In general there is no simple way in getting graphics onto the topsheet. The explanation I have gotten from professional printing companies is, that the topsheet and base plastics are very tough and durable industrial plastics made for application of durability, hence also from the chemical viewpoint they will be tough and resistant against reacting with any ink.
In general when you select a method, you might experience these issues:
- the ink seems to stick to the topsheet but when you laminate it and pull, the topsheet comes off. The binding is weak! (solvent/UV)
- The ink bleeds during lamination and pressing (solvent/UV)
- there is warping/shading (sublimation)
In general you have to do testing in any case first to see if the ink will stick or if the ink will bleed, or if you ahve any other issues. Some systems work better then others.
There are several ways people have tried toget the graphics onto the topheet,
– Digital printing with solvent ink, UV curable ink, Epoxy inks etc. TPU/ABS topsheet works with solent ink systems, some. UV ink requires a primer on the topsheet first. Epoxy ink would work on all without a primer! Primer can be found from Berlac Basler group.
– Sublimation or heat transfer: The ink goes deep into the topsheet and stays there. TPU/ABS topsheet or extruded base does not support this transfer type!
– Silk screen printing. This method works well with all topsheets, the ink type suggested by manufacturer is Basler lacke / berlac ink type 63. I also know Nazdar has some epoxy inks.
– Printing on a substrate or a cloth which is an inlay to the topsheet (goes under the topsheet).
For topsheets available, here are the options,
PBT: This one is white, and is suitable for sublimation only. It gives fantastic results.
PA nylon: PA is suitable for sublimation as well. You should be able to screen print on it as well for the clear version. For white background you have to back print on it or go for the white version of the topsheet. Direct digital printing so far is unsure, if you decide UV or Latex printing, please make sure you use primer, and test bounding with epoxy!
TPU/ABS: The ABS component in this topsheet reacts chemically with solvant ink. Typically white is not printable, so it becomes see thru, unless you can find someone who can print white. So this one you can print with solvant ink. Also screen printing should be ok. Please test several printers as some work well and some dont.
we know from some customers that printer are working well as follows:
For PE you can use a clear Basler 63 system as a primer and print into the Basler layer.
PE base material: It works with sublimation for sintered bases! If you wish to try direct digital printing like UV or Latex, try with primer first, then test bounding with epoxy.
Digital printing
In general Iv tried UV printing. I did not have big success, ink does not stick well to the topsheet! A primer is needed, a back coating primer from Berlac/Basler or Nazdar is needed. Primer is a epoxy primer and takes about 24h to cure. Its extra work. Make sure you test a lot first.
If you can somehow print with epoxy ink on the topsheet, this will work but so far I have not found anyone who can do this. I know some facories use Screen Truepress W3200.
As for solvent ink, some printers will work and some will not. Also Iv had issues with some printers that the colors will bleed during pressing or lamination.
Isosport has not been succesful in digitally printing on PA topshets. The latest update is that soome of the topshets suchas ICP 8210 PA might be printed on with a Latex printe (which is quite expensive), however no guaranty for good results.
Solvent ink printing seems to be the best for TPU/ABS topsheet on the ABS part, and on PE bases with primer.
The main problem is that if you print digitally the ink might stick to the topsheet and seem to be ok, however the bound between ink and the topsheet is so weak, that after the process of lamination, the ink will seperate from the topsheet and your topsheet will fall off.
Any topsheet with ABS component in it will react well with solvent ink. As far as I know, this is how signs are made. One drawback to pure ABS is that it is UV sensitive, it might give yellowing if the topsheet is not threated with some kind of varnish.
So in general unless you have a Latex printer you can test, or unless you use a ABS topsheet, or some epoxy system, digital printing is hard to accomplish. This is why many people simply choose to modify their press to support sublimation, and get a Epson SC t3200 printer for sublimation or similar.
The results from a digital printing on a transparent topsheet are transparent graphics, so if you dont for your internal layup to be visible you will have to backprint with some white pigmented epoxy or similar. Nadzar has epoxy inks used for this, white in color. It is expoy ink for silk screening.
Inlay
Printing on an inlay should be doable. The main properties of the inlay should be that it will bind to epoxy on both sides and that it will receive ink well. It should also be strong in a way that you can not rip it appart when you pull on the two sides (topsheet will pull one way and the glassfabric on the other side will pull another way). Also you need to think about that your inlay will not absorb moisture and delaminalte later on.
Printing on cotton or bamboo or similar cloth material (say 100gms) can be done by some companies, or you can try to set it up on your printer. Thin cloth inlays are successfully used in surfboards, however quite often they also give a see thru result.
Another method I hear about is printing on paper. I have had bad results with delamination this way. Make sure you experiment before you go with this method.
Sublimation should be possible on PBT-polyester inlay fabric.
Tissue paper or rice paper are also widely used but are hard to deal with. Tissue paper is a cheap and simple way for a small builder. You need some acidic free tissue paper, a spray adhesive and some printer paper. You spray the adhesive to your printer paper, attach the tissue paper and cut it quickly to shape, put it in the printer, print. Once it is printed you need to be quick to remove the tissue paper from the printer paper. It is now ready!
As long as the fabric/inlay has some small holes where the epoxy can penetrate, this should improve the bound to the topsheet and minimize delamination.
The thickness of the inlay and density will determine the see thru and the white in the graphics.
Silk screen printing
Silk screen printing on a topsheet is not my favorite (unless you can find waterbased epoxy inks or similar). In this method you create a screen for each color and the you put your screen over the topsheet and press the color thru the screen. Once this color dries, you go to the next screen for the next color, and in the end you have a topsheet impregnated with all the graphics.
It is mainly for larger production, the initial setup cost is high and you have little degree of freedom in making custom graphics. You also need some strong epoxy chemicals which are both hasardeous to you and the environment.
White color is doable.
Sublimation
Read more here: https://www.junksupply.com/sublimation-heat-transfer-of-graphics-on-plastics/
Sublimation printing or heat transfer is the method where the ink is transfered onto the tophseet in a pressurized heated press. The molecules of ink go deeply into the topsheet and are hard to get out or scratch off. I prefer this method for several reasons. Beyond the not so bad setup investment, the method works on several topsheets such as PA and PBT and some ptex. The ink is water based and hence environmentally and health friendly. The waste is minimum. It is suitable for custom graphics.
The startup cost is not so great, as you can modify your press to support temperature of 130-160C for short time, and get a printer such as Epson SC T3200 that supports sublimation.
White colors are not doable, so any graphics with white component is done on a white topsheet – PBT or white PA nylon.