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Screen printing emulsion: 3 types of emulsion
The screen printing emulsion is a photosensitive liquid mixture (of varying composition, depending on the type of emulsion), which is applied to a screen printingAfter the engraving process, it allows you to create a printing matrix. In this article, we'll explain how it works, what types of screen printing emulsion there are and the main steps for emulsifying.
⧗ reading time - 12 to 14 minutes ⧗
What is screen printing emulsion?
Screen printing emulsion is used in the indirect method, where the matrix is engraved directly onto the screen in a sequence of steps.
It is sensitive to light (depending on the emulsion, it can be sensitive to any light or to UV light), which allows it to be used in the photosensitization process. When exposed to UV light, the emulsion reacts and hardens in the areas that receive light. Conversely, the areas not exposed to light (blocked with the photolithium) do not harden and are removed with water during the development process, creating a design/image on the screen.
The choice of screen printing emulsion is important to guarantee the quality and durability of the matrix. There are different types of emulsion, with different exposure times, ink resistance, suitability for the type of ink, sensitivity to light, among other characteristics. Each type of screen printing emulsion may be more suitable for certain types of printing and substrates.
In the following video, you'll learn how the screen printing emulsion should be applied to the screen.
video by Luís Eustáquio
Function and at what stage of the process is it applied?
Screen printing emulsion is a fundamental element in the indirect method of the screen printing process. The aim is to create a precise and durable (but always limited) matrix that allows the ink to pass through the screen in a controlled and quality manner onto the substrate.
Emulsions are sensitive to UV light and require a light source to harden and form a matrix.
During the process, the screen printing emulsion is applied to the screen mesh, forming a uniform, thin layer. After drying, the screen is then exposed to light with a photolitho, which contains the design/image to be printed. The photolitho is placed between the light source and the emulsion in order to block the light in the desired areas. As a result, the light hardens the exposed areas of the emulsion and the remaining area, protected from the light, does not harden. After exposure to light, the screen is washed with water, which removes the unhardened emulsion, creating the design/image of the photolitho.
At this stage, the screen is ready for printing. The ink applied to the screen, pulling with a squeegeeIt will pass through to the substrate only in the areas where the emulsion has not hardened.
The screen printing emulsion plays an important role in the quality of the print, as it must be able to withstand the pressure and friction of the squeegee, as well as resisting the type of ink used (plastisol, solvent-based, etc.). A good quality screen printing emulsion must be able to hold the matrix for several prints without wearing out or losing detail.
What is screen printing?
7 main steps of the indirect method with screen printing emulsion
After preparing the screen-printing emulsion (if necessary), we move on to the die engraving stage, which includes a series of phases. These are the main steps:
- Screen printing It must be in good condition, with the mesh well tensioned. You should wash/clean it with a degreaser, whether it's a new screen or an old one.
- Emulsify Apply the screen printing emulsion to the mesh (washed, degreased and dried), using a scraper, in a thin, even layer.
- Drying After application, the screen must remain in a dark environment for the emulsion to dry. Preferably in a horizontal position.
- Photolithography You need a photolitho that blocks out the light and creates a matrix.
- UV exposure The emulsified canvas is exposed to UV light along with the photolithograph. The photolitho must be positioned between the emulsified canvas and the light in order to block the desired areas. The opaque areas of the photolitho block the light, which does not fall on the emulsion. The emulsion, where no light has hit it, will not harden and will be removed in the wash.
- Washing/Revelation - At this stage, the screen is washed with water to reveal the matrix. The emulsion blocked by the photolithographic design, which is not exposed to light, will come off with water. Conversely, the remaining parts react chemically to the light, harden and become water-resistant, sticking to the screen.
- Drying/Return to display - After the canvas has dried and is free of traces of water, we recommend exposing it to UV light for twice as long as it was initially exposed. If you want to save energy, you can leave it in the sun.
Another method?
The stencil method stands out for its simple approach, unlike the indirect method. It consists of cutting directly into the matrix, thus defining the areas where the paint will be applied. The stencil can be made from different materials, such as paper.
This technique is particularly effective for projects that are simple, don't involve a great deal of complexity or many print runs.
3 types of screen printing emulsion
The three main types of screen printing emulsion are diazo-based, dual cure and photopolymer. Each one has its own characteristics and the most suitable applications.
Diazo-based screen printing emulsions are bi-component, made up separately of the emulsion (which is not sensitized) and diazo, which is a chemical compound that is sensitive to and activated by light. Prior preparation is required to mix the two components.
Due to their composition, photopolymer emulsions are ready to use and no components need to be added. In this sense, they are easier to use than diazo-based emulsions, as they require no prior preparation. Also due to their composition, they are more sensitive to light and therefore generally require shorter exposure times and less margin for error.
Dual cure emulsions combine the properties of a diazo emulsion and a photopolymer. They are bi-component, made up of emulsion and diazo, but the emulsion is pre-sensitized. This means that after mixing (prior preparation is also required to mix the two components) a mixture with two doubly sensitized elements is created.
Photopolymer and Dual Cure emulsions are capable of producing detailed and sharp images. They are known for their high resistance to abrasion as well as solvents, which makes them ideal for printing on a variety of substrates. Both can be water and solvent resistant (suitable for various types of inks), while diazo is generally water or solvent resistant and not both.
All types of screen printing emulsion have different variations and brands available on the market, each with its own characteristics and specific properties. The choice of screen printing emulsion will depend on the type of material to be printed on, the ink used, the complexity of the design, as well as exposure and washing conditions. However, personal preference will always weigh more heavily. Once you've found the right light exposure time, with a specific emulsion, and you've had positive printing results, you'll still want to work with the same solution. As long as it suits all your projects (type of substrate, type of ink, etc.).
Bichromate Emulsion?
Perhaps you've heard of the existence of a bichromate emulsion? Potassium bichromate is a chemical compound that was once widely used as a component in screen printing emulsions. However, potassium bichromate is toxic and carcinogenic, and its use has been discouraged and even banned in many countries. Screen printing emulsion manufacturers have been replacing it with other safer and less environmentally harmful emulsions, creating emulsions that do not contain chromates in their composition.
Are there any emulsions that are less harmful to the environment and health?
It's a difficult question to answer when it comes to chemical compositions. Any knowledge of the subject may be insufficient.
To minimize risks and environmental impact, it is important to follow safety guidelines, such as wearing personal protective equipment, adequate ventilation and adopting responsible practices, regardless of the type of emulsion you use. This requires adopting the measures indicated by each manufacturer. The use of a mask, gloves and goggles may be necessary.
Expiration date?
The shelf life of screen printing emulsions can vary depending on the manufacturer and storage conditions, but in general, diazo, dual cure and photopolymer emulsions have different shelf lives.
Diazo emulsions generally have a shorter shelf life after mixing with the diazo, which is usually a few weeks. Dual cure emulsions, on the other hand, can have a slightly longer shelf life after mixing, but no more than 6-8 weeks. Finally, photopolymer emulsions have a longer shelf life compared to diazo and dual cure emulsions, and can last several months or even more than a year if stored properly.
However, it is important to follow the manufacturer's instructions and check the expiry date indicated on the packaging of each screen printing emulsion, as they may have different expiry dates depending on the type or manufacturer. In addition, shelf life can be affected by external factors such as temperature and humidity. It is therefore important to store emulsions properly and to check the quality of the emulsion before each use.
Council
Every time you start using a screen printing emulsion, write the date on the packaging. That way, over several uses, you can better calculate and understand the emulsion's behavior and lifespan, depending on how it is stored.
Once opened, the diazo and dual cure emulsion can be stored tightly closed in the fridge (without creating ice). This way it can last longer than stored in a less cool place.
When stored in the fridge, and when you want to use it, you can remove the emulsion beforehand and leave it at room temperature, so that it can't be used cold.
Preparing the screen printing emulsion
Photopolymer-based emulsions are ready to use, while diazo (and dual cure) emulsions require preparation. These emulsions are bi-component and the various elements need to be mixed. Generally, distilled water needs to be added to the diazo (powder), mixed well and then added to the emulsion. The two components must be mixed together very well (preferably with a plastic spatula) and sealed, then left to stand for no longer than the time indicated by the manufacturer.
This preparation should preferably be carried out in a dark room with suitable lighting (e.g. yellow light, so that the recording process does not start).
Depending on the emulsion/manufacturer, there may be variations and you should always check the instructions and advice.
Council
When preparing diazo (or dual cure) emulsion, you should wear protective equipment such as gloves, goggles and a mask. It is advisable to always read the protective measures indicated by the manufacturer on the product packaging.
3 Types of screen printing emulsion: Pros and Cons
Diazo
Pros
- Cheaper
- Greater exposure latitude
Cons
- Requires prior preparation
- Exposure time can be long
- Shorter shelf life
- Generally resistant to water or solvents and not both
- Lower quality for fine details
Dual Cure
Pros
- High resistance to abrasion (including solvents)
- Combines Diazo and Photopolymer characteristics
- Greater versatility in applications
- Durability
- Sharp, detailed images
- Greater exposure latitude
Cons
- Requires prior preparation
- Longer exposure time than photopolymer
- Limited shelf life after mixing
Photopolymer
Pros
- Ready to use, without preparation
- High light sensitivity = Shorter exposure time (can work with weak light sources)
- Longer shelf life
- Sharp, detailed images
Cons
- High light sensitivity = lower exposure latitude (you can easily underexpose or overexpose)
- Use in a suitable dark room
What screen printing emulsion is used at FICA?
The emulsion
In the workshop we use (and resell) a dual cure screen printing emulsion from the Italian brand Saati Grafic HU Blue range.
It is a screen printing emulsion with high resistance to abrasion and solvents. It has excellent print definition on any mesh. It is suitable for printing with UV-curable, plastisol, solvent-based and water-based inks.
According to the manufacturer, stored and sealed in its original container at a temperature of 20-25°C, it will retain its original properties for up to 18 months from the date of production. After mixing, this shelf life reduces.
PROS High resistance and suitable for all types of paint.
CONS Once mixed, the sensitized emulsion should be stored in a cool place and used within a month or so.
Is the matrix infinite?
No. Any matrix engraved on a screen with screen printing emulsion is not infinite. The concept, and positive point, of a screen is that it can be reused. Which means you can remove the emulsion and re-emulsify it.
This also means that, no matter how resistant it is, once we start using the screen, the emulsion will eventually lose resistance and come off little by little. However, if you look after it properly, you can make hundreds of prints with the same matrix.
Screen printing emulsion (dual cure) lasts a long time if you follow a few tips and adopt good practices. In the case of large print runs, you may have to make more than one exposure. In our experience, an engraved screen is capable of reproducing up to 500 units (this may vary).
Council
Paint should always be cleaned immediately after use. First remove the excess paint with a spatula. Then, using a super-soft sponge moistened with water (for water-based paints), run it over the canvas without rubbing, so that the paint comes off more easily. Wash the sponge and go over the paint areas again, rubbing gently. Repeat these steps until the paint has come off.
Whenever you use adhesive tape, it is preferable to choose a solvent-free one. Ideally, the adhesive tape should be removed immediately after using the canvas, otherwise, over time, it can be very difficult to remove the adhesive tape and it will leave traces stuck to the canvas. In this case, use a damp sponge to remove the tape, rubbing moderately, but it may not come off.
If, during use, small dots of emulsion start to come out that don't interfere with the design, you should block them with adhesive tape on the side of the canvas in contact with the substrate.
Conclusion
In conclusion, the screen printing emulsion plays a key role in the process of engraving a matrix, (on the screen printing screen), when UV light is blocked during exposure.
The choice between emulsions, taking into account exposure times, resistance, type of ink, type of light source (exposure unit) and experience, can be important in guaranteeing print quality.
The dual cure emulsion guarantees high quality abrasion resistance and fine detail. At the same time, it has greater exposure latitude, which makes it more user-friendly when engraving the matrix, especially if you're a beginner. However, prior preparation and a shorter lifespan are drawbacks.
Photopolymer emulsion has a longer shelf life and requires no prior preparation, which makes it more attractive for those who don't record regularly.
Of the three types, diazo emulsion has the greatest number of drawbacks. But it can easily be used for matrices with less detail, as long as it is suitable for the type of solvent used in the paint.
Correct storage, following expiry dates, and adopting responsible practices and other advice are imperative. By focusing on resistance, proper storage and responsible practices, it is possible to ensure consistent emulsion performance, which is fundamental to success in the process.
Light sensitivity, correct preparation (when necessary) and the choice between different types of emulsion contribute directly to the quality and durability of the matrix, positively influencing the final print.
One of the biggest challenges when using any screen printing emulsion is the exposure time. We stress that any aspect can alter the exposure time. Starting with the emulsion itself, which can be more or less sensitive to light.
The type of light can mean different distances between the light source and the screen. The power and level of UV will also affect the length of exposure time.
The type of photolitho, and the quality and level of opacity of the photolitho, will influence the exposure due to its ability to block out light.
If we add the number of layers of emulsion (1, 2 or more layers), we add another factor to the equation, which will directly influence the duration of the exposure.
Therefore, a detailed understanding of these elements and the implementation of good practices are essential to achieving consistent, quality results.
Proper use in the printing process, especially when cleaning, is extremely important.
Finally, we would like to stress that we are not concluding that the screen printing emulsion we use is the best. However, during our journey and experiences, it was the emulsion that guaranteed the best results for the type of projects we have.
We remember that experience and experimentation are important for finding the best solutions for the characteristics of each person's project.
Screens with engraving
At FICA Oficina Criativa, in addition to selling screen printing canvases, we also offer an exhibition/engraving service. Screen prices vary according to size and number of threads
Screen printing material
In addition to screen-printing services, you can find various materials and consumables in the store: screens, squeegees, scrapers, emulsion, hinges, adhesive spray, water-based inks.