Handling and Storage
Next, let’s focus on the actual handling and storage of the containers both before use and when leaving as a partial container for use later. Again, both the TDS and MSDS, as well as the warning label, spell out proper storage conditions. Regardless of the product, the containers should be kept in a cool, dry, well-ventilated area. Normally temperatures above 50°F and below 120°F are acceptable. Insure that all lids are secured tightly to prevent evaporation and to keep moisture out. When only using a partial container, it is critical that for any urethane product (moisture sensitive) the headspace is capped with inert gas or dry air. This will prevent water contamination which will affect the quality of the product. Always look closely at the manufacturing and expiration dates marked on container labels. Do not use the expired product and always practice FIFO (First in first out) to ensure the oldest product is used first before newer lots.
Mixing the Adhesive
As you handle and mix the adhesive before coating or laminating, several steps and precautions should be taken to ensure quality. Always refer to the TDS (Technical Data Sheet) for proper mix ratio, application solids, diluting solvent, etc. Calculate the amount of adhesive needed for the job and only mix that amount (plus waste), or only mix amount that can be used in a normal 8-hour shift. It is often advisable to premix water-based container for 5-15 minutes before pulling out material, this is not necessary for solvent-based products. Always use urethane grade diluting solvent and ensure this remains moisture-free with the use of an inert gas blanket or desiccant tubes. Weigh adhesive using calibrated floor or benchtop balances at the proper ratio.
Mixing should be done in a round container, using mixing blade 1/3 the diameter of the container with a mild, off-center vortex to insure proper mixing but avoiding trapped air. The addition of co-reactant and diluting solvent should be done while mixing. Once proper viscosity/solids have been achieved, mixed/diluted material can be pumped into the application pan using a low shear-type pump. Examples are diaphragm, peristaltic, centrifugal, or positive displacement pumps. Recirculation is advised for longer runs to help minimize possible foaming. Keep return distance short with a return below the fluid level. Keep return as far from intake as possible. While filtering is not usually needed, it can be used to collect and debris our foam that has been generated and can be as simple as cheese cloth. Solids/viscosity should be monitored throughout the run and adjusted as needed to ensure consistent coating weight. Appearance is also maintained during the run.
By reading, understanding and following both the supplied documentation and above guidelines the various adhesives and coatings can be used safely and applied accurately. Proper handling ensures not only worker safety but will help give high quality, high performing adhesive laminations or coated products. Proper handling and storage also will help ensure the products will perform throughout manufactured shelf life and enable the reuse of partial containers. Any questions can always be answered by referring to the proper manufacturers' technical or regulatory departments for clarification.