The correct use of polyurethane adhesives for flexible packaging is crucial for ensuring the quality of the composite film and preventing problems such as delamination and blistering. The core lies in the three major steps: ingredient preparation, machine loading, and curing. At the same time, common misunderstandings should be avoided.
Before use, precise ingredient measurement is required: first, confirm that the adhesive model matches the packaging requirements, distinguish between the main agent and the curing agent, and strictly weigh according to the proportion. Estimation based on experience is not allowed. Deviation in the ratio will result in incomplete drying of the adhesive layer, brittleness, or insufficient peel strength. When measuring the ingredients, start by adding the main agent and then the curing agent, stir at medium speed for 5-10 minutes. If there is no solvent type, stir more evenly. After mixing, use it within the applicable period. For solvent-based adhesives, use within 4-8 hours; for non-solvent-based adhesives, within 2-4 hours. If the adhesive becomes thick and starts to bubble, stop using immediately.
When performing the on-machine compounding process, it is necessary to pay attention to details: for solvent-based compounds, high-purity ethyl acetate should be used for dilution, and the concentration should be controlled as required. The drying temperature should be 60-80℃ to ensure no residue; for non-solvent-based compounds, heating to 30-50℃ is necessary, and the adhesive application amount should be controlled at 1.0-2.5g/m². The corona value of the substrate should meet the standards. The operating environment should be protected from water and moisture, as moisture can damage the curing of the adhesive layer.
The aging process cannot be omitted. At room temperature of 25℃, it needs to be aged for 24 to 72 hours. In an aging chamber at 40-50℃, it needs to be aged for 12 to 24 hours. The sterilization bag needs to be extended to more than 48 hours. Insufficient aging will result in delamination and bag rupture during sterilization.
In addition, it is strictly prohibited to mix different types of adhesives. Unused adhesives should be sealed for storage to prevent moisture and dampness. After compounding, the product must be left to mature for at least 12 hours before being bagged and filled, in order to ensure the quality of the flexible packaging compounding.
