Pigment-based vs encapsulated pigment inkjet inks: a comparison

Digital decoration has changed the way ceramic surfaces are designed and produced. It allows us to reproduce complex graphics, work with greater flexibility and develop finishes that, just a few years ago, were difficult to transfer from a screen to an industrial production line.

But behind inkjet printing lies a decision that influences both the aesthetic result and part of the production process: which ink technology should we use?

When we talk about pigment-based inkjet inks and occlusion pigments, we are not actually dealing with two completely opposing technologies. Occlusion pigments are also ceramic pigments, but they have a particular structure: the component responsible for the colour is encapsulated within a crystalline matrix that protects it.

For this reason, throughout this comparison we will use the term pigmented ceramic inks to refer to inkjet formulations based on conventional micronised ceramic pigments, and occlusion pigments or encapsulated pigments when referring specifically to this second family.

Rather than asking which solution is better, there is a more useful question to consider: what do we need to achieve on our surface, and which option is best suited to that objective?

In this comparison, we analyse the main differences between both technologies and the variables we need to consider before taking an ink into production.

What is the difference between pigmented ceramic inks and occlusion pigments?

The difference begins with the structure of the pigment itself.

In pigmented ceramic inks, colour comes from solid ceramic pigment particles dispersed in a liquid vehicle. In industrial formulations, correctly controlling the size and distribution of these particles is essential to ensure that the ink can circulate and be jetted consistently through the printheads.

Occlusion pigments, on the other hand, incorporate the component responsible for colour within a crystalline structure that acts as a protective matrix. This architecture influences both their behaviour during ink preparation and their subsequent response during firing.

We are therefore not simply talking about two different formulations designed to achieve exactly the same result. The pigment structure influences how it can be adapted to inkjet printing, the colour possibilities it offers and its behaviour within the ceramic system.

How pigmented ceramic inks work

A pigmented ink contains inorganic ceramic pigment particles distributed within a liquid medium. To adapt them to inkjet printing, these particles must have a very tightly controlled particle size and remain properly dispersed.

From there, other fundamental ink properties come into play, including viscosity, surface tension and stability both during storage and continuous operation in the printing machine.

These parameters are particularly critical in digital ceramic decoration, as inkjet technology requires pigments with reduced particle sizes, dispersion stability and suitable rheological properties to ensure correct droplet formation and prevent printing issues.

Source: sciencedirect.com

In our digital ceramic inks, we work with average particle sizes below 1 µm, viscosity values between 8 and 15 mPa·s at 25°C, and surface tension between 25 and 35 mN/m. We control these parameters, together with the physicochemical stability of the formulation, to achieve stable and reproducible behaviour during printing.

The ink is deposited onto the surface and, subsequently, the pigment must withstand and interact correctly with the ceramic system during firing in order to develop the intended colour result.

That is why a pigmented ink cannot be assessed solely by the colour we see before firing. Its true behaviour becomes apparent when the ink, glaze, substrate and firing cycle work together.

How occlusion pigments work

In occlusion pigments, also known as encapsulated pigments or inclusion pigments, the component responsible for colour is confined within a protective crystalline matrix.

This structure makes it possible to isolate the chromophore from certain chemical and thermal interactions that occur during the ceramic process. In other words, the outer matrix does not necessarily generate the colour itself; instead, it helps protect the phase responsible for developing it.

When we want to incorporate this type of pigment into a ceramic inkjet ink, an additional challenge arises. We not only need to achieve a particle size compatible with the printing system; we must do so without compromising the occlusion structure.

For this reason, factors such as particle size, milling, dispersion and stability become particularly important when developing an inkjet formulation based on this type of pigment.

Pigmented inks vs occlusion pigments: the main differences

When we compare both solutions, we can see that the differences extend beyond pigment composition. Let us look at the factors that can have the greatest influence on development or production decisions.

Colour range and colour intensity

Conventional pigmented ceramic inks offer a well-established colour range for digital decoration and make it possible to work with a wide variety of shades, combinations and effects.

Occlusion pigments offer a different advantage. Their protective structure makes them particularly suitable for certain colour systems in which the component responsible for colour needs to be isolated from the ceramic environment in order to maintain its behaviour during firing.

This does not mean that an occlusion pigment will always provide greater colour intensity.

The result depends on multiple factors: the nature of the pigment, degree of encapsulation, concentration, glaze composition, substrate and thermal conditions.

Particle size and compatibility with inkjet printheads

Particle size is one of the most important variables in any pigmented inkjet ink. To achieve stable printing, we need to work with a particle size distribution that is compatible with the printhead being used. An oversized particle, agglomeration or unstable dispersion can affect the ink’s behaviour during jetting.

In conventional pigmented inks, micronisation allows us to adapt the pigment to the ranges required for digital printing.

With occlusion pigments, the challenge can be greater. We not only need to achieve sufficiently small particles; we also need to prevent the size-reduction process from compromising the structure that encapsulates the chromophore.

For this reason, the compatibility between pigment, particle size distribution, formulation and inkjet printhead needs to be studied as a complete system.

There is no single particle size that is suitable for every system. The reference point should always be the specific printing technology and the actual conditions of the production line.

Resistance of the pigment structure during ink preparation

In a pigmented ink, one of the main objectives of milling is to reduce and homogenise particle size until a distribution suitable for inkjet printing is achieved.

When we work with occlusion pigments, we need to add another requirement: preserving their protective structure throughout this process.

Overly aggressive milling can alter the encapsulating matrix and leave the colour-producing component we are trying to protect more exposed.

Preparing an ink with occlusion pigments therefore requires us to find the right balance between three variables:

• Particle size suitable for inkjet printing

• Correct pigment dispersion

• Integrity of the occlusion structure

It is not simply a matter of making the pigment smaller. It is about ensuring that it retains the properties we are looking for once it has been adapted to the printing system.

Graphic distribution and design reproduction

In digital printing, definition does not depend solely on the nature of the pigment.

Droplet formation and stability, particle size distribution, viscosity, surface tension, printhead technology, interaction with the surface and printing parameters all contribute to the final result.

Correctly adjusted pigmented ceramic inks can reproduce details, veins, patterns and gradients with precision.

With occlusion pigments, we also aim for stable graphic performance, but first we need to ensure that the particle size distribution and formulation are compatible with the printing technology being used.

Stability and behaviour during inkjet printing

In pigmented inks, we need to pay particular attention to particle size distribution, dispersion, sedimentation, viscosity and surface tension to ensure stable printing.

With occlusion pigments, we need to control these same variables while also taking into account the additional constraints created by their particular structure.

In both cases, the objective is the same: to achieve stability and repeatability throughout production, maintaining consistent performance in the machine as well as a consistent colour result.

After analysing these factors, we can summarise the main differences between both technologies as follows:

How ceramic inkjet inks influence the production process

A colour chart can help us choose a direction. But it does not tell us how an ink will behave after hours of printing, how it will react with our ceramic glaze or whether the shade will remain consistent when certain production conditions change.

Interaction between ink, substrate and glaze

The same ink can produce different results when we change the substrate, glaze or application conditions.

The particles responsible for colour come into contact with the ceramic system and may undergo interactions during firing that modify the final colour development.

In occlusion pigments, the protective matrix is designed to isolate the chromophore from its surroundings to a certain extent. But this does not mean that the pigment is independent of the rest of the system.

The glaze, substrate, temperature and firing conditions continue to influence the final result.

That is why, when we develop a surface, we do not work with an isolated ink alone. We work with the relationship between all the materials and processes involved.

Colour development during firing

What we print before the kiln is not necessarily what we will see afterwards.

The thermal cycle activates the transformations that consolidate the ceramic result. Maximum temperature, firing time, atmosphere, glaze and substrate composition, and the nature of the pigment can all influence the outcome.

With pigmented inks, we need the pigment to retain or correctly develop its colour properties within the ceramic system.

This explains why comparing two inks solely in their liquid state only gives us part of the picture.

Repeatability and control of the industrial result

Achieving an attractive piece in the laboratory is only the beginning. The challenge comes when we need to reproduce that result consistently across thousands of square metres.

This is where variables such as the following come into play:

• Ink stability over extended periods

• Continuous printhead performance

• Application consistency

• Interaction with the glaze or substrate

• Variations in temperature and production-line conditions

• Colour repeatability after firing

The formulation needs to perform reliably alongside all of these variables.

And when we incorporate an occlusion pigment, we need to add one more question: does it maintain its structure and colour response after undergoing the entire process required to turn it into a stable industrial ink?

What should we evaluate before choosing an inkjet ink?

Before recommending a formulation, we need to understand both the result you want to achieve and the actual conditions of your production line.

Some of the factors we need to evaluate include:

• Aesthetic and colour result: shade, intensity, graphic definition, depth and the finish we want to achieve.

• Substrate characteristics: composition, absorption and behaviour during firing.

• Glaze and other applied materials: their interaction with the ink can modify colour development and the final surface result.

• Firing cycle: maximum temperature, duration and thermal conditions of production.

• Available inkjet technology: printhead type, printing parameters and application conditions.

• Ink properties: particle size distribution, viscosity, surface tension, stability and compatibility with the printing system.

• Subsequent processes: polishing, lapping or other treatments that may modify the surface.

• Industrial validation: the performance achieved in the laboratory needs to be maintained when we take the solution into real production conditions.

At Kerafrit, we work from this global perspective. We formulate, apply, fire, measure and fine-tune together with you until we find the right balance between aesthetic intention and industrial stability.

Because a technically correct ink is not enough. It needs to perform reliably within your process and help you create the surface you have in mind.