Analysis and Solutions for Large Grainy Effect in UV Flatbed Printer White Ink

Analysis and Solutions for Large Grainy Effect in UV Flatbed Printer White Ink

Table of content.

White ink contains a high proportion of titanium dioxide (TiO₂) to achieve strong opacity. Due to its physical properties, white ink is inherently more prone to sedimentation, impurities, and graininess compared to colored inks.

When obvious graininess appears in the print result, troubleshooting should generally focus on the following two aspects:

 

I. White UV Ink Quality Issues

1. Root Causes

• Characteristics of Titanium Dioxide
 Titanium dioxide has a high specific gravity and settles easily. Poor-quality ink often has weak dispersion stability, causing pigment agglomeration and severe sedimentation.

• High Impurity Content
 Low-grade ink may contain excessive impurities introduced during production or inadequately milled large pigment particles.

• Poor Stability
 Inferior ink formulations may result in layering, clumping, or chemical reactions that generate sediment.

 

 

2. Consequences

• High Risk of Printhead Clogging
 Large particles and sediment can easily block nozzles, accelerate printhead wear, and significantly shorten printhead lifespan.

• Poor Print Quality
 Uneven ink droplets lead to visible graininess, rough surfaces, color inconsistency, ink starvation, or stringing.

• Increased Maintenance Costs
 More frequent printhead cleaning and filter replacement are required, leading to increased downtime.

 

 

3. Long-Term Solutions

▲ Upgrade Ink Quality (Fundamental Solution)
 Choose reputable, market-proven white ink brands.

High-quality white ink features:

  • Better dispersion stability (reduced sedimentation)

  • Finer pigment milling (smaller particle size)

  • Stricter impurity control

  • Good compatibility with your printer model and printhead

 

 

4. Temporary Preventive Measures

▲ Use high-quality filters (typically 5–10 micron level).

▲ Shorten replacement cycles.
 Low-quality white ink clogs filters more quickly. Replace the main ink tank filters, secondary filters, and pre-printhead filters more frequently than when using premium white or color ink. Adjust the maintenance schedule based on ink supplier recommendations and actual usage (printing volume, downtime duration).

▲ Strengthen daily maintenance:

  • Perform regular printhead cleaning and moisturizing procedures.

  • Before long shutdown periods, thoroughly clean the white ink circulation system and properly maintain printhead moisture protection.

 

 

II. Print Curve (Waveform / Dot Setting) Mismatch

1. Root Causes

• Ink Droplets Too Large
 “Large-dot” or “coarse-dot” printing curves are often used to achieve higher opacity or faster speed. While they provide strong coverage and productivity, larger droplets spread more visibly on the substrate, resulting in noticeable graininess.

• Curve Not Matched to Ink or Substrate
 The selected waveform has not been optimized for the specific white ink brand, batch, or substrate being used.

 

 

2. Solutions

▲ Switch to a finer print curve.
 Prefer “small-dot” or “medium-dot” waveforms. These produce smaller droplets, resulting in finer ink points on the substrate, significantly reducing graininess and improving surface smoothness.

▲ Trade speed for quality.
 Using small-dot curves usually reduces printing speed, but this is necessary to achieve a smooth and refined white ink layer.

▲ Conduct waveform testing and optimization.
 Before mass production, print test strips using different small- or medium-dot waveforms on the target substrate. Evaluate:

  • Opacity

  • Surface smoothness (graininess level)

  • Adhesion

  • Curing performance

Select the curve with the best overall balance.
 If the printer manufacturer or ink supplier provides optimized white ink curves for specific substrates, prioritize those options.

▲ Consider increasing Pass count.
 Under sufficient opacity conditions, increasing the number of passes (carriage movements) can help distribute ink more evenly and reduce visible graininess, though printing speed must be balanced accordingly.

 

 

Application of Ink Cartridge Stirring Function

Importance of Stirring

▲ Critical for White Ink
 Stirring is essential for white ink and effectively reduces sedimentation issues.

 

 

Operating Methods

Automatic Stirring System:
 Before each printing session—especially after long downtime—activate the automatic white ink circulation and stirring function for 5–15 minutes (refer to ink and equipment manuals for exact duration). This ensures titanium dioxide sediment is fully dispersed.

Manual Stirring (If No Automatic System):

  • Shake the ink bottle or ink bag manually for at least 2–3 minutes before refilling or after long downtime.

  • Ensure no visible sediment remains at the bottom.

  • If machine structure allows and it is safe to do so, carefully stir the internal white ink system manually.

 

 

Installing a Stirring Device

▲ Strongly recommended: Install an automatic stirring device (circulation pump or built-in agitator) in the white ink system.

This is a long-term solution to prevent sedimentation, ensure stable printing performance, and extend printhead lifespan. Continuous, gentle stirring maintains ink uniformity and significantly improves reliability.

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