At present, the commonly used composite adhesives in flexible packaging industry mainly include solvent-free adhesives, water-based adhesives and solvent-based adhesives. Developed countries in Europe and America attach great importance to environmental protection, and solvent-free adhesives and water-based adhesives are mainly used in the composite production of flexible packaging. In most countries in Asia and Africa, solvent-based adhesives are still the main soft packaging manufacturers. For example, in Japan, where the soft packaging industry is relatively developed, solvent-based adhesives account for more than 90% of the market.
Types and characteristics of adhesives
The three types of adhesives commonly used in flexible packaging industry have their own characteristics and corresponding application fields. The following is a brief analysis and summary of their advantages and disadvantages.
1. Solvent adhesive
There are mainly two-component polyester adhesives, two-component polyether adhesives, two-component polychloroprene adhesives and alcohol-soluble polychloroprene adhesives.
(1) Advantages
① It has a wide range of applicable substrates, and basically has good adhesion to materials commonly used in flexible packaging compounding.
② Good initial adhesion and high composite strength.
③ The composite film has high transparency and good flexibility, which meets the requirements of post-processing procedures and product packaging.
④ Heat resistance, cold resistance and medium resistance are the best among all kinds of adhesives.
⑤ It is safe, hygienic and odorless, and meets the requirements of FDA standards and the relevant provisions of VOC.
⑥ Good operability and relatively low requirements for equipment and operators.
(2) Disadvantages
① Volatile organic solvents are harmful to human body and also pollute the environment.
② The incomplete reaction of free TDI (toluene diisocyanate) in some ester-soluble adhesives is harmful to human body.
③ There is a small amount of solvent residue in the composite membrane, which may pollute the packaging contents.
2.Aqueous hot melt adhesive
Water-based adhesives for soft packaging composite mainly include water-based polyurethane adhesives and water-based acrylic adhesives.
(1) Advantages
① It does not pollute the environment and is beneficial to environmental protection.
② It can be used on middle and high speed compound machines.
③No solvent residue, and the transparency of the composite film is high.
④ The composite strength of aluminized film is good, and the aluminized layer will not be damaged or transferred.
⑤ The coating amount is small (as low as 1,6g/㎡), and the comprehensive use cost is low.
⑥ It has good adaptability to alcohol-soluble ink.
(2) Disadvantages
① Not suitable for heavy-duty packaging and high-temperature cooking packaging.
② The requirements for the surface properties of the film are relatively harsh, and the requirements for the surface tension are high.
③The energy consumption is high and the production efficiency is low, which requires the composite equipment to have strong heating and exhaust capacity (the temperature should reach 60℃ ~ 100℃).
④ The composite strength decays with time.
⑤ The corrosion of composite equipment is serious.
⑥ When composite aluminized film is applied, the aluminized layer is easy to be corroded.
3.Solvent-free adhesive
Solvent-free adhesives for soft packaging composite mainly include single-component, two-component and UV-curable adhesives.
(1)Advantage
① Non-toxic, environment-friendly, solvent-free, no environmental pollution, in line with FDA standards.
② Safe operation, no need to take fire and explosion prevention measures.
③Less glue coating, simple compounding process, and compounding speed up to 200 m ~ 300 m/min.
④ Save energy. After gluing, it is not necessary to heat and dry in the drying tunnel, and the energy consumption will not increase due to waste gas incineration or recovery.
⑤ The composite product does not have the problem of solvent residue or migration, so it will not pollute the contents and is suitable for food packaging.
⑥ The solid content can reach 100%, and the comprehensive use cost of users is low.
(2)Disadvantage
① The investment of solvent-free composite equipment is large, and the coating system is complicated, and a heating device is needed.
② The viscosity of glue solution is high, and the storage time after mixing is short.
③ Low initial adhesion and long curing time.
④ The precision of the tension system of composite equipment is required to be high, and the operating level of operators is also required to be high.
⑤ The requirements for the flatness and thickness of the composite substrate are strict, and the surface tension of the film is large.
⑥ The composite strength decays with time.
⑦ When some packaging products (pesticide bags, high temperature resistant retort pouch, etc.) with high quality requirements are compounded, their properties and compounding quality can not reach the level of ester-soluble polychloroprene adhesive.
