Assuming your operators are not radically adjusting the ink on press and that your ink supplier is supplying the correct formulation to suit your anilox, plates and substrate you may need to look at your driers.  Maintaining the right velocity, balance and direction of air between decks is critical if it is not to end up being directed onto the plate cylinder, which will cause the ink to dry on the plate.

     Driers can become easily blocked over time with ink, and substrates and dampers may be adjusted during regular maintenance and not correctly reset. You can check the velocity of the air from your driers and this should be routinely checked to ensure it complies with the manufacturer’s recommendations.

     You did not mention if this was common on all decks or just one or more. If it appears to be on only a few of the decks then it is almost certainly more of a mechanical issue, i.e. dampers opened to wide, angled incorrectly, improperly balanced, or some sort of blockage could be causing air to be deflected onto the cylinder or cylinders causing the premature drying of the ink on your plates.

     Also, double check that one or more operators are not putting additives into the ink to help speed up drying. This can and will also contribute to ink drying on the plate if carried out to any excess. If this is the case you need to start with fresh ink as any used stock may be contaminated and will continue to cause the same problem.

      The stock or label substrate is the material to which an adhesive layer is applied with the base being the component that is printed or other processes applied to create a label. From its very humble paper format there are now many options including: Polyester, (PET) Polypropylene, Vinyl, (PLA) Polylactic Acid, Polymide, Polyacrylate, Polyolefin, Polystyrene and of course paper itself.

     Each has specific properties such as resistance to decay, moisture, ozone resistance, heat, chemicals, UV exposure, and more. The adhesives consist of rubber, acrylic and silicone, which again all have different properties. They also come in permanent, semi- permanent, removable, ultra removable, freezer permanent and tamper evident formats.

     The release liner (backing) acts as a carrier for the label. It also protects the adhesive layer, staying with the label until it is ready to be applied. A release coating is applied to the liner that will allow it to separate from the adhesive. Although silicone is the most common release coating, silicone free liners are now available for clean room environments.

     The liner can be in paper or synthetic, which is becoming more popular. Liners can be butt cut, back scored or have pin feed holes on the left- and right-hand edges. Many face stocks also have a topcoat applied to make them more receptive to different inks, coatings and print systems, not just flexo. The stock can also be glossy, matte or even colored.

     You can then add an over lamination, varnish or other specialty coatings to give the label even more resistance to environmental conditions, chemicals etc. I have given you a very brief explanation but you probably already know it is a much more complex subject, and you should use the expertise of your stock vendor to help you determine what will be best for you and your customer.