Study on Special Adhesive for Alcohol-soluble Polyurethane Coating on Aluminum (I)

With the development of society and the improvement of people’s living standards, the application of aluminized films in flexible packaging has become more widespread. There are two kinds of commonly used aluminizing film materials, one is polypropylene aluminized film, abbreviated as VMCPP, one is aluminized aluminized film, referred to as VMPET, and the two aluminized films have the following characteristics:

1. The appearance of a metallic luster, a strong reflection of light, increase the visual effect of the packaging. 2. After the film has been plated with aluminum, it can greatly improve its barrier properties and can extend the shelf life of packaged goods.
3. Good processing performance. Compared with aluminum foil, aluminum-plated film is not easy to wrinkle and break.

Although there are many advantages in the application of aluminized films on flexible packaging, there are certain deficiencies. I personally think there are two points:

1. The aluminum-plated aluminum layer is easily transferred, resulting in a decrease in the composite strength of the composite film. This is because domestic aluminizing film manufacturers generally do not apply primer to the surface of plastic film when producing aluminized films. The combination between aluminum and film depends only on the polarity of the molecules, and the binding force of the polarity itself is very low. , so the aluminum layer is easy to fall off. Because the polarity of PET is higher than that of CPP, the composite strength of VMPET and other films is higher than that of VMCPP and other films. Another reason is the adhesive itself. I have done experiments with the same aluminized film and the same production process. As a result, it has been found that the degree of transfer of the aluminum layer is not the same and there is a large difference in the composite strength.

2. When the aluminized film is subjected to dry composite processing, white spots are likely to occur, especially at the white ink and the yellow ink. One of the most important reasons is the poor leveling property of the adhesive. For the ester soluble adhesive, if the quality of the adhesive is good, the dry basis weight of the adhesive is 2.5-3.0 g/sq. In meters, the desired surface effect can be achieved. If the quality of the adhesive is poor, the dry basis weight of the glue can reach 2.8-3.5 g/m2 to achieve the desired effect.

For the aluminized film in the composite process, if the aluminum layer is transferred to reduce the composite strength, many research and development adhesives manufacturers have conducted many years of research, and successively launched different brands of ester-soluble aluminum plating. Special adhesives for films, some brands can achieve certain effects, and some have no obvious effect.

The authors conducted trials on aluminized films for five domestic brands of ester-soluble adhesives. Among them, the three brands A, B, and C are common ester-soluble adhesives, and the D and E brands are ester-soluble aluminum-plated adhesives. The test process, materials, and strength are as follows:

Experimental equipment and materials: OPP printing, VMCPP, VMPET, dry laminating machine, network roller (120#, 60μ), tensile machine.

Experimental process: glue concentration 30%, compound pressure 5KG, three-stage drying temperature 60°C, 70°C, 80°C, compound temperature 65°C, machine speed 85m/min, aging temperature 50°C, aging time 48 hours.

Phenomenon: The aluminum layer of the aluminized film of the A brand adhesive composite product is severely transferred, and the white ink has white spots. The aluminum layer of the aluminized film of the product of the B and C brand adhesive transfer 80%, and there is no white spot at the position of the white ink. The aluminum layer of the aluminum alloy film of the D brand adhesive composite product is hardly transferred, and the white ink does not have a white dot at the position, but the stickiness of the aged colloid is somewhat similar to the one-component adhesive. E brand adhesive composite product aluminum film transfer of 20% of the aluminum layer, white ink does not have white spots.

(to be continued)