Principles and Applications of Siphon Ink Supply System

1. Siphon Ink Supply System

A siphon ink supply system is an ink delivery method that operates based on the principle of atmospheric pressure difference.

2. Siphon

A siphon is a physical phenomenon in which a liquid rises automatically within a tube. It is caused by a pressure difference formed inside the tube. When one end of the tube is immersed in liquid, and the other end is positioned lower, the liquid will flow upward automatically until equilibrium is reached.

3. Siphon Ink Supply

Siphon ink supply is a method of delivering ink using the siphon principle and is commonly used in continuous ink supply systems (CISS) for inkjet printers.
In this system, an external ink bottle is connected to the printer’s ink cartridge via ink tubes. Using the siphon effect, ink continuously flows from the ink bottle into the cartridge, enabling an uninterrupted ink supply.

4. Siphon Principle

The siphon principle is based on the principle of communicating vessels. When the siphon tube is completely filled with liquid and contains no air, the liquid level at the inlet side is higher, while the outlet is initially sealed. At this point, the pressure inside the tube is uniform.
Once the outlet is opened, the higher liquid level and greater pressure at the inlet side push the liquid to flow continuously through the tube and exit from the outlet.

5. Siphon Phenomenon

The siphon phenomenon results from intermolecular attraction between liquid molecules combined with a difference in gravitational potential energy. The pressure difference created by the liquid column causes the liquid to rise and then flow to a lower position.

In inkjet printers, the siphon ink supply operates based on this physical phenomenon. Ink in the cartridge is connected to the nozzle through ink tubes, forming a liquid circulation system.
Specifically, ink in the cartridge first flows into the ink tube under gravity. As the ink descends inside the tube, one end of the tube remains immersed in ink while the other end is positioned at the lower nozzle location. Due to this height difference, the liquid rises automatically, creating a siphon effect. The ink is drawn upward through the tube and then, under printer control, ejected through the nozzles.

6. Siphon Ink Supply vs. Traditional Gravity Ink Supply

Compared with traditional gravity-fed ink systems, the siphon ink supply has the following advantages:

① It ensures continuous ink delivery and prevents printing interruption caused by an empty cartridge.
② It provides better control of ink flow rate, ensuring proper pressure at the nozzle for improved print quality.
③ It reduces ink splashing and uneven ink ejection, thereby enhancing overall print quality.

7. Precautions for Siphon Ink Path Connections

① Proper coordination between the printhead and waveform is required to generate suitable pressure and jetting speed for optimal print results.
② Connections between the ink cartridge and ink tubes must remain airtight to prevent ink leakage or evaporation.
③ Ink viscosity must be appropriate; viscosity that is too high or too low will negatively affect the siphon effect.

8. Siphon Ink Supply Method (Working Conditions)

To generate a siphon effect, the outlet of the bent tube must be lower than the inlet.

Let the liquid level at the inlet be plane A and the liquid level at the outlet be plane B. Atmospheric pressure acting upward on both planes is P₀. However, in the right-side tube below plane A, there is a liquid column of height h. Therefore, the pressure at plane A inside the right tube is:

P = P₀ − ρgh

Since P₀ > P, this pressure difference causes the liquid to flow toward the right tube and eventually exit at point B.

Note:
The formula for liquid pressure is:
p = ρgh

Where:

• p = liquid pressure (Pa)
  

• ρ = liquid density (kg/m³)
  

• g = gravitational acceleration (≈ 9.8 m/s²)
  

• h = liquid depth (m)
  
  

To create a meniscus negative pressure at the nozzle surface, the ink level in the cartridge must be set lower than the nozzle surface due to ink surface tension.

9. Applications of the Siphon Ink Supply Method

① When the ink cartridge is positioned behind the carriage, and its liquid level must be lower than the nozzle surface, the machine can only be used for roll-to-roll printing.
② When the ink cartridges are positioned at one or both ends of the machine and connected to the printhead via drag chains, the printer can be designed for either roll-to-roll printing or flatbed material printing.

PS:
The typical liquid level difference is approximately 70 mm.

Siphon Ink Supply System: Principle Analysis and Applications

1. Principle Analysis of the Siphon Ink Supply System

Principle:
The siphon ink supply system is an ink delivery mechanism commonly used in printers (especially large-format printers or continuous ink supply systems). Its core principle is to utilize the liquid level difference, combined with gravity and atmospheric pressure, to achieve stable and continuous ink supply from an external large-capacity ink tank to the internal printhead.

According to the Kelvin equation, the relationship between the negative pressure at the printhead surface, ink properties, and the printhead is as follows:

ΔP=4×γ×cos⁡θR×K\Delta P = \frac{4 \times \gamma \times \cos\theta}{R \times K}ΔP=R×K4×γ×cosθ

• ΔP: Pressure at the nozzle surface during droplet formation

• γ: Surface tension of the ink

• θ: Contact angle at the printhead

• R: Radius of the nozzle

• K: Constant

 

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2. Effect of Temperature on Surface Tension

For most liquids (including water and ink), the surface tension coefficient (σ) decreases as temperature increases. This occurs because:

• Higher temperature weakens intermolecular attraction forces

• Gas-phase molecules exert stronger pulling forces on surface molecules

• The tendency of the surface to contract decreases

Unit conversion:
1 mN/m = 1 dyn/cm

Typical variation:
Within a temperature range of several tens of degrees Celsius, the surface tension of most organic solvents decreases by approximately 0.1–0.3 mN/m per 1°C increase.

 

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3. Surface Tension Data Acquisition

Surface Tension of Common Liquids

★ How to obtain accurate ink data:

1. Consult the Technical Data Sheet (TDS)
   Request from the ink supplier. It typically provides surface tension values at 20°C or 25°C, sometimes including temperature correction coefficients.

2. Experimental Measurement
   Use a surface tension tester (e.g., ring method, platinum plate method) or dyne pens.
   Testing should be conducted under controlled temperature conditions, ensuring stable solvent evaporation.

(TDS = Technical Data Sheet, a document detailing product specifications, performance, usage conditions, safety, storage, and testing information.)

 

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4. Estimation Example (Water-Based Ink)

Assume a water-based ink with the following data:

• Surface tension at 20°C: σ₍₂₀₎ = 35.0 mN/m

• Estimated decrease: 0.15 mN/m per 1°C increase

Using this, approximate surface tension values at other temperatures can be calculated.

Estimated Surface Tension vs Temperature

 

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Note

This estimation method is only applicable to the same ink formulation with relatively stable composition and under conditions where temperature variations are not significant.

 

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5. Application Differences of Inks with Different Viscosities

• Water-based inks generally have higher surface tension than solvent-based inks.

• For inks with the same surface tension, larger nozzle diameters require greater siphon height differences.

• The siphon height difference is also affected by pressure fluctuations, viscosity, and fluid density.

• Printing pressure fluctuation range: ±0.2 kPa
  (Smaller fluctuations indicate a more stable ink supply system.)

• The secondary ink tank significantly affects the ink inlet of the printhead, mainly due to liquid level fluctuations:

ΔH=a×Wg\Delta H = \frac{a \times W}{g}ΔH=ga×W

• ΔH: Liquid level fluctuation height

• a: Carriage acceleration

• W: Ink tank width

• g: Gravitational acceleration

 

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6. Key Pressure Factors in Siphon Ink Systems

a. Static Pressure

The meniscus pressure at the nozzle surface, i.e., the pressure detected at the ink inlet when the printhead is stationary.

 

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b. Dynamic Pressure

1. Pressure fluctuations caused by liquid level changes in the secondary ink tank during carriage movement

2. Dynamic disturbances caused by cable chain movement compressing ink tubes

If pressure is not released in time, it propagates into the printhead, increasing internal pressure and forcing ink out of the nozzles, leading to ink accumulation (flooding) on the nozzle surface

 

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c. Cleaning Pressure

1. During positive pressure cleaning, ensure the pressure remains within the printhead’s tolerance range

2. During pressure release (returning to atmospheric pressure), the speed of pressure change is critical

If pressure drops too quickly, external air may be drawn into the nozzle, causing ink break (misfiring) after cleaning