Analysis and Research on the best way to improve t

2022-08-03
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Analysis and Research on the ways to improve the fastness of printing ink

from the analysis of the formation mechanism and test methods of printing adhesion fastness, we can better understand the ways to improve the fastness of printing adhesion (mainly on the discussion of polydilute hydrocarbon films)

1. Selection of raw materials in the production of plastic films, raw materials containing no or less plastic additives shall be selected. We can judge the presence of additives according to the relevant technical data on the brand, performance and application of the resin. When raw materials containing more additives have to be used, they should also be mixed with raw materials without additives. The reason for this choice is that the additives folded out during the forming process and placement will form an oil film, thus weakening the adhesion of the ink on the film

2. Modification of raw materials 1) blending modification: blending polyolefins with polymers with good printing properties to improve printing properties is a newly developed and attractive method. For example, the modification of high-density polyethylene with polyacrylic acid resin greatly improves the adhesion of the ink to polyethylene. When 5-20% polymethylmethacrylate (PMMA) is added, the above adhesion is increased by seven times. For another example, when chlorinated polyethylene containing a large amount of chlorine is used for industrial mixing, only a small amount of chlorine can significantly improve the adhesion between polyethylene and oil black. When 5%cpe-55 was added, the adhesion between the blend and ink was three times higher than that of pure HDPE. In addition, according to relevant reports, some processing aids (rheological modifiers, etc.) of plastic polymers can not only increase output and eliminate melt fracture, but also improve printing adhesion. The reason why adding polyacrylic acid resin or chlorinated polypropylene can improve the printability of HDPE is that they are poorly miscible with HDPE. When they first form a dispersed phase in the HDPE based blend system and occupy the surface of the film, it is obviously conducive to bonding with the ink. 2) Grafting modification: grafting modification is to use radiation and other methods to make polyolefin components undergo grafting reaction, so as to make the polyolefin macromolecule chain band polar, and then improve the wettability of the material to the ink. For example, the printability of linear density polyethylene was improved by grafting maleic anhydride or acrylic acid

3) modification by other methods: for example, adding a small amount of maleic acid or its anhydride into polyolefin can also greatly improve the ink fastness of polyolefin films. 3. fastness of printing ink layer ink also plays a decisive role in the fastness of printing ink layer. Of course, the corresponding ink should be used for different substrates. For example, nitrocellulose porphyrin resin ink can be used for cellophane; Chlorinated polypropylene resin ink can be used for polypropylene film; Polyamide resin ink can be used for polyethylene film, etc. In production, we often add a certain amount of solvent in order to adjust the viscosity and volatilization speed of ink

two problems should be paid attention to here: 1) when adding solvent, the solvent with low surface tension should be selected as far as possible to reduce the surface tension of the whole ink system, so as to improve the wettability of the printing film. 2) When the working solid content is too high, the wetting effect will be correspondingly low, which will affect the ink fastness. On the contrary, if too much solvent is added, it will relatively reduce the effective components of the adhesion between the ink and the film, which will also cause a decline in fastness. In order to solve the contradiction between the fastness of the ink layer and the volatilization speed of the ink, the resin (rubber (information, market)) corresponding to the ink or other appropriate compatible bonding resin or rubber can be added to the diluent or the ink. This can also improve the fastness of the ink layer to a certain extent. At the same time, if the ink is placed for too long or mixed with impurities, the connecting material will deteriorate. Therefore, fresh ink should be used as much as possible or the deteriorated ink should be replaced in time

4. Surface treatment from the analysis of ink adhesion fastness mechanism, it can be known that further modification of ink and film can improve the ink adhesion fastness. However, for the sake of cost, the commonly used method is surface treatment of printing film. For PVC, cellophane, polyester, nylon and other films, due to their high surface tension, they can be directly printed when the requirements for printed products are not high (in fact, due to the improvement of customer requirements in recent years, these materials must be treated before printing), while the surface tension of untreated polyolefin films is very low, such as 31 dyne for PE and 29 dyne for PP, which should be increased to 38 dyne 2 for printing, This requires surface treatment of the film. The methods of plastic surface treatment include flame treatment, chemical treatment, solvent treatment and corona treatment, but corona treatment is widely used for polyolefin films. The reasons why corona treatment can improve ink fastness are analyzed by taking polyethylene film as an example. 1) Due to ionization, the oxygen in the air generates ozone, which makes the surface oxidized. The molecular chains of polyethylene on the surface layer may generate carbonyl, carboxyl, hydroxyl and other p-terminal active electrodes. Nitrogen in the air is also ionized into plasma and interacts with polyethylene molecules to generate amine type genes on the polyethylene molecular chain, and can continue to oxidize to generate a series of nitrogen-containing compounds

as a result, the polarity and wettability of the molecules on the surface of the polyethylene film are enhanced, thus improving the ink. Therefore, the system has high precision adhesion. 2) Eliminate some invisible oil (impurities, additives, oligomers, etc.) from the film surface, so that the ink can be in close contact with the film. 3) Because of the impact, the surface is roughened, and the mechanical wedge function is realized. 4) As the surface of the film is heated, the activity of the molecular chain intensifies, that is, the degree of surface activity increases. 5) Under the action of high voltage electric field, the charge in the molecule of the non-conductive plastic film will shift, and the induced charge will be formed on the surface. The existence of this induced charge can generate library attraction with the polar ink molecules, which also plays a role in improving the fastness of the printing ink layer. The following problems should be paid attention to during corona treatment: 1) after corona treatment, it should be used in a short time. Otherwise, if the polar groups are combined with water molecules in the air, the wettability will be reduced and the adhesion fastness of the printing ink layer will be damaged. Therefore, qualified films should be stored in a dry and low temperature warehouse; Check and test again when using. 2) For cold films, high-power electronic surface treatment is required. The cold film shall be preheated with iodine tungsten infrared ray before treatment. 3) If only one side printing is required, only one side corona treatment shall be carried out. Otherwise, it is easy to cause adhesion after printing. 4) At high temperature, if the treatment time is too long, the adhesion tends to decrease. This may be due to the decomposition products on the surface, forming a weak boundary layer in the most widely used conventional plastic granulator equipment

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