SCREEN PRINTING 101


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WHAT IS SCREEN PRINTING?

 

Screen printing is the best and fastest process for printing into garments plus other products and definitely the most affordable when it comes to large quantities. Just like with a stencil, the screen printing technique consists of pressing ink through apertures to create a printed design onto a huge variety of surfaces and materials. Also known as serigraphy, serigraph printing or silkscreen, this form of decoration is a great way to personalize your products. It’s a very basic process that has unlimited outcomes. Is the most common and widely used form of decoration in the industry and currently accounts for over half of the apparel decoration activity in the US. 

The basic idea of screen printing consists of your design being transferred onto a mesh screen stretched across a frame and your product is placed under the screen. Ink is then pressed across the screen with a rubber blade or squeegee either manually or by a machine one color at a time onto the product. Finally, each printed piece is either air dried, placed under UV lights or ran through a high temperature conveyor dryer to cure the inks.

One of the great benefits of screen printing is that it can be applied to almost any material and the most common are fabric and paper. If you own a t-shirt with a design on it, it’s probably been screen printed. As well as artistic uses on paper, it has a range of exciting commercial applications and promotional items like mugs, bottles, cups, mouse pads, hats, flags, signs, display stands, towels, bandanas, bags, etc. It’s also used in a miniature level on high-tech things like circuit boards and medical devices.

There is the misconception that screen printed graphics need to be bold, simple and can’t have much detail, but we can now easily achieve highly detailed multi colored prints like full color photographs or artistic illustrations and get the same resolution as a digital print with longer durability, a more vibrant look and best of all at a lower cost when you need prints in bulk.

an animation of the screen printing process at the psylo graphics shop

 

THE BENEFITS OF SCREEN PRINTING:

 

  • Better pricing and faster than digital, heat transfer or sublimation on medium and long runs. 
  • It’s easy and cost effective to print large quantities so the more you print the less expensive it becomes.
  • You can adapt to your budget. Screen printing offers the flexibility of choosing different options that will reduce cost and still achieve great results.
  • It can be applied to a wide range of surfaces and materials. 
  • More vibrant and vivid colors for your designs.
  • The inks used in screen printing are more durable and better quality. 
  • You have the option of choosing different types of inks for different materials, finish and look.
  • You can match any Pantone color.
  • You can explore different options by manipulating the screen printing process and achieve custom results.
  • You can do it yourself. With the right materials and tools, screen printing can be done easily at home.

 

THE PROCESS

 

Technically speaking the serigraphy process consists of ink being transferred through the openings of a mesh onto a substrate. The ink passes through the apertures of the mesh except in areas made impermeable to the ink by a blocking cured emulsion. These apertures are defined by the shape of the design to print. A squeegee is moved across the mesh while applying pressure to fill the open mesh openings with ink. This causes the ink to wet the receiving surface after the squeegee has passed. One color is printed at a time so several screens are needed to create a full color design. Screens must be registered or lined up so all the colors are printed in the exact same position and match the original design. Once all the colors have been printed the inks need to be cured. Different materials and inks require different methods. Some inks are air dried and some need to be exposed to UV lights or high temperatures to be cured and adhere properly to the container.

Below we’ll explain in detail the whole process required to achieve the perfect screen printed product in this 15 steps…

 

SELECT YOUR BLANK OR SUBSTRATE:

samples of blanks to be used for screen printing

The first thing we need to decide is on what are we going to print. Different materials, inks, size and placements will require different types of screen, mesh and emulsion. So we need to define what is the product we want to decorate and make sure we use the right tools prior to production and get the best results without complications.

If we want to print on a shirt for example we need to define: 

1. Style: Tanks, hoodies or tees have very different sizes, cuts, shapes and materials which will give you more decoration possibilities or limitations that need to be taken into account.

2. Color: Dark colored shirts with light colored prints will require an undercoat of white plastisol ink or the use of discharge inks.

3. Material: Different fabric materials like cotton, polyester or rayon can or cannot be treated with certain inks which will define the mesh count, the emulsion and the inks to use.

4. Placement, shape and size of the print: Different sizes, shapes and placements like the chest, a sleeve or the inside of the neck  of the shirt will require different screens and pallets and the position of the graphic on the screen will change. If the prints are small you can burn several graphics in the same screen and tape over the graphics you are not printing. The more decoration placements on your product the more time it has to go under the press requiring more time and materials. 

5. Quantities: Defining quantities will help determine the amount of ink needed and the time and energy to complete the full run.

 

It is mandatory to create a virtual mock up of your finalized product with all the specifications about your blank and decorations details and placements prior to production. If you can’t or don’t know how to do this Psylo Graphics can help you create one for you at no charge with your screen printing order.

 

ART PREPARATION

a sample of color separation, a step of the screen printing process

1.  Convert to a digital format: If your art is in a physical form only we need to scan it or take a high quality picture of it so we can manipulate it with software. Make sure that your image is scanned at a minimum resolution of 300 DPI at the actual size that wants to be printed or bigger. You can also get great results with a high definition camera with plenty of light and a tripod. Your files can be saved and provided as JPG, PNG, PDF, TIFF or AI. 

2.  Size, Resolution and Adjustments: Before making adjustments and separating colors the art must be 100% sized and at 300 DPI resolution. Increasing the DPI resolution of a low res image won’t improve the quality of your image. Most of the images you find online are low res and not optimal for printing. Make sure that your graphics look crisp and clean even when you zoom in at the actual print size or closer. For better results the design must be high-contrast and the edges shouldn’t be pixelated. If you can’t or don’t know how to do this Psylo Graphics can help you make your graphics look sharp and ready for high quality screen printing.

3.  Color Separation: One separate sheet of film and one screen for each color ink is needed for your product. So we need to separate all the colors of your design and output them as 100% black for proper burning of the graphic on the screen. Grays and gradients are acquired by using halftone dots that mixed with the color of the substrate or other inks create new tones and colors. There are different color separation techniques depending of the art and final look desired. The most common ones are spot color, halftone, 4 color process and index color separation. Psylo Graphics offers free color separations with every order.

 

PRINT FILMS POSITIVES

Film positives are reusable transparent sheets the designs are printed onto using an inkjet printer. The design needs to be as dark as possible, so that it blocks light from the exposure unit to the areas behind the design. Crosshairs or targets to the corners of multiple color designs are added so that we can align the screens properly and have proper registrationIt’s also important to include the name of the color with the targets so you can label each screen easily. After the screens are burned and registered we can block the targets and color information with tape or emulsion so they don’t become part of the print. With certain rips and apps we can also control the patterns, size, angle and shape of the dots that will create the halftones and gradients of the design. This is used to create different looks or to optimize the image for the screen mesh count and or ink to be used. After the image present on the film positive is transferred to the screen we can store the films and use them again and again for future runs.

 

CHOOSE YOUR INK

samples of buckets of ink used in the screen printing process

Before we can get our screens ready we need to know what type of ink we want to use for our project. There’s a vast range of ink options and they have different densities and formulas that will determine the mesh count of the screen to use and also the type of emulsion to coat the screen with. For example a metallic or glittery ink is very dense and contains big particles or flakes to create the desired shimmery effect, therefor we need to use a low mesh count so the particles can pass through the openings of the mesh easily. A finely threaded mesh will block some or most of this metallic ink and the print will look faded. The most common inks used for textiles are plastisol, water base and discharge. For paper, stickers and signs there’s acrylic, vinyl and enamel. There’s also a lot of specialty inks that create all kinds of effects and textures like glow in the dark inks, gel, reflective, puff, high density, suede, sparkle, etc. To learn more about screen printing inks and choose the right one for your project please go here

 

SELECT YOUR SCREEN AND EMULSION

samples of screens and emulsions used in the screen printing process

Screens are basically stencils made of finely threaded mesh stretched out and attached to a metal or wooden frame. Synthetic threads are commonly used in the making of mesh for screen printing and polyester is the most popular material. There are also different types of mesh size which will determine the outcome and look of the finished design on the material. The higher the mesh count of the screen, then the higher amount of detail that it can hold, given that it is burned properly.

Before we coat the screen we want to use for our project we need to consider:

Size: The screen needs to be considerably bigger than the graphic to print. You want to have a minimum margin of 4 inches all around your graphic to have comfortable room for the ink, squeegee and flow bar. Screen frames can be custom made at any size, common sizes are 18″x20″, 20″x24″, and 24″x31″, but there are companies willing to make screens to any size needed. It’s recommended to use the same size screen for all the colors in the same set up for easier registration. 

Mesh Count: Mesh count is determined by how many threads of mesh are crossing per square inch. The higher the mesh count, the finer the threads and holes are in the screen. The most standard mesh sizes are 110 & 156 but in any professional screen shop you’ll find screens with mesh counts from 86 to 355. Lower mesh count screens are used for thicker inks like metallic gold, silver, white, etc, as one wants to avoid clogging and lay down more of these inks since they are often printed on dark apparel. Higher mesh count screens are better for process printing, index separations and detailed prints with tiny halftones. A higher mesh also helps prevent bleeding problems with thinner inks.

Emulsion: Emulsion is a photosensitive liquid which has the consistency of honey and that is ‘scooped’ across the mesh and left to dry for about a day in the dark. This results in a thin coat of gel over the screen that once it’s exposed to light it hardens in the exposed areas but leaves the unexposed parts soft and easy to wash off creating the stencil for the design. Different types of emulsions are required for different inks and they have different exposure ranges and exposure times. 

 

COAT SCREENS WITH EMULSION

a 2d animation of the coating step of the screen printing process

Once we’ve decided what ink, screen, mesh count and emulsion we want to use for our project, we’re ready to coat our screens. Emulsion is applied on both sides of the screen using a scoop coater, the result should be a thin, evenly spread layer of emulsion. After the screen is coated it needs to be kept in darkness in a dark or red lit room just like developing photographs, as any light could start exposing the screen. All moisture needs to be removed from the emulsion. A fan, heater or a dehumidifier can be used to speed up the process. 

 

“BURN” THE GRAPHIC ON THE SCREEN

an image of a graphic being "burned" into a screen for the screen printing process

Placement: The film positive is now placed and taped on top of emulsion-covered screen according to the print placement on your product, the press and the support pallet that you will be using for your run. The idea is to do most of the registration work before aligning the screens on the press so rulers and guides are used to place the designs on the screen in the most accurate way. If the prints are small and you are NOT using discharge inks you can burn more than one graphic in one screen and tape over the ones you are not printing. 

Exposure: Once the film positives are properly placed on the screen in a dark environment we need to expose them to bright light. At Psylo Graphics we use a professional high wattage metal halide bulb exposure unit to achieve the best results and get most of the graphic details but you can use any source of UV light, bulbs designed for growing plants or even the sun. The time of exposure changes depending of the emulsion and the intensity of the light is exposed to. It can range from 1 minute to 45 minutes. 

 

WASH OFF UNEXPOSED EMULSION AND DRY

a water hose spraying water to wash off the emulsion for the screen printing process

Immediately after the exposure time is complete, the film positive is removed carefully and the screen is washed with a low pressure shower or water spray. The emulsion areas that were NOT exposed to light thanks to the blocking black design present in the film positives will be still soft and wash off easily resulting in a proper stencil in the mesh making the areas permeable to ink. The emulsion areas that were exposed to the light will harden into the screen and make it impermeable to the ink. After the soft emulsion has been completely washed off and the negative image that comes out on the screen matches whats present on the film positive we leave the screens out in the sun for a few minutes to dry off and harden the remaining emulsion even more. 

 

PREPARE INK

samples of ink during the ink preparation step of the screen printing process

While the screens are drying in the sun we can start preparing the ink. At this point we should have already decided about the type of ink and color we want to use. Amount of ink is calculated based on the size of the screen, the size and shape of the design and the quantity of items and amount of hits to print. You want to have enough ink to keep the screen flooded but you don’t want to have too much left over specially if you are using discharge inks because they can not be stored. For very large orders that require lots of ink it’s best to prepare the ink in batches for easier handling and better control of the mix and texture. Ink must be very well mixed, soft, chunk free and at the right temperature so it goes through the mesh smoothly without clogging. Colors are mixed to match what we see on the digital version of the design, a printout or a Pantone color number if requested. Ink colors can change slightly after being applied to the substrate and cured so you want to make sure that you do a few tests on the actual product you are printing before you’ re done mixing the ink and start with production.

 

SET UP SCREENS FOR PRINTING

screens for screen printing being set up

Tape edges and other unwanted apertures: Once the screens are completely moisture free, we tape the edges with a glue residue free tape (like painter’s tape) to reinforce the border between the emulsion and the frame of the screen. All areas of the screen must be completely impermeable to the ink except the stencil area with the design to print. Targets, color labels and other small unwanted apertures in the screens can be blocked with more emulsion or tape. 

Press Set Up: There are a number of different presses, including manual and automatic styles. At Psylo Graphics we use automatic rotary 10 color carousel presses, as this allows several different screens to work at once. For multi-colored prints, this sort of printer can also be used to apply the separate color layers in quick succession. Print ready screens are now clamped on to the press in order following the right sequence for your print. Flashed under-bases (if needed) are printed first, then light colors and dark colors at the end of the sequence. Different sequences can alter the final look of the print and we can play with the order in which the colors are printed to achieve the desired results.

Registration: After the screens are set up in the right sequence and position we need to micro-register the colors using the crosshair targets as a guide and position all the screens in the exact location where all the targets fall on the same place and the colors of the design don’t overlap each other at all. Each color lines up perfect with the next so you end up with one cohesive, flawless design. Several tests on recycled paper or rags might be needed to have the colors perfectly registered and match the original art. Once all the colors are properly registered we are ready to start printing.

 

SELECT SQUEEGEE

squeegees used in the screen printing process

A squeegee is a half inch thick rubber blade attached to a metal, plastic or wooden handle. It’s used to pull the ink across the screen and lay down the paint by pushing the ink through the mesh. They come in many sizes and the stiffness and sharpness of the blade affect the print considerably. One must choose the right length and density to achieve the best results…

Size: The length of the squeegee to be used should be a couple of inches smaller tan the mesh screen or about 4 inches wider than the graphic to print, as this will give better coverage.

Hardness: Screen printing squeegees come in a few different “durometers” (a metric used for hardness) based on the ink type and mesh count of the screen. The color of the rubber usually defines the density and hardness for the screen. Red and orange squeegees are usually softer, yellow ones are in the middle of the spectrum and then green and blue are the hardest. A stiffer and sharper squeegee lays down less ink than a softer rounded squeegee. A softer, more yielding rubber squeegee is often used when printing less detailed designs or when printing onto fabric. A firmer rubber blade is better for printing intricate designs with lots of detail as it ensures all the nooks and crannies in the stencil receive an even layer of ink. 

 

PREPARE PALLET OR SUPPORTING SURFACE

various pallets used in the screen printing process

The surface supporting the substrate to be printed is commonly referred to as a pallet and also needs to be prepared before production. It needs to be clean and marked for proper alignment and registration…

Coating: Pallets should be coated with a wide ‘pallet tape’. This serves to protect the ‘pallet’ from any unwanted ink leaking through the screen and potentially staining the ‘pallet’ or transferring unwanted ink onto the next substrate.

Glue or Vacuum: The substrate to print should adhere momentarily to the surface so it stays still and in place during the printing of all colors. This is very important specially for  For fabrics a special light transparent glue is applied to the pallet that makes them stick to the surface without leaving residue. A coat of glue should last for several blanks. For paper you can use a light coat of spray glue or some presses come with a vacuum system that sucks the paper against the surface and makes it stay put.

Marks Or Wedges: In order to print your art consistently on the same exact location you want to add marks or wedges to the surface supporting the substrate to be printed. These marks will help you load your blanks correctly every time onto the pallet. You can use laser guides, pencil or tape. 

This last action concludes what in the screen printing industry is referred as the “Set Up”, the process which includes all the steps involved in color separationfilm printsscreen shootingink mix and registration. When this entire process is done each product is printed from the same screen set whether it’s a quantity of one or one thousand. Again, once the set up is complete, it’s easy to print large quantities. So, the more you print, the less expensive it becomes. And, unfortunately, the set up for screen printing is too time-consuming and simply not at all cost effective for small jobs – like one t-shirt or just a few signs. In some instances, you’d pay more for the setup fee than for your order. 

 

START PRINTING

animation of a squeegee during the screen printing process

Now that every step of preparation and the press set up has been completed we are ready with production…

Pour Inks: Pour enough ink into the screen to flood the whole printing area and have enough ink for a whole batch of prints. It’s more convenient to add extra ink and have some left over than risking not having enough ink for a whole batch and damaging some of the prints with poor coverage. Also keeping your screens flooded and wet avoids the ink getting dry and clogging the mesh. 

Load Blank: Load your blanks onto the pallet or place on the supporting surface carefully making sure it’s aligned with your marks and that it stays put.

Print: Once the screens and blanks are aligned, the screen is lowered down onto the printing board leaving a small off contact around 1/8th of an inch of space in between the mesh and the blank. The squeegee is then pulled over the full length of the stencil with adequate pressure at a 70 degree angle. This presses the ink through the open areas of the stencil, imprinting the design on the product underneath. The amount of squeegee pressure will affect the results and it will change depending on the mesh, the ink, the substrate and the results you are looking for. The screen is then lift back up and we can see the print. In the case of multi-colored items, the colors must be applied in individual layers, using separate stencils for each ink. The printed item is removed from the pallet or board for curing and the process is repeated for the whole batch of blanks to be printed.

 

CURING

a series of curing machinery, used in the screen printing process

Some inks like enamel or vinyl are dried and cured by air but garments printed with plastisol, water base or discharge inks are run through a large dryer at a specific temperature. This bakes the print onto the item which results in a colour fast product. Carefully remove your product from the platen and set to dry or heat cure. If you’re using plastisol ink it will take about 30 seconds at around 320 degrees Fahrenheit, but follow the instructions provided on your ink bottles. Once dry your custom printed shirts are ready to be worn!

 

FINISHING

samples of the products finished after undergoing the screen printing process

After your items are cured they’re ready to be grouped and stored. Apparel is grouped in dozens by sizes, colors, styles and printed designs. If you want to have them ready for retail sales we can fold and bag them for you. We can also sew woven labels, patches or decorate with embroidery. Size stickers or labels can be added to your product as well as hang tags or any other type of information or promotional stationary. To learn more about about this extra services that we can provide please go here.

When production is over we need to clean up our squeegees and screens, collect any left over ink and get the press ready for the next batch. Screens can be cleaned and stored for future use with the same graphic or if we want to burn a new graphic we need to remove the cured emulsion with special chemicals and repeat the same process over and over using the same frame and mesh for a very long time.