3.1 Toray System
Toray waterless printing system is mainly composed of three parts: no watermark version, waterless ink and temperature control system on the printing press.
(1) Toray without watermark version
The Toray waterless version has two types, negative and positive. At present, the most used type is the negative image type without watermark.
Toray has no watermark version with three main layers.
a) Aluminium substrate, base layer (approximately 0.5 to 1 mm).
b) Photosensitive resin layer (approximately 3 to 3.5 μm): A diazo photosensitive material. The positive-type photosensitive layer is a photosensitive combination type, and the negative-type photosensitive layer is a photosensitive decomposition-type functional structure.
c) Silica gel layer (approximately 2 μm): Strong ink repellency, as a blank on the plate.
d) Cover film (protective layer, about 6 μm): In order to increase the adhesion of the film and the plate at the time of printing, the surface of the cover layer was processed into a 2 μm concave-convex shape.
e) In order to bond the aluminum plate and the photosensitive layer (diazo photosensitive material), the photosensitive layer (diazo photosensitive material) and the silica gel layer well, they are also coated with a photosensitive diazonium compound as a raw material. Gluing layer.
According to the type of Toray waterless version, the print volume varies from 100000 to 600000 prints. The amount of print depends on other factors.
Like the traditional PS version, the Toray waterless version can be regenerated.
(2) Plate-making step: Waterless offset printing The key to plate-making development is to cut off the silica gel layer corresponding to the graphic part. The shear force is stronger than the adhesion between the silicone layer and the photo-sensitive layer in the graphic part. Applying it to the interface between the two layers can remove the graphic part of the silicone layer.
a) Imposition: Films for waterless printing can be either negative or positive. The so-called imposition is the process of pasting and fixing the film on the printing plate according to certain requirements and operating specifications. The imposition should be based on the film and lithographic type to determine whether to use light blocking film.
b) Exposure: The Toray waterless version is exposed using a conventional UV light source exposure device and a light source. The exposure time is also about 60 seconds. The negative-pattern waterless version passes through the UV light of the film during exposure, penetrates the silicone rubber layer, and reaches the photosensitive resin layer. The photosensitive resin in the graphic part absorbs UV light and reacts and falls off at the junction of the photosensitive resin and the silicone rubber layer. This kind of reaction is very fine, and the printing plate is also very easy to get high resolution. When the number of screen lines is 175 lines/inch, it can reproduce 0.5% to 99.5% of the dots.
c) In addition to the protective film: Toray waterless version after exposure, but also need to be processed. Prior to processing the plate, the protective film on the silicone layer must be removed.
d) Swelling: The development processing equipment is unique to the system and uses special chemical and mechanical methods to process the plates. The photosensitive layer of the graphic part is swollen with the appropriate PPG (polypropylene glycol) and PEG (polyethylene glycol), ie TORAY PA-1 pretreatment solution, and the silicone layer is floated, so that the adhesive force between the two layers is greatly increased. Weakened. The blank part cannot afford chemical changes.
e) Mechanical peeling: If a negative image is used, the photosensitive portion is peeled off and the unexposed portion (ie, the blank portion) retains the silicone layer; if a positive image is used, the photosensitive portion hardens, and the unexposed portion falls off to form the graphic portion. The puffed waterless version is uniformly applied with shear force to the interface of the swollen silicone layer by the nylon brush, and the silicone layer of the printed part is peeled off. Thus, the watermark printing process has not been completed, and the waterless version is manufactured as such. .
f) Staining: The developed waterless version can be printed without dyeing. The dyeing function is mainly used to identify and check the quality of the printing plate.
One point to be emphasized here is that waterless offset printing produces a flat gravure plate. The non-graphic part of the plate is an ink-repellant silicone rubber layer. In the graphic part, the silicone rubber layer is removed, leaving the ink absorbing. The resin layer forms an "ink-absorbing hole" structure. These "ink-absorbing holes" provide a supporting net wall as the ink is transferred from the printing plate to the blanket cylinder. In this way, in the process of ink transfer, the dot enlargement formed under the effect of the printing pressure is very small, and the faithful reproduction of the graphic and picture is basically achieved.
(to be continued)
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