Process of PUR (polyurethane) hot melt adhesive in plastic packaging box

PUR hot melt adhesive, that is, reactive polyurethane hot melt adhesive, its main component is polyurethane prepolymer with -NCO group. The reaction principle of PUR hot melt adhesive is: the colloid is heated and melted into a liquid state and then coated on the surface of the substrate. After the two layers of substrates are bonded together, the PUR hot melt adhesive can undergo an irreversible chemical reaction with the moisture in the air. Form a high molecular polymer with extremely high cohesion. 

PUR hot melt adhesive has the following outstanding advantages
(1) The stability is better. Ordinary hot melt adhesives become liquid after being heated and melted, and then turn back to solid when the temperature cools to room temperature, but PUR hot melt adhesives are different, and they will undergo further irreversible reactions to form a cross-linked substance. Therefore, compared with ordinary hot melt adhesives, PUR hot melt adhesives have better stability. 
(2) The use temperature is low. Compared with ordinary hot-melt adhesives, PUR hot-melt adhesives can be used at a relatively low temperature, thus effectively avoiding the problem of thermal deformation during the gluing process of transparent plastic packaging boxes. 

(3) Other performance advantages. Based on the reaction principle of PUR hot melt adhesive, it can be known that it forms a polymer film with high cohesive strength after cross-linking with moisture in the air, which makes PUR hot melt adhesive more resistant to solvents and aging than ordinary hot melt adhesives. The performance is excellent, and the low temperature resistance and high temperature resistance of PUR hot melt adhesive products are better than ordinary hot melt adhesives. 

PUR hot melt adhesive transparent plastic packaging process control points

In order to give full play to the advantages of PUR hot melt adhesives in transparent plastic packaging box gluing boxes, process control must be strengthened in the gluing box production process, especially the following aspects. 
1. Handling of materials
The surface energy of materials such as PET, PP or PVC should not be lower than 38mN/m. If the surface energy of the material is low, it must be used after surface pretreatment. 
2. Control of the amount of glue applied
In the process of pasting boxes, the amount of glue applied must be strictly controlled, not too much or too little. Too much will easily make the film whitish; too little will easily lead to poor adhesion, which will eventually affect the carrying capacity of the transparent plastic packaging box. 
3. Pressurize the finished product
After the finished product bonded by PUR hot melt adhesive, it must be fully pressurized after it goes off-line, otherwise the unreacted PUR hot melt adhesive will easily generate air bubbles, resulting in poor bonding. the
4. Guaranteed curing conditions
The finished product of PUR hot melt adhesive paste should be placed under suitable temperature and humidity conditions after offline to ensure the full curing of PUR hot melt adhesive. Generally, the suitable curing temperature is 22 ° C ~ 35 ° C, and the curing humidity is 50 % ~ 80 %, the curing time is 24 to 48 hours.