How are adhesives selected to ensure the quality of composite packaging bags?

In the composite processing of packaging bags, the adhesive is one of the key factors affecting product quality. The choice of different adhesives for composite packaging bags will directly affect the quality and efficiency of production, which is also a concern for many enterprises that have a demand for composite packaging bags.

How to choose the right adhesive product to ensure quality? Shunxingyuan Packaging, a professional flexible packaging manufacturer, has compiled and summarized the following aspects for your reference based on its experience in producing composite packaging bags.

I. Select the adhesive according to the requirements of the packaging product

Different post-processing temperatures of packaging products require different adhesives.

Common temperature classifications include steaming at 135℃ for 30min, steaming at 121℃ for 30min, boiling at 85℃ for 30min, room temperature, freezing, and deep freezing.

The selection principle is to consider suitable varieties while meeting processing conditions. Choosing higher-than-necessary adhesives will lead to waste and increased costs.

If the product requires 135℃ for 30min, an adhesive that meets this temperature requirement must be selected; if the product only requires steaming at 121℃ for 30min, there is no need to use an adhesive that can withstand 135℃.

II. Select the adhesive according to the structure of the composite packaging

Composite packaging uses a variety of materials, including BOPP (glossy film, pearlescent film, matte film), PET, BOPA, AL, aluminum-plated film (VMPET, VMCPP, VMPE, etc.), CPP, PE, etc.

Single PE films vary greatly. Different PE film thicknesses and resins result in different PE film properties, requiring different adhesives.

For example, when using ordinary adhesives for aluminum-plated film lamination, the peel strength is generally only (0.3-0.6) N/15mm, and the aluminum transfer is serious.

If such packaging bags are used to package irregular solid objects (such as tea) and then vacuum-packed, after a period of time, large bubbles will appear on the surface of the packaging bag, which is delamination of the aluminum-plated composite film.

Therefore, it is necessary to find ways to improve the peel strength of the aluminum-plated composite film and solve the problem of aluminum transfer. One way is to use a special adhesive for aluminum-plated film lamination.

III. Select the adhesive according to the dry lamination equipment

In dry lamination production, it is found that the same adhesive has different effects when used by different manufacturers. There are many reasons for this, one of which is the different equipment used.

Select the adhesive according to the equipment's tension system.

If the equipment's tension control system is poor, the control accuracy of the tension is not high, and the tracking feedback is poor, then when selecting the adhesive, the adhesive with good initial tack should be selected to reduce the formation of tunnels. Conversely, if the tension control system is good, the initial tack of the adhesive can be slightly lower, and tunnels will not appear, which will not affect the yield.

Select the adhesive according to the operating speed of the equipment.

If the operating speed of the equipment is very high, then when selecting the adhesive, an adhesive with lower viscosity should be selected. If the viscosity is too high, a large number of bubbles will be generated in the glue trough, seriously affecting the coating state of the adhesive and thus affecting the product quality.

Conversely, if the operating speed is low, the viscosity of the adhesive can be higher.

IV. Select the adhesive according to the working concentration of the adhesive

Under the same speed and other process conditions, the higher the working concentration of the adhesive, the better the economic performance, transparency, and other quality factors.

Generally, the higher the solid content of the adhesive, the higher the working concentration. For an adhesive with a solid content of 50%, the working concentration is 20%~30%; while for an adhesive with a solid content of 75%, the working concentration is 30%~40%.

Example (adhesive dry base: 2.5g/㎡):

Scheme A:

Using an adhesive with a solid content of 50%, the working concentration is 25%, and the wet glue amount is 10g/㎡.

Scheme B:

Using an adhesive with a solid content of 75%, the working concentration is 40%, and the wet glue amount is 6.25g/㎡.

Scheme A consumes 3.75 g/㎡ more ethyl acetate than Scheme B, approximately 0.03375 yuan/㎡. If the 3.75 g/㎡ of ethyl acetate is completely volatilized, a certain amount of heat must be consumed, affecting production efficiency.

Therefore, when selecting an adhesive, it is best to use a high-solid-content adhesive and use the highest possible working concentration to achieve better economic performance and production efficiency, while the transparency and other indicators of the composite film will be better.

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