What is a Moisture Meter?
A moisture meter is used to measure the residual water content of the emulsion before exposure.

When the emulsion is dried the water content ideally must fall below 4% and be no higher that 6%. If the water content is higher than 6% the emulsion will not cure properly during exposure.

We need water to reclaim mesh, degrease the mesh and develop the image. However, we do not want it in the emulsion just before it is exposed. A “dried” emulsion that still contains high moisture content will not react fully to the Ultra Violet light used for exposure. This shows itself by the photopositive sticking to the emulsion when you try to remove it or the emulsion sticking to the glass. When you come to wash out the image some of the emulsion outside the image area will wash away. When you come to print with the stencil, it will break down, because it is soft. Additionally there are likely to be excessive pinholes. The sensitiser reacting with the water content and not the emulsion causes all this. Incomplete curing is even more pronounced when you are using fast reacting emulsions of the type that are used in direct projection.

When do we use it?
The moisture meter is used to measure the water content of the emulsion before exposure of the stencil.

Firstly, check the moisture content of the dried emulsion. You can do this with the contact moisture meter. This is not expensive and very easy to use. The reading should be less than 4%. Anything above 6% will mean that it will be impossible to cure the emulsion fully no matter how long you expose it. If it is below 4%, you will obtain a robust stencil that will perform very well.

If it is above the 4 – 6% range providing your drying oven is adequate the stencil can be placed back in the oven and dried until the moisture content is correct.

If you cannot get the moisture content below 6%, you probably have a serious fault in your process. The possible causes are:-

• A drying regime that does not take the relative humidity of the environment low enough.
• Excessive levels of humidity in the shop through water sprays used in reclamation, degreasing and development.
• The weather.

You will need to isolate these processes from drying and exposure. If you are in a high humidity region, the use of dehumidifiers is necessary. You may think 4% moisture content is low but if you do not maintain it, you will compromise your stencil quality with the resulting losses in production.

Advantages
High quality reliable stencils:

Supplier
PDS Consulting
Innovation Way
Barnsley
South Yorkshire
S75 3RQ
Telephone: 01226 249590
Facsimile: 01226 294797

Email: info@pdsconsulting.co.uk
Website: www.pdsconsulting.co.uk

Contact: Peter Kiddell or Carol Swift

Cost
£499.00 +VAT
Carriage extra
Delivery 4 weeks

Contact PDS Consulting for information on test and measurement equipment you should have in your stencil and screen print shop.