Industry expert Tony Palmer shares some top tips on wet-on-wet printing with plastisol ink
So, you’ve laid down your pristine white base layer using the high-tension mesh with a superb EOM coating and the fancy new composite blade. Next, you flash and get the underbase just dry enough to start laying down the 11 colours on top. It’s at this point that most of us reach for the coffee pot, put on the lucky shirt and try to figure out the intricacies of a multi-colour job on a dark shirt. Should you even have said yes to this job? Should you have argued with the customer to change it to a two-colour silhouette design? Should you have gone down the transfer route? The design has toned edges but surely the addition of a garment colour bleed would be OK? Maybe this is the perfect job to get the DTG machine finally paying for itself?
No, it seems that the whole of the multiverse is working against you because the run size is 3,000, and the shirts are a great vintage purple colour with just enough man-made fibres in them to make them allergic to almost anything other than multi- colour direct screen print. There’s nothing else for it, you’ll have to knuckle down and get it printed. You approach the press wearing your lucky shirt (the one from the batch of 1,000 that you stayed up all night printing and packing, delivered to the event and secured the next order for 10,000 – you are a printer, superstition beats logic every time!). With 12 more screens to place in the press, you frantically work out how many heads you have and where you can put the five flash cure units. Then, disaster strikes! To run this job you must remove four of the flash cure units and use the print heads instead, if you want to keep a cooling station after the base flash. The prospect of running a 12-colour job with only one flash strikes instant fear. Will it smudge? Will it pick off? Will it pinhole? Do you have sufficient silicone spray on hand? Maybe you still have a tub of flow thinner from 1987! That will help, right?
Fail to prepare, prepare to fail
Flashes, spots, dryers, heaters – these wonderful additions to a printer’s arsenal are valuable assets, but are you always using them correctly? When printing on a manual carousel, flashing every colour takes no extra time, and it’s arguably more difficult not to flash. However, on an automatic machine the addition of a flash can actually cause more problems than it solves. The number one use of flash curers is to dry the base white layer to ensure that the colours you lay down on top remain bright and make the print ‘pop’. When a base layer is applied onto the fabric and gelled, the base white should be touch-dry but not cured. It should resemble a tomato: firm to the touch, but still wet and squishy underneath.
Flash curers are wonderful additions to a printer’s arsenal, but multiple flashes are not necessary for successful wet-on-wet plastisol printing
Be careful not to over-flash, though: countless problems arise from an over-flashed base layer. Plastisol ink has a gel temperature: it gels when it hits this temperature and then it becomes wet again as the temperature continues to rise, until it hits its second phase – the curing phase. It’s very difficult to tell from touching alone if a base layer has been over-cured or under-cured as both feel wet to the touch.
Many print shops are now using multiple flashes on dark and even light shirts. But is the use of these flash curers actually necessary, or are they being used as an expensive cure to a problem that could be addressed early in the path from design to press?
The truth is that most problems with a multi-colour job can be solved before they happen – and they don’t require multiple flash curers…
Colour order This is important and can help a job to look cleaner and run more easily. Try to use the old technique of smallest area to largest area: this is a guide and should be manipulated according to brightness, design intricacies and the use of tones to create the appearance of more colours (as if 12 wasn’t enough!).
Mesh counts Why is that colour on that particular mesh? Is it because it’s all you have that is clean? What’s the tension of that mesh? High mesh counts with high tension are a necessity for multi-colour prints. Allowing for a little personal preference and, of course, adapting to the level of detail or line count, I wouldn’t go lower than a 90 as the strength of the colour comes from that pristine base that goes down first. Using the higher mesh count allows you to control ink deposit while also stopping the ink from smudging on the base white. The last colour can use a lower mesh count as nothing else is going over the top, which is perfect for keeping whites bright or yellows super opaque.
Blade choice Most commonly, blade selection is made using the same, age-old, tried-and-tested method that has served print professional for decades – “Which ones are clean?” Better instead to consider some more important variables… The hardness (shore) of the squeegee blade is of extreme importance when printing wet-on-wet as it controls two elements – the amount of ink laid down and the amount of force applied on wet ink to avoid pick-up from the previous screen. Start the job with your hardest blade and work your way through, getting softer and softer. The last colour should have the softest blade in your shop, as this blade will be pressing down on 11 colours sitting atop a solid white base that is designed specifically for the purpose of making plastisol run along it (and making that ‘mmpppaahh’ sound that all printers hate).
Progressive angles are a key factor in reducing the blurriness and maintaining the flow of a job without resorting to multiple flash curers
The last colour can use a lower mesh count as nothing else is going over the top, which is perfect for keeping yellows super opaque
Squeegee angle Progressive angles are a key factor in reducing the blurriness and maintaining the flow of a job without the need to resort to multiple flash curers. Start with that rock-hard blade in the first colour and use a straight angle of around 5 degrees – it won’t hurt anything because you’ll be printing onto that pristine tomato-skin base white. Progressively add angle until the last colour, with the softest blade, when you should use the steepest angle: 25 degrees or more.
Squeegee pressure Squeegee pressure plays an integral part in a finely tuned print set-up on press. Using the same theory as the blade selection and angle application, pressure should also be progressive. Reduce the pressure on these wet colours by backing oto the point where the ink doesn’t clear the mesh and then adding just one turn of pressure. Avoid double-stroking as this will add more ink than you need. It may look nice when it first goes down, but once it has been pressed by another five sets of blades it will run along the base white faster than the catcher runs for the exit at the end of the shift.
Heat management This is a major factor in ensuring a print job runs smoothly. Let it go cold and the ink starts to go sticky, keep adding heat and the ink starts to go sticky, too hot and the boards leave a little battle scar burn on the belly of the loaders.
Keep your cool
Multi-colour printing can be difficult and demanding, I have certainly felt like throwing the squeegee blades through the closest window and just sitting in a dark corner of the screen room and gently rocking myself back to normality when a multi-colour job starts to get too hot on the press. So try to keep cool and be persistent. Solve the problems before they hit the press and then sit back and watch the machine knocking out beautiful little works of art. Take great pride in knowing that you printed those little masterpieces using just one flash and progressive angles. But also prepare to be ostracised from polite society if, when you see one of these shirts worn in public, you persist in telling the wearer all about the advantages of using 30 newton screens and a 65/90/65 composite blade.
Tony Palmer has been in the garment decoration industry for over 30 years and is now an independent print consultant working closely with print shops to get the most from existing processes and techniques. Tony is passionate about keeping and enhancing production skill levels within the industry. He is the owner and consultant at Palmprint Consultants, offering practical help and assistance to garment decorators all over the globe.