The "pit" that must be recognized by the advanced road of the intaglio ink
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As we all know, the printing of cigarette packets is mainly gravure printing, while the traditional gravure printing uses solvent-based inks, which is the “culprit” of the residual solvent of cigarette packets. The water-based ink uses water as the main solvent and water-based ink instead of solvent-based ink. It can effectively solve the problem of high residual solvent of cigarette packets.
In the following, taking a cigarette package product of the author company as an example, the application of gravure aqueous ink in the field of cigarette package printing is discussed.
Process improvement program
The printing scheme of the cigarette packet box product is: 4-color pattern + 2-color solid spot color + glazing (as shown in FIG. 1). Among them, the spot color part of the field accounts for about 90% of the total area of the product, and it is changed to water-based ink printing; the 4-color pattern is still printed with solvent-based ink.
The purpose of this process improvement is to solve the problem of high solvent residue in the cigarette packet box product. In view of the disadvantages of slow drying speed and poor leveling in the ground, compared with solvent-based inks, the ratio of the first to the first is The larger area of the spot color section was improved.
Process adjustment
In view of the two shortcomings of slow drying speed of water-based ink and poor leveling in the field, our company has adjusted the process as follows.
1. Slow drying speed
Drying performance is one of the main indicators of water-based inks. The drying speed of the aqueous ink is slower than that of the solvent-based ink, and once the drying is insufficient, an ink sticking phenomenon occurs. The solution is as follows:
When the printing speed is kept at 156 m/min, the drying temperature is raised from the original 52 ° C to 62 ° C;
Change to shallow net, change the depth of the gravure cell from the original 53μm to 43μm.
After the above process adjustment, the drying performance of the aqueous ink has been improved to some extent.
2. Poor leveling in the field
Water-based inks use water as the main solvent, but the surface tension of water is large, which makes the wetting of printing materials and pigments difficult, resulting in poor leveling of the final printed products. The solution is as follows:
Ink suppliers cooperate with our company to carry out relevant tests, adjust the formulation of water-based inks, reduce the surface tension of water-based inks, and enable the water-based inks to fully wet and level on the paper surface, and transfer them more evenly;
Adjust the ratio of water to ethanol, increase the viscosity of water-based ink and strictly control the viscosity change, increase the oven temperature, increase the amount of blowing, and ensure that the water-based ink is completely dried;
In the gravure process, a new amount of ink is added in a small number of ways to ensure the stability of the pH of the aqueous ink.
Comparison of indicators before and after improvement
1. Comparison of solvent residues
Ten samples of cigarette packs before and after the improvement were randomly selected and tested according to YC/T 207-2014 "Determination of Solvent Residues in Tobacco Paper by Headspace-Gas Chromatography/Mass Spectrometry". The solvent residue comparison is shown in Table 1.
It can be seen from Table 1 that the residual amount of the tobacco packet solvent after the process improvement is significantly reduced, which effectively solves the problem of high solvent residue of the cigarette packet box product.
2. Comparison of printing quality indicators
Samples of cigarette packs before and after improvement were randomly selected and tested according to GB/T 7705-2008 "Platinum Printed Matter" and GB/T 18348-2008 "Inspection of Printed Barcode Symbol Quality of Commodity Barcodes", samples of cigarette packs A comparison of several major printing quality indicators is shown in Table 2.
It can be seen from Table 2 that after the replacement of the water-based ink, the printing quality of the cigarette packet product can also be guaranteed.
Benefit Analysis
(1) Although the price of the aqueous ink is slightly higher than that of the solvent type ink, the coating amount (the amount of ink consumed per unit printing area) is relatively small. It has been tested that the use of aqueous inks can reduce the coating amount by about 10% compared to solvent-based inks, that is, the printing of the same number and size of printed inks, the consumption of aqueous inks is reduced by about 10% compared to solvent-based inks. Moreover, the solution for cleaning the intaglio plate is also changed from organic solvent to water, reducing the amount of organic solvent used. Therefore, water-based inks are more economical from the perspective of resource consumption.
(2) When printing with solvent-based ink, a certain solvent evaporation time is required after the product is produced. After the water-based ink is used, the printed product can be directly sealed and delivered without additional space and time for solvent evaporation. Not only shortens the production cycle, increases production efficiency, but also saves production space.
(3) After the process is improved, the volatile organic compounds emitted during the printing process and the cleaning process of the cigarette packet box product are significantly reduced, the environment of the production workshop is greatly improved, and the health of the operator is beneficial.
Precautions
(1) When solving the problem of slow drying speed of water-based ink, when setting specific parameters, the printing speed, gravure depth, oven power and wind speed should be comprehensively considered according to the situation of the printing equipment.
(2) Since the aqueous ink is insoluble in water after drying, it is necessary to keep the intaglio plate roller in a rotating state in the ink tank when the printing is stopped in the middle.
(3) Thinner ratio: Generally, the ratio of ethanol to water in the aqueous ink diluent is between 1:1 and 4:1, but it should be noted that when increasing the proportion of water, it is necessary to consider the addition of water. Quantity, if the amount of water added is too much, one will produce too many bubbles, and the second will lead to incomplete drying of the ink, resulting in sticky or ink anti-sticking of the printed product.
(4) The diluent of the aqueous ink is ethanol and water, and the diluent of the solvent type ink is n-propyl acetate. The two thinners on the production site should be clearly marked, stored separately, and added separately.
(5) Water-based inks are prone to false shadows when printing small characters and lines, and the dots are easy to increase and deform. Therefore, it is necessary to refine the small characters and lines in advance when making plates, and then adjust the dots according to their own equipment and printing conditions.
(6) In the process of gravure printing, after the aqueous ink is circulated for a long time, the performance of the water-based ink is reduced due to the decrease of the binder or the evaporation of the amine substance, resulting in deterioration of the leveling property in the field. When the problem is slight, a large amount of new ink can be added to solve the problem; if the problem is serious, if the water-based ink is contaminated, it is necessary to replace the new ink. Therefore, in the production process, try to match the water-based ink as needed, do not adjust.