Liquid Coating: Coating Technology for Print Protection
Liquid coating machine
The liquid laminator is actually a coating device. From the most basic point of view, the print must first be fed into the laminator, then coated, and finally entered. The intermediate and final steps in the lamination process depend primarily on the type of coating you choose. It can be either a UV-curable coating or an aqueous or solvent-based coating. For example, substrates that have undergone UV coating must be processed by the drying unit prior to export, while substrates coated with water-based coatings can be selected to add an infrared drying process based on the automation level of the laminator. Increase the drying effect of prints
In order to meet the different needs of users, liquid laminating machines also have a variety of different configurations and sizes. In today's printing market, people can choose manual or automatic laminating machines, or they can choose to use sheet-fed or web laminating machines.
UV laminating machines are generally classified as reverse roller or three-roll systems. Aqueous laminating machines generally apply the coating to a substrate, and then use a wire rod (a cylindrical metering rod) to reduce the thickness of the coating to a suitable level. A squeegee or similar device can be used to scrape off the paint from the back of the substrate.
Ike Harris, president of Daige, said: “This is not a roller coating but a wipe on the substrate. When people need precise coating, special metering is often used in the laboratory. In addition, this metering rod is also suitable for use in the aqueous coating process of manual and large roll-to-roll coaters, which enables the coater to produce a smooth and uniform coating on the substrate. The coating."
Roller coaters can use multiple ink rollers to transfer printed images and complete the task of coating them. From entering the roll coater, the substrate is either dried by UV or IR, or dried naturally, but the latter takes a long time. Printer transporters integrated with some coaters—usually conveyors—feed the coated substrates in a timely manner to a drying or curing system. As an alternative, one can also place the aqueous coated image horizontally so that it dries faster. This method is usually used on manual coaters. Harris pointed out that waterborne coatings take about 20 to 25 minutes to dry.
Many recently introduced UV liquid laminators can cure coatings at high speeds, sometimes at speeds of up to 100 feet per minute. In addition, they can also be designed to be very compact in order to achieve space-saving purposes. For example, the total length of such a device can be controlled within 5 feet, which also includes the length of the conveyor, because only then can the laminator quickly process the material.
The characteristics and number of jobs determine the type of liquid laminator you need. If you want to print a banner pattern on grid plastic or print POP images on textiles, it is best to choose an aqueous coating system because the depressions in the printed surface of the material must be filled with liquid paint.
Protective coatings and their applications
With the ever-increasing awareness of environmental protection in printing plants, UV coating has rapidly gained acceptance in recent years. Most of the UV coatings currently used for printing images do not contain VOCs (Volatile Organic Compounds), so they can easily be converted into solids without any volatilization. Waterborne coatings typically consist of 70% water and 30% resin, so it takes a long time after coating to allow moisture to evaporate before the substrate is rolled up or piled up. Tatum believes that people should consider the evaporation factor when calculating the cost of waterborne coating.
The advantages of waterborne coating come mainly from the latest advances in its formulation technology. Just a few years ago, the VOC content in waterborne coatings was as high as 2-3 pounds per gallon. Today, the VOC content of many coatings has dropped dramatically. According to Tatum, high VOC content is one of the major causes of yellowing of printed images. Therefore, he suggested that people use non-stearate type resins in waterborne coatings to reduce the solvent content.
Although waterborne and UV curable coatings have made great strides, solvent-based coatings still have a place in the liquid film market. David Conrad, equipment product manager at Neschen USA, said solvent-based coating still dominates the sign production field. Flexible panels are best suited for solvent-based coating because they prevent the image from becoming brittle or cracking over time. Products printed on rigid substrates are more suitable for UV coating because UV coatings do not have the extended properties exhibited by other coatings, and because of this, these coatings are not suitable for body image (below). protection.
The body image needs to be coated with ductile materials because the coating must be able to adapt to rivets, curved surfaces and other special surface conditions. The body image shown in the figure uses an aqueous liquid film. Tatum explained: “If you want to protect the image of your vehicle and boat, you must use a paint that has at least 150% elongation, because it needs to take care of rivets, intricate curves, and other irregular printing surfaces. In this case, once the coating is broken, the printed image will also fall apart.†In general, one should select the aqueous or solvent-based coating for the substrate depending on its coverage or flexibility requirements. It should also be borne in mind that knowing the high solids content in UV coatings is not conducive to their use on textiles and other special substrates. When it comes to this, we must remind those who intend to use inkjet printers to produce fine art and photography: You should pay special attention to using liquid laminators to protect printed images.
Waterproof canvas needs water-based coating. This type of canvas absorbs a large amount of ink, so that there is almost no possibility of water damage. Manelski pointed out that if the images printed on the waterproof canvas are not covered by liquid, it is difficult to maintain a long time.
Another type of canvas, called swollen canvas, requires the application of a solvent-based material on the surface of the substrate because the ink penetrating the surface of the substrate can easily become a water-destroying problem under the influence of surrounding moisture. Although swellable canvases are more prone to such failures than water-resistant canvases.
Other products that are suitable for liquid conformance include doors, furniture, walls, decorations, and food packaging. For the above products and those with traditional use of printed images, you must be careful when choosing coating formulations. Let's focus on the effective method of choosing paint for prints.
Choose the right liquid
It is well known that UV light can cure UV inks and coatings, but it also prevents UV liquid coatings from providing protection for printed images. Any kind of UV inhibitor will affect the curing of the coating. Therefore, the original purpose of the UV liquid coating was to prevent the printed image from being scratched and scratched. Tatum pointed out that the use of UV-cured coatings on images produced by UV inkjet printers is very good. In most cases, he said, aqueous coatings are not suitable for UV inkjet prints because the cured UV inks can form a non-stick surface.
Another issue to be aware of is that aqueous liquid coatings, like water-based screen printing inks, also contain certain solvents. We mentioned earlier that the VOC content of these coatings will decrease over time, but even so, you should keep a copy of the Chemical Safety Data Sheet for each waterborne coating you use.
Solvent-based liquid coatings are mostly used on water-based prints. Their formulations may contain UV absorbers and stabilizers that prevent polymer aging caused by photooxidation and high temperatures. Solvent-based coatings can also contain some leveling agents that act to increase the smoothness of the coating surface.
Cost factor
The cost of replacing a plastic film with a liquid coating is a concern. According to Conrad, the cost of protecting the image with a liquid coating is approximately 0.02-0.03 USD/m2 (for short-term use of display images) or 0.30-0.38 USD/m2 (for long-term use of images printed on demand).
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