Common Printing Principles and Process Overview (1)

Letterpress platemaking has a variety of methods. The selenium on the metal plate can be used to etch the letterpress plate, and the photographic plate can also be printed on the photosensitive resin to form a letterpress plate. There is also electronic engraving. The machine is engraved into a relief printing plate; the prepared relief plate can be copied into a relief printing plate by casting method, and the plate making method is selected according to requirements in use.

One, copper zinc plate

By photographing, the image on the manuscript is reproduced as a negative film, and the image of the negative film is dried on a copper plate or a zinc plate coated with a photosensitive layer. After developing the film, ferric chloride is used. Or nitric acid will etch away the blank part of the printing plate, and get the embossed graphic printing plate.

Metal plates are generally made of copper plates to produce high-quality photos and photos of continuously adjusted nets. Zinc plates are used for making maps or simple patterns. Zinc plates contain microcrystalline zinc plates, suitable for powder-free corrosion, and can also be used instead of copper plates. Powdered zinc plate is suitable for powder corrosion. The powder zinc plate used for making relief plates is an alloy. Contains 99% of zinc, 0.2-0.5% of lead, 0.2-0.35% of cadmium, 0.012-0.02% of iron. The microcrystalline zinc plate contains 99% zinc, 0.02-0.10% aluminum, and 0.05-0.15% magnesium.

The plate making process flow is: sheet preparation → printing → corrosion → full-page → proofing.

1. Plate preparation

Select a suitable copper plate or zinc plate, cut to the required size, remove the surface of the oil, oxide film, scars, water stains, trachoma and so on. The method of removal can be grinded with light, soft, charcoal without knots or cracks. The milled plate surface also produces a very fine streak, which can increase the adsorption of the photosensitive liquid. The ground metal plate is placed on a baking plate to transfer the chrome glue photosensitive liquid to the drying plate for drying.

The chrome glue photosensitive liquid is made of a mixture of dichromate (ammonium dichromate, potassium dichromate, etc.) and a high molecular material (gelatin, polyvinyl alcohol, etc.).

2. Printing

Shaiban is carried out in the stencil, the main surface of the metal plate coated with a photosensitive liquid is in close contact with the negative image of the cathode, and the method of close adhesion is pressurized with a sponge pad, and some methods of vacuum sealing are used after the close contact. When exposure is performed, only the part of the image on the negative film can be transmitted through the light to expose the photosensitive layer to light-insoluble material that becomes insoluble in water. An image is formed on the metal plate, and the photosensitive layer in other parts of the plate surface is not affected by light. As a result, the photosensitive layer is not denatured and can still dissolve in water.

The exposure time is determined by factors such as the density and transparency of the film, the thickness of the line, the properties of the photosensitive solution, the thickness of the sensory layer, the composition and strength of the light source, and the distance from the printing machine to the light source.

After the exposure is completed, the metal plate is developed by rinsing with water, so that the photosensitive layer of the part that has not been exposed to light is dissolved in water, and only the shadow mask formed by the hardened adhesive layer remains on the plate surface after the development, so that the image is clearly discernible. The surface of the board can be coated with methyl violet solution for dyeing, and can play a role as a firm film to prevent degumming.

In order for the hardened adhesive layer (ie, the image portion) on the plate surface to be able to adapt to the corrosion of the next process, the corrosion resistance of the hardened layer must be increased. Therefore, the hardened layer is baked and baked until the layer is brownish. The baking plate requires a uniform layout. If the baking plate is insufficient, the adhesive layer is not completely dehydrated and hardened, and it is orange-yellow. This will reduce the corrosion resistance and cause partial degumming during the etching. For example, if the baking plate is too long and the adhesive layer is black, then The adhesive layer cannot be adsorbed tightly on the surface of the plate and loses its anti-corrosion properties, resulting in full degumming. The roasted plate can be repaired after cooling.

The purpose of the revision is to remove the unnecessary resist film on the plate thoroughly and cleanly, and maintain and trim the required image to make it have anti-corrosion properties.

3. Corrosion

The purpose of the corrosion is to keep the graphic part of the hardened adhesive layer undisturbed, and the blank part of the adhesive-free layer erodes after etching, so that the graphic part is still on the same plane and is higher than the blank part to achieve the letterpress. Printing requirements.

Corrosion General copper plate is corroded with ferric chloride solution. Its chemical reaction formula is:

2FeCl3+Cu→2FeCl2+CuCl2

The zinc plate is corroded by a dilute nitric acid solution. Its chemical reaction formula is as follows:

4Zn+1-10HNO3→4Zn(NO3)2+N2O+5H2O

The corrosion results of these solutions on the metal plate not only vertically erodes the blank portion but also causes side etching of the image portion, thereby reducing the printing plate's resistance to printing, and producing powder in order to prevent side corrosion. Red powder) corrosion and no powder corrosion two methods.

(1) Powder etching process

The process of powder corrosion is: Before starting corrosion, anti-acid paint should be applied on the back of the metal plate to protect the back. The corrosion is carried out in the corrosive machine. When the side of the picture starts to appear, the side must be protected so that no side corrosion will occur during the process of continued corrosion, so that the fine lines will be finely deformed. After the initial corrosion is completed, the cleaning is performed. , Full pouring of ammonium chromate solution, pouring ammonium chromate solution is due to the effect of ammonium dichromate is hydrophilic oleophobic, in the recessed blank part of the anti-oil effect, does not make the concave part of the ink. Then, ink is applied to the protruding film portion of the film to further protect the graphic portion.

Side protection, using the graphics around the sides were brushed with pink powder. After baking the red powder was dissolved into a corrosion layer, red powder is a red resin made from the red resin of the fruit of the blood tree, low melting point, insoluble in water, soluble It has corrosion resistance in ethanol, ether and oils.

After the red powder is cooled by the baking plate, it can be etched a second time. When the new side continues to be generated, the previous method is repeated. The powder brushing, etching, dressing, and powdering are usually repeated 4 to 5 times to achieve Corrosion depth requirements, due to many times the results of the red powder, so that the side of the map is a ladder-like, this type of plate is not suitable for printing, the country, the final need to be completely etched, so that the side of the graphic step removed, forming a slope The side can be used for printing. Due to the complex operation of the process and the poor working conditions, the powder-free etching process has been adopted.


(2) Powderless etching process

Non-powder corrosion is performed in powderless etching maching. It is an etching process that adds chemical additives as side protectants in the etching solution. The additive consists of an organic solvent and a surfactant. The organic solvent is mainly composed of diethylbenzene, benzene, kerosene, etc. It has acid resistance but cannot be mixed with water. After adding the surfactant, the water and the active agent form an oil-in-water emulsion under mechanical stirring. liquid. After the oil film on the plate surface, the tension is reduced, and the protective film is formed during the etching process. The adhesion of the protective film on the plate surface is different. In the graphic part, the presence of the photosensitive film layer, the adhesion of the protective film is large. However, the blank part has less adhesion. In the process of corrosion, the vertical spraying force of the etching solution is great, destroying the protective film of the layout, performing deep etching, and the sides of the graphic part are protected and formed. Uniform side.

No powder corrosion can be completed at one time, and the image side remains intact, so the no-powder corrosion has the advantages of fast plate making speed, good graphic side slope, low labor intensity, and high plate-making quality. Therefore, the powder corrosion process is gradually powder-free. Corrosion under the Arts Center instead.

4. The full-page full-length version is a corrosion-resistant copper-zinc flexo plate. The unwanted part is drilled or drilled deep to prevent dirt from picking up during printing. As long as it can accommodate the blank part of the drill bit, it must be drilled. The closer the text is to the better, the plane to be drilled requires a flat, uniform and beautiful appearance, and the depth of the drill meets the printing requirements.

For example, the plates that are put together are to be separated one by one. In addition, the plate must be assembled together with the movable type, so the plate must be equipped with a bottom plate, the bottom plate is supported by a wooden tray or a metal bottom plate, and the metal tray can be recycled. The angle of the bottom bracket should be 90. It is easy to make imposition, and the thickness of the bottom bracket should be the same. The height of the plate should be the same as the height of the typeface after adding the bottom plate, but the height should not be high or low, and the cardboard can be corrected on the back of the bottom pad.

Paste the plate on the metal tray or nail it on the wooden tray for printing.

5. Proofing

The purpose of proofing is to check and prevent the reversal or placement of the image, in order to check the quality, such as the quality of corrosion. To solve the problems found in the proofing, take appropriate measures to solve it, or take the whole corrosion, or take a partial corrosion, or use a needle stroke, knife carving, etc., so that the quality meets the original requirements.

Second, photosensitive resin letterpress

Photopolymer relief plate (photopolymer relief plate) is a synthetic polymer material as a film-forming agent, unsaturated organic compounds as a photocrosslinker to produce a photosensitive plate with a relief. Photosensitive resin under the irradiation of ultraviolet light. A photocrosslinking reaction occurs between molecules, thereby forming a relief image with some insolubility. It is combined with phototypesetting technology, which increases the speed of plate making, discards the lead alloy plate, makes the cold row more perfect, and creates a new way for letterpress printing.

Photosensitive resin letterpress plate making process flow is as follows:

Text Manuscript → Phototypes → Photographs

Line Originals → Photos → Imposition → Resin Relief

Continuous tune originals → Screen capture

From the above process flow, it can be seen that if the photographing output is a film, the photographing process can be omitted.

The photosensitive resin relief plate has many kinds of plates, and can be classified into two types of liquid-curing type and solid-hardening type before resin molding.

1. Liquid-curable photosensitive resin letterpress

Liquid-curable photosensitive resin letterpress, referred to as a liquid resin plate, is a viscous, transparent liquid that is photoreceptor-resin and cross-linked to a solid state after photosensitized.

(1) Composition of Liquid Curable Type Photosensitive Resin Relief

The resin is an unsaturated resin obtained by polycondensation of aliphatic and aromatic saturated and unsaturated polycarboxylic acids and glycols.

The crosslinking agent is cross-linked under the action of ultraviolet light to become a solid, commonly used are acrylic acid, acrylamide, ethylene glycol dimethacrylate, ethylene glycol acrylate and the like.

Photoinitiators, also called photosensitizers, are vehicles for transmitting light energy in photopolymerization reactions, mainly benzoin and its ethers.

The polymerization inhibitor is a substance that suppresses the occurrence of a dark reaction and is usually p-phenylenediamine.

(2) Main process flow of liquid resin relief forming

The main technical process of the liquid resin relief printing is: paving → exposure → rinsing → drying and post-exposure

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