Kiwo PolyCol Stack TDS


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PolyCol Stack

Description:

POLYCOL STACK is a presensitized SBQ-photopolymer emulsion used to produce stencils with emulsion over mesh build-up of 100 to 1000+ microns. The high viscosity and high solids content of this emulsion enable the coating of a very thick stencil for applications using High Density Ink systems, as well as extremely fast exposure speed to crosslink quickly through the thick build-up of emulsion.

Sensitizing:

Pre-sensitized -- ready to use.

Mesh preparation:

To achieve a good stencil, the mesh must be degreased with a commercial degreaser such as KIWO Degreaser 1:20 or PREGAN A9 and must be free of dirt, dust, ink residues and ghost images. Rinse the screen thoroughly using low water pressure to remove any degreaser remaining on the screen. A foaming degreaser such as KIWO DEGREASER 1:20 or PREGAN A9 helps to determine proper and complete rinsing. See KIWO DEGREASER 1:20 or PREGAN A9 technical data sheets for details.

Base Coating:

POLYCOL STACK is recommended specifically for printing with High Density Ink systems. This application requires very thick emulsion build-up on mesh counts of 40 - 156 THREADS PER INCH (16 - 60 threads per cm).
POLYCOL STACK can achieve 50 to 200 microns of emulsion build-up with simple base coating.
Procedure

Start by coating 1 or 2 coats with a round edged coating trough on the substrate side of the screen to fill in the mesh openings.

Finish by coating wet-on-wet coats on the squeegee side of the screen with a round edge coating trough to build-up the emulsion coating to the desired thickness or limit thickness.

Dry the screen in a hortizontal position with the PRINT SIDE DOWN (See "Drying the BASE Coat: 6.5’ for more details).

Each mesh count will have a limit to the amount of emulsion applied from the squeegee side of the screen before the emulsion will drip off of the screen. The number of passes on the squeegee side of the screen will vary. A simple step coating test can determine the coating limits. (see ‘Step Coating Test' below for directions for conducting a coating test)
The number of squeegee side passes will not only be influenced by the mesh count, but also by trough fill level, coating speed and coating trough pressure.

Trough fill level:

A full coating trough will deposit more emulsion onto a screen compared to a quarter full coating trough. As the coating trough is depleted, less and less emulsion flows onto the screen. Since you are trying to produce a thick emulsion build-up quickly, the coating trough should be completely full before starting to coat. In addition, the coarse mesh counts used in this process use a lot of emulsion; the coating trough fill level needs to be checked and/or filled after coating each screen. Ideally, the trough is filled to the same level for each screen to keep a consistant deposit from screen to screen.

Coating speed:

A slower coating speed of the coating trough allows for more emulsion to flow onto and through the mesh resulting in a thicker emulsion build-up compared to a fast coating speed. The screen coater needs to maintain a consistant speed from the bottom to the top of the screen and also from screen to screen.
Note: A very slow coating speed can lead to processing problems. To achieve a very thick build-up, the screen maker needs to deposit as much emulsion as possible without the emulsion running down the screen. If the coating speed is TOO SLOW, the screen maker may only be able to deposit 1 or 2 passes of emulsion before the emulsion begins to run down the screen. Medium to fast coating speeds may allow the screen maker to apply more wet-on-wet coats. The screens should then be moved to the drying area. (See ‘Drying the BASE Coat: 6.5’ for more details)

Coating Trough Pressure:

When the screen maker applies various amounts of pressure from the coating trough to the screen, the emulsion deposit will vary. The screen maker needs to be sure the coating trough pressure remains consistant from side-to-side and top-to-bottom of the screen, as well as from screen to screen.

Automatic and Manual Coating:

Both automatic and manual coating techniques can be used for base coating. An automatic coating machine such as the KIWOMAT^TM is recommended to control coating speed and coating pressure to achieve a greater consistancy of coating from screen to screen.

Coating Recommendations:

The following table (next page) gives emulsion over mesh build-up results for the recommended coating procedure for the following mesh counts. The screens were coated with an automatic coater at a pressure of 3 bar and a speed of approx. 500 cm/min. Again, a ‘Step Coating Test’ is recommended to find the optimal coating procedure for the specific user. Contact KIWO for additional information.

Mesh Count	Recommended Wet-on-Wet Coating for Max. Build-Up	Approx. EOM
60/145 white	1-2 coats on print side, round edge 5 coats on squeegee side, round edge	110 um
83/64 yellow	1-2 coats on print side, round edge 3 coats on squeegee side, round edge	175 um
92/100 white	1-2 coats on print side, round edge 5 coats on squeegee side, round edge	95 um
110/80 white	1-2 coats on print side, round edge 5 coats on squeegee side, round edge	100 um
110/80 yellow	1-2 coats on print side, round edge 5 coats on squeegee side, round edge	100 um

Step Coating Test:

A quick coating test should be conducted to determine the maximum amount of coats applied to the squeegee side of the screen for base coating.

1. Start by coating 1 or 2 coats with a round edged coating trough on the substrate side of the screen to fill in the mesh openings.
2. Coat one wet-on-wet on the squeegee side of the screen with a round edge coating trough to begin to build-up the emulsion coating.
3. Apply a second coat starting 1/5^th of the way up the screen. The screen now has two different emulsion thicknesses.
4. Apply a third coat starting 2/5^th of the way up the screen. The screen now has three different emulsion thicknesses.
5 Apply a forth coat starting 3/5^th of the way up the screen. The screen now has four different emulsion thicknesses.
6 Apply a fifth coat starting 4/5^th of the way up the screen. The result should be 5 different coating thicknesses on one screen.

Figure 1: step test coating from the squeegee side.

7. Dry the screen in a hortizontal position with the PRINT SIDE DOWN (See "Drying the Base Coat: 6.5’ for more details).

8. Evaluate the screen to determine the maximum number of squeegee side coats that can be applied before the emulsion runs or drips. In addition, measure the emulsion build-up with a thickness gauge, such as the KIWO STENCIL THICKNESS GAUGE, to determine the emulsion build-up, EOM, for each coating.

9. Use the tested, ideal coating technique for all screens with the same mesh count.

Additional Emulsion Build-up:

There are 3 different face coating techniques to achieve extremely thick emulsion over mesh (EOM). Each ‘Face Coating’ technique is detailed separately following the main body of information. In addition, the advantages and disadvantages are described with the specific coating instructions.
The separate face coating instructions are: (a) Face Coating WITHOUT a Shim, (b) Face Coating WITH a Shim, and (c) Pouring With a Shim.

Drying of the coated screen:

The drying time is affected by temperature, relative humidity and air flow. The screens must be dried thoroughly before exposing to achieve highest resistance to inks. A temperature of 86°-104°F (30°-40°C) at a relative humidity between 30%- 50% and a moderate airflow are optimum conditions. Drying at room temperature and uncontrolled conditions may lead to inconsistent results and varying screen resistance.

Drying the BASE Coat:

Dry the screen in complete darkness, or under safelight conditions, with the screen in a level and horizontal position with the PRINT side DOWN. To achieve maxiumum build-up with the wet-on-wet base coats, the drying conditions need to be optimized as stated previously. The faster the drying – the thicker the base coat thickness can be coated. If a screen is dried at room temperature with a relative humidity above 50%, the emulsion will dry slower and have a greater chance of running or dripping on the screen; therefore less emulsion can be coated onto a slow drying screen to reduce the chance of dripping or running. With elevated temperatures and low relative humidiity, the emulsion dries faster with less unwanted dripping of the emulsion; a thicker deposit can be applied to the screen.

Drying the FACE Coat:

Dry the screen in complete darkness, or under safelight conditions, with the screen in a level and horizontal position with the SQUEEGEE side DOWN.
When drying the base coat, water evaporates from both sides of the screen. After face coating on the print side of the screen, water mainly evaporates from the wet surface – the print side of the screen.
When the face coating is applied in a relatively thin layer, the water throughout the face coat dries quickly. Processing several thinner face coats may take only a few hours.
As the face coat deposit increases, drying time increases for two reasons. First, the drying increases because there is physically more emulsion deposited on the screen. Second, the upper most layers of a thick deposit face coat dries before the inner layers dry. It is more difficult for the water from the inner layers of emulsion to evaporate from the stencil since the outer most layers have started to dry. An excessively thick face coating (with a shim greater than 500 microns) will take much longer to dry than if several layers of relatively thin face coats were applied.

Exposure:

Expose with Ultra Violet light at a wavelength of 320 - 380 nm. A metal halide lamp provides best results. Due to the many variables that determine the actual exposure time accurate estimates for specific process environments are not possible, however the following example has been generated to offer a starting point to test for proper exposure.
Lamp: 5000 Watt metal halide at 50" distance, with a narrow reflector. Intensity of the Light Source for estimated exposure time is 15.35 mW/cm² @ 300-400 Nm and 34.4 mW/cm².
The correct exposure time for your equipment and mesh selection, must be determined through exposure tests using a step exposure or an exposure calculator such as the KIWO EXPOSURE CALCULATOR or KIWO EXPOSURE STEP WEDGE.
Underexposed screens will be slimy with under exposed emulsion on the squeegee side during developing. At the correct exposure time, the emulsion has completely hardened. Overexposure will lead to loss of detail. Correctly exposed screens will withstand high tap water pressure during washout. Contact KIWO if you have further questions regarding exposure time.

Developing/Washout:

Develop the screen using at least full tap water pressure and a medium spray pattern – for best results, use a pressure washer and a medium to high pressure sprayer to develop screens. Adjust the water temperature to lukewarm or slightly colder.
Rinse thoroughly from both sides of the screen to saturate the emulsion. Spray with medium or high pressure from the squeegee side of the screen for 30 to 60 seconds. Turn the screen around to the print side of the screen and continue to spray the screen with medium to high pressure. Continuously move the sprayer around the screen, do not concentrate the high pressure spray in one area of the screen for longer than a few seconds (10 to 30 seconds).

Mesh Type	Mesh Thickness (um)	Emulsion Thickness (EOM, um)	Exposure Duration (seconds)
60/145 white	250	100	450
60/145white	250	200	500
60/145 white	250	400	600
83/64 yellow	100	100	500
83/64 yellow	100	200	550
83/64 yellow	100	400	625
92/100 yellow	150	100	525
92/100 yellow	150	200	575
92/100 yellow	150	400	750
110/80 white	125	100	400
110/80 white	125	200	475
110/80 white	125	400	575
110/80 yellow	125	100	600
110/80 yellow	125	200	700
110/80 yellow	125	400	875

A pressure washer with 1200 psi at a distance of 6" is desired for developing. When higher levels of pressure are used, increase the distance of the pressure washer to the screen. At 3000 psi, the distance should be no closer than 18" to the screen.
Vacuum off any excess water or blot it off with newsprint paper. This will prevent under exposed emulsion from running into the image area.

Post-exposure:

Postexposing the screen after developing and drying can be very effective. Postexposure times should be 1-2 times the original exposure time.

Post-hardening (chemically:)

The emulsion can be chemically post hardened using HARDENER HP to improve water resistance. HARDENER HP improves the water resistance, but the emulsion remains reclaimable. See HARDENER HP Technical Data Sheet for application details.

Blockout/Touch-up:

When printing with plastisol inks, re-touching or blocking out can be done with KIWO BLOCKOUT and KIWO TOUCHUP. For water resistant stencils block out and re-touch with KIWOFILLER WR/MV or use POLYCOL STACK for re-touching and blocking out (dry thoroughly and re-expose completely prior to using HARDENER AWR).

Decoating:

POLYCOL STACK can be decoated with emulsion removers such as KIWO STENCIL REMOVER. Before decoating, ensure the screen is completely cleaned of ink or ink cleaning chemical residues. If water beads up on the stencil, degrease the screen prior to decoating. See the KIWO STENCIL REMOVER Technical Data Sheet for details.

Haze Removing:

When under-exposed, the emulsion can cause emulsion haze after reclaiming. To remove haze, use KIWO HAZE REMOVER or PREGAN PASTE. Use the haze removing products with the KIWO INK WASH and haze remover activator or KIWO ULTIMATE INK WASH. These products are also very effective at removing ink haze. See separate Technical Data Sheets for these additional products for more details.

Physical Properties:

Viscosity : approx.: 10,000 mPas
Solids content: 36%
Color: whitish
Storage: 1 year at 20°C/68°F
Potlife: 1 year at 20°C/68°F
Pre-coated screens: 8 weeks in complete darkness at 20°C/68°F
Freezing: protect against freezing
VOC: none
TLV: n/a
HMIS rating: Health -- 1
Flammability -- 0
Reactivity – 0

Packaging:

1 US Gallon, 5 US Gallon, 32 Gallon drums

Additional information:

For additional product information, please visit www.kiwo.com or call PCS at (919) 266-4463.

Thank you for choosing KIWO.

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