Atomic Layer Deposition: Protection for Coins and Watches

The coin and watch industries are two traditional technology branches which can hugely benefit from Atomic Layer Deposition (ALD) technology.

ALD is a potential protection method for both numismatic and circulation coins, preventing them from the damage caused by corrosion and oxidation. The application of traditional protection techniques like lacquering may result in rippling effects and yellowing. Material waste and a negative environmental impact are often also the unwanted side effects of treatments based on wet chemistry. All these issues can be easily addressed with Picosun’s proven ALD technology.

Advantages of ALD Coating Technique

ALD is a gas phase coating technique, forming films on the nanoscale thickness with high structural integrity, conformality, uniformity, and repeatability. The advantages of this sophisticated thin film coating technique include:

  • 100% conformal, dense, crack, defect, and pinhole-free films
  • Low material wastage
  • Possibility to use non-toxic, non-allergenic oxide coating materials
  • Applies coating without causing damage to the coin surface
  • Environmentally safe as it does not produce adverse process waste
  • Comparatively low processing temperatures
  • Absence of undesired optical side effects
  • Film thickness and homogeneity can be exactly controlled
  • Desired coating can be achieved with much thinner layers
  • Does not cause heat damage even to sensitive metals

ALD Films for Minting Applications

ALD technology applies a homogenous coating at the microstructural level over the surface of a coin, thereby protecting the surface from ambient air, sweat, dirt, and moisture. It is possible to apply either a colored or a transparent film based on the film thickness and material. For coins, it is desired to preserve their original appearance which is why transparent coatings are typically preferred.

The ALD film formation process involves chemisorption reactions of gaseous precursors over the surface of the substrate to be coated. The characteristics of the ALD technology allow it to treat the processed objects more gently than other available techniques. In addition, the use of low processing temperatures and safe precursors enable processing of even the most sensitive materials.

The type of coin is the decisive factor in the selection of ALD process and materials. For instance, a very thin single oxide layer provides sufficient protection for numismatic collector coins. However, a carefully customized nanolaminate structure of a combination of oxide materials can provide the robust protection required for circulation coins.

Picosun provides completely automatic ALD coating systems to treat large batches of coins. The production-optimized, high throughput PICOSUN™ P-series production ALD systems deliver high process quality for up to thousands of items in a single run at a low cost of ownership.

Figures 1 and 2 show the PICOSUN™ P-1000 ultra-large scale production ALD tool and PICOSUN™ P-300B large scale production ALD tool, respectively.

A PICOSUN™ P- 300B production ALD system equipped with the feature of industrial robot sample handling and loading is presented in Figure 3.

PICOSUN™ P-1000 ultra-large scale production ALD tool

Figure 1. PICOSUN™ P-1000 ultra-large-scale production ALD tool

PICOSUN™ P-300B large scale production ALD tool

Figure 2. PICOSUN™ P-300B large scale production ALD tool

A PICOSUN™ P-300B production ALD system with industrial robot sample handling and loading.

Figure 3. A PICOSUN™ P-300B production ALD system with industrial robot sample handling and loading.

The steps involved in the application of ALD protective coating for a batch of circulation coins using the P-300B reactor are illustrated in Figures 4, 5, 6, 7, and 8.

Coins before coating

Figure 4. Coins before coating

Loading into the PICOSUN™ P-300B reaction chamber

Figure 5. Loading into the PICOSUN™ P-300B reaction chamber

After coating

Figure 6. After coating

Removal from the sample holder, packing for shipment

Figure 7. Removal from the sample holder, packing for shipment

Coins ready to be shipped to the customer

Figure 8. Coins ready to be shipped to the customer

ALD Protective Coatings for Watches

Opposite to the minting applications of ALD, the color tuning capability of the technology [MT1] is highly desirable in the wristwatch and timepiece industry. Here again, the unique characteristics of ALD coatings such as uniformity, conformality, structural integrity with always homogenous color tone in unique metallic hues make them the coating method of choice.

Apart from their color tuning capability, ALD coatings also provide protection against wear, tarnishing, and corrosion. Significant reduction in material consumption is another advantage of the ALD technology, as it achieves the desired result using much thinner films.

For luxury articles such as designer jewelry and watches, the cost associated with the application of an ALD coating is insignificant when compared to their overall cost of production. However, it also possible to coat low and medium-price items with the help of rapid and economical processing on large batch ALD tools. For instance, a PICOSUN™ P-300B batch ALD reactor allows the processing of at least 3000 coins or 1000 watch dials in a single run.

ALD coated watch dials and bracelets are shown in Figures 9 and 10.

ALD coated watch dials (Picture credit HE-Arc, Switzerland)

Figure 9. ALD coated watch dials. Image Credit: HE-Arc, Switzerland)

ALD coated bracelets (Picture credit HE-Arc, Switzerland)

Figure 10. ALD coated bracelets. Image Credit: HE-Arc, Switzerland

Conclusion

Picosun has several clients in the watch and minting industries all across the world. Austrian Mint, one of the key European customers, applies industrial-scale protective coating for coins using Picosun’s ALD technology.

This information has been sourced, reviewed and adapted from materials provided by Picosun Oy.

For more information on this source, please visit Picosun Oy.

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