What happens when the ink layer is not strong after compounding and the ink layer is transferred when peeling off?
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Many packaging materials have exquisite patterns and necessary textual descriptions, all of which are printed with ink, and the ink layer is between the film and the sublayer film. Since the ink layer is protected by the surface film, it is not afraid of abrasion and scraping, and there is no disadvantage that the printing ink is easy to fall. However, there is a case where the ink layer is transferred at the time of peeling after the compounding, and the fastness between the original base film (usually mostly BOPP, PET or BOPA film) is poor, and the peeling force exhibited is also low. In another case, after the contents of the composite bag are filled with certain contents, especially the contents of the aromatic, pungent or surface active substances are stored for one or two weeks or months, the ink layer is automatically layered, even It shows the phenomenon that the ink is sticky. There are several reasons why the ink layer is not strong and the ink layer is transferred during peeling.
(1) The surface treatment strength of the base film before printing is insufficient, and the surface tension is low, even less than 38 mN/m.
Although the ink used is a printing ink, its printing fastness is not high, and it is easy to be pulled down when it is peeled off with a tape. If this is the case, the base film with a surface tension that meets the printing requirements must be used, at least greater than 38 mN/m, or reprocessed to greater than 38 mN/m.
(2) The printing fastness of the ink is acceptable. When the tape is peeled and peeled off, it cannot be pulled down. However, when peeling off after compounding, the ink layer is transferred again, and the peeling force is also low.
This phenomenon is not the cause of the surface tension of the base film. We know that the fastness between the ink and the substrate is achieved by the affinity between the binder and the substrate in the ink. The affinity is polar attraction, dipole moment, intermolecular attraction or dispersion force. The comprehensive manifestation, strictly speaking, is a physical force, not a chemical bond of a chemical structure.
The adhesive used in the compounding, the fastness between it and the two adherends, in addition to the same physical force as the ink, plus another chemical bonding force that is much larger than the physical force. Therefore, the fastness between the ink layer and the sub-layer film is generally greater than the fastness between the ink layer itself and the substrate film. Therefore, at the time of peeling, most of the ink layers are removed from the original substrate film and transferred. However, a good ink exhibits a high peeling force and does not transfer 100%; a bad ink will transfer 100% and the peeling force is small.
(3) Special inks must be used to fundamentally guarantee quality.
First of all, the composite ink must be used in the composite material, and the surface printing ink cannot be used. The connecting material of the printing ink is composed of chlorinated polypropylene, vinyl chloride-vinyl acetate copolymer, chloroacetic acid copolymer and MP-45 resin (imported resin for printing ink), which is compounded at present. The most used BOPP film in the material has good affinity. As long as the surface tension of the BOPP film is higher, the printing fastness is satisfactory, especially the quality of the polyurethane ink is better.
The connecting material of the surface printing ink is mostly a single polyamide resin, and the ink is not suitable for the printing of the composite product. Because of the cost considerations, we have found that some small factories use surface-printing inks to make composite products. Most of their products have ink layer transfer and peeling force is extremely small.
The higher-grade composite ink printed in the printing is a two-component polyurethane ink, which is of the same type as the two-component polyurethane adhesive used in the composite, and has better fastness to various printing base films than the former printing ink. It is much larger, and has ideal printing fastness to BOPP, PET, OPA, aluminum foil and other substrates. It is also very suitable for composite adhesives. As long as the ratio is used properly, the ink also has high temperature resistance and resistance to medium corrosion. It is the most ideal ink for solving the problem of ink layer transfer and peeling force.
(4) Under the premise that the ink type is a one-component printing composite ink, if you want to improve the printing fastness, avoid 100% ink layer transfer, and maintain a slightly higher peel strength, you can add 5% to the composite ink. (mass fraction) of "curing agent".
This "curing agent" is a curing agent in a versatile two-component ink, and is generally a "curing agent" in a two-component polyurethane adhesive used in dry compounding. The information reported by the unit using this method shows that this method has practical effects. However, it must be stated here that this method can be used only in the case of printing ink of good quality and without alcohol, and this method cannot be used if the ink contains a solvent of active hydrogen such as alcohol.
(5) In addition to the ink factor, it is also possible to use a kind of adhesive which has strong permeability and can increase the fastness of the ink and the base film when selecting a composite adhesive.
The adhesive contains a rubber compound with a smaller molecular weight, which is more easily transported by the solvent than the large molecular weight rubber to the surface of the base film, so that the ink not only depends on the physical structure between itself and the base film. Combine the force, and also add the chemical bond force of the adhesive to achieve higher fastness.
If the contents of the erosive effect are packaged, the high-quality oil of the medium-resistant type should be carefully considered due to the effect of the medium on the ink causing stickiness and separation. Because this phenomenon is a quality accident that cannot be detected before the composite bag is shipped from the factory, it will appear after a long period of packaging of the goods, and the loss caused by this will not be recovered. Therefore, in this case, the use of ink, must be more careful and more careful.