Flexible plate making

There are two types of flexographic plates: flexographic plates and photosensitive resins. The materials they use and the methods used to make them are all different.

First, the rubber version of the rubber plate is made of natural rubber or synthetic rubber and is made by hand-carving or moulding.
1. Hand-engraving method This is a kind of plate-making method used for making flexographic plates, similar to engraving rubber seals. First, the painted pattern and text are inversely attached to the surface of the rubber plate, which is then carefully carved into a relief plate. The sculpted rubber is then affixed to the plate cylinder of the rotary printing press and printed. Hand-sculpting is slow and has poor accuracy. Only some corrugated cartons, packaging kraft paper, textile bags and Other plastic packaging with simple patterns can be printed. Paste can use 501 or 502 adhesive or double-sided tape.
2. Molding method Molding method is divided into three steps:
(1) Preparation of metal relief (original). Photographic platemaking method is used to photograph the manuscript of the manuscript as negative film negative. The sensitized film is coated on the surface of the metal plate (copper and zinc), and metal relief plate is formed by printing, developing, and etching.
(2) Press the template. With the metal letterpress as the original plate, a thermosetting resin (phenolic resin) is used as a material on a press machine, and a concave stencil is formed by heating and pressing.
(3) Squeeze rubber relief. A rubber sheet (natural rubber or synthetic rubber) is laid over the concave stencil and vulcanized, molded, and cured to make a rubber plate. According to the thickness required for printing, the back of the printing plate can be ground and printed.
The graphic precision of the molded rubber plate is better than that of the hand-carved rubber plate. A template can repeatedly compress multiple rubber plates, but the process is complicated, costly and inefficient.

Second, photosensitive resin flexo photosensitive resin flexo is a high elastic polymer. The plate making time is short, the cost is low, and the printing force is high. This photographic plate undergoes photopolymerization upon irradiation with ultraviolet light to become an insoluble reticular polymer, and portions not irradiated with light are washed away by the solution during development to form an embossed relief.
1. The structure of a photosensitive resin flexographic plate It consists of a plate base, an adhesive layer, a photosensitive adhesive layer, and a protective layer.
(1) Edition base. It is the carrier of the plate. Requires good transparency, smoothness, and low scaling. General use of PET sheet for the base, but also for the base metal aluminum.
(2) Adhesive layer. It is the adhesive material between the photo resist layer and the substrate. Generally, it is applied on the surface of the substrate first, and after it is dried, the photosensitive layer is coated.
(3) photosensitive layer. It consists of resin, cross-linking agent, photoinitiator and polymerization inhibitor. The resins are unsaturated and rubbery polymers such as polybutadiene, butadiene-styrene copolymers, trimethylol triacrylate, and the like. The crosslinker can change the unsaturated polyester from a linear structure into a network structure. When using cross-linking agents, care should be taken with the resin. Commonly used photoinitiators are benzophenone, benzalkonone (benzoin) and the like. The photosensitive resin plate is a prefabricated plate. In order to prevent thermal reaction and dark reaction and ensure the quality of the plate, a polymerization inhibitor is added to the photosensitive resin to inhibit the polymerization reaction of the photosensitive resin, such as hydroquinone and p-methoxybenzene. Phenol, gallic acid and so on.

Table 30-1 Several Commonly Used Flexible Plates

product name

2. The main technical parameters of the flexo (1) size. The web size and thickness of the plate are selected according to the needs of the printed product and the conditions of the printing equipment and materials. For example, the GS type flexo plate produced by the Shanghai Institute of Printing Technology has two sizes: 450×550 mm and 450×720 mm. The thickness of the plate is 2-2.5 mm (thick) and 0.8-1.1 mm (thin). Table 30-2 shows the varieties and specifications of the Cyrel version of the United States.

Table 30-2 Specifications and Thickness of CyreL

(2) Flatness error is ±2.0-2.5 filaments. The printing pressure is about 0.1 MPa.
(3) Resolution up to 48-60 lines/cm.
(4) The absorption spectrum was 380 nm.
(5) The finest independent line is 0.175mm.
(6) The smallest individual diameter is 0.25mm.
The depth of the (7) version is 0.76-1.10mm.
The (8) version has a hardness of 35-50 degrees Shore.
(9) Surface tension 20-40 dyn/cm.
(10) The storage period is 1 year.
3. Flexo platemaking process (1) process flow
(2) Originals. The manuscript used to prepare the flexo should have the following conditions:
1 The darkness of the pattern and text should be deep, and it should be consistent and black and white. If the outline of the graphic is dark and blurred, it will affect the effect of the negative film.
2) Reduce the size of the manuscript. The fine strokes of the graphic and text should be clear, and the phenomenon of loss and disappearance should not occur when it is reduced.
3Continuously adjusting the contrast of photos should be moderate.
4 The fine strokes of the manuscript on the manuscript should be thick enough to avoid blurring due to the expansion of the flexographic ink during printing.
5 In the design of the original, it is necessary to avoid the appearance of a large area of ​​dense colors on the same color plate, as well as clear screening images. In order to control the amount of ink and the color of the ink during printing, and ensure the printing quality, the fine-grained and fine-grained layers of the screen are separated from each other in the design.
(3) Making Yin picture. Ordinary line drawing drafts or phototype drafts can be used to make negative editions. Photosensitive film should use high-contrast film or color film. The density of the non-graphic part of the Yin picture is greater than 3.5, and the density of the graphic part (transparent part) is less than 0.05. If the contrast of the negative image is small and the density is not high, the fog density at the transparent part will affect the quality of the flexographic production. Flexo printing is direct printing (positive printing). The graphic on the printing plate is reversed. Therefore, the negative image must be a positive image. Yin pictures can also be obtained by photographic color screening or electronic color separation screening. However, the flexible version of the cable is generally thicker than the lithographic screen and is generally controlled at 30-45 lines/cm.
(4) Auxiliary exposure (back flash exposure). Auxiliary exposure, also known as pre-exposure, is to give full exposure from the back of the printing plate, so that the photosensitive layer on the north side of the photosensitive layer becomes sensitized into a hardened layer. The auxiliary exposure time is determined by the required depth of the layout. The auxiliary exposure time is proportional to the thickness of the plate base; the auxiliary exposure time is inversely proportional to the embossed depth of the plate relief.
(5) Main exposure (front exposure). The main exposure is to expose the photosensitive layer on the plate through the negative image. First, the protective film of the flexographic plate was removed, and the negative film negative was placed on the surface of the flexographic plate and evacuated to make it close. The light source is activated, and the ultraviolet light passes through the negative plate to photosensitize the flexographic plate, and photo-crosslinking occurs, so that the light-receiving photosensitive polymer layer becomes an insoluble substance and constitutes an image. The main exposure determines the sharpness and angular gradient of the graphic text. Inadequacy and excessiveness will affect the quality of the print. The influencing factors are as follows: 1 The photographic performance of the flexographic printing plate: The sensitization performance of the flexographic plates of different manufacturers is not the same. The same manufacturer, due to different production batch numbers and time, will also be slightly different; 2 Translucent conditions of the shade pictures: The transparency and density contrast state of the picture and the transparency are inversely proportional to the exposure time. The higher the density, the longer the exposure time. In addition, the structural state of the layout graphic, such as patterns, color blocks, and line versions, has different exposure times. The finer the dots, the longer the exposure time; 3 The embossing depth of the printing plate is different, and the exposure time is also different. For example, the emboss depth of plastic printing is 0.4-0.5 mm, and the emboss depth of thick printing plate is 1-2 mm. The longer the dark exposure time, the spectral distribution range of the 4 light source output should be consistent with the spectral range of the printed absorption. Near-ultraviolet light is generally used. The plate-making time for several flexo plates is shown in Table 30-3.

Table 30-3 Platemaking time for several flexo plates

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