Why Glow Paint & Ink Develop Hard Sedimentation After Storage

Many customers encounter a very common problem when developing glow-in-the-dark paint, glow ink, or other luminous coating products.

When the product is first made, the dispersion looks good and there may be no obvious abnormality. However, after a period of storage, visible sediment gradually appears at the bottom. In some cases, it may even form hard sedimentation or compact settling, making it increasingly difficult to stir and redisperse.

This situation is especially common in high-loading glow pigment systems.

Many people’s first reaction is usually:

• “Is there something wrong with the glow pigment itself?”
• “Is the particle size too large?”
• “Should we reduce the loading ratio?”

In most cases, however, the main cause of sedimentation is not the glow pigment itself. It is more closely related to the anti-settling system design of the entire paint or ink formulation.

Glow pigment has a density of around 3.6 g/cm³, which is significantly higher than most paint and ink systems. Once added into a coating system, the particles naturally have a strong tendency to settle. For this type of glow paint formulation, building an effective anti-settling system is usually more important than simply replacing the glow pigment.

So, how can sedimentation in glow paint or glow ink be improved?

1. First Direction: Choose an Anti-Settling Agent That Matches the Coating System

The first step is usually to choose an anti-settling agent that matches the specific coating or ink system being used, and then observe its anti-settling performance.

If the system can form a relatively soft sedimentation layer, remain easy to redisperse after storage, and still meet the final viscosity requirements for printing or application, then the same anti-settling system can usually continue to be used.

2. Second Direction: Add a Solid Thickener That Can Build a Structural Network

If the anti-settling agent alone does not provide satisfactory results, another direction is to consider combining it with a solid thickener that can help build a structural network in the system.

One commonly used option is:

Fumed Silica

Its function is not simply to increase viscosity. More importantly, it can help form a non-Newtonian structure within the system. Together with the anti-settling agent, this structure can improve the suspension ability of the particles and help reduce sedimentation.

However, it should be noted that fumed silica may slightly reduce the gloss of the printed or coated layer and create a mild matte effect.

If the final product has high gloss requirements, other solid thickeners that can also build a structural network may be considered.

About the Addition Level

There is usually no fixed addition ratio for anti-settling agents or thickeners. The amount needs to be estimated and tested according to the target viscosity of the final paint or ink.

Because printing methods, coating systems, solvent ratios, and application requirements vary greatly, there is no universal viscosity standard for finished glow paint or glow ink.

For reference, in our own water-based acrylic glow paint:

• Glow pigment particle size: around 30 μm
• Glow pigment loading: 40%
• Viscosity: KU 90–100, measured by Stormer viscometer

However, different systems may use different viscosity testing methods, so this data should be used only as a reference.

3. The Influence of Particle Size

The particle size of glow pigment is indeed an important factor affecting sedimentation speed.

In general:

• Smaller particles settle more slowly.
• Larger particles settle more quickly.

At the same time, it is important to note that reducing particle size usually also leads to lower brightness.

Therefore, whether it is necessary to switch to a smaller particle size product should be evaluated through testing. The final choice needs to balance several factors, including sedimentation speed, printing suitability, and glow performance.

4. The Influence of Storage Time

Storage time is also an important factor affecting sedimentation behavior.

In general, we recommend controlling the storage period of mixed glow paint to within around one year.

Within a reasonable storage period, a certain degree of sedimentation does not necessarily mean the product has failed. As long as it can be stirred again and restored to a uniform dispersion state, it can usually still be used normally.

5. The Influence of Glow Pigment Loading

The glow pigment loading ratio itself is usually not the main factor that determines sedimentation speed.

A higher loading level may make sedimentation look more obvious, mainly because the total amount of powder in the system increases, making the deposited layer at the bottom easier to observe.

Final Thoughts

In glow paint or glow ink systems, sedimentation itself does not necessarily mean that the formulation has failed.

The more important questions are:

• Does it form hard sedimentation that cannot be redispersed?
• Does it affect the final printing or application performance?
• Does it affect the final glow effect?

In most cases, instead of directly replacing the glow pigment, it is better to start by optimizing the anti-settling design of the entire system. This may include the anti-settling agent, structural thickener, viscosity, and storage conditions.

Because different applications vary greatly, such as ink, paint, plastic, screen printing, and spraying, there is no single fixed solution that works for every system.

If you are developing a glow product and encountering similar issues, you are welcome to share the following information:

• Whether the system is water-based or solvent-based
• The resin type
• The glow pigment loading ratio
• The viscosity requirement
• The expected storage time
• The printing or application method

We can discuss a more suitable adjustment direction based on your specific application.