During the production and use of flexible packaging, some quality problems related to the peel strength are often encountered, and the peel strength is closely related to the adhesion of the ink. Ink adhesion is often mentioned, but some aspects are often overlooked when it is used.
1. There are differences in the adhesion of inks with different hues
Generally, in the same model, the adhesion between gold and silver inks, white inks and printing substrates is relatively low, and there is enough awareness, but not enough attention is paid to the different adhesion of other colors. Because in general roll film and bag making products, inks of various colors can meet the requirements.
High-demand products and some special usages should be selected for each color. It is impossible to promote the use of other inks of this type in similar products because a certain type of ink of a certain color can meet the peel strength and subsequent processing requirements of the product. . For example, a customer produces BOPP/AL/PE structure drug roll film packaging, which is used on a roller vertical packaging machine. After being tested by the pharmaceutical factory, the green ink can be used normally. So the blue ink was directly used in the same product, and the blue ink heat-sealed delamination phenomenon occurred during use. After testing, there is a big gap between the peel strength of green ink and blue ink. The heat-seal delamination phenomenon is generally considered to be related to the adhesion and heat resistance of the ink, and the pigment will affect the adhesion and resistance of the ink. However, the roller vertical packaging method is prone to layer separation, and the composite film used for packaging mostly uses PET as the outer layer.
2. Low adhesion between inks of different systems
For example, the peeling force between the surface printing ink and the inner printing composite ink is low. There is another manifestation of low adhesive force. The detected peeling force is relatively large. When the post-processing is heated and extruded, the adhesive force does not work and the material is delaminated. Such cohesion can be called "false strength". In other words, there is no strong bond between the two layers of ink, which is similar to the non-drying bond of adhesive. For example: A customer uses polyurethane general-purpose ink for large-area spot colors in BOPP/AL/PE, and chlorinated polypropylene white ink as the base. The test peel strength is 2.9N/15mm, which is higher than the 2N/15mm requirement of the packaging film manufacturer. However, not only delamination occurs during heat sealing, but also the BOPP shrinks at the edge of the composite film, and the white ink layer leaks out. This shrinkage is not caused by BOPP's heat intolerance, but a manifestation of "false strength". As shown in the diagram.
Inks from different systems are mixed. For example, the modified surface printing ink can be used as the bottom printing composite white ink; the alcohol-water white ink can be used as the bottom printing of the chloropropane type and the polyurethane type ink. This mix is determined by the performance of specific inks and is mostly used for light packaging.
3. Some inner printing compound color inks do not spread white, and when compounding aluminum foil or aluminized film, the strength is low or no strength
Although this phenomenon has been clearly stated for a long time, similar problems always occur. When encountering such a product, just choose the applicable ink. Pay attention to the influence of different adhesives when choosing ink.
4. Remaining ink affects adhesion
Some manufacturers often add all the previous remaining ink at one time during production. If the amount of remaining ink is large, it cannot meet the stripping requirements of high-standard products.
Factors that reduce ink adhesion include too thick ink layer, too thin ink blending, too much solvent residue, low surface tension of the film, moisture absorption of the film, ink deterioration, etc., and attention should be paid to control during production.
