The real deal

As counterfeiting continues to grow, Nano4u explains the significance of covert injection moulded ‘watermark’ features for authentication of moulded medical parts

Counterfeit products are on the increase and in the case of medical products the issue is not just one of loss of income or litigation problems, but also a risk to human life. How can a manufacturer prove that a product is its own genuine product or a fake? How can a user or distributor verify that a product is genuine?

A new way of treating hardened steel tooling, developed by Nano4u, allows for holograms and covert verification features to be directly injection moulded onto plastic parts. These can be visible holograms that change with viewing angle, or hidden diffractive features that reconstruct an optical image when a laser pointer is directed at them. Without knowledge of the presence and location of the hidden features, the user is unaware of them. When a user knows where and how to look, a verification check can easily be carried out.

One advantage of this new technology is that the holographic structures can readily be incorporated into existing steel tooling by surface structuring an existing steel tool insert or an ejector pin surface. Because the structure is part of the hardened steel, it has high durability and has been proven to last for over a million injection moulding shots.

The process has already been used with polymers ranging from commodity plastics like polypropylene and HDPE in the packaging industry, to filled engineering polymers such as PPS in the electronics industry. A recent example of this technology, demonstrated at some recent medical exhibitions, is the microfluidic lab-on-a-chip component.

This is a micro-moulded part, designed as a two-shot moulding. The picture shows only the first shot assembly (the second shot moulds an elastomeric surround around the first part). The micro-mould for the part, made by Micro Systems (UK) has a number of small ejector pins, and one of these is structured with the diffractive security feature.

The pin with the authentication feature is positioned in the centre of the ‘O’ in the logo on the plastic part. The ejector pin has a tip diameter of 0.8mm, making it the smallest ejector pin so far structured using this technology and a truly “covert” authentication feature. Larger ejector pins and inserts up to 40mm diameter can also be structured in this way.

When a laser pointer is fired through the centre of the “O” on the plastic, an image is reconstructed, which in this case shows a 2D barcode (pictured). Depending on the diffractive optics design, this feature could be a logo, or lettering, or some other shape. When examined closely under a microscope on the plastic in the ejector pin witness area, all that is visible is a seemingly random pattern of tiny  squares and micron-scale lines.

These types of diffractive features also work on opaque plastics, where the reconstruction of the hidden image using the laser is done in reflection instead of transmission. The effect also works with red wavelength lasers, but because the human eye is about 20x more sensitive to green, a green laser is preferred. Depending on the ambient lighting, the image is either clearer or weaker.

Application of this new technology allows producers of medical devices and pharmaceutical packaging to easily implement a solution that add security to the serialisation practices that are becoming standard in the industry. Unlike serialisation codes, these features cannot easily be copied or removed.