What should be paid attention to when choosing hot melt adhesive?
Published on Oct. 08, 2019
The use of cartons in the packaging of goods has been extensive, and the quality of cardboard and printing has also increased. However, the traditional sealing method using tape paper or even tying has obviously lagged behind, which not only affects the appearance of the overall packaging, but also has great defects in durability and theft prevention. At present, as a new type of carton and carton packaging, the hot melt adhesive for paper carton has begun to partially replace the traditional bundling and tape packaging, which is applied to carton packaging and wine, dairy, etc. The corrugated box on the outer packaging of the product. Because of the advantages of good packaging quality, beautiful appearance, low cost, and good anti-theft effect, the hot melt adhesive sealing box has become increasingly popular for the application of hot melt adhesive sealing. In view of the fact that hot-melt adhesive sealing is a new technical method, some problems will inevitably occur in the use. Therefore, it is necessary to pay attention to the characteristics and use technology of the hot melt adhesive to ensure the quality of the plastic box.
Hot Melt Adhesive for Paper Carton
The main characteristics of hot melt adhesive and its advantages in corrugated box plastic tank
Hot melt adhesives mainly include EVA hot melt adhesives and PUR hot melt adhesives. EVA hot melt adhesive is an early use product, which has the advantages of fast bonding, low price, easy operation (reversible) and easy storage. However, due to the influence of solvents, low temperature and high temperature, the EVA hot melt adhesive has defects such as poor durability, large amount of application, low adhesive strength, and less material to be adapted. For this reason, a moisture reaction was developed. The curable polyurethane reactive hot melt adhesive (PUR) promotes hardening by moisture in the air, effectively improving the deficiency of the EVA hot melt. The latest aging-resistance hot melt adhesive can be adapted to different paper thicknesses, coating conditions and printing inks. Its adhesive strength is 40% to 60% higher than that of ordinary EVA adhesives. The thickness of PUR film is higher than that of standard EVA. Glue can be reduced by 50% or less, and PUR hot melt is unique in that it can firmly bond coated paper and many other materials, including varnish coating, UV cured layer, plastic film and so on.
Thermosetting Printing Ink
PUR hot melt adhesives are mass-produced PUR top polymers with active terminal groups. Crosslinking reactions occur when the active terminal mass is exposed to moist air or the humidity of the paper reaches a certain level. Once the top polymer is wetted, it penetrates well into the paper for higher tack and higher paper pull. After cross-linking, the PUR film exhibits a high inherent strength (cohesion), which results in a very durable adhesive film. PUR films are not only insensitive to thermosetting printing ink and solvents, but also have excellent durability. PUR is a polymer compound with a urethane bond (NH-CO-0), and the end of the molecular chain is in the form of an isocyanate group. The basic composition of PUR is a polyol with an active hydrogen at the end (polyester). And a polyether diol (chain extender) and an isocyanate-based addition polymer. According to the rigid molecular segment formed by the reaction of the diol and the isocyanate group (cohesive force between molecules), the flexible molecular segment (van der Waals gravitation) formed by the reaction of the polyol with the isocyanate group is balanced. In order to obtain a PUR adhesive which is both rigid and soft, and an irreversible crosslinking reaction (urea bond, allophanate chain, titration bonding) when the isocyanate group and the moisture in the air meet, Thereby a strong adhesive layer is formed. Active PUR (Polyurethane Reactive) Hot melt adhesive is a wet reactive hot melt adhesive that begins to melt at 90 degrees Celsius and solidifies upon cooling. Further, since moisture and moisture such as air and paper generate a crosslinking reaction, once the reaction is completed, the adhesive strength, heat resistance, cold resistance, solvent resistance, and recyclability are exhibited. It promotes hardening by the moisture in the air, which is the main feature of PUR hot melt adhesive. One of the most important aspects of PUR becoming a standard hot melt adhesive is its high viscosity. However, compared with EVA, PUR also has shortcomings such as poor operability, long hardening time, and limited mechanical speed. It takes a long time in the early adhesive effect, and cross-linking with outdoor air causes cross-linking. Reaction, so a special glue applicator that blocks air is required.