Leary said there are two primary solutions for coating […]
Leary said there are two primary solutions for coating challenges. One option is to collaborate with the adhesive supplier to find a more aggressive formula that will work with the carton’s existing coatings. Most adhesive suppliers have a range of options for the different types of coated stock in the current market. Another option is to use a plasma treating system to change the surface tension of the area requiring glue, creating a stronger bond by enhancing adhesive penetration into the board. Davis recommends testing the surface tension of the coating using a dyne kit. “Prior to committing to a job, it is recommended to condut dyne tests and handgluing quality assurance testing with samples. Also, it is encouraged to knock out the glue tabs whenever possible,” he said. Davis also explained that, generally speaking, a reading below 40 dyne is borderline for waterbased adhesives, while some laminating and coating applications require surface energies of 50 dynes or more. “When using waterbased adhesive, it is important for at least one of the surface areas to be porous, as nonporous substrates will trap the adhesive between the two surfaces, delaying setup time because the water has no place to go,” he explained. “
For skive coated areas, see if a chemical primer or surface treatment such as corona, plasma or flame treatment will raise the surface tension of the coating.” Jeff Wilcox, product manager of PPC Technologies & Solutions LLC (PPCTS), said that many times there will be coatings covering the glue lap or panel of a carton blank. These coatings can be UV or polybased, foil, varnish, ink, laminates or simply the stock itself. Whatever the coating, it can alter the surface tension of the substrate, and it will affect the glue’s ability to bond. “Specialty glue can be ordered from the glue supplier; however, it is possible that each different coating will require a different formula and, on top of that, specialty glues can be costly, so keep the size of the order and how often it will be used in mind,” Wilcox said. Many times – if repeating orders will be processed – the glue manufacturer will work with the customer to decrease these costs. There are several other ways to remedy a glue bond issue, and Wilcox recommends using a skiver – generally used to improve the glue bond of side seamstyle cartons – because it cannot be attached in a way that will be helpful for the glue bond on automatic lock bottomstyle cartons. “Some skivers have a replaceable razor blade or something similar that will remove the top layer of the substrate. This is very effective, but could be costly – upwards of $70,000. Other skivers have a grinder with a highspeed carbide cutter.
These systems also are very effective and will cost considerably less, with prices typically under $7,500,” Wilcox said. He recommends using a skiver in conjunction with a vacuum and filter system to prevent airborne particulates from either being inhaled or collecting onto the machinery. Wilcox also recommends the plasma treatment system. Plasma is generated by highvoltage electricity applied to a tungsten carbide electrode. The electrode is housed in a stainless steel tip plasma head and inert gas, such as compressed air, is blown over it. The reaction creates a plasma flame, which can be directed to a small area(s) of the carton and will change the surface tension of the substrate enough for it to be able to accept glue. Plasma heads also can be attached inline with each other to effectively increase operating speeds or treated areas. Verify that the plasma system is CEcertified and has an automatic stop feature that shuts off the plasma flame if the folder/gluer stops. Look for an individual on/off switch for each plasma head, so the heads not in use can be turned off. Because the plasma flame is affected by the amount of air passing over the electrode, a low air pressure alert also is good to have. “The cost of plasma treatment systems varies widely, depending on where it’s manufactured, the features it has and its warranty” Wilcox said. “Generally, the price of a good system can start at about $10,000.”