High opacity white – a must for digital inkjet label printing
High opacity white for digital inkjet label conversion is a hot topic, why? Is white ink really important?
The importance of white ink
Having a high opacity white ink in your digital printing armory can be the difference between producing ‘okay’ labels, which are acceptable for use on only a handful of applications and crisp, detailed and vibrant labels that are ‘fit for purpose’ for a wide range of vertical markets. Labels produced with a poor white simply won’t carry much commercial credibility.
What is commercial credibility?
Commercial credibility for white ink is an important consideration when choosing a digital press. The white needs to be printing consistently even across the web. Then it needs to have an opacity capable of overlaying other colors without reducing the impact of the label. The white needs to be white, not grey. The color of the white ink should be as close as possible to your target press condition.
Then there are other technical factors such as a broad adhesion range on a wide range of substrates, scratch resistance, light fastness and ink to ink/ink to substrate interactions.
Let’s dive a little deeper into these factors.
Applying a back white lets any image or text printed on top of it to really stand out against the packaging or product it is to be applied to.
If the white ink has too thin an ink film it will lack the pigment required to achieve relevant opacity. Colours will appear muted and brand impact affected.
Often printing processes, not just digital, need to print slower or “double” hit the white in order
to achieve an acceptable result. Obviously a double layer adds to the ink costs and can restrict overall productivity but is often due to the unique challenges of white ink.
The challenges of jetting a high opacity white
Ink
Formulating a successful white ink solution presents several unique engineering challenges.
The pigment materials used in white ink are typically titanium dioxide (TiO2). This is because titanium dioxide has unique optical properties such as whiteness and opacity. This is due to many factors of which particle size and refractive index are the most important. It is difficult to get the particle size small enough without the ink appearing grey.
In order to jet a fluid it must have the correct viscosity at the operating temperature. In order to jet white ink you must maintain the viscosity and yet have the particles small enough and have enough particles to achieve the desired coverage at the correct production speed.
It is for precisely this reason that the ink, ink delivery system and print heads must be designed as an integrated unit each part carefully chosen and fit for purpose. The inking system must maintain the ink’s viscosity at the correct level ensuring temperature is consistent and ink is circulated to maintain homogenization. Yet ensure it is suitable to deliver ink to the head array. This is why FFEI’s Graphium includes a custom designed ink delivery system and Xaar 1001/2 printheads. The Xaar 1001/2 handles a wide range of fluid viscosities easily, including white ink and varnishes,
Print heads for white ink
The Xaar 1001/2 incorporates both TF Technology™ (ink recirculation) and the unique Hybrid Side Shooter™ architecture so that ink can flow directly past the back of the nozzle during drop ejection.
The Xaar 1001/2 can jet fluids within a viscosity range of 7 to 50 cP. And yet maintain a minimum droplet size of 6pl. This enables the widest choice of ink and substrates providing greater versatility in print applications. Ink recirculation in the head work with the ink system which means that air bubbles and dust particles present in the ink are carried away. Radically improving the reliability, even in the harshest industrial environment. Ink recirculation keeps the ink in constant motion and prevents sedimentation and nozzle blocking particularly in heavily pigmented inks.
Our specialist Fujifilm Uvijet Graphium™ UV inks have been carefully specified and matched to the Xaar 1001/2 to deliver reliable jetting performance and allow Graphium to print with market leading white ink performance. Achieving salable output at high speed in a single pass.
Substrates
A range of effects can be achieved on different substrates with a high opacity white.
- Raised tactile screen print like effect. Controlled by UV cure.
- Extremely detailed and sharp text, excellent ‘ink on ink, varnish on ink interactions’ or overprinting due to low silicon and use of partial cure LED lamps.
- Flat litho type effect when finished with Fujifilm Matt varnish.
- Can be used with clear, metallic, coloured, fluorescent, iridescent, uncoated, textured and holographic substrates for wide range of metallic process
- Tints of white ink can be used in conjunction with metallic substrates for de-metallisation effects, controlling the gloss of the underlying substrate to create unique effects.
- Can be used as a primer to ensure consistent printing quality across wider range of substrates
- Can be used to increase the glossiness and vibrancy of printed colours.
- Can be used to ensure consistent ISO standard printing on custom substrates. New substrates can be on target with little or no additional profiling.
Points to consider when designing with white ink
White ink needs to be considered as a spot colour not just paper white. Therefore considerable care needs to be taken during the design stages. Often prepress are left to generate the white separations correctly. Creative use of white, non white and tint areas and the object the label is applied to can really lift a label into something with spectacular impact.
Often a white ink separation needs to be technically designed too. Either it is trapped to appear marginally smaller than the overprinted object. Or is designed to halo the object allowing a label to be clearly visible against a wide variety of background colors. Then we must also not use white on very small objects. This is why FFEI believe that hardware must be supported by the best software. FFEI Realpro toolkit includes high end white and rich black generation tools, which do not just generate the separation but can also control undercuts and spread very accurately allowing minimum objects and details to be excluded and even tints mirrors by the white ink. Furthermore Realpro applies the white in a separate layer thus ensuring that none of the original label design is touched.
Conclusion
With so many contributing factors to consider when printing white, you need the right partners – ink design, integration, manufacturing, ink and software – to define the ultimate solution. With Graphium, FFEI have done just that.
