How to solve quality issues such as small ink dots, small crystal points, and wavy lines on the surface of packaging bags?

Many companies, when using packaging bags to package products, will find small flaws on the packaging bags upon close observation, such as small ink dots, small crystal points, wave patterns, small gray dots, small white dots, and small scar points. What causes this? Are there any solutions?

Today, Shunxingyuan Packaging, a professional flexible packaging manufacturer, will clarify that these small flaws can generally be well solved during production, and let's see how to avoid the appearance of these flaws during production.

1、 Small ink dots

Small ink dots are less likely to appear immediately after lamination, unless there are impurities.

Aluminum-plated film may exhibit this phenomenon after a period of lamination. This is because the ink corrodes the aluminum. When the ink exhibits a certain acidity or alkalinity, and the amount of adhesive is small and cannot form a continuous layer, this situation may occur.

2、 Small gray dots (i.e., small solid dots)

There are two possibilities for the appearance of small gray dots: one is that uneven rollers cause adhesive spots, and the other is that uneven ink causes uncompressed ink spots.

Both possibilities are related to the process and can be solved by adjusting the process, i.e., increasing the thickness of the adhesive application.

3、 Small white dots

These are prone to appear when the surface ink changes color, mostly appearing in the composite of aluminum-plated film.

There are two reasons for the appearance of small white dots: firstly, the covering power of the ink itself is not strong or uneven, especially white ink, allowing the aluminum color to penetrate, and places without aluminum color penetration form small white dots; secondly, due to process reasons, the oven temperature (especially the first oven) is too high or the adhesive application is too thick, causing the surface of the adhesive layer to solidify in the first oven, and when the ethyl acetate is pushed out in the second and third ovens, it squeezes the adhesive, revealing the original color of the ink.

The solution is to improve the ink covering power or adjust the suitable temperature of the first, second, and third ovens, gradually increasing the temperature to avoid excessively high temperature in the first oven.

4、 Small crystal points

Small crystal points occur more frequently on transparent films, with both concave and convex types, and different causes: convex small crystal points are mostly due to adhesive preparation reasons. If the correct adhesive mixing order (adding diluent first, then curing agent) is not followed, adding the curing agent first and then the diluent, small crystal points will generally appear after ten or so hours. It may also be because the machine has been used for a long time without being cleaned.

The method to eliminate small crystal points is to strictly follow the correct adhesive mixing method, and the machine must be cleaned after use; for concave small crystal points, observe carefully with a magnifying glass, and you will find small bubbles inside, which is mainly caused by excessive water content. Note that the water content of the diluent must not exceed

5、 Small scar points

Small scar points refer to points larger than the above-mentioned small points, with a convex periphery and a concave center. This is mainly due to uneven film activation treatment. The same scar points also appear during printing, and may also be caused by excessive activation time.

6、 Wave patterns

Wave patterns are prone to occur on white films, mainly because the molecular weight of the adhesive is uneven. After passing through the hot oven and hot roller, the elastic high molecular chains contract, and the contraction of molecules with different molecular weights is inconsistent. This uneven internal contraction causes wave patterns. In this case, the cause should be considered from the adhesive.

7、 Influence of film on surface quality

Due to various reasons such as the surface smoothness and uniformity of the film, similar phenomena to the above six may occur. To distinguish whether it is caused by the film or the above six situations, the unlaminated film can be carefully observed with a magnifying glass.

Since the transparent adhesive is between the two layers of film, forming a composite film together with the two layers of film, using a magnifying glass to enlarge the small spots and waves on the film, many situations require careful observation to find the problem.

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