Bluecoat - 414 Photo Screen Emulsion
In the process of rotary screen engraving it is the emulsion that forms the link between the image & the screen & playing a vital role. Quality of the image, mechanical resistance to all printing paste, the runability & Photo efficiency are the outstanding features of Bluecoat 414 - PHOTO SCREEN EMULSION. For exposing the screen following procedure is to be followed.
Preparing & Applying
Take 1 Kg of Bluecoat 414 Emulsion in a clean vessel & also take 50 ml. of sensitizer. Mix them together for sometime till the colour of Emulsion is changed to light uniform green. Viscosity of the Emulsion can be changed by adding DISTILLED WATER depending upon mesh of the screen & technique of coating - i.e. machine coating or hand coating. Filter this emulsion with bolting cloth & close the vessel for 1 hour in cool dark place so that all the air bubbles are disappeared.
A completely grease free screen is required in order to achieve good fixing of Emulsion to the screen. Even if the screen is being used for the first time it is required to be degreased with the degreaser, by giving good rinse & immersion in degreaser & subsequent cleaning with pressure of water. Allow it to dry in a dust free area.
Direct Emulsion Coating requires skill to produce uniform pinhole free coating. Bluecoat 414 Emulsion can be applied to a screen by using circular rubber squeegee. It should be verified that the rubber of the squeegee has constant & correct hardness, elasticity & diameter & even after prolonged use it maintains elasticity & it is not broken or cracked.
There are two methods of coating Photo Emulsion viz. Machine Coating & hand coating.
In this method Emulsion is applied automatically to screen in single action & one cycle of operation from top to bottom & it forms smooth adhesion between emulsion & screen so that practically no touching is required & pinholes hardly ever occur. Viscosity of the emulsion can be diluted by adding distilled water to suit the machine coating.
In this type of technique round rings are inserted on both sides of rings & it is placed on floor in upright position & after that emulsion is applied to screen at even speed by using circular rubber squeegee from bottom to top at a even speed & put the screen in dryer. Depending upon the mesh of the screen additional 3 to 4 coats are required by repeating the above procedure.
Drying & Exposing
After applying the emulsion the screen is transferred to dryer & dried by heating air approximately 30° C. & drying it to a relative humidity at 40%. In case of hand coating, if you are coating the screen for 2nd & 3rd time, it is important that the first coat be thoroughly dried before the subsequent coat is applied. Moisture remain present in coated screen even when the screen feels dry to touch.
Exposing is one of the most important factors in achieving fine image & sharpness. The important aspect is deciding exposing time which depends on mesh of the screen, thickness of coating, light source for Photography & image pattern. Photo Emulsion is extremely sensitive to ultraviolet light & takes little time for photography. If exposing machines are fitted with metal halogen lamps or xenon lamps then exposing time of 2 to 4 minutes are sufficient. Thus time of exposing varies from 2 minutes to 7 minutes depending upon light sources & exposure should himself determine time for photography.
Immediately after exposure, the screen is taken for developing where it is immersed in a cool water for 5 to 10 minutes. The lacquer not exposed is removed into tank with rubber foam thoroughly both from inside & outside the screen till the image comes out clearly. Use of spray gun is desirable for removal of excess lacquer left behind after developing in the tank. Open areas in the screen are checked under tubelight on touching stand & closed by means of brush.
After the screen is developed & dried (at room temperature) it is kept in polymeriser (Heater) for curing. The temperature in the chamber should be 170° C. to 180° C. throughout & constant & screen should be kept for at least one & half hour which ensures complete resistance to chemicals.
It should be ensured that temperature is maintained throughout, in the chamber. Generally it happens that temperature in the chamber varies considerably between top & bottom. To eliminate this it is desirable to turn the screen after 45 minutes.
It should be observed that colour of the screen is uniform throughout from top to bottom after curing, otherwise screen is under-cured & creates problem of leakage. It is here that the screen acquires its final chemical & mechanical properties.
The last stage in the process of preparing the screen for printing is gluing of endring from both the side so that it can resist considerable amount of force during printing speed.
An engraving is more than just the sum total of film, screen & emulsion. Even if each of these product is individually of the highest quality, it is you-person on the job - who contributes the 100% to the ultimate quality of the engraved screen.
Keep the container closed & away from sunlight.
12 months, if container is properly closed.
We recommend that before using our product in full scale production, the customer should make his own tests to determine the suitability of the product for his own purpose under his own operating conditions. Since the circumstances under which our product is stored, handled & used, are beyond our control, we cannot assume any responsibility of their use by the customer.