聚焦纺织品印花产业的商机与未来
2021.05.20-22 Poly World Trade Center Expo
 

Transfer Printing: Down to the “Nitty Gritty”

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This article goes into the process of the transfer printing technique, the advantages and disadvantages of choosing this method, a little of the history, some examples, a myth buster session, and a handy FAQ to boot.



How does Transfer Printing Work?


Depending on the technique the process differs, but the most general form of transfer printing happens with a soft, elastomeric stamp. The process operates in three steps:


Inks (also called microdevices) are prepared on the donor substrate in an ordered and releasable manner. (Usually through wet chemical etching or dry etching).


An elastomeric stamp is used to retrieve inks from the donor substrate. During this process, a proper preload is applied to the stamp to ensure the conformal contact between stamp and ink, which makes it adhesive enough to retrieve inks from the donor substrate. The process can be either selective (if you are looking for precise manipulation of the inks) or non-selective (for high throughput).


The inked stamp is printed onto the receiver substrate. The removal of the stamp completes the transfer printing process. The printing mode can be non-selective or selective.


While the retrieval-printing process above applies mostly to techniques that require the use of transfer papers, some techniques; such as CAD-Cut Vinyl, use solvent releasable tapes or thermal releasable tapes instead of stamps, simplifying the process.


For sublimation printing, a special kind of ink is used that evaporates when heat is applied. It is therefore unique in this way because the gas joins the polyester, becoming part of the material instead of just attaching to it.


Different Kinds of Transfers


Did you know that there are actually so many ways to do transfer printing? Have a look at some of the most popular transfer printing techniques.


Plastisol


Named after the ink used, plastisol-transfers are a great choice for company logos, labels, text and designs where fine detail and vibrancy of colour is the priority. It is often confused with screen-printing because it is practically the same process with the only difference being that this time we print onto transfer paper instead of the garment. It is also very similar to water-based transfers, but the ink doesn’t contain PVC which makes it more environmentally friendly.


This type of heat transfer is known for its vibrant colours, but it cannot print too many at once. Generally no more than four. However, the colours are particularly bold and very durable. Unlike other inks, Plastisol has a very soft feeling with the capability of a much finer level of detail. When heat-pressed, the transfer is allowed to cool before the backing is removed, (hence ‘Cold Peel’) which allows easy application and suitability for most types of garment. This is the most popular of all transfer techniques.


Stretch Litho


Litho, named after lithography, is the latest technology in the transfer world. It is a great combination of digital and screen-printing. As first printed onto paper, litho transfer retains the details of the artwork better than other techniques. Paper is a smoother substrate than fabric, so the dot of colour does not bleed as much as when touching the paper´s surface, as it does on fabric.


Sublimation


When you want to decorate 100%-polyester shirts, sublimation transfers are a full-colour solution that is also cost-efficient. The process of this technique differs from the others because it works with an ink that turns to gas whenever it’s heated. The gas joins directly to the garment, becoming part of the polyester instead of just attaching to it. Therefore, it does not add any extra layer on top of the fabric, which makes it work best on white or very light coloured garments.


Nonetheless, the sublimation process is quite similar to heat-transfer paper, since it involves printing said design onto a sheet of sublimation paper (in this case) and pressing it to a garment with a heat press.


Bonus! Sublimation not only works on polyester fabrics – it also works on a wide variety of hard surfaces which first have a poly-coated layer.


Sublimation transfer can produce long-lasting images, on the other hand, it is limited by the materials it is compatible with. Due to the nature of the inks, this technique only works on fabrics made out of polyester. Yet, sublimation also works on a wide variety of poly-coated hard surfaces, so it can be used for mugs and other promotional items as well. A particularly popular technique all round! However, it is easy to recognise because any fold or crease on the T-shirt will remain white – a problem found in the area under the sleeves.


CAD-Cut Vinyl


The CAD-cut (Computer-Aided Design) vinyl transfer printing is a method of heat-transferring onto T-shirts and clothing. It is most commonly used for printing the numbers, names, and logos onto sports T-shirts. It prints directly onto printable vinyl or nylon, which is ideal for garment printing of one to three colours. It is known for its durable, matt or gloss finish, and available in many colours and patterns. Moreover, with no set-up time, it’s faster and easier than screen-printing!

The transfer is usually cut into a number or name and then applied to the garment with an application tape, which allows you to heat press right away.


To customise clothes further with this technique, different vinyl colours and textures can be used. Along with plain block-colour, cool effects such as polka-dots, chevrons, animal-print, demin, camo, leather and stripes are available too. By layering pieces of vinyl, you can also create unique effects. To keep its pristine condition and to prevent it from peeling off after washes, choosing the right vinyl applied right way is also vital.


The different Stages of Transfer Printing


Unlike other techniques such as DTG, screen-printing or embroidery, the process of transfer printing varies with the type of transfer performed.


Step 1: Image selection


Depending on the type of transfer, the artwork is handled in a different way. Techniques like plastisol or litho allow for complex (with many colours) images to be printed in detail. While processes like CAD-cut vinyl require simple vector shapes so they can be ‘read’ and cut by the computer. That being said, regardless of the type of transfer, it is recommended for the original file to be saved in high-quality (300 dpi) to ensure the best possible result!


After all, the artwork requirements are equal to the different types of transfer printing. Most of the transferring process works with Pantone colours, which requires careful selection when using the design software. Moreover the artwork must be saved in vectors in AI, EPS and PDF formats. After that, all should be converted to strokes and the artwork must be done in the actual size of the final print. Be aware not to put gradients and shades.


Step 2: Print your artwork


Once the design has been selected, it will be printed on the transfer material. Place the transfer paper onto an inkjet printer through the software of the cutter or plotter machine. Make sure to adjust the graphics to the size of the print as desired.


It is advisable to use professional heat transfer paper as this will give the image a high-quality finish. It lasts longer and won’t fade, bleed or peel. Cheap papers usually leave a line around where the design has been cut and have a shiny finish, which many find unpleasant.


Differences between the technologies for step 2:

CAD Cut Vinyl: unlike printing the artwork on a transfer paper, this technique allows you to print directly onto a printable vinyl or nylon.


DST: when printing the artwork, instead of using ink, the artwork will be digitally laser-printed on a transfer paper.Sublimation Printing: instead of transfer paper, sublimation paper will be used during this process.


Step 3: Cutting


After the artwork is printed, carefully load the printed transfer medium into a cutter/plotter. Then the machine will detect and cut the medium into the shape of the graphic.


Once the cutting process is complete, do not forget to remove the unwanted parts by using a weeder tool. Double-check if the print looks how you want it to be on the T-shirt!


Step 4: Weeding (Optional)


When working with vinyl, the design must be cut from the material. This process can be automated or done by hand. A computer is used to control the process to ensure the cut is perfect. After that, the excess will be picked out. This process is known as weeding.


Some types of transfers such as CAD-Cut Vinyl need this step others do not. Basically, this refers to the excess of material left after the design has been cut off.


Step 5: Pressing onto the Garment


The paper is pressed against the fabric using the heat press and is left for the heat to do its job. Ensure that the shirt is placed straight and the graphic is centralized to avoid a crooked print.


Though, there are several things to take in account on the heat press machine before printing. For example, the optimum temperature depends on the transfer medium and the type of fabric used. Usually, 155’C to 180’C is good. The pressure should not be too high or too low. When pressing, follow the instructions stated on your medium to avoid over-pressing and leaving burn marks on your garment.


Nowadays a more elaborate version of the simple iron-on method is used by most of the professional T-shirt printers. Yet, the basics did not change! The heat transfer machine releases a certain amount of pressure while holding the garment in place with a consistent temperature that allows the colour pigments to be transferred from one surface to another.


Differences between the technologies for step 4:

Plastisol Heat Transfer: there are two options for this technology: hot-split transfers and cold transfers. While the heat transfer press is being set between 166’C and 177’C, press the heat transfer onto the substrate for 10 to 12 seconds. If your option is hot-split transfer, you will immediately peel off the paper, which makes the ink split into two, depositing some on the substrate, while leaving the remainder on the paper.


This option provides a softer feel. For the cold transfer option, you will let the substrate and the transfer paper to cool for about 40 seconds before the peeling process. Then, the entire plastisol transfer will remain well on the shirt.


DST (Digital Screen Transfer): before this step, DST requires additional steps compared to other technologies which are placing DST film on a platter and applying white base and DST adhesive. After applying, place the DST film for 5 to 7 seconds in a heat press set at 120’C with light pressure. Then, set it between 125’C to 140’C with medium pressure to transfer the artwork to a garment.


Sublimation printing: when the sublimation ink is heated, the ink turns from a solid to a gas that embeds itself into the polyester fabric.


Step 6: Cool Off


When the required amount of time has passed, lift the print and leave the garment alone to cool off. If everything goes as planned, you will have before you a quality T-shirt with your very own design!


Differences between the technologies for step 5

Sublimation printing: in step 5, the ink turns to gas while being embedded into the polyester fabric. During this step, the gas goes back to solid and becomes a permanent part of the fabric. So in this case, there is no difference in feeling between the printed image and the rest of the fabric, since the transferred design does not add an additional layer on top.