When experienced screen printers first started their venture, little did they realized the factors involved in properly curing their prints. Under-cured ink is the most common problem found in the print shops today. If you too are screen printers, you would know of the stories of how people tried to cure their t-shirts in their kitchen oven.
Many use flash cure or buy a heat gun from local hardware, in spite of the fact that people use a heat gun to bake and strip-away paint. It didn’t take much time for them to realize that these ideas were only making their production suffer.
Although there are many creative ways to cure your screen printed t-shirt, the best and most recommended solution is to employ a conveyor dryer if you are looking to build a professional screen printing shop.
The Right Curing for the Right Type of Ink-Screen Prints
There is really no substitute for conveyor dryer when you are looking for long-term success and produce high-quality prints. It is the most financially viable option for you. However, you need to find a dryer that best fits your workspace and your work process and production quantity.
You also have to make sure that you are using the right curing techniques based on the ink you are using. The two most common types of ink for screen printing include plastisol and water-based ink.
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|For plastisol ink, the curing has to be done at 320° F, some as low as 280° F. Plastisol is the industry standard for creating opaque and durable prints. Here, you have to check the datasheet from the manufacturer of each plastisol ink you use.
||On the other hand, water-based ink uses water as a solvent to hold the pigment. This means, it demands complete evaporation for a proper cure, so it needs a longer dwell time of at least 90 seconds to several minutes. The curing temperature may range from 300° F to 360° F. using additives you could bring it down to as low as 200° F to 280° F. For the best results it is logical to check the technical sheet from the manufacturer.|
Process of Proper Curing
01. Fabric vs Temperature
Not all fabrics require the same curing temperature. Set your oven to different printing profiles based on fabric type, fabric color, fabric thickness, and
ink application. Understand the rate at which the garments heat up. For instance, polyester heats faster than cotton shirts. Similarly, manage your oven heat settings for different types of garments.
Weather is also an important consideration while fixing the temperature of your oven. Most importantly, keep records of different dryer temperature for different garments, at various times in a day especially during weather changing conditions.
For faster prints, you may try running the conveyor drier with the oven set too hot. Remember, this may damage your fabric. With anything fast, you are just wasting your energy and resources like fabric and printing ink. It is better to slow the speed of the conveyor and for gradual heating that prints your shirts.
02. Dwelling Period
The dwelling period is the time a shirt is in the oven chamber under the exposure of heat. This is where the curing process starts. Many neglect the curing process due to the hasty production of printed t-shirts that eventually lacks print quality and washes away easily.
It is similar to baking a cake where providing heat for a longer period of time cooks it perfect for a fluffy and spongy texture. In a similar manner, apply the recommended cure temperature that maintains the ink to remain under heat for a longer period of time known as the dwelling period.
Ink films are thin. Only 3-5 seconds are recommended to keep it under the oven heat for proper curing. It may go up to 60 seconds to ensure the ink is properly cured especially for larger and thicker prints.
03. Avoid Excessive Flash
Flash is the short term application of heat in between print stages to quickly dry the ink before applying a new ink color over the previous ink layer.
Overflsahing or applying excessive temperature can cause damage to the fabric and ink as well. Most flash temperature ranges between 90 degrees Celcius to 108 degrees Celcius.
Excessive flash causes the inks to be sticky that results in distorted or hazy designs.
04. Controlling Dye-Migration
Too much heating during the curing process causes some of the ink to bleed/seep through the garment. This is called Dye-migration is During the decoration process, you can control dye-migration by using correct inks and lowering the temperature.
Another reliable method of controlling dye-migration is to use an ink that blocks the bleeding by absorbing migrating dyes before they get to the subsequent layer of ink and cause discoloration.
You can use low-bleed white ink under the lower curing process that may control the bleeding to some extent
Putting it Through The Test
If you follow your manufacturer’s recommendation completely, it will overwhelm you to decide what to do and what not to.
01. Washing Test
The best way to ensure that the cure is perfect you need to put it through the test such as a wash test. It is still one of the best methods to ensure that you did the curring properly and also the fact that the dryer is working properly.
Many screen printers do it only when they are dealing with a big order or when the type of garment used is prone to have defects such as special effects, gel inks, etc. You can do it simply – you put it through the laundry just like one does in the real world. If the print stays on without showing any defects, you can rest assure that the curing is perfect.
If you find that some of the print colors have washed off, you can conclude that the ink wasn’t properly cured. The amount of print degraded will give you an idea of how insufficient the cure was. Many manufacturers wait for nearly 24 to 48 hours before doing a wash test to get more accurate results.
However, it is worth noting that you cannot prevent 100% of the print from deteriorating, you need to determine the best and acceptable tolerance of deterioration before shipping it to customers. Many print businesses conduct a wash test from time to time to see if their dryer is working properly.
02. Stretching Test
Another common curing test is the stretch test in which you will have to stretch the t-shirt to one half the stretch capacity. If the print doesn’t crack when you relax the fabric, you can be sure that the ink is cured.
Note: A 100% polyester jersey has no elasticity and not eligible for the stretch test to determine curing quality.
One more thing, all inks are not equally designed and manufactured. Some focus on durability and toughness while others on softness and elongation.
Stretch test is the quickest and easiest method to check the curing quality. For testing, you need to select a print area that is 5cm long . Stretch it slowly until you see a crack on the image, record the stretched length vs cracking point.
Note: The cracking values may vary for different types of fabric, their density and ink deposit.
03. Rubbing Test
Rub the colored portion of the fabric with a white cock test cloth. Then assess the color transfers on the white cloth using the AATCC 9
Step Chromatic Transference Scale or Gray Scale (ISO International standard 105/A03). The preferred crock dry scale by major brands is 3 to 4.
Some print shops use simple white cloth for this test. However, it is recommended to use white crock test cloth for meaningful results.
Limitations: Fabric with white prints cannot be assessed with this test.
Common Issues With Print Curing
The most common issues with today’s organic blends are bleeding in which dye gets trapped under the ink, thereby discoloring it. Other issues such as ghosting also arise which creates a soft halo around the print. Then there is the problem of see-through prints.
There is also the problem of shrinkage and scorching which have led screen printers to look for inks that they can cure at low temperatures.
Getting the right cure can be a tough task but with a solid understanding of the basic curing needs and tests you can get the result you crave for. Plus, if you have a print shop, you need to automate the process with a web-to-print solution to make your production much faster, easier and in a cost-effective manner.
Does water-based ink need to be cured? Yes, it is necessary to cure water-based ink but it usually takes longer. Although you can use heat guns and flash dryers, it is recommended to run water-based ink printed shirts to a conveyor dryer.
Will screen printing ink washout? Even after fully curing the t-shirt, the ink will eventually wash out sooner or later. Moreover, it depends on the fabric such as if it’s a cotton substrate it will take longer to cure than other fabrics and will also wash out much later.
In conclusion, not only inks but also the printers that greatly contribute to the print quality. You must have knowledge and skill about the printing machines and tools to properly cure the ink.
Finally, you must protect your garments from over-heating during the printing and curing processs, and quality decorated apparel to your customers.
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