COATING OF NEON TUBES
There are two methods for coating neon tubes;
- Dust coating (dry method)
- Suspension coating (wet method)
Below you will find more information about above two methods.
The application of phosphor powder, according to the Philips suspension method.
- After bending the tubes, the tubes have to be rinsed with a mixture of water and fluorine
- The tubes have to be well dried before applying the phosphor
- The suspension consists of 2/3Ltr thinner, 1/3 liters of binder and 600 gr. phosphor powder
- The bottles with the suspension are mixed at least 24 hours on a bullet blender/ mill
- Afterwards, one side of the tube is closed with a cork, at the other side of the tube suspension is poured in, enough to cover the whole inside of the tube
- While shaking the suspension through the tube, you will get a thin layer of suspension on the inside of the tube, excess suspension is poured back into the bottle
- Now the tube have to be dried with a hairfohn until the layer is dry
- First, one soak a sponge with binder B1 or put glass beads (pearls) in the Binder B1
- Secondly, then one let the sponge go through the inside of the tube using air pressure or shake the moisture glass pearls through the inside of the tube, so that the inside of the tube is fully covered with binder B1. Note: air pressure is not needed when using glass pearls.
- After finishing above step, one put phosphor in the tube and shake the phosphor through the tube till the inside is fully covered with the phosphor powder.
- When the inside of the tube is fully covered with phosphor powder, the tube have to dry and will be ready to processed.
- First, a check should be considered to see if the suspension layer is not too thick or too thin
- The thicker layer on the bottom of the tube may not be wider than about 1/ 8 of the circumference of the tube
- The tubes are placed in an oven at a temperature of about 450 ºC
- The oven should be fitted with a vent that allows thinner and binder to be evaporated
- The tubes remain about 10 minutes at 450 ºC in the oven, than the oven is cooled off
- As a result of the evaporation of the thinner of the suspension, every 3 to 8 tubes about 30CC thinner has to be added
- Coating of the tubes will be done after bending the tubes
- For the wet method an oven is needed, therefore, the dry method is more cost economical
- For both methods different binders must be used.
– For dustcoating – Binder B1
– For suspension coating – Binder B23
Thinner is only needed when applying the Suspenion Method
- A thin layer at the back of the tube
In this case, the suspension has too much dilution and binder should be added.
leave the bottle of suspension about 24 hours, remove a part of the liquid and add the same part of binder.
- A thick layer at the back of the tube
This means that the suspension is too thick, dilute with a mixture of binder: thinner = 1: 2 .
- A thick layer in the tube
Now there is too much binder in the suspension and thinner should be added.
- A thin layer in the tube
There’s too little phosphor powder in the suspension.
Leave the bottle with a suspension for some time, so that the powder drops to the bottom of the bottle.
Now, a part of the mixture of binder and thinner should be drained.
Note: the above is a theoretical approach, a lot depends on experience.