UV Printing on Wood
Wood is considered one of the most traditional materials for just about any furniture, signage, or construction project, but it has always been a material that’s hard to work with. When it comes to painting wood, its porous nature and generally inconsistent surface quality make it necessary to apply paint in several coats – a tedious and time-consuming task. In this article, we’re taking a look at UV printing technology and how it can make printing on wood a lot faster and more reliable.
What makes wood such a difficult substrate for printing? As anybody who has ever painted on wood can tell you, it is rarely a straightforward task. The porous nature of wood means that a portion of the paint, whether it is solvent-based or water-based, gets absorbed into the wood. This ends up making the layer of paint look washed-out or less vibrant than intended, thus the need to apply paint in several coats.
There’s also the problem of lack of consistency. Not all wood products are made of a single, solid piece of wood. A lot of wood fixtures used nowadays are classified as particle boards or medium density fiberboards. These are made of very small wood fibers held in place by a binder. MDFs and particle boards are much more absorbent and have poor surface consistency – a quality that is difficult to conceal with solvent-based or water-based paint.
UV printing bridges this gap by providing a technology that allows for rapid curing of paint on wood surfaces. This process uses a special UV ink which is a combination of standard ink with polymer chemistry. Through photoinitiators in the ink, curing of the ink is achieved almost instantaneously upon exposure to UV light.
Advantages of UV printing
One thing you need to know about UV printing on wood is that it requires special equipment. Most UV printing is done on flatbed printers that work similarly to inkjet printers but has integrated UV LED lights for curing. UV ink is also a bit more expensive than standard ink, as one would expect. Given these considerations, what advantages does UV printing technology offer?
The idea behind UV printing is that you only need a single pass to paint a wood substrate. Without the need for multiple coats, UV printing can significantly shorten the turnaround time for wood painting projects. There’s also the fact that curing paint using UV is virtually an instant process – a huge upgrade compared to the several hours it takes for solvent-based paint to dry.
- Better surface consistency
A key factor in the difficulty of achieving good surface consistency when painting wood is the fact that wood is very porous. When wood absorbs a solvent-based paint, imperfections on the surface of the wood tend to become more visible. This is also the reason why multiple coats of paint are needed when painting wood to reduce the effects of surface inconsistencies.
UV printing addresses this gap through the near-instant UV curing technique. Typically, UV curing starts as soon as the ink hits the substrate, giving minimal time for the ink to be absorbed into the wood surface. This helps in concealing surface imperfections and making the finished painted surface look more consistent and vibrant.
- More flexible
As mentioned, UV ink is a product that combines traditional ink composition with polymer chemistry. This provides greater freedom in terms of controlling the physical and chemical properties of UV ink, making it more compatible with a greater variety of substrates. Moreover, the same flatbed printer used for UV printing in wood can also be used for other materials such as plastics, fabric, and certain types of metals.
- Produces fewer pollutants
A majority of printing applications today still use solvent-based inks. Common solvents used in inks include pentane, benzene, toluene, acetone, isopropyl alcohol, and tetrahydrofuran (THF). Solvents were preferred because they are effective in evenly dispersing coloring pigments and dry relatively quickly on account of their low boiling points.
The problem with solvent-based inks is that they just aren’t environmentally friendly. The solvents used in these inks typically come from petroleum-derived and non-sustainable sources. When the solvents evaporate, they contribute to the planet’s level of volatile organic compounds (VOCs) which have an impact on global warming.
If you’re concerned about making your products more sustainable, then switching over to UV printing is one of the few viable solutions. It’s not a perfect alternative but it significantly reduces the environmental footprint of your printing process.
Despite the initial capital expense of switching to UV printing, the increased throughput and better quality of UV printing is enough to justify the cost in many cases.
Tips on High-Quality Printing
Despite the superiority of UV printing, it’s not a foolproof technique. UV printing can still fail without careful consideration of several factors during the printing process. To make sure that you get the best out of UV printing with wood, here are some things to watch out for:
1. Selecting the best wood type
While there isn’t a specific type of wood that works best with UV printing, UV printed projects tend to look better on wood that has no dark spots or grains. Should this not be the case, then a white pre-coat may be needed to make sure that the color of the UV ink pops. UV printing is equally compatible with both solid wood pieces and composite wooden boards such as MDFs and particle boards.
2. Keep the surface of the wood clean
More important than the type of wood used for UV printing is the need for the wood surface to be kept clean. Any imperfections on the wood surface, such as loose wood fibers, can compromise how well the UV ink sticks. If needed, it would be ideal to sand the wood surface smooth and wipe it down with a tack cloth to remove any loose fibers or sawdust.
3. Control the head height
To maximize accuracy, the printhead of a UV printer typically sits very close to the wooden surface – less than 1/10 of an inch in most cases. This makes it crucial to use a workpiece with as level a surface as possible, lest the printhead gets damaged by abrasion. It is also good practice to clean the printhead regularly to remove any loose fibers which can get stuck to the printhead during the UV printing process.
Pre-treatment and Post-treatment
Depending on the intended application of the UV printed product, some pre-treatment and post-treatment of the wood workpiece may be in order.
An important part of pre-treatment is making sure that the wood is as smooth as level as possible. This removes any loose fibers and surface imperfections which could compromise how well the ink adheres to the wood surface or damage the printhead. This can be done via a combination of sanding, sandblasting, and wiping down with a damp cloth.
In some cases, a primer or pre-coat can be applied to a wood surface prior to UV printing. This is a means of neutralizing the effect of any surface imperfection on the wood surface, preventing any potential issues with adhesion or abrasion. Most pre-coats are done using a clear primer, but white ones can also be used for workpieces with excessively dark spots or grains.
Post-treatment is done to protect the cured layer of UV inks from the erosive effects of the outdoor elements. This is essential for applications such as outdoor signages or for projects that will be subject to repeated abrasion, such as wood walls or floor panels. It is common practice for a post-treatment coating to be applied to an entire wooden piece to prevent damage due to moisture and UV exposure.
If you’re using a third-party paint as post-treatment for a UV printed project, then any clear water-based polyurethane sealer will do. Some UV printers can also provide post-treatment if they have a provision for clear ink.
UV printing essentially makes wood as versatile a medium as any painting canvas. No longer does printing on wood need to be restricted by the complexity of multiple coats and long drying times. This opens up huge opportunities for digital printing on wood. UV printing is economical both for large-scale production and low-volume orders, making it a suitable technology both for commercial and personalized products.
With the variety of UV printers available today, there are now opportunities for a wide range of wooden projects that can be UV printed. Businesses who strive for a rustic image benefit from using wooden signages for their brands with the extra crispness that UV printing brings to the table. We have also seen guitars, skateboards, and longboards which have been impressively personalized by 3D printing.
The interior design industry has greatly benefited from UV printing technology. With UV printing, wooden wall panels and floorboards can be customized with artwork without an artist having to do it by hand. This technique can also be used to jazz up wooden furniture. Smaller items in the house like photo frames and coasters can also be personalized with UV printing.
UV printing just might be the ultimate technology for the customization of wood pieces. By combining digital printing with UV inks, a customized wood project can now be done in just a few minutes. There are still limitations to the technology, but it’s pretty clear that these limitations are far out shadowed by its potential.