Beginners guide to screen-printing for T-shirts...

Beginners guide to screen-printing for T-shirts...

Screen printing has been around for half a century and will probably last another half-century unless digital printing takes a leap forward and can do some of the things that currently can only be achieved with screens.

If you are just starting out, deciding on the correct process for your brand or project, it is useful for you to know what the process is and what it can do.

Here is a quick run-down which is actually not that quick because this is quite complicated when you break it down.

1 What is a screen?

It is very simple and consists of 2 parts. Usually an aluminium frame which comes in various sizes with a tensioned mesh insert, glued to each edge to create a 'drum tight' object that looks like a picture frame with no picture.

The frame sizes are often 2 inches thick and then usually 21 x 24 inches in overall size but they can be bigger or smaller.

The mesh is a variable and the choice of mesh used depends on the print objective. An example of a simple objective would be 'do I need a heavy deposit or a light deposit of ink?'.

The correct choice of mesh would determine the outcome for heavy or light deposit. A courser mesh gets more ink down and finer mesh gets less ink down and can produce better detail.

The mesh is pulled extremely tight into the frame before it is glued into position and this tension relaxes as a screen ages and this means they need to be replaced periodically.

Aluminium frames with tensioned fabric

2 How is my design put onto a screen?

Before your image can be 'burned' onto a screen, the screen needs to be coated in a material that can take on the shape of your design. This is usually done using a liquid emulsion that is applied as a thin coat to the mesh and allowed to dry in a specially controlled environment, usually a heat cupboard.

Once the emulsion is dried, it can be placed on a light box to burn your design onto the screen.

This involves using a thin, clear plastic sheet with your artwork printed on from an image-setter or desktop printer. This is called an acetate or a 'separation'.

The artwork is then placed on the top glass section of a special lightbox, the screen is placed over the artwork and the whole unit is closed and vacuum sealed and then the screen with emulsion is exposed to an ultra violet light source for a set period of time, usually a few minutes so that the emulsion can react chemically with the UV light to become hardened and non-water soluable where the light has been able to hit the screen. The artwork that is placed between the screen and the light box blocks the light to the emulsion and this area can be washed out using a pressure hose.

Each colour in your design requires this process and when it is completed you have a number of screens that then need to be placed into a screen printing carousel in the right order to achieve the desired outcome.This this is called 'setting up' and is where the skill and experience of the screen-printer comes into play as a different setup configuration can result in a different outcome and can even result in a total failure if it is done incorrectly. 

3 What is setting up?

A print carousel is a circular construction of steel and aluminium and plastic.

There are numerous manufacturers of this equipment to suit all budgets. Some have features that make the job of setting up easier but these features come at an extra cost.

It takes about 5 minutes on average to set up each colour. This includes putting in ink and squeegees. Therefore it can take 50 minutes to an hour to set up a 10 colour job. Lot's of things can upset that average though.

There are automated carousels and manual carousels.

An automated carousel can print up to 600 shirts an hour while a manual machine can do approx 120 shirts an hour depending on the skill of the operator and the type of job.

There are reasons why you would choose a manual over automatic.

The basic concept is that each of your screens gets slotted into the carousel in the correct order so that each one is printed sequentially onto the surface of the t-shirt.

Once slotted into position, the screens must be 'registered' to a template so that they all print in the right area of the shirt.

Each colour needs to fit together like a jigsaw puzzle so that the culmination of printing each colour separately results in a finished image of composite colours unifying to make a single design.

Completing the 'setup' process also involves the fitting of squeegees into the print head of the carousel and also putting ink in the screen.

Setting up a 10 colour automatic screen print machine.

4 What is ink?

Ink is a liquid carrier of colour.

They can be made of an oil based plasticiser or can be water based.

Most t shirt printers prefer to use the oil based products because they are easier to work with which makes it quicker and less stressful to setup and run the job.

Water based inks tend to dry out in the screen during the print process and this is a problem for printers. Fine halftones (very small detail) are difficult to achieve and Pantone colour matches ( industry specific colour matching) are almost impossible on dark shirts.

Oil based products are considered less favourable to your 'ethical' buyer but recent accreditations by the Soil Association and by the Global Organic Textile Standard for a plastisol ink called PIONEER now make them a possibility if you have an environmentally aware buying agenda.

They have had a number of chemical components removed to satisfy an audit and stamp of approval by these two leading environmental auditors.

Other than the differences in environmental impact between the two ink systems, there are look and feel differences too.

Water based inks have a softer feel but lack the vibrancy and longevity of plastisols.

Once an ink is laid onto the shirt it needs to be 'cured'.

Both ink systems require a long tunnel dryer which subjects the garment and ink to a controlled heat at a controlled amount of time. Usually 160 degrees celsius for about 2 minutes.

Screen printing inks are often matched to Pantone colours

5 How does the ink get onto the garment?

The screen is basically like a stencil. That thing you made at school and then placed over a piece of paper then painted over it then removed it and saw that it left the shape of your stencil/design.

The ink is squeezed or rather 'sheered' through the stencil by pushing it through with a piece of specially constructed rubber called a squeegee, which has a sharp right angle edge to it to force the ink through the stencil aperture in a controlled manner. This 'sheering' is called a squeegee stroke.

The 'stroke' can be repeated two or three times to increase ink coverage. Sometimes the ink is partially cured on the garment while it is 'in place' on the carousel so that the next stroke puts ink down onto a more stable surface resulting in a brighter/thicker deposit.

The squeegee drag, pushing ink through the screen

6 Why do I want screen printing instead of digital or vinyl or transfer?

There are a few reasons why screen printing is going to be better for your project.

1 It is still the most economically sensible process for large print runs. If you read the guff above you will remember that an automatic print carousel can print 600 shirts an hour. This means they are cheaper to produce and therefore you will pay less per unit.

Screen printers like big print runs because once it's set up it is easy money and a whole day of printing a single order is better for them than setting up and taking down multiple jobs in a day which causes 'downtime'. Printing vinyl is slow and costly and so is transfers. Digital printing can only really achieve 150 an hour at best at the moment although this is improving each year.

2 It still gives the best finish for dark inks on light shirts, especially for white ink. Some of the really high-end digital machines like the Kornit are catching up and can produce bright deposits of ink but they still do not quite match the look and feel that a good screen print can achieve with smoothness and vibrancy.

3 There is much better colour control with screen printing.Inks are mixed by hand using formulas, weights and measures. Digital transfer and vinyl printing still cannot match the accuracy for Pantone matching and digital is still a few years off from being able to compete.

7 Conclusion

Even though you are now armed with the basics you may still need some advice.

There are plenty of projects where even the most experienced account manager at a print workshop will dither and ping pong from one process to the other when working out what might be the best process at that time for that project.

This is because there are variables and sometimes it is not just t shirts that are being printed,it can be sweats and hoodies and joggers and sportswear etc... this can cause some head scratching.

Talk to your account manager, they will get you to where you need to go.

Author:Arron Harnden

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Comments 1

Guest - Pratik Shah on Saturday, 13 April 2019 11:33
Nice blog Thank you sharing with us

Thank you for sharing this blog.

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