In the field of printing, from the perspective of environmental protection, all products containing PVC components, including plastic melt inks, will gradually be left out, and the use of water-based inks will become more and more common. But the problem is that printers are already used to using plastic melt inks. They use water-based inks in the same way and evaluate the printing effect of water-based inks in the same way. This is an absolutely wrong concept. Compare water-based inks, and introduce in detail how to use water-based inks.
Manufacture of environmentally friendly plastic melt ink
Although plastic melt inks are not as good as water-based inks in terms of touch, hygroscopicity and breathability, people still hope to have a PVC-free plastic melt ink replacement product, and the printed images have characteristics such as touch, visual sense and tensile deformation. Similar to plastic melt ink, this idea is deeply ingrained in the clothing printing industry, because the clothing printed by plastic melt ink has too much and too much influence on consumers. Consumers not only accept this kind of clothing, but also expect it Can last. In the future, apparel consumers may require printed patterns to still look like fabrics and feel soft as water-based inks, or printed patterns appear to be worn out as if they were plastic melt inks. Uncured completely washed off part of water.
Customers are always correct. In order to meet the needs of customers, ink manufacturers produce imitation plastic melt inks. The printing effect is similar to plastic melt inks, but the stretchability is very good. Many garments in Australia now use imitation plastics. It is undesirable that the melt-printed inks are not convenient to use, so ink manufacturers still spend their energy on the research and production of water-based inks.
In order to encourage printers to use water-based inks instead of plastic melt inks, manufacturers of water-based inks have indeed made some efforts. They have invested in many aspects, such as advertising, participating in exhibitions, and conducting product promotion lectures.
The reason why plastic melt ink is accepted by most printers is because it is easy to operate and welcomed by customers. When it comes to the convenience of plastic melt ink, it mainly means that it will not dry on the screen, and is not limited by time. Sometimes the ink can be placed on the screen for a weekend or even two weeks without drying, and the printer can continue For printing, the water-based ink placed on the screen for a long time will evaporate and the ink will dry. Therefore, the printer will not discard the plastic melt ink and use the water-based ink anyway, which makes the work more difficult. Some small garment printers believe that if the government does not allow the use of plastic melt inks one day, they will have to leave the business behind closed doors.
If only water-based inks are allowed, some large-scale clothing printing factories can only lose their business and find other ways to make money. For these reasons, ink manufacturers strive to research and develop aqueous inks with the printing characteristics of plastic melt inks instead of producing an aqueous ink to replace plastic melt inks. With the government's policy to reduce the use of plastic melt inks, ink manufacturers mainly target most plastic melt ink manufacturers to produce easy-to-use water-based inks. As long as the printers cooperate actively, water-based inks are also easy to operate.
The general transparent water-based ink is very easy to flow, and can be printed continuously without drying on the screen, but the problem is that if the water-based ink is treated as a plastic melt ink, the water-based ink will eventually block the mesh. In order to make the plastic melt ink The user uses the water-based ink smoothly, and the ink manufacturer conducts a new research. For the ink manufacturer, the most difficult problem to solve is that the general plastic melt ink printing steps are completely unsuitable for the printing process of water-based ink. The ordinary plastic melt ink printing step, we call it the worst printing scheme (abbreviated as WCS).
We used 230T silk screen for the experiment. The lines in the printed image ranged from half a millimeter to a few millimeters. Of course, there were also on-site tests. The experiment was conducted at room temperature, with a relative humidity of 30%. In the process, when the ink color begins to darken, we add a little water to prevent the ink from clogging the screen. If you print the one color ink, do not re-cover the ink on the screen, just like printing plastic melt ink, then After printing for about 4 minutes, the water-based ink will block the screen, and the ends of some thin lines cannot be printed. After 2 minutes, 50% of the thin lines or more lines will not be printed. If the printing time of water-based ink is long, the washing fastness of the printed fabric will decrease.
Water-based ink printing
In order to maximize the printing time of water-based inks, it is best to avoid fine lines or dot images in the printed images. In particular, when printing with covering water-based inks and discharge inks, the width of the image lines should not be less than 1.5mm . When printing water-based inks on black fabrics, printers are advised to consider the reverse, that is, printing black inks on white fabrics, because water-based inks are very breathable and feel good, customers will not have a sense of weight when wearing this type of clothing.
Some covering water-based inks can be wet-pressed and wet-printed on a white base material, but according to the characteristics and printing equipment of existing water-based inks, water-based inks will fail after a period of time, because the WCS printing schemes cover inks Very inappropriate. We use 156T silk screen to print white base material and print patterns on the white base material at room temperature with a relative humidity of 35%. After printing each color, ensure that the ink is overlaid on the screen and from time to time. Add water to it, so that it can be printed for 4 hours, and 0.5 mm wide lines can not be printed at both ends, and 1 mm wide lines are well printed.
If one color is printed and the ink is not overlaid on the screen, the line with a width of 0.5 mm will not be printed after 8 minutes of printing, and the line thinner than 2 mm will not be printed completely after 12 minutes. It is a big problem for printers who often use plastic melt ink to print. Of course, the experiment here is just a comparison and does not reflect the printing characteristics of other covering inks or water-based inks.
Using existing screen printing conditions, printing workers based on plastic melt ink can use discharge ink to print on dark clothing. Discharge ink should be printed on the clothing that can be discharged and the ink should be dried for a long enough time to obtain good washing fastness. At the same time, the printing color is good and the printed image feels good. Even if the drying time is long enough, the wash fastness of garments printed with discharge inks is still not as good as the wash fastness of garments printed with normally cured plastic melt inks, but if we want to use discharge inks instead of plastic melt inks, and If the feel of the printed image is not high, we can print a layer of transparent protective oil on the image printed by the discharge ink to solve the problem of poor wash fastness. So far there is no effective chemical agent that can reduce the curing time of discharge ink. [next]
To prevent the stencil from breaking, and adjust the screen production process
Stencil rupture is a frequent failure of printing water-based inks. Therefore, use a water-resistant photosensitive emulsion, complete exposure and complete drying to enhance the water resistance of the stencil. It is recommended to use a hardener, especially when printing discharge inks. Hardener.
But through experiments, the above reason seems to be outdated, because when implementing the WCS scheme to clean the screens clogged with water-based ink, it is not as expected, that is, the use of Ulano ’s water-resistant photosensitive emulsion and hardener , And the exposure is correct, but when cleaning the screen clogged with water-based ink, the stencil where the thin lines are still broken. In this case, the experts used water seal oil, which is usually used on wooden decks. The experts applied the water seal oil on the screen with a cloth, dried the image part, and dried it with a drying box. Screen drying, before the end of the work every day, use the same method to process the screen again, so that not only does the template not break, but also the place clogged with ink is easy to clean. Experts have tested some variables, so the water seal oil is included in the screen auxiliary materials, and the water seal oil must be used before printing. When printing with water-based ink, the following auxiliary materials are required:
Water seal oil: This material can be purchased in construction stores, coated on the screen before printing and processed after the printing is completed every day.
Water-resistant tape: It is very important to use suitable tape. When the tape is sealed, the air should be fully removed to ensure sufficient adhesion.
Multifunctional cleaning agent: This multifunctional cleaning agent is packaged as a spray and is available on the market. It can not only clean dry ink, but also spray lightly on the back of the screen to open the clogged mesh.
Screen cleaner: If the multifunctional cleaner cannot remove dirt, you can use screen cleaner to clean the screen.
Nail polish: available in supermarkets. Nail polish can quickly seal the pinhole on the template, and the nail polish is water resistant. Color nail polish is better than colorless nail polish.
Buckets and sponges: For printing with water-based inks, you should prepare multiple buckets of water (one bucket of water per color ink) and some sponges. This is very convenient for cleaning dirt, especially when printing discharge inks, you need to wash the ink on your hands.
Paper towels or rags: After cleaning the screen, you need to dry the screen with a paper towel or rag. When printing discharge ink, be sure to wipe the back of the screen with a paper towel.
Plastic film: In the printing gap, in order to prevent the water-based ink from drying on the screen, the plastic film can be covered on the screen.
Avoid ink drying on the screen
Before printing, we must consider what method to avoid the ink drying on the screen, especially to prevent the ink from drying on the image part. The key to the success and failure of printing water-based ink is the proper operation of the ink. When printing plastic melt ink, the printer may not need to consider the drying problem of the plastic melt ink. The plastic melt ink can be placed on the screen without disregarding it until the ink is added or the ink is removed. Printing water-based inks needs to develop the habit of paying close attention to inks. If you are not ready to print, do not put ink on the screen. Try to eliminate the factors that make the ink dry. For example, the fan of the printing workshop is best to turn off.
Tips for cleaning screens
If printing is completed or it takes a long time to continue printing, you need to scrape the ink from the image part of the screen to the bottom of the screen, and wipe the image part of the screen with a damp sea surface. You can also use a screen cleaner Wash the image part to prevent the ink from drying on the screen, and finally put the ink back into the packaging jar. If the non-image part of the screen still has ink or dirt, it will have little effect on reprinting. All dirt on the screen will be removed during the screen recovery process.
New method for drying water-based ink
The equipment used to cure plastic melt inks is not suitable for the curing of water-based inks. In addition to discharge inks, other water-based inks contain chemical cross-linking agents, and water-based inks must be sufficiently dried to ensure the wash fastness of printed images. Some printing plants choose air drying for the curing of water-based inks. Some printing plants directly contact the printed matter with a hot platform before the ink is dried to evaporate the water, and then put the printed matter into the oven.
Before the paper is coated, the drying equipment should be used to remove the moisture from the paper. This drying equipment is also suitable for removing moisture from the water-based ink. Perhaps the most reasonable way to get rid of water is to avoid adding water to printing. So if it is possible to print transparent inks on light or white fabrics, this means that fine screen printing of transparent inks will be used and there will be very little moisture. [next]
Adjust printing process or means
Printing water-based inks should not be handled like printing plastic melt inks. In general, the screen pitch has little effect on the printing of water-based inks, and the use of glue with moderate hardness, the minimum printing pressure is the key to water-based ink printing. When printing discharge ink, the printing pressure of the squeegee is required to be large, and the faster the printing speed, the better the effect. This can be done by several trial printings and then recording the best results.
Some plastic-melt ink products are not as soft as plastic-melt inks. You can use printing hood printing oil, adding chemical cross-linking agents and other methods to improve the printing feel and improve the washing fastness of printed images. A German company began printing water-based inks on fabrics a few years ago. Instead of flash curing, they used ultra-low temperature methods to cure water-based inks.
Production of equipment suitable for water-based ink printing
At present, most textile printing equipment is mainly based on plastic melt ink printing. Water-based ink drying oven should have airflow to accelerate the drying speed of ink. However, most infrared ovens have no airflow. If the airflow is increased, the drying temperature will be decline.
Flash curing is very effective for drying plastic melt inks printed on dark clothing, but it is not suitable for drying water-based inks, because plastic melt inks can be flash cured in only 10 to 15 seconds, and water-based inks are always Nor will it have this feature. In Europe, ultra-low temperature printing platforms have been used to freeze water-based inks. Some years ago, some people used hot printing platforms to print water-based inks, but this did not change the printer ’s insistence on using plastic melt inks.
If the printer's concept changes and he wants to use water-based ink, equipment manufacturers will consider the problem of water-based ink drying on the screen when producing the printing press. If one day the printer uses water-based inks to print textiles, equipment manufacturers will consider the possibility of designing an automatic closing device for the screen. When the printing is stopped, the screen is automatically closed, and the ink will not dry on the screen.
If the external conditions that accelerate the drying of the water-based ink are eliminated, the printer needs to consider how to slow down the drying speed of the ink rather than adding more retarder. Because too much retarder will reduce the washing fastness of clothing, not to mention that ink manufacturers have added a certain amount of retarder when producing ink. In order to prevent the ink from drying when printing water-based inks without cross-linking agents, some printers cover the screen with a plastic film or wrap the entire screen with a plastic bag, and then go home from work or weekends before going to work Remove the plastic film or plastic bag to continue printing.
When printing with water-based ink, use plastic film to cover the screen, and add some water to the ink from time to time to make the ink shiny. This is a very effective method to prevent the ink from drying. Discharge inks and covering water-based inks, even if they are not dry, will gel with time. Therefore, when printing is resumed, wipe the image portion of the screen with a damp sponge to start the ink flow again. This method is not suitable for inks containing catalysts or low-temperature chemical cross-linking agents, because the catalysts or cross-linking agents will solidify and deteriorate.
in conclusion
Since it is impossible for water-based ink to penetrate into every thread of the fabric, it is normal to see the printed image break when the fabric is stretched. This is normal, and customers should admit this fact if they require the water-based ink to print the fabric. Can not be compared with the printing effect and printing feel of plastic melt ink.
Once the printer has mastered the skills of water-based ink printing, water-based ink is not just a substitute for plastic melt ink. Monochrome pedal sports caps printed with reflective water-based ink are sold for $ 50 each, while plastic melt The market price of six-color T-shirts printed with ink is only $ 5. Which print order are you willing to accept? People who regularly do running exercises will definitely stand in line to buy T-shirts printed with reflective ink, because wearing reflective T-shirts is obvious in the dark, and it is easy to be noticed, which makes runners more secure.
When printing plastic melt ink on cotton cloth, the printed image cannot be ironed, and clothing printed with water-based ink can not only iron, but also dry clean. In short, the advantages of printing with water-based ink are many, so the printer may wish to try it in person.
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