In this article, we will discuss UV inks and what to consider Choosing the Right Digital Ink. Decorators prefer digital printers and inks because of the ability to print on different types of materials.
Do certain materials need specialized UV ink? Unlike traditional printing inks, which are substrate-specific, UV inkjet inks are used to print on a wide range of materials. Despite their potential substrate specificity, these inks categorize themselves according to the rigidity of the material they print on.
Ink surface tension vs Hard good (materials) surface Energy
For digital printing inks to stick to a surface, their surface tension must be equal to or less than the surface energy of the material. To put it another way, the ink can appropriately wet the material’s surface when the material’s surface energy is greater than the ink’s surface tension.
Surface tension is a property of a liquid’s surface that enables it to resist external forces. Hard goods or solids do not have surface tension because the molecules are tightly packed; they have surface energy. Surface energy is the energy associated with creating a new surface on a solid material. Therefore, the ink’s surface tension must equal or be less than the material’s surface energy for good adhesion.
When an ink has a lower surface tension than the hard good it is applied to, it spreads more easily and makes better contact with the surface, which leads to improved adhesion.
Dyne is the unit of measurement for surface tension and force (surface energy).
Therefore, these forces directly impact the adhesion and durability of UV-cured inks. Understanding surface tension or dyne levels will enable a decorator to pick the correct specialized ink, which will result in the best print and adhesion results possible.
Digital printing ink to consider
As previously mentioned, the formulation of digital inks is not substrate-specific but rather based on the printhead and the rigidity of the printing material. Therefore, there is no specific Tritan® ink category for Tritan products, which are made of durable, BPA-free plastic. This type of ink is rigid and has the correct surface tension characteristics, which are lower than the surface energy of Tritan plastics. These characteristics enable the ink to perfectly bond to the Tritan material and any other material with similar surface energy.
The major categories of ultraviolet inks include rigid, neutral, and flexible inks. When printing on sport bottles, for example, it is important to consider using neutral or flexible UV inks. The imprints made with these types of inks are flexible and will resist cracking when squeezed.
On the other hand, when printing on rigid materials such as glass, ceramics, metals, powder-coated metals, or coated drinkware, consider rigid ink.
The major factor to consider when choosing ink is your product mix. If 80% of your products are rigid materials, then use rigid UV ink. If you are not sure of your product mix, then consider a neutral UV ink because it will allow you the flexibility to print both flexible and rigid materials. The goal is to minimize ink changeover.
Alternatively, you can consider having two machines: one to cover 80% of your most popular items and another with different ink to cover the remaining 20% of items.
Choose the right digital ink for specific materials
The printhead and printing materials should be considered when choosing ink. A rigid UV-curable ink is ideal for printing on hard materials. However, if you want to maximize the number of materials that you can print, consider using neutral ink.
Because there are only three categories of UV inks, it is challenging to find an ink that has lower surface tension than the surface energy of all materials. As a result, it is important to use pre-treatments to increase the number of items that you can print with specific ink.
For example, those printing on Tritan® but are not using our inks can use the Natron® G1 UV adhesion promoter to achieve permanent ink adhesion. If you use our Natron 314 Series UV ink, you do not need to use a digital primer on Tritan. The 314 Series is formulated for use with Ricoh Gen 5 and Ricoh Gen 6. Lastly, we also offer other inks for Ricoh Gen 5i, Epson DX5, DX7, and Epson i3200 printheads.
UV Ink pre-treatments
UV inks and ink pre-treatments complement each other. Pre-treatments commonly known as adhesion promoters ensure proper ink adhesion. There are two types of pretreatments: chemical and mechanical methods. Both types contribute to increasing the surface energy of the material.
Mechanical pre-treatments include plasma, coronal, and flame. Chemical pre-treatments include wipe-on, sprayable, and jettable digital primers. It is important to note that adhesion promoters, apart from jettable primers, decrease efficiency and therefore increase cost.
UV printing does not require post-treatment, e.g., thermal cure. By choose the right digital ink for your specific print head and combining it with the proper pretreatment, you will always achieve excellent printing results.
Testing for strong bond
There are several ways in which a specific ink adheres onto a material (substrate or surface). These adhesion properties are ink and material specific. The ink absorbs into porous materials. Examples of porous materials include natural surfaces such as wood and paper.
In other materials, such as simple plastics like polycarbonate, the ink solvent dissolves and latches onto the surface, thereby creating a permanent chemical bond.
Lastly, mechanical adhesion occurs when the ink interlocks with the material’s surface. This is the UV ink that bonds onto metals, glass, tiles, Aluminum Composite Material (ACM), acrylics, varnished surfaces, and most complex plastics. Most mechanical bonding cases require adhesion promoters or pre-treatment for excellent ink adhesion.
Examples of ink adhesion failures include cracking, peeling, flaking, and blistering. Therefore, it is important to test ink-substrate bond strength and durability according to the American Society for Testing and Materials (ASTM) standardized adhesion tests. Examples of these tests include the scratch test and the tape tests. At Boston Industrial Solutions, Inc., we offer these and many more additional ink adhesion tests depending on the item, process, and customer requirements.
How to choose the right digital ink for your product
Efficiency is the most important consideration when purchasing a UV printing machine. You must select the proper ink for the machine and the materials you are printing to achieve this level of efficiency.
The challenge is that more than 90% of UV printer vendors do not manufacture the ink used in the equipment they sell. As a result, some suppliers are unable to provide printing and adhesion guidance due to a lack of understanding about ink adhesion.
As a result, it is critical to purchase your UV ink from Boston Industrial Solutions, Inc., who have extensive expertise in inks, coatings, and materials.
We not only examine the materials, but we also create custom inks and primers for unusual materials as needed—a feat that few firms can equal. Furthermore, we provide free adhesion testing, which is accompanied by a detailed report outlining the ink and pretreatment choices utilized on each tested product.
Finally, our experience with equipment and ink manufacture enables us to help you choose the right digital ink and adhesion promoters for printing on various difficult-to-print surfaces. Visit our support hub to learn more about digital inks.
