With anything in life, there is struggle. Oftentimes getting back to the basics in any given situation will provide you with a solution to that problem. The Direct to Garment (DTG) market is no different. Being in the direct to garment industry since 2004, there have been major changes in printing equipment but the basics of DTG has remained the same. Understanding how your printer functions is a crucial element in operating a successful DTG printing business.
One common concern DTG manufacturers, suppliers, operators and owners have is maintenance. Most maintenance procedures include cleaning a wiper blade, capping station, spit station, encoders, cleaning around the print head, oiling the head rail and shaking your white ink. Some of these are performed daily and others weekly or monthly.
Effectively performing your maintenance will ensure continual and uninterrupted performance of your equipment. At the beginning of your day, operators are encouraged to shake their white ink, initiate a head cleaning (performed by the system itself) and print a nozzle check. The nozzle check will help determine whether your system is functioning properly and as simple as it sounds, can help diagnose where there could potentially be issues. We’ll go a little deeper into this when discussing the ink delivery system, but the first and simplest diagnosis comes by cleaning your encoder(s).
Encoders: There are many types of encoders, but with direct to garment systems, there are usually two optical encoders used. An optical encoder is either a strip or a disc that appear gray in color. The coloration actually comes from printing extremely thin black lines in a row, usually beginning at over one thousand across a span of one inch. The first is typically called an encoder strip, encoder scale or linear encoder. This is the strip that is behind the print head carriage and runs left to right. There is an encoder sensor behind the carriage that reads these lines so it knows the position of the head at all times and when to fire a nozzle.
A dirty or scratched linear encoder will cause printing problems during printing. These problems could include unwanted lines being printed, mis-registered prints, the print head carriage traveling further than its allowed distance and other strange issues. In these cases, the system is not able to understand where the positioning of the head is and where the nozzles need to fire due to a miscount of these lines. Cleaning this strip off throughout normal maintenance procedures will prevent many of these types of issues occurring.
The second optical encoder is almost always a disc and it keeps the positioning of the platen movement correct. Most of the time this disc is hidden and not exposed so cleaning is not necessary. If it can be seen, then chances are cleaning it would be necessary. The linear encoder effects prints from left to right, whereas the rotary encoder effects prints from top to bottom. If there is an inconsistency with prints in this manner and you can see the rotary encoder, cleaning it off with a lint free cloth with isopropyl alcohol should fix the issue, if it doesn’t contact the manufacturer or distributor for additional assistance.
Outside of the various features offered, all direct to garment equipment have five basic areas in the ink delivery system: a supply source, ink lines, dampers (or cartridges), print head(s), and capping station/pump. Some may include filters or degassing systems that need to be taken into account, but most operate with the five basic areas mentioned here. Understanding the cause and effect for each area will give you the ability to quickly diagnose and overcome the issue(s).
Ink Delivery System: When DTG first exploded on the market, companies offered a bulk ink system. Even though consumers consider a bulk ink system to be a money saver, the problems that can be associated with an open system oftentimes outweigh the perceived savings. An open or bulk system is simply containers in which you pour ink into. If your system is used infrequently, waterbased inks can evaporate causing the ink to change its viscosity or thickness. The inks for your system are designed to be used with the associated print head and any change in the inks can cause persistent issues.
Another concern for an open bulk system is when ink bottle caps are opened, dry ink around the bottle rim can fall into the container, causing issues for your dampers. If your printer has an open ink system, it is imperative that in addition to your maintenance procedures, be sure to clean around the openings on your containers with a damp cloth. This simple step can help avoid dried ink from falling into your ink supply.
Positioning of your ink system also has a tremendous effect on the performance of your system. If your system allows for a change of positioning of your ink supply, finding the correct height can be found through trial and error. If you have an open container system that is six to eight inches high, as the ink is being used, the amount of ink in the container changes and causes a difference of pressure in your system. This causes you to either need to constantly change your ink system positioning or continuously maintain a certain amount of ink your system at all times. Bagged ink is much simpler to find this position since a bag laying flat doesn't change the height of ink remaining.
To find the correct position, a good starting point would be to level out your ink supply even with the bottom of your print head or the top of your platen. The reason your ink system may be adjustable is your elevation to sea level can have an effect on performance. The higher your elevation the less pressure internally there would be so your ink supply may need to be higher to force more pressure into the system since most are gravity fed. Very rarely do we see the need for your ink supply to go above the bottom of the print head. Some of the newer systems on the market are pressurized and this may not apply. Be sure to talk to your manufacturer or supplier about proper ink supply heights.
If your ink source is too high, as your system is printing there could be drops of ink on your shirt. This is almost always an indicator of too much pressure in your system which would most likely be attributed to this scenario. Even though there may not be any unwanted drops, too much pressure could also cause the system to appear to be clogged or nozzles dropping out, resulting in a banded or print where the color is not correct. If you are fighting this issue, the first thing to do would be to move the print head to the center and look at the bottom surface of the head. If you see ink build up on the head surface or specifically on the row of nozzles, then your nozzles are being blocked from a buildup of ink. Performing a system head clean should bring this back to 100% but without adjusting your ink delivery, this would be a constant struggle.
If your ink source is too low, then more force is being pulled backwards and not allowing the ink to flow into the dampers properly. This would cause what is known as ink starvation. The effect is similar to the nozzles being blocked when your source is too high, but looking at the bottom of the head should show a clean surface. If this is the case, then chances are as the nozzles drop out and the head is firing ink, it could be drying out your nozzles leading to head clogs that can be difficult or time consuming to work out. Each manufacturer or distributor may have a different method to recovering nozzles and it's suggested to contact them in these cases.
Now that we know the cause and effect of the ink source positioning, depending on which direction you need to move the source's position, it's good to work in small increments. If there was dripping, then I would move the ink source down about 1/4" and try again. Continue to do this until the dripping and/or buildup on the head's surface disappears. Of course the same goes for dropped out or clogged nozzles from the ink source being too low. If your system has an ink source where the height that cannot be changed but you have an open cartridge, then it would be good to invest in closed or sealed ink cartridges. Chances are, this would increase the performance and reliability of your printer.
Ink Lines: Most of the DTG printers available today were designed as paper printers with no ink lines. When ink lines were added to the systems there was no provision for a circulation of white ink. Color inks tend to not be an issue but if white ink sits unmoved in ink lines over a period of time it could harden in the lines causing that channel to not print. This is one reason we do nozzle checks daily. What we refer to as a channel of ink is the nozzle rows for that color. If a channel drops out, then technically that color isn't printing. This drop out could be related to a clogged ink line, which is very difficult to break free and almost always results in changing your ink line(s). This is why most companies advocate that the operator print daily even if it is a sample shirt. Once again, check with your manufacturer or distributor for proper procedures.
Dampers or Cartridges: Since the ink lines directly connect to the dampers or cartridges, determining if the issues are either the ink lines or dampers takes a little trial and error. Most of the older converted DTG systems have a cartridge with ink lines attached to them. The cartridges sit on top of the print head itself. These types of cartridges have an electronic chip on the end. A damper would not have this chip and will perform much better than a cartridge. When the print head moves, the internal pressure increases and decreases rapidly, a damper equalizes this pressure since the source is coming from the damper itself. As ink flows into the damper, it goes through a filter, a reservoir then the print head. If the ink is not properly filtered or has dried ink from an open system, these filters can clog quickly causing nozzles or full channels to drop out. This is why a proper ink source using high quality and properly filtered inks makes a tremendous difference with performance.
At the beginning of your day, if a nozzle check is performed and a channel is not printing, use the proper procedure from your manufacturer to recover your nozzles. If after they have been recovered and the channel drops out shortly after you begin printing, chances are the damper is not performing correctly. Recover the channel again and if the same results are seen, then change the damper.
Most of these types of systems have either three or four channels of white ink printing. In a four channel system, it's possible to print three channels of white ink at 100% and achieve solid and bright white ink. If a nozzle check is not performed and one of these channels are not printing, the damper may not be functioning. This would not allow the ink to flow through the ink lines causing a clogging in the line itself. Performing a nozzle check will allow you to know if the ink is flowing properly and aid in preventing a costly repair.
Print Head(s): There are several types of print heads on the market but the most widely used systems utilize a single head with eight channels of ink. The top portion of the print head is called the manifold. This is where the spikes push into the dampers allowing the ink to be released into the head. As the ink travels through the manifold, it passes through a filter before it reaches the head itself. If the ink lines and dampers are not clogged but you cannot recover the ink channel or most of the nozzles in that channel, there is a good possibility the manifold filter is clogged. There are methods to recover the manifold called backflushing, but if this doesn't solve the issue, changing the manifold itself should solve the problem. Of course, if the manifold isn't the issue either, it may be time for a new print head.
Most print heads have over a thousand nozzles on the surface of the nozzle plate. Each nozzle is the thickness of a human hair, so it's no wonder improper ink handling during processing can cause ill effects. It’s not always the ink itself but air bubbles entrapped between the nozzle plate and the inside head cavity as the cause of blocked nozzles. To determine if you are experiencing a print head clog or an air bubble, print a nozzle check then perform a basic system head clean. Perform a second nozzle check and compare the two. If the nozzles are now printing, it could have been air bubbles or a clog, but if the same nozzles are dropped out, it would indicate a head clog. If the nozzle is now firing but others are dropped out, chances are it's an air bubble traveling inside the head.
Most of the time a head clean will address this issue but try to refrain from doing too many consecutive head cleans. After around the fourth head cleaning, you could be creating a foaming inside of the head which would make the head appear worse than before. Oftentimes you can let the head sit for 30-45 minutes and the foam would dissipate and perform as normal. Since all systems could be slightly different and they may not use the same type of print head, contact the manufacturer or distributor for proper procedures.
Capping Station/Pump: Capping stations typically are comprised of three elements, the cap top, wiper blade and pump. They may all be contained within one unit or they could be separated. The function of the capping station is to pull ink through the lines during cleanings, to keep the head surface clean from ink or debris and to stop the head from drying out. Part of the maintenance could also include what is called wet capping. At the end of the day, placing a little cleaning liquid in the cap and parking the head over the station also can aid in keeping the head from drying out. Be sure to check with the manufacturer or distributor to ensure this is a proper procedure to use. Not all dampers will stop a back flow of ink or prohibit the ink from flowing into a waste container.
The cap top has hard rubber or polymer seals and should be free from any nicks, cuts or ink build up. Clean this daily with a foam swab and cleaning solution to avoid nicks or ink buildup. When the head sits on the cap top but the seal is compromised, the pump may not pull properly and/or the nozzle plate could be exposed to air. If the head is exposed for prolonged periods with no use, the nozzles can easily dry out, once again causing clogs. During your normal maintenance procedures, be sure to examine and clean the cap top thoroughly.
Cleaning the wiper blade takes very little time, but a dirty blade can wreak havoc on any direct to garment system. If the blade is not cleaned properly, dry ink will be pushed back into the nozzles. The effect would be packing dried or thickened ink into these nozzles and possibly not allowing for recovery. A dirty wiper blade could also leave the surface of the head with ink build up blocking the nozzles from firing properly. If the wiper blade is in this condition, it may be simpler to replace it.
The pump, as mentioned before, pulls ink through the system. With inkjet systems, head cleans are necessary to keep the ink flowing and the nozzles firing properly. If the pump is not pulling correctly but everything else seems to be functioning, then the effect is the entire head will have poor performance. The pump is usually not the first thing looked at as the cause since they have a low failure rate, but it is something to keep in consideration when determining printing issues. It’s important to note, a pump will not effect a single channel in a multi-channel head. When a single channel is not performing properly, it’s better to start from the ink source and work your way towards the capping station in diagnosing the problem.
If at any point in your ink delivery system there are additional filters, an ink circulating system and/or degassing units, you would want to check these areas as well. But again, beginning at the ink source itself and working your way through the system will allow for quicker troubleshooting.
Understanding the basic principles of how an inkjet system works, specifically direct to garment, can simplify your printing process. This simplifying can lead to more confidence in printing and far less down time resulting in higher profits and happier employees and customers.