It is the printer’s responsibility to keep an eye on the mechanical functionality of the machine. As with all machines, breakdown or failure of mechanical parts can happen at any time. This can range from clamps coming loose to total machine failure.
Whilst going around checking inks, the printer can listen out for any irregular noises, which may indicate that beginning of a failure, notify maintenance if you see or hear anything suspicious.
The printer should check the flash units to ensure they are reaching the sufficient temperature and not getting too hot, also ensure the correct zones are operating
Monitor the state of the mesh, look for tears and holes. Other problems might include:
Because screens are subject to wear and tear, the emulsion, which provides the mask for the stencil, can break down. This usually presents itself as small pinholes in the same place on every print. Unaddressed area of breakdown will increase as the screen wears.
Any examples of this type of undesirable print outside the main print area can be rectified by placing a “mask” such as tape over the hole.
Stencils can also suffer from blockages. Build up on the back of a screen can encroach the stencil area therefore, this must also be looked out for, as it will compromise the integrity of the stencil. Any occurrences can be eliminated by simply stopping the machine and cleaning the back of the affected screen(s)
An example of “build up” on the back of a screen can be seen below:
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Often within a batch of garments, there are loose foreign bodies, such as pieces of cotton that can end up lying within the print area on the shirt. The problem with these bodies is that if they are within the print area, the capillary action of the screen will lift said items from the shirt and they will become part of the stencil. This can be easily remedied by removing the offending item from the stencil. However, due to the nature of how the print press is set up, it may be anything up to 20 shirts before this is spotted, so the best way to eliminate this situation is prevention. Therefore, the loader must keep an eye on the surface of the shirt, and quickly remove any pieces of loose material before the machine indexes.
Foreign bodies may also get onto the pallet, and because screen-printing is designed for printing onto flat surfaces, any textures on the board can create uneven surfaces, which can sometimes show up on the print.
Pallets can get a build-up of foreign objects, such as cotton or lint, that are loose on the shirt and with the glue on the pallets, these become stuck in place. Large foreign objects on the pallet will affect the surface of the print and where seen these should be removed.
Registration is the fixed relationship between each colour contained within any one print. It can be affected by:
Insufficient supplies of glue where the shirt moves in between colours.
Machine failure where either the screen or the pallet is not locked into the correct position prior to print action taking place.
Excessive flashing.
Stretching of the mesh due to excessive pressure, excessive heat or too much ink.
Wrong off-contact setting.
Please note, as specified earlier, it is the printer’s responsibility to administer all of these checking procedures.
To aid with this, they are also expected to make regular visits, selecting random garments from the feed-in point of the dryer, and spend sufficient time to do full random checks.
At the same time, this provides the opportunity to monitor the off-loader to ensure they are administering all during run checking procedures and loading the garments into the dryer in the correct manner.
Although ironing marks are a result of the process of flashing and mechanical
squeegee action, these markings must be reduced as much as possible.
This can be done by: -
i) Reduced pressure on each squeegee.
ii) Different size of squeegees to dissipate the marks.
Setting the wrong front or back position for the squeegee or flow bar may result in parts of print missing or the appearance of unwanted lines.
It is important to check that all the elements contained within a colour visual are present on the completed shirt. Look out for discolouration of a complex image with a definitive horizontal line.
Flashing is a process, which in effect quick dries the surface of the ink, thus allowing subsequent inks to print on the garment without blurring. It is done with the use of an external heating element that switches on and off at a set time to compliment the indexing of the machine. If not set right, this can mean under flashing, thus not dried and results in issues with opacity and curing. Over flashing can result in the scorching of garments and the print itself.
During a production run the printer should allocate the time to establish the next print run and this might include:
Identifying and collecting the stock
Identifying and collecting the ink
Identifying and collecting the screens
Identifying and collecting the sample
Reading and understanding the job information
Preparing for the next job to minimise the “down time” between jobs