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What You Should Know About Ink Filtration?

Filtration stands as a crucial step in the ink manufacturing process, yet experience has taught us that relying solely on your supplier’s ink filter doesn’t exempt you from filtration within your system. Ink transforms over time, and without adequate protection, these changes can wreak havoc on your system’s functionality. In this article, we delve into the significance of ink filters across various types of ink supplies and offer guidance on selecting the appropriate filter and its placement to safeguard your system’s performance. Join us as we explore the critical role of filtration in preserving the integrity of your printing system and maximizing its longevity.

Types of Ink Filters

When it comes to ink filters, the choices are abundant. One of the simplest options is the woven metal mesh, which is essentially cut directly from the woven fabric. The filtering capabilities of this type of filter depend on factors such as the gauge of the wire and the number of overlapping mesh layers. Filters are typically categorized by grid count, indicating the number of openings per unit distance, akin to print resolution. The illustration below illustrates how the intersecting threads of the braid determine porosity, and how altering the number of thread meshes impacts the effective particle size of the filter.

These mesh screens are weldable into stainless steel housings to create a filtration unit. Known for their exceptional chemical compatibility, they are well-suited for applications involving strong acidity, high solvency, or elevated temperatures, particularly inks. While these filters excel at removing larger contaminants, their limited surface area increases the likelihood of clogging over time.

Presently, the majority of inkjet machines available utilize polymer membrane filters, with one popular variant being the capsule filter. Capsules are frequently integrated into ink systems as fill filters to strain ink before entering the system or as recirculation filters (as depicted in the schematic below). Similar to filters employed in ink manufacturing processes, capsule filters are pleated to enhance surface area and consist of multiple layers to prolong their lifespan before experiencing notable flow reduction.

capsule filter

Another variant is the disc filter, primarily employed as a last-chance filter (LCF). Positioned after the ink reservoir, disc filters strain ink before it reaches the printhead, a particularly prevalent practice in multi-pass printers equipped with end-shooter (non-circulating) printheads. These filters are also frequently utilized in laboratory environments due to their cost-effective interchangeability between different inks. While disc filters have the propensity to clog relatively swiftly, they are less prevalent in recirculating systems, although some applications still incorporate them to this day.

disc filter

In conclusion, the filtration systems in most inkjet machines predominantly feature polymer membrane capsules or disc filters, selected based on the volume of ink passing through them. However, for enhanced durability in environments with elevated temperatures or exposure to potent chemicals, metal mesh filters offer a viable alternative. By carefully considering the specific requirements of each application, printer manufacturers can optimize filtration efficiency and ensure reliable performance in diverse operating conditions.

Ink Filter Pore Size

Determining the appropriate aperture size for your ink supply is crucial, especially considering that certain printheads come equipped with built-in filters as part of their design. For instance, the Seiko 508GS, Konica Minolta KM1024i, and Dimatix Samba printheads feature integrated metal mesh filters within the ink channels, while the Dimatix Q-Class and Ricoh MH series printheads incorporate perforated membranes within the individual ink channels. Opting for a suitable filter size within your ink supply serves as a prudent decision, serving as a final barrier to safeguard the nozzles and other internal components, thereby extending the lifespan of your printheads. By implementing the appropriate filtration system, you can ensure optimal performance and longevity of your printing equipment.

When it comes to colored ink formulations, a prevalent filled filter size ranges between 5-6 μm, whereas for dyes, a 1 μm filter suffices. In recirculation systems, employing a 10 μm filter can prolong the replacement interval while effectively safeguarding the nozzle. However, for white inks, particle deposition can lead to clumping, rendering a 10 μm filter susceptible to clogging, thus necessitating the use of a larger-sized filter. Additionally, specialty inks like those containing metal flakes may encounter issues with smaller filter pore sizes, warranting careful consideration and potentially requiring larger filter sizes to mitigate problems effectively. Tailoring the filter size to match the specific ink formulation ensures optimal performance and longevity of the printing system.

In some cases, it may be possible and/or desirable to use a staged filtration regime. In this scheme, often used in ink manufacturing, the filtration is stepped down 20um -> 10um -> 5um, for example. Although slightly costlier from a periodic service perspective, this approach can result in a decreased failure rate with time (and associated reliability) and still ultimately protect the head.

In certain scenarios, employing a staged filtration regime may be both feasible and advantageous. This filtration approach, commonly utilized in ink manufacturing processes, involves a stepped-down filtration sequence, such as 20 μm -> 10 μm -> 5 μm. Despite potentially incurring slightly higher periodic service costs, this method offers several benefits. By progressively reducing particle size at each stage of filtration, the likelihood of system failure over time decreases, enhancing overall reliability. Moreover, this approach effectively safeguards the printhead, ensuring optimal performance while mitigating the risk of ink-related issues. Ultimately, implementing a staged filtration regime offers a proactive strategy to maintain system integrity and prolong equipment lifespan, thereby optimizing operational efficiency and minimizing downtime.

In conclusion, the primary function of a filter is to safeguard the integrity of the nozzle, making it imperative to utilize the smallest hole size feasible. Ideally, the filter’s pore size should be smaller than the nozzle diameter to ensure effective protection against contaminants. By adhering to this principle and selecting appropriately sized filters, users can significantly reduce the risk of nozzle clogging and prolong the lifespan of their printheads. Prioritizing nozzle protection through meticulous filter selection ultimately contributes to the sustained reliability and optimal performance of printing systems.

Ink Filter Failure

The occurrence of filter failure often serves as a prevalent culprit behind printing issues. As previously highlighted, inadequate meniscus pressure can trigger a decline in pressure, leading to erratic volume output or, in severe cases, nozzle suction of air, resulting in cessation of spraying. Additionally, excessive strain or prolonged operation of the pump, coupled with insufficient system refilling, signals a telltale sign that the fill filter necessitates replacement. Recognizing these indicators is crucial in promptly addressing filter-related issues to maintain optimal printer performance and mitigate potential disruptions in printing operations. Regular monitoring and timely replacement of filters are essential practices to uphold system integrity and prevent filter-related complications from impacting print quality and efficiency.

Various issues arising from filter failure are contingent upon the system’s design, including the types of pumps utilized and their driving mechanisms. Integrating pressure sensors into the system can effectively monitor its characteristics and promptly alert operators to error conditions. Although this enhancement may elevate the system’s cost, it proves far superior to compromising performance or encountering ink level surges within the machine. By proactively implementing monitoring mechanisms, operators can preemptively address potential issues, thereby safeguarding system integrity and ensuring consistent printing performance. The investment in such monitoring technologies ultimately contributes to enhanced reliability and longevity of the printing system, outweighing the initial costs incurred.

It’s essential to consider the potential risks posed to the ink by filtration itself. In high-flow applications, the ink undergoes significant shear forces as it traverses the filter, potentially exceeding anticipated levels. Over time, these shear forces can adversely affect ink stability, leading to unforeseen consequences. Before conducting tests with a customer, it’s advisable to evaluate the system using the actual fluids intended for use. This proactive approach ensures compatibility and helps mitigate any adverse effects on ink stability, ultimately enhancing the reliability and performance of the printing system. By conducting thorough testing beforehand, operators can preemptively address any potential issues and deliver optimal results to customers.

In conclusion, filters serve a critical role in safeguarding printheads and preventing failures in other parts of the system from causing irreparable damage. It’s crucial to recognize that filters are not merely accessories but integral components that require careful consideration in system design, ongoing monitoring, and regular maintenance. By incorporating filters into printing systems, operators can proactively mitigate risks and prolong the lifespan of printheads, ensuring consistent performance and minimizing downtime. Viewing filters as essential components rather than optional add-ons underscores their importance in maintaining system integrity and achieving reliable printing results. Effective design, monitoring, and maintenance of filters are essential practices for optimizing system performance and maximizing operational efficiency.

 

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