In this article we run through the things you'll need to have and know for successful halftone photomasks. For your convienience we have created open in new window hyperlinks throughout the article so that you can go to the resourse being discussed.
We also offer a halftone mask production service for those not wanting to go through the mask making process and just want the pre-mask mask ready to blast.
Equipment
Artwork
First of all you will either need graphics software to create half tone images. The most common software is Adobe Photo Shop or CorelDraw. There are other options which you'll find online.
Mask Processing and Application
Next you will need exquipment to Expose and Wash Out you mask. An Inkjet Printer and Inkjet film to print your artwork film for exposure.
To make the mask you will need a UV Exposure system , washout hose , washout board and warm water. There are other items such as Wire wheel and burnishing tool that we recomend and we also suggest you consider the Start Up Kit which provides you with everything you need including some SR3000 - 3mil Resist that will be used to make the masks.
Sandblasting
We recomend using a fine grade Aluiminium Oxide such as 150 Grit. Any sandblasting machine can do the job but a pressure pot blaster is best. Vacuum blasters can work but you run the risk of lifting the mask as the brushes run over the surface.
Process
Create the Artwork
Creating the half tone image corectly is the most important part of the process. You need to consider removing the background, what colour surface the etching is going on. dark coloured stone requires (burcs help)
For full instructions on creating a half tone downlod our Half Tone Production Guide here
Producing the Photo Mask.
- Make sure your artwork is printed on quality inkjet film and is black and clear only.
- During the development process do not allow exteranl UV light to make contact with the SR3000 mask.
- The light must travel through the inkjet film onto the SR3000 Mask
- Exposure time is critical. Always use the recomended settings. Too much or too little exposure will ruin the mask.
- You must use warm water (shower temperature) to wash the mask out
- We strongly recomend that you use our proven washout hose and washout board for the wash out process for the best results.
- An A4 halftone mask should take about 3 minutes to wash out. Keep the spray nozzle about 15cm away from the resist and spray evenly over the surface.
Applying the Mask to Substrate
It is very important to have a clean surface as you are sticking thousands of small dots onto the stone, glass etc.
When placing PhotoMask onto substrate make sure you are happy with the position before applying pressure. It is re-positionable as long you have not applies much pressure. Once you are happy with the positioning then apply light pressure to secure the position.
Use the a Burnisher to press the PhotoMask down onto the surface. Apply plenty of pressure and push any air bubbles out as much as possible. Then remove the clear plastic cover sheet.
Use the wire wheel and cut the membrane to let any air escape. Now check over the mask and press down on it to push the mask down onto the substrate surface. It is critical to get the mask fimly adhered to the surface. When pressing do not turn you hand or finget pad in a squishing motion. Just press straight down. Check over the mask to make sure it is secured everywhere against the surface. mask up any edges that may get blasted by mistake.
Blasting
We recomend a fine grit like 150 grit aluminium oxide. We also recomend a blast pressure of around 30psi. Keep the nozzle about 10cm away from the stone surface.
It is very important to direct the blast nozzle perpendicular (90o to the surface) while blasting. If you blast at an angle you are likely to lift some resist and the job will be ruined. So stay perpendicular and about 10cm away with the blasting nozzle
Blast in a nice even flowing motion from one side to the other working your way down the area. Do a few passes and try different flow angles to get every part of the etching area. DO NOT go very deep as you will a) distort the engraving and b) risk blow outs.
Clean Up
If you are going to paint fill the etching leave the mask on and blow dust off them spray the image with 3 light coates of paint. Leave to dry and then peel off the resist.
Conclusion
Halftone etching is not hard as long as you follow these simple rules. You can pourchase the Start Up Kit that gives you everything you need to get the job done. Alternatively, if you don't want to go through the mask producing process then ProBlast can make the masks for you.
Half tone etching looks fantastic and is a premium product that customers will pay handsomly for.