Pretreating and Curing the Pretreatment for 100% Black Polyester Printing

customerMarch 18, 2019

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  • You will typically need MORE pretreatment than a standard 100% cotton garment. Try starting your testing with 30-40 grams of ULTRA pretreatment.
  • This means the shirt is going to be WET!
  • Try Hover Curing...... this will require NO cover sheet and keep the dreaded heat press marks from showing.
  • But prior to placing the garment on the heating platen, pre-press the platen for 10-20 seconds to really get the rubber on the bottom hot, then place the shirt on the heating platen and hover. The heat from the bottom will help cure the ink from the underside while the hovering cures from the top. It will speed up the curing and result in a no-contact, better cured print.
  • Depending on the gap distance of your heat press to the garment surface, time will vary until it is dried and ready to print. DO NOT OVER CURE! This will make the garment permanently stiff.
  • Try 356F and start with 2-3 minutes. This will most likely not be enough, but remove the shirt and repress the rubber platen to get rid of any moisture and re-heat it.

NOTICE: The garment is going to be REALLY stiff...... the flexibility will return after 15-30 minutes of sitting out and returning to standard room temperature. Do not try printing while the shirt is stiff..... you need the pliability to fit your platen best.

I want to show everyone how important it is to ensure that your DTG ink is properly cured when printing on 100% poly garments.

Figure 1 shows two different shirts with the same image printed. The garment is a 100% black polyester fabric with the Image Armor E-SERIES inks. This picture is after just one wash and dry cycle.

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In this case we were testing hover curing and wanted to show exactly what happens with a properly cured in film and one that was only partially cured. The left shirt was hover cured much longer than the shirt on the right. As you can see, the partially cured ink caused ink failure after just the first wash. Uncured ink will not wash well. It will start to flake off and the image will degrade very quickly with subsequent washes.

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This is a closeup of uncured ink that has been washed. The durability of uncured ink is greatly diminished and will result in almost instantaneous ink film failure when washed. Figure 2 is a closeup of the under cured ink. Under cured ink does not have the wash characteristics of durability that properly cured ink produces. Typically with Image Armor inks, you need to cure at 356F for 35 seconds on cotton and blended shirts. On polyester fabrics, that time and temperature can possibly cause dye migration and a discoloration of the white ink from the dyes in the fabric. The ink can be cured at slightly lower temperatures, however the time under heat usually will increase with the amount of ink applied - it is a balance of getting the entire ink film to temperature (above 315F, removing the moisture - a balance of time and temperature - and to a point, pressure if a heat press is used).

The point of this article is to show you the telltale signs of uncured or under cured ink. It is of the highest importance that you need to ensure that all moisture from the ink film is removed and the entire ink film reaches cure temperature. Make sure, especially if you are trying to print 100% black polyester fabrics, that you do your testing prior to running any production runs. Proper testing, printing, and washing on fabrics like black polyester will help bring your shop to the front edge of what is possible with DTG white ink printing.

PRINTING

The printing process is relatively straight forward like the pretreating process, however some printers and RIPs may be better suited for printing white ink on polyester fabrics than others. Loading the shirt onto the platen is a very crucial part of this process. You want to be able to thread the shirt onto the platen for optimal performance of the print. If your printer platen only allows you to lay the entire shirt onto the platen you will run into some issues with ink passing through the first layer of the shirt and depositing onto the inside of the back of the shirt. This happens because the weave of most polyester fabrics are not a super-tight weave leaving a lot of open air areas between the threads. DTG printer ink can not bridge this gap and thus the ink will just jet through onto whatever is behind it. In this case, the inside of the back of the shirt.

One solution is to utilize a slip sheet in between the layers of the shirt. However, this can cause issues due to the amount of ink being deposited. The ink will soak the paper and cause it to swell and possibly bubble up, raising the surface of the shirt enough that you might run into a head strike. Due to the high concentration of pretreatment a head strike can quickly clog up nozzles in a print head and possibly leading to a replacement of the printhead.

A close-up of the printed shirt reveals the open mesh weave of the athletic polyester shirt. This makes the ink look pin holed or less white than normal due to the black of the shirt showing through these holes.

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The main point is you want to lay down as much white ink as possible on the first pass for the underbase. You will need to apply typically more ink than on a 100% cotton shirt. How much white ink you can lay down in a single pass will be dependent upon the printer and the RIP. Some printers, like the Epson PRO series printers (i.e. 3880) will not allow as much ink to be deposited as say an Epson 3000 printer. You will have to do independent testing with the type of printer you have and the RIP.

Working on conjunction with the amount of ink the printer can physically lay down is the RIP. The RIP will also limit how much ink you can deposit. Polyester will require 1.5-3 times the white ink to achieve a great looking finished product when compared to a 100% cotton shirt. Of course, testing with your own equipment and settings will be required. Laying down too much white ink can result in the white ink not being "kicked over"enough and then when the CMYK is applied it will look great on the printer platen, but when you heat press the ink it will blend into the white causing a dulling and image clarity degradation. So, finding the optimal amount of white ink for your printer will take some testing.

You DO NOT want to deposit a lot of white ink on the second, or highlight pass. This is because all the pretreatment has been used up in kicking over the initial deposit of white ink. The addition of printing more white ink will result in a serious wicking of moisture and components from the ink onto the surrounding fibers. The ink will either "spider out" or create a halo around the image which may or may not wash out after printing. Many times, when depositing a lot of white ink on the underbase, you will still get this halo effect. This will usually wash out in the first wash and is most noticeable on lighter colored garments.

We have found that certain colors of polyester, especially red and maroon, will most likely still dye migrate during the curing process and even after the cure has been completed. This is something we are still working on, however it is still going to be an ongoing issue in dealing with our water based inks.

Washing of the Garment

We would highly recommend washing the garment prior to wearing obviously as with any DTG printed shirt. However, the wash characteristics are extremely favorable due to the way we formulated the E-SERIES inks. Other than regular washing techniques suggested for the specific fabric, we really do not have any other requirements for good washing. As long as the ink is cured it will wash extremely well. We tested our shirts in the extreme of washing - hot water during the wash and high during the drying of the shirt. For optimal results, warm to cold water washing and hang drying of the garment will result in the longest life of the shirt and print.

Making it All Happen

Due to the nature of the E-SERIES inks, we have been able to achieve really good results while printing on black 100% polyester fabrics. In fact, some look as good or better than screen printed designs and could easily pass for standard screen printing. There is still a lot of work to do to perfect this process, but we are making great strides to achieve an industry wide, easy to accomplish task. We've only been able to do this with the Image Armor inks and not any other brands within the Epson re-purposed printers. So, you no longer need to be confined to just cotton shirts. Let the power of the E-SERIES inks open new doors and profit opportunities for your business.

 

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