Liquid Coating: Print Protection Coating Technology

For screen printers that have introduced large-format inkjet devices, laminators have become a must-have for postpress equipment. The original purpose of the film was to provide a barrier between the printed images to prevent them from being worn out during repeated use. The laminating machine used in the printing industry is mainly to cover the surface of the printed product with a film to prevent the image from being scratched and damaged by chemicals. However, there is another use for the laminator, which is to apply a protective liquid coating to the print. Liquid film coating technology is the focus of this article, we will focus on to introduce the equipment, coating type, application range and its benefits related to this postpress process.

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. Enhances 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 conveyor belts—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.

According to Jim Tatum, president of Advanced Finishing Solutions, the use of a UV liquid laminator to machine this textile material is not optimal because the laminating equipment will apply it to the print at very high speeds. A thin layer of paint. Under given operating parameters, this coating has almost no chance of filling the depressions on the surface of the substrate.

Tatum pointed out: "In this way, only part of the images you have obtained has been coated and cured. When severe weather conditions and other destructive factors occur, the coating will not protect the image at all." On the other hand, the aqueous liquid laminating machine evenly coats the surface of the substrate with the coating, so that the depressions in the image can also be properly protected. [next]

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 protection of body images.

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 [Encyclopedia]. 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."

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