In the practical application of DTF pigment white ink inks, the claim of “no sedimentation” is considered a false proposition. The core reason lies in the irreconcilable contradictions between the physical properties of titanium dioxide, the functional requirements of the ink, and the laws of materials science—sedimentation is a thermodynamically spontaneous trend, and existing technologies can only delay it, not completely eliminate it. This can be explained in the following four aspects:
1. The physical properties of titanium dioxide determine that “sedimentation is a spontaneous trend”
Titanium dioxide (especially rutile-type) has a density of about 4.2 g/cm³, while the solvent system (water, alcohols, etc.) of white ink heat transfer inks has a density of only 1–1.2 g/cm³, with a density difference of more than 3 times between the two. According to Stokes’ law of sedimentation:
The sedimentation velocity of particles is proportional to the density difference between the particles and the solvent, and inversely proportional to the viscosity of the solvent.
This means that titanium dioxide particles in the ink will inevitably have a sedimentation tendency due to gravity. As long as there is a density difference, it is impossible to completely offset this thermodynamically spontaneous sedimentation trend through materials. Even if the particles are dispersed to the nanoscale (e.g., below 100 nm) with dispersants to improve short-term stability, long-term standing (for more than one month) will still lead to gradual sinking of particles due to “weakened Brownian motion and slow agglomeration,” resulting in irreversible sedimentation. It is just a matter of time.
2. There is a natural contradiction between the “fluidity” and “anti-sedimentation” requirements of the ink
White ink heat transfer inks need to meet the requirement of printing fluency: the nozzle aperture is usually 20–50 μm, so the ink viscosity must not be too high (generally 10–30 mPa·s for water-based systems and 5–15 mPa·s for oil-based systems); otherwise, it will block the nozzle or cause uneven ink ejection.
However, “anti-sedimentation” requires high viscosity or strong structural support (such as thixotropic systems), and high viscosity directly conflicts with printing fluidity:
- If the viscosity is significantly increased to prevent sedimentation (e.g., exceeding 50 mPa·s), the ink cannot be smoothly ejected through the nozzle, losing its printing function;
- If only relying on the charge or steric hindrance of dispersants, although low viscosity can be maintained, particles will still settle slowly due to the density difference, especially when standing still, as there is a lack of shear force to break agglomeration.
This “contradiction in functional requirements” determines that the ink must make a compromise between “printability” and “anti-sedimentation”. It is impossible to pursue absolute no sedimentation at the expense of printing performance, so sedimentation can only be delayed rather than eliminated.
3. The role of additives is to “delay” rather than “eliminate”, with inherent limitations
The core function of existing anti-sedimentation materials (dispersants, suspending agents, etc.) is to prolong the sedimentation cycle, but they cannot break through physical laws:
- Limited adsorption stability of dispersants: Dispersants are adsorbed on the surface of titanium dioxide through physical adsorption (rarely chemical adsorption). If the ink system changes (such as pH fluctuation, temperature rise, or solvent volatilization), the dispersants may desorb. For example:
- In low-temperature environments, the molecular chains of dispersants curl, weakening the steric hindrance and making particles prone to agglomeration;
- After long-term storage, some dispersants may be “competitively adsorbed” by impurities on the surface of titanium dioxide (such as iron ions, calcium, and magnesium ions), losing their dispersing effect.
- The structural support of suspending agents will decay over time: The thixotropic networks formed by xanthan gum, fumed silica, etc., will have gradually relaxed hydrogen bonds or interparticle forces after long-term standing or repeated freezing and thawing, reducing the strength of the network structure. As a result, the “binding force” on titanium dioxide weakens, eventually leading to sedimentation.
- High titanium dioxide content amplifies instability: To ensure hiding power, white ink heat transfer inks usually contain 20%–40% titanium dioxide, which is much higher than that in ordinary inks (5%–15%). In high-concentration particle systems, the distance between particles is shorter, the collision probability is higher, and the risk of agglomeration increases exponentially over time. Even if the initial dispersion is perfect, local agglomeration and sedimentation are inevitable after several months.
4. The complexity of practical application scenarios accelerates the inevitability of sedimentation
There are many variables in the storage, transportation, and use environments of white ink heat transfer inks, which further amplify the inevitability of sedimentation:
- Temperature fluctuations: High temperatures in summer (above 30°C) accelerate solvent volatilization and dispersant aging; low temperatures in winter (below 0°C) may cause the suspending agents to freeze and demulsify, destroying the stability of the system;
- Mechanical vibration: Bumps during transportation may cause titanium dioxide particles to agglomerate under shear force, making them more likely to settle after standing;
- Open use: When printing, the ink is exposed to the air, and solvent volatilization increases the concentration of titanium dioxide, raising the risk of agglomeration.
These uncontrollable factors in practical scenarios make “absolute no sedimentation” completely unachievable in industrial applications. Even if there is no sedimentation in the short term under laboratory conditions, sedimentation will inevitably occur in actual circulation.
Conclusion: “No sedimentation” violates the laws of materials science and is an idealized misunderstanding
The “no sedimentation” of white ink heat transfer inks is essentially an idealized goal that violates the laws of thermodynamics and fluid mechanics. The density difference between titanium dioxide and solvents, the printing fluidity requirements of the ink, and the limitations of additives jointly determine that sedimentation is an “inevitable trend”. Existing technologies can only extend the sedimentation cycle to meet practical needs (such as no obvious sedimentation within 1–3 months, which can be restored by shaking before use).
Therefore, white ink heat transfer inks claiming to be “no sedimentation” either ignore the actual scenario of long-term storage or sacrifice printing performance (such as ultra-high viscosity that makes them unusable), and problems will inevitably emerge in applications.