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.
Tatum explains: “To get the same coverage as UV coating, you have to coat the substrate with more paint; therefore your costs will increase as well. The benefit of UV coatings is that it allows you to use a reverse A roll coating system or a three-roll coating system is applied and the coating it forms is very thin, typically between 6 and 20 microns."
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 fall apart."
In general, one should choose either 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.
Jim Manelski, president of BullDogProducts, said: “If you are printing on water-based printers like Epson, Roland, Hewlett-Packard, and Canon – using water-based inks – then you need to apply a liquid film to the prints to prevent it from breaking the water. Failure (due to the presence of chemical components or other substances on wet or dry ink film, which causes the printing ink or ink component to penetrate into areas that should not be reached during operation) or exposure to ultraviolet light. There are currently two types of problems. The canvas can be used on water-based printers, and everyone can choose different coating methods depending on the type of canvas."
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 swelled canvas is more prone to such failures than water resistant canvases, Manelski claims that he prefers the former because in most cases it can produce a wider color gamut.
Manelski believes that liquid laminators are a key factor in protecting delicate prints because they can significantly reduce the likelihood of prints being contaminated by dust and other substances. For example, liquid paint can easily entrain small particles in the air during the process of being sprayed onto the print surface, thus causing permanent contamination of the image. He said: "The liquid laminator can solve this problem very effectively because you are exposed to dry products during the operation."
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.
Harris recommends that customers using solvent-based or environmentally-friendly solvent inks use aqueous liquid film. He said: "If you apply aqueous coating on outdoor prints, you will find it can easily absorb the paint, because these substrates have been pre-coated before."
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).
As Harris puts it: "The cost of plastic film is somewhere between $0.35 and $0.60. So you can save a lot of money by using liquid film."
The price of consumables is a factor that must be taken into account. In addition, waste generation and disposal costs are also issues that cannot be ignored.
Tatum explained: “Every print that needs plastic film must be processed by a laminator, and you can hardly find a plastic film that matches the size of the print. Therefore, you will certainly have a lot of corners remaining. And you also need to use a certain amount of labor to deal with them. The liquid laminating machine not only has a very fast operating speed, but also does not give you any waste and garbage."
Is it the best time to use liquid film?
In general, the film is mainly popular in the field of inkjet printing. But now many screen printing companies have introduced digital imaging technology, so it is time for you to use new solutions to protect large-format inkjet prints. The price of a liquid laminating machine depends to a large extent on the type of equipment you choose. The price of UV systems is generally higher than that of aqueous coating systems because they use UV-curing lamps and the processing speed of prints is also faster. In many cases, the UV coater paper is only a little cheaper than a waterborne coating system that processes five times its own width.
Tatum said: "Primary waterborne coating systems are not expensive, if you can afford it, then you can easily transition to UV systems - you can experience speed, cost and stackability and other aspects The benefit of this system. The only disadvantage of UV coating is that it is not as flexible and flexible as water-based coating."