Let’s go back to basics. Screen printing is also a stencil method of print making in which a design is imposed on a screen of polyester or other fine mesh, with blank areas coated with an impermeable substance, and ink is forced into the mesh openings of the mesh by the fill blade or squeegee and onto the printing surface during the squeegee stroke.
Emulsion is the means of making impermeable substance. Light sensitive, thick liquid which coats the screen. When the screen is exposed the emulsion hardens and unexposed areas drop out to leave the stencil.
So you have your positive artwork
Now this process is one of the most tricky in screen printing and needs to be done thoroughly and carefully. Never skip on any step especially drying.
It is very important to degrease the screen prior to coating the screen with emulsion and exposing the artwork. A screen that is not degreased will have problems exposing and increase the chance of pinholes, the emulsion will not adhere to the screen properly and might washout before the image can be seen. The emulsion could also not wash out at all. Make sure you let it dry thoroughly before you coat it with emulsion.
There are many emulsions on the market and every printer will have their preferred type and brand. Some emulsions come pre sensitised and ready for use and some will need mixing. Our emulsion is a 2 part emulsion, its comes with sensitizer.
Shelf life is different depending on when the sensitizer is added . Separately both parts can last from 12-24 months. Once mixed the emulsion lasts 6-8 weeks (its life can be prolonged slightly if it is stored in a cold place, like the fridge).
Always make sure you have chosen the right emulsion if you are using Plastisol inks / Solvent inks you need a Solvent resistant emulsion like Ulano Proclaim or if you are using Waterbased inks you need a water resistant emulsion like Ulano 925wr. We also sell Autosol emulsion, which is a good dual purpose emulsion, it can be used with both waterbased and solvent inks.
Make sure you are doing all parts of the emulsion and exposure process in a light safe environment with NO outside or bright light. This includes mixing your emulsion, coating your screens, drying screens, exposure, and washout (as soon as screen is exposed as long as you wash it out straight away this is not a problem)..
A costing trough is the best way to get an even coverage of emulsion. Always check to make sure the coating trough has a straight edge and no damage otherwise you will get poor coverage and you can snag the mesh.
Here are a few things to watch out for if your images are not washing out correctly:
That you are not coating your emulsion too thick. One coat both sides should do it, with a nice even spread. There are sometimes where you may need some extra coats e.g. printing transfers and printing white onto a dark garment but you will need to adjust the exposure time.
That your film positive is very opaque and dark. If you hold it up to a light and can see through it, you need to double print your film to achieve a more opaque image.
That there is positive contact between your screen mesh and your positive film. If the film is not pressed completely against your mesh then you will get light reflection between your positive and your screen which will result in a blurry and not clear image. That’s why the glass is so important.
That you are exposing your screen for the correct amount of time, which will depend on the exposure system you are using. If you are unclear on exposure times please feel free to ask us. The simple run of thumb is – if the emulsions washes off too easily and you start to lose the stencil then the screen is underexposed and if after prolonged washing the stencil does not come through they you are likely to have overexposed the screen.
After you coat your screen, you want it to be COMPLETELY dry before you expose the screen.
To transfer your image onto your screen you will need to use an exposure unit. There are many different exposure unit set ups on the market and each has a different light source. Each having different light sources. UV, halide and halogen are very popular in the UK. Our Wicked exposure lamp has a 1000 watt halogen light source and is provided will all waterbased and Plastisol kits.
We also sell Actinic and Metal Halide exposure units which are able to expose quicker (typical exposure time is 2 minutes for an Actinic unit and 16 minutes for the lamp depending on size of the screen) than the cheaper lamp solution. Some units include built in drying cabinets making the whole process a lot faster.
A very large part of your decision if you are new to screen printing will be your budget and space. Exposure units vary dramatically in price. The WPS Lamp is small and compact,
After exposing and rinsing out your exposure, you want your screen to thoroughly dry (and ideally harden your screen, by exposing it to the sun or your exposure unit) before inking and printing. This process is often called double baking.
Before inking you need to use blocking tape (can use brown tape or professional blocking tape) to cover up areas on the screen not covered by the emulsion. Also fix any pinholes either using blocking tape or using screen filler which is a liquid emulsion, make sure you choose the right one as there are different versions for solvent and water resistant stencils.
Now you are ready to print
When you get bigger there are other options like the Revolutionary Riso QS200 Designed for the Professional Printer which prints directly from your computer onto a screen. Then the whole process takes under 5 minutes!
We are often asked “what is the best exposure unit for my screen printing business?”
Like always what seems a simple question does not have a simple answer. So we thought we would put this guide together to help work through your requirements and to come up with the right answer for you.
Let us first look at what YOU for YOUR Screen Printing business. Think about these considerations and questions?
We are going to do our best to avoid baffling techy jargon so if this is all new to you we suggest that to take a look ‘Is screen printing for me article’ and our video tutorial which will help you understand the basics.
Now let us look at the Exposure Unit solutions from simple to heavy duty.
Very simple solution, there are thousands out there, which are used every day. Good for hobbyists / home printers who make a handful of screens per day. Comes as part of our Essential and Mid range screen printing kits.
Pro: Very Cost Effective, can create excellent stencils and you can expose large screens. Note that the lamp does not have a vacuum therefore you need to ensure that the positive is tight and intimate with the screen. To do this you use sheet of glass (the heavier the better) which ensures that the film positive and screen are very tight. This Exposure Unit uses halogen bulbs (1000W) which are powerful and cheap to replace.
Cons: Very Slow (10 – 20 minutes depending on screen size), requires space (large cupboards are ideal), the printer has to time the stencil exposure – there is nothing ‘hi tech’ about the lamp solution but it works.
The WPS Mini Exposure Unit uses proven “Actinic” tubes in a tight array. This exposure unit comes with a yellow pilot light which you use to position the film positive with the screen. The unit comes with an integrated timer (you can set multiple programs) and vacuum which is extremely easy to use. We have used these units for a number of years and have been pleasantly surprised at the quality of stencil produced even with very difficult artwork. Typical exposure times from 140 – 300 seconds depending on what kind of emulsion and the number of coats you are using.
Ideal for small print shops, schools and colleges. You can also purchase the unit with a drying cabinet which really does improve production with a relatively small footprint.
Pros: Very easy to use, very tight vacuum, and uses proven technology giving high quality stencils. Different sizes of exposure unit available to accommodate different frame sizes.
Cons: Potentially tube units do not produce stencils as sharp as from a single light source. With tube units, light comes from multiple angles, potentially undercutting the positive during exposure which can result in the loss of fine detail. However we have not experienced many issues at all with this kind of unit.
These units can be used in a high production environment e.g. 50 – 70 screens per days. However do budget to replace the bulbs on a regular basis as they will gradually degrade.
The WPS LED Mini Exposure Unit, consist of UV LED technology positioned in a tight array, similar format to the “Actinic” version. It comes with a yellow pilot light which you use to position the film positive with the screen. The unit comes with an integrated timer (you can set multiple programs) and vacuum which is extremely easy to use. LED technology has started to make inroads into the screen printing industry, so the technology is relatively new and is continuing to be developed. Like the standard unit it also available with a built in drying cabinet which is great for increasing production and reducing mess.
Pros: Very quick (30 – 300 seconds depending on emulsion / number of coats etc.), Very easy to use, very tight vacuum, LED technology using low power, does not generate heat, is long lasting (stated to be very long life) and produces high quality stencils. Different sizes of exposure unit available to accommodate different frame sizes.
Cons: Initial purchase price higher than Actinic units. The LED array emits light from multiple angles undercutting the positive during exposure which can result in the loss of fine detail. However with LED technology this seems less of a problem than tube units and is commonly not considered a problem for the vast numbers of printers (99.9%). LED technology is new and is continuing be developed.
Ideal for small / mid, large screen printing shops and educational establishments who need to produce lots of screens quickly. These units are designed for high production environments. We tend sell this units to printers who have invested in direct to screen technology.
The Heavy Duty Unit uses a single point Metal Halide bulb, they come in lots of different configurations with different bulb ratings and features such as integrators (measures the quantity of light reaching the screen and adjusts the exposure if there are any voltage fluctuations or to compensate for deteriorating bulbs) and rapid start-up – it can take time for a metal halide bulb to get to the correct operating temperature. These units are fast and give very accurate stencils. Metal Halide is still probably the most popular light source used for mid and large screen printers.
Pros: Very fast (depending on the power options you choose) and can come with advanced features so you can produce large numbers of stencils quickly, consistently and accurately. Often used in heavy industry environments and for used for multi applications e.g. exposing print plates. Different sizes of exposure unit available to accommodate different frame sizes.
Cons: Metal Halide bulbs are expensive (£200 – £400 common prices), generate heat and consume much more energy than LED units (LED exposure units typically use 1/5 of the energy of a metal halide unit). Many screen printers are moving over to LED technology.
When choosing an exposure unit take some time and think about your current and future screen printing requirements. There are lots of exposure units to choose from all giving different levels of production capability and quality. The exposure units with combined drying cabinets are very cost effective and increase productivity. If you are looking to replace an older unit e.g. metal halide unit then we would highly recommend that you consider LED units.
Please feel free to contact us to discuss your requirements and we can help you to find the right exposure solution for your needs.
Starting out and want to know the fundamentals of screen printing?
Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate. A fill blade or squeegee is moved across the screen stencil, forcing or pumping ink into the mesh openings for transfer by capillary action during the squeegee stroke.
Screen printing is also a stencil method of print making in which a design is imposed on a screen of polyester or other fine mesh, with blank areas coated with an impermeable substance, and ink is forced into the mesh openings of the mesh by the fill blade or squeegee and onto the printing surface during the squeegee stroke. It is also known as silkscreen, serigraphy, and serigraph printing. You can also have more than one colour printing, for example you could have a striped printing
You need to follow the ‘exposing process’.
Firstly you need to make your artwork positive, then coat your screen with emulsion. Once that is done you are ready to expose your artwork onto the screen using an exposure lamp or unit.
We find that this can be the most tricky part of the screen printing process. For more details check out our buyers guide and YouTube videos.
Sometimes it is the simplest things that mess up your screen printing! We sell a variety of printing platens, brackets and hold downs suitable to keep all substrates(what you are printing on) still from textiles to paper.
Our MDF platens are great value and easy to clean with a strong melamine white surface. Our platen sizes range from children to adult mega and we also sell a sleeve platen and vacuum board.
We also sell two types of platen attachment brackets which are sold separately. The 50mm is for use with our wicked presses and carousels and the 75mm is for use with larger printing arms on floor standing Hopkins carousels.
Our aluminium platens which are ideal for floor standing carousels are very hard wearing and long lasting and can help you to avoids warping caused by flash drying.
We sell a range of Weiss hold downs for printing onto caps, jackets and umbrellas. These hold downs can fit other carousels but we need to know the arm sizes.
Our vacuum boards are ideal for printing posters, banners and stickers and their warp resistant frame makes for for longer durability. This board is a must with our 2, 4 and 6 colour printing presses for single and multi coloured prints. We also sell the Weiss Vacuum platen and motor which can be used with other brands of carousel.