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Recyclable flexible packaging solvent-free lamination adhesive is polyurethane resin, abbreviated as polyurethane ester, which is a polymer compound containing amino ester (- NHCOO -) units in its molecular structure. Solvent free adhesives are divided into two-component and single component.
In two-component systems, component A is generally an isocyanate terminated polyurethane resin, while component B is a hydroxyl terminated polymer. The two components are mixed in a certain ratio and coated, compounded, rolled, and matured on a solvent-free laminating machine to complete the flexible packaging laminating process.
The single component is polyurethane resin capped with isocyanate, which relies on water or moisture to complete curing.
The degree to which temperature affects the rate of chemical reactions can refer to the following formulas and rules:
(1) Arrhenius equation: This is an empirical formula for the relationship between the rate constant of a chemical reaction and temperature, written as k=Ae Ea/RT (exponential formula). K is the rate constant, R is the molar gas constant, T is the thermodynamic temperature, Ea is the apparent activation energy, and A is the pre exponential factor (also known as the frequency factor). This law applies not only to all elementary reactions, but also to a large number (not all) of complex reactions.
(2) Van Hoff rule: This rule refers to most chemical reactions, where the reaction rate increases with temperature. Experiments have shown that for homogeneous thermochemical reactions, the reaction rate increases by 2-4 times for every 10K increase in reaction temperature. Although the van’t Hoff rule is not accurate, it is still useful for roughly calculating the change in reaction rate with temperature when data is lacking. The curing reaction of solvent-free adhesives, the reaction between isocyanates and hydroxyl groups, and the reaction between isocyanates and water, gradually accelerate with increasing temperature, and the reaction rate is very low below 10 ℃. When the curing temperature is constant, the composite roll film in winter is affected by room temperature, resulting in a lower overall temperature. The actual curing temperature and reaction rate of the lamination adhesive are also affected. Therefore, it is recommended to extend the curing time in winter
When recyclable material is more difficult in lamination than conventional materials, we will recommend engineers to spend more time in aging for lower temperature.
If in summer, with high temperature and humidity, the reaction between water and isocyanates accelerates, this effect will further expand. Therefore, in the summer flexible packaging composite workshop, attention should be paid to cooling and dehumidification, protection of the outer packaging of the film, sealing of the adhesive tank, or adjusting the adhesive ratio appropriately and increasing the amount of isocyanate components. Take the above measures to ensure the smooth progress of the adhesive curing reaction, while the opposite is true in winter
(1) The reaction rate of component A and component B gradually accelerates with the increase of temperature. It is recommended to increase the aging temperature without affecting other properties;
(2) When the curing temperature is low, the reaction is slow. In winter, due to the need for preheating time for film rolling, it is recommended to extend the curing time;
(3) The isocyanate of polyurethane adhesive reacts with moisture, and the relative humidity affects the adhesive ratio, dryness, heat resistance, bonding performance, appearance, etc. It is recommended to cool down and dehumidify or increase the isocyanate component during high temperature and humidity in summer, and the opposite is true in winter;
(4) The relative humidity is the same, the temperature is different, and the moisture content in the air is different; The humidity in the air varies greatly between summer and winter.
Longdapac is the leading recyclable mono-material PE pouches factory in China. Our engineers spent couple years to improve the lamination process of mono-material PE bags. And now the quality is as good as the conventional materials.