Effect of additives on the performance of film flexographic ink
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Flexo ink is called green printing material because it does not produce volatile organic solvents when printing. However, at present, flexo inks account for only 3% to 5% of the market in the field of flexible packaging printing. However, for the safety of packaging, flexo inks should be promoted in soft packaging, especially for baby products, packaging for women's products, and food. In applications such as packaging, this puts higher demands on the performance of flexo inks, forcing the industry to develop and use new flexographic water-based inks. Additives are one of the important components of flexo inks, which are essential for the performance of flexo inks and for improving the quality of flexo printing. In this paper, the effects of different additives such as wetting agent, leveling agent, defoaming agent, filming aid, wax emulsion and pH adjuster on the performance of film flexographic ink are discussed and discussed.
Effect of wetting agent and leveling agent on the performance of film flexo ink
Films such as BOPP are non-absorbent materials with low surface energy. The film flexo ink has a large surface tension and is not ideal for wetting the film non-absorbent material. Adding a suitable wetting agent and leveling agent to the film flexo ink can reduce the static surface tension and dynamic surface tension of the water-based ink, impart excellent wettability and leveling properties to the ink, and improve the spread of the ink on the film surface. Improve the wetting and leveling effect of the ink film. In addition, when high-speed printing is used, the intermolecular distance between the ink and the film surface is rapidly reduced instantaneously. It is also required to add a suitable and efficient wetting agent and leveling agent with low foaming properties for better and faster wetting. Film surface.
Experiments were carried out with 20 kinds of wetting agents and 10 leveling agents from BYK, TEGO, Corning Chemical (China) Co., Ltd. and Air Chemical Company. The experimental results show that the ink leveling effect of the ink on the surface of the film is best when the amount of the wetting agent W4 (organic silicone) and the leveling agent L5 (organic) of the air chemical company are 0.3% and 0.2%, respectively. The ink film is more delicate, and the ink with the added L5 has the best proofing effect.
Effect of Defoamer on the Properties of Film Flexo Ink
Since the film flexo ink contains a foaming surfactant such as a wetting agent, a leveling agent, an emulsifier, etc., excessive bubbles in the ink mixing stage may affect the ink dispersion, and a large amount of bubbles generated in the printing stage may reduce the quality of the printed matter. Therefore, defoamer is an indispensable auxiliary in water-based inks. In the ink dispensing stage of the film flexo ink and during the printing process, the defoaming agent acts to eliminate foam and inhibit foam generation. The defoaming agent not only controls the defoaming speed of the ink distribution and printing stage, but also has good compatibility with the ink system, and does not cause surface defects such as shrinkage of the ink film, orange peel, needle eye, etc., to ensure the smooth progress of the printing process. And print quality.
In order to study the effect of defoamer on the performance of film flexo ink, four different types of mineral oil, non-silicon polymer, polysiloxane and polyether siloxane were selected by dispersing air. Gradient experiments were carried out with 20 defoamers from different manufacturers. Use RK manual flexo proofing machine and IGT flexo proofing machine to perform proofing and printing on BOPP. The experimental results show that the polyether siloxane defoamer F1 has a fast defoaming speed in the film flexographic ink system, but it will cause surface defects such as shrinkage, orange peel and pinhole in the ink film; Defoamer F10 has a fast defoaming speed in the film flexographic ink system, and the leveling and recoating effect is good. The ink film is fine and does not cause the above surface defects. When the amount of F10 added is 0.3% (mass parts), The foaming effect is the best; the sample without the defoaming agent is not well dispersed due to too many bubbles in the ink mixing stage, and the foam disappears slowly after the end of the ink mixing, and the effect is poor. Adding anti-foaming agent F1, F10 ink and ink without anti-foaming agent proofing effect comparison. Therefore, it is necessary to add suitable defoaming agent to film flexo ink, but the amount of antifoaming agent should be guaranteed. Under the premise that the bubble effect is the best, the less the better.
Effect of Filming Aids on the Properties of Film Flexo Ink
The film-forming auxiliary agent greatly promotes the film formation of the film flexo ink, but the film-forming auxiliary agent is an organic solvent, which has a negative impact on the environment. As people's awareness of environmental protection and regulatory standards continue to be stricter, film-forming auxiliaries will develop toward high boiling point, multi-functionality, low odor, multi-component and low toxicity, safe and acceptable biodegradability. .
The high-boiling film-forming auxiliary agent is added to the film flexographic ink formulation to promote the film formation of the film, and better meet the performance requirements of the film flexo ink. However, the high-boiling film-forming auxiliary has a slower volatilization rate and a longer retention time in the ink film. Compared with the low-boiling film-forming auxiliary agent, it has a certain negative influence on the hardness and stain resistance of the ink film. Therefore, multi-functional non-ionic film-forming surfactants can be selected to reduce the surface tension of the ink and ensure low foaming, and also reduce the minimum film forming temperature (MFFT) of the ink, which meets the emission requirements of VOCs.
The non-ionic film-forming surfactants D1 and D2 of Air Chemical Company were selected for experiments. The experimental results show that the two film-forming auxiliaries improve the leveling, film-forming and smash resistance of the ink, and are not added. Compared with the ink of the film additive, the inks added with D1 and D2 have better leveling effect and the ink film is more delicate. In addition, the samples of the same ink sample were dried at 50 ° C for 5 minutes, 10 minutes, 15 minutes, and 30 minutes, respectively. The results show that the ink film has a great improvement in adhesion fastness and enthalpy resistance as the drying time is extended. This may be because the addition of the filming aid reduces the minimum film forming temperature (MFFT) of the ink. The drying time is lengthened, and the film-forming auxiliary agent is released more thoroughly, so that the film forming property of the ink film is improved.
Effect of wax emulsion on the performance of film flexo ink
The addition of an aqueous wax emulsion to the film flexo ink can reduce the ink friction coefficient and improve the slip of the ink, thereby improving the abrasion resistance, scratch resistance, surface hydrophobicity, chemical resistance and stain resistance of the ink film. Sex and anti-blocking.
The wax emulsion with excellent performance recommended by many manufacturers was selected for experiments. The preliminary experiment verified that Wengkel's wax emulsion WE5 had the best effect in formula ink. Samples proofed with ink without added wax emulsion, damaged under 揉搓5, rubbed back and forth once with rough paper, the ink layer was completely destroyed, and the adhesion fastness of the ink film tape (detected with 3M tape) was also slightly poor. After adding 2% WE5 (WE5 solid content is 50%), the ink has a great improvement in the tamper resistance, abrasion resistance and adhesion fastness. There is no damage to the ink film to 100, and the sample is rubbed back and forth with rough paper. 5 times, the ink layer was not damaged, and the adhesion fastness of the ink film tape was also improved. Figure 4 is a comparison of ink proofing effects of an ink with a wax emulsion WE5 and an unwaxed emulsion.
Effect of pH Adjuster on the Properties of Film Flexo Ink
For film flexo inks in which the film-forming resin is an acrylic resin, the change in pH will directly affect the viscosity of the ink. The pH adjusting agent is mainly ammonia, and after the printing ink is transferred to the printing material, the ammonia film is cross-linked to form a salt with the release of ammonia, so that the adhesion fastness of the ink film is better. The pH of the ink was adjusted using an organic amine pH adjuster AMP-95 and a volatile aqueous ammonia, and the drying test was performed. The test shows that the film flexo ink prepared by using AMP-95 has a slow evaporation rate of amine, a long initial drying time, and good resolubility, which meets the requirements of "slow drying, fast drying" of the flexographic aqueous ink; The film flexo ink prepared by using ammonia water is very volatile, and the initial drying time is extremely fast, and the printing process is very easy to cause blocking.
When the pH is 8.0 to 9.5, the ink performance is the best. The pH value is too low (below 8.0), the viscosity of the ink increases, the resolubility decreases, the drying speed increases, the plate and the anilox roll are easily blocked; the pH is too high (above 9.5), the viscosity of the ink is lowered, and the resolubility is improved. The drying speed is slow, which is easy to cause quality problems such as smudging on the back side of the printed matter and mixing the previous color ink when printing one color. Therefore, in the actual printing operation, it is necessary to monitor the pH value of the film flexo ink in real time, and control it between 8.0 and 9.5 to ensure that the ink has good slow drying on the printing plate (slow drying) and good on the film surface. Drying speed (dry and fast).