All isocyanate solvent-less adhesives are a two component mixture.
Step one is ensure the adhesive is mixed properly, manually weighing the two components at the beginning of the shift is extremely important. The A part is mixed with the B part to create bonds and shear. The resulting mixed adhesive will still have reactive groups that will react with moisture on the web surface and moisture that was present in the air during lamination. This reaction creates Urea. Polyurea is extremely heat and chemical resistant. The first reaction between the A and B part is very fast. The adhesive builds molecular weight very quickly and creates bonds and film structure (shear). The second reaction after the A and B parts has been mixed is with moisture. The moisture reaction is 10 times slower than the initial reaction between the A and B parts. Moisture is present on the film surface and in the air. There is an abundance of moisture in Summer months but in Winter as you begin to heat the plant, the moisture is dried from the air and the relative humidity drops to levels below the recommended levels of 35% RH. The drier the air the longer it will take your laminate to ultimately cure, unless the roll can be kept warm and the isocyanate active. To speed the moisture reaction and resulting final cure, ensure the plant air has a relative humidity of at least 35% and store the roll in storage at 35C. This will result in a cure time that is similar to hot summer months. Keep in mind, strong bonds are not an indication of final cure. The shear resistance of the adhesive is gained with the reaction between A and B parts. The ultimate test is can the laminate withstand heat, which is gained through the reaction with moisture and the formation of Urea within the adhesive layer. PA films lamination are hygroscopic and will compete for moisture in the laminate with the adhesive.
When laminating with Nylon it is important to remember, if humidity levels are below 35% the cure time can also be extended by up to 50% or more. All adhesive cure begins when the two films are brought together in the lamination nip. There must be enough heat transfer to penetrate through both webs. A good measuring tool is to measure the temperature of the rewound roll during the run. The roll should register a minimum temp of 35C.
