Stencil Application

Contenu réductible

Why is it better to do a perpendicular stretch than a bias/angled stretch (on mesh)?

Mesh is stronger and can achieve a more stable tension when stretched perpendicular to the frame. The better aligned the threads are to the frame, the more stable the mesh will be. Stretching on an angle isn’t necessarily bad but it requires a lower tension stretch to avoid screen breakage.

Before RIP programs, screen mesh was stretched to an angle like 22º or 61º to eliminate moiré. Today, we adjust these angles with the artwork positives.

How important is screen abrading and screen degreasing?

It is important to abrade a new screen mesh to help the stencil to adhere well.

You must use Screen Degreaser to remove screen grease or debris prior to emulsion coating. Screen degreasing helps stencil to adhere well and support the tonal design.

It also avoids the occurrence of unnecessary pinholes. Do not use dishwashing soap as it contains lanolin (oil) content.

Abrade with soft brush, degrease with a degreaser.

What is the right method to coat a screen mesh with stencil (emulsion)?

Before coating the stencil, it is advisable to do the following:

1. Ensure that the mesh has a good tension stretch.

2. Ensure that the screen mesh has been properly degreased for better stencil adhesion.

3. De-air the bubbles of the stencil after mixing for at least 2 hours before use.

To apply:

1. In a dark room (with red light/blue light), use a coater that is 1″ – 2″ bigger than your design. Pour in the de-aired stencil. Evenly bring the stencil emulsion to the lip of the coater.

2. The frame should be in a slightly slanted position (for easy maneuvering of the coater), start coating from the bottom to the top by exerting pressure to push the emulsion to coat the mesh.

To scoop out the excess, set the frame to an upright position. Start coating at the substrate side first (i.e. 2x), then twist to coat the squeegee side (i.e. 2x), with the same procedure.

4. For re-coating, repeat the same process. The substrate side is always thicker and should be the last to be coated.

5. Once done, leave to dry in a clean, dark, dust-free area, with low humidity. Drying time will depend on your drying area and thickness of coating as well as the humidity level of the area.

How many coats/pass of stencil (emulsion) should be applied on the screen mesh?

The number of coating for the emulsion will depend on the following:

1. Thread diameter of your screen mesh. Thicker thread diameter means more coating.

2. The mesh opening. Bigger mesh opening means more coating.

3. The thin or thick lip of your emulsion (trough) coater. Thin lip means more coating.

4. Photo emulsion viscosity. Low viscosity means more coating.

Usually, 2 coats/pass per side is good enough but it is best to consider the elements as seen above.

Is the exposure time for water-resist emulsion and solvent-resist emulsion similar?

Photo Flash SRK (solvent-resist) would need a longer exposure time than the Photo Flash 300K (water-resist). On average, you need 2x more of your usual exposure time.

How important is monitoring the exposure time of the stencil (emulsion)?

CORRECT EXPOSURE TIME controls dot size with a correct round pattern & opening.

OVEREXPOSED STENCIL decreases the size of the dots, resulting in less opening area as well as losing of finer details due to light under-cutting. It also causes poor stencil adhesion due to over-hardening.

UNDEREXPOSED STENCIL will not hold up tones/dot image resulting in poor and irregular opening area. It causes premature stencil breakdown (will wash off) with the squeegee side having a softer and low run durability.

Why is the design losing details on the stencil?

To achieve full design details, ensure the following:

1. The artwork must have high density in the film.

2. The mesh is stretched with high tension.

3. The exposure bulb wattage has enough strength for the halftone details.

4. The frame is not warped, as the stencil needs to be in full contact with the art film.

5. The stencil coating is neither too thin nor too thick.

6. The stencil is fully dried before subjecting it to exposure.

7. The exposure time is correct. Overexposed stencil will harden and lead to loss of details, while underexposed stencil will make stencil soft and lead to wash off.

Why is it harder to develop a screen on low mesh count than on a regular mesh count (100-120 mesh)?

* A stencil that is difficult to develop would mean it has exceeded its exposure time.

* A stencil that washes off too easily on the other hand means it lacks exposure time, or that the stencil is not dry enough when subjected to immediate exposure.

Lower mesh counts (60 - 85) would need more coating on its printing and squeegee side, therefore it would require longer drying and exposure time due to the thicker coating.

Exposure time also varies on the mesh diameter and mesh opening (S thread has bigger opening while HD thread size has a smaller opening, despite it having same mesh count).

The mesh tension of your frame, the kind of exposure unit, the wattage, age of bulb, distance, and the design process such as solid or halftones are some factors to be considered as well when developing stencil (emulsion).

Why is the exposed stencil gradually washing off every time it's being cleaned?

Before a production run, it is recommended that the developed stencil be re-exposed as soon as it is wiped dry. Re-exposing your stencil will help to strengthen your stencil.

Why are some halftone details clogged with shiny spots after screen developing?

It is important to properly wipe the mesh dry with a chamois cloth every time the screen is washed. The shiny portions that are blocking the ink from pushing through are called water scum (dried water trapped in the mesh opening).

What will happen if the sensitizer and pigment load is decreased contrary to the recommended percentage load?

* Putting in less sensitizer would mean shorter exposure time.

* Putting too much sensitizer would hardened the stencil, hence it will require longer exposure time. Currently, sensitizer used is of diazo powder or a dual cure.

Adding pigment into the stencil (emulsion) helps distribute light evenly during stencil exposure.

What causes the sensitizer to harden?

Proper storage plays a big role on the quality of the sensitizer. High heat and humidity can cause a reaction with the sensitizer, making it hard and difficult to dissolve in water.

How long can a mixed stencil (emulsion) with sensitizer be kept in storage?

In a cool and dry storage, a mixed stencil emulsion can last 3-4 weeks and can still be used for stencil exposure.

If it is stored in an area with high heat and humidity, the mixture may thicken overtime rendering it ineffective for use.

The website FAQ page(s) contain questions frequently asked over the years and may be updated from time to time. The answers are provided as reference and it is intended to be helpful and of assistance. Under no circumstances should any information contained herein be construed as legal advices.