly uses magnetron plasma multi-arc vacuum sputtering technology. The core principle is: under vacuum conditions, low-voltage, high-current arc discharge is used to evaporate the target material through gas discharge, ionizing both the evaporated material and the gas. Then, using the acceleration effect of the electric field, the evaporated material and its reaction products are deposited onto the surface of the workpiece.
Coating non-metal surfaces like ceramics is much trickier than coating conductive materials like metals. Since ceramics don’t conduct electricity, metal ions can’t deposit and bond the way they do on metal substrates. The fix is to add an ion cleaning system and a middle transition layer before the actual coating. By first depositing a metal transition layer, like titanium or chromium, the functional coating that comes next can stick firmly.
1.2.Typical Device Setup
Taking the 1400-type multi-arc magnetron coating machine used for ceramic tile coating as an example, the equipment mainly includes the following parts:
Vacuum chamber: 1400 mm in diameter, 1600 mm in height, made of 304 stainless steel with a double-layer water-cooled jacket structure.
Vacuum system: composed of a diffusion pump (pumping speed 9400 L/s), Roots pump (300 L/s), mechanical pumps , and a sustaining pump. It takes less than 30 minutes to pump from atmospheric pressure to working vacuum when empty, with a ultimate vacuum of up to 5×10⁻⁴ Pa.
Multi-arc targets: 12 in total, titanium cathodes sized φ90mm×40mm, individually powered and ignited independently.
Magnetron sputtering coating target: 1, with an internal magnetic field strength above 5000 Gauss.
Workpiece rotating fixture: 5-axis design, supporting both revolution and rotation to ensure uniform coating on the tile surface.
Ion bombardment system: DC 3000V, 5kW high-voltage bombardment power supply for pre-coating cleaning and activation.
Heating and temperature control system: 3 U-shaped infrared heating tubes, using PID-controlled silicon modules for temperature control.
2.The complete process of vacuum coating for ceramic tiles
(1) Substrate pretreatment and drying. Cleaning the surface of the tile is fundamental for coating quality. Usually, a clean cotton cloth with distilled water is used to wipe the surface to remove dust and grease. To improve efficiency and reduce the heating time in the vacuum chamber, the treated tiles need to be baked in an oven at around 250°C for at least 20 minutes, ensuring that all adsorbed water on the tile surface is completely evaporated.
(2) Loading and vacuuming. Quickly place the dried tiles onto the workpiece rack in the vacuum chamber. Start the rotation system to ensure it runs smoothly, then close the furnace door. The vacuuming is done in stages: first, use a mechanical pump and a Roots pump for a quick rough vacuum; when the vacuum reaches about 2×10⁻¹ Pa, switch to a diffusion pump for fine vacuuming, ultimately reaching a vacuum level around 3×10⁻³ Pa.
(3) Workpiece heating and degassing. Once the vacuum level is achieved, start rotating the workpieces and turn on the heating power. The tile temperature gradually rises (usually not exceeding 400°C). This heating step helps drive out any residual gas inside the substrate, preventing the outgassing from affecting the coating quality later.
(4) Ion cleaning and titanium base layer deposition. Argon is introduced, and the high-voltage bombardment system is activated to perform ion cleaning on the surface of the tiles. The bombardment voltage is generally 400-500V, and you can observe the discharge phenomenon through the viewing window to judge the cleaning effect. After cleaning is complete, adjust the current to 10-12A and the voltage to 600-800V to deposit a layer of titanium base on the tile surface, lasting about 2-3 minutes.
(5) Multi-arc deposition of titanium nitride (gold) or titanium (silver). After the titanium base layer is deposited, reduce the argon and fill with high-purity nitrogen. Under a vacuum of about 3×10⁻¹Pa to 6×10⁻¹Pa, start the multi-arc target for titanium nitride deposition for about 3-5 minutes to get a gold-like coating. If a silver effect is needed, just keep depositing the titanium layer in a argon atmosphere.
(6) Cooling and taking out. Once coating is complete, turn off the arc source and gases in order, let the workpiece cool down slightly, then fill with air up to atmospheric pressure, open the furnace and take out the product. A full production cycle takes about 15 to 20 minutes.
3.Core Strengths and Application Value
Outstanding decorative effect. Vacuum coating can create pure gold, silver, or rainbow colors on the surface of tiles, with even color and bright gloss. The surface shape can also be pre-designed according to design needs, and after coating, unwanted parts can be removed by polishing to produce artistic products with vivid textures and bright colors. Christoc tiles from Italy's Gardenia use PVD technology for gold and silver coating, effectively replicating the look of precious materials.
Significantly improved durability. Titanium nitride (TiN) and zirconium nitride (ZrN) coatings can reach thicknesses of 0.7 to 1.6 μm, and tests show they have good scratch resistance and corrosion stability, making them suitable for high humidity, daily washing, and household chemical cleaners. The coating adheres well, has a dense structure, and maintains long-lasting gloss.
Environmental protection and cost advantages. Compared with traditional real gold leafing or gold water printing, vacuum coating doesn’t use precious metal materials, produces no pollution, has a short processing time, and is low-cost, making it suitable for large-scale industrial production. The coating process takes place in a vacuum chamber, so there’s no pollution or noise.
Wide potential for functionality. Besides decorative purposes, by doping antibacterial elements like silver or copper into the PVD coating, the tile surfaces can gain significant sterilizing properties, making them suitable for medical spaces with strict hygiene requirements, such as operating rooms and patient wards.
4.Technical Challenges and Development Trends
Vacuum coating for ceramic tiles still faces some challenges. The difference in thermal expansion between the ceramic substrate and the metal coating can affect the long-term stability of the coating. Plus, the equipment is pretty expensive and requires operators to have good process control skills.
As high-ionization sputtering technologies like HiPIMS become more mature and domestic equipment improves, vacuum coating for ceramic tiles will expand further. It will evolve from just decorative coatings to 'functional coatings' that also offer antibacterial, self-cleaning, and wear-resistant properties, giving a big boost to the transformation and upgrading of the building ceramics industry.
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