Silk screen printing plate equipment (2)

2. Photographic photographic film.

The photographic photographic film is a photographic material for making a screen plate master. Photographic film is divided into silver salt photosensitive film and non-silver salt photosensitive film. At present, the domestic plate-making photography generally uses silver salt film.

1 The structure of the photosensitive sheet. Plate-making photographic film, as shown in Figure 2-92, is mainly composed of film base, emulsion layer, anti-halation, protective layer and the like.

Film base, also known as support, commonly used film base with glass plate and transparent plastic film, with glass plate as the film base called hard film, is now not used; transparent plastic film base is called film. The base size is stable, the surface should be smooth and the thickness should be uniform.

Emulsion layers are mostly composed of photosensitive silver salts, gelatin, and pigments. Silver salt is the main component of the emulsion, commonly used silver salt silver bromide, silver iodide, etc., and its photochemical reaction can occur when exposed to light.

The role of gelatin is to distribute the silver salt evenly without sinking, forming a stable emulsion.

The role of the pigment is to increase the color-sensitive properties of the emulsion, making it an emulsion for the perception of shade.

The role of the antihalation layer is to prevent the halo phenomenon from occurring.

The role of the protective layer is to prevent the emulsifier from being scratched and damaged.

2 The type and use of the photosensitive film. Sensitive film according to the photosensitive range is divided into color blindness, positive color film, full-color film three, as shown in Figure 2-93.

a. Color blindness. The color-blind film has a color sensing wavelength range of 330-480 nm, i.e., sensitive to blue, violet, and ultraviolet light, blunted to green light, and hardly sensitive to red light and yellow light. It is often used to shoot ray strips and text originals.

b. Positive color film. Orthochromes, commonly known as red lights, can sense blue, violet, yellow, and green light, and the color sensing wavelength range is 330 to 600 nm. It does not feel red, so it can be operated under a red security light.

c. Full-color film. The full-color film can sense all color lights in the visible spectrum, and the color sensing wavelength range is 330-700 nm, which can be used for color separation of various color originals.

According to the requirements of the copying process, the photosensitive sheets are distinguished by gamma and special hard, hard, medium and soft types:

Special hard film, gamma ratio greater than 5, can be used for direct screen color separation.

Hard film, contrast ratio is about 3  5, lack of intermediate levels, for shooting lines, text bottom.

Neutral film, gamma ratio is about 2, the color separation film negative tone, rich levels, can be used for the contrast of natural color normal and negative originals.

Soft film, gamma ratio of about 1, rich low-key levels, suitable for shooting black and white photo manuscripts.

Different manufacturers mark the performance of the photosensitive film on the package with different symbols.

For example, the southern brand plate film, "N" for color blindness, "P" for full color, "O" for positive color; "S" for special hard, "A" for hard, " B" indicates a neutral tablet, and "C" indicates a soft tablet. On the packaging, if printed "SP" is a full-color hard film, "PA" is a full-color rigid film, "PB" is a full-color neutral film, "PC" is a full-color soft film, "OA ” is a positive-color hard film, “OB” is a positive-color neutral film, “OC” is a positive-color soft film, and “SO” is a positive-color hard film.

Huaguang plate making film, "E" for positive color film, "Q" for full color film; "600" for special hard film, "350" for neutral film, "160" for medium soft film, with "100" indicates a soft sheet.

Table 2-30 describes the photographic performance and use of the Southern license plate printed film for the reader's reference.

Table 2-30 Main properties of domestic films

Performance Index Variety Sensitivity Contrast Factor Fog Density Maximum Density Latitude
PA Hard full color 13±2 3.50±0.50 <0.06 >3.50 >0.80
PB neutral full color 17±2 1.75±0.25 <0.08 >2.80 >1.10
PC round full color 20±2 1.15±0.15 <0.10 >2.00 >1.50
SP special hard full color 6±2 <5.50 >0.06 >3.80
OA rigid positive color 10±2 3.50±0.50 <0.06 >3.50 >0.80
OB neutral color 13±2 1.75±0.25 <0.08 >2.80 >1.10
OC soft positive color 17±2 1.20±0.20 <0.10 >2.00 >1.50
SO special hard positive color 2±1 <6.00 >0.05 >3.80