Tamper evident labels have features that show if a label has been removed or if removal has been attempted.
Security labels have features that make the label difficult to copy or can show if certain things have happened to the product.
Tamper evident features:
- Security slits/cuts. This is the most basic form of tamper evidence. A series of cuts are included in the label causing the label to tear if removal is attempted – this means the label cannot be replaced without evidence of its prior removal being visible. The most common application for this would be in supermarket price labelling.
- Fragile or ultra-destruct materials. These materials are weaker than the adhesive bond to the substrate. This means that when they are removed, they come away in small pieces that would be impossible to fit back together. Perhaps the best of these is ultra-destruct vinyl which is incredibly fragile with a strong adhesive but its fragility can make it too difficult to use in some circumstances (it cannot self-support so must be adhered to a surface with no holes or depressions). Other alternatives are made from paper, polyethylene and polypropylene. The polypropylene version is strong and very easy to handle but when removal is attempted it splits into two layers leaving a layer stuck down and the printed top layer peeled away.
- Reveal materials. These are usually made from polyester which gives enhanced durability and temperature resistance. When removed they reveal a residue that stays stuck to the substrate in either a pattern such as chequerboard or a message such as VOID.
- Reveal no residue materials. These are similar to the standard reveal materials but the pattern is only evident in the material once the label is removed. No residue is left on the substrate and the label should come away clean. This is particularly useful when labelling items that are checked and sealed on a regular basis such as in Customs, or when security checking buildings and sealing doors, cupboards and drawers etc.
- Red lamination or a red background prevents photocopying.
- Holographic images. These are extremely difficult to duplicate (think banknotes and credit cards). They come in standard patterns with a range of messages e.g. “Valid” and are generally a random scatter print and are ideal for low to medium volumes, or they can come in a bespoke design that can be scatter print or a registered image e.g. a logo or crest. The bespoke ones are the most secure but come at a high cost to originate and with a minimum order of holograms tend to rule out most low and medium volume applications.
- Thermochromatic ink which changes colour at a set temperature. The change can be temporary or permanent. These are useful for detecting if a product has been exposed to a temperature – e.g. quality control in the sterilization process, or for checking on misuse of a product for warranty purposes.
- Photochromic ink which changes colour when exposed to UV light. The change in colour is reversible. The ink can be clear or black and looks like either no print (clear) or standard black in normal light but changes in UV light. This is a good covert way of adding information to a label to check if a printed label is genuine or counterfeit. The information can be in variable data such as a serial number.
- Check digits – these are algorithms within a barcode or sequential number designed to produce a number that is difficult to make up. A good example of this is the 16 digit number across the middle of a credit card. Part of the number is an answer to an algorithm of the rest of the numbers. Because the number contains a calculation with an answer that needs to be correct to make a valid sequence it is almost impossible to just make up a number. Check digits can be from a range of standard algorithms or can be bespoke.
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