News & Events
Haze removers and how to use them
David Parker, Marketing Manager at MacDermid Autotype takes a further look at screen stains and how to deal with them.
We are all aware that using dirty, stained screens can lead to low quality prints and expensive stencil breakdown. We are also aware of the wide range of stains that can be created due to the variety of inks, emulsions and stencils used in screen printing. So how do you select the right cleaning product for the stain removal task in hand?
As discussed in the previous issue, screen stains can be caused by a number of factors; such as dried-in inks, fused (locked-in) stencils and/or Diazo stains. It is therefore, important to choose a haze remover that is right for these stains and for the way your shop works. This guide answers many commonly asked questions about which type of haze remover to use and how to use it.
Firstly though, a word of caution. Haze removers are formulated using powerful chemical blends, so always read the Safety Data Sheet before use and make sure you wear the Personal Protective Equipment (PPE) that is recommended.
Can I prevent my ink from staining?
Most inks can be removed completely without staining the mesh, but only if they are cleaned immediately after printing with a good quality screen wash solvent.
Screen wash cleaning solvents are specially formulated to combine high cleaning power with a low evaporation rate, so they work efficiently and stay longer on the screen. We recommend using the special screen cleaning brushes to apply screen wash solvents. These brushes have soft, chemically resistant fibres with flagged ends that help hold the solvent without dripping and they will not damage even the finest mesh fibres.
How to use screen wash cleaning solvents
Brush the screen wash thoroughly into both sides of the screen until all the ink is dissolved and then immediately rinse with cold water before using a High Pressure Gun. It is important to rinse off all traces of the cleaning chemicals before you use the High Pressure Gun.
How can I remove difficult ink stains?
Some inks simply stain the mesh fibres worse than others, or they have been left to dry into the mesh. So when you need a bit more cleaning power than a screen washalone, you can use a special solvent/low caustic cleaner. The powerful solvent blend in this type of cleaner is combined with a low caustic content (<5%) to increase its cleaning efficiency.
How to use solvent/low caustic cleaners
Use the brush to work the cleaner into both sides of the screen, ensuring that all the stain is covered, wait five minutes and then rinse with cold water before using a High Pressure Gun.
What is the best way to remove everyday ink & stencil stains?
A low caustic/hypochlorite, general purpose haze remover is the ideal product for everyday use. These thickened liquids are a blend of low caustic (<10%) and hypochlorite that are ‘activated’ on the screen with a special screen wash solvent immediately before rinsing. They work exceptionally well on Diazo and fused stencil stains and the application of the screen wash helps to remove dried-in ink stains, making them ideal as a general purpose cleaner for regular use.
How to use low caustic/hypochlorite cleaners
They are typically supplied as a thickened liquid so you can apply them to the screen with a brush. Or, for ease of use on larger screens, an old coating trough works really well as long as you rinse it out after use and don’t expect to use it for coating emulsion again!
For optimum results it is best to allow the screen to dry overnight and then ‘activate’ it the following morning with a suitable screen wash solvent, rinse well with cold water and then finish off with a High Pressure Gun. This method is ideal if you have a number of screens that need to be de-hazed at one time.
For quicker haze removal of light stains, the coated screen can be ‘force dried’ with a cold (NOT HOT) air fan and then ‘activated’ with a screen wash immediately before rinsing off and then blasting with the gun.
Finally, for very light stains, you can use the five minute method where you apply the haze remover to the mesh, followed immediately by the activator and you then mix the two on the screen with the brush. Wait five minutes before rinsing and then blasting. These low caustic/hypochlorite cleaners are probably the most versatile of the haze removers and therefore one of the most popular.
What about removing the more stubborn ink & stencil stains?
When multiple stains have been left to build up on the mesh, or you are using a ‘difficult’ ink, then it is best to select a medium caustic/powerful solvent haze remover (20% to 25% caustic). These are highly effective against most common screen stains and screens can even look ‘like new again’ in under ten minutes. These haze removers can also be ‘activated’ with a screen wash immediately before rinsing to help remove heavy ink stains.
How to use a medium caustic/solvent haze remover
Usually they are supplied as a thickened liquid making brushing onto the screen much easier than a conventional paste. Use the brush, or an old coating trough to apply the haze remover to both sides of the dry mesh.
Leave on the screen for up to ten minutes and then rinse off with a low pressure water spray. Finally blast the entire screen with a High Pressure Gun.
How to remove the very difficult ink & stencil stains
Occasionally you get a screen that you just can’t get clean with conventional haze removers and it is time to wheel out the big guns. There are some very strong caustic and solvent haze remover pastes (>25% caustic) that are designed for occasional use on these very stubborn stains. Basically when nothing else works, that is the time to try these high caustic/solvent blend haze removers.
How to use high caustic/solvent haze remover pastes
It is usually most effective to apply these to a wet mesh using a brush as they are too thick to apply with a trough. Let them stand for an absolute maximum of eight minutes before rinsing off with a cold water spray, then use a High Pressure Gun. This type of haze remover should only be used occasionally, as repeated application of a very strong caustic to polyester can weaken the mesh.
Important: As stated earlier, always read the Safety Data Sheet and wear the recommended PPE safety equipment when using any haze remover.
Summary: Selecting which haze remover to use is a lot like choosing which kitchen cleaner to buy, it all depends on what you are trying to clean.
For example, you would use a mild detergent cleaner for work tops, but you know that you will need a strong caustic cleaner for the oven. Some stains are simply harder to remove than others. The same is true for screen printing.
Having a range of haze removers in your shop will ensure that you maximise the overall cleaning efficiency, whilst minimising the potential for mesh damage or operator risk.
Quite simply, choosing the right product for each job can save you time, money and quite a bit of frustration!
Finally, the costs of mesh re-stretching are often a significant proportion of screen making costs. Using the right haze remover to prolong screen life and to minimise quality issues can be one of the most cost effective decisions you can make.
For more information on the MacDermid Autotype range of Haze Removers click hereBack to News & Events