Your Mini Guide to Choose the Right Screen Printing Emulsion
The journey to great screen printing begins with printing techniques, printing equipment, screen fabrics, and screen printing emulsion.
Understanding different types of screen printing emulsions and the one you are utilizing for your printing business is crucial to your print quality. Any wrong choice can disturb the quality of the result and hamper your productivity. For example, coating the screen might take you hours with a thick emulsion as well as increase your drying time. You cannot sit and say that the screen is drying when you need quality output without any delay.
When it comes to applying the emulsion on your screen, you should use an emulsion scoop coater to spread an even layer on the emulsion sheet. Now, it depends on the type of emulsion as well as your type of job to get the work right. For instance, some emulsion hardens while others might show difficulties in the coating.
To get the best screen printing result, you first need to understand your emulsion. Be it liquid emulsion, hybrid emulsion, or direct emulsion, all require a certain amount of UV light exposure to recover. Knowing about these will help you choose the best one for your project, let's have a look,
Types of Emulsions
Basically, there are three types of emulsions that can be used in screen printing. Based on the type of photosensitizers, photopolymer emulsions can be classified as,
Diazo Sensitized Photo Emulsion
Diazo emulsions can be considered a new addition to the printing inks or emulsion arena. These emulsions replaced bichromate emulsions which were in the league years ago.
Diazo emulsions offer two major advantages,
- Safer to use because of zero mercury content
- Longer shelf life than bichromate emulsions
Diazo emulsions have an increased shelf life up to 6 weeks which makes it easy to use and coat. With the help of diazo, you can store your screen in screen racks without any fear. These also provide hardness to the screen along with abrasion resistance.
However, diazo emulsions also come up with a few problems. One of the biggest concerns while using diazo is that it stains the mesh. Nonetheless, if you expose the screen and expose the emulsion, it will reduce your chances of staining. Apart from this, you can also observe fuzzy edges while using diazo on your screen printers.
The elemental component of diazo is polyvinyl alcohol and polyvinyl acetate which has to be added by the user prior to application. You will need to mix your photosensitizer with resin manually to prepare your emulsion. In addition, it can take up to 15 minutes to cure.
Diazo are cheaper as compared to other emulsions in the market and are becoming a popular choice.
Dual-cure Emulsions
Dual-cure stands for a system that makes use of two systems in one. One out of the two sensitizers is a diazo added by the customer. So, you can consider dual-cure a modified version of diazo emulsion.
It offers certain advantages over conventional diazo,
- It has a high solid content making up to 30-45% of solids.
- Unlike diazo, it has a wide exposure
- It provides a high resolution up to 50-micron lines
- Wide variety of solvent resistance
The biggest advantage of using two sensitizers in one is the creation of a solid bond that provides better imaging and stencil strength. You can also prepare an emulsion without diazo but adding diazo can help you in creating a quality stencil. You can also use them with water-based and solvent-based inks.
Similar to the diazo emulsion, dual-cure also contains polyvinyl alcohol and polyvinyl acetate along with some other components including urethane acrylates, photo initiators, and diazo. The addition of these components provides faster exposure, quicker build-up, and higher resolution compared to the diazo emulsion system.
The special components in dual-cure are difficult to manufacture which turns it towards an expensive emulsion type.
Pure Photopolymer Emulsion System
Pure photopolymer emulsion system is also called "one pot" as there is no need to add a diazo sensitizer. It is the easiest emulsion system asking you to open the lid and start coating. In addition to this, you also don't have to worry about the shelf life because a photopolymer can be used to make stencils up to two years from the date of manufacture.
Unlike other emulsion systems, photopolymer offers a lesser exposure time which can be counted in seconds rather than minutes. You need to take care of the exposure speed while creating a stencil with a photopolymer as it will dry quickly.
The high solid content of this emulsion makes you to coat a thick E.O.M (emulsion over mesh) easily. So, you can achieve thickness in limited coats. Apart from this, you can also observe lesser pinholes as compared to the diazo system.
A pure photopolymer is composed of photoactive polyvinyl alcohol, polyvinyl acetate, urethane acrylate monomers, oligomers, and photoinitiators.
How to Choose the Right Emulsion for Your Job?
When it comes to selecting the right emulsion, a lot of factors are needed to be considered. For instance, the basic requirement of any screen printing operation is quality which any of the three emulsions can provide.
If you are new into the play, the diazo emulsion can be the best-suited option for you among the three as it is cheaper and easy to work in your initial days of learning. Dual cure emulsion tends to be difficult to work because of its quick dry time. However, it can also provide you with the refined finish you are looking for.
The second thing you need to consider while choosing your emulsion is its water resistance. Apart from this, the viscosity of emulsion and solid content also play a major role in governing your outcome.
The size of your screen mesh also defines your results. For example, a higher mesh count screens require a thin emulsion. On the other hand, a thin emulsion cannot coat a screen of lower mesh count as it will result in pinholes in your print.
In the end, pay some heed to your manufacturer’s recommendation. The ink manufacturers recommend emulsion types that are compatible with their inks. As the screen printing results depend on the type and quality of ink, as well as the emulsion, you need to pay concern in choosing the suitable option for your job.
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