PHOTOGRAPHIC EMULSION (DIRECT PROCESS)
PRODUCT:
Screen printing emulsion to be sensitized with Bichromate.
APPLICATION:
For the preparation of screen stencils for the sign printing with water based inks and textile printing ( plastisol, water based, sublimation or reactive inks ).
PROPERTIES:
- High resistance to water based inks and mineral spirits.
- Sensitizable with bichromate, can be exposed with all types of lamps.
- Economic emulsion ideal for large size printing.
CHARACTERISTICS:
| SCREEN FOTO ACQUA | |
|---|---|
| Resistant to: | Water based, plastisols |
| Definition: | Very good |
| Resolution: | Very good |
| Sensitizer: | Bichromate |
| Color: | Pink or Green |
| Solid Content: | 46% |
| Post-exposure: | No |
| Reclaiming: | Good |
| Use on meshes: | from 42 to 120 threads/cm |
| Pot Life: | 24 months |
| Pot Life of Sensitized Emulsion: | 4 days |
| Shelf Life of Coated Meshes: | 4 hours |
Note: Do not store below freezing (32ºF)
INSTRUCTIONS:
ChoOSING THE MESH:
The correct choice of mesh is extremely important. The mesh is the structure that supports the photographic layer, determines the ink deposit and can affect the print definition and resolution.
To choose the ideal mesh, the following factors must be observed:
a - Thread Material: Determines the physical and chemical properties of the mesh: flexibility, dimensional stability, abrasion resistance, and resistance to chemical products. The mesh can be made of nylon (good flexibility), polyester (excellent dimensional stability) or metallic (maximum dimensional stability and anti-static effect due to its electrical conductibility).
b - Mesh Count (number of threads per inch): Determines the ink deposit on the substrate. This factor is also related to the adhesion of the emulsion layer. For thicker ink deposits, we suggest coarser meshes. For finer detail, use a mesh count which will ensure that the smallest dot of the screen is supported by at least two threads of the mesh in each direction.
c - Thread type: Due to its precision and ink flow characteristics, only use mesh made with monofilament threads.
d - Thread diameter: Influences the physical properties of the mesh (mechanical resistance), the ink flow and the resolution of the finest details.
e - Color: Dyed meshes (yellow or orange) avoid light diffraction thus allowing better image definition and resolution.
MESH STRETCHING:
Stretch the mesh according to the values recommended by the fabric manufacturer. Each type of mesh has its proper tension value. Use pneumatic equipment or retensionable frames for better control of the final tension.
For stretch and glue, it is recommended to use the DECAFIX Adhesive (Two Components or Instant Dry), which provides a strong and permanent adhesion of all types of meshes on wood, aluminum or iron frames. After the curing time the adhesive is completely resistant to all solvents used in screen printing.
MESH PREPARATION:
Before coating the emulsion, clean the mesh throughly to guarantee the uniformity of the layer, a perfect adhesion of the emulsion and to increase the durability of the stencil.
For the removal of grease contaminants and dust particles, use DECAPREP or HB10 Degreaser (paste or gel): Apply it on the wet stencil, over the whole surface - on both sides of the mesh. Rinse well with water, including the frames. After the treatment do not touch the mesh.
For coarser meshes, the adhesion of the emulsion can be improved by pre-treating the fabric with HB12 Abrasive Paste, which increases the surface area of the threads besides cleaning.
SENSITIZING:
Due to the characteristics of bichromate, sensitize only the quantity of emulsion that will be used in a period of up to 4 days period. Add the sensitizer to the emulsion in the proportion of 10 parts of emulsion for each part of sensitizer (in volume). Stir well. Leave it resting for a period of 2 hours to eliminate air bubbles.
COATING:
For manual coating, use a AGABE APLIC® Coating Through, made with anodized aluminum with plastic ends. Adequate design for easier handling and cleaning after use. Different edges allow thicker or thinner coats. The shape of the ends allows an adequate contact to the screen.
Always use a coater long enough to cover the whole image area of the stencil. Never use a smaller coater in parallel passes which will create a layer of irregular thickness.
With the screen in a vertical position, slightly tilted, coat the emulsion 1 or 2 times on the print side, and 2 to 4 times on the squegee side (without drying).
The ideal stencil thickness ranges from 10 to 25% of the mesh thickness. In special applications, different thickness can be used. We advise the use of a thickness gauge for perfect process control.
After the emulsion is dried, more emulsion can be coated on the print side to improve stencil flatness or making the layer a little thicker.
DRYING:
Dry the emulsion completely with the print side down. The drying time depends on the type of fabric, type of emulsion and coating thickness.
The dryer should have a filter for the incoming hot air. The exhaust air should not be recirculated to the work area. Bichromate sensitized emulsions should not be dried over 37ºC (99ºF). If a drier is not available leave the coated screens to dry in a clean, dry and dark place.
For thicker stencils on coarser meshes, the drying time is longer.
If the emulsion is sensitized with Bichromate, expose and washout the stencil as soon as it is dry. After a few hours the emulsion will harden, even if it has not been exposed to light.
ExpoSURE TO UV LIGHT (Copying the image):
The photographic stencil becomes insoluble in water when exposed to light. An image can be created if a mask is placed between the stencil and the light source. The perfect image reproduction depends on some factors:
• Positive (film):
Observe the quality of the positive. The dark areas must be opaque (optical density over 3.2) to block completely the light. The remaining areas must be transparent and free of dust and dirt, to avoid light filtering and pinholes in the stencil. The use of translucent films such as those commonly used for laser or inkjet printers is not recommended for precision work. It is best to use transparent photographic films.
Use positives with at least 1200 DPI resolution. With less definition the edges of the final print will not be sharp.
Place the positive on the print side of the screen and fix it with adhesive tape. The opaque layer of the positive should be in contact with the screen printing emulsion.
Maintain a perfect contact of the positive to the stencil during exposure. Otherwise there will be a space in which light will penetrate and cause loss of resolution. It is advisable to use a vacuum frame.
• Light Source:
Type: If the emulsion is sensitized with Diazo, use a light source that radiates UV Light such as metal halide or halogen lamps.
Geometry: To achieve a perfect image definition and resolution and a uniform hardening of the emulsion, the distance between the light source and the surface for the stencil should be, at least, equal to the diagonal measurements of the screen. Larger distances reduces the loss of image resolution. The use of several tube lamps produces a diffuse and unfocused light, therefore making these inadequate for detail copying.
• Exposure time:
The exposure time is extremely important because it determines the quality of definition, the level of resolution and the durability of the stencil.
During the exposure, the print side of the stencil reacts initially with the light rays. After some time, the hardening also reaches the inner layer of the emulsion. If the exposure time is insufficient (under exposed stencil), the squegee side of the emulsion layer will not be completely hard and will dissolve during wash out. If the exposure time is too long (over exposure) the light difraction will cause the loss of detail and of edge sharpness.
The correct exposure time depends on the mesh count, thread diameter, fabric color, type and thickness of the photographic layer, power and age of the UV lamp, distance between lamp and stencil, correct drying of the emulsion and positive quality (transparency and opacity levels).
To determine the ideal time, use the Agabe Test Positive. With this test, you may also evaluate the sharpness of the image and measure the loss of resolution.
The following table shows the recommended exposure times for SCREEN FOTO ACQUA for the following parameters and may be used as a basis for initial tests.
Obs: SS - Squeegee Side / PS - Print Side
If the conditions are not the same as indicated, the following correction factors can be used to adjust the exposure time (multiply the time by the correciton factor.
LAMP POWER (METAL HALIDE)
| Power | Correction factor |
|
|---|---|---|
| MH 500 Watts | 10,00 | 10 times longer than 5kW |
| MH 1000 Watts = 1kW | 5,00 | 5 times longer than 5kW |
| MH 2000 Watts = 2kW |
2,50 | 2,5 times longer than 5kW |
| MH 3000 Watts = 3kW | 1,67 | 1,67 times longer than 5kW |
| MH 4000 Watts = 4kW |
1,25 | 1,25 times longer than 5kW |
| MH 7000 Watts = 7kW | 0,71 | 0,71 times longer than 5kW |
COATING PROCESS
| From - To | Correction Factor |
|---|---|
| From 1PS + 1SS to 1PS + 2SS | Multiply by 1,33 |
| 1PS+1SS -> 2PS+2SS | Multiply by 1,50 |
| 1PS+1SS -> 2PS+3SS | Multiply by 1,00 |
| 1PS+2SS -> 2PS+2SS | Multiply by 1,25 |
| 1PS+2SS -> 2PS+3SS | Multiply by 1,33 |
| 1PS+2SS -> 1PS+1SS | Multiply by 0,67 |
| 2PS+3SS -> 2PS+2SS | Multiply by 0,75 |
| 2PS+3SS -> 1PS+2SS | Multiply by 0,57 |
| 2PS+3SS -> 1PS+1SS | Multiply by 0,50 |
MESH COUNT
| Number of Threads | Correction Factor |
|---|---|
| 455 | Multiply by 0,75 |
| 420 | Multiply by 0,85 |
| 355 | Multiply by 0,90 |
| 305 | Multiply by 1,00 |
| 230 | Multiply by 1,20 |
| 195 | Multiply by 1,60 |
| 107 | Multiply by 2,00 |
| 81 | Multiply by 2,50 |
DISTANCE BETWEEN STENCIL AND LIGHT SOURCE
| From - To | Correction Factor |
|---|---|
| From 100 to 60cm | Multiply by 0,36 |
| 100 90 | Multiply by 0,81 |
| 100 110 | Multiply by 1,21 |
| 100 120 | Multiply by 1,44 |
| 100 150 | Multiply by 2,25 |
| 100 180 | Multiply by 3,24 |
| 100 200 | Multiply by 4,00 |
| 100 225 | Multiply by 5,06 |
| 100 250 | Multiply by 6,25 |
MESH COLOR
| From - To | Correction Factor |
|---|---|
| White to Yellow | Multiply by 1,5 - 2,0 |
| White to Metallic | Multiply by 2,5 - 4,0 |
AMBIENT CONDITIONS
| From normal to | Correction Factor |
|---|---|
| High temperature and humidity | Multiply by 1,3 - 1,8 |
WASHING OUT:
Wash out the screen evenly, using a soft water spray over both sides of the whole stencil. Wash until the image fully appears and the non exposed areas are free from residues. Use higher pressure only on the print side. To guarantee uniform wash out with details, it is suggested to rotate the screen and spread the water in several directions.
For thick stencils or coarse meshes, the screens can be left submerged for 5 minutes prior to using the water jet. The use of slightly warm water helps to dissolve unexposed emulsion.
Evaluate the quality of the stencil, observing the Agabê Test Positive, to control exposure time, definition and resolution.
After washing out, apply the Liquid Light Exposure Enhancer HB70 on the stencil while still wet. Begin on the squeegee side using a soft sponge or spray. Wait some seconds and rinse it. This product reacts with the stencil completing the light exposure, fixing the emulsion and preventing residues to run down in open areas.
FINISHING:
Dry the screen completely. Seal the edges of the stencil, registration marks and the Test Positive with block out chosen. Dry the stencil with hot air. For plastisols and water based inks, block the screen edges with HB20 Acqua Permanent Block Out or with the emulsion itself. In this case, re-expose the screen again.
POST TREATMENT:
Hardening: To increase the stencil resistance to abrasion and water based products, use catalyst HB74 or hardeners HB72 or HB76.
RECLAIMING (for reusing the screen):
Use HB52 Ink Remover to eliminate any ink residues that create a barrier that block the action of the stencil decoaters. Apply the product using a nylon brush and wash it with running water.
Following this step, use HB50 Stencil Decoater to remove the emulsion layer. For best results, wet the screen with water and apply HB50 (paste or gel) on the squeegee side. Leave it on for a few minutes (do not let it dry on the screen). Wash it with running water and use high pressure water on the squeegee side.
Stencils made several months before or hardened with HB72, HB74, HB76 or other catalyst are difficult to decoat. However, some of them may be reclaimed using the Ink Remover HB52 again after the using of the HB50 Decoater.
To remove the so called ghost images (mesh threads dyed by the printing ink) use HB54 Haze Remover mixed with HB52 Ink Remover. Apply the remover HB52 on both sides of the dry mesh with a nylon brush, followed by the Haze Remover HB54 mixing both products on the stencil until the stains are fully covered. Leave it for 15 minutes. Wash the stencil well using running water, prior to using high pressure jets.
Obs.: Before using the cleaning products read the Technical manuals for detailed instructions and consult the Material Safety Data Sheets.
CAUTION:
The emulsion does not present risks if the basic principles of work safety and hygiene are followed.
The bichromate sensitizer is toxic and not biodegradable. Avoid contact with eyes and skin. Wash spills with water. Wear protective gloves and goggles.
Check if local health and environmental regulations allow the use of bichromate.
OTHER INFORMATION:
The information on this document are base on the best of our current knowledge. This product is solely intended for industrial use. No warranties are made or implied. Agabe will not be held liable for claims related to any party´s use or reliance on information or recommendation contained herein.