Comparison of the use of plastic melt inks and water-based inks in printing

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 common. But the problem is that printers have become accustomed to the use of 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. This paper will deal with plastic melt inks. Water-based inks are compared and the use of aqueous inks is described in detail.

Manufacturing environmentally friendly plastic melt ink

Although plastic melt inks are inferior to water-based inks in terms of handfeel, hygroscopicity, and breathability, there is still a desire for a plastic-free ink-free alternative to PVC, where the printed image is characterized by feel, feel, and tensile deformation. Similar to the plastic melt ink, this idea is already ingrained in the garment printing industry because the clothing printed with plastic melt ink has too great influence on the consumers. Consumers not only accept such clothing, but also look forward to it. Lasting. In the future, clothing consumers may require the printed pattern to remain as cloth-like visually, feel as soft as water-based ink, or the printed pattern appears to be worn out as if it were a plastic melt ink. Uncured completely washed off part of it.

The customer is always right. In order to meet the needs of customers, ink manufacturers produce plastic melt inks. The printing effect is similar to that of plastic melt inks, but the stretchability is very good. Nowadays, many clothing in Australia are used for plastics. The printing of melt inks is not ideal because such plasticized melt inks are inconvenient to use, so ink manufacturers still devote their energies to 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 do have some work. They invest in many aspects, such as advertising, attending exhibitions, and conducting product promotion seminars.

The reason why plastic melt ink is accepted by most printers is because it is easy to operate and is welcomed by customers. When it comes to the convenience of plastic melt ink, it mainly means that it will not dry on the screen, not subject to time constraints, sometimes the ink can be placed on the screen for a weekend or even two weeks without drying, the printer can then For printing, the water-based ink will be evaporated on the screen for a long time, and the ink will dry out. Therefore, the printer is not willing to discard the plastic ink and use the water-based ink anyway, which makes it more difficult for one's own work. Some small-scale clothing printers think that if one day the government does not allow the use of plastic melt ink, they only leave the business behind closed doors.

If only water-based inks are allowed, some of the larger clothing printers can only lose their business and look for other ways to make money. For these reasons, ink manufacturers are striving to develop water-based inks that have the printing properties of plastic melt inks instead of producing a water-based ink to replace the melt-molding ink. With the government's policy of reducing the use of plastic melt inks, ink manufacturers mainly produce inks that are easy to use for most plastic melt ink manufacturers. As long as the printers actively cooperate with them, water-based inks are also easy to handle.

General transparent water-based inks can easily flow and can be continuously printed without drying on the screen, but the problem is that if the water-based ink is treated like a plastic melt ink, the water-based ink will eventually block the mesh, in order to make the melt ink Users are using water-based inks smoothly. The ink manufacturers re-study the research. For ink manufacturers, the most difficult problem to solve is that the printing and use procedures of general plastic-melt inks are completely unsuitable for the printing process of water-based inks. The printing step of ordinary plastic melt ink, we call it the worst printing scheme (abbreviated as WCS).

We use 230T wire mesh for experiments. The lines in the printed image range from a half millimeter to a few millimeters. Of course, there are also experiments. The experiment is conducted at room temperature, the relative humidity is 30%, and the printing ink is a general black transparent water-based ink. During the process, when the color of the ink begins to darken, we add a little water to prevent the ink from blocking the screen plate. If we print a single color ink and do not re-apply the ink to the screen, just like printing plastic melt ink, when About 4 minutes after printing, the water-based ink will block the screen, and some thin lines will not be printed on both ends. After 2 minutes, 50% of thin lines or more lines will not be printed. Water-based inks take a long time to print, and the wash fastness of printed fabrics 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 for printed images. In particular, when printing with masking water-based inks and discharge inks, the image line width must not be less than 1.5 mm. . When printing water-based inks on black fabrics, it is recommended that printers in turn consider that black inks are printed on white fabrics because the water-based inks have good air permeability and feel, and customers don't feel heavy when they wear such garments.

Some maskable water-based inks can be wet-on-wet printed on white substrates, but according to the characteristics of existing water-based inks and printing equipment, water-based inks will fail after printing for some time because of the WCS printing scheme for masking inks. Very inappropriate. We used a 156T screen to print a white material at a relative humidity of 35% at room temperature and print a pattern on a white substrate. After each color is printed, we ensure that the ink re-applies to the screen, and from time to time we go to the ink. Add water, so that you can print for 4 hours, and the 0.5 mm wide line can only be printed on both sides, and 1 mm wide lines print well.

If one color is printed and the ink is not overlaid on the screen, the 0.5 mm wide line will not be printed after 8 minutes of printing, and the line thinner than 2 mm will not print completely after 12 minutes. It is a big problem for printing workers who often use plastic melt ink to print. Of course, the experiment here is only a comparison and does not reflect the printing characteristics of other hiding inks or water-based inks.

Utilizing existing screen printing conditions, printers based on plastic melt inks can use discharge inks to print on dark garments. Discharge ink should be printed on clothing that can be discharged and the drying time of the ink should be long enough to obtain good wash fastness, good color printing at the same time, and good feeling of printed image. Even if the drying time is long enough, the washfastness of garments printed with discharge ink is still not as good as the fastness of garments printed with normal cured plastic melt inks, but if we use discharge inks instead of plastic melt inks, and If the feel of the printed image is not high enough, we can print a layer of transparent protective oil on the printed image 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.

Prevents stencil breakage and adjusts screen making process

The stencil break is a fault that often occurs in the printing water-based ink. Therefore, it is necessary to use a water-resistant sensitizing emulsion, and the exposure is complete and dry completely, so that the water resistance of the stencil is enhanced. It is recommended to use a hardener, especially when printing and discharging the ink. Hardener.

However, through experimentation, the above reason seems to be outdated, because the implementation of the WCS scheme to clean the screen block of water-based ink blockage is not as expected, that is, the use of Ulano's water-resistant emulsion and hardener. , And the exposure is correct, but when cleaning the screen blocked by water-based ink, there is still a break in the stencil where the thin lines are located. In this case, the experts used sealant oil, which is usually used on wooden decks. The experts used a cloth to coat the sealant on the screen, partially dried the image, and used a drying box. The screen plate is dried, and before the end of work every day, the screen plate is processed again in the same way so that the plate is not broken, and the place blocked by the ink is also easy to clean. Experts passed tests on a number of variables, so they included water seal oil in the screen auxiliary materials, and they must use water seal oil before printing. When printing with aqueous ink, the following auxiliary materials are required:

Water seal oil: This material can be purchased in a construction shop, coated on a screen before printing and processed after the end of printing every day.

Water resistant tape: It is very important to use suitable tape. When the tape is sealed, the air should be fully expelled to ensure adequate adhesion.

Multi-Functional Cleaner: This multi-purpose cleaner is a spray package that is commercially available. Not only can it clean the dried ink, it can be lightly sprayed on the back of the screen to open the blocked mesh.

Screen cleaner: If the multifunctional cleaner cannot remove dirt, you can use a screen cleaner to clean the screen.

Nail polish: available at the supermarket. Nail polish can quickly seal the needles on the stencil and the nail polish resists water. Color nail polish is better than colorless nail polish.

Buckets and Sponges: For printing with aqueous inks, multiple buckets of water (one bucket of ink per color) and some sponges should be prepared, which is very convenient for cleaning dirt, especially when printing printing and discharging inks. It is necessary to wash the ink contaminated by hands.

Paper towels or rags: After cleaning the screen, it is necessary to dry the screen with a paper towel or a rag. When printing the ink, be sure to dry the back of the screen with a paper towel.

Plastic film: In the printing gap, to prevent the water-based ink from drying on the screen, the plastic film can be covered on the screen.

Avoid ink on the screen

Before printing, it must be considered what method to use to prevent the ink from drying on the screen, in particular to prevent the ink from drying at the image portion. The key to the success and failure of printing aqueous ink is the proper operation of the ink. When printing plastic melt ink, the printer can not consider the dry-solid problem of the plastic melt ink, and the melted ink can be placed on the screen without the tube, until the ink is added or the ink is removed and no longer printed. The printing water-based inks need to develop a habit of paying close attention to the ink. If you do not want to print, do not put ink on the screen. Try to eliminate the factors that make the ink dry. For example, the fan in the printing shop is best turned off.

Tips for cleaning screens

If the printing is finished or the printing needs to be continued for a long time, then the ink needs to be scraped from the image portion of the screen to the bottom of the screen, and the screen portion is wiped with a damp sea surface. If necessary, a screen cleaning agent can also be used. The image was washed to prevent the ink from drying on the screen and finally the ink was put back into the can. If the non-image part of the screen still contains ink or dirt, this will have little effect on reprinting. All the dirt on the screen will be removed during screen recovery.

A new method for drying water-based inks

The equipment for curing plastic melt inks is not suitable for the curing of aqueous inks. In addition to discharging inks, other water-based inks contain chemical cross-linking agents. Water-based inks only get sufficient drying to ensure the fastness of printed images. Some printing plants choose air-drying methods for curing water-based inks. Some printers place the prints directly in contact with a hot stage before the ink dries, allowing water to evaporate, and then placing the prints in the oven.

Before the paper is coated, the moisture in the paper is removed by a drying device. This drying device is also suitable for water elimination in the aqueous ink. Perhaps the most reasonable way to remove moisture is to avoid adding water to the printing. So if it is possible to print a clear ink on a light or white fabric, this means using a fine screen-printed clear ink, which will have little moisture.

Adjust the printing process or means

Printing water-based inks do not operate like printing plastic melt inks. In general, the net distance has little effect on the printing of water-based inks, but the use of a moderate hardness of the squeegee, the printing pressure is the key to the water-based ink printing. When printing a discharge ink, the printing pressure of the squeegee is required to be large, and the faster the printing speed is, the better the effect is. This can be done by several trial prints and then record the best results.

Some products that mimic melt inks are not as soft as plastic melt inks. They can use printing mask oil, chemical cross-linking agents and other methods to improve the printing touch and improve the fastness of printed images. A German company began printing water-based inks on fabrics a few years ago. Instead of flash curing, they use ultra-low temperature methods to cure aqueous inks.

Production of equipment suitable for aqueous ink printing

At present, most textile printing equipment is based on plastic melt ink printing. The drying of the water-based ink should have airflow to accelerate the drying of the ink. In most infrared ovens, there is no air flow. If the air flow is increased, the drying temperature will increase. decline.

Flash curing is very effective for the drying of plastic printing inks printed on dark clothing, but it is not suitable for the drying of water-based inks, because it takes only 10 seconds to 15 seconds for the plastic ink to be cured by flash, and the aqueous ink is forever It will not have this feature. In Europe, ultra-low temperature printing platforms were used to freeze water-based inks. Some years ago, some people had used hot printing platforms to print water-based inks, but this did not change the idea of ​​printers insisting on the use of plastic melt inks.

If the concept of the printer is changed and the use of water-based ink is desired, equipment manufacturers will consider the problem of water-based ink drying on the screen when producing the printing machine. If one day printers use water-based inks to print textiles, equipment manufacturers may consider that an automatic closing device may be designed for the screens. When the printing is stopped, the screens are automatically closed and the ink is not dried on the screens.

If the external conditions that accelerate the drying of water-based inks are eliminated, the printer needs to consider how to slow the drying of the ink rather than adding more retarder. Because too much retarder will reduce the washing fastness of clothing, not to mention the ink manufacturer has added a certain amount of retarder in the production of ink. Some printers print inks containing no cross-linking agent to prevent them from drying out. They use plastic film to cover the screen or use plastic bags to cover the entire screen. Then they come home from work or over the weekend, and then go to work. Remove the plastic film or plastic bag to continue printing.

When printing with a water-based ink, a plastic film is used to cover the screen, and a little water is added to the ink from time to time to make the ink glossy. This is a very effective method for preventing the ink from drying. Dyeing inks and hiding water-based inks will gel over time even if they are not dry, so when you restart printing, wipe the screen part of the screen with a damp sponge to make the ink flow again. This method is not suitable for inks containing catalysts or low temperature chemical crosslinkers because the catalyst or crosslinker will coagulate and deteriorate.

in conclusion

Since it is impossible for water-based ink to permeate into each thread of the fabric, it is normal for the printed image to be broken when the fabric is stretched. This is normal, and customers should acknowledge this fact if they require water-based ink to print the fabric. Can not be compared with the printing effect of plastic melt ink, printing feel.

Once the printer has mastered the technique of water-based ink printing, water-based ink is not only a substitute for plastic melt ink, a monochrome sports car with a reflective water-based ink to sell to one of the 50 US dollars, and plastic melt The market price of six-tone T-shirts for printing inks is only 5 US dollars. Which print order would you like to accept? Runners who exercise regularly will surely stand in teams to buy T-shirts printed with reflective ink, because they wear reflective T-shirts. Obviously in the dark, it is easy to be noticed, giving runners a sense of security.

Printed plastic printing ink on the cotton cloth, its printed image can not be ironed, and water-based ink printed clothing can not only iron, but also dry cleaning. In short, the advantages of printing with aqueous ink are many, so the printer may wish to try it for himself.

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