Film Assembly

          

Film Assembly

            It is the process of assembling all pieces of film containing the image that will be carried on the same printing plate and securing them on a astolon sheet that will hold them in appropriate/proper position during the platemaking process. The assembled positive films are called a flat. After the flat is prepared it is generally tested on inexpensive photosensitive material to check the image position and to ensure that undesired light reaches the plate. This process is called proofing, if the proof is approved the flat can be placed in contact with a printing plate and light can be passed through the plate to make the plate for printing.

            The pasting/stripping artist uses a variety of tools like T Square, Triangle, Cutting tools, Blades, Knifes to trim films. For greater accuracy an ordinary needle is used to make the masking sheet when laying out a window. Water colour brushes with no. 0,2,4,6 are used. A pair of scissors, a low powered magnifying glass(10x), pencils to 2hetch and 4hetch, pencil eraser, felt tip marking pens for labeling flats are used.

            For negatives the masking sheet that does not passed light to printing plate must be used. The most commonly used are golden rod paper, which blocks actinic light (any light that exposes blue light and ultra violet light sensitive emulsion) because of its colour. The job that requires greater accuracy uses orange or red colour vinyl masking sheet. To positive striping masking sheet and film must pass light in all areas except the image area. Most positive striping is done on clear acetate support sheet or astolon sheet. Opaque is a liquid material used to cover pin holes and other unwanted details on film negative. Red opaque is easier to apply. Old tools mentioned above should be centrally placed near light tables for easy usage.

Imposition: - It refers to the placement of images in the correct position on the printing plate so they will be printed on the desired location on the final printed sheet. Several types of imposition are commonly used. They depends on the following factors:-

1.      The design, folding, trimming and binding.

2.      The type and the size of the machine in press.

3.      The type of paper grain direction.

Masking Sheet: - The position of the image on the printing plate is determined by the film’s position on the masking sheet. Care must be taken in placing the film images on the masking sheet. The masking sheet is generally dark in colour which doesn’t allow light to pass through.

The cylinder line: - It identifies the area of the masking sheet that covers the part of litho palte clamped to the plate cylinder.

The gripper margin: - it is the area of the mechanical gripper hold by the mechanical fingers that holds the sheet during printing.

The plate center line: - This is the center of the plate cylinder for the guidance for plate fixing.